JPH0146874B2

JPH0146874B2 -

Info

Publication number: JPH0146874B2
Application number: JP54173321A
Authority: JP
Inventors: Tomio Sonehara
Original assignee: Seiko Epson Corp
Current assignee: Seiko Epson Corp
Priority date: 1979-12-26
Filing date: 1979-12-26
Publication date: 1989-10-11
Also published as: JPS5692591A

Description

[Detailed description of the invention]

本発明は、電界による液晶の相転移現象を応用
した、液晶表示装置に関する。電界による液晶の相転移現象で、現在表示装置
に応用されているのは、コレステリツク―ネマチ
ツク相転移現象がある。このコレステリツク―ネ
マチツク相転移現象を生じる液晶を透明電極を有
する２枚の基板間に挾持したセルに於いては、分
子の配列が印加電界に対し、１対１に対応しない
つまり、増加電界に対する構造と減少電界に対す
る構造が一致しない電界範囲が存在する。横軸に
印加電界強度、縦軸に配列を表わすパラメータを
とつてみれば、ヒステリシスを描く。このこと
は、印加電圧に対する誘電率、又は、色素分子に
平行、垂直な偏光に対し吸収の異なる二色性色素
を添加した、いわゆるゲスト―ホスト型液晶表示
装置の印加電圧に対する透過率を描いてみれば、
明白である。このヒステリシスを描く中間状態は、電界を上
昇させて印加した場合、非常に不安定である。ヒ
ステリシスをとる電圧と電圧零を切換えて表示の
オン・オフをすると、電界の印加されたオン状態
は再現性のある構造をとらないため、表示にむら
を生じ、かつ不安定であり、表示品位が低下して
しまう。この中間状態を避けるためには、ヒステ
リシスが生じない、さらに高い電界を加え駆動を
行なう必要がある。しかしこの方法は、不必要に
高い電圧を印加し続けることから、電力を余分に
消費する。本発明は、このような欠点を解消したものであ
る。本発明は、情報表示のための電圧印加と、次の
情報表示のための電圧印加の間の１周期内に、す
くなくとも１回、ヒステリシスをとり得ない高電
圧を該液晶セルに印加することにより、直接印加
ではヒステリシスを生じる電圧でも、安定な表示
を得る方法を提供するものである。以下、実施例に基づき本発明を詳しく説明す
る。第１図は、二色性色素を添加したコレステリ
ツク―ネマチツク相転移を生じる液晶を、対向す
る２枚の透明電極間に挾持したセルの印加電圧と
透過率の関係図である。第１図で、V₁は透過率
変化の10％での電圧、V₂は電界減少時にネマチ
ツク相をとりうる臨界電圧、V₃はヒステリシス
を生じない臨界電圧を示している。使用した２枚の透明電極は、ラビング等の通の
平行配向処理を施され、液晶は第２図に示すよう
に、無電界時にはコレステリツク相をとり、電界
印加時には透明電極に対し液晶分子が垂直に配向
したネマチツク相をとる。なお、第１図に示した
電圧―透過率特性を得た液晶及び色素は、第１表
に示す通りである。 The present invention relates to a liquid crystal display device that applies a phase transition phenomenon of liquid crystal caused by an electric field. Among the phase transition phenomena of liquid crystals caused by electric fields, the cholesteric-nematic phase transition phenomenon is currently applied to display devices. In a cell in which a liquid crystal that exhibits this cholesteric-nematic phase transition phenomenon is sandwiched between two substrates having transparent electrodes, the arrangement of molecules does not correspond one-to-one to the applied electric field. There exists an electric field range in which the structures for decreasing electric fields do not match. If we take the applied electric field strength on the horizontal axis and the parameter representing the arrangement on the vertical axis, hysteresis is depicted. This describes the dielectric constant with respect to applied voltage, or the transmittance with respect to applied voltage of a so-called guest-host type liquid crystal display device in which a dichroic dye is added that has different absorption for light polarized parallel to and perpendicular to the dye molecules. If you look,
It's obvious. This intermediate state depicting hysteresis is highly unstable when an increasing electric field is applied. When the display is turned on and off by switching between a voltage with hysteresis and a zero voltage, the on-state with an electric field applied does not have a reproducible structure, resulting in uneven and unstable display, resulting in poor display quality. will decrease. In order to avoid this intermediate state, it is necessary to drive by applying a higher electric field that does not cause hysteresis. However, this method continues to apply an unnecessarily high voltage, consuming excess power. The present invention eliminates these drawbacks. The present invention is characterized by applying a high voltage that does not cause hysteresis to the liquid crystal cell at least once within one cycle between applying a voltage for displaying information and applying a voltage for displaying the next information. , provides a method for obtaining stable display even at voltages that would cause hysteresis when directly applied. Hereinafter, the present invention will be explained in detail based on Examples. FIG. 1 is a diagram showing the relationship between the applied voltage and the transmittance of a cell in which a dichroic dye-added liquid crystal exhibiting a cholesteric-nematic phase transition is sandwiched between two opposing transparent electrodes. In FIG. 1, V ₁ is the voltage at 10% of the transmittance change, V ₂ is the critical voltage at which a nematic phase can be taken when the electric field decreases, and V ₃ is the critical voltage at which hysteresis does not occur. The two transparent electrodes used were subjected to parallel alignment treatment such as rubbing, and as shown in Figure 2, the liquid crystal takes a cholesteric phase when no electric field is applied, and when an electric field is applied, the liquid crystal molecules are perpendicular to the transparent electrodes. It takes on a nematic phase oriented to . The liquid crystals and dyes from which the voltage-transmittance characteristics shown in FIG. 1 were obtained are shown in Table 1.

【表】第２図に示した液晶セルに印加する電圧は、第
３図に示すように、２段階の電圧V_ON1とV_ON2に
よつて与えられる。ここでV_ON1，V_ON2はV_ON1≧
V₃＞V_ON2＞V₂の関係を満足している。情報表示にあたつて、まずV_ON1の電圧が該液
晶セルに印加され、第１図に於ける領域３をと
る。領域３は、透明電極に対し液晶分子が垂直に
配向したネマチツク状態である。液晶の応答性に
応じた時間t₁（この場合は０℃で100m sec）V_ON1
を印加した後、次にV_ON2に印加電圧を減ずる。
以後、表示状態を消去するまでV_ON1の電圧印加
でも該液晶セル内の液晶は、透明電極に対し垂直
に配向したネマチツク相を安定にとることができ
る。この状態は、第１図中領域２に対応してい
る。情報表示状態を消去する場合は、V_ON2より電
圧を減じ、V₁以下とすればよい。V₁以下の電圧
では、該液晶セル内の液晶は、第１図の領域１に
対応した第２図ａに示すコレステリツク相をと
る。さらに本発明は、コレステリツク―ネマチツク
相転移現象に限定されることなく、例えば、スメ
クチツクＡ―スメクチツクＣ相転移現象のような
電界による構造の変化に、ヒステリシスを有する
液晶にも適用される。以上の例にみられるように、電界による構造の
変化にヒステリシスを有する液晶を用いた液晶表
示体を駆動する際に、ヒステリシスをとらない高
電圧を情報表示と次の情報表示の間に加えること
により、電力消費の少ない、表示の安定した液晶
表示装置を得ることができる。上述の如く本発明は、一対の基板間に液晶が封
入され、該基板の液晶が接する側に透明電極が形
成され、該液晶は電圧に対しヒステリシスを有す
る相転移現象を生ずる液晶である液晶表示装置に
おいて、該液晶には二色性色素が添加されてな
り、情報表示状態にあつては、該液晶がヒステリ
シスを生じない臨界電圧以上であつて、かつ点燈
電圧を越えた第１の電圧を初期の期間該液晶に印
加し、続いて該液晶がネマチツク相をとりうる臨
界電圧まで下げた第２電圧を印加し、情報表示の
消去状態にあつては、該液晶がヒステリシスを生
じない電圧以下の第３の電圧を非点燈電圧として
該液晶に印加してなるようにしたから、従来の相
転移現象を有する液晶にみられたフオーカルコニ
ツク状態を回避することができるので、液晶の混
濁状態が発生することがない。従つて、情報表示
状態における液晶の完全な透明状態と、非表示状
態における二色性色素の完全な発色状態とのみが
得られ、明瞭な表示を得ることができるものであ
る。[Table] The voltage applied to the liquid crystal cell shown in FIG. 2 is given by two levels of voltages V _ON1 and V _ON2 , as shown in FIG. Here, V _ON1 and V _ON2 are V _ON1 ≧
The relationship V ₃ > V _ON2 > V ₂ is satisfied. When displaying information, first a voltage of V _ON1 is applied to the liquid crystal cell, which takes area 3 in FIG. Region 3 is in a nematic state in which liquid crystal molecules are aligned perpendicularly to the transparent electrode. Time t ₁ depending on the responsiveness of the liquid crystal (in this case, 100 m sec at 0°C) V _ON1
After applying , then reduce the applied voltage to V _ON2 .
Thereafter, even when the voltage V _ON1 is applied until the display state is erased, the liquid crystal in the liquid crystal cell can stably assume a nematic phase aligned perpendicular to the transparent electrode. This state corresponds to region 2 in FIG. When erasing the information display state, the voltage may be reduced from V _ON2 to V ₁ or less. At voltages below _V1 , the liquid crystal in the liquid crystal cell assumes the cholesteric phase shown in FIG. 2a, which corresponds to region 1 in FIG. Further, the present invention is not limited to the cholesteric-nematic phase transition phenomenon, but is also applicable to liquid crystals having hysteresis due to structural changes caused by electric fields, such as the smectic A-smectic C phase transition phenomenon. As seen in the above example, when driving a liquid crystal display using a liquid crystal that has hysteresis when changing its structure due to an electric field, a high voltage without hysteresis is applied between one information display and the next information display. Accordingly, a liquid crystal display device with low power consumption and stable display can be obtained. As described above, the present invention provides a liquid crystal display in which a liquid crystal is sealed between a pair of substrates, a transparent electrode is formed on the side of the substrate in contact with the liquid crystal, and the liquid crystal is a liquid crystal that causes a phase transition phenomenon having hysteresis with respect to voltage. In the device, a dichroic dye is added to the liquid crystal, and when the liquid crystal is in an information display state, a first voltage that is equal to or higher than a critical voltage at which hysteresis does not occur and exceeds a lighting voltage is applied. is applied to the liquid crystal for an initial period, and then a second voltage lowered to a critical voltage at which the liquid crystal can assume a nematic phase is applied, and in the erased state of information display, a voltage at which the liquid crystal does not cause hysteresis is applied. Since the following third voltage is applied to the liquid crystal as a non-lighting voltage, it is possible to avoid the focal conic state observed in conventional liquid crystals having a phase transition phenomenon. No turbidity occurs. Therefore, only a completely transparent state of the liquid crystal in the information display state and a completely colored state of the dichroic dye in the non-display state can be obtained, and a clear display can be obtained.

[Brief explanation of drawings]

第１図は、二色性色素を添加したコレステリツ
ク―ネマチツク相転移を生じる液晶を、ラビング
による平行配向処理を施した２枚の相対する透明
電極間に挾持した液晶セルの印加実効電圧と透過
率の関係を示すものである。１は領域１、２は領域２、３は領域３を示す。
第２図は、コレステリツク―ネマチツク相転移に
於ける液晶分子の配向状態を示すものである。ａ
は無電界状態、ｂは電界印加状態である。４は透
明電極基板、５は液晶分子、６６は電源を示す。
第３図は、液晶セルに印加される電圧波形の１つ
の例を示している。図中、ONと記したところ
が、電界を印加した表示状態である。７は、30Hz
以上誘電緩和周波数以下の矩形波を示す。 Figure 1 shows the applied effective voltage and transmittance of a liquid crystal cell in which a dichroic dye-added liquid crystal that exhibits a cholesteric-nematic phase transition is sandwiched between two opposing transparent electrodes that have been subjected to parallel alignment treatment by rubbing. This shows the relationship between 1 indicates area 1, 2 indicates area 2, and 3 indicates area 3.
FIG. 2 shows the alignment state of liquid crystal molecules during cholesteric-nematic phase transition. a
b is a state in which no electric field is applied, and b is a state in which an electric field is applied. 4 is a transparent electrode substrate, 5 is a liquid crystal molecule, and 66 is a power source.
FIG. 3 shows one example of a voltage waveform applied to a liquid crystal cell. In the figure, the area marked ON is the display state in which an electric field is applied. 7 is 30Hz
The above shows a rectangular wave below the dielectric relaxation frequency.

Claims

[Claims]

1. A liquid crystal display device in which a liquid crystal is sealed between a pair of substrates, a transparent electrode is formed on the side of the substrate in contact with the liquid crystal, and the liquid crystal is a liquid crystal that exhibits a cholesteritschnematic phase transition phenomenon having hysteresis with respect to voltage. A dichroic dye is added to the liquid crystal, and when the liquid crystal is in an information display state, a first voltage which is equal to or higher than a critical voltage at which the liquid crystal does not cause hysteresis and exceeds the lighting voltage is applied as an initial voltage. A second voltage lowered to a critical voltage at which the liquid crystal can assume a nematic phase is applied for a period of A liquid crystal display device characterized in that a third voltage is applied to the liquid crystal as a non-lighting voltage.