JP4338059B2 - Liquid crystal composition - Google Patents
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- JP4338059B2 JP4338059B2 JP14970698A JP14970698A JP4338059B2 JP 4338059 B2 JP4338059 B2 JP 4338059B2 JP 14970698 A JP14970698 A JP 14970698A JP 14970698 A JP14970698 A JP 14970698A JP 4338059 B2 JP4338059 B2 JP 4338059B2
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Description
【0001】
【発明の属する利用分野】
本発明は液晶表示素子の分野で有用な二色性色素を含む液晶組成物に関する。
【0002】
【従来の技術】
液晶材料に少量の二色性色素を添加した組成物は、ゲストホスト(以後GHと称する)と称される液晶表示素子に使用される。このGHは液晶表示素子の重要な形式の一つであり、特にカラ−液晶表示素子の光利用効率を高める方法として着目されている。たとえば、三原色各々のハルマイヤー型GHセルを積層したGH型液晶表示素子、二色のハルマイヤー型GHセルの間に偏光板を挿入して積層したGH型液晶表示素子、三原色各々のGH液晶を二層型または三層型セルで積層したGH型液晶表示素子、等の各種GH型液晶表示素子が注目されている。近年は特に省エネルギ−や携帯機器に於ける電池駆動時間の確保の点から反射型の液晶表示素子が着目されている。反射型の液晶表示素子ではバックライト等の補助光源がないため、光利用効率の高いこれらGH型液晶表示素子が有望視されている。
【0003】
一方、GHに使用される二色性色素としては、これまでアゾ系色素、アントラキノン系色素等で二色性を有する優れた材料が開発され、これらの材料は多くの液晶材料中で二色性を示すことが、アレキサンダー ヴィ. イバシュチェンコ(Alexander V. Ivashchenko)著、ダイクロイックダイズ フォオ リキッドクリスタル ディスプレイズ(DICHROIC DYES for LIQUID CRYSTAL DISPLAYS)第165〜337頁、シーアールシープレス(CRC Press)等に記載されている。
【0004】
しかしながら、二色性色素の吸収スペクトル形状と吸光係数は、GH方式でカラ−表示を行う際に大きな影響を与える。 すなわち、表示可能な色調を増やし演色性を確保するためには各原色を独立に制御する必要があり、吸収波長の重複の少ない色素を組み合わせる必要がある。吸収波長の重複により各原色は完全に独立に制御出来ず、表現できる色の範囲は狭まり、また余計な吸収によって光利用効率も低下していた。
吸収波長の重複を避けるためには各色の吸収ピ−ク波長の選定も重要であるが、一般的に色素の吸収ピークは幅広いため、吸収ピ−ク波長の選定だけではどうしても幾分かの重複部分が発生する。そこで、吸収スペクトル形状は重複部分を減らすために光吸収ピークの波長幅が少しでも狭い色素が特に有用である。
また、十分なコントラストを確保するために、二色性色素の吸光係数は大きいほど好ましい。すなわち、吸光係数の大きな二色性色素は、わずかな使用量で鮮明な液晶表示素子を提供することができるが、吸光係数の小さな二色性色素を使用した場合、ある一定のコントラストを出すために多くの量の色素を使用せねばならず、経済的であるとはいえない。従来のキノン系色素では光吸収の波長幅は比較的狭いものの、吸光係数は比較的小さく、アゾ系色素では吸光係数は比較的大きいものの、光吸収ピークの波長幅は比較的広い。従来の液晶組成物の中に含まる二色性色素では、大きな吸光係数と光吸収ピークの波長幅が狭いという特性を同時に兼ね備えたものは見出せていないのが現状である。
【0005】
【発明が解決しようとする課題】
本発明の目的は、吸光係数が大きく、かつ光吸収ピ−クの波長幅が狭く、同時に二色性を示す色素を含む液晶組成物を得ることである。
【0006】
【課題を解決するための手段】
本発明者らは、上記の課題を解決すべく鋭意検討を続けた結果、ある種のベンゾジフラノン系化合物が吸光係数が大きく、かつ吸収半値幅が小さく、同時に二色比を示すことを見出し、本発明を完成するに至った。
すなわち、本発明は、下記一般式(I)
【0007】
【化2】
【0008】
(式中、AおよびBは、それぞれ独立して水素原子若しくは少なくとも1つの基で置換されていてもよい、ベンゼン、ナフタレン、ビフェニル、チオフェン、ベンゾチオフェン、チアゾール、ベンゾチアゾールまたはベンゾイソチアゾールを表し、nは0を表す。)で示される二色性色素を少なくとも1つ含むことを特徴とする液晶組成物に関するものである。
【0009】
【発明の実施の形態】
本発明において、一般式(I)におけるAおよびB上の置換基の中、置換されていてもよい基としては、水酸基、置換されていてもよい、C1〜C12アルキル基、C1〜C12アルコキシ基、C1〜C12アルコキシC1〜C12アルキル基、C1〜C12アルキルカルボニル基、C1〜C12アルコキシカルボニルC1〜C12アルキル基、フェニルアルキル基若しくはC1〜C12アルコキシC1〜C12アルコキシカルボニルC1〜C12アルキル基、あるいは−O−R1−Q(ここで、R1はメチレン基またはC1〜C12アルキルカルボニルオキシ基で置換されていてもよい直鎖若しくは分枝のC2〜C6アルキレン基を表し、Qは置換されていてもよい、5員環または6員環の飽和若しくは不飽和の残基を表す。)、ハロゲン原子、ニトロ基、アミノ基、アシルアミノ基、C1〜C12アルキルアミノ基、ジC1〜C12アルキルアミノ基、アシル基、アシロキシ基、置換されていてもよいアルケニル基、等が挙げられる。
【0010】
また、上記のQの5員環または6員環の飽和残基としては、テトラヒドロフリル基、テトラヒドチエニル基、テトラヒドロピラニル基、ピペリジル基、ピロリジル基、ピペラジル基、モルホニル基、ヘキサヒドロアゼピニル基、シクロヘキシル基等が挙げられ、Qの5員環または6員環の不飽和残基としては。フリル基、チエニル基、ピロリル基、ピリジル基、ピラニル基、チアゾリル基、オキサゾリル基、ピラゾリル基、ピラジル基、イミダゾリル基、チアジアゾリル基、s-トリアジニル基、ベンゾフラニル基、ベンゾチエニル基、インドリル基、ベンズオキサゾリル基、ベンゾイミダゾリル基、ベンゾチアゾリル基、シクロヘキセニレン基、等が挙げられる。
【0011】
上記の一般式(I)におけるAおよびB上の置換基において、ハロゲン原子は、フッ素原子、塩素原子、臭素原子および沃素原子を意味し、アシルアミノ基としては、アセチルアミノ基等が挙げられ、アシロキシ基としては、下記一般式
【0012】
【化3】
【0013】
[式中、Tは、C1〜C4アルキル基、フェニル基、フェノキシ基またはC1〜C4アルコキシ基を表す。]
で示される基、等が挙げられる。
【0014】
本発明で用いられる一般式(I)で示される二色性色素の具体例を次に示す。
【0015】
【化4】
(E−1)
【0017】
【化6】
(E−3)
【0018】
【化7】
(E−4)
【0019】
【化8】
(E−5)
【0020】
尚、一般式(I)で示される化合物は、特開平3−72571号公報、特開平8−48893号公報、英国公開特許第2299811号明細書等に記載の方法またはこれらに準ずる方法にて製造できる。
【0021】
本発明において、一般式(I)で示される二色性色素を少なくとも1つ含む液晶組成物は、液晶性物質を含有し液晶相を示す。
【0022】
液晶相の種類としてはネマチック相、コレステリック相、スメクティック相、ディスコティック相、等の公知の相を使用することができるが、GHに使用するためにはネマチック相、コレステリック相、スメクティック相が好ましく、ネマチック相が特に好ましい。これらの相は含有する液晶性物質によってほぼ決まるが、少量の添加物により相が変化する場合も有る。このような例としては少量の旋光性物質によってコレステリック相が現れる場合が挙げられる。また本発明の液晶組成物の誘電率異方性は正でも負でもよく、目的の液晶表示素子の形式に合わせて選択することができる。
【0023】
安定な液晶相を広い温度範囲で発現させるために、本発明の液晶組成物中の液晶性物質の含有量は、通常、80重量%以上が好ましく、90重量%以上がさらに好ましく、95重量%以上が特に好ましい。また、液晶性物質は単一の化合物でも複数の化合物の混合物でも使用することができるが、安定な液晶相を広い温度範囲で発現させるために一般に複数の化合物を混合して使用することが好ましい。具体的な液晶性物質としては、液晶デバイスハンドブック;日本学術振興会第142委員会編(1989年)第152〜192頁、同第715〜722頁等に記載されたようなネマティック相あるいはスメクティック相を示すビフェニル系、フェニルシクロヘキサン系、フェニルピリミジン系、シクロヘキシルシクロヘキサン系、等の各種の化合物または混合物を使用することができる。また、好ましい化合物としては、下記表1に例示されるものが使用できる。
【0024】
【化9】
【0025】
[式中、VおよびWは、それぞれ、アルキル基、アルコキシ基、アルコキシアルキル基、アルキルフェニル基、アルコキシアルキルフェニル基、アルコキシフェニル基、アルキルシクロヘキシル基、アルコキシアルキルシクロヘキシル基、アルキルシクロヘキシルフェニル基、シアノフェニル基、シアノ基、ハロゲン原子、フルオロメチル基、フルオロメトキシ基、アルキルフェニルアルキル基、アルコキシフェニルアルキル基、アルキルシクロヘキシルアルキル基、アルコキシアルコキシヘキシルアルキル基、アルコキシフェニルアルキル基、またはアルキルシクロヘキシルフェニルアルキル基を表し、これらのアルキル鎖およびアルコキシ鎖中に光学活性中心を有しても良い。またVおよびW中のフェニル基またはフェノキシ基は、シアノ基、フッ素原子、塩素原子、等のハロゲン原子でさらに置換されてもよい。また、上記各構造式中のフェニル基は、1個〜4個のフッ素原子、塩素原子、等のハロゲン原子、シアノ基でさらに置換されてもよい。Uは水素原子、ハロゲン原子またはシアノ基を表す。]
【0026】
また、従来のシアノ基を含有した液晶化合物の替わりに、−F,−CF3、−OCF3、などのフッ素原子またはフッ素原子含有基などの置換基を有するいわいるフッ素系液晶性物質が薄膜トランジスタ方式液晶ディスプレイ(TFT・LCD)に好ましいとされており、これらのフッ素系液晶性物質も本発明の液晶組成物に用いることができる。
【0027】
本発明の液晶組成物に含まれる化合物の純度は色素の種類や合成方法により若干異なるが、通常90〜100%の範囲が使用でき、好ましくは98〜100%の範囲が、さらに好ましくは99〜100%の範囲が、特に好ましく99.5〜100%の範囲が使用される。
【0028】
本発明の液晶組成物の作製方法としては、成分である二色性色素、液晶性物質等を混合することにより得られる。混合の方法には公知の方法が用いられる。例えば、液晶性物質を加熱して等方性液体に融解させ、これに一般式(I)で示される二色性色素を混合して溶解する方法等が挙げられる。
【0029】
【実施例】
以下本発明の実施例を示すが、本発明はこれらによって限定されるものではない。
実施例
(二色比の測定)
二色比(R)の測定は、一般式(I)で示される二色性色素を含む液晶組成物を測定セルに注入し、この測定セルの偏光吸収スペクトルを測定することにより行った。測定セルは2枚の石英製基板により作成した。各石英製基板の片面にはポリイミド配向膜(日立化成製、LX1400)を約20nm塗布し加熱を行った後、一方向に布でラビング処理した。この石英製基板を2枚配向膜面を内側にして貼り合わせた。この時、周辺部にスペ−サを含む接着剤を塗布し、これを硬化させることにより2枚の石英製基板の間隔が17〜24μmの液晶セルとした。この時、2枚の石英製基板のラビング方向が互いに平行の関係となるように貼り合わせた測定セルに本発明の液晶組成物を注入して測定を行った。
【0030】
ここで二色比とは特定の波長における、測定セルのラビング方向に平行な偏光方向に平行な方向に偏光した光に対する吸光度(A1)と、測定セルのラビング方向に垂直な方向の偏光した光に対する吸光度(A2)を測定し、以下の数1で示される数式により求めたものであり、測定セルのラビング方向に平行な方向に変更した光に対する偏光吸収スペクトルのピーク波長での値を用いた。吸光度の値としては、一般式(I)で示される二色性色素を含まない同様の液晶組成物を注入した測定セルによる吸収を差し引いて、含まれる一般式(I)で示される二色性色素そのものの吸収を用いた。
【0031】
【数1】
R=A1/A2
【0032】
特に、液晶セルの偏光方向に垂直な方向の偏光の吸収スペクトルのピ−ク波長での値を用いた。吸光度の値としては、液晶セル基材による吸収を差し引いて、液晶組成物そのものの吸収を用いた。液晶セルは2枚の石英製基板により作製した。石英製基板にはポリイミド配向膜(日立化成製、LX1400)を約20nm塗布し加熱してイミド化を行った後、一方向にラビングした。この石英製基板を2枚配向膜面を内側にして貼り合わせた。この時、周辺部にスペ−サを含む接着剤を塗布し、これを硬化させることにより2枚の石英製基板の間隔が17〜24μmの液晶セルとした。この時、2枚の石英製基板のラビング方向が互いに平行の関係となるように貼り合わせた。この測定セルに本発明の液晶組成物を注入して測定を行った。その結果、表1に示すようにE−1、E−3〜E−5の化合物は、何れも二色性を有していた。
【0033】
【表1】
【0034】
(吸光係数と吸収半値幅の測定)
吸光係数は下記数2で示される数式より求めた。ここでMは二色性色素の分子量、Rは二色性色素の二色比、A2は前記の意味を表わす。fは液晶組成物E7の比重、eは液晶組成物E7中での二色性色素の濃度(%)、dはセル厚(μm)を意味する。なお%は重量%を意味する。
【0035】
【数2】
吸光係数=(M×(R+1)2×A2×1000)/(4×f×R2×e×d)
【0036】
吸収半値幅は、液晶セルの偏光方向に垂直な方向の偏光の吸収スペクトルにのある特定の吸収ピ−クについて、その吸収ピ−クの半分の高さを示す左右二つ波長W1およびW2から下記数3で示される数式により算出される。また、吸収スペクトル上における吸収半値幅について図1に具体的に示す。
【0037】
【数3】
吸収半値幅=|W1−W2|
【0038】
本発明の一般式(I)に含まれるE−5で示される化合物と、比較化合物G−1およびG−2に関する測定結果を表2に示す。
【0039】
【化10】
(G−1)
【0040】
【化11】
(G−2)
【0041】
【表2】
【0042】
表2から、本発明で用いられる二色性色素は、大きな吸光係数と小さな吸収半値幅の2つの特性を同時に有することがわかった。
【0043】
【発明の効果】
本発明の液晶組成物は、吸光係数が大きくかつ吸収半値幅が小さいため、これを使用した液晶表示素子は多彩で鮮明な色調を表示でき、工業的価値が大きい。
【図面の簡単な説明】
【図1】図1はE−5と液晶組成物E7(メルク社製)との混合物を注入した液晶セルの偏光吸収スペクトル、図中において
1:測定セルのラビング方向に平行な方向に偏光した光に対する吸収スペクトル2:測定セルのラビング方向に垂直な方向に偏光した光に対する吸収スペクトル3:W1
4:W2
5:吸収半値幅
6:吸収ピーク
を意味する。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal composition containing a dichroic dye useful in the field of liquid crystal display elements.
[0002]
[Prior art]
A composition obtained by adding a small amount of a dichroic dye to a liquid crystal material is used for a liquid crystal display element called a guest host (hereinafter referred to as GH). This GH is one of the important types of liquid crystal display elements, and is particularly attracting attention as a method for increasing the light utilization efficiency of color liquid crystal display elements. For example, a GH type liquid crystal display element in which Halmer-type GH cells of three primary colors are stacked, a GH type liquid crystal display element in which a polarizing plate is inserted between two color Halmeier type GH cells, and a GH liquid crystal in each of the three primary colors Various GH type liquid crystal display elements such as GH type liquid crystal display elements laminated in a two-layer type or three-layer type cell are attracting attention. In recent years, a reflection type liquid crystal display element has attracted attention especially in terms of energy saving and securing of battery driving time in portable devices. Since a reflective liquid crystal display element does not have an auxiliary light source such as a backlight, these GH liquid crystal display elements with high light utilization efficiency are promising.
[0003]
On the other hand, as dichroic dyes used in GH, excellent materials having dichroism such as azo dyes and anthraquinone dyes have been developed, and these materials are dichroic among many liquid crystal materials. Can be shown by Alexander V. It is described by Alexander V. Ivashchenko, dichroic soybean for liquid crystal displays (DICROIC DYES for LIQUID CRYSTAL DISPLAYS) pp. 165 to 337, CRC Press and the like.
[0004]
However, the absorption spectrum shape and extinction coefficient of the dichroic dye have a great influence when color display is performed by the GH method. That is, in order to increase the color tone that can be displayed and to ensure color rendering, it is necessary to control each primary color independently, and it is necessary to combine dyes with little overlap of absorption wavelengths. Each primary color could not be controlled completely independently due to the overlap of absorption wavelengths, and the range of colors that could be expressed was narrowed, and the light utilization efficiency was also reduced due to extra absorption.
Although it is important to select the absorption peak wavelength of each color in order to avoid the overlap of the absorption wavelength, the absorption peak of the dye is generally wide. Part occurs. Therefore, a dye having a narrow wavelength width of the light absorption peak is particularly useful in order to reduce the overlapping portion of the absorption spectrum shape.
Moreover, in order to ensure sufficient contrast, the larger the extinction coefficient of the dichroic dye, the better. That is, a dichroic dye having a large extinction coefficient can provide a clear liquid crystal display element with a small amount of use, but when a dichroic dye having a small extinction coefficient is used, a certain contrast is obtained. It is not economical because a large amount of pigment must be used. Conventional quinone dyes have a relatively narrow light absorption wavelength range, but the absorption coefficient is relatively small, while azo dyes have a relatively large absorption coefficient, but the wavelength width of the light absorption peak is relatively wide. As for the dichroic dyes contained in the conventional liquid crystal composition, no dichroic dye having both a large absorption coefficient and a characteristic that the wavelength width of the light absorption peak is narrow has not been found at present.
[0005]
[Problems to be solved by the invention]
An object of the present invention is to obtain a liquid crystal composition containing a dye having a large extinction coefficient and a narrow wavelength width of a light absorption peak and simultaneously exhibiting dichroism.
[0006]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have found that certain benzodifuranone-based compounds have a large extinction coefficient and a small absorption half-value width and simultaneously exhibit a dichroic ratio. The invention has been completed.
That is, the present invention provides the following general formula (I)
[0007]
[Chemical formula 2]
[0008]
Wherein A and B each independently represent a hydrogen atom or at least one group, which may be substituted with benzene, naphthalene, biphenyl, thiophene, benzothiophene, thiazole, benzothiazole or benzoisothiazole, and n represents 0. The liquid crystal composition is characterized in that it contains at least one dichroic dye represented by formula (1).
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the present invention, among the substituents on A and B in formula (I), examples of the optionally substituted group include a hydroxyl group, an optionally substituted C1-C12 alkyl group, and a C1-C12 alkoxy group. C1-C12 alkoxy C1-C12 alkyl group, C1-C12 alkylcarbonyl group, C1-C12 alkoxycarbonyl C1-C12 alkyl group, phenylalkyl group or C1-C12 alkoxy C1-C12 alkoxycarbonyl C1-C12 alkyl group, or- O—R 1 —Q (wherein R 1 represents a linear or branched C 2 to
[0010]
The saturated residue of the above-mentioned Q 5-membered or 6-membered ring includes tetrahydrofuryl group, tetrahydrthienyl group, tetrahydropyranyl group, piperidyl group, pyrrolidyl group, piperazyl group, morphonyl group, hexahydroazepi Nyl group, cyclohexyl group, etc. are mentioned, and as a 5-membered ring or 6-membered ring unsaturated residue of Q. Furyl group, thienyl group, pyrrolyl group, pyridyl group, pyranyl group, thiazolyl group, oxazolyl group, pyrazolyl group, pyrazyl group, imidazolyl group, thiadiazolyl group, s-triazinyl group, benzofuranyl group, benzothienyl group, indolyl group, benzoxa A zolyl group, a benzimidazolyl group, a benzothiazolyl group, a cyclohexenylene group, and the like can be given.
[0011]
In the substituents on A and B in the above general formula (I), the halogen atom means a fluorine atom, a chlorine atom, a bromine atom and an iodine atom, and examples of the acylamino group include an acetylamino group. As the group, the following general formula:
[Chemical 3]
[0013]
[Wherein, T represents a C1-C4 alkyl group, a phenyl group, a phenoxy group, or a C1-C4 alkoxy group. ]
And the like, and the like.
[0014]
Specific examples of the dichroic dye represented by the general formula (I) used in the present invention are shown below.
[0015]
[Formula 4]
(E-1)
[0017]
[Chemical 6]
(E-3)
[0018]
[Chemical 7]
(E-4)
[0019]
[Chemical 8]
(E-5)
[0020]
The compound represented by the general formula (I) is produced by the method described in JP-A-3-72571, JP-A-8-48893, British Published Patent No. 2299811 or the like, or a method analogous thereto. it can.
[0021]
In the present invention, the liquid crystal composition containing at least one dichroic dye represented by formula (I) contains a liquid crystal substance and exhibits a liquid crystal phase.
[0022]
As the type of liquid crystal phase, known phases such as nematic phase, cholesteric phase, smectic phase, discotic phase, etc. can be used, but nematic phase, cholesteric phase, smectic phase are preferred for use in GH, A nematic phase is particularly preferred. These phases are almost determined by the liquid crystal substance contained, but the phase may be changed by a small amount of additives. An example of this is the case where the cholesteric phase appears with a small amount of optically rotatory material. The dielectric anisotropy of the liquid crystal composition of the present invention may be positive or negative, and can be selected according to the type of the target liquid crystal display element.
[0023]
In order to develop a stable liquid crystal phase in a wide temperature range, the content of the liquid crystal substance in the liquid crystal composition of the present invention is usually preferably 80% by weight or more, more preferably 90% by weight or more, and 95% by weight. The above is particularly preferable. Further, the liquid crystalline substance can be used as a single compound or a mixture of a plurality of compounds, but it is generally preferable to use a mixture of a plurality of compounds in order to develop a stable liquid crystal phase in a wide temperature range. . Specific liquid crystalline substances include the liquid crystal device handbook; nematic phase or smectic phase as described in Japan Society for the Promotion of Science 142nd Committee (1989), pages 152-192, pages 715-722, etc. Various compounds or mixtures such as biphenyl, phenylcyclohexane, phenylpyrimidine, cyclohexylcyclohexane and the like can be used. Moreover, as a preferable compound, what is illustrated by following Table 1 can be used.
[0024]
[Chemical 9]
[0025]
[Wherein, V and W are an alkyl group, an alkoxy group, an alkoxyalkyl group, an alkylphenyl group, an alkoxyalkylphenyl group, an alkoxyphenyl group, an alkylcyclohexyl group, an alkoxyalkylcyclohexyl group, an alkylcyclohexylphenyl group, and a cyanophenyl, respectively. Represents a group, a cyano group, a halogen atom, a fluoromethyl group, a fluoromethoxy group, an alkylphenylalkyl group, an alkoxyphenylalkyl group, an alkylcyclohexylalkyl group, an alkoxyalkoxyhexylalkyl group, an alkoxyphenylalkyl group, or an alkylcyclohexylphenylalkyl group. These alkyl chains and alkoxy chains may have an optically active center. In addition, the phenyl group or phenoxy group in V and W may be further substituted with a halogen atom such as a cyano group, a fluorine atom, or a chlorine atom. In addition, the phenyl group in each structural formula above may be further substituted with 1 to 4 halogen atoms such as fluorine atom, chlorine atom, and cyano group. U represents a hydrogen atom, a halogen atom or a cyano group. ]
[0026]
Further, in place of the conventional liquid crystal compound containing a cyano group, a so-called fluorine-based liquid crystalline substance having a substituent such as a fluorine atom or a fluorine atom-containing group such as —F, —CF 3 , —OCF 3 , etc. It is considered preferable for a liquid crystal display (TFT / LCD), and these fluorine-based liquid crystalline substances can also be used in the liquid crystal composition of the present invention.
[0027]
The purity of the compound contained in the liquid crystal composition of the present invention varies slightly depending on the type of dye and the synthesis method, but usually 90 to 100% can be used, preferably 98 to 100%, and more preferably 99 to 99%. A range of 100% is particularly preferred, and a range of 99.5 to 100% is used.
[0028]
The method for producing the liquid crystal composition of the present invention can be obtained by mixing dichroic dyes, liquid crystal substances and the like as components. A known method is used as the mixing method. For example, there is a method in which a liquid crystalline substance is heated to melt into an isotropic liquid, and a dichroic dye represented by the general formula (I) is mixed and dissolved therein.
[0029]
【Example】
Examples of the present invention will be described below, but the present invention is not limited thereto.
Example (measurement of dichroic ratio)
The dichroic ratio (R) was measured by injecting a liquid crystal composition containing a dichroic dye represented by the general formula (I) into a measurement cell and measuring the polarization absorption spectrum of the measurement cell. The measurement cell was made of two quartz substrates. A polyimide alignment film (LX1400, manufactured by Hitachi Chemical Co., Ltd., about 20 nm) was applied to one side of each quartz substrate, heated, and then rubbed with a cloth in one direction. Two quartz substrates were bonded together with the alignment film surface inside. At this time, an adhesive containing a spacer was applied to the peripheral portion and cured to obtain a liquid crystal cell having a distance between two quartz substrates of 17 to 24 μm. At this time, the measurement was performed by injecting the liquid crystal composition of the present invention into a measurement cell bonded so that the rubbing directions of the two quartz substrates were parallel to each other.
[0030]
Here, the dichroic ratio means the absorbance (A 1 ) for light polarized in a direction parallel to the polarization direction parallel to the rubbing direction of the measurement cell at a specific wavelength, and polarization in a direction perpendicular to the rubbing direction of the measurement cell. The absorbance (A 2 ) for light was measured and obtained by the following mathematical formula 1. The value at the peak wavelength of the polarization absorption spectrum for light changed in a direction parallel to the rubbing direction of the measurement cell was obtained. Using. As the value of absorbance, the dichroism represented by the general formula (I) contained by subtracting the absorption by the measurement cell injected with the same liquid crystal composition not containing the dichroic dye represented by the general formula (I). Absorption of the dye itself was used.
[0031]
[Expression 1]
R = A 1 / A 2
[0032]
In particular, the value at the peak wavelength of the absorption spectrum of polarized light in a direction perpendicular to the polarization direction of the liquid crystal cell was used. As the absorbance value, the absorption of the liquid crystal composition itself was used by subtracting the absorption by the liquid crystal cell substrate. The liquid crystal cell was produced with two quartz substrates. A quartz alignment film (manufactured by Hitachi Chemical Co., Ltd., LX1400) was applied to a quartz substrate at about 20 nm, heated to imidize, and then rubbed in one direction. Two quartz substrates were bonded together with the alignment film surface inside. At this time, an adhesive containing a spacer was applied to the peripheral portion and cured to obtain a liquid crystal cell having a distance between two quartz substrates of 17 to 24 μm. At this time, the two quartz substrates were bonded so that the rubbing directions were parallel to each other. Measurement was performed by injecting the liquid crystal composition of the present invention into the measurement cell. As a result, as shown in Table 1, all of the compounds E-1 , E-3 to E-5 had dichroism.
[0033]
[Table 1]
[0034]
(Measurement of extinction coefficient and half-width of absorption)
The extinction coefficient was obtained from the mathematical formula represented by the following formula 2. Here, M is the molecular weight of the dichroic dye, R is the dichroic ratio of the dichroic dye, and A 2 is as defined above. f is the specific gravity of the liquid crystal composition E7, e is the concentration (%) of the dichroic dye in the liquid crystal composition E7, and d is the cell thickness (μm). % Means% by weight.
[0035]
[Expression 2]
Absorption coefficient = (M × (R + 1) 2 × A2 × 1000) / (4 × f × R 2 × e × d)
[0036]
The half width of absorption is the two left and right wavelengths W 1 and W indicating the height of half of the absorption peak for a specific absorption peak in the absorption spectrum of polarized light in a direction perpendicular to the polarization direction of the liquid crystal cell. It is calculated from 2 by the mathematical formula shown by the following formula 3. Further, FIG. 1 specifically shows the absorption half width on the absorption spectrum.
[0037]
[Equation 3]
Absorption half-width = | W 1 −W 2 |
[0038]
Table 2 shows the measurement results regarding the compound represented by E-5 and the comparative compounds G-1 and G-2 contained in the general formula (I) of the present invention.
[0039]
Embedded image
(G-1)
[0040]
Embedded image
(G-2)
[0041]
[Table 2]
[0042]
From Table 2, it was found that the dichroic dye used in the present invention has two characteristics of a large extinction coefficient and a small absorption half width at the same time.
[0043]
【The invention's effect】
Since the liquid crystal composition of the present invention has a large extinction coefficient and a small absorption half-value width, a liquid crystal display device using the liquid crystal composition can display a variety of clear colors and has a great industrial value.
[Brief description of the drawings]
FIG. 1 is a polarization absorption spectrum of a liquid crystal cell injected with a mixture of E-5 and a liquid crystal composition E7 (manufactured by Merck). In FIG. 1, the light is polarized in a direction parallel to the rubbing direction of the measurement cell. Absorption spectrum for light 2: Absorption spectrum for light polarized in a direction perpendicular to the rubbing direction of the measurement cell 3: W 1
4: W 2
5: Absorption half-value width 6: Absorption peak.
Claims (1)
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