JP3612893B2 - Image forming apparatus - Google Patents

Description

【００３１】
（電界依存性）
沿面タイプの２層構造ＥＰＤＭロールについて、半導電層中に分散されるカーボンブラックの配合量を変更して、抵抗水準の異なるＥＰＤＭロールに１ｋＶ，２ｋＶ，３ｋＶ，４ｋＶ，５ｋＶの電圧を印加した時の抵抗値を図９に示す。抵抗値の計測は、前述した図８Ａに示す方法に従って求めた。なお、図中の●印で示すロールの印加電圧１ｋＶでの抵抗値（ｌｏｇ Ω）は８．５であり、○印で示すロールの抵抗値は９．６である。図９に示すように、本発明の沿面タイプ転写ロールでは、印加電圧１ｋＶと５ｋＶで抵抗値が約０．５桁ほど異なり、電界依存性が比較的小さい。
比較例として単層構造の発泡ＥＰＤＭロールについて、ロール中に分散されるカーボンブラックの配合量を変更して、抵抗水準の異なる発泡ＥＰＤＭロールに１ｋＶ，２ｋＶ，３ｋＶ，４ｋＶ，５ｋＶの電圧を印加した時の抵抗値を図１０に示す。抵抗値の計測は、前述した図８Ｂに示す方法に従って求めた。なお、図１０中の▲印で示すロールの印加電圧１ｋＶでの抵抗値は７．２であり、△印で示すロールの抵抗値は８．３であり、■印で示すロールの抵抗値は１０．４である。図１０に示すように、比較例の各ＥＰＤＭ転写ロールでは、印加電圧１ｋＶと５ｋＶで抵抗値が約１桁ほど異なり、電界依存性の大きいことが分かる。
【００３２】
表１に示す本発明の沿面タイプＥＰＤＭロールおよび比較例３の発泡ＥＰＤＭロールのバイアス電圧と転写電流の関係を図１１に示す。
例えば、転写電流２０〜４０μＡを確保できる電圧の範囲は、単層の発泡ＥＰＤＭロールでは０．５ｋＶであるのに対して、沿面タイプの２層構造ＥＰＤＭロールでは１．４ｋＶである。すなわち、沿面タイプの転写ロールでは、電界依存性の大きい転写電流を確保するために必要な電圧の範囲（転写ラチチュード）が広くなる。
【００３３】
本発明の沿面タイプ転写ロールにおいて、前述の図６に示す８点で計測された抵抗値ｒ_１〜ｒ_８を表面抵抗率で１０^８ Ω／□とし、そのうち１点の抵抗値ｒ_５ だけが他の部位より１桁低い（１０^７ Ω／□）場合と、２点の抵抗値ｒ_５，ｒ_６が他の部位より１桁低い場合について、電極ロールを転写部に対向する位置（１８０°）と１３５°の位置に配設したときのロールの抵抗値を前述の図８Ａに示す方法に従って求めた。得られた抵抗値の変動を表２に示す。
上記抵抗値ｒ_１〜ｒ_８の計測方法は、図１２に示すように、直径１２ｍｍ，長さ３３０ｍｍの２本のＳＵＳ製金属ロールを、長さ３２５ｍｍの上記転写ロール表面にその円周方向に１０ｍｍ離して０．２ｍｍの食い込み量で接触させ、金属ロール間に１ｋＶの電圧（Ｖ）を印加して行われた。そして、電圧の印加から１０秒後の電流値（Ｉ）を読み取って、下記の式により表面抵抗率ρｓ を求めた。
ρｓ ＝ ＬＶ／ＧＩ
Ｌ：転写ロールの長さ（ｃｍ）
Ｇ：２本の金属ロール間の距離（ｃｍ）
【００３４】
【表２】

【００３５】
上記の表２をグラフ化したもの、すなわち転写ロールに圧接する電極ロールが転写部に対して１８０°の位置と１３５°の位置に配設された場合の転写ロールの抵抗値の変動を図１３に示す。図１３において、実線は８点中１点の抵抗値が低い場合であり、破線は８点中２点の抵抗値が低い場合である。また、●印は電極ロールを転写部に対して１８０°の位置に配設させた場合であり、○印は１３５°の位置に配設させた場合である。
表２，図１３に示すように、転写部に対向する位置にバイアス電圧を印加することにより、転写部に対する転写ロールの周方向における抵抗値のバラツキの影響を低減することができる。
【００３６】
実施例２
（画像形成装置Ｕ_２ ）
図１４は本発明の画像形成装置として中間転写ベルトを備えたデジタルカラー複写機の全体図である。なお、図７に示す画像形成装置と重複する説明は省略することにする。
図１４において、前記画像書込手段３が構成要素２１〜２８から構成される。像担持体１の周囲には、図７に示す画像形成装置と同様に、帯電器２、現像装置４、各色のトナー像を前記中間転写ベルト１２に転写する一次転写ロール１１、クリーニング装置８が配置されている。
中間転写ベルト１２は、前記ベルト搬送ロール１３ａ，１３ｂ，１３ｃおよびバックアップロール１４に張架され、像担持体１表面に当接しながらその接線方向に移動する。本実施例では、転写ベルト１２を張架する各ロール（１３，１４）のうち、転写ベルト１２が矢印Ｂ方向に移動するよう、ベルト搬送ロール１３ｂを駆動ロールとし、他のロール（１３ａ，１３ｃ，１４）は従動ロールとして構成されている。また、転写ベルト１２の撓みを防止するために、搬送ロール１３ｃの軸はバネ（図示せず）によって方向Ｃに付勢されている。
【００３７】
中間転写ベルト１２の裏面側には、前記一次転写ロール１１が像担持体１表面と転写ベルト１２とが接触する一次転写部に接離可能に配置されている。一方、未定着トナー像を担持する転写ベルト１２の表面側には、バックアップロール１４およびベルト搬送ロール１３ａに対向して、それぞれ前記二次転写ロール１５およびベルトクリーナ１６が配置されている。ロール１４，１５が対向する前者の部位が二次転写部となる。
また、バックアップロール１４とベルト搬送ロール１３ａとの間には、二次転写されたトナー像を担持する用紙Ｐを転写ベルト１２から剥がす剥離爪３７が配置されている。上記二次転写ロール１５表面には、ポリウレタンで成形されたクリーニングブレード３８が常時当接していて、二次転写時等で付着したトナー粒子や紙粉等の異物が除去される。
図４，１４に示すように、一次転写ロール１１には、電圧印加手段１０ｂとしての電源に接続した電極ロール９ｂが圧接していて、２ｋＶのバイアス電圧が印加される。また、二次転写ロール１５には、電圧印加手段１０ｃに接続した電極ロール９ｃが圧接していて、−２ｋＶのバイアス電圧が印加される。
【００３８】
（画像形成装置Ｕ_２ の作用）
前述した画像形成装置Ｕ_１ と同様にして、第１色目のＹ色のトナー像に現像され、同トナー像が一次転写部へ移動する。一次転写部において、一次転写ロール１１は中間転写ベルト１２を介して像担持体１に押圧した状態にある。そして、電極ロール９ｂからトナー像の帯電極性と逆極性の転写電圧を印加させることにより、Ｙ色のトナー像を静電的に中間転写ベルト１２に吸着させつつ、転写ベルト１２の矢印Ｂ方向の移動で一次転写させる。
中間転写ベルト１２は、Ｙトナー像を吸着担持したまま像担持体１と同一の速度で移動する。１色目のＹトナー像の転写が終了すると、転写ベルト１２におけるＹトナー像の転写開始位置が一次転写部に到達する迄に、光書込制御装置２７からの出力によりグリーン（Ｇ）のフィルタで色分解された光像に対応する静電潜像の書込が開始される。そして、Ｙトナー像を担持した転写ベルト１２の上記転写開始位置が一次転写部に到達すると、一次転写ロール１１によって２色目のＭトナー像の転写が行われる。続いて、Ｃ，Ｋ色の静電潜像が順次現像器４ｃ，４ｋにより可視化され、Ｃ，Ｋトナー像の転写が上記Ｍトナー像の転写と同様に行われる。
このようして、各色に重ね合わされた多重トナー像が中間転写ベルト１２上に形成される。各色のトナー像が中間転写ベルト１２に一次転写された後に、クリーニング装置８のブレードにより、像担持体１の表面はクリーニングされる。また、各色のトナー像が転写ベルト１２上に一次転写されるまで、転写ベルト１２の表面側に配置された前記二次転写ロール１５，剥離爪３７およびベルトクリーナ１６は、転写ベルト１２から離間した退避位置に保持されている。
【００３９】
一方、給紙トレイ６から給紙された用紙Ｐは、中間転写ベルト１２上に転写された各色（Ｙ，Ｍ，Ｃ，Ｋ）の多重トナー像が二次転写部に移動してくるのと同期して、前記レジロール３３から二次転写部に搬送される。
二次転写部において、二次転写ロール１５は中間転写ベルト１２を介してバックアップロール１４に押圧した状態にある。そして、搬送されてきた用紙Ｐは、ロール１４，１５間の圧接搬送および転写ベルト１２の移動によって二次転写部を通過する。この際、電極ロール９ｃからトナー像の帯電極性と同極性の転写電圧の印加による静電反撥により、転写ベルト１２に吸着担持されていたトナー像が転写ベルト１２表面から用紙Ｐに二次転写される。また、二次転写ロール１５がバックアップロール１４に押圧すると、二次転写ロール１５表面に付着したトナー粒子等の異物は、前記クリーニングブレード３８により除去される。
【００４０】
ここで、単色画像を形成する場合は、中間転写ベルト１２上に一次転写された例えばＫ色のトナー像が二次転写部に移動してきた時、直ちにトナー像は用紙Ｐに転写される。複数色の画像を形成する場合は、多色トナー像が二次転写部に移動してきた時、トナー像を用紙Ｐに転写すればよい。この多色画像の転写の場合は、各色のトナー像が一次転写部でズレることなく正確に一致するよう、前述のとおり、像担持体１の回転と中間転写ベルト１２の移動とを同期させている。
上述のようにして、トナー像が所望の色相に転写された用紙Ｐは、剥離爪３７の作動により中間転写ベルト１２から剥離され、搬送ベルト３４に載置されて定着装置７に搬送される。その後、定着処理された用紙Ｐは排紙トレイ３６に排出される。二次転写が完了すると、転写ベルト１２は、二次転写部の下流に設けられたベルトクリーナ１６によりクリーニングされ、次の転写に備える。
【００４１】
（一次転写部および二次転写部）
図１４に示した画像形成装置における一次および二次転写部材の具体的な構成は次のとおりである。
一次転写ロール（１１）として２層構造のウレタンゴムロールを用いた。この一次転写ロール（１１）は、図４Ａに示す発泡ゴム層（１１ｂ）および半導電層（１１ｃ）のゴム材料がウレタンゴムで構成され、試験室環境下における印加電圧１ｋＶでの抵抗値が１０^７．７ Ωである以外は、図７に示す前記転写ロール（５）と同様である。
中間転写ベルト（１２）としては、厚さ８０μｍで表面抵抗率１０^１２Ω／□のポリイミド樹脂を用いた。バックアップロール（１４）としては、厚さ６．５ｍｍに成形された外径２８ｍｍの導電性シリコーンゴムが用いられた。その硬度はアスカーＣで６２°であり、表面抵抗率は１０^９ Ω／□であった。
二次転写ロール（１５）としては、外径がバックアップロール（１４）と同径の２層構造のＥＰＤＭロールを用いた。このロール（１５）は、外径１５ｍｍのＳＵＳ製シャフト（１５ａ）を用い、ＥＰＤＭにカーボンブラックを分散させた膜厚１ｍｍの半導電層（１５ｃ）で表面が被覆された絶縁性発泡ＥＰＤＭゴム層（１５ｂ）からなる。その硬度はアスカーＣで４０°であり、試験室環境下における印加電圧１ｋＶでの抵抗値は１０^４．３Ωであった。この転写ロール（１５）をニッブ幅３．０ｍｍでバックアップロール（１４）に押圧させた。
電極部材（９ｃ）として、直径１２ｍｍのＳＵＳ３１４製金属ロールを用い、喰い込み量０．２ｍｍで転写ロール（１５）に圧接させた。また、電圧印加手段（１０ｃ）からは、電極部材（９ｃ）を通じて−２ｋＶの転写電圧が印加されるように構成されている。
【００４２】
【発明の効果】
本発明の画像形成装置は、２層構造の転写ロールが、環境変動による抵抗値の変動の小さい電子導電性のカーボンブラックを分散させた半導電層で絶縁性ロールを被覆した沿面タイプのロールからなり、転写ロールには電極部材を圧接させている。そのため、従来の転写ロールと比較して、上記沿面ロールの周面に沿って転写部に流れる電流経路を長くとることが可能である。
したがって、転写電流のロールの周方向における抵抗値のバラツキの影響を低減することができるだけでなく、転写電流の変化を小さくすることが可能であるので、転写部での電圧依存性を低減することができる。しかも、電界依存性の大きい転写電流を確保するのに必要な転写ラチチュードを広くとることができる。このように、環境変動や電圧変動にかかわらず、一定の転写電流を安定して流すことが可能であるので、高画質の画像を安定して得ることのできる。
本発明においては、電極部材の配設位置を転写部に対向させることによって、上記電流経路が最も長くなるので、抵抗値のバラツキおよび電圧依存性を最も低減させることができる。
【図面の簡単な説明】
【図１】図１Ａは本発明の画像形成装置の概略構成図であり、図１Ｂはその転写部の拡大図である。
【図２】本発明の別の画像形成装置の概略構成図である。
【図３】本発明の更に別の画像形成装置の概略構成図である。
【図４】転写ロールとして本発明における沿面タイプのロールを用いた場合の転写部の拡大図であって、図４Ａ，図４Ｂはそれぞれ一次転写部および二次転写部の拡大図である。
【図５】沿面タイプの転写ロールの電流経路を示す説明図である。
【図６】沿面タイプの転写ロールを周方向に８分割した場合に、バイアス電圧印加位置とロールの抵抗値が計測される転写部の位置を示す説明図である。
【図７】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８】転写ロールの抵抗値を計測する方法を示す説明図である。
【図９】沿面タイプのＥＰＤＭ転写ロールの電界依存性を示すグラフである。
【図１０】従来の発泡ＥＰＤＭ転写ロールの電界依存性を示すグラフである。
【図１１】本発明および比較例における転写ロールのバイアス電圧と転写電流の関係を示すグラフである。
【図１２】ロールの表面抵抗率計測方法を示す説明図である。
【図１３】転写部に対して１８０°の位置と１３５°の位置に電極ロールを配設した場合の転写ロールの抵抗値の変動を示すグラフである。
【図１４】本発明の別の実施例として示す画像形成装置の全体図である。
【図１５】従来の画像形成装置の概略構成図である。
【符号の説明】
Ｕ_１，Ｕ_２…画像形成装置、Ｐ…記録媒体（用紙）、１…像担持体、４…現像装置、５…転写ロール、５ｂ…絶縁性ゴム層、５ｃ…半導電層、９…電極部材（電極ロール）、１０…電圧印加手段、１１…一次転写ロール、１２…中間転写ベルト、１４…バックアップロール、１５…二次転写ロール。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic system, such as an electrophotographic copying machine, a laser printer, a facsimile, and a composite device thereof. More specifically, the present invention relates to an image forming apparatus of a type that electrostatically transfers a toner image formed on an image carrier using a transfer roll onto a transfer medium such as paper or an intermediate transfer member.
[0002]
[Prior art]
In an image forming apparatus using an electrophotographic system, demands for environmental measures, noise measures, cost reduction, and the like are further increased. As a technology that meets these requirements, in place of a corona discharger that charges the image carrier composed of a photosensitive drum or the like, or transfers a toner image formed on the image carrier, etc. Various bias roll type image forming apparatuses using a semiconductive roll for charging and transferring have been proposed.
This contact-type semiconductive roll generates almost no corona products such as ozone, and does not require a large high-voltage power supply. Therefore, it is possible to improve the fixing efficiency by turning the power consumption to the fixing device. In addition, it is possible to reduce the weight and speed of the image forming apparatus.
As an image forming apparatus using a semiconductive roll, for example, as shown in FIG. 15, the surface of the photosensitive drum 01 is charged to a predetermined potential by a charging roll 02, and then subjected to image exposure L to form an electrostatic latent image. The electrostatic latent image is developed and visualized by the developing device 03 to form a toner image, and the toner image formed on the photosensitive drum 01 is transferred onto the transfer paper 05 by the transfer roll 04, so that it is necessary. An electrophotographic apparatus capable of forming the image is widely known. The surface of the photosensitive drum 01 on which the toner image transfer process has been completed is cleaned of residual toner by the cleaning device 06, and is prepared for the next image forming process.
[0003]
Semiconductive rolls constituting the charging roll and transfer roll of the image forming apparatus include elastic materials such as NBR, EPDM (ethylene propylene diene rubber), urethane rubber, silicone rubber, carbon black, organic electrolyte, or inorganic electrolyte. Sponge rolls that have been imparted with conductivity by dispersing conductive materials such as gas and foamed by gas foaming or chemical foaming are used.
In such a semiconductive roll, the electrical characteristics vary greatly depending on the conductive material. The conductive substance is classified into an ionic conductive type in which an electrolyte is added to an elastic material and an electronic conductive type in which nonionic carbon black or the like is dispersed.
An ion conductive type semiconductive roll is desirable because the change in electrical resistance value inside the roll is extremely small. On the other hand, the electrical resistance varies greatly with changes in temperature and humidity. For example, a high temperature and high humidity environment (H / H environment) of 28 ° C. and 85% RH and a low temperature and low humidity environment (L / L) of 10 ° C. and 15% RH. There is a problem that the difference in resistance value (log Ω) from the L environment reaches 1.5 to 2 digits.
In the case of an electronic conductive type using carbon black, the variation of the electric resistance value with respect to environmental changes in temperature and humidity is small. On the other hand, due to the instability of dispersibility of carbon black, for example, the variation in the resistance value (log Ω) inside the roll is as large as one digit. In addition, since the voltage dependency is large, there is a problem that the transfer current in the transfer portion greatly fluctuates due to voltage fluctuation.
[0004]
The following measures have been taken against this problem. For example, a two-layered transfer elastic roller having a different resistance level in which a high resistance surface layer is coated on a low resistance elastic layer to reduce resistance fluctuations in an H / H environment and an L / L environment is a special feature. This is proposed in Kaihei 3-202885. Japanese Patent Laid-Open No. 5-332352 proposes a semiconductive roller in which two types of carbon black, channel black and furnace black, are blended to reduce variation in volume resistance in the semiconductive region. Further, Japanese Patent Application Laid-Open No. 7-98549 proposes a conductive roller in which a change in resistance value due to environmental fluctuations and voltage fluctuations is reduced by the combined use of a surfactant and carbon black.
However, these rollers have a problem in that a constant transfer current necessary for the transfer portion cannot be stably supplied in accordance with environmental fluctuations and voltage fluctuations.
[Problems to be solved by the invention]
[0005]
As described above, the semiconductive roll in the prior art has a small variation in resistance inside the transfer roll required for an image forming apparatus that transfers an unfixed toner image onto a transfer medium, and has an H / H environment and an L / L environment. The electrical resistance value fluctuation at the time was small, and the requirement that the voltage dependency was small could not be satisfied. That is, there is a problem that a constant transfer current required in the transfer portion cannot be stably supplied regardless of environmental fluctuations or voltage fluctuations.
Therefore, the present invention is intended to solve the above-described problems, and uses a semiconductive roll having a small variation in electric resistance value in the H / H environment and the L / L environment as the transfer roll, By reducing the influence of the resistance value variation and voltage dependency inside the roll at a constant level, a constant transfer current required in the transfer part can be flowed stably regardless of environmental fluctuations and voltage fluctuations, resulting in high-quality images. It is an object of the present invention to provide an image forming apparatus capable of stably obtaining the above.
[0006]
[Means for Solving the Problems]
The inventor has conducted extensive studies to solve the above problems, and as a transfer roll, the surface is composed of a semiconductive layer in which electronically conductive carbon black is dispersed, and the transfer current flows along the roll surface. Obtaining the knowledge that the use of a flowing two-layer creeping surface type semiconductive roll reduces the change in transfer current due to variations in roll resistance and the voltage dependence at the transfer portion, and has led to the present invention. It is.
That is, the image forming apparatus of the present invention includes an image carrier that forms an electrostatic latent image according to image information, a developing device that visualizes the electrostatic latent image formed on the image carrier as a toner image with toner, A transfer roll for transferring a toner image carried on the image carrier to a recording medium, an electrode member for pressing the transfer roll and applying a bias voltage to the roll, and a voltage applying means for electrically connecting to the electrode member The transfer roll comprises an insulating roll disposed so as to be able to come into contact with and separated from the image carrier and coated with a semiconductive layer in which carbon black is dispersed,The electrode member is disposed at a position facing the image carrier at 180 ° ± 10 ° through the transfer roll.
The image forming apparatus of the present invention includes an image carrier that forms an electrostatic latent image according to image information, a developing device that visualizes the electrostatic latent image formed on the image carrier as a toner image with toner, A primary transfer roll for primary transfer of the toner image carried on the image carrier to the intermediate transfer body; a bias roll for secondary transfer of the unfixed toner image carried on the intermediate transfer body to the recording medium; A backup roll that supports the intermediate transfer member from the back surface, and the primary transfer roll is an insulating roll covered with a semiconductive layer in which carbon black is dispersed, and an electrode that applies a bias voltage to the primary transfer roll. The member is in pressure contact, and voltage application means is electrically connected to the electrode member, and the electrode member faces the image carrier at 180 ° ± 10 ° through the primary transfer roll. It is arranged in location.
The image forming apparatus of the present invention also includes the image carrier and the developing device, a primary transfer device that primarily transfers the toner image carried on the image carrier to the intermediate transfer member, and an unfixed image carried on the intermediate transfer member. A secondary transfer roll for secondary transfer of the toner image to the recording medium, and a backup roll for supporting the intermediate transfer member from the back surface thereof, facing the secondary transfer roll,The secondary transfer roll is an insulating roll coated with a semiconductive layer in which carbon black is dispersed. An electrode member for applying a bias voltage is in pressure contact with the secondary transfer roll, and voltage applying means is electrically connected to the electrode member. And the electrode member is disposed at a position facing the backup roll at 180 ° ± 10 ° via the secondary transfer roll.Consists of configuration.
[0007]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail mainly based on the drawings.
The image forming apparatus of the present invention is not particularly limited as long as it is an electrophotographic apparatus using a transfer roll as a transfer device. For example, the image forming apparatus may be an ordinary monocolor image forming apparatus or a single image carrier such as a photosensitive drum. The present invention is applied to a color image forming apparatus that supports multiple toner images, an intermediate transfer type color image forming apparatus, and a tandem type color image forming apparatus in which a plurality of image carriers having developing units for respective colors are arranged in series. .
In the image forming apparatus shown in each drawing, components having the same function are given the same numbers.
[0008]
FIG. 1A is a schematic configuration diagram of the color image forming apparatus which carries a multiple toner image on an image carrier. In FIG. 1A, after the surface of the image carrier 1 composed of a photosensitive drum rotating in the direction of the arrow is uniformly charged by a charger 2, electrostatic charging of the first color is performed by an image writing means 3 such as a laser beam. A latent image is formed. The electrostatic latent image is formed with a toner image visualized by the developing device 4 containing toner corresponding to the color. In the same manner, the second, third, and fourth color toner images are sequentially superimposed on the image carrier 1 on which the first color toner image is formed. A multiple toner image is obtained.
The multiple toner images are electrostatically transferred collectively to a recording medium (hereinafter, represented by paper P) supplied from the paper feed tray 6 to the transfer portion pressed by the transfer roll 5 against the image carrier 1 at a predetermined timing. Is done. The paper P on which the toner image has been transferred is peeled off from the image carrier 1, and then conveyed to the fixing device 7, subjected to heating / pressurizing processing, and discharged outside the apparatus.
After the transfer, the image carrier 1 is freed of residual toner and residual charges by the cleaning device 8 and the like, and is ready for the next image forming process.
[0009]
The developing device 4 includes a plurality of developing devices 4 containing toner corresponding to the electrostatic latent images of the respective colors.₁~ 4₄Have That is, each developing device contains toner of each color of yellow (Y), magenta (M), cyan (C), and black (K).
The transfer roll 5 is disposed so as to be able to come into contact with and separate from the image carrier 1 and is configured to press the image carrier 1 at the time of transferring the multiple toner images onto the paper P. Further, an electrode member 9 a that applies a bias voltage having a polarity opposite to that of the toner is pressed against the transfer roll 5. Further, voltage application means (power source) 10a is electrically connected to the electrode member 9a. FIG. 1B is an enlarged view of a transfer portion that the transfer roll 5 presses against the image carrier 1 and will be described in detail later.
[0010]
FIG. 2 is a schematic configuration diagram of the color image forming apparatus of the intermediate transfer system provided with an intermediate transfer belt as an intermediate transfer member. The image forming apparatus shown in FIG. 2 forms a first color toner image in the same manner as the color image forming apparatus shown in FIG. This toner image is primarily transferred to the intermediate transfer belt 12 by the action of an electric field generated between the image carrier 1 and the primary transfer device 11 ′. Thereafter, in the same manner, second, third, and fourth color toner images are formed each time the image carrier 1 is rotated, and sequentially transferred onto the intermediate transfer belt 12.
The intermediate transfer belt 12 is stretched around a plurality of belt support rollers (13a, 13b, 13c) and a backup roll 14, and moves in the direction of the arrow while contacting the surface of the image carrier 1. The primary transfer is performed when the toner image on the image carrier 1 passes through a primary transfer portion in which the primary transfer device 11 ′ is disposed to face the image carrier 1. In this way, an unfixed multiple toner image is carried on the intermediate transfer belt 12.
A bias roll 15 ′ and a belt cleaner 16 are respectively arranged at positions facing the backup roll 14 and the belt transport roll 13 a via the intermediate transfer belt 12. The backup roll 14 may support the intermediate transfer belt 12 from the back surface, and the backup roll 14 may be in contact with the illustrated earth roll 17.
[0011]
On the other hand, the paper P is conveyed from the paper feed tray 6 at a predetermined timing to the secondary transfer portion where the bias roll 15 ′ presses against the backup roll 14. When the paper P passes between the roll 14 and the roll 15 ′, the multiple toner image carried on the intermediate transfer belt 12 is secondarily transferred to the paper P. The paper P onto which the multiple toner images are transferred at once is conveyed to the fixing device 7, heated and pressurized, and discharged outside the apparatus.
Residual toner and charges are removed from the image carrier 1 after the primary transfer by a cleaning device 8 and the like, and residual toner is removed from the intermediate transfer belt 12 after the secondary transfer by a belt cleaner 16 to prepare for the next image forming process. .
When forming a multicolor image other than full color in the image forming apparatus shown in FIGS. 1 and 2, toner corresponding to the multicolor image is accommodated in two or three developing devices. Further, the image writing means 3 subjected to image processing so as to form a single-color electrostatic latent image forms an electrostatic latent image on the image carrier 1, and only the toner corresponding to the color is developed by the developing device 4. The above-described image forming apparatus can be applied to a monocolor image forming apparatus. Further, the intermediate transfer belt 12 shown in FIG. 2 can be replaced with a known intermediate transfer drum.
[0012]
FIG. 3 is a schematic configuration diagram of the tandem type color image forming apparatus. In this image forming apparatus, a developing device containing toner of each color is arranged on a plurality of image carriers 1 arranged in series, and the toner images of each color are sequentially primary transferred onto the intermediate transfer belt 12 as shown in FIG. Different from the color image forming apparatus shown in FIG.
That is, the image carrier 1₁~ 1₄The surface of the charger 2₁~ 2₄Image writing means 3 for converting the original image into electrical signals for each color after being uniformly charged by₁~ 3₄Thus, an electrostatic latent image for each color is formed. Each electrostatic latent image is a developing unit 4 containing toner corresponding to its color.₁~ 4₄As a result, the toner images of the respective colors are formed. Also, the primary transfer device 11 '₁~ 11 '₄Are image carriers 1 respectively.₁~ 1₄The toner images of each color are electrostatically and sequentially primary transferred onto the intermediate transfer belt 12. This primary transfer is performed when the intermediate transfer belt 12 carrying the toner image of the first color passes the second and subsequent primary transfer portions. The subsequent secondary transfer is the same as the color image forming apparatus shown in FIG. 2, although the paper feed tray 6 and the fixing device 7 are not shown in FIG.
In the image forming apparatus shown in FIG. 3, two image carriers are arranged, and the developing device 4₁~ 4₄Among them, by arranging two appropriate developing devices on each image carrier, it is possible to use as a double tandem type full color image forming apparatus. Further, the intermediate transfer belt 12 is replaced with a sheet conveying belt, and the secondary transfer member or the like (14 to 17) is omitted, and the sheet is directly conveyed to the plurality of transfer units, thereby forming a multicolor image. Can do.
[0013]
In the image forming apparatus of the present invention shown in FIGS. 1 to 3, a corona charger can be used as the charger 2 in place of the illustrated charging roll. As the primary transfer device 11 ′, a roll member, a transfer blade, or the like that presses against the image carrier 1 during primary transfer is used in addition to a corona transfer device such as a corotron shown in the figure.
The intermediate transfer belt 12 shown in FIGS. 2 and 3 is a belt formed to have a thickness of 0.05 to 0.15 mm. The surface resistivity is obtained by mixing an appropriate amount of a conductive agent such as carbon black into various resins or rubber materials. 10⁸  -10¹⁵It is adjusted to the range of Ω / □. Examples of the various resins include acrylic resin, polyvinyl chloride, polyester, polycarbonate, and polyimide.
The backup roll 14 shown in FIGS. 2 and 3 forms the counter electrode of the bias roll 15 ′. The layer structure of the backup roll 14 may be either a single layer or a multilayer. For example, in the case of a single layer structure, it is composed of a roll in which an appropriate amount of conductive fine powder such as carbon black is blended in silicone rubber, urethane rubber, EPDM or the like. In the case of a two-layer structure, a roll in the case of a single layer whose volume resistivity is appropriately adjusted is used as a lower layer, and the outer peripheral surface is constituted by a conductive surface layer coated with, for example, a fluorine-based resin. Examples of the fluororesin include FEP (TFE-HFP copolymer), PFA, and the like. The hardness of the backup roll is preferably in the range of 60 to 75 ° with Asker C.
[0014]
The bias roll 15 ′ is normally separated from the transfer belt 12, and when the toner image carried on the transfer belt 12 is secondarily transferred to the paper P, the bias roll 15 ′ is pressed against the transfer belt 12 and is transferred to the backup roll 14. It arrange | positions so that contact / separation is possible so that it may press. The bias roll 15 'is composed of a low resistance roll in which an appropriate amount of a conductive agent such as carbon black is blended in a rubber material such as silicone rubber, urethane rubber, EPDM, etc. In some cases, the bias roll 15' may be a metal roll.
In the image forming apparatus of the present invention shown in FIGS. 2 and 3, the primary transfer unit 11 '(11'₁~ 11 '₄) And the bias roll 15 ', the creeping type two-layer structure transfer roll described below is used.
[0015]
FIG. 4 is an enlarged view of a transfer portion when the primary transfer roll 11 and the secondary transfer roll 15 according to the present invention are used as the primary transfer device 11 ′ and the bias roll 15 ′ shown in FIGS. Here, FIG. 4A is an enlarged view of the primary transfer portion that the primary transfer roll 11 presses against the image carrier 1 via the intermediate transfer belt 12. FIG. 4B is an enlarged view of the secondary transfer portion where the secondary transfer roll 15 presses against the backup roll 14 via the paper P and the intermediate transfer belt 12.
Each of the creeping type transfer rolls (5, 11, 15) has an insulating rubber layer (5b, 11b, 15b) fixed to the shaft (5a, 11a, 15a) as shown in FIG. 1B and FIG. ) Comprises an insulating roll (hereinafter referred to as a creeping roll) covered with a semiconductive layer (5c, 11c, 15c) in which carbon black is dispersed.
The shaft does not need to be particularly conductive, and any member can be used as long as it has rigidity. The insulating rubber layer has a volume resistivity of 10¹¹The rubber material is composed of a rubber material of Ωcm or more, and examples of the rubber material include EPDM, urethane rubber, silicone rubber, NBR, and chloroprene rubber. These rubber materials may be two or more kinds of blend rubbers.
The semiconductive layer is composed of the above rubber material or resin material in which electronic conductive carbon black is dispersed as a conductive agent. As the carbon black, acetylene black, ketjen black (manufactured by Lion Aguso), thermal black, Vulcan XC (manufactured by Cabot), or a mixture thereof is used. Examples of the resin material include PFA, polyvinylidene fluoride, nylon, and polycarbonate. Furthermore, as a constituent material of the semiconductive layer, a conductive paint in which carbon black is dispersed, for example, a urethane paint, acrylic paint, or fluorine-based paint in which carbon black is dispersed can be used.
[0016]
The outer diameter of the creeping roll in the present invention is generally in the range of 16 to 24 mm in the case of the transfer roll (5) and the primary transfer roll (11), and in the range of 25 to 32 mm in the case of the secondary transfer roll (15). Is preferred. The hardness of each transfer roll is preferably in the range of 20 to 50 ° in terms of Asker C hardness.
The volume resistivity of the creeping roll is 10 in the case of the roll (5, 11).⁶-10⁹Ωcm range, preferably 10⁷-10⁸In the range of Ωcm, 10 for the roll (15)³-10⁶Ωcm range, preferably 10⁴-10⁵It is in the range of Ωcm. These volume resistivities can be adjusted mainly by the selection of the rubber material constituting the insulating rubber layer and the carbon black dispersed in the semiconductive layer and the blending amount thereof.
The thickness of the semiconductive layer is preferably in the range of 0.4 to 0.6 mm in the case of the roll (5, 11) and in the range of 0.4 to 1.2 mm in the case of the roll (15). When the film thickness is less than 0.4 mm, it is difficult to stably form the surface semiconductive layer. On the other hand, if the film thickness is thicker than the above value, the hardness of the creeping roll increases, and it becomes difficult to ensure a predetermined nip pressure and nib width at the transfer portion.
[0017]
Examples of the electrode member 9 (9a to 9c) include a metal roll, a conductive rubber roll, a metal plate, a conductive resin plate, and a conductive brush. Especially, the metal roll and conductive rubber roll which rotate with a creeping roll are used preferably.
The material constituting the metal roll or the metal plate is not particularly limited as long as it is an electrically conductive metal or alloy, and for example, stainless steel (SUS), copper, aluminum, or the like is used. The conductive rubber roll has a volume resistivity of 10 in which a conductive agent such as carbon black is dispersed in an appropriate rubber material.²It consists of a low resistance roll of Ωcm or less. Similarly, the conductive resin plate is a low-resistance plate in which a conductive agent such as carbon black is dispersed in a fluorine resin such as PTFE, PFA, and PVDF, a resin material such as an acrylic resin, a polyamide resin, and a urethane resin. As the conductive brush, both a rotating type in which a conductive fiber brush roll rotates and a stationary type fixed to a plate can be used.
From the voltage application means 10 (10a to 10c), a voltage of 1 to 5 kV is applied to the transfer roll 5 and a bias voltage of 1 to 7 kV (absolute value) is applied to the primary transfer roll 11 and the secondary transfer roll 15 through the electrode member 9. Is done. For example, if the bias voltage is lower than 1 kV, the intensity of the electric field for transferring the unfixed toner image on the intermediate transfer belt 12 onto the paper P is not sufficient. On the other hand, when the voltage is higher than the above numerical value, the transfer electric field becomes too high, causing Paschen discharge between the intermediate transfer belt 12 and the paper P, causing a defective image quality and a decrease in transfer efficiency due to toner charging abnormality. Become. Further, the secondary transfer roll 15 is not preferable because the change in the surface resistivity of the backup roll 14 becomes large when used for a long period of time.
[0018]
When the creeping roll is the transfer roll 5 or the primary transfer roll 11, the electrode member 9 is disposed at a position opposite to the image carrier 1 by 180 ± 10 °, particularly 180 ° via the roll (5, 11). It is preferable. Further, in the case of the secondary transfer roll 15, it is preferable that the electrode member 9 is disposed through the roll 15 at a position facing the backup roll 14 by 180 ± 10 °, particularly 180 °.
When the electrode member 9 is disposed so as to be opposed by about 180 ° as described above, the conduction path of the current flowing from the electrode member 9 to each transfer portion at the time of transfer becomes the longest, so the influence of the resistance variation in the creeping roll, The voltage dependency in the transfer portion can be greatly reduced. Furthermore, since the pressing direction of the electrode member 9 coincides with the creeping roll and the axis of the image carrier (photosensitive drum) 1 or the backup roll 14, the electrode member 9 can be stably pressed against the creeping roll.
[0019]
The operation of the present invention is as follows.
The creeping type two-layer structure transfer roll (5, 11, 15) was coated with a semiconductive layer in which carbon black having a small resistance variation between the H / H environment and the L / L environment was dispersed as a conductive agent. It consists of an insulating roll. Since the electrode member 9 is pressed against the creeping roll, a current flows to the transfer portion along the peripheral surface of the creeping roll by the transfer bias applied to the creeping roll.
Therefore, by separating the position of the electrode member 9 that applies the voltage to the creeping roll from the transfer portion, the current conduction path can be made longer than in the conventional example in which the voltage is applied to the conductive shaft. .
As a result, it is possible to reduce the influence of resistance variation in the circumferential direction of the roll of current flowing through the transfer portion. In addition, since the electric field strength in the transfer portion is inversely proportional to the distance from the position where the bias voltage is applied, even if the voltage fluctuates, it is possible to reduce the change in the transfer current in the transfer portion. That is, the voltage dependency at the transfer portion can be reduced.
[0020]
Furthermore, by arranging the electrode member 9 so as to face the transfer portion by 180 °, the conduction path from the transfer voltage application position to the transfer portion is 3.14 (when voltage is applied to the shaft). Circumference ratio π) times. Therefore, when the creeping roll having the same outer diameter is used, the current conduction path becomes the longest, and the effect of reducing the voltage dependency at the transfer portion described above appears greatly. Moreover, the influence of local resistance variation in the circumferential direction of the transfer roll (5, 14, 18) can be reduced.
FIG. 5 is an explanatory diagram showing a current path of a creeping type two-layer structure transfer roll, and a current i flowing through the transfer portion is i = i.₁  + I₂It is represented by
[0021]
For example, as shown in FIG. 6, when the creeping roll is divided into eight in the circumferential direction, the resistance value of each part is represented by r.₁, R₂, R₃, R₄, R₅, R₆, R₇, R₈Assuming that the resistance value R of the creeping roll at the transfer portion (5) when a bias voltage is applied to the position (1)₁  Can be represented by a parallel circuit of the following formula (1).
1 / R₁= 1 / (r₁+ R₂+ R₃+ R₄) + 1 / (r₅+ R₆+ R₇+ R₈(1)
Further, the resistance value R of the creeping roll at the transfer section (6) when the roll rotates and a bias voltage is applied to the position (2).₂Can be represented by a parallel circuit of the following equation (2).
1 / R₂= 1 / (r₂+ R₃+ R₄+ R₅) + 1 / (r₆+ R₇+ R₈+ R₁(2)
Further, the resistance value R of the creeping roll at the transfer portion {circle around (1)} when the roll is rotated 180 ° from the position {circle around (1)} and a bias voltage is applied to the position {circle around (5)}.₅Can be represented by a parallel circuit of the following formula (3), and R₁And R₅Are equal.
1 / R₅= 1 / (r₅+ R₆+ R₇+ R₈) + 1 / (r₁+ R₂+ R₃+ R₄(3)
8 divided resistance value r₁~ R₈Among them, even if the resistance value at only one point is different, the resistance value R in the circumferential direction of the creeping roll is equal. Thus, by arranging the position of the electrode member 9 so as to oppose the transfer portion, current unevenness due to resistance variation in the circumferential direction of the creeping roll can be reduced.
[0022]
【Example】
EXAMPLES Hereinafter, although an Example demonstrates this invention concretely, this invention is not limited to the following Example.
Example 1
(Image forming apparatus U₁  )
FIG. 7 is an overall view of a digital color copying machine that carries multiple toner images on an image carrier as an image forming apparatus of the present invention. In addition, the same number is attached | subjected to what has the function similar to the component of the image forming apparatus shown in FIG.
In FIG. 7, the light emitted from the document illumination lamp 22 moving along the lower surface of the document (not shown) placed on the platen 21 and reflected by the document is moved by the moving mirror unit 23, the lens 24, and the fixed mirror. 25 is converged on the CCD of the image reading unit. The CCD converts the original image into an electrical signal for each color by a large number of photoelectric conversion elements and filters of three colors of red (R), green (G), and blue (B). This electric signal is input to the image processing circuit 26, and the image processing circuit 26 has an image memory for converting the original image reading signal input for each color into a digital signal and storing it. The optical writing control device 27 reads out the image data of the image processing circuit 26 at a predetermined timing and outputs it to the light beam writing device 28. The light beam writing device 28 writes an electrostatic latent image corresponding to each color on the image carrier 1 composed of a photosensitive drum rotating in the direction of arrow A. These numbers 21 to 28 constitute the image writing means 3.
[0023]
Around the image carrier 1, there are a charger 2 for uniformly charging the surface thereof, a developing device 4 for developing the electrostatic latent image written on the image carrier 1 into a toner image of each color, and a multiple toner image of each color. A transfer roll 5 for transferring the toner onto the paper P, and a cleaner unit (cleaning device) 8 having a static eliminator and a cleaning blade are arranged.
The developing device 4 includes developing devices 4y, 4m, 4c, and 4k that store toners of the colors Y, M, C, and K, and develops and visualizes the electrostatic latent image with the toners of the colors. . The transfer roll 5 is in pressure contact with an electrode roll 9a connected to a power source as the voltage applying means 10a.
Image forming apparatus U₁  An extractable paper feed tray 6 is provided at the lower part of the main body, and a pickup roller 29 is disposed above the paper feed tray 6. On the downstream side of the pickup roller 29, a pair of feed rolls 30 that prevent double feeding of the paper P, a paper transport roll 31, a guide member 32 that guides the paper P, and a registration roll 33 are sequentially arranged.
On the downstream side of the transfer portion where the transfer roll 5 presses against the image carrier 1, a conveyance belt 34 for conveying the paper P carrying the transferred toner image and the unfixed toner image on the paper P are sequentially fixed. The fixing device 7, a pair of discharge rolls 35 for discharging the paper P on which the fixed image is formed to the outside of the apparatus, and a paper discharge tray 36 for placing the discharged paper P are disposed.
[0024]
(Image forming apparatus U₁  Action)
The surface of the image carrier 1 rotating in the direction of arrow A is uniformly charged by the charger 2, and an electrostatic latent image is written by the light beam writing device 28. The electrostatic latent image on the image carrier 1 is developed into an unfixed toner image by the developing device 4. In this toner image formation, the first color toner image is formed first, and then the second to fourth color toner images are formed each time the image carrier 1 rotates for a predetermined time. In this embodiment, Y, M, C, and K toner images are sequentially formed.
Here, the optical writing control device 27 reads the first Y-color digital signal corresponding to the optical image color-separated by the blue (B) filter first, and sends it to the optical beam writing device 28. Output. The writing device 28 writes an electrostatic latent image corresponding to the Y color on the surface of the image carrier 1. The electrostatic latent image corresponding to the Y color is developed into a visualized toner image of the Y color by the developing device 4y in the developing device 4.
After the development of the first Y toner image was completed, the color was separated by the green (G) filter by the output from the optical writing controller 27 in synchronization with the Y electrostatic latent image writing start position. Writing of the electrostatic latent image corresponding to the optical image is started. The developing unit 4m develops the M toner image of the second color on the image carrier 1 that carries the Y toner image. Subsequently, the electrostatic latent image of C color corresponding to the light image color-separated by the red (R) filter is developed by the developing device 4c. Finally, the digital signal image-processed to the K color of the fourth color is read from the optical writing control device 27 and output to the optical beam writing device 28. The writing device 28 writes an electrostatic latent image corresponding to K color on the surface of the image carrier 1, and the developing device 4 k develops the toner image visualized in K color.
In this way, a multiple toner image superimposed on each color is formed on the image carrier 1. During this time, the transfer roll 5 is held at a retracted position separated from the image carrier 1.
[0025]
On the other hand, the paper P stored in the paper feed tray 6 is picked up one by one by a pickup roller 29 at a predetermined timing, fed by a pair of feed rolls 30 and a paper transport roll 31, and once by a pair of registration rolls 33. Stopped. The paper P is then conveyed from the registration roll 33 to the transfer unit in synchronization with the movement of the multiple toner images of each color (Y, M, C, K) carried on the image carrier 1 to the transfer unit. The
At this time, the transfer roll 5 is pressed against the image carrier 1. The paper P conveyed to the transfer unit passes through the transfer unit by pressure contact conveyance between the image carrier 1 and the transfer roll 5. At this time, the multiple toner images carried on the image carrier 1 are collectively transferred onto the paper P by applying a transfer voltage having a polarity opposite to the charging polarity of the toner image from the electrode roll 9a.
Although the transfer of the full-color image has been described above, in the case of forming a single-color image, for example, when the K-color toner image transferred onto the image carrier 1 moves to the transfer portion, the toner image is immediately transferred to the paper P. Transcribed. When forming a multi-color image, it is only necessary to select a desired hue and transfer the toner image onto the paper P when the multi-color toner image superimposed on those colors has moved to the transfer section.
As described above, the paper P on which the toner image is transferred to a desired hue is placed on the transport belt 34 and transported to the fixing device 7. In this fixing device 7, after fixing an unfixed toner image and fixing it to a permanent image, the paper P is discharged to a paper discharge tray 36 by a pair of paper discharge rollers 35. When the transfer process is completed, the image carrier 1 is cleaned by the cleaning device 8 to prepare for the next image forming process.
[0026]
(Transfer part)
The specific configuration of the transfer unit in the color image forming apparatus shown in FIG. 7 is as follows.
As the image carrier (1), an OPC photosensitive drum having an outer diameter of 84 mm whose surface was coated with polycarbonate was used. As the transfer roll (5), a two-layer EPDM roll having an outer diameter of 21 mm, in which a semiconductive layer (5c) was formed on the extruded foamed EPDM rubber layer (5b) by a tube extrusion molding method, was used. Specifically, a foamed EPDM rubber layer (5b) having a surface coated with a semiconductive layer (5c) having a thickness of 0.5 mm in which carbon black is dispersed in EPDM using a shaft made of SUS having an outer diameter of 12 mm (5b). ). Its hardness is 30 ° in Asker C, and the resistance value at an applied voltage of 1 kV in a laboratory environment (23 ° C., 55% RH) is 10^7.5Ω. This transfer roll (5) was pressed against the image carrier (1) with a nib width of 3.5 mm.
As the electrode member (9a), a metal roll made of SUS314 having a diameter of 12 mm was used and pressed against the transfer roll (5) with a biting amount of 0.2 mm. Further, a bias voltage of +2 kV is applied from the voltage applying means (10a) through the electrode member (9a).
[0027]
(Electrical characteristics of transfer roll)
For creeping type transfer rolls (5), electricity at an applied voltage of 100 V and 1 kV under H / H environment (28 ° C., 85% RH), laboratory environment and L / L environment (10 ° C., 15% RH). The resistance value was measured.
As shown in FIG. 8A, the resistance value is measured by bringing a SUS metal roll having a diameter of 12 mm longer than the transfer roll into contact with the transfer roll with a biting amount of 0.2 mm, and a SUS metal roll having a diameter of 28 mm at the opposite position. Was carried out by applying the above-mentioned voltage between two metal rolls. Then, the current value 10 seconds after the application of the voltage was read, and the resistance value was obtained by Ohm's formula (R = V / I).
Furthermore, in the measurement method shown in FIG. 8A, the minimum and maximum values of the current when the roll is rotated once while rotating a metal roll having a diameter of 28 mm to which a voltage of 1 kV is applied in a test room environment at 10 rpm. The variation in resistance value was obtained from the difference.
[0028]
As comparative examples, 1) an ion conductive type urethane foam roll having an outer diameter of 21 mm, 2) a carbon black dispersed type urethane foam roll, and 3) a carbon black dispersed type foamed EPDM roll as a transfer roll, The electrical resistance values at an applied voltage of 100 V and 1 kV were measured under the / H environment, the laboratory environment, and the L / L environment.
In Comparative Example 1, a volume resistivity of 10 using quaternary ammonium perchlorate as an ionic conductive agent is used.^8.0A foamed urethane roll obtained by molding an Ωcm 2 mold was used. In Comparative Examples 2 and 3, the volume resistivity obtained by extrusion molding was 10^7.3A foamed urethane roll and foamed EPDM roll of Ωcm 2 were used.
As shown in FIG. 8B, the resistance value of each transfer roll is measured by constantly pressing a SUS metal roll having a diameter of 28 mm on the transfer roll with a biting amount of 0.5 mm, and the metal shaft of the transfer roll and the metal roll. The above voltage was applied between the two and the current value 10 seconds after the voltage application was read, and the resistance value was obtained by the Ohm equation. Further, the variation in the resistance value is obtained from the difference between the minimum value and the maximum value of the current when the metal roll makes one turn in the measurement method shown in FIG. 8B, similarly to the measurement of the transfer roll (5). It was.
[0029]
Table 1 shows the resistance value (log Ω) of the roll measured in each environment where the test room environment is expressed as “N / N”, the environmental variation of the resistance value, the voltage dependence of the resistance value, and the variation of the resistance value. Indicates. In addition, the environmental fluctuation of the resistance value in Table 1 is represented by the difference between the resistance values measured in the H / H and L / L environments at the applied voltage of 1 kV. Further, the voltage dependency of the resistance value is represented by the difference between the resistance values at 100 V and 1 kV in the environment having the largest fluctuation range among the roll resistance values measured in each environment.
As can be seen from Table 1 below, the creeping type transfer roll of the present invention gave good results with respect to environmental variations in resistance, voltage dependence, and variations in resistance. On the other hand, in the ion conductive type roll of Comparative Example 1, although the voltage dependency and variation of the resistance value are small, the resistance value greatly changed with the environmental change. Further, in the electronic conductive type rolls of Comparative Examples 2 and 3, although the change in the resistance value with respect to the environmental change was small, the variation in the resistance value was large and the voltage dependence of the resistance value was also large.
[0030]
[Table 1]

[0031]
(Electric field dependence)
For creeping type two-layer EPDM rolls, when the amount of carbon black dispersed in the semiconductive layer is changed and voltages of 1 kV, 2 kV, 3 kV, 4 kV, 5 kV are applied to EPDM rolls with different resistance levels The resistance values are shown in FIG. The resistance value was measured according to the method shown in FIG. 8A described above. In the drawing, the resistance value (log Ω) at an applied voltage of 1 kV of the roll indicated by ● is 8.5, and the resistance value of the roll indicated by ◯ is 9.6. As shown in FIG. 9, in the creeping type transfer roll of the present invention, the resistance values differ by about 0.5 digits between the applied voltages of 1 kV and 5 kV, and the electric field dependency is relatively small.
As a comparative example, for a foam EPDM roll having a single layer structure, the amount of carbon black dispersed in the roll was changed, and voltages of 1 kV, 2 kV, 3 kV, 4 kV, and 5 kV were applied to the foamed EPDM rolls having different resistance levels. The resistance value at the time is shown in FIG. The resistance value was measured according to the method shown in FIG. 8B described above. In FIG. 10, the resistance value of the roll indicated by ▲ at an applied voltage of 1 kV is 7.2, the resistance value of the roll indicated by △ is 8.3, and the resistance value of the roll indicated by ■ is 10.4. As shown in FIG. 10, in each EPDM transfer roll of the comparative example, it can be seen that the resistance value differs by about one digit at the applied voltage of 1 kV and 5 kV, and the electric field dependency is large.
[0032]
FIG. 11 shows the relationship between the bias voltage and the transfer current of the creeping type EPDM roll of the present invention shown in Table 1 and the foamed EPDM roll of Comparative Example 3.
For example, the voltage range capable of securing a transfer current of 20 to 40 μA is 0.5 kV for a single-layer foamed EPDM roll, whereas it is 1.4 kV for a creeping type two-layer EPDM roll. That is, in the creeping type transfer roll, a voltage range (transfer latitude) necessary for securing a transfer current having a large electric field dependency is widened.
[0033]
In the creeping type transfer roll of the present invention, the resistance value r measured at the eight points shown in FIG.₁~ R₈The surface resistivity is 10⁸  Ω / □, one point resistance value r₅  Only one order of magnitude lower than the rest (10⁷  Ω / □) and resistance value r at two points₅, R₆Is 1 digit lower than the other part, the resistance value of the roll when the electrode roll was disposed at the position (180 °) facing the transfer portion and the position of 135 ° was determined according to the method shown in FIG. 8A described above. . Table 2 shows the variation of the obtained resistance value.
Resistance value r₁~ R₈As shown in FIG. 12, the measurement method of FIG. 12 includes two SUS metal rolls having a diameter of 12 mm and a length of 330 mm, spaced by 10 mm in the circumferential direction on the surface of the transfer roll having a length of 325 mm, and a bite of 0.2 mm. The contact was made in an amount, and a voltage (V) of 1 kV was applied between the metal rolls. Then, the current value (I) 10 seconds after the application of the voltage was read, and the surface resistivity ρs was determined by the following equation.
ρs = LV / GI
L: Length of transfer roll (cm)
G: Distance between two metal rolls (cm)
[0034]
[Table 2]

[0035]
The graph of Table 2 above, that is, the fluctuations in the resistance value of the transfer roll when the electrode roll pressed against the transfer roll is disposed at a position of 180 ° and a position of 135 ° with respect to the transfer portion is shown in FIG. Shown in In FIG. 13, the solid line indicates a case where the resistance value at one of the eight points is low, and the broken line indicates a case where the resistance value at two of the eight points is low. Further, the mark ● represents the case where the electrode roll is disposed at a position of 180 ° with respect to the transfer portion, and the mark ◯ represents the case where the electrode roll is disposed at a position of 135 °.
As shown in Table 2 and FIG. 13, by applying a bias voltage to a position facing the transfer portion, it is possible to reduce the influence of variation in resistance value in the circumferential direction of the transfer roll with respect to the transfer portion.
[0036]
Example 2
(Image forming apparatus U₂  )
FIG. 14 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. Note that description overlapping with the image forming apparatus shown in FIG. 7 is omitted.
In FIG. 14, the image writing means 3 is composed of constituent elements 21 to 28. Around the image carrier 1, similarly to the image forming apparatus shown in FIG. 7, there are a charger 2, a developing device 4, a primary transfer roll 11 that transfers toner images of each color to the intermediate transfer belt 12, and a cleaning device 8. Has been placed.
The intermediate transfer belt 12 is stretched around the belt conveying rolls 13a, 13b, 13c and the backup roll 14, and moves in the tangential direction while contacting the surface of the image carrier 1. In this embodiment, among the rolls (13, 14) that stretch the transfer belt 12, the belt transport roll 13b is used as a drive roll and the other rolls (13a, 13c) so that the transfer belt 12 moves in the direction of arrow B. 14) are configured as driven rolls. Further, in order to prevent the transfer belt 12 from being bent, the shaft of the transport roll 13c is urged in the direction C by a spring (not shown).
[0037]
On the back side of the intermediate transfer belt 12, the primary transfer roll 11 is disposed so as to be able to contact and separate from a primary transfer portion where the surface of the image carrier 1 and the transfer belt 12 are in contact with each other. On the other hand, on the surface side of the transfer belt 12 carrying the unfixed toner image, the secondary transfer roll 15 and the belt cleaner 16 are arranged to face the backup roll 14 and the belt transport roll 13a, respectively. The former part where the rolls 14 and 15 are opposed serves as a secondary transfer part.
Further, a separation claw 37 for separating the sheet P carrying the second transferred toner image from the transfer belt 12 is disposed between the backup roll 14 and the belt conveyance roll 13a. A cleaning blade 38 made of polyurethane is always in contact with the surface of the secondary transfer roll 15, and foreign particles such as toner particles and paper dust adhered during the secondary transfer are removed.
As shown in FIGS. 4 and 14, an electrode roll 9b connected to a power source as a voltage applying means 10b is pressed against the primary transfer roll 11, and a bias voltage of 2 kV is applied thereto. The secondary transfer roll 15 is in pressure contact with the electrode roll 9c connected to the voltage applying means 10c, and a bias voltage of -2 kV is applied.
[0038]
(Image forming apparatus U₂  Action)
Image forming apparatus U described above₁  In the same manner as described above, the first color Y toner image is developed, and the toner image moves to the primary transfer portion. In the primary transfer portion, the primary transfer roll 11 is pressed against the image carrier 1 via the intermediate transfer belt 12. Then, by applying a transfer voltage having a polarity opposite to the charging polarity of the toner image from the electrode roll 9b, the Y-color toner image is electrostatically attracted to the intermediate transfer belt 12, and the transfer belt 12 in the direction of arrow B is applied. Primary transfer by movement.
The intermediate transfer belt 12 moves at the same speed as the image carrier 1 while adsorbing and carrying the Y toner image. When the transfer of the Y toner image of the first color is completed, the output from the optical writing control device 27 is filtered by a green (G) filter until the transfer start position of the Y toner image on the transfer belt 12 reaches the primary transfer portion. Writing of the electrostatic latent image corresponding to the color-separated light image is started. When the transfer start position of the transfer belt 12 carrying the Y toner image reaches the primary transfer portion, the M toner image of the second color is transferred by the primary transfer roll 11. Subsequently, the electrostatic latent images of C and K are sequentially visualized by the developing devices 4c and 4k, and the transfer of the C and K toner images is performed in the same manner as the transfer of the M toner image.
In this way, a multiple toner image superimposed on each color is formed on the intermediate transfer belt 12. After the toner images of the respective colors are primarily transferred to the intermediate transfer belt 12, the surface of the image carrier 1 is cleaned by the blade of the cleaning device 8. Further, the secondary transfer roll 15, the peeling claw 37, and the belt cleaner 16 disposed on the surface side of the transfer belt 12 are separated from the transfer belt 12 until the toner images of the respective colors are primarily transferred onto the transfer belt 12. It is held in the retracted position.
[0039]
On the other hand, on the paper P fed from the paper feed tray 6, the multiple toner images of each color (Y, M, C, K) transferred onto the intermediate transfer belt 12 move to the secondary transfer portion. In synchronism, the toner is conveyed from the registration roll 33 to the secondary transfer unit.
In the secondary transfer portion, the secondary transfer roll 15 is pressed against the backup roll 14 via the intermediate transfer belt 12. Then, the conveyed paper P passes through the secondary transfer portion by pressure contact conveyance between the rolls 14 and 15 and movement of the transfer belt 12. At this time, the toner image adsorbed and supported on the transfer belt 12 is secondarily transferred from the surface of the transfer belt 12 to the paper P by electrostatic repulsion by applying a transfer voltage having the same polarity as the charging polarity of the toner image from the electrode roll 9c. The Further, when the secondary transfer roll 15 is pressed against the backup roll 14, foreign matters such as toner particles adhering to the surface of the secondary transfer roll 15 are removed by the cleaning blade 38.
[0040]
Here, in the case of forming a single color image, for example, when a K-color toner image primarily transferred onto the intermediate transfer belt 12 moves to the secondary transfer portion, the toner image is immediately transferred onto the paper P. When forming a multi-color image, the toner image may be transferred onto the paper P when the multi-color toner image moves to the secondary transfer portion. In the case of this multi-color image transfer, as described above, the rotation of the image carrier 1 and the movement of the intermediate transfer belt 12 are synchronized so that the toner images of the respective colors are accurately matched without being shifted at the primary transfer portion. Yes.
As described above, the paper P on which the toner image is transferred to a desired hue is peeled off from the intermediate transfer belt 12 by the operation of the peeling claw 37, placed on the transport belt 34, and transported to the fixing device 7. Thereafter, the fixed paper P is discharged to the paper discharge tray 36. When the secondary transfer is completed, the transfer belt 12 is cleaned by a belt cleaner 16 provided downstream of the secondary transfer portion to prepare for the next transfer.
[0041]
(Primary transfer section and secondary transfer section)
The specific configuration of the primary and secondary transfer members in the image forming apparatus shown in FIG. 14 is as follows.
A two-layer urethane rubber roll was used as the primary transfer roll (11). In the primary transfer roll (11), the rubber material of the foam rubber layer (11b) and the semiconductive layer (11c) shown in FIG. 4A is made of urethane rubber, and the resistance value at an applied voltage of 1 kV in a test room environment is 10^7.7Except for Ω, it is the same as the transfer roll (5) shown in FIG.
The intermediate transfer belt (12) has a thickness of 80 μm and a surface resistivity of 10¹²An Ω / □ polyimide resin was used. As the backup roll (14), a conductive silicone rubber having an outer diameter of 28 mm and having a thickness of 6.5 mm was used. Its hardness is 62 ° in Asker C, and the surface resistivity is 10⁹It was Ω / □.
As the secondary transfer roll (15), an EPDM roll having a two-layer structure having the same outer diameter as that of the backup roll (14) was used. This roll (15) uses an SUS shaft (15a) having an outer diameter of 15 mm, and an insulating foamed EPDM rubber layer whose surface is coated with a 1 mm thick semiconductive layer (15c) in which carbon black is dispersed in EPDM. (15b). Its hardness is 40 ° in Asker C, and the resistance value at an applied voltage of 1 kV in a test room environment is 10^4.3Ω. The transfer roll (15) was pressed against the backup roll (14) with a nib width of 3.0 mm.
As the electrode member (9c), a metal roll made of SUS314 having a diameter of 12 mm was used and pressed against the transfer roll (15) with a biting amount of 0.2 mm. The voltage application means (10c) is configured to apply a transfer voltage of -2 kV through the electrode member (9c).
[0042]
【The invention's effect】
In the image forming apparatus of the present invention, a transfer roll having a two-layer structure is a creeping type roll in which an insulating roll is coated with a semiconductive layer in which electronic conductive carbon black having a small resistance variation due to environmental fluctuations is dispersed. Thus, an electrode member is pressed against the transfer roll. Therefore, as compared with the conventional transfer roll, it is possible to take a longer current path through the transfer portion along the peripheral surface of the creeping roll.
Therefore, not only can the influence of the variation of the resistance value in the circumferential direction of the roll of the transfer current be reduced, but also the change in the transfer current can be reduced, so that the voltage dependency at the transfer portion is reduced. Can do. In addition, the transfer latitude required to secure a transfer current having a large electric field dependency can be widened. As described above, a constant transfer current can be stably supplied regardless of environmental fluctuations and voltage fluctuations, and thus a high-quality image can be stably obtained.
In the present invention, since the current path becomes the longest by making the electrode member arrangement position facing the transfer portion, the variation in resistance value and the voltage dependency can be reduced most.
[Brief description of the drawings]
FIG. 1A is a schematic configuration diagram of an image forming apparatus of the present invention, and FIG. 1B is an enlarged view of a transfer portion thereof.
FIG. 2 is a schematic configuration diagram of another image forming apparatus of the present invention.
FIG. 3 is a schematic configuration diagram of still another image forming apparatus of the present invention.
FIGS. 4A and 4B are enlarged views of a transfer portion when a creeping type roll according to the present invention is used as a transfer roll, and FIGS. 4A and 4B are enlarged views of a primary transfer portion and a secondary transfer portion, respectively.
FIG. 5 is an explanatory diagram showing a current path of a creeping type transfer roll.
FIG. 6 is an explanatory diagram showing a bias voltage application position and a position of a transfer portion where a resistance value of the roll is measured when a creeping type transfer roll is divided into eight in the circumferential direction.
FIG. 7 is an overall view of an image forming apparatus shown as an embodiment of the present invention.
FIG. 8 is an explanatory diagram showing a method for measuring a resistance value of a transfer roll.
FIG. 9 is a graph showing the electric field dependence of a creeping type EPDM transfer roll.
FIG. 10 is a graph showing electric field dependence of a conventional foamed EPDM transfer roll.
FIG. 11 is a graph showing a relationship between a bias voltage of a transfer roll and a transfer current in the present invention and a comparative example.
FIG. 12 is an explanatory diagram showing a method for measuring the surface resistivity of a roll.
FIG. 13 is a graph showing fluctuations in the resistance value of the transfer roll when electrode rolls are disposed at a position of 180 ° and a position of 135 ° with respect to the transfer portion.
FIG. 14 is an overall view of an image forming apparatus shown as another embodiment of the present invention.
FIG. 15 is a schematic configuration diagram of a conventional image forming apparatus.
[Explanation of symbols]
U₁, U₂DESCRIPTION OF SYMBOLS ... Image forming apparatus, P ... Recording medium (paper), 1 ... Image carrier, 4 ... Developing device, 5 ... Transfer roll, 5b ... Insulating rubber layer, 5c ... Semiconductive layer, 9 ... Electrode member (electrode roll) DESCRIPTION OF SYMBOLS 10 ... Voltage application means, 11 ... Primary transfer roll, 12 ... Intermediate transfer belt, 14 ... Backup roll, 15 ... Secondary transfer roll

Claims (3)

An image carrier that forms an electrostatic latent image according to image information, a developing device that visualizes the electrostatic latent image formed on the image carrier as a toner image with toner, and a toner image carried on the image carrier. A transfer roll that transfers to a recording medium, an electrode member that presses against the transfer roll and applies a bias voltage to the roll, and a voltage applying means that is electrically connected to the electrode member. An image forming apparatus comprising an insulating roll disposed so as to be able to contact and separate from each other and covered with a semiconductive layer in which carbon black is dispersed , wherein the electrode member is disposed on the image carrier via the transfer roll. The image forming apparatus disposed at a position facing each other at 180 ° ± 10 °. An image carrier that forms an electrostatic latent image according to image information, a developing device that visualizes the electrostatic latent image formed on the image carrier as a toner image with toner, and a toner image carried on the image carrier. A primary transfer roll for primary transfer to the intermediate transfer member, a bias roll for secondary transfer of an unfixed toner image carried on the intermediate transfer member to a recording medium, and an intermediate transfer member supported from the back surface facing the bias roll The primary transfer roll is an insulating roll coated with a semiconductive layer in which carbon black is dispersed, and an electrode member for applying a bias voltage is in pressure contact with the primary transfer roll, and a voltage is applied to the electrode member. the application means an image forming apparatus were electrically connected, the electrode member, through said first transfer roller, distribution at a position facing at 180 ° ± 10 ° with respect to the image bearing member It has been the image forming apparatus. An image carrier that forms an electrostatic latent image according to image information, a developing device that visualizes the electrostatic latent image formed on the image carrier as a toner image with toner, and a toner image carried on the image carrier. A primary transfer device for primary transfer to the intermediate transfer body, a secondary transfer roll for secondary transfer of an unfixed toner image carried on the intermediate transfer body to a recording medium, and an intermediate transfer body facing the secondary transfer roll The secondary transfer roll comprises an insulating roll covered with a semiconductive layer in which carbon black is dispersed, and an electrode member for applying a bias voltage is pressed against the secondary transfer roll. together, an image forming apparatus were electrically connected with a voltage application means to the electrode member, said electrode member, via the second transfer roller, in a position opposed at 180 ° ± 10 ° with respect to the backup roll Set by said image forming apparatus.

Images