JP2006011256A

JP2006011256A - Fixing device

Info

Publication number: JP2006011256A
Application number: JP2004191453A
Authority: JP
Inventors: Keisuke Abe; 敬介阿部; Kazuhisa Kenmochi; 和久剱持; Masashi Komata; 将史小俣
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 2004-06-29
Filing date: 2004-06-29
Publication date: 2006-01-12

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fixing device capable of improving uniformity of the image quality on one recording medium. <P>SOLUTION: The fixing device which has a heating body 24, a rotating body 21 to be heated by the heating body, and a pressure member 10 pressed against the rotating body to form a nip part N, and clamps and conveys a recording medium P carrying an unfixed image S with the nip part to fix the unfixed image to the recording medium has a control means 31 of controlling the heating body to a specified target set temperature. The control means has a mode, in which 1st target set temperature up to right immediately prior to the recording medium plunging into the nip part is set to be lower than 2nd target set temperature after the recording medium rushes in the nip part. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

本発明は、記録媒体に担持させた未定着画像を加熱定着させる定着装置に関するものである。 The present invention relates to a fixing device that heat-fixes an unfixed image carried on a recording medium.

電子写真方式を利用したレーザプリンタ、複写機、ファクシミリ等の画像形成装置においては、記録媒体に担持させた未定着トナー画像を加熱定着させる画像加熱定着装置（以下、定着装置と記す）が搭載されている。この定着装置の加熱方式、構成として、熱ローラ方式、フィルム加熱方式、電磁誘導加熱方式などが知られている。 2. Description of the Related Art Image forming apparatuses such as laser printers, copiers, and facsimiles using an electrophotographic system are equipped with an image heating fixing device (hereinafter referred to as a fixing device) that heats and fixes an unfixed toner image carried on a recording medium. ing. As a heating method and configuration of the fixing device, a heat roller method, a film heating method, an electromagnetic induction heating method, and the like are known.

熱ローラ方式の定着装置は、弾性層を有したローラ対に加熱体（ヒータ）を内蔵させ、ローラ表面が所定の温度を保つように温度制御し、未定着トナー画像を担持した記録媒体を、ローラ対の接触部に形成される定着ニップ部に挟持搬送させ、加熱および加圧して、トナー画像を記録媒体に定着させる。 A heat roller type fixing device incorporates a heating body (heater) in a roller pair having an elastic layer, controls the temperature so that the roller surface maintains a predetermined temperature, and a recording medium carrying an unfixed toner image, The toner image is fixed on the recording medium by being nipped and conveyed to a fixing nip formed at the contact portion of the roller pair, and heated and pressurized.

それに対して、フィルム加熱方式（特許文献１参照）の定着装置は、板状の加熱体であるヒータを内側に有し、それに摺動して回転する耐熱性の定着フィルムと、該定着フィルムに圧接して定着ニップ部を形成する加圧ローラなどで構成され、未定着トナーを担持する記録媒体を上記定着ニップ部で挟持搬送し、トナーを加熱定着する。 On the other hand, the fixing device of the film heating method (see Patent Document 1) has a heater which is a plate-shaped heating body inside, a heat-resistant fixing film which slides and rotates on the heater, and the fixing film. The recording medium is composed of a pressure roller that is pressed to form a fixing nip portion, and holds a recording medium carrying unfixed toner at the fixing nip portion to heat and fix the toner.

このようなフィルム加熱方式の定着装置においては、低熱容量の加熱体、定着フィルムを用いて、加圧ローラ側の加熱手段を省くことで、従来の熱ローラ方式に比べ、省電力化が図れ、クイックスタート性に優れている。 In such a film heating type fixing device, by using a low heat capacity heating body and a fixing film, by omitting the heating means on the pressure roller side, power saving can be achieved compared to the conventional heat roller type, Excellent quick start.

定着ニップ部において記録媒体に未定着トナー画像を加熱定着させる定着プロセスにおいては、未定着トナー画像の記録媒体への定着のさせ方によって出力画像の画質に影響を与えることが知られている。 In a fixing process in which an unfixed toner image is heated and fixed on a recording medium at a fixing nip portion, it is known that the image quality of an output image is affected by the manner in which the unfixed toner image is fixed to the recording medium.

定着プロセスにおける代表的なパラメータは温度、圧力、速度等が挙げられるが、特に温度制御に関しては、従来、上記のフィルム加熱方式の定着装置においては、記録媒体上のトナー画像に直接接触する定着フィルム表面の温度が、トナーを加熱定着するのに適した所定の温度（定着温度）を保つように、加熱体の発熱量を制御する方法が取られている。 Typical parameters in the fixing process include temperature, pressure, speed, etc. In particular, with regard to temperature control, in the conventional film heating type fixing device, a fixing film that directly contacts a toner image on a recording medium. A method of controlling the amount of heat generated by the heating body is employed so that the surface temperature is kept at a predetermined temperature (fixing temperature) suitable for heat-fixing the toner.

また、定着フィルム表面を上記の所定温度に保つための加熱体の目標設定温度は、記録媒体の条件すなわち記録媒体のサイズ、厚み、表面性などの種類毎に変更することはあっても、１種類の記録媒体を定着処理する間は、所定の値に固定して温度制御がなされている。これはフィルム加熱方式の定着装置に限らず、電磁誘導加熱方式（特許文献２）の定着装置のように熱応答性がよく、記録媒体の裏面に接する加圧部材側の加熱手段を省いた定着装置にも同様のことが言える。
特開昭６３−３１３１８２特開平１０−３０１４１５ Further, the target set temperature of the heating body for maintaining the fixing film surface at the above-mentioned predetermined temperature may vary depending on the conditions of the recording medium, that is, the size, thickness, surface property, etc. of the recording medium. During the fixing process of the type of recording medium, the temperature is controlled at a fixed value. This is not limited to a film heating type fixing device, but has a good thermal response, such as an electromagnetic induction heating type (Patent Document 2) fixing device, and fixing without a heating means on the pressure member side in contact with the back surface of the recording medium. The same is true for the device.
JP-A-63-313182 JP-A-10-301415

しかし、上記の定着装置では、何れも記録媒体上の未定着トナー画像と接する側の定着ローラあるいは定着フィルムなどの加熱回転体の表面温度を一定に保つ温度制御を行っており、記録媒体においてトナー画像面（記録媒体表面）の裏側（記録媒体裏面）に接する加圧部材としての加圧ローラの表面温度については考慮されていない。 However, in each of the fixing devices described above, temperature control is performed to keep the surface temperature of a heating rotating body such as a fixing roller or a fixing film on the side in contact with an unfixed toner image on the recording medium constant. The surface temperature of the pressure roller as a pressure member in contact with the back side (recording medium back surface) of the image surface (recording medium surface) is not considered.

加熱体の目標設定温度が常に一定の従来の温度制御では、フィルム加熱方式や電磁誘導加熱方式のように加熱手段を有していない加圧ローラの表面温度は、記録媒体がニップ部に突入した直後に大幅に低下する。以後、記録媒体がニップ部を通過する過程で、加圧ローラの熱は記録媒体に奪われていき、徐々に温度が低下していく。特に加圧ローラの周長毎に顕著な温度低下が起こるが、これは最初に記録媒体が定着ニップ部に突入した時点で起こる、加圧ローラ表面の温度低下の履歴を残しているためであり、後続の記録媒体が定着ニップ部に順次に突入するのに伴って次第にその履歴は消えてゆくため、温度低下幅は徐々に小さくなって加圧ローラ表面温度は記録媒体を含めた熱平衡状態へと落ち着く。 In the conventional temperature control in which the target set temperature of the heating body is always constant, the surface temperature of the pressure roller that does not have a heating means like the film heating method or the electromagnetic induction heating method, the recording medium enters the nip portion. Immediately after that, it drops significantly. Thereafter, as the recording medium passes through the nip portion, the heat of the pressure roller is taken away by the recording medium, and the temperature gradually decreases. In particular, a significant temperature drop occurs for each circumference of the pressure roller, because this is because a history of temperature drop on the pressure roller surface that occurs when the recording medium first enters the fixing nip part remains. Since the history gradually disappears as the subsequent recording medium sequentially enters the fixing nip portion, the temperature decrease width gradually decreases, and the pressure roller surface temperature reaches a thermal equilibrium state including the recording medium. And calm down.

加熱回転体と同様に加圧ローラからも記録媒体裏面から記録媒体を通して記録媒体表面のトナーへ熱を伝えている。加圧ローラの温度が低下すると、記録媒体表面のトナーへ伝わる熱量が減少し、トナーの溶融が抑えられて溶け広がらないので、トナーの投影面積が小さくなり、且つ凹凸が残ることから、濃度、グロスが低下する。またトナーの溶融不足により定着性も低下する。記録媒体がニップ部を通過する際、記録媒体先端がニップ部に突入した時点から加圧ローラの温度は徐々に低下するため、出力画像は先端から徐々に濃度、グロスが低下してしまう。特に加圧ローラ周長に相当する位置毎に温度低下幅が大きいため、それに対応した位置で濃度、グロスの低下が目立ち、同一記録媒体上で均一な画質が得られない。 Similarly to the heating rotator, heat is transmitted from the pressure roller to the toner on the surface of the recording medium from the back surface of the recording medium through the recording medium. When the temperature of the pressure roller is decreased, the amount of heat transmitted to the toner on the surface of the recording medium is reduced, the toner is prevented from melting and does not spread, and the projected area of the toner is reduced and unevenness remains. Gross decreases. In addition, fixability is also lowered due to insufficient melting of the toner. When the recording medium passes through the nip portion, the temperature of the pressure roller gradually decreases from the time when the leading end of the recording medium enters the nip portion, and the density and gloss of the output image gradually decrease from the leading end. In particular, since the temperature decrease range is large at each position corresponding to the circumferential length of the pressure roller, the density and gloss decrease conspicuously at the corresponding position, and uniform image quality cannot be obtained on the same recording medium.

一方、加熱回転体は加熱体を有し、常に熱が供給されるので、加圧ローラほど大きな温度低下は起こらない。その結果、記録媒体がニップ部を通過している最中にトナーに与えられる加熱回転体からの熱量、すなわち記録媒体表面から与えられる熱量と、加圧ローラからの熱量、すなわち記録媒体裏面から与えられる熱量のバランスが崩れていく。特にフィルム定着方式等のように低熱容量の加熱体、定着フィルムを用いる等して熱応答性が向上した定着装置においては、この現象が顕著に起こり、記録媒体表面、裏面からの熱量のバランスの変化により、濃度、グロスが変化する。 On the other hand, since the heating rotator has a heating body and is always supplied with heat, the temperature does not decrease as much as the pressure roller. As a result, while the recording medium passes through the nip portion, the amount of heat from the heating rotating body applied to the toner, that is, the amount of heat applied from the surface of the recording medium, and the amount of heat from the pressure roller, that is, applied from the back surface of the recording medium. The balance of the amount of heat generated will be lost. This phenomenon is particularly noticeable in fixing devices that have improved thermal responsiveness by using a low heat capacity heating element or a fixing film, such as a film fixing method, and the balance of the amount of heat from the front and back surfaces of the recording medium. The density and gloss change due to the change.

以下に記録媒体表面、裏面からの熱量バランスが濃度とグロスに影響を与える仕組みを説明する。記録媒体表面からの熱はトナー層の上層部分の溶融を進め、溶融が進行するほどトナー上層は溶け広がるため、投影面積が広くなり、平滑性が上がるため、濃度、グロスが向上する。しかし、トナー上層の溶融が進行しすぎると、ホットオフセットなどの弊害を生じる。一方、記録媒体裏面からの熱はトナー層の下層部分の溶融を進める。溶融が進行するほどトナー下層は溶け広がるので、記録媒体表面からの熱と同様の効果が得られるが、さらに、トナー下層は軟らかくなって紙繊維に絡みつくという効果がある。その結果、トナー層全体の定着性を確保することができる。しかし、トナー下層の溶融が進行しすぎると、過度に軟らかくなったトナーは紙の繊維間へ落ち込んでいき、紙繊維を露出させ、その凹凸を露にしてしまう。すると定着性は確保できるものの、濃度、グロスが低下してしまう。以上のことから、記録媒体表面、裏面からの熱量バランスを制御することにより、定着性、濃度、グロス等の画質を制御することができる。言い換えると記録媒体表面、裏面からの熱量バランスが変化すると、画質が変化してしまうことになる。 A mechanism in which the heat balance from the front and back surfaces of the recording medium affects the density and gloss will be described below. The heat from the surface of the recording medium advances the melting of the upper layer portion of the toner layer, and as the melting progresses, the toner upper layer melts and spreads, so that the projected area increases and the smoothness increases, and the density and gloss improve. However, if the melting of the toner upper layer proceeds too much, problems such as hot offset occur. On the other hand, the heat from the back surface of the recording medium advances the melting of the lower layer portion of the toner layer. As the melting progresses, the toner lower layer melts and spreads, so that the same effect as the heat from the surface of the recording medium can be obtained. However, the toner lower layer becomes soft and entangles with the paper fibers. As a result, the fixability of the entire toner layer can be ensured. However, if the melting of the toner lower layer proceeds too much, the toner that has become excessively soft falls into the fibers of the paper, exposing the paper fibers and exposing the concavities and convexities. As a result, the fixing property can be secured, but the density and gloss are lowered. From the above, it is possible to control image quality such as fixability, density, and gloss by controlling the heat balance from the front and back surfaces of the recording medium. In other words, the image quality changes if the heat balance from the front and back surfaces of the recording medium changes.

従って、記録媒体のニップ部通過中に加圧ローラ温度が低下することを予測して、総熱量を補うために単純に目標設定温度を高くしても、記録媒体表面、裏面からの熱量バランスが崩れていく状況は変わらないため、同一記録媒体上での画質の不均一性を解決することはできない。またホットオフセット等の弊害も生じる。 Therefore, even if the target set temperature is simply increased in order to compensate for the total heat quantity by predicting that the pressure roller temperature decreases while the recording medium passes through the nip portion, the heat quantity balance from the front surface and the back surface of the recording medium is maintained. Since the collapsed situation does not change, it is not possible to solve the non-uniformity of image quality on the same recording medium. In addition, adverse effects such as hot offset also occur.

本発明は、上記の課題を解決するためになされたものであり、記録媒体に担持させた未定着画像を加熱定着させる定着装置について、同一記録媒体上で画質の均一性を向上させ得る定着装置を提供することを目的とする。 The present invention has been made to solve the above-described problem, and a fixing device that can heat and fix an unfixed image carried on a recording medium can improve the uniformity of image quality on the same recording medium. The purpose is to provide.

本発明に係る定着装置の代表的な構成は、
加熱体と、前記加熱体によって加熱される加熱回転体と、前記加熱回転体に圧接しニップ部を形成する加圧部材と、を有し、未定着画像を担持する記録媒体を前記ニップ部で挟持搬送して未定着画像を記録媒体に定着する定着装置において、
前記加熱体を所定の目標設定温度に温調する制御手段を有し、前記制御手段は、前記記録媒体がニップ部に突入する直前までの第１の目標設定温度を、該記録媒体がニップ部に突入した後の第２の目標設定温度よりも低くするモードを有することを特徴とする定着装置、
である。 A typical configuration of the fixing device according to the present invention is as follows.
A heating member, a heating rotator heated by the heating member, and a pressure member that presses against the heating rotator to form a nip portion, and a recording medium carrying an unfixed image is formed at the nip portion. In a fixing device for nipping and conveying and fixing an unfixed image on a recording medium,
Control means for adjusting the temperature of the heating body to a predetermined target set temperature, wherein the control means has a first target set temperature immediately before the recording medium enters the nip portion, and the recording medium has a nip portion. A fixing device having a mode of lowering the second target set temperature after entering
It is.

本発明によれば、記録媒体がニップ部に突入する直前までの第１の目標設定温度を、該記録媒体がニップ部に突入した後の第２の目標設定温度よりも低くするので、記録媒体のニップ部突入直後に加圧部材表面温度が急激に低下するのを防ぐことができる。それにより、記録媒体の未定着画像側面の裏側からの熱量が急激に減少するのを防ぎ、記録媒体の未定着画像側面とその裏側面からの熱量のバランスを一定に保ち、同一記録媒体上での濃度、グロス変化を抑えて画質の均一性を向上させることができる。また、加圧部材表面の温度低下を避けるために、単純に目標設定温度を上げることによるホットオフセット発生を防ぎ、また、記録媒体の通過前に過剰な加熱をすることが無いため、必要以上に温度が上昇するのを避けられ、消費電力を抑えることができる。 According to the present invention, the first target set temperature until immediately before the recording medium enters the nip portion is made lower than the second target set temperature after the recording medium enters the nip portion. It is possible to prevent the pressure member surface temperature from rapidly decreasing immediately after entering the nip portion. As a result, the amount of heat from the back side of the unfixed image side of the recording medium is prevented from abruptly decreasing, and the balance between the amount of heat from the unfixed image side surface of the recording medium and the back side is kept constant. The uniformity of image quality can be improved by suppressing changes in density and gloss. Also, in order to avoid a temperature drop on the pressure member surface, hot offset generation by simply raising the target set temperature is prevented, and excessive heating is not required before passing the recording medium. Temperature rise can be avoided and power consumption can be suppressed.

以下、本発明の実施例を図面に基づいて説明する。 Embodiments of the present invention will be described below with reference to the drawings.

（１）画像形成装置例
図４は本発明に係る定着装置として画像加熱定着装置を含む、画像形成装置の構成の一例を示す図である。本実施例の画像形成装置は転写方式電子写真プロセスを用いたレーザビームプリンタである。 (1) Example of Image Forming Apparatus FIG. 4 is a diagram showing an example of the configuration of an image forming apparatus including an image heating and fixing apparatus as the fixing apparatus according to the present invention. The image forming apparatus of this embodiment is a laser beam printer using a transfer type electrophotographic process.

図４において、１０１は装置本体Ｍに回転自在に支持されている潜像担持体（像担持体）としての感光ドラムであり、駆動手段（不図示）によって矢印方向へ所定のプロセススピードで回転している。 In FIG. 4, reference numeral 101 denotes a photosensitive drum as a latent image carrier (image carrier) that is rotatably supported by the apparatus main body M, and is rotated at a predetermined process speed in the direction of an arrow by a driving means (not shown). ing.

感光ドラム１０１の周囲には、その回転方向に沿って、帯電ローラ（転写手段）１０２、レーザ露光装置（露光手段）１０３、現像装置（現像手段）１０５、転写ローラ（転写手段）１０６、クリーニング装置（クリーニング手段）１０７がその順に配設されている。 Around the photosensitive drum 101, along the rotation direction, a charging roller (transfer means) 102, a laser exposure device (exposure means) 103, a development device (development means) 105, a transfer roller (transfer means) 106, and a cleaning device. (Cleaning means) 107 are arranged in that order.

感光ドラム１０１は、帯電ローラ１０２により、所定の極性および電位に一様に帯電される。その後、その表面に対しレーザ光学系等のレーザ露光装置１０３から画像情報に基づいたレーザＬがミラー１０４等を介して露光され、露光部分の電荷が除去されて該感光ドラム１０１上に静電潜像が形成される。 The photosensitive drum 101 is uniformly charged to a predetermined polarity and potential by a charging roller 102. Thereafter, a laser L based on image information is exposed to the surface from a laser exposure device 103 such as a laser optical system through a mirror 104 or the like, and the charge in the exposed portion is removed, and electrostatic latent images are formed on the photosensitive drum 101. An image is formed.

静電潜像は現像装置１０５によって現像される。現像装置１０５は現像ローラ１０５ａを有しており、この現像ローラに現像バイアスを印加し、感光ドラム１０１上の静電潜像にトナーを付着させることで、静電潜像がトナー像として可視化（顕像化）される。 The electrostatic latent image is developed by the developing device 105. The developing device 105 includes a developing roller 105a. By applying a developing bias to the developing roller and attaching toner to the electrostatic latent image on the photosensitive drum 101, the electrostatic latent image is visualized as a toner image ( Visualized).

一方、所定のタイミングで給紙ローラ１０９により、給紙カセット１０８から記録媒体Ｐが給紙され、搬送ローラ１１０等により、感光ドラム１０１と転写ローラ１０６とによって形成される転写ニップ部Ｔｎへと搬送される。転写ローラ１０６には、転写バイアスが印加され、これにより感光ドラム１０１上のトナー像が順次記録媒体Ｐ上に転写される。 On the other hand, the recording medium P is fed from the paper feed cassette 108 by the paper feed roller 109 at a predetermined timing, and conveyed to the transfer nip Tn formed by the photosensitive drum 101 and the transfer roller 106 by the conveyance roller 110 or the like. Is done. A transfer bias is applied to the transfer roller 106, whereby the toner images on the photosensitive drum 101 are sequentially transferred onto the recording medium P.

転写によって表面に未定着トナー画像を担持した記録媒体Ｐは転写ニップ部Ｔｎを出た後、感光ドラム１０１から分離されて、搬送ガイド１１１に沿って定着装置１１２へ送り込まれ、ここで未定着トナー画像が加熱・加圧されて記録媒体Ｐ表面に定着される。なお、定着装置１１２の構成については次の（２）項で詳しく説明する。 The recording medium P carrying the unfixed toner image on the surface by the transfer exits the transfer nip portion Tn, is separated from the photosensitive drum 101, and is sent along the conveyance guide 111 to the fixing device 112. The image is heated and pressurized and fixed on the surface of the recording medium P. The configuration of the fixing device 112 will be described in detail in the next section (2).

未定着トナー画像が定着された記録媒体Ｐは、搬送ローラ１１３、排紙ローラ１１４によって装置本体Ｍ上の排紙トレイ１１５上に搬送・排出される。 The recording medium P on which the unfixed toner image is fixed is transported and discharged onto a paper discharge tray 115 on the apparatus main body M by a transport roller 113 and a paper discharge roller 114.

一方、トナー像転写後の感光ドラム１０１は、記録媒体Ｐに転写されないで表面に残ったトナーがクリーニング装置１０７のクリーニングブレード１０７ａによって除去され、次の画像形成に備える。 On the other hand, the toner remaining on the surface of the photosensitive drum 101 after the toner image transfer without being transferred to the recording medium P is removed by the cleaning blade 107a of the cleaning device 107 to prepare for the next image formation.

（２）定着装置１１２
図１は本実施例の画像加熱定着装置の一例を示す概略構成模型図である。本実施例に示す画像加熱定着装置(以下、定着装置と記す)１１２はフィルム加熱方式の定着装置である。 (2) Fixing device 112
FIG. 1 is a schematic configuration model diagram showing an example of an image heating and fixing apparatus of this embodiment. An image heating fixing device (hereinafter referred to as a fixing device) 112 shown in this embodiment is a film heating type fixing device.

本例の定着装置１１２は、加圧ローラ駆動式であり、加熱体(ヒータ)２４を保持させた加熱体支持体としてのステー２２に、加熱回転体としての円筒状の定着フィルム２１を介して加圧部材である加圧ローラ１０を所定の押圧力をもって圧接させ、加熱体２４との間に定着ニップ部Ｎを形成している。 The fixing device 112 of this example is a pressure roller drive type, and a stay 22 as a heating body support holding a heating body (heater) 24 is connected to a stay 22 as a heating rotator via a cylindrical fixing film 21. A pressure roller 10, which is a pressure member, is brought into pressure contact with a predetermined pressing force, and a fixing nip portion N is formed between the heating member 24.

回転駆動制御回路３０は、加圧ローラ１０を回転駆動するモータと、これを制御するＣＰＵなどを備えてなり、ＣＰＵがプリント信号Ｓ１を入力してモータを起動させ、該モータによって加圧ローラ１０を矢印ｂ方向（反時計方向）に回転駆動させる。この加圧ローラ１０の回転による定着フィルム２１外面との摺動摩擦力により定着フィルム２１に回転力が作用し、定着フィルム２１は加熱体２４を保持させたステー２２の外回りを矢印ｃ方向（時計方向）に回転する。制御手段としての加熱体駆動制御回路３１は、給電装置と、これを制御するＣＰＵなどを備えてなり、ＣＰＵがプリント信号Ｓ１を入力して給電装置をオン・オフ制御することにより加熱体２４の基板表面側に設けた発熱抵抗体２４ｂを通電加熱させて、加熱体２４を所定の目標設定温度に温調制御し、該加熱体によって定着フィルム２１をその温度に加熱する。 The rotation drive control circuit 30 includes a motor that rotationally drives the pressure roller 10 and a CPU that controls the motor. The CPU inputs a print signal S1 to start the motor, and the pressure roller 10 is activated by the motor. Is driven to rotate in the direction of arrow b (counterclockwise). A rotational force acts on the fixing film 21 by the sliding frictional force with the outer surface of the fixing film 21 due to the rotation of the pressure roller 10, and the fixing film 21 moves around the stay 22 holding the heating body 24 in the direction of arrow c (clockwise). ). The heating body drive control circuit 31 as a control means includes a power feeding device and a CPU that controls the power feeding device, and the CPU inputs a print signal S1 to turn on / off the power feeding device, thereby controlling the heating body 24. The heating resistor 24b provided on the substrate surface side is energized and heated, the temperature of the heating body 24 is controlled to a predetermined target set temperature, and the fixing film 21 is heated to that temperature by the heating body.

この状態において、未定着トナー画像Ｓを担持した記録媒体Ｐを定着ニップ部Ｎで挟持搬送することで、加熱体２４の熱が定着フィルム２１を介して記録媒体Ｐに付与され、未定着トナー画像Ｓが記録媒体Ｐ面に熱定着される。 In this state, the recording medium P carrying the unfixed toner image S is nipped and conveyed by the fixing nip portion N, whereby the heat of the heating body 24 is applied to the recording medium P via the fixing film 21, and the unfixed toner image S is thermally fixed on the surface of the recording medium P.

定着ニップ部Ｎを通過した記録材Ｐは定着フィルム２１の面から曲率分離されて排紙される。 The recording material P that has passed through the fixing nip N is separated from the surface of the fixing film 21 by the curvature and discharged.

加圧ローラ１０は金属（アルミあるいは鉄など）の芯金１１と、その外側にシリコンゴム等で形成された弾性層１２と、該弾性層１２の表面を被覆する離型性層１３から成る。 The pressure roller 10 includes a metal core 11 made of metal (aluminum or iron), an elastic layer 12 formed of silicon rubber or the like on the outside, and a releasable layer 13 covering the surface of the elastic layer 12.

弾性層１２としては、シリコンゴム等で形成されたソリッドゴム層、あるいは断熱効果を持たせるためシリコンゴムを発泡させ形成されたスポンジゴム層、あるいはシリコンゴム層内に中空のフィラーを分散させ、硬化物内に気泡部分を持たせ、断熱作用を高めた気泡ゴム層などが用いられる。 As the elastic layer 12, a solid rubber layer formed of silicon rubber or the like, a sponge rubber layer formed by foaming silicon rubber to have a heat insulating effect, or a hollow filler is dispersed in the silicon rubber layer and cured. A bubble rubber layer or the like having a bubble portion in an object to enhance a heat insulating function is used.

離型性層１３は、パーフルオロアルコキシ樹脂（ＰＦＡ）、ポリテトラフルオロエチレン樹脂（ＰＴＦＥ）、テトラフルオロエチレン−ヘキサフルオロプロピレン樹脂（ＦＥＰ）等のフッ素系樹脂、あるいはＧＬＳラテックスコーティングを施したものであってもよく、また該離型性層１３はチューブを被覆させたものでも、表面を塗料でコートしたものであってもよい。 The releasable layer 13 is a fluorine resin such as perfluoroalkoxy resin (PFA), polytetrafluoroethylene resin (PTFE), tetrafluoroethylene-hexafluoropropylene resin (FEP), or a GLS latex coating. The releasable layer 13 may be a tube coated or a surface coated with a paint.

本実施例では、芯金１１はアルミ芯金、弾性層１２はシリコンゴム、離型性層１３はＰＦＡであり、加圧ローラ１０の外形は２０ｍｍ、弾性層１２の厚さは３．５ｍｍのものを用いた。 In this embodiment, the core 11 is an aluminum core, the elastic layer 12 is silicon rubber, the releasable layer 13 is PFA, the pressure roller 10 has an outer shape of 20 mm, and the elastic layer 12 has a thickness of 3.5 mm. A thing was used.

定着フィルム２１は、耐熱樹脂を円筒状に形成したものであり、周長に余裕を持ってステー２２に外嵌されている。本例に示す定着フィルム２１は、耐熱性、断熱性を有するポリイミド、ポリアミドイミド、ＰＥＥＫ、ＰＥＳ、ＰＰＳ、ＰＦＡ、ＰＴＦＥ、ＦＥＰ等を基層とし、表層にはＰＦＡ、ＰＴＦＥ、ＦＥＰ、シリコーン樹脂等の離型性の良い耐熱樹脂を混合または単独で被覆してある。 The fixing film 21 is formed of a heat-resistant resin in a cylindrical shape, and is externally fitted to the stay 22 with a margin in circumference. The fixing film 21 shown in this example is made of polyimide, polyamideimide, PEEK, PES, PPS, PFA, PTFE, FEP, etc. having heat resistance and heat insulation, and the surface layer is made of PFA, PTFE, FEP, silicone resin, etc. Heat-resistant resin with good releasability is mixed or coated alone.

ステー２２は、液晶ポリマー、フェノール樹脂、ＰＰＳ，ＰＥＥＫ等の耐熱性と、摺動性を具備した耐熱性樹脂により断面略半円形樋型に形成されている。 The stay 22 is formed in a substantially semi-circular saddle shape with a heat resistant resin having a heat resistance such as a liquid crystal polymer, a phenol resin, PPS, and PEEK and a sliding property.

加熱体２４は、アルミナ等でできた基板２４ａの表面に、通電発熱体２４ｂとして例えばＡｇ／Ｐｄ（銀パラジウム）等の電気抵抗材料をスクリーン印刷等により塗工し、その上に表面保護層２４ｃとしてガラスやフッ素樹脂等がコートされている。 The heating body 24 is formed by applying an electric resistance material such as Ag / Pd (silver palladium) as an energization heating element 24b on the surface of a substrate 24a made of alumina or the like by screen printing or the like, and a surface protective layer 24c thereon. As such, glass or fluororesin is coated.

（３）加熱体２４の温度制御
次に加熱体２４の温度制御について述べる。加熱体２４の発熱量の制御は、基板２４ａの背面側に設けられた温度検知手段としてのサーミスタ２３により検知される検知温度情報を元に、所定の目標設定温度が維持されるように加熱体２４への通電量を制御することで実現される。 (3) Temperature control of heating body 24 Next, temperature control of the heating body 24 will be described. Control of the amount of heat generated by the heating body 24 is performed so that a predetermined target set temperature is maintained based on detected temperature information detected by the thermistor 23 as temperature detecting means provided on the back side of the substrate 24a. This is realized by controlling the energization amount to 24.

本発明の要点は、記録媒体Ｐの定着ニップ部Ｎ通過中において、記録媒体Ｐの未定着トナー画像Ｓの担持面(以下、記録媒体表面と記す)に対して裏面側からの熱量を一定に保つこと、すなわち本実施例においては、定着装置１１２の温度制御を加圧ローラ１０の表面温度を基準に行うことであり、加圧ローラ１０の表面温度を記録媒体Ｐのニップ部Ｎ通過前および通過中で常に飽和温度Ｔ_ｓを保つため、記録媒体Ｐの定着ニップ部Ｎ突入前と後で、加熱体２４の目標設定温度を変更することである。ここで言う飽和温度Ｔ_ｓとは定着ニップ部Ｎを記録媒体Ｐが通過している状態における飽和温度であって、加圧ローラ１０と、加熱回転体２０と、記録媒体Ｐとが、熱平衡状態になったときの温度である。記録媒体通過時の飽和温度Ｔ_ｓは加熱体２４の目標設定温度に対応した値をとるものであるが、ここではそれが記録媒体Ｐ上の未定着トナー画像Ｓを定着するために最適な温度となるようにする。 The main point of the present invention is that the amount of heat from the back side is kept constant with respect to the carrying surface of the unfixed toner image S of the recording medium P (hereinafter referred to as the recording medium surface) while passing through the fixing nip N of the recording medium P. That is, in this embodiment, the temperature control of the fixing device 112 is performed based on the surface temperature of the pressure roller 10, and the surface temperature of the pressure roller 10 is set before passing through the nip portion N of the recording medium P and to keep always the saturation temperature T _s in passing, and after the fixing nip portion N inrush front of the recording medium P, is to change the target setting temperature of the heating member 24. The saturation temperature T _{s mentioned} here is a saturation temperature in a state where the recording medium P passes through the fixing nip portion N, and the pressure roller 10, the heating rotator 20, and the recording medium P are in a thermal equilibrium state. This is the temperature when The saturation temperature T _s at the time of passing through the recording medium takes a value corresponding to the target set temperature of the heating body 24, but here, it is the optimum temperature for fixing the unfixed toner image S on the recording medium P. To be.

記録媒体Ｐの定着ニップ部Ｎ通過中における加熱体２４の目標設定温度(第２の目標設定温度)をＴ_ｔ１とすると、記録媒体Ｐのニップ部Ｎ通過前は記録媒体Ｐに熱を奪われることがない分、記録媒体通過時の加圧ローラ飽和温度Ｔ_ｓを維持するためには、加熱体２４の発熱量を減らす必要があるため、そのときの目標設定温度(第１の目標設定温度)をＴ_ｔ０（＜Ｔ_ｔ１）とする。 If the target set temperature (second target set temperature) of the heating body 24 while the recording medium P passes through the fixing nip N is T _t1 , the recording medium P is deprived of heat before passing through the nip N of the recording medium P. Therefore, in order to maintain the pressure roller saturation temperature T _s when passing through the recording medium, it is necessary to reduce the amount of heat generated by the heating element 24. Therefore, the target set temperature (first target set temperature) ) _Is T _t0 (<T _t1 ).

図１（ｉ）および（ｉｉ）は本実施例と従来例における温調制御の説明図であり、以下、これを用いて説明する。 FIGS. 1 (i) and (ii) are explanatory views of temperature control in the present embodiment and the conventional example, and will be described below using this.

図１（ｉ）において、ｄは従来の温度制御で用いる加熱体２４の目標設定温度であって常にＴ_ｔ１で固定されている。ｂはそのときの加圧ローラ１０表面温度の変化を示したものである。 In FIG. 1I, d is a target set temperature of the heating body 24 used in the conventional temperature control, and is always fixed at T _t1 . b shows the change in the surface temperature of the pressure roller 10 at that time.

横軸（時間軸）上の原点０からＡ_０にかけては、記録媒体Ｐの定着ニップ部Ｎ突入前であって、加熱体２４は目標設定温度Ｔ_ｔ１で加熱され、加圧ローラ１０の表面温度は、横軸（時間軸）上の原点０からＡ_０にかけて昇温し、Ａ_０において記録媒体Ｐが定着ニップ部Ｎに突入する。その際、加圧ローラ１０は記録媒体Ｐに熱を奪われるため、急激な温度低下が起こる。 Is subjected A ₀ from the origin 0 on the horizontal axis (time axis), a fixing nip portion N inrush front of the recording medium P, the heating member 24 is heated at a target set temperature T _t1, the surface temperature of the pressure roller 10 the temperature was raised from the origin 0 on the horizontal axis (time axis) toward a _0, the recording medium P in a ₀ rushes into the fixing nip portion N. At that time, since the pressure roller 10 is deprived of heat by the recording medium P, a rapid temperature drop occurs.

これは記録媒体Ｐのニップ部突入前に、加圧ローラ１０が過度に熱せられ、その表面温度と記録媒体通過時の飽和温度Ｔ_ｓの温度差が大きくなっているためで、この温度差が大きいほど加圧ローラ１０の温度低下幅が大きくなる。加圧ローラ１０の表面温度は、最初の突入時の急激な温度低下の履歴を持っているために、加圧ローラ２周目開始時Ａ_１において、更に低下してしまう。このようにして、加圧ローラ１０の表面温度は、その周長ごとに顕著な温度低下を示し、次第に記録媒体通過時の飽和温度Ｔ_ｓへ近づいていく。なお、Ａ_２は加圧ローラ３周目開始時を示す。 This is because the pressure roller 10 is heated excessively before the nip portion of the recording medium P enters, and the temperature difference between the surface temperature and the saturation temperature T _s when passing through the recording medium becomes large. The larger the temperature is, the larger the temperature drop of the pressure roller 10 is. Since the surface temperature of the pressure roller 10 has a history of a rapid temperature drop at the time of first entry, it further decreases at the start A ₁ of the second round of the pressure roller. In this way, the surface temperature of the pressure roller 10, shows a significant temperature drop per its circumference, gradually approaches the saturation temperature T _s at the time of the recording medium passage. A ₂ represents the start of the third round of the pressure roller.

これに対し、ｃは本実施例の温度制御で用いる加熱体２４の目標設定温度であり、記録媒体Ｐの定着ニップ部Ｎ突入前（図１（ｉ）：原点０〜Ａ_０）はＴ_ｔ０（＜Ｔ_ｔ１）、定着ニップ部Ｎ突入後（図１（ｉ）：Ａ_０以後）はＴ_ｔ１とする。ａはそのときの温度制御による加圧ローラ１０の表面温度の変化を示したものである。 On the other hand, c is a target set temperature of the heating body 24 used in the temperature control of the present embodiment, and before the fixing nip portion N of the recording medium P enters (FIG. 1 (i): origin _{0 to A 0} ), T _t0. (<T _t1 ), after entering the fixing nip N (FIG. 1 (i): after A ₀ ), T _t1 . a shows the change of the surface temperature of the pressure roller 10 by the temperature control at that time.

加圧ローラ１０の表面温度は、記録媒体Ｐの定着ニップ部Ｎ突入前の段階で、記録媒体通過時の飽和温度Ｔ_ｓに向かって温度上昇する。これは、記録媒体Ｐの定着ニップ部Ｎ突入前の目標設定温度Ｔ_ｔ０は定着ニップ部Ｎ突入後の目標設定温度Ｔ_ｔ１よりも低いためであり、過度に熱せられることが無く、突入時に記録媒体通過時の飽和温度Ｔ_ｓとの温度差が無いので、急激な温度低下は起こらず、突入後もほぼ記録媒体通過時の飽和温度Ｔ_ｓを維持する。また加圧ローラ１０表面に温度低下の履歴が残ることが無いため、それ以後も記録媒体通過時の飽和温度Ｔ_ｓを維持することができる。 The surface temperature of the pressure roller 10 rises toward the saturation temperature T _s when the recording medium passes before the recording medium P enters the fixing nip N. This is because the target set temperature T _t0 before entering the fixing nip portion N of the recording medium P is lower than the target set temperature T _t1 after entering the fixing nip portion N. Since there is no temperature difference from the saturation temperature T _s when passing through the medium, there is no sudden temperature drop, and the saturation temperature T _s when passing through the recording medium is substantially maintained even after entering the recording medium. The pressurized because there is never pressure roller 10 History temperature drop on the surface is left, thereafter also can maintain the saturation temperature T _s at the time of the recording medium passage.

図２（ｉｉ）は、例えばトナーの種類等が変更されて、トナー溶融に最適な温度すなわち目標設定温度Ｔ_ｔ１、Ｔ_ｔ０が図１（ｉ）に示す目標設定温度よりも低くなった場合の温度制御の説明図である。この場合、加圧ローラ１０表面の記録媒体通過時の飽和温度Ｔ_ｓが新たな最適温度と一致するように、加熱体２４の目標設定温度Ｔ_ｔ０、Ｔ_ｔ１を図１（ｉ）のときよりも下げることで、対応できる。 FIG. 2 (ii) shows a case where, for example, the type of toner is changed and the optimum temperature for melting the toner, that is, the target set temperatures T _t1 and T _t0 are lower than the target set temperatures shown in FIG. It is explanatory drawing of temperature control. In this case, the target set temperatures T _t0 and T _t1 of the heating body 24 are set as compared with those in FIG. 1 (i) so that the saturation temperature T _s when the pressure roller 10 surface passes through the recording medium coincides with the new optimum temperature. Can also be reduced.

図２（ｉ）および（ｉｉ）に示した加熱体２４の温度制御に対応した温度制御モードを実行する加熱体駆動制御回路３１の温度制御フローチャートを図３に示す。 FIG. 3 shows a temperature control flowchart of the heating element drive control circuit 31 that executes a temperature control mode corresponding to the temperature control of the heating element 24 shown in FIGS. 2 (i) and (ii).

加熱体駆動制御回路３１ではＣＰＵがプリント信号Ｓ１を入力することによって温度制御モードをスタートする。ステップＳ_１において目標設定温度Ｔ_ｔ０で加熱体２４の温度制御を行う。記録媒体Ｐが定着ニップ部Ｎに突入したか否かを判断し（Ｓ_２）、突入したのなら（ＹＥＳ）目標設定温度をＴ_ｔ１に変更する（Ｓ_３）。記録媒体Ｐが定着ニップ部Ｎを完全に通過したか否かを判断し（Ｓ_４）、完全に通過したら（ＹＥＳ）終了する。 In the heating element drive control circuit 31, the CPU starts the temperature control mode by inputting the print signal S1. Controlling the temperature of the heating member 24 at a target setting temperature _{T t0} in step _{S 1.} It is determined whether or not the recording medium P has entered the fixing nip N (S ₂ ), and if it has entered (YES), the target set temperature is changed to T _t1 (S ₃ ). It is determined whether or not the recording medium P has completely passed through the fixing nip N (S ₄ ).

上記フローチャートにおいて、記録媒体Ｐが定着ニップ部Ｎに突入したことを判断する場合の構成例として、例えば定着装置１１２の定着ニップ部Ｎの記録媒体導入側に導入検知センサ３３（図１）を設け、このセンサで記録媒体Ｐの先端を検知し、その検知信号に基づいてＣＰＵで記録媒体Ｐの定着ニップ部突入を判断させるようにしてよい。記録媒体Ｐが定着ニップ部Ｎを完全に通過したことを判断する場合の構成例として、例えば定着装置１１２の定着ニップ部Ｎの記録媒体排出側に排出検知センサ３４（図１）を設け、このセンサで記録媒体Ｐの後端を検知し、その検知信号に基づいてＣＰＵで記録媒体Ｐの定着ニップ部突入を判断させるようにしてよい。 In the above flowchart, as an example of a configuration in which it is determined that the recording medium P has entered the fixing nip N, an introduction detection sensor 33 (FIG. 1) is provided on the recording medium introduction side of the fixing nip N of the fixing device 112, for example. The leading edge of the recording medium P may be detected by this sensor, and the CPU may determine whether the fixing nip portion of the recording medium P has entered based on the detection signal. As a configuration example for determining that the recording medium P has completely passed through the fixing nip N, for example, a discharge detection sensor 34 (FIG. 1) is provided on the recording medium discharge side of the fixing nip N of the fixing device 112. The rear end of the recording medium P may be detected by a sensor, and the CPU may determine whether the recording medium P has entered the fixing nip based on the detection signal.

本実施例では記録媒体Ｐとして坪量７５ｇのＬｅｔｔｅｒ普通紙を用いた。これをある一定の目標設定温度で温度制御した定着装置の定着ニップ部Ｎに通紙し、紙の後端が定着ニップ部Ｎを抜けたときの加圧ローラ表面温度をＴ_ｓとして、Ｔ_ｓ〜９０℃となるような加熱体２４の目標設定温度をＴ_ｔ１〜１７５℃とした。 In the present embodiment, Letter plain paper having a basis weight of 75 g was used as the recording medium P. This is passed through the fixing nip N of the fixing device whose temperature is controlled at a certain target set temperature, and the pressure roller surface temperature when the trailing edge of the paper passes through the fixing nip N is T _s , T _s The target set temperature of the heating body 24 to be ˜90 ° C. was T _t1 ˜175 ° C.

また、この値をもとに記録媒体Ｐの定着ニップ部Ｎ突入前の目標設定温度をＴ_ｔ０〜１４５℃に定めた。Ｔ_ｔ１とＴ_ｔ０の差ΔＴ_ｔ０＝Ｔ_ｔ１−Ｔ_ｔ０〜３０℃は、紙のニップ部突入直後に起こる、最も急激で且つ大きな加圧ローラの表面温度低下幅とほぼ同等の値であることに対応している。 Further, based on this value, the target set temperature before entering the fixing nip N of the recording medium P is set to T _{t0 to} 145 ° C. The difference ΔT _t0 = T _t1 −T _t0 -30 ° C. between T _t1 and T _t0 is almost the same value as the most rapid and large pressure roller surface temperature drop that occurs immediately after entering the nip portion of the paper. It corresponds to.

なお、飽和温度Ｔ_ｓは定着フィルムや加圧ローラ、記録媒体の種類（サイズ、厚さ、表面性）により異なるため、使用する定着フィルム、加圧ローラ、記録媒体の種類ごとに飽和温度Ｔ_ｓを測定して定め、それに従って加熱体２４の目標設定温度Ｔ_ｔ０、Ｔ_ｔ１を決定する。 Since the saturation temperature T _s varies depending on the type of fixing film, pressure roller, and recording medium (size, thickness, surface property), the saturation temperature T _s varies depending on the type of fixing film, pressure roller, and recording medium to be used. Is measured and determined, and the target set temperatures T _t0 and T _t1 of the heating body 24 are determined accordingly.

またトナー溶融に最適な加圧ローラ表面温度はトナーの種類ごとに異なるため、その温度と一致させるべき飽和温度Ｔ_ｓの値もトナーごとに変更する。 Further, since the pressure roller surface temperature optimum for melting the toner differs depending on the type of toner, the value of the saturation temperature T _s to be matched with the temperature is also changed for each toner.

図２（ii）に示している加圧ローラ表面温度Ｔ_ｓ、目標設定温度Ｔ_ｔ０、Ｔ_ｔ１は、より溶融粘度の低いトナーの場合の例として当てはまる。トナー溶融粘度が低ければ、ホットオフセット等の弊害を避けるため、設定温度も低めに調整する必要がある。一例として、トナー溶融に最適な加圧ローラ表面温度Ｔ_ｓ〜８５℃としたときの目標設定温度は、Ｔ_ｔ０〜１６５℃、Ｔ_ｔ１〜１４０℃となる。 The pressure roller surface temperature T _s and target set temperatures T _t0 and T _t1 shown in FIG. 2 (ii) are applicable as an example in the case of a toner having a lower melt viscosity. If the toner melt viscosity is low, it is necessary to adjust the set temperature to be low in order to avoid adverse effects such as hot offset. As an example, the target set temperatures when the pressure roller surface temperature T _{s to} 85 ° C. is optimal for toner melting are T _{t0 to} 165 ° C. and T _{t1 to} 140 ° C.

本実施例の定着装置によれば、記録媒体Ｐの定着ニップ部Ｎ通過前および通過中において、加圧ローラ１０の表面温度は記録媒体通過時の飽和温度Ｔ_ｓを保つことができる。その結果、記録媒体裏面からの熱量が一定となり、記録媒体表面と裏面からの熱量のバランスを一定に保てることから、定着後の画像濃度、グロスを均一にすることができる。また、加圧ローラ１０表面の温度低下を避けるために、単純に目標設定温度を上げることによるホットオフセット発生を防ぎ、また、記録媒体Ｐの定着ニップ部Ｎ通過前に過剰な加熱をすることが無いため、加圧ローラ１０表面温度は記録媒体通過時の飽和温度Ｔ_ｓを超えて余分に温度が上昇することが無く、消費電力を抑えることができる。 According to the fixing device of the present embodiment, in the fixing nip N passes before and during passage of the recording medium P, the surface temperature of the pressure roller 10 can maintain the saturation temperature T _s at the time of passing the recording medium. As a result, the amount of heat from the back surface of the recording medium becomes constant, and the balance between the amount of heat from the front surface and the back surface of the recording medium can be kept constant, so that the image density and gloss after fixing can be made uniform. Further, in order to avoid a temperature drop on the surface of the pressure roller 10, it is possible to prevent the occurrence of hot offset by simply raising the target set temperature, and to heat the recording medium P before passing through the fixing nip portion N. not because the pressure roller 10 surface temperature without being excessively temperature rises above the saturation temperature T _s at the time of passing the recording medium, power consumption can be suppressed.

すなわち、記録媒体Ｐが定着ニップ部Ｎに突入する直前までの目標設定温度Ｔ_ｔ０を、該記録媒体がニップ部に突入した後の目標設定温度Ｔ_ｔ１よりも低くするので、記録媒体Ｐのニップ部突入直後に加圧ローラ表面温度が急激に低下するのを防ぐことができる。それにより、記録媒体裏面側からの熱量が急激に減少するのを防ぎ、記録媒体表面と裏面からの熱量のバランスを一定に保ち、同一記録媒体Ｐ上での濃度、グロス変化を抑えて画質の均一性を向上させることができる。また、加圧ローラ表面の温度低下を避けるために、単純に目標設定温度を上げることによるホットオフセット発生を防ぎ、また、記録媒体の通過前に過剰な加熱をすることが無いため、必要以上に温度が上昇するのを避けられ、消費電力を抑えることができる。 That is, the target set temperature T _t0 until the recording medium P immediately before entering the fixing nip portion N is set lower than the target set temperature T _t1 after the recording medium enters the nip portion. It is possible to prevent the pressure roller surface temperature from rapidly decreasing immediately after the part enters. As a result, the amount of heat from the back side of the recording medium is prevented from abruptly decreasing, the balance of the amount of heat from the front and back surfaces of the recording medium is kept constant, and changes in density and gloss on the same recording medium P are suppressed to improve image quality. Uniformity can be improved. Also, in order to avoid the temperature drop on the pressure roller surface, hot offset generation by simply raising the target set temperature is prevented, and there is no excessive heating before passing the recording medium. Temperature rise can be avoided and power consumption can be suppressed.

また、目標設定温度Ｔ_ｔ０、Ｔ_ｔ１のそれぞれを、加圧ローラ１０の表面温度が、記録媒体Ｐのニップ部通過中に該加圧ローラが達する熱平衡状態の温度を維持するように定めるので、記録媒体Ｐのニップ部通過前および通過中において、加圧ローラ１０の表面温度は、定着フィルム２１と、加圧ローラ１０と、記録媒体Ｐから決まる熱平衡温度を保つことができる。その結果、記録媒体裏面からの熱量が一定となり、記録媒体表面と裏面からの熱量のバランスを一定に保てることから、定着後の画像濃度、グロスを均一にすることができる。また、加圧ローラ表面の温度低下を避けるために、単純に目標設定温度を上げることによるホットオフセット発生を防ぎ、また、記録媒体の通過前に過剰な加熱をすることが無いため、記録媒体通過時の飽和温度（熱平衡温度）を超えて余分に温度が上昇するのを避けられ、消費電力を抑えることができる。 Further, each of the target set temperatures T _t0 and T _t1 is determined so that the surface temperature of the pressure roller 10 maintains the temperature of the thermal equilibrium state reached by the pressure roller while passing through the nip portion of the recording medium P. Before and during the passage of the recording medium P through the nip portion, the surface temperature of the pressure roller 10 can maintain a thermal equilibrium temperature determined by the fixing film 21, the pressure roller 10, and the recording medium P. As a result, the amount of heat from the back surface of the recording medium becomes constant, and the balance between the amount of heat from the front surface and the back surface of the recording medium can be kept constant, so that the image density and gloss after fixing can be made uniform. Also, in order to avoid a temperature drop on the pressure roller surface, hot offset generation by simply raising the target set temperature is prevented, and there is no excessive heating before passing the recording medium. It is possible to prevent the temperature from rising excessively beyond the saturation temperature (thermal equilibrium temperature), and to reduce power consumption.

また、目標設定温度Ｔ_ｔ０、Ｔ_ｔ１のそれぞれを、記録媒体のサイズ、厚さ、表面性などの種類毎に、前記加圧部材の表面温度が、記録媒体のニップ部通過中に該加圧部材が達する熱平衡状態の温度を維持するように定めるので、加圧ローラ表面の温度を記録媒体Ｐの種類に応じた最適な熱平衡温度に保つことができる。それにより記録媒体の種類に応じて、記録媒体裏面から最適な熱量を安定して供給でき、記録媒体表面と裏面からの熱量のバランスを一定に保てることから、定着後の画像濃度、グロスを均一にすることができる。また、加圧ローラ表面の温度低下を避けるために、単純に目標設定温度を上げることによるホットオフセット発生を防ぎ、また、記録媒体の通過前に過剰な加熱をすることが無いため、記録媒体通過時の飽和温度（熱平衡温度）を超えて余分に温度が上昇するのを避けられ、消費電力を抑えることができる。 Further, each of the target set temperatures T _t0 and T _t1 is determined depending on the type, such as the size, thickness, and surface property of the recording medium. Since the temperature of the thermal equilibrium state reached by the member is determined to be maintained, the temperature of the pressure roller surface can be maintained at the optimum thermal equilibrium temperature according to the type of the recording medium P. As a result, the optimum amount of heat can be stably supplied from the back side of the recording medium according to the type of the recording medium, and the balance between the amount of heat from the front and back sides of the recording medium can be kept constant, so that the image density and gloss after fixing are uniform. Can be. Also, in order to avoid a temperature drop on the pressure roller surface, hot offset generation by simply raising the target set temperature is prevented, and there is no excessive heating before passing the recording medium. It is possible to prevent the temperature from rising excessively beyond the saturation temperature (thermal equilibrium temperature), and to reduce power consumption.

また、サーミスタ２３の検知温度に基づいて加熱体２４の発熱量を制御し、加熱体２４を目標設定温度Ｔ_ｔ０、Ｔ_ｔ１にそれぞれ温調するので、加圧ローラの表面温度を熱平衡状態の温度に保つことができる。 Further, the amount of heat generated by the heating element 24 is controlled based on the temperature detected by the thermistor 23, and the heating element 24 is adjusted to the target set temperatures T _t0 and T _t1 , respectively. Can be kept in.

（その他）
（１）本発明の定着装置は、フィルム加熱方式の定着装置に限らず、電磁誘導加熱方式等のように熱応答性がよく、記録媒体の裏面に接する加圧部材側の加熱手段を省いた定着装置にも適用できる。この場合、記録媒体の定着ニップ部通過前および通過中において、記録媒体裏面からの熱量を一定に保つように、励磁コイルと磁性体コアとを具備する磁束発生手段（加熱体）によって電磁誘導発熱性金属層を含む定着フィルム（加熱回転体）を電磁誘導加熱させる目標設定温度を変化させることで同様の効果が得られる。 (Other)
(1) The fixing device of the present invention is not limited to a film heating type fixing device, and has good thermal response, such as an electromagnetic induction heating method, and omits the heating means on the pressure member side in contact with the back surface of the recording medium. It can also be applied to a fixing device. In this case, before and during passage of the recording medium through the fixing nip, electromagnetic induction heat is generated by magnetic flux generation means (heating body) having an exciting coil and a magnetic core so as to keep the amount of heat from the back surface of the recording medium constant. The same effect can be obtained by changing the target set temperature for electromagnetic induction heating of the fixing film (heating rotator) including the conductive metal layer.

（２）加熱体による加熱回転体の加熱は本実施例の内部加熱方式に限られず、加熱体を加熱回転体の外部に配設した外部加熱方式の装置構成にすることもできる。 (2) The heating of the heating rotator by the heating element is not limited to the internal heating method of the present embodiment, and an external heating type apparatus configuration in which the heating member is disposed outside the heating rotator can be employed.

実施例１の定着装置の概略構成模型図。FIG. 3 is a schematic configuration model diagram of the fixing device according to the first exemplary embodiment. 加熱体の目標設定温度と加圧ローラ表面温度の変化を説明する図。The figure explaining the change of the target setting temperature of a heating body and the pressure roller surface temperature. 定着装置の温度制御フローチャート。6 is a temperature control flowchart of the fixing device. 定着装置を具備する画像形成装置の概略構成模型図。1 is a schematic configuration model diagram of an image forming apparatus including a fixing device.

Explanation of symbols

１０‥‥加圧ローラ
１１‥‥芯金
１２‥‥弾性層
１３‥‥離型性層
２１‥‥定着フィルム
２２‥‥ステ−
２３‥‥サーミスタ
２４‥‥加熱体
３１‥‥加熱体駆動制御回路
Ｓ‥‥トナー
Ｐ‥‥記録媒体
Ｎ‥‥定着ニップ部 DESCRIPTION OF SYMBOLS 10 ... Pressure roller 11 ... Core metal 12 ... Elastic layer 13 ... Releasable layer 21 ... Fixing film 22 ... Stage
23 ... Thermistor 24 ... Heating element 31 ... Heating element drive control circuit S ... Toner P ... Recording medium N ... Fixing nip

Claims

A heating member, a heating rotator heated by the heating member, and a pressure member that presses against the heating rotator to form a nip portion, and a recording medium carrying an unfixed image is formed at the nip portion. In a fixing device for nipping and conveying and fixing an unfixed image on a recording medium,
Control means for adjusting the temperature of the heating body to a predetermined target set temperature, wherein the control means has a first target set temperature immediately before the recording medium enters the nip portion, and the recording medium has a nip portion. A fixing device having a mode in which the temperature is lower than a second target set temperature after entering the printer.

The first and second target set temperatures are determined such that the surface temperature of the pressure member maintains a temperature in a thermal equilibrium state reached by the pressure member while passing through the nip portion of the recording medium. The fixing device according to claim 1.

The first and second target set temperatures are respectively applied to the surface temperature of the pressurizing member while the recording medium passes through the nip portion for each type of the recording medium such as size, thickness, and surface property. The fixing device according to claim 1, wherein the fixing device is determined so as to maintain a temperature in a thermal equilibrium state reached by the pressure member.

The temperature detection means further detects the temperature of the heating body, and the control means sets the heating body to the first target set temperature and the second target set temperature based on the detected temperature of the temperature detection means. The fixing device according to claim 1, wherein the temperature is adjusted.