负性液晶材料电压保持率的研究

VHR study in negative dielectric anisotropy liquid crystal mixture

电压保持率(VHR)是表征液晶材料信赖性特性的重要参数之一,液晶材料的线残像特性与VHR相关。本文着重探讨了负性液晶材料在搭配不同PI材料,在不同电压、不同温度时VHR的表现。通过使用由不同PI材料制备的测试盒测量液晶材料在不同电压和温度下的VHR,从而得出负性液晶材料在不同条件下VHR的变化趋势。实验结果表明,测试盒的VHR值受到液晶材料和PI材料的共同影响。|Δε|较大的液晶材料VHR相对较低。在常温时,伴随充电电压升高,测试盒VHR呈下降趋势;而在高温时趋势相反,伴随充电电压升高,VHR呈上升趋势。|Δε|较高的液晶材料含有较多极性成分,易出现相对较低的VHR。常温时,离子运动较慢,伴随充电电压升高测试盒离子析出持续增加,离子析出增加会使测试盒VHR呈下降趋势。而高温时,离子活性较强,测试盒会析出大量离子,而大量离子不纯物的存在会使液晶盒在充电放时产生直流电残留,伴随充电电压升高,直流电残留电会更加严重,因此导致测试盒伴随VHR呈上升趋势。

Voltage holding ratio is one important reliability property of liquid crystal mixture,especially relatively higher VHR value can generally relate to better line image sticking performance.In this paper,we focus on studying the effect of alignment material,charging voltage and temperature on LC mixture＇s VHR dependency.The experiment is based on test cell measurement result.We use test cell which is made by different PI material for measuring VHR of negativeΔεLC mixture in various voltage and temperature conditions.Experimental results indicate that test cell＇s VHR can be influenced by both LC material and PI material.First,the LC mixture with large｜Δε｜has related low VHR.In room temperature measurement result,VHR goes down with charging voltage increasing.In high temperature,we have a reversed trend,VHR goes up with charging voltage increasing.Mixture with large｜Δε｜has more polar component which may cause a related low VHR.In room temperature case,higher charging voltage generates more ionic impurity and the increasing of ionic impurity causesVHR drop.In high temperature case,test cell has much more ionic impurity naturally than room temperature and it causes a residual DC during test cell charge-release cycle.With the increasing of charging voltage,test cell shows VHR goes up and test cell＇s residual DC becomes much worse.