JP5017987B2

JP5017987B2 - Optical film

Info

Publication number: JP5017987B2
Application number: JP2006260319A
Authority: JP
Inventors: 城柴田
Original assignee: Toppan Inc
Current assignee: Toppan Inc
Priority date: 2006-09-26
Filing date: 2006-09-26
Publication date: 2012-09-05
Anticipated expiration: 2026-09-26
Also published as: JP2008083148A

Description

本発明は有機ＥＬに関し、有機ＥＬ素子の光取り出し効率を向上させる構造を有する有機ＥＬ用光学フィルムおよびそれを用いた光学用転写シートに関する。 The present invention relates to an organic EL, and relates to an organic EL optical film having a structure that improves the light extraction efficiency of an organic EL element, and an optical transfer sheet using the same.

有機ＥＬ素子は、自発光による広視野角、高速応答も可能、薄型軽量なことからディスプレイや照明として期待されている。近年携帯電話やデジタルカメラのディスプレイとして実用化され盛んに開発が行われている。 The organic EL element is expected as a display or illumination because it has a wide viewing angle by self-emission, a high-speed response, and is thin and light. In recent years, it has been put into practical use as a display for mobile phones and digital cameras and has been actively developed.

有機ＥＬ素子は一般的に正孔輸送層、発光層、電子輸送層を電極で挟んだ構造である。電極間に電界をかけ、電子、正孔を注入し発光層で励起子を生成し、再結合することで発光する。励起子には一重項状態と三重項状態があり、一重項状態と三重項状態の発生確率は量子的に１：３であり、三重項状態の発光を利用する燐光発光材料を用いた場合でも発光効率は最大７５％となってしまう。更に、屈折率は有機層が１．７程度、透明電極は２．０、空気が１．０であるので素子界面での全反射が起こり、実際に素子外部に取り出せる光は発光する光の２０％程度になってしまい、合わせるとエネルギー変換効率として１５％が上限となってしまう。 An organic EL element generally has a structure in which a hole transport layer, a light emitting layer, and an electron transport layer are sandwiched between electrodes. An electric field is applied between the electrodes, electrons and holes are injected, excitons are generated in the light emitting layer, and light is emitted by recombination. The exciton has a singlet state and a triplet state, the generation probability of the singlet state and the triplet state is 1: 3, and even when a phosphorescent material that uses triplet state emission is used. The luminous efficiency is 75% at the maximum. Further, since the refractive index is about 1.7 for the organic layer, 2.0 for the transparent electrode, and 1.0 for air, total reflection occurs at the element interface, and light that can actually be extracted outside the element is 20 of the emitted light. When combined, the upper limit is 15% as the energy conversion efficiency.

この取り出し効率を改善する方法としては、素子側面に反射面を形成し全反射により素子側面方向に進む光を前方に反射させる方法、例えば特許文献１があるが、大面積に形成することが困難で実用的ではない。他には、回折格子やゾーンプレートを用いて、屈折、回折により、光の進行方向を変える、例えば特許文献２があるが、ある程度の効果はあるものの全反射を完全には防ぐことは出来ない。したがって、有機ＥＬの光取り出し方法は未だ不十分であり、取り出し方法の更なる改善が高効率化には不可欠である。
特開２００５−３２７５２２号公報特許第２９９１１８３号公報 As a method for improving the extraction efficiency, there is a method of forming a reflection surface on the side surface of the element and reflecting light traveling forward in the direction of the element side surface by total reflection, for example, Patent Document 1, but it is difficult to form a large area. It is not practical. In addition, there is, for example, Patent Document 2 that uses a diffraction grating or a zone plate to change the traveling direction of light by refraction and diffraction. However, although there is some effect, total reflection cannot be completely prevented. . Therefore, the light extraction method of organic EL is still insufficient, and further improvement of the extraction method is indispensable for high efficiency.
JP 2005-327522 A Japanese Patent No. 2911183

本発明は、上記の技術的背景を考慮してなされたものであって、有機ＥＬ素子の光取り出し効率を向上させる構造を有する有機ＥＬ用光学フィルムおよびそれを用いた光学用転写シートを提供することを課題とするものである。 The present invention has been made in consideration of the above technical background, and provides an organic EL optical film having a structure for improving the light extraction efficiency of an organic EL element, and an optical transfer sheet using the same. This is a problem.

上記の課題の解決手段として、請求項１に係る発明は、基材上に微細凹凸構造層を有する光学フィルムであって、前記基材上の前記微細凹凸構造層の凹凸形成面上に、表面保護層が形成されており、前記表面保護層の屈折率が、前記微細凹凸構造層の屈折率よりも小さく、前記微細凹凸構造が基材から遠ざかる方向に向かって断面積が減少し、前記表面保護層が、フッ素樹脂からなり、前記微細凹凸構造のピッチが５０ｎｍから３５０ｎｍであり、前記微細凹凸構造の高低差が５０ｎｍから５μｍであり、前記表面保護層側の面上に粘着層、保護フィルムが順次積層され、前記表面保護層側とは他方の基材面上に平坦化層、バリア層、透明電極層が順次積層されたことを特徴とする光学フィルムである。 As a means for solving the above problems, the invention according to claim 1 is an optical film having a fine concavo-convex structure layer on a substrate, wherein the surface is formed on the concavo-convex formation surface of the fine concavo-convex structure layer on the substrate. A protective layer is formed, a refractive index of the surface protective layer is smaller than a refractive index of the fine concavo-convex structure layer, and a cross-sectional area decreases in a direction in which the fine concavo-convex structure moves away from the substrate, and the surface The protective layer is made of a fluororesin, the pitch of the fine concavo-convex structure is from 50 nm to 350 nm, the height difference of the fine concavo-convex structure is from 50 nm to 5 μm, and the adhesive layer and the protective film are on the surface on the surface protective layer side Are sequentially laminated, and the surface protective layer side is an optical film characterized in that a planarizing layer, a barrier layer, and a transparent electrode layer are sequentially laminated on the other substrate surface .

本発明の光学フィルムを貼り付けるまたは基板とすることで光取り出し効率を容易に向上することが可能である。また、ＥＬの発光波長により凹凸のピッチを最適に設定することでその光に最適な光の取出しが可能になる。さらに、取り出し効率が高くなると、同じ輝度を得るのに、本発明の光学フィルムを用いることで低い電力で負荷をかけずに寿命を延ばすことが可能になることや、低い輝度の材料の使用も可能になり、高輝度、長寿命という問題に発光材料以外から貢献できること、そして低消費電力化できることはデバイスとして魅力があり非常に有効である。 The light extraction efficiency can be easily improved by attaching the optical film of the present invention or using the substrate. In addition, by setting the concave / convex pitch optimally according to the emission wavelength of the EL, it is possible to extract the light optimal for the light. Furthermore, when the extraction efficiency is increased, the same brightness can be obtained by using the optical film of the present invention to extend the life without applying a load with low power, and the use of a material with low brightness. Being able to contribute to the problems of high brightness and long life from other than the light emitting material, and being able to reduce power consumption is attractive and extremely effective as a device.

以下、本発明の実施形態の一例について図面を参照して説明する。本発明の光学フィルムは、微細凹凸構造のピッチを可視光の波長より小さい５０ｎｍから３５０ｎｍにし、基材フィルム４から遠ざかる方向に向かって断面積が減少する構造にすることで、可視光にとって明確な屈折率差を有する界面がなくなり、膜厚方向に連続的に屈折率が変化している状態を作り出せ、全反射を抑えることが可能になる。保護フィルム１，６は実際の使用時には剥がすため、本発明の光学フィルムの表面は微細凹凸構造または微細凹凸構造層上に積層された低屈折率の表面保護層２である。表面保護層２は防汚性、耐薬品性を付加し微細凹凸構造を保護するために用い、フッ素樹脂はその特性がよく、透明で低屈折率の材料であり適している。できるだけ屈折率の低い材料を用いることで、表面保護層と空気との界面で全反射が起こりにくくし、取り出し効率を大きく低下させず表面を保護する効果が得られる。さらに両面に微細凹凸構造を形成することで基材フィルムから空気まで連続に屈折率が変化するだけでなく、この光学フィルムを基板とする有機ＥＬ素子から空気まで屈折率が連続的に変化するようになり、取り出し効率が改善する。基材フィルムの両面にある微細凹凸構造は同じ形状でも異なるものでも良い。有機ＥＬ素子は凹凸に影響を受けるので平坦化層を導入している。また、有機層は酸素に影響を受けるため、バリア層を設けている。バリア層はＳｉＮやＳｉＯ、ＳｉＯ₂等が有効であるが特に指定するものではない。 Hereinafter, an example of an embodiment of the present invention will be described with reference to the drawings. In the optical film of the present invention, the pitch of the fine concavo-convex structure is changed from 50 nm to 350 nm, which is smaller than the wavelength of visible light, and the cross-sectional area decreases in the direction away from the base film 4. An interface having a difference in refractive index is eliminated, and a state in which the refractive index continuously changes in the film thickness direction can be created, and total reflection can be suppressed. Since the protective films 1 and 6 are peeled off during actual use, the surface of the optical film of the present invention is the surface protective layer 2 having a low refractive index laminated on the fine concavo-convex structure or the fine concavo-convex structure layer. The surface protective layer 2 is used to add antifouling properties and chemical resistance to protect the fine concavo-convex structure, and the fluororesin has good characteristics and is a transparent, low refractive index material and suitable. By using a material having a refractive index as low as possible, total reflection hardly occurs at the interface between the surface protective layer and air, and the effect of protecting the surface can be obtained without greatly reducing the extraction efficiency. Furthermore, by forming fine concavo-convex structures on both sides, not only the refractive index continuously changes from the base film to the air, but also the refractive index continuously changes from the organic EL element using this optical film as a substrate to the air. Thus, the extraction efficiency is improved. The fine concavo-convex structure on both surfaces of the base film may be the same shape or different. Since the organic EL element is affected by unevenness, a planarization layer is introduced. In addition, since the organic layer is affected by oxygen, a barrier layer is provided. As the barrier layer, SiN, SiO, SiO ₂ or the like is effective, but is not particularly specified.

図１に微細凹凸構造を形成した光学フィルムの構造を示す。基材フィルムは透明であることと微細構造を成形する材料との密着性が良いことが必要である。また微細凹凸構造形成にＵＶや熱を使う場合、ＵＶ透過性や耐熱性が必要である。屈折率は成形樹脂と基材フィルムが近い方がその界面での反射、屈折が少なく取り出し効果は大きくなる。構造について、ピッチは可視光よりも狭くする必要があり、少なくとも３５０ｎｍよりも狭い必要がある。逆に５０ｎｍより狭いと屈折率を連続的に変化させるための凹凸を高くしなければならず、アスペクト比が大きくなり、成形が難しく実用的ではない。高さに関しては屈折率を連続的に変化させるため少なくとも５０ｎｍ以上が必要で、成形性、実用性から５μｍ以下が適当である。実際には有機ＥＬの発光波長により最適に適宜決定する必要がある。微細凹凸構造は屈折率を連続的に変化させるため、断面形状は凸部が底部から上部に向かい断面積が減少するものが好適であり、円錐が望ましいが特に限定するものではない。また、面内の配置についても特に指定するものではない。粘着材、保護フィルムについては、剥離性がよく粘着材が微細構造、基材フィルムに糊残りがないものである必要がある。表面保護層について、微細構造層とは屈折率が連続的に変化していて全反射が抑えられているが、空気との界面では全反射が起こってしまうので、できるだけ屈折率が空気に近いすなわち屈折率が低い材料が必要である。 FIG. 1 shows the structure of an optical film having a fine relief structure. The base film must be transparent and have good adhesion to the material for forming the microstructure. Further, when UV or heat is used for forming the fine concavo-convex structure, UV transparency and heat resistance are required. The closer the molding resin and the base film are to the refractive index, the less the reflection and refraction at the interface, and the greater the extraction effect. For the structure, the pitch should be narrower than visible light, and at least narrower than 350 nm. Conversely, if it is narrower than 50 nm, the unevenness for continuously changing the refractive index must be increased, the aspect ratio becomes large, and molding is difficult and impractical. The height is required to be at least 50 nm in order to continuously change the refractive index, and is preferably 5 μm or less in view of moldability and practicality. Actually, it is necessary to determine the optimum optimally according to the emission wavelength of the organic EL. Since the fine concavo-convex structure continuously changes the refractive index, the cross-sectional shape is preferably such that the convex portion decreases from the bottom toward the top and the cross-sectional area decreases, and a cone is desirable, but is not particularly limited. Also, there is no particular designation for the in-plane arrangement. About an adhesive material and a protective film, it is necessary for the adhesive material to have good releasability, the adhesive material has a fine structure, and the base film has no adhesive residue. Regarding the surface protective layer, the refractive index is continuously changed from that of the microstructure layer and total reflection is suppressed, but total reflection occurs at the interface with air, so that the refractive index is as close to air as possible. A material with a low refractive index is required.

以下、具体的な実施例を挙げて本発明を説明する。 Hereinafter, the present invention will be described with specific examples.

微細凹凸構造はピッチ２００ｎｍ高さ３００ｎｍの構造で電子線描画により形成したレジスト版から電鋳によりＮｉ原版を作製した。易接着ＰＥＴフィルム東洋紡製Ａ４３００を基材フィルムとして、基材フィルムとＮｉ原版の間にアクリル系ＵＶ硬化樹脂を挟み密着させＵＶを照射することで微細凹凸構造を基材フィルム上に転写した。保護フィルムは日東電工製Ｒ−１００を使用し、微細凹凸構造を転写したフィルムに貼り付けた。
この光学フィルムをＳｉＮバリア層／ＩＴＯ透明電極／有機層（赤色発光、波長６２０ｎｍ）／Ａｇ合金電極／ガラスの有機ＥＬ素子上に貼り付け評価したところ、光学フィルムのない状態に比べると外部量子効率が２倍に改善した。 The fine concavo-convex structure was a structure having a pitch of 200 nm and a height of 300 nm, and a Ni original plate was produced by electroforming from a resist plate formed by electron beam drawing. An easy-adhesion PET film A4300 manufactured by Toyobo was used as a base film, and an acrylic UV curable resin was sandwiched between the base film and the Ni original plate, and the fine concavo-convex structure was transferred onto the base film by irradiation with UV. The protective film used was R-100 manufactured by Nitto Denko, and was attached to the film to which the fine concavo-convex structure was transferred.
When this optical film was attached and evaluated on an organic EL element of SiN barrier layer / ITO transparent electrode / organic layer (red light emission, wavelength 620 nm) / Ag alloy electrode / glass, the external quantum efficiency was compared with the state without the optical film. Improved twice.

本発明の光学フィルムの一例の一部を示す断面図である。It is sectional drawing which shows a part of example of the optical film of this invention. 本発明の光学フィルムの他の例の一部を示す断面図である。It is sectional drawing which shows a part of other example of the optical film of this invention.

Explanation of symbols

１保護フィルム
２表面保護層
３微細凹凸構造層
４基材フィルム
５粘着材層
６保護フィルム
７微細凹凸構造層
８平坦化層
９バリア層
１０透明電極 DESCRIPTION OF SYMBOLS 1 Protective film 2 Surface protective layer 3 Fine uneven structure layer 4 Base film 5 Adhesive material layer 6 Protective film 7 Fine uneven structure layer 8 Planarizing layer 9 Barrier layer 10 Transparent electrode

Claims

An optical film having a fine concavo-convex structure layer on a substrate, wherein a surface protective layer is formed on the concavo-convex formation surface of the fine concavo-convex structure layer on the substrate, and the refractive index of the surface protective layer is The refractive index of the fine concavo-convex structure layer is smaller than the refractive index of the fine concavo-convex structure layer, the cross-sectional area decreases in a direction away from the substrate, the surface protective layer is made of a fluororesin, and the pitch of the fine concavo-convex structure is 50 nm to 350 nm, the height difference of the fine concavo-convex structure is 50 nm to 5 μm, an adhesive layer and a protective film are sequentially laminated on the surface of the surface protective layer side, and the surface protective layer side is the other substrate optical film characterized in that a planarizing layer on the surface, the barrier layer, the transparent electrode layer are sequentially stacked.