JP2004111352A - Surface light source device and light guide used therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface light source device of high quality which has a uniformity ration of illuminance without unevenness of luminance even when a relatively small number of punctiform primary light sources are used. <P>SOLUTION: In the surface light source device, a light guide of rectangular shape has an incident light end surface 41 for receiving incident light from a primary nearly punctiform light source, and a light emitting surface 43 for emitting the incident light. A plurality of lens arrays, which extends from the light emitting surface 43 to at least a part of the incident light end surface 41 in an opposite direction, has an asymmetrical cross-sectional face, and has at least a curved part, are formed nearly in parallel on the surface light source device. <P>COPYRIGHT: (C)2004,JPO

Description

【数２】

導光体４に形成する指向性光出射機構の具体例としては、一次光源２を略中心とする弧状にレンズ列を形成したもの、一次光源２を略中心とする放射状にレンズ列を形成したもの、導光体４を構成する帯状の異屈折率層を一次光源２を略中心とする放射状に形成したもの、導光体４を構成する帯状の異屈折率層を一次光源２を略中心とする弧状に形成したものでなどが挙げられる。中でも、一次光源２を略中心とする弧状にレンズ列を形成したものが、導光体４中を一次光源２を略中心とする放射状に伝搬する光の方向が大幅に変化することなく光出射面４３から出射されるため、光偏向素子６によって殆どの光を所望の方向に偏向することができ、輝度が高く、輝度の均一性に優れた面光源装置が提供できることから好ましい。これは、ＸＹ面内では導光体４中を伝搬する光の方向が一次光源２を略中心とする放射状であり大幅に変化することがなく、かくして光出射面４３から出射される殆どの光を光偏向素子６によって所望の方向に偏向することができ、輝度が高く、輝度の均一性に優れた面光源装置が提供できるからである。
【００２１】
本発明においては、一次光源２としてＬＥＤ等の略点状光源を使用するため、導光体４に入射した光は、光出射面４３と略同一の平面内において一次光源２を略中心とした放射状に導光体４中を伝搬する。このような放射状に伝搬する光に対して、弧状に形成したレンズ列（弧状レンズ列）を一次光源２を取り囲むように略弧状に並列して配置することにより、導光体４中を放射状に伝搬する光の殆どが弧状レンズ列に対して略垂直方向に入射することになるため、その伝搬方向に関わらず効率よく所望の方向に出射させることができ、伝搬方向を維持しやすくなるとともに、導光体４の光出射面４３の全領域で出射光を効率良く特定の方向に向けることができ、輝度の均一性を向上させることができる。弧状レンズ列は、導光体４中を伝搬する光の分布に応じてその弧状の程度を選定し、導光体４中を放射状に伝搬する光の殆どが弧状レンズ列に対して垂直方向に入射するようにすることが好ましい。このような弧状レンズ列としては、断面形状が三角形状、弧状、半円状、多角形状等の形状のものを形成することができる。
【００２２】
指向性光出射機構としてこのような弧状レンズ列を形成する場合、形成する弧状レンズ列の径方向の分布は、連続して形成することもできるし、隣接する弧状レンズ列の間に平坦部を介して離散的にすることもできる。弧状レンズ列を連続して形成した場合、弧状レンズ列から出射した後に、隣接する弧状レンズ列に入射する光が存在する場合があり、このような光が多量に存在する場合には導光体４から出射する出射光の出射光分布の乱れが大きくなり、光偏向素子６によって所望の方向に偏向されない光が多くなることにより、輝度の低下を招く場合がある。このような場合には、弧状レンズ列を離散的に形成することにより、隣接する弧状レンズ列に入射する光を低減することができ、導光体４から出射する出射光からの出射光分布の乱れによる輝度の低下を抑止することができる。
【００２３】
一次光源としてのＬＥＤ２を本実施形態のように導光体４の１つのコーナー部に配置した場合には、ＬＥＤ２の光の指向性の方向と導光体４の長辺とのなす角度を図５に示すように３７〜４５度の範囲とすることが好ましく、さらに好ましくは３９〜４２度の範囲である。これは、ＬＥＤ２の光の指向性の方向と導光体４の長辺とのなす角が３７度未満であると、導光体４の短辺とのなす角度が大きくなり、ＬＥＤ２の光の指向性の方向と短辺との間の領域の輝度むらを防ぐことが困難となる傾向にあるためであり、この角度が４５度を超えるとＬＥＤ２の光の指向性の方向と短辺との間の領域が長辺との間の領域に比べ増大するため、ＬＥＤ２の光の指向性の方向と短辺との間の領域の輝度減少を防ぐことが困難となる傾向にあるためである。
【００２４】
このようにＬＥＤ２が導光体４のコーナー部に配置された場合には、図６、７に示したように導光体４の光出射面４３にＬＥＤ２を取り囲むようにして多数のレンズ列を略弧状に並列して形成することが好ましい。なお、本発明においては、図７に示したように導光体４として光出射面４３が略台形形状をなし、その底辺がなす１つのコーナー部にＬＥＤ２を配置することもできる。
【００２５】
本発明においては、一次光源としてのＬＥＤ２の配置は、本実施形態のようにコーナー部に限らず、図８、９に示したような配置をすることもできる。図８は、ＬＥＤ２が導光体４の裏面に設けられた凹部または貫通孔内に導光体４との間に空気層または透明物質を介して設置され、導光体４の光出射面４３にＬＥＤ３を取り囲むようにして多数のレンズ列を略円弧状に並列して形成したものである。図９は、導光体４の１つの端縁に複数個のＬＥＤ２を配置し、導光体４の光入射端面４１のＬＥＤ２と対向する部分にレンズ列４２が形成されている。この場合には、光入射端面４１の中央付近に位置するＬＥＤと対向する位置には左右対称の断面形状を有するレンズ列４２２を形成し、光入射端面４１の両端付近に位置するＬＥＤと対向する位置には左右非対称の断面形状を有するレンズ列４２１を形成することにより、導光体４の光出射面全体で輝度の均斉度を向上させることができる。
【００２６】
光偏向素子６は、導光体４の光出射面４３上に配置されている。光偏向素子６の２つの主面は、それぞれ全体としてＸＹ面と平行に位置する。２つの主面のうち一方（導光体の光出射面４３側に位置する主面）は入光面６１とされており、他方が出光面６２とされている。光偏向素子６は、導光体４からの出射光を目的の方向に偏向（変角）させる機能を果たすものであり、少なくとも一方の面に２つの面を有する多くのプリズム列が平行に配列して形成されたレンズ面を有するレンズシート等を使用することができる。
【００２７】
本発明においては、一次光源２としてＬＥＤ等の略点状光源を使用しているため、導光体４に入射した光は、光出射面４３と同一の平面内において一次光源２を略中心とした放射状に導光体４中を伝搬し、光出射面４３から出射する出射光も同様に一次光源２を中心とした放射状に出射する。このような放射状に出射する出射光を、その出射方向に関わらず効率よく所望の方向に偏向させるためには、光偏向素子６に形成するプリズム列を一次光源２を取り囲むように略弧状に並列して配置する。このように、プリズム列を一次光源２を取り囲むように略弧状に並列して配置することにより、光出射面４３から放射状に出射する光の殆どが光偏向素子６のプリズム列に対して垂直方向に入射するため、導光体４の光出射面４３の全領域で出射光を効率良く特定の方向に向けることができ、輝度の均一性を向上させることができる。
【００２８】
光偏向素子６に形成する略弧状のプリズム列は、導光体４中を伝搬する光の分布に応じてその弧状の程度を選定し、光出射面４３から放射状に出射する光の殆どが光偏向素子６のプリズム列に対して垂直方向に入射するようにすることが好ましい。具体的には、ＬＥＤ等の点状光源を略中心とした同心円状に円弧の半径が少しずつ大きくなるように並列して配置されたものが挙げられ、プリズム列の半径の範囲は、面光源システムにおける点状光源の位置と、液晶表示エリアに相当する面光源の有効エリアとの位置関係や大きさによって決定される。
【００２９】
また、光偏向素子６に形成されるプリズム列のパターンは、一次光源２の配置方法に応じて、光出射面４３から放射状に出射する光の殆どが光偏向素子６のプリズム列に対して略垂直方向に入射するようなパターンとなるように、適宜設定することができる。さらに、光偏向素子６に形成するプリズム列は、導光体４の光出射面４３に対面して光偏向素子６の入光面６１に形成してもよいし、出光面６２に形成してもよし、入光面６１と出光面６２の両面に形成してもよい。導光体４からの指向性の高い出射光を効率よく所望の方向に偏向させ、高い輝度を得るためには、光偏向素子６の入光面６１にプリズム列を形成することが好ましい。
【００３０】
入光面６１にプリズム列を形成した光偏向素子６を導光体４の光出射面４３に配置した場合には、光出射面４３から出射した出射光は、プリズム列の一次光源２に近い方の面から光偏向素子６に入射し、一次光源２に遠い方の面で内面反射し所望の方向に偏向された後、光偏向素子６の出光面６２から出射する。このため、導光体４の光出射面４３から出射した出射光の指向性をほぼ維持した状態でその出射方向を所望の方向に変えることができ、光の利用効率が高くなるとともに、輝度の高い面光源システムとすることができる。
【００３１】
導光体４の光出射面４３から出射する出射光は、出射光分布のピ−ク光が光出射面４３に対して１０〜５０度傾いた方向であるため、プリズム列の一次光源２から遠い方の面と光偏向素子６の基準平面のなす角度は４０〜８０度であることが好ましく、より好ましくは５０〜６５度、さらに好ましくは５５〜６５度である。これは、一次光源２から遠い方の面と光偏向素子６の基準平面のなす角度をこの範囲とすることにより、このような指向性を持つ導光体４からの出射光を、光偏向素子６の出光面６２の法線方向の近傍に偏向して出射することができるためである。ここで、光偏向素子６の基準平面とは、光偏向素子６のプリズム列が形成された面が平滑であると仮定した時の平面とする。
【００３２】
一方、導光体４中を伝搬する光の一部は、導光体４の末端まで到達し、その端面で反射して戻ってくる光が存在する。このような光は、導光体４の光入射面に向かって導光体４中を伝搬し、導光体４に形成された指向性光出射機構により光出射面４３から出射される。このような出射光は、光偏向素子６の一次光源２から遠い側のプリズム面から入射し、一次光源２に近い側のプリズム面で内面反射し所望の方向に偏向た後され、光偏向素子６の出射光面６２から出射する。このような出射光も、出射光分布のピ−ク光が光出射面４３に対して１０〜５０度傾いた方向であるため、このような出射光が比較的多い場合には、プリズム列の一次光源２に近い方のプリズム面と光偏向素子６の基準平面のなす角度も、一次光源２から遠い方のプリズム面と同様に４０〜８０度であることが好ましく、より好ましくは５０〜６５度、さらに好ましくは５５〜６５度である。
【００３３】
光偏向素子６の基準平面に対する２つのプリズム面のなす角度は同一としてもよく、異ならせることもできる。両角度を異ならせる場合には、その差が１０度以下であることが好ましく、より好ましくは５度以下、さらに好ましくは２度以下である。
【００３４】
本発明において、携帯電話や携帯情報端末等のような携帯用電子機器の面光源システムのように、消費電力の低減化と高輝度化の要求が非常に高い用途では、光偏向素子６に形成するプリズム列の断面形状を、プリズム面を凸状の曲面あるいは多角面形状とすることにより、プリズム面で内面反射する際に所望方向へ集中するように偏向させることができ、より指向性の高い集中光として出射されるため、消費電力あたりの輝度を高めることができ、低消費電力化および高輝度化をより高めることができる。
【００３５】
本発明の導光体４及び光偏向素子６は、光透過率の高い合成樹脂から構成することができる。このような合成樹脂としては、メタクリル樹脂、アクリル樹脂、ポリカーボネート系樹脂、ポリエステル系樹脂、塩化ビニル系樹脂、環状ポリオレフィン樹脂が例示できる。特に、メタクリル樹脂が、光透過率の高さ、耐熱性、力学的特性、成形加工性に優れており、最適である。このようなメタクリル樹脂としては、メタクリル酸メチルを主成分とする樹脂であり、メタクリル酸メチルが８０重量％以上であるものが好ましい。導光体４及び光偏光素子６の粗面の表面構造やプリズム列等の表面構造を形成するに際しては、透明合成樹脂板を所望の表面構造を有する型部材を用いて熱プレスすることで形成してもよいし、スクリーン印刷、押出成形や射出成形等によって成形と同時に形状付与してもよい。また、熱あるいは光硬化性樹脂等を用いて構造面を形成することもできる。更に、ポリエステル系樹脂、アクリル系樹脂、ポリカーボネート系樹脂、塩化ビニル系樹脂、ポリメタクリルイミド系樹脂等からなる透明フィルムあるいはシート等の透明基材上に、活性エネルギー線硬化型樹脂からなる粗面構造またレンズ列配列構造を表面に形成してもよいし、このようなシートを接着、融着等の方法によって別個の透明基材上に接合一体化させてもよい。活性エネルギー線硬化型樹脂としては、多官能（メタ）アクリル化合物、ビニル化合物、（メタ）アクリル酸エステル類、アリル化合物、（メタ）アクリル酸の金属塩等を使用することができる。
【００３６】
光反射素子８としては、例えば表面に金属蒸着反射層を有するプラスチックシートを用いることができる。また、導光体４の側端面（光入射端面４１を除く）にも反射部材を付することが好ましい。
【００３７】
一次光源２としては、消費電力等の点からＬＥＤ光源が好ましいが、ハロゲンランプ等のような他の略点状の光源を用いることもできる。また、略点状の一次光源２としては、単色光のもの、赤、緑、青の３原色の波長の光を有する白色光源等を用いることができる。本発明においては、このような一次光源２として略点状の光源を１個または複数個使用することができる。また、１つのコーナー部または端面に複数の略点状の光源を近接して配置する場合には、複数の略点状の光源をアレイ化したＬＥＤアレイ等を点状光源として使用することができる。
【００３８】
一次光源２としては、目的や要求特性に応じて、最適の発光パターン（出射光分布）のものを用いることが好ましい。一般的には、一次光源２の前方の輝度が他の部分より高くなる現象を緩和するために、導光体４の光出射面４３に平行な方向（ａ方向）での発光パターンの広がりは大きいことが好ましく、発光パターンのピーク半値幅が１２０〜１８０度程度であるものが好ましい。導光体４の端面に一次光源２を設置する場合は、ａ方向の広がりが大きい発光パターンのものを使用することが好ましく、ピーク半値幅が１４０〜１８０度程度であるものが好ましい。また、導光体４のコーナー部に一次光源２を設置する場合は、導光体４中に入射した光が導光体４のａ方向において全面に向かって広がることが好ましく、入射した光の広がり角度が導光体４の面の広がりにほぼ一致することが好ましい。このため、光を入射する導光体２のコーナーの角度が９０度である場合には一次光源２のａ方向の発光パターンのピーク半値幅が６０〜１２０度程度であるものが好ましく、コーナーの角度が４５度である場合には一次光源２のａ方向の発光パターンのピーク半値幅が２０〜７０度程度であるものが好ましい。
【００３９】
また、一次光源２の光出射面４３に垂直な方向（ｂ方向）の発光パターンは、そのピーク半値幅が１０〜１２０度程度であることが好ましい。これは、ｂ方向が広すぎると光は一次光源２の近傍で出射しやすくなり輝度の均一性が低下する傾向にあり、ｂ方向の発光パターンが狭すぎると導光体４からの出射率が小さくなり輝度が低下する傾向にあるためである。
【００４０】
【実施例】
以下、実施例によって本発明を具体的に説明する。
実施例１
導光体の作製
鏡面仕上げをした４８ｍｍ×３４ｍｍ、厚さ３ｍｍの真鍮板の表面に、ピッチ３０μｍで、断面形状が頂角１６０度の断面二等辺三角形で、４８ｍｍ×３４ｍｍの四角形状の１つのコーナー近傍を中心とした円弧状プリズム列を同心円状に形成し、隣接する円弧状プリズム列間に３０〜２００μｍの平坦部を中心部より徐々に間隔が狭くなるように形成した円弧状プリズムパターンを４０ｍｍ×３０ｍｍの有効領域に切削加工した金型を得た。得られた金型と、鏡面仕上げをした４８ｍｍ×３４ｍｍ、厚さ３ｍｍの真鍮板を用いて射出成形を行い、長辺４８ｍｍ、短辺３４ｍｍ、厚み０．８ｍｍの矩形の導光板を得た。射出成形の材料としては、ポリメチルメタクリレ−トを用いた。
【００４１】
得られた導光体は、一方の面が平滑面で、他方の面に図６に示したような円弧状プリズムパターンが形成されていた。この導光体の円弧状プリズム列の中心となるコーナー部を端面長さ４ｍｍの平面状に切り欠き部を形成し光入射端面とした。この光入射端面全面に、図１１に示したような半径１５μｍの四分の一円と、長径が２５μｍで短径が１５μｍの四分の一楕円とを組み合わせた形状のレンズ列と、幅１０μｍの平面とからなるレンズ列パターン形成した金型を用いて加熱転写した。
【００４２】
光偏向素子の作製
鏡面仕上げをした４８ｍｍ×３４ｍｍ、厚さ３ｍｍの真鍮板の表面に、ピッチ５０μｍで、断面形状が６５．４度の頂角を挟む２つの傾斜面が曲率半径４００μｍの凸状曲面である略二等辺三角形で、４８ｍｍ×３４ｍｍの四角形状の１つのコーナー近傍を中心とした円弧状プリズム列を同心円状に並列して連設した円弧状プリズムパターンを切削加工した金型を得た。得られた金型にアクリル系紫外線硬化性組成物を注入し、１８８μｍのポリエステルフィルム（東洋紡社製Ａ４０００、屈折率１．６００）を重ね合わせた後、高圧水銀ランプを用いてポリエステルフィルムを通して紫外線を照射しアクリル系紫外線硬化性組成物を硬化し、金型から剥離しプリズムシートを得た。得られたプリズムシートは、ポリエステルフィルムの片面に、屈折率１．５２８の紫外線硬化樹脂からなり、ピッチ５０μｍで、６５．４度の頂角を挟む２つのプリズム面が曲率半径４００μｍの凸状曲面である略二等辺三角形で、１つのコーナー近傍を中心とする同心円状の円弧状プリズム列が並列して連設した円弧状プリズムパターンが形成されていた。
【００４３】
面光源システムの作製
得られた導光体の円弧状プリズムパターンが形成された面側に光拡散反射フィルム（辻本電機製作所社製ＳＵ−１１９）を設置し、導光体の光出射面となる平滑面側に、得られたプリズムシ−トを円弧状プリズムパターンを形成した面が導光体側となり、形成した円弧状プリズム列の中心となるコーナー部が導光体の切り欠き部と重なるように設置した。また、導光体の切り欠き部には、導光体の光出射面と平行方向のピーク半値幅が１１５度（±５７．５度）、垂直方向のピーク半値幅１１０度（±５５度）のＬＥＤ光源１個を、ＬＥＤ光源の指向性の方向と導光体の長辺とのなす角が４０度となるように設置し、１５ｍＡの電流を流した。
【００４４】
評価
得られた面光源システムを点灯し観察したところ、輝度むらの発現はほとんど視認されない良好な外観であった。
【００４５】
【発明の効果】
以上のように、本発明によれば、比較的少ない数の点状光源を一次光源として使用した場合であっても、輝度むらのない均斉度のとれた高品位の面光源装置を提供することができる。
【図面の簡単な説明】
【図１】本発明の面光源装置を示す分解斜視図である。
【図２】本発明の導光体の光入射端面の拡大斜視図である。
【図３】本発明の導光体の光入射端面の拡大斜視図である。
【図４】本発明の導光体の光入射端面の拡大斜視図である。
【図５】導光体に対する一次光源の位置を示す説明図である。
【図６】本発明の面光源装置の一実施態様を示す斜視図ある。
【図７】本発明の面光源装置の一実施態様を示す斜視図ある。
【図８】本発明の面光源装置の一実施態様を示す斜視図ある。
【図９】本発明の面光源装置の一実施態様を示す斜視図ある。
【図１０】本発明の光入射端面に形成するレンズ列の形状を示す断面図である。
【図１１】本発明の光入射端面に形成するレンズ列の形状を示す断面図である。
【図１２】本発明の光入射端面に形成するレンズ列の形状を示す断面図である。
【図１３】従来の面光源装置における導光体中での光の拡がり方を示す説明図である。
【符号の説明】
２　　　ＬＥＤ
４　　　導光体
４１　　光入射端面
４２　　光入射端面に形成されたレンズ列
４２１　非対称レンズ列
４２２　対称レンズ列
４３　　光出射面
６　　　光偏向素子
６１　　入光面
６２　　出光面
８　　　光反射素子[0001]
TECHNICAL FIELD OF THE INVENTION
INDUSTRIAL APPLICABILITY The present invention is used as a liquid crystal display device used for a notebook personal computer or a liquid crystal television, a display of a portable electronic device such as a mobile phone, a portable information terminal, a portable game machine, and an indicator of various electric / electronic devices. The present invention relates to a surface light source device suitable for a relatively small liquid crystal display device using a substantially point-like primary light source such as an LED and a light guide used therein, and more particularly to a high-quality illumination having a high degree of uniformity of luminance. The present invention relates to a surface light source device that can be provided.
[0002]
Problems to be solved by the prior art and the invention
In recent years, liquid crystal display devices have been widely used as monitors for portable notebook personal computers and the like, or as display units for liquid crystal televisions and video-integrated liquid crystal televisions, and in various other fields. The liquid crystal display device basically includes a backlight unit and a liquid crystal display element unit. As a backlight unit, an edge light type backlight is frequently used from the viewpoint of downsizing of a liquid crystal display device. Conventionally, as a backlight, at least one end face of a rectangular plate-shaped light guide is used as a light incidence end face, and a linear or rod-shaped primary light source such as a straight tube fluorescent lamp is arranged along the light incidence end face. And introducing light emitted from the primary light source into the inside of the light guide from the light incident end face of the light guide and emitting the light from one of the two main surfaces of the light guide. Is widely used.
[0003]
On the other hand, in recent years, portable electronic devices such as mobile phones, portable information terminal devices and portable game machines, or liquid crystal display devices having relatively small screen dimensions such as indicators of various electric and electronic devices have been reduced in size and power consumption. Reduction is desired. Therefore, in order to reduce power consumption, a light emitting diode (LED) which is a point light source is used as a primary light source of the backlight. As a backlight using an LED as a primary light source, for example, as described in JP-A-7-270624, a plurality of LEDs are used to exhibit the same function as that using a linear primary light source. They are arranged one-dimensionally along the light incident end face of the light guide. By using a primary light source based on a one-dimensional array of a plurality of LEDs in this manner, it is possible to obtain a required light amount and uniformity of luminance distribution over the entire screen.
[0004]
Further, in the case of a small liquid crystal display device, further reduction in power consumption is required, and in order to meet this demand, it is necessary to reduce the number of LEDs used. However, if the number of LEDs is reduced, the distance between the light emitting points becomes longer, so that the area of the light guide close to the area between the adjacent light emitting points is enlarged, and light is emitted from this light guide area in a required direction. The light intensity decreases. This leads to non-uniform luminance distribution in the viewing direction on the light emitting surface of the surface light source device (that is, non-uniform luminance uniformity). In Japanese Patent Publication No. 7-27137, a light guide having a rough light exit surface is used, and a prism sheet in which a large number of prism rows are arranged is formed such that the prism surface faces the light guide. A method has been proposed in which the distribution of emitted light is narrowed in order to reduce the power consumption of the backlight and to reduce the brightness as much as possible, by arranging the light on the light emitting surface. However, in such a backlight, although high brightness can be obtained with low power consumption, when the number of LEDs used is reduced, the unevenness of the brightness distribution of the light emitted from the light guide is easily recognized through the prism sheet. Met.
[0005]
The cause of the non-uniformity of the luminance distribution is that the light emitted from each LED arranged on the light incident end face of the light guide has directivity, and furthermore, the light is guided by the refraction effect when entering the light guide. This is because the spread of the light that has entered the body is relatively small, and as shown in FIG. 13, dark portions are generated in the regions on both ends of the LED. In particular, when the number of LEDs to be used is reduced or the LEDs are installed close to the light guide in order to reduce power consumption, dark portions become noticeable. As described above, in the conventional backlight using a point light source as the primary light source, it has been difficult to achieve both reduction in power consumption and maintenance of uniformity of luminance.
[0006]
Further, even in a backlight using a linear light source such as between cold cathodes as a primary light source, a light guide corner near the both ends of a linear or rod-shaped primary light source, or adjacent to a light incident end face of the light guide. There is a problem that a sufficient amount of light does not reach a region near the side end surface, and the luminance of these portions and regions is likely to be reduced. As a method of eliminating such a dark portion near the incident surface, for example, Japanese Patent Application Laid-Open No. H10-153778 proposes a method of roughening the surface of the light guide near the incident surface. In a backlight using a point light source such as an LED as a primary light source, such a method cannot sufficiently eliminate the dark part as described above.
[0007]
Therefore, an object of the present invention is to eliminate unevenness in brightness uniformity due to the use of a small number of point-like primary light sources for reducing power consumption of the surface light source device as described above, and to achieve high quality. An object of the present invention is to provide a surface light source device.
[0008]
[Means for Solving the Problems]
That is, the light guide for a surface light source device of the present invention is a rectangular light guide having a light incident end surface for receiving light from a substantially point-shaped primary light source and a light exit surface for emitting incident light. At least a part of the light-incident end face extends from the light-emitting face in the direction of the opposite face, has a cross-section that is asymmetric, and has a plurality of lens rows that are at least partially curvilinearly formed substantially in parallel. It is characterized by the following. Further, a surface light source device of the present invention is characterized by comprising the above light guide and a light deflecting element arranged on the light exit surface side of the light guide.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0010]
FIG. 1 is an exploded perspective view showing one embodiment of a surface light source device according to the present invention. As shown in FIG. 1, the surface light source device of the present embodiment includes an LED 2 as a substantially point-shaped primary light source, a light emitted from the LED 2, which is incident from a light incident end face, guides the light, and guides the light. A light guide 4 in the form of a rectangular plate in an XY plane, and a light deflector 6 and a light reflector 8 disposed adjacent to the light guide 4.
[0011]
The light guide 4 has two upper and lower main surfaces and an edge connecting the outer peripheral edges of the main surfaces, and one corner of the edge is cut out to be a light incident end surface, and the LED 2 is arranged. A light incident end face 41 corresponding to a position where the LED 2 is arranged is formed at the incident end edge of the light guide 4. As shown in FIG. 2, the light incident end face 41 extends at least at a position facing the LED 2 from the light emitting surface in the direction of the surface on the opposite side, the cross section is asymmetrical, and at least a part is curved. A plurality of lens rows 42 are formed substantially in parallel. When the light incident end face 41 is a flat surface, the light distribution of the light incident on the light guide 4 is narrower than that of the light emitted from the LED 2 due to the refraction when the light enters the light guide 4. By forming such a lens array 42 on the light incident end face 41, the light distribution of the light incident on the light guide 4 can be broadened. Further, by making the cross-sectional shape of the lens array 42 asymmetric, it is possible to adjust the amount of light emitted in each direction, and it is possible to increase the uniformity of luminance on the entire light emitting surface of the light guide 4. Furthermore, at least a part of the lens array 42 is formed with a curved surface in order to generate various refraction angles and efficiently widen the light distribution of light incident on the light guide 4.
[0012]
If the pitch of the lens array 42 is too large with respect to the LED 3, the refracting action of the lens array 42 is uniquely determined by the relative positional relationship with the LED 2, and spots due to the spread of light rays due to the positional relationship are visually recognized. Therefore, it is preferable that the pitch of the lens rows 42 is small. However, if the pitch is too small, shape transfer becomes difficult or the shape accuracy is reduced. Therefore, the pitch is preferably set to 10 to 200 μm, more preferably 20 μm. -100 μm, more preferably 30-60 μm.
[0013]
The preferred cross-sectional shape of the lens array 42 is an asymmetric shape composed of a combination of at least two different curves, for example, a shape obtained by combining two different curved surfaces, a combination of two or more different spherical or aspherical shapes. Shape, a combination of two or more different spherical and aspherical shapes, a shape composed of an arc and a part of an ellipse, an approximately quarter circle and an approximately ellipse Examples include a combined shape, a shape obtained by combining two substantially quarter ellipses having different major axes and minor axes, and the like. In addition, the substantially quarter circle and the substantially elliptical ellipse refer to a substantially quarter shape of the whole circle and ellipse. The cross-sectional shape of the lens array 42 is determined by a desired light distribution of light incident on the light guide 4. For example, when a wide light distribution is required, the light traveling direction is set to be a short axis. An elliptical shape is preferred.
[0014]
Specifically, those having a lens shape as shown in FIGS. FIG. 10 shows that one lens unit has different major and minor axes obtained by combining a quarter ellipse with a major axis of 20 μm and a minor axis of 15 μm and a quarter ellipse with a major axis of 30 μm and a minor axis of 15 μm. It has a shape combining two substantially quarter ellipses. FIG. 11 shows that one lens unit includes a lens having a shape obtained by combining a quarter circle having a radius of 15 μm, a quarter ellipse having a major axis of 25 μm and a minor axis of 15 μm, and a plane having a width of 10 μm. Things. FIG. 12 shows that one lens unit is a combination of a quarter ellipse having a major axis of 17 μm and a minor axis of 16 μm and a quarter ellipse having a major axis of 34 μm and a minor axis of 17 μm. The lens comprises a plurality of lenses having a flat portion, and a plane having an angle of 21 degrees with the lens forming surface. The cross-sectional shape of the lens array 42 may be partially straight. By making a part of the cross-sectional shape of the lens array 42 straight as described above, the shaping stability of the shape of the lens array 42 is improved, and the light distribution of the light incident on the light guide 4 is easily controlled. it can.
[0015]
Further, in the present invention, a plane portion or a curved portion may be formed between adjacent lens rows 42 as shown in FIG. The light distribution of light can be adjusted by adjusting the length of a plane portion or the like formed between the lens rows 42, and an optimal light distribution for achieving uniform luminance can be obtained. In this case, the width of the flat surface or the curved surface to be formed is preferably smaller than the pitch of the lens array 42 in consideration of the effect of expanding the light distribution of the lens array 42, and is preferably, for example, about 5 to 100 μm. It is more preferably in the range of 5 to 50 μm, and still more preferably in the range of 7 to 30 μm. A portion having a straight cross section may be a lens end as shown in FIG. Further, the lens array 42 may be formed only in a portion facing the arranged LEDs 2, or may be formed in a part of the light incident end face as shown in FIG. 4 and the other portions may be flat. In this case, the ratio of the length of the flat portion to the length of the light incident end face is preferably 30% or less, and more preferably 15 to 20%.
[0016]
One of the two main surfaces (the upper surface in the figure) of the light guide 4 is a light emission surface 43 and the other main surface is a back surface. At least one main surface of the light emitting surface 43 or the rear surface is provided with light guided in the light guide 4 in a direction inclined with respect to the light emitting surface 43 (that is, a direction inclined with respect to the XY plane). Is provided. As the directional light emitting mechanism, for example, an uneven shape is formed on at least one surface of the light emitting surface 43 and the back surface of the light guide 4, or a structure in which the refractive index is different from that of the base material in the light guide 4. For example, a directional light emitting mechanism can be formed by incorporating light diffusing fine particles having a different refractive index from the base material. These directional light emitting mechanisms can be formed in the light guide 4 by combining a plurality of directional light emitting mechanisms. The light incident on the light guide 4 changes its incident angle on the light emitting surface 43 while propagating through the light guide 4 by such a directional light emitting mechanism, and the incident angle on the light emitting surface 43. Is smaller than the critical angle, the light exits from the light exit surface 43.
[0017]
When the directional light emitting mechanism is formed by making the surface of the light guide 4 uneven, a lens surface in which a number of lens arrays such as a prism array, a lenticular lens array, and a V-shaped groove are formed in parallel, Alternatively, a rough surface (mat surface) may be used. In the light guide 4 provided with such a directional light emission mechanism, the direction of the peak emission light in the emission light distribution of the emission light emitted from the light emission surface 43 is an angle of 10 to 50 degrees with the light emission surface 43. It is preferable that the half width of the emission light distribution is 10 to 40 degrees.
[0018]
In the present invention, the average inclination angle θa according to ISO 4287 / 1-1984 is preferably in the range of 2 to 12 degrees, and more preferably in the range of 3 to 10 degrees, for the rough surface or the lens surface as the directional light emitting mechanism. It is. This is because if the average inclination angle θa is less than 2 degrees, the light emission rate of the light guide 4 becomes small, the light emission amount becomes insufficient, and the luminance tends to decrease. If θa exceeds 12 degrees, the light emission rate of the light guide 4 is large, the amount of light emitted near the primary light source 2 is large, and the uniformity of luminance in the light emission surface 43 tends to decrease. is there. In the present invention, the average inclination angle θa of the rough surface or the lens surface may be uniform within the surface of the light guide 4 or may be changed continuously, intermittently, or partially. For example, in order to improve the uniformity of luminance in the light emitting surface 43, it is preferable to increase the average inclination angle θa as the distance from the primary light source 2 increases. Further, when there is a portion where the luminance is partially reduced in the light emitting surface 43, the average inclination angle θa of the portion is increased, or when there is a portion where the luminance is partially increased. By reducing the average inclination angle θa of the portion, the amount of emitted light can be partially controlled to achieve uniform brightness.
[0019]
The average inclination angle θa of the rough surface or the lens surface formed on the light guide 4 is measured in accordance with ISO 4287 / 1-1984 using a stylus type surface roughness meter, and the coordinates in the measurement direction are represented by x. Can be obtained from the obtained inclination function f (x) using the following equations (1) and (2). Here, L is the measured length, and Δa is the tangent of the average inclination angle θa.
[0020]
(Equation 1)

(Equation 2)

As a specific example of the directional light emitting mechanism formed in the light guide 4, a lens array is formed in an arc shape having the primary light source 2 substantially at the center, and a lens array is formed in a radial shape having the primary light source 2 at the center. The light guide 4 has a band-shaped different refractive index layer formed radially around the primary light source 2, and the light guide 4 has a band different refractive index layer substantially centered on the primary light source 2. And those formed in an arc shape. Above all, a lens array formed in an arc shape with the primary light source 2 substantially at the center is used to emit light without largely changing the direction of light propagating radially around the primary light source 2 in the light guide 4. Since the light is emitted from the surface 43, most of the light can be deflected in a desired direction by the light deflecting element 6, and a surface light source device with high luminance and excellent luminance uniformity can be provided. This is because, in the XY plane, the direction of light propagating through the light guide 4 is radial with the primary light source 2 being substantially at the center, and does not change significantly. Can be deflected in a desired direction by the light deflecting element 6, and a surface light source device with high luminance and excellent uniformity of luminance can be provided.
[0021]
In the present invention, since a substantially point-like light source such as an LED is used as the primary light source 2, the light incident on the light guide 4 is substantially centered on the primary light source 2 in the same plane as the light exit surface 43. The light propagates radially in the light guide 4. For such radially propagating light, a lens array formed in an arc shape (arc-shaped lens array) is arranged in parallel in a substantially arc shape so as to surround the primary light source 2, so that the inside of the light guide 4 is radially formed. Since most of the propagating light is incident on the arc-shaped lens array in a substantially vertical direction, it can be efficiently emitted in a desired direction regardless of the propagation direction, and the propagation direction can be easily maintained. Outgoing light can be efficiently directed to a specific direction in the entire region of the light emitting surface 43 of the light guide 4, and the uniformity of luminance can be improved. The arc-shaped lens array selects the degree of its arc shape in accordance with the distribution of light propagating in the light guide 4, and most of the light propagating radially in the light guide 4 is perpendicular to the arc-shaped lens array. It is preferable that the light is incident. As such an arc-shaped lens array, one having a cross-sectional shape such as a triangle, an arc, a semicircle, and a polygon can be formed.
[0022]
When such an arc-shaped lens array is formed as a directional light emitting mechanism, the radial distribution of the formed arc-shaped lens array can be formed continuously, or a flat portion can be formed between adjacent arc-shaped lens arrays. Can be discrete via When the arc-shaped lens array is formed continuously, there is a case where there is light incident on an adjacent arc-shaped lens array after exiting from the arc-shaped lens array. Dispersion of the outgoing light of the outgoing light emitted from the light 4 increases, and the amount of light that is not deflected in a desired direction by the light deflecting element 6 increases, which may cause a decrease in luminance. In such a case, by forming the arc-shaped lens arrays discretely, light incident on the adjacent arc-shaped lens arrays can be reduced, and the distribution of the emitted light from the emitted light emitted from the light guide 4 can be reduced. It is possible to suppress a decrease in luminance due to disturbance.
[0023]
When the LED 2 as the primary light source is disposed at one corner of the light guide 4 as in this embodiment, the angle between the direction of the light directivity of the LED 2 and the long side of the light guide 4 is shown. As shown in FIG. 5, the angle is preferably in the range of 37 to 45 degrees, and more preferably in the range of 39 to 42 degrees. This is because if the angle between the direction of the light directivity of the LED 2 and the long side of the light guide 4 is less than 37 degrees, the angle between the short side of the light guide 4 and the light of the LED 2 becomes large. This is because it tends to be difficult to prevent luminance unevenness in a region between the direction of the directivity and the short side. If this angle exceeds 45 degrees, the difference between the direction of the light directivity of the LED 2 and the short side is reduced. This is because the region between the short sides is larger than the region between the long sides, and it tends to be difficult to prevent a decrease in luminance in the region between the direction of light directivity of the LED 2 and the short sides.
[0024]
When the LEDs 2 are arranged at the corners of the light guide 4 as described above, a large number of lens rows are arranged on the light exit surface 43 of the light guide 4 so as to surround the LEDs 2 as shown in FIGS. It is preferable to form them in parallel in a substantially arc shape. In the present invention, as shown in FIG. 7, the light emitting surface 43 of the light guide 4 may have a substantially trapezoidal shape, and the LED 2 may be arranged at one corner formed by the base.
[0025]
In the present invention, the arrangement of the LEDs 2 as the primary light source is not limited to the corner portion as in the present embodiment, but may be the arrangement shown in FIGS. FIG. 8 shows that the LED 2 is installed between the light guide 4 and an air layer or a transparent substance in a recess or a through hole provided on the back surface of the light guide 4, and the light exit surface 43 of the light guide 4 is provided. A large number of lens rows are formed in parallel in a substantially arc shape so as to surround the LED 3. In FIG. 9, a plurality of LEDs 2 are arranged on one edge of the light guide 4, and a lens array 42 is formed on a portion of the light incident end face 41 of the light guide 4 facing the LED 2. In this case, a lens array 422 having a symmetrical cross-sectional shape is formed at a position facing the LED located near the center of the light incident end face 41, and faces the LEDs located near both ends of the light incident end face 41. By forming a lens array 421 having an asymmetrical cross-sectional shape at the position, the uniformity of luminance can be improved over the entire light exit surface of the light guide 4.
[0026]
The light deflecting element 6 is arranged on the light exit surface 43 of the light guide 4. The two main surfaces of the light deflecting element 6 are respectively positioned as a whole in parallel with the XY plane. One of the two main surfaces (the main surface located on the light exit surface 43 side of the light guide) is a light incident surface 61, and the other is a light exit surface 62. The light deflecting element 6 has a function of deflecting (deflecting) the light emitted from the light guide 4 in a target direction. Many prism rows having two surfaces on at least one surface are arranged in parallel. A lens sheet having a lens surface formed as described above can be used.
[0027]
In the present invention, since a substantially point light source such as an LED is used as the primary light source 2, the light incident on the light guide 4 is substantially centered on the primary light source 2 in the same plane as the light exit surface 43. The emitted light propagating radially through the light guide 4 and emitted from the light emitting surface 43 is also emitted radially around the primary light source 2. In order to efficiently deflect such emitted light in a desired direction irrespective of the emission direction, prism rows formed in the light deflecting element 6 are arranged in a substantially arc shape so as to surround the primary light source 2. And place it. In this way, by arranging the prism arrays in parallel in a substantially arc shape so as to surround the primary light source 2, most of the light radially emitted from the light exit surface 43 is perpendicular to the prism array of the light deflecting element 6. , The emitted light can be efficiently directed in a specific direction in the entire area of the light emitting surface 43 of the light guide 4, and the uniformity of luminance can be improved.
[0028]
The substantially arc-shaped prism array formed on the light deflecting element 6 selects the degree of the arc in accordance with the distribution of light propagating in the light guide 4, and almost all of the light emitted radially from the light exit surface 43 is light. It is preferable that the light is incident on the prism array of the deflecting element 6 in the vertical direction. Specifically, there is a concentric circle arranged substantially in parallel with a point light source such as an LED so that the radius of the arc is gradually increased. The range of the radius of the prism array is a surface light source. It is determined by the positional relationship and size between the position of the point light source in the system and the effective area of the surface light source corresponding to the liquid crystal display area.
[0029]
Also, the pattern of the prism array formed on the light deflecting element 6 is such that most of the light radially emitted from the light exit surface 43 is substantially equal to the prism array of the light deflecting element 6 depending on the arrangement method of the primary light source 2. It can be set appropriately so as to have a pattern which is incident in the vertical direction. Further, the prism array formed on the light deflecting element 6 may be formed on the light entrance surface 61 of the light deflecting element 6 facing the light exit surface 43 of the light guide 4 or may be formed on the light exit surface 62. Alternatively, it may be formed on both the light incident surface 61 and the light exit surface 62. In order to efficiently deflect outgoing light having high directivity from the light guide 4 in a desired direction and obtain high luminance, it is preferable to form a prism array on the light incident surface 61 of the light deflector 6.
[0030]
When the light deflecting element 6 in which the prism array is formed on the light incident surface 61 is arranged on the light emitting surface 43 of the light guide 4, the emitted light emitted from the light emitting surface 43 is close to the primary light source 2 of the prism array. The light enters the light deflecting element 6 from one side, is reflected internally by the surface farther from the primary light source 2, is deflected in a desired direction, and then exits from the light exit surface 62 of the light deflecting element 6. For this reason, it is possible to change the emission direction to a desired direction while maintaining the directivity of the emission light emitted from the light emission surface 43 of the light guide 4, thereby increasing the light use efficiency and improving the luminance. A high surface light source system can be provided.
[0031]
The light emitted from the light exit surface 43 of the light guide 4 is directed from the primary light source 2 of the prism array because the peak light of the emitted light distribution is inclined by 10 to 50 degrees with respect to the light exit surface 43. The angle between the far surface and the reference plane of the light deflecting element 6 is preferably 40 to 80 degrees, more preferably 50 to 65 degrees, and even more preferably 55 to 65 degrees. This is because, by setting the angle formed between the surface far from the primary light source 2 and the reference plane of the light deflecting element 6 in this range, the light emitted from the light guide 4 having such directivity can be converted to the light deflecting element. This is because the light can be deflected to the vicinity of the normal direction of the light emitting surface 62 of the light emitting device 6 and emitted. Here, the reference plane of the light deflecting element 6 is a plane when it is assumed that the surface of the light deflecting element 6 where the prism rows are formed is smooth.
[0032]
On the other hand, a part of the light propagating in the light guide 4 reaches the end of the light guide 4, and there is light reflected by the end face and returned. Such light propagates through the light guide 4 toward the light incident surface of the light guide 4 and is emitted from the light emission surface 43 by the directional light emission mechanism formed on the light guide 4. Such outgoing light enters from the prism surface farther from the primary light source 2 of the light deflector 6, is internally reflected by the prism surface closer to the primary light source 2, is deflected in a desired direction, and is deflected in a desired direction. The light exits from the exit light surface 62 of FIG. Such emitted light also has a direction in which the peak light of the emitted light distribution is inclined by 10 to 50 degrees with respect to the light emitting surface 43. Therefore, when the amount of such emitted light is relatively large, the prism row is not formed. The angle between the prism surface closer to the primary light source 2 and the reference plane of the light deflecting element 6 is also preferably 40 to 80 degrees, more preferably 50 to 65 degrees, similar to the prism surface farther from the primary light source 2. Degrees, more preferably 55 to 65 degrees.
[0033]
The angle formed by the two prism surfaces with respect to the reference plane of the light deflecting element 6 may be the same or may be different. When the two angles are different, the difference is preferably 10 degrees or less, more preferably 5 degrees or less, and still more preferably 2 degrees or less.
[0034]
In the present invention, when the demand for reduction of power consumption and high brightness is extremely high, such as a surface light source system of a portable electronic device such as a mobile phone or a portable information terminal, the light deflection element 6 is formed. The cross-sectional shape of the prism array to be formed can be deflected so as to concentrate in a desired direction when the prism surface is internally reflected by the prism surface by making the prism surface a convex curved surface or a polygonal surface shape, and a higher directivity is obtained. Since the light is emitted as concentrated light, luminance per power consumption can be increased, and power consumption can be reduced and luminance can be increased.
[0035]
The light guide 4 and the light deflecting element 6 of the present invention can be made of a synthetic resin having a high light transmittance. Examples of such a synthetic resin include a methacrylic resin, an acrylic resin, a polycarbonate resin, a polyester resin, a vinyl chloride resin, and a cyclic polyolefin resin. In particular, methacrylic resin is optimal because of its high light transmittance, heat resistance, mechanical properties, and moldability. Such a methacrylic resin is a resin containing methyl methacrylate as a main component, and is preferably a resin having 80% by weight or more of methyl methacrylate. When forming the surface structure of the rough surface of the light guide 4 and the light polarizing element 6 and the surface structure such as the prism rows, the transparent synthetic resin plate is formed by hot pressing using a mold member having a desired surface structure. The shape may be provided simultaneously with the molding by screen printing, extrusion molding, injection molding, or the like. Further, the structural surface can also be formed by using a heat or light curable resin. Further, on a transparent substrate such as a transparent film or sheet made of a polyester resin, an acrylic resin, a polycarbonate resin, a vinyl chloride resin, a polymethacrylimide resin, etc., a rough surface structure made of an active energy ray-curable resin. Further, a lens array structure may be formed on the surface, or such a sheet may be joined and integrated on a separate transparent substrate by a method such as adhesion or fusion. As the active energy ray-curable resin, polyfunctional (meth) acrylic compounds, vinyl compounds, (meth) acrylates, allyl compounds, metal salts of (meth) acrylic acid, and the like can be used.
[0036]
As the light reflection element 8, for example, a plastic sheet having a metal deposition reflection layer on the surface can be used. Further, it is preferable that a reflection member is also provided on the side end surface of the light guide 4 (excluding the light incident end surface 41).
[0037]
As the primary light source 2, an LED light source is preferable in terms of power consumption and the like, but other substantially point-like light sources such as a halogen lamp can also be used. Further, as the substantially point-shaped primary light source 2, a monochromatic light source, a white light source having light of three primary colors, red, green, and blue, and the like can be used. In the present invention, one or a plurality of substantially point light sources can be used as the primary light source 2. When a plurality of substantially point-like light sources are arranged close to one corner or end face, an LED array or the like in which a plurality of substantially point-like light sources are arrayed can be used as the point-like light source. .
[0038]
As the primary light source 2, it is preferable to use one having an optimum light emission pattern (emission light distribution) according to the purpose and required characteristics. Generally, in order to alleviate the phenomenon that the luminance in front of the primary light source 2 becomes higher than other portions, the spread of the light emission pattern in the direction (a direction) parallel to the light exit surface 43 of the light guide 4 is limited. It is preferable that the width is large, and the peak half width of the light emission pattern is about 120 to 180 degrees. When the primary light source 2 is installed on the end face of the light guide 4, it is preferable to use a light emission pattern having a large spread in the a-direction, and a light emission pattern having a peak half width of about 140 to 180 degrees is preferable. When the primary light source 2 is installed at the corner of the light guide 4, it is preferable that the light incident on the light guide 4 spreads toward the entire surface of the light guide 4 in the direction a. It is preferable that the spread angle substantially matches the spread of the surface of the light guide 4. For this reason, when the angle of the corner of the light guide 2 into which light is incident is 90 degrees, it is preferable that the peak half-value width of the light emission pattern in the a direction of the primary light source 2 is about 60 to 120 degrees. When the angle is 45 degrees, it is preferable that the peak half width of the light emission pattern of the primary light source 2 in the direction a is about 20 to 70 degrees.
[0039]
Further, it is preferable that the emission pattern in the direction (b direction) perpendicular to the light emission surface 43 of the primary light source 2 has a peak half-value width of about 10 to 120 degrees. This is because if the b direction is too wide, light tends to be emitted near the primary light source 2 and the uniformity of luminance tends to decrease. If the light emission pattern in the b direction is too narrow, the emission rate from the light guide 4 is reduced. This is because the brightness tends to decrease and the brightness tends to decrease.
[0040]
【Example】
Hereinafter, the present invention will be specifically described with reference to examples.
Example 1
Fabrication of light guide
On the surface of a mirror-finished 48 mm x 34 mm, 3 mm thick brass plate, with a pitch of 30 µm, a cross-sectional shape is an isosceles triangle with a vertex angle of 160 degrees, centered around one corner of a square of 48 mm x 34 mm An arcuate prism pattern is formed concentrically, and a flat portion of 30 to 200 μm is formed between adjacent arcuate prism lines so as to gradually narrow the interval from the center. A die cut in the area was obtained. Injection molding was performed using the obtained mold and a mirror-finished 48 mm × 34 mm, 3 mm thick brass plate to obtain a rectangular light guide plate having a long side of 48 mm, a short side of 34 mm, and a thickness of 0.8 mm. Polymethyl methacrylate was used as a material for injection molding.
[0041]
The resulting light guide had a smooth surface on one side and an arc-shaped prism pattern as shown in FIG. 6 formed on the other side. A corner portion of the light guide, which is the center of the arc-shaped prism array, was formed as a light incident end surface by forming a notch in a plane having an end surface length of 4 mm. A lens array having a shape obtained by combining a quarter circle having a radius of 15 μm as shown in FIG. 11, a quarter ellipse having a major axis of 25 μm and a minor axis of 15 μm, and a width of 10 μm, as shown in FIG. Heat transfer was performed using a mold having a lens array pattern formed of the flat surface.
[0042]
Fabrication of light deflection element
On a 48 mm × 34 mm mirror-finished brass plate having a thickness of 3 mm, approximately two convex surfaces having a pitch of 50 μm and a cross-sectional shape having an apex angle of 65.4 degrees are convex curved surfaces having a radius of curvature of 400 μm. A mold was obtained by cutting an arc-shaped prism pattern in which arc-shaped prism rows each having an isosceles triangle and being arranged concentrically in parallel with arc-shaped prism rows centered on one corner of a square of 48 mm × 34 mm. An acrylic UV curable composition was injected into the obtained mold, and a 188 μm polyester film (A4000, manufactured by Toyobo Co., refractive index: 1.600) was superimposed. Ultraviolet rays were passed through the polyester film using a high-pressure mercury lamp. Irradiation was performed to cure the acrylic ultraviolet curable composition, and the composition was separated from the mold to obtain a prism sheet. The obtained prism sheet is made of a UV curable resin having a refractive index of 1.528 on one side of a polyester film, and has a pitch of 50 μm, and two prism faces sandwiching a 65.4 degree apex angle have a convex curved surface with a radius of curvature of 400 μm. In this case, an arc-shaped prism pattern was formed in which substantially concentric arc-shaped prism rows centered around one corner were arranged in parallel.
[0043]
Fabrication of surface light source system
A light diffusing reflection film (SU-119, manufactured by Tsujimoto Electric Co., Ltd.) was installed on the surface of the obtained light guide on which the arc-shaped prism pattern was formed, and on the smooth surface side of the light guide, which became the light emission surface, The obtained prism sheet was placed so that the surface on which the arc-shaped prism pattern was formed was on the light guide side, and the corner portion, which was the center of the formed arc-shaped prism row, overlapped the cutout portion of the light guide. In the notch of the light guide, the peak half width in the direction parallel to the light exit surface of the light guide is 115 degrees (± 57.5 degrees), and the peak half width in the vertical direction is 110 degrees (± 55 degrees). Was set such that the angle between the direction of the directivity of the LED light source and the long side of the light guide was 40 degrees, and a current of 15 mA was passed.
[0044]
Evaluation
When the obtained surface light source system was turned on and observed, the appearance of luminance unevenness was good and the appearance was hardly visually recognized.
[0045]
【The invention's effect】
As described above, according to the present invention, even when a relatively small number of point-like light sources are used as primary light sources, it is possible to provide a high-quality surface light source device having uniformity without luminance unevenness. Can be.
[Brief description of the drawings]
FIG. 1 is an exploded perspective view showing a surface light source device of the present invention.
FIG. 2 is an enlarged perspective view of a light incident end face of the light guide of the present invention.
FIG. 3 is an enlarged perspective view of a light incident end face of the light guide of the present invention.
FIG. 4 is an enlarged perspective view of a light incident end face of the light guide of the present invention.
FIG. 5 is an explanatory diagram showing a position of a primary light source with respect to a light guide.
FIG. 6 is a perspective view showing one embodiment of the surface light source device of the present invention.
FIG. 7 is a perspective view showing an embodiment of the surface light source device of the present invention.
FIG. 8 is a perspective view showing one embodiment of the surface light source device of the present invention.
FIG. 9 is a perspective view showing one embodiment of the surface light source device of the present invention.
FIG. 10 is a cross-sectional view showing the shape of a lens array formed on the light incident end face of the present invention.
FIG. 11 is a cross-sectional view showing the shape of a lens array formed on the light incident end face of the present invention.
FIG. 12 is a cross-sectional view showing the shape of a lens array formed on the light incident end face of the present invention.
FIG. 13 is an explanatory diagram showing how light spreads in a light guide in a conventional surface light source device.
[Explanation of symbols]
2 LED
4 Light guide
41 ° light incidence end face
42 ° Lens array formed on the light incident end face
421 asymmetric lens array
422 ° symmetric lens array
43 ° light exit surface
6 Light deflection element
61 Light incident surface
62 ° light emitting surface
8 Light reflection element

Claims (11)

In a rectangular light guide having a light incident end surface for receiving light from a substantially point-shaped primary light source and a light exit surface for emitting incident light, at least a portion of the light incident end surface is exposed from the light exit surface. A light guide for a surface light source device, wherein a plurality of lens rows extending in the direction of the opposite surface, having an asymmetric cross section, and having at least a part of a curved line are formed substantially in parallel. 2. The light guide for a surface light source device according to claim 1, wherein the lens array is formed at least at a portion of the light incident end face facing the primary light source. 3. 2. The lens array according to claim 1, wherein a lens array having a symmetrical cross section is formed near the center of the incident end face, and a lens array having an asymmetrical cross section is formed near both ends of the incident end face. 3. Light guide for surface light source device. The light guide for a surface light source device according to claim 1, wherein the lens array has a shape obtained by combining at least two different curved surfaces. The light guide for a surface light source device according to claim 1, wherein the lens array has a shape obtained by combining at least two different spherical surfaces and / or aspheric surfaces. The light guide for a surface light source device according to claim 1, wherein the lens array has a cross-sectional shape formed by a part of an arc and an ellipse. The light guide for a surface light source device according to claim 1, wherein the lens array has a cross-sectional shape obtained by combining a quarter circle and a quarter ellipse. 2. The light guide for a surface light source device according to claim 1, wherein the lens array has a cross-sectional shape obtained by combining two quarter ellipses. 3. The light guide for a surface light source device according to any one of claims 1 to 8, wherein a flat portion or a curved portion that is narrower than the width of each lens row unit is formed between adjacent lens rows. The light guide for a surface light source device according to claim 1, wherein the light incident end face is formed at a corner of the light guide. A surface light source device comprising: the light guide according to any one of claims 1 to 10; and a light deflecting element disposed on a light exit surface side of the light guide.

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