JP4405697B2 - Image forming method, image forming apparatus, and process cartridge - Google Patents

Description

（式中、Ｒ５とＲ６は同一であっても異なっていても良く、各々、直鎖または分岐したアルキル基、アルケニル基、アルコキシル基、ハロゲン原子、ニトロ基、シアノ基、アミノ基、カルボキシル基及び水酸基からなる群から選ばれる置換基を示し、ｍ及びｎは０〜５の整数を示す。）
【００５９】
また中でも、下記一般式（２）で示されるベンジル酸のアルミニウム化合物であることがより好ましい。
【００６０】
【化２】

（式中、Ｒ５とＲ６は同一であっても異なっていても良く、各々、直鎖または分岐したアルキル基、アルケニル基、アルコキシル基、ハロゲン原子、ニトロ基、シアノ基、アミノ基、カルボキシル基及び水酸基からなる群から選ばれる置換基を示し、ｍ及びｎは０〜５の整数を示す。又、Ｙは１価のカチオン、水素、リチウム、ナトリウム、カリウム、アンモニウム及びアルキルアンモニウムを示す。）
【００６１】
またさらにスルホン酸含有アクリルアミドを含有させることも好ましい。例えば、２−アクリルアミドプロパンスルホン酸、２−アクリルアミド−ｎ−ブタンスルホン酸、２−アクリルアミド−ｎ−ヘキサンスルホン酸、２−アクリルアミド−ｎ−オクタンスルホン酸、２−アクリルアミド−ｎ−ドデカンスルホン酸、２−アクリルアミド−ｎ−テトラデカンスルホン酸、２−アクリルアミド−２−メチルプロパンスルホン酸、２−アクリルアミド−２−フェニルプロパンスルホン酸、２−アクリルアミド−２,２,４−トリメチルペンタンスルホン酸、２−アクリルアミド−２−メチルフェニルエタンスルホン酸、２−アクリルアミド−２−（４−クロロフェニル）プロパンスルホン酸、２−アクリルアミド−２−カルボキシメチルプロパンスルホン酸、２−アクリルアミド−２−（２−ピリジル）プロパンスルホン酸、２−アクリルアミド−１−メチルプロパンスルホン酸、３−アクリルアミド−３−メチルブタンスルホン酸、２−メタクリルアミド−ｎ−デカンスルホン酸、２−メタクリルアミド−ｎ−テトラデカンスルホン酸などを挙げることができる。好ましくは２−アクリルアミド−２−メチルプロパンスルホン酸が挙げられる。
【００６２】
樹脂被覆層への負帯電性の物質の添加量は、樹脂被覆層用結着樹脂１００質量部に対して１〜１００質量部とすることが好ましい。１質量部未満では添加による帯電安定性の向上が見られず、１００質量部を超えると樹脂被覆層用結着樹脂中での存在量が過剰となって元の樹脂被覆層用結着樹脂の特性を損ない被覆層強度の低下を招きやすい。
【００６３】
本発明における樹脂被覆層を負帯電性の物質を含有したものとするさらに好ましい手段として、本発明に先駆け、特開平１０−３２６０４０号公報、特開平１１−０５２７１１号公報等において、従来トナーの正帯電性制御剤として知られている第４級アンモニウム塩化合物、すなわち、それ自体が鉄粉に対して正帯電性である第４級アンモニウム塩化合物と、樹脂被覆層用結着樹脂として、特に樹脂被覆層用結着樹脂の一部又は全てが、その分子構造中に、少なくとも−ＮＨ₂基、＝ＮＨ基、−ＮＨ−結合のいずれかを有するものとを用いて現像剤担持体の樹脂被覆層を形成すると、第４級アンモニウム塩化合物が樹脂被覆層用結着樹脂中に取り込まれ、正帯電性トナーに対して樹脂（樹脂被覆層）自身が強いネガ帯電性を示し、良好な帯電付与性を示すことを見出し、これを現像剤担持体として現像装置に用いることで非常に良好な画像が得られる旨の提案を行っている。
【００６４】
この方法の優れた点は、例えば、トナーに帯電を付与するためにシリカ、フッ素樹脂粉末、負帯電性制御剤を樹脂被覆層に添加する前述の系と比較して、樹脂被覆層用結着樹脂の溶媒中に第４級アンモニウム塩化合物が溶け込んで樹脂中に均一に存在させることができるため、樹脂被覆層を形成した場合、樹脂層全体が均一な負帯電性材料となり、シリカ添加系のようにマトリックス的に分散しているものに比較して現像剤担持体全体が均一且つ良好な帯電付与性を示すことと、さらには粉末添加系ではないので、機械的強度すなわち耐久性が良好である点にある。
【００６５】
本発明者らは、これら開示された技術をさらに検討していった結果、負帯電性現像剤を用いる場合において、特に本発明に用いられるような球形〜略球形を有し、さらには表面への磁性粉体などの露出の少ない、過剰な電荷を有しやすい現像剤を用いる場合に、樹脂被覆層に第４級アンモニウム塩化合物を添加することで、現像剤の過剰な電荷の発生を抑制し好適な帯電特性が得られることを見出した。つまり従来トナーの正帯電性制御剤として知られている第４級アンモニウム塩化合物、すなわち、それ自体が鉄粉に対して正帯電性である第４級アンモニウム塩化合物を用い、添加量を適切な量に設定することによって、さらに樹脂被覆層用結着樹脂として、樹脂被覆層用結着樹脂の一部又は全てが、その分子構造中に、−ＮＨ₂基、＝ＮＨ基、−ＮＨ−結合のいずれかを有するものを用いて現像剤担持体の樹脂被覆層を形成することによって、本発明における磁性現像剤に対し、過剰な電荷を有する現像剤の発生や、現像剤担持体表面への現像剤の強固な付着を有効に防止し、摩擦帯電量を好適なレベルに帯電可能であることを見出した。
【００６６】
高転写効率の利点を有する重合法により製造された、本発明におけるトナーの帯電特性を向上させるための検討を行った結果、現像剤担持体の樹脂被覆層を上記構成とすることで、現像剤の帯電量を安定させ、現像ムラやブロッチ、カブリやチャージアップによる画像濃度低下などの発生を防止することができる。
【００６７】
本発明に好適に使用される第４級アンモニウム塩化合物としては、鉄粉に対して正帯電性を有するものが用いられる。例えば、下記一般式３で表される化合物が挙げられる。
【００６８】
【化３】

【００６９】
（式中のＲ１、Ｒ２、Ｒ３、Ｒ４は、各々、置換基を有しても良いアルキル基、置換基を有しても良いアリール基、アルアルキル基を表し、Ｒ１〜４は各々同一でもあるいは異なっていてもよい。Ｘ^-は酸の陰イオンを表す。）
これに対し、例えば下記式４で表されるような、それ自身が鉄粉に対して負帯電性を有する含フッ素４級アンモニム塩化合物についても検討を行ったが、該化合物の添加では本発明の所期の目的が達成されないことがわかった。即ち、下記式４で表される化合物は、電子吸引性の強いフッ素樹脂原子が構造中にあるので、それ自身が鉄粉に対して負帯電性を有するが、本発明の場合と同様に、該化合物を樹脂被覆層用結着樹脂中に分散させた樹脂組成物を用いて樹脂被覆層を形成しても、それ自身が鉄粉に対して正帯電性である第４級アンモニウム塩化合物を含有させたほどには、効果は得られなかった。
【００７０】
【化４】

【００７１】
本発明に好適に用いられる、それ自身が鉄粉に対して正帯電性である第４級アンモニウム塩化合物としては、具体的には、下記一般式５〜式１２のものが挙げられるが、勿論、本発明は、これらに限定されるものではない。
【００７２】
【化５】

【００７３】
【化６】

【００７４】
【化７】

【００７５】
【化８】

【００７６】
【化９】

【００７７】
【化１０】

【００７８】
【化１１】

【００７９】
【化１２】

【００８０】
上記に示したような本発明で使用する第４級アンモニウム塩化合物の添加量は、樹脂被覆層用結着樹脂１００質量部に対して１〜１００質量部とすることが好ましい。１質量部未満では添加による帯電安定性の向上が見られず、１００質量部を超えると樹脂被覆層用結着樹脂中での存在量が過剰となって元の樹脂の特性を損ない被膜強度の低下を招きやすい。
【００８１】
本発明に用いられる現像剤担持体の樹脂被覆層に用いられる樹脂被覆層用結着樹脂は、特に限定されないが、樹脂被覆層用結着樹脂の一部又は全部がその分子構造中に少なくとも−ＮＨ₂基、＝ＮＨ基、もしくは−ＮＨ−結合のいずれかの構造を有していることが好ましい。このような樹脂被覆層用結着樹脂を用いて樹脂被覆層を形成することで、本発明の効果が発揮されやすい。本発明において、現像剤担持体の樹脂被覆層として上記のような構成のものを用いると、樹脂被覆層自身の帯電付与性が変化することについての明確な理由は定かではないが、鉄粉に対して正帯電性である第４級アンモニウム塩化合物及び、−ＮＨ₂基、＝ＮＨ基、もしくは−ＮＨ−結合の少なくとも一つの構造を有している樹脂被覆層用結着樹脂を用いて樹脂被覆層を形成することにより樹脂被覆層用結着樹脂の構造中に第４級アンモニウム塩が取り込まれる。その際、正極性を有する第４級アンモニウム塩の元の構造が失われ、これらを取り込んだ樹脂被覆層用結着樹脂が均一且つ十分な帯電性を有するようになり、帯電の安定化に寄与するためではないかと考えられる。
【００８２】
本発明に用いられる現像剤担持体は樹脂被覆層の体積抵抗を調整する為、被覆層用結着樹脂中に導電性微粉末を分散含有させても良い。このような導電性微粉末としては、個数平均粒径２０μｍ以下が好ましく、１０μｍ以下がより好ましい。被覆層用結着樹脂表面に形成される凹凸を避けるためには、個数平均粒径１μｍ以下の導電性微粉末を用いることがより好ましい。
【００８３】
本発明における導電性微粉末の平均粒径は、ベックマンコールター社製、ＬＳ−２３０型レーザ回折式粒度分布測定装置にリキッドモジュールを取付けて０．０４〜２０００μｍの測定範囲で測定する。測定法としては、純水１０ｍｌに微量の界面活性剤を添加し、これに導電性微粉末の試料１０ｍｇを加え、超音波分散機（超音波ホモジナイザー）にて１０分間分散した後、測定時間９０秒、測定回数１回で測定する。
【００８４】
本発明で使用される導電性微粉末としては、ファーネスブラック、ランプブラック、サーマルブラック、アセチレンブラック、チャンネルブラック等のカーボンブラック；酸化チタン、酸化スズ、酸化亜鉛、酸化モリブデン、チタン酸カリウム、酸化アンチモン及び酸化インジウム等の金属酸化物等；アルミニウム、銅、銀、ニッケル等の金属、グラファイト、金属繊維、炭素繊維等の無機系充填剤等が挙げられる。
【００８５】
上述した樹脂被覆層中の導電性微粉末の添加量としては、被覆層用結着樹脂１００量部に対して１００質量部以下の範囲が好ましい結果を与える。より好ましい添加量は４０質量部である。添加量が１００質量部を越えると被膜強度の低下が起こり易く、また多量の非帯電性粒子の添加は、トナーの帯電量の低下が生じうる。
【００８６】
本発明に用いられる現像剤担持体の樹脂被覆層の構成として、さらに潤滑性物質を樹脂被覆層中に分散させることで、より本発明の効果が促進されるので好ましい。潤滑性物質としては、例えばグラファイト、二硫化モリブデン、窒化硼素、雲母、フッ化グラファイト、銀−セレン化ニオブ、塩化カルシウム−グラファイト、滑石、ステアリン酸亜鉛等の脂肪酸金属塩等が挙げられ、特にグラファイトが被覆層の導電性を損なわないので好ましく用いられる。これらの潤滑性物質は、個数平均粒径が好ましくは０．２〜２０μｍ程度、より好ましくは０．３〜１５μｍのものを使用するのがよい。
【００８７】
本発明における潤滑性物質の平均粒径は、導電性微粉末の粒径測定と同様に、ベックマンコールター社製、ＬＳ−２３０型レーザ回折式粒度分布測定装置にリキッドモジュールを取付けて０．０４〜２０００μｍの測定範囲で測定する。
上記潤滑性物質の添加量としては、被覆層用結着樹脂１００質量部に対して１０〜１２０質量部の範囲で特に好ましい結果を与える。添加量が１２０質量部を越える場合は被覆層強度の低下が生じ易く、また非帯電性の添加物を多量に添加することは、トナーの帯電量の低下が発生する。逆に１０質量部未満では現像剤担持体へのトナー付着防止に対する添加効果を得ることができにくい。
【００８８】
また、現像剤担持体の樹脂被覆層は、前述した添加物質に加えて、球状粒子を樹脂被覆層中に分散させることで、表面粗さを安定化させ、現像剤担持体上の現像剤コート量を最適化することが可能である。該球状粒子は、現像剤担持体の被覆層表面に均一な表面粗度を保持させると同時に、被覆層表面が摩耗した場合でも被覆層の表面粗度の変化が少なく、且つ現像剤汚染や現像剤融着を発生しにくくする効果がある。
【００８９】
本発明に使用される球状粒子としては、個数平均粒径が０．３〜３０μｍ、好ましくは２〜２０μｍである。球状粒子の個数平均粒径が０．３μｍ未満では表面に均一な粗さを付与する効果とそれにより帯電性能を安定化させる効果が少なく、現像剤への迅速且つ均一な帯電が不十分となる。さらに、現像剤の搬送が不安定となることや、被覆層の磨耗による搬送性のさらなる低下で現像剤の帯電不良、現像剤汚染及び現像剤融着が発生し、ゴーストの悪化、画像濃度低下を生じやすくなるため好ましくない。個数平均粒径が３０μｍを越える場合には、被覆層表面の粗さが大きくなり過ぎ、現像剤の搬送量が大きくなり、現像剤規制部での規制が十分に行われにくくなり、現像剤の帯電が十分に行なわれにくくなって画質の低下反転カブリの増加など不具合が起こりやすい。さらには、被覆層の機械的強度が低下し膜の耐久性が低下するため好ましくない。
【００９０】
球状粒子の個数平均粒径は、導電性微粉末の粒径測定と同様に、ベックマンコールター社製、ＬＳ−２３０型レーザ回折式粒度分布測定装置を用いて測定する。
【００９１】
球状粒子は、真密度が３ｇ／ｃｍ³以下、好ましくは２．７ｇ／ｃｍ³以下、より好ましくは０．９〜２．３ｇ／ｃｍ³であることが良い。即ち、球状粒子の真密度が３ｇ／ｃｍ³を越える場合には、被覆層中での球状粒子の分散性が不十分となる為、被覆層表面に均一な粗さを付与しにくくなる。また、塗料の保存安定性が良くないため、ここでも均一表面凹凸を有する摩擦帯電付与部材表面が得にくくなる。球状粒子の真密度が０．９ｇ／ｃｍ³より小さい場合にも、被覆層中での球状粒子の分散性および保存安定性が不十分となる傾向がある。
球状粒子の真密度は、乾式密度計アキュビック１３３０（島津製作所製）を用いて測定する。
【００９２】
本発明に於いて球状粒子における「球状」とは、粒子の長径／短径の比が１．０〜１．５程度を意味しており、本発明において好ましくは、長径／短径の比が１．０〜１．２の粒子を使用することが良い。球状粒子の長径／短径の比が１．５を越える場合には、被覆層表面粗さの不均一化が発生し、トナーの迅速且つ均一な帯電化及び導電性被覆層の強度の点で好ましくない。
【００９３】
本発明に用いられる球状粒子は、公知の球状粒子が使用可能である。例えば、球状の樹脂粒子、球状の金属酸化物粒子、球状の炭素化物粒子などがある。球状の樹脂粒子は、例えば、懸濁重合、分散重合法等により得られるものであり、より少ない添加量で好適な表面粗さが得られ、更に均一な表面形状が得られやすい。この様な球状粒子としては、ポリアクリレート、ポリメタクリレート等のアクリル系樹脂粒子、ナイロン等のポリアミド系樹脂粒子、ポリエチレン、ポリプロピレン等のポリオレフィン系樹脂粒子、シリコン系樹脂粒子、フェノール系樹脂粒子、ポリウレタン系樹脂粒子、スチレン系樹脂粒子、ベンゾグアナミン粒子等が挙げられる。粉砕法により得られた樹脂粒子を熱的にあるいは物理的な球形化処理を行ってから用いてもよい。
【００９４】
球状粒子の表面に無機微粉末を付着させて、あるいは固着させて用いてもよい。この様な無機微粉末としては、ＳｉＯ₂、ＳｒＴｉＯ₃、ＣｅＯ₂、ＣｒＯ、Ａｉ₂Ｏ₃、ＺｎＯ、ＭｇＯの如き酸化物、Ｓｉ₃Ｎ₄等の窒化物、ＳｉＣ等の炭化物、ＣａＳＯ₄、ＢａＳＯ₄、ＣａＣＯ₃等の硫酸塩、炭酸塩等が挙げられる。
【００９５】
球状粒子に付着させる無機微粉末は、カップリング剤により処理して用いても良い。特に結着樹脂との密着性を向上させる目的、あるいは粒子に疎水性を与える等の目的でカップリング剤処理された無機微粉末を付着させた球状粒子を用いることが好ましい。このようなカップリング剤としては、例えば、シランカップリング剤、チタンカップリング剤、ジルコアルミネートカップリング剤等がある。より具体的には、シランカップリング剤としては、ヘキサメチルジシラザン、トリメチルシラン、トリメチルクロルシラン、トリメチルエトキシシラン、ジメチルジクロルシラン、メチルトリクロルシラン、アリルジメチルクロルシラン、アリルフェニルジクロルシラン、ベンジルジメチルクロルシラン、ブロムメチルジメチルクロルシラン、α−クロルエチルトリクロルシラン、β−クロルエチルトリクロルシラン、クロルメチルジメチルクロルシラン、トリオルガノシリルメルカプタン、トリメチルシリルメルカプタン、トリオルガノシリルアクリレート、ビニルジメチルアセトキシシラン、ジメチルジエトキシシラン、ジメチルジメトキシシラン、ジフェニルジエトキシシラン、ヘキサメチルジシロキサン、1,3-ジビニルテトラメチルジシロキサン、1,3-ジフェニルテトラメチルジシロキサン、及び１分子当たり２〜１２個のシロキサン単位を有し、末端に位置する単位にそれぞれ１個宛の硅素原子に結合した水酸基を含有したジメチルポリシロキサン等が挙げられる。
【００９６】
このように球状粒子表面に対してカップリング剤で処理された無機微粉末を付着させることにより、樹脂被覆層中への分散性、樹脂被覆層表面の均一性、樹脂被覆層の耐汚染性、トナーへの帯電付与性、樹脂被覆層の耐磨耗性等を向上させることができる。
【００９７】
また、本発明に使用する球状粒子は導電性であることがより好ましい。即ち、球状粒子に導電性を持たせることによって、その導電性のゆえに粒子表面にチャージが蓄積しにくく、現像剤付着の軽減や現像剤への帯電付与性を向上させることができるからである。本発明において、球状粒子の導電性としては、体積抵抗値が１０⁶Ωｃｍ以下、より好ましくは１０^-3〜１０⁶Ωｃｍの導電性球状粒子であることが好ましい。
【００９８】
本発明において、球状粒子の体積抵抗が１０⁶Ωｃｍを超えると、摩耗によって被覆層表面に露出した球状粒子を核として現像剤の汚染や融着を発生しやすくなるとともに、迅速且つ均一な帯電が行われにくくなるため、好ましくない。
【００９９】
このような導電性球状粒子を得る方法としては、以下に示す様な方法が好ましいが、必ずしもこれらの方法に限定されるものではない。
【０１００】
本発明に使用される特に好ましい導電性球状粒子を得る方法としては、例えば、球状の樹脂粒子やメソカーボンマイクロビーズを焼成して炭素化及び／又は黒鉛化して得た低密度且つ良導電性の球状の炭素化物粒子を得る方法が挙げられる。
そして、球状の樹脂粒子に用いられる樹脂としては、例えば、フェノール樹脂、ナフタレン樹脂、フラン樹脂、キシレン樹脂、ジビニルベンゼン重合体、スチレン−ジビニルベンゼン共重合体、ポリアクリロニトリル等が挙げられる。
【０１０１】
また、メソカーボンマイクロビーズは、通常、中ピッチを加熱焼成していく過程で生成する球状結晶を多量のタール、中油、キノリン等の溶剤で洗浄することによって製造することができる。
【０１０２】
より好ましい導電性球状粒子を得る方法としては、フェノール樹脂、ナフタレン樹脂、フラン樹脂、キシレン樹脂、ジビニルベンゼン重合体、スチレン−ジビニルベンゼン共重合体、ポリアクリロニトリル等の球状の樹脂粒子表面に、メカノケミカル法によってバルクメソフェーズピッチを被覆し、被覆された粒子を酸化性雰囲気化で熱処理した後に不活性雰囲気下又は真空下で焼成して炭素化及び／又は黒鉛化し、導電性球状の炭素化物粒子を得る方法が挙げられる。この方法で得られる球状の炭素化物粒子は、黒鉛化して得られる球状の炭素化物粒子の被覆部の結晶化が進んだものとなるので導電性が向上し、より好ましい。
【０１０３】
上記した方法で得られる導電性球状の炭素化物粒子は、いずれの方法でも、焼成条件を変化させることによって得られる球状の炭素化物粒子の導電性を制御することが可能であり、本発明において好ましく使用される。又、上記の方法で得られる球状炭素粒子は、場合によっては、更に導電性を高めるために導電性球状粒子の真密度が３ｇ／ｃｍ³を越えない範囲で、導電性の金属及び／または金属酸化物のメッキを施していても良い。
【０１０４】
本発明で使用される導電性球状粒子を得る他の方法としては、球状の樹脂粒子からなる芯粒子に対して、芯粒子の粒径より小さい粒径の導電性微粒子を適当な配合比で機械的に混合することによって、ファンデルワールス力及び静電気力の作用により、芯粒子の周囲に均一に導電性微粒子を付着した後、例えば機械的衝撃力を付与することによって生ずる局部的温度上昇により芯粒子表面を軟化させ、芯粒子表面に導電性微粒子を成膜して導電化処理した球状の樹脂粒子を得る方法が挙げられる。
【０１０５】
本発明に使用される導電性球状粒子を得る他の方法として、球状の樹脂粒子中に導電性微粒子を均一に分散させることにより、導電性微粒子が分散された導電性球状粒子を得る方法が挙げられる。球状の樹脂粒子中に導電性微粒子を均一に分散させる方法としては、例えば、球状の樹脂粒子に用いられる結着樹脂と導電性微粒子とを混練して導電性微粒子を分散させた後、冷却固化し、所定の粒径に粉砕し、機械的処理及び熱的処理により球形化して導電性球状粒子を得る方法；又は、球状の樹脂粒子に用いられる重合性単量体中に重合開始剤、導電性微粒子及びその他の添加剤を加え、分散機によって均一に分散させた単量体組成物を、分散安定剤を含有する水相中に攪拌機等によって所定の粒径になるように懸濁させて重合を行い、導電性微粒子が分散された球状粒子を得る方法；が挙げられる。
【０１０６】
次に本発明に用いられる現像剤担持体の構成について説明する。
【０１０７】
現像剤担持体は基体とそれを取り巻いて被覆する樹脂被覆層とからなる。基体の形状としては、円筒状部材、円柱状部材、ベルト状部材等がある。ドラムに非接触の現像方法においては金属の円筒状部材が好ましく用いられ、具体的には金属製の円筒管が好ましく用いられる。金属製円筒管は主としてステンレススチール、アルミニウムおよびその合金等の非磁性のものが好適に用いられる。また、ドラムに直接接触させる現像方法の場合の基体としては、ウレタン、ＥＰＤＭ、シリコン等のゴムやエラストマーを含む層構成を有する円筒状部材が好ましく用いられる。
【０１０８】
また、磁性現像剤を用いる本発明においては、現像剤を現像剤担持体上に磁気的に吸引かつ保持するために、磁石が内設されているマグネットローラ等を現像剤担持体内に配置する。その場合、基体を円筒状としその内部にマグネットローラを配置すればよい。
本発明の樹脂被覆層を形成する方法については、特に限定されず、通常の方法によって行える。例えば、現像剤担持体の基材に、上記被覆層用結着樹脂及び上記第４級アンモニウム塩化合物等を含有する塗布液をディッピング法、スプレー法、はけ塗り法などの方法で塗布し乾燥させれば、本発明に用いられる現像剤担持体が得られる。
【０１０９】
＜２＞本発明に用いられる現像剤
次に本発明において、静電潜像から可視画像としてのトナー像を得るために用いられる現像剤（以下、「トナー」ともいう）について説明する。
【０１１０】
本発明に用いられるトナーは、結着樹脂成分及び磁性粉体を少なくとも含有するトナー粒子と、無機微粉体と、該無機微粉体よりも大きくトナーよりも小さい平均粒径の導電性微粉体とを有し、上記式（１）により求められる平均円形度が０．９７０以上であり、実質的に磁性粉体が表面に露出していない磁性トナーである。
【０１１１】
まず、トナーの円形度について説明する。
【０１１２】
円形度が０．９７０以上のトナー（トナー粒子群で構成される粉体）から構成されるトナーは転写性に非常に優れている。これはトナー粒子と感光体との接触面積が小さく、鏡像力やファンデルワールス力等に起因するトナー粒子の感光体への付着力が低下するためと考えられる。従って、このようなトナーを用いれば転写率が高く、転写残トナーが非常に低減するため、帯電部材と感光体との圧接部におけるトナーが非常に少なく、トナー融着が防止され、画像欠陥が著しく抑制されるものと考えられる。
【０１１３】
さらに、円形度が０．９７０以上のトナー粒子は表面のエッジ部がほとんど無いため、帯電部材と感光体との圧接部において摩擦が低減され、感光体表面の削れが抑制されるとも考えられる。
【０１１４】
これらの効果は、転写中抜けの発生しやすい接触転写工程を含む画像形成方法においては、より顕著となって現れる。
【０１１５】
本発明におけるトナーの円形度は、トナー粒子の形状を定量的に表現する簡便な方法として用いたものであり、本発明では東亜医用電子（株）製フロー式粒子像測定装置ＦＰＩＡ−１０００型を用いて測定を行い、下式（２）を用いて算出し、さらに下式（３）で示すように測定された全粒子の円形度の総和を全粒子数（ｍ）で除した値を平均円形度（ａｍ）と定義する。
【０１１６】
【数６】
円形度（ａｉ）＝Ｌ₀／Ｌ 式（２）
（式中、Ｌ₀は磁性トナー粒子像と同じ投影面積をもつ円の周囲長を示し、Ｌは磁性トナー粒子の投影像の周囲長を示す。）
【０１１７】
【数７】

ここで粒子投影面積とは二値化されたトナー粒子像の面積であり、粒子投影像の周囲長とは該トナー粒子像のエッジ点を結んで得られる輪郭線の長さと定義する。
【０１１８】
本発明における円形度は現像剤粒子の凹凸の度合いを示す指標であり、トナー粒子が完全な球形の場合に１．０００を示し、表面形状が複雑になる程、円形度は小さな値となる。
【０１１９】
なお、本発明で用いる測定装置である「ＦＰＩＡ−１０００」は、各粒子の円形度を算出後、平均円形度及びモード円形度の算出に当たって、粒子を得られた円形度によって、円形度０．４０〜１．００を６１分割したクラスに分け、分割点の中心値と頻度を用いて平均円形度の算出を行う算出法を用いている。しかしながら、この算出法で算出される平均円形度の各値と、上述した各粒子の円形度を直接用いる算出式によって算出される平均円形度の各値との誤差は、非常に少なく、実質的には無視できる程度のものであり、本発明においては、算出時間の短縮化や算出演算式の簡略化の如きデータの取り扱い上の理由で、上述した各粒子の円形度を直接用いる算出式の概念を利用し、一部変更したこのような算出法を用いても良い。
【０１２０】
測定手順としては、以下の通りである。
【０１２１】
界面活性剤約０．１ｍｇを溶解している水１０ｍｌに、磁性トナー約５ｍｇを分散させて分散液を調製し、超音波（２０ＫＨｚ、５０Ｗ）を分散液に５分間照射し、分散液濃度を５０００〜２万個／μｌとして、前記装置により測定を行い、平均円形度を求める。
【０１２２】
また、本発明における磁性トナーは、実質的に磁性粉体が表面に露出していないものであり、具体的には、Ｘ線光電子分光分析により測定される磁性トナー粒子の表面に存在する炭素元素の含有量（Ａ）に対する鉄元素の含有量（Ｂ）の比（Ｂ／Ａ）が、０．００１未満であることが好ましい。
【０１２３】
すなわち接触帯電工程を含む画像形成方法において、トナー粒子表面に磁性粉体が露出している磁性トナーを用いた場合、露出した磁性粉体による感光体の削れがより顕著となって現れやすいためである。しかしながら、上述の如き（Ｂ／Ａ）が０．００１未満である、すなわち磁性粉体がトナー粒子表面に実質的にほとんど露出していない磁性トナーを用いれば、帯電部材によりトナーが感光体表面に圧接されても感光体表面が削れることはほとんど無く、感光体の削れやトナー融着を著しく低減させることが可能となる。
【０１２４】
なお、磁性トナー表面に存在する炭素元素の含有量（Ａ）に対する鉄元素の含有量（Ｂ）の比（Ｂ／Ａ）は、ＥＳＣＡ（Ｘ線光電子分光分析）により表面組成分析を行い算出することができる。
【０１２５】
本発明では、ＥＳＣＡの装置および測定条件は、下記の通りである。
使用装置：ＰＨＩ社製 １６００Ｓ型 Ｘ線光電子分光装置
測定条件：Ｘ線源 ＭｇＫα（４００Ｗ）
分光領域 ８００μｍφ
本発明では、測定された各元素のピーク強度から、ＰＨＩ社提供の相対感度因子を用いて表面原子濃度を算出する。本測定はトナーを超音波洗浄し、磁性トナー粒子表面に付着している無機微粉体等を除去した後、磁気力にて分離し、乾燥し測定することが好ましい。
【０１２６】
なお、粒子内部の特定の部分のみに磁性粉体粒子が含有されている特殊なトナーは、特開平７−２０９９０４号公報においても既に開示されている。しかしながら、特開平７−２０９９０４号公報においては、開示されているトナーの円形度に関する言及がなされていない。
【０１２７】
本発明の画像形成方法においては、特定の円形度を有するトナーの使用が必須要素であり、特開平７−２０９９０４号公報に記載されているようなトナーを本発明の使用形態で用いても同じような効果が発現するかどうかは不明である。特開平７−２０９９０４号公報において開示されているトナー構成を要約すれば、トナー粒子表面付近に磁性粉体粒子の存在しない樹脂層が一定量以上の厚みで形成されている構造から成るものであり、これは、磁性粉体粒子が存在しないトナー表層部分がかなりの割合で存在することを意味している。しかしながら言い換えると、このようなトナーは、例えば平均粒径が１０μｍと小さい場合、磁性粉体粒子が存在しうる容積が小さくなるため、十分な量の磁性粉体粒子を内包しにくいということでもある。しかも、こういったトナーでは、トナーの粒度分布において粒径の大きいトナー粒子と小さい粒子とでは磁性粉体粒子の存在しない表面樹脂層の割合が異なり、従って、内包される磁性粉体含有量も異なるため、現像性や転写性もトナーの粒径によって異なってしまい、粒径に依存する、選択現像性が見られやすい。従って、こういった磁性トナーで長期に渡り印字を行うと、磁性粉体を多く含み現像されにくい粒子、即ち粒径の大きなトナー粒子が残りやすく、画像濃度及び画質の低下、さらには定着性の悪化にもつながる。
【０１２８】
従って、本発明においてはトナー粒子中の磁性粉体の分散状態を以下のような好ましい分散状態にすればよい。トナー粒子中における好ましい磁性粉体分散状態とは、磁性粉体粒子が凝集せずになるべくトナー粒子全体に均一に存在する状態である。即ち、トナーの体積平均粒径をＣ、透過型電子顕微鏡（ＴＥＭ）を用いた磁性トナーの断層面観察において、磁性粉体とトナー粒子表面との距離の最小値をＤとしたとき、Ｄ／Ｃ≦０．０２である磁性トナーを用いることもまた、本発明における特徴の一つである。
【０１２９】
本発明で、Ｄ／Ｃ≦０．０２に調整する方法としては、磁性粉体の表面処理剤の種類や処理の均一性を制御することなどが挙げられる。
【０１３０】
本発明における磁性トナーの体積平均粒径Ｃは、後述するコールターマルチサイザー等にて、またＤは、以下のように測定することができる。ＴＥＭによる具体的な観察方法としては、常温硬化性のエポキシ樹脂中へ観察すべきトナー粒子を十分に分散させた後、温度４０℃の雰囲気中で２日間硬化させ得られた硬化物を、そのままあるいは凍結して、ダイヤモンド歯を備えたミクロトームにより薄片状のサンプルとして観察する方法が好ましい。
【０１３１】
本発明の画像形成方法において、更に高画質化のため、より微小な潜像ドットを忠実に現像するためには、トナーの重量平均粒径が３〜１０μｍ、更には４〜８μｍであることが好ましい。重量平均粒径が３μｍよりも小さいトナーに於いては、転写効率の低下から感光体上の転写残トナーが多くなり、接触帯電工程での感光体の削れやトナー融着の抑制が難しくなる傾向がある。さらに、トナー全体の表面積が増えることに加え、トナーの流動性及び攪拌性が低下し、個々のトナー粒子を均一に帯電させることが困難となることからカブリや転写性が悪化傾向となり、削れや融着以外にも画像の不均一ムラの原因となりやすいため、本発明で使用するトナーには好ましくない。また、トナーの重量平均粒径が１０μｍを越える場合には、文字やライン画像に飛び散りが生じやすく、高解像度が得られにくい。さらに画像形成装置が高解像度になっていくと８μｍ以上のトナーは１ドットの再現が悪化する傾向にある。
【０１３２】
トナーの平均粒径はコールターカウンターＴＡ−II型あるいはコールターマルチサイザー（ベックマンコールター社製）等種々の方法で測定可能であるが、本発明においてはコールターマルチサイザー（ベックマンコールター社製）を用い、個数分布、体積分布を出力するインターフェイス（日科機製）及びＰＣ９８０１パーソナルコンピューター（ＮＥＣ製）を接続し、電解液は１級塩化ナトリウムを用いて１％ＮａＣｌ水溶液を調整する。たとえば、ＩＳＯＴＯＮ Ｒ−II（コールターサイエンティフィックジャパン社製）が使用できる。
【０１３３】
測定法としては、前記電解水溶液１００〜１５０ｍｌ中に分散剤として界面活性剤、好ましくはアルキルベンゼンスルフォン酸塩を０．１〜５ｍｌ加え、更に測定試料を２〜２０ｍｇ加える。試料を懸濁した電解液は超音波分散器で約１〜３分間分散処理を行い、前記コールターマルチサイザーによりアパーチャーとして１００μｍアパーチャーを用いて、２μｍ以上のトナー粒子の体積、個数を測定して体積分布と個数分布とを算出する。
【０１３４】
それから、本発明に係わる体積分布から求めた体積基準の重量平均粒径（Ｄ４）を求める。
【０１３５】
本発明においては、トナー粒子を重合法、特に懸濁重合法で製造した後、無機微粉体と導電性微粉体を混合添加することにより無機微粉体と導電性微粉体を表面に付着させ、本発明の磁性トナーとすることが好ましい。この懸濁重合法においては、結着樹脂成分となる重合性単量体、磁性粉体および着色剤（更に必要に応じて重合開始剤、架橋剤、荷電制御剤、その他の添加剤）を均一に溶解または分散させて重合性単量体系とした後、この重合性単量体系を分散安定剤が含有される連続層（例えば水系媒体）中に適当な撹拌器を用いて分散し同時に重合反応を行わせ、所望の粒径を有するトナーを得るものである。この懸濁重合法で得られるトナー（以後重合トナー）は、個々のトナー粒子形状がほぼ球形に揃っているため、円形度が０．９７０以上という本発明に必須な物性要件を満たすトナーが得られやすい。なお、本発明において水系媒体とは、水を主要成分としている媒体である。具体的には、水系媒体として水そのもの、水に少量の界面活性剤を添加したもの、水にｐＨ調製剤を添加したもの、水に有機溶剤を添加したものが挙げられる。
【０１３６】
しかしながら、重合トナー中に通常の磁性粉体を含有させても、粒子表面からの磁性粉体の露出を抑えることは難しい。さらにはトナー粒子の流動性及び帯電特性が著しく低下するだけでなく、懸濁重合トナーの製造時に磁性粉体と水との相互作用が強いことにより、平均円形度が０．９７０以上のトナーが得られ難い。これは、第一に磁性粉体粒子は一般的に親水性であるためにトナー表面に存在しやすいこと、第二に水溶媒撹拌時に磁性粉体が乱雑に動き、それに単量体から成る懸濁粒子表面が引きずられ、形状が歪んで円形になりにくいこと等が原因と考えられる。こういった問題を解決するためには磁性粉体粒子の有する表面特性の改質が重要である。磁性粉体が優れた疎水性と分散性を有するために、本発明において重合トナーに用いられる磁性粉体は、表面が水系媒体中で磁性粉体を一次粒径となるように分散しつつカップリング剤を加水分解しながら処理された磁性粉体であるのが好ましい。この疎水化処理方法は気相中で処理するより、磁性粉体粒子同士の合一が生じにくく、また疎水化処理による磁性粉体粒子間の帯電反発作用が働き、磁性粉体はほぼ一次粒子の状態で表面処理される。
【０１３７】
該磁性粉体を重合トナー用の材料として用いた場合、トナー粒子中への分散性が非常に良好となり、磁性粉体がトナー粒子表面に露出することも無くほぼ球形に近い磁性トナーを得ることができる。即ち、平均円形度が０．９７０以上、さらにＸ線光電子分光分析により測定される磁性トナーの表面に存在する炭素元素の含有量（Ａ）に対する（Ｂ）の比（Ｂ／Ａ）が０．００１未満という磁性トナーを得ることが可能となる。
【０１３８】
本発明に係わる磁性粉体の表面処理において使用できるカップリング剤としては、例えば、シランカップリング剤、チタンカップリング剤等が挙げられる。その処理量は磁性粉体１００質量部に対して、０．０５〜２０質量部、好ましくは０．１〜１０質量部とするのが良い。
【０１３９】
こうして得られる磁性粉体は粒子の凝集が見られず、個々の粒子表面が均一に疎水化処理されているため、重合トナー用の材料として用いた場合、トナー粒子中への分散性が非常に良好である。しかもトナー粒子表面からの露出が無く、ほぼ球形に近い重合トナーが得られる。
【０１４０】
本発明におけるトナーに用られる磁性粉体は、結着樹脂成分１００質量部に対して、１０〜２００質量部用いることが好ましい。さらに好ましくは２０〜１８０質量部用いることが良い。１０質量部未満ではトナーの着色力が乏しく、カブリの抑制も困難である。一方、２００質量部を越えると、現像剤担持体への磁力による保持力が強まり現像性が低下したり、個々のトナー粒子への磁性粉体の均一な分散が難しくなるだけでなく、定着性が低下してしまう傾向がある。
【０１４１】
本発明に用いられる磁性粉体としては、マグネタイト、マグヘマイト、フェライト等の磁性酸化鉄、鉄、コバルト、ニッケル等の金属或いはこれらの金属とアルミニウム、コバルト、銅、鉛、マグネシウム、錫、亜鉛、アンチモン、ベリリウム、ビスマス、カドミウム、カルシウム、マンガン、セレン、チタン、タングステン、バナジウム等の金属の合金及びその混合物が挙げられるが、主にマグネタイトからなるものが好ましい。
【０１４２】
磁性粉体の形状としては、８面体、６面体、球形、針状、燐片状などがあるが、８面体、６面体、球形、不定型等の異方性の少ないものが画像濃度を高める上で好ましい。こういった磁性粉体の形状はＳＥＭなどによって確認することができる。磁性粉体の平均粒径としては０．０１〜１．０μｍが好ましく、さらに好ましくは０．０５〜０．５μｍが好ましい。平均粒径が０．０１μｍ未満の場合、黒色度の低下が顕著となり、白黒用トナーの着色剤としては着色力が不十分となるうえに、複合酸化物粒子どうしの凝集が強くなるため、分散性が悪化する傾向となる。一方、平均粒径が１．０μｍを越えてしまうと、一般の着色剤と同様に着色力が不足するようになる。加えて、特に小粒径トナー用の着色剤として使用する場合、個々のトナー粒子に同個数の磁性粉体を分散させることが確率的に困難となり、分散性が悪化しやすい。なお、磁性粉体の平均粒径は、透過型電子顕微鏡を用いて測定できる。具体的には、測定するトナーの粉体サンプルを透過型電子顕微鏡で観察し、視野中の１００個の磁性粉体粒子径を測定し、個数平均粒径を求め平均粒径とする。
【０１４３】
さらにまた、磁性粉体以外に他の着色剤を併用しても良い。併用し得る着色材料としては、磁性あるいは非磁性無機化合物、公知の染料及び顔料が挙げられる。具体的には、例えば、コバルト、ニッケルなどの強磁性金属粒子、またはこれらにクロム、マンガン、銅、亜鉛、アルミニウム、希土類元素などを加えた合金、ヘマタイトなどの粒子、チタンブラック、ニグロシン染料／顔料、カーボンブラック、フタロシアニン等が挙げられる。これらもまた、磁性粉体と同様にカップリング剤で表面を処理して用いても良い。
【０１４４】
本発明に係わるトナーは、離型剤を含有することも好ましい使用形態の一つである。
【０１４５】
転写材上に転写されたトナー像はその後、熱・圧力等のエネルギーにより転写材上に定着され、半永久的画像が得られる。この際、熱ロール式定着が一般に良く用いられる。
【０１４６】
先述したように、重量平均粒径が１０μｍ以下のトナーを用いれば非常に高精細な画像を得ることができるが、粒径の細かいトナー粒子は紙等の転写材を使用した場合に紙の繊維の隙間に入り込み、熱定着用ローラからの熱の受け取りが不十分となり、低温オフセットが発生しやすい。しかしながら、本発明に係わるトナーにおいて、離型剤として適正量の離型剤を含有させることにより、高解像性と耐オフセット性を両立させつつ感光体の削れを防止することが可能となる。
【０１４７】
本発明に係わるトナーに使用可能な離型剤としては、パラフィンワックス、マイクロクリスタリンワックス、ペトロラクタム等の石油系ワックス及びその誘導体、モンタンワックス及びその誘導体、フィッシャートロプシュ法による炭化水素ワックス及びその誘導体、ポリエチレンに代表されるポリオレフィンワックス及びその誘導体、カルナバワックス、キャンデリラワックス等天然ワックス及びその誘導体などで、誘導体には酸化物や、ビニル系モノマーとのブロック共重合物、グラフト変性物を含む。さらには、高級脂肪族アルコール、ステアリン酸、パルミチン酸等の脂肪酸、あるいはその化合物、酸アミドワックス、エステルワックス、ケトン、硬化ヒマシ油及びその誘導体、植物系ワックス、動物性ワックス等示差熱分析における吸熱ピークを４５℃以上１１０℃以下、更には５０℃以上９０℃以下の範囲に有するものが好ましい。
【０１４８】
離型剤を使用する際の含有量としては、トナー全体に対して０．５〜５０質量％の範囲が好ましい。含有量が０．５質量％未満では低温オフセット抑制効果に乏しく、５０質量％を超えてしまうと長期間の保存性が悪化すると共に、他のトナー材料の分散性が悪くなり、トナーの流動性の悪化や画像特性の低下につながる。
【０１４９】
本発明の画像形成方法に関わるトナーには、荷電特性を安定化するために荷電制御剤を配合しても良い。荷電制御剤としては、公知のものが利用でき、特に帯電スピードが速く、かつ、一定の帯電量を安定して維持できる荷電制御剤が好ましい。さらに、トナーを直接重合法を用いて製造する場合には、重合阻害性が低く、水系分散媒体への可溶化物が実質的にない荷電制御剤が特に好ましい。具体的な化合物としては、負帯電性荷電制御剤としてサリチル酸、アルキルサリチル酸、ジアルキルサリチル酸、ナフトエ酸、ダイカルボン酸等の芳香族カルボン酸の金属化合物、アゾ染料あるいはアゾ顔料の金属塩または金属錯体、スルホン酸又はカルボン酸基を側鎖に持つ高分子型化合物、ホウ素化合物、尿素化合物、ケイ素化合物、カリックスアレーン等が挙げられる。荷電制御剤をトナーに含有させる方法としては、トナー粒子内部に添加する方法と外添する方法がある。これらの荷電制御剤の使用量としては、結着樹脂成分の種類、他の添加剤の有無、分散方法を含めたトナー製造方法によって決定されるもので、一義的に限定されるものではないが、好ましくは結着樹脂成分１００質量部に対して０．１〜１０質量部、より好ましくは０．１〜５質量部の範囲で用いられる。
【０１５０】
本発明の画像形成方法に関わるトナーの懸濁重合法による製造方法を説明する。
【０１５１】
本発明に関わる重合トナーに使用される重合性単量体系を構成する重合性単量体としては以下のものが挙げられる。
【０１５２】
重合性単量体としては、スチレン、ｏ−メチルスチレン、ｍ−メチルスチレン、ｐ−メチルスチレン、ｐ−メトキシスチレン、ｐ−エチルスチレン等のスチレン系単量体；アクリル酸メチル、アクリル酸エチル、アクリル酸ｎ−ブチル、アクリル酸イソブチル、アクリル酸ｎ−プロピル、アクリル酸ｎ−オクチル、アクリル酸ドデシル、アクリル酸２−エチルヘキシル、アクリル酸ステアリル、アクリル酸２−クロルエチル、アクリル酸フェニル等のアクリル酸エステル類；メタクリル酸メチル、メタクリル酸エチル、メタクリル酸ｎ−プロピル、メタクリル酸ｎ−ブチル、メタクリル酸イソブチル、メタクリル酸ｎ−オクチル、メタクリル酸ドデシル、メタクリル酸２−エチルヘキシル、メタクリル酸ステアリル、メタクリル酸フェニル、メタクリル酸ジメチルアミノエチル、メタクリル酸ジエチルアミノエチル等のメタクリル酸エステル類；その他のアクリロニトリル、メタクリロニトリル、アクリルアミド等の単量体が挙げられる。
【０１５３】
これらの重合性単量体は単独、または混合して使用し得る。上述の重合性単量体の中でも、スチレンまたはスチレン誘導体を単独で、あるいはほかの単量体と混合して使用する事がトナーの現像特性及び耐久性の点から好ましい。
【０１５４】
本発明に係わる重合トナーの製造においては、重合性単量体系に樹脂を添加して重合しても良い。例えば、重合性単量体では水溶性のため水性懸濁液中では溶解して乳化重合を起こすため使用できないアミノ基、カルボン酸基、水酸基、スルホン酸基、グリシジル基、ニトリル基等親水性官能基含有の単量体成分をトナー中に導入したい時には、これらとスチレンあるいはエチレン等ビニル化合物とのランダム共重合体、ブロック共重合体、あるいはグラフト共重合体等の形にして、あるいはポリエステル、ポリアミド等の重縮合体、ポリエーテル、ポリイミン等重付加重合体の形にして使用すればよい。こうした極性官能基を含む高分子重合体をトナー中に共存させると、前述のワックス成分を相分離させ、より内包化が強力となり、耐オフセット性、耐ブロッキング性、低温定着性の良好なトナーを得ることができる。このような極性官能基を含む高分子重合体を使用する場合、その平均分子量は５，０００以上が好ましく用いられる。５，０００以下、特に４，０００以下では、本重合体が表面付近に集中し易い事から、現像性、耐ブロッキング性等に悪い影響が起こり易くなり好ましくない。
【０１５５】
また、極性重合体としては特にポリエステル系の樹脂が好ましい。
【０１５６】
また、材料の分散性や定着性、あるいは画像特性の改良等を目的として上記以外の樹脂を重合性単量体系中に添加しても良く、用いられる樹脂としては、例えば、ポリスチレン、ポリビニルトルエンなどのスチレン及びその置換体の単重合体；スチレン−プロピレン共重合体、スチレン−ビニルトルエン共重合体、スチレン−ビニルナフタリン共重合体、スチレン−アクリル酸メチル共重合体、スチレン−アクリル酸エチル共重合体、スチレン−アクリル酸ブチル共重合体、スチレン−アクリル酸オクチル共重合体、スチレン−アクリル酸ジメチルアミノエチル共重合体、スチレン−メタアクリル酸メチル共重合体、スチレン−メタアクリル酸エチル共重合体、スチレン−メタアクリル酸ブチル共重合体、スチレン−メタクリル酸ジメチルアミノエチル共重合体、スチレン−ビニルメチルエーテル共重合体、スチレン−ビニルエチルエーテル共重合体、スチレン−ビニルメチルケトン共重合体、スチレン−ブタジエン共重合体、スチレン−イソプレン共重合体、スチレン−マレイン酸共重合体、スチレン−マレイン酸エステル共重合体などのスチレン系共重合体；ポリメチルメタクリレート、ポリブチルメタクリレート、ポリ酢酸ビニル、ポリエチレン、ポリプロピレン、ポリビニルブチラール、シリコン樹脂、ポリエステル樹脂、ポリアミド樹脂、エポキシ樹脂、ポリアクリル酸樹脂、ロジン、変性ロジン、テンペル樹脂、フェノール樹脂、脂肪族または脂環族炭化水素樹脂、芳香族系石油樹脂などが単独或いは混合して使用できる。
【０１５７】
これら樹脂の添加量としては、重合性単量体１００質量部に対し１〜２０質量部が好ましい。１質量部未満では添加効果が小さく、一方２０質量部以上添加すると重合トナーの種々の物性設計が難しくなる傾向がある。
【０１５８】
さらに、重合性単量体を重合して得られるトナーの分子量範囲とは異なる分子量の重合体を重合性単量体系中に溶解して重合すれば、分子量分布の広い、耐オフセット性の高いトナーを得ることが出来る。
【０１５９】
本発明の画像形成方法に関わる重合トナーの製造において使用される重合開始剤としては、重合反応時に半減期０．５〜３０時間であるものを、重合性単量体に対し０．５〜２０質量部の添加量で重合反応を行うと、分子量１万〜１０万の間に極大を有する重合体が得られ、トナーに望ましい強度と適当な溶融特性を与えることが出来る。重合開始剤例としては、２，２'−アゾビス−（２，４−ジメチルバレロニトリル）、２，２'−アゾビスイソブチロニトリル、１，１'−アゾビス（シクロヘキサン−１−カルボニトリル）、２，２'−アゾビス−４−メトキシ−２，４−ジメチルバレロニトリル、アゾビスイソブチロニトリル等のアゾ系またはジアゾ系重合開始剤、ベンゾイルパーオキサイド、メチルエチルケトンパーオキサイド、ジイソプロピルパーオキシカーボネート、クメンヒドロパーオキサイド、２，４−ジクロロベンゾイルパーオキサイド、ラウロイルパーオキサイド、ｔ−ブチルパーオキシ２−エチルヘキサノエート等の過酸化物系重合開始剤が挙げられる。
【０１６０】
本発明の画像形成方法に関わる重合トナーを製造する際は、架橋剤を添加しても良く、好ましい添加量としては、重合性単量体系に対して０．００１〜１５質量％である。
【０１６１】
ここで架橋剤としては、主として２個以上の重合可能な二重結合を有する化合物が用いられ、例えば、ジビニルベンゼン、ジビニルナフタレン等のような芳香族ジビニル化合物；例えばエチレングリコールジアクリレート、エチレングリコールジメタクリレート、１，３−ブタンジオールジメタクリレート等のような二重結合を２個有するカルボン酸エステル；ジビニルアニリン、ジビニルエーテル、ジビニルスルフィド、ジビニルスルホン等のジビニル化合物；及び３個以上のビニル基を有する化合物；が単独もしくは混合物として用いられる。
【０１６２】
本発明の画像形成方法に関わる重合トナーの製造方法では、一般に上述のトナー組成物、すなわち重合性単量体に磁性粉体、離型剤、可塑剤、荷電制御剤、架橋剤、場合によって着色剤等トナーとして必要な成分及びその他の添加剤、例えば重合反応で生成する重合体の粘度を低下させるために入れる有機溶媒、高分子重合体、分散剤等を適宜加えて、ホモジナイザー、ボールミル、コロイドミル、超音波分散機等の分散機に依って均一に溶解または分散させた重合性単量体系を、分散安定剤を含有する水系媒体中に懸濁する。この時、高速撹拌機もしくは超音波分散機のような高速分散機を使用して一気に所望のトナー粒子のサイズとするほうが、得られるトナー粒子の粒径がシャープになる。重合開始剤添加の時期としては、重合性単量体に他の添加剤を添加する時同時に加えても良いし、水系媒体中に懸濁する直前に混合しても良い。又、造粒直後、重合反応を開始する前に重合性単量体あるいは溶媒に溶解した重合開始剤を加える事も出来る。
【０１６３】
造粒後は、通常の撹拌機を用いて、粒子状態が維持され且つ粒子の浮遊・沈降が防止される程度の撹拌を行えば良い。
【０１６４】
本発明の画像形成方法に関わる重合トナーを製造する場合には、分散安定剤として公知の界面活性剤や有機・無機分散剤が使用でき、中でも無機分散剤が有害な超微粉を生じ難く、その立体障害性により分散安定性を得ているので反応温度を変化させても安定性が崩れ難く、洗浄も容易でトナーに悪影響を与え難いので、好ましく使用できる。こうした無機分散剤の例としては、燐酸カルシウム、燐酸マグネシウム、燐酸アルミニウム、燐酸亜鉛等の燐酸多価金属塩、炭酸カルシウム、炭酸マグネシウム等の炭酸塩、メタ硅酸カルシウム、硫酸カルシウム、硫酸バリウム等の無機塩、水酸化カルシウム、水酸化マグネシウム、水酸化アルミニウム、シリカ、ベントナイト、アルミナ等の無機酸化物等が挙げられる。
【０１６５】
これらの無機分散剤は、重合性単量体１００質量部に対して、０．２〜２０質量部を単独で使用する事が望ましいが、超微粒子を発生し難いもののトナーを微粒化するには不十分であるので、０．００１〜０．１質量部の界面活性剤を併用しても良い。
【０１６６】
界面活性剤としては、例えばドデシルベンゼン硫酸ナトリウム、テトラデシル硫酸ナトリウム、ペンタデシル硫酸ナトリウム、オクチル硫酸ナトリウム、オレイン酸ナトリウム、ラウリル酸ナトリウム、ステアリン酸ナトリウム、ステアリン酸カリウム等が挙げられる。
【０１６７】
これら無機分散剤を用いる場合には、そのまま使用しても良いが、より細かい粒子を得るため、水系媒体中にて該無機分散剤粒子を生成させることが好ましい。例えば、燐酸カルシウムの場合、高速撹拌下、燐酸ナトリウム水溶液と塩化カルシウム水溶液とを混合して水不溶性の燐酸カルシウムを生成させることにより、より均一で細かな分散が可能となる。このとき、同時に水溶性の塩化ナトリウム塩が副生するが、水系媒体中に水溶性塩が存在すると、重合性単量体の水への溶解が抑制されて、乳化重合に依る超微粒トナーが発生し難くなるので、より好都合である。重合反応終期に残存重合性単量体を除去する時には障害となることから、水系媒体を交換するか、イオン交換樹脂で脱塩したほうが良い。無機分散剤は、重合終了後酸あるいはアルカリで溶解して、ほぼ完全に取り除くことが出来る。
【０１６８】
前記重合工程においては、重合温度は４０℃以上、一般には５０〜９０℃の温度に設定して重合を行う。この温度範囲で重合を行うと、内部に封じられるべき離型剤やワックスの類が、相分離により析出して内包化がより完全となる。残存する重合性単量体を消費するために、重合反応終期ならば、反応温度を９０〜１５０℃にまで上げる事は可能である。
【０１６９】
本発明においてトナーは、流動化剤として無機微粉体が添加されることも重要である。無機微粉体は、トナーの流動性改良及びトナー粒子の帯電均一化のために添加されるが、無機微粉体を疎水化処理するなどの処理によってトナーの帯電量の調整、環境安定性の向上等の機能を付与することも好ましい形態である。
【０１７０】
無機微粉体は平均１次粒径４〜８０ｎｍが好ましい。平均１次粒径が８０ｎｍよりも大きい場合、或いは８０ｎｍ以下の無機微粉体が添加されていない場合には、転写残トナーが帯電部材へ付着した際に帯電部材に固着し易くなり、安定して良好な帯電特性を得ることが困難である。また、良好なトナーの流動性が得られず、トナー粒子への帯電付与が不均一になり易く、カブリの増大、画像濃度の低下、トナー飛散等の問題を避けられない。無機微粉体の平均１次粒径が４ｎｍよりも小さい場合には、無機微粉体の凝集性が強まり、１次粒子ではなく解砕処理によっても解れ難い強固な凝集性を持つ粒度分布の広い凝集体として挙動し易く、凝集体の現像、像担持体或いは現像担持体等を傷つけるなどによる画像欠陥を生じ易くなる。
【０１７１】
トナー粒子の帯電分布をより均一とするためには無機微粉体の平均１次粒径は６〜３５ｎｍであることがより良い。
【０１７２】
本発明において、無機微粉体の平均１次粒径の測定は以下のように行う。走査型電子顕微鏡により拡大撮影したトナーの写真で、更に走査型電子顕微鏡に付属させたＸＭＡ等の元素分析手段によって無機微粉体の含有する元素でマッピングされたトナーの写真を対照しつつ、トナー表面に付着或いは遊離して存在している無機微粉体の１次粒子を１００個以上測定し、個数平均粒径を求めることにより測定出来る。
【０１７３】
本発明で用いられる無機微粉体としては、シリカ、アルミナ、チタニアなどが使用できる。
【０１７４】
例えば、シリカとしてはケイ素ハロゲン化物の蒸気相酸化により生成されたいわゆる乾式法又はヒュームドシリカと称される乾式シリカ、及び水ガラス等から製造されるいわゆる湿式シリカの両者が使用可能であるが、表面及びシリカ微粉体の内部にあるシラノール基が少なく、またＮａ₂Ｏ、ＳＯ₃ ^2-等の製造残滓の少ない乾式シリカの方が好ましい。また乾式シリカにおいては、製造工程において例えば、塩化アルミニウム、塩化チタン等他の金属ハロゲン化合物をケイ素ハロゲン化合物と共に用いることによって、シリカと他の金属酸化物の複合微粉体を得ることも可能でありそれらも包含する。
【０１７５】
平均１次粒径が４〜８０ｎｍの無機微粉体の添加量は、トナー粒子に対して０．１〜３．０質量％であることが好ましく、添加量が０．１質量％未満ではその効果が十分ではなく、３．０質量％以上では定着性が悪くなる傾向がある。
【０１７６】
無機微粉体は、疎水化処理された物であることが高温高湿環境下での特性から好ましい。トナーに添加された無機微粉体が吸湿すると、トナー粒子の帯電量が著しく低下し、トナー飛散が起こり易くなるからである。
【０１７７】
疎水化処理の処理剤としては、シリコーンワニス、各種変性シリコーンワニス、シリコーンオイル、各種変性シリコーンオイル、シラン化合物、シランカッブリング剤、その他有機硅素化合物、有機チタン化合物等の処理剤を単独で或いは併用して処理しても良い。
【０１７８】
その中でも、シリコーンオイルにより処理したものが好ましく、より好ましくは、無機微粉体を疎水化処理すると同時或いは処理した後に、シリコーンオイルにより処理したものが高湿環境下でもトナー粒子の帯電量を高く維持し、トナー飛散を防止する上でよい。
【０１７９】
具体的には、例えば第一段反応としてシリル化反応を行い、シラノール基を化学結合により消失させた後、第二段反応としてシリコーンオイルにより表面に疎水性の薄膜を形成することができる。
【０１８０】
上記シリコーンオイルは、２５℃における粘度が１０〜２００，０００ｍｍ²／ｓのものが、さらには３，０００〜８０，０００ｍｍ²／ｓのものが好ましい。１０ｍｍ²／ｓ未満では、無機微粉体に安定性が無く、熱および機械的な応力により、画質が劣化する傾向がある。２００，０００ｍｍ²／ｓを超える場合は、均一な処理が困難になる傾向がある。
【０１８１】
使用されるシリコーンオイルとしては、例えばジメチルシリコーンオイル、メチルフェニルシリコーンオイル、α−メチルスチレン変性シリコーンオイル、クロルフェニルシリコーンオイル、フッ素変性シリコーンオイル等が特に好ましい。
【０１８２】
シリコーンオイルの処理の方法としては、例えばシラン化合物で処理された無機微粉体とシリコーンオイルとをヘンシェルミキサー等の混合機を用いて直接混合してもよいし、無機微粉体にシリコーンオイルを噴霧する方法を用いてもよい。あるいは適当な溶剤にシリコーンオイルを溶解あるいは分散せしめた後、シリカ微粉体を加えて混合し溶剤を除去する方法でもよい。無機微粉体の凝集体の生成が比較的少ない点で噴霧機を用いる方法がより好ましい。
【０１８３】
シリコーンオイルの処理量は無機微粉体１００質量部に対し１〜２３質量部、好ましくは５〜２０質量部が良い。
【０１８４】
シリコーンオイルの量が少なすぎると良好な疎水性が得られず、多すぎるとカブリ発生等の不具合が生ずることがある。
【０１８５】
本発明で用いられる平均１次粒径が８０ｎｍ以下の無機微粉体は、ＢＥＴ法で測定した窒素吸着による比表面積が２０〜２５０ｍ²／ｇ範囲内のものが好ましく、より好ましくは４０〜２００ｍ²／ｇのものが更に良い。
【０１８６】
比表面積はＢＥＴ法に従って、比表面積測定装置オートソーブ１（湯浅アイオニクス社製）を用いて試料表面に窒素ガスを吸着させ、ＢＥＴ多点法を用いて比表面積を算出することにより求められる。
【０１８７】
また、本発明におけるトナーは、無機微粉体の個数平均１次粒径よりも大きく、トナーの重量平均粒径よりも小さい導電性微粉体を有していることが好ましい。個数平均１次粒径、重量平均粒径は同じ尺度で比較するものではないが、無機微粉体は導電性微粉体より比較的小さく、また導電性微粉体はトナーより比較的小さいので、本発明においては、導電性微粉体の大きさを比較する一つの指標としてこれらを用いた。
【０１８８】
導電性微粉体は、体積平均粒径が０．１〜１０μｍであることが好ましく良い。導電性微粉体の体積平均粒径が小さいと、現像性の低下を防ぐために導電性微粉体のトナー全体に対する含有量を小さく設定することが好ましい。導電性微粉体の体積平均粒径が０．１μｍ未満では、導電性微粉体の有効量を確保できず、帯電工程において、接触帯電部材への絶縁性の転写残トナーへの付着・混入による帯電阻害に打ち勝ち像担持体の帯電を良好に行わせるのに十分な量の導電性微粉体を、帯電部材と像担持体との当接部或いはその近傍の帯電領域に介在させることができず、帯電不良を生じ易くなる。この観点から、導電性微粉体の体積平均粒径は好ましくは０．１５μｍ以上、更に好ましくは０．２μｍ以上、５μｍ以下が良い。
【０１８９】
また、導電性微粉体の体積平均粒径が１０μｍよりも大きいと、帯電部材から脱落した導電性微粉体は静電潜像を書き込む露光光を遮光或いは拡散し、静電潜像の欠陥を生じ画像品位を低下させる傾向がある。更に、導電性微粉体の体積平均粒径が大きいと、単位重量当りの粒子数が減少するため、帯電部材からの導電性微粉体の脱落等による減少、劣化を考慮して導電性微粉体を帯電部材と像担持体との当接部或いはその近傍の帯電領域に逐次に導電性微粉体が供給し続け介在させるために、また、接触帯電部材が導電性微粉体を介して像担持体への緻密な接触性を維持し良好な帯電性を安定して得るためには、導電性微粉体のトナー全体に対する含有量を大きくしなければならない。しかし、導電性微粉体の含有量を大きくしすぎると、特に高湿環境下で、現像性を低下させ、画像濃度低下やトナー飛散を生ずる。このような観点から、導電性微粉体の体積平均粒径は好ましくは５μｍ以下が良い。
【０１９０】
導電性微粉体のトナー全体に対する含有量は、０．１〜１０質量％であることが好ましい。導電性微粉体のトナー全体に対する含有量が０．１質量％よりも少ないと、接触帯電部材への絶縁性の転写残トナーへの付着・混入による帯電阻害に打ち勝って像担持体の帯電を良好に行わせるのに十分な量の導電性微粉体を、帯電部材と像担持体との当接部或いはその近傍の帯電領域に介在させることができず、帯電性が低下し帯電不良を生じやすい。また、含有量が１０質量％よりも多い場合では、現像同時クリーニングによって回収される導電性微粉体が多くなりすぎることによる現像部でのトナーの帯電能、現像性を低下させ、画像濃度低下やトナー飛散を生じやすい。導電性微粉体のトナー全体に対する含有量は、０．２〜５質量％であることが好ましく良い。
【０１９１】
また、導電性微粉体の抵抗は１０⁹Ωｃｍ以下が好ましい。導電性微粉体の抵抗が１０⁹Ωｃｍよりも大きいと導電性微粉体を帯電部材と像担持体との当接部或いはその近傍の帯電領域に介在させ、接触帯電部材の導電性微粉体を介しての像担持体への緻密な接触性を維持させても、良好な帯電性を得るための帯電促進効果が得られにくい。
【０１９２】
更に、導電性微粉体の抵抗が１０⁶Ωｃｍ以下であることが、接触帯電部材への絶縁性の転写残トナーへの付着・混入による帯電阻害に打ち勝って像担持体の帯電をより良好に行わせる上で良い。
【０１９３】
導電性微粉体の帯電促進効果を十分に引き出し、良好な帯電性を安定して得るためには、導電性微粉体の抵抗が、接触帯電部材の表面部或いは像担持体との接触部の抵抗よりも小さいことが好ましい。
【０１９４】
また、導電性微粉体は透明、白色或いは淡色の導電性微粉体であることが、転写材上に転写される導電性微粉体の色再現性への影響が防止されるため好ましく良い。静電潜像形成工程における露光光の妨げとならない意味でも、導電性微粉体は、透明、白色或いは淡色の導電性微粉体であることがよく、より好ましくは、導電性微粉体の露光光に対する透過率が３０％以上であることが良い。
【０１９５】
本発明においては、導電性微粉体の光透過性については以下の手順で測定することができる。片面に接着層を有する透明のフィルムに、導電性微粉体を一層分固定した状態で透過率を測定する。光はシートの鉛直方向から照射し、フィルム背面に透過した光を集光し光量を測定する。フィルムのみと導電性微粉体を付着したときの光量から正味の光量として導電性微粉体の透過率を算出する。実際にはＸ−Ｒｉｔｅ社製３１０Ｔ透過型濃度計を用いて測定する。
【０１９６】
また、導電性微粉体は非磁性であることが好ましい。導電性微粉体が非磁性であることで、透明、白色または淡色の導電性微粉体が得られやすい。反対に、磁性を有する導電性微粉体は、透明、白色または淡色とすることが困難である。また、現像剤担持のために磁気力による現像剤の搬送及び保持を行う画像形成法においては、磁性を有する導電性微粉体は現像されにくいため、像担持体上への導電性微粉体の供給が不足したり、現像剤担持体表面に導電性微粉体が蓄積することにより、トナー粒子の現像を妨げる等の弊害を起こし易い。更に、磁性トナー粒子に磁性を有する導電性微粉体を添加すると、磁気的凝集力によりトナー粒子から導電性微粉体が遊離しにくくなる傾向があり、導電性微粉体の像担持体上への供給性が低下し易い。
【０１９７】
本発明における導電性微粉体としては、例えばカーボンブラック、グラファイトなどの炭素微粉体；銅、金、銀、アルミニウム、ニッケルなどの金属微粉体；酸化亜鉛、酸化チタン、酸化スズ、酸化アルミニウム、酸化インジウム、酸化珪素、酸化マグネシウム、酸化バリウム、酸化モリブデン、酸化鉄、酸化タングステンなどの金属酸化物；硫化モリブデン、硫化カドミウム、チタン酸カリなどの金属化合物、あるいはこれらの複合酸化物などが必要に応じて粒度及び粒度分布を調整することで使用できる。これらの中でも酸化亜鉛、酸化スズ、酸化チタン等の導電性無機酸化物微粉体が特に好ましい。
【０１９８】
また、導電性無機酸化物微粉体の抵抗値を制御する等の目的で、アンチモン、アルミニウムなどの元素をドープした金属酸化物、導電性材料を表面に有する微粉体なども使用できる。例えば酸化スズ・アンチモンで表面処理された酸化チタン微粉体、アンチモンがドープされた酸化第二スズ微粉体、あるいは酸化第二スズ微粉体などである。
【０１９９】
市販の酸化スズ・アンチモン処理された導電性酸化チタン微粉体としては、例えばＥＣ−３００（チタン工業株式会社）、ＥＴー３００、ＨＪ−１、ＨＩ−２（以上、石原産業株式会社）、Ｗ−Ｐ（三菱マテリアル株式会社）などが挙げられる。
【０２００】
市販のアンチモンドープの導電性酸化スズとしては、例えばＴ−１（三菱マテリアル株式会社）やＳＮ−１００Ｐ（石原産業株式会社）などが、また市販の酸化第二スズとしては、ＳＨ−Ｓ（日本化学産業株式会社）などが挙げられる。
【０２０１】
上記導電性微粉体の体積平均粒径の測定法を例示する。コールター社製、ＬＳ-２３０型レーザー回折式粒度分布測定装置にリキッドモジュールを取り付けて０．０４〜２０００μｍの粒径を測定範囲とし、得られる体積基準の粒度分布より導電性微粉体の体積平均粒径を算出する。測定手順としては、純水１０ｃｃに微量の界面活性剤を添加し、これに導電性微粉体の試料１０ｍｇを加え、超音波分散機（超音波ホモジナイザー）にて１０分間分散した後、測定時間９０秒、測定回数１回で測定する。
【０２０２】
トナーからの測定においては、純水１００ｇに対して、微量の界面活性剤を添加してトナー２〜１０ｇを加え、超音波分散機（超音波ホモジナイザー）にて１０分間分散した後、遠心分離機等により、トナー粒子と上記導電性微粉体を分離する。磁性トナーの場合は磁石を利用することもできる。分離した分散液を測定時間９０秒、測定回数１回で測定する。
【０２０３】
本発明において、導電性微粉体の粒度の調整方法としては、導電性微粉体の１次粒子が製造時において所望の粒度が得られるように製造法、製造条件を設定する方法以外にも、一次粒子の小さな粒子を凝集させる方法、一次粒子の大きな粒子を粉砕する方法或いは分級による方法等が可能であり、更には、所望の粒度の基材粒子の表面の一部もしくは全部に導電性粒子を付着或いは固定化する方法、所望の粒度の粒子に導電性成分が分散された形態を有する導電性粒子を用いる方法等も可能であり、これらの方法を組み合わせて導電性微粉体の粒度を調整することも可能である。
【０２０４】
導電性微粉体の粒子が凝集体として構成されている場合の粒径は、その凝集体としての平均粒径として定義される。導電性微粉体は、１次粒子の状態で存在するばかりでなく２次粒子の凝集した状態で存在することも問題はない。どのような凝集状態であれ、凝集体として帯電部材と像担持体との当接部或いはその近傍の帯電領域に介在し、帯電補助或いは促進の機能が実現できればその形態は問わない。
【０２０５】
本発明において、導電性微粉体の抵抗測定は、錠剤法により測定し正規化して求めることができる。即ち、底面積２．２６ｃｍ²の円筒内に凡そ０．５ｇの粉体試料を入れ上下電極に１５ｋｇの加圧を行うと同時に１００Ｖの電圧を印加し抵抗値を計測、その後正規化して比抵抗を算出する。
【０２０６】
本発明に用いられるトナーには、実質的な悪影響を与えない範囲内で更に他の添加剤、例えばテフロン粉末、ステアリン酸亜鉛粉末、ポリフッ化ビニリデン粉末の如き滑剤粉末、あるいは酸化セリウム粉末、炭化硅素粉末、チタン酸ストロンチウム粉末などの研磨剤、あるいは例えば酸化チタン粉末、酸化アルミニウム粉末などの流動性付与剤、ケーキング防止剤、また、逆極性の有機微粒子、及び無機微粒子を現像性向上剤として少量用いる事もできる。これらの添加剤も表面を疎水化処理して用いることも可能である。
【０２０７】
＜３＞本発明の画像形成方法及び画像形成装置
本発明の画像形成方法は、帯電部材に電圧を印加し、像担持体を帯電させる帯電工程と、帯電された像担持体に、静電潜像を形成させる静電潜像形成工程と、下記（ａ）〜（ｄ）を含む現像工程と、
（ａ）現像容器内に収容されている現像剤を現像剤担持体上に担持させる工程；
（ｂ）該現像剤担持体上の現像剤の層厚を現像剤層厚規制部材により規制する工程；（ｃ）層厚を規制された前記現像剤を前記現像剤担持体と像担持体とが対向する現像領域へ担持搬送する工程；（ｄ）現像剤担持体上の現像剤を像担持体上の静電潜像に転移させてトナー像を形成する工程；
前記像担持体表面に形成されたトナー像を転写材に静電転写する転写工程と、前記転写材上に転写されたトナー像を加熱・定着する定着工程と、を有する画像形成方法において、前記現像工程は、トナー像を転写材上に転写した後に像担持体に残留した現像剤を回収するクリーニング工程を兼ねており、前記現像剤は上記の磁性現像剤を用い、前記現像剤担持体は上記現像剤担持体を用いる画像形成方法である。
また、本発明の画像形成装置は、本発明の画像形成方法を用いたものである。
【０２０８】
本発明における帯電工程は、像担持体と当接部を形成して接触する帯電部材に電圧を印加することにより像担持体を帯電する工程であり、かつ、少なくとも帯電部材と像担持体との当接部及び／又はその近傍に、前記トナー中に含有の導電性微粉体が現像工程で像担持体に付着し転写工程の後も像担持体上に残留し持ち運ばれて介在している。
【０２０９】
以下に本発明の画像形成方法を用いた画像形成装置について図を用いて説明するが、本発明はこれらに限定されない。
【０２１０】
図１は、磁性一成分現像剤を用いた本発明の現像装置の模式図を示す。図１において、公知のプロセスにより形成された静電潜像を保持する像担持体、例えば、電子写真感光ドラム１は、矢印Ｂ方向に回転される。現像剤担持体としての現像スリーブ８は、現像容器としてのホッパー３によって供給された磁性トナーを有する現像剤４を担持して、矢印Ａ方向に回転することによって、現像スリーブ８と感光ドラム１とが対向している現像領域Ｄに現像剤４を搬送する。図１に示すように、現像スリーブ８内には、現像剤４を現像スリーブ８上に磁気的に吸引且つ保持する為に、磁石が内接されているマグネットローラ５が配置されている。
【０２１１】
本発明において現像装置で用いられる現像スリーブ８は、上述の現像剤担持体を用いれば良く、具体的には基体としての金属円筒管６上に被覆された樹脂被覆層７を有する。ホッパー３中には、現像剤４を攪拌するための攪拌翼１０が設けられている。１１は現像スリーブ８とマグネットローラ５とが非接触状態にあることを示す間隙である。
【０２１２】
現像剤４は、現像剤相互間及び現像スリーブ８上の樹脂被覆層７との摩擦により、感光ドラム１上の静電潜像を現像することが可能な摩擦帯電電荷を得る。図１の例では、現像領域Ｄに搬送される現像剤４の層厚を規制するために、現像剤層厚規制部材としてウレタンゴム、シリコーンゴム等のゴム弾性を有する材料、或いはリン青銅、ステンレス鋼等の金属弾性を有する材料の弾性板からなる現像剤層厚規制部材２を使用し、現像スリーブ８に対してカウンター方向に現像剤を介し弾性的に圧接することによって現像剤の薄層を形成している。この様にして、現像スリーブ８上に形成される現像剤４の薄層の厚みは、現像領域Ｄにおける現像スリーブ８と感光ドラム１との間の最小間隙よりも更に薄いものであることが好ましい。
【０２１３】
現像スリーブ８に対する現像剤層厚規制部材２の当接圧力は線圧５〜５０ｇ／ｃｍであることが、現像剤の規制を安定化させ、現像剤層厚を好適にさせることが出来る点で好ましい。現像剤層厚規制部材の当接圧力が線圧５ｇ／ｃｍ未満の場合には、現像剤の規制が弱くなり、カブリやトナーもれの原因となり、線圧５０ｇ／ｃｍを超える場合には、トナーへのダメージが大きくなり、トナー劣化やスリーブ及びブレードへの融着の原因となり易い。
【０２１４】
上記現像スリーブ８に担持された一成分系現像剤４を飛翔させる為、上記現像スリーブ８にはバイアス手段としての電源９により交番バイアス電圧が印加される。この現像バイアスとして直流電圧を使用するときに、静電潜像の画像部（現像剤４が付着して可視化される領域）の電位と背景部の電位との間の値の電圧を現像スリーブ８に印加するのが好ましい。現像された画像の濃度を高め、或は階調性を向上するためには、現像スリーブ８に交番バイアス電圧を印加し、現像領域Ｄに向きが交互に反転する振動電界を形成してもよい。この場合には、上記した現像画像部電位と背景部電位の中間の値を有する直流電圧成分を重畳した交番バイアス電圧を現像スリーブ８に印加するのが好ましい。
【０２１５】
高電位部と低電位部を有する静電潜像の高電位部にトナーを付着させて可視化する、所謂、正規現像の場合には、静電潜像の極性と逆極性に帯電するトナーを使用する。高電位部と低電位部を有する静電潜像の低電位部にトナーを付着させて可視化する、所謂、反転現像の場合には、静電潜像の極性と同極性に帯電するトナーを使用する。高電位、低電位というのは、絶対値による表現である。これらいずれの場合にも、現像剤４は少なくとも現像スリーブ８との摩擦により帯電される。
【０２１６】
図はあくまでも本発明における現像装置を模式的に例示したものであり、現像剤容器（ホッパー３）の形状、攪拌翼１０の有無、磁極の配置に様々な形態があることは言うまでもない。
【０２１７】
図２は本発明における別の形態の現像装置の模式図を示す。図２では現像剤層厚規制部材を現像スリーブ８に対して順方向に現像剤を介し弾性的に圧接したものである。
【０２１８】
本発明は、これらの現像手段、像保持体、帯電手段を一体化してプロセスカートリッジとして用いることもできる。
図３を参照しながら、図１で例示した本発明の現像剤担持体を有する現像装置を使用した画像形成装置の一例について説明する。先ず、一次帯電手段としての接触（ローラ）帯電手段１８により像担持体としての感光ドラム１の表面を負極性に帯電させ、レーザ光の露光１２によるイメージスキャニングにより静電潜像が感光ドラム１上に形成される。次に、現像剤層厚規制部材２を有し、現像剤担持体としての現像スリーブ８が具備されている現像装置によって、上記静電潜像が、現像容器としてのホッパー３内のトナーを有する負帯電性一成分系現像剤４によって反転現像される。
【０２１９】
図３に示す様に、現像領域Ｄにおいて感光ドラム１は現像スリーブに接地されており、現像スリーブ８には電源９により交番バイアス、パルスバイアス及び／又は直流バイアスが印加されている。次に、転写材Ｐが搬送されて転写部に来ると、転写手段としての接触（ローラ）転写手段１３により転写材Ｐの背面（感光ドラム側と反対面）から電圧印加手段２０で帯電されることにより、感光ドラム１の表面上に形成されている現像画像が接触転写手段１３で転写材Ｐ上へ転写される。
次に、感光ドラム１から分離された転写材Ｐは、定着手段としての加熱加圧ローラ定着器１５に搬送され、該定着器によって転写材Ｐ上の現像画像の定着処理がなされる。
【０２２０】
上記の一連の工程において、感光ドラム（即ち、像担持体）１は感光層及び導電性基体を有するものであり、矢印Ｂ方向に動く。現像スリーブ８は、現像領域Ｄにおいて感光ドラム１の表面と同方向（矢印Ａ方向）に進む様に回転する。ホッパー３内の一成分系現像剤４は現像スリーブ８上に担持され、且つ現像スリーブ８の表面との摩擦及び／又はトナー同士の摩擦によって、例えば、マイナスのトリボ電荷が与えられる。更に、現像剤層厚規制部材１２により、現像剤層の厚さを薄く（３０〜３００μｍ）且つ均一に規制して、現像領域Ｄにおける感光ドラム１と現像スリーブ８との間隙よりも薄い現像剤層を形成させる。
【０２２１】
現像スリーブ８は像担持体に対して１００〜１０００μｍの離間距離を有して対向して設置されることが好ましい。現像スリーブ８の像担持体に対する離間距離が１００μｍよりも小さいと、離間距離の振れに対するトナーの現像特性の変化が大きくなるため、安定した画像性を満足する画像形成装置を量産することが困難となる。現像スリーブ８の像担持体に対する離間距離が１０００μｍよりも大きいと、現像装置への転写残トナーの回収性が低下し、回収不良によるカブリを生じ易くなる。また、像担持体上の静電潜像に対するトナーの追従性が低下するために、解像性の低下、画像濃度の低下等の画質低下を招く。好ましくは１２０〜５００μｍがよい。
【０２２２】
また、現像スリーブ８の回転速度を調整することによって、現像スリーブ８の表面速度が感光ドラム１の表面の速度と実質的に等速、もしくはそれに近い速度となる様にすることが好ましい。現像領域Ｄにおいて、現像スリーブ８に現像バイアス電圧として、交番バイアス又はパルスバイアスを電源９により印加してもよい。現像スリーブ８と潜像保持体との間に、少なくともピークトゥーピークの電界強度で３×１０⁶〜１０×１０⁶Ｖ／ｍ、周波数１００〜５０００Ｈｚの交番電界を現像バイアスとして印加することが好ましく良い。
【０２２３】
現像領域Ｄにおける現像剤の移転に際し、感光ドラム１の表面の静電気力、及び交番バイアス又はパルスバイアスの如き現像バイアス電圧の作用によって、現像剤は静電潜像側に移転する。ここで現像同時クリーニング画像形成方法において、トナー粒子に導電性微粉体を外部添加した場合の画像形成プロセス中でのトナー粒子及び導電性微粉体の挙動について説明する。
【０２２４】
トナーに含有させた導電性微粉体は、現像工程における像担持体側の静電潜像の現像時にトナー粒子とともに適当量が像担持体側に移行する。
【０２２５】
像担持体上のトナー像は転写工程において転写材側に転移する。像担持体上の導電性微粉体も一部は転写材側に付着するが残りは像担持体上に付着保持されて残留する。トナーと逆極性の転写バイアスを印加して転写を行う場合には、トナーは転写材側に引かれて積極的に転移するが、像担持体上の導電性微粉体は導電性であることで転写材側には積極的には転移せず、一部は転写材側に付着するものの残りは像担持体上に付着保持されて残留する。
【０２２６】
クリーナを用いない画像形成方法では、転写後の像担持体面に残存の転写残トナーおよび上記の残存導電性微粉体は、像担持体と接触帯電部材の当接部である帯電部に像担持体面の移動でそのまま持ち運ばれて接触帯電部材に付着・混入する。
【０２２７】
従って、像担持体と接触帯電部材との当接部に導電性微粉体が介在した状態で像担持体の接触帯電が行われる。
【０２２８】
この導電性微粉体の存在により、接触帯電部材への転写残トナーの付着・混入による汚染にかかわらず、接触帯電部材の像担持体への緻密な接触性と接触抵抗を維持できるため、該接触帯電部材による像担持体の帯電を良好に行わせることができる。
【０２２９】
また、接触帯電部材に付着・混入した転写残トナーは、帯電部材から像担持体へ印加される帯電バイアスによって、帯電バイアスと同極性に帯電を揃えられて接触帯電部材から徐々に像担持体上に吐き出され、像担持体面の移動とともに現像部に至り、現像工程において現像同時クリーニング（回収）される。
【０２３０】
更に、画像形成が繰り返されることで、トナーに含有させてある導電性微粉体が、現像部で像担持体面に移行し該像担持面の移動により転写部を経て帯電部に持ち運ばれて帯電部に逐次に導電性微粉体が供給され続けるため、帯電部において導電性微粉体が脱落等で減少したり、劣化するなどしても、帯電性の低下が生じることが防止されて良好な帯電性が安定して維持される。
【０２３１】
本発明の画像形成方法における帯電工程は、像担持体（被帯電体）に、ローラ型（帯電ローラ）、ファーブラシ型、磁気ブラシ型、ブレード型等の導電性の帯電部材（接触帯電部材・接触帯電器）を接触させ、この接触帯電部材に所定の帯電バイアスを印加して被帯電体面を所定の極性・電位に帯電させる接触帯電装置を用いる。接触帯電部材に対する印加帯電バイアスは直流電圧のみでも良好な帯電性を得ることが可能であるが、直流電圧に交番電圧（交流電圧）を重畳してもよい。
【０２３２】
交番電圧の波形としては、正弦波、矩形波、三角波等適宜使用可能である。また、直流電源を周期的にオン／オフすることによって形成されたパルス波であっても良い。このように交番電圧の波形としては周期的にその電圧値が変化するようなバイアスが使用できる。
【０２３３】
本発明においては、帯電部材が、帯電部材と像担持体との間に導電性微粉体を介在させる当接部を設ける上で弾性を有することが好ましく、帯電部材に電圧を印加することにより像担持体を帯電するために導電性であることが好ましい。従って、帯電部材は弾性導電ローラ、磁性粒子を磁気拘束させた磁気ブラシ部を有し、該磁気ブラシ部を被帯電体に接触させた磁気ブラシ接触帯電部材或いは導電性繊維から構成される帯電ブラシであることが好ましく良い。
【０２３４】
弾性導電ローラの硬度は、硬度が低すぎると形状が安定しないために被帯電体との接触性が悪くなり、更に、帯電部材と像担持体との当接部に導電性微粉体を介在させることで弾性導電ローラ表層を削り或いは傷つけ、安定した帯電性が得られにくい。また、硬度が高すぎると被帯電体との間に帯電当接部を確保できないだけでなく、被帯電体表面へのミクロな接触性が悪くなるので、アスカーＣ硬度で２５〜５０度が好ましい範囲である。
【０２３５】
弾性導電ローラは弾性を持たせて被帯電体との十分な接触状態を得ると同時に、移動する被帯電体を充電するに十分低い抵抗を有する電極として機能することが重要である。一方では被帯電体にピンホールなどの欠陥部位が存在した場合に電圧のリークを防止する必要がある。被帯電体として電子写真用感光体を用いた場合、十分な帯電性と耐リークを得るには１０³〜１０⁸Ωの抵抗であることが良く、より好ましくは１０⁴〜１０⁷Ωの抵抗であることが良い。
【０２３６】
ローラ抵抗は、ローラの芯金に総圧１ｋｇの加重がかかるよう直径３０ｍｍの円筒状アルミドラムにローラを圧着した状態で、芯金とアルミドラムとの間に１００Ｖを印加して、計測できる。
【０２３７】
例えば、弾性導電ローラは芯金上に可撓性部材としてのゴムあるいは発泡体の中抵抗層を形成することにより作成される。中抵抗層は樹脂（例えばウレタン）、導電性物質（例えばカーボンブラック）、硫化剤、発泡剤等により処方され、芯金の上にローラ状に形成する。その後必要に応じて切削、表面を研磨して形状を整え、弾性導電ローラを作成することができる。該ローラ表面は導電性微粉体を介在させるために微少なセルまたは凹凸を有していることが好ましい。
【０２３８】
弾性導電ローラの材質としては、弾性発泡体に限定するものでは無く、弾性体の材料として、エチレン−プロピレン−ジエンポリエチレン（ＥＰＤＭ）、ウレタン、ブタジエンアクリロニトリルゴム（ＮＢＲ）、シリコーンゴムや、イソプレンゴム等に抵抗調整のためにカーボンブラックや金属酸化物等の導電性物質を分散したゴム材や、またこれらを発泡させたものがあげられる。また、導電性物質を分散せずに、或いは導電性物質と併用してイオン導電性の材料を用いて抵抗調整をすることも可能である。
【０２３９】
弾性導電ローラは像担持体としての被帯電体に対して弾性に抗して所定の押圧力で圧接させて配設し、弾性導電ローラと像担持体の当接部である帯電当接部を形成させる。この帯電当接部幅は特に制限されるものではないが、弾性導電ローラと像担持体の安定して密な密着性を得るため１ｍｍ以上、より好ましくは２ｍｍ以上が良い。
【０２４０】
また、接触帯電部材としての帯電ブラシは、一般に用いられている繊維に導電材を分散させて抵抗調整されたものが用いられる。繊維としては、一般に知られている繊維が使用可能であり、例えばナイロン、アクリル、レーヨン、ポリカーボネート、ポリエステル等が挙げられる。導電材としては、一般に知られている導電材が使用可能であり、例えば、ニッケル、鉄、アルミニウム、金、銀等の導電性金属或いは酸化鉄、酸化亜鉛、酸化スズ、酸化アンチモン、酸化チタン等の導電性金属の酸化物、更にはカーボンブラック等の導電粉が挙げられる。なおこれら導電材は必要に応じ疎水化、抵抗調整の目的で表面処理が施されていてもよい。使用に際しては、繊維との分散性や生産性を考慮して選択して用いる。
【０２４１】
接触帯電部材として帯電ブラシを用いる場合には、固定型と回動可能なロール状のものがある。ロール状帯電ブラシとしては、例えば導電性繊維をパイル地にしたテープを金属製の芯金にスパイラル状に巻き付けてロールブラシとすることができる。導電性繊維は、繊維の太さが１〜２０デニール（繊維径１０〜５００μｍ程度）、ブラシの繊維の長さは１〜１５ｍｍ、ブラシ密度は１平方インチ当たり１万〜３０万本（１平方メートル当たり１．５×１０⁷〜４．５×１０⁸本程度）のものが好ましく用いられる。
【０２４２】
帯電ブラシは、極力ブラシ密度の高い物を使用することが好ましく、１本の繊維を数本〜数百本の微細な繊維から作ることも好ましく良い。例えば、３００デニール／５０フィラメントのように３００デニールの微細な繊維を５０本束ねて１本の繊維として植毛することも可能である。しかしながら、本発明においては、直接注入帯電の帯電ポイントを決定しているのは、主には帯電部材と像担持体との帯電当接部及びその近傍の導電性微粉体の介在密度に依存しているため、帯電部材の選択の範囲は広められている。
【０２４３】
帯電ブラシの抵抗値は、弾性導電ローラの場合と同様に十分な帯電性と耐リークを得るには１０³〜１０⁸Ωの抵抗であることが良く、より好ましくは１０⁴〜１０⁷Ωの抵抗であることが良い。
【０２４４】
帯電ブラシの材質としては、ユニチカ（株）製の導電性レーヨン繊維ＲＥＣ−Ｂ、ＲＥＣ−Ｃ、ＲＥＣ−Ｍ１、ＲＥＣ−Ｍ１０、さらに東レ（株）製のＳＡ−７、日本蚕毛（株）製のサンダーロン、カネボウ製のベルトロン、クラレ（株）製のクラカーボ、レーヨンにカーボンを分散したもの、三菱レーヨン（株）製のローバル等があるが、環境安定性の点でＲＥＣ−Ｂ、ＲＥＣ−Ｃ、ＲＥＣ−Ｍ１、ＲＥＣ−Ｍ１０が特に好ましく良い。
【０２４５】
また、接触帯電部材が可撓性を有していることが接触帯電部材と像担持体の当接部において導電性微粉体が像担持体に接触する機会を増加させ、高い接触性を得ることができ、直接注入帯電性を向上させる点で好ましく良い。つまり、接触帯電部材が導電性微粉体を介して密に像担持体に接触して、接触帯電部材と像担持体の当接部に存在する導電性微粉体が像担持体表面を隙間なく摺擦することで、接触帯電部材による像担持体の帯電は導電性微粉体の存在により放電現象を用いない安定かつ安全な直接注入帯電が支配的となり、従来のローラ帯電等では得られなかった高い帯電効率が得られ、接触帯電部材に印加した電圧とほぼ同等の電位を像担持体に与えることができる。
【０２４６】
更に、当接部を形成する帯電部材の表面の移動速度と像担持体の表面の移動速度には、相対的速度差を設けることが好ましい。接触帯電部材と像担持体の当接部において導電性微粉体が像担持体に接触する機会を格段に増加させ、より高い接触性を得ることができる、直接注入帯電性を向上させる点で好ましく良い。
【０２４７】
接触帯電部材と像担持体との当接部に導電性微粉体を介在させることにより、導電性微粉体の潤滑効果（摩擦低減効果）により接触帯電部材と像担持体との間に大幅なトルクの増大及び接触帯電部材及び像担持体表面の顕著な削れ等を伴うことなく速度差を設けることが可能となる。
【０２４８】
速度差を設ける構成としては、接触帯電部材を回転駆動させて像担持体と該接触帯電部材に速度差を設けることができる。
【０２４９】
帯電部に持ち運ばれる像担持体上の転写残トナーを接触帯電部材に一時的に回収し均すために、接触帯電部材と像担持体は互いに逆方向に移動させることが好ましく良い。接触帯電部材の回転方向を像担持体表面の移動方向とは逆方向に回転するように構成することが望ましい。即ち、逆方向回転で像担持体上の転写残トナーを一旦引き離し帯電を行うことにより優位に直接注入帯電を行うことが可能である。
【０２５０】
帯電部材を像担持体表面の移動方向と同じ方向に移動させて速度差をもたせることも可能であるが、直接注入帯電の帯電性は像担持体の周速と帯電部材の周速の比に依存するため、逆方向と同じ周速比を得るには順方向では帯電部材の回転数が逆方向の時に比べて大きくなるので、帯電部材を逆方向に移動させる方が回転数の点で有利である。ここで記述した周速比は、
周速比（%）＝（帯電部材周速−潜像保持体周速）／潜像保持体周速×100
である（帯電部材周速は当接部において帯電部材表面が潜像保持体表面と同じ方向に移動するとき正の値である）。
【０２５１】
相対速度差を示す指標としては、次式で表される相対移動速度比がある。
相対移動速度比（％）＝｜（Ｖｃ−Ｖｐ）／Ｖｐ｜×１００
（式中、Ｖｃは帯電部材表面の移動速度、Ｖｐは像担持体表面の移動速度であり、Ｖｃは、当接部において帯電部材表面が像担持体表面と同じ方向に移動するとき、Ｖｐと同符号の値とする。）
相対移動速度比は、１０〜５００％であることが好ましく、２０〜４００％であることがより好ましい。相対移動速度比が、上記範囲よりも小さすぎる場合には、接触帯電部材と像担持体との接触確率を増加させることが十分にはできず、直接注入帯電による像担持体の帯電性を維持することが難しい場合がある。更に、上述の像担持体と接触帯電部材との接触部に介在する導電性微粉体の量を接触帯電部材と像担持体との摺擦によって制限することにより像担持体の帯電阻害を抑制する効果、及び転写残トナー粒子のパターンを均し現像同時クリーニングでの現像剤の回収性を高める効果が十分には得られない場合もある。相対移動速度比が、上記範囲よりも大きすぎる場合には、帯電部材の移動速度を高めることとなるために、像担持体と接触帯電部材との接触部に持ち連ばれた現像剤成分が飛散することによる装置内の汚染を生じ易く、像担持体及び接触帯電部材が摩耗し易くなるあるいは傷の発生を生じ易くなり短寿命化する傾向がある。
また、帯電部材の移動速度が０である場合（帯電部材が静止している状態）は、帯電部材の像担持体との接触点が定点となるため、帯電部材の像担持体への接触部の摩耗または劣化を生じ易く、像担持体の帯電阻害を抑制する効果及び転写残トナー粒子のパターンを均し現像同時クリーニングでの現像剤の回収性を高める効果が低下しやすく好ましくない。
【０２５２】
像担持体と接触帯電部材との当接部における導電性微粉体の介在量は、少なすぎると、該導電性微粉体による潤滑効果が十分に得られず、像担持体と接触帯電部材との摩擦が大きくて接触帯電部材を像担持体に速度差を持って回転駆動させることが困難である。つまり、駆動トルクが過大となるし、無理に回転させると接触帯電部材や像担持体の表面が削れてしまう傾向がある。更に導電性微粉体による接触機会増加の効果が得られないこともあり十分な帯電性能が得られにくい。一方、介在量が多過ぎると、導電性微粉体の接触帯電部材からの脱落が著しく増加し作像上に悪影響が出やすい。
【０２５３】
実験によると導電性微粉体の介在量は１０³個／ｍｍ²以上が好ましく、より好ましくは１０⁴個／ｍｍ²以上が良い。１０³個／ｍｍ²より低いと十分な潤滑効果と接触機会増加の効果が得られず帯電性能の低下が生じやすい。１０⁴個／ｍｍ²より低いと転写残トナーが多い場合に帯電性能の低下が生じやすい。
【０２５４】
導電性微粉体の塗布密度範囲は、導電性微粉体をどれぐらいの密度で像担持体上に塗布することで均一帯電性の効果が得られるかでも決定される。
【０２５５】
帯電時は少なくともこの記録解像度よりは均一な接触帯電が必要なことは言うまでもない。しかしながら人間の目の視覚特性に関して、空間周波数が１０ｃｙｃｌｅｓ／ｍｍ以上では、画像上の識別諧調数が限りなく１に近づいていく、すなわち濃度ムラを識別できなくなる。この特性を積極的に利用すると、像担持体上に導電性微粉体を付着させた場合、少なくとも像担持体上で１０ｃｙｃｌｅｓ／ｍｍ以上の密度で導電性微粉体を存在させ、直接注入帯電を行えば良いことになる。たとえ導電性微粉体の存在しないところにミクロな帯電不良が発生したとしても、その帯電不良によって発生する画像上の濃度ムラは、人間の視覚特性を越えた空間周波数領域に発生するため、画像上では問題は無いことになる。
【０２５６】
導電性微粉体の塗布密度が変化したときに、画像上に濃度ムラとしての帯電不良が認知されるかどうかについては、導電性微粉体をわずかにでも塗布されれば（例えば１０個／ｍｍ²）、帯電ムラ発生の抑制に効果が認められるが、画像上の濃度ムラが人間にとって許容可能かどうかと言う点においてはまだ不十分である。
【０２５７】
ところがその塗布量を１０²個／ｍｍ²以上すると、画像の客観評価において急激に好ましい結果が得られるようになる。更に、塗布量を１０³個／ｍｍ²以上増加させていくことにより、帯電不良に起因する画像上の問題点は皆無となる。
【０２５８】
直接注入帯電方式による帯電では、放電帯電方式とは根本的に異なり、帯電部材が感光体に確実に接触する事で帯電が行われている訳であるが、たとえ導電性微粉体を像担持体上に過剰に塗布したとしても、接触できない部分は必ず存在する。ところが本発明の人間の視覚特性を積極的に利用した導電性微粉体の塗布を行うことで、実用上この問題点を解決する。
【０２５９】
しかしながら、直接注入帯電方式を現像同時クリーニング画像形成における像担持体の一様帯電として適用する場合には、転写残トナーの帯電部材への付着或いは混入による帯電特性の低下が生ずる。転写残トナーの帯電部材への付着及び混入を抑制し、または転写残トナーの帯電部材への付着或いは混入による帯電特性への悪影響に打ち勝って、良好な直接注入帯電を行うには、像担持体と接触帯電部材との当接部における導電性微粉体の介在量が１０⁴個／ｍｍ²以上であることが好ましく良い。
【０２６０】
塗布密度上限値は導電性微粉体の粒径によっても変わってくるために、一概にはいえないが、強いて記述するならば、導電性微粉体が像担持体上に１層均一に塗布される量が上限である。それ以上塗布されても効果が向上するわけではなく逆に、露光光源を遮ったり、散乱させたりという弊害が生じる。
【０２６１】
導電性微粉体の量は、５×１０⁵個／ｍｍ²を超えると、導電性微粉体の像担持体への脱落が著しく増加し、導電性微粉体自体の光透過性を問わず、像担持体への露光量不足が生じる。５×１０⁵個／ｍｍ²以下では脱落する粒子量も低く抑えられ露光の阻害を改善できる。該介在量範囲において像担持体上に脱落した粒子の存在量を測ると１０²〜１０⁵個／ｍｍ²であったことから、作像上弊害がない該存在量としては１０⁴〜５×１０⁵個／ｍｍ²の介在量が好ましい。
【０２６２】
帯電当接部での導電性微粉体の介在量及び静電潜像形成工程での像担持体上の導電性微粉体存在量の測定方法について述べる。導電性微粉体の介在量は接触帯電部材と像担持体の接触面部を直接測ることが望ましいが、当接部を形成する接触帯電部材の表面と像担持体の表面には速度差を設けている場合、接触帯電部材に接触する前に像担持体上に存在した粒子の多くは逆方向に移動しながら接触する帯電部材に剥ぎ取られることから、本発明では接触面部に到達する直前の接触帯電部材表面の粒子量をもって介在量とする。
【０２６３】
具体的には、以下の通りである。帯電バイアスを印加しない状態で像担持体及び弾性導電ローラの回転を停止し、像担持体及び弾性導電ローラの表面をビデオマイクロスコープ（ＯＬＹＭＰＵＳ製ＯＶＭ１０００Ｎ）及びデジタルスチルレコーダ（ＤＥＬＴＩＳ製ＳＲ−３１００）で撮影する。弾性導電ローラについては、弾性導電ローラを像担持体に当接させるのと同じ条件でスライドガラスに当接させ、スライドガラスの背面からビデオマイクロスコープにて接触面を１０００倍の対物レンズで１０箇所以上撮影する。得られたデジタル画像から個々の微粉体を領域分離するため、ある閾値を持って２値化処理し、微粉体の存在する領域の数を所望の画像処理ソフトを用いて計測する。また、像担持体上の存在量についても像担持体上を同様のビデオマイクロスコープにて撮影し同様の処理を行い計測する。
【０２６４】
また、本発明の画像形成方法においては、像担持体の最表面層の体積抵抗が、１×１０⁹Ωｃｍ以上１×１０¹⁴Ωｃｍ以下が好ましく、該範囲の体積抵抗であることにより、より良好な帯電性を与えることができる。電荷の直接注入による帯電方式においては、被帯電体側の抵抗を下げることでより効率良く電荷の授受が行えるようになる。このためには、最表面層の体積抵抗値としては１×１０¹⁴Ωｃｍ以下であることが好ましく良い。一方、像担持体として静電潜像を一定時間保持する必要するためには、最表面層の体積抵抗値としては１×１０⁹Ωｃｍ以上であることが好ましく良い。
【０２６５】
更に、像担持体が電子写真感光体であり、該電子写真感光体の最表面層の体積抵抗が１×１０⁹Ωｃｍ以上１×１０¹⁴Ωｃｍ以下であることにより、プロセススピードの速い装置においても、十分な帯電性を与えることができより好ましい。
【０２６６】
また、像担持体はアモルファスセレン、ＣｄＳ、ＺｎＯ₂、アモルファスシリコン又は有機系感光物質の様な光導電絶縁物質層を持つ感光ドラムもしくは感光ベルトであることが好ましく、アモルファスシリコン感光層、又は有機感光層を有する感光体が特に好ましく用いられる。
【０２６７】
有機感光層としては、電荷発生物質及び電荷輸送性能を有する物質を同一層に含有する単一層型でもよく、又は電荷輸送層と電荷発生層を有する機能分離型感光層であっても良い。導電性基体上に電荷発生層、次いで電荷輸送層の順で積層されている構造の積層型感光層は好ましい例の一つである。
【０２６８】
像担持体の表面抵抗を調整することで、更に安定して像担持体の均一な帯電を行うことができる。
【０２６９】
像担持体の電荷注入をより効率化或いは促進する目的で、電子写真感光体の表面に電荷注入層を設けることも好ましい。電荷注入層は、結着樹脂中に導電性微粒子を分散させた形態が好ましい。
【０２７０】
電荷注入層を設ける形態としては、例えば、
（i）セレン、アモルファスシリコン等の無機感光体もしくは単一層型有機感光体の上に、電荷注入層を設ける、
（ii）機能分離型有機感光体の電荷輸送層としての、電荷輸送剤と結着樹脂からなる表面層に、電荷注入層としての機能を兼ねさせる（例えば、電荷輸送層として結着樹脂中に電荷輸送剤と導電性微粒子を分散させる、あるいは電荷輸送剤自体もしくはその存在状態によって、電荷輸送層に電荷注入層としての機能を持たせる）、
（iii）機能分離型有機感光体上に最表面層として電荷注入層を設ける等があるが、最表面層の体積抵抗が好ましい範囲にあることが重要である。
【０２７１】
電荷注入層としては、例えば、金属蒸着膜等の無機材料の層、あるいは導電性微粒子を結着樹脂中に分散させた導電性微粒子分散樹脂層等によって構成され、蒸着膜は蒸着、導電性微粒子分散樹脂層はディッピング塗工法、スプレー塗工法、ロールコート塗工法及びビーム塗工法等の適当な塗工法にて塗工することによって形成される。また、絶縁性の結着樹脂に光透過性の高いイオン導電性を持つ樹脂を混合もしくは共重合させて構成するもの、または中抵抗で光導電性のある樹脂単体で構成するものでもよい。
【０２７２】
この中でも、像担持体の最表面層が、少なくとも金属酸化物からなる導電性微粒子（以下、「酸化物導電性微粒子」と表記する）が分散された樹脂層であることが好ましい。すなわち、像担持体の最表面層をこのような構成にすることにより、電子写真感光体の表面の抵抗を下げてより効率良く電荷の授受を行うことができ、かつ表面の抵抗を下げたことで像担持体が静電潜像を保持している間に潜像電荷が拡散することによる潜像のボケもしくは流れを抑制できるため好ましい。
【０２７３】
上記酸化物導電性微粒子が分散された樹脂層の場合、分散された粒子による入射光の散乱を防ぐために、入射光の波長よりも酸化物導電性微粒子の粒径の方が小さいことが好ましい。従って、分散される酸化物導電性微粒子の粒径としては０．５μｍ以下であることが好ましい。酸化物導電性微粒子の含有量は、最外層の総重量に対して２〜９０質量％が好ましく、５〜７０質量％がより好ましい。酸化物導電性微粒子の含有量が上記範囲よりも少なすぎる場合には、所望の体積抵抗値を得にくくなる。また、含有量が上記範囲よりも多すぎる場合には、膜強度が低下してしまうため、電荷注入層が削り取られやすくなり、感光体の寿命が短くなる傾向があり、また抵抗が低くなりすぎてしまうことによって潜像電位が流れることによる画像不良を生じやすくなる。
【０２７４】
また、電荷注入層の層厚は０．１〜１０μｍが好ましく、潜像の輪郭のシャープさを得る上では５μｍ以下であることがより好ましく、電荷注入層の耐久性の点からは１μｍ以上であることがより好ましい。
電荷注入層の結着樹脂は、電荷注入層の下層（例えば電荷輸送層）に用いられる結着樹脂と同じとすることも可能であるが、この場合には電荷注入層の塗工時に下層の塗工面を乱してしまう可能性があるため、形成方法を特に選択する必要がある。
【０２７５】
なお、本発明における像担持体の最表面層の体積抵抗値の測定方法は、表面に金を蒸着させターボリエチレンテレフタレート（ＰＥＴ）フィルム上に像担持体の最表面層と同様の組成からなる層を作成し、これを体積抵抗測定装置（ヒューレットパッカード社製４１４０Ｂ ｐＡ ＭＡＴＥＲ）にて、温度２３℃、湿度６５％の環境で１００Ｖの電圧を印加して測定することにより行う。
【０２７６】
また、本発明においては、像担持体表面に離型性を付与することが好ましく、像担持体表面の水に対する接触角は８５度以上であることが好ましい。より好ましくは像担持体表面の水に対する接触角は９０度以上である。
【０２７７】
像担持体表面が高い接触角を有することは、像担持体表面がトナー粒子に対して高い離型性を有することを示す。この効果により、現像同時クリーニング工程においては現像剤の回収効率が向上する。また、転写残トナー量を著しく減少させることができるため、転写残トナーによる像担持体の帯電性低下を抑制することもできる。
【０２７８】
像担持体表面に離型性を付与する手段としては、例えば、
▲１▼膜を構成する樹脂自体に表面エネルギーの低いものを用いる、
▲２▼撥水、親油性を付与するような添加剤を加える、
▲３▼高い離型性を有する材料（滑剤微粒子）を粉体状にして分散する、
が挙げられる。▲１▼の表面エネルギーの低い樹脂は、樹脂の構造中にフッ素含有基、シリコーン含有基を導入することにより得られる。▲２▼の添加剤としては、界面活性剤が挙げられる。▲３▼の滑剤微粒子としては、ポリ４フッ化エチレン、ポリフッ化ビニリデン及びフッ化カーボン等のフッ素原子を含むフッ素系樹脂、シリコーン系樹脂又はポリオレフィン系樹脂等を用いることが挙げられる。
【０２７９】
これらの手段によって像担持体表面の水に対する接触角を８５度以上とすることが可能である。
この中でも像担持体の最表面層が、少なくともフッ素系樹脂、シリコーン系樹脂又はポリオレフィン系樹脂から選ばれる少なくとも１種以上の材料からなる滑剤微粒子が分散された層であることが好ましい。特に、ポリ４フッ化エチレンやポリフッ化ビニリデン等の含フッ素樹脂を用いることが好適である。本発明においては、▲３▼の滑剤微粒子としてフッ素系樹脂を離型性粉体として用いた場合には、最表面層への分散が好適である。
【０２８０】
これらの滑剤微粒子を最表面層に含有させるためには、結着樹脂中に該粉体を分散させた層を感光体最表面に設けるか、あるいは、樹脂を主体として構成されている有機感光体であれば、新たに表面層を設けなくても最表面層に該粉体を分散させれぱ良い。
【０２８１】
上記滑剤微粒子の像担持体の表面層への添加量は、表面層総重量に対して、１〜６０質量％であることが好ましく、２〜５０質量％であることがより好ましい。添加量が上記範囲よりも少なすぎると転写残トナーが充分に減少せず、現像同時クリーニング装置での現像剤の回収効率が充分でない。添加量が上記範囲よりも大きすぎると膜の強度が低下したり、感光体への入射光量が著しく低下して像担持体の帯電性を損ねたりするため好ましくない。該粉体の粒径については、画質の面から１μｍ以下であることが好ましく、０．５μｍ以下であることがより好ましい。粒径が上記範囲よりも大きすぎると入射光の散乱によりラインの切れが悪くなりやすく、解像性を損ねやすい。
【０２８２】
本発明において、接触角の測定は純水を用い、装置は協和界面科学（株）製接触角計ＣＡ−ＤＳ型を用いて行う。
【０２８３】
本発明に用いられる像担持体としての感光体の好ましい様態のひとつを以下に説明する。導電性基体としては、アルミニウム又はステンレス等の金属；アルミニウム合金又は酸化インジウム−酸化錫合金による被膜層を有するプラスチック；導電性粒子を含浸させた紙又はプラスチック；導電性ポリマーを有するプラスチック；の円筒状シリンダー及びフィルムが用いられる。
【０２８４】
これら導電性基体上には、感光層の接着性向上、塗工性改良、基体の保護、基体上に欠陥の被覆、基体からの電荷注入性改良または感光層の電気的破壊に対する保護を目的として導電層や下引き層を設けても良い。
【０２８５】
導電層は、金属や金属酸化物粒子を含有する樹脂層であり、膜厚は１０〜３０μｍが好ましい。
【０２８６】
下引き層は、ポリビニルアルコール、ポリ−Ｎ−ビニルイミダゾール、ポリエチレンオキシド、エチルセルロース、メチルセルロース、ニトロセルロース、エチレン−アクリル酸コポリマー、ポリビニルブチラール、フェノール樹脂、カゼイン、ポリアミド、共重合ナイロン、ニカワ、ゼラチン、ポリウレタン又は酸化アルミニウム等の材料によって形成される。下引き層の膜厚は通常０．１〜１０μｍ、好ましくは０．１〜３μｍが良い。
【０２８７】
電荷発生層は、アゾ系顔料、フタロシアニン系顔料、インジゴ系顔料、ペリレン系顔料、多環キノン系顔料、スクワリリウム色素、ピリリウム塩類、チオピリリウム塩類、トリフェニルメタン系色素又はセレンや非晶質シリコン等の無機物質等の電荷発生物質を適当な結着樹脂に分散し塗工する、あるいは蒸着により形成する。なかでもフタロシアニン系顔料が感光体感度を本発明に適合する感度に調整するうえで好ましい。結着樹脂としては、例えば、ポリカーボネート樹脂、ポリエステル樹脂、ポリビニルブチラール樹脂、ポリスチレン樹脂、アクリル樹脂、メタクリル樹脂、フェノール樹脂、シリコーン樹脂、エポキシ樹脂、酢酸ビニル樹脂等が挙げられる。電荷発生層中に含有される結着樹脂の量は８０質量％以下、好ましくは０〜４０質量％であることが良い。電荷発生層の膜厚は５μｍ以下、特には０．０５〜２μｍが好ましい。
【０２８８】
電荷輸送層は、電界の存在下で電荷発生層から電荷キャリアを受け取り、これを輸送する機能を有している。電荷輸送層は電荷輸送物質を必要に応じて結着樹脂と共に溶剤中に溶解し、塗工することによって形成され、その膜厚は一般的には５〜４０μｍである。電荷輸送物質としては、主鎖または側鎖にビフェニレン、アントラセン、ピレン及びフェナントレン等の多環芳香族化合物；インドール、カルバゾール、オキサジアゾール及びピラゾリンの如き含窒素環式化合物；ヒドラゾン化合物；スチリル化合物；セレン；セレン−テルル；非晶質シリコン；硫化カドニウム等が挙げられる。
【０２８９】
これら電荷輸送物質を分散させる結着樹脂としては、ポリカーボネート樹脂、ポリエステル樹脂、ポリメタクリル酸エステル、ポリスチレン樹脂、アクリル樹脂及びポリアミド樹脂等の樹脂；ポリ−Ｎ−ビニルカルバゾール及びポリビニルアントラセン等の有機光導電性ポリマーが挙げられる。
【０２９０】
表面層として、前述のように電荷注入をより効率化或いは促進するために樹脂中に導電性微粒子を分散させた層を設けてもよい。表面層の樹脂としては、ポリエステル、ポリカーボネート、アクリル樹脂、エポキシ樹脂、フェノール樹脂、あるいはこれらの樹脂の硬化剤が単独あるいは２種以上組み合わされて用いられる。導電性微粒子の例としては、金属又は金属酸化物が挙げられる。好ましくは、酸化亜鉛、酸化チタン、酸化スズ、酸化アンチモン、酸化インジウム、酸化ビスマス、酸化スズ被膜酸化チタン、スズ被膜酸化インジウム、アンチモン被膜酸化スズ又は酸化ジルコニウム等の酸化物導電性微粒子がある。これらは単独で用いても２種以上を混合して用いても良い。
【０２９１】
本発明においては、像担持体の帯電面に静電潜像を形成する静電潜像形成手段が、像露光手段であることが好ましい。静電潜像形成のための画像露光手段としては、デジタル的な静電潜像を形成するレーザ走査露光手段に限定されるものではなく、通常のアナログ的な画像露光やＬＥＤなどの他の発光素子でも構わないし、蛍光燈等の発光素子と液晶シャッター等の組み合わせによるものなど、画像情報に対応した静電潜像を形成できるものであるなら構わない。
【０２９２】
【実施例】
以下、本発明を製造例及び実施例により具体的に説明するが、これらは本発明を何ら限定するものではない。尚、以下の配合における部数は全て質量部である。
【０２９３】
＜１＞感光体の製造
負帯電用の有機光導電性物質を用いた感光体（以下「ＯＰＣ感光体」と表記する）を製造した。感光体の基体には、直径２４ｍｍのアルミニウム製のシリンダーを用いた。このシリンダー上に下記の各層を浸漬塗布することにより順次積層して感光体を作製した。
【０２９４】
第１層は導電層であり、アルミニウム基体の欠陥等をならすため、またレーザ露光の反射によるモアレの発生を防止するために設けられている厚さ約２０μｍの導電性粒子分散樹脂層（酸化錫及び酸化チタンの粉末をフェノール樹脂に分散したものを主体とする）である。
【０２９５】
第２層は正電荷注入防止層（下引き層）であり、アルミニウム基体から注入された正電荷が感光体表面に帯電された負電荷を打ち消すのを防止する役割を果たし、メトキシメチル化ナイロンによって１０⁶Ωｃｍ程度に抵抗調整された厚さ約１μｍの中抵抗層である。
【０２９６】
第３層は電荷発生層であり、ジスアゾ系の顔料をブチラール樹脂に分散した厚さ約０．３μｍの層であり、レーザ露光を受けることによって正負の電荷対を発生する。
【０２９７】
第４層は電荷輸送層であり、ポリカーボネート樹脂にヒドラゾン化合物を分散した厚さ約２５μｍの層であり、Ｐ型半導体である。従って、感光体表面に帯電された負電荷はこの層を移動することはできず、電荷発生層で発生した正電荷のみを感光体表面に輸送することができる。
【０２９８】
第５層は電荷注入層であり、光硬化性のアクリル樹脂に導電性酸化スズ微粒子及び粒径約０．２５μｍの四フッ化エチレン樹脂粒子を分散したものである。具体的には、樹脂に対して、アンチモンをドーピングし低抵抗化した粒径約０．０３μｍの酸化スズ粒子を１００質量％、更に四フッ化エチレン樹脂粒子を２０質量％、分散剤を１．２質量％分散したものである。このようにして調製した塗工液をスプレー塗工法にて厚さ約２．５μｍに塗工して電荷注入層とした。
【０２９９】
このようにして得られた感光体の最表面層における体積抵抗は、５×１０¹²Ωｃｍ、感光体表面の水に対する接触角は、１０３度であった。
【０３００】
＜２＞磁性粉体の製造
（磁性粉体の製造例１）
硫酸第一鉄水溶液中に、鉄イオンに対してｌ．０〜１．１当量の苛性ソーダ溶液を混合し、水酸化第一鉄を含む水溶液を調製した。水溶液のｐＨを９前後に維持しながら、空気を吹き込み、８０〜９０℃で酸化反応を行い、種晶を生成させるスラリー液を調製した。次いで、このスラリー液に当初のアルカリ量（苛性ソーダのナトリウム成分）に対し０．９〜１．２当量となるよう硫酸第一鉄水溶液を加えた後、スラリー液をｐＨ８に維持して、空気を吹込みながら酸化反応をすすめ、酸化反応後に生成した磁性酸化鉄粒子を洗浄、濾過して一旦取り出した。この時、含水サンプルを少量採取し、含水量を計っておいた。次に、この含水サンプルを乾燥せずに別の水系媒体中に再分散させた後、再分散液のｐＨを約６に調整し、十分攪拌しながらシランカップリング剤（ｎ−Ｃ₁₀ Ｈ₂₁Ｓｉ（ＯＣＨ₃）₃）を磁性酸化鉄に対し１．０質量部（磁性酸化鉄の量は含水サンプルから含水量を引いた値として計算した）添加し、カップリング処理を行った。生成した疎水性酸化鉄粒子を常法により洗浄、濾過、乾燥し、次いで若干凝集している粒子を解砕処理して、磁性粉体１を得た。
（磁性粉体の製造例２）
磁性粉体の製造例１と同様に酸化反応を進め、酸化反応後に生成した磁性酸化鉄粒子を洗浄、濾過後、表面処理を行わずに、乾燥し、凝集している粒子を解砕処理し磁性粉体２を得た。
＜３＞導電性微粉体の調製
（導電性微粉体の例１）
体積平均粒径２．７μｍの導電性酸化亜鉛（抵抗１．５×１０⁴Ωｃｍ）を導電性微粉体１として用いた。この導電性微粉体は、走査型電子顕微鏡にて観察したところ、０．１〜０．３μｍの酸化亜鉛１次粒子と１〜４μｍの凝集体からなっていた。
【０３０１】
後述する実施例１の画像形成装置で画像露光に用いられるレーザビームスキャナの露光光波長７４０ｎｍにあわせて、波長７４０ｎｍの光源を用いて、この波長域における透過率を、Ｘ−Ｒｉｔｅ社製３１０Ｔ透過型濃度計を用い測定したところ、この導電性微粉体の透過率はおよそ３５％であった。
【０３０２】
（導電性微粉体の例２）
導電性微粉体１から分級操作により体積平均粒径０．７μｍの導電性酸化亜鉛（抵抗 ２．８×１０⁴Ωｃｍ）を得た。これを導電性微粉体２として用いた。
【０３０３】
（導電性微粉体の例３）
体積平均粒径２．８μｍの導電性酸化スズ（抵抗 ２．２×１０⁵Ωｃｍ）を導電性微粉体３として用いた。
【０３０４】
（導電性微粉体の例４）
体積平均粒径３．１μｍの導電性酸化チタン（抵抗 ３．４×１０⁶Ωｃｍ）を導電性微粉体４として用いた。
【０３０５】
＜４＞現像剤の製造
（現像剤の製造例１）
イオン交換水７０９ｇに０．１Ｍ−Ｎａ₃ＰＯ₄水溶液４５１ｇを投入し６０℃に加温した後、１．０Ｍ−ＣａＣｌ₂水溶液６７．７ｇを徐々に添加してＣａ₃（ＰＯ₄）₂を含む水系媒体を得た。
・スチレン ８０部
・ｎ−ブチルアクリレート ２０部
・不飽和ポリエステル樹脂 ３部
・飽和ポリエステル樹脂 ３部
・負荷電性制御剤（モノアゾ染料系のＦｅ化合物） １.５部
・磁性粉体１ ９０部
上記処方をアトライター（三井三池化工機（株））を用いて均一に分散混合した。
【０３０６】
この単量体組成物を６０℃に加温し、そこにベヘニン酸ベヘニルを主体とするエステルワックス（ＤＳＣにおける吸熱ピークの極大値７２℃）６部を添加混合溶解し、これに重合開始剤2,2'-アゾビス（2,4-ジメチルバレロニトリル）［ｔ1/2＝１４０分、６０℃条件下］５ｇを溶解した。
【０３０７】
前記水系媒体中に上記重合性単量体系を投入し、６０℃、Ｎ₂雰囲気下においてＴＫ式ホモミキサー（特殊機化工業（株））にて１０，０００ｒｐｍで１５分間撹拌し、造粒した。その後パドル撹拌翼で撹拌しつつ、６０℃で６時間反応させた。その後液温を８０℃とし更に４時間撹拌を続けた。反応終了後、８０℃で更に２時間蒸留を行い、その後、懸濁液を冷却し、塩酸を加えてＣａ₃（ＰＯ₄）₂を溶解し、濾過、水洗、乾燥して重量平均粒径６．７μｍのトナー粒子を得た。
【０３０８】
このトナー１００部と、上記導電性微粉体１ ２部と、一次粒径８ｎｍのシリカにヘキサメチルジシラザンで表面を処理し処理後のＢＥＴ値が２５０ｍ²／ｇの疎水性シリカ微粉体１．１部とをヘンシェルミキサー（三井三池化工機（株））で混合して、現像剤１を調製した。また、トナー粒子、現像剤の粒径、円形度、Ｂ／Ａ値、Ｄ／Ｃは、上記実施の形態に示した方法で測定した。現像剤１の物性を表１に示す。
【０３０９】
【表１】

【０３１０】
（現像剤の製造例２）
現像剤の製造例１において、磁性粉体１に代えて磁性粉体２を９０部使用する以外は同様の手法により、重量平均粒径７．３μｍのトナー粒子を得た。現像剤２の物性を表１に示す。
【０３１１】
（現像剤の製造例３）
現像剤の製造例１において、導電性微粉体１に代えて導電性微粉体２を使用する以外は同様の手法により、重量平均粒径６．７μｍのトナー粒子を得た。現像剤３の物性を表１に示す。
【０３１２】
（現像剤の製造例４）
現像剤の製造例１において、導電性微粉体１に代えて導電性微粉体３を使用する以外は同様の手法により、重量平均粒径６．７μｍのトナー粒子を得た。現像剤４の物性を表１に示す。
【０３１３】
（現像剤の製造例５）
現像剤の製造例１において、導電性微粉体１に代えて導電性微粉体４を使用する以外は同様の手法により、重量平均粒径６．７μｍのトナー粒子を得た。現像剤５の物性を表１に示す。
【０３１４】
（現像剤の製造例６）
現像剤の製造例１において、導電性微粉体１を添加しない以外は同様にして現像剤６を調製した。現像剤６の物性を表１に示す。
【０３１５】
【実施例１】
＜現像スリーブの製造＞
現像スリーブの製造について述べる。
【０３１６】
下記材料をφ２ｍｍのジルコニア粒子にて３時間サンドミルを用いて分散を行い、その後ジルコニア粒子を篩いで分離し、メタノールで固形分を３６％に調整し塗料１を得た。

第４級アンモニウム塩化合物（１）の鉄粉との摩擦帯電量は、市販の摩擦帯電量測定器（東芝ケミカル製ＴＢ−２００型）を用いてブローオフ法により求めたところ、正極性であった。また球状粒子として、球状炭素粒子Ａを用いた。物性を表２に示す。個数平均粒径５．２μｍ、真密度１．５１ｇ／ｃｍ³、体積抵抗７．５×１０^-2Ωｃｍ、長径／短径比が１．１５であった。
【０３１７】
塗料１をスプレー法にて直径１６ｍｍのＡｌ円筒体上に約１０μｍの樹脂被覆層を形成させ、次いで熱風乾燥器により１５０℃／３０分間加熱・硬化させ現像剤担持体（１）を作製した。表３に塗料処方及び現像剤担持体の物性を示す。
【０３１８】
【表２】

【０３１９】
【表３】

【０３２０】
＜画像形成装置＞
画像形成装置として、ＬＢＰ−１７６０を改造したものを用いた。本改造機は、転写式電子写真プロセスを利用した現像同時クリーニングプロセス（クリーナーレスシステム）のレーザプリンタ（記録装置）である。クリーニングブレードの如きクリーニング部材を有するクリーニングユニットを除去したプロセスカードリッジを有し、現像剤としては磁性一成分系現像剤を使用し、現像剤担持体上の現像剤層と像担持体が非接触となるよう配置された装置である。
【０３２１】
一次帯電部材として導電性カーボンを分散しナイロン樹脂で被覆されたゴムローラ帯電器を前述した電荷注入層を有する感光体に当接させ（当接圧６０ｇ／ｃｍ）、直流電圧−７００Ｖｄｃに交流電圧２．０ｋＶｐｐを重畳したバイアスを印加して感光体上を一様に帯電させる。一次帯電に次いで、レーザ光で画像部分を露光することにより静電潜像を形成させる。
【０３２２】
この時、暗部電位Ｖｄ＝−７００Ｖ、明部電位ＶＬ＝−１５０Ｖとした。感光ドラムと現像スリーブとの間隙は２９０μｍとし、現像磁極８５ｍＴ（８５０ガウス）、現像剤層厚規制部材として厚み１．０ｍｍ、自由長１．０ｍｍのシリコーンゴム製ブレードを２９．４Ｎ／ｍ（３０ｇ／ｃｍ）の線圧で当接させた。
【０３２３】
次いで、現像バイアスとして直流バイアス成分Ｖｄｃ＝−５００Ｖ、重畳する交流バイアス成分Ｖｐｐ＝１６００Ｖ、ｆ＝２０００Ｈｚを用いた。また、現像スリーブの周速は感光体周速（９４ｍｍ／ｓｅｃ）に対して順方向に１１０％のスピード（１０３ｍｍ／ｓｅｃ）とした。
【０３２４】
また転写ローラ（導電性カーボンを分散したエチレン−プロピレンゴム製、導電性弾性層の体積抵抗値１０⁸Ωｃｍ、表面ゴム硬度２４゜、直径２０ｍｍ、当接圧５９Ｎ／ｍ（６０ｇ／ｃｍ））を感光体周速（９４ｍｍ／ｓｅｃ）に対して等速とし、転写バイアスは直流１．５ｋＶとした。
【０３２５】
定着方法としてはＬＢＰ−１７６０のオイル塗布機能のない、フィルムを介してヒータにより加熱加圧定着する方式の定着装置を用いた。この時加圧ローラはフッ素系樹脂の表面層を有するものを使用し、ローラの直径は３０ｍｍであった。また、定着温度は１８０℃、当接幅を７ｍｍに設定した。
【０３２６】
＜画像評価＞
現像剤として現像剤１を使用し、２４℃、１０％ＲＨの常温低湿（Ｎ／Ｌ）及び３０℃、８０％ＲＨの高温高湿（Ｈ／Ｈ）環境下において画出し試験を行った。転写材としては７５ｇ／ｍ²の紙を使用した。その結果、初期において高い転写性を示し、文字やラインの転写中抜けもなく、非画像へのカブリのない良好な画像が得られた。
【０３２７】
次に、印字面積比率５％の横ラインのみからなる画像パターンで耐久性の評価を行った。得られた結果を表４、表５に示す。
【０３２８】
下記に挙げる評価項目について耐久試験評価を行った。
（１）画像濃度
画出しは、２４℃、１０％ＲＨの常温低湿（Ｎ／Ｌ）及び３０℃、８０％ＲＨの高温高湿（Ｈ／Ｈ）環境下にて、１万５千枚（１５ｋ）まで行った。初期濃度は画だし２０枚目の濃度とした。ベタ黒画像濃度を、反射濃度ＲＤ９１８（マクベス社製）で測定して、５点の平均値をとって画像濃度とした。
【０３２９】
（２）トナー帯電量（Ｑ／Ｍ）及びトナー搬送量（Ｍ／Ｓ）
現像スリーブ上に担持されたトナーを、金属円筒管と円筒フィルターにより吸引捕集し、その際金属円筒管を通じてコンデンサーに蓄えられた電荷量Ｑ、捕集されたトナー重量Ｍと、トナーを吸引した面積Ｓから、単位重量当たりの電荷量Ｑ／Ｍ（ｍＣ／ｋｇ）と単位面積当たりのトナー重量Ｍ／Ｓ（ｍｇ／ｃｍ²）を計算し、それぞれトナー帯電量（Ｑ／Ｍ）、トナー搬送量（Ｍ／Ｓ）とした。
【０３３０】
（３）カブリ
カブリの測定は、東京電色社製のＲＥＦＬＥＣＴＭＥＴＥＲ ＭＯＤＥＬ ＴＣ−６ＤＳを使用して測定した。フィルターは、グリーンフィルターを用い、カブリは下記の式より算出した。
カブリ（反射率）（％）＝標準紙上の反射率（％）−サンプル非画像部の反射率（％）
カブリは、２．０％以下であれば良好な画像である。
【０３３１】
（４）感光体の削れ及びトナー融着
画出し終了後、感光体ドラム表面の傷及び傷へのトナーの固着の発生状況とハーフトーン画像での黒点あるいは白抜けを目視により評価した。
Ａ：非常に良好（未発生）
Ｂ：良好（わずかに傷の発生が見られるが、画像への影響はない）
Ｃ：普通（トナー固着や傷があるが、画像への影響は少ない）
Ｄ：悪い（傷に沿ってトナー固着が多く、縦スジ状の画像欠陥を生じる）
【０３３２】
（５）帯電ムラ
転写残トナーによる一次帯電不良に起因する画像不良、即ち帯電ムラはハーフトーン画像上で評価した。ハーフトーン画像上に現れる濃淡差（ムラ）を目視で下記の基準で評価した。
○：濃淡差が全く見られない。
○△：軽微な濃淡差が見られる。
△：濃淡差がやや見られるが実用可。
×：濃淡差が顕著に見られ、実用不可。
【０３３３】
（６）被覆層の耐汚染性
耐久後の現像剤担持体表面をＳＥＭで観察し、トナー汚染の程度を下記の基準で評価した。
○：軽微な汚染が観察される。
○△：やや汚染が観察される。
△：部分的に汚染が観察される。
×：著しい汚染が観察される。
【０３３４】
（７）転写率
転写効率は、ベタ黒画像転写後の感光体上の転写残トナーをマイラーテープによりテーピングしてはぎ取り、紙上に貼ったもののマクベス濃度の値をＣ、転写後定着前のトナーの載った紙上にマイラーテープを貼ったもののマクベス濃度をＤ、未使用の紙上に貼ったマイラーテープのマクベス濃度をＥとした時、近似的に以下の式で計算した。
【０３３５】
【数８】

【０３３６】
転写効率は９０％以上であれば問題の無い画像である。
【０３３７】
【表４】

【０３３８】
【表５】

【０３３９】
【実施例２】
現像剤として現像剤２を使用し、実施例１と同様の画像形成方法で耐久試験評価を行ったところ、非常に良好な結果が得られた。結果を表４、表５に示す。
【０３４０】
【実施例３】
現像剤として現像剤３を使用し、実施例１と同様の画像形成方法で耐久試験評価を行ったところ、良好な結果が得られた。結果を表４、表５に示す。
【比較例１】
現像剤として現像剤６を使用し、実施例１と同様の画像形成方法で耐久試験評価を行った。結果を表４、表５に示す。ページ内の濃度ムラが大きな画像が得られた。
【０３４１】
【比較例２】
直径１６ｍｍのＡｌ円筒管にサンドブラスト処理を施し、表面粗さＲａ１．１８μｍになる様に表面を粗して、比較例の現像スリーブ（１５）を得た。この現像スリーブについて、現像剤１を用いて実施例１と同様に耐久試験評価を行った。結果を表４、表５に示す。各環境においてベタ黒画像濃度低下が発生した。表３に現像剤担持体（１５）の塗料処方及び物性を示す。
【比較例３】
比較例２と同様にサンドブラスト処理を施した現像スリーブ（表面粗さＲａ１．１８μｍ）について、現像剤２を用いて実施例１と同様に耐久試験評価を行った。結果を表４、表５に示す。
【０３４２】
【実施例４】
現像スリーブの樹脂被覆層の作製において、式６で示される第４級アンモニウム塩化合物とした以外は実施例１と同様にして塗料を作製し、現像剤担持体（２）を得た。式６で示される４級アンモニウム塩化合物を実施例１と同様に鉄粉を用いたブローオフにより帯電量を測定したところ、正極性であった。表３に現像剤担持体（２）の塗料処方及び物性を示す。
現像剤担持体（２）と現像剤１を用いて実施例１と同様に耐久試験評価を行った。表４、表５に示したように良好な結果が得られた。
【０３４３】
【実施例５】
現像剤担持体（２）及び現像剤２を用いて実施例１と同様にして耐久試験評価を行った。結果を表４、表５に示す。実用上問題のない結果が得られた。
【０３４４】
【比較例４】
現像剤担持体（２）及び現像剤６を使用し、実施例１と同様の画像形成方法で耐久試験評価を行った。結果を表４、表５に示す。ページ内の濃度ムラが大きな画像が得られた。
【０３４５】
【実施例６】
現像スリーブの樹脂被覆層の作製において、式７で示される第４級アンモニウム塩化合物とした以外は実施例１と同様にして塗料を得、現像剤担持体（３）を作製した。式７で示される第４級アンモニウム塩化合物を実施例１と同様に鉄粉を用いたブローオフにより帯電量を測定したところ、正極性であった。表３に現像剤担持体（３）の塗料処方及び物性を示す。
現像剤担持体（３）と現像剤１を用いて実施例１と同様に耐久試験評価を行った。表４、表５に示したように良好な結果が得られた。
【０３４６】
【実施例７】
現像剤担持体（３）及び現像剤２を用いて実施例１と同様にして耐久試験評価を行った。結果を表４、表５に示す。実用上問題のない結果が得られた。
【０３４７】
【実施例８】
実施例１において、現像スリーブの樹脂被覆層に用いる式５で示される第４級アンモニウム塩化合物の添加量を３０質量部から１０質量部に変えて塗料を作製した以外は同様にして現像剤担持体（４）を得た。表３に現像剤担持体（４）の塗料処方及び物性を示す。
【０３４８】
現像剤担持体（４）と現像剤１を用いて実施例１と同様にして耐久試験評価を行った。結果を表４、表５に示す。
【０３４９】
【実施例９】
実施例１において、現像スリーブの樹脂被覆層に用いる式５で示される第４級アンモニウム塩化合物の添加量を３０質量部から５０質量部に変えて塗料を作製した以外は同様にして現像剤担持体（５）を得た。表３に現像剤担持体（５）の塗料処方及び物性を示す。
【０３５０】
現像剤担持体（５）と現像剤１を用いて実施例１と同様にして耐久試験評価を行った。結果を表４、表５に示す。
【０３５１】
【実施例１０】
現像スリーブの樹脂被覆層に用いる球状粒子として、実施例１において用いた個数平均粒径５．２μｍの球状炭素粒子の代わりに、個数平均粒径５．０μｍのＰＭＭＡ粒子（Ｂ）を用いた以外は、実施例１と同様にして現像剤担持体（６）を作製した。このＰＭＭＡ粒子は、真密度１．１６ｇ／ｃｍ³、体積抵抗１０¹⁵Ωｃｍ以上、長径／短径比が１．１２であった。表３に現像剤担持体（６）の塗料処方及び物性を示す。
【０３５２】
現像剤担持体（６）を用いて実施例１と同様の耐久試験評価を行った。結果を表４、表５に示す。
【０３５３】
【実施例１１】
現像剤担持体の樹脂被覆層の作製において、グラファイトに変えて窒化硼素を用いた以外は現像剤担持体（１）の製造とほぼ同様にして現像剤担持体（７）を作製した。用いた原料は以下の通りである。

現像剤担持体（７）と現像剤１を用いて、実施例１と同様に耐久試験評価を行った。
【０３５４】
結果を表４、表５に示す。
【０３５５】
【実施例１２】
下記の材料により作製された樹脂被覆層用の塗料を用いた以外は、現像剤担持体（１）と同様にして現像剤担持体（８）を作製し、該現像剤担持体（８）と現像剤１を用いて、実施例１と同様に耐久試験評価を行った。

結果を表４、表５に示す。
【０３５６】
【実施例１３】
下記の材料により作製された樹脂被覆層用の塗料を用いた以外は、同様にして現像剤担持体（９）を作製し、該現像剤担持体（９）と現像剤１を用いて、実施例１と同様に耐久試験評価を行った。
・ウレタン樹脂（固形分４０％） ３７５部
・カーボン １５部
・グラファイト ８５部
・式５で示される４級アンモニウム塩化合物 ３０部
・球状炭素粒子（Ａ） ３０部
・メタノール １３０部
結果を表４、表５に示す。
【０３５７】
【実施例１４】
下記の材料により作製された樹脂被覆層用の塗料を用いた以外は、同様にして現像剤担持体（１０）を作製し、該現像剤担持体（１０）と現像剤１を用いて、実施例１と同様に耐久試験評価を行った。

結果を表４、表５に示す。
【０３５８】
【実施例１５】
現像剤担持体の製造において、樹脂被覆層を負帯電性とするための物質として、ベンジル酸２ｍｏｌとアルミニウム原子１ｍｏｌからなるベンジル酸のアルミニウム化合物を用い、具体的には表３に示す材料を用いて樹脂被覆層用の塗料を作製し、現像剤担持体（１１）を得た。該現像剤担持体（１１）と現像剤１を用いて、実施例１と同様に耐久試験評価を行った。結果を表４、５に示す。
【０３５９】
【実施例１６】
現像剤担持体の製造において、樹脂被覆層を負帯電性とするための物質として、アルミニウム原子１ｍｏｌに代えてホウ素原子１ｍｏｌとベンジル酸２ｍｏｌとからなるベンジル酸ホウ素化合物を用い、具体的には表３に示す材料を用いて樹脂被覆層用の塗料を作製し、現像剤担持体（１２）を得た。該現像剤担持体（１２）と現像剤１を用いて、実施例１と同様に耐久試験評価を行った。結果を表４、５に示す。
【０３６０】
【実施例１７】
現像剤担持体の製造において、樹脂被覆層を負帯電性とするための物質として、３，５−ジターシャリーブチルサリチル酸のＣｒ錯体を用い、具体的には表３に示す材料を用いて樹脂被覆層用の塗料を作製し、現像剤担持体（１３）を得た。該現像剤担持体（１３）と現像剤１を用いて、実施例１と同様に耐久試験評価を行った。結果を表４、５に示す。
【０３６１】
【実施例１８】
現像剤担持体の製造において、樹脂被覆層を負帯電性とするための物質として、式５で示される４級アンモニウム塩化合物の代わりに、クロルフェノールを含むアゾナフトールのクロム錯体とした以外は同様にして、現像剤担持体（１４）を作成し、実施例１と同様に耐久試験評価を行った。なお、クロルフェノールを含むアゾナフトールのクロム錯体の鉄粉との摩擦帯電量を実施例１と同様にブローオフ法により求めたところ、負極性であった。結果を表４、５に示す。
【実施例１９、２０】
実施例１で用いた現像剤担持体１と導電性微粉体として酸化スズおよび酸化チタンを用いた現像剤４、５を使用して、実施例１と同様の画像形成方法で耐久試験評価を行ったところ、良好な結果が得られた。結果を表４、表５に示す。
【比較例５、６】
比較例２と同様にサンドブラスト処理を施した現像剤スリーブと現像剤４および５を用いて、実施例１と同様の画像形成方法で耐久試験評価を行った。結果を表４、表５に示す。
【０３６２】
【発明の効果】
本発明によれば、現像剤に対して過剰帯電（チャージアップ）させることなく安定して適切な帯電付与を行うことができ、現像剤を好適なトリボにコントロールすることのできる画像形成方法を提供することができる。
【０３６３】
さらには、従来安定した帯電付与が困難であった重合法により製造された現像剤を用いた場合においても、好適なトリボにコントロールすることのできる画像形成方法を提供することができる。
【０３６４】
また、現像剤担持体表面への融着防止など耐汚染性に優れ、濃度低下やカブリの少ない高品位な画像を長期の画出し耐久において、安定した画像形成方法を提供することができる。
【０３６５】
また、本発明は転写性に優れ、転写残現像剤の回収性に優れた現像同時クリーニング画像形成を可能とする画像形成方法を提供することができる。
【図面の簡単な説明】
【図１】 本発明の画像形成方法に用いる現像装置の構成例を示す模式図である。
【図２】 本発明の画像形成方法に用いる現像装置の別の構成例を示す模式図である。
【図３】 本発明の画像形成方法を用いた画像形成装置の構成例を示す模式図である。
【符号の説明】
１ 電子写真感光ドラム（像担持体）
２ 現像剤層厚規制部材
３ ホッパー
４ 現像剤
５ マグネットローラ
６ 金属円筒管
７ 樹脂被膜層
８ 現像スリーブ（現像剤担持体）
９ 電源
１０ 攪拌翼
１１ 間隙
１２ 露光
１３ 接触転写手段
１４ 電圧印加手段
１５ 加熱加圧ローラ定着器
１７ イレース露光
１８ 接触帯電手段[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming method, an image forming apparatus, a process cartridge, and the image forming method for developing and developing a latent image formed on an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric. The present invention relates to a developing device used in the apparatus.
[0002]
[Prior art]
Conventionally, many methods are known as electrophotographic methods. Generally, a charging process for charging an image carrier using a photoconductive substance and an electrostatic latent image are formed on the charged image carrier. A developing process for developing the electrostatic latent image formed on the image carrier, a transferring process for transferring the developed image to a transfer material by a transfer means, and a transfer process on the transfer material. The target copy is obtained through a fixing step of heating and fixing the transferred image.
[0003]
Development methods in electrophotography are mainly divided into a one-component development method and a two-component development method. In recent years, since it is necessary to reduce the size of a copying apparatus for the purpose of reducing the weight and size of an electrophotographic apparatus, a developing apparatus using a one-component developer is often used. For example, as a developing method using a one-component developer, a jumping developing method is proposed in Japanese Patent Application Laid-Open No. 55-18656.
[0004]
However, the above developing method has an unstable factor related to the magnetic developer used. This is because a considerable amount of fine magnetic powder is mixed and dispersed in the magnetic developer, and a part of the magnetic powder is exposed on the surface of the toner particles. This affects the chargeability, and as a result, causes fluctuation or deterioration of various characteristics required for the developer such as development characteristics and durability of the magnetic developer.
[0005]
When the magnetic developer containing the conventional magnetic powder is used, the above-mentioned problem occurs because the magnetic powder is exposed on the surface of the toner particles. That is, the magnetic powder fine particles having a relatively low resistance compared to the resin constituting the toner particles are exposed on the surface of the toner particles, thereby reducing the developer charging performance, the developer fluidity, In long-term use, image deterioration such as a decrease in image density and occurrence of uneven density due to the separation of the magnetic powder due to rubbing between the developers or with the developer layer thickness regulating member is caused.
[0006]
Conventionally, toner particles are produced by melting and mixing a binder resin, a colorant, and the like, uniformly dispersing, pulverizing with a fine pulverizer, and classifying with a classifier to produce toner particles having a desired particle size (pulverization method). However, there is a limit to the range of materials that can be used to reduce the toner particle size. For example, the resin colorant dispersion must be sufficiently brittle and capable of being finely pulverized by an economically usable production apparatus. From this requirement, in order to make the resin colorant dispersion brittle, when the resin colorant dispersion is actually finely pulverized at a high speed, particles having a wide particle size range are easily formed, and in particular, a relatively large proportion of fine particles ( There arises a problem that excessively pulverized particles) are included therein. Further, such a highly brittle material is often more susceptible to fine pulverization or powdering when used as a developer in a printer or the like, and the generation of such fine particles is a toner on the photosensitive member and developer carrying member. Adhesion is likely to occur, causing image defects.
[0007]
Further, in the pulverization method, it is difficult to completely disperse solid fine particles such as a magnetic substance or a colorant into a resin, and depending on the degree of dispersion, it may cause an increase in fog and a decrease in image density. . Further, the pulverization method inherently exposes the magnetic fine particles to the surface of the toner particles, and thus tends to be disadvantageous for increased fog, fluidity of the developer, and charging stability under harsh environments.
[0008]
In order to overcome the above-mentioned problem of toner particles by a pulverization method, a method for producing toner particles by a suspension polymerization method has been proposed. Since this manufacturing method does not go through a pulverization step, it is not necessary to impart brittleness to the developer, and further, a material that can use a large amount of a low softening point material that could not be used in the conventional pulverization method. The range of choices expands. Toner particles by suspension polymerization (hereinafter referred to as polymerized toner) can be easily made into fine particles, and the resulting toner particles have a spherical shape, which is excellent in fluidity and advantageous for high image quality. It becomes.
[0009]
On the other hand, as an image forming method, many methods such as an electrostatic recording method, a magnetic recording method, and a toner jet method are known. In general, after the transfer, the above-described steps are repeated through a cleaning process in which the developer remaining on the image carrier without being transferred to the transfer material is cleaned by various methods and stored in a waste developer container as a waste developer. The image forming method is used.
[0010]
For this cleaning step, a method is used in which the developer remaining on the transfer is mechanically scraped or damped and collected in a waste developer container. However, since the image forming apparatus is inevitably increased in size to have an apparatus for performing such a cleaning process, it becomes a bottleneck when aiming to make the apparatus compact. Furthermore, in view of saving resources, reducing waste, and effective use of toner, a system without waste developer, a system excellent in fixing property and offset resistance has been desired.
[0011]
  On the other hand, as a system without waste developer, a technique called simultaneous development cleaning or cleanerless has been proposed. However, the conventional technology related to simultaneous development cleaning or cleanerless is disclosed in Japanese Patent Application Laid-Open No. 5-2287.TheThe main focus is on memory and negative memory. However, as the use of electrophotography progresses, it is necessary to transfer toner images to various transfer materials. In this sense, the transfer images are not satisfactory.
[0012]
Further, as a development method preferably applied to simultaneous development cleaning or cleanerless, conventionally, in the simultaneous development cleaning that essentially does not have a cleaning device, a configuration in which the surface of the image carrier is rubbed with a developer and a development sleeve is essential. For this reason, many contact development methods in which the toner or developer carrier contacts the image carrier have been studied. This is because it is considered that a configuration in which the toner or developer carrying member comes into contact with and rubs the image carrying member in order to collect the transfer residual developer in the developing means is considered advantageous. However, the simultaneous development cleaning or cleaner-less process using the contact development method causes toner deterioration, development sleeve surface deterioration, photoreceptor surface deterioration or wear, etc. due to long-term use, and sufficient solutions have been made to durability characteristics. Absent. Therefore, a development simultaneous cleaning method by a non-contact development method is desired.
[0013]
Various methods for forming a latent image on an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric are also known. For example, in electrophotography, an electric latent image is formed by performing image pattern exposure after uniformly charging a photoconductor using a photoconductive material as an image carrier to the required polarity and potential. The method to do is common.
[0014]
Conventionally, a corona charger (corona discharger) has often been used as a charging device that uniformly charges (including static elimination processing) an image carrier to a required polarity and potential. In recent years, as a charging device for an object to be charged such as an image carrier, a contact charging device has been proposed and put into practical use because it has advantages such as low ozone and low power as compared with a corona charger.
[0015]
There are two types of contact charging mechanisms (charging mechanism, charging principle): (1) discharge charging mechanism and (2) direct injection charging mechanism, depending on which is dominant. The characteristic of appears.
[0016]
In the contact charging device, a roller charging method using a charging roller as a contact charging member is preferable in terms of charging stability and is widely used. The charging mechanism in the conventional roller charging system is dominated by the discharge charging mechanism (1).
[0017]
The charging roller has elasticity in order to obtain a certain contact state with the member to be charged, but has a large frictional resistance, and is often driven by the member to be charged or with a slight speed difference. Therefore, even if direct injection charging is attempted, a decrease in absolute charging ability, lack of contactability, contact unevenness due to the roller shape, and charging unevenness due to deposits on the object to be charged cannot be avoided.
[0018]
In the method of charging by applying only the DC voltage to the contact charging member (DC charging method), in order to obtain the photoreceptor surface potential Vd required for electrophotography, the charging roller has a charging start voltage in addition to Vd. The above DC voltage is required. However, in DC charging, the resistance value of the contact charging member fluctuates due to environmental fluctuations, etc., and the charging start voltage fluctuates when the film thickness changes due to the photoconductor being scraped. Difficult to make. For this reason, in order to achieve further uniform charging, a voltage obtained by superimposing an AC component on a DC voltage corresponding to a desired Vd is applied to the contact charging member as disclosed in Japanese Patent Application Laid-Open No. 63-149669. An “AC charging method” is used. This is for the purpose of smoothing the potential due to AC, and the potential of the charged body converges to Vd, which is the center of the peak of the AC voltage, and is not affected by disturbances such as the environment. However, even in such a contact charging device, the essential charging mechanism uses a discharge phenomenon from the contact charging member to the photosensitive member, so that the voltage applied to the contact charging member is photosensitive as described above. A value higher than the body surface potential is required, and a trace amount of ozone is generated.
[0019]
Further, when AC charging is performed for uniform charging, generation of further ozone, generation of vibration noise (AC charging sound) between the contact charging member and the photosensitive member due to the electric field of the AC voltage, and surface of the photosensitive member due to discharge Deterioration of the surface becomes remarkable, which is a new problem.
[0020]
Among the contact charging methods, the charging mechanism of the fur brush charging is dominated by the discharge charging mechanism (1) described above, and charging is performed using a discharge phenomenon by applying a high charging bias.
[0021]
On the other hand, the charging mechanism of the magnetic brush charging is dominated by the direct injection charging mechanism (2). By using conductive magnetic particles constituting the magnetic brush portion having a particle diameter of 5 to 50 μm and providing a sufficient speed difference from the photoreceptor, uniform direct injection charging is possible. Magnetic brush charging makes it possible to obtain a charging potential substantially proportional to the applied bias. However, there are also disadvantages such as a complicated device configuration and conductive magnetic particles constituting the magnetic brush portion falling off and adhering to the photoreceptor.
[0022]
Here, consider the case where these contact charging methods are applied to a simultaneous development cleaning method and a cleanerless image forming method. In the simultaneous development cleaning method and the cleanerless image forming method, since there is no cleaning member, the transfer residual developer remaining on the photosensitive member comes into contact with the contact charging member as it is, and is attached or mixed. Further, in the case of a charging method in which the discharge charging mechanism is dominant, adhesion to the charging member is also deteriorated due to developer deterioration due to discharge energy. When commonly used insulating toner adheres to or mixes with the contact charging member, the chargeability is lowered.
[0023]
In the case of a charging method in which the discharge charging mechanism is dominant, this decrease in chargeability of the member to be charged occurs abruptly since the toner layer adhering to the surface of the contact charging member becomes a resistance that inhibits the discharge voltage. On the other hand, in the case of a charging method in which the direct injection charging mechanism is dominant, the transfer residual developer adhering to or mixed in reduces the contact probability between the surface of the contact charging member and the object to be charged. Chargeability decreases.
[0024]
This reduction in the uniform chargeability of the object to be charged reduces the contrast and uniformity of the electrostatic latent image after image exposure, thereby reducing the image density or increasing the fog.
[0025]
Further, in the simultaneous development cleaning method and the cleanerless image forming method, the charge polarity and charge amount of the transfer residual developer on the photoreceptor are controlled, and the transfer residual developer is stably recovered in the development process. The point is not to deteriorate the development characteristics, and the charging polarity and the charge amount of the residual transfer developer are controlled by the charging member.
[0026]
This will be specifically described by taking a general laser printer as an example. In the case of reversal development using a charging member for applying a negative polarity voltage, a negatively charged photosensitive member and a negatively charging developer, the toner image visualized by the positive polarity transfer member is transferred to the transfer material in the transfer process. However, depending on the relationship between the type of transfer material (difference in thickness, resistance, dielectric constant, etc.) and the image area, the charging polarity of the developer remaining in the transfer varies from plus to minus. However, due to the negative polarity charging member for charging the negatively chargeable photoconductor, even if the developer remaining on the transfer surface as well as the surface of the photoconductor is swung to the positive polarity in the transfer process, it is uniformly negative. The charging polarity can be made uniform. Therefore, when reversal development is used as a developing method, a dark portion potential that is charged with a negative charge remains in the bright portion potential portion of the developer to be developed and the transfer residual developer is not to be developed. Is attracted toward the developer carrying member due to the development electric field, and the untransferred developer is recovered without remaining on the photosensitive member having the dark portion potential. That is, by controlling the charging polarity of the developer remaining on the transfer simultaneously with the charging of the photosensitive member by the charging member, the simultaneous development cleaning and the cleanerless image forming method are established.
[0027]
However, if the transfer residual developer adheres to or mixes with the contact charging member beyond the ability to control the developer charge polarity of the contact charging member, the charge polarity of the transfer residual developer cannot be made uniform, and the developer carrying It becomes difficult to collect the developer by the body. Even if the developer carrying member is collected by mechanical force such as rubbing, if the charge of the residual transfer developer is not evenly arranged, the chargeability of the developer on the developer carrying member is adversely affected. Adversely affect the development characteristics.
[0028]
In other words, in the simultaneous development cleaning and cleanerless image forming methods, the charge control characteristics of the transfer residual developer when passing through the charging member and the adhesion / mixing characteristics to the charging member are closely linked to the durability characteristics and the image quality characteristics. ing.
[0029]
Japanese Patent Laid-Open No. 5-150539 discloses that in an image forming method using a contact charging method, toner particles and silica fine particles that could not be blade-cleaned after repeated image formation for a long time adhere to and accumulate on the surface of the charging means. In order to prevent charging inhibition due to the above, it is disclosed that the developer contains at least visible particles and conductive particles having an average particle size smaller than the visible particles. However, the contact charging or proximity charging used here is based on a discharge charging mechanism, and has the above-described problems due to discharge charging. In addition, when applied to a cleanerless image forming apparatus, compared to the case where a cleaning mechanism is provided, a large amount of conductive fine particles and the transfer residual developer have an influence on the chargeability due to passing through the charging step, and these large amounts. No consideration has been given to the recoverability of the conductive fine particles and the residual transfer developer in the development process, and the influence of the collected conductive fine particles and the residual transfer developer on the development characteristics of the developer. Further, when the direct injection charging mechanism is applied to the contact charging, a necessary amount of the conductive fine particles is not supplied to the contact charging member, resulting in a charging failure due to the influence of the transfer residual developer.
[0030]
Further, in the proximity charging, it is difficult to uniformly charge the photosensitive member with a large amount of conductive fine particles and a transfer residual developer, and an effect of leveling the pattern of the transfer residual developer cannot be obtained. A pattern ghost for shielding the image exposure is generated. Further, when the power supply is interrupted or a paper jam occurs during image formation, the contamination inside the apparatus with toner becomes significant.
[0031]
In addition, some commercially available electrophotographic printers use a roller member that contacts the photoconductor between the transfer process and the charging process, and assists or controls the transfer residual developer recovery during development. There is also a device. Such an image forming apparatus exhibits a good development simultaneous cleaning property and can greatly reduce the amount of waste developer, but the cost is increased and the advantage of the simultaneous development cleaning is impaired in terms of miniaturization.
[0032]
In contrast, in Japanese Patent Application Laid-Open No. 10-307456, a toner containing toner particles and electrically conductive charge accelerating particles having a particle size equal to or less than ½ of the toner particle size is developed simultaneously with development using a direct injection charging mechanism. An image forming apparatus applied to a cleaning image forming method is disclosed. According to this proposal, it is possible to obtain a developing simultaneous cleaning image forming apparatus that can greatly reduce the amount of waste toner without generating a discharge product, and is advantageous for downsizing at low cost. Alternatively, a good image that does not cause diffusion can be obtained.
[0033]
In JP-A-10-307421, a toner containing conductive particles having a particle size that is 1/50 to 1/2 of the toner particle size is used for a simultaneous development cleaning image forming method using a direct injection charging mechanism. An image forming apparatus is disclosed in which the conductive particles are applied to have a transfer promoting effect.
[0034]
Furthermore, in Japanese Patent Application Laid-Open No. 10-307455, the particle size of the conductive fine powder is set to 10 nm in order to make the particle size of the conductive fine powder smaller than the size of one pixel of the constituent pixels and to obtain better charging uniformity. It is described that it is set to ˜50 μm.
[0035]
In Japanese Patent Laid-Open No. 10-307457, in consideration of human visual characteristics, the conductive particles are made to be about 5 μm or less, preferably 20 nm to 5 μm in order to make it difficult to visually recognize the influence on the image of the poorly charged portion. It is described to do.
[0036]
Further, according to Japanese Patent Laid-Open No. 10-307458, the particle size of the conductive fine powder is set to be equal to or smaller than the toner particle size, thereby inhibiting the development of the toner at the time of development, or the development bias is applied via the conductive fine powder. Leakage of the image, eliminating defects in the image, and setting the particle size of the conductive fine powder to be larger than 0.1 μm. A developing simultaneous cleaning image forming method using a direct injection charging mechanism that solves the adverse effect of light shielding and realizes excellent image recording is described.
[0037]
According to Japanese Patent Laid-Open No. 10-307456, a conductive fine powder is externally added to the toner, and the conductive fine powder contained in the toner is at least at the contact portion between the flexible contact charging member and the image carrier. However, it adheres to the image carrier in the development process and remains on the image carrier after the transfer process and is carried and intervened to obtain a good image that does not cause poor charging and light exposure. A developing simultaneous cleaning image forming apparatus capable of performing the above is disclosed.
[0038]
However, these proposals also have room for further improvement in order to improve stable performance and resolution in repeated use over a long period of time.
[0039]
Furthermore, it is difficult to adjust the charge of the polymerized toner, and various measures such as improvement of charging characteristics by external additives have been made. However, durability stability such as non-uniformity of developer charging and occurrence of fusion to the sleeve surface is also included. The problems related to are not fully resolved.
[0040]
Further, as the copying is repeated, the developer is repeatedly rubbed against the developer carrier, so that a non-development material such as an additive for improving the fluidity of the developer is deposited on the developer carrier or developed. Since the low softening point substance in the developer forms a film on the sleeve, there is a problem that the surface state of the developer carrier changes and the developability of the developer changes.
[0041]
Furthermore, there is room for further improvement in the charging failure of the developer on the developer carrying member due to the effect of recovery of the charge accelerating particles and the transfer residual developer in repeated use over a long period of time.
[0042]
Improvements such as prevention of these charging failures, improvement of charging uniformity, and suppression of developer contamination and developer fusion are desired.
[0043]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide an image forming method, an image forming apparatus, a process cartridge, and a developing device that solve the above-described problems. More specifically, an image forming method, an image forming apparatus, a process cartridge, and a charging device capable of preventing charging failure when using toner particles by a polymerization method having a substantially spherical shape and having a quick, uniform and stable charge imparting property to a developer, and A developing device used in the image forming apparatus is provided.
[0044]
Another object of the present invention is that it is possible to significantly reduce the amount of waste developer without generating discharge products, to enable simultaneous development cleaning image formation that is advantageous for downsizing at low cost, and to be repeated over a long period of time. Another object of the present invention is to provide an image forming method, an image forming apparatus, a process cartridge, and a developing device used for the image forming apparatus that can provide a good image without causing a charging failure even in use.
[0045]
Another object of the present invention is to provide an image forming method, an image forming apparatus, a process cartridge, and an image forming apparatus capable of forming an image at the same time as the development cleaning with excellent transferability and excellent recovery of the transfer residual developer. It is to provide a developing device.
[0046]
[Means for Solving the Problems]
  The present invention is as follows.
(1) A voltage is applied to the charging member,A charging member to which a voltage is applied is brought into contact with the image carrier,A charging step for charging the image carrier, an electrostatic latent image forming step for forming an electrostatic latent image on the charged image carrier, a development step including the following (a) to (d), (a) (C) a step of supporting the developer contained in the developer container on the developer carrier; (b) a step of regulating the layer thickness of the developer on the developer carrier by a developer layer thickness regulating member; And (d) a step of carrying and transporting the developer whose layer thickness is regulated to a developing region where the developer carrying member and the image carrying member are opposed to each other; (d) the developer on the developer carrying member is statically moved on the image carrying member. A step of forming a toner image by transferring to an electrostatic latent image; a transfer step of electrostatically transferring the toner image formed on the surface of the image carrier onto a transfer material; and heating and transferring the toner image transferred onto the transfer material A fixing step for fixing, and the developing step transfers the toner image onto a transfer material. It also serves as a cleaning step for recovering the developer remaining on the image carrier later, and the developer includes toner particles containing at least a binder resin component and magnetic powder, and inorganic fine powder on the toner particle surface; A conductive fine powder having an average particle size larger than that of the inorganic fine powder and smaller than that of the developer, the average circularity determined by the following formula (1) is 0.970 or more, and is substantially a magnetic powder. Is a negatively chargeable magnetic developer that is not exposed on the surface,The toner particles are toner particles obtained by suspension polymerization of a polymerizable monomer system including at least a polymerizable monomer serving as a binder resin component and a magnetic powder in an aqueous medium,The developer carrier comprises a substrate and a resin coating layer formed on the substrate, and the resin coating layer is a negatively chargeable resin coating layer containing at least a negatively chargeable substance. An image forming method.
[0047]
[Expression 4]
Circularity a = L₀/ L (1)
(Where L₀Indicates the perimeter of a circle having the same projected area as the particle image, and L indicates the perimeter of the projected image of the particle. )
(2) The binder resin for the coating layer of the resin coating layer may be partially or entirely -NH₂(1) The image forming method having at least one of a group, a = NH group, and a -NH- bond.
(3) The image forming method according to (1) or (2), wherein the binder resin for the coating layer of the resin coating layer contains at least a phenol resin.
(4) The phenol resin is a phenol resin produced by adding and condensing phenols and aldehydes using a nitrogen-containing compound as a catalyst.₂(3) The image forming method according to (3), which is a phenol resin having any one of a group, ═NH group, and —NH— bond.
(5) The image forming method according to any one of (1) to (4), wherein the resin coating layer contains a quaternary ammonium salt compound that is positively charged with respect to at least iron powder.
(6) The image forming method according to any one of (1) to (4), wherein the resin coating layer contains a benzylic acid compound.
(7) The image forming method according to any one of (1) to (6), wherein the resin coating layer is a conductive resin coating layer in which conductive fine powder is further dispersed in the coating layer binder resin.
(8) The magnetic powder is mainly composed of magnetite, and the ratio of the iron element content (B) to the carbon element content (A) present on the toner particle surface (measured by X-ray photoelectron spectroscopy) ( The image forming method according to any one of (1) to (7), wherein B / A) is less than 0.001.
(9) The volume average particle diameter of the magnetic developer is C, and the minimum value of the distance between the magnetic powder and the toner particle surface in the tomographic plane observation of the magnetic developer using a transmission electron microscope (TEM) is D. When D / C ≦ 0.02, image formation according to any one of (1) to (8)Method.
(10)The conductive fine powder of the magnetic developer has a volume resistance of 10⁹Ωcm or less (1) ~(9)Any one of the image forming methods.
(11)The conductive fine powder of the magnetic developer has a volume resistance of 10⁶Ωcm or less (1) ~(9)Any one of the image forming methods.
(12)The conductive fine powder of the magnetic developer is nonmagnetic (1) to(11)Any one of the image forming methods.
(13)The developer has toner particles and a volume average particle size of 0.1 μm to10 μm(1) to (1) having conductive fine powder(12)Any one of the image forming methods.
(14)The charging step is a step of charging the image carrier by applying a voltage to a charging member that is in contact with the image carrier through the conductive fine powder.(13)Any one of the image forming methods.
(15)In the charging step, the conductive fine powder contained in the magnetic developer adheres to the image carrier in the development step and remains on the image carrier after the transfer step, so that at least the contact between the charging member and the image carrier. Interspersed and / or transported in the vicinity(14)Image forming method.
(16)The conductive fine powder is fine particles containing at least one oxide selected from zinc oxide, tin oxide and titanium oxide (1) to(15)Any one of the image forming methods.
(17)A process cartridge for visualizing an electrostatic latent image formed on an image carrier as a toner image by a developer and transferring the visualized developer image to a transfer material, the process cartridge comprising: An image carrier for carrying an electrostatic latent image, and the image carrierIn contact with the image carrierThe electrostatic latent image formed on the image carrier and the electrostatic latent image formed on the image carrier is visualized as a toner image by developing with a developer, and the toner image is transferred to a transfer material. And at least developing means for recovering the developer remaining on the image carrier, and the developing device and the latent image carrier are integrated and detachably attached to the image forming apparatus main body. The developer includes toner particles containing at least a binder resin component and a magnetic powder, inorganic fine powder on the surface of the toner particles, and larger than the inorganic fine powder than the developer. Negatively chargeable magnetism having a conductive powder having a small average particle diameter, an average circularity obtained by the above formula (1) of 0.970 or more, and substantially no magnetic powder is exposed on the surface Developer,The toner particles are toner particles obtained by suspension polymerization of a polymerizable monomer system including at least a polymerizable monomer serving as a binder resin component and a magnetic powder in an aqueous medium,The developing device includes a developer container for accommodating a developer, a developer carrier for supporting the magnetic developer accommodated in the developer container and transporting the developer to a development region, and the developer carrier At least a developer layer thickness regulating member for regulating the layer thickness of the developer carried on the substrate, wherein the developer carrier comprises a substrate and a resin coating layer formed on the substrate, The process cartridge, wherein the resin coating layer is a negatively chargeable resin coating layer containing at least a negatively chargeable substance.
(18)Apply voltage to the charging member,A charging member to which a voltage is applied is brought into contact with the image carrier,A charging unit for charging the image carrier, an electrostatic latent image forming unit for forming an electrostatic latent image on the charged image carrier, a developer container for containing a developer, and a developer container accommodated in the developer container Development means having at least a developer carrying member for carrying the developer being carried and transporting it to the development area, and a developer layer thickness regulating member for regulating the layer thickness of the developer carried on the developer carrying member An image forming apparatus comprising: a transfer unit that electrostatically transfers a toner image formed on the surface of the image carrier to a transfer material; and a fixing unit that heats and fixes the toner image transferred onto the transfer material. The developing means visualizes the electrostatic latent image formed on the image carrier as a toner image by developing with a developer, and after the toner image is transferred to a transfer material, Collects developer remaining on image carrier The developer includes toner particles containing at least a binder resin component and a magnetic powder, an inorganic fine powder on the surface of the toner particle, and an average larger than the inorganic fine powder and smaller than the developer. A negatively chargeable magnetic developer having a conductive fine powder having a particle size and having an average circularity of 0.970 or more determined by the above formula (1), and the magnetic powder is not substantially exposed on the surface. AndThe toner particles are toner particles obtained by suspension polymerization of a polymerizable monomer system including at least a polymerizable monomer serving as a binder resin component and a magnetic powder in an aqueous medium,The developer carrier comprises a substrate and a resin coating layer formed on the substrate, and the resin coating layer is a negatively chargeable resin coating layer containing at least a negatively chargeable substance. An image forming apparatus.
[0048]
DETAILED DESCRIPTION OF THE INVENTION
The present invention also serves as a cleaning step of collecting the developer remaining on the image carrier after the development step transfers the toner image onto the transfer material,
The developer includes toner particles containing at least a binder resin component and a magnetic powder, inorganic fine powder on the surface of the toner particles, and conductive fine powder having an average particle size larger than the inorganic fine powder and smaller than the developer. A magnetic developer having an average circularity determined by the following formula (1) of 0.970 or more and substantially no magnetic powder exposed on the surface;
The developer carrier comprises a substrate and a resin coating layer formed on the substrate,
The resin coating layer contains at least a negatively chargeable substance.
[0049]
[Equation 5]
Circularity a = L₀/ L (1)
(Where L₀Indicates the perimeter of a circle having the same projected area as the particle image, and L indicates the perimeter of the projected image of the particle. )
In the image forming method of the simultaneous development cleaning method in which the developing process for developing the electrostatic latent image also serves as the cleaning process for collecting the developer remaining on the image carrier after the image is transferred to the transfer material, There has been a demand for a developer having a high transfer efficiency characteristic with little residual developer.
[0050]
In general, the developer produced by the polymerization method has a smaller contact area between the toner particles and the photoconductor than the developer produced by the conventional jet milling method, and the toner particles are exposed to the photoconductor. Adhesive strength is considered to be reduced, and transferability is greatly improved and transfer efficiency is greatly improved. On the other hand, coloring materials such as carbon and magnetic powder used for magnetic developer are taken into toner particles. Therefore, since these additives do not function as sites for leaking the charge generated on the toner particle surface, the developer is likely to be charged up. In the present invention, as a developer used in the image forming method of the simultaneous development cleaning system that also serves as a cleaning process for collecting the developer remaining on the image carrier after the developed toner image is transferred to a transfer material in the developing process, charging is promoted. Although particles with conductive fine powder added are used, even when such a developer is used, it is difficult for the charge to leak, so development unevenness, blotches, and developer concentration due to fixing of the developer carrier Degradation is likely to occur. Furthermore, the developer tends to be poorly charged on the developer carrying member due to the effect of collecting the charge accelerating particles and the transfer residual developer in repeated use.
[0051]
  In order to improve these charging characteristics and the like, a method of adding various inorganic fine powders as external additives to toner particles has been proposed, but a sufficient method has not been obtained yet.
<1> Developer carrier in the present invention
  Therefore, as a result of repeated investigations on the surface of the developer carrying member that imparts triboelectric charge to the developer, a resin coating layer is formed on the substrate of the developer carrying member, and the formed resin coating layerButBy containing at least a negatively chargeable substance, in the simultaneous development cleaning method, a developer having an excessive charge relative to the negatively chargeable developer produced by the polymerization method, and the surface of the developer carrier It has been found that it is possible to effectively prevent strong adhesion of the developer to the toner and to charge the triboelectric charge to a suitable level.
[0052]
As the binder resin for resin coating used in the resin coating layer in the present invention, known resins can be used. For example, thermoplastic resins such as styrene resins, vinyl resins, polyethersulfone resins, polycarbonate resins, polyphenylene oxide resins, polyamide resins, fluororesins, fiber resins, acrylic resins, epoxy resins, polyester resins, alkyd resins Thermal or photo-curable resins such as phenol resin, melamine resin, polyurethane resin, urea resin, silicone resin, polyimide resin, etc. can be used. Among them, those having releasability such as silicone resin, fluorine resin, or polyether sulfone resin, polycarbonate resin, polyphenylene oxide resin, polyamide resin, phenol resin, polyester resin, polyurethane resin, styrene resin, acrylic resin Those having excellent mechanical properties are more preferred.
[0053]
Among these, negatively chargeable silicone resins, fluororesins, and the like are preferable, and they may be used in combination with other binder resins for the purpose of increasing mechanical strength.
-NH together with quaternary ammonium salt that is positively charged to iron powder₂It is preferable to use a binder resin having at least one structure of a group, ═NH group, or —NH— bond.
[0054]
-NH₂As the substance having a group, R-NH₂Or a polyamine having them, RCO-NH₂Or a polyamide having them. As the substance having ═NH group, a secondary amine represented by R═NH or a polyamine having them, (RCO)₂Secondary amides represented by = NH or polyamides having them may be mentioned. Examples of the substance having an —NH— bond include polyurethane having an —NHCOO— bond in addition to the above-described polyamine, polyamide and the like. As the binder resin for the coating layer, an industrially synthesized resin containing one or more of the above substances as a copolymer or a copolymer is suitably used. Of these, from the viewpoint of versatility, phenol resins, polyamide resins, urethane resins and the like produced by adding and condensing phenols and aldehydes using a nitrogen-containing compound as a catalyst can be preferably used.
[0055]
  Examples of the nitrogen-containing compound used as a catalyst in the production of a phenol resin include acidic catalysts and basic catalysts. Examples of acidic catalysts include ammonium sulfate, ammonium phosphate, ammonium sulfamate, ammonium carbonate, ammonium acetate, maleic acid. Examples thereof include ammonium salts such as ammonium acid or amine salts. Examples of basic catalysts include ammonia, dimethylamine, diethylamine, diisopropylamine, diisobutylamine, diamylamine, trimethylamine, triethylamine, tri-n-butylamine, triamylamine, dimethylbenzylamine, diethylbenzylamine, dimethylaniline, diethyl Aniline, N, N-di-n-butylaniline, N, N-diamilaniline, N, N-di-t-amylaniline, N-methylethanolamine, N-ethylethanolamine, diethanolamine, triethanolamine, dimethylethanolamine, diethylethanolamine, ethyldiethanolamine, n-butyldiethanolamine, di-Amino compounds such as n-butylethanolamine, triisopropanolamine, ethylenediamine, hexamethylenetetramine, pyridine such as pyridine, α-picoline, β-picoline, 2,4-lutidine, 2,6-lutidine, and derivatives thereof, quinoline compounds Imidazole such as imidazole, 2-methylimidazole, 2,4-dimethylimidazole, 2-ethyl-4-methylimidazole, 2-phenylimidazole, 2-phenyl-4-methylimidazole, 2-heptadecylimidazole, etc. Is mentioned.
[0056]
It is also preferable to add a negatively charged substance to these known binder resins.
As such a negatively charged substance, conventionally known substances can be used. For example, in addition to silica powder and fluororesin powder, there are organometallic complexes, chelate compounds, monoazo metal complexes, acetylacetone metal complexes, aromatic hydroxycarboxylic acid, and aromatic dicarboxylic acid metal complexes. In addition, there are aromatic hydroxycarboxylic acids, aromatic mono- and polycarboxylic acids and their metal salts, anhydrides, esters, and phenol derivatives such as bisphenol.
[0057]
Among these, the following compounds are preferably used in order to charge the developer satisfactorily.
Examples include benzylic acid aluminum compounds, boron compounds, zinc compounds, and chromium compounds.
Examples of the benzylic acid compound include an aluminum compound of benzylic acid having an unsubstituted group or a substituent represented by the following general formula (1).
[0058]
[Chemical 1]

(Wherein R5 and R6 may be the same or different, and each represents a linear or branched alkyl group, alkenyl group, alkoxyl group, halogen atom, nitro group, cyano group, amino group, carboxyl group and A substituent selected from the group consisting of a hydroxyl group is shown, and m and n are integers of 0 to 5.)
[0059]
Among these, an aluminum compound of benzyl acid represented by the following general formula (2) is more preferable.
[0060]
[Chemical 2]

(Wherein R5 and R6 may be the same or different, and each represents a linear or branched alkyl group, alkenyl group, alkoxyl group, halogen atom, nitro group, cyano group, amino group, carboxyl group and A substituent selected from the group consisting of a hydroxyl group, m and n each represent an integer of 0 to 5. Y represents a monovalent cation, hydrogen, lithium, sodium, potassium, ammonium or alkylammonium.
[0061]
  It is also preferable to further contain sulfonic acid-containing acrylamide. For example, 2-acrylamidopropanesulfonic acid, 2-acrylamide-n-butanesulfonic acid, 2-acrylamide-n-hexanesulfonic acid, 2-acrylamide−n−Octane sulfonic acid, 2−Acrylamide−n-dodecanesulfonic acid, 2-acrylamide-n-tetradecanesulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid, 2-acrylamido-2-phenylpropanesulfonic acid, 2-acrylamide−2,2,4-trimethylpentanesulfonic acid, 2-acrylamido-2-methylphenylethanesulfonic acid, 2-acrylamido-2- (4-chlorophenyl) propanesulfonic acid, 2-acrylamido-2-carboxymethylpropanesulfonic acid, 2-acrylamido-2- (2-pyridyl) propanesulfonic acid, 2-acrylamido-1-methylpropanesulfonic acid, 3-acrylamido-3-methylbutanesulfonic acid, 2-methacrylamide-n-decanesulfonic acid, 2−And methacrylamide-n-tetradecanesulfonic acid. Preferably, 2-acrylamido-2-methylpropanesulfonic acid is used.
[0062]
The amount of the negatively chargeable substance added to the resin coating layer is preferably 1 to 100 parts by mass with respect to 100 parts by mass of the binder resin for the resin coating layer. If the amount is less than 1 part by mass, the charging stability is not improved by addition. If the amount exceeds 100 parts by mass, the amount in the binder resin for the resin coating layer becomes excessive, and the amount of the original binder resin for the resin coating layer is reduced. The characteristics are impaired and the strength of the coating layer is likely to decrease.
[0063]
As a more preferable means for making the resin coating layer in the present invention contain a negatively chargeable substance, prior to the present invention, in Japanese Patent Application Laid-Open No. 10-3204040, Japanese Patent Application Laid-Open No. 11-052711, etc. Quaternary ammonium salt compounds known as charge control agents, that is, quaternary ammonium salt compounds which are themselves positively charged with respect to iron powder, and as a binder resin for resin coating layers, particularly resins Part or all of the binder resin for the coating layer has at least —NH in its molecular structure.₂When a resin coating layer of a developer carrier is formed using a group having any of a group, ═NH group, and —NH— bond, the quaternary ammonium salt compound is incorporated into the binder resin for the resin coating layer. , Found that the resin (resin coating layer) itself exhibits a strong negative chargeability and a good charge imparting property with respect to the positively chargeable toner, and is very good when used as a developer carrier in a developing device. A proposal to obtain a good image.
[0064]
The superiority of this method is, for example, that the binder for the resin coating layer is compared with the above-described system in which silica, fluororesin powder, and a negative charge control agent are added to the resin coating layer in order to impart charge to the toner. Since the quaternary ammonium salt compound is dissolved in the resin solvent and can be uniformly present in the resin, when the resin coating layer is formed, the entire resin layer becomes a uniform negatively chargeable material, Thus, the entire developer-carrying member exhibits a uniform and good charge imparting property as compared with the one dispersed in a matrix, and further, since it is not a powder addition system, mechanical strength, that is, durability is good. There is a point.
[0065]
As a result of further investigation of these disclosed techniques, the present inventors have found that when a negatively chargeable developer is used, the developer has a spherical shape to a substantially spherical shape particularly used in the present invention, and further to the surface. When using a developer with low exposure and easy to have an excess charge such as magnetic powder, the addition of a quaternary ammonium salt compound to the resin coating layer suppresses the generation of excess charge in the developer. It has been found that suitable charging characteristics can be obtained. In other words, a quaternary ammonium salt compound known as a positive charge control agent for conventional toners, that is, a quaternary ammonium salt compound that itself is positively charged with respect to iron powder, is used in an appropriate amount. By setting the amount, as a binder resin for the resin coating layer, a part or all of the binder resin for the resin coating layer may be —NH₂By forming a resin coating layer of a developer carrying member using a group having any of a group, ═NH group, and —NH— bond, a developer having an excess charge relative to the magnetic developer in the present invention is used. It has been found that generation and strong adhesion of the developer to the surface of the developer carrying member can be effectively prevented, and the triboelectric charge can be charged to a suitable level.
[0066]
As a result of investigations for improving the charging characteristics of the toner of the present invention produced by a polymerization method having the advantage of high transfer efficiency, the developer covering member has a resin coating layer having the above-described structure. The charging amount of the toner can be stabilized, and development unevenness, blotches, fogging, and image density reduction due to charge-up can be prevented.
[0067]
As the quaternary ammonium salt compound suitably used in the present invention, those having positive chargeability with respect to iron powder are used. For example, the compound represented by the following general formula 3 is mentioned.
[0068]
[Chemical Formula 3]

[0069]
(In the formula, R1, R2, R3, and R4 each represent an alkyl group that may have a substituent, an aryl group that may have a substituent, and an aralkyl group, and R1 to 4 may be the same. Or it may be different X^-Represents an anion of an acid. )
On the other hand, for example, a fluorine-containing quaternary ammonium salt compound having a negative chargeability with respect to iron powder as represented by the following formula 4 was also examined. It was found that the intended purpose was not achieved. That is, since the compound represented by the following formula 4 has a fluorine resin atom having a strong electron-withdrawing property in the structure, the compound itself has a negative chargeability with respect to iron powder, but as in the case of the present invention, Even when a resin coating layer is formed using a resin composition in which the compound is dispersed in a binder resin for a resin coating layer, a quaternary ammonium salt compound that itself is positively charged with respect to iron powder. The effect was not acquired so much that it was contained.
[0070]
[Formula 4]

[0071]
Specific examples of the quaternary ammonium salt compound that is preferably used in the present invention and is positively charged with respect to iron powder include the following general formulas 5 to 12. However, the present invention is not limited to these.
[0072]
[Chemical formula 5]

[0073]
[Chemical 6]

[0074]
[Chemical 7]

[0075]
[Chemical 8]

[0076]
[Chemical 9]

[0077]
[Chemical Formula 10]

[0078]
Embedded image

[0079]
Embedded image

[0080]
The addition amount of the quaternary ammonium salt compound used in the present invention as described above is preferably 1 to 100 parts by mass with respect to 100 parts by mass of the binder resin for the resin coating layer. When the amount is less than 1 part by mass, the charging stability is not improved by the addition, and when it exceeds 100 parts by mass, the amount of the resin in the binder resin for the resin coating layer becomes excessive and the properties of the original resin are impaired. It tends to cause a decline.
[0081]
The binder resin for the resin coating layer used for the resin coating layer of the developer carrying member used in the present invention is not particularly limited, but a part or all of the binder resin for the resin coating layer is at least − in the molecular structure. NH₂It preferably has any structure of a group, ═NH group, or —NH— bond. By forming the resin coating layer using such a binder resin for the resin coating layer, the effect of the present invention is easily exhibited. In the present invention, when the resin coating layer of the developer carrier is used as described above, there is no clear reason for the change in charge imparting property of the resin coating layer itself. A quaternary ammonium salt compound that is positively charged and -NH₂In the structure of the binder resin for the resin coating layer, the resin coating layer is formed using the binder resin for the resin coating layer having at least one structure of a group, = NH group, or -NH- bond. Quaternary ammonium salts are incorporated. At that time, the original structure of the quaternary ammonium salt having positive polarity is lost, and the binder resin for the resin coating layer incorporating these has a uniform and sufficient chargeability, contributing to stabilization of charging. It is thought that it is to do.
[0082]
In order to adjust the volume resistance of the resin coating layer, the developer carrier used in the present invention may contain conductive fine powder dispersed in the binder resin for the coating layer. Such conductive fine powder preferably has a number average particle size of 20 μm or less, and more preferably 10 μm or less. In order to avoid unevenness formed on the surface of the binder resin for coating layer, it is more preferable to use conductive fine powder having a number average particle diameter of 1 μm or less.
[0083]
The average particle size of the conductive fine powder in the present invention is measured in a measurement range of 0.04 to 2000 μm by attaching a liquid module to an LS-230 type laser diffraction particle size distribution measuring device manufactured by Beckman Coulter. As a measuring method, a trace amount of surfactant is added to 10 ml of pure water, 10 mg of a conductive fine powder sample is added thereto, and the mixture is dispersed for 10 minutes with an ultrasonic disperser (ultrasonic homogenizer). Measured once per second and number of measurements.
[0084]
The conductive fine powder used in the present invention includes carbon black such as furnace black, lamp black, thermal black, acetylene black, channel black; titanium oxide, tin oxide, zinc oxide, molybdenum oxide, potassium titanate, antimony oxide. And metal oxides such as indium oxide; metals such as aluminum, copper, silver and nickel; inorganic fillers such as graphite, metal fibers and carbon fibers.
[0085]
As the addition amount of the conductive fine powder in the resin coating layer described above, a preferable range is 100 parts by mass or less with respect to 100 parts by mass of the binder resin for the coating layer. A more preferable addition amount is 40 parts by mass. When the addition amount exceeds 100 parts by mass, the coating strength is liable to decrease, and the addition of a large amount of non-chargeable particles can cause a decrease in the charge amount of the toner.
[0086]
As the constitution of the resin coating layer of the developer carrying member used in the present invention, it is preferable to further disperse the lubricating substance in the resin coating layer because the effect of the present invention is further promoted. Examples of the lubricating substance include graphite, molybdenum disulfide, boron nitride, mica, graphite fluoride, silver-niobium selenide, calcium chloride-graphite, talc, and fatty acid metal salts such as zinc stearate. Is preferably used because it does not impair the conductivity of the coating layer. These lubricating substances preferably have a number average particle diameter of preferably about 0.2 to 20 μm, more preferably 0.3 to 15 μm.
[0087]
In the present invention, the average particle size of the lubricating substance is 0.04 to 0.04 to the liquid particle size distribution measuring device manufactured by Beckman Coulter, LS-230, as in the case of measuring the particle size of the conductive fine powder. Measure in the measuring range of 2000 μm.
As the addition amount of the lubricating substance, a particularly preferable result is given in the range of 10 to 120 parts by mass with respect to 100 parts by mass of the binder resin for the coating layer. When the addition amount exceeds 120 parts by mass, the strength of the coating layer tends to be lowered, and when a large amount of non-chargeable additive is added, the charge amount of the toner is lowered. On the other hand, if the amount is less than 10 parts by mass, it is difficult to obtain the effect of preventing the toner from adhering to the developer carrier.
[0088]
Further, the resin coating layer of the developer carrying body stabilizes the surface roughness by dispersing spherical particles in the resin coating layer in addition to the additive substances described above, and the developer coating on the developer carrying body. It is possible to optimize the amount. The spherical particles maintain a uniform surface roughness on the surface of the coating layer of the developer carrier, and at the same time, even when the surface of the coating layer is worn, there is little change in the surface roughness of the coating layer. There is an effect of making it difficult to cause agent fusion.
[0089]
The spherical particles used in the present invention have a number average particle size of 0.3 to 30 μm, preferably 2 to 20 μm. If the number average particle size of the spherical particles is less than 0.3 μm, the effect of imparting uniform roughness to the surface and the effect of stabilizing the charging performance thereby are small, and the rapid and uniform charging to the developer becomes insufficient. . In addition, the developer transport becomes unstable, and further deterioration in transportability due to wear of the coating layer causes developer charging failure, developer contamination, and developer fusion, resulting in ghost deterioration and image density reduction. Is liable to occur, which is not preferable. When the number average particle diameter exceeds 30 μm, the surface roughness of the coating layer becomes too large, the developer transport amount becomes large, and it is difficult to sufficiently regulate the developer regulating section. Charging is difficult to perform sufficiently, and problems such as deterioration in image quality and increase in reversal fog are likely to occur. Furthermore, it is not preferable because the mechanical strength of the coating layer decreases and the durability of the film decreases.
[0090]
The number average particle diameter of the spherical particles is measured using a LS-230 type laser diffraction particle size distribution measuring device manufactured by Beckman Coulter, in the same manner as the particle diameter measurement of the conductive fine powder.
[0091]
Spherical particles have a true density of 3 g / cm^ThreeOr less, preferably 2.7 g / cm^ThreeOr less, more preferably 0.9 to 2.3 g / cm^ThreeIt is good to be. That is, the true density of the spherical particles is 3 g / cm.^ThreeIn the case where it exceeds 1, the dispersibility of the spherical particles in the coating layer becomes insufficient, so that it becomes difficult to impart uniform roughness to the surface of the coating layer. Also, since the storage stability of the paint is not good, it is difficult to obtain the surface of the triboelectric charge imparting member having uniform surface irregularities. The true density of the spherical particles is 0.9 g / cm^ThreeEven when it is smaller, the dispersibility and storage stability of the spherical particles in the coating layer tend to be insufficient.
The true density of the spherical particles is measured using a dry densitometer Accuvic 1330 (manufactured by Shimadzu Corporation).
[0092]
In the present invention, the term “spherical” in the spherical particles means that the ratio of the major axis / minor axis of the particles is about 1.0 to 1.5. In the present invention, the ratio of major axis / minor axis is preferably It is preferable to use particles of 1.0 to 1.2. When the ratio of the major axis / minor axis of the spherical particles exceeds 1.5, the surface roughness of the coating layer becomes non-uniform, which leads to rapid and uniform charging of the toner and the strength of the conductive coating layer. It is not preferable.
[0093]
As the spherical particles used in the present invention, known spherical particles can be used. Examples include spherical resin particles, spherical metal oxide particles, and spherical carbonized particles. Spherical resin particles are obtained, for example, by suspension polymerization, dispersion polymerization, and the like, and a suitable surface roughness can be obtained with a smaller addition amount, and a more uniform surface shape can be easily obtained. Examples of such spherical particles include acrylic resin particles such as polyacrylate and polymethacrylate, polyamide resin particles such as nylon, polyolefin resin particles such as polyethylene and polypropylene, silicon resin particles, phenol resin particles, and polyurethane resins. Examples thereof include resin particles, styrene resin particles, and benzoguanamine particles. The resin particles obtained by the pulverization method may be used after thermally or physically spheroidizing.
[0094]
An inorganic fine powder may be attached to the surface of the spherical particles or may be fixed. Such inorganic fine powder includes SiO 2₂, SrTiO_Three, CeO₂, CrO, Ai₂O_Three, Oxides such as ZnO and MgO, Si_ThreeN_FourNitride such as SiC, carbide such as SiC, CaSO_Four, BaSO_Four, CaCO_ThreeAnd sulfates, carbonates and the like.
[0095]
The inorganic fine powder attached to the spherical particles may be used after being treated with a coupling agent. In particular, it is preferable to use spherical particles to which an inorganic fine powder treated with a coupling agent is attached for the purpose of improving the adhesion to the binder resin or imparting hydrophobicity to the particles. Examples of such a coupling agent include a silane coupling agent, a titanium coupling agent, and a zircoaluminate coupling agent. More specifically, silane coupling agents include hexamethyldisilazane, trimethylsilane, trimethylchlorosilane, trimethylethoxysilane, dimethyldichlorosilane, methyltrichlorosilane, allyldimethylchlorosilane, allylphenyldichlorosilane, benzyl. Dimethylchlorosilane, bromomethyldimethylchlorosilane, α-chloroethyltrichlorosilane, β-chloroethyltrichlorosilane, chloromethyldimethylchlorosilane, triorganosilylmercaptan, trimethylsilylmercaptan, triorganosilylacrylate, vinyldimethylacetoxysilane, dimethyldi Ethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, hexamethyldisiloxane, 1,3-divinyltetramethyldi Loxane, 1,3-diphenyltetramethyldisiloxane, and dimethylpolysiloxane containing 2 to 12 siloxane units per molecule, each containing a hydroxyl group bonded to one silicon atom at each terminal unit Etc.
[0096]
By attaching the inorganic fine powder treated with the coupling agent to the spherical particle surface in this way, dispersibility in the resin coating layer, uniformity of the resin coating layer surface, stain resistance of the resin coating layer, The charge imparting property to the toner, the abrasion resistance of the resin coating layer, and the like can be improved.
[0097]
The spherical particles used in the present invention are more preferably conductive. That is, by imparting conductivity to the spherical particles, it is difficult to accumulate charges on the particle surface due to the conductivity, and it is possible to reduce the adhesion of the developer and improve the charge imparting property to the developer. In the present invention, the volume resistance value is 10 as the conductivity of the spherical particles.⁶Ωcm or less, more preferably 10^-3-10⁶The conductive spherical particles are preferably Ωcm.
[0098]
In the present invention, the volume resistance of the spherical particles is 10⁶If it exceeds Ωcm, the developer is likely to be contaminated and fused with spherical particles exposed on the surface of the coating layer due to wear, and it is difficult to perform quick and uniform charging.
[0099]
As a method for obtaining such conductive spherical particles, the following methods are preferable, but are not necessarily limited to these methods.
[0100]
As a method of obtaining particularly preferable conductive spherical particles used in the present invention, for example, low density and good conductivity obtained by carbonizing and / or graphitizing by firing spherical resin particles or mesocarbon microbeads. A method for obtaining spherical carbonized particles may be mentioned.
Examples of the resin used for the spherical resin particles include phenol resin, naphthalene resin, furan resin, xylene resin, divinylbenzene polymer, styrene-divinylbenzene copolymer, polyacrylonitrile, and the like.
[0101]
In addition, mesocarbon microbeads can be usually produced by washing spherical crystals formed in the process of heating and firing the medium pitch with a large amount of solvents such as tar, medium oil, and quinoline.
[0102]
As a more preferable method for obtaining conductive spherical particles, the surface of spherical resin particles such as phenol resin, naphthalene resin, furan resin, xylene resin, divinylbenzene polymer, styrene-divinylbenzene copolymer, polyacrylonitrile, etc. is mechanochemical. The bulk mesophase pitch is coated by the method, and the coated particles are heat-treated in an oxidizing atmosphere and then calcined in an inert atmosphere or vacuum to be carbonized and / or graphitized to obtain conductive spherical carbonized particles. A method is mentioned. Spherical carbonized particles obtained by this method are more preferable because the conductivity of the spherical carbonized particles obtained by graphitization is improved because crystallization of the coating portion has progressed.
[0103]
The conductive spherical carbonized particles obtained by the above-described method can control the conductivity of the spherical carbonized particles obtained by changing the firing conditions in any method, and are preferable in the present invention. used. In addition, in some cases, the spherical carbon particles obtained by the above method have a true density of the conductive spherical particles of 3 g / cm in order to further increase the conductivity.^ThreeThe conductive metal and / or metal oxide may be plated within a range not exceeding.
[0104]
As another method for obtaining the conductive spherical particles used in the present invention, the conductive fine particles having a particle size smaller than the particle size of the core particles with respect to the core particles made of the spherical resin particles are machined at an appropriate blending ratio. When the conductive particles are uniformly mixed around the core particles by the action of van der Waals force and electrostatic force, the core is increased due to a local temperature rise caused by, for example, applying mechanical impact force. Examples include a method of obtaining spherical resin particles obtained by softening the particle surface, forming conductive fine particles on the core particle surface, and conducting the conductive treatment.
[0105]
Another method for obtaining the conductive spherical particles used in the present invention is to obtain conductive spherical particles in which the conductive fine particles are dispersed by uniformly dispersing the conductive fine particles in the spherical resin particles. It is done. As a method for uniformly dispersing the conductive fine particles in the spherical resin particles, for example, the binder resin used for the spherical resin particles and the conductive fine particles are kneaded to disperse the conductive fine particles, and then cooled and solidified. A method of obtaining conductive spherical particles by pulverizing to a predetermined particle size and spheronizing by mechanical treatment and thermal treatment; or a polymerization initiator, conductive agent in a polymerizable monomer used for spherical resin particles; The finely divided fine particles and other additives are added, and the monomer composition uniformly dispersed by a disperser is suspended in an aqueous phase containing a dispersion stabilizer so as to have a predetermined particle diameter by a stirrer or the like. And a method of performing polymerization to obtain spherical particles in which conductive fine particles are dispersed.
[0106]
Next, the configuration of the developer carrying member used in the present invention will be described.
[0107]
The developer carrying member includes a substrate and a resin coating layer surrounding and covering the substrate. Examples of the shape of the substrate include a cylindrical member, a columnar member, and a belt-like member. In the developing method without contact with the drum, a metal cylindrical member is preferably used, and specifically, a metal cylindrical tube is preferably used. As the metal cylindrical tube, nonmagnetic materials such as stainless steel, aluminum and alloys thereof are preferably used. In addition, as a substrate in the development method in which the drum is brought into direct contact, a cylindrical member having a layer structure including rubber or elastomer such as urethane, EPDM, or silicon is preferably used.
[0108]
In the present invention using a magnetic developer, in order to magnetically attract and hold the developer on the developer carrier, a magnet roller or the like in which a magnet is provided is disposed in the developer carrier. In that case, the substrate may be cylindrical and a magnet roller may be disposed inside the substrate.
The method for forming the resin coating layer of the present invention is not particularly limited, and can be performed by a normal method. For example, a coating liquid containing the binder resin for the coating layer and the quaternary ammonium salt compound is applied to the base material of the developer carrier by a method such as dipping, spraying, or brushing and drying. Then, the developer carrying member used in the present invention can be obtained.
[0109]
<2> Developer used in the present invention
Next, in the present invention, a developer (hereinafter also referred to as “toner”) used for obtaining a toner image as a visible image from an electrostatic latent image will be described.
[0110]
The toner used in the present invention comprises toner particles containing at least a binder resin component and a magnetic powder, an inorganic fine powder, and a conductive fine powder having an average particle size larger than that of the inorganic fine powder and smaller than that of the toner. The magnetic toner has an average circularity determined by the above formula (1) of 0.970 or more and substantially no magnetic powder is exposed on the surface.
[0111]
First, the circularity of the toner will be described.
[0112]
A toner composed of toner having a circularity of 0.970 or more (powder composed of toner particle groups) is very excellent in transferability. This is presumably because the contact area between the toner particles and the photoconductor is small, and the adhesion force of the toner particles to the photoconductor due to mirror image force, van der Waals force, or the like is reduced. Therefore, if such a toner is used, the transfer rate is high and the residual toner is greatly reduced. Therefore, the toner in the pressure contact portion between the charging member and the photosensitive member is very little, toner fusion is prevented, and image defects are prevented. It is considered to be significantly suppressed.
[0113]
Further, since toner particles having a circularity of 0.970 or more have almost no edge portion on the surface, it is considered that friction is reduced at the press contact portion between the charging member and the photosensitive member, and the surface of the photosensitive member is suppressed.
[0114]
These effects are more prominent in an image forming method including a contact transfer process in which transfer loss is likely to occur.
[0115]
The circularity of the toner in the present invention is used as a simple method for quantitatively expressing the shape of the toner particles. In the present invention, the flow type particle image measuring device FPIA-1000 manufactured by Toa Medical Electronics Co., Ltd. is used. Measured using the following formula (2), and the average of the values obtained by dividing the total roundness of all particles measured by the following formula (3) by the total number of particles (m) Defined as circularity (am).
[0116]
[Formula 6]
Circularity (ai) = L₀/ L Formula (2)
(Where L₀Indicates the perimeter of a circle having the same projected area as the magnetic toner particle image, and L indicates the perimeter of the projected image of the magnetic toner particles. )
[0117]
[Expression 7]

Here, the particle projection area is the area of the binarized toner particle image, and the peripheral length of the particle projection image is defined as the length of the contour line obtained by connecting the edge points of the toner particle image.
[0118]
In the present invention, the circularity is an index indicating the degree of unevenness of the developer particles, and is 1.000 when the toner particles are perfectly spherical. The more complicated the surface shape, the smaller the circularity.
[0119]
In addition, “FPIA-1000”, which is a measuring apparatus used in the present invention, calculates the circularity of each particle, and then calculates the average circularity and the mode circularity. A calculation method is used in which 40 to 1.00 is divided into 61 classes, and the average circularity is calculated using the center value and frequency of the division points. However, there is very little error between each value of the average circularity calculated by this calculation method and each value of the average circularity calculated by the above-described calculation formula that directly uses the circularity of each particle. In the present invention, the calculation formula directly using the circularity of each particle described above is used for reasons of data handling such as shortening the calculation time and simplifying the calculation formula. Such a calculation method that is partially changed using the concept may be used.
[0120]
The measurement procedure is as follows.
[0121]
A dispersion is prepared by dispersing about 5 mg of a magnetic toner in 10 ml of water in which about 0.1 mg of a surfactant is dissolved, and ultrasonic waves (20 KHz, 50 W) are irradiated to the dispersion for 5 minutes to adjust the concentration of the dispersion. Measurement is performed with the above apparatus at 5000 to 20,000 / μl, and the average circularity is obtained.
[0122]
Further, the magnetic toner in the present invention is one in which the magnetic powder is not substantially exposed on the surface, and specifically, carbon elements present on the surface of the magnetic toner particles measured by X-ray photoelectron spectroscopy analysis. The ratio (B / A) of the iron element content (B) to the iron content (A) is preferably less than 0.001.
[0123]
That is, in the image forming method including the contact charging process, when the magnetic toner having the magnetic powder exposed on the surface of the toner particles is used, the photoconductor scraping due to the exposed magnetic powder becomes more prominent and tends to appear. is there. However, if (B / A) as described above is less than 0.001, that is, if magnetic toner in which the magnetic powder is substantially not exposed on the surface of the toner particles is used, the toner is brought to the surface of the photoreceptor by the charging member. Even when pressed, the surface of the photoreceptor is hardly scraped off, and it is possible to significantly reduce the scraping of the photoreceptor and toner fusion.
[0124]
The ratio (B / A) of the iron element content (B) to the carbon element content (A) present on the magnetic toner surface is calculated by performing surface composition analysis by ESCA (X-ray photoelectron spectroscopy). be able to.
[0125]
In the present invention, the ESCA apparatus and measurement conditions are as follows.
Equipment used: 1600S type X-ray photoelectron spectrometer manufactured by PHI
Measurement conditions: X-ray source MgKα (400W)
Spectral region 800μmφ
In the present invention, the surface atomic concentration is calculated from the measured peak intensity of each element using a relative sensitivity factor provided by PHI. This measurement is preferably performed by ultrasonically cleaning the toner and removing the inorganic fine powder and the like adhering to the surface of the magnetic toner particles, separating by magnetic force, and drying.
[0126]
A special toner in which magnetic powder particles are contained only in a specific portion inside the particles has already been disclosed in Japanese Patent Laid-Open No. 7-209904. However, Japanese Patent Laid-Open No. 7-209904 does not mention the circularity of the disclosed toner.
[0127]
In the image forming method of the present invention, the use of a toner having a specific circularity is an essential element, and the same toner can be used in the usage form of the present invention as described in JP-A-7-209904. It is unclear whether such an effect is manifested. To summarize the toner structure disclosed in Japanese Patent Application Laid-Open No. 7-209904, the toner layer has a structure in which a resin layer having no magnetic powder particles is formed with a certain thickness or more near the surface of the toner particles. This means that the toner surface layer portion where no magnetic powder particles are present is present in a considerable proportion. However, in other words, when the average particle diameter is as small as 10 μm, for example, the volume in which the magnetic powder particles can exist is small, so that it is difficult to enclose a sufficient amount of the magnetic powder particles. . Moreover, in such a toner, the ratio of the surface resin layer in which the magnetic powder particles are not present differs between the toner particles having a large particle size and the small particles in the toner particle size distribution. Since they differ, the developability and transferability also vary depending on the particle size of the toner, and selective developability that depends on the particle size is likely to be seen. Therefore, when printing is performed with such a magnetic toner for a long period of time, particles that contain a large amount of magnetic powder and are difficult to develop, that is, toner particles having a large particle size are likely to remain, and the image density and image quality are lowered. It also leads to deterioration.
[0128]
Therefore, in the present invention, the dispersion state of the magnetic powder in the toner particles may be set to the following preferable dispersion state. A preferable magnetic powder dispersion state in the toner particles is a state in which the magnetic powder particles are present uniformly throughout the toner particles as much as possible without aggregation. That is, when the volume average particle diameter of the toner is C, and the tomographic surface observation of the magnetic toner using a transmission electron microscope (TEM) is D, the minimum value of the distance between the magnetic powder and the toner particle surface is D / The use of a magnetic toner satisfying C ≦ 0.02 is also one of the features of the present invention.
[0129]
In the present invention, the method of adjusting D / C ≦ 0.02 includes controlling the kind of surface treatment agent for magnetic powder and the uniformity of treatment.
[0130]
The volume average particle size C of the magnetic toner in the present invention can be measured by a Coulter Multisizer described later, and D can be measured as follows. As a specific observation method by TEM, after sufficiently dispersing toner particles to be observed in a room temperature curable epoxy resin, a cured product obtained by curing in an atmosphere at a temperature of 40 ° C. for 2 days is used as it is. Alternatively, a method of freezing and observing as a flaky sample with a microtome equipped with diamond teeth is preferable.
[0131]
In the image forming method of the present invention, the toner should have a weight average particle diameter of 3 to 10 [mu] m, more preferably 4 to 8 [mu] m in order to faithfully develop finer latent image dots for higher image quality. preferable. For toners with a weight average particle size smaller than 3 μm, the transfer residual toner on the photoconductor increases due to a decrease in transfer efficiency, and it tends to be difficult to suppress photoconductor scraping and toner fusion in the contact charging process. There is. Furthermore, in addition to an increase in the entire surface area of the toner, the fluidity and agitation of the toner are lowered, and it becomes difficult to uniformly charge the individual toner particles. Other than fusing, it tends to cause non-uniform image unevenness, which is not preferable for the toner used in the present invention. When the weight average particle diameter of the toner exceeds 10 μm, the characters and line images are likely to be scattered and high resolution is difficult to obtain. In addition, as the image forming apparatus becomes higher in resolution, toner of 8 μm or more tends to deteriorate the reproduction of one dot.
[0132]
The average particle diameter of the toner can be measured by various methods such as Coulter Counter TA-II type or Coulter Multisizer (manufactured by Beckman Coulter, Inc.). In the present invention, a Coulter Multisizer (manufactured by Beckman Coulter, Inc.) is used. An interface for outputting distribution and volume distribution (manufactured by Nikka) and a PC9801 personal computer (manufactured by NEC) are connected, and a 1% NaCl aqueous solution is prepared using first-grade sodium chloride as the electrolyte. For example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used.
[0133]
As a measuring method, 0.1 to 5 ml of a surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 ml of the electrolytic aqueous solution, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the volume and number of toner particles of 2 μm or more are measured using the 100 μm aperture as the aperture by the Coulter Multisizer. Distribution and number distribution are calculated.
[0134]
Then, the volume-based weight average particle diameter (D4) obtained from the volume distribution according to the present invention is obtained.
[0135]
In the present invention, toner particles are produced by a polymerization method, particularly a suspension polymerization method, and then the inorganic fine powder and the conductive fine powder are mixed and added to adhere the inorganic fine powder and the conductive fine powder to the surface. The magnetic toner of the invention is preferred. In this suspension polymerization method, a polymerizable monomer, a magnetic powder and a colorant (a polymerization initiator, a cross-linking agent, a charge control agent, and other additives as required) are uniformly used as a binder resin component. After dissolving or dispersing in a polymerizable monomer system, the polymerizable monomer system is dispersed in a continuous layer (for example, an aqueous medium) containing a dispersion stabilizer using a suitable stirrer and simultaneously subjected to a polymerization reaction. To obtain a toner having a desired particle size. The toner obtained by this suspension polymerization method (hereinafter referred to as “polymerized toner”) has toner particles that are substantially spherical in shape, so that a toner satisfying the physical property requirement essential for the present invention of circularity of 0.970 or more is obtained. It is easy to be done. In the present invention, the aqueous medium is a medium containing water as a main component. Specific examples of the aqueous medium include water itself, water added with a small amount of a surfactant, water added with a pH adjusting agent, and water added with an organic solvent.
[0136]
However, even if normal magnetic powder is contained in the polymerized toner, it is difficult to suppress exposure of the magnetic powder from the particle surface. Further, not only the fluidity and charging characteristics of the toner particles are remarkably lowered, but also the toner having an average circularity of 0.970 or more is obtained due to the strong interaction between the magnetic powder and water during the production of the suspension polymerization toner. It is difficult to obtain. This is because, firstly, the magnetic powder particles are generally hydrophilic, so they tend to be present on the toner surface, and secondly, the magnetic powder moves randomly when the aqueous solvent is stirred, and the magnetic powder particles are suspended from the monomer. It is considered that the turbid particle surface is dragged, the shape is distorted, and it is difficult to form a circle. In order to solve these problems, it is important to modify the surface characteristics of the magnetic powder particles. Since the magnetic powder has excellent hydrophobicity and dispersibility, the magnetic powder used for the polymerized toner in the present invention is a cup with the surface dispersed in an aqueous medium so that the magnetic powder has a primary particle size. It is preferably a magnetic powder that is treated while hydrolyzing the ring agent. This hydrophobic treatment method is less likely to cause coalescence between the magnetic powder particles than the treatment in the gas phase, and the electrostatic repulsion action between the magnetic powder particles by the hydrophobic treatment works, so that the magnetic powder is almost primary particles. Surface treatment in the state of.
[0137]
When the magnetic powder is used as a material for polymerized toner, the dispersibility in the toner particles becomes very good, and the magnetic powder is not exposed on the surface of the toner particles to obtain a magnetic toner that is almost spherical. Can do. That is, the average circularity is 0.970 or more, and the ratio (B / A) of (B) to the content (A) of carbon element present on the surface of the magnetic toner measured by X-ray photoelectron spectroscopy is 0. A magnetic toner of less than 001 can be obtained.
[0138]
Examples of the coupling agent that can be used in the surface treatment of the magnetic powder according to the present invention include a silane coupling agent and a titanium coupling agent. The treatment amount is 0.05 to 20 parts by mass, preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the magnetic powder.
[0139]
In the magnetic powder thus obtained, no particle aggregation is observed, and the surface of each particle is uniformly hydrophobized. Therefore, when used as a material for polymerized toner, the dispersibility in the toner particles is extremely high. It is good. Moreover, there is no exposure from the surface of the toner particles, and a polymer toner that is almost spherical can be obtained.
[0140]
The magnetic powder used for the toner in the present invention is preferably used in an amount of 10 to 200 parts by mass with respect to 100 parts by mass of the binder resin component. More preferably, 20 to 180 parts by mass are used. If it is less than 10 parts by mass, the coloring power of the toner is poor, and it is difficult to suppress fogging. On the other hand, when the amount exceeds 200 parts by mass, not only the retention by the magnetic force on the developer carrying member is increased and the developability is lowered, but it is difficult not only to uniformly disperse the magnetic powder into individual toner particles, but also the fixability. Tends to decrease.
[0141]
Examples of the magnetic powder used in the present invention include magnetic iron oxides such as magnetite, maghemite and ferrite, metals such as iron, cobalt and nickel or these metals and aluminum, cobalt, copper, lead, magnesium, tin, zinc and antimony. And alloys of metals such as beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, vanadium, and mixtures thereof, but those mainly composed of magnetite are preferred.
[0142]
The shape of the magnetic powder includes octahedrons, hexahedrons, spheres, needles, flakes, and the like, but those having less anisotropy such as octahedrons, hexahedrons, spheres, and irregular shapes increase the image density. Preferred above. The shape of such magnetic powder can be confirmed by SEM or the like. The average particle size of the magnetic powder is preferably 0.01 to 1.0 μm, more preferably 0.05 to 0.5 μm. When the average particle size is less than 0.01 μm, the blackness is remarkably lowered, the coloring power is insufficient as a colorant for black and white toner, and the aggregation of the composite oxide particles becomes strong, so that Tend to deteriorate. On the other hand, when the average particle size exceeds 1.0 μm, the coloring power becomes insufficient as in the case of a general colorant. In addition, particularly when used as a colorant for small-diameter toners, it is probabilistically difficult to disperse the same number of magnetic powders in individual toner particles, and the dispersibility tends to deteriorate. The average particle size of the magnetic powder can be measured using a transmission electron microscope. Specifically, a powder sample of the toner to be measured is observed with a transmission electron microscope, the diameter of 100 magnetic powder particles in the field of view is measured, and the number average particle diameter is obtained to obtain the average particle diameter.
[0143]
In addition to the magnetic powder, other colorants may be used in combination. Examples of coloring materials that can be used in combination include magnetic or nonmagnetic inorganic compounds, and known dyes and pigments. Specifically, for example, ferromagnetic metal particles such as cobalt and nickel, or alloys obtained by adding chromium, manganese, copper, zinc, aluminum and rare earth elements to these, particles such as hematite, titanium black, nigrosine dye / pigment , Carbon black, phthalocyanine and the like. These may also be used by treating the surface with a coupling agent in the same manner as the magnetic powder.
[0144]
The toner according to the present invention also contains a release agent, which is one of preferable usage forms.
[0145]
The toner image transferred onto the transfer material is then fixed on the transfer material with energy such as heat and pressure to obtain a semi-permanent image. At this time, heat roll type fixing is generally used.
[0146]
As described above, if a toner having a weight average particle size of 10 μm or less is used, a very high-definition image can be obtained. However, a toner particle having a small particle size is a paper fiber when a transfer material such as paper is used. , The heat receiving from the heat fixing roller becomes insufficient, and low temperature offset is likely to occur. However, in the toner according to the present invention, by including an appropriate amount of the release agent as the release agent, it is possible to prevent the photoconductor from being scraped while achieving both high resolution and offset resistance.
[0147]
As the release agent usable in the toner according to the present invention, petroleum wax such as paraffin wax, microcrystalline wax, petrolactam and derivatives thereof, montan wax and derivatives thereof, hydrocarbon wax and derivatives thereof by Fischer-Tropsch method, Polyolefin waxes typified by polyethylene and derivatives thereof, natural waxes and derivatives thereof such as carnauba wax and candelilla wax, and the derivatives include oxides, block copolymers with vinyl monomers, and graft modified products. Furthermore, endotherms in differential thermal analysis such as higher fatty alcohols, fatty acids such as stearic acid and palmitic acid, or compounds thereof, acid amide waxes, ester waxes, ketones, hydrogenated castor oil and derivatives thereof, plant waxes, animal waxes, etc. What has a peak in the range of 45 degreeC or more and 110 degrees C or less, Furthermore, 50 degreeC or more and 90 degrees C or less is preferable.
[0148]
The content when the release agent is used is preferably in the range of 0.5 to 50% by mass with respect to the whole toner. If the content is less than 0.5% by mass, the effect of suppressing the low temperature offset is poor, and if it exceeds 50% by mass, the long-term storage stability is deteriorated, the dispersibility of other toner materials is deteriorated, and the toner fluidity is deteriorated. Leading to deterioration and deterioration of image characteristics.
[0149]
In the toner relating to the image forming method of the present invention, a charge control agent may be blended in order to stabilize the charge characteristics. As the charge control agent, a known one can be used, and a charge control agent that has a high charging speed and can stably maintain a constant charge amount is particularly preferable. Further, when the toner is produced using a direct polymerization method, a charge control agent having a low polymerization inhibitory property and substantially free from a solubilized product in an aqueous dispersion medium is particularly preferable. Specific compounds include metal compounds of aromatic carboxylic acids such as salicylic acid, alkyl salicylic acid, dialkyl salicylic acid, naphthoic acid and dicarboxylic acid, metal salts or metal complexes of azo dyes or azo pigments as negatively chargeable charge control agents, Examples thereof include a polymer compound having a sulfonic acid or carboxylic acid group in the side chain, a boron compound, a urea compound, a silicon compound, and calixarene. As a method of incorporating a charge control agent into the toner, there are a method of adding it inside the toner particles and a method of adding it externally. The amount of these charge control agents used is determined by the toner production method including the type of the binder resin component, the presence or absence of other additives, and the dispersion method, and is not limited uniquely. The amount is preferably 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the binder resin component.
[0150]
A method for producing toner by suspension polymerization related to the image forming method of the present invention will be described.
[0151]
Examples of the polymerizable monomer constituting the polymerizable monomer system used in the polymerized toner according to the present invention include the following.
[0152]
Examples of the polymerizable monomer include styrene monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, and p-ethylstyrene; methyl acrylate, ethyl acrylate, Acrylate esters such as n-butyl acrylate, isobutyl acrylate, n-propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, and phenyl acrylate Class; methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, Methacrylic acid dimethyl aminoethyl, methacrylic acid esters such as diethylaminoethyl methacrylate; and other acrylonitrile, methacrylonitrile, and the like monomers acrylamide.
[0153]
These polymerizable monomers can be used alone or in combination. Among the polymerizable monomers described above, styrene or a styrene derivative is preferably used alone or mixed with other monomers from the viewpoint of the developing characteristics and durability of the toner.
[0154]
In the production of the polymerized toner according to the present invention, the polymerization may be performed by adding a resin to the polymerizable monomer system. For example, hydrophilic monomers such as amino groups, carboxylic acid groups, hydroxyl groups, sulfonic acid groups, glycidyl groups, and nitrile groups cannot be used because polymerizable monomers dissolve in water and cause emulsion polymerization due to water solubility. When it is desired to introduce a group-containing monomer component into the toner, a random copolymer, a block copolymer, or a graft copolymer of these and a vinyl compound such as styrene or ethylene, or a polyester or polyamide And the like in the form of a polycondensation product such as a polyaddition polymer such as polyether or polyimine. When such a polymer containing a polar functional group is allowed to coexist in the toner, the above-mentioned wax component is phase-separated and the encapsulation becomes stronger, and a toner having good offset resistance, blocking resistance, and low-temperature fixability can be obtained. Obtainable. When using such a high molecular polymer containing a polar functional group, the average molecular weight is preferably 5,000 or more. If it is 5,000 or less, particularly 4,000 or less, the present polymer is likely to concentrate near the surface, and this tends to adversely affect developability, blocking resistance, etc., which is not preferred.
[0155]
The polar polymer is particularly preferably a polyester resin.
[0156]
In addition, resins other than those described above may be added to the polymerizable monomer system for the purpose of improving the dispersibility and fixability of the material or image characteristics. Examples of the resin used include polystyrene and polyvinyltoluene. Styrene and its substituted homopolymers: styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer Polymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-dimethylaminoethyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer , Styrene-butyl methacrylate copolymer, Styrene-dimethyl methacrylate Noethyl copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-maleic acid Styrene copolymers such as copolymers, styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, silicone resin, polyester resin, polyamide resin, epoxy resin Polyacrylic acid resin, rosin, modified rosin, temper resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin and the like can be used alone or in combination.
[0157]
As addition amount of these resin, 1-20 mass parts is preferable with respect to 100 mass parts of polymerizable monomers. If the amount is less than 1 part by mass, the effect of addition is small, while if it is added in an amount of 20 parts by mass or more, various physical properties of the polymerized toner tend to be difficult to design.
[0158]
Furthermore, if a polymer having a molecular weight different from the molecular weight range of the toner obtained by polymerizing the polymerizable monomer is dissolved and polymerized in the polymerizable monomer system, the toner has a wide molecular weight distribution and high offset resistance. Can be obtained.
[0159]
As the polymerization initiator used in the production of the polymerized toner related to the image forming method of the present invention, those having a half-life of 0.5 to 30 hours at the time of the polymerization reaction are 0.5 to 20 with respect to the polymerizable monomer. When the polymerization reaction is carried out with an addition amount of parts by mass, a polymer having a maximum between 10,000 and 100,000 in molecular weight can be obtained, and the toner can have desirable strength and suitable melting characteristics. Examples of polymerization initiators include 2,2′-azobis- (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile) Azo or diazo polymerization initiators such as 2,2′-azobis-4-methoxy-2,4-dimethylvaleronitrile, azobisisobutyronitrile, benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, Examples thereof include peroxide-based polymerization initiators such as cumene hydroperoxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide, and t-butylperoxy 2-ethylhexanoate.
[0160]
When producing the polymerized toner relating to the image forming method of the present invention, a crosslinking agent may be added, and the preferred addition amount is 0.001 to 15% by mass with respect to the polymerizable monomer system.
[0161]
Here, as the crosslinking agent, a compound having two or more polymerizable double bonds is mainly used, for example, an aromatic divinyl compound such as divinylbenzene, divinylnaphthalene, etc .; for example, ethylene glycol diacrylate, ethylene glycol diester Carboxylic acid ester having two double bonds such as methacrylate, 1,3-butanediol dimethacrylate, etc .; Divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide, divinyl sulfone, etc .; and having three or more vinyl groups Are used alone or as a mixture.
[0162]
In the method for producing a polymerized toner relating to the image forming method of the present invention, generally, the above-described toner composition, that is, a polymerizable monomer, a magnetic powder, a release agent, a plasticizer, a charge control agent, a crosslinking agent, and optionally colored. Components necessary for the toner and other additives and other additives such as organic solvents, polymer polymers, dispersants, etc. that are added to reduce the viscosity of the polymer produced by the polymerization reaction, are added as appropriate, homogenizer, ball mill, colloid A polymerizable monomer system uniformly dissolved or dispersed by a dispersing machine such as a mill or an ultrasonic dispersing machine is suspended in an aqueous medium containing a dispersion stabilizer. At this time, the particle size of the obtained toner particles becomes sharper by using a high-speed disperser such as a high-speed stirrer or an ultrasonic disperser to obtain a desired toner particle size at a stretch. The polymerization initiator may be added at the same time as other additives are added to the polymerizable monomer, or may be mixed immediately before being suspended in the aqueous medium. Further, a polymerization initiator dissolved in a polymerizable monomer or a solvent can be added immediately after granulation and before starting the polymerization reaction.
[0163]
After granulation, stirring may be performed using a normal stirrer to such an extent that the particle state is maintained and the particles are prevented from floating and settling.
[0164]
In the case of producing a polymerized toner related to the image forming method of the present invention, known surfactants and organic / inorganic dispersants can be used as dispersion stabilizers, and among them, inorganic dispersants are less likely to produce harmful ultra fine powders. Since dispersion stability is obtained due to steric hindrance, the stability is not easily lost even if the reaction temperature is changed, and the toner can be preferably used because it is easy to wash and does not adversely affect the toner. Examples of such inorganic dispersants include polyvalent metal phosphates such as calcium phosphate, magnesium phosphate, aluminum phosphate and zinc phosphate, carbonates such as calcium carbonate and magnesium carbonate, calcium metasuccinate, calcium sulfate and barium sulfate. Examples thereof include inorganic salts, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, silica, bentonite, inorganic oxides such as alumina.
[0165]
These inorganic dispersants are desirably used alone in an amount of 0.2 to 20 parts by mass with respect to 100 parts by mass of the polymerizable monomer. However, in order to atomize a toner that hardly generates ultrafine particles. Since it is insufficient, 0.001 to 0.1 parts by mass of a surfactant may be used in combination.
[0166]
Examples of the surfactant include sodium dodecylbenzene sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, sodium oleate, sodium laurate, sodium stearate, potassium stearate and the like.
[0167]
When these inorganic dispersants are used, they may be used as they are, but in order to obtain finer particles, it is preferable to generate the inorganic dispersant particles in an aqueous medium. For example, in the case of calcium phosphate, more uniform and fine dispersion can be achieved by mixing a sodium phosphate aqueous solution and a calcium chloride aqueous solution under high speed stirring to produce water-insoluble calcium phosphate. At this time, a water-soluble sodium chloride salt is produced as a by-product at the same time. However, if a water-soluble salt is present in the aqueous medium, dissolution of the polymerizable monomer in water is suppressed, and an ultrafine toner based on emulsion polymerization is produced. Since it becomes difficult to generate | occur | produce, it is more convenient. Since it becomes an obstacle when removing the remaining polymerizable monomer at the end of the polymerization reaction, it is better to replace the aqueous medium or desalinate with an ion exchange resin. The inorganic dispersant can be almost completely removed by dissolving with an acid or alkali after completion of the polymerization.
[0168]
In the polymerization step, the polymerization is performed at a polymerization temperature of 40 ° C. or higher, generally 50 to 90 ° C. When the polymerization is carried out in this temperature range, the release agent or wax to be sealed inside is precipitated by phase separation, and the encapsulation becomes more complete. In order to consume the remaining polymerizable monomer, it is possible to raise the reaction temperature to 90 to 150 ° C. at the end of the polymerization reaction.
[0169]
In the present invention, it is also important that the toner is added with inorganic fine powder as a fluidizing agent. The inorganic fine powder is added to improve the fluidity of the toner and to make the charge of the toner particles uniform. However, adjustment of the charge amount of the toner, improvement of environmental stability, etc. by treatment such as hydrophobizing the inorganic fine powder. It is also a preferable form to provide the function.
[0170]
The inorganic fine powder preferably has an average primary particle size of 4 to 80 nm. When the average primary particle size is larger than 80 nm, or when inorganic fine powder of 80 nm or less is not added, when the transfer residual toner adheres to the charging member, the toner easily adheres to the charging member and is stable. It is difficult to obtain good charging characteristics. In addition, good toner fluidity cannot be obtained, and charging to toner particles is likely to be uneven, and problems such as increased fog, decreased image density, and toner scattering cannot be avoided. When the average primary particle size of the inorganic fine powder is smaller than 4 nm, the agglomeration property of the inorganic fine powder is strengthened, and the coagulability of the particle size distribution having a strong agglomeration property that is difficult to be solved by the pulverization treatment instead of the primary particles. It tends to behave as an aggregate, and image defects are likely to occur due to development of aggregates, damage to the image carrier or development carrier, and the like.
[0171]
In order to make the charge distribution of the toner particles more uniform, the average primary particle size of the inorganic fine powder is preferably 6 to 35 nm.
[0172]
In the present invention, the average primary particle size of the inorganic fine powder is measured as follows. The surface of the toner is contrasted with a photograph of the toner magnified by a scanning electron microscope, and a photograph of the toner mapped with elements contained in the inorganic fine powder by an elemental analysis means such as XMA attached to the scanning electron microscope. It can be measured by measuring 100 or more primary particles of inorganic fine powder adhering to or released from the surface and determining the number average particle size.
[0173]
Silica, alumina, titania and the like can be used as the inorganic fine powder used in the present invention.
[0174]
For example, as silica, both a so-called dry method produced by vapor phase oxidation of silicon halide or a dry silica called fumed silica, and a so-called wet silica produced from water glass or the like can be used. There are few silanol groups on the surface and inside the silica fine powder, and Na₂O, SO_Three ^2-For example, dry silica with less production residue is preferred. In dry silica, it is also possible to obtain composite fine powders of silica and other metal oxides by using other metal halogen compounds such as aluminum chloride and titanium chloride together with silicon halogen compounds in the production process. Is also included.
[0175]
The addition amount of the inorganic fine powder having an average primary particle size of 4 to 80 nm is preferably 0.1 to 3.0% by mass with respect to the toner particles, and the effect is obtained when the addition amount is less than 0.1% by mass. However, the fixing property tends to be poor at 3.0% by mass or more.
[0176]
The inorganic fine powder is preferably a hydrophobized product in view of characteristics in a high temperature and high humidity environment. This is because when the inorganic fine powder added to the toner absorbs moisture, the charge amount of the toner particles is remarkably reduced, and the toner is easily scattered.
[0177]
As treatment agents for hydrophobic treatment, treatment agents such as silicone varnish, various modified silicone varnishes, silicone oil, various modified silicone oils, silane compounds, silane coupling agents, other organic silicon compounds, and organic titanium compounds may be used alone or in combination. And may be processed.
[0178]
Among these, those treated with silicone oil are preferable, and more preferably, the inorganic fine powder is treated with silicone oil at the same time or after treatment to maintain the charge amount of toner particles high even in a high humidity environment. In addition, it is good for preventing toner scattering.
[0179]
Specifically, for example, a silylation reaction is performed as a first stage reaction, and after silanol groups are eliminated by chemical bonding, a hydrophobic thin film can be formed on the surface with silicone oil as a second stage reaction.
[0180]
The silicone oil has a viscosity at 25 ° C. of 10 to 200,000 mm.²/ S, even 3,000-80,000mm²/ S is preferred. 10mm²If it is less than / s, the inorganic fine powder is not stable and the image quality tends to deteriorate due to heat and mechanical stress. 200,000mm²If it exceeds / s, uniform processing tends to be difficult.
[0181]
As the silicone oil used, for example, dimethyl silicone oil, methylphenyl silicone oil, α-methylstyrene modified silicone oil, chlorophenyl silicone oil, fluorine modified silicone oil and the like are particularly preferable.
[0182]
As a method for treating the silicone oil, for example, the inorganic fine powder treated with the silane compound and the silicone oil may be directly mixed using a mixer such as a Henschel mixer, or the silicone oil is sprayed onto the inorganic fine powder. A method may be used. Alternatively, after dissolving or dispersing silicone oil in an appropriate solvent, a fine silica powder may be added and mixed to remove the solvent. A method using a sprayer is more preferable in that the formation of inorganic fine powder aggregates is relatively small.
[0183]
The treatment amount of the silicone oil is 1 to 23 parts by mass, preferably 5 to 20 parts by mass with respect to 100 parts by mass of the inorganic fine powder.
[0184]
If the amount of silicone oil is too small, good hydrophobicity cannot be obtained, and if it is too large, problems such as fogging may occur.
[0185]
  The inorganic fine powder having an average primary particle size of 80 nm or less used in the present invention is obtained by nitrogen adsorption measured by the BET method.RuSpecific surface area of 20-250m²/ G is preferable, more preferably 40-200m²/ G is even better.
[0186]
The specific surface area is determined according to the BET method by adsorbing nitrogen gas to the sample surface using a specific surface area measuring device Autosorb 1 (manufactured by Yuasa Ionics) and calculating the specific surface area using the BET multipoint method.
[0187]
The toner in the present invention preferably has a conductive fine powder that is larger than the number average primary particle diameter of the inorganic fine powder and smaller than the weight average particle diameter of the toner. Although the number average primary particle size and the weight average particle size are not compared on the same scale, the inorganic fine powder is relatively smaller than the conductive fine powder, and the conductive fine powder is relatively smaller than the toner. In, these were used as one index for comparing the size of the conductive fine powder.
[0188]
The conductive fine powder preferably has a volume average particle size of 0.1 to 10 μm. When the volume average particle size of the conductive fine powder is small, it is preferable to set the content of the conductive fine powder with respect to the entire toner to be small in order to prevent the developability from decreasing. When the volume average particle size of the conductive fine powder is less than 0.1 μm, an effective amount of the conductive fine powder cannot be secured, and charging due to adhesion / mixing of the insulating transfer residual toner to the contact charging member in the charging process. A sufficient amount of conductive fine powder to overcome the inhibition and charge the image bearing member satisfactorily cannot be interposed in the contact portion between the charging member and the image bearing member or in the vicinity of the charged region. It becomes easy to cause charging failure. From this viewpoint, the volume average particle size of the conductive fine powder is preferably 0.15 μm or more, more preferably 0.2 μm or more and 5 μm or less.
[0189]
If the volume average particle size of the conductive fine powder is larger than 10 μm, the conductive fine powder dropped from the charging member blocks or diffuses the exposure light for writing the electrostatic latent image, resulting in a defect in the electrostatic latent image. There is a tendency to reduce image quality. Furthermore, since the number of particles per unit weight decreases when the volume average particle size of the conductive fine powder is large, the conductive fine powder is reduced in consideration of the decrease or deterioration due to dropping of the conductive fine powder from the charging member. In order to continuously supply and intervene the conductive fine powder in the contact area between the charging member and the image carrier or in the vicinity of the charged region, the contact charging member is also connected to the image carrier via the conductive fine powder. In order to maintain the fine contact property and stably obtain good chargeability, it is necessary to increase the content of the conductive fine powder with respect to the entire toner. However, if the content of the conductive fine powder is excessively increased, developability is deteriorated, particularly in a high humidity environment, resulting in a decrease in image density and toner scattering. From such a viewpoint, the volume average particle diameter of the conductive fine powder is preferably 5 μm or less.
[0190]
The content of the conductive fine powder with respect to the whole toner is preferably 0.1 to 10% by mass. When the content of the conductive fine powder in the whole toner is less than 0.1% by mass, the charging of the image carrier is excellent by overcoming the charging inhibition due to the adhesion and mixing of the insulating transfer residual toner to the contact charging member. A sufficient amount of conductive fine powder to be applied to the contact portion between the charging member and the image bearing member or in the vicinity of the charging region cannot be provided, and the charging property is lowered and charging failure is likely to occur. . Further, when the content is more than 10% by mass, the conductive fine powder recovered by the simultaneous development cleaning is excessively increased, so that the toner chargeability and developability in the developing portion are lowered, and the image density is lowered. Prone to toner scattering. The content of the conductive fine powder with respect to the whole toner is preferably 0.2 to 5% by mass.
[0191]
The resistance of the conductive fine powder is 10⁹Ωcm or less is preferable. Resistance of conductive fine powder is 10⁹If it is greater than Ωcm, the conductive fine powder is interposed in the contact area between the charging member and the image carrier or in the vicinity of the charging region, and the fineness to the image carrier through the conductive fine powder of the contact charging member is high. Even if the contact property is maintained, it is difficult to obtain a charge promoting effect for obtaining good chargeability.
[0192]
Furthermore, the resistance of the conductive fine powder is 10⁶If it is Ωcm or less, the charging of the image bearing member can be performed more satisfactorily by overcoming charging inhibition due to adhesion / mixing of the insulating transfer residual toner to the contact charging member.
[0193]
In order to sufficiently extract the charge-promoting effect of the conductive fine powder and stably obtain good chargeability, the resistance of the conductive fine powder is the resistance of the surface portion of the contact charging member or the contact portion with the image carrier. Is preferably smaller.
[0194]
Further, it is preferable that the conductive fine powder is a transparent, white or light-colored conductive fine powder because the influence on the color reproducibility of the conductive fine powder transferred onto the transfer material is prevented. The conductive fine powder is also preferably a transparent, white or light-colored conductive fine powder, more preferably for the exposure light of the conductive fine powder, in the sense that it does not interfere with the exposure light in the electrostatic latent image forming step. The transmittance is preferably 30% or more.
[0195]
In the present invention, the light transmittance of the conductive fine powder can be measured by the following procedure. The transmittance is measured with a conductive fine powder fixed to one layer on a transparent film having an adhesive layer on one side. Light is irradiated from the vertical direction of the sheet, and the light transmitted through the back of the film is collected and the amount of light is measured. The transmittance of the conductive fine powder is calculated as a net light amount from the light amount when only the film and the conductive fine powder are attached. Actually, measurement is performed using a 310T transmission densitometer manufactured by X-Rite.
[0196]
The conductive fine powder is preferably nonmagnetic. Since the conductive fine powder is non-magnetic, it is easy to obtain a transparent, white or light-colored conductive fine powder. On the other hand, it is difficult to make the conductive fine powder having magnetism transparent, white or pale. Further, in the image forming method in which the developer is transported and held by magnetic force for supporting the developer, the conductive fine powder having magnetism is difficult to be developed, so that the conductive fine powder is supplied onto the image carrier. Or the accumulation of conductive fine powder on the surface of the developer carrier tends to cause problems such as hindering development of toner particles. Further, when magnetic conductive fine powder is added to the magnetic toner particles, the conductive fine powder tends to be difficult to be separated from the toner particles due to magnetic cohesive force, and the supply of the conductive fine powder onto the image carrier. It is easy to deteriorate.
[0197]
Examples of the conductive fine powder in the present invention include carbon fine powder such as carbon black and graphite; metal fine powder such as copper, gold, silver, aluminum and nickel; zinc oxide, titanium oxide, tin oxide, aluminum oxide and indium oxide. Metal oxides such as silicon oxide, magnesium oxide, barium oxide, molybdenum oxide, iron oxide, and tungsten oxide; metal compounds such as molybdenum sulfide, cadmium sulfide, and potassium titanate, or composite oxides thereof, as required It can be used by adjusting the particle size and particle size distribution. Among these, conductive inorganic oxide fine powders such as zinc oxide, tin oxide, and titanium oxide are particularly preferable.
[0198]
  Further, for the purpose of controlling the resistance value of the conductive inorganic oxide fine powder, a metal oxide doped with an element such as antimony or aluminum, a fine powder having a conductive material on its surface, or the like can be used. For example, titanium oxide fine powder surface-treated with tin oxide / antimony, antimonyButDoped stannic oxide fine powder or stannic oxide fine powder.
[0199]
As commercially available tin oxide / antimony-treated conductive titanium oxide fine powder, for example, EC-300 (Titanium Industry Co., Ltd.), ET-300, HJ-1, HI-2 (above, Ishihara Sangyo Co., Ltd.), W -P (Mitsubishi Materials Corporation).
[0200]
Examples of commercially available antimony-doped conductive tin oxide include T-1 (Mitsubishi Materials Corporation) and SN-100P (Ishihara Sangyo Co., Ltd.), and examples of commercially available stannic oxide include SH-S (Japan). Chemical Industry Co., Ltd.).
[0201]
A method for measuring the volume average particle diameter of the conductive fine powder will be exemplified. A liquid module is attached to a LS-230 type laser diffraction particle size distribution measuring device manufactured by Coulter, Inc., and a particle size of 0.04 to 2000 μm is set as a measurement range, and the volume average particle size of the conductive fine powder is obtained from the obtained volume-based particle size distribution. Calculate the diameter. As a measurement procedure, a trace amount of surfactant is added to 10 cc of pure water, 10 mg of a conductive fine powder sample is added thereto, and the mixture is dispersed for 10 minutes with an ultrasonic disperser (ultrasonic homogenizer), and then measured for 90 hours. Measured once per second and number of measurements.
[0202]
In measurement from toner, a trace amount of surfactant is added to 100 g of pure water, 2 to 10 g of toner is added, and the mixture is dispersed for 10 minutes with an ultrasonic disperser (ultrasonic homogenizer), and then a centrifuge. The toner particles and the conductive fine powder are separated by, for example. In the case of magnetic toner, a magnet can be used. The separated dispersion is measured with a measurement time of 90 seconds and a single measurement.
[0203]
In the present invention, as a method for adjusting the particle size of the conductive fine powder, in addition to the method of setting the production method and production conditions so that the primary particles of the conductive fine powder have a desired particle size at the time of production, A method of agglomerating small particles, a method of pulverizing large particles of primary particles, a method of classification, etc. are possible, and further, conductive particles are applied to a part or all of the surface of a base particle having a desired particle size. A method of attaching or fixing, a method of using conductive particles having a form in which a conductive component is dispersed in particles of a desired particle size, and the like are possible, and these methods are combined to adjust the particle size of the conductive fine powder. It is also possible.
[0204]
The particle diameter in the case where the conductive fine powder particles are formed as an aggregate is defined as an average particle diameter of the aggregate. There is no problem that the conductive fine powder exists not only in the state of primary particles but also in the state of aggregation of secondary particles. In any aggregated state, any form can be used as long as the aggregate is interposed in the contact portion between the charging member and the image carrier or in the vicinity of the charged region and can realize a charge assisting or promoting function.
[0205]
In the present invention, the resistance of the conductive fine powder can be determined by measuring and normalizing by the tablet method. That is, the bottom area 2.26cm²A powder sample of about 0.5 g is placed in the cylinder, and 15 kg of pressure is applied to the upper and lower electrodes. At the same time, a voltage of 100 V is applied to measure the resistance value, and then normalized to calculate the specific resistance.
[0206]
The toner used in the present invention may further contain other additives such as Teflon powder, zinc stearate powder, polyvinylidene fluoride powder, cerium oxide powder, silicon carbide within a range that does not have a substantial adverse effect. A small amount of a polishing agent such as powder or strontium titanate powder, or a fluidity imparting agent such as titanium oxide powder or aluminum oxide powder, an anti-caking agent, organic fine particles having opposite polarity, and inorganic fine particles are used in small amounts as a developability improver. You can also do things. These additives can also be used after hydrophobizing the surface.
[0207]
<3> Image forming method and image forming apparatus of the present invention
The image forming method of the present invention includes a charging step of applying a voltage to the charging member to charge the image carrier, an electrostatic latent image forming step of forming an electrostatic latent image on the charged image carrier, A development step comprising (a) to (d);
(A) a step of carrying the developer contained in the developer container on the developer carrying member;
(B) a step of regulating the developer layer thickness on the developer carrier by a developer layer thickness regulating member; (c) the developer having the regulated layer thickness, the developer carrier and the image carrier; (D) a step of transferring the developer on the developer carrier to an electrostatic latent image on the image carrier to form a toner image;
An image forming method comprising: a transfer step of electrostatically transferring a toner image formed on the surface of the image carrier to a transfer material; and a fixing step of heating and fixing the toner image transferred onto the transfer material. The developing step also serves as a cleaning step for collecting the developer remaining on the image carrier after the toner image is transferred onto the transfer material. The developer uses the magnetic developer described above, and the developer carrier is An image forming method using the developer carrying member.
The image forming apparatus of the present invention uses the image forming method of the present invention.
[0208]
The charging step in the present invention is a step of charging the image carrier by applying a voltage to a charging member that forms a contact portion with the image carrier and contacts, and at least between the charging member and the image carrier. The conductive fine powder contained in the toner adheres to the image carrier in the development process and remains on the image carrier after the transfer process and is carried around the contact part and / or the vicinity thereof. .
[0209]
Hereinafter, an image forming apparatus using the image forming method of the present invention will be described with reference to the drawings. However, the present invention is not limited to these.
[0210]
FIG. 1 is a schematic view of a developing device of the present invention using a magnetic one-component developer. In FIG. 1, an image carrier that holds an electrostatic latent image formed by a known process, for example, an electrophotographic photosensitive drum 1 is rotated in the direction of arrow B. The developing sleeve 8 as a developer carrying member carries the developer 4 having magnetic toner supplied by a hopper 3 as a developing container and rotates in the direction of arrow A, whereby the developing sleeve 8, the photosensitive drum 1, The developer 4 is transported to the developing area D facing each other. As shown in FIG. 1, a magnet roller 5 in which a magnet is inscribed is disposed in the developing sleeve 8 in order to magnetically attract and hold the developer 4 on the developing sleeve 8.
[0211]
The developing sleeve 8 used in the developing device in the present invention may use the developer carrier described above, and specifically has a resin coating layer 7 coated on a metal cylindrical tube 6 as a substrate. In the hopper 3, a stirring blade 10 for stirring the developer 4 is provided. Reference numeral 11 denotes a gap indicating that the developing sleeve 8 and the magnet roller 5 are not in contact with each other.
[0212]
The developer 4 obtains a triboelectric charge capable of developing the electrostatic latent image on the photosensitive drum 1 by friction between the developers and the resin coating layer 7 on the developing sleeve 8. In the example of FIG. 1, in order to regulate the layer thickness of the developer 4 conveyed to the development region D, a material having rubber elasticity such as urethane rubber or silicone rubber, phosphor bronze, stainless steel or the like as the developer layer thickness regulating member. The developer layer thickness regulating member 2 made of an elastic plate made of a material having metal elasticity such as steel is used, and a thin layer of developer is formed by elastically pressing the developer sleeve 8 in the counter direction via the developer. Forming. Thus, the thickness of the thin layer of the developer 4 formed on the developing sleeve 8 is preferably thinner than the minimum gap between the developing sleeve 8 and the photosensitive drum 1 in the developing region D. .
[0213]
The contact pressure of the developer layer thickness regulating member 2 with respect to the developing sleeve 8 is a linear pressure of 5 to 50 g / cm in that the regulation of the developer can be stabilized and the developer layer thickness can be made suitable. preferable. When the contact pressure of the developer layer thickness regulating member is less than the linear pressure of 5 g / cm, the regulation of the developer becomes weak, causing fogging and toner leakage, and when the linear pressure exceeds 50 g / cm, The damage to the toner is increased, and this tends to cause toner deterioration and fusion to the sleeve and blade.
[0214]
In order to cause the one-component developer 4 carried on the developing sleeve 8 to fly, an alternating bias voltage is applied to the developing sleeve 8 by a power source 9 as bias means. When a DC voltage is used as the developing bias, a voltage having a value between the potential of the image portion of the electrostatic latent image (the region visualized with the developer 4 attached) and the potential of the background portion is set as the developing sleeve 8. It is preferable to apply to. In order to increase the density of the developed image or to improve the gradation, an alternating bias voltage may be applied to the developing sleeve 8 to form an oscillating electric field whose direction is alternately reversed in the developing region D. . In this case, it is preferable to apply to the developing sleeve 8 an alternating bias voltage in which a DC voltage component having an intermediate value between the developed image portion potential and the background portion potential is superimposed.
[0215]
In the case of so-called regular development, toner that is charged with the opposite polarity to the polarity of the electrostatic latent image is used for visualization by attaching toner to the high potential portion of the electrostatic latent image having a high potential portion and a low potential portion. To do. In the case of so-called reversal development, a toner that is charged to the same polarity as the polarity of the electrostatic latent image is used for visualization by attaching toner to the low potential portion of the electrostatic latent image having a high potential portion and a low potential portion. To do. High potential and low potential are expressions based on absolute values. In any of these cases, the developer 4 is charged at least by friction with the developing sleeve 8.
[0216]
The drawing schematically illustrates the developing device according to the present invention, and it goes without saying that there are various forms in the shape of the developer container (hopper 3), the presence or absence of the stirring blade 10, and the arrangement of the magnetic poles.
[0217]
FIG. 2 is a schematic view of a developing device according to another embodiment of the present invention. In FIG. 2, the developer layer thickness regulating member is elastically pressed against the developing sleeve 8 through the developer in the forward direction.
[0218]
In the present invention, these developing means, image carrier, and charging means can be integrated and used as a process cartridge.
With reference to FIG. 3, an example of an image forming apparatus using the developing device having the developer carrier of the present invention illustrated in FIG. 1 will be described. First, the surface of the photosensitive drum 1 as an image carrier is negatively charged by a contact (roller) charging unit 18 as a primary charging unit, and an electrostatic latent image is formed on the photosensitive drum 1 by image scanning by laser beam exposure 12. Formed. Next, the electrostatic latent image has toner in the hopper 3 as a developing container by the developing device having the developer layer thickness regulating member 2 and provided with the developing sleeve 8 as the developer carrying member. Reversal development is performed by the negatively chargeable one-component developer 4.
[0219]
As shown in FIG. 3, in the developing region D, the photosensitive drum 1 is grounded to the developing sleeve, and an alternating bias, a pulse bias, and / or a direct current bias is applied to the developing sleeve 8 by a power source 9. Next, when the transfer material P is conveyed and arrives at the transfer portion, it is charged by the voltage application means 20 from the back surface (the surface opposite to the photosensitive drum side) of the transfer material P by the contact (roller) transfer means 13 as the transfer means. As a result, the developed image formed on the surface of the photosensitive drum 1 is transferred onto the transfer material P by the contact transfer means 13.
Next, the transfer material P separated from the photosensitive drum 1 is conveyed to a heat and pressure roller fixing device 15 as a fixing unit, and a fixing process of the developed image on the transfer material P is performed by the fixing device.
[0220]
  In the above series of steps, the photosensitive drum (that is, the image carrier) 1 has a photosensitive layer and a conductive substrate, and moves in the direction of arrow B. The developing sleeve 8 rotates so as to proceed in the same direction (arrow A direction) as the surface of the photosensitive drum 1 in the developing region D. The one-component developer 4 in the hopper 3 is carried on the developing sleeve 8, and friction with the surface of the developing sleeve 8 and / orOrFor example, negative triboelectric charge is given by friction between toners. Further, the developer layer thickness regulating member 12 makes the developer layer thin (30 to 300 μm) and uniformly regulated so that the developer is thinner than the gap between the photosensitive drum 1 and the developing sleeve 8 in the developing region D. A layer is formed.
[0221]
The developing sleeve 8 is preferably installed facing the image carrier with a separation distance of 100 to 1000 μm. If the separation distance of the developing sleeve 8 from the image carrier is less than 100 μm, the change in the developing characteristics of the toner with respect to the fluctuation of the separation distance becomes large, and it is difficult to mass-produce an image forming apparatus that satisfies stable image quality. Become. If the separation distance of the developing sleeve 8 from the image carrier is greater than 1000 μm, the recoverability of the transfer residual toner to the developing device is lowered, and fogging due to poor recovery tends to occur. Further, since the followability of the toner with respect to the electrostatic latent image on the image carrier is lowered, the image quality is lowered such as a lower resolution and a lower image density. Preferably 120-500 micrometers is good.
[0222]
Further, it is preferable to adjust the rotation speed of the developing sleeve 8 so that the surface speed of the developing sleeve 8 is substantially equal to or close to the speed of the surface of the photosensitive drum 1. In the developing region D, an alternating bias or a pulse bias may be applied to the developing sleeve 8 by a power source 9 as a developing bias voltage. Between the developing sleeve 8 and the latent image holder, at least a peak-to-peak electric field strength of 3 × 10⁶-10x10⁶It is preferable to apply an alternating electric field of V / m and a frequency of 100 to 5000 Hz as a developing bias.
[0223]
When the developer is transferred in the development area D, the developer is transferred to the electrostatic latent image side due to the electrostatic force on the surface of the photosensitive drum 1 and the action of a developing bias voltage such as an alternating bias or a pulse bias. Here, the behavior of the toner particles and the conductive fine powder during the image forming process when the conductive fine powder is externally added to the toner particles in the simultaneous development image forming method will be described.
[0224]
An appropriate amount of the conductive fine powder contained in the toner is transferred to the image carrier side together with the toner particles during development of the electrostatic latent image on the image carrier side in the development process.
[0225]
The toner image on the image carrier is transferred to the transfer material side in the transfer process. Part of the conductive fine powder on the image carrier also adheres to the transfer material side, but the rest remains attached to and held on the image carrier. When a transfer bias having a polarity opposite to that of the toner is applied, the toner is attracted to the transfer material side and actively transferred. However, the conductive fine powder on the image carrier is conductive. The transfer material does not actively transfer to the transfer material side, and a part of the material adhering to the transfer material side remains attached to and held on the image carrier.
[0226]
In an image forming method that does not use a cleaner, the residual transfer toner remaining on the image carrier surface after transfer and the above-mentioned residual conductive fine powder are transferred to the image carrier surface on the charging portion that is the contact portion between the image carrier and the contact charging member. It is carried as it is and adheres to and mixes with the contact charging member.
[0227]
Accordingly, contact charging of the image carrier is performed in a state where the conductive fine powder is interposed in the contact portion between the image carrier and the contact charging member.
[0228]
Due to the presence of the conductive fine powder, the contact charging member can be kept in close contact with the image bearing member and contact resistance regardless of contamination due to the adhesion or mixing of the transfer residual toner to the contact charging member. It is possible to satisfactorily charge the image carrier with the charging member.
[0229]
Further, the transfer residual toner adhering to and mixed in the contact charging member is uniformly charged with the same polarity as the charging bias by the charging bias applied from the charging member to the image carrier, and gradually moves from the contact charging member onto the image carrier. As the image carrier surface moves, it reaches the developing section and is simultaneously cleaned (collected) in the development process.
[0230]
Furthermore, by repeating the image formation, the conductive fine powder contained in the toner moves to the image carrier surface at the developing unit and is carried to the charging unit via the transfer unit by the movement of the image carrying surface and charged. Since the conductive fine powder is continuously supplied to the part, even if the conductive fine powder decreases or deteriorates in the charging part due to dropout or the like, it is prevented that the chargeability is reduced, and good charging is achieved. Sex is stably maintained.
[0231]
In the image forming method of the present invention, the charging step is carried out on an image bearing member (charged member) by using a conductive charging member (contact charging member, A contact charging device is used in which a contact charging device is contacted and a predetermined charging bias is applied to the contact charging member to charge the surface of the object to be charged to a predetermined polarity and potential. The charging electrification bias applied to the contact charging member can obtain good chargeability only with a DC voltage, but an alternating voltage (AC voltage) may be superimposed on the DC voltage.
[0232]
As the waveform of the alternating voltage, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Further, it may be a pulse wave formed by periodically turning on / off a DC power source. In this way, a bias that changes the voltage value periodically can be used as the waveform of the alternating voltage.
[0233]
In the present invention, the charging member preferably has elasticity in providing a contact portion for interposing the conductive fine powder between the charging member and the image carrier, and the image is obtained by applying a voltage to the charging member. In order to charge the carrier, it is preferably conductive. Therefore, the charging member has an elastic conductive roller, a magnetic brush portion in which magnetic particles are magnetically constrained, and a magnetic brush contact charging member in which the magnetic brush portion is in contact with a member to be charged or a charging brush composed of conductive fibers. It is preferable that it is.
[0234]
If the hardness of the elastic conductive roller is too low, the shape is not stable, so that the contact property with the charged body is deteriorated, and further, conductive fine powder is interposed at the contact portion between the charging member and the image carrier. As a result, the surface layer of the elastic conductive roller is scraped or damaged, and it is difficult to obtain stable chargeability. Further, if the hardness is too high, a charging contact portion cannot be secured between the charged body and the micro-contact property to the surface of the charged body is deteriorated, so that the Asker C hardness is preferably 25 to 50 degrees. It is a range.
[0235]
It is important that the elastic conductive roller has elasticity to obtain a sufficient contact state with the member to be charged, and at the same time functions as an electrode having a sufficiently low resistance to charge the moving member to be charged. On the other hand, it is necessary to prevent voltage leakage in the case where a defect site such as a pinhole exists in the member to be charged. When an electrophotographic photosensitive member is used as the member to be charged, 10 is necessary to obtain sufficient chargeability and leakage resistance.^Three-10⁸The resistance is preferably Ω, more preferably 10^Four-10⁷The resistance should be Ω.
[0236]
The roller resistance can be measured by applying 100 V between the core metal and the aluminum drum in a state where the roller is pressed against a cylindrical aluminum drum having a diameter of 30 mm so that a total pressure of 1 kg is applied to the core metal of the roller.
[0237]
For example, the elastic conductive roller is formed by forming a middle resistance layer of rubber or foam as a flexible member on a cored bar. The middle resistance layer is formulated with a resin (for example, urethane), a conductive material (for example, carbon black), a sulfurizing agent, a foaming agent, and the like, and is formed in a roller shape on the core metal. Thereafter, the elastic conductive roller can be prepared by cutting and polishing the surface as necessary to adjust the shape. The roller surface preferably has minute cells or irregularities in order to interpose conductive fine powder.
[0238]
The material of the elastic conductive roller is not limited to the elastic foam. Examples of the elastic material include ethylene-propylene-diene polyethylene (EPDM), urethane, butadiene acrylonitrile rubber (NBR), silicone rubber, and isoprene rubber. In addition, a rubber material in which a conductive material such as carbon black or a metal oxide is dispersed for resistance adjustment, or a foamed material thereof can be used. It is also possible to adjust the resistance using an ion conductive material without dispersing the conductive substance or in combination with the conductive substance.
[0239]
The elastic conductive roller is arranged to be pressed against the object to be charged as an image carrier against the elasticity with a predetermined pressing force, and a charging contact portion which is a contact portion between the elastic conductive roller and the image carrier is provided. Let it form. The width of the charging contact portion is not particularly limited, but is preferably 1 mm or more, more preferably 2 mm or more in order to obtain a stable and close adhesion between the elastic conductive roller and the image carrier.
[0240]
In addition, as the charging brush as the contact charging member, a brush whose resistance is adjusted by dispersing a conductive material in commonly used fibers is used. As the fiber, generally known fiber can be used, and examples thereof include nylon, acrylic, rayon, polycarbonate, polyester and the like. As the conductive material, generally known conductive materials can be used. For example, conductive metal such as nickel, iron, aluminum, gold, silver or iron oxide, zinc oxide, tin oxide, antimony oxide, titanium oxide, etc. The conductive metal oxides, and further conductive powders such as carbon black. These conductive materials may be subjected to surface treatment for the purpose of hydrophobization and resistance adjustment as necessary. In use, it is selected in consideration of dispersibility with fibers and productivity.
[0241]
When a charging brush is used as the contact charging member, there are a fixed type and a rotatable roll type. As the roll-shaped charging brush, for example, a tape having conductive fibers in a pile ground can be wound around a metal core bar in a spiral shape to form a roll brush. The conductive fiber has a fiber thickness of 1 to 20 denier (fiber diameter of about 10 to 500 μm), a brush fiber length of 1 to 15 mm, and a brush density of 10,000 to 300,000 per square inch (1 square meter) 1.5 × 10 per⁷~ 4.5 × 10⁸About this) is preferably used.
[0242]
It is preferable to use a charging brush having as high a brush density as possible, and it is also preferable to make one fiber from several to several hundreds of fine fibers. For example, it is possible to bundle 50 fine fibers of 300 denier, such as 300 denier / 50 filament, and plant the fibers as one fiber. However, in the present invention, the charging point for direct injection charging is determined mainly depending on the charging contact portion between the charging member and the image carrier and the density of the conductive fine powder in the vicinity thereof. Therefore, the range of selection of the charging member is widened.
[0243]
The resistance value of the charging brush is 10 to obtain sufficient charging property and leakage resistance as in the case of the elastic conductive roller.^Three-10⁸The resistance is preferably Ω, more preferably 10^Four-10⁷The resistance should be Ω.
[0244]
As materials for the charging brush, conductive rayon fibers REC-B, REC-C, REC-M1, and REC-M10 manufactured by Unitika Co., Ltd., SA-7 manufactured by Toray Industries, Inc., Nippon Kashige Co., Ltd. There are Sanderlon made by Kanebo, Beltron made by Kanebo, Kuraray made by Kuraray Co., Ltd., carbon dispersed in rayon, and Roval made by Mitsubishi Rayon Co., Ltd. REC-B, REC in terms of environmental stability. -C, REC-M1, and REC-M10 are particularly preferable.
[0245]
In addition, the flexibility of the contact charging member increases the chance that the conductive fine powder contacts the image carrier at the contact portion between the contact charging member and the image carrier, thereby obtaining high contact properties. This is preferable from the viewpoint of improving direct injection chargeability. That is, the contact charging member comes into close contact with the image carrier via the conductive fine powder, and the conductive fine powder present at the contact portion between the contact charging member and the image carrier slides on the surface of the image carrier without any gap. By rubbing, the charging of the image carrier by the contact charging member is dominated by stable and safe direct injection charging without using the discharge phenomenon due to the presence of the conductive fine powder, which was not obtained by conventional roller charging or the like. Charge efficiency can be obtained, and a potential substantially equal to the voltage applied to the contact charging member can be applied to the image carrier.
[0246]
Furthermore, it is preferable to provide a relative speed difference between the moving speed of the surface of the charging member forming the contact portion and the moving speed of the surface of the image carrier. It is preferable from the viewpoint of improving direct injection charging property, which can greatly increase the chance that the conductive fine powder contacts the image carrier at the contact portion between the contact charging member and the image carrier, and can obtain higher contactability. good.
[0247]
By interposing the conductive fine powder in the contact portion between the contact charging member and the image carrier, a significant torque is generated between the contact charging member and the image carrier due to the lubricating effect (friction reduction effect) of the conductive fine powder. Thus, it is possible to provide a speed difference without increasing the contact speed and notably scraping the surface of the contact charging member and the image carrier.
[0248]
As a configuration in which the speed difference is provided, the contact charging member can be rotationally driven to provide the speed difference between the image carrier and the contact charging member.
[0249]
In order to temporarily collect and level the transfer residual toner on the image carrier carried by the charging unit on the contact charging member, it is preferable to move the contact charging member and the image carrier in opposite directions. It is desirable that the rotation direction of the contact charging member is configured to rotate in the direction opposite to the moving direction of the image carrier surface. That is, it is possible to preferentially perform direct injection charging by once separating the transfer residual toner on the image carrier by reverse rotation and performing charging.
[0250]
Although it is possible to move the charging member in the same direction as the moving direction of the image carrier surface to give a speed difference, the charging property of direct injection charging is the ratio of the peripheral speed of the image carrier to the peripheral speed of the charging member. Therefore, in order to obtain the same peripheral speed ratio as in the reverse direction, the rotation speed of the charging member is larger in the forward direction than in the reverse direction. Therefore, it is advantageous in terms of the rotation speed to move the charging member in the reverse direction. It is. The peripheral speed ratio described here is
Peripheral speed ratio (%) = (charging member peripheral speed−latent image carrier circumferential speed) / latent image carrier circumferential speed × 100
(The charging member peripheral speed is a positive value when the surface of the charging member moves in the same direction as the surface of the latent image holding member at the contact portion).
[0251]
  As an index indicating the relative speed difference, there is a relative movement speed ratio represented by the following equation.
Relative moving speed ratio (%) = | (Vc−Vp) / Vp | × 100
(Where Vc is the moving speed of the charging member surface, Vp is the moving speed of the image carrier surface, and Vc is Vp when the charging member surface moves in the same direction as the image carrier surface at the contact portion.WhenThe value is the same sign. )
  The relative movement speed ratio is preferably 10 to 500%, more preferably 20 to 400%. If the relative movement speed ratio is too smaller than the above range, the contact probability between the contact charging member and the image carrier cannot be increased sufficiently, and the chargeability of the image carrier by direct injection charging is maintained. It may be difficult to do. Further, the charging inhibition of the image carrier is suppressed by limiting the amount of the conductive fine powder interposed in the contact portion between the image carrier and the contact charging member by sliding between the contact charging member and the image carrier. In some cases, the effect and the effect of improving the recoverability of the developer in the simultaneous development cleaning by leveling the pattern of the transfer residual toner particles may not be sufficiently obtained. If the relative movement speed ratio is too larger than the above range, the movement speed of the charging member will be increased, so that the developer component held in contact with the contact portion between the image carrier and the contact charging member is scattered. As a result, the inside of the apparatus is likely to be contaminated, and the image carrier and the contact charging member are likely to be worn or scratches are liable to occur, resulting in a short life.
  Further, when the moving speed of the charging member is 0 (in a state where the charging member is stationary), the contact point of the charging member with the image carrier becomes a fixed point. This is not preferable because the effect of suppressing the charging inhibition of the image carrier and the effect of leveling the pattern of the residual toner particles and improving the recoverability of the developer in the simultaneous development cleaning are liable to decrease.
[0252]
If the amount of the conductive fine powder intervened at the contact portion between the image carrier and the contact charging member is too small, the lubricating effect of the conductive fine powder cannot be sufficiently obtained. It is difficult to rotationally drive the contact charging member to the image carrier with a speed difference due to the large friction. That is, the driving torque becomes excessive, and if it is forcibly rotated, the surface of the contact charging member or the image carrier tends to be scraped. Furthermore, the effect of increasing the contact opportunity due to the conductive fine powder may not be obtained, and it is difficult to obtain sufficient charging performance. On the other hand, if the amount of inclusion is too large, dropping of the conductive fine powder from the contact charging member is remarkably increased, which tends to adversely affect image formation.
[0253]
According to experiments, the amount of conductive fine powder intervened is 10^ThreePiece / mm²Or more, more preferably 10^FourPiece / mm²The above is good. 10^ThreePiece / mm²If it is lower, a sufficient lubrication effect and an effect of increasing the contact opportunity cannot be obtained, and the charging performance tends to be lowered. 10^FourPiece / mm²If it is lower, charging performance is likely to deteriorate when there is a large amount of untransferred toner.
[0254]
The coating density range of the conductive fine powder is also determined by the density of the conductive fine powder applied to the image carrier to obtain the effect of uniform charging.
[0255]
Needless to say, at the time of charging, contact charging more uniform than at least the recording resolution is required. However, regarding the visual characteristics of the human eye, when the spatial frequency is 10 cycles / mm or more, the identification gradation number on the image approaches 1 as much as possible, that is, density unevenness cannot be identified. By actively utilizing this characteristic, when conductive fine powder is adhered on the image carrier, the conductive fine powder is present at least at a density of 10 cycles / mm or more on the image carrier, and direct injection charging is performed. It will be good. Even if a micro charge failure occurs in the absence of conductive fine powder, the density unevenness on the image caused by the charge failure occurs in the spatial frequency region exceeding the human visual characteristics. Then there will be no problem.
[0256]
As to whether or not a charging failure as density unevenness is recognized on the image when the coating density of the conductive fine powder is changed, the conductive fine powder is applied even slightly (for example, 10 particles / mm).²), Which is effective in suppressing the occurrence of charging unevenness, but is still insufficient in terms of whether density unevenness on the image is acceptable to humans.
[0257]
However, the coating amount is 10²Piece / mm²As a result, a favorable result is rapidly obtained in the objective evaluation of the image. Furthermore, the coating amount is 10^ThreePiece / mm²By increasing the above, there is no problem on the image due to the charging failure.
[0258]
Charging by the direct injection charging method is fundamentally different from the discharge charging method, and charging is performed by reliably contacting the charging member to the photosensitive member. There is always a part that cannot be touched even if it is applied excessively. However, this problem is practically solved by applying the conductive fine powder that positively utilizes the human visual characteristics of the present invention.
[0259]
However, when the direct injection charging method is applied as uniform charging of the image carrier in the image development simultaneous cleaning image formation, charging characteristics are deteriorated due to adhesion or mixing of the transfer residual toner to the charging member. To carry out good direct injection charging by suppressing the adhesion and mixing of the transfer residual toner to the charging member or overcoming the adverse effect on the charging characteristics due to the adhesion or mixing of the transfer residual toner to the charging member, The amount of conductive fine powder intervening at the contact portion between the contact charging member and the contact charging member is 10^FourPiece / mm²The above is preferable.
[0260]
Since the upper limit of the coating density varies depending on the particle size of the conductive fine powder, it cannot be generally stated. However, if it is described forcibly, the conductive fine powder is uniformly coated on the image carrier. The amount is the upper limit. Even if it is applied more than that, the effect is not improved, and conversely, the exposure light source is blocked or scattered.
[0261]
The amount of conductive fine powder is 5 × 10^FivePiece / mm²Exceeding the value causes the drop of the conductive fine powder to the image carrier to remarkably increase, resulting in insufficient exposure of the image carrier regardless of the light transmittance of the conductive fine powder itself. 5 × 10^FivePiece / mm²In the following, the amount of dropped particles can be kept low, and the inhibition of exposure can be improved. When the abundance of particles dropped on the image carrier in the amount range is 10²-10^FivePiece / mm²Therefore, the abundance that is not harmful to image formation is 10^Four~ 5x10^FivePiece / mm²Is preferable.
[0262]
A method for measuring the amount of conductive fine powder interposed at the charging contact portion and the amount of conductive fine powder present on the image carrier in the electrostatic latent image forming step will be described. It is desirable to directly measure the contact surface between the contact charging member and the image carrier while the amount of the conductive fine powder intervenes. However, there is a speed difference between the surface of the contact charging member forming the contact portion and the surface of the image carrier. In the present invention, since most of the particles existing on the image carrier before contacting the contact charging member are peeled off by the charging member that contacts while moving in the opposite direction, in the present invention, the contact immediately before reaching the contact surface portion is performed. The amount of particles on the surface of the charging member is defined as the intervening amount.
[0263]
Specifically, it is as follows. The rotation of the image carrier and the elastic conductive roller is stopped without applying the charging bias, and the surface of the image carrier and the elastic conductive roller is observed with a video microscope (OLYMPUS OVM1000N) and a digital still recorder (DELTIS SR-3100). Take a picture. With respect to the elastic conductive roller, the elastic conductive roller is brought into contact with the slide glass under the same conditions as in contact with the image carrier, and the contact surface is set at 10 positions with a 1000 × objective lens from the back surface of the slide glass with a video microscope. Shoot above. In order to separate individual fine powders from the obtained digital image, binarization processing is performed with a certain threshold value, and the number of areas where fine powders are present is measured using desired image processing software. Also, the abundance on the image carrier is measured by photographing the image carrier with the same video microscope and performing the same processing.
[0264]
In the image forming method of the present invention, the volume resistance of the outermost surface layer of the image carrier is 1 × 10.⁹Ωcm or more 1 × 10¹⁴Ωcm or less is preferable, and by having a volume resistance in this range, better chargeability can be provided. In the charging method using direct injection of charges, charges can be exchanged more efficiently by reducing the resistance on the charged object side. For this purpose, the volume resistance of the outermost layer is 1 × 10¹⁴It is preferable that it is Ωcm or less. On the other hand, in order to hold an electrostatic latent image as an image carrier for a certain time, the volume resistance value of the outermost surface layer is 1 × 10.⁹It is preferable that it is Ωcm or more.
[0265]
Further, the image bearing member is an electrophotographic photosensitive member, and the volume resistance of the outermost surface layer of the electrophotographic photosensitive member is 1 × 10.⁹Ωcm or more 1 × 10¹⁴When it is Ωcm or less, sufficient chargeability can be imparted even in an apparatus having a high process speed, which is more preferable.
[0266]
The image carrier is amorphous selenium, CdS, ZnO.₂A photosensitive drum or a photosensitive belt having a photoconductive insulating material layer such as amorphous silicon or an organic photosensitive material is preferable, and an amorphous silicon photosensitive layer or a photosensitive member having an organic photosensitive layer is particularly preferably used.
[0267]
The organic photosensitive layer may be a single layer type containing a charge generation material and a material having charge transport performance in the same layer, or may be a function-separated type photosensitive layer having a charge transport layer and a charge generation layer. A laminated photosensitive layer having a structure in which a charge generation layer and then a charge transport layer are laminated in this order on a conductive substrate is one preferred example.
[0268]
By adjusting the surface resistance of the image carrier, the image carrier can be uniformly charged more stably.
[0269]
It is also preferable to provide a charge injection layer on the surface of the electrophotographic photosensitive member for the purpose of making the charge injection of the image carrier more efficient or accelerating. The charge injection layer preferably has a form in which conductive fine particles are dispersed in a binder resin.
[0270]
As a form of providing the charge injection layer, for example,
(I) A charge injection layer is provided on an inorganic photoreceptor such as selenium or amorphous silicon or a single layer organic photoreceptor.
(Ii) The surface layer composed of the charge transport agent and the binder resin as the charge transport layer of the function-separated organic photoconductor also serves as the charge injection layer (for example, in the binder resin as the charge transport layer) The charge transporting agent and the conductive fine particles are dispersed, or the charge transporting agent itself or its presence state makes the charge transporting layer a function as a charge injection layer),
(Iii) Although a charge injection layer is provided as the outermost surface layer on the function-separated organic photoreceptor, it is important that the volume resistance of the outermost surface layer is in a preferable range.
[0271]
The charge injection layer is composed of, for example, a layer of an inorganic material such as a metal vapor deposition film, or a conductive fine particle dispersed resin layer in which conductive fine particles are dispersed in a binder resin. The dispersed resin layer is formed by coating by an appropriate coating method such as a dipping coating method, a spray coating method, a roll coating method, or a beam coating method. Further, it may be configured by mixing or copolymerizing an insulating binder resin with a resin having high light transmittance and ion conductivity, or may be configured by a single resin having medium resistance and photoconductivity.
[0272]
Among these, the outermost surface layer of the image carrier is preferably a resin layer in which conductive fine particles (hereinafter referred to as “oxide conductive fine particles”) made of at least a metal oxide are dispersed. In other words, by configuring the outermost surface layer of the image bearing member in this way, the surface resistance of the electrophotographic photosensitive member can be reduced to transfer charges more efficiently, and the surface resistance can be reduced. Thus, it is preferable because blurring or flow of the latent image due to diffusion of the latent image charge can be suppressed while the image carrier holds the electrostatic latent image.
[0273]
In the case of the resin layer in which the oxide conductive fine particles are dispersed, the particle diameter of the oxide conductive fine particles is preferably smaller than the wavelength of the incident light in order to prevent scattering of incident light by the dispersed particles. Therefore, the particle diameter of the oxide conductive fine particles to be dispersed is preferably 0.5 μm or less. The content of the oxide conductive fine particles is preferably 2 to 90% by mass, and more preferably 5 to 70% by mass with respect to the total weight of the outermost layer. When the content of the oxide conductive fine particles is too smaller than the above range, it is difficult to obtain a desired volume resistance value. Also, if the content is too much above the above range, the film strength will decrease, so the charge injection layer will be easily scraped off, the life of the photoreceptor tends to be shortened, and the resistance will be too low. As a result, an image defect is likely to occur due to the flow of the latent image potential.
[0274]
The layer thickness of the charge injection layer is preferably 0.1 to 10 μm, more preferably 5 μm or less for obtaining the sharpness of the latent image, and 1 μm or more from the viewpoint of durability of the charge injection layer. More preferably.
The binder resin for the charge injection layer may be the same as the binder resin used for the lower layer of the charge injection layer (for example, the charge transport layer). Since the coated surface may be disturbed, it is necessary to select a formation method in particular.
[0275]
In the present invention, the volume resistance value of the outermost surface layer of the image carrier is a layer having a composition similar to that of the outermost layer of the image carrier on a turbo-ethylene terephthalate (PET) film by depositing gold on the surface. This is performed by applying a voltage of 100 V in a volume resistance measuring device (4140B pA MATER manufactured by Hewlett-Packard Company) in an environment of a temperature of 23 ° C. and a humidity of 65%.
[0276]
In the present invention, it is preferable to impart releasability to the surface of the image carrier, and the contact angle of water on the surface of the image carrier is preferably 85 degrees or more. More preferably, the contact angle of water on the surface of the image carrier is 90 degrees or more.
[0277]
A high contact angle on the surface of the image carrier indicates that the surface of the image carrier has a high releasability with respect to toner particles. This effect improves the developer recovery efficiency in the simultaneous development cleaning step. Further, since the amount of transfer residual toner can be significantly reduced, it is possible to suppress a decrease in chargeability of the image carrier due to the transfer residual toner.
[0278]
As a means for imparting releasability to the image carrier surface, for example,
(1) Use a resin having a low surface energy as the resin itself constituting the film.
(2) Add additives that impart water repellency and lipophilicity.
(3) Disperse the material having high releasability (lubricant fine particles) in powder form.
Is mentioned. The resin (1) having a low surface energy can be obtained by introducing a fluorine-containing group or a silicone-containing group into the resin structure. Surfactant is mentioned as an additive of (2). Examples of (3) lubricant fine particles include the use of fluorine-containing resins, silicone-based resins or polyolefin-based resins containing fluorine atoms such as polytetrafluoroethylene, polyvinylidene fluoride and carbon fluoride.
[0279]
By these means, the contact angle with respect to the water on the surface of the image carrier can be set to 85 degrees or more.
Among these, it is preferable that the outermost surface layer of the image carrier is a layer in which lubricant fine particles made of at least one material selected from at least fluorine resin, silicone resin, or polyolefin resin are dispersed. In particular, it is preferable to use a fluorine-containing resin such as polytetrafluoroethylene or polyvinylidene fluoride. In the present invention, when a fluororesin is used as the releasable powder as the lubricant fine particles of (3), the dispersion to the outermost layer is preferable.
[0280]
In order to contain these lubricant fine particles in the outermost surface layer, a layer in which the powder is dispersed in a binder resin is provided on the outermost surface of the photosensitive member, or an organic photoreceptor mainly composed of a resin. If so, the powder may be dispersed in the outermost surface layer without providing a new surface layer.
[0281]
  The addition amount of the lubricant fine particles to the surface layer of the image carrier is preferably 1 to 60% by mass, and more preferably 2 to 50% by mass with respect to the total weight of the surface layer. If the addition amount is too smaller than the above range, the transfer residual toner is not sufficiently reduced, and the developer recovery efficiency in the simultaneous development cleaning apparatus is not sufficient. If the addition amount is too larger than the above range, the strength of the film is lowered, or the amount of incident light on the photosensitive member is remarkably lowered to impair the chargeability of the image carrier. The particle size of the powder is preferably 1 μm or less from the viewpoint of image quality, and more preferably 0.5 μm or less.preferable.If the particle diameter is too larger than the above range, the line breakage tends to be deteriorated due to scattering of incident light, and the resolution is easily impaired.
[0282]
In the present invention, the contact angle is measured using pure water, and the apparatus is a contact angle meter CA-DS manufactured by Kyowa Interface Science Co., Ltd.
[0283]
One preferred embodiment of the photoreceptor as an image carrier used in the present invention will be described below. As the conductive substrate, a cylindrical shape of a metal such as aluminum or stainless steel; a plastic having a coating layer of aluminum alloy or indium oxide-tin oxide alloy; paper or plastic impregnated with conductive particles; plastic having a conductive polymer; Cylinders and films are used.
[0284]
On these conductive substrates, for the purpose of improving the adhesion of the photosensitive layer, improving the coating property, protecting the substrate, coating defects on the substrate, improving the charge injection from the substrate, or protecting the photosensitive layer from electrical breakdown. A conductive layer or an undercoat layer may be provided.
[0285]
The conductive layer is a resin layer containing metal or metal oxide particles, and the film thickness is preferably 10 to 30 μm.
[0286]
Undercoat layer is polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, methyl cellulose, nitrocellulose, ethylene-acrylic acid copolymer, polyvinyl butyral, phenol resin, casein, polyamide, copolymer nylon, glue, gelatin, polyurethane Alternatively, it is formed of a material such as aluminum oxide. The thickness of the undercoat layer is usually 0.1 to 10 μm, preferably 0.1 to 3 μm.
[0287]
The charge generation layer is composed of azo pigments, phthalocyanine pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, squarylium dyes, pyrylium salts, thiopyrylium salts, triphenylmethane dyes, selenium, amorphous silicon, etc. A charge generating material such as an inorganic material is dispersed in an appropriate binder resin and applied, or is formed by vapor deposition. Of these, phthalocyanine pigments are preferred for adjusting the sensitivity of the photoreceptor to a sensitivity suitable for the present invention. Examples of the binder resin include polycarbonate resin, polyester resin, polyvinyl butyral resin, polystyrene resin, acrylic resin, methacrylic resin, phenol resin, silicone resin, epoxy resin, and vinyl acetate resin. The amount of the binder resin contained in the charge generation layer is 80% by mass or less, preferably 0 to 40% by mass. The thickness of the charge generation layer is preferably 5 μm or less, particularly preferably 0.05 to 2 μm.
[0288]
The charge transport layer has a function of receiving charge carriers from the charge generation layer in the presence of an electric field and transporting them. The charge transport layer is formed by dissolving a charge transport material in a solvent together with a binder resin as required, and coating, and the film thickness is generally 5 to 40 μm. Examples of charge transport materials include polycyclic aromatic compounds such as biphenylene, anthracene, pyrene and phenanthrene in the main chain or side chain; nitrogen-containing cyclic compounds such as indole, carbazole, oxadiazole and pyrazoline; hydrazone compounds; styryl compounds; Selenium; selenium-tellurium; amorphous silicon; cadmium sulfide.
[0289]
Examples of binder resins for dispersing these charge transport materials include polycarbonate resins, polyester resins, polymethacrylic acid esters, polystyrene resins, acrylic resins, and polyamide resins; and organic photoconductive materials such as poly-N-vinylcarbazole and polyvinylanthracene. A functional polymer.
[0290]
As the surface layer, a layer in which conductive fine particles are dispersed in a resin may be provided in order to make charge injection more efficient or promote as described above. As the resin for the surface layer, polyester, polycarbonate, acrylic resin, epoxy resin, phenol resin, or curing agents for these resins may be used alone or in combination of two or more. Examples of the conductive fine particles include metals and metal oxides. Preferably, there are oxide conductive fine particles such as zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, tin oxide-coated titanium oxide, tin-coated indium oxide, antimony-coated tin oxide, or zirconium oxide. These may be used alone or in combination of two or more.
[0291]
In the present invention, the electrostatic latent image forming means for forming an electrostatic latent image on the charging surface of the image carrier is preferably an image exposure means. The image exposure means for forming the electrostatic latent image is not limited to the laser scanning exposure means for forming a digital electrostatic latent image, and other light emission such as normal analog image exposure and LEDs. It does not matter as long as it can form an electrostatic latent image corresponding to image information, such as a combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter.
[0292]
【Example】
EXAMPLES Hereinafter, although a manufacture example and an Example demonstrate this invention concretely, these do not limit this invention at all. In addition, all the parts in the following mixing | blending are a mass part.
[0293]
<1> Manufacture of photoconductor
A photoconductor using an organic photoconductive material for negative charging (hereinafter referred to as “OPC photoconductor”) was produced. An aluminum cylinder having a diameter of 24 mm was used as the substrate of the photoreceptor. The following layers were sequentially laminated on this cylinder by dip coating to prepare a photoreceptor.
[0294]
The first layer is a conductive layer, and is provided with a conductive particle-dispersed resin layer (tin oxide) having a thickness of about 20 μm, which is provided for leveling defects on the aluminum substrate and preventing the occurrence of moire due to reflection of laser exposure. And mainly titanium oxide powder dispersed in a phenol resin.
[0295]
The second layer is a positive charge injection preventing layer (undercoat layer), which serves to prevent the positive charge injected from the aluminum substrate from canceling the negative charge charged on the surface of the photoreceptor. 10⁶This is a medium resistance layer having a thickness of about 1 μm, the resistance of which is adjusted to about Ωcm.
[0296]
  The third layer is a charge generation layer that contains disazo pigments.TheIt is a layer having a thickness of about 0.3 μm dispersed in a chillal resin, and generates positive and negative charge pairs upon receiving laser exposure.
[0297]
The fourth layer is a charge transport layer, which is a layer having a thickness of about 25 μm in which a hydrazone compound is dispersed in a polycarbonate resin, and is a P-type semiconductor. Accordingly, negative charges charged on the surface of the photoreceptor cannot move through this layer, and only positive charges generated in the charge generation layer can be transported to the surface of the photoreceptor.
[0298]
The fifth layer is a charge injection layer, in which conductive tin oxide fine particles and tetrafluoroethylene resin particles having a particle size of about 0.25 μm are dispersed in a photocurable acrylic resin. Specifically, 100 mass% of tin oxide particles having a particle size of about 0.03 μm, doped with antimony and reduced in resistance to the resin, 20 mass% of tetrafluoroethylene resin particles, and 1. 2% by mass dispersed. The coating solution thus prepared was applied to a thickness of about 2.5 μm by a spray coating method to form a charge injection layer.
[0299]
The volume resistance of the outermost surface layer of the photoreceptor thus obtained is 5 × 10¹²The contact angle with respect to water on the surface of the photoreceptor was 103 degrees.
[0300]
<2> Production of magnetic powder
(Production example 1 of magnetic powder)
  In ferrous sulfate aqueous solution, l. An aqueous solution containing ferrous hydroxide was prepared by mixing 0 to 1.1 equivalents of caustic soda solution. While maintaining the pH of the aqueous solution at around 9, air was blown and an oxidation reaction was performed at 80 to 90 ° C. to prepare a slurry liquid for generating seed crystals. Subsequently, after adding ferrous sulfate aqueous solution so that it may become 0.9-1.2 equivalent with respect to the original alkali amount (sodium component of caustic soda) to this slurry liquid, the slurry liquid is maintained at pH 8 and air is supplied. The oxidation reaction was promoted while blowing, and the magnetic iron oxide particles produced after the oxidation reaction were washed, filtered, and taken out once. At this time, a small amount of water-containing sample was collected and the water content was measured. Next, the water-containing sample is re-dispersed in another aqueous medium without drying, and then the pH of the re-dispersed liquid is adjusted to about 6.AdjustmentThe silane coupling agent (n-C_TenH_{twenty one}Si (OCH_Three)_Three) Was added to the magnetic iron oxide in an amount of 1.0 part by mass (the amount of the magnetic iron oxide was calculated as a value obtained by subtracting the water content from the water-containing sample), and the coupling treatment was performed. The produced hydrophobic iron oxide particles were washed, filtered and dried by a conventional method, and then the slightly agglomerated particles were pulverized to obtain a magnetic powder 1.
(Production example 2 of magnetic powder)
As in magnetic powder production example 1, the oxidation reaction proceeds, the magnetic iron oxide particles generated after the oxidation reaction are washed, filtered, dried without surface treatment, and the aggregated particles are crushed. Magnetic powder 2 was obtained.
<3> Preparation of conductive fine powderMade
(Example 1 of conductive fine powder)
  Conductive zinc oxide having a volume average particle size of 2.7 μm (resistance: 1.5 × 10^FourΩcm) was used as the conductive fine powder 1. When this conductive fine powder was observed with a scanning electron microscope, it consisted of zinc oxide primary particles of 0.1 to 0.3 μm and aggregates of 1 to 4 μm.
[0301]
In accordance with the exposure light wavelength of 740 nm of the laser beam scanner used for image exposure in the image forming apparatus of Example 1 to be described later, the transmittance in this wavelength range is set to 310T transmission manufactured by X-Rite Co., Ltd. When measured using a mold densitometer, the transmittance of the conductive fine powder was about 35%.
[0302]
(Example 2 of conductive fine powder)
Conductive zinc oxide having a volume average particle size of 0.7 μm by classification operation from conductive fine powder 1 (resistance 2.8 × 10^FourΩcm) was obtained. This was used as the conductive fine powder 2.
[0303]
(Example 3 of conductive fine powder)
Conductive tin oxide having a volume average particle size of 2.8 μm (resistance 2.2 × 10^FiveΩcm) was used as the conductive fine powder 3.
[0304]
(Example 4 of conductive fine powder)
Conductive titanium oxide having a volume average particle diameter of 3.1 μm (resistance: 3.4 × 10⁶Ωcm) was used as the conductive fine powder 4.
[0305]
<4> Production of developer
(Developer Production Example 1)
0.1M-Na in 709g of ion-exchanged water_ThreePO_FourAfter adding 451 g of aqueous solution and heating to 60 ° C., 1.0 M-CaCl₂Gradually add 67.7 g of aqueous solution and add Ca_Three(PO_Four)₂An aqueous medium containing was obtained.
・ 80 parts of styrene
・ N-butyl acrylate 20 parts
・ Unsaturated polyester resin 3 parts
・ Saturated polyester resin 3 parts
-Negative charge control agent (monoazo dye-based Fe compound) 1.5 parts
・ 90 parts of magnetic powder 1
The above formulation was uniformly dispersed and mixed using an attritor (Mitsui Miike Chemical Co., Ltd.).
[0306]
This monomer composition was heated to 60 ° C., and 6 parts of ester wax mainly composed of behenyl behenate (maximum endothermic peak of 72 ° C. in DSC) was added, mixed and dissolved therein, and polymerization initiator 2 was added thereto. , 2'-azobis (2,4-dimethylvaleronitrile) [t1 / 2 = 140 minutes, at 60 ° C] was dissolved.
[0307]
The polymerizable monomer system is charged into the aqueous medium, 60 ° C., N₂In an atmosphere, the mixture was stirred for 15 minutes at 10,000 rpm with a TK homomixer (Special Machine Industries Co., Ltd.) and granulated. Thereafter, the mixture was reacted at 60 ° C. for 6 hours while stirring with a paddle stirring blade. Thereafter, the liquid temperature was raised to 80 ° C., and stirring was further continued for 4 hours. After completion of the reaction, distillation is further performed at 80 ° C. for 2 hours, after which the suspension is cooled, hydrochloric acid is added and Ca_Three(PO_Four)₂Was dissolved, filtered, washed with water, and dried to obtain toner particles having a weight average particle diameter of 6.7 μm.
[0308]
100 parts of this toner, 12 parts of the above conductive fine powder, silica having a primary particle diameter of 8 nm and a surface treated with hexamethyldisilazane have a BET value of 250 m.²Developer 1 was prepared by mixing 1.1 parts of / g hydrophobic silica fine powder with a Henschel mixer (Mitsui Miike Chemical Co., Ltd.). Further, the particle diameter, circularity, B / A value, and D / C of the toner particles and developer were measured by the methods described in the above embodiments. Table 1 shows the physical properties of Developer 1.
[0309]
[Table 1]

[0310]
(Developer Production Example 2)
A toner particle having a weight average particle diameter of 7.3 μm was obtained in the same manner as in Developer Production Example 1 except that 90 parts of magnetic powder 2 was used instead of magnetic powder 1. Table 1 shows the physical properties of Developer 2.
[0311]
(Developer Production Example 3)
Toner particles having a weight average particle diameter of 6.7 μm were obtained in the same manner as in Developer Production Example 1 except that conductive fine powder 2 was used instead of conductive fine powder 1. Table 1 shows the physical properties of Developer 3.
[0312]
(Developer Production Example 4)
Toner particles having a weight average particle diameter of 6.7 μm were obtained in the same manner as in Developer Production Example 1 except that conductive fine powder 3 was used instead of conductive fine powder 1. Table 1 shows the physical properties of Developer 4.
[0313]
(Developer Production Example 5)
Toner particles having a weight average particle diameter of 6.7 μm were obtained in the same manner as in Developer Production Example 1 except that conductive fine powder 4 was used instead of conductive fine powder 1. Table 1 shows the physical properties of Developer 5.
[0314]
(Developer Production Example 6)
Developer 6 was prepared in the same manner as in Developer Production Example 1 except that conductive fine powder 1 was not added. Table 1 shows the physical properties of Developer 6.
[0315]
[Example 1]
<Manufacture of developing sleeve>
The production of the developing sleeve will be described.
[0316]
The following materials were dispersed with zirconia particles having a diameter of 2 mm using a sand mill for 3 hours, after which the zirconia particles were separated by sieving, and the solid content was adjusted to 36% with methanol to obtain paint 1.

The triboelectric charge amount of the quaternary ammonium salt compound (1) with the iron powder was positive when determined by the blow-off method using a commercially available triboelectric charge meter (TB-200 manufactured by Toshiba Chemical). . Further, spherical carbon particles A were used as the spherical particles. The physical properties are shown in Table 2. Number average particle diameter 5.2 μm, true density 1.51 g / cm^ThreeVolume resistance 7.5 × 10^-2The Ωcm and the major axis / minor axis ratio were 1.15.
[0317]
The coating material 1 was formed by spraying a resin coating layer of about 10 μm on an Al cylinder having a diameter of 16 mm, and then heated and cured at 150 ° C./30 minutes with a hot air drier to produce a developer carrier (1). Table 3 shows the paint formulation and the physical properties of the developer carrier.
[0318]
[Table 2]

[0319]
[Table 3]

[0320]
<Image forming apparatus>
As the image forming apparatus, a modified LBP-1760 was used. This remodeling machine is a laser printer (recording apparatus) of a simultaneous development cleaning process (cleanerless system) using a transfer type electrophotographic process. It has a process cartridge from which a cleaning unit having a cleaning member such as a cleaning blade is removed, a magnetic one-component developer is used as a developer, and the developer layer on the developer carrier and the image carrier are not in contact with each other. It is an apparatus arranged to become.
[0321]
A rubber roller charger in which conductive carbon is dispersed as a primary charging member and coated with nylon resin is brought into contact with the above-described photoreceptor having a charge injection layer (contact pressure 60 g / cm), and an AC voltage of 2 to a DC voltage of −700 Vdc is obtained. A bias superimposed with 0.0 kVpp is applied to uniformly charge the photosensitive member. Subsequent to primary charging, an electrostatic latent image is formed by exposing the image portion with laser light.
[0322]
At this time, the dark portion potential Vd = −700 V and the light portion potential VL = −150 V. The gap between the photosensitive drum and the developing sleeve is 290 μm, a developing magnetic pole of 85 mT (850 gauss), a developer layer thickness regulating member of a thickness of 1.0 mm and a free length of 1.0 mm of a silicone rubber blade of 29.4 N / m (30 g) / Cm).
[0323]
Next, a DC bias component Vdc = −500 V, an overlapping AC bias component Vpp = 1600 V, and f = 2000 Hz were used as the developing bias. The peripheral speed of the developing sleeve was 110% (103 mm / sec) in the forward direction with respect to the peripheral speed of the photosensitive member (94 mm / sec).
[0324]
Also, a transfer roller (made of ethylene-propylene rubber in which conductive carbon is dispersed, the volume resistance value of the conductive elastic layer is 10⁸Ωcm, surface rubber hardness of 24 °, diameter of 20 mm, contact pressure of 59 N / m (60 g / cm)) were set to a constant speed with respect to the peripheral speed of the photoreceptor (94 mm / sec), and the transfer bias was set to 1.5 kV DC.
[0325]
As a fixing method, there was used a fixing device of LBP-1760 which does not have an oil application function and which is fixed by heating and pressing with a heater through a film. At this time, a pressure roller having a fluororesin surface layer was used, and the diameter of the roller was 30 mm. The fixing temperature was set to 180 ° C., and the contact width was set to 7 mm.
[0326]
<Image evaluation>
The developer 1 was used as a developer, and an image-drawing test was performed in a room temperature low humidity (N / L) environment of 24 ° C., 10% RH and a high temperature high humidity environment (H / H) of 30 ° C., 80% RH. . 75g / m as transfer material²Paper was used. As a result, a high transferability was exhibited in the initial stage, no transfer of characters or lines was lost during transfer, and a good image without fogging on non-images was obtained.
[0327]
Next, durability was evaluated with an image pattern consisting only of horizontal lines with a printing area ratio of 5%. The obtained results are shown in Tables 4 and 5.
[0328]
Durability test evaluation was performed on the evaluation items listed below.
(1) Image density
Image drawing is performed up to 15,000 sheets (15k) in a room temperature and low humidity (N / L) of 24 ° C, 10% RH and a high temperature and high humidity (H / H) environment of 30 ° C and 80% RH. It was. The initial density is the density of the 20th image. The solid black image density was measured with a reflection density RD918 (manufactured by Macbeth), and an average value of five points was taken as an image density.
[0329]
(2) Toner charge amount (Q / M) and toner transport amount (M / S)
The toner carried on the developing sleeve is sucked and collected by a metal cylindrical tube and a cylindrical filter. At that time, the charge amount Q stored in the condenser, the collected toner weight M, and the toner are sucked through the metal cylindrical tube. From the area S, the charge amount Q / M per unit weight (mC / kg) and the toner weight M / S per unit area (mg / cm²) And calculated as toner charge amount (Q / M) and toner transport amount (M / S), respectively.
[0330]
(3) fog
The fog was measured using a REFECTMETER MODEL TC-6DS manufactured by Tokyo Denshoku. The filter used was a green filter, and fog was calculated from the following formula.
Fog (reflectance) (%) = reflectance on standard paper (%) − reflectance of sample non-image area (%)
If the fog is 2.0% or less, a good image is obtained.
[0331]
(4) Photoreceptor scraping and toner fusion
After completion of image printing, scratches on the surface of the photosensitive drum and the occurrence of toner sticking to the scratches and black spots or white spots in the halftone images were visually evaluated.
A: Very good (not generated)
B: Good (slight scratches are seen but there is no effect on the image)
C: Normal (there is toner adhesion and scratches, but there is little effect on the image)
D: Poor (a lot of toner adheres along the flaw and causes a vertical stripe-like image defect)
[0332]
(5) Uneven charging
Image defects due to primary charging defects due to transfer residual toner, that is, charging unevenness, were evaluated on halftone images. The difference in density (unevenness) appearing on the halftone image was visually evaluated according to the following criteria.
○: No difference in density is observed.
○ △: A slight difference in density is observed.
Δ: A slight difference in shading is seen, but practical use is possible.
X: A difference in shading is noticeable and impractical.
[0333]
(6) Contamination resistance of the coating layer
The surface of the developer carrying member after durability was observed with an SEM, and the degree of toner contamination was evaluated according to the following criteria.
○: Slight contamination is observed.
○ △: Some contamination is observed.
Δ: Contamination is partially observed.
X: Significant contamination is observed.
[0334]
(7) Transfer rate
The transfer efficiency is determined by tapering the transfer residual toner on the photoconductor after the solid black image transfer with a Mylar tape and pasting it on the paper. The Macbeth density value is C, and the Mylar is applied on the paper with the toner after the fixing before the transfer. When the Macbeth concentration of the tape affixed was D, and the Macbeth concentration of Mylar tape affixed on unused paper was E, the following formula was used for approximation.
[0335]
[Equation 8]

[0336]
If the transfer efficiency is 90% or more, the image has no problem.
[0337]
[Table 4]

[0338]
[Table 5]

[0339]
[Example 2]
When developer 2 was used as a developer and durability test evaluation was performed by the same image forming method as in Example 1, a very good result was obtained. The results are shown in Tables 4 and 5.
[0340]
[Example 3]
When the developer 3 was used as the developer and the durability test evaluation was performed by the same image forming method as in Example 1, good results were obtained. The results are shown in Tables 4 and 5.
[Comparative Example 1]
The developer 6 was used as a developer, and durability test evaluation was performed by the same image forming method as in Example 1. The results are shown in Tables 4 and 5. An image with large density unevenness in the page was obtained.
[0341]
[Comparative Example 2]
A 16 mm diameter Al cylindrical tube was sandblasted to roughen the surface to a surface roughness Ra of 1.18 μm to obtain a developing sleeve (15) of a comparative example. The development sleeve was evaluated for durability using the developer 1 in the same manner as in Example 1. The results are shown in Tables 4 and 5. A solid black image density drop occurred in each environment. Table 3 shows the coating formulation and physical properties of the developer carrier (15).
[Comparative Example 3]
For the developing sleeve (surface roughness Ra 1.18 μm) subjected to sandblasting in the same manner as in Comparative Example 2, durability test evaluation was performed in the same manner as in Example 1 using Developer 2. The results are shown in Tables 4 and 5.
[0342]
[Example 4]
A coating material was prepared in the same manner as in Example 1 except that the quaternary ammonium salt compound represented by Formula 6 was used in the preparation of the resin coating layer of the developing sleeve, and a developer carrier (2) was obtained. When the charge amount of the quaternary ammonium salt compound represented by Formula 6 was measured by blow-off using iron powder in the same manner as in Example 1, it was positive. Table 3 shows the coating formulation and physical properties of the developer carrier (2).
Durability test evaluation was performed in the same manner as in Example 1 using the developer carrier (2) and developer 1. As shown in Tables 4 and 5, good results were obtained.
[0343]
[Example 5]
Durability test evaluation was performed in the same manner as in Example 1 using the developer carrier (2) and developer 2. The results are shown in Tables 4 and 5. A practically acceptable result was obtained.
[0344]
[Comparative Example 4]
Using the developer carrying member (2) and the developer 6, durability test evaluation was performed by the same image forming method as in Example 1. The results are shown in Tables 4 and 5. An image with large density unevenness in the page was obtained.
[0345]
[Example 6]
A coating material was obtained in the same manner as in Example 1 except that the quaternary ammonium salt compound represented by Formula 7 was used in the production of the resin coating layer of the developing sleeve, and a developer carrier (3) was produced. When the charge amount of the quaternary ammonium salt compound represented by Formula 7 was measured by blow-off using iron powder in the same manner as in Example 1, it was positive. Table 3 shows the coating formulation and physical properties of the developer carrier (3).
Durability test evaluation was performed in the same manner as in Example 1 using the developer carrier (3) and developer 1. As shown in Tables 4 and 5, good results were obtained.
[0346]
[Example 7]
Durability test evaluation was performed in the same manner as in Example 1 using the developer carrier (3) and the developer 2. The results are shown in Tables 4 and 5. A practically acceptable result was obtained.
[0347]
[Example 8]
In Example 1, a developer was carried in the same manner except that the amount of the quaternary ammonium salt compound represented by Formula 5 used for the resin coating layer of the developing sleeve was changed from 30 parts by mass to 10 parts by mass to prepare a paint. Body (4) was obtained. Table 3 shows the coating formulation and physical properties of the developer carrier (4).
[0348]
Durability test evaluation was performed in the same manner as in Example 1 using the developer carrier (4) and developer 1. The results are shown in Tables 4 and 5.
[0349]
[Example 9]
In Example 1, a developer was carried in the same manner except that the amount of the quaternary ammonium salt compound represented by formula 5 used for the resin coating layer of the developing sleeve was changed from 30 parts by mass to 50 parts by mass. Body (5) was obtained. Table 3 shows the coating formulation and physical properties of the developer carrier (5).
[0350]
Durability test evaluation was performed in the same manner as in Example 1 using the developer carrier (5) and developer 1. The results are shown in Tables 4 and 5.
[0351]
[Example 10]
As the spherical particles used for the resin coating layer of the developing sleeve, PMMA particles (B) having a number average particle size of 5.0 μm were used instead of the spherical carbon particles having a number average particle size of 5.2 μm used in Example 1. Produced a developer carrying member (6) in the same manner as in Example 1. The PMMA particles have a true density of 1.16 g / cm.^Three, Volume resistance 10¹⁵The major axis / minor axis ratio was 1.12 or more. Table 3 shows the coating formulation and physical properties of the developer carrier (6).
[0352]
The same durability test evaluation as in Example 1 was performed using the developer carrier (6). The results are shown in Tables 4 and 5.
[0353]
Example 11
A developer carrier (7) was produced in substantially the same manner as the developer carrier (1) except that boron nitride was used instead of graphite in the production of the resin carrier layer of the developer carrier. The raw materials used are as follows.

Using the developer carrier (7) and the developer 1, durability test evaluation was performed in the same manner as in Example 1.
[0354]
The results are shown in Tables 4 and 5.
[0355]
Example 12
A developer carrying body (8) was produced in the same manner as the developer carrying body (1) except that the coating material for the resin coating layer produced from the following materials was used, and the developer carrying body (8) Using developer 1, the durability test was evaluated in the same manner as in Example 1.

The results are shown in Tables 4 and 5.
[0356]
Example 13
A developer carrier (9) was prepared in the same manner except that the coating material for the resin coating layer made of the following materials was used, and the developer carrier (9) and developer 1 were used. The durability test was evaluated in the same manner as in Example 1.
-Urethane resin (solid content 40%) 375 parts
・ 15 parts of carbon
・ 85 parts of graphite
30 parts of quaternary ammonium salt compound represented by formula 5
・ Spherical carbon particles (A) 30 parts
・ Methanol 130 parts
The results are shown in Tables 4 and 5.
[0357]
Example 14
A developer carrier (10) was prepared in the same manner except that the coating material for the resin coating layer made of the following materials was used, and the developer carrier (10) and developer 1 were used. The durability test was evaluated in the same manner as in Example 1.

The results are shown in Tables 4 and 5.
[0358]
Example 15
In the production of the developer carrier, an aluminum compound of benzylic acid composed of 2 mol of benzylic acid and 1 mol of aluminum atoms is used as a substance for making the resin coating layer negatively charged, and specifically, the materials shown in Table 3 are used. Thus, a paint for the resin coating layer was prepared to obtain a developer carrier (11). Using this developer carrying member (11) and developer 1, durability test evaluation was performed in the same manner as in Example 1. The results are shown in Tables 4 and 5.
[0359]
Example 16
In the production of the developer carrying member, a benzyl acid boron compound composed of 1 mol of boron atom and 2 mol of benzyl acid is used instead of 1 mol of aluminum atom as a substance for making the resin coating layer negatively charged. A coating material for the resin coating layer was prepared using the material shown in No. 3 to obtain a developer carrier (12). Using the developer carrying member (12) and developer 1, durability test evaluation was performed in the same manner as in Example 1. The results are shown in Tables 4 and 5.
[0360]
[Example 17]
In the production of the developer carrying member, a 3,5-ditertiary butylsalicylic acid Cr complex is used as a substance for making the resin coating layer negatively chargeable. Specifically, the materials shown in Table 3 are used for resin coating. A layer coating material was prepared to obtain a developer carrier (13). Using the developer carrying member (13) and developer 1, durability test evaluation was performed in the same manner as in Example 1. The results are shown in Tables 4 and 5.
[0361]
Example 18
In the production of the developer carrying member, the same applies except that the azonaphthol chromium complex containing chlorophenol is used instead of the quaternary ammonium salt compound represented by Formula 5 as a material for making the resin coating layer negatively charged. Thus, a developer carrier (14) was prepared, and the durability test was evaluated in the same manner as in Example 1. In addition, when the triboelectric charge amount with the iron powder of the chromium complex of the azonaphthol containing chlorophenol was calculated | required by the blow-off method similarly to Example 1, it was negative polarity. The results are shown in Tables 4 and 5.
Examples 19 and 20
Using the developer carrier 1 used in Example 1 and developers 4 and 5 using tin oxide and titanium oxide as conductive fine powder, durability test evaluation was performed by the same image forming method as Example 1. As a result, good results were obtained. The results are shown in Tables 4 and 5.
[Comparative Examples 5 and 6]
Durability test evaluation was performed by the same image forming method as in Example 1, using a developer sleeve subjected to sandblasting as in Comparative Example 2 and Developers 4 and 5. The results are shown in Tables 4 and 5.
[0362]
【The invention's effect】
According to the present invention, there is provided an image forming method capable of stably applying appropriate charge without overcharging (charging up) the developer and controlling the developer to a suitable tribo. can do.
[0363]
Furthermore, it is possible to provide an image forming method that can be controlled to a suitable tribo even when a developer produced by a polymerization method that has conventionally been difficult to impart stable charge.
[0364]
Further, it is possible to provide a stable image forming method with excellent anti-contamination property such as prevention of fusing to the surface of the developer carrying member, and high-quality images with little reduction in density and fogging in the long-term image output durability.
[0365]
In addition, the present invention can provide an image forming method that enables the development simultaneous cleaning image formation that is excellent in transferability and excellent in recoverability of a transfer residual developer.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating a configuration example of a developing device used in an image forming method of the present invention.
FIG. 2 is a schematic diagram showing another configuration example of a developing device used in the image forming method of the present invention.
FIG. 3 is a schematic diagram illustrating a configuration example of an image forming apparatus using the image forming method of the present invention.
[Explanation of symbols]
1 Electrophotographic photosensitive drum (image carrier)
2 Developer layer thickness regulating member
3 Hopper
4 Developer
5 Magnet roller
6 Metal cylindrical tube
7 Resin coating layer
8 Development sleeve (developer carrier)
9 Power supply
10 Stirring blade
11 gap
12 Exposure
13 Contact transfer means
14 Voltage application means
15 Heating and pressure roller fixing device
17 Erase exposure
18 Contact charging means

Claims (48)

The charging member a voltage is applied to, by contacting the charging member to which a voltage is applied to the image bearing member, a charging step of charging the image bearing member, the charged image carrier to form an electrostatic latent image An electrostatic latent image forming step;
A development step including the following (a) to (d);
(A) a step of supporting the developer contained in the developer container on the developer carrying member; (b) a step of regulating the layer thickness of the developer on the developer carrying member by a developer layer thickness regulating member. (C) a step of carrying and transporting the developer having a regulated layer thickness to a developing region where the developer carrying member and the image carrying member are opposed to each other; (d) the developer on the developer carrying member being an image carrying member; Transferring to the electrostatic latent image above to form a toner image;
A transfer step of electrostatically transferring a toner image formed on the surface of the image carrier to a transfer material;
A fixing step of heating and fixing the toner image transferred onto the transfer material,
The developing step also serves as a cleaning step of collecting the developer remaining on the image carrier after the toner image is transferred onto the transfer material,
The developer includes toner particles containing at least a binder resin component and a magnetic powder, inorganic fine powder on the surface of the toner particles, and conductive fine powder having an average particle size larger than the inorganic fine powder and smaller than the developer. A negatively chargeable magnetic developer having an average circularity of 0.970 or more determined by the following formula (1) and having substantially no magnetic powder exposed on the surface thereof:
The toner particles are toner particles obtained by suspension polymerization of a polymerizable monomer system including at least a polymerizable monomer serving as a binder resin component and a magnetic powder in an aqueous medium,
The developer carrier comprises a substrate and a resin coating layer formed on the substrate,
The image forming method, wherein the resin coating layer is a negatively chargeable resin coating layer containing at least a negatively chargeable substance.
[Expression 1]
Circularity a = L ₀ / L (1)
(In the formula, L ₀ represents the perimeter of a circle having the same projected area as the particle image, and L represents the perimeter of the projected image of the particle.) 2. The binder resin for a coating layer of the resin coating layer is partially or wholly at least one of —NH ₂ group, ═NH group, and —NH— bond in the molecular structure. Image forming method.   The image forming method according to claim 1, wherein the binder resin for the coating layer of the resin coating layer contains at least a phenol resin. The phenol resin is a phenol resin produced by adding and condensing phenols and aldehydes using a nitrogen-containing compound as a catalyst. In the structure, -NH ₂ group, = NH group, or -NH- 4. The image forming method according to claim 3, wherein the image forming method is a phenol resin having any one of bonds.   The image forming method according to claim 1, wherein the resin coating layer contains a quaternary ammonium salt compound that is positively charged with respect to at least iron powder.   The image forming method according to claim 1, wherein the resin coating layer contains a benzylic acid compound.   The image forming method according to claim 1, wherein the resin coating layer is a conductive resin coating layer in which conductive fine powder is further dispersed in a binder resin for a coating layer.   The magnetic powder is mainly composed of magnetite, and the ratio of the content of iron element (B) to the content of carbon element (A) present on the toner particle surface (B / A) measured by X-ray photoelectron spectroscopy. ) Is less than 0.001. The image forming method according to claim 1.   When the volume average particle diameter of the magnetic developer is C, and the minimum value of the distance between the magnetic powder and the toner particle surface in the tomographic surface observation of the magnetic developer using a transmission electron microscope (TEM) is D, The image forming method according to claim 1, wherein D / C ≦ 0.02. The image forming method according to any one of claims 1 to 9, wherein the conductive fine powder of the magnetic developer has a volume resistance of 10 ⁹ Ωcm or less. The image forming method according to any one of claims 1 to 9, wherein the conductive fine powder of the magnetic developer has a volume resistance of 10 ⁶ Ωcm or less.   The image forming method according to claim 1, wherein the conductive fine powder of the magnetic developer is nonmagnetic.   The image according to claim 1, wherein the developer includes toner particles and conductive fine powder having a volume average particle diameter of 0.1 μm to 10 μm. Forming method.   The charging step is a step of charging the image carrier by applying a voltage to a charging member that forms a contact portion with the image carrier through contact with the conductive fine powder. The image forming method according to any one of the above.   In the charging step, the conductive fine powder contained in the magnetic developer adheres to the image carrier in the development step and remains on the image carrier after the transfer step, so that at least the contact between the charging member and the image carrier. The image forming method according to claim 14, wherein the image forming method is interposed in and / or near the contact portion.   The image according to claim 1, wherein the conductive fine powder contains at least one oxide selected from fine particles containing at least zinc oxide, tin oxide, and titanium oxide. Forming method. A process cartridge for visualizing an electrostatic latent image formed on an image carrier as a toner image with a developer and transferring the visualized developer image onto a transfer material,
The process cartridge includes an image carrier for carrying an electrostatic latent image, charging means for contacting the image carrier and charging the image carrier, and an electrostatic latent image formed on the image carrier. A developing means for visualizing the image as a toner image by developing with a developer and collecting the developer remaining on the image carrier after the toner image is transferred to a transfer material; Having at least
The developing device and the latent image carrier are integrated, and are configured to be detachably attached to the image forming apparatus main body,
The developer includes toner particles containing at least a binder resin component and a magnetic powder, inorganic fine powder on the surface of the toner particles, and conductive fine powder having an average particle size larger than the inorganic fine powder and smaller than the developer. A negatively chargeable magnetic developer having an average circularity of 0.970 or more determined by the following formula (1) and having substantially no magnetic powder exposed on the surface thereof:
The toner particles are toner particles obtained by suspension polymerization of a polymerizable monomer system including at least a polymerizable monomer serving as a binder resin component and a magnetic powder in an aqueous medium,
The developing device includes a developer container for accommodating a developer, a developer carrier for supporting the magnetic developer accommodated in the developer container and transporting the developer to a development region, and the developer carrier At least a developer layer thickness regulating member for regulating the layer thickness of the developer carried on
The developer carrier comprises a substrate and a resin coating layer formed on the substrate,
The process cartridge, wherein the resin coating layer is a negatively chargeable resin coating layer containing at least a negatively chargeable substance.
[Expression 2]
Circularity a = L ₀ / L (1)
(In the formula, L ₀ represents the perimeter of a circle having the same projected area as the particle image, and L represents the perimeter of the projected image of the particle.) The binder resin for a coating layer of the resin coating layer has at least one of —NH ₂ group, ═NH group, and —NH— bond in its molecular structure. Process cartridge.   The process cartridge according to claim 17 or 18, wherein the binder resin for the coating layer of the resin coating layer contains at least a phenol resin. The phenol resin is a phenol resin produced by adding and condensing phenols and aldehydes using a nitrogen-containing compound as a catalyst. In the structure, -NH ₂ group, = NH group, or -NH- The process cartridge according to claim 19, wherein the process cartridge is a phenol resin having any one of bonds.   The process cartridge according to any one of claims 17 to 20, wherein the resin coating layer contains a quaternary ammonium salt compound that is positively charged with respect to at least iron powder.   The process cartridge according to any one of claims 17 to 20, wherein the resin coating layer contains a benzylic acid compound.   The process cartridge according to any one of claims 17 to 22, wherein the resin coating layer is a conductive resin coating layer in which conductive fine powder is further dispersed and contained in a binder resin for a coating layer.   The magnetic powder is mainly composed of magnetite, and the ratio of the content of iron element (B) to the content of carbon element (A) present on the toner particle surface (B / A) measured by X-ray photoelectron spectroscopy. ) Is less than 0.001. The process cartridge according to any one of claims 17 to 23.   When the volume average particle diameter of the magnetic developer is C, and the minimum value of the distance between the magnetic powder and the toner particle surface in the tomographic surface observation of the magnetic developer using a transmission electron microscope (TEM) is D, The process cartridge according to claim 17, wherein D / C ≦ 0.02. The process cartridge according to any one of claims 17 to 25, wherein the conductive fine powder of the magnetic developer has a volume resistance of 10 ⁹ Ωcm or less. The process cartridge according to any one of claims 17 to 25, wherein the conductive fine powder of the magnetic developer has a volume resistance of 10 ⁶ Ωcm or less.   The process cartridge according to any one of claims 17 to 27, wherein the conductive fine powder of the magnetic developer is non-magnetic.   The process according to any one of claims 17 to 28, wherein the developer includes toner particles and conductive fine powder having a volume average particle diameter of 0.1 µm to 10 µm. cartridge.   30. The charging unit is a unit that charges the image carrier by applying a voltage to a charging member that forms a contact portion with the image carrier through contact with the conductive fine powder. The process cartridge according to any one of the above.   The conductive fine powder contained in the magnetic developer adheres to the image carrier during development and remains on the image carrier after transfer, at least at the contact portion and / or in the vicinity of the charging member and the image carrier. The process cartridge according to claim 30, wherein the process cartridge is interposed.   The process according to any one of claims 17 to 31, wherein the conductive fine powder contains at least one oxide selected from fine particles containing at least zinc oxide, tin oxide, and titanium oxide. cartridge. The charging member a voltage is applied to, by contacting the charging member to which a voltage is applied to the image bearing member, a charging means for charging said image bearing member,
An electrostatic latent image forming means for forming an electrostatic latent image on a charged image carrier;
A developer container for containing the developer, a developer carrier for carrying the developer contained in the developer container and transporting it to the development region, and a developer layer carried on the developer carrier Development means having at least a developer layer thickness regulating member for regulating the thickness;
Transfer means for electrostatically transferring a toner image formed on the surface of the image carrier to a transfer material;
An image forming apparatus comprising: a fixing unit that heats and fixes the toner image transferred onto the transfer material;
The developing means visualizes the electrostatic latent image formed on the image carrier as a toner image by developing with a developer, and after the toner image is transferred to a transfer material, A means for collecting the developer remaining on the carrier;
The developer includes toner particles containing at least a binder resin component and a magnetic powder, inorganic fine powder on the surface of the toner particles, and conductive fine powder having an average particle size larger than the inorganic fine powder and smaller than the developer. A negatively chargeable magnetic developer having an average circularity of 0.970 or more determined by the following formula (1) and having substantially no magnetic powder exposed on the surface thereof:
The toner particles are toner particles obtained by suspension polymerization of a polymerizable monomer system including at least a polymerizable monomer serving as a binder resin component and a magnetic powder in an aqueous medium,
The developer carrier comprises a substrate and a resin coating layer formed on the substrate,
The image forming apparatus, wherein the resin coating layer is a negatively chargeable resin coating layer containing at least a negatively chargeable substance.
[Equation 3]
Circularity a = L ₀ / L (1)
(In the formula, L ₀ represents the perimeter of a circle having the same projected area as the particle image, and L represents the perimeter of the projected image of the particle.) 34. The binder resin for a coating layer of the resin coating layer, part or all of which has at least one of —NH ₂ group, ═NH group, and —NH— bond in its molecular structure. Image forming apparatus.   The image forming apparatus according to claim 33 or 34, wherein the binder resin for the coating layer of the resin coating layer contains at least a phenol resin. The phenol resin is a phenol resin produced by adding and condensing phenols and aldehydes using a nitrogen-containing compound as a catalyst. In the structure, -NH ₂ group, = NH group, or -NH- 36. The image forming apparatus according to claim 35, wherein the image forming apparatus is a phenol resin having any one of bonds.   The image forming apparatus according to any one of claims 33 to 36, wherein the resin coating layer contains a quaternary ammonium salt compound that is positively charged with respect to at least iron powder.   The image forming apparatus according to any one of claims 33 to 36, wherein the resin coating layer contains a benzylic acid compound.   The image forming apparatus according to any one of claims 33 to 38, wherein the resin coating layer is a conductive resin coating layer in which conductive fine powder is further dispersed in the coating layer binder resin.   The magnetic powder is mainly composed of magnetite, and the ratio of the content of iron element (B) to the content of carbon element (A) present on the toner particle surface (B / A) measured by X-ray photoelectron spectroscopy. 40) is less than 0.001. The image forming apparatus according to any one of claims 33 to 39.   When the volume average particle diameter of the magnetic developer is C, and the minimum value of the distance between the magnetic powder and the toner particle surface in the tomographic surface observation of the magnetic developer using a transmission electron microscope (TEM) is D, The image forming apparatus according to claim 33, wherein D / C ≦ 0.02. The image forming apparatus according to any one of claims 33 to 41, wherein the conductive fine powder of the magnetic developer has a volume resistance of 10 ⁹ Ωcm or less. The image forming apparatus according to any one of claims 33 to 41, wherein the conductive fine powder of the magnetic developer has a volume resistance of 10 ⁶ Ωcm or less.   44. The image forming apparatus according to any one of claims 33 to 43, wherein the conductive fine powder of the magnetic developer is non-magnetic.   The image according to any one of claims 33 to 44, wherein the developer has toner particles and conductive fine powder having a volume average particle diameter of 0.1 µm to 10 µm. Forming equipment.   46. The charging unit is a unit that charges the image carrier by applying a voltage to a charging member that forms a contact portion with the image carrier through contact with the conductive fine powder. The image forming apparatus according to claim 1.   The conductive fine powder contained in the magnetic developer adheres to the image carrier during development and remains on the image carrier after transfer, at least at the contact portion and / or in the vicinity of the charging member and the image carrier. The image forming apparatus according to claim 46, wherein the image forming apparatus is carried and interposed.   The image according to any one of claims 33 to 47, wherein the conductive fine powder contains at least one oxide selected from fine particles containing at least zinc oxide, tin oxide, and titanium oxide. Forming equipment.

Images