Anti counterfeiting function of liquid crystal ink

Introduction to the anti-counterfeiting function of liquid crystal ink

first, the composition and process of liquid crystal ink

liquid crystal ink originated in the United States in the 1970s. Later, with the gradual maturity of its technology and the continuous expansion of the printing market, liquid crystal ink printing has developed rapidly in the United States, Japan and other countries, and the scope of application is also expanding. From the perspective of manufacturing method, liquid crystal ink belongs to the type of microcapsule structure ink. From the perspective of application, it belongs to the category of thermotropic ink with heat sensitivity on anti-counterfeiting printing ink. However, from the perspective of the characteristics of liquid crystal ink, it mainly uses the characteristics of liquid crystal temperature sensitive discoloration

liquid crystal ink is mainly composed of water-soluble resin, liquid crystal capsule, additives, binder and defoamer. It is prepared by dispersing liquid crystal and additives enclosed in microcapsules in binder. It changes the direction of ordered pari molecules due to the temperature sensitivity of liquid crystals in the ink layer, so that the optical characteristics of selectively reflecting light of specific wavelengths show color changes, rather than using ink layer pigments to form color graphics and texts

when the liquid crystal is irradiated by natural light, artificial white light, and colored light of a certain wavelength, the reflection is strengthened due to refraction. As the temperature rises, the color of the liquid crystal changes from the color of long wavelength to the color of short wavelength (that is, it changes according to red green cyan). The color formation mechanism of the liquid crystal is formed by the selective reflection of the liquid crystal to the light of a specific wavelength

the liquid crystal must be printed on the black and dark background, and the ready-made liquid crystal can reflect - 100 ~ ＋ 700 ℃. The accuracy is 0.50 degrees Celsius. Because the arrangement of liquid crystal molecules is not as firm as the crystal structure, it is easy to be affected by external stimuli such as electric field, magnetic field, temperature, stress and adsorbed impurities, which changes its various optical properties. Liquid crystal inks apply this characteristic of liquid crystal

because liquid crystal is an organic compound between liquid and crystal, it cannot be directly added to the connecting material like ordinary ink. In order to prevent the liquid crystal from being polluted by its compounds and ensure the color rendering effect, it is necessary to wrap the liquid crystal in the microsphere capsule, and then mix it with the connecting material to make the so-called microcapsule ink. Microcapsules in liquid crystal inks are different from those in foaming and fragrance inks

the microcapsule of foaming ink is a foaming agent (or low boiling point liquefied gas). After heating, the foaming agent in the microcapsule emits a large amount of gas (or low boiling point liquefied gas expansion) to increase the volume of the microcapsule and play a foaming role. In addition, the foaming ink is added with pigments, which can be printed into various colors of foaming graphics and texts, and has the dual function of foaming and coloring

fragrance has a 10 point high-end and high-grade name - the microcapsule in cyclotron ink is characterized by not being crushed and damaged during printing. After printing into finished products, it is required to press and tear them with nails, pencils, etc. to make them easy to damage, so as to achieve the purpose of emitting fragrance. The microcapsule in the liquid crystal ink attaches the liquid crystal in the capsule to the ink layer through the connecting material

II. Printing technical requirements of liquid crystal ink

liquid crystal ink can be printed with silk or intaglio, but silk printing is better. The key of liquid crystal printing technology is to display liquid crystals with bright colors at different temperatures, and to form a series of color temperature range values. Liquid crystal microcapsules should be small and uniform, and the capsule wall should be transparent and thin. When mixed with ink, it is required to be solvent resistant, stable, reliable and long-life; Ensure that the liquid crystal microcapsules are not crushed during the printing process; The surface is covered with protective film, etc

1. Plate making

the number of wire mesh should be 100-175 mesh, which should be selected according to the requirements of ink microcapsule diameter and ink layer thickness. Because silk liquid crystal microcapsule ink is water-soluble. Therefore, the photosensitive adhesive with strong water resistance should be used in plate making

2. Printing

the following points should be paid attention to when printing with liquid crystal ink:

(1) the printing plate should be filled with enough ink at one time, and the ink should be evenly fed. It is best not to supplement the ink midway to prevent foaming

(2) in case of blockage and blistering during printing, stop the machine immediately to eliminate it and thoroughly clean it with alcohol water

(3) the printing pressure should be moderate. Low pressure, insufficient ink on the printing substrate; If the pressure is too high, the liquid crystal capsule will burst, affecting the color effect

(4) in order to make the printing part color obviously, the printing background color should be black or dark tone, and the bottom layer can use water-soluble ink or organic solvent ink. Printing methods include printing, offset printing and gravure printing. When using organic solvent ink, it must be fully dried after printing, and the ink film must not remain organic solvent, otherwise it will react with liquid crystal and affect the chromogenic effect

(5) note that the ink layer should be smooth and bright, and the thickness of the ink layer should be controlled to 15 ~ 35 μ m. To improve the hair color effect

(6) printing color sequence arrangement. You can use black (or dark) ink to print the background color first, and then use liquid crystal ink to print the desired pattern; You can also print the bottom with liquid crystal ink first, and then cover the negative pattern required for printing with water-soluble black (or dark color) ink

3. Post press processing

(1) the best drying method is natural drying, which can also be used at 40 ℃ 3 The preparation and utilization of ultra-fine functional materials should not be accelerated by the technology of heat sealing and drying. It is heated to high temperature and dried rapidly

(2) do not press hard when stacking printed matter. Try not to stack and overlap too much after drying, and do not add too much local pressure when cutting, so as to avoid the liquid crystal microcapsules being pressure-sensitive

(3) when using liquid crystal ink, the color change temperature range should be determined according to the purpose of use and the durability of liquid crystal should be considered according to the purpose. In order to improve the wear resistance, temperature resistance, gas insulation and maintain its gloss of the ink layer surface, the surface can be coated with gloss paint or pasted with protective film

III. anti counterfeiting function of liquid crystal ink

liquid crystal ink is a new ink material that has great vitality and needs to be developed. Its printing application range is very wide. In terms of its function, it is mainly used for temperature display and hair color change

temperature display: as long as it is a substrate with temperature display requirements, such as thermometer, body temperature, automatic temperature recorder, testing machinery and testing instruments. At present, liquid crystal printing paper tape is also used as a disposable thermometer in foreign countries

hair color changes: advertisements, trademark labels, arts and crafts, commemorative medals, jewelry and other decorations and anti-counterfeiting printing products. If it is used to print calendar pictures on the path of resource-saving development, it will show different colors with the change of temperature in the four seasons

if printed into a children's album, the picture color can be changed with children's pointing and touching; Printed into trademarks, wrapping paper, etc., and pasted on some products that are afraid of heat, you can differentiate according to the variable resolution 1 of the pattern color, and understand the quality changes of the internal items. For example, if the bright picture on the candy wrapping paper turns gray, you should eat the candy as soon as possible, otherwise it will melt. Printing liquid crystal pattern on the container can display the humidity of the items in the container. On large items that are expensive, afraid of heat and cold, liquid crystal printing can be used as a reminder card of storage temperature

as for the use of liquid crystal ink as anti-counterfeiting ink, it mainly uses the characteristics of temperature sensitive discoloration of liquid crystal. Now it has also played a great role in the field of anti-counterfeiting packaging and decoration, and its anti-counterfeiting effect is also relatively ideal