Liquid crystal is an intermediate state that certain organic substances are present 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, so that the liquid crystal not only has the fluidity and surface tension of the liquid, but also exhibits the optical properties of some crystals, such as a temperature higher than the liquid crystal phase temperature At the upper limit, the liquid crystal becomes an ordinary transparent liquid and loses its optical properties. If the temperature is lower than the lower limit of the liquid crystal phase temperature, the liquid crystal becomes an ordinary crystal and loses its fluidity. Nematic liquid crystals in liquid crystals are used as display materials in the electronics industry, and cholesteric liquid crystals can be used for temperature indication.
The liquid crystal is irradiated by natural light and artificial white light, and the color light of a certain wavelength enhances reflection due to refraction phenomenon, and as the temperature rises, the color changes from a long wavelength to a short wavelength (ie, changes from red to green to blue). The color forming mechanism of liquid crystals is due to the selective reflection of light of a specific wavelength by the liquid crystal. The liquid crystal must be printed on a black or dark background, and now the liquid crystal can react between -10°C and +70°C with an accuracy of ±0.5°C.
During printing, the liquid crystal is encapsulated in microcapsules and ink is added for printing. Liquid crystal encapsulation has the following advantages: It can prevent the contamination of the liquid crystal itself; It can play a protective role, extend the service life, and facilitate long-term preservation; It can improve the printability. The amount of liquid crystal added to the ink is 40% of the total amount of ink, and the diameter of the capsule is between 10 and 30 microns.
Printing methods can be screen printing or gravure printing can be, in the screen printing liquid crystals should pay attention to: After the printing ink layer needs to have a considerable thickness, it is generally used 40 to 70 lines / cm stainless steel mesh, nylon mesh or polyester mesh; Since the screen liquid crystal microcapsule ink is water-soluble, therefore, the plate-making needs to use a strong water-resistant sensitizer; the micro-capsule ink is easy to plug the plate hole, and the plate should be washed frequently; the pressure of the squeegee should be smaller during operation; It is best to use natural drying, and it is not possible to use accelerated heating and drying; the dried printed matter should not be stacked in large quantities, and the cutting and the like should not be subjected to excessive partial pressure.
When using a liquid crystal ink, the color temperature range should be determined according to the purpose of use and the durability of the liquid crystal should be taken into account depending on the use.
The key to liquid crystal printing technology is: it can display brightly colored liquid crystals at different temperatures, and it should be a series at the color and humidity threshold; the production technology of liquid crystal microcapsules is also key, microcapsules must be made small and uniform, and the capsules should be transparent. In addition, thin, ink-containing inks require solvent resistance, stability, reliability, and long life; during the printing process, it is also necessary to ensure that the liquid crystal microcapsules are not crushed; the surface is covered with a protective film.
The purpose of liquid crystal printing: printed calendar pictures, the screen will change in different colors throughout the year in different colors; printed into a children's album, with the child's pointing touch to change the color of the picture; printed trademarks, wrapping paper, etc., posted in some The products that are afraid of heat can understand the changes in the quality of the contents in accordance with the changes in the pattern colors. For example, the vivid screen on the candy wrapper becomes dark, you should eat the candy as soon as possible, or you must melt it. The liquid crystal pattern printed on the container can display the temperature of the contents in the container. On large items such as precious, heat-sensitive and cold, the liquid crystal printing can be used as a reminder card for storing the temperature; the liquid crystal printing paper tape is also used as a disposable body temperature in foreign countries. Test meter.
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