Liquid crystal ink printing and its application
Liquid crystal ink is a new type of special ink that originated in the United States in the 1970s. It refers to the addition of compounds with crystalline properties to the ink. Liquid crystal ink belongs to the type of microcapsule structure ink in terms of production method; in terms of application, it belongs to the category of thermosensitive thermochromic ink. 1 Composition of liquid crystal ink The liquid crystal ink is mainly composed of water-soluble resin, liquid crystal capsules, additives, linking materials, defoaming agents, etc. It is prepared by dispersing liquid crystal and additives enclosed in microcapsules in the linking materials. The main components are as follows. 1) LCD Liquid crystal is a substance that has liquid fluidity and has the same chemical properties as crystal. Very sensitive to electric field, magnetic field, temperature, chemical environment and stress. 2) Capsule Since liquid crystal is an organic compound between liquid and crystal, it is not like ordinary ink that can be directly added to the binder. In order to prevent the liquid crystal from being contaminated by other substances and to ensure the color rendering effect, the liquid crystal needs to be wrapped in microcapsules, and then mixed with the connecting material to make microcapsule ink. The wall of the microcapsule is composed of gelatin, gum arabic, formaldehyde, acetic acid, sodium hydroxide and so on. 3) Other The water-soluble resin is mainly acrylic copolymer emulsion, which has good durability and mechanical strength; the connection material is water-based resin, commonly used are water-soluble polyvinyl alcohol, hydrosol resin; defoamer is glycerin. 2 Preparation of liquid crystal ink Mix 1 part of gelatin and 12.1 parts of distilled water into an aqueous solution, add 70% cholesteryl nonanolate, 25% cholesteryl chloride, 5% cholesteryl cinnamate to the liquid crystal melt when heated to 55 ° C, and then use a blender to mix it Disperse into particles with a diameter of 15-30μm. In another container, mix 1 part of gum arabic and 95.6 parts of distilled water according to the quality, the temperature is controlled at 55 ° C, and slowly add the gelatin aqueous solution to adjust the pH to 4.85. When the mixed solution is cooled to 15 ° C, it is mixed with a 25% aqueous solution of pentylene glycol, washed and dehydrated with a dehydrating machine to become a concentrated capsule slurry, and then mixed with a 10% aqueous solution of polyvinyl alcohol to make a liquid crystal microcapsule ink. 3 Color rendering mechanism of liquid crystal ink The liquid crystal forms a spiral structure as a whole, and when light enters from the direction of the spiral axis parallel to the plane, it is divided into left-handed light and right-handed light. The light of one component is transmitted, and the light of the other component is totally reflected. This phenomenon is called circularly polarized dichroism. The cholesteric liquid crystal has a strong rotation in the wavelength region on both sides of the selective light scattering band, and the directions of optical rotation in the light scattering band are different from left to right. Because the pitch of most cholesteric liquid crystals has a strong dependence on temperature, so as long as the temperature changes slightly, the wavelength (color) of the scattered light will change greatly. In layman's terms, the color-forming mechanism of liquid crystal is formed by the selective reflection of light of a specific wavelength. Liquid crystal inks make use of such characteristics of liquid crystals, so that under the influence of weak current and temperature, the crystal lattice changes to show light and dark patterns and colors. The reaction temperature of liquid crystals is -100 to 700 ° C.
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