JP3745389B2 - Parallel beam expansion type surface light source device - Google Patents

Description

上式（１），（２）は各々いわゆる積分形及び微分形の表現であって、物理的な意味は等価である。なお、このＥは濁度と呼ばれることもある。
一方、媒体内に分布した不均一構造によって光散乱が起こる場合の散乱光強度は、縦偏光の入射光に対して出射光の大半が縦偏光である通常の場合（ＶV 散乱）には、次式（３）で表される。
【００１６】
【数２】

自然光を入射させた場合には、Ｈh 散乱を考慮して、式（３）の右辺に（１＋cos²Φ）／２を乗じた次式を考えれば良いことが知られている。
【００１７】
【数３】

ここで、λ0 は入射光の波長、ν＝（２πｎ）／λ0 、ｓ＝２sin （Φ／２）である。また、ｎは媒体の屈折率、Φは散乱角、＜η2 ＞は媒体中の誘電率ゆらぎ２乗平均（以下、＜η2 ＞＝τとして、τを適宜使用する。）であり、γ（ｒ）は相関関数と呼ばれるものである。相関関数γ（ｒ）は、次式（６）で表わされる。
【００１８】
そして、Ｄｅｂｙｅによると、媒体の屈折率不均一構造が界面を持ってＡ相とＢ相に分かれて分散している場合には、相関関数γ（ｒ）、相関距離ａ、誘電率ゆらぎ２乗平均τの関係について次の式（７），（８）が成立する。
【００１９】
【数４】

不均一構造が半径Ｒの球状界面で構成されているとみなせば、相関距離ａは次式で表される。
【００２０】
【数５】

相関関数γ（ｒ）についての式（６）を用い、式（５）に基づいて自然光を媒体に入射させた時の有効散乱照射パラメータＥを計算すると結果は次のようになる。
【００２１】
【数６】

以上述べた関係から、相関距離ａ及び誘電率ゆらぎ２乗平均τを変化させることにより、散乱光強度、散乱光強度の角度依存性及び有効散乱照射パラメータＥを制御することが可能であることが判る。
図１は、横軸に相関距離ａ、縦軸に誘電率ゆらぎ２乗平均τをとり、有効散乱照射パラメータＥを一定にする条件を表わす曲線を、Ｅ＝５０［cm^-1］及びＥ＝１００［cm^-1］の場合について描いたものである。
【００２２】
一般に、Ｅが大きければ散乱能が大きく、Ｅが小さければ散乱能が小さい、換言すれば透明に近くなる。Ｅ＝０は全く散乱の無いことに対応する。
従って、一般には、大寸法の平行光束化素子にはＥの小さな光散乱導光体を用い、小寸法の面光源装置にはＥの大きな平行光束化素子を用いることが好ましいと言うことが出来る。
上記基準を考慮に入れて本願発明で使用される平行光束化素子の有効散乱照射パラメータＥのレンジを定めると、Ｅ＝０．５〜５０［cm^-1］の程度となる。
一方、相関距離ａは、平行光束化素子に用いる光散乱導光体内部における個々の散乱現象における散乱光の方向特性に深く関わっている量である。即ち、上記（３）式乃至（５）式の形から推察されるように、光散乱導光体内部における光散乱は一般に前方散乱性を帯びているが、前方散乱性の強さが相関距離ａによって変化する。
【００２３】
図２は、これをａの２つの値について例示したグラフである。同図において、横軸は散乱角度Φ（入射光線の進行方向をΦ＝０°とした。）を表わし、縦軸は自然光を仮定した場合の規格化散乱光強度、即ち、上記（５）式をΦ＝０°に対して規格化した値、Ｖvh（Φ）／Ｖvh（０）を表わしている。
同図に併記されているように、ａ＝０．１３μｍの場合、即ち、上記（９）式による粒径算値で２Ｒ＝０．２μｍの場合には、Φに関する緩やかな減少関数を表わすグラフが得られるが、ａ＝１．３μｍ、同（９）式による粒径換算値で２Ｒ＝２．０μｍの場合には、Φが小さい値にある領域内で急激に減少する関数を表わすグラフが得られる。
【００２４】
このように、光散乱導光体内の屈折率の不均一構造によって生ずる散乱は、基本的には前方散乱の性格を有しているが、相関距離ａの値が小さくなるに従って前方散乱性が弱まり、個々の散乱過程における散乱角度の範囲が広がる傾向が生じて来る。これは実験的にも確認済みの事柄である。
【００２５】
以上の議論は、平行光束化素子を構成する光散乱導光体内部に分布した屈折率不均一構造による散乱現象そのものに着目した場合に成り立つものであるが、光散乱導光体で構成される平行光束化素子の光取出面から実際に出射される光の方向特性を評価する為には、光取出面における全反射の現象と光出射時の透過率（平行光束化素子から同素子外への脱出率）を併せて考慮する必要がある。
【００２６】
基礎的な光学理論によって全反射の条件として良く知られているように、光散乱導光体の内部側から光取出面に光が入射した時、光散乱導光体内外の媒質の屈折率によって決まる臨界角αc （ここでは、光取出面に立てた法線方向を０°とする。）を入射角が上回る場合には、外部（空気層）への出射（脱出）が起らない。本願発明に使用される代表的な材料であるＰＭＭＡ（屈折率１．４９２）では、αc ＝４２°となる。
【００２７】
後述するように、本願発明で平行光束化素子のマトリックス材料として好適に使用される通常の樹脂材料の屈折率は、１．４〜１．７の範囲にあるので、実際的なαc の範囲は、３６．０°〜４５．６°の程度の値となる。
【００２８】
上述したように、光散乱導光体内部における散乱は前方散乱性を示すから、光取出面の側方に光入射面をとる通常のケースでは、光入射面から入射した光が不均一構造に遭遇して発生した１次散乱光が直ちに上記臨界角条件を満たすことは稀であると考えられる。
【００２９】
従って、光取出面からの光出射には、光散乱導光体内部における多重散乱過程や、光散乱導光体の背面側の界面あるいは反射部材による反射過程を経た光が上記臨界角条件を満たして外部に出射されるという現象が大きく関与しているものと考えるべきである。
【００３０】
そうだとすると、臨界角条件を満たす光に注目した場合には、個々の散乱現象の属性である前方散乱性は相当程度薄められ、光の進行方向分布には相当の拡がりが生じている筈である。その結果、光散乱導光体で構成された平行光束化素子から出射される光の方向特性は、臨界角条件を満たした光の光取出面における透過率（脱出率）の角度依存性に大きく左右されることになる。
【００３１】
一般に、臨界角条件をぎりぎりで満たすような入射角をもって媒体界面に入射した光の界面透過率は極めて低い。例えば、アクリル樹脂−空気界面の場合、Ｐ偏光成分４０％程度、Ｓ偏光成分２０％程度である。そして、入射角が臨界角を下回る角度が増加するに従って光透過等は急激に上昇し、５°乃至１０°以上下回った条件ではほぼ一定となる。アクリル樹脂−空気界面の場合では、Ｐ偏光成分９０％以上、Ｓ偏光成分８５％以上となる。
【００３２】
以上のことから、アクリル樹脂の場合で言えば、光取出面への入射角が３５°〜４０°前後の光が、平行光束化素子の光取出面からの光出射に最も大きく寄与しているものと考えられる。屈折に関するスネルの法則を考慮すると、光取出面がアクリル樹脂−空気界面である場合、３５°〜４０°前後の入射角で光取出面に入射した光は、光取出面に空気側から立てた法線に対して６５°付近から前後数度程度の範囲内に収まる方向へ向けて出射される。
【００３３】
平行光束化素子を構成する光散乱導光体にアクリル樹脂以外の材料を使用した場合でも、実際的な材料の屈折率の範囲は１．４〜１．７の程度であるから、上記角度に数度程度のずれを見込めば、全く同様の議論が成立する。
【００３４】
即ち、平行光束化素子の光取出面からの出射光は、粗く見積って光取出面表面に対して２０°〜３０°前後も立ち上がった方向に明瞭な指向性を有する光となる。
【００３５】
但し、ここで注意すべきことは、相関距離ａの値が余り小さくなると、個々の散乱過程における前方散乱性が薄れ、一次散乱のみで後方散乱を含む広範囲の散乱光が発生するようになる為に、このような指向性を与える前提条件が崩れてしまうことである。本願発明では、このような現象が顕著とならないような光散乱導光体（以下、「指向出射性の光散乱導光体」と呼ぶ。）で構成された平行光束化素子を使用する。この条件を考慮した場合の相関距離ａの下限値は０．０６μｍの程度である。
【００３６】
一方、図１から判るように、相関距離ａが大きい程有効散乱照射パラメータＥの値を大きくすることが難しくなる傾向がある。本願発明では、この条件をも考慮に入れて、平行光束化素子を構成する光散乱導光体の相関距離ａの値の実際的な範囲として、０．０６μｍ〜３５μｍを選択した。光散乱導光体を異屈折率粒子を分散させた場合には、（９）式から、粒子径０．１μｍ〜５４μｍの範囲がこれに対応することになる。
【００３７】
このような条件で一様な散乱能を与えられた楔形状の指向出射性の平行光束化素子の厚みが大きい側の側面を光入射面として、通常の蛍光ランプ等の光源（一般には、光供給手段）からの光を入射させると、平行光束化素子の表裏両面から指向性の光束が出射される。その一方の面が平行光束化素子の光取出面として用いられる。他方の面には適宜反射性の部材を配置して光の散逸を防止することが好ましい。
【００３８】
平行光束化素子の光取出面から出射した光は、上述したように、光取出面に対して２０°から３０°前後立ち上がった方向に指向性を有している。ところが、液晶表示装置のバックライト光源の用途をはじめとして、面光源装置には正面あるいはこれに近い方向から見た明るさが要求されることが多い。また、平行光束化素子の光取出面から出射される平行光束の断面積は、光取出面の大きさより小さくなるから、比較的大きな断面積の光束を必要とする場合には、それに合わせて平行光束化素子のサイズも大型化する必要が生じる。
【００３９】
本願発明では、このような不都合を回避する為に平行光束化素子から出射された平行光束を該平行光束の伝播方向に対して傾斜配置された表裏二重プリズム反射素子の反射面で反射させることによって、平行光束の伝播方向を所定の方向、例えば、面光源装置全体の延在方向に対して垂直な方向（以下、単に「正面方向」と言う。）に転換させると共に、光束の断面積を拡大させる。
【００４０】
ここで、平行光束化素子が楔形状断面の光散乱導光体で構成されていることの光学的な意義について説明しておく。
図３は、本願発明で使用される楔形状の平行光束化素子の楔形断面を表わす図であり、その内部における繰り返し反射の様子が、光入射面から平行光束化素子内部に取り込まれる光線の光路を光線Ｂ0 で代表させる形で記されている。
【００４１】
符号１は「作用」の欄で述べた散乱特性を有する光散乱導光体で構成された平行光束化素子を表わしており、楔形状の断面積の大きな方の側端部に形成された光入射面２に臨んで蛍光ランプＬ（一般には、光供給手段であるが、以下、蛍光ランプでこれを代表させる。）が配置されている。蛍光ランプＬから出射されて平行光束化素子１内に入射される光を代表する代表光線Ｂ0 の伝播方向は、図示したように、平行光束化素子の延在方向と小さな角度をなしているものと考えることが出来る。
【００４２】
この光線Ｂ0 の挙動を考察してみると、入射面２から平行光束化素子１内に入射した光線Ｂ0 は、一定割合で散乱による方向転換を受けながら、図示したように光取出面３とこれに対して傾斜した裏面４において反射を繰り返しながら、平行光束化素子１の厚みの薄い末端部６へ近づいていく。面４，５の内側表面における反射は正反射であるから、個々の反射における入射角と反射角は等しい（θ1 ，θ2 ，θ3 ・・・・）。ここで、光取出面３における各回の反射に注目すると、θ2 ＞θ4 ＞θ6 ・・・の関係が成立していることが判る。
【００４３】
更に、各反射時における界面透過率を考えてみると、光散乱導光体の指向出射性の場合と同様の議論によって、θi ＞αc （臨界角；ＰＭＭＡ−空気界面で４２°）の条件では全反射が起こり、θi がαc を下回ると透過率が急上昇し、θi が所定値（ＰＭＭＡ−空気界面で３５°前後）以下で透過率はほぼ一定となる。図では、θ2 ＞αc ＞θ4 ＞θ6 の関係によって、出射光Ｂ4 ，Ｂ6 が生じている様子が描かれている。
【００４４】
このような効果は、代表光線Ｂ0 （無散乱光）に限らず、１次散乱光や多重散乱光についても程度の差はあっても同様に生じている筈であるから、平行光束化素子１全体としては光入射面２から遠ざかる程光取出面３からの光出射率を高める効果を生んでいるものと考えられる。この効果を、光入射面２からの距離ｘの関数ｆ（ｘ）で評価すると、ｆ（ｘ）はｘに関する増加関数である。一方、光入射面２に近い部分では光源Ｌに近いという効果が直接光、散乱光いずれについても働く。この近接効果をｇ（ｘ）で評価すれば、ｇ（ｘ）は減少関数となる。
【００４５】
従って、近接効果ｇ（ｘ）がｆ（ｘ）によって相殺され、より遠くまで光を導いた上で光取出面３から光を出射させる傾向が生まれることになる。また、平行光束化素子１内の光が光取出面３に入射する機会も、楔形状の効果によって入射面２から遠ざかるにつれて増大する傾向を持ちつつ全体的に増大すると考えられるから、光取出面３全体に亙って輝度レベルを一段と向上させる効果も生じているものと思われる。
【００４６】
両面３，４のなす角度ψに絶対的な制限は特にないが、明るさのレベル、均一度、指向特性等を考慮した実際的な範囲としては、０．５°≦ψ≦５°が考えられる。また、傾斜した裏面４（場合によっては光取出面３）を曲面とすることにより、反射角θ1 、θ2 、θ3 ・・・・の増大推移を制御し、より望ましい特性を実現することも可能である。
【００４７】
ここで述べたような効果は、裏面４に沿って反射体５を配置した場合にも同様に成立することは明らかである。平行光束化を阻害しない観点から、この反射体５は拡散反射性の反射体よりも正反射性を有する反射体であることが好ましい。
【００４８】
なお、平行光束化素子を含む平行光束出射部と組み合わせて配置される表裏二重プリズム反射素子の反射面の形状や配置方向の選択、並びに平行光束化素子を構成する光散乱導光体の材料・製法については、次記実施例の中で述べることとする。
【００４９】
【実施例】
図４は、本願発明の基本配置に相当する構成を備えた面光源装置を液晶表示装置のバックライト光源として使用した実施例を、要部断面図の形で表わしたものであり、拡大化機能を分かりやすくする為に、実際的な寸法データが例示的に併記されている。
【００５０】
同図において、符号Ｆで示された部分は平行光束出射部であり、蛍光ランプＬと背面側から蛍光ランプＬを取り囲むように設けられた反射体Ｒ、平行光束化素子１から構成されている。平行光束化素子１は、楔形状の断面を有する光散乱導光体で構成されており、ここでは、ポリメチルメタクリレート（ＰＭＭＡ）中にシリコーン系樹脂材料（屈折率＝１．４３４５）を０．１ｗｔ％の割合で一様に分散させたものが使用されている。
【００５１】
裏面４の長さサイズは図中に示した通り３８ｍｍであり、入射面２側の端部の厚みは８．０ｍｍである。末端部６の厚みは０．２ｍｍ程度とする。幅については適宜の値（例えば、２００ｍｍ）とすることが出来る。
【００５２】
蛍光ランプＬは平行光束化素子１の入射面２から１ｍｍ離して配置されておりその直径は８ｍｍ、長さは平行光束化素子１の幅とほぼ等しいものとする。反射体Ｒは入射面２から入射する光量を出来るだけ多くする為に適宜配置されるもので、例えば、酸化防止の為の表面処理を施した銀箔が使用される。
平行光束化素子１の裏面４にも、正反射性の反射体が設けられている。この反射体５は、平行光束化素子１とは別体の反射部材（例えば、銀箔シート）であっても良く、また、裏面４上に形成された反射膜（例えばＡｇ蒸着膜、Ａｌ蒸着膜等）であっても良い。銀箔シートのように、紫外線による反射性能の劣化の恐れがある反射部材を用いる場合には、裏面４への固着手段として紫外線吸収性の接着剤を用いることが好ましい。後述するように、平行光束化素子１はプラスチック材料の射出成形技術によって製造することが実用的であり、反射部材の固着に際してインモールド法を適用することが可能である。
【００５３】
蛍光ランプＬからの放射光及び反射体Ｒによる反射光は、光散乱導光体で構成された平行光束化素子１の光入射面２から平行光束化素子１の内部に進入し、光散乱作用を受けながら、末端部６へ向けて導光される。「作用」の欄で詳しく説明したように、この過程を通して平行光束化素子１の光取出面３からは、平行化された光束（以下、単に「平行光束」と言う。）が出射される。符号Ｇ1 は、この平行光束を代表する光線である。代表光線Ｇ1 の出射角β（光取出面３に立てた垂線から測ることとする。）は、「作用」の欄で述べたように、６５°前後となる。
【００５４】
符号ＰＲは、平行光束出射部から出射される平行光束のほぼ全量を受光する位置に、平行光束の伝播方向（即ち、代表光線Ｇ1 の伝播方向）に対して所定角度傾斜して配置された表裏二重プリズム反射素子である。この表裏二重プリズム反射素子ＰＲは、次に述べる平行光束の断面積拡大機能と伝播方向転換機能を有しており、平行光束出射部Ｆからの平行光束のほぼ全量は、図中上方へ向けて反射される。
【００５５】
表裏二重プリズム反射素子ＰＲからの反射光束の光路には、適当な散乱能を与えられた光拡散板ＤＦが配置されており、更にその上方には液晶パネル部ＬＰが配置されている。液晶パネル部ＬＰは、偏光透過軸を直交させた２枚の偏光子２１，２３の間に液晶セル部２２を挟んだ基本構成を有している。
【００５６】
このような配置により、平行光束出射部Ｆから供給された平行光束は、表裏二重プリズム反射素子ＰＲで上方に向かう拡大された反射光束に転換されて光拡散板ＤＦに入射する。この光拡散板ＤＦは、表裏二重プリズム反射素子ＰＲの反射光束の指向性を適宜緩和調整すると共に、表裏二重プリズム反射素子ＰＲにおける反射過程で発生する可能性のある微細なレベルでの明るさのムラを除去する為に適宜使用されるものであり、場合によっては、省略あるいは透明板に代えることも有り得る。
【００５７】
光拡散板ＤＦを通過して、適度に指向性を緩和調整された平行光束は、液晶パネル部ＬＰに入射し、バックライト光としての役割を果たす。平行光束の持つ指向性と均一性によって、所望の観察方向（ここでは、正面方向）から見た表示品位に優れた液晶表示画面が実現される。また、光拡散板ＤＦに付与する散乱能の強さを調整することによって、明るい表示画面が観察される方向の幅を適宜調整することも可能である。
【００５８】
次に、表裏二重プリズム反射素子ＰＲの構造と機能について説明する。図５は上記実施例に使用されている表裏二重プリズム反射素子ＰＲの符号３０で示した部分を拡大描示した断面図であり、光線Ｇ1 で代表される平行光束ＦＬ１の反射の様子が併記されている。同図に示されているように、表裏二重プリズム反射素子ＰＲの表裏には、プリズム状の起伏を構成する繰り返し傾斜面Ｈ，Ｈ’，Ｊ，Ｊ’が形成されている。また、裏面からの光の透過散逸を防止する為に、適宜ＡｌあるいＡｇ等の蒸着膜ＶＬが形成されている。表裏二重プリズム反射素子ＰＲを構成する材料には任意の透明光学材料が使用可能であるが、平行光束化素子１のマトリックスに使用される材料と同じ材料、例えばＰＭＭＡ（ポリメチルメタクリレート）を使用すれば、経済的に有利である。
【００５９】
代表光線Ｇ1 の伝播方向と表裏各面の傾斜面のＨ，Ｈ’及びＪ，Ｊ’の傾斜角の間には次の条件が成立していることが望ましい。換言すれば、この条件を満たすように、平行光束化素子１と表裏二重プリズム反射素子ＰＲの材料（屈折率）、平行光束化素子１と表裏二重プリズム反射素子ＰＲの姿勢関係、傾斜面Ｈ，Ｈ’及びＪ，Ｊ’の傾斜角度を選択することが好ましい。
【００６０】
（１）各傾斜面Ｈ’と光線Ｇ1 の伝播方向が平行であること。
（２）各傾斜面Ｊは、Ｈから入射した屈折光束のほぼ全量を受ける位置に延在していること。
【００６１】
（３）各傾斜面Ｈ’は、各傾斜面Ｈから入射した屈折光束の面Ｊ（蒸着膜との界面）における正反射光束のほぼ全量を受ける位置に延在していること。
【００６２】
（４）各傾斜面Ｈにおける正反射光束ＦＬ２と、各傾斜面Ｈ’から出射される光束ＦＬ３を各々代表する光線Ｇ2 ，Ｇ3 がほぼ平行であり、且つ、 所望の出射方向にほぼ合致していること。
【００６３】
このような条件を常に厳密に満足させることは難しいが、少なくとも、希望する出射方向が正面方向から大幅にはずれない範囲では、近似的な満足を得ることは容易である。例えば、表裏二重プリズム反射素子ＰＲの平行光束化素子１に対する姿勢の調整と、表裏二重プリズム反射素子ＰＲの屈折率選択だけで、相当の幅で出射方向を調整することが出来る。
【００６４】
好ましくは、上記条件を満たすように設計された表裏二重プリズム反射素子ＰＲの表裏面における反射作用によって、光線Ｇ1 で代表される入射光束ＦＬ１は各面Ｈにおける正反射光束ＦＬ２（Ｇ2 で代表）と各面Ｈ’からの屈折出射光束ＦＬ３（Ｇ3 で代表）に分割され、その断面積が拡大される（ＦＬ１→ＦＬ２＋ＦＬ３）。なお、各面Ｈにおける反射／透過の割合を調整する為に、半透光膜を各面Ｈ上に形成することも考えられる。また、偏光成分（Ｐ偏光成分とＳ偏光成分）の各面Ｈにおける反射／透過の割合の差が液晶表示面の明るさのムラになって現われる場合には、繰り返し斜面Ｈ，Ｈ’，Ｊ，Ｊ’の繰り返しピッチを小さくし、光拡散板ＤＦに与える散乱能を強くすることが有効である。
【００６５】
上記実施例に関する以上の議論は、主として平行光束化素子１の光入射面２から見て縦断方向（紙面に沿った方向、以下単に「縦断方向」と言う。）に注目したものであるが、平行光束化素子１の光入射面２から見て横断方向（紙面に垂直な方向、以下単に「横断方向」と言う）について、光束の伝播方向を整えて、面光源装置の横断方向側方への光の散逸を防止することが望まれる場合には、平行光束化素子１の光取出面３に臨んで光出射方向修正手段が設けることが出来る。
【００６６】
この光出射方向修正手段は、平行光束化素子１と一体、別体いずれの形態で設けても良い。図６は、前者の例を示した斜視図であり、図７は、後者の例を示した斜視図である。
各図において、符号ＣＲ，ＣＲ’は平行光束化素子１の光取出面３側に縦断方向に配向して形成されたプリズム状の起伏列であり、図６では平行光束化素子１の光取出面３の表面がこれを兼ねている。また、図７では、起伏列ＣＲ’を形成した別体の光出射方向修正素子７が配置された形態が示されている。符号２，３，４，５は、図４と同じく各々光入射面、光取出面、裏面及び反射体（銀箔）を表わしている。
【００６７】
図６、図７いずれの配置においても、光入射面２から平行光束化素子１内に進入した光は、「作用」の欄で述べたように、縦断方向について平行化され、６５度前後の出射角をもって光取出面３から出射される（矢印群３ｆで表示）。ここで、この出射時の横断方向についての光路を考えて見ると、平行光束化素子１に与えられた散乱能によって伝播方向に相当の拡がりが存在していると考えられる（矢印群３ｆ’で表示）。
【００６８】
縦断方向に配向して形成された各図におけるプリズム状起伏列は、このような横断方向の光束伝播方向の拡がりを抑制して、光の三次元的に平行性を向上させるものであり、この作用を通して光の横断方向側方への散逸を防止する上で有効なものである。
【００６９】
図８は、各図における横断方向（光入射側から見て左右幅方向）の光出射方向修正機能を説明する図であり、平行光束化素子１あるいは光出射方向修正素子７を符号８で示された方向に沿って切りとった断面を表わしている。同図において、方向にバラツキがある符号Ｂ1 〜Ｂ3 で示された光線は、平行光束化素子１または光出射方向修正素子７から外部へ出射される直前の光を代表している。
【００７０】
先ず、左右方向に近い進行方向を有する光線Ｂ1 ，Ｂ2 は、図示されているように、起伏面ＣＲあるいはＣＲ’を構成するプリズム面Ｃａ，Ｃｂの一方から一旦空気層ＡＲへ出射されるが、その相当部分は他方のプリズム面Ｃｂ，Ｃａで正反射し、横断方向成分がほぼ除去されて光線Ｂ1 ’，Ｂ2 ’として出射される。
【００７１】
一方、横断方向成分が乏しい光線Ｂ3 は、図示されているように、一方のプリズム面Ｃａで反射されてから、他方のプリズム面Ｃｂを通過して一旦空気層ＡＲへ出射されるが、その相当部分は隣接したプリズム面Ｃａで正反射され、横断方向成分の乏しい状態を保った光線Ｂ3 ’として出射されるものと考えることが出来る。このような屈折作用によって、図６、図７において矢印群３ｆで示されているような方向に伝播する光の割合が増加し、矢印群３ｆ’で示されているように横断方向側方へそれる光の割合が減少するから、結局、平行光束出射部Ｆから供給される光束の平行度が三次元的に改善される。
【００７２】
なお、平行光束化素子１あるいは光出射方向修正素子７に通常の材料（例えば、ＰＭＭＡ）を使用した場合、光出射方向修正機能を良好に発揮させる上で好適なプリズム頂角（プリズム面Ｃａ，Ｃｂのなす角度）の大きさは、８０°〜１１０°の程度である。
【００７３】
また、以上の説明では、光源として棒状の蛍光ランプが用いられているが、本願発明が光源の種類、形状等に格別の制限を設けるものでないことは、本願発明の原理とこれまで説明事項に照らして明らかであろう。例えば、光拡散性の面光源の光を平行光束化素子の光入射面から入射させても良いし、発光ダイオードアレイからの複数ビームを入射光として、これを均一な平行光束に変換することも可能である。
【００７４】
更に、図４の配置を対向した向きで並列配置し、２灯式としてほぼ倍のサイズの拡大光束を生成する面光源装置を構成しても良い。
【００７５】
最後に、本願発明に使用される平行光束化素子を構成する光散乱導光体の材料及び製造方法について説明する。
本願発明で使用する平行光束化素子を構成する光散乱導光体のベースには、ポリマー材料をベースとした種々のものが利用可能である。これらポリマーの代表的なものを下記の表１及び表２に示した。
【００７６】
【表１】

【００７７】
【表２】

このようなポリマー材料をベースとする平行光束化素子は、次のような製造法によって製造することが可能である。
先ず、その１つは、２種類以上のポリマーを混練する工程を含む成形プロセスを利用する方法である。
即ち、２種類以上の屈折率の相互に異なるポリマー材料（任意形状で良い。工業的には、例えばペレット状のものが考えられる。）を混合加熱して、練り合わし（混練工程）、混練された液状材料を射出成形機の金型内に高圧で射出注入し、冷却固化することによって成形された平行光束化素子を金型から取り出せば金型形状に対応した形状の平行光束化素子を得ることが出来る。
【００７８】
混練された２種類以上の異屈折率のポリマーは完全には混ざり合うことなく固化するので、それらの局所的濃度に不均一（ゆらぎ）が生まれて固定され、一様な散乱能が与えられる。
また、混練された材料を押し出し成形機のシリンダー内に注入し、通常のやり方で押し出せば目的とする成形物を得ることが出来る。
【００７９】
これらポリマーブレンドの組合せや混合割合については、非常に幅広い選択が可能であり、屈折率差、成形プロセスで生成される屈折率不均一構造の強さや性質（散乱照射パラメータＥ、相関距離ａ、誘電率ゆらぎ２乗平均τ等）を考慮して決定すれば良い。なお、使用し得るポリマー材料の代表的なものは前記表１及び表２に示されている。
【００８０】
平行光束化素子を構成する材料の製造法の別の１つは、ポリマー材料中に屈折率の異なる（０．００１以上の屈折率差）粒子状材料を一様に混入分散させるものである。
そして、粒子状材料の一様混入に利用可能な方法の１つにサスペンション重合法と呼ばれる方法がある。即ち、粒子状材料をモノマー中に混入し、湯中に懸濁させた状態で重合反応を行なわせると、粒子状材料が一様に混入されたポリマー材料を得ることが出来る。これを原材料に用いて成形を行なえば、所望の形状の平行光束化素子が製造される。
【００８１】
また、サスペンション重合を種々の粒子状材料とモノマーの組合せ（粒子濃度、粒径、屈折率等の組合せ）について実行し、複数種類の材料を用意しておき、これを選択的にブレンドして成形を行なえば、多様な特性の平行光束化素子を製造することが出来る。また、粒子状材料を含まないポリマーをブレンドすれば、粒子濃度を簡単に制御することが出来る。
【００８２】
粒子状材料の一様混入に利用可能な方法の他の１つは、ポリマー材料と粒子状材料を混練するものである。この場合も、種々の粒子状材料とポリマーの組合せ（粒子濃度、粒径、屈折率等の組合せ）で混練・成形（ペレット化）を行なっておき、これらを選択的にブレンドして平行光束化素子を成形製造することにより、多様な特性の平行光束化素子を得ることが出来る。
【００８３】
また、上記のポリマーブレンド法と粒子状材料混入方法を組み合わせることも可能である。例えば、屈折率の異なるポリマーのブレンド・混練時に粒子状材料を混入させることが考えられる。
【００８４】
以下、製造法の幾つかの実例を挙げておく。
＜製造例１＞
メタクリル樹脂のペレット（旭化成製、デルベット８０Ｎ）に粒径０．８μｍのシリコーン系樹脂粉体（東芝シリコーン製、トスパール１０８）を０．３ｗｔ％添加し、ミキサーで混合分散させた後、押し出し機でストランド状に押し出し、ペレタイザーでペレット化することにより、シリコーン系樹脂粉体が均一に分散されたペレットを調製した。
【００８５】
このペレットを射出成形機を用い、シリンダー温度２３０゜Ｃ〜２６０゜Ｃ、型温度５０゜Ｃの条件で成形して、縦３８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍ迄徐々に変化した楔型の平行光束化素子を得た。
【００８６】
製造された平行光束化素子の相関距離はａ＝０．５３μｍであり、有効散乱照射パラメータの前記（１１）式による見積計算値はＥ＝１２．６[cm^-1]であった。
【００８７】
＜製造例２＞
ＭＭＡに粒径０．８μｍのシリコーン系樹脂粉体（東芝シリコーン製、トスパール１０８）を０．３ｗｔ％添加し、公知のサスペンション重合法により、該粉体が均一に分散した球状粒子を得た。これを製造例１と同様にペレタイザーでペレット化することにより、シリコーン系樹脂粉体が均一に分散されたペレットを調製した。
【００８８】
以下、製造例１と同じ条件で同型の楔状平行光束化素子を得た。この平行光束化素子は、製造例１で作製された平行光束化素子と外観上全く区別がつかないものであった。そして、相関距離はａ＝０．５３μｍであり、有効散乱照射パラメータの前記（１１）式による見積値はＥ＝１２．６[cm^-1]であった。
【００８９】
＜製造例３＞
ポリメチルメタクリレート（ＰＭＭＡ）にポリスチレン（ＰＳｔ）を０．５ｗｔ％添加し、Ｖ型タンブラーを用いて１０分間、次いでヘンシェルミキサーを用いて５分間混合した。これを径３０ｍｍの２軸押し出し機［ナカタニ機械（株）製］を使って、シリンダー温度２２０゜Ｃ〜２５０゜Ｃ、スクリュー回転数７５ｒｐｍ、吐出量６ｋｇ／ｈｒの条件で融解混合してペレットを作成した。
【００９０】
このペレットを射出成形機を用い、シリンダー温度２２０゜Ｃ〜２５０゜Ｃ、型温度６５゜Ｃ、射出速度中速、射出圧力ショートショット圧プラス１０ｋｇ／ｃｍ2 の条件で成形して、縦３８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍ迄徐々に変化した楔型の平行光束化素子を得た。
【００９１】
＜製造例４＞
ＭＭＡ（メチルメタクリレート）に粒径２μｍのシリコーン系樹脂粉体（東芝シリコーン製、トスパール１２０）を各々０．０５ｗｔ％、０．０８ｗｔ％、０．１０ｗｔ％、０．１５ｗｔ％を加えて均一に分散した４種類の試料と粒子無添加のＭＭＡ試料を用意し、計５種類の試料の各々にラジカル重合開始剤としてベンゾイルパーオキサイド（ＢＰＯ）０．５ｗｔ％、連鎖移動剤としてｎ―ラウリルメルカプタン（ｎ−ＬＭ）を０．２ｗｔ％加え、７０℃で２４時間注型重合させて縦３８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍ迄徐々に変化した楔型の平行光束化素子を１枚づつ作製した。
【００９２】
＜製造例５＞
ＭＭＡ（メチルメタクリレート）にシリコーンオイルを０．０２５ｗｔ％加えて均一に分散させ、ラジカル重合開始剤としてベンゾイルパーオキサイド（ＢＰＯ）を０．５ｗｔ％、連鎖移動剤としてｎ―ブチルメルカプタン（ｎ−ＢＭ）を０．２ｗｔ％、各々加え、７０℃で３０分間にわたりゾル化を行なった上で、更に６５℃で２４時間注型重合させて縦３８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍまで徐々に変化した楔型の平行光束化素子を作製した。
【００９３】
＜製造例６＞
ＰＭＭＡ（ポリメチルメタクリレート）に粒径２μｍのシリコーン系樹脂粉体（東芝シリコーン製、トスパール１２０）を０．０８ｗｔ％加え、Ｖ型タンブラを用いて１０分間、次いでヘンシェルミキサを用いて５分間混合した。これを２軸押し出し機で溶融混合（シリンダ温度２２０℃〜２５０℃）・押出成形して、ペレットを作製した。
【００９４】
このペレットを射出成形機を用いてシリンダ温度２２０℃〜２５０℃の条件で射出成形し、縦３８ｍｍ、横８５ｍｍで厚さが長辺方向に３．８ｍｍから０．２ｍｍまで徐々に変化した楔型の平行光束化素子を作製した。
【００９５】
【発明の効果】
本願発明によれば、従来のレンズや曲面鏡を利用した方法では困難であった無秩序な方向性を有する光束の平行化と拡大化が同時に達成される。また、その際に得られる平行光束は、そのフラックス断面の強度プロファイルの平坦度が高いことも従来の方法には期待し得なかった利点である。
【００９６】
更に、本願発明では、光入射面側から見て横断方向に関しても平行度を向上させる技術手段を提供したので、非平行性の光束を３次元的な意味で高い平行性を有する拡大光束に変換することも可能となった。
【００９７】
従って、比較的小型の平行光束化素子を用いて、大きな断面積を有する平行光束を生成する面光源装置を構成することが出来る。
【００９８】
このような諸利点は、液晶表示装置のバックライト光源への適用に際して特に有利に作用する。
【図面の簡単な説明】
【図１】横軸に相関距離ａ、縦軸に誘電率ゆらぎ２乗平均τをとって有効散乱照射パラメータＥを一定にする条件を表わす曲線を、Ｅ＝５０［cm^-1］及びＥ＝１００［cm^-1］の場合について描いたものである。
【図２】相関距離ａによって平行光束化素子を構成する光散乱導光体の前方散乱性の強さが変化することを説明するグラフである。
【図３】本願発明で使用される楔形状の平行光束化素子の楔形断面を表わす図であり、その内部における繰り返し反射の様子が、光入射面から平行光束化素子内部に取り込まれる光線の光路を光線Ｂ0 で代表させる形で記されている。
【図４】本願発明の基本配置に相当する構成を備えた面光源装置を液晶表示装置のバックライト光源として使用した実施例を、要部断面図の形で表わしたものである。
【図５】実施例に使用されている表裏二重プリズム反射素子の一部を拡大描示した断面図であり、光線Ｇ1 で代表される平行光束ＦＬ１の反射の様子が併記されている。
【図６】平行光束化素子と一体に設けられた光出射方向修正手段について説明する斜視図である。
【図７】平行光束化素子と別体に設けられた光出射方向修正手段（光出射方向修正素子）について説明する斜視図である。
【図８】図６、図７に示した光出射方向修正手段の光出射方向修正機能を説明する図である。
【符号の説明】
１ 平行光束化素子
２ 光入射面
３ 光取出面
３ｆ，３ｆ’ 出射光
４ 裏面
５ 平行光束化素子裏面側に設けられた反射体（銀箔）
６ 平行光束化素子の末端部（末端面）
７ 光出射方向修正素子
２１，２３ 偏光子
２２ 液晶セル部
ＡＲ 空気層
ＣＲ，ＣＲ’ プリズム状起伏
ＤＦ 光拡散板
Ｆ 平行光束出射部
Ｌ 蛍光ランプ
ＬＰ 液晶表示パネル部
ＰＲ 表裏二重プリズム反射素子
Ｒ 蛍光ランプ背面側に設けられた反射体（銀箔）
ＶＬ ＡｌあるいＡｇ等の蒸着膜[0001]
[Industrial application fields]
The present invention relates to a surface light source device that is advantageous when applied to a backlight light source unit or the like of a liquid crystal display device, and more specifically, has an enlarged cross-sectional area for light from a normal light source such as a fluorescent lamp. In addition, the present invention relates to a surface light source device that can be converted into a uniform light beam with high parallelism and emitted.
The present invention can be applied to any application that requires a parallel light beam having a relatively large cross-sectional area in addition to the application to the backlight light source unit of the liquid crystal display device. The present invention can be effectively used for various types of devices used for the purpose of light and information transmission.
[0002]
[Prior art]
Conventionally, when it is necessary to convert a non-parallel light beam into a light beam having a high degree of parallelism, an optical system made up of a lens or a curved mirror (such as a parabolic mirror) is usually used. The beam collimation technology using this lens or curved mirror is a light beam that is emitted from a non-parallel beam source (single or multiple light source elements or optical fiber exit end, etc.) in multiple directions. Parallelizing using the function of convergence or light divergence.
[0003]
Therefore, the non-parallel light source has only one of the properties of diverging (for example, a single point light source) or convergence (for example, a large number of directional point light sources arranged at one point). It can be an effective collimating means, but it can collimate light beams that cannot be defined by one of divergent or convergent properties, such as light emitted from multiple light sources in multiple directions. It was difficult to make it.
[0004]
In addition, when using an optical system consisting of a lens or concave mirror, it is theoretically difficult to flatten the light intensity profile (light intensity distribution on the beam cross section) of the collimated light beam (usually near the optical axis) It is a Gaussian-type profile with a peak of), and is not suitable for use to obtain a parallel light beam with uniform light intensity.
[0005]
Furthermore, in order for the lens and curved mirror to exhibit the light convergence / divergence function, it is necessary to ensure a sufficient distance along the optical axis direction, so it is generally difficult to reduce the depth dimension of the entire apparatus. .
[0006]
As a technology that is completely different from the technology using an optical system composed of these lenses and concave mirrors, a technology is known in which light incident from the side using a light scatterer is emitted from the light extraction surface on the front side. (For example, JP-A-2-221926, JP-A-4-145485, and Japanese Utility Model Laid-Open No. 51-89888), these techniques are based on the progress of light by the light scattering action applied to the inside of the light guide or to the surface region. This is to secure the amount of light emitted from the light extraction surface by making the direction as random as possible, and is not based on the technical problem of collimating the light emitted from the light extraction surface.
[0007]
Thus, in the past, it was difficult to generate a parallel light beam having a uniform profile, so in addition to the parallelism of the light beam and the uniformity of the profile, the size of the light beam cross-sectional area was simultaneously secured. It was even more difficult to do.
[0008]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a parallel light beam expansion type light source device capable of generating a collimated light beam having an expanded cross-sectional area with high uniformity in incident light.
[0009]
In addition, the present invention provides a surface light source capable of responding to the use of a backlight light source of a liquid crystal display device, for which there is an increasing demand for higher image quality and a larger screen by providing such a parallel light flux expanding type light source device It is intended to provide an apparatus.
[0010]
Furthermore, the present invention intends to provide the surface light source device provided with means for achieving the collimated light flux at a three-dimensional level or means for reducing the degree of directivity of the collimated light flux. To do.
[0011]
[Means for Solving the Problems]
In the present invention, first, as a technical means for achieving the above basic object, And having On one side The first reflecting surface having a repeatedly inclined surface shape that reflects a part of incident light from the outside On the other side The second reflecting surface having a repetitive inclined surface shape that reflects at least part of the internal incident light A front and back double prism reflecting element,
To the side of the double prism reflector The collimated light beam is directed toward the first reflecting surface, and the incident angle when the light propagating in the direction representative of the propagation direction of the collimated light beam is incident on the first reflecting surface is 0. In an attitude that outputs so as not to become Placed Tabira Row beam exit When With
The parallel light beam emitting portion has an effective scattering irradiation parameter E [cm ^-1 ] Is in the range of 0.5 ≦ E ≦ 50, and the correlation function γ (r) of the refractive index inhomogeneous structure that produces the light scattering ability is expressed as γ (r) = exp [−r / a] (where r Is a wedge-shaped cross section having a uniform scattering ability in which the value of the correlation distance a [μm] is in the range of 0.06 ≦ a ≦ 35 when approximated by the distance between two points in the light scattering light guide). A parallel luminous element comprising a light-scattering light guide including a volume region, and a light incident means disposed on the end face side of the relatively large wedge-shaped cross section of the parallel luminous element,
The front and back double prism reflecting element is the first Reflective surface The collimated light beam incident on the first Reflective surface And the second Reflective surface Reflected in ,in front First Reflective surface To From outside As a collimated beam with an enlarged cross-sectional area compared to the incidence , Outward from the first reflective surface The present invention proposes a “parallel light flux expanding type surface light source device characterized in that it emits” (structure described in claim 1).
[0012]
here Compared to the above basic configuration, brightness uniformity is further improved and the degree of directivity is adjusted and relaxed Therefore, a light diffusing plate can be disposed in the optical path of the reflected light beam from the front and back double prism reflecting elements. .
[0013]
Furthermore, in each of the above-described configurations, it is viewed from the light incident surface side of the parallel light beam forming element. Width Direction (below , " Cross direction " Also To tell. In order to improve the three-dimensional parallelism by adjusting the propagation direction of the light beam emitted from the parallel light beam emitting portion, the above-described configuration includes “seeing from the light incident surface side of the parallel light beam converting element”. Width 3. The light emission direction correcting means for correcting the light emission direction characteristic of the direction is provided facing the light emission surface of the parallel beam forming element of the parallel beam emitting unit. It is proposed to impose the requirement of “surface light source device described in 1).
[0014]
[Action]
In the present invention, a light beam having a relatively small cross-sectional area whose propagation direction is aligned using a parallel light beam generation element including a volume region having a wedge-shaped cross section provided with uniform scattering power is relatively The light is incident on a front and back double prism reflecting element having a reflecting surface having a large area and is taken out in the form of a reflected light beam having a relatively large cross-sectional area.
Therefore, first, the scattering irradiation parameter E and the correlation distance a used in describing the scattering characteristics of the light scattering light guide constituting the parallel light flux generating element in the present invention will be described with reference to Debye's theory. .
When light having an intensity I0 is transmitted through the medium by y (cm) and the intensity is attenuated to I due to scattering therebetween, the effective scattering irradiation parameter E is defined by the following equation (1) or (2).
[0015]
[Expression 1]

The above formulas (1) and (2) are expressions of so-called integral type and differential type, respectively, and their physical meanings are equivalent. This E is sometimes called turbidity.
On the other hand, the scattered light intensity when light scattering occurs due to the non-uniform structure distributed in the medium is as follows in the normal case (VV scattering) where most of the emitted light is longitudinally polarized with respect to longitudinally polarized incident light. It is represented by Formula (3).
[0016]
[Expression 2]

When natural light is incident, (1 + cos) is added to the right side of Equation (3) in consideration of Hh scattering. ² It is known that the following equation multiplied by (Φ) / 2 may be considered.
[0017]
[Equation 3]

Here, λ0 is the wavelength of incident light, ν = (2πn) / λ0, and s = 2sin (Φ / 2). Further, n is the refractive index of the medium, Φ is the scattering angle, <η 2> is the mean square of the dielectric constant fluctuation in the medium (hereinafter, τ is appropriately used as <η 2> = τ), and γ (r ) Is called a correlation function. The correlation function γ (r) is expressed by the following equation (6).
[0018]
According to Debye, when the refractive index inhomogeneous structure of the medium has an interface and is divided and dispersed into an A phase and a B phase, the correlation function γ (r), the correlation distance a, and the dielectric constant fluctuation square. The following equations (7) and (8) are established for the relationship of the average τ.
[0019]
[Expression 4]

If it is considered that the non-uniform structure is constituted by a spherical interface having a radius R, the correlation distance a is expressed by the following equation.
[0020]
[Equation 5]

Using the expression (6) for the correlation function γ (r) and calculating the effective scattering irradiation parameter E when natural light is incident on the medium based on the expression (5), the result is as follows.
[0021]
[Formula 6]

From the relationship described above, it is possible to control the scattered light intensity, the angle dependence of the scattered light intensity, and the effective scattering irradiation parameter E by changing the correlation distance a and the dielectric constant fluctuation mean square τ. I understand.
FIG. 1 shows a curve representing a condition for making the effective scattering irradiation parameter E constant by taking the correlation distance a on the horizontal axis and the mean square τ of the dielectric constant fluctuation on the vertical axis, and E = 50 [cm ^-1 ] And E = 100 [cm ^-1 ] Is drawn.
[0022]
Generally, if E is large, the scattering power is large, and if E is small, the scattering power is small, in other words, it becomes close to transparency. E = 0 corresponds to no scattering at all.
Therefore, in general, it can be said that it is preferable to use a light-scattering light guide with a small E for a large-dimension parallel luminous element, and to use a parallel-emission element with a large E for a small-sized surface light source device. .
When the range of the effective scattering irradiation parameter E of the collimating beam used in the present invention is determined in consideration of the above criteria, E = 0.5 to 50 [cm ^-1 ].
On the other hand, the correlation distance a is an amount that is deeply related to the directional characteristics of the scattered light in each scattering phenomenon inside the light scattering light guide used in the parallel luminous element. That is, as inferred from the above formulas (3) to (5), the light scattering inside the light scattering light guide is generally forward scattering, but the strength of the forward scattering is the correlation distance. Varies with a.
[0023]
FIG. 2 is a graph illustrating this for two values of a. In the figure, the horizontal axis represents the scattering angle Φ (the traveling direction of the incident light is Φ = 0 °), and the vertical axis represents the normalized scattered light intensity when natural light is assumed, that is, the above equation (5). Represents a value normalized with respect to Φ = 0 °, Vvh (Φ) / Vvh (0).
As shown in the figure, when a = 0.13 μm, that is, when the calculated particle diameter is 2R = 0.2 μm according to the above equation (9), a graph showing a gradual decrease function with respect to Φ. In the case where a = 1.3 μm and the particle size converted value by the equation (9) is 2R = 2.0 μm, a graph representing a function that rapidly decreases in a region where Φ is small is obtained. can get.
[0024]
Thus, the scattering caused by the non-uniform structure of the refractive index in the light-scattering light guide basically has the character of forward scattering, but the forward scattering property becomes weaker as the value of the correlation distance a becomes smaller. There is a tendency that the range of the scattering angle in each scattering process is widened. This has been confirmed experimentally.
[0025]
The above discussion is valid when focusing on the scattering phenomenon itself due to the refractive index non-uniform structure distributed inside the light-scattering light guide constituting the collimating beam forming element. In order to evaluate the directional characteristics of the light actually emitted from the light extraction surface of the parallel light beam generation element, the phenomenon of total reflection on the light extraction surface and the transmittance at the time of light emission (from the parallel light beam generation element to the outside of the element) (Escape rate) must also be considered.
[0026]
As is well known as a condition of total reflection by basic optical theory, when light enters the light extraction surface from the inside of the light scattering light guide, it depends on the refractive index of the medium inside and outside the light scattering light guide. When the incident angle exceeds the determined critical angle αc (here, the normal direction set up on the light extraction surface is 0 °), emission (escape) to the outside (air layer) does not occur. In PMMA (refractive index: 1.492) which is a representative material used in the present invention, αc = 42 °.
[0027]
As will be described later, since the refractive index of a normal resin material suitably used as the matrix material of the parallel beam forming element in the present invention is in the range of 1.4 to 1.7, the practical range of αc is , 36.0 ° to 45.6 °.
[0028]
As described above, since the scattering inside the light scattering light guide shows forward scattering, the light incident from the light incident surface has a non-uniform structure in the normal case where the light incident surface is located on the side of the light extraction surface. It is considered rare that the first-order scattered light encountered and encountered immediately satisfies the critical angle condition.
[0029]
Therefore, in the light emission from the light extraction surface, light that has undergone multiple scattering processes inside the light scattering light guide or the reflection process by the interface on the back side of the light scattering light guide or the reflecting member satisfies the above critical angle condition. It should be considered that the phenomenon of being emitted to the outside is greatly involved.
[0030]
If so, when focusing on light satisfying the critical angle condition, the forward scattering property, which is an attribute of each scattering phenomenon, is considerably diminished, and the distribution of light traveling direction should be considerably spread. . As a result, the direction characteristic of the light emitted from the collimating light beam forming element composed of the light scattering light guide is greatly dependent on the angle dependency of the transmittance (escape rate) on the light extraction surface of the light satisfying the critical angle condition. It will be influenced.
[0031]
In general, the interface transmittance of light incident on the medium interface with an incident angle that satisfies the critical angle condition is extremely low. For example, in the case of an acrylic resin-air interface, the P polarization component is about 40% and the S polarization component is about 20%. Then, as the angle at which the incident angle is less than the critical angle increases, the light transmission and the like rapidly increase, and becomes substantially constant under the condition of 5 ° to 10 ° or less. In the case of the acrylic resin-air interface, the P polarization component is 90% or more and the S polarization component is 85% or more.
[0032]
From the above, in the case of acrylic resin, light having an incident angle on the light extraction surface of around 35 ° to 40 ° contributes most to light emission from the light extraction surface of the parallel light flux conversion element. It is considered a thing. In consideration of Snell's law regarding refraction, when the light extraction surface is an acrylic resin-air interface, light incident on the light extraction surface at an incident angle of about 35 ° to 40 ° is raised from the air side on the light extraction surface. The light is emitted in a direction that falls within a range of around several degrees from around 65 ° to the normal.
[0033]
Even when a material other than acrylic resin is used for the light-scattering light guide constituting the collimated beam forming element, the practical range of the refractive index of the material is about 1.4 to 1.7. The same argument can be made if a deviation of several degrees is expected.
[0034]
In other words, the light emitted from the light extraction surface of the parallel beam forming element is roughly estimated and becomes light having clear directivity in a direction rising about 20 ° to 30 ° with respect to the light extraction surface.
[0035]
However, it should be noted here that if the value of the correlation distance a becomes too small, the forward scattering property in each scattering process is reduced, and a wide range of scattered light including backscattering is generated only by the primary scattering. In addition, the precondition for giving such directivity is broken. In the present invention, a parallel light beam forming element configured by a light scattering light guide (hereinafter referred to as a “directional light-emitting light scattering light guide”) that does not cause such a phenomenon is used. When this condition is taken into consideration, the lower limit value of the correlation distance a is about 0.06 μm.
[0036]
On the other hand, as can be seen from FIG. 1, the larger the correlation distance a, the more difficult it is to increase the value of the effective scattering irradiation parameter E. In the present invention, taking this condition into consideration, 0.06 μm to 35 μm is selected as the practical range of the correlation distance a of the light scattering light guides constituting the parallel light beam forming element. When different refractive index particles are dispersed in the light scattering light guide, the range of the particle diameter of 0.1 μm to 54 μm corresponds to this from the equation (9).
[0037]
A wedge-shaped directional emitting collimating beam collimating element provided with uniform scattering power under these conditions is used as a light incident surface, and a light source such as a normal fluorescent lamp (generally, light When the light from the supply means is incident, directional light beams are emitted from both the front and back surfaces of the parallel light beam generating element. One of the surfaces is used as a light extraction surface of the parallel light beam forming element. It is preferable that a reflective member is appropriately disposed on the other surface to prevent light dissipation.
[0038]
As described above, the light emitted from the light extraction surface of the parallel beam forming element has directivity in the direction rising from about 20 ° to about 30 ° with respect to the light extraction surface. However, the brightness of the surface light source device is often required from the front or a direction close thereto, including the use of the backlight light source of the liquid crystal display device. In addition, since the cross-sectional area of the parallel light beam emitted from the light extraction surface of the parallel light beam generating element is smaller than the size of the light extraction surface, if a light beam having a relatively large cross-sectional area is required, the cross-sectional area is parallel to that. It is necessary to increase the size of the luminous element.
[0039]
In the present invention, in order to avoid such inconvenience, the parallel luminous flux emitted from the parallel luminous flux element is reflected by the reflecting surface of the front and back double prism reflecting elements arranged to be inclined with respect to the propagation direction of the parallel luminous flux. Thus, the propagation direction of the parallel light flux is changed to a predetermined direction, for example, a direction perpendicular to the extending direction of the entire surface light source device (hereinafter simply referred to as “front direction”), and the cross-sectional area of the light flux is changed. Enlarge.
[0040]
Here, the optical significance that the parallel light beam forming element is formed of a light scattering light guide having a wedge-shaped cross section will be described.
FIG. 3 is a diagram showing a wedge-shaped cross section of a wedge-shaped parallel beam forming element used in the present invention, and the state of repeated reflection in the inside is the optical path of a light beam taken into the parallel beam generating element from the light incident surface. Is represented by a ray B0.
[0041]
Reference numeral 1 represents a parallel beam-forming element composed of a light-scattering light guide having the scattering characteristics described in the “Action” column, and light formed at the side end portion having the larger wedge-shaped cross-sectional area. A fluorescent lamp L (generally a light supply means, which will be represented by a fluorescent lamp hereinafter) is arranged facing the incident surface 2. The propagation direction of the representative light beam B0 representative of the light emitted from the fluorescent lamp L and incident into the parallel light flux forming element 1 forms a small angle with the extending direction of the parallel light flux forming element as shown in the figure. Can be considered.
[0042]
Considering the behavior of the light beam B0, the light beam B0 that has entered the parallel beam forming element 1 from the incident surface 2 undergoes a change of direction due to scattering at a constant rate, and the light extraction surface 3 and the light extraction surface 3 as shown in FIG. While approaching the back surface 4 inclined with respect to the parallel light-reflecting element 1, the parallel light beam generating element 1 approaches the thin end portion 6. Since the reflection on the inner surfaces of the surfaces 4 and 5 is regular reflection, the incident angle and the reflection angle in each reflection are equal (θ1, θ2, θ3,...). Here, when attention is paid to each reflection on the light extraction surface 3, it can be seen that the relationship θ2>θ4> θ6...
[0043]
Further, considering the interface transmittance at the time of each reflection, under the condition of θi> αc (critical angle: 42 ° at the PMMA-air interface), the same discussion as in the case of the directivity of the light scattering light guide When total reflection occurs and θi falls below αc, the transmittance increases rapidly, and when θi is equal to or less than a predetermined value (around 35 ° at the PMMA-air interface), the transmittance is almost constant. In the figure, a state in which the outgoing lights B4 and B6 are generated by the relationship of θ2>αc>θ4> θ6 is depicted.
[0044]
Such an effect is not limited to the representative light beam B0 (non-scattered light), but the primary scattered light and the multiple scattered light should be produced in the same way, although there is a difference in degree. As a whole, it is considered that as the distance from the light incident surface 2 increases, the light emission rate from the light extraction surface 3 increases. If this effect is evaluated by a function f (x) of the distance x from the light incident surface 2, f (x) is an increasing function with respect to x. On the other hand, in the portion close to the light incident surface 2, the effect of being close to the light source L works for both direct light and scattered light. If this proximity effect is evaluated by g (x), g (x) becomes a decreasing function.
[0045]
Accordingly, the proximity effect g (x) is canceled out by f (x), and a tendency to emit light from the light extraction surface 3 after guiding the light farther is generated. In addition, it is considered that the opportunity for the light in the collimated light flux forming element 1 to enter the light extraction surface 3 is increased as a whole with a tendency to increase as the distance from the incident surface 2 increases due to the wedge-shaped effect. It seems that the effect of further improving the luminance level over the entire 3 is also produced.
[0046]
There is no absolute limitation on the angle ψ formed by the two surfaces 3 and 4, but 0.5 ° ≦ ψ ≦ 5 ° is considered as a practical range in consideration of brightness level, uniformity, directivity, and the like. It is done. Further, by making the inclined back surface 4 (in some cases the light extraction surface 3) a curved surface, it is possible to control the increasing transition of the reflection angles θ1, θ2, θ3,. is there.
[0047]
It is clear that the effect described here is similarly realized when the reflector 5 is arranged along the back surface 4. From the viewpoint of not hindering the parallel luminous flux, the reflector 5 is preferably a reflector having specular reflection rather than a diffuse reflection reflector.
[0048]
In addition, selection of the shape and arrangement direction of the reflecting surface of the front and back double prism reflecting elements arranged in combination with the parallel beam emitting part including the parallel beam generating element, and the material for the light scattering light guide constituting the parallel beam generating element -The manufacturing method will be described in the following examples.
[0049]
【Example】
FIG. 4 shows an embodiment in which a surface light source device having a configuration corresponding to the basic arrangement of the present invention is used as a backlight light source of a liquid crystal display device in the form of a cross-sectional view of an essential part. In order to make it easier to understand, actual dimensional data is also shown by way of example.
[0050]
same In the figure In this case, the portion indicated by the symbol F is a parallel light beam emitting portion, which is composed of a fluorescent lamp L, a reflector R provided so as to surround the fluorescent lamp L from the back side, and the parallel light beam converting element 1. The parallel luminous element 1 is composed of a light scattering light guide having a wedge-shaped cross section, and here, a silicone resin material (refractive index = 1.4345) in a polymethyl methacrylate (PMMA) is set to 0.00. What is uniformly dispersed at a rate of 1 wt% is used.
[0051]
The length size of the back surface 4 is 38 mm as shown in the figure, and the thickness of the end portion on the incident surface 2 side is 8.0 mm. The thickness of the terminal part 6 shall be about 0.2 mm. The width can be an appropriate value (for example, 200 mm).
[0052]
The fluorescent lamp L is arranged at a distance of 1 mm from the incident surface 2 of the parallel luminous element 1 and has a diameter of 8 mm and a length substantially equal to the width of the parallel luminous element 1. The reflector R is appropriately disposed in order to increase the amount of light incident from the incident surface 2 as much as possible. For example, a silver foil subjected to surface treatment for preventing oxidation is used.
A specular reflective body is also provided on the back surface 4 of the parallel luminous element 1. The reflector 5 may be a reflecting member (for example, a silver foil sheet) that is separate from the parallel luminous element 1, and a reflecting film (for example, an Ag deposited film or an Al deposited film) formed on the back surface 4. Etc.). When using a reflective member such as a silver foil sheet that may deteriorate the reflection performance due to ultraviolet rays, it is preferable to use an ultraviolet-absorbing adhesive as means for fixing to the back surface 4. As will be described later, it is practical to manufacture the parallel luminous flux element 1 by an injection molding technique of a plastic material, and an in-mold method can be applied when the reflecting member is fixed.
[0053]
The radiated light from the fluorescent lamp L and the reflected light from the reflector R enter the parallel luminous element 1 from the light incident surface 2 of the parallel luminous element 1 constituted by the light scattering light guide, and light scattering action. Then, the light is guided toward the end portion 6. As described in detail in the section of “Action”, a collimated light beam (hereinafter, simply referred to as “parallel light beam”) is emitted from the light extraction surface 3 of the parallel light beam converting element 1 through this process. Reference numeral G1 is a light beam representing this parallel light beam. The emission angle β (measured from the vertical line standing on the light extraction surface 3) of the representative light beam G1 is about 65 ° as described in the section “Action”.
[0054]
The symbol PR is arranged in a position inclined at a predetermined angle with respect to the propagation direction of the parallel light beam (that is, the propagation direction of the representative light beam G1) at a position where almost all of the parallel light beam emitted from the parallel light beam emitting portion is received. It is a double prism reflecting element. This front / back double prism reflecting element PR has the function of expanding the cross-sectional area of parallel light beams and the function of changing the direction of propagation described below, and almost all of the parallel light beams from the parallel light beam emitting portion F are directed upward in the figure. And reflected.
[0055]
A light diffusing plate DF having an appropriate scattering ability is disposed in the optical path of the reflected light beam from the front and back double prism reflecting elements PR, and a liquid crystal panel LP is disposed further above. The liquid crystal panel portion LP has a basic configuration in which a liquid crystal cell portion 22 is sandwiched between two polarizers 21 and 23 whose polarization transmission axes are orthogonal to each other.
[0056]
With such an arrangement, the parallel light beam supplied from the parallel light beam emitting portion F is converted into an enlarged reflected light beam directed upward by the front and back double prism reflecting element PR and is incident on the light diffusion plate DF. This light diffusion plate DF appropriately adjusts the directivity of the reflected light beam of the front and back double prism reflecting element PR, and at a fine level that may occur in the reflection process of the front and back double prism reflecting element PR. It is used appropriately to remove the unevenness of the thickness, and may be omitted or replaced with a transparent plate depending on the case.
[0057]
The parallel light flux that has passed through the light diffusing plate DF and has been moderately relaxed and adjusted in directivity is incident on the liquid crystal panel portion LP and serves as backlight light. Due to the directivity and uniformity of the parallel light flux, a liquid crystal display screen with excellent display quality viewed from a desired observation direction (here, the front direction) is realized. In addition, by adjusting the intensity of the scattering power applied to the light diffusion plate DF, the width in the direction in which a bright display screen is observed can be appropriately adjusted.
[0058]
Next, the structure and function of the front and back double prism reflecting element PR will be described. FIG. 5 is an enlarged sectional view of the portion indicated by reference numeral 30 of the front and back double prism reflecting element PR used in the above embodiment, and the state of reflection of the parallel light beam FL1 represented by the light beam G1 is also shown. Has been. As shown in the drawing, repeated inclined surfaces H, H ′, J, and J ′ constituting prismatic undulations are formed on the front and back surfaces of the front and back double prism reflecting elements PR. Further, in order to prevent the transmission and dissipation of light from the back surface, a vapor deposition film VL such as Al or Ag is appropriately formed. Although any transparent optical material can be used as the material constituting the front and back double prism reflecting element PR, the same material as that used for the matrix of the parallel beam converting element 1, for example, PMMA (polymethyl methacrylate) is used. This is economically advantageous.
[0059]
It is desirable that the following condition is satisfied between the propagation direction of the representative ray G1 and the inclination angles of H, H ′ and J, J ′ of the inclined surfaces of the front and back surfaces. In other words, so as to satisfy this condition, the material (refractive index) of the parallel luminous element 1 and the front and back double prism reflecting element PR, the posture relationship between the parallel luminous element 1 and the front and back double prism reflecting element PR, and the inclined surface It is preferable to select the inclination angles of H, H ′ and J, J ′.
[0060]
(1) The propagation direction of each inclined surface H ′ and the light beam G1 is parallel.
(2) Each inclined surface J extends to a position that receives almost the entire amount of the refractive light beam incident from H.
[0061]
(3) Each inclined surface H ′ extends to a position where almost all of the regular reflected light beam is received on the surface J (interface with the vapor deposition film) of the refracted light beam incident from each inclined surface H.
[0062]
(4) The specularly reflected light beam FL2 on each inclined surface H and the light beams G2 and G3 representing the light beam FL3 emitted from each inclined surface H ′ are substantially parallel and substantially coincide with the desired emission direction. Being.
[0063]
Although it is difficult to always satisfy such conditions strictly, it is easy to obtain approximate satisfaction at least in a range where the desired emission direction does not deviate significantly from the front direction. For example, the emission direction can be adjusted with a considerable width only by adjusting the posture of the front and back double prism reflecting element PR with respect to the parallel luminous element 1 and selecting the refractive index of the front and back double prism reflecting element PR.
[0064]
Preferably, the incident light beam FL1 represented by the light beam G1 is reflected by the regular reflection light beam FL2 (represented by G2) on each surface H by the reflection action on the front and back surfaces of the front and back double prism reflecting elements PR designed to satisfy the above conditions. Are divided into refracted and emitted light beams FL3 (represented by G3) from each surface H ', and their cross-sectional areas are enlarged (FL1 → FL2 + FL3). In order to adjust the ratio of reflection / transmission on each surface H, a semi-transparent film may be formed on each surface H. Further, when the difference in the ratio of reflection / transmission on each surface H of the polarization component (P polarization component and S polarization component) appears as uneven brightness of the liquid crystal display surface, the inclined surfaces H, H ′, J are repeatedly formed. , J ′ is effective to reduce the repetition pitch and to increase the scattering power applied to the light diffusion plate DF.
[0065]
The above discussion regarding the above embodiment mainly focuses on the longitudinal direction (the direction along the paper surface, hereinafter simply referred to as “longitudinal direction”) when viewed from the light incident surface 2 of the parallel light beam splitter 1. In the transverse direction as viewed from the light incident surface 2 of the parallel light beam forming element 1 (direction perpendicular to the paper surface, hereinafter simply referred to as “transverse direction”), the propagation direction of the light flux is adjusted, and the lateral direction side of the surface light source device. When it is desired to prevent the light from being dissipated, a light exit direction correcting means can be provided to face the light extraction surface 3 of the parallel beam converting element 1.
[0066]
This light emission direction correcting means may be provided in the form of a single unit or a separate unit with the parallel beam forming element 1. FIG. 6 is a perspective view showing the former example, and FIG. 7 is a perspective view showing the latter example.
In each figure, symbols CR and CR ′ are prism-like undulations formed in the longitudinal direction on the light extraction surface 3 side of the parallel beam-forming element 1, and in FIG. The surface of the surface 3 also serves as this. Further, FIG. 7 shows a form in which a separate light emitting direction correcting element 7 having a undulating row CR ′ is arranged. Reference numerals 2, 3, 4, and 5 represent the light incident surface, the light extraction surface, the back surface, and the reflector (silver foil) as in FIG.
[0067]
6 and 7, the light that has entered the collimated light beam splitter 1 from the light incident surface 2 is collimated in the longitudinal direction as described in the section of “action”, and is about 65 degrees. The light is emitted from the light extraction surface 3 with an emission angle (indicated by an arrow group 3f). Here, when considering the optical path in the transverse direction at the time of emission, it is considered that there is a considerable spread in the propagation direction due to the scattering power given to the parallel light beam converting element 1 (in the arrow group 3f ′). display).
[0068]
The prismatic undulation rows in each figure formed oriented in the longitudinal direction suppress the spread of the light flux propagation direction in the transverse direction and improve the parallelism of the light in three dimensions. This is effective in preventing light from escaping in the transverse direction through the action.
[0069]
8 shows the transverse direction in each figure. (Horizontal width direction when viewed from the light incident side) FIG. 2 is a diagram for explaining the light emission direction correcting function of FIG. 2 and shows a cross section obtained by cutting the parallel beam forming element 1 or the light emission direction correcting element 7 along the direction indicated by reference numeral 8. In the figure, the light beams indicated by reference numerals B1 to B3 having variations in directions represent the light immediately before being emitted from the parallel light flux conversion element 1 or the light emission direction correcting element 7 to the outside.
[0070]
First, as shown in the drawing, the light beams B1 and B2 having a traveling direction close to the left-right direction are once emitted from one of the prism surfaces Ca and Cb constituting the undulating surface CR or CR 'to the air layer AR. The corresponding portion is specularly reflected by the other prism surfaces Cb and Ca, and the transverse component is substantially removed and emitted as light beams B1 'and B2'.
[0071]
On the other hand, as shown in the drawing, the light beam B3 having a poor transverse direction component is reflected by one prism surface Ca, then passes through the other prism surface Cb, and is emitted to the air layer AR. The portion is specularly reflected by the adjacent prism surface Ca, and can be considered to be emitted as a light beam B 3 ′ that maintains a poor transverse direction component. Due to such a refraction action, the proportion of light propagating in the direction as indicated by the arrow group 3f in FIGS. 6 and 7 is increased, and as indicated by the arrow group 3f ′, laterally in the transverse direction. Since the ratio of the deviating light is reduced, the parallelism of the light beam supplied from the parallel light beam emitting portion F is eventually improved three-dimensionally.
[0072]
In addition, when a normal material (for example, PMMA) is used for the collimating beam forming element 1 or the light emitting direction correcting element 7, a prism apex angle (prism surface Ca, The angle of Cb is about 80 ° to 110 °.
[0073]
In the above description, a rod-like fluorescent lamp is used as the light source. However, the fact that the present invention does not place any particular restrictions on the type, shape, etc. of the light source is based on the principle of the present invention and the explanations so far. It will be clear in the light. For example, the light of a light diffusing surface light source may be incident from the light incident surface of the parallel light beam forming element, or a plurality of beams from the light emitting diode array may be used as incident light and converted into a uniform parallel light beam. Is possible.
[0074]
Furthermore, the arrangement of FIG. 4 may be arranged in parallel so as to face each other, and a two-lamp type surface light source device that generates an expanded light beam of almost double size may be configured.
[0075]
Finally, the material and manufacturing method of the light-scattering light guide constituting the collimated beam forming element used in the present invention will be described.
Various bases based on polymer materials can be used as the base of the light-scattering light guide constituting the collimating beam used in the present invention. Representative examples of these polymers are shown in Tables 1 and 2 below.
[0076]
[Table 1]

[0077]
[Table 2]

Such a parallel luminous element based on a polymer material can be manufactured by the following manufacturing method.
First, one of them is a method using a molding process including a step of kneading two or more kinds of polymers.
That is, two or more kinds of different polymer materials having different refractive indexes (may be in any shape. Industrially, for example, pellets are considered) are mixed and heated, kneaded (kneading step), and kneaded. The parallel light beam forming element having a shape corresponding to the mold shape can be obtained by injecting the liquid material into the mold of the injection molding machine at a high pressure and cooling and solidifying it to take out the formed parallel light beam generating element from the mold. I can do it.
[0078]
Since the two or more kinds of kneaded polymers having different refractive indexes are solidified without being mixed completely, nonuniformity (fluctuation) is generated and fixed in their local concentration, and uniform scattering ability is given.
The kneaded material can be poured into a cylinder of an extrusion molding machine and extruded in the usual manner to obtain a desired molded product.
[0079]
The combination and mixing ratio of these polymer blends can be selected from a very wide range, including the difference in refractive index and the strength and properties of the refractive index non-uniform structure generated in the molding process (scattering irradiation parameter E, correlation distance a, dielectric). It may be determined in consideration of the rate fluctuation mean square τ). The typical polymer materials that can be used are shown in Tables 1 and 2 above.
[0080]
Another method for producing the material constituting the parallel beam forming element is to uniformly mix and disperse particulate materials having different refractive indexes (refractive index difference of 0.001 or more) in the polymer material.
One of the methods that can be used for uniform mixing of the particulate material is a method called a suspension polymerization method. That is, when the particulate material is mixed in the monomer and the polymerization reaction is performed in a state of being suspended in hot water, a polymer material in which the particulate material is uniformly mixed can be obtained. If molding is performed using this as a raw material, a parallel luminous element having a desired shape is manufactured.
[0081]
Suspension polymerization is performed for various particulate materials and monomer combinations (combination of particle concentration, particle size, refractive index, etc.), multiple types of materials are prepared, and these are selectively blended to form. If this is done, it is possible to manufacture parallel luminous flux elements having various characteristics. Moreover, if the polymer which does not contain a particulate material is blended, particle concentration can be easily controlled.
[0082]
Another method available for uniform mixing of particulate material is to knead the polymer material and particulate material. Also in this case, kneading and forming (pelletizing) are performed by combining various particulate materials and polymers (combination of particle concentration, particle size, refractive index, etc.), and these are selectively blended to produce parallel light fluxes. By forming and manufacturing the element, it is possible to obtain a parallel luminous element having various characteristics.
[0083]
It is also possible to combine the polymer blend method and the particulate material mixing method. For example, it can be considered that a particulate material is mixed during blending and kneading of polymers having different refractive indexes.
[0084]
Hereinafter, some examples of the production method will be given.
<Production Example 1>
Add 0.3 wt% of silicone resin powder (Toshiba Silicone, Tospearl 108) with a particle size of 0.8μm to methacrylic resin pellets (Asahi Kasei, Delvette 80N), mix and disperse with a mixer, Extruded into a strand and pelletized with a pelletizer to prepare pellets in which silicone resin powder was uniformly dispersed.
[0085]
The pellets were molded using an injection molding machine under conditions of a cylinder temperature of 230 ° C. to 260 ° C. and a mold temperature of 50 ° C., and the length was 38 mm, the width was 85 mm, and the thickness was 3.8 mm to 0.00 mm in the long side direction. A wedge-shaped parallel luminous element that gradually changed to 2 mm was obtained.
[0086]
The correlation distance of the manufactured parallel luminous element is a = 0.53 μm, and the estimated calculation value of the effective scattering irradiation parameter according to the equation (11) is E = 12.6 [cm. ^-1 ]Met.
[0087]
<Production Example 2>
To MMA, 0.3 wt% of a silicone-based resin powder having a particle size of 0.8 μm (manufactured by Toshiba Silicone, Tospearl 108) was added, and spherical particles in which the powder was uniformly dispersed were obtained by a known suspension polymerization method. This was pelletized with a pelletizer in the same manner as in Production Example 1 to prepare pellets in which silicone resin powder was uniformly dispersed.
[0088]
Thereafter, the same type of wedge-shaped parallel luminous flux element was obtained under the same conditions as in Production Example 1. This parallel luminous element was indistinguishable from the parallel luminous element produced in Production Example 1 in appearance. The correlation distance is a = 0.53 μm, and the estimated value of the effective scattering irradiation parameter according to the equation (11) is E = 12.6 [cm. ^-1 ]Met.
[0089]
<Production Example 3>
0.5 wt% of polystyrene (PSt) was added to polymethyl methacrylate (PMMA) and mixed for 10 minutes using a V-type tumbler and then for 5 minutes using a Henschel mixer. Using a 30-mm diameter twin screw extruder (Nakatani Machinery Co., Ltd.), the pellets were melted and mixed under the conditions of a cylinder temperature of 220 ° C to 250 ° C, a screw speed of 75 rpm, and a discharge rate of 6 kg / hr. Created.
[0090]
This pellet is molded using an injection molding machine under the conditions of a cylinder temperature of 220 ° C. to 250 ° C., a mold temperature of 65 ° C., an injection speed of medium speed, an injection pressure of short shot pressure plus 10 kg / cm 2, and a length of 38 mm. A wedge-shaped parallel luminous element having a thickness of 85 mm and a thickness gradually changing from 3.8 mm to 0.2 mm in the long side direction was obtained.
[0091]
<Production Example 4>
Disperse uniformly by adding 0.05 wt%, 0.08 wt%, 0.10 wt%, and 0.15 wt% of a silicone resin powder (made by Toshiba Silicone, Tospearl 120) to MMA (methyl methacrylate). 4 types of samples and MMA samples without added particles were prepared. In each of the 5 types of samples, 0.5 wt% of benzoyl peroxide (BPO) as a radical polymerization initiator and n-lauryl mercaptan (n -LM) was added at 0.2 wt%, and cast polymerization was performed at 70 ° C. for 24 hours, and the wedge-shaped parallel light flux was gradually changed from 3.8 mm to 0.2 mm in the long side direction at a length of 38 mm and a width of 85 mm. Each of the control elements was produced.
[0092]
<Production Example 5>
0.025 wt% of silicone oil is added to MMA (methyl methacrylate) and dispersed uniformly, 0.5 wt% of benzoyl peroxide (BPO) as a radical polymerization initiator, and n-butyl mercaptan (n-BM) as a chain transfer agent 0.2 wt% of each was added, and after solification was performed at 70 ° C. for 30 minutes, cast polymerization was further performed at 65 ° C. for 24 hours, and the length was 38 mm, the width was 85 mm, and the thickness was 3.8 mm in the long side direction. A wedge-shaped parallel luminous element that gradually changed from 0.2 mm to 0.2 mm was produced.
[0093]
<Production Example 6>
0.08 wt% of a silicone resin powder (Toshiba Silicone, Tospearl 120) having a particle size of 2 μm was added to PMMA (polymethyl methacrylate), and mixed for 10 minutes using a V-type tumbler, and then mixed for 5 minutes using a Henschel mixer. . This was melt-mixed (cylinder temperature 220 ° C. to 250 ° C.) and extruded using a biaxial extruder to produce pellets.
[0094]
This pellet was injection molded using an injection molding machine at a cylinder temperature of 220 ° C. to 250 ° C., and was wedge-shaped with a length of 38 mm, a width of 85 mm, and a thickness gradually changing from 3.8 mm to 0.2 mm in the long side direction. The parallel luminous element was produced.
[0095]
【The invention's effect】
According to the present invention, collimation and enlargement of a light beam having disordered directionality, which has been difficult with a method using a conventional lens or curved mirror, can be achieved at the same time. In addition, the parallel light beam obtained at that time has an advantage that the flatness of the intensity profile of the flux cross section is high, which cannot be expected from the conventional method.
[0096]
Furthermore, in the present invention, a technical means for improving the parallelism in the transverse direction when viewed from the light incident surface side is provided, so that the non-parallel light beam is converted into an expanded light beam having high parallelism in a three-dimensional sense. It became possible to do.
[0097]
Therefore, it is possible to configure a surface light source device that generates a parallel light beam having a large cross-sectional area using a relatively small parallel light beam generating element.
[0098]
Such advantages are particularly advantageous when the liquid crystal display device is applied to a backlight light source.
[Brief description of the drawings]
FIG. 1 is a curve showing a condition for making an effective scattering irradiation parameter E constant by taking a correlation distance a on a horizontal axis and a mean square τ of dielectric constant fluctuation on a vertical axis, and E = 50 [cm ^-1 ] And E = 100 [cm ^-1 ] Is drawn.
FIG. 2 is a graph for explaining that the intensity of forward scattering of the light-scattering light guide constituting the parallel light beam changing element varies depending on the correlation distance a.
FIG. 3 is a diagram showing a wedge-shaped cross section of a wedge-shaped parallel beam forming element used in the present invention, in which the state of repeated reflection inside is the optical path of a light beam taken into the parallel beam generating element from the light incident surface Is represented by a ray B0.
FIG. 4 shows an embodiment in which a surface light source device having a configuration corresponding to the basic arrangement of the present invention is used as a backlight light source of a liquid crystal display device in the form of a cross-sectional view of a main part.
FIG. 5 is a cross-sectional view showing a part of the front and back double prism reflecting elements used in the embodiment in an enlarged manner, and shows a state of reflection of a parallel light beam FL1 represented by a light beam G1.
FIG. 6 is a perspective view for explaining a light emission direction correcting means provided integrally with a parallel luminous element.
FIG. 7 is a perspective view for explaining light exit direction correcting means (light exit direction correcting element) provided separately from the parallel luminous flux generating element.
8 is a diagram for explaining a light emission direction correcting function of the light emission direction correcting means shown in FIGS. 6 and 7. FIG.
[Explanation of symbols]
1 Parallel luminous element
2 Light incident surface
3 Light extraction surface
3f, 3f 'outgoing light
4 Back side
5 Reflector (silver foil) provided on the back side of the parallel luminous element
6 End part (end face) of collimating beam
7 Light exit direction correcting element
21,23 Polarizer
22 Liquid crystal cell part
AR air layer
CR, CR 'Prism-like relief
DF light diffusion plate
F Parallel beam exit
L fluorescent lamp
LP LCD panel
PR Front and back double prism reflector
R Reflector (silver foil) provided on the back side of the fluorescent lamp
Vapor deposited film such as VL Al or Ag

Claims (3)

While have a planar spread, on one surface, has a first reflecting surface of the repeated inclined surface shape that reflects part of incident light from the outside, on the other side, at least one internal incident light A front and back double prism reflecting element having a second reflecting surface having a repetitive inclined surface shape that reflects the portion ;
The light propagating in the direction representative of the propagation direction of the collimated light beam is directed to the first reflecting surface toward the side of the front and back double prism reflecting elements . and a Yukimitsu Taira bundle emitting portion incident angle is disposed in a posture to be output so as not to 0 ° when entering the reflecting surface,
The parallel light beam emitting portion has a value of an effective scattering irradiation parameter E [cm ⁻¹ ] in a range of 0.5 ≦ E ≦ 50, and a correlation function γ (r) of a refractive index nonuniform structure that generates light scattering ability. The value of the correlation distance a [μm] when approximated by γ (r) = exp [−r / a] (where r is the distance between two points in the light scattering light guide) is 0.06 ≦ a ≦ 35. A parallel luminous element comprising a light-scattering light guide including a volume region having a wedge-shaped cross section provided with uniform scattering power in a range, and a cross-sectional area of the wedge-shaped cross section of the parallel luminous element is relatively Including a light incident means arranged on the larger end face side,
The front and rear dual prism reflecting elements, said first collimated light beam incident on the reflecting surface of, reflected by the reflecting surface and the second reflecting surface of the first, previous SL first reflecting surface A parallel light flux expanding type surface light source device that emits a collimated light beam having a cross-sectional area that is larger than that when incident from the outside toward the outside from the first reflecting surface . 2. The parallel light flux expanding type surface light source device according to claim 1 , wherein a light diffusing plate is disposed in an optical path of a reflected light beam from the front and back double prism reflecting elements .   Light exit direction correcting means for correcting the light exit direction characteristic in the left-right width direction when viewed from the light incident surface side of the parallel beam generating element is provided facing the light exit surface of the parallel beam generating element of the parallel beam emitting unit. The surface light source device according to claim 1, wherein the surface light source device is provided.

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