JP3643344B2 - Fixing means of image forming apparatus capable of duplex printing - Google Patents

Description

【０００６】
表１を見てわかるとおり、１００枚程度を両面印刷すると、感光体ドラムの表面温度は６０℃前後まで上昇し、それ以後は６０℃前後で推移する。※１の不具合は、現像領域での表面電位が低下したことによる画像カブリの発生と思われる。
【０００７】
※２の不具合は、感光体ドラム温度が６０℃前後になることにより、表面のトナーの温度もガラス転移温度近くなり、感光体ドラム表面に付着しやすくなることが原因であると思われる。
【０００８】
定着性の評価は、手で擦って、定着トナー画像がはがれるか否かの２段階評価で行った。ここでは定着性は、特に問題は発生していない。
【０００９】
上記問題を解決するために、一般的には片面印刷のみの定着の設定温度より低い設定温度で、両面印刷を行う技術が取り入れられている。多くの画像形成装置ではこれを適用することにより上記問題は解決することができる。しかし今回の実験で用いた、スタックレスであり、感光体ドラムの温度特性が激しく、トナーのガラス転移温度が低い、印刷枚数が多いなどの条件が重なった場合には、上記従来技術によっても不具合が発生することが分かった。上記で説明した従来技術による画像形成装置で、連続両面印刷を行ったときの用紙温度、各場所での温度を表２に記載する。尚本確認実験２での条件は以下の通りである。
・室温／湿度：２８℃／５０％
・搬送速度：３５０ｍｍ／ｓｅｃ、４０枚／ｍｉｎ（Ａ４サイズ横通し）
・感光体ドラム径：φ６０ｍｍ
・感光体ドラムヒータ温度：４５℃（４５℃以上でＯＦＦする制御）
・熱ローラ：熱ローラ温度が１８０℃からヒータをＯＮせず連続１００枚印刷したときに、約４０℃の温度低下が見られるものを使用。
・熱ローラ温度：１６０±５℃（１５５℃以下でＯＮ／１７５℃以上でＯＦＦ）
・通紙方法：６枚づつ交互の両面印刷、Ａ４サイズ普通紙を横方向に通紙
【００１０】
【表２】

【００１１】
表２を見てわかるとおり、５０枚程度を両面印刷すると、感光体ドラムの表面温度は５０℃前後まで上昇し、それ以後は５０℃前後で推移する。感光体ドラムの温度上昇もかなり抑えられ、確認実験１で発生したような画像カブリや、クリーニング不良などの欠点は解消されているいることわかる。
【００１２】
しかし、初期数枚程度の定着性が悪いことが確認できた。これは画像形成装置の、感光体ドラムや搬送路などが冷えた状態で、定着温度を低い設定にしてしまうと定着性が悪くなることが原因であると思われる。
【００１３】
上記２つ目の問題を解決するには、両面印刷時の温度設定をもう少し高く設定するなどすれば解消するかもしれないが、既に感光体ドラムの温度推移からこれ以上の温度に上げることは危険である。
【００１４】
【課題を解決するための手段】
上記の課題を解決するために、本願第１の発明は、両面印刷可能な画像形成装置に設けられ、用紙に転写されたトナー画像を熱と圧力により定着する定着手段において、連続して両面印刷する時には、熱ローラの表面の目標温度を所定の枚数を印刷する毎に定着性能を満足しかつ片面印刷時の目標温度である第１の定着温度から感光体ドラムの温度を所定の範囲に維持できる第２の定着温度へ所定の間隔の温度づつ複数の段階を経て推移させ、この第２の定着温度になるとこの温度で維持する制御手段を有することを特徴とする定着手段を用いる。
【００１６】
本願第３の発明は、前記制御手段は、同じ所定の枚数毎に同じ所定の温度だけ段階的に下げる制御を行うことを特徴とする第１、２の発明に記載の定着手段を用いる。
【００１７】
【作用】
本願第１〜３の発明は、両面印刷時には、最初から所定枚数の印刷の間は、定着温度は片面時と同等の温度設定のため、定着性能は確保され、途中で徐々に定着温度を両面印刷時の設定温度に近づけることにより、感光体ドラムの温度上昇も解決できる。
【００１８】
【発明の実施形態】
本発明の一実施形態が採用される両面印字可能な画像形成装置が両面に画像を印刷する動きを図１に基づいて説明する。同図面において、給紙カセット１から給紙ローラ１１で１枚づつ給紙された用紙は、搬送路２１を経て、レジスト部２２で先端を整えられ待機し、所定のタイミングで画像形成手段４へ搬送され、当該画像形成手段４で形成されたトナー画像が転写手段４５で用紙の第１面に転写される。第１面に未定着トナー画像を転写された用紙は、搬送路２４により定着手段５の熱ローラ５１と圧ローラ５２の間のニップ部に搬送され、前記２つのローラが挟持し加熱することにより第１面の未定着トナー画像が定着される。次に当該第１面に画像を有する用紙は分岐手段６により上流側搬送路２５を経てスイッチバック手段７へ受け渡され、当該スイッチバック手段７内で搬送方向を変えられて下流側搬送路２６へ受け渡される。このとき前記スイッチバック手段７内の用紙はガイド手段８により幅方向を所定の位置にガイドされる。続いて当該第１面に画像を有する用紙は前記下流側搬送路２６から下搬送路２７搬送され、当該下搬送路２７では前記ガイド手段８により搬送されつつつ幅方向をガイドされ、垂直搬送路２８を経て再び前記レジスト部２２で先端を整えられ待機し、所定のタイミングで前記画像形成手段４へ搬送され、当該画像形成手段４で形成されたトナー画像が前記転写手段４５で用紙の第２面に転写される。第２面に未定着トナー画像を転写された用紙は、前記搬送路２４により前記定着手段５の前記熱ローラ５１と前記圧ローラ５２の間のニップ部に搬送され、前記２つのローラが挟持し加熱することにより第２面の未定着トナー画像が定着される。ここまでで両面に画像を印刷された用紙は前記分岐手段６により、排紙部２９を経て、排紙トレイ９に排出される。
【００１９】
本発明の特徴である前記定着手段５の温度設定の制御について図２に基づき説明する。当該定着手段５は、内部にハロゲンランプなどのヒータ５１１を内蔵する、アルミなどの熱伝導性に優れる基材５１２からなる熱ローラ５１と、熱伝導性のよいアルミなどのローラ５２１の周囲が耐熱性のウレタンゴムでできた弾性層５２２で覆われ、さらに外周はＰＴＦＥなどのフッ素系樹脂の離型層を持った圧ローラと、前記熱ローラの表面温度を検知する温度検知手段５３と、ヒータ５１１の電源５４と、前記ヒータ５１１のＯＮ／ＯＦＦをするスイッチング手段５５、及びこれらを制御する定着温度制御手段から構成されている。本実施形態の画像形成装置の定着手段の温度制御は、用紙の片面のみの印刷時、及び通常の安定待機状態においては、１８０±５℃での設定温度で推移している。この場合は、前記温度検知手段５３の検知した値から換算される前記熱ローラ５１の表面温度が、制御したい温度から決定される第１の定着閾値（この場合は１７５℃）を下回ったときは前記スイッチング手段をＯＮして前記熱ローラ５１の温度を上げ、制御したい温度から決定される第２の定着閾値（この場合は１８５℃）を上回ったときには前記スイッチング手段をＯＦＦして前記熱ローラ５１の温度が用紙や空気に熱を奪われて下がるという、スレッシュホールド制御を行っている。
【００２０】
本実施形態の両面印刷時には、以下の表３の定着温度制御テーブルに基づく温度制御を行っている。尚この表３において、所定枚数は１０枚ずつ、第１の定着温度は１８０°、第２の定着温度は１６０°、所定の間隔の温度は２°ずつ下げる制御に使われるものである。
【００２１】
【表３】

【００２２】
上記で説明した本発明による画像形成装置で、連続両面印刷を行ったときの用紙温度、各場所での温度を表４に記載する。尚本確認実験３での条件は以下の通りである。
・室温／湿度：２８℃／５０％
・搬送速度：３５０ｍｍ／ｓｅｃ、４０枚／ｍｉｎ（Ａ４サイズ横通し）
・感光体ドラム径：φ６０ｍｍ
・感光体ドラムヒータ温度：４５℃（４５℃以上でＯＦＦする制御）
・熱ローラ：熱ローラ温度が１８０℃からヒータをＯＮせず連続１００枚印刷したときに、約４０℃の温度低下が見られるものを使用。
・熱ローラ温度：表３に基づくスレッシュホールド制御
・通紙方法：６枚づつ交互の両面印刷、Ａ４サイズ普通紙を横方向に通紙
【００２３】
【表４】

【００２４】
上記表４の結果から明らかなように、感光体ドラムの温度の上昇を抑えつつ、定着性をクリアできることが分かった。
【００２５】
【発明の効果】
本件の発明を採用すれば、スタックレス方式の両面印刷可能な画像形成装置特有の感光体ドラムの温度上昇を、定着性を確保しつつ実現できる。
【図面の簡単な説明】
【図１】従来技術及び本発明のスタックレス方式の両面印刷可能な画像形成装置の概略図である。
【図２】本発明の定着手段の概略図である。
【符号の説明】
４；画像形成手段
５；定着手段
５１；熱ローラ
５２；圧ローラ
７；スイッチバック手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a copying machine, a laser printer, a facsimile, and the like, and more particularly to a fixing unit of an image forming apparatus using an electrophotographic technique.
[0002]
[Prior art]
A conventional image forming apparatus capable of duplex printing will be described with reference to FIG. In the drawing, the sheets fed one by one from the sheet feeding cassette 1 by the sheet feeding roller 11 pass through the conveyance path 21, have their leading ends adjusted by the registration unit 22, and wait for the image forming unit 4 at a predetermined timing. The toner image conveyed and formed by the image forming unit 4 is transferred to the first surface of the paper by the transfer unit 45. The sheet on which the unfixed toner image is transferred to the first surface is conveyed by the conveyance path 24 to the nip portion between the heat roller 51 and the pressure roller 52 of the fixing unit 5, and the two rollers sandwich and heat the sheet. The unfixed toner image on the first side is fixed. Next, the sheet having an image on the first surface is transferred by the branching unit 6 to the switchback unit 7 through the upstream conveyance path 25, and the conveyance direction is changed in the switchback unit 7 to change the downstream conveyance path 26. It is handed over to. Subsequently, the sheet having an image on the first surface passes through the downstream side conveyance path 26, the lower conveyance path 27, and the vertical conveyance path 28, and is re-adjusted at the registration unit 22 and waits, and the image formation is performed at a predetermined timing. The toner image conveyed to the means 4 and formed by the image forming means 4 is transferred to the second surface of the paper by the transfer means 45. The sheet on which the unfixed toner image is transferred to the second surface is conveyed to the nip portion between the heat roller 51 and the pressure roller 52 of the fixing unit 5 through the conveyance path 24, and the two rollers sandwich the sheet. The unfixed toner image on the second surface is fixed by heating. Thus far, the paper on which images are printed on both sides is discharged by the branching unit 6 to the paper discharge tray 9 via the paper discharge unit 29.
[0003]
[Problems to be solved by the invention]
However, according to such a conventional method, when both sides are continuously printed, the sheet on which the image is transferred onto the first side is first fixed with the toner image by the fixing unit and naturally becomes a high temperature. The sheet on which the image is printed on the first side is immediately conveyed again to the image forming unit 4 so that the image is transferred to the second side of the sheet at a high temperature. When it does, heat is transferred and the temperature rises gradually. For example, when 100 sheets of double-sided printing are performed, the surface temperature of the photosensitive drum 41 rises to about 60 ° C. When the temperature of the photosensitive drum 41 rises to around 60 ° C., the surface potential in the developing area of the photosensitive drum 41 decreases. In addition, the toner used in the image forming unit 4 starts to aggregate on the surface of the photosensitive drum 41 and image defects occur. Furthermore, various problems such as a reduction in the cleaning performance of the cleaning unit due to the influence of the heat of the photosensitive drum 41 have occurred.
[0004]
Table 1 shows the sheet temperature and the temperature at each location when continuous duplex printing is performed in the conventional image forming apparatus described above. The conditions in this confirmation experiment 1 are as follows.
Room temperature / humidity: 28 ° C / 50%
・ Conveying speed: 350mm / sec, 40 sheets / min (A4 size sideways)
・ Photosensitive drum diameter: φ60mm
-Photoconductor drum heater temperature: 45 ° C (control to turn off at 45 ° C or higher)
-Heat roller: Use a roller that shows a temperature drop of about 40 ° C when printing 100 sheets continuously without heating the heater from 180 ° C.
-Heat roller temperature: 180 ± 5 ° C (ON at 175 ° C or lower / OFF at 185 ° C or higher)
-Paper feeding method: 6-sheet alternating double-sided printing, A4 size plain paper is passed in the horizontal direction.
[0005]
[Table 1]

[0006]
As can be seen from Table 1, when double-sided printing is performed on about 100 sheets, the surface temperature of the photosensitive drum rises to around 60 ° C., and thereafter changes to around 60 ° C. * The first problem seems to be the occurrence of image fogging due to a decrease in surface potential in the development area.
[0007]
The problem of * 2 seems to be due to the fact that when the temperature of the photosensitive drum is around 60 ° C., the temperature of the toner on the surface is also close to the glass transition temperature, and it tends to adhere to the surface of the photosensitive drum.
[0008]
The fixing property was evaluated by a two-step evaluation of whether or not the fixed toner image is peeled off by rubbing by hand. Here, there is no particular problem with the fixing property.
[0009]
In order to solve the above problem, generally, a technique for performing duplex printing at a set temperature lower than the set temperature for fixing only for single-sided printing is adopted. In many image forming apparatuses, the above problem can be solved by applying this. However, if the stackless, photoconductor drum temperature characteristics, the toner glass transition temperature is low, the number of printed sheets, etc. used in this experiment overlap, the above-mentioned conventional technique also fails. Was found to occur. Table 2 shows the sheet temperature and the temperature at each location when continuous duplex printing is performed in the conventional image forming apparatus described above. The conditions in the confirmation experiment 2 are as follows.
Room temperature / humidity: 28 ° C / 50%
・ Conveying speed: 350mm / sec, 40 sheets / min (A4 size sideways)
・ Photosensitive drum diameter: φ60mm
-Photoconductor drum heater temperature: 45 ° C (control to turn off at 45 ° C or higher)
-Heat roller: Use a roller that shows a temperature drop of about 40 ° C when printing 100 sheets continuously without heating the heater from 180 ° C.
-Heat roller temperature: 160 ± 5 ° C (ON at 155 ° C or below / OFF at 175 ° C or above)
・ Passing method: Alternate double-sided printing every 6 sheets, passing A4 size plain paper in the horizontal direction [0010]
[Table 2]

[0011]
As can be seen from Table 2, when about 50 sheets are printed on both sides, the surface temperature of the photosensitive drum rises to around 50 ° C., and thereafter changes to around 50 ° C. It can be seen that the temperature rise of the photosensitive drum is considerably suppressed, and the defects such as the image fogging and the poor cleaning that have occurred in the confirmation experiment 1 are solved.
[0012]
However, it was confirmed that the fixability of the initial few sheets was poor. This is considered to be caused by poor fixability when the fixing temperature is set to a low level in a state where the photosensitive drum or the conveyance path of the image forming apparatus is cooled.
[0013]
To solve the second problem, it may be solved by setting the temperature setting for double-sided printing a little higher, but it is dangerous to raise the temperature of the photosensitive drum to a temperature higher than this. It is.
[0014]
[Means for Solving the Problems]
In order to solve the above-described problems, the first invention of the present application provides a double-sided printing continuously in a fixing unit provided in an image forming apparatus capable of double-sided printing and fixing a toner image transferred onto paper by heat and pressure. When a predetermined number of sheets are printed, the target temperature of the surface of the heat roller satisfies the fixing performance, and the temperature of the photosensitive drum is maintained within a predetermined range from the first fixing temperature, which is the target temperature for single-sided printing. it is trend through a temperature increments plurality of stages of a predetermined interval to the second fixing temperature, the fixing means When this second fixing temperature, comprising a control means for maintaining at this temperature is used.
[0016]
A third invention of the present application uses the fixing means according to the first and second inventions, wherein the control means performs a control for stepwise lowering by the same predetermined temperature for every same predetermined number of sheets.
[0017]
[Action]
According to the first to third aspects of the present invention, during double-sided printing, since the fixing temperature is set to the same temperature as during single-sided printing from the beginning, the fixing performance is ensured, and the fixing temperature is gradually increased on both sides. By bringing the temperature close to the set temperature at the time of printing, the temperature rise of the photosensitive drum can be solved.
[0018]
DETAILED DESCRIPTION OF THE INVENTION
A movement in which an image forming apparatus capable of duplex printing that employs an embodiment of the present invention prints an image on both sides will be described with reference to FIG. In the drawing, the sheets fed one by one from the sheet feeding cassette 1 by the sheet feeding roller 11 pass through the conveyance path 21, are adjusted in the leading edge by the registration unit 22, and wait for the sheet to the image forming unit 4 at a predetermined timing. The toner image conveyed and formed by the image forming unit 4 is transferred to the first surface of the paper by the transfer unit 45. The sheet on which the unfixed toner image is transferred to the first surface is conveyed by the conveyance path 24 to the nip portion between the heat roller 51 and the pressure roller 52 of the fixing unit 5, and the two rollers sandwich and heat the sheet. The unfixed toner image on the first side is fixed. Next, the sheet having an image on the first surface is transferred by the branching unit 6 to the switchback unit 7 through the upstream conveyance path 25, and the conveyance direction is changed in the switchback unit 7 to change the downstream conveyance path 26. It is handed over to. At this time, the sheet in the switchback means 7 is guided to a predetermined position in the width direction by the guide means 8. Subsequently, the sheet having the image on the first surface is conveyed from the downstream conveyance path 26 to the lower conveyance path 27, and is guided in the width direction while being conveyed by the guide unit 8 in the lower conveyance path 27, and the vertical conveyance path After 28, the front end of the resist unit 22 is adjusted again and waits, and the toner image formed by the image forming unit 4 is transferred to the image forming unit 4 at a predetermined timing. It is transferred to the surface. The sheet on which the unfixed toner image is transferred to the second surface is conveyed to the nip portion between the heat roller 51 and the pressure roller 52 of the fixing unit 5 through the conveyance path 24, and the two rollers sandwich the sheet. The unfixed toner image on the second surface is fixed by heating. Thus far, the paper on which images are printed on both sides is discharged by the branching unit 6 to the paper discharge tray 9 via the paper discharge unit 29.
[0019]
The temperature setting control of the fixing unit 5 which is a feature of the present invention will be described with reference to FIG. The fixing unit 5 includes a heat roller 51 including a heater 512 such as a halogen lamp and made of a base material 512 having excellent heat conductivity such as aluminum, and a roller 521 made of aluminum having good heat conductivity. A pressure roller covered with an elastic layer 522 made of a conductive urethane rubber and having a fluororesin release layer such as PTFE on the outer periphery, a temperature detecting means 53 for detecting the surface temperature of the heat roller, and a heater The power supply 54 of 511, the switching means 55 which turns ON / OFF the said heater 511, and the fixing temperature control means which controls these are comprised. The temperature control of the fixing unit of the image forming apparatus of the present embodiment changes at a set temperature of 180 ± 5 ° C. during printing on only one side of the paper and in a normal stable standby state. In this case, when the surface temperature of the heat roller 51 converted from the value detected by the temperature detecting means 53 falls below the first fixing threshold value (175 ° C. in this case) determined from the temperature to be controlled. The switching means is turned on to raise the temperature of the heat roller 51. When a second fixing threshold (185 ° C. in this case) determined from the temperature to be controlled is exceeded, the switching means is turned off and the heat roller 51 is turned on. Threshold control is performed so that the temperature of the paper drops as paper and air are deprived of heat.
[0020]
During double-sided printing according to the present embodiment, temperature control is performed based on the fixing temperature control table shown in Table 3 below. In Table 3, the predetermined number is 10 sheets, the first fixing temperature is 180 °, the second fixing temperature is 160 °, and the temperature at a predetermined interval is decreased by 2 °.
[0021]
[Table 3]

[0022]
Table 4 shows the sheet temperature and the temperature at each location when continuous duplex printing is performed in the image forming apparatus according to the present invention described above. The conditions in this confirmation experiment 3 are as follows.
Room temperature / humidity: 28 ° C / 50%
・ Conveying speed: 350mm / sec, 40 sheets / min (A4 size sideways)
・ Photosensitive drum diameter: φ60mm
-Photoconductor drum heater temperature: 45 ° C (control to turn off at 45 ° C or higher)
-Heat roller: Use a roller that shows a temperature drop of about 40 ° C when printing 100 continuous sheets without heating the heater from 180 ° C.
Heat roller temperature: Threshold control based on Table 3. Paper feeding method: Alternate double-sided printing every six sheets, A4 size plain paper is passed in the horizontal direction.
[Table 4]

[0024]
As is apparent from the results in Table 4 above, it was found that the fixability can be cleared while suppressing the temperature rise of the photosensitive drum.
[0025]
【The invention's effect】
By adopting the present invention, it is possible to realize the temperature rise of the photosensitive drum peculiar to the image forming apparatus capable of double-sided printing of the stackless method while securing the fixing property.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an image forming apparatus capable of duplex printing of a prior art and the present invention.
FIG. 2 is a schematic view of a fixing unit of the present invention.
[Explanation of symbols]
4; image forming means 5; fixing means 51; heat roller 52; pressure roller 7; switchback means

Claims (2)

In a fixing unit provided in an image forming apparatus capable of double-sided printing and fixing a toner image transferred to paper by heat and pressure,
When performing continuous double-sided printing, the target temperature of the surface of the heat roller satisfies the fixing performance from the first fixing temperature that is the target temperature for single-sided printing and prints the temperature of the photosensitive drum every time a predetermined number of sheets are printed. Fixing means characterized by having a control means for making a transition to a second fixing temperature that can be maintained within a predetermined range through a plurality of stages at a temperature of a predetermined interval and maintaining the temperature at this second fixing temperature. . 2. The fixing unit according to claim 1 , wherein the control unit performs control to stepwise decrease the same predetermined temperature for each same predetermined number of sheets.

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