JP4083271B2

JP4083271B2 - Liquid crystal display

Info

Publication number: JP4083271B2
Application number: JP01124298A
Authority: JP
Inventors: 義則樋口
Original assignee: 東芝松下ディスプレイテクノロジー株式会社
Priority date: 1998-01-23
Filing date: 1998-01-23
Publication date: 2008-04-30
Anticipated expiration: 2018-01-23
Also published as: JPH11212088A

Description

【０００１】
【発明の属する技術分野】
本発明は、導光板を棒状光源にて照射して面状の照射光を得る光照射装置を用い液晶表示素子を照射して成る液晶表示装置に関する。
【０００２】
【従来の技術】
液晶表示装置において、側面に螢光放電管等の棒状光源を有し、この光源からの光を導光板内を伝搬しながら面状の光に変換し出射する事により、液晶表示素子を背面から照射透過し画像表示を行う光照射装置にあっては、従来より図５に示す様な装置を用いていた。即ち、光透過率の高い樹脂等からなり背面に反射板２を有する導光板１の一側に、反射鏡３で囲われた棒状蛍光管４を近接配置し、棒状蛍光管４から導光板１に入射された光を導光板１と空気との界面で全反射を繰り返しながら棒状蛍光管４から遠ざかる方向に伝搬し、この間、導光板１に配置される複数の散乱ドット６により生じる乱反射により、その一部を導光板１の出射面から拡散フィルム７を透過して液晶表示素子５方向に照射していた。
【０００３】
ここで散乱ドット６は、酸化チタン（ＴｉＯ）等の顔料を含むインキを導光板１表面にシルク印刷により塗布したり、導光板１表面に伝搬される光の波長に比べ十分高い凹凸を形成する等してなっている。散乱ドット６は、全反射により導光板１中を伝搬する光に対して、その全反射を阻害することにより導光板１から出射させるものであり、導光板１からの出射光量は、導光板１を伝搬する光量と散乱ドット６の散乱能率により決まる。又導光板１を伝搬する光は、順次散乱ドット６での乱反射により外部に出射されながら伝搬されるので、棒状蛍光管４から遠ざかるに従いその光量が低減される。
【０００４】
このため従来は、棒状蛍光管４から遠ざかるに従い散乱ドット６の面積や数を増大し、光量が低減される分を補正して、導光板１からの出射光量の均一化を図っていた。
【０００５】
【発明が解決しようとする課題】
上記従来の装置にあっては、散乱ドットは導光板に印刷されたり、導光板表面に作りつけられたりと導光板に固定されており、所定の位置における散乱能率も棒状蛍光管から遠く成るに従い増大された状態で固定され、導光板１からの出射光量はどの位置でもほぼ均一とされていた。一方、実際の表示画像は、その輝度が全面にわたり均一では無く、その場面に応じて、ある部分はで暗く又別のある部分では明るい等の輝度分布を有している。
【０００６】
しかしながら従来の光照射装置では導光板からの出射光量が均一に設定されている事から、画像の場面に応じた輝度は、液晶表示素子の透過率によってのみ制御されていた。このため最大輝度を高めようとすると、例えその高輝度を必要とされる部分が一部であったとしても、棒状蛍光管の輝度を高くする事により導光板全体からの出射輝度を明るくしなければ得られず、従来から、液晶表示装置の消費電力に占める光照射装置の消費電力の割合が約２／３にも達するにも拘わらず、更に消費電力の増大を招いてしまうと言う問題を生じていた。
【０００７】
しかも、従来の散乱能率が固定の散乱ドットは、導光板全面に渡り均一な輝度を得るためのドットの大きさや数等を経験的に作られる事が多く、実験により試行錯誤を繰り返しながら決定されるため、その開発に時間を要すると言う問題も有していた。
【０００８】
そこで本発明は上記課題を解決するもので、消費電力の増大を招く事無く、液晶表示素子の各部分において導光板から実際の画像の輝度に見合った輝度を得られ、又光散乱パターンの設計にかかる時間の短縮を図る事が出来る液晶表示装置を提供することを目的とする。
【００１０】
【課題を解決するための手段】
本発明は上記課題を解決するための手段として、電極を有し互いに対向する電極基板の間隙に表示液晶組成物を封入してなる液晶表示素子と、この液晶表示素子と略同等の面積を有し一側より入射された光を面状に出射する出射面を有する平板状の導光板と、この導光板の所定の一側面に隣接し前記導光板を照射する棒状光源と、前記出射面に対して平行に配置され光散乱能率を液晶表示素子の走査に応じて部分的に切り替え可能な可変散乱パターンを有する可変散乱手段とを設けるものである。
【００１１】
上記構成により本発明は、画像上必要とする部分の可変散乱パターンの光散乱能率を液晶表示素子の走査に応じて切り替える事により、画像全体の光量を増大する事無く、必要とする部分のみの輝度を高め或いは低減出来、消費電力の増大を生じる事無く必要な輝度を得る事により、経済的でありながら画像再現性を向上するものである。
【００１２】
【発明の実施の形態】
以下本発明を、図１乃至図３に示す実施の形態を参照して説明する。
【００１３】
先ず本実施の形態に使用される光拡散液晶組成物について述べる。光拡散液晶組成物としてはＰＤＬＣ（ＰｏｌｙｍｅｒＤｉｓｐｅｒｓｅｄＬｉｑｕｉｄＣｒｙｓｔａｌ）、ＬＥＦＤ（ＬａｔｅｒａｌＥｌｅｃｔｒｉｃＦｉｅｌｄＤｉｆｆｒａｃｔｉｏｎ）、ＰＮＬＣ（ＰｏｌｙｍｅｒＮｅｔｗｏｒｋＬｉｑｕｉｄＣｒｙｓｔａｌ）、ＮＣＡＰ（ＮｅｍａｔｃＣｕｒｖｉｌｉｎｅａｒＬｉｑｕｉｄＣｒｙｓｔａｌ）、ＰＳＣＴ（ＰｏｌｙｍｅｒＳｔａｂｉｌｉｚｅｄＣｈｏｌｅｓｔｅｒｉｃＴｅｘｔｕｒｅ）、ＬＣＰＧ（ＬｉｑｕｉｄＣｒｙｓｔａｌＰｈａｓｅＧｒａｔｉｎｇ）、ＴＤ−ＴＤＢ（ＴｗｏＤｏｍａｉｎＴｕｎａｂｌｅＢｉｒｅｆｒｉｎｇｅｎｃｅＤｉｆｆｒａｃｔｉｖｅ）等がある。
【００１４】
例えば、ＰＤＬＣ（ＰｏｌｙｍｅｒＤｉｓｐｅｒｓｅｄＬｉｑｕｉｄＣｒｙｓｔａｌ：ポリマー分散液晶）は、プラスチック中に液晶を微少な泡状に分散させて封入したものであり、電界を印加しないときには白濁しているが、電界印加により透明となる特性を有している。封入された液晶分子は泡の中で動く事が出来、外部から電界を作用させない状態ではバラバラの方向を向いている。液晶分子は屈折率異方性を持っており、バラバラの状態では光の進行方向に対して周囲のプラスチックと屈折率が異なるため見かけ上白濁した拡散板であるかの様に見える。
【００１５】
プラスチックの厚さ方向に交流電界を印加し、液晶分子の方向を揃えてやると、光の進行方向に対して周囲のプラスチック材料と屈折率がほぼ等しい状態にすることが出来、あたかも同一材料で出来た透明板であるかのように取り扱うことが出来る。
【００１６】
一方例えばＬＥＦＤ（ＬａｔｅｒａｌＥｌｅｃｔｒｉｃＦｉｅｌｄＤｉｆｆｒａｃｔｉｏｎ）は、電界を印加しないときは透明であり、電界印加時には白濁されると言う特性を有している。
【００１７】
次に上記ＰＤＬＣを用いて成る光拡散液晶素子にて導光板の光を散乱し、液晶表示素子を照射する本発明の実施の形態について述べる。液晶表示装置８の液晶表示素子１０は、信号線及び走査線の交点に設けられる薄膜トランジスタにて駆動される画素電極を有するアレイ基板１０ａ及び対向電極を有する対向基板１０ｂ間に表示液晶組成物１０ｃを封入してなっている。液晶表示素子１０の背面には、反射鏡１１により集光される棒状光源である蛍光管１２からの光を、導光板１３にて、液晶表示素子１０側に照射する光照射装置１４が設けられている。
【００１８】
導光板１３の出射面の反対面には導光板１３内を伝搬される光を出射面に散乱するための可変散乱手段である光拡散液晶素子１７が設けられている。この光拡散液晶素子１７は、プラスチックやガラス等からなる第１の透明基板１８ａ上にアルミニウム（Ａｌ）やＩｎｄｉｕｍＴｉｎＯｘｉｄｅ（以下ＩＴＯと略称する。）等からなり蛍光管１２と平行に設けられる走査電極１８ｂがパターン形成される走査電極基板１８と、プラスチックやガラス等からなる第２の透明基板２０ａ上にＩＴＯからなる対向電極２０ｂが形成される対向電極基板２０の間に光拡散液晶組成物であるＰＤＬＣ２１を封入して成っている。これにより光拡散液晶素子１７は、走査電極１８ｂの形状に沿ってパターン形成される蛍光管１２と平行な可変散乱パターンを有する。
【００１９】
走査電極１８ｂの接続端子１８ｃは、液晶表示素子１０の駆動回路（図示せず）を制御する制御装置２４に接続される。走査電極１８ｂは制御装置２４により、液晶表示素子１０の走査信号と同期して走査され、各可変散乱パターン毎に光拡散液晶素子１７への電圧印加をオン／オフ制御するように成っている。これによりオン時には光拡散液晶素子１７は透明にされ散乱能率を低減され、オフ時には光拡散液晶素子１７は白濁され散乱能率を増大する様切り換えられる。又２２は、拡散シートである。
【００２０】
次に光照射装置１４の製造方法について述べる。第１の透明基板１８ａに走査電極１８ｂをパターン形成し、第２の透明基板２０ａに対向電極２０ｂを形成する。いずれかの基板１８、２０周囲に紫外線硬化樹脂を塗布し、走査電極基板１８及び対向電極基板２０を間隙を保持して対向して貼り合わせセルを形成する。セルの間隙にＰＤＬＣ２２を注入し、全面に紫外線を照射し紫外線硬化樹脂を硬化させ光拡散液晶素子１７を製造する。光拡散液晶素子１７を導光板１３に重ね、反対の出射面に拡散シート２２を重ね、反射鏡１１、蛍光管１２を組み込み光照射装置１４を完成する。
【００２１】
この様にして成る光照射装置１４による液晶表示素子１０への光照射について述べる。電圧が印加されない状態では、光拡散液晶素子１７は、全面が白濁されており、蛍光管１２の点灯により導光板１３を伝搬する光を散乱し、液晶表示素子１０を照射する様に設定されている。そして液晶表示素子１０の画像表示操作に伴い蛍光管１２が点灯されると、この蛍光管１２から入射された光は導光板１３内を全反射を繰り返しながら伝搬する間に光拡散液晶素子１７により散乱され出射面から外部に出射され液晶表示素子１０を照射する。
【００２２】
液晶表示素子１０は、駆動装置（図示せず）からの画像情報信号により、走査線が順次走査され、信号線からの信号情報に応じた画像を表示する。これに伴い、光拡散液晶素子１７の走査電極１８ｂには、液晶表示素子１０の走査線への走査信号に同期して制御信号が入力され、光拡散液晶素子１７は各パターン毎にオン／オフ制御される。
【００２３】
即ち、表示画像全面にて均一な輝度を得たい場合は、図３（ａ）に示すように、蛍光管１２から遠くなるに従い、電圧印加する走査電極１８ｂの密度を低減し、透明部分Ｃを減少して印加電圧オフの白濁部分ｗを増加する。又、輝度分布を有する場面にあっては図３（ｂ）に示す様に、明るい画像に対応する部分［Ａ］の光拡散液晶素子１７への印加電圧をオフし光拡散液晶素子１７を白濁部分ｗとしたままとしその部分の散乱能率を増大し、導光板１３内の光を散乱して液晶表示素子１０側に出射する一方暗い画像に対応する部分［Ｂ］の光拡散液晶素子１７に電圧を印加する事により光拡散液晶素子１７を透明部分Ｃにして散乱能率を下げ、導光板１３内の光を散乱する事無く伝搬し、表示画像の輝度に則した照射を行う事となる。
【００２４】
このように構成すれば、光拡散液晶素子１７の走査電極１８ｂをオン／オフ制御して、可変散乱パターン毎に散乱能率を切り換える事により蛍光管１２からの光は、必要な部分では部分的に出射し、不要な部分では出射を押さえることが出来るので、従来に比し余分な出射が無く、高い輝度を必要とする場合にはその部分の拡散能率を上げて部分的に明るく出来る。従って従来の様に高輝度を得るために蛍光管１２の消費電力を増大する必要が無く、経済的でありながら、画像再現性の向上を図れる。又、光拡散液晶素子１７の走査電極１８ｂにより形成される散乱パターンの散乱能率は、パターンの配置や大きさ等を考慮する事無く、画像に応じた印加電圧制御により容易に変動出来、従来のように開発に時間を要する事無く画像に適した散乱パターンを容易に得る事ができる。しかも光拡散液晶素子１７のオン／オフ制御は、液晶表示素子１０の制御の様に微細である必要が無いことから、印加する交流電圧の周波数も十分低減出来、その消費電力はごく小さくてすみ、低電力化を損なう事も無い。
【００２５】
尚本発明は上記実施の形態に限られるものでなく、その趣旨を変えない範囲での変更は可能であって、例えば実施の形態の光拡散液晶素子の走査は、液晶表示素子の走査線と同期をとる事無く、走査線とは別制御により蛍光管側から順次走査する等しても良いし、その電圧制御も印加電圧をオン／オフ制御するのみではなく、画像再現性を更に向上するために、印加する電圧や電流の大きさ、周波数、パルス波形のデューティ比等を調整する事により、光拡散液晶素子の散乱能率をより細かく調整するようにしても良い。例えば、ＰＤＬＣを用いて成る光拡散液晶素子にて棒状光源から遠くなるにつれ印加電圧を小さくして散乱能率を増大し、導光板全面にわたり均一な出射光を得る様にしても良い。
【００２６】
又、光拡散液晶素子に用いる光拡散液晶組成物も、電圧印加時に白濁し、印加しないときは透明となるＬＥＦＤ等を用いても良く、このＬＥＦＤを用いて散乱が必要な部分にのみ電圧を印加し白濁させる様制御すれば、より低消費電力での駆動が可能となる。又、可変散乱パターンの形状及びその制御方法等任意であり、走査電極をマトリクス状に形成し、画像表示素子のマトリクス画像と同期して、その散乱能率を調整する事により、画像再現性を向上する等しても良い。
【００２７】
更に導光板内の光をより効率的に面状に出射させるための散乱パターンとして、可変散乱パターンと固定散乱パターンとを併用してもよく、例えば図４に示す他の変形例のように、アルミナ（Ａｌ₂Ｏ₃）を分散して成る樹脂にて導光板２６表面に白色ドットからなる固定散乱パターン２７を印刷し、更に実施の形態で述べた、ストライプ状の可変散乱パターン２８ａを有する光拡散液晶素子２８を重ねる事により、導光板２６内の光をより効率的且つ再現性良く散乱するようにしても良い。
【００２８】
【発明の効果】
以上説明したように本発明によれば、導光板を伝搬する光を、散乱能率を変動可能な可変散乱手段にて散乱し平面状に出射する事により、従来の様に、開発に時間を要する固定散乱パターンを、導光板に印刷等により作りつける事無く容易に均等な出射輝度を得る事が出来る。又、輝度分布を有し、部分的に高輝度を要求される場面においては、従来の様に、導光板全面の輝度を向上する事無く、可変散乱パターン毎に散乱能率を適宜変動することにより表示画像に応じて容易に表示輝度を調整出来、高輝度が要求される場合にも、画像上の高輝度に対応する可変散乱パターン部分の散乱能率を上げ、他の部分は散乱しない様容易に調整設定出来、導光板全体としてはその輝度を押さえられるので、消費電力を増大する事無く部分的に必要な輝度を容易に得る事が出来、経済性を損なう事無く画像輝度の再現性を向上できる。
【図面の簡単な説明】
【図１】本発明の実施の形態の液晶表示装置を示す概略側面図である。
【図２】本発明の実施の形態の液晶表示装置を示す概略分散斜視図である。
【図３】本発明の実施の形態の光照射装置の出射状況を示し、（ａ）は均一輝度を得る場合、（ｂ）は輝度分布を得る場合の概略説明図である。
【図４】本発明の他の変形例の導光板及び光拡散液晶素子を示す概略分散斜視図である。
【図５】従来の光照射装置を示す概略側面図である。
【符号の説明】
８…液晶表示装置
１０…液晶表示素子
１１…反射鏡
１２…螢光管
１３…導光板
１４…光照射装置
１７…光拡散液晶素子
１８…走査電極基板
１８ｂ…走査電極
２０…対向電極基板
２１…ＰＤＬＣ
２２…拡散シート[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device formed by irradiating the liquid crystal display device using the light irradiation equipment to obtain a planar illumination light is irradiated with the light guide plate in the rod-shaped light sources.
[0002]
[Prior art]
A liquid crystal display device has a rod-shaped light source such as a fluorescent discharge tube on the side surface, and converts the light from the light source into a planar light while propagating through the light guide plate, thereby allowing the liquid crystal display element to be emitted from the back surface. Conventionally, an apparatus as shown in FIG. 5 has been used for a light irradiation apparatus that transmits and transmits an image. That is, a rod-like fluorescent tube 4 surrounded by a reflecting mirror 3 is arranged close to one side of a light guide plate 1 made of a resin having a high light transmittance and having a reflection plate 2 on the back surface. Is propagated in a direction away from the rod-like fluorescent tube 4 while repeating total reflection at the interface between the light guide plate 1 and air, and during this time, due to irregular reflection caused by the plurality of scattering dots 6 arranged on the light guide plate 1, A part of the light was transmitted through the diffusion film 7 from the light exit surface of the light guide plate 1 and irradiated toward the liquid crystal display element 5.
[0003]
Here, the scattering dots 6 are coated with an ink containing a pigment such as titanium oxide (TiO) on the surface of the light guide plate 1 by silk printing, or have unevenness sufficiently higher than the wavelength of light propagated to the surface of the light guide plate 1. It has become equal. The scattering dot 6 emits the light propagating through the light guide plate 1 by total reflection from the light guide plate 1 by inhibiting the total reflection, and the amount of light emitted from the light guide plate 1 is determined by the light guide plate 1. And the scattering efficiency of the scattering dots 6. Further, since the light propagating through the light guide plate 1 is propagated while being emitted to the outside due to irregular reflection at the scattering dots 6, the amount of light is reduced as the distance from the rod-like fluorescent tube 4 increases.
[0004]
For this reason, conventionally, as the distance from the rod-like fluorescent tube 4 increases, the area and number of the scattering dots 6 are increased, and the amount of light that is reduced is corrected to make the amount of light emitted from the light guide plate 1 uniform.
[0005]
[Problems to be solved by the invention]
In the above-mentioned conventional apparatus, the scattering dots are fixed to the light guide plate by being printed on the light guide plate or built on the surface of the light guide plate, and the scattering efficiency at a predetermined position is also farther from the rod-like fluorescent tube. The amount of light emitted from the light guide plate 1 is almost uniform at any position. On the other hand, the actual display image has a luminance distribution such that the luminance is not uniform over the entire surface, and depending on the scene, one part is dark and the other part is bright.
[0006]
However, in the conventional light irradiation device, the amount of light emitted from the light guide plate is set uniformly, so that the luminance according to the scene of the image is controlled only by the transmittance of the liquid crystal display element. For this reason, when trying to increase the maximum brightness, even if there is only a part where the high brightness is required, the brightness emitted from the entire light guide plate must be increased by increasing the brightness of the rod-shaped fluorescent tube. Conventionally, there is a problem that power consumption increases even though the ratio of the power consumption of the light irradiation device to the power consumption of the liquid crystal display device reaches about 2/3. It was happening.
[0007]
Moreover, conventional scattering dots with a fixed scattering efficiency are often created empirically in terms of the size and number of dots to obtain uniform brightness over the entire surface of the light guide plate, and are determined through repeated trial and error through experiments. Therefore, it has a problem that it takes time to develop it.
[0008]
The present invention therefore also that to solve the above problems, without increasing the power consumption, resulting luminance commensurate with the luminance of the actual image from the light guide plate in each of the liquid crystal display device, the Matahikari scattering pattern an object of the present invention is to provide it can Ru liquid crystal display device to shorten the time required for design.
[0010]
[Means for Solving the Problems]
As means for solving the above-mentioned problems, the present invention provides a liquid crystal display element in which a display liquid crystal composition is sealed in a gap between electrode substrates having electrodes and facing each other, and an area substantially equal to the liquid crystal display element. A flat light guide plate having an output surface for emitting light incident from one side in a plane, a rod-shaped light source that irradiates the light guide plate adjacent to a predetermined side surface of the light guide plate, and the output surface. A variable scattering means having a variable scattering pattern which is arranged in parallel with the light scattering efficiency and can be partially switched according to the scanning of the liquid crystal display element is provided.
[0011]
With the above configuration, the present invention switches the light scattering efficiency of the variable scattering pattern of the necessary portion on the image in accordance with the scanning of the liquid crystal display element , so that only the necessary portion is increased without increasing the light amount of the entire image. The luminance can be increased or decreased, and the necessary luminance can be obtained without increasing the power consumption, thereby improving the image reproducibility while being economical.
[0012]
DETAILED DESCRIPTION OF THE INVENTION
The present invention will be described below with reference to the embodiments shown in FIGS.
[0013]
First, the light diffusing liquid crystal composition used in the present embodiment will be described. PDLC as a light diffusing liquid crystal composition (Polymer Dispersed LiquidCrystal), LEFD (Lateral Electric Field Diffraction), PNLC (Polymer Network Liquid Crystal), NCAP (Nematc Curvilinear Liquid Crystal), PSCT (Polymer Stabilized Cholesteric Texture), LCPG (Liquid Crystal Phase Grading) and TD-TDB (Two Domain Tunable Birefringence Differential).
[0014]
For example, PDLC (Polymer Dispersed Liquid Crystal) is a liquid in which liquid crystal is dispersed in plastic in a fine bubble shape and encapsulated, and is white turbid when no electric field is applied. It has the characteristic which becomes. The encapsulated liquid crystal molecules can move in the bubbles, and face the different directions when no electric field is applied from the outside. The liquid crystal molecules have refractive index anisotropy, and in a disjoint state, the refractive index is different from that of the surrounding plastic with respect to the light traveling direction, so that it looks as if it is a turbid diffuser plate.
[0015]
By applying an alternating electric field in the plastic thickness direction and aligning the liquid crystal molecules in the same direction, the refractive index of the surrounding plastic material can be made almost equal to the light traveling direction. It can be handled as if it were a transparent plate.
[0016]
On the other hand, for example, LEFD (Lateral Electric Field Diffraction) has a characteristic that it is transparent when an electric field is not applied and is clouded when an electric field is applied.
[0017]
Next, an embodiment of the present invention in which light from the light guide plate is scattered by the light diffusion liquid crystal element using the PDLC and the liquid crystal display element is irradiated will be described. The liquid crystal display element 10 of the liquid crystal display device 8 includes a display liquid crystal composition 10c between an array substrate 10a having pixel electrodes driven by thin film transistors provided at intersections of signal lines and scanning lines and a counter substrate 10b having counter electrodes. It is enclosed. On the back surface of the liquid crystal display element 10, there is provided a light irradiation device 14 that irradiates light from the fluorescent tube 12, which is a rod-shaped light source condensed by the reflecting mirror 11, to the liquid crystal display element 10 side by the light guide plate 13. ing.
[0018]
A light diffusing liquid crystal element 17 which is a variable scattering means for scattering light propagating through the light guide plate 13 to the exit surface is provided on the opposite surface of the light guide plate 13 to the exit surface. The light diffusing liquid crystal element 17 is a scanning made of aluminum (Al), Indium Tin Oxide (hereinafter abbreviated as ITO) or the like and provided in parallel with the fluorescent tube 12 on a first transparent substrate 18a made of plastic, glass or the like. A light diffusing liquid crystal composition is formed between the scanning electrode substrate 18 on which the electrode 18b is patterned and the counter electrode substrate 20 on which the counter electrode 20b made of ITO is formed on the second transparent substrate 20a made of plastic or glass. A PDLC 21 is enclosed. Thus, the light diffusion liquid crystal element 17 has a variable scattering pattern parallel to the fluorescent tube 12 that is patterned along the shape of the scanning electrode 18b.
[0019]
The connection terminal 18c of the scanning electrode 18b is connected to a control device 24 that controls a drive circuit (not shown) of the liquid crystal display element 10. The scanning electrode 18b is scanned by the control device 24 in synchronization with the scanning signal of the liquid crystal display element 10, and the voltage application to the light diffusing liquid crystal element 17 is controlled on / off for each variable scattering pattern. As a result, when the light is turned on, the light diffusion liquid crystal element 17 is made transparent to reduce the scattering efficiency, and when it is turned off, the light diffusion liquid crystal element 17 is clouded and switched so as to increase the scattering efficiency. Reference numeral 22 denotes a diffusion sheet.
[0020]
Next, a method for manufacturing the light irradiation device 14 will be described. The scanning electrode 18b is patterned on the first transparent substrate 18a, and the counter electrode 20b is formed on the second transparent substrate 20a. An ultraviolet curable resin is applied around one of the substrates 18 and 20, and the scan electrode substrate 18 and the counter electrode substrate 20 are opposed to each other while holding a gap to form a bonded cell. PDLC 22 is injected into the cell gap, and the entire surface is irradiated with ultraviolet rays to cure the ultraviolet curable resin, thereby manufacturing the light diffusing liquid crystal element 17. The light diffusion liquid crystal element 17 is overlaid on the light guide plate 13, the diffusion sheet 22 is overlaid on the opposite emission surface, the reflecting mirror 11 and the fluorescent tube 12 are incorporated, and the light irradiation device 14 is completed.
[0021]
The light irradiation to the liquid crystal display element 10 by the light irradiation device 14 thus configured will be described. In a state where no voltage is applied, the light diffusing liquid crystal element 17 is set to illuminate the liquid crystal display element 10 by scattering the light propagating through the light guide plate 13 when the fluorescent tube 12 is turned on. Yes. When the fluorescent tube 12 is turned on in accordance with the image display operation of the liquid crystal display element 10, the light incident from the fluorescent tube 12 is transmitted by the light diffusion liquid crystal element 17 while propagating through the light guide plate 13 while repeating total reflection. The liquid crystal display element 10 is irradiated after being scattered and emitted to the outside from the emission surface.
[0022]
In the liquid crystal display element 10, scanning lines are sequentially scanned by an image information signal from a driving device (not shown), and an image corresponding to the signal information from the signal line is displayed. Accordingly, a control signal is input to the scanning electrode 18b of the light diffusing liquid crystal element 17 in synchronization with the scanning signal to the scanning line of the liquid crystal display element 10, and the light diffusing liquid crystal element 17 is turned on / off for each pattern. Be controlled.
[0023]
That is, when it is desired to obtain uniform brightness over the entire display image, as shown in FIG. 3A, as the distance from the fluorescent tube 12, the density of the scanning electrode 18b to which voltage is applied is reduced, and the transparent portion C is formed. Decrease and increase the cloudy portion w of the applied voltage off. In a scene having a luminance distribution, as shown in FIG. 3B, the voltage applied to the light diffusing liquid crystal element 17 in the portion [A] corresponding to the bright image is turned off to make the light diffusing liquid crystal element 17 cloudy. While the portion w is left as it is, the scattering efficiency of the portion is increased, the light in the light guide plate 13 is scattered and emitted to the liquid crystal display element 10 side, while the light diffusion liquid crystal element 17 in the portion [B] corresponding to the dark image By applying a voltage, the light diffusing liquid crystal element 17 is made to be a transparent portion C, the scattering efficiency is lowered, light in the light guide plate 13 is propagated without being scattered, and irradiation according to the luminance of the display image is performed.
[0024]
With this configuration, the scanning electrode 18b of the light diffusing liquid crystal element 17 is turned on / off to switch the scattering efficiency for each variable scattering pattern, so that the light from the fluorescent tube 12 is partially in a necessary portion. Outgoing and unnecessary emission can be suppressed at an unnecessary portion, so that there is no extra emission compared to the conventional case, and when high luminance is required, the diffusion efficiency of the portion can be increased to make it partially bright. Therefore, it is not necessary to increase the power consumption of the fluorescent tube 12 in order to obtain high luminance as in the conventional case, and the image reproducibility can be improved while being economical. Further, the scattering efficiency of the scattering pattern formed by the scanning electrode 18b of the light diffusing liquid crystal element 17 can be easily changed by controlling the applied voltage according to the image without considering the arrangement and size of the pattern. Thus, a scattering pattern suitable for an image can be easily obtained without requiring time for development. In addition, since the on / off control of the light diffusing liquid crystal element 17 does not need to be as fine as the control of the liquid crystal display element 10, the frequency of the applied AC voltage can be sufficiently reduced, and the power consumption is very small. There is no loss of power reduction.
[0025]
Note that the present invention is not limited to the above-described embodiment, and can be changed without departing from the spirit thereof. For example, the scanning of the light diffusing liquid crystal element of the embodiment can be performed with the scanning line of the liquid crystal display element. Without synchronization, scanning from the fluorescent tube side may be sequentially performed by control different from the scanning line, and the voltage control is not only on / off control of the applied voltage, but further improves image reproducibility. Therefore, the scattering efficiency of the light diffusing liquid crystal element may be adjusted more finely by adjusting the magnitude of the applied voltage or current, the frequency, the duty ratio of the pulse waveform, and the like. For example, in a light diffusing liquid crystal element using PDLC, the applied voltage may be decreased as the distance from the rod-shaped light source is increased to increase the scattering efficiency, and uniform emitted light may be obtained over the entire surface of the light guide plate.
[0026]
Further, the light diffusing liquid crystal composition used for the light diffusing liquid crystal element may also use LEFD or the like which becomes cloudy when voltage is applied and becomes transparent when voltage is not applied, and the voltage is applied only to a portion where scattering is required using this LEFD. If the application is controlled so as to make it cloudy, driving with lower power consumption becomes possible. In addition, the shape of the variable scattering pattern and its control method are arbitrary, and the image reproducibility is improved by forming the scanning electrodes in a matrix and adjusting the scattering efficiency in synchronization with the matrix image of the image display device. You may do it.
[0027]
Furthermore, as a scattering pattern for emitting light in the light guide plate more efficiently in a planar shape, a variable scattering pattern and a fixed scattering pattern may be used together. For example, as in another modification shown in FIG. A light having a stripe-like variable scattering pattern 28a described in the embodiment, in which a fixed scattering pattern 27 made of white dots is printed on the surface of the light guide plate 26 with a resin in which alumina (Al ₂ O ₃ ) is dispersed. By overlapping the diffusion liquid crystal element 28, the light in the light guide plate 26 may be scattered more efficiently and with good reproducibility.
[0028]
【The invention's effect】
As described above, according to the present invention, the light propagating through the light guide plate is scattered by the variable scattering means capable of changing the scattering efficiency and emitted in a planar shape, so that development takes time as in the conventional case. Equal emission brightness can be easily obtained without forming a fixed scattering pattern on the light guide plate by printing or the like. Also, in scenes that have a luminance distribution and partially require high luminance, the scattering efficiency is appropriately changed for each variable scattering pattern without improving the luminance of the entire surface of the light guide plate as in the past. The display brightness can be easily adjusted according to the display image, and even when high brightness is required, the scattering efficiency of the variable scattering pattern part corresponding to the high brightness on the image is increased, and other parts are not easily scattered. Adjustment can be set, and the brightness of the light guide plate as a whole can be suppressed. Therefore, it is possible to easily obtain the required brightness without increasing power consumption, improving the reproducibility of image brightness without sacrificing economy. it can.
[Brief description of the drawings]
FIG. 1 is a schematic side view showing a liquid crystal display device according to an embodiment of the present invention.
FIG. 2 is a schematic dispersed perspective view showing a liquid crystal display device according to an embodiment of the present invention.
FIGS. 3A and 3B are schematic explanatory diagrams showing the emission state of the light irradiation apparatus according to the embodiment of the present invention, in which FIG. 3A shows a uniform luminance and FIG. 3B shows a luminance distribution.
FIG. 4 is a schematic dispersed perspective view showing a light guide plate and a light diffusion liquid crystal element according to another modification of the present invention.
FIG. 5 is a schematic side view showing a conventional light irradiation apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 8 ... Liquid crystal display device 10 ... Liquid crystal display element 11 ... Reflector 12 ... Fluorescent tube 13 ... Light guide plate 14 ... Light irradiation apparatus 17 ... Light-diffusion liquid crystal element 18 ... Scan electrode substrate 18b ... Scan electrode 20 ... Counter electrode substrate 21 ... PDLC
22 ... Diffusion sheet

Claims

A liquid crystal display element in which a display liquid crystal composition is sealed in a gap between electrode substrates having electrodes and opposed to each other, and light incident from one side is emitted in a planar shape having substantially the same area as this liquid crystal display element A flat light guide plate having a light emitting surface, a rod-like light source that irradiates the light guide plate adjacent to a predetermined side surface of the light guide plate, and a light scattering efficiency that is disposed in parallel to the light emitting surface. A liquid crystal display device comprising: variable scattering means having a variable scattering pattern that can be partially switched according to scanning of an element.

The liquid crystal display device according to claim 1, further comprising a fixed scattering unit including a fixed scattering pattern having a fixed light scattering efficiency on the light exit surface side of the light guide plate.

The liquid crystal display element is arranged in a matrix and has a plurality of pixels driven line-sequentially, and the light scattering efficiency of the variable scattering pattern can be partially switched in synchronization with the cycle of the line-sequential driving. The liquid crystal display device according to claim 1 or 2.