JP4104938B2 - Composition for vertical alignment film and method for producing vertical alignment film - Google Patents
Composition for vertical alignment film and method for producing vertical alignment film Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は、液晶表示素子に使用する液晶配向膜に関し、さらに詳しくは、液晶を垂直配向させることのできるラビングレスの垂直配向膜に関する。
【0002】
【従来の技術】
液晶表示素子においては、従来ツイステッドネマティックモードの液晶表示素子が広く使用されていたが、近年、コントラスト比が高く、視野角依存性の小さい表示方式として、負の誘電異方性を有する液晶分子を基板に対して垂直に配向(以下、ホメオトロピック配向と略す。)させた、垂直配向モードの液晶表示素子の開発が盛んに行われている。
この垂直配向モードの液晶表示素子を表示させるためには、液晶分子に方位角方向の配向規制力を与え、電圧印加時に液晶分子が基板面に対して平行に配向(以下、ホモジニアス配向と略す。)するときの方位を制御しなければならず、そのためには、電圧無印加時の液晶分子を、その分子軸が基板面内の一定の方位に、基板面法線に対して一定のプレチルト角を持つように配向させることが必要である。
【0003】
液晶分子にプレチルト角を与える方法としては、液晶セルの基板内面に表面をラビング処理したポリイミド等の垂直配向膜を設けて、液晶分子に基板面法線方向に対するプレチルト角を与える方法が知られているが、液晶表示画面に筋状の輝度むらが発生しやすく、表示品位が低下してしまう。
【0004】
これに対し、特開平9−211468号公報には、長鎖の直鎖状アルキル基を有するポリイミド系やシランカップリング剤の垂直配向膜用組成物を基板上に塗布した後、該塗膜表面に、254nmや313nmといった短波長の非偏光の紫外線を、斜め方向から照射して得た垂直配向膜を液晶セルの基板内面に設けて、液晶分子に基板面法線に対するプレチルト角を与える方法が開示されている。
しかし、この方法で得られるプレチルト角は、1°未満と小さく、その結果、電圧印加時に、液晶表示素子に配向欠陥が生じたり、電圧応答速度が遅くなるといった問題があった。また、この方法は、短波長の紫外線で長鎖アルキル基の一部を分解又は切断して、長鎖アルキル基の向きを基板面内の一定の方位に揃えることによって、液晶分子にプレチルト角を与える方法であるが、このとき生じた分解生成物により電圧保持率等の液晶表示素子特性が低下するといった問題もあった。
【0005】
【発明が解決しようとする課題】
本発明が解決しようとする課題は、液晶分子を、その分子軸が基板面内の一定の方位に、基板面法線に対して大きなプレチルト角を持つように配向させることができ、且つ、電圧保持率が低下せず、優れた液晶表示素子特性を与えることのできる、垂直配向モードの液晶表示素子に使用する垂直配向膜用組成物、及び、該垂直配向膜用組成物を使用した垂直配向膜の製造方法を提供することにある。
【0006】
【課題を解決するための手段】
本発明は、液晶表示素子用の垂直配向膜用組成物に、紫外線で光配向させて液晶分子の分子軸をホモジニアス配向させる機能を有するアゾ化合物を添加することによって、基板面内の方位角方向への配向力が付与された垂直配向膜を得ることができ、上記課題を解決した。
即ち、本発明は、無極性の長鎖アルキル基又は脂環式構造を有する液晶表示素子用の垂直配向膜用組成物であって、一般式(1)で表されるアゾ化合物を0.5〜50質量%含有することを特徴とする垂直配向膜用組成物、及び、該垂直配向膜用組成物を有機溶剤に溶解し、基板上に塗布し、有機溶剤を除去した後、斜め方向から非偏光の紫外線を照射する垂直配向膜の製造方法を提供する。
【0007】
【化2】
【0008】
(式中、R1は各々独立して、ヒドロキシ基、(メタ)アクリロイルオキシ基、(メタ)アクリルアミド基、ビニルオキシ基、ビニルオキシカルボニル基、ビニルイミノカルボニル基、ビニルイミノカルボニルオキシ基、ビニル基、イソプロペニルオキシ基、イソプロペニルオキシカルボニル基、イソプロペニルイミノカルボニル基、イソプロペニルイミノカルボニルオキシ基、イソプロペニル基、又はエポキシ基を表す。R2は、−(A−B−A)m−(D)n−で表される連結基を表し、R3は、−(D)n−(A−B−A)m−で表される連結基を表す。ここで、Aは、炭素原子数20以下の二価の炭化水素基を表し、Bは、−O−、−CO−O−、−OCO−、−CONH−、−NHCO−、−NHCO−O−、又は−OCONH−を表し、mは0〜3の整数を表す。Dは、mが0のとき、炭素原子数20以下の二価の炭化水素基を表し、mが1〜3の整数のとき、−O−、−CO−O−、−OCO−、−CONH−、−NHCO−、−NHCO−O−、又は−OCONH−を表し、nは0又は1を表す。但し、m=n=0の場合は、R 2 及びR 3 は単結合を表す。R4は各々独立して、ハロゲン原子、カルボキシ基、ハロゲン化メチル基、ハロゲン化メトキシ基、シアノ基、ニトロ基、メトキシ基、又はメトキシカルボニル基を表す。但し、カルボキシ基はアルカリ金属と塩を形成していてもよい。R5は各々独立して、カルボキシ基、スルホ基、ニトロ基、アミノ基、又はヒドロキシ基を表す。但し、カルボキシ基又はスルホ基はアルカリ金属と塩を形成していてもよい。)
【0009】
【発明の実施の形態】
一般式(1)において、R1は、(メタ)アクリロイルオキシ基、(メタ)アクリルアミド基、ビニルオキシ基、ビニルオキシカルボニル基、ビニルイミノカルボニル基、ビニルイミノカルボニルオキシ基、ビニル基、イソプロペニルオキシ基、イソプロペニルオキシカルボニル基、イソプロペニルイミノカルボニル基、イソプロペニルイミノカルボニルオキシ基、イソプロペニル基、又はエポキシ基を表す。からなる群から選ばれる重合性基である場合には、本発明の垂直配向膜用組成物(以下、本発明の垂直配向膜用組成物と略す。)を光配向後、熱重合や光重合によって配向を固定化することができ、耐熱性に優れた配向膜を得ることができ、好ましい。中でも、(メタ)アクリロイルオキシ基、又は(メタ)アクリルアミド基が好ましい。
【0010】
一般式(1)において、R1で表されるヒドロキシ基や重合性基は、R2及びR3で表される連結基を介して、隣接するフェニレン基と連結している。連結基R2及び連結基R3のうち、Aで表される二価の炭化水素基としては、プロピレン基、へプチレン基等の炭素原子数3〜20のアルキレン基、メチレン基、トリメチレン基、ペンタメチレン基等の炭素原子数1〜20のポリメチレン基、シクロプロピレン基、シクロヘキシレン基等の炭素原子数3〜20のシクロアルキレン基、フェニレン基、ナフチレン基等の炭素原子数6〜20のアリーレン基等が挙げられる。
【0011】
一般式(1)において、R4のハロゲン原子としては、フッ素原子や塩素原子が、ハロゲン化メチル基としては、トリクロロメチル基やトリフルオロメチル基等が、ハロゲン化メトキシ基としては、クロロメトキシ基やトリフルオロメトキシ基等が挙げられる。中でも、R4がカルボキシ基であると、基板に対する付着性が高い。カルボキシ基は、リチウム、ナトリウム、カリウム等のアルカリ金属と塩を形成していても良い。
【0012】
一般式(1)において、R5は、カルボキシ基又はスルホ基であると基板に対する付着性が高く好ましい。また、カルボキシ基及びスルホ基は、リチウム、ナトリウム、カリウム等のアルカリ金属と塩を形成していても良い。
【0013】
一般式(1)で表されるアゾ化合物は、偏光、もしくは基板面に対して斜め方向からの光を照射すると容易に配向し、且つ、ガラスやITO等の基板に対し成膜性や付着性に優れる。具体的には、下記構造のアゾ化合物を挙げることができる。
【0014】
【化3】
【0015】
【化4】
【0016】
【化5】
【0017】
【化6】
【0018】
例えば、前記(a)で表されるアゾ化合物は、1,2−ニトロベンゼンスルホン酸の水酸化ナトリウム水溶液に、亜鉛粉末と硫酸ナトリウム水溶液を加え、次に塩酸を添加して3,3’−ベンジジンジスルホン酸を合成し、これに、亜硝酸ナトリウムを反応させて、ジアゾニウム化合物としてから、2−ヒドロキシ安息香酸を反応させて得られる。
【0019】
また、前記(b)で表されるアゾ化合物は、前記(a)で表されるアゾ化合物の両末端のヒドロキシ基に、アクリル酸クロライドを反応させて得られる。
【0020】
前記一般式(1)で表されるアゾ化合物は、液晶表示素子用の垂直配向膜用組成物(以下、本発明で使用する垂直配向膜用組成物Aと略す。)に添加して使用する。
本発明で使用する垂直配向膜用組成物Aは、基板上に塗膜として設けることで、液晶分子の分子軸をホメオトロピック配向させる機能を有するものであればよい。具体的には、例えば、レシチン、シラン系界面活性剤、チタネート系界面活性剤、ピリジニウム塩系高分子界面活性剤、n−オクタデシルトリエトキシシラン等のシランカップリング系垂直配向膜用組成物、長鎖アルキル基や脂環式構造を側鎖に有する可溶性ポリイミドや長鎖アルキル基や脂環式構造を側鎖に有するポリアミック酸等のポリイミド系垂直配向膜用組成物が挙げられる。本発明においては、前記垂直配向膜用組成物Aとして、ジェイエスアール(株)製のポリイミド系垂直配向膜用組成物「JALS−2021」や「JALS−204」、日産化学工業(株)製の「RN−1517」や「SE−1211」等の市販品をそのまま使用することができる。
【0021】
前記垂直配向膜用組成物Aは、無極性の長鎖アルキル基や脂環式構造を有しており、例えば不揮発分濃度が1%程度となるように有機溶剤に溶解し、基板上にスピンコーティング法等の方法で塗工した後、有機溶剤を除去すると、無極性の長鎖アルキル基や脂環式構造が塗膜表面付近に分布した垂直配向膜を得ることができる。該垂直配向膜は、塗膜表面が疎水性であるので、液晶分子の分子軸をホメオトロピック配向させることができる。
【0022】
中でも、ポリイミド系の垂直配向膜用組成物は、前記一般式(1)で表されるアゾ化合物と混合しやすく、基板に塗布しやすいことや、耐熱性に優れた垂直配向膜が得られることから特に好ましい。ポリイミド系の垂直配向膜用組成物として、長鎖アルキル基や脂環式構造を側鎖に有するポリアミック酸を使用する場合は、本発明の垂直配向膜用組成物を基板上に塗布した後に加熱焼成して、ポリアミック酸をイミド化させる。
【0023】
前記一般式(1)で表されるアゾ化合物は、本発明の垂直配向膜用組成物の0.5〜50%を占める量を添加する。前記アゾ化合物の添加量が0.5%未満では、大きいプレチルト角を得ることが難しく、一方、前記アゾ化合物の添加量が50%を越えてしまうと、液晶分子を垂直配向させることが困難になる。中でも、本発明の垂直配向膜用組成物の1%〜35%を占める量を添加することが好ましい。
【0024】
本発明の垂直配向膜用組成物を基板上に塗布し、偏光、もしくは膜面に対して斜め方向から非偏光を照射することで、液晶分子を垂直配向させ、且つ大きなプレチルト角を与えることのできる光配向膜を得ることができる。
前記一般式(1)で表されるアゾ化合物は、アゾ基が吸収する波長の偏光を照射すると、偏光方向に対して一定の方向に再配列、即ち光配向する。従って、前記一般式(1)で表されるアゾ化合物からなる組成物を基板上に塗布後、偏光を照射した塗膜は、液晶分子の分子軸をホモジニアス配向させることができる。
本発明の垂直配向膜用組成物は、本発明で使用する垂直配向膜用組成物Aに、前記一般式(1)で表されるアゾ化合物を添加しているので、これを基板上に塗布し、偏光、もしくは膜面に対して斜め方向から非偏光を照射して、前記一般式(1)で表されるアゾ化合物を光配向させた垂直配向膜は、ホメオトロピック配向した液晶分子に、基板面法線から一定の方向に大きなプレチルト角を与えることができる。
【0025】
また、従来の技術では、短波長の紫外線で長鎖アルキル基を切断することによって、液晶分子を配向させるのに対して、本発明においては、紫外線照射によるアゾ化合物の再配列によって液晶分子を配向させる。即ち、長鎖アルキル基を切断する必要がない。
【0026】
次に、本発明の垂直配向膜用組成物を使用して、垂直配向膜を製造する方法の例を述べる。
本発明の垂直配向膜用組成物は溶媒に溶解して使用する。この際溶媒は特に限定されないが、N−メチルピロリドン、N,N,−ジメチルホルムアミド、ブチルセロソルブ、γ−ブチロラクトン、クロロベンゼン、ジメチルスルホキシド、ジメチルアセトアミド、テトラヒドロフラン、トルエン、エチレングリコールモノブチルエーテル等が一般的に用いられる。中でもブチルセロソルブ、γ−ブチロラクトン、N−メチルピロリドン、N,N−ジメチルホルムアミドの溶液はガラス等の基板に対する塗布性が良好で、均一な膜が得られることから特に好ましい。これらの溶剤は、塗布性や、塗布後の溶剤の揮発速度を考慮して選択することが好ましく、2種類以上を混合して使用することもできる。
【0027】
本発明に使用する基板は、液晶配向膜を有する液晶表示素子に通常使用する基板であって、特に液晶表示素子製造時の加熱に耐えうる耐熱性を有するものが好ましい。そのような基板としてはガラスや耐熱性のポリマーからなる基板が挙げられる。
通常は、その表面にITO等の透明電極や薄膜トランジスタ等を設けて使用する。
【0028】
基板上に、スピンコーティング法、印刷法、ダイコーティング法、ディッピング法等の方法によって本発明の垂直配向膜用組成物の溶液を塗布し、乾燥後、得られた塗膜の光配向操作を行う。
【0029】
本発明の垂直配向膜用組成物を塗布、乾燥して得られる塗膜の光配向は、塗膜に直線偏光や楕円偏光等の偏光、もしくは膜面に対して斜めの方向から非偏光を照射することによって行う。偏光は、偏光フィルタを使用するので光強度が減少する傾向にある。これに対し、膜面に対して斜め方向から非偏光を照射する方法には、照射装置に偏光フィルタを必要とせず、大きな強度の照射光が得られ、光配向のための照射時間を短縮することができるという利点がある。
照射する光は、一般式(1)で表されるアゾ化合物が吸収を有する波長領域の光であり、具体的には波長が350〜400nmの範囲の紫外線が特に好ましい。具体的には、キセノンランプ、高圧水銀ランプ、超高圧水銀ランプ、メタルハライドランプ等の紫外光源からの光を偏光フィルタやグラントムソン、グランテーラー等の偏光プリズムを通すことで紫外線の直線偏光を得ることができる。また、偏光、非偏光のいずれを使用する場合でも、照射する光は、ほぼ平行光であることが特に好ましい。本発明の垂直配向膜用組成物は、超高圧水銀ランプ等の最も強度の大きい発光波長である365nmを使用して効率よく光配向させることができる。
【0030】
一般式(1)で表されるアゾ化合物が重合性基を有する場合は、光配向操作後、重合性基を重合させることによって、より耐熱性に優れた配向膜を得ることができる。重合方法としては、熱重合、又は光重合が挙げられる。このとき、必要に応じて公知慣用の重合開始剤を使用することが好ましい。
熱重合開始剤としては、例えば、ベンゾイルパーオキサイド、2,4-ジクロロベンゾイルパーオキサイド、1,1-ジ(ターシャリーブチルパーオキシ)−3,3,5−トリメチルシクロヘキサン、2,2’−アゾビスイソブチロニトリル、テトラメチルチウラムジスルフィド等が挙げられる。又、光重合開始剤としては、例えば、1−ヒドロキシシクロヘキシルフェニルケトン、2−メチル−1−[(メチルチオ)フェニル]−2−モリホリノプロパン−1、ベンジルジメチルケタール、アシルフォスフィンオキシド等が挙げられる。
重合性基を熱重合させるには、本発明の垂直配向膜用組成物を塗布乾燥させ、光配向操作をしたのち、加熱する。加熱温度は100〜300℃が好ましく、100〜200℃がさらに好ましい。
一方、重合性基を光重合させるには、本発明の垂直配向膜用組成物を塗布乾燥させ、光配向操作をしたのち、一般式(1)で表されるアゾ化合物のアゾベンゼン構造が吸収しない波長である、200〜320nmの波長の光を照射する。
【0031】
本発明で使用する垂直配向膜用組成物Aがポリアミック酸の場合は、本発明の垂直配向膜用組成物を基板に塗布した後、又は、本発明の垂直配向膜用組成物を塗布乾燥させ、光配向操作した後、加熱焼成してポリアミック酸をイミド化させる。このときの加熱温度は150℃〜250℃が好ましい。
このとき、一般式(1)で表されるアゾ化合物として、前記式(b)、(c)、又は(d)で表される化合物のような、重合性基を有する化合物を選択すると、光配向操作した後に加熱焼成することで、イミド化と熱重合を同時にすることができる。
【0032】
次に、前記製造方法により作製した垂直配向膜を使用し、液晶表示素子を得る方法の一例を以下に述べる。
例えば、偏光膜、位相差膜、反射膜、ITO電極等を設けた透明基板上の、ITO電極面に、本発明の垂直配向膜用組成物の有機溶媒溶液を塗布し、乾燥させ、光配向操作を行う。このとき、一般式(1)で表されるアゾ化合物が重合性基を有する場合は、さらに光照射もしくは加熱によって重合性基を重合させ、配向を固定化する。このようにして、前記基板上に垂直配向膜を作製する。
次に、得られた基板の、該垂直配向膜を設けた面を内側にし、スペーサーを介して、公知の方法により貼り合わせて、液晶セルを作製する。得られた液晶セルの二枚の基板の間隙に液晶を注入して、液晶表示素子を製造することができる。
本発明の垂直配向膜の製造方法により得られた垂直配向膜を設けた液晶表示素子は、長鎖アルキル基等の分解生成物を有さないので、高い電圧保持率を有する。
【0033】
【実施例】
以下、実施例および比較例を用いて本発明をさらに詳細に説明する。
【0034】
[合成例1]
1,2−ニトロベンゼンスルホン酸20.3gを100mlの水に溶かし、水酸化ナトリウム25gを加えた。これを50〜80℃に加熱し、亜鉛粉末25gを少しずつ添加し、更に硫酸ナトリウム5gを160mlの水に溶かしたものを沸騰させて加えた。その後、未反応の亜鉛粉末をろ過し、ろ液に30%塩酸90mlを加えた。冷却後、沈殿物をろ別し、水洗後、水で再結晶することにより、3,3’−ベンジジンジスルホン酸12gを得た。
次に、3,3’−ベンジジンジスルホン酸8.6gに2%塩酸230mlを加え、0〜5℃に保ちながら亜硝酸ナトリウム0.5gの水溶液を少しずつ滴下し、2時間反応させてジアゾニウム溶液を得た。次に2−ヒドロキシ安息香酸6.9gを300mlの5%炭酸ナトリウム水溶液に溶かし、これに前記ジアゾニウム溶液を徐々に滴下した。1時間反応させた後、20%食塩水を加えて沈殿物を得た。この沈殿物を、エタノールと水の混合溶媒で再結晶させて、4.8gの式(2)で表されるアゾ化合物を得た。
【0035】
【化7】
【0036】
[合成例2]
4−ヒドロキシ安息香酸13.8g、ヨウ化カリウム2.5gに、44mlのエタノールと8.4gの水酸化ナトリウムを溶解させた水44mlを加え撹拌し溶解させた。これに6−クロロ−1−ヘキサノール13.6gを徐々に滴下し、16時間還流した。冷却後、撹拌しながら希塩酸を加えて中和させ、得られた沈殿物をろ別し、水で洗浄し、乾燥させ、式(3)で表される化合物22gを得た。
【0037】
【化8】
【0038】
次に、ディーンスターク水分離器を備えた反応容器に、式(3)で表される化合物を11g、アクリル酸13.3g、トルエン42ml、n−ヘキサン18ml、テトラヒドロフラン26ml、ヒドロキノン0.6g、p−トルエンスルホン酸2.7gを仕込み、撹拌しながら加熱し、生成する水を分離しながら、5時間還流させた。室温まで冷却後、水100mlで洗浄し、酢酸エチル50mlを加えた。次に、40mlの飽和炭酸水素ナトリウム水溶液で洗浄した後、水相が中性になるまで水で洗浄し、最後に有機溶媒を減圧留去した。得られた粗生成物を、トルエンとヘキサンの混合溶媒で再結晶することにより、式(4)で表される化合物約11gを得た。
【0039】
【化9】
【0040】
アニソール2.0gをジクロロメタン中で臭化アセチル2.0gと反応させた後、溶媒を留去した。得られた化合物2.5gをN,N−ジメチルホルムアミドに溶かし、これに合成例1で得られた式(2)で表される化合物1.6gを加え、トリエチルアミンの存在下で反応させた。次に、式(4)で表される化合物0.6gを加え、1−エチル−3−(3−ジメチルアミノプロピル)−カルボイミド塩酸塩の存在下で反応させた。溶媒を留去した後、得られた粗生成物をアニソールに溶解し、トリフルオロ酢酸を添加して反応させた。最後に溶媒を留去後、ヘキサンで洗浄することで、式(5)で表されるアゾ化合物0.1gを得た。
【0041】
【化10】
【0042】
[実施例1]
合成例1で得られた式(2)で表されるアゾ化合物の1.3%N,N,−ジメチルホルムアミド(以下、DMFと略す。)溶液を1質量部、ジェイエスアール(株)製のポリイミド系垂直配向膜用組成物「JALS−2021」1質量部、DMF1質量部を混合し、垂直配向膜用組成物とした。該垂直配向膜用組成物を、スピンコーターでITO電極付きガラス基板のITO電極面に均一に塗布し、190℃で1.5時間加熱した。得られた塗膜表面に、最も大きい強度が365nmである超高圧水銀ランプを使用し、干渉フィルタを通して得られた、エネルギー密度40mW/cm2の非偏光の平行紫外光を、基板法線に対して30°の角度から、積算光量が5J/cm2となるように照射し、該基板のITO電極上に垂直配向膜を作成した。
【0043】
次に、該垂直配向膜付基板の外縁部に直径5μmのスチレンビーズを含んだ熱硬化性接着剤を液晶注入口が残るように塗布し、もう一枚の垂直配向膜付基板を、配向面が相対し、かつ照射した斜め非偏光の入射面が反平行となるように重ね合わせて圧着し、接着剤を90分間150℃に加熱して硬化させた。次いで、液晶注入口よりメルク社製の誘電率異方性が負の液晶組成物「MLC−6609」を、120℃で注入し、エポキシ系接着剤で液晶注入口を封止し、液晶表示素子Aを得た。
【0044】
液晶表示素子Aのプレチルト角を、回転結晶法[T.J.Schuffer,et al.,J.Appl.Phys.,vol.48,1783(1977)]により測定した。その結果、プレチルト角は基板法線に対して1.5°であった。
【0045】
液晶表示素子の、電圧印加による液晶の応答速度の測定は次のようにして行った。測定に使用した装置を、図1に示す。最初に、偏光方向が互いに直交する二枚の偏光板2と4の間に、液晶表示素子3を、光配向のために照射した紫外光の偏光方向7が、それぞれの偏光板の偏光方向の45°の角度をなすように配置した。次に、He−Neレーザー発振装置1から発振された633nm波長のレーザー光を、液晶表示素子3の基板面、ならびに偏光板2及び4の面に対し、法線方向から照射した。このとき、液晶表示素子3の電極間に、1KHzの交流電場を断続的に印加した。交流電場を印加しないときは暗状態、印加したときは明状態となるが、この透過光の強度の変化を、フォトダイオード5で検出し、その出力変化をオシロスコープ9で測定し、暗状態から明状態の変化時間を液晶の応答速度とした。このようにして測定した液晶表示素子Aの液晶の応答速度は16msecであった。
【0046】
次に、液晶表示素子Aの電圧保持率を測定した。電圧保持率は、該液晶表示素子のITO電極間に、80℃の環境下、5Vの電圧を64μsec間印加し、その後16msec経過した時の電極間の電圧を測定し、印加電圧5Vに対する百分率で表した。その結果、電圧保持率は96%であった。
【0047】
[実施例2]
合成例2で得られた式(5)で表されるアゾ化合物の1.0%N−メチルピロリドン(以下、NMPと略す。)溶液を1質量部、ジェイエスアール(株)製のポリイミド系垂直配向膜用組成物「JALS−204」1質量部、和光純薬工業(株)製の熱重合開始剤「V−65」0.02質量部、及び、1質量部のNMPを混合し、垂直配向膜用組成物とした。該垂直配向膜用組成物を、スピンコーターでITO電極付きガラス基板のITO電極面に均一に塗布し、100℃で10分間乾燥した。得られた塗膜表面に実施例1と同様にして平行紫外光を照射した後、190℃で1.5時間加熱してポリイミド系垂直配向膜用組成物の焼成と、式(5)で表されるアゾ化合物の重合とを同時に行い、該基板のITO電極上に垂直配向膜を作成した。
【0048】
得られた垂直配向膜付き基板を使用し、実施例1と同様の方法で液晶表示素子Bを作成した。液晶表示素子Bのプレチルト角の測定を行った結果、プレチルト角は基板法線方向に対して1.4°であった。
次に、実施例1と同様の方法で、液晶表示素子Bの電圧印加による液晶の応答速度の測定を行った結果、応答時間は20msecであった。
また、実施例1と同様の方法で、液晶表示素子Bの電圧保持率の測定を行ったところ、電圧保持率の値は95%であった。
【0049】
[比較例1]
ジェイエスアール(株)製のポリイミド系垂直配向膜用組成物「JALS−2021」1質量部とDMF1質量部を混合し、垂直配向膜用組成物とした。該垂直配向膜用組成物を、スピンコーターでITO電極付きガラス基板のITO電極面に均一に塗布し、190℃で1.5時間加熱した。得られた塗膜表面に、超高圧水銀ランプを使用し、干渉フィルタを通して得られた、波長313nm、エネルギー密度30mW/cm2の非偏光の平行紫外光を、基板法線に対して30°の角度から、積算光量が5J/cm2となるように照射し、垂直配向膜を作成した。
【0050】
得られた垂直配向膜付き基板を使用し、実施例1と同様の方法で液晶表示素子Cを作成した。液晶表示素子Cのプレチルト角の測定を行った結果、プレチルト角は基板法線方向に対して0.4°であった。
次に、実施例1と同様の方法で、液晶表示素子Cの電圧印加による液晶の応答速度の測定を行った結果、応答時間は118msecであった。
また、実施例1と同様の方法で、液晶表示素子Cの電圧保持率を測定したところ、電圧保持率は89%であった。
【0051】
この結果、実施例1及び2で得られた液晶表示素子A及びBは、比較例1で得られた液晶表示素子Cと比較して、プレチルト角が大きく、液晶の応答速度もはやかった。
【0052】
【発明の効果】
本発明の垂直配向膜用組成物を基板上に塗布し、偏光、もしくは膜面に対して斜め方向から非偏光を照射することで、液晶分子に大きなプレチルトを与えることのできる垂直配向膜を得ることができる。
即ち、本発明の垂直配向膜用組成物は、一般式(1)で表されるアゾ化合物を含有しているので、偏光、もしくは膜面に対して斜め方向からの非偏光を照射して該アゾ化合物を光配向させることで、ホメオトロピック配向した液晶分子に、基板面法線から一定の方向に比較的大きなプレチルト角を与えることができる。
本発明においては、短波長の紫外線を照射して長鎖アルキル基を分解することなく、液晶分子にプレチルト角を与えることができるので、本発明の垂直配向膜用組成物を使用して得られる液晶表示素子は高い電圧保持率を示す。
【図面の簡単な説明】
【図1】液晶表示素子の応答速度の測定装置を模式的に表した。
【符号の説明】
1 He−Neレーザー発振装置
2 偏光板
3 液晶表示素子
4 偏光板
5 フォトダイオード
6 偏光板2の偏光方向
7 光配向のために照射した紫外線の偏光方向
8 偏光板4の偏光方向
9 オシロスコープ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal alignment film used for a liquid crystal display element, and more particularly to a rubbing-less vertical alignment film capable of vertically aligning liquid crystals.
[0002]
[Prior art]
Conventionally, twisted nematic mode liquid crystal display elements have been widely used as liquid crystal display elements, but in recent years, liquid crystal molecules having negative dielectric anisotropy have been used as a display method with a high contrast ratio and a small viewing angle dependency. 2. Description of the Related Art A vertical alignment mode liquid crystal display element that has been aligned perpendicularly to a substrate (hereinafter abbreviated as homeotropic alignment) has been actively developed.
In order to display the liquid crystal display element in the vertical alignment mode, the alignment regulating force in the azimuth direction is applied to the liquid crystal molecules, and the liquid crystal molecules are aligned in parallel to the substrate surface when a voltage is applied (hereinafter abbreviated as homogeneous alignment). ) To control the orientation of the liquid crystal molecules when no voltage is applied, the molecular axis of the liquid crystal molecules in a certain orientation in the substrate plane, and a constant pretilt angle with respect to the substrate surface normal. It is necessary to orient so that it has.
[0003]
As a method for giving a pretilt angle to liquid crystal molecules, a method is known in which a vertical alignment film such as polyimide whose surface is rubbed is provided on the inner surface of a liquid crystal cell to give the liquid crystal molecules a pretilt angle with respect to the normal direction of the substrate surface. However, streaky luminance unevenness is likely to occur on the liquid crystal display screen, and the display quality is degraded.
[0004]
On the other hand, JP-A-9-21468 discloses a composition for a vertical alignment film of a polyimide or silane coupling agent having a long-chain linear alkyl group on a substrate, and then the surface of the coating film. In addition, there is a method in which a vertical alignment film obtained by irradiating a non-polarized ultraviolet ray having a short wavelength such as 254 nm or 313 nm from an oblique direction is provided on the inner surface of the substrate of the liquid crystal cell to give the liquid crystal molecules a pretilt angle with respect to the normal to the substrate surface. It is disclosed.
However, the pretilt angle obtained by this method is as small as less than 1 °. As a result, when a voltage is applied, there is a problem that an alignment defect occurs in the liquid crystal display element or the voltage response speed becomes slow. In addition, this method decomposes or cuts a part of the long-chain alkyl group with ultraviolet rays having a short wavelength, and aligns the direction of the long-chain alkyl group with a certain direction in the substrate surface, thereby giving the liquid crystal molecules a pretilt angle. However, the decomposition product generated at this time has a problem that the liquid crystal display element characteristics such as the voltage holding ratio deteriorate.
[0005]
[Problems to be solved by the invention]
The problem to be solved by the present invention is that liquid crystal molecules can be aligned so that their molecular axes have a large pretilt angle with respect to the normal to the substrate surface in a certain orientation within the substrate surface, and voltage A composition for a vertical alignment film used for a liquid crystal display element in a vertical alignment mode capable of giving excellent liquid crystal display element characteristics without lowering the retention rate, and a vertical alignment using the composition for a vertical alignment film It is to provide a method for manufacturing a film.
[0006]
[Means for Solving the Problems]
The present invention provides a composition for a vertical alignment film for a liquid crystal display device by adding an azo compound having a function of photo-aligning with ultraviolet rays and homogeneously aligning the molecular axes of liquid crystal molecules, whereby the azimuth direction in the substrate plane A vertical alignment film to which an alignment force is applied can be obtained, and the above-described problems have been solved.
That is, the present inventionA composition for a vertical alignment film for a liquid crystal display device having a nonpolar long-chain alkyl group or an alicyclic structure,A vertical alignment film composition containing 0.5 to 50% by mass of the azo compound represented by the general formula (1), and the vertical alignment film compositionDissolved in organic solvents,Provided is a method for producing a vertical alignment film, which is applied on a substrate and after removing an organic solvent, followed by irradiation with non-polarized ultraviolet rays from an oblique direction.
[0007]
[Chemical 2]
[0008]
(Wherein R1Each independently represents a hydroxy group, a (meth) acryloyloxy group, a (meth) acrylamide group, a vinyloxy group, a vinyloxycarbonyl group, a vinyliminocarbonyl group, a vinyliminocarbonyloxy group, a vinyl group, an isopropenyloxy group, an iso A propenyloxycarbonyl group, an isopropenyliminocarbonyl group, an isopropenyliminocarbonyloxy group, an isopropenyl group, or an epoxy group is represented. R2Is-(A-B-A)m-(D)n-Represents a linking group represented by R3Is-(D)n-(A-B-A)m-Represents a linking group represented by-. Where A isLess than 20 carbon atomsRepresents a divalent hydrocarbon group, B represents —O—, —CO—O—, —OCO—, —CONH—, —NHCO—, —NHCO—O—, or —OCONH—, and m represents 0. Represents an integer of ~ 3. D is when m is 0,Less than 20 carbon atomsRepresents a divalent hydrocarbon group, and when m is an integer of 1 to 3, -O-, -CO-O-, -OCO-, -CONH-, -NHCO-, -NHCO-O-, or -OCONH -Represents n, and 0 represents 0 or 1.However, when m = n = 0, R 2 And R 3 Represents a single bond.R4Each independently represents a halogen atom, a carboxy group, a halogenated methyl group, a halogenated methoxy group, a cyano group, a nitro group, a methoxy group, or a methoxycarbonyl group. However, the carboxy group may form a salt with an alkali metal. R5Each independently represents a carboxy group, a sulfo group, a nitro group, an amino group, or a hydroxy group. However, the carboxy group or the sulfo group may form a salt with the alkali metal. )
[0009]
DETAILED DESCRIPTION OF THE INVENTION
In the general formula (1), R1Are (meth) acryloyloxy group, (meth) acrylamide group, vinyloxy group, vinyloxycarbonyl group, vinyliminocarbonyl group, vinyliminocarbonyloxy group, vinyl group, isopropenyloxy group, isopropenyloxycarbonyl group, isopropenyl It represents an iminocarbonyl group, an isopropenyliminocarbonyloxy group, an isopropenyl group, or an epoxy group. In the case of a polymerizable group selected from the group consisting of: after photoalignment of the composition for vertical alignment film of the present invention (hereinafter abbreviated as composition for vertical alignment film of the present invention), thermal polymerization or photopolymerization. The orientation can be fixed by this, and an alignment film having excellent heat resistance can be obtained, which is preferable. Among these, a (meth) acryloyloxy group or a (meth) acrylamide group is preferable.
[0010]
In the general formula (1), R1A hydroxy group or a polymerizable group represented by2And R3It connects with the adjacent phenylene group through the coupling group represented by these. Linking group R2And linking group R3Among them, the divalent hydrocarbon group represented by A includes an alkylene group having 3 to 20 carbon atoms such as propylene group and heptylene group, 1 carbon atom such as methylene group, trimethylene group and pentamethylene group. Examples thereof include cycloalkylene groups having 3 to 20 carbon atoms such as polymethylene group, cyclopropylene group and cyclohexylene group having ˜20, and arylene groups having 6 to 20 carbon atoms such as phenylene group and naphthylene group.
[0011]
In the general formula (1), R4Examples of the halogen atom include a fluorine atom and a chlorine atom, the halogenated methyl group includes a trichloromethyl group and a trifluoromethyl group, and the halogenated methoxy group includes a chloromethoxy group and a trifluoromethoxy group. . Above all, R4When is a carboxy group, adhesion to the substrate is high. The carboxy group may form a salt with an alkali metal such as lithium, sodium or potassium.
[0012]
In the general formula (1), R5Is preferably a carboxy group or a sulfo group because of high adhesion to the substrate. The carboxy group and the sulfo group may form a salt with an alkali metal such as lithium, sodium, or potassium.
[0013]
The azo compound represented by the general formula (1) is easily oriented when irradiated with polarized light or light from an oblique direction with respect to the substrate surface, and has film formability and adhesion to a substrate such as glass or ITO. Excellent. Specific examples include azo compounds having the following structure.
[0014]
[Chemical Formula 3]
[0015]
[Formula 4]
[0016]
[Chemical formula 5]
[0017]
[Chemical 6]
[0018]
For example, the azo compound represented by (a) is prepared by adding zinc powder and sodium sulfate aqueous solution to 1,2-nitrobenzenesulfonic acid sodium hydroxide aqueous solution, and then adding hydrochloric acid to 3,3′-benzidine. It is obtained by synthesizing disulfonic acid and reacting it with sodium nitrite to form a diazonium compound and then reacting with 2-hydroxybenzoic acid.
[0019]
The azo compound represented by (b) is obtained by reacting acrylic acid chloride with the hydroxy groups at both ends of the azo compound represented by (a).
[0020]
The azo compound represented by the general formula (1) is used by adding to a composition for vertical alignment film for liquid crystal display elements (hereinafter abbreviated as composition A for vertical alignment film used in the present invention). .
The composition A for vertical alignment film used in the present invention may be any as long as it has a function of homeotropic alignment of the molecular axes of liquid crystal molecules by providing it as a coating film on a substrate. Specifically, for example, a composition for a silane coupling-based vertical alignment film such as lecithin, a silane-based surfactant, a titanate-based surfactant, a pyridinium salt-based polymer surfactant, and n-octadecyltriethoxysilane, Examples thereof include a composition for a polyimide-based vertical alignment film such as a soluble polyimide having a chain alkyl group or an alicyclic structure in the side chain, or a polyamic acid having a long chain alkyl group or an alicyclic structure in the side chain. In the present invention, as the vertical alignment film composition A, polyimide vertical alignment film compositions “JALS-2021” and “JALS-204” manufactured by JSR Co., Ltd., manufactured by Nissan Chemical Industries, Ltd. Commercial products such as “RN-1517” and “SE-1211” can be used as they are.
[0021]
The composition A for vertical alignment films has a nonpolar long-chain alkyl group and an alicyclic structure, and is dissolved in an organic solvent so that the nonvolatile content concentration is about 1%, and spins on the substrate. When the organic solvent is removed after coating by a coating method or the like, a vertical alignment film in which nonpolar long-chain alkyl groups and alicyclic structures are distributed in the vicinity of the coating film surface can be obtained. Since the surface of the vertical alignment film is hydrophobic, the molecular axes of liquid crystal molecules can be homeotropically aligned.
[0022]
Among them, the polyimide-based composition for a vertical alignment film can be easily mixed with the azo compound represented by the general formula (1), can be easily applied to a substrate, and a vertical alignment film excellent in heat resistance can be obtained. Is particularly preferred. When a polyamic acid having a long chain alkyl group or an alicyclic structure in the side chain is used as a polyimide-based composition for a vertical alignment film, heating is performed after the composition for a vertical alignment film of the present invention is applied on a substrate. Baking to imidize the polyamic acid.
[0023]
The azo compound represented by the general formula (1) is added in an amount that occupies 0.5 to 50% of the composition for a vertical alignment film of the present invention. If the added amount of the azo compound is less than 0.5%, it is difficult to obtain a large pretilt angle. On the other hand, if the added amount of the azo compound exceeds 50%, it becomes difficult to vertically align liquid crystal molecules. Become. Especially, it is preferable to add the quantity which occupies 1%-35% of the composition for vertical alignment films of this invention.
[0024]
By applying the composition for vertical alignment film of the present invention on a substrate and irradiating polarized light or non-polarized light from an oblique direction with respect to the film surface, liquid crystal molecules are vertically aligned and a large pretilt angle is given. A photoalignment film that can be obtained can be obtained.
When the azo compound represented by the general formula (1) is irradiated with polarized light having a wavelength that is absorbed by the azo group, the azo compound is rearranged in a certain direction with respect to the polarization direction, that is, photo-aligned. Therefore, the coating film irradiated with polarized light after coating the composition comprising the azo compound represented by the general formula (1) on the substrate can make the molecular axes of liquid crystal molecules homogeneously align.
In the composition for vertical alignment film of the present invention, the azo compound represented by the general formula (1) is added to the composition A for vertical alignment film used in the present invention. The vertical alignment film in which the azo compound represented by the general formula (1) is photo-aligned by irradiating polarized light or non-polarized light from an oblique direction with respect to the film surface is applied to liquid crystal molecules that are homeotropically aligned. A large pretilt angle can be given in a certain direction from the substrate surface normal.
[0025]
In the conventional technique, the liquid crystal molecules are aligned by cleaving long-chain alkyl groups with short-wave ultraviolet light, whereas in the present invention, liquid crystal molecules are aligned by rearrangement of azo compounds by ultraviolet irradiation. Let That is, there is no need to cleave long chain alkyl groups.
[0026]
Next, an example of a method for producing a vertical alignment film using the composition for vertical alignment film of the present invention will be described.
The composition for vertical alignment films of the present invention is used after being dissolved in a solvent. In this case, the solvent is not particularly limited, but N-methylpyrrolidone, N, N, -dimethylformamide, butyl cellosolve, γ-butyrolactone, chlorobenzene, dimethyl sulfoxide, dimethylacetamide, tetrahydrofuran, toluene, ethylene glycol monobutyl ether and the like are generally used. It is done. Among them, a solution of butyl cellosolve, γ-butyrolactone, N-methylpyrrolidone, and N, N-dimethylformamide is particularly preferable because it has a good coatability on a substrate such as glass and a uniform film can be obtained. These solvents are preferably selected in consideration of applicability and the volatilization rate of the solvent after application, and two or more types can be mixed and used.
[0027]
The substrate used in the present invention is a substrate usually used for a liquid crystal display element having a liquid crystal alignment film, and particularly preferably has a heat resistance capable of withstanding heating during the production of the liquid crystal display element. Examples of such a substrate include a substrate made of glass or a heat resistant polymer.
Usually, a transparent electrode such as ITO, a thin film transistor or the like is provided on the surface.
[0028]
A solution of the composition for vertical alignment film of the present invention is applied onto a substrate by a method such as spin coating, printing, die coating, dipping, and the like, and after drying, the photo-alignment operation of the obtained coating film is performed. .
[0029]
The coating film obtained by applying and drying the composition for vertical alignment film of the present invention is irradiated with polarized light such as linearly polarized light and elliptically polarized light, or non-polarized light from a direction oblique to the film surface. By doing. Polarization tends to decrease the light intensity because a polarizing filter is used. On the other hand, the method of irradiating non-polarized light from the oblique direction with respect to the film surface does not require a polarizing filter in the irradiating device, so that irradiation light with high intensity can be obtained and the irradiation time for photo-alignment is shortened. There is an advantage that you can.
The light to be irradiated is light in a wavelength region in which the azo compound represented by the general formula (1) has absorption, and specifically, ultraviolet light having a wavelength in the range of 350 to 400 nm is particularly preferable. Specifically, linearly polarized ultraviolet light is obtained by passing light from an ultraviolet light source such as a xenon lamp, a high-pressure mercury lamp, an ultra-high pressure mercury lamp, or a metal halide lamp through a polarizing prism such as a polarizing filter, Glan Thompson, or Grand Taylor. Can do. Moreover, it is particularly preferable that the irradiated light is substantially parallel light regardless of whether polarized light or non-polarized light is used. The composition for vertical alignment films of the present invention can be efficiently photo-aligned using 365 nm, which is the emission wavelength with the largest intensity, such as an ultra-high pressure mercury lamp.
[0030]
When the azo compound represented by the general formula (1) has a polymerizable group, an alignment film having more excellent heat resistance can be obtained by polymerizing the polymerizable group after the photo-alignment operation. Examples of the polymerization method include thermal polymerization and photopolymerization. At this time, it is preferable to use a known and usual polymerization initiator as necessary.
Examples of the thermal polymerization initiator include benzoyl peroxide, 2,4-dichlorobenzoyl peroxide, 1,1-di (tertiary butyl peroxy) -3,3,5-trimethylcyclohexane, 2,2′-azo. Examples thereof include bisisobutyronitrile and tetramethylthiuram disulfide. Examples of the photopolymerization initiator include 1-hydroxycyclohexyl phenyl ketone, 2-methyl-1-[(methylthio) phenyl] -2-morpholinopropane-1, benzyl dimethyl ketal, and acylphosphine oxide. Can be mentioned.
In order to thermally polymerize the polymerizable group, the composition for vertical alignment film of the present invention is applied and dried, subjected to a photo-alignment operation, and then heated. The heating temperature is preferably from 100 to 300 ° C, more preferably from 100 to 200 ° C.
On the other hand, in order to photopolymerize the polymerizable group, the azobenzene structure of the azo compound represented by the general formula (1) does not absorb after coating and drying the composition for vertical alignment film of the present invention and performing photoalignment operation. Irradiate light having a wavelength of 200 to 320 nm.
[0031]
When the composition A for vertical alignment films used in the present invention is a polyamic acid, the composition for vertical alignment films of the present invention is applied to a substrate, or the composition for vertical alignment films of the present invention is applied and dried. After the photo-alignment operation, the polyamic acid is imidized by heating and baking. The heating temperature at this time is preferably 150 ° C to 250 ° C.
At this time, when a compound having a polymerizable group such as the compound represented by the formula (b), (c), or (d) is selected as the azo compound represented by the general formula (1), Imidization and thermal polymerization can be performed simultaneously by heating and firing after the orientation operation.
[0032]
Next, an example of a method for obtaining a liquid crystal display element using the vertical alignment film produced by the above production method will be described below.
For example, an organic solvent solution of the composition for vertical alignment film of the present invention is applied to a surface of an ITO electrode on a transparent substrate provided with a polarizing film, a retardation film, a reflective film, an ITO electrode, etc., dried, and photo-aligned Perform the operation. At this time, when the azo compound represented by the general formula (1) has a polymerizable group, the polymerizable group is further polymerized by light irradiation or heating to fix the orientation. In this way, a vertical alignment film is formed on the substrate.
Next, the surface of the obtained substrate on which the vertical alignment film is provided is set inward, and bonded together by a known method through a spacer to produce a liquid crystal cell. A liquid crystal display element can be manufactured by injecting liquid crystal into a gap between two substrates of the obtained liquid crystal cell.
The liquid crystal display element provided with the vertical alignment film obtained by the method for producing a vertical alignment film of the present invention does not have a decomposition product such as a long chain alkyl group, and thus has a high voltage holding ratio.
[0033]
【Example】
Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.
[0034]
[Synthesis Example 1]
20.3 g of 1,2-nitrobenzenesulfonic acid was dissolved in 100 ml of water, and 25 g of sodium hydroxide was added. This was heated to 50 to 80 ° C., 25 g of zinc powder was added little by little, and 5 g of sodium sulfate dissolved in 160 ml of water was boiled and added. Thereafter, unreacted zinc powder was filtered, and 90 ml of 30% hydrochloric acid was added to the filtrate. After cooling, the precipitate was filtered off, washed with water, and recrystallized with water to obtain 12 g of 3,3'-benzidine disulfonic acid.
Next, 230 ml of 2% hydrochloric acid is added to 8.6 g of 3,3′-benzidine disulfonic acid, and an aqueous solution of 0.5 g of sodium nitrite is added dropwise little by little while keeping the temperature at 0 to 5 ° C. to react for 2 hours to obtain a diazonium solution Got. Next, 6.9 g of 2-hydroxybenzoic acid was dissolved in 300 ml of 5% aqueous sodium carbonate solution, and the diazonium solution was gradually added dropwise thereto. After reacting for 1 hour, 20% saline was added to obtain a precipitate. This precipitate was recrystallized with a mixed solvent of ethanol and water to obtain 4.8 g of an azo compound represented by the formula (2).
[0035]
[Chemical 7]
[0036]
[Synthesis Example 2]
To 13.8 g of 4-hydroxybenzoic acid and 2.5 g of potassium iodide, 44 ml of water in which 44 ml of ethanol and 8.4 g of sodium hydroxide were dissolved was added and stirred to dissolve. To this, 13.6 g of 6-chloro-1-hexanol was gradually added dropwise and refluxed for 16 hours. After cooling, dilute hydrochloric acid was added to neutralize while stirring, and the resulting precipitate was filtered off, washed with water and dried to obtain 22 g of the compound represented by formula (3).
[0037]
[Chemical 8]
[0038]
Next, in a reaction vessel equipped with a Dean-Stark water separator, 11 g of the compound represented by formula (3), 13.3 g of acrylic acid, 42 ml of toluene, 18 ml of n-hexane, 26 ml of tetrahydrofuran, 0.6 g of hydroquinone, p -2.7 g of toluenesulfonic acid was charged, heated with stirring, and refluxed for 5 hours while separating generated water. After cooling to room temperature, it was washed with 100 ml of water, and 50 ml of ethyl acetate was added. Next, after washing with 40 ml of saturated aqueous sodium hydrogen carbonate solution, the mixture was washed with water until the aqueous phase became neutral, and finally the organic solvent was distilled off under reduced pressure. The obtained crude product was recrystallized with a mixed solvent of toluene and hexane to obtain about 11 g of a compound represented by the formula (4).
[0039]
[Chemical 9]
[0040]
After reacting 2.0 g of anisole with 2.0 g of acetyl bromide in dichloromethane, the solvent was distilled off. 2.5 g of the obtained compound was dissolved in N, N-dimethylformamide, and 1.6 g of the compound represented by the formula (2) obtained in Synthesis Example 1 was added thereto, and reacted in the presence of triethylamine. Next, 0.6 g of the compound represented by the formula (4) was added and reacted in the presence of 1-ethyl-3- (3-dimethylaminopropyl) -carbomido hydrochloride. After the solvent was distilled off, the resulting crude product was dissolved in anisole and reacted by adding trifluoroacetic acid. Finally, the solvent was distilled off, followed by washing with hexane to obtain 0.1 g of an azo compound represented by the formula (5).
[0041]
Embedded image
[0042]
[Example 1]
1 part by weight of a 1.3% N, N, -dimethylformamide (hereinafter abbreviated as DMF) solution of the azo compound represented by the formula (2) obtained in Synthesis Example 1 was manufactured by JSR Corporation. 1 part by mass of a polyimide-based vertical alignment film composition “JALS-2021” and 1 part by mass of DMF were mixed to obtain a composition for vertical alignment film. The composition for a vertical alignment film was uniformly applied to the ITO electrode surface of the glass substrate with an ITO electrode by a spin coater and heated at 190 ° C. for 1.5 hours. An energy density of 40 mW / cm obtained through an interference filter using an ultrahigh pressure mercury lamp having a maximum intensity of 365 nm on the surface of the obtained coating film.2Non-polarized parallel ultraviolet light from an angle of 30 ° with respect to the substrate normal is 5 J / cm.2Then, a vertical alignment film was formed on the ITO electrode of the substrate.
[0043]
Next, a thermosetting adhesive containing styrene beads having a diameter of 5 μm is applied to the outer edge of the substrate with the vertical alignment film so that the liquid crystal injection port remains, and another substrate with the vertical alignment film is formed on the alignment surface. Were opposed and pressed so that the irradiated obliquely polarized non-polarized light incident surface was antiparallel, and the adhesive was heated at 150 ° C. for 90 minutes to be cured. Next, a liquid crystal composition “MLC-6609” having a negative dielectric anisotropy made by Merck is injected from a liquid crystal injection port at 120 ° C., and the liquid crystal injection port is sealed with an epoxy-based adhesive. A was obtained.
[0044]
The pretilt angle of the liquid crystal display element A is determined by the rotational crystal method [T. J. et al. Schuffer, et al. , J .; Appl. Phys. , Vol. 48, 1783 (1977)]. As a result, the pretilt angle was 1.5 ° with respect to the substrate normal.
[0045]
The liquid crystal display device was measured for the response speed of liquid crystal by voltage application as follows. The apparatus used for the measurement is shown in FIG. First, between the two polarizing plates 2 and 4 whose polarization directions are orthogonal to each other, the polarization direction 7 of the ultraviolet light irradiated on the liquid crystal display element 3 for photo-alignment is the polarization direction of each polarizing plate. They were arranged at an angle of 45 °. Next, a laser beam having a wavelength of 633 nm oscillated from the He—Ne laser oscillation device 1 was applied to the substrate surface of the liquid crystal display element 3 and the surfaces of the polarizing plates 2 and 4 from the normal direction. At this time, an alternating electric field of 1 KHz was intermittently applied between the electrodes of the liquid crystal display element 3. When an AC electric field is not applied, it is in a dark state, and when it is applied, it is in a bright state. The change in the intensity of the transmitted light is detected by the photodiode 5, and the output change is measured by the oscilloscope 9. The change time of the state was defined as the response speed of the liquid crystal. The response speed of the liquid crystal of the liquid crystal display element A measured in this way was 16 msec.
[0046]
Next, the voltage holding ratio of the liquid crystal display element A was measured. The voltage holding ratio is a percentage of the applied voltage of 5 V measured by applying a voltage of 5 V for 64 μsec between the ITO electrodes of the liquid crystal display element in an environment of 80 ° C. for 64 μsec and then 16 msec. expressed. As a result, the voltage holding ratio was 96%.
[0047]
[Example 2]
1 part by mass of a 1.0% N-methylpyrrolidone (hereinafter abbreviated as NMP) solution of the azo compound represented by the formula (5) obtained in Synthesis Example 2 and a polyimide-based vertical product manufactured by JSR Corporation. The composition for alignment film “JALS-204” 1 part by mass, Wako Pure Chemical Industries, Ltd. thermal polymerization initiator “V-65” 0.02 part by mass, and 1 part by mass of NMP are mixed, It was set as the composition for alignment films. The composition for vertical alignment film was uniformly applied on the ITO electrode surface of the glass substrate with ITO electrode by a spin coater and dried at 100 ° C. for 10 minutes. The obtained coating film surface was irradiated with parallel ultraviolet light in the same manner as in Example 1, and then heated at 190 ° C. for 1.5 hours to sinter the polyimide vertical alignment film composition, and represented by the formula (5) Polymerization of the azo compound to be performed was performed simultaneously to form a vertical alignment film on the ITO electrode of the substrate.
[0048]
A liquid crystal display element B was prepared in the same manner as in Example 1 using the obtained substrate with a vertical alignment film. As a result of measuring the pretilt angle of the liquid crystal display element B, the pretilt angle was 1.4 ° with respect to the normal direction of the substrate.
Next, as a result of measuring the response speed of the liquid crystal by applying a voltage to the liquid crystal display element B in the same manner as in Example 1, the response time was 20 msec.
Further, when the voltage holding ratio of the liquid crystal display element B was measured in the same manner as in Example 1, the value of the voltage holding ratio was 95%.
[0049]
[Comparative Example 1]
1 part by mass of composition “JALS-2021” for polyimide-based vertical alignment film manufactured by JSR Co., Ltd. and 1 part by mass of DMF were mixed to obtain a composition for vertical alignment film. The composition for a vertical alignment film was uniformly applied to the ITO electrode surface of the glass substrate with an ITO electrode by a spin coater and heated at 190 ° C. for 1.5 hours. The obtained coating film surface was obtained through an interference filter using an ultrahigh pressure mercury lamp, wavelength 313 nm, energy density 30 mW / cm.2Non-polarized parallel ultraviolet light from an angle of 30 ° with respect to the substrate normal is 5 J / cm.2In this way, a vertical alignment film was prepared.
[0050]
A liquid crystal display element C was prepared in the same manner as in Example 1 using the obtained substrate with a vertical alignment film. As a result of measuring the pretilt angle of the liquid crystal display element C, the pretilt angle was 0.4 ° with respect to the normal direction of the substrate.
Next, as a result of measuring the response speed of the liquid crystal by applying a voltage to the liquid crystal display element C in the same manner as in Example 1, the response time was 118 msec.
Further, when the voltage holding ratio of the liquid crystal display element C was measured by the same method as in Example 1, the voltage holding ratio was 89%.
[0051]
As a result, the liquid crystal display elements A and B obtained in Examples 1 and 2 had a larger pretilt angle and a liquid crystal response speed no longer than that of the liquid crystal display element C obtained in Comparative Example 1.
[0052]
【The invention's effect】
By applying the composition for vertical alignment film of the present invention on a substrate and irradiating polarized light or non-polarized light from an oblique direction with respect to the film surface, a vertical alignment film capable of giving a large pretilt to liquid crystal molecules is obtained. be able to.
That is, since the composition for vertical alignment films of the present invention contains the azo compound represented by the general formula (1), the composition is irradiated with polarized light or non-polarized light from an oblique direction with respect to the film surface. By photo-aligning the azo compound, a relatively large pretilt angle can be given to the homeotropically aligned liquid crystal molecules in a certain direction from the normal to the substrate surface.
In the present invention, a pretilt angle can be given to liquid crystal molecules without irradiating short-wave ultraviolet rays to decompose long-chain alkyl groups, so that the liquid crystal molecules can be obtained using the vertical alignment film composition of the present invention. The liquid crystal display element exhibits a high voltage holding ratio.
[Brief description of the drawings]
FIG. 1 schematically shows an apparatus for measuring the response speed of a liquid crystal display element.
[Explanation of symbols]
1 He-Ne laser oscillator
2 Polarizing plate
3 Liquid crystal display elements
4 Polarizing plate
5 Photodiode
6 Polarization direction of polarizing plate 2
7 Polarization direction of ultraviolet rays irradiated for photo-alignment
8 Polarization direction of polarizing plate 4
9 Oscilloscope
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