JP3880459B2 - Image forming apparatus - Google Patents

Description

【００６９】
これらの結果から分かるように、１次転写ローラ５の硬度を柔らかくすることによって、中間転写ベルト７と感光体ドラム１との両者の密着性が向上し、１次転写ローラと中間転写ベルトとの間に生じる空隙をなくし、異常放電を防止することができ、画像不良を防止することができる。
【００７０】
そして、本発明者らの検討の結果、１次転写ローラ５の硬度を変えた時、上記実験結果を示すグラフ中の画像不良発生領域（Ａ）と、画像不良が起きないか若しくは画像不良が実用上問題にならないレベルである領域とを分ける境界線は、θａとＲｍａｘとの１次関数で表される式、
θａ＝Ｂ−０．０１７４×Ｒｍａｘ
におけるＢに影響を及ぼしていることが分かった。即ち、１次転写ローラ５の硬度を柔らかくすることでＢの値が大きくなり、中間転写ベルト７の使用可能領域を広げることができる。
【００７１】
但し、硬度を５°以下にすると、発泡体の場合にはスポンジのセル径を大きくせざるを得ず、セル内での放電劣化や、スポンジ表面と中間転写ベルト７との摺擦による表面劣化を招くため、好ましくない。
【００７２】
次に、１次転写ローラ５の感光体ドラム１に対する加圧力と画像不良との関係について検討を行った。以下の検討は、１次転写ローラ５の硬度を１０°に固定し、加圧力を４．９Ｎと、１４．７Ｎにした時の画像レベルを評価したものである。加圧力４．９Ｎ、１４．７Ｎの時の結果を、それぞれ図６、図７に示す。又、その実験結果を表２にまとめる。
【００７３】
【表２】

【００７４】
これらの結果から分かるように、１次転写ローラ５の感光体ドラム１に対する加圧力を上げることによって、中間転写ベルト７と感光体ドラム１、及び、中間転写ベルト７と１次転写ローラ５との密着性を上げ、画像不良を防止することができる。
【００７５】
そして、本発明者らの検討の結果、１次転写ローラ５の感光体ドラム１に対する加圧力を変えた時、上記実験結果を示すグラフ中の画像不良発生領域（Ａ）と、画像不良が起きないか若しくは画像不良が実用上問題にならないレベルである領域とを分ける境界線は、θａとＲｍａｘとの１次関数で表される式、
θａ＝Ｂ−０．０１７４×Ｒｍａｘ
におけるＢに影響を及ぼしていることが分かった。即ち、１次転写ローラ５の感光体ドラム１に対する加圧力を上げることでＢの値が大きくなり、中間転写ベルト７の使用可能領域を広げることができる。
【００７６】
しかしながら、加圧力を上げ過ぎると、感光体ドラム１の傷が発生するという弊害を招くことがあるため、この弊害とのバランスをとる必要がある。
【００７７】
以上の検討結果から、以下のことが分かった。
（１）画像不良の発生しない中間転写体の表面状態は、Ｒｍａｘとθａとで定義することが有効である。そして、画像不良が発生する領域と、中間転写体の使用可能領域とを分ける境界線は、
θａ＝Ｂ−０．０１７４×Ｒｍａｘ（Ｂは係数） ・・・（１）
の関係式で表される。
（２）上記式１中の係数Ｂは、１次転写部材の硬度と、１次転写部材の像担持体に対する加圧力とにより定義される。
【００７８】
次に、１次転写部材の硬度と、１次転写部材の像担持体に対する加圧力との関数である、上記式１中の係数Ｂについて更に考察する。
【００７９】
上記結果（図４〜図７）にあるように、係数Ｂは、１次転写部材の硬度が低い程、又加圧力が高い程大きくなる１次関数的挙動を示すため、アスカーＣ硬度をＲ（°）、加圧力をＰ（Ｎ）とすると、係数Ｂは下記式、
Ｂ＝α×（Ｐ＋γ）／（Ｒ＋β） （但しα、β、γは係数） ・・・（２）
で表されると考えられる。
【００８０】
上記式２中の係数α、β、γの値を、既にＢ、Ｐ、Ｒの各値が分かっている、上記検討結果におけるθａとＲｍａｘとの複数の境界線（図３〜７に示されている。）に当てはめて、３元１次方程式で求めると、α＝２．３５５、β＝９４．２、γ＝１１．４となる。
よって、係数Ｂは下記式、
Ｂ＝２．３５５×（Ｐ＋１１．４）／（Ｒ＋９４．２）
となる。
【００８１】
よって、中間転写体の使用可能境界線を表す式は、下記式、
θａ＝２．３５５×（Ｐ＋１１．４）／（Ｒ＋９４．２）−０．０１７４×Ｒｍａｘ
のように表すことができる。
【００８２】
これらの結果から、画像不良の発生を防止するために必要な、中間転写体の表面粗さの指標を表すθａとＲｍａｘとの関係は、下記式、
θａ＜２．３５５×（Ｐ＋１１．４）／（Ｒ＋９４．２）−０．０１７４×Ｒｍａｘ
Ｐ：転写部材の像担持体への加圧力（Ｎ）
Ｒ：転写部材のアスカーＣ硬度（°）
となる。
【００８３】
ところで、例えば上記検討に用いた画像形成装置１００において、θａが０．００５より小さくなると、１次転写ニップＴ近傍での空気抜けの空隙がなく画像が尾引いたり、又、感光体ドラム１と中間転写ベルト７との接触面積が過大になり、中間転写ベルト７の表面上にトナーが付着固着する、所謂、フィルミング現象が発生し、その部分が転写抜けする画像不良が発生した。従って、θａは０．００５以上にすることが好ましい。
【００８４】
つまり、θａは、以下に示す範囲内にすることが好ましい。
【００８５】
０．００５≦θａ＜２．３５５×（Ｐ＋１１．４）／（Ｒ＋９４．２）−０．０１７４×Ｒｍａｘ
（但し、Ｒｍａｘは２０μｍ以下）
【００８６】
尚、上記条件により、実用上問題とならない程度まで画像不良を回避することができるが、より好ましくは、この実用上問題とならない程度の軽微な画像不良が発生する領域をも除くように、更に、Ｒｍａｘ≦１２（μｍ）、且つ、θａ≦０．２４（°）に規定する。これにより、実質的に画像不良が全く起きない中間転写体の表面形状の条件を規定することが可能である。
【００８７】
以下に、θａ、Ｒｍａｘ、表面抵抗率、体積抵抗率の定義及び測定についての説明を行う。
【００８８】
平均傾斜角θａは、図２に示したように、基準長さＷの範囲内における、凹凸の高さの変化（Ｈ₁、Ｈ₂、・・・）の和を、前記基準長さで割った値を角度単位で表したものである。即ち、基準長さが同じ時に平均傾斜角θａが大きいほど、表面の凹凸がより急峻であることを表している。
【００８９】
【数１】

【００９０】
更に、θａは基準長さ内での凹凸の全ての極大点、極小点を検出し、それらの高低差を全て加算して導出する値であるから、表面が粗く、凹凸の数が多いほどθａの値は大きくなるという特徴を併せ持つ指標である。つまり、平均傾斜角θａが小さい値であることは、凹凸の頻度が低く、且つ、数少ない表面の凹凸がなだらかであるということ、即ち、表面性に優れた材質であることを意味する。
【００９１】
このように、本発明によれば、凹凸の高さを最大高さＲｍａｘで規定し、一方、最大高さのみでは表現できない表面の凹凸の広がりを平均傾斜角θａという指標で規定する。
【００９２】
（測定方法）
上記各実験例における中間転写ベルト７（Ｉ、ＩＩ、ＩＩＩ）の特性、即ち、最大高さＲｍａｘ、平均傾斜角θａ、体積抵抗率及び表面抵抗率の測定は、以下に従って行った。
（１）最大高さＲｍａｘ、平均傾斜角θａ
Ｓｕｒｆｃｏｒｄｅｒ ＳＥ−３４００（小坂研究所製）にて、評価長さ（基準長さ）２．５ｍｍ、送り速さ０．５ｍｍ、フィルタ２ＣＲ、カットオフλｃ０．８ｍｍの条件にもとに測定を行った。３回測定を行い、それらの加算平均を測定値とした。
（２）表面抵抗率、体積抵抗率
デジタル超高抵抗計Ｒ８３４０Ａ（アドバンテスト社製、プローブは同社製Ｒ１２７０２Ａを用いた）にて、１０秒除電した後、印加電圧１００Ｖにて１０秒印加した後の表面抵抗率を測定した。測定環境は２３℃、５０％ＲＨ。測定は同一ベルトのうち６箇所について行った。
【００９３】
以上、本実施例の如く、中間転写ベルト７の最大高さＲｍａｘのみならず、平均傾斜角度θａをも規定することで、中間転写ベルト７の表面形状による画像劣化を回避して、高品位画像を形成することができる。
【００９４】
尚、本発明は、図８を参照して説明したような、像担持体に順次形成される各色成分の画像情報に応じた静電潜像を、複数の現像手段によって順次トナー像として現像し、このトナー像を中間転写体上に積層して転写し、その後一括して転写材に転写する画像形成装置にも当然適用可能である。
【００９５】
又、上記実施例では、中間転写体はベルト状であるとして説明したが、本発明はこれに限定されるものではない。上述のように、ベルト状の中間転写体によって装置設計の自由度が高まり、装置の小型化、省スペース性の点で優れている。しかし、当業者には周知のように、中間転写体として、ドラム状基材を上記中間転写ベルトと同様の材料で被覆したり、或いはドラム形状の外縁部を形成する枠体に上記中間転写ベルトと同様の材料からなるシート部材を張設して構成される中間転写ドラムを採用する場合にも、本発明を適用することができ、同様の効果を得ることができる。
【００９６】
更に、本発明は、像担持体の帯電方式、像露光方式、現像方式などを何ら上記実施例のものに限定するものではない。
【００９７】
【発明の効果】
以上説明したように、本発明によれば、中間転写体を挟んだ像担持体と転写部材との接触を一様にし、中間転写体の表面形状による画像不良を回避して、高品位画像を形成し得る画像形成装置を提供することができる。
【図面の簡単な説明】
【図１】本発明を適用し得る画像形成装置の一例の概略構成図である。
【図２】中間転写体の転写面を形成する材料の表面形状を表す平均傾斜角θａを説明するための図である。
【図３】実験例の結果を示すグラフ図である。
【図４】実験例の結果を示すグラフ図である。
【図５】実験例の結果を示すグラフ図である。
【図６】実験例の結果を示すグラフ図である。
【図７】実験例の結果を示すグラフ図である。
【図８】本発明を適用し得る画像形成装置の他の例の概略構成図である。
【図９】従来の画像形成装置における課題を説明するための、（ａ）中間転写体、（ｂ）１次転写部を示す模式図である。
【図１０】従来の画像形成装置における課題を説明するための中間転写体の突起と転写電界との関係を示す模式図である。
【図１１】従来の画像形成装置における課題を説明するための（ａ）ベタ画像における画像不良、（ｂ）ハーフトーン画像における画像不良を示す模式図である。
【符号の説明】
１ 像担持体
２ 帯電手段
３ 露光手段
４ 現像手段
５ １次転写部材
６，７ 中間転写体（中間転写ベルト）
８ ２次転写手段
９ 定着手段[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic system, an electrostatic recording type copying machine, a facsimile, a printer, and the like, and more particularly, an intermediate transfer system for transferring an image formed by a developer formed on an image carrier to an intermediate transfer body. The present invention relates to an image forming apparatus.
[0002]
[Prior art]
Conventionally, for example, an image forming apparatus as shown in FIG. 8 is known as an electrophotographic image forming apparatus.
[0003]
The image forming apparatus 200 of FIG. 8 includes a drum-type electrophotographic photosensitive member that is an image carrier, that is, a photosensitive drum 1. The photosensitive drum 1 is rotatably supported and is driven to rotate in the direction of the arrow in the drawing by a driving means (not shown). Around the photosensitive drum 1, a charging unit 2, an exposure unit 3, a developing unit 4, and a cleaning unit 10 are provided. Further, an intermediate transfer belt 6 as an intermediate transfer member is provided adjacent to the photosensitive drum 1, and a primary transfer member 5 is disposed opposite to the intermediate transfer belt 6.
[0004]
The photoreceptor drum 1 is configured by forming an organic photoreceptor (OPC) layer on the outer peripheral surface of a cylindrical aluminum cylinder. The charging roller 2 is configured by providing a conductive rubber layer and a medium resistance surface layer on a mandrel. The charging roller 2 is disposed in contact with the surface of the photosensitive drum 1, and a DC bias and a superimposed bias (charging bias) of an AC bias are applied to the charging roller 2 to uniformly charge the surface of the photosensitive drum 1. Let The exposure unit 3 emits a laser beam in accordance with a signal according to image information input to the laser driver, and irradiates the uniformly charged surface of the photosensitive drum 1. As a result, an electrostatic latent image is formed on the surface of the photosensitive drum 1.
[0005]
The developing means 4 is a rotatable rotary developer that stores developing devices 4Y, 4M, 4C, and 4K that develop toner images of yellow (Y), magenta (M), cyan (C), and black (K) colors. It is a vessel. When developing the electrostatic latent image of each color component, the rotary developer 4 rotates to move the developer containing the developer of each color component to a position facing the photosensitive drum 1. As a result, a developer of a color corresponding to the electrostatic latent image of each color component is attached to form a developer image (toner image).
[0006]
The intermediate transfer belt 6 is stretched around four rollers including a driving roller 61, a tension roller 62, a driven roller 63, and a primary transfer roller 5, and is moved (rotated and driven) in the direction of the arrow in the figure. The photosensitive drum 1 is formed on the photosensitive drum 1 by applying a primary transfer electric field to a primary transfer roller 5 as a primary transfer member disposed at a position facing the photosensitive drum 1 across the intermediate transfer belt 6. The toner image of each color component is sequentially transferred onto the intermediate transfer belt 6. Further, a secondary transfer roller 8 as a secondary transfer unit is disposed at a position facing the driven roller 63 with the intermediate transfer belt 6 interposed therebetween. Then, by applying a secondary transfer electric field to the secondary transfer roller 8, the toner images stacked on the intermediate transfer belt 6 are collectively transferred onto the transfer material S.
[0007]
The cleaning means 10 for the photosensitive drum 1 is disposed downstream of the primary transfer portion T in the driving direction of the photosensitive drum 1, and is not transferred to the intermediate transfer belt 6 in the primary transfer portion T and is transferred to the photosensitive drum 1. The remaining transfer residual toner is removed.
[0008]
The cleaning means 11 for the intermediate transfer belt 6 is disposed downstream of the secondary transfer portion T ′ in the driving direction of the intermediate transfer belt 6, and is not transferred to the transfer material S at the secondary transfer portion T ′. The toner remaining on the transfer is removed.
[0009]
The fixing unit (fixing device) 9 has two rollers, a fixing roller 91 and a pressure roller 92, and fixes the toner image transferred to the transfer material S by heating and pressing.
[0010]
The operation of the image forming apparatus 200 having the above configuration will be further described. First, the photosensitive drum 1 is rotationally driven in the direction of the arrow in the figure, and a charging bias is applied to the charging roller 2 to make the surface of the photosensitive drum 1 uniform. Charge. Next, as the first color, for example, in accordance with image information of a yellow (Y) color component, the exposure unit 3 exposes the photosensitive drum 1 to form a yellow component electrostatic latent image. Here, the rotary developing device 4 is rotated, and the yellow developing device 4Y containing yellow toner as a developer is disposed at a position facing the photosensitive drum 1. Usually, a superimposed bias (development bias) of DC and AC voltage is applied to the developer carrying member (developing roller) provided in the yellow developing device 4Y, and yellow toner is applied to the electrostatic latent image on the photosensitive drum 1. This is adhered to form a yellow toner image. Next, the yellow toner image formed on the photosensitive drum 1 is transferred onto the intermediate transfer belt 6 by applying a primary transfer bias to the primary transfer roller 5.
[0011]
Similarly, magenta (M), cyan (C), and black (K) color component toner images are sequentially formed on the photosensitive drum 1 and then sequentially transferred and laminated on the intermediate transfer belt 6. A four-color toner image is formed thereon.
[0012]
On the other hand, the transfer material S stored in the cassette 12 serving as a transfer material storage unit is separated and supplied into the apparatus by the pickup roller 13 and transferred to the intermediate transfer belt 6 by the conveying roller pair 14 and the registration roller pair 15. In synchronization with the toner image, the toner image is conveyed to the secondary transfer portion T ′.
[0013]
In this way, the four color toner layers on the intermediate transfer belt 6 are transferred at a predetermined timing by applying a secondary transfer bias to the secondary transfer roller 8 in the secondary transfer portion T ′. Are collectively transferred.
[0014]
The toner image transferred to the transfer material S is fixed by the fixing device 9 and becomes a full-color permanent image. Thereafter, the transfer material S is discharged out of the apparatus by the conveying roller pair 16, the discharge roller pair 17, and the like.
[0015]
Prior to the use of the intermediate transfer type image forming process as described above, multiple transfer in which each color toner image is sequentially transferred and stacked on a transfer material electrostatically adsorbed onto a transfer material conveyance means such as a conveyance belt. The method was adopted. In such a multiple transfer system of toner images onto a transfer material, the image quality is excellent in the material properties of the transfer material, such as the size, thickness, surface roughness of the transfer material, and non-uniformity due to the presence of voids in the transfer material. The evil was heavily dependent.
[0016]
On the other hand, according to the intermediate transfer method, since the toner layer is laminated on the intermediate transfer body based on the resin, which is more uniform as a material, it is possible to avoid image deterioration due to material characteristics of the transfer material. The image quality can be improved.
[0017]
There are mainly two types of intermediate transfer members, a drum body and a belt body. In particular, by selecting a belt body, the degree of freedom in designing the machine body is increased, so that a reduction in size and space saving of the image forming apparatus can be expected.
[0018]
[Problems to be solved by the invention]
However, even in the intermediate transfer method, the uniformity of the material of the intermediate transfer member to which the toner image is transferred in the primary transfer is required.
[0019]
Taking the intermediate transfer belt as an example, for example, from the viewpoint of the surface roughness of the intermediate transfer belt, if the surface roughness is large, as shown in FIG. Will do. At this time, as shown in FIG. 9B, for example, the photosensitive drum and the primary transfer roller are not uniformly contacted with the intermediate transfer belt between the protrusions, so that the transfer electric field is insufficient. There is a risk of becoming.
[0020]
As shown in FIG. 10, the transfer efficiency of dots forming an image is lowered at a location where a transfer electric field shortage occurs as described above. For example, in the case of a solid image, as shown in FIG. 11A, there is a possibility that an image having a locally low density (shaded portion) may be formed. In particular, when a halftone image is formed with small dots of area gradation, if there is a wide area where the transfer electric field is insufficient at the location where the protrusion of the intermediate transfer belt is present, as shown in FIG. Such small dots are not transferred at all, and there is a risk of image defects due to dot-like white spots in the halftone image.
[0021]
The present invention has been made in view of the above circumstances. That is, an object of the present invention is to form a high-quality image by making the contact between the image carrier and the transfer member sandwiching the intermediate transfer member uniform, avoiding image defects due to the surface shape of the intermediate transfer member. An image forming apparatus is provided.
[0022]
[Means for Solving the Problems]
  The above object is achieved by the image forming apparatus according to the present invention. In summary, The present inventionIs
  An image carrier for carrying a developer image;
  Image forming means for forming a developer image on the image carrier;
  An intermediate transfer member to which a developer image on the image carrier is transferred;
  The developer image on the image carrier is disposed at a position opposite to the image carrier via the intermediate transfer member, and presses the intermediate transfer member toward the image carrier and is applied with a voltage. Is primarily transferred to the intermediate transfer member.PrimaryA transfer member;
  The developer image on the intermediate transfer member is secondarily transferred to a transfer material.SecondaryTranscription means;
In an image forming apparatus having
  The maximum height representing the surface shape of the intermediate transfer body onto which the developer image is transferred is Rmax (μm),
  The average inclination angle representing the surface shape of the intermediate transfer member onto which the developer image is transferred is θa (°),
  The pressing force of the primary transfer member against the intermediate transfer member is P (N),
  Asker C hardness of the primary transfer member is R (°),
When
0.005 ≦ θa <2.355 × (P + 11.4) / (R + 94.2) −0.0174 × Rmax
An image forming apparatus characterized by satisfying the above relationship.
[0024]
  The present inventionAccording to one embodiment, the maximum height Rmax is in a range of 20 (μm) or less, and,otherAccording to the embodiment, the ten-point average roughness Rz (μm) representing the surface shape of the intermediate transfer body onto which the developer image is transferred is in the range of 0.05 (μm) to 10 (μm).
[0025]
  The present inventionAccording to another embodiment, the volume resistivity of the intermediate transfer member is 10⁶(Ω · cm) or more, 10¹²(Ω · cm) or less, and according to another embodiment, the intermediate transfer member has a surface resistivity of 10⁸(Ω / □) or more, 10¹⁴(Ω / □) The following range.
[0026]
  The present inventionThe intermediate transfer member may be belt-shaped. In one embodiment, the intermediate transfer member is formed of a polyimide resin. In the present invention,PrimaryThe transfer member may have a roller shape.
[0027]
  The present inventionThe image forming apparatus includes: the image carrier, the image forming unit, and thePrimaryA plurality of transfer members, and sequentially transferring the developer images formed on the respective image carriers on the intermediate transfer member in order,SecondarySecondary transfer may be collectively performed on a transfer material by a transfer unit.
[0028]
DETAILED DESCRIPTION OF THE INVENTION
The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.
[0029]
Example 1
An example of an image forming apparatus to which the present invention can be applied will be described with reference to FIG. An image forming apparatus 100 in FIG. 1 is an electrophotographic color image forming apparatus (color laser printer).
[0030]
In the image forming apparatus 100 shown in FIG. 1, each color component of yellow (Y), magenta (M), cyan (C), and black (K) is sequentially arranged in the moving direction along the flat portion of the intermediate transfer belt 7. The image forming units Py, Pm, Pc, and Pk, which are the image forming units, are disposed. Since the basic configuration of each image forming unit is the same, the details of the image forming unit will be described only for the yellow image forming unit Py.
[0031]
The yellow image forming unit Py has a drum-type electrophotographic photosensitive member (photosensitive drum) 1Y as an image carrier. The photoconductor drum 1Y is formed by laminating a photoconductor layer, a charge transport layer, and a surface protective layer using an aluminum cylinder having a diameter of 30 mm as a base layer. The surface protective layer is made of a material in which fine particles of tin oxide are dispersed in a photo-curable acrylic resin, and the surface of the photoreceptor drum 1Y is uniformly charged by injecting electric charges.
[0032]
The yellow image forming unit Py includes a charging roller 2Y which is a charge injection charger as a charging unit. By applying a charging bias in which a DC bias of −700 V and an AC bias of 1.5 kVp-p are superimposed on the charging roller 2Y, the surface of the photosensitive drum 1Y is uniformly charged to −700V.
[0033]
Above the photosensitive drum 1Y, a laser beam scanner 3Y as image exposure means is disposed. The laser beam scanner 3Y scans and exposes the surface of the uniformly charged photoreceptor drum 1Y according to image information, and forms an electrostatic latent image of a yellow color component on the surface.
[0034]
The electrostatic latent image formed on the photosensitive drum 1Y is developed with toner as a developer by the developing unit 4Y. That is, the one-component non-magnetic contact developer 4Y as the developing means includes a developing roller 4Ya as a developer carrying member, a regulating blade 4Yb as a developer amount regulating member, and a non-magnetic one-component developer as a developer. Contains yellow toner. The developing roller 4Ya supplied with the yellow toner is in light pressure contact with the photosensitive drum 1Y in the developing portion, and is rotated with a speed difference in the forward direction with respect to the photosensitive drum 1Y. The yellow toner conveyed to the developing unit by the developing roller 4Ya adheres to the electrostatic latent image formed on the photosensitive drum 1Y by applying a developing bias of −300 V to the developing roller 4Ya. As a result, a visible image (yellow toner image) is formed on the photosensitive drum 1Y.
[0035]
In this embodiment, an image forming unit for forming a developer image on an image carrier is constituted by a charging roller 2Y as a charging unit, a laser beam scanner 3Y as an exposure unit, and a developing device 4Y as a developing unit.
[0036]
The intermediate transfer belt 7, which is an intermediate transfer body, is stretched around a driving roller 71, a tension roller 72, and a driven roller 73. ] (Rotation drive). The yellow toner image that has reached the primary transfer portion (primary transfer nip) Ty is a primary transfer roller serving as a primary transfer member that is pressed against the photosensitive drum 1Y via the intermediate transfer belt 7. The image is transferred onto the intermediate transfer belt 7 by 5Y. The primary transfer roller 5Y has a volume resistivity of 10 by dispersing carbon black in EPDM rubber.^FiveWhat was made into the roller shape by making it electrically conductive so that it would be about Ω · cm was used. Then, for example, about 500 V is applied to the primary transfer roller 5Y as a primary transfer bias by constant voltage control.
[0037]
Similarly, the image forming operation described above is performed in each of the magenta (M), cyan (C), and black (K) units Pm, Pc, and Pk as the intermediate transfer belt 7 is moved. Four color toner images of yellow, magenta, cyan, and black are stacked. The four color toner layers are conveyed along with the movement of the intermediate transfer belt 7 and are transferred onto the transfer material S conveyed at a predetermined timing by the secondary transfer roller 8 as the secondary transfer means in the secondary transfer portion T ′. Batch transfer. The secondary transfer roller 8 is made of foamed rubber similar to the primary transfer rollers 5Y, 5M, 5C, and 5K, and has a volume resistivity of 10⁸The resistance is adjusted to be about Ω · cm. For example, 3 kV is applied to the secondary transfer roller 8 as a secondary transfer bias by constant voltage control.
[0038]
The transfer material S is stored in a cassette 12 which is a transfer material storage portion, separated and supplied into the apparatus by a pickup roller 13, and transferred to the intermediate transfer belt 7 by a conveying roller pair 14 and a registration roller pair 15. In synchronization with the toner image, the toner image is conveyed to the secondary transfer portion T ′.
[0039]
The toner image transferred to the transfer material S is fixed by the fixing device 9 and becomes, for example, a full-color permanent image. The fixing device 9 includes a fixing roller 91 including a heating unit and a pressure roller 92, and fixes the unfixed toner image on the transfer material S by heating and pressing.
[0040]
Thereafter, the transfer material S is discharged out of the apparatus by the conveying roller pair 16, the discharge roller pair 17, and the like.
[0041]
A cleaning blade 11 as a cleaning unit for the intermediate transfer belt 7 is disposed downstream of the secondary transfer portion T ′ in the driving direction of the intermediate transfer belt 7 and is transferred to the transfer material S at the secondary transfer portion T ′. Instead, the transfer residual toner remaining on the intermediate transfer belt 7 is removed. Further, the transfer residual toner remaining on each of the photosensitive drums 1Y to 1K after the transfer of the toner image is removed by a cleaning unit or collected in each of the developing units 4Y to 4K when a cleaner-less mechanism is used. Is done.
[0042]
The charging potential, the developing bias, the primary transfer bias, and the secondary transfer bias vary depending on the external environment such as temperature and humidity, the type of the transfer material S, and the like, and are limited to the above values. is not.
[0043]
The intermediate transfer belt 7 can be manufactured using a resin material such as polyimide, ethylene-tetrafluoroethylene copolymer (ETFE), polyvinylidene fluoride (PVdF), polycarbonate (PC), or polyethylene terephthalate (PET). it can.
[0044]
In this embodiment, the intermediate transfer belt 7 is made of a polyimide resin as a base and has a thickness of 80 μm. In particular, when the polyimide used in this example is used as a material, the polyamic acid solution is coated on the outer peripheral surface or inner peripheral surface of a cylindrical mold by a dipping method, a centrifugal method, a coating method, etc., and dried. It can be prepared by filming and heat treatment to imidize the polyamic acid. Of course, the present invention does not limit the method for producing the intermediate transfer member. Further, the surface shape (surface roughness) of the surface to which the image of the intermediate transfer belt 7 is transferred is adjusted by the surface roughness of the mold when the intermediate transfer belt is molded, the firing temperature during the heat treatment, and the like. Can do.
[0045]
Further, the resistance of the intermediate transfer belt 7 of this embodiment was adjusted by dispersing carbon black. The volume resistivity of the intermediate transfer belt 7 is 10⁶-10¹²It is in the range of Ω · cm, and the surface resistivity is 10⁸-10¹⁴It is preferably in the range of Ω / □. The volume resistivity of the intermediate transfer belt 7 is 10¹²If it exceeds Ω · cm, the intermediate transfer belt 7 may be charged up and cause image defects when continuously driven. In order to prevent this, it is necessary to provide a static elimination mechanism, which leads to a complicated configuration and an increase in cost. On the other hand, the volume resistivity of the intermediate transfer belt 7 is 10⁶If it is smaller than Ω · cm, for example, a bias flows to an unintended adjacent primary transfer portion in the primary transfer portions Ty to Tk, which may cause image defects due to insufficient transfer bias.
[0046]
10¹⁴Since the intermediate transfer belt 7 having a high surface resistivity exceeding Ω / □ has a high charge holding capability, it peels off when the transfer material S leaves the intermediate transfer belt 7 after passing through the secondary transfer portion T ′. There is a possibility that electric discharge occurs and an image defect occurs. Meanwhile, 10⁸In the intermediate transfer belt 7 having a surface resistivity smaller than Ω / □, for example, toner may be scattered in an unintended place when a dot image is formed. This is a phenomenon in which the toner that forms the edge of the dot scatters due to the transfer electric field wrapping around the area where the toner is not present due to the presence of the lower layer toner. This phenomenon causes the lower limit of the surface resistivity of the intermediate transfer belt 7 to be 10%.⁸It can be avoided by setting Ω / □.
[0047]
Further, since the intermediate transfer belt 7 removes the transfer residual toner that has not been transferred to the transfer material S at the secondary transfer portion T ′ by bringing a cleaning means such as a cleaning blade 11 into contact therewith, the intermediate transfer belt 7 has a sufficient surface. It is preferable to manufacture such that the point average roughness Rz (based on JIS B 0601. The same applies hereinafter) is 0.05 μm or more and 10 μm or less. More preferably, the ten-point average roughness Rz is 2 μm or more and 10 μm or less. The smooth intermediate transfer belt 7 having an Rz smaller than 0.05 μm has a problem that the cleaning blade 11 is turned over, particularly in a high humidity environment. On the other hand, in the intermediate transfer belt 7 in which Rz exceeds 10 μm, toner particles may enter the surface irregularities, and cleaning failure may occur.
[0048]
Hereinafter, the relationship between the surface property of the intermediate transfer belt 7 and the occurrence of image defects will be described in more detail with reference to some experimental examples. Here, three types of intermediate transfer belts 7 (I, II, and III) having different surface properties are put into the above-described image forming apparatus 100, and conditions under which image defects due to the surface property of the intermediate transfer belt 7 can be prevented. investigated. In the following description, regarding elements common to the image forming units Py, Pm, Pc, and Pk, a subscript Y (y indicating that the element belongs to each image forming unit, unless particularly distinguished. ), M (m), C (c), and K (k) are omitted.
[0049]
As an index representing the surface shape of the surface onto which the image of the intermediate transfer belt 7 is transferred, a maximum height Rmax (conforming to JIS B 0601, the same applies hereinafter) as shown in FIG. 2 and an average inclination angle θa were measured. . A method for measuring the maximum height Rmax, the average inclination angle θa, the volume resistivity, and the sheet resistivity will be described later.
[0050]
Explaining the setting of conditions at the time of examination, the intermediate transfer belt 7 and the primary transfer roller 5 having the following specifications were used.
Intermediate transfer belt 7 (I, II, III)
Material: Semiconductive polyimide resin
Thickness: 80 μm
Volume resistivity: 10⁹Ω · cm
Surface resistivity: 10¹²Ω / □
Elastic modulus: 5GPa
・ Primary transfer roller 5
Material: Semi-conductive urethane sponge
Outer diameter: φ16 (core metal φ8)
Resistance value: 10⁶Ω (when applied voltage is 50V)
Hardness: 10 ° (ASKER C hardness (hereinafter the same); load 49N)
The pressure applied to the photosensitive drum 1 by the primary transfer roller 5 via the intermediate transfer belt 7 was 7.8N.
[0051]
Three intermediate transfer belts 7 (I, II, III) are inserted into the image forming apparatus 100 having the above specifications, and a halftone image having a density of 0.3 to 0.6 (measured by Xrite 404 manufactured by Xrite). A3 size recording paper CLC80 (Nippon Paper Industries basis weight 80g / m²) When 10 sheets were output continuously (to form a toner image on the entire surface of the intermediate transfer belt), it was confirmed that image defects occurred at several locations corresponding to the position of the intermediate transfer belt 7 (output 10 sheets continuously) Therefore, the image defect repeated at the cycle of the intermediate transfer belt was confirmed.)
[0052]
At this time, on the surface of the intermediate transfer belt 7, the protrusions of the I belt, the II belt, the II belt, the III belt, and the III belt are visually checked, and marking is performed with tracing paper. Identification of the occurrence point of Furthermore, the maximum height Rmax and the average inclination angle θa were measured for these marking locations.
[0053]
Then, image evaluation was performed using these intermediate transfer belts 7, and the state of the image corresponding to the marking portion was visually observed to evaluate the level of image failure.
[0054]
FIG. 3 shows the relationship between the image defect level and the index θa representing the surface roughness of the intermediate transfer belt 7 and Rmax. In the figure, ◯ indicates that no image defect occurred, △ indicates that a minor image defect has occurred but is acceptable level for practical use, and ▲ indicates that an unacceptable level image defect has occurred. , Respectively. In this study, it is possible to determine that white spots are approximately φ200 μm or more, but the appearance may vary depending on the minimum dot diameter of the image, the image processing method, and the like.
[0055]
Conventionally, it has been known that an image defect occurs unless the surface roughness of the intermediate transfer member is set to a predetermined value or less.
[0056]
For example, Japanese Patent Application Laid-Open No. 8-160763 discloses that the sum of the maximum height Rmax of the first image carrier (photosensitive drum) and the maximum height Rmax of the intermediate transfer member is 20 μm or less.
[0057]
Japanese Patent Laid-Open No. 7-271201 discloses that the surface roughness of the intermediate transfer member is such that Rz, which is a ten-point average roughness substantially the same as the size of the toner particles, is 5 μm or more and 20 μm or less. .
[0058]
As shown in FIG. 3, as a result of the above-described experiment, it is found that the maximum height Rmax is 29.00 μm (θa is 0.577 °), and an image defect occurs at the protrusion having the maximum height exceeding 20 μm. As a result of the above-mentioned results and further studies by the present inventors, it has been found that the surface roughness of the surface on which the image of the intermediate transfer member is transferred preferably has a maximum height Rmax of 20 μm or less.
[0059]
On the other hand, Japanese Patent Application Laid-Open No. 2000-155476 discloses an intermediate transfer member from the viewpoint that if the surface roughness of the transfer surface of the intermediate transfer member is large, toner particles enter the irregularities of the intermediate transfer member and transfer properties deteriorate. The transfer surface has a center line average roughness Ra of 0.35 μm or less and a maximum height Rmax of 5 μm or less.
[0060]
However, from the results of the above experimental examples, for example, the maximum height Rmax is 13.51 μm (θa is 0.118 °), and the protrusions (intermediate transfer belt) having a surface roughness smaller than that of the toner particles used in this embodiment. It can be seen that even with the measured value (II), a slight image defect occurs although it is not a practical problem.
[0061]
Based on the above results, the present inventors have conducted many experimental studies, and as a condition for preventing image defects, in addition to defining the maximum height Rmax of the protrusion on the surface of the intermediate transfer member, the shape of the protrusion (spreading) It has been found that it is necessary to define θa representing a state as in FIG.
[0062]
In FIG. 3, when the occurrence state of the image defect was examined, it was found that the area (A) indicated by the hatched portion in FIG. 3 was the image defect occurrence area. The boundary line of this region can be substantially expressed by a linear function of Rmax and θa.
[0063]
That is, a part other than the region (A) indicated by the hatched portion in FIG.
θa <0.434−0.0174 × Rmax
In this area, it can be said that no image defect occurs or the image defect does not cause a practical problem.
[0064]
As described above, in the image forming apparatus 100 used for the above-described examination, the maximum height Rmax ≦ 20 μm of the intermediate transfer belt 7 and the average inclination angle θa <0.434−0.0174 × Rmax are set. Image defects caused by the material of the intermediate transfer belt 7 such as white spots in the tone image can be avoided.
[0065]
The inventors of the present invention have further studied the relationship between the surface shape of the intermediate transfer member and the image defect as a factor that affects the close contact state between the intermediate transfer member and the image carrier. Focusing on the hardness and pressing conditions, the following investigations were made.
[0066]
First, in the image forming apparatus 100 used for the above examination, the pressure applied to the photosensitive drum of the primary transfer roller 5 as a primary transfer member is fixed at 7.8 N, and the hardness is two types other than the above (35 °). , 20 °).
[0067]
The results when the hardness is 35 ° and 20 ° are shown in FIGS. 4 and 5, respectively. The above experimental results are summarized in Table 1.
[0068]
[Table 1]

[0069]
As can be seen from these results, by softening the hardness of the primary transfer roller 5, the adhesion between the intermediate transfer belt 7 and the photosensitive drum 1 is improved, and the primary transfer roller and the intermediate transfer belt are separated from each other. The gap generated between them can be eliminated, abnormal discharge can be prevented, and image defects can be prevented.
[0070]
As a result of the study by the present inventors, when the hardness of the primary transfer roller 5 is changed, an image defect occurrence area (A) in the graph showing the experimental results, and no image defect occurs or an image defect occurs. A boundary line that divides a region that is a level that does not cause a problem in practice is an expression represented by a linear function of θa and Rmax,
θa = B−0.0174 × Rmax
It was found that B was affected. That is, by softening the hardness of the primary transfer roller 5, the value of B increases and the usable area of the intermediate transfer belt 7 can be expanded.
[0071]
However, if the hardness is 5 ° or less, in the case of foam, the cell diameter of the sponge has to be increased, and discharge deterioration within the cell or surface deterioration due to rubbing between the sponge surface and the intermediate transfer belt 7 This is not preferable.
[0072]
Next, the relationship between the pressure applied to the photosensitive drum 1 by the primary transfer roller 5 and the image defect was examined. The following examination evaluates the image level when the hardness of the primary transfer roller 5 is fixed at 10 ° and the pressure is 4.9N and 14.7N. The results when the applied pressure is 4.9 N and 14.7 N are shown in FIGS. 6 and 7, respectively. The experimental results are summarized in Table 2.
[0073]
[Table 2]

[0074]
As can be seen from these results, by increasing the pressure applied to the photosensitive drum 1 by the primary transfer roller 5, the intermediate transfer belt 7 and the photosensitive drum 1, and the intermediate transfer belt 7 and the primary transfer roller 5. Adhesion can be increased and image defects can be prevented.
[0075]
As a result of the study by the present inventors, when the pressure applied to the photosensitive drum 1 by the primary transfer roller 5 is changed, an image defect occurrence region (A) in the graph showing the experimental result and an image defect occur. The boundary line that divides the region where there is no image defect or a level that does not cause a problem in practice is an expression represented by a linear function of θa and Rmax,
θa = B−0.0174 × Rmax
It was found that B was affected. That is, by increasing the pressure applied to the photosensitive drum 1 by the primary transfer roller 5, the value B increases, and the usable area of the intermediate transfer belt 7 can be expanded.
[0076]
However, if the pressurizing force is increased too much, there is a possibility that the photosensitive drum 1 may be damaged. Therefore, it is necessary to balance this adverse effect.
[0077]
From the above examination results, the following was found.
(1) It is effective to define the surface state of the intermediate transfer member where no image defect occurs by Rmax and θa. And the boundary line that separates the area where the image defect occurs and the usable area of the intermediate transfer member is
θa = B−0.0174 × Rmax (B is a coefficient) (1)
It is expressed by the relational expression.
(2) The coefficient B in the above formula 1 is defined by the hardness of the primary transfer member and the pressure applied to the image carrier of the primary transfer member.
[0078]
Next, the coefficient B in the above formula 1 as a function of the hardness of the primary transfer member and the pressure applied to the image carrier of the primary transfer member will be further considered.
[0079]
As shown in the above results (FIGS. 4 to 7), the coefficient B shows a linear function behavior that increases as the hardness of the primary transfer member decreases and as the pressing force increases. (°), and the applied pressure is P (N), the coefficient B is the following formula:
B = α × (P + γ) / (R + β) (where α, β, and γ are coefficients) (2)
It is considered that
[0080]
The values of the coefficients α, β, and γ in Equation 2 above are the boundary lines (shown in FIGS. 3 to 7) between θa and Rmax in the above examination results for which the values of B, P, and R are already known. In this case, α = 2.355, β = 94.2, and γ = 11.4.
Therefore, the coefficient B is the following formula:
B = 2.355 × (P + 11.4) / (R + 94.2)
It becomes.
[0081]
Therefore, the formula representing the usable boundary line of the intermediate transfer member is the following formula:
θa = 2.355 × (P + 11.4) / (R + 94.2) −0.0174 × Rmax
It can be expressed as
[0082]
From these results, the relationship between θa and Rmax, which is an indicator of the surface roughness of the intermediate transfer member, necessary for preventing the occurrence of image defects, is expressed by the following equation:
θa <2.355 × (P + 11.4) / (R + 94.2) −0.0174 × Rmax
P: Pressure applied to the image carrier of the transfer member (N)
R: Asker C hardness (°) of transfer member
It becomes.
[0083]
  By the way, in the image forming apparatus 100 used for the above examination, for example, when θa is smaller than 0.005, there is no air gap in the vicinity of the primary transfer nip T, and the image is tailed. The contact area with the intermediate transfer belt 7 becomes excessive, so that a so-called filming phenomenon occurs in which toner adheres and adheres to the surface of the intermediate transfer belt 7, and an image defect occurs in which that portion is not transferred. Therefore, θa is preferably 0.005 or more.Yes.
[0084]
That is, θa is preferably within the range shown below.
[0085]
0.005 ≦ θa <2.355 × (P + 11.4) / (R + 94.2) −0.0174 × Rmax
(However, Rmax is 20 μm or less)
[0086]
Note that the above conditions can avoid image defects to the extent that they do not cause a problem in practice, but more preferably, so as to exclude areas where minor image defects that do not cause a problem in practice occur. , Rmax ≦ 12 (μm) and θa ≦ 0.24 (°). As a result, it is possible to define the condition of the surface shape of the intermediate transfer member so that substantially no image defect occurs.
[0087]
The definition and measurement of θa, Rmax, surface resistivity, and volume resistivity will be described below.
[0088]
As shown in FIG. 2, the average inclination angle θa is a change in height of the unevenness within the range of the reference length W (H₁, H₂,...), And the value obtained by dividing the sum by the reference length is expressed in angle units. That is, the larger the average inclination angle θa when the reference length is the same, the steeper surface unevenness is.
[0089]
[Expression 1]

[0090]
Further, θa is a value derived by detecting all the maximum and minimum points of the unevenness within the reference length and adding all the height differences thereof, so that the surface becomes rougher and the number of unevenness is larger. This is an index that has the feature that the value of increases. In other words, a small value of the average inclination angle θa means that the unevenness frequency is low and the surface unevenness is few, that is, the material is excellent in surface property.
[0091]
As described above, according to the present invention, the height of the unevenness is specified by the maximum height Rmax, while the spread of the surface unevenness that cannot be expressed only by the maximum height is specified by the index of the average inclination angle θa.
[0092]
(Measuring method)
The characteristics of the intermediate transfer belt 7 (I, II, III) in each of the above experimental examples, that is, the maximum height Rmax, the average inclination angle θa, the volume resistivity, and the surface resistivity were measured as follows.
(1) Maximum height Rmax, average inclination angle θa
Measurement was performed with Surfcorder SE-3400 (manufactured by Kosaka Laboratories) under the conditions of evaluation length (reference length) 2.5 mm, feed speed 0.5 mm, filter 2CR, cutoff λc 0.8 mm. . The measurement was performed three times, and the average of these was used as the measurement value.
(2) Surface resistivity, volume resistivity
After removing electricity for 10 seconds with a digital ultrahigh resistance meter R8340A (manufactured by Advantest Corporation, R12702A manufactured by Advantest), the surface resistivity after 10 seconds application at an applied voltage of 100 V was measured. The measurement environment is 23 ° C. and 50% RH. Measurements were made at six locations on the same belt.
[0093]
As described above, by defining not only the maximum height Rmax of the intermediate transfer belt 7 but also the average inclination angle θa as in this embodiment, image deterioration due to the surface shape of the intermediate transfer belt 7 can be avoided, and a high-quality image can be obtained. Can be formed.
[0094]
In the present invention, as described with reference to FIG. 8, the electrostatic latent image corresponding to the image information of each color component sequentially formed on the image carrier is sequentially developed as a toner image by a plurality of developing means. Of course, the present invention can also be applied to an image forming apparatus in which the toner image is laminated and transferred onto an intermediate transfer member and then transferred to a transfer material in a batch.
[0095]
In the above embodiment, the intermediate transfer member has been described as having a belt shape, but the present invention is not limited to this. As described above, the belt-shaped intermediate transfer member increases the degree of freedom in device design, and is excellent in terms of downsizing and space saving of the device. However, as is well known to those skilled in the art, as the intermediate transfer member, the intermediate transfer belt is coated on a drum-like base material with the same material as the intermediate transfer belt, or on a frame that forms a drum-shaped outer edge. The present invention can also be applied to the case where an intermediate transfer drum constituted by stretching a sheet member made of the same material as that described above, and the same effect can be obtained.
[0096]
Furthermore, the present invention does not limit the charging method, image exposure method, development method, etc. of the image carrier to those of the above-described embodiments.
[0097]
【The invention's effect】
As described above, according to the present invention, the contact between the image carrier and the transfer member sandwiching the intermediate transfer member is made uniform, image defects due to the surface shape of the intermediate transfer member are avoided, and a high-quality image is obtained. An image forming apparatus that can be formed can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus to which the present invention can be applied.
FIG. 2 is a diagram for explaining an average inclination angle θa representing a surface shape of a material forming a transfer surface of an intermediate transfer member.
FIG. 3 is a graph showing the results of an experimental example.
FIG. 4 is a graph showing the results of an experimental example.
FIG. 5 is a graph showing the results of an experimental example.
FIG. 6 is a graph showing the results of an experimental example.
FIG. 7 is a graph showing the results of an experimental example.
FIG. 8 is a schematic configuration diagram of another example of an image forming apparatus to which the present invention can be applied.
FIGS. 9A and 9B are schematic diagrams illustrating (a) an intermediate transfer member and (b) a primary transfer unit for explaining problems in a conventional image forming apparatus.
FIG. 10 is a schematic diagram showing a relationship between a protrusion of an intermediate transfer member and a transfer electric field for explaining a problem in a conventional image forming apparatus.
FIGS. 11A and 11B are schematic diagrams illustrating (a) an image defect in a solid image and (b) an image defect in a halftone image for explaining problems in a conventional image forming apparatus.
[Explanation of symbols]
1 Image carrier
2 Charging means
3 Exposure means
4 Development means
5 Primary transfer member
6,7 Intermediate transfer member (intermediate transfer belt)
8 Secondary transfer means
9 Fixing means

Claims (9)

An image carrier for carrying a developer image;
Image forming means for forming a developer image on the image carrier;
An intermediate transfer member to which a developer image on the image carrier is transferred;
The developer image on the image carrier is disposed at a position opposite to the image carrier via the intermediate transfer member, and presses the intermediate transfer member toward the image carrier and is applied with a voltage. A primary transfer member for primary transfer to the intermediate transfer member;
Secondary transfer means for secondary transfer of the developer image on the intermediate transfer member to a transfer material;
In an image forming apparatus having
The maximum height representing the surface shape of the intermediate transfer body onto which the developer image is transferred is Rmax (μm),
The average inclination angle representing the surface shape of the intermediate transfer member onto which the developer image is transferred is θa (°),
The pressing force of the primary transfer member against the intermediate transfer member is P (N),
Asker C hardness of the primary transfer member is R (°),
When
0.005 ≦ θa <2.355 × (P + 11.4) / (R + 94.2) −0.0174 × Rmax
An image forming apparatus satisfying the relationship: The image forming apparatus according to claim 1 , wherein the maximum height Rmax is in a range of 20 (μm) or less. The ten-point average roughness Rz (μm) representing the surface shape of the intermediate transfer member onto which the developer image is transferred is in the range of 0.05 (μm) to 10 (μm). Item 3. The image forming apparatus according to Item 1 or 2 . The image according to any one of claims 1 to 3 , wherein the volume resistivity of the intermediate transfer member is in a range of 10 ⁶ (Ω · cm) to 10 ¹² (Ω · cm). Forming equipment. The surface resistivity of the intermediate transfer member, 10 ⁸ (Ω / □) or more, 10 ¹⁴ (Ω / □) following ranges image forming apparatus according to any one of claims 1-4. The intermediate transfer member, the image forming apparatus according to any one of claims 1-5, characterized in that the belt-shaped. The image forming apparatus according to claim 6 , wherein the intermediate transfer member is formed of a polyimide resin. The primary transfer member, the image forming apparatus according to any one of claims 1-7, characterized in that the roller-shaped. It said image bearing member has a plurality of said image forming means and the primary transfer member after the developer image formed on the image carriers are sequentially overlaid primary transfer onto the intermediate transfer member, the secondary the image forming apparatus according to any one of claims 1-8, characterized in that the secondary transfer collectively to a transfer material by a transfer means.

Images