JP2009186828A

JP2009186828A - Image forming apparatus

Info

Publication number: JP2009186828A
Application number: JP2008027843A
Authority: JP
Inventors: Katsuya Kawagoe; 克哉川越
Original assignee: Ricoh Co Ltd
Current assignee: Ricoh Co Ltd
Priority date: 2008-02-07
Filing date: 2008-02-07
Publication date: 2009-08-20

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus which is capable of suppressing the occurrence of toner scattering and a void and the wear of an image carrying belt. <P>SOLUTION: A belt guide member 8 projects the intermediate transfer belt portion 1A toward a side of a recording medium sheet S being transferred to the transfer roller 3, by pressing the rear surface 1b of an intermediate transfer belt portion 1A on the upstream side in the transfer direction (direction of A) of the intermediate transfer belt 1, through the endless-shaped belt 7, from a press-contact potion (nip portion) 5 where a transfer roller 3 comes into press-contact with an opposing roller 16 through an intermediate transfer belt 1 and an endless-shaped belt 7, and the belt guide member is fixedly arranged. The endless-shaped belt 7 is stretched on the opposing roller 16 and the belt guide member 8 and the rear surface 1b of the intermediate transfer belt 1 comes into press-contact with the belt guide member 8 through the endless-shaped belt 7, to be pressed by the belt guide member 8. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

本発明は、無端状の像担持ベルトの表面にトナー像を形成し、そのトナー像を転写手段によって転写材上に転写する画像形成装置に関する。 The present invention relates to an image forming apparatus that forms a toner image on the surface of an endless image bearing belt and transfers the toner image onto a transfer material by a transfer unit.

電子複写機、プリンタ、ファクシミリ或いはその少なくとも２つの機能を備えた複合機等として構成される上記形式の画像形成装置は従来から周知である。像担持ベルトは、例えば、現像装置によって表面にトナー像が形成される感光体ベルトや、感光体からトナー像を転写される中間転写ベルトなどから構成される。
図５は、像担持ベルトが中間転写ベルトとして構成された従来の画像形成装置の転写部の構成を示す概略図である。ここに示した中間転写ベルト１は、図５には示していないローラと図５に示した１つのローラ（以下対向ローラという）２との複数のローラに張架されて矢印Ａ方向に移送駆動され、その表面に、図示していない感光体から互いに異なる色のトナー像が順先重ね合されて転写される。図５に示した矢印Ｅ方向に回転する対向ローラ２には、中間転写ベルト１を介して転写手段の一例である転写ローラ３が対向配置されている。中間転写ベルト１の表面のトナー像を転写用紙等の記録媒体からなる転写材Ｐ上に転写する時は、転写ローラ３は、図５に示すように、中間転写ベルト１を介して対向ローラ２に圧接する。このとき転写ローラ３は矢印Ｆ方向に回転し、この転写ローラ３と中間転写ベルト１との間を、転写材Ｐが矢印Ｂ方向に移動する。このように転写ローラ３は、中間転写ベルト１と転写材Ｐとを介して対向ローラ２に圧接する。このとき転写ローラ３には、中間転写ベルト１の表面に形成されたトナー像のトナー帯電極性と逆極性の転写電圧が印加され、これにより中間転写ベルト１の表面に当接しながら矢印Ｂ方向に移動する転写材Ｐの表面に中間転写ベルト１上のトナー像が転写される。対向ローラ２と転写ローラ３との圧接部（ニップ部）５を通過した転写材Ｐは、図示していない定着装置を通り、このときその表面に転写されたトナー像が転写材Ｐ上に定着される。 An image forming apparatus of the above type configured as an electronic copying machine, a printer, a facsimile machine, or a multifunction machine having at least two functions thereof has been conventionally known. The image carrying belt is composed of, for example, a photosensitive belt on which a toner image is formed by a developing device, an intermediate transfer belt on which a toner image is transferred from the photosensitive body, and the like.
FIG. 5 is a schematic diagram showing a configuration of a transfer unit of a conventional image forming apparatus in which an image carrying belt is configured as an intermediate transfer belt. The intermediate transfer belt 1 shown here is stretched around a plurality of rollers, a roller not shown in FIG. 5 and one roller (hereinafter referred to as a counter roller) 2 shown in FIG. Then, toner images of different colors are sequentially superimposed on the surface of the photoconductor (not shown) and transferred. A transfer roller 3, which is an example of a transfer unit, is opposed to the opposing roller 2 that rotates in the direction of arrow E shown in FIG. When transferring the toner image on the surface of the intermediate transfer belt 1 onto a transfer material P made of a recording medium such as transfer paper, the transfer roller 3 is connected to the opposing roller 2 via the intermediate transfer belt 1 as shown in FIG. Pressure contact. At this time, the transfer roller 3 rotates in the direction of arrow F, and the transfer material P moves in the direction of arrow B between the transfer roller 3 and the intermediate transfer belt 1. Thus, the transfer roller 3 is in pressure contact with the counter roller 2 via the intermediate transfer belt 1 and the transfer material P. At this time, a transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the surface of the intermediate transfer belt 1 is applied to the transfer roller 3, thereby causing the transfer roller 3 to contact the surface of the intermediate transfer belt 1 in the direction of arrow B. The toner image on the intermediate transfer belt 1 is transferred onto the surface of the moving transfer material P. The transfer material P that has passed through the pressure contact portion (nip portion) 5 between the opposing roller 2 and the transfer roller 3 passes through a fixing device (not shown). At this time, the toner image transferred to the surface is fixed on the transfer material P. Is done.

上述のように、転写材Ｐは、対向ローラ２と転写ローラ３との間に、その入口側Ｉから送り込まれて搬送されるが、このとき、その入口側Ｉの領域には中間転写ベルト１と転写材Ｐとによってくさび状のギャップＧが区画形成される。その際、転写ローラ３には、前述の転写電圧が印加されているので、対向ローラ２と転写ローラ３との圧接部５の近傍に位置する転写材Ｐ１の部分もトナーの帯電極性と逆極性に帯電する。このため、中間転写ベルト１上のトナーが、矢印Ｃで示すように、転写材Ｐの表面に静電的に飛び散って付着する。このような現象は「トナー散り」とも称せられているが、係るトナー散りが発生すると、圧接部５を通過した転写材表面には、転写されたトナー像のまわりに、上述のように飛び散ったトナーがにじんだ状態で付着し、これによってトナー像の画質が劣化する。 As described above, the transfer material P is fed between the opposed roller 2 and the transfer roller 3 and conveyed from the entrance side I. At this time, the intermediate transfer belt 1 is in the region on the entrance side I. And a transfer material P form a wedge-shaped gap G. At this time, since the transfer voltage described above is applied to the transfer roller 3, the portion of the transfer material P1 located in the vicinity of the pressure contact portion 5 between the opposing roller 2 and the transfer roller 3 is also opposite in polarity to the charging polarity of the toner. Is charged. Therefore, the toner on the intermediate transfer belt 1 electrostatically scatters and adheres to the surface of the transfer material P as indicated by an arrow C. Such a phenomenon is also referred to as “toner scattering”. When such toner scattering occurs, the surface of the transfer material that has passed through the press contact portion 5 scatters around the transferred toner image as described above. The toner adheres in a blurred state, which deteriorates the image quality of the toner image.

上述の不具合は、像担持ベルトが感光体ベルトや誘電体ベルトより成り、転写材Ｐが中間転写体又は記録媒体よりなる場合にも同様に生じるものであるが、中間転写ベルト１は、通常、その体積抵抗率が例えば１０^８Ωｃｍ乃至１０^１３Ωｃｍ程度の中抵抗体よりなることが多く、かかる中間転写ベルト１を用いた場合には、上述のトナー散りの発生が顕著となる。その原因としては、中抵抗体よりなる中間転写ベルト１の表面にトナーが静電的に密着する力は、絶縁体とトナーとの静電的な密着力よりも弱く、トナーが中間転写ベルト１の表面に比較的動きやすい状態で付着していることが挙げられる。特に中間転写ベルト１の表面に複数色のトナー像が重ねて形成されている場合、中間転写ベルト１上の単位面積当りのトナー量が多くなるため、特に最上層のトナーが非常に動きやすい状態となっている。このように動きやすい状態でトナーが付着している中間転写ベルト１の表面と、帯電した転写材Ｐが微小のギャップＧをもって対向すると、中間転写ベルト１上のトナーが転写材上に静電的に飛翔しやすくなり、前述のトナー散りが発生しやすくなるのである。 The above-mentioned problems occur in the same manner when the image carrying belt is composed of a photosensitive belt or a dielectric belt, and the transfer material P is composed of an intermediate transfer body or a recording medium. The volume resistivity is often made of a medium resistor having a volume resistivity of about 10 ⁸ Ωcm to 10 ¹³ Ωcm, for example. When such an intermediate transfer belt 1 is used, the above-described toner scattering becomes remarkable. As a cause thereof, the force that the toner is electrostatically adhered to the surface of the intermediate transfer belt 1 made of the intermediate resistor is weaker than the electrostatic adhesion force between the insulator and the toner, and the toner is transferred to the intermediate transfer belt 1. It is mentioned that it adheres to the surface of the surface in a relatively mobile state. In particular, when a plurality of color toner images are formed on the surface of the intermediate transfer belt 1, the amount of toner per unit area on the intermediate transfer belt 1 increases, so that the toner on the uppermost layer is particularly easy to move. It has become. When the surface of the intermediate transfer belt 1 to which the toner adheres in such a state that it is easy to move and the charged transfer material P face each other with a minute gap G, the toner on the intermediate transfer belt 1 is electrostatically applied onto the transfer material. The above-described toner scattering is likely to occur.

そこで、図６に示すように、矢印Ｆ方向に回転する転写ローラ３に対向した矢印Ｅ方向に回転する対向ローラ２と、中間転写ベルト１を支持するもう１つのガイドローラ４との間の中間転写ベルト部分１Ａが、圧接部５へ移動する転写材Ｐの移動方向Ｂに対してほぼ平行となるように、ガイドローラ４を配置し、圧接部５よりも像担持ベルトの移動方向上流側に大きく離れた個所で転写材Ｐが中間転写ベルト１の表面に当接し始めるように構成することが考えられる。このようにすれば、圧接部５の近傍に至った転写材Ｐの部分６が、転写ローラ３に印加された電圧の影響を受けて帯電したとき、当該転写材部分Ｐ１は既に中間転写ベルト１の表面に密着しているので、中間転写ベルト１の表面のトナーが転写材部分Ｐ１に飛翔することはなく、或いは飛翔するトナー量は極めて少なくなる。このようにしてトナー散りの発生を抑えることができる。 Therefore, as shown in FIG. 6, an intermediate between the opposing roller 2 rotating in the direction of arrow E facing the transfer roller 3 rotating in the direction of arrow F and another guide roller 4 supporting the intermediate transfer belt 1. The guide roller 4 is disposed so that the transfer belt portion 1A is substantially parallel to the moving direction B of the transfer material P moving to the press contact portion 5, and is located upstream of the press contact portion 5 in the moving direction of the image carrier belt. It can be considered that the transfer material P is configured to start to come into contact with the surface of the intermediate transfer belt 1 at a location far away. In this way, when the portion 6 of the transfer material P that reaches the vicinity of the press contact portion 5 is charged under the influence of the voltage applied to the transfer roller 3, the transfer material portion P1 has already been transferred to the intermediate transfer belt 1. Therefore, the toner on the surface of the intermediate transfer belt 1 does not fly to the transfer material portion P1, or the amount of toner to fly becomes extremely small. In this way, the occurrence of toner scattering can be suppressed.

ところで、対向ローラ２とガイドローラ４との間を近接させるために、中間転写ベルト１を支持する対向ローラ２及びガイドローラ４の径を小さくすると、これらの対向ローラ２とガイドローラ４を通過する中間転写ベルト１にカールぐせがつき、これによって中間転写ベルト１から転写材Ｐにトナー像が転写されるときに転写むらが発生し、転写されたトナー像の画質が劣化する。また転写ローラ３に対向する対向ローラ２の径が小さすぎると、転写材搬送方向における圧接部５の距離（ニップ幅）が小さくなり、転写効率が低下する恐れもある。従って、これらの対向ローラ２及びガイドローラ４の径をあまり小さくすることはできない。
上述の理由により、対向ローラ２及びガイドローラ４の径を大きくすると、転写材Ｐが圧接部５に至る前に中間転写ベルト１の表面に密着する密着部の距離Ｄが大きくなり、圧接部５から、転写材Ｐの移動方向上流側に大きく離れた位置で、転写材Ｐが中間転写ベルト１に接触し始めることになる。その際、中間転写ベルト１に当接した転写材Ｐの部分中の転写材移動方向上流側の部分６は、転写ローラ３から大きく離れているので、この転写材部分６は、転写ローラ３に印加された電圧の影響により帯電していないか、帯電していたとしても、その電位は極めて低くなっている。従って、この転写材部分６は、中間転写ベルト１の表面に静電的に強く吸着し合った状態で密着することはない。 By the way, if the diameters of the counter roller 2 and the guide roller 4 that support the intermediate transfer belt 1 are reduced in order to make the counter roller 2 and the guide roller 4 close to each other, they pass through the counter roller 2 and the guide roller 4. The intermediate transfer belt 1 is curled, thereby causing uneven transfer when the toner image is transferred from the intermediate transfer belt 1 to the transfer material P, and the image quality of the transferred toner image is deteriorated. If the diameter of the facing roller 2 facing the transfer roller 3 is too small, the distance (nip width) of the press contact portion 5 in the transfer material conveyance direction is reduced, and there is a possibility that transfer efficiency is lowered. Therefore, the diameters of the facing roller 2 and the guide roller 4 cannot be made too small.
For the above-described reasons, when the diameters of the opposing roller 2 and the guide roller 4 are increased, the distance D of the close contact portion that comes into close contact with the surface of the intermediate transfer belt 1 before the transfer material P reaches the press contact portion 5 increases. Therefore, the transfer material P starts to contact the intermediate transfer belt 1 at a position far away from the upstream side in the moving direction of the transfer material P. At this time, the portion 6 on the upstream side in the transfer material moving direction in the portion of the transfer material P that is in contact with the intermediate transfer belt 1 is far away from the transfer roller 3. Even if it is not charged or charged due to the influence of the applied voltage, its potential is very low. Therefore, the transfer material portion 6 does not adhere to the surface of the intermediate transfer belt 1 in a state where it is strongly adsorbed electrostatically.

しかし、このため、中間転写ベルト１に発生したわずかなカールによる表面の凹凸やたるみなどに、転写材部分６が追従して密着しきれず、また転写材部分６が中間転写ベルト１に対してわずかにずれ動くことがある。これによって中間転写ベルト１の表面と転写材部分６との間に存するトナー像の一部が乱され、この乱れにより、圧接部５を通過した転写材Ｐ上に転写されているトナー像の濃度が局部的に薄くなった画像抜けが発生し、その画質が劣化するおそれがある。この画像抜けは、一般に白色の転写材Ｐが多用されていることから「白抜け」とも称せられている。特に、中間転写ベルト１と転写材Ｐとの間にて速度が公差範囲でずれてしまう場合は、この密着部にて画像ずれが発生しやすく、Ｄ寸法は大きくすることが難しくなる。
これらの問題を解決するため、本発明者らは、特許文献１に記載したように、中間転写ベルト部分１Ａを転写材Ｐ側に突出させて当接する湾曲面を有するベルト案内部材を、対向ローラ３の上流側に配置固定して、中間転写ベルト部分Ｐ１を形成してトナー散りの発生を抑制すると共に、転写材部分６の長さを可及的に小さくすることによって白抜けの発生を抑制することを提案した。
特開２００２−８２５４３公報 However, for this reason, the transfer material portion 6 cannot follow the surface unevenness or sagging due to slight curl generated in the intermediate transfer belt 1 and cannot be adhered to the intermediate transfer belt 1, and the transfer material portion 6 is slightly in contact with the intermediate transfer belt 1. May move. As a result, a part of the toner image existing between the surface of the intermediate transfer belt 1 and the transfer material portion 6 is disturbed, and due to this disorder, the density of the toner image transferred onto the transfer material P that has passed through the press contact portion 5 is disturbed. However, there is a possibility that an image dropout that is locally thin occurs and the image quality deteriorates. This image omission is generally referred to as “white omission” because white transfer material P is generally used. In particular, when the speed is deviated within a tolerance range between the intermediate transfer belt 1 and the transfer material P, an image misalignment is likely to occur at the contact portion, and it is difficult to increase the D dimension.
In order to solve these problems, as described in Patent Document 1, the present inventors use a belt guide member having a curved surface that protrudes and contacts the intermediate transfer belt portion 1A toward the transfer material P side as a counter roller. 3 is arranged and fixed on the upstream side to form an intermediate transfer belt portion P1 to suppress the occurrence of toner scattering, and the length of the transfer material portion 6 is made as small as possible to suppress the occurrence of white spots. Proposed to do.
JP 2002-82543 A

しかしながら、特許文献１記載の場合には、無端状の中間転写ベルト１の裏面が固定されたベルト案内部材に常に摺擦されながら移送されるため、中間転写ベルト１の裏面の磨耗による摩耗粉が発生し、磨耗粉が中間転写ベルト１の表面に付着することによる転写不良や、磨耗粉によってトナー像が転写される中間転写ベルトの表面に傷が発生して画像不良が発生するという問題点があることが判明した。
本発明は、上記実情を考慮してなされたものであり、トナー散りの発生及び白抜けの発生を抑制すると共に、像担持ベルトの摩耗を抑制することが可能な画像形成装置を提供することを目的とする。 However, in the case of Patent Document 1, since the back surface of the endless intermediate transfer belt 1 is transferred while being constantly rubbed against the belt guide member to which the endless intermediate transfer belt 1 is fixed, abrasion powder due to wear on the back surface of the intermediate transfer belt 1 is generated. There is a problem that the transfer failure due to the generated abrasion powder adhering to the surface of the intermediate transfer belt 1 and the surface of the intermediate transfer belt to which the toner image is transferred due to the abrasion powder are scratched to cause image defects. It turned out to be.
The present invention has been made in view of the above circumstances, and provides an image forming apparatus capable of suppressing the occurrence of toner scattering and the occurrence of white spots and the wear of an image bearing belt. Objective.

上記課題を解決するために、請求項１の発明は、複数のローラに張架されて移送駆動され、表面にトナー像が形成される無端状の像担持ベルトと、当該像担持ベルトを介して、前記複数のローラ中の１つのローラに対向して配置され、前記像担持ベルトの表面に形成されたトナー像のトナー帯電極性と逆極性の転写電圧を印加する転写手段とを有し、前記像担持ベルトの表面に当接しながら前記転写手段と前記１つのローラとの間を移動する転写材上に、前記転写手段から前記転写電圧を印加することによって像担持ベルト表面のトナー像を転写する画像形成装置において、前記１つのローラと前記転写手段との対向領域よりも前記像担持ベルトの移送方向上流側の像担持ベルト部分の裏面を押圧して当該像担持ベルト部分を、前記転写手段に移送中の転写材の側へ突出させるベルト案内部材を固定配置し、当該ベルト案内部材と前記１つのローラとの間に、無端状ベルトを張架し、当該無端状ベルトを前記ベルト案内部材と前記１つのローラとによって前記像担持ベルトの裏面に当接させて当該像担持ベルトの移送と共に前記無端状ベルトが移送されることを特徴とする。 In order to solve the above-mentioned problems, an invention according to claim 1 is directed to an endless image carrier belt that is stretched and driven by a plurality of rollers to form a toner image on the surface, and the image carrier belt through the image carrier belt. A transfer unit disposed opposite to one of the plurality of rollers and applying a transfer voltage having a polarity opposite to a toner charging polarity of a toner image formed on the surface of the image bearing belt, The toner image on the surface of the image carrier belt is transferred by applying the transfer voltage from the transfer unit onto a transfer material that moves between the transfer unit and the one roller while being in contact with the surface of the image carrier belt. In the image forming apparatus, the back surface of the image carrier belt portion on the upstream side in the transfer direction of the image carrier belt with respect to a region where the one roller and the transfer device are opposed to each other is pressed to place the image carrier belt portion on the transfer device. A belt guide member that protrudes toward the transfer material being transferred is fixedly arranged, an endless belt is stretched between the belt guide member and the one roller, and the endless belt is connected to the belt guide member. The one end roller is brought into contact with the back surface of the image carrying belt, and the endless belt is moved along with the transfer of the image carrying belt.

また、請求項２の発明は、請求項１記載の画像形成装置において、前記無端状ベルトは、１０^７Ωｃｍ〜１０^１０Ωｃｍの体積抵抗値を有することを特徴とする。
また、請求項３の発明は、請求項１又は２記載の画像形成装置において、前記無端状ベルトは、前記像担持ベルトと当接する面に植毛体が形成されていることを特徴とする。
また、請求項４の発明は、請求項１乃至３のいずれか１項記載の画像形成装置において、前記ベルト案内部材は、前記像担持ベルト部分を、前記転写手段に移送中の転写材の側へ突出させる向きに湾曲する湾曲面を有し、当該湾曲面の曲率半径を１０ｍｍ以上に設定したことを特徴とする。
また、請求項５の発明は、請求項４記載の画像形成装置において、前記ベルト案内部材の湾曲面は、前記像担持ベルトの全幅を押圧する押圧面を有していることを特徴とする。 According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the endless belt has a volume resistance value of 10 ⁷ Ωcm to ^{10 10} Ωcm.
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the endless belt has a flocked body formed on a surface in contact with the image carrying belt.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects of the present invention, the belt guide member includes a side of a transfer material that is transferring the image carrying belt portion to the transfer unit. It has a curved surface that curves in the direction of projecting to the side, and the curvature radius of the curved surface is set to 10 mm or more.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the curved surface of the belt guide member has a pressing surface for pressing the entire width of the image bearing belt.

また、請求項６の発明は、請求項１乃至５のいずれか１項記載の画像形成装置において、前記像担持ベルトは、前記ベルト案内部材と転写手段との間に前記転写材と密着する密着部分を有し、当該密着部分の前記像担持ベルトの移動方向に沿う長さが２ｍｍ〜３０ｍｍ以内に設定されることを特徴とする。
また、請求項７の発明は、請求項１乃至６のいずれか１項記載の画像形成装置において、前記転写手段は、転写ローラであり、当該転写ローラに前記像担持ベルトの表面に形成されたトナー像のトナー帯電極性と逆極性の転写電圧を印加することにより、移動する前記転写材上に像担持ベルト表面のトナー像を転写することを特徴とする。
また、請求項８の発明は、請求項１乃至７のいずれか１項記載の画像形成装置において、前記像担持ベルトは、感光体表面に形成されたトナー像が一次転写される無端状の中間転写ベルトであり、前記転写材は記録媒体であることを特徴とする。 According to a sixth aspect of the present invention, in the image forming apparatus according to any one of the first to fifth aspects, the image carrying belt is in close contact with the transfer material between the belt guide member and the transfer unit. And the length of the contact portion along the moving direction of the image carrying belt is set within 2 mm to 30 mm.
According to a seventh aspect of the present invention, in the image forming apparatus according to any one of the first to sixth aspects, the transfer means is a transfer roller, and is formed on the surface of the image bearing belt on the transfer roller. The toner image on the surface of the image bearing belt is transferred onto the moving transfer material by applying a transfer voltage having a polarity opposite to the toner charging polarity of the toner image.
According to an eighth aspect of the present invention, in the image forming apparatus according to any one of the first to seventh aspects, the image carrying belt is an endless intermediate to which a toner image formed on the surface of the photoreceptor is primarily transferred. A transfer belt, wherein the transfer material is a recording medium.

本発明によれば、前記１つのローラと前記転写手段との対向領域よりも前記像担持ベルトの移動方向上流側の像担持ベルト部分の裏面を押圧して当該像担持ベルト部分を、前記転写手段に移送中の転写材の側へ突出させるベルト案内部材を固定配置し、当該ベルト案内部材と前記１つのローラとの間に、無端状ベルトを張架し、当該無端状ベルトを前記ベルト案内部材と１つのローラとによって前記像担持ベルトの裏面に当接させて当該像担持ベルトの移送と共に前記無端状ベルトが移送されることによって、トナー散りの発生及び白抜けの発生を抑制すると共に、像担持ベルトの摩耗を抑制することが可能な画像形成装置を提供することができる。 According to the present invention, the back surface of the image carrier belt portion on the upstream side in the moving direction of the image carrier belt with respect to the region where the one roller and the transfer device are opposed is pressed to place the image carrier belt portion on the transfer device. A belt guide member that protrudes toward the transfer material being transferred is fixedly disposed, an endless belt is stretched between the belt guide member and the one roller, and the endless belt is connected to the belt guide member. And one roller are brought into contact with the back surface of the image carrier belt and the endless belt is transferred along with the transfer of the image carrier belt, thereby suppressing the occurrence of toner scattering and white spots. It is possible to provide an image forming apparatus capable of suppressing the wear of the support belt.

以下、図面を参照して、本発明の実施形態を詳細に説明する。
図１は、本発明による一実施形態の画像形成装置である複写機の概略構成を示す図である。図中符号１００は複写機本体、２００はそれを載せる給紙テーブル、３００は複写機本体１００上に取り付けるスキャナ、４００はさらにその上に取り付ける原稿自動搬送装置（ＡＤＦ）である。
複写機本体１００には、中央に、無端状の中間転写ベルト１を設ける。中間転写ベルト１は、図１に示す通り、図示例では駆動ローラ１４、支持ローラ１５及び対向ローラ１６に張架されて駆動ローラ１４の駆動回転によって図中時計回り（矢印Ａ方向）に回転移送可能となっている。そして、対向ローラ１６には、後述するトナー散りと白抜け防止機構３０が配設されている。また、この図示例では、支持ローラ１５の左に、トナー像を記録媒体シートＳに転写後に中間転写ベルト１上に残留する残留トナーを除去する中間転写体クリーニング装置１７が設けられている。また、駆動ローラ１４と支持ローラ１５間に張り渡した中間転写ベルト１上には、その搬送方向に沿って、ブラック、シアン、マゼンタ、イエローの４色のトナー像を形成する画像形成手段１８Ｂ、１８Ｃ、１８Ｍ、１８Ｙを横に並べて配置してタンデム画像形成装置２０を構成する。このタンデム画像形成装置２０の上には、図１に示すように、さらに露光装置２１を設ける。 Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a diagram showing a schematic configuration of a copying machine which is an image forming apparatus according to an embodiment of the present invention. In the figure, reference numeral 100 is a copying machine main body, 200 is a paper feed table on which it is placed, 300 is a scanner mounted on the copying machine main body 100, and 400 is an automatic document feeder (ADF) further mounted thereon.
The copying machine main body 100 is provided with an endless intermediate transfer belt 1 in the center. As shown in FIG. 1, the intermediate transfer belt 1 is stretched around a driving roller 14, a support roller 15, and a counter roller 16 in the illustrated example, and is rotated and transferred clockwise (in the direction of arrow A) in the drawing by driving rotation of the driving roller 14. It is possible. The counter roller 16 is provided with a toner scattering and white spot prevention mechanism 30 which will be described later. In the illustrated example, an intermediate transfer body cleaning device 17 is provided on the left side of the support roller 15 to remove residual toner remaining on the intermediate transfer belt 1 after the toner image is transferred to the recording medium sheet S. Further, on the intermediate transfer belt 1 stretched between the driving roller 14 and the support roller 15, an image forming unit 18B that forms toner images of four colors of black, cyan, magenta, and yellow along the conveying direction. The tandem image forming apparatus 20 is configured by arranging 18C, 18M, and 18Y side by side. An exposure device 21 is further provided on the tandem image forming apparatus 20 as shown in FIG.

画像形成手段１８Ｂ、１８Ｃ、１８Ｍ、１８Ｙには、それぞれ、ドラム状の感光体４０Ｂ、４０Ｃ、４０Ｍ、４０Ｙが備えられており、これらの周囲に、これらの感光体４０Ｂ、４０Ｃ、４０Ｍ、４０Ｙの表面をそれぞれ一様に帯電する帯電装置３７、現像装置３８Ｂ、３８Ｃ、３８Ｍ、３８Ｙ及びクリーニング装置３９が備えられている。そして、このようにして帯電された感光体４０Ｂ、４０Ｃ、４０Ｍ、４０Ｙの表面に露光装置２１からの光線によってそれぞれの色に対応する画像情報に基づく静電潜像が形成され、これらの静電潜像に対して、それぞれの色のトナーを収容した現像装置３８Ｂ、３８Ｃ、３８Ｍ、３８Ｙからそれぞれの色のトナーが供給されてそれぞれの感光体４０Ｂ、４０Ｃ、４０Ｍ、４０Ｙ上にそれぞれブラック、シアン、マゼンタ、イエローのトナー像を形成する。このようにして形成されたトナー像は、中間転写ベルト１上に転写ローラ６２によってトナー像のトナー帯電極性と逆極性の転写電圧が印加されて転写される。このようにして中間転写ベルト１上にトナー像を転写した後に残存する感光体４０Ｂ、４０Ｃ、４０Ｍ、４０Ｙ上のトナーは、クリーニング装置３９で除去されて一連の画像形成工程が終了する。 The image forming units 18B, 18C, 18M, and 18Y are provided with drum-shaped photoreceptors 40B, 40C, 40M, and 40Y, respectively, and around these photoreceptors 40B, 40C, 40M, and 40Y. A charging device 37 for uniformly charging the surface, developing devices 38B, 38C, 38M, and 38Y and a cleaning device 39 are provided. Then, electrostatic latent images based on image information corresponding to the respective colors are formed on the surfaces of the photoreceptors 40B, 40C, 40M, and 40Y thus charged by light rays from the exposure device 21, and these electrostatic images are formed. With respect to the latent image, the respective color toners are supplied from the developing devices 38B, 38C, 38M, and 38Y containing the respective color toners, and black and cyan are respectively applied to the respective photoreceptors 40B, 40C, 40M, and 40Y. , Magenta and yellow toner images are formed. The toner image thus formed is transferred onto the intermediate transfer belt 1 by applying a transfer voltage having a polarity opposite to the toner charging polarity of the toner image by the transfer roller 62. The toner on the photoreceptors 40B, 40C, 40M, and 40Y remaining after the toner image is transferred onto the intermediate transfer belt 1 in this manner is removed by the cleaning device 39, and a series of image forming steps is completed.

一方、中間転写ベルト１を挟んでタンデム画像形成装置２０と反対の側には、２次転写装置２２を備える。２次転写装置２２は、図示例では、駆動ローラ２３及び転写ローラ３とに、無端状ベルトである２次転写ベルト２４を張架して構成されている。そして、中間転写ベルト１、後述する無端状ベルト７及び２次転写ベルト２４を介して転写ローラ３を対向ローラ１６に押し当てて配置し、中間転写ベルト１の表面１ａ（図２参照）上のトナー像をトナー像のトナー帯電極性と逆極性の転写電圧を転写ローラ３から印加して転写材である紙やプラスチック等からなる記録媒体シートＳに転写する。
２次転写装置２２の横には、記録媒体シートＳ上に２次転写装置２２によって転写された未定着トナー像を定着する定着装置２５を設ける。定着装置２５は、無端状ベルトである定着ベルト２６に加圧ローラ２７を押し当てて構成する。なお、図示例では、このような２次転写装置２２および定着装置２５の下に、上述したタンデム画像形成装置２０と平行に、記録媒体シートＳの両面にトナー像を記録すべく記録媒体シートＳを反転するシート反転装置２８を備える。 On the other hand, a secondary transfer device 22 is provided on the opposite side of the intermediate transfer belt 1 from the tandem image forming device 20. In the illustrated example, the secondary transfer device 22 is configured such that a secondary transfer belt 24 that is an endless belt is stretched around a driving roller 23 and a transfer roller 3. Then, the transfer roller 3 is pressed against the opposing roller 16 via the intermediate transfer belt 1, an endless belt 7 and a secondary transfer belt 24, which will be described later, and placed on the surface 1a (see FIG. 2) of the intermediate transfer belt 1. The toner image is transferred to a recording medium sheet S made of paper, plastic, or the like as a transfer material by applying a transfer voltage having a polarity opposite to the toner charging polarity of the toner image from the transfer roller 3.
A fixing device 25 for fixing the unfixed toner image transferred by the secondary transfer device 22 on the recording medium sheet S is provided beside the secondary transfer device 22. The fixing device 25 is configured by pressing a pressure roller 27 against a fixing belt 26 that is an endless belt. In the illustrated example, a recording medium sheet S is recorded under both the secondary transfer device 22 and the fixing device 25 so as to record a toner image on both surfaces of the recording medium sheet S in parallel with the tandem image forming apparatus 20 described above. Is provided with a sheet reversing device.

さて、このカラー複写機を用いてコピーをとるときは、原稿自動搬送装置４００の原稿台３０上に原稿をセットする。または、原稿自動搬送装置４００を開いてスキャナ３００のコンタクトガラス３２上に原稿をセットし、原稿自動搬送装置４００を閉じてそれで押さえる。そして、不図示のスタートスイッチを押すと、原稿自動搬送装置４００に原稿をセットしたときは、原稿を搬送してコンタクトガラス３２上へと移動した後、他方コンタクトガラス３２上に原稿をセットしたときは、直ちにスキャナ３００を駆動し、第１走行体３３および第２走行体３４を走行する。そして、第１走行体３３で光源から光を発射するとともに原稿面からの反射光をさらに反射して第２走行体３４に向け、第２走行体３４のミラーで反射して結像レンズ３５を通して読取りセンサ３６に入光して原稿内容を読み取る。 Now, when making a copy using this color copying machine, a document is set on the document table 30 of the automatic document feeder 400. Alternatively, the automatic document feeder 400 is opened, a document is set on the contact glass 32 of the scanner 300, and the automatic document feeder 400 is closed and pressed by it. When a start switch (not shown) is pressed, when a document is set on the automatic document feeder 400, the document is transported and moved onto the contact glass 32, and then the document is set on the other contact glass 32. Immediately drives the scanner 300 and travels through the first traveling body 33 and the second traveling body 34. Then, the first traveling body 33 emits light from the light source and further reflects the reflected light from the document surface toward the second traveling body 34, and is reflected by the mirror of the second traveling body 34 and passes through the imaging lens 35. The light enters the reading sensor 36 and reads the contents of the original.

また、不図示のスタートスイッチを押すと、不図示の駆動モータで駆動ローラ１４を回転駆動して支持ローラ１５を従動回転し、中間転写ベルト１をＡ方向に移送して回転搬送する。同時に、画像形成手段１８Ｂ、１８Ｃ、１８Ｍ、１８Ｙで、前述のように、それぞれのドラム状の感光体４０Ｂ、４０Ｃ、４０Ｍ、４０Ｙを矢印方向に回転して各感光体４０Ｂ、４０Ｃ、４０Ｍ、４０Ｙ上にそれぞれ、ブラック、シアン、マゼンタ、イエローの単色のトナー像を形成する。そして、中間転写ベルト１の移送とともに、それらの単色のトナー像を転写ローラ６２でトナー像のトナー帯電極性と逆極性の転写電圧を印加中間転写ベルト１の表面上に順次重複させて転写して中間転写ベルト１上に合成カラートナー像を形成する。 When a start switch (not shown) is pressed, the drive roller 14 is driven to rotate by a drive motor (not shown), the support roller 15 is driven to rotate, and the intermediate transfer belt 1 is transported in the direction A for rotation. At the same time, with the image forming units 18B, 18C, 18M, and 18Y, as described above, the respective drum-shaped photoconductors 40B, 40C, 40M, and 40Y are rotated in the directions of the arrows, and the respective photoconductors 40B, 40C, 40M, and 40Y A monochrome toner image of black, cyan, magenta, and yellow is formed on each of them. Then, along with the transfer of the intermediate transfer belt 1, these single color toner images are transferred onto the surface of the intermediate transfer belt 1 by sequentially transferring a transfer voltage having a polarity opposite to the toner charging polarity of the toner image on the surface of the intermediate transfer belt 1. A synthetic color toner image is formed on the intermediate transfer belt 1.

一方、不図示のスタートスイッチを押すと、給紙テーブル２００の給紙ローラ４２の１つを選択回転し、ペーパーバンク４３に多段に備える給紙カセット４４の１つから記録媒体シートＳを繰り出し、分離ローラ４５で１枚ずつ分離して給紙路４６に入れ、搬送ローラ４７で搬送して複写機本体１００内の給紙路４８に導き、レジストローラ４９に突き当てて止める。または、給紙ローラ５０を回転して手差しトレイ５１上の記録媒体シートＳを繰り出し、分離ローラ５２で１枚ずつ分離して手差し給紙路５３に入れ、同じくレジストローラ４９に突き当てて止める。
そして、中間転写ベルト１上の合成カラートナー像にタイミングを合わせてレジストローラ４９を回転し、中間転写ベルト１と２次転写装置２２との間に記録媒体シートＳを送り込み、２次転写装置２２で転写して記録媒体シートＳ上にカラートナー像を記録する。トナー像転写後の記録媒体シートＳは、２次転写装置２２で搬送して定着装置２５へと送り込み、定着装置２５で定着ベルト２６によって加熱され、同時に加圧ローラ２７で加圧されて転写トナー像を定着した後、切換爪５５で切り換えて排出ローラ５６で排出し、排紙トレイ５７上にスタックする。または、切換爪５５で切り換えて記録媒体シートＳをシート反転装置２８に入れ、そこで反転して再び２次転写装置２２の位置へと導き、裏面にもトナー像を記録して後、排出ローラ５６で排紙トレイ５７上に排出する。
一方、画像転写後の中間転写ベルト１は、中間転写体クリーニング装置１７で、トナー像を記録媒体シートＳに転写後に中間転写ベルト１上に残留する残留トナーを除去し、タンデム画像形成装置２０による再度の画像形成に備える。 On the other hand, when a start switch (not shown) is pressed, one of the paper feed rollers 42 of the paper feed table 200 is selectively rotated, and the recording medium sheet S is fed out from one of the paper feed cassettes 44 provided in multiple stages in the paper bank 43. The paper is separated one by one by the separation roller 45 and put into the paper feed path 46, transported by the transport roller 47, guided to the paper feed path 48 in the copying machine main body 100, and abutted against the registration roller 49 and stopped. Alternatively, the sheet feeding roller 50 is rotated to feed out the recording medium sheets S on the manual feed tray 51, separated one by one by the separation roller 52, put into the manual feed path 53, and abutted against the registration roller 49 and stopped.
Then, the registration roller 49 is rotated in synchronization with the composite color toner image on the intermediate transfer belt 1, and the recording medium sheet S is fed between the intermediate transfer belt 1 and the secondary transfer device 22, and the secondary transfer device 22. And a color toner image is recorded on the recording medium sheet S. The recording medium sheet S after the transfer of the toner image is conveyed by the secondary transfer device 22 and sent to the fixing device 25, heated by the fixing belt 26 by the fixing device 25, and simultaneously pressed by the pressure roller 27 to be transferred toner. After fixing the image, the image is switched by the switching claw 55, discharged by the discharge roller 56, and stacked on the discharge tray 57. Alternatively, the recording medium sheet S is switched to the sheet reversing device 28 by switching with the switching claw 55, reversed there and led again to the position of the secondary transfer device 22, and after recording the toner image on the back surface, the discharge roller 56. Is discharged onto the discharge tray 57.
On the other hand, the intermediate transfer belt 1 after image transfer is removed by the intermediate transfer body cleaning device 17 to remove residual toner remaining on the intermediate transfer belt 1 after the toner image is transferred to the recording medium sheet S. Prepare for image formation again.

ここで、本実施形態に係る２次転写装置２２においては、前述のトナー散りと白抜けの発生を抑制するために、トナー散りと白抜け防止機構３０が採用されている。このトナー散りと白抜け防止機構３０について図２〜図４に基づいて説明する。図２は、本発明による一実施形態にトナー散りと白抜け防止機構の概略構成を示す図、図３は、後述するトナー散りと白抜け防止機構における中間転写ベルトと記録媒体シートＳとの密着部距離Ｄと散りトナー数および画像抜け発生率との関係を示すグラフ、図４は、本発明による一実施形態の後述するトナー散りと白抜け防止機構で使用される無端状ベルトの概略構成を示す断面図である。 Here, in the secondary transfer device 22 according to the present embodiment, the toner scattering and white spot prevention mechanism 30 is employed in order to suppress the occurrence of the toner scattering and white spot described above. The toner scattering and white spot prevention mechanism 30 will be described with reference to FIGS. FIG. 2 is a diagram showing a schematic configuration of a toner scattering and white spot prevention mechanism according to an embodiment of the present invention, and FIG. 3 is a diagram showing a close contact between an intermediate transfer belt and a recording medium sheet S in the toner scattering and white spot prevention mechanism described later. FIG. 4 is a graph showing the relationship between the part distance D, the number of scattered toners, and the image loss occurrence rate, and FIG. 4 shows a schematic configuration of an endless belt used in a toner scattering and white spot prevention mechanism described later according to an embodiment of the present invention. It is sectional drawing shown.

本実施形態に係るトナー散りと白抜け防止機構３０においては、図２に明示するように、中間転写ベルト１を張架する対向ローラ１６と、転写手段の一例である転写ローラ３とを中間転写ベルト１を介して対向配置している。そして、転写ローラ３と中間転写ベルト１及び後述する無端状ベルト７を介して対向ローラ１６と圧接する圧接部（ニップ部）５よりも中間転写ベルト１の移送方向（Ａ方向）の上流側の中間転写ベルト部分１Ａの裏面１ｂを無端状ベルト７を介して押圧して、中間転写ベルト部分１Ａを転写ローラ３に移送中の記録媒体シートＳ側に突出させるベルト案内部材８が固定配置されている。従って、中間転写ベルト１は、ベルト案内部材８によって案内されて、中間転写ベルト部分１ＡでＢ方向から搬送された記録媒体シートＳと密着して密着部９を形成し、密着部９によって、前述のような転写ローラ３からの転写電圧の影響によるトナー散りを抑制可能となっている。 In the toner scattering and white spot prevention mechanism 30 according to the present embodiment, as clearly shown in FIG. 2, the counter roller 16 that stretches the intermediate transfer belt 1 and the transfer roller 3 that is an example of a transfer unit are intermediate-transferred. Opposing to each other via the belt 1. The intermediate transfer belt 1 in the transport direction (A direction) is more upstream than the pressure contact portion (nip portion) 5 that is in pressure contact with the opposing roller 16 via the transfer roller 3, the intermediate transfer belt 1, and an endless belt 7 described later. A belt guide member 8 that presses the back surface 1b of the intermediate transfer belt portion 1A through the endless belt 7 and projects the intermediate transfer belt portion 1A to the transfer roller 3 toward the recording medium sheet S is fixedly disposed. Yes. Accordingly, the intermediate transfer belt 1 is guided by the belt guide member 8 and is in close contact with the recording medium sheet S conveyed from the B direction by the intermediate transfer belt portion 1A to form the close contact portion 9. Thus, the toner scattering due to the influence of the transfer voltage from the transfer roller 3 can be suppressed.

また、対向ローラ１６とベルト案内部材８とには、無端状ベルト７が張架されており、中間転写ベルト１の裏面１ｂは、無端状ベルト７を介してベルト案内部材８と圧接してベルト案内部材８によって押圧されるようになっている。そして、無端状ベルト７は、中間転写ベルト１の移送に伴い、矢印Ｅ方向に回転する対向ローラ１６と矢印Ｆ方向に回転する転写ローラ３との圧接によって矢印Ｊ方向に回転移送されるようになっている。従って、中間転写ベルト１の裏面１ｂは、ほぼ同一速度で移送される無端状ベルト７と当接するので、中間転写ベルト１の裏面１ｂがベルト案内部材８との摺接を避けることが可能となって、ベルト案内部材８による中間転写ベルト１の裏面からの摩耗粉の発生を抑制することができる。その結果、摩耗粉による白抜け、即ち画像抜けの発生が抑制されることになる。
ベルト案内部材８は、中間転写ベルト１の裏面１ｂに、無端状ベルト７を介してその全幅に亘って押圧する板状部材より成り、硬質樹脂又は金属などの剛性の大なる材料によって構成されている。そして、かかる案内部材８は、転写ユニットフレーム（図示せず）や、画像形成装置本体のフレームなどに固定支持されている。ここで中間転写ベルト１の裏面１ｂとは、トナー像が転写される表面１ａと反対側の面である。 Further, an endless belt 7 is stretched between the opposing roller 16 and the belt guide member 8, and the back surface 1 b of the intermediate transfer belt 1 is in pressure contact with the belt guide member 8 via the endless belt 7. It is pressed by the guide member 8. The endless belt 7 is rotated and transferred in the arrow J direction by the pressure contact between the opposing roller 16 rotating in the arrow E direction and the transfer roller 3 rotating in the arrow F direction as the intermediate transfer belt 1 is transferred. It has become. Accordingly, the back surface 1b of the intermediate transfer belt 1 comes into contact with the endless belt 7 transported at substantially the same speed, so that the back surface 1b of the intermediate transfer belt 1 can avoid sliding contact with the belt guide member 8. Thus, the generation of abrasion powder from the back surface of the intermediate transfer belt 1 by the belt guide member 8 can be suppressed. As a result, the occurrence of white spots due to wear powder, that is, the occurrence of missing images is suppressed.
The belt guide member 8 is composed of a plate-like member that is pressed across the entire width of the intermediate transfer belt 1 via the endless belt 7 and is made of a highly rigid material such as hard resin or metal. Yes. The guide member 8 is fixedly supported by a transfer unit frame (not shown), a frame of the image forming apparatus main body, or the like. Here, the back surface 1b of the intermediate transfer belt 1 is a surface opposite to the front surface 1a onto which the toner image is transferred.

無端状ベルト７は、図４に示すように、基材７ａの表面に植毛体７ｂが植設されており、この植毛体７ｂが中間転写ベルト１の裏面１ｂと当接するようになっている。従って、無端状ベルト７と中間転写ベルト１の裏面１ｂとの当接は、滑らかな状態で当接し、仮に無端状ベルト７の移送速度と中間転写ベルト１の移送速度にずれが生じたとしても、無端状ベルト７によって中間転写ベルト１の裏面１ｂが摩耗されることを抑制することができる。また、この例の場合、無端状ベルト７の抵抗値を中抵抗（１０^７Ωｃｍ〜１０^１０Ωｃｍ）としている。無端状ベルト７が中抵抗ベルト部材であるため、無端状ベルト７に電荷が溜まることによる異常画像の発生を防ぐことができる。また、抵抗が低すぎないために、転写ローラ３から無端状ベルト７へ電流が逃げてしまうことによる転写不良を防ぐことができる。 As shown in FIG. 4, the endless belt 7 has a flocked body 7 b planted on the surface of the base material 7 a, and the flocked body 7 b comes into contact with the back surface 1 b of the intermediate transfer belt 1. Accordingly, the contact between the endless belt 7 and the back surface 1b of the intermediate transfer belt 1 is in a smooth state, and even if a deviation occurs between the transfer speed of the endless belt 7 and the transfer speed of the intermediate transfer belt 1. The endless belt 7 can prevent the back surface 1b of the intermediate transfer belt 1 from being worn. In this example, the resistance value of the endless belt 7 is set to a medium resistance (10 ⁷ Ωcm to ^{10 10} Ωcm). Since the endless belt 7 is a medium resistance belt member, it is possible to prevent the occurrence of an abnormal image due to the accumulation of electric charge on the endless belt 7. Further, since the resistance is not too low, it is possible to prevent a transfer failure due to the current escaping from the transfer roller 3 to the endless belt 7.

上述の如き無端状ベルト７とベルト案内部材８を圧接部５の入口側Ｉに設けることによって、その無端状ベルト７と圧接部５との間の中間転写ベルト部分１Ａを、記録媒体シートＳの移動方向に対してほぼ平行な状態にすることができ、対向ローラ１６と転写ローラ３とがトナー像の転写時に圧接する圧接部５よりも、中間転写ベルト１の移動方向上流側において、記録媒体シートＳが中間転写ベルト１の表面に当接し始めることができる。このような記録媒体シートＳと中間転写ベルト１との当接タイミングが得られるように、固定配置されたベルト案内部材８が、圧接部５よりも中間転写ベルト１の移動方向上流側の中間転写ベルト部分１Ａの裏面を押圧して、その中間転写ベルト部分を転写ローラ３に移送中の記録媒体シートＳの側へ突出させている。また、本実施形態においては、無端状ベルト７が対向ローラ１６及びベルト案内部材８に張架されており、これにより、前述のＤ寸法を短く保つことができる。無端状ベルト７が少なくとも対向ローラ１６とベルト案内部材８にて張架しているため、圧接部５に無端状ベルト７をより近づけることができ、また、対向ローラ１６に無端状ベルト７を張架した状態にて転写するために、対向ローラ１６に抵抗を持たせる必要がなくなり、コストダウンとなる。 By providing the endless belt 7 and the belt guide member 8 on the inlet side I of the press contact portion 5 as described above, the intermediate transfer belt portion 1A between the endless belt 7 and the press contact portion 5 is placed on the recording medium sheet S. The recording medium can be in a substantially parallel state with respect to the moving direction, and on the upstream side of the moving direction of the intermediate transfer belt 1 with respect to the pressing portion 5 where the opposing roller 16 and the transfer roller 3 are pressed when the toner image is transferred. The sheet S can begin to contact the surface of the intermediate transfer belt 1. In order to obtain such a contact timing between the recording medium sheet S and the intermediate transfer belt 1, the belt guide member 8 that is fixedly arranged is intermediate transfer on the upstream side in the moving direction of the intermediate transfer belt 1 with respect to the press contact portion 5. The back surface of the belt portion 1A is pressed so that the intermediate transfer belt portion protrudes toward the recording medium sheet S being transferred to the transfer roller 3. Further, in the present embodiment, the endless belt 7 is stretched around the opposing roller 16 and the belt guide member 8, whereby the aforementioned D dimension can be kept short. Since the endless belt 7 is stretched by at least the opposing roller 16 and the belt guide member 8, the endless belt 7 can be brought closer to the press contact portion 5, and the endless belt 7 is stretched to the opposing roller 16. Since the transfer is performed in a laid state, it is not necessary to provide resistance to the opposing roller 16 and the cost is reduced.

上記構成により、前述の図６に示した画像形成装置の場合と同様に、圧接部５の近傍に至った転写材部分Ｐ１が転写ローラ３に印加された電圧に基づいて帯電したとき、その部分Ｐ１は中間転写ベルト１の表面に密着しているので、中間転写ベルト１の表面１ａのトナーが転写材部分８の表面に静電的に移行しても、これが飛翔して移行することはない。或いは飛翔するトナーの量は極めて少なくなる。これにより、トナー散りの発生を効果的に抑え、記録媒体シートＳ上に転写されたトナー像の画質を向上させることができる。しかも、図６に示した例では、ガイドローラ４によって上述の作用を得るように構成されているので、前述のように、中間転写ベルト１に静電的に強く密着しない転写材部分６が存在したが、図１及び図２に示した例では、ガイドローラ４ではなく、これとは別のベルト案内部材８を用いて記録媒体シートＳが早期に中間転写ベルト１の表面に当接するように構成したので、中間転写ベルト１に静電的に強く密着しない転写材部分６をなくすことができる。無端状ベルト７及びベルト案内部材８は、ガイドローラ７とは異なり、その形状やサイズ、或いはその設置位置を実質的に自由に設定できるので、中間転写ベルト１に静電的に強く密着しない転写材部分６が存在しなくなるように、圧接部５に至る前に記録媒体シートＳが中間転写ベルト１の表面に密着する密着部９の距離Ｄを設定できるのである。これにより、図６に示した構成の場合に生じていたトナー像の乱れの発生を抑え、記録媒体シートＳ上に転写されたトナー像に画像抜け（所謂白抜け）が発生する不具合を効果的に抑制することができる。 With the above configuration, as in the case of the image forming apparatus shown in FIG. 6 described above, when the transfer material portion P1 that has reached the vicinity of the press contact portion 5 is charged based on the voltage applied to the transfer roller 3, that portion. Since P1 is in close contact with the surface of the intermediate transfer belt 1, even if the toner on the surface 1a of the intermediate transfer belt 1 is electrostatically transferred to the surface of the transfer material portion 8, it does not fly and transfer. . Alternatively, the amount of flying toner is extremely small. Thereby, the occurrence of toner scattering can be effectively suppressed and the image quality of the toner image transferred onto the recording medium sheet S can be improved. In addition, in the example shown in FIG. 6, since the above-described action is obtained by the guide roller 4, there is a transfer material portion 6 that does not adhere to the intermediate transfer belt 1 electrostatically and strongly as described above. However, in the example shown in FIGS. 1 and 2, the recording medium sheet S is brought into contact with the surface of the intermediate transfer belt 1 at an early stage by using a belt guide member 8 other than the guide roller 4 instead of the guide roller 4. Since it is configured, it is possible to eliminate the transfer material portion 6 that is not electrostatically strongly adhered to the intermediate transfer belt 1. Unlike the guide roller 7, the endless belt 7 and the belt guide member 8 can be substantially freely set in shape, size, or installation position thereof, so that the transfer is not electrostatically strongly adhered to the intermediate transfer belt 1. The distance D of the contact portion 9 where the recording medium sheet S adheres to the surface of the intermediate transfer belt 1 before reaching the press contact portion 5 can be set so that the material portion 6 does not exist. This suppresses the occurrence of toner image disturbance that has occurred in the case of the configuration shown in FIG. 6, and effectively eliminates the problem of image omission (so-called white omission) in the toner image transferred onto the recording medium sheet S. Can be suppressed.

上述の距離Ｄは、これが長くなりすぎると、図６に示した画像形成装置のように、転写されたトナー像中に画像抜けが発生しやすくなり、逆にこの距離Ｄが短すぎるとトナー散りが発生しやすくなる。図３は、一方の縦軸に、転写されたフルカラーのライントナー像１０ｍｍにつき発生する散りトナーの数をとり、他方の縦軸に、転写されたトナー像の画像抜けの発生率をとり、横軸には、上記密着部の距離Ｄをとって示したグラフであり、実線Ｘは距離Ｄに対応する散りトナーの数を表わし、鎖線Ｙは距離Ｄに対応する画像抜け発生率を表わしている。このグラフから判るように、圧接部５に至る前に転写材４が中間転写ベルト１の表面に密着する密着部の中間転写ベルト移動方向に沿う距離Ｄが２ｍｍ以上で３０ｍｍ以下、好ましくは５ｍｍ以上で２０ｍｍ以下であると、トナー散りと、画像抜けの発生を共に減少させ、トナー像の画質が高められることを理解できる。 If the distance D is too long, image loss is likely to occur in the transferred toner image as in the image forming apparatus shown in FIG. 6, and conversely if the distance D is too short, the toner scatters. Is likely to occur. In FIG. 3, the vertical axis represents the number of scattered toner generated per 10 mm of the transferred full-color line toner image, and the vertical axis represents the occurrence rate of image omission in the transferred toner image. The axis is a graph showing the distance D of the contact portion. The solid line X represents the number of scattered toners corresponding to the distance D, and the chain line Y represents the image loss occurrence rate corresponding to the distance D. . As can be seen from this graph, the distance D along the intermediate transfer belt moving direction of the contact portion where the transfer material 4 is in close contact with the surface of the intermediate transfer belt 1 before reaching the press contact portion 5 is 2 mm or more and 30 mm or less, preferably 5 mm or more. It can be understood that when the thickness is 20 mm or less, both toner scattering and image omission are reduced, and the image quality of the toner image is improved.

また、図２から判るように、ベルト案内部材８は、中間転写ベルト１の表面側に突出する向きに湾曲面８ａが形成された断面円弧状を有しているが、湾曲面８ａの曲率半径Ｒは、１０ｍｍ以上、好ましくは１５ｍｍ以上に設定されている。曲率半径Ｒをこのように大きく設定することにより、無端状ベルト７によって案内されながら走行する中間転写ベルト１にカールぐせができることを防止し、乃至は抑制でき、中間転写ベルト１のカールぐせに基因するトナー像の転写むらの発生を抑えることができる。
また、無端状ベルト７の裏面に当接する側のベルト案内部材８の湾曲面８ａに植毛処理を施しておくと、その植毛によって、無端状ベルト７とベルト案内部材８とに作用する摩擦力を減少させることができ、無端状ベルト７とベルト案内部材８の経時的な摩耗を効果的に抑制することができる。
なお、本実施形態においては、転写手段として転写ローラ３を使用しているが、スコロトロン等の転写チャージャや、無端状転写ベルトや転写ブラシ等であっても良い。により行っているが、転写装置をチャージャやベルト体としてもよい。 As can be seen from FIG. 2, the belt guide member 8 has a circular arc shape in which a curved surface 8a is formed in a direction protruding toward the front surface side of the intermediate transfer belt 1, but the curvature radius of the curved surface 8a. R is set to 10 mm or more, preferably 15 mm or more. By setting the radius of curvature R to be large in this way, it is possible to prevent or suppress curling of the intermediate transfer belt 1 running while being guided by the endless belt 7, which is caused by curling of the intermediate transfer belt 1. The occurrence of uneven toner image transfer can be suppressed.
In addition, if the curved surface 8a of the belt guide member 8 that is in contact with the back surface of the endless belt 7 is subjected to a flocking treatment, a frictional force acting on the endless belt 7 and the belt guide member 8 is generated by the flocking. Thus, wear with time of the endless belt 7 and the belt guide member 8 can be effectively suppressed.
In this embodiment, the transfer roller 3 is used as a transfer unit, but a transfer charger such as a scorotron, an endless transfer belt, a transfer brush, or the like may be used. However, the transfer device may be a charger or a belt body.

本発明による一実施形態の画像形成装置である複写機の概略構成を示す断面図である。1 is a cross-sectional view illustrating a schematic configuration of a copying machine that is an image forming apparatus according to an embodiment of the present invention. 本発明による一実施形態にトナー散りと白抜け防止機構の概略構成を示す断面図である。1 is a cross-sectional view illustrating a schematic configuration of a toner scattering and white spot prevention mechanism according to an embodiment of the present invention. トナー散りと白抜け防止機構における中間転写ベルトと記録媒体シートＳとの密着部距離Ｄと散りトナー数および画像抜け発生率との関係を示すグラフ図である。FIG. 6 is a graph showing a relationship between a contact distance D between the intermediate transfer belt and the recording medium sheet S in the toner scattering and white spot prevention mechanism, the number of scattered toners, and an image missing rate. 本発明による一実施形態のトナー散りと白抜け防止機構で使用される無端状ベルトの概略構成を示す断面図である1 is a cross-sectional view illustrating a schematic configuration of an endless belt used in a toner scattering and white spot prevention mechanism according to an embodiment of the present invention. 従来の画像形成装置の転写部の構成を示す概略図である。FIG. 10 is a schematic diagram illustrating a configuration of a transfer unit of a conventional image forming apparatus. 従来の他の実施形態に係る画像形成装置の転写部の構成を示す概略図である。FIG. 10 is a schematic diagram illustrating a configuration of a transfer unit of an image forming apparatus according to another conventional embodiment.

Explanation of symbols

１中間転写ベルト、１Ａ中間転写ベルト部分、２対向ローラ、３転写ローラ、４ガイドローラ、５圧接部、６転写材部分、７無端状ベルト、７ｂ植毛体、８ベルト案内部材、８ａ湾曲面、９密着部、１４駆動ローラ、１５支持ローラ、１６対向ローラ、１８Ｂ、１８Ｃ、１８Ｍ、１８Ｙ画像形成手段、２１露光装置、２２２次転写装置、２５定着装置、３７帯電装置、３８Ｂ、３８Ｃ、３８Ｍ、３８Ｙ現像装置、３９クリーニング装置、４０Ｂ、４０Ｃ、４０Ｍ、４０Ｙ感光体 DESCRIPTION OF SYMBOLS 1 Intermediate transfer belt, 1A Intermediate transfer belt part, 2 Opposite roller, 3 Transfer roller, 4 Guide roller, 5 Pressure contact part, 6 Transfer material part, 7 Endless belt, 7b Hair transplant body, 8 Belt guide member, 8a Curved surface, DESCRIPTION OF SYMBOLS 9 Contact part, 14 Drive roller, 15 Support roller, 16 Opposed roller, 18B, 18C, 18M, 18Y Image forming means, 21 Exposure device, 22 Secondary transfer device, 25 Fixing device, 37 Charging device, 38B, 38C, 38M , 38Y Developing device, 39 Cleaning device, 40B, 40C, 40M, 40Y

Claims

An endless image carrier belt that is stretched and driven by a plurality of rollers and forms a toner image on the surface thereof, and is disposed opposite to one of the plurality of rollers via the image carrier belt And a transfer means for applying a transfer voltage having a polarity opposite to the toner charging polarity of the toner image formed on the surface of the image carrying belt, while being in contact with the surface of the image carrying belt and the 1 In an image forming apparatus for transferring a toner image on the surface of an image bearing belt by applying the transfer voltage from the transfer unit onto a transfer material that moves between two rollers.
A transfer material that is moving the image carrier belt portion to the transfer device by pressing the back surface of the image carrier belt portion on the upstream side in the transfer direction of the image carrier belt relative to a region where the one roller and the transfer device are opposed to each other The belt guide member that protrudes toward the side is fixedly arranged,
An endless belt is stretched between the belt guide member and the one roller, and the endless belt is brought into contact with the back surface of the image carrying belt by the belt guide member and the one roller. An image forming apparatus, wherein the endless belt is transferred along with the transfer of the image carrying belt.

The image forming apparatus according to claim 1.
The image forming apparatus, wherein the endless belt has a volume resistance value of 10 ⁷ Ωcm to ^{10 10} Ωcm.

The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein the endless belt has a flocked body formed on a surface in contact with the image carrying belt.

The image forming apparatus according to any one of claims 1 to 3,
The belt guide member has a curved surface that curves in a direction in which the image carrying belt portion protrudes toward the transfer material being transferred to the transfer means, and the curvature radius of the curved surface is set to 10 mm or more. An image forming apparatus.

The image forming apparatus according to claim 4.
The image forming apparatus according to claim 1, wherein the curved surface of the belt guide member has a pressing surface for pressing the entire width of the image carrying belt.

The image forming apparatus according to claim 1,
The image carrying belt has a close contact portion that is in close contact with the transfer material between the belt guide member and the transfer unit, and a length along the moving direction of the image carrying belt of the close contact portion is within 2 mm to 30 mm. An image forming apparatus that is set.

The image forming apparatus according to claim 1,
The transfer means is a transfer roller, and an image on the moving transfer material is applied to the transfer roller by applying a transfer voltage having a polarity opposite to the toner charge polarity of the toner image formed on the surface of the image bearing belt. An image forming apparatus for transferring a toner image on a surface of a carrier belt.

The image forming apparatus according to claim 1,
The image forming apparatus, wherein the image carrying belt is an endless intermediate transfer belt onto which a toner image formed on the surface of a photoreceptor is primarily transferred, and the transfer material is a recording medium.