JP4081212B2 - Sealant composition for liquid crystal display device and liquid crystal display device using the sealant - Google Patents

Description

【００１８】
まず、熱硬化型エポキシ系シール剤の硬化過程は、大まかには以下の工程に分類される。
【００１９】
（工程１）：シール剤の所定厚さを得るため、圧力と熱を加える工程（表１において、「本キュア」と記載）。
【００２０】
（工程２）：圧力負荷を解除してもシール剤の厚さが変化しない（一般的に「タックフリー」という）時間だけシール剤に熱を加える工程（表１において、「１０分間」と記載）。
【００２１】
（工程３）：圧力を解除した後、材料を完全に硬化するため、熱を加える工程（表１において、「アフターキュア」と記載）。
【００２２】
これに対し、紫外線硬化型シール剤の硬化過程は、大まかには以下の工程に分類される。
【００２３】
（工程１）：紫外線照射（６０００ｍＪ／ｃｍ²）により材料の約８０％が硬化し、タックフリーとなる工程。
【００２４】
（工程２）：アフターキュア（１２０℃）により材料を完全に硬化する工程。
【００２５】
前記の硬化過程に基づいて、シール剤中の残留応力の計算を行うと、熱硬化型シール剤のトータルの残留応力値（約１．２２ｋｇｆ／ｍｍ²）は、紫外線硬化型シール剤のトータルの残留応力値（−０．０１８ｋｇｆ／ｍｍ²）より２桁程大きい数値を示している。従って、熱硬化型シール剤では紫外線硬化型シール剤に比較して、それの硬化過程でシール剤中に発生する残留応力が大きくなって、シール剤の接着性に悪影響を及ぼす懸念があると、本願発明者は考えた。
【００２６】
以上の計算結果は、次に示す考察よって妥当なものであると考えられる。
【００２７】
熱硬化型エポキシ系シール剤の場合には（図２）、シール剤３の温度が１５０℃に達しないと、シール剤３の硬化は促進されないため、シール剤３の温度がこの温度に達するまで、ガラス基板１、２の歪み（延び）に追随して、このガラス基板１、２に接着するシール剤３は自由に変形できる（図２（ａ））。このような状態であれば、ガラス基板１、２もシール剤３も自由に変形できるため、ガラス基板１、２の内部やシール剤３の内部に応力エネルギは保存されない。しかし、一旦、シール剤３の温度１５０℃で熱硬化型シール剤３の硬化が完了した後にあっては、このシール剤３は固化され、かつシール剤３とガラス基板１、２は接着されている（図２（ｂ））。よってこのガラス基板１、２を室温にもどす際には、ガラス基板１、２の収縮度合とシール剤３の収縮度合が、両者の熱膨張係数の相違に起因して異なるため、互いに接着固定されたシール剤３とガラス基板１、２の間に応力（シール剤３の幅方向の応力）が発生する。この応力が残留応力としてシール剤３とガラス基板内部１、２に保存されると考えられる（図２（ｃ））。図中の矢印は各部が受ける力の方向を示す。
【００２８】
一方、紫外線硬化型シール剤の場合には（図３）、シール剤３を加熱処理する前に、紫外線照射によってシール剤３の約８０％が硬化される（図３（ａ））。これにより、紫外線照射の後にはシール剤３はある程度固化され、かつガラス基板はシール剤３に接着されている（図３（ｂ））。従って、その後にこのガラス基板１、２を加熱・冷却しても、少なくともシール剤３の塗布された部分のシール剤３の膨張・収縮は、ガラス基板１、２の膨張・冷却に追随する。このことは、ガラス基板１、２に加熱と冷却を施したとしても、最終的にガラス基板１、２の温度を初期温度にすれば、ガラス基板１、２とシール剤３の接着状態は加熱前の初期状態に戻るため、両者間に応力を発生させる要因はなく、ガラス基板１、２の内部とシール剤３の内部に残留応力は保存されないと考えられる（図３（ｃ））。
【００２９】
（紫外線硬化型シール剤の問題点の把握）
以上に述べたように、紫外線硬化型シール剤を用いると、硬化過程に伴って発生する残留応力を大幅に低減できるため、液晶表示装置の剥離不良が改善されるはずであると、本願発明者は考えた。
【００３０】
しかし市販の紫外線硬化型シール剤を使用した場合、次に述べる問題点が顕在化した。
【００３１】
ノート型のパーソナルコンピュータにおいては、表示部周辺の表示に寄与しない額縁の幅を狭くするという要求があり（これを、狭額縁化という。）、この狭額縁化のため、ＴＦＴ基板の配線端子６の上であって、かつカラーフィルタ基板の周辺ブラックマスク５の下に紫外線硬化型シール剤３を配置させる設計を行った（図４を参照）。このためカラーフィルタ基板側では、紫外線硬化型シール剤全面がクロム（Ｃｒ）やアルミ（Ａｌ）金属のブラックマスク５に遮光されているので、紫外線硬化型シール剤３の硬化には、ＴＦＴ基板側から光を照射することを要する。しかし一方、ＴＦＴ基板上に形成された配線端子６も遮光機能を有するため、配線端子６の上に形成されたシール剤に光照射がなされない。
【００３２】
図４に示された線Ｖ−Ｖに部分の断面斜視図（図５）を用いて、この問題をより詳細に説明すると、液晶表示装置４の周辺部には、液晶分子を駆動する電圧を供給するため、複数の配線端子６からなる配線端子群が設けられており、この配線端子群の材質は、クロム（Ｃｒ）やアルミ（Ａｌ）の金属薄膜であって、遮光性を有している。市販の紫外線硬化型シール剤でもある程度加熱硬化作用を持っているが、もしこのシール剤３が加熱だけでは完全に硬化しないとすると、配線端子６の上に設けられたシール剤３については、光照射されないため光硬化の促進はされず、熱硬化の促進も期待できないことになる。このことは、基板の接着不良の要因となるほか、未硬化シール剤３の液晶中への溶解による液晶材料汚染や配向膜汚染という問題も引き起こす。従って、紫外線照射のみでも完全に硬化し、かつ加熱のみでも完全に硬化する２元硬化性シール剤の開発を行うべきであるとの結論に至った。なお、図５では、シール剤３とブラックマスク５の間に有機膜７を設けている。
【００３３】
本発明の２元硬化性シール剤の特徴は、この課題を解決するため、シール剤組成物中の有機過酸化物が、加熱によってラジカルを生成して光カチオン開始剤のカチオン生成を促進し、エポキシ化合物の加熱硬化を促進させる点にある。以下、その構成と物性を詳細に説明する。
【００３４】
（２元硬化性シール剤の構成と物性について）
タルク粒子の表面上の原子が分子レベルでエポキシ化合物と結合してその表面がエポキシ化合物で覆われたハイブリッド状態のタルク粒子とは、特開平１０−９５９０１号公報に開示されているメカノケミカル方法（たとえば、加熱処理、撹拌処理、ボールミル処理、シュレッダー処理、超音波処理）でタルク表面に物理的エネルギーを与えてその表面を活性化処理し、強く結合させたエポキシ化合物で被覆された粒子のことをいう。好ましい例として、商品名エピコート８２８（油化シェル（株））、エピコート８０７（油化シェル（株））、ＨＢＥ１００（新日本理化（株））などのエポキシ化合物とタルク粒子とのハイブリッド化物をあげることができる。
【００３５】
このようなタルク粒子をエポキシ化合物で覆ったハイブリッド状態のタルク粒子を使用することにより、本発明の２元硬化性シール剤は柔軟性と靱性とをもつとともに、圧縮永久ひずみも小さい。さらに、このタルク粒子の表面は非親水性のエポキシ化合物で覆われているので、２元硬化性シール剤の耐水性・耐湿性が飛躍的に向上する。さらに従来の充填材のようにシランカップリング剤等で表面を改質していないので、シランカップリング剤等が溶出して液晶材料を汚染することが原因となる表示不良は引き起こされない。このハイブリッド状態のタルク粒子の添加量は、２元硬化性シール剤中１０〜７０重量％が好ましい。１０重量％未満では靱性などの前述の性能をこのシール剤に付与できず、７０重量％を超えると、このシール剤の粘度が高くなり細い線状に基板に塗布することが困難になるからである。
【００３６】
紫外線硬化性アクリル樹脂組成物は、アクリル酸エステル樹脂と光ラジカル開始剤とを含有する周知の紫外線硬化性組成物であればよい。このような組成物は、たとえば前述の特開昭５５−４１４８８号公報に詳細に記載されている。本発明では紫外線硬化性アクリル樹脂組成物の原料または組成を特別に限定するものではないが、好ましいアクリル酸エステル樹脂として、ヒドロキシ基を分子内に有する化学構造のエポキシアクリレートをあげることができる。一般にエポキシアクリレートは、他のアクリル酸エステル樹脂に比べて接着強度が高いからである。
【００３７】
紫外線硬化性エポキシ樹脂組成物は、エポキシ基を有する化合物とオニウム塩などに代表される光カチオン開始剤とを含有する周知の紫外線硬化性エポキシ樹脂組成物であればよい。このような組成物は前述の特開昭６１−２３３７１９号公報、特開昭６１−５１０２４号公報に詳細に記載されている。本発明では紫外線硬化性エポキシ樹脂組成物の原料または組成を特別に限定するものではない。好ましいオニウム塩としては、ジアゾニウム塩、ヨードニウム塩、スルホニウム塩などをあげることができ、使用するエポキシ化合物と相溶するオニウム塩が好ましいといえる。また、紫外線硬化性エポキシ樹脂組成物と紫外線硬化性アクリル樹脂組成物との混合比は６：４〜８．５：１．５が好ましい。このような混合比の範囲において、後述するようなシール層の物性を得ることができるからである。
【００３８】
有機過酸化物は周知の有機過酸化物であればよく、本発明では特定の有機過酸化物に限定するものではない。本発明の２元硬化性シール剤においてこの有機過酸化物は特異な作用効果を発揮する。
【００３９】
一般に有機過酸化物はラジカル重合の開始剤と考えられており、アクリル樹脂組成物の加熱硬化には利用できるが、エポキシ樹脂組成物の加熱硬化には利用されることはなかった。しかし、有機過酸化物は、紫外線照射後の加熱工程における紫外線硬化性エポキシ樹脂組成物に対して硬化温度を下げかつ硬化速度を早める効果があることを発見した。この効果は、有機過酸化物のラジカルがオニウム塩のカチオン生成に何らかの作用をしているためと推定する。有機過酸化物の添加量は、シール剤組成物中０．１〜１０重量％が好ましい。０．１重量％未満では前述のオニウム塩のカチオン生成が促進されず、１０重量％を超えるとシール剤組成物の保存安定性を損なうからである。
【００４０】
前述の成分構成による２元硬化性シール剤は、従来の紫外線硬化性アクリル樹脂組成物と加熱硬化性エポキシ樹脂組成物との混合系のシール剤組成物に比べて、紫外線照射だけでも完全硬化することが可能であり、加熱だけでも完全硬化が可能である。もし紫外線の透過しない陰影部が存在しても、このシール剤は低い加熱温度で短時間に確実に完全硬化し、未硬化成分が液晶材料へ溶出するような心配もない。さらに、硬化後のシール層は強靱な弾性体で剥離強度が高く、圧縮永久歪みが小さく耐水性が強いので、優れた耐久性を発揮する。
【００４１】
２元硬化性シール剤の物性を、
１）硬化前の２５℃での粘度が５０，０００〜８０，０００ｍＰａ・ｓ
２）硬化前のチクソトロピック性が回転粘度型の回転数１ｒｐｍと回転数１０ｒｐｍにおける粘度比で１．５〜３．０
３）硬化時の体積収縮が３％以下
４）硬化温度が低く、かつ硬化時間を短くする
５）硬化後のヤング率を１０００〜３０００ＭＰａ
となるようにした。
【００４２】
２元硬化性シール剤の物性を前述のようにするには、紫外線硬化性アクリル樹脂組成物と紫外線硬化性エポキシ樹脂組成物との混合系で構成し、その混合比を６：４〜８．５：１．５にすることにより達成することができる。また、２元硬化性シール剤の接着力をアップさせるため、アクリル酸エステル樹脂としてエポキシアクリレートを使用することが好ましい。また低い硬化温度及び早い硬化速度にするために紫外線硬化性にし、かつ有機過酸化物を添加して前述のとおり硬化性をさらに改善した。
【００４３】
本発明の２元硬化性シール剤組成物の配合例を表２に示す。
【００４４】
【表２】

【００４５】
（２元硬化性シール剤の強度試験結果）
図６に、従来の紫外線硬化型シール剤と対比しながら、２元硬化性シール剤の強度試験結果を示す。図中、Ａは本発明の２元硬化性シール剤、Ｂは従来の紫外線硬化型シール剤１、Ｃは従来の紫外線硬化型シール剤２の破壊靱性値を示す。図６から明らかなように、２元硬化性シール剤の強度の破壊靱性値は、従来の紫外線硬化型シール剤のそれに比較して高く、時間の経過に伴って両者の破壊靱性値の差異は大きくなっている。強度試験の実施は、接着度に与える影響の大きい条件、具体的には、温度６０℃、湿度９０％ＲＨの高温・高湿の環境条件（以下、「耐湿試験」という。）でなされた。試験サンプルについては、液晶表示装置の一対のガラス基板間にシール剤を挟んだ状態で、これを硬化させて製作した。図６の横軸は、経過時間（基板の硬化接着時からの時間）を示し、縦軸は高温高湿処置後の破壊靱性値（以下、「耐湿強度」という。）を示す。
【００４６】
２元硬化性シール剤では、初期状態（経過時間ゼロの状態）において耐湿強度が高く、かつ時間経過によってその耐湿強度が劣化しない。これに比べて、従来の紫外線硬化型シール剤では、初期状態において耐湿強度は高いものの、時間が経過すると、耐湿強度の劣化が見られる。たとえば、２種の紫外線硬化型シール剤の耐湿強度はいずれも、５００時間の経過後において、初期状態の耐湿強度の約１／５程度であった。なお、約０．１５ｋｇｆ／ｍｍ^2/3以上の耐湿強度がなければ、液晶表示装置の製造の歩留まりや製品の信頼性の点で支障をきたすにもかかわらず、従来の紫外線硬化型シール剤ではこの条件を満足することは難しい。
【００４７】
以上の強度試験結果により、本発明の２元硬化性シール剤によって液晶表示装置の耐湿強度の改善を図れることが明らかになった。
【００４８】
実施の形態２
液晶表示装置の強度試験方法を、図７と図８を参照しながら説明する。
【００４９】
図７は、強度試験用のサンプルを液晶表示装置から切り取ることを説明する概念図である。図７に示すように、液晶表示装置４の基板端から矩形状サンプル８を切り取る。このサンプル８の大きさについては、その長手方向長さを１００ｍｍ、幅方向の長さを２５ｍｍ、厚さを１０ｍｍと統一した。サンプル８は、図８に示すようなアルミ製の治具１８に固定され、サンプル８の基板を互いに剥がす方向（図中の矢印方向）に、このアルミ製の治具１８を引っ張る。
【００５０】
この引っ張り試験の条件は、試験温度（環境温度）２５℃、引っ張り速度１ｍｍ／ｍｉｎである。
【００５１】
この試験方法は、破壊力学の分野において広く用いられるＤＣＢ（Double Cantilever Beam）試験に基づくものである。液晶表示装置の構成を考えると、ガラス基板の厚さが基板間の隙間に対して充分大きいので、基板間の隙間を一種のき裂とみなした評価が可能と考え、き裂を評価するパラメータとして、破壊靭性値（Fracture Toughness）を使用した。破壊靭性値は、この強度試験から得られる破断強度（実測値）を用いて応力計算によって導く。
【００５２】
この試験方法によれば、液晶表示装置の強度を数値化でき、強度評価の客観化を図ることができる。
【００５３】
なお、ＤＣＢ試験の測定値と液晶表示装置の破壊状況観察とによって、ＤＣＢ試験の測定値が０．１５ｋｇｆ／ｍｍ^2/3以上であれば、製造工程や製品において実用上問題の無いことが分かった。
【００５４】
【実施例】
以下、図面を参照しながら、強度試験の具体例を説明する。
【００５５】
１．液晶表示装置の構成
図９は、有機膜をカラーフィルタ基板に設けたＩＰＳパネルの断面図を、図１０は、有機膜をＴＦＴ基板に設けた画素平坦化パネルの断面図を示す。
【００５６】
まず、図９に示されたＩＰＳパネルの構成を説明する。
【００５７】
図９は、基板に平行方向（横方向）の電界を印加するＩＰＳパネルの断面図である。
【００５８】
ガラス基板１においては、その基板１上に横方向電界を生成するスイッチング素子９が形成され、その素子９上に配向制御膜１０が形成されている。一方、液晶（図示せず）を介してガラス基板１に対向するガラス基板２では、その基板２上にブラックマスク１１およびカラーフィルター１２が形成され、更に、このブラックマスク１１およびカラーフィルター１２を覆うようにオーバーコート膜１３が設けられいる。そして基板１と同様、基板２のスイッチング素子９の上にも配向制御膜１０が形成されている。なおここで、ブラックマスク１１の材質には、たとえば、遮光性を持つ金属膜や遮光性を有する顔料が用いられる。またオーバーコート膜１３の材質には、たとえば、熱もしくは光で硬化するアクリル系樹脂、エポキシ系樹脂等の有機膜が用いられる。
【００５９】
これらの基板１、２は互いに、約４〜５μｍのギャップを保った状態で対向配置されている。このギャップの量は、表示領域内に配置された表示内スペーサ１４の直径と、基板１、２の周辺のシール剤３の内部に配置されたシール内スペーサ１５の直径によって一義的に決定される。なおここで、シール剤３の材質は、熱硬化型シール剤または前記の本発明の２元硬化性シール剤であり、これをスクリーン印刷法やディスペンサ法によって、基板１上に環状に塗布し形成する。その後、基板１と基板２を約４μｍのギャップを保って保持させ、このシール剤３を硬化させた後、このギャップの領域に液晶を注入し液晶表示装置を完成させる。
【００６０】
次に、図１０に示された画素平坦化パネルの構成を説明する。
【００６１】
図１０は、有機膜によって画素電極が平坦化処理された画素平坦化パネルの断面図である。但し、図９の液晶表示装置と同じ構成を有する箇所の説明を省略する。
【００６２】
透明画素電極として機能するＩＴＯ膜（図示せず）の平坦化を図るため、基板１上に画素平坦化膜１６が、厚さ約１０μｍ形成されている。この画素平坦化膜１６の材質としては、たとえば、感光性を持つアクリル系樹脂等の有機膜が用いられる。また、基板１に垂直方向の電界を発生させるため、基板１側の画素平坦化膜１６上にＩＴＯ膜（図示せず）が設けられると共に、基板２側にもＩＴＯ膜１７が設けられている。そして、このＩＴＯ膜１７が保護膜としての機能も兼ね備えるため、基板２上に別途、オーバーコート膜を形成することを要しない。すなわち、シール剤３はブラックマスク１１と直接に接触している。
【００６３】
２．サンプル測定
ＩＰＳパネル、画素平坦化パネルについて、本発明の２元硬化性シール剤を用いて、液晶表示装置の破壊靭性値を測定した。さらに、この２元硬化性シール剤の技術的効果と対比するため、熱硬化型シール剤（たとえば、エポキシ系シール剤）を使用した液晶表示装置の破壊靭性値の測定値も併記した。表１には、２元硬化型シール剤と熱硬化型シール剤のそれぞれにつき、両者の物性値と硬化条件とを記載している。具体的には、熱硬化型シール剤の硬化では、１５０℃、１０分で本キュアした後、１５０℃、６０分でアフターキュアする。２元硬化性シール剤の硬化では、６０００ｍＪ／ｃｍ²の紫外線照射の後、１２０℃、６０分でアフターキュアする。
【００６４】
液晶表示装置の破壊靭性値の測定結果を図１１に示す。図１１の破壊靭性値データでは、ＩＰＳパネルと画素平坦化パネルを、それぞれ１０パネルづつ準備し、これらのパネルの端部から所定の矩形形状（長手方向長さを１００ｍｍ、幅方向の長さを２５ｍｍ、厚さを１０ｍｍ）サンプルを切り取り、切り取りサンプル各１０個の強度を測定した結果を、データの平均値および最少値で比較している。
【００６５】
図中Ｄは平均値をＥは最小値を示し、Ｆ〜Ｉはパネル構造とシール剤の組合せのケースを示す。Ｆ、Ｇは図９に示したＩＰＳパネル、Ｈ、Ｉは図１０に示した画素平坦化パネル、Ｆ、Ｈは熱硬化型シール材、Ｇ、Ｉは２元硬化型シール剤の組合せを示す。
【００６６】
３．測定結果の評価
この測定結果により、以下（１）〜（４）の結果を得ることができた。
【００６７】
（１）２元硬化性シール剤を使用すると、ＩＰＳパネル（図９）と画素平坦化パネル（図１０）のいずれでも破壊靱性値の平均値は一定であり、かつその数値は製品スペックの破壊靭性値（０．１５ｋｇｆ／ｍｍ^2/3）を越えている。
【００６８】
（２）２元硬化性シール剤を使用すると、ＩＰＳパネルと画素平坦化パネルのいずれも、それらの破壊靱性値の平均値と最少値とがほぼ一致し、破壊靱性値のサンプルによるばらつきが殆どみられない。
【００６９】
（３）熱硬化型シール剤を使用すると、ＩＰＳパネルの破壊靭性値の平均値は高いものの、その最少値は低いという結果を得た。すなわち、破壊靱性値のばらつきが大きい。
【００７０】
（４）熱硬化型シール剤を使用すると、画素平坦化パネルの破壊靱性値の平均値が低かった。すなわち、熱硬化型シール剤を使って製造したパネルの破壊靱性値は、２元硬化型シール剤を使った場合のそれと比べかなり劣ることが判明した。
【００７１】
前記実験結果の現象を解明するため、破壊面の断面観察を行った。
【００７２】
図１２は、熱硬化型シール剤を使用したＩＰＳパネルにおいて、破壊靱性値の低いサンプルの破壊状況を説明する図である。
【００７３】
図１３は、２元硬化型シール剤を使用したＩＰＳパネルにおいて、サンプルの破壊状況を説明する図であり、図１２の破壊状況と対比するものである。
【００７４】
ここで、図１２（ａ）と図１３（ａ）では、カラーフィルターが形成された基板（以下、この基板を「カラーフィルター基板」という）の断面図を示し、図１２（ｂ）と図１３（ｂ）では、スイッチング素子が形成された基板（以下、この基板を「アレイ基板」という）を示している。
【００７５】
図１２（ａ）、図１２（ｂ）によると、アレイ基板１とカラーフィルター基板２の剥離が、シール剤３の形成された領域において、シール剤３上のオーバーコート膜１３の表面とブラックマスク５の表面の境界に沿って観察された（以下、この剥離現象を「界面破壊」という）。そして、アレイ基板１側のシール剤３の上にオーバーコート膜１３が観察された（図１２（ｂ））。
【００７６】
これに対して、図１３（ａ）、図１３（ｂ）によると、シール剤３は、アレイ基板１側およびカラーフィルター基板２側の両方で観察されるので、アレイ基板１とカラーフィルター基板２の剥離はシール剤３の内部で生じたと推察される（以下、この剥離現象を「凝集破壊」をいう）。
【００７７】
すなわち、オーバーコート膜１３のような有機膜とブラックマスク５のような無機膜の界面は、接着力が弱く、熱硬化型シール剤を使用する場合には、この界面にそって界面剥離が発生したものと思われる。
【００７８】
またＩＰＳパネルの他、画素平坦化パネルにおいても同様に、熱硬化型シール剤を用いたパネルであって、破壊靱性値が最低のパネルについては、オーバーコート膜１３（有機膜）とブラックマスク５（無機膜）の境界面で界面破壊が観察され、破壊靱性値の大きいパネルについては、凝集破壊が発生していた。なお、全サンプル中の約２０％は界面破壊であった。
【００７９】
以上の実験結果から本願発明者は、シール剤の相違から次の知見を得た。
【００８０】
（１）熱硬化型シール剤のサンプルでは、有機膜（オーバーコート膜）と無機膜（ブラックマスク）の界面破壊が発生する。一方、２元硬化型シール剤では、このような界面破壊はみられない。したがって、シール剤の加熱過程で有機膜と無機膜の界面に接着上の問題が発生するものと考えられる。
【００８１】
（２）２元硬化型シール剤では、いずれのサンプルも界面破壊が発生しないので、有機膜（オーバーコート膜）を使用する液晶表示装置においては、２元硬化型シール剤を選別することが不可欠である。
【００８２】
なおこれらの知見は、有機膜を使わない液晶表示装置については、従来より熱硬化型シール剤で接着しても問題にならないという事実とも整合性があり、また、この知見によって、熱硬化型シール剤の残留応力が２元硬化型シール剤のそれに比べて大きい（したがって、熱硬化型シール剤は好ましくない）という数値計算の妥当性も確認された。
【００８３】
【発明の効果】
本発明のシール剤組成物の特徴は紫外線照射で完全硬化することが可能であるが、紫外線の非透過の陰影部が存在しても、低い加熱温度で短時間に硬化する点にある。
【００８４】
したがって、本発明の請求項１にかかわるシール剤組成物によれば、硬化後に強靱な弾性体で剥離強度が高く、しかも圧縮永久歪みが小さく耐水性の強い液晶表示装置用シール剤を得ることができる。
【００８５】
本発明の請求項２〜５にかかわる液晶表示装置によれば、基板間のシール部を紫外線を遮光する配線端子群と遮光膜とが共存する基板周辺に設けても、前記のシール剤組成物を使用することにより、シール剤組成物を低照射の紫外線照射および低い加熱温度で短時間に完全硬化できる。
【００８６】
また、本発明の請求項２〜５にかかわる液晶表示装置によれば、シール層に発生する内部応力を低くできるため、接着信頼性と耐久性の高い液晶表示装置を得ることができる。
【図面の簡単な説明】
【図１】数値計算用のモデルを示す断面図である。
【図２】熱硬化型シール剤を基板接着に使用した場合に、シール剤内部、基板内部の残留応力生成過程を説明する概念断面図である。
【図３】紫外線硬化型シール剤を基板接着に使用した場合に、残留応力の発生を回避できることを説明するための概念断面図である。
【図４】液晶表示装置の平面概念図である。
【図５】図４に示された線Ｖ−Ｖ箇所の断面斜視図である。
【図６】２元硬化性シール剤の強度試験結果を示す図である。
【図７】サンプル切り取りを説明する概念図である。
【図８】サンプル引っ張り試験を説明する概念図である。
【図９】有機膜をカラーフィルタ基板に設けたＩＰＳパネルの断面図である。
【図１０】有機膜をＴＦＴ基板に設けた画素平坦化パネルの断面図である。
【図１１】液晶表示装置の破壊靭性値の測定結果を示す図である。
【図１２】液晶表示装置の界面破壊の状態を説明する概念断面図である。
【図１３】液晶表示装置の凝集破壊の状態を説明する概念断面図である。
【図１４】熱硬化型エポキシシール剤で基板を接着した液晶表示装置の断面図である。
【図１５】液晶表示装置において、熱硬化型エポキシシール剤の接着性の問題を説明する図である。
【符号の説明】
１、２、１０１、１０４ ガラス基板
３ シール剤
４ 液晶表示装置
６ 配線端子
７ 有機膜
８ サンプル
９、１０２ スイッチング素子
１６ 画素平坦化膜
１７ ＩＴＯ膜
１８ 治具
１０、１０３、１０８ 配向制御膜
５、１１、１０５ ブラックマスク
１２、１０６ カラーフィルター
１３、１０７ オーバーコート膜
１０９ 熱硬化型エポキシ系シール剤
１４、１５、１１０、１１１ スペーサ[0001]
BACKGROUND OF THE INVENTION
The present invention provides a two-curing sealant composition for a liquid crystal display device that is completely cured by ultraviolet rays and is also completely cured by heating, and a pair of substrates bonded together using this sealant, thereby providing a seal. The present invention relates to a liquid crystal display device that prevents deterioration of adhesive strength.
[0002]
[Prior art]
In a liquid crystal display device using TN (Twisted Nematic) liquid crystal, a technique for improving the viewing angle and the aperture ratio has been actively researched and developed.
[0003]
For example, an active matrix liquid crystal display device (hereinafter referred to as “IPS panel”) using a lateral electric field parallel to the substrate has been proposed for widening the field of view, and an organic flattening film is placed on the liquid crystal driving element to improve the aperture ratio. A liquid crystal display device (hereinafter referred to as a “transmissive pixel flattening panel”) is proposed.
[0004]
Each of these liquid crystal display devices includes an organic film having a thickness of about 1 μm or more, and in the case of a large liquid crystal display device such as a liquid crystal display device for a notebook computer or a liquid crystal display device for a monitor, For bonding the glass substrate, a sealing agent composition composed of two components, an ultraviolet curable resin and a heat curable resin, is used. It is possible to manufacture a liquid crystal display device by bonding and sealing two substrates by ultraviolet irradiation and heating with a sealing agent composition composed of two components, an ultraviolet curable resin and a heat curable resin. 53-22753, JP-A-55-41488, and JP-A-58-105124. In addition, it is possible to bond and seal a substrate covered with an organic layer, a ceramic layer or a chromium layer with an ultraviolet curable sealant composition, as disclosed in JP-A-5-127175 and JP-A-8-234214. This is disclosed in Japanese Laid-Open Patent Application No. 10-96936.
[0005]
[Problems to be solved by the invention]
In the following, the problems of the prior art will be described using an IPS panel as an example.
[0006]
FIG. 14 shows a cross-sectional view of an IPS panel using a thermosetting epoxy sealant for substrate bonding. On the glass substrate 101, a switching element 102 that generates an electric field in the horizontal direction (parallel to the glass substrate) and an alignment control film 103 that controls the alignment direction of liquid crystal molecules are formed. Further, a black mask 105 made of a chromium material, a color filter 106, an overcoat film 107 made of an acrylic material and functioning as a protective film, and an alignment control film 108 are formed on the glass substrate 104 facing the glass substrate 101. Has been. Then, the glass substrate 101 and the glass substrate 104 are bonded to each other with a gap interval of about 4 μm by the thermosetting epoxy sealant 109, and the gap is filled with liquid crystal. The diameter of the mixed spacer 110 in the thermosetting epoxy sealant 109 and the diameter of the spacer 111 in the display area are adjusted so that the gap amount between the substrates 101 and 104 can be made substantially equal. .
[0007]
In the process of manufacturing such an IPS panel, peeling failure frequently occurred between the glass substrate 101 and the glass substrate 104. Therefore, the inventor of the present application analyzed the cause of the peeling and predicted a phenomenon as shown in FIG. Specifically, in the manufacturing process of the IPS panel, there is a step of applying a force in the direction of arrow J shown in FIG. 15 to the element driving terminal portion around the glass substrate 101, and peeling occurs in this step. It is thought that there is. When the peeled IPS panel was observed, the surface of the peeled portion 113 was generated at the interface between the overcoat film 107 and the black mask 105.
[0008]
The present invention has been made to solve the above-described problems, and a first object of the present invention is to completely cure only with ultraviolet rays in order to eliminate substrate peeling that has occurred during the manufacturing process of a liquid crystal display device. At the same time, it is to obtain a binary curable sealing agent composition for a liquid crystal display device that is completely cured only by heating.
[0009]
The second object of the present invention is to use the above-mentioned sealing agent composition to completely cure a sealing agent for substrate adhesion only by ultraviolet rays or heating alone, thereby causing problems due to poor adhesion of the sealing agent. It is in the point of obtaining a liquid crystal display device that eliminates the above.
[0010]
[Means for Solving the Problems]
A sealing agent composition for a liquid crystal display device which is one of the inventions of the present application includes (1) an ultraviolet curable acrylic resin composition comprising a photo radical initiator and an acrylate resin, and (2) a photo cation initiator. An ultraviolet curable epoxy resin composition comprising an epoxy resin, (3) an organic peroxide, and (4) atoms on the surface of the talc particles are bonded to the epoxy compound at the molecular level so that the surface is covered with the epoxy compound. And talc particles in a hybrid state, and having a dual curability of ultraviolet rays and heating.
[0011]
The liquid crystal display device, which is another invention of the present application, has a light-shielding wiring terminal group composed of a plurality of wiring terminals provided in the periphery of the first glass substrate, and straddles the surface of the first glass substrate. A sealant formed on the wiring terminal group and having both UV curable property and heat curable property; a second glass substrate facing the first glass substrate through the sealant; and a second glass substrate; A liquid crystal display device provided with a light-shielding film disposed between sealants and shielding the entire surface of the sealant, wherein the sealant composition comprises (1) an ultraviolet curable composition comprising a photoradical initiator and an acrylate resin. An acrylic resin composition; (2) an ultraviolet curable epoxy resin composition comprising a photocationic initiator and an epoxy resin; (3) an organic peroxide; and (4) a hybrid state in which the surface is covered with an epoxy compound. Tal It characterized in that it contains the particles.
[0012]
Here, an organic film may be provided between the light shielding film and the sealant or between the wiring terminal group and the sealant.
[0013]
The material of the wiring terminal group is, for example, chromium metal or aluminum metal.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiment 1
(Understanding the problems of thermosetting sealants)
Numerical calculation (simulation) of the residual stress between the sealant and the substrate generated during the curing process of the sealant was performed. A numerical calculation model is shown in FIG. In order to reduce the calculation load, a two-dimensional simplified model was adopted in which a gap of about 4 μm was formed between a pair of opposed glass substrates 1 and 2 and a sealant 3 was interposed in the gap. In addition, as the physical property data of the glass substrates 1 and 2 used in the calculation, the longitudinal elastic modulus (7450 kgf / mm ² ), Linear expansion coefficient (48 × 10 ^-7 /.Degree. C.) and substrate thickness (1.1 mm) are employed.
[0015]
The longitudinal elastic modulus, linear expansion coefficient, and thickness of the glass substrates 1 and 2 are Eg, αg, and hg, respectively, and the longitudinal elastic modulus, linear expansion coefficient, and thickness of the sealing agent 3 are Es, αs, and hs, respectively. Assuming that the difference between the temperature at which 3 is cured and the room temperature is Δt, the theoretical formula for calculating the residual stress is as follows.
(1) When curing sealant 3
σs = 2 (αg−αs) Δt · hg · Es · Eg / (2Eg · hg + Es · hs) (1)
(2) When the sealant 3 is cured and returned to room temperature (cooling)
σs = 2 (αg−αs) (− Δt) · hg · Es · Eg / (2Eg · hg + Es · hs) (2)
[0016]
Here, the curing process of the thermosetting sealant and the ultraviolet curable sealant will be described with reference to Table 1.
[0017]
[Table 1]

[0018]
First, the curing process of the thermosetting epoxy sealant is roughly classified into the following steps.
[0019]
(Step 1): A step of applying pressure and heat to obtain a predetermined thickness of the sealant (described as “this cure” in Table 1).
[0020]
(Step 2): The step of applying heat to the sealant for the time that the thickness of the sealant does not change even when the pressure load is released (generally referred to as “tack-free”) (described as “10 minutes” in Table 1) ).
[0021]
(Step 3): After releasing the pressure, a step of applying heat to completely cure the material (described as “after cure” in Table 1).
[0022]
On the other hand, the curing process of the ultraviolet curable sealant is roughly classified into the following processes.
[0023]
(Step 1): UV irradiation (6000 mJ / cm ² ) To cure about 80% of the material and become tack-free.
[0024]
(Step 2): A step of completely curing the material by after-cure (120 ° C.).
[0025]
When the residual stress in the sealant is calculated based on the above curing process, the total residual stress value of the thermosetting sealant (about 1.22 kgf / mm ² ) Is the total residual stress value (−0.018 kgf / mm) of the ultraviolet curable sealant. ² The figure is about two digits larger than Therefore, in the thermosetting sealing agent, compared with the ultraviolet curable sealing agent, there is a concern that the residual stress generated in the sealing agent during the curing process becomes larger, and the adhesiveness of the sealing agent may be adversely affected. The present inventor has considered.
[0026]
The above calculation results are considered to be appropriate based on the following consideration.
[0027]
In the case of a thermosetting epoxy sealant (FIG. 2), if the temperature of the sealant 3 does not reach 150 ° C., the curing of the sealant 3 is not accelerated, so that the temperature of the sealant 3 reaches this temperature. Following the distortion (extension) of the glass substrates 1 and 2, the sealing agent 3 adhered to the glass substrates 1 and 2 can be freely deformed (FIG. 2A). In such a state, since the glass substrates 1 and 2 and the sealing agent 3 can be freely deformed, stress energy is not stored inside the glass substrates 1 and 2 or inside the sealing agent 3. However, once the curing of the thermosetting sealing agent 3 is completed at a temperature of 150 ° C., the sealing agent 3 is solidified and the sealing agent 3 and the glass substrates 1 and 2 are bonded. (FIG. 2B). Therefore, when the glass substrates 1 and 2 are returned to room temperature, the degree of shrinkage of the glass substrates 1 and 2 and the degree of shrinkage of the sealant 3 are different due to the difference in thermal expansion coefficient between them, and are thus bonded and fixed to each other. Stress (stress in the width direction of the sealant 3) is generated between the sealant 3 and the glass substrates 1 and 2. It is considered that this stress is stored as residual stress in the sealant 3 and the glass substrate interiors 1 and 2 (FIG. 2C). The arrows in the figure indicate the direction of force received by each part.
[0028]
On the other hand, in the case of an ultraviolet curable sealant (FIG. 3), about 80% of the sealant 3 is cured by ultraviolet irradiation before the sealant 3 is heated (FIG. 3A). Thereby, after ultraviolet irradiation, the sealing agent 3 is solidified to some extent, and the glass substrate is bonded to the sealing agent 3 (FIG. 3B). Therefore, even if the glass substrates 1 and 2 are heated / cooled thereafter, the expansion / contraction of the sealing agent 3 at least in the portion where the sealing agent 3 is applied follows the expansion / cooling of the glass substrates 1 and 2. This means that even when the glass substrates 1 and 2 are heated and cooled, if the glass substrates 1 and 2 are finally set to the initial temperature, the bonding state between the glass substrates 1 and 2 and the sealant 3 is heated. Since it returns to the previous initial state, there is no factor causing stress between them, and it is considered that the residual stress is not preserved inside the glass substrates 1 and 2 and inside the sealant 3 (FIG. 3C).
[0029]
(Understanding the problems of UV curable sealants)
As described above, when an ultraviolet curable sealant is used, the residual stress generated during the curing process can be greatly reduced. Thought.
[0030]
However, when a commercially available UV curable sealant is used, the following problems have become apparent.
[0031]
In a notebook personal computer, there is a demand for narrowing the width of a frame that does not contribute to display around the display unit (this is called narrowing the frame). For this narrowing of the frame, the wiring terminals 6 of the TFT substrate are required. The ultraviolet curable sealant 3 was arranged below the peripheral black mask 5 of the color filter substrate (see FIG. 4). For this reason, on the color filter substrate side, the entire surface of the ultraviolet curable sealant is shielded from light by the black mask 5 made of chromium (Cr) or aluminum (Al) metal. It is necessary to irradiate light from. However, since the wiring terminal 6 formed on the TFT substrate also has a light shielding function, the sealing agent formed on the wiring terminal 6 is not irradiated with light.
[0032]
This problem will be described in more detail with reference to a cross-sectional perspective view (FIG. 5) of a portion taken along the line V-V shown in FIG. 4. A voltage for driving liquid crystal molecules is applied to the peripheral portion of the liquid crystal display device 4. In order to supply, a wiring terminal group composed of a plurality of wiring terminals 6 is provided, and the material of the wiring terminal group is a metal thin film of chromium (Cr) or aluminum (Al), and has a light shielding property. Yes. Commercially available UV-curing sealants have a certain degree of heat-curing action, but if this sealant 3 is not completely cured by heating alone, the sealant 3 provided on the wiring terminal 6 will Since it is not irradiated, photocuring is not promoted, and heat curing cannot be expected. This causes a problem of adhesion failure of the substrate, and also causes problems of liquid crystal material contamination and alignment film contamination due to dissolution of the uncured sealing agent 3 in the liquid crystal. Accordingly, it has been concluded that a binary curable sealant that is completely cured only by ultraviolet irradiation and that is completely cured only by heating should be developed. In FIG. 5, an organic film 7 is provided between the sealing agent 3 and the black mask 5.
[0033]
In order to solve this problem, the binary curable sealant of the present invention is characterized in that the organic peroxide in the sealant composition generates radicals by heating to promote cation generation of the photocation initiator, This is to promote heat curing of the epoxy compound. Hereinafter, the configuration and physical properties will be described in detail.
[0034]
(Configuration and physical properties of binary curable sealant)
A talc particle in a hybrid state in which atoms on the surface of the talc particle are bonded to an epoxy compound at a molecular level and the surface is covered with the epoxy compound is a mechanochemical method disclosed in JP-A-10-95901. For example, heat treatment, agitation treatment, ball mill treatment, shredder treatment, ultrasonic treatment) gives physical energy to the talc surface to activate the surface, and the particles are coated with a strongly bonded epoxy compound. Say. Preferable examples include hybrids of epoxy compounds and talc particles such as trade name Epicoat 828 (Oilized Shell Co., Ltd.), Epicoat 807 (Oilized Shell Co., Ltd.), HBE100 (New Nippon Rika Co., Ltd.), and the like. be able to.
[0035]
By using talc particles in a hybrid state in which such talc particles are covered with an epoxy compound, the binary curable sealant of the present invention has flexibility and toughness and also has a small compression set. Furthermore, since the surface of the talc particles is covered with a non-hydrophilic epoxy compound, the water resistance and moisture resistance of the binary curable sealant are dramatically improved. Further, since the surface is not modified with a silane coupling agent or the like as in the case of a conventional filler, a display defect caused by the silane coupling agent or the like eluting and contaminating the liquid crystal material is not caused. The addition amount of the talc particles in the hybrid state is preferably 10 to 70% by weight in the binary curable sealant. If it is less than 10% by weight, the above-mentioned performance such as toughness cannot be imparted to this sealant, and if it exceeds 70% by weight, the viscosity of this sealant becomes high and it becomes difficult to apply it to a thin line. is there.
[0036]
The ultraviolet curable acrylic resin composition may be a known ultraviolet curable composition containing an acrylic ester resin and a photo radical initiator. Such a composition is described in detail in, for example, the above-mentioned JP-A-55-41488. In the present invention, the raw material or composition of the ultraviolet curable acrylic resin composition is not particularly limited, but a preferable acrylic ester resin is an epoxy acrylate having a chemical structure having a hydroxy group in the molecule. This is because epoxy acrylate generally has higher adhesive strength than other acrylic ester resins.
[0037]
The ultraviolet curable epoxy resin composition may be a known ultraviolet curable epoxy resin composition containing a compound having an epoxy group and a photocationic initiator represented by an onium salt. Such compositions are described in detail in the above-mentioned JP-A-61-233719 and JP-A-61-1524. In the present invention, the raw material or composition of the ultraviolet curable epoxy resin composition is not particularly limited. Preferred onium salts include diazonium salts, iodonium salts, sulfonium salts and the like, and it can be said that onium salts that are compatible with the epoxy compound used are preferred. The mixing ratio of the ultraviolet curable epoxy resin composition and the ultraviolet curable acrylic resin composition is preferably 6: 4 to 8.5: 1.5. This is because the physical properties of the sealing layer as described later can be obtained within such a range of the mixing ratio.
[0038]
The organic peroxide may be a well-known organic peroxide, and is not limited to a specific organic peroxide in the present invention. In the binary curable sealant of the present invention, this organic peroxide exhibits a unique action and effect.
[0039]
In general, an organic peroxide is considered as an initiator for radical polymerization and can be used for heat curing of an acrylic resin composition, but has not been used for heat curing of an epoxy resin composition. However, it has been discovered that organic peroxides have the effect of lowering the curing temperature and increasing the curing rate relative to the ultraviolet curable epoxy resin composition in the heating step after ultraviolet irradiation. This effect is presumed to be because the radicals of the organic peroxide have some effect on the cation formation of the onium salt. The amount of the organic peroxide added is preferably 0.1 to 10% by weight in the sealant composition. If the amount is less than 0.1% by weight, the cation formation of the onium salt is not promoted, and if it exceeds 10% by weight, the storage stability of the sealant composition is impaired.
[0040]
The binary curable sealant having the above-described component configuration is completely cured even by ultraviolet irradiation alone, as compared with a conventional sealant composition of a mixed system of an ultraviolet curable acrylic resin composition and a heat curable epoxy resin composition. It is possible to cure completely by heating alone. Even if there is a shade part that does not transmit ultraviolet rays, this sealing agent is completely cured in a short time at a low heating temperature, and there is no concern that the uncured component will elute into the liquid crystal material. Further, the cured seal layer is a tough elastic body, has high peel strength, has a small compression set, and has a high water resistance, and thus exhibits excellent durability.
[0041]
The physical properties of the binary curable sealant
1) Viscosity at 25 ° C. before curing is 50,000 to 80,000 mPa · s.
2) The thixotropic property before curing is 1.5 to 3.0 in terms of viscosity ratio at a rotational viscosity of 1 rpm and a rotational frequency of 10 rpm.
3) Volume shrinkage during curing is 3% or less
4) Low curing temperature and shorten curing time
5) Young's modulus after curing is 1000 to 3000 MPa.
It was made to become.
[0042]
In order to make the physical properties of the binary curable sealing agent as described above, it is composed of a mixed system of an ultraviolet curable acrylic resin composition and an ultraviolet curable epoxy resin composition, and the mixing ratio is 6: 4-8. This can be achieved by setting the ratio to 5: 1.5. Moreover, in order to improve the adhesive force of a binary curable sealing agent, it is preferable to use an epoxy acrylate as an acrylic ester resin. Further, in order to obtain a low curing temperature and a high curing rate, the composition was made ultraviolet curable, and an organic peroxide was added to further improve the curability as described above.
[0043]
Table 2 shows formulation examples of the binary curable sealant composition of the present invention.
[0044]
[Table 2]

[0045]
(Strength test result of binary curable sealant)
FIG. 6 shows the strength test result of the binary curable sealant while comparing with the conventional ultraviolet curable sealant. In the figure, A is the binary curable sealant of the present invention, B is the conventional UV curable sealant 1, and C is the fracture toughness value of the conventional UV curable sealant 2. As is clear from FIG. 6, the strength fracture toughness value of the binary curable sealant is higher than that of the conventional ultraviolet curable sealant, and the difference between the two fracture toughness values over time is as follows. It is getting bigger. The strength test was performed under conditions that have a large effect on the degree of adhesion, specifically, high-temperature and high-humidity environmental conditions (hereinafter referred to as “humidity resistance test”) at a temperature of 60 ° C. and a humidity of 90% RH. The test sample was manufactured by curing a sealing agent between a pair of glass substrates of a liquid crystal display device. The horizontal axis in FIG. 6 represents the elapsed time (time from the time when the substrate is cured and bonded), and the vertical axis represents the fracture toughness value after high-temperature and high-humidity treatment (hereinafter referred to as “moisture resistance strength”).
[0046]
The binary curable sealant has high moisture resistance in the initial state (zero elapsed time) and does not deteriorate with time. Compared to this, the conventional ultraviolet curable sealant has high moisture resistance in the initial state, but the moisture resistance is deteriorated over time. For example, the moisture resistance strength of the two types of ultraviolet curable sealants was about 1/5 of the moisture resistance strength in the initial state after 500 hours had elapsed. In addition, about 0.15kgf / mm ^2/3 Without the above moisture resistance, it is difficult to satisfy this condition with a conventional ultraviolet curable sealant, although it impedes the production yield of liquid crystal display devices and the reliability of products.
[0047]
From the above strength test results, it became clear that the moisture resistance strength of the liquid crystal display device can be improved by the binary curable sealant of the present invention.
[0048]
Embodiment 2
A strength test method of the liquid crystal display device will be described with reference to FIGS.
[0049]
FIG. 7 is a conceptual diagram illustrating that a sample for strength test is cut out from the liquid crystal display device. As shown in FIG. 7, a rectangular sample 8 is cut out from the substrate end of the liquid crystal display device 4. Regarding the size of the sample 8, the length in the longitudinal direction was unified as 100 mm, the length in the width direction was 25 mm, and the thickness was unified as 10 mm. The sample 8 is fixed to an aluminum jig 18 as shown in FIG. 8, and the aluminum jig 18 is pulled in a direction in which the substrates of the sample 8 are peeled from each other (in the direction of the arrow in the figure).
[0050]
The conditions for this tensile test are a test temperature (environmental temperature) of 25 ° C. and a tensile speed of 1 mm / min.
[0051]
This test method is based on a DCB (Double Cantilever Beam) test widely used in the field of fracture mechanics. Considering the configuration of the liquid crystal display device, the thickness of the glass substrate is sufficiently large relative to the gap between the substrates, so it is considered possible to evaluate the gap between the substrates as a kind of crack, and the parameter for evaluating the crack Fracture toughness values (Fracture Toughness) were used. The fracture toughness value is derived by stress calculation using the fracture strength (measured value) obtained from this strength test.
[0052]
According to this test method, the strength of the liquid crystal display device can be digitized, and the strength evaluation can be made objective.
[0053]
The measured value of the DCB test is 0.15 kgf / mm based on the measured value of the DCB test and the observation of the destruction state of the liquid crystal display device. ^2/3 If it was above, it turned out that there is no practical problem in a manufacturing process or a product.
[0054]
【Example】
Hereinafter, specific examples of the strength test will be described with reference to the drawings.
[0055]
1. Configuration of liquid crystal display device
FIG. 9 is a cross-sectional view of an IPS panel in which an organic film is provided on a color filter substrate, and FIG. 10 is a cross-sectional view of a pixel flattening panel in which an organic film is provided on a TFT substrate.
[0056]
First, the configuration of the IPS panel shown in FIG. 9 will be described.
[0057]
FIG. 9 is a cross-sectional view of an IPS panel that applies a parallel (lateral) electric field to the substrate.
[0058]
In the glass substrate 1, a switching element 9 that generates a lateral electric field is formed on the substrate 1, and an orientation control film 10 is formed on the element 9. On the other hand, in the glass substrate 2 facing the glass substrate 1 through a liquid crystal (not shown), a black mask 11 and a color filter 12 are formed on the substrate 2 and further covers the black mask 11 and the color filter 12. Thus, an overcoat film 13 is provided. Similar to the substrate 1, the orientation control film 10 is also formed on the switching element 9 of the substrate 2. Here, as the material of the black mask 11, for example, a light-shielding metal film or a light-shielding pigment is used. As the material of the overcoat film 13, for example, an organic film such as an acrylic resin or an epoxy resin that is cured by heat or light is used.
[0059]
These substrates 1 and 2 are arranged to face each other while maintaining a gap of about 4 to 5 μm. The amount of the gap is uniquely determined by the diameter of the in-display spacer 14 disposed in the display area and the diameter of the in-seal spacer 15 disposed in the sealant 3 around the substrates 1 and 2. . Here, the material of the sealant 3 is a thermosetting sealant or the above-described binary curable sealant of the present invention, which is formed by applying it on the substrate 1 in a ring shape by a screen printing method or a dispenser method. To do. Thereafter, the substrate 1 and the substrate 2 are held with a gap of about 4 μm and the sealant 3 is cured, and then liquid crystal is injected into the gap region to complete a liquid crystal display device.
[0060]
Next, the configuration of the pixel flattening panel shown in FIG. 10 will be described.
[0061]
FIG. 10 is a cross-sectional view of a pixel flattening panel in which pixel electrodes are flattened with an organic film. However, description of portions having the same configuration as the liquid crystal display device of FIG. 9 is omitted.
[0062]
In order to flatten an ITO film (not shown) that functions as a transparent pixel electrode, a pixel flattening film 16 is formed on the substrate 1 to a thickness of about 10 μm. As the material of the pixel flattening film 16, for example, an organic film such as a photosensitive acrylic resin is used. In order to generate an electric field in the vertical direction on the substrate 1, an ITO film (not shown) is provided on the pixel flattening film 16 on the substrate 1 side, and an ITO film 17 is also provided on the substrate 2 side. . Since the ITO film 17 also has a function as a protective film, it is not necessary to separately form an overcoat film on the substrate 2. That is, the sealing agent 3 is in direct contact with the black mask 11.
[0063]
2. Sample measurement
About the IPS panel and the pixel flattening panel, the fracture toughness value of the liquid crystal display device was measured using the binary curable sealant of the present invention. Furthermore, in order to contrast with the technical effect of this binary curable sealant, the measurement value of the fracture toughness value of a liquid crystal display device using a thermosetting sealant (for example, epoxy sealant) is also shown. Table 1 shows the physical property values and curing conditions of each of the binary curable sealant and the thermosetting sealant. Specifically, in the curing of the thermosetting sealant, after the main curing at 150 ° C. for 10 minutes, the after-curing is performed at 150 ° C. for 60 minutes. 6000 mJ / cm for the curing of the binary curable sealant ² After UV irradiation, after cure at 120 ° C. for 60 minutes.
[0064]
The measurement result of the fracture toughness value of the liquid crystal display device is shown in FIG. In the fracture toughness value data of FIG. 11, 10 IPS panels and 10 pixel flattening panels are prepared, and a predetermined rectangular shape (length in the longitudinal direction is 100 mm, length in the width direction is set from the end portions of these panels. 25 mm, 10 mm in thickness) Samples were cut, and the results of measuring the strength of 10 cut samples were compared with the average value and the minimum value of the data.
[0065]
In the figure, D represents an average value, E represents a minimum value, and F to I represent a combination of a panel structure and a sealant. F and G are IPS panels shown in FIG. 9, H and I are pixel flattening panels shown in FIG. 10, F and H are thermosetting sealing materials, and G and I are combinations of binary curable sealing agents. .
[0066]
3. Evaluation of measurement results
From the measurement results, the following results (1) to (4) could be obtained.
[0067]
(1) When a binary curable sealant is used, the average value of the fracture toughness value is constant in both the IPS panel (FIG. 9) and the pixel flattening panel (FIG. 10), and the value is the breakdown of the product specifications. Toughness value (0.15kgf / mm ^2/3 )
[0068]
(2) When a binary curable sealant is used, the average value and the minimum value of the fracture toughness values of both the IPS panel and the pixel flattening panel are almost the same, and there is almost no variation in the fracture toughness value among samples. I can't see.
[0069]
(3) When the thermosetting sealant was used, the average value of the fracture toughness value of the IPS panel was high, but the minimum value was low. That is, the variation in fracture toughness value is large.
[0070]
(4) When the thermosetting sealant was used, the average value of the fracture toughness value of the pixel flattening panel was low. That is, it was found that the fracture toughness value of the panel manufactured using the thermosetting sealant was considerably inferior to that obtained when using the binary curable sealant.
[0071]
In order to elucidate the phenomenon of the experimental results, a cross section of the fracture surface was observed.
[0072]
FIG. 12 is a diagram for explaining a fracture state of a sample having a low fracture toughness value in an IPS panel using a thermosetting sealant.
[0073]
FIG. 13 is a diagram for explaining the destruction state of the sample in the IPS panel using the binary curable sealant, and contrasts with the destruction state of FIG.
[0074]
Here, FIGS. 12A and 13A are cross-sectional views of a substrate on which a color filter is formed (hereinafter, this substrate is referred to as a “color filter substrate”). FIG. 12B and FIG. (B) shows a substrate on which switching elements are formed (hereinafter, this substrate is referred to as an “array substrate”).
[0075]
According to FIGS. 12A and 12B, the surface of the overcoat film 13 on the sealing agent 3 and the black mask in the region where the sealing agent 3 is formed are peeled off from the array substrate 1 and the color filter substrate 2. 5 was observed along the boundary of the surface (hereinafter, this peeling phenomenon is referred to as “interface fracture”). An overcoat film 13 was observed on the sealant 3 on the array substrate 1 side (FIG. 12B).
[0076]
On the other hand, according to FIG. 13A and FIG. 13B, the sealant 3 is observed on both the array substrate 1 side and the color filter substrate 2 side. It is inferred that this peeling occurred inside the sealing agent 3 (hereinafter, this peeling phenomenon is referred to as “cohesive failure”).
[0077]
That is, the interface between the organic film such as the overcoat film 13 and the inorganic film such as the black mask 5 has a weak adhesive force, and when a thermosetting sealant is used, interface peeling occurs along this interface. It seems to have done.
[0078]
Similarly, in the pixel flattening panel as well as the IPS panel, the panel using the thermosetting sealant and having the lowest fracture toughness value is the overcoat film 13 (organic film) and the black mask 5. Interfacial fracture was observed at the interface of (inorganic film), and cohesive fracture occurred in panels having a large fracture toughness value. In addition, about 20% in all samples was interface fracture.
[0079]
From the above experimental results, the present inventor has obtained the following knowledge from the difference in the sealant.
[0080]
(1) In the thermosetting sealant sample, interface breakdown between the organic film (overcoat film) and the inorganic film (black mask) occurs. On the other hand, such interfacial destruction is not observed in the binary curable sealant. Therefore, it is considered that an adhesion problem occurs at the interface between the organic film and the inorganic film during the heating process of the sealant.
[0081]
(2) In the case of a dual-curing sealant, no interface breakdown occurs in any sample. Therefore, in a liquid crystal display device using an organic film (overcoat film), it is essential to select a dual-curing sealant. It is.
[0082]
These findings are consistent with the fact that liquid crystal display devices that do not use organic films can be bonded with a thermosetting sealant so far. The validity of the numerical calculation that the residual stress of the agent is larger than that of the binary curable sealant (thus, the thermosetting sealant is not preferable) was also confirmed.
[0083]
【The invention's effect】
The sealant composition of the present invention can be completely cured by ultraviolet irradiation, but is cured in a short time at a low heating temperature even when there is a non-transparent shade of ultraviolet rays.
[0084]
Therefore, according to the sealant composition according to claim 1 of the present invention, it is possible to obtain a sealant for a liquid crystal display device having a strong elastic body after peeling, a high peel strength, a small compression set and a high water resistance. it can.
[0085]
According to the liquid crystal display device according to claims 2 to 5 of the present invention, even if the sealing portion between the substrates is provided around the substrate where the wiring terminal group for shielding ultraviolet rays and the light shielding film coexist, the sealing agent composition described above By using this, the sealant composition can be completely cured in a short time with low irradiation of ultraviolet rays and a low heating temperature.
[0086]
In addition, according to the liquid crystal display device according to claims 2 to 5 of the present invention, since the internal stress generated in the seal layer can be lowered, a liquid crystal display device having high adhesion reliability and durability can be obtained.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing a model for numerical calculation.
FIG. 2 is a conceptual cross-sectional view for explaining a residual stress generation process inside the sealing agent and inside the substrate when a thermosetting sealing agent is used for bonding the substrate.
FIG. 3 is a conceptual cross-sectional view for explaining that the occurrence of residual stress can be avoided when an ultraviolet curable sealant is used for substrate adhesion.
FIG. 4 is a conceptual plan view of a liquid crystal display device.
FIG. 5 is a cross-sectional perspective view taken along line VV shown in FIG. 4;
FIG. 6 is a view showing a strength test result of a binary curable sealant.
FIG. 7 is a conceptual diagram illustrating sample cutting.
FIG. 8 is a conceptual diagram illustrating a sample tensile test.
FIG. 9 is a cross-sectional view of an IPS panel in which an organic film is provided on a color filter substrate.
FIG. 10 is a cross-sectional view of a pixel flattening panel in which an organic film is provided on a TFT substrate.
FIG. 11 is a diagram showing measurement results of fracture toughness values of a liquid crystal display device.
FIG. 12 is a conceptual cross-sectional view illustrating a state of interface breakdown in a liquid crystal display device.
FIG. 13 is a conceptual cross-sectional view illustrating a state of cohesive failure of a liquid crystal display device.
FIG. 14 is a cross-sectional view of a liquid crystal display device in which a substrate is bonded with a thermosetting epoxy sealant.
FIG. 15 is a diagram for explaining a problem of adhesiveness of a thermosetting epoxy sealant in a liquid crystal display device.
[Explanation of symbols]
1, 2, 101, 104 Glass substrate
3 Sealing agent
4 Liquid crystal display device
6 Wiring terminal
7 Organic membrane
8 samples
9, 102 Switching element
16 Pixel flattening film
17 ITO film
18 Jig
10, 103, 108 Orientation control film
5, 11, 105 Black mask
12, 106 Color filter
13, 107 Overcoat film
109 Thermosetting epoxy sealant
14, 15, 110, 111 Spacer

Claims (5)

It has a binary curing property by ultraviolet rays and heating,
(1) an ultraviolet curable acrylic resin composition comprising a photo radical initiator and an acrylate resin;
(2) an ultraviolet curable epoxy resin composition comprising a photocationic initiator and an epoxy resin;
(3) an organic peroxide;
(4) A talc particle in a hybrid state in which atoms on the surface of the talc particle are bonded to an epoxy compound at a molecular level and the surface is covered with the epoxy compound;
A sealant composition for a liquid crystal display device, comprising: A light-shielding wiring terminal group consisting of a plurality of wiring terminals provided in the periphery of the first glass substrate, formed on the wiring terminal group so as to straddle the surface of the first glass substrate, A sealing agent having both heat-curing properties, a second glass substrate facing the first glass substrate through the sealing agent, and being disposed between the second glass substrate and the sealing agent; A liquid crystal display device comprising a light-shielding film that shields the entire surface, wherein the sealing agent composition comprises:
(1) an ultraviolet curable acrylic resin composition comprising a photo radical initiator and an acrylate resin;
(2) an ultraviolet curable epoxy resin composition comprising a photocationic initiator and an epoxy resin;
(3) an organic peroxide;
(4) talc particles in a hybrid state whose surface is covered with an epoxy compound;
A liquid crystal display device comprising: The liquid crystal display device according to claim 2, wherein an organic film is provided between the light shielding film and the sealant. The liquid crystal display device according to claim 2, wherein an organic film is provided between the wiring terminal group and the sealant. The liquid crystal display device according to claim 2, wherein the wiring terminal group or the light shielding film is made of chromium metal or aluminum metal.

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