JP3809699B2 - Lenticular lens sheet - Google Patents

Description

【００１８】
（式中、ｘはレンズ中心からピッチ方向への距離、Ｃは曲率半径の逆数、Ｋは円錐定数、Ｄ、Ｅ、Ｆ、Ｇはそれぞれ４次から１０次までの項の係数を表す。）
で表される曲線等の場合も包含する。
【００１９】
本発明によれば、入射側レンチキュラーレンズのレンズ深さが、このレンチキュラーレンズシートを用いて構成される背面投写型スクリーンの有効画面範囲の中央部に比して端部で０．９８以上となっているので、レンチキュラーレンズシートの端部において入射側レンチキュラーレンズに入射した光が出射側レンチキュラーレンズへ入射するときのその入射角θ₁が過度に大きくなることはなく、中央部での入射角θ₀と同等になる。したがって光のけられを防止し、カラーシフトを低減させ、かつ全光線透過率も向上させることが可能となる。また、中央部に対する端部のレンズ深さの比の上限は１．１０となっているので、水平拡散性の減少によるカットオフ現象を防止することも可能となる。
【００２０】
なお、このような効果は、本発明のレンチキュラーレンズシートを、３つのＣＲＴを使用してカラーの光学像を映す背面投写型スクリーンに使用する場合だけに得られるものではない。本発明のレンチキュラーレンズシートを使用した背面投写型スクリーンは、ＣＲＴだけでなく、ＬＣＤやＤＭＤを光源とした場合でも全光線透過率を向上させることができ、また、水平拡散性を増大させてカットオフ現象を防止することができる。
【００２１】
【発明の実施の形態】
以下、本発明を図面に基づいて詳細に説明する。なお、各図中、同一符号は、同一又は同等の構成要素を表している。
【００２２】
図１は、本発明の一態様のレンチキュラーレンズシート１０Ａの幅方向の断面図である。同図に示したように、このレンチキュラーレンズシート１０Ａは、光線の入射側面に入射側レンチキュラーレンズ１１を有し、光線の出射側面にも出射側レンチキュラーレンズ１２を有する両面レンチキュラーレンズシートであり、光線の出射側面上の、入射側レンチキュラーレンズ１１の非集光部に光吸収層１３を設けたものである。
【００２３】
入射側レンチキュラーレンズ１１及び出射側レンチキュラーレンズ１２は、それぞれシリンドリカルレンズをシートの幅方向に並列させた形状を有している。ここで、入射側レンチキュラーレンズ１１を構成するシリンドリカルレンズは、その曲率半径につき、シート中央部（即ち、このレンチキュラーレンズシートを用いて構成される背面投写型スクリーンの有効画面範囲中央部）での曲率半径Ｒi₀に対して、シート中央部からシートの幅方向の距離がｘであるシート周辺部での曲率半径Ｒi_xがｘの増加に伴い単調に小さくなり、それに応じてシート周辺部のレンズ深さｈi_xのシート中央部のレンズ深さｈi₀に対する比が単調に増加している。そして、このレンチキュラーレンズシートを用いて構成される背面投写型スクリーンの有効画面範囲では、その両端部の入射側レンチキュラーレンズのレンズ深さｈi₁がいずれも中央部のレンズ深さｈi₀に対して０．９８以上１．１０以下となっている。
【００２４】
このように入射側レンチキュラーレンズシートの端部のレンズ深さをシート中央部のレンズ深さに対して特定の関係に設定することにより、後述するようにカラーシフトを低減し、また全光線透過率を向上させることができる。
【００２５】
なお、このレンチキュラーレンズシート１０Ａにおいては、入射側レンチキュラーレンズ１１の頂部と出射側レンチキュラーレンズ１２の頂部との距離であるシート厚については、シート中央部のシート厚ｔ₀とシート中央部から幅方向の距離がｘであるシート周辺部のシート厚ｔ_xとは略等しく、シートの全幅にわたって均一となっている。
【００２６】
このレンチキュラーレンズシート１０Ａの中央部と周辺部とのそれぞれにおける光線Ｌの透過状態を図１にあわせて示す。
【００２７】
この図１のレンチキュラーレンズシート１０Ａによれば、レンチキュラーレンズシートを構成する入射側レンチキュラーレンズ１１のシリンドリカルレンズのレンズ深さにつき、シート中央部に対してシート周辺部が０．９８以上に形成されている。したがって、従来の両面レンチキュラーレンズシートのように、入射側レンチキュラーレンズの曲率半径が、シート中央部に対してシート周辺部で数％程度も小さくなり、それに応じてレンズ深さがシート中央部に比してシート周辺部で数％程度大きくなっているものに比して光吸収層１３による光のけられを防止でき、カラーシフトを低減させ、また、全光線透過率を向上させることが可能となる。また、このレンチキュラーレンズシート１０Ａによれば、入射側レンチキュラーレンズ１１のシリンドリカルレンズのレンズ深さが、シート中央部に対してシート周辺部で１．１０以下に形成されているので、カットオフ現象を防止することができる。
【００２８】
さらにこのレンチキュラーレンズシート１０Ａによれば、レンチキュラーレンズシートの厚みが中央部と周辺部とで略等しいので、中央部のシート厚みに比して周辺部のシート厚みが数％程度薄く形成されている従来の両面レンチキュラーレンズシートに比して、よりいっそうカラーシフトを低減させ、全光線透過率を向上させることが可能となる。
【００２９】
図１のレンチキュラーレンズシート１０Ａの製造方法としては、例えば、成形品の逆型形状を有する平板状の金型を２枚用意し、この間に加熱した樹脂を挟み込み、加圧、冷却する所謂プレス法や、成形品の逆型形状を有する１組の賦形ロール間にダイから溶融した樹脂を流し、押圧、冷却する押出成形法等を用いることができる。
【００３０】
中でも、押出成形法は、レンズ深さやシート厚等をシートの幅方向に徐々に変化させることができるので、本発明のレンチキュラーレンズシートの製造方法として有用である。押出成形法でレンズ深さを制御する場合のより具体的方法としては、例えば、押出に用いるダイの温度を中央部と周辺部とで均一にするか、又は中央部を周辺部に比して５〜１０℃高くすることが好ましい。なおこのようにダイの温度を制御すると、ダイ周辺部から比較的温度の低い樹脂が押し出されるので、シート周縁部に使用できない部分が生じる場合があるが、この場合にはその部分を切除すればよい。
【００３１】
また、プレス法や押出成形法を従来例にしたがって行うと、得られるレンチキュラーレンズシートは、周辺部の厚さが中央部に比して数％程度薄くなるので、周辺部と中央部とのシート厚さを同等とするためには、成形時に中央部に対して周辺部の厚さが増加するように厚さ制御を行うことが好ましい。より具体的には、例えば、押出成形法で成形する場合、賦形ロールと樹脂との間にある樹脂だまり（所謂バンク）をレンチキュラーレンズシート中央部に対して周辺部で増やす。また、さらに、押出成形法で成形する場合、１組の賦形ロールのうちの少なくとも１本をクラウニングロールとしてもよい。この場合、ロールのクラウニング量は、中央部と周辺部とのバンクにもよるが、これらのクラウニング量を変えない場合、１ｍ当たり２０μｍ以上とすることが好ましい。
【００３２】
本発明は、上述のレンチキュラーレンズシート１０Ａの他、入射側レンチキュラーレンズのシート中央部でのレンズ深さｈi₀とスクリーンの有効画面範囲端部でのレンズ深さｈi₁が
０．９８≦ｈi₁／ｈi₀≦１．１０
を満たしている限り、種々の態様をとることができる。
【００３３】
たとえば、本発明において、入射側レンチキュラーレンズを構成するシリンドリカルレンズのレンズ断面の形状は真円形状に限らず、例えば、楕円、次の高次式
【００３４】
【数２】

【００３５】
（式中、ｘはレンズ中心からピッチ方向への距離、Ｃは曲率半径の逆数、Ｋは円錐定数、Ｄ、Ｅ、Ｆ、Ｇはそれぞれ４次から１０次までの項の係数を表す。）
で表される曲線等とすることができる。
【００３６】
また、入射側レンチキュラーレンズのレンズ深さｈ_xの変化の態様としては、上述の例のように、ｘの増加に伴い単調に変化する場合に限らず、ステップ状に変化する場合も包含する。
【００３７】
レンチキュラーレンズシートのシート厚に関し、図１のレンチキュラーレンズシート１０Ａにおいては、その中央部のシート厚と周辺部のシート厚とが略等しいが、本発明においてはレンチキュラーレンズシートの厚み分布はこれに限らない。好ましくは、カラーシフトを低減させ、全光線透過率をあげる点から、シート中央部のシート厚に対するシート周辺部のシート厚の比が０．９８〜１．１０倍程度の範囲となるようにする。なお、シート中央部のシート厚に対するシート周辺部のシート厚の比を大きくすると、レンチキュラーレンズシートの周辺部において入射側レンチキュラーレンズに入射した光が出射側レンチキュラーレンズへ入射するときのその入射角θ₁が小さくなるので、全光線透過率をいっそう高めることができ、反対に、シート中央部のシート厚に対するシート周辺部のシート厚の比を小さくすると水平拡散角を広くすることができる。したがって、シート中央部のシート厚に対するシート周辺部のシート厚の比は当該レンチキュラーレンズシートへの要求特性に応じて適宜定めることができる。
【００３８】
本発明のレンチキュラーレンズシートは、従来のレンチキュラーレンズシートと同様に、図５に示したように、フレネルレンズと組み合わせて背面投写型スクリーンに使用することができる。この場合、フレネルレンズとしては、従来より背面投写型スクリーンに使用されているものを使用することができる。
【００３９】
また、本発明のレンチキュラーレンズシートを用いた背面投写型スクリーンは、ＣＲＴだけでなく、ＬＣＤやＤＭＤを光源とした場合でも全光線透過率をあげることができるので、好ましく使用することができる。
【００４０】
【実施例】
以下、本発明を実施例に基づいて具体的に説明する。
【００４１】
実施例１
（１）レンチキュラーレンズシートの作製
両面レンチキュラーレンズシートであって、出射側面には入射側レンチキュラーレンズによる非集光部に光吸収層を有するものを、クラウニングロールを使用する押出成形法により製造した。この場合、レンチキュラーレンズシートを構成する樹脂としては、ポリメチルメタクリレートを使用した。また、押出条件としては、ダイ温度をダイ周辺部に対してダイ中央部で５℃上げ、バンクをロール中央部に対して周辺部で１０％程度増加させた。
【００４２】
これにより、シートの全高＝１５００ｍｍ、全幅＝１０００ｍｍ、入射側レンチキュラーレンズ１１のピッチ（ｐ）＝０．７８ｍｍ、入射側レンチキュラーレンズのシート中央部が近似曲率半径Ｒｉ₀＝０．３２０ｍｍ、レンズ深さｈi₀＝０．３００ｍｍの楕円、入射側レンチキュラーレンズのシート端部が近似曲率半径Ｒｉ₁＝０．３２０ｍｍ、レンズ深さｈi₁＝０．３００の楕円、出射側レンチキュラーレンズシート１２のピッチ（ｐ）＝０．３６ｍｍ、出射側レンチキュラーレンズシートのシート中央部が近似曲率半径Ｒｏ₀＝０．２２０ｍｍの楕円、出射側レンチキュラーレンズシートのシート端部が近似曲率半径Ｒｏ₁＝０．２２０ｍｍの楕円、レンチキュラーレンズシートの中央部のシート厚ｔ₀＝０．９３０ｍｍ、端部のシート厚ｔ₁＝０．９３０ｍｍのレンチキュラーレンズシートを成形した。
【００４３】
次に、成型したレンチキュラーレンズシートに対して、光吸収層１３を常法により印刷し（ストライプの幅０．３２ｍｍ）、実施例のレンチキュラーレンズシートを得た。
【００４４】
（２）評価
（2-1）カラーシフト
フレネルレンズとして、焦点距離ｆ＝９００ｍｍのレンズを用意し、上述のレンチキュラーレンズシートと組み合わせて背面投写型スクリーンを形成した（幅約１２５０ｍｍ、高さ約９５０ｍｍ）。このスクリーンを市販の背面投写型プロジェクタテレビ（T0SHIBA AMERICA CONSUMER PRODUCTS.,INC.製、モデル名TP61E90）に取り付けた。そして、このテレビセットに全白信号を入力し、図２に示すように、テレビセット２０のスクリーン５の中心から水平方向に向かって左側６００ｍｍの位置（Ａ）を、３ｍ離れたスクリーン正面の位置（Ｂ）及び水平方向反時計回りに６０°移動した位置（Ｃ）で観察することにより、カラーシフトを次のように評価した。
【００４５】
まず、青色、緑色の光源をカバーで覆い、赤色光をスクリーンに射出した場合のスクリーンからの出射輝度をＢ位置で測定した（Ｒ₀［ｎｉｔ］）。次に、赤色、緑色の光源をカバーで覆い、青色光のスクリーンからの出射輝度を同様に測定した（Ｂ₀［ｎｉｔ］）。
【００４６】
測定位置をＣ位置に移し、Ｂ位置での測定と同様に、赤色光の出射輝度Ｒ₆₀［ｎｉｔ］と青色光の出射輝度Ｂ₆₀［ｎｉｔ］を測定した。
【００４７】
そして、次式にしたがってスクリーン５の中心から左側６００ｍｍの位置（Ａ）での色変化の大きさを表すカラーシフトＣＳ_{(600mm,60 ° )}を求めた。
【００４８】
【数３】
ＣＳ_{(600mm,60 ° )}＝２０log（（Ｒ₆₀／Ｒ₀）／（Ｂ₆₀／Ｂ₀））［ｄＢ］
この結果を表１に示す。
【００４９】
（2-2）全光線透過率
上述のカラーシフトの測定と同様に、レンチキュラーレンズシートを背面投写型プロジェクターテレビに取り付け、このテレビセットのスクリーンの中心から水平方向に向かって左側６００ｍｍの位置について、ＡＳＴＭ Ｄ−１００３にしたがい、全光線透過率Ｔ_tを測定した。
【００５０】
この結果を表１に示す。
【００５１】
実施例２〜５、比較例１〜３
実施例と略同様にして、表１及び表２に示す形状のレンチキュラーレンズシートを作製し、そのカラーシフトと全光線透過率とを測定した。これらの結果を表１及び表２に示す。
【００５２】
【表１】

【００５３】
【表２】

【００５４】
表１及び表２から入射側レンチキュラーレンズのレンズ深さについて、シート中央部のレンズ深さｈi₀に対するシート端部のレンズ深さｈi₁の比(ｈi₁／ｈi₀)が０．９８〜１．１０である実施例のレンチキュラーレンズシートによれば、カラーシフトを低減させ、全光線透過率を向上させられることがわかる。
【００５５】
これに対して、レンズ深さの比(ｈi₁／ｈi₀)が０．９８より小さい比較例１では、カラーシフトが大きく、全光線透過率も劣っていることがわかる。
【００５６】
レンズ深さの比(ｈi₁／ｈi₀)が１．１０を超える比較例２では、カラーシフトや全光線透過率は実施例と同程度であるが、水平方向で拡散光が急激に低下するカットオフがあり、好ましくないことがわかる。
【００５７】
さらに、レンズ深さの比(ｈi₁／ｈi₀)が１．１０を超え、シート端部のシート厚が薄くなっている比較例３では、カラーシフトが極めて大きく、全光線透過率も極めて低いことがわかる。
【００５８】
【発明の効果】
本発明のレンチキュラーレンズシートによれば、カラーシフトを低減させることができ、また、シートの全光線透過率を向上させて光の利用効率を向上させることができる。
【図面の簡単な説明】
【図１】本発明のレンチキュラーレンズシートの断面図及びその光線追跡図である。
【図２】カラーシフトの測定方法の説明図である。
【図３】一般的な背面投写型テレビジョンの概略構成図である。
【図４】一般的な背面投写型テレビジョンにおける光線説明図である。
【図５】一般的な背面投写型テレビジョンで使用されるスクリーンの斜視図である。
【図６】従来の両面レンチキュラーレンズシートの断面図である。
【図７】従来の片面レンチキュラーレンズシートの断面図及びその光線追跡図である。
【図８】両面レンチキュラーレンズシートのシート厚さを変化させた場合の断面図及びその光線追跡図である。
【符号の説明】
１ ＣＲＴ
２ 投写レンズ
３ フレネルレンズ
４ レンチキュラーレンズシート
５ 背面投写型スクリーン
１０ｘ 片面レンチキュラーレンズシート
１０、１０Ａ 両面レンチキュラーレンズシート
１ 入射側レンチキュラーレンズ
２ 出射側レンチキュラーレンズ
３ 光吸収層
２０ テレビセット[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a lenticular lens sheet used for a rear projection screen.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, as a method for displaying an image on a large screen, a method of enlarging and projecting an optical image from a CRT or liquid crystal panel onto a rear projection screen using a projection lens is known. FIG. 3 is a schematic configuration diagram of a general rear projection television that forms an image by this method, FIG. 4 is an explanatory diagram of light rays, and FIG. 5 is used in the rear projection television of FIG. It is a perspective view of the screen to do.
[0003]
In the rear projection television shown in the figure, the optical images from the CRT 1 of R (red), G (green), and B (blue) installed in the cabinet 6 are magnified by the projection lens 2, and reflected by the reflecting mirror. 7 is reflected on the rear projection type screen 5 composed of the Fresnel lens 3 and the lenticular lens sheet 4. Here, the Fresnel lens 3 has a function of substantially directing incident light in the direction in which the observer is positioned, and the lenticular lens sheet 4 transmits light emitted from the Fresnel lens 3 at a predetermined angle in the horizontal and vertical directions. It is dispersed at an appropriate distribution ratio to widen the viewing angle within a predetermined range.
[0004]
However, in such a display device, the color of the image on the screen is changed by changing the observation position of the screen 5 in the horizontal direction due to the concentrated angle ε of the projection light of each of the CRT 1 of R, G, B. (See FIG. 4). That is, in the normal CRT 1 arrangement, the green is located in the center and the red and blue are shifted to the left and right, so that the color of red or blue becomes stronger when the observation position is changed to the left or right. Such a phenomenon is called color shift.
[0005]
Therefore, in order to reduce the color shift, as shown in FIG. 6, conventionally, as the lenticular lens sheet, an incident side lenticular lens 11 in which a plurality of cylindrical lenses are arranged in parallel on the light incident side surface is formed, and the cylindrical surface is also formed on the output side surface. It is known to use a double-sided lenticular lens sheet 10 in which a light-emitting layer 13 is formed on the non-light-collecting portion of the incident-side lenticular lens 11 on the light-exiting side. It has been.
[0006]
On the other hand, as a method for producing a lenticular lens sheet, a thermoplastic resin extrusion molding method is currently employed because of its high productivity. In this method, the temperature is adjusted 5 to 10 ° C. higher than the central portion at the end of the die so that smooth extrusion can be performed over the entire width of the die. This is to compensate for the pressure drop in the manifold at the end by the decrease in viscosity.
[0007]
[Problems to be solved by the invention]
However, in order to make the die temperature higher at the end than at the center, the radius of curvature of the cylindrical lens constituting the lenticular lens sheet is not equal over the entire width of the lenticular lens sheet, and is several at the end relative to the center. The actual situation is that the percentage is smaller, which is different from the expected shape.
[0008]
Therefore, in the central part of the lenticular lens sheet, the thickness of the sheet is determined so that the incident side lenticular lens condenses on the exit side surface of the sheet, and light is incident on the non-condensing part of the incident side lenticular lens on the exit side surface of the sheet. When the absorption layer is provided, at the end of the lenticular lens sheet, so-called light scuffing occurs in which light incident from the incident side lenticular lens is blocked by the light absorption layer from being emitted from the emission side lenticular lens. There has been a problem that the light transmittance of the sheet is remarkably lowered and the screen image becomes dark.
[0009]
Regarding this problem of light scattering, a single-sided lenticular lens sheet (that is, an incident-side lenticular lens is provided on the incident side of the light beam, and a flat exit surface is provided at a portion where light incident on the incident-side lenticular lens exits. For the lenticular lens sheet provided), the thickness of the lenticular lens sheet with respect to the central portion is adjusted so that the radius of curvature of the cylindrical lens constituting the lenticular lens sheet becomes smaller at the end portion with respect to the central portion. It has been proposed to form thinly at the end (Japanese Utility Model Publication No. 63-44819).
[0010]
However, even if such a method is effective for a single-sided lenticular lens sheet, as shown in FIG. 6, in a double-sided lenticular lens sheet 10 in which lenticular lenses 11 and 12 are provided on both the incident side and the exit side. Since the total light transmittance is lowered, it is not an effective means. That is, like the single-sided lenticular lens sheet 10x shown in FIG. 7, the incident side lenticular lens 11 is provided on the incident side surface of the light beam, but the output side lenticular lens is not provided on the incident side surface of the light beam. In the lenticular lens sheet in which the light absorption layer 13 is formed on the emission side, the emission side of the light beam is changed from the emission side S ₀ at the initial position to the emission side S ₁ at the position of the broken line. Even if the thickness of the lenticular lens sheet is decreased from t ₀ to t ₁ by changing the incident angle of the light L with respect to the emission side surfaces S ₀ and S ₁ of the sheet does not change as θ ₀ = θ ₁ , and therefore the emission side surface The transmittance of the light L at S ₀ and S ₁ is not changed by reducing the thickness of the sheet.
[0011]
On the other hand, in the double-sided lenticular lens sheet 10 in which the lenticular lenses 11 and 12 are respectively formed on the light incident side surface and the light emission side surface as shown in FIG. 6, as shown in FIG. When the sheet thickness is reduced from t ₀ to t ₁ by changing from the emission side S ₀ to the emission side S ₁ at the position indicated by the broken line, the incidence of the light beam L on the emission side S ₀ before the sheet thickness is reduced. With respect to the angle θ ₀ , the incident angle θ ₁ of the light beam L with respect to the exit side S ₁ after the sheet thickness is reduced increases, and thus the reflectance at the exit side S ₁ increases, and in some cases the exit side S S The amount of light totally reflected at ₁ and transmitted through the sheet is significantly reduced. Therefore, this lenticular lens sheet has a problem that an observed image becomes dark.
[0012]
The present invention is to solve the above-described problems of the prior art, and in a double-sided lenticular lens sheet capable of reducing color shift with respect to a single-sided lenticular lens sheet, the light formed on the exit side of the sheet An object is to improve the light utilization efficiency by preventing the scattering of light by the absorbing layer and also improving the total light transmittance of the sheet.
[0013]
[Means for Solving the Problems]
When manufacturing the double-sided lenticular lens sheet by the extrusion molding method, the lens depth of the cylindrical lens constituting the incident side lenticular lens sheet is adjusted at the center of the sheet by adjusting the resin temperature, the extrusion amount, and the like. On the other hand, it can be made higher than a specific ratio at the periphery of the sheet, which can solve the problem of light scattering due to the light absorption layer on the light exit surface, and can improve the total light transmittance. The headline and the present invention have been completed.
[0014]
That is, the present invention has an incident side lenticular lens having a shape in which cylindrical lenses are arranged in parallel in the sheet width direction on the light incident side surface, and an exit side in a shape in which cylindrical lenses are arranged in parallel in the sheet width direction on the emission side surface. Effective for a rear projection screen having a lenticular lens and a double-sided lenticular lens sheet in which the top of the exit side lenticular lens sheet is formed at a substantially condensing position of the entrance side lenticular lens. When the lens depth of the incident side lenticular lens at the center of the screen range is hi ₀ and the lens depth of the incident side lenticular lens at the end of the effective screen range is hi1,
0.98 ≦ hi ₁ / hi ₀ ≦ 1.10.
Is satisfied ,
From the effective screen range center of the screen, the lens depth of said incident side lenticular lens is taken as h i _x in the position of the distance x in a direction perpendicular to the longitudinal direction of the cylindrical lenses constituting the incident side lenticular lens, a screen The lenticular lens sheet is characterized in that h i _x / h i ₀ monotonously decreases or increases as x increases within the effective screen range .
[0015]
Here, the lens depth of the cylindrical lens constituting the incident side lenticular lens refers to the lens surface of the cylindrical lens from the lens trough that is a boundary line between adjacent ones of the plurality of cylindrical lenses constituting the incident side lenticular lens. Is the height to the top of the lens, which is the part most protruding to the light source side. Therefore, when each cylindrical lens has a perfect circular cross-sectional shape and the pitch of each cylindrical lens is equal, the lens depth increases as the curvature radius of the cylindrical lens decreases.
[0016]
In the present invention, the lens cross section of the cylindrical lens is not limited to a perfect circle, and for example, the lens cross section is an ellipse or the following higher order formula:
[Expression 1]

[0018]
(Where x is the distance from the lens center in the pitch direction, C is the reciprocal of the radius of curvature, K is the conic constant, and D, E, F, and G are the coefficients of the fourth to tenth terms, respectively.)
The case of a curve represented by
[0019]
According to the present invention, the lens depth of the incident side lenticular lens is 0.98 or more at the end compared to the central portion of the effective screen range of the rear projection screen configured using this lenticular lens sheet. Therefore, the incident angle θ ₁ when the light incident on the incident side lenticular lens at the end of the lenticular lens sheet enters the output side lenticular lens does not become excessively large, and the incident angle θ at the center portion Equivalent to ₀ . Therefore, it is possible to prevent the light from shifting, to reduce the color shift, and to improve the total light transmittance. Further, since the upper limit of the ratio of the lens depth at the end to the center is 1.10, it becomes possible to prevent the cut-off phenomenon due to the decrease in horizontal diffusivity.
[0020]
Such an effect cannot be obtained only when the lenticular lens sheet of the present invention is used for a rear projection screen that projects a color optical image using three CRTs. The rear projection screen using the lenticular lens sheet of the present invention can improve the total light transmittance not only with a CRT but also with an LCD or DMD as a light source, and also increases the horizontal diffusivity to cut it. The off phenomenon can be prevented.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the drawings. In addition, in each figure, the same code | symbol represents the same or equivalent component.
[0022]
FIG. 1 is a cross-sectional view in the width direction of a lenticular lens sheet 10A of one embodiment of the present invention. As shown in the figure, this lenticular lens sheet 10A is a double-sided lenticular lens sheet having an incident-side lenticular lens 11 on the incident side of the light beam and an output-side lenticular lens 12 on the light-exiting side. The light absorption layer 13 is provided on the non-condensing part of the incident side lenticular lens 11 on the exit side surface.
[0023]
The incident side lenticular lens 11 and the emission side lenticular lens 12 each have a shape in which cylindrical lenses are juxtaposed in the width direction of the sheet. Here, the cylindrical lens constituting the incident side lenticular lens 11 has a curvature at the center of the sheet (that is, at the center of the effective screen range of the rear projection screen configured using this lenticular lens sheet) with respect to the radius of curvature. with respect to the radial Ri _0, the radius of curvature Ri _x in the sheet periphery is the distance from the sheet central portion in the width direction of the sheet x is monotonously reduced with an increase in x, the lens depth of the sheet periphery accordingly The ratio of the height _{h i x} to the lens depth _{h i 0} at the center of the sheet monotonously increases. And, in the effective screen range of the rear projection screen configured using this lenticular lens sheet, the lens depth hi ₁ of the incident side lenticular lens at both ends thereof is relative to the lens depth hi _{0 of the} central portion. It is 0.98 or more and 1.10 or less.
[0024]
In this way, by setting the lens depth at the end of the incident side lenticular lens sheet to a specific relationship with the lens depth at the center of the sheet, the color shift is reduced as described later, and the total light transmittance is also achieved. Can be improved.
[0025]
In the lenticular lens sheet 10A, the sheet thickness, which is the distance between the top of the incident-side lenticular lens 11 and the top of the exit-side lenticular lens 12, is the sheet thickness t _{0 at the} center of the sheet and the width direction from the center of the sheet. Is substantially equal to the sheet thickness t _{x at the} periphery of the sheet where the distance is x, and is uniform over the entire width of the sheet.
[0026]
The transmission state of the light beam L at each of the central portion and the peripheral portion of the lenticular lens sheet 10A is shown in FIG.
[0027]
According to the lenticular lens sheet 10A of FIG. 1, with respect to the lens depth of the cylindrical lens of the incident side lenticular lens 11 constituting the lenticular lens sheet, the sheet peripheral part is formed at 0.98 or more with respect to the sheet central part. Yes. Therefore, like the conventional double-sided lenticular lens sheet, the radius of curvature of the incident side lenticular lens is about several percent smaller at the periphery of the sheet than the center of the sheet, and the lens depth is correspondingly smaller than that at the center of the sheet. As a result, it is possible to prevent the light absorption by the light absorption layer 13 from being increased by several percent at the periphery of the sheet, to reduce the color shift, and to improve the total light transmittance. Become. Further, according to the lenticular lens sheet 10A, the lens depth of the cylindrical lens of the incident side lenticular lens 11 is formed to be 1.10 or less at the sheet peripheral portion with respect to the sheet central portion, so that the cut-off phenomenon is prevented. Can be prevented.
[0028]
Furthermore, according to this lenticular lens sheet 10A, since the thickness of the lenticular lens sheet is substantially equal between the central portion and the peripheral portion, the thickness of the peripheral portion is about several percent thinner than the thickness of the central portion. Compared with a conventional double-sided lenticular lens sheet, the color shift can be further reduced and the total light transmittance can be improved.
[0029]
As a manufacturing method of the lenticular lens sheet 10A of FIG. 1, for example, a so-called pressing method in which two flat plate molds having a reverse shape of a molded product are prepared, and a heated resin is sandwiched between them and pressed and cooled. Alternatively, an extrusion molding method in which a molten resin is poured from a die between a pair of shaping rolls having a reverse shape of a molded product, pressed, and cooled can be used.
[0030]
Among them, the extrusion molding method is useful as a method for producing the lenticular lens sheet of the present invention because the lens depth, the sheet thickness, and the like can be gradually changed in the sheet width direction. As a more specific method for controlling the lens depth by the extrusion molding method, for example, the temperature of the die used for extrusion is made uniform between the central part and the peripheral part, or the central part is compared with the peripheral part. It is preferable to make it 5-10 degreeC high. If the temperature of the die is controlled in this way, a resin having a relatively low temperature is pushed out from the periphery of the die, so that there may be a portion that cannot be used in the peripheral portion of the sheet, but in this case, if that portion is cut off Good.
[0031]
In addition, when the pressing method or extrusion molding method is performed according to the conventional example, the resulting lenticular lens sheet has a thickness of about several percent thinner than the central portion, so the sheet of the peripheral portion and the central portion In order to make the thicknesses equal, it is preferable to control the thickness so that the thickness of the peripheral part increases with respect to the central part during molding. More specifically, for example, when molding is performed by an extrusion molding method, a resin pool (so-called bank) between the shaping roll and the resin is increased at the peripheral portion with respect to the central portion of the lenticular lens sheet. Furthermore, when molding by an extrusion molding method, at least one of a set of shaping rolls may be a crowning roll. In this case, although the crowning amount of the roll depends on the bank of the central part and the peripheral part, it is preferable that the roll crowning amount is 20 μm or more per meter when the crowning amount is not changed.
[0032]
In the present invention, in addition to the above-described lenticular lens sheet 10A, the lens depth hi ₀ at the center of the incident side lenticular lens and the lens depth hi ₁ at the end of the effective screen range of the screen are 0.98 ≦ hi _1. / Hi ₀ ≦ 1.10
As long as the above is satisfied, various modes can be adopted.
[0033]
For example, in the present invention, the shape of the lens cross-section of the cylindrical lens constituting the incident side lenticular lens is not limited to a perfect circle, but may be an ellipse, for example,
[Expression 2]

[0035]
(Where x is the distance from the lens center in the pitch direction, C is the reciprocal of the radius of curvature, K is the conic constant, and D, E, F, and G are the coefficients of the fourth to tenth terms, respectively.)
Or a curve represented by
[0036]
Further, the mode of change of the lens depth h _x of the incident side lenticular lens is not limited to the case of changing monotonously as x increases as in the above example, but includes the case of changing in a stepped manner.
[0037]
With respect to the sheet thickness of the lenticular lens sheet, in the lenticular lens sheet 10A of FIG. 1, the sheet thickness at the center and the sheet thickness at the peripheral part are substantially equal. However, in the present invention, the thickness distribution of the lenticular lens sheet is not limited to this. Absent. Preferably, in order to reduce the color shift and increase the total light transmittance, the ratio of the sheet thickness at the sheet peripheral part to the sheet thickness at the sheet central part is in a range of about 0.98 to 1.10 times. . When the ratio of the sheet thickness at the sheet peripheral part to the sheet thickness at the sheet central part is increased, the incident angle θ when the light incident on the incident side lenticular lens in the peripheral part of the lenticular lens sheet enters the output side lenticular lens _{Since 1} becomes smaller, the total light transmittance can be further increased. Conversely, if the ratio of the sheet thickness at the sheet peripheral portion to the sheet thickness at the sheet central portion is decreased, the horizontal diffusion angle can be increased. Therefore, the ratio of the sheet thickness at the sheet peripheral part to the sheet thickness at the sheet central part can be appropriately determined according to the required characteristics of the lenticular lens sheet.
[0038]
Like the conventional lenticular lens sheet, the lenticular lens sheet of the present invention can be used in a rear projection screen in combination with a Fresnel lens, as shown in FIG. In this case, a Fresnel lens that has been conventionally used for a rear projection screen can be used.
[0039]
In addition, the rear projection screen using the lenticular lens sheet of the present invention can be preferably used because it can increase the total light transmittance not only with a CRT but also with an LCD or DMD as a light source.
[0040]
【Example】
Hereinafter, the present invention will be specifically described based on examples.
[0041]
Example 1
(1) Production of Lenticular Lens Sheet A double-sided lenticular lens sheet having a light-absorbing layer in the non-light-collecting portion of the incident side lenticular lens on the exit side was produced by an extrusion method using a crowning roll. In this case, polymethyl methacrylate was used as the resin constituting the lenticular lens sheet. Moreover, as extrusion conditions, the die temperature was increased by 5 ° C. at the center of the die with respect to the periphery of the die, and the bank was increased by about 10% at the periphery of the center of the roll.
[0042]
Thereby, the total height of the sheet = 1500 mm, the total width = 1000 mm, the pitch (p) of the incident side lenticular lens 11 is 0.78 mm, the central portion of the sheet of the incident side lenticular lens has an approximate curvature radius Ri ₀ = 0.320 mm, and the lens depth. An ellipse with hi ₀ = 0.300 mm, the sheet end of the incident side lenticular lens has an approximate curvature radius Ri ₁ = 0.320 mm, an ellipse with a lens depth hi ₁ = 0.300, and the pitch of the exit side lenticular lens sheet 12 (p ) = 0.36 mm, an ellipse having an approximate curvature radius Ro ₀ = 0.220 mm at the center of the exit side lenticular lens sheet, an ellipse having an approximate curvature radius Ro ₁ = 0.220 mm at the end of the exit side lenticular lens sheet, central portion of the sheet thickness t ₀ = 0.930mm of the lenticular lens sheet, the end sheet It was molded lenticular lens sheet bets thickness t ₁ = 0.930mm.
[0043]
Next, the light absorption layer 13 was printed on the molded lenticular lens sheet by a conventional method (stripe width 0.32 mm) to obtain the lenticular lens sheet of the example.
[0044]
(2) Evaluation (2-1) As a color shift Fresnel lens, a lens having a focal length f = 900 mm was prepared, and a rear projection screen was formed in combination with the above-described lenticular lens sheet (width about 1250 mm, height about 950 mm). ). This screen was attached to a commercially available rear projection projector TV (T0SHIBA AMERICA CONSUMER PRODUCTS., INC., Model name TP61E90). Then, an all white signal is input to this television set, and as shown in FIG. 2, the position 600A on the left side from the center of the screen 5 of the television set 20 toward the horizontal direction (A) is the position on the front of the screen 3 m away. By observing at (B) and the position (C) moved 60 ° in the counterclockwise direction in the horizontal direction, the color shift was evaluated as follows.
[0045]
First, the blue and green light sources were covered with a cover, and the luminance emitted from the screen when red light was emitted to the screen was measured at the B position (R ₀ [nit]). Next, the red and green light sources were covered with a cover, and the emission luminance from the blue light screen was measured in the same manner (B ₀ [nit]).
[0046]
The measurement position was moved to the C position, and the emission luminance R ₆₀ [nit] of red light and the emission luminance B ₆₀ [nit] of blue light were measured in the same manner as the measurement at the B position.
[0047]
Then, a color shift CS _{(600 mm, 60 ° )} representing the magnitude of the color change at the position (A) 600 mm on the left side from the center of the screen 5 was determined according to the following equation.
[0048]
[Equation 3]
CS _{(600 mm, 60 ° )} = 20 log ((R ₆₀ / R ₀ ) / (B ₆₀ / B ₀ )) [dB]
The results are shown in Table 1.
[0049]
(2-2) Total light transmittance Similar to the above-described measurement of color shift, a lenticular lens sheet is attached to a rear projection projector TV, and the position of 600 mm on the left side from the center of the screen of this TV set in the horizontal direction. The total light transmittance T _t was measured according to ASTM D-1003.
[0050]
The results are shown in Table 1.
[0051]
Examples 2-5, Comparative Examples 1-3
In substantially the same manner as in the examples, lenticular lens sheets having the shapes shown in Table 1 and Table 2 were prepared, and the color shift and total light transmittance were measured. These results are shown in Tables 1 and 2.
[0052]
[Table 1]

[0053]
[Table 2]

[0054]
From Tables 1 and 2, regarding the lens depth of the incident side lenticular lens, the ratio (hi ₁ / hi ₀ ) of the lens depth hi _{1 at} the sheet end to the lens depth hi ₀ at the center of the sheet is 0.98 to 1. It can be seen that according to the lenticular lens sheet of Example 10.10, the color shift can be reduced and the total light transmittance can be improved.
[0055]
On the other hand, it can be seen that in Comparative Example 1 in which the lens depth ratio (hi ₁ / hi ₀ ) is smaller than 0.98, the color shift is large and the total light transmittance is inferior.
[0056]
In Comparative Example 2 in which the lens depth ratio (hi ₁ / hi ₀ ) exceeds 1.10, the color shift and the total light transmittance are the same as those in the example, but the diffused light rapidly decreases in the horizontal direction. It turns out that there is a cut-off, which is not preferable.
[0057]
Further, in Comparative Example 3 in which the lens depth ratio (hi ₁ / hi ₀ ) exceeds 1.10 and the sheet thickness at the sheet edge is thin, the color shift is extremely large and the total light transmittance is also extremely low. I understand that.
[0058]
【The invention's effect】
According to the lenticular lens sheet of the present invention, the color shift can be reduced, and the light utilization efficiency can be improved by improving the total light transmittance of the sheet.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a lenticular lens sheet of the present invention and a ray tracing diagram thereof.
FIG. 2 is an explanatory diagram of a color shift measurement method.
FIG. 3 is a schematic configuration diagram of a general rear projection television.
FIG. 4 is an explanatory diagram of light rays in a general rear projection television.
FIG. 5 is a perspective view of a screen used in a general rear projection television.
FIG. 6 is a cross-sectional view of a conventional double-sided lenticular lens sheet.
FIG. 7 is a sectional view of a conventional single-sided lenticular lens sheet and a ray tracing diagram thereof.
FIG. 8 is a cross-sectional view and its ray tracing diagram when the sheet thickness of a double-sided lenticular lens sheet is changed.
[Explanation of symbols]
1 CRT
2 projection lens 3 Fresnel lens 4 lenticular lens sheet 5 rear projection screen 10x single-sided lenticular lens sheet 10, 10A double-sided lenticular lens sheet 1 incident side lenticular lens 2 outgoing side lenticular lens 3 light absorbing layer 20 television set

Claims (4)

An incident side lenticular lens having a shape in which cylindrical lenses are arranged in parallel in the width direction of the sheet on the incident side surface of the light beam, and an exit side lenticular lens having a shape in which cylindrical lenses are arranged in parallel in the width direction of the sheet on the exit side surface, In a double-sided lenticular lens sheet in which the top of the exit-side lenticular lens sheet is formed at a substantially condensing position of the entrance-side lenticular lens, the incident at the center of the effective screen range of the rear projection screen configured using this lenticular lens sheet When the lens depth of the side lenticular lens is hi ₀ and the lens depth of the incident side lenticular lens at the end of the effective screen range is hi ₁ ,
0.98 ≦ hi ₁ / hi ₀ ≦ 1.10.
Is satisfied ,
From the effective screen range center of the screen, the lens depth of said incident side lenticular lens is taken as h i _x in the position of the distance x in a direction perpendicular to the longitudinal direction of the cylindrical lenses constituting the incident side lenticular lens, a screen The lenticular lens sheet is characterized in that h i _x / h i ₀ monotonously decreases or increases with an increase in _x within the effective screen range . 2. The lenticular lens sheet according to claim 1, wherein a ratio of a sheet thickness at a sheet peripheral part to a sheet thickness at a sheet central part is 0.98 to 1.10.   The lenticular lens sheet according to claim 1 or 2 formed by extrusion molding.   The lenticular lens sheet according to claim 3, wherein the crowning amount of the shaping roll used for extrusion molding is 20 µm or more per meter.

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