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Abstract摘要
We have developed a new structure for True wide In-cell IPS(Twin IPS) panel which consists of a positive C plate in the cell.
我们已经开发出一种新的结构，真正的宽结构（IPS双IPS）面板，其中包括系统中重要的C盘。 This positive C plate is made of a UV polymerizable Liquid Crystalon the color filter substrate as a retardation film. TWin IPS of20.1”VGA has improved diagonal viewing performance without anyadditional layer in the cell.
1. Introduction介绍
As a LCD panel has become larger, the diagonal lightleakage of IPS mode has been given a considerable attention for aTV application[1]. 液晶面板已经变得比以前更大，因此IPS模式的对角线的光泄漏的问题一直是在亚洲电视应用程序获得了相当大的重视。 In order to solve the light leakage of diagonaldirection, IPS mode needs a retardation film such as a biaxial filmor a combined film using positive C plate and A plate[1,2]. Severalgroups already improved the black level of a diagonal direction inIPS mode by the compensation of the retardation film[3,4].Common material used for a compensator is stretched retardationfilm, which is put on the outside of a cell. Owing to stretchingprocess of common compensation film, it is difficult to manufacturea large size of the retardation film with high productivity and costcompetitiveness.The in-cell retardation film is one of effective ways to makea retardation film which has optical anisotropy and forms a film bycoating and polymerization of polymerizable liquid crystal (LC)[5,6]. According to the alignment of polymerizable LCs, it can beused for A plate, O plate, negative C plate and positive C plate. Sothey used to be applied to transflective mode and VA mode ascompensation films of in-cell type[7]. However, because the A plateand negative C plate require an alignment layer, rubbing andpatterning process, these application can not induce a highproducitivity and cost competitiveness.In this paper, we suggest the new structure of TWin IPSwhich has a positive C plate as a retardation film on the color filtersubstrate. It is made by a simple process using a non-rubbedalignment layer and improves the angular performance in the blacklevel of a diagonal direction with a high thermal stability.
2. Experiments试验 http://www.ukassignment.org/dxcoursework/
2.1 Structure of TWin IPS panelIPS mode requires A plate and positive C plate tocompensate the diagonal light leakage. 双IPS IPS面板模式的结构，需要一个C盘和面板来解决对角线漏光的问题。If A plate consisting of.polymerizable LC would be used for compensation film, it alsocould not realize high productivity. Therefore A plate is not apolymerizable liquid crystal in this proposal structure. Here, onlypositive C plate adapted in the cell as an compensator using apolymerizable LCs. Because it can have a vertical orientationwithout an alignment layer, it does not require an additional processsuch as coating an alignment layer and rubbing process. So it makesa retardation film with high productivity. As shown in figure 1, theA plate stretched type is attached out of a cell and positive C plateconsisting of polymerizable LC is located in a cell.正如图1中所示，THEA拉伸式盘状附加的是位于小区之间的正C板的愈合性的液晶面板。
Thermal stability of positive C plate.The C plate in a cell must have a thermal stability to get theoptimization of retardation because the C plate has an experience ofhigh temperature(200~250℃) in the process of curing an alignmentlayer. We has measured the heat stability of a C plate after heattreatment(230℃,1hr.). As a result, the change of retardation is lowerthan 5% of an initial retardation. The positive C plate of TWin IPSis stable enough to hold the retardation during the cell process.2.3 Retardation of positive C plate in TWin IPS.In TWin IPS structure, positive C plate consists of apolymerizable LC and is formed by coating and curing on the colorfilter substrate. It is relatively easy to form because a polymerizable LC has been aligned vertically without any additional process suchas mechanical rubbing. Figure 2 shows that the retardation profile issymmetric and positive C plate has a vertical orientation without atilted angle. Because Rth of C plate depends on the thickness of Cplate, Rth can controlled by changing a thickness of C plate. Inorder to compensate diagonal light leakage of IPS mode, theretardation of C plate needs to match with that of an A plate out ofcell. So various positive C plates are evaluated to optimizeretardation in this experiment.
3. Result & Discussion3.1 SimulationIn order to optimize retardation of A plate and positive Cplate of TWin IPS structure as shown in Figure 1, a lot ofsimulations are progressed. The retardation range of A plate (Re) isbetween 80 and 160nm and that of a positive C plate (Rth) isbetween 40 and 150nm. From the result of simulation, the diagonalluminance of a black level decreases initially and then increasesgradually as Rth of C plate has increased from 40nm to 150nm. Onthe other hand, color shift increases initially and then decreases.Therefore, Re and Rth are selected to optimize both blackluminance and color shift of a black level for the minimized thetrade off between the diagonal light leakage and color shift of theblack level. Figure 3 and Figure 4 show that the angularperformance of black level and color shift on the (a) normal IPSwithout compensator and (b) TWin IPS by using optimized Re andRth. Base on the this results, TWin IPS panel of 20.1”VGA has beenmade with the optimum retardation combination of A plate andpositive C plate.
3.2 The characterization of TWin IPS panelThe retardation fixed by the simulation applies to a TWinIPS of 20.1”VGA panel. Figure 5 shows that the contrast ratio isimproved comparing TWin IPS to normal IPS. In case of Twin IPS,the minimum contrast ratio is 40:1 in all directions, which is higherthan minimum contrast ratio of 10:1 of a normal IPs.A diagonal light leakage of a black level disappeared and isnot detected by eyes. It shows that TWin IPS has an improvedviewing angle for each of the four quadrants relatively. Figure 6 andFigure 7 show that color shift of a black level is also improved. Incase of a normal IPS, color shift of diagonal direction is very higher than that of horizontal and vertical direction. There is a lot ofdifference between diagonal and horizontal direction. However, incase of TWin IPS, the difference of color shift between diagonal andhorizontal is small comparing to a normal IPS. TWin IPS has a lowcolor shift of diagonal direction, which is the half of a normal IPS.Figure 8 is the pictures of the improvement in angular performancewith TWin IPS. The viewing angle for each of the four quadrantsshown in Figure 8 is 60o. Clearly an improvement of image qualityis observed with TWin IPS.
图8中所示的四个象限中的每个的视野角为60°。明显改善双IPS中图像的质量。 |
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