Application of the hottest chemical anti-counterfe

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The application of chemical anti-counterfeiting materials in printing inks

I. Introduction

in order to meet the needs of the development of socialist market economy and commodity anti-counterfeiting, the anti-counterfeiting industry has gradually formed and developed. In recent years, the research and development of national defense counterfeiting technology and the production and use of anti-counterfeiting technology products have developed rapidly. According to preliminary statistics, nearly 1000 enterprises and institutions in China are engaged in the research, development, production and sales of anti-counterfeiting technology and its products. The annual output value of anti-counterfeiting products has reached more than one billion yuan, forming an emerging industry of anti-counterfeiting technology products

the anti-counterfeiting technology involves many scientific fields, such as optics, infrared technology, chemistry, electromagnetism, computer technology, spectrum technology, printing technology, pattern code technology, packaging technology, etc., which belongs to an interdisciplinary frontier discipline. Among them, chemical anti-counterfeiting materials and technology is one of the most basic anti-counterfeiting technologies. It includes various anti-counterfeiting technologies using chemical materials and technologies, among which anti-counterfeiting ink technology occupies a very important position and plays an irreplaceable role. Here, combined with the experience and experience in the research and implementation of anti-counterfeiting technology in recent years, the application of functional chemical anti-counterfeiting materials in printing inks is discussed

II. Types of anti-counterfeiting inks

the so-called anti-counterfeiting inks are special printing inks processed by adding anti-counterfeiting materials with special properties into the ink binder. Printing inks can be divided into relief, intaglio, silk screen, offset and water-based flexographic inks according to the printing form; According to different substrates, it can be divided into iron printing ink, ink, plastic ink, etc. Here, the popular anti-counterfeiting inks in the market and our recently developed anti-counterfeiting inks are classified according to the anti-counterfeiting functions of the products. At present, the products include UV fluorescent ink, infrared excitation anti-counterfeiting ink, sunlight excitation color changing ink, thermal anti-counterfeiting ink (thermochromic ink), friction color changing ink, pressure-sensitive color changing ink, humidity sensitive color changing ink, reactive color changing ink, intelligent anti-counterfeiting ink - accelerating the transformation from labor-intensive to technology capital intensive industrial structure, multi-functional or comprehensive anti-counterfeiting ink (laser holography plus fluorescent anti-counterfeiting ink), etc, The specific implementation is mainly in the form of ink printing on tickets, product trademarks and packaging. This kind of anti-counterfeiting technology is characterized by simple implementation, low cost, good concealment, bright colors, convenient inspection (even the color can be changed by hand temperature), strong reproducibility and various color changes. It is the preferred anti-counterfeiting technology for banknotes, tickets and trademarks in various countries

1. UV fluorescent ink

special ink that can emit visible light (nm) under ultraviolet (nm) irradiation. According to the wavelength of the excitation light source, it can be divided into short wave ultraviolet excitation fluorescent anti-counterfeiting printing ink (excitation wavelength is 254nm) and long wave ultraviolet excitation fluorescent anti-counterfeiting printing ink (excitation wavelength is 365nm). According to whether the ink has color, it can be divided into colored fluorescent ink and colorless fluorescent ink. Among them, there are three kinds of commonly used fluorescent materials according to their composition. First, organic fluorescent materials are unsaturated molecules with large conjugates, which are mostly excited by sunlight and used for decoration with obvious colors. They have poor fluorescence stability and are easy to be oxidized and decomposed; Secondly, inorganic fluorescent materials synthesized at high temperature are luminescent materials used for fluorescent screens and fluorescent tubes. They have good radiation resistance and high stability, but they are difficult to disperse in oily media, difficult to synthesize, and poor water resistance; Third, chemically synthesized rare earth organic complexes as fluorescent materials, which is the focus of this paper. Conventional organorare earth fluorescent complexes have the advantages of simple preparation, easy dispersion, dissolution and refinement in oily media, colorless under visible light, and strong fluorescence under ultraviolet excitation. In recent years, the research reports and patent applications of organorare earth complex fluorescent materials have gradually increased. However, most of their shortcomings are poor stability, low efficiency of light energy conversion or high cost of preparation supported by National Natural Science Foundation of China, 973 program, 863 program, international cooperation program and other projects, so they can be applied in practice less. The patent applications (Japanese public license, (a), 1988) of Mitsui and Kimo keifu, etc., each disclose a complex fluorescent material, but there are serious fluorescent stability problems

Chemical principle of luminescence and energy transfer of fluorescent rare earth complexes: in organic rare earth complexes, as an energy absorbing group, there is generally strong absorption in the ultraviolet region (nm), while the absorption of rare earth metal ions as the luminescence center is very weak in this region. When the organic ligand of the complex absorbs light energy, it transitions from the ground state S0 to the excited singlet state S1, and soon transfers the energy to the triplet excited state through the jump of a non radiative system. If the triplet energy is higher than the excited state energy of metal ions emitting fluorescence, it can transfer the energy to gold ions and emit characteristic fluorescence. The energy transfer process of rare earth complex fluorescence is shown in Figure 1

Figure 1 Schematic diagram of the energy transfer process of rare earth complex fluorescence

this fluorescence generation process shows that when different complex organic groups are introduced around the luminous central ion, their surrounding environment is changed, and the symmetry of the adjacent electric field is changed, which will directly affect the fluorescence intensity of the complex. This is very important for improving the fluorescence efficiency and fluorescence stability of rare earth complexes

recently, researchers at Peking University have synthesized several organic fluorescent compounds, which are stilbene derivatives, naphthalene ethylene derivatives, tetraphenyltriene derivatives, etc

2. Infrared excitation luminescence materials

the reason why the import and export of non-ferrous metals in China have increased against the trend. Optical materials refer to up conversion luminescence materials, which emit visible light under the irradiation of far-infrared light (such as 980 nm). Because the early infrared laser recognizer was not easy to produce, it affected the promotion of this technology. At present, Peking University has launched this anti-counterfeiting technology series, including infrared anti-counterfeiting ink, infrared printing ink, infrared recognizer, etc

3. Color changing anti-counterfeiting ink excited by sunlight

anti counterfeiting printing ink that can emit visible light (nm) under sunlight. This kind of ink is discolored by sunlight on the surface, and it is also discolored by ultraviolet radiation in essence. Recently, our company has successfully developed several sunlight induced color changing anti-counterfeiting inks. These inks have color changing effect under sunlight (also under ultraviolet light), which can change from colorless to purple, blue, yellow and other colors, and can also be designed to change from colored to colored. They are the rookie and wonderful flowers in anti-counterfeiting materials. Its color changing principle is shown in the figure below (omitted)

when sunlight or ultraviolet light (UV) irradiates the anti-counterfeiting ink, the photosensitive material in the ink is excited, and its molecular structure changes, resulting in the change of appearance color. When the external stimulation (sunlight or ultraviolet light) is removed, the photosensitive material molecules in the ink return to the original ground state, and the ink returns to the original color. These photosensitive material molecules are a kind of colorless isomeric organic compounds, which contain two localized bond systems that only absorb ultraviolet light. When the c=o in the photosensitive material molecule is excited and decomposed by the ultraviolet light in the nm band, the two localized bond systems become an delocalized bond system, and the delocalized bond system absorbs some visible light, thus producing some recording data color

4. Thermal anti-counterfeiting ink (thermochromic anti-counterfeiting ink or temperature change anti-counterfeiting ink)

ink that can change color under the action of heating. According to the temperature required for color change, it can be divided into hand temperature color change anti-counterfeiting ink and high-temperature color change anti-counterfeiting ink. Hand temperature color changing anti-counterfeiting ink refers to the ink that can change color under the action of ℃ temperature; High temperature color changing anti-counterfeiting ink refers to the ink that can change color under the action of ℃ or even higher temperature. According to the difference of color changing ways, it can be divided into single color changing reversible, multi color changing reversible, single color changing irreversible and multi color changing irreversible thermosensitive anti-counterfeiting inks. Our company has developed five hand temperature single color changing reversible inks. The color changing methods are as follows: Rose Red becomes colorless, purplish red becomes colorless, blue becomes colorless, green becomes colorless, orange red becomes colorless, and can also be designed as colored into various other colors; Three kinds of high-temperature single color reversible anti-counterfeiting inks, color changing methods are: pink to blue, yellow to red, red to black, etc. Thermochromic substances can be divided into inorganic salts, coordination compounds, organic substances (dye molecules) and liquid crystal polymers. The discoloration principle of thermochromic substances is as follows:

I. reversible discoloration principle:

① crystal transformation

the thermochromic effect caused by the change of crystal structure of some inorganic substances, such as:

Hg I2 (red, orthorhombic system) HgI2 (yellow, orthorhombic system), (137 ℃)

its reversible discoloration mechanism is that its crystal structure can undergo reversible changes

② pH change type

after some substances are mixed with higher fatty acids and heated to a certain temperature, the carboxyl protons in the acid are activated and interact with these substances, causing changes in pH and obvious color changes. When the carboxyl protons recover after cooling, the color of these substances also recovers. For example, the thermochromic material composed of stearic acid and bromophenol blue in a certain proportion is yellow below 55 ℃ and reversible change of blue above 55 ℃

③ loss of crystal water

inorganic thermochromic substances are mainly salts or compound salts of transition metals such as silver, mercury, copper, cobalt, nickel, etc., or compounds formed with water, hexamethylene tetramine, ethylenediamine, etc. Their thermal decomposition reaction, water loss when the aqueous salt changes temperature or water absorption in the opposite direction; Hydration and dehydration of salt are accompanied by color changes during temperature change. The most common compounds are cobalt, nickel and copper, such as:

coc12? 6H2O (pink) coc12 (blue) + 6H2O (g), (35 ℃)

co Br2? 10H2O? 2Y (pink) Co Br2 (blue violet) +10h2o (g), (40 ℃)

where y is hexamethylenetetramine c6h12n4, and the dehydration of salt is a thermal decomposition reaction. During the cooling process, anhydrous salt absorbs moisture from the air and can recover to the primary color, so it is a reversible thermal color process

④ changes in molecular structure

some organic thermochromic substances change their molecular structure when heated, resulting in changes in appearance color, mainly including the balance movement between acid base, ketone enol, and lactimide lactam. For example, when studying an organic compound containing mercury, the movement of the double bond position and hydrogen transfer in its molecule are the main reasons for the color change. It can be expressed by the following formula:

⑤ chemical reaction

in addition, the discoloration effect of some organic thermochromic substances is caused by chemical reactions between components. It is mainly composed of three functional components, namely, electron donor, electron acceptor and solvent. These three factors together determine the color depth and temperature range of the system. This kind of reversible thermochromic materials have obvious advantages over other thermochromic materials in terms of the selectivity of color change temperature, the freedom of color combination, the degree of color change and price. For example, the thermochromic material composed of indole red, octyl p-carboxyvanillic acid and glyceryl laurate in a certain proportion is pink, and the reversible change is white when heated to 45 ℃

⑥ liquid crystal types

some types of liquid crystals produce new different crystal phases after heating. Thus, the reflection, refraction and absorption of light are different, making its color change. If cholesteryl propionate cholesteryl oleate is coated with a certain proportion of color glue and pigment, its color will be different above and below a certain temperature. Nematic liquid crystal, dish liquid

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