The function of liquid crystal ink and its application in screen printing

Liquid crystal ink is a kind of new ink material with great vitality and yet to be developed. Its range of printing applications is very wide. In terms of its functions, it is mainly used in the two major directions of temperature display and hair color change.

Temperature display: Mainly thermometers, body temperature, automatic temperature recorders, testing machines and testing instruments, etc. have temperature display requirements of the substrate. At present, foreign countries also use liquid crystal printing tape as a one-time body temperature tester.

Hair color changes: advertising, trademark labels, arts and crafts, medals, jewelry and other accessories and security printing products. If used for printing calendar pictures, it will show different colors as the temperature of the four seasons changes; if it is printed into a children's album, it can change the color of the picture with the touch of the child's fingertips; printed trademarks, Wrapping Paper, etc., are affixed to some products that are afraid of heat , According to the change of pattern color, to understand the quality of the contents of the contents, such as the candy on the bright paper screen becomes gray, you should eat candy as soon as possible, or to dissolve. A liquid crystal pattern is printed on the container to display the humidity of the contents of the container. On large items such as precious, heat-resisting and cold, the liquid crystal printing can be used as a reminder card for preserving the temperature. As for the use of liquid crystal ink as a forgery-proof ink, the main use is the use of the characteristic of temperature-sensitive discoloration of liquid crystals, and now it has also played a significant role in the field of anti-counterfeiting packaging and decoration, and its anti-counterfeiting effect is also ideal.

Liquid crystal inks can be screen or gravure, but silk screens are better. The key to liquid crystal printing technology is the ability to display brightly colored liquid crystals at different temperatures, and to make a series of color temperature values. The liquid crystal microcapsules have to be small and uniform, the capsule wall is transparent and thin, and the ink is incorporated, and the solvent resistance is required to be stable, reliable, and long-lived; the liquid crystal microcapsules are also not to be crushed during the printing process, and the surface is covered with a protective film.

1. Plate making

The number of screen meshes is 100-175 mesh, which is selected according to the requirements of ink microcapsule diameter and ink layer thickness. 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.

2. Printing

The following points should be noted when printing LCD inks:

(1) The printing plate should be filled with enough ink at a time, and the ink should be evenly distributed. It is best not to fill the ink in the middle to prevent foaming.

(2) When plugging or blistering is found during printing, it is necessary to stop the machine immediately and thoroughly clean it with alcohol.

(3) The printing pressure should be moderate. The pressure is small and the amount of ink on the printing substrate is insufficient. If the pressure is too high, the liquid crystal capsule will be broken and affect 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. The bottom layer can be water-soluble inks, organic solvent inks can also be used. Printing methods available screen printing, offset printing, gravure. When organic solvent ink is used, it must be fully dried after printing. The organic solvent should not remain in the ink film, otherwise it will react with the liquid crystal and affect the color effect.

(5) Pay attention to the smoothness and smoothness of the ink layer. The thickness of the ink layer should be controlled to 15~35μm to improve the color effect.

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

3. Post-press processing

(1) The drying method is preferably natural drying. It can also be dried by hot air at about 40 degrees Celsius, and it must not be accelerated and the high temperature of heating should be drastically dried;

(2) Do not press the printed matter when it is stacked. After drying, try not to pile too much overlap, when breaking, etc. should not be too large partial pressure, so as not to be liquid crystal microcapsules are crushed;

(3) When using liquid crystal inks, the temperature range of the discoloration should be determined according to the purpose of use and the durability of the liquid crystal should be considered 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.

Source: Silk Screen Printing Industry Channel

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