JP4070011B2

JP4070011B2 - Method of manufacturing foamed conductive rubber roller for image forming apparatus and transfer roller

Info

Publication number: JP4070011B2
Application number: JP2002228774A
Authority: JP
Inventors: 竜太浦野; 正幸橋本; 満奥田
Original assignee: Canon Chemicals Inc
Current assignee: Canon Chemicals Inc
Priority date: 2002-08-06
Filing date: 2002-08-06
Publication date: 2008-04-02
Anticipated expiration: 2022-08-06
Also published as: JP2004069980A

Description

【０００１】
【発明の属する技術分野】
本発明は、電子写真方式を利用した複写機やプリンター等の画像形成装置で用いられる画像形成装置用導電性ゴムローラの製造方法に関するものであり、特に、電子写真感光体に当接して用いられる転写ローラに関するものである。
【０００２】
【従来の技術】
従来、複写機やプリンター等のＯＡ機器の画像形成装置においては、コロナ放電により高電圧を印加する非接触型の帯電法が用いられていた。しかしながら、この帯電法ではコロナ放電に伴い有害なオゾンが発生する問題があった。そこで近年では、電圧印加した導電性ゴムローラを電子写真感光体表面に押し当て、絶縁体表面を帯電する接触帯電方式を用いた画像形成が主流となっており、画像形成の中心であるＯＰＣ等の電子写真感光体を用いた感光ドラム廻りに帯電、転写等の各工程別に導電性ゴムローラが用いられている。
【０００３】
また、導電性ゴムローラにおいては、ドラムとの密着性を高めるため上記特性のほかに適度に低硬度であることが望まれている。ローラ硬度が高い場合、感光ドラム等とのニップ幅が小さくなるため、例えば、転写ローラの場合、転写率が低下したり、電子写真感光体の表面の摩耗や損傷により画像の欠陥を生じ易い。また、硬度が低過ぎる場合は、柔らか過ぎて圧縮永久歪が大きくなり耐久性が劣るほか、搬送力が強くなり過ぎ画像に欠陥を生じ易い。
【０００４】
導電性ゴムローラの低硬度化の方法としては、軟化剤や可塑剤等の各種添加剤を用いている方法が挙げられるが、軟化剤や可塑剤等を添加した導電性ゴムローラを感光ドラムと接触使用した場合、導電性ゴムローラ内から低分子量の各種添加剤がブリードアウトし電子写真感光体表面に付着することで、画像劣化や電子写真感光体汚染等を起こすという問題が生じ易い。
【０００５】
そのため、導電性ゴムローラの低硬度化は、一般的に、化学発泡剤を用いて発泡弾性ゴムローラを得る方法が用いられている。
【０００６】
上記導電性ゴムローラに用いるゴム材料としては、アクリロニトリルブタジエンゴム（ＮＢＲ）やエピクロルヒドリンゴム等の極性ゴムを用いる手法が一般的である。極性ゴムは、ポリマー内に存在する極性基の作用により導電性をもつため、抵抗のばらつきが小さく、また電気抵抗の電圧依存性が小さいことから導電性ゴムローラに適していることが知られている。
【０００７】
しかしながら、アクリロニトリルブタジエンゴムやエピクロルヒドリンゴム等を主成分とする導電性ゴムローラの場合、極性ゴムであるため電子写真感光体表面を被膜している極性樹脂と馴染み易く、電子写真感光体表面に貼り付き、画像劣化や電子写真感光体汚染等を起こすという問題を生じ易い。
【０００８】
そこで、このような上記の問題点を解決する方法として、ローラ表面にオゾンや紫外線を照射することで表面を改質する方法（特開平８−２９２６４０号公報及び特開平１１−１４９２０１号公報等）や非極性ゴムをブレンドする方法が提案されている。しかしながら、オゾンや紫外線を照射する方法は貼り付き防止に効果があるものの、人体に悪影響を与える恐れもあり、また、設備も高価である。
【０００９】
また、非極性ゴムとのブレンドの場合、非極性ゴムと電子写真感光体表面の樹脂被膜との極性の違いにより馴染みにくく、その結果、アクリロニトリルブタジエンゴムやエピクロルヒドリンゴムと電子写真感光体表面との接触が緩和され、電子写真感光体表面との貼り付かないローラが得られる。また、イオン導電系ゴム材の特徴である抵抗のばらつきが小さく、電気抵抗の電圧依存性が小さいという特性を保持した導電性ゴムローラを得ることができる。
【００１０】
【発明が解決しようとする課題】
しかしながら、極性ゴムであるアクリロニトリルブタジエンゴムやエピクロルヒドリンゴムと非極性ゴムからなるゴム組成物の場合、両者が非相溶性であり、また、加硫速度や発泡速度が異なるため、均一に発泡させることが困難である問題を有していた。
【００１１】
本発明の目的は、前述の事情に鑑みなされたものであり、接触使用しても電子写真感光体への貼り付きや汚染がなく、かつ抵抗値の環境依存性の小さい低硬度の画像形成装置用導電性ゴムローラの製造方法及び転写ローラを提供することである。
【００１２】
【課題を解決するための手段】
本発明に従って、導電性芯材上に発泡ゴム層が設けられている画像形成装置用発泡導電性ゴムローラの製造方法において、
該発泡ゴム層のゴム組成物のゴム成分が、少なくともエチレンプロピレンジエンゴム（Ａ）、エピクロルヒドリンゴム（Ｂ）及びアクリロニトリルブタジエンゴム（Ｃ）を含有しており、該ゴム組成物のゴム成分１００質量部に対し、化学発泡剤としてアゾジカルボンアミドが５〜１５質量部含有され、かつ、下記条件
（１）該（Ａ）の全ゴム成分の合計１００質量部に対する割合が１０質量部以上３０質量部以下、
（２）該（Ｂ）の（Ｂ）、（Ｃ）の合計１００質量部に対する割合が５質量部以上２５質量部未満、
を満たし、かつ、１６０℃で３０分間の条件で加硫曲線と発泡圧曲線を測定して得た加硫進行率について、
（３）該ゴム組成物の発泡進行率１０％における加硫進行率が５〜２７％、
（４）該ゴム組成物の発泡進行率９０％における加硫進行率が４８〜８５％、
を満たすゴム組成物を、
加熱手段として加硫缶を用いた直接加圧蒸気、設定加熱温度１５０〜１７０℃で加硫させることを特徴とする画像形成装置用発泡導電性ゴムローラの製造方法が提供される。
また、本発明に従って、電子写真感光体上の静電荷像を現像剤により現像する画像形成装置に用いられる転写ローラにおいて、該転写ローラが電子写真感光体上に相対して配置される上記に記載の製造方法により得られた画像形成装置用発泡導電性ゴムローラであることを特徴とする転写ローラが提供される。
【００１３】
【発明の実施の形態】
以下、本発明の導電性ゴムローラについて詳述する。本発明の発泡導電性ゴムローラは、導電性芯材上に発泡ゴム層が設けられている発泡導電性ゴムローラである。本発明に使用するゴム組成物中のゴム成分は、少なくとも非極性ゴム（Ａ）、エピクロルヒドリンゴム（Ｂ）及びアクリロニトリルブタジエンゴム（Ｃ）を含有し、その配合割合は非極性ゴム（Ａ）の全ゴム成分の合計１００質量部に対する割合が１０質量部以上３０質量部以下であり、エピクロルヒドリンゴム（Ｂ）及びアクリロニトリルブタジエンゴム（Ｃ）の合計１００質量部に対するエピクロルヒドリンゴム（Ｂ）の割合が５質量部以上２５質量部未満である。また、上記ゴム組成物の発泡進行率１０％における加硫進行率が５〜２７％、発泡進行率９０％における加硫進行率が４８〜８５％である。
【００１４】
上記ゴム成分中の非極性ゴム（Ａ）の種類は、電子写真感光体に対し貼り付きや汚染がないものであれば、特に限定されるものではない。例えば、エチレンプロピレンゴム、エチレンゴム、エチレンブタジエンゴム及びブタジエンゴム等が挙げられるが、特に耐オゾン性や耐熱性の面で優れているエチレンプロピレンジエンゴムが好ましい。
【００１５】
上記非極性ゴムの添加量は、全ゴム成分１００質量部に対して１０質量部以上３０質量部以下であり、より好ましくは１５質量部以上２５質量部以下である。非極性ゴムが１０質量部未満の場合、アクリロニトリルブタジエンゴムやエピクロルヒドリンゴムと電子写真感光体表面との接触を緩和する効果が弱く、電子写真感光体表面に貼り付いたり、電子写真感光体汚染を生じる。また、非極性ゴムが３０質量部を超える場合、電子写真感光体への貼り付きや汚染に効果があるものの、ローラ抵抗が高くなるため、転写ローラとしての機能を損ない、転写不良による画像ムラを生じてしまう。そのためローラ抵抗としては、最も抵抗が高くなる低温低湿環境においても１×１０^１０Ω未満が好ましい。
【００１６】
上記ゴム成分中のエピクロルヒドリンゴム（Ｂ）とアクリロニトリルブタジエンゴム（Ｃ）は、抵抗調整を目的として添加される。アクリロニトリルブタジエンゴムのアクリロニトリル含有量や、エピクロルヒドリンゴムのエチレンオキサイドとエピクロルヒドリンの共重合比率は、各ローラで所望する電気抵抗等の諸特性を有していれば、特に限定されるものではない。
【００１７】
上記エピクロルヒドリンゴム（Ｂ）とアクリロニトリルブタジエンゴム（Ｃ）の添加割合は、エピクロルヒドリンゴム（Ｂ）及びアクリロニトリルブタジエンゴム（Ｃ）の合計１００質量部に対するエピクロルヒドリンゴム（Ｂ）の割合が５質量部以上２５質量部未満である。エピクロルヒドリンゴムが５質量部未満の場合、抵抗値はほとんど変化せず、また、２５質量部以上の場合、抵抗の環境変動が大きいエピクロルヒドリンゴムの割合が増すため、ローラ抵抗の環境変動が大きくなる。ローラ抵抗の環境変動が大きい場合、抵抗の変化に合わせて印加電圧を制御する必要があり、また、抵抗変化に耐えうる電源を搭載する必要がありコスト面や装置の小型化に影響する。そのため、ローラ抵抗の環境変動は、低温・低湿と高温・高湿の環境下の抵抗変動桁で１．３０以下が好ましい。
【００１８】
本発明において、上記ゴム組成物の発泡進行率１０％における加硫進行率が５〜２７％、発泡進行率９０％における加硫進行率が４８〜８５％であることが重要である。
【００１９】
発泡進行率１０％における加硫進行率が５％より小さい場合は、発泡進行率９０％における加硫進行率にかかわらず、発泡反応と加硫反応のバランスにおいて、発泡反応が先行してしまうため、ゴム表面からガスが抜けて発泡不足になり、硬度が高くなり、電子写真感光体の表面の摩耗や損傷により画像の欠陥を生じる。
【００２０】
そのため、ローラの硬度としては、φ６ｍｍの導電性芯材に４ｍｍ厚の発泡ゴム層を設けた発泡導電性ゴムローラにおいては、アスカーＣ硬度で２０°〜４０°が好ましく、より好ましくは２５°〜３５°である。
【００２１】
発泡進行率１０％における加硫進行率が２７％を超える場合は、発泡進行率９０％における加硫進行率にかかわらず、発泡反応と加硫反応のバランスにおいて、加硫反応が先行してしまうため、ゴムの粘度が上がり、発泡し難いため発泡ガスが押さえこまれ発泡不足となり、硬度が高くなってしまう。
【００２２】
また、発泡進行率１０％における加硫進行率が５〜２７％の範囲内であっても、発泡進行率９０％における加硫進行率が４８％より小さい場合は、発泡反応と加硫反応のバランスが崩れ、ゴム表面から発泡ガスが抜け発泡不良になり、低硬度のローラが得難くなってしまう。また、発泡進行率９０％における加硫進行率が、８５％を超える場合は、ゴムの粘度が高く発泡し難くなるため発泡ガスが押さえ込まれ発泡不足となり、硬度が高くなってしまう。
【００２３】
また、化学発泡剤としては、アゾジカルボンアミドが挙げられる。
【００２４】
４、４’−オキシビス（ベンゼンスルホニルヒドラジド）やパラトルエンスルホニルヒドラジドを用いた場合、分解温度が低いため発泡の進行が早くなり、上記の加硫速度と発泡速度のバランスを調整し難く、また、ジニトロソペンタメチレンテトラミンの場合は、分解副生成物として毒性のあるホルムアルデヒドやアミン臭の強いヘキサメチレンテトラミンが発生するため、本発明で使用する発泡剤としてはアゾジカルボンアミドである。
【００２５】
アゾジカルボンアミドの添加量は特に限定されるものではないが、ゴム成分１００質量部に対し５〜１５質量部添加する。アゾジカルボンアミドの添加量が５質量部より少ない場合、発生ガス量が少ないため発泡不足となり硬度が高くなり易い。また、アゾジカルボンアミドの添加量が１５質量部を超えて添加した場合は、発生ガス量が多過ぎるため、発泡セル径が大きくなり、硬度が低過ぎて圧縮永久歪が大きくなり、画像に欠陥を生じ易い。
【００２６】
また、本発明の発泡導電性ゴムローラに使用されるゴム組成物には、一般のゴムに使用されるその他の成分を必要に応じて含有させることができる。例えば、硫黄や有機含硫黄化合物等の加硫剤、各種加硫促進剤、カーボンブラック、炭酸カルシウムやクレー、シリカ、タルク等の各種充填剤、可塑等の加工助剤、各種老化防止剤、酸化亜鉛やステアリン酸等の加硫助剤、尿素等の各種発泡助剤、導電性調整のための各種イオン導電剤等が必要に応じて含有される。
【００２７】
加硫剤や加硫促進剤は特に限定するものでないが、上記ゴム組成物の発泡進行率１０％における加硫進行率が５〜２７％、発泡進行率９０％における加硫進行率が４８〜８５％である様にする必要がある。
【００２８】
本発明の発泡導電性ゴムローラは、上述のゴムに必要に応じて各種添加剤を配合して混練し、チューブ状に押出し成形した後、加硫を行い、これに金属製の芯材を挿入し、所望の形状に研磨することで得られる。金属製の芯材としては、従来用いられているアルミニウムやステンレス等が挙げられる。
【００２９】
加硫方法について特に限定されるものではなく、例えば加硫缶を用いた直接加圧蒸気加硫、金型を熱盤でプレスするプレス加硫、熱風炉を用いた熱風加硫及びマイクロ波加硫等が挙げられるが、ゴム材料に対して均一に熱が伝わり易く、また均一な発泡体を得易い直接加圧蒸気加硫がより好ましい。加硫缶を用いた直接加圧蒸気加硫の加硫条件は、通常１４０〜１８０℃、１０〜１２０分で行われるが、本発明においては１５０〜１７０℃で加硫する。１５０℃より低い温度で加硫した場合、加硫反応、発泡反応いずれも遅くなるため発泡セル径が大きくなり易く、硬度が低過ぎて圧縮永久歪が大きくなり、画像に欠陥を生じ易い。また、１７０℃より高い温度で加硫する場合は、一般的な加硫缶では出力性能上困難であるため、より高価な装置が必要となりコストアップの要因になってしまう。
【００３０】
【実施例】
以下に、具体的な実施例を挙げて本発明をより詳細に説明するが、本発明は、これら実施例に限定するものではない。なお、実施例中の配合量の単位は質量部である。
【００３１】
各実施例及び比較例において、表１に示す配合割合で原材料をオープンロールで混練を行いゴム組成物を作製した。
【００３２】
【表１】
【００３３】
【表２】
【００３４】
上記実施例において、エチレンプロピレンジエンゴムには「エスプレン５０５Ａ；住友化学工業（株）社製」を、エピクロルヒドリンゴムには「ゼクロン３１０１（エチレンオキサイド含量３１ｍｏｌ％）；日本ゼオン（株）社製」を、アクリロニトリルブタジエンゴムには「ニポールＤＮ４０１Ｌ（アクリロニトリル含量１８質量％）；日本ゼオン（株）社製」を使用した。また、重質炭酸カルシウムには「スーパーＳＳＳ；丸尾カルシウム（株）社製」を、カーボンブラックには「旭＃３５；旭カーボン（株）社製」を、酸化亜鉛には「酸化亜鉛２種；ハクスイテック（株）社製」を、ステアリン酸には「ステアリン酸Ｓ；花王（株）社製」を、硫黄には「サルファックス２００Ｓ；鶴見化学（株）社製」を使用した。また、ジベンゾチアジルジスルフィドには「ノクセラーＤＭ；大内振興化学（株）社製」を、２−メルカプトベンゾチアゾールには「ノクセラーＭ−ｐ；大内振興化学（株）社製」を使用した。また、アゾジカルボンアミドには「ビニホールＡＣ＃ＬＱ；永和化成（株）社製」を、尿素には「セルペーストＡ；永和化成（株）社製」を使用した。
【００３５】
なお、実施例及び比較例の発泡導電性ゴムローラは、押出し機を用いてチューブ状にゴム組成物を押出した後、加硫缶にて表１に記した加硫温度で３０分間加硫を行いチューブ状のゴム加硫物を作製し、次いでφ６ｍｍの導電性芯体を前記チューブ状のゴム加硫物の内径部に圧入し、ローラ状の成形体を得た。この成形体を外径がφ１４ｍｍになるように研磨し、作製した。
【００３６】
また、発泡進行率１０％における加硫進行率、発泡進行率９０％における加硫進行率、抵抗、抵抗の環境変動桁、硬度、貼り付き等に関する特性は、以下の方法により測定した。
【００３７】
＜発泡進行率１０％における加硫進行率、発泡進行率９０％における加硫進行率＞
発泡圧測定機能付ロータレス加硫試験機ＭＤＲ２０００Ｐ（アルファテクノロジーズ社製）を用いて、１６０℃で３０分間の条件で加硫曲線と発泡圧曲線を測定し、発泡進行率１０％における加硫進行率、発泡進行率９０％における加硫進行率を算出した。また、発泡進行率１０％における加硫進行率が５〜２７％である場合を○、それ以外を×、発泡進行率９０％における加硫進行率が４８〜８５％である場合を○、それ以外を×とした。
【００３８】
＜ローラ電気抵抗＞
低温低湿のＬ／Ｌ環境（１５℃／１０％ＲＨ）、常温常湿のＮ／Ｎ環境（２３℃／５０％ＲＨ）、高温高湿のＨ／Ｈ環境（３２．５℃／８０％ＲＨ）において、導電性ゴムローラの芯体に総圧５００ｇの荷重が掛かるように外径３０ｍｍのアルミニウム製ドラムに圧着し、０．５Ｈｚで回転させた状態で、芯体とアルミドラムとの間に５００Ｖの電圧を印加しながら抵抗値を測定した。なお、評価基準は、低温低湿の環境下での抵抗値が１×１０^１０Ωより低い場合を○、１×１０^１０Ω以上の場合を×とした。
【００３９】
＜ローラ電気抵抗の環境変動桁＞
上記ローラ電気抵抗を測定した時のＬ／Ｌ環境における抵抗値（Ｒ_{（Ｌ／Ｌ）}）とＨ／Ｈ環境における抵抗値（Ｒ_{（Ｈ／Ｈ）}）から抵抗の環境変動桁（ｌｏｇＲ_{（Ｌ／Ｌ）}−ｌｏｇＲ_{（Ｈ／Ｈ）}）を算出し、環境変動桁１．３０以下を○、１．３０を超える場合を×とした。
【００４０】
＜硬度＞
導電性ゴムローラ端部の導電性芯材を軸受で受けた状態で、芯体に総圧５００ｇの荷重とともにアスカーＣ型スプリング式硬さ試験機（高分子計器（株）製）の押し針を押し付けてアスカーＣ硬度を測定した。なお、評価基準はアスカーＣ硬度２５°〜３５°の場合を◎、アスカーＣ硬度２０°〜２４°又は３６°〜４０°を○、アスカーＣ硬度４０°を超える場合やアスカーＣ硬度２０°より小さい場合を×とした。
【００４１】
＜電子写真感光体への貼り付き＞
導電性ローラをヒューレッドパッカード製レーザージェット４０５０用の感光ドラムに片側荷重５００ｇとなるように接触させ、４０℃／９５％ＲＨ環境下に２４０時間放置した後、電子写真感光体の汚染状態を目視により確認し、接触跡が認められない場合を○、接触跡が認められる場合を×とした。
【００４２】
【表３】
【００４３】
【表４】
【００４４】
【表５】
【００４５】
表３〜表５に示される実験の結果より、実施例１〜３及び比較例１、２より本発明の導電性ゴムローラにおいては、エチレンプロピレンジエンゴムの全ゴム成分に対する割合が質量比で１０以上３０以下が好ましいことが分かる。すなわち、エチレンプロピレンジエンゴムの質量比が１０未満である比較例１では電子写真感光体に貼り付いて不良であり、また、エチレンプロピレンジエンゴムの質量比が３０を超える比較例２の場合、電子写真感光体への貼り付き防止は良好であるが、低温低湿の環境下におけるローラの抵抗が１×１０^１０Ωを超えるため不良である。
【００４６】
次に、実施例４〜７及び比較例３、４より、エピクロルヒドリンゴム、アクリロニトリルブタジエンゴムの合計に対するエピクロルヒドリンゴムの割合が質量比で５以上２５未満が好ましいことが分かる。質量比が５未満の比較例３は低温低湿の環境下におけるローラの抵抗が１×１０^１０Ωを超えるため不良である。また、質量比が２５である比較例４は抵抗の環境変動桁が大きく不良である。
【００４７】
次に、実施例１、比較例５〜８から低硬度のローラを得るには、ゴム組成物の発泡進行率１０％における加硫進行率が５〜２７％、発泡進行率９０％における加硫進行率が４８〜８５％であることが適していることが分かる。
【００４８】
発泡進行率１０％における加硫進行率が５％より小さい比較例５では、発泡反応と加硫反応のバランスにおいて、発泡反応が先行してしまうため、ゴム表面からガスが抜けて発泡不足になり、硬度が高くなり不良である。
【００４９】
また、発泡進行率１０％における加硫進行率が２７％を超える比較例６では、発泡反応と加硫反応のバランスにおいて、加硫反応が先行してしまうため、ゴムの粘度が上がり、発泡し難いため発泡ガスが押さえ込まれ発泡不足となり、硬度が高くなり不良である。
【００５０】
また、発泡進行率１０％における加硫進行率が５〜２７％であっても、発泡進行率９０％における加硫進行率が４８〜８５％を満たさない比較例７や比較例８の場合も、発泡反応と加硫反応のバランスが崩れ、ガス抜けや発泡ガスの押さえ込みが生じ硬度が高くなり不良である。
【００５１】
実施例１、８、９及び参考例１よりアゾジカルボンアミドの添加量は、５〜１５質量部が好ましいことが分かる。アゾジカルボンアミドの添加量が１５質量部を超えて添加した参考例１の場合は、アゾジカルボンアミドの添加量が５〜１５質量部である実施例１、８、９より発生ガス量が多いため、発泡セル径が大きくなり、硬度が低くなる傾向にある。
【００５２】
実施例１、参考例２、実施例１２、１３より、加硫条件温度は１５０〜１７０℃が好ましいことが分かる。１５０℃より低い温度で加硫した参考例２は、１５０〜１７０℃の温度で加硫した実施例１、１２、１３よりも加硫反応、発泡反応いずれも遅くなるため発泡セル径が大きくなり、硬度が低くなる傾向にある。
【００５３】
【発明の効果】
以上説明したように、本発明の製造方法により得られた画像形成装置用導電性ゴムローラは、電子写真感光体に接触使用しても貼り付かず、また電子写真感光体汚染がない。また、抵抗値の環境依存性が小さく、かつ低硬度であるため接触部材との密着性が高い。そのため、本発明の製造方法により得られた発泡導電性ゴムローラは、電子写真装置において電子写真感光体上に相対して用いられる、特に転写ローラに好適なものである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method of manufacturing a conductive rubber roller for an image forming apparatus used in an image forming apparatus such as a copying machine or a printer using an electrophotographic method , and in particular, a transfer used in contact with an electrophotographic photosensitive member. It is about Roller.
[0002]
[Prior art]
Conventionally, in image forming apparatuses for office automation equipment such as copying machines and printers, a non-contact charging method in which a high voltage is applied by corona discharge has been used. However, this charging method has a problem that harmful ozone is generated with corona discharge. Therefore, in recent years, image formation using a contact charging method in which a conductive rubber roller to which voltage is applied is pressed against the surface of the electrophotographic photosensitive member to charge the surface of the insulator has become the mainstream, and OPC, which is the center of image formation, has become the mainstream. A conductive rubber roller is used around each photosensitive drum using an electrophotographic photosensitive member for each process such as charging and transfer.
[0003]
In addition, the conductive rubber roller is desired to have a moderately low hardness in addition to the above characteristics in order to improve the adhesion to the drum. When the roller hardness is high, the nip width with the photosensitive drum or the like becomes small. For example, in the case of a transfer roller, the transfer rate is reduced, and image defects are likely to occur due to wear or damage on the surface of the electrophotographic photosensitive member. On the other hand, if the hardness is too low, the compression set is too soft and the compression set becomes large and the durability is inferior, and the conveying force becomes too strong and the image is liable to be defective.
[0004]
Examples of the method for reducing the hardness of the conductive rubber roller include a method using various additives such as a softener and a plasticizer. The conductive rubber roller added with the softener and the plasticizer is used in contact with the photosensitive drum. In this case, various additives having a low molecular weight bleed out from the conductive rubber roller and adhere to the surface of the electrophotographic photosensitive member, so that problems such as image deterioration and electrophotographic photosensitive member contamination are likely to occur.
[0005]
For this reason, a method of obtaining a foamed elastic rubber roller using a chemical foaming agent is generally used to reduce the hardness of the conductive rubber roller.
[0006]
As a rubber material used for the conductive rubber roller, a technique using a polar rubber such as acrylonitrile butadiene rubber (NBR) or epichlorohydrin rubber is generally used. It is known that polar rubber is suitable for a conductive rubber roller because it has conductivity due to the action of polar groups present in the polymer, and therefore has little variation in resistance and voltage dependency of electrical resistance is small. .
[0007]
However, in the case of a conductive rubber roller mainly composed of acrylonitrile butadiene rubber or epichlorohydrin rubber, it is easy to become familiar with the polar resin coating the surface of the electrophotographic photosensitive member because it is a polar rubber, and is attached to the surface of the electrophotographic photosensitive member. Problems such as image deterioration and electrophotographic photoreceptor contamination are likely to occur.
[0008]
Therefore, as a method for solving the above-described problems, a method of modifying the surface by irradiating the roller surface with ozone or ultraviolet rays (JP-A-8-292640 and JP-A-11-149201). And a method of blending non-polar rubber has been proposed. However, although the method of irradiating ozone and ultraviolet rays is effective in preventing sticking, there is a risk of adversely affecting the human body, and the equipment is expensive.
[0009]
Also, in the case of blending with nonpolar rubber, it is difficult to adapt due to the difference in polarity between the nonpolar rubber and the resin coating on the surface of the electrophotographic photosensitive member. As a result, contact between the acrylonitrile butadiene rubber or epichlorohydrin rubber and the surface of the electrophotographic photosensitive member is difficult. Is reduced, and a roller that does not stick to the surface of the electrophotographic photosensitive member can be obtained. In addition, it is possible to obtain a conductive rubber roller that retains the characteristics that the variation in resistance, which is a characteristic of the ion conductive rubber material, is small and the voltage dependency of electrical resistance is small.
[0010]
[Problems to be solved by the invention]
However, in the case of a rubber composition comprising acrylonitrile butadiene rubber, which is a polar rubber, or epichlorohydrin rubber and a non-polar rubber, both are incompatible, and the vulcanization speed and foaming speed are different, so that it can be uniformly foamed. Had a problem that was difficult.
[0011]
An object of the present invention has been made in view of the above-described circumstances, and is a low-hardness image forming apparatus that does not stick to or contaminate an electrophotographic photosensitive member even when used in contact with each other, and has a small resistance dependency on the environment. it is to provide a manufacturing method and a transfer roller of use conductive rubber roller.
[0012]
[Means for Solving the Problems]
According to the present invention, in a method for producing a foamed conductive rubber roller for an image forming apparatus, wherein a foamed rubber layer is provided on a conductive core material,
The rubber component of the rubber composition of the foam rubber layer contains at least ethylene propylene diene rubber (A), epichlorohydrin rubber (B) and acrylonitrile butadiene rubber (C), and 100 parts by mass of the rubber component of the rubber composition On the other hand, 5 to 15 parts by mass of azodicarbonamide is contained as a chemical foaming agent, and the ratio to the total 100 parts by mass of all the rubber components of the following condition (1) (A) is 10 parts by mass or more and 30 parts by mass or less. ,
(2) The ratio of (B) (B) and (C) to 100 parts by mass in total is 5 parts by mass or more and less than 25 parts by mass,
And the progress of vulcanization obtained by measuring the vulcanization curve and the foaming pressure curve at 160 ° C. for 30 minutes,
(3) The rubber composition has a vulcanization progress rate of 5 to 27% at a foaming progress rate of 10%,
(4) The rubber composition has a vulcanization progress rate of 48 to 85% at a foaming progress rate of 90%,
A rubber composition that satisfies
There is provided a method for producing a foamed conductive rubber roller for an image forming apparatus, characterized in that vulcanization is carried out at a set pressure of 150 to 170 ° C. by directly pressurized steam using a vulcanizing can as a heating means.
According to the present invention, in the transfer roller used in the image forming apparatus for developing the electrostatic image on the electrophotographic photosensitive member with a developer, the transfer roller is disposed relative to the electrophotographic photosensitive member. A transfer roller is provided which is a foamed conductive rubber roller for an image forming apparatus obtained by the manufacturing method.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the conductive rubber roller of the present invention will be described in detail. The foamed conductive rubber roller of the present invention is a foamed conductive rubber roller in which a foamed rubber layer is provided on a conductive core material. The rubber component in the rubber composition used in the present invention contains at least a nonpolar rubber (A), an epichlorohydrin rubber (B) and an acrylonitrile butadiene rubber (C), and the blending ratio thereof is the total amount of the nonpolar rubber (A). and the ratio is less than 30 parts by mass or more 1 0 part by weight to the total 100 parts by mass of the rubber component, the ratio is 5 mass of epichlorohydrin rubber (B) and epichlorohydrin rubber per 100 total parts by weight of the acrylonitrile-butadiene rubber (C) (B) Part or more and less than 25 parts by mass . The rubber composition has a vulcanization progress rate of 5 to 27% at a foaming progress rate of 10% and a vulcanization progress rate of 48 to 85% at a foaming progress rate of 90%.
[0014]
The kind of nonpolar rubber (A) in the rubber component is not particularly limited as long as it does not stick to or contaminate the electrophotographic photosensitive member. Examples include ethylene propylene rubber, ethylene rubber, ethylene butadiene rubber, and butadiene rubber, and ethylene propylene diene rubber that is particularly excellent in terms of ozone resistance and heat resistance is preferable.
[0015]
The addition amount of the non-polar rubber, the total rubber relative to 100 parts by weight of the component is 30 parts by weight or more 1 0 parts by mass, more preferably not more than 25 parts by mass or more 15 parts by weight. If the non-polar rubber is less than 10 mass parts, weak effect of mitigating contact with acrylonitrile-butadiene rubber and epichlorohydrin rubber and an electrophotographic photosensitive member surface, or stick to the surface of the electrophotographic photoreceptor, an electrophotographic photoreceptor contamination Arise. Also, if a non-polar rubber is more than 30 parts by weight, although the effect on the sticking and contamination of the electrophotographic photosensitive member, the roller resistance increases, impairing the function as a transfer roller, image irregularity due to transfer failure Will occur. Therefore, the roller resistance is preferably less than 1 × 10 ¹⁰ Ω even in a low temperature and low humidity environment where the resistance is highest.
[0016]
The epichlorohydrin rubber (B) and the acrylonitrile butadiene rubber (C) in the rubber component are added for the purpose of resistance adjustment. The acrylonitrile content of the acrylonitrile butadiene rubber and the copolymerization ratio of ethylene oxide and epichlorohydrin of the epichlorohydrin rubber are not particularly limited as long as they have various properties such as electrical resistance desired by each roller.
[0017]
The ratio of the epichlorohydrin rubber (B) and the acrylonitrile butadiene rubber (C) is such that the ratio of the epichlorohydrin rubber (B) to the total 100 parts by mass of the epichlorohydrin rubber (B) and the acrylonitrile butadiene rubber (C) is 5 parts by mass or more and 25 masses. Less than part . When epichlorohydrin rubber is less than 5 parts by mass, the resistance value hardly changes, were or, if more than 2 5 parts by weight, the proportion of the resistance of the environmental change is large epichlorohydrin rubber increases, the environmental variation of roller resistance growing. When the roller resistance has a large environmental fluctuation, it is necessary to control the applied voltage in accordance with the change in resistance, and it is necessary to mount a power source that can withstand the resistance change, which affects the cost and downsizing of the apparatus. Therefore, the environmental fluctuation of the roller resistance is preferably 1.30 or less in terms of resistance fluctuation digits under the low temperature / low humidity and high temperature / high humidity environments.
[0018]
In the present invention, it is important that the rubber composition has a vulcanization progress rate of 5 to 27% at a foaming progress rate of 10% and a vulcanization progress rate of 48 to 85% at a foaming progress rate of 90%.
[0019]
When the vulcanization progress rate is less than 5% when the foaming progress rate is 10%, the foaming reaction precedes the balance between the foaming reaction and the vulcanization reaction regardless of the vulcanization progress rate when the foaming progress rate is 90%. The gas escapes from the rubber surface, resulting in insufficient foaming, increased hardness, and image defects due to wear and damage on the surface of the electrophotographic photosensitive member.
[0020]
Therefore, the hardness of the roller is preferably 20 ° to 40 °, more preferably 25 ° to 35 in terms of Asker C hardness in a foamed conductive rubber roller in which a foamed rubber layer having a thickness of 4 mm is provided on a conductive core material of 6 mm. °.
[0021]
When the vulcanization progress rate at a foaming progress rate of 10% exceeds 27%, the vulcanization reaction precedes the balance between the foaming reaction and the vulcanization reaction, regardless of the vulcanization progress rate at the foaming progress rate of 90%. For this reason, the viscosity of the rubber is increased and foaming is difficult, so the foaming gas is suppressed, foaming is insufficient, and the hardness is increased.
[0022]
Further, even if the vulcanization progress rate at a foaming progress rate of 10% is within a range of 5 to 27%, if the vulcanization progress rate at a foaming progress rate of 90% is smaller than 48%, the foaming reaction and the vulcanization reaction The balance is lost, and the foaming gas is released from the rubber surface, resulting in poor foaming, making it difficult to obtain a low-hardness roller. Further, when the vulcanization progress rate at a foam progress rate of 90% exceeds 85%, the viscosity of the rubber is so high that it is difficult to foam, so the foaming gas is suppressed, foaming becomes insufficient, and the hardness increases.
[0023]
As the chemical blowing agents include azodicarbonamide Ami de.
[0024]
When 4,4′-oxybis (benzenesulfonyl hydrazide) or paratoluenesulfonyl hydrazide is used, since the decomposition temperature is low, the progress of foaming is accelerated, and it is difficult to adjust the balance between the vulcanization speed and the foaming speed. In the case of dinitrosopentamethylenetetramine, toxic formaldehyde or hexamethylenetetramine having a strong amine odor is generated as a decomposition by-product, so azodicarbonamide is used as the blowing agent used in the present invention .
[0025]
The addition amount of azodicarbonamide is not particularly limited, it added 5-15 parts by weight based on 100 parts by mass of the rubber component. When the amount of azodicarbonamide added is less than 5 parts by mass, the amount of gas generated is small, so foaming is insufficient and the hardness tends to increase. In addition, when the amount of azodicarbonamide added exceeds 15 parts by mass, the amount of generated gas is too large, the foam cell diameter becomes large, the hardness is too low and the compression set becomes large, resulting in a defect in the image. It is easy to produce.
[0026]
Moreover, the rubber composition used for the foamed conductive rubber roller of the present invention can contain other components used for general rubber, if necessary. For example, vulcanizing agents such as sulfur and organic sulfur compounds, various vulcanization accelerators, carbon black, various fillers such as calcium carbonate, clay, silica, talc, processing aids such as plastics, various anti-aging agents, oxidation Vulcanization aids such as zinc and stearic acid, various foaming aids such as urea, various ionic conductive agents for adjusting conductivity, and the like are contained as necessary.
[0027]
The vulcanizing agent and vulcanization accelerator are not particularly limited, but the rubber composition has a vulcanization progress rate of 5 to 27% at a foaming progress rate of 10% and a vulcanization progress rate of 48 to 90% at a foaming progress rate of 90%. It needs to be 85%.
[0028]
The foamed conductive rubber roller of the present invention is blended with various additives as necessary in the above-mentioned rubber, kneaded, extruded into a tube shape, vulcanized, and inserted with a metal core. It can be obtained by polishing into a desired shape. Examples of the metal core material include conventionally used aluminum and stainless steel.
[0029]
The vulcanization method is not particularly limited. For example, direct pressure steam vulcanization using a vulcanization can, press vulcanization in which a mold is pressed with a hot platen, hot air vulcanization using a hot air furnace, and microwave vulcanization. Sulfur and the like can be mentioned, but direct pressure steam vulcanization is more preferable because heat can be uniformly transmitted to the rubber material and a uniform foam can be easily obtained. Vulcanization conditions of direct pressurized vapor vulcanization using the vulcanizing is usually 140 to 180 ° C., carried out at 10 to 120 minutes, you vulcanized at 150-170 ° C. in the present invention. When vulcanized at a temperature lower than 150 ° C., both the vulcanization reaction and the foaming reaction are slowed, so the foam cell diameter tends to be large, the hardness is too low and the compression set is large, and the image tends to be defective. Further, when vulcanizing at a temperature higher than 170 ° C., it is difficult in terms of output performance with a general vulcanizing can, so that a more expensive device is required, which causes an increase in cost.
[0030]
【Example】
Hereinafter, the present invention will be described in more detail with reference to specific examples. However, the present invention is not limited to these examples. In addition, the unit of the compounding quantity in an Example is a mass part.
[0031]
In each Example and Comparative Example, the raw materials were kneaded with an open roll at the blending ratio shown in Table 1 to prepare a rubber composition.
[0032]
[ Table 1 ]
[0033]
[Table 2]
[0034]
In the above examples, “Esprene 505A; manufactured by Sumitomo Chemical Co., Ltd.” is used for the ethylene propylene diene rubber, and “Zeklon 3101 (ethylene oxide content 31 mol%); manufactured by Nippon Zeon Co., Ltd.” is used for the epichlorohydrin rubber. As the acrylonitrile butadiene rubber, “NIPOL DN401L (acrylonitrile content: 18% by mass); manufactured by Nippon Zeon Co., Ltd.” was used. “Super SSS; manufactured by Maruo Calcium Co., Ltd.” for heavy calcium carbonate, “Asahi # 35; manufactured by Asahi Carbon Co., Ltd.” for carbon black, and “Zinc oxide 2 types” for zinc oxide "Hakusui Tech Co., Ltd." was used, "Stearic acid S; Kao Corporation" was used for stearic acid, and "Sulfax 200S; Tsurumi Chemical Co., Ltd." was used for sulfur. In addition, “Noxeller DM; manufactured by Ouchi Shinko Chemical Co., Ltd.” was used for dibenzothiazyl disulfide, and “Noxeller Mp; manufactured by Ouchi Shinko Chemical Co., Ltd.” was used for 2-mercaptobenzothiazole. . In addition, “Vinole AC # LQ; made by Eiwa Kasei Co., Ltd.” was used for azodicarbonamide, and “Cell Paste A; made by Eiwa Kasei Co., Ltd.” was used for urea.
[0035]
The foamed conductive rubber rollers of the examples and comparative examples were vulcanized for 30 minutes at the vulcanization temperature described in Table 1 with a vulcanizer after extruding the rubber composition into a tube shape using an extruder. A tube-shaped rubber vulcanizate was produced, and then a conductive core having a diameter of 6 mm was press-fitted into the inner diameter portion of the tube-shaped rubber vulcanizate to obtain a roller-shaped molded body. This molded body was prepared by polishing so that the outer diameter was 14 mm.
[0036]
Moreover, the characteristics regarding the vulcanization progress rate at the foaming progress rate of 10%, the vulcanization progress rate at the foaming progress rate of 90%, the resistance, the environmental variation digit of the resistance, the hardness, and the sticking were measured by the following methods.
[0037]
<Vulcanization progress rate at 10% foaming progress rate, vulcanization progress rate at 90% foam progress rate>
Using a rotorless vulcanization tester MDR2000P (manufactured by Alpha Technologies Co., Ltd.) with a foam pressure measurement function, the vulcanization curve and the foam pressure curve were measured at 160 ° C. for 30 minutes, and the vulcanization progress rate at a foam progress rate of 10% The vulcanization progress rate at a foam progress rate of 90% was calculated. Further, the case where the vulcanization progress rate when the foaming progress rate is 10% is 5 to 27% is ◯, the case where the vulcanization progress rate is 90% and the vulcanization progress rate when the foaming progress rate is 90% is 48 to 85%. Except for x.
[0038]
<Roller electrical resistance>
Low-temperature and low-humidity L / L environment (15 ° C / 10% RH), normal temperature and normal humidity N / N environment (23 ° C / 50% RH), high-temperature and high-humidity H / H environment (32.5 ° C / 80% RH) ), The core of the conductive rubber roller is pressure-bonded to an aluminum drum having an outer diameter of 30 mm so that a total pressure of 500 g is applied, and rotated at 0.5 Hz, and 500 V is applied between the core and the aluminum drum. The resistance value was measured while applying a voltage of. In addition, the evaluation criteria were set to ○ when the resistance value in a low-temperature and low-humidity environment is lower than 1 × 10 ¹⁰ Ω, and × when the resistance value is 1 × 10 ¹⁰ Ω or more.
[0039]
<Environmental fluctuation digits of roller electrical resistance>
From the resistance value (R _{(L / L)} ) in the L / L environment when the roller electrical resistance is measured and the resistance value (R _{(H / H)} ) in the H / H environment, the resistance fluctuation digits (logR _{(L / L)} −logR _{(H / H)} ) was calculated, and an environmental fluctuation figure of 1.30 or less was marked with ◯, and a value exceeding 1.30 was marked with ×.
[0040]
<Hardness>
With the conductive core material at the end of the conductive rubber roller received by the bearing, press the push needle of Asker C-type spring hardness tester (manufactured by Kobunshi Keiki Co., Ltd.) with a total pressure of 500g on the core. Asker C hardness was measured. The evaluation criteria are ◎ when the Asker C hardness is 25 ° to 35 °, ○ when the Asker C hardness is 20 ° to 24 ° or 36 ° to 40 °, and when the Asker C hardness exceeds 40 ° or from the Asker C hardness of 20 °. When small, it was set as x.
[0041]
<Attaching to electrophotographic photoreceptor>
A conductive roller is brought into contact with a photosensitive drum for Hewlett Packard laser jet 4050 at a load of 500 g on one side and left in a 40 ° C./95% RH environment for 240 hours, and then the electrophotographic photoreceptor is visually inspected for contamination. When the contact mark was not recognized, it was marked as ◯, and the case where the contact mark was recognized was marked as x.
[0042]
[Table 3]
[0043]
[ Table 4 ]
[0044]
[Table 5]
[0045]
From the results of the experiments shown in Tables 3 to 5, from Examples 1 to 3 and Comparative Examples 1 and 2, in the conductive rubber roller of the present invention, the ratio of ethylene propylene diene rubber to all rubber components is 10 or more by mass ratio. It can be seen that 30 or less is preferable. That is, the comparative example 1 in which the mass ratio of the ethylene propylene diene rubber is less than 10 is not good because it adheres to the electrophotographic photosensitive member, and the comparative example 2 in which the mass ratio of the ethylene propylene diene rubber exceeds 30 Although prevention of sticking to a photographic photoreceptor is good, the resistance of the roller in a low-temperature and low-humidity environment exceeds 1 × 10 ¹⁰ Ω, which is poor.
[0046]
Next, it can be seen from Examples 4 to 7 and Comparative Examples 3 and 4 that the ratio of epichlorohydrin rubber to the total of epichlorohydrin rubber and acrylonitrile butadiene rubber is preferably 5 or more and less than 25 by mass ratio. Comparative Example 3 with a mass ratio of less than 5 is defective because the resistance of the roller in a low temperature and low humidity environment exceeds 1 × 10 ¹⁰ Ω. Further, Comparative Example 4 having a mass ratio of 25 has a large resistance variation digit of resistance, which is unsatisfactory.
[0047]
Next, in order to obtain a low hardness roller from Example 1 and Comparative Examples 5 to 8, the rubber composition has a vulcanization progress rate of 5 to 27% at a foaming progress rate of 10% and a vulcanization at a foaming progress rate of 90%. It can be seen that it is suitable that the progress rate is 48 to 85%.
[0048]
In Comparative Example 5 in which the vulcanization progress rate is less than 5% at the foaming progress rate of 10%, the foaming reaction precedes in the balance between the foaming reaction and the vulcanization reaction, so the gas escapes from the rubber surface and the foaming is insufficient. , The hardness becomes high and is poor.
[0049]
Further, in Comparative Example 6 in which the vulcanization progress rate at a foaming progress rate of 10% exceeds 27%, the vulcanization reaction is preceded in the balance between the foaming reaction and the vulcanization reaction. Since it is difficult, foaming gas is suppressed, foaming is insufficient, hardness increases, and it is defective.
[0050]
Further, even when the vulcanization progress rate at a foaming progress rate of 10% is 5 to 27%, the vulcanization progress rate at a foaming progress rate of 90% does not satisfy 48 to 85%. The balance between the foaming reaction and the vulcanization reaction is lost, and the outgassing and the suppression of the foaming gas occur, resulting in a high hardness and a failure.
[0051]
From Examples 1 , 8 , 9 and Reference Example 1 , it can be seen that the addition amount of azodicarbonamide is preferably 5 to 15 parts by mass. In the case of Reference Example 1 in which the addition amount of azodicarbonamide exceeds 15 parts by mass, the amount of generated gas is larger than in Examples 1, 8, and 9 in which the addition amount of azodicarbonamide is 5 to 15 parts by mass. The foam cell diameter tends to increase and the hardness tends to decrease.
[0052]
From Example 1, Reference Example 2, and Examples 12 and 13, it can be seen that the vulcanization temperature is preferably 150 to 170 ° C. In Reference Example 2 vulcanized at a temperature lower than 150 ° C., both the vulcanization reaction and the foaming reaction are slower than those of Examples 1, 12, and 13 vulcanized at a temperature of 150 to 170 ° C., so that the foam cell diameter becomes larger. , The hardness tends to be low.
[0053]
【The invention's effect】
As described above, the conductive rubber roller for an image forming apparatus obtained by the production method of the present invention does not stick even when used in contact with the electrophotographic photosensitive member, and there is no contamination of the electrophotographic photosensitive member. Moreover, since the environmental dependency of the resistance value is small and the hardness is low, the adhesion with the contact member is high. Therefore, the foamed conductive rubber roller obtained by the production method of the present invention is suitable for use as a transfer roller, which is used relative to the electrophotographic photosensitive member in the electrophotographic apparatus.

Claims

In the method of manufacturing a foamed conductive rubber roller for an image forming apparatus in which a foamed rubber layer is provided on the conductive core material,
The rubber component of the rubber composition of the foam rubber layer contains at least ethylene propylene diene rubber (A), epichlorohydrin rubber (B) and acrylonitrile butadiene rubber (C), and 100 parts by mass of the rubber component of the rubber composition On the other hand, 5 to 15 parts by mass of azodicarbonamide is contained as a chemical foaming agent, and the ratio to the total 100 parts by mass of all the rubber components of the following condition (1) (A) is 10 parts by mass to 30 parts by mass. ,
(2) The ratio of (B) (B) and (C) to 100 parts by mass in total is 5 parts by mass or more and less than 25 parts by mass,
And the progress of vulcanization obtained by measuring the vulcanization curve and the foaming pressure curve at 160 ° C. for 30 minutes,
(3) The rubber composition has a vulcanization progress rate of 5 to 27% at a foaming progress rate of 10%,
(4) The rubber composition has a vulcanization progress rate of 48 to 85% at a foaming progress rate of 90%,
A rubber composition that satisfies
A method for producing a foamed conductive rubber roller for an image forming apparatus, characterized in that vulcanization is carried out at a set pressure of 150 to 170 ° C. using direct pressure steam using a vulcanizing can as a heating means.

The transfer roller used in an image forming apparatus for developing with a developer an electrostatic image on the electrophotographic photosensitive member, by the method according to claim 1 wherein said transfer roller is arranged relative to the electrophotographic photosensitive member A transfer roller, which is a foamed conductive rubber roller for an image forming apparatus obtained .