JP2004325686A - Electrophotographic photoreceptor and image forming apparatus equipped with the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrophotographic photoreceptor having excellent cleaning property and durability and capable of forming a high-quality image even for long-term use by specifying the ranges of hardness and surface free energy of the photosensitive layer. <P>SOLUTION: In the photoreceptor 1 comprising a conductive support body 3 and a photosensitive layer 7 formed on the conductive support body 3, the photosensitive layer 7 is specified to have ≥20 Vickers hardness (HV) and 28 to 35 mN/m of surface free energy (γ). The obtained photoreceptor has excellent wear resistance, a long life for use and excellent cleaning performance because foreign substances hardly deposit on the surface of the photoreceptor or foreign substances are easily made to leave from the surface. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

ここで、γ_１：物質１の表面自由エネルギー
γ_２：物質２の表面自由エネルギー
γ_１ ^ｄ，γ_２ ^ｄ：物質１，物質２の双極子成分
γ_１ ^ｐ，γ_２ ^ｐ：物質１，物質２の分散成分
γ_１ ^ｈ，γ_２ ^ｈ：物質１，物質２の水素結合成分
【００１７】
被測定対象の固体物質における前述の式（２）に示す各成分の表面自由エネルギー（γ^ｄ，γ^ｐ，γ^ｈ）は、各成分の表面自由エネルギーが既知である試薬を使用し、その試薬との付着性を測定することによって算出できる。したがって、物質１および物質２のそれぞれについて、各成分の表面自由エネルギーを求め、さらに各成分の表面自由エネルギーから式（３）によって物質１と物質２との界面自由エネルギーを求めることができる。
【００１８】
このようにして求められる固体と固体との間の界面自由エネルギーの考え方に基づいて、光導電層がアモルファスＳｉ系で構成される電子写真感光体の表面自由エネルギー（γ）を３５〜６５ｍＮ／ｍまたは３５〜５５ｍＮ／ｍに規定することによって、電子写真感光体のクリーニング性と耐久性とを改善することが、従来技術として開示されている（たとえば、特許文献４，５参照）。
【００１９】
また光導電層が有機感光材料で構成される電子写真感光体についても、表面自由エネルギーを３５乃至６５ｍＮ／ｍの範囲に規定することによって、電子写真感光体表面のクリーニング性を向上し、長寿命化の実現されることが、従来技術として開示されている（特許文献６参照）。
【００２０】
しかしながら、本発明者らの調査によれば、従来技術に開示される範囲である３５〜６５ｍＮ／ｍの表面自由エネルギー（γ）を有する電子写真感光体を用いて、たとえば記録紙に対して実際に画像形成する実写性能試験を行ったところ、電子写真感光体表面において、紙粉などの異物との接触によると思われる傷の発生が確認された。またその傷に起因するクリーニング不良によって、記録紙に転写した画像上に黒すじが発生することを確認した。
【００２１】
さらに、特許文献６に開示される従来技術においては、電子写真感光体の耐久にともなう表面自由エネルギーの変化量（Δγ）を規定しているけれども、電子写真感光体の初期特性たとえば表面自由エネルギー（γ）を規定することによっては変化量Δγを定められないこと、また画像形成する際の環境や転写材の材質などの諸条件に依存して変動量Δγが変化することを考慮すると、実際の電子写真感光体の設計において、変動量Δγは不確定な要素を多分に含み設計基準として適さないという問題がある。
【００２２】
【特許文献１】
特開２００１−２４９４７４号公報
【特許文献２】
特開平４−９０６６号公報
【特許文献３】
特開昭６０−２２１３１号公報
【非特許文献１】
北崎寧昭、畑敏雄外；「Ｆｏｒｋｅｓ式の拡張と高分子固体の表面張力の評価」、日本接着協会誌、日本接着協会、１９７２年、Ｖｏｌ．８、Ｎｏ．３、ｐ．１３１−１４１
【特許文献４】
特開２００２−１３１９５７号公報
【特許文献５】
特開２００２−２２９２３４号公報
【特許文献６】
特開平１１−３１１８７５号公報
【００２３】
【発明が解決しようとする課題】
本発明の目的は、感光層の硬さおよび表面自由エネルギーの範囲を規定することによって、クリーニング性および耐久性に優れ、長時間の使用に際しても高品質な画像を形成することのできる電子写真感光体およびそれを備える画像形成装置を提供することである。
【００２４】
【課題を解決するための手段】
本発明は、導電性支持体と導電性支持体上に設けられる感光層とを備える電子写真感光体において、
前記感光層の硬さが、ビッカース硬さで２０以上であり、かつ前記感光層の表面の表面自由エネルギー（γ）が、２８ｍＮ／ｍ以上、３５ｍＮ／ｍ以下であることを特徴とする電子写真感光体である。
【００２５】
本発明に従えば、電子写真感光体は、感光層の硬さがビッカース硬さで２０以上であり、感光層表面の表面自由エネルギーが、２８ｍＮ／ｍ以上、３５ｍＮ／ｍ以下になるように設定される。ここで言うビッカース硬さは、日本工業規格（ＪＩＳ）Ｚ２２４４に規定されるものである。電子写真感光体における感光層の硬さを、ビッカース硬さで２０以上の範囲に設定することによって、電子写真感光体の感光層は充分な機械的強度を有するようになるので、クリーニング工程における機械的磨耗に対して充分な耐久寿命を発現させることができる。
【００２６】
さらに、ここで言う電子写真感光体の感光層の表面自由エネルギーは、前述したＦｏｒｋｅｓの拡張理論により算出導き出したものである。電子写真感光体の感光層の表面自由エネルギーは、電子写真感光体の表面に対するたとえばトナーや紙粉などの濡れ性すなわち付着力の指標である。表面自由エネルギーを前記好適な範囲に設定することによって、特にトナーに対しては現像に必要な程度の付着力を発現するにも関らず過度の付着力を抑制し、また紙粉等の異物に対する付着力を抑制することができるので、電子写真感光体表面から過剰のトナーや異物が除去され易くなる。このようにして、現像性能を低下させることなく、クリーニング性能を向上させることが可能になる。
【００２７】
したがって、表面は充分な硬さを有して耐磨耗性に優れ、かつ表面に異物が付着しにくくまた表面から異物を離脱させ易いクリーニング性能に優れる電子写真感光体が実現される。このような電子写真感光体は、耐久寿命が長く、長期間安定して形成画像に品質低下を生じさせることがない。
【００２８】
また本発明は、前記電子写真感光体の感光層は、電荷発生物質を含む電荷発生層と、電荷輸送物質を含む電荷輸送層とが積層されて構成されることを特徴とする。
【００２９】
本発明に従えば、電子写真感光体の感光層は、電荷発生物質を含む電荷発生層と、電荷輸送物質を含む電荷輸送層とが積層されて構成される。このように感光層を複数層が積層されるタイプにすることによって、各層を構成する材料およびその組合せの自由度が増すので、電子写真感光体表面の表面自由エネルギー値を所望の範囲に設定することが容易になる。
【００３０】
また本発明は、前記いずれかの電子写真感光体を備えることを特徴とする画像形成装置である。
【００３１】
本発明に従えば、画像形成装置には、クリーニング性能および耐磨耗性に優れ、耐久寿命の長い電子写真感光体が備えられる。したがって、長期間に亘り安定して画質低下のない画像形成が可能であり、かつメンテナンス頻度の少ない画像形成装置が提供される。
【００３２】
【発明の実施の形態】
図１は本発明の実施の一形態である電子写真感光体１の構成を簡略化して示す部分断面図である。電子写真感光体１（以後、感光体と略称する）は、導電性素材からなる導電性支持体３と、導電性支持体３上に積層される下引層４と、下引層４上に積層される層であって電荷発生物質を含む電荷発生層５と、電荷発生層５の上にさらに積層される層であって電荷輸送物質を含む電荷輸送層６とを含む。電荷発生層５と電荷輸送層６とは、感光層７を構成する。
【００３３】
導電性支持体３は、円筒形状を有し、（ａ）アルミニウム、ステンレス鋼、銅、ニッケルなどの金属材料、（ｂ）ポリエステルフィルム、フェノール樹脂パイプ、紙管などの絶縁性物質の表面にアルミニウム、銅、パラジウム、酸化錫、酸化インジウムなどの導電性層を設けたものが好適に用いられ、その体積抵抗が１０^１０Ω・ｃｍ以下の導電性を有するものが好ましい。導電性支持体３には、前述の体積抵抗を調整する目的で表面に酸化処理が施されてもよい。導電性支持体３は、感光体１の電極としての役割を果たすとともに他の各層４，５，６の支持部材としても機能する。なお導電性支持体３の形状は、円筒形に限定されることなく、板状、フイルム状およびベルト状のいずれであってもよい。
【００３４】
下引層４は、たとえば、ポリアミド、ポリウレタン、セルロース、ニトロセルロース、ポリビニルアルコール、ポリビニルピロリドン、ポリアクリルアミド、アルミニウム陽極酸化被膜、ゼラチン、でんぷん、カゼイン、Ｎ−メトキシメチル化ナイロンなどによって形成される。また酸化チタン、酸化錫、酸化アルミニウムなどの粒子を下引層４中に分散させてもよい。下引層４の膜厚は、約０．１〜１０μｍに形成される。この下引層４は、導電性支持体３と感光層７との接着層としての役割を果たすとともに、導電性支持体３から電荷が感光層７へ流込むのを抑制するバリア層としても機能する。このように下引層４は感光体１の帯電特性を維持するように作用するので、感光体１の寿命を延ばすことができる。
【００３５】
電荷発生層５は、公知の電荷発生物質を含んで構成することができる。電荷発生物質には、可視光を吸収してフリー電荷を発生するものであれば、無機顔料、有機顔料および有機染料のいずれをも用いることができる。無機顔料としては、セレンおよびその合金、ヒ素−セレン、硫化カドミウム、酸化亜鉛、アモルファスシリコン、その他の無機光導電体が挙げられる。有機顔料としては、フタロシアニン系化合物、アゾ系化合物、キナクリドン系化合物、多環キノン系化合物、ペリレン系化合物などが挙げられる。有機染料としては、チアピリリウム塩、スクアリリウム塩などが挙げられる。前述の電荷発生物質の中でもフタロシアニン系化合物が好適に用いられ、特にチタニルフタロシアニン化合物を用いることが最適であり、良好な感度特性、帯電特性および再現性が得られる。
【００３６】
前述の列挙した顔料および染料の他に、電荷発生層５には、化学増感剤または光学増感剤を添加してもよい。化学増感剤として、電子受容性物質、たとえば、テトラシアノエチレン、７，７，８，８−テトラシアノキノジメタンなどのシアノ化合物、アントラキノン、ｐ−ベンゾキノンなどのキノン類、２，４，７−トリニトロフルオレノン、２，４，５，７−テトラニトロフルオレノンなどのニトロ化合物が挙げられる。光学増感剤として、キサンテン系色素、チアジン色素、トリフェニルメタン系色素などの色素が挙げられる。
【００３７】
電荷発生層５は、前述の電荷発生物質をバインダ樹脂とともに、適当な溶媒中に分散させ、下引層４上に積層し、乾燥または硬化させて成膜する。バインダ樹脂としては、具体的に、ポリアリレート、ポリビニルブチラール、ポリカーボネート、ポリエステル、ポリスチレン、ポリ塩化ビニル、フェノキシ樹脂、エポキシ樹脂、シリコーン、ポリアクリレートなどが挙げられる。溶媒としては、イソプロピルアルコール、シクロヘキサノン、シクロヘキサン、トルエン、キシレン、アセトン、メチルエチルケトン、テトラヒドロフラン、ジオキサン、ジオキソラン、エチルセロソルブ、酢酸エチル、酢酸メチル、ジクロロメタン、ジクロロエタン、モノクロルベンゼン、エチレングリコールジメチルエーテルなどが挙げられる。
【００３８】
なお溶媒は、前述のものに限定されることなく、アルコール系、ケトン系、アミド系、エステル系、エーテル系、炭化水素系、塩素化炭化水素系、芳香族系のうちから選択されるいずれかの溶媒系を、単独または混合して用いてもよい。ただし、電荷発生物質の粉砕およびミリング時の結晶転移に基づく感度低下、およびポットライフによる特性低下を考慮した場合、無機や有機顔料において結晶転移を起こしにくいシクロヘキサノン、１，２−ジメトキシエタン、メチルエチルケトン、テトラヒドロキノンのいずれかを用いることが好ましい。
【００３９】
電荷発生層５の形成には、真空蒸着法、スパッタリング法、ＣＶＤ法などの気相堆積法や塗布方法などを適用することができる。塗布方法を用いる場合、電荷発生物質をボールミル、サンドグラインダ、ペイントシェイカ、超音波分散機などによって粉砕して溶剤に分散し、必要に応じてバインダ樹脂を加えた塗布液を、公知の塗布法によって下引層４上に塗布する。下引層４の形成される導電性支持体３が円筒状の場合、塗布法にはスプレイ法、垂直型リング法、浸漬塗布法などを用いることができる。電荷発生層５の膜厚は、約０．０５〜５μｍであることが好ましく、より好ましくは約０．１〜１μｍである。
【００４０】
なお下引層４の形成されている導電性支持体３の形状がシートの場合、塗布法にはアプリケータ、バーコータ、キャスティング、スピンコートなどを用いることができる。
【００４１】
電荷輸送層６は、公知の電荷輸送物質と結着樹脂とを含んで構成することができる。電荷発生層５に含まれる電荷発生物質で発生した電荷を受け入れ、これを輸送する能力を有するものであればよい。電荷輸送物質としては、たとえばポリ−Ｎ−ビニルカルバゾールおよびその誘導体、ポリ−ｇ−カルバゾリルエチルグルタメートおよびその誘導体、ポリビニルピレン、ポリビニルフェナントレン、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、９−（ｐ−ジエチルアミノスチリル）アントラセン、１，１−ビス（４−ジベンジルアミノフェニル）プロパン、スチリルアントラセン、スチリルピラゾリン、ピラゾリン誘導体、フェニルヒドラゾン類、ヒドラゾン誘導体、トリフェニルアミン系化合物、テトラフェニルジアミン系化合物、スチルベン系化合物、３−メチル−２−ベンゾチアゾリン環を有するアジン化合物等の電子供与性物質が挙げられる。
【００４２】
電荷輸送層６を構成する結着樹脂としては、電荷輸送物質と相溶性を有するものであればよく、たとえば、ポリカーボネートおよび共重合ポリカーボネート、ポリアリレート、ポリビニルブチラール、ポリアミド、ポリエステル、エポキシ樹脂、ポリウレタン、ポリケトン、ポリビニルケトン、ポリスチレン、ポリアクリルアミド、フェノール樹脂、フェノキシ樹脂およびポリスルホン樹脂、それらの共重合樹脂などが挙げられる。これらの樹脂を単独または２種以上混合して用いてもよい。前述の結着樹脂の中でもポリスチレン、ポリカーボネートおよび共重合ポリカーボネート、ポリアリレート、ポリエステルなどの樹脂は、１０^１３Ω以上の体積抵抗率を有し、成膜性や電位特性などにも優れている。
【００４３】
またこれらの材料を溶解させる溶剤は、メタノールやエタノールなどのアルコール類、アセトン、メチルエチルケトンやシクロヘキサノンなどのケトン類、エチルエーテル、テトラヒドロフラン、ジオキサンやジオキソランなどのエーテル類、クロロホルム、ジクロロメタンやジクロロエタンなどの脂肪族ハロゲン化炭化水素、ベンゼン、クロロベンゼンやトルエンなどの芳香族類などを用いることができる。
【００４４】
電荷輸送層６を形成するための電荷輸送層用塗布液は、結着樹脂溶液中へ電荷輸送物質を溶解して調製される。電荷輸送層６に占める電荷輸送物質の割合は、３０〜８０重量％の範囲が好ましい。電荷発生層５上への電荷輸送層６の形成は、前述の下引層４上に電荷発生層５を形成したのと同様にして行われる。電荷輸送層６の膜厚は、１０〜５０μｍが好ましく、より好ましくは１５〜４０μｍである。
【００４５】
また、電荷輸送層６には、１種以上の電子受容性物質や色素を含有させることによって、感度の向上を図り繰返し使用時の残留電位の上昇や疲労などを抑えるようにしてもよい。電子受容性物質としては、たとえば無水コハク酸、無水マレイン酸、無水フタル酸、４−クロルナフタル酸無水物などの酸無水物、テトラシアノエチレン、テレフタルマロンジニトリルなどのシアノ化合物、４−ニトロベンズアルデヒドなどのアルデヒド類、アントラキノン、１−ニトロアントラキノンなどのアントラキノン類、２，４，７−トリニトロフルオレノン、２，４，５，７−テトラニトロフルオレノンなどの多環または複素環ニトロ化合物が挙げられ、これらを化学増感剤として用いることができる。
【００４６】
色素としては、たとえば、キサンテン系色素、チアジン色素、トリフェニルメタン色素、キノリン系顔料、銅フタロシアニンなどの有機光導電性化合物が挙げられ、これらを光学増感剤として用いることができる。
【００４７】
さらに、電荷輸送層６には、公知の可塑剤を含有させることによって、成形性、可撓性および機械的強度を向上させるようにしてもよい。可塑剤としては、二塩基酸エステル、脂肪酸エステル、リン酸エステル、フタル酸エステル、塩素化パラフィン、エポキシ型可塑剤などが挙げられる。また、感光層７には、必要に応じてポリシロキサンなどのゆず肌防止のためのレベリング剤、耐久性向上のためフェノール系化合物、ハイドロキノン系化合物、トコフェロール系化合物、アミン系化合物などの酸化防止剤、紫外線吸収剤などを含有してもよい。
【００４８】
前述のように構成される感光体１の感光層７の硬さは、ＪＩＳ−Ｚ２２４４に規定されるビッカース硬さ（測定荷重３０ｍＮ）で２０以上になるように制御設定され、かつ感光層７表面の表面自由エネルギー（γ）は、拡張Ｆｏｒｋｅｓ理論によって算出される値が、２８ｍＮ／ｍ以上、３５ｍＮ／ｍ以下になるように制御設定される。
【００４９】
ビッカース硬さが２０未満では、感光体１表面の残留物を除去するために圧接されるクリーニングブレードによる擦過、およびクリーニングブレードと感光体１表面の残留物とによる機械的研磨によって感光層７が著しく磨耗し、感光体１の寿命が極端に短くなる。したがって、ビッカース硬さで２０以上とした。なお感光体１の感光層７のビッカース硬さは、３５以下であることが好ましい。感光層７のビッカース硬さが、３５を超えると、脆さの弊害が現れることによる。
【００５０】
また表面自由エネルギーが３５ｍＮ／ｍを超えると、トナーや紙粉などの感光体表面に対する付着力が増大するのでクリーニング性が悪化する。表面自由エネルギーが２８ｍＮ／ｍ未満になると、トナーと感光体１表面との付着力が低下するので、装置内へのトナー飛散および感光体１上のトナー画像部以外の部分に付着した微粉トナーの記録紙への移行により画像かぶりが発生する。したがって、表面自由エネルギーは、２８〜３５ｍＮ／ｍが好適である。
【００５１】
感光層７のビッカース硬さの前述範囲への制御設定は、感光層７に含まれる結着樹脂に硬さの高い樹脂を用いたり、より高分子の樹脂を用いることによって実現できる。また感光層７の結着樹脂を架橋することによっても実現できる。
【００５２】
また感光層７の表面自由エネルギーの前述範囲への制御設定は、以下のようにして行われる。比較的低い表面自由エネルギー値を有する、たとえばポリテトラフルオロエチレン（略称ＰＴＦＥ）を代表とするフッ素系材料、ポリシロキサン系材料などを、感光層７に導入し、その含有量を調整することによって実現できる。また感光層７に含まれる電荷発生物質、電荷輸送物質および結着樹脂の種類、これらの組成比を変化させることによっても実現できる。また感光層７を形成する際の乾燥温度を調整することによっても実現できる。
【００５３】
このようにして制御設定される感光体１表面の表面自由エネルギーは、前述のように表面自由エネルギーの双極子成分、分散成分および水素結合成分が既知である試薬を使用し、その試薬との付着性を測定することによって求められる。具体的には、試薬に純水、ヨウ化メチレン、α−ブロモナフタレンを使用し、接触角計ＣＡ−Ｘ（商品名；協和界面株式会社製）を用いて、感光体２表面に対する接触角を測定し、測定結果に基づき表面自由エネルギー解析ソフトＥＧ−１１（商品名；協和界面株式会社製）を用いて各成分の表面自由エネルギーを算出することができる。なお試薬は、前述の純水、ヨウ化メチレン、α−ブロモナフタレンに限定されるものではなく、双極子成分、分散成分、水素結合成分が適宜な組合せの試薬を用いてもよい。また測定方法も、前述の方法に限定されるものではなく、たとえばウィルヘルミ法（つり板法）やドゥ・ヌイ法などが用いられてもよい。
【００５４】
以下感光体１における静電潜像形成動作について簡単に説明する。感光体１に形成される感光層７は、帯電器などでたとえば負に一様に帯電され、帯電された状態で電荷発生層５に吸収波長を有する光が照射されると、電荷発生層５中に電子および正孔の電荷が発生する。正孔は、電荷輸送層６に含まれる電荷輸送材料によって感光体１表面に移動されて表面の負電荷を中和し、電荷発生層５中の電子は、正電荷が誘起された導電性支持体３の側に移動し、正電荷を中和する。このように、感光層７には、露光された部位の帯電量と露光されなかった部位の帯電量とに差異が生じて静電潜像が形成される。
【００５５】
図２は、本発明の実施の第２の形態である感光体８の構成を簡略化して示す部分断面図である。本実施の形態の感光体８は、実施の第１形態の感光体１に類似し、対応する部分については同一の参照符号を付して説明を省略する。感光体８において注目すべきは、導電性支持体３上に単層からなる感光層９が形成されることである。
【００５６】
感光層９は、実施の第１形態の感光体１に用いるのと同様の電荷発生物質、電荷輸送物質、結着樹脂などを用いて形成される。結着樹脂中に電荷発生物質および電荷輸送物質を分散したり、電荷輸送物質を含む結着樹脂中に電荷発生物質を顔料粒子の形で分散させたりして調製した感光層用塗布液を用い、実施の第１形態の感光体１における電荷発生層５を形成するのと同様の方法によって単層の感光層が導電性支持体３上に形成される。本実施の形態の単層型感光体８は、オゾン発生が少ない正帯電型画像形成装置用の感光体として好適であり、また塗布されるべき感光層９が一層のみであるので、製造原価および歩留が電荷発生層および電荷輸送層の積層して構成される積層型に比べて優れている。
【００５７】
図３は、本発明の他の実施の形態である画像形成装置２の構成を簡略化して示す配置側面図である。画像形成装置２は、実施の第１形態の感光体１を備えることを特徴とする。なお、本発明の画像形成装置は、実施の第２形態の感光体８を備える構成であってもよい。
【００５８】
図３を参照して感光体１を備える画像形成装置２の構成および画像形成動作について説明する。本実施の形態として例示する画像形成装置２は、デジタル複写機２である。
【００５９】
デジタル複写機２は、大略スキャナ部１１と、レーザ記録部１２とを含む構成である。スキャナ部１１は、透明ガラスからなる原稿載置台１３と、原稿載置台１３上へ自動的に原稿を供給搬送するための両面対応自動原稿送り装置（ＲＡＤＦ）１４と、原稿載置台１３上に載置された原稿の画像を走査して読取るための原稿画像読取りユニットであるスキャナユニット１５とを含む。このスキャナ部１１にて読取られた原稿画像は、画像データとして画像データ入力部へと送られ、画像データに対して所定の画像処理が施される。ＲＡＤＦ１４は、ＲＡＤＦ１４に備わる原稿トレイ上に複数枚の原稿を一度にセットし、セットされた原稿を１枚ずつ自動的に原稿載置台１３上へ給送する装置である。
【００６０】
スキャナユニット１５は、原稿面上を露光するランプリフレクターアセンブリ１６と、原稿からの反射光像を光電変換素子（略称ＣＣＤ）２３に導くために原稿からの反射光を反射する第１反射ミラー１７を搭載する第１走査ユニット１８と、第１反射ミラー１７からの反射光像をＣＣＤ２３に導くための第２および第３反射ミラー１９，２０を搭載する第２走査ユニット２１と、原稿からの反射光像を前述の各反射ミラー１７，１９，２０を介して電気的画像信号に変換するＣＣＤ２３上に結像させるための光学レンズ２２と、前記ＣＣＤ２３とを含む構成である。
【００６１】
スキャナ部１１は、ＲＡＤＦ１４とスキャナユニット１５との関連動作によって、原稿載置台１３上に読取るべき原稿を順次給送載置させるとともに、原稿載置台１３の下面に沿ってスキャナユニット１５を移動させて原稿画像を読取るように構成される。第１走査ユニット１８は、原稿載置台１３に沿って原稿画像の読取り方向（図３では紙面に向って右から左）に一定速度Ｖで走査され、また第２走査ユニット２１は、その速度Ｖに対して２分の１（Ｖ／２）の速度で同一方向に平行に走査される。この第１および第２走査ユニット１８，２１の動作によって、原稿載置台１３上に載置された原稿画像を１ライン毎に順次ＣＣＤ２３へ結像させて画像を読取ることができる。
【００６２】
原稿画像をスキャナユニット１５で読取って得られた画像データは、各種画像処理が施された後、メモリに一旦記憶され、出力指示に応じてメモリ内の画像を読出してレーザ記録部１２に転送して記録媒体である記録紙上に画像を形成させる。
【００６３】
レーザ記録部１２は、記録紙の搬送系３３と、レーザ書込みユニット２６と、画像を形成するための電子写真プロセス部２７とを備える。レーザ書込みユニット２６は、前述のスキャナユニット１５にて読取られてメモリに記憶された後にメモリから読出される画像データ、または外部の装置から転送される画像データに応じてレーザ光を出射する半導体レーザ光源と、レーザ光を等角速度偏向するポリゴンミラーと、等角速度で偏向されたレーザ光が電子写真プロセス部２７に備えられる感光体１上で等角速度で偏向されるように補正するｆ−θレンズなどを含む。
【００６４】
電子写真プロセス部２７は、前述の感光体１の周囲に帯電器２８、現像器２９、転写器３０、クリーニング器３１が、矢符３２で示す感光体１の回転方向の上流側から下流側に向ってこの順番に備えられる。前述のように感光体１は、帯電器２８によって一様に帯電され、帯電された状態でレーザ書込みユニット２６から出射される原稿画像データに対応するレーザ光によって露光される。露光されることによって感光体１表面に形成される静電潜像は、現像器２９から供給されるトナーによって現像され、可視像であるトナー画像となる。感光体１表面に形成されたトナー画像は、後述する搬送系３３によって供給される記録紙上に転写器３０によって転写される。
【００６５】
このとき、感光体１表面の表面自由エネルギーが、好適な範囲に設定されているので、トナー画像を形成するトナーは、感光体１表面から記録紙上へ容易に移行転写されて残留トナーが発生しにくく、また転写時に接触する記録紙の紙粉なども感光体１表面に付着しにくい。したがって、転写後の感光体１表面を清掃するために設けられるクリーニング器３１のクリーニングブレード３１ａの研磨能力を弱く設定することができ、またクリーニングブレード３１ａの感光体１表面に対する当接圧力も小さく設定することができる。また、感光体１表面にトナーや異物の付着が無く、常に清浄な状態に保たれるので、画質の良好な画像を長期間安定して形成することが可能になる。さらに、感光体１の感光層７はビッカース硬さが好適な範囲に設定されているので、クリーニングブレード３１ａによる擦過およびクリーニングブレード３１ａと残留物との機械的研磨による磨耗が抑えられるので、感光体１の寿命が延長される。
【００６６】
記録紙の搬送系３３は、記録紙Ｐを収容するカセット３４と、カセット３４内の記録紙Ｐを１枚ずつ分離送給する給紙ユニット３５と、給紙ユニット３５によってカセット３４から送給される記録紙Ｐを搬送系３３内の所定の位置に搬送する複数の搬送ローラ３６とを備える。前述の転写器３０の記録紙Ｐ搬送方向下流側には定着器３７が設けられる。
【００６７】
転写器３０によってトナー画像が転写された記録紙は、搬送系３３によって定着器３７へと搬送され、定着器３７によってトナー画像が定着処理される。トナー画像が定着処理された記録紙は、搬送ローラ３６によって排紙カセット３８に排紙されて、デジタル複写機２における一連の画像形成動作が終了する。
【００６８】
このデジタル複写機２には、前述のようにトナーが過度に付着することなく、また異物が付着しにくく、クリーニング器３１によって容易にクリーニングすることのできるクリーニング性に優れる感光体１が備えられるので、長期間に亘り安定して画質低下のない画像形成が可能であり、かつ感光体１の寿命が長くクリーニング器３１も簡易なものですむことから低コストでメンテナンス頻度の少ない装置の提供が実現される。
【００６９】
（実施例）
以下本発明の実施例について説明する。なお、本発明は、以下に説明する実施例に限定されるものではない。
【００７０】
まず、直径：３０ｍｍ、長さ：３２６．３ｍｍのアルミニウム製導電性支持体上に種々の条件にて感光層を形成し、実施例および比較例として準備した感光体について説明する。なお実施例中では、ビッカース硬さをＨＶ、表面自由エネルギーをγと略記する。
【００７１】
（実施例のＳ１〜Ｓ３感光体）
（Ｓ１感光体）
酸化チタン（ＴＴＯ５５Ａ：石原産業社製）７重量部および共重合ナイロン（ＣＭ８０００：東レ社製）１３重量部を、メチルアルコール１５９重量部と１，３−ジオキソラン１０６重量部との混合溶剤に加え、ペイントシェーカにて８時間分散処理して下引層用塗布液を調整した。この塗布液を塗布槽に満たし、導電性支持体を浸漬後引上げ、自然乾燥して層厚１μｍの下引層を形成した。
【００７２】
オキソチタニルフタロシアニン３重量部とブチラール樹脂（ＢＬ−１：積水化学社製）２重量部とを、メチルエチルケトン２４５重量部に混合し、ペイントシェーカにて分散して電荷発生層用塗布液を調整した。この塗布液を、下引層の場合と同様の浸漬塗布法にて前述の下引層上に塗布し、 自然乾燥して層厚０．４μｍの電荷発生層を形成した。
【００７３】
電荷輸送物質として下記構造式（Ｉ）で示されるエナミン系化合物５重量部、ポリカーボネート樹脂（Ｇ４００：出光興産株式会社製）５重量部、同じくポカーボネート樹脂（ＧＨ５０３：出光興産株式会社製）５重量部、スミライザーＢＨＴ（住友化学株式会社製）０．０５重量部を混合し、テトラヒドロフラン４７重量部を溶剤として電荷輸送層用塗布液を調整した。この塗布液を、浸漬塗布法にて前述の電荷発生層上に塗布し、１３０℃で１時間乾燥して層厚２８μｍの電荷輸送層を形成した。このようにしてＳ１感光体を作製した。
【００７４】
【化１】

【００７５】
（Ｓ２感光体）
Ｓ１感光体と同様にして下引層および電荷発生層を形成した。次いで電荷輸送物質として下記構造式（ＩＩ）で示されるブタジエン系化合物を５重量部、４種類のポリカーボネート樹脂、Ｊ５００（出光興産株式会社製）２．４重量部、Ｇ４００（出光興産株式会社製）１．６重量部、ＧＨ５０３（出光興産株式会社製）１．６重量部、ＴＳ２０２０（帝人化成株式会社製）２．４重量部、さらにスミライザーＢＨＴ（住友化学株式会社製）０．２５重量部を混合し、テトラヒドロフラン４９重量部を溶剤として電荷輸送層用塗布液を調整した。この塗布液を、浸漬塗布法にて電荷発生層上に塗布し、１３０℃で１時間乾燥して層厚２８μｍの電荷輸送層を形成した。このようにしてＳ２感光体を作製した。
【００７６】
【化２】

【００７７】
（Ｓ３感光体）
Ｓ１感光体と同様にして下引層および電荷発生層を形成した。次いで電荷輸送物質として前記構造式（ＩＩ）で示されるブタジエン系化合物を３．５重量部、下記構造式（ＩＩＩ）で示されるスチリル系化合物を１．５重量部、４種類のポリカーボネート樹脂、Ｊ５００（出光興産株式会社製）２．２重量部、Ｇ４００（出光興産株式会社製）２．２重量部、ＧＨ５０３（出光興産株式会社製）１．８重量部、ＴＳ２０２０（帝人化成株式会社製）１．８重量部、さらにスミライザーＢＨＴ（住友化学株式会社製）１．５重量部を混合し、テトラヒドロフラン５５重量部を溶剤として電荷輸送層用塗布液を調整した。この塗布液を、浸漬塗布法にて電荷発生層上に塗布し、１２０℃で１時間乾燥して層厚２８μｍの電荷輸送層を形成した。このようにしてＳ３感光体を作製した。
【００７８】
【化３】

【００７９】
（比較例のＲ１〜Ｒ３感光体）
（Ｒ１感光体）
Ｓ１感光体と同様にして下引層および電荷発生層を形成した。次いで、電荷輸送層形成に際し、ポリカーボネート樹脂の一部に代えて、γの低い樹脂であるＰＴＦＥを用いた以外は、Ｓ１感光体と同様にして塗布液を調整した。この塗布液を、浸漬塗布法にて電荷発生層上に塗布し、１２０℃で１時間乾燥して層厚２８μｍの電荷輸送層を形成した。このようにしてＲ１感光体を作製した。
【００８０】
（Ｒ２感光体）
Ｓ１感光体と同様にして下引層および電荷発生層を形成した。次いで電荷輸送物質として前記構造式（ＩＩ）で示されるブタジエン系化合物を５重量部、３種類のポリカーボネート樹脂、Ｇ４００（出光興産株式会社製）２．４重量部、ＴＳ２０２０（帝人化成株式会社製）４重量部、Ｖｙｌｏｎ２９０（東洋紡株式会社製）１．６重量部、さらにスミライザーＢＨＴ（住友化学株式会社製）０．２５重量部を混合し、テトラヒドロフラン４９重量部を溶剤として電荷輸送層用塗布液を調整した。この塗布液を、浸漬塗布法にて電荷発生層上に塗布し、１３０℃で１時間乾燥して層厚２８μｍの電荷輸送層を形成した。このようにしてＲ２感光体を作製した。
【００８１】
（Ｒ３感光体）
Ｓ１感光体と同様にして下引層および電荷発生層を形成した。次いで、電荷輸送層形成に際し、ポリカーボネート樹脂に、Ｇ４００（出光興産株式会社製）８重量部を用いた以外は、Ｒ２感光体と同様にして塗布液を調整した。この塗布液を、浸漬塗布法にて電荷発生層上に塗布し、１３０℃で１時間乾燥して層厚２８μｍの電荷輸送層を形成した。このようにしてＲ３感光体を作製した。
【００８２】
以上のように、Ｓ１〜Ｓ３感光体およびＲ１〜Ｒ３感光体の作製において、電荷輸送層用塗布液に含まれる樹脂の種類および含有比率を変化させるとともに、塗布後の乾燥温度を変化させることによって、感光体表面のＨＶおよびγが所望の値になるように調整した。これらの感光体表面のＨＶは、微小硬度測定器Ｈ１０００Ｃ（Ｈ．ＦＩＳＣＨＥＲ社製）および解析ソフトＷＩＮ−ＨＣＵ（Ｈ．ＦＩＳＣＨＥＲ社製）によって求め、感光体表面のγは、接触角測定機ＣＡ−Ｘ（協和界面株式会社製）および解析ソフトＥＧ−１１（協和界面株式会社製）によって求めた。
【００８３】
実施例のＳ１〜Ｓ３感光体および比較例のＲ１〜Ｒ３感光体を、試験用に改造したデジタル複写機ＡＲ−４５０（シャープ株式会社製）に搭載することによって、画像品質および耐磨耗性の評価試験を行った。次に、評価方法について説明する。
【００８４】
［画像品質］
前述のデジタル複写機ＡＲ−４５０に備わるクリーニング器のクリーニングブレードが、感光体に当接する当接圧力、いわゆるクリーニングブレード圧を初期線圧で２１ｇｆ／ｃｍ（２．０６×１０^−１Ｎ／ｃｍ）に調整した。温度：２５℃、相対湿度：５０％の常温／常湿（Ｎ／Ｎ：Ｎｏｒｍａｌ Ｔｅｍｐｅｒａｔｕｒｅ／Ｎｏｒｍａｌ Ｈｕｍｉｄｉｔｙ）環境中で、前記複写機を用いて、記録紙上に白べた画像および黒べた画像を形成した。得られた白べた画像および黒べた画像を目視観察し、画像品質を評価した。次いで前記条件下において、所定パターンの画像を記録紙１０万枚に形成した後、記録紙上に白べた画像および黒べた画像を形成した。得られた白べた画像および黒べた画像を目視観察して、１０万枚の画像形成後における画像品質を評価した。
【００８５】
画像品質の評価基準は以下のようである。
○：良好。白べた画像へのかぶり、黒すじの発生および黒べた画像の画像濃度低下なし。
×：不良。白べた画像に多数のかぶり、黒すじ発生または黒べた画像の画像濃度が著しく低下。
【００８６】
［耐磨耗性］
感光体作製時における感光層の膜厚ｄ０と、前述の画像品質評価試験において記録紙１０万枚に画像形成した後に装置から取出した感光体の膜厚ｄ１とをそれぞれ測定し、両測定値の差である膜べり量Δｄ（＝ｄ０−ｄ１）を求めた。膜べり量Δｄが小さい程、耐磨耗性が優れると評価した。なお膜厚は、膜厚計ＭＣＰＤ２０００（大塚電子株式会社製）によって測定した。
【００８７】
［評価結果］
評価結果を表１に合わせて示す。ＨＶが本発明範囲内の２０以上であるけれども、γが本発明範囲外の２８未満である比較例のＲ１感光体は、膜減り量Δｄが小さいけれども、１０万枚の画像形成後における白ベた画像へのかぶりの発生が見られ、画像品質不良であった。またこのときの画像形成装置内のトナー飛散による汚れがひどく、これがかぶりの発生に影響したものと推察される。
【００８８】
ＨＶが本発明範囲内の２０以上であるけれども、γが本発明範囲外の３５超えである比較例のＲ２感光体は、ＨＶが高いので膜べり量Δｄが小さいけれども、１０万枚の画像形成後の白ベた画像に多数の黒すじが発生し、画像品質不良であった。感光体表面のγすなわち付着力が大きいので、残留トナーのクリーニング不良によるトナーのフィルミングなどが発生したものである。
【００８９】
γが本発明範囲内の２８〜３５ｍＮ／ｍであるけれども、ＨＶが本発明範囲外の２０未満である比較例のＲ３感光体は、感光層のＨＶが低いので膜減り量Δｄが極端に大きい。また１０万枚の画像形成後の白ベた画像へのかぶり発生、黒ベた画像に若干の濃度低下が見られた。
【００９０】
一方、ＨＶが本発明範囲内の２０以上であり、かつγが本発明範囲内の２８〜３５ｍＮ／ｍである実施例のＳ１〜Ｓ３感光体は、膜減り量Δｄが比較的小さく、初期から１０万枚の画像形成後まで、良好な品質の画像を得ることが出来た。
【００９１】
【表１】

【００９２】
【発明の効果】
本発明によれば、電子写真感光体は、感光層の硬さがビッカース硬さで２０以上であり、感光層表面の表面自由エネルギーが、２８ｍＮ／ｍ以上、３５ｍＮ／ｍ以下になるように設定される。電子写真感光体における感光層の硬さを、ビッカース硬さで２０以上の範囲に設定することによって、電子写真感光体の感光層は充分な機械的強度を有するようになるので、クリーニング工程における機械的磨耗に対して充分な耐久寿命を発現させることができる。
【００９３】
電子写真感光体の感光層の表面自由エネルギーを前記好適な範囲に設定することによって、特にトナーに対しては現像に必要な程度の付着力を発現するにも関らず過度の付着力を抑制し、また紙粉等の異物に対する付着力を抑制することができるので、電子写真感光体表面から過剰のトナーや異物が除去され易くなる。このようにして、現像性能を低下させることなく、クリーニング性能を向上させることが可能になる。
【００９４】
したがって、表面は充分な硬さを有して耐磨耗性に優れ、かつ表面に異物が付着しにくくまた表面から異物を離脱させ易いクリーニング性能に優れる電子写真感光体が実現される。このような電子写真感光体は、耐久寿命が長く、長期間安定して形成画像に品質低下を生じさせることがない。
【００９５】
また本発明によれば、電子写真感光体の感光層は、電荷発生物質を含む電荷発生層と、電荷輸送物質を含む電荷輸送層とが積層されて構成される。このように感光層を複数層が積層されるタイプにすることによって、各層を構成する材料およびその組合せの自由度が増すので、電子写真感光体表面の表面自由エネルギー値を所望の範囲に設定することが容易になる。
【００９６】
また本発明によれば、画像形成装置には、クリーニング性能および耐磨耗性に優れ、耐久寿命の長い電子写真感光体が備えられる。したがって、長期間に亘り安定して画質低下のない画像形成が可能であり、かつメンテナンス頻度の少ない画像形成装置が提供される。
【図面の簡単な説明】
【図１】本発明の実施の一形態である電子写真感光体１の構成を簡略化して示す部分断面図である。
【図２】本発明の実施の第２の形態である感光体８の構成を簡略化して示す部分断面図である。
【図３】本発明の他の実施の形態である画像形成装置２の構成を簡略化して示す配置側面図である。
【図４】付着濡れの状態を例示する側面図である。
【符号の説明】
１，８ 感光体
２ 画像形成装置
３ 導電性支持体
４ 下引層
５ 電荷発生層
６ 電荷輸送層
７，９ 感光層
１１ スキャナ部
１２ レーザ記録部
１３ 原稿載置台
１４ ＲＡＤＦ
１５ スキャナユニット
１８ 第１走査ユニット
２１ 第２走査ユニット
２２ 光学レンズ
２３ ＣＣＤ
２６ レーザ書込みユニット
２７ 電子写真プロセス部
２８ 帯電器
２９ 現像器
３０ 転写器
３１ クリーニング器
３３ 搬送系
３４ カセット
３５ 給紙ユニット
３７ 定着器
３８ 排紙カセット[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an electrophotographic photosensitive member used for an electrophotographic image forming apparatus such as a copying machine and an image forming apparatus including the same.
[0002]
[Prior art]
2. Description of the Related Art Electrophotographic image forming apparatuses have been widely used not only for copying machines but also for printers and the like, which are output means of computers and the like, whose demand has been remarkably growing in recent years. 2. Description of the Related Art In an electrophotographic image forming apparatus, a photosensitive layer of an electrophotographic photosensitive member provided in the apparatus is uniformly charged by a charger, and is exposed to, for example, a laser beam corresponding to image information. A fine particle developer called toner is supplied from a developing device to the latent image to form a toner image. Although the formed toner image is transferred to a transfer material such as recording paper by a transfer means, not all of the toner on the surface of the electrophotographic photosensitive member is transferred to the recording paper and transferred. Remains on the body surface. In addition, the paper dust of the recording paper that comes into contact with the electrophotographic photosensitive member during development may remain while being attached to the electrophotographic photosensitive member.
[0003]
Such residual toner and attached paper dust on the surface of the electrophotographic photoreceptor adversely affect the quality of an image to be formed, and thus are generally removed by a cleaning device. In recent years, a cleaning device has a cleaning blade provided so as to be in contact with the surface of an electrophotographic photosensitive member, and the surface of the electrophotographic photosensitive member is rubbed by the cleaning blade as the electrophotographic photosensitive member rotates. What removes residue on the surface is the mainstream.
[0004]
When the cleaning blade rubs the surface of the electrophotographic photosensitive member during cleaning of the electrophotographic photosensitive member by the cleaning device, foreign matters such as toner and paper powder remaining on the surface of the electrophotographic photosensitive member cause the cleaning blade and the electrophotographic photosensitive member to be removed. In between, the surface of the electrophotographic photosensitive member is mechanically polished, so that the surface of the electrophotographic photosensitive member is worn. Therefore, in order to prolong the service life of the electrophotographic photoreceptor, abrasion resistance capable of withstanding mechanical polishing is required. Hardness is one of the characteristics used as an index for evaluating the abrasion resistance of an electrophotographic photosensitive member.
[0005]
As a conventional technique for defining an electrophotographic photosensitive member by hardness, there is a technology using a resin having a Vickers hardness of 15 or more as a base resin used as a cylindrical base of the electrophotographic photosensitive member (see Patent Document 1). However, the technique disclosed in Patent Literature 1 regulates the hardness of the cylindrical substrate to prevent the outer peripheral surface of the substrate from being damaged at the time of demolding after the molding of the substrate or at the time of handling during the subsequent process. Thus, the coating property of the photosensitive layer can be ensured, and a good photosensitive layer can be formed to improve the printing performance. Therefore, Patent Document 1 does not disclose a technique for improving abrasion resistance when cleaning the surface of an electrophotographic photosensitive member.
[0006]
Another conventional technique relates to a relationship between a layer thickness of a photosensitive layer of an electrophotographic photosensitive member and a normal speed of a transfer paper supplied to be in contact with the surface of the electrophotographic photosensitive member with respect to the electrophotographic photosensitive member. There is one that defines the Vickers hardness of a photosensitive layer (see Patent Document 2). However, as in the technique disclosed in Patent Literature 2, merely by specifying the hardness of the electrophotographic photoreceptor can improve the abrasion life, but does not reduce paper dust or the like on the surface of the electrophotographic photoreceptor. Since the problem of adhesion of the residual toner is not solved, there is a problem that a cleaning failure occurs, and a black streak or a white background fog occurs in the image transferred to the recording paper due to the cleaning failure.
[0007]
It is considered that the phenomenon of poor cleaning is caused by the mutual adhesion force, which is related to the properties of the toner particles and the surface properties of the electrophotographic photosensitive member. Therefore, in order to improve the cleaning property of the electrophotographic photosensitive member, it is essential to control the cleaning property focusing on the surface properties of the electrophotographic photosensitive member itself.
[0008]
The cleaning of the electrophotographic photoreceptor is performed by removing a force exceeding an adhesive force between the electrophotographic photoreceptor surface and the adhered residual toner from the surface of the electrophotographic photoreceptor by acting on the residual toner. is there. Therefore, it can be said that the lower the wettability of the electrophotographic photosensitive member surface, the easier the cleaning. The wettability of the surface of the electrophotographic photoreceptor, that is, the adhesive force can be represented by using surface free energy (synonymous with surface tension) as an index. The surface free energy (γ) is a phenomenon that an intermolecular force, which is a force acting between molecules constituting a substance, occurs on the outermost surface.
[0009]
The toner adheres and fuses to the surface of the electrophotographic photosensitive member, and the remaining toner without being transferred to the transfer material spreads in a film form on the surface of the electrophotographic photosensitive member while repeating a process from charging to cleaning. The phenomenon corresponds to “adhesion wetting” in the wettability.
[0010]
FIG. 4 is a side view illustrating a state of adhesion and wetting. In the adhesion wetting shown in FIG. 4, the relationship between wettability and surface free energy (γ) is expressed by Young's equation (1).
γ₁= Γ₂・ Cos θ + γ₁₂                              … (1)
Where γ₁： Surface free energy of material 1 surface
γ₂： Surface free energy of material 2 surface
γ₁₂： Interface free energy between substance 1 and substance 2
θ: contact angle of substance 2 with substance 1
[0011]
From equation (1), it can be seen from the equation (1) that reducing the wettability of the substance 2 with respect to the substance 1, that is, increasing the θ to make the substance less wet, requires the interface free energy γ related to the wetting work between the electrophotographic photosensitive member and the foreign matter.₁₂And the surface free energy γ₁And γ₂Is achieved by reducing
[0012]
In the formula (1), when considering the adhesion of the toner to the surface of the electrophotographic photosensitive member, the substance 1 may be the electrophotographic photosensitive member and the substance 2 may be the toner. Therefore, when cleaning the actual electrophotographic photosensitive member, the surface free energy γ of the electrophotographic photosensitive member₁, The wettability on the right side of the equation (1), that is, the state of adhesion of the toner to the electrophotographic photosensitive member can be controlled.
[0013]
Therefore, as a conventional technique for defining the surface state of the electrophotographic photosensitive member, there is a technique using a contact angle with pure water (for example, see Patent Document 3). However, as for the wetting between a solid and a liquid, the contact angle θ can be measured as shown in FIG. 4 described above, but in the case of a solid and a solid like an electrophotographic photosensitive member and a toner, , The contact angle θ cannot be measured. Therefore, the above-mentioned prior art can be applied to the wettability between the surface of the electrophotographic photoreceptor and pure water, but cannot sufficiently explain the relationship between the wettability of the toner with respect to solids and the cleaning property.
[0014]
Wettability between solids can be represented by the interfacial free energy between the solids. Regarding the interfacial free energy between a solid and a solid, it is said that Forkes's theory describing nonpolar intermolecular forces can be further extended to components due to polar or hydrogen-bonded intermolecular forces (Non-Patent Document) 1). According to the extended Forkes theory, the surface free energy of each substance is obtained by two or three components. The surface free energy in the case of the adhesion wetting corresponding to the toner on the surface of the electrophotographic photosensitive member can be obtained by three components.
[0015]
The surface free energy between solid substances will be described below. In the extended Forkes theory, it is assumed that the addition rule of the surface free energy shown in Expression (2) holds.
γ = γ^d+ Γ^p+ Γ^h                                    … (2)
Where γ^d： Dipole component (wetting by polarity)
γ^p: Dispersion component (non-polar wetting)
γ^h: Hydrogen bond component (wetting by hydrogen bond)
[0016]
When the addition rule of equation (2) is applied to the Forkes theory, the interface free energy γ between substance 1 and substance 2 which are both solids₁₂Is obtained as in Expression (3).

Where γ₁: Surface free energy of substance 1
γ₂: Surface free energy of substance 2
γ₁ ^d, Γ₂ ^d： Dipole components of substance 1 and substance 2
γ₁ ^p, Γ₂ ^p: Dispersion component of substance 1 and substance 2
γ₁ ^h, Γ₂ ^h： Hydrogen bonding component of substance 1 and substance 2
[0017]
In the solid substance to be measured, the surface free energy (γ^d, Γ^p, Γ^h) Can be calculated by using a reagent whose surface free energy of each component is known, and measuring the adhesion to the reagent. Therefore, for each of the substance 1 and the substance 2, the surface free energy of each component can be obtained, and further, the interface free energy between the substance 1 and the substance 2 can be obtained from the surface free energy of each component by the equation (3).
[0018]
Based on the concept of the interfacial free energy between the solids determined in this way, the surface free energy (γ) of the electrophotographic photoreceptor in which the photoconductive layer is made of amorphous Si is 35 to 65 mN / m. Alternatively, improvement of the cleaning property and durability of an electrophotographic photoreceptor by regulating the density to 35 to 55 mN / m has been disclosed as a conventional technique (for example, see Patent Documents 4 and 5).
[0019]
Also, for an electrophotographic photoreceptor in which the photoconductive layer is made of an organic photosensitive material, the surface free energy is specified in the range of 35 to 65 mN / m, so that the cleaning property of the electrophotographic photoreceptor surface is improved and a long life is achieved. It is disclosed as a conventional technology that the realization is realized (see Patent Document 6).
[0020]
However, according to a study by the present inventors, it has been found that an electrophotographic photosensitive member having a surface free energy (γ) of 35 to 65 mN / m, which is a range disclosed in the related art, is used for, for example, a recording paper. When an actual photographing performance test was performed to form an image on the surface of the electrophotographic photosensitive member, it was confirmed that a scratch was considered to be caused on the surface of the electrophotographic photosensitive member due to contact with foreign matter such as paper dust. In addition, it was confirmed that black streaks were generated on the image transferred to the recording paper due to cleaning failure caused by the scratch.
[0021]
Further, in the prior art disclosed in Patent Document 6, although the amount of change in surface free energy (Δγ) associated with the durability of the electrophotographic photosensitive member is specified, the initial characteristics of the electrophotographic photosensitive member, such as surface free energy (Δγ), are defined. Considering that the amount of change Δγ cannot be determined by defining γ) and that the amount of change Δγ changes depending on various conditions such as the environment during image formation and the material of the transfer material, In the design of the electrophotographic photosensitive member, there is a problem that the variation Δγ includes an uncertain element in many cases and is not suitable as a design standard.
[0022]
[Patent Document 1]
JP 2001-249474 A
[Patent Document 2]
JP-A-4-9066
[Patent Document 3]
JP-A-60-22131
[Non-patent document 1]
Kitazaki, Y. and Hata, T .; "Expansion of Forkes equation and evaluation of surface tension of polymer solid", Journal of the Adhesion Society of Japan, Adhesion Society of Japan, 1972, Vol. 8, No. 3, p. 131-141
[Patent Document 4]
JP 2002-131957 A
[Patent Document 5]
JP 2002-229234 A
[Patent Document 6]
JP-A-11-31875
[0023]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic photosensitive member capable of forming a high-quality image even when used for a long period of time by defining a range of hardness and surface free energy of a photosensitive layer, thereby being excellent in cleaning property and durability. An object of the present invention is to provide a body and an image forming apparatus including the body.
[0024]
[Means for Solving the Problems]
The present invention provides an electrophotographic photosensitive member including a conductive support and a photosensitive layer provided on the conductive support,
Electrophotography wherein the hardness of the photosensitive layer is 20 or more in Vickers hardness, and the surface free energy (γ) of the surface of the photosensitive layer is 28 mN / m or more and 35 mN / m or less. It is a photoconductor.
[0025]
According to the present invention, the electrophotographic photosensitive member is set so that the hardness of the photosensitive layer is 20 or more in Vickers hardness and the surface free energy of the surface of the photosensitive layer is 28 mN / m or more and 35 mN / m or less. Is done. The Vickers hardness referred to here is specified in Japanese Industrial Standard (JIS) Z2244. By setting the hardness of the photosensitive layer in the electrophotographic photoreceptor to a range of 20 or more in terms of Vickers hardness, the photosensitive layer of the electrophotographic photoreceptor has sufficient mechanical strength. It is possible to develop a sufficient durable life against mechanical wear.
[0026]
Further, the surface free energy of the photosensitive layer of the electrophotographic photosensitive member is calculated and derived according to Forkes's extended theory. The surface free energy of the photosensitive layer of the electrophotographic photosensitive member is an index of the wettability of, for example, toner or paper powder, that is, the adhesion to the surface of the electrophotographic photosensitive member. By setting the surface free energy in the above-described preferred range, excessive adhesive force is suppressed despite developing an adhesive force necessary for development, especially for toner, and foreign matter such as paper dust Therefore, excessive toner and foreign matter can be easily removed from the surface of the electrophotographic photosensitive member. Thus, the cleaning performance can be improved without lowering the developing performance.
[0027]
Therefore, an electrophotographic photoreceptor having a surface having sufficient hardness and excellent abrasion resistance, and having excellent cleaning performance in which foreign matter is not easily attached to the surface and foreign matter is easily detached from the surface is realized. Such an electrophotographic photoreceptor has a long durable life and does not cause quality deterioration in a formed image stably for a long time.
[0028]
Further, the invention is characterized in that the photosensitive layer of the electrophotographic photosensitive member is formed by laminating a charge generation layer containing a charge generation substance and a charge transport layer containing a charge transport substance.
[0029]
According to the present invention, the photosensitive layer of the electrophotographic photoreceptor is configured by laminating a charge generation layer containing a charge generation substance and a charge transport layer containing a charge transport substance. By making the photosensitive layer a type in which a plurality of layers are laminated, the degree of freedom of the materials constituting each layer and the combination thereof is increased, so that the surface free energy value of the electrophotographic photosensitive member surface is set to a desired range. It becomes easier.
[0030]
According to another aspect of the invention, there is provided an image forming apparatus including any one of the electrophotographic photosensitive members.
[0031]
According to the present invention, the image forming apparatus is provided with an electrophotographic photosensitive member having excellent cleaning performance and abrasion resistance and a long durable life. Therefore, it is possible to provide an image forming apparatus that can stably form an image without deterioration in image quality over a long period of time and that requires less maintenance.
[0032]
BEST MODE FOR CARRYING OUT THE INVENTION
FIG. 1 is a partial cross-sectional view showing a simplified structure of an electrophotographic photosensitive member 1 according to an embodiment of the present invention. An electrophotographic photoreceptor 1 (hereinafter abbreviated as a photoreceptor) includes a conductive support 3 made of a conductive material, an undercoat layer 4 laminated on the conductive support 3, and an undercoat layer 4 on the undercoat layer 4. The charge generation layer includes a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material and further stacked on the charge generation layer. The charge generation layer 5 and the charge transport layer 6 constitute the photosensitive layer 7.
[0033]
The conductive support 3 has a cylindrical shape, and (a) a metal material such as aluminum, stainless steel, copper, or nickel; and (b) aluminum on a surface of an insulating material such as a polyester film, a phenol resin pipe, or a paper tube. One provided with a conductive layer of copper, palladium, tin oxide, indium oxide, or the like is preferably used and has a volume resistance of 10¹⁰Those having conductivity of Ω · cm or less are preferable. The surface of the conductive support 3 may be oxidized for the purpose of adjusting the volume resistance described above. The conductive support 3 functions as an electrode of the photoconductor 1 and also functions as a support member for the other layers 4, 5, and 6. The shape of the conductive support 3 is not limited to a cylindrical shape, but may be any one of a plate shape, a film shape, and a belt shape.
[0034]
The undercoat layer 4 is formed of, for example, polyamide, polyurethane, cellulose, nitrocellulose, polyvinyl alcohol, polyvinylpyrrolidone, polyacrylamide, anodized aluminum film, gelatin, starch, casein, N-methoxymethylated nylon, or the like. Further, particles such as titanium oxide, tin oxide, and aluminum oxide may be dispersed in the undercoat layer 4. The undercoat layer 4 has a thickness of about 0.1 to 10 μm. The undercoat layer 4 functions as an adhesive layer between the conductive support 3 and the photosensitive layer 7 and also functions as a barrier layer that suppresses charge from flowing from the conductive support 3 into the photosensitive layer 7. I do. As described above, the undercoat layer 4 acts to maintain the charging characteristics of the photoconductor 1, so that the life of the photoconductor 1 can be extended.
[0035]
The charge generation layer 5 can include a known charge generation substance. As the charge generating substance, any of inorganic pigments, organic pigments, and organic dyes can be used as long as they absorb visible light and generate free charges. Inorganic pigments include selenium and its alloys, arsenic-selenium, cadmium sulfide, zinc oxide, amorphous silicon, and other inorganic photoconductors. Examples of the organic pigment include a phthalocyanine compound, an azo compound, a quinacridone compound, a polycyclic quinone compound, and a perylene compound. Examples of the organic dye include a thiapyrylium salt and a squarylium salt. Among the above-described charge generating substances, a phthalocyanine-based compound is suitably used, and particularly, a titanyl phthalocyanine compound is optimally used, and good sensitivity characteristics, charging characteristics, and reproducibility can be obtained.
[0036]
In addition to the above-mentioned pigments and dyes, a chemical sensitizer or an optical sensitizer may be added to the charge generation layer 5. Examples of the chemical sensitizer include electron accepting substances such as cyano compounds such as tetracyanoethylene and 7,7,8,8-tetracyanoquinodimethane, quinones such as anthraquinone and p-benzoquinone, and 2,4,7. And nitro compounds such as trinitrofluorenone and 2,4,5,7-tetranitrofluorenone. Examples of the optical sensitizer include dyes such as xanthene dyes, thiazine dyes, and triphenylmethane dyes.
[0037]
The charge generation layer 5 is formed by dispersing the above-described charge generation substance together with a binder resin in a suitable solvent, laminating the undercoat layer 4, drying or curing the film. Specific examples of the binder resin include polyarylate, polyvinyl butyral, polycarbonate, polyester, polystyrene, polyvinyl chloride, phenoxy resin, epoxy resin, silicone, and polyacrylate. Examples of the solvent include isopropyl alcohol, cyclohexanone, cyclohexane, toluene, xylene, acetone, methyl ethyl ketone, tetrahydrofuran, dioxane, dioxolan, ethyl cellosolve, ethyl acetate, methyl acetate, dichloromethane, dichloroethane, monochlorobenzene, ethylene glycol dimethyl ether, and the like.
[0038]
The solvent is not limited to those described above, and may be any one selected from alcohol, ketone, amide, ester, ether, hydrocarbon, chlorinated hydrocarbon, and aromatic. May be used alone or as a mixture. However, in consideration of a decrease in sensitivity due to crystal transition during milling and milling of the charge generating material, and a decrease in characteristics due to pot life, cyclohexanone, 1,2-dimethoxyethane, methyl ethyl ketone, which hardly causes crystal transition in inorganic or organic pigments, It is preferable to use any of tetrahydroquinone.
[0039]
For forming the charge generation layer 5, a vapor deposition method such as a vacuum evaporation method, a sputtering method, and a CVD method, a coating method, and the like can be applied. When using the coating method, the charge generating substance is pulverized by a ball mill, a sand grinder, a paint shaker, an ultrasonic disperser or the like and dispersed in a solvent, and a coating liquid to which a binder resin is added if necessary is applied by a known coating method. Is applied on the undercoat layer 4. When the conductive support 3 on which the undercoat layer 4 is formed is cylindrical, a spraying method, a vertical ring method, a dip coating method, or the like can be used as a coating method. The thickness of the charge generation layer 5 is preferably about 0.05 to 5 μm, and more preferably about 0.1 to 1 μm.
[0040]
When the conductive support 3 on which the undercoat layer 4 is formed is a sheet, an applicator, a bar coater, casting, spin coating, or the like can be used as a coating method.
[0041]
The charge transport layer 6 can include a known charge transport substance and a binder resin. Any material can be used as long as it has the ability to accept charges generated by the charge generation material contained in the charge generation layer 5 and transport the charges. Examples of the charge transport material include poly-N-vinylcarbazole and its derivatives, poly-g-carbazolylethylglutamate and its derivatives, polyvinylpyrene, polyvinylphenanthrene, oxazole derivatives, oxadiazole derivatives, imidazole derivatives, and 9- ( (p-Diethylaminostyryl) anthracene, 1,1-bis (4-dibenzylaminophenyl) propane, styrylanthracene, styrylpyrazoline, pyrazoline derivative, phenylhydrazone, hydrazone derivative, triphenylamine-based compound, tetraphenyldiamine-based compound And stilbene-based compounds, and azine compounds having a 3-methyl-2-benzothiazoline ring.
[0042]
The binder resin constituting the charge transport layer 6 may be any resin that is compatible with the charge transport material. Examples thereof include polycarbonate and copolymerized polycarbonate, polyarylate, polyvinyl butyral, polyamide, polyester, epoxy resin, polyurethane, Examples thereof include polyketone, polyvinyl ketone, polystyrene, polyacrylamide, phenol resin, phenoxy resin, polysulfone resin, and copolymer resins thereof. These resins may be used alone or in combination of two or more. Among the binder resins described above, resins such as polystyrene, polycarbonate and copolycarbonate, polyarylate, and polyester are 10%.^ThirteenIt has a volume resistivity of Ω or more and is excellent in film-forming properties and potential characteristics.
[0043]
Solvents that dissolve these materials include alcohols such as methanol and ethanol, ketones such as acetone, methyl ethyl ketone and cyclohexanone, ethers such as ethyl ether, tetrahydrofuran, dioxane and dioxolan, and aliphatics such as chloroform, dichloromethane and dichloroethane. Halogenated hydrocarbons, benzene, aromatics such as chlorobenzene and toluene can be used.
[0044]
The coating solution for the charge transport layer for forming the charge transport layer 6 is prepared by dissolving a charge transport material in a binder resin solution. The proportion of the charge transport material in the charge transport layer 6 is preferably in the range of 30 to 80% by weight. The formation of the charge transport layer 6 on the charge generation layer 5 is performed in the same manner as the formation of the charge generation layer 5 on the undercoat layer 4 described above. The thickness of the charge transport layer 6 is preferably from 10 to 50 μm, and more preferably from 15 to 40 μm.
[0045]
The charge transport layer 6 may contain one or more kinds of electron-accepting substances or dyes so as to improve sensitivity and suppress an increase in residual potential and fatigue during repeated use. Examples of the electron accepting substance include acid anhydrides such as succinic anhydride, maleic anhydride, phthalic anhydride, and 4-chloronaphthalic anhydride; cyano compounds such as tetracyanoethylene and terephthalmalondinitrile; 4-nitrobenzaldehyde; Aldehydes, anthraquinones, anthraquinones such as 1-nitroanthraquinone, and polycyclic or heterocyclic nitro compounds such as 2,4,7-trinitrofluorenone and 2,4,5,7-tetranitrofluorenone. Can be used as a chemical sensitizer.
[0046]
Examples of the dye include an organic photoconductive compound such as a xanthene dye, a thiazine dye, a triphenylmethane dye, a quinoline pigment, and copper phthalocyanine, and these can be used as an optical sensitizer.
[0047]
Further, the charge transport layer 6 may contain a known plasticizer to improve moldability, flexibility, and mechanical strength. Examples of the plasticizer include dibasic acid esters, fatty acid esters, phosphoric acid esters, phthalic acid esters, chlorinated paraffins, and epoxy-type plasticizers. In addition, the photosensitive layer 7 may have a leveling agent such as polysiloxane for preventing yuzu skin, if necessary, and an antioxidant such as a phenol compound, a hydroquinone compound, a tocopherol compound or an amine compound for improving durability. , An ultraviolet absorber or the like.
[0048]
The hardness of the photosensitive layer 7 of the photosensitive member 1 configured as described above is controlled and set so as to be 20 or more in Vickers hardness (measured load: 30 mN) specified in JIS-Z2244, and the surface of the photosensitive layer 7 Is controlled and set so that the value calculated by the extended Forkes theory becomes 28 mN / m or more and 35 mN / m or less.
[0049]
If the Vickers hardness is less than 20, the photosensitive layer 7 is markedly formed by rubbing with a cleaning blade pressed against the surface of the photoreceptor 1 and mechanical polishing by the cleaning blade and the residue on the surface of the photoreceptor 1. As a result, the life of the photoconductor 1 becomes extremely short. Therefore, the Vickers hardness was set to 20 or more. The Vickers hardness of the photosensitive layer 7 of the photosensitive member 1 is preferably 35 or less. If the Vickers hardness of the photosensitive layer 7 exceeds 35, the problem of brittleness appears.
[0050]
On the other hand, if the surface free energy exceeds 35 mN / m, the adhesion of toner and paper powder to the surface of the photoreceptor is increased, so that the cleaning property is deteriorated. When the surface free energy is less than 28 mN / m, the adhesive force between the toner and the surface of the photoconductor 1 is reduced, so that the toner scatters into the apparatus and the fine powder toner adhering to a portion other than the toner image portion on the photoconductor 1 is removed. Image fog occurs due to transfer to recording paper. Therefore, the surface free energy is preferably from 28 to 35 mN / m.
[0051]
The control setting of the Vickers hardness of the photosensitive layer 7 to the above-mentioned range can be realized by using a resin having a high hardness as the binder resin contained in the photosensitive layer 7 or using a higher molecular weight resin. It can also be realized by crosslinking the binder resin of the photosensitive layer 7.
[0052]
The control setting of the surface free energy of the photosensitive layer 7 to the above-mentioned range is performed as follows. A material having a relatively low surface free energy value, such as a fluorine-based material such as polytetrafluoroethylene (abbreviated as PTFE) or a polysiloxane-based material, is introduced into the photosensitive layer 7 and the content thereof is adjusted. it can. It can also be realized by changing the types of the charge generating substance, the charge transporting substance and the binder resin contained in the photosensitive layer 7 and the composition ratio thereof. It can also be realized by adjusting the drying temperature when forming the photosensitive layer 7.
[0053]
The surface free energy of the surface of the photoreceptor 1 controlled and set as described above uses a reagent whose dipole component, dispersion component and hydrogen bonding component of the surface free energy are known as described above, and adheres to the reagent. It is determined by measuring gender. Specifically, using pure water, methylene iodide, and α-bromonaphthalene as reagents, and using a contact angle meter CA-X (trade name; manufactured by Kyowa Interface Co., Ltd.), the contact angle with respect to the surface of the photoreceptor 2 is determined. The surface free energy of each component can be calculated using the surface free energy analysis software EG-11 (trade name; manufactured by Kyowa Interface Co., Ltd.) based on the measurement results. The reagent is not limited to the above-described pure water, methylene iodide, and α-bromonaphthalene, and a reagent having an appropriate combination of a dipole component, a dispersion component, and a hydrogen bonding component may be used. Also, the measurement method is not limited to the above-described method, and for example, the Wilhelmy method (hanging plate method), the de Nui method, or the like may be used.
[0054]
Hereinafter, the operation of forming an electrostatic latent image on the photoconductor 1 will be briefly described. The photosensitive layer 7 formed on the photoreceptor 1 is, for example, uniformly and negatively charged by a charger or the like. When the charge generation layer 5 is irradiated with light having an absorption wavelength in the charged state, the charge generation layer 5 is charged. Electron and hole charges are generated therein. The holes are transferred to the surface of the photoreceptor 1 by the charge transporting material contained in the charge transporting layer 6 to neutralize the negative charges on the surface, and the electrons in the charge generating layer 5 are converted into conductive supports on which the positive charges are induced. It moves to the side of the body 3 and neutralizes the positive charge. As described above, in the photosensitive layer 7, an electrostatic latent image is formed due to a difference between the charge amount of the exposed portion and the charge amount of the unexposed portion.
[0055]
FIG. 2 is a partial cross-sectional view showing a simplified configuration of a photoconductor 8 according to a second embodiment of the present invention. The photoconductor 8 of the present embodiment is similar to the photoconductor 1 of the first embodiment, and the corresponding portions are denoted by the same reference numerals and description thereof will be omitted. It should be noted that the photosensitive layer 8 has a single-layer photosensitive layer 9 formed on the conductive support 3.
[0056]
The photosensitive layer 9 is formed using the same charge generation substance, charge transport substance, binder resin, and the like as those used for the photoconductor 1 of the first embodiment. Using a coating solution for a photosensitive layer prepared by dispersing a charge generating substance and a charge transporting substance in a binder resin, or dispersing a charge generating substance in the form of pigment particles in a binder resin containing the charge transporting substance. A single-layer photosensitive layer is formed on the conductive support 3 by the same method as that for forming the charge generation layer 5 in the photosensitive member 1 of the first embodiment. The single-layer type photoreceptor 8 of the present embodiment is suitable as a photoreceptor for a positively-charged image forming apparatus that generates less ozone, and has only one photosensitive layer 9 to be applied. The yield is superior to that of the stacked type in which the charge generation layer and the charge transport layer are stacked.
[0057]
FIG. 3 is an arrangement side view showing a simplified configuration of an image forming apparatus 2 according to another embodiment of the present invention. The image forming apparatus 2 includes the photoconductor 1 according to the first embodiment. Note that the image forming apparatus of the present invention may be configured to include the photoconductor 8 of the second embodiment.
[0058]
The configuration and image forming operation of the image forming apparatus 2 including the photoconductor 1 will be described with reference to FIG. The image forming apparatus 2 exemplified as the present embodiment is a digital copying machine 2.
[0059]
The digital copying machine 2 has a configuration including a scanner unit 11 and a laser recording unit 12. The scanner unit 11 includes a document table 13 made of transparent glass, a double-sided automatic document feeder (RADF) 14 for automatically feeding and transporting the document onto the document table 13, and a document table 13 mounted on the document table 13. And a scanner unit 15 which is a document image reading unit for scanning and reading an image of a placed document. The document image read by the scanner unit 11 is sent to the image data input unit as image data, and predetermined image processing is performed on the image data. The RADF 14 is a device for setting a plurality of documents at a time on a document tray provided in the RADF 14 and automatically feeding the set documents one by one onto the document table 13.
[0060]
The scanner unit 15 includes a lamp reflector assembly 16 that exposes the surface of the original, and a first reflection mirror 17 that reflects the reflected light from the original in order to guide a reflected light image from the original to a photoelectric conversion element (CCD) 23. A first scanning unit 18 mounted thereon, a second scanning unit 21 mounted with second and third reflecting mirrors 19 and 20 for guiding a reflected light image from the first reflecting mirror 17 to the CCD 23, and a reflected light from a document. The configuration includes an optical lens 22 for forming an image on a CCD 23 that converts an image into an electric image signal via the above-described reflection mirrors 17, 19, and 20, and the CCD 23.
[0061]
The scanner unit 11 sequentially feeds and places the documents to be read on the document table 13 by moving the scanner unit 15 along the lower surface of the document table 13 by the related operation of the RADF 14 and the scanner unit 15. It is configured to read a document image. The first scanning unit 18 scans the original image at a constant speed V along the original mounting table 13 in the reading direction of the original image (right to left as viewed in FIG. 3), and the second scanning unit 21 Are scanned in parallel in the same direction at a speed of 1/2 (V / 2). By the operation of the first and second scanning units 18 and 21, the image of the document placed on the document table 13 can be sequentially formed on the CCD 23 line by line to read the image.
[0062]
The image data obtained by reading the original image by the scanner unit 15 is temporarily stored in a memory after being subjected to various image processing, and the image in the memory is read out according to an output instruction and transferred to the laser recording unit 12. To form an image on recording paper as a recording medium.
[0063]
The laser recording unit 12 includes a recording paper transport system 33, a laser writing unit 26, and an electrophotographic processing unit 27 for forming an image. The laser writing unit 26 is a semiconductor laser that emits a laser beam in accordance with image data read from the memory after being read by the above-described scanner unit 15 and stored in the memory, or image data transferred from an external device. A light source, a polygon mirror that deflects the laser light at an equal angular velocity, and an f-θ lens that corrects the laser light deflected at an equal angular velocity on the photoreceptor 1 provided in the electrophotographic process unit 27 so as to be deflected at an equal angular velocity. Including.
[0064]
The electrophotographic process unit 27 includes a charger 28, a developing unit 29, a transfer unit 30, and a cleaning unit 31 around the photoconductor 1 from the upstream side to the downstream side in the rotation direction of the photoconductor 1 indicated by an arrow 32. Be prepared in this order towards you. As described above, the photoreceptor 1 is uniformly charged by the charger 28, and is exposed by the laser beam corresponding to the document image data emitted from the laser writing unit 26 in the charged state. The electrostatic latent image formed on the surface of the photoconductor 1 by being exposed is developed by the toner supplied from the developing device 29, and becomes a visible toner image. The toner image formed on the surface of the photoconductor 1 is transferred by a transfer unit 30 onto a recording sheet supplied by a transport system 33 described later.
[0065]
At this time, since the surface free energy of the surface of the photoreceptor 1 is set in a suitable range, the toner for forming the toner image is easily transferred and transferred from the surface of the photoreceptor 1 onto the recording paper to generate residual toner. It is also difficult for paper powder or the like of recording paper that comes into contact during transfer to adhere to the surface of the photoconductor 1. Therefore, the polishing ability of the cleaning blade 31a of the cleaning device 31 provided for cleaning the surface of the photoreceptor 1 after the transfer can be set weakly, and the contact pressure of the cleaning blade 31a on the surface of the photoreceptor 1 can be set small. can do. Further, since the surface of the photoreceptor 1 is kept free of toner and foreign matter and is always kept in a clean state, it is possible to stably form an image having good image quality for a long period of time. Further, since the Vickers hardness of the photosensitive layer 7 of the photosensitive member 1 is set in a suitable range, abrasion by the cleaning blade 31a and abrasion due to mechanical polishing of the cleaning blade 31a and the residue are suppressed. 1 is extended.
[0066]
The recording paper transport system 33 is fed from the cassette 34 by the cassette 34 for accommodating the recording paper P, the paper feeding unit 35 for separating and feeding the recording paper P in the cassette 34 one by one, and the paper feeding unit 35. And a plurality of transport rollers 36 for transporting the recording paper P to a predetermined position in the transport system 33. A fixing device 37 is provided downstream of the transfer device 30 in the transport direction of the recording paper P.
[0067]
The recording paper onto which the toner image has been transferred by the transfer device 30 is conveyed to a fixing device 37 by a conveyance system 33, and the toner image is fixed by the fixing device 37. The recording sheet on which the toner image has been fixed is discharged to a discharge cassette 38 by the conveying roller 36, and a series of image forming operations in the digital copying machine 2 is completed.
[0068]
As described above, the digital copying machine 2 is provided with the photosensitive member 1 which does not excessively adhere to the toner, hardly adheres foreign matter, and has excellent cleaning properties which can be easily cleaned by the cleaning device 31. It is possible to stably form an image without deterioration in image quality over a long period of time, and to provide a low-cost and low-maintenance apparatus because the life of the photosensitive member 1 is long and the cleaning device 31 is simple. Is done.
[0069]
(Example)
Hereinafter, embodiments of the present invention will be described. The present invention is not limited to the embodiments described below.
[0070]
First, photosensitive members prepared by forming photosensitive layers on an aluminum conductive support having a diameter of 30 mm and a length of 326.3 mm under various conditions and prepared as examples and comparative examples will be described. In the examples, Vickers hardness is abbreviated as HV and surface free energy is abbreviated as γ.
[0071]
(S1 to S3 photoreceptors of Examples)
(S1 photoreceptor)
7 parts by weight of titanium oxide (TTO55A: manufactured by Ishihara Sangyo) and 13 parts by weight of copolymerized nylon (CM8000: manufactured by Toray Industries, Inc.) were added to a mixed solvent of 159 parts by weight of methyl alcohol and 106 parts by weight of 1,3-dioxolane, The coating solution for the undercoat layer was prepared by performing a dispersion treatment with a paint shaker for 8 hours. This coating solution was filled in a coating tank, and the conductive support was dipped and pulled up, followed by natural drying to form an undercoat layer having a thickness of 1 μm.
[0072]
3 parts by weight of oxotitanyl phthalocyanine and 2 parts by weight of a butyral resin (BL-1 manufactured by Sekisui Chemical Co., Ltd.) were mixed with 245 parts by weight of methyl ethyl ketone, and dispersed by a paint shaker to prepare a coating solution for a charge generation layer. This coating solution was applied onto the undercoat layer by the same dip coating method as in the case of the undercoat layer, and was naturally dried to form a 0.4 μm-thick charge generation layer.
[0073]
5 parts by weight of an enamine compound represented by the following structural formula (I), 5 parts by weight of a polycarbonate resin (G400: manufactured by Idemitsu Kosan Co., Ltd.), and 5 parts by weight of a polycarbonate resin (GH503: manufactured by Idemitsu Kosan Co., Ltd.) And 0.05 parts by weight of SUMILIZER BHT (manufactured by Sumitomo Chemical Co., Ltd.), and 47 parts by weight of tetrahydrofuran as a solvent to prepare a coating solution for a charge transport layer. This coating solution was applied on the above-described charge generation layer by a dip coating method, and dried at 130 ° C. for 1 hour to form a charge transport layer having a thickness of 28 μm. Thus, an S1 photoreceptor was manufactured.
[0074]
Embedded image

[0075]
(S2 photoreceptor)
An undercoat layer and a charge generation layer were formed in the same manner as the S1 photoreceptor. Next, 5 parts by weight of a butadiene compound represented by the following structural formula (II) as a charge transport material, four types of polycarbonate resins, 2.4 parts by weight of J500 (manufactured by Idemitsu Kosan Co., Ltd.), and G400 (manufactured by Idemitsu Kosan Co., Ltd.) 1.6 parts by weight, 1.6 parts by weight of GH503 (manufactured by Idemitsu Kosan Co., Ltd.), 2.4 parts by weight of TS2020 (manufactured by Teijin Chemicals Limited), and 0.25 part by weight of Sumilizer BHT (manufactured by Sumitomo Chemical Co., Ltd.) The mixture was mixed to prepare a charge transport layer coating solution using 49 parts by weight of tetrahydrofuran as a solvent. This coating solution was applied onto the charge generation layer by a dip coating method, and dried at 130 ° C. for 1 hour to form a charge transport layer having a thickness of 28 μm. Thus, an S2 photoreceptor was manufactured.
[0076]
Embedded image

[0077]
(S3 photoreceptor)
An undercoat layer and a charge generation layer were formed in the same manner as the S1 photoreceptor. Next, 3.5 parts by weight of a butadiene compound represented by the structural formula (II), 1.5 parts by weight of a styryl compound represented by the following structural formula (III) as a charge transporting substance, four kinds of polycarbonate resins, J500 2.2 parts by weight (made by Idemitsu Kosan Co., Ltd.), 2.2 parts by weight of G400 (made by Idemitsu Kosan Co., Ltd.), 1.8 parts by weight of GH503 (made by Idemitsu Kosan Co., Ltd.), TS2020 (manufactured by Teijin Chemicals Ltd.) 1 0.8 part by weight and 1.5 parts by weight of Sumilizer BHT (manufactured by Sumitomo Chemical Co., Ltd.) were mixed, and a coating solution for a charge transport layer was prepared using 55 parts by weight of tetrahydrofuran as a solvent. This coating solution was applied on the charge generation layer by a dip coating method, and dried at 120 ° C. for 1 hour to form a charge transport layer having a thickness of 28 μm. Thus, an S3 photoreceptor was manufactured.
[0078]
Embedded image

[0079]
(R1 to R3 photoconductors of comparative examples)
(R1 photoreceptor)
An undercoat layer and a charge generation layer were formed in the same manner as the S1 photoreceptor. Next, a coating solution was prepared in the same manner as the S1 photoreceptor except that PTFE, which is a low γ resin, was used instead of a part of the polycarbonate resin when forming the charge transport layer. This coating solution was applied on the charge generation layer by a dip coating method, and dried at 120 ° C. for 1 hour to form a charge transport layer having a thickness of 28 μm. Thus, an R1 photoreceptor was manufactured.
[0080]
(R2 photoreceptor)
An undercoat layer and a charge generation layer were formed in the same manner as the S1 photoreceptor. Next, 5 parts by weight of a butadiene compound represented by the structural formula (II) as a charge transporting substance, three types of polycarbonate resins, 2.4 parts by weight of G400 (manufactured by Idemitsu Kosan Co., Ltd.), and TS2020 (manufactured by Teijin Chemicals Limited) 4 parts by weight, 1.6 parts by weight of Vylon 290 (manufactured by Toyobo Co., Ltd.) and 0.25 parts by weight of Sumilizer BHT (manufactured by Sumitomo Chemical Co., Ltd.) were mixed, and 49 parts by weight of tetrahydrofuran was used as a solvent to prepare a coating solution for a charge transport layer. It was adjusted. This coating solution was applied on the charge generation layer by a dip coating method, and dried at 130 ° C. for 1 hour to form a charge transport layer having a thickness of 28 μm. Thus, an R2 photoreceptor was produced.
[0081]
(R3 photoreceptor)
An undercoat layer and a charge generation layer were formed in the same manner as the S1 photoreceptor. Next, a coating solution was prepared in the same manner as in the case of the R2 photoreceptor except that 8 parts by weight of G400 (manufactured by Idemitsu Kosan Co., Ltd.) was used as the polycarbonate resin when forming the charge transport layer. This coating solution was applied on the charge generation layer by a dip coating method, and dried at 130 ° C. for 1 hour to form a charge transport layer having a thickness of 28 μm. Thus, an R3 photoreceptor was produced.
[0082]
As described above, in the production of the S1 to S3 photoreceptors and the R1 to R3 photoreceptors, by changing the type and the content ratio of the resin contained in the charge transport layer coating liquid, and by changing the drying temperature after coating, And HV and γ of the photoreceptor surface were adjusted to desired values. The HV of the surface of the photoreceptor is obtained by using a micro hardness measuring instrument H1000C (manufactured by H. FISCHER) and analysis software WIN-HCU (manufactured by H. FISCHER), and the γ of the surface of the photoreceptor is determined by a contact angle measuring machine CA-. X (manufactured by Kyowa Interface Co., Ltd.) and analysis software EG-11 (manufactured by Kyowa Interface Co., Ltd.).
[0083]
By mounting the S1 to S3 photoconductors of the examples and the R1 to R3 photoconductors of the comparative examples on a digital copying machine AR-450 (manufactured by Sharp Corporation) modified for testing, image quality and abrasion resistance were improved. An evaluation test was performed. Next, an evaluation method will be described.
[0084]
[Image quality]
The contact pressure of the cleaning blade of the cleaning device provided in the above-mentioned digital copying machine AR-450 is brought into contact with the photoreceptor, that is, the so-called cleaning blade pressure at an initial linear pressure of 21 gf / cm (2.06 × 10^-1N / cm). In the environment of normal temperature / normal humidity (N / N: Normal Temperature / Normal Humidity) with a temperature of 25 ° C. and a relative humidity of 50%, a white solid image and a black solid image were formed on recording paper using the copying machine. . The obtained solid white image and solid black image were visually observed to evaluate the image quality. Next, under the above conditions, an image having a predetermined pattern was formed on 100,000 sheets of recording paper, and then a white solid image and a black solid image were formed on the recording paper. The obtained solid white image and solid black image were visually observed, and the image quality after forming 100,000 sheets of images was evaluated.
[0085]
The evaluation criteria for image quality are as follows.
：: good. No fogging of black solid images, no black streaks, and no decrease in image density of black solid images.
X: Poor. Many fogs and black streaks occur on the solid white image, or the image density of the solid black image is significantly reduced.
[0086]
[Abrasion resistance]
The film thickness d0 of the photosensitive layer at the time of manufacturing the photoconductor and the film thickness d1 of the photoconductor taken out of the apparatus after forming an image on 100,000 sheets of recording paper in the above-described image quality evaluation test were measured. The difference Δd (= d0−d1), which is the difference in film thickness, was determined. It was evaluated that the smaller the film thickness Δd, the better the abrasion resistance. The film thickness was measured by a film thickness meter MCPD2000 (manufactured by Otsuka Electronics Co., Ltd.).
[0087]
[Evaluation results]
The evaluation results are shown in Table 1. Although the HV is 20 or more within the range of the present invention, and γ is less than 28 outside the range of the present invention, the R1 photoreceptor of Comparative Example has a small film loss Δd, but has a white background after forming 100,000 sheets of an image. Fogging was observed on the resulting image, and the image quality was poor. In addition, it is presumed that dirt due to toner scattering in the image forming apparatus at this time was severe, and this affected fogging.
[0088]
The R2 photoreceptor of the comparative example in which HV is 20 or more within the range of the present invention but γ is more than 35 outside the range of the present invention has a high HV and thus has a small amount of film slip Δd. Many black streaks occurred in the later solid white image, resulting in poor image quality. Since the surface of the photoreceptor has a large γ, that is, an adhesive force, filming of the toner due to defective cleaning of the residual toner has occurred.
[0089]
Although the γ is 28 to 35 mN / m within the range of the present invention, the HV of the comparative example having an HV of less than 20 outside the range of the present invention has an extremely large film reduction amount Δd because the HV of the photosensitive layer is low. . Further, fogging occurred on a white solid image after 100,000 sheets of the image were formed, and a slight decrease in density was observed in the black solid image.
[0090]
On the other hand, the S1 to S3 photoreceptors of Examples in which HV is 20 or more within the range of the present invention and γ is 28 to 35 mN / m within the range of the present invention have a relatively small film reduction amount Δd, and Good image quality could be obtained up to 100,000 sheets after image formation.
[0091]
[Table 1]

[0092]
【The invention's effect】
According to the present invention, the electrophotographic photoreceptor is set so that the hardness of the photosensitive layer is 20 or more in Vickers hardness and the surface free energy of the surface of the photosensitive layer is 28 mN / m or more and 35 mN / m or less. Is done. By setting the hardness of the photosensitive layer in the electrophotographic photoreceptor to a range of 20 or more in terms of Vickers hardness, the photosensitive layer of the electrophotographic photoreceptor has sufficient mechanical strength. It is possible to develop a sufficient durable life against mechanical wear.
[0093]
By setting the surface free energy of the photosensitive layer of the electrophotographic photoreceptor in the above-described preferred range, excessive adhesive force is suppressed even though toner develops an adhesive force necessary for development. In addition, since the adhesion to foreign matter such as paper dust can be suppressed, excess toner and foreign matter are easily removed from the surface of the electrophotographic photosensitive member. Thus, the cleaning performance can be improved without lowering the developing performance.
[0094]
Therefore, an electrophotographic photoreceptor having a surface having sufficient hardness and excellent abrasion resistance, and having excellent cleaning performance in which foreign matter is not easily attached to the surface and foreign matter is easily detached from the surface is realized. Such an electrophotographic photoreceptor has a long durable life and does not cause quality deterioration in a formed image stably for a long time.
[0095]
According to the invention, the photosensitive layer of the electrophotographic photoreceptor is formed by laminating a charge generation layer containing a charge generation substance and a charge transport layer containing a charge transport substance. By making the photosensitive layer a type in which a plurality of layers are laminated, the degree of freedom of the materials constituting each layer and the combination thereof is increased, so that the surface free energy value of the electrophotographic photosensitive member surface is set to a desired range. It becomes easier.
[0096]
Further, according to the present invention, the image forming apparatus is provided with an electrophotographic photoreceptor having excellent cleaning performance and abrasion resistance and a long durable life. Therefore, it is possible to provide an image forming apparatus that can stably form an image without deterioration in image quality over a long period of time and that requires less maintenance.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing a simplified configuration of an electrophotographic photosensitive member 1 according to an embodiment of the present invention.
FIG. 2 is a partial cross-sectional view showing a simplified configuration of a photoconductor 8 according to a second embodiment of the present invention.
FIG. 3 is an arrangement side view showing a simplified configuration of an image forming apparatus 2 according to another embodiment of the present invention.
FIG. 4 is a side view illustrating a state of adhesion and wetting;
[Explanation of symbols]
1,8 photoconductor
2 Image forming apparatus
3 conductive support
4 Undercoat layer
5 charge generation layer
6 charge transport layer
7,9 photosensitive layer
11 Scanner section
12 Laser recording unit
13 Document Placement Table
14 RADF
15 Scanner unit
18 First scanning unit
21 Second scanning unit
22 Optical lens
23 CCD
26 Laser writing unit
27 Electrophotographic Process Department
28 Charger
29 Developer
30 Transfer device
31 Cleaning device
33 Transport system
34 cassettes
35 Paper feed unit
37 Fixing unit
38 paper output cassette

Claims (3)

An electrophotographic photoreceptor comprising a conductive support and a photosensitive layer provided on the conductive support,
Electrophotography wherein the hardness of the photosensitive layer is 20 or more in Vickers hardness, and the surface free energy (γ) of the surface of the photosensitive layer is 28 mN / m or more and 35 mN / m or less. Photoconductor. The photosensitive layer,
2. The electrophotographic photoreceptor according to claim 1, wherein a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material are laminated. An image forming apparatus comprising the electrophotographic photosensitive member according to claim 1.

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