JP4401694B2 - Image forming apparatus - Google Patents

Description

【００３８】
さて、ここで上記二つのサンプルについて感光体表面の摩擦係数を測定した。図５は、この２つのサンプルについて感光体表面に塗布した後の経過時間に対する感光体表面の摩擦係数をプロットしたものである。なお、摩擦係数の測定は、オイラーベルト法によるものである。感光体表面に保護物質３０を塗布した直後は、塗布量により摩擦係数が異なるが、ある程度の時間経過により摩擦係数が同程度となることがわかる。本実験によれば、ある程度の時間経過後に摩擦係数が約０．１となった。この程度の低い摩擦係数であれば、機械的磨耗による感光体表面の膜厚削れを防止することが可能である。
【００３９】
表１及び図５の結果から、ステアリン酸亜鉛を潤滑剤として塗布して感光体表面を低摩擦係数化するためには、塗布量が０．０００２［ｍｇ/ｍｍ２］で十分であるが、感光体表面を交流印加放電では顕著となる化学的劣化から保護するためには塗布量を０．００１６［ｍｇ/ｍｍ２］より多くする必要があることがわかる。すなわち感光体を低摩擦係数化するための条件と感光体表面を交流印加放電では顕著となる化学的劣化から保護するための条件とは異なっており、交流印加放電では顕著となる化学的劣化から保護するための条件は従来技術からは導き出せないことがわかる。本出願人の検討により、低摩擦係数作用を得るために必要なステアリン酸亜鉛の存在状態と放電による感光体表面の劣化を防止するために必要なステアリン酸亜鉛の存在状態とは異なることが明らかになった。
【００４０】
〔実験例４〕
次に、交流印加放電では顕著となる感光体表面の膜厚削れ量がＡＣ電圧のピークツーピーク電圧値Ｖｐｐ（以下、単に「Ｖｐｐ」という）、すなわち帯電部材に印加する交流成分の振幅値に比例することを示す実験例について説明する。
図３（ａ）に示すような感光体１、帯電装置２、塗布装置３０から構成される装置により以下の実験を行った。機械的磨耗に起因する感光体表面の劣化を発生させないために、予め帯電ローラ２ａと保護物質塗布装置３０以外の感光体に当接する部材を全て取り払った。そして、Ｖｐｐを変えて、連続１００時間感光体１表面を交流印加放電により帯電させたときの膜厚削れ量を測定した。実験条件は以下のとおりである。
【００４１】
（実験条件）
帯電条件：
Ｖｐｐ（ＡＣ電圧のピークツーピーク電圧値）＝２．２、２．６、３．０［ｋＶ］
ｆ（ＡＣ電圧の周波数）＝１３５０［Ｈｚ］
ＤＣ電圧値＝−６００［Ｖ］
感光体表面の移動速度ｖ＝１１３［ｍｍ／ｓ］
保護物質：ステアリン酸亜鉛
帯電時間：１００時間
【００４２】
図６は、Ｖｐｐに対する連続１００時間の放電により帯電された後の感光体表面の膜厚削れ量をプロットしたものである。図より、感光体表面の膜厚削れ量は、Ｖｐｐに比例していることがわかる。また、Ｖｐｐが約１．９[ｋＶ]のときに膜厚削れ量が０となることがわかる。
【００４３】
この点について、本出願人は以下のように考えている。ＡＣ電圧を印加した時、帯電部材に印加する電圧が所定の値以上とならないと帯電部材表面と感光体表面との間で放電が開始されない事が知られている。本出願人の研究によれば、非接触帯電の場合、帯電部材表面と被帯電表面との最近接距離をＧｐ［μｍ］としたときに帯電部材に印加する電圧が数８に示す値以上となると帯電部材表面と感光体表面との間で放電が開始される。以下、この値を放電開始電圧Ｖｔｈと記す。
＜数８＞ Ｖｔｈ＝３１２＋６．２×（ｄ／ε_opc＋Ｇｐ／ε_air）＋√（７７３７．６×ｄ／ε_opc）
ここで、ｄは感光体の膜厚［μｍ］、εopcは感光体の比誘電率、εairは感光体と帯電部材の間の空間における比誘電率である。
Ｖｐｐが上記Ｖｔｈの２倍以上となったときに帯電部材と感光体との間で双方向に放電が発生する。
本実験例では帯電ローラと感光体との間のギャップは５０［μｍ］、感光体の比誘電率は約３、感光体の膜厚は３０［μｍ］、感光体と帯電部材の間の空間における比誘電率は約１であったので、上記式にこれらを当てはめるとＶｔｈ＝９６２［Ｖ］となる。帯電部材に印加する電圧が９６２［Ｖ］以上となると帯電部材表面と感光体表面との間で放電が開始され、またＶｐｐが約１９２４［Ｖ］を越えるとＡＣ電圧による放電が開始されると考えられる。放電現象として支配的なのはＡＣ電圧によって生じる双方向放電であり、このためＶｐｐが約１.９［ｋＶ］を越えると感光体の膜厚削れが始まると考えられる。
【００４４】
〔実験例５〕
次に、交流印加放電では顕著となる感光体表面の膜厚削れ量がＡＣ電圧の周波数ｆに比例することを示す実験例について説明する。
本実験例に用いた装置の基本的な構成及び実験条件は、上記実験例４のものと同様であるが、帯電条件と感光体表面の移動速度が上記実験例４とは異なっている。すなわち、上記実験例４では、ＡＣ電圧の周波数ｆを固定してＶｐｐを変化させているが、本実験例ではＶｐｐを固定しＡＣ電圧の周波数ｆを変化させている。
【００４５】
（実験条件）
帯電条件：
Ｖｐｐ（ＡＣ電圧のピークツーピーク電圧値）＝２．２［ｋＶ］
ｆ（ＡＣ電圧の周波数）＝５００、９００、１４００、２０００、４０００［Ｈｚ］
ＤＣ電圧値＝−６００［Ｖ］
感光体表面の移動速度ｖ＝１０４［ｍｍ／ｓ］
保護物質：ステアリン酸亜鉛
帯電時間：１００時間
【００４６】
図７は、ＡＣ電圧の周波数ｆに対して上記放電により連続１００時間の帯電した後の感光体表面の膜厚削れ量をプロットしたものである。図より、感光体表面の膜厚削れ量は、ＡＣ電圧の周波数ｆに比例していることがわかる。
【００４７】
本実験例及び上記実験例４の結果より、感光体膜厚の減少は帯電条件により変動（具体的にはＶｐｐ、ｆに比例）することが明らかとなった。
そこで、本出願人は感光体膜厚の減少には以下の関係があると予測した。すなわち、▲１▼Ｖｐｐ−２×Ｖｔｈに比例し、▲２▼ＡＣ電圧の周波数ｆに比例し、かつ▲３▼感光体表面の移動速度ｖに反比例する、と予測した。▲３▼の予測をした理由は、感光体の移動速度が遅いと、同じ帯電条件でも単位面積あたりに照射される放電エネルギーが大きくなると考えられるからである。そして後述する実験例６により、この予測の妥当性を確認し、さらに接触又は近接させて配置した帯電部材による交流印加放電では顕著となる被帯電体の化学的劣化を防止するために被帯電体に塗布すべき保護物質の量に関する以下の知見を得た。
【００４８】
帯電部材により被帯電体を帯電させる領域において、ＸＰＳにより検出される被帯電体最表面を構成する物質の全元素の元素個数総和に対する、ＸＰＳにより検出される保護物質の特定元素の元素個数割合[％]を、次の数９以上とすることにより、接触又は近接させて配置した帯電部材による交流印加放電では顕著となる被帯電体表面の変質を防止することが可能となる。
＜数９＞ １．５２×１０^{− 4}×｛Ｖｐｐ−２×Ｖｔｈ｝×ｆ／ｖ×Ｎ_α
ここで、ＶｐｐはＡＣ電圧のピークツーピーク電圧値［単位：Ｖ］、ｆは帯電部材に印加する交流成分の周波数［単位：Ｈｚ］、ｖは被帯電体表面の移動速度［単位：ｍｍ／ｓｅｃ］、Ｎαは保護物質を構成する元素のうち特定元素の１分子中における元素個数である。
また、Ｖｔｈは放電開始電圧であり、上記数８により求められる。
【００４９】
さらに、帯電部材により被帯電体を帯電させる領域において、ＸＰＳにより検出される被帯電体最表面を構成する物質の全元素の元素個数総和に対する、ＸＰＳにより検出される保護物質の特定元素の元素個数割合[％]を、次の数１０以上とすることにより被帯電体の膜厚削れを防止することができる。
＜数１０＞ ２．２２×１０^{− 4}×｛Ｖｐｐ−２×Ｖｔｈ｝×ｆ／ｖ×Ｎ_α
【００５０】
【発明の実施の形態】
〔実施形態１〕
以下、本発明を画像形成装置に適用した一の実施形態について説明する。まず、図８を用いてこの画像形成装置が備える画像形成ユニットの基本的な構成について説明する。図において、この画像形成ユニットは、被帯電部材である像担持体としてのドラム状の感光体１、帯電装置２、感光体１上に静電潜像を書き込むための露光装置３、現像装置４、感光体１表面の像形成物質を除去するクリーニング装置７などにより構成されている。
【００５１】
このような構成の画像形成装置において、感光体１は図示しない駆動装置により回転駆動され、その表面が帯電装置２により所定の極性に帯電される。次いで、外部から読み込まれた画像情報に基づいて上記露光装置３が駆動され、これによって感光体１の帯電領域（画像形成領域）に静電潜像が形成される。この静電潜像は、現像装置４から供給される現像剤（トナー）によって現像されて可視像としてのトナー像となる。
【００５２】
一方、この感光体１上へのトナー像の形成が行われている間に、不図示の給紙部から記録媒体としての転写紙が感光体１に向けて給送される。この転写紙は、感光体１上のトナー像に重ね合わされるタイミングで感光体１と対向配置されている転写装置５に送り出され、転写ニップＴ１で感光体１上のトナー像が転写せしめられる。その後、感光体１から機械的に分離された後、定着装置６に搬送され、トナー像が定着される。
【００５３】
上記転写ニップＴ１を通過した後の感光体１表面に残留した残留トナーは、上記クリーニング装置８によって感光体１上から除去され回収される。そして、転写残トナーが除去された後の感光体表面の残留電荷は、除電装置９により除去される。
【００５４】
次に、本実施形態に係る放電劣化防止手段について説明する。本実形態に係る画像形成装置には、図８に示すように保護物質３２を感光体表面に供給するための保護物質供給手段として、保護物質塗布装置３０を設けている。この保護物質塗布装置３０は、クリーニング装置７に対して感光体１の回転方向下流側、帯電装置２に対して感光体１の回転方向上流側に感光体１と対向するように設けられている。保護物質塗布装置３０は、塗布部材としてのファーブラシ３１、保護物質３２、保護物質をファーブラシ方向に押圧するための加圧バネ３３とを備えている。保護物質３２はバー状に成型された固体状となっている。ファーブラシ３１は感光体表面にブラシ先端が当接しており、軸を中心に回転することによって保護物質３２を一端ブラシに汲み上げ、感光体表面との当接位置までブラシ上に担持搬送して感光体表面に塗布する。バー上に成形された個体保護物質３２は、加圧バネ３３によって所定の圧力で保護物質３２がファーブラシ３１側に押圧されている。これにより、経時的に保護物質３２がファーブラシ３１に掻き削られて減少した場合でも、常にファーブラシ３１に対して微量の保護物質３２を均一に供給することができる。
【００５５】
以上、保護物質塗布装置３０により保護物質３２を塗布する方法について説明したが、保護物質３２を感光体１表面上に適切な状態で存在させることができる手段であればいかなる方法を用いてもよい。たとえば、保護物質３２をトナーに内添、外添するなどして感光体表面に移行させる方法を採用することもできる。ただし、その場合には画像濃度や画像パターンによって感光体表面上の保護物質３２の存在量にムラが生じやすくなり、これを補うために必要以上の保護物質を塗布する必要が生じる。本実施形態のように感光体表面に保護物質３２を塗布する方法は、画像濃度や画像パターンなど種々の条件によって変化することなく、また、感光体表面に安定して保護物質３２を分布させることができるのでより好ましい。
【００５６】
次に本実施形態で用いられる帯電装置２について詳しく説明する。本実施形態に係る帯電装置は非接触となるよう近接させて対向配置した帯電部材による交流印加放電により感光体を帯電せしめている。なお、接触させて対向配置した帯電部材による交流印加放電により感光体を帯電せしめる方法がある。この方法を適用する場合には、感光体表面と帯電部材との接触性を向上させ、かつ感光体に機械的ストレスを与えない弾性部材を用いることが好ましい。ただし、弾性部材を用いると、帯電ニップ幅が広くなり、これに起因して帯電ローラ側に保護物質が付着しやすくなることがある。よって、被帯電体の高耐久化には非接触により帯電させる方が有利である。
【００５７】
図９は、帯電装置２と感光体１の概略説明図である。帯電装置２は、帯電部材としての帯電ローラ２ａ、スペーサ２２、スプリング１５、電源１６とからなる。帯電ローラ２ａには、軸部２１ａと帯電部としてのローラ部２１ｂとがある。このうちローラ部２１ｂは、感光体１に対向して感光体表面を帯電する機能を担っており、軸部２１ａの回転によって回動可能なように構成されている。帯電ローラ表面の帯電部２１ｂが感光帯表面に対して微小な間隙で対向配置するよう帯電ローラに間隙保持部材であるスペーサ２２を設けている。このスペーサ２２により、感光体１表面のうち画像が形成される画像形成領域１１に対向する部分は感光体１と非接触となるよう配設されている。ローラ部２１ｂの長手方向の寸法は、感光体１の画像形成領域よりも長く設定されており、感光体１の非画像形成領域１２にスペーサ２２を当接せしめることにより、上記微小なギャップ１４を形成している。このスペーサ２２を介して帯電ローラ２ａは、感光体１表面に連れまわって回転するようになっている。微小ギャップ１４は、帯電ローラ部２１ｂと感光体１との最近接部が１〜１００［μｍ］となるように構成されている。この最近接距離は、３０〜６５［μｍ］であることがさらに好ましい。本実施形態１の装置では、５０［μｍ］となるように配設した。
軸部２１ａには、帯電ローラ２ａを被帯電体へ向けて押圧するためのスプリング１５が取り付けられている。これにより上記微小ギャップ１４を精度良く維持することが可能となる。
【００５８】
帯電ローラ２ａは、帯電用の電源１６が接続されており、感光体１表面と帯電ローラ２ａ表面との間の微小な空隙において、交流印加放電により感光体１表面を均一に帯電せしめる。本実施形態では、直流成分であるＤＣ電圧に交流成分であるＡＣ電圧が重畳された交番電圧が帯電ローラ２ａの帯電部へ印加されるようになっている。交番電圧を用いることにより、微小なギャップ変動に起因する帯電電位のバラツキなどの影響が抑制され、均一な帯電が可能となる。
【００５９】
上記帯電ローラ２ａは、円柱状を呈する導電性支持体としての芯金と、この芯金の外周面上に形成された抵抗調整層とから構成される。本実施形態では、帯電ローラ２ａの直径を１０［ｍｍ］とした。
【００６０】
帯電ローラ２ａの表面は、例えばゴム部材などの既知の材料を用いることができるが、樹脂材料で構成することがより好ましい。ゴム部材を用いると、ゴムの吸水や、たわみの発生により、感光体１との微小な間隙を維持することが困難となるからである。作像条件によっては帯電ローラ２ａの中央部のみが感光体表面に突発的に接触する可能性がある。このような局所的、突発的な帯電ローラ２ａの感光体１への接触による感光体表面層の乱れに対応することは困難である。従って、非接触帯電方式により感光体を帯電する場合には、帯電ローラと感光体との微小間隙を均一に維持することができる硬質の材料を用いることがより好ましい。
【００６１】
＜帯電ローラ表層＞帯電ローラ２ａの表面が硬質な材料としては、例えば、以下のようなものを用いることができる。抵抗調整層として、高分子型イオン導電剤が分散する熱可塑性樹脂組成物（ポリエチレン、ポリプロピレン、ポリメタクリル酸メチル、ポリスチレン及びその共重合体等）により形成し、抵抗調整層の表面を硬化剤により硬化皮膜処理されたものなどである。硬化皮膜処理は、例えば、イソシアネート含有化合物を含む処理溶液に抵抗調整層を浸漬させることにより行うことができる。あるいは、抵抗調整層の表面に改めて硬化処理皮膜層を形成してもよい。
【００６２】
本実施形態に用いられる感光体１は負帯電性の有機感光体であり、直径３０［ｍｍ］のドラム状導電性支持体上に感光層等を設けたものである。図１０は、本実施形態に用いた感光体を表す断面図である。基層としての導電性支持体５０上に、絶縁層である下引き層５１が設けられている。そして、その上に感光層としての電荷発生層（ＣＧＬ）５２、電荷輸送層（ＣＴＬ）５３が設けられている。さらにその上に表面保護層（ＦＲ）５４が積層されている。
【００６３】
＜導電性支持体５０＞導電性支持体としては、体積抵抗１０¹⁰Ω・ｃｍ以下の導電性を示すものを用いることができる。例えば、アルミニウム、ニッケル、クロム、ニクロム、銅、金、銀、白金などの金属、酸化スズ、酸化インジウムなどの金属酸化物を、蒸着またはスパッタリングにより、フィルム状もしくは円筒状のプラスチック、紙に被覆したもの、あるいは、アルミニウム、アルミニウム合金、ニッケル、ステンレスなどの板およびそれらを、押し出し、引き抜きなどの工法で素管化後、切削、超仕上げ、研摩などの表面処理した管などを使用することができる。また、特開昭５２−３６０１６号公報に開示されたエンドレスニッケルベルト、エンドレスステンレスベルトも導電性支持体として用いることができる。
【００６４】
この他、上記支持体上に導電性粉体を適当な結着樹脂に分散して塗工したものについても、本発明の導電性支持体として用いることができる。この導電性粉体としては、カーボンブラック、アセチレンブラック、またアルミニウム、ニッケル、鉄、ニクロム、銅、亜鉛、銀などの金属粉、あるいは導電性酸化スズ、ＩＴＯなどの金属酸化物粉体などがあげられる。また、同時に用いられる結着樹脂には、ポリスチレン、スチレン−アクリロニトリル共重合体、スチレン−ブタジエン共重合体、スチレン−無水マレイン酸共重合体、ポリエステル、ポリ塩化ビニル、塩化ビニル−酢酸ビニル共重合体、ポリ酢酸ビニル、ポリ塩化ビニリデン、ポリアリレート樹脂、フェノキシ樹脂、ポリカーボネート、酢酸セルロース樹脂、エチルセルロース樹脂、ポリビニルブチラール、ポリビニルホルマール、ポリビニルトルエン、ポリ−Ｎ−ビニルカルバゾール、アクリル樹脂、シリコーン樹脂、エポキシ樹脂、メラミン樹脂、ウレタン樹脂、フェノール樹脂、アルキッド樹脂などの熱可塑性、熱硬化性樹脂または光硬化性樹脂が挙げられる。このような導電性層は、これらの導電性粉体と結着樹脂を適当な溶剤、例えば、テトラヒドロフラン、ジクロロメタン、メチルエチルケトン、トルエンなどに分散して塗布することにより設けることができる。
さらに、適当な円筒基体上にポリ塩化ビニル、ポリプロピレン、ポリエステル、ポリスチレン、ポリ塩化ビニリデン、ポリエチレン、塩化ゴム、テフロン（登録商標）などの素材に前記導電性粉体を含有させた熱収縮チューブによって導電性層を設けてなるものも、本発明の導電性支持体として良好に用いることができる。
【００６５】
次に感光層について説明する。感光層は単層でも積層でもよいが、説明の都合上、先ず電荷発生層と電荷輸送層とからなる積層構成の場合から述べる。
【００６６】
＜電荷発生層５２＞電荷発生層は、電荷発生物質を主成分とする層である。電荷発生層には公知の電荷発生物質を用いることが可能であり、その代表として、モノアゾ顔料、ジスアゾ顔料、トリスアゾ顔料、ペリレン系顔料、ペリノン系顔料、キナクリドン系顔料、キノン系縮合多環化合物、スクアリック酸系染料、他のフタロシアニン系顔料、ナフタロシアニン系顔料、アズレニウム塩系染料等が挙げられ、これらは有用に用いられる。これら電荷発生物質は単独でも、２種以上混合して用いることも可能である。
【００６７】
電荷発生層は、電荷発生物質を必要に応じて結着樹脂とともに適当な溶剤中にボールミル、アトライター、サンドミル、超音波などを用いて分散し、これを導電性支持体上、あるいは下引き層上に塗布し、乾燥することにより形成される。
【００６８】
電荷発生層には、必要に応じて結着樹脂中に上記電荷発生物質を分散させることができる。用いることができる結着樹脂の例としては、ポリアミド、ポリウレタン、エポキシ樹脂、ポリケトン、ポリカーボネート、シリコーン樹脂、アクリル樹脂、ポリビニルブチラール、ポリビニルホルマール、ポリビニルケトン、ポリスチレン、ポリスルホン、ポリ−Ｎ−ビニルカルバゾール、ポリアクリルアミド、ポリビニルベンザール、ポリエステル、フェノキシ樹脂、塩化ビニル−酢酸ビニル共重合体、ポリ酢酸ビニル、ポリフェニレンオキシド、ポリアミド、ポリビニルピリジン、セルロース系樹脂、カゼイン、ポリビニルアルコール、ポリビニルピロリドン等が挙げられる。結着樹脂の量は、電荷発生物質１００重量部に対し０〜５００重量部、好ましくは１０〜３００重量部が適当である。結着樹脂の添加は、分散前あるいは分散後どちらでも構わない。
【００６９】
ここで用いられる溶剤としては、イソプロパノール、アセトン、メチルエチルケトン、シクロヘキサノン、テトラヒドロフラン、ジオキサン、エチルセルソルブ、酢酸エチル、酢酸メチル、ジクロロメタン、ジクロロエタン、モノクロロベンゼン、シクロヘキサン、トルエン、キシレン、リグロイン等が挙げられるが、特にケトン系溶媒、エステル系溶媒、エーテル系溶媒が良好に使用される。これらは単独で用いても２種以上混合して用いてもよい。
【００７０】
電荷発生層は、電荷発生物質、溶媒及び結着樹脂を主成分とするが、その中には、増感剤、分散剤、界面活性剤、シリコーンオイル等のいかなる添加剤が含まれていても良い。
【００７１】
塗布液の塗工法としては、浸漬塗工法、スプレーコート、ビートコート、ノズルコート、スピナーコート、リングコート等の方法を用いることができる。
電荷発生層の膜厚は、０.０１〜５［μｍ］程度が適当であり、好ましくは０.１〜２［μｍ］である。
【００７２】
＜電荷輸送層５３＞電荷輸送層は、電荷輸送物質および結着樹脂を適当な溶剤に溶解ないし分散し、これを電荷発生層上に塗布、乾燥することにより形成できる。また、必要により単独あるいは２種以上の可塑剤、レベリング剤、酸化防止剤等を添加することもできる。
【００７３】
電荷輸送物質には、正孔輸送物質と電子輸送物質とがある。
電子輸送物質としては、例えばクロルアニル、ブロムアニル、テトラシアノエチレン、テトラシアノキノジメタン、２，４，７−トリニトロ−９−フルオレノン、２，４，５，７−テトラニトロ−９−フルオレノン、２，４，５，７−テトラニトロキサントン、２，４，８−トリニトロチオキサントン、２，６，８−トリニトロ−４Ｈ−インデノ〔１，２−ｂ〕チオフェン−４−オン、１，３，７−トリニトロジベンゾチオフェン−５，５−ジオキサイド、ベンゾキノン誘導体等の電子受容性物質が挙げられる。
【００７４】
正孔輸送物質としては、ポリ−Ｎ−ビニルカルバゾールおよびその誘導体、ポリ−γ−カルバゾリルエチルグルタメートおよびその誘導体、ピレン−ホルムアルデヒド縮合物およびその誘導体、ポリビニルピレン、ポリビニルフェナントレン、ポリシラン、オキサゾール誘導体、オキサジアゾール誘導体、イミダゾール誘導体、モノアリールアミン誘導体、ジアリールアミン誘導体、トリアリールアミン誘導体、スチルベン誘導体、α−フェニルスチルベン誘導体、ベンジジン誘導体、ジアリールメタン誘導体、トリアリールメタン誘導体、９−スチリルアントラセン誘導体、ピラゾリン誘導体、ジビニルベンゼン誘導体、ヒドラゾン誘導体、インデン誘導体、ブタジェン誘導体、ピレン誘導体等、ビススチルベン誘導体、エナミン誘導体等、その他公知の材料が挙げられる。これらの電荷輸送物質は単独、または２種以上混合して用いられる。
【００７５】
結着樹脂としては、ポリスチレン、スチレン−アクリロニトリル共重合体、スチレン−ブタジエン共重合体、スチレン−無水マレイン酸共重合体、ポリエステル、ポリ塩化ビニル、塩化ビニル−酢酸ビニル共重合体、ポリ酢酸ビニル、ポリ塩化ビニリデン、ポリアリレート樹脂、フェノキシ樹脂、ポリカーボネート、酢酸セルロース樹脂、エチルセルロース樹脂、ポリビニルブチラール、ポリビニルホルマール、ポリビニルトルエン、ポリ−Ｎ−ビニルカルバゾール、アクリル樹脂、シリコーン樹脂、エポキシ樹脂、メラミン樹脂、ウレタン樹脂、フェノール樹脂、アルキッド樹脂等の熱可塑性または熱硬化性樹脂が挙げられる。
【００７６】
電荷輸送物質の量は結着樹脂１００重量部に対し、２０〜３００重量部、好ましくは４０〜１５０重量部が適当である。また、電荷輸送層の膜厚は解像度・応答性の点から、２５［μｍ］以下とすることが好ましい。下限値に関しては、使用するシステム（特に帯電電位等）に異なるが、５［μｍ］以上が好ましい。
【００７７】
ここで用いられる溶剤としては、テトラヒドロフラン、ジオキサン、トルエン、ジクロロメタン、モノクロロベンゼン、ジクロロエタン、シクロヘキサノン、メチルエチルケトン、アセトンなどが用いられる。これらは単独で使用しても２種以上混合して使用しても良い。
【００７８】
次に感光層が単層構成の場合について述べる。感光層は、前述の電荷発生物質、電荷輸送物質、結着樹脂等を適当な溶剤に溶解ないし分散し、これを導電性支持体５０上ないし下引き層５１上に塗布、乾燥することによって形成できる。電荷輸送物質を含有させずに、電荷発生物質と結着樹脂とから構成してもよい。また、必要により可塑剤やレベリング剤、酸化防止剤等を添加することもできる。
【００７９】
結着樹脂としては先に電荷輸送層で挙げた結着樹脂のほかに、電荷発生層で挙げた結着樹脂を混合して用いてもよい。もちろん、先に挙げた高分子電荷輸送物質も良好に使用できる。結着樹脂１００重量部に対する電荷発生物質の量は５〜４０重量部が好ましく、電荷輸送物質の量は０〜１９０重量部が好ましく、さらに５０〜１５０重量部であるればより好ましい。
【００８０】
感光層は、電荷発生物質、結着樹脂を電荷輸送物質とともにテトラヒドロフラン、ジオキサン、ジクロロエタン、シクロヘキサン等の溶媒を用いて分散機等で分散した塗工液を、浸漬塗工法やスプレーコート、ビードコート、リングコートなどで塗工して形成できる。感光層の膜厚は、５〜２５［μｍ］程度が適当である。
【００８１】
＜下引き層５１＞本実施形態に係る感光体においては、導電性支持体と感光層との間に下引き層を設けることができる。下引き層は一般には樹脂を主成分とするが、これらの樹脂はその上に感光層を溶剤で塗布することを考えると、一般の有機溶剤に対して耐溶剤性の高い樹脂であることが望ましい。このような樹脂としては、ポリビニルアルコール、カゼイン、ポリアクリル酸ナトリウム等の水溶性樹脂、共重合ナイロン、メトキシメチル化ナイロン等のアルコール可溶性樹脂、ポリウレタン、メラミン樹脂、フェノール樹脂、アルキッド−メラミン樹脂、エポキシ樹脂等、三次元網目構造を形成する硬化型樹脂等が挙げられる。下引き層にはモアレ防止、残留電位の低減等のために酸化チタン、シリカ、アルミナ、酸化ジルコニウム、酸化スズ、酸化インジウム等で例示できる金属酸化物の微粉末顔料を加えてもよい。また、これらの下引き層は、前述の感光層の如く適当な溶媒及び塗工法を用いて形成することができる。更に本発明の下引き層として、シランカップリング剤、チタンカップリング剤、クロムカップリング剤等を使用することもできる。この他、本発明の下引き層には、Ａｌ2Ｏ3を陽極酸化にて設けたものや、ポリパラキシリレン（パリレン）等の有機物やＳｉＯ2、ＳｎＯ2、ＴｉＯ2、ＩＴＯ、ＣｅＯ2等の無機物を真空薄膜作成法にて設けたものも良好に使用できる。このほかにも公知のものを用いることができる。下引き層の膜厚は０〜５［μｍ］が適当である。
【００８２】
＜保護層５４＞感光体の最表面層に機械的磨耗を防止するために保護層５４を設けることも可能である。例えば耐磨耗性を向上させるためにアモルファスシリコンで表面コートした感光体や、電荷輸送層のさらに表面にアルミナや酸化スズ等を分散させた最表面層を設けた有機感光体などを用いる事もできる。
【００８３】
以上説明したように、本実施形態に用いることができる感光体１の構成は特定の構成に限定されるものではない。導電性支持体の上に電荷発生物質と電荷輸送物質を主成分とする感光層のみを設けた１層構成や、導電性支持体の上に電荷発生物質を主成分とする電荷発生層と電荷輸送物質を主成分とする電荷輸送層とが積層された構成や、導電性支持体の上に電荷発生物質と電荷輸送物質を主成分とする感光層を設け、その上に更に保護層を設けた構成や、導電性支持体の上に電荷発生物質を主成分とする電荷発生層と電荷輸送物質を主成分とする電荷輸送層とを積層し、その電荷輸送層の上に保護層を設けた構成や、導電性支持体の上に電荷輸送物質を主成分とする電荷輸送層と電荷発生物質を主成分とする電荷発生層とを積層し、その電荷発生層の上に保護層を設けた構成など、種々の層構成を有する感光体に適用可能である。
【００８４】
感光体表面の存在する微量の保護物質３２の量を測定する事は困難であるが、本出願人は保護物質３２中の特徴的な元素を測定する事によって感光体表面に必要な保護物質に関する知見を得る事に成功した。測定は、ＰＨＩ社製Ｑｕａｎｔｕｍ２０００型 走査型Ｘ線光電子分光装置（ＸＰＳ）により、Ｘ線源ＡｌＫα、分析領域１００［μｍ］φの条件で行った。
【００８５】
図１１（ａ）に示すように、保護物質３２が感光体１表面上に部分的覆われている場合には、測定される表面元素は、保護物質３２と感光体を構成する保護層５４や電荷輸送層５３を構成する元素が検出される。この場合、測定領域中において、保護物質３２に由来する表面元素割合が高いほど保護物質３２が感光体表面を覆っている割合が高いことになる。一方、図１１（ｂ）に示すように、保護物質３２が感光体表面を均一に覆い、かつ深さ方向の測定領域よりも厚く保護物質が塗布されている場合には、ＸＰＳにより測定される表面元素は全て保護物質３２に由来することになる。また、図１１（ｃ）に示すように、保護物質３２が感光体表面を均一に覆っているが、深さ方向の測定領域よりも保護物質が薄く塗布されている場合には、ＸＰＳによって測定される表面元素は保護物質と感光体を構成する他の層に由来するものとなる。
【００８６】
一例として、保護物質３２としてのステアリン酸亜鉛を感光体表面へ塗布した二つのサンプルについて、ＸＰＳにより測定した結果について説明する。測定は、感光体最表面から深さ２０から５０[Å]に存在する直径１００［μｍ］の円内において行った。ここで、ＸＰＳにより測定される感光体表面領域は少なくとも炭素元素（Ｃ）、酸素元素（Ｏ）、シリコン元素（Ｓｉ）、亜鉛元素（Ｚｎ）及び水素元素（Ｈ）のみから構成されている。また、亜鉛元素（Ｚｎ）は、ステアリン酸亜鉛以外の構成物質には存在しないように構成されている。なお、水素元素（Ｈ）は、ＸＰＳによる測定では検出されない。
【００８７】
表２は、上記二つのサンプルについてＸＰＳにより検出される感光体表面を構成する物質の全元素の元素個数総和に対する、ＸＰＳにより検出される各元素の元素個数割合［％］を示したものである。
【表２】

上述した通り、亜鉛元素（Ｚｎ）は、ステアリン酸亜鉛にのみ存在するので、この亜鉛元素（Ｚｎ）の元素個数割合［％］からＸＰＳにより検出されるステアリン酸亜鉛の元素個数割合［％］、及びステアリン酸亜鉛を構成する各元素のＸＰＳにより検出される元素個数割合［％］を求めることができる。ステアリン酸亜鉛は、分子式が［ＣＨ_３（ＣＨ_２）_１６ＣＯＯ］_２Ｚｎであり、１の亜鉛元素（Ｚｎ）に対し炭素元素（Ｃ）が３６、酸素元素（Ｏ）が４、水素元素（Ｈ）が７０存在する。このうち水素元素（Ｈ）はＸＰＳでは検出されない。従って、感光体表面を構成する物質のＸＰＳにより検出される全元素の元素個数総和に対するステアリン酸亜鉛のＸＰＳにより検出される元素個数割合［％］は、亜鉛元素（Ｚｎ）の元素個数割合［％］に炭素、酸素、亜鉛の各元素の総和である４１を乗じることにより求められる。また、感光体表面を構成する物質のＸＰＳにより検出される全元素の元素個数総和に対するステアリン酸亜鉛のＸＰＳにより検出される各構成元素の元素個数割合［％］は、亜鉛の元素個数割合［％］に一分子中に存在する各元素の元素個数を乗じることにより求められる。表３は、表２の結果からステアリン酸亜鉛、及びそれ以外の保護層５４や電荷輸送層５３に由来する物質の各元素の元素個数割合を示したものである。
【表３】

測定領域において、サンプル１ではＸＰＳにより検出されるステアリン酸亜鉛の元素個数割合は、８．６［％］となる。また、サンプル２では、ＸＰＳにより検出されるステアリン酸亜鉛の元素個数割合は９８．４［％］となる。サンプル２では、感光体表面はほぼステアリン酸亜鉛に覆われていることになる。なお、ステアリン酸亜鉛以外の保護物質を使用した場合であっても、感光体には存在しない特徴的な元素が保護物質中に含まれていれば保護物質の量に関する知見を得ることが出来る。
【００８８】
〔実験例６〕
次に、交流印加放電では顕著となる感光体の膜厚削れが▲１▼Ｖｐｐ−２×Ｖｔｈに比例し、▲２▼ＡＣ電圧の周波数ｆに比例し、かつ▲３▼感光体表面の移動速度ｖに反比例することを示す実験結果について説明する。
本実験例に用いた装置の基本的な構成及び実験条件は、上記実験例４のものと同様であるが、本実験例ではＶｐｐ，ＡＣ電圧の周波数ｆ、感光体表面の移動速度ｖ、保護物質の供給量を変えながら感光体表面の劣化の有無を調べた。具体的には、100時間連続で帯電部材へ電圧を印加させ、保護物質の供給量に対して感光体表面の白濁、膜厚減少の有無をしらべた。また、各条件において、保護物質が実際にどれだけ供給されているのかを知るために、帯電部材へ電圧を印加しない状態で、保護物質のみ供給したサンプルを膜厚減少量測定用とは別に作成し、ＸＰＳにより感光体表面上の亜鉛元素（Ｚｎ）の存在量（元素個数割合）を測定した。亜鉛元素（Ｚｎ）の測定値（元素個数割合）は、帯電部材への電圧印加をせずにステアリン酸亜鉛を塗布し続け、5時間経過した段階での感光体表面を測定した場合の値である。
【００８９】
（実験条件）
帯電条件：
Ｖｐｐ（ＡＣ電圧のピークツーピーク電圧値）＝２１２０、３０００［Ｖ］
ｆ（ＡＣ電圧の周波数）＝８７７．２、１３５０［Ｈｚ］
ＤＣ電圧値＝−６００［Ｖ］
感光体表面の移動速度ｖ＝１２５、１８５［ｍｍ／ｓ］
保護物質：ステアリン酸亜鉛
【００９０】
本実施形態で使用した感光体１では保護物質の直下層は機械的磨耗を防止するための保護層５４であり、その下層は電荷輸送層５３であるが、これらの層には亜鉛が存在しないので、測定された亜鉛元素（Ｚｎ）の元素個数割合は全て保護物質であるステアリン酸亜鉛に由来している。
【００９１】
表４は、Ｘ、感光体速度ｖ、Ｖｐｐ、ＡＣ電圧の周波数ｆの条件を変えて実験を行ったときの、感光体表面状態（白濁の有無と膜厚減少量）とＸＰＳにより検出された亜鉛元素（Ｚｎ）の元素個数割合［％］の結果を示したものである。但しＸは、数１１である。
＜数１１＞ Ｘ＝{Ｖｐｐ−２×Ｖｔｈ}×ｆ／ｖ
【００９２】
図１２は、表４の実験結果に基づき、Ｘに対して、放電領域のＸＰＳにより検出される感光体最表面を構成する物質の全元素の元素個数総和に対する、ＸＰＳにより検出される亜鉛元素の元素個数割合[％]をプロットしたものである。この図より、放電による感光表面の劣化（白濁）を防止するために必要な亜鉛元素（Ｚｎ）の元素個数割合は、次の数１２以上存在させる必要があることがわかる。さらに、放電による感光表面の膜厚削れを防止するために必要な亜鉛元素（Ｚｎ）の元素個数割合は、次の数１３以上存在させる必要があることがわかる。
＜数１２＞ １．５２×１０^-4×｛Ｖｐｐ−２×Ｖｔｈ｝×ｆ／ｖ
＜数１３＞ ２．２２×１０^-4×｛Ｖｐｐ−２×Ｖｔｈ｝×ｆ／ｖ
【００９３】
こうして得られた亜鉛元素の含有割合に基づいて、感光体表面の劣化を防止するために必要なＸＰＳにより検出されるステアリン酸亜鉛の存在量を算出すると以下のようになる。すなわち、ＸＰＳにより検出される感光体最表面を構成する物質の全元素の元素個数総和に対するＸＰＳにより検出されるステアリン酸亜鉛の元素個数割合[％]を数１４以上とすれば、感光体の劣化（白濁）が防止できる。さらに、亜鉛元素の含有割合に基づいて、ＸＰＳにより検出される感光体最表面を構成する物質の全元素の元素個数総和に対するＸＰＳにより検出されるステアリン酸亜鉛の元素個数割合[％]を数１５以上とすれば、膜厚削れもほとんど発生しない。
＜数１４＞ ６．２３×１０^{- ３}×｛Ｖｐｐ−２×Ｖｔｈ｝×ｆ／ｖ
＜数１５＞ ９．１０×１０^{- ３}×｛Ｖｐｐ−２×Ｖｔｈ｝×ｆ／ｖ
【００９４】
交流印加放電では顕著となる感光体表面の化学的劣化がステアリン酸亜鉛の塗布量によって変動する理由については、次のように考えられる。感光体表面の放電領域では放電により発生した粒子（電子、励起分子、イオン、プラズマなど）のエネルギーが感光体表面層に照射される。このエネルギーが感光体表面を構成する分子の結合エネルギーに共鳴、吸収され、電荷輸送層は樹脂分子鎖の切断による分子量低下、高分子鎖の絡み合い度の低下などの化学的劣化を生じ膜厚を減少させてしまうと考えられる。
一方、感光体表面に保護物質が存在すると、放電によって発生した粒子のエネルギーが直接照射されるのは保護物質であるため、感光体自身は放電によって発生した粒子の直接照射を免れることになる。従って、保護物質自身が放電により発生した粒子のエネルギーを吸収し、感光体表面の化学的劣化を緩和すると考えられる。図３に示した実験においても、感光体１の保護物質がない領域Ｂの感光体表面は感光体を構成する分子の残骸が分析から検出されているのに対して、保護物質のある領域Ａでは感光体を構成する分子の残骸が検出されおらず、保護物質の下の感光体表面は劣化していなかった。そして領域Ａでは、保護物質として供給したステアリン酸亜鉛が化学的に変化し、分解した物質が検出された。
【００９５】
このような検討によれば、上記保護物質３２としては種々の物質を用いることが可能である。本実施形態の画像形成装置において用いられているステアリン酸亜鉛は保護物質３２の一例であり、各種の脂肪酸塩、ワックス、シリコンオイル等他の物質を保護物質３２として用いることが可能である。
脂肪酸塩のうちでも脂肪酸金属塩は、金属元素がＸＰＳによって測定される特徴的な元素となりやすく、塗布量などの条件を設定する上で測定が行いやすい。したがって本実施形態のように帯電条件に応じて最適な量の保護物質を感光体表面に供給する装置を設計する上で好適である。
【００９６】
脂肪酸としてはウンデシル酸、ラウリン酸、トリデシル酸、ミリスチン酸、パルミチン酸、ペンダデシル酸、ステアリン酸、ヘプタデシル酸、アラキン酸、モンタン酸、オレイン酸、アラキドン酸、カプリル酸、カプリン酸、カプロン酸などが挙げられ、その金属塩としては亜鉛、鉄、銅、マグネシウム、アルミニウム、カルシウムなどの金属との塩が挙げられる。
【００９７】
保護物質としてはステアリン酸亜鉛のようなラメラ結晶紛体を使用すると好適である。ラメラ結晶は両親媒性分子が自己組織化した層状構造を有しており、剪断力が加わると層間にそって結晶が割れて滑りやすい。この作用が低摩擦係数化に効果があるのであるが、放電からの感光体表面保護の観点から見た場合にも、せん断力を受けて均一に感光体表面を覆っていくラメラ結晶の特性は少量の保護物質によって効果的に感光体表面を覆うことが出来るので保護物質として望ましい。
【００９８】
ラメラ結晶の性質を充分に利用して放電から感光体表面を保護するためには、保護物質塗布装置３０の回転速度と感光体表面の回転速度とを異ならしめ、せん断力を作用させつつ保護物質を塗布する事が望ましい。
また本発明のように放電による劣化から感光体表面を保護する事を目的とした時には、保護物質塗布装置３０はクリーニング装置と帯電装置との中間に設ける事が望ましい。放電領域に到達する前にクリーニング装置によって保護物質が除去されてしまうことを防止するためである。
【００９９】
なお、例えば感光体上に塗付された保護物質がステアリン酸亜鉛である場合には、放電による劣化により粘性を発生する。他の種々の保護物質を使用する場合においても劣化した保護物質は速やかに感光体上から除去することが一般に望ましいと考えられる。かかる観点からは、感光体表面から劣化した保護物質３２を除去する除去部材を設けることが望ましい。また劣化した保護部材は現像領域において現像装置内に混入することがある。このような保護物質の混入はトナー帯電量の変動を引き起こす可能性があるので、変動に強い2成分磁気ブラシ現像を用いる事が望ましい。
【０１００】
以下に、感光体１表面の化学的劣化を防止することができる本実施形態にかかる具体的な手段について説明する。図１３は、感光体１表面の化学的劣化を防止するための電装部を示すブロック図である。同図において、コントローラ（メイン制御部）１１０は、ＣＰＵ、ＲＡＭ、及びＲＯＭを有しており、感光体表面の化学的劣化を防止するための制御を司っている。ＲＯＭは、後述するプログラムが記録されている。ＣＰＵは、ＲＡＭを適宜利用しながらこのプログラムを実行する。コントローラ１１０には、ファーブラシ３１の回転速度と感光体１表面に供給される保護物質３２の量とを対応させた第一のテーブル１０１と、温湿度検出器１００によって検出された帯電ローラ２ａ周囲の環境と帯電条件とを対応させた第二のテーブル１０２と、ファーブラシ３１の回転速度を制御する塗布制御部１０３と、帯電条件を制御する帯電制御部１０４と、帯電条件に応じて必要な保護部材の量を算出する演算部１０５とを備えている。また、コントローラ１１０には温湿度検出器１００や、帯電装置２、保護物質塗布装置３０などが電気的に接続されている。第一のテーブル１０１や、第二のテーブル１０２は、ＲＯＭに構成するようにしてもよい。また、演算部１０５は、この演算手順のプログラムをＲＯＭに記録しておき、ＣＰＵでこのプログラムを実行することにより実現するように構成してもよい。
【０１０１】
第一のテーブル１０１は、感光体１表面の化学的劣化が起きないために必要とされる感光体表面上に塗布すべきステアリン酸亜鉛を塗布するために、上記ＸＰＳによる測定の結果得られるZnの元素割合とファーブラシの回転速度とが対応させられたデーターを有している。第二のテーブル１０２は、帯電ローラ周囲の環境が変化する事によって放電開始電圧が変化した場合でも確実にAC電圧による放電を発生可能なように、温湿度値と放電に必要なＶｐｐの値とを対応させたデーターを有している。演算部１０５は、帯電条件に応じて必要な保護部材の量を算出するために上記式１１又は、式１２に従って必要な亜鉛の元素個数割合［％］を算出可能なように設定されている。
【０１０２】
図１４は、ブラシの回転速度と帯電条件を決めるための手順に関するフローチャートである。コントローラ１１０は、画像形成開始指令が入力されたことに伴って帯電を開始させるに先立ち、温湿度検出器により帯電装置周辺の温度及び湿度（環境条件）を検知する（ステップ１）。次に、ステップ１の検知結果に基づいて予め第二のテーブル１０２に記憶されている帯電条件（Ｖｐｐ値）を選択し、帯電条件として設定する（ステップ２）。そして、ステップ２により設定された帯電条件に応じて感光体１表面の劣化が発生しないために塗布されるステアリン酸亜鉛の亜鉛の元素個数割合［％］を演算部１０５により算出する（ステップ３）。ステップ３により算出された亜鉛の元素個数割合［％］から、感光体表面に所望の保護物質が塗布されるように、第一のテーブル１０１からファーブラシの回転速度を選択し、回転速度として設定する（ステップ４）。次に、ステップ４により設定された回転速度となるように塗布制御部１０３においてファーブラシを回転駆動する（ステップ５）。最後に、帯電制御部において帯電部材に印加する電圧を制御しつつ帯電を開始させる。以上の手順を実行するためのプログラムが前述のようにＲＯＭに記録されている。
【０１０３】
このような制御手段を設けることにより、環境に応じて帯電条件を変化させた場合においても、最適な保護物質を感光体表面に供給して感光体の劣化を防止させる事が可能となる。
【０１０４】
なお上記式１０に従って必要なステアリン酸亜鉛の元素割合を算出する場合には、感光体の膜厚が減少していることを加味してＶｔｈを算出する必要がある。そこでコントローラはさらに、累積放電時間を記憶するための記憶手段と累積放電時間から感光体の膜厚を導くための第３のテーブルを持ち、第３のテーブルによって累積放電時間に対応した感光体膜厚を導き出してＶｔｈを計算する。
【０１０５】
また本実施形態の画像形成装置では、図３（ａ）の点線で囲示すように感光体１、帯電装置２、保護物質塗布装置３０とが一体に構成され、画像形成装置本体から着脱可能なプロセスカートリッジ２００として構成されている。かかるプロセスカートリッジ２００は一体に交換されるので、塗布装置３０に含有される保護物質の量、感光体の初期膜厚などを相互に適切な量に設定する事が容易であり、本発明に適している。
【０１０６】
［実施形態２］
次に、上記実施形態の画像形成装置における別の実施形態２について説明する。本実施形態２の画像形成装置の基本的な構成及び動作は、上記実施形態１と同様であるが、クリーニング装置の構成が上記実施形態とは異なっている。すなわち、上記実施形態１の画像形成装置では、専用のクリーニング装置７が設けられているが、本実施形態２の画像形成装置ではこのクリーニング装置７を取り除き、転写残トナーを現像装置４を用いて回収する方式を採用している。この現像装置回収方式では、クリーニングとは別の目的で設置されている現像装置４をクリーニング手段として利用するため、別個独立に上記のようなクリーニング装置を設ける必要がなく、装置の小型化に大きく貢献することができる。帯電ローラ２ａは、ゴム材料により構成され、感光体１表面に接触せしめる（接触帯電方式（Ｇｐ＝０［μｍ］））ように構成した。
【０１０７】
転写残トナーは、感光体１と対向して設けられた現像装置に再び運ばれ、そこで回収されることになる。かかる構成においては、保護物質塗布装置３０により感光体表面に保護物質を塗布する領域においても転写残トナーが存在することになる。この転写残トナーが存在する部分においては、保護物質を塗布することができない。そのため、保護物質塗布装置３０により保護物質が塗布せしめられた後の感光体表面は、転写残トナーが付着している部分と保護物質が塗布された部分とが混在することになる。
しかしながら、交流印加放電では顕著となる感光体表面劣化を保護するためには何らかの物質が感光体表面に存在していればよい。従って、保護物質３２の代わりにトナーが感光体表面に存在していても感光体表面の化学的劣化を防止することができる。すなわち、転写残トナーの影響を考慮せずに、亜鉛の元素個数割合［％］を上記数１２以上とすれば感光体１表面の白濁を防止でき、亜鉛の元素個数割合［％］を上記数１３以上とすれば感光体の膜厚削れを防止できる。
【０１０８】
ところで、このような現像装置回収方式を採用した画像形成装置においては、感光体上の転写残トナーを現像領域まで搬送する間に、その転写残トナーが保護物質塗布装置３０や接触式帯電ローラ２ａと接触することになる。そのため、保護物質塗布装置３０や帯電ローラ２ａに転写残トナーが付着することがある。かかる場合、感光体１表面上にトナーも保護物質３２も存在しない領域ができることになる。このような領域が多くなることにより、放電による感光体表面（保護層５４や電荷輸送層５３等）の化学的劣化が発生する。そこで、本実施形態では、保護物質塗布装置３０に負の電圧を印加する。例えば、保護物質塗布装置３０にー１０００[Ｖ]程度の電圧を印加させる。これにより、感光体１上のトナーは強く負帯電して感光体１への付着力（鏡像力）が強まる。その結果、トナーが保護物質塗布装置３０や帯電ローラ２ａへの移動を抑制し、放電から感光体１表面を保護することが容易となる。
【０１０９】
本実施形態に係る画像形成装置においては、従来一般的に使用されているクリーニングブレードのエッジ部分を感光体表面に当接させてクリーニングを行う方式によるクリーニング装置を設ける必要がない。クリーニングブレードレスにすることにより、感光体表面に加わる負荷を低減でき、感光体の駆動系に加わる駆動負荷を少なくできる。
なお、転写後に感光体表面に残留した転写残トナーのうち、帯電バイアスと同極性に帯電した正規帯電トナーとは逆極性の逆帯電トナーを、保護物質塗布装置３０に対して感光体表面の移動方向上流側にブラシ部材等の一次保持手段により感光体表面から回収して保持するように構成してもよい。このように逆帯電トナーを回収、保持することで、逆帯電トナーが帯電部材に付着するのを防ぐことができる。そして、その保持した逆帯電トナーを、一の画像形成を終えてから次の画像形成を行うまでの間などの所定のタイミングで、感光体表面に戻す。このようにして感光体上に戻された逆帯電トナーは、現像装置で回収されたり、被転写体やこれを搬送するための搬送部材などに転移されたりする。戻された逆帯電トナーが帯電領域を通過する間は、帯電バイアスの印加を停止したり、帯電ローラ２aを感光体から離間させたりすることにより、逆帯電トナーが帯電ローラ２a等に付着しないように構成している。ブラシ部材の感光体表面へ摺擦する摺擦力はクリーニングブレードに比べて小さくできるので、ブラシ部材を用いても感光体の寿命を長くすることができる。
【０１１０】
なお本発明は図１に示したような画像形成装置のみに適用されるものではなく、接触又は近接させて配置した帯電部材による交流印加放電を用いて被帯電体表面を帯電させる画像形成装置一般に使用可能である。
【０１１１】
以上、実施形態１及び実施形態２によれば、帯電部材を接触又は近接させて配置する方式において、交流印加放電では顕著となる感光体表面の化学的劣化を帯電条件に応じて保護物質を所望量存在させることにより、以下の効果を得ることができる。
ＸＰＳにより検出される感光体体最表面を構成する物質の全元素の元素個数総和に対する、ＸＰＳにより検出されるステアリン酸亜鉛の亜鉛元素（Ｚｎ）の元素個数割合[％]を、上記数１２以上とすることにより、交流印加放電では顕著となる感光体表面の変質（白濁）を防止することができる。
また、ＸＰＳにより検出される感光体最表面を構成する物質の全元素の元素個数総和に対する、ＸＰＳにより検出されるステアリン酸亜鉛の亜鉛元素（Ｚｎ）の元素個数割合[％]を、上記数１３以上とすることにより、交流印加放電では顕著となる感光体表面の膜厚削れを防止することができる。
また、ＸＰＳにより検出される感光体体最表面を構成する物質の全元素の元素個数総和に対する、ＸＰＳにより検出される保護物質としてのステアリン酸亜鉛を構成する元素個数割合[％]を、上記数１４以上とすることにより交流印加放電では顕著となる感光体表面の変質（白濁）を防止することができる。
また、ＸＰＳにより検出される感光体体最表面を構成する物質の全元素の元素個数総和に対する、ＸＰＳにより検出される保護物質としてのステアリン酸亜鉛を構成する元素個数割合[％]を、上記数１５以上とすることにより、交流印加放電では顕著となる感光体表面の膜厚削れを防止することができる。
また、保護物質としてラメラ結晶紛体を用いている。これにより、剪断力を受けて層間で保護物質がへき開して感光体表面に広がるので、より均一に塗布することができる。
また、実施形態１に係る画像形成装置は、帯電ローラと感光体を非接触により帯電する方式を採用している。これにより、帯電ローラへの保護物質の付着を防止して、保護物質の感光体上の存在量を安定させることができる。
また、実施形態１に係る画像形成装置は、帯電ローラの表面層を樹脂材料により構成している。これにより、帯電部材の変形が抑制され、保護物質の存在量が局所的、突発的に乱されるのを抑制することができる。
また、実施形態１、２に係る画像形成装置は、保護物質を感光体表面に塗布するための塗布装置を有し、この感光体１と塗布装置３０のブラシローラ部３１との接触部における両者の回転速度を異ならしめるように設定している。これにより、保護物質としてのラメラ結晶紛体がへき開によってより広がりやすくなるので、感光体表面に保護物質をより効率的に塗布することができる。
また、実施形態１、２においては、帯電部材周囲の環境状態を検出する環境検出手段と、環境検出手段による検出結果に基づいて感光体への保護物質を存在させる量を制御する保護物質供給量制御部とを有している。これにより、温度や湿度が変動しても、保護物質の最適な量を感光体に供給することが可能となり、感光体の化学的劣化を防止することができる。
また、実施形態２においては、クリーニングブレードを設けず、転写残トナーを現像装置を用いて回収する方式を採用している。また、現像装置４に対して感光体１の移動方向下流側であって帯電装置２に対して感光体１表面の移動方向上流側に残留した像形成物質を帯電させるための帯電部材を設け、かつ、ステアリン酸亜鉛に含まれる亜鉛元素の元素個数割合［％］を上記数１２または数１３に適合するように感光体表面にステアリン酸亜鉛を塗布している。かかる構成により、転写残トナーを感光体上に鏡像力で固定することが可能となり、トナー及びステアリン酸亜鉛の存在によって、放電による感光体表面の化学的劣化を防止することができる。
また、実施形態１及び２においては、帯電装置２、感光体１、帯電装置３０からなるプロセスカートリッジを、画像形成装置に対して着脱可能に構成している。かかるプロセスカートリッジは一体に交換されるので、塗布装置３０に含有される保護物質の量、感光体の初期膜厚などを相互に適切な量に設定する事が容易である。
【０１１２】
【発明の効果】
本発明によれば、接触又は近接させて配置した帯電部材による交流印加放電を利用して感光体を帯電させる場合において、感光体表面の化学的劣化を防止することができるという優れた効果がある。
【図面の簡単な説明】
【図１】（ａ）は、感光体の断面図。
（ｂ）は、放電によって感光体表面が劣化する場合の感光体表面の状態を示した説明図。
【図２】従来技術の不具合発生に関する実験結果を示す図。
【図３】（ａ）は、本発明の効果を確かめるための実験装置の概略構成図。
（ｂ）は、感光体表面を保護層形成部と非形成部とに分けた状態の説明図。
【図４】帯電時間に対する感光体表面の膜厚削れ量をプロットしたグラフ。
【図５】２通りの塗布量でステアリン酸亜鉛塗布を行ったときの、時間に対する感光体表面摩擦係数をプロットしたグラフ。
【図６】Ｖｐｐに対して、感光体表面の膜厚削れ量をプロットしたグラフ。
【図７】ＡＣ電圧の周波数ｆに対して、感光体表面の膜厚削れ量をプロットしたグラフ。
【図８】実施形態１に係る画像形成装置の要部の説明図。
【図９】実施形態１に係る画像形成装置に用いる帯電装置の概略構成図。
【図１０】実施形態１に係る感光体の断面図。
【図１１】（ａ）は、保護物質が部分的に塗布されていることを示す説明図。
（ｂ）は、保護物質が均一に塗布され、かつ最表面層から２０から５０[Å]以上塗布されていることを示す説明図。
（ｃ）は、保護物質が均一に塗布され、かつ最表面層から２０から５０[Å]以下塗布されていることを示す説明図。
【図１２】実験例６に係るＸに対して、Ｚｎ元素個数割合をプロットしたグラフ。
【図１３】実施形態１に係る保護物質を最適に塗布するための制御図。
【図１４】実施形態１に係る帯電を開始するための手順に関するフローチャート図。
【符号の説明】
１ 感光体
２ 帯電装置
２ａ 帯電ローラ
４ 現像装置
３０ 保護物質塗布装置
３１ ファーブラシ
３２ 保護物質
１００ 温湿度検出器
１０３ 塗布制御部
１０４ 帯電制御部
２００ プロセスカートリッジ[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a charging device that includes a movable body to be charged and a charging member that is disposed opposite to and in contact with the body to be charged, and charges the body to be charged by applying a voltage containing an AC component to the charging member. Image forming apparatus havingIn placeIt is related.
[0002]
[Prior art]
In an electrophotographic image forming apparatus, a charging unit is used for various purposes. For example, uniform charging of the surface of the photoconductor performed before forming an electrostatic latent image on the surface of the photoconductor as an image bearing member, which is a charged body, and equalizing the potential of the charged region in the photoconductor after image transfer. For this purpose, a charging means is provided for static elimination or the like. In some cases, a charging unit is also provided for charging the transfer material for applying a predetermined potential to the transfer material, which is a member to be charged that has been conveyed to the transfer region. As these charging means, there has been conventionally used a corona charging method using corona discharge.
[0003]
In the corona charging method, a charge wire is disposed close to a member to be charged, and a high voltage is applied to the charge wire to cause a corona discharge between the charge wire and the member to be charged. Is charged.
However, in the case of the corona charging method, discharge products such as ozone and nitrogen oxide (NOx) are generated with corona discharge. Since the discharge-generating substance may form a film of nitric acid or nitrate that adversely affects image formation on the surface of the photoreceptor, it is desirable to avoid the occurrence of the substance if possible.
[0004]
Therefore, in recent years, in place of the corona charging method, the development of a contact charging method or a proximity charging method in which the generation of a discharge generating material is small and charging can be performed with low power has been active. In these methods, a charging member such as a roller, a brush, or a blade is brought into contact with or in close proximity to a charged member such as a photosensitive member, and a voltage is applied to the charging member to charge the surface of the charged member. It is. According to this method, compared to the corona charging method, the generation of a discharge generation material is small, and low power can be realized, so that the utility is high. In addition, since a large charging device is not required, the device can be miniaturized, which meets the needs for miniaturization of the device.
[0005]
In these systems, since the charge is applied to the charged object by discharging to the charged object directly or through a minute gap, the problem of poor charging uniformity due to discharge unevenness becomes a problem. Thus, an AC voltage superposition charging method has been proposed in which a voltage obtained by superimposing an alternating voltage on a direct current voltage is applied to a charged body to charge the charged body (see Patent Document 1). In this method, an alternating voltage is superimposed on a direct current voltage, thereby facilitating discharge by instantaneously and continuously applying a voltage that greatly exceeds the breakdown voltage to the charged body.
[0006]
On the other hand, the following proposals have been made, for example, in order to prevent film thickness shaving on the surface of the photoreceptor. For example, the surface of the photoconductor is coated with amorphous silicon carbide, or an inorganic material such as alumina is dispersed in the charge transport layer (CTR) on the surface of the organic photoconductor (see Patent Documents 2 and 3).
[0007]
Patent Documents 4, 5, 6, and 7 disclose means for applying zinc stearate to the surface of the photoreceptor, as in a specific embodiment of the means for preventing deterioration of the charged object surface in the means for solving the problems described later. Has been proposed. According to the proposals in Patent Documents 4 and 5, it is possible to reduce the coefficient of friction on the surface of the photoconductor and prevent the cleaning of the surface of the photoconductor. The proposals in Patent Documents 6 and 7 are intended to prevent foreign matters from easily attaching to the surface of the photoreceptor, and use of zinc stearate to prevent hazards caused by contact charging or proximity charging. In the above, the present invention is approximated.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 5-150564
[Patent Document 2]
JP 2002-207308 A
[Patent Document 3]
JP 2002-229227 A
[Patent Document 4]
JP 2002-55580 A
[Patent Document 5]
JP 2002-244487 A
[Patent Document 6]
JP 2002-244516 A
[Patent Document 7]
JP 2002-156877 A
[0009]
[Problems to be solved by the invention]
In the contact charging method or the proximity charging method described above, there is a problem in that the surface of the object to be charged is chemically deteriorated when the object to be charged is charged by using a discharge generated by applying a voltage containing an AC component. From experiments to be described later, it was found that this chemical deterioration (thickness shaving, etc.) on the surface of the member to be charged occurs even when there is no mechanical rubbing.
[0010]
As the film thickness of the photosensitive layer constituting the photoconductor progresses, it tends to promote reduction in the charged potential of the photoconductor, deterioration in photosensitivity, background contamination due to scratches on the surface of the photoconductor, reduction in image density, or deterioration in image quality. Becomes stronger. Preventing deterioration of the photoreceptor surface is a particularly important issue in today's high demand for higher image quality.
[0011]
According to the proposals in Patent Documents 2 and 3, it is possible to improve the durability of the photosensitive member against mechanical wear. However, in the method in which the charging member as described above is arranged in contact or close proximity, the AC application discharge is notable. It is impossible to prevent chemical deterioration of the surface of the photoreceptor. Further, in the proposals of Patent Documents 4 and 5, there is a possibility that chemical deterioration of the surface of the photosensitive member, which becomes noticeable with AC applied discharge, cannot be prevented in the method in which the charging member is arranged in contact with or in close proximity. The presence state of zinc stearate required on the surface of the photoreceptor to prevent chemical deterioration of the surface of the photoreceptor due to such discharge is different from that for reducing the friction coefficient (see Experimental Example 2). Because. In the proposals in Patent Documents 6 and 7, no means for preventing chemical deterioration (thickness shaving, etc.) on the surface of the photoconductor is described. The state of the presence of an appropriate protective substance on the surface of the photoreceptor in the discharge region for preventing ()) has not been studied.
[0012]
In the image forming apparatus, there are cases where control is performed so that the apparatus operates optimally by changing charging conditions (charging voltage, etc.) according to environmental conditions such as temperature and humidity. It is presumed that the degree of progress of chemical degradation on the surface of the photoreceptor varies depending on the charging conditions. Therefore, if the existence state of the protective substance on the member to be charged that can appropriately prevent the chemical deterioration of the surface of the photosensitive member according to the charging condition can be grasped, the durability of the member to be charged can be further increased. Seem.
[0013]
  The present invention has been made in view of the above problems, and an object of the present invention is to charge the object to be charged by using an AC applied discharge by a charging member arranged in contact with or close to the charging member. Image forming apparatus capable of preventing chemical deterioration of charged surfacePlaceIs to provide.
[0014]
[Means for Solving the Problems]
  In order to achieve the above object, an image forming apparatus according to a first aspect of the present invention includes a movable object to be charged and a charging member disposed in contact with or in close proximity to the object to be charged, and the charging member has an alternating current. In an image forming apparatus having a charging device that applies a voltage containing a component to charge the object to be charged, zinc stearate as a protective substance for preventing deterioration of the surface of the object to be charged due to the charging is applied to the object. An environment detecting means for detecting an environmental condition around the charging member, the detection means being present on the charged body, and based on a detection result by the environment detecting means.Based on a charge control unit that controls a voltage applied to the charging member, and a voltage value applied to the charging memberA protective substance supply amount control unit for controlling the amount of zinc stearate present in the object to be charged, and an X-ray photoelectron spectrometer (XPS) in a region where the object to be charged is charged by the charging member. The element number ratio [%] of the specific element of the zinc stearate detected by the XPS with respect to the total element number of all elements of the substance constituting the outermost surface of the object to be detected detected by the following equation: It is characterized by that.
  <Equation 1> 1.52 × 10 −4 × {Vpp−2 × Vth} × f / v × Nα
(Where Vpp is the peak-to-peak voltage value [unit: V] of the AC voltage, f is the frequency of the AC component applied to the charging member [unit: Hz], and v is the moving speed of the surface of the member to be charged [unit: mm] / Sec], Nα is the number of elements in one molecule of the specific element among the elements constituting the protective substance.
  Vth is a discharge start voltage, and is obtained by the following equation (2).
  <Equation 2> Vth = 312 + 6.2 × (d / εopc + Gp / εair) + √ (7737.6 × d / εopc)
  In this case, d is the film thickness [unit: μm] of the member to be charged, εopc is the relative dielectric constant of the member to be charged, εair is the relative dielectric constant in the space between the member to be charged and the charging member, and Gp is the surface of the charging member. The closest distance to the surface of the member to be charged [unit: μm]. )
  According to a second aspect of the present invention, there is provided a movable member to be charged and a charging member disposed oppositely in contact with or close to the member to be charged, and a voltage containing an AC component is applied to the charging member. In an image forming apparatus having a charging device for charging the member to be charged, zinc stearate as a protective material for preventing deterioration of the surface of the member to be charged due to the charging is present on the member to be charged, After the start of formation, in the region where the charged body is charged by the charging member, the total number of elements of all the elements constituting the charged body outermost surface detected by an X-ray photoelectron spectrometer (XPS) is The element number ratio [%] of the specific element of the zinc stearate detected by the XPS is expressed as follows:3Based on the calculation result, the amount of zinc stearate to be present in the object to be charged is calculated.More than 3A protective substance supply amount control unit for controlling is provided.
  <Number3> 1.52 × 10 −4 × {Vpp−2 × Vth} × f / v × Nα
  (Where Vpp is the peak-to-peak voltage value [unit: V] of the AC voltage, f is the frequency of the AC component applied to the charging member [unit: Hz], and v is the moving speed of the surface of the member to be charged [unit: mm] / Sec], Nα is the number of elements in one molecule of a specific element among elements constituting zinc stearate.
  Vth is a discharge start voltage, and the following number4It is calculated by.
  <Number4> Vth = 312 + 6.2 × (d / εopc + Gp / εair) + √ (7737.6 × d / εopc)
  In this case, d is the film thickness [unit: μm] of the member to be charged, εopc is the relative dielectric constant of the member to be charged, εair is the relative dielectric constant in the space between the member to be charged and the charging member, and Gp is the surface of the charging member. The closest distance to the surface of the member to be charged [unit: μm]. )
[0015]
  According to a third aspect of the present invention, in the image forming apparatus of the first or second aspect, the element number ratio [%] of the specific element is5It is characterized by the above.
  <Number5> 2.22 × 10^{− Four}* {Vpp-2 * Vth} * f / v * N_α
[0016]
  According to a fourth aspect of the present invention, there is provided the image forming apparatus according to the first or second aspect, wherein the XPS with respect to the total number of elements of all the elements constituting the surface of the charged body detected by the XPS is used. The ratio of the number of elements constituting the zinc stearate to be detected [%] is expressed as follows:6It is characterized by the above.
  <Number6> 1.52 × 10^{− Four}* {Vpp-2 * Vth} * f / v * N_β
(Nβ: a value obtained by subtracting the number of hydrogen elements from the total number of elements constituting one molecule of zinc stearate.)
[0017]
  An image forming apparatus according to a fifth aspect is the image forming apparatus according to the third aspect, wherein the image forming apparatus is detected by the XPS with respect to the total number of all elements of the substance constituting the outermost surface of the charged body detected by the XPS. The ratio of the number of elements constituting the zinc stearate [%]7It is characterized by the above.
  <Number7> 2.22 × 10^{− Four}* {Vpp-2 * Vth} * f / v * N_β
[0018]
  Claims6The image forming apparatus according to claim 1.2 or 3In the image forming apparatus,UpThe specific elementzincAnd Nα is 1.
[0020]
  An image forming apparatus according to a seventh aspect is the4 or 5In the image forming apparatus, Nβ is 41.
[0022]
  Claims8The image forming apparatus of claim 1, 2, 3, 4, 5, 6.Or 7In this image forming apparatus, the closest distance between the charging member and the member to be charged is 1 to 100 [μm].
[0023]
  Claims9The image forming apparatus of claim8In the image forming apparatus, the surface layer of the charging member is made of a resin material.
[0024]
  Claims10The image forming apparatus of claim1, 2, 3, 4, 5, 6, 7, 8, or 9In the image forming apparatus, a protective substance supply member for applying the protective substance to the surface of the object to be charged is provided, the surface of the protective substance supply member and the surface of the object to be charged are brought into contact, and the protective substance at the contact portion The moving speed between the surface of the supply member and the surface of the member to be charged is set differently.
[0026]
  Claim11The image forming apparatus of claim 1, 2, 3, 4, 5, 6, 7, 8, 9.Or 10In this image forming apparatus, the electrostatic latent image of the image carrier is provided with a charging member arranged in contact with or close to the image carrier and means for removing the image forming substance remaining on the surface of the image carrier. A developing device that develops an image; and the image carrier surface downstream of the developing device in the moving direction of the image carrier surface and upstream of the charging member in the moving direction of the image carrier surface. And charging means for charging the remaining image forming substance.
[0028]
  Claims 1 to11In the present invention, for the reason considered from the experiment described below, in the method of charging an object to be charged using an AC applied discharge by a charging member arranged in contact or in proximity, the surface of the object to be charged is chemically treated. Deterioration can be prevented.
[0029]
[Experimental Example 1]
The present applicant conducted the following experiment in order to investigate the deterioration state of the surface of the photosensitive member as a member to be charged, which becomes conspicuous in the AC applied discharge by the charging member arranged in contact or close to the charging member. In order to eliminate deterioration of the surface of the photoreceptor due to mechanical wear, the charging member 2a is disposed in a non-contact manner with respect to the surface of the photoreceptor 1 as shown in FIG. Further, all members that contact the photosensitive member 1 were removed. The roller-shaped charging member 2a (hereinafter referred to as “charging roller 2a”) capable of rotating in a non-contact manner to which a voltage obtained by superimposing an alternating current (AC) voltage bias on a direct current (DC) bias is applied for about 150 hours. The photoreceptor 1 was continuously charged. As shown in FIG. 1A, the photoreceptor 1 used in this experiment is provided with an undercoat layer 51 that is an insulating layer on a base layer 50. Furthermore, a charge generation layer (CGL) 52, a charge transport layer (CTL) 53, and a surface protective layer (FR) 54 are sequentially laminated thereon.
[0030]
FIG. 2 is a plot of the amount of film thickness shaving on the surface of the photoreceptor 1 with respect to the charging time. From this figure, it can be seen that the film thickness of the photosensitive member 1 decreases as the charging time increases. It is presumed that chemical deterioration of the surface of the photosensitive member 1 after charging, which becomes noticeable in the AC applied discharge, has occurred, and the film thickness has been reduced as shown in FIG. Although the details of the mechanism that causes chemical degradation of the surface of the charged body, which becomes noticeable in the AC applied discharge by the charging member arranged in contact or close to each other, are under investigation, the photosensitive body as the charged body after the charging in Experimental Example 1 Analysis of the body 1 surface revealed the following facts. A carboxylic acid considered to be a decomposition product of polycarbonate, which is a binder resin constituting the charge transport layer 53 and the surface protective layer 54, was detected.
[0031]
Since the components constituting the photoconductor 1 are considered to have been decomposed, the mechanism of the film thickness reduction of the photoconductor 1 can be considered as follows.
When the surface protective layer 54 on the surface of the photoconductor 1 is irradiated with energy of particles (ozone, electrons, excited molecules, ions, plasma, etc.) generated by discharge by a charging member arranged in contact or in proximity, this energy is exposed to light. Resonant and absorbed by the binding energy of the molecules constituting the surface protective layer 54 and the like on the surface of the body 1. And it induces chemical degradation such as a decrease in the degree of entanglement of the polymer chains forming the outermost surface layer, a decrease in molecular weight due to the cleavage of the resin molecular chains, and evaporation of the resin and decomposition products. With such chemical deterioration, it is estimated that the outermost surface layer on the surface of the photoreceptor 1 is gradually shaved.
[0032]
The film thickness reduction is considered to be caused by the energy of particles generated by the discharge by the charging member arranged in contact with or close to the film. Therefore, this is not a problem peculiar to polycarbonate, which is a substance forming the surface protective layer 54 and the charge transport layer 53 in Experimental Example 1, and it is considered that the same phenomenon occurs in the photoreceptor 1 using other materials.
[0033]
[Experimental example 2]
Next, a description will be given of an experimental example showing that the chemical deterioration of the surface of the photoreceptor, which becomes noticeable in alternating current application discharge, can be suppressed by the presence of a protective substance on the photoreceptor. FIG. 3A is a schematic configuration of an experimental apparatus for confirming that the chemical degradation of the surface of the photoconductor 1 that becomes remarkable in the AC applied discharge is suppressed by the presence of the protective substance 32 on the photoconductor 1. FIG. In order to compare the deterioration state of the surface of the photoconductor due to the presence or absence of the protective material 32, as shown in FIG. 3B, a region A in which the protective material is applied on the surface of the photoconductor ) And a non-coated area B (the right half in the photoconductor width direction in the figure). Specifically, the protective material coating device 30 (the configuration and operation will be described in the embodiment) is disposed so as to be applied only to the left half surface region in the width direction of the photoreceptor 1 using the fur brush 31. Only the area A was coated with zinc stearate as the protective substance 32.
In order not to cause deterioration of the surface of the photoreceptor 1 due to mechanical wear, all members other than the charging roller 2a and the protective material coating device 30 were removed in advance. Then, the charging device 2 and the protective material coating device 30 were continuously driven together with the photoconductor 1, and the deterioration state of the surface of the photoconductor 1 was examined. The experimental conditions are as follows.
[0034]
(Experimental conditions)
Charging conditions:
Vpp (peak-to-peak voltage value of AC voltage) = 2.12 [kV]
f (frequency of AC voltage) = 877.2 [Hz]
DC voltage value = −660 [V]
Moving speed of photoreceptor surface v = 125 [mm / s]
Line speed of fur brush 31 = 216 [mm / sec]
Protective substance 32: Zinc stearate
[0035]
FIG. 4 is a plot of the amount of film thickness shaving on the surface of the photoreceptor against the charging time. From the figure, it can be seen that the amount of film scraping increases as the charging time increases.
The following facts were found when the film thickness of the photoconductor 1 after the experiment was continuously performed for 200 hours was compared with the film thickness of the photoconductor 1 before the experiment. In the region B where the protective material 32 is not applied, the film thickness is reduced by 2.5 [μm], whereas in the region A where the protective material 32 is applied, 1/8 of the reduced film thickness of the region B is applied. Reduced to:
Further, when the surface of the photoconductor 1 after the above experiment was continuously performed for 200 hours was visually observed, in the region B where the protective material 32 was not applied, the surface of the photoconductor 1 was turned white and deteriorated. On the other hand, in the area A where the protective substance 32 is applied, the same mirror surface as the surface of the new photoreceptor 1 before the experiment was held.
From these results, it has been clarified that chemical deterioration of the surface of the photoreceptor, which becomes noticeable in alternating current application discharge, can be suppressed by applying a protective substance to the surface of the photoreceptor 1.
[0036]
[Experimental Example 3]
Next, the conditions for suppressing the chemical deterioration of the surface of the photoreceptor 1 that becomes remarkable in the AC applied discharge are the conditions for reducing the friction coefficient of the photoreceptor surface proposed in the above-mentioned documents 4 and 5. Will be described experimental examples showing different.
Experimental conditions are basically the same as in Experimental Example 2. However, the non-existing region B of the protective material 32 is not provided on the surface of the photoconductor, but the protective material 32 is applied to the entire region (region A and region B) on the surface of the photoconductor so that the desired abundance is as follows. The point is different. The coating amount of zinc stearate as a protective substance on the surface of the photoconductor is set to 0.0002 [mg / mm2] and 0.0016 [mg / mm2]. The presence or absence of occurrence was examined.
[0037]
The results are shown in Table 1. When zinc stearate was applied at 0.0002 [mg / mm 2], the film thickness on the surface of the photoconductor was scraped and the surface of the photoconductor was deteriorated. On the other hand, when zinc stearate was applied at 0.0016 [mg / mm 2], the film thickness on the surface of the photoconductor was not scraped and the surface of the photoconductor was not deteriorated. When the coating amount is 0.0002 [mg / mm 2], the coating amount is insufficient, and the surface deterioration of the photosensitive member, which becomes noticeable with AC applied discharge, cannot be suppressed. On the other hand, when the coating amount is 0.0016 [mg / mm 2], it can be said that the coating amount for that purpose is satisfied.
[Table 1]

[0038]
Here, the friction coefficient of the surface of the photoreceptor was measured for the above two samples. FIG. 5 is a plot of the coefficient of friction of the photoreceptor surface versus the elapsed time after application to the photoreceptor surface for these two samples. The coefficient of friction is measured by the Euler belt method. Immediately after the protective material 30 is applied to the surface of the photoconductor, the friction coefficient varies depending on the amount of application, but it can be seen that the friction coefficient becomes comparable after a certain period of time. According to this experiment, the coefficient of friction became about 0.1 after a certain period of time. With such a low coefficient of friction, it is possible to prevent the film thickness from being removed on the surface of the photoreceptor due to mechanical wear.
[0039]
From the results shown in Table 1 and FIG. 5, a coating amount of 0.0002 [mg / mm2] is sufficient to apply zinc stearate as a lubricant to reduce the coefficient of friction on the surface of the photoreceptor. It can be seen that the coating amount needs to be larger than 0.0016 [mg / mm 2] in order to protect the body surface from chemical deterioration that becomes remarkable in the AC applied discharge. That is, the conditions for lowering the coefficient of friction of the photoconductor and the conditions for protecting the surface of the photoconductor from the chemical degradation that becomes noticeable in AC applied discharge are different. It can be seen that the conditions for protection cannot be derived from the prior art. According to the applicant's investigation, it is clear that the presence state of zinc stearate necessary for obtaining a low coefficient of friction action is different from the presence state of zinc stearate necessary for preventing deterioration of the photoreceptor surface due to electric discharge. Became.
[0040]
[Experimental Example 4]
Next, the film thickness scraping amount on the surface of the photoreceptor, which becomes noticeable in the AC applied discharge, is the AC voltage peak-to-peak voltage value Vpp (hereinafter simply referred to as “Vpp”), that is, the amplitude value of the AC component applied to the charging member. An experimental example showing proportionality will be described.
The following experiment was performed using an apparatus including the photoconductor 1, the charging device 2, and the coating device 30 as shown in FIG. In order not to cause deterioration of the surface of the photosensitive member due to mechanical wear, all members that contact the photosensitive member other than the charging roller 2a and the protective substance coating device 30 were removed in advance. Then, the Vpp was changed, and the amount of film thickness scraping was measured when the surface of the photoreceptor 1 was charged by alternating current discharge for 100 consecutive hours. The experimental conditions are as follows.
[0041]
(Experimental conditions)
Charging conditions:
Vpp (peak-to-peak voltage value of AC voltage) = 2.2, 2.6, 3.0 [kV]
f (frequency of AC voltage) = 1350 [Hz]
DC voltage value = −600 [V]
Movement speed of photoreceptor surface v = 113 [mm / s]
Protective substance: Zinc stearate
Charging time: 100 hours
[0042]
FIG. 6 is a plot of the amount of film thickness shaving on the surface of the photoreceptor after being charged by 100 hours of continuous discharge against Vpp. From the figure, it can be seen that the film thickness shaving amount on the surface of the photoreceptor is proportional to Vpp. It can also be seen that the amount of film thickness reduction is 0 when Vpp is about 1.9 [kV].
[0043]
  In this regard, the present applicant considers as follows. It is known that when an AC voltage is applied, discharge does not start between the charging member surface and the photoreceptor surface unless the voltage applied to the charging member exceeds a predetermined value. According to the applicant's research, in the case of non-contact charging, the voltage applied to the charging member is several when the closest distance between the charging member surface and the surface to be charged is Gp [μm].8When the value becomes equal to or greater than the value shown in FIG. Hereinafter, this value is referred to as a discharge start voltage Vth.
  <Number8> Vth = 312 + 6.2 × (d / ε_opc+ Gp / ε_air) + √ (7737.6 × d / ε)_opc)
  Here, d is the film thickness [μm] of the photosensitive member, εopc is the relative dielectric constant of the photosensitive member, and εair is the relative dielectric constant in the space between the photosensitive member and the charging member.
  When Vpp is equal to or greater than twice the above Vth, a bidirectional discharge occurs between the charging member and the photosensitive member.
  In this experimental example, the gap between the charging roller and the photoconductor is 50 [μm], the relative permittivity of the photoconductor is about 3, the film thickness of the photoconductor is 30 [μm], and the space between the photoconductor and the charging member. Since the relative dielectric constant at is about 1, when these are applied to the above equation, Vth = 962 [V]. When the voltage applied to the charging member is 962 [V] or higher, discharge is started between the surface of the charging member and the surface of the photosensitive member, and when Vpp exceeds about 1924 [V], discharge by AC voltage is started. Conceivable. The dominant discharge phenomenon is bi-directional discharge caused by AC voltage. For this reason, it is considered that when the Vpp exceeds about 1.9 [kV], the film thickness of the photoreceptor starts to be reduced.
[0044]
[Experimental Example 5]
Next, a description will be given of an experimental example showing that the film thickness shaving amount on the surface of the photosensitive member, which is noticeable in AC applied discharge, is proportional to the frequency f of the AC voltage.
The basic configuration and experimental conditions of the apparatus used in this experimental example are the same as those in the experimental example 4, but the charging conditions and the moving speed of the photosensitive member surface are different from those in the experimental example 4. That is, in Experimental Example 4, the frequency f of the AC voltage is fixed and Vpp is changed, but in this experimental example, Vpp is fixed and the frequency f of the AC voltage is changed.
[0045]
(Experimental conditions)
Charging conditions:
Vpp (peak-to-peak voltage value of AC voltage) = 2.2 [kV]
f (frequency of AC voltage) = 500, 900, 1400, 2000, 4000 [Hz]
DC voltage value = −600 [V]
Moving speed of photoreceptor surface v = 104 [mm / s]
Protective substance: Zinc stearate
Charging time: 100 hours
[0046]
FIG. 7 is a plot of the amount of film thickness shaving on the surface of the photoreceptor after charging for 100 consecutive hours by the above discharge against the frequency f of the AC voltage. From the figure, it can be seen that the film thickness shaving amount on the surface of the photoreceptor is proportional to the frequency f of the AC voltage.
[0047]
From the results of the present experimental example and the above experimental example 4, it has been clarified that the decrease in the thickness of the photosensitive member varies depending on the charging conditions (specifically, proportional to Vpp and f).
Therefore, the present applicant has predicted that the reduction in the thickness of the photosensitive member has the following relationship. That is, it was predicted that (1) proportional to Vpp-2 × Vth, (2) proportional to the frequency f of the AC voltage, and (3) inversely proportional to the moving speed v of the photoreceptor surface. The reason for the prediction of (3) is that if the moving speed of the photosensitive member is slow, it is considered that the discharge energy irradiated per unit area increases even under the same charging conditions. The validity of this prediction is confirmed by Experimental Example 6 to be described later, and in order to prevent chemical deterioration of the charged body, which becomes remarkable in the AC applied discharge by the charging member arranged in contact with or close to the charged body. The following knowledge about the amount of the protective substance to be applied to was obtained.
[0048]
  In the region where the member to be charged is charged by the charging member, the ratio of the number of elements of the specific element of the protective material detected by XPS to the total number of all elements of the material constituting the outermost surface of the member to be detected detected by XPS [ %] The next number9By doing so, it becomes possible to prevent the surface of the charged body from being significantly deteriorated in the AC applied discharge by the charging member arranged in contact with or close to the charging member.
  <Number9> 1.52 × 10^{− Four}* {Vpp-2 * Vth} * f / v * N_α
  Here, Vpp is the peak-to-peak voltage value [unit: V] of the AC voltage, f is the frequency of the AC component applied to the charging member [unit: Hz], and v is the moving speed of the surface of the member to be charged [unit: mm / mm]. sec], Nα is the number of elements in one molecule of the specific element among the elements constituting the protective substance.
  Vth is the discharge start voltage,8It is calculated by.
[0049]
  Furthermore, in the region where the member to be charged is charged by the charging member, the number of elements of the specific element of the protective material detected by XPS with respect to the total number of elements of all the elements constituting the surface of the member to be charged detected by XPS Percentage [%], next number10By doing so, it is possible to prevent the thickness of the member to be charged from being reduced.
  <Number10> 2.22 × 10^{− Four}* {Vpp-2 * Vth} * f / v * N_α
[0050]
DETAILED DESCRIPTION OF THE INVENTION
[Embodiment 1]
Hereinafter, an embodiment in which the present invention is applied to an image forming apparatus will be described. First, a basic configuration of an image forming unit provided in the image forming apparatus will be described with reference to FIG. In the figure, this image forming unit includes a drum-shaped photosensitive member 1 as an image carrier as a member to be charged, a charging device 2, an exposure device 3 for writing an electrostatic latent image on the photosensitive member 1, and a developing device 4. A cleaning device 7 for removing an image forming substance on the surface of the photoreceptor 1 is used.
[0051]
In the image forming apparatus having such a configuration, the photosensitive member 1 is rotationally driven by a driving device (not shown), and the surface thereof is charged to a predetermined polarity by the charging device 2. Next, the exposure device 3 is driven based on image information read from the outside, whereby an electrostatic latent image is formed in the charged area (image forming area) of the photoreceptor 1. This electrostatic latent image is developed by a developer (toner) supplied from the developing device 4 and becomes a toner image as a visible image.
[0052]
On the other hand, while the toner image is being formed on the photoreceptor 1, transfer paper as a recording medium is fed toward the photoreceptor 1 from a paper supply unit (not shown). This transfer paper is sent to the transfer device 5 disposed opposite to the photoconductor 1 at the timing when it is superimposed on the toner image on the photoconductor 1, and the toner image on the photoconductor 1 is transferred at the transfer nip T1. Thereafter, the toner image is mechanically separated from the photoreceptor 1 and then conveyed to the fixing device 6 to fix the toner image.
[0053]
Residual toner remaining on the surface of the photoreceptor 1 after passing through the transfer nip T1 is removed from the photoreceptor 1 by the cleaning device 8 and collected. Then, the residual charge on the surface of the photoreceptor after the transfer residual toner is removed is removed by the static eliminator 9.
[0054]
Next, the discharge deterioration preventing means according to this embodiment will be described. In the image forming apparatus according to this embodiment, as shown in FIG. 8, a protective substance applying device 30 is provided as a protective substance supply unit for supplying the protective substance 32 to the surface of the photoreceptor. The protective substance coating device 30 is provided to face the photoconductor 1 on the downstream side in the rotation direction of the photoconductor 1 with respect to the cleaning device 7 and on the upstream side in the rotation direction of the photoconductor 1 with respect to the charging device 2. . The protective substance application device 30 includes a fur brush 31 as an application member, a protective substance 32, and a pressure spring 33 for pressing the protective substance in the fur brush direction. The protective material 32 is in a solid shape formed into a bar shape. The fur brush 31 has a brush tip in contact with the surface of the photoconductor. When the fur brush 31 rotates around the shaft, the protective material 32 is pumped up to one end of the brush, and is carried on the brush to a contact position with the surface of the photoconductor. Apply to body surface. The solid protective substance 32 molded on the bar is pressed against the fur brush 31 by a pressure spring 33 at a predetermined pressure. Thereby, even when the protective material 32 is scraped off by the fur brush 31 and decreases over time, a small amount of the protective material 32 can always be uniformly supplied to the fur brush 31.
[0055]
The method for applying the protective substance 32 using the protective substance applying apparatus 30 has been described above. However, any method may be used as long as the protective substance 32 can be present in an appropriate state on the surface of the photoreceptor 1. . For example, it is possible to adopt a method in which the protective substance 32 is transferred to the surface of the photosensitive member by internal addition or external addition to the toner. However, in that case, the presence of the protective substance 32 on the surface of the photosensitive member tends to be uneven depending on the image density and image pattern, and it is necessary to apply an excessive protective substance to compensate for this. The method of applying the protective material 32 on the surface of the photoconductor as in this embodiment distributes the protective material 32 stably on the surface of the photoconductor without changing depending on various conditions such as image density and image pattern. Is more preferable.
[0056]
Next, the charging device 2 used in this embodiment will be described in detail. In the charging device according to the present embodiment, the photosensitive member is charged by AC applied discharge by charging members that are arranged close to each other so as to be non-contact. There is a method in which the photosensitive member is charged by AC applied discharge by a charging member arranged in contact with and opposed to each other. When this method is applied, it is preferable to use an elastic member that improves the contact between the surface of the photoreceptor and the charging member and does not apply mechanical stress to the photoreceptor. However, when an elastic member is used, the charging nip width becomes wide, and the protective material may easily adhere to the charging roller side due to this. Therefore, it is more advantageous to charge the object to be charged without contact.
[0057]
FIG. 9 is a schematic explanatory diagram of the charging device 2 and the photoreceptor 1. The charging device 2 includes a charging roller 2a as a charging member, a spacer 22, a spring 15, and a power source 16. The charging roller 2a has a shaft portion 21a and a roller portion 21b as a charging portion. Of these, the roller portion 21b has a function of charging the surface of the photoconductor facing the photoconductor 1, and is configured to be rotatable by the rotation of the shaft portion 21a. A spacer 22 as a gap holding member is provided on the charging roller so that the charging portion 21b on the surface of the charging roller is opposed to the photosensitive belt surface with a small gap. By the spacer 22, a portion of the surface of the photoconductor 1 facing the image forming region 11 where an image is formed is disposed so as not to contact the photoconductor 1. The length of the roller portion 21b in the longitudinal direction is set to be longer than the image forming area of the photoreceptor 1, and the minute gap 14 is formed by bringing the spacer 22 into contact with the non-image forming area 12 of the photoreceptor 1. Forming. The charging roller 2 a is rotated along the surface of the photosensitive member 1 through the spacer 22. The minute gap 14 is configured such that the closest portion between the charging roller portion 21b and the photosensitive member 1 is 1 to 100 [μm]. The closest distance is more preferably 30 to 65 [μm]. In the apparatus of the first embodiment, it is arranged to be 50 [μm].
A spring 15 for pressing the charging roller 2a toward the member to be charged is attached to the shaft portion 21a. As a result, the minute gap 14 can be maintained with high accuracy.
[0058]
The charging roller 2a is connected to a power source 16 for charging, and uniformly charges the surface of the photosensitive member 1 by alternating current application discharge in a minute gap between the surface of the photosensitive member 1 and the surface of the charging roller 2a. In the present embodiment, an alternating voltage in which an AC voltage that is an AC component is superimposed on a DC voltage that is a DC component is applied to the charging unit of the charging roller 2a. By using the alternating voltage, the influence of variations in charging potential caused by minute gap fluctuations is suppressed, and uniform charging becomes possible.
[0059]
The charging roller 2a includes a cored bar as a conductive support having a cylindrical shape and a resistance adjusting layer formed on the outer peripheral surface of the cored bar. In the present embodiment, the charging roller 2a has a diameter of 10 [mm].
[0060]
For example, a known material such as a rubber member can be used for the surface of the charging roller 2a, but it is more preferable to use a resin material. This is because, when a rubber member is used, it is difficult to maintain a minute gap with respect to the photoreceptor 1 due to water absorption of the rubber and generation of deflection. Depending on the image forming conditions, only the central portion of the charging roller 2a may suddenly contact the surface of the photoreceptor. It is difficult to cope with such disturbance of the surface layer of the photoreceptor due to the local and sudden contact of the charging roller 2a with the photoreceptor 1. Therefore, when charging the photoconductor by the non-contact charging method, it is more preferable to use a hard material that can maintain a uniform gap between the charging roller and the photoconductor.
[0061]
<Charging roller surface layer> As a material having a hard surface of the charging roller 2a, for example, the following materials can be used. The resistance adjustment layer is formed from a thermoplastic resin composition (polyethylene, polypropylene, polymethyl methacrylate, polystyrene, or a copolymer thereof, etc.) in which a polymer type ion conductive agent is dispersed, and the surface of the resistance adjustment layer is formed with a curing agent. For example, a cured film. The cured film treatment can be performed, for example, by immersing the resistance adjusting layer in a treatment solution containing an isocyanate-containing compound. Alternatively, a cured film layer may be formed again on the surface of the resistance adjustment layer.
[0062]
The photosensitive member 1 used in this embodiment is a negatively charged organic photosensitive member, in which a photosensitive layer or the like is provided on a drum-shaped conductive support having a diameter of 30 [mm]. FIG. 10 is a cross-sectional view showing the photoreceptor used in this embodiment. An undercoat layer 51 which is an insulating layer is provided on the conductive support 50 as a base layer. Further, a charge generation layer (CGL) 52 and a charge transport layer (CTL) 53 as a photosensitive layer are provided thereon. Furthermore, a surface protective layer (FR) 54 is laminated thereon.
[0063]
<Conductive support 50> As the conductive support, volume resistance 10^TenThose having conductivity of Ω · cm or less can be used. For example, a metal such as aluminum, nickel, chromium, nichrome, copper, gold, silver, platinum, or a metal oxide such as tin oxide or indium oxide is coated on a film or cylindrical plastic or paper by vapor deposition or sputtering. Can be used, such as aluminum, aluminum alloy, nickel, stainless steel plates and the like, and pipes that have been surface treated by cutting, superfinishing, polishing, etc. . Further, endless nickel belts and endless stainless steel belts disclosed in JP-A-52-36016 can also be used as the conductive support.
[0064]
In addition, those obtained by dispersing and coating conductive powder in an appropriate binder resin on the support can also be used as the conductive support of the present invention. Examples of the conductive powder include carbon black, acetylene black, metal powder such as aluminum, nickel, iron, nichrome, copper, zinc and silver, or metal oxide powder such as conductive tin oxide and ITO. It is done. The binder resin used at the same time is polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer. , Polyvinyl acetate, polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinyl carbazole, acrylic resin, silicone resin, epoxy resin, Examples thereof include thermoplastic, thermosetting resins, and photocurable resins such as melamine resin, urethane resin, phenol resin, and alkyd resin. Such a conductive layer can be provided by dispersing and coating these conductive powder and binder resin in a suitable solvent such as tetrahydrofuran, dichloromethane, methyl ethyl ketone, and toluene.
Furthermore, it is electrically conductive by a heat-shrinkable tube in which the conductive powder is contained in a material such as polyvinyl chloride, polypropylene, polyester, polystyrene, polyvinylidene chloride, polyethylene, chlorinated rubber, Teflon (registered trademark) on a suitable cylindrical substrate. Those provided with a conductive layer can also be used favorably as the conductive support of the present invention.
[0065]
Next, the photosensitive layer will be described. The photosensitive layer may be a single layer or a multilayer, but for convenience of explanation, first, a case of a multilayer structure including a charge generation layer and a charge transport layer will be described.
[0066]
<Charge generation layer 52> The charge generation layer is a layer mainly composed of a charge generation material. Known charge generation materials can be used for the charge generation layer, and representative examples thereof include monoazo pigments, disazo pigments, trisazo pigments, perylene pigments, perinone pigments, quinacridone pigments, quinone condensed polycyclic compounds, Squalic acid dyes, other phthalocyanine pigments, naphthalocyanine pigments, azulenium salt dyes and the like can be mentioned, and these are useful. These charge generation materials can be used alone or in combination.
[0067]
In the charge generation layer, the charge generation material is dispersed in a suitable solvent together with a binder resin as necessary using a ball mill, attritor, sand mill, ultrasonic wave, etc., and this is dispersed on the conductive support or the undercoat layer. It is formed by coating on top and drying.
[0068]
In the charge generation layer, the charge generation material can be dispersed in the binder resin as necessary. Examples of binder resins that can be used include polyamide, polyurethane, epoxy resin, polyketone, polycarbonate, silicone resin, acrylic resin, polyvinyl butyral, polyvinyl formal, polyvinyl ketone, polystyrene, polysulfone, poly-N-vinylcarbazole, poly Examples include acrylamide, polyvinyl benzal, polyester, phenoxy resin, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, polyphenylene oxide, polyamide, polyvinyl pyridine, cellulose resin, casein, polyvinyl alcohol, and polyvinyl pyrrolidone. The amount of the binder resin is suitably 0 to 500 parts by weight, preferably 10 to 300 parts by weight with respect to 100 parts by weight of the charge generating material. The binder resin may be added before or after dispersion.
[0069]
Examples of the solvent used here include isopropanol, acetone, methyl ethyl ketone, cyclohexanone, tetrahydrofuran, dioxane, ethyl cellosolve, ethyl acetate, methyl acetate, dichloromethane, dichloroethane, monochlorobenzene, cyclohexane, toluene, xylene, ligroin and the like. In particular, ketone solvents, ester solvents, and ether solvents are preferably used. These may be used alone or in combination of two or more.
[0070]
The charge generation layer is mainly composed of a charge generation material, a solvent, and a binder resin, and may contain any additive such as a sensitizer, a dispersant, a surfactant, and silicone oil. good.
[0071]
As a coating method for the coating solution, a dip coating method, spray coating, beat coating, nozzle coating, spinner coating, ring coating, or the like can be used.
The film thickness of the charge generation layer is suitably about 0.01 to 5 [μm], preferably 0.1 to 2 [μm].
[0072]
<Charge transport layer 53> The charge transport layer can be formed by dissolving or dispersing a charge transport material and a binder resin in a suitable solvent, and applying and drying the solution on the charge generation layer. Further, if necessary, two or more kinds of plasticizers, leveling agents, antioxidants and the like can be added.
[0073]
Charge transport materials include hole transport materials and electron transport materials.
Examples of the electron transporting material include chloroanil, bromoanil, tetracyanoethylene, tetracyanoquinodimethane, 2,4,7-trinitro-9-fluorenone, 2,4,5,7-tetranitro-9-fluorenone, 2,4 , 5,7-tetranitroxanthone, 2,4,8-trinitrothioxanthone, 2,6,8-trinitro-4H-indeno [1,2-b] thiophen-4-one, 1,3,7-tri Examples thereof include electron-accepting substances such as nitrodibenzothiophene-5,5-dioxide and benzoquinone derivatives.
[0074]
Examples of the hole transport material include poly-N-vinylcarbazole and derivatives thereof, poly-γ-carbazolylethyl glutamate and derivatives thereof, pyrene-formaldehyde condensates and derivatives thereof, polyvinylpyrene, polyvinylphenanthrene, polysilane, oxazole derivatives, Oxadiazole derivatives, imidazole derivatives, monoarylamine derivatives, diarylamine derivatives, triarylamine derivatives, stilbene derivatives, α-phenylstilbene derivatives, benzidine derivatives, diarylmethane derivatives, triarylmethane derivatives, 9-styrylanthracene derivatives, pyrazolines Derivatives, divinylbenzene derivatives, hydrazone derivatives, indene derivatives, butadiene derivatives, pyrene derivatives, bisstilbene derivatives, enamine derivatives, etc. Other known materials may be used. These charge transport materials may be used alone or in combination of two or more.
[0075]
Examples of the binder resin include polystyrene, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyester, polyvinyl chloride, vinyl chloride-vinyl acetate copolymer, polyvinyl acetate, Polyvinylidene chloride, polyarylate resin, phenoxy resin, polycarbonate, cellulose acetate resin, ethyl cellulose resin, polyvinyl butyral, polyvinyl formal, polyvinyl toluene, poly-N-vinylcarbazole, acrylic resin, silicone resin, epoxy resin, melamine resin, urethane resin And thermoplastic or thermosetting resins such as phenol resins and alkyd resins.
[0076]
The amount of the charge transport material is appropriately 20 to 300 parts by weight, preferably 40 to 150 parts by weight, based on 100 parts by weight of the binder resin. The thickness of the charge transport layer is preferably 25 [μm] or less from the viewpoint of resolution and responsiveness. Regarding the lower limit, although it differs depending on the system to be used (particularly charging potential, etc.), 5 [μm] or more is preferable.
[0077]
As the solvent used here, tetrahydrofuran, dioxane, toluene, dichloromethane, monochlorobenzene, dichloroethane, cyclohexanone, methyl ethyl ketone, acetone and the like are used. These may be used alone or in combination of two or more.
[0078]
Next, the case where the photosensitive layer has a single layer structure will be described. The photosensitive layer is formed by dissolving or dispersing the above-described charge generation material, charge transport material, binder resin, etc. in an appropriate solvent, and applying and drying the solution on the conductive support 50 or the undercoat layer 51. it can. You may comprise from a charge generation material and binder resin, without containing a charge transport material. Moreover, a plasticizer, a leveling agent, antioxidant, etc. can also be added as needed.
[0079]
As the binder resin, in addition to the binder resin previously mentioned in the charge transport layer, the binder resin mentioned in the charge generation layer may be mixed and used. Of course, the polymer charge transport materials mentioned above can also be used favorably. The amount of the charge generating material with respect to 100 parts by weight of the binder resin is preferably 5 to 40 parts by weight, and the amount of the charge transporting material is preferably 0 to 190 parts by weight, and more preferably 50 to 150 parts by weight.
[0080]
The photosensitive layer is formed by dip coating, spray coating, bead coating, a coating solution in which a charge generating material and a binder resin are dispersed together with a charge transporting material using a solvent such as tetrahydrofuran, dioxane, dichloroethane, and cyclohexane. It can be formed by coating with a ring coat or the like. The film thickness of the photosensitive layer is suitably about 5 to 25 [μm].
[0081]
<Undercoat layer 51> In the photoreceptor according to this embodiment, an undercoat layer can be provided between the conductive support and the photosensitive layer. In general, the undercoat layer is mainly composed of a resin. However, considering that the photosensitive layer is coated with a solvent on these resins, the resin may be a resin having high solvent resistance with respect to a general organic solvent. desirable. Examples of such resins include water-soluble resins such as polyvinyl alcohol, casein, and sodium polyacrylate, alcohol-soluble resins such as copolymer nylon and methoxymethylated nylon, polyurethane, melamine resin, phenol resin, alkyd-melamine resin, and epoxy. Examples thereof include a curable resin that forms a three-dimensional network structure such as a resin. A metal oxide fine powder pigment exemplified by titanium oxide, silica, alumina, zirconium oxide, tin oxide, indium oxide and the like may be added to the undercoat layer in order to prevent moire and reduce residual potential. Further, these undercoat layers can be formed using an appropriate solvent and coating method as in the above-described photosensitive layer. Furthermore, a silane coupling agent, a titanium coupling agent, a chromium coupling agent, or the like can be used as the undercoat layer of the present invention. In addition, for the undercoat layer of the present invention, a vacuum thin film made of Al2O3 provided by anodic oxidation, organic substances such as polyparaxylylene (parylene), and inorganic substances such as SiO2, SnO2, TiO2, ITO, CeO2 is prepared. Those provided by law can also be used satisfactorily. In addition, known ones can be used. The thickness of the undercoat layer is suitably from 0 to 5 [μm].
[0082]
<Protective layer 54> A protective layer 54 may be provided on the outermost surface layer of the photoreceptor in order to prevent mechanical wear. For example, it is possible to use a photoreceptor whose surface is coated with amorphous silicon in order to improve wear resistance, or an organic photoreceptor provided with an outermost surface layer in which alumina, tin oxide or the like is further dispersed on the surface of the charge transport layer. it can.
[0083]
As described above, the configuration of the photoreceptor 1 that can be used in the present embodiment is not limited to a specific configuration. A single layer configuration in which only a photosensitive layer mainly composed of a charge generation material and a charge transport material is provided on a conductive support, or a charge generation layer and a charge mainly composed of a charge generation material on a conductive support. A structure in which a charge transport layer mainly composed of a transport material is laminated, or a photosensitive layer mainly composed of a charge generation material and a charge transport material is provided on a conductive support, and a protective layer is further provided thereon. A charge generation layer mainly composed of a charge generation material and a charge transport layer mainly composed of a charge transport material are laminated on a conductive support, and a protective layer is provided on the charge transport layer. A charge transport layer mainly composed of a charge transport material and a charge generation layer composed mainly of a charge generation material on a conductive support, and a protective layer is provided on the charge generation layer. The present invention can be applied to photoreceptors having various layer configurations such as those described above.
[0084]
Although it is difficult to measure the amount of a small amount of the protective substance 32 present on the surface of the photoreceptor, the present applicant relates to the protective substance necessary for the surface of the photoreceptor by measuring characteristic elements in the protective substance 32. We succeeded in obtaining knowledge. The measurement was performed using a Quantum 2000 scanning X-ray photoelectron spectrometer (XPS) manufactured by PHI under the conditions of an X-ray source AlKα and an analysis region 100 [μm] φ.
[0085]
As shown in FIG. 11A, when the protective material 32 is partially covered on the surface of the photosensitive member 1, the surface element to be measured is the protective layer 54 and the protective layer 54 constituting the photosensitive member. Elements constituting the charge transport layer 53 are detected. In this case, in the measurement region, the higher the surface element ratio derived from the protective substance 32, the higher the ratio of the protective substance 32 covering the photoreceptor surface. On the other hand, as shown in FIG. 11B, when the protective material 32 uniformly covers the surface of the photoreceptor and the protective material is applied thicker than the measurement region in the depth direction, the measurement is performed by XPS. All surface elements are derived from the protective substance 32. In addition, as shown in FIG. 11C, the protective material 32 uniformly covers the surface of the photoreceptor, but when the protective material is applied thinner than the measurement region in the depth direction, the measurement is performed by XPS. The surface element to be generated is derived from the protective material and other layers constituting the photoconductor.
[0086]
As an example, the results of measurement by XPS of two samples in which zinc stearate as the protective substance 32 is applied to the surface of the photoreceptor will be described. The measurement was performed in a circle having a diameter of 100 [μm] existing at a depth of 20 to 50 [Å] from the outermost surface of the photoreceptor. Here, the surface area of the photoreceptor measured by XPS is composed of at least carbon element (C), oxygen element (O), silicon element (Si), zinc element (Zn), and hydrogen element (H). Further, the elemental zinc (Zn) is configured not to be present in constituent materials other than zinc stearate. Note that the hydrogen element (H) is not detected by the XPS measurement.
[0087]
Table 2 shows the element number ratio [%] of each element detected by XPS to the total number of elements of all elements constituting the surface of the photoreceptor detected by XPS for the two samples. .
[Table 2]

As described above, since zinc element (Zn) exists only in zinc stearate, the element number ratio [%] of zinc stearate detected by XPS from the element number ratio [%] of this zinc element (Zn), And the element number ratio [%] detected by XPS of each element which comprises zinc stearate can be calculated | required. Zinc stearate has the molecular formula [CH₃(CH₂)₁₆COO]₂There are 36 carbon elements (C), 4 oxygen elements (O), and 70 hydrogen elements (H) with respect to one zinc element (Zn). Of these, hydrogen element (H) is not detected by XPS. Accordingly, the ratio of the number of elements detected by XPS of zinc stearate to the total number of elements of all elements detected by XPS of the substance constituting the surface of the photoreceptor is the ratio of the number of elements of zinc element (Zn) [%]. ] Is multiplied by 41 which is the sum of carbon, oxygen and zinc elements. In addition, the element number ratio [%] of each constituent element detected by XPS of zinc stearate to the total element number of all elements detected by XPS of the substance constituting the photoreceptor surface is the element number ratio [%] of zinc. ] Is multiplied by the number of each element present in one molecule. Table 3 shows the ratio of the number of elements of each element of the zinc stearate and other substances derived from the protective layer 54 and the charge transport layer 53 from the results of Table 2.
[Table 3]

In the measurement region, in sample 1, the ratio of the number of elements of zinc stearate detected by XPS is 8.6 [%]. In sample 2, the element number ratio of zinc stearate detected by XPS is 98.4 [%]. In sample 2, the photoreceptor surface is almost covered with zinc stearate. Even when a protective substance other than zinc stearate is used, knowledge about the amount of the protective substance can be obtained if a characteristic element that does not exist in the photoreceptor is contained in the protective substance.
[0088]
[Experimental Example 6]
Next, the film thickness reduction of the photosensitive member, which is noticeable in AC applied discharge, is proportional to (1) Vpp-2 × Vth, (2) proportional to the frequency f of the AC voltage, and (3) movement of the photosensitive member surface. An experimental result showing that it is inversely proportional to the speed v will be described.
The basic configuration and experimental conditions of the apparatus used in this experimental example are the same as those of the experimental example 4, but in this experimental example, Vpp, the frequency f of the AC voltage, the moving speed v of the photoreceptor surface, the protection. The presence or absence of deterioration of the photoreceptor surface was examined while changing the amount of substance supplied. Specifically, a voltage was applied to the charging member continuously for 100 hours, and the presence or absence of white turbidity or film thickness reduction on the surface of the photosensitive member with respect to the supply amount of the protective substance was examined. In addition, in order to know how much of the protective substance is actually supplied under each condition, a sample supplied with only the protective substance without applying voltage to the charging member is created separately from the film thickness reduction measurement Then, the abundance (ratio of the number of elements) of zinc element (Zn) on the surface of the photoreceptor was measured by XPS. The measured value (ratio of the number of elements) of zinc element (Zn) is the value when the surface of the photoconductor is measured after 5 hours have passed and zinc stearate has been applied without applying voltage to the charging member. is there.
[0089]
(Experimental conditions)
Charging conditions:
Vpp (peak-to-peak voltage value of AC voltage) = 2120, 3000 [V]
f (frequency of AC voltage) = 877.2, 1350 [Hz]
DC voltage value = −600 [V]
Moving speed of photoreceptor surface v = 125, 185 [mm / s]
Protective substance: Zinc stearate
[0090]
In the photoreceptor 1 used in this embodiment, the immediate lower layer of the protective material is a protective layer 54 for preventing mechanical wear, and the lower layer is a charge transport layer 53, but these layers do not contain zinc. Therefore, all the measured element number ratios of zinc element (Zn) are derived from zinc stearate which is a protective substance.
[0091]
  Table 4 shows the surface state of the photoconductor (whether there is white turbidity and the amount of decrease in film thickness) and XPS detected when the experiment was performed while changing the conditions of X, photoconductor speed v, Vpp, and AC voltage frequency f. The result of the element number ratio [%] of zinc element (Zn) is shown. Where X is a number11It is.
  <Number11> X = {Vpp-2 × Vth} × f / v
[0092]
  FIG. 12 is a graph showing the results of the experimental results shown in Table 4 with respect to the zinc element detected by XPS with respect to the total number of elements of all the elements constituting the outermost surface of the photoreceptor detected by XPS in the discharge region. The element number ratio [%] is plotted. From this figure, the ratio of the number of elements of zinc element (Zn) necessary for preventing deterioration (white turbidity) of the photosensitive surface due to discharge is as follows.12It turns out that it is necessary to exist above. Furthermore, the element number ratio of zinc element (Zn) necessary to prevent film thickness abrasion on the photosensitive surface due to discharge is the following number:13It turns out that it is necessary to exist above.
  <Number12> 1.52 × 10^-Four* {Vpp-2 * Vth} * f / v
  <Number13> 2.22 × 10^-Four* {Vpp-2 * Vth} * f / v
[0093]
  Based on the content ratio of zinc element thus obtained, the amount of zinc stearate detected by XPS necessary for preventing deterioration of the photoreceptor surface is calculated as follows. That is, the ratio of the number of elements of zinc stearate detected by XPS [%] to the total number of elements of all the elements constituting the outermost surface of the photoreceptor detected by XPS is a number.14If it is set as above, deterioration (white turbidity) of the photoreceptor can be prevented. Further, based on the content ratio of the zinc element, the element number ratio [%] of zinc stearate detected by XPS to the total number of elements of all elements constituting the outermost surface of the photoreceptor detected by XPS15If it is above, film thickness scraping hardly occurs.
  <Number14> 6.23 × 10^{- 3}* {Vpp-2 * Vth} * f / v
  <Number15> 9.10 × 10^{- 3}* {Vpp-2 * Vth} * f / v
[0094]
The reason why the chemical deterioration of the surface of the photoreceptor, which becomes noticeable in the AC applied discharge, varies depending on the coating amount of zinc stearate, is considered as follows. In the discharge region on the surface of the photoconductor, the energy of particles (electrons, excited molecules, ions, plasma, etc.) generated by the discharge is applied to the photoconductor surface layer. This energy resonates and is absorbed by the binding energy of the molecules that make up the surface of the photoreceptor, and the charge transport layer undergoes chemical degradation such as molecular weight reduction due to resin molecular chain scission and polymer chain entanglement, resulting in film thickness reduction. It is thought that it will decrease.
On the other hand, if a protective substance is present on the surface of the photoreceptor, it is the protective substance that is directly irradiated with the energy of the particles generated by the discharge, so that the photoreceptor itself is free from direct irradiation of the particles generated by the discharge. Therefore, it is considered that the protective substance itself absorbs the energy of the particles generated by the discharge and alleviates chemical deterioration of the surface of the photoreceptor. In the experiment shown in FIG. 3 as well, the surface of the photosensitive member B in the region B where no protective substance is present on the photosensitive member 1 is detected from the analysis of molecular debris constituting the photosensitive member, whereas the region A where the protective material is present. However, molecular debris constituting the photoconductor was not detected, and the photoconductor surface under the protective material was not deteriorated. In region A, zinc stearate supplied as a protective substance was chemically changed, and a decomposed substance was detected.
[0095]
According to such examination, various substances can be used as the protective substance 32. Zinc stearate used in the image forming apparatus according to the present embodiment is an example of the protective substance 32, and other substances such as various fatty acid salts, waxes, and silicone oil can be used as the protective substance 32.
Among the fatty acid salts, the fatty acid metal salt is easily a characteristic element in which the metal element is measured by XPS, and is easy to measure when setting conditions such as the coating amount. Therefore, it is suitable for designing an apparatus for supplying an optimal amount of a protective substance to the surface of the photosensitive member according to the charging conditions as in this embodiment.
[0096]
Examples of fatty acids include undecyl acid, lauric acid, tridecyl acid, myristic acid, palmitic acid, pendadecyl acid, stearic acid, heptadecyl acid, arachidic acid, montanic acid, oleic acid, arachidonic acid, caprylic acid, capric acid, caproic acid, etc. Examples of the metal salt include salts with metals such as zinc, iron, copper, magnesium, aluminum, and calcium.
[0097]
It is preferable to use a lamellar crystal powder such as zinc stearate as the protective substance. A lamellar crystal has a layered structure in which amphipathic molecules are self-organized, and when a shearing force is applied, the crystal breaks along the layers and is slippery. This action is effective for lowering the coefficient of friction, but when viewed from the viewpoint of protecting the photoreceptor surface from electric discharge, the characteristics of lamellar crystals that uniformly cover the photoreceptor surface under shearing force are as follows: Since the surface of the photoreceptor can be effectively covered with a small amount of protective material, it is desirable as a protective material.
[0098]
In order to fully protect the surface of the photoreceptor from electric discharge by fully utilizing the properties of the lamellar crystals, the protective material is applied while the rotational speed of the protective material coating device 30 is different from the rotational speed of the surface of the photoreceptor, and the shearing force is applied. It is desirable to apply.
In addition, when the object is to protect the surface of the photoreceptor from deterioration due to discharge as in the present invention, it is desirable to provide the protective substance coating device 30 between the cleaning device and the charging device. This is to prevent the protective material from being removed by the cleaning device before reaching the discharge region.
[0099]
For example, when the protective material applied on the photoreceptor is zinc stearate, viscosity is generated due to deterioration due to discharge. Even when other various protective substances are used, it is generally considered desirable to quickly remove the deteriorated protective substance from the photoreceptor. From such a viewpoint, it is desirable to provide a removing member for removing the deteriorated protective substance 32 from the surface of the photoreceptor. In addition, the deteriorated protective member may be mixed in the developing device in the developing region. Since mixing of such protective substances may cause fluctuations in the toner charge amount, it is desirable to use a two-component magnetic brush development that is resistant to fluctuations.
[0100]
Hereinafter, specific means according to the present embodiment capable of preventing chemical deterioration of the surface of the photoreceptor 1 will be described. FIG. 13 is a block diagram showing an electrical component for preventing chemical deterioration of the surface of the photoreceptor 1. In the figure, a controller (main control unit) 110 includes a CPU, a RAM, and a ROM, and performs control for preventing chemical deterioration of the surface of the photoreceptor. The ROM stores a program to be described later. The CPU executes this program while appropriately using the RAM. The controller 110 includes a first table 101 that associates the rotational speed of the fur brush 31 with the amount of the protective substance 32 supplied to the surface of the photosensitive member 1, and the surroundings of the charging roller 2 a detected by the temperature / humidity detector 100. The second table 102 in which the environment and the charging condition are associated with each other, the application control unit 103 that controls the rotation speed of the fur brush 31, the charging control unit 104 that controls the charging condition, and the necessary one depending on the charging condition And an arithmetic unit 105 that calculates the amount of the protective member. The controller 110 is electrically connected to the temperature / humidity detector 100, the charging device 2, the protective substance coating device 30, and the like. The first table 101 and the second table 102 may be configured in a ROM. The calculation unit 105 may be configured to be realized by recording a program of the calculation procedure in a ROM and executing the program by the CPU.
[0101]
The first table 101 is Zn obtained as a result of the measurement by XPS in order to apply zinc stearate to be applied on the surface of the photoreceptor, which is necessary to prevent chemical deterioration of the surface of the photoreceptor 1. The element ratio and the rotation speed of the fur brush correspond to each other. The second table 102 shows the temperature / humidity value and the Vpp value necessary for the discharge so that the discharge due to the AC voltage can be surely generated even when the discharge start voltage changes due to the environment around the charging roller. It has data corresponding to. The calculation unit 105 is set so as to be able to calculate the zinc element number ratio [%] required according to the above formula 11 or formula 12 in order to calculate the amount of the protective member required according to the charging conditions.
[0102]
FIG. 14 is a flowchart regarding a procedure for determining the rotation speed of the brush and the charging condition. The controller 110 detects the temperature and humidity (environmental conditions) around the charging device with a temperature / humidity detector prior to starting charging in response to the input of the image formation start command (step 1). Next, the charging condition (Vpp value) stored in advance in the second table 102 is selected based on the detection result of step 1 and set as the charging condition (step 2). Then, in accordance with the charging condition set in step 2, since the surface of the photoconductor 1 is not deteriorated, the element number ratio [%] of zinc stearate applied is calculated by the calculation unit 105 (step 3). . The rotation speed of the fur brush is selected from the first table 101 and set as the rotation speed so that a desired protective substance is applied to the surface of the photoreceptor from the ratio of the number of elements of zinc calculated in step 3 [%]. (Step 4). Next, the fur brush is rotationally driven in the application control unit 103 so as to achieve the rotational speed set in step 4 (step 5). Finally, charging is started while controlling the voltage applied to the charging member in the charging control unit. A program for executing the above procedure is recorded in the ROM as described above.
[0103]
By providing such a control means, even when the charging condition is changed according to the environment, it is possible to supply the optimum protective substance to the surface of the photoconductor to prevent deterioration of the photoconductor.
[0104]
When calculating the necessary element ratio of zinc stearate according to the above formula 10, it is necessary to calculate Vth taking into account that the film thickness of the photoreceptor is reduced. Therefore, the controller further has storage means for storing the accumulated discharge time and a third table for deriving the film thickness of the photoreceptor from the accumulated discharge time, and the photoreceptor film corresponding to the accumulated discharge time by the third table. The thickness is derived and Vth is calculated.
[0105]
In the image forming apparatus according to the present embodiment, the photosensitive member 1, the charging device 2, and the protective substance applying device 30 are integrally configured as shown by a dotted line in FIG. The process cartridge 200 is configured. Since the process cartridge 200 is replaced integrally, it is easy to set the amount of the protective substance contained in the coating device 30 and the initial film thickness of the photosensitive member to an appropriate amount, which is suitable for the present invention. ing.
[0106]
[Embodiment 2]
Next, another embodiment 2 of the image forming apparatus of the above embodiment will be described. The basic configuration and operation of the image forming apparatus according to the second embodiment are the same as those of the first embodiment, but the configuration of the cleaning device is different from that of the first embodiment. That is, in the image forming apparatus of the first embodiment, the dedicated cleaning device 7 is provided. However, in the image forming apparatus of the second embodiment, the cleaning device 7 is removed, and the transfer residual toner is developed using the developing device 4. A collection method is adopted. In this developing device collection method, since the developing device 4 installed for a purpose other than cleaning is used as a cleaning means, there is no need to provide a separate cleaning device as described above, greatly reducing the size of the device. Can contribute. The charging roller 2a is made of a rubber material and is configured to come into contact with the surface of the photoreceptor 1 (contact charging method (Gp = 0 [μm])).
[0107]
  The transfer residual toner is transported again to the developing device provided opposite to the photoreceptor 1 and collected there. In such a configuration, the transfer residual toner exists also in a region where the protective material is applied to the surface of the photosensitive member by the protective material coating device 30. A protective substance cannot be applied to a portion where the transfer residual toner exists. For this reason, on the surface of the photoreceptor after the protective substance is applied by the protective substance applying device 30, a portion where the transfer residual toner is adhered and a portion where the protective substance is applied are mixed.
  However, in order to protect the photoreceptor surface deterioration that becomes remarkable in the AC applied discharge, it is sufficient that some substance is present on the photoreceptor surface. Therefore, even when toner is present on the surface of the photoreceptor instead of the protective material 32, chemical deterioration of the surface of the photoreceptor can be prevented. That is, the element number ratio [%] of zinc is set to the above number without considering the influence of the transfer residual toner.12With the above, it is possible to prevent white turbidity on the surface of the photoreceptor 1, and the ratio of the number of zinc elements [%] to the above.Equation 13If it is set as above, the film thickness abrasion of a photoreceptor can be prevented.
[0108]
By the way, in the image forming apparatus adopting such a developing device collecting system, the transfer residual toner is transferred to the protective substance coating device 30 and the contact-type charging roller 2a while the transfer residual toner on the photosensitive member is conveyed to the development region. Will be in contact with. Therefore, transfer residual toner may adhere to the protective substance coating device 30 and the charging roller 2a. In such a case, an area where neither toner nor protective substance 32 exists on the surface of the photoreceptor 1 is formed. By increasing the number of such regions, chemical deterioration of the photoreceptor surface (such as the protective layer 54 and the charge transport layer 53) due to discharge occurs. Therefore, in this embodiment, a negative voltage is applied to the protective substance coating apparatus 30. For example, a voltage of about −1000 [V] is applied to the protective substance coating apparatus 30. As a result, the toner on the photoreceptor 1 is strongly negatively charged, and the adhesion (mirror force) to the photoreceptor 1 is increased. As a result, the toner is prevented from moving to the protective substance coating device 30 and the charging roller 2a, and it becomes easy to protect the surface of the photoreceptor 1 from discharge.
[0109]
In the image forming apparatus according to the present embodiment, there is no need to provide a cleaning device that performs cleaning by bringing the edge portion of a cleaning blade that is generally used conventionally into contact with the surface of the photoreceptor. By eliminating the cleaning blade, the load applied to the surface of the photoconductor can be reduced, and the drive load applied to the drive system of the photoconductor can be reduced.
Of the transfer residual toner remaining on the surface of the photoconductor after the transfer, the reversely charged toner having the opposite polarity to the normal charged toner charged to the same polarity as the charging bias is moved to the protective material applying device 30 on the surface of the photoconductor. It may be configured to be recovered from the surface of the photoreceptor and held by a primary holding means such as a brush member on the upstream side in the direction. By collecting and holding the reversely charged toner in this way, it is possible to prevent the reversely charged toner from adhering to the charging member. Then, the held reversely charged toner is returned to the surface of the photosensitive member at a predetermined timing such as after the completion of one image formation until the next image formation. The reversely charged toner returned onto the photosensitive member in this manner is collected by the developing device, or transferred to a transfer target or a transport member for transporting the transfer target. While the returned reversely charged toner passes through the charging region, the application of the charging bias is stopped or the charging roller 2a is separated from the photosensitive member so that the reversely charged toner does not adhere to the charging roller 2a or the like. It is configured. Since the rubbing force of the brush member rubbing against the surface of the photoconductor can be made smaller than that of the cleaning blade, the life of the photoconductor can be extended even if the brush member is used.
[0110]
Note that the present invention is not applied only to the image forming apparatus as shown in FIG. 1, and is generally used to charge the surface of an object to be charged by using an AC applied discharge by a charging member arranged in contact with or close to the surface. It can be used.
[0111]
  As described above, according to the first and second embodiments, in the method in which the charging member is disposed in contact with or close to the surface, the chemical degradation of the surface of the photoreceptor, which becomes remarkable in the AC applied discharge, is desired depending on the charging condition. The following effects can be acquired by making it exist.
  The element number ratio [%] of zinc stearate (Zn) detected by XPS to the total number of elements of all the elements constituting the outermost surface of the photoconductor detected by XPS is the above number.12By doing so, it is possible to prevent alteration (white turbidity) of the surface of the photoreceptor, which becomes remarkable in AC applied discharge.
  In addition, the number ratio [%] of the zinc element (Zn) of zinc stearate detected by XPS to the total number of elements of all the elements constituting the outermost surface of the photoreceptor detected by XPS is the above number.13By setting it as the above, the film thickness abrasion of the surface of a photoreceptor which becomes remarkable by alternating current application discharge can be prevented.
  Further, the ratio of the number of elements constituting zinc stearate as a protective substance detected by XPS to the total number of elements of all elements constituting the outermost surface of the photoreceptor detected by XPS [%]14By doing so, it is possible to prevent alteration (white turbidity) of the surface of the photoreceptor, which becomes noticeable in AC applied discharge.
  Further, the ratio of the number of elements constituting zinc stearate as a protective substance detected by XPS to the total number of elements of all elements constituting the outermost surface of the photoreceptor detected by XPS [%]15By doing so, it is possible to prevent film thickness shaving on the surface of the photoreceptor, which becomes noticeable in AC applied discharge.
  In addition, lamellar crystal powder is used as a protective substance. As a result, the protective substance is cleaved between the layers by receiving a shearing force and spreads on the surface of the photoreceptor, so that it can be applied more uniformly.
  The image forming apparatus according to the first embodiment employs a method in which the charging roller and the photosensitive member are charged in a non-contact manner. Thereby, adhesion of the protective substance to the charging roller can be prevented, and the abundance of the protective substance on the photoreceptor can be stabilized.
  In the image forming apparatus according to the first embodiment, the surface layer of the charging roller is made of a resin material. Thereby, deformation of the charging member can be suppressed, and the amount of the protective substance present can be suppressed from being disturbed locally and suddenly.
  In addition, the image forming apparatus according to the first and second embodiments includes a coating device for coating the surface of the photosensitive member with a protective substance, and both the contact portion between the photosensitive member 1 and the brush roller portion 31 of the coating device 30. The rotation speed is set to be different. As a result, the lamellar crystal powder as the protective substance is more easily spread by cleavage, so that the protective substance can be more efficiently applied to the surface of the photoreceptor.
  In the first and second embodiments, an environment detection unit that detects an environmental state around the charging member, and a protective substance supply amount that controls the amount of the protective substance present on the photoconductor based on the detection result of the environment detection unit. And a control unit. As a result, even if the temperature and humidity fluctuate, it is possible to supply an optimal amount of the protective material to the photoconductor, and to prevent chemical deterioration of the photoconductor.
  In the second embodiment, a cleaning blade is not provided and a transfer residual toner is collected using a developing device. Further, a charging member is provided for charging the image forming substance remaining on the downstream side in the moving direction of the photosensitive member 1 with respect to the developing device 4 and on the upstream side in the moving direction of the surface of the photosensitive member 1 with respect to the charging device 2. And the element number ratio [%] of the zinc element contained in the zinc stearate is the above number.12Or number13Zinc stearate is applied to the surface of the photoreceptor so as to conform to the above. With this configuration, it is possible to fix the transfer residual toner on the photoconductor with a mirror image force, and the presence of the toner and zinc stearate can prevent chemical deterioration of the photoconductor surface due to electric discharge.
  In the first and second embodiments, the process cartridge including the charging device 2, the photoreceptor 1, and the charging device 30 is configured to be detachable from the image forming apparatus. Since such process cartridges are replaced together, it is easy to set the amount of the protective substance contained in the coating device 30 and the initial film thickness of the photosensitive member to an appropriate amount.
[0112]
【The invention's effect】
According to the present invention, there is an excellent effect that chemical deterioration of the surface of the photoconductor can be prevented when the photoconductor is charged using AC applied discharge by a charging member arranged in contact or close to the photoconductor. .
[Brief description of the drawings]
FIG. 1A is a cross-sectional view of a photoreceptor.
(B) is an explanatory view showing the state of the surface of the photoreceptor when the surface of the photoreceptor is deteriorated by discharge.
FIG. 2 is a diagram showing experimental results related to occurrence of defects in the prior art.
FIG. 3A is a schematic configuration diagram of an experimental apparatus for confirming the effect of the present invention.
(B) is explanatory drawing of the state which divided the photoreceptor surface into the protective layer formation part and the non-formation part.
FIG. 4 is a graph in which the amount of film thickness shaving on the surface of a photoreceptor is plotted against charging time.
FIG. 5 is a graph plotting the photoreceptor surface friction coefficient with respect to time when zinc stearate is applied in two application amounts.
FIG. 6 is a graph in which the amount of film thickness shaving on the surface of the photoreceptor is plotted against Vpp.
FIG. 7 is a graph in which the amount of film thickness shaving on the surface of the photoreceptor is plotted against the frequency f of the AC voltage.
FIG. 8 is an explanatory diagram of a main part of the image forming apparatus according to the first embodiment.
FIG. 9 is a schematic configuration diagram of a charging device used in the image forming apparatus according to the first embodiment.
FIG. 10 is a cross-sectional view of a photoconductor according to the first exemplary embodiment.
FIG. 11A is an explanatory view showing that a protective substance is partially applied.
(B) is explanatory drawing which shows that the protective substance is apply | coated uniformly and 20-50 [Å] or more is applied from the outermost surface layer.
(C) is explanatory drawing which shows that the protective substance is apply | coated uniformly and 20-50 [Å] or less is applied from the outermost surface layer.
12 is a graph plotting the number ratio of Zn elements with respect to X according to Experimental Example 6. FIG.
FIG. 13 is a control diagram for optimally applying the protective substance according to the first embodiment.
FIG. 14 is a flowchart regarding a procedure for starting charging according to the first embodiment;
[Explanation of symbols]
1 Photoconductor
2 Charging device
2a Charging roller
4 Development device
30 Protective substance applicator
31 Fur Brush
32 Protective substances
100 Temperature / humidity detector
103 Application control unit
104 Charging controller
200 process cartridge

Claims (11)

Movable object to be charged;
An image forming apparatus comprising: a charging member disposed in contact with or in proximity to the member to be charged; and a charging device that charges the member to be charged by applying a voltage containing an AC component to the charging member.
Zinc stearate as a protective substance for preventing deterioration of the surface of the member to be charged due to the charging is present on the member to be charged;
An environment detection means for detecting an environmental condition around the charging member; a charge control section for controlling a voltage applied to the charging member based on a detection result by the environment detection means;
A protective substance supply amount control unit that controls the amount of zinc stearate to be present in the member to be charged based on a voltage value applied to the charging member;
In the region where the object to be charged is charged by the charging member, the XPS detects the total number of all elements of the substance constituting the surface of the object to be charged, which is detected by an X-ray photoelectron spectrometer (XPS). The image forming apparatus characterized in that the number ratio [%] of the specific element of the zinc stearate is set to the following number 1 or more.
<Equation 1> 1.52 × 10 −4 × {Vpp−2 × Vth} × f / v × Nα
(Where Vpp is the peak-to-peak voltage value [unit: V] of the AC voltage, f is the frequency of the AC component applied to the charging member [unit: Hz], and v is the moving speed of the surface of the member to be charged [unit: mm] / Sec], Nα is the number of elements in one molecule of a specific element among elements constituting zinc stearate.
Vth is a discharge start voltage, and is obtained by the following equation (2).
<Equation 2> Vth = 312 + 6.2 × (d / εopc + Gp / εair) + √ (7737.6 × d / εopc)
In this case, d is the film thickness [unit: μm] of the member to be charged, εopc is the relative dielectric constant of the member to be charged, εair is the relative dielectric constant in the space between the member to be charged and the charging member, and Gp is the surface of the charging member. The closest distance to the surface of the member to be charged [unit: μm]. ) Movable object to be charged;
An image forming apparatus comprising: a charging member disposed in contact with or in proximity to the member to be charged; and a charging device that charges the member to be charged by applying a voltage containing an AC component to the charging member.
Zinc stearate as a protective substance for preventing deterioration of the surface of the member to be charged due to the charging is present on the member to be charged;
After the start of image formation, in the region where the charged body is charged by the charging member, the total number of elements of all the elements constituting the charged body outermost surface detected by the X-ray photoelectron spectrometer (XPS) is detected. The number ratio [%] of the specific element of the zinc stearate detected by the XPS is calculated based on the following number 3;
An image forming apparatus comprising: a protective substance supply amount control unit that controls the amount of zinc stearate to be present in the member to be charged to several 3 or more based on a calculation result.
<Equation 3> 1.52 × 10 −4 × {Vpp−2 × Vth} × f / v × Nα
(Where Vpp is the peak-to-peak voltage value [unit: V] of the AC voltage, f is the frequency of the AC component applied to the charging member [unit: Hz], and v is the moving speed of the surface of the member to be charged [unit: mm] / Sec], Nα is the number of elements in one molecule of a specific element among elements constituting zinc stearate.
Vth is a discharge start voltage, and is obtained by the following equation (4).
<Equation 4> Vth = 312 + 6.2 × (d / εopc + Gp / εair) + √ (7737.6 × d / εopc)
In this case, d is the film thickness [unit: μm] of the member to be charged, εopc is the relative dielectric constant of the member to be charged, εair is the relative dielectric constant in the space between the member to be charged and the charging member, and Gp is the surface of the charging member. The closest distance to the surface of the member to be charged [unit: μm]. ) The image forming apparatus according to claim 1 or 2,
An image forming apparatus, wherein the number ratio [%] of the specific element is set to the following number 5 or more.
<Equation 5> 2.22 × 10 −4 × {Vpp−2 × Vth} × f / v × Nα The image forming apparatus according to claim 1 or 2,
The ratio of the number of elements constituting the zinc stearate detected by XPS to the sum of the number of all elements of the substance constituting the outermost surface of the object to be detected detected by XPS is expressed by the following equation 6 An image forming apparatus characterized by the above.
<Equation 6> 1.52 × 10 −4 × {Vpp−2 × Vth} × f / v × Nβ
(Nβ: a value obtained by subtracting the number of hydrogen elements from the total number of elements constituting one molecule of zinc stearate.) The image forming apparatus according to claim 3.
The ratio of the number of elements constituting the zinc stearate detected by XPS to the total number of elements of the elements constituting the outermost surface of the material to be charged detected by XPS [%] An image forming apparatus characterized by the above.
<Equation 7> 2.22 × 10 −4 × {Vpp−2 × Vth} × f / v × Nβ The image forming apparatus according to claim 1, 2 or 3.
An image forming apparatus, wherein the specific element is zinc and the Nα is 1. The image forming apparatus according to claim 4 or 5,
The image forming apparatus according to claim 1, wherein Nβ is 41. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6 or 7.
An image forming apparatus, wherein a closest distance between the charging member and the member to be charged is 1 to 100 [μm]. The image forming apparatus according to claim 8.
An image forming apparatus, wherein a surface layer of the charging member is made of a resin material. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, or 9.
A protective substance supply member for applying the protective substance on the surface of the object to be charged is provided, the surface of the protective substance supply member and the surface of the object to be charged are brought into contact with each other, and the surface of the protective substance supply member at the contact portion An image forming apparatus, wherein the moving speed with respect to the surface of a charged body is set differently. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10.
A developing device for developing an electrostatic latent image on the image carrier, comprising: a charging member disposed in contact with or close to the image carrier; and means for removing an image forming substance remaining on the surface of the image carrier. And an image forming substance remaining on the surface of the image carrier on the downstream side in the movement direction of the surface of the image carrier with respect to the developing device and upstream in the movement direction of the surface of the image carrier with respect to the charging member. An image forming apparatus comprising: charging means for charging .

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