JPH09179386A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To effectively use a photoreceptor having a high γ-characteristic, to obtain excellent sensitivity with respect to an optical digital signal and to form a sharp image by providing an auxiliary exposure means between an image exposure means and a developing means. SOLUTION: An electrifying means 2 electrifies the photoreceptor 1 and the image exposure means 3 writes a latent image pattern on the photoreceptor 1 charged by the electrifying means 2, with an exposure in such a degree that a potential is not attenuated at a developing position. Then, the auxiliary exposure means 4 is disposed on the rear stage of the image exposure means 3 and executes the uniform auxiliary exposure of the photoreceptor 1, so that only in the image exposure part Ze of the latent image pattern written by the image exposure means 3, the potential is selectively attenuated at the developing position. Further, the developing means 5 makes the latent image pattern formed by the image exposure means 3 and the auxiliary exposure means 4 a visible image. Thus, the auxiliary exposure means 4 is provided between the image exposure means 3 and the developing means 5, besides the image exposure means 3, so that the photoreceptor 1 after an image exposure has a uniform full-surface exposure, to selectively attenuate the potential only in the image exposure part.

Description

【発明の詳細な説明】Detailed Description of the Invention

【０００１】[0001]

【発明の属する技術分野】この発明は、電子写真方式を
用いて感光体上に画像を形成する複写機、静電記録装
置、ファクシミリ、伝送装置、レーザプリンタ等の画像
形成装置に係り、特に、所謂ハイガンマ（Ｈｉｇｈ−
γ）特性の感光体を用いたタイプの画像形成装置の改良
に関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, an electrostatic recording apparatus, a facsimile, a transmission apparatus and a laser printer, which forms an image on a photosensitive member by using an electrophotographic method, and more particularly, The so-called high gamma (High-
The present invention relates to improvement of an image forming apparatus of a type using a photoconductor having γ) characteristics.

【０００２】[0002]

【従来の技術】電子写真技術は、画像形成速度の迅速
性、乾式現像であること、記録密度が高いこと等の特徴
を生かし、現在普通紙複写機、レーザプリンタ、ファク
シミリ等の画像形成装置として実用化されている。電子
写真プロセスは、帯電、露光、現像、転写、定着、クリ
ーニングの基本過程により構成されるが、感光体はこの
中で帯電、露光による潜像形成を担う重要な部品であ
る。2. Description of the Related Art Electrophotographic technology is currently used as an image forming apparatus for plain paper copying machines, laser printers, facsimiles, etc., because of its features such as rapid image forming speed, dry development, and high recording density. It has been put to practical use. The electrophotographic process is composed of the basic processes of charging, exposing, developing, transferring, fixing and cleaning, and the photoconductor is an important part responsible for latent image formation by charging and exposing.

【０００３】電子写真用感光体に求められる特性には帯
電性、光導電性等が求められ、これらは電子写真プロセ
スにおける潜像形成の支配的要因である。電子写真にお
ける像形成は、均一に帯電し感光体表面の電荷を、光照
射により選択的に消失させることにより達成される。The characteristics required of the electrophotographic photoreceptor are chargeability, photoconductivity, and the like, which are the dominant factors for latent image formation in the electrophotographic process. Image formation in electrophotography is achieved by uniformly charging and selectively eliminating the charge on the photoreceptor surface by light irradiation.

【０００４】現在まで実用化された代表的な電子写真用
感光体は大きく分けてアモルファスセレン及びその合
金を含むアモルファスカルコゲナイド系材料、酸化亜
鉛、硫化カドミウムなどのＩＩ−ＩＶ属無機化合物系材
料、高分子ならびに低分子有機化合物の樹脂分散系等
の有機光導電体（ＯＰＣ：Organic Photoconductor）、
アモルファスシリコン系材料が挙げられる。１９７０
年代までは感光体は無機系で独占されていたが、１９７
０年前半からのＯＰＣの出現により電子写真用感光体は
大きな転換点を迎え、従来の無機系感光体の殆どがＯＰ
Ｃに置き換わる方向に進み始めた。このＯＰＣの特徴的
なものとしては分光感度設計が容易であるため、レーザ
プリンタの出現により新たに要求されるところとなっ
た。すなわち、記録光源の主流が半導体レーザであるた
め、感光体が７８０ｍｍ単色光感度に優れることが挙げ
られる。Typical electrophotographic photoreceptors which have been put into practical use until now are roughly classified into amorphous chalcogenide materials containing amorphous selenium and its alloys, II-IV group inorganic compound materials such as zinc oxide and cadmium sulfide, and Organic photoconductor (OPC) such as resin dispersion system of molecules and low molecular weight organic compounds,
Amorphous silicon materials can be used. 1970
Until the 1960s, photoconductors were monopolized by inorganic materials, but in 197
With the advent of OPC from the first half of the year, electrophotographic photoconductors have reached a major turning point, and most of the conventional inorganic photoconductors are OP.
It started to move in the direction of replacing C. A characteristic of this OPC is that it is easy to design the spectral sensitivity, and it has become a new requirement with the advent of laser printers. That is, since the mainstream of the recording light source is a semiconductor laser, the photoconductor has excellent monochromatic light sensitivity of 780 mm.

【０００５】この因子がなぜ重要であるかを説明する。
従来、電子写真技術はアナログ光学系を光源に用いた普
通紙複写機としてのみ実用化されていた。しかし、１９
８０年代に入るとコンピュータの出力機器としてこの技
術が盛んに応用され始めた。これに加えて普通紙のデジ
タル化、カラー化が急速に進展するところとなった。こ
れらのシステムでは、デジタル光学系を使用するので、
このシステムに使用される光源に対応した十分な感度を
持つことが感光体に要求される。つまり特定な波長の単
色光に対して十分な感度を有することが重要となる。特
に、デジタル用光源としては半導体レーザが多く用いら
れており、その多くは安価で量産性に優れた７００〜９
００ｎｍの間にピークを持つ単色光に大きな感度を持つ
感光体が開発されてきた。この結果デジタル光学系を用
いた電子写真システム用の感光体としてＯＰＣが多く占
められるようになった。Explain why this factor is important.
Conventionally, electrophotographic technology has been put into practical use only as a plain paper copying machine using an analog optical system as a light source. But 19
In the 1980s, this technology began to be actively applied as a computer output device. In addition to this, the digitization and colorization of plain paper has come to the forefront. Since these systems use digital optics,
The photoreceptor is required to have sufficient sensitivity corresponding to the light source used in this system. That is, it is important to have sufficient sensitivity to monochromatic light of a specific wavelength. In particular, a semiconductor laser is often used as a light source for digital use, and most of them are 700 to 9 that are inexpensive and excellent in mass productivity.
Photoconductors having a large sensitivity to monochromatic light having a peak in the range of 00 nm have been developed. As a result, OPC has come to be widely used as a photoconductor for an electrophotographic system using a digital optical system.

【０００６】現在主流となっているＯＰＣは電荷輸送材
を高濃度で樹脂中に溶解した電荷輸送層と電荷発生顔料
を高濃度で樹脂中に分散した電荷発生層とからなる、積
層型ＯＰＣである。この型のＯＰＣは、感光体の光導電
性の基本機能を分割独立させたもので、材料の選択に余
裕が広がり、結果として感光体性能の飛躍的向上を達成
した。特にに無金属フタロシアニン、銅フタロシアニ
ン、チタニルフタロシアニン、マグネシュウムフタロシ
アニン、バナジルフタロシアニンなどのフタロシアニン
顔料を用いた有機感光体はデジタル用に適するものとし
て知られている。The OPC currently in the mainstream is a laminated OPC comprising a charge transport layer in which a charge transport material is dissolved in a resin in a high concentration and a charge generation layer in which a charge generating pigment is dispersed in a resin in a high concentration. is there. In this type of OPC, the photoconductive basic function of the photoreceptor is divided and independent, and the selection of materials is expanded, and as a result, the performance of the photoreceptor is dramatically improved. In particular, organic photoreceptors using phthalocyanine pigments such as metal-free phthalocyanine, copper phthalocyanine, titanyl phthalocyanine, magnesium phthalocyanine, and vanadyl phthalocyanine are known to be suitable for digital applications.

【０００７】しかし、この積層型のＯＰＣの大きな問題
点は帯電特性が負帯電であることにある。負帯電型ＯＰ
Ｃは利用するシステムからの大量なオゾン発生という問
題点を抱える。このため、正帯電型のＯＰＣも例えば
「T.NakagaWa et al, JapanHardcopy′88 l.Ozawa
et al,Japan Hardcopy′88等」のように研究され始め、
１９８０年代後半に普通複写機用ＯＰＣとして実用化さ
れた。However, a major problem with this laminated OPC is that the charging characteristic is negative charging. Negatively charged OP
C has a problem that a large amount of ozone is generated from the system used. For this reason, positively charged OPCs are also described in, for example, “T. NakagaWa et al, Japan Hardcopy′88 l. Ozawa.
et al, Japan Hardcopy '88 etc. "
It was put to practical use as an OPC for ordinary copying machines in the latter half of the 1980s.

【０００８】また、正帯電単層型ＯＰＣの研究もなさ
れ、新たな特性を持つものが例えば「S.Johnson et a
l.,IS＆T′s Seventh International congress on Adva
nces in Non-impact Printing Technologies ,'91 S.
Tsuchiya et al.,ibit,'91」のように提案されてきた。
これらは共に感光層中に電荷輸送剤を含まない、顔料を
樹脂中に分散した感光体である。したがって、従来の積
層型に比べて層形成の点で低価格になる。また、これら
は正帯電型であることを最大の特徴としている。更に、
これらの感光体のもう一つの大きな特徴にＨｉｇｈ−γ
特性を挙げることができる。このＨｉｇｈ−γ特性と
は、感光体の電位減衰曲線中の直線的電位減衰部分の傾
きが大きいことを表しており、この特性がデジタル方式
による画像形成に特に有利であると提案されている。Further, studies on positively charged single layer type OPC have been made, and those having new characteristics are described in, for example, "S. Johnson et a.
l., IS & T ′s Seventh International congress on Adva
nces in Non-impact Printing Technologies, '91 S.
Tsuchiya et al., Ibit, '91 ”.
These are both photoconductors in which a pigment is dispersed in a resin without a charge transporting agent in the photosensitive layer. Therefore, the price is lower than that of the conventional laminated type in terms of layer formation. Further, the most characteristic of these is that they are positively charged. Furthermore,
Another major feature of these photoconductors is High-γ
The characteristics can be mentioned. The High-γ characteristic means that the slope of the linear potential decay portion in the potential decay curve of the photoconductor is large, and it is proposed that this characteristic is particularly advantageous for digital image formation.

【０００９】従来ドット露光を行うスポット光の光エネ
ルギ分布は裾長のガウス分布となる。この裾長のエネル
ギ分布を有するドット露光を入射光量に応じて電位減衰
が開始される感光体上に照射して像形成を行えば、裾長
のドット露光がそのまま再現され、ドット周辺にぼけを
生じ、解像力の悪いドット画像が形成される。そこで、
例えば特開平１−１６９４５４号公報には弱露光時には
殆ど電位減衰が現れず、光量を増やしある光量になると
急峻な電位減衰特性を示す所謂Ｈｉｇｈ−γ感光体が提
案されている。前記公報ではドット露光が裾長のガウス
分布であってもシャープなドット状の潜像が形成される
ことが記載されている。Conventionally, the light energy distribution of spot light used for dot exposure is a Gaussian distribution with a skirt length. If dot exposure with this hem length energy distribution is applied to the photoconductor where the potential decay starts according to the amount of incident light to form an image, the hem length dot exposure will be reproduced as it is, and blurring will occur around the dots. Occurs, and a dot image with poor resolution is formed. Therefore,
For example, Japanese Patent Application Laid-Open No. 1-169454 proposes a so-called High-γ photoconductor that shows almost no potential attenuation during weak exposure and shows steep potential attenuation characteristics when the amount of light increases and reaches a certain amount of light. The above-mentioned publication describes that even if the dot exposure has a Gaussian distribution with a hem length, a sharp dot-shaped latent image is formed.

【００１０】また、単層型ＯＰＣにＨｉｇｈ−γ特性が
出現する現象は以前よりインダクション効果として知ら
れている。このインダクション効果とは、図８に示すよ
うに、感光体への光照射後、電位減衰までに時間遅れを
生じる現象であり、樹脂分散型感光体固有の特性であ
る。この現象は、露光初期において、発生したキャリア
がトラップに捕獲されるため電位減衰にあまり寄与しな
いが、その後発生キャリア数が多くなるに従ってトラッ
プが埋めつくされ、キャリアの輸送が急激に起こり大き
な電位減衰が生じるためと推察される。この結果、高い
ガンマ値を示すことになる。従来にあっては、前記イン
ダクション効果はリニアな感光特性を得ようとする場合
には不適と考えられていたため、インダクション効果を
低減化するという開発がなされていたが、最近、前述し
たように、インダクション効果（感光体を帯電、露光し
た時の表面電位の減衰過程が露光量増加に対して始めは
緩やかに減衰するが次第に露光量を増加させていくと急
激な電位減衰を示すという点）を積極的に利用し、デジ
タル方式（二値化）による画像形成を行なおうとする動
きが出てきた。Further, the phenomenon that the High-γ characteristic appears in the single layer type OPC has been known as an induction effect from before. As shown in FIG. 8, the induction effect is a phenomenon in which there is a time delay until the potential decays after the photoconductor is irradiated with light, and is a characteristic peculiar to the resin dispersion type photoconductor. This phenomenon does not contribute much to potential decay because generated carriers are trapped in traps at the beginning of exposure, but traps are filled up as the number of generated carriers increases thereafter, and carrier transport rapidly occurs and large potential decay occurs. It is presumed that this occurs. As a result, a high gamma value is exhibited. In the past, the induction effect was considered unsuitable when trying to obtain a linear photosensitivity, so there was a development to reduce the induction effect, but recently, as mentioned above, Induction effect (the point that the decay process of the surface potential when the photoreceptor is charged and exposed is gradually attenuated with the increase of the exposure amount, but shows a rapid potential decrease as the exposure amount is gradually increased). There has been a movement to actively use and form images by digital methods (binarization).

【００１１】[0011]

【発明が解決しようとする課題】しかしながら、前述し
たＨｉｇｈ−γ特性を持った単層型感光体にあっては、
露光部位で露光によって発生したキャリアはトラップに
捕獲されトラップが埋め尽くされるまで電位減衰に寄与
しないため、前記Ｈｉｇｈ−γ特性の単層型感光体は従
来の積層型感光体に比べて感度が低いという欠点があ
り、この種のＨｉｇｈ−γ特性を持った単層型感光体に
おいて感度不足を補うために各種増感方式が提案されて
いる。However, in the above-mentioned single layer type photoreceptor having the High-γ characteristic,
Since the carriers generated by the exposure at the exposed portion are trapped by the traps and do not contribute to the potential decay until the traps are filled up, the single layer type photoreceptor having the High-γ characteristic has lower sensitivity than the conventional laminated type photoreceptor. However, various sensitization methods have been proposed in order to compensate the lack of sensitivity in the single-layer type photoconductor having this type of High-γ characteristic.

【００１２】従来における第一の増感方式としては、帯
電と同時または直後の位置に補助露光装置を設け、帯電
後の感光体に均一な補助露光を行い、次工程で露光する
像露光装置の光量を底上げすることにより増感を行って
いるものがある（例えば特開平３−１８１９６４号，特
開平４一５０８７４号公報参照）。また、第二の増感方
式としては、像露光装置からの増露光光路と同じ光路の
位置に補助露光装置を設け、像露光と同時に均一な補助
露光を行い、像露光の光量を底上げすることにより増感
を行っているものがある（例えば特開平１−１７２８６
３号公報参照）。更に、第三の増感方式としては、帯電
装置の背後から帯電と同時にデジタル露光を行い、現像
装置前に補助露光装置を設けて均一な補助露光を行い、
像露光の光量を底上げすることにより増感を行っている
ものがある（例えば特開平４−５０８７５号公報参
照）。As the first conventional sensitization method, an auxiliary exposure device is provided at the same time as or immediately after charging, and the photosensitive member after charging is uniformly subjected to auxiliary exposure, and is exposed in the next step. There are some types in which sensitization is performed by raising the light amount (see, for example, JP-A-3-181964 and JP-A-41- 50874). As the second sensitization method, an auxiliary exposure device is provided at the same optical path as the sensitized exposure optical path from the image exposure device, and uniform auxiliary exposure is performed simultaneously with the image exposure to raise the light amount of the image exposure. Some of them are sensitized according to Japanese Patent Laid-Open No. 17286/1989.
(See Japanese Patent Publication No. 3). Furthermore, as the third sensitization method, digital exposure is performed simultaneously from the back of the charging device at the same time as charging, and an auxiliary exposure device is provided in front of the developing device to perform uniform auxiliary exposure.
In some cases, sensitization is performed by raising the light amount of image exposure (see, for example, Japanese Patent Laid-Open No. 4-50875).

【００１３】しかしながら、従来の第一の増感方式（帯
電と同時または帯電直後の位置で均一な補助露光を行う
方式）にあっては、補助露光により感光体では電位の暗
減衰が開始し始めるので、像露光時の帯電電位が不安定
になり易いばかりか、補助露光の光量は像露光前までに
電位減衰することがない光量以下であり、かつ、現像装
置直前までに像露光部の部位が電位減衰しさらに非画像
部が電位減衰しない光量でなくてはならず、補助露光の
光量制御が極めて困難になるという技術的課題があっ
た。However, in the first conventional sensitization method (method in which uniform auxiliary exposure is performed at the same time as charging or immediately after charging), dark attenuation of the potential starts on the photosensitive member due to auxiliary exposure. Therefore, not only the charging potential during image exposure is likely to become unstable, but the light amount of auxiliary exposure is less than the light amount that does not cause potential attenuation before image exposure, and the part of the image exposure unit is located just before the developing device. However, there is a technical problem that it is very difficult to control the light amount of the auxiliary exposure because the light amount must be such that the potential is attenuated and the non-image portion is not attenuated.

【００１４】また、第二の増感方式（像露光と同じ光路
に補助露光装置を設けて像露光と同時に均一な補助露光
を行う方式）では、像露光と補助露光の光とが干渉して
しまい、高画質な微細ｄｏｔを再現するには問題があっ
た。In the second sensitization method (a method in which an auxiliary exposure device is provided in the same optical path as image exposure to perform uniform auxiliary exposure simultaneously with image exposure), the image exposure light and the auxiliary exposure light interfere with each other. Therefore, there is a problem in reproducing a high-quality fine dot.

【００１５】更に、第一及び第二の増感方式のように、
補助露光装置を現像装置よりも前工程に設けるほど像露
光によって光照射が行われなかった部位もインダクショ
ン効果の影響で現像位置で電位減衰し易くなってしまう
ため、像露光における光照射部位と非光照射部位との分
離が難しくなってしまう。また、像露光による光照射部
位と非光照射部位との間に大きな電位ギャップを生じさ
せるために、弱い露光光量で補助露光を行なうと増感率
は低くなってしまい、効果的な増感を行えなかった。ゆ
えに、補助露光装置を現像装置直前から上流側に設ける
ほど増感効果は低くなり、像露光による非光照射部位の
電位が不安定になってしまい、高解像度の画像を忠実に
再現するには問題があった。Further, like the first and second sensitization methods,
As the auxiliary exposure device is provided in a step prior to the developing device, the potential of the light-irradiated portion due to the image exposure is likely to be attenuated at the developing position due to the effect of the induction effect. Separation from the light irradiation site becomes difficult. Further, in order to generate a large potential gap between the light-irradiated portion and the non-light-irradiated portion by image exposure, if the auxiliary exposure is performed with a weak exposure light amount, the sensitization rate becomes low, resulting in effective sensitization. I couldn't. Therefore, the sensitization effect becomes lower as the auxiliary exposure device is provided immediately upstream of the developing device from the upstream side, and the potential of the non-light-irradiated portion due to image exposure becomes unstable, so that a high-resolution image can be faithfully reproduced. There was a problem.

【００１６】更にまた、第三の増感方式（帯電装置の背
後から帯電と同時にデジタル露光を行い、現像装置前で
均一な補助露光を行う方式）では、像露光を行った感光
体部位に更に電界を加えることになるため、キャリアの
トラップの状態を変化させてしまうことになり、高解像
度の画像を忠実に再現するには問題があった。Furthermore, in the third sensitization system (a system in which digital exposure is performed simultaneously with charging from the back of a charging device and uniform auxiliary exposure is performed in front of a developing device), the photosensitive member portion subjected to image exposure is further exposed. Since an electric field is applied, the state of carrier traps is changed, and there is a problem in faithfully reproducing a high-resolution image.

【００１７】本発明は、以上のような技術的課題を解決
するためになされたものであって、Ｈｉｇｈ−γ特性を
持つ感光体を有効に利用し、デジタル光信号に対して良
好な感度を持ち、鮮明な画像形成を可能とした画像形成
装置を提供するものである。The present invention has been made in order to solve the above technical problems, and effectively utilizes a photoconductor having a High-γ characteristic to obtain good sensitivity to digital optical signals. The present invention provides an image forming apparatus which has a vivid image formation.

【００１８】[0018]

【課題を解決するための手段】すなわち、本発明は、図
１に示すように、一様帯電された表面電位Ｖpが現像位
置である露光量Ａ0を境として急激に減衰する電位減衰
特性の感光体１を用いた画像形成装置において、前記感
光体１を帯電する帯電手段２と、この帯電手段２にて帯
電された感光体１に対して現像位置で電位減衰しない程
度の露光量で潜像パターンを書き込む像露光手段３と、
この像露光手段３の後段側に配設され、当該像露光手段
３により書き込まれた潜像パターンのうち像露光部Ｚe
のみ選択的に現像位置で電位減衰するように前記感光体
１を均一に補助露光する補助露光手段４と、前記像露光
手段３及び補助露光手段４にて形成された潜像パターン
を可視像化する現像手段５とを備えたことを特徴とす
る。That is, according to the present invention, as shown in FIG. 1, a photosensitive member having a potential decay characteristic in which a uniformly charged surface potential Vp is rapidly attenuated at an exposure amount A0 which is a developing position. In an image forming apparatus using the body 1, a latent image is formed by a charging unit 2 that charges the photoconductor 1 and an exposure amount that does not attenuate the potential of the photoconductor 1 charged by the charging unit 2 at a developing position. An image exposure means 3 for writing a pattern,
Of the latent image patterns written by the image exposing means 3, the image exposing portion Ze is provided at the rear side of the image exposing means 3.
Auxiliary exposure means 4 for uniformly auxiliary exposing the photoreceptor 1 so as to selectively attenuate the potential at the developing position, and the latent image pattern formed by the image exposure means 3 and the auxiliary exposure means 4 as a visible image. And a developing means 5 for converting the same into a form.

【００１９】このような技術的手段において、感光体１
としては、ある露光量Ａ0を境として急激に電位減衰す
る電位減衰特性を備えたものであれば全て適用対象であ
り、例えばＸ型無金属フタロシアニンとバインダ樹脂か
らなる単層型有機感光体などが挙げられる。また、感光
体１の形態についてもドラム状、ベルト状を問わない。
また、帯電手段２、像露光手段３及び現像手段５につい
ては公知の各種デバイスを使用できることは勿論であ
る。In such a technical means, the photoreceptor 1
As for, as long as it has a potential attenuation characteristic that abruptly attenuates the potential at a certain exposure amount A0, it is applicable, for example, a single layer type organic photoconductor made of X-type metal-free phthalocyanine and a binder resin. Can be mentioned. Also, the form of the photoreceptor 1 may be a drum shape or a belt shape.
It is needless to say that various known devices can be used for the charging unit 2, the image exposing unit 3, and the developing unit 5.

【００２０】また、補助露光手段４としては、感光体１
の幅方向に沿って均一露光を施せるものであれば、感光
体１の幅方向に沿って延びる棒状光源を初め、多数の発
光素子を配列したものなど適宜選定して差し支えない。
また、補助露光手段４からの照射光量は、使用する感光
体１の種類、像露光手段３との位置関係、像露光手段３
の照射光量を考慮して適宜選定することが必要であり、
補助露光手段４としては、使用する感光体１に対して最
適な光量を提供できるように、コントローラやスリット
等によりその照射光量を調節し得るものが好ましい。As the auxiliary exposure means 4, the photoconductor 1 is used.
As long as uniform exposure can be performed in the width direction, the rod-shaped light source extending in the width direction of the photoconductor 1 and a plurality of light emitting elements arranged can be appropriately selected.
Further, the amount of light emitted from the auxiliary exposure unit 4 depends on the type of the photoconductor 1 used, the positional relationship with the image exposure unit 3, and the image exposure unit 3.
It is necessary to select it in consideration of the irradiation light amount of
As the auxiliary exposure unit 4, it is preferable that the irradiation amount of light can be adjusted by a controller, a slit, or the like so that an optimum amount of light can be provided to the photoconductor 1 to be used.

【００２１】更に、補助露光手段４の配設位置について
は、像露光手段３の後段側で現像手段５の前段側であれ
ば適宜選定して差し支えないが、現像時における潜像電
位を安定させるという観点からすれば、可能な限り現像
手段５寄りに配設することが好ましい。但し、現像手段
５寄りに補助露光手段４を配設した場合には、現像手段
５からのトナークラウドで補助露光手段４が汚れるとい
う懸念があるため、現像手段５側にトナークラウドの発
生を封じ込める手段（現像ハウジングの周囲にシール部
材を設けたり，トナークラウド回収装置を付設する等）
を設けたり、あるいは、補助露光手段４側にトナークラ
ウドの付着防止手段（清掃手段やトナー電荷と反発する
バイアス印加手段）を設けることが好ましい。Further, the position of the auxiliary exposure means 4 may be appropriately selected as long as it is located after the image exposure means 3 and before the development means 5, but the latent image potential during development is stabilized. From this point of view, it is preferable to dispose it as close to the developing unit 5 as possible. However, when the auxiliary exposure unit 4 is arranged near the developing unit 5, there is a concern that the auxiliary exposure unit 4 will be contaminated by the toner cloud from the developing unit 5, so the generation of the toner cloud can be contained on the developing unit 5 side. Means (providing a seal member around the developing housing, attaching a toner cloud collecting device, etc.)
Alternatively, it is preferable to provide a toner cloud adhesion preventing means (cleaning means or bias applying means that repels toner charge) on the auxiliary exposure means 4 side.

【００２２】次に、上述した技術的手段の作用について
説明する。本発明において、感光体１は一様帯電された
表面電位Ｖpが現像位置である露光量Ａ0を境として急激
に減衰する電位減衰特性を備えている。このような電位
減衰特性の感光体１において、帯電手段２が帯電した後
に像露光手段３が像露光を施すと、像露光によって光を
照射された部位は直ちに電位減衰が起こらずある時間の
遅れをもって減衰が起こり、現像位置では減衰が終了し
ない。ここで、像露光の次の工程で補助露光手段４によ
る全面補助露光をある一定光量にて行うと、前記像露光
によって光照射が行われた部位の電位減衰を加速させ、
現像位置で減衰を終了させることができる。Next, the operation of the above-mentioned technical means will be described. In the present invention, the photoconductor 1 has a potential attenuation characteristic in which the uniformly charged surface potential Vp is rapidly attenuated at the exposure amount A0 at the developing position. In the photoconductor 1 having such a potential decay characteristic, when the image exposure means 3 performs image exposure after the charging means 2 is charged, the portion irradiated with light by the image exposure does not immediately undergo potential decay and is delayed by a certain time. Attenuation occurs at the developing position and does not end at the developing position. Here, when the entire surface auxiliary exposure by the auxiliary exposure means 4 is performed with a certain constant light amount in the step subsequent to the image exposure, the potential attenuation of the portion irradiated with light by the image exposure is accelerated,
The decay can be terminated at the development position.

【００２３】一方、像露光によって光照射が行われなか
った部位は全面補助露光によって初めて光エネルギを受
けるため、この部位は直ちに電位減衰が起こらずある時
間の遅れをもって減衰するので、次工程の現像時におい
てはまだ殆ど電位低下は見られない。これにより像露光
による光照射部と非光照射部との間に大きな電位ギャッ
プが生じることになり、この状態で、現像手段５にて前
記潜像（光照射部と非光照射部）を現像することによ
り、像露光に応じたトナー像が形成される。On the other hand, the area not irradiated with light by the image exposure receives light energy for the first time by the whole surface auxiliary exposure, so that this area is not immediately attenuated in potential and is attenuated with a certain time delay. Almost no decrease in the electric potential is seen yet. As a result, a large potential gap is generated between the light irradiation portion and the non-light irradiation portion due to image exposure, and in this state, the latent image (light irradiation portion and non-light irradiation portion) is developed by the developing means 5. By doing so, a toner image corresponding to the image exposure is formed.

【００２４】[0024]

【発明の実施の形態】以下、添付図面に示す実施の形態
に基づいてこの発明を詳細に説明する。図２はこの発明
が適用された画像形成装置の実施の一形態を示す。同図
において、符号２１はある露光量を境として急激に電位
減衰する電位減衰特性（Ｈｉｇｈ−γ特性）を持つ単層
型有機感光体、２２は感光体２１を正帯電する帯電装
置、２３は帯電された感光体２１上に光照射して静電潜
像（本実施の形態では画像部露光のネガ潜像）を形成す
る像露光装置であり、例えば半導体レーザとポリゴンミ
ラーを内蔵するレーザ光発生器が用いられる。更に、符
号２４は像露光装置２３の後段側に設けられて感光体２
１を均一補助露光する補助露光装置である。また、符号
２５は感光体２１上に形成された静電潜像を感光体２１
の帯電極性と同じ極性電荷を持つトナーで可視像化する
現像装置、２６は感光体２１上のトナー像を記録紙２７
に転写させるコロトロンなどの転写装置、２８は感光体
２１に静電吸着した記録紙２７を剥離するコロトロンな
どの用紙剥離装置、２９は記録紙２７上の未定着トナー
像を定着する定着装置、３０は感光体２１上の残留トナ
ーなどの残留物を除去するクリーナ、３１は感光体２１
上の残留電荷を除去する除電装置である。BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be described below in detail based on the embodiments shown in the accompanying drawings. FIG. 2 shows an embodiment of an image forming apparatus to which the present invention is applied. In the figure, reference numeral 21 is a single-layer type organic photoconductor having a potential attenuation characteristic (High-γ characteristic) in which the potential is rapidly attenuated at a certain exposure amount, 22 is a charging device for positively charging the photoconductor 21, and 23 is a charging device. This is an image exposure device that irradiates the charged photoconductor 21 with light to form an electrostatic latent image (in the present embodiment, a negative latent image for image area exposure). For example, a laser beam including a semiconductor laser and a polygon mirror is provided. A generator is used. Further, reference numeral 24 is provided on the rear side of the image exposure device 23 and
1 is an auxiliary exposure apparatus for uniformly auxiliary exposing 1. Reference numeral 25 denotes an electrostatic latent image formed on the photoconductor 21.
A developing device that visualizes with a toner having the same charge as the charging polarity of the recording paper 27, and a toner image on the photoconductor 21 on the recording paper 27.
A transfer device such as a corotron for transferring the image onto the recording paper 27; a paper separating device such as a corotron for separating the recording paper 27 electrostatically attracted to the photoconductor 21; a fixing device 29 for fixing an unfixed toner image on the recording paper 27; Is a cleaner that removes residual toner and other residues on the photoconductor 21, 31 is the photoconductor 21
This is a static eliminator that removes the residual charge above.

【００２５】本実施の形態において、感光体２１として
は、Ｘ型無金属フタロシアニンをバインダ樹脂に分散さ
せた単層型有機感光体が用いられている。具体的にはＸ
型無金属フタロシアニン（大日本インキ（株）製）、フ
ァーストゲンブルー（Fastgen Blue）を感材とした正帯
電単層型感光体を試作した。上記感光体の詳細に関して
は既に特開平３−２８７１７１号公報に開示されてい
る。また、本実施の形態において、感光体形状はアルミ
ニウム製のドラム本体を用い、ドラム状に製作した。こ
のように構成された単層型感光体２１では、電荷移動の
主体はホールなので表面を正帯電して使用する。In the present embodiment, a single-layer organic photoconductor in which X-type non-metallic phthalocyanine is dispersed in a binder resin is used as the photoconductor 21. Specifically, X
A positively charged single-layer type photoconductor was prepared by using a type metal-free phthalocyanine (manufactured by Dainippon Ink and Chemicals, Inc.) and Fastgen Blue as a photosensitive material. The details of the photoreceptor have already been disclosed in JP-A-3-287171. Further, in the present embodiment, the photosensitive member was manufactured in a drum shape using an aluminum drum main body. In the single-layer type photoreceptor 21 configured as described above, since charges are mainly transferred by holes, the surface is positively charged before use.

【００２６】この樹脂分散単層型感光体２１の電位減衰
特性を図３（ａ）（ｂ）に示す。図３（ａ）の実線は樹
脂分散単層型感光体２１の明減衰特性を示すもので、帯
電した後、光照射した際、表面電位の露光量による光減
衰過程が初めは徐々に緩やかな減衰を示し、さらに光量
を増加すると緩やかな減衰間に続いて急激に表面電位が
減衰するというカーブになっている。一方、図３（ｂ）
の実線は樹脂分散単層型感光体２１の暗減衰特性を示す
もので、所定電位に帯電した後の経時的変化が初めは緩
やかな減衰を示し、続いて時間経過に従って急激な減衰
を示し表面電位が降下していくというカーブになってい
る。The potential attenuation characteristics of this resin-dispersed single-layer type photosensitive member 21 are shown in FIGS. 3 (a) and 3 (b). The solid line in FIG. 3A shows the light attenuation characteristic of the resin-dispersed single-layer photosensitive member 21. When light is irradiated after charging, the light attenuation process due to the exposure amount of the surface potential becomes gradually gentle at first. The curve shows a decay, and when the light amount is further increased, the surface potential is abruptly attenuated following a gradual decay. On the other hand, FIG.
The solid line indicates the dark decay characteristics of the resin-dispersed single-layer photoreceptor 21. The change over time after charging to a predetermined potential shows a gradual decay at first, followed by a rapid decay with the passage of time. The curve shows that the potential drops.

【００２７】ここで、従来の積層型感光体の明暗減衰特
性（図３（ａ）（ｂ）で点線で示す）と本実施の形態に
用いた樹脂分散単層型感光体２１の明暗減衰特性と比較
する。なお、積層型感光体は表面電位が負帯電に帯電さ
れ、樹脂分散単層型感光体２１は正帯電に帯電される
為、図３の積層型感光体においては絶対値としての電位
を用いた。図３から分かるように、従来の積層型感光体
の感度特性は照射光に対して感度領域が比較的全領域反
応するのに対し、本実施の形態に係る単層型感光体で
は、ある照射光量までは露光しても表面電位が緩やかに
減衰し、ある照射光量を境にして光量が増加すると表面
電位が急激に減衰する状態になっていることが理解され
る。Here, the light-dark attenuation characteristics of the conventional laminated type photoreceptor (shown by dotted lines in FIGS. 3A and 3B) and the light-dark attenuation characteristic of the resin dispersion single layer type photoreceptor 21 used in the present embodiment. Compare with. The surface potential of the multilayer photoconductor is negatively charged and the resin dispersed single-layer photoconductor 21 is positively charged. Therefore, the potential as an absolute value was used in the multilayer photoconductor of FIG. . As can be seen from FIG. 3, the sensitivity characteristics of the conventional laminated photoreceptor are such that the sensitivity region relatively reacts to the irradiation light over the entire region, whereas the single layer photoreceptor according to the present embodiment has a certain irradiation characteristic. It is understood that the surface potential attenuates gently even after exposure to the light amount, and the surface potential abruptly attenuates when the light amount increases after a certain irradiation light amount.

【００２８】前記のような明減衰特性及び暗減衰特性が
Ｓ字カーブ状に変曲点を持ってオンオフ的に変化する感
度特性である感光体としては、酸化亜鉛を樹脂分散させ
た単層型感光体やフタロシアニンを樹脂分散させた有機
感光体でも報告されているが、露光時の感光体表面電位
が減衰を始める緩和時間が長いことや、帯電に必要な電
荷が多く必要で有ったり、繰り返し使用時の電位保持性
能や感度の変化が大きく、実用に適さないものであっ
た。そこで、本実施の形態では、これらの諸問題を克服
し、実用レベルでの感度特性を有するものとして、Ｘ型
無金属フタロシアニンを樹脂に分散させた単層型感光体
を使用することにした。As the photoconductor having the above-described light attenuation characteristic and dark attenuation characteristic, which are sensitivity characteristics in which an S-shaped curve has an inflection point and changes on and off, a single layer type in which zinc oxide is dispersed in a resin is used. It has been reported that the photoconductor or the organic photoconductor in which phthalocyanine is resin-dispersed, but the relaxation time that the photoconductor surface potential starts to decay at the time of exposure is long, and a large amount of charge required for charging is required, It was not suitable for practical use due to large changes in potential holding performance and sensitivity during repeated use. Therefore, in the present embodiment, a single-layer type photoconductor in which an X-type non-metallic phthalocyanine is dispersed in a resin is used as a type which overcomes these problems and has a sensitivity characteristic at a practical level.

【００２９】また、本実施の形態において、補助露光装
置２４は現像装置２５寄りに配設されており、感光体２
１の幅方向に沿って延びる棒状光源であって感光体２１
の幅方向略全域に亘って均一に露光するもので、例えば
スリットの開度を変更することにより照射光量を調節す
るようになっている。本実施の形態において、像露光装
置２３は、直ちに電位減衰しない程度の露光量で潜像パ
ターンを書き込むものであり、補助露光装置２４の均一
露光量としては、像露光装置２３にて書き込まれた潜像
パターン（光照射部，非光照射部）が補助露光装置２４
位置にて補助露光を受けたときに、前記潜像の光照射部
が電位減衰し、一方、潜像の非光照射部が少なくとも現
像装置２５位置に到達しても電位減衰しない程度のもの
が選定される。Further, in the present embodiment, the auxiliary exposure device 24 is disposed near the developing device 25, and the photoconductor 2
1 is a rod-shaped light source extending in the width direction of the photosensitive member 21.
Is uniformly exposed over substantially the entire width direction, and the irradiation light amount is adjusted by changing the opening of the slit, for example. In the present embodiment, the image exposure device 23 writes the latent image pattern with an exposure amount that does not cause the potential to be immediately attenuated, and the uniform exposure amount of the auxiliary exposure device 24 is written by the image exposure device 23. The latent image pattern (light irradiation portion, non-light irradiation portion) is the auxiliary exposure device 24.
When the auxiliary exposure is performed at the position, the light irradiation part of the latent image is attenuated in potential, while the non-light irradiation part of the latent image is not attenuated in potential even at least at the developing device 25 position. Selected.

【００３０】ここで、本実施の形態で用いられる像露光
装置２３及び補助露光装置２４の露光量を選定する上
で、本実施の形態で用いられる感光体２１の露光量と遅
れて減衰を開始するまでの時間との関係を実験にて調
べ、その結果を図４に示す。同図において、縦軸は感光
体２１の表面電位を示し、横軸は露光部位が現像位置到
達後からの時間を示している。実験方法は直径３０ｍｍ
のＨｉｇｈ−γ特性の感光体２１をプロセススピード５
６ｍｍ／ｓｅｃのマシーンに搭載し、像露光装置２３に
て所定の露光量で均一露光を行った後に現像位置まで感
光体２１を回転させて停止させ、その後の感光体２１の
表面電位を夫々測定した。なお、本実験において、帯電
位置から現像位置までの感光体２１の移動時間は０．８
４秒、露光位置から現像位置までの感光体２１の移動時
間は０．４秒である。Here, in selecting the exposure amounts of the image exposure device 23 and the auxiliary exposure device 24 used in this embodiment, the attenuation is started after the exposure amount of the photoconductor 21 used in this embodiment. The relationship with the time required to do so was investigated experimentally, and the results are shown in FIG. In the figure, the vertical axis represents the surface potential of the photoconductor 21, and the horizontal axis represents the time after the exposed portion reaches the developing position. Experimental method is 30mm in diameter
Process speed 5 with high-γ photoconductor 21
It is mounted on a 6 mm / sec machine, and after uniform exposure with a predetermined exposure amount by the image exposure device 23, the photoconductor 21 is rotated to a developing position and stopped, and then the surface potential of the photoconductor 21 is measured. did. In this experiment, the moving time of the photoconductor 21 from the charging position to the developing position is 0.8.
The moving time of the photoconductor 21 from the exposure position to the developing position is 0.4 seconds in 4 seconds.

【００３１】この結果、本実施の形態における感光体２
１は露光量の大きさによって露光後減衰するまでの時間
が変化することが理解され、露光量と露光後減衰するま
での時間との関係は、図５に示すように、比例関係を示
すことが分かった。なお、図５の横軸は露光後ＶL（光
照射部電位）が１００Ｖに減衰するまでの時間を示す。
従って、図５に示すような露光量減衰特性を考慮し、像
露光装置２３及び補助露光装置２４の露光量が適宜選定
される。As a result, the photoconductor 2 in this embodiment is
1 indicates that the time until attenuation after exposure changes depending on the magnitude of the exposure amount, and the relationship between the exposure amount and the time until attenuation after exposure shows a proportional relationship, as shown in FIG. I understood. The horizontal axis of FIG. 5 shows the time until VL (light irradiation portion potential) after exposure is attenuated to 100V.
Therefore, the exposure amounts of the image exposure device 23 and the auxiliary exposure device 24 are appropriately selected in consideration of the exposure amount attenuation characteristics as shown in FIG.

【００３２】次に、本実施の形態に係る画像形成装置の
作像プロセスについて説明する。先ず、帯電装置２２
は、前記したＨｉｇｈ−γ特性の感光体２１を所定極性
（本実施の形態では正極性）に一様に帯電し、像露光装
置２３がデジタル信号に応じた像露光を行う。このと
き、像露光による光照射部は直ちに電位減衰が起こら
ず、ある時間の遅れをもって減衰が起こるが、前記光照
射部の電位減衰が起こらない段階で、次の工程である補
助露光装置２４による補助露光工程が行われる。この補
助露光工程では、感光体２１全面がある一定光量にて均
一露光され、前記像露光による光照射部の電位減衰する
までの時間が短縮され、前記像露光による光照射部では
急激に電位減衰が進行する。一方、像露光による非光照
射部は全面補助露光において初めて光エネルギを受ける
ため、この部位における光減衰が起こるまでにはかなり
の時間を要し、次工程の現像装置２５による現像工程に
おいてはまだ殆ど電位低下は見られない。従って、像露
光による光照射部と非光照射部との間に大きな電位ギャ
ップが生じ、これを現像装置２５にて現像することによ
り、像露光に応じた潜像パターンに対応したトナー像が
正確に形成される。Next, an image forming process of the image forming apparatus according to this embodiment will be described. First, the charging device 22
, Uniformly charges the photoconductor 21 having the above-mentioned High-γ characteristic to a predetermined polarity (positive in this embodiment), and the image exposure device 23 performs image exposure according to a digital signal. At this time, the light irradiation portion due to the image exposure does not immediately undergo the potential attenuation, and the attenuation occurs with a certain time delay, but at the stage where the potential attenuation of the light irradiation portion does not occur, the auxiliary exposure device 24, which is the next step, is used. An auxiliary exposure process is performed. In this auxiliary exposure process, the entire surface of the photoconductor 21 is uniformly exposed with a certain amount of light, and the time until the potential of the light irradiation portion due to the image exposure is attenuated is shortened, and the potential of the light irradiation portion due to the image exposure is rapidly attenuated. Progresses. On the other hand, since the non-light-irradiated portion by the image exposure receives the light energy for the first time in the whole surface auxiliary exposure, it takes a considerable time until the light attenuation in this portion occurs, and the development step by the developing device 25 in the next step still does not occur. Almost no potential drop is seen. Therefore, a large potential gap is generated between the light-irradiated portion and the non-light-irradiated portion due to the image exposure, and by developing this with the developing device 25, the toner image corresponding to the latent image pattern according to the image exposure is accurately obtained. Is formed.

【００３３】図６は上述した作像プロセスにおける感光
体の表面電位変化を比較の形態と共に示すものである。
図６（ａ）は比較の形態１（補助露光を行なわない形
態）に係る画像形成装置の帯電、露光、現像位置におけ
る像露光による光照射部（実線）と非光照射部（破線）
との変化状態を示し、同図（ｂ）は本実施の形態に係る
画像形成装置の帯電、露光、補助露光、現像位置におけ
る像露光による光照射部（実線）と非光照射部（破線）
との変化状態を示し、同図（ｃ）は比較の形態２（帯電
と同時に補助露光を行う形態）に係る画像形成装置の帯
電、露光、現像位置における像露光による光照射部（実
線）と非光照射部（破線）との変化状態を示す。尚、い
ずれの形態においても、帯電位置と露光位置との間は
０．４秒、帯電位置と現像位置との間は０．８４秒であ
る。FIG. 6 shows a change in the surface potential of the photosensitive member in the above-mentioned image forming process together with a comparative form.
FIG. 6A shows a light irradiation portion (solid line) and a non-light irradiation portion (broken line) by image exposure at the charging, exposure, and development positions of the image forming apparatus according to the first comparative example (a mode in which auxiliary exposure is not performed).
FIG. 2B shows a change state of a light irradiation part (solid line) and a non-light irradiation part (broken line) by charging, exposure, auxiliary exposure, and image exposure at the developing position of the image forming apparatus according to the present embodiment.
And (c) shows a light irradiation portion (solid line) by image exposure at the charging, exposure, and development positions of the image forming apparatus according to the comparative mode 2 (mode in which auxiliary exposure is performed simultaneously with charging). The change state with a non-light irradiation part (broken line) is shown. In any case, the interval between the charging position and the exposure position is 0.4 seconds, and the interval between the charging position and the developing position is 0.84 seconds.

【００３４】これらの形態のうち、本実施の形態によれ
ば、像露光による光照射部は現像位置の手前で電位減衰
し、像露光による非光照射部は現像位置では電位減衰し
ておらず、両者間の電位コントラストは充分に確保され
る。これに対し、比較の形態１にあっては、像露光によ
る光照射部及び非光照射部ともに前記現像位置において
は未だ電位減衰しておらず、両者間の電位コントラスト
を確保できない。このため、充分な電位コントラストを
確保するには現像位置を更に下流側へ移動することが必
要になってしまう。また、比較の形態２にあっては、像
露光による光照射部と非光照射部とを前記現像位置にお
いて電位的に分離することは可能であるが、像露光によ
る非光照射部は上流側での補助露光の影響で現像位置で
電位減衰し始め、電位的に不安定である。このため、現
像位置で電位を安定させるには弱い光量で補助露光を行
わなければならず、増感の効果が減少してしまう。Among these modes, according to the present embodiment, the light irradiation part by image exposure has its potential attenuated before the developing position, and the non-light irradiation part by image exposure has no potential attenuation at the developing position. , The potential contrast between them is sufficiently secured. On the other hand, in the first comparative example, the potential of both the light-irradiated portion and the non-light-irradiated portion by image exposure has not yet been attenuated at the developing position, and the potential contrast between them cannot be secured. Therefore, in order to secure a sufficient potential contrast, it becomes necessary to move the developing position further downstream. Further, in the second comparative embodiment, it is possible to electrically separate the light irradiation portion by image exposure and the non-light irradiation portion at the developing position, but the non-light irradiation portion by image exposure is on the upstream side. The potential begins to decay at the developing position due to the influence of the auxiliary exposure, and the potential is unstable. Therefore, in order to stabilize the potential at the developing position, it is necessary to perform auxiliary exposure with a weak light amount, and the effect of sensitization decreases.

【００３５】このように、本実施の形態に係る画像形成
装置によれば、像露光装置２３の露光量を増大させず
に、高コントラストの潜像電位ギャップを得ることが可
能になる。このため、像露光装置２３の光源である半導
体レーザとして照射光量の大きいものを使用する必要が
なく、しかも、露光時間を不必要に長くする必要がなく
なり、画像形成装置のコストアップ及びプロセススピー
ドの低減は有効に抑えられるほか、潜像パターンに対応
した高コントラストの潜像電位ギャップが得られる分、
高解像度のトナー像が得られる。よって、本実施の形態
に係る画像形成装置は、高速デジタル電子写真装置や高
解像度な電子写真装置に良好に適用されることが理解さ
れる。As described above, according to the image forming apparatus of the present embodiment, it is possible to obtain a latent image potential gap with high contrast without increasing the exposure amount of the image exposure device 23. Therefore, it is not necessary to use a semiconductor laser having a large irradiation light amount as a light source of the image exposure device 23, and it is not necessary to unnecessarily lengthen the exposure time, which increases the cost and process speed of the image forming apparatus. Reduction can be suppressed effectively, and a high-contrast latent image potential gap corresponding to the latent image pattern can be obtained.
A high resolution toner image is obtained. Therefore, it is understood that the image forming apparatus according to the present embodiment is favorably applied to a high speed digital electrophotographic apparatus and a high resolution electrophotographic apparatus.

【００３６】図７は本実施の形態に係る画像形成装置の
現像装置直前に全面露光を実施した場合の効果を説明す
るための説明図であり、横軸は補助露光装置通過後の時
間（ｓｅｃ）、縦軸は感光体の表面電位（Ｖ）を夫々示
す。像露光装置の光源として７８０ｎｍのＬＤ（レーザ
ダイオード，１０ｅｒｇ）を使用し、補助露光装置とし
て７００ｎｍのＬＥＤ（ライト エミッティング ダイオ
ード）を使用した。同図において、各グラフは、夫々補
助露光を行わない場合における像露光光照射部（実線
Ｉ）及び像露光非光照射部（破線Ｉ’）、７００ｎｍの
ＬＥＤにて約１５ｅｒｇの光で補助露光を行った場合に
おける像露光光照射部（実線ＩＩ）及び像露光非光照射
部（破線ＩＩ’）、７００ｎｍのＬＥＤにて約３０ｅｒ
ｇの光で補助露光を行った場合における像露光光照射部
（実線ＩＩＩ）及び像露光非光照射部（破線ＩＩＩ’）
について補助露光装置通過後の時間と表面電位との関係
を示す。FIG. 7 is an explanatory diagram for explaining the effect when the entire surface exposure is performed immediately before the developing device of the image forming apparatus according to the present embodiment, and the horizontal axis represents the time (sec) after passing through the auxiliary exposure device. ), The vertical axis represents the surface potential (V) of the photoconductor. A 780 nm LD (laser diode, 10 erg) was used as a light source of the image exposure device, and a 700 nm LED (light emitting diode) was used as an auxiliary exposure device. In the figure, each graph shows the image exposure light irradiation part (solid line I) and the image exposure non-light irradiation part (broken line I ′) when the auxiliary exposure is not performed, and the auxiliary exposure with light of about 15 erg by the 700 nm LED. The image exposure light irradiation part (solid line II) and the image exposure non-light irradiation part (broken line II ′) in the case of performing
Image exposure light irradiation part (solid line III) and image exposure non-light irradiation part (broken line III ′) in the case of performing auxiliary exposure with g light
The relationship between the time after passing through the auxiliary exposure device and the surface potential is shown.

【００３７】これから明らかなように、補助露光の光量
を増加させていくとそれに応じて感度も増加し、少ない
像露光量でも現像位置までに電位減衰させることができ
る。しかし、破線ＩＩＩ’のように、補助露光光量が強
すぎると、像露光非光照射部の電位が現像位置で不安定
となるため、強すぎる補助露光光量であることは好まし
くなく、また、補助露光装置が現像装置よりも前工程の
例えば帯電位置などに設けられると、帯電位置から現像
位置に至るまでの時間が増すため、この間で補助露光に
よる電位減衰が現像位置前に発生してしまうことが考え
られ、補助露光位置は現像装置直前が好ましいことが分
かった。本実施の形態では７００ｎｍのＬＥＤで約１５
ｅｒｇの光で補助露光を行った（実線ＩＩ／破線Ｉ
Ｉ’）の設定が最も好ましく、少ない露光量でも十分な
電位ギャップを得ることが可能となる。As is apparent from this, as the light amount of the auxiliary exposure is increased, the sensitivity is also increased accordingly, and the potential can be attenuated to the developing position even with a small image exposure amount. However, as indicated by a broken line III ′, if the auxiliary exposure light amount is too strong, the potential of the image exposure non-light irradiation portion becomes unstable at the developing position. Therefore, it is not preferable that the auxiliary exposure light amount is too strong. If the exposure device is provided at a charging position in a step before the developing device, for example, the time from the charging position to the developing position is increased, and during this time, potential attenuation due to auxiliary exposure occurs before the developing position. Therefore, it was found that the auxiliary exposure position is preferably immediately before the developing device. In this embodiment, about 700 nm LED has about 15
Auxiliary exposure was performed with light of erg (solid line II / broken line I
The setting of I ') is most preferable, and it becomes possible to obtain a sufficient potential gap even with a small exposure amount.

【００３８】また、補助露光装置が帯電直後、像露光と
同位置、現像装置直前の夫々の位置に設けられた時の１
ｋ（１０００）枚プリント時の画質変化を以下の表１に
示す。1 when the auxiliary exposure device is provided immediately after charging, at the same position as the image exposure, and immediately before the developing device.
Table 1 below shows changes in image quality when printing k (1000) sheets.

【００３９】[0039]

【表１】 [Table 1]

【００４０】Ｈｉｇｈ−γ特性の感光体は繰り返し使用
時の電位保持性能や感度の変化が大きくいままでに様々
な改善が行われてきた。今回使用しているＨｉｇｈ−γ
特性の感光体はこれらの諸問題を実用レベルで克服した
ものではあるが、繰り返し帯電と露光と転写とを行うと
若干ではあるが感光体の感度は上がり、電位は早く減衰
しインダクション効果が加速される傾向がある。High-γ characteristic photoconductors have large changes in potential holding performance and sensitivity during repeated use, and various improvements have been made so far. High-γ used this time
Although the photoconductor with the characteristics overcomes these problems at a practical level, the sensitivity of the photoconductor rises slightly, and the potential decays quickly and the induction effect accelerates when the charging, exposure and transfer are repeated. Tend to be.

【００４１】帯電直後に補助露光装置を設けた形態（比
較の形態２）にあっては、補助露光装置が現像装置から
離れた位置にあるため、電位減衰特性の変化の影響を大
きく受ける。帯電位置で受けた補助露光の光により像露
光による光照射部も現像装置直前で電位減衰してしまい
カブリが発生してしまった。In the mode (comparative mode 2) in which the auxiliary exposure device is provided immediately after charging, since the auxiliary exposure device is located away from the developing device, it is greatly affected by the change in the potential attenuation characteristic. Due to the auxiliary exposure light received at the charging position, the light irradiating portion due to the image exposure is also attenuated in potential immediately before the developing device, causing fog.

【００４２】また、像露光と同位置に補助露光装置を設
けた形態（比較の形態３）にあっては、補助露光装置と
現像装置までの時間はかなり短くなるため上記に比べれ
ば電位減衰特性の変化の影響を受けにくい。しかし、若
干ではあるが感度は上がり、画像は潰れがちになってい
る。Further, in the form (comparative form 3) in which the auxiliary exposure device is provided at the same position as the image exposure, the time between the auxiliary exposure device and the developing device is considerably shortened, and therefore the potential decay characteristic is compared to the above. Less susceptible to changes in. However, the sensitivity is slightly increased, and the image tends to be crushed.

【００４３】これに対し、現像装置直前に補助露光装置
を設けた本実施の形態にあっては、補助露光装置と現像
装置までの時間はさらに短くなるため、電位減衰特性の
変化の影響を受けることはなく、１ドットの再現性やラ
ダーの潰れや１ドットラインの線幅に変化はない。ま
た、像露光による非光照射部に照射する補助露光装置の
露光量は、直後にある現像装置までに減衰しなければよ
いので、帯電直後に補助露光装置を設けた比較の形態２
や露光と同時に補助露光装置を設けた比較の形態３に比
べて強い光量で補助露光が行える。ゆえに、本実施の形
態は比較の形態２，３に比べて増感率が高くなる。On the other hand, in the present embodiment in which the auxiliary exposure device is provided immediately before the developing device, the time between the auxiliary exposure device and the developing device is further shortened, so that it is affected by the change in the potential attenuation characteristic. There is no change in the reproducibility of 1 dot, the collapse of the ladder, or the line width of the 1 dot line. Further, since the exposure amount of the auxiliary exposure device which irradiates the non-light irradiation part by image exposure does not have to be attenuated by the developing device immediately after, a comparative form 2 in which the auxiliary exposure device is provided immediately after charging
The auxiliary exposure can be performed with a larger amount of light as compared with Comparative Example 3 in which the auxiliary exposure device is provided simultaneously with the exposure. Therefore, in the present embodiment, the sensitization rate is higher than in the comparative forms 2 and 3.

【００４４】[0044]

【発明の効果】以上説明してきたように、本発明によれ
ば、Ｈｉｇｈ−γ特性の感光体において、像露光手段と
は別に像露光手段と現像手段との間に補助露光手段を設
け、像露光後の感光体に均一な全面露光を行い、像露光
部のみ選択的に電位を減衰させるようにしたので、像露
光手段の露光光量を増大させることなく、像露光による
光照射部と非光照射部との間の電位コントラストを充分
且つ確実に確保することができる。このため、従来の増
感方式に比べ、Ｈｉｇｈ−γ特性の感光体を４〜８倍の
光感度を持つものとして効果的に使用することができ、
Ｈｉｇｈ−γ特性の感光体に対して少ない露光光量で高
解像度の画像を確実に得ることができる。特に、補助露
光手段を現像手段寄りに配設するようにすれば、補助露
光手段と現像手段との間の位置関係を考慮することな
く、感光体の特性に応じて補助露光手段の露光量を選択
すればよいので、感光体に対する感度の調整が容易にな
り、しかも、像露光による非光照射部については補助露
光を施した後一定時間内では電位減衰が殆ど起こらない
ので、安定した暗部電位を確実に得ることができる。As described above, according to the present invention, in the photoreceptor having the High-γ characteristic, the auxiliary exposure means is provided between the image exposure means and the developing means in addition to the image exposure means. Since the photosensitive body after exposure is uniformly exposed on the whole surface, and the potential is selectively attenuated only in the image exposure portion, the light irradiation portion and the non-light irradiation portion by the image exposure are not increased without increasing the exposure light amount of the image exposure means. It is possible to ensure a sufficient and sure potential contrast with the irradiation unit. Therefore, compared to the conventional sensitization method, a photoreceptor having a High-γ characteristic can be effectively used as one having a photosensitivity of 4 to 8 times,
It is possible to reliably obtain a high-resolution image with a small amount of exposure light for a photoreceptor having a High-γ characteristic. In particular, if the auxiliary exposure unit is arranged closer to the developing unit, the exposure amount of the auxiliary exposure unit can be adjusted according to the characteristics of the photoconductor without considering the positional relationship between the auxiliary exposure unit and the developing unit. It is easy to adjust the sensitivity to the photoconductor because it can be selected.Moreover, the non-light-irradiated portion by image exposure hardly loses potential within a fixed time after the auxiliary exposure, so that the stable dark portion potential can be obtained. Can be surely obtained.

【００４５】本発明において、Ｈｉｇｈ−γ特性の感光
体として、Ｘ型無金属フタロシアニンとバインダ樹脂か
らなるものを用いた場合には、前述した効果を確実に発
揮することができる。In the present invention, when the high-γ characteristic photoconductor made of X-type metal-free phthalocyanine and the binder resin is used, the above-mentioned effects can be surely exhibited.

【図面の簡単な説明】[Brief description of the drawings]

【図１】 本発明に係る画像形成装置の構成を示す説明
図である。FIG. 1 is an explanatory diagram illustrating a configuration of an image forming apparatus according to the present invention.

【図２】 本発明が適用された画像形成装置の実施の一
形態を示す説明図である。FIG. 2 is an explanatory diagram illustrating an embodiment of an image forming apparatus to which the present invention has been applied.

【図３】 （ａ）は実施の形態で用いられる感光体の明
減衰特性、（ｂ）はその暗減衰特性を示す説明図であ
る。FIG. 3A is an explanatory diagram showing a light attenuation characteristic of a photoreceptor used in the embodiment, and FIG. 3B is an explanatory diagram showing its dark attenuation characteristic.

【図４】 実施の形態で用いられた感光体の露光光量に
よる電位減衰変化を示すグラフ図である。FIG. 4 is a graph showing a potential attenuation change of the photoconductor used in the embodiment according to the exposure light amount.

【図５】 実施の形態で用いられた感光体の露光量と露
光後ＶL１００Ｖに減衰するまでの時間との関係を示す
グラフ図である。FIG. 5 is a graph showing the relationship between the exposure amount of the photoconductor used in the embodiment and the time until it decays to VL100V after exposure.

【図６】 実施の形態に係る画像形成装置の作像プロセ
スにおける像露光による光照射部及び非光照射部の電位
変化を示す説明図である。FIG. 6 is an explanatory diagram showing potential changes of a light irradiation portion and a non-light irradiation portion due to image exposure in an image forming process of the image forming apparatus according to the exemplary embodiment.

【図７】 実施の形態に係る補助露光装置の働きを説明
するためのグラフ図である。FIG. 7 is a graph diagram for explaining the operation of the auxiliary exposure apparatus according to the embodiment.

【図８】 単層型感光体のインダクション効果による電
位減衰特性を示すグラフ図である。FIG. 8 is a graph showing a potential decay characteristic of a single-layer type photoconductor due to an induction effect.

【符号の説明】[Explanation of symbols]

１…感光体，２…帯電手段，３…像露光手段，４…補助
露光手段，５…現像手段DESCRIPTION OF SYMBOLS 1 ... Photoconductor, 2 ... Charging means, 3 ... Image exposure means, 4 ... Auxiliary exposure means, 5 ... Developing means

Claims (2)

【特許請求の範囲】[Claims] 【請求項１】 一様帯電された表面電位（Ｖp）が現像
位置である露光量（Ａ0）を境として急激に減衰する電
位減衰特性の感光体（１）を用いた画像形成装置におい
て、 前記感光体（１）を帯電する帯電手段（２）と、この帯
電手段（２）にて帯電された感光体（１）に対して現像
位置で電位減衰しない程度の露光量で潜像パターンを書
き込む像露光手段（３）と、この像露光手段（３）の後
段側に配設され、当該像露光手段（３）により書き込ま
れた潜像パターンのうち像露光部（Ｚe）のみ選択的に
現像位置で電位減衰するように前記感光体（１）を均一
に補助露光する補助露光手段（４）と、前記像露光手段
（３）及び補助露光手段（４）にて形成された潜像パタ
ーンを可視像化する現像手段（５）とを備えたことを特
徴とする画像形成装置。1. An image forming apparatus using a photoconductor (1) having a potential attenuation characteristic, wherein the uniformly charged surface potential (Vp) is rapidly attenuated at an exposure amount (A0) which is a developing position. A charging unit (2) for charging the photoconductor (1) and a latent image pattern are written on the photoconductor (1) charged by the charging unit (2) with an exposure amount such that the potential is not attenuated at the developing position. The image exposure means (3) and only the image exposure part (Ze) of the latent image pattern provided by the image exposure means (3) disposed behind the image exposure means (3) are selectively developed. An auxiliary exposure means (4) for uniformly auxiliary exposing the photoconductor (1) so as to attenuate the potential at a position, and a latent image pattern formed by the image exposure means (3) and the auxiliary exposure means (4). Image formation comprising a developing means (5) for making a visible image Location. 【請求項２】 請求項１記載のものにおいて、前記感光
体（１）はＸ型無金属フタロシアニンとバインダ樹脂か
らなる単層型有機感光体であることを特徴とする画像形
成装置。2. The image forming apparatus according to claim 1, wherein the photoconductor (1) is a single-layer organic photoconductor composed of an X-type metal-free phthalocyanine and a binder resin.