JP4129724B2 - Liquid crystal display device and electronic apparatus using the same - Google Patents

Description

【００５９】
そして、通常の方法により９０°ツイストのＴＮセルを作製して上記ゲストホスト液晶を注入した後、上基板及び下基板の外面側に日東電工社製の偏光板ＳＥＧ１４２５ＤＵ（商品名、偏光度：９９．９％）を貼り付けた。この際、上下の偏光板の透過軸は、それぞれ上基板の配向膜のラビング方向，下基板の配向膜のラビング方向に平行となるようにしている。
【００６０】
なお、セルギャップは、式（３）により、液晶層のリタデーションΔｎｄがＧ（緑）の光に対して最適となる大きさとし、液晶セルＣ１，Ｃ２のセル厚（液晶層厚）をそれぞれ４．０４μｍ，４．１６μｍとなるように構成した（表２参照）。すなわち、液晶セルＣ１，Ｃ２のリタデーションΔｎｄはそれぞれ４８５ｎｍ，４９９ｎｍとなり、５５０ｎｍ付近の波長の光に対して透過表示時のコントラストが最大となるようになっている。
【００６１】
また、各液晶セルＣ１，Ｃ２について、上記液晶に混合するトータルの色素濃度ｃをそれぞれ３．６ｗｔ％，３．３ｗｔ％とし、光の吸収量（簡単のため、色素濃度ｃ×液晶層厚みｄとして計算している）が各液晶セルＣ１，Ｃ２についてそれぞれ１４．５，１３．７となるようにしている。
【００６２】
【表２】

【００６３】
さらに、図７に示すように、下基板１３と下偏光板２８との間に配置する位相補償層６０として、ポリカーボネイト製の二枚の位相差フィルム（第１位相差板６１，第２位相差板６２）を使用した。これらの第１位相差板６１，第２位相差板６２には、５９０ｎｍの波長の光に対する位相差がそれぞれ４６０ｎｍ，２２０ｎｍのものを用いている。
【００６４】
また、図７に示すように、第１位相差板６１，第２位相差板６２の遅相軸を、下偏光板２８の透過軸に対してそれぞれθ１，θ２だけ傾けて配置している。この角度θ１，θ２は、液晶セルＣ１についてはそれぞれ３２°，３３°、液晶セルＣ２についてはそれぞれ２７°，３８°とし、液晶の旋光による波長分散をより良く補償するとともに下偏光板２８から入射した直線偏光の偏光面を９０°だけ回転させるようにしている。なお、二色性色素の吸収によって偏光状態が変化するため、色素濃度の異なる液晶セルＣ１と液晶セルＣ２とでは、光学特性が最適となるθ１，θ２の条件が若干異なっている。
【００６５】
また、式（１）においてＮを１とした効果を調べるために、液晶層のリタデーションΔｎｄが式（１）でＮを２とした式に基づいて設定される二種類の比較用のセル（比較セルＤ１，比較セルＤ２）を作製した。比較セルＤ１，Ｄ２の液晶層はそれぞれ１０．８μｍ，１１．２μｍとされ、いずれもＧ（緑）の光に対して最適な透過率が得られるようになっている。また、比較セルＤ１の液晶は二色性色素を混合しない通常のＴＮセルとし、比較セルＤ２では色素濃度ｃを１．３ｗｔ％として光の吸収量が液晶セルＣ１と略同一となるように構成している。
【００６６】
さらに、位相補償層６０の有無による透過表示時のコントラストの変化について調べるために、位相補償層６０を設けない比較用のセル（第３比較セルＤ３，第４比較セルＤ４）を作製した。すなわち、比較セルＤ３，Ｄ４は、それぞれ液晶セルＣ１，Ｃ２の構成において、第１位相差板及び第２位相差板を省いた構成となっている。なお、下基板１３に入射する光の偏光方向が上記液晶セルＣ１，Ｃ２と同一となるように、これらの比較セルＤ３，Ｄ４では、下偏光板２８の透過軸を下基板１３の配向膜のラビング方向に対して直交するように配置している。
【００６７】
なお、上記の各セルＣ１，Ｃ２，Ｄ１〜Ｄ４において、反射特性と透過特性とを独立に調べるために、全面反射層を有するセルと反射層が全くないセルとの二種類を作製した。
そして、輝度計を用いてこれらのセルの反射特性及び透過特性を評価した。なお、輝度計はセル正面に配置され、セルの表示面から垂直に出射された光の輝度を測定するようになっている。そして、測定値に基づいて反射率及び透過率を算出している。
【００６８】
〔階調反転に関する特性評価〕
まず、階調反転に対する効果を調べるために、反射層を有するセルを用いて０〜５Ｖまで電圧を印加しながら反射率を測定した。その結果、図１１に示すように、比較セルＤ１では、印加電圧が０Ｖ〜１．３Ｖの範囲では反射率に変化はなく、１．３Ｖ付近で一旦増大した後、１．５Ｖ付近で反射率は減少し始めた。そして、印加電圧が２．１Ｖ付近で反射率は増大に転じ、印加電圧が３．４Ｖ以降で反射率は略一定の値となった。
【００６９】
本来、二色性色素を含まない比較セルＤ１の構成では、印加電圧の有無に関わらず常に明表示を示すはずであり、ここでの反射率の変化は、純粋にリタデーションΔｎｄと旋光性との関係として説明される。つまり、１．５Ｖ〜２．１Ｖ印加時の反射率の落ち込みは、電圧印加に伴う旋光性の低下によって反射光が一部上偏光板に吸収されたことに起因していると考えられる。なお、印加電圧１．３Ｖ〜１．５Ｖでの反射率の増大は実効的なΔｎｄが式（２）を満たすような旋光性の高い状態になっていることに起因すると思われる。
【００７０】
比較セルＤ２では、比較セルＤ１が示す反射率のカーブと比較して、１．８Ｖ〜３Ｖ印加時に反射率に落ち込みが見られる。落ち込みが見られた印加電圧の領域は上記比較セルＤ１において反射率の低下が見られたのと略同じ電圧領域であり、ここでの反射率の落ち込みも旋光性の消失の過程で生じる階調反転現象として説明できる。
これに対して、液晶セルＣ１では、電圧の増加に伴って反射率は増大し続け、階調反転のない良好な反射特性が得られた。また、５Ｖ印加時の反射率は２５％程度となり、色素を混合した分反射率は低下しているものの、許容される範囲と考えられる。
【００７１】
〔透過率及びコントラストに関する特性評価〕
次に、透過表示における透過率及びコントラストの評価を行なうために、反射層のないセルを用いて、０〜５Ｖまで電圧を印加しながら透過率を測定した。その結果、図１２に示すように、比較セルＤ２，Ｄ３に関しては、４Ｖ印加時（明表示）に２８％程度の透過率を示すものの、０Ｖ（暗表示）の透過率は０．５％程度あり、コントラストは５５程度となった（表３参照）。
【００７２】
【表３】

【００７３】
これに対して、液晶セルＣ１では４Ｖ印加時（明表示）の透過率と０Ｖ（暗表示）の透過率とはそれぞれ２５．１％，０．０６５％となり、比較セルＤ２に比べて暗表示の輝度（光り抜け）が一桁程度改善された。これにより、コントラストは３８６に向上し、透過表示として十分な表示特性が得られた。また、液晶セルＣ１では位相補償層を設けたことと色素を混合したこととにより明表示における透過率は若干低下しているが、それほど大幅な低下ではなく、許容できる範囲である。また、図１６に示したような円偏光を利用する従来の半透過反射型液晶表示装置の場合には、反射部をなくして画素全体を透過部にしたとしても、最大２５％の透過率しか得られないことと比較すると、リサイクル光の利用により明るい表示が得られたと考えられる。
【００７４】
色素濃度を薄くしたセルＣ２，Ｄ４についても上記と同様の測定を行なった。その結果、図１３に示すように、４Ｖ印加時（明表示）の透過率はセルＣ２，Ｄ４についてそれぞれ２６．７３％，２８．１７％となり、色素濃度の濃い上記セルＣ１，Ｄ３に比べていずれも１．５％程度の改善が見られた（表３参照）。なお、セルＣ２については０Ｖ（暗表示）の透過率が０．０８８％と若干高くなったため、コントラストは３０４に低下したが、十分許容できる範囲と考えられる。
【００７５】
また、上述の暗表示における光抜けの改善効果を詳しく調べるために、分光透過率測定を行った。その結果、図１４に示すように、液晶セルＣ１では可視光（４００ｎｍ〜７００ｎｍ）の広い波長範囲で波長分散の補償された均一な透過率が得られることがわかる。これにより、液晶セルＣ１では透過特性が可視光の略全範囲で最適化され、比較セルＤ３に比べて光抜けが大幅に低減された極めて良好な暗状態が得られることがわかる。
【００７６】
セルＣ２，Ｄ４についても同様の測定を行った結果、図１５に示すように、いずれのセルＣ２，Ｄ４についても色素濃度の濃い上記セルＣ１，Ｄ３に比べて若干透過率が増大している。これは、上記セルＣ１，Ｄ３では位相補償層によっても補償しきれずに液晶層に楕円偏光として入射した光は二色性色素によってある程度吸収されていたのに対して、色素濃度の薄いセルＣ２，Ｄ４ではこのような効果が弱まったためと考えられる。
【００７７】
【発明の効果】
以上、詳細に説明したように、本発明の構成によれば、反射表示では液晶による光の旋光性と二色性色素による光の吸収を、透過表示では液晶による旋光性のみを利用することによって、反射表示及び透過表示の表示特性を共に向上させることができる。
また、透過表示部と反射表示部との同時刻における液晶の配向状態は基本的に同じでよく、複雑な構成を必要としないため、製造を容易にすることができる。
さらに、透過表示領域に液晶層の旋光による波長分散を補償する位相補償層が設けられているため、透過表示において高いコントラストを得ることができる。
【図面の簡単な説明】
【図１】 本発明の一実施形態の液晶表示装置の概略構成を示す断面図である。
【図２】 同、液晶表示装置の表示原理を説明するための図であって、表示原理の説明に必要な構成要素のみを示す図である。
【図３】 同、液晶表示装置の表示原理を説明するための図であって、表示原理の説明に必要な構成要素のみを示す図である。
【図４】 同、液晶表示装置の表示原理を説明するための図であって、表示原理の説明に必要な構成要素のみを示す図である。
【図５】 同、液晶表示装置の表示原理を説明するための図であって、表示原理の説明に必要な構成要素のみを示す図である。
【図６】 同、液晶表示装置の表示原理を説明するための図であって、表示原理の説明に必要な構成要素のみを示す図である。
【図７】 本発明の実施例の液晶表示装置の概略斜視図であり、構成部材の光学軸の配置を示す図である。
【図８】 本発明に係る電子機器の一例を示す斜視図である。
【図９】 本発明に係る電子機器の他の例を示す斜視図である。
【図１０】 本発明に係る電子機器のさらに他の例を示す斜視図である。
【図１１】 本発明の実施例の液晶表示装置における反射率を示す図である。
【図１２】 本発明の実施例の液晶表示装置における透過率を示す図である。
【図１３】 本発明の実施例の液晶表示装置における透過率を示す図である。
【図１４】 本発明の実施例の液晶表示装置における暗表示の分光透過率を示す図である。
【図１５】 本発明の実施例の液晶表示装置における暗表示の分光透過率を示す図である。
【図１６】 従来の液晶表示装置の一例の概略構成を示す断面図である。
【図１７】 同、液晶表示装置の表示原理を説明するための図であって、表示原理の説明に必要な構成要素のみを示す図である。
【符号の説明】
１０ 液晶表示装置
１１ 液晶セル
１２ バックライト
１３ 下基板
１４ 上基板
１６ 液晶層
１８ 半透過反射層
１８ａ 開口部
２４，３３ 配向膜
２８ 下偏光板
３６ 上偏光板
５０ カラーフィルタ
６０ 位相補償層
Ｒ 反射表示領域
Ｔ 透過表示領域
Ｓ 二色性色素分子
Ｌ 液晶分子[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device and an electronic apparatus, and more particularly to a transflective liquid crystal display device that can display a sufficiently bright display not only in a reflection mode but also in a transmission mode. It is.
[0002]
[Prior art]
Conventionally, a liquid crystal display device has been proposed in which external light is used in a bright place in the same manner as a normal reflective liquid crystal display device, and in a dark place, the display can be visually recognized by an internal light source. This liquid crystal display device adopts a display method that has both a reflection mode and a transmission mode, and by switching to one of the display methods according to the surrounding brightness, even when the surroundings are dark while reducing power consumption Clear display can be performed. Hereinafter, in this specification, this type of liquid crystal display device is referred to as a “transflective liquid crystal display device”. As one form of the transflective liquid crystal display device, a reflective film in which an opening for light transmission is formed in a metal film such as aluminum is provided on the inner surface of the lower substrate, and this reflective film functions as a transflective film. Proposed. In the present specification, the liquid crystal side surface of each substrate constituting the liquid crystal display device is referred to as an “inner surface”, and the opposite surface is referred to as an “outer surface”.
[0003]
FIG. 16 shows an example of a transflective liquid crystal display device using this type of transflective film.
In this liquid crystal display device 100, a liquid crystal layer 103 is sandwiched between a pair of glass substrates 101 and 102, and a transflective layer 104 having an opening 104 a on the inner surface of the lower substrate 101, a transparent electrode 108, and an alignment film 107. Is formed. On the other hand, a transparent electrode 112 and an alignment film 113 are formed on the inner surface of the upper substrate 102.
[0004]
Further, on the outer surface side of the upper substrate 102, two retardation plates 118 and 119 (these retardation plates function as a quarter-wave plate 120) and an upper polarizing plate 114 are disposed, and the outer surface of the lower substrate 101. On the side, a quarter-wave plate 115 and a lower polarizing plate 116 are provided. Further, a backlight 117 including a light source 122, a light guide plate 123, a reflection plate 124 and the like is disposed below the lower polarizing plate 116. The quarter-wave plates 115 and 120 can convert linearly polarized light into substantially circularly polarized light in a certain wavelength band.
[0005]
The display principle of the transflective liquid crystal display device 100 shown in FIG. 16 will be described below with reference to FIG. Note that FIG. 17 shows only the components necessary for the explanation of the display principle among the components of the liquid crystal display device of FIG.
First, when performing dark display, a voltage is applied to the liquid crystal layer 103 (turned on) so that there is no phase difference in the liquid crystal layer 103. In the reflective display, light incident from above the upper polarizing plate 114 passes through the upper polarizing plate 114 and then becomes linearly polarized light perpendicular to the paper surface when the transmission axis of the upper polarizing plate 114 is perpendicular to the paper surface. After passing through the / 4 wavelength plate 120, it becomes counterclockwise circularly polarized light and passes through the liquid crystal layer 103. Then, when reflected on the surface of the semi-transmissive reflective layer 104, the rotation direction is reversed to become clockwise circularly polarized light, transmitted through the liquid crystal layer 103, transmitted through the quarter wavelength plate 120, and then linearly polarized light parallel to the paper surface. Become. Here, since the upper polarizing plate 114 has a transmission axis perpendicular to the paper surface, the reflected light is absorbed by the upper polarizing plate 114 and does not return to the outside (observer side), resulting in dark display.
[0006]
On the other hand, in transmissive display, the light emitted from the backlight 117 is linearly polarized parallel to the paper after passing through the lower polarizing plate 116 when the transmission axis of the lower polarizing plate 116 is parallel to the paper. After passing through the quarter-wave plate 115, it becomes clockwise circularly polarized light and passes through the liquid crystal layer 103. Then, after the clockwise circularly polarized light passes through the quarter-wave plate 120, it becomes linearly polarized light parallel to the paper surface, and is absorbed by the upper polarizing plate 114 as in the reflection mode, resulting in dark display.
[0007]
Next, in the case of performing bright display, the voltage is not applied to the liquid crystal layer 103 (off state), and the phase difference due to the birefringence effect in the liquid crystal layer 103 at this time is set to ¼ wavelength. Keep it. In the reflective display, the counterclockwise circularly polarized light incident from above the upper polarizing plate 114 and transmitted through the upper polarizing plate 114 and the quarter-wave plate 120 is transmitted through the liquid crystal layer 103 and is transmitted through the semi-transmissive reflective layer 104. When the light reaches the surface, it becomes linearly polarized light parallel to the paper surface. Then, when the light is reflected by the surface of the semi-transmissive reflective layer 104 and transmitted through the liquid crystal layer 103, the light is again counterclockwise circularly polarized light, and after passing through the quarter wavelength plate 120, becomes linearly polarized light perpendicular to the paper surface. Here, since the upper polarizing plate 114 has a transmission axis perpendicular to the paper surface, the reflected light passes through the upper polarizing plate 114 and returns to the outside (observer side), thereby providing a bright display.
[0008]
On the other hand, in the transmissive display, the clockwise circularly polarized light incident from the backlight 117 and transmitted through the lower polarizing plate 116 and the quarter-wave plate 115 is a straight line perpendicular to the paper surface when transmitted through the liquid crystal layer 103. It becomes polarized light. When the linearly polarized light perpendicular to the paper plane is transmitted through the quarter-wave plate 120, it becomes counterclockwise circularly polarized light. Since the upper polarizing plate 114 has a transmission axis perpendicular to the paper surface, Only the linearly polarized light perpendicular to the paper surface is transmitted through the upper polarizing plate 114 and becomes bright display.
[0009]
[Problems to be solved by the invention]
As described above, according to the liquid crystal display device 100 shown in FIGS. 16 and 17, although the display can be visually recognized regardless of the presence or absence of external light, the brightness of the transmissive display is insufficient compared to the reflective display. was there.
One of the causes is that, as described in the explanation of the display principle with reference to FIG. 17, in the case of performing bright display by transmissive display, it is transmitted through the liquid crystal layer 103 and the quarter-wave plate 120 and is incident on the upper polarizing plate 114. This is because almost half of the circularly polarized light is absorbed by the upper polarizing plate 114 and does not contribute to display.
[0010]
Another cause is that light emitted from the backlight 117 does not pass through the opening 104a of the transflective layer 104 and is reflected by the back surface of the transflective layer 104 in the rotation direction. Is inverted to become counterclockwise circularly polarized light, and when it passes through the quarter-wave plate 115, it becomes linearly polarized light perpendicular to the paper surface. The linearly polarized light is absorbed by the lower polarizing plate 116 having a transmission axis parallel to the paper surface. That is, of the light emitted from the backlight 117, the light that has not passed through the opening 104 a passes through the lower polarizing plate 116 without being absorbed by the lower polarizing plate 116 and returns to the backlight 117. For example, this return light is emitted again toward the liquid crystal cell, but actually, after being reflected by the back surface of the transflective layer 104, almost all of the light is absorbed by the lower polarizing plate 116 and cannot be reused. is there.
[0011]
By the way, a liquid crystal to which a dichroic dye is added, that is, a so-called guest-host liquid crystal is well known. When this guest-host liquid crystal is used in a transflective liquid crystal display device, light passes through the liquid crystal layer twice in the reflective display portion, whereas light passes through the liquid crystal layer in the transmissive display portion. Since it is only once, the amount of light absorbed by the dichroic dye differs between the reflective display portion and the transmissive display portion. Therefore, when the dye density is adjusted so that a sufficient contrast can be obtained in the transmissive display, only a reflective display with a very low reflectance can be obtained. On the contrary, when the dye density is adjusted so that sufficient brightness and appropriate contrast can be obtained in the reflective display, there is a problem that the contrast becomes very low in the transmissive display.
[0012]
As described above, when the guest-host liquid crystal is applied to a transflective liquid crystal display device, it is difficult to obtain good optical characteristics in both reflective display and transmissive display. A method for solving this problem is disclosed in Japanese Patent Application Laid-Open No. 11-242226. However, in this method, it is essential that the liquid crystal alignment state at the same time be different between the reflective display portion and the transmissive display portion. For this reason, there is a drawback that the apparatus configuration is complicated and manufacturing is difficult.
[0013]
The present invention has been made in order to solve the above problems, and in a transflective liquid crystal display device capable of both reflective display and transmissive display, improves display characteristics in both display modes, An object of the present invention is to provide a liquid crystal display device capable of obtaining high contrast in transmissive display. It is another object of the present invention to provide an electronic apparatus including a liquid crystal display unit that improves display characteristics in both display modes of reflection display and transmission display and increases contrast in transmission display.
[0014]
[Means for Solving the Problems]
In order to achieve the above object, a liquid crystal display device of the present invention has a liquid crystal layer sandwiched between a pair of substrates facing each other, and has a transmissive display region and a reflective display region in one dot region. In the reflective liquid crystal display device, a first polarizing plate is provided on the outer surface side of one of the pair of substrates and a second polarizing plate is provided on the outer surface side of the other substrate of the pair of substrates, Between the second polarizing plate and the other substrate, the wavelength dispersion due to the optical rotation of the liquid crystal layer is compensated or relaxed, and the polarization direction of the linearly polarized light incident from the second polarizing plate is changed to that of the other substrate. A phase compensation layer that converts in a direction substantially perpendicular to the alignment direction of liquid crystal molecules adjacent to the inner surface is provided, and the liquid crystal layer includes a liquid crystal composition having a positive dielectric anisotropy mixed with a dichroic dye, The liquid crystal molecules of the liquid crystal layer are the pair of substrates. The substrate is twisted approximately 90 ° in a plane parallel to the substrate surface, and the transmission axis direction of the first polarizing plate and the alignment direction of the liquid crystal molecules adjacent to the inner surface of the one substrate are approximately parallel. And
[0015]
The operation at the time of dark display in the transmission mode of this configuration will be described with reference to FIG. FIG. 2 is a diagram for explaining the principle of the present invention, in which a liquid crystal layer 16 containing a dichroic dye S is sandwiched between upper and lower substrates 14 and 13, and polarizing plates are provided on the outer surface sides of the substrates 14 and 13, respectively. 6 schematically shows a transflective liquid crystal display device in which a transflective layer 18 is formed on the inner surface side of the lower substrate 13.
Here, the liquid crystal molecules L of the liquid crystal layer 16 are twisted by approximately 90 ° in a plane parallel to the substrate surface between the upper substrate 14 and the lower substrate 13 when a non-selection voltage is applied, and on the inner surface side of the upper substrate 14. The alignment direction of the liquid crystal molecules L in contact therewith is substantially parallel to the transmission axis of the upper polarizing plate (first polarizing plate) 36. For comparison, the liquid crystal display device is divided into a left portion where no phase compensation layer is provided and a right portion where the phase compensation layer 60 is interposed between the lower substrate 13 and the lower polarizing plate 28. However, the transmission axis of each lower polarizing plate (second polarizing plate) 28 is arranged at an appropriate angle with respect to the alignment direction of the liquid crystal molecules L in contact with the inner surface side of the lower substrate 13, and polarization of light incident on the liquid crystal layer 16. The direction is substantially perpendicular to the orientation direction.
[0016]
According to this configuration, in the transmissive display, the light that has been transmitted through the lower polarizing plate 28 and becomes linearly polarized light is, due to the phase compensation layer 60, the polarization direction of the liquid crystal molecules L that are in contact with the inner surface of the lower substrate 28. It is converted so as to be substantially vertical (see the right part of FIG. 2). Then, when this light passes through the liquid crystal layer 16, the polarization direction is rotated by 90 ° and becomes almost perpendicular to the transmission axis of the upper polarizing plate 36.
In addition, since the phase of the light is shifted in advance in a direction to compensate or relax the wavelength dispersion due to the optical rotation of the liquid crystal layer 16 before passing through the liquid crystal layer 16, the total amount of light when reaching the upper polarizing plate 36 is increased. The amount of phase shift is smaller than that when the phase compensation layer 60 is not provided (see the left part of FIG. 2). As a result, the polarization state of the light reaching the upper polarizing plate 36 becomes closer to linearly polarized light as compared with the case where the phase compensation layer 60 is not provided, and light is prevented from being lost and a good dark display is obtained.
[0017]
Ideally, the wavelength dispersion due to the optical rotation of the liquid crystal is completely compensated over a wide wavelength range of visible light, so that the upper polarizing plate is reached as shown in the right part of FIG. All of the R, G, and B light is linearly polarized light containing no elliptically polarized light component, and the amount of emitted light can be made zero. Thereby, light omission in dark display can be effectively suppressed, and contrast in transmissive display can be improved.
[0018]
Although not shown, in this configuration, the reflection display uses the optical rotation by the liquid crystal and the light absorption by the dichroic dye S, so that the light of such a dye can be adjusted by adjusting the dye concentration. It is possible to simultaneously improve the display characteristics of both reflective display that performs display using absorption and transmissive display that uses only the optical rotation of light. Further, since circularly polarized light is not used for transmissive display, there is no component absorbed by the upper polarizing plate during bright display, and the transmissive display can be brightened. Furthermore, in the liquid crystal display device of the present invention, the alignment state of the liquid crystal at the same time in the transmissive display unit and the reflective display unit may be basically the same, and a complicated configuration is not required.
[0019]
The liquid crystal display device of the present invention is a transflective liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates facing each other, and a transmissive display region and a reflective display region are included in one dot region. A first polarizing plate is provided on the outer surface side of one substrate of the pair of substrates and a second polarizing plate is provided on the outer surface side of the other substrate of the pair of substrates, Between the second polarizing plate and the other substrate, Compensating or mitigating chromatic dispersion due to optical rotation of the liquid crystal layer , For linearly polarized light (wavelength λ) incident from the second polarizing plate Forms a phase difference of approximately λ And maintains the polarization state of the linearly polarized light The liquid crystal layer includes a liquid crystal composition having a positive dielectric anisotropy mixed with a dichroic dye, and the liquid crystal molecules of the liquid crystal layer are disposed between the pair of substrates. The second polarizing plate is twisted by approximately 90 ° in a plane parallel to the surface, and the transmission axis direction of the first polarizing plate is substantially parallel to the alignment direction of liquid crystal molecules adjacent to the inner surface of the first substrate. And the alignment direction of the liquid crystal molecules adjacent to the inner surface of the other substrate is substantially perpendicular.
[0020]
That is, in this configuration, the transmission axis of the lower polarizing plate is substantially perpendicular to the alignment direction of the liquid crystal molecules in contact with the inner surface of the lower substrate, and the phase difference formed by the phase compensation layer is approximately λ and is incident from the lower polarizing plate. The polarization state of linearly polarized light is maintained. Even with this configuration, the light incident on the liquid crystal layer from the lower polarizing plate has a polarization direction that is substantially perpendicular to the alignment direction of the liquid crystal molecules in contact with the inner surface of the lower substrate, and the phase is wavelength dispersion due to the optical rotation of the liquid crystal. It is possible to make a state shifted in a direction in which is compensated or relaxed. Therefore, the same operational effects as described above can be obtained, and the contrast of transmissive display can be improved.
[0021]
Furthermore, the liquid crystal display device of the present invention is a transflective liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates facing each other, and a transmissive display region and a reflective display region are included in one dot region. A first polarizing plate is provided on the outer surface side of one substrate of the pair of substrates and a second polarizing plate is provided on the outer surface side of the other substrate of the pair of substrates, Between the second polarizing plate and the other substrate, Compensating or mitigating chromatic dispersion due to optical rotation of the liquid crystal layer , For linearly polarized light (wavelength λ) incident from the second polarizing plate A phase compensation layer that forms a phase difference of approximately λ / 2 is provided, and the liquid crystal layer includes a liquid crystal composition having a positive dielectric anisotropy mixed with a dichroic dye, and the liquid crystal molecules of the liquid crystal layer include The pair of substrates is twisted approximately 90 ° in a plane parallel to the substrate surface, and the transmission axis direction of the first polarizing plate and the alignment direction of the liquid crystal molecules adjacent to the inner surface of the one substrate are approximately The angle formed between the slow axis of the phase compensation layer and the alignment direction of the liquid crystal molecules adjacent to the inner surface of the other substrate is θ, and the transmission axis of the second polarizing plate and the other substrate The angle between the alignment direction of the liquid crystal molecules in contact with the inner surface is approximately 2θ.
[0022]
According to this configuration, in the transmissive display, the light that has been transmitted through the lower polarizing plate and becomes linearly polarized light is rotated by the phase compensation layer by 2θ. The direction is substantially perpendicular to the alignment direction of the liquid crystal molecules in contact with the inner surface of the lower substrate. Therefore, this configuration can achieve the same effects as described above, and improve the contrast of transmissive display.
[0023]
The value of θ is preferably about 45 °. According to this configuration, in transmissive display, light that has been transmitted through the lower polarizing plate and converted into linearly polarized light becomes linearly polarized light with the polarization plane rotated by approximately 90 ° when transmitted through the phase compensation layer. Of the linearly polarized light, the light reflected by the back surface of the transflective layer is transmitted through the phase compensation layer, rotated again by 90 ° on the polarization plane, and returned to the lower polarizing plate. At this time, since the polarization direction of the linearly polarized light and the transmission axis of the lower polarizing plate are parallel, the linearly polarized light passes through the lower polarizing plate as it is. For this reason, the light reflected by the transflective layer can be reused to contribute to transmissive display, and a bright display is possible.
[0024]
Moreover, it is preferable to arrange | position a phase compensation layer in an outer surface side rather than a semi-transmissive reflective layer. According to this configuration, a bright display can be obtained without reducing the luminance in the reflective display. Of course, the phase compensation layer may be provided only in the transmissive display region. This configuration does not reduce the brightness of the reflective display.
The retardation value Δnd (Δn: refractive index anisotropy, d: liquid crystal layer thickness) of the liquid crystal layer may satisfy Δnd = 0.866 · λ (λ: 380 nm to 780 nm). According to this configuration, high display quality without gradation inversion can be obtained in reflective display. The basis for Δnd = 0.866 · λ will be described later in the section of [Embodiment of the Invention].
[0025]
The phase compensation layer may be configured as a combination of a plurality of retardation plates. According to this structure, the freedom degree of the member selection at the time of matching retardation of a phase compensation layer with respect to a liquid crystal layer increases.
A color filter may be provided between the upper substrate and the lower substrate. According to this configuration, it is possible to realize a liquid crystal display device capable of clear color display in both reflective display and transmissive display.
An electronic apparatus according to the present invention includes the liquid crystal display device according to the present invention.
According to this configuration, it is possible to provide an electronic apparatus including a liquid crystal display unit that is bright in both reflective display and transmissive display and particularly has high contrast in transmissive display.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, an embodiment of the present invention will be described. FIG. 1 is a cross-sectional view showing a schematic configuration of a liquid crystal display device of the present embodiment, and FIGS. 3 to 6 are diagrams for explaining the display principle. FIG. 8 is a diagram illustrating only components necessary for explaining the display principle, and FIGS. 8 to 10 are diagrams illustrating examples of electronic apparatuses including the liquid crystal display device. This embodiment is an example of an active matrix type transflective color liquid crystal display device. In all the following drawings, the film thicknesses and dimensional ratios of each component are appropriately changed in order to make the drawings easy to see. It is.
[0027]
As shown in FIG. 1, the liquid crystal display device 10 of the present embodiment includes a liquid crystal cell 11 and a backlight 12 (illumination device). The liquid crystal cell 11 has a lower substrate 13 and an upper substrate 14 facing each other, and a dielectric anisotropy obtained by adding a dichroic dye S to a space sandwiched between the upper substrate 14 and the lower substrate 13 is positive. A liquid crystal layer 16 is formed by sealing TN liquid crystal. The backlight 12 is disposed on the rear surface side of the liquid crystal cell 11 (the outer surface side of the lower substrate 13). The dichroic dye S in the present embodiment is added to the liquid crystal and aligned in the same direction as the liquid crystal molecules L. The dichroic dye S is a so-called P-type dichroic dye, and exhibits a maximum absorbance with respect to linearly polarized light parallel to the alignment direction of the liquid crystal molecules L, and is a straight line perpendicular to the alignment direction of the liquid crystal molecules L. Shows minimum absorbance for polarized light.
[0028]
A transflective layer 18 made of a highly reflective metal film such as aluminum, silver, or an alloy thereof is formed on the inner surface side of the lower substrate 13 made of a translucent material such as glass or plastic. The transflective layer 18 is provided with an opening 18a for transmitting the light emitted from the backlight 12 for each dot. Of the formation region of the transflective layer 18, a metal film is actually formed. The existing portion constitutes the reflective display region R, and the opening 18a constitutes the transmissive display region T.
[0029]
A color filter 50 having R (red), G (green), and B (blue) dye layers 51 to 53 is provided on the inner surface side of the lower substrate 13 so as to cover the transflective layer 18. It has been. A pixel electrode 23 made of a transparent conductive film such as ITO (Indium Tin Oxide) is formed on the color filter 50, and an alignment film 24 made of polyimide or the like is laminated so as to cover the pixel electrode 23. A phase compensation layer 60 is provided on the outer surface side of the lower substrate 13, and a lower polarizing plate 28 is provided on the outer surface side of the phase compensation layer 60.
[0030]
For the phase compensation layer 60, a member having a wavelength dispersion substantially opposite to the wavelength dispersion caused by the optical rotation of the liquid crystal layer 16 such as polycarbonate or PVA is used, and the wavelength dispersion characteristics due to the optical rotation of the liquid crystal layer 16 are compensated or relaxed. ing. That is, in the phase compensation layer 60 and the liquid crystal layer 16, the phase shift directions when linearly polarized light is converted into elliptically polarized light are opposite to each other (that is, the rotation directions of the ellipses are opposite to each other), The light that has passed through the lower polarizing plate 28 and has become linearly polarized light is converted into elliptically polarized light whose phase is shifted in a direction that compensates or relaxes the wavelength dispersion caused by the rotation of the liquid crystal layer 16 in advance by the phase compensation layer 60. ing.
[0031]
When this elliptically polarized light is transmitted through the twist-aligned liquid crystal layer 16, the phase thereof is shifted in the opposite direction to the above-described shift direction by the liquid crystal layer 16. Thus, the light reaching the upper polarizing plate 36 can be changed to elliptically polarized light slightly deviated from linearly polarized light.
It is desirable that such chromatic dispersion compensation or relaxation be performed in a wide wavelength region of visible light, but it is not necessarily performed in the entire visible light range, and relaxation is performed in a part of the visible light wavelength region. Even just being done is effective.
[0032]
In addition, the phase compensation layer 60 is configured as a λ / 2 plate that rotates the polarization plane of the linearly polarized light incident from the lower polarizing plate 28 by 90 °, thereby improving the light utilization efficiency of the backlight and enabling a brighter display. Yes. That is, the light emitted from the backlight and transmitted through the lower polarizing plate 28 to become linearly polarized light becomes linearly polarized light whose polarization plane is rotated by approximately 90 ° when transmitted through the phase compensation layer 60. Of the linearly polarized light, the light reflected by the back surface of the transflective layer 18 is transmitted through the phase compensation layer 60, rotated again by 90 ° on the polarization plane, and returned to the lower polarizing plate 28. At this time, since the polarization direction of the linearly polarized light and the direction of the transmission axis of the lower polarizing plate 28 are parallel, the linearly polarized light is transmitted as it is without being absorbed by the lower polarizing plate 28 and returns to the backlight 12. And since it is reflected by the reflecting plate 40 on the lower surface of the backlight 12 and is emitted again toward the liquid crystal cell 11, the light reflected on the back surface of the transflective layer 18 can be reused to contribute to transmissive display. It can be done.
[0033]
The phase compensation layer 60 may be configured by combining a plurality of retardation plates. As a result, the degree of freedom in selecting a member when aligning retardation with the liquid crystal is increased, and chromatic dispersion due to the rotation of the liquid crystal can be easily compensated in a wide wavelength region.
The lower substrate 13 is composed of a pixel switching element such as a TFT, an element substrate on which a data line, a scanning line, etc. are formed. However, the pixel switching element, the data line, the scanning line, etc. are not shown in FIG. To do.
On the other hand, a common electrode 32 made of a transparent conductive film such as ITO and an alignment film 33 made of polyimide or the like are sequentially laminated on the inner surface side of the upper substrate 14 made of a translucent material such as glass or plastic. An upper polarizing plate 36 is provided on the outer surface side of the upper substrate 14.
[0034]
Both the alignment films 33 and 24 on the upper substrate 14 side and the lower substrate 13 side are subjected to a horizontal alignment process such as a rubbing process, and the alignment direction of the alignment film 33 on the upper substrate 14 side is a direction parallel to the paper surface in FIG. The alignment direction of the alignment film 24 on the lower substrate 13 side is set to a direction perpendicular to the paper surface in FIG. For this reason, the liquid crystal molecules L and the dichroic dye molecules S of the liquid crystal layer 16 are approximately 90 ° in a plane parallel to the substrate surface between the upper substrate 14 and the lower substrate 13 when a non-selective voltage is applied (voltage off). It is in a twisted state.
The transmission axis direction of the upper polarizing plate 36 is set in a direction parallel to the paper surface in FIG. 1, and the transmission axis direction of the lower polarizing plate 28 is set in a direction perpendicular to the paper surface in FIG. That is, the transmission axis direction of the upper polarizing plate 36 and the alignment direction of the liquid crystal molecules L in contact with the inner surface of the upper substrate 14 are substantially parallel, and the transmission axis direction of the lower polarizing plate 28 and the liquid crystal molecules L in contact with the inner surface of the lower substrate 13. Is substantially parallel to the orientation direction.
[0035]
Further, the retardation Δnd of the liquid crystal layer 16 (Δn: refractive index anisotropy of the liquid crystal layer 16, d: thickness of the liquid crystal layer) is expressed as follows: λ is the wavelength of visible light passing through the liquid crystal layer 16, and N is a natural number. It is set so as to satisfy Expression (2).
Δnd = λ / 2 · (4N ² -1) ^0.5 ... (1)
[0036]
Expression (1) is generally known as a technique for minimizing the amount of transmitted light when the voltage is turned off in transmissive display, whereby high contrast can be obtained. In addition, when Δnd is large, when the voltage is gradually applied to the liquid crystal layer from the state where no voltage is applied, a phenomenon in which the display once becomes bright and then becomes dark again (gradation inversion phenomenon) is observed. Therefore, in the liquid crystal display device of this embodiment, the value of N is set to 1 so that the retardation Δnd of the liquid crystal layer 16 satisfies the following formula (2).
Δnd = 0.866λ (2)
[0037]
In other words, in order for TN liquid crystal to fully exhibit optical rotation, Δnd needs to satisfy the following Morgan condition (3), but in the process where effective Δnd decreases with voltage application, Since the propagating light is not sufficiently rotated and becomes elliptically polarized light, the light deviated from the polarization axis of the polarizing plate is partially absorbed by the polarizing plate and becomes dark.
Δnd> 2λ (3)
Such a gradation reversal phenomenon occurs even when the display is viewed from the front, and particularly appears at the time of reflective display in which light passes through the liquid crystal layer twice, which causes a reduction in visibility. In particular, when the effective Δnd at the same voltage is large, the degree of elliptically polarized light increases, and the drop in brightness at the time of gradation inversion increases. By minimizing the value of N, the amount of decrease in luminance due to such gradation inversion is minimized. In addition, since the liquid crystal layer thickness d is reduced, effects such as high luminance, high speed response, and low threshold voltage, which are found in a normal TN liquid crystal, can be obtained.
[0038]
The value of Δnd has a certain width with λ being a visible light wavelength range of 380 nm to 780 nm, and is set to an optimum value based on required specifications such as contrast. For example, high contrast can be obtained by matching λ in the above formula (2) with a wavelength of light close to G (green) having high visibility.
The backlight 12 includes a light source 37, a reflection plate 38, and a light guide plate 39, and light transmitted through the light guide plate 39 is transmitted to the liquid crystal cell 11 on the lower surface side (the side opposite to the liquid crystal panel 1) of the light guide plate 39. A reflecting plate 40 for emitting light toward the side is provided.
[0039]
Hereinafter, the display principle of the liquid crystal display device 10 of the present embodiment will be described with reference to FIGS.
First, when performing dark display in the reflection mode (see FIG. 3), the liquid crystal layer 16 is not applied with a voltage (non-selection voltage application state), and the liquid crystal molecules L and the dichroic dye molecules S are placed between the upper and lower substrates. In this state, the twist orientation is approximately 90 °. Light incident from above the upper polarizing plate 36 becomes linearly polarized light parallel to the paper surface after passing through the upper polarizing plate 36 because the transmission axis of the upper polarizing plate 36 is parallel to the paper surface.
[0040]
The linearly polarized light rotates while being absorbed by the dichroic dye molecule S along the twist of the liquid crystal molecule L, reaches the transflective layer 18 and is reflected. While being absorbed by the molecule S, it rotates and returns. At this time, the R and B lights transmitted through the dye layers 51 to 53 become elliptically polarized light slightly deviated from linearly polarized light due to the wavelength dispersion caused by the rotation of the liquid crystal layer 16. Therefore, such an elliptically polarized component is sufficiently absorbed by the dichroic dye S and a good dark display can be obtained.
[0041]
Next, when bright display is performed in the reflection mode (see FIG. 4), a voltage is applied to the liquid crystal layer 16 (selection voltage application state), and the liquid crystal molecules L and the dichroic dye molecules S are placed on the substrate surface. It is assumed that it stands up in a substantially normal direction. In this case, the linearly polarized light parallel to the paper surface incident from above the upper polarizing plate 36 is hardly absorbed by the dichroic dye molecules S during the reciprocation of the liquid crystal layer 16, and does not rotate. Return to 36. Therefore, since this light passes through the upper polarizing plate 36 and returns to the outside (observer side), a bright display is obtained.
[0042]
On the other hand, when dark display is performed in the transmission mode (see FIG. 5), the alignment of the liquid crystal molecules L and the dichroic dye molecules S is set in the same manner as in the dark display in the reflection mode. The light incident from the backlight 12 passes through the lower polarizing plate 28 and then becomes linearly polarized light (that is, R, G, and B linearly polarized light) perpendicular to the paper surface, passes through the phase compensation layer 60 and passes through the polarization surface. It is rotated 90 °. Further, when the R, G, and B linearly polarized light passes through the phase compensation layer 60, the phase is shifted in a direction that compensates or relaxes the chromatic dispersion caused by the rotation of the liquid crystal, and the R, B, linearly polarized light is linearly polarized light. Are converted to elliptically polarized light that are opposite to each other and slightly shifted from each other.
[0043]
When these R, G, and B light enters the liquid crystal layer 16, the polarization plane of each of the R, G, and B linearly polarized light is rotated by about 90 ° due to the optical rotation of the liquid crystal, and the rotation of the liquid crystal. Due to the chromatic dispersion, the R and B elliptical polarizations are shifted in phase in the direction opposite to the phase shift due to the phase compensation layer 60, and the total phase shift amount becomes smaller than that without the phase compensation layer 60. As a result, all of the R, G, and B light reaches the upper substrate 14 side as light close to linearly polarized light. Since the polarization direction of these linearly polarized light is orthogonal to the transmission axis direction of the upper polarizing plate 36, it is almost completely absorbed by the upper polarizing plate 36, and an extremely good dark display is obtained.
[0044]
Next, when the bright display is performed in the transmission mode (see FIG. 6), the orientation of the liquid crystal molecules L and the dichroic dye molecules S is substantially perpendicular to the substrate surface as in the case of the bright display in the reflection mode. The state of orientation is set. The light incident from the backlight 12 passes through the lower polarizing plate 28 and then becomes linearly polarized light (that is, R, G, and B linearly polarized light) perpendicular to the paper surface, passes through the phase compensation layer 60 and passes through the polarization surface. It is rotated 90 °. In addition, when the R, G, and B linearly polarized light passes through the phase compensation layer 60, the G polarization state does not change, and the R, B linearly polarized light is slightly shifted from the linearly polarized light. Converted to polarized light.
[0045]
The R, G, and B light passes through the liquid crystal layer 16 that has lost its optical rotation, and passes through the upper polarizing plate 36 having a transmission axis parallel to the polarization direction, thereby providing a bright display. At this time, since the R and B lights contain an elliptically polarized component, they are slightly absorbed by the dichroic dye S and the upper polarizing plate 36. However, a decrease in luminance due to this hardly causes a problem in display.
Of the linearly polarized light that passes through the lower polarizing plate 28 and is parallel to the paper surface, the light reflected by the back surface of the transflective layer 18 passes through the phase compensation layer 60 and rotates again by 90 °. The light returns to the backlight 12 without being absorbed by the polarizing plate 28. Then, the light is reflected by the reflecting plate 40 on the lower surface of the backlight 12 and emitted again toward the liquid crystal cell 11 to be reused.
[0046]
In the liquid crystal display device 10 of the present embodiment, both the optical rotatory power of the liquid crystal and the absorption of the light by the dichroic dye are used in the reflective display, and only the optical rotatory power of the liquid crystal is used in the transmissive display. Thus, the display characteristics of both the reflective display and the transmissive display can be independently improved. In other words, the reflection display uses the guest-host mode, and the contrast is adjusted by the addition amount of the dichroic dye, while the transmissive display uses only the optical rotation of the light due to the twist of the liquid crystal alignment, regardless of the dichroic dye. Since the TN mode is used, a high contrast can be easily obtained independently of the contrast of the reflective display.
[0047]
The addition amount of the dichroic dye S is preferably smaller than that in the normal guest-host mode from the viewpoint of improving the brightness in the reflective display, and the brightness of the bright display from the viewpoint of improving the contrast in the transmissive display. It is preferable that the amount is as long as the thickness is not impaired. The reason for this is that, in the case of the present embodiment, in the reflective display, not only the absorption by the dye is used, but also the optical rotation of the light of the liquid crystal is used together. This is because if there are many dyes, the amount of absorption in bright display increases even if the molecules are vertically aligned, and the brightness of bright display decreases in both reflective display and transmissive display.
[0048]
On the other hand, in transmissive display, when performing dark display, elliptically polarized light that is slightly deviated from linearly polarized light without being fully compensated for chromatic dispersion by the phase compensation layer 60 is absorbed by the dichroic dye S, and light loss in dark display is lost. This is because it can be effectively prevented. For this reason, the addition amount of the dichroic dye S is set to an optimum value in accordance with required specifications such as brightness and contrast.
[0049]
Further, in the liquid crystal display device 10 of the present embodiment, since circularly polarized light is not used for transmissive display, there is no component absorbed by the upper polarizing plate 36 during bright display, and on the back side of the transflective layer 18 in the reflective display region R. Since there is no component in which the reflected light is absorbed by the lower polarizing plate 28, the light can be reused and the transmissive display can be brightened.
Furthermore, in the liquid crystal display device of the present embodiment, the alignment state of the liquid crystal molecules at the same time in the transmissive display region T and the reflective display region R may be basically the same, and a complicated configuration is not required. Easy.
[0050]
In addition, since the liquid crystal layer thickness is set so that the retardation value Δnd of the liquid crystal layer 16 satisfies the above formula (3), in the reflective display, a display with excellent visibility without gradation inversion can be obtained. In transmissive display, a bright and high-contrast display can be obtained.
Further, in the transmissive display, the wavelength dispersion due to the rotation of the liquid crystal layer 16 is compensated by the phase compensation layer 60, so that the brightness of the dark display can be further reduced and the contrast can be greatly improved.
[0051]
[Electronics]
An example of an electronic apparatus including the liquid crystal display device of the above embodiment will be described.
FIG. 8 is a perspective view showing an example of a mobile phone. In FIG. 8, reference numeral 1000 denotes a mobile phone body, and reference numeral 1001 denotes a liquid crystal display unit using the liquid crystal display device of the above embodiment.
[0052]
FIG. 9 is a perspective view showing an example of a wristwatch type electronic apparatus. In FIG. 9, reference numeral 1100 indicates a watch body, and reference numeral 1101 indicates a liquid crystal display unit using the liquid crystal display device of the above embodiment.
[0053]
FIG. 10 is a perspective view showing an example of a portable information processing apparatus such as a word processor or a personal computer. In FIG. 10, reference numeral 1200 denotes an information processing apparatus, reference numeral 1202 denotes an input unit such as a keyboard, reference numeral 1204 denotes an information processing apparatus main body, and reference numeral 1206 denotes a liquid crystal display unit using the liquid crystal display device of the above embodiment.
[0054]
Since the electronic apparatus shown in FIGS. 8 to 10 includes a liquid crystal display unit using the liquid crystal display device of the above embodiment, a bright and excellent display can be obtained regardless of the reflection mode and the transmission mode. An electronic device having a display portion with high contrast in transmissive display can be realized.
[0055]
The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, the present invention is not limited to the active matrix transflective color liquid crystal display device as in the above embodiment, but can also be applied to a passive matrix method, a dot matrix method, and a monochrome display liquid crystal display device. is there.
Further, the phase compensation layer 60 is not necessarily provided at a position between the lower polarizing plate 28 and the lower substrate 13, and may be provided in the transmissive display region.
[0056]
【Example】
In order to demonstrate the effect of the present invention, the inventors actually manufactured a liquid crystal display device having a configuration according to the present invention, and measured transmittance, reflectance, and contrast. The results are reported below.
[0057]
In this example, two types of liquid crystal cells C1 and C2 with different dye concentrations c (wt%) were produced.
In manufacturing the liquid crystal cells C1 and C2, a liquid crystal composition having a positive dielectric anisotropy having a small amount of a chiral substance added to MJ96411 (trade name, manufactured by Merck & Co., Inc.) was used. The refractive index anisotropy Δn of this liquid crystal composition is 0.12 with respect to light having a wavelength of 589 nm.
Further, as the dichroic dye, four kinds of dyes (manufactured by Mitsubishi Chemical Corporation) shown in Table 1 below were used and mixed at the mixing ratio shown in Table 1 to obtain a black dye. And this black pigment | dye was mixed with the said liquid crystal by predetermined | prescribed density | concentration c (wt%), and it was set as the guest host liquid crystal.
[0058]
[Table 1]

[0059]
Then, a 90 ° twisted TN cell was prepared by a normal method and the guest host liquid crystal was injected. Then, a polarizing plate SEG1425DU (trade name, polarization degree: 99 manufactured by Nitto Denko Corporation) was formed on the outer surface side of the upper substrate and the lower substrate. 9%). At this time, the transmission axes of the upper and lower polarizing plates are parallel to the rubbing direction of the alignment film on the upper substrate and the rubbing direction of the alignment film on the lower substrate, respectively.
[0060]
It should be noted that the cell gap is set to a size at which the retardation Δnd of the liquid crystal layer is optimal for G (green) light according to the equation (3), and the cell thickness (liquid crystal layer thickness) of the liquid crystal cells C1 and C2 is 4. It comprised so that it might become 04 micrometers and 4.16 micrometers (refer Table 2). That is, the retardations Δnd of the liquid crystal cells C1 and C2 are 485 nm and 499 nm, respectively, so that the contrast at the time of transmissive display is maximized with respect to light having a wavelength near 550 nm.
[0061]
Further, for each of the liquid crystal cells C1 and C2, the total dye concentration c mixed with the liquid crystal is 3.6 wt% and 3.3 wt%, respectively, and the amount of light absorption (dye concentration c × liquid crystal layer thickness d for simplicity). However, the liquid crystal cells C1 and C2 are 14.5 and 13.7, respectively.
[0062]
[Table 2]

[0063]
Further, as shown in FIG. 7, two retardation films (a first retardation plate 61 and a second retardation film) made of polycarbonate are used as a phase compensation layer 60 disposed between the lower substrate 13 and the lower polarizing plate 28. A plate 62) was used. As the first retardation plate 61 and the second retardation plate 62, those having phase differences of 460 nm and 220 nm with respect to light having a wavelength of 590 nm are used.
[0064]
Further, as shown in FIG. 7, the slow axes of the first retardation plate 61 and the second retardation plate 62 are inclined with respect to the transmission axis of the lower polarizing plate 28 by θ1 and θ2, respectively. The angles θ1 and θ2 are 32 ° and 33 ° for the liquid crystal cell C1 and 27 ° and 38 ° for the liquid crystal cell C2, respectively, so that the wavelength dispersion caused by the rotation of the liquid crystal is better compensated and incident from the lower polarizing plate 28. The plane of polarization of the linearly polarized light is rotated by 90 °. Since the polarization state changes due to absorption of the dichroic dye, the conditions of θ1 and θ2 at which the optical characteristics are optimal are slightly different between the liquid crystal cell C1 and the liquid crystal cell C2 having different dye concentrations.
[0065]
Further, in order to investigate the effect of setting N to 1 in the formula (1), two types of comparison cells (comparison) in which the retardation Δnd of the liquid crystal layer is set based on the formula in which N is set to 2 in the formula (1) Cell D1 and comparative cell D2) were prepared. The liquid crystal layers of the comparison cells D1 and D2 are 10.8 μm and 11.2 μm, respectively, so that the optimum transmittance can be obtained for G (green) light. Further, the liquid crystal of the comparative cell D1 is a normal TN cell in which no dichroic dye is mixed, and the comparative cell D2 is configured such that the dye concentration c is 1.3 wt% and the light absorption amount is substantially the same as that of the liquid crystal cell C1. is doing.
[0066]
Furthermore, in order to investigate the change in contrast during transmissive display depending on the presence or absence of the phase compensation layer 60, comparative cells (third comparison cell D3 and fourth comparison cell D4) without the phase compensation layer 60 were produced. That is, the comparison cells D3 and D4 have a configuration in which the first retardation plate and the second retardation plate are omitted from the configuration of the liquid crystal cells C1 and C2, respectively. In these comparison cells D3 and D4, the transmission axis of the lower polarizing plate 28 is set to the alignment film of the lower substrate 13 so that the polarization direction of the light incident on the lower substrate 13 is the same as that of the liquid crystal cells C1 and C2. They are arranged so as to be orthogonal to the rubbing direction.
[0067]
In each of the cells C1, C2, D1 to D4 described above, two types of cells, a cell having an entire reflective layer and a cell having no reflective layer, were prepared in order to independently examine the reflection characteristics and the transmission characteristics.
Then, the reflection characteristics and transmission characteristics of these cells were evaluated using a luminance meter. The luminance meter is arranged in front of the cell and measures the luminance of light emitted vertically from the display surface of the cell. Then, the reflectance and transmittance are calculated based on the measured values.
[0068]
[Characteristic evaluation regarding gradation inversion]
First, in order to investigate the effect on gradation inversion, the reflectance was measured while applying a voltage from 0 to 5 V using a cell having a reflective layer. As a result, as shown in FIG. 11, in the comparative cell D1, there is no change in the reflectance when the applied voltage is in the range of 0V to 1.3V, and after increasing once near 1.3V, the reflectance near 1.5V. Began to decline. The reflectance started to increase when the applied voltage was around 2.1 V, and the reflectance became a substantially constant value after the applied voltage was 3.4 V.
[0069]
Originally, in the configuration of the comparative cell D1 that does not include the dichroic dye, the bright display should always be displayed regardless of the presence or absence of the applied voltage, and the change in reflectance here is purely between the retardation Δnd and the optical rotation. Explained as a relationship. That is, it is considered that the drop in reflectance when 1.5 V to 2.1 V is applied is due to the fact that the reflected light is partially absorbed by the upper polarizing plate due to a decrease in optical rotation accompanying voltage application. The increase in reflectance at an applied voltage of 1.3 V to 1.5 V is considered to be due to the fact that the optical rotation is high so that the effective Δnd satisfies the formula (2).
[0070]
In the comparison cell D2, a drop in reflectance is observed when 1.8V to 3V is applied, as compared to the reflectance curve indicated by the comparison cell D1. The region of the applied voltage where the drop was observed is substantially the same voltage region as that in which the reflectance was lowered in the comparative cell D1, and the drop in the reflectance here is also a gradation generated in the process of loss of optical rotation. This can be explained as an inversion phenomenon.
On the other hand, in the liquid crystal cell C1, the reflectance continued to increase as the voltage increased, and good reflection characteristics without gradation inversion were obtained. Further, the reflectivity when 5 V is applied is about 25%, and although the reflectivity is decreased by mixing the dye, it is considered to be an allowable range.
[0071]
[Characteristic evaluation regarding transmittance and contrast]
Next, in order to evaluate the transmittance and contrast in the transmissive display, the transmittance was measured using a cell without a reflective layer while applying a voltage from 0 to 5V. As a result, as shown in FIG. 12, regarding the comparative cells D2 and D3, although the transmittance is about 28% when 4V is applied (bright display), the transmittance at 0V (dark display) is about 0.5%. Yes, the contrast was about 55 (see Table 3).
[0072]
[Table 3]

[0073]
On the other hand, in the liquid crystal cell C1, the transmittance when 4V is applied (bright display) and the transmittance at 0V (dark display) are 25.1% and 0.065%, respectively, which is darker than that of the comparative cell D2. The brightness (light loss) has been improved by an order of magnitude. Thereby, the contrast was improved to 386, and display characteristics sufficient for transmissive display were obtained. Further, in the liquid crystal cell C1, the transmittance in the bright display is slightly lowered due to the provision of the phase compensation layer and the mixing of the pigment, but it is not so much reduced and is in an allowable range. Further, in the case of the conventional transflective liquid crystal display device using circularly polarized light as shown in FIG. 16, even if the reflective portion is eliminated and the entire pixel is made a transmissive portion, the transmittance is only 25% at maximum. It is considered that bright display was obtained by using recycled light as compared with the case where it was not obtained.
[0074]
Measurements similar to those described above were performed for the cells C2 and D4 having a reduced pigment concentration. As a result, as shown in FIG. 13, the transmittance when 4V is applied (bright display) is 26.73% and 28.17% for the cells C2 and D4, respectively, which is higher than that of the cells C1 and D3 having a high pigment concentration. In all cases, an improvement of about 1.5% was observed (see Table 3). Note that the transmittance of 0V (dark display) for cell C2 was slightly increased to 0.088%, and thus the contrast decreased to 304, but is considered to be a sufficiently acceptable range.
[0075]
Further, in order to examine in detail the effect of improving light leakage in the above-described dark display, spectral transmittance measurement was performed. As a result, as shown in FIG. 14, it can be seen that the liquid crystal cell C1 can obtain a uniform transmittance with compensated chromatic dispersion in a wide wavelength range of visible light (400 nm to 700 nm). Thus, it can be seen that the liquid crystal cell C1 has a transmission characteristic optimized in substantially the entire range of visible light, and a very good dark state in which light leakage is significantly reduced as compared with the comparative cell D3.
[0076]
As a result of performing the same measurement for the cells C2 and D4, as shown in FIG. 15, the transmittance of the cells C2 and D4 is slightly increased as compared with the cells C1 and D3 having a high pigment concentration. This is because in the cells C1 and D3, light incident as elliptically polarized light on the liquid crystal layer without being compensated by the phase compensation layer was absorbed to some extent by the dichroic dye, whereas the cells C2 and D2 having a low dye concentration were used. It is thought that this effect was weakened in D4.
[0077]
【The invention's effect】
As described above in detail, according to the configuration of the present invention, by utilizing the optical rotatory power of the liquid crystal and the absorption of the light by the dichroic dye in the reflective display, by using only the optical rotatory power of the liquid crystal in the transmissive display. Both the display characteristics of the reflective display and the transmissive display can be improved.
In addition, the alignment state of the liquid crystal in the transmissive display portion and the reflective display portion at the same time may be basically the same, and a complicated configuration is not required, so that manufacturing can be facilitated.
Furthermore, since a phase compensation layer that compensates for wavelength dispersion caused by optical rotation of the liquid crystal layer is provided in the transmissive display region, high contrast can be obtained in transmissive display.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a schematic configuration of a liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is a diagram for explaining the display principle of the liquid crystal display device, and showing only the components necessary for explaining the display principle.
FIG. 3 is a diagram for explaining the display principle of the liquid crystal display device, and showing only the components necessary for explaining the display principle.
FIG. 4 is a diagram for explaining the display principle of the liquid crystal display device, and showing only the components necessary for explaining the display principle.
FIG. 5 is a diagram for explaining the display principle of the liquid crystal display device, and showing only the components necessary for explaining the display principle.
FIG. 6 is a diagram for explaining the display principle of the liquid crystal display device, and showing only the components necessary for explaining the display principle.
FIG. 7 is a schematic perspective view of a liquid crystal display device according to an embodiment of the present invention, and is a diagram illustrating an arrangement of optical axes of constituent members.
FIG. 8 is a perspective view showing an example of an electronic apparatus according to the invention.
FIG. 9 is a perspective view showing another example of an electronic apparatus according to the invention.
FIG. 10 is a perspective view showing still another example of the electronic apparatus according to the invention.
FIG. 11 is a diagram showing reflectance in a liquid crystal display device according to an embodiment of the present invention.
FIG. 12 is a diagram showing transmittance in a liquid crystal display device according to an embodiment of the present invention.
FIG. 13 is a diagram showing the transmittance in the liquid crystal display device according to the embodiment of the present invention.
FIG. 14 is a diagram showing spectral transmittance of dark display in the liquid crystal display device according to the embodiment of the present invention.
FIG. 15 is a diagram illustrating spectral transmittance of dark display in the liquid crystal display device according to the embodiment of the present invention.
FIG. 16 is a cross-sectional view showing a schematic configuration of an example of a conventional liquid crystal display device.
FIG. 17 is a diagram for explaining the display principle of the liquid crystal display device, and showing only the components necessary for explaining the display principle.
[Explanation of symbols]
10 Liquid crystal display device
11 Liquid crystal cell
12 Backlight
13 Lower substrate
14 Upper substrate
16 Liquid crystal layer
18 Transflective layer
18a opening
24, 33 Alignment film
28 Lower polarizing plate
36 Upper Polarizer
50 color filter
60 Phase compensation layer
R Reflective display area
T Transparent display area
S Dichroic dye molecule
L Liquid crystal molecules

Claims (10)

A transflective liquid crystal display device having a liquid crystal layer sandwiched between a pair of substrates facing each other and having a transmissive display region and a reflective display region in one dot region,
A first polarizing plate is provided on an outer surface side of one substrate of the pair of substrates, and a second polarizing plate is provided on an outer surface side of the other substrate of the pair of substrates, and the second polarizing plate and the other substrate And compensating or mitigating chromatic dispersion caused by optical rotation of the liquid crystal layer, and aligning the polarization direction of the linearly polarized light incident from the second polarizing plate with the alignment direction of liquid crystal molecules adjacent to the inner surface of the other substrate. A phase compensation layer that converts in a substantially vertical direction is provided,
The liquid crystal layer includes a liquid crystal composition having a positive dielectric anisotropy mixed with a dichroic dye, and the liquid crystal molecules of the liquid crystal layer are substantially in a plane parallel to the substrate surface between the pair of substrates. A liquid crystal display device, wherein the liquid crystal display device is twisted by 90 °, and the alignment direction of liquid crystal molecules adjacent to the inner surface of the one substrate is substantially parallel to the first polarizing plate. A transflective liquid crystal display device having a liquid crystal layer sandwiched between a pair of substrates facing each other and having a transmissive display region and a reflective display region in one dot region,
A first polarizing plate is provided on an outer surface side of one substrate of the pair of substrates, and a second polarizing plate is provided on an outer surface side of the other substrate of the pair of substrates, and the second polarizing plate and the other substrate And compensates or relaxes the chromatic dispersion caused by the optical rotation of the liquid crystal layer, and forms a phase difference of approximately λ with respect to the linearly polarized light (wavelength λ) incident from the second polarizing plate . A phase compensation layer that maintains the polarization state is provided,
The liquid crystal layer includes a liquid crystal composition having a positive dielectric anisotropy mixed with a dichroic dye, and the liquid crystal molecules of the liquid crystal layer are substantially in a plane parallel to the substrate surface between the pair of substrates. 90 ° twisted, the transmission axis direction of the first polarizing plate and the alignment direction of the liquid crystal molecules adjacent to the inner surface of the first substrate are substantially parallel, and the transmission axis direction of the second polarizing plate and the other A liquid crystal display device characterized by being substantially perpendicular to an alignment direction of liquid crystal molecules adjacent to an inner surface of a substrate. A transflective liquid crystal display device having a liquid crystal layer sandwiched between a pair of substrates facing each other and having a transmissive display region and a reflective display region in one dot region,
A first polarizing plate is provided on an outer surface side of one substrate of the pair of substrates, and a second polarizing plate is provided on an outer surface side of the other substrate of the pair of substrates, and the second polarizing plate and the other substrate between, as well as compensation or relax the wavelength dispersion by the optical rotation of the liquid crystal layer, a phase compensation generally forms a phase difference of lambda / 2 with respect to linearly polarized light which is incident (wavelength lambda) from said second polarizer Layers are provided,
The liquid crystal layer includes a liquid crystal composition having a positive dielectric anisotropy mixed with a dichroic dye, and the liquid crystal molecules of the liquid crystal layer are substantially in a plane parallel to the substrate surface between the pair of substrates. 90 ° twisted, the transmission axis direction of the first polarizing plate and the alignment direction of the liquid crystal molecules close to the inner surface of the one substrate are substantially parallel, and the slow axis of the phase compensation layer and the other substrate The angle between the alignment direction of the liquid crystal molecules adjacent to the inner surface of the substrate is θ, and the angle between the transmission axis of the second polarizing plate and the alignment direction of the liquid crystal molecules in contact with the inner surface of the other substrate is approximately 2θ. A liquid crystal display device.   4. The liquid crystal display device according to claim 3, wherein an angle [theta] formed between the slow axis of the phase compensation layer and the transmission axis of the second polarizing plate is about 45 [deg.].   The liquid crystal display device according to claim 2, wherein the transflective layer is disposed closer to the liquid crystal layer than the phase compensation layer.   The liquid crystal display device according to claim 2, wherein the phase compensation layer is provided only in the transmissive display region.   The retardation value Δnd (Δn: refractive index anisotropy, d: liquid crystal layer thickness) of the liquid crystal layer is Δnd = 0.866 · λ (λ: 380 nm to 780 nm). 7. The liquid crystal display device according to any one of items 6.   The liquid crystal display device according to claim 1, wherein the phase compensation layer is configured as a combination of a plurality of retardation plates.   The liquid crystal display device according to claim 1, wherein a color filter is provided between the pair of substrates.   An electronic apparatus comprising the liquid crystal display device according to claim 1.

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