JP2005201931A

JP2005201931A - Image forming apparatus

Info

Publication number: JP2005201931A
Application number: JP2004005062A
Authority: JP
Inventors: Hiroyuki Suzuki; 啓之鈴木; Makoto Nakamura; 良中村
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2004-01-13
Filing date: 2004-01-13
Publication date: 2005-07-28

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which performs electrification by using a plurality of magnetic brush electrifiers, and prevents the degradation of the electrostatic chargeability in particular, in a 1st magnetic brush electrifier. <P>SOLUTION: The image forming apparatus in which a photoreceptor is electrified by using an electrifying member, and an electrostatic latent image is formed on the photoreceptor by an image exposure means, is equipped with a developing means for forming a toner image by developing the latent image by a developer carrier to carry developer, and forms an image by transferring the toner image on transfer material. The electrifying member is constituted of a plurality of contact electrifying members each of which is a magnetic brush electrifier using magnetic particles. The 1st magnetic brush electrifier stores a larger amount of magnetic particles than other magnetic brush electrifiers. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

本発明は被記録画像や画像データに対応して像担持体に形成された静電潜像を、現像剤により現像して用紙等に記録する画像形成装置に関する。 The present invention relates to an image forming apparatus that develops an electrostatic latent image formed on an image carrier corresponding to a recorded image and image data with a developer and records the image on a sheet or the like.

従来、電子写真方式や静電記録方式を用いた画像形成装置は、数多く考案されているが図４を用いて概略構成ならびに動作について簡単に説明する。図４に示した画像形成装置において、コピー開始信号が入力されると感光体ドラム１がコロナ帯電器３により所定の電位になるように帯電される。一方、原稿台１０上におかれた原稿Ｇに対し原稿照射用ランプ、短焦点レンズアレイ、ＣＣＤセンサーが一体のユニット９となって原稿を照射しながら走査することにより、その照明走査光の原稿面反射光が、短焦点レンズアレイによって結像されてＣＣＤセンサーに入射される。ＣＣＤセンサーは受光部、転送部、出力部より構成されている。ＣＣＤ受光部において光信号が電荷信号に変えられ、転送部でクロックパルスに同期して順次出力部へ転送され、出力部において電荷信号を電圧信号に変換し、増幅、低インピーダンス化して出力する。得られたアナログ信号は周知の画像処理を行ってデジタル信号に変換してプリンター部に送られる。プリンター部においては、上記の画像信号を受けてＯＮ、ＯＦＦ発光されるＬＥＤ露光手段２により感光ドラム１面上に、原稿画像に対応した静電潜像を形成する。 Conventionally, many image forming apparatuses using an electrophotographic system or an electrostatic recording system have been devised, but the schematic configuration and operation will be briefly described with reference to FIG. In the image forming apparatus shown in FIG. 4, when a copy start signal is input, the photosensitive drum 1 is charged by the corona charger 3 so as to have a predetermined potential. On the other hand, the original G of the illumination scanning light is scanned by irradiating the original G on the original table 10 while irradiating the original as a unit 9 including an original irradiating lamp, a short focus lens array, and a CCD sensor. The surface reflected light is imaged by the short focus lens array and is incident on the CCD sensor. The CCD sensor includes a light receiving unit, a transfer unit, and an output unit. The optical signal is converted into a charge signal in the CCD light receiving unit, and sequentially transferred to the output unit in synchronization with the clock pulse in the transfer unit. The charge signal is converted into a voltage signal in the output unit, amplified and reduced in impedance, and output. The obtained analog signal is subjected to known image processing, converted into a digital signal, and sent to the printer unit. In the printer section, an electrostatic latent image corresponding to the original image is formed on the surface of the photosensitive drum 1 by the LED exposure means 2 that receives the image signal and emits light ON and OFF.

次にこの静電潜像をトナー粒子を収容した現像器４にて現像し、感光ドラム１上にトナー像を得る。このようにして、感光ドラム１上に形成されたトナー像は、転写装置７によって転写材上に静電転写される。その後転写材は、静電分離されて定着器６へと搬送され、熱定着されて画像が出力される。一方、トナー像転写後の感光ドラム１の面は、クリーナー５によって転写残りトナー等の付着汚染物の除去、必要に応じて像露光の光メモリを除去する前露光手段８による露光を受けて繰り返し画像形成に使用される。上記のようにして画像形成される、電子写真画像形成装置に用いられる、感光体としては、有機感光体やアモルファスシリコン系感光体（以下、「ａ−Ｓｉ系感光体」と称する）。等がよく用いられているが、前記ａ−Ｓｉ系感光体は、表面硬度が高く、半導体レーザなどに高い感度を示し、しかも繰返し使用による劣化もほとんど認められないことから、高速複写機やレーザービームプリンタ（ＬＢＰ）などの電子写真用感光体として用いられている。前記のａ−Ｓｉ系感光体を帯電する方法としては、コロナ放電を用いたコロナ帯電方式、導電性ローラを用い直接放電で帯電を行うローラ帯電方式、磁性粒子等により接触面積を充分に取り電荷を感光体表面に直接注入することにより帯電を行う注入帯電方式などがある。この中で、コロナ帯電方式やローラ帯電方式は放電を用いるため放電生成物が表面に付着しやすく、またａ−Ｓｉ系感光体は表面高度が非常に高く磨耗しにくいため放電生成物が表面に残存しやすく、高湿環境下等で水分の吸着等による静電潜像が形成された感光体表面上の電荷の面方向へ移動に伴う画像流れ現象が発生しやすい。これに対して、前記注入帯電方式は放電を積極的に用いることはせずに感光体表面に接触した部分から直接電荷を注入する帯電方式であるため前記の画像流れといった現象は発生しにくい。上記のａ−Ｓｉ系感光体はその製造方法が、ガスを高周波やマイクロ波でプラズマ化して固体化し、アルミシリンダー上に堆積させて成膜するため、プラズマが均一でないと周方向や長手方向に膜厚ムラや組成ムラができてしまう。これにより、従来から現像部において、数１０Ｖ程度の電位ムラが発生してしまっていた。これは、膜厚ムラにより静電容量の違いができ帯電能の差が生じるの現象とともに、前周の光メモリーを消すために用いる前露光による帯電−現像間での暗状態での電位減衰（以降、暗減衰と呼ぶ）が、膜厚や組成の違いによって差が生じ現像部における電位ムラをより増大させることにより発生する。前述の暗減衰は、ａ−Ｓｉ系感光体を用いた場合、有機感光体に比べ暗状態でも非常に大きく、更に像露光の光メモリーによる電位減衰が増大するため、前周の光メモリーを消すための帯電前の前露光手段が必要となる。このため、帯電−現像間での暗減衰は非常に大きくなり、１００〜２００Ｖ程度の電位減衰が生じる。このとき前述の膜厚ムラ、組成ムラにより、数１０Ｖの電位ムラが発生してしまっていた。 Next, the electrostatic latent image is developed by a developing device 4 containing toner particles, and a toner image is obtained on the photosensitive drum 1. In this manner, the toner image formed on the photosensitive drum 1 is electrostatically transferred onto the transfer material by the transfer device 7. Thereafter, the transfer material is electrostatically separated and conveyed to the fixing device 6 where it is thermally fixed and an image is output. On the other hand, the surface of the photosensitive drum 1 after the transfer of the toner image is repeatedly subjected to exposure by the pre-exposure means 8 that removes adhering contaminants such as toner remaining after transfer by the cleaner 5 and, if necessary, the optical memory for image exposure. Used for forming. As the photoconductor used in the electrophotographic image forming apparatus for forming an image as described above, an organic photoconductor or an amorphous silicon photoconductor (hereinafter referred to as “a-Si photoconductor”). However, the a-Si photoconductor has a high surface hardness, a high sensitivity to a semiconductor laser, etc., and almost no deterioration due to repeated use. It is used as an electrophotographic photoreceptor such as a beam printer (LBP). As a method for charging the a-Si photosensitive member, a corona charging method using corona discharge, a roller charging method in which charging is performed by direct discharge using a conductive roller, a contact area sufficiently obtained by magnetic particles, etc. There is an injection charging method in which charging is performed by directly injecting the toner onto the surface of the photoreceptor. Of these, the corona charging method and roller charging method use discharge, so that the discharge product is likely to adhere to the surface, and the a-Si photoconductor has a very high surface height and is difficult to wear. It tends to remain, and an image flow phenomenon due to movement of charges on the surface of the photoreceptor on which an electrostatic latent image is formed due to moisture adsorption or the like in a high humidity environment is likely to occur. On the other hand, the injection charging method is a charging method in which charges are directly injected from a portion in contact with the surface of the photoreceptor without actively using discharge, and thus the phenomenon of image flow is unlikely to occur. The above-described a-Si photoconductor is manufactured by plasmaizing gas with high frequency or microwave and solidifying it, and depositing it on an aluminum cylinder to form a film. Film thickness unevenness and composition unevenness are generated. As a result, potential unevenness of about several tens of volts has conventionally occurred in the developing section. This is due to the phenomenon that the electrostatic capacity varies due to uneven film thickness, resulting in a difference in charging ability, as well as the potential attenuation in the dark state between the charge and development by the pre-exposure used to erase the optical memory in the previous circumference ( Hereinafter, this is referred to as dark decay), which occurs when a difference occurs due to a difference in film thickness or composition and potential unevenness in the developing portion is further increased. When the a-Si type photoconductor is used, the dark decay described above is much larger even in the dark state than the organic photoconductor, and further the potential decay due to the optical memory for image exposure is increased. Therefore, pre-exposure means before charging is required. For this reason, the dark decay between charging and development becomes very large, and a potential decay of about 100 to 200 V occurs. At this time, potential unevenness of several tens of volts was generated due to the above-described film thickness unevenness and composition unevenness.

このような電位ムラが生じると、静電容量の大きなａ−Ｓｉ系感光体は有機感光体に比べてコントラストも小さいため影響を大きく受けてしまい、濃度ムラも顕著になってしまう。このような問題点に対して、例えば複数回帯電を行うという方法が有効である（例えば特許文献１参照）。前述の光メモリーによる暗減衰の増大は複数帯電を行うことにより、第１の帯電で光メモリーを大幅に軽減できるため、第２の帯電を行った後には暗減衰を少なくすることが可能となる。これに伴い、電位ゴーストや電位ムラが大幅に良化される。ここで複数回の帯電を行う際に注入帯電方式を用いると帯電能が高く、電位収束性が高いため、電位ゴーストや電位ムラについて大きく改善される。また注入帯電方式は前記のように放電をほとんど用いないため、画像流れも発生しにくい。注入帯電器としては例えば磁性粒子を用いた磁気ブラシ帯電器が有効である。磁気ブラシ帯電器は磁性粒子の接触点によって帯電を行うため、帯電を行うための表面積が広く汚染に強い利点がある。このため長期にわたる耐久を行っても帯電性能を維持することが可能である。しかし、複数の磁気ブラシ帯電器を用いた場合には、マグネットローラ等高価な部品を複数必要としコストが高くなるため、通常の帯電器以上に交換間隔を長くすることが望まれる。更に、用いる感光体がａ−Ｓｉ系感光体のように高寿命の感光体の場合には、帯電器等の感光体周りのパーツを高寿命化していくことがランニングコストの低減に大きな効果となる。これに対し、前記のように磁性粒子を用いた磁気ブラシ帯電器は、粒子を用いるため感光体に接触する比表面積がローラ帯電等の接触帯電器に比べて大きいため汚染に強く、また、ローラ帯電等のように通電で抵抗が大幅にアップするようなことがないため帯電器寿命は長いが、長期にわたり耐久を行っていくとクリーナをすり抜けた外添剤やトナーが少しずつ混入してくるため、磁性粒子の表面を徐々に汚染し少しずつではあるが帯電性が低下してくる。 When such potential unevenness occurs, the a-Si type photoconductor having a large electrostatic capacity is affected by a large contrast because the contrast is smaller than that of the organic photoconductor, and the density nonuniformity becomes remarkable. For such a problem, for example, a method of charging a plurality of times is effective (see, for example, Patent Document 1). The increase in dark attenuation due to the optical memory described above can reduce the optical memory greatly by the first charging by performing a plurality of charging, and therefore it is possible to reduce the dark attenuation after performing the second charging. . Along with this, potential ghost and potential unevenness are greatly improved. Here, when charging is performed a plurality of times, if an injection charging method is used, charging ability is high and potential convergence is high, so that potential ghost and potential unevenness are greatly improved. In addition, since the injection charging method uses almost no discharge as described above, image flow hardly occurs. For example, a magnetic brush charger using magnetic particles is effective as the injection charger. Since the magnetic brush charger is charged by the contact point of the magnetic particles, it has an advantage that it has a large surface area for charging and is resistant to contamination. For this reason, it is possible to maintain charging performance even after long-term durability. However, when a plurality of magnetic brush chargers are used, a plurality of expensive parts such as magnet rollers are required and the cost is increased. Therefore, it is desirable to make the replacement interval longer than a normal charger. Furthermore, when the photoconductor to be used is a photoconductor having a long life such as an a-Si type photoconductor, extending the life of parts around the photoconductor such as a charger has a great effect on reducing the running cost. Become. On the other hand, the magnetic brush charger using magnetic particles as described above uses particles, so that the specific surface area in contact with the photosensitive member is larger than that of a contact charger such as roller charging, and is resistant to contamination. The life of the charger is long because there is no significant increase in resistance due to energization unlike charging, but external additives and toner that have passed through the cleaner will gradually be mixed in as the durability is extended over a long period of time. For this reason, the surface of the magnetic particles is gradually contaminated, and the charging property is gradually reduced.

この磁性粒子の汚染は複数の磁気ブラシ帯電器を用いる場合には、第１の磁気ブラシ帯電器がより顕著である。これは、クリーナをすり抜けた外添剤やトナーは第１の磁気ブラシ帯電器でほとんど捕獲されるため、第２の磁気ブラシ帯電器以降には多くは到達しないためである。
特開２００３−１７３０７０号公報 This magnetic particle contamination is more noticeable in the first magnetic brush charger when a plurality of magnetic brush chargers are used. This is because the external additive and the toner that have passed through the cleaner are almost captured by the first magnetic brush charger, and therefore do not reach much after the second magnetic brush charger.
JP 2003-173070 A

そこで、本発明の目的としては複数の磁気ブラシ帯電器において帯電を行う構成において、特に第１の磁気ブラシ帯電器における帯電能の低下を防ぐことを目的としている。 Accordingly, an object of the present invention is to prevent a decrease in charging ability in the first magnetic brush charger, particularly in a configuration in which charging is performed in a plurality of magnetic brush chargers.

本発明においては、上記のように複数の磁気ブラシ帯電器において帯電を行う場合に、第１の磁気ブラシ帯電器が汚染しやすいことに対して第１の磁気ブラシ帯電器の磁性粒子の担持量を、他の帯電器に比べて多くすることにより実現している。磁性粒子の担持量を多くし循環させることにより、外添剤やトナーが混入した場合の汚染による抵抗アップを大幅に低減する事が可能となる。 In the present invention, in the case where charging is performed in a plurality of magnetic brush chargers as described above, the amount of magnetic particles carried by the first magnetic brush charger is in contrast to that the first magnetic brush charger is likely to be contaminated. This is realized by increasing the number of the chargers compared to other chargers. By increasing the amount of magnetic particles carried and circulating, it is possible to greatly reduce resistance increase due to contamination when external additives and toner are mixed.

以上説明のように、本発明のように第１の磁気ブラシ帯電器の磁性粒子担持量を第２の磁気ブラシ帯電器の磁性粒子担持量に比べ充分に多くしてやることにより、帯電器の寿命を充分に長くすることができ、コストが多少高くてもランニングコストの面では充分に安くすることができた。またサービスマンのメンテナンス間隔についても広く設定することが可能となり、アモルファスシリコン感光体の高寿命である特徴を充分に生かすことが可能となった。 As described above, the life of the charger can be increased by increasing the amount of magnetic particles carried by the first magnetic brush charger as compared with the amount of magnetic particles carried by the second magnetic brush charger as in the present invention. It was possible to make it sufficiently long, and even if the cost was somewhat high, it was possible to make it sufficiently cheap in terms of running cost. In addition, it is possible to set a wide maintenance interval for service personnel, and it is possible to make full use of the long-life characteristics of the amorphous silicon photoconductor.

（実施例１）
本実施例においては、ポジ帯電のアモルファスシリコン感光体を２つの磁気ブラシ帯電器により帯電する場合について述べる。また、本実施例においては図１に示すような画像形成装置を用いている。帯電工程に磁気ブラシ帯電器を３０、３１に示すように２つ設け、２回帯電を行うこと以外は従来例と同様の工程にて画像出力が可能となっている。 (Example 1)
In this embodiment, a case where a positively charged amorphous silicon photosensitive member is charged by two magnetic brush chargers will be described. In this embodiment, an image forming apparatus as shown in FIG. 1 is used. As shown in 30 and 31, two magnetic brush chargers are provided in the charging process, and image output is possible in the same process as in the conventional example except that charging is performed twice.

図５は、本実施例において用いたポジ帯電性のａ−Ｓｉ系感光体の構造を示す模式的な断面図である。図５に示すａ−Ｓｉ系感光体は、Ａｌなどからなる導電性支持体２０１と、導電性支持体２０１の表面上に順次堆積された感光層２０５（電荷注入阻止層２０２および光導電性を示す光導電層２０３）と表面層２０４とからなる。ここで、電荷注入阻止層２０２は導電性支持体２０１から光導電層２０３への電荷の注入を阻止するためのものであり、必要に応じて設けられる。また、光導電層２０３は少なくともシリコン原子を含む非晶質材料で構成され、光導電性を示すものである。さらに、表面層２０４はシリコン原子と炭素原子（さらに、必要により水素原子あるいはハロゲン原子またはその両方の原子）を含み、電子写真装置における潜像を保持する能力をもつものである。ａ−Ｓｉ系感光体はその製造方法が、ガスを高周波やマイクロ波でプラズマ化して固体化し、アルミシリンダー上に堆積させて成膜するため、プラズマが均一でないと膜厚ムラや組成ムラができてしまう。これにより、従来から現像部において、数１０Ｖ程度の電位ムラが発生してしまっていた。これは、膜厚ムラにより静電容量の違いができ帯電能の差が生じるの現象とともに、前周の光メモリーを消すために用いる前露光による帯電−現像間での電位減衰が、膜厚や組成によって差が生じ現像部における電位ムラをより増大させることにより発生する。 FIG. 5 is a schematic cross-sectional view showing the structure of the positively chargeable a-Si photoconductor used in this example. The a-Si photoconductor shown in FIG. 5 includes a conductive support 201 made of Al or the like, and a photosensitive layer 205 (a charge injection blocking layer 202 and a photoconductive layer) sequentially deposited on the surface of the conductive support 201. A photoconductive layer 203) and a surface layer 204. Here, the charge injection blocking layer 202 is for blocking charge injection from the conductive support 201 to the photoconductive layer 203, and is provided as necessary. The photoconductive layer 203 is made of an amorphous material containing at least silicon atoms and exhibits photoconductivity. Further, the surface layer 204 contains silicon atoms and carbon atoms (and, if necessary, hydrogen atoms and / or halogen atoms) and has the ability to hold a latent image in an electrophotographic apparatus. The production method of a-Si photoconductors is that the gas is solidified by high-frequency or microwave plasma, and is deposited on an aluminum cylinder to form a film. End up. As a result, potential unevenness of about several tens of volts has conventionally occurred in the developing section. This is because the difference in electrostatic capacity due to film thickness unevenness and the difference in charging ability occur, as well as the potential attenuation between charging and developing due to pre-exposure used for erasing the optical memory on the previous circumference. A difference occurs depending on the composition, and this is caused by further increasing the potential unevenness in the developing portion.

上記の光メモリーについて説明すると、ａ−Ｓｉ系感光体を帯電し像露光を行うと光キャリアを生成し電位を減衰させる。しかしこのとき、ａ−Ｓｉ系感光体は多くのタングリングボンド（未結合手）を有しており、これが局在準位となって光キャリアの一部を捕捉してその走行性を低下させ、あるいは光生成キャリアーの再結合確率を低下させる。したがって、画像形成プロセスにおいて、露光によって生成された光キャリアの一部は、次工程の帯電時にａ−Ｓｉ系感光体に電界がかかると同時に局在準位から開放され、露光部と非露光部とでａ−Ｓｉ系感光体の表面電位に差が生じて、これが最終的に光メモリーとなる。 The optical memory will be described. When an a-Si photosensitive member is charged and image exposure is performed, a photocarrier is generated and the potential is attenuated. However, at this time, the a-Si-based photoconductor has many tangling bonds (unbonded hands), which become localized levels and capture a part of the optical carrier to reduce the running property. Or reduce the recombination probability of photogenerated carriers. Therefore, in the image forming process, a part of the photocarrier generated by exposure is released from the localized level at the same time as an electric field is applied to the a-Si photoconductor during charging in the next process, and the exposed portion and the non-exposed portion. Thus, a difference occurs in the surface potential of the a-Si photoconductor, which finally becomes an optical memory.

そこで、前露光工程において均一露光を行うことによりａ−Ｓｉ系感光体内部に潜在する光キャリアを過多にし全面で均一になるようにして、光メモリーを消去することが一般的である。このとき、前露光源８から発する前露光の光量を増やしたり、前露光の波長をａ−Ｓｉ系感光体８の分光感度ピーク（約６８０〜７００ｎｍ）に近づけることにより、より効果的に光メモリ（ゴースト）を消去することが可能である。 Therefore, in general, the optical memory is erased by performing uniform exposure in the pre-exposure step so that the optical carriers latent in the a-Si photosensitive member are excessive and uniform over the entire surface. At this time, the amount of pre-exposure emitted from the pre-exposure source 8 is increased, or the wavelength of the pre-exposure is brought closer to the spectral sensitivity peak (about 680 to 700 nm) of the a-Si photosensitive member 8, thereby more effectively optical memory ( (Ghost) can be erased.

しかしながら、上記のようにａ−Ｓｉ系感光体に例えば膜厚ムラが存在すると、光導電層間にかかる電界が異なるため、上記局在準位からの光キャリアの開放に差が生じ、膜厚が薄い部分ほど電位減衰が大きく、帯電部でたとえ均一に帯電できたとしても、現像部では電位ムラが生じてしまう。また、帯電能についても膜厚が薄い部分ほど静電容量が大きくなるため不利となり、帯電能が低下してくると上記の現像部での帯電ムラはより顕著となってしまう。この電位ムラは、画像露光を行った場合にも残り、現像行程を行うと特に目に認識されやすい低濃度領域で顕著な濃度ムラとして現れる。 However, for example, if there is unevenness in the film thickness of the a-Si photosensitive member as described above, the electric field applied between the photoconductive layers is different, so that a difference occurs in the release of photocarriers from the localized level, and the film thickness is The thinner the portion, the greater the potential attenuation. Even if the charging portion can be uniformly charged, potential unevenness occurs in the developing portion. Further, the charging ability is disadvantageous because the smaller the film thickness, the larger the electrostatic capacity, which is disadvantageous. When the charging ability is lowered, the charging unevenness in the developing section becomes more remarkable. This potential unevenness remains even when image exposure is performed, and appears as remarkable density unevenness particularly in a low density region that is easily recognized by the eyes when the development process is performed.

また、ａ−Ｓｉ系感光体は膜厚が一定の場合においても製法上周方向や長手方向について組成ムラができやすく光キャリアの発生量が面内で差が生じ、前記と同様に暗減衰が面方向で一定にならないことによる電位ムラは生じる場合が多かった。 In addition, even in the case where the film thickness is constant, the composition of the a-Si type photoconductor tends to cause uneven composition in the circumferential direction and the longitudinal direction, and the amount of generated photocarriers is different in the surface. In many cases, potential non-uniformity occurs due to non-uniformity in the surface direction.

このような、光キャリアに起因される暗減衰や電位ムラを軽減する方法として複数回帯電を行う方法がある。第１の帯電において光キャリアを大幅に減らすことにより、第２の帯電後の暗減衰を大幅に軽減することが可能になるため、電位ムラや電位ゴーストを大幅に改善できる。 As a method of reducing such dark attenuation and potential unevenness caused by the optical carrier, there is a method of charging a plurality of times. By significantly reducing the number of optical carriers in the first charging, the dark decay after the second charging can be greatly reduced, so that potential unevenness and potential ghost can be greatly improved.

ここで、前述のａ−Ｓｉ系感光体の帯電部材としては、従来からコロナ帯電を用いた装置が実用化されている。しかし、ａ−Ｓｉは比誘電率が１１〜１２と有機感光体に比べ大きいため、静電容量が大きくなり、それに伴い帯電能の低下、放電による潜像の流れによる画像流れ等が発生しやすくなる。 Here, as a charging member for the a-Si photosensitive member, a device using corona charging has been put to practical use. However, since a-Si has a relative dielectric constant of 11 to 12 which is larger than that of the organic photoreceptor, the capacitance is increased, and accordingly, the charging ability is lowered, and the image flow due to the flow of the latent image due to the discharge is likely to occur. Become.

これに対して、帯電部材として導電性ローラーやファーブラシローラー、磁性粒子を担持したマグネットローラ等を用いた、接触帯電部材を用い感光体に対して十分な接触状態を保つ条件で、ａ−Ｓｉ系感光体を帯電すると、ａ−Ｓｉ系感光体表面が１０^９〜１０^１４Ω・ｃｍの材質からなる層により形成されていることにより、接触帯電部材に印加したバイアスのうちの直流成分とほぼ同等の帯電電位を像担持体表面に得ることが可能である。このような帯電方法は、放電を用いずに電荷を直接感光体に注入し帯電を行うため、注入帯電と称する。この注入帯電を用いれば、像担持体への帯電がコロナ帯電器を用いて行われるような放電現象を利用しないので完全なオゾンレスかつ、低電力消費型帯電が可能となり注目されてきている。また、帯電能の低下や画像流れが防止できるとともに、印加した電圧近傍に帯電されるため電位の制御を行うことも容易となる。 In contrast to this, a-Si is used under the condition that a contact charging member is used to maintain a sufficient contact state with the photosensitive member using a conductive roller, a fur brush roller, a magnet roller carrying magnetic particles, or the like as a charging member. When the photoconductor is charged, the surface of the a-Si photoconductor is formed of a layer made of a material of 10 ⁹ to 10 ¹⁴ Ω · cm, so that it is almost equal to the DC component of the bias applied to the contact charging member. It is possible to obtain an equivalent charging potential on the surface of the image carrier. Such a charging method is referred to as injection charging because charging is performed by directly injecting a charge into the photoreceptor without using discharge. If this injection charging is used, a discharge phenomenon in which the image carrier is charged by using a corona charger is not used, and therefore, complete ozone-less and low power consumption type charging becomes possible. In addition, a decrease in charging ability and image flow can be prevented, and the potential can be easily controlled because the charging is performed in the vicinity of the applied voltage.

図２中、３０及び３１は本実施例において用いた磁気ブラシ方式の注入帯電器である。本実施例においては磁気ブラシ帯電器を感光体回転方向に対し２つ設けている。このとき本実施例においては、第１の磁気ブラシ帯電器３０内には磁性粒子が２００ｇ収容され、第２の磁気ブラシ帯電器３１内には磁性粒子が６０ｇ担持されている。また、第１の磁気ブラシ帯電器３０内には、磁性粒子規制手段近傍に磁性粒子を撹拌する撹拌部材３０５が設けられている。 In FIG. 2, reference numerals 30 and 31 denote magnetic brush type injection chargers used in this embodiment. In this embodiment, two magnetic brush chargers are provided with respect to the rotation direction of the photosensitive member. At this time, in this embodiment, 200 g of magnetic particles are accommodated in the first magnetic brush charger 30 and 60 g of magnetic particles are carried in the second magnetic brush charger 31. In the first magnetic brush charger 30, a stirring member 305 for stirring magnetic particles is provided in the vicinity of the magnetic particle regulating means.

磁気ブラシ方式の注入帯電器は導電性の磁性粒子を直接マグネット、あるいは、マグネットを内包するスリーブ上に磁気的に拘束させ、停止、あるいは、回転しながら像担持体に接触させ、これに電圧を印加することによって帯電が開始される。本実施例で用いた磁気ブラシ帯電器３０、３１は、内部に図２のように４極構成の固定マグネット３０２が設けられ、回転自在の非磁性の帯電スリーブ３０３上に、磁性粒子規制手段３０１によって規制された帯電用磁性粒子３０４が磁界によってブラシ状に形成されて、非磁性スリーブ３０３の回転にともない帯電用磁性粒子３０４が搬送される。また、上記帯電スリーブ３４は感光ドラム１に対しカウンター方向に回転しており、感光ドラム１の回転速度３００ｍｍ／ｓｅｃに対し磁気ブラシ帯電器３０、３１は２５０ｍｍ／ｓｅｃで回転している。上記帯電スリーブ３０３に、帯電電圧を印加することにより、帯電用磁性粒子３０４から電荷が感光ドラム１上に与えられ、帯電電圧に対応した電位に近い値に帯電される。 The magnetic brush type injection charger directly confins the conductive magnetic particles on the magnet or the sleeve containing the magnet, and stops or rotates it to contact the image carrier and apply voltage to it. Charging is started by application. The magnetic brush chargers 30 and 31 used in this embodiment are provided with a fixed magnet 302 having a four-pole configuration inside as shown in FIG. 2, and a magnetic particle regulating means 301 on a rotatable nonmagnetic charging sleeve 303. The magnetic particles 304 for charging restricted by the magnetic field are formed in a brush shape by a magnetic field, and the magnetic particles for charging 304 are conveyed as the nonmagnetic sleeve 303 rotates. The charging sleeve 34 is rotated in the counter direction with respect to the photosensitive drum 1, and the magnetic brush chargers 30 and 31 are rotated at 250 mm / sec with respect to the rotational speed of the photosensitive drum 1 of 300 mm / sec. By applying a charging voltage to the charging sleeve 303, a charge is applied from the charging magnetic particles 304 onto the photosensitive drum 1, and the charging sleeve 303 is charged to a value close to a potential corresponding to the charging voltage.

磁気ブラシ帯電器３０、３１において、感光ドラム１に対して形成される帯電用磁性粒子３０４の接触ニップ幅は４ｍｍになるよう調整されている。また、帯電用磁性粒子としては、粒径が平均粒径が１０〜１００μｍ、飽和磁化が２０〜２５０ｅｍｕ／ｃｍ^３、抵抗が１０^２〜１０^１０Ω・ｃｍのものが、好ましく感光ドラムにピンホールのような絶縁の欠陥が存在することを考慮すると１０^６Ω・ｃｍ以上のものを用いることが好ましい。帯電性能を良くするにはできるだけ抵抗の小さいものを用いる方がよいので、本実施例においては、平均粒径２５μｍ、飽和磁化２００ｅｍｕ／ｃｍ^３、抵抗が５×１０^６Ω・ｃｍの帯電用磁性粒子を用いた。また本実施例において用いた帯電用磁性粒子は、フェライト表面を酸化、還元処理して抵抗調整を行ったものを用いている。 In the magnetic brush chargers 30 and 31, the contact nip width of the charging magnetic particles 304 formed on the photosensitive drum 1 is adjusted to 4 mm. The charging magnetic particles preferably have an average particle size of 10 to 100 μm, a saturation magnetization of 20 to 250 emu / cm ³ , and a resistance of 10 ² to 10 ¹⁰ Ω · cm. In view of the existence of such an insulation defect, it is preferable to use one having a resistance of 10 ⁶ Ω · cm or more. In order to improve the charging performance, it is better to use the one having as small resistance as possible. In this example, the charging magnetism having an average particle diameter of 25 μm, a saturation magnetization of 200 emu / cm ³ , and a resistance of 5 × 10 ⁶ Ω · cm. Particles were used. Further, the magnetic particles for charging used in this example are those obtained by adjusting the resistance by oxidizing and reducing the ferrite surface.

ここで、帯電用磁性粒子の抵抗値は、底面積が２２８ｍｍ^２の金属セルに帯電用磁性粒子を２ｇ入れた後、６．６Ｋｇ／ｃｍ^２で加重し、１００Ｖの電圧を印加して測定している。 Here, the resistance value of the magnetic particles for charging is measured by putting 2 g of the magnetic particles for charging into a metal cell having a bottom area of 228 mm ² , then applying a voltage of 100 V, applying a weight of 6.6 Kg / cm ^2. ing.

また、本実施例において磁気ブラシ帯電器に対して印加したバイアスは、第１の磁気ブラシ帯電器には５５０Ｖの直流電圧を、第２の磁気ブラシ帯電器には５００Ｖの直流電圧を非磁性スリーブに対して印加している。このように電圧を印加して帯電工程を行うと、第１の磁気ブラシ帯電器により５５０Ｖ近傍まで帯電された後に、ａ−Ｓｉ感光体の場合には暗減衰による電位減衰が生じ、第２の磁気ブラシ帯電器の帯電直前においては５００Ｖ弱に減衰している。引き続き第２の磁気ブラシ帯電器で帯電を行うと、第１の磁気ブラシ帯電器によって５００Ｖ弱に帯電が施されているため、帯電ニップ内においては印加電圧に収束させるための帯電時間が充分取れるため、電位ムラのない均一な帯電状態が実現できる。また、第１の磁気ブラシ帯電において帯電した後に暗減衰を起こしているため、光キャリアを大幅に減らすことができ、第２の帯電後の暗減衰を大幅に軽減することが可能になる。このため、暗減衰の差によって生じる電位ムラや帯電不良による電位ムラ等について大幅に改善することができる。 Further, in the present embodiment, the bias applied to the magnetic brush charger is 550V DC voltage for the first magnetic brush charger and 500V DC voltage for the second magnetic brush charger. Is applied. When the charging process is performed by applying a voltage in this way, after the first magnetic brush charger is charged to near 550 V, in the case of an a-Si photosensitive member, potential decay due to dark decay occurs, and the second Immediately before the charging of the magnetic brush charger, it is attenuated to less than 500V. When the second magnetic brush charger is subsequently charged, the first magnetic brush charger is charged to less than 500V, so that a sufficient charging time can be taken to converge to the applied voltage in the charging nip. Therefore, a uniform charged state without potential unevenness can be realized. In addition, since dark decay occurs after charging in the first magnetic brush charging, it is possible to significantly reduce the optical carrier, and it is possible to greatly reduce the dark decay after the second charging. For this reason, it is possible to significantly improve the potential unevenness caused by the difference in dark attenuation, the potential unevenness due to charging failure, and the like.

ここで、本実施例においては前記のように、第１の磁気ブラシ帯電器には磁性粒子が２００ｇ担持され、第２の磁気ブラシ帯電器には磁性粒子が６０ｇ担持されている。図６は、画像比率７％の原稿を出力し耐久を行った場合の現像位置における電位の推移をあらわしており、図７は、前記条件における電位ムラの推移をあらわしている。比較例として、第１の磁気ブラシ帯電器、第２の磁気ブラシ帯電器ともに磁性粒子が６０ｇ担持されている場合と、第１の磁気ブラシ帯電器に磁性粒子が６０ｇ担持され、第２の磁気ブラシ帯電器に磁性粒子が２００ｇ担持されている場合について検討したところ、図６、図７のように第１の磁気ブラシ帯電器に２００ｇ、第２の磁気ブラシ帯電器に６０ｇ磁性粒子を収容した本実施例の場合は他の比較例に比べ帯電電位の推移及び電位ムラの推移について良好であることがわかる。 In this embodiment, as described above, 200 g of magnetic particles are carried on the first magnetic brush charger, and 60 g of magnetic particles are carried on the second magnetic brush charger. FIG. 6 shows changes in potential at the development position when a document having an image ratio of 7% is output and durability is applied, and FIG. 7 shows changes in potential unevenness under the above conditions. As a comparative example, both the first magnetic brush charger and the second magnetic brush charger carry 60 g of magnetic particles, and the first magnetic brush charger carries 60 g of magnetic particles, and the second magnetic brush charger The case where 200 g of magnetic particles are carried on the brush charger was examined. As shown in FIGS. 6 and 7, 200 g of magnetic particles were accommodated in the first magnetic brush charger and 60 g of magnetic particles were accommodated in the second magnetic brush charger. In the case of this example, it can be seen that the transition of the charging potential and the transition of the potential unevenness are better than those of the other comparative examples.

これは、磁性粒子の汚染は第１の磁気ブラシ帯電器において顕著であるため、比較例のように第１の磁気ブラシ帯電器のキャリア容量が６０ｇと少ない場合には１０万枚程度までは問題なく帯電できるが、それ以降第１の磁気ブラシ帯電器の帯電能が徐々に帯電能が低下してきてしまう。第１の磁気ブラシ帯電器の帯電能が低下してきてしまうと、第２の磁気ブラシ帯電器の帯電能が高い場合でも、前述の複数帯電によって光キャリアを低減する効果が低くなるため帯電電位が低下してしまう。また、第１の磁気ブラシ帯電器の帯電能が低くなり帯電電位ムラが大きくなってしまうと第２の磁気ブラシ帯電器で充分にならすことができなくなり電位ムラも増加してしまう。このため、比較例の第１の磁気ブラシ帯電器に磁性粒子が６０ｇ担持され、第２の磁気ブラシ帯電器に磁性粒子が２００ｇ担持されトータルでは本実施例と同量の磁性粒子を担持していても、帯電電位や電位ムラに差が生じてしまう。 This is because the contamination of the magnetic particles is remarkable in the first magnetic brush charger, and therefore, when the carrier capacity of the first magnetic brush charger is as small as 60 g as in the comparative example, there is a problem up to about 100,000 sheets. However, after that, the charging ability of the first magnetic brush charger gradually decreases. If the charging capability of the first magnetic brush charger is reduced, even if the charging capability of the second magnetic brush charger is high, the effect of reducing the optical carrier due to the above-described multiple charging is reduced, so the charging potential is reduced. It will decline. Further, if the charging capability of the first magnetic brush charger becomes low and the charging potential unevenness becomes large, the second magnetic brush charger cannot be sufficiently smoothed and the potential unevenness increases. For this reason, 60 g of magnetic particles are carried on the first magnetic brush charger of the comparative example, and 200 g of magnetic particles are carried on the second magnetic brush charger, so that the total amount of magnetic particles is carried as in this embodiment. However, there is a difference in charging potential and potential unevenness.

本実施例のように第１の磁気ブラシ帯電器に２００ｇ、第２の磁気ブラシ帯電器に６０ｇ磁性粒子を収容した場合には、第１の磁気ブラシ帯電器の磁性粒子の容量を多くし循環させる構成をとったことにより、汚染の影響を大幅に低減することが可能となり長期にわたり帯電能を維持することが可能になったため、複数帯電のメリットである光キャリアの低減が実現できるとともに電位ムラについても第１の帯電時にも均一帯電が可能なため、第２の帯電器で更にならすことにより充分に低いレベルを維持することが可能となった。 When 200 g magnetic particles are accommodated in the first magnetic brush charger and 60 g magnetic particles are accommodated in the second magnetic brush charger as in this embodiment, the capacity of the magnetic particles in the first magnetic brush charger is increased to circulate. By adopting this configuration, it is possible to significantly reduce the influence of contamination and maintain the charging ability over a long period of time, so that it is possible to reduce the optical carrier, which is the merit of multiple charging, and to realize potential unevenness. In addition, since uniform charging is possible during the first charging, a sufficiently low level can be maintained by further leveling with the second charger.

第２の磁気ブラシ帯電器の磁性粒子の汚染は第１の磁気ブラシ帯電器の磁性粒子の汚染に比べ少ないため、磁性粒子の担持量は第１の磁気ブラシ帯電器に比べ少なくて構わないが、比較例の第１の磁気ブラシ帯電器、第２の磁気ブラシ帯電器ともに磁性粒子が６０ｇ担持されている場合と、第１の磁気ブラシ帯電器に磁性粒子が６０ｇ担持され、第２の磁気ブラシ帯電器に磁性粒子が２００ｇ担持されている場合について比較すると、第２の磁気ブラシ帯電器の磁性粒子担持量が２００ｇの方が若干良好なことから、第２の磁気ブラシ帯電器の磁性粒子も若干は汚染が生じていることがわかる。本実施例においては５０万枚の耐久で評価したため、第２の磁気ブラシ帯電器の磁性粒子容量を６０ｇとしたが、例えば１００万枚の寿命を目指す場合等には第２の磁気ブラシ帯電器の磁性粒子の担持量も、それあわせて多少増やす必要がある。ただし、その場合においても第１の磁気ブラシ帯電器の磁性粒子はより汚染しやすくなるので、磁性粒子の担持量は少なくとも第２の磁気ブラシ帯電器の磁性粒子担持量よりも充分に多いことが必要となる。 Since the contamination of the magnetic particles of the second magnetic brush charger is less than the contamination of the magnetic particles of the first magnetic brush charger, the amount of magnetic particles supported may be less than that of the first magnetic brush charger. The first magnetic brush charger and the second magnetic brush charger of the comparative example both carry 60 g of magnetic particles, and the first magnetic brush charger carries 60 g of magnetic particles, and the second magnetic brush charger When the case where 200 g of magnetic particles are carried on the brush charger is compared, the amount of magnetic particles carried by the second magnetic brush charger is slightly better when 200 g is used. It can also be seen that there is some contamination. In this embodiment, since the durability was evaluated for 500,000 sheets, the magnetic particle capacity of the second magnetic brush charger was set to 60 g. However, for example, when the life of 1 million sheets is aimed, the second magnetic brush charger The amount of the magnetic particles supported needs to be increased accordingly. However, even in that case, the magnetic particles of the first magnetic brush charger are more likely to be contaminated, so that the amount of magnetic particles carried is at least sufficiently larger than the amount of magnetic particles carried by the second magnetic brush charger. Necessary.

（実施例２）
実施例１においては、図２ように第１の磁気ブラシ帯電器の非磁性スリーブ内のマグネットについて、４極構成のマグネットを用いたが、本実施例においては図３ように５極構成のマグネットを用いた。具体的には撹拌部材３０５近傍に同極の反発極を設け非磁性スリーブ上にコーティングされた磁性粒子を磁力によって剥ぎ取る構成になっている。このように反発極を設けた５極構成のマグネットを用いると、磁性粒子の循環が良好に行なわれ一部の磁性粒子のみ汚染が促進するのを防止することが可能となる。本実施例のような構成をとることにより、実施例１と比較しても同等以上の耐久性を保つことが可能となり、長期にわたり高安定、高精度の帯電を行うことが可能となった。 (Example 2)
In the first embodiment, as shown in FIG. 2, the magnet in the non-magnetic sleeve of the first magnetic brush charger is a four-pole magnet. In this embodiment, a five-pole magnet is used as shown in FIG. Was used. Specifically, a repulsive pole having the same polarity is provided in the vicinity of the stirring member 305, and the magnetic particles coated on the nonmagnetic sleeve are peeled off by a magnetic force. When a magnet having a five-pole configuration having a repulsive pole is used, it is possible to prevent the contamination of only some of the magnetic particles by promoting the circulation of the magnetic particles. By adopting the configuration as in the present embodiment, it is possible to maintain durability equal to or higher than that of the first embodiment, and it is possible to perform highly stable and highly accurate charging over a long period of time.

実施例１、２においては、磁気ブラシ帯電器について、非磁性スリーブ内に固定マグネットを設け非磁性スリーブを回転させることにより、磁性粒子を搬送する構成をとったが、本発明はこのような構成に限られるものではなく、例えばマグネットローラに直接磁性粒子を担持してマグネットローラ自体の回転により磁性粒子を搬送する構成や、非磁性スリーブ内に回転するマグネットローラが配置され、マグネットローラの回転方向の逆方向に磁性粒子が搬送されることにより帯電を行う方法等においても適応可能である。複数の磁気ブラシ帯電器によって帯電工程を行う構成において、磁気ブラシ帯電器に収容される磁性粒子の量が第１の磁気ブラシ帯電器について、他の磁気ブラシ帯電器と比較して多い場合のすべての場合において効果が得られる。また、本実施例１、２においては、磁気ブラシ帯電器が２つの場合について述べたが、例えば３つ以上の磁気ブラシ帯電器で帯電を行う場合についても、第１の磁気ブラシ帯電器に収容される磁性粒子が最も多い場合について本発明は適用される。 In the first and second embodiments, the magnetic brush charger is configured to convey the magnetic particles by providing a fixed magnet in the nonmagnetic sleeve and rotating the nonmagnetic sleeve. However, the present invention has such a configuration. For example, a configuration in which magnetic particles are directly carried on the magnet roller and the magnetic particles are conveyed by rotation of the magnet roller itself, or a rotating magnet roller is disposed in the non-magnetic sleeve, and the rotation direction of the magnet roller is arranged. This method can also be applied to a method in which charging is performed by transporting magnetic particles in the opposite direction. In the configuration in which the charging process is performed by a plurality of magnetic brush chargers, all the cases where the amount of magnetic particles accommodated in the magnetic brush charger is larger than the other magnetic brush chargers in the first magnetic brush charger In this case, an effect is obtained. In the first and second embodiments, the case where there are two magnetic brush chargers has been described. However, for example, charging with three or more magnetic brush chargers is also accommodated in the first magnetic brush charger. The present invention is applied to the case where the most magnetic particles are used.

本発明の実施例１、２において用いた画像形成装置の概略図Schematic diagram of an image forming apparatus used in Examples 1 and 2 of the present invention 本発明の実施例１において用いた磁気ブラシ帯電器の概略図Schematic of the magnetic brush charger used in Example 1 of the present invention 本発明の実施例１において用いた磁気ブラシ帯電器の概略図Schematic of the magnetic brush charger used in Example 1 of the present invention 従来例において用いた画像形成装置の概略図Schematic of the image forming apparatus used in the conventional example アモルファスシリコン感光体の層構成の一例を示す断面図Sectional view showing an example of layer structure of amorphous silicon photoconductor 実施例１において用いた磁性粒子容量と帯電電位の関係を示す概略図Schematic diagram showing the relationship between the magnetic particle capacity and charging potential used in Example 1 実施例１において用いた磁性粒子容量と電位ムラの関係を示す概略図Schematic showing the relationship between magnetic particle capacity and potential unevenness used in Example 1

Explanation of symbols

１感光ドラム
２ＬＥＤ露光手段
３コロナ帯電器
３０、３１、３２磁気ブラシ帯電器
４現像装置
５クリーナー
６定着器
７転写装置
８前露光ランプ
９スキャナユニット
１０原稿台 DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 LED exposure means 3 Corona charger 30, 31, 32 Magnetic brush charger 4 Developing device 5 Cleaner 6 Fixing device 7 Transfer device 8 Pre-exposure lamp 9 Scanner unit 10 Document stand

Claims

Developing means for charging a photosensitive member by a charging member, forming an electrostatic latent image on the photosensitive member by an image exposure unit, and developing the latent image by a developer carrying member carrying a developer to form a toner image. An image forming apparatus for forming an image by transferring the toner image to a transfer material, wherein the charging member comprises a plurality of contact charging members, each charging member is a magnetic brush charger using magnetic particles, In addition, the amount of magnetic particles accommodated in the magnetic brush charger is larger in the first magnetic brush charger than in other magnetic brush chargers.

The image forming apparatus according to claim 1, wherein the photoconductor includes amorphous silicon.