Application of Chemical Anti-counterfeit Material in Printing Ink

I. Introduction

In order to meet the needs of the development of the socialist market economy and the anti-counterfeiting of commodities, the anti-counterfeiting industry has gradually developed. In recent years, the research and development of anti-counterfeiting technology in China and the production and use of anti-counterfeiting technology products have developed rapidly. According to preliminary statistics, there are nearly 1,000 enterprises engaged in research, development, production and sales of anti-counterfeit technologies and products in China. The annual output value of anti-counterfeit products has reached More than one billion yuan has formed a new industry of anti-counterfeiting technology products.

Anti-counterfeiting technology involves many fields of science, such as optics, infrared technology, chemistry, electromagnetics, computer technology, spectroscopy, printing technology, pattern code technology, packaging technology, etc., belonging to a cross-cutting discipline. Among them, chemical anti-counterfeit materials and technologies are one of the most basic technologies for anti-counterfeiting. It includes a variety of anti-counterfeiting technologies using chemical materials and technologies, among which the anti-counterfeiting ink technology occupies a very important position and has an irreplaceable role. Here, combined with the experience and experience in the research and implementation of anti-counterfeiting technology in recent years, talk about the application of functional chemical anti-counterfeiting materials in printing inks.

Second, security ink type

The so-called anti-counterfeiting inks, special printing materials with special properties are added to the ink binder, and special printing inks are processed through special processes. Printing inks can be divided into letterpress, gravure, silkscreen, offset printing, and water-based flexographic printing inks according to the printing format. According to the different substrates, printing inks, press inks, and plastic inks can be classified. Here, the anti-counterfeiting features implemented by products classify the currently popular anti-counterfeiting inks on the market and our recent development. Current products include UV fluorescent inks, infrared excitation security inks, sunlight-induced color-changing inks, thermal security inks (thermochromic inks), friction color inks, pressure-sensitive color-changing inks, humidity-sensitive color-changing inks, reaction color-changing inks, and smart security inks. , Multi-function or comprehensive security ink (laser hologram plus fluorescent anti-counterfeiting ink) and so on, the specific implementation of ink printing in the ticket, product trademarks and packaging. This type of anti-counterfeiting technology is characterized by simple implementation, low cost, good concealment, bright colors, easy inspection (even hand-warming color changeable), strong reproducibility, and diverse color changes. It is the first choice for counterfeiting of banknotes, tickets and trademarks in various countries. technology.

1. Ultraviolet fluorescent ink can emit visible light (400-800nm) special ink under ultraviolet light (200-400nm) irradiation. According to the different wavelength of the excitation light source, it can be divided into short-wave ultraviolet excitation fluorescence anti-forgery printing ink (excitation wavelength of 254nm) and long-wave ultraviolet excitation fluorescence anti-forgery printing ink (excitation wavelength of 365nm). According to the color of the ink is divided into colored fluorescent ink and colorless fluorescent ink two. Among the commonly used fluorescent materials, there are mainly three types according to their composition. First, organic fluorescent materials are unsaturated molecules with large conjugates, most of which are excited by sunlight. They are used for decorative colors with poor fluorescence stability and are easily oxidized and decomposed. Second, inorganic fluorescent materials synthesized with high temperature are used. The luminescent materials for fluorescent screens and fluorescent tubes have good resistance to radiation and high stability, but are difficult to disperse in oily media, have high difficulty in synthesis, and have poor water resistance; Thirdly, chemically synthesized rare earth organic complexes are used as fluorescent materials. The focus of this article. Conventional organic rare earth fluorescent complexes have simple preparation, are easy to disperse, dissolve, and refine in oily media, are colorless under visible light, and have strong fluorescence effects under ultraviolet light excitation. In recent years, research reports and patent applications for organic rare earth complex fluorescent materials have gradually increased. However, most of their shortcomings are poor stability, low light energy conversion efficiency, or high preparation cost, so they can be used less practically. Patent applications by Japanese Mitsui and Seki Kaifu et al. (Japanese Laid-Open Patent, (A), 1988) each disclose a complex fluorescent material, but both have a serious problem of fluorescence stability.

Luminescent and energy transfer chemical principles of fluorescent rare earth complexes: In organic rare earth complexes, energy absorbing groups generally have strong absorption in the ultraviolet region (200-400 nm), and rare earth metal ions as luminescent centers are present here. Interval absorption is weak. When the complex organic ligand absorbs light energy, it jumps from the ground state S0 to the excited singlet state S1, and quickly passes through a non-radiative system to transfer energy to the triplet excited state, if the triplet state energy is higher than Metal ions emit fluorescent excited state energy, which can transfer energy to gold ions and emit characteristic fluorescence. The energy transfer process of the rare earth complex fluorescence is shown in FIG.

Figure 1. Schematic diagram of the energy transfer process of rare earth complexes fluorescing

The fluorescence generation process shows that: When different complex organic groups are introduced into the surrounding of the luminescent center ions, their surrounding environments are changed, and the symmetry of adjacent electric fields is changed, the fluorescence intensity of the complex will be directly affected. This is 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 tristyryl derivatives, vinyl naphthalene ethylene derivatives, and tetraphenyltriene derivatives.

2. Infrared excitation luminescent material

Infrared excitation luminescent material refers to an up-converting luminescent material that emits visible light under irradiation of far-infrared light (eg, 980 nm). As the early infrared laser recognizer is not easy to produce, it affects the promotion of this technology. At present, Peking University has launched this series of anti-counterfeiting technologies, including infrared anti-counterfeiting inks, infrared inks, and infrared recognition devices.

3. Daylight excitation color change security ink

Under the sunlight, it can emit visible light (400-800nm) anti-counterfeiting printing ink. This ink is discolored on the surface due to the action of sunlight and is essentially discolored by ultraviolet light. Recently, our company has successfully developed several kinds of sunlight-induced color-changing anti-counterfeiting inks. These inks can change color from colorless to violet, blue and yellow under sunlight (also under UV light), and can also be designed as From colored to colored changes, it is a rookie in the security material. The principle of color change is shown below (slightly)

When sunlight or ultraviolet (UV) light is irradiated onto the security ink, the photosensitive material in the ink is excited, and its molecular structure changes, resulting in a change in appearance color. When the external stimulus (solar or ultraviolet light) is removed, the photosensitive material in the ink returns to its original ground state and the ink returns to its original color. These photoactive material molecules are a class of colorless isomer organics that contain two localized pi-bond systems that only absorb ultraviolet light. When -C=O in the photosensitizing material molecule is decomposed by excitation with ultraviolet light in the wavelength band of 300-360 nm, the two localized pi-bond systems become a delocalized pi-bond system, and this delocalized pi-bond system absorbs Some kind of visible light, which produces a certain color.

4. Thermal security ink (thermochromic security ink or temperature change security ink)

Under the effect of heating, the ink can change color effect. According to the different temperature required for discoloration, it can be divided into hand-temperature anti-counterfeiting ink, high-temperature anti-counterfeiting ink. Hand-type color change security ink, refers to the effect of temperature at 26-32 °C, can produce discoloration effect of the ink; high-temperature color anti-counterfeit ink, refers to the 40-100 °C or even higher temperature, the effect of discoloration of the ink . According to the difference in color change, it can be divided into single color reversible, multi-color reversible, single color irreversible and multi-color irreversible thermal ink. Our company has developed five kinds of hand-temperature single-color reversible ink, color change methods are: rose red becomes colorless, purple becomes colorless, blue colorless, green colorless, orange red colorless can also be designed as colored Into a variety of other colors; three high-temperature single color reversible security ink, color change methods: pink blue, yellow red, red and black. Thermochromic substances can be classified into inorganic salts, coordination compounds, organic substances (dye molecules) and liquid crystal polymers. The principle of discoloration of thermochromic substances is as follows:

I. Reversible color change principle:

Crystallization changes in the crystal structure of certain inorganic substances caused by the thermochromic effect, such as:

Hg I2 (red, tetragonal) → HgI2 (yellow, orthorhombic), (137°C)

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

2 PH value change Some substances mixed with higher fatty acids, and when heated to a certain temperature, the carboxy protons in the acid are activated and react with these substances, causing changes in pH, resulting in significant color changes. When the carboxy protons are restored after cooling, the color of these substances also recovers. Thermochromic materials such as stearic acid and bromophenol blue have a proportion of less than 55°C yellow, and a blue reversible change above 55°C.

3 Loss of Crystallization Water The inorganic thermochromic substances are mainly transition metals such as salts, double salts of silver, mercury, copper, cobalt, nickel, etc., or compounds formed with water, hexamethylenetetramine, ethylenediamine, and the like. Their thermal decomposition reaction, dehydration when the hydrated salt temperature changes, or water absorption in the reverse direction; hydration and dehydration of the salt during the temperature change accompanied by color changes, the most common are cobalt, nickel, copper compounds, such as:
CoC12 ?6H2O (pink) → CoC12 (blue) +6H2O (g), (35°C)

Co Br2?10H2O?2Y (Pink)→Co Br2 (Blue Violet) +10H2O (g), (40°C)

Among them, Y is hexamethylenetetramine C6H12N4, and the water loss of the salt is a thermal decomposition reaction. During the cooling process, the anhydrous salt can absorb moisture from the air to recover the primary color, and thus is a reversible thermal color process.

4 Molecular structure changes Some organic thermochromic substances cause changes in molecular structure caused by heat, resulting in changes in the appearance of color, including acid-alkali, keto-enol, lactam-lactam, etc., the balance between the movement. For example, when studying a table for a mercury-containing organic compound, the intramolecular double bond position shift and hydrogen transfer are the main causes of color change. The following formula can be used:

5 Chemical reactions In addition, the discoloration effect of some organic thermochromic substances is caused by chemical reactions between the components. It consists mainly of three functional components, namely the electron donor, the electron acceptor and the solvent. The three together determine the color depth of the system, the temperature range. This kind of reversible thermochromic material has obvious advantages over other thermochromic materials in terms of the selectivity of discoloration temperature, the degree of freedom of color combination, the obvious degree of color change, and the price. For example, bismuth red, octadecyl octadecanoate and glycerol triglyceride compose the thermochromic material in a certain proportion to a reversible change from pink heating to 45°C to white.

6 LCD type

Some types of liquid crystals generate new and different crystal phases after they are heated. As a result, the reflection, refraction, and absorption of light are different, and the color changes. For example, when the proportion of cholesteryl propionate, cholesterol, and oleate is determined in a certain proportion, the colors produced by the colorant and the pigment are different at a certain temperature and below. Nematic liquid crystals, discotic liquid crystals, and cholesteric liquid crystals all have this effect.

II. Irreversible color change principle

Sulfates, nitrates, phosphates, chromates, sulfides, oxides, and azos of certain pigments such as lead, chromium, nickel, cobalt, iron, cadmium, barium, zinc, manganese, molybdenum, barium, magnesium, etc. Dyes, phthalocyanine dyes, methylene methane dyes, and the like, the discoloration of these pigments or dyes are irreversible chemical changes such as sublimation, melting, thermal decomposition, combination, oxidation, and reduction reactions that occur spontaneously. For example, pink cobalt oxalate is oxidatively decomposed at around 300°C to produce black cobalt oxide.

There are many substances that can generate thermochromic substances, but they are truly suitable for the production of thermochromic security inks. The following conditions must be met:
1 The color change has high sensitivity and shows a clear color change in a short time; the color contrast between the front and rear is large, such as red to blue, blue to white, and yellow to blue.
2 appropriate color temperature. The discoloration temperature should be controlled between 40°C and 100°C.
3 good stability. Under the influence of temperature, humidity, light, etc. under different climatic conditions, sensitive and effective during the use period should be guaranteed.

5. Smart security ink

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