Characteristics and printing technology of the hot

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Characteristics and printing technology of liquid crystal ink

in the field of ink, liquid crystal temperature variable materials are the most interesting. It mainly causes the change of optical properties through the change of lattice

I. composition and characteristics of liquid crystal

generally, solid substances become liquids when heated to the melting point. However, some substances with special molecular structure do not directly change from solids to liquids, but first go through an intermediate state. This intermediate state, which does not belong to ordinary solids, liquids and gases, is called the fourth state of matter. Its appearance is a fluid turbid liquid with liquid fluidity and surface tension, and at the same time it has the birefringence of optical anisotropy unique to crystals. This kind of substance that can have both liquid and crystal properties in a certain temperature range is called liquid crystal, which is generally divided into nematic, smectic, cholesteric and heteromorphic types

nematic. Many filamentous optical patterns can be seen by polarizing microscope. This liquid crystal still shows positive refraction, its viscosity is small, and it is rich in fluidity

smectic form. Rod like molecules form a layered structure, and the molecules are arranged in parallel with each other. The force between the molecular layers of this arrangement is relatively weak, and it is easy to slide between them, so the smectic liquid crystal presents two-dimensional fluid properties and has high viscosity characteristics

cholesteric type. Most of them are compounds derived from cholesterol. The liquid crystal as a whole forms a helical structure and has birefringence. It is the main type of liquid crystal ink

heteromorphic liquid crystal. It is also divided into reentrant liquid crystal and disc liquid crystal. Reentrant liquid crystal is a liquid crystal with the same phase again in the process of phase transition. Disc liquid crystal is a kind of liquid crystal whose molecular structure is disc-shaped

liquid crystal is an intermediate state of some organic substances in a certain temperature range. In this state, due to the special orientation of the molecular arrangement, the molecular motion also has a specific law. For example, if the humidity is higher than the upper limit of the liquid crystal phase temperature, the liquid crystal will become an ordinary transparent liquid and lose its optical properties. If the temperature is lower than the lower limit of the liquid crystal phase temperature, it will become an ordinary crystal and lose its fluidity

II. 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 orderly arranged molecules due to the temperature sensing of liquid crystal in the ink layer, so as to selectively reflect the visible light of specific wavelength and absorb the optical characteristics of other wavelengths to show color changes, rather than using the ink layer pigments to form color graphics and text. 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 the refraction phenomenon. 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 forming mechanism of the liquid crystal is due to the selective reflection of the liquid crystal to the light of a specific wavelength. The liquid crystal must be printed on the black or dark background. Now the liquid crystal can reflect -100~+700 degrees Celsius. 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 will change its various optical properties. This characteristic of liquid crystal is applied under liquid crystal ink

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 chemicals to ensure the color 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 `; Microcapsules; Type ink

microcapsules in liquid crystal inks are different from those in foaming and fragrance inks. The microcapsule of foaming ink is filled with foaming agent (or low boiling point liquefied gas). After trying to simulate leather and other effects of 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. Microcapsules in scented ink are characterized by not being crushed and damaged during printing, but they are required to be pressed and torn with nails, pencils, etc. after printing into products, so that they are easy to be damaged, so as to achieve the purpose of emitting fragrance. The microcapsules in the liquid crystal ink fix the liquid crystal in the capsule in the ink layer through the connecting material

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

2. Printing

when printing with liquid crystal ink, pay attention to the following points:

through internal technological innovation and mergers and acquisitions of other enterprises (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 replenish 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 hair color of the printing part obvious, the printing background color should be black or dark tone. The bottom layer can be 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 color development 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 print the required negative pattern with water-soluble black (or dark color) ink to cover it

3. Post press processing

(1) the best drying method is natural drying, or hot air drying at about 40 degrees Celsius. Do not accelerate and heat up the high temperature for rapid drying

Nike cooperates with many stakeholders (2) don't put too much pressure on the stacking of printed matter. After drying, try not to stack and overlap too much, and do not add too much local pressure when cutting, so as to avoid crushing the liquid crystal microcapsules

(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

IV. market prospect 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 in two directions: temperature display and hair color change

temperature display: it is mainly the 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 change. 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, it will show different colors with the change of temperature in the four seasons; If it is 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 understand the quality changes of the internal items according to the changes of pattern color. 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

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