JP3950591B2

JP3950591B2 - Rubber roller and manufacturing method thereof

Info

Publication number: JP3950591B2
Application number: JP24585099A
Authority: JP
Inventors: 之則永田; 昌明原田
Original assignee: Canon Inc
Current assignee: Canon Inc
Priority date: 1999-08-31
Filing date: 1999-08-31
Publication date: 2007-08-01
Anticipated expiration: 2019-08-31
Also published as: JP2001062849A

Description

【０００１】
【発明の属する技術分野】
本発明は、芯金の外周面上に発泡ゴム層と非発泡ゴム層の二層からなる弾性体を形成したゴムローラとその製造方法に関する。より具体的には、例えば、電子写真プロセスを利用した画像形成装置に用いられる種々のゴムローラ、すなわち、帯電・転写ローラ、現像ローラ、あるいは、搬送ローラ、画像定着ローラ、中間転写体などに好適に利用できるゴムローラ、ならびにその製造方法に関する。
【０００２】
【従来の技術】
電子写真プロセスにおいて、帯電・転写プロセスでは、感光体表面の帯電には、従来、非接触型のコロナ放電が利用されたいた。このコロナ放電時には、オゾンなどが発生すること、また、発生したオゾンなどは、感光体表面の劣化を進行させる要因となることが判明している。更に、コロナ放電に利用されるワイヤーに汚れが付着すると、感光体表面の帯電に不均一を生じさせ、例えば、画像白抜けや黒すじを引き起こすなど、画像品質に影響を与えるという問題点を有している。
【０００３】
従来から、このコロナ放電に代わる感光体表面の帯電の手法として、接触帯電・転写の手法が、多くの研究者により研究されてきている。図１に、これらの研究により提案されている、接触帯電・転写部材を用いる電子写真装置構成の一例を模式的に示す断面図を示す。この装置構成において、被帯電体は、像担持体であり、具体的には、アルミニウムなどを用いる導電性の基体層とその外周表面上にアモルファスシリコンなどで形成される光導電層の二層からなるドラム型の感光体１である。この感光体１と接するように、ローラ形状の帯電部材２が設置され、感光体１表面を所定の電位に一様に帯電させる。
【０００４】
このローラ形状の帯電部材２、つまり帯電ローラは、中心部の芯金と、その外周に形成される導電性弾性体の層からなっている。この帯電ローラ２は、バネなどを利用する圧着手段により、感光体１に所定の圧接力でもって圧接され、それに伴い、感光体１の回転に従動回転する。一方、帯電ローラ２の芯金部に、直流または直流＋交流バイアスを印加し、感光体１を所定の電位に接触帯電させる。この際、良好なコピー画像を得るためには、感光体１の表面が均一な電位に帯電される必要があり、つまり、帯電ローラ２の均一な接触状態と、導電性の均一性が必要である。帯電された感光体１の表面は、レーザー、ＬＥＤなどを光源とする露光手段３を用い、画像情報を露光することにより、目的の画像情報に対応する静電潜像を形成する。
【０００５】
次いで、前記静電潜像上に、現像手段４によるトナーの塗布を施し、トナー画像として可視像化する。感光体１の表面に形成されているトナー画像は、転写材５（コピー用紙など）の裏面から、転写部材６（転写ローラ）による前記トナーと逆極性の帯電を行うことで、転写材５の表面に転写する。トナー画像の転写後、転写材５は感光体１表面と分離され、先に設置される定着部材７（定着ローラ）において、熱、圧着により画像の固着がなされる。他方、像転写の後、感光体１の表面は、クリーニング手段８により、一連の転写工程で、表面に残留している残留トナーなどの付着物を除去され、再び清浄な面に復される。この繰り返しにより、連続的に電子写真プロセスが行える。
【０００６】
この種の装置においては、図１に示すように、例えば、帯電部材２、転写部材６、定着部材７などにローラが用いられる。例えば、帯電ローラなどは、両端において回転可能に支持される芯金と、その芯金の外周に円柱状に設けられる導電性の弾性体層から構成される。このように、例えば、帯電ローラに利用される導電性弾性体は、上述するように交流成分を印加する際、その交流成分に起因する帯電音を抑制するため、さらには、常に圧接している感光体表面を傷つけることがないようにするため、表面の硬度を低くし、また、抵抗を調整したものが利用される。具体的には、硬度が低い発泡体に、導電粒子を分散させるなどして、所望の導電性と硬度を達成することが多い。
【０００７】
発泡体自体の表面は、一般に表面粗さが粗くなる傾向を持ち、それに伴い、感光体との接触が不均一になると、放電が不均一となり易い。接触を密にするため、圧接力を増すと、繰り返し使用していく間に、感光体表面が不均一に摩耗したり、削れたりすることが起こり易くなり、寿命を短くするといった弊害もある。この発泡体自体の性質に由来する不具合を除くため、発泡体を用いた導電性の弾性体表面に、導電性の塗料を塗工したり、あるいは、表面の滑らかな導電性チューブで被覆するなど、被覆層を形成する方法も適用されている。この被覆層により、表面粗さを改善する、また、ローラ抵抗の調整を行っている。
【０００８】
導電性弾性体に発泡体を利用したローラを製造する方法には、発泡体のポリマー原料と発泡剤、ならびに各種添加剤を配合し、混練した原料組成物を円筒状に押し出したものを、加硫・発泡させた後、前記の円筒状の中心に芯金を圧入し、所望の外径となるように外周を研磨し、整える方法や、予め芯金が中心に位置するように配置した成形金型を用い、前記金型の内部に芯金とともに前記原料組成物を入れ、成形金型を加熱して、加硫・発泡させることにより、所定の外径を持つ円筒状の発泡弾性体を芯金の周囲に形成する方法が知られている。
【０００９】
これらの方法で作製した発泡体ローラは、上で述べたように表面の欠陥などをなくし、表面粗さを改善する目的で、例えば、被覆層の塗工がなされるが、表面のあれたものでは、被覆層の層厚を厚くする必要があり、その結果、ローラ硬度が高くなってしまうなどの問題が生じることもある。
【００１０】
適度な層厚の被覆層を形成する手法として、発泡体の表面粗さが十分に小さくない場合に、発泡体となる発泡材料と被覆層となる非発泡材料とを、別々の押し出し機を用いて、同時一体的に同心円筒状に形成した後、加硫することで、内部の発泡層を覆う非発泡層を設ける構造のローラを作製する方法も知られている。
【００１１】
仮に、外部の非発泡層がない場合には、発泡体の原料組成物、つまり、発泡材料は発泡反応の開始とともに、発泡構造を形成するセルとその隣接するセルとの隙間には窪みが生じ、この微少な凹凸を表面に残したまま膨張し、金型内壁に押し付けられる。この押し付けによるローラ表面形成時に、大半の表面凹凸は、押しつぶされるが、局部的な押し付け不足で若干の凹凸が残る、しわが残ることも少なくない。また、たまたま、表面にセルが露出してしまい、セルの跡がピンホールを形成することもある。一方、外部に非発泡層があると、例え、隣接するセルに隙間があっても、外側の非発泡層に支えられ、金型内壁に押し付けられた際、微少な凹凸やしわの残留・発生が抑えられ、従って、表面粗さの少ないローラが得られ、有用な方法である。
【００１２】
しかしながら、内側の発泡層と外側の非発泡層の間で、層の厚さ、ムーニー粘度、ならびに加硫速度のバランスを失すると、内側の発泡層となる発泡材料が十分に発泡ができないという事態が起こり、外径精度が低下する、あるいは、軸の振れが増大するなど、形状精度が低下する。また、十分に発泡倍率が高まらないと、硬度が高くなってしまう、逆に、非発泡層による支えが不十分であると、発泡によるガスは、非発泡層を突き抜け、表面にピンホールを生じさせ、却って、表面を荒らす結果となってしますなど、なお、問題を内在するものである。
【００１３】
表面のピンホール発生を防ぐ手段には、発泡時に気泡が外部に抜ける現象に対処するために、特開平１０−１５６９１７号公報に記載するように、非発泡層のスコーチタイムを発泡層のスコーチタイムより短く設定する方法もあるが、その条件では、非発泡層の厚さが厚すぎると、十分発泡倍率が高まらないという事態を引き起こす可能性もある。
【００１４】
【発明が解決しようとする課題】
従来より、適度なローラ硬度を保ちつつ、表面粗さを改善し、かつ形状精度も向上させる試みはなされているが、なお、改善の余地を残すものである。例えば、再現性よく、適度なローラ硬度を保ちつつ、表面粗さの改善も図れる弾性体ローラの製造方法の提案は、なお望まれている。
【００１５】
本発明は、上記の課題を解決するもので、本発明の目的は、成形金型を用いて、再現性よく作製が可能であり、表面粗さが小さく、また、形状精度も高い発泡体ゴムローラ、ならびにその製造方法を提供することにある。より具体的には、本発明の目的は、例えば、電子写真装置などに用いるゴムローラに適するローラ硬度を保ちつつ、表面粗さが小さく、また、形状精度も高い発泡体ゴムローラ、ならびに、前記発泡体ゴムローラを成形金型を用いて、再現性よく作製することを可能とする製造方法を提供することにある。さらに、本発明は、電子写真装置などに用いるゴムローラ、特に、電子写真用感光体の帯電に用いられる帯電部材用のゴムローラにおいて、上記の特性を満たす発泡体ゴムローラ、ならびにその製造方法を提供することにある。
【００１６】
【課題を解決するための手段】
本発明者らは、上記の課題を解決すべく、発泡体ゴムローラの作製に用いる原料組成物の性状、加硫と発泡条件を種々に変え、得られるゴムローラの特性を比較・検討する研究を進めた。その結果、成形金型を用いて、芯金の外周に、内側に発泡層を、外側に非発泡層を有する二層構造の円筒状弾性体層を形成する際、発泡層の原料である未加硫未発泡原料組成物と非発泡層の原料である未加硫非発泡原料組成物を、未加硫非発泡原料組成物の加硫速度を未加硫未発泡原料組成物の加硫速度より遅くし、さらに、未加硫非発泡原料組成物のムーニー粘度を未加硫未発泡原料組成物のムーニー粘度より低くすると、成形されたローラの表面粗さは十分に小さくなり、同時に、外径精度や振れなどの形状精度も高く、適度なローラ硬度が再現性よく得られることを見出し、係る知見に基づき、本発明を完成するに至った。
【００１７】
すなわち、本発明のゴムローラは、芯金の外周に、内側に発泡ゴム層を、その外側に非発泡ゴム層を持つ同心円筒状の弾性体が形成されてなるゴムローラであって、
前記発泡ゴム層は、発泡体のポリマー原料と発泡剤を配合し、混練してなる未加硫未発泡原料組成物を加硫ならびに発泡させて得られる発泡ゴムを材質とし、
前記非発泡ゴム層は、ポリマー原料を配合し、混練してなる未加硫非発泡原料組成物を加硫して得られる非発泡ゴムを材質とし、
前記未加硫非発泡原料組成物の加硫速度を、前記未加硫未発泡原料組成物の加硫速度より遅くし、ならびに、前記未加硫非発泡原料組成物のムーニー粘度を、前記未加硫未発泡原料組成物のムーニー粘度より小さくし、
前記未加硫非発泡原料組成物を、前記未加硫未発泡原料組成物の外周上に一体的に同時に押し出し形成される同心円筒状の積層体となし、前記同心円筒状の積層体の内に前記芯金は、軸中心を一致させて配置され、
前記同心円筒状の積層体の外周より大きい、所定の円筒状内周面を有し、かつ前記芯金を前記円筒状内周面の同心軸上に保持するための蓋体を両端に有する円筒状の成形金型を用い、
前記芯金と一体に配置してなる前記積層体を、前記成形金型内に配置し、加硫ならびに発泡の処理を施し、
前記発泡に伴い、前記積層体の外周面を前記成形金型の内周面に押し付け、成形してなる内側に発泡ゴム層を、その外側に非発泡ゴム層を持つ同心円筒状の弾性体ゴム層を有することを特徴とするゴムローラである（但し、前記加硫速度は、ＪＩＳＫ６３００に基づき、Ａ法の加硫試験を、１６０℃、振れ角１度の条件で行った測定結果から算定したｔ 30 の値とし、かつ、前記ムーニー粘度は、ＪＩＳＫ６３００に基づき、ムーニー粘度試験を行って求めたＭＬ (1+4) １００℃の値とする）。
【００１８】
また、本発明のゴムローラの製造方法は、芯金の外周に、内側に発泡ゴム層を、その外側に非発泡ゴム層を持つ同心円筒状の弾性体が形成されてなるゴムローラの製造方法であって、
（ｉ）前記発泡ゴム層の原料としての、発泡体のポリマー原料と発泡剤を配合し混練してなる未加硫未発泡原料組成物を、前記非発泡ゴム層の原料としての、ポリマー原料を配合してなる未加硫非発泡原料組成物の外周上に一体的に同時に押し出し同心円筒状の積層体となし、前記同心円筒状の積層体の内に前記芯金を、軸中心を一致させて配置する工程；及び
（ ii ）前記同心円筒状の積層体の外周より大きい、所定の円筒状内周面を有し、かつ前記芯金を前記円筒状内周面の同心軸上に保持するための蓋体を両端に有する円筒状の成形金型を用い、前記工程（ｉ）で調製した、前記芯金と一体に配置した前記積層体を、前記成形金型内に配置し、加硫ならびに発泡の処理を施す工程；及び
（ iii ）前記発泡に伴い、前記積層体の外周面を前記成形金型の内周面に押し付け、成形してなる内側に発泡ゴム層を、その外側に非発泡ゴム層を持つ同心円筒状の弾性体ゴム層を形成する工程、を有するゴムローラの製造方法において、
前記未加硫非発泡原料組成物の加硫速度を、前記未加硫未発泡原料組成物の加硫速度より遅くし、ならびに、前記未加硫非発泡原料組成物のムーニー粘度を、前記未加硫未発泡原料組成物のムーニー粘度より小さくしていることを特徴とするゴムローラの製造方法である（但し、前記加硫速度は、ＪＩＳＫ６３００に基づき、Ａ法の加硫試験を、１６０℃、振れ角１度の条件で行った測定結果から算定したｔ 30 の値とし、かつ、前記ムーニー粘度は、ＪＩＳＫ６３００に基づき、ムーニー粘度試験を行って求めたＭＬ (1+4) １００℃の値とする）。
【００１９】
なお、本発明のゴムローラにおいては、前記発泡ゴム層中の発泡セル径に対して、前記非発泡ゴム層の厚さを、前記セル径の５０％以上とするのが好ましい。また、本発明のゴムローラにおいては、前記発泡ゴム層および前記非発泡ゴム層がともに導電性を有する構成とすることもできる。加えて、本発明のゴムローラは、前記弾性体ゴム層の外周面上に、一層又は二層以上の導電性の被覆薄膜層を塗工して設ける構造とすることもできる。
【００２０】
上記の本発明のゴムローラにおいて、前記芯金の外周に形成される円筒状の弾性体を、導電性を有するものとすると、例えば、電子写真用感光体表面に接触配置し、前記感光体の帯電に用いる帯電ローラに好適に利用できる。
【００２１】
【発明の実施の形態】
本発明のゴムローラは、そのロール部の主要な構成要素である弾性体層を、主に弾性を与える発泡ゴム層と、その外側に一体に形成され、ロール部の表面形状を支配する非発泡ゴム層が、同心円筒状の二層構造をとる構成としたものである。その外面形状は、前記未加硫未発泡原料組成物を発泡ゴム層とすべく、発泡処理を行う際、所定の形状寸法、ならびに、平滑な内表面に形成されている成形金型を用いて、発泡に伴う押し付けにより形成されるものである。すなわち、本発明のゴムローラにおける外形形状は、本来、前記成形金型の内面形状により、その概略は規定されるものである。
【００２２】
従って、本発明のゴムローラは、そのロール部における断面を模式的に示すと、図２に、一例を示す構成をとっている。前記金型を用いて成形された弾性体層の表面に、さらに、一層または二層以上の被覆薄膜層を塗工して設けると、その断面は、例えば、図３に模式的に示す形状となる。図２ならびに図３において、芯金１０には、金属を用いることが多いが、例えば、導電性樹脂など、導電性を持つ材料を用いることもできる。この芯金１０の外周に、二層構造をとる弾性体層として、発泡ゴム層１１と非発泡ゴム層１２が同心円筒状に形成されている。図３では、弾性体層の外周面上に、さらに一層または二層以上の被覆薄膜層１３が設けられている。通常、非発泡ゴム層１２の厚さは、発泡ゴム層１１の厚さより有意に薄くなるように形成され、被覆薄膜層１３の総膜厚も、発泡ゴム層１１の厚さより十分に薄くなるように選択する。
【００２３】
つまり、前記被覆薄膜層１３は、例えば、電子写真用感光体表面に接触配置し、前記感光体の帯電に用いる帯電ローラでは、導電性塗料を塗工した被覆膜、あるいは、導電性薄膜で形成される導電性チューブによる被覆などで形成する。帯電ローラでは、ローラ表面における電位を均一にするため、前記の導電性材料からなる被覆薄膜層を設け、ローラ表面内の導電率をより高める構成とされる。また、電子写真装置において、転写部材として利用する際にも、前記帯電ローラと同様に、ローラ表面における電位を均一にするため、前記の導電性材料からなる被覆薄膜層を設け、ローラ表面内の導電率をより高める構成とされる。あるいは、熱、圧力を加え、転写されたトナー画像の定着を行う、定着部材に利用されるローラでは、熱等に対する耐久性を増す被膜などを、前記被覆薄膜層１３として設けるとよい。このように、前記被覆薄膜層１３は、使用目的に応じて、適宜所望の特性を持つ薄膜層を選択するとよい。
【００２４】
図３に示す構成をとると、ローラの最表面には、被覆薄膜層１３が設けられ、表面形状、表面粗さなどは、被覆薄膜層１３を形成する前の非発泡ゴム層１２の表面形状、表面粗さより、若干の改善が見られる。しかしながら、被覆薄膜層１３の膜厚は、ローラ表面内で均一となるように形成され、また、多くの場合、非発泡ゴム層１２の表面形状、表面粗さが、ローラの最表面の形状、表面粗さに反映される程度に薄いものである。
【００２５】
本発明のゴムローラは、例えば、以下に述べる手順により製造することができる。
【００２６】
先ず、非発泡ゴム層用の未加硫非発泡原料組成物を、発泡ゴム層用の未加硫未発泡原料組成物の外周上に一体的に同時に押し出し形成される同心円筒状の積層体となし、前記同心円筒状の積層体の内に芯金を、軸中心を一致させて配置したものを作製する。前記同心円筒状の積層体の形成は、図４に示すような二種の原料組成物を同時に、単一の押し出しヘッドから押し出すことが可能な装置を用いて行う。図４に示す装置は、発泡ゴム層用の押し出し機１４と非発泡ゴム層用の押し出し機１５、その中心に配置される押し出しヘッド１６から構成される。押し出しヘッド１６内は、例えば、図５に示す構成を採っている。同心状に、未加硫未発泡原料組成物の流路２０と、その周囲に未加硫非発泡原料組成物の流路１９が設けられ、それぞれ、発泡ゴム層用の押し出し機１４と非発泡ゴム層用の押し出し機１５から、原料組成物が所望の供給量で押し出される。押し出しヘッド１６の中心には、円筒状積層体の穴径に相当するニップル１７、円筒状積層体の外径を規定するダイス１８がセットされる。ダイス１８の直前で、未加硫未発泡原料組成物の流路２０と、その周囲に未加硫非発泡原料組成物の流路１９とから供給される原料組成物は、所定の膜厚比に積層される。すなわち、発泡ゴム層用の押し出し機１４と非発泡ゴム層用の押し出し機１５からの吐出速度（回転数）を調整して、所定の膜厚比とする。
【００２７】
ダイス１８から押し出し成形された円筒状積層体は、その中心穴に芯金を軸を一致させて配置し、一体化する。長さ寸法は、最終的なロール長に応じて、所定の長さに揃えて、切断する。次いで、芯金と一体化された円筒状積層体は、例えば、図６に示す成形金型内において、発泡・加硫処理を行い、弾性体とされ、同時に、その外形の成形がなされる。
【００２８】
図６に示す成形金型の一例では、同心円筒状の金型本体２１と両端の蓋体２２から構成されている。蓋体２２には、芯金を保持する孔が穿ってあり、同心円筒状の金型本体２１の中心軸上に、芯金を配置する芯金保持部材の機能を持つ。また、蓋体２２には、発泡・加硫処理に伴う体積膨張により金型内から追い出されるガスを逃すため、ガス抜き孔２３が設けられている。成形金型の内面は、滑らかな表面とされ、また、その内径は、作製すべきゴムローラの外径に対応させて設定する。
【００２９】
発泡・加硫処理の際、円筒状の積層体は、均一な温度となるように、成形金型の加熱を行う。例えば、加熱は、図７にその形状を模式的に示す加熱盤中に、成形金型を装着して行うなどする。図７に示す加熱盤は、二分割された蓄熱ブロック（熱盤）２６から構成され、中央に、成形金型を挿入する空孔部２５が形成されている。予め、加熱盤を所定温度に予熱しておき、芯金と一体化した積層体を保持した成形金型を挿入し、加熱を行う。
【００３０】
加熱により、発泡ならびに加硫が進み、発泡により内層の発泡ゴム層が所望の発泡倍率に達すると、上層の非発泡ゴム層は、成形金型の内面へ押し付けがなされ、規定される形状に成形される。非発泡ゴム層の加硫が進んだ時点で、加熱を終了し、冷却後金型から外し、一連のゴムローラ作製工程が終了する。なお、得られた弾性体層の表面に、さらに被覆薄膜層を設ける際には、後工程として、被覆材料の塗工などを行い、ゴムローラ完成品とされる。
【００３１】
本発明の製造方法においては、非発泡ゴム層の原料に用いる未加硫非発泡原料組成物の加硫速度は、発泡ゴム層の原料に用いる未加硫未発泡原料組成物の加硫速度より遅くされ、また、非発泡ゴム層の原料に用いる未加硫非発泡原料組成物のムーニー粘度は、発泡ゴム層の原料に用いる未加硫未発泡原料組成物のムーニー粘度より小さくされている。このため、加熱を始めると、先ず、未加硫未発泡原料組成物の発泡が進み始めし、また、加硫も開始する。この時、未加硫非発泡原料組成物の加硫速度は、より遅くされているので、架橋形成に伴う粘性の上昇、硬化はより緩やかに進行する。また、未加硫非発泡原料組成物のムーニー粘度は、より小さくされているので、内側の未加硫未発泡原料組成物が発泡して、占有体積が膨張する際、全くその妨げにはならない。つまり、未加硫非発泡原料組成物の流動性は、この段階では、未加硫未発泡原料組成物の流動性より高いので、内側の未加硫未発泡原料組成物の発泡に起因する膨張に従って、より速やかに変形できるので、上層に未加硫非発泡原料組成物が存在してない場合と、遜色のない程度に発泡が進行する。
【００３２】
仮に、上層に未加硫非発泡原料組成物が存在してない場合には、未加硫未発泡原料組成物の極く表層で形成されたセルは、時に、その表面を突き破り、気泡が外部に抜ける現象がある。本発明においては、その粘度はより小さなものではあるが、上層に未加硫非発泡原料組成物の層が存在しているので、極く表層で形成されたセルが、その表面を突き破る現象を抑制する作用を持つ。また、仮に、気泡が未加硫未発泡原料組成物の表面から抜けた際にも、上層にある未加硫非発泡原料組成物の層はより高い流動性を持つので、気泡が放出された後に残る穴跡をより速やかにまた容易に満たし、ピンホール状の跡を残すこともない。
【００３３】
上記の気泡が外部に抜ける際には、セル内圧により、表面にドーム状盛り上がり、この部分では、粘性のみでセルの表層が維持されている。セルの径の半ば以上に、ドーム状盛り上がりが成長すると、セルの底部分において、それまでセル内圧に抗するように加わっている外力により、押し出されるため、急速に気泡が外部に抜けていく。従って、上層として、未加硫非発泡原料組成物層が、平均セル径の５０％以上の厚さを有すると、未加硫未発泡原料組成物の表面（界面）が、セルの径の半ば以上に、ドーム状に盛り上がるまでは、気泡が外部に抜けるのを抑制する働きをする。一方、セルの径の半ば以上に、ドーム状に盛り上がり、未加硫未発泡原料組成物の表層に穴が生ずると、未加硫非発泡原料組成物層はより粘度が小さいので、速やかに、気泡は、未加硫未発泡原料組成物の表面（界面）を脱し、未加硫非発泡原料組成物層内を通過し、外部に抜ける可能性がある。この時、未加硫非発泡原料組成物層内には、気泡が占めていた空孔が残るが、より流動性が高いので、その空孔は速やかに埋められ、解消することになる。従って、未加硫非発泡原料組成物層の厚さ、つまり、非発泡ゴム層の膜厚は、発泡ゴム層内のセル平均径の５０％以上とすると、より好ましい。非発泡ゴム層の膜厚が、セル平均径の５０％未満であっても、上記の効果は相当の範囲では保持されるが、膜厚がより薄くなるにつれ、効果は減少していく。
【００３４】
未加硫未発泡原料組成物の発泡が進み、成形金型の内面に押し付けられると、それ以上の径方向の膨張は抑えられる。なお、未加硫未発泡原料組成物自体は、含まれる発泡剤は、均一に分散されるように混練されているものの、発泡反応自体は多分に偶発的な契機で開始する反応であり、若干の疎密が伴う。発泡が密な部分は、先に成形金型の内面に達し、径方向の膨張は抑えられ、疎な部分は、遅れて成形金型の内面に達する。その間、密な部分では、軸方向の膨張はなお進行しており、時に、未加硫未発泡原料組成物の表面（界面）では、この密な部分と疎な部分の境に微細なしわが形成されることがある。また、上述するように、未加硫未発泡原料組成物の表面（界面）に達したセルによるドーム状の盛り上がりに伴い、極めて微細な凹凸も存在する。未加硫非発泡原料組成物は、より流動性に富むので、これら未加硫未発泡原料組成物の表面（界面）に生成している微細な凹みやしわを満たし、平坦化が容易になされる。なお、これら微細な凹みやしわは、通常、高々発泡ゴム層内のセル平均径の５０％程度でしかなく、未加硫非発泡原料組成物層の厚さ、つまり、非発泡ゴム層の膜厚は、発泡ゴム層内のセル平均径の５０％以上とすると、平坦化はより確実なものとなる。また、多くの場合、押し付けにより、なお流動性を残す未加硫未発泡原料組成物自体による埋め込み効果もあり、上記の微細な凹凸やしわは、発泡ゴム層内のセル平均径の５０％に満たない変異でしかないので、未加硫非発泡原料組成物層の厚さ、つまり、非発泡ゴム層の膜厚が、発泡ゴム層内のセル平均径の５０％に満たない場合にも、相当な範囲で平坦化が達成される。この表面平坦化が達成された時点で、より加硫速度が遅い未加硫非発泡原料組成物においても、加硫が進行して、流動性を失い、弾性体層の表面形状は、滑らかな金型の内面と一致したものとなる。
【００３５】
以上に説明するとおり、本発明においては、より加硫速度が遅く、また、ムーニー粘度がより小さい未加硫非発泡原料組成物を上層に有するので、成形金型への押し付けにより成形される弾性体層表面は、気泡の抜けた跡に当たるピンホール様の表面欠陥がなく、さらには、表面粗さが極めて小さく、外径のバラツキがないゴムローラとなる。このより加硫速度が遅く、また、ムーニー粘度がより小さい未加硫非発泡原料組成物を上層に利用することによる作用は、未加硫非発泡原料組成物層の厚さ、つまり、非発泡ゴム層の膜厚がより厚くなっても、本質的に損なわれるものではない。しかしながら、非発泡ゴム層は、内部にセル構造がないので、通常、発泡ゴム層程の弾性を示さず、樹脂の硬度は比較的に高いものとなる。樹脂の硬度が高いと、非発泡ゴム層の膜厚が増すにつれ、全体として、ローラの硬度は増していく。この点を考慮すると、特別の理由がない限り、非発泡ゴム層の膜厚は、発泡ゴム層内のセル平均径の５０％の値に対して、桁違いに厚くならない範囲とするとより好ましい。従って、非発泡ゴム層の膜厚は、発泡ゴム層内のセル平均径の１０数倍以下、あるいは、数倍程度、例えば、２〜３倍を超えない範囲に選択すると一般により好ましいものとなる。
【００３６】
本発明のゴムローラは、上層に用いる非発泡ゴム層の膜厚を薄くすることができ、低硬度なローラを得ることが可能であり、また、表面に欠陥がなく、形状の均一性も高いものであるので、例えば、弾性体層を導電性材質とするとき、周内での抵抗ムラなども小さくできるので、電子写真装置において、感光体表面と接触させて、その帯電に利用する帯電部材（帯電ローラ）やコピー用紙上へのトナー画像転写に利用する転写部材（転写ローラ）に、より適するものである。
【００３７】
上記発泡ゴム層の原料に用いる未加硫未発泡原料組成物、ならびに非発泡ゴム層の原料に用いる未加硫非発泡原料組成物に用いられる原料ポリマーは、目的とするローラの用途に応じて選択するが、例えば、天然ゴム、ブタジエンゴム、スチレンブタジエンゴム（ＳＢＲ）、ニトリルゴム（アクリロニトリル-ブタジエンゴム）、エチレン-プロピレンゴム（ＥＰＤＭ：エチレン-プロピレン-ジエン三元共重合体）、エチレン-プロピレンゴム（ＥＰＭ）、クロロプレンゴム（ＣＲ）、ニトリルブタジエンゴム（ＮＢＲ）、エピクロロヒドリンゴム、ブチルゴム、シリコンゴム、ウレタンゴム、フッ素ゴム、塩素ゴムなど、汎用される各種のポリマーから選択するとよい。具体的には、未加硫未発泡原料組成物、ならびに未加硫非発泡原料組成物が、それぞれその加硫速度とムーニー粘度が上記の条件を満たすように、上記の各種ポリマーから選択する、あるいは、組み合わせるとよい。
【００３８】
発泡ゴム層の原料に用いる未加硫未発泡原料組成物には、発泡剤が添加されるが、原料ポリマーの種類、加硫条件、その架橋温度などに応じて、所望の発泡倍率が得られる添加量、発泡剤種類を選択する。例えば、有機発泡剤として、ＡＤＣＡ（アゾジカルボンアミド）系、ＤＰＴ（ジニトロソペンタメチレンテトラアミン）系、ＴＳＨ（p-トルエンスルホニルヒドラジド）系、ＯＢＳＨ（オキシビスベンゼンスルフェニルヒドラジド）系などが挙げられる。前記の有機発泡剤を用いる際には、通常、上記の原料ポリマー１００重量部に対して、発泡剤の添加量を２〜３０重量部の範囲に選択する。また、場合に応じて、無機発泡剤を用いることも可能であり、例えば、重炭酸ナトリウム、炭酸アンモニウムなどが挙げられる。また、前記発泡剤に加えて、適宜発泡助剤を添加することもできる。
【００３９】
未加硫未発泡原料組成物、ならびに未加硫非発泡原料組成物には、用いる原料ポリマーの種類に応じて、加硫剤として、硫黄、あるいは、非硫黄加硫剤である、金属酸化物、有機過酸化物などから、所望の加硫速度を得る上で、適するものを添加する。また、加硫剤の添加量に応じて、公知の加硫促進剤から適するものを選択し、所望の架橋密度が得られるように適宜添加量を選び、添加する。さらに、各種の加硫促進助剤を添加することもなされる。
【００４０】
発泡ゴム層ならびに非発泡ゴム層を導電性とする際には、原料組成物中の原料ポリマー中に、導電性粉末を分散させる。例えば、多用される導電粉としては、カーボンブラック、導電性カーボンなどのカーボン類、グラファイト、ＴｉＯ₂、ＳｎＯ₂、ＺｎＯなどの導電性金属酸化物、ＳｎＯ₂とＳｂ₂Ｏ₃の固溶体、ＺｎＯとＡｌ₂Ｏ₃の固溶体などの前記金属酸化物との複合酸化物、Ｃｕ、Ａｇなどの金属粉、導電性の繊維などを挙げることができる。所望の導電率に応じ、また、用いる導電粉材料の比重に応じて、原料ポリマー１００重量部に対して、導電粉の添加量を５〜２００重量部の範囲で選択して、適宜添加する。
【００４１】
その他、原料組成物には、無機充填剤、例えば、カーボンブラック、タルク、クレーなどを添加することもあり、また、原料組成物の混練や、その後の押し出しによる円筒形状の形成などに利する、プロセスオイル、軟化剤などを必要に応じて、適宜添加する。
【００４２】
本発明の製造方法においては、上記の各成分を添加し、混練した未加硫非発泡原料組成物ならびに未加硫未発泡原料組成物は、未加硫非発泡原料組成物の加硫速度を、未加硫未発泡原料組成物の加硫速度より遅くし、ならびに、未加硫非発泡原料組成物のムーニー粘度を、未加硫未発泡原料組成物のムーニー粘度より小さくする。前記の条件を満たすように、原料ポリマーの種類、その他の添加成分を選択し、また、含有量を調整する。加硫速度は、実際に加硫を行う条件、温度において、予め測定し、その値を比較すべきものではあるが、一般に、ＪＩＳ等において規定される加硫試験に準拠して、代表値を求め、その代表値が前記条件を満たすものであってよい。僅かな条件の差異があっても、加硫速度の大小関係は概ね保存されるので、加硫速度の大小関係に有意な差異がある限り、問題を生ずることはない。同じく、ムーニー粘度に関しても、ＪＩＳ等において規定されるムーニー粘度試験に準拠して、代表値を求め、その代表値が前記条件を満たすものであってよい。
【００４３】
例えば、加硫速度の代表値として、ＪＩＳＫ６３００に基づき、Ａ法の加硫試験を、１６０℃、振れ角１度（ＪＳＲキュラストメータIII型）の条件で行い、測定結果から算定したｔ30の値を用いることができる。また、例えば、ムーニー粘度の代表値として、同じくＪＩＳＫ６３００に基づき、ムーニー粘度試験を行い、ＭＬ(1+4)１００℃の値を求め、このＭＬ(1+4)１００℃の値を用いることができる。
【００４４】
本発明においては、例えば、未加硫未発泡原料組成物の加硫速度を、前記ｔ30の値において、１．５〜８の範囲に選択するとき、未加硫非発泡原料組成物の加硫速度を、前記ｔ30の値において、２〜１２の範囲に選択して、その際、未加硫非発泡原料組成物の加硫速度が、未加硫未発泡原料組成物の加硫速度のおよそ１．２〜３倍となるように選択すると、より好ましい結果が得られる。同時に、例えば、未加硫未発泡原料組成物のムーニー粘度を、前記ＭＬ(1+4)１００℃の値において、２８〜３６の範囲に選択するとき、未加硫非発泡原料組成物の前記ＭＬ(1+4)１００℃の値において、１５〜４０の範囲に選択して、その際、未加硫非発泡原料組成物のムーニー粘度が、未加硫未発泡原料組成物のムーニー粘度の０．８〜０．３倍となるように選択すると、より好ましい結果が得られる。
【００４５】
本発明のゴムローラは、上記の弾性体層の外周面上に被覆薄膜層を設けることができる。例えば、前記被覆薄膜層として、導電性被膜を形成する際には、被膜の材質として、例えば、Ｎ−メチルメトキシ化ナイロン、ポリビニルブチラール、ポリエチレン、ポリ酢酸ビニル、ポリスチレン、ポリブタジエン、ポリアミド、ポリイミド、ポリウレタン、ポリエステル、シリコン樹脂など、さらには、エピクロロヒドリン、ウレタン、クロロプレン、アクリロニトリル-ブタジエン系のゴムなどを利用することができる。これらから選択した被膜材料に、導電率を所望の値に調節するため、導電性顔料、例えば、カーボンブラックやカーボングラファイト、酸化チタン、酸化亜鉛などを適量添加するとよい。例えば、上記導電性被膜材料を塗工により、被膜形成する際には、これらの被膜成分物質を溶剤などに溶解または分散して、塗料状にし、被膜厚さに応じて、デッピング、スプレーコート、ロールコートなどの手段から適する手段を選択し、ローラの外周に均一に塗工するとよい。
【００４６】
被覆薄膜層の膜厚は、その被覆目的に応じて、適宜選択すべきものであるが、本発明においては、目的とする機能が維持される限り、より薄い膜厚を選択するのが一般に好ましい。すなわち、一般に、被覆薄膜層を設けると、その膜厚が増すに従って、ローラ硬度の上昇を引き起こす傾向があり、不要な高硬度化を防ぐためには、被覆の目的を損なわない範囲で、より薄い膜厚を選択するのが一般に好ましい。
【００４７】
【実施例】
以下、具体例を挙げて、本発明のゴムローラ、その製造方法について、より詳しく説明する。なお、下記する具体例では、主に電子写真感光体に接触配置させて、この感光体表面の帯電に用いる帯電ローラに適する、導電性のローラ部をゆうするゴムローラに適用した事例を述べるが、本発明は、これら具体例によりなんら限定されるものではない。
【００４８】
（実施例１）
本実施例は、感光体表面の帯電に用いる帯電ローラの作製例であり、また、作製された帯電ローラが、成形されたローラの表面粗さは十分に小さくなり、同時に、外径精度や振れなどの形状精度も高く、適度なローラ硬度が再現性よく得られていることを検証した例である。
【００４９】
本実施例においては、非発泡ゴム層用の未加硫非発泡原料組成物は、原料ポリマーとして、エチレン-プロピレン-ジエン三元共重合体（商品型番：EPT4045 三井石油化学（株）製）を、導電剤（導電粉）として、ケッチェンブラック（商品型番：ケッチェンブラックEC 三菱化学（株）製））あるいはＳＲＦカーボンブラック（商品型番：旭＃３５旭カーボン社製）を、軟化剤として、パラフィンオイルを、架橋剤（加硫剤）として、硫黄を、加硫促進剤として、メルカプトベンゾチアゾール（Ｍ）ならびにシクロヘキシルベンゾチアゾールスルフェンアミド（ＣＢＳ）を、加硫促進助剤として、酸化鉛とステアリン酸を、それぞれ用い、各成分の含量（重量部）を、表１に示す値とした。混練には、オープンロールを用い、均一な組成物とした。
【００５０】
また、発泡ゴム層用の未加硫未発泡原料組成物は、原料ポリマーとして、エチレン-プロピレン-ジエン三元共重合体（商品型番：EPT8075E 三井石油化学（株）製）を、導電剤（導電粉）として、ケッチェンブラック（商品型番：ケッチェンブラックEC 三菱化学（株）製））あるいはＳＲＦカーボンブラック（商品型番：旭＃３５旭カーボン社製）を、軟化剤として、パラフィンオイルを、架橋剤（加硫剤）として、硫黄を、加硫促進剤として、メルカプトベンゾチアゾール（Ｍ）、ジブチルジチオカルバミン酸亜鉛（ＺｎＢＤＣ）、テトラメチルチウラムジスルフィド（ＴＭＴＤ）、ならびにシクロヘキシルベンゾチアゾールスルフェンアミド（ＣＢＳ）を、加硫促進助剤として、酸化鉛とステアリン酸を、発泡剤として、ＡＤＣＡおよびＯＢＳＨを、それぞれ用いて、各成分の含量（重量部）を、表１に示す値とした。混練には、オープンロールを用い、均一な組成物とした。
【００５１】
この非発泡ゴム層用の未加硫非発泡原料組成物、ならびに発泡ゴム層用の未加硫未発泡原料組成物について、その加硫速度の指標値として、ＪＩＳＫ６３００に基づき、Ａ法の加硫試験を、１６０℃、振れ角１度（ＪＳＲキュラストメータIII型）の条件で行い、測定結果から算定したｔ30の値を用いて、代表値とした。また、ムーニー粘度の指標値として、同じくＪＩＳＫ６３００に基づき、ムーニー粘度試験を行い、ＭＬ(1+4)１００℃の値を用い、代表値とした。前記加硫速度およびムーニー粘度の代表値を、表１に併せて示す。この代表値の比較からも判るとおり、本実施例において用いた、未加硫非発泡原料組成物の加硫速度は、未加硫未発泡原料組成物の加硫速度より有意に遅く、ならびに未加硫非発泡原料組成物のムーニー粘度は、未加硫未発泡原料組成物のムーニー粘度より有意に低いことが確認される。
【００５２】
上記の非発泡ゴム層用の未加硫非発泡原料組成物、ならびに発泡ゴム層用の未加硫未発泡原料組成物を用い、図４に示す押し出し機と図５に示す押し出しヘッドを利用し、内径がφ7.75mmのダイと外径がφ5.0mmのニップルをヘッドにセットして、同時一体的に押し出しを行い、円筒状の積層体を形成した。成形金型の空孔部の長さ224mmに合わせて、その内部に収まるように、円筒状の積層体の長さをおよそ同じ長さでカットした。
【００５３】
図４に示す押し出し機において、非発泡ゴム層用の未加硫非発泡原料組成物の押し出しは、スクリュー径φ50mmの押し出し機を、発泡ゴム層用の未加硫未発泡原料組成物の押し出しは、スクリュー径φ75mmの押し出し機を、それぞれ用い、二つの押し出し機の回転比をφ50：φ75＝１：３に設定することで、発泡ゴム層と非発泡ゴム層の原料組成物厚さを調整した。
【００５４】
芯金は、予めその表面に導電性の接着剤を塗布しておき、得られた円筒状の積層体の中心穴内に挿入して、芯金と円筒状の積層体の組み上げを行った。その後、図６に模式的に示すように、成形金型の両端に設けられる蓋体に、前記芯金末端を軸心を一致させて固定し、金型内部に積層体を配置した。この成形金型を、予め１８０℃に予熱してある図７の加熱盤に挿入し、１５分間加熱して、加硫・発泡処理を施した。その結果、直径φ6mmの芯金の表面に、外形寸法が、長さ224mm、直径φ12mmであり、用いた金型の内面寸法、直径φ12.3mmに一致する弾性体層が形成された。表面の非発泡ゴム層の平均厚さは100μmであり、内部の発泡ゴム層の平均セル径は、153μmであった。従って、非発泡ゴム層の膜厚は、発泡ゴム層のセル径の、およそ６５％に当たる。
【００５５】
なお、前記の平均セル径は、発泡ゴム層の断面を顕微鏡などで観察し、視野内にある種々の大きさに見えるセル断面のうち、最大径のものから、１０個程度の形が整っているものを選び、そのセル径の測定値を平均した値である。セル断面形状が、真円から大きく歪み、楕円状となっているものは、長径と短径の単純平均をセル径の測定値とした。
【００５６】
なお、本実施例で利用した成形金型の形状・構成を、図６に模式的に示す。金型本体２１は、外径φ26mm、その内面は、内径φ12.3mmの円筒状であり、両端には、ローラの芯金を挿入保持する穴を穿った蓋体（芯金保持部材）２２が装着される。この蓋体２２が装着した状態で、内面の長さは、上記のとおり224mmよりやや長くなる。蓋体２２には、内部のガスの抜け道となるガス抜き孔２３が設けられている。ローラの弾性体層となる、円筒状の積層体２４は、中心の芯金を蓋体２２により保持することで、金型内面と軸心を一致させて、配置される。一方、加熱盤は、図７にその形状を模式的に示すとおり、二分割される蓄熱ブロックからなり、分割面には、前記成形金型の外形寸法に合わせた空孔部２５が形成されている。成形金型を挿入すると、その外周から均一な加熱がなされる。
【００５７】
以上の手順で作製されるゴムローラの外径精度、表面粗さを評価した。押し出し機で作製される円筒状の積層体自体のばらつきをも考慮し、Ｎ＝１０本について平均値を求めた。外径については、ゴムローラの両端５ｍｍの部分を除いた範囲について、非接触型のレーザー測長機を用いて、外径を測定し、最大値と最小値の差を、外径精度とした。なお、本実施例程度の外径を持つ、帯電ローラにおいては、外径精度が0.1mm以下であれば、良好とされる。
【００５８】
さらに、上記の手順で作製されたゴムローラの表面に、導電性被膜層を塗工して、電子写真装置で用いる帯電ローラに調製した。導電性被膜層の被覆には、ポリウレタンを水中に分散させたポリウレタン液に対して、ｐＨ５〜６に調整して、粉末状の酸化錫をその界面の電気的反発力で分散させた導電性酸化錫スラリーとして、酸化錫を固体分比で３０％相当分散させてなる導電性酸化錫添加ポリウレタン塗料を用いた。表面をシランカップリング剤で処理したローラ表面上は、前記塗料を塗工し、熱風炉内で１２０℃で、３０分間の加熱・乾燥処理を行って、厚さ４０μｍの導電性薄膜の被覆を行った。最終的に、ローラ自体の抵抗が、１０×１０⁶Ωの帯電ローラとした。
【００５９】
また、作製した帯電ローラについて、上記の導電性薄膜を被覆した後、表面粗さを測定したところ、表面粗さは、Ｒｚ＝０．８９μｍであり、被覆前の弾性体層の表面粗さを反映するものであった。
【００６０】
加えて、作製した帯電ローラの抵抗について、周内の均一性を検討するため、図８に模式的に示す評価装置を用いて、周方向に関し、ローラの抵抗分布を測定した。図８に示す評価装置では、アルミニウム製のドラム２９に帯電ローラ２７が圧接するように、芯金２８端部に加圧力ｆ＝５００ｇを加えてある。この圧接した状態で、帯電ローラ２７はドラム２９に従動して、回転させる。芯金２８を介して、電源３０から、ドラム２９との間に電圧DC 100Vを印加し、帯電ローラ２７を回転させつつ、ローラの抵抗を測定した。周方向について、ローラの抵抗の測定値に基づき、周方向について、その最大値Ｒｍａｘと最小値Ｒｍｉｎの比を求めた。比Ｒｍａｘ／Ｒｍｉｎは、１．３であった。
【００６１】
本実施例で作製された、上記導電性薄膜被覆付きの帯電ローラを、電子写真装置（型式：LBP-320 Canon製）に組み込み、１５℃、１０ＲＨの環境下で実際の画像を出力したところ、帯電ローラの外径の不均一（外径精度不足）や表面の欠陥に由来すると報告されている画像不良の発生は見出されなかった。
【００６２】
後に述べる従来方法で作製した、比較例１〜３、ならびに、比較例４において作製した帯電ローラと比較した。まず、導電性薄膜被覆前における弾性体層の外径精度については、表２に併せて示す。本実施例と同じく、弾性体層が発泡ゴム層と非発泡ゴム層の二層構造である、比較例１〜３において調製したローラと比較して、本実施例のローラは、外径精度が有意に向上し、0.1mm以下の良好な水準となっている。
【００６３】
【表１】

【００６４】
【表２】

（実施例２）
本実施例では、上記の実施例１と異なり、発泡ゴム層用の未加硫未発泡原料組成物において、原料ポリマーとして、エチレン-プロピレン-ジエン三元共重合体（商品型番：EPT8075E 三井石油化学（株）製）に代えて、エチレン-プロピレン-ジエン三元共重合体（商品型番：EPT4045 三井石油化学（株）製）を用い、それに伴い、軟化剤として添加する、パラフィンオイルの含有量を調整した。一方、非発泡ゴム層用の未加硫非発泡原料組成物は、実施例１に用いたものと同じ組成とした。用いた発泡ゴム層用の未加硫未発泡原料組成物、ならびに非発泡ゴム層用の未加硫非発泡原料組成物について、その成分組成（重量部）を表１に併せて示す。
【００６５】
また、実施例１に記載する方法に従い、各原料組成物の加硫速度、ムーニー粘度を評価し、その結果も、表１に併せて示す。この代表値の比較からも判るとおり、本実施例においても、用いた未加硫非発泡原料組成物の加硫速度は、未加硫未発泡原料組成物の加硫速度より有意に遅く、ならびに未加硫非発泡原料組成物のムーニー粘度は、未加硫未発泡原料組成物のムーニー粘度より有意に低いことが確認される。ただし、実施例１と比べると、ムーニー粘度の差異は、より小さくなっている。
【００６６】
実施例１の手順に準じて、円筒状の積層体を図４に示す押し出し機を用いて作製した。非発泡ゴム層用の未加硫非発泡原料組成物の押し出しは、スクリュー径φ50 mmの押し出し機を、発泡ゴム層用の未加硫未発泡原料組成物の押し出しは、スクリュー径φ75mmの押し出し機を、それぞれ用い、二つの押し出し機の回転比をφ50：φ75＝１：３に設定することで、発泡ゴム層と非発泡ゴム層の原料組成物厚さを調整した。その後、実施例１の手順に従い、円筒状の積層体と芯金の一体化、加硫・発泡処理を施し、弾性体層の形成を行った。なお、円筒状積層体の寸法、用いた成形金型は、実施例１と同じ設計寸法とした。得られた弾性体層の外形寸法は、実施例１と本質的に同じであり、また、実施例１に記載する方法で、発泡ゴム層中の平均セル径、ならびに、非発泡ゴム層の平均膜厚を測定した。本実施例では、表面の非発泡ゴム層の平均厚さは100μmであり、内部の発泡ゴム層の平均セル径は、151μmであった。従って、非発泡ゴム層の膜厚は、発泡ゴム層のセル径の、およそ６６％に当たる。
【００６７】
また、作製した弾性体層の外径精度に関しても、実施例１の評価法により測定した。評価された弾性体層の外径精度は、表２に併せて示す。本実施例のローラは、その外径精度は、上記実施例１のローラにおける外径精度よりは僅かに劣る結果ではあった。この僅かな差異はあるものの、弾性体層が発泡ゴム層と非発泡ゴム層の二層構造である、比較例１〜３において調製したローラと比較して、本実施例のローラは、実施例１のローラと同じく、外径精度が有意に向上し、0.1mm以下の良好な水準となっている。
【００６８】
さらに、実施例１と同じ手順・条件で、導電性薄膜の被覆を行い、最終的に、ローラ自体の抵抗が、およそ１０×１０⁶Ωの帯電ローラとした。実施例１に記載される評価方法に準じて、本実施例で作製した帯電ローラの抵抗についても、周内の均一性を評価したところ、比Ｒｍａｘ／Ｒｍｉｎは、１．３であった。それに対応して、本実施例で作製された、上記導電性薄膜被覆付きの帯電ローラを、電子写真装置（型式：LBP-320 Canon製）に組み込み、１５℃、１０ＲＨの環境下で実際の画像を出力したところ、実施例１の帯電ローラと同じく、帯電ローラの外径の不均一（外径精度不足）や表面の欠陥に起因する画像不良の発生は見出されなかった。
【００６９】
（実施例３）
本実施例では、発泡ゴム層用の未加硫未発泡原料組成物、ならびに、非発泡ゴム層用の未加硫非発泡原料組成物は、実施例１で用いたものと同じ組成とした。
【００７０】
実施例１の手順に準じて、円筒状の積層体を図４に示す押し出し機を用いて作製した。非発泡ゴム層用の未加硫非発泡原料組成物の押し出しは、スクリュー径φ50mmの押し出し機を、発泡ゴム層用の未加硫未発泡原料組成物の押し出しは、スクリュー径φ75mmの押し出し機を、それぞれ用い、但し、二つの押し出し機の回転比をφ50：φ75＝１：４に設定することで、非発泡ゴム層の原料組成物厚さを実施例１より薄くなるように調整した。その後、実施例１の手順に従い、円筒状の積層体と芯金の一体化、加硫・発泡処理を施し、弾性体層の形成を行った。なお、円筒状積層体の寸法、用いた成形金型は、実施例１と同じ設計寸法とした。得られた弾性体層の外形寸法は、実施例１と本質的に同じであり、また、実施例１に記載する方法で、発泡ゴム層中の平均セル径、ならびに、非発泡ゴム層の平均膜厚を測定した。本実施例では、設計したとおり、表面の非発泡ゴム層の平均厚さは60μmとなっており、内部の発泡ゴム層の平均セル径は、159μmであった。従って、非発泡ゴム層の膜厚は、発泡ゴム層のセル径の、およそ３８％に当たる。
【００７１】
また、弾性体層の表面を観察すると、実施例２のローラにおいては、相当の頻度で、微細な表面荒れが見出された。具体的には、非発泡ゴム層の表面には、微少なしわが見られる部分があり、さらには、下層の発泡ゴム層において、セルが潰れた跡に当たるピンホール状の窪みの発生も見られた。これらの微細な表面荒れにより、表面粗さは、実施例１のローラ弾性体層表面と比較し、より大きなものとなっていた。
【００７２】
また、作製した弾性体層の外径精度に関しても、実施例１の評価法により測定した。評価された弾性体層の外径精度は、表２に併せて示す。本実施例のローラは、その外径精度は、上記実施例１のローラにおける外径精度よりは僅かであるが、有意に劣る結果ではあった。この外径精度における差異は、前記の微少なしわやピンホール状の窪みに対応して、外径の局所的な変動を反映しているものである。しかしながら、弾性体層が発泡ゴム層と非発泡ゴム層の二層構造である、比較例１〜３において調製したローラと比較して、本実施例のローラでも、外径精度は有意に向上していると判断され、従って、0.1mm以下の良好な水準は維持されている。
【００７３】
さらに、実施例１と同じ手順・条件で、導電性薄膜の被覆を行い、最終的に、ローラ自体の抵抗が、およそ１０×１０⁶Ωの帯電ローラとした。この被覆薄膜層を形成した結果、前記の微少なしわやピンホール状の窪みを被覆材料が埋め込み、平滑化がなされた。この帯電ローラとした段階では、その表面粗さ、外径精度ともに、実施例１で作製した帯電ローラと比較しても、遜色のない程度となっていた。
【００７４】
実施例１に記載される評価方法に準じて、本実施例で作製した帯電ローラの抵抗についても、周内の均一性を評価したところ、比Ｒｍａｘ／Ｒｍｉｎは、１．４であった。本実施例で作製された、上記導電性薄膜被覆付きの帯電ローラを、電子写真装置（型式：LBP-320 Canon製）に組み込み、１５℃、１０ＲＨの環境下で実際の画像を出力したところ、実施例１の帯電ローラと同じく、帯電ローラの外径の不均一（外径精度不足）や表面の欠陥に起因する画像不良の発生は見出されなかった。
【００７５】
（比較例１〜３）
比較例１〜３において用いた、発泡ゴム層用の未加硫未発泡原料組成物、ならびに、非発泡ゴム層用の未加硫非発泡原料組成物の組成（重量部）を、表１に対比のため、併せて示した。また、実施例１に記載する方法に従い、各原料組成物の加硫速度、ムーニー粘度を評価し、その結果も、表１に併せて示す。比較例１〜３において、比較例２を除き、用いた未加硫非発泡原料組成物の加硫速度は、未加硫未発泡原料組成物の加硫速度より早く、ならびに、比較例１を除き、未加硫非発泡原料組成物のムーニー粘度は、未加硫未発泡原料組成物のムーニー粘度より高いことが確認される。
【００７６】
実施例１の手順に準じて、円筒状の積層体を図４に示す押し出し機を用いて作製した。非発泡ゴム層用の未加硫非発泡原料組成物の押し出しは、スクリュー径φ50mmの押し出し機を、発泡ゴム層用の未加硫未発泡原料組成物の押し出しは、スクリュー径φ75mmの押し出し機を、それぞれ用い、二つの押し出し機の回転比をφ50：φ75＝１：３に設定することで、各原料組成物の厚さを調整した。その後、実施例１の手順に従い、円筒状の積層体と芯金の一体化、加硫・発泡処理を施し、弾性体層の形成を行った。なお、円筒状積層体の寸法、用いた成形金型は、実施例１と同じ設計寸法とした。
【００７７】
得られた弾性体層の外形寸法は、実施例１と概ね同じであった。また、実施例１に記載する方法で、発泡ゴム層中の平均セル径、ならびに、非発泡ゴム層の平均膜厚を測定した。本比較例では、設計したとおり、表面の非発泡ゴム層の平均厚さは100μmとなっており、一方、各比較例における未加硫未発泡原料組成物の組成に応じて、内部の発泡ゴム層の平均セル径は、120〜150μmの範囲で分布するものであった。
【００７８】
また、作製した弾性体層の外径精度に関しても、実施例１の評価法により測定した。評価された弾性体層の外径精度は、表２に併せて示す。比較例１〜３のローラは、その外径精度は、いずれも、0.1mmを有意に超えており、良好な水準はではないものであった。
【００７９】
また、弾性体層の表面を観察すると、比較例１〜３のローラにおいては、高い頻度で、明確な表面荒れが見出された。具体的には、非発泡ゴム層の表面には、微少なしわや凹凸が幾つかの部分で見られた。あるいは、下層の発泡ゴム層から伝播してきて、表面でセルが潰れた跡に当たるピンホール状の窪みの発生も多く見られた。上述した低い外径精度の要因は、表面に生成した凹凸しわやピンホール状の窪みに対応して、外径の局所的な変動を反映しているものであった。
【００８０】
すなわち、これらの表面荒れは、発泡ゴム層における局所的な発泡の不均一、異常発泡や発泡不足に由来する凹凸が、上層の非発泡ゴム層にまでその影響を及ぼした結果であった。
【００８１】
さらに、実施例１と同じ手順・条件で、導電性薄膜の被覆を行い、最終的に、ローラ自体の抵抗が、およそ１０×１０⁶Ωの帯電ローラとした。この導電性薄膜被覆付きの帯電ローラを、電子写真装置（型式：LBP-320 Canon製）に組み込み、１５℃、１０ＲＨの環境下で実際の画像を出力したところ、異常発泡などを反映した表面の欠陥に起因し、画像不良の発生するローラが多数見出された。
【００８２】
（比較例４）
上記の実施例２において用いた、発泡ゴム層用の未加硫未発泡原料組成物と同じものを用いて、上層の非発泡ゴム層を設けない、ゴムローラを作製した。すなわち、実施例２に記載する一連の手順に準じるものの、上層の非発泡ゴム層となる原料組成物は、押し出し機に投入しなかった。
【００８３】
作製された弾性体層について、実施例１に記載する方法に従い、その外径精度を評価し、対比のため、結果を表２に示す。
【００８４】
また、実施例２と同様に、導電性薄膜の被覆を行い、最終的に、ローラ自体の抵抗が、およそ１０×１０⁶Ωの帯電ローラとした。被覆層を形成した後であっても、ローラ表面の表面粗さは、Ｒｚ＝４．１μmであった。作製した帯電ローラの抵抗について、周内の均一性を評価したところ、比Ｒｍａｘ／Ｒｍｉｎは、１．８にも達していた。この帯電ローラを、電子写真装置（型式：LBP-320 Canon製）に組み込み、１５℃、１０ＲＨの環境下で実際の画像を出力したところ、帯電ローラ周内の抵抗ムラに起因すると判断される、画像不良の発生が、１０本中、２本の頻度で見られた。
【００８５】
【発明の効果】
本発明のゴムローラは、弾性体層を発泡ゴム層とその上層に膜厚が薄い非発泡ゴム層を同心円筒状に形成したものであり、発泡ゴム層用の未加硫未発泡原料組成物と非発泡ゴム層用の未加硫非発泡原料組成物を用い、一体的に同時に押し出し形成する積層体を加熱し、加硫ならびに発泡処理を行い製造するので、発泡ゴム層内での異常発泡や発泡不足が生じ難く、結果として、異常発泡や発泡不足に由来する表面の欠陥ならびに表面粗さが極めて少ないものとできる。従って、表面粗さが十分小さく、また、外径精度も高く、ローラ硬度自体も適正なゴムローラとなる。特に、本発明の製造方法によれば、このように良質な品質を持つゴムローラが、一体的に同時に押し出し形成する積層体を用いて、単一の加熱処理で作製できるので、その生産性は高く、かつ、再現性よく製造することができる利点を持つ。加えて、本発明のゴムローラでは、上記するように弾性体層の表面は、そのままでも、外径精度は高く、また、表面荒れもなく、表面粗さも十分に小さいものであり、表面粗さや表面荒れを改善する目的で被覆膜層を表面に設ける必要がないものである。仮に、例えば、表面の耐摩耗性の改善、あるいは、表面の導電率の更なる均一化などの目的で、被覆薄膜層を表面に設ける際にも、その膜厚を必要最小限に抑えることが可能となる。例えば、帯電ローラに適用すると、被覆薄膜層に起因するローラ硬度の上昇を抑えることができ、硬度を低く保ちつつ、導電性の均一化が図られ、抵抗ムラの少ない帯電ローラを、再現性よく製造することができる。
【図面の簡単な説明】
【図１】本発明のゴムローラを接触帯電部材、転写部材などに利用することが可能な、電子写真装置の構成と、各ゴムローラの役割を模式的に示す図である。
【図２】本発明のゴムローラの一例を示す図であり、弾性体層の構成を説明する模式図である。
【図３】表面に被覆薄膜層を設けた本発明のゴムローラの一例における構成を説明する模式図である。
【図４】円筒状の積層体形成に利用する押し出し機の構成を模式的に示す図である。
【図５】円筒状の積層体形成に利用する押し出しヘッドの構成を模式的に示す断面図である。
【図６】ゴムローラの製造に用いる成形金型、円筒状の積層体と一体化した芯金を保持する状態を模式的に示す断面図である。
【図７】成形金型の加熱に利用される加熱盤の一例を模式的に示す図である。
【図８】帯電ローラの抵抗測定器の構成を模式的に示す図である。
【符号の説明】
１感光体（像担持体）
２帯電部材（帯電ローラ）
３露光手段
４現像部材
５転写部材（転写ローラ）
６転写材
７定着部材
８クリーニング部材
９トナー
１０芯金
１１発泡ゴム層
１２非発泡ゴム層
１３被覆薄膜層
１４押し出し機（発泡ゴム層用）
１５押し出し機（非発泡ゴム層用）
１６押し出しヘッド
１７ニップル
１８ダイス
１９未加硫非発泡原料組成物の流路
２０未加硫未発泡原料組成物の流路
２１成形金型本体
２２蓋体（芯金保持部材）
２３ガス抜き孔
２４円筒状の積層体
２５空孔部（成形金型挿入用）
２６熱盤（蓄熱ブロック）
２７帯電ローラ（導電性ゴムローラ）
２８芯金
２９アルミニウムドラム
３０電源[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a rubber roller in which an elastic body composed of two layers of a foamed rubber layer and a non-foamed rubber layer is formed on the outer peripheral surface of a cored bar, and a method for manufacturing the same. More specifically, for example, it is suitable for various rubber rollers used in an image forming apparatus using an electrophotographic process, that is, a charging / transfer roller, a developing roller, a conveyance roller, an image fixing roller, an intermediate transfer member, and the like. The present invention relates to a rubber roller that can be used and a method for manufacturing the same.
[0002]
[Prior art]
In the electrophotographic process, in the charging / transfer process, a non-contact type corona discharge has been conventionally used for charging the surface of the photoreceptor. During this corona discharge, it has been found that ozone and the like are generated, and that the generated ozone and the like cause deterioration of the photoreceptor surface. Furthermore, if dirt adheres to the wire used for corona discharge, the surface of the photoconductor is unevenly charged. For example, it causes image white spots and black streaks, which affects the image quality. is doing.
[0003]
Conventionally, a contact charging / transfer technique has been studied by many researchers as a method for charging the surface of a photoreceptor in place of the corona discharge. FIG. 1 is a sectional view schematically showing an example of the configuration of an electrophotographic apparatus using a contact charging / transfer member proposed by these studies. In this apparatus configuration, the object to be charged is an image carrier. Specifically, the object to be charged is composed of a conductive base layer using aluminum or the like and a photoconductive layer formed of amorphous silicon or the like on the outer peripheral surface thereof. This is a drum-type photoreceptor 1. A roller-shaped charging member 2 is installed so as to be in contact with the photosensitive member 1 and uniformly charges the surface of the photosensitive member 1 to a predetermined potential.
[0004]
The roller-shaped charging member 2, that is, the charging roller, is composed of a cored bar at the center and a layer of a conductive elastic body formed on the outer periphery thereof. The charging roller 2 is pressed against the photosensitive member 1 with a predetermined pressing force by a pressing means using a spring or the like, and accordingly, the charging roller 2 is rotated by the rotation of the photosensitive member 1. On the other hand, a direct current or a direct current + alternating current bias is applied to the core part of the charging roller 2 to charge the photoreceptor 1 to a predetermined potential. At this time, in order to obtain a good copy image, the surface of the photoconductor 1 needs to be charged to a uniform potential, that is, a uniform contact state of the charging roller 2 and conductivity uniformity are necessary. is there. The charged surface of the photoreceptor 1 is exposed to image information using an exposure unit 3 using a laser, LED, or the like as a light source, thereby forming an electrostatic latent image corresponding to the target image information.
[0005]
Next, toner is applied on the electrostatic latent image by the developing means 4 to form a visible image as a toner image. The toner image formed on the surface of the photosensitive member 1 is charged from the back surface of the transfer material 5 (copy paper or the like) with a polarity opposite to that of the toner by the transfer member 6 (transfer roller). Transfer to the surface. After the transfer of the toner image, the transfer material 5 is separated from the surface of the photoreceptor 1 and the image is fixed by heat and pressure on a fixing member 7 (fixing roller) that is installed first. On the other hand, after the image transfer, the surface of the photoconductor 1 is cleaned again by a cleaning unit 8 in a series of transfer steps to remove adhered toner and other residual matters remaining on the surface. By repeating this, the electrophotographic process can be continuously performed.
[0006]
In this type of apparatus, as shown in FIG. 1, for example, rollers are used for the charging member 2, the transfer member 6, the fixing member 7, and the like. For example, the charging roller or the like is composed of a core bar that is rotatably supported at both ends, and a conductive elastic body layer provided in a columnar shape on the outer periphery of the core bar. Thus, for example, when applying an alternating current component as described above, the conductive elastic body used for the charging roller is further kept in pressure contact to suppress the charging noise caused by the alternating current component. In order not to damage the surface of the photoreceptor, a material having a reduced surface hardness and adjusted resistance is used. Specifically, desired conductivity and hardness are often achieved by dispersing conductive particles in a foam having low hardness.
[0007]
The surface of the foam itself generally has a tendency to have a rough surface, and accordingly, if the contact with the photoconductor becomes nonuniform, the discharge tends to be nonuniform. Increasing the pressure contact force in order to make the contact densely causes the surface of the photoconductor to be unevenly worn or scraped during repeated use, and there is a problem that the life is shortened. In order to eliminate problems due to the properties of the foam itself, the surface of the conductive elastic body using the foam is coated with a conductive paint or covered with a smooth conductive tube. A method of forming a coating layer is also applied. This coating layer improves the surface roughness and adjusts the roller resistance.
[0008]
In the method of manufacturing a roller using a foam as a conductive elastic body, a polymer raw material of foam, a foaming agent, and various additives are blended, and a kneaded raw material composition extruded into a cylindrical shape is added. After vulcanizing and foaming, press the core metal into the center of the cylinder, polish the outer circumference to the desired outer diameter, and arrange the core metal in advance so that it is centered A cylindrical foamed elastic body having a predetermined outer diameter is obtained by using a mold, placing the raw material composition together with the cored bar inside the mold, heating the molding mold, and vulcanizing and foaming. A method of forming around a metal core is known.
[0009]
As described above, the foam roller produced by these methods is coated with a coating layer, for example, with the purpose of eliminating surface defects and improving the surface roughness. Then, it is necessary to increase the thickness of the coating layer, and as a result, problems such as an increase in roller hardness may occur.
[0010]
As a method for forming a coating layer with an appropriate layer thickness, when the surface roughness of the foam is not sufficiently small, a foaming material that becomes the foam and a non-foaming material that becomes the coating layer are used using separate extruders. There is also known a method of manufacturing a roller having a structure in which a non-foamed layer covering an internal foamed layer is formed by vulcanization after simultaneously forming a concentric cylindrical shape.
[0011]
If there is no external non-foamed layer, the foam raw material composition, that is, the foamed material, has a depression in the gap between the cell forming the foamed structure and the adjacent cell as the foaming reaction starts. The fine irregularities are left on the surface and are expanded and pressed against the inner wall of the mold. When the roller surface is formed by this pressing, most of the surface irregularities are crushed. However, it is not uncommon for some irregularities to remain and wrinkles to remain due to insufficient local pressing. Also, it happens that the cell is exposed on the surface, and the trace of the cell may form a pinhole. On the other hand, if there is a non-foamed layer on the outside, even if there is a gap between adjacent cells, even if there is a gap between the cells, when the outer wall is supported by the outer non-foamed layer and pressed against the inner wall of the mold, minute irregularities and wrinkles remain and occur. Therefore, a roller having a low surface roughness can be obtained, which is a useful method.
[0012]
However, if the balance of the layer thickness, Mooney viscosity, and vulcanization speed is lost between the inner foam layer and the outer non-foam layer, the foam material that becomes the inner foam layer cannot sufficiently foam. Occurs, the accuracy of the outer diameter decreases, or the shape accuracy decreases, such as an increase in shaft deflection. Also, if the expansion ratio is not sufficiently increased, the hardness will be increased. Conversely, if the support by the non-foamed layer is insufficient, the foaming gas will penetrate the non-foamed layer and cause a pinhole on the surface. However, the problem is inherent, such as causing the surface to become rough.
[0013]
As a means for preventing the occurrence of pinholes on the surface, the scorch time of the non-foamed layer is changed to the scorch time of the foamed layer as described in Japanese Patent Application Laid-Open No. 10-156917 in order to deal with the phenomenon that bubbles escape to the outside during foaming. There is a method of setting the length shorter, but under such conditions, if the thickness of the non-foamed layer is too thick, there is a possibility that the foaming ratio may not be sufficiently increased.
[0014]
[Problems to be solved by the invention]
Conventional attempts have been made to improve surface roughness and shape accuracy while maintaining an appropriate roller hardness, but leave room for improvement. For example, there is still a demand for a method for manufacturing an elastic roller capable of improving surface roughness while maintaining appropriate roller hardness with good reproducibility.
[0015]
The present invention solves the above-mentioned problems, and an object of the present invention is to provide a foam rubber roller that can be produced with good reproducibility using a molding die, has a small surface roughness, and high shape accuracy. And a method of manufacturing the same. More specifically, an object of the present invention is, for example, a foam rubber roller having a small surface roughness and high shape accuracy while maintaining a roller hardness suitable for a rubber roller used in an electrophotographic apparatus, and the foam. An object of the present invention is to provide a manufacturing method that enables a rubber roller to be manufactured with good reproducibility using a molding die. Furthermore, the present invention provides a foam rubber roller satisfying the above-mentioned characteristics in a rubber roller used for an electrophotographic apparatus or the like, particularly a charging member rubber roller used for charging an electrophotographic photoreceptor, and a method for producing the same. It is in.
[0016]
[Means for Solving the Problems]
In order to solve the above-mentioned problems, the present inventors have advanced research to compare and examine the properties of the resulting rubber roller by variously changing the properties, vulcanization and foaming conditions of the raw material composition used for producing the foam rubber roller. It was. As a result, when a cylindrical elastic body layer having a two-layer structure having a foam layer on the inside and a non-foam layer on the outside is formed on the outer periphery of the core metal using a molding die, The vulcanized unfoamed raw material composition and the unvulcanized non-foamed raw material composition that is the raw material of the non-foamed layer, the vulcanization speed of the unvulcanized non-foamed raw material composition, the vulcanization speed of the unvulcanized unfoamed raw material composition If the Mooney viscosity of the unvulcanized unfoamed raw material composition is made lower than the Mooney viscosity of the unvulcanized unfoamed raw material composition, the surface roughness of the molded roller becomes sufficiently small, and at the same time, The present inventors have found that shape accuracy such as diameter accuracy and runout is high, and that moderate roller hardness can be obtained with good reproducibility, and based on such knowledge, the present invention has been completed.
[0017]
  That is, the rubber roller of the present invention is a rubber roller in which a concentric cylindrical elastic body having a foam rubber layer on the inside and a non-foam rubber layer on the outside is formed on the outer periphery of the core metal,
  The foam rubber layer comprises a foam polymer material and a foaming agent.BlendedThe material is foam rubber obtained by vulcanizing and foaming the unvulcanized unfoamed raw material composition obtained by kneading,
  The non-foamed rubber layer is a polymer raw materialBlendedThe non-foamed rubber obtained by vulcanizing the unvulcanized unfoamed raw material composition obtained by kneading,
  The vulcanization rate of the unvulcanized unfoamed raw material composition is made slower than the vulcanization rate of the unvulcanized unfoamed raw material composition, and the Mooney viscosity of the unvulcanized unfoamed raw material composition Less than the Mooney viscosity of the vulcanized unfoamed raw material composition,
  The unvulcanized non-foamed raw material composition is formed as a concentric cylindrical laminate integrally and simultaneously extruded on the outer periphery of the unvulcanized unfoamed raw material composition. The cored bar is arranged with its axis center aligned,
  A cylinder having a predetermined cylindrical inner peripheral surface that is larger than the outer periphery of the concentric cylindrical laminate and having lids at both ends for holding the cored bar on the concentric shaft of the cylindrical inner peripheral surface Using a shaped mold,
  The laminate formed integrally with the core metal is placed in the molding die, subjected to vulcanization and foaming treatment,
  Along with the foaming, the outer peripheral surface of the laminate is pressed against the inner peripheral surface of the molding die, a foamed rubber layer is formed on the inner side, and a non-foamed rubber layer is formed on the outer side. It is a rubber roller characterized by having a layer(However, the vulcanization rate was calculated based on JIS K 6300, which was calculated from the measurement results obtained by performing the vulcanization test of Method A under the conditions of 160 ° C. and 1 degree deflection angle. 30 And the Mooney viscosity was determined by performing a Mooney viscosity test based on JIS K 6300. (1 + 4) A value of 100 ° C.).
[0018]
  Further, the method for producing the rubber roller of the present invention includes:A method of manufacturing a rubber roller in which a concentric cylindrical elastic body having a foam rubber layer on the inside and a non-foam rubber layer on the outside is formed on the outer periphery of the core metal,
  (I) An unvulcanized unfoamed raw material composition obtained by blending and kneading a foam polymer raw material and a foaming agent as a raw material for the foamed rubber layer, and a polymer raw material as a raw material for the non-foamed rubber layer. The unvulcanized non-foamed raw material composition thus formed is integrally and simultaneously extruded on the outer periphery to form a concentric cylindrical laminate, and the core metal is aligned in the center of the concentric cylindrical laminate. And placing; and
  ( ii ) It has a predetermined cylindrical inner peripheral surface that is larger than the outer periphery of the concentric cylindrical laminate, and has lids at both ends for holding the cored bar on the concentric shaft of the cylindrical inner peripheral surface. Using a cylindrical molding die, the step of arranging the laminate prepared integrally with the core metal prepared in the step (i) in the molding die and subjecting it to vulcanization and foaming; as well as
  ( iii ) With the foaming, the outer peripheral surface of the laminate is pressed against the inner peripheral surface of the molding die, and a concentric cylindrical elastic body having a foamed rubber layer on the inside and a non-foamed rubber layer on the outside is formed. Forming a rubber layer, in a method for manufacturing a rubber roller,
  The vulcanization rate of the unvulcanized unfoamed raw material composition is made slower than the vulcanization rate of the unvulcanized unfoamed raw material composition, and the Mooney viscosity of the unvulcanized unfoamed raw material composition This is a method for producing a rubber roller, characterized in that it is smaller than the Mooney viscosity of the vulcanized unfoamed raw material composition (however, the vulcanization speed is based on JIS K 6300 and the vulcanization test of method A is 160 T calculated from the measurement results obtained under the conditions of ℃ and deflection angle of 1 degree. 30 And the Mooney viscosity was determined by performing a Mooney viscosity test based on JIS K 6300. (1 + 4) A value of 100 ° C.).
[0019]
In the rubber roller of the present invention, it is preferable that the thickness of the non-foamed rubber layer is 50% or more of the cell diameter with respect to the foamed cell diameter in the foamed rubber layer. In the rubber roller of the present invention, the foamed rubber layer and the non-foamed rubber layer can both be electrically conductive. In addition, the rubber roller of the present invention may have a structure in which one or two or more conductive coating thin film layers are coated on the outer peripheral surface of the elastic rubber layer.
[0020]
In the rubber roller of the present invention described above, if the cylindrical elastic body formed on the outer periphery of the core metal has conductivity, for example, it is placed in contact with the surface of the electrophotographic photoreceptor, and charging of the photoreceptor is performed. It can utilize suitably for the charging roller used for.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
The rubber roller of the present invention comprises an elastic body layer, which is a main component of the roll portion, a foam rubber layer that mainly gives elasticity, and a non-foam rubber that is integrally formed on the outside and governs the surface shape of the roll portion. The layer has a concentric cylindrical two-layer structure. The outer shape of the unvulcanized unfoamed raw material composition is a foamed rubber layer using a molding die that is formed on a smooth inner surface when performing foaming treatment. It is formed by pressing accompanying foaming. That is, the outline of the outer shape of the rubber roller of the present invention is essentially defined by the inner shape of the molding die.
[0022]
Therefore, when the cross section in the roll part is typically shown, the rubber roller of this invention takes the structure which shows an example in FIG. When the surface of the elastic body layer formed using the mold is further coated with one or more coating thin film layers, the cross section thereof is, for example, the shape schematically shown in FIG. Become. 2 and 3, a metal is often used for the cored bar 10, but a conductive material such as a conductive resin can also be used. A foamed rubber layer 11 and a non-foamed rubber layer 12 are formed in a concentric cylindrical shape on the outer periphery of the metal core 10 as an elastic body layer having a two-layer structure. In FIG. 3, one or more coating thin film layers 13 are provided on the outer peripheral surface of the elastic layer. Usually, the thickness of the non-foamed rubber layer 12 is formed so as to be significantly thinner than the thickness of the foamed rubber layer 11, and the total film thickness of the covering thin film layer 13 is also sufficiently thinner than the thickness of the foamed rubber layer 11. Select
[0023]
In other words, the coating thin film layer 13 is, for example, a contact roller disposed on the surface of an electrophotographic photoreceptor, and a charging roller used for charging the photoreceptor is a coating film coated with a conductive paint or a conductive thin film. It is formed by covering with a conductive tube to be formed. In the charging roller, in order to make the potential on the roller surface uniform, a coating thin film layer made of the above-described conductive material is provided to further increase the conductivity in the roller surface. In addition, when used as a transfer member in an electrophotographic apparatus, similarly to the charging roller, in order to make the potential on the roller surface uniform, a coating thin film layer made of the conductive material is provided, The conductivity is further increased. Alternatively, in the roller used as a fixing member that fixes the transferred toner image by applying heat and pressure, a film that increases durability against heat or the like may be provided as the coating thin film layer 13. Thus, as the covering thin film layer 13, a thin film layer having desired characteristics may be appropriately selected according to the purpose of use.
[0024]
When the configuration shown in FIG. 3 is taken, a coated thin film layer 13 is provided on the outermost surface of the roller, and the surface shape, surface roughness, etc. are the surface shape of the non-foamed rubber layer 12 before forming the coated thin film layer 13. Some improvement is seen from the surface roughness. However, the film thickness of the coating thin film layer 13 is formed to be uniform within the roller surface, and in many cases, the surface shape and surface roughness of the non-foamed rubber layer 12 are the shape of the outermost surface of the roller, It is thin enough to be reflected in the surface roughness.
[0025]
The rubber roller of the present invention can be manufactured, for example, by the procedure described below.
[0026]
First, a non-foamed non-foamed raw material composition for a non-foamed rubber layer and a concentric cylindrical laminate formed by simultaneously and integrally extruding the outer periphery of an unvulcanized unfoamed raw material composition for a foamed rubber layer; None, in which the cored bar is disposed in the concentric cylindrical laminate so that the axial centers coincide with each other. The concentric cylindrical laminate is formed using an apparatus capable of simultaneously extruding two kinds of raw material compositions as shown in FIG. 4 from a single extrusion head. The apparatus shown in FIG. 4 includes an extruder 14 for a foamed rubber layer, an extruder 15 for a non-foamed rubber layer, and an extrusion head 16 disposed at the center thereof. The inside of the extrusion head 16 has taken the structure shown, for example in FIG. Concentrically, a flow path 20 for the unvulcanized unfoamed raw material composition and a flow path 19 for the unvulcanized non-foamed raw material composition are provided around it, respectively, and an extruder 14 for the foamed rubber layer and the non-foamed foam respectively. The raw material composition is extruded from the rubber layer extruder 15 at a desired supply amount. At the center of the extrusion head 16, a nipple 17 corresponding to the hole diameter of the cylindrical laminate and a die 18 that defines the outer diameter of the cylindrical laminate are set. Immediately before the die 18, the raw material composition supplied from the unvulcanized unfoamed raw material composition flow path 20 and the unvulcanized non-foamed raw material composition flow path 19 around it has a predetermined film thickness ratio. Is laminated. That is, the discharge rate (number of rotations) from the extruder 14 for the foamed rubber layer and the extruder 15 for the non-foamed rubber layer is adjusted to obtain a predetermined film thickness ratio.
[0027]
The cylindrical laminated body extruded from the die 18 is arranged by integrating a cored bar with its axis aligned in the center hole. The length is cut to a predetermined length according to the final roll length. Next, the cylindrical laminated body integrated with the core metal is subjected to foaming and vulcanization treatment in, for example, a molding die shown in FIG. 6 to be an elastic body, and at the same time, its outer shape is molded.
[0028]
The example of the molding die shown in FIG. 6 includes a concentric cylindrical die body 21 and lid bodies 22 at both ends. The lid body 22 has a hole for holding the cored bar, and has a function of a cored bar holding member for arranging the cored bar on the central axis of the concentric cylindrical mold body 21. The lid 22 is provided with a gas vent hole 23 for releasing the gas expelled from the mold due to the volume expansion accompanying the foaming / vulcanizing process. The inner surface of the molding die is a smooth surface, and the inner diameter is set corresponding to the outer diameter of the rubber roller to be manufactured.
[0029]
During the foaming / vulcanization treatment, the cylindrical laminate is heated so that the temperature becomes uniform. For example, the heating is performed by mounting a molding die in a heating plate whose shape is schematically shown in FIG. The heating plate shown in FIG. 7 is composed of a heat storage block (heat plate) 26 divided into two, and a hole 25 for inserting a molding die is formed at the center. A heating plate is preheated to a predetermined temperature in advance, a molding die holding a laminated body integrated with a core metal is inserted, and heating is performed.
[0030]
By heating, foaming and vulcanization proceed, and when the foamed inner rubber layer reaches the desired foaming ratio by foaming, the upper non-foamed rubber layer is pressed against the inner surface of the molding die and molded into the prescribed shape. Is done. When the vulcanization of the non-foamed rubber layer proceeds, the heating is finished, and after cooling, it is removed from the mold, and a series of rubber roller manufacturing steps is finished. In addition, when a coating thin film layer is further provided on the surface of the obtained elastic body layer, a coating material is applied as a subsequent process to obtain a finished rubber roller product.
[0031]
In the production method of the present invention, the vulcanization rate of the unvulcanized non-foamed raw material composition used as the raw material for the non-foamed rubber layer is greater than the vulcanization rate of the unvulcanized unfoamed raw material composition used as the raw material for the foamed rubber layer. The Mooney viscosity of the unvulcanized non-foamed raw material composition used for the raw material of the non-foamed rubber layer is made smaller than the Mooney viscosity of the unvulcanized unfoamed raw material composition used for the raw material of the foamed rubber layer. For this reason, when heating is started, foaming of the unvulcanized unfoamed raw material composition starts to proceed, and vulcanization is also started. At this time, since the vulcanization speed of the unvulcanized non-foaming raw material composition is made slower, the viscosity increase and curing accompanying the cross-linking formation proceed more slowly. Also, since the Mooney viscosity of the unvulcanized non-foamed raw material composition is made smaller, it does not interfere at all when the inner unvulcanized unfoamed raw material composition expands and the occupied volume expands. . In other words, the fluidity of the unvulcanized unfoamed raw material composition is higher than the fluidity of the unvulcanized unfoamed raw material composition at this stage, and therefore expansion due to foaming of the inner unvulcanized unfoamed raw material composition. Therefore, the foaming progresses to the extent that it is not inferior to the case where the unvulcanized unfoamed raw material composition is not present in the upper layer.
[0032]
If the unvulcanized unfoamed raw material composition is not present in the upper layer, the cell formed by the very surface layer of the unvulcanized unfoamed raw material composition sometimes breaks through its surface, and the bubbles are external. There is a phenomenon that falls off. In the present invention, although the viscosity is smaller, since the layer of the unvulcanized unfoamed raw material composition exists in the upper layer, the cell formed by the very surface layer breaks through the surface. Has an inhibitory effect. In addition, even if the bubbles escape from the surface of the unvulcanized unfoamed raw material composition, the upper unlayered layer of the unvulcanized non-foamed raw material composition has higher fluidity, so that the bubbles were released. The remaining hole marks are filled more quickly and easily, and no pinhole-shaped marks are left.
[0033]
When the bubbles escape to the outside, a dome shape rises on the surface due to the internal pressure of the cell, and the surface layer of the cell is maintained only by viscosity in this portion. When the dome-shaped bulge grows to more than half the cell diameter, the bottom portion of the cell is pushed out by the external force applied so far against the internal pressure of the cell, so that the bubbles rapidly escape to the outside. Therefore, when the unvulcanized unfoamed raw material composition layer has a thickness of 50% or more of the average cell diameter as the upper layer, the surface (interface) of the unvulcanized unfoamed raw material composition is half the cell diameter. As described above, the air bubbles are prevented from escaping to the outside until they rise to a dome shape. On the other hand, when the surface of the unvulcanized unfoamed raw material composition rises to a dome shape more than half of the cell diameter, and the unvulcanized unfoamed raw material composition layer has a lower viscosity, The bubbles may escape from the surface (interface) of the unvulcanized unfoamed raw material composition, pass through the unvulcanized non-foamed raw material composition layer, and escape to the outside. At this time, pores occupied by bubbles remain in the unvulcanized non-foamed raw material composition layer. However, since the fluidity is higher, the pores are quickly filled and eliminated. Therefore, the thickness of the unvulcanized non-foamed raw material composition layer, that is, the thickness of the non-foamed rubber layer is more preferably 50% or more of the average cell diameter in the foamed rubber layer. Even if the film thickness of the non-foamed rubber layer is less than 50% of the average cell diameter, the above effect is maintained in a considerable range, but the effect decreases as the film thickness becomes thinner.
[0034]
When foaming of the unvulcanized unfoamed raw material composition proceeds and is pressed against the inner surface of the molding die, further expansion in the radial direction is suppressed. In addition, although the unvulcanized unfoamed raw material composition itself is kneaded so that the foaming agent contained is uniformly dispersed, the foaming reaction itself is a reaction that starts with an accidental chance, With sparse and dense. The portion where the foaming is dense first reaches the inner surface of the molding die, the radial expansion is suppressed, and the sparse portion reaches the inner surface of the molding die with a delay. Meanwhile, in the dense part, the axial expansion is still progressing, and sometimes fine wrinkles are formed at the boundary between the dense part and the sparse part on the surface (interface) of the unvulcanized unfoamed raw material composition. May be. Further, as described above, extremely fine irregularities are also present along with the dome-like swelling caused by the cells that have reached the surface (interface) of the unvulcanized unfoamed raw material composition. Since the unvulcanized unfoamed raw material composition is more fluid, it fills the fine dents and wrinkles generated on the surface (interface) of these unvulcanized unfoamed raw material compositions and is easily flattened. The These fine dents and wrinkles are usually only about 50% of the average cell diameter in the foamed rubber layer, and the thickness of the unvulcanized non-foamed raw material composition layer, that is, the film of the non-foamed rubber layer If the thickness is 50% or more of the average cell diameter in the foamed rubber layer, flattening is more reliable. Further, in many cases, there is also an embedding effect by the unvulcanized unfoamed raw material composition itself that still retains fluidity by pressing, and the fine irregularities and wrinkles are 50% of the average cell diameter in the foamed rubber layer. Since the variation is only less than, even when the thickness of the unvulcanized unfoamed raw material composition layer, that is, the film thickness of the non-foamed rubber layer is less than 50% of the cell average diameter in the foamed rubber layer, Flattening is achieved in a considerable range. When this surface flattening is achieved, even in an unvulcanized non-foamed raw material composition having a slower vulcanization rate, vulcanization proceeds and loses fluidity, and the surface shape of the elastic layer is smooth. It matches the inner surface of the mold.
[0035]
As described above, in the present invention, the upper layer has an unvulcanized non-foamed raw material composition having a slower vulcanization speed and a smaller Mooney viscosity, so that it is formed by pressing on a molding die. The body layer surface has no pinhole-like surface defects corresponding to traces of air bubbles, and is a rubber roller having extremely small surface roughness and no variation in outer diameter. The effect of using an unvulcanized non-foamed raw material composition having a slower vulcanization speed and a smaller Mooney viscosity as the upper layer is the thickness of the unvulcanized non-foamed raw material composition layer, that is, non-foamed. Even if the film thickness of the rubber layer becomes thicker, it is not essentially damaged. However, since the non-foamed rubber layer does not have a cell structure inside, the non-foamed rubber layer usually does not exhibit elasticity as much as the foamed rubber layer, and the resin has a relatively high hardness. When the hardness of the resin is high, the hardness of the roller as a whole increases as the film thickness of the non-foamed rubber layer increases. Considering this point, unless there is a special reason, the film thickness of the non-foamed rubber layer is more preferably in a range that does not increase by an order of magnitude with respect to the value of 50% of the average cell diameter in the foamed rubber layer. Therefore, it is generally more preferable that the film thickness of the non-foamed rubber layer is selected to be not more than ten times the average cell diameter in the foamed rubber layer, or several times, for example, a range not exceeding 2-3 times. .
[0036]
The rubber roller of the present invention can reduce the film thickness of the non-foamed rubber layer used for the upper layer, and can obtain a low-hardness roller, and there is no defect on the surface and the shape is highly uniform. Therefore, for example, when the elastic body layer is made of a conductive material, resistance unevenness in the circumference can be reduced, so that in an electrophotographic apparatus, a charging member (which is used for charging by contacting with the surface of the photoreceptor) It is more suitable for a transfer member (transfer roller) used for transferring a toner image onto a charging roller or a copy sheet.
[0037]
The raw polymer used in the unvulcanized unfoamed raw material composition used as the raw material for the foamed rubber layer and the unvulcanized non-foamed raw material composition used as the raw material for the non-foamed rubber layer depends on the intended use of the roller. For example, natural rubber, butadiene rubber, styrene butadiene rubber (SBR), nitrile rubber (acrylonitrile-butadiene rubber), ethylene-propylene rubber (EPDM: ethylene-propylene-diene terpolymer), ethylene-propylene It may be selected from various polymers such as rubber (EPM), chloroprene rubber (CR), nitrile butadiene rubber (NBR), epichlorohydrin rubber, butyl rubber, silicon rubber, urethane rubber, fluorine rubber, and chlorine rubber. Specifically, the unvulcanized unfoamed raw material composition, and the unvulcanized non-foamed raw material composition are selected from the above-mentioned various polymers so that the vulcanization speed and Mooney viscosity satisfy the above conditions, Or it is good to combine.
[0038]
A foaming agent is added to the unvulcanized unfoamed raw material composition used as the raw material for the foam rubber layer, and a desired foaming ratio can be obtained depending on the type of raw material polymer, vulcanization conditions, the crosslinking temperature, and the like. Select the amount and type of foaming agent. Examples of organic foaming agents include ADCA (azodicarbonamide), DPT (dinitrosopentamethylenetetraamine), TSH (p-toluenesulfonyl hydrazide), OBSH (oxybisbenzenesulfenyl hydrazide), and the like. . When using the said organic foaming agent, the addition amount of a foaming agent is normally selected in the range of 2-30 weight part with respect to 100 weight part of said raw material polymers. Moreover, according to the case, it is also possible to use an inorganic foaming agent, for example, sodium bicarbonate, ammonium carbonate, etc. are mentioned. Moreover, in addition to the said foaming agent, a foaming adjuvant can also be added suitably.
[0039]
In the unvulcanized unfoamed raw material composition and the unvulcanized non-foamed raw material composition, depending on the type of raw material polymer used, sulfur or a metal oxide that is a non-sulfur vulcanizing agent is used as a vulcanizing agent. In addition, an organic peroxide or the like that is suitable for obtaining a desired vulcanization rate is added. Further, a suitable vulcanization accelerator is selected according to the addition amount of the vulcanizing agent, and the addition amount is appropriately selected and added so as to obtain a desired crosslinking density. Furthermore, various vulcanization acceleration aids are also added.
[0040]
When making the foamed rubber layer and the non-foamed rubber layer conductive, conductive powder is dispersed in the raw material polymer in the raw material composition. For example, frequently used conductive powders include carbons such as carbon black and conductive carbon, graphite, TiO₂, SnO₂, ZnO and other conductive metal oxides, SnO₂And Sb₂O_ThreeSolid solution of ZnO and Al₂O_ThreeExamples thereof include composite oxides with the above metal oxides such as solid solutions, metal powders such as Cu and Ag, and conductive fibers. Depending on the desired conductivity and depending on the specific gravity of the conductive powder material to be used, the addition amount of the conductive powder is selected in the range of 5 to 200 parts by weight with respect to 100 parts by weight of the raw material polymer and added as appropriate.
[0041]
In addition, an inorganic filler such as carbon black, talc, or clay may be added to the raw material composition, which is useful for kneading the raw material composition or forming a cylindrical shape by subsequent extrusion. Process oil, softener, etc. are added as necessary.
[0042]
In the production method of the present invention, the unvulcanized unfoamed raw material composition and the unvulcanized unfoamed raw material composition added and kneaded with each of the above components have the vulcanization rate of the unvulcanized non-foamed raw material composition. The vulcanization speed of the unvulcanized unfoamed raw material composition is made slower than that, and the Mooney viscosity of the unvulcanized nonfoamed raw material composition is made smaller than the Mooney viscosity of the unvulcanized unfoamed raw material composition. In order to satisfy the above conditions, the type of raw material polymer and other additive components are selected, and the content is adjusted. The vulcanization speed should be measured in advance under the conditions and temperature at which vulcanization is actually performed, and the values should be compared. In general, a representative value is obtained based on the vulcanization test specified in JIS. The representative value may satisfy the above condition. Even if there is a slight difference in conditions, the magnitude relationship between the vulcanization speeds is generally preserved, so that there is no problem as long as there is a significant difference in the magnitude relation between the vulcanization speeds. Similarly, regarding the Mooney viscosity, a representative value may be obtained in accordance with a Mooney viscosity test specified in JIS or the like, and the representative value may satisfy the above condition.
[0043]
For example, as a representative value of vulcanization rate, based on JIS K 6300, a vulcanization test of Method A was performed at 160 ° C. under a swing angle of 1 degree (JSR Clastometer Type III), and calculated from the measurement result t30 Can be used. Further, for example, as a representative value of Mooney viscosity, a Mooney viscosity test is also performed based on JIS K 6300, a value of ML (1 + 4) 100 ° C. is obtained, and this value of ML (1 + 4) 100 ° C. is used. be able to.
[0044]
In the present invention, for example, when the vulcanization rate of the unvulcanized unfoamed raw material composition is selected in the range of 1.5 to 8 in the value of t30, the vulcanized unvulcanized raw material composition is vulcanized. The speed is selected within the range of 2 to 12 in the value of t30. At this time, the vulcanization speed of the unvulcanized unfoamed raw material composition is approximately the vulcanization speed of the unvulcanized unfoamed raw material composition. If it is selected to be 1.2 to 3 times, a more preferable result is obtained. At the same time, for example, when the Mooney viscosity of the unvulcanized unfoamed raw material composition is selected within the range of 28 to 36 at the ML (1 + 4) value of 100 ° C., the uncured unfoamed raw material composition In the value of ML (1 + 4) 100 ° C., the range of 15 to 40 is selected. At that time, the Mooney viscosity of the unvulcanized unfoamed raw material composition is the same as the Mooney viscosity of the unvulcanized unfoamed raw material composition. If it is selected to be 0.8 to 0.3 times, a more preferable result is obtained.
[0045]
The rubber roller of this invention can provide a coating thin film layer on the outer peripheral surface of said elastic body layer. For example, when a conductive film is formed as the coating thin film layer, the material of the film is, for example, N-methylmethoxylated nylon, polyvinyl butyral, polyethylene, polyvinyl acetate, polystyrene, polybutadiene, polyamide, polyimide, polyurethane. Polyester, silicone resin, and the like, and epichlorohydrin, urethane, chloroprene, acrylonitrile-butadiene rubber, and the like can be used. An appropriate amount of a conductive pigment such as carbon black, carbon graphite, titanium oxide, or zinc oxide may be added to the coating material selected from these in order to adjust the conductivity to a desired value. For example, when a film is formed by coating the conductive film material, these film component substances are dissolved or dispersed in a solvent or the like to form a paint, and depending on the film thickness, dipping, spray coating, A suitable means may be selected from means such as roll coating, and the coating may be performed uniformly on the outer periphery of the roller.
[0046]
The film thickness of the coated thin film layer should be appropriately selected according to the purpose of coating, but in the present invention, it is generally preferable to select a thinner film thickness as long as the intended function is maintained. That is, generally, when a coating thin film layer is provided, as the film thickness increases, the roller hardness tends to increase, and in order to prevent unnecessary high hardness, a thinner film can be used as long as the purpose of coating is not impaired. It is generally preferred to select a thickness.
[0047]
【Example】
Hereinafter, the rubber roller of the present invention and the manufacturing method thereof will be described in more detail with specific examples. In the specific example described below, an example will be described in which the electrophotographic photosensitive member is mainly disposed in contact with a rubber roller having a conductive roller portion suitable for a charging roller used for charging the surface of the photosensitive member. The present invention is not limited to these specific examples.
[0048]
Example 1
The present embodiment is an example of producing a charging roller used for charging the surface of the photosensitive member. The surface of the produced charging roller is sufficiently small, and at the same time, the outer diameter accuracy and runout are reduced. This is an example in which it has been verified that a high degree of shape accuracy is obtained and an appropriate roller hardness is obtained with good reproducibility.
[0049]
In this example, the unvulcanized non-foamed raw material composition for the non-foamed rubber layer is made of an ethylene-propylene-diene terpolymer (product model number: EPT4045, Mitsui Petrochemical Co., Ltd.) as the raw material polymer. As a conductive agent (conductive powder), ketjen black (product model number: ketjen black EC manufactured by Mitsubishi Chemical Corporation)) or SRF carbon black (product model number: Asahi # 35 manufactured by Asahi Carbon Co., Ltd.) is used as a softener. Paraffin oil as a crosslinking agent (vulcanizing agent), sulfur as a vulcanization accelerator, mercaptobenzothiazole (M) and cyclohexyl benzothiazole sulfenamide (CBS) as a vulcanization acceleration aid, lead oxide and Stearic acid was used, and the content (parts by weight) of each component was set to the values shown in Table 1. For kneading, an open roll was used to obtain a uniform composition.
[0050]
In addition, the unvulcanized unfoamed raw material composition for the foam rubber layer is obtained by using an ethylene-propylene-diene terpolymer (product model number: EPT8075E manufactured by Mitsui Petrochemical Co., Ltd.) as a raw material polymer and a conductive agent (conductive Ketjen Black (product model number: manufactured by Mitsubishi Chemical Co., Ltd.)) or SRF carbon black (product model number: manufactured by Asahi # 35 Asahi Carbon Co., Ltd.) as a softener, and paraffin oil as a softener Sulfur as vulcanizing agent (vulcanizing agent), mercaptobenzothiazole (M), zinc dibutyldithiocarbamate (ZnBDC), tetramethylthiuram disulfide (TMTD), and cyclohexyl benzothiazole sulfenamide (CBS) as vulcanization accelerators As a vulcanization accelerator, lead oxide and stearic acid as foaming agents, ADCA and O The SH, using respectively, the content (parts by weight) of each component was a value shown in Table 1. For kneading, an open roll was used to obtain a uniform composition.
[0051]
With respect to the unvulcanized unfoamed raw material composition for the non-foamed rubber layer and the unvulcanized unfoamed raw material composition for the foamed rubber layer, as an index value of the vulcanization rate, based on JIS K 6300, The vulcanization test was conducted under the conditions of 160 ° C. and a swing angle of 1 degree (JSR curlastometer type III), and the value of t30 calculated from the measurement result was used as a representative value. In addition, as an index value of Mooney viscosity, a Mooney viscosity test was performed based on JIS K 6300, and a value of ML (1 + 4) 100 ° C. was used as a representative value. The typical values of the vulcanization speed and Mooney viscosity are also shown in Table 1. As can be seen from the comparison of the representative values, the vulcanization rate of the unvulcanized non-foamed raw material composition used in this example is significantly slower than the vulcanization rate of the unvulcanized unfoamed raw material composition, and It is confirmed that the Mooney viscosity of the vulcanized non-foamed raw material composition is significantly lower than the Mooney viscosity of the unvulcanized unfoamed raw material composition.
[0052]
Using the unvulcanized unfoamed raw material composition for the non-foamed rubber layer and the unvulcanized unfoamed raw material composition for the foamed rubber layer, the extruder shown in FIG. 4 and the extrusion head shown in FIG. 5 were used. A die having an inner diameter of φ7.75 mm and a nipple having an outer diameter of φ5.0 mm were set on the head, and extrusion was performed simultaneously and integrally to form a cylindrical laminate. The length of the cylindrical laminate was cut to approximately the same length so as to fit within the hole portion length of 224 mm of the molding die.
[0053]
In the extruder shown in FIG. 4, the unvulcanized unfoamed raw material composition for the non-foamed rubber layer is extruded using an extruder with a screw diameter of 50 mm, and the unvulcanized unfoamed raw material composition for the foamed rubber layer is extruded. The thickness of the raw material composition of the foamed rubber layer and the non-foamed rubber layer was adjusted by using an extruder with a screw diameter of φ75 mm and setting the rotation ratio of the two extruders to φ50: φ75 = 1: 3. .
[0054]
The cored bar was previously coated with a conductive adhesive and inserted into the center hole of the obtained cylindrical laminate to assemble the cored bar and the cylindrical laminate. Thereafter, as schematically shown in FIG. 6, the core metal ends were fixed to lid bodies provided at both ends of the molding die so that the axes coincide with each other, and the laminate was disposed inside the die. This molding die was inserted into the heating plate of FIG. 7 preheated to 180 ° C. and heated for 15 minutes to perform vulcanization / foaming treatment. As a result, an elastic body layer having an outer dimension of 224 mm in length and a diameter of φ12 mm on the surface of the core metal having a diameter of φ6 mm and an inner surface dimension of the used mold and a diameter of φ12.3 mm was formed. The average thickness of the non-foamed rubber layer on the surface was 100 μm, and the average cell diameter of the internal foamed rubber layer was 153 μm. Therefore, the film thickness of the non-foamed rubber layer corresponds to approximately 65% of the cell diameter of the foamed rubber layer.
[0055]
The average cell diameter is obtained by observing the cross section of the foamed rubber layer with a microscope or the like, and having about 10 pieces from the maximum diameter among the cell cross sections that appear in various sizes in the field of view. This is the average value of the measured cell diameters. When the cell cross-sectional shape is greatly distorted from a perfect circle and is elliptical, the simple average of the major axis and the minor axis was taken as the measured value of the cell diameter.
[0056]
FIG. 6 schematically shows the shape and configuration of the molding die used in the present example. The mold body 21 has a cylindrical shape with an outer diameter of φ26 mm and an inner surface of an inner diameter of φ12.3 mm, and lid bodies (core metal holding members) 22 having holes for inserting and holding the core metal of the roller are provided at both ends. Installed. With the lid 22 attached, the length of the inner surface is slightly longer than 224 mm as described above. The lid body 22 is provided with a gas vent hole 23 that serves as a passage for the internal gas. A cylindrical laminated body 24 serving as an elastic body layer of the roller is disposed so that the inner surface of the mold coincides with the axis center by holding the central core metal by the lid body 22. On the other hand, the heating panel is composed of a heat storage block that is divided into two parts, as schematically shown in FIG. 7, and a hole 25 that matches the outer dimensions of the molding die is formed on the divided surface. Yes. When the molding die is inserted, uniform heating is performed from the outer periphery.
[0057]
The outer diameter accuracy and surface roughness of the rubber roller produced by the above procedure were evaluated. Taking into account the variation of the cylindrical laminate itself produced by the extruder, an average value was obtained for N = 10. As for the outer diameter, the outer diameter was measured using a non-contact type laser length measuring instrument in the range excluding the 5 mm both ends of the rubber roller, and the difference between the maximum value and the minimum value was defined as the outer diameter accuracy. It should be noted that the charging roller having the outer diameter of the present embodiment is good if the outer diameter accuracy is 0.1 mm or less.
[0058]
Further, a conductive coating layer was applied to the surface of the rubber roller produced by the above procedure to prepare a charging roller for use in an electrophotographic apparatus. For the coating of the conductive coating layer, conductive oxidation in which a polyurethane liquid in which polyurethane is dispersed in water is adjusted to pH 5 to 6 and powdered tin oxide is dispersed by the electric repulsive force at the interface. As the tin slurry, a conductive tin oxide-added polyurethane coating in which tin oxide was dispersed in an amount corresponding to 30% in terms of solid content was used. The surface of the roller treated with a silane coupling agent is coated with the paint, and heated and dried at 120 ° C. for 30 minutes in a hot air oven to coat a conductive thin film having a thickness of 40 μm. went. Finally, the resistance of the roller itself is 10 × 10⁶An Ω charging roller was used.
[0059]
Further, when the surface roughness of the manufactured charging roller was measured after coating the conductive thin film, the surface roughness was Rz = 0.89 μm, and the surface roughness of the elastic body layer before coating was measured. It was a reflection.
[0060]
In addition, in order to examine the uniformity in the circumference of the resistance of the manufactured charging roller, the resistance distribution of the roller was measured in the circumferential direction using an evaluation apparatus schematically shown in FIG. In the evaluation apparatus shown in FIG. 8, a pressing force f = 500 g is applied to the end of the cored bar 28 so that the charging roller 27 is pressed against the aluminum drum 29. In this pressure contact state, the charging roller 27 is driven by the drum 29 and rotated. A voltage DC 100 V was applied between the power source 30 and the drum 29 via the core metal 28, and the resistance of the roller was measured while rotating the charging roller 27. In the circumferential direction, the ratio between the maximum value Rmax and the minimum value Rmin was obtained in the circumferential direction based on the measured value of the resistance of the roller. The ratio Rmax / Rmin was 1.3.
[0061]
When the charging roller with the conductive thin film coating prepared in this example was incorporated into an electrophotographic apparatus (model: LBP-320 manufactured by Canon) and an actual image was output in an environment of 15 ° C. and 10 RH, The occurrence of image defects reported to be caused by non-uniform outer diameter of the charging roller (insufficient outer diameter accuracy) or surface defects was not found.
[0062]
Comparison was made with the charging rollers produced in Comparative Examples 1 to 3 and Comparative Example 4 produced by the conventional method described later. First, Table 2 shows the accuracy of the outer diameter of the elastic layer before coating with the conductive thin film. Similar to this example, the roller of this example has an outer diameter accuracy compared to the rollers prepared in Comparative Examples 1 to 3, in which the elastic layer has a two-layer structure of a foamed rubber layer and a non-foamed rubber layer. Significantly improved, with a good level of 0.1mm or less.
[0063]
[Table 1]

[0064]
[Table 2]

(Example 2)
In this example, unlike Example 1 above, in the unvulcanized unfoamed raw material composition for the foamed rubber layer, an ethylene-propylene-diene terpolymer (product model number: EPT8075E Mitsui Petrochemical Co., Ltd.) was used as the raw material polymer. (Inc.) instead of using an ethylene-propylene-diene terpolymer (product model number: EPT4045, Mitsui Petrochemical Co., Ltd.) It was adjusted. On the other hand, the unvulcanized non-foaming raw material composition for the non-foamed rubber layer had the same composition as that used in Example 1. Table 1 shows the component composition (parts by weight) of the unvulcanized unfoamed raw material composition for the foamed rubber layer and the unvulcanized nonfoamed raw material composition for the non-foamed rubber layer.
[0065]
Moreover, according to the method described in Example 1, the vulcanization speed and Mooney viscosity of each raw material composition were evaluated, and the results are also shown in Table 1. As can be seen from the comparison of the representative values, also in this example, the vulcanization rate of the unvulcanized unfoamed raw material composition used was significantly slower than the vulcanization rate of the unvulcanized unfoamed raw material composition, and It is confirmed that the Mooney viscosity of the unvulcanized unfoamed raw material composition is significantly lower than the Mooney viscosity of the unvulcanized unfoamed raw material composition. However, compared to Example 1, the difference in Mooney viscosity is smaller.
[0066]
According to the procedure of Example 1, a cylindrical laminate was produced using the extruder shown in FIG. Extruding unvulcanized unfoamed raw material composition for non-foamed rubber layer is an extruder with a screw diameter of φ50 mm. Extruding unvulcanized unfoamed raw material composition for foamed rubber layer is an extruder with a screw diameter of φ75 mm. Were used, and the rotation ratio of the two extruders was set to φ50: φ75 = 1: 3, thereby adjusting the thickness of the raw material composition of the foamed rubber layer and the non-foamed rubber layer. Then, according to the procedure of Example 1, the cylindrical laminated body and the core metal were integrated, vulcanized and foamed, and an elastic body layer was formed. The dimensions of the cylindrical laminate and the molding die used were the same design dimensions as in Example 1. The outer dimensions of the obtained elastic body layer are essentially the same as those of Example 1, and the average cell diameter in the foamed rubber layer and the average of the non-foamed rubber layer were measured by the method described in Example 1. The film thickness was measured. In this example, the average thickness of the non-foamed rubber layer on the surface was 100 μm, and the average cell diameter of the internal foamed rubber layer was 151 μm. Therefore, the film thickness of the non-foamed rubber layer corresponds to approximately 66% of the cell diameter of the foamed rubber layer.
[0067]
Further, the outer diameter accuracy of the produced elastic body layer was also measured by the evaluation method of Example 1. Table 2 shows the outer diameter accuracy of the evaluated elastic layer. The outer diameter accuracy of the roller of this example was slightly inferior to the outer diameter accuracy of the roller of Example 1 described above. Although there is this slight difference, the roller of this example is different from the roller prepared in Comparative Examples 1 to 3 in which the elastic body layer has a two-layer structure of a foamed rubber layer and a non-foamed rubber layer. As with the No. 1 roller, the outer diameter accuracy is significantly improved, and is a good level of 0.1 mm or less.
[0068]
Further, the conductive thin film is coated in the same procedure and conditions as in Example 1, and finally the resistance of the roller itself is about 10 × 10⁶An Ω charging roller was used. According to the evaluation method described in Example 1, the uniformity of the circumference of the charging roller manufactured in this example was also evaluated. As a result, the ratio Rmax / Rmin was 1.3. Correspondingly, the charging roller with the conductive thin film coating prepared in this example is incorporated into an electrophotographic apparatus (model: LBP-320 manufactured by Canon), and an actual image is obtained in an environment of 15 ° C. and 10 RH. As in the charging roller of Example 1, the occurrence of image defects due to non-uniform outer diameter of the charging roller (insufficient outer diameter accuracy) and surface defects were not found.
[0069]
(Example 3)
In this example, the unvulcanized unfoamed raw material composition for the foamed rubber layer and the unvulcanized nonfoamed raw material composition for the non-foamed rubber layer were the same as those used in Example 1.
[0070]
According to the procedure of Example 1, a cylindrical laminate was produced using the extruder shown in FIG. For extruding the unvulcanized unfoamed raw material composition for the non-foamed rubber layer, an extruder with a screw diameter of φ50 mm is used. For extruding the unvulcanized unfoamed raw material composition for the foamed rubber layer, an extruder with a screw diameter of φ75 mm is used. However, the raw material composition thickness of the non-foamed rubber layer was adjusted to be thinner than that in Example 1 by setting the rotation ratio of the two extruders to φ50: φ75 = 1: 4. Then, according to the procedure of Example 1, the cylindrical laminated body and the core metal were integrated, vulcanized and foamed, and an elastic body layer was formed. The dimensions of the cylindrical laminate and the molding die used were the same design dimensions as in Example 1. The outer dimensions of the obtained elastic body layer are essentially the same as those of Example 1, and the average cell diameter in the foamed rubber layer and the average of the non-foamed rubber layer were measured by the method described in Example 1. The film thickness was measured. In this example, as designed, the average thickness of the non-foamed rubber layer on the surface was 60 μm, and the average cell diameter of the foamed rubber layer on the inside was 159 μm. Therefore, the film thickness of the non-foamed rubber layer corresponds to approximately 38% of the cell diameter of the foamed rubber layer.
[0071]
Further, when the surface of the elastic layer was observed, the surface roughness of the roller of Example 2 was found with a considerable frequency. Specifically, on the surface of the non-foamed rubber layer, there was a portion where minute wrinkles were seen, and in the lower foamed rubber layer, the occurrence of pinhole-shaped depressions corresponding to the collapsed cells was also observed. . Due to these fine surface roughnesses, the surface roughness was larger than that of the roller elastic body layer surface of Example 1.
[0072]
Further, the outer diameter accuracy of the produced elastic body layer was also measured by the evaluation method of Example 1. Table 2 shows the outer diameter accuracy of the evaluated elastic layer. The outer diameter accuracy of the roller of this example was slightly lower than the outer diameter accuracy of the roller of Example 1, but the result was significantly inferior. This difference in outer diameter accuracy reflects local fluctuations in the outer diameter corresponding to the fine wrinkles and pinhole-shaped depressions. However, compared with the rollers prepared in Comparative Examples 1 to 3, in which the elastic layer has a two-layer structure of a foam rubber layer and a non-foam rubber layer, the outer diameter accuracy is significantly improved even with the roller of this example. Therefore, a good level of 0.1 mm or less is maintained.
[0073]
Further, the conductive thin film is coated in the same procedure and conditions as in Example 1, and finally the resistance of the roller itself is about 10 × 10⁶An Ω charging roller was used. As a result of forming this coating thin film layer, the above-mentioned fine wrinkles and pinhole-shaped depressions were filled with a coating material and smoothed. At the stage of making this charging roller, the surface roughness and outer diameter accuracy were comparable to those of the charging roller produced in Example 1.
[0074]
According to the evaluation method described in Example 1, the resistance within the circumference of the charging roller produced in this example was also evaluated, and the ratio Rmax / Rmin was 1.4. When the charging roller with the conductive thin film coating prepared in this example was incorporated into an electrophotographic apparatus (model: LBP-320 manufactured by Canon) and an actual image was output in an environment of 15 ° C. and 10 RH, As in the charging roller of Example 1, no occurrence of image defects due to non-uniform outer diameter (insufficient outer diameter accuracy) or surface defects was found.
[0075]
(Comparative Examples 1-3)
Table 1 shows the composition (parts by weight) of the unvulcanized unfoamed raw material composition for the foamed rubber layer and the unvulcanized nonfoamed raw material composition for the non-foamed rubber layer used in Comparative Examples 1 to 3. For comparison, it is also shown. Moreover, according to the method described in Example 1, the vulcanization speed and Mooney viscosity of each raw material composition were evaluated, and the results are also shown in Table 1. In Comparative Examples 1 to 3, except for Comparative Example 2, the vulcanization rate of the unvulcanized unfoamed raw material composition used was faster than the vulcanization rate of the unvulcanized unfoamed raw material composition. Except for this, it is confirmed that the Mooney viscosity of the unvulcanized unfoamed raw material composition is higher than the Mooney viscosity of the unvulcanized unfoamed raw material composition.
[0076]
According to the procedure of Example 1, a cylindrical laminate was produced using the extruder shown in FIG. For extruding the unvulcanized unfoamed raw material composition for the non-foamed rubber layer, an extruder with a screw diameter of φ50 mm is used. For extruding the unvulcanized unfoamed raw material composition for the foamed rubber layer, an extruder with a screw diameter of φ75 mm is used. The thickness of each raw material composition was adjusted by setting the rotation ratio of the two extruders to φ50: φ75 = 1: 3. Then, according to the procedure of Example 1, the cylindrical laminated body and the core metal were integrated, vulcanized and foamed, and an elastic body layer was formed. The dimensions of the cylindrical laminate and the molding die used were the same design dimensions as in Example 1.
[0077]
The outer dimensions of the obtained elastic body layer were substantially the same as those in Example 1. Further, the average cell diameter in the foamed rubber layer and the average film thickness of the non-foamed rubber layer were measured by the method described in Example 1. In this comparative example, as designed, the average thickness of the non-foamed rubber layer on the surface is 100 μm. On the other hand, depending on the composition of the unvulcanized unfoamed raw material composition in each comparative example, the internal foamed rubber The average cell diameter of the layer was distributed in the range of 120 to 150 μm.
[0078]
Further, the outer diameter accuracy of the produced elastic body layer was also measured by the evaluation method of Example 1. Table 2 shows the outer diameter accuracy of the evaluated elastic layer. The rollers of Comparative Examples 1 to 3 each had an outer diameter accuracy significantly exceeding 0.1 mm, which was not a good level.
[0079]
Moreover, when the surface of the elastic body layer was observed, clear surface roughness was found at a high frequency in the rollers of Comparative Examples 1 to 3. Specifically, fine wrinkles and irregularities were observed in several portions on the surface of the non-foamed rubber layer. Alternatively, many occurrences of pinhole-shaped depressions that propagated from the lower foamed rubber layer and hit the trace of the cells being crushed on the surface were also observed. The factors of the low outer diameter accuracy described above reflect local fluctuations in the outer diameter corresponding to the uneven wrinkles and pinhole-shaped depressions generated on the surface.
[0080]
That is, these surface roughnesses were the result of unevenness due to local non-uniform foaming, abnormal foaming or insufficient foaming in the foamed rubber layer, which affected the upper non-foamed rubber layer.
[0081]
Further, the conductive thin film is coated in the same procedure and conditions as in Example 1, and finally the resistance of the roller itself is about 10 × 10⁶An Ω charging roller was used. This charging roller with a conductive thin film coating was incorporated into an electrophotographic apparatus (model: LBP-320 Canon), and an actual image was output in an environment of 15 ° C. and 10 RH. Many rollers have been found that have image defects due to defects.
[0082]
(Comparative Example 4)
Using the same unvulcanized unfoamed raw material composition for the foamed rubber layer used in Example 2 above, a rubber roller without an upper non-foamed rubber layer was prepared. That is, although it followed the series of procedures described in Example 2, the raw material composition to be the upper non-foamed rubber layer was not put into the extruder.
[0083]
About the produced elastic body layer, the outer diameter accuracy was evaluated according to the method described in Example 1, and the results are shown in Table 2 for comparison.
[0084]
Similarly to Example 2, the conductive thin film is coated, and finally the resistance of the roller itself is about 10 × 10.⁶An Ω charging roller was used. Even after the coating layer was formed, the surface roughness of the roller surface was Rz = 4.1 μm. As a result of evaluating the uniformity in the circumference of the resistance of the manufactured charging roller, the ratio Rmax / Rmin reached 1.8. When this charging roller is incorporated into an electrophotographic apparatus (model: LBP-320 manufactured by Canon) and an actual image is output under an environment of 15 ° C. and 10 RH, it is determined that the charging roller is caused by uneven resistance in the periphery of the charging roller. The occurrence of image defects was observed at a frequency of 2 out of 10.
[0085]
【The invention's effect】
The rubber roller of the present invention is an elastic layer in which a foamed rubber layer and a non-foamed rubber layer having a thin film thickness are formed concentrically on top of the foamed rubber layer, and an unvulcanized unfoamed raw material composition for the foamed rubber layer, Using the unvulcanized unfoamed raw material composition for the non-foamed rubber layer, the laminated body that is extruded and formed at the same time is heated and vulcanized and foamed to produce. Insufficient foaming hardly occurs, and as a result, surface defects and surface roughness resulting from abnormal foaming and insufficient foaming can be made extremely small. Therefore, a rubber roller having a sufficiently small surface roughness, high outer diameter accuracy, and appropriate roller hardness is obtained. In particular, according to the manufacturing method of the present invention, a rubber roller having such a high quality can be produced by a single heat treatment using a laminated body that is integrally formed by extrusion at the same time, so that its productivity is high. And it has the advantage that it can be manufactured with good reproducibility. In addition, in the rubber roller of the present invention, as described above, the surface of the elastic body layer has a high outer diameter accuracy, no surface roughness, and the surface roughness is sufficiently small. It is not necessary to provide a coating film layer on the surface for the purpose of improving roughness. For example, when the coating thin film layer is provided on the surface for the purpose of, for example, improving the wear resistance of the surface or further uniforming the conductivity of the surface, the film thickness can be minimized. It becomes possible. For example, when applied to a charging roller, it is possible to suppress an increase in roller hardness due to the coated thin film layer, and to maintain a low hardness while achieving uniform conductivity, a charging roller with less resistance unevenness can be reproduced with high reproducibility. Can be manufactured.
[Brief description of the drawings]
FIG. 1 is a diagram schematically illustrating the configuration of an electrophotographic apparatus that can use a rubber roller of the present invention as a contact charging member, a transfer member, and the role of each rubber roller.
FIG. 2 is a diagram illustrating an example of a rubber roller according to the present invention, and is a schematic diagram illustrating a configuration of an elastic body layer.
FIG. 3 is a schematic view illustrating a configuration in an example of a rubber roller of the present invention in which a coating thin film layer is provided on the surface.
FIG. 4 is a diagram schematically showing the configuration of an extruder used for forming a cylindrical laminate.
FIG. 5 is a cross-sectional view schematically showing a configuration of an extrusion head used for forming a cylindrical laminated body.
FIG. 6 is a cross-sectional view schematically showing a state where a molding die used for manufacturing a rubber roller and a cored bar integrated with a cylindrical laminated body are held.
FIG. 7 is a view schematically showing an example of a heating plate used for heating a molding die.
FIG. 8 is a diagram schematically illustrating a configuration of a resistance measurement device for a charging roller.
[Explanation of symbols]
1 Photoconductor (image carrier)
2 Charging member (charging roller)
3 Exposure means
4 Development member
5 Transfer member (transfer roller)
6 Transfer material
7 Fixing member
8 Cleaning member
9 Toner
10 cored bar
11 Foam rubber layer
12 Non-foamed rubber layer
13 Coating thin film layer
14 Extruder (for foam rubber layer)
15 Extruder (for non-foamed rubber layer)
16 Extrusion head
17 Nipple
18 dice
19 Flow path of unvulcanized unfoamed raw material composition
20 Flow path of unvulcanized unfoamed raw material composition
21 Mold body
22 Lid (core metal holding member)
23 Degassing holes
24 Cylindrical laminate
25 Hole part (for inserting mold)
26 Heating board (heat storage block)
27 Charging roller (conductive rubber roller)
28 cored bar
29 Aluminum drum
30 power supply

Claims

A rubber roller in which a concentric cylindrical elastic body having a foamed rubber layer on the inside and a non-foamed rubber layer on the outside is formed on the outer periphery of the core metal,
The foamed rubber layer is made of foamed rubber obtained by vulcanizing and foaming an unvulcanized unfoamed raw material composition obtained by blending and kneading a foam polymer raw material and a foaming agent,
The non-foamed rubber layer is made of a non-foamed rubber obtained by vulcanizing an unvulcanized non-foamed raw material composition obtained by blending and kneading a polymer raw material,
The vulcanization rate of the unvulcanized unfoamed raw material composition is made slower than the vulcanization rate of the unvulcanized unfoamed raw material composition, and the Mooney viscosity of the unvulcanized unfoamed raw material composition Less than the Mooney viscosity of the vulcanized unfoamed raw material composition,
The unvulcanized non-foamed raw material composition is formed as a concentric cylindrical laminate integrally and simultaneously extruded on the outer periphery of the unvulcanized unfoamed raw material composition. The cored bar is arranged with its axis center aligned,
A cylinder having a predetermined cylindrical inner peripheral surface that is larger than the outer periphery of the concentric cylindrical laminate and having lids at both ends for holding the cored bar on the concentric shaft of the cylindrical inner peripheral surface Using a shaped mold,
The laminate formed integrally with the core metal is placed in the molding die, subjected to vulcanization and foaming treatment,
Along with the foaming, the outer peripheral surface of the laminate is pressed against the inner peripheral surface of the molding die, a foamed rubber layer is formed on the inner side, and a non-foamed rubber layer is formed on the outer side. A rubber roller having a layer (however, the vulcanization speed is calculated based on a measurement result obtained by performing a vulcanization test of Method A under the conditions of 160 ° C. and a deflection angle of 1 degree based on JIS K 6300. And the Mooney viscosity is ML (1 + 4) 100 ° C. obtained by conducting a Mooney viscosity test based on JIS K 6300 ) .

The rubber roller according to claim 1, wherein a thickness of the non-foamed rubber layer is 50% or more of the cell diameter with respect to a foamed cell diameter in the foamed rubber layer.

3. The rubber roller according to claim 1 , further comprising one or more conductive coating thin film layers on an outer peripheral surface of the non-foamed rubber layer . 4.

The rubber roller according to claim 1, wherein both the foamed rubber layer and the non-foamed rubber layer have conductivity .

An image forming apparatus using an electrophotographic process, wherein the rubber roller according to claim 4 is used as a charging roller that is disposed in contact with the surface of an electrophotographic photosensitive member and is used for charging the photosensitive member. Image forming apparatus .

A method for producing a rubber roller in which a concentric cylindrical elastic body having a foam rubber layer on the inside and a non-foam rubber layer on the outside is formed on the outer periphery of the core metal,
(I) An unvulcanized unfoamed raw material composition obtained by blending and kneading a foam polymer raw material and a foaming agent as a raw material for the foamed rubber layer, and a polymer raw material as a raw material for the non-foamed rubber layer. The unvulcanized non-foamed raw material composition thus formed is integrally and simultaneously extruded on the outer periphery to form a concentric cylindrical laminate, and the core metal is aligned in the center of the concentric cylindrical laminate. Arranging the steps;
( ii ) It has a predetermined cylindrical inner peripheral surface that is larger than the outer periphery of the concentric cylindrical laminate, and has lids at both ends for holding the cored bar on the concentric shaft of the cylindrical inner peripheral surface. Using a cylindrical molding die, the step of arranging the laminate prepared integrally with the core metal prepared in the step (i) in the molding die and subjecting it to vulcanization and foaming; as well as
( iii ) With the foaming, the outer peripheral surface of the laminate is pressed against the inner peripheral surface of the molding die, and a concentric cylindrical elastic body having a foamed rubber layer on the inside and a non-foamed rubber layer on the outside is formed. Forming a rubber layer, in a method for producing a rubber roller,
The vulcanization rate of the unvulcanized unfoamed raw material composition is made slower than the vulcanization rate of the unvulcanized unfoamed raw material composition, and the Mooney viscosity of the unvulcanized unfoamed raw material composition A method for producing a rubber roller, characterized in that it is smaller than the Mooney viscosity of the vulcanized unfoamed raw material composition ( However, the vulcanization rate was calculated based on JIS K 6300, and was calculated from the measurement results obtained by performing the vulcanization test of Method A under the conditions of 160 ° C. and a swing angle of 1 degree. 30 And the Mooney viscosity was determined by performing a Mooney viscosity test based on JIS K 6300. (1 + 4) A value of 100 ° C.).