LCD liquid crystal development technology knowledge

- Aug 21, 2018-

            

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Main parameters affecting liquid crystal performance: clearing point; refractive index Δn; threshold voltage; purity; viscosity constant K; dielectric constant ε; pitch ρ


Factory adaptive test method and judgment standard for liquid crystal: Resistivity: A. Test method: Test the resistance value of the liquid crystal to be tested with a high resistance meter. B. Judging criteria: The test results are within the scope of product requirements (the factory standard ≥ 8X107). Photoelectric properties: A, test method: test the product, and test its photoelectric performance. B. Judgment criteria: The Von and Voff values of the test samples are consistent with the supplier parameters, and the viewing angle, contrast, and background color meet the requirements of the production product. Clear highlights: A. Test method: Heat the liquid crystal to be tested and measure the temperature at which it reaches the clearing point. B. Judgment criteria: The temperature of the measurement result is consistent with the clearing point temperature provided by the supplier. UV resistance: A. Test method: The liquid crystal test product to be tested is placed under the sealing UV machine, and irradiated twice according to the UV intensity and time specified by the sealing process to test the photoelectric performance change before and after the irradiation. B. Judging criteria: After UV irradiation, the Voff value rises within 0.1V (low voltage liquid crystal is within 0.15V), the current value changes within 2 times, and the contrast drop is not obvious. Reliability: A. Test method: Test the liquid crystal to be tested and test its reliability performance. B. Judging criteria: The photoelectric performance changes after the reliability test are within the product requirements.


According to the display type: TN type liquid crystal, STN type liquid crystal, HTN type liquid crystal; according to clear points: ordinary liquid crystal, wide temperature type liquid crystal;

  LCD selection rules: According to the customer's required background color, select the appropriate Δn range of liquid crystal categories, and then according to the customer's IC circuit data, select the appropriate voltage range of the liquid crystal category, meet the above conditions of the liquid crystal, according to a reasonable proportion After use, you can meet customer requirements.


How to use the liquid crystal: The liquid crystal should be fully stirred before use to infuse it. Add liquid crystal of solid chiral agent, heat it to 60 degrees Celsius, then quickly cool to room temperature and stir well. Moreover, it cannot be left for too long during use. Especially for low threshold voltage liquid crystals, since low threshold voltage liquid crystals have these different characteristics, the following aspects should be paid attention to when using these liquid crystals: The liquid crystal should be fully stirred before use, and the prepared liquid crystal should be put into production immediately and minimized. Allow to store the storage time to avoid chromatographic phenomena. The liquid crystal should be covered with blackout and stored as much as possible within one shift (eight hours). The incomplete liquid crystal needs to be recycled and re-tested for voltage. Generally, as the time increases, the driving voltage increases. After the liquid crystal is taken from the original bottle, the original bottle should be covered and sealed in time to reduce the time of exposure to the air. The time exposed to the air is generally too long, which will increase the leakage current of the liquid crystal. The liquid crystal display empty box for filling the threshold voltage is preferably from the PI solid baking to the liquid filling process, and the empty storage box with the production time within 24 hours is used, and the filling operation generally uses a relatively low perfusion speed. The low threshold voltage liquid crystal must be covered with a suitable hood when sealing, and should be kept away from the ultraviolet source as much as possible during the entire liquid crystal filling period except during the curing of the sealing glue. Otherwise, the wrong direction and the increase of the threshold voltage will occur near the ultraviolet ray. Liquid crystal is an organic polymer substance, which is easily dissolved in various solvents or reacts with other chemicals. Liquid crystal itself is also a good solvent, so it should be kept away from otherization during use and storage.