JP3763369B2 - Fixing device - Google Patents

Description

【００６４】
上記表１の結果により、スリット間隔；Ｌは１１０ｍｍ以下が最適であることが分かる。スリット間隔；Ｌを１２０ｍｍ以上に設定すると、理論上はスリット部でシートの膨張や撓みを吸収することが可能であるが、実際には膨張が一部分に集中し、スリット幅；ΔＬが広い場合、上述したスリット間隔；Ｌではシートの撓みを吸収できないことが理解できる。
【００６５】
すなわち、耐熱性シートのスリット間隔を１１０ｍｍ以下にすることにより、耐熱性シートの撓みを確実に防止することができる。それゆえ、安定した定着につながる。
【００６６】
次に、定着ローラ５２は紙を通紙方向に搬送するために紙搬送力が必要である。これについて、（ａ）白紙通紙、（ｂ）１００％黒ベタ印字紙通紙の２種類の場合に必要な紙搬送力を図４に基づいて説明する。図３は図４の紙搬送力の測定方法を示す斜視図である。但し、１００％黒ベタ印字紙とは、定着ローラ５２側は未定着トナー像２による黒ベタであり、耐熱性シート５４側は定着が終了した定着像３による黒ベタとする。
【００６７】
定着ローラ５２と耐熱性シート５４との間に白紙（１２８ｇ）を挿入する。定着ローラ５２を回転させ、定着ローラ温度を１４０度に温度調節し、用紙１を搬送する。このとき、用紙１に取り付けたバネばかり６３を引っ張ると、定着ローラ５２が回転中に用紙１の搬送が停止する。その後、徐々にバネばかり６３の引っ張り力を弱めると、再び用紙１が搬送され始める。用紙１が再搬送され始めた時点でのバネばかり６３の値を紙搬送力とした。
【００６８】
（ａ）白紙通紙の場合、紙搬送を行うためには、
μ１（ｔ１・ｍ）・ｐ＞（ｔ２・ｍ）・ｐ＋Ｍｐ ・・・（１）
μ１ ：定着ローラ５２のコート材と用紙１との間の摩擦係数
μ２ ：耐熱性シート５４材と用紙１との間の摩擦係数
ｐ：用紙１に加えられた加圧力
Ｍｐ：用紙１の抵抗力と搬送力
の関係が満足されていなければならない。即ち、μ１＞μ２の関係を満たしていなければならない。但し、摩擦係数μ１はコート材の温度及び材料に依存する係数である。同様に、摩擦係数μ２はシート材の温度及び材料に依存する係数である。つまり、耐熱性シート５４と用紙１との摩擦係数μ２より、定着ローラ５２と用紙１との摩擦係数μ１を大きくすることによって、安定した紙搬送を行うことができ、通紙不良が少なくなる。
【００６９】
本実施例では摩擦係数μ２が０．１、加圧力ｐが１４００ｇｆ、搬送力Ｍｐが１００ｇｆであり、このとき摩擦係数μ１は０．１７以上必要となる。また、摩擦係数μ２が０．１、加圧力ｐが１０００ｇｆ、搬送力Ｍｐが１００ｇｆであり、このとき摩擦係数μ１は０．２以上必要となる。さらに、摩擦係数μ２が０．１の場合は、摩擦係数μ１は０．２５以上必要となる。従って、耐熱性シート材５４は摩擦係数μ２が小さい材料が良く、加圧力ｐは大きいほうが良いことになる。しかし、加圧力ｐが大きすぎると、摩擦トルクが大きくなり、装置全体としてコストアップにつながる。
【００７０】
次に、（ｂ）１００％黒ベタ印字紙通紙の場合は、
μＣ（ｔ１・ｍ）・ｐ＞μｓ（ｔ２・ｍ）・ｐ＋Ｍｐ ・・・（２）
Ｆ２・Ｆ２′＞Ｆ３＞Ｆ１ ・・・（３）
μＣ：定着ローラ５２のコート材と用紙１との間の摩擦係数
μＳ：耐熱性シート５４材と用紙１との間の摩擦係数
ｐ：用紙１に加えられる加圧力
Ｍｐ：用紙１の抵抗力と搬送力
Ｆ１：コート材と表面張力（耐離型性）
Ｆ２：定着ローラ５２側の用紙１とトナーとの表面張力（耐離型性）
Ｆ２′：耐熱性シート５４側の用紙１とトナーとの表面張力（耐離型性）
Ｆ３：シート材とトナーとの表面張力（耐離型性）
上記（２）、（３）の関係を同時に満足していなければならない。但し、上記白紙通紙の場合と同様に、摩擦係数μＣ・μＳ、表面張力Ｆ１・Ｆ２・Ｆ２′・Ｆ３は、それぞれ温度及び材料によって決まる。
【００７１】
ところで、トナーの流動性は温度によって変化し、温度が高いと他物質との表面張力及び摩擦係数は大きくなる。従って、１００％黒ベタ印字紙通紙の場合は、白紙の場合より条件が厳しくなる。つまり、μＳ＞μ２となり、白紙の場合より摩擦係数μＳ、即ち、紙搬送力Ｍｐの大きいコート材が必要となる。
【００７２】
次に、上記構成により通紙試験を行ったときの通紙状態の評価を行った。このとき、黒トナー濃度１．４の両面黒ベタ紙（定着面：未定着黒ベタ、シート面：定着黒ベタ）を用いた。定着ローラ５２の離型性、耐熱性及び搬送性を兼ねたものであり、その搬送力が１７０ｇｆ、２５０ｇｆ、３００ｇｆ、５００ｇｆ、１５００ｇｆの５種類のものを使用した。また、通紙は通紙間隔が３秒であるマルチプリント（非通紙状態の３秒間は１４０度の温度調節）と通紙間隔が６０秒であるシングルマルチプリント（非通紙状態の６０秒間は温調オフ）とで行い、それぞれ通紙速度２５ｍｍ／ｓｅｃで行った。この結果を表２に示す。
【００７３】
【表２】

【００７４】
この結果、紙搬送力が３００ｇｆ、５００ｇｆ、１５００ｇｆのとき、マルチプリント及びシングルマルチプリントの通紙性は良好であった。さらに、本定着装置のライフである６０Ｋ相当時間を定着ローラ温度１４０度で空回転（耐熱性シートとは摩擦）を行った。即ち、本実施例に用いたレーザービームプリンタは４枚／ｍｉｎプリントであるので、１５００ｍｉｎ（２５０ｈｏｕｒ）を、通紙なしでローラ表面温度１４０度で回転続けたところ、紙搬送力が約１０％低下した。この理由は、定着ローラ５２と耐熱性シート５４（本実施例ではＰＴＦＥ）との摩擦及びＰＴＦＥシート５４から定着ローラ５２のコート層側にＰＴＦＥが移行するという２つの大きな理由が考えられる。
【００７５】
これにより、定着ローラ５２に持たせる紙搬送力として３００ｇｆ以上が望ましい。この結果、最低紙搬送力を決定することでどのような種類の用紙に対しても通紙不良を起こすことなく、安定した通紙を行うことができる。また、上記最低紙搬送力に近い値を紙搬送力とすることで、トナーとの離型性が良好な定着ローラ５２を得ることができる。従って、紙搬送力は約３５０ｇｆが最適値である。
【００７６】
以上の説明においては、定着ローラ５２の長手方向、つまり回転軸方向においてほぼ均一に加熱されている場合において耐熱性シート５４が膨張し、耐熱性シート５４に設けたスリット幅；ΔＬがゼロになることで、耐熱性シート５４の歪み等による波打ちや、反り等を緩和（吸収）し、これらの影響をなくしている。これにより、定着ローラ５２に圧接される耐熱性シート５４とのニップ幅を所定の値に維持でき、定着状態を良好に行える。
【００７７】
しかし、耐熱性シート５４の材質や、その製法において、定着ローラ５２の回転軸方向での温度分布が均一であっても、スリット５４ａ等を設けても、熱膨張によりスリット幅；ΔＬがゼロにならない場合や、部分的な波打ちや反り等が発生し、定着ローラ５２に耐熱性シート５４が均一なニップ幅にて圧接しなくなることがある。
【００７８】
また、定着ローラ５２においても、回転軸方向に全域において均一な温度分布になることはなく、多少の温度差が生じており、これにより上述したような耐熱性シート５４による部分的な波打ちや反りが生じることとなる。
【００７９】
耐熱性シート５４の製法の一例を示せば、耐熱性に優れた合成樹脂材料、例えばポリイミド（ＰＩ）をベースに離型性及び耐熱性の良好な合成樹脂、例えばＰＦＡ（四フッ素化エチレン＝パーフロロアルクルビニールエーテル共重合樹脂）や、ＲＴＦＥ（四フッ素化エチレン樹脂）等のフッ素樹脂を混ぜた合成樹脂にて作成している。
【００８０】
そこで、上述した合成樹脂材料をまず円柱形状に形成した後、桂剥きにしてロール状態にシート形状に形成する。この場合、桂剥きにしたロール形状のシートはどうしても巻癖が生じるため、そのままでは耐熱性シート５４として利用できない。
【００８１】
そのため、巻癖が生じたロール形状のシートをフラット形状にするために加熱ローラで均一に張力を加えながら圧延させる。そしてシート材の内部の残留応力を除去するために熱処理される。例えば、３００℃以上の雰囲気中で５時間放置される。
【００８２】
こうしてフラット形状になった源反シートに対して耐熱性シート５４を作成するために金型等で打ち抜き所定の形状の耐熱性シート５４が作成される。例えば本実施形態においては、図１３に示すとおり長さ２３１ｍｍ、幅１４ｍｍ、厚さ０．３ｍｍの耐熱性シート５４を作成し、スリットを設けることなく切り目５４ｂを、ピッチ；Ｐを１．４１ｍｍ、切り目の長さ；ｄを８ｍｍに形成した。ここで、本発明による切れ目５４ｂは、スリット５４ａとは別に、そのスリット幅を有しないものであり、単に切り筋が形成されるものである。
【００８３】
上述のように作成した耐熱性シート５４の場合、温度膨張係数が安定しない。そのため、定着ローラ５２の回転軸方向の温度分布が一定であっても、シート５４の熱膨張が一定しなくなり、部分的に波打ち等が生じる。また、定着時にシート５４に加えられる熱は均一ではなくスリットをもうけた場合のスリット幅；ΔＬ、スリット間隔；Ｌは材料の製造ロットによってその最適値が変動する場合がある。そのため、スリットを設ける場合に定着時（高温時）にスリット幅；ΔＬが完全なゼロにならない場合がある。そのため、その部分で定着ムラが発生する。
【００８４】
この点、図１３の上述した切れ目５４ｂを所定のピッチで形成した耐熱性シート５４では高温時、つまり、定着ローラ５２にて定着を行える状態において、図１４に示すように耐熱性シート５４が長手方向、つまり定着ローラ５２の回転軸方向に膨張するが、それと直交する方向への熱膨張はなく、部分的な波打ちや反り等がなく、当初のニップ幅；ｎ（本実施形態においては１．５ｍｍ）の変化がみられなかった。つまり、上述した耐熱性シート５４においては、切れ目５４ｂを所定のピッチで形成した場合に、定着ローラ５２が加熱され定着状態においても最適なニップ幅；ｎを確保でき、定着を常時安定させることができる。
【００８５】
下記表３には耐熱性シート５４に形成する切り目５４ｂのピッチ；Ｐを変えて加工した結果を示している。つまり、切り目５４ｂのピッチ；Ｐを短くすると、熱膨張等を緩和する効果が高まる一方、加工ムラが生じる。これはシート５４の厚さにより変化する。この加工ムラは切り目５４ｂを形成する時に、隣接して形成された切り目５４ｂに影響され歪んだり、一定幅のピッチにならないムラ等である。また、切り目５４ｂのピッチ；Ｐが長くなると、熱膨張等を緩和できずにピッチに応じて定着ムラが発生する。
【００８６】
【表３】

【００８７】
また、耐熱性シート５４の厚さが０．３ｍｍにおいて、切り目５４ｂを加工した場合において、シート厚さの２倍以下のピッチでは均一な切り目５４ｂの加工が困難となる。また、１０倍を越える場合では切り目５４ｂのピッチ；Ｐで定着の光沢ムラが生じ定着後には見苦しい画像となる。
【００８８】
以上のことから、切り目５４ｂは、そのピッチ；Ｐを短くすることで、定着ローラ５２による熱にて耐熱性シート５４が膨張する時に、シートの波打ちやうねり、あるいは反り等の影響を受けることなく、定着ローラ５２に所定のニップ幅を維持して、安定した定着を行える。
【００８９】
一方、切り目５４ｂのピッチ；Ｐにおいては、短くすると切れ目の加工ムラが発生し、これによる定着ムラが発生する。そのため、耐熱性シート５４の厚さの２倍以上に設定することで、加工ムラをなくし、安定した定着を可能にしている。しかも、耐熱性シート５４の厚さの１０倍以下のピッチ；Ｐによる切り目５４ｂを形成することで、定着ムラを解消できる。
【００９０】
よって、耐熱性シート５４の温度膨張係数が安定しない場合においては、上述したように定着装置を構成する耐熱性シート５４にスリットを設けずに切り目５４ｂを所定ピッチで設けることで、熱膨張等による耐熱性シート５４の波打ち等をなくし、安定した定着を可能にしている。
【００９１】
続いて、耐熱性シート５４は、上述したロール形状に形成した後、フラット形状のシートにする源反の製造工程で、シートの長手方向に張力が加えられる。例えば図１５に示すように矢印方向に張力を加えられたシートは、その両端部には中央部とは異なる図示する残留応力を残す。この残留応力を除去するための熱処理が施されても完全に除去できるものではない。そのため、定着装置を構成する耐熱性シート５４をその部分において作成すれば、定着加熱や定着加圧時に、その耐熱性シート５４はその応力を緩和する方向に形状を変形しようとする。そのため、耐熱性シート５４が大きく変形し、定着不良が生じることになる。
【００９２】
特に図１５に示すシート源反に対し、図１６（ａ）に示すように横方向に打ち抜き耐熱性シート５４を作成した場合、長手方向の両端部は定着ローラ５２による定着加熱、定着加圧により伸びることによって応力を緩和できる。中央部はそのようなことはなく伸びない。この差はスリット５４ａや切り目５４ｂを形成した耐熱性シートに対し、その幅やピッチの寸法不安定の原因となる。
【００９３】
常温で打ち抜き加工された耐熱性シート５４のスリット幅；ΔＬや切り目は、定着加熱、定着加圧により中央と両端部でその寸法が変化してしまう。これにより波打ちやうねり、さらに反り等として部分的に生じ、定着ローラ５２への耐熱性シート５４の接触状態が安定せず、ニップ幅等が不安定になり、定着不良を生じる。
【００９４】
これを解決するためには製品寸法に対し十分に長い幅の源反シートを作成し、その両端部を使用しないという方法がある。例えば、長手方向において２３１ｍｍの耐熱性シート５４を作成する場合、図１６（ａ）に示すように約３００ｍｍ幅のシートを作成する必要がある。そのためには、まず高さ３００ｍｍの円柱状の上述した合成樹脂材料を作成する必要があり、これが製造上かなり困難となる。また、両端部約３５ｍｍ、合計で約７０ｍｍの部分は、製品化されず廃棄となるため耐熱性シートを作成する時のコストアップの要因ともなる。
【００９５】
そこで、シート源反に対し、図１６（ｂ）に示すように縦方向に打ち抜いて耐熱性シート５４を作成した場合、定着加熱、定着加圧により耐熱性シートは縮むことにより残留応力を緩和する。その縮みは、耐熱性シートの長手方向に均一でありスリット５４ａ、切り目５４ｂの寸法変化が出たとしてもそれは均等になる。また、高さ１５０ｍｍの円柱の合成樹脂材料であっても、十分に２４０ｍｍを越える耐熱性シート５４を作成することができる。これにより、定着装置を構成する耐熱性シート５４の作成するコストが低減する。
【００９６】
このようにして作成された耐熱性シート５４を用いて定着装置を構成した場合、５００枚〜１０００枚の連続印刷を行うと耐熱性シート５４は、長時間定着ローラ５２による熱にて高温状態にさらされる。しかもその温度は一定ではなく、定着を行う通紙中には用紙１を介して定着ローラ５２の熱を受け紙間では定着ローラ５２から直に熱を受ける。また加圧部、いわゆる定着ローラ５２と耐熱性シート５４とが接触するニップ部は、紙間で直に定着ローラ５２に加圧されるが、ニップ部以外は定着ローラ５２からの熱が伝わりにくい。
【００９７】
この熱ストレスの不均一さが耐熱性シート５４の反りや歪み、波打ちの発生原因となる。耐熱性シート５４の通紙上流側は、フレームに粘着性材料で固定されており、シートの反り、歪み、波打ちは発生しにくい。シートの通紙下流側は不均一な熱ストレスの影響を受けやすくシートの波打ちが発生しやすい。波打ちが発生した場合、その波打ち形状がニップ部まで達していると定着圧が不均一となり定着不良が生じる。
【００９８】
このような不具合をなくすために、本発明においては耐熱性シート５４に切り目５４ｂを形成し、この切り目５４ｂにて緩和するようにしている。そこで、この切り目５４ｂの長さ、つまり用紙１を搬送する方向の長さについての実験結果を下記表４に示した。特に、切り目５４ｂは、短いと熱等による膨張による影響を十分に緩和できずに、定着不良が生じる結果となった。
【００９９】
【表４】

【０１００】
これに対して、切り目５４ｂを十分に長く形成すれば、熱による膨張を吸収して、耐熱性シート５４の波打ち等による症状が解消され、安定した定着が可能となる。
【０１０１】
そこで、耐熱性シート５４に形成される切り目５４ｂと、該耐熱性シート５４が定着ローラ５２に接触するニップ幅（＝約１．５ｍｍ）との関係について示した結果が上記表４である。この結果から切り目５４ｂの中央部に定着ローラ５４を当接させた場合において、切り目５４ｂの長さは、ニップ幅の２倍以上の時に良好な定着結果が得られた。
【０１０２】
なお、耐熱性シート５４は、用紙１の搬送方向の長さ（幅）が、本実施例においては１４ｍｍであれば、それ以上の長さにはならない。しかも、耐熱性シート５４の一端がフレーム等に固着されるため、切れ目５４ｂは少なくとも１０ｍｍ以下に設定する必要がある。これは、耐熱性シート５４の幅に応じて決めればよいことである。
【０１０３】
また、上述した耐熱性シート５４に設ける切り目５４ｂについては、用紙１の搬送方向に平行に形成しているが、多少傾斜するように形成してもよい。さらに、上述した切り目５４ｂの長さは図１２に示した切り目５４ｂにおいても適用すれば、好適な結果を得ることができる。
【０１０４】
【発明の効果】
請求項１記載の発明によれば、定着ローラと加圧部材との間にスリットを有した耐熱性シートを設け、前記定着ローラと耐熱性シートとの間に前記記録材を搬送させる構成である。
【０１０５】
これにより、定着ローラによって、高温に加熱されても耐熱性シートの膨張による撓みや歪みを吸収することができるので、用紙搬送トルクを増大させることなく、耐熱性シートの確実な歪み補正が行え、良好な定着を行うことができる。また、加圧部材には定着ローラの回転によるせん断力は作用しない。それゆえ、加圧部材は変形することがなく、耐久性が向上する。さらに加圧部材にはせん断力が働かないので、加圧部材を固定するための接着面積を考慮する必要がない。従って、加圧部材は必要最低限の大きさにすることができるので、装置の小型化が可能となり、コストの低減につながる。
【０１０６】
請求項２記載の発明によれば、耐熱性シートのスリットは記録材の搬送方向に対し傾斜しているので、加圧部材によって加圧されても、加圧効果を損なうことなく、トナーの定着性を向上させることができる。
【０１０７】
また、スリットと用紙搬送の摩擦力を分散することができる。それゆえ、加圧部材は変形することがなく、耐久性が向上し、用紙搬送に大きなトルクを必要としない。従って、モータや電源の小型化が可能となりコスト及び消費電力の低減につながる。
【０１０８】
結局、耐熱性シートの反りを防止することができ、用紙搬送トルクを増大させることなく、耐熱性シートの確実な歪み補正が行え、良好な定着を行うことができる。
【０１０９】
請求項３記載の発明によれば、耐熱性シートに設けられたスリットの長手方向に対し、中央部に定着ローラを当接することによって、温度の安定性が良くなり、スリット幅、スリット間隔の設定が確実に行える。
【０１１０】
すなわち、耐熱性シートの疲労を軽減でき、耐熱性シートの表面温度を均一に維持することが可能であり、耐熱性シートの反りを防止することができ、用紙搬送トルクを増大させることなく、耐熱性シートの確実な歪み補正が行え、良好な定着を行うことができる。
【０１１１】
請求項４記載の発明によれば、耐熱性シートのスリット間にスリットと平行に切り目を設けたことにより、切り目が耐熱性シートの撓みや歪みを吸収することによって、スリット幅、スリットの間隔設定が容易に行える。
【０１１２】
すなわち、耐熱性シートの疲労を軽減でき、耐熱性シートの表面温度を均一に維持することが可能であり、良好な定着を行うことができる。
【０１１３】
また本発明の定着装置によれば、特に耐熱性シートに所定のピッチで切り目を設けることでも十分に耐熱性シートの熱による膨張を緩和し、安定した定着を行える。
【図面の簡単な説明】
【図１】本発明に係る定着装置の説明図である。
【図２】上記定着装置が適用されるレーザービームプリンタの概略構成図である。
【図３】紙搬送力の測定方法を示す斜視図である。
【図４】（ａ）上記定着装置における定着ローラの紙搬送力の測定状態で、用紙が白紙の場合を示す説明図である。
（ｂ）上記定着装置における定着ローラの紙搬送力の測定状態で、用紙が１００％黒ベタ印字の場合を示す説明図である。
【図５】本発明の耐熱性シートの正面図である。
【図６】上記耐熱性シートを定着の設定温度に加熱した状態の正面図である。
【図７】上記耐熱性シートの設けたスリットを傾斜させたものである。
【図８】上記耐熱性シートに当接する定着ローラの当接部を示したものである。
【図９】上記耐熱性シートに当接する定着ローラの当接部とニップを示したものである。
【図１０】上記耐熱性シートのスリットの形状を略三角形状にしたものである。
【図１１】上記耐熱性シートのスリットの形状を略三角形状にしたものである。
【図１２】上記耐熱性シートのスリット間に切り目を設けたものである。
【図１３】本発明の他の実施形態による耐熱性シートを示す平面図である。
【図１４】図１３による耐熱性シートの熱等による膨張状態を示す平面図である。
【図１５】本発明にかかる耐熱性シートを作成する過程において残留する応力状態を示す図である。
【図１６】形成したフラット状態の源反シートに対して、耐熱性シートを作成する状態を示すものであって、（ａ）は源反シートに対して横抜きに打ち抜く状態を示した平面図、（ｂ）は本発明による源反シートに対して縦抜きに打ち抜く状態を示した平面図である。
【図１７】従来の加圧パッド方式の定着装置の構造図である。
【図１８】従来の加圧シート方式の定着装置の構造図である。
【図１９】従来の加圧パッド方式に耐熱シートを用いた定着装置の構造図である。
【図２０】（ａ）像ながれのない画像を表す図である。
（ｂ）像ながれのある画像を表す図である。
【符号の説明】
１ 用紙
２ 未定着トナー像
３ 定着像
１０ 給紙部
１１ 給紙トレイ
１２ 給紙ローラ
１３ 用紙分離摩擦板
１４ 加圧バネ
１５ 用紙検知アクチュエータ
１６ 用紙検知センサー
１７ 制御回路
２０ 画像形成装置
２１ 感光体
２２ 転写ローラ
２３ 帯電部材
２４ 現像ローラ
２５ 現像ユニット
２６ クリーニングユニット
３０ レーザー走査部
３１ レーザーダイオード発光ユニット
３２ 走査ミラー
３３ 走査ミラーモータ
３４ レーザー光
３５・３６・３７ 反射ミラー
４１・４２ 用紙搬送ローラ
５０ 定着装置
５１ 加圧部材
５２ 定着ローラ
５３ 下フレーム
５４ 耐熱シート
５４ａ スリット
５４ｂ 切れ目
５５ ヒーターランプ
５６ Ｌ曲げ板金
５７ 定着前ガイド
６０ 軸受け
６１ 上フレーム
６２ 定着ガイド
６３ バネばかり
１０１ 用紙
１０２ 未定着トナー像
１１１ 押圧部材
１１２ 定着ローラ
１１２ａ 中空ローラ
１１２ｂ 被覆層
１１３ 下フレーム
１１４ 被覆層
１１６ 加圧板
１１７ 軸
１１８ 加圧スプリング
１２１ 圧力ウエブ部材
１２２ 定着ローラ
１２２ａ 中空ローラ
１２２ｂ 被覆層
１２３ フレーム
１２８ コイルスプリング[0001]
[Industrial application fields]
The present invention relates to a fixing device used in an apparatus using an electrophotographic process, such as an electrophotographic copying machine, the same printer, and the same facsimile.
[0002]
[Prior art]
Conventionally, a fixing device used in an apparatus using an electrophotographic process, such as an electrophotographic copying machine, the same printer, and the same facsimile, includes a fixing roller and a pressure roller that is in pressure contact with the fixing roller. A roller system is generally used in which both are heated and a recording material is conveyed and fixed between the pair of rollers.
[0003]
However, in the above roller system, the pair of rollers must be rotated in synchronization. Further, since it is necessary to support the rollers in a freely rotatable manner, the structure becomes complicated, the cost is increased, and the apparatus is increased in size.
[0004]
In order to solve this problem, a pressure pad system is used in which a non-rotating pressing member is pressed against the fixing roller instead of the pressing roller, and a recording material is carried between the fixing roller and the pressing member to perform fixing. This is disclosed in Japanese Patent Publication No. 55-36996.
[0005]
In addition, a pressure sheet system is used in which a pressure web member is brought into pressure contact with the fixing roller at a predetermined winding angle instead of the pressure roller, and a recording material is carried between the fixing roller and the pressure web member for fixing. It is disclosed in Japanese Laid-Open Patent Publication No. 1-344481.
[0006]
Also, a method proposed by the same applicant, in which a heat-resistant sheet is provided between the fixing roller and the pressure member by a pressure pad method, and a recording material is carried between the fixing roller and the heat-resistant sheet for fixing. Japanese Patent Application No. 7-44647 discloses a heat radiating member formed of aluminum foil or the like on the outside of the heat-resistant sheet.
[0007]
An example of a pressure pad type fixing device will be described with reference to FIG. The fixing roller 112 is configured by providing a coating layer 112b having a large friction coefficient such as silicon rubber on the peripheral surface of a hollow roller 112a made of aluminum. A pressing member 111 is provided on the lower surface of the fixing roller 112.
[0008]
Further, the surface facing the fixing roller 112, that is, the pressing surface is constituted by a coating layer 114 made of a material having a small friction coefficient such as tetrafluoroethylene resin. The pressing member 111 is fixed to the upper surface of the pressure plate 116 supported by the shaft 117, and is pressed against the fixing roller 112 by a pressure spring 118 with a predetermined pressure. Then, the sheet 101 having the unfixed toner image 102 is conveyed between the fixing roller 112 and the pressing member 111 to be fixed.
[0009]
An example of a fixing device using a pressure sheet system will be described with reference to FIG. The fixing roller 122 is configured by providing a coating layer 122b having a large friction coefficient such as silicon rubber on the peripheral surface of a hollow roller 122a made of aluminum. One end portion of the pressure web member 121 is locked to the frame 123, and the opposite end portion is stretched with a predetermined tension by a coil spring 128 and is pressed against the fixing roller 122 at a predetermined winding angle α. Then, the sheet 101 having the unfixed toner image 102 is conveyed between the fixing roller 122 and the pressure web 121 to be fixed.
[0010]
An example of a fixing device using a heat-resistant sheet for the pressure pad method will be described with reference to FIG. The fixing roller 112 is coated with a synthetic resin material having good releasability, paper transportability, and heat resistance, for example, heat resistant rubber having a large friction coefficient such as silicon rubber, on the entire outer peripheral surface of a thin aluminum cylinder. Yes. A pressure member 111 is provided on the lower surface of the fixing roller 112.
[0011]
Further, a heat resistant sheet 114 fixed to the lower frame 113 with a heat resistant double-sided tape is inserted between the fixing roller 112 and the pressure member 111. The heat-resistant sheet 114 is a synthetic resin material having good releasability and heat resistance on a glass fiber (100 μm) base material, such as PFA (tetrafluoroethylene = perfluoroalkylene vinyl ether copolymer resin), PTFE (tetrafluoroester). A coating or impregnation (thickness: 100 μm) of a fluorine resin such as an ethylene resin is used. Then, the sheet 101 having the unfixed toner image is conveyed between the fixing roller 112 and the heat resistant sheet 114 and fixed. Further, a metal foil such as aluminum is provided below the heat resistant sheet 114, and the metal foil is bonded to the frame.
[0012]
[Problems to be solved by the invention]
However, in the fixing device using the pressure pad method,
(1) Since the adhesive strength of the covering layer 114 to the pressing member 111 is weak, it is quickly worn and peeled by sliding with the fixing roller 112.
[0013]
(2) At the time of pre-rotation before carrying in the paper 101 or non-passage such as between papers during continuous paper feed, a shearing force acts on the pressing member 111 by the rotation of the fixing roller 112, and the pressing member 111 is deformed. End up.
[0014]
(3) If the bonding area between the pressing member 111 and the pressing plate 116 is increased in order to increase the bonding strength between the pressing member 111 and the pressing plate 116, the pressing member 111 becomes larger and the cost increases.
[0015]
(4) If the hardness of the pressing member 111 is too high, a sufficient nip width cannot be obtained, and uneven fixing tends to occur in the longitudinal direction of the fixing roller 112. On the contrary, if the hardness of the pressing member 111 is too low, permanent deformation is likely to occur.
[0016]
(5) Since the pressing member 111 and the covering layer 114 are fixed to the pressure plate 116, the paper conveyance has to rely on the conveyance force of the fixing roller 112, and it is difficult to carry the paper and the poor paper passing tends to occur. .
[0017]
(6) In order to satisfy both the releasability and the paper conveyance performance which are opposite to each other only with the coating layer 112b coated on the fixing roller 112, a large conveyance force is required, and optimization of the conveyance force is required. Is done.
[0018]
Has the problem.
[0019]
In the fixing device using the pressure sheet method,
(1) In order to obtain a sufficient fixing force (fixing strength), it is necessary to increase the winding angle α of the pressure web member 121 with respect to the fixing roller 122, and the curling of the sheet 101 after fixing becomes large.
[0020]
{Circle around (2)} The pressure distribution in the longitudinal direction of the pressure web member 121 with respect to the fixing roller 122 tends to be non-uniform, and uneven fixing tends to occur.
[0021]
Has the problem.
[0022]
In addition, a fixing device using a heat-resistant sheet as a pressure pad is
(1) Since the heat-resistant synthetic resin is formed on the glass fiber, the thickness is increased, so that an appropriate nip cannot be secured and good fixing cannot be obtained.
[0023]
(2) Due to the above configuration, the glass fiber and the synthetic resin have different expansion coefficients depending on the temperature, so that warping occurs during heating (a heat dissipation device such as a metal stay is required).
[0024]
(3) At the time of pre-rotation before carrying the paper 101 or non-sheet passing such as between sheets during continuous paper passing, a shearing force acts on the pressing member 111 by the rotation of the fixing roller 112, and the pressing member 111 is deformed. End up.
[0025]
(4) If the hardness of the pressing member 111 is too high, a sufficient nip width cannot be obtained, and uneven fixing tends to occur in the longitudinal direction of the fixing roller 112. On the contrary, if the hardness of the pressing member 111 is too low, permanent deformation is likely to occur.
[0026]
(5) In order to satisfy both the releasability and the paper conveyance performance which are opposite to each other only with the coating layer 112b coated on the fixing roller 112, a large conveyance force is required, and optimization of the conveyance force is required. Is done.
[0027]
Has the problem.
[0028]
In addition, as common to the pressure pad method and the pressure sheet method,
(1) When a sheet on which a toner image is recorded on the back side (hereinafter referred to as a back sheet) is fixed during double-sided printing or the like, sliding between the back side of the sheet and the pressing member 111 or the pressure web 121 The toner image on the back side of the paper flows (hereinafter referred to as image flow), and the toner on the back side of the paper and the pressing member 111 or the pressure web 121 are welded to cause jamming.
[0029]
Has the problem.
[0030]
[Means for Solving the Problems]
The fixing device according to claim 1 includes a fixing roller and a pressure member disposed in pressure contact with an outer peripheral surface of the fixing roller, and an unfixed toner image is formed between the fixing roller and the pressure member. In a fixing device for fixing an unfixed toner image on the recording material by conveying the recording material having the recording material, the heat-resistant sheet positioned between the fixing roller and the pressure member and pressed against the fixing roller Of this heat-resistant sheet In contact with the fixing roller , Cuts with no slit width A contact width between the heat-resistant sheet and the fixing roller, which is at least twice the contact width in the conveyance direction of the recording material, Do not reach the end of the heat-resistant sheet , At a predetermined pitch of 2 to 10 times the thickness of the heat-resistant sheet In the fixing device, the recording material is formed and conveyed between the fixing roller and the heat-resistant sheet.
[0031]
The fixing device according to claim 2, A plurality of slits whose slit width becomes zero due to expansion of the heat-resistant sheet when heated by the fixing roller at a predetermined temperature are in contact with the fixing roller of the heat-resistant sheet pressed against the fixing roller, Formed parallel to the cut The fixing device according to claim 1.
[0032]
The fixing device according to claim 3, wherein the fixing roller is in contact with a central portion with respect to a longitudinal direction of a slit provided in the heat resistant sheet. 2 The fixing device described.
[0036]
DETAILED DESCRIPTION OF THE INVENTION
The embodiment of the present invention will be described with reference to FIGS. 1 to 12 and FIG. 20 as follows. The fixing device according to the embodiment of the present invention will be described when applied to a laser printer.
[0037]
As shown in FIG. 2, the laser printer includes a paper feeding unit 10, an image forming apparatus 20, a laser scanning unit 30, and a fixing device 50 of the present invention. The paper feeding unit 10 conveys the paper 1 to the image forming apparatus 20 inside the printer, and the image forming apparatus 20 transfers the toner image onto the conveyed paper 1. The sheet 1 is further conveyed, and the toner is fixed on the sheet by the sheet 1 and the fixing device 50. Thereafter, the paper is discharged out of the printer by the paper transport rollers 41 and 42. That is, the sheet 1 follows the path indicated by the arrow A indicated by the thick line in the drawing.
[0038]
The paper feed unit 10 includes a paper feed tray 11, a paper feed roller 12, a paper separation friction plate 13, a pressure spring 14, a paper detection actuator 15, a paper detection sensor 16, and a control circuit 17.
[0039]
The sheets 1 loaded in the sheet feed tray 11 receive a print command from a host computer (not shown) connected to the outside, and are fed one by one by the action of the sheet feed roller 12, the sheet separation friction plate 13, and the pressure spring 14. Paper is fed and fed sequentially into the printer. For the fed paper 1, the paper detection actuator 15 is tilted and output to the paper detection optical sensor 16 as an electrical signal to instruct the start of image printing. The control circuit 17 activated by the operation of the paper detection actuator 15 sends an image signal to the laser diode light emitting unit 31 of the laser scanning unit 30 to control lighting / non-lighting of the light emitting diode.
[0040]
The laser scanning unit 30 includes the laser diode light emitting unit 31, a scanning mirror 32, a scanning mirror motor 33, and reflection mirrors 35, 36, and 37.
[0041]
The scanning mirror 32 is rotated at a high speed and a constant speed by a scanning mirror motor 33. That is, in FIG. 2, the laser beam 34 scans in a direction perpendicular to the paper surface. The laser beam 34 irradiated from the laser diode light emitting unit 31 is irradiated to the photoconductor 21 described later via the reflection mirrors 35, 36, and 37. At this time, the laser beam 34 is selectively exposed on the photosensitive member 21 based on the lighting / non-lighting information from the control circuit 17.
[0042]
The image forming apparatus 20 includes a photoreceptor 21, a transfer roller 22, a charging member 23, a developing roller 24, a developing unit 25, and a cleaning unit 26. By exposing the surface of the photosensitive member charged to a predetermined potential by the charging member 23 in advance by the laser beam 34, the surface potential of the photosensitive member is selectively discharged to form an electrostatic latent image. The toner used for development is accumulated in the development unit 25. The toner to which electric charge is given by appropriate stirring in the developing unit 25 adheres to the surface of the developing roller 24, and electrostatic latent potential is generated by the action of the developing bias voltage applied to the developing roller 24 and the electric field generated by the photoreceptor surface potential. A toner image corresponding to the image can be formed on the photoreceptor 21.
[0043]
The sheet 1 conveyed from the sheet feeding unit 10 is sent between the photosensitive member 21 and the transfer roller 22. The toner on the photoconductor 21 is electrically attracted and transferred to the paper 1 by the action of an electric field applied by the transfer voltage applied to the transfer roller 22. At this time, the toner on the photosensitive member 21 is transferred to the paper 1 by the transfer roller 22 and the untransferred toner is collected by the cleaning unit 26.
[0044]
Thereafter, the sheet 1 is conveyed to the fixing device 50. Therefore, temperature and pressure are applied by the pressure member 51 and the fixing roller 52 maintained at 170 ° C. Then, the toner dissolves on the paper 1 and is fixed to the paper 1 to form a wall image. The sheet 1 is transported by the sheet transport rollers 41 and 42 and discharged outside the apparatus. The fixing device 50 will be described in detail below.
[0045]
As shown in FIG. 1, the fixing device 50 includes a pressing member 51, a fixing roller 52, and a lower frame 53. The fixing roller 52 is coated with a heat-resistant rubber having a good paper-carrying property such as silicone rubber on the entire outer peripheral surface of a thin-walled aluminum cylindrical body, such as a synthetic resin material having good releasability, paper-carrying property, and heat-resistance. It is a thing. A heater lamp 55 is inserted in the shaft core portion of the fixing roller 52.
[0046]
Near both ends of the fixing roller 52, semicircular bearings 60 (Esvea SS745, manufactured by Starlight Industry Co., Ltd.) are arranged perpendicular to the fixing roller shaft. The bearing 60 is fitted in a fixing cover 59 (Remapet: manufactured by Mitsubishi Yuka Co., Ltd.) made of a heat resistant resin. The fixing cover 59 is configured to be pressurized from the upper frame 61 via a pressure spring having a pressure of 1200 gf.
[0047]
The pressure member 51 is silicon sponge rubber (silicon sponge rubber TL4400: manufactured by Inoac Co., Ltd.) having a thickness of 2 mm, and has an Asker C hardness of about 30 degrees. The pressure member 51 is located between the L-bending sheet metal 56 (SECC: thickness t1) and the outer peripheral surface of the fixing roller 52, and is pressed by the action of the pressure spring 58. The pressing member 51 is fixed on the L-bending sheet metal 56 with a heat-resistant double-sided tape (double-sided tape 5302A: manufactured by Nitto Kogyo Co., Ltd.). Further, the pressing member 51 is fitted into a boss protruding from the lower frame 53 in the vicinity of both end portions of the L-bending sheet metal 56 and is fixed to the lower frame 53.
[0048]
Between the pressure member 51 and the fixing roller 52, a heat-resistant sheet 54, which is fixed to the lower frame 53 with a heat-resistant double-sided tape, is inserted. The heat-resistant sheet 54 is a synthetic resin material having good releasability and heat resistance, such as fluorine resin such as PFA (ethylene tetrafluoride = bar fluorocarbon resin vinyl ether resin), PTFE (tetrafluoroethylene resin), etc. Coating or impregnation (thickness 300 μm). In the present embodiment, a PTA sheet (general coefficient of friction with aluminum of 0.04 to 0.1) provided with a slit 54a is used as the heat resistant sheet 54.
[0049]
In the lower frame 53, the upstream side (side into which the paper 1 is inserted) from the fixing roller 52 is substantially higher than the downstream side by the thickness of the pressure member 51 and the heat-resistant sheet 54. An L-bending sheet metal 56 is fitted into the boundary portion of the height. The upstream side is a pre-fixing guide 57 that guides the loading of the paper 1, and the downstream side is a fixing guide 62 that guides the discharge of the paper 1 that has been fixed.
[0050]
The above configuration is as follows. The sheet 1 with the unfixed toner image 2 moves in the sheet passing direction (arrow B direction), and passes through the nip portion between the fixing roller 52 and the heat resistant sheet 54 by the pre-fixing guide 57. At this time, the unfixed toner image 2 electrostatically adhering to the paper 1 is fixed to the paper 1 by the heat and pressure of the fixing roller 52, and desired characters and drawings are formed. Thereafter, it passes over the fixing guide 62 and is discharged. With such a configuration, final fixing of the electrophotographic process is performed.
[0051]
Next, the heat resistant sheet will be described with reference to FIGS.
[0052]
The heat-resistant sheet 54 is made of the above-described synthetic resin material, such as PFA or PTFE. In this embodiment, the thickness is 300 μm, and the slit width ΔL is 1.2 mm and the slit interval L is 80 mm as shown in FIG. Is adopted. This thickness is determined by the nip width with the fixing roller 52, and the life of the fixing device 60K can be maintained by the strength of the pressure member 51, the hardness of the heat-resistant sheet 54, and the amount of wear due to friction with the fixing roller 54. Is set to In addition, the slit width and the slit interval are set by a set temperature of the fixing roller and a thermal expansion coefficient peculiar to the resin depending on the temperature.
[0053]
In the case of a conventional heat-resistant sheet, the heat-resistant sheet expands due to heating from the fixing roller and the surface is bent or distorted, so that the pressure is not uniform between the fixing roller 54 and the pressure member 51. As a result, satisfactory fixing was not performed, and there was a problem of fixing failure such as image flow (see FIGS. 20A and 20B). In addition, when used for a long period of time, there is a problem that the heat-resistant sheet is bent and distorted by heat and becomes permanent.
[0054]
According to the present invention, the set heat-resistant sheet 54 gradually begins to expand with the temperature rise T of the fixing roller 52 (fixing roller surface temperature−outside air temperature). Further, as the temperature continues to rise, the surface of the heat resistant sheet 54 bends as it expands. Then, when the set temperature of the fixing roller 52 is reached, as shown in FIG. 6, the expanded portion and the surface deflection of the expanded heat-resistant sheet 54 are absorbed by the slit portion 54a due to the pressure difference, and the slit width: ΔL = 0. The expanded portion and the deflection of the heat resistant sheet 54 are all absorbed by the slit 54a. Therefore, the optimum nip width can be ensured while maintaining the pressing force of the pressing member without using a heat radiating device or increasing the thickness of the heat resistant sheet 54. Therefore, good fixing can be performed.
[0055]
FIG. 7 shows the slit 54 a provided in the heat resistant sheet 54 inclined with respect to the paper transport direction. By providing the slit portion 54a with an inclination, even if a fixing failure occurs due to use beyond the life or for some other reason, the fixing failure is not noticeable because it is not on the same line with respect to the paper transport direction. Accordingly, the slit width 54a, the slit interval, and the fixing roller can be easily set. Further, by inclining the slit, it is possible to prevent warping of the end of the slit 54a of the heat-resistant sheet 54, and to prevent an increase in conveyance torque.
[0056]
FIG. 8 shows the fixing roller 52 in contact with the longitudinal center of the slit 54. A contact portion of the fixing roller 52 is indicated by a one-dot chain line. By providing the fixing roller 52 at the center of the slit 54, there is no problem that causes an increase in conveyance torque such as warping of the end of the heat resistant sheet 54. FIG. 9 shows a state in which the fixing roller 52 is heated. The heat conduction (surface temperature) of the entire heat-resistant sheet 54 is uniform, and the slit 54a can reliably absorb expansion and bending due to heat, and the slit width and slit interval can be easily set. Accordingly, it is possible to maintain a stable fixing temperature without increasing the sheet conveyance torque.
[0057]
10 and 11, the shape of the slit 54a of the heat-resistant slit 54 is substantially triangular or quadrangular. By distorting the shape of the slit 54a as described above, it is possible to reliably absorb the expanded portion of the heat-resistant sheet 54 due to heat. Further, fatigue of the heat resistant sheet 54 due to expansion and contraction of the heat resistant sheet can be reduced. Further, fatigue at the cut end of the slit portion can be reduced, and problems such as permanent distortion can be solved. Therefore, it is possible to perform stable fixing throughout the life.
[0058]
In FIG. 12, a plurality of cuts 54 b are provided between the slits 54 a of the heat resistant sheet 54. In the case of a heat-resistant sheet having no cuts 54b, when a thick sheet such as an envelope or a postcard is passed, the sheet part in contact with the end of the sheet is distorted, and fixing failure occurs in that part. Therefore, when a plurality of cuts 54b are provided between the slits, absorption can be performed by the plurality of cuts 54b if the heat-resistant sheet is slightly bent or distorted. Therefore, even when thick paper is passed, the sheet can be prevented from being bent, and reliable fixing can be performed.
[0059]
And the cut provided between the slits of the heat-resistant sheet is provided only in the central portion in the recording material conveyance direction, so that the heat-resistant sheet can be prevented from warping or bending due to the cut. In addition, the surface temperature of the heat resistant sheet is stabilized. Therefore, it is possible to maintain a uniform surface temperature of the heat-resistant sheet without causing a load fluctuation of the fixing roller, and it is possible to prevent the heat-resistant sheet from warping and increase the paper conveyance torque. Therefore, it is possible to surely correct the distortion of the heat-resistant sheet and to perform good fixing.
[0060]
Next, an experiment of fixing property by changing the slit width and the slit interval was performed.
[0061]
In this example, the expansion coefficient of PTFE is 10 × 10. ^-Five When setting was performed at an outside air temperature of 20 ° C. and a fixing roller surface temperature of 170 ° C., the slit width at normal temperature; ΔL was set to 1.2 mm, and the slit interval; L was set to 80 mm. The slit width and slit interval are obtained from the following equations.
[0062]
Δ L = α ・ L ・ T
Δ L: Slit width at room temperature (mm)
α: Expansion coefficient by material (1 / ° C)
L: Slit spacing at room temperature (mm)
T: Temperature rise of heat resistant sheet (° C)
(Fixing roller surface temperature-outside air temperature)
As described above, when the slit width; ΔL is heated by the fixing roller 52 having a surface temperature of 170 degrees at normal temperature, the slit width; ΔL becomes zero, and the fixing is possible. Further, the experiment was performed by changing the slit width; ΔL and the slit interval;
[0063]
[Table 1]

[0064]
From the results in Table 1 above, it can be seen that the optimum slit interval; L is 110 mm or less. If the slit interval; L is set to 120 mm or more, it is theoretically possible to absorb the expansion and deflection of the sheet at the slit portion, but in reality, the expansion is concentrated in a part, and the slit width; It can be understood that the above-described slit interval; L cannot absorb sheet deflection.
[0065]
That is, by making the slit interval of the heat resistant sheet 110 mm or less, it is possible to reliably prevent the heat resistant sheet from being bent. Therefore, it leads to stable fixing.
[0066]
Next, the fixing roller 52 needs a paper conveying force to convey the paper in the paper feeding direction. With respect to this, the paper conveyance force required for two types of (a) white paper passing and (b) 100% black solid printing paper passing will be described with reference to FIG. FIG. 3 is a perspective view showing a method for measuring the paper conveying force of FIG. However, 100% black solid printing paper is solid black with the unfixed toner image 2 on the fixing roller 52 side, and solid black with the fixed image 3 after fixing on the heat resistant sheet 54 side.
[0067]
A blank paper (128 g) is inserted between the fixing roller 52 and the heat resistant sheet 54. The fixing roller 52 is rotated, the temperature of the fixing roller is adjusted to 140 degrees, and the paper 1 is conveyed. At this time, if only the spring 63 attached to the paper 1 is pulled, the conveyance of the paper 1 is stopped while the fixing roller 52 is rotating. Thereafter, when the tension of the spring 63 is gradually weakened, the paper 1 starts to be conveyed again. The value of the spring 63 at the time when the sheet 1 starts to be conveyed again is defined as the sheet conveying force.
[0068]
(A) In the case of blank paper passing, in order to carry paper,
μ1 (t1 · m) · p> (t2 · m) · p + Mp (1)
μ1: Coefficient of friction between the coating material of the fixing roller 52 and the paper 1
μ2: Coefficient of friction between the heat-resistant sheet 54 and the paper 1
p: Pressure applied to paper 1
Mp: Resistance and transport force of paper 1
The relationship must be satisfied. That is, the relationship of μ1> μ2 must be satisfied. However, the friction coefficient μ1 is a coefficient depending on the temperature and material of the coating material. Similarly, the friction coefficient μ2 is a coefficient depending on the temperature and material of the sheet material. That is, by increasing the friction coefficient μ1 between the fixing roller 52 and the paper 1 than the friction coefficient μ2 between the heat-resistant sheet 54 and the paper 1, stable paper conveyance can be performed and sheet passing defects are reduced.
[0069]
In this embodiment, the friction coefficient μ2 is 0.1, the applied pressure p is 1400 gf, and the conveying force Mp is 100 gf. At this time, the friction coefficient μ1 needs to be 0.17 or more. Further, the friction coefficient μ2 is 0.1, the applied pressure p is 1000 gf, and the conveying force Mp is 100 gf. At this time, the friction coefficient μ1 needs to be 0.2 or more. Further, when the friction coefficient μ2 is 0.1, the friction coefficient μ1 needs to be 0.25 or more. Therefore, the heat-resistant sheet material 54 is preferably a material having a small friction coefficient μ2, and the pressure force p is preferably large. However, if the pressure p is too large, the friction torque increases, leading to an increase in the cost of the entire apparatus.
[0070]
Next, in the case of (b) 100% black solid printing paper passing,
μC (t1 · m) · p> μs (t2 · m) · p + Mp (2)
F2 / F2 ′>F3> F1 (3)
μC: Coefficient of friction between the coating material of the fixing roller 52 and the paper 1
μS: Coefficient of friction between the heat-resistant sheet 54 and the paper 1
p: Pressure applied to paper 1
Mp: Resistance and transport force of paper 1
F1: Coating material and surface tension (Release resistance)
F2: Surface tension between the sheet 1 on the fixing roller 52 side and the toner (release resistance)
F2 ′: surface tension between the paper 1 on the heat-resistant sheet 54 side and the toner (release resistance)
F3: Surface tension between sheet material and toner (release resistance)
The above relationships (2) and (3) must be satisfied at the same time. However, the friction coefficient μC · μS and the surface tensions F1, F2, F2 ′, and F3 are determined by the temperature and the material, respectively, as in the case of the above-mentioned blank paper passing.
[0071]
By the way, the fluidity of the toner varies depending on the temperature. When the temperature is high, the surface tension and the coefficient of friction with other substances increase. Therefore, the condition is more severe in the case of passing 100% black solid printing paper than in the case of blank paper. That is, μS> μ2, and a coating material having a larger coefficient of friction μS, that is, a paper conveying force Mp than that of blank paper is required.
[0072]
Next, the paper passing state when the paper passing test was performed with the above-described configuration was evaluated. At this time, double-sided black solid paper having a black toner density of 1.4 (fixed surface: unfixed black solid, sheet surface: fixed black solid) was used. The fixing roller 52 has the releasability, heat resistance, and transportability, and five types of transport forces of 170 gf, 250 gf, 300 gf, 500 gf, and 1500 gf were used. Also, multi-printing with a paper passing interval of 3 seconds (temperature adjustment of 140 degrees for 3 seconds in a non-paper passing state) and single multi-printing with a paper passing interval of 60 seconds (60 seconds in a non-paper passing state). The temperature adjustment was performed at a sheet feeding speed of 25 mm / sec. The results are shown in Table 2.
[0073]
[Table 2]

[0074]
As a result, when the paper conveying force was 300 gf, 500 gf, and 1500 gf, the multi-printing and single multi-printing properties were good. Further, idling rotation (friction with the heat-resistant sheet) was performed at a fixing roller temperature of 140 degrees for a time corresponding to 60K, which is the life of the fixing device. That is, since the laser beam printer used in this example is printing at 4 sheets / min, when the roller surface temperature continues to rotate for 1500 min (250 hours) at a roller surface temperature of 140 degrees, the paper conveying force is reduced by about 10%. did. There are two main reasons for this: friction between the fixing roller 52 and the heat-resistant sheet 54 (PTFE in this embodiment) and PTFE moving from the PTFE sheet 54 to the coating layer side of the fixing roller 52.
[0075]
Accordingly, it is desirable that the paper conveyance force provided to the fixing roller 52 is 300 gf or more. As a result, by determining the minimum paper conveyance force, it is possible to perform stable paper feeding without causing poor paper feeding on any type of paper. In addition, by setting the paper conveyance force to a value close to the minimum paper conveyance force, it is possible to obtain the fixing roller 52 with good releasability from the toner. Accordingly, the optimum value for the paper conveying force is about 350 gf.
[0076]
In the above description, when the fixing roller 52 is heated substantially uniformly in the longitudinal direction, that is, in the rotation axis direction, the heat resistant sheet 54 expands and the slit width provided in the heat resistant sheet 54; ΔL becomes zero. As a result, undulations and warpage caused by distortion of the heat-resistant sheet 54 are alleviated (absorbed), and these effects are eliminated. Thereby, the nip width with the heat resistant sheet 54 pressed against the fixing roller 52 can be maintained at a predetermined value, and the fixing state can be satisfactorily performed.
[0077]
However, in the material of the heat-resistant sheet 54 and its manufacturing method, even if the temperature distribution in the direction of the rotation axis of the fixing roller 52 is uniform or the slit 54a is provided, the slit width; ΔL becomes zero due to thermal expansion. Otherwise, partial undulation or warping may occur, and the heat-resistant sheet 54 may not come into pressure contact with the fixing roller 52 with a uniform nip width.
[0078]
Also, the fixing roller 52 does not have a uniform temperature distribution in the entire region in the direction of the rotation axis, and a slight temperature difference is generated, which causes partial waving and warping by the heat-resistant sheet 54 as described above. Will occur.
[0079]
If an example of the manufacturing method of the heat resistant sheet 54 is shown, the heat resistance Excellent Synthetic resin materials such as polyimide (PI) as a base and good release properties and heat resistance such as PFA (tetrafluorinated ethylene = perfluoroalkyl vinyl ether copolymer resin) and RTFE (tetrafluorinated ethylene resin) ) Synthetic resin mixed with fluororesin In Have created.
[0080]
Therefore, the above-described synthetic resin material is first formed into a cylindrical shape, and then peeled off from the katsura to form a sheet in a roll state. In this case, the roll-shaped sheet stripped with katsura cannot be used as the heat-resistant sheet 54 as it is because the curl is inevitably generated.
[0081]
Therefore, in order to make a roll-shaped sheet with curled wrinkles into a flat shape, it is rolled while uniformly applying tension with a heating roller. And it heat-processes in order to remove the residual stress inside a sheet | seat material. For example, it is left for 5 hours in an atmosphere of 300 ° C. or higher.
[0082]
A heat-resistant sheet 54 having a predetermined shape is punched out with a mold or the like in order to create the heat-resistant sheet 54 with respect to the source sheet having a flat shape. For example, in this embodiment, FIG. A heat resistant sheet 54 having a length of 231 mm, a width of 14 mm, and a thickness of 0.3 mm is prepared as shown in FIG. 5B, the slit 54b is formed without any slit, the pitch; P is 1.41 mm, the length of the cut; d is 8 mm. Formed. Here, apart from the slit 54a, the cut 54b according to the present invention does not have the slit width, and a cut line is simply formed.
[0083]
In the case of the heat resistant sheet 54 prepared as described above, the temperature expansion coefficient is not stable. For this reason, even if the temperature distribution in the rotation axis direction of the fixing roller 52 is constant, the thermal expansion of the sheet 54 does not become constant, and undulation or the like partially occurs. Further, the heat applied to the sheet 54 at the time of fixing is not uniform, and the optimum value of the slit width; ΔL, slit interval; L varies depending on the production lot of the material. Therefore, when a slit is provided, the slit width; ΔL may not be completely zero at the time of fixing (at high temperature). Therefore, uneven fixing occurs at that portion.
[0084]
This point, FIG. In the heat-resistant sheet 54 in which the above-described cuts 54b are formed at a predetermined pitch, at a high temperature, that is, in a state where the fixing roller 52 can perform fixing, FIG. As shown in FIG. 2, the heat-resistant sheet 54 expands in the longitudinal direction, that is, in the direction of the rotation axis of the fixing roller 52, but there is no thermal expansion in the direction orthogonal thereto, there is no partial undulation or warping, and the initial nip width. N ( Book In the embodiment, no change of 1.5 mm) was observed. That is, in the above-described heat-resistant sheet 54, when the cuts 54b are formed at a predetermined pitch, the fixing roller 52 is heated so that an optimum nip width n can be secured even in a fixing state, and fixing can be always stabilized. it can.
[0085]
Table 3 below shows the results of processing by changing the pitch P of the notches 54b formed in the heat resistant sheet 54. That is, turn off R When the pitch of the eyes 54b; P is shortened, the effect of alleviating thermal expansion and the like is enhanced, while processing unevenness occurs. This varies depending on the thickness of the sheet 54. This processing unevenness is cut off R When forming the eye 54b, the cut formed adjacently. R It is affected by the eyes 54b and is distorted or unevenness that does not become a constant pitch. Also, turn off R When the pitch of the eyes 54b; P becomes longer, the thermal expansion or the like cannot be relaxed, and fixing unevenness occurs according to the pitch.
[0086]
[Table 3]

[0087]
When the heat-resistant sheet 54 has a thickness of 0.3 mm, R When the stitches 54b are machined, a uniform cut is obtained at a pitch less than twice the sheet thickness. R It becomes difficult to process the eyes 54b. In addition, when it exceeds 10 times, the pitch 54b of the cuts 54b causes uneven gloss of the fixing, resulting in an unsightly image after fixing.
[0088]
From the above, turn off R By reducing the pitch P, the eyes 54b are not affected by the undulation, undulation, or warp of the sheet when the heat-resistant sheet 54 is expanded by heat from the fixing roller 52. Stable fixing can be performed while maintaining a predetermined nip width.
[0089]
On the other hand R If the pitch of the eyes 54b; P is shortened, uneven machining of the cut occurs. Shi As a result, uneven fixing occurs. Therefore, by setting the thickness of the heat-resistant sheet 54 to be twice or more, the processing unevenness is eliminated and stable fixing is possible. Moreover, the thickness of the heat-resistant sheet 54 is 10%. Double The following pitch; cut by P R By forming the eyes 54b, fixing unevenness can be eliminated.
[0090]
Therefore, when the thermal expansion coefficient of the heat resistant sheet 54 is not stable, the heat resistant sheet 54 constituting the fixing device is cut without providing a slit as described above. R Providing the eyes 54b at a predetermined pitch eliminates undulation of the heat-resistant sheet 54 due to thermal expansion or the like, and enables stable fixing.
[0091]
Subsequently, the heat-resistant sheet 54 is formed into the above-described roll shape, and then a flat sheet. In Tension is applied in the longitudinal direction of the sheet in the manufacturing process of the source fabric. For example, as shown in FIG. 15, a sheet applied with tension in the direction of the arrow leaves a residual stress in the figure different from the central portion at both ends. Even if heat treatment for removing this residual stress is performed, it cannot be completely removed. Therefore, if the heat-resistant sheet 54 constituting the fixing device is formed in that portion, the heat-resistant sheet 54 tends to change its shape in a direction to relieve the stress at the time of fixing heating or fixing pressure. For this reason, the heat resistant sheet 54 is greatly deformed and fixing failure occurs.
[0092]
In particular, when the heat resistant sheet 54 is punched in the lateral direction as shown in FIG. 16A against the sheet source shown in FIG. 15, both end portions in the longitudinal direction are heated by fixing heat and fixing pressure by the fixing roller 52. Stress can be relieved by stretching. The central part is not like that and does not stretch. This difference causes dimensional instability of the width and pitch of the heat-resistant sheet in which the slits 54a and the cuts 54b are formed.
[0093]
The slit width; ΔL and cuts of the heat-resistant sheet 54 punched at room temperature change in dimensions at the center and both ends due to fixing heating and fixing pressure. As a result, undulations, undulations, warping, and the like occur in part, the contact state of the heat resistant sheet 54 to the fixing roller 52 is not stable, the nip width becomes unstable, and fixing failure occurs.
[0094]
In order to solve this, there is a method in which a source sheet having a sufficiently long width with respect to the product dimensions is prepared and both end portions thereof are not used. For example, when creating a heat resistant sheet 54 having a length of 231 mm in the longitudinal direction, it is necessary to create a sheet having a width of about 300 mm as shown in FIG. For that purpose, it is necessary to first produce the above-described synthetic resin material having a columnar shape with a height of 300 mm, which is considerably difficult in production. In addition, both end portions of about 35 mm, which is about 70 mm in total, are discarded without being commercialized, which causes a cost increase when producing a heat-resistant sheet.
[0095]
Therefore, when the heat resistant sheet 54 is formed by punching in the longitudinal direction with respect to the sheet source, as shown in FIG. 16B, the heat resistant sheet shrinks due to fixing heating and fixing pressure, thereby relieving the residual stress. . The shrinkage is uniform in the longitudinal direction of the heat-resistant sheet, and the slit 54a, cut 54b Even if there is a dimensional change, it will be equal. Further, even with a cylindrical synthetic resin material having a height of 150 mm, the heat-resistant sheet 54 sufficiently exceeding 240 mm can be produced. Thereby, the cost for producing the heat resistant sheet 54 constituting the fixing device is reduced.
[0096]
When the fixing device is configured using the heat-resistant sheet 54 thus prepared, the heat-resistant sheet 54 is kept in a high temperature state by heat from the fixing roller 52 for a long time when 500 to 1000 sheets are continuously printed. Exposed. In addition, the temperature is not constant, and the fixing roller 52 receives heat through the sheet 1 during the sheet passing for fixing, and directly receives heat from the fixing roller 52 between the sheets. In addition, a pressurizing portion, that is, a nip portion where the fixing roller 52 and the heat-resistant sheet 54 are in contact with each other is directly pressed by the fixing roller 52 between sheets, but heat from the fixing roller 52 is difficult to be transmitted except in the nip portion. .
[0097]
This non-uniformity of thermal stress causes warpage, distortion, and undulation of the heat-resistant sheet 54. The upstream side of the heat-resistant sheet 54 is fixed to the frame with an adhesive material, and the warp, distortion, and undulation of the sheet are unlikely to occur. The downstream side of the sheet is likely to be affected by uneven thermal stress, and the sheet is likely to corrugate. When undulation occurs, if the undulation shape reaches the nip portion, the fixing pressure becomes non-uniform and fixing failure occurs.
[0098]
In order to eliminate such problems, in the present invention, the heat-resistant sheet 54 is cut. R The eye 54b is formed and this cut R The eye 54b relaxes. So this cut R Table 4 below shows the experimental results regarding the length of the eyes 54b, that is, the length in the direction in which the paper 1 is conveyed. Especially R If the eye 54b is short, the influence of expansion due to heat or the like cannot be sufficiently mitigated, resulting in poor fixing.
[0099]
[Table 4]

[0100]
In contrast, R If the eyes 54b are formed sufficiently long, the expansion due to heat is absorbed, and the symptom due to the waving of the heat-resistant sheet 54 is eliminated, and stable fixing becomes possible.
[0101]
Therefore, the cut formed on the heat-resistant sheet 54 R Table 4 shows the results of the relationship between the eyes 54b and the nip width (= about 1.5 mm) at which the heat-resistant sheet 54 contacts the fixing roller 52. From this result, when the fixing roller 54 was brought into contact with the center of the cut 54b, a good fixing result was obtained when the length of the cut 54b was more than twice the nip width.
[0102]
Note that the heat-resistant sheet 54 does not have a longer length if the length (width) in the conveyance direction of the paper 1 is 14 mm in this embodiment. Moreover, the heat-resistant sheet 54 one end Is fixed to a frame or the like, the cut 54b needs to be set to at least 10 mm or less. This can be determined according to the width of the heat-resistant sheet 54.
[0103]
Also, the cut provided on the heat-resistant sheet 54 described above. R The eyes 54b are formed parallel to the conveyance direction of the paper 1, but may be formed to be slightly inclined. In addition, R The length of the eye 54b is the cut length shown in FIG. R If it is applied to the eye 54b, a favorable result can be obtained.
[0104]
【The invention's effect】
According to the first aspect of the present invention, a heat resistant sheet having a slit is provided between the fixing roller and the pressure member, and the recording material is conveyed between the fixing roller and the heat resistant sheet. .
[0105]
As a result, the fixing roller can absorb the bending and distortion caused by the expansion of the heat-resistant sheet even when heated to a high temperature, so that the distortion of the heat-resistant sheet can be reliably corrected without increasing the paper conveyance torque. Good fixing can be performed. Further, a shearing force due to the rotation of the fixing roller does not act on the pressure member. Therefore, the pressure member is not deformed and the durability is improved. Further, since the shearing force does not act on the pressure member, it is not necessary to consider the bonding area for fixing the pressure member. Therefore, since the pressure member can be made to the minimum necessary size, the apparatus can be miniaturized and the cost can be reduced.
[0106]
According to the second aspect of the present invention, since the slit of the heat resistant sheet is inclined with respect to the recording material conveyance direction, the toner can be fixed without impairing the pressurizing effect even when the pressurizing member is pressed. Can be improved.
[0107]
Further, the frictional force between the slit and the sheet conveyance can be dispersed. Therefore, the pressure member is not deformed, the durability is improved, and a large torque is not required for paper conveyance. Therefore, it is possible to reduce the size of the motor and the power supply, leading to reduction in cost and power consumption.
[0108]
Eventually, the heat-resistant sheet can be prevented from warping, and the distortion of the heat-resistant sheet can be surely corrected without increasing the sheet conveying torque, and good fixing can be performed.
[0109]
According to the third aspect of the invention, the stability of the temperature is improved by contacting the fixing roller at the center with respect to the longitudinal direction of the slit provided in the heat resistant sheet, and the slit width and the slit interval are set. Can be done reliably.
[0110]
That is, the fatigue of the heat-resistant sheet can be reduced, the surface temperature of the heat-resistant sheet can be kept uniform, the warp of the heat-resistant sheet can be prevented, and heat resistance can be increased without increasing the paper conveyance torque. The sheet can be reliably corrected for distortion and can be fixed satisfactorily.
[0111]
According to the invention described in claim 4, the slit width and the slit interval are set by providing the cut between the slits of the heat-resistant sheet in parallel with the slit, and the cut absorbs the deflection and distortion of the heat-resistant sheet. Can be done easily.
[0112]
That is, fatigue of the heat-resistant sheet can be reduced, the surface temperature of the heat-resistant sheet can be kept uniform, and good fixing can be performed.
[0113]
Further, according to the fixing device of the present invention, the heat-resistant sheet is cut at a predetermined pitch. R Providing the eyes sufficiently relaxes the expansion of the heat-resistant sheet due to heat, and enables stable fixing.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a fixing device according to the present invention.
FIG. 2 is a schematic configuration diagram of a laser beam printer to which the fixing device is applied.
FIG. 3 is a perspective view illustrating a method for measuring a paper conveying force.
FIG. 4A is an explanatory diagram illustrating a case where a sheet is a blank sheet in a measurement state of a sheet conveying force of a fixing roller in the fixing device.
FIG. 6B is an explanatory diagram illustrating a case where the paper is 100% black solid printing in a measurement state of the paper conveyance force of the fixing roller in the fixing device.
FIG. 5 is a front view of the heat-resistant sheet of the present invention.
FIG. 6 is a front view showing a state in which the heat-resistant sheet is heated to a preset fixing temperature.
FIG. 7 shows an inclined slit provided with the heat-resistant sheet.
FIG. 8 illustrates a contact portion of a fixing roller that contacts the heat resistant sheet.
FIG. 9 illustrates a contact portion and a nip of a fixing roller that contacts the heat resistant sheet.
FIG. 10 is a diagram in which the slit shape of the heat-resistant sheet is formed into a substantially triangular shape.
FIG. 11 is a view in which the slit shape of the heat-resistant sheet is substantially triangular.
FIG. 12 is a view in which cuts are provided between the slits of the heat-resistant sheet.
FIG. 13 is a plan view showing a heat resistant sheet according to another embodiment of the present invention.
14 is a plan view showing an expanded state of the heat-resistant sheet according to FIG. 13 due to heat or the like. FIG.
FIG. 15 is a diagram showing a residual stress state in the process of producing a heat resistant sheet according to the present invention.
FIG. 16 is a plan view showing a state in which a heat-resistant sheet is prepared with respect to a formed source sheet in a flat state, and FIG. (B) is the top view which showed the state punched out vertically with respect to the source fabric sheet | seat by this invention.
FIG. 17 is a structural diagram of a conventional pressure pad type fixing device.
FIG. 18 is a structural diagram of a conventional pressure sheet type fixing device.
FIG. 19 is a structural diagram of a fixing device using a heat-resistant sheet in a conventional pressure pad method.
FIG. 20A is a diagram illustrating an image without image drift.
(B) It is a figure showing the image with image drift.
[Explanation of symbols]
1 paper
2 Unfixed toner image
3 Fixed image
10 Paper feeder
11 Paper tray
12 Paper feed roller
13 Paper separation friction plate
14 Pressure spring
15 Paper detection actuator
16 Paper detection sensor
17 Control circuit
20 Image forming apparatus
21 photoconductor
22 Transfer roller
23 Charging member
24 Development roller
25 Development unit
26 Cleaning unit
30 Laser scanning unit
31 Laser diode light emitting unit
32 Scanning mirror
33 Scanning mirror motor
34 Laser light
35 ・ 36 ・ 37 Reflection mirror
41.42 Paper transport rollers
50 Fixing device
51 Pressure member
52 Fixing roller
53 Lower frame
54 Heat-resistant sheet
54a slit
54b cut
55 Heater lamp
56 L bent sheet metal
57 Pre-fixing guide
60 bearings
61 Upper frame
62 Fixing Guide
63 Spring only
101 paper
102 Unfixed toner image
111 Pressing member
112 Fixing roller
112a Hollow roller
112b Coating layer
113 Lower frame
114 Coating layer
116 Pressure plate
117 axis
118 Pressure spring
121 Pressure web member
122 Fixing roller
122a Hollow roller
122b coating layer
123 frames
128 coil spring

Claims (3)

A fixing roller and a pressure member disposed in pressure contact with the outer peripheral surface of the fixing roller, and conveying a recording material having an unfixed toner image between the fixing roller and the pressure member; In a fixing device for fixing an unfixed toner image on the recording material,
A heat-resistant sheet positioned between the fixing roller and the pressure member and pressed against the fixing roller is provided, and a cut having no slit width is formed at a contact portion of the heat-resistant sheet with the fixing roller. The contact width between the heat-resistant sheet and the fixing roller is not less than twice the contact width in the conveyance direction of the recording material, and the thickness of the heat-resistant sheet is set so as not to reach the end of the heat-resistant sheet. On the other hand, the fixing device is formed at a predetermined pitch of 2 times or more and less than 10 times, and the recording material is conveyed between the fixing roller and the heat resistant sheet . A plurality of slits whose slit width becomes zero due to expansion of the heat-resistant sheet when heated by the fixing roller at a predetermined temperature at a contact portion of the heat-resistant sheet pressed against the fixing roller with the fixing roller, The fixing device according to claim 1, wherein the fixing device is formed in parallel with the cut line. The fixing device according to claim 2, wherein the fixing roller is in contact with a central portion with respect to a longitudinal direction of a slit provided in the heat resistant sheet.

Images