JP3552001B2 - Image forming apparatus, bias roll thereof, and method of manufacturing the same - Google Patents

Description

転写画質
○ ： 画質欠陥の発生なし
× ： 画質欠陥の発生あり
− ： 用紙の汚れがひどく、評価せず
用紙裏面の汚れ
○ ： １回
△ ： ２〜４回
× ： ５回以上
【００４７】
バイアスロールの硬度が４５°より高い比較例１では、転写画質のホローキャラクタ等の画質欠陥が発生し、転写画質が不良となった。また、実施例１，２および比較例１から明らかなように、バイアスロール表面を表面エネルギーの小さい材料で被覆することにより、バイアスロールへのトナーの付着力が小さくなり、クリーニングブレードによるスクレープ作用を充分に発揮させることができるので、用紙裏面の汚れがない。
また、コーティング層を被覆しないでスキン層を表面層とした比較例２においては、バイスロールの１回の回転では同ロールに付着したトナーを充分に除去することができなかった。一方、バイアスロールとして、発泡シリコーンゴム，発泡ＥＰＤＭを用いた比較例３，４では、発泡ゴムの摩擦係数が大きいため、クリーニングブレードによる負荷トルクが０．１１Ｎｍと大きくなる。その結果、図３に示す画像形成装置において、中間転写ベルトが駆動ローラ（ベルト搬送ロール２４）でスリップして回らないというトラブルが発生した。
【００４８】
（発泡ロールおよびバイアスロールの体積抵抗率）
発泡ロール（すなわち、芯金と前記芯金の外周面に固定されたＥＰＤＭ系発泡ゴム材料または発泡ウレタンゴムを構成成分とするコア層と前記コア層の表面粗さおよび硬度を調節するスキン層とを有するロール）およびバイアスロール（すなわち、発泡ロールおよびコーティング層を有するロール）の体積抵抗率の測定方法を図４に示す。
各ロールの測定方法は、ロールの軸方向３ヶ所（中央部，両端部５０ｍｍ）に２４．５ｍｍ幅(ｗ)の銅テープをロールの円周方向に巻き付け、ロールの芯金と銅テープとの間に２０Ｖの電圧(Ｖ)を印加し、電圧の印加から１０秒後の電流値(Ｉ)を読み取って、下記の式により体積抵抗率ρv(Ωcm）を求めた。
ρv ＝ ２πｗＶ／Ｉ・ｌｎ（ｒ2／ｒ1）
ここで、ｒ1 ： 芯 金の外径(１５ｍｍ)
ｒ2 ： ロールの外径(２８ｍｍ)

【００４９】
表２，３には、図４に示す測定方法に従って測定されたコーティング層被覆前後の発泡ゴムロールの体積抵抗率（ｌｏｇρｖ）の他に、ロール硬度およびロール外径を示す。なお、本発明の実施例および比較例に示す各ロールの体積抵抗率は、上記測定方法に従って求められたものである。
また、表中に示すロール抵抗のバラツキを表す標準偏差値は、各１０本のロールに対してそれぞれ図４に示すロールの軸方向３ヶ所について測定し、計３０回の試験から得られた体積抵抗率により求めた。
下記の表２，３に示すように、体積抵抗率のバラツキは発泡ゴムロールのコーティング層の被覆により小さくなっており、ロール硬度は被覆によってもバラツキの小さいことが分かる。
【００５０】
【表２】

【表３】

【００５１】
実施例３
カーボンブラックを１５ｗｔ％含有するシリコーンゴムに２，５−ジメチル−２，５−ジ（ｔ−ブチルパーオキシ）ヘキサン、発泡剤、シリカを配合した発泡シリコーンゴムコンパウンドを２本ロールで混練した。この混練物を押出機で外径１５ｍｍのＳＵＳ製芯金（２ａ）に圧入して成形した後、金型内において２３０℃で３時間加熱して発泡・加硫することにより、コア層（ｂ）とスキン層（２ｃ）を同時成形した。成形された外径２８ｍｍの発泡ゴムロール表面を研磨して、表面粗さＲｚが１２μｍで厚さが１００μｍのスキン層（２ｃ）を形成した。
さらに、カーボンブラックを２０ｗｔ％含有したＦＥＰ系導電塗料（前記ＧＬＳ−２１３Ｒ）をスキン層（２ｃ）表面にスプレー法により塗布した後、２１０℃で１０分間加熱・硬化して、膜厚１５μｍのコーティング層（２ｄ）を形成した。この時のコーティング層（２ｄ）の表面粗さＲｚは９μｍであった。
このようにして製造された３層構造のバイアスロール（２）において、コア層中の平均セル径は１００μｍであり、硬度は３５°であった。また、発泡ゴムロール（２ｂ，２ｃ）の体積抵抗率は１０^５．３ Ωｃｍであり、コーティング層（２ｄ）の体積抵抗率は１０^２．１ Ωｃｍであり、バイアスロール（２）の体積抵抗率は１０^４．６ Ωｃｍであった。
【００５２】
実施例４
スキン層（２ｃ）の表面粗さＲｚが１７μｍとなるように研磨加工した以外は、実施例３と同様にしてバイアスロール（２）を製造した。得られたバイアスロール（２）表面、すなわちコーティング層（２ｄ）の表面粗さＲｚは１２μｍであった。
実施例５
スキン層（２ｃ）の表面粗さＲｚが２０μｍとなるように研磨加工した以外は、実施例３と同様にしてバイアスロール（２）を製造した。形成されたコーティング層（２ｄ）の表面粗さＲｚは１５μｍであった。
【００５３】
比較例５
スキン層（２ｃ）の表面粗さＲｚが２２μｍとなるように研磨加工すると共に、コーティング層（２ｄ）を膜厚１０μｍに形成した以外は、実施例３と同様にして硬度３３°のバイアスロール（２）を製造した。この時のコーティング層（２ｄ）の表面粗さＲｚは１８μｍであった。
比較例６
スキン層（２ｃ）の表面粗さＲｚが２６μｍとなるように研磨加工した以外は、実施例３と同様にしてバイアスロール（２）を製造した。形成されたコーティング層（２ｄ）の表面粗さＲｚは２２μｍであった。
【００５４】
実施例３〜５および比較例５，６のバイアスロールについて、転写画質および用紙裏面の汚れを評価した。評価基準は前記「バイアスロールの二次転写試験」の場合と同じである。その結果を下記の表４に示す。また、スキン層の表面粗さ（Ｒｚ）とコーティング層の膜厚および表面粗さ（Ｒｚ）をまとめて表４に示す。
なお、各バイアスロールの物性は、上記表面粗さおよび比較例５の硬度を除いて、実施例３に示したものと全て同一である。
【表４】

【００５５】
コーティング層の膜厚を１０μｍ，１５μｍ，２０μｍ，２５μｍおよび３０μｍに形成したバイアスロールにおいて、スキン層の表面粗さ（Ｒｚ）を変化させたときに形成されるコーティング層の表面粗さ（Ｒｚ）を図５に示す。これらのバイアスロールは、前記実施例３に示した方法に準じて製造された。図５において、上記コーティング層の膜厚は、１０μｍ：●、１５μｍ：○、２０μｍ：■、２５μｍ：□、３０μｍ：▲の符号で示される。
図５から明らかなように、スキン層の表面粗さを２０μｍ以下に調整して、膜厚を１５〜３０μｍの範囲でコーティング層を形成すると、その表面粗さが１５μｍ以下のバイアスロールを安定して製造することができる。このようなバイアスロールは、表面が平滑でありかつ表面エネルギーの小さい材質で構成されているため、表４に示したとおり、二次転写時に用紙裏面がトナーで汚染されるようなことがない。
【００５６】
【発明の効果】
本発明の画像形成装置およびバイアスロールは、芯金の外周面にスキン層を介してＥＰＤＭ系発泡ゴム材料または発泡ウレタンゴムを構成成分とするコア層を表面エネルギーの小さい材料を構成成分とするコーティング層で被覆した３層構造からなる。あるいは、芯金の外周面に固定されたコア層が発泡ゴム材料で構成され、スキン層を介して形成されるコーティング層が表面粗さ１５μｍ以下の表面エネルギーの小さい材料で構成された３層構造からなる。したがって、バイアスロール表面に発泡セルによる凹凸がなく平滑であるため、トナーが付着し難く、たとえトナーが付着したとしてもクリーニングブレード等で容易に除去することができる。
また、表面コーティング層の膜厚が５〜３０μｍの範囲にあるので、低硬度のバイアスロールが安定して得られるため、ライン画像が中抜けするホローキャラクタの画質欠陥を発生するようなことがなく、高品質の転写画像が得られる。
本発明の画像形成装置用バイアスロールの製造方法によれば、硬度２０〜４５°の範囲内でバイアスロールが安定して得られ、均一な厚さのスキン層を確実に形成することができるだけでなく、コーティング層の膜厚の調節も容易である。
【図面の簡単な説明】
【図１】本発明の画像形成装置における二次転写部の概略構成図である。
【図２】表面エネルギーの尺度となる接触角の説明図である。
【図３】本発明の一実施例として示す画像形成装置の全体図である。
【図４】発泡ゴムロールおよびバイアスロールの体積抵抗率の測定方法を示す説明図である。
【図５】コーティング層の膜厚の相違によるバイアスロールにおけるスキン層の表面粗さとコーティング層の表面粗さの関係を示すグラフである。
【図６】従来の画像形成装置における二次転写部の説明図である。
【符号の説明】
Ｕ…画像形成装置、Ｐ…用紙（記録媒体）、１…中間転写ベルト、２…バイアスロール、２ａ…芯金、２ｂ…コア層、２ｃ…スキン層、２ｄ…コーティング層、３…バックアップロール、１９…像担持体、２１…現像ユニット（現像装置）。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic method, such as an electrophotographic copying machine, a laser printer, a facsimile, and a composite OA device thereof. More specifically, an image forming apparatus in which a toner image formed on an image carrier is once primarily transferred to an intermediate transfer belt, and then this is secondarily transferred to a recording medium such as paper to obtain a reproduced image. The present invention also relates to a bias roll for secondary-transferring a primary-transferred toner image to a recording medium and a method for manufacturing the same.
[0002]
[Prior art]
An image forming apparatus using an electrophotographic method forms a uniform charge on an image carrier made of a photoconductor made of an inorganic or organic photoconductive material, and forms an electrostatic charge with a laser beam or the like that modulates an image signal. After forming the latent image, the electrostatic latent image is developed with the charged toner to obtain a visualized toner image. Then, the required reproduced image is obtained by transferring the toner image via an intermediate transfer member or directly onto a recording medium such as paper.
In a method in which a toner image formed on an image carrier is primarily transferred to an intermediate transfer member, and a toner image on the intermediate transfer member is secondarily transferred to a recording medium, a conductive bias roll is used. 2. Description of the Related Art A bias roll type image forming apparatus that presses a recording medium against an intermediate transfer body and electrostatically transfers a toner image by the action of an electric field is known. The bias roller transfer method in which electrostatic transfer is performed while applying a transfer voltage to a conductive bias roll includes a backup roll that receives a pressing force of the bias roll and forms a transfer current passage.
[0003]
Conventional examples of the image forming apparatus employing the above method are disclosed in, for example, JP-A-6-95521 and JP-A-6-124049.
FIG. 6 is an explanatory diagram of a secondary transfer unit in the transfer device disclosed in the former publication. In the figure, the intermediate transfer member 01 is stretched by a backup roll 02 and a plurality of support rollers 03, and moves in the direction of the arrow. In the secondary transfer section, a bias roll 05 for applying a transfer voltage from the power supply 04 to the backup roll 02 and a roll pressed against the backup roll 02 to form a path for a transfer current based on the transfer voltage are formed. An electrode roll (earth roll) 06 is provided. As the bias roll 05, a metal roll made of aluminum is used. Then, when a transfer voltage is applied between the bias roll 05 and the backup roll 02 from the power supply 04, the toner image on the intermediate transfer body 01 is transferred to the paper P.
Further, the latter publication discloses an image forming apparatus in which a bias roll (transfer roller) is formed by a cored bar and a next elastic member covering the outer peripheral surface thereof. As the elastic member, a conductive agent is dispersed to reduce the volume resistivity to 10⁷  -10¹⁰Elastic body made of EPDM set to Ωcm, or volume resistivity 10⁸-10⁹Volume resistivity 10 coated with PFA tube of Ωcm⁸-10⁹Ωcm epichlorohydrin rubber is used.
[0004]
[Problems to be solved by the invention]
However, in the transfer device disclosed in JP-A-6-95521 using a metal roll as the bias roll, the paper P is pressed against the backup roll 02 by the bias roll 05 via the intermediate transfer member 01, so that the electric field of the electric field is reduced. The load of the pressing force by the bias roll 05 concentrates on the secondary transfer portion where the toner image is electrostatically transferred by the action. For this reason, the toner image may be aggregated, the charge density may be increased, and a discharge may be generated inside the toner layer to change the polarity of the toner. Due to such factors, the above-described conventional technique has a problem in that an image quality defect of a hollow character in which a line image is missing occurs.
As a countermeasure against this problem, it is necessary to make the bias roll low in Asker C hardness in the range of 20 to 45 °. Methods for reducing the hardness of the rubber material include a) a method of blending a low molecular component such as a plasticizer into the rubber material, and b) a method of forming the rubber material into a foam. However, the former method a) of blending low molecular components is not preferable because the low molecular components oozing from the roll surface adversely affect image quality as contaminants.
[0005]
In the transfer device disclosed in Japanese Patent Laid-Open No. 6-95521, the intermediate transfer member 01 is also provided between the time when the sheet P passes through the bias roll 05 and the time when the next sheet P is conveyed to the bias roll 05. The toner remaining on the sheet P is transferred to the bias roll 05, which causes a problem that the paper P is stained on the back side. In order to solve this problem, for example, c) a method of cleaning the bias roll with a cleaning blade or the like; d) an electric field in the direction in which the toner is displaced to the image carrier during non-transfer is applied between the bias roll and the image carrier. A method of forming the same has been proposed.
However, in the method c), when the hardness of the bias roll is relatively low as in the method b), it is difficult to sufficiently exert the scraping action of the cleaning blade. On the other hand, when the bias roll is made of a rubber material having a large friction coefficient, such as urethane rubber or EPDM (ethylene propylene diene rubber) disclosed in the above-mentioned Japanese Patent Application Laid-Open No. 6-124049, the bias roll is rubbed by the blade. Is not practical because of damage to the motor or an increase in rotational torque.
In the method d), since the bias roll is pressed against the image carrier and deforms in a concave shape, the attached toner is pressed by the bias roll and easily aggregates. Therefore, a high electric field is required for sufficient cleaning, which is not preferable.
[0006]
As a countermeasure for preventing such back contamination of the recording medium, there is a method of coating a foamed rubber body with a fluorine-based resin as described in the above method b).
For example, Japanese Patent Application Laid-Open No. 6-149097 discloses that for the purpose of preventing contamination of the photosensitive drum surface by a bleed component such as a plasticizer, the surface of a foamed elastic material such as silicone rubber or urethane rubber is made of a fluorine resin or a silicone resin. A transfer roller partially coated with fine patches is disclosed.
Japanese Patent Application Laid-Open No. 6-175470 discloses a conductive film layer formed of a soluble fluororesin containing a conductive material for the purpose of preventing the appearance of a network-like image due to uneven charging of a member to be charged under a low humidity environment. Discloses a conductive roll coated with a foamed elastic material layer such as EPDM.
However, since the foamed elastic body has a large surface roughness due to the unevenness of the foamed cells remaining on the surface, even if the surface is coated with a fluorine-based resin, the cleaning blade sufficiently exerts a scraping action. Can not.
[0007]
For example, a roller transfer device in which a resin having good releasability is coated on a rubber lining layer in order to sufficiently exert a scraping action is disclosed in JP-A-4-208973. Similarly, a fluorine-based resin having a small surface energy, such as the above-mentioned PFA (Tetrafluoroethylene-Perfluoroalkyl vinyl etherCopolymer) There is a method of coating the tube material on the foamed elastic body. In order to coat this tube material on a rubber roll, for example, the following method is known.
One method e) is to process a predetermined film material into a tube shape, inflate by press-fitting a fluid such as air from the inside thereof, insert a rubber roll therein, and then reduce the pressure of the fluid to shrink. Then, there is a processing method of forming a surface layer. As another method f), the tube material is stretched on the inner surface of a cylindrical mold and attached in a tube shape, and a liquid rubber material is poured into the tube material, and then vulcanized and cured to form a film-coated rubber roll. There is a method of molding.
[0008]
Since the tube (film) material used in both of the above-mentioned processing methods is given an elongation of 50 to 200% during processing, the characteristics of the tube material include a deformation amount of 50 to 200% in the elastic region. Need. In order to cover the tube material without breaking the tube material within the range of the elongation, the thickness cannot be less than 50 μm.
However, when a rubber material is coated with a tube material thicker than 50 μm, the hardness (Asker C) of the rubber roll increases by about 15 to 20 °. Therefore, there is a problem that it is not possible to stably obtain a low-hardness, Asker C 20-45 ° bias roll that satisfies the above-described hardness condition for avoiding the occurrence of the hollow character.
[0009]
As described above, in the conventional bias roller transfer method, since a bias roll having both hardness and surface characteristics was not obtained, the toner transferred to the bias roll during non-transfer was removed to remove the back stain on the recording medium. There is no effective means to prevent this, and there is a problem that high quality images cannot be obtained.
Therefore, the present invention is to solve the above-mentioned problem, and it is possible to reliably prevent the paper from being contaminated by the toner transferred to the bias roll during non-transfer or the like, and to obtain a high-quality image. It is an object of the present invention to provide a possible image forming apparatus and a bias roll thereof and a method of manufacturing the same.
[0010]
[Means for Solving the Problems]
The inventor of the present invention has conducted intensive studies on a means capable of efficiently removing toner transferred to a bias roll in a bias roller transfer method for secondary transfer of a toner image using an intermediate transfer member. By interposing a skin layer between the surface layer and the foamed elastic body, it was possible to reduce the hardness of the bias roll, the film thickness of the surface layer, and the surface roughness to a mutually satisfactory range. The present invention has been made based on the above.
That is, the image forming apparatus of the present invention includes an image carrier on which an electrostatic latent image corresponding to image information is formed, and a developing device for visualizing the electrostatic latent image formed on the image carrier as a toner image with toner. An intermediate transfer belt on which a toner image carried on an image carrier is primarily transferred, a bias roll for secondary transfer of an unfixed toner image on the intermediate transfer belt to a recording medium, and an intermediate transfer belt facing the bias roll. And a backup roll supporting the back from the back surface, the bias roll, the core layer and a core layer of EPDM foam rubber material or urethane foam rubber fixed to the outer peripheral surface of the core metal,Adjust the surface roughness and hardness of the core layerA skin layer, comprising a coating layer having a thickness of 5 to 30 μm and comprising a material having a small surface energy having a contact angle of 90 ° or more with a water droplet when indicated by wettability of water,
The volume resistivity of the material layer between the core metal and the outer surface of the skin layer calculated assuming that the material layer between the core metal and the outer surface of the skin layer is uniform (hereinafter referred to as “foaming roll”) Is 10). ^Four -10 ⁷ Ω cm Wherein the volume resistivity of the coating layer is a value lower than the volume resistivity of the foam roll and 10 ^Two -10 ^Five Ω cm And the volume resistivity of the material layer between the core metal and the outer surface of the coating layer calculated assuming that the material layer between the core metal and the outer surface of the coating layer is a uniform material layer. (Hereinafter referred to as “volume resistivity of the bias roll”) is a value lower than the volume resistivity of the foam roll and 10 ^Four -10 ⁷ Ω cm In the range ofThe hardness of the bias roll is in the range of 20 to 45 ° in Asker C hardness.
The present invention also includes the above-mentioned bias roll and a method for manufacturing the same.
[0011]
The image forming apparatus of the present invention further includes the above-described image carrier, a developing device, an intermediate transfer belt, a bias roll and a backup roll, and the bias roll is fixed to a cored bar and an outer peripheral surface of the cored bar. A core layer comprising a foamed rubber material as a component,Adjust the surface roughness and hardness of the core layerA skin layer, comprising a coating layer having a thickness of 5 to 30 μm and comprising a material having a small surface energy having a contact angle of 90 ° or more with a water droplet when indicated by wettability of water,
The foamed roll has a volume resistivity of 10 ^Four -10 ⁷ Ω cm Wherein the volume resistivity of the coating layer is a value lower than the volume resistivity of the foam roll and 10 ^Two -10 ^Five Ω cm And the volume resistivity of the bias roll is a value lower than the volume resistivity of the foam roll and 10 ^Four -10 ⁷ Ω cm In the range ofThe surface roughness Rz of the coating layer is 15 μm or less, and the hardness of the bias roll is in the range of 20 to 45 ° in Asker C hardness.
The present invention further includes the above-mentioned bias roll.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail.
FIG. 1 is an explanatory diagram of a secondary transfer unit in the image forming apparatus of the present invention. In FIG. 1, a backup roll 3 is disposed at a position opposite to a bias roll 2 via an intermediate transfer belt 1 carrying an unfixed toner image that has been primarily transferred, and the backup roll 3 holds the intermediate transfer belt 1 from the back. To support. An electrode roll 4 for applying a transfer voltage to the bias roll 2 is pressed against the backup roll 3. The bias roll 2 is grounded, and the electrode roll 4 is connected to a power supply 5. A cleaning blade 6 made of polyurethane or the like is in contact with the surface of the bias roll 2.
The intermediate transfer belt 1 is a belt formed by mixing an appropriate amount of a conductive agent such as carbon black with various resins or rubber materials and molding the same to a thickness of, for example, 0.05 to 0.15 mm.⁸  -10¹⁴Adjusted to the range of Ω / □. Examples of various resins include acrylic resin, polyvinyl chloride, polyester, polycarbonate, polyamide, and polyimide.
[0013]
The bias roll 2 constituting the transfer electrode is separated from the transfer belt 1 while the toner image carried on the image carrier is primarily transferred onto the intermediate transfer belt 1, and the toner image carried on the transfer belt 1 is Is transferred onto a recording medium such as paper P (hereinafter, represented by paper P), and is pressed against the transfer belt 1 and pressed against the backup roll 3.
The bias roll 2 is made of a material having low surface energy via a skin layer 2c on a core layer 2b composed of a rubber material such as an EPDM foam rubber material or a urethane foam rubber material fixed to the outer peripheral surface of a cored bar 2a. Has a three-layer structure in which a coating layer 2d is used as a component. When the surface roughness Rz of the coating layer 2d is equal to or less than a predetermined value described later, the core layer 2b can be made of an arbitrary foamed rubber material. A conductive agent is dispersed in these layers (2b to 2d) to adjust the resistance.
Examples of the conductive agent dispersed in each layer include metals or alloys such as carbon black, graphite, copper, aluminum, copper alloy, stainless steel (SUS), tin oxide, zinc oxide, titanium oxide, indium oxide, antimony oxide, and titanium. Potassium salt, SnO₂  -In₂O₃Composite oxide, SnO₂  -Sb₂O₅Fine powder such as a conductive metal oxide such as a composite oxide is used. Among them, carbon black is preferable because of its good dispersibility in rubber materials and various resins.
[0014]
In the bias roll, between the core metal and the outer surface of the coating layerVolume resistivity of the material layer between the core metal and the outer surface of the coating layer calculated assuming that the material layer is a homogeneous material(Hereinafter referred to as the volume resistivity of the bias roll) is 10^Four-10⁷Ωcm range. This volume resistivity is 10^Four If it is lower than Ωcm, an air gap may be generated between the sheet conveyed at the time of the secondary transfer and the bias roll, in which case discharge occurs. On the other hand, when the volume resistivity is 10⁷ If it is higher than Ωcm, the balance with the resistance of the backup roll is lost, and the transfer latitude at which a high-quality toner image can be maintained is narrowed. In any case, if the volume resistivity of the bias roll is not in the above range, there is a possibility that poor image quality may occur.^4.5-10⁶Ωcm.
The hardness of the bias roll is in the range of 20 to 45 ° in terms of Asker C hardness (hereinafter, hardness is represented by Asker C). That is, when the foamed rolls (2b, 2c) are coated with a thin film of a material having a small surface energy in which a conductive agent is dispersed, manufacturing a roll having a hardness of less than 20 ° is disadvantageous in cost. On the other hand, when the hardness is higher than 45 °, the nip pressure with the intermediate transfer belt pressed through the paper is unnecessarily increased, and the graininess of image quality is deteriorated, and a hollow character is generated, that is, a line image is hollow. Become like
[0015]
The core metal functions as an electrode and a support member of the bias roll, and is made of, for example, a metal or alloy such as aluminum, iron, copper alloy, or SUS, iron plated with chromium, nickel, or the like, synthetic resin, or the like. It is made of a conductive material. The outer diameter of the core is usually in the range of 10 to 20 mm.
As described above, the core layer is made of a conductive agent-dispersed EPDM rubber material or urethane rubber foam. Here, the EPDM rubber material means EPDM alone or a blend rubber with another rubber material containing EPDM by 50% by weight or more. Further, when the later-described surface roughness Rz of the coating layer is 15 μm or less, it is not limited to the above-mentioned foam, and any foamed rubber material can be used. Specific examples thereof include, in addition to the above EPDM and urethane rubber, isoprene rubber, chloroprene rubber, butyl rubber, epichlorohydrin rubber, norbornene rubber, silicone rubber, fluorine rubber, acrylic rubber, SBR (styrene-butadiene rubber), NBR ( Foamed rubber materials such as acrylonitrile-butadiene rubber) and acrylonitrile-butadiene-styrene rubber, and a blended material thereof may be used. Among them, silicone rubber, urethane rubber, EPDM and the like are preferably used.
[0016]
The thickness of the core layer is preferably in the range of 4 to 10 mm. The size of the bubbles formed in the core layer differs depending on the type of the rubber material, the foam molding method, and the like, and the average cell diameter is generally adjusted to a range of 40 to 1200 μm. In order to manufacture a bias roll having predetermined hardness and surface characteristics, for example, the average cell diameter is in the range of 50 to 300 μm in the case of EPDM foam rubber material, and in the range of 50 to 1000 μm in the case of foam urethane rubber. Respectively.
If the average cell diameter is smaller than 40 μm, not only a bias roll having stable characteristics cannot be obtained, but also the hardness of the bias roll becomes higher than 45 °. On the other hand, if the average cell diameter is larger than 1200 μm, the internal structure of the bias roll will vary, making it impossible to obtain a bias roll having stable volume resistivity and hardness.
[0017]
The skin layer covering the surface of the core layer is provided to eliminate unevenness due to foam cells on the surface of the bias roll and to adjust the hardness of the bias roll within the range of 20 to 45 °. The skin layer is formed by: i) coating a non-foamed rubber material dispersed with a conductive agent on the surface of the core layer, ii) coating and adhering the film or tube (hereinafter, represented by a tube) to the surface of the core layer, and iii). When a non-foamed elastic material containing a conductive agent, a foaming agent and the like is foamed and molded, it is formed by molding a dense surface layer simultaneously with the core layer.
The rubber material constituting the skin layer is not particularly limited, and the same non-foamed rubber material as illustrated as a component of the core layer is used. In particular, it is preferable to use the same rubber material as the foam of the core layer. In this case, the adhesion between the two layers is good, and when the above-mentioned molding method iii) is employed, the core layer and the skin layer can be molded simultaneously.
[0018]
In order to adjust the surface roughness and hardness of the bias roll, the thickness of the skin layer is generally preferably in the range of 10 μm to 1.50 mm. For example, when the foam is an EPDM foam rubber material, the thickness is preferably in the range of 10 to 800 μm, and when the foam is urethane foam, it is preferably in the range of 10 μm to 1.50 mm. In the method of forming the skin layer, i) when the rubber material is coated on the surface of the core layer, it is generally in the range of 0.10 to 1.50 mm, for example, 0.20 to 0 in the case of EPDM foam rubber material. The thickness of each of the skin layers may be adjusted within a range of 0.80 mm and in the range of 0.20 to 1.50 mm in the case of urethane foam rubber. ii) When adhering the tube material to the core layer surface, a tube material having a thickness in the range of 50 to 500 μm is used. iii) When molded simultaneously with the core layer, a skin layer having a thickness in the range of 10 to 200 μm can be easily formed.
Further, the surface roughness Rz of the skin layer is preferably set to 20 μm or less. In that case, a coating layer having a surface roughness Rz of 15 μm or less can be easily formed.
[0019]
The coating layer is made of a material having a low surface energy in which a conductive agent is dispersed.
Here, as described above, the “material having a small surface energy” has a contact angle with a water droplet of 90 ° or more when indicated by wettability of water. The wettability of water is expressed by using a material of the semiconductive coating layer before dispersing the conductive agent as a test piece and using a contact angle between a plane of the test piece and a water drop as a scale. More specifically, when a water droplet is placed on the surface of the test piece, the surface tension γs of the test piece, the interfacial tension γi between the liquid and the test piece, and the surface tension γl of the liquid balance, and as shown in FIG. Form the shape of At this time, if the influence of gravity is negligible, the following Young's equation holds. That is, the “material having a small surface energy” in the present invention means a material having the contact angle θ of 90 ° or more.
γs = γi + γlcosθ
[0020]
Examples of a material having a small surface energy include polytetrafluoroethylene (tetrafluoroethylene: TFE), polyvinylidene fluoride, polychlorotrifluoroethylene, PFA, an ethylene-TFE copolymer, and a TFE-hexafluoropropylene copolymer (FEP). ), Fluorine-based resins such as ethylene-chlorotrifluoroethylene copolymer, TFE-PFA copolymer, PFA-FEP copolymer, polydimethylsiloxane, polymethylphenylsiloxane, dimethylsiloxane-methylphenylsiloxane copolymer, Examples include silicone rubber or resin such as dimethylsiloxane-methylvinylsiloxane copolymer and dimethylsiloxane-methyltrifluoropropylsiloxane copolymer. These materials have a characteristic that the toner is difficult to adhere to the surface of the bias roll because the surface energy is small.
The thickness of the coating layer is in the range of 5 to 30 μm. In the secondary transfer section, the pressing and rotation of the bias roll to the backup roll are repeated via the paper and the intermediate transfer belt, so that if the film thickness is less than 5 μm, the coating layer is worn and the skin layer is worn. May be exposed. On the other hand, when the film thickness exceeds 30 μm, when the skin layer is coated with the above-described material containing a conductive agent by a coating method, liquid dripping easily occurs on the surface, and it is difficult to stably form a smooth and uniform coating film. It becomes. When the thickness of the coating layer is in the above range, a bias roll having a hardness in the range of 20 to 45 ° can be obtained stably.
[0021]
The surface of the bias roll is desirably smooth in order to sufficiently exhibit the scraping action of the cleaning boot blade. In the present invention, the surface roughness Rz of the coating layer is generally adjusted to 15 μm or less. However, according to the bias roll in which the core layer is made of the EPDM foam rubber material or the urethane foam rubber, since the back stain of the paper due to the incomplete scraping action does not occur, the surface roughness Rz of the coating layer is not necessarily 15 μm or less. There is no need to adjust.
The coating layer having such a surface roughness Rz can be easily formed by employing a coating method such as a spray method. According to the coating method, a coating layer having a surface roughness Rz of 15 μm or less is formed on a skin layer having a surface roughness Rz of 20 μm or less by adjusting the film thickness to a range of 15 to 30 μm.
When the surface roughness Rz of the coating layer to be formed is larger than 15 μm, the surface roughness Rz is set to 15 μm by appropriately setting the polishing conditions such as the feed speed of the grindstone, the rotation speed of the bias roll, and other processing times. The following can be adjusted. This is the same when adjusting the surface roughness Rz of the skin layer to 20 μm or less. In the present invention, the surface roughness Rz refers to a value determined according to a ten-point average roughness according to JIS B 0610.
[0022]
In the above-mentioned bias roll, between the core metal and the outer surface of the skin layerVolume resistivity(Hereinafter referred to as the volume resistivity of the foamed rubber roll) is 10^Four-10⁷Ωcm range and the volume resistivity of the coating layer is 10^Two-10^FiveIt is preferable to set the range to Ωcm.
For this purpose, the ratio of the conductive agent blended in the foaming roll is in the range of 5 to 30 wt%, and the ratio of the conductive agent blended in the coating layer is in the range of 10 to 30 wt%, although it depends on the type of the conductive agent. Is preferred. If the mixing ratio is outside the above ranges, it is not only difficult to adjust the volume resistivity of the bias roll to the desired range, but if the mixing ratio exceeds 30 wt%, for example, the hardness of the bias roll becomes 45%. ° may be higher.
By setting the volume resistivity of the foaming roll and the coating layer within the above range, the volume resistivity of the bias roll obtained by synthesizing these resistances can be adjusted to the above-described 10 value.^Four-10⁷It can be set arbitrarily within the range of Ωcm. Therefore, it is possible to provide a degree of freedom for the volume resistivity of the foam roll.
[0023]
The backup roll 3 constituting the counter electrode is a roll in which an appropriate amount of the conductive agent is mixed with an insulating rubber roll of EPDM, silicone rubber, urethane rubber, or the like. Its surface resistivity is 10⁸  -10¹⁰The hardness is preferably in the range of Ω / □ and the hardness is in the range of 58 to 73 °.
The material of the electrode roll 4 is not particularly limited as long as it is a metal or alloy having good electrical conductivity, and for example, SUS, copper, aluminum, or the like is used. From the electrode roll 4, a transfer voltage of −2 to −5 kV is applied to the bias roll 2 through the backup roll 3. When the transfer voltage is lower than 2 kV (absolute value), the intensity of the electric field for transferring the unfixed toner image on the intermediate transfer belt 1 to the sheet P is not sufficient. On the other hand, if the voltage is higher than 5 kV, the change in the surface resistivity of the backup roll 3 is undesirably large during long-term use.
In the above secondary transfer section, the electrode roll 4 is not necessarily a necessary member, and for example, a core provided on the backup roll 3 can be used as an electrode member.
[0024]
The bias roll of the present invention can be manufactured, for example, as follows, depending on the difference between the methods i) to iii) for forming the skin layer.
i) Method of coating and molding non-foamed rubber material dispersed with conductive agent on the surface of core layer
In order to adjust the conductivity and hardness, a conductive agent such as carbon black, a filler such as a metal oxide or a non-metal oxide, a foaming agent, a vulcanizing agent, etc., an unfoamed EPDM rubber material or a urethane rubber material, etc. To prepare a foamed rubber compound. In order to form a foamed elastic body having predetermined conductivity and hardness, it is important to adjust the amount of foaming agent and the foaming conditions.
Next, after kneading the foamed rubber compound with an extruder, it is heated to foam and vulcanize the rubber material, thereby forming a tubular foamed elastic body. Thereafter, the core metal is pressed into the cavity of the foamed elastic body and fixed, and the surface of the foamed elastic body is polished as necessary to form a core layer.
Next, the core metal is positioned at the center of the mold, and the rubber compound excluding the foaming agent is coated on the outer peripheral surface of the core layer by a tube crosshead extruder, or the outer peripheral surface of the core layer and the inner surface of the mold are separated from each other. After pouring, a skin layer is formed on the outer peripheral surface of the core layer by vulcanization. At this time, the thickness of the skin layer is generally 0.10 to 1.50 mm, for example, 0.20 to 0.80 mm when the foam is a foamed EPDM rubber material, and when the foam is urethane foam. Molded to 0.20 to 1.50 mm. Note that the rubber material in the rubber compound does not necessarily need to match the material of the core layer. Further, when the surface roughness Rz of the formed skin layer is larger than 20 μm, it is preferable to perform polishing as needed. The same applies to the following methods ii) and iii).
[0025]
The formed foamed rubber roll is then coated with a dispersion of a conductive agent such as carbon black in a material having a small surface energy on the skin layer surface to form a coating layer having a thickness of 5 to 30 μm.
Examples of the dispersion include an aqueous emulsion paint containing a urethane-modified TFE resin (Emuralon 345E: manufactured by Nippon Acheson Co., Ltd.) and a paint containing a TFE-PFA copolymer (Belflon: manufactured by Nippon Oil & Fats Co., Ltd.) In addition, those mixed with carbon black are preferable. These paints are used as a two-part type that crosslinks at a relatively low temperature from room temperature to 150 ° C. Further, an FEP-based conductive paint (GLS-213R: manufactured by Daikin Industries, Ltd.) is also preferably used.
The method for applying the dispersion is not particularly limited, and examples thereof include a brush coating method, a spray method, a dipping method, and a roll coater method. Among them, the spraying method sprays a dispersion liquid from a sprayer while rotating around a metal core to which a foamed rubber roll is fixed, and the formation of a coating layer is simple. In addition, the film thickness can be easily adjusted. When the surface roughness Rz of the formed coating layer is larger than 15 μm, it is preferable to perform polishing. In particular, when the core layer is made of a rubber material other than the EPDM foam rubber material or the urethane foam rubber, the following methods ii) and iii) are the same, but the surface roughness Rz is adjusted to 15 μm or less. Polishing is performed.
[0026]
ii) A method of coating and bonding a tube material in which a conductive agent is dispersed to the surface of a core layer
A smooth tube material having a thickness of about 50 to 500 μm is attached to the inner surface of the cylindrical mold. Next, the same foamed rubber compound as in the above method i) is injected into the inside of the tube material, and then foamed and vulcanized to form a core layer, and at the same time, the core layer and the tube material are bonded. If the adhesion between the tube material to be the skin layer and the core layer is poor, it is preferable to apply an adhesive in advance to the inner surface of the tube material. Thereafter, a coating layer is formed in the same manner as in the method i).
iii) A method of molding a skin layer simultaneously with a core layer during molding of an unfoamed rubber compound A foamed rubber compound is prepared in the same manner as in the above method i), and the kneaded product is extruded by an extruder and sent to a crosshead. Wrap around the outer surface of the gold. Next, the foamed rubber compound is heated by supporting the cored metal in the mold, and the foamed elastic body is fixed to the cored metal to form a core layer, and at the same time, a thickness of 10 to 200 μm is formed on the inner surface of the mold. , A dense skin layer is formed. Thereafter, a coating layer is formed in the same manner as in the method i).
Further, instead of the above-mentioned coating method, the above-mentioned methods e) and f) of coating a tube material having a small surface energy after coating the skin layer on the core layer formed as described above or on the foamed rubber roll are adopted. May be.
[0027]
The operation of the present invention is as follows. The numbers in parentheses correspond to the components of the numbers shown in FIG.
The electrostatic latent image formed on the image carrier (19) according to the image information is developed by the toner in the developing device (21) and is visualized as an unfixed toner image. This toner image is transferred to the intermediate transfer belt 1 in the primary transfer section while being carried on the image carrier (19). When transferring a multicolor image, the primary transfer is repeated for each color of the toner stored in the developing device (21).
When the primary transfer of the toner image from the image carrier (19) onto the intermediate transfer belt 1 is completed and the intermediate transfer belt 1 carrying the toner image of a desired hue moves to the secondary transfer unit, The sheet P is conveyed to the secondary transfer section in synchronization with the transfer. At this time, the bias roll 2 is in pressure contact with the transfer belt 1 whose back surface is supported by the backup roll 3. Then, when the paper P passes through the secondary transfer portion while receiving a pressure contact force between the bias roll 2 and the backup roll 3, for example, a transfer voltage having the same polarity as the charged polarity of the toner image is applied from the electrode roll 4. As a result, the toner image carried on the transfer belt 1 is secondarily transferred to the sheet P from the surface of the intermediate transfer belt 1.
[0028]
According to the image forming apparatus of the first aspect and the bias roll of the fifth aspect, the bias roll 2 includes a core layer 2b, a skin layer 2c, and a surface, each of which has a foamed rubber material as a constituent component on an outer peripheral surface of a cored bar 2a. It has a three-layer structure in which a coating layer 2d containing a material having low energy as a component is laminated. Therefore, since the surface of the bias roll 2 is coated with a material having a small surface energy without irregularities due to the foam cells, the toner transferred to the bias roll 2 during non-transfer can be easily removed by a cleaning member such as the cleaning blade 6. Can be removed.
Further, since the thickness of the coating layer 2d is in the range of 5 to 30 μm, the roll hardness required as the transfer roll can be stably obtained in the range of 20 to 45 °. Therefore, in a state where the bias roll 2 is pressed against the intermediate transfer belt 1 via the paper P, the load of the pressing force by the bias roll 2 is concentrated in the secondary transfer portion that electrostatically transfers the toner image by the action of the electric field. Therefore, the image quality defect of the hollow character in which the line image is missing does not occur.
In addition, the volume resistivity of the bias roll 2 is 10⁴-10⁷Because of the range of Ωcm, a high quality transfer image can be obtained by the action of an appropriate transfer electric field in the secondary transfer portion for transferring the unfixed toner image on the intermediate transfer belt 1 to the paper P.
[0029]
Further, according to claim 1According to the image forming apparatus of the present invention, the volume resistivity of the bias roll 2 required for forming the above-mentioned high quality transfer image is 10^Four-10⁷In order to obtain Ωcm, the foamed rolls (2b, 2c) have a volume resistivity higher than that of the bias roll by 10%.^Four-10⁷Ωcm, and the volume resistivity of the coating layer 2d is 10^Two-10^FiveIt is set in the range of Ωcm. Therefore, compared to the variation of the volume resistivity of the core layer 2b, the volume resistivity of the bias roll 2 obtained by synthesizing the foamed roll and the coating layer 2d is 10%.^Four-10⁷The variation (standard deviation) of Ωcm can be further reduced.
[0030]
Claim 2According to the image forming apparatus of the present invention, the average cell diameter of the core layer 2b containing the EPDM foamed rubber material as a component is in the range of 50 to 300 μm, and the thickness of the skin layer 2c containing the EPDM rubber material as a component. Is in the range of 10 to 800 μm, the resin component of the coating layer 2d is a fluorine-based resin, and carbon black is dispersed in each layer (2b to 2d) as a conductive agent. Therefore, in combination with the setting of the thickness of the coating layer 2d in the range of 5 to 30 μm, the hardness of the bias roll 2 as the transfer roll can be more stably obtained in the range of 20 to 45 °. . In addition, the bias roll 2 is made of an inexpensive material.
Claim 3According to the image forming apparatus of the present invention, the average cell diameter of the core layer 2b containing urethane foam as a component is in the range of 50 to 1000 μm, and the thickness of the skin layer 2c containing urethane rubber as a component is 10 μm to 1 μm. .50 mm, the resin component of the coating layer 2d is a fluorine-based resin, and carbon black as a conductive agent is dispersed in each of the layers (2b to 2d). Therefore, as in the case of the second aspect, the hardness of the bias roll 2 is more stably obtained in the range of 20 to 45 °.
According to the bias roll for an image forming apparatus of the invention according to claim 4, a core metal and a core layer composed of an EPDM foamed rubber material or urethane foam fixed to the outer peripheral surface of the cored bar,Adjust the surface roughness and hardness of the core layerA skin layer, comprising a coating layer having a thickness of 5 to 30 μm and comprising a material having a small surface energy having a contact angle of 90 ° or more with a water droplet when indicated by wettability of water,
The foamed roll has a volume resistivity of 10 ^Four -10 ⁷ Ω cm Wherein the volume resistivity of the coating layer is a value lower than the volume resistivity of the foam roll and 10 ^Two -10 ^Five Ω cm And the volume resistivity of the bias roll is a value lower than the volume resistivity of the foam roll and 10 ^Four -10 ⁷ Ω cm In the range ofThe hardness of the bias roll is in the range of 20 to 45 ° in Asker C hardness. By using the bias roll for an image forming apparatus according to the fourth aspect, the image forming apparatus according to the first aspect can be obtained.
[0031]
Claim 5The invention isA method for manufacturing a bias roll for an image forming apparatus according to claim 4.Forming a core layer of a foamed EPDM rubber material in which carbon black is dispersed on the outer periphery of a core metal, extruding at least an EPDM rubber material containing carbon black, and then heating to form a thickness. The core layer is covered with a skin layer having a thickness of 0.20 to 0.80 mm, and a fluorine resin in which carbon black is dispersed is applied to the surface of the skin layer to perform coating processing.
According to the method of manufacturing a bias roll for an image forming apparatus according to the fifth aspect of the present invention, a carbon black-dispersed EPDM rubber material is extruded to form a foamed core layer 2b and a non-foamed skin layer 2c. Thereafter, a carbon black-dispersed fluorine-based resin liquid is applied to the surface of the skin layer 2c to form a coating layer 2d. Therefore, the hardness of the bias roll 2 can be stably obtained within the above range. Further, the thickness of the skin layer 2c can be uniformly and reliably formed within the range of 0.20 to 0.80 mm, and the thickness of the coating layer 2d can be easily adjusted by applying a fluorine-based resin solution. Can be.
According to a sixth aspect of the present invention, in the method for manufacturing a bias roll according to the fourth aspect, a core layer of a foamed urethane rubber material in which carbon black is dispersed is formed on the outer periphery of the core metal, and then fixed to the outer peripheral surface of the core metal. After placing the core layer in the mold and injecting a liquid urethane rubber material containing at least carbon black between the surface of the core layer and the inner surface of the mold, the urethane rubber material is heated to a thickness of 0 mm. It is characterized in that a skin layer of .20 to 1.50 mm is formed, and a fluorine resin in which carbon black is dispersed is applied to the surface of the skin layer for coating.
According to the method of manufacturing a bias roll for an image forming apparatus of the invention, the core layer is formed by foaming a carbon black-dispersed urethane rubber material, and then the carbon black is formed between the core layer surface and the mold inner surface. After a dispersed liquid urethane rubber material is injected and heated to form a skin layer, a fluorine-based resin liquid dispersed with carbon black is applied to the surface of the skin layer 2c to form a coating layer 2d. Therefore, similarly to the fifth aspect of the present invention, the hardness of the bias roll 2 can be stably obtained within the above range. In addition, the thickness of the skin layer 2c can be uniformly and reliably formed within the range of 0.20 to 1.50 mm, and the thickness of the coating layer 2d can be easily adjusted by applying a fluorine-based resin solution. Can be.
[0032]
An image forming apparatus according to a seventh aspect of the present invention and a bias roll according to the ninth aspect of the present invention, wherein the core layer 2b comprises various foamed rubber materials as constituent components, The surface roughness Rz is further limited to 15 μm or less. Therefore, the same effects as those of the first and fifth aspects of the invention are achieved. In addition, since the surface of the bias roll 2 is smooth, toner transferred to the bias roll 2 during non-transfer can be reliably removed by a cleaning member such as the cleaning blade 6.
According to the image forming apparatus of claim 8, when the coating layer 2d having a film thickness in the range of 15 to 30 μm is formed on the skin layer 2c having the surface roughness Rz of 20 μm or less, for example, by a coating method. A bias roll 2 having a surface roughness Rz of 15 μm or less is obtained. Such a surface roughness Rz can be obtained without being affected by the materials of the core layer 2b and the skin layer 2c. Therefore, the eighth aspect of the invention has the same effect as the seventh aspect of the invention.
[0033]
【Example】
Hereinafter, the present invention will be described specifically with reference to Examples, but the present invention is not limited to the following Examples.
(Image forming device)
FIG. 3 is an overall view of a digital color copying machine provided with an intermediate transfer belt as an image forming apparatus of the present invention.
3, light emitted from a document illumination lamp 12 moving along the lower surface of a document (not shown) placed on a platen 11 and reflected by the document is reflected by a movable mirror unit 13, a lens 14, and a fixed mirror. The light is converged on the CCD of the image reading unit via the line 15. The CCD converts the original image into an electric signal for each color by using a number of photoelectric conversion elements and filters of three colors of red (R), green (G), and blue (B). The electric signal is input to the image processing circuit 16, and the image processing circuit 16 has an image memory that converts the original image reading signal input for each color into a digital signal and stores it.
[0034]
The optical writing control device 17 reads out the image data of the image processing circuit 16 at a predetermined timing and outputs it to the light beam writing device 18. The light beam writing device 18 writes an electrostatic latent image corresponding to each color on an image carrier 19 composed of a photosensitive drum rotating in the direction of arrow A. Around the image carrier 19, a charging charger 20 for uniformly charging the surface thereof, a developing unit 21 for developing an electrostatic latent image written on the image carrier 19 into a toner image of each color, A transfer corotron 22, which primarily transfers a toner image to the intermediate transfer belt 1, a cleaner unit 23 having a static eliminator and a cleaning blade are provided.
The developing unit 21 has a developing device containing toner of each color of black (K), yellow (Y), magenta (M), and cyan (C), and develops the electrostatic latent image with the toner of each color. And visualize it.
The intermediate transfer belt 1 is stretched around the backup roll 3 and the belt transport rolls 24, 25, 26 pressed by the electrode roll 4, and moves in the tangential direction while abutting on the surface of the image carrier 19. In this embodiment, of the rolls (3, 24 to 26) that stretch the transfer belt 1, the belt transport roll 24 is used as a drive roll so that the transfer belt 1 moves in the direction of arrow B, and the other rolls (3 to 24) are moved. , 25, 26) are configured as driven rolls. Further, in order to prevent the transfer belt 1 from bending, the shaft of the belt transport roll 26 is urged in the direction C by a spring (not shown).
[0035]
On the back side of the intermediate transfer belt 1, the transfer corotron 22 is disposed at a primary transfer portion where the image carrier 19 and the surface of the transfer belt 1 are in contact. On the other hand, the bias roll 2 and the belt cleaner 27 are disposed on the front side of the transfer belt 1 carrying the unfixed toner image, facing the backup roll 3 and the belt transport roll 24, respectively. A portion where the bias roll 2 and the backup roll 3 face each other is a secondary transfer portion.
Further, between the backup roll 3 and the belt transport roll 24, a separation claw 28 for separating the sheet P carrying the secondary-transferred toner image from the transfer belt 1 is arranged. A cleaning blade 6 made of urethane rubber is always in contact with the surface of the bias roll 2 to remove foreign matters such as toner particles and paper powder attached during secondary transfer or the like.
[0036]
An extractable paper feed tray 29 is provided at a lower portion of the image forming apparatus U main body, and a pickup roller 30 is disposed above the paper feed tray 29. Downstream of the pickup roller 30, a pair of feed rolls 31, a paper transport roll 32, a guide member 33 for guiding the paper P, and a registration roll 34 are sequentially arranged.
On the downstream side of the secondary transfer section, a transport belt 35 for transporting a sheet P carrying the secondary-transferred toner image sequentially, a fixing device 36 for fixing an unfixed toner image on the sheet P, a fixed image A pair of discharge rolls 37 for discharging the paper P on which the paper P is formed outside the apparatus, and a paper discharge tray 38 for placing the discharged paper P are arranged.
[0037]
(Operation of Image Forming Apparatus)
The surface of the image carrier 19 rotating in the direction of arrow A is uniformly charged by the charging charger 20. An electrostatic latent image is written on the uniformly charged image carrier 19 by the light beam writing device 18. The electrostatic latent image on the image carrier 19 is developed by the developing unit 21 into an unfixed toner image. In the formation of the toner image, the first color toner image is formed first, and thereafter, every time the image carrier 19 rotates once, the second to fourth color toner images are formed. In this embodiment, K, Y, M, and C color toner images are sequentially formed. After the toner image is transferred onto the intermediate transfer belt 1, the surface of the image carrier 19 is cleaned by the blade of the cleaner unit 23.
Here, the optical writing control device 17 first reads out the digital signal of K color of the first color and outputs it to the light beam writing device 18. The writing device 18 writes an electrostatic latent image corresponding to K color on the surface of the image carrier 19. The electrostatic latent image corresponding to the K color is developed by the developing unit K in the developing unit 21 into a visualized toner image of the K color, and moves to the primary transfer unit. In the primary transfer section, a K-color toner image that has reached the primary transfer section is applied to the toner image from the transfer corotron 22 disposed on the back side of the intermediate transfer belt 1 by applying an electric field having a polarity opposite to the charging polarity of the toner image. While being electrostatically attracted to the intermediate transfer belt 1, the primary transfer is performed by moving the intermediate transfer belt 1 in the direction of arrow B.
[0038]
The intermediate transfer belt 1 moves at the same cycle as the image carrier 19 while holding the K toner image by suction. When the transfer of the K toner image of the first color is completed, the output of the optical writing controller 17 outputs the Y color of the second color until the transfer start position of the K toner image on the transfer belt 1 reaches the primary transfer portion. Writing of the electrostatic latent image is started. When the transfer start position of the transfer belt 1 carrying the K toner image reaches the primary transfer portion, the transfer corotron 22 transfers the second color Y toner image. Subsequently, the transfer of the M toner image and the C toner image is performed in the same manner as the transfer of the Y toner image.
In this way, a multiple toner image superimposed on each color is formed on the intermediate transfer belt 1. Until the toner images of each color are primarily transferred onto the intermediate transfer belt 1, the bias roll 2, the release claw 28, and the belt cleaner 27 disposed on the surface side of the transfer belt 1 are retracted away from the intermediate transfer belt 1. Held in position.
[0039]
On the other hand, the paper P stored in the paper feed tray 29 is taken out one by one at a predetermined timing by a pickup roller 30, fed by a pair of feed rolls 31 and a paper transport roll 32, and temporarily once by a pair of registration rolls 34. Stopped. The paper P is then transferred from the registration roll 34 to the secondary transfer section in synchronization with the transfer of the multiple toner images of each color (K, Y, M, C) transferred onto the intermediate transfer belt 1 to the secondary transfer section. Transported to the department.
In the secondary transfer section, the bias roll 2 is in pressure contact with the backup roll 3 via the transfer belt 1. Then, the conveyed paper P passes through the secondary transfer section by the press-contact conveyance between the rolls 2 and 3 and the movement of the transfer belt 1. At this time, due to electrostatic repulsion caused by application of a transfer voltage having the same polarity as the charge polarity of the toner image from the electrode roll 4, the toner image adsorbed and carried on the transfer belt 1 is transferred from the surface of the intermediate transfer belt 1 to the paper P Transcribed. When the bias roll 2 is pressed against the backup roll 3, foreign matter such as toner particles attached to the surface of the bias roll 2 is removed by the cleaning blade 6.
[0040]
Although the transfer of a full-color image has been described above, in the case of forming a single-color image, when the toner image of, for example, K primarily transferred onto the intermediate transfer belt 1 moves to the secondary transfer portion, the toner image is immediately The image is transferred to the sheet P. When an image of a plurality of colors is formed, desired hue is selected, and when the multicolor toner image superimposed on those colors moves to the secondary transfer unit, the toner image may be transferred to the paper P. . In the case of the transfer of the multicolor image, the rotation of the image carrier 19 and the movement of the intermediate transfer belt 1 are synchronized as described above so that the toner images of the respective colors exactly match without shifting at the primary transfer portion. I have.
As described above, the paper P on which the toner image has been transferred to the desired hue is peeled by the operation of the peeling claw 28, placed on the transport belt 35, and transported to the fixing device 36. Then, after fixing the unfixed toner image to the permanent image in the fixing device 36, the sheet P is discharged to a discharge tray 38 by a pair of discharge rollers 37. When the secondary transfer is completed, the surface of the intermediate transfer belt 1 is cleaned by a belt cleaner 27 provided downstream of the secondary transfer unit to prepare for the next transfer.
[0041]
(Secondary transfer member)
The specific configuration of the secondary transfer member in the image forming apparatus shown in FIG. 3 is as follows.
The intermediate transfer belt (1) has a thickness of 80 μm and a surface resistivity of 10¹²Ω / □ polyimide was used. As the bias roll (2), a core layer (2b), a skin layer (2c), and a coating layer (2d) were formed on a SUS cored bar (2a) having an outer diameter of 15 mm, as shown in "Production of bias roll" below. ) Were used, and a roll having a length of 325 mm and an outer diameter of 28 mm was used.
As the backup roll (3), a conductive silicone rubber molded to a thickness of 6.5 mm was used. Its hardness is 62 ° and its surface resistivity is 10⁹  Ω / □. The outer diameter of the backup roll (3) is 28 mm, which is the same diameter as the bias roll (2). A SUS metal roll having a diameter of 12 mm was used as the electrode roll (4).
[0042]
(Manufacture of bias roll)
The bias roll shown in the examples was manufactured as follows. The following "parts" means "parts by weight" with respect to 100 parts by weight of the rubber material.
Example 1
100 parts of a rubber material (EPDM EP33: manufactured by Nippon Synthetic Rubber Co., Ltd.) containing 1.5% by weight of sulfur as a vulcanizing agent and 0.6% by weight of tetramethylthiuram disulfide as a vulcanization accelerator, and Ketjen Black (a conductive agent) Composition ratio of 14 parts of Lion Aguso Co., Ltd., 20 parts of FT Carbon (manufactured by Asahi Carbon Co., Ltd.), 6 parts of p, p'-oxy-bis (benzenesulfonylhydrazide) as a blowing agent and 6 parts of mineral oil as a softening agent Was kneaded with a kneader and a roll.
This kneaded product was extruded into a tube shape by an extruder, and the mixture was heated in a vulcanizer at a temperature of 126 ° C. and a pressure of 1.5 kg / cm.²It was foamed and vulcanized by heating under the pressurized steam of G. A SUS core metal (2a) having an outer diameter of 15 mm was pressed into the cavity of the obtained foamed elastic body, and the surface of the foamed elastic body was polished to form a core layer (2b) having an outer diameter of 28 mm.
[0043]
Next, 10 parts of Ketjen black and 25 parts of FT carbon were added to 100 parts of a rubber material (NE40; manufactured by Nippon Synthetic Rubber Co., Ltd.) in which NBR and EPDM were blended at a weight ratio of 4: 6, and kneaded. did. This kneaded material was coated on the outer peripheral surface of the core layer (2b) by a tube cloth head extruder. At this time, the outer diameter of the core layer was reduced to 27.5 mm due to the pressurization of the tube material. This tube material is put in a vulcanizer at a temperature of 127 ° C. and a pressure of 1.55 kg / cm.²It was heated under the pressurized steam of G, vulcanized and adhered to the core layer. Thereafter, the surface of the roll was polished to obtain dimensions, and the outer diameter of the foamed rubber roll (2b, 2c) having the skin layer (2c) adhered to the outer peripheral surface of the core layer was set to 28 mm.
Further, an aqueous emulsion paint of the urethane-modified TFE resin containing carbon black (Emulalon 345E) was applied to the surface of the skin layer (2c) by a spray method, and then heated and cured at 100 ° C. for 35 minutes to obtain a film having a thickness of 15 μm. A coating layer (2d) was formed.
Thus, a bias roll (2) having a three-layer structure was manufactured. In this bias roll, most of the cell diameter in the core layer was in the range of 50 to 300 μm, and the hardness of the foamed rubber roll and the bias roll was 36 ° and 40 °, respectively. The volume resistivity of the foamed rubber roll, the coating layer and the bias roll is 10^5.78Ωcm, 10^4.55Ωcm, 10Ω^5.32cm.
[0044]
Example 2
A kneaded product obtained by blending a foaming agent with an elastic material having a composition ratio of 100 parts of polyether urethane and 15 parts of carbon black is extruded into a tube shape by an extruder, which is heated and foamed and vulcanized. A foamed elastic body was formed. A SUS cored bar (2a) having an outer diameter of 15 mm coated with a hot-melt type adhesive was press-fitted into the cavity of the foamed elastic body, and then heated and bonded. To form a core layer (2b) having an outer diameter of 25.5 mm.
A urethane elastic material similar to the above elastic material was used except that the formed core layer was concentrically positioned in a mold having an inner diameter of 28 mm and a foaming agent was removed between the outer peripheral surface of the core layer and the inner surface of the mold. Injected. Next, the inside of the mold was heated to 160 ° C. for vulcanization, and the elastic material was fixed to the outer peripheral surface of the core layer. Thereafter, the surface of the molded foam rubber roll was polished to form a skin layer (2c) having a surface roughness Rz of 20 μm and a thickness of 1.25 mm. Further, a coating layer (2d) was formed in the same manner as in Example 1. At this time, the surface roughness Rz of the coating layer (2d) was 15 μm.
Thus, a bias roll (2) having a three-layer structure was manufactured. In the bias roll (2), most of the cell diameter in the core layer was in the range of 0.2 to 1.0 mm, and the hardness of the foamed rubber roll and the bias roll was 30 ° and 36 °, respectively. The volume resistivity of the foamed rubber roll, the coating layer and the bias roll is 10^5.46Ωcm, 10^4.55Ωcm, 10^5.18Ωcm.
[0045]
(Secondary transfer test of bias roll)
The image forming apparatus shown in FIG. 3 equipped with the bias rolls of the first and second embodiments is operated to evaluate the transfer image quality and the stain on the back surface of the sheet, and further measure the load torque due to the load of the cleaning blade (6) of the bias roll. did. The results are shown in Table 1 below.
Further, as Comparative Examples 1 to 4, 1) a bias in which a 50 μm-thick PFA tube was directly coated without forming a skin layer on a core layer made of a foamed silicone rubber instead of the bias roll of the above-described embodiment. Roll, 2) a bias roll composed of silicone rubber as the core layer and skin layer foamed without coating the coating layer, 3) a bias roll composed of only the foamed silicone rubber core layer, and 4) a foamed EPDM. Each of the vise rolls consisting only of the core layer was used for the above test. Table 1 shows the results. The “dirt on the back surface of the paper” in Table 1 was evaluated by the number of rotations of a vise roll required for removing the toner.
[0046]
[Table 1]

Transfer image quality
: No image quality defect occurred
×: Image quality defect occurred
−: The paper is very dirty, not evaluated
Dirt on the back of the paper
○: Once
△: 2 to 4 times
×: 5 times or more
[0047]
In Comparative Example 1 in which the hardness of the bias roll was higher than 45 °, an image quality defect such as a hollow character of the transfer image quality occurred, and the transfer image quality was poor. Further, as is apparent from Examples 1 and 2 and Comparative Example 1, by coating the surface of the bias roll with a material having a small surface energy, the adhesion of the toner to the bias roll is reduced, and the scraping action of the cleaning blade is reduced. Since it can be sufficiently exhibited, there is no stain on the back surface of the paper.
Further, in Comparative Example 2 in which the skin layer was the surface layer without coating the coating layer, the toner adhered to the vice roll could not be sufficiently removed by one rotation of the vise roll. On the other hand, in Comparative Examples 3 and 4 using foamed silicone rubber and foamed EPDM as the bias rolls, the friction coefficient of the foamed rubber is large, so that the load torque by the cleaning blade is as large as 0.11 Nm. As a result, in the image forming apparatus shown in FIG. 3, a trouble occurred in which the intermediate transfer belt did not slip around the driving roller (the belt transport roll 24) and did not rotate.
[0048]
(Foam roll andBias roll volume resistivity)
Foam roll (That is, a roll having a cored bar, a core layer fixed to the outer peripheral surface of the cored bar, made of EPDM foamed rubber material or urethane rubber, and a skin layer for adjusting the surface roughness and hardness of the core layer.) And bias roll (That is, a foamed roll and a roll having a coating layerFIG. 4 shows a method for measuring the volume resistivity of ()).
The measurement method of each roll is as follows. A copper tape of 24.5 mm width (w) is wound around the roll in three circumferential directions (central part, both ends 50 mm) in the circumferential direction of the roll, and the roll core metal and the copper tape are wound together. During this period, a voltage (V) of 20 V was applied, and the current value (I) 10 seconds after the application of the voltage was read, and the volume resistivity ρv (Ωcm) was determined by the following equation.
ρv = 2πwV / I · ln (r2 / r1)
Here, r1 is the outer diameter of the core metal (15 mm)
r2: Roll outer diameter (28mm)

[0049]
Tables 2 and 3 show the roll hardness and the roll outer diameter, in addition to the volume resistivity (logρv) of the foamed rubber roll before and after coating the coating layer measured according to the measurement method shown in FIG. In addition, the volume resistivity of each roll shown in Examples and Comparative Examples of the present invention was determined according to the above-described measurement method.
In addition, the standard deviation value representing the variation of the roll resistance shown in the table was measured at three axial positions of the roll shown in FIG. 4 for each of ten rolls, and the volume obtained from a total of 30 tests was performed. It was determined by resistivity.
As shown in Tables 2 and 3 below, it can be seen that the dispersion of the volume resistivity is reduced by the coating of the coating layer of the foamed rubber roll, and the roll hardness is also small by the coating.
[0050]
[Table 2]

[Table 3]

[0051]
Example 3
A foamed silicone rubber compound in which 2,5-dimethyl-2,5-di (t-butylperoxy) hexane, a foaming agent and silica were blended with a silicone rubber containing 15% by weight of carbon black was kneaded with two rolls. This kneaded product is pressed into a SUS cored bar (2a) having an outer diameter of 15 mm by an extruder, molded, and then heated at 230 ° C. for 3 hours in a mold to foam and vulcanize to form a core layer (b). ) And the skin layer (2c) were simultaneously molded. The surface of the molded foam rubber roll having an outer diameter of 28 mm was polished to form a skin layer (2c) having a surface roughness Rz of 12 μm and a thickness of 100 μm.
Further, an FEP-based conductive paint (the above-mentioned GLS-213R) containing 20% by weight of carbon black is applied to the surface of the skin layer (2c) by a spray method, and then heated and cured at 210 ° C. for 10 minutes to form a coating having a thickness of 15 μm. A layer (2d) was formed. At this time, the surface roughness Rz of the coating layer (2d) was 9 μm.
In the bias roll (2) having a three-layer structure manufactured as described above, the average cell diameter in the core layer was 100 μm, and the hardness was 35 °. The volume resistivity of the foamed rubber roll (2b, 2c) is 10^5.3Ωcm, and the volume resistivity of the coating layer (2d) is 10^2.1  Ωcm, and the volume resistivity of the bias roll (2) is 10^4.6Ωcm.
[0052]
Example 4
A bias roll (2) was manufactured in the same manner as in Example 3, except that the skin layer (2c) was polished so that the surface roughness Rz became 17 μm. The surface roughness Rz of the surface of the obtained bias roll (2), that is, the coating layer (2d) was 12 μm.
Example 5
A bias roll (2) was manufactured in the same manner as in Example 3, except that the skin layer (2c) was polished so that the surface roughness Rz became 20 μm. The surface roughness Rz of the formed coating layer (2d) was 15 μm.
[0053]
Comparative Example 5
The surface roughness Rz of the skin layer (2c) is 22 μm.To beA bias roll (2) having a hardness of 33 ° was manufactured in the same manner as in Example 3 except that polishing was performed and the coating layer (2d) was formed to a film thickness of 10 μm. At this time, the surface roughness Rz of the coating layer (2d) was 18 μm.
Comparative Example 6
A bias roll (2) was manufactured in the same manner as in Example 3, except that the skin layer (2c) was polished so as to have a surface roughness Rz of 26 μm. The surface roughness Rz of the formed coating layer (2d) was 22 μm.
[0054]
With respect to the bias rolls of Examples 3 to 5 and Comparative Examples 5 and 6, the transfer image quality and the stain on the back surface of the paper were evaluated. The evaluation criteria are the same as those in the case of the “bias roll secondary transfer test”. The results are shown in Table 4 below. Table 4 summarizes the surface roughness (Rz) of the skin layer, the film thickness and the surface roughness (Rz) of the coating layer.
The physical properties of each bias roll were the same as those shown in Example 3 except for the surface roughness and the hardness of Comparative Example 5.
[Table 4]

[0055]
In a bias roll in which the coating layer has a thickness of 10 μm, 15 μm, 20 μm, 25 μm, and 30 μm, the surface roughness (Rz) of the coating layer formed when the surface roughness (Rz) of the skin layer is changed is adjusted. As shown in FIG. These bias rolls were manufactured according to the method described in Example 3. In FIG. 5, the film thickness of the coating layer is indicated by the symbols of 10 μm: ●, 15 μm: ○, 20 μm: Δ, 25 μm: □, 30 μm: ▲.
As is apparent from FIG. 5, when the surface roughness of the skin layer is adjusted to 20 μm or less and the coating layer is formed in the thickness range of 15 to 30 μm, the bias roll having the surface roughness of 15 μm or less is stabilized. Can be manufactured. Since such a bias roll is made of a material having a smooth surface and a small surface energy, as shown in Table 4, the back surface of the paper is not contaminated with toner during the secondary transfer.
[0056]
【The invention's effect】
The image forming apparatus and the bias roll of the present invention are provided with a core layer composed of an EPDM foamed rubber material or a urethane foamed rubber via a skin layer on the outer peripheral surface of a cored bar and a coating having a material having a small surface energy as a component. It has a three-layer structure covered with layers. Alternatively, a three-layer structure in which a core layer fixed to the outer peripheral surface of a cored bar is made of a foamed rubber material, and a coating layer formed via a skin layer is made of a material having a surface roughness of 15 μm or less and a small surface energy. Consists of Accordingly, since the surface of the bias roll is smooth without irregularities due to the foam cells, the toner does not easily adhere, and even if the toner adheres, the toner can be easily removed with a cleaning blade or the like.
In addition, since the thickness of the surface coating layer is in the range of 5 to 30 μm, a low-hardness bias roll can be stably obtained. And a high quality transfer image can be obtained.
According to the method of manufacturing a bias roll for an image forming apparatus of the present invention, a bias roll can be stably obtained within a hardness range of 20 to 45 °, and a skin layer having a uniform thickness can be reliably formed. In addition, it is easy to adjust the thickness of the coating layer.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a secondary transfer unit in an image forming apparatus of the present invention.
FIG. 2 is an explanatory diagram of a contact angle which is a measure of surface energy.
FIG. 3 is an overall view of an image forming apparatus shown as one embodiment of the present invention.
FIG. 4 is an explanatory view showing a method of measuring the volume resistivity of a foamed rubber roll and a bias roll.
FIG. 5 is a graph showing the relationship between the surface roughness of the skin layer and the surface roughness of the coating layer in the bias roll depending on the difference in the thickness of the coating layer.
FIG. 6 is an explanatory diagram of a secondary transfer unit in a conventional image forming apparatus.
[Explanation of symbols]
U: image forming apparatus, P: paper (recording medium), 1: intermediate transfer belt, 2: bias roll, 2a: core metal, 2b: core layer, 2c: skin layer, 2d: coating layer, 3: backup roll, 19: image carrier, 21: developing unit (developing device).

Claims (9)

An image carrier on which an electrostatic latent image corresponding to image information is formed, a developing device for visualizing the electrostatic latent image formed on the image carrier as a toner image with toner, and a toner image carried on the image carrier From the intermediate transfer belt on which the primary transfer is performed, a bias roll for secondarily transferring the unfixed toner image on the intermediate transfer belt to the recording medium, and a backup roll for supporting the intermediate transfer belt from the back surface opposite to the bias roll. The bias roll is configured to adjust the surface roughness and hardness of the core layer and the core layer composed of the EPDM foam rubber material or the urethane foam rubber fixed to the outer peripheral surface of the core bar and the core layer. For example, a coating layer having a thickness of 5 to 30 μm and comprising a material having a small surface energy having a contact angle of 90 ° or more with a skin layer and a water droplet when expressed by wettability of water. ,
The volume resistivity of the material layer between the core metal and the outer surface of the skin layer calculated assuming that the material layer between the core metal and the outer surface of the skin layer is uniform (hereinafter referred to as “foaming roll”) volume resistivity "of.) is 10 ⁴ to 10 in the range of ^{7 Ω} · cm, and the volume resistivity of the coating layer is at a lower value than the volume resistivity of the foamed roll 10 ² to 10 ⁵ Omega cm And the volume resistivity of the material layer between the core metal and the outer surface of the coating layer calculated assuming that the material layer between the core metal and the outer surface of the coating layer is a uniform material layer. (hereinafter, referred to as "volume resistivity of the bias roll.") is in the range of and 10 ⁴ ~10 ⁷ Ω cm at a value lower than the volume resistivity of the foamed roll, and hardness Asker C hardness of the bias roll Characterized by being in the range of 20 to 45 ° Device. 2. The bias roll according to claim 1, wherein the core layer is made of the EPDM foamed rubber material having an average cell diameter of 50 to 300 μm in which carbon black is dispersed, and the skin layer is made of EPDM having a thickness of 10 to 800 μm in which carbon black is dispersed. An image forming apparatus comprising a rubber-based material and a coating layer comprising a fluorine-based resin in which carbon black is dispersed. 2. The bias roll according to claim 1, wherein the core layer is made of the urethane foam rubber having an average cell diameter of 50 to 1000 [mu] m in which carbon black is dispersed, and the skin layer is urethane having a thickness of 10 [mu] m to 1.50 mm in which carbon black is dispersed. An image forming apparatus comprising a rubber and a coating layer comprising a fluororesin in which carbon black is dispersed. A core metal, a core layer composed of an EPDM foamed rubber material or a urethane foam rubber fixed to the outer peripheral surface of the core metal, a skin layer for adjusting the surface roughness and hardness of the core layer, and water wetting. A coating layer having a thickness of 5 to 30 μm having a material having a small surface energy having a contact angle with a water droplet of 90 ° or more when expressed as a property,
The volume resistivity of the foamed roll is in the range of 10 ⁴ ~10 ⁷ Ω · cm, the volume resistivity of the coating layer is and 10 ² ~10 ⁵ Ω cm at a value lower than the volume resistivity of the foamed roll in the range, the range of the bias volume resistivity of the roll and at a lower value than the volume resistivity of the foamed roll 10 ⁴ ~10 ⁷ Ω cm, and 20 to the hardness of the bias roll Asker C hardness A bias roll for an image forming apparatus for secondary-transferring a toner image on an intermediate transfer belt onto a sheet, wherein the bias roll is in a range of 45 °. After forming a core layer of a foamed EPDM-based rubber material in which carbon black is dispersed, an EPDM-based rubber material containing at least carbon black is extruded, and then heated to a thickness of 0.1 mm. 5. The method for manufacturing a bias roll according to claim 4, wherein the core layer is covered with a skin layer having a thickness of 20 to 0.80 mm, and a fluorine-based resin in which carbon black is dispersed is applied to the surface of the skin layer for coating. . A core layer of a foamed urethane rubber material in which carbon black is dispersed is formed on the outer periphery of the core metal, and then the core layer fixed to the outer peripheral surface of the core metal is positioned in the mold, and the surface of the core layer and the inner surface of the mold are formed. After injecting a liquid urethane rubber material containing at least carbon black between them, the urethane rubber material is heated to form a skin layer having a thickness of 0.20 to 1.50 mm, and further, fluorine containing carbon black is dispersed. 5. The method for manufacturing a bias roll according to claim 4, wherein a coating process is performed by applying a base resin to the surface of the skin layer. An image carrier on which an electrostatic latent image corresponding to image information is formed, a developing device for visualizing the electrostatic latent image formed on the image carrier as a toner image with toner, and a toner image carried on the image carrier From the intermediate transfer belt on which the primary transfer is performed, a bias roll for secondarily transferring the unfixed toner image on the intermediate transfer belt to the recording medium, and a backup roll for supporting the intermediate transfer belt from the back surface opposite to the bias roll. The bias roll comprises a cored bar, a core layer composed of a foamed rubber material fixed to the outer peripheral surface of the cored bar, a skin layer for adjusting the surface roughness and hardness of the core layer, and water. Consisting of a coating layer having a thickness of 5 to 30 μm containing a material having a small surface energy having a contact angle of 90 ° or more with a water droplet when expressed in terms of wettability,
The volume resistivity of the foamed roll is in the range of 10 ⁴ ~10 ⁷ Ω · cm, the volume resistivity of the coating layer is and 10 ² ~10 ⁵ Ω cm at a value lower than the volume resistivity of the foamed roll in the range, the range of the bias roll and at a lower value than the volume resistivity of the volume resistivity of the foamed roll 10 ⁴ ~10 ⁷ Ω cm, the surface roughness Rz of the coating layer be 15μm or less And the hardness of the bias roll is in the range of 20 to 45 ° in Asker C hardness. 8. The image forming apparatus according to claim 7, wherein the surface roughness Rz of the skin layer is not more than 20 [mu] m, and the thickness of the coating layer is in a range of 15 to 30 [mu] m. A core metal, a core layer composed of a foamed rubber material fixed to the outer peripheral surface of the core metal, a skin layer for adjusting the surface roughness and hardness of the core layer , A coating layer having a thickness of 5 to 30 μm and a material having a small surface energy having a contact angle of 90 ° or more with a water droplet,
The volume resistivity of the foamed roll is in the range of 10 ⁴ ~10 ⁷ Ω · cm, the volume resistivity of the coating layer is and 10 ² ~10 ⁵ Ω cm at a value lower than the volume resistivity of the foamed roll in the range, the range of the bias volume resistivity of the roll and at a lower value than the volume resistivity of the foamed roll 10 ⁴ ~10 ⁷ Ω cm,
An image forming apparatus for secondary-transferring a toner image on an intermediate transfer belt onto paper, wherein the surface roughness Rz of the coating layer is 15 μm or less and the hardness is in the range of 20 to 45 ° in Asker C hardness. For bias roll.

Images