Anti-counterfeit printing ink in security packaging printing

Anti-counterfeit printing is an important market for current printing, and it is widely used in many fields such as banknotes, securities, and commodity packaging, and plays a very important role in safeguarding goods. Anti-counterfeit printing mainly uses materials (inks, paper, etc.) for anti-counterfeiting and printing technology for anti-counterfeiting. Most of the printing technologies used in security printing are the continuous progress of screen printing technology and the unique advantages of screen printing. It has also begun to occupy a place in the field of security printing, especially in card printing, lottery printing, and commodities. The anti-counterfeit packaging printing has fully exhibited satisfactory results.

At present, there are many kinds of anti-counterfeiting inks developed, but according to the characteristics of screen printing, the most suitable inks for screen printing are the following:

1. LCD ink

Liquid crystal ink is a new type of special ink originated from the United States in the 1970s. It refers to the addition of a compound with crystalline properties to the ink. From the production method, it also belongs to the type of microcapsule structure ink, from the application point of view, is a thermochromic temperature-induced color ink, but from the perspective of the characteristics of liquid crystal ink, mainly the use of liquid crystal thermochromic characteristics. The liquid crystal ink is mainly composed of a water-soluble resin, a liquid crystal capsule, an auxiliary agent, a binder, and an antifoaming agent. The liquid crystal ink is prepared by dispersing the liquid crystals, additives and the like enclosed in the microcapsules in a binder. The liquid crystal ink does not constitute a color image with the ink layer pigment, but utilizes the temperature change of the liquid crystal in the ink layer to cause a change in the molecular direction, thereby selectively reflecting visible light of a specific wavelength, absorbing optical characteristics of other wavelength light, thereby rendering color Variety. The color forming mechanism of the liquid crystal is formed by selective reflection of light of a specific wavelength, and the liquid crystal must be printed on a black or dark background. Since the molecular arrangement of the liquid crystal is not as strong as the crystal structure, it is easily influenced by the external environment and its optical properties are changed. The liquid crystal ink utilizes this property of the liquid crystal, so that under the influence of the weak current and the temperature of the liquid crystal, the crystal lattice changes to show bright and dark patterns and colors.

The liquid crystal ink printing method is preferably screen printing, so that the printed product has a reversible reaction or an irreversible reaction printing method. The key to liquid crystal printing technology is the ability to display brightly colored liquid crystals at different temperatures, and to make series in the color temperature range. The production technology of liquid crystal microcapsules is also critical. The microcapsules have to be small and uniform, and the capsule wall is transparent and thin. The ink is incorporated and requires solvent resistance, stability, reliability, and long life; and the liquid crystal microcapsules are not to be protected during the printing process. Crush; surface covered with protective film. The amount of liquid crystal added to the ink is 40% of the total amount of ink, and the diameter of the capsule is preferably 10 to 3 μm. The screen used for the printing of liquid crystal ink is generally a nylon screen or a polyester screen. If a large amount of ink is required for the printing plate, a stainless steel screen plate may be used. According to the requirements of ink microcapsule diameter and ink layer thickness, generally choose 100~175 mesh. Since the screen liquid crystal microcapsule ink is water-soluble, the photosensitive resist which has strong water resistance should be used when making the plate.

Please pay attention to the following issues when printing screen printing inks:

1 In each printing, there must be enough ink on the plate to give the ink even, and it is best not to fill the ink halfway to prevent foaming.

2 The microcapsule ink tends to clog the screen plate. If a plugging or blistering phenomenon is found, the machine should be shut down immediately and thoroughly cleaned with alcohol.

3 The printing pressure should be moderate. The pressure is low and the amount of ink on the substrate is insufficient, which affects the color effect. When the pressure is too high, the liquid crystal capsules are broken, thereby reducing the color effect.

4 In order to make the color of the printing part obvious, the black color or dark tone should be used for the printing background color. Background color can be water-soluble ink or organic solvent ink, printing methods available screen printing, offset printing, gravure. When organic solvent inks are used, they must be fully dried after printing to avoid the organic solvent remaining in the ink film and react with the liquid crystals to affect the coloring effect.

5 The printing process should pay attention to the smoothness of the ink layer, and the thickness is controlled at 15~35μm.

6 Reasonably arrange the printing color sequence. Firstly, the background color can be printed with black (or dark) ink, and then the desired pattern can be printed with liquid crystal ink; or the desired negative pattern can be printed with water-soluble black (or dark color) ink after printing the substrate first with the liquid crystal ink. cover.

7 The printed matter is preferably dried naturally. It can also be dried with hot air at about 40°C. Avoid rapid heating and high temperature drying.

In addition, when the printed matter is not stacked, it should not be heavily pressed. After drying, it should not be piled up as much as possible. When cutting, it is also not appropriate to add excessive partial pressure to prevent the liquid crystal microcapsules from being crushed. When using liquid crystal inks, the color temperature range should also be determined according to the purpose of use, and the durability of the liquid crystals should be taken into consideration according to the use. In order to improve the surface wear resistance, temperature resistance, gas barrier and maintain its gloss, the surface can be coated with varnish or protective film.

2. Magnetic ink

Magnetic ink anti-counterfeiting principle is the use of magnetic colorants, such as iron oxide or iron oxide added cobalt and other chemical substances, the use of magnetic detection detector detects the magnetic signal and decoding. Magnetic is produced by the magnetic pigment contained in the ink. The best magnetic pigments are Fe3O4 (black) and Fe2O3 (brown). Most of these pigments are needle-like crystals smaller than micrometers. The size and shape of these particles make them extremely easy to arrange in the magnetic field and obtain relatively high residual magnetism. This kind of residual magnetism is symbolized and digitally processed inside the automatic processing device. The friction function realizes the discrimination function. The binder for magnetic ink is generally an alkyd resin. Other pigments can also be added to obtain different colors of ink. The most prominent feature of magnetic ink is the deep color appearance and simple detection equipment.

3. Thermochromic ink

Thermochromic ink, also called temperature-sensitive ink, is a special ink that can change color with temperature. The anti-counterfeit principle of the thermal ink is that the color material uses a substance whose color changes with temperature. In recent years, some research institutes and manufacturers at home and abroad have successively developed thermochromic inks with different characteristics. Now, there are three types of thermochromic inks: color reversible, color irreversible, and memory. The reversible type means that when the thermochromic discoloration occurs, the heat source can be restored to its original shape once the ink color is removed. The type of discoloration can be divided into sublimation, melting, thermal decomposition, oxidation and curing reactions, mainly due to the loss of crystal water after the conversion of crystal form or due to PH. The value changes and changes color, so when the heat source is eliminated, it can be restored to its original state. The irreversible type is that when the color changing pigment in the printing ink is heated, a physical or chemical change occurs, the original physical and chemical properties are changed, and thus the color change occurs. Therefore, the color of the ink cannot be restored to the original color when the heat source is withdrawn. Memory type has memory function.

Thermochromic inks can be used for screen printing, gravure printing, and flexo printing, especially for screen printing. Screen printing is suitable for printing materials of any shape, especially for substrates with small batches but special shapes. When printing thermochromic inks, attention should be paid to the relationship between the thickness of the ink layer and the effect of temperature-sensitive color change, and at the same time, the viscosity, volatility, etc. of the ink must also be considered because these characteristics affect not only the printing process but also the color rendering effect; Drying should be careful, it is best not to use heat drying method, in addition thermal ink is not suitable for direct printing on aluminum foil material.

4. Photochromic ink

Photochromic inks, also called photochromic inks, are photochromic or photoactive compounds that are added to the ink. In the sun, the ink can change from colorless to colored, or from orange to black, etc., and can generally be divided into common type and UV type. . Ordinary type means that under the effect of ordinary daylight and strong light, the color of the ink will change, and it will return to its original shape after leaving the light source. It looks like it is discolored under the sun, and it is essentially changed by ultraviolet radiation. The color changing wavelength is 400~800nm. The application of this kind of ink in packaging and decoration not only can improve the grade of goods, increase interest, but also highlight the anti-counterfeiting effect. UV type ink is colorless or does not change color under the irradiation of ordinary light sources, but it will show bright red, orange, yellow, green and green fluorescence under UV light (UV light) irradiation. Most large denomination banknotes are printed using this kind of ink, and authenticity can be revealed under the effect of a counterfeit money detector.

In screen printing, thermochromic and photochromic inks can be transferred to different substrates, such as paper, cloth, nylon, plastic, metal, glass, ceramics, etc., by screen printing. It has the characteristics of sensitive to external conditions, obvious changes and rapid recovery. It is the ideal material for anti-counterfeiting technology and interesting gifts. It has broad development and application value.

5. Fluorescent ink

The fluorescent ink is made of a fluorescent material dissolved in the corresponding resin. Fluorescent pigments are generally coarser particles, and the types of binders are also more. Different binders will produce different fluorescence. When using fluorescent inks, it should be ensured that it has sufficient concentration, and the ink layer on the prints is a little thicker. Satisfactory fluorescence effect is guaranteed. Fluorescent inks are printed brightly after screen printing, and the decorating effect is very good. Under the action of visible light and ultraviolet rays, it can give off glittering fluorescence. Fluorescent ink can be self-aligned, different formulations can get different fluorescence effects, and its anti-counterfeiting effect is better. However, fluorescent inks have poor light resistance, and prints used outdoors are not effective.

6. Storage and Phosphorescent Inks

The light-storing pigments are prepared using certain zinc sulfide/copper phosphors, calcium sulfide/germanium phosphors, etc. having a phosphorescent effect in inorganic phosphors. Inorganic fluorescent substances are generated by crystals. If the crystals are broken due to pressurization, resulting in reduced luminosity, screen printing is generally suitable. Ink carriers and fluorescent substances are mixed during use. Phosphorescent inks are characterized by the ability to absorb light and emit light at a certain wavelength within a certain period of time. The pigment of this ink is a zinc sulfide containing a small amount of impurities (such as cadmium zinc sulfide), which is afraid of acid and alkali, and therefore requires neutral resins such as cyclohexanone resin, cellulose ester and ether. In addition, heavy metals, desiccants, and drying oils should not be added to the ink to avoid damaging the pigment material. The link material used requires transparency and UV light transmission. This type of ink is mainly used for printing advertisements, signage, etc. However, if phosphorescent inks and fluorescent inks are used in anti-counterfeit packaging printing, they can receive very good packaging decoration and anti-counterfeiting effects.

7. Printing ink

The printing ink is mainly composed of pigments, fillers, binders, etc. The choice of pigments is an important step in determining the hue and vividness of printed products. Many manufacturers and ink manufacturers have customized special inks for printing of each product. Its formula is kept confidential by the ink factory. For example, the “China” and “Peony” cigarettes produced by the Shanghai Cigarette Factory are printed with special inks that are specially customized at the Shanghai ink factory. This type of ink does not know that the detailed formula is difficult to tune, and therefore has a better anti-counterfeit effect.

8. Composite ink

After mixing two or more anti-counterfeit inks in a certain proportion, composite inks with new properties can be developed. If the ink formulations are not fully understood, it will be difficult to imitate them.

9. Other security screen printing ink

Plastic security ink. Applicable to PP, PVC, PE, PS, ABS, PC and other plastic products, with 150 ~ 200 mesh polyester net, each kilogram of ink can be printed 20 ~ 30m. , Dry naturally or at 130 °C for 3 minutes.

Metal, glass, ceramic security ink. Suitable for printing on metal temperature signs, color-changing glass ware, color changing milk cups and ceramic tea sets, etc., with 70 to 100 mesh polyester mesh, 10 to 20 square meters per kilogram of ink, and drying conditions of 25, 48, or 120 degrees Celsius. 45min.

Glass, ceramic decal transfer paper security special ink. Applicable to the printing of glass and ceramic decals, with a 150 to 200 mesh polyester web, and the drying conditions are 200°C and 20 minutes after water transfer.

Water-based security inks and printing pastes. Applicable to printing on paper, cotton, knitted fabrics, T-shirts, sportswear, etc., with 80 to 150 mesh polyester mesh, printing about 20m2 per kilogram of ink (cotton fabric will be less than this number), drying conditions 130 °C, 3min

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