Principle and application of anti-counterfeiting ink
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Anti-counterfeiting ink is one of the most important technical branches of anti-counterfeiting technology. It involves many disciplines, such as optics, chemistry, electromagnetics, computer technology, spectroscopy, printing technology, etc. It belongs to a cross-edge discipline. Among them, chemical anti-counterfeiting materials and technology are the basic technology of anti-counterfeiting inks, occupying a very important position in research and application. Ink anti-counterfeiting technology is a highly practical technology in the field of anti-counterfeiting, valuable securities and trademark packaging. It can meet the requirements of the public's first-line anti-counterfeiting identification, and also meet the identification and supervision of second- and third-line senior experts and management departments. Requirements.
First, the concept and type of anti-counterfeiting ink
Anti-counterfeiting ink refers to the ink with anti-counterfeiting effect, that is, special anti-counterfeiting material added into the ink connecting material, special ink processed by special process, which is also composed of three parts: coloring material, connecting material and ink additive. The anti-counterfeiting ink relies on the special functions of the coloring materials and the connecting materials in the ink to provide anti-counterfeiting effects.
Anti-counterfeiting inks can be divided into embossed, gravure, silk screen, offset and water-based flexo inks according to the printing form. Anti-counterfeiting inks can be classified into paper ink, printing iron ink, newsprint ink, plastic ink, etc. according to the substrate.
Anti-counterfeiting inks are classified according to their anti-counterfeiting functions. The main ones are as follows: 1 thermochromic anti-counterfeiting ink, the principle is that the color material adopts color change with temperature; 2 photochromic anti-counterfeiting ink, the principle is to add photochromism to the ink. Or a light-activated compound; 3 moisture-sensitive color-changing anti-counterfeiting ink, the principle is to add a color change color change substance in the color material; 4 pressure-sensitive color-changing anti-counterfeiting ink, the principle is to add pressure-induced color-changing compound or micro-capsule into the ink; Ultraviolet fluorescent anti-counterfeiting ink, the principle is to add visible fluorescent compound with ultraviolet light excitation in the ink; 6 infrared fluorescent anti-counterfeiting ink, the principle is to add visible fluorescent compound excited by infrared light in the ink; 7 anti-reflection anti-counterfeiting ink, in The ink is added with a chemical reaction to the chemical substance for alteration; 8 visual color-changing anti-counterfeiting ink, the color material adopts multi-layer interference optical film; 9 magnetic anti-counterfeiting ink, the color material is magnetic substance such as iron oxide and oxidation The iron is doped with cobalt and the like. These anti-counterfeiting inks are characterized by the implementation of different external conditions, mainly using light, heat, and spectral detection to observe the color change of the ink print to achieve anti-counterfeiting purposes.
Second, the category of anti-counterfeiting ink
1. UV fluorescent anti-counterfeiting ink
It can emit visible light (wavelength 400-800μm) special ink under ultraviolet light (wavelength 200~400μm). According to the different wavelengths of the excitation light source, it can be divided into short-wave ultraviolet light excitation fluorescent anti-counterfeiting ink and long-wave ultraviolet light excitation fluorescent anti-counterfeiting ink. Generally, the short-wave ultraviolet light is used to excite the visible violet anti-counterfeiting printing ink, the excitation wavelength is 254 μm, and the long-wave ultraviolet light excites the visible fluorescent anti-counterfeiting printing ink, and the excitation wavelength is 365 μm.
According to the color of the printing ink, it is divided into two types: colored fluorescent ink and colorless fluorescent ink. The former is to add a fluorescent compound to the colored ink, the latter is added to the colorless ink, the former printed image is visible to the naked eye, and the latter is invisible.
The components of the ultraviolet fluorescent ink are mainly phosphors, and the commonly used fluorescent materials are mainly classified into three according to their composition. 1 organic fluorescent material is an unsaturated molecule with large conjugated body, mostly excited by sunlight, its fluorescence stability is poor, easy to oxidize and decompose; 2 inorganic fluorescent material synthesized by high temperature, good radiation resistance, high stability, but in oily medium It is difficult to disperse, has high synthesis difficulty and poor water resistance; 3 chemically synthesized rare earth organic complex is a fluorescent material and is the main material of anti-counterfeiting ink. Commonly used organic rare earth complexes have simple preparation, are easy to disperse, dissolve and refine in oily medium, and are colorless under visible light, and exhibit strong fluorescence effect under ultraviolet light excitation.
In recent years, China's UV fluorescent inks have developed rapidly. Successfully developed colored (explicit) UV fluorescent inks and colorless (invisible) UV fluorescent inks. These fluorescent inks can emit red fluorescence and blue fluorescence under specific ultraviolet light. , yellow fluorescence and green fluorescence.
The tax stamp on the invoice is printed with colored UV fluorescent ink. The tax stamp on the invoice during the day is the same as the general unit seal. When the invoice is illuminated with purple light in the dark and dull place, the tax chapter is bright red, and generally The chapter of the unit is black.
2. Thermal anti-counterfeiting ink
The thermal anti-counterfeiting ink is an ink that can change color under the action of temperature. It is usually divided into reversible and irreversible thermochromic anti-counterfeiting inks, usually referred to as a discoloration temperature of 34 ° C to 100 ° C. According to the temperature required for discoloration, it can be divided into hand temperature discoloration anti-counterfeiting ink and high temperature discoloration anti-counterfeiting ink. The hand temperature discoloration anti-counterfeiting ink refers to an ink which can change color at a temperature of 34 ° C to 36 ° C; the high-temperature discoloration anti-counterfeiting ink refers to an ink which can cause a discoloration effect at a temperature of 40 ° C to 100 ° C or higher. It is true that it is suitable for the production of thermal-resistant anti-counterfeiting inks. It must have the following conditions: high color sensitivity and vivid color change in a short time; proper color temperature, color temperature should be controlled at 40 ° C ~ 100 ° C; good stability, In different climatic conditions, it should be sensitive and effective during the period of use.
2.1. Reversible thermochromic anti-counterfeiting ink. The invertible color can be produced either from an organic compound or from an inorganic compound.
Organic compound reversible color mechanism: The reversible color of organic compounds is caused by the change of molecular structure with the change of temperature, that is, the movement between electron donor and electron acceptor; two spatial configurations or two The crystal structure changes to each other; the molecules are subjected to thermal ring opening or radical generation to cause ink color change.
2.2. irreversible thermochromic compounds. The non-reversible color compound refers to a compound whose color after heating discoloration cannot be restored when it is cooled. For example: cobalt chloride penta-ammonium dichloride, which changes from room temperature pink to 120 ° C purple, 170 ° C sky blue, higher than 230 ° C black, when cooled to room temperature, it still remains corresponding to The highest temperature color, the ink made of the thermochromic compound as a color material is called a thermal anti-counterfeiting ink, and can also be called a thermochromic ink. Temperature-changing color-changing inks have been widely used in China. Temperature-sensitive inks are used to test temperature quickly, accurately, and simply. No special auxiliary equipment is required, and operators do not need special training to operate.
The heat-sensitive anti-counterfeiting ink is easy to detect and suitable for mass identification, and is widely used in the packaging of brand-name products, especially cigarette packages. The disadvantage is that the color printing effect of offset printing and embossing is poor, and the screen printing and gravure printing effects are good.
3. Photochromic anti-counterfeiting ink
Under sunlight, the ink changes from colorless to colored, but can be reduced to a colorless anti-counterfeiting ink after the light source is removed. The ink is discolored on the surface due to the action of sunlight, and is substantially discolored by ultraviolet light. At present, several kinds of sunlight-activated color-changing anti-counterfeiting inks have been successfully developed in China. Their anti-counterfeiting features are color-changing effects under sunlight, which can change from colorless to purple, blue, yellow, etc., and can also be designed from colored to colorless. .
The photochromic ink has the advantages of convenient identification and good anti-counterfeiting performance, and has been widely used. The disadvantage is that the offset printing and embossing effects are poor.
4. Magnetic anti-counterfeiting ink
The magnetic anti-counterfeiting ink is an anti-counterfeiting printing ink prepared by using a magnetic powder material (cobalt-doped in iron oxide and iron oxide) as a functional component. It is the most commonly used anti-counterfeiting ink. Its outstanding feature is the dark color of the appearance, the detection instrument is simple, and it is mostly used for anti-counterfeiting of bills and documents. Magnetic inks are characterized by characteristic and non-characteristic. The so-called characteristic magnetic ink means that the magnetic powder in the ink contains a specific magnetic signal, while the non-characteristic magnetic ink means that the magnetic powder in the ink does not contain a specific magnetic signal, and only magnetic.
Magnetic inks In addition to banks and postal applications for magnetic ink letter recognition, there are also readers, also known as optical scanners, which are devices that use optical principles to recognize alphabetic symbols. Another main use is to print tape strips on shopping credit cards, shopping cards, meal ticket magnetic cards, IC cards and visit cards. The magnetic ink is used for anti-counterfeiting packaging, which is mainly printed with magnetic ink at a certain position of the packaging, and is detected by special means, thereby achieving the purpose of anti-counterfeiting, and the printing method is generally lithographic printing and embossing.
5. Visual color change security ink
Visual color-changing anti-counterfeiting ink is a high-tech security anti-counterfeiting ink that can be printed by traditional engraving gravure method. It does not require complicated or additional testing equipment to distinguish the authenticity. It is suitable for banknotes, trademarks, securities, packaging and printing. Visual color-changing anti-counterfeiting inks are very concealed and difficult to decipher. They are security inks developed for fast-developing color reproduction technologies such as laser scanning color separation machines and color copiers.
The principle of visual color-changing anti-counterfeiting ink is: when the angle of view changes by 60°, two distinct colors are produced. The first color is seen when it is totally reflected, that is, the color seen at a viewing angle of 90°. When twisted 60° to a viewing angle of 30°, the first color is cancelled and the second color is strengthened.
6. Pressure sensitive anti-counterfeiting ink
The pressure sensitive anti-counterfeiting ink refers to an ink which can appear in color under the action of pressure or friction. It is made by adding special chemical reagents or color-changing substances to the ink. A colored or invisible graphic printed with such an ink. When rubbed or pressed with a hard object or tool, chemical pressure change or microcapsule rupture dye appears to appear in color (red, blue, black, Green, purple, yellow, etc.). The displayed color can be selected and designed according to the user's requirements.
7. Anti-alteration anti-counterfeiting ink
The anti-alteration anti-counterfeiting ink refers to an ink having a color developing chemical reaction for the chemical substance for coating. Print the invoice and the shading of all valuable securities with anti-altering ink. When encountering the correction fluid such as Xiaoziling, these shading disappears or discolors and the traces of the alteration are found.
Anti-counterfeiting ink anti-counterfeiting principle: 1 Use pigments that can be discolored by encountering Xiaoziling or other correction fluids, such as some salt-based dyes, and print the shading of the amount of securities. 2 Use anti-altering inks such as biphenol, which can be discolored by encountering Xiaoziling or other chemicals. The check uppercase column printed with this ink, etc., will change color or appear "obsolete" if it encounters Xiaoziling or other correction fluid.
Third, anti-counterfeiting inks need to pay attention to the printing
1. Many anti-counterfeiting inks are colorless inks, that is, they are colorless or white in the printed matter. Therefore, before printing such inks, the ink rollers, ink fountains, and ink knives must be cleaned to avoid imprinting of the printed products and affect the anti-counterfeiting effect. .
2. Many anti-counterfeiting inks have poor alcohol resistance, such as fluorescent and thermal inks. Therefore, it is best not to use alcohol dampening when using such inks.
3. Due to the limitation of raw material characteristics, many anti-counterfeiting inks are inferior to ordinary inks in offset printing. Therefore, it is necessary to increase the amount of printing in the printing to strengthen the product inspection to prevent the difference in ink color from affecting product quality and anti-counterfeiting effect.
4. Since direct irradiation of 254nm ultraviolet light will harm human skin and eyes, when using short-wave fluorescence, product testing must use a detection device with a protective device to avoid affecting health.