JP2004093638A - Thermal fixing device and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To eliminate trouble such as tailing remarkably appearing at the edge of an image, that means, the tailing in belt shape in a thermal fixing device having constitution where recording material P on which an unfixed toner image T is formed is introduced into a fixing nip part N formed by the press-contact of a 1st rotating body 10 corresponding to the front surface side of the recording material being the unfixed toner image carrying surface side of the recording material with a 2nd rotating body 20 corresponding to the back surface side of the recording material being an opposite surface side to the unfixed toner image carrying surface side so as to be held and fed, so that the unfixed toner image is thermally fixed on the recording material, and DC voltage is applied to the 1st and the 2nd rotating bodies while the recording material passes through the fixing nip part. <P>SOLUTION: An optional time difference is given to timing to start the application of DC voltage to the 1st and the 2nd rotating bodies 10 and 20. As for the application of the DC voltage to the respective rotating bodies 10 and 20, a desired DC voltage value is applied through the voltage values of a plurality of steps. <P>COPYRIGHT: (C)2004,JPO

Description

【０１１８】
表１に示したように、従来の定着バイアスの印加タイミングでは、プリント開始直後の１枚目の定着尾引きの発生が良くないことが分かる。これは、定着回転体である定着フィルム１０と加圧回転体である加圧ローラ２０の各々の回転体１０・２０への定着バイアスが印加されていない状態から、定着バイアスを印加することで形成される約１２００Ｖの電位差により形成される電界を打ち消す向きに生じる逆向きの電界の形成による生じる逆極性の電荷により、定着バイアスによる定着尾引きの抑止効果が小さくなるためである。
【０１１９】
比較して、本発明の第１の実施例では、プリント開始直後の１枚目でも、定着尾引きの発生抑止効果が高く、発明の効果が現れていることが分かる。
【０１２０】
本実施例では、定着バイアスを印加する順番として、加圧ローラ２０から先に定着バイアスの印加を実施するものとした。ここで、加圧ローラ２０から先に定着バイアスを印加した理由に関して、再度詳細に記す。
【０１２１】
本実施例で用いた加熱定着装置では、定着回転体としての定着フィルム１０の表層に用いている離型層１０ｃはフッ素樹脂材をコーティングして形成したものであり、コーティングの特性上、▲１▼．コーティング膜厚の厚み、▲２▼．極微小なピンホールの発生、に起因してフッ素樹脂材料自体よりも低い体積抵抗値のコーティング層となっている。
【０１２２】
対して、加圧ローラ２０の表層に用いている離型層２３はフッ素樹脂からなるチューブを被覆して形成したものであり、フッ素樹脂材料と同等の体積抵抗値を有する絶縁体であるため、加圧ローラ２０に定着バイアスを印加した時に生じる電界を打ち消す向きに生じる逆向きの電界による逆極性の電荷量が多く生じることになるため、その逆極性の電荷の影響による定着回転体としての定着フィルム１０と加圧回転体としての加圧ローラ２０との回転体間の電位差への影響を滅してから、記録材を定着ニップに導きたいため、定着フィルム１０に先行して加圧ローラ２０に定着バイアスを印加させる構成をとったほうが、定着尾引きの抑止効果が高まることになる。
【０１２３】
そこで、本実施例では加圧ローラ２０に先行して定着バイアスを印加するものとした。
【０１２４】
これは、定着フィルム１０と加圧ローラ２０の表層に用いる材料の体積抵抗値、及び、その表層の成型方法、などに左右されるものであり、用いる加熱定着装置に応じて、定着ローラ１０、若しくは、加圧ローラ２０の何れかを先行して定着バイアスを印加するように設定すれば本実施例で説明した効果は期待できるものである。
【０１２５】
また、定着バイアスを印加するタイミングに関しても、定着フィルム１０と加圧ローラ２０の表層に用いる材料の体積抵抗値、及び、その表層の成型方法、などで左右されるものであり、用いる加熱定着装置に応じて、任意に選択すれば良いものである。
【０１２６】
〈第２の実施例〉
以下に、本発明に係る第２の実施例を示す。第２の実施例は、定着回転体である定着フィルム１０、及び、加圧回転体である加圧ローラ２０への定着バイアスの印加手段として、所望の定着バイアス値よりも小さな複数段階の定着バイアス値を経てから、所望の定着バイアス値に設定することで、一度に印加する定着バイアス値を小さく抑え、定着バイアス電源の負荷を小さくし、定着バイアス印加時に流れる電流のオーバーシュートの発生をなくし、定着回転体表面の電位を安定化させることで帯状に発生する定着尾引きを抑止するものである。
【０１２７】
先に述べた、従来の技術や第１の実施例と、相違ない箇所に関しては記述・説明を省略し、本実施例での特徴となる点についてのみ説明を行うものとする。また、本実施例で用いた画像形成装置、加熱定着装置、及び、それらを構成する各部材は同様のものを用いた。
【０１２８】
本実施例では、図８に示したように、定着バイアスとして印加するバイアス値を、所望の定着バイアス値より小さいバイアス値の印加を経てから、所望の定着バイアス値を印加するものとしている。
【０１２９】
具体的に、定着フィルム１０には、最初に−４００Ｖの直流電圧を印加した後、１５０ミリ秒経過後に、所望の−７００Ｖの直流電圧の印加へと切り替えている。加圧ローラ２０には、最初に＋２５０Ｖの直流電圧を印加した後、同じく１５０ミリ秒経過後に、所望となる＋５００Ｖの直流電圧の印加へと切り替えている。そして、定着ニップ部に記録材が搬送される直前には、定着フィルム１０、及び、加圧ローラ２０には、定着尾引きを抑止するために所望となる定着バイアスとして、１２００Ｖの電位差による電界が形成されている。
【０１３０】
定着フィルム１０に印加する上記の定着バイアスの切替は、図９に示したように、第１の電源７７と給電ブラシ７８の間に、高抵抗体として１０〜１００ＭΩ程度の抵抗Ｒを設け、この抵抗Ｒを介して電源７７から給電ブラシ７８に定着バイアスを印加する経路と、抵抗Ｒを介さないで定着バイアスを印加する経路とを、制御回路部８３で切替え制御されるスィッチング素子やリレーなどの切替部材８５によって切替えることで行なわせた。第２の電源８２から加圧ローラ２０に印加する上記の定着バイアスの切替も上記と同様の経路切替え構成で行なわせた。
【０１３１】
また、図１０に、比較例として用いた従来例での定着バイアス印加の手法である一度に所望の定着バイアス値を印加した場合と、本実施例で用いた複数段階を経た後に所望となる定着バイアス値を印加する場合での、定着フィルムと加圧ローラの給電ブラシに流れる電流の推移をモニターした結果の概念図を示した。
【０１３２】
図から分かるように、一度に所望となる定着バイアス値を印加した場合は、流れる電流値が定常状態で流れる電流値よりも大きな電流値が流れる電流のオーバーシュート現象が発生した後、定常状態で流れる電流値に落ち着いていることが分かる。
【０１３３】
これは、定着フィルム１０や加圧ローラ２０を形成している各部材はある一定の体積抵抗値を有した材料であり、特に表層の離型層に用いられるフッ素系の樹脂は高抵抗体若しくは絶縁体であるため、これらの各回転体に所望となる定着バイアスを印加するために定着バイアス電源は、より多くの電流を流すことで所望の電位に収束しようとしているために発生している現象である。
【０１３４】
これは定着フィルム１０や加圧ローラ２０が、ある容量を持ったコンデンサとして考えると分かりやすい。この容量分が電荷で満たされるまでは、より大きな電流が流れることになり、容量分が電荷で満たされると定常状態の電流値として落ち着くものである。
【０１３５】
対して、本実施例では、所望とする直流電圧値よりも小さな定着バイアスを印加した後、所望とする定着バイアス値へと切り替えているため、上述した電流のオーバーシュートを小さく抑えることが可能となっていることが分かる。
【０１３６】
次に、オーバーシュートを小さく抑えた場合の効果について説明する。
【０１３７】
定着フィルム１０や加圧ローラ２０は、定着バイアスが印加されることで発生する電界を打ち消す逆向きの電界が生じる性質を有していることは先に述べたとおりである。
【０１３８】
そのため、オーバーシュートが大きくなると、そのオーバーシュートによって生じる電界も大きくなり、それを打ち消す逆向きに定着ニップ部下流側で定着フィルム１０と加圧ローラ２０が分離する際に生じる電界も強いものとなり、そのタイミングで定着フィルム１０や加圧ローラ２０の表層に生じる逆極性の電荷量も多くなることになり、その逆極性の電荷の影響をうけて定着フィルム１０や加圧ローラ２０の表層にあらわれる電位も乱れ、そのタイミングでは定着尾引きやオフセットを抑止するために印加している定着バイアスの効果がなくなることになる。
【０１３９】
これは、表層として絶縁体であるフッ素樹脂系のチューブを被覆している加圧ローラ２０で特に顕著にあらわれる。そのため、発明が解決しようとする課題の項で図１４を用いて説明したように、ある一定巾での帯状の定着尾引きが生じることになる。
【０１４０】
図１１に、定着フィルム１０と加圧ローラ２０の表面電位をモニターした結果の概略図を示した。この図から、本発明の第２の実施例での定着バイアスの印加制御のほうが、電流のオーバーシュートが小さくなっていることが分かる。
【０１４１】
次に、本発明の実施例と従来の実施形態例での、帯状の定着尾引きの抑止効果を確認した結果を表２に記す。効果の確認は、先の実施例１と同様の確認にて行った。
【０１４２】
【表２】

【０１４３】
表２に示したように、従来の実施形態では発生していた帯状の定着尾引きの発生が、本実施例では発生することなく、常に良好な画像が得られることが実証された。
【０１４４】
〈第３の実施例〉
上記第２の実施例での説明では、定着バイアス値を２段階として切り替えるものとしたが、定着バイアスの印加タイミングは定着フィルムと加圧ローラで同期させた実施系で説明、効果の確認を行ったが、先に述べた第１の実施例で説明したように、定着フィルムと加圧ローラへの定着印加バイアスのタイミングをずらした系で実施すれば、定着尾引きの発生抑止効果が高まるのは言うまでもない。
【０１４５】
以上のように、画像形成装置の高速化に伴い、よりシビアとなる定着尾引きの発生を抑止する効果を高めた加熱定着装置を、定着バイアス電源のオーバースペックをすることなく、確立し提供することが達成できる。
【０１４６】
〈その他〉
１）加熱体としてのセラミックヒータ１１の構成形態は実施例のものに限られないことは勿論である。また、ヒータ１１は必ずしも定着ニップ部Ｎに位置していなくてもよい。例えば、ヒータ１１を定着ニップ部Ｎよりもフィルム移動方向上流側に位置させて配設することも出来る。
【０１４７】
２）フィルム加熱方式の加熱定着装置は、実施例のものは加圧用回転体駆動方式であるが、エンドレスの定着フィルムの内周面に駆動ローラを設け、フィルムにテンションを加えながら駆動する方式の装置であってもよい。
【０１４８】
３）本発明において加熱定着装置はフィルム加熱方式に限られるものではなく、熱ローラ方式の装置であってもよい。要するに、加熱部材と加圧部材とのニップで画像を担持した記録材を挟持搬送させて記録材上の画像を加熱する像加熱装置であればよい。
【０１４９】
４）本発明の加熱定着装置には、未定着画像を記録材上に永久画像として加熱定着させる定着装置ばかりでなく、未定着画像を記録材上に仮定着させる像加熱装置、画像を担持した記録材を再加熱してつや等の画像表面性を改質する像加熱装置なども包含される。
【０１５０】
５）画像形成装置の作像方式は電子写真方式に限られず、静電記録方式、磁気記録方式等であってもよいし、また転写方式でも直接方式でもよい。
【０１５１】
【発明の効果】
以上説明したように本発明によれば、未定着トナー画像が形成された記録材を、該記録材の未定着トナー画像担持面側である記録材表面側に対応する第１の回転体と、未定着トナー画像担持面側とは反対面側である記録材裏面側に対応する第２の回転体との圧接で形成される定着ニップ部に導入して挟持搬送させることにより、未定着トナー画像を記録材上に加熱定着させ、記録材が定着ニップ部を通過中には、第１と第２の回転体には直流電圧を印加する構成を有した加熱定着装置について、画像先端に顕著に現れる尾引き、帯状に発生する尾引きの問題を解消することができる。
【図面の簡単な説明】
【図１】画像形成装置例の概略構成図
【図２】加熱定着装置部分の拡大模型図
【図３】定着フィルムの層構成模型図
【図４】定着ニップ部部分の拡大横断面模型図
【図５】加熱用ヒータ（セラミックヒータ）の構成説明図
【図６】第１の実施例における定着バイアス制御の説明図（その１）
【図７】第１の実施例における定着バイアス制御の説明図（その２）
【図８】第２の実施例における定着バイアス制御の説明図（その１）
【図９】定着バイアス切替え構成の説明図
【図１０】第２の実施例における定着バイアス制御の説明図（その２）
【図１１】第２の実施例における定着バイアス制御の説明図（その３）
【図１２】加熱定着装置の概念図
【図１３】定着尾引きの概念図（その１）
【図１４】定着尾引きの概念図（その２）
【符号の説明】
１・・プロセスカートリッジ、２・・感光ドラム、３・・帯電ローラ、４・・現像装置、５・・転写ローラ、６・・クリーニング部材、７・・加熱定着装置、１０・・定着部材、１１・・加熱部材（加熱用ヒータ）、１１ａ・・セラミック基板、１１ｂ、１１ｃ・・通電発熱抵抗層、１１ｄ・・薄肉ガラス保護層、１１ｅ・・摺動層、１１ｆ、１１ｇ、１１ｈ・・電極、１２・・ステイホルダー、１３・・定着回転体（定着フィルム）、１３ａ・・導電プライマー層、１３ｂ・・表層（離型層）、１４・・温度検知素子、１５・・サーモプロテクタ、１７・・フランジ、１８・・コネクタ、２０・・加圧ローラ、２１・・加圧ローラ芯金、２２・・加圧ローラ弾性層、２３・・加圧ローラ離型層、２５・・加圧バネ、２６・・加圧ローラ駆動用ギア、２７・・定着入口ガイド、２８・・ダイオード、７６・・定着排紙センサ、７７・・定着バイアス電源、７８・・給電ブラシ、７９・・導電性ブラシ、Ｎ・・定着ニップ、Ｌ・・レーザビーム、Ｐ・・記録材、ｔ・・未定着トナー像、Ｓ・・記録材搬送基準[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a heat fixing device applied to an image forming apparatus using an electrophotographic method, an electrostatic recording method, or the like.
[0002]
More specifically, the recording material on which the unfixed toner image is formed is provided by: a first rotating body corresponding to the recording material surface side, which is the unfixed toner image carrying surface side of the recording material; The unfixed toner image is heat-fixed on the recording material by being introduced into a fixing nip formed by pressure contact with a second rotating body corresponding to the back side of the recording material opposite to the side opposite to the fixing member. The present invention relates to an improvement in a heat fixing device having a configuration in which a DC voltage is applied to the first and second rotating bodies while the recording material passes through the fixing nip.
[0003]
[Prior art]
Typical examples of the above-described heat fixing device include a heat roller type and a film heating type, and are widely used.
[0004]
FIG. 12 is a schematic diagram of the heat fixing device. P is a recording material on which an unfixed toner image T is formed. Reference numeral 100 denotes a first rotating body corresponding to the surface of the recording material P on the side of the unfixed toner image carrying surface of the recording material P, and 200 denotes a recording material on the side opposite to the surface of the recording material P on which the unfixed toner image carries the image. This is the second rotating body corresponding to the back side. More specifically, in a heat roller type heat fixing device, the first rotating body 100 is a heat roller (fixing roller, heat roller) that is heated to a predetermined temperature by a built-in heat source such as a halogen heater. In the case of a film-heating type heating / fixing apparatus, a cylindrical or endless belt-shaped heat-resistant thin film (fixing film) or sleeve (fixing sleeve) heated by a heating member (heating body) such as a ceramic heater in contact with the inner surface. ). Hereinafter, the first rotating body 100 is referred to as a fixing rotating body. The second rotating body 200 is an elastic pressure roller including a cored bar, an elastic layer, a surface release layer, and the like. Hereinafter, the second rotating body 200 is referred to as a pressure rotating body.
[0005]
The fixing rotator 100 and the pressing rotator 200 are pressed against each other with a predetermined pressing force against the elasticity of the elastic layer of the pressing rotator 200 to form a fixing nip portion (heating nip) N having a predetermined width. Thus, both the rotating bodies 100 and 200 are rotated in the direction of the arrow.
[0006]
The recording material P on which the unfixed toner image T is formed is introduced into the fixing nip N, and is nipped and conveyed in the fixing nip N. In the process of nipping and transporting the recording material P in the fixing nip N, the unfixed toner image T on the recording material P is permanently fixed to the surface of the recording material P by heating by the fixing rotator 100 and pressing force of the fixing nip N. It is established as. The recording material P that has exited from the fixing nip N is separated from the fixing rotating body 100, and is discharged and conveyed while being nipped between the fixing discharge roller pairs 61 and 61a.
[0007]
By the way, with the recent development of the computer industry, demand for printers has been increasing worldwide, and printers have been used in various countries around the world. As a result, the paper type used as the recording material P is also rich in various types such as thickness, surface properties, basis weight, etc., and at the same time, the time required to discharge the first recording material in combination with the high speed of the image forming apparatus. From the viewpoint of shortening the printing time (called the first printout time) and achieving sufficient fixing performance even with various recording materials, it is necessary to raise the fixing temperature and adjust the film heating method. In the heat fixing apparatus, satisfactory fixing performance has been ensured by increasing the amount of heat applied to the recording material from the heating element, such as improving the thermal conductivity of a fixing film as a fixing rotating body.
[0008]
In addition, the demand for image quality by users has increased, and an image forming apparatus having improved dot reproducibility formed by toner and excellent in gradation has been developed. As one means for implementing this, the particle size of the toner is further reduced. The demand for higher image quality has been achieved by increasing the particle size.
[0009]
Under the circumstances described above, various problems of image defects have also occurred in the fixing step in the image forming process. However, by developing new technologies corresponding to the problems, solutions and improvements have been made.
[0010]
For example, in the heat fixing device shown in FIG. 12, when the recording material P enters the fixing nip portion N, the unfixed toner image T on the recording material P scatters in a band shape on the rear side in the recording material traveling direction. A defect phenomenon (hereinafter, referred to as fixing tailing) may occur. When the recording material P enters the fixing nip portion N, the unfixed portion on the recording material P is located upstream of the fixing nip portion N in the recording material conveyance direction (hereinafter, referred to as the fixing nip portion upstream side). This is a phenomenon in which the toner image T scatters, is subsequently heat-fixed in the fixing nip N, becomes a toner image fixed on the recording material P, and becomes a scattered scattered image as shown in FIG.
[0011]
It is considered that the cause of the above-mentioned tailing is water vapor generated when the moisture contained in the recording material P is rapidly heated in the fixing nip portion N. That is, the generated water vapor evaporates into the space near the fixing nip portion, but easily escapes in the direction of the arrow H in FIG. 12 in the space upstream of the fixing nip portion, and the generated water vapor urges the recording material P Is generated when the unfixed toner image T is blown off.
[0012]
Further, in the fixing tailing, the amount of heat supplied to the recording material P passing through the fixing nip N has to be increased with an increase in the speed of the image forming apparatus, and the amount of generated steam increases, and the amount of generated steam increases. When the force of the generated water vapor is also increased, the unfixed toner image is blown off more strongly, and fixing tailing is likely to occur.
[0013]
Further, the water vapor easily escapes in the direction opposite to the traveling direction of the recording material P (since the water vapor generated upstream of the fixing nip portion is blocked by the fixing nip portion), so that the scattering, which is a phenomenon of fixing tailing, occurs. Is a phenomenon that the horizontal line parallel to the direction of the recording material makes it more conspicuous, and the amount of toner on the toner image forming the horizontal line becomes more conspicuous. is there.
[0014]
As an effective means for preventing the above-mentioned fixing tailing, it has been proposed to increase the holding power of an unfixed toner image on a recording material.
[0015]
As an example, a fixing bias having the same polarity as that of the toner is applied to the conductive member layer of the fixing rotator 100 from a fixing bias power supply 77 serving as a power supply means via a power supply brush 78, and at the same time, a contact is made with the back surface of the recording material downstream of the fixing nip. By setting a conductive brush 79 to be grounded and grounding to GND, the effect of suppressing fixing tailing is aimed at.
[0016]
In the configuration described above, if the recording material P present in the fixing nip portion N is in contact with the conductive brush 79, the recording material P and the conductive brush 79 are transferred from the fixing rotating body 100 via the recording material P. Thus, a current path to GND is formed. By forming such a current path, a voltage drop is caused between the fixing rotator 100 and the recording material P, and between the recording material P and the conductive brush 79, and an electric field generated at this time is recorded. By acting as a holding force of the toner T on the material P, tailing of the fixing is prevented.
[0017]
In addition, the core of the pressurizing rotating body 200 is grounded via the diode 80 so that electric charges of the opposite polarity to the toner flow from the ground side, so that the toner holding force from the back surface of the recording material is increased. are doing.
[0018]
It is needless to say that the same effect can be obtained by making the fixing paper discharging roller 61 conductive and grounding instead of the conductive brush 79.
[0019]
In an image forming apparatus capable of speeding up in recent years, since the fixing tailing is likely to occur as described above, a larger fixing bias is applied to suppress the occurrence of the fixing tailing even when the speed is increased. It has been forced to apply.
[0020]
Further, as a technique for increasing the effect of suppressing these offsets, a fixing bias having a polarity opposite to that of the toner is applied not only to the fixing rotator 100 but also to the pressing rotator 200 so that the fixing rotator 100 and the fixing rotator 100 are applied. There is a configuration in which an offset is prevented by more positively forming an electric field for holding the unfixed toner T on the recording material P between the pressure rotators 200.
[0021]
The fixing bias value applied to the pressing rotator 200 has to be increased to a larger value as in the case of the fixing film described above.
[0022]
[Problems to be solved by the invention]
However, the following problems have occurred.
[0023]
▲ 1 ▼. When a fixing bias for forming an electric field between the fixing rotator 100 and the pressing rotator 200 forming the fixing nip portion N is applied to each rotator, a releasing layer used as a surface layer of each rotator is formed. Surface layer (often coated with a thin-walled tube made of a fluorine-based resin with excellent release properties or coated with a fluorine-based resin) is a high-resistance or insulator Therefore, when the fixing rotator 100 and the pressing rotator 200 that are in contact with each other in the fixing nip N are separated on the downstream side of the fixing nip, the electric field formed in the fixing nip N is canceled. Directionally, charge transfer occurs in the surface layer of each of the rotating bodies 100 and 200. That is, a positive charge is generated on the surface of the surface of the fixing rotator 100, and a negative charge is generated on the surface of the pressing rotator 200. This tendency becomes remarkable in the pressurized rotating body 200 which covers a fluororesin-based tube as an insulator as a surface layer of the rotating body.
[0024]
Therefore, the effect of the electric field due to the fixing bias applied for the purpose of holding the unfixed toner image T on the recording material P is reduced due to the influence of the charge of the opposite polarity, and the above-described fixing tailing phenomenon is suppressed. The effect is reduced, and a fixing tailing phenomenon occurs.
[0025]
In addition, the amount of the opposite polarity charge generated at this time is such that the larger the electric field formed in the fixing nip portion, the larger the electric field generated in the direction to cancel the electric field, so that the amount of the generated reverse charge is large. Become.
[0026]
This is because in a high-speed image forming apparatus, a larger fixing bias is applied to suppress the occurrence of fixing tailing, the potential difference between the fixing film and the pressure roller is increased, and the electric field between the fixing film and the pressure roller is increased. This has a big bearing on having to make the bigger.
[0027]
▲ 2 ▼. Conventionally, the timing for applying a fixing bias for forming an electric field between the fixing rotator 100 and the pressing rotator 200 that form the fixing nip N is set immediately before the recording material P reaches the fixing nip N. , And when the recording material P reaches the fixing nip N, a desired electric field is formed.
[0028]
Using such a configuration, an image forming apparatus capable of forming images at 45 sheets per minute (LTR size vertical conveyance, process speed of 266 mm / sec) as a high-speed image forming apparatus is used. To prevent this, the DC voltage applied to each of the rotators 100 and 200 is not set so that the strength of the electric field formed between the fixing rotator 100 and the pressing rotator 200 becomes stronger (larger). It turned out to be bad.
[0029]
This is because, in an image forming apparatus with a high speed, the time required for the recording material P to pass through the fixing nip portion N is also shortened. Since the amount of heat applied to the recording material must be increased, as a result, the amount of water vapor generated from the recording material and the force of the generated water vapor become strong, so that the fixing tailing tends to occur, and the fixing tailing also occurs. The occurrence level will also be worsened.
[0030]
Even in such a high-speed image forming apparatus, a stronger electric field must be formed between the pair of rotating members 100 and 200 forming the fixing nip portion N in order to provide a heat fixing device that does not cause fixing tailing. Have to be.
[0031]
(3). By forming a stronger electric field as described above, it is possible to suppress the occurrence of fixing tailing, but on the other hand, the following problems have become apparent.
[0032]
In order to form a stronger electric field, it is necessary to apply a larger DC voltage to each of the fixing rotating body 100 and the pressing rotating body 200. When a larger DC voltage is applied, more current flows to satisfy the electric capacity of each of the rotating bodies 100 and 200. Therefore, during a transition from a state where no DC voltage is applied to each of the rotating bodies 100 and 200 to a state where a desired voltage is applied, a phenomenon in which more current flows instantaneously (current overshoot) occurs. After passing through, the desired voltage is settled.
[0033]
As described above, since each of the rotating bodies 100 and 200 employs a fluororesin (insulator) having excellent releasability as a surface layer, when a voltage is applied and an electric field is formed, the fixing nip portion is formed. When the fixing rotator 100 and the pressing rotator 200 are separated on the downstream side, an electric field is generated in a direction to cancel the electric field, and the polarity of each of the rotators 100 and 200 is opposite to the polarity applied by the fixing bias. Will be accumulated.
[0034]
Since the overshoot of the current flowing in each of the rotating bodies 100 and 200 becomes excessive, it is instantaneous (several hundred milliseconds depending on the specification of the high-voltage power supply). The potential difference larger than the potential difference required to prevent the occurrence of the image formation is generated for a very short time. However, since the image forming apparatus is also operated at a high speed, it cannot be ignored when considering the fixing rotating body 100 and the pressing rotating body 200. It will be something.
[0035]
Due to this, a stronger electric field than desired is formed in the fixing nip portion N, and the amount of charge of the opposite polarity generated when each of the rotating bodies 100 and 200 separates on the downstream side of the fixing nip portion is also reduced. It will be big. Under the influence of the opposite polarity charge, a portion having a potential lower than a desired potential is generated on the fixing rotating body 100 and the pressing rotating body 200, and a phenomenon that the electric field is partially weakened occurs. Oops.
[0036]
As described above, since the desired electric field is not formed for a very short time, it has a certain width on the recording material P and is orthogonal to the recording material conveyance direction, as shown in FIG. A belt-like fixing tail is generated.
[0037]
This phenomenon occurs because the DC current flowing into each of the rotating bodies 100 and 200 momentarily overshoots, and is a band-like fixing tail. If the overshoot of the current can be prevented, the phenomenon occurs. Can be suppressed.
[0038]
To achieve this, it is possible to eliminate the transient current by setting the capacity of the power transformer that generates the fixing bias to a larger capacity power transformer, but this can be achieved. A power transformer, which is not desirable in terms of product cost.
[0039]
In addition, with the recent miniaturization of image forming apparatuses, it is necessary to reduce the size of an electric board on which electric components (resistance, IC, transistor, power transformer, etc.) are mounted. It is difficult to implement a mounted power transformer (the size of the power transformer also naturally increases) due to restrictions on the electric board.
[0040]
The present invention relates to a recording material on which an unfixed toner image is formed as described above, comprising: a first rotating body corresponding to a recording material surface side which is an unfixed toner image carrying surface side of the recording material; An unfixed toner image is recorded by being introduced into a fixing nip portion formed by press contact with a second rotating body corresponding to the back side of the recording material opposite to the toner image carrying surface side and nipped and conveyed. A heat fixing device having a configuration in which a DC voltage is applied to the first and second rotating bodies while the recording material is passing through the fixing nip portion while the recording material is passing through the fixing nip portion. An object of the present invention is to solve the problem of tailing that appears remarkably and tailing that occurs in a band shape.
[0041]
[Means for Solving the Problems]
The present invention is a heat fixing device and an image forming apparatus characterized by the following constitutions.
[0042]
(1) A recording material on which an unfixed toner image is formed is provided by a first rotating body corresponding to a recording material surface side which is an unfixed toner image carrying surface side of the recording material, and an unfixed toner image carrying surface side. Is introduced into a fixing nip formed by pressure contact with a second rotating body corresponding to the reverse side of the recording material, and nipped and conveyed to heat and fix an unfixed toner image on the recording material. A heating and fixing device configured to apply a DC voltage to the first and second rotating members while the recording material passes through the fixing nip;
The timing at which the application of the DC voltage to the first and second rotating bodies starts to be started has an arbitrary time difference.
[0043]
(2) The timing at which the application of the DC voltage to the first and second rotating bodies is started is the time before the leading end of the recording material introduced into the fixing nip reaches the fixing nip. Then, the application is started to the first and second rotating bodies, and the application is also started to the other rotating body until the leading end of the recording material reaches the fixing nip with a time difference. The heating according to (1), wherein a DC voltage is applied to each of the first and second rotating bodies at a timing when the recording material is nipped and conveyed to the fixing nip portion. Fixing device.
[0044]
(3) The recording material on which the unfixed toner image is formed is divided into a first rotating body corresponding to the recording material surface side which is the unfixed toner image carrying surface side of the recording material, and an unfixed toner image carrying surface side. Is introduced into a fixing nip formed by pressure contact with a second rotating body corresponding to the reverse side of the recording material, and nipped and conveyed to heat and fix an unfixed toner image on the recording material. A heating and fixing device configured to apply a DC voltage to the first and second rotating members while the recording material passes through the fixing nip;
The heating and fixing device is characterized in that the application of a DC voltage to each of the rotating bodies applies a desired DC voltage value through a plurality of voltage values.
[0045]
(4) The recording material on which the unfixed toner image is formed is divided into a first rotating body corresponding to the recording material surface side, which is the unfixed toner image carrying surface side of the recording material, and an unfixed toner image carrying surface side. Is introduced into a fixing nip formed by pressure contact with a second rotating body corresponding to the reverse side of the recording material, and nipped and conveyed to heat and fix an unfixed toner image on the recording material. A heating and fixing device configured to apply a DC voltage to the first and second rotating members while the recording material passes through the fixing nip;
The timing of starting the application of the DC voltage to each of the first and second rotating bodies is given an arbitrary time difference, and the application of the DC voltage to each rotating body is performed in a plurality of voltage values. A heating and fixing device for applying a desired DC voltage value.
[0046]
(5) The setting of the DC voltage value having a plurality of steps to be applied to the rotating body is performed by changing from a voltage value smaller than a desired DC voltage value to a larger value to a desired DC voltage value. The heat fixing device according to (3) or (4), wherein
[0047]
(6) A DC voltage having the same polarity as the toner is applied to the first rotating body corresponding to the recording material front side, and a DC voltage having the opposite polarity to the toner is applied to the second rotating body corresponding to the recording material rear side. The fixing device according to any one of (1) to (5), wherein the voltage is applied.
[0048]
(7) An electrode member that is in contact with the back side of the recording material is provided downstream of the fixing nip in the recording material conveyance direction, and the electrode member is electrically grounded. Any one of (1) to (6), wherein a DC voltage having the same polarity as the DC voltage applied to the second rotating body corresponding to the material rear surface side is applied. 2. The heat fixing device according to 1.
[0049]
(8) The heat fixing device according to (7), wherein the electrode member is a conductive brush.
[0050]
(9) A pair of rollers as a recording material transport holding member is provided downstream of the fixing nip portion in the recording material transport direction, and the roller in contact with the recording material back surface of the roller pair is electrically conductive. The heat fixing device according to any one of (1) to (8), wherein the heat fixing device is provided and is electrically grounded.
[0051]
(10) The first rotating body corresponding to the recording material surface side is a flexible member formed at least from a base layer serving as a base material, a surface layer serving as a release layer, and an adhesive layer between the base layer and the release layer. It is constituted by a hollow rotating body having a property, is heated by a heating member inscribed in the inside of the hollow rotating body, and a DC voltage is applied to the rotating body through the adhesive layer. (1) The heat fixing device according to any one of (1) to (9).
[0052]
(11) The second rotating body corresponding to the back side of the recording material includes a metal core, a rubber layer as an elastic layer, and a surface layer as a release layer from the center outward. The heat fixing device according to any one of (1) to (10), wherein the application of the DC voltage to the rotating body is performed via a metal core or directly on a surface layer.
[0053]
(12) In an image forming apparatus having an image forming unit that forms an unfixed toner image on a recording material and a heat fixing unit that heats and fixes the unfixed toner image on the recording material,
The image forming apparatus, wherein the heat fixing unit is the heat fixing device according to any one of (1) to (11).
[0054]
<Operation>
▲ 1 ▼. That is, by changing the strength of the electric field formed between the first and second rotating members forming the fixing nip portion stepwise with an arbitrary time difference, the amount of change in the electric field at one time is suppressed. Thus, control is performed so that the amount of charges of opposite polarity generated when the first rotating body and the second rotating body are separated downstream of the fixing nip portion is reduced.
[0055]
As an advantage, the electric field formed in the fixing nip portion can be always optimized, and a heat fixing device that can always suppress the occurrence of the fixing tailing phenomenon can be provided.
[0056]
▲ 2 ▼. The specific setting of the DC voltage (fixing bias) to be applied to each of the first and second rotating bodies starts from a fixing bias value smaller than a desired fixing bias value, and is set for a predetermined time (several hundred milliseconds). After the lapse of time, by switching to the desired fixing bias value, the formation of an electric field stronger than the desired electric field caused by the overshoot of the current generated when the fixing bias is applied is prevented, and the electric field is generated in a direction to cancel the electric field. Provided is a heating / fixing device which eliminates unevenness of a potential difference generated for a very short time due to generation of charges of opposite polarity, and which can effectively prevent a band-like fixing tailing caused by unevenness of a potential difference in a fixing nip portion. It is possible to do.
[0057]
BEST MODE FOR CARRYING OUT THE INVENTION
<First embodiment>
(1) Example of image forming apparatus
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to the present embodiment. The image forming apparatus of this embodiment is a laser printer using an electrophotographic process, and is of a detachable type with a process cartridge and capable of outputting 45 sheets of LTR size per minute as a recording material. It also has an image resolution of 600 dpi (dot per inch).
[0058]
Reference numeral 2 denotes a photosensitive drum on which a photosensitive material such as OPC, amorphous Se, amorphous Si, or the like is formed on a cylindrical element tube such as aluminum or nickel.
[0059]
The photosensitive drum 2 is driven to rotate in the direction of the arrow, and its surface is first uniformly charged by a charging roller 3 as a charging device.
[0060]
Next, the uniformly charged surface of the rotating photosensitive drum 2 is subjected to laser beam scanning exposure L by the laser scanner unit 81 to form an electrostatic latent image of image information. The laser beam scanning exposure L on the photosensitive drum 2 is performed by reflecting a laser beam whose lighting is controlled in accordance with image information by a polygon mirror rotating in a laser scanner unit 81.
[0061]
This electrostatic latent image is developed and visualized by the developing device 4. As a developing method, a jumping developing method, a two-component developing method, an FEED developing method, or the like is used, and a combination of image exposure and reversal developing is often used.
[0062]
The visualized toner image is transferred from the photosensitive drum 2 onto a recording material (transfer material) P conveyed at a predetermined timing from a paper feed mechanism by a transfer roller 5 as a transfer device.
[0063]
The recording material P is picked up from a selected upper or lower cassette 72 of the paper feed mechanism by a paper feed roller pair 73, sent through a paper feed path 74 to a registration roller pair 75 that detects the leading edge of the paper, After matching the timing with the toner image as a visible image on the photosensitive drum 2, the toner image is conveyed to a transfer nip, which is a contact portion between the photosensitive drum 2 and the transfer roller 5. At this time, the recording material P is nipped and conveyed between the photosensitive drum 2 and the transfer roller 5 with a constant pressing force.
[0064]
The recording material P on which the toner image has been transferred at the transfer nip is separated from the surface of the photosensitive drum 2 and is conveyed to the fixing device 7 where it is fixed as a permanent image, and is discharged to the discharge tray 70 via the discharge roller pair 71. Will be done.
[0065]
On the other hand, the transfer residual toner remaining on the photosensitive drum 2 is removed from the surface of the photosensitive drum by the cleaning member 6, and the photosensitive drum 2 is repeatedly used for image formation.
[0066]
The printer of this embodiment is a process cartridge 1 in which the four process devices of the photosensitive drum 2, the charging roller 3, the developing device 4, and the cleaning device 6 are collectively attached to and detached from the printer main body.
[0067]
(2) Heat fixing device 7
1) Overall configuration of the heat fixing device 7
FIG. 2 is a schematic cross-sectional view of the schematic configuration of the heat fixing device 7. The heat fixing device 7 of the present embodiment employs a film heating method using a cylindrical (endless belt-shaped) fixing film as a fixing rotator disclosed in Japanese Patent Application Laid-Open Nos. 4-44075 to 44083 and 4-20498 to 204984. , A heating and fixing device of a pressing rotary member driving system.
[0068]
Reference numeral 10 denotes a cylindrical (endless belt-shaped) fixing film as a first rotating body, that is, a fixing rotating body. As shown in FIG. 3, the fixing film 10 includes a base layer 10a made of a heat-resistant resin or a metal and a surface layer 10c as a release layer laminated on the outer peripheral surface thereof via a conductive primer layer (adhesive layer) 10b. And a flexible thin rotating body having a small heat capacity as a whole. This fixing film 10 will be described in more detail in section 2) below.
[0069]
The fixing film 10 is loosely fitted to a heat insulating stay holder 12 having a ceramic heater 11 as a heater for heating (heating member, heating element) fixedly held on the lower surface. The ceramic heater 11 will be described in more detail in section 3) below.
[0070]
The heat-insulating stay holder 12 is a member that holds the heating heater 11 and also serves as a conveyance guide for the rotating fixing film 10 and that prevents heat radiation to the opposite side of the fixing nip, and includes a liquid crystal polymer, a phenol resin, It is formed of PPS, PEEK, or the like. In this embodiment, a heat insulating stay holder made of a liquid crystal polymer is used.
[0071]
Reference numeral 20 denotes a second rotating body, that is, an elastic pressing roller as a pressing rotating body. The pressure roller 20 includes a metal core 21, an elastic layer 22 formed by foaming heat-resistant rubber such as silicon rubber or fluorine rubber or silicon rubber formed outside the metal core 21, and further thereon. A release layer 23 of PFA, PTFE, FEP, or the like is formed.
[0072]
The pressure roller 20 is pressed against the lower surface of the heater 11 held by the heat insulating stay holder 12 with a total pressure of 127 N by a pressure spring as a pressing means (not shown) with the fixing film 10 interposed therebetween. A fixing nip portion N having a width is formed.
[0073]
The pressure roller 20 is rotated at a predetermined peripheral speed in a counterclockwise direction indicated by an arrow in FIG. 2 by transmitting a rotational force from a drive system to a pressure roller drive gear (not shown) fixed to a cored bar 21. . The rotational force acts on the cylindrical fixing film 10 by the frictional contact between the outer surface of the pressure roller 20 and the fixing film 10 at the fixing nip portion N by the rotational driving of the pressing roller 20, and the fixing film 10 The inner surface of the heat-insulating stay holder 12 is driven to rotate clockwise as indicated by an arrow while the inner surface thereof is in close contact with the downward surface of the heater 11 while sliding.
[0074]
Although not shown in the figure, a flange member is provided at the end of the heat insulating stay holder 12 for receiving the end of the rotating fixing film 13 to regulate the longitudinal position and restricting the fixing film from moving in the axial direction. It is set up. As a material used for the flange member, as a material having excellent heat resistance, relatively poor thermal conductivity and excellent slipperiness, a resin containing glass fiber such as PPS, liquid crystal polymer, PET, PI, PA, etc. Is used.
[0075]
Further, since the fixing film 10 rotates while rubbing against the internal heater 11 and the heat insulating stay holder 12, it is necessary to reduce the frictional resistance between the heater 11 and the heat insulating stay holder 12 and the fixing film 10. There is. Therefore, a small amount of heat-resistant grease is applied as a lubricant to the surfaces of the heater 11 and the heat insulating stay holder 12. Thus, the fixing film 10 can rotate smoothly.
[0076]
The pressure roller 20 is rotated and driven, whereby the cylindrical fixing film 10 is driven to rotate, and the heater 11 is energized, and the temperature of the heater 11 rises to a predetermined temperature and the temperature is controlled. In this state, the recording material P carrying the unfixed toner image T is introduced between the fixing film 10 and the pressure roller 20 in the fixing nip portion N while being guided along the heat-resistant fixing entrance guide 27, and is introduced. In the portion N, the toner image bearing surface side of the recording material P is in close contact with the outer surface of the fixing film 10, and the fixing nip N is conveyed together with the film 10. In this nipping and conveying process, the heat of the heater 11 is applied to the recording material P via the fixing film 10, and the unfixed toner image T on the recording material P is heated and pressed onto the recording material P to be fused and fixed. .
[0077]
The recording material P that has passed through the fixing nip portion N is separated from the fixing film 13 by curvature, and a conductive brush 79 as an electrode member that comes into contact with the back surface of the recording material, a fixing discharge sensor 76, a pair of fixing discharge rollers 61, 61a, and a discharge The paper is discharged to the paper discharge tray 70 via the paper roller pair 71. The conductive brush 79 is electrically grounded via a diode 80.
[0078]
The fixing / discharge sensor 76 is a sensor for determining whether or not the recording material exists in the fixing nip portion, and outputs a signal used for controlling the power supply to the heater 11 and detecting the retention of the recording material in the fixing nip. is there. The fixing paper discharge sensor 76 is provided as a sensor that is turned ON when a recording material is present on the fixing paper discharge sensor 76, and is provided very close to the fixing nip portion. It can also be used as an indicator of the presence of material.
[0079]
Reference numeral 77 denotes a first power supply for applying a fixing bias having the same polarity as that of the toner to the fixing film 10 as a fixing rotating body. That is, a part of the primer layer 10b of the fixing film 10 in the longitudinal direction is exposed in the circumferential direction as shown in FIG. 3, and the fixing film surface has a negative polarity of the same polarity as the toner for the purpose of tailing and preventing offset. A DC voltage of -700 V is applied as a fixing bias from a power supply 77 via a power supply brush 78 so as to maintain the potential. This fixing bias prevents the unfixed toner T on the recording material P from being transferred (offset) onto the fixing film 10.
[0080]
Reference numeral 82 denotes a second power supply for applying a fixing bias having a polarity opposite to that of the toner to the pressure roller 20 as a pressure rotating body. Similarly to the above-described fixing film 10, the pressing roller 20 has a second core attached to the pressing roller core 21 in order to form an electric field with the fixing film 10 for the purpose of tailing and offset prevention. By applying a DC voltage of +500 V from the power supply 82, the potential of the surface of the pressure roller is set to be positive with the opposite polarity to that of the toner, and the holding power of the toner from the back surface of the recording material is increased. A configuration in which a fixing bias is directly applied to the surface layer of the pressure roller may be employed.
[0081]
In addition, the conductive brush 79 and the fixing discharge roller 61 provided immediately after the fixing nip portion are grounded to the body frame (GND), and a positive DC voltage for supplying power to the pressure roller 20 is applied. By forming a current circuit from the fixing film 10 to the conductive brush 78 and the fixing discharge roller 61 via the recording material P, the effect of suppressing phenomena such as fixing tailing and offset is improved. There is also an embodiment of an image forming apparatus in which the following is taken.
[0082]
In this embodiment, a diode 80 is provided between the conductive brush 79 and the main frame (GND) with the main frame side being the anode side.
[0083]
Reference numeral 83 denotes a control circuit of the image forming apparatus, which controls an image forming operation sequence of the entire image forming apparatus. The first and second power supplies 77 and 82 control the application timing and output of the fixing bias to the fixing film 10 and the pressure roller 20 according to the control program set in the control circuit unit 83, respectively. The control of the fixing bias will be described later in detail in section (3).
[0084]
In the heat fixing device of the film heating type using such a thin fixing film 10, the pressing roller 20 having an elastic layer presses the ceramic roller as a heater due to the high rigidity of the ceramic heater. The flat surface of the heater 11 is flattened at the pressure contact portion to form a fixing nip portion N having a predetermined width, and only the fixing nip portion N is heated to achieve a quick start. This realizes heat fixing that achieves large energy saving without energizing the power.
[0085]
2) Fixing film 10
The first rotating body, that is, the cylindrical heat-resistant fixing film 10 serving as a fixing rotating body, has a thickness of a total thickness because the heat of the heater 11 is efficiently applied to the recording material P as the material to be heated in the fixing nip portion N. The thickness is as thin as 100 μm or less, preferably 20 to 70 μm.
[0086]
As described above, the fixing film 11 has a three-layer structure including a film base layer 10a, a primer layer 10b, and a release layer 10c. The film base layer 10a side is the heater 11 side, and the release layer 10c side is pressurized. The roller 20 side. The film base layer 10a is made of polyimide, polyamide imide, PEEK, or the like having a higher insulating property than a glass protective layer 10c described later of the heater 11, has heat resistance, high elasticity, and has a flexible thickness of about 25 to 65 μm. It is formed as a resin film. Further, mechanical strength such as tear strength of the entire fixing film is maintained by the film base layer 10a. The primer layer 10b is formed of a thin layer having a thickness of about 2 to 6 μm, and is provided with conductivity by dispersing carbon, metal oxide, or the like so as to serve as an electrically conductive path to prevent charging of the fixing film 10, Generally, it is a conductive primer layer. The release layer 13c is a toner offset prevention layer to which the toner adheres to the fixing film, and is formed by coating a fluororesin such as PFA, PTFE, and FEP to a thickness of about 10 μm. The release layer 10c also disperses carbon and metal oxide during release to impart conductivity by reducing charge on the surface layer of the fixing film and preventing phenomena such as electrostatic offset which is widely known in electrophotography. That is common.
[0087]
More specifically, as the base layer 10a, heat-resistant resin such as polyimide, polyamide-imide, PEEK (polyetheretherketone) having heat resistance and thermoplasticity, or SUS (stainless steel) having heat resistance and high heat conductivity, Al It is formed of a metal material such as (aluminum), Ni (nickel), Ti (titanium), Zn (zinc), etc., alone or in combination.
[0088]
In the case of the resin base layer 10a, a high thermal conductive powder such as BN (boron nitride), alumina, or Al may be mixed in order to improve thermal conductivity. Further, in order to form the base layer 10a having sufficient strength and excellent durability for forming the long-life fixing film 10, a thickness of about 25 μm or more is required. Therefore, the total thickness of the fixing film 10 is optimally 25 μm or more and 100 μm or less.
[0089]
Further, in order to prevent offset and secure the separation property of the recording material, the surface layer 13c has a PFA (tetrafluoroethylene perfluoroalkylvinyl ether copolymer), PTFE (polytetrafluoroethylene), and FEP (tetrafluoroethylene hexafluoropropylene copolymer). Fluorine resin having good releasability, such as coalescing), is mixed or coated alone or coated.
[0090]
The fixing film 10 used in the present embodiment has a total thickness of 60 μm so that the temperature can be raised to a fixing-possible temperature in a very short time, and the base layer 10a is a heat-resistant, thermoplastic resin film of polyimide. The thickness of the base layer 10a was set to 45 μm and the outer diameter was set to approximately φ25 mm in order to endure thermal stress and mechanical stress and to have sufficient strength to form a long-life fixing rotating body.
[0091]
On the base layer 10a, a conductive primer layer (adhesive layer) 10b in which a suitable amount of a conductive material such as carbon is dispersed is applied to a thickness of 5 μm.
[0092]
On the conductive primer layer 10b, PFA is used as a fluororesin having high releasability and high heat resistance in order to prevent adhesion of toner and paper powder and to secure the separating property of the recording material P from the fixing film 10. Is applied in a thickness of 10 μm by a dipping coating method to form a release layer 10c, and the base layer 10a, the primer layer 10b, and the release layer 10c form a fixing film 10 of approximately φ25 mm.
[0093]
3) heater 11 for heating
Generally, a ceramic heater is used for the heater 11. FIG. 4 is an enlarged cross-sectional model surface of the fixing nip portion N including the heater 11 in the present embodiment, and FIG. 5 is a configuration explanatory view of the heater 11.
[0094]
For example, alumina (Al ₂ O ₃ ), Etc., on the surface (the surface facing the fixing film) of the ceramic substrate 11a having high electrical insulation, good thermal conductivity, and low heat capacity along the substrate length (the direction perpendicular to the paper surface of FIG. 4). Ag / Pb) ・ Ta ₂ A heating and heating resistance layer 11b of N or the like is formed by applying a thin strip of about 10 μm in thickness and about 4 mm in width by screen printing or the like, and the surface on which the heating resistance layer is formed is rubbed with the fixing film 10. It is covered with a thin glass protective layer (glass coat) 11c that can withstand the heat. The glass protective layer 11c is formed to have a thickness of about 50 μm in order to satisfy the pressure-resistant insulation between the current-carrying resistance layer 11b of the heater 11 and the conductive primer layer 10b of the fixing film 10. In the heater 11, the energization and heating resistance layer 11b is energized by a power supply (not shown) from the electrodes 11f and 11g to generate heat, and the entire heater including the ceramic substrate 11a and the glass protection layer 11c is heated. The temperature rises rapidly.
[0095]
The temperature rise of the heater 11 is detected by a temperature detection element 14 arranged on the back of the heater, and the temperature detection information is fed back to the power supply control unit (not shown) from the electrodes 11h and 11i. The energization control unit controls energization of the energization heating resistance layer 11c so that the heater temperature detected by the temperature detection element 14 is maintained at a predetermined substantially constant temperature (fixed temperature adjustment temperature). That is, the heater 11 is heated and adjusted to a predetermined fixing temperature.
[0096]
As a method of controlling the power supply to the current-carrying resistance layer 11c, a wave number control method of controlling the input power by the wave number of the AC voltage, a phase control method of supplying a current to the next zero cross after a predetermined delay time from the zero cross of the AC voltage, and the like are applied. Is done.
[0097]
Further, on the back surface of the heater, a temperature detecting element 14 such as a thermistor and a temperature fuse for shutting off the power supply to the energized heat generating resistance layer 11b of the heater at the time of runaway or a thermo protector 15 such as a thermo switch are in contact. The image forming apparatus is arranged in a conveyance area of a recording material having a minimum width that can be conveyed.
[0098]
Regarding the temperature detecting element 14, even when a recording material having a minimum width that can be conveyed by the image forming apparatus main body is conveyed, the toner image on the recording material is appropriately fixed without causing a problem such as defective fixing and high-temperature offset. In order to heat and fix at a proper fixing temperature, the recording material is provided within the minimum transport area of the recording material. On the other hand, even when the recording material having the minimum width is conveyed, the thermo protector 15 is overheated in the non-conveying region having a smaller thermal resistance than the conveying region when the recording material having the minimum width is conveyed. It is provided in the recording material minimum conveyance area so as not to cause a problem such as shutting out of energization due to malfunction of the thermoprotector.
[0099]
(3) Fixing bias control
FIG. 6 or FIG. 6 shows a control of applying a fixing bias to a fixing film 10 as a fixing rotator and a pressing roller 20 as a pressing rotator sequentially with an arbitrary time difference. 7 will be described. This control is performed by the control circuit unit 83. That is, the control circuit unit 83 controls the application timing of the fixing bias from the first and second power supplies 77 and 82 to the fixing film 10 and the pressure roller 20 by a predetermined time difference according to the control program set therein.
[0100]
FIG. 6 is an explanatory diagram of the application timing of the fixing bias to the fixing film 10 and the pressure roller 20 as compared with the conventional example. The signal of the fixing / discharge sensor 76 (FIG. 2) in the figure is a signal that is turned on while the recording material P reaches the sensor 76 as described above, and the recording material P is almost applied to the fixing nip portion N. Is coincident with the timing at which.
[0101]
As shown in FIG. 6, the conventional application timing of the fixing bias is such that immediately before the recording material P reaches the fixing nip portion N, the fixing bias to the fixing film 10 and the pressing roller 20 is started to be applied simultaneously. I have.
[0102]
Therefore, as described in the section of the problem to be solved by the invention, in the fixing nip portion N, an electric field for canceling the electric field formed between the fixing film 10 and the pressure roller 20 is generated downstream of the fixing nip portion. Is generated when the fixing film 10 and the pressure roller 20 are separated from each other, and a charge having a polarity opposite to the potential on the surface layer of each rotating body of the fixing film 10 and the pressure roller 20 is generated in the fixing nip portion. become.
[0103]
This is because, as described above, a pressure roller that covers a fluororesin-based tube, which is an insulator, as a surface layer rather than the fixing film 10 whose surface layer is formed by coating, spray coating, dipping, or the like. At 20, the generation of charges in the opposite direction becomes noticeable. Due to the influence of the charge of the opposite polarity, the electric field due to the fixing bias applied to prevent the tailing of the fixing becomes smaller than desired.
[0104]
In order to confirm this, FIG. 7 is a conceptual diagram showing a result of measuring electric charges generated on the surface layers of the fixing film 10 and the pressure roller 20 as a surface potential. As shown in FIG. 7, at the same time as the application of the fixing bias, the surface potentials of the fixing film 10 and the pressure roller 20 pass through an unstable state before stably settling at a desired potential, and then reach a desired level of about 1200 V. It can be seen that the potential difference calms down. If the recording material reaches the fixing nip before converging to the potential difference of about 1200 V, an electric field for suppressing the occurrence of fixing tailing is not formed, so that fixing tailing occurs. .
[0105]
As already described in the section of the problem to be solved, in the heat fixing device which has achieved high speed, in order to obtain the optimum fixing property, the fixing temperature must be adjusted to a higher temperature. Since the amount of water vapor increases and the generated steam becomes stronger, it is necessary to form a stronger electric field due to a larger potential difference between the fixing rotating members 10 as compared with the conventional heat fixing device. Therefore, the opposite electric field generated when the fixing film 10 as the fixing rotator and the pressing roller 20 as the pressing rotator are separated on the downstream side of the fixing nip to cancel the stronger electric field is also increased. Also, since the amount of charges of the opposite polarity is increased, the effect of the fixing bias applied for the purpose of suppressing the tailing of the fixing and the offset is reduced.
[0106]
Therefore, in order to reduce the strength of the electric field in the opposite direction generated in the direction of canceling the electric field formed to suppress fixing tailing and offset, the amount of change in the potential difference formed by the fixing bias is suppressed to a small value. It is the gist of the present invention to control the potential difference formed between the pair of fixing rotations so that the electric field generated in the opposite direction is also weakened by reducing the intensity of the electric field generated in accordance with the above.
[0107]
Here, the recording material is transferred to the fixing nip so that the electric field formed between the fixing rotator 10 and the pressing rotator 20 converges to a desired potential difference before the recording material reaches the fixing nip. Although an effect can be expected by delaying the transport timing, as described in the section of the related art, as described in the section of the related art, it is a recent trend to shorten the time until the first image is output (reduced first printout). This is an essential item in the image forming apparatus described above, and delaying the timing of transporting the recording material to the fixing nip portion, which hinders this, impairs the convenience of the user. It is a measure that can not be done.
[0108]
Next, the content of the first embodiment of the present invention, that is, the amount of change in the electric field generated by suppressing the change in the potential difference generated when the fixing bias is applied to be small, is reduced, and the amount of change in the electric field is reduced. A description will be given of the content of suppressing the electric field in the opposite direction to a small value and also reducing the amount of charges of the opposite polarity generated.
[0109]
As shown in FIG. 6, in this embodiment, the application of a DC voltage of +500 V as a fixing bias to the pressure roller 20 is started about 300 ms before the recording material P reaches the fixing nip N. .
[0110]
At this time, since the potential difference between the fixing film 10 and the pressure roller 20 is about 500 V, the electric field formed between the fixing film 10 and the pressure roller 20 is smaller than the 1200 V of the comparative example according to the potential difference. , About 40% as 500/1200. Therefore, the strength of the reverse electric field generated when the fixing film 10 and the pressure roller 20 are separated on the downstream side of the fixing nip portion is small, and the amount of the opposite polarity charge generated there is also small. Thus, the effect of the fixing bias applied to the pressure roller 20 can be made to act more efficiently.
[0111]
Next, about 170 milliseconds after the application of the fixing bias to the pressure roller 20, the application of a DC high voltage of -700 V as a fixing bias to the fixing film 10 was started. The potential difference between the fixing film 10 and the pressure roller 20 that changes at this moment is about 700 V, which is 700/1200 compared to the comparative example, which can be about 60%. As in the case of the roller, the reverse electric field generated in the direction to cancel the electric field can be weak. As an effect thereof, similarly to the case of the pressure roller, the effect of the fixing bias applied to the fixing film can be made more efficient, so that fixing tailing and offset can be prevented.
[0112]
Here, the time difference between the application of the bias of the pressure roller 20 and the application of the bias to the fixing film 10 is set to 170 ms because the application of the bias is started 170 ms after the bias is applied to the pressure roller 20. Since the portion that has been moved exceeds the downstream side of the fixing nip portion (separates from the fixing film), the influence of the accumulation of the opposite polarity charge due to the effect of the potential difference due to the application of the fixing bias to the pressure roller 20 is eliminated, and the fixing is started next. This is to further enhance the effect of the bias.
[0113]
As described above, the effect of the application timing of the fixing bias in the above-described first embodiment of the present invention as an image forming apparatus was confirmed by the occurrence of fixing tailing. Confirmation was made on the recording material, image pattern, and environment in which fixing tailing is likely to occur. Product name sold by Canon Sales Co., Ltd. as a recording material: Office planner, A4 size, 64 g / m ² Was left in a high-temperature, high-humidity environment for a long time, and used as a recording material that had sufficiently absorbed moisture.
[0114]
As described above, as described above, a 6-dot horizontal line (a line of approximately 25 μm) and a space of 30 dots (a non-printing region of approximately 130 μm) are repeated as a region where fixing tailing is likely to occur.
[0115]
The environment was 30 ° C./80% as a high-temperature and high-humidity environment in which the recording material was left.
[0116]
Table 1 shows the results of the confirmation.
[0117]
[Table 1]

[0118]
As shown in Table 1, it can be seen that the occurrence of the tailing of the first sheet immediately after the start of printing is not good with the conventional fixing bias application timing. This is achieved by applying a fixing bias from a state in which no fixing bias is applied to each of the rotating bodies 10 and 20 of the fixing film 10 as the fixing rotating body and the pressing roller 20 as the pressing rotating body. This is because the effect of suppressing the fixing tailing due to the fixing bias is reduced by the charge of the opposite polarity caused by the formation of the electric field in the opposite direction generated in the direction to cancel the electric field formed by the potential difference of about 1200 V.
[0119]
In comparison, in the first embodiment of the present invention, it can be seen that the effect of suppressing the occurrence of fixing tailing is high even on the first sheet immediately after the start of printing, and the effect of the present invention appears.
[0120]
In the present embodiment, the order of applying the fixing bias is such that the application of the fixing bias is performed first from the pressing roller 20. Here, the reason why the fixing bias is applied first from the pressure roller 20 will be described in detail again.
[0121]
In the heat fixing device used in the present embodiment, the release layer 10c used as the surface layer of the fixing film 10 as the fixing rotating body is formed by coating a fluororesin material. ▼. Coating thickness, (2). Due to the generation of extremely minute pinholes, the coating layer has a lower volume resistance value than the fluororesin material itself.
[0122]
On the other hand, the release layer 23 used as the surface layer of the pressure roller 20 is formed by covering a tube made of a fluororesin, and is an insulator having a volume resistance value equivalent to that of the fluororesin material. Since a large amount of charges of the opposite polarity is generated due to the opposite electric field generated in the direction of canceling the electric field generated when the fixing bias is applied to the pressure roller 20, fixing as a fixing rotating body due to the influence of the charges of the opposite polarity is performed. Since it is desired to guide the recording material to the fixing nip after eliminating the influence on the potential difference between the film 10 and the pressure roller 20 as the pressure roller and the pressure roller 20, the recording material is applied to the pressure roller 20 prior to the fixing film 10. A configuration in which a fixing bias is applied increases the effect of suppressing fixing tailing.
[0123]
Therefore, in this embodiment, the fixing bias is applied prior to the pressing roller 20.
[0124]
This depends on the volume resistance value of the material used for the surface layer of the fixing film 10 and the pressure roller 20, and the method of molding the surface layer, and the like. Alternatively, if any one of the pressure rollers 20 is set to apply the fixing bias in advance, the effect described in this embodiment can be expected.
[0125]
The timing of applying the fixing bias also depends on the volume resistance value of the material used for the surface layer of the fixing film 10 and the pressure roller 20 and the molding method of the surface layer. May be arbitrarily selected according to the above.
[0126]
<Second embodiment>
Hereinafter, a second embodiment according to the present invention will be described. In the second embodiment, as a means for applying a fixing bias to the fixing film 10 as a fixing rotating body and the pressing roller 20 as a pressing rotating body, a plurality of fixing biases smaller than a desired fixing bias value are used. After that, by setting the desired fixing bias value, the fixing bias value applied at a time is reduced, the load on the fixing bias power supply is reduced, and the occurrence of overshoot of the current flowing when the fixing bias is applied is eliminated. By stabilizing the potential of the surface of the fixing rotator, the fixing tailing which occurs in a belt shape is suppressed.
[0127]
The description and description of the portions that are not different from the above-described conventional technology and the first embodiment will be omitted, and only the features that are the features of the present embodiment will be described. Further, the same image forming apparatus, heat fixing apparatus, and members constituting the same used in this embodiment were used.
[0128]
In this embodiment, as shown in FIG. 8, a desired fixing bias value is applied after a bias value applied as a fixing bias is smaller than a desired fixing bias value.
[0129]
Specifically, after a DC voltage of -400 V is first applied to the fixing film 10, the application is switched to a desired DC voltage of -700 V after 150 ms. After a DC voltage of +250 V is first applied to the pressure roller 20, the application is switched to the desired DC voltage of +500 V after a lapse of 150 ms. Immediately before the recording material is conveyed to the fixing nip portion, an electric field due to a potential difference of 1200 V is applied to the fixing film 10 and the pressure roller 20 as a fixing bias that is desired to suppress fixing tailing. Is formed.
[0130]
As shown in FIG. 9, the switching of the fixing bias applied to the fixing film 10 is performed by providing a resistance R of about 10 to 100 MΩ between the first power supply 77 and the power supply brush 78 as a high resistance body. A path for applying the fixing bias from the power supply 77 to the power supply brush 78 via the resistor R and a path for applying the fixing bias without passing through the resistor R are switched by the control circuit unit 83 such as switching elements and relays. Switching was performed by the switching member 85. The above-described fixing bias applied from the second power source 82 to the pressure roller 20 was also switched by the same path switching configuration as described above.
[0131]
FIG. 10 shows a case where a desired fixing bias value is applied at a time, which is a method of applying a fixing bias in a conventional example used as a comparative example, and a case where a desired fixing bias value is applied after a plurality of steps used in this embodiment. The conceptual diagram of the result of monitoring the transition of the current flowing through the power supply brush of the fixing film and the pressure roller when a bias value is applied is shown.
[0132]
As can be seen from the figure, when a desired fixing bias value is applied at a time, a current value that flows is larger than a current value flowing in a steady state. It can be seen that the flowing current value is settled.
[0133]
This is because each member forming the fixing film 10 and the pressure roller 20 is a material having a certain volume resistance value. In particular, the fluorine-based resin used for the surface release layer is a high-resistance material or The phenomenon that occurs because the fixing bias power supply is trying to converge to the desired potential by applying more current to apply the desired fixing bias to each of these rotating bodies because it is an insulator It is.
[0134]
This is easy to understand when the fixing film 10 and the pressure roller 20 are considered as a capacitor having a certain capacity. Until this capacity is filled with electric charges, a larger current flows, and when the capacity is filled with electric charges, the current value in the steady state is settled.
[0135]
On the other hand, in the present embodiment, since the fixing bias is switched to the desired fixing bias value after applying the fixing bias smaller than the desired DC voltage value, the above-described current overshoot can be suppressed to a small value. You can see that it is.
[0136]
Next, the effect when the overshoot is kept small will be described.
[0137]
As described above, the fixing film 10 and the pressure roller 20 have a property of generating an electric field in the opposite direction to cancel the electric field generated by applying the fixing bias.
[0138]
Therefore, when the overshoot increases, the electric field generated by the overshoot also increases, and the electric field generated when the fixing film 10 and the pressure roller 20 are separated on the downstream side of the fixing nip to reverse the electric field also increases. At this timing, the amount of charge of the opposite polarity generated on the surface of the fixing film 10 and the pressure roller 20 also increases, and the potential appearing on the surface of the fixing film 10 and the surface of the pressure roller 20 is affected by the charge of the opposite polarity. At that time, the effect of the fixing bias applied to suppress the tailing of the fixing and the offset is lost.
[0139]
This is particularly noticeable in the case of the pressure roller 20 which covers a fluororesin-based tube which is an insulator as a surface layer. Therefore, as described with reference to FIG. 14 in the section of the problem to be solved by the invention, a belt-shaped fixing tail with a certain width occurs.
[0140]
FIG. 11 is a schematic diagram showing the results of monitoring the surface potentials of the fixing film 10 and the pressure roller 20. From this figure, it can be seen that the current overshoot is smaller in the fixing bias application control in the second embodiment of the present invention.
[0141]
Next, Table 2 shows the results of confirming the effect of suppressing the belt-like fixing tailing in the examples of the present invention and the conventional embodiment. The effect was confirmed in the same manner as in Example 1 above.
[0142]
[Table 2]

[0143]
As shown in Table 2, it was proved that a belt-like fixing tail did not occur in the conventional embodiment but occurred in the present embodiment, and that a good image was always obtained.
[0144]
<Third embodiment>
In the description of the second embodiment, the fixing bias value is switched in two steps. However, the application timing of the fixing bias is described in an embodiment in which the fixing film and the pressure roller are synchronized, and the effect is confirmed. However, as described in the first embodiment described above, when the fixing bias is applied to the fixing film and the pressure roller in a system in which the timing of the bias is shifted, the effect of suppressing the occurrence of fixing tailing is enhanced. Needless to say.
[0145]
As described above, with the increase in the speed of the image forming apparatus, a heating and fixing apparatus that has an enhanced effect of suppressing the occurrence of severe tailing without fixing is established without providing an overspec of the fixing bias power supply. Can be achieved.
[0146]
<Others>
1) Needless to say, the configuration of the ceramic heater 11 as a heating element is not limited to the embodiment. Further, the heater 11 does not necessarily have to be located at the fixing nip portion N. For example, the heater 11 may be disposed so as to be located upstream of the fixing nip portion N in the film moving direction.
[0147]
2) The heat fixing device of the film heating type is a rotary driving device for pressing in the embodiment, but a driving roller is provided on the inner peripheral surface of the endless fixing film, and the film is driven while applying tension to the film. It may be a device.
[0148]
3) In the present invention, the heat fixing device is not limited to the film heating system, but may be a heat roller system. In short, any image heating apparatus that heats the image on the recording material by nipping and conveying the recording material carrying the image in the nip between the heating member and the pressing member may be used.
[0149]
4) The heat fixing device of the present invention includes not only a fixing device that heats and fixes an unfixed image on a recording material as a permanent image, but also an image heating device that tentatively fixes an unfixed image on a recording material, and carries an image. An image heating device for improving the image surface properties such as gloss by reheating the recording material is also included.
[0150]
5) The image forming method of the image forming apparatus is not limited to the electrophotographic method, and may be an electrostatic recording method, a magnetic recording method, or the like, or may be a transfer method or a direct method.
[0151]
【The invention's effect】
As described above, according to the present invention, a recording material on which an unfixed toner image is formed includes: a first rotating body corresponding to a recording material surface side which is an unfixed toner image carrying surface side of the recording material; An unfixed toner image is introduced by being introduced into a fixing nip formed by press contact with a second rotating body corresponding to the back side of the recording material opposite to the unfixed toner image carrying surface, and nipped and transported. Is heated and fixed on the recording material, and while the recording material is passing through the fixing nip portion, the first and second rotating bodies are applied with a DC voltage. The problem of the trailing that appears and the trailing that occurs in the form of a strip can be solved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus.
FIG. 2 is an enlarged model diagram of a heat fixing device part.
FIG. 3 is a schematic diagram of a layer structure of a fixing film.
FIG. 4 is an enlarged cross-sectional model view of a fixing nip portion.
FIG. 5 is an explanatory diagram of a configuration of a heater for heating (ceramic heater).
FIG. 6 is an explanatory diagram (part 1) of fixing bias control in the first embodiment.
FIG. 7 is an explanatory diagram of a fixing bias control in the first embodiment (part 2).
FIG. 8 is an explanatory diagram of fixing bias control in a second embodiment (part 1).
FIG. 9 is an explanatory diagram of a fixing bias switching configuration.
FIG. 10 is an explanatory diagram of fixing bias control in the second embodiment (part 2).
FIG. 11 is an explanatory diagram of the fixing bias control in the second embodiment (part 3).
FIG. 12 is a conceptual diagram of a heat fixing device.
FIG. 13 is a conceptual diagram of fixing tailing (part 1).
FIG. 14 is a conceptual diagram of fixing tailing (part 2).
[Explanation of symbols]
1. process cartridge, 2. photosensitive drum, 3. charging roller, 4. developing device, 5. transfer roller, 6. cleaning member, 7. heating fixing device, 10. fixing member, 11 ..Heating members (heating heaters), 11a..Ceramic substrate, 11b, 11c. 12. Stay holder, 13 ... Fixing rotating body (fixing film), 13a ... Conductive primer layer, 13b ... Surface layer (release layer), 14 ... Temperature sensing element, 15 ... Thermo protector, 17 ... Flange, 18 connector, 20 pressure roller, 21 pressure roller core, 22 pressure roller elastic layer, 23 pressure roller release layer, 25 pressure spring, 26 ..Pressurizing roller drive Gear, 27 fixing entrance guide, 28 diode, 76 fixing discharge sensor, 77 fixing bias power supply, 78 power supply brush, 79 conductive brush, N fixing fuse nip, L .Laser beam, P ... Recording material, t..Unfixed toner image, S..Recording material conveyance standard

Claims (12)

The recording material on which the unfixed toner image is formed is placed on the first rotating body corresponding to the recording material surface side, which is the unfixed toner image carrying surface side of the recording material, and the surface opposite to the unfixed toner image carrying surface. The non-fixed toner image is heated and fixed on the recording material by being introduced into a fixing nip formed by pressure contact with a second rotating body corresponding to the back side of the recording material. Is a heating fixing device having a configuration in which a DC voltage is applied to the first and second rotating bodies while passing through the fixing nip portion,
The timing at which the application of the DC voltage to the first and second rotating bodies starts to be started has an arbitrary time difference. The start of the application of the DC voltage to the first and second rotating bodies is started at a point before the leading end of the recording material introduced into the fixing nip reaches the fixing nip. And start applying the voltage to the second rotating member, and start applying the voltage to the other rotating member by a time difference until the leading end of the recording material reaches the fixing nip portion. 2. The heat fixing device according to claim 1, wherein a DC voltage is applied to each of the first and second rotating bodies at a timing when the recording material is nipped and conveyed in the fixing nip portion. The recording material on which the unfixed toner image is formed is placed on the first rotating body corresponding to the recording material surface side, which is the unfixed toner image carrying surface side of the recording material, and the surface opposite to the unfixed toner image carrying surface. The non-fixed toner image is heated and fixed on the recording material by being introduced into a fixing nip formed by pressure contact with a second rotating body corresponding to the back side of the recording material. Is a heating fixing device having a configuration in which a DC voltage is applied to the first and second rotating bodies while passing through the fixing nip portion,
The heating and fixing device is characterized in that the application of a DC voltage to each of the rotating bodies applies a desired DC voltage value through a plurality of voltage values. The recording material on which the unfixed toner image is formed is placed on the first rotating body corresponding to the recording material surface side, which is the unfixed toner image carrying surface side of the recording material, and the surface opposite to the unfixed toner image carrying surface. The non-fixed toner image is heated and fixed on the recording material by being introduced into a fixing nip formed by pressure contact with a second rotating body corresponding to the back side of the recording material. Is a heating fixing device having a configuration in which a DC voltage is applied to the first and second rotating bodies while passing through the fixing nip portion,
The timing of starting the application of the DC voltage to each of the first and second rotating bodies is given an arbitrary time difference, and the application of the DC voltage to each rotating body is performed in a plurality of voltage values. A heating and fixing device for applying a desired DC voltage value. The setting of the DC voltage value having a plurality of steps to be applied to the rotating body is performed by changing from a voltage value smaller than a desired DC voltage value to a larger value to reach a desired DC voltage value. 5. The heat fixing device according to claim 3, wherein the heat fixing device is a heat fixing device. Apply a DC voltage of the same polarity as the toner to the first rotating body corresponding to the recording material front side, and apply a DC voltage of the opposite polarity to the toner to the second rotating body corresponding to the recording material rear side. The heat fixing device according to any one of claims 1 to 5, wherein An electrode member that is in contact with the back side of the recording material is provided downstream of the fixing nip in the recording material conveyance direction, and the electrode member is electrically grounded, or the back surface of the recording material. 7. The heat fixing device according to claim 1, wherein a DC voltage having the same polarity as a DC voltage applied to the second rotating body corresponding to the first rotating body is applied. apparatus. The heat fixing device according to claim 7, wherein the electrode member is a conductive brush. A roller pair as a recording material transport holding member is provided downstream of the fixing nip portion in the recording material transport direction, and a roller in contact with the recording material back surface of the roller pair is electrically conductive. 9. The heat fixing device according to claim 1, wherein the heat fixing device is configured to be electrically grounded. The first rotating body corresponding to the recording material surface side has flexibility formed at least from a base layer serving as a base material, a surface layer serving as a release layer, and an adhesive layer between the base layer and the release layer. It is constituted by a hollow rotating body, is heated by a heating member inscribed inside the hollow rotating body, and a DC voltage is applied to the rotating body through the adhesive layer. Item 10. The heat fixing device according to any one of Items 1 to 9. The second rotating body corresponding to the back side of the recording material is composed of a metal core, a rubber layer as an elastic layer, and a surface layer as a release layer from the center to the outside. The heat fixing device according to any one of claims 1 to 10, wherein the application of the DC voltage is performed via a metal core or directly on a surface layer. In an image forming apparatus having an image forming unit that forms an unfixed toner image on a recording material and a heat fixing unit that heats and fixes the unfixed toner image on the recording material,
An image forming apparatus, wherein the heat fixing unit is the heat fixing device according to claim 1.

Images