Security ink performance and printing a

Anti-counterfeiting ink is one of the most important technical branches of anti-counterfeiting technology. There are many subject areas involved, such as optics, chemistry, electromagnetics, computer technology, spectroscopy, printing technology, etc., belonging to a cross border discipline. Among them, chemical anti-counterfeiting materials and technologies are the basic technologies of anti-counterfeit inks and occupy a very important position in research and application. Ink anti-counterfeiting technology is a highly practical technology in the field of ticket security, securities and trademark packaging. It can meet the requirements of the public's first-line anti-counterfeiting identification, and can also meet the requirements for the identification and supervision of second- and third-line senior experts and management departments. The request.

First, the concept and type of security ink

Anti-counterfeiting ink refers to the ink with anti-counterfeiting effect, that is, adding special anti-counterfeiting material to the ink connecting material, and special ink processed through special process. It is also composed of three parts: color material, connecting material and ink auxiliary agent. Anti-counterfeit inks rely on the special functions of pigments and binders in inks to provide anti-counterfeiting effects.

Anti-counterfeiting ink can be divided into embossing, gravure, silk screen, offset printing and water-based flexo printing ink according to the printing form. Anti-counterfeiting inks can be divided into paper inks, iron printing inks, newsprint inks, and plastic inks according to different substrates.

Security ink according to its anti-counterfeiting features, mainly in the following categories: 1 Thermochromic anti-counterfeiting ink, the principle is that the color of the material with the color change with temperature; 2 photosensitive anti-counterfeiting ink, the principle is to add photochromic ink Or light-activated compounds; 3 Humidity change color security ink, the principle is in the color material to add color with humidity changes in the material; 4 pressure sensitive anti-counterfeiting ink, the principle is to add pressure-induced discoloration of the compound in the ink or microcapsules; 5 UV fluorescent anti-counterfeiting ink, the principle is to add in the ink with ultraviolet light visible fluorescent compounds; 6 infrared fluorescent anti-counterfeiting ink, the principle is to add in the ink with infrared light excitation visible fluorescent compounds; 7 anti-flood security ink, in The ink is provided with a substance that has a color-developing chemical reaction to the chemical substances used for altering; 8 visual color-change proof inks; the color material is a multi-layered interference optically-clipped film; 9 magnetic anti-counterfeit inks are pigmented with magnetic substances such as iron oxides and oxides. Cobalt and other iron. These security inks are characterized by the implementation of different external conditions, the main use of light, heat, spectral detection and other forms, to observe the color change of ink samples to achieve anti-counterfeiting purposes.

Second, the category of security ink

1. UV fluorescent security ink

In the ultraviolet (wavelength 200 ~ 400μm) irradiation, can emit visible light (wavelength 400 ~ 800μm) special ink. According to different wavelengths of the excitation light source, it can be divided into short-wave ultraviolet light excitation fluorescence anti-counterfeiting ink and long-wave ultraviolet light excitation fluorescence anti-counterfeiting ink. Generally refers to the short-wave ultraviolet light excitation visible violet anti-counterfeiting printing ink, excitation wavelength of 254μm, long-wave ultraviolet light excitation visible fluorescence anti-counterfeit printing ink, excitation wavelength of 365μm.

According to whether the color of printing ink is divided into colored fluorescent ink, colorless fluorescent ink two. The former is the addition of a fluorescent compound to a colored ink, the latter being added to a colorless ink. The former print is visible to the naked eye and the latter is invisible.

The composition of the UV fluorescent ink is mainly phosphor, and there are mainly three types of commonly used fluorescent materials according to their composition. 1 Organic fluorescent materials are unsaturated molecules with large conjugates, most of which are excited by sunlight. They have poor fluorescence stability and are easily oxidized and decomposed. 2 Inorganic fluorescent materials synthesized by high temperature, good resistance to radiation and high stability, but in oily media Hard to disperse, difficult to synthesize, poor water resistance; 3 chemical synthesis of rare earth organic complexes for fluorescent materials, is the main material of security ink. The commonly used organic rare earth complex has a simple preparation, is easy to disperse, dissolve, and refine in an oily medium, is colorless under visible light, and exhibits strong fluorescence effect under ultraviolet light excitation.

In recent years, China's UV fluorescent inks have developed rapidly, and successfully developed colored (visible) ultraviolet fluorescent inks and colorless (stealth) ultraviolet fluorescent inks. These fluorescent inks can emit red fluorescence and blue fluorescence, respectively, under specific ultraviolet light irradiation. , yellow fluorescence and green fluorescence.

The tax stamp on the invoice is printed with colored UV fluorescent ink. During the daytime, the tax stamp on the invoice is the same as that of the general unit stamp. When the invoice is illuminated with violet light in a dark and dark place, the tax stamp is bright red. The chapter of the unit appears black.

2. Thermal security ink

Thermal anti-counterfeiting inks are inks that can change color under the effect of temperature. Usually divided into reversible and irreversible thermal color security ink, usually referred to the color temperature is 34 °C ~ 100 °C. According to the different temperature required for discoloration, it can be divided into hand-warming anti-counterfeit inks and high-temperature anti-counterfeit inks.

Hand-warm anti-counterfeiting inks refer to inks that can produce discoloration at temperatures of 34°C to 36°C. High-temperature discoloration anti-counterfeit inks are inks that can change color at 40°C to 100°C or even higher temperatures. True conformity to the production of heat-change anti-counterfeit inks must meet the following conditions: high color sensitivity, showing a clear color change in a short period of time; proper color temperature, color temperature should be controlled at 40 °C ~ 100 °C; good stability, Under different climatic conditions, it should be sensitive and effective during the use period.

1 Reversible thermal discoloration security ink. Reversible discoloration can occur either from organic compounds or from inorganic compounds.

Mechanism of reversible discoloration of organic compounds: Reversible discoloration of organic compounds is due to changes in molecular structure with changes in temperature, ie movement between the electron donor and the electron receiver; two spatial configurations or two The crystal structure is interconverted; the molecule undergoes thermal ring opening or generates free radicals, which causes the color of the ink to change.

2 Irreversible thermochromic compounds. The irreversible color-changing compound refers to a compound whose color cannot be restored when the color after heating is discolored upon cooling. For example: Cobalt chloride pentaamine dichloride, which changes from pink at room temperature to purple at 120°C, sky blue at 170°C, black above 230°C, and when cooled to room temperature, it remains corresponding to The color of the highest temperature, the ink produced with the thermochromic compound as the color material is called a thermal security ink, and it can also be called a temperature-change color ink. The temperature-change color ink has begun to be widely used in China. The test temperature of the temperature-change color ink used for printing is rapid, accurate and simple. No special auxiliary equipment is required. In addition, the operator can operate without special training.

The heat-sensitive anti-counterfeiting ink is easy to detect and suitable for mass identification. It is widely used in the packaging of brand-name products, especially cigarette packaging. The disadvantage is offset printing, embossing color effect is poor, the use of screen printing, gravure printing effect is good.

(to be continued)