JP4056917B2 - Projection screen and projection display device - Google Patents

Description

【００３９】
また、観察側の面が平坦面とすると、プリズムレンズ１１３から出射する光線の出射角θ₅ とシート内での映像光の進む角度θ₄ との間には、下記式が成立する。
ｓｉｎθ₄ ＝ｓｉｎθ₅ ／ｎ
ただし、γ＝φ＋λ−π／２≧０である。
γが負の時は、プリズムの第１の面の形状が逆テーパーになってフレネルレンズ及びフレネルレンズ成形型が事実上製造できなくなるからである。θ₄ が略零とすると、φは、θ₁ について単調減少するので、γは、入射角θ₁ の大きい外周部で、負になりやすい。プリズムの第１面（入射面）が逆テーパーにならない為の条件は、下記式で表される。
ｃｏｓ^-1｛ｃｏｓ（θ₁）／ｎ｝／２≦λ
【００４０】
一方、プリズムレンズ１１３のフレネル中心に近い場所では、第１の面に入射した後、第２の面で全反射せず、迷光となる光が存在する。そこで、図１１に示すように、１つのプリズム内での入射光線が迷光となる部分と有効な光となる部分との境界の位置を通過する光、すなわち、第１の面から入射して、丁度プリズムの谷部へと屈折する光について考察する。プリズムの第１の面への入射角度をθ₂ 、プリズムの第１の面の屈折角度をθ₃ 、プリズムレンズ１１３のレンズピッチ（フレネルレンズのピッチ）をｐ、プリズムの第２の面で全反射し好適に利用できる部分をｅ₁ 、プリズムの第２の面で全反射できずに迷光になる部分をｅ₂ 、プリズムの高さをｈ、プリズムの第１の面の迷光となる部分と有効な部分の境界の高さをｓとすると、有効な部分ｅ₁ は、以下の式で表される。
ｅ₁ ＝（ｈ−ｓ）×（ｔａｎ（φ＋λ−π／２）＋ｔａｎθ₁ ）
【００４１】
ここで、プリズムの高さｈと、プリズムの第１の面の迷光となる部分と有効な部分の境界の高さｓは、それぞれ、以下の式により表すことができる。
ｈ＝ｐ×ｔａｎ（φ＋λ）×ｔａｎφ／（ｔａｎ（φ＋λ）−ｔａｎφ）
ｓ＝−ｐ×ｔａｎ（φ＋λ）／（１＋ｔａｎ（φ＋λ）×ｔａｎ（φ＋λ＋θ₃ ））
また、θ₃ ＝ａｒｃｓｉｎ｛ｓｉｎ（θ₁ ＋φ＋λ）／ｎ｝である。
【００４２】
図１１より、明らかにｅ₁ ≦ｐである。ピッチに対する有効部の比ｅ₁ ／ｐは、入射角θ₁ が大きい程大きくなり、あるところでｅ₁ ＝ｐとなる。そのところより入射角度θ₁ が大きいところでは、プリズムの第１の面より入射し、第２の面で全反射しないで観察側の面に向かう迷光となる光が存在しない領域となる。
【００４３】
図５は、プリズムの頂角に対する迷光の存在する入射光の角度の境界と、第１の面が逆テーパーになる入射光の角度を、出射角θ₅ ＝０で、レンズ部分の屈折率が１．５５について、計算した結果を示した図である。
【００４４】
図５において、２本の線に囲まれた内側では、フレネル中心に近い場所での迷光もなく、かつ、フレネル中心から遠い場所での、第１の面の逆テーパーもない領域である。例えば、プリズム頂角３５°の時には、レンズの許容入光角はおよそ４５〜６０°程度であることが示される。一方、プリズム頂角が４５°の場合には、たとえ真下からの映像光でも、入光面が垂直で反射面が４５°となり、光のロスはなくなる。従って、フレネル中心に近い場所での迷光防止を重視すれば、プリズム頂角は、小さい方が好ましく、逆に、フレネル中心から遠い場所での、第１の面が逆テーパーとなることを防止することを重視すれば、プリズム頂角は、大きい方が好ましい。
従って、全反射プリズムの頂角３０°〜４５°の範囲で、フレネル中心に近い場所では、プリズムの頂角を小さくし、フレネル中心から遠いところでは、プリズムの頂角を大きくすることで、フレネル中心に近いところから遠いところまで、良好なフレネルレンズを得ることが出来る。
【００４５】
そしてまた、上記のように構成されたプロジェクションスクリーンの観察者側に、さらにＡＲ、ＡＧ、ＡＳ、ＨＣ、防汚、センサー等の機能を付与することも望ましい形態である。ここで、上記のＡＲ、ＡＧ、ＡＳ、ＨＣ、防汚、センサーについての機能概要を説明する。先ず、ＡＲとはアンチリフレクションの略で、例えばレンズ表面に入光する光の反射率を抑える機能を有するフィルムをラミネートしたり、レンズ表面を直接ＡＲ処理することにより得られる。ＡＧとはアンチグレアの略で、レンズの防眩性機能を有するフィルムをラミネートしたり、レンズ表面を直接ＡＧ処理することにより得られる。ＡＳとはアンチスタティックの略で、レンズ表面に帯電防止用のフィルムをラミネートしたり、レンズ表面を直接ＡＳ処理することにより得られる。ＨＣとはハードコートの略で、レンズ表面の強度を増して傷等がつかないような耐摩耗性フィルムをラミネートしたり、レンズ表面を直接ＨＣ処理することにより得られる。防汚とはレンズ表面に汚れが付着することを防止するフィルム等をラミネートしたり、レンズ表面を直接、防汚処理することにより得られる。そして、センサーとはタッチセンサー等の機能の付与を意味するものである。
【００４６】
（第２実施形態）
図２は、本発明によるプロジェクションスクリーンの第２実施形態を示す図である。
この実施の形態のプロジェクションスクリーン２１は、ベースシート２３の入光側表面にプリズムの位置により頂角λ２が角度変化している同心円状の全反射プリズム２２が形成され、ベースシート２３の出光側表面に、単位レンズとして断面が台形状の高屈折率部２５とＶ字形状の低屈折率部２６で構成されるレンチキュラーレンズ２４が形成されている。全反射プリズム２２の頂角λ２は、３０°〜４５°の角度範囲内で、同心円の中心に近い側（図面下側）の頂角よりも同心円の中心からより遠い側（図面上側）の頂角の方が大きくなるように、連続的に角度を変えてある。
【００４７】
台形状レンチキュラーレンズ２４は下底を入光部、上底を出光部とし、所定の屈折率を有する材料で形成されており、隣接する単位レンズ間のＶ字形状の部分２６は台形状部分２５よりも低い屈折率を有する材料で形成されており、Ｖ字形状部分２６と台形状部分２５との界面による全反射効果を用いて映像光を拡散させているレンズである。
【００４８】
図２の紙面右手前側下方に映像光源（図示せず）があり、斜め上方に向けて投射された映像光は全反射プリズム２２に入光し、全反射してスクリーン面に対して略直交する方向へ出光する映像光に変換されてプリズム２２から出光後、台形状のレンチキュラーレンズ２４の台形の下底側から入光し、台形状の高屈折率部２５とＶ字形状の低屈折率部２６との界面で全反射して出光し、紙面左側奥の観察者（図示せず）に達する。
【００４９】
図３は、第２実施形態におけるプロジェクションスクリーンの水平断面模式図である。
レンチキュラーレンズ２４は単位レンズの断面が台形状２５であり、隣接する台形間のＶ字形状の低屈折率部２６にはレンチキュラーレンズ２４を構成する物質より低い屈折率を有する物質が充填されている。台形状高屈折率部２５とＶ字形状低屈折率部２６との界面での全反射効果を利用する為、Ｖ字形状部２６の物質としては、台形状レンズ２５を構成する物質よりも相対的に低い屈折率を有していればよく、特に材料は限定されないが、例えば、低屈折率の合成樹脂材料等が用いられる。
【００５０】
上記の低屈折率の合成樹脂材料は、光吸収作用があることが好ましく、レンチキュラーレンズ２４の台形斜面部を透過した光を、光吸収作用を有するＶ字形状部２６で吸収することができる。
【００５１】
光吸収作用を有するＶ字形状部２６は、低屈折率樹脂中に染料、顔料、又は着色された樹脂微粒子よりなる光吸収粒子を混入することにより形成することができる。
【００５２】
なお、第１実施形態及び第２実施形態において説明した本発明によるプロジェクションスクリーンは、入光面側で光源に近い側（フレネルレンズ中心に近い側）の端部において、スクリーンへの映像光の入射角θ₁ が３５°以上、好ましくは４５°以上で、５０°以下となるようなプロジェクションディスプレイ装置に好適に用いることができる。
【００５３】
（第３実施形態）
第１及び第２実施形態では、プロジェクションスクリーン全面に渡ってプリズムの頂角が連続的に変化している例を示した。
しかし、プリズムを製造する成形型の製造上は、全ての位置においてプリズムの頂角を変化させることは、非常に多くの加工工程を必要とすることになる。したがって、第１及び第２実施形態に示すプロジェクションスクリーンを製造する成形型の加工費用が高額となり、結果的にプロジェクションスクリーンも高価格になってしまう。
そこで、プロジェクションスクリーン全面に渡ってプリズムの頂角を連続的に変化させるのではなく、プリズムの頂角が大きい領域と頂角が小さい領域、及びこれらの間に頂角が変化する領域を設けることとし、成形型の製造が困難なプリズムの頂角が変化する領域を少なくした。
【００５４】
第３実施形態におけるプロジェクションスクリーン１１１は、第１及び第２実施形態における全反射円弧状プリズムの形状を変更した形態であるので、第１及び第２実施形態と共通する機能を有する部分の説明は、適宜省略する。
図９は、第３実施形態におけるプロジェクションスクリーンを説明する図である。図９（ａ）は、プロジェクションスクリーンを入光面側（プリズムレンズ１１３側）から見た図であり、図９（ｂ）は、側面から見た図である。
本実施形態におけるプロジェクションスクリーン１１１は、第１及び第２実施形態と同様に最入光面側に同心円状で中心（フレネル中心）が画面上にない全反射プリズムが形成されたプリズムシート（フレネルレンズシート）１１３が設けられている。
【００５５】
図１０は、本実施形態におけるプロジェクションスクリーン１１１を示す斜視図である。
プリズムレンズ１１３のさらに観察側には、レンチキュラーレンズ１１５が設けられている。なお、レンチキュラーレンズ１１５の具体的な形態は、図１０（ａ）に示すような第１実施形態と同様な形態（１１５Ａ）であってもよいし、図１０（ｂ）に示すような第２実施形態と同様な形態（１１５Ｂ）であってもよい。
【００５６】
図９に戻って、映像光源１１２は、プロジェクションスクリーンを入光面側から見たときにプリズムレンズ１１３の同心円と同じ高さとなる位置に設けられている。
プリズムレンズ１１３の入光側の面に形成されているプリズムは、同心円の中心からの距離により領域Ａ１，Ａ２，Ａ３の３領域に分けることができる。
領域Ａ１は、同心円の中心からの距離ｒ１よりも中心に近い位置にある第１の頂角固定領域であり、プリズムの頂角は、λ１で一定である。
領域Ａ２は、同心円の中心からの距離ｒ２よりも中心から遠い位置にある第２の頂角固定領域であり、プリズムの頂角は、λ２で一定である。
ここで、λ１とλ２とを比較すると、λ２の方がλ１よりも角度が大きくなっている（λ２＞λ１）。
【００５７】
領域Ａ３は、領域Ａ１と領域Ａ２とに挟まれた位置（同心円の中心からの距離ｒ１よりも中心から遠く、距離ｒ２よりも中心に近い位置）にある頂角変化領域（第１の頂角変化部）であり、プリズムの頂角がλ１〜λ２に変化する領域である。
領域Ａ３は、第２の面の角度が変化せずに、第１の面の角度が徐々に変化することにより、頂角がλ１〜λ２に徐々に変化するようになっている。
【００５８】
仮に領域Ａ３を設けずに、領域Ａ１と領域Ａ２のみを設けたとすると、スクリーン上のある位置において急に、λ１からλ２にプリズム頂角が変わってしまう。そうすると、その部分で、頂角だけでなく、第２の面（全反射面）の角度も急に変わる。しかも、中心側から外周側へ向けて徐々に面の角度が小さくなっていたものが、その位置では、逆に面の角度が大きくなるため、その境界がはっきりと観察される。そこで、本実施形態では、第２の面の角度が逆行しないように、第２の面の角度が一定の領域Ａ３を形成した。
【００５９】
図１２は、出射角θ₅ ＝０で、プリズムの頂角を３５°と４５°としたときの、入射角に対する、レンズ角度φの計算結果を示す図である。
例えば、フレネル中心に近い場所では、プリズムの頂角を３５°とし、フレネル中心から遠い場所では、プリズムの頂角を４５°とする場合を考える。この場合、仮に入射角５０°で急にプリズムの頂角を変えるとすると、中心部側から徐々にレンズ角度が小さくなっていたものが、その点で急に２．６°大きくなる。このようにしてしまうと、映像観察時にその境界が観察される可能性があり、好ましくない。
【００６０】
そこで、本実施形態では、図１２に実線で示したように、プリズム頂角を３５°から４５°へ変える場合には、例えば、入射角が５２．５°から５９．２°の範囲において、レンズ角（スクリーン面に対する第２の面の角度）が５７°一定であって、スクリーン面に対する第１の面の角度を徐々に変えることによりプリズム頂角を３５°から徐々に４５°へと変えるようにした。
【００６１】
また、本実施形態では、第１の面の逆テーパーを起こさず、鏡面である部分と粗面である部分とが形成されないようにするために、第１の面がスクリーン面に対する垂線に対して少なくとも１／１０００°以上外側（光源側）を向いているようにし、成形型の抜け勾配を確保するようにしている。したがって、第１の面（１１３ａ）は、表面の粗さがスクリーン全面に渡って均一である。
【００６２】
このようにすることにより、プリズムシート（フレネルレンズシート）の成形型の製造を容易に行うことができると共に、プリズムの頂角の変化を観察されにくくすることができる。
【００６３】
（第４実施形態）
第４実施形態は、第３実施形態をさらに改良し、プリズムの頂角の変化をさらに観察されにくくした形態である。したがって、ここでは、簡単のため第３実施形態と異なる部分のみ説明を行うものとする。
図１３は、第４実施形態におけるプロジェクションスクリーンを説明する図である。なお、図１３は、図９と同様に示している。
第４実施形態におけるフレネルレンズ２１３では、第３実施形態における領域Ａ１，Ａ２，Ａ３に相当する領域Ａ１’，Ａ２’，Ａ３’を有している。さらに、領域Ａ３’と領域Ａ１’及び領域Ａ２’との間に、それぞれ、領域Ａ４，Ａ５を有している。
【００６４】
本実施形態における領域Ａ４，Ａ５は、第３実施形態における領域Ａ１とＡ３との境界部、及び、領域Ａ２とＡ３との境界部の付近に所定の幅を持って設けられている。したがって、本実施形態における領域Ａ１’，Ａ２’，Ａ３’は、この領域Ａ４，Ａ５が存在する分だけ第３実施形態における領域Ａ１，Ａ２，Ａ３よりも狭くなっている。
【００６５】
第３実施形態における領域Ａ３では、第２の面の角度が変化せずに、第１の面の角度が徐々に変化することにより、頂角がλ１〜λ２に徐々に変化ようにした。しかし、この場合であっても、領域Ａ３と領域Ａ１，Ａ２との境界部分では、第２の面の角度（φ）の変化率の変化が他の部分に比べて大きく、プリズム形状の設定によっては、この境界部が目立ってしまうおそれがある。
そこで、本実施形態では、この境界部分を中心として所定の幅の領域に、第２の面の角度が徐々に変化する領域Ａ４，Ａ５（第２及び第３の頂角変化部）を設け、境界部が目立つことを防止している。
このように、第２の面の角度が一定な領域Ａ３’の両側に、第２の面の角度の変化率をなめらかに変化させる領域Ａ４，Ａ５を設けることで、映像観察上の違和感を更に低減させることができる。
【００６６】
本実施形態では、この領域Ａ４，Ａ５において、領域Ａ１’，Ａ２’，Ａ３’における第２の面の角度の変化を数式化し、これをスプライン補完して領域Ａ４，Ａ５における第２の面の角度の変化量を決定している。このスプライン補完の具体的な形態は、後述する実施例において説明する。
なお、この領域Ａ４，Ａ５においても、入射角度が、ともに、図５に示した２本の線の内側になければならない。
【００６７】
【実施例】
（実施例１）
実施例１は、第１実施形態に示したプロジェクションスクリーンの具体的な形態である。
図１に示す、プロジェクションスクリーンの形態図に基づきプロジェクションスクリーンの実施例について述べる。このプロジェクションスクリーンは５０インチ用で、全反射プリズムは同心円状で、その中心が画面上にない円弧状であり、円弧の半径は画面の下側中央で８００ｍｍ、プリズムピッチは１００μｍ、プリズム高さは１５０μｍとし、全反射プリズムの頂角は、スクリーンの下端で最もプリズム中心に近い部分の頂角を３７°、スクリーンの上端で最もプリズム中心から遠い部分の頂角を４０°とし、３７°〜４０°の範囲で連続的にプリズム頂角を変化させた。全反射プリズムは、ＮＣ旋盤により切削加工して得られる円弧状プリズム金型を用い、アクリル製のベースシート上の紫外線硬化性樹脂を成型加工することにより、厚さ２ｍｍのプリズムシートを得た。
【００６８】
次に、レンチキュラーレンズ製造用の円筒状のロール金型により、ピッチ１４０μｍでレンズ横径が１４０μｍ、レンズ縦径が１００μｍの半楕円形状で、レンズ高さが５０μｍのレンチキュラーレンズを押出し成型にて作製し、水平拡散角が半値角で３５°、垂直拡散角が半値角で１５°の特性を得た。なお、このレンチキュラーレンズシートの押出し成型の際に、耐衝撃性アクリル樹脂等に極微量の黒色染料及び拡散剤を混合することによりレンチキュラーレンズシートの透過率を７０％とし、外光等の反射防止効果及び拡散効果を付加した。
【００６９】
上記の、全反射プリズムシートとレンチキュラーレンズシートを組み合わせてプロジェクションスクリーンを構成した。
【００７０】
本実施例のプロジェクションスクリーンは、入射角の許容幅が広く、表面輝度の低下やコントラストの低下もなく、高画質の映像が得られた。
【００７１】
（実施例２）
実施例２は、第２実施形態に示したプロジェクションスクリーンの具体的な形態である。
図２に示すプロジェクションスクリーンの形態図に基づき、プロジェクションスクリーンの実施例について述べる。このプロジェクションスクリーン装置はスクリーン下方より打ち上げる投射系で、光源はＬＣＤライトバルブを用いており、入射角は下端で４５°、上端で６０°、プロジェクションスクリーンは５０インチである。
【００７２】
全反射プリズムは同心円状で、その中心は画面上にない円弧状であり、円弧の半径は画面の下側中央で８００ｍｍ、プリズムピッチは１００μｍ、プリズム高さは１５０μｍとし、全反射プリズムの頂角は、スクリーンの下端で最もプリズム中心に近い部分の頂角を３７°、スクリーンの上端で最もプリズム中心から遠い部分の頂角を４０°とし、３７°〜４０°の範囲でプリズム頂角を連続的に変化させた。全反射プリズムは、厚さ０．２ｍｍのアクリルフィルムをベースフィルムとし、ＮＣ旋盤により切削加工して得られる円弧状プリズム金型で、紫外線硬化性樹脂を用いて、所定条件のもとに露光し硬化させて、プリズムシートを作製した。
【００７３】
続いて、プリズムシートの反対側の面に断面が台形状のレンチキュラーレンズを形成し、さらに隣接する台形間のＶ字形状部分に光吸収粒子を含む低屈折率樹脂を充填した。台形状の高屈折率部の材料としてエポキシアクリレート、Ｖ字形状の低屈折率部としてウレタンアクリレート、光吸収粒子として大日精化工業（株）製「ラブコロール」（登録商標）を使用した。「ラブコロール」の平均粒径は８μｍで、添加量は４５重量％とした。台形状の高屈折率部のレンズピッチは５０μｍで屈折率は１．５７、Ｖ字形状の低屈折率部の屈折率は１．４８であった。また、台形の上底長さと、Ｖ字部の三角形底辺の長さを等しくなるようにし、いわゆるブラックストライプ率が５０％とし、Ｖ字部三角形の頂角を２０°に設定した。
【００７４】
上記の構成の全反射プリズムレンズとレンチキュラーレンズが１枚のシートの表裏に形成されたプロジェクションスクリーンは、透過率が８０％、反射率が５％、ゲインが４であった。また、垂直視野角（半値角：ある方向から観視したときの輝度が正面から観視したときの半分になる角度）は１２°、水平視野角（半値角）は２５°であった。
【００７５】
本実施例のプロジェクションスクリーンは、入射角の許容幅が広く、表面輝度の低下やコントラストの低下もなく、高画質の映像が得られた。
【００７６】
（実施例３）
実施例３は、実施例２をさらに改良した実施例である。
このプロジェクションスクリーンの構成は、上記の実施例２の、レンチキュラーレンズの前の最観察者側に、厚さ０．１ｍｍのＡＲコートフィルムをラミネートすること以外は同様のものであり、反射率は１．５％に改善できる。
【００７７】
（実施例４）
実施例４は、実施例１に示したプロジェクションスクリーンを用いた背面投射型のプロジェクションディスプイ装置の実施例である。
図４（ａ）に示すプロジェクションディスプイ装置３０は、映像光源としてＬＣＤライトバルブ３２を用い、上方に向かって、スクリーン下端に入射する映像光の入射角θ₁₁＝４５°、スクリーン上端に入射する映像光の入射角θ₁₀＝６０°となるようにプロジェクションスクリーン３１に映像を投射するシステムである。この場合、プロジェクションスクリーンと映像光源との水平状態での距離は略８０ｃｍである。
【００７８】
（実施例５）
実施例５は、実施例４に示した背面投射型のプロジェクションディスプイ装置の投射方向及び映像光源を変更した実施例である。
背面投射型プロジェクションディスプレイ装置の別な形態として、図４（ｂ）に示すように、映像光源にＤＭＤ用光源４２を用い、下方に向かって、８０インチのスクリーン上端に入射する映像光の入射角θ₂₀＝４５°、スクリーン下端に入射する映像光の入射角θ₂₁＝７０°、となるように映像をプロジェクションスクリーン４１上に投射する。この場合、プロジェクションスクリーンと映像光源との水平状態での距離は略７０ｃｍである。
【００７９】
（実施例６）
実施例６は、第３実施形態に示したプロジェクションスクリーンの具体的な形態である。
画面サイズ５５インチ（１６：９）、投射距離３４０ｍｍ、スクリーン面に対して光源の位置が画面下端より２５０ｍｍ下方に存在している薄型背面投射型のプロジェクションディスプイ装置（テレビ用）の透過型スクリーンを下記のようにして作成した。このプロジェクションスクリーンの下端中央部（フレネル中心からの距離２５０ｍｍ）への入射光の角度θ₁ は３６．３°、上端隅（フレネル中心からの距離１１１６ｍｍ）への入射光の角度θ₁ は、７３．０°である。
【００８０】
第３実施形態において説明した全反射タイプのフレネルレンズシート（プリズムシート）を、硬化後の屈折率が１．５５の紫外線硬化型樹脂を用いて作製した。出射角度θ₅ を零（垂直出射）、フレネル中心に近い側のプリズム先端角度λを３５°、遠い側の先端角度λを４０°とし、フレネル中心からの距離ｒ１＝５２９．６ｍｍ（入射角度５７．３°）からｒ２＝６０５．９ｍｍ（入射角度６０．７°）において、レンズ角度φを５５．２５°で一定とした。
【００８１】
図１４は、実施例６，７におけるフレネルレンズシートのプリズム先端角度が３５°から４０°へと変わる近傍のプリズム先端角度λの変化を示す図である。
図１５は、実施例６，７におけるフレネルレンズシートのプリズム先端角度が３５°から４０°へと変わる近傍のフレネルレンズ角度φの変化を示す図である。
図１４，１５において、実線が実施例６の場合を示している。
【００８２】
（実施例７）
実施例７は、第４実施形態に示したプロジェクションスクリーンの具体的な形態であり、実施例６をさらに改良したものである。
実施例６と同一のプロジェクションディスプイ装置用に、フレネル中心からの距離５００ｍｍから６５０ｍｍのフレネルレンズのレンズ角度φを５ノードのスプライン補完関数を用いて決定した以外は、実施例６と同様の全反射タイプのフレネルレンズを作製した。プリズム先端角度λの変化とフレネルレンズ角度φの変化を実施例６と同様に図１４及び図１５に破線により示した。以下に使用したスプライン関数式と定数を示す。
【００８３】
【数２】

【００８４】
また、パラメータは、以下の表に示す通りである。
【００８５】
【表１】

【００８６】
スプライン補完関数によってレンズ角φを決定後、下記式により入射面の角度γ及びプリズム頂角λを計算した。
【００８７】
【数３】

【００８８】
実施例６及び実施例７との比較用に従来技術による例として、比較例１及び比較例２に示すフレネルレンズシートを作製した。
（比較例１）
実施例６と同一のプロジェクションディスプイ装置用に、プリズム先端角度を４０°で一定のフレネルレンズシートを比較例１として作製した。
【００８９】
（比較例２）
実施例６と同一のプロジェクションディスプイ装置用に、フレネル中心からの距離が５４４ｍｍ（入射角５８．０°）のところより内側では、プリズム先端角度λが３５°で一定のフレネルレンズを作製した。このフレネルレンズでは、フレネル中心からの距離が５４４ｍｍのところより外側では、前記フレネルレンズの計算式では、γ＜０となるため、この場所より外側においても、投射光を垂直出射させるために、第１面（入射面）が垂直で、フレネルレンズの角度φを下記式により決定される値とした。
φ＝｛ａｒｃｓｉｎ（ｃｏｓθ１／ｎ）＋π／２｝／２
このフレネルレンズは、フレネル中心からの距離が５４４ｍｍのところより外側では、第１面（入射面）には、フレネルレンズの金型を切削したときに切削痕が形成されるために粗面となっており、また、プリズムの先端角度は、徐々に３５°より大きくなっている。
【００９０】
（実施例６，７及び比較例１，２の比較評価）
実施例６、実施例７と比較例１、比較例２のフレネルレンズシートをレンチキュラーレンズシートと組み合わせて透過型スクリーンを構成し、上述の、画面サイズ５５インチ（アスペクト比は１６：９）、投射距離３４０ｍｍ、スクリーン面に対して光源の位置が画面下端より２５０ｍｍ下方に存在している薄型背面投射型のプロジェクションディスプイ装置に実装して比較評価を行った。
実施例６及び実施例７による背面投射型スクリーンは、共に均一で良好な画面であった。
【００９１】
一方、比較例１の背面投射型スクリーンでは、画面下部中央付近が他のフレネルレンズを用いた背面投射型スクリーンに比べてやや暗く、また、ゴーストが観察された。
比較例２の背面投射型スクリーンでは、フレネル中心からの距離が５４４ｍｍのところの第１面の角度が変わる境界が観察された。
【００９２】
（変形形態）
以上説明した実施形態に限定されることなく、種々の変形や変更が可能であって、それらも本発明の均等の範囲内である。
（１）各実施形態において、全反射プリズムシート（フレネルレンズシート）及びプロジェクションスクリーンの形状を具体的に示したが、これに限らず、頂角を変えた中心が画面上にない同心円状の全反射プリズムシートは、考えられる構成を全てとることができ、また、プロジェクションスクリーンも考えられる構成を全てとることができる。
【００９３】
（２）各実施形態において、プロジェクションスクリーンには、観察者側にさらに拡散剤を混入した拡散シートを張り合わせてもよい。
【００９４】
（３）第２〜第４実施形態において、プロジェクションスクリーンには、観察者側にさらに、ＡＲ、ＡＧ、ＡＳ、ＨＣ、防汚、センサー等の機能を付与してもよい。
【００９５】
（４）各実施形態において、プロジェクションディスプイ装置は、映像光源からプロジェクションスクリーンに対して直接映像光を投射する例を示したが、これに限らず、たとえば、図１６に示すように、映像光源からの映像光を鏡に反射させてからプロジェクションスクリーンへ投射するようにしてもよい。
【００９６】
【発明の効果】
以上詳しく説明したように、本発明によれば、以下の効果を奏することができる。
（１）映像光源からプロジェクションスクリーンへ上方あるいは下方へ映像を投射する投射系を備えたプロジェクションディスプレイ装置において、プロジェクションスクリーンの最入光面側に頂角が位置によって角度変化している全反射円弧状プリズムを設けることにより、入射光の許容幅を広くし、表面輝度の低下やコントラストの低下がなく、映像光源より平行に映像を投射した場合と同等レベルの高画質のプロジェクションスクリーン及びプロジェクションディスプレイ装置が得られる。
【００９７】
（２）プリズムの頂角が所定の角度で一定である第１の頂角固定領域と、頂角が第１の頂角固定領域の頂角とは異なる所定の角度で一定である第２の頂角固定領域と、頂角が変化している頂角変化領域とを設けたので、全反射プリズムシートの製造に使用する成形型の製造が容易になり、高画質なプロジェクションスクリーン及びプロジェクションディスプレイ装置をより安価にすることができる。
【００９８】
（３）頂角変化領域は、第１の頂角変化部と第１及び第２の頂角固定領域との間に、第１の面及び第２の面のいずれも変化することにより頂角が変化する第２及び第３の頂角変化部を有するので、各領域の境界部分をより目立たなくすることができ、さらなる高画質化を図ることができる。
【００９９】
（４）第１の面は、スクリーン面に対する垂線に対して１／１０００度以上の抜け勾配を有しているので、迷光を無くして映像光のロスを防ぐことができる。また、成形型が逆テーパーとならないので、成形型の作製が容易であり、プリズムの離型も容易に行うことができる。
【０１００】
（５）第１の面は、表面の粗さがスクリーン全面に渡って均一であるので、位置により像にむらが生じることなく、高画質な像を観察することができる。
【図面の簡単な説明】
【図１】本発明によるプロジェクションスクリーンの第１実施形態を示す部分形態図である。
【図２】本発明によるプロジェクションスクリーンの第２実施形態を示す図である。
【図３】第２実施形態におけるプロジェクションスクリーンの水平断面模式図である。
【図４】本発明の映像光源からの映像をプロジェクションスクリーン上に投射する状態を説明する図である。
【図５】プリズムの頂角に対する迷光の存在する入射光の角度の境界と、第１の面が逆テーパーになる入射光の角度を、出射角θ₅ ＝０で、レンズ部分の屈折率が１．５５について、計算した結果を示した図である。
【図６】一般的なプロジェクションスクリーンを説明する図である。
【図７】全反射プリズムの頂角を大きくした場合の映像光の光路である。
【図８】全反射プリズムの頂角を小さくした場合の映像光の光路である。
【図９】第３実施形態におけるプロジェクションスクリーンを説明する図である。
【図１０】本実施形態におけるプロジェクションスクリーン１１１を示す斜視図である。
【図１１】本実施形態におけるプリズムレンズ１１３の一部を拡大して示した断面図である。
【図１２】出射角θ₅ ＝０で、プリズムの頂角を３５°と４５°としたときの、入射角に対する、レンズ角度φの計算結果を示す図である。
【図１３】第４実施形態におけるプロジェクションスクリーンを説明する図である。
【図１４】実施例６，７におけるフレネルレンズシートのプリズム先端角度が３５°から４０°へと変わる近傍のプリズム先端角度λの変化を示す図である。
【図１５】実施例６，７におけるフレネルレンズシートのプリズム先端角度が３５°から４０°へと変わる近傍のフレネルレンズ角度φの変化を示す図である。
【図１６】プロジェクションディスプイ装置の変形形態を示す図である。
【符号の説明】
１ プロジェクションスクリーン
２ 全反射円弧状プリズム
３ プリズムシート
４ レンチキュラーレンズ
５ レンチキュラーレンズシート
２１ プロジェクションスクリーン
２２ 全反射円弧状プリズム
２３ ベースシート
２４ レンチキュラーレンズ
２５ 台形状高屈折率部
２６ Ｖ字形状低屈折率部
３０ プロジェクションディスプレイ装置
３１ プロジェクションスクリーン
３２ 液晶ライトバルブ
４０ プロジェクションディスプレイ装置
４１ プロジェクションスクリーン
４２ ＤＭＤ用光源
７２ 全反射プリズム
８２ 全反射プリズム
１００ プロジェクションスクリーン
１０１ フレネルレンズシート
１０１ｂ フレネルレンズ
１０２ レンチキュラーレンズシート
１１１，２１１ プロジェクションスクリーン
１１２ 映像光源
１１３，２１３ フレネルレンズ
１１３ａ 第１の面
１１３ｂ 第２の面
１１５，１１５Ａ，１１５Ｂ レンチキュラーレンズ
Ａ１，Ａ１’ 領域（第１の頂角固定領域）
Ａ２，Ａ２’ 領域（第２の頂角固定領域）
Ａ３，Ａ３’ 領域〔頂角変化領域（第１の頂角変化部）〕
Ａ４ 領域（第２の頂角変化部）
Ａ５ 領域（第３の頂角変化部）[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a projection screen and a projection display apparatus suitable for obliquely projecting and observing an image from an image light source having a cell structure such as an LCD (Liquid Crystal Display), a DMD (Digital Micro-mirror Device), or the like. It is about.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, there has been known a rear projection type projection display apparatus that uses three CRTs of red, green, and blue as image light sources and uses a transmissive projection screen as a projection screen. In general, a projection screen is composed of a Fresnel lens sheet and a lenticular lens sheet, and is used to form an image of image light from a projector on the projection screen to obtain a diffusing surface with directivity. It is what is done. As shown in FIG. 6, the projection screen 100 is disposed on the observation side of the Fresnel lens sheet 101 in which a circular type Fresnel lens 101b is formed on the light output side, and horizontally on the light incident side. A lenticular lens for diffusion is formed, and a lenticular lens sheet 102 having a black stripe on the light output side is provided.
[0003]
The Fresnel lens has a function of forming grooves having a predetermined angle at a predetermined pitch in a transparent resin material such as acrylic, and condensing light diffused radially from the image light source to the front.
[0004]
A lenticular lens is a lens for obtaining diffused light that has directivity in the horizontal direction. Cylindrical lens-shaped lenses are regularly formed in a vertical direction on a single plane, and the light distribution characteristics in the horizontal direction. It has a function that can be expanded.
[0005]
In recent years, instead of the projection method using three CRTs of red, green, and blue, a projection display apparatus that projects an image on a projection screen from an image light source having a cell structure such as an LCD or DMD, and observes the image Needs such as are increasing. In such a single-lens rear projection television using an LCD, DMD, or the like, since a method in which image light is incident substantially perpendicularly to the center of the projection screen is generally used, a CRT is used. It needed almost the same depth as the rear projection TV.
[0006]
On the other hand, as one of the projection display devices, the projection screen and the projection can be greatly reduced in thickness by projecting the image obliquely on the projection screen and observing the image without losing the quality of the image. Attempts have been made with regard to the system from various fields such as Patent Document 1 and Patent Document 2.
[0007]
[Patent Document 1]
Japanese Patent Laid-Open No. 61-208041
[Patent Document 2]
JP 2000-180967 A
[0008]
[Problems to be solved by the invention]
In the case of a projection screen using a total reflection Fresnel lens used in such a projection system, on the side close to the light source, that is, close to the center of the Fresnel, as shown in FIG. A part of the light was not totally reflected by the total reflection surface, but was lost and became stray light, causing problems such as a double image (ghost). In FIG. 7, the optical path of normal image light is L10, and L11 indicates a component that becomes stray light. Such stray light is generated more as the apex angle of the total reflection prism is larger, and is smaller as the total reflection prism is smaller.
[0009]
On the other hand, on the side far from the light source, that is, far from the center of the Fresnel, as shown in FIG. 8, when the apex angle of the total reflection prism 82 is small, the incident light side surface of the prism becomes a reverse taper, and the incident light L22 is totally absorbed. After reflection on the reflecting surface, the light hits the incident surface again and is reflected to become stray light, causing a problem of loss of image light. For comparison, L21 shows the case of normal light. Furthermore, it is difficult to produce a mold with a reverse-tapered prism, and there is a problem that the mold and the prism are reversely released even in lens molding, which makes it difficult to release the prism. When a die is cut and a prism is manufactured using the die, the reverse taper of the first surface of the prism is impossible in terms of die cutting, so a cut mark is formed on the first surface. The resulting vertical rough surface. For this reason, the portion where the first surface is a mirror surface and the portion where the surface is rough are present on the same prism sheet, and the appearance of the image is different (observed as image unevenness) near this boundary. There was a problem that. As described above, the conventional projection screen disclosed in Patent Document 1 has a problem that the allowable width of the incident angle at which the image light is not lost is narrow.
[0010]
Therefore, the present invention eliminates the loss of image light due to stray light, further increases the allowable angle of incidence, does not decrease the surface brightness and does not decrease the contrast, and projects the image quality vertically from the image light source to the center of the projection screen. A projection screen and a projection display device that maintain the same level as the above and have a good contrast are provided.
[0011]
[Means for Solving the Problems]
  The present invention solves the above problems by the following means. For ease of understanding, the reference numerals corresponding to the embodiments of the present invention are used for explanation, but the present invention is not limited thereto..
[0013]
  Claim 1The invention ofRear projection type projection display device (30, 30) having a projection system for projecting an image upward or downward from the image light source (32, 42, 112) to the projection screen (1, 21, 31, 41, 100, 111, 211). 40), and a total reflection prism (2, 22, 72, 82) in which the apex angle of the prism is changed depending on the position of the prism is provided concentrically on the most incident light surface side of the screen. , The center of the concentric circle is not on the screen,In the apex angle of the concentric total reflection prism, the apex angle on the far side is larger than the apex angle on the side close to the center of the concentric circle.The apex angle of the prism was changed according to the position of the prism so thatThis is a projection screen characterized by that.
[0014]
  Claim 2The invention ofClaim 1In the projection screen described above, the vertex angle of the total reflection prism (2, 22, 72, 82) with the vertex angle changed is changed depending on the position of the prism within a range of 30 ° to 45 °. Is a projection screen.
[0015]
  Claim 3The invention ofClaim 1 or claim 2The projection screen according to the item 1, wherein the apex angle changes continuously.
[0016]
  Claim 4The invention ofClaims 1 to 3The projection screen according to any one of the preceding claims, wherein the apex angle is fixed at a predetermined angle, the first apex angle fixing region (A1, A1 '), and the apex angle is the first apex angle fixing. A second apex angle fixed region (A2, A2 ′) that is constant at a predetermined angle different from the apex angle of the region, and an apex angle change region (A3, A3 ′, A4, A5) in which the apex angle changes And a projection screen characterized by comprising:
[0017]
  Claim 5The invention ofClaim 4The total reflection prism may include a first surface (113a) that refracts incident video light projected from the projection system, and total reflection of the image light from the first surface in the observation direction. The apex angle is formed by an angle formed by the first surface and the second surface, and the apex angle changing region includes the second surface (113b). The first apex angle changing portion (A3, A3 ′) in which the apex angle changes continuously by changing the absolute angle of the first surface continuously without changing the absolute angle of the surface. It is a projection screen characterized by having.
[0018]
  Claim 6The invention ofClaim 5In the projection screen described in (1), the apex angle changing region includes the first surface (113a) and the first apex angle changing portion between the first apex angle changing unit and the first and second apex angle fixing regions. The projection screen is characterized by having second and third apex angle changing portions (A4, A5) in which the apex angle changes by changing any of the two surfaces (113b).
[0019]
  The invention of claim 7Claim 5 or claim 6In the projection screen described in (1), the first surface (113a) has a draft angle of 1/1000 degrees or more with respect to a perpendicular to the screen surface.
[0020]
  The invention of claim 8Claim 5The projection screen according to any one of claims 1 to 7, wherein the first surface (113a) has a uniform surface roughness over the entire screen. .
[0021]
  Claim 9The invention of claim 1 starts from claim 1.Claim 8The projection screen according to any one of the above, wherein a lenticular lens (4, 24, 115, 115A, 115B) is provided closer to the viewer than the total reflection prism having a different apex angle. Projection screen.
[0022]
  Claim 10The invention ofClaim 9In the projection screen described in (1), the lenticular lens (24, 115B) is a projection screen characterized in that a unit lens has a trapezoidal cross section.
[0023]
  Claim 11The invention ofClaim 10The projection screen according to claim 1, wherein the lower base of the trapezoidal lenticular lens (24, 115B) is a light incident part and the upper base is a light emission part.
[0024]
  Claim 12The invention ofClaim 10 or Claim 11In the projection screen described in (1), the trapezoidal lenticular lens (24, 115B) is formed of a material having a predetermined refractive index, and the cross section between adjacent unit lenses has a V-shaped portion more than the trapezoidal portion. A projection screen, characterized in that it is a lenticular lens made of a material having a low refractive index and using a total reflection effect by the interface between the V-shaped part and the trapezoidal part.
[0025]
  Claim 13The invention ofClaim 12In the projection screen described in (1), the V-shaped low refractive index portion of the trapezoidal lenticular lens (24, 115B) has a light absorbing action.
[0026]
  Claim 14The invention ofClaim 13The projection screen according to claim 1, wherein the light absorbing action is caused by mixing light absorbing particles in a low refractive index resin.
[0027]
  Claim 15The invention of claim 1 starts from claim 1.Claim 14In the projection screen according to any one of the above, the lenticular lens (24) and the total reflection prism (22) with the apex angle changed are formed on the front and back of one sheet (23). This is a characteristic projection screen.
[0028]
  Claim 16The invention of claim 1 starts from claim 1.Claim 155. The projection screen according to any one of the above, wherein a diffusion sheet is further provided on the viewer side.
[0029]
  Claim 17The invention of claim 1 starts from claim 1.Claim 16The projection screen according to any one of the above, wherein the observer side has at least one function of AR, HC, AS, AG, antifouling, and a sensor. is there.
[0030]
  Claim 18The invention of claim 1 starts from claim 1.Claim 17The projection screen (1, 21, 31, 41, 100, 111, 211) described in any one of the above, an image light source (32, 42, 112), and image light from the image light source is converted into the projection screen. And a projection system for projecting to the projection display device.
[0031]
(Function)
In the rear projection type projection display apparatus, when the incident angle of the image light to the projection screen is up or down at all positions, a total reflection prism can be arranged on the light incident surface side. . At this time, if the total reflection prism is a concentric circular arc prism with no center on the screen, the optical axis can be corrected only on the light incident surface side. The apex angle of the concentric total reflection prism is such that the apex angle on the side farther from the center of the concentric circle is larger than the apex angle on the side near the center of the concentric circle within a certain angle range. By changing the angle, it is possible to eliminate loss of image light due to stray light and widen the allowable range of incident angles.
[0032]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in more detail with reference to the drawings.
The projection screen of the present invention is provided with a total reflection prism in which the apex angle of the prism is changed depending on the position of the prism on the most incident light surface side of the screen. When using a lenticular lens, the prism surface and the lenticular lens surface may be composed of separate prism sheets and lenticular lens sheets, respectively, and the prism surface and the lenticular lens surface may be configured on the front and back of one sheet. In the present invention, any case can be implemented. As the lenticular lens of the present invention, either a lens whose unit lens has a semi-elliptical cross section or a trapezoidal lens can be used. In addition to the above-described configuration, an embodiment in which an observer is further provided with a diffusion sheet is also included in the embodiment of the present invention. Furthermore, instead of using the lenticular lens, a diffusion sheet or a bead screen can be used.
[0033]
(First embodiment)
FIG. 1 is a partial view showing a first embodiment of a projection screen according to the present invention.
The projection screen 1 according to this embodiment includes a prism sheet 3 on which a total reflection prism 2 having a concentric circular shape whose center is not on the screen and having the apex angle λ changed depending on the position on the most incident light surface side, and the prism. The lenticular lens sheet 5 is further provided on the observation side of the sheet 3, and a lenticular lens 4 for horizontal diffusion is formed on the light incident side. In FIG. 1, the prism sheet 3 and the lenticular lens sheet 5 are shown separated from each other for easy understanding.
[0034]
A plurality of concentric total reflection prisms 2 are arranged in an arc shape with a prism pitch of 100 to 200 μm and a prism height of 150 to 300 μm. In FIG. 1, the apex angle λ of the prism is 30 ° or more and 45 °. It is preferable to make it below, and it changes with the position of the prism within this angular range. The apex angle λ of the total reflection prism 2 is within the angle range of 30 ° to 45 °, and the apex on the side farther from the center of the concentric circle (upper side of the drawing) than the apex angle on the side closer to the center of the concentric circle (lower side of the drawing). The angle is continuously changed so that the corner becomes larger.
[0035]
Note that arrows (solid lines) in FIG. 1 are output from image light sources such as LCDs and DMDs, and projected from the incident light of the image light projected through a projection system (projection optical system) (not shown) to the projection screen. It shows the optical path up to. Next, the optical path will be described. First, by setting the incident light and the prism angle, the incident light enters from the incident surface side of the concentric total reflection prism 2, is totally reflected by the total reflection surface, and is emitted vertically from the prism sheet 3, and the lenticular lens 4. The light path is such that the light enters the light and exits vertically from the lenticular lens sheet 5 to the observation side.
[0036]
The lenticular lens 4 shown in FIG. 1 is, for example, a semi-elliptical shape having a pitch of 140 μm, a lens lateral diameter of 140 μm, and a lens vertical diameter of 100 μm, a lens height of 50 μm, and a horizontal diffusion angle of 20 to 50 ° with a half-value angle. Can be used.
[0037]
Here, a specific shape of the prism in the present embodiment will be described.
FIG. 11 is an enlarged cross-sectional view showing a part of the prism lens 113 in the present embodiment.
The image light from the light source has different incident angles (incident angles with respect to the prism lens sheet surface) θ depending on the position of the prism sheet.₁The light enters the first surface (113a) of the prism of the prism sheet. The image light incident on the first surface is incident on the first surface, is totally reflected by the second surface (113b), and travels almost vertically to the surface on the observation side.
Therefore, the lens angle (angle of the second surface) φ of the total reflection type Fresnel lens used in the present invention is the incident angle θ.₁, N is the refractive index of the material of the Fresnel lens, and θ is the angle at which the image light travels with respect to the normal of the sheet after being reflected by the second surface of the prism._FourIf the tip angle (vertical angle) of the prism is λ, it is expressed by the following equation.
[0038]
[Expression 1]

[0039]
If the observation side surface is a flat surface, the output angle θ of the light beam emitted from the prism lens 113_FiveAnd the angle θ of the image light in the seat_FourThe following formula is established between
sinθ_Four= Sinθ_Five/ N
However, γ = φ + λ−π / 2 ≧ 0.
This is because when γ is negative, the shape of the first surface of the prism is inversely tapered, so that the Fresnel lens and the Fresnel lens mold cannot be manufactured in practice. θ_FourIs approximately zero, φ is θ₁Γ is the angle of incidence θ₁It tends to be negative at the large outer periphery. The condition for preventing the first surface (incident surface) of the prism from being reversely tapered is expressed by the following equation.
cos^-1{Cos (θ₁) / N} / 2 ≦ λ
[0040]
On the other hand, in a place near the Fresnel center of the prism lens 113, there is light that becomes stray light without being totally reflected by the second surface after entering the first surface. Therefore, as shown in FIG. 11, the incident light in one prism enters the position of the boundary between the part that becomes stray light and the part that becomes effective light, that is, incident from the first surface, Consider the light that refracts just into the valley of the prism. The angle of incidence on the first surface of the prism is θ₂, The refraction angle of the first surface of the prism is θ_Three, P is the lens pitch of the prism lens 113 (Pitch of the Fresnel lens), and e is the portion that can be suitably used by being totally reflected by the second surface of the prism.₁, The part which becomes stray light without being totally reflected by the second surface of the prism e₂, Where h is the height of the prism, and s is the height of the boundary between the stray light portion and the effective portion of the first surface of the prism, the effective portion e₁Is represented by the following equation.
e₁= (H−s) × (tan (φ + λ−π / 2) + tan θ₁)
[0041]
Here, the height h of the prism and the height s of the boundary between the stray light portion and the effective portion of the first surface of the prism can be expressed by the following equations, respectively.
h = p × tan (φ + λ) × tanφ / (tan (φ + λ) −tanφ)
s = −p × tan (φ + λ) / (1 + tan (φ + λ) × tan (φ + λ + θ)_Three))
And θ_Three= Arcsin {sin (θ₁+ Φ + λ) / n}.
[0042]
From FIG. 11, clearly e₁≦ p. Ratio of effective part to pitch e₁/ P is the incident angle θ₁The larger the value, the larger₁= P. Incident angle θ from there₁Is large, the light is incident from the first surface of the prism, and is a region where there is no stray light traveling toward the observation side surface without being totally reflected by the second surface.
[0043]
FIG. 5 shows the angle between the incident light where stray light exists with respect to the apex angle of the prism and the angle of the incident light where the first surface is inversely tapered._FiveFIG. 10 is a diagram illustrating a calculation result when = 0 and a refractive index of a lens portion is 1.55.
[0044]
In FIG. 5, the area surrounded by the two lines is a region where there is no stray light near the Fresnel center and no reverse taper of the first surface at a position far from the Fresnel center. For example, when the prism apex angle is 35 °, the allowable incident light angle of the lens is about 45 to 60 °. On the other hand, when the prism apex angle is 45 °, even with image light from directly below, the light incident surface is vertical and the reflection surface is 45 °, and light loss is eliminated. Therefore, if importance is placed on prevention of stray light near the center of the Fresnel, it is preferable that the prism apex angle is small, and conversely, the first surface at a place far from the center of the Fresnel is prevented from being reversely tapered. If this is emphasized, the prism apex angle is preferably larger.
Accordingly, in the range of the apex angle of the total reflection prism from 30 ° to 45 °, the apex angle of the prism is reduced at a location close to the Fresnel center, and the apex angle of the prism is increased at a location far from the Fresnel center. A good Fresnel lens can be obtained from a location close to the center to a location far away.
[0045]
In addition, it is also desirable to provide functions such as AR, AG, AS, HC, antifouling, and sensors to the observer side of the projection screen configured as described above. Here, an outline of the functions of the AR, AG, AS, HC, antifouling, and sensor will be described. First, AR is an abbreviation for anti-reflection, and is obtained, for example, by laminating a film having a function of suppressing the reflectance of light incident on the lens surface, or by directly AR processing the lens surface. AG is an abbreviation for anti-glare and can be obtained by laminating a film having an anti-glare function of a lens or by directly performing AG treatment on the lens surface. AS is an abbreviation for anti-static, and can be obtained by laminating an antistatic film on the lens surface or by directly AS-treating the lens surface. HC is an abbreviation for hard coat, and is obtained by laminating a wear-resistant film that increases the strength of the lens surface and does not cause scratches, or by directly treating the lens surface with HC. Antifouling is obtained by laminating a film or the like that prevents dirt from adhering to the lens surface, or by directly antifouling the lens surface. And a sensor means provision of functions, such as a touch sensor.
[0046]
(Second Embodiment)
FIG. 2 is a diagram showing a second embodiment of the projection screen according to the present invention.
In the projection screen 21 of this embodiment, a concentric total reflection prism 22 whose apex angle λ2 is changed by the position of the prism is formed on the light incident side surface of the base sheet 23, and the light exiting side surface of the base sheet 23 is formed. In addition, a lenticular lens 24 composed of a high refractive index portion 25 having a trapezoidal cross section and a V-shaped low refractive index portion 26 is formed as a unit lens. The apex angle λ2 of the total reflection prism 22 is within the angle range of 30 ° to 45 °, and the apex on the side farther from the center of the concentric circle (upper side of the drawing) than the apex angle on the side closer to the center of the concentric circle (lower side of the drawing). The angle is continuously changed so that the corner becomes larger.
[0047]
The trapezoidal lenticular lens 24 is formed of a material having a predetermined refractive index with a lower base as a light entrance portion and an upper base as a light exit portion. A V-shaped portion 26 between adjacent unit lenses is a trapezoidal portion 25. It is a lens that is made of a material having a lower refractive index and diffuses image light by using the total reflection effect by the interface between the V-shaped portion 26 and the trapezoidal portion 25.
[0048]
There is an image light source (not shown) below the right front side of the sheet of FIG. 2, and the image light projected obliquely upward enters the total reflection prism 22 and is totally reflected and substantially orthogonal to the screen surface. After being converted to image light that is emitted in the direction and emitted from the prism 22, the light enters the trapezoidal lenticular lens 24 from the lower bottom side of the trapezoid, and the trapezoidal high refractive index portion 25 and the V-shaped low refractive index portion. The light is totally reflected at the interface with the light 26 and emitted, and reaches an observer (not shown) at the back left side of the drawing.
[0049]
FIG. 3 is a schematic horizontal sectional view of a projection screen according to the second embodiment.
The cross section of the lenticular lens 24 is a trapezoidal shape 25, and a V-shaped low refractive index portion 26 between adjacent trapezoids is filled with a material having a lower refractive index than the material constituting the lenticular lens 24. . In order to use the total reflection effect at the interface between the trapezoidal high refractive index portion 25 and the V-shaped low refractive index portion 26, the material of the V-shaped portion 26 is more relative to the material constituting the trapezoidal lens 25. However, the material is not particularly limited, and for example, a synthetic resin material having a low refractive index is used.
[0050]
The synthetic resin material having a low refractive index preferably has a light absorbing action, and the light transmitted through the trapezoidal slope portion of the lenticular lens 24 can be absorbed by the V-shaped portion 26 having the light absorbing action.
[0051]
The V-shaped portion 26 having a light absorbing action can be formed by mixing light absorbing particles made of dyes, pigments, or colored resin fine particles in a low refractive index resin.
[0052]
Note that the projection screen according to the present invention described in the first embodiment and the second embodiment has the incident light incident on the screen at the end of the light incident surface side closer to the light source (side closer to the center of the Fresnel lens). Angle θ₁Can be suitably used for a projection display device in which the angle is 35 ° or more, preferably 45 ° or more and 50 ° or less.
[0053]
(Third embodiment)
In the first and second embodiments, an example is shown in which the apex angle of the prism continuously changes over the entire projection screen.
However, in manufacturing a mold for manufacturing a prism, changing the apex angle of the prism at all positions requires a great number of processing steps. Therefore, the processing cost of the mold for manufacturing the projection screen shown in the first and second embodiments is high, and as a result, the projection screen is also expensive.
Therefore, instead of continuously changing the apex angle of the prism over the entire projection screen, provide a region where the apex angle of the prism is large, a region where the apex angle is small, and a region where the apex angle changes between them. Thus, the region where the apex angle of the prism, which is difficult to manufacture the mold, is reduced.
[0054]
Since the projection screen 111 in the third embodiment is a form in which the shape of the total reflection arc-shaped prism in the first and second embodiments is changed, description of a part having a function common to the first and second embodiments will be given. This is omitted as appropriate.
FIG. 9 is a diagram for explaining a projection screen according to the third embodiment. 9A is a view of the projection screen as viewed from the light incident surface side (prism lens 113 side), and FIG. 9B is a view as viewed from the side surface.
As in the first and second embodiments, the projection screen 111 according to the present embodiment is a prism sheet (Fresnel lens) in which a total reflection prism that is concentric and has no center (Fresnel center) on the screen is formed on the most incident light surface side. Sheet) 113 is provided.
[0055]
FIG. 10 is a perspective view showing the projection screen 111 in the present embodiment.
On the further observation side of the prism lens 113, a lenticular lens 115 is provided. The specific form of the lenticular lens 115 may be the same form (115A) as the first embodiment as shown in FIG. 10 (a) or the second form as shown in FIG. 10 (b). The form (115B) similar to the embodiment may be used.
[0056]
Returning to FIG. 9, the image light source 112 is provided at the same height as the concentric circle of the prism lens 113 when the projection screen is viewed from the light incident surface side.
The prism formed on the light incident side surface of the prism lens 113 can be divided into three regions A1, A2, and A3 according to the distance from the center of the concentric circle.
The area A1 is a first apex angle fixed area located closer to the center than the distance r1 from the center of the concentric circle, and the apex angle of the prism is constant at λ1.
The area A2 is a second apex angle fixed area located farther from the center than the distance r2 from the center of the concentric circle, and the apex angle of the prism is constant at λ2.
Here, when comparing λ1 and λ2, the angle of λ2 is larger than that of λ1 (λ2> λ1).
[0057]
The region A3 is an apex angle changing region (first apex angle) located at a position sandwiched between the regions A1 and A2 (a position farther from the center than the distance r1 from the center of the concentric circle and closer to the center than the distance r2). This is a region where the apex angle of the prism changes from λ1 to λ2.
In the area A <b> 3, the apex angle gradually changes from λ <b> 1 to λ <b> 2 by gradually changing the angle of the first surface without changing the angle of the second surface.
[0058]
If only the area A1 and the area A2 are provided without providing the area A3, the prism apex angle suddenly changes from λ1 to λ2 at a certain position on the screen. Then, not only the apex angle but also the angle of the second surface (total reflection surface) changes suddenly at that portion. In addition, the angle of the surface gradually decreases from the center side toward the outer peripheral side, but at that position, the angle of the surface increases conversely, so that the boundary is clearly observed. Therefore, in the present embodiment, the region A3 in which the angle of the second surface is constant is formed so that the angle of the second surface does not reverse.
[0059]
FIG. 12 shows the output angle θ_FiveIt is a figure which shows the calculation result of lens angle (phi) with respect to an incident angle when = 0 and the vertex angle of a prism is 35 degrees and 45 degrees.
For example, consider a case where the apex angle of the prism is 35 ° near the Fresnel center and the apex angle of the prism is 45 ° far from the Fresnel center. In this case, if the apex angle of the prism is suddenly changed at an incident angle of 50 °, the lens angle gradually decreases from the center side, but suddenly increases by 2.6 ° at that point. If it does in this way, the boundary may be observed at the time of image observation, and it is not preferable.
[0060]
Therefore, in the present embodiment, as shown by the solid line in FIG. 12, when the prism apex angle is changed from 35 ° to 45 °, for example, in the range of the incident angle from 52.5 ° to 59.2 °, The lens angle (the angle of the second surface with respect to the screen surface) is constant 57 °, and the prism apex angle is gradually changed from 35 ° to 45 ° by gradually changing the angle of the first surface with respect to the screen surface. I did it.
[0061]
Further, in the present embodiment, the first surface is not perpendicular to the screen surface in order to prevent the first surface from being inversely tapered and to prevent a mirror surface portion and a rough surface portion from being formed. At least 1/1000 ° or more is directed outward (light source side) so as to ensure a mold exit gradient. Therefore, the roughness of the surface of the first surface (113a) is uniform over the entire screen.
[0062]
By doing in this way, the shaping | molding die of a prism sheet (Fresnel lens sheet) can be manufactured easily, and the change of the apex angle of a prism can be made hard to be observed.
[0063]
(Fourth embodiment)
In the fourth embodiment, the third embodiment is further improved, and the change in the apex angle of the prism is further difficult to observe. Accordingly, only the parts different from the third embodiment will be described here for simplicity.
FIG. 13 is a diagram for explaining a projection screen according to the fourth embodiment. FIG. 13 shows the same as FIG.
The Fresnel lens 213 in the fourth embodiment has areas A1 ', A2', A3 'corresponding to the areas A1, A2, A3 in the third embodiment. Further, regions A4 and A5 are provided between the region A3 'and the regions A1' and A2 ', respectively.
[0064]
The regions A4 and A5 in the present embodiment are provided with a predetermined width in the vicinity of the boundary between the regions A1 and A3 and the boundary between the regions A2 and A3 in the third embodiment. Accordingly, the regions A1 ', A2', A3 'in the present embodiment are narrower than the regions A1, A2, A3 in the third embodiment by the presence of the regions A4, A5.
[0065]
In the region A3 in the third embodiment, the apex angle is gradually changed from λ1 to λ2 by gradually changing the angle of the first surface without changing the angle of the second surface. However, even in this case, the change in the change rate of the angle (φ) of the second surface is larger at the boundary portion between the region A3 and the regions A1 and A2 than at the other portions. There is a risk that this boundary portion will be noticeable.
Therefore, in the present embodiment, regions A4 and A5 (second and third apex angle changing portions) in which the angle of the second surface gradually changes are provided in a region having a predetermined width around the boundary portion, The boundary is prevented from being noticeable.
As described above, by providing the regions A4 and A5 that smoothly change the change rate of the angle of the second surface on both sides of the region A3 ′ where the angle of the second surface is constant, the sense of incongruity in image observation is further increased. Can be reduced.
[0066]
In the present embodiment, in the regions A4 and A5, the change in the angle of the second surface in the regions A1 ′, A2 ′, and A3 ′ is mathematically expressed, and this is spline-complemented to correct the second surface in the regions A4 and A5. The amount of change in angle is determined. A specific form of this spline interpolation will be described in an embodiment described later.
Also in these areas A4 and A5, both incident angles must be inside the two lines shown in FIG.
[0067]
【Example】
Example 1
Example 1 is a specific form of the projection screen shown in the first embodiment.
An embodiment of the projection screen will be described based on the schematic diagram of the projection screen shown in FIG. This projection screen is for 50 inches, the total reflection prism is concentric, and its center is an arc shape not on the screen, the radius of the arc is 800 mm at the lower center of the screen, the prism pitch is 100 μm, and the prism height is The apex angle of the total reflection prism is 37 °, the apex angle of the portion closest to the prism center at the lower end of the screen is 37 °, and the apex angle of the portion farthest from the prism center at the upper end of the screen is 40 °. The prism apex angle was continuously changed in the range of °. As the total reflection prism, an arc-shaped prism mold obtained by cutting with an NC lathe was used, and an ultraviolet curable resin on an acrylic base sheet was molded to obtain a prism sheet having a thickness of 2 mm.
[0068]
Next, a lenticular lens having a pitch of 140 μm, a lens lateral diameter of 140 μm, a lens vertical diameter of 100 μm, and a lens height of 50 μm is produced by extrusion molding using a cylindrical roll mold for manufacturing a lenticular lens. The horizontal diffusion angle was 35 ° as a half-value angle, and the vertical diffusion angle was 15 ° as a half-value angle. At the time of extrusion molding of this lenticular lens sheet, the transmittance of the lenticular lens sheet is set to 70% by mixing a very small amount of black dye and a diffusing agent with impact-resistant acrylic resin, etc., thereby preventing reflection of outside light, etc. Added effect and diffusion effect.
[0069]
A projection screen was constructed by combining the total reflection prism sheet and the lenticular lens sheet.
[0070]
The projection screen of this example had a wide allowable angle of incidence, and did not have a decrease in surface brightness or a contrast, and a high-quality image was obtained.
[0071]
(Example 2)
Example 2 is a specific form of the projection screen shown in the second embodiment.
An embodiment of the projection screen will be described based on the schematic diagram of the projection screen shown in FIG. This projection screen device is a projection system launched from below the screen, and the light source uses an LCD light valve. The incident angle is 45 ° at the lower end, 60 ° at the upper end, and the projection screen is 50 inches.
[0072]
The total reflection prism is concentric, and its center is an arc shape not on the screen. The radius of the arc is 800 mm at the lower center of the screen, the prism pitch is 100 μm, the prism height is 150 μm, and the apex angle of the total reflection prism , The apex angle of the portion closest to the prism center at the lower end of the screen is 37 °, the apex angle of the portion farthest from the prism center at the upper end of the screen is 40 °, and the prism apex angle is continuously in the range of 37 ° to 40 °. Changed. The total reflection prism is an arc prism mold obtained by cutting with an NC lathe using an acrylic film with a thickness of 0.2 mm as a base film, and is exposed to UV curable resin under specified conditions. Curing was performed to prepare a prism sheet.
[0073]
Subsequently, a lenticular lens having a trapezoidal cross section was formed on the opposite surface of the prism sheet, and a V-shaped portion between adjacent trapezoids was filled with a low refractive index resin containing light absorbing particles. Epoxy acrylate was used as the material for the trapezoidal high refractive index portion, urethane acrylate was used as the V-shaped low refractive index portion, and “Love Collol” (registered trademark) manufactured by Dainichi Seika Kogyo Co., Ltd. was used as the light absorbing particle. The average particle diameter of “Love Color” was 8 μm, and the amount added was 45% by weight. The trapezoidal high refractive index portion had a lens pitch of 50 μm and a refractive index of 1.57, and the V-shaped low refractive index portion had a refractive index of 1.48. Further, the upper base length of the trapezoid is made equal to the length of the triangle base of the V-shaped portion, the so-called black stripe ratio is set to 50%, and the apex angle of the V-shaped triangle is set to 20 °.
[0074]
The projection screen in which the total reflection prism lens and the lenticular lens having the above configuration are formed on the front and back of one sheet had a transmittance of 80%, a reflectance of 5%, and a gain of 4. The vertical viewing angle (half-value angle: the angle at which the luminance when viewed from a certain direction is half that when viewed from the front) was 12 °, and the horizontal viewing angle (half-value angle) was 25 °.
[0075]
The projection screen of this example had a wide allowable angle of incidence, and did not have a decrease in surface brightness or a contrast, and a high-quality image was obtained.
[0076]
(Example 3)
Example 3 is an example in which Example 2 is further improved.
The configuration of this projection screen is the same as in Example 2 except that an AR coat film having a thickness of 0.1 mm is laminated on the most observer side in front of the lenticular lens, and the reflectance is 1 It can be improved to 5%.
[0077]
Example 4
The fourth embodiment is an embodiment of a rear projection type projection display apparatus using the projection screen shown in the first embodiment.
The projection display device 30 shown in FIG. 4A uses an LCD light valve 32 as an image light source, and an incident angle θ of image light incident on the lower end of the screen upward.₁₁= 45 °, incident angle θ of image light incident on the upper end of the screen_TenThis is a system for projecting an image on the projection screen 31 so as to be 60 °. In this case, the distance in the horizontal state between the projection screen and the image light source is approximately 80 cm.
[0078]
(Example 5)
Example 5 is an example in which the projection direction and the image light source of the rear projection type projection display apparatus shown in Example 4 are changed.
As another form of the rear projection type projection display device, as shown in FIG. 4 (b), the DMD light source 42 is used as the image light source, and the incident angle of the image light incident on the upper end of the 80-inch screen downward. θ₂₀= 45 °, incident angle θ of image light incident on the lower end of the screen_{twenty one}An image is projected on the projection screen 41 so that = 70 °. In this case, the horizontal distance between the projection screen and the image light source is approximately 70 cm.
[0079]
(Example 6)
Example 6 is a specific form of the projection screen shown in the third embodiment.
A transmissive screen of a thin rear projection type projection display device (for television) having a screen size of 55 inches (16: 9), a projection distance of 340 mm, and a light source position 250 mm below the screen bottom. Was made as follows. Angle θ of incident light to the center of the lower end of the projection screen (distance 250 mm from the center of Fresnel)₁Is 36.3 °, the angle θ of the incident light to the upper corner (distance 1116 mm from the center of Fresnel)₁Is 73.0 °.
[0080]
The total reflection type Fresnel lens sheet (prism sheet) described in the third embodiment was manufactured using an ultraviolet curable resin having a refractive index after curing of 1.55. Output angle θ_FiveIs zero (vertical emission), the prism tip angle λ on the side closer to the Fresnel center is 35 °, the tip angle λ on the far side is 40 °, and the distance from the Fresnel center r1 = 529.6 mm (incident angle 57.3 °) From r2 = 605.9 mm (incident angle 60.7 °), the lens angle φ was made constant at 55.25 °.
[0081]
FIG. 14 is a graph showing changes in the prism tip angle λ in the vicinity where the prism tip angle of the Fresnel lens sheet in Examples 6 and 7 changes from 35 ° to 40 °.
FIG. 15 is a diagram illustrating a change in Fresnel lens angle φ in the vicinity where the prism tip angle of the Fresnel lens sheet in Examples 6 and 7 changes from 35 ° to 40 °.
14 and 15, the solid line shows the case of the sixth embodiment.
[0082]
(Example 7)
Example 7 is a specific form of the projection screen shown in the fourth embodiment, and is a further improvement of Example 6.
For the same projection display apparatus as in Example 6, the lens angle φ of the Fresnel lens having a distance from the Fresnel center of 500 mm to 650 mm was determined using a 5-node spline interpolation function. A reflection type Fresnel lens was produced. The change in the prism tip angle λ and the change in the Fresnel lens angle φ are shown by broken lines in FIGS. The spline function equations and constants used are shown below.
[0083]
[Expression 2]

[0084]
The parameters are as shown in the following table.
[0085]
[Table 1]

[0086]
After determining the lens angle φ by the spline interpolation function, the incident surface angle γ and the prism apex angle λ were calculated by the following equations.
[0087]
[Equation 3]

[0088]
For comparison with Example 6 and Example 7, Fresnel lens sheets shown in Comparative Example 1 and Comparative Example 2 were produced as examples according to the prior art.
(Comparative Example 1)
For the same projection display apparatus as in Example 6, a Fresnel lens sheet having a constant prism tip angle of 40 ° was produced as Comparative Example 1.
[0089]
(Comparative Example 2)
For the same projection display device as that of Example 6, a constant Fresnel lens with a prism tip angle λ of 35 ° was produced inside a distance from the center of Fresnel of 544 mm (incident angle 58.0 °). In this Fresnel lens, when the distance from the center of the Fresnel is outside 544 mm, the calculation formula of the Fresnel lens is γ <0. One surface (incident surface) was vertical, and the angle φ of the Fresnel lens was determined by the following equation.
φ = {arcsin (cos θ1 / n) + π / 2} / 2
This Fresnel lens has a rough surface on the first surface (incident surface) when the distance from the center of the Fresnel is 544 mm, because a cut mark is formed when the mold of the Fresnel lens is cut. In addition, the tip angle of the prism is gradually larger than 35 °.
[0090]
(Comparative evaluation of Examples 6 and 7 and Comparative Examples 1 and 2)
A transmission type screen is formed by combining the Fresnel lens sheets of Example 6, Example 7, Comparative Example 1, and Comparative Example 2 with a lenticular lens sheet, and the above-mentioned screen size is 55 inches (aspect ratio is 16: 9), projection. It was mounted on a thin rear projection type projection display apparatus having a distance of 340 mm and the position of the light source 250 mm below the lower end of the screen for comparative evaluation.
The rear projection screens according to Example 6 and Example 7 were both uniform and good screens.
[0091]
On the other hand, in the rear projection screen of Comparative Example 1, the vicinity of the lower center of the screen was slightly darker than the rear projection screen using other Fresnel lenses, and ghosts were observed.
In the rear projection type screen of Comparative Example 2, a boundary where the angle of the first surface changes at a distance of 544 mm from the Fresnel center was observed.
[0092]
(Deformation)
The present invention is not limited to the embodiment described above, and various modifications and changes are possible, and these are also within the equivalent scope of the present invention.
(1) In each embodiment, the shapes of the total reflection prism sheet (Fresnel lens sheet) and the projection screen are specifically shown. However, the present invention is not limited to this, and all the concentric circular shapes whose centers are not on the screen are not limited to this. The reflection prism sheet can take all possible configurations, and the projection screen can also take all possible configurations.
[0093]
(2) In each embodiment, the projection screen may be bonded with a diffusion sheet mixed with a diffusing agent on the viewer side.
[0094]
(3) In the second to fourth embodiments, the projection screen may be further provided with functions such as AR, AG, AS, HC, antifouling, and a sensor on the viewer side.
[0095]
(4) In each embodiment, an example in which the projection display device directly projects image light from the image light source onto the projection screen has been described. However, the present invention is not limited to this. For example, as illustrated in FIG. The image light from the image may be reflected on a mirror and projected onto the projection screen.
[0096]
【The invention's effect】
As described above in detail, according to the present invention, the following effects can be obtained.
(1) In a projection display device having a projection system for projecting an image from an image light source to a projection screen upward or downward, a total reflection arc shape in which the apex angle changes depending on the position on the most incident light surface side of the projection screen By providing a prism, the allowable range of incident light is widened, and there is no reduction in surface brightness or contrast, and a projection screen and a projection display device with high image quality equivalent to the case of projecting images in parallel from an image light source. can get.
[0097]
(2) a first apex angle fixed region where the apex angle of the prism is constant at a predetermined angle, and a second apex angle which is constant at a predetermined angle different from the apex angle of the first apex angle fixed region Since the apex angle fixing region and the apex angle changing region in which the apex angle is changed are provided, it becomes easy to manufacture a mold used for manufacturing a total reflection prism sheet, and a high-quality projection screen and projection display device Can be made cheaper.
[0098]
(3) The apex angle changing region is changed by changing both the first surface and the second surface between the first apex angle changing portion and the first and second apex angle fixing regions. Since the second and third apex angle changing portions change, the boundary portion of each region can be made less conspicuous and the image quality can be further improved.
[0099]
(4) Since the first surface has a draft angle of 1/1000 degrees or more with respect to the normal to the screen surface, it is possible to eliminate stray light and prevent loss of image light. Further, since the mold does not have an inverse taper, the mold can be easily manufactured and the prism can be easily released.
[0100]
(5) Since the surface of the first surface is uniform over the entire screen, it is possible to observe a high-quality image without causing unevenness in the image depending on the position.
[Brief description of the drawings]
FIG. 1 is a partial view showing a first embodiment of a projection screen according to the present invention.
FIG. 2 is a diagram showing a second embodiment of the projection screen according to the present invention.
FIG. 3 is a schematic horizontal sectional view of a projection screen according to a second embodiment.
FIG. 4 is a diagram illustrating a state in which an image from an image light source according to the present invention is projected on a projection screen.
FIG. 5 shows the angle of incident light where stray light exists with respect to the apex angle of the prism and the angle of incident light whose first surface is inversely tapered;_FiveFIG. 10 is a diagram illustrating a calculation result when = 0 and a refractive index of a lens portion is 1.55.
FIG. 6 is a diagram illustrating a general projection screen.
FIG. 7 is an optical path of image light when the apex angle of the total reflection prism is increased.
FIG. 8 is an optical path of image light when the apex angle of the total reflection prism is reduced.
FIG. 9 is a diagram illustrating a projection screen according to a third embodiment.
FIG. 10 is a perspective view showing a projection screen 111 in the present embodiment.
FIG. 11 is an enlarged cross-sectional view showing a part of a prism lens 113 in the present embodiment.
FIG. 12 is an output angle θ._FiveIt is a figure which shows the calculation result of lens angle (phi) with respect to an incident angle when = 0 and the vertex angle of a prism is 35 degrees and 45 degrees.
FIG. 13 is a diagram illustrating a projection screen according to a fourth embodiment.
14 is a graph showing changes in the prism tip angle λ in the vicinity where the prism tip angle of the Fresnel lens sheet in Examples 6 and 7 changes from 35 ° to 40 °. FIG.
15 is a graph showing changes in the Fresnel lens angle φ in the vicinity where the prism tip angle of the Fresnel lens sheet in Examples 6 and 7 changes from 35 ° to 40 °. FIG.
FIG. 16 is a diagram showing a modification of the projection display device.
[Explanation of symbols]
1 Projection screen
2 Total reflection arc prism
3 Prism sheet
4 Lenticular lens
5 Lenticular lens sheet
21 Projection screen
22 Total reflection arc prism
23 Base sheet
24 Lenticular lens
25 trapezoidal high refractive index part
26 V-shaped low refractive index part
30 Projection display device
31 Projection screen
32 Liquid crystal light valve
40 Projection display device
41 Projection screen
42 Light source for DMD
72 Total reflection prism
82 Total Reflection Prism
100 projection screen
101 Fresnel lens sheet
101b Fresnel lens
102 Lenticular lens sheet
111, 211 projection screen
112 Image light source
113,213 Fresnel lens
113a first surface
113b second side
115,115A, 115B Lenticular lens
A1, A1 'region (first apex angle fixed region)
A2, A2 'region (second apex angle fixed region)
A3, A3 'region [vertical angle change region (first vertical angle change part)]
A4 area (second apex angle change part)
A5 region (third apex angle change part)

Claims (18)

A screen used in a rear projection type projection display device having a projection system for projecting an image from an image light source to a projection screen upward or downward,
A total reflection prism in which the apex angle of the prism is changed depending on the position of the prism is provided concentrically on the most incident light surface side of the screen, and the center of the concentric circle is not on the screen,
In the apex angle of the concentric total reflection prism, the apex angle of the prism was changed depending on the position of the prism so that the apex angle on the side farther than the apex angle near the center of the concentric circle is larger.
Projection screen featuring The projection screen according to claim 1,
The apex angle of the total reflection prism with the apex angle changed is changed by the position of the prism within a range of 30 ° to 45 °,
Projection screen featuring The projection screen according to claim 1 or 2,
The apex angle is continuously changing;
Projection screen featuring In the projection screen of any one of Claim 1 to Claim 3,
A first apex angle fixing region in which the apex angle is constant at a predetermined angle;
A second apex angle fixed region in which the apex angle is constant at a predetermined angle different from the apex angle of the first apex angle fixed region;
An apex angle changing region in which the apex angle changes;
Having
Projection screen featuring The projection screen according to claim 4,
The total reflection prism includes a first surface that refracts incident video light projected from the projection system;
A second surface that totally reflects the image light from the first surface in the observation direction;
Have
The apex angle is formed by an angle formed by the first surface and the second surface,
In the apex angle change region, the apex angle changes continuously by changing the angle of the first surface with respect to the screen surface continuously without changing the angle of the second surface with respect to the screen surface. Having a first apex angle changing portion;
Projection screen featuring The projection screen according to claim 5,
The apex angle changing region is between the first apex angle changing portion and the first and second apex angle fixing regions,
Having both second and third apex angle changing portions in which the apex angle changes by changing both the first surface and the second surface;
Projection screen featuring In the projection screen according to claim 5 or 6 ,
The first surface has a draft angle of 1/1000 degrees or more with respect to a normal to the screen surface;
Projection screen featuring The projection screen according to any one of claims 5 to 7,
The first surface has a uniform surface roughness over the entire screen;
Projection screen featuring In the projection screen according to any one of claims 1 to 8,
A lenticular lens is provided on the viewer side from the total reflection prism with the apex angle changed,
Projection screen featuring The projection screen according to claim 9, wherein
In the lenticular lens, the unit lens has a trapezoidal cross section;
Projection screen featuring The projection screen according to claim 10, wherein
The lower base of the trapezoidal lenticular lens is the light entrance part, and the upper base is the light exit part,
Projection screen featuring The projection screen according to claim 10 or 11,
The trapezoidal lenticular lens is formed of a material having a predetermined refractive index, and the cross section between adjacent unit lenses is formed of a material having a refractive index lower than that of the trapezoidal portion. A lenticular lens using a total reflection effect by an interface between the V-shaped portion and the trapezoidal portion;
Projection screen featuring The projection screen according to claim 12,
The V-shaped low refractive index portion of the trapezoidal lenticular lens has a light absorbing action;
Projection screen featuring The projection screen according to claim 13.
The light absorbing action is due to mixing light absorbing particles in the low refractive index resin,
Projection screen featuring The projection screen according to any one of claims 1 to 14,
The lenticular lens and the total reflection prism having a different apex angle are formed on the front and back of one sheet;
Projection screen featuring The projection screen according to any one of claims 1 to 15,
Providing a further diffusion sheet on the viewer side,
Projection screen featuring The projection screen according to any one of claims 1 to 16,
The observer must have at least one function among AR, HC, AS, AG, antifouling, and sensor.
Projection screen featuring The projection screen according to any one of claims 1 to 17,
An image light source,
A projection system for projecting image light from the image light source onto the projection screen;
A projection display device comprising:

Images