JP4161166B2 - Organic EL head, manufacturing method thereof, and image forming apparatus using the same - Google Patents

Description

【００４４】
また、正孔輸送層４として、次の化学式２で示されるＰＥＤＯＴ−ＰＰＳ（ｐｏｌｙｅｔｈｙｌｅｎｅ ｄｉｏｘｙｔｈｉｏｐｈｅｎｅ／ｐｏｌｙｓｔｙｒｅｎｅ ｓｕｌｐｈｏｎａｔｅ）を使用する。
【００４５】
【化２】

【００４６】
このように、本発明においては、有機ＥＬ層を高分子系の材料で液相法により形成している。ここで、低分子系の材料も液相法により有機ＥＬ層として構成できなかどうかを検討する。低分子系の材料も溶剤に溶けることから、液相法により塗布することは可能である。
【００４７】
しかしながら、低分子系の材料は、結晶性が高いので、成膜時にすぐ結晶化して凝集し、均一な膜にはならないという特性がある。このため、本発明においては、液相法で成膜する有機ＥＬ層には、低分子系の材料を採用していない。
【００４８】
図１の構成では、基板１からみて下側に陽極２を、上側に陰極６を配置している。次に、このような電極配置とした理由について説明する。図１においては、陽極を上側に形成する場合には、有機ＥＬ層を形成した後にＩＴＯをスパッタ法で処理することになる。
【００４９】
このように、ＩＴＯ分子を有機材料の上に高速で飛ばすことになると、有機材料が劣化するという問題が生じる。陽極材料であるＩＴＯを液相法で形成することも可能であるが、液相法を使用してＩＴＯを形成した場合でも、製造工程で加熱処理が必要となる。このため、有機材料の劣化が避けられないという問題が生じる。
【００５０】
このため、本発明においては、有機材料を熱で劣化させないように、有機材料の上に蒸着で形成可能な金属材料が使用されている。この金属材料は、仕事関数が小さなＡｌなどが使用され、陰極を形成している。
【００５１】
本発明においては、前記のように反射層２と半透明反射層７とにより、微小光共振器を構成している。次に、微小光共振器を構成することによる利点を、図３、図４の光強度分布特性図で説明する。図３、図４は、最大値を１とした場合の光強度の相対分布を示すものである。
【００５２】
図３は、微小光共振器構造を採用しない場合の特性図である。有機ＥＬ素子の発光面は、完全拡散光源に近く、この場合の光強度の角度分布は、略球面状の分布となる。また、図４は、図１の微小光共振器構造を採用した場合の特性図である。この場合の光強度の角度分布は、角度０の方向（正面方向）に指向性が強められた特性が得られている。すなわち、像担持体方向の光分布強度が大きくなる。
【００５３】
したがって、微小光共振器構造を採用することにより、光の拡散を抑制し、露光スポットの広がりが少なくなる。すなわち、光の放射角を小さくすることができるので、クロストークを防止することができる。また、発光波長の半値幅を狭くしてピーク波長の出力を強めて発光効率を向上させることができる。このような微小光共振器構造による光学的な特性は、発光部で発光する光の方向が共振方向に揃えられる作用があるために得られている。
【００５４】
本発明の実施形態について、有機ＥＬヘッド各部の諸元を表１に示す。
【００５５】
【表１】

【００５６】
表１は、発光ピーク波長が６３６ｎｍにおける有機ＥＬヘッドの各部の諸元を示している。誘電体多層膜からなる半透明反射層（誘電体ミラー）７は、一対のＳｉＯ₂とＴｉＯ₂からなる層を３層積層して形成されている。また、誘電体多層膜からなる反射層（誘電体ミラー）２は、一対のＳｉＯ₂とＴｉＯ₂からなる層を８層積層して形成されている。
【００５７】
反射層２および半透明反射層７に使用されるＳｉＯ₂は、屈折率が１.４５、厚さが１０９.７（ｎｍ）、光学長が１５９（ｎｍ）、光学長／波長が０.２５である。また、ＴｉＯ₂は、屈折率が２.３、厚さが６９.１（ｎｍ）、光学長が１５９（ｎｍ）、光学長／波長が０.２５である。
【００５８】
なお、表１は各反射層に使用される誘電体多層膜の特性の一例を示すものである。本発明においては、誘電体多層膜の層数、各層の層厚、材質などを適宜選定することにより、反射率が１に近い値とすることができる。このため、発光層の出力光は無駄な面から射出することなく、出力光の有効利用を図ることができる。
【００５９】
正孔輸送層４の材料であるＰＥＤＯＴ−ＰＳＳは、屈折率が１.５１、厚さが１０５.３（ｎｍ）、光学長が１５９（ｎｍ）、光学長／波長が０.２５である。発光層５の材料であるＭＥＨ−ＰＰＶは、屈折率が１.７、厚さが９３.５（ｎｍ）、光学長が１５９（ｎｍ）、光学長／波長が０.２５である。
【００６０】
また、陽極に用いるＩＴＯは、屈折率が１.９、厚さが１６７.４（ｎｍ）、光学長が３１８（ｎｍ）、光学長／波長が０.５の特性である。陰極６に使用されるアルミニューム（Ａｌ）は、屈折率が０.７６、厚さが０.５（ｎｍ）以下のものである。
【００６１】
本発明においては、上記のような構成の有機ＥＬヘッドを、例えば電子写真方式のカラー画像を形成する画像形成装置の露光ヘッドとして用いることができる。図５は、有機ＥＬアレイ露光ヘッドの一例を模式的に示す平面図である。
【００６２】
この実施形態の有機ＥＬアレイ露光ヘッド１５は、２列のアレイ１６、１６’が平行で相互の画素が千鳥状になるように配列されている。各アレイ１６、１６’は直線状に配置された多数の画素１７からなるが、各画素１７の構成は同じである。各画素１７は、有機ＥＬヘッド１８と、その有機ＥＬヘッド１８の発光を制御するＴＦＴ１９とから構成される。
【００６３】
図６は、図５で説明した有機ＥＬアレイ露光ヘッドを用いた画像形成装置の一例を示す正面図である。この画像形成装置は、同様な構成の４個の有機ＥＬアレイ露光ヘッド１Ｋ、１Ｃ、１Ｍ、１Ｙを、対応する同様な構成である４個の感光体ドラム４１Ｋ、４１Ｃ、４１Ｍ、４１Ｙの露光位置にそれぞれ配置した、タンデム方式の画像形成装置として構成されている。
【００６４】
図６に示すように、この画像形成装置は、駆動ローラ５１と従動ローラ５２とテンションローラ５３とが設けられており、テンションローラ５３でテンションを加えて張架されて、図示矢印方向（反時計方向）へ循環駆動される中間転写ベルト５０を備えている。この中間転写ベルト５０に対して所定間隔で配置された４個の像担持体としての外周面に感光層を有する感光体４１Ｋ、４１Ｃ、４１Ｍ、４１Ｙが配置される。
【００６５】
前記符号の後に付加されたＫ、Ｃ、Ｍ、Ｙはそれぞれ黒、シアン、マゼンタ、イエローを意味し、それぞれ黒、シアン、マゼンタ、イエロー用の感光体であることを示す。他の部材についても同様である。感光体４１Ｋ、４１Ｃ、４１Ｍ、４１Ｙは、中間転写ベルト５０の駆動と同期して図示矢印方向（時計方向）へ回転駆動される。
【００６６】
各感光体４１（Ｋ、Ｃ、Ｍ、Ｙ）の周囲には、それぞれ感光体４１（Ｋ、Ｃ、Ｍ、Ｙ）の外周面を一様に帯電させる帯電手段（コロナ帯電器）４２（Ｋ、Ｃ、Ｍ、Ｙ）と、この帯電手段４２（Ｋ、Ｃ、Ｍ、Ｙ）により一様に帯電させられた外周面を感光体４１（Ｋ、Ｃ、Ｍ、Ｙ）の回転に同期して順次ライン走査する本発明の上記のような有機ＥＬアレイ露光ヘッド１（Ｋ、Ｃ、Ｍ、Ｙ）が設けられている。
【００６７】
また、この有機ＥＬアレイ露光ヘッド１（Ｋ、Ｃ、Ｍ、Ｙ）で形成された静電潜像に現像剤であるトナーを付与して可視像（トナー像）とする現像装置４４（Ｋ、Ｃ、Ｍ、Ｙ）と、この現像装置４４（Ｋ、Ｃ、Ｍ、Ｙ）で現像されたトナー像を一次転写対象である中間転写ベルト５０に順次転写する転写手段としての一次転写ローラ４５（Ｋ、Ｃ、Ｍ、Ｙ）と、転写された後に感光体４１（Ｋ、Ｃ、Ｍ、Ｙ）の表面に残留しているトナーを除去するクリーニング手段としてのクリーニング装置４６（Ｋ、Ｃ、Ｍ、Ｙ）とを有している。
【００６８】
ここで、各有機ＥＬアレイ露光ヘッド１（Ｋ、Ｃ、Ｍ、Ｙ）は、図６に示すように対応する感光体４１（Ｋ、Ｃ、Ｍ、Ｙ）の表面から所定距離だけ離れて、有機ＥＬアレイ露光ヘッド１（Ｋ、Ｃ、Ｍ、Ｙ）のアレイ方向が感光体ドラム４１（Ｋ、Ｃ、Ｍ、Ｙ）の母線に沿うように設置される。そして、各有機ＥＬアレイ露光ヘッド１（Ｋ、Ｃ、Ｍ、Ｙ）の発光エナルギーピーク波長と、感光体４１（Ｋ、Ｃ、Ｍ、Ｙ）の感度ピーク波長とは略一致するように設定されている。
【００６９】
現像装置４４（Ｋ、Ｃ、Ｍ、Ｙ）は、例えば、現像剤として非磁性一成分トナーを用いるもので、その一成分現像剤を例えば供給ローラで現像ローラへ搬送し、現像ローラ表面に付着した現像剤の膜厚を規制ブレードで規制し、その現像ローラを感光体４１（Ｋ、Ｃ、Ｍ、Ｙ）に接触あるいは押厚させて感光体４１（Ｋ、Ｃ、Ｍ、Ｙ）の電位レベルに応じて現像剤を付着させることによりトナー像として現像するものである。
【００７０】
このような４色の単色トナー像形成ステーションにより形成された黒、シアン、マゼンタ、イエローの各トナー像は、一次転写ローラ４５（Ｋ、Ｃ、Ｍ、Ｙ）に印加される一次転写バイアスにより中間転写ベルト５０上に順次一次転写され、中間転写ベルト５０上で順次重ね合わされてフルカラーとなったトナー像は、二次転写ローラ６６において用紙等の記録媒体Ｐに二次転写され、定着部である定着ローラ対６１を通ることで記録媒体Ｐ上に定着され、排紙ローラ対６２によって、装置上部に形成された排紙トレイ６８上へ排出される。
【００７１】
なお、図６中、６３は多数枚の記録媒体Ｐが積層保持されている給紙カセット、６４は給紙カセット６３から記録媒体Ｐを一枚ずつ給送するピックアップローラ、６５は二次転写ローラ６６の二次転写部への記録媒体Ｐの供給タイミングを規定するゲートローラ対、６６は中間転写ベルト５０との間で二次転写部を形成する二次転写手段としての二次転写ローラ、６７は二次転写後に中間転写ベルト５０の表面に残留しているトナーを除去するクリーニング手段としてのクリーニングブレードである。
【００７２】
図６で用いる有機ＥＬアレイ露光ヘッド１（Ｋ、Ｃ、Ｍ、Ｙ）は、図１に示したように各有機ＥＬ発光部上に、インクジェット方式により所定の焦点距離の凸マイクロレンズ８が形成されてなるものであるが、凸マイクロレンズ８に代えてボールレンズを用いる構成としても良い。
【００７３】
この際に、ボールレンズは誘電体多層膜７に接着して取り付けても良いし、陰極層６の凹所内の誘電体多層膜７上に単に載置する構成としても良い。このように、図６の画像形成装置は、書き込み手段として図１に示した有機ＥＬヘッドを用いているので、レーザ走査光学系を用いた構成とする場合と比較して、装置の小型化を図ることができる。
【００７４】
以上、本発明の有機ＥＬアレイ露光ヘッドとその作製方法及びそれを用いた画像形成装置を実施例に基づいて説明したが、本発明はこれら実施例に限定されず種々の変形が可能である。
【００７５】
【発明の効果】
以上の説明から明らかなように、本発明においては、光学系を有する有機ＥＬヘッドを液相法、特にインクジェット法により容易に構成することができる。また、微小光共振構造と組み合わせることにより、光の放射角を小さくすることができるので、クロストークを防止することができる。
【００７６】
また、反射層として機能する誘電体多層膜は、層数、各層の層厚、材質などを調整することにより、反射率を略１（０.９９９）に近づけることが可能となり、有機ＥＬヘッドの不要な面からの光の漏出を防止することができる。更に、陰極側から光を射出することと組み合わせて、発光部とマイクロレンズとの距離を短くすることができるので、光の利用効率が向上する。なお、本発明の有機ＥＬヘッドを用いることにより、画像形成装置の小型化が図れる。
【図面の簡単な説明】
【図１】本発明に基づく有機ＥＬヘッドの一例を示す縦断正面図である。
【図２】インクジェット方式におけるピエゾジェット方式のヘッドの構成例を示す断面図である。
【図３】光放射強度分布の特性図である。
【図４】本発明による光放射強度分布を示す特性図である。
【図５】有機ＥＬアレイ露光ヘッドの概略構成を示す平面図である。
【図６】本発明の有機ＥＬヘッドを配置したタンデム方式の画像形成装置の概略構成を示す正面図である。
【符号の説明】
１…基板
２…誘電体多層膜からなる反射層
３…陽極
４…正孔輸送層
５…発光層
６…陰極
７…誘電体多層膜からなる半透明反射層
８…マイクロレンズ
９…隔壁（バンク）
１０…有機ＥＬアレイ
１１…隔壁の穴
１５…有機ＥＬアレイ露光ヘッド
１６、１６‘…アレイ
１７…画素
１８…有機ＥＬヘッド
１９…ＴＦＴ
２１…ヘッド
２２…ノズルプレート
２３…振動板
２４…仕切部材（リザーバープレート）
２５…インク室
２６…ノズル孔
２８…圧電素子
２９…電極
１（Ｋ、Ｃ、Ｍ、Ｙ）…有機ＥＬアレイ露光ヘッド
４１（Ｋ、Ｃ、Ｍ、Ｙ）…感光体ドラム
４２（Ｋ、Ｃ、Ｍ、Ｙ）…帯電手段（コロナ帯電器）
４４（Ｋ、Ｃ、Ｍ、Ｙ）…現像装置
４５（Ｋ、Ｃ、Ｍ、Ｙ）…一次転写ローラ
４６（Ｋ、Ｃ、Ｍ、Ｙ）…クリーニング装置
５０…中間転写ベルト
５１…駆動ローラ
５２…従動ローラ
５３…テンションローラ
６１…定着ローラ対
６２…排紙ローラ対
６３…給紙カセット
６４…ピックアップローラ
６５…ゲートローラ対
６６…二次転写ローラ
６７…クリーニングブレード
６８…排紙トレイ
Ｐ…記録媒体[0001]
BACKGROUND OF THE INVENTION
The present invention has a structure in which the organic EL film is formed by a liquid phase method, the reflectance of the reflective layer is brought close to 1, and the light utilization efficiency is improved by adopting a micro optical resonator structure. The present invention relates to a head, a manufacturing method thereof, and an image forming apparatus using the head.
[0002]
[Prior art]
Conventionally, in an image forming apparatus for writing a latent image on an image carrier, an apparatus using a laser scanning optical system is used as a writing unit. Further, an LED array is also known as a writing means.
[0003]
The apparatus using the laser scanning optical system has a problem in that various optical parts such as lenses are required, so that the apparatus becomes large and high-speed processing is limited. In addition to the problem that the LED array is used, in addition to the problem that the substrate and the driver are expensive, there is a problem that the configuration becomes complicated because a rod array lens is required to form an image on the image carrier. It was.
[0004]
In recent years, attempts have been made to use an organic EL (organic electroluminescent element) array as the writing means. In Japanese Patent Application Laid-Open No. 2000-77184, a light emitting layer is formed by organic EL, and the anode side is made of SiO₂TiO₂For example, a micro-optical resonator structure is formed between a semi-transparent reflective layer formed of the above and a cathode layer using Mg, Al, etc., to increase luminous efficiency.
[0005]
In Japanese Patent Laid-Open No. 2000-77188, the light emission efficiency is further enhanced by constituting the micro optical resonator structure and using a microlens. Japanese Patent Application Laid-Open No. 2000-77188 describes a method of creating a microlens on the top surface of the substrate by the in-o method, a method using a photoresist on the back surface of the substrate, or a replica method. By aligning the microlenses thus created, an organic EL array having an optical resonator structure is deposited by vapor deposition.
[0006]
[Problems to be solved by the invention]
In the prior art described in JP 2000-77184 A and JP 2000-77188 A, SiO2, TiO₂A micro-optical resonator structure is configured between a translucent layer formed by the above method and a cathode using Mg, Al, or the like. When such a micro optical resonator structure is employed, the light emission intensity increases as the reflectance on the non-light emitting side is closer to 1.
[0007]
However, in each of the above prior arts, the cathode layer on the side that does not emit light uses a metal such as Mg or Al, so the upper limit of the reflectance is determined by the spectral reflection characteristics of the material. Further, the reflectivity is lowered depending on the state of the metal surface, and there is a problem that it is difficult to increase the reflectivity to the limit of 0.999 or more.
[0008]
By the way, as a method for forming the organic EL layer, a liquid phase method such as an ink jet method or a spin coating method and a vapor deposition method are employed. When the liquid phase method is employed, the surface smoothness tends to be worse than when the vapor deposition method is employed. In each of the above prior arts, when the organic EL layer is formed by a liquid phase method, the cathode layer functioning as the reflective layer is deposited on the organic EL layer with a certain thickness, so that the cathode layer has smoothness. There was a problem that the reflectivity decreased due to deterioration.
[0009]
In addition, Japanese Patent Application Laid-Open No. 2000-77188 in which a microlens is integrated with an organic EL array has a problem that the microlens material is restricted. Furthermore, in this example, since the organic EL layer is formed by vapor deposition, there is a problem that the selectivity of the material of the organic EL layer is narrow.
[0010]
The present invention has been made in view of such problems of the prior art, and its purpose is to form a structure in which an organic EL film is formed by a liquid phase method, and the reflectance of the reflective layer is close to 1. To provide an organic EL head in which the utilization efficiency of light is improved by adopting a minute optical resonator structure, a manufacturing method thereof, and an image forming apparatus using the organic EL head.
[0011]
[Means for Solving the Problems]
The organic EL head of the present invention that achieves the above object is formed at a predetermined height with a substrate, a reflective layer made of a dielectric multilayer film formed on the substrate, and a hole on the reflective layer. An opaque partition,
In the hole of the partition,
  An anode formed on the reflective layer;
  An organic EL light emitting layer formed on the anode;
  A cathode formed of a metal thin film having a thickness for transmitting light on the organic EL light emitting layer;
  A translucent reflective layer composed of a dielectric multilayer film having a number of laminated layers formed on the cathode and smaller than that of the reflective layer;
  On the translucent reflective layerBy inkjet methodWith the formed micro lens
Have
The reflective layer and the semi-transparent reflective layer constitute a micro-optical resonator, which is transmitted through the semi-transparent reflective layer and emits output light from the micro lens.
[0012]
  This organic EL head is characterized in that the organic EL is formed by a liquid phase method.
[0013]
  The organic EL head of the present invention includes a step of forming a reflective layer made of a dielectric multilayer film on a substrate, and a step of forming an opaque partition wall having a predetermined height with a hole on the reflective layer.
HaveIn the hole of the partition,
  Forming an anode on the reflective layer;
  Forming an organic EL light emitting layer on the anode by a liquid phase method;
  Forming a cathode by depositing a metal thin film having a thickness of transmitting light on the organic EL light emitting layer by vapor deposition;
  Forming a translucent reflective layer comprising a dielectric multilayer film having a smaller number of layers on the cathode than the reflective layer;
  On the translucent reflective layerBy inkjet methodForming a microlens and,
HaveThe reflective layer and the semitransparent reflective layer constitute a micro optical resonator, and an organic EL head that transmits the semitransparent reflective layer and emits output light from the microlens is manufactured.
[0015]
The image forming apparatus of the present invention includes the organic EL head having the above characteristics as an exposure head for writing an image on an image carrier.
[0016]
  Further, the image forming apparatus is an image forming apparatus in which at least two or more image forming stations each including a charging unit, an exposure head, a developing unit, and a transfer unit are provided around an image carrier. .
[0017]
In the present invention, an organic EL head having an optical system can be easily constructed by a liquid phase method, particularly an ink jet method. Further, by combining with a minute optical resonance structure, the light emission angle can be reduced and crosstalk can be prevented.
[0018]
In addition, in the dielectric multilayer film functioning as a reflective layer, the reflectance can be brought close to approximately 1 (0.999) by adjusting the number of layers, the layer thickness of each layer, the material, and the like. Leakage of light can be prevented. Furthermore, in combination with emitting light from the cathode side, the distance between the light emitting portion and the microlens can be shortened, so that the light utilization efficiency is improved. Note that the size of the image forming apparatus can be reduced by using the organic EL head of the present invention.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, examples of the organic EL head of the present invention will be described based on the manufacturing method thereof. FIG. 1 is a longitudinal sectional front view showing an example of the organic EL head 10. In FIG. 1, a dielectric multilayer reflective layer (dielectric mirror) 2 is formed on a substrate 1 made of glass or resin film by sputtering.
[0020]
The reflective layer 2 made of this dielectric multilayer film is, for example, a pair of SiO 2₂And TiO₂It is formed by laminating a plurality of layers, for example, eight layers. The reflection layer 2 made of such a dielectric multilayer film according to the present invention has a reflectivity of about 0.999, and a reflection layer with extremely good reflection characteristics can be obtained.
[0021]
Next, the holes 11 corresponding to the light emitting portions of the organic EL head 10 are formed, and the partition walls (bumps) 9 are formed at a predetermined height. The partition wall 9 can be formed by an arbitrary method such as a photolithography method or a printing method as disclosed in Japanese Patent Application Laid-Open No. 2000-353594.
[0022]
For example, when the lithography method is used, an organic material is applied in accordance with the bump height by a predetermined method such as spin coating, spray coating, roll coating, die coating, dip coating, and a resist layer is applied thereon. Then, a mask is applied in accordance with the shape of the partition wall 9, and the resist is exposed and developed to leave a resist matched to the shape of the partition wall 9. Finally, the partition wall material is etched to remove the partition wall material other than the mask.
[0023]
Further, the bump (convex portion) may be formed of two or more layers in which the lower layer is made of an inorganic material and the upper layer is made of an organic material. Further, as disclosed in JP-A-2000-323276, the material constituting the partition wall 9 is not particularly limited as long as it has durability against the solvent of the EL material, but it is made Teflon by fluorocarbon gas plasma treatment. For example, organic materials such as acrylic resin, epoxy resin, and photosensitive polyimide are preferable. The laminated partition which made inorganic materials, such as liquid glass, the lower layer may be sufficient. The partition wall 9 is desirably black or opaque by mixing carbon black or the like with the above material.
[0024]
Next, immediately before the organic EL light emitting layer ink composition is applied, the substrate provided with the partition walls 9 is subjected to continuous plasma treatment of oxygen gas and fluorocarbon gas plasma. Thereby, for example, the polyimide surface constituting the partition wall 9 is water repellent, and the wettability of the substrate side for finely patterning the ink jet droplets can be controlled. As an apparatus for generating plasma, an apparatus for generating plasma in a vacuum or an apparatus for generating plasma in the atmosphere can be used similarly.
[0025]
Next, the anode 3 is formed on the reflective layer 2 made of a dielectric multilayer film by sputtering. The anode 3 is made of a light transmissive and conductive material. As a material having such characteristics, a material having a large work function such as ITO (indium tin oxide) is used.
[0026]
Next, the hole transport layer 4 is formed on the anode 3 by an ink jet method. Further, after forming the hole transport layer 4 in the hole 11, the ink composition is discharged from the head of the ink jet printing apparatus into the hole 11, and patterning is applied on the light emitting layer of each pixel. After coating, the solvent is removed and heat treatment is performed to form the light emitting layer 5.
[0027]
The organic EL layer of the hole transport layer 4 and the light emitting layer 5 is prepared by applying the ink composition by the ink jet method as described above, but instead of the ink jet method, a known spin coating method or dip method is used. Other liquid phase methods can also be used.
[0028]
As materials used for the hole transport layer 4 and the light emitting layer 5, various known EL materials described in, for example, JP-A Nos. 10-12377 and 2000-323276 can be used. Detailed description thereof is omitted.
[0029]
Next, the cathode 6 is formed by vapor deposition. As the material of the cathode 6, for example, Al is used. The cathode 6 of the present invention is formed with a thin film portion 6a having a thickness in the hole 11 of the partition wall 9 that allows light to pass therethrough so that the cross-sectional shape is concave.
[0030]
A translucent reflective layer 7 made of a plurality of dielectric multilayer films is formed on the bottom of the recess of the cathode 6 by sputtering. The translucent reflective layer 7 made of this dielectric multilayer film is composed of a pair of SiO 2₂And TiO₂For example, three layers are laminated. The translucent reflective layer 7 formed of such a dielectric multilayer film according to the present invention has a reflectance of about 0.9.
[0031]
Next, a microlens 8 is formed on the translucent reflective layer 7 made of a dielectric multilayer film by an inkjet method. In this process, the transparent ink composition for the microlens is discharged from the head 21 (FIG. 2) of the ink jet printing apparatus into the recess of the cathode 6 formed in the hole 11 of the partition wall 9, and patterning is applied. Post-curing is performed to form a convex microlens 8 on the organic EL light emitting portion of each pixel.
[0032]
The radius of curvature of the surface of the microlens 8 formed into a convex shape, that is, the focal length, is the ejection amount of the ink composition, the diameter of the hole, the surface tension of the transparent ink composition for the microlens, and the repellency to the dielectric multilayer film 7. It is determined by the degree of aqueousity, the amount of shrinkage when the ink composition is cured, and the like. In the present invention, as described above, output light is emitted from the microlens 8 through the thin metal film cathode 6 that transmits light and the translucent reflective layer 7 made of a dielectric multilayer film on the light emitting layer 5. Yes. For this reason, since the distance from the light emitting layer 5 to the microlens 8 is shortened, light absorption and attenuation are reduced before reaching the image carrier, and light utilization efficiency is improved.
[0033]
Here, the ink jet system used in the present invention is based on a piezo jet system that discharges an ink composition using mechanical energy of a piezoelectric element or the like, and bubbles are generated using the thermal energy of a heater, and the generation of the bubbles Any of the thermal methods for discharging the ink composition may be used (“Fine Imaging and Hard Copy” 1999.1.7 (Corona Co., Ltd.), edited by the Japan Photography Society and the Imaging Society of Japan Joint Publishing Committee). 43).
[0034]
FIG. 2 is a cross-sectional view illustrating a configuration example of a piezo jet head. The inkjet head 21 includes, for example, a stainless steel nozzle plate 22 and a diaphragm 23, and both are joined via a partition member (reservoir plate) 24. A plurality of ink chambers 25 and liquid reservoirs (not shown) are formed between the nozzle plate 22 and the vibration plate 23 by the partition member 24. The interiors of the ink chamber 25 and the liquid reservoir are filled with the ink composition, and the ink chamber 25 and the liquid reservoir communicate with each other through a supply port.
[0035]
Further, the nozzle plate 22 is provided with nozzle holes 26 for jetting the ink composition from the ink chamber 25 in a jet form. On the other hand, the ink jet head 21 is formed with an ink introduction hole for supplying the ink composition to the liquid reservoir. A piezoelectric element 28 is bonded to the surface of the vibration plate 23 opposite to the surface facing the ink chamber 25 so as to correspond to the position of the ink chamber 25.
[0036]
The piezoelectric element 28 is positioned between the pair of electrodes 29 and bends so that the piezoelectric element 28 protrudes outward when energized. As a result, the volume of the ink chamber 25 increases. Therefore, the ink composition corresponding to the increased volume in the ink chamber 25 flows from the liquid reservoir through the supply port.
[0037]
Next, when energization to the piezoelectric element 28 is released, both the piezoelectric element 28 and the diaphragm 23 return to their original shapes. As a result, the space also returns to the original volume, so that the pressure of the ink composition inside the ink chamber 25 increases, and the ink composition is ejected from the nozzle hole 26 toward the substrate 1 provided with the partition wall 9.
[0038]
By the way, the organic EL light emitting section as described above has a property of being easily deteriorated by moisture. In order to prevent such moisture intrusion, it is desirable to apply a transparent protective layer to the entire surface of the substrate after the microlenses 8 are formed. As a material for the transparent protective layer, for example, an epoxy resin, an acrylic resin, liquid glass, or the like can be used.
[0039]
In FIG. 1, of the output light emitted from the light emitting layer 5, the reflected light of the reflective layer 2 made of a dielectric multilayer film passes through the thin film portion 6 a of the cathode 6 and is translucent reflective layer 7 made of a dielectric multilayer film. , Passes through the translucent reflective layer 7 and is emitted from the microlens 8 to the outside. As such a configuration, the reflective layer 2 and the translucent reflective layer 7 constitute a micro optical resonator structure.
[0040]
Thus, in this invention, the thin film part 6a is formed in the cathode 6, and light is permeate | transmitted by this thin film part 6a. In other words, unlike the prior art, the cathode is not formed to have a predetermined thickness and the cathode reflects light. For this reason, even when the organic EL layers of the hole transport layer 4 and the light emitting layer 5 are formed by a liquid phase method such as an inkjet method, the portion of the cathode in contact with the organic EL layer transmits light as a thin film. Even if the cathode is formed by vapor deposition, there is no problem that the reflectance is lowered due to the smoothness of the contact portion between the EL layer and the cathode.
[0041]
In the present invention, the organic EL layer can be formed by a liquid phase method such as a dip method in addition to the ink jet method. For this reason, there is an advantage that patterning of the light emitting layers of the three colors becomes easy.
[0042]
Next, materials of the organic EL layer used for the hole transport layer 4 and the light emitting layer 5 in FIG. 1 will be described. As the light-emitting layer 5, MEH-PPV {poiy [2-methoxy-5- (2′-ethyl-hexyloxy) -1,4-phenylene vinylene]} represented by the following chemical formula 1 is used.
[0043]
[Chemical 1]

[0044]
As the hole transport layer 4, PEDOT-PPS (polyethylene dioxythiophene / polystyrene sulfate) represented by the following chemical formula 2 is used.
[0045]
[Chemical 2]

[0046]
Thus, in the present invention, the organic EL layer is formed of a polymer material by a liquid phase method. Here, it is examined whether or not a low molecular material can be formed as an organic EL layer by a liquid phase method. Since a low molecular weight material is also soluble in a solvent, it can be applied by a liquid phase method.
[0047]
However, since low molecular weight materials have high crystallinity, they have a characteristic that they are crystallized and aggregated immediately during film formation and do not form a uniform film. For this reason, in this invention, the low molecular material is not employ | adopted for the organic EL layer formed into a film by a liquid phase method.
[0048]
In the configuration of FIG. 1, the anode 2 is disposed on the lower side and the cathode 6 is disposed on the upper side when viewed from the substrate 1. Next, the reason why such an electrode arrangement is used will be described. In FIG. 1, when the anode is formed on the upper side, the ITO is processed by sputtering after the organic EL layer is formed.
[0049]
As described above, when the ITO molecules are blown onto the organic material at a high speed, there arises a problem that the organic material is deteriorated. It is possible to form the anode material ITO by a liquid phase method, but even when the ITO is formed by using the liquid phase method, heat treatment is required in the production process. For this reason, the problem that deterioration of an organic material cannot be avoided arises.
[0050]
For this reason, in the present invention, a metal material that can be formed on the organic material by vapor deposition is used so that the organic material is not deteriorated by heat. As this metal material, Al or the like having a small work function is used to form a cathode.
[0051]
In the present invention, as described above, the reflective layer 2 and the translucent reflective layer 7 constitute a micro optical resonator. Next, advantages of configuring the minute optical resonator will be described with reference to the light intensity distribution characteristic diagrams of FIGS. 3 and 4 show the relative distribution of the light intensity when the maximum value is 1. FIG.
[0052]
FIG. 3 is a characteristic diagram when the minute optical resonator structure is not employed. The light emitting surface of the organic EL element is close to a completely diffusing light source, and the angular distribution of the light intensity in this case is a substantially spherical distribution. FIG. 4 is a characteristic diagram when the micro-optical resonator structure of FIG. 1 is adopted. The angular distribution of the light intensity in this case has a characteristic in which directivity is enhanced in the direction of angle 0 (front direction). That is, the light distribution intensity in the direction of the image carrier increases.
[0053]
Therefore, by adopting the minute optical resonator structure, the diffusion of light is suppressed and the spread of the exposure spot is reduced. That is, since the light emission angle can be reduced, crosstalk can be prevented. Moreover, the half-value width of the emission wavelength can be narrowed to increase the output of the peak wavelength, and the emission efficiency can be improved. The optical characteristics of such a minute optical resonator structure are obtained because the direction of the light emitted from the light emitting unit is aligned with the resonance direction.
[0054]
Table 1 shows the specifications of each part of the organic EL head according to the embodiment of the present invention.
[0055]
[Table 1]

[0056]
Table 1 shows the specifications of each part of the organic EL head at an emission peak wavelength of 636 nm. The translucent reflective layer (dielectric mirror) 7 made of a dielectric multilayer film is composed of a pair of SiO₂And TiO₂It is formed by laminating three layers made of The reflective layer (dielectric mirror) 2 made of a dielectric multilayer film is composed of a pair of SiO 2₂And TiO₂It is formed by laminating 8 layers made of
[0057]
SiO used for the reflective layer 2 and the translucent reflective layer 7₂Has a refractive index of 1.45, a thickness of 109.7 (nm), an optical length of 159 (nm), and an optical length / wavelength of 0.25. TiO₂Has a refractive index of 2.3, a thickness of 69.1 (nm), an optical length of 159 (nm), and an optical length / wavelength of 0.25.
[0058]
Table 1 shows an example of the characteristics of the dielectric multilayer film used for each reflective layer. In the present invention, the reflectance can be made close to 1 by appropriately selecting the number of layers of the dielectric multilayer film, the layer thickness of each layer, the material, and the like. For this reason, the output light of the light emitting layer can be effectively used without being emitted from a useless surface.
[0059]
PEDOT-PSS which is a material of the hole transport layer 4 has a refractive index of 1.51, a thickness of 105.3 (nm), an optical length of 159 (nm), and an optical length / wavelength of 0.25. MEH-PPV which is a material of the light emitting layer 5 has a refractive index of 1.7, a thickness of 93.5 (nm), an optical length of 159 (nm), and an optical length / wavelength of 0.25.
[0060]
In addition, ITO used for the anode has a refractive index of 1.9, a thickness of 167.4 (nm), an optical length of 318 (nm), and an optical length / wavelength of 0.5. Aluminum (Al) used for the cathode 6 has a refractive index of 0.76 and a thickness of 0.5 (nm) or less.
[0061]
In the present invention, the organic EL head having the above-described configuration can be used as an exposure head of an image forming apparatus that forms an electrophotographic color image, for example. FIG. 5 is a plan view schematically showing an example of the organic EL array exposure head.
[0062]
The organic EL array exposure head 15 of this embodiment is arranged so that the two arrays 16 and 16 'are parallel and the pixels are staggered. Each array 16, 16 ′ is composed of a large number of pixels 17 arranged in a straight line, and the configuration of each pixel 17 is the same. Each pixel 17 includes an organic EL head 18 and a TFT 19 that controls light emission of the organic EL head 18.
[0063]
FIG. 6 is a front view showing an example of an image forming apparatus using the organic EL array exposure head described in FIG. This image forming apparatus includes four organic EL array exposure heads 1K, 1C, 1M, and 1Y having the same configuration, and corresponding exposure positions of four photosensitive drums 41K, 41C, 41M, and 41Y having the same configuration. Are arranged as tandem type image forming apparatuses.
[0064]
As shown in FIG. 6, this image forming apparatus is provided with a drive roller 51, a driven roller 52, and a tension roller 53. The tension roller 53 applies tension to the image forming apparatus and stretches it in the direction indicated by the arrow (counterclockwise). The intermediate transfer belt 50 is circulated and driven in the direction). Photosensitive members 41K, 41C, 41M, and 41Y having photosensitive layers are arranged on the outer peripheral surface as four image carriers arranged at predetermined intervals with respect to the intermediate transfer belt 50.
[0065]
K, C, M, and Y added after the reference sign mean black, cyan, magenta, and yellow, respectively, and indicate that the photoconductors are black, cyan, magenta, and yellow, respectively. The same applies to other members. The photoreceptors 41K, 41C, 41M, and 41Y are rotationally driven in the direction indicated by the arrow (clockwise) in synchronization with the driving of the intermediate transfer belt 50.
[0066]
Around each photoconductor 41 (K, C, M, Y), charging means (corona charger) 42 (K) for uniformly charging the outer peripheral surface of the photoconductor 41 (K, C, M, Y), respectively. , C, M, Y) and the outer peripheral surface uniformly charged by the charging means 42 (K, C, M, Y) are synchronized with the rotation of the photoconductor 41 (K, C, M, Y). Thus, the organic EL array exposure head 1 (K, C, M, Y) as described above of the present invention for sequentially scanning the lines is provided.
[0067]
Further, a developing device 44 (K) that applies toner as a developer to the electrostatic latent image formed by the organic EL array exposure head 1 (K, C, M, Y) to form a visible image (toner image). , C, M, Y) and a primary transfer roller 45 as transfer means for sequentially transferring the toner image developed by the developing device 44 (K, C, M, Y) to the intermediate transfer belt 50 as a primary transfer target. (K, C, M, Y) and a cleaning device 46 (K, C, Y) as a cleaning unit for removing the toner remaining on the surface of the photoreceptor 41 (K, C, M, Y) after being transferred. M, Y).
[0068]
Here, each organic EL array exposure head 1 (K, C, M, Y) is separated from the surface of the corresponding photoreceptor 41 (K, C, M, Y) by a predetermined distance as shown in FIG. The organic EL array exposure head 1 (K, C, M, Y) is installed so that the array direction is along the bus line of the photosensitive drum 41 (K, C, M, Y). The light emission energy peak wavelength of each organic EL array exposure head 1 (K, C, M, Y) and the sensitivity peak wavelength of the photoconductor 41 (K, C, M, Y) are set so as to substantially match. ing.
[0069]
The developing device 44 (K, C, M, Y) uses, for example, a non-magnetic one-component toner as a developer, and the one-component developer is conveyed to the developing roller by a supply roller, for example, and adheres to the surface of the developing roller. The film thickness of the developed developer is regulated by a regulation blade, and the potential of the photoreceptor 41 (K, C, M, Y) is adjusted by bringing the developing roller into contact with or pushing the photoreceptor 41 (K, C, M, Y). The toner image is developed by attaching a developer according to the level.
[0070]
The black, cyan, magenta, and yellow toner images formed by the four-color single-color toner image forming station are intermediated by the primary transfer bias applied to the primary transfer roller 45 (K, C, M, Y). The toner image, which is sequentially primary transferred onto the transfer belt 50 and sequentially superposed on the intermediate transfer belt 50 to become a full color, is secondarily transferred to a recording medium P such as paper by a secondary transfer roller 66, and serves as a fixing unit. The toner is fixed on the recording medium P by passing through the fixing roller pair 61, and is discharged onto a paper discharge tray 68 formed in the upper part of the apparatus by a paper discharge roller pair 62.
[0071]
In FIG. 6, reference numeral 63 denotes a paper feed cassette in which a large number of recording media P are stacked and held, 64 denotes a pickup roller for feeding the recording media P one by one from the paper feed cassette 63, and 65 denotes a secondary transfer roller. A pair of gate rollers for defining the supply timing of the recording medium P to the secondary transfer portion 66, a secondary transfer roller 66 as a secondary transfer means for forming a secondary transfer portion with the intermediate transfer belt 50, 67 Is a cleaning blade as a cleaning means for removing the toner remaining on the surface of the intermediate transfer belt 50 after the secondary transfer.
[0072]
In the organic EL array exposure head 1 (K, C, M, Y) used in FIG. 6, a convex microlens 8 having a predetermined focal length is formed on each organic EL light emitting unit by an ink jet method as shown in FIG. However, a ball lens may be used in place of the convex microlens 8.
[0073]
At this time, the ball lens may be attached by being attached to the dielectric multilayer film 7 or may simply be placed on the dielectric multilayer film 7 in the recess of the cathode layer 6. Thus, since the image forming apparatus of FIG. 6 uses the organic EL head shown in FIG. 1 as the writing means, the size of the apparatus can be reduced as compared with the configuration using the laser scanning optical system. You can plan.
[0074]
The organic EL array exposure head of the present invention, the manufacturing method thereof, and the image forming apparatus using the same have been described based on the embodiments. However, the present invention is not limited to these embodiments and can be variously modified.
[0075]
【The invention's effect】
As is clear from the above description, in the present invention, an organic EL head having an optical system can be easily configured by a liquid phase method, particularly an ink jet method. Further, by combining with a minute optical resonance structure, the light emission angle can be reduced, so that crosstalk can be prevented.
[0076]
In addition, the dielectric multilayer film functioning as a reflective layer can be made to have a reflectance close to about 1 (0.999) by adjusting the number of layers, the layer thickness of each layer, the material, and the like. Leakage of light from unnecessary surfaces can be prevented. Furthermore, in combination with emitting light from the cathode side, the distance between the light emitting portion and the microlens can be shortened, so that the light utilization efficiency is improved. Note that the size of the image forming apparatus can be reduced by using the organic EL head of the present invention.
[Brief description of the drawings]
FIG. 1 is a longitudinal sectional front view showing an example of an organic EL head according to the present invention.
FIG. 2 is a cross-sectional view illustrating a configuration example of a piezo jet head in an ink jet method.
FIG. 3 is a characteristic diagram of a light emission intensity distribution.
FIG. 4 is a characteristic diagram showing a light emission intensity distribution according to the present invention.
FIG. 5 is a plan view showing a schematic configuration of an organic EL array exposure head.
FIG. 6 is a front view illustrating a schematic configuration of a tandem type image forming apparatus in which the organic EL head of the present invention is disposed.
[Explanation of symbols]
1 ... Board
2 ... Reflective layer made of dielectric multilayer
3 ... Anode
4 ... Hole transport layer
5 ... Light emitting layer
6 ... Cathode
7: Translucent reflective layer made of dielectric multilayer film
8 ... Micro lens
9 ... Bank (bank)
10 ... Organic EL array
11 ... Hall of partition wall
15 ... Organic EL array exposure head
16, 16 '... array
17 ... Pixel
18 ... Organic EL head
19 ... TFT
21 ... Head
22 ... Nozzle plate
23 ... Diaphragm
24 ... Partition member (reservoir plate)
25. Ink chamber
26 ... Nozzle hole
28: Piezoelectric element
29 ... Electrode
1 (K, C, M, Y): Organic EL array exposure head
41 (K, C, M, Y) ... photosensitive drum
42 (K, C, M, Y): Charging means (corona charger)
44 (K, C, M, Y) ... developing device
45 (K, C, M, Y) ... primary transfer roller
46 (K, C, M, Y) ... Cleaning device
50. Intermediate transfer belt
51. Driving roller
52. Followed roller
53 ... Tension roller
61. Fixing roller pair
62 ... Paper discharge roller pair
63: Paper cassette
64 ... Pickup roller
65 ... Gate roller pair
66. Secondary transfer roller
67 ... Cleaning blade
68 ... Output tray
P ... Recording medium

Claims (5)

A substrate,
A reflective layer made of a dielectric multilayer film formed on the substrate;
An opaque partition wall having a hole on the reflective layer and formed at a predetermined height;
In the hole of the partition,
An anode formed on the reflective layer;
An organic EL light emitting layer formed on the anode;
A cathode formed of a metal thin film having a thickness for transmitting light on the organic EL light emitting layer;
A translucent reflective layer composed of a dielectric multilayer film having a number of laminated layers formed on the cathode and smaller than that of the reflective layer;
A microlens formed by an inkjet method on the translucent reflective layer;
An organic EL head characterized in that a minute optical resonator is constituted by the reflective layer and the semitransparent reflective layer, and the output light is emitted from the microlens through the semitransparent reflective layer. Characterized in that the organic EL is formed by a liquid phase method, according to claim 1 the organic EL head according. Forming a reflective layer made of a dielectric multilayer film on a substrate;
Forming an opaque partition wall having a predetermined height with a hole on the reflective layer;
In the hole of the partition wall ,
Forming an anode on the reflective layer;
Forming an organic EL light emitting layer on the anode by a liquid phase method;
Forming a cathode by depositing a metal thin film having a thickness of transmitting light on the organic EL light emitting layer by vapor deposition;
Forming a translucent reflective layer comprising a dielectric multilayer film having a smaller number of layers on the cathode than the reflective layer;
Forming a microlens on the translucent reflective layer by an inkjet method ;
And forming an organic EL head that constitutes a micro optical resonator with the reflective layer and the semi-transparent reflective layer, transmits the semi-transparent reflective layer, and emits output light from the micro lens. A method for producing an organic EL head. The organic EL head of any one of claims 1 2, characterized in that it comprises as an exposure head for writing an image on an image bearing member, the image forming apparatus. The image forming apparatus, characterized in that an image forming apparatus provided at least two charging means around, the exposure head, developing means, an image forming station which arranged transfer means of the image bearing member, according to claim 4 The image forming apparatus described.

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