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JP2012103300A - Image forming device - Google Patents

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JP2012103300A
JP2012103300A JP2010249311A JP2010249311A JP2012103300A JP 2012103300 A JP2012103300 A JP 2012103300A JP 2010249311 A JP2010249311 A JP 2010249311A JP 2010249311 A JP2010249311 A JP 2010249311A JP 2012103300 A JP2012103300 A JP 2012103300A
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intermediate transfer
transfer belt
region
sheet member
station
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Yasunari Obara
泰成 小原
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Canon Inc
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Canon Inc
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Abstract

【課題】中間転写方式の一次転写部における転写部材としてシート部材を用いたカラー画像形成装置において、一次転写部のシート部材の位置関係を各ステーションにおいて適正に配置することで新たな部材を追加することなく装置の長寿命化を達成する。
【解決手段】シート部材32a〜32dは、中間転写ベルト13を介して感光体1a〜1dと中間転写ベルト13とシート部材32a〜32dとが接触して形成される第１領域と、該第１領域よりも中間転写ベルト13の回転方向下流側でシート部材32a〜32dが中間転写ベルト13に接触し、且つ感光体1a〜1dと中間転写ベルト13とが離間する第２領域とを有し、複数のシート部材32a〜32dのうち中間転写ベルト13の回転方向において最下流側に配置されるシート部材32ｄの第２領域の中間転写ベルト13の回転方向の長さが最も長いことを特徴とする。
【選択図】図１In a color image forming apparatus using a sheet member as a transfer member in a primary transfer portion of an intermediate transfer method, a new member is added by appropriately arranging the positional relationship of the sheet member of the primary transfer portion at each station. Long life of the device is achieved without any problems.
Sheet members (32a to 32d) include first regions formed by contact between photosensitive members (1a to 1d), an intermediate transfer belt (13), and sheet members (32a to 32d) via an intermediate transfer belt (13). The sheet members 32a to 32d are in contact with the intermediate transfer belt 13 on the downstream side in the rotation direction of the intermediate transfer belt 13 with respect to the region, and the photosensitive members 1a to 1d and the intermediate transfer belt 13 are separated from each other. The length of the second region of the sheet member 32d disposed on the most downstream side in the rotation direction of the intermediate transfer belt 13 among the plurality of sheet members 32a to 32d is the longest in the rotation direction of the intermediate transfer belt 13. .
[Selection] Figure 1

Description

本発明は、複写機あるいはプリンタなどの電子写真方式の画像形成装置に関し、特に、像担持体、帯電手段、および現像手段などを含む画像形成ユニットを複数個有し、多色画像を形成する画像形成装置に関するものである。   BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer, and more particularly to an image having a plurality of image forming units including an image carrier, a charging unit, a developing unit, and the like to form a multicolor image. The present invention relates to a forming apparatus.

従来、例えば電子写真方式を用いる画像形成装置では、像担持体としての電子写真感光体（以下、「感光体」という）上にトナー画像を形成する。そして、トナーの正規の帯電極性とは逆極性の電界を転写手段に与え、転写ベルトに担持されている転写材又は中間転写ベルトの表面に、感光体に担持されているトナー画像を静電的に転移させる転写工程が行われる。   Conventionally, for example, in an image forming apparatus using an electrophotographic system, a toner image is formed on an electrophotographic photosensitive member (hereinafter referred to as “photosensitive member”) as an image carrier. Then, an electric field having a polarity opposite to the normal charging polarity of the toner is applied to the transfer means, and the toner image carried on the photosensitive member is electrostatically applied to the surface of the transfer material carried on the transfer belt or the intermediate transfer belt. A transfer step of transferring to is performed.

そのため、転写ベルトや中間転写ベルトなどの移動可能なベルト体を備えた画像形成装置では、転写手段に対して転写工程に必要な電圧を印加する電圧印加手段が設けられる。   For this reason, in an image forming apparatus including a movable belt body such as a transfer belt or an intermediate transfer belt, a voltage applying unit that applies a voltage necessary for the transfer process to the transfer unit is provided.

この一例として、画像形成部を複数備え、画像形成部内の感光体上に形成されたトナー画像をそれぞれ中間転写ベルトに転写した後、ベルト回転方向下流側で転写材へ一括して転写をおこなう、いわゆる中間転写方式の画像形成装置が普及している。感光体から中間転写ベルトへの転写を一次転写、その後の転写材への一括転写を二次転写と呼ぶ。   As an example of this, a plurality of image forming units are provided, and each toner image formed on the photoreceptor in the image forming unit is transferred to an intermediate transfer belt, and then transferred collectively to a transfer material on the downstream side in the belt rotation direction. A so-called intermediate transfer type image forming apparatus is widely used. Transfer from the photoreceptor to the intermediate transfer belt is called primary transfer, and subsequent batch transfer to the transfer material is called secondary transfer.

中間転写ベルトを用いた画像形成装置では、一次転写部材として、中間転写ベルトを挟んで感光体の対向位置（ベルト体の裏面側）に、電圧印加手段としての高圧電源に接続された転写ローラなどの接触転写部材を配置している。ここで、一次転写部材を含む画像形成部をステーションと呼び、ベルト回転方向の上流側から順に第１ステーション、第２ステーション、第３ステーション、第４ステーションのように呼ぶ。   In an image forming apparatus using an intermediate transfer belt, as a primary transfer member, a transfer roller connected to a high voltage power source as a voltage application unit at a position facing the photoconductor (back side of the belt body) with the intermediate transfer belt interposed therebetween The contact transfer member is arranged. Here, the image forming unit including the primary transfer member is referred to as a station, and is referred to as a first station, a second station, a third station, and a fourth station in order from the upstream side in the belt rotation direction.

ところが、転写ローラを用いた画像形成装置では、ベルト体と転写ローラとの接触領域が転写ローラの撓みの影響などにより長手方向で不均一となることがある。従って、転写工程に必要な電流がベルト体と転写ローラとの接触領域の長手方向で不均一となり、転写不良などの画像不良を引き起こす場合がある。   However, in an image forming apparatus using a transfer roller, the contact area between the belt body and the transfer roller may be uneven in the longitudinal direction due to the influence of the deflection of the transfer roller. Therefore, the current required for the transfer process becomes non-uniform in the longitudinal direction of the contact area between the belt body and the transfer roller, which may cause image defects such as transfer defects.

このような問題に対して、特許文献１には、一次転写部材として、シート部材を用いた構成が提案されている。より具体的には、シート部材の裏面に弾性部材を配置し、ベルト体に対してシート部材を加圧配置することで、ベルト体に均一な転写ニップ部を得るようにした転写部材が提案されている。このようなシート部材を用いた転写部材は、各ステーションにおいて、感光体、ベルト体、およびシート部材の位置関係が同じになるように配置されており、装置の小型化と簡略化を図ることができる。   For such a problem, Patent Document 1 proposes a configuration using a sheet member as a primary transfer member. More specifically, a transfer member has been proposed in which an elastic member is disposed on the back surface of the sheet member and the sheet member is pressurized and disposed on the belt body to obtain a uniform transfer nip portion on the belt body. ing. The transfer member using such a sheet member is arranged so that the positional relationship among the photosensitive member, the belt member, and the sheet member is the same at each station, so that the apparatus can be reduced in size and simplified. it can.

特開２００８−３１００６０号公報JP 2008-31060 A

しかしながら、特許文献１のように、シート部材を各ステーションにおいて感光体とベルト体、およびシート部材の位置関係が同じになるように配置した画像形成装置では、次のような問題があった。   However, as in Patent Document 1, the image forming apparatus in which the sheet member is arranged so that the positional relationship between the photosensitive member, the belt member, and the sheet member is the same at each station has the following problems.

ベルト体とシート部材が接触するベルト体の回転方向の長さが何れのステーションでも比較的短いと、ベルト体へ過剰に供給された電荷が中和されない。これにより、ベルト体の回転方向下流側のステーションやベルト体を張架する張架部材の位置で剥離放電による画像不良が発生する。   If the length in the rotation direction of the belt body in contact with the belt body and the sheet member is relatively short at any station, the charge excessively supplied to the belt body is not neutralized. As a result, an image defect due to peeling discharge occurs at a station on the downstream side in the rotation direction of the belt body or a position of the stretching member that stretches the belt body.

これは、高抵抗のベルト体が接触している感光体や張架部材等の対向部材から分離する際に、それらの離間過程で急激に増加するエアーギャップにかかる電圧が放電閾値を超えるためであり、剥離放電と呼ばれる現象である。   This is because the voltage applied to the air gap, which increases rapidly in the separation process, exceeds the discharge threshold when separating from the opposing member such as the photosensitive member or the stretching member that the high-resistance belt is in contact with. There is a phenomenon called peeling discharge.

この剥離放電によりトナー画像が乱され、「放電跡」が発生する。「放電跡」を防止する方法として、各ステーションの転写ニップ部のベルト体の回転方向下流側において、ベルト体に近接した位置に除電針などの除電器を配置し、ベルト体上の電荷を除去することが考えられるが、装置が大型化する上にコストアップを招いてしまう。   This peeling discharge disturbs the toner image and generates a “discharge mark”. As a method to prevent “discharge traces”, a static eliminator such as a static eliminator is placed near the belt body at the downstream side of the belt nip in the transfer nip of each station to remove the charge on the belt body. However, this increases the size of the apparatus and increases the cost.

逆に、ベルト体とシート部材とが接触するベルト体の回転方向の長さが、何れのステーションでも比較的長いと、各ステーション通過後のベルト体上の電荷が不足し、ベルト体上にトナーを保持することができず、いわゆる「トナーの飛び散り」が発生してしまう。   On the contrary, if the length of the belt body in which the belt body and the sheet member are in the rotation direction is relatively long at any station, the charge on the belt body after passing through each station is insufficient, and the toner on the belt body Cannot be held, and so-called “toner scattering” occurs.

また、シート部材とベルト体との接触面積が増加するために、長期間使用後の装置の駆動トルクが増大し、異なる色を重ねて転写する際に発生する「色ムラ」が顕著になったり、最終的に安定したベルト体の搬送が出来なくなる。特に、長期使用によってベルト体の抵抗値が変動する場合には、上記「放電跡」や「トナーの飛び散り」といった画像不良の改善を両立させるのは困難であり、装置寿命が短くなっていた。   Further, since the contact area between the sheet member and the belt body increases, the driving torque of the apparatus after long-term use increases, and “color unevenness” that occurs when different colors are transferred in a superimposed manner becomes noticeable. Finally, the belt cannot be stably conveyed. In particular, when the resistance value of the belt body fluctuates due to long-term use, it is difficult to achieve both improvement in image defects such as “discharge traces” and “toner scattering”, and the life of the apparatus is shortened.

ベルト体を含む部材をユニット化し、交換可能とすることで高画質を長期にわたり維持することはできるが、ユーザがユニットを交換する手間と頻度が増えてしまうという問題がある。   Although it is possible to maintain high image quality over a long period of time by making the member including the belt unit into a unit and making it replaceable, there is a problem that the time and effort for the user to replace the unit increases.

以上のように、各ステーションにおいて感光体とベルト体、およびシート部材の位置関係が同じになるように配置した従来の画像形成装置では装置の長寿命化が困難であった。   As described above, it is difficult to extend the life of the conventional image forming apparatus in which the positional relationship between the photosensitive member, the belt member, and the sheet member is the same at each station.

本発明は、上記課題を解決するためになされたもので、長期間にわたって使用しても画像不良を防止できる画像形成装置を提供することを目的とする。   SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus that can prevent image defects even when used for a long period of time.

上記目的を達成するため本発明に係る代表的な構成は、トナー画像を担持する複数の像担持体と、回転可能なベルト体と、前記複数の像担持体上のトナー画像を前記ベルト体の表面に転写する複数の転写部材と、を有し、前記ベルト体の移動中に前記複数の転写部材は回転せずに前記ベルト体の裏面に接触する画像形成装置において、前記転写部材には画像形成中にトナーと逆極性のバイアス電圧が印加されており、前記転写部材は、前記ベルト体を介して前記像担持体と前記ベルト体と前記転写部材とが接触して形成される第１領域と、前記第１領域よりも前記ベルト体の回転方向下流側で前記転写部材が前記ベルト体に接触し、且つ前記像担持体と前記ベルト体とが離間する第２領域とを有し、前記複数の転写部材のうち前記ベルト体の回転方向において最下流側に配置される転写部材の前記第２領域の前記ベルト体の回転方向の長さが最も長いことを特徴とする。   In order to achieve the above object, a representative configuration according to the present invention includes a plurality of image carriers that carry a toner image, a rotatable belt body, and a toner image on the plurality of image carriers that is attached to the belt body. A plurality of transfer members that transfer to the front surface, and the plurality of transfer members do not rotate during the movement of the belt body and contact the back surface of the belt body. A bias voltage having a polarity opposite to that of the toner is applied during the formation, and the transfer member is formed by contacting the image carrier, the belt body, and the transfer member via the belt body. And a second region where the transfer member is in contact with the belt body on the downstream side in the rotational direction of the belt body from the first region, and the image carrier and the belt body are separated from each other, Of the plurality of transfer members, the belt body The length of the rotational direction of said belt member in the second region of the transfer member disposed at the most downstream side and wherein the longest in the rolling direction.

上記構成によれば、複数の転写部材のうちベルト体の回転方向において最下流側に配置される転写部材の第２領域のベルト体の回転方向の長さが最も長い。これにより、ベルト体が最下流側に配置される転写部材に接触する時間が最も長くなる。これにより該転写部材に印加されるバイアス電圧によりベルト体上の電荷量の減少が最も大きくなる。これにより該ベルト体と該ベルト体を張架する張架部材との間で剥離放電が発生しない。これにより、トナー画像に「放電跡」と呼ばれる画像不良が発生することを防止できる。これにより、早期に発生していた画像不良を遅延でき、装置の長寿命化が達成できる。   According to the above configuration, the length in the rotation direction of the belt body in the second region of the transfer member arranged on the most downstream side in the rotation direction of the belt body among the plurality of transfer members is the longest. Thereby, the time for the belt body to contact the transfer member disposed on the most downstream side is the longest. As a result, the reduction in the amount of charge on the belt body is maximized by the bias voltage applied to the transfer member. As a result, no peeling discharge occurs between the belt body and the stretching member that stretches the belt body. Thereby, it is possible to prevent an image defect called “discharge trace” from occurring in the toner image. As a result, image defects that have occurred at an early stage can be delayed, and the life of the apparatus can be extended.

本発明に係る画像形成装置の構成を示す断面説明図である。1 is an explanatory cross-sectional view illustrating a configuration of an image forming apparatus according to the present invention. 本発明に係る画像形成装置の第１実施形態における一次転写部材の近傍の構成を示す断面説明図である。FIG. 3 is an explanatory cross-sectional view illustrating a configuration in the vicinity of the primary transfer member in the first embodiment of the image forming apparatus according to the invention. 第１実施形態における一次転写部材の作用を説明する図である。It is a figure explaining the effect | action of the primary transfer member in 1st Embodiment. 第１実施形態における中間転写ベルト上の電荷量と画像不良との関係を説明する図である。FIG. 6 is a diagram illustrating a relationship between an amount of charge on the intermediate transfer belt and an image defect in the first embodiment. 第１実施形態で長期使用状態における中間転写ベルト上の電荷量と画像不良との関係を説明する図である。FIG. 6 is a diagram illustrating a relationship between an amount of charge on an intermediate transfer belt and an image defect in a long-term use state according to the first embodiment. 第１実施形態において転写部材の第２領域のベルト体の回転方向の長さを変更した場合の画像評価結果を説明する図である。It is a figure explaining the image evaluation result at the time of changing the length of the rotation direction of the belt body of the 2nd field of a transfer member in a 1st embodiment. 本発明に係る画像形成装置の第２実施形態における中間転写ベルト上の電荷量と画像不良との関係を説明する図である。FIG. 10 is a diagram illustrating a relationship between an amount of charge on an intermediate transfer belt and an image defect in the second embodiment of the image forming apparatus according to the present invention.

以下、図を用いて本発明に係る画像形成装置について説明する。   The image forming apparatus according to the present invention will be described below with reference to the drawings.

まず、図１〜図６を用いて本発明に係る画像形成装置の第１実施形態の構成について説明する。尚、本実施形態では、第１ステーション６ａをイエロー（Ｙ）、第２ステーション６ｂをマゼンタ（Ｍ）、第３ステーション６ｃをシアン（Ｃ）、第４ステーション６ｄをブラック（Ｂｋ）としている。以下、記述の煩雑化を防ぐために、イエロー、マゼンタ、シアン、ブラックの４つのステーション６ａ〜６ｄをステーション６で代表させて説明するものとし、関連する次の各プロセス手段についても同様とする。   First, the configuration of the first embodiment of the image forming apparatus according to the present invention will be described with reference to FIGS. In the present embodiment, the first station 6a is yellow (Y), the second station 6b is magenta (M), the third station 6c is cyan (C), and the fourth station 6d is black (Bk). Hereinafter, in order to prevent the description from becoming complicated, the four stations 6a to 6d of yellow, magenta, cyan, and black will be described as representative by the station 6, and the same applies to the following respective process means.

各ステーション６では、トナー画像を担持する複数の像担持体となる電子写真感光体（以下、単に「感光体」という）１と、帯電手段としての帯電ローラ２を有する。更に、感光体１上の転写残トナーをクリーニングするクリーニングユニット３と、現像手段としての現像ユニット８を有する。現像ユニット８は、現像スリーブ４、現像剤となるトナー５、現像剤塗布ブレード７からなり、これらは、一体型のプロセスカートリッジ９として構成される。11は露光手段であり、レーザー光からなる走査ビーム12を多面鏡によって走査させるスキャナユニットまたはＬＥＤ（発光ダイオード）アレイから構成され、画像信号に基づいて変調された走査ビーム12を感光体１上に照射する。   Each station 6 includes an electrophotographic photosensitive member (hereinafter simply referred to as “photosensitive member”) 1 serving as a plurality of image carriers that carry toner images, and a charging roller 2 as a charging unit. Further, the image forming apparatus includes a cleaning unit 3 for cleaning the transfer residual toner on the photosensitive member 1 and a developing unit 8 as a developing unit. The developing unit 8 includes a developing sleeve 4, a toner 5 as a developer, and a developer coating blade 7, and these are configured as an integrated process cartridge 9. Reference numeral 11 denotes exposure means, which is composed of a scanner unit or LED (light emitting diode) array that scans a scanning beam 12 made of laser light with a polygon mirror, and a scanning beam 12 modulated based on an image signal is applied to the photoreceptor 1. Irradiate.

また、各感光体１に対向して張架部材となる駆動ローラ14、テンションローラ15及び二次転写対向ローラ24により回転可能に張架されたベルト体となる中間転写ベルト13が配置されている。そして、複数の感光体１上（像担持体上）のトナー画像を中間転写ベルト13の表面に転写する複数の転写手段となる一次転写部材30が設けられている。複数の一次転写部材30は中間転写ベルト13の移動中に回転せずに該中間転写ベルト13の裏面に接触する複数の転写部材となるシート部材32を有する。   In addition, an intermediate transfer belt 13 that is a belt member that is rotatably stretched by a driving roller 14 that serves as a stretching member, a tension roller 15, and a secondary transfer facing roller 24 that is opposed to each photoconductor 1 is disposed. . A primary transfer member 30 is provided as a plurality of transfer means for transferring toner images on the plurality of photoreceptors 1 (on the image carrier) onto the surface of the intermediate transfer belt 13. The plurality of primary transfer members 30 have a plurality of sheet members 32 that serve as a plurality of transfer members that do not rotate during the movement of the intermediate transfer belt 13 and contact the back surface of the intermediate transfer belt 13.

帯電ローラ２には、該帯電ローラ２への電圧供給手段である帯電バイアス電源20が接続されている。現像スリーブ４には、該現像スリーブ４への電圧供給手段である現像バイアス電源21が接続されている。一次転写部材30には、該一次転写部材30への電圧供給手段として画像形成中にトナーと逆極性のバイアス電圧を印加する一次転写電源22が接続されている。中間転写ベルト13を介して二次転写対向ローラ24に対向する二次転写ローラ25には、該二次転写ローラ25への電圧供給手段である二次転写電源26が接続されている。   The charging roller 2 is connected to a charging bias power source 20 that is a voltage supply means to the charging roller 2. The developing sleeve 4 is connected to a developing bias power source 21 that is a voltage supply means to the developing sleeve 4. The primary transfer member 30 is connected to a primary transfer power source 22 that applies a bias voltage having a polarity opposite to that of the toner during image formation as a voltage supply unit to the primary transfer member 30. A secondary transfer power source 26 that is a voltage supply means to the secondary transfer roller 25 is connected to the secondary transfer roller 25 that faces the secondary transfer counter roller 24 via the intermediate transfer belt 13.

次に感光体１上の画像形成動作について説明する。画像形成動作がスタートすると、感光体１ａ〜１ｄや中間転写ベルト13等は所定の画像形成プロセススピード（例えば１００mm/sec）で図１の矢印方向にそれぞれ回転を始める。感光体１は帯電ローラ２によって一様に負極性に帯電され、続いて露光手段11からの走査ビーム12によって画像情報に従った静電潜像が形成される。非露光部の感光体１上の電位を暗部電位、露光部の感光体１上の電位を明部電位という。   Next, an image forming operation on the photoreceptor 1 will be described. When the image forming operation starts, the photoreceptors 1a to 1d, the intermediate transfer belt 13 and the like start to rotate in the direction of the arrow in FIG. 1 at a predetermined image forming process speed (for example, 100 mm / sec). The photosensitive member 1 is uniformly charged to the negative polarity by the charging roller 2, and then an electrostatic latent image according to the image information is formed by the scanning beam 12 from the exposure unit 11. The potential on the non-exposed portion of the photoreceptor 1 is referred to as a dark portion potential, and the potential on the exposed portion of the photoreceptor 1 is referred to as a bright portion potential.

現像ユニット８内のトナー５は、現像剤塗布ブレード７によって負極性に帯電されて現像スリーブ４に塗布される。そして、現像スリーブ４には、現像バイアス電源21よりバイアス電圧が印加される。感光体１が回転して該感光体１上に形成された静電潜像が現像スリーブ４に到達すると、静電潜像は負極性のトナー５によって可視像化される。そして、感光体１ａ上には第１色目（本実施形態では、イエロー（Ｙ））のトナー画像が形成される。尚、感光体１上の画像形成動作については、第２〜第４ステーション６ｂ〜６ｃについても第１ステーション６ａと同様の構成としているので説明は省略する。   The toner 5 in the developing unit 8 is charged to the negative polarity by the developer application blade 7 and applied to the developing sleeve 4. A bias voltage is applied to the developing sleeve 4 from a developing bias power source 21. When the photosensitive member 1 rotates and the electrostatic latent image formed on the photosensitive member 1 reaches the developing sleeve 4, the electrostatic latent image is visualized by the negative toner 5. Then, a toner image of the first color (in this embodiment, yellow (Y)) is formed on the photoreceptor 1a. The image forming operation on the photoconductor 1 is the same as that of the first station 6a in the second to fourth stations 6b to 6c, and the description thereof is omitted.

トナー画像担持体である中間転写ベルト13は、４つの感光体１ａ〜１ｄの全てに対して当接するように配置される。中間転写ベルト13は、その張架部材として二次転写対向ローラ24、駆動ローラ14、テンションローラ15の３本のローラにより支持されており、所定のテンションが維持されるようになっている。また、中間転写ベルト13は駆動ローラ14を図１の矢印方向に回転駆動させることにより図１の矢印方向に回転する感光体１ａ〜１ｄに対して順方向に略等速度で移動する。一次転写部材30は、中間転写ベルト13を挟んで感光体１と反対側に配置されている。   The intermediate transfer belt 13 that is a toner image carrier is disposed so as to abut against all of the four photoconductors 1a to 1d. The intermediate transfer belt 13 is supported by three rollers, that is, a secondary transfer counter roller 24, a driving roller 14, and a tension roller 15 as a stretching member, so that a predetermined tension is maintained. Further, the intermediate transfer belt 13 is driven at a substantially constant speed in the forward direction with respect to the photoreceptors 1a to 1d rotating in the arrow direction of FIG. 1 by rotating the drive roller 14 in the arrow direction of FIG. The primary transfer member 30 is disposed on the opposite side of the photoreceptor 1 with the intermediate transfer belt 13 in between.

各一次転写部材30は、図２に示すように、弾性部材31と可撓性を有するシート部材32からなり、該シート部材32は中間転写ベルト13と弾性部材31との間に挟持されている。一次転写部材30は中間転写ベルト13を介して感光体１と該中間転写ベルト13とシート部材32とが接触して形成される第１領域Ａを有する。   As shown in FIG. 2, each primary transfer member 30 includes an elastic member 31 and a flexible sheet member 32, and the sheet member 32 is sandwiched between the intermediate transfer belt 13 and the elastic member 31. . The primary transfer member 30 has a first area A formed by contacting the photoreceptor 1, the intermediate transfer belt 13 and the sheet member 32 with the intermediate transfer belt 13 interposed therebetween.

そして、該第１領域Ａよりも中間転写ベルト13の回転方向下流側（図２の右側）でシート部材32が中間転写ベルト13に接触し、且つ感光体１と中間転写ベルト13とが離間する第２領域Ｂを有している。   Then, the sheet member 32 contacts the intermediate transfer belt 13 on the downstream side in the rotation direction of the intermediate transfer belt 13 from the first area A (right side in FIG. 2), and the photosensitive member 1 and the intermediate transfer belt 13 are separated from each other. It has the 2nd field B.

本実施形態では、複数のシート部材32のうちの中間転写ベルト13の回転方向において第４ステーション６ｄのシート部材32ｄが最下流側に配置される。第４ステーション６ｄのシート部材32ｄの第２領域Ｂの中間転写ベルト13の回転方向の長さ（以下、単に、「第２領域Ｂの長さ」という）Ｌ４を他の各ステーション６ａ〜６ｃのシート部材32ａ〜32ｃの第２領域Ｂの長さＬ１〜Ｌ３よりも長く構成している。 In the present embodiment, the sheet member 32d of the fourth station 6d is arranged on the most downstream side in the rotation direction of the intermediate transfer belt 13 among the plurality of sheet members 32. The length L 4 in the rotation direction of the intermediate transfer belt 13 in the second area B of the sheet member 32d of the fourth station 6d (hereinafter simply referred to as “the length of the second area B”) L4 is set to each of the other stations 6a to 6c. constitute greater than the length L 1 ~L 3 of the second region B of the sheet member 32 a to 32 c.

即ち、最下流側に配置される第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４が最も長くなるように設定されている。その理由については、後で詳細に説明する。 That is set so that the length L 4 of the second region B of the sheet member 32d of the fourth station 6d disposed on the most downstream side becomes longest. The reason will be described in detail later.

各色の感光体１上に形成されたトナー画像は、それぞれのシート部材32ａ〜32ｄにトナーと逆極性の電圧を印加することで、順に中間転写ベルト13にトナー画像を転写していき、中間転写ベルト13上に多重画像が形成される。   The toner images formed on the photosensitive members 1 of the respective colors are transferred to the intermediate transfer belt 13 in order by applying a voltage having a polarity opposite to that of the toner to the respective sheet members 32a to 32d. Multiple images are formed on the belt 13.

その後、露光による静電潜像の作像に合わせて、給送カセット16に積載されている転写材Ｐは、給送ローラ17により給送され、図示しない搬送ローラによりレジストローラ18まで搬送される。そして、転写材Ｐは中間転写ベルト13上のトナー画像に同期してレジストローラ18によって、中間転写ベルト13と二次転写ローラ25とで形成される当接ニップ部Ｎへ搬送される。その後、二次転写ローラ25には二次転写電源26により、トナーと逆極性の電圧印加を行い、転写材Ｐ上に中間転写ベルト13上に担持された４色の多重トナー画像が一括して二次転写される。   Thereafter, the transfer material P loaded on the feeding cassette 16 is fed by the feeding roller 17 and conveyed to the registration roller 18 by a conveying roller (not shown) in accordance with the electrostatic latent image formation by exposure. . The transfer material P is conveyed to a contact nip portion N formed by the intermediate transfer belt 13 and the secondary transfer roller 25 by the registration roller 18 in synchronization with the toner image on the intermediate transfer belt 13. Thereafter, a voltage having a polarity opposite to that of the toner is applied to the secondary transfer roller 25 by a secondary transfer power source 26, and the four-color multiple toner images carried on the intermediate transfer belt 13 on the transfer material P are collectively displayed. Secondary transferred.

尚、本実施形態では、二次転写ローラ25は外径直径８mmのニッケルメッキ鋼棒に抵抗値を１０８Ω、厚み５mmに調整したＮＢＲ（ニトリルブタジエンゴム）の発泡スポンジ体で覆った外径直径１８mmのものを用いた。また、二次転写ローラ25は、中間転写ベルト13に対して、５g/cm〜１５g/cm程度の線圧で当接させ、且つ中間転写ベルト13の移動方向に対して順方向に略等速度で回転するように配置した。 In this embodiment, the secondary transfer roller 25 has an outer diameter covered with a nickel-plated steel rod having an outer diameter of 8 mm and a foamed sponge of NBR (nitrile butadiene rubber) adjusted to a resistance value of 10 8 Ω and a thickness of 5 mm. The one with a diameter of 18 mm was used. Further, the secondary transfer roller 25 is brought into contact with the intermediate transfer belt 13 with a linear pressure of about 5 g / cm to 15 g / cm, and is substantially constant in the forward direction with respect to the moving direction of the intermediate transfer belt 13. It was arranged to rotate at.

一方、二次転写を終えた後、中間転写ベルト13上に残留した転写残トナーは、中間転写ベルト13に当接配置されたベルトクリーニング手段27により、その表面から除去・回収される。本実施形態の画像形成装置ではベルトクリーニング手段27としてウレタンゴム等で形成された弾性を有するクリーニングブレードを用いた。   On the other hand, after the secondary transfer is completed, the transfer residual toner remaining on the intermediate transfer belt 13 is removed and collected from the surface by the belt cleaning means 27 disposed in contact with the intermediate transfer belt 13. In the image forming apparatus according to the present embodiment, an elastic cleaning blade formed of urethane rubber or the like is used as the belt cleaning unit 27.

二次転写終了後の転写材Ｐは定着装置19へと搬送され、転写材Ｐ上にトナー画像が固着されて画像形成物として画像形成装置外へと排出される。中間転写ベルト13の構成としては、厚さ１００μｍ、体積抵抗率１０１0Ω・ｃｍのポリイミド樹脂を用いている。 After the completion of the secondary transfer, the transfer material P is conveyed to the fixing device 19 where the toner image is fixed on the transfer material P and is discharged out of the image forming apparatus as an image formed product. As a configuration of the intermediate transfer belt 13, a polyimide resin having a thickness of 100 μm and a volume resistivity of 10 10 Ω · cm is used.

また、張架部材としての駆動ローラ14は、アルミニウム芯金にカーボンを導電剤として分散した抵抗１０４Ω、肉厚が１．０mmのＥＰＤＭ（エチレン−プロピレン−ジエン三元共重合体）ゴムを被覆した外径直径２５mmのものを用いている。張架部材としてのテンションローラ15は、外径直径２５mmのアルミニウムの金属棒を用いており、テンションは片側１９．６Ｎ、総圧３９．２Ｎとしている。張架部材としての二次転写対向ローラ24は、アルミニウム芯金にカーボンを導電剤として分散した抵抗１０４Ω、肉厚０．５mmのＥＰＤＭゴムを被覆した外径直径２５mmのものを用いている。 The driving roller 14 as a tension member is made of EPDM (ethylene-propylene-diene terpolymer) rubber having a resistance of 10 4 Ω and a thickness of 1.0 mm, in which carbon is dispersed in an aluminum core as a conductive agent. A coated outer diameter of 25 mm is used. The tension roller 15 as a tension member uses an aluminum metal rod having an outer diameter of 25 mm, and the tension is 19.6 N on one side and the total pressure is 39.2 N. The secondary transfer counter roller 24 as a stretching member is a roller having an outer diameter of 25 mm and coated with an EPDM rubber having a resistance of 10 4 Ω and a thickness of 0.5 mm in which carbon is dispersed as a conductive agent in an aluminum core. .

次に、一次転写部材30が設けられた一次転写部の構成について図２を用いてさらに詳しく説明する。図２は、各ステーション６の一次転写部材30の近傍を拡大した断面説明図である。弾性部材31は、絶縁性のウレタンスポンジであり、肉厚３mm、幅６mm、長さ２３０mmの略直方体形状に構成したものを用いている。硬度はアスカーＣ 硬度計（４．９Ｎ（５００gf）荷重）で３０°である。ただし、必ずしも上記のような弾性部材31である必要はなく、シート部材32をバックアップできる部材であれば、さらに硬度の高い部材を用いても良い。   Next, the configuration of the primary transfer portion provided with the primary transfer member 30 will be described in more detail with reference to FIG. FIG. 2 is an explanatory cross-sectional view enlarging the vicinity of the primary transfer member 30 of each station 6. The elastic member 31 is an insulative urethane sponge having a substantially rectangular parallelepiped shape with a wall thickness of 3 mm, a width of 6 mm, and a length of 230 mm. The hardness is 30 ° with an Asker C hardness meter (4.9 N (500 gf) load). However, the elastic member 31 is not necessarily required as described above, and a member having higher hardness may be used as long as the member can back up the sheet member 32.

シート部材32は、体積抵抗率が１０６Ω・ｃｍ（導電率：１０−４Ｓ/ｍ）であり、厚み１５０μｍの樹脂性シートを用いている。本実施形態では、シート部材32として酢酸ビニルシートを用いている。他に、ポリカーボネイト(PC)、ポリフッ化ビニリデン(PVDF)、ポリエチレンテレフタレート(PET)、ポリイミド(PI)、ポリエチレン(PE)、ポリアミド(PA)などのシートを用いても良い。シート部材32には、一次転写電源22が接続され、画像形成動作中は５００Ｖの電圧が印加されている。 The sheet member 32 is a resin sheet having a volume resistivity of 10 6 Ω · cm (conductivity: 10 −4 S / m) and a thickness of 150 μm. In the present embodiment, a vinyl acetate sheet is used as the sheet member 32. In addition, sheets of polycarbonate (PC), polyvinylidene fluoride (PVDF), polyethylene terephthalate (PET), polyimide (PI), polyethylene (PE), polyamide (PA), etc. may be used. A primary transfer power source 22 is connected to the sheet member 32, and a voltage of 500 V is applied during the image forming operation.

また、図２において一点鎖線ｍは、感光体１の中心Ｃから下ろした垂線である。弾性部材31は、感光体１の中心Ｃ位置よりも中間転写ベルト13の回転方向下流側（図２の右側）に１mmずれた位置で、図示しない加圧バネにより感光体１側に総圧が９．８Ｎで加圧されている。中間転写ベルト13を介して弾性部材31を感光体１に圧接する位置を感光体１の中心Ｃ位置よりも中間転写ベルト13の回転方向下流側にずらす。これにより、感光体１の回転方向上流側では不要な電界の影響は少なくなり、感光体１上のトナー画像の画質を比較的忠実に保ちながらトナー画像が転写可能となる。   In FIG. 2, an alternate long and short dash line m is a perpendicular drawn from the center C of the photoreceptor 1. The elastic member 31 is displaced by 1 mm from the center C position of the photosensitive member 1 to the downstream side in the rotation direction of the intermediate transfer belt 13 (the right side in FIG. 2). Pressurized at 9.8N. The position where the elastic member 31 is pressed against the photosensitive member 1 via the intermediate transfer belt 13 is shifted from the center C position of the photosensitive member 1 to the downstream side in the rotation direction of the intermediate transfer belt 13. As a result, the influence of an unnecessary electric field is reduced on the upstream side in the rotation direction of the photosensitive member 1, and the toner image can be transferred while maintaining the image quality of the toner image on the photosensitive member 1 relatively faithfully.

ここで、図２に示すように、中間転写ベルト13の回転方向上流側（図２の左側）から、中間転写ベルト13とシート部材32との接触点のうち最上流側の接触点を境界位置ａとする。感光体１と中間転写ベルト13との接触点のうち最下流側の接触点を境界位置ｂとする。中間転写ベルト13とシート部材32の端部33との接触点を境界位置ｃとする。そして、境界位置ａと境界位置ｂとで挟まれるニップ領域を第１領域Ａとする。即ち、感光体１と中間転写ベルト13とシート部材32とが全て接触しているニップ領域を第１領域Ａとする。そして、境界位置ｂと境界位置ｃとで挟まれるニップ領域を第２領域Ｂと定義する。   Here, as shown in FIG. 2, the contact point on the most upstream side of the contact points between the intermediate transfer belt 13 and the sheet member 32 is defined as the boundary position from the upstream side in the rotation direction of the intermediate transfer belt 13 (left side in FIG. 2). a. Of the contact points between the photoreceptor 1 and the intermediate transfer belt 13, the contact point on the most downstream side is defined as a boundary position b. A contact point between the intermediate transfer belt 13 and the end portion 33 of the sheet member 32 is defined as a boundary position c. A nip region sandwiched between the boundary position a and the boundary position b is defined as a first region A. That is, a nip region where all of the photosensitive member 1, the intermediate transfer belt 13, and the sheet member 32 are in contact is defined as a first region A. A nip region sandwiched between the boundary position b and the boundary position c is defined as a second region B.

次に、一次転写部材30が設けられる一次転写部におけるニップ部の第１領域Ａおよび第２領域Ｂの機能について図３を用いてより詳しく説明する。図３は中間転写ベルト13とシート部材32とが接触する第１領域Ａおよび第２領域Ｂの断面を拡大した図である。   Next, the functions of the first area A and the second area B of the nip portion in the primary transfer portion provided with the primary transfer member 30 will be described in more detail with reference to FIG. FIG. 3 is an enlarged view of the first region A and the second region B where the intermediate transfer belt 13 and the sheet member 32 are in contact with each other.

画像形成動作中はシート部材32に電圧が印加されており、感光体１上のトナー画像は第１領域Ａの中間転写ベルト13の回転方向上流側（図３の左側）の空隙において中間転写ベルト13へ飛翔する。   During the image forming operation, a voltage is applied to the sheet member 32, and the toner image on the photosensitive member 1 is transferred to the intermediate transfer belt in the gap on the upstream side (left side in FIG. 3) in the rotation direction of the intermediate transfer belt 13 in the first region A. Fly to 13.

また、感光体１と中間転写ベルト13とシート部材32が全て３層に接する第１領域Ａは最も電界が強いため、シート部材32から中間転写ベルト13へトナーと逆極性の電荷が移動する（図３のｈ）。この第１領域Ａでは、トナー総電荷量に勝る電荷が中間転写ベルト13へ供給され、この電荷により、トナーは中間転写ベルト13の表面に保持される。   Further, since the electric field is the strongest in the first region A where the photosensitive member 1, the intermediate transfer belt 13 and the sheet member 32 are all in contact with the three layers, the charge having the opposite polarity to the toner moves from the sheet member 32 to the intermediate transfer belt 13 ( FIG. 3 h). In the first region A, a charge that exceeds the total toner charge amount is supplied to the intermediate transfer belt 13, and the toner is held on the surface of the intermediate transfer belt 13 by this charge.

次に、中間転写ベルト13が回転方向下流側（図３の右側）へ搬送されるに伴い、供給された電荷も下流側へ移動する（図３のｉ）。そして、第２領域Ｂまで移動すると、中間転写ベルト13と感光体１との離間距離が次第に大きくなるため、中間転写ベルト13の電位は該中間転写ベルト13の回転方向下流側（図３の右側）ほど上昇する。   Next, as the intermediate transfer belt 13 is transported to the downstream side in the rotational direction (right side in FIG. 3), the supplied charge also moves downstream (i in FIG. 3). When the intermediate transfer belt 13 moves to the second region B, the separation distance between the intermediate transfer belt 13 and the photosensitive member 1 gradually increases, so that the potential of the intermediate transfer belt 13 is downstream in the rotation direction of the intermediate transfer belt 13 (right side in FIG. 3). ).

その結果、第２領域Ｂの下流側領域では中間転写ベルト13とシート部材32の電位は逆転し、中間転写ベルト13の電荷の一部はシート部材32へ逆流する（図３のｊ）。逆流した電荷は、電界の作用で中間転写ベルト13の回転方向上流側（図３の左側）へ還流する（図３のｋ）。   As a result, in the downstream region of the second region B, the potentials of the intermediate transfer belt 13 and the sheet member 32 are reversed, and a part of the charge of the intermediate transfer belt 13 flows back to the sheet member 32 (j in FIG. 3). The backflowed electric charge returns to the upstream side (left side in FIG. 3) in the rotation direction of the intermediate transfer belt 13 by the action of the electric field (k in FIG. 3).

また、中間転写ベルト13に残留した電荷は、さらに該中間転写ベルト13の回転方向下流側（図３の右側）へ搬送される（図３のｌ）。このような現象がおきるのは、シート部材32の体積抵抗率が中間転写ベルト13の体積抵抗率に比べて十分小さいためである。   Further, the electric charge remaining on the intermediate transfer belt 13 is further conveyed downstream in the rotation direction of the intermediate transfer belt 13 (right side in FIG. 3) (l in FIG. 3). Such a phenomenon occurs because the volume resistivity of the sheet member 32 is sufficiently smaller than the volume resistivity of the intermediate transfer belt 13.

第２領域Ｂではシート部材32へ電荷が逆流するため、中間転写ベルト13上の電荷量Ｑは該中間転写ベルト13の回転方向下流側（図３の右側）に進むにつれて以下の数１式のように減少する。尚、以下の数１式において、Ｑ０は図３に示す境界位置ｂにおける中間転写ベルト13上の電荷量であり、τは該中間転写ベルト13の電気的な時定数である。 In the second region B, since the charge flows back to the sheet member 32, the charge amount Q on the intermediate transfer belt 13 is expressed by the following equation 1 as it advances downstream in the rotation direction of the intermediate transfer belt 13 (right side in FIG. 3). To decrease. In Equation 1 below, Q 0 is the amount of charge on the intermediate transfer belt 13 at the boundary position b shown in FIG. 3, and τ is the electrical time constant of the intermediate transfer belt 13.

［数１］
Ｑ＝Ｑ０ exp（−ｔ／τ） [Equation 1]
Q = Q 0 exp (−t / τ)

図４は、中間転写ベルト13上の電荷量の時間推移を示している。図４はシート部材32の第２領域Ｂが中間転写ベルト13の回転方向下流側（図３の右側）方向に十分長いとした場合の電荷量の減少カーブである。実際にはシート部材32の第２領域Ｂの長さＬによって中間転写ベルト13上の電荷量Ｑの減少は停止する。即ち、第２領域の長さをＬ（mm）、画像形成プロセススピードをＶｐ（mm/sec）とすると、中間転写ベルト13が境界位置ｂ通過後にシート部材32に接触している時間｛Ｌ／Ｖｐ｝（sec）で中間転写ベルト13上の電荷量Ｑの減少は停止する。その後、第２領域Ｂを通過した後の中間転写ベルト13上の電荷量Ｑは殆んど変化しない。   FIG. 4 shows the time transition of the charge amount on the intermediate transfer belt 13. FIG. 4 is a charge amount decrease curve when the second region B of the sheet member 32 is sufficiently long in the direction downstream of the rotation direction of the intermediate transfer belt 13 (right side in FIG. 3). Actually, the decrease in the charge amount Q on the intermediate transfer belt 13 is stopped by the length L of the second region B of the sheet member 32. That is, when the length of the second region is L (mm) and the image forming process speed is Vp (mm / sec), the time during which the intermediate transfer belt 13 is in contact with the sheet member 32 after passing the boundary position b {L / The decrease in the charge amount Q on the intermediate transfer belt 13 stops at Vp} (sec). Thereafter, the charge amount Q on the intermediate transfer belt 13 after passing through the second region B hardly changes.

シート部材32の第２領域Ｂの長さＬが比較的短い（中間転写ベルト13が境界位置ｂ通過後にシート部材32に接触している時間が短い）場合には、中間転写ベルト13上の電荷量Ｑの減少は小さい。該中間転写ベルト13がシート部材32の第２領域Ｂを通過すると、中間転写ベルト13と感光体１との間の静電容量が小さくなる。   When the length L of the second region B of the sheet member 32 is relatively short (the time during which the intermediate transfer belt 13 is in contact with the sheet member 32 after passing the boundary position b is short), the charge on the intermediate transfer belt 13 The decrease in quantity Q is small. When the intermediate transfer belt 13 passes through the second region B of the sheet member 32, the electrostatic capacity between the intermediate transfer belt 13 and the photoreceptor 1 becomes small.

このために中間転写ベルト13の電位が上昇し、該中間転写ベルト13と感光体１との間で剥離放電が発生する。この場合、トナー画像に「放電跡」と呼ばれる画像不良が発生してしまう。図４中の一点鎖線ｄはトナー画像に「感光体における放電跡」が発生する中間転写ベルト13上の電荷量Ｑを示し、ｄ´はその時の中間転写ベルト13が境界位置ｂ通過後の経過時間を示している。   For this reason, the potential of the intermediate transfer belt 13 rises, and peeling discharge occurs between the intermediate transfer belt 13 and the photoreceptor 1. In this case, an image defect called “discharge trace” occurs in the toner image. In FIG. 4, the alternate long and short dash line d indicates the amount of charge Q on the intermediate transfer belt 13 where the “discharge mark on the photoconductor” occurs in the toner image, and d ′ indicates the time after the intermediate transfer belt 13 has passed the boundary position b. Shows time.

逆に、シート部材32の第２領域Ｂの長さＬが比較的長い（中間転写ベルト13が境界位置ｂ通過後にシート部材32に接触している時間が長い）場合には、中間転写ベルト上の電荷量Ｑの減少は大きい。   Conversely, when the length L of the second region B of the sheet member 32 is relatively long (the time during which the intermediate transfer belt 13 is in contact with the sheet member 32 after passing through the boundary position b) is long, The decrease in the charge amount Q is large.

すると該中間転写ベルト13上の電荷量Ｑが単位面積当たりのトナー総電荷量よりも少なくなる。するとトナーを中間転写ベルト13の表面に保持することが困難になる。この場合、中間転写ベルト13上で「トナーの飛び散り」と呼ばれる画像不良が発生する。   Then, the charge amount Q on the intermediate transfer belt 13 becomes smaller than the total toner charge amount per unit area. Then, it becomes difficult to hold the toner on the surface of the intermediate transfer belt 13. In this case, an image defect called “toner scattering” occurs on the intermediate transfer belt 13.

図４中の一点鎖線ｅはシート部材32の第２領域Ｂの中間転写ベルト13の回転方向下流側（図３の右側）の該中間転写ベルト13上で「トナーの飛び散り」が発生する中間転写ベルト13上の電荷量Ｑを示す。ｅ´はその時の中間転写ベルト13が境界位置ｂ通過後の経過時間を示す。   4 represents an intermediate transfer in which “scattering of toner” occurs on the intermediate transfer belt 13 on the downstream side in the rotation direction of the intermediate transfer belt 13 in the second region B of the sheet member 32 (right side in FIG. 3). The amount of charge Q on the belt 13 is shown. e ′ indicates the elapsed time after the intermediate transfer belt 13 passes through the boundary position b.

従って、図４から感光体１への剥離放電が無く、且つ中間転写ベルト13上のトナーの飛び散りが無い場合の各ステーション６のシート部材32の第２領域Ｂの長さＬは以下の条件となる。即ち、中間転写ベルト13が境界位置ｂ通過後にシート部材32に接触している時間｛Ｌ／Ｖｐ｝が、｛ｄ´＜Ｌ／Ｖｐ＜ｅ´｝の範囲内に収まるようにすれば良い。   Therefore, the length L of the second region B of the sheet member 32 of each station 6 when there is no peeling discharge from the photoreceptor 1 in FIG. 4 and no toner is scattered on the intermediate transfer belt 13 is as follows. Become. That is, the time {L / Vp} during which the intermediate transfer belt 13 is in contact with the sheet member 32 after passing through the boundary position b may be set within the range of {d ′ <L / Vp <e ′}.

中間転写ベルト13の回転方向最下流側（図１の右側）に第４ステーション６ｄがある。この場合には、該第４ステーション６ｄよりも更に中間転写ベルト13の回転方向下流側（図１の右側）に該中間転写ベルト13を回転可能に張架するための駆動ローラ14が配置されている。このため他のステーション６ａ，６ｂ，６ｃとは事情が異なる。   There is a fourth station 6d on the most downstream side in the rotation direction of the intermediate transfer belt 13 (the right side in FIG. 1). In this case, a driving roller 14 for rotatably suspending the intermediate transfer belt 13 is disposed downstream of the fourth station 6d in the rotation direction of the intermediate transfer belt 13 (right side in FIG. 1). Yes. For this reason, the situation differs from the other stations 6a, 6b, 6c.

即ち、第４ステーション６ｄを通過した中間転写ベルト13が高電位であると、該中間転写ベルト13と駆動ローラ14との間で剥離放電を起こし、トナーを担持する中間転写ベルト13の表面に急激な電界ムラを生じる。その結果、トナー画像が乱される。   That is, if the intermediate transfer belt 13 that has passed through the fourth station 6d is at a high potential, a peeling discharge occurs between the intermediate transfer belt 13 and the driving roller 14, and the surface of the intermediate transfer belt 13 that carries toner is suddenly applied. Cause uneven electric field. As a result, the toner image is disturbed.

この現象は、他のステーション６ａ，６ｂ，６ｃで中間転写ベルト13と感光体１との間で発生する剥離放電によりトナー画像が乱される「感光体における放電跡」よりも早期に見られる現象であり、「駆動ローラにおける放電跡」と呼ぶ。駆動ローラ14と中間転写ベルト13との間で発生する剥離放電が、感光体１と中間転写ベルト13との間で発生する剥離放電よりも早期におこる理由は以下の通りである。   This phenomenon is seen earlier than the “discharge mark on the photosensitive member” in which the toner image is disturbed by the peeling discharge generated between the intermediate transfer belt 13 and the photosensitive member 1 at the other stations 6a, 6b, and 6c. It is called “discharge trace on the driving roller”. The reason why the peeling discharge generated between the driving roller 14 and the intermediate transfer belt 13 occurs earlier than the peeling discharge generated between the photoreceptor 1 and the intermediate transfer belt 13 is as follows.

中間転写ベルト13上の電荷量Ｑが同じであっても該中間転写ベルト13と感光体１とのニップ部近傍における感光体１は表層樹脂層の分圧が大きく、感光体１と中間転写ベルト13との電位差が比較的小さい。図４中の一点鎖線ｆはトナー画像に「駆動ローラにおける放電跡」が発生する中間転写ベルト13上の電荷量Ｑを示し、ｆ´はその時の中間転写ベルト13が境界位置ｂ通過後の経過時間を示している。   Even if the charge amount Q on the intermediate transfer belt 13 is the same, the photosensitive member 1 in the vicinity of the nip portion between the intermediate transfer belt 13 and the photosensitive member 1 has a large partial pressure of the surface resin layer, and the photosensitive member 1 and the intermediate transfer belt The potential difference from 13 is relatively small. In FIG. 4, the alternate long and short dash line f indicates the amount of charge Q on the intermediate transfer belt 13 where the “discharge mark on the driving roller” is generated in the toner image, and f ′ indicates the passage of the intermediate transfer belt 13 at that time after passing the boundary position b. Shows time.

従って、図４から駆動ローラ14への剥離放電が無く、且つ感光体１への剥離放電も無く、且つ中間転写ベルト13上のトナーの飛び散りも無い場合の第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４は以下の条件となる。中間転写ベルト13が境界位置ｂ通過後にシート部材32ｄに接触している時間｛Ｌ／Ｖｐ｝が、｛ｆ´＜Ｌ４／Ｖｐ＜ｅ´｝の範囲内に収まるようにすれば良い。 Accordingly, from FIG. 4, when there is no peeling discharge to the driving roller 14, no peeling discharge to the photosensitive member 1, and no toner scattering on the intermediate transfer belt 13, the sheet member 32d of the fourth station 6d has a second one. The length L 4 of the two regions B is as follows. The time {L / Vp} during which the intermediate transfer belt 13 is in contact with the sheet member 32d after passing through the boundary position b may be set within the range of {f ′ <L 4 / Vp <e ′}.

以後同様に、第１ステーション６ａのシート部材32ａの第２領域Ｂの長さをＬ１とする。第２ステーション６ｂのシート部材32ｂの第２領域Ｂの長さをＬ２とする。第３ステーション６ｃのシート部材32ｃの第２領域Ｂの長さをＬ３とする。第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さをＬ４とする。 Similarly thereafter, the length of the second region B of the sheet member 32a of the first station 6a and L 1. The length of the second region B of the sheet member 32b of the second station 6b and L 2. The length of the second region B of the sheet member 32c of the third station 6c and L 3. The length of the second region B of the sheet member 32d of the fourth station 6d and L 4.

また、各ステーション６のシート部材32の第２領域Ｂの適切な長さＬを決める際には、以下の２点を考慮する必要がある。一つは、シート部材32が中間転写ベルト13の駆動トルクへ与える影響である。   Further, when determining an appropriate length L of the second region B of the sheet member 32 of each station 6, the following two points need to be considered. One is the influence of the sheet member 32 on the driving torque of the intermediate transfer belt 13.

シート部材32と中間転写ベルト13との接触面積が増加すると、該中間転写ベルト13の駆動トルクが変動するためトナー画像に「色ムラ」と呼ばれる画像不良が発生する。「色ムラ」とは、感光体１と中間転写ベルト13との周速度差が変動し、その周速度差が大きいときにトナー画像が引き伸ばされ、周速度差が小さいときにはトナー画像の引き伸ばしが小さいために画像ムラが生じる現象である。   When the contact area between the sheet member 32 and the intermediate transfer belt 13 increases, the driving torque of the intermediate transfer belt 13 fluctuates, so that an image defect called “color unevenness” occurs in the toner image. “Color unevenness” means that the toner image is stretched when the peripheral speed difference between the photoreceptor 1 and the intermediate transfer belt 13 is large and the peripheral speed difference is large, and the toner image is not stretched when the peripheral speed difference is small. This is a phenomenon in which image unevenness occurs.

よって、シート部材32と中間転写ベルト13とが接触する該シート部材32の第２領域Ｂの長さＬは，できるだけ短く設定する必要がある。   Therefore, the length L of the second region B of the sheet member 32 where the sheet member 32 and the intermediate transfer belt 13 are in contact with each other needs to be set as short as possible.

もう一つは、長期使用にともなう中間転写ベルト13の抵抗値変動を考慮する必要がある。例えば、ポリイミド樹脂にカーボンブラック、グラファイト、または金属酸化物といった電子導電剤を分散させて中抵抗となるように調整した中間転写ベルト13は、転写工程における通電状態が長時間継続すると、通電劣化により抵抗値が上昇する傾向がある。   The other is to consider fluctuations in the resistance value of the intermediate transfer belt 13 with long-term use. For example, the intermediate transfer belt 13 that is adjusted to have a medium resistance by dispersing an electronic conductive agent such as carbon black, graphite, or metal oxide in a polyimide resin is subjected to deterioration due to current deterioration when the current supply state in the transfer process continues for a long time. The resistance value tends to increase.

図５に転写材Ｐとして、Ａ４サイズの普通紙を１００×１０３枚通紙した後の中間転写ベルト13上の電荷量Ｑの時間推移（図５の破線カーブ）を図４のグラフに重ねて示す。図５のように中間転写ベルト13の抵抗値上昇によって中間転写ベルト13の電気的な時定数τが長くなる。このため該中間転写ベルト13が境界位置ｂ通過後に「感光体における放電跡」、「駆動ローラにおける放電跡」が発生する経過時間は、使用初期に比べてそれぞれｄ´→ｄ″と長くなり、ｆ´→ｆ″と長くなる。また、「トナーの飛び散り」は何れのステーション６においても使用初期のほうが電荷が速く減少するので経過時間ｅ´よりも短い時間とする必要がある。 In FIG. 5, the time transition of the charge amount Q on the intermediate transfer belt 13 after passing 100 × 10 3 sheets of A4 size plain paper as the transfer material P (broken line curve in FIG. 5) is superimposed on the graph in FIG. Show. As shown in FIG. 5, the electrical time constant τ of the intermediate transfer belt 13 becomes longer due to the increase in the resistance value of the intermediate transfer belt 13. For this reason, after the intermediate transfer belt 13 passes through the boundary position b, the elapsed time when the “discharge mark on the photosensitive member” and the “discharge mark on the driving roller” are generated becomes d ′ → d ″, respectively, longer than in the initial use. f ′ → f ″ becomes longer. Further, the “toner scattering” needs to be shorter than the elapsed time e ′ because the electric charge is reduced faster in the initial stage of use at any station 6.

従って、図５から第１〜第３ステーション６ａ〜６ｃにおける「感光体における放電跡」を防止するためには、中間転写ベルト13が境界位置ｂ通過後にシート部材32ａに接触している時間｛Ｌ１／Ｖｐ｝が、｛ｄ″＜Ｌ１／Ｖｐ＜ｅ´｝の範囲内に収まること。 Therefore, in order to prevent “discharge traces on the photosensitive member” in the first to third stations 6a to 6c from FIG. 5, the time {L of the intermediate transfer belt 13 in contact with the sheet member 32a after passing the boundary position b {L 1 / Vp} falls within the range of {d ″ <L 1 / Vp <e ′}.

且つ、中間転写ベルト13が境界位置ｂ通過後にシート部材32ｂに接触している時間｛Ｌ２／Ｖｐ｝が、｛ｄ″＜Ｌ２／Ｖｐ＜ｅ´｝の範囲内に収まること。且つ、中間転写ベルト13が境界位置ｂ通過後にシート部材32ｃに接触している時間｛Ｌ３／Ｖｐ｝が、｛ｄ″＜Ｌ３／Ｖｐ＜ｅ´｝の範囲内に収まるようにすれば良い。 Further, the time {L 2 / Vp} in which the intermediate transfer belt 13 is in contact with the sheet member 32 b after passing the boundary position b falls within the range of {d ″ <L 2 / Vp <e ′}. The time {L 3 / Vp} in which the intermediate transfer belt 13 is in contact with the sheet member 32c after passing the boundary position b may be set within the range of {d ″ <L 3 / Vp <e ′}.

同様に、図５から第４ステーション６ｄにおける「駆動ローラにおける放電跡」を防止するためには中間転写ベルト13が境界位置ｂ通過後にシート部材32ｄに接触している時間｛Ｌ４／Ｖｐ｝が、｛ｆ″＜Ｌ４／Ｖｐ＜ｅ´｝の範囲内に収まるようにすれば良い。 Similarly, the time {L 4 / Vp} during which the intermediate transfer belt 13 is in contact with the sheet member 32d after passing through the boundary position b in order to prevent “the trace of discharge on the driving roller” at the fourth station 6d from FIG. , {F ″ <L 4 / Vp <e ′}.

その他、中間転写ベルト13上の電荷量Ｑを左右する因子として各ステーション６間の離間距離ならびに第４ステーション６ｄと駆動ローラ14との離間距離がある。図１に示すように、各ステーション６間の離間距離ならびに第４ステーション６ｄと駆動ローラ14との離間距離が略同程度の離間距離であれば中間転写ベルト13上の電荷量Ｑには関係しない。   Other factors that influence the charge amount Q on the intermediate transfer belt 13 include the separation distance between the stations 6 and the separation distance between the fourth station 6 d and the driving roller 14. As shown in FIG. 1, if the separation distance between the stations 6 and the separation distance between the fourth station 6d and the driving roller 14 are substantially the same separation distance, the charge amount Q on the intermediate transfer belt 13 is not related. .

以上のことを考慮して、本実施形態では各ステーション６のシート部材32の第２領域Ｂの長さＬを以下の条件とした。中間転写ベルト13の回転方向最下流側（図１の右側）の第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４が、他のステーション６ａ〜６ｃのシート部材32ａ〜32ｃの第２領域Ｂの長さＬ１〜Ｌ３と比べて最も長くなるようにした。 In consideration of the above, in this embodiment, the length L of the second region B of the sheet member 32 of each station 6 is set as follows. Farthest downstream side in the rotation direction of the intermediate transfer belt 13 length L 4 of the second region B of the sheet member 32d of the fourth station 6d of (right side in FIG. 1), the sheet member 32a~32c other stations 6a~6c It was set to be longest in comparison with the length L 1 ~L 3 of the second region B.

具体的な各ステーション６のシート部材32の第２領域Ｂの長さＬは、実際の画像形成装置においてシート部材32の長さＬを変えて画像評価をおこなって決定した。以下に評価方法について説明する。   The specific length L of the second region B of the sheet member 32 of each station 6 was determined by performing image evaluation while changing the length L of the sheet member 32 in an actual image forming apparatus. The evaluation method will be described below.

＜評価方法＞
画像形成プロセススピードが１００mm/secの画像形成装置を用いて、初期とＡ４サイズの普通紙を１００×１０３枚通紙後の「トナーの飛び散り」、「感光体における放電跡」、「駆動ローラにおける放電跡」、「色ムラ」について評価をおこなった。 <Evaluation method>
Using an image forming apparatus with an image forming process speed of 100 mm / sec, “toner splatter”, “discharge trace on photoconductor”, “driving roller” after passing 100 × 10 3 sheets of A4 size plain paper at the initial stage and A4 size Evaluation of “discharge traces” and “color unevenness”.

評価は次のような手順でおこなった。まず、図６に示すように、第２ステーション６ｂ以外の第１、第３、第４ステーション６ａ，６ｃ，６ｄのシート部材32ａ，32ｃ，32ｄの第２領域Ｂの長さＬ１＝Ｌ３＝Ｌ４＝１．８mmで固定した。 The evaluation was performed according to the following procedure. First, as shown in FIG. 6, the length L 1 = L 3 of the second region B of the sheet members 32a, 32c, 32d of the first, third, fourth stations 6a, 6c, 6d other than the second station 6b. = L 4 = fixed at 1.8 mm.

第２ステーション６ｂのシート部材32ｂの第２領域Ｂの長さＬ２を変えて「感光体における放電跡」と「トナーの飛び散り」を初期と通紙後において評価した。そして、第１〜第３ステーション６ａ〜６ｃのシート部材32ａ〜32ｃのそれぞれの第２領域Ｂの長さＬ１〜Ｌ３を決定した（ステップＳ１）。 By changing the length L 2 second region B of the sheet member 32b of the second station 6b as a "discharge traces the photoconductor" and "toner scattering" were evaluated after the initial and the feed. Then, to determine the length L 1 ~L 3 of each of the second region B of the sheet member 32a~32c of the first to third station 6 a to 6 c (step S1).

次に、第１〜第３ステーション６ａ〜６ｃのシート部材32ａ〜32ｃのそれぞれの第２領域Ｂの長さＬ１〜Ｌ３を前記ステップＳ１で決定したそれぞれの第２領域Ｂの長さＬ１＝Ｌ２＝Ｌ３＝２．０mmで固定した。第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４を変えて「駆動ローラにおける放電跡」と「色ムラ」を初期と通紙後において評価した。そして、第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４を決定した（ステップＳ２）。 Next, the lengths L 1 to L 3 of the second regions B of the sheet members 32a to 32c of the first to third stations 6a to 6c are determined as the lengths L of the second regions B determined in step S1. 1 = L 2 = L 3 = 2.0 mm and fixed. By changing the length L 4 second region B of the sheet member 32d of the fourth station 6d as "discharge traces in drive roller" a "color unevenness" was evaluated after the initial and the feed. Then, to determine the length L 4 of the second region B of the sheet member 32d of the fourth station 6d (Step S2).

通紙テストは、１５℃／１０％Ｒｈ（相対湿度）の低温、低湿環境において、ゼロックス社製4204（坪量７５ｇ）の普通紙を通紙することによりおこない、所定の間隔で画像サンプルを取得して画像良好を「○」とし、画像不良を「×」として判定した。「トナーの飛び散り」は、印字サンプルを拡大観察して評価した。「感光体における放電跡」、「駆動ローラにおける放電跡」は、単色のハーフトーン画像上に放電模様が発生しているか否かを目視で評価をおこなった。「色ムラ」は、レッド色など複数色のトナーを混色させたライン画像を目視により評価しておこなった。   The paper-passing test is performed by passing 4204 (basis weight 75g) plain paper made by Xerox Corporation in a low-temperature, low-humidity environment of 15 ° C / 10% Rh (relative humidity), and image samples are acquired at predetermined intervals. Thus, the image quality was determined as “◯” and the image defect was determined as “x”. “Toner scattering” was evaluated by magnifying the print sample. The “discharge trace on the photoconductor” and the “discharge trace on the drive roller” were evaluated by visual observation of whether or not a discharge pattern was generated on a monochrome halftone image. “Color unevenness” was performed by visually evaluating a line image obtained by mixing a plurality of colors of toner such as red.

＜評価結果＞
図６に評価結果を一覧で示す。まず、ステップＳ１において、第２ステーション６ｂのシート部材32ｂの第２領域Ｂの長さＬ２を変えたテストからＬ２＝２．０mmとした。即ち、通紙後に「感光体における放電跡」が見られない第２ステーション６ｂのシート部材32ｂの第２領域Ｂの長さＬ２として評価項目の全てが画像良好「○」であったＬ２＝２．０mmとした。 <Evaluation results>
FIG. 6 shows a list of evaluation results. First, in step S1, L 2 = 2.0 mm was obtained from a test in which the length L 2 of the second region B of the sheet member 32b of the second station 6b was changed. That, L 2 all evaluation items as the length L 2 of the second region B of the sheet member 32b of the second station 6b is not observed "discharge marks the photoconductor" after the sheet passing is an image good "○" = 2.0 mm.

次に、ステップＳ２において、第１〜第３ステーション６ａ〜６ｃのシート部材32ａ〜32ｃのそれぞれの第２領域Ｂの長さＬ１＝Ｌ２＝Ｌ３＝２．０mmとした。第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４を変えたテストからＬ４＝２．５mmとした。即ち、通紙後に「駆動ローラにおける放電跡」が見られない第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４は評価結果が画像良好「○」であった２．４mm以上である。 Next, in step S2, the length L 1 = L 2 = L 3 = 2.0 mm of each second region B of the sheet members 32a to 32c of the first to third stations 6a to 6c was set. Was L 4 = 2.5 mm from the test with different length L 4 of the second region B of the sheet member 32d of the fourth station 6d. That is, the length L 4 of the second region B of the sheet member 32d of the fourth station 6d where “the discharge trace on the driving roller” is not seen after the sheet is passed is an evaluation result of “Good” of 2.4 mm or more. It is.

同じく「色ムラ」が見られない第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４は評価結果が画像良好「○」であった２．６mm以下であった。このことから、２．４mmと２．６mmとの間をとって第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４＝２．５mmとした。 Similarly, the length L 4 of the second region B of the sheet member 32d of the fourth station 6d in which no “color unevenness” is seen was 2.6 mm or less where the evaluation result was “good”. Therefore, the length L 4 of the second region B of the sheet member 32d of the fourth station 6d is set to 2.5 mm between 2.4 mm and 2.6 mm.

また、ステップＳ３において、第１〜第３ステーション６ａ〜６ｃのシート部材32ａ〜32ｃのそれぞれの第２領域Ｂの長さＬ１＝Ｌ２＝Ｌ３＝２．２mmとした。第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４の長さを変えたテストから第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４は２．２mm以上で「色ムラ」が見られた。 In step S3, the length L 1 = L 2 = L 3 = 2.2 mm of each second region B of the sheet members 32a to 32c of the first to third stations 6a to 6c is set. Fourth length L 4 of the length Length L 4 of the second region B of the sheet member 32d stations 6d from the test with different second region B of the sheet member 32d of the fourth station. 6d 2.2mm or more “Color unevenness” was observed.

このため、全てのステーション６でシート部材32の第２領域Ｂの長さＬを２．２mmとすることはできなかった。これにより、本実施形態では、第１〜第３ステーション６ａ〜６ｃのシート部材32ａ〜32ｃのそれぞれの第２領域Ｂの長さＬ１＝Ｌ２＝Ｌ３＝２．０mmに設定した。第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４＝２．５mmに設定することでＡ４サイズの普通紙を１００×１０３枚通紙をおこなっても画像不良の発生を防止することができた。 For this reason, the length L of the second region B of the sheet member 32 cannot be set to 2.2 mm at all the stations 6. Thus, in this embodiment, set to the first to the respective lengths L 1 = L 2 = L 3 = 2.0mm in the second region B of the sheet member 32a~32c third station 6 a to 6 c. By setting the length L 4 of the second region B of the sheet member 32d of the fourth station 6d to 2.5 mm, the occurrence of image defects can be prevented even when 100 × 10 3 sheets of A4 size plain paper are passed. We were able to.

[比較例]
比較例として、各ステーション６で感光体１と中間転写ベルト13とシート部材23との位置関係が同一になるように配置した。そして、第１〜第４ステーション６ａ〜６ｄのシート部材32ａ〜32ｄのそれぞれの第２領域Ｂの長さＬ１＝Ｌ２＝Ｌ３＝Ｌ４＝２．０mmとした。この場合には、初期の画像は良好であったが、Ａ４サイズの普通紙を５０×１０３枚通紙後に「駆動ローラにおける放電跡」が発生した。 [Comparative example]
As a comparative example, each station 6 is arranged so that the positional relationship among the photosensitive member 1, the intermediate transfer belt 13, and the sheet member 23 is the same. Then, the first to the respective lengths L 1 = L 2 = L 3 = L 4 = 2.0mm in the second region B of the sheet member 32a~32d of the fourth station 6 a to 6 d. In this case, the initial image was satisfactory, but “discharge trace on the driving roller” occurred after 50 × 10 3 sheets of A4 size plain paper was passed.

＜シート部材の第２領域Ｂの長さの判別方法＞
各ステーション６におけるシート部材32の第２領域Ｂの長さＬは以下の方法によって判別できる。同じ長さのシート部材32を用いている場合、各ステーション６におけるシート部材32の第２領域Ｂの長さＬがどれだけ異なるかは以下のようにして求める。シート部材32にバイアス電圧を印加した状態で中間転写ベルト13を回転させた時に中間転写ベルト13がシート部材32に摺動して形成される摺擦跡の長さを測定する。これにより、シート部材32の第２領域Ｂの長さＬの相対的な違いがわかる。また、同じ長さのシート部材32を用いているか不明な場合でも、各ステーション６の断面観察をおこなうことで、シート部材32の第２領域Ｂの長さＬを比較することができる。 <Determination method of length of second region B of sheet member>
The length L of the second region B of the sheet member 32 at each station 6 can be determined by the following method. When the sheet member 32 having the same length is used, how much the length L of the second region B of the sheet member 32 in each station 6 is different is obtained as follows. When the intermediate transfer belt 13 is rotated in a state where a bias voltage is applied to the sheet member 32, the length of the rubbing trace formed when the intermediate transfer belt 13 slides on the sheet member 32 is measured. Thereby, the relative difference of the length L of the 2nd field B of sheet member 32 is understood. Even when it is unclear whether the sheet member 32 having the same length is used, the length L of the second region B of the sheet member 32 can be compared by observing the cross section of each station 6.

以上、本実施形態では、第１〜第３ステーション６ａ〜６ｃのシート部材32ａ〜32ｃのそれぞれの第２領域Ｂの長さＬを同一としたが、必ずしも同じである必要はない。また、中間転写ベルト13としてベース樹脂中に電子導電剤を分散させた中間転写ベルト13について説明をおこなったが、導電剤としてアルカリ金属塩等のイオン導電剤を使用した中間転写ベルト13に対しても有効である。   As described above, in the present embodiment, the lengths L of the second regions B of the sheet members 32a to 32c of the first to third stations 6a to 6c are the same, but they are not necessarily the same. Further, the intermediate transfer belt 13 in which the electronic conductive agent is dispersed in the base resin as the intermediate transfer belt 13 has been described, but the intermediate transfer belt 13 using an ionic conductive agent such as an alkali metal salt as the conductive agent is described. Is also effective.

次に、本発明に係る画像形成装置の第２実施形態について図７を用いて説明する。尚、前記第１実施形態で説明した同一機能を有する部材には同一符号を付して説明は省略する。本実施形態では、前記第１実施形態に比べて画像形成プロセススピードがより高速（画像形成プロセススピード：２００mm/sec）とされる画像形成装置に適用した一例について説明する。   Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. In addition, the same code | symbol is attached | subjected to the member which has the same function demonstrated in the said 1st Embodiment, and description is abbreviate | omitted. In the present embodiment, an example applied to an image forming apparatus in which the image forming process speed is higher than that in the first embodiment (image forming process speed: 200 mm / sec) will be described.

画像形成プロセススピードが高速であっても中間転写ベルト13へ供給する電荷量を前記第１実施形態と略同じにするため、本実施形態の中間転写ベルト13は電子導電剤の量を増やして抵抗値を小さくしている。その結果、転写部材となるシート部材32の中間転写ベルト13への接触面積は略同程度のままで高速化に対応できる。また、シート部材32へ印加するバイアス電圧も大きくする必要がない。しかし、中間転写ベルト13の電気的な時定数τが短くなるため、前記第１実施形態よりも、さらに適正にシート部材32の第２領域Ｂの長さＬを設定する必要がある。   In order to make the amount of charge supplied to the intermediate transfer belt 13 substantially the same as that in the first embodiment even when the image forming process speed is high, the intermediate transfer belt 13 of this embodiment increases the amount of the electronic conductive agent to increase resistance. The value is reduced. As a result, the contact area of the sheet member 32 serving as a transfer member with the intermediate transfer belt 13 remains substantially the same, and the speed can be increased. Further, it is not necessary to increase the bias voltage applied to the sheet member 32. However, since the electrical time constant τ of the intermediate transfer belt 13 is shortened, it is necessary to set the length L of the second region B of the sheet member 32 more appropriately than in the first embodiment.

本実施形態のような画像形成装置の一次転写では、中間転写ベルト13の抵抗値変動があっても均一な転写を行えるようにするために、画像形成前などの非画像形成時に、シート部材32に定電流バイアス電圧を印加してインピーダンス検知をおこなう。そして、画像形成中に所定の定電圧を印加するように制御したＡＴＶＣ（Active Transfer Voltage Control）制御が各ステーション６毎におこなわれる。   In the primary transfer of the image forming apparatus as in the present embodiment, the sheet member 32 is used during non-image formation such as before image formation in order to perform uniform transfer even if the resistance value of the intermediate transfer belt 13 varies. Impedance detection is performed by applying a constant current bias voltage to. Then, ATVC (Active Transfer Voltage Control) control is performed for each station 6 so as to apply a predetermined constant voltage during image formation.

中間転写ベルト13の回転方向最上流側（図１の左側）に配置された第１ステーション６ａと、それよりも下流側に配置された第２ステーション６ｂ以降とで画像形成中に同じように定電圧制御をおこなう。第１ステーション６ａは、その上流側に電圧印加部材がない。このために、図３に示す感光体１と中間転写ベルト13とシート部材32とが全て３層で接触している第１領域Ａを通過した後における中間転写ベルト13上に担持される電荷量Ｑが他の第２〜第４ステーション６ｂ〜６ｄよりも僅かに少ない。   The first station 6a disposed on the most upstream side in the rotation direction of the intermediate transfer belt 13 (left side in FIG. 1) and the second station 6b and the subsequent stations disposed on the downstream side thereof are similarly determined during image formation. Perform voltage control. The first station 6a has no voltage application member on the upstream side. Therefore, the amount of charge carried on the intermediate transfer belt 13 after passing through the first region A in which the photosensitive member 1, the intermediate transfer belt 13, and the sheet member 32 shown in FIG. Q is slightly less than the other second to fourth stations 6b to 6d.

各ステーション６に設けられる複数の転写部材となるシート部材32のうち中間転写ベルト13の回転方向において最上流側（図１の左側）に配置される第１ステーション６ａのシート部材32ａの第２領域Ｂの長さＬ１を以下の条件とする。 The second region of the sheet member 32a of the first station 6a disposed on the most upstream side (left side in FIG. 1) in the rotational direction of the intermediate transfer belt 13 among the plurality of sheet members 32 serving as transfer members provided in each station 6. the following condition a length L 1 of B.

第１ステーション６ａよりも下流側（図１の右側）に配置される他のステーション６ｂ〜６ｄの各シート部材32ｂ〜32ｄの第２領域Ｂの長さＬ２〜Ｌ４よりも第１ステーション６ａのシート部材32ａの第２領域Ｂの長さＬ１を短くする。 The first downstream side of the station 6a second region first station 6a than the length L 2 ~L 4 of B of each sheet member 32b~32d other stations 6b~6d disposed (right side in FIG. 1) shortening of the second region B of the sheet member 32a of the length L 1.

即ち、最上流側（図１の左側）に配置される第１ステーション６ａのシート部材32ａの第２領域Ｂの中間転写ベルト13の回転方向（図３の左右方向）の長さＬ１を最も短くする。 That is, the length L 1 in the rotation direction (left-right direction in FIG. 3) of the intermediate transfer belt 13 in the second region B of the sheet member 32a of the first station 6a arranged on the most upstream side (left side in FIG. 1) is maximized. shorten.

これにより、最上流側（図１の左側）に配置される第１ステーション６ａにおける画像不良の発生タイミングを、それよりも下流側（図１の右側）に配置される他のステーション６ｂ，６ｃ，６ｄにおける画像不良の発生タイミングと同等とすることが出来る。   Thereby, the occurrence timing of the image defect in the first station 6a arranged on the most upstream side (left side in FIG. 1) is set to the other stations 6b, 6c, It can be equivalent to the occurrence timing of the image defect in 6d.

以後、第１ステーション６ａと，第２ステーション６ｂとを例にとり、上記のように設定した理由を説明する。図７は前述した図４及び図５と同じように、一次転写部材30が設けられた一次転写部における各シート部材32の第２領域Ｂが中間転写ベルト13の回転方向下流側（図２の右側）方向に十分長いと仮定した。その場合における中間転写ベルト13上の電荷量Ｑの時間推移を示したグラフである。   Hereinafter, the reason for setting as described above will be described by taking the first station 6a and the second station 6b as an example. 7 is similar to FIGS. 4 and 5 described above, the second region B of each sheet member 32 in the primary transfer portion provided with the primary transfer member 30 is downstream in the rotational direction of the intermediate transfer belt 13 (see FIG. 2). It was assumed that it was long enough in the (right) direction. 7 is a graph showing the time transition of the charge amount Q on the intermediate transfer belt 13 in that case.

図７における電荷量Ｑ０は、第１ステーション６ａの境界位置ｂにおける中間転写ベルト13上に担持された電荷量Ｑであり、図７に示す実線の曲線は第１ステーション６ａにおける中間転写ベルト13上に担持される電荷量Ｑが減衰する様子を表している。 Charge amount Q in FIG. 7 0 is the charge amount Q that is carried on the intermediate transfer belt 13 at the boundary position b of the first station 6a, the intermediate transfer belt 13 at the first station 6a is solid curve shown in FIG. 7 It shows how the charge amount Q carried thereon is attenuated.

また、図７における電荷量Ｑ１は、第２ステーション６ｂの境界位置ｂにおける中間転写ベルト13上に担持された電荷量Ｑであり、図７に示す破線の曲線は第２ステーション６ｂにおける中間転写ベルト13上に担持される電荷量Ｑが減衰する様子を表している。 The charge amount Q 1 in FIG. 7, a charge amount Q that is carried on the intermediate transfer belt 13 at the boundary position b of the second station 6b, the dashed curve shown in FIG. 7 is an intermediate transfer in the second station 6b This shows how the charge amount Q carried on the belt 13 is attenuated.

また、図７中の一点鎖線ｄはトナー画像に「感光体における放電跡」が発生する中間転写ベルト13上の電荷量Ｑを示し、ｄ´，ｄ″はその時の各第１、第２ステーション６ａ，６ｂにおいて中間転写ベルト13が境界位置ｂ通過後の経過時間をそれぞれ示している。   7 indicates the amount of charge Q on the intermediate transfer belt 13 at which the “discharge mark on the photosensitive member” is generated in the toner image, and d ′ and d ″ are the first and second stations at that time. 6a and 6b show the elapsed time after the intermediate transfer belt 13 passes the boundary position b.

図７中の一点鎖線ｅはシート部材32の第２領域Ｂの中間転写ベルト13の回転方向下流側（図３の右側）の該中間転写ベルト13上で「トナーの飛び散り」が発生する中間転写ベルト13上の電荷量Ｑを示す。ｅ´，ｅ″はその時の各第１、第２ステーション６ａ，６ｂにおいて中間転写ベルト13が境界位置ｂ通過後の経過時間をそれぞれ示す。   In FIG. 7, an alternate long and short dash line e indicates an intermediate transfer in which “scattering of toner” occurs on the intermediate transfer belt 13 on the downstream side in the rotation direction of the intermediate transfer belt 13 in the second region B of the sheet member 32 (right side in FIG. 3). The amount of charge Q on the belt 13 is shown. e ′ and e ″ indicate the elapsed time after the intermediate transfer belt 13 has passed the boundary position b in the first and second stations 6a and 6b, respectively.

図７に示すように、中間転写ベルト13の回転方向において最上流側（図１の左側）に第１ステーション６ａが配置される。第１ステーション６ａの境界位置ｂにおける中間転写ベルト13上に担持される電荷量Ｑ０が、それよりも下流側に配置される第２ステーション６ｂの境界位置ｂにおける中間転写ベルト13上に担持される電荷量Ｑ１よりも僅かに小さい。 As shown in FIG. 7, the first station 6 a is arranged on the most upstream side (left side in FIG. 1) in the rotation direction of the intermediate transfer belt 13. Charge amount Q 0 which is carried on the intermediate transfer belt 13 at the boundary position b of the first station 6a may be carried on the intermediate transfer belt 13 at the boundary position b of the second station 6b to which it is arranged downstream of the that is slightly smaller than the charge amount Q 1.

このため、第１ステーション６ａで画像不良が発生しない適正な範囲は図７の横軸で示される時間軸の時間の短い側（図７の左側）に寄る。従って、長期使用において最上流側（図１の左側）に配置される第１ステーション６ａにおける画像不良の発生タイミングを、それよりも下流側（図１の右側）に配置される他のステーション６ｂ，６ｃ，６ｄにおける画像不良の発生タイミングと同等とする。   Therefore, an appropriate range in which no image defect occurs in the first station 6a is closer to the shorter time side (left side in FIG. 7) of the time axis indicated by the horizontal axis in FIG. Therefore, the image defect occurrence timing at the first station 6a arranged on the most upstream side (left side in FIG. 1) in the long-term use is set to the other stations 6b arranged on the downstream side (right side in FIG. 1). The timing is the same as the occurrence timing of image defects in 6c and 6d.

そのために、本実施形態では第１ステーション６ａのシート部材32ａの第２領域Ｂの長さＬ１を、第２ステーション６ｂのシート部材32ｂの第２領域Ｂの長さＬ２よりも短くしている。 Therefore, in this embodiment the length L 1 of the second region B of the sheet member 32a of the first station 6a, shorter than the length L 2 of the second region B of the sheet member 32b of the second station 6b Yes.

即ち、本実施形態では、以下の関係が成り立つように各ステーション６のシート部材32の第２領域Ｂの長さＬを設定している。最下流側（図１の右側）に第４ステーション６ｄが配置される。第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４を、それよりも上流側に配置される他の第１〜第３ステーション６ａ〜６ｃの各シート部材32ａ〜32ｃの第２領域Ｂの長さＬ１〜Ｌ３よりも長く設定する。その理由は、前記第１実施形態で説明しているので、その説明は省略する。 That is, in the present embodiment, the length L of the second region B of the sheet member 32 of each station 6 is set so that the following relationship is established. The fourth station 6d is arranged on the most downstream side (right side in FIG. 1). Fourth second region B of the sheet member 32d stations 6d length L 4, each of the second sheet member 32a~32c other first to third stations 6a~6c it is disposed upstream of the It is set to be longer than the lengths L 1 to L 3 of the region B. The reason is described in the first embodiment, and the description thereof is omitted.

本実施形態では、最上流側（図１の左側）に配置される第１ステーション６ａのシート部材32ａの第２領域Ｂの長さＬ１＝１．９mmに設定する。その下流側（図１の右側）に配置される第２ステーション６ｂのシート部材32ｂの第２領域Ｂの長さＬ２＝２．０mmに設定する。 In the present embodiment, the length L 1 of the second region B of the sheet member 32a of the first station 6a arranged on the most upstream side (left side in FIG. 1) is set to 1.9 mm. The length L 2 of the second region B of the sheet member 32b of the second station 6b arranged on the downstream side (right side in FIG. 1) is set to 2.0 mm.

更にその下流側（図１の右側）に配置される第３ステーション６ｃのシート部材32ｃの第２領域Ｂの長さＬ３＝２．１mmに設定する。更にその下流側で最下流側（図１の右側）に配置される第４ステーション６ｄのシート部材32ｄの第２領域Ｂの長さＬ４＝２．５mmに設定する。 Further, the length L 3 of the second region B of the sheet member 32c of the third station 6c arranged on the downstream side (right side in FIG. 1) is set to 2.1 mm. Further, the length L 4 of the second region B of the sheet member 32d of the fourth station 6d arranged on the most downstream side (the right side in FIG. 1) is set to 2.5 mm on the downstream side.

そして、前記第１実施形態と同様にＡ４サイズの普通紙を２００×１０３枚以上通紙をおこなって同様な評価をおこなった結果、良好な画像を維持できることが判明した。 As in the first embodiment, it was found that a good image can be maintained as a result of performing a similar evaluation by passing 200 × 10 3 or more A4 size plain papers.

以上のように、各ステーション６におけるシート部材32の第２領域Ｂの長さＬを適正にすることで、従来のように除電針などの部材をシート部材32の第２領域Ｂの下流側に設ける必要もなく、従来よりも良好な画像を長期間にわたって維持することが可能になる。   As described above, by making the length L of the second region B of the sheet member 32 in each station 6 appropriate, a member such as a static elimination needle is placed downstream of the second region B of the sheet member 32 as in the past. It is not necessary to provide an image, and it is possible to maintain a better image than before for a long period of time.

１，１ａ〜１ｄ …感光体(像担持体)
13 …中間転写ベルト(ベルト体)
32，32ａ〜32ｄ …シート部材(転写部材)
Ａ …第１領域
Ｂ …第２領域 1, 1a to 1d: Photoconductor (image carrier)
13 ... Intermediate transfer belt (belt body)
32, 32a to 32d ... Sheet member (transfer member)
A ... 1st area | region B ... 2nd area | region

Claims (2)

トナー画像を担持する複数の像担持体と、回転可能なベルト体と、前記複数の像担持体上のトナー画像を前記ベルト体の表面に転写する複数の転写部材と、を有し、前記ベルト体の移動中に前記複数の転写部材は回転せずに前記ベルト体の裏面に接触する画像形成装置において、
前記転写部材には画像形成中にトナーと逆極性のバイアス電圧が印加されており、
前記転写部材は、
前記ベルト体を介して前記像担持体と前記ベルト体と前記転写部材とが接触して形成される第１領域と、
前記第１領域よりも前記ベルト体の回転方向下流側で前記転写部材が前記ベルト体に接触し、且つ前記像担持体と前記ベルト体とが離間する第２領域と、
を有し、
前記複数の転写部材のうち前記ベルト体の回転方向において最下流側に配置される転写部材の前記第２領域の前記ベルト体の回転方向の長さが最も長いことを特徴とする画像形成装置。 A plurality of image carriers that carry toner images; a rotatable belt body; and a plurality of transfer members that transfer toner images on the plurality of image carriers to the surface of the belt body. In the image forming apparatus in which the plurality of transfer members do not rotate and contact the back surface of the belt body during movement of the body,
A bias voltage having a polarity opposite to that of the toner is applied to the transfer member during image formation.
The transfer member is
A first region formed by contacting the image carrier, the belt body and the transfer member via the belt body;
A second region in which the transfer member is in contact with the belt body on the downstream side in the rotation direction of the belt body from the first region, and the image carrier and the belt body are separated from each other;
Have
An image forming apparatus, wherein the length of the second region of the transfer member arranged on the most downstream side in the rotation direction of the belt body among the plurality of transfer members is the longest in the rotation direction of the belt body. トナー画像を担持する複数の像担持体と、回転可能なベルト体と、前記複数の像担持体上のトナー画像を前記ベルト体の表面に転写する複数の転写部材と、を有し、前記ベルト体の移動中に前記複数の転写部材は回転せずに前記ベルト体の裏面に接触する画像形成装置において、
前記転写部材には画像形成中にトナーと逆極性のバイアス電圧が印加されており、
前記転写部材は、
前記ベルト体を介して前記像担持体と前記ベルト体と前記転写部材とが接触して形成される第１領域と、
前記第１領域よりも前記ベルト体の回転方向下流側で前記転写部材が前記ベルト体に接触し、且つ前記像担持体と前記ベルト体とが離間する第２領域と、
を有し、
前記複数の転写部材のうち前記ベルト体の回転方向において最上流側に配置される転写部材の前記第２領域の前記ベルト体の回転方向の長さが最も短いことを特徴とする画像形成装置。 A plurality of image carriers that carry toner images; a rotatable belt body; and a plurality of transfer members that transfer toner images on the plurality of image carriers to the surface of the belt body. In the image forming apparatus in which the plurality of transfer members do not rotate and contact the back surface of the belt body during movement of the body,
A bias voltage having a polarity opposite to that of the toner is applied to the transfer member during image formation.
The transfer member is
A first region formed by contacting the image carrier, the belt body and the transfer member via the belt body;
A second region in which the transfer member is in contact with the belt body on the downstream side in the rotation direction of the belt body from the first region, and the image carrier and the belt body are separated from each other;
Have
An image forming apparatus, wherein a length of the second region of the transfer member arranged on the most upstream side in the rotation direction of the belt body among the plurality of transfer members is the shortest in the rotation direction of the belt body.
JP2010249311A 2010-11-08 2010-11-08 Image forming device Pending JP2012103300A (en)

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