JP2004226446A - Image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method which permits a high transfer efficiency of toner, causes no fogging of toner and can correspond to a cleanerless process too, in an image forming method using an AC contact charging process used with a contact charging magnetic brush. <P>SOLUTION: Carriers contain at least binder resin and magnetic metal oxide particles and satisfy inequation (1): -6.0 R+300≤M≤-3.0 R+350, 5≤R≤30 (1). In the inequation (1), R denotes number-average particle size (μm) of magnetic carrier particles and M denotes saturation magnetization (emu/cm<SP>3</SP>) of the magnetic carrier particles. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

Ｒ：磁性キャリア粒子の個数平均粒径（μｍ）
Ｍ：磁性キャリア粒子の飽和磁化（ｅｍｕ／ｃｍ^３）
【００２４】
本発明における現像方式には、現像剤として二成分系現像剤を用い、現像剤磁気ブラシが潜像担持体に接触して摺擦しつつ交番電界をかけながら現像を行う、いわゆる接触二成分系ＡＣ現像を行い、かつ現像剤担持体が、円筒状の非磁性スリーブと該非磁性スリーブに内包されている磁石とを有し、且つ、該磁石が回転駆動するように構成されていることが最適である。これは、前述したように、ハーフトーン再現性に優れた高画質トナー画像を得るためである。
【００２５】
また、該潜像担持体の表面抵抗が１×１０^１０〜１×１０^１６Ωである電荷注入層が存在し、これに接触帯電する部材で一次帯電を行うことで、オゾンの発生を抑制することができる。特に、磁性粒子を用いた帯電磁気ブラシを使用することで、より、均一な帯電が可能となる。
【００２６】
さらに、二成分系現像剤を構成する磁性キャリアの磁気力を軟磁性体、硬磁性体を混合してコントロールし、かつ実質的に現像磁性キャリアを高抵抗化することにより、トナーカブリとキャリア付着を防止しつつ、ハーフトーン再現性の良好な、高画質画像が得られる。
【００２７】
また、以上のような構成の画像形成装置に、重合法によって製造されるトナーを使用することにより、高転写効率で、カブリのないトナーによりクリーナーレスの画像形成方法も併せて達成することができる。
【００２８】
以下、本発明の好ましい実施の形態を挙げて、本発明を更に詳細に説明する。
【００２９】
本発明者らが詳細な検討を行ったところ、本発明における潜像担持体の電荷注入層の表面抵抗は、１×１０^１０〜１×１０^１６Ωであることが必要であり、より好ましくは１×１０^１２〜１×１０^１５Ωの範囲にあることが好ましいことがわかった。電荷注入層の表面抵抗が１×１０^１０Ω未満である場合、接触帯電部材から注入される電荷が電荷注入層の表面で保持されずに、反転現像系の電子写真プロセスでは結果として画像流れと呼ばれる現象を引き起こすことがあった。これはとくに高湿下で多く見られた。電荷注入層の表面の抵抗が１×１０^１６Ωを超える場合は、電荷が十分に注入されず、潜像担持体の帯電不良領域に不必要にトナーが乗ってしまういわゆる帯電ポジコーストが発生することがある。
【００３０】
また、以上のように潜像担持体の電荷注入層の表面抵抗が１×１０^１０Ω〜１×１０^１６Ωの範囲にあっても、注入帯電部材の比抵抗が適当な範囲になければ、適正に帯電は行われない。これは注入帯電部材の構成によって調整される必要があるが、例えば磁性粒子で構成される帯電ブラシローラを用いる場合、１×１０^５〜１×１０^８Ωｃｍの比抵抗の磁性体で構成された帯電ブラシローラが良好な帯電性を示す。
【００３１】
帯電磁気ブラシローラを構成する磁性体は、例えば鉄、コバルト、ニッケルなど磁性金属や、その化合物を用いることができる。これらを適切なコート樹脂でコートするか、あるいは酸化処理、還元処理などを行って、上記の比抵抗に調整する必要がある。例えば、水素還元処理したＺｎ−Ｃｕフェライト、酸化処理したマグネタイトなどを用いることができる。また、磁性金属酸化物と導電性微粒子とをバインダー樹脂中に分散させたバインダー型の磁性粒子、あるいは該バインダー型磁性粒子を適切なコート樹脂でコートしたものを用いることもできる。
【００３２】
潜像担持体の電荷注入層としては、絶縁性でかつ透光性のバインダー樹脂中に導電性の微粒子を分散したものが好ましく用いられる。この電荷注入層を、電圧を印加された帯電磁気ブラシが接触することで、あたかも潜像担持体の導電基体に対して導電粒子が無数の独立したフロート電極のように存在し、これらのフロート電極が形成するコンデンサーに充電を行うような作用を期待することができる。従って、接触帯電部材に印加した電圧と潜像担持体表面電位は等しい値に収束し、印加する電圧も最小限のもので良いという効果も認められた。
【００３３】
前述したように、高画質化を達成するために接触二成分系現像プロセス、ＡＣ現像バイアスを用いたとき、以上のように電荷注入層の表面抵抗が１×１０^１０Ω〜１×１０^１６Ωの範囲にある潜像担持体を用いるとき、従来のような鉄粉キャリアやフェライトに樹脂コートを施した磁性キャリアを現像剤に使用すると、キャリア付着やトナーカブリが著しく発生することが見受けられた。
【００３４】
これは、表面の比抵抗が比較的低い潜像担持体と、従来の鉄粉キャリアやフェライトキャリアのような比抵抗の低い現像磁性キャリアを合わせて使用する場合、潜像担持体上の潜像の電位が、接触して摺擦する現像磁性キャリア粒子を介してリークしてその電位を現像バイアス電位に近づくように変化させてしまい、その結果、カブリ取り電位が低くなり、
トナーカブリを発生する。また、現像バイアスがキャリアに注入され、それが原因でキャリア付着も同時に起こりやすくなっていることがわかった。
【００３５】
従って、キャリアとして特有の磁気特性を有する磁性キャリアを用い、且つ、比抵抗が十分に高く、磁性キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量を制御した磁性キャリア粒子を用いれば、十分な画像濃度が得られ、キャリア付着の発生がなく、
しかも、その特性を耐久維持できることを知見して本発明に至った。
【００３６】
更に、上記特有の磁気特性を有する磁性キャリアとしては、熱硬化性のバインダー樹脂を用いて重合法によって得られる球形の樹脂キャリアであって、且つ、磁気特性の異なる２種以上の磁性金属酸化物を組み合わせて用い、これらが分散した状態の磁性体分散型樹脂キャリアを使用することが有効であることもわかった。
【００３７】
以下、これらについて更に詳細に説明する。
【００３８】
磁性キャリアについて本発明者らが詳細に検討した結果、トナー粒径が１乃至１０μｍのごとき小粒径化したときに、磁性キャリアとして個数平均粒径が５〜３０μｍのものを使用することが好適であることがわかった。即ち、この場合に、個数平均粒径が５μｍよりも小さい磁性キャリアを使用すると、現像磁気ブラシが潜像担持体に接触しつつ現像が行なわれる、所謂、接触現像を行なったときに、後述する本発明で採用する磁気特性を有する磁性キャリアを使用したとしてもキャリア付着を免れることができない。一方、個数平均粒径が３０μｍよりも大きい磁性キャリアを用いた場合には、磁性キャリアの表面積が小さくなるために、キャリア表面を好ましいトナー濃度で保持することができなくなる結果、トナーカブリの原因となったり、十分な画像濃度が得られない場合がある。
【００３９】
更に、前述したように、上記のような小粒径のトナーを用いる場合には、現像剤担持体内部に配置されている磁石が回転駆動して二成分系現像剤を現像部へと搬送する構成の現像方法を用いることによって、十分な画像濃度が得られることが知られているが、本発明者らの更なる検討の結果、このときに、磁気特性を適宜に制御した磁性キャリアを使用すれば、ハーフトーン再現性に優れ、高い画像濃度を保ちつつ、キャリア付着の発生を有効に防止でき、しかも、その性能を耐久維持できることがわかった。そして、キャリアの磁気特性としては、具体的に、１０キロエルステッドの磁場における飽和磁化が１００乃至３００ｅｍｕ／ｃｍ^３であり、残留磁化が１５乃至１５０ｅｍｕ／ｃｍ^３であることが重要であり、またさらに、磁性キャリア粒径とキャリアの飽和磁化が密接に関係していることも見いだした。磁性キャリアの粒径が５乃至３０μｍである場合に以下の関係式を満足する領域の飽和磁化を有するキャリアを用いることでキャリア付着、ハーフトーン画質の再現性、画像濃度をバランスよく良好にすることが可能となった。
【００４０】

Ｒ：磁性キャリア粒子の個数平均粒径（μｍ）
Ｍ：磁性キャリア粒子の飽和磁化（ｅｍｕ／ｃｍ^３）
【００４１】
−６．０Ｒ＋３００＞Ｍなる場合には、後述するがキャリア粒子をいくら高抵抗化してもキャリア付着を防止することが困難となる。また、Ｍ＞−３．０Ｒ＋３５０なる場合には、現像磁気ブラシが粗になり、ハーフトーン再現性に劣り、トナー劣化を促進させるようになる。
【００４２】
又、使用する磁性キャリアの残留磁化については、１５ｅｍｕ／ｃｍ^３よりも低い場合は、二成分系現像剤が現像剤担持体上で良好に転がることができず、本発明の所期の目的である画像濃度の向上を達成することができなくなり、一方、磁性キャリアの残留磁化が１５０ｅｍｕ／ｃｍ^３よりも高い場合には、現像剤担持体の磁場から離れたところでもキャリア同士の磁化による凝集が大きいため、トナーの劣化が避けられず、耐久特性が悪くなる。
【００４３】
また、本発明の磁性キャリアにおいては、磁気特性と共にキャリア粒子の比抵抗が重要である。即ち、２５乃至５００Ｖ印加時に５．０×１０^１３Ω・ｃｍ以上という高い比抵抗を有することが必須であることも見いだした。いずれの電圧印加時において５．０×１０^１３Ω・ｃｍより低い比抵抗を示すキャリアは現像バイアスがキャリアを介して潜像電位を低下させ、画像の劣化を生じさせたり、カブリを生じたり、また、キャリア自身が電荷を注入されることによりキャリア付着を生じたりする場合がある。
【００４４】
そして、本発明者らの更なる検討によれば、上記のような特有の磁気特性を有し、且つ、本発明の所期の目的を容易に達成し得る磁性キャリアを効率的に得るためには、少なくとも磁性体を含む磁性金属酸化物粒子をバインダー樹脂に分散させた、所謂、磁性体分散型の樹脂キャリアを用い、その構成材料として、熱硬化性のバインダー樹脂と磁気特性の異なる２種以上の磁性金属酸化物を少なくとも用い、重合法によって作製することが有効であることがわかった。
【００４５】
そして、上記２種以上の磁性金属酸化物の組み合わせとして、残留磁化が小さい、所謂、軟磁性で比較的飽和磁化の高い磁性金属酸化物粒子と、残留磁化が大きい、所謂、硬磁性の磁性金属酸化物粒子を混合して用いることが有効であることを見いだした。
【００４６】
更に、これらの磁性体を分散させるバインダー樹脂として、フェノール樹脂やメラミン樹脂等の熱硬化性の樹脂を用い、且つ、重合法によって作製した磁性キャリアを用いることが有効であることがわかった。即ち、かかる磁性キャリアは、硬く強度に優れ、しかも球形であるので、このような磁性キャリアを用いれば、現像器内での磁気的シェア等によるキャリア破壊が有効に防止されて、キャリア付着の発生が抑制され、又、その形状が球形であるために、現像剤担持体上で転がり易く、トナーを良好な状態で現像部に供給することが可能となるため、本発明の所期の目的である画像濃度の向上を更に達成できる。
【００４７】
さらに、表面近傍に非磁性金属酸化物粒子を含有した層を設けることで、磁性キャリアの前述した高抵抗化が計れるようになった。その高抵抗化の目安として、該磁性キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量が０．００１〜５．０質量％であることことが本発明において必要であることを見いだした。
【００４８】
さらに、該磁性キャリアは、シリコーン系の樹脂層をコーティングして用いることで、より流動性に優れ、帯電性に優れ、強度をさらに高めることができる。
【００４９】
また、本発明に好適に用いることのできるトナーとしては、重量平均粒径が１〜１０μｍであり、個数基準の変動係数が０〜３５％であることが好ましい。
【００５０】
即ち、本発明のキャリアと良好に帯電を行うために小粒径トナーであり、そのときの粒度分布がシャープであることが必要であることがわかった。さらに、流動性を高め、帯電性を良好にするために個数平均粒径が０．２μｍ以下の無機微粒子、０．２μｍ以下の有機微粒子またはそれらの混合物を含有した小粒径トナーを用いることが好ましい。
【００５１】
さらに、該トナーは、粒子全体、または一部が重合法により形成され、該トナーの形状係数ＳＦ−１が１００〜１３０であることがさらに流動性を高め、高画質化を計るために好ましい。このような小粒径のトナーを効率的に得るためには、懸濁重合や乳化重合、分散重合等の重合法を用いてトナーを製造することが好ましい。
【００５２】
以下、本発明の画像形成方法において好適に使用できる上記のような態様の磁性キャリアについて説明する。
【００５３】
この場合に用いることができる金属酸化物としては、軟磁性体粒子として、例えば、ＭＯ・Ｆｅ_２Ｏ_３又はＭＦｅ_２Ｏ_４の一般式で表される、マグネタイト、ソフトフェライト等を好ましく用いることができる。式中のＭとしては、２価或いは１価の金属イオン、例えば、Ｍｎ，Ｆｅ，Ｎｉ，Ｃｏ，Ｃｕ，Ｍｇ，Ｚｎ，Ｃｄ，Ｌｉ等が相当し、更に、Ｍは、単独或いは複数の金属として用いることができる。このようなものとしては、例えば、マグネタイト、γ酸化鉄、Ｍｎ−Ｚｎ系フェライト、Ｎｉ−Ｚｎ系フェライト、Ｍｎ−Ｍｇ系フェライト、Ｃａ−Ｍｇ系フェライト、Ｌｉ系フェライト、Ｃｕ−Ｚｎ系フェライトと言った鉄系磁性酸化物を挙げることができる。
【００５４】
又、上記した軟磁性の金属酸化物粒子と共に用いる硬磁性金属酸化物粒子としては、例えば、ＢａＦｅ_１２Ｏ_１９，ＳｒＦｅ_１２Ｏ_１９で表されるバリウムフェライト、ストロンチウムフェライト等を挙げることができる。更に、磁気特性や電気抵抗等の調整のために、上記金属酸化物以外にも、Ｍｇ、Ａｌ、Ｓｉ、Ｃａ、Ｓｃ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｎ、Ｓｒ、Ｙ、Ｚｒ、Ｎｂ、Ｍｏ、Ｃｄ、Ｓｎ、Ｂａ、Ｐｂ等の金属を、単独或いは複数用いた非磁性の金属酸化物を併用することもできる。
【００５５】
尚、上記で言うソフトフェライトとは、軟磁性のフェライトであって、その保磁力Ｈｃが１００エルステッド以下のものを意味する。
【００５６】
上記の金属酸化物を樹脂に分散してコアとする場合、磁性を示す金属酸化物の個数平均粒径はキャリア粒径によっても変わるが、０．０２〜２μｍまでのものが好ましく用いることができる。また、２種以上の金属酸化物を分散させて用いる場合、磁性を示す金属酸化物の個数平均粒径は０．０２〜２μｍまでのものが用いることができ、他方の非磁性金属酸化物の個数平均粒径は０．０５〜５μｍのものが使用できる。この場合、磁性粒子（粒径ｒ_ａ）に対して他方の非磁性金属酸化物（粒径ｒ_ｂ）の粒径比ｒ_ｂ／ｒ_ａは１倍を超えることが好ましく、１倍を超え５倍以下であることがより好ましい。１．０倍以下であると比抵抗の低い磁性金属酸化物粒子が表面に出やすくなり、キャリアコアの抵抗を十分に上げることができず、本発明のキャリア付着を防止する効果が得られにくくなる。また、５．０倍を超えると樹脂中への金属酸化物粒子の取り込みが上手くいかなくなる場合もあり、キャリアの強度が低下し、キャリア破壊を引き起こしやすくなる。
【００５７】
また、キャリア粒子表面近傍に存在させる非磁性の酸化物の例としては、例えばＡｌ_２Ｏ_３、ＳｉＯ_２、ＣａＯ、ＴｉＯ_２、Ｖ_２Ｏ_５、ＣｒＯ_２、ＭｎＯ_２、Ｆ_２Ｏ_３、ＣｏＯ、ＮｉＯ、ＣｕＯ、ＺｎＯ、ＳｒＯ、Ｙ_２Ｏ_３、ＺｒＯ_２系等を使用することができる。
【００５８】
また、樹脂に分散して用いる金属酸化物の比抵抗は、磁性粒子が１×１０^３Ωｃｍ以上の範囲のものを使用でき、特に、２種以上の金属酸化物を混合して用いる場合には、磁性を示す粒子が１×１０^３Ωｃｍ以上の範囲のものであり、他方の非磁性金属酸化物粒子は磁性粒子よりも高い比抵抗を有するものを用いることが必要である。好ましくは本発明に用いる他方の非磁性金属酸化物の比抵抗は、１×１０^８Ωｃｍ以上のものが好ましく用いられる。磁性粒子の比抵抗が１×１０^３Ωｃｍ未満であると、分散する金属酸化物の含有量を減量しても所望のキャリア比抵抗が得られない。また、２種以上の金属酸化物を分散する場合には粒径の大きな非磁性金属酸化物の比抵抗が１×１０^８Ωｃｍ未満であると、
キャリアコアの比抵抗を十分に高めることができず、本発明の効果が得られにくくなる。
【００５９】
本発明の金属酸化物分散樹脂コアの金属酸化物の総含有量は、５０質量％〜９９質量％である。金属酸化物の量が５０質量％未満であると、帯電性が不安定になり、特に低温低湿環境下においてキャリアが帯電し、その残留電荷が残存しやすくなるために微粉トナーや外添削等がキャリア表面に付着しやすくなる。また、９９質量％を超えるとキャリア強度が低下して、耐久によるキャリアの割れなどの問題を生じやすくなる。
【００６０】
また、本発明で使用する金属酸化物分散樹脂コアに含有される金属酸化物は、親油化処理されていることが好ましい。親油化処理された金属酸化物はバインダー樹脂中に分散させコア粒子を形成する場合、均一でかつ高密度でバインダー樹脂中に取り込まれることが可能となる。特に、重合法でコア粒子を形成する場合は球形で表面が平滑な粒子を得るために、また、粒度分布をシャープにするために重要である。
【００６１】
親油化処理はシラン系カップリング剤やチタネート系カップリング剤などのカップリング剤で金属酸化物を処理するか、界面活性剤を含む水性溶媒中に金属酸化物を分散させることにより表面を親油化する等の方法がある。
【００６２】
ここでいうシラン系カップリング剤としては、疎水性基、アミノ基あるいはエポキシ基を有するものを用いることができる。疎水性基をもつシラン系カップリング剤として例えば、ビニルトリクロルシラン、ビニルトリエトキシシラン、ビニルトリス（β−メトキシ）シラン等を挙げることができる。アミノ基をもつシラン系カップリング剤としては、γ−アミノプロピルエトキシシラン、Ｎ−β（アミノエチル）−γ−アミノプロピルトリメトキシシラン、Ｎ−β（アミノエチル）−γ−アミノプロピルメチルジメトキシシラン、Ｎ−フェニル−γ−アミノプロピルトリメトキシシラン等が挙げられる。エポキシ基をもつシラン系カップリング剤としては、γ−グリシドキシプロピルメチルジエトキシシラン、γ−グリシドキシプロピルトリェトキシシラン、β−（３，４−エポキシシクロヘキシル）トリメトキシシラン等が挙げられる。
【００６３】
チタネート系カップリング剤としては、例えば、イソプロピルトリイソステアロイルチタネート、イソプロピルトリトデシルベンセンスルホニルチタネート、イソプロピルトリス（ジオクチルピロホスフェート）チタネート等を挙げることができる。
【００６４】
界面活性剤としては、市販の界面活性剤をそのまま使用することができる。
【００６５】
上述した本発明の磁性キャリアを製造する方法としては、少なくとも重合性モノマーと２種以上の磁性金属酸化物とを含む組成物を混合して造粒し、モノマーを重合させて、直接、キャリアを得る方法がある。重合に用いられる重合性モノマーとしては、先に挙げたフェノール樹脂やメラミン樹脂等の熱硬化性樹脂原料であるビニル系モノマー、例えばフェノール樹脂の場合は、フェノール類とアルデヒド類、尿素樹脂の場合は、尿素とアルデヒド類、メラミン樹脂の場合は、メラミンとアルデヒド類や、その他の、エポキシ樹脂の出発原料となるビスフェノール類とエピクロルヒドリン等が用いられる。例えば、硬化系フェノール樹脂を用いた磁性キャリアの具体的な製造方法としては、水性媒体中で、重合性モノマーであるフェノール類とアルデヒド類を、塩基性触媒の存在下、先に挙げたような磁性金属酸化物、好ましくは親油化処理した磁性金属酸化物を入れて、単量体モノマーを重合させることによって、直接、磁性体分散型の球状の樹脂キャリアを得る。
【００６６】
本発明の磁性キャリアは、キャリアと共に用いるトナーの帯電量に合わせて、更に、その表面が適当なコート樹脂で被覆されているものであることが好ましい。
【００６７】
この際に使用するコート樹脂としては、絶縁性樹脂であることが好ましい。この場合に使用し得る絶縁性樹脂としては、熱可塑性の樹脂であっても熱硬化性樹脂であってもよい。
【００６８】
具体的には、例えば、熱可塑性の樹脂としては、ポリスチレン、ポリメチルメタクリレートやスチレン−アクリル酸共重合体等のアクリル樹脂、スチレン−ブタジエン共重合体、エチレン−酢酸ビニル共重合体、ポリ塩化ビニル、ポリ酢酸ビニル、ポリフッ化ビニリデン樹脂、フルオロカーボン樹脂、ハーフロロカーボン樹脂、溶剤可溶性ハーフロロカーボン樹脂、ポリビニルアルコール、ポリビニルアセタール、ポリビニルピロリドン、石油樹脂、セルロース、酢酸セルロース、硝酸セルロース、メチルセルロース、ヒドロキシメチルセルロース、ヒドロキシメチルセルロース、ヒドロキシプロピルセルロース等のセルロース誘導体、ノボラック樹脂、低分子量ポリエチレン、飽和アルキルポリエステル樹脂、ポリエチレンテレフタレート、ポリブチレンテレフタレート、ポリアリレートと言った芳香族ポリエステル樹脂、ポリアミド樹脂、ポリアセタール樹脂、ポリカーボネート樹脂、ポリエーテルスルホン樹脂、ポリスルホン樹脂、ポリフェニレンサルファイド樹脂、ポリエーテルケトン樹脂等を挙げることができる。
【００６９】
又、熱硬化性樹脂としては、具体的には、例えば、フェノール樹脂、変性フェノール樹脂、マレイン樹脂、アルキド樹脂、エポキシ樹脂、アクリル樹脂、或いは、無水マレイン酸とテレフタル酸と多価アルコールとの重縮合によって得られる不飽和ポリエステル、尿素樹脂、メラミン樹脂、尿素−メラミン樹脂、キシレン樹脂、トルエン樹脂、グアナミン樹脂、メラミン−グアテミン樹脂、アセトグアナミン樹脂、グリプタール樹脂、フラン樹脂、シリコーン樹脂、ポリイミド、ポリアミドイミド樹脂、ポリエーテルイミド樹脂、ポリウレタン樹脂等を挙げることができる。
【００７０】
上述した樹脂は、単独でも使用できるが、夫々を混合して使用してもよい。又、熱可塑性樹脂に硬化剤等を混合し硬化させて使用することもできる。
【００７１】
特に好ましい形態は、シリコーン系の硬化樹脂であることである。帯電量をコントロールするためにアミノ基を含有するシラン化合物等を混合して用いるとより好ましい。
【００７２】
更に、本発明の磁性キャリアは、真比重が３．０〜４．９ｇ／ｃｍ^３であるとき好適に用いることができる。即ち、真比重が３．０ｇ／ｃｍ^３未満である磁性キャリアは、実質的に、キャリアの重量に占める樹脂の割合が５０％以上であるような樹脂分の多いキャリアを意味しており、強度面で問題を生じる場合がある。一方、真比重が４．９ｇ／ｃｍ^３より大きい場合には、キャリアの磁気特性にもよるが、現像器内でのトナーに与えるシェアが大きくなる傾向があり、耐久時にトナー劣化を引き起こす恐れがあり、バインダー成分が不足となり強度低下が起こる場合もある。
【００７３】
本発明の画像形成方法は、該二成分系現像剤を現像剤担持体上に担持して現像部へと搬送し、該現像部において、現像剤担持体上に二成分系現像剤の磁気ブラシを形成し、該磁気ブラシを潜像担持体に接触させて潜像担持体上に形成されている静電潜像を現像する工程において、上記現像剤担持体が、円筒状の非磁性スリーブと該非磁性スリーブに内包されている磁石とを有し、且つ、該磁石が回転駆動するように構成されているが必要である。
【００７４】
即ち、本発明における磁性キャリアは、着磁して用いる。その際、現像剤担持体である非磁性スリーブの中に磁石が配設され、それが高速回転することにより、現像剤が現像部へと搬送される。
【００７５】
本発明の磁性キャリアを着磁する方法としては、公知の方法でできる。好ましくは、保磁力の３倍以上の磁場中で磁化して用いることが好ましい。
【００７６】
本発明の画像形成方法における接触二成分系ＡＣ現像方式で、現像剤磁気ブラシに印加する交番電界は５００Ｈｚ〜５０００Ｈｚであることが好適である。印加する交番電界が５００Ｈｚ未満である場合、いかに本発明のごとき実質的に高抵抗の現像磁性キャリアであっても、現像磁性キャリアを通じて電荷が潜像担持体に注入されてしまい、キャリア付着してしまう場合があった。また、印加する交番電界が５０００Ｈｚを超える場合、電界に対してトナーが追随できず画質低下を招きやすい。
【００７７】
印加する交番電界としては、従来の正弦波、三角波あるいは矩形波を用いることができるが、波形を適切に制御した交番電界を用いることもできる。例えば、潜像担持体から現像剤担持体にトナーを向かわせる第１電圧と現像剤担持体から潜像担持体にトナーを向かわせる第２電圧と、該第１電圧と第２電圧の間の第３電圧で波形のパターンを形成させるような交番電界を用いることができるが、このような場合も、その波形の繰り返しパターン１周期に対して周波数が本発明における交番電界の周波数の範囲、すなわち５００Ｈｚ〜５０００Ｈｚであることが好適である。
【００７８】
本発明の画像形成方法に用いられるトナーは、重量平均粒径が１〜１０μｍの範囲であることが好適である。１０μｍを超えるトナー粒径では、潜像を現像する粒子１個が大きくなるために、本発明の目的である高精細なトナー像は得られないことになる。
【００７９】
ところで、本発明の画像形成方法に、クリーナーレスプロセスを組み合わせることが可能であるが、前述したように、接触帯電部材に磁気ブラシローラを用いて、これにクリーナーレスプロセスを組み合わせた場合、磁気ブラシ中にトナーが混入したとき、その帯電特性が変化してしまうという問題点がある。
【００８０】
このような問題を避けるため、本発明の画像形成方法にクリーナーレスプロセスを組み合わせる場合には、転写効率が９５％以上であるトナーが必須であり、より好ましくは９８％以上であるトナーを用いるのが良い。
【００８１】
転写効率は、ベタ黒画像を現像させたのち紙上に転写させ、その単位面積当りの転写されたトナー重量（Ｔ１）と、転写されずに潜像担持体上に残ったトナー重量（Ｔ２）を測定し、下記の式
転写効率（％）＝１００×Ｔ１／（Ｔ１＋Ｔ２）
により計算することにより算出した。
【００８２】
このため、本発明の画像形成方法に、クリーナーレスプロセスを組み合わせる場合には、トナーの一部又は全部が重合法により製造されていることが好ましい。また、適切な外添剤がトナーの周囲に存在していることが好ましい。重合法により製造されたトナーは一般に球形度が高く、そのため潜像担持体上に少ない接触面積で置かれるため転写効率が高い。
【００８３】
また、外添剤は潜像担持体とトナー粒子とのスペーサーの役割を果たし、トナーの転写性を上げることができる。また、球形度が高いことセトナーの摩擦帯電が良好になり、帯電不良によるトナーカブリもなくなるため、カブリトナーが転写されずに接触帯電磁気ブラシに混入することも避けることができる。
【００８４】
トナーの外添剤としては、従来用いられてきた外添剤を使用することができ、無機微粒子又は有機微粒子、あるいはそれらの混合物を使うことができる。それら外添剤は、ＢＥＴ法による比表面積が１００ｍ^２／ｇ以上であることが好ましい。比表面積が１００ｍ^２／ｇ未満であると、トナーの流動性が無くなり、トナーの転写性を十分に向上させることができない。
【００８５】
また、本発明の画像形成方法においては現像剤担持体は、その表面形状が
０．２μｍ≦中心線平均粗さ（Ｒａ）≦５．０μｍ
１０μｍ≦凹凸の平均間隔（Ｓｍ）≦８０μｍ
０．０５≦Ｒａ／Ｓｍ≦０．５
上記条件を満足することが好ましい。
【００８６】
Ｒａ及びＳｍとは、ＪＩＳ−Ｂ０６０１及びＩＳＯ４６８に記載される中心線平均粗さ及び凹凸の平均間隔を規定する値で次式により求められる。
【００８７】
【数１】

【００８８】
Ｒａが０．２μｍより小さいと、現像剤の搬送性が不十分なため耐久による画像むらや画像の濃度むらが発生しやすくなる。Ｒａが５μｍを超えると、現像剤の搬送性には優れるものの、ブレード等の現像剤搬送量規制部における規制力が大きくなりすぎるために外部添加剤が摺擦による劣化を受けて耐久時の画質が低下する。
【００８９】
Ｓｍが８０μｍより大きくなると、現像剤担持体上への現像剤が保持されにくくなるために画像濃度が低くなってしまう。このＳｍの与える原因について詳細は不明であるが、現像剤担持体の搬送量規制部等で現像剤担持体との滑りが起こっていることから、凹凸の間隔が広くなりすぎると現像剤が密にパッキングされた塊として作用し、その力が現像剤担持体−現像剤間の保持力を上回ると考えられる。Ｓｍが１０μｍ未満であると、担持体表面の凹凸の多くが現像剤平均粒径より小さくなるため、凹部に入り込む現像剤の粒度選択性が生じ、現像剤微粉成分による融着が発生しやすくなる。また製造的にも困難である。
【００９０】
さらに上記の観点より現像剤担持体上の凸部の高さと凹凸の間隔から求められる凸・凹の傾斜（≒ｆ（Ｒａ／Ｓｍ））が本発明の場合重要な原因となる。本発明では
０．０５≦Ｒａ／Ｓｍ≦０．５
であることが好ましく、より好ましくは０．０７以上０．３以下である。
【００９１】
Ｒａ／Ｓｍが０．０５未満であると、現像剤の現像剤担持体上への保持力が弱いため現像剤担持体へ現像剤が保持されにくくなるので現像剤規制部で搬送量が制御されず、結果として画像むらが生じる。Ｒａ／Ｓｍが０．５を超えると、現像剤担持体表面の凹部に入った現像剤が他の現像剤と循環しにくくなるため現像剤融着が発生する。
【００９２】
現像剤担持体の長さ方向にさらに溝（いわゆるローレット）を数本加工せしめることで、さらに流動性に優れた現像剤をも現像剤担持体に均一にコーティングすることが容易になった。
【００９３】
本発明におけるＲａ及びＳｍの測定は、接触式表面粗さ測定器ＳＥ−３３００（小坂研究所社製）を用い、ＪＩＳ−Ｂ０６０１に準拠して行った。
【００９４】
本発明の所定の表面粗さを有する現像剤担持体を製造する方法としては、例えば不定形・定形粒子を砥粒として用いたサンドブラスト法、スリーブ円周方向に凹凸を形成するためにサンドペーパーでスリーブ面を軸方向に擦るサンドペーパー法、化学処理による方法、弾性樹脂でコート後樹脂凸部を形成する方法等を用いることができる。
【００９５】
以下に、本発明で用いる測定方法について述べる。
【００９６】
本発明に用いるトナー粒子の粒径の測定は、レーザースキャン型粒度分布測定装置（ＣＩＳ−１００ＧＡＬＡＩ社製）を用いて、０．４μｍから６０μｍの範囲内で測定を行う。試料は、水１００ｍｌに界面活性剤（アルキルベンゼンスルホン酸塩）０．２ｍｌ加えた溶液にトナー０．５乃至２ｍｇを抑え、超音波分散器で２分間分散した後、マグネットスターラーを入れたキュービックセルに水を８割程度入れ、その中に分超音波散した試料をピペットで１、２滴添加する。これから得られる重量平均粒径、個数平均粒径Ｄｎ、個数分布基準のＳ．Ｄ．（標準偏差）をもとに、重量平均粒径、変動係数を求める。
【００９７】
変動係数（％）＝Ｓ．Ｄ．／Ｄｎ×１００
【００９８】
磁性キャリアの粒径については、走査電子顕微鏡（１００〜５，０００倍）によりランダムに粒径０．１μｍ以上の磁性キャリア粒子を３００個以上抽出し、ニレコ社（株）製の画像処理解析装置Ｌｕｚｅ×３により解析し、個数平均の水平方向フェレ径をもってキャリアの個数平均粒子径とした。
【００９９】
又、磁性キャリアの磁気特性は、理研電子（株）製の振動磁場型磁気特性自動記録装置ＢＨＶ−３０を用いて測定した。キャリア粉体の磁気特性値は、１０キロエルステッドの外部磁場を作り、飽和磁化、及びそこから０エルステッドに戻したときの残留磁化を求めた。磁性キャリアの測定用サンプルは、円筒状のプラスチック容器に充分密になるようにパッキングした状態で作製する。この状態で磁化モーメントを測定し、更に、上記で充填した試料の実際の重量を測定して磁化の強さ（ｅｍｕ／ｇ）を求める。次いで、キャリア粒子の真比重を、乾式自動密度計アキュピック１３３０（島津製作所（株）社製）により求め、磁化の強さ（ｅｍｕ／ｇ）に真比重を掛けることで、本発明で規定する単位体積あたりの磁化の強さ（ｅｍｕ／ｃｍ^３）を求める。
【０１００】
本発明における磁性キャリアの比抵抗の測定は、本発明において、磁性キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量は以下の方法により求めることができる。
【０１０１】
５１のビーカーに３１の脱イオン水を入れ、水温が４５〜５０℃まで加温する。４００ｍｌの脱イオン水と２５ｇの磁性キャリア粒子を混合しスラリー状にして、８０５ｍｌの脱イオン水で水洗しながら全てを５１ビーカー中に加える。次いで、前期５１ビーカー中の溶液温度を５０℃、撹拌スピードを２００ｒｐｍに保ちながら、特級硫酸６９５ｍｌを前期５１ビーカー中に加え、溶解を開始する。溶解開始から１時問後に溶解液を２０ｍｌサンプリングして、０．１μｍメンブランフィルターで濾過して濾液を採取する。
【０１０２】
濾液の１０ｍｌを計りとり、プラズマ発光分光（ＩＣＰ）によって、鉄元素の溶解濃度を定量する。
【０１０３】
一方、該溶解液の濾液１０ｍｌにイオン交換水１００ｍｌを加えて、０．１ＮのＫＭｎＯ４水溶液を用いて滴定し、微紅色の着色を終点として滴定量を求める。並行してブランクテストを行い、次式により磁性キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量を求めることができる。
【０１０４】
【数２】

【０１０５】
以下に本発明で使用した摩擦帯電量の測定方法を記載する。トナーとキャリアを所定の混合比になるように混合し、夕一ブラミキサーで１２０秒混合する。この現像剤を底部に６３５メッシュの導電性スクリーンを装着した金属製の容器にいれ、吸引機で吸引し、吸引前後の重量差と容器に接続されたコンデンサーに蓄積された電位から摩擦帯電量を求める。この際、吸引圧を２５０ｍｍＨｇとする。この方法によって、摩擦帯電量を下記式を用いて算出する。
Ｑ（μＣ／ｇ）＝（Ｃ×Ｖ）×（Ｗ_１−Ｗ_２）^−１
（式中Ｗ_１は吸引前の重量でありＷ_２は吸引後の重量であり、Ｃはコンデンサーの容量、及びＶはコンデンサーに蓄積された電位である。）
【０１０６】
本発明で用いた静電潜像担持体の表面抵抗の測定方法について述べる。潜像担持体表面に、有効電極長さ２ｃｍで、電極間距離１２０μｍのくし型電極を金蒸着し、抵抗測定装置（ヒューレットパッカード社製４１４０ＢｐＡＭＡＴＥＲ）にて１００Ｖの電圧を印加させて測定する。
【０１０７】
【実施例】
以下、本発明の実施例について具体的に説明するが、本発明はこれに限定されるものではない。
【０１０８】
（トナーの製造）
［トナー１］
プロポキシ化ビスフェノールとフマル酸を
縮合して得られたポリエステル樹脂 １００質量部
Ｃ．Ｉ．ピグメントブルー１５：３ ５質量部
ジ−ｔｅｒｔ−ブチルサリチル酸のクロム錯塩 ４質量部
これらを固定槽式乾式混合機により混合し、ベント口を吸引ポンプに接続し吸引しつつ、二軸押し出し機にて溶融混練を行った。
【０１０９】
この溶融混練物を、ハンマーミルにて粗砕し、１ｍｍメッシュパスのトナー組成物の粗砕物を得た。更に、この粗砕物を機械式粉砕機により、重量平均径２０〜３０μｍまで粉砕を行った後、旋回流中の粒子間衝突を利用したジェットミルにて粉砕を行った後、多段割分級機により分級を行ってシアン着色粒子を得た。
【０１１０】
又、このトナー組成物１００質量部に対して、ＢＥＴ法による比表面積が２００ｍ^２／ｇである疎水性酸化チタンを１．８質量部外添してトナー１を得た。得られた粒子は、重量平均粒径４．８μｍであった。個数分布の変動係数は、２８％であった。
【０１１１】
［トナー２］
イオン交換水７１０質量部に、０．１Ｍ−Ｎａ_３ＰＯ_４水溶液４５０質量部を投入し、６０℃に加温した後、ＴＫ式ホモミキサー（特殊機化工業製）を用いて、１２，０００ｒｐｍにて撹拌した。これに１．０Ｍ−ＣａＣｌ_２水溶液７５質量部を徐々に添加し、均一且つ微細に分散された状態のＣａ_３（ＰＯ_４）_２を含む水系媒体を調製した。
【０１１２】
スチレン １６０質量部
ｎ−ブチルアクリレート ３５質量部
Ｃ．Ｉ．ピグメントブルー１５：３ １５質量部
ジ−ｔｅｒｔ−ブチルサリチル酸のアルミ錯塩 １５質量部
飽和ポリエステル（酸価１４、ピーク分子量；８０００） １０質量部
エステルワックス（融点７０℃） ５０質量部
【０１１３】
一方、上記材料を混合してを６０℃に加温し、ＴＫ式ホモミキサー（特殊機化工業製）を用いて、１２，０００ｒｐｍにて均一に溶解、分散した。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）１０質量部を溶解し、重合性モノマーを含む組成物を調製した。
【０１１４】
次に、前記で予め調製しておいた水系媒体中に、得られた重合性モノマーを含む組成物を投入し、６０℃のＮ２雰囲気下において、ＴＫ式ホモミキサーにて１０，０００ｒｐｍで１０分間撹拌して、該組成物を造粒した。その後、パドル撹拌翼で撹拌しつつ、８０℃に昇温し、１０時間反応させた。重合反応終了後、減圧下で残存モノマーを留去し、冷却後、塩酸を加えてリン酸カルシウムを溶解させた後、ろ過、水洗、乾燥をして、シアン着色懸濁粒子を得た。
【０１１５】
その後、多段割分級機により分級を２回行った。この着色粒子１００質量部に対して、ＢＥＴ法による比表面積が２００ｍ^２／ｇである疎水性酸化チタンを３．５質量部外添して、重合法により製造されたトナー２を得た。得られた粒子は重量平均粒径３．１μｍであった。個数分布の変動係数は、１８％であった。
【０１１６】
［トナー３］
トナー１の多分割分級機による分級条件を変化させること以外はトナー１と同様にしてシアン着色粒子を製造した。このシアン着色粒子１００質量部に対して、ＢＥＴ法による比表面積が２００ｍ^２／ｇである疎水性酸化チタンを１．８質量部外添して、粉砕法により製造されたトナー３を得た。得られた粒子の重量平均粒径は、５．２μｍであった。個数分布の変動係数は、３７％であった。
【０１１７】
（キャリアの製造）
［キャリア１］
先ず、個数平均粒径０．２５μｍのマグネタイト粉と、個数平均粒径０．２５μｍのバリウムフェライト粉、個数平均粒径０．４０μｍのヘマタイト粉に対して、夫々４．８質量％のシラン系カップリング剤（３−（２−アミノエチルアミノプロピル）ジメトキシシラン）を加え、容器内で１０００℃以上で高速混合撹拌して金属酸化物微粒子の親油化処理を行った。
・フェノール １０質量部
・ホルムアルデヒド溶液 ６質量部
（ホルムアルデヒド４０％、メタノール１０％、水５０％）
・親油化処理したマグネタイト ７２質量部
・親油化処理したバリウムフェライト １８質量部
・親油化処理したヘマタイト １０質量部
上記材料と、２８％アンモニア水５質量部、水１０質量部をフラスコに入れ、撹拌、混合しながら３０分間で８５℃まで昇温・保持し、３時間重合反応させて硬化させた。
【０１１８】
さらに先述と同様に（３−（２−アミノエチルアミノプロピル）ジメトキシシラン）で親油化処理した個数平均粒径０．２０μｍのヘマタイト粉を１．５質量部、フェノールを１質量部、ホルムアルデヒド溶液を０．４質量部加え、さらに３時間重合反応させた。
【０１１９】
その後、３０℃まで冷却し、更に水を添加した後、上澄み液を除去し、沈殿物を水洗した後、風乾した。次いで、これを減圧下（５ｍｍＨｇ以下）、５０〜６０℃の温度で乾燥して、球状の粒子を得た。
【０１２０】
更に、上記で得られた粒子の表面に、以下の方法で熱硬化性のシリコーン樹脂をコートした。その際、キャリアコア粒子表面のコート樹脂量が１．５質量％になるように、トルエンを溶媒として１０質量％のキャリアコード溶液を作製した。このコート溶液を剪断応力を連続して加えながら溶媒を７０℃で揮発させて、キャリアコア表面へのコートを行った。このコート磁性キャリア粒子を２００℃で３時間撹拌しながら熱処理し、冷却後、解砕した後、２００メッシュの篩で分級して、キャリア１を得た。
【０１２１】
得られたキャリア１の個数平均粒径は２２．０μｍであった。更に、得られたキャリアを１０キロエルステッドの磁場をかけ、その磁気特性を測定した。１０キロエルステッドにおける飽和磁化は２４８ｅｍｕ／ｃｍ^３であり、残留磁化は２４．８ｅｍｕ／ｃｍ^３であった。又、キャリア１の真比重は３．５５ｇ／ｃｍ３であった。また、キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量は、２．１質量％であった。
【０１２２】
［キャリア２］
先ず、個数平均粒径０．２５μｍのマグネタイト粉と、個数平均粒径０．２７μｍのストロンチウムフェライト粉、個数平均粒径０．４０μｍのヘマタイト粉に対して、夫々４．８質量％のシラン系カップリング剤（３−（２−アミノェチルアミノプロピル）ジメトキシシラン）を加え、容器内で１００℃以上で高速混合撹拌してキャリア１と同様に金属酸化物微粒子の親油化処理を行った。
・フェノール １２質量部
・ホルムアルデヒド溶液 ７質量部
（ホルムアルデヒド４０％、メタノール１０％、水５０％）
・親油化処理したマグネタイト ４２質量部
・親油化処理したストロンチウムフェライト ２８質量部
・親油化処理したヘマタイト ３０質量部
上記材料と、２８％アンモニア水６質量部、水１２質量部をフラスコに入れ、撹拌、混合しながら３０分間で８５℃まで昇温・保持し、３時間重合反応させて硬化させた。
【０１２３】
さらにキャリア１と同様に親油化処理した個数平均粒径０．２０μｍのヘマタイト粉を１．５質量部、フェノールを１質量部、ホルムアルデヒド溶液を０．４質量部加え、さらに３時間重合反応させた。
【０１２４】
その後キャリア１と同様にして球状の粒子を得た。
【０１２５】
更に、上記で得られた粒子の表面に、キャリア１と同様に熱硬化性のシリコーン樹脂をコートしてキャリア２を得た。
【０１２６】
得られたキャリア２の個数平均粒径は２９．３μｍであった。１０キロエルステッドにおける飽和磁化は１８１ｅｍｕ／ｃｍ^３であり、残留磁化は３０．１ｅｍｕ／ｃｍ^３であった。又、キャリア１の真比重は３．６０ｇ／ｃｍ^３であった。また、キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量は、１．２質量％であった。
【０１２７】
［キャリア３］
キャリア１で用いた親油化処理したマグネタイトとバリウムフェライトとを用い、以下の処方で重合を行った。
・フェノール １０質量部
・ホルムアルデヒド溶液 ６質量部
（ホルムアルデヒド４０％、メタノール１０％、水５０％）
・親油化処理したマグネタイト ９０質量部
・親油化処理したバリウムフェライト １０質量部
上記材料と、２８％アンモニア水４質量部、水８質量部をフラスコに入れ、撹拌、混合しながら３０分間で８５℃まで昇温・保持し、３時間重合反応させて硬化させた。さらにキャリア１と同様に親油化処理した個数平均粒径０．２８μｍのヘマタイト粉を１．５質量部、フェノールを１質量部、ホルムアルデヒド溶液を０．４質量部加え、さらに３時間重合反応させた。
【０１２８】
その後キャリア１と同様にして球状の粒子を得た。
【０１２９】
更に、上記で得られた粒子の表面に、キャリア１と同様に熱硬化性のシリコーン樹脂をコートしてキャリア３を得た。
【０１３０】
得られたキャリア３の個数平均粒径は１５．７μｍであった。１０キロエル子テッドにおける飽和磁化は２８１ｅｍｕ／ｃｍ^３であり、残留磁化は１９．５ｅｍｕ／ｃｍ^３であった。又、キャリア１の真比重は３．５８ｇ／ｃｍ^３であった。また、キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量は、４．４質量％であった。
【０１３１】
［キャリア４］
個数平均粒径０．２５μｍの銅亜鉛フェライト粉と、個数平均粒径０．２５μｍのバリウムフェライト粉、個数平均粒径０．４０μｍのヘマタイト粉に対し、夫々３．８質量％のシラン系カップリング剤（３−（２−アミノエチルアミノプロピル）ジメトキシシラン）を加え、容器内で１００℃以上で、高速混合撹拌して金属酸化物微粒子の親油化処理を行った。
・フェノール １２質量部
・ホルムアルデヒド溶液 ７質量部
（ホルムアルデヒド４０％、メタノール１０％、水５０％）
・親油化処理した銅亜鉛フェライト ２４質量部
・親油化処理したバリウムフェライト ５６質量部
・親油化処理したヘマタイト ２０質量部
上記材料と、２８％アンモニア水６質量部、水１２質量部をフラスコに入れ、撹拌、混合しながら３０分間で８５℃まで昇温・保持して、３時間で反応・硬化させた。
【０１３２】
さらにキャリア１で用いたヘマタイト粉を１．０質量部、フェノールを１質量部、ホルムアルデヒド溶液を０．４質量部加え、さらに３時間重合反応させた。
【０１３３】
その後キャリア１と同様にして球状の粒子を得た。
【０１３４】
更に、上記で得られた粒子の表面に、キャリア１と同様に熱硬化性のシリコーン樹脂をコートしてキャリア４を得た。
【０１３５】
得られたキャリア４の個数平均粒径は２８．１μｍであった。１０キロエルステッドにおける飽和磁化は１８２ｅｍｕ／ｃｍ^３であり、残留磁化は５２．１ｅｍｕ／ｃｍ^３であった。又、キャリア１の真比重は３．５３ｇ／ｃｍ^３であった。また、キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量は、０．２質量％であった。
【０１３６】
［キャリア５］
先ず、個数平均粒径０．４０μｍのマグネタイト粉と、個数平均粒径０．４１μｍのバリウムフェライト粉に対して、夫々３．０質量％のシラン系カップリング剤（３−（２−アミノエチルアミノプロピル）ジメトキシシラン）を加え、キャリア１と同様に容器内で１００℃以上で高速混合撹拌して金属酸化物微粒子の親油化処理を行った。
・フェノール １０質量部
・ホルムアルデヒド溶液 ６質量部
（ホルムアルデヒド４０％、メタノール１０％、水５０％）
・親油化処理したマグネタイト ６０質量部
・親油化処理したバリウムフェライト ４０質量部
上記材料と、２８％アンモニア水５質量部、水１０質量部をフラスコに入れ、撹拌・混合しながら３０分間で８５℃まで昇温・保持し、３時間重合反応させて硬化させた。
【０１３７】
その後、３０℃まで冷却し、更に水を添加した後、上澄み液を除去し、沈殿物を水洗した後、風乾した。次いで、これを減圧下（５ｍｍＨｇ以下）、５０〜６０℃の温度で乾燥して、球状の粒子を得た。
【０１３８】
更に、上記で得られた粒子の表面に、キャリア１と同様な方法で熱硬化性のシリコーン樹脂をコートしてキャリア５を得た。
【０１３９】
得られたキャリア４の個数平均粒径は２０．３μｍであった。１０キロエルステッドにおける飽和磁化は２５５ｅｍｕ／ｃｍ^３であり、残留磁化は４５．９ｅｍｕ／ｃｍ^３であった。又、キャリア１の真比重は３．５８ｇ／ｃｍ^３であった。また、キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量は、８．８質量％であった。
【０１４０】
［キャリア６］
モル比で、Ｆｅ_２Ｏ_３＝５０モル％、ＣｕＯ＝２７モル％、ＺｎＯ＝２３モル％になるように秤量し、ボールミルを用いて混合を行った。これを仮焼した後、ボールミルにより粉砕を行い、さらにスプレードライヤーにより造粒を行った。これを焼結し、さらに分級してキャリアコア粒子を得た。
【０１４１】
更に、上記で得られた粒子の表面に、キャリア１と同様な方法で熱硬化性のシリコーン樹脂をコートしてキャリア５を得た。
【０１４２】
得られたキャリア４の個数平均粒径は３８．１μｍであった。１０キロエルステッドにおける飽和磁化は３２５ｅｍｕ／ｃｍ^３であり、残留磁化は０．４ｅｍｕ／ｃｍ^３であった。又、キャリア１の真比重は５．０２ｇ／ｃｍ^３であった。また、キャリア粒子表面の溶出鉄元素濃度に対するＦｅ（ＩＩ）含有量は、０．１質量％であった。
【０１４３】
＜接触帯電磁性ブラシ用磁性粒子＞
（コア粒子）水素還元Ｚｎ−Ｃｕフェライト ２００質量部
（個数平均粒径４８．０μｍ、比抵抗５×１０^６Ωｃｍ）
（コート樹脂溶液）
ポリカーボネート １．０質量部
エポキシ変性シリコーン樹脂 １．０質量部
導電性酸化チタン ４．０質量部
４フッ化エチレン樹脂粒子（０．２５μｍ） ０．２質量部
キシレン溶液 １４．０質量部
以上のコート樹脂溶液の各処方をガラスビーズをいれたペイントシェイカーで２時間分散させ、コート樹脂溶液を作製した。これを上記のコア粒子に、前述したスピラコータを用いてコートし、１５０℃で１時間乾燥させた。得られた接触帯電磁性ブラシ用磁性粒子の比抵抗は８．９×１０^６Ωｃｍ、個数平均粒径は４８．３μｍであった。１キロエルステッドにおける磁化の強さ＝２６２．１ｅｍｕ／ｃｍ^３であった（磁性粒子の真比重は５．０２ｇ／ｃｍ^３）。
【０１４４】
ここで用いた接触帯電磁性ブラシ用磁性粒子の比抵抗と個数平均粒径は、前述した現像用磁性キャリアの該特性の測定方法によった。
【０１４５】
＜実施例１＞
キャリア１を１０キロエルステッドの磁場で着磁を行い、トナー１とキャリア１を、トナー濃度８％となるように混合し、二成分系現像剤を作製した。このとき、トナーの帯電量は−３５．１μＣ／ｇであった。
【０１４６】
この二成分系現像剤を用いて、キヤノン（株）製フルカラー複写機ＣＬＣ５００の改造機で画像出し試験を行なった。この現像部周辺の模式図を図１に示し、これをもって説明する。図中、１１は感光ドラム、１２は現像スリーブ、１３は、現像スリーブ１２内に回転可能な状態で配置されたマグネットローラ、１４は現像剤を現像スリーブ１２に一定厚さに供給するための規制ブレード、１５は現像剤を現像スリーブ１２から剥がすために配置された剥離ブレード、１６は撹拌スクリュー、１７はトナーを供給するホッパーである。
【０１４７】
又、現像スリーブ１２は、感光ドラム１１に対する再近接距離が５５０μｍになるように配設され、現像剤が感光ドラム１１に対して接触する状態で現像できるように構成されている。現像スリーブ１２は外径３２ｍｍであり、内部のマグネットローラ１３は多極１０００ガウスの磁力で８極が、ほぼ均等な位置に配置されている。感光ドラム１１は、矢印方向に１６０ｍｍ／ｓｅｃで回転する。又、マグネットローラ１３は、矢印方向に２５００ｒ．ｐ．ｍで高速回転する。又、現像スリーブ１２は、マグネットローラ１３とは逆の矢印方向に１００ｍｍ／ｓｅｃで回転し、トナー１とキャリア１とを含む二成分系現像剤は、現像スリーブ１２上で転がりつつ、現像スリーブ回転方向に搬送される。
【０１４８】
なお、現像スリーブ１２は、ＣＬＣ５００の現像器内で用いられている現像スリーブ（材質：ＳＵＳ、日立金属社製、３２φ）の表面をニューマプラスター（不二製作所製）を用いてサンドブラストし、Ｒａ＝２．１μｍ，Ｓｍ：２９．７μｍのブラストスリーブ（Ｒａ／Ｓｍ＝０．０７）としたものを用いた。
【０１４９】
現像スリーブ１２には、直流電圧及び交流電圧が重畳して印加される。本実施例では、直流電圧Ｖｄｃ＝−４５０Ｖに対して、交流電圧Ｖｐｐ＝２，０００Ｖ、周波数Ｖｆ＝２，２００Ｈｚを重畳したものを現像バイアスとした。又、現像コントラストとしてＶｃｏｎｔを３５０Ｖ、カブリとりバイアスＶｂａｃｋを８０Ｖとした。
【０１５０】
接触帯電部材２１に印加する電圧としては、−５６０ＶのＤＣバイアスを用いた。
【０１５１】
なお、感光ドラムとしてはアルミニウム製のφ８０のドラム上に以下の機能層を５層もったＯＰＣ感光体を用いた。
【０１５２】
アルミ基層側から順に第１層は下引き層、第２層は正電荷注入防止層、第３層は電荷発生層、第４層は電荷輸送層であり、第５層が電荷注入層である。この電荷注入層は光硬化性のアクリル樹脂にＳｎＯ_２超微粒子、さらに接触帯電部材と感光体との接触時間を増加させて、均一な帯電を行うために４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、アンチモンをドーピングし、低抵抗化した粒径約０．０３μｍのＳｎＯ_２粒子を樹脂に対して７０質量％、さらに粒径０．２５μｍの４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。この感光ドラムの表面抵抗は１×１０^１２Ωであった。
【０１５３】
上記の現像条件で画像出しを行った。この結果、ハーフトーン再現性に非常に優れ、ベタ画像の濃度が高い優れた画像が得られた。さらに、キャリア付着による画像部、非画像部の画像の乱れやトナーカブリは認められなかった。
【０１５４】
なお、べタ黒画像を感光ドラムから紙上に転写する際のトナー転写効率を測定すると、９９．４％であり、クリーナーレスプロセスにも十分対応できるレベルであった。実際、クリーナーを取り外して１万枚の画像出し耐久を行ったところ、帯電磁気ブラシの帯電性にまったく変化はなく、帯電ゴーストなどは見られなかった。
【０１５５】
本実施例の結果を表２に示す。以下の実施例及び比較例の結果も表２に示す。
【０１５６】
＜実施例２＞
キャリア２を１０キロエルステッドの磁場で着磁を行い、トナー１とキャリア２を用いて、実施例１と同様にしてトナー濃度５％となるように混合し、二成分系現像剤を作製した。トナー帯電量は−３５．７μＣ／ｇであった。
【０１５７】
実施例１と全て同じ条件で画像出し試験を行なったところ、実施例１と同様にキャリア付着やカブリ等による画像汚れがなく、ハーフトーン再現性も問題なく、画像濃度が充分である良好な結果が得られた。トナー転写効率は９７．６％と良好なものであった。
【０１５８】
＜実施例３＞
キャリア３を１０キロエルステッドの磁場で着磁を行い、トナー２とキャリア３を用いて、実施例１と同様にしてトナー濃度５％となるように混合し、二成分系現像剤を作製した。トナー帯電量は−４１．０μＣ／ｇであった。
【０１５９】
実施例１と全て同じ条件で画像出し試験を行なったところ、実施例１と同様に画像濃度、キャリア付着やカブリ等の画像汚れがない良好な結果が得られた。特にハーフトーン再現性には優れていた。又、画像出し耐久試験の結果も良好なものであった。また、転写効率は、９９．７％であった。
【０１６０】
クリーナーを取り外して１万枚の画像出し耐久を行ったところ、実施例１と同様に良好であった。
【０１６１】
＜実施例４＞
キャリア４を１０キロエルステッドの磁場で着磁を行い、トナー１とキャリア４を用いて、実施例２と同様にしてトナー濃度５％となるように混合し、二成分系現像剤を作製した。トナー帯電量は−３１．８μＣ／ｇであった。
【０１６２】
実施例１と全て同じ条件で画像出し試験を行なったところ、実施例１と同様にキャリア付着、カブリも良好で、画像濃度が充分である良好な結果が得られた。また、転写効率は、９８．８％であった。又、画像出し耐久試験の結果も良好なものであった。
【０１６３】
＜比較例１＞
キャリア５を１０キロエルステッドの磁場で着磁を行い、トナー１とキャリア５を用いて、実施例１と同様にして二成分系現像剤を作製した。トナー帯電量は−３２．５μＣ／ｇであった。
【０１６４】
実施例１と全て同じ条件で画像出し試験を行なったところ、画像濃度は充分なレベルであったが、カブリが若干発生し、キャリア付着による汚れが発生した。また、転写効率は、９３．１％であった。又、画像出し耐久試験の結果、カブリトナーによる感光体の帯電不良が起こり、途中で止めた。
【０１６５】
＜比較例２＞
トナー１とキャリア６を用いて、実施例１と同様にして二成分系現像剤を作製した。トナー帯電量は−３２．９μＣ／ｇであった。
【０１６６】
実施例１と全て同じ条件で画像出し試験を行なったところ、キャリア付着が見られ、カブリも発生し、また、画像濃度の薄い画像しか得られなかった。現像部を観察すると、現像剤の流動性が悪くかった。また、転写効率は、９０．４％であった。又、画像出し耐久試験の結果、カブリトナーによる感光体の帯電不良が起こり、途中で止めた。
【０１６７】
実施例及び比較例で使用したトナー及び磁性キャリアの物性値を、下記の表１にまとめて示した。
【０１６８】
【表１】

【０１６９】
［評価］
実施例及び比較例で使用した表１に示した物性を有するトナー及び磁性キャリアからなる二成分系現像剤を用いて行なった画出し試験の評価は、下記の方法及び下記の基準で行なった。
【０１７０】
（１）キャリア付着：
ベタ白画像を画出しし、現像部とクリーナ部との間の感光ドラム上の部分を透明な接着テープを密着させてサンプリングし、５ｃｍ×５ｃｍ中の感光ドラム上に付着していた磁性キャリア粒子の個数をカウントし、１ｍｍ^２あたりの付着キャリアの個数を算出した。
◎：０．１個／ｍｍ^２未満
○：０．１〜０．５個／ｍｍ^２未満
△：０．５〜２．０個／ｍｍ^２未満
×：２．０個／ｍｍ^２以上
【０１７１】
（２）画像濃度：
画像濃度は、ＳＰＩフィルターを装着したマクベス社製マクベスカラーチェッカーＲＤ−１２５５を使用して、普通紙上に形成されたべタ画像の相対濃度として測定した。
◎：１．６以上
○：１．５〜１．６未満
△：１．４〜１．５未満
×：１．４未満
【０１７２】
（３）カブリ：
画出し前の普通紙の平均反射率Ｄｒ（％）を、東京電色株式会社製デンシトメータＴＣ−６ＭＣによって測定した。一方、普通紙上にベタ自画像を画出しし、次いでベタ自画像の反射率Ｄｓ（％）を測定した。カブリ（％）は、これらの測定値から、下記式によって算出し、下記の基準で評価した。
ｆｏｇ（％）＝Ｄｒ（％）−Ｄｓ（％）
◎：１．０％未満
○：１．０〜１．５未満
△：１．５〜２．０未満
×：２．０以上
【０１７３】
（４）ハーフトーンドット再現性：
画像のハーフトーン部（潜像スポット径１５μｍ）の感光ドラム上に現像されたドットを、ＣＣＤを搭載した実体顕微鏡（×１００）を用いて、パソコン上にイメージデータとして取り込んだ。ついで、このドットのピクセル面積を算出して、これを１００個積算して平均値ａと標準偏差Ｓを算出した。このドットのピクセル面積の標準偏差Ｓを平均値で割った値Ｓ／ａをドット再現性の評価値として用い、以下の基準で評価した。
◎ ：０．０５未満
○ ：０．０５〜０．１未満
△ ：０．１〜０．１５未満
△×：０．１５〜０．２未満
× ：０．２以上
【０１７４】
評価結果は、下記の表２にまとめて示した。
【０１７５】
【表２】

【０１７６】
【発明の効果】
以上、説明したように、本発明によれば、潜像担持体に帯電部材を接触させて帯電させる接触帯電装置を有する画像形成方法において、非常に高抵抗で、特有の磁気特性を有する磁性キャリアを用いて接触二成分系ＡＣ現像を行うことで、キャリア付着の発生が有効に防止されると共に、カブリのない、ハーフトーン再現性にも優れ、かつ高い画像濃度を得ることが可能な画像形成方法が提供される。
【図面の簡単な説明】
【図１】本発明の実施例において用いた二成分系現像装置の説明に用いた概略図である。
【符号の説明】
１１．感光ドラム
１２．現像スリーブ
１３．マグネットローラ
１４．規制ブレード
１５．剥離ブレード
１６．撹拌スクリュー
１７．ホッパー
２１．接触帯電部材
２２．露光装置[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming method including a contact charging device for bringing a charging member into contact with a latent image carrier and charging the latent image carrier in an electrophotographic method, an electrostatic recording method, or the like, and using a two-component developer in a developing process.
[0002]
[Prior art]
In electrophotography, an electrostatic latent image formed on a latent image carrier is developed with toner, and then transferred and fixed on transfer paper. As a developing method in this case, a two-component developing method using a two-component developer consisting of a toner and a magnetic carrier as a developer, or a one-component developing method using a one-component developer without using a magnetic carrier are currently used. Although a system and the like are known, when higher image quality and higher speed are required, a two-component developing system is suitably used.
[0003]
In the two-component developing method, a two-component developer composed of a toner and a magnetic carrier forms a spike called a developing magnetic brush on a developer carrier, and this developing magnetic brush is used in a developing process. There is known a so-called contact development in which the latent image carrier is brought into contact with the latent image carrier, and a so-called non-contact development in which development is performed without contacting the latent image carrier. Usually, when high image quality and high density are required, the former contact development is often used.
[0004]
On the other hand, a typical recent technology relating to a developer is a method of reducing the particle size of a toner and a magnetic carrier. For example, in JP-A-58-184157, in a developing process in which a two-component developer magnetic brush rubs the surface of a latent image carrier, a toner having an average particle size of 10 μm or less and a toner having an average particle size of 5 to 30 μm are used. It is stated that when a magnetic carrier is used, a sufficiently high image quality can be achieved.
[0005]
However, when the particle size of the toner is small, the charge amount increases, and the adhesion to the carrier due to van der Waals force and the like also increases. There is a problem that the concentration becomes low.
[0006]
In order to solve these problems, a developing method is used in which a two-component developer is transported to a developing unit by rotating a magnet disposed inside the developer carrier, and a certain amount of residual magnetization is used as a carrier. It is known that, when a developing brush is selected, the developing is performed while the developing magnetic brush rotates on the developer carrier, so that the developing efficiency can be increased and the image density can be increased.
[0007]
As the magnetic carrier used here, barium ferrite, strontium ferrite or the like composed of a single hard magnetic material has been used, but when used alone, the specific resistance of the carrier particles is low, and in contact development, It is used by being coated with a resin so as not to leak the bias applied from the developer carrier. However, this causes inconvenience when the coating material comes off.
[0008]
In addition, due to a demand for a reduction in the particle size of the carrier and the like, for example, as disclosed in Japanese Patent Publication No. 59-224416, a resin carrier of a magnetic material dispersion type has been developed. Further, as disclosed in Japanese Patent Application Laid-Open No. 10-268575, spherical naked coalesced particles have been proposed in order to control magnetic properties freely and to increase resistance.
[0009]
However, when the toner is small and the carrier particles are also small, the image density is high, and the specific resistance is still insufficient to sufficiently prevent the carrier from adhering, and a sufficiently satisfactory magnetic carrier has not been obtained.
[0010]
By the way, before forming an electrostatic latent image on a latent image carrier, a process called so-called primary charging for uniformly charging the entire surface of the latent image carrier is performed. So-called corona chargers using discharge have been used.
[0011]
However, in recent years, contact charging devices have been put to practical use instead. This aims at low ozone, low power, and downsizing of the apparatus, and a conductive roller or a magnetic brush roller is used as a charging member. As a charging method, in order to perform contact charging smoothly and uniformly and without being affected by environmental fluctuations, a voltage in which an AC component is superimposed is applied to a charging member as described in JP-A-63-149669. It is desirable to do.
[0012]
Even in such a contact charging device, the essential charging mechanism uses a discharge phenomenon from the charging member to the latent image carrier, so that generation of ozone is inevitable, and the voltage applied to the charging member is Is required to be at least a value equal to or higher than the desired latent image carrier surface potential. When the charging using the AC component as described above is performed, vibration or abnormal noise due to an electric field, generation of the latent image carrier There were problems such as deterioration.
[0013]
In order to solve such a problem, charging by direct injection of charge into the latent image carrier has been desired. In order to inject charges directly to the surface of the latent image carrier, a charging member having a low resistance value is used, and a long charging time is applied to charge the charged charges to the trap level of the charges existing on the surface of the latent image carrier. There is a way. However, in such a charging method, the specific resistance of the charging member is 1 × 10³On the premise that it is very low, that is, less than Ωcm, there is a problem that a large charge leak is caused to a flaw or a pinhole generated on the surface of the latent image carrier. Also, the time required for performing sufficient charging was not at a practical level.
[0014]
Therefore, Japanese Patent Application Laid-Open No. Hei 6-3921 discloses a method in which a charge injection layer is provided on the surface of a latent image carrier and charges are injected into the charge injection layer using a contact charging member. This makes it possible to solve the above-mentioned problems in the contact charging device.
[0015]
As the charging member used in the contact charging device as described above, a magnetic brush roller which can make a large contact nip with the latent image carrier and can uniformly contact the surface of the latent image carrier is particularly preferably used.
[0016]
In a contact charging device using a magnetic brush roller, it is necessary that the magnetic particles constituting the magnetic brush contact each other to form a conductive path, and the charge flowing through this conductive path charges the surface of the latent image carrier, It is charged, but when impurities are mixed in the magnetic brush, there is a problem that its charging characteristics change. For example, when a relatively large amount of toner particles or the like is mixed into the magnetic brush for some reason, such a problem may be realized. Recently, a cleaner-less process has been proposed in which the waste toner recovery portion is omitted in order to realize a reduction in the size of the entire apparatus and simplification of maintenance. The toner remaining on the magnetic brush is mixed with a high probability without being cleaned.
[0017]
Further, by using the contact two-component developing process and the AC developing bias as described above to improve the image quality, the core resistance of the iron powder carrier, ferrite carrier and the like as in the prior art can be reduced to 1 × 10 5⁹When a magnetic carrier obtained by applying a resin coat to a low-resistance core such as Ωcm or less is used as a developer, carrier adhesion and toner fogging occur, and these toners and the developing magnetic carrier are mixed into the contact charging member. In some cases, the contact charging ability became insufficient.
[0018]
Japanese Patent Application Laid-Open No. 6-222676 discloses an image forming apparatus using a contact charging process of a charged magnetic brush, in which the resistance of a magnetic carrier used for a developer is made higher than the magnetic particles used for a charged magnetic brush, and the alternating current of charging and developing is performed. Although proposals have been made to use a common voltage power supply, particularly when a contact two-component development process is used, the resistance is controlled by changing the ferrite particle coating material described in the specification, and When it is used for magnetic particles for an electromagnetic brush and a developing magnetic carrier for a two-component developer, high image quality cannot be achieved.
[0019]
For the above reasons, an image forming method which can achieve low ozone generation using a contact two-component AC developing process which is excellent in fine line reproducibility and can obtain an image with high image density has not been put to practical use. .
[0020]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming method which solves the above-mentioned problems, and in particular, provides an image forming method using a two-component developer and a contact charging process.
[0021]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming method capable of suppressing generation of ozone, preventing the occurrence of carrier adhesion, and obtaining a high-quality toner image having excellent halftone reproducibility.
[0022]
SUMMARY OF THE INVENTION It is an object of the present invention to provide an image forming method using a contact AC charging process using a contact charging magnetic brush, wherein the toner has a high transfer efficiency, has no toner fog, and can cope with a cleanerless process. To provide.
[0023]
[Means for Solving the Problems]
The present invention has a surface resistance of 1 × 10¹⁰~ 1 × 10¹⁶A charging step of charging an electrostatic latent image carrier having a charge injection layer of Ω by a magnetic brush composed of magnetic particles;
A latent image forming step of forming an electrostatic latent image on the electrostatic latent image carrier having the charged charge injection layer by exposure;
A developing step of developing the electrostatic latent image formed on the electrostatic latent image carrier having the charge injection layer with the toner of a two-component developer having a magnetic carrier and a toner;
In the image forming method having
The magnetic carrier contains at least a binder resin and magnetic metal oxide particles, and the specific resistance of the magnetic carrier particles is 5.0 × 10 5 when a voltage of 25 V to 500 V is applied.^ThirteenΩcm or more,
The saturation magnetization of the magnetic carrier particles at 10 kOe is 100 to 300 emu / cm.³And the residual magnetization is 25 to 150 emu / cm.³And
The true specific gravity of the magnetic carrier particles is 3.0 to 4.9 g / cm.³And
The Fe (II) content with respect to the concentration of the eluted iron element on the surface of the magnetic carrier particles is 0.001 to 5.0% by mass,
The present invention relates to an image forming method satisfying the following expression.

R: Number average particle size of magnetic carrier particles (μm)
M: saturation magnetization of magnetic carrier particles (emu / cm³)
[0024]
In the developing method of the present invention, a so-called contact two-component system is used, in which a two-component developer is used as a developer, and a developer magnetic brush performs development while applying an alternating electric field while rubbing and contacting the latent image carrier. It is optimal that the AC developing is performed and the developer carrier has a cylindrical non-magnetic sleeve and a magnet included in the non-magnetic sleeve, and the magnet is configured to be driven to rotate. It is. This is to obtain a high quality toner image having excellent halftone reproducibility as described above.
[0025]
Further, the surface resistance of the latent image carrier is 1 × 10¹⁰~ 1 × 10¹⁶Occurrence of ozone can be suppressed by providing a charge injection layer of Ω and performing primary charging with a member that is in contact with the charge injection layer. In particular, the use of a charged magnetic brush using magnetic particles enables more uniform charging.
[0026]
In addition, the magnetic force of the magnetic carrier constituting the two-component developer is controlled by mixing a soft magnetic material and a hard magnetic material, and by substantially increasing the resistance of the developed magnetic carrier, toner fog and carrier adhesion are improved. And a high-quality image with good halftone reproducibility can be obtained.
[0027]
In addition, by using a toner manufactured by a polymerization method in the image forming apparatus having the above-described configuration, a cleaner-less image forming method can be achieved with toner having high transfer efficiency and no fog. .
[0028]
Hereinafter, the present invention will be described in more detail by way of preferred embodiments of the present invention.
[0029]
As a result of detailed studies by the present inventors, the surface resistance of the charge injection layer of the latent image carrier in the present invention was 1 × 10¹⁰~ 1 × 10¹⁶Ω, more preferably 1 × 10¹²~ 1 × 10^FifteenIt turned out that it is preferable to be in the range of Ω. The surface resistance of the charge injection layer is 1 × 10¹⁰If it is less than Ω, the charge injected from the contact charging member is not retained on the surface of the charge injection layer, and as a result, a phenomenon called image deletion may occur in the electrophotographic process of the reversal development system. This was particularly common under high humidity. The resistance of the surface of the charge injection layer is 1 × 10¹⁶If it exceeds Ω, the charge is not sufficiently injected, and a so-called charged positive coast may occur in which the toner unnecessarily rides on the poorly charged area of the latent image carrier.
[0030]
As described above, the surface resistance of the charge injection layer of the latent image carrier is 1 × 10¹⁰Ω ~ 1 × 10¹⁶Even if it is within the range of Ω, charging is not performed properly unless the specific resistance of the injection charging member is within an appropriate range. This needs to be adjusted by the configuration of the injection charging member. For example, when a charging brush roller made of magnetic particles is used, 1 × 10⁵~ 1 × 10⁸A charging brush roller made of a magnetic material having a specific resistance of Ωcm shows good charging properties.
[0031]
As the magnetic material constituting the charged magnetic brush roller, for example, a magnetic metal such as iron, cobalt, and nickel, or a compound thereof can be used. It is necessary to coat these with an appropriate coat resin or to perform an oxidation treatment, a reduction treatment, or the like to adjust the specific resistance to the above. For example, hydrogen-reduced Zn-Cu ferrite, oxidized magnetite, or the like can be used. Binder-type magnetic particles in which a magnetic metal oxide and conductive fine particles are dispersed in a binder resin, or particles obtained by coating the binder-type magnetic particles with an appropriate coat resin can also be used.
[0032]
As the charge injection layer of the latent image carrier, a material in which conductive fine particles are dispersed in an insulating and translucent binder resin is preferably used. By contacting the charge injection layer with a charged magnetic brush to which a voltage has been applied, conductive particles are present as if there were countless independent floating electrodes with respect to the conductive substrate of the latent image carrier. Can be expected to charge the capacitor formed by. Therefore, it was also recognized that the voltage applied to the contact charging member and the surface potential of the latent image carrier converged to the same value, and the effect of applying only a minimum voltage was recognized.
[0033]
As described above, when the contact two-component developing process and the AC developing bias are used to achieve high image quality, the surface resistance of the charge injection layer is 1 × 10¹⁰Ω ~ 1 × 10¹⁶When using a latent image carrier in the range of Ω, if a magnetic carrier obtained by applying a resin coat to a conventional iron powder carrier or ferrite is used as a developer, carrier adhesion and toner fogging are remarkably generated. Was.
[0034]
This is because when a latent image carrier having a relatively low specific resistance on the surface and a developing magnetic carrier such as a conventional iron powder carrier or ferrite carrier having a low specific resistance are used together, the latent image carrier on the latent image carrier is used. Is leaked through the developing magnetic carrier particles that are in contact with and rubbing, and the potential is changed so as to approach the developing bias potential. As a result, the fog removing potential decreases,
Generates toner fog. In addition, it was found that the developing bias was injected into the carrier, which caused carrier adhesion to occur at the same time.
[0035]
Therefore, if a magnetic carrier having a specific magnetic property is used as the carrier, and the magnetic carrier particles having a sufficiently high specific resistance and controlling the Fe (II) content with respect to the concentration of the eluted iron element on the surface of the magnetic carrier particles are used, Sufficient image density is obtained, no carrier adhesion occurs,
In addition, the inventors have found that the characteristics can be maintained in a durable manner, and have reached the present invention.
[0036]
Further, the magnetic carrier having the above-mentioned specific magnetic characteristics is a spherical resin carrier obtained by a polymerization method using a thermosetting binder resin, and two or more magnetic metal oxides having different magnetic characteristics. It was also found that it is effective to use a combination of these and use a magnetic material-dispersed resin carrier in which these are dispersed.
[0037]
Hereinafter, these will be described in more detail.
[0038]
The present inventors have studied the magnetic carrier in detail, and as a result, when the toner particle size is reduced to 1 to 10 μm, it is preferable to use a magnetic carrier having a number average particle size of 5 to 30 μm. It turned out to be. That is, in this case, when a magnetic carrier having a number average particle size smaller than 5 μm is used, the developing is performed while the developing magnetic brush is in contact with the latent image carrier. Even if a magnetic carrier having the magnetic characteristics employed in the present invention is used, carrier adhesion cannot be avoided. On the other hand, when a magnetic carrier having a number average particle diameter larger than 30 μm is used, the surface area of the magnetic carrier becomes small, so that the carrier surface cannot be maintained at a preferable toner concentration. Or a sufficient image density may not be obtained.
[0039]
Further, as described above, when the toner having the small particle diameter as described above is used, the magnet disposed inside the developer carrier is driven to rotate to convey the two-component developer to the developing unit. It is known that a sufficient image density can be obtained by using the developing method having the above configuration, but as a result of further studies by the present inventors, at this time, a magnetic carrier having appropriately controlled magnetic characteristics was used. Thus, it has been found that the carrier can effectively prevent the occurrence of carrier adhesion while maintaining excellent image reproducibility and high image density, and can maintain its performance in a durable manner. As the magnetic characteristics of the carrier, specifically, the saturation magnetization in a magnetic field of 10 kOe is 100 to 300 emu / cm.³And the residual magnetization is 15 to 150 emu / cm.³It was also found that the particle diameter of the magnetic carrier and the saturation magnetization of the carrier were closely related. When the particle diameter of the magnetic carrier is 5 to 30 μm, by using a carrier having a saturation magnetization in a region satisfying the following relational expression, the carrier adhesion, the reproducibility of halftone image quality, and the image density are improved in a well-balanced manner. Became possible.
[0040]

R: Number average particle size of magnetic carrier particles (μm)
M: saturation magnetization of magnetic carrier particles (emu / cm³)
[0041]
When −6.0R + 300> M is satisfied, it will be difficult to prevent carrier adhesion even if the resistance of the carrier particles is increased, as will be described later. When M> −3.0R + 350, the developing magnetic brush becomes coarse, the halftone reproducibility is poor, and the toner deterioration is promoted.
[0042]
The residual magnetization of the magnetic carrier used was 15 emu / cm.³If it is lower than 2, the two-component developer cannot be rolled well on the developer carrier, and the intended improvement in image density, which is the intended object of the present invention, cannot be achieved. Residual magnetization of carrier is 150 emu / cm³If it is higher than the magnetic field of the developer carrying member, aggregation of the carriers due to magnetization is large even at a distance from the magnetic field of the developer carrying member.
[0043]
In the magnetic carrier of the present invention, the specific resistance of the carrier particles is important together with the magnetic characteristics. That is, 5.0 × 10 when a voltage of 25 to 500 V is applied.^ThirteenIt has also been found that it is essential to have a high specific resistance of Ω · cm or more. 5.0 × 10 at any voltage application^ThirteenCarriers exhibiting a resistivity lower than Ωcm cause the developing bias to lower the latent image potential via the carrier, causing image deterioration, fogging, and the carrier itself being injected with electric charge. Carrier adhesion may occur.
[0044]
According to further studies by the present inventors, in order to efficiently obtain a magnetic carrier having the above-described specific magnetic characteristics and capable of easily achieving the intended object of the present invention. Uses a so-called magnetic material-dispersed resin carrier in which magnetic metal oxide particles containing at least a magnetic material are dispersed in a binder resin, and as a constituent material, a thermosetting binder resin and two types having different magnetic properties. It has been found that it is effective to use at least the above-mentioned magnetic metal oxide and produce it by a polymerization method.
[0045]
As a combination of the two or more magnetic metal oxides, a so-called soft magnetic and relatively high saturation magnetization magnetic metal oxide particle and a so-called hard magnetic magnetic metal having a large residual magnetization are used. It has been found that it is effective to use a mixture of oxide particles.
[0046]
Furthermore, it has been found that it is effective to use a thermosetting resin such as a phenol resin or a melamine resin as a binder resin for dispersing these magnetic substances, and to use a magnetic carrier produced by a polymerization method. That is, since such a magnetic carrier is hard, has excellent strength, and is spherical, the use of such a magnetic carrier effectively prevents carrier destruction due to a magnetic shear or the like in a developing device and causes carrier adhesion. Is suppressed, and because the shape is spherical, it is easy to roll on the developer carrying member, and it is possible to supply the toner to the developing section in a good state. A certain improvement in image density can be further achieved.
[0047]
Further, by providing a layer containing non-magnetic metal oxide particles near the surface, the above-described resistance increase of the magnetic carrier can be measured. As a measure for increasing the resistance, it has been found that it is necessary in the present invention that the Fe (II) content relative to the concentration of the eluted iron element on the surface of the magnetic carrier particles is 0.001 to 5.0% by mass. .
[0048]
Further, by coating the magnetic carrier with a silicone resin layer, the magnetic carrier can be more excellent in fluidity, excellent in chargeability, and further enhanced in strength.
[0049]
The toner that can be suitably used in the present invention preferably has a weight average particle diameter of 1 to 10 μm and a coefficient of variation on a number basis of 0 to 35%.
[0050]
That is, it was found that the toner having a small particle size was required to have a sharp particle size distribution in order to favorably charge the carrier of the present invention. Furthermore, in order to enhance the fluidity and improve the chargeability, it is possible to use a small particle size toner containing inorganic fine particles having a number average particle size of 0.2 μm or less, organic fine particles having a particle size of 0.2 μm or less, or a mixture thereof. preferable.
[0051]
Further, it is preferable that the whole or a part of the toner is formed by a polymerization method, and the shape factor SF-1 of the toner is from 100 to 130, in order to further enhance fluidity and to achieve high image quality. In order to efficiently obtain a toner having such a small particle diameter, it is preferable to manufacture the toner using a polymerization method such as suspension polymerization, emulsion polymerization, or dispersion polymerization.
[0052]
Hereinafter, the magnetic carrier of the above-described embodiment which can be suitably used in the image forming method of the present invention will be described.
[0053]
As the metal oxide that can be used in this case, soft magnetic particles such as MO.Fe₂O₃Or MFe₂O₄Magnetite, soft ferrite, etc. represented by the following general formula can be preferably used. M in the formula corresponds to a divalent or monovalent metal ion, for example, Mn, Fe, Ni, Co, Cu, Mg, Zn, Cd, Li, and the like. Can be used as Examples of such materials include magnetite, γ-iron oxide, Mn-Zn-based ferrite, Ni-Zn-based ferrite, Mn-Mg-based ferrite, Ca-Mg-based ferrite, Li-based ferrite, and Cu-Zn-based ferrite. Iron-based magnetic oxides.
[0054]
Hard magnetic metal oxide particles used together with the above soft magnetic metal oxide particles include, for example, BaFe₁₂O₁₉, SrFe₁₂O₁₉And barium ferrite and strontium ferrite. Further, in order to adjust magnetic properties, electric resistance, etc., in addition to the above metal oxides, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Metals such as Sr, Y, Zr, Nb, Mo, Cd, Sn, Ba, and Pb may be used alone or in combination with a non-magnetic metal oxide.
[0055]
The soft ferrite mentioned above is a soft magnetic ferrite having a coercive force Hc of 100 Oe or less.
[0056]
When the above metal oxide is dispersed in a resin to form a core, the number average particle size of the metal oxide exhibiting magnetism varies depending on the carrier particle size, but those having a particle size of up to 0.02 μm can be preferably used. . When two or more kinds of metal oxides are used in a dispersed state, those having a number average particle diameter of from 0.02 to 2 μm can be used for the metal oxide exhibiting magnetism. Those having a number average particle size of 0.05 to 5 μm can be used. In this case, the magnetic particles (particle size r_a) To the other non-magnetic metal oxide (particle size r_b) Particle size ratio r_b/ R_aIs preferably more than 1 time, more preferably more than 1 time and 5 times or less. When the ratio is 1.0 or less, magnetic metal oxide particles having a low specific resistance are likely to be exposed on the surface, and the resistance of the carrier core cannot be sufficiently increased, so that the effect of preventing carrier adhesion of the present invention is hardly obtained. Become. On the other hand, when the ratio exceeds 5.0 times, the incorporation of the metal oxide particles into the resin may not be successful, and the strength of the carrier may be reduced, and the carrier may be easily broken.
[0057]
Examples of the non-magnetic oxide to be present near the carrier particle surface include, for example, Al₂O₃, SiO₂, CaO, TiO₂, V₂O₅, CrO₂, MnO₂, F₂O₃, CoO, NiO, CuO, ZnO, SrO, Y₂O₃, ZrO₂A system or the like can be used.
[0058]
The specific resistance of the metal oxide used as dispersed in the resin is as follows.³Ωcm or more can be used. In particular, when two or more kinds of metal oxides are mixed and used, particles exhibiting magnetism are 1 × 10³It is necessary to use a non-magnetic metal oxide particle having a specific resistance higher than that of the magnetic particle. Preferably, the specific resistance of the other nonmagnetic metal oxide used in the present invention is 1 × 10⁸Ωcm or more is preferably used. The specific resistance of the magnetic particles is 1 × 10³If it is less than Ωcm, a desired carrier specific resistance cannot be obtained even if the content of the dispersed metal oxide is reduced. When two or more metal oxides are dispersed, the specific resistance of the nonmagnetic metal oxide having a large particle size is 1 × 10⁸If it is less than Ωcm,
The specific resistance of the carrier core cannot be sufficiently increased, and it is difficult to obtain the effects of the present invention.
[0059]
The total content of the metal oxide in the metal oxide-dispersed resin core of the present invention is 50% by mass to 99% by mass. When the amount of the metal oxide is less than 50% by mass, the chargeability becomes unstable, and the carrier is charged particularly in a low-temperature and low-humidity environment, and the residual charge tends to remain. It easily adheres to the carrier surface. On the other hand, if the content exceeds 99% by mass, the strength of the carrier decreases, and problems such as cracking of the carrier due to durability tend to occur.
[0060]
The metal oxide contained in the metal oxide-dispersed resin core used in the present invention is preferably subjected to lipophilic treatment. When the lipophilic metal oxide is dispersed in a binder resin to form core particles, it can be uniformly and densely incorporated into the binder resin. Particularly, when the core particles are formed by a polymerization method, it is important to obtain spherical particles having a smooth surface and to sharpen the particle size distribution.
[0061]
In the lipophilic treatment, the metal oxide is treated with a coupling agent such as a silane coupling agent or a titanate coupling agent, or the surface is made hydrophilic by dispersing the metal oxide in an aqueous solvent containing a surfactant. There is a method such as oiling.
[0062]
As the silane-based coupling agent here, those having a hydrophobic group, an amino group or an epoxy group can be used. Examples of the silane coupling agent having a hydrophobic group include vinyltrichlorosilane, vinyltriethoxysilane, and vinyltris (β-methoxy) silane. Examples of a silane coupling agent having an amino group include γ-aminopropylethoxysilane, N-β (aminoethyl) -γ-aminopropyltrimethoxysilane, and N-β (aminoethyl) -γ-aminopropylmethyldimethoxysilane. , N-phenyl-γ-aminopropyltrimethoxysilane and the like. Examples of the silane coupling agent having an epoxy group include γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltriethoxysilane, β- (3,4-epoxycyclohexyl) trimethoxysilane and the like. .
[0063]
Examples of the titanate-based coupling agent include isopropyl triisostearoyl titanate, isopropyl tritodecylbenzenesulfonyl titanate, and isopropyl tris (dioctyl pyrophosphate) titanate.
[0064]
As the surfactant, a commercially available surfactant can be used as it is.
[0065]
As a method for producing the above-described magnetic carrier of the present invention, a composition containing at least a polymerizable monomer and two or more magnetic metal oxides is mixed and granulated, and the monomer is polymerized. There is a way to get it. As the polymerizable monomer used for polymerization, a vinyl monomer which is a thermosetting resin raw material such as a phenol resin or a melamine resin described above, such as a phenol resin, phenols and aldehydes, and a urea resin. In the case of urea and aldehydes and melamine resin, melamine and aldehydes, and other bisphenols and epichlorohydrin, which are starting materials for epoxy resins, are used. For example, as a specific method for producing a magnetic carrier using a curable phenol resin, in an aqueous medium, phenols and aldehydes that are polymerizable monomers, in the presence of a basic catalyst, as described above. A magnetic metal oxide, preferably a lipophilized magnetic metal oxide, is charged and a monomer monomer is polymerized to directly obtain a magnetic material-dispersed spherical resin carrier.
[0066]
The magnetic carrier of the present invention is preferably one whose surface is further coated with an appropriate coat resin in accordance with the charge amount of the toner used together with the carrier.
[0067]
The coating resin used at this time is preferably an insulating resin. In this case, the insulating resin that can be used may be a thermoplastic resin or a thermosetting resin.
[0068]
Specifically, for example, thermoplastic resins include polystyrene, acrylic resins such as polymethyl methacrylate and styrene-acrylic acid copolymer, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, and polyvinyl chloride. , Polyvinyl acetate, polyvinylidene fluoride resin, fluorocarbon resin, half-lorocarbon resin, solvent-soluble half-lorocarbon resin, polyvinyl alcohol, polyvinyl acetal, polyvinylpyrrolidone, petroleum resin, cellulose, cellulose acetate, cellulose nitrate, methylcellulose, hydroxymethylcellulose, hydroxymethylcellulose , Cellulose derivatives such as hydroxypropyl cellulose, novolak resin, low molecular weight polyethylene, saturated alkyl polyester resin, polyethylene terephthalate Polybutylene terephthalate, polyarylate and said aromatic polyester resins, polyamide resins, polyacetal resins, polycarbonate resins, polyethersulfone resins, polysulfone resins, polyphenylene sulfide resins, polyether ketone resins.
[0069]
As the thermosetting resin, specifically, for example, a phenol resin, a modified phenol resin, a maleic resin, an alkyd resin, an epoxy resin, an acrylic resin, or a mixture of maleic anhydride, terephthalic acid, and a polyhydric alcohol Unsaturated polyester obtained by condensation, urea resin, melamine resin, urea-melamine resin, xylene resin, toluene resin, guanamine resin, melamine-guanatemine resin, acetoguanamine resin, gliptal resin, furan resin, silicone resin, polyimide, polyamideimide Resins, polyetherimide resins, polyurethane resins, and the like can be given.
[0070]
The above-mentioned resins can be used alone or in combination. It is also possible to mix and cure a curing agent or the like with a thermoplastic resin before use.
[0071]
A particularly preferred embodiment is a silicone-based cured resin. In order to control the charge amount, it is more preferable to use a mixture of a silane compound containing an amino group and the like.
[0072]
Further, the magnetic carrier of the present invention has a true specific gravity of 3.0 to 4.9 g / cm.³When it is, it can be used suitably. That is, the true specific gravity is 3.0 g / cm.³The magnetic carrier having a value of less than substantially means a carrier having a high resin content such that the ratio of the resin to the carrier weight is 50% or more, and may cause a problem in strength. On the other hand, the true specific gravity is 4.9 g / cm³If it is larger, it depends on the magnetic properties of the carrier, but the share given to the toner in the developing unit tends to be large, and there is a possibility that the toner will be deteriorated at the time of durability, and the binder component will be insufficient and the strength will decrease. In some cases.
[0073]
In the image forming method of the present invention, the two-component developer is carried on a developer carrier, and is conveyed to a developing section. In the developing section, a magnetic brush of the two-component developer is provided on the developer carrier. In the step of developing the electrostatic latent image formed on the latent image carrier by contacting the magnetic brush with the latent image carrier, the developer carrier includes a cylindrical non-magnetic sleeve. And a magnet contained in the non-magnetic sleeve, and the magnet is required to be rotationally driven.
[0074]
That is, the magnetic carrier in the present invention is used after being magnetized. At that time, a magnet is provided in a non-magnetic sleeve, which is a developer carrier, and rotates at a high speed, so that the developer is transported to the developing unit.
[0075]
A known method can be used to magnetize the magnetic carrier of the present invention. Preferably, it is preferably magnetized and used in a magnetic field three times or more the coercive force.
[0076]
In the contact two-component AC developing system in the image forming method of the present invention, the alternating electric field applied to the developer magnetic brush is preferably 500 Hz to 5000 Hz. When the alternating electric field to be applied is less than 500 Hz, no matter how substantially the resistance of the developed magnetic carrier as in the present invention, the charge is injected into the latent image carrier through the developed magnetic carrier, and the carrier adheres. There was a case. Further, when the applied alternating electric field exceeds 5000 Hz, the toner cannot follow the electric field and the image quality is liable to be deteriorated.
[0077]
As the alternating electric field to be applied, a conventional sine wave, triangular wave or rectangular wave can be used, but an alternating electric field whose waveform is appropriately controlled can also be used. For example, a first voltage that directs toner from the latent image carrier to the developer carrier, a second voltage that directs toner from the developer carrier to the latent image carrier, and a voltage between the first voltage and the second voltage An alternating electric field that forms a waveform pattern with the third voltage can be used. In such a case, the frequency is within the range of the frequency of the alternating electric field in the present invention for one cycle of the waveform repetition pattern, that is, It is preferable that the frequency be 500 Hz to 5000 Hz.
[0078]
The toner used in the image forming method of the present invention preferably has a weight average particle size in a range of 1 to 10 μm. If the toner particle size exceeds 10 μm, one particle for developing the latent image becomes large, so that a high-definition toner image, which is the object of the present invention, cannot be obtained.
[0079]
By the way, it is possible to combine a cleaner-less process with the image forming method of the present invention. However, as described above, when a magnetic brush roller is used for the contact charging member and the cleaner-less process is combined therewith, the magnetic brush is used. There is a problem that when toner is mixed in the toner, the charging characteristics thereof change.
[0080]
In order to avoid such a problem, when a cleanerless process is combined with the image forming method of the present invention, a toner having a transfer efficiency of 95% or more is essential, and more preferably, a toner having a transfer efficiency of 98% or more is used. Is good.
[0081]
The transfer efficiency is determined by calculating the weight of the transferred toner per unit area (T1) and the weight of the toner remaining on the latent image carrier without transfer (T2) after the solid black image is developed and then transferred onto paper. Measure and use the following formula
Transfer efficiency (%) = 100 × T1 / (T1 + T2)
Was calculated by the following formula.
[0082]
For this reason, when a cleanerless process is combined with the image forming method of the present invention, it is preferable that a part or all of the toner is manufactured by a polymerization method. It is preferable that an appropriate external additive is present around the toner. The toner produced by the polymerization method generally has a high sphericity, and is therefore placed on the latent image carrier with a small contact area, so that the transfer efficiency is high.
[0083]
Further, the external additive plays a role of a spacer between the latent image carrier and the toner particles, and can improve the transferability of the toner. Further, since the sphericity is high, the frictional charging of the set toner becomes good, and the toner fog due to poor charging is also eliminated, so that it is possible to prevent the fog toner from being transferred and being mixed into the contact charging magnetic brush.
[0084]
As the external additive of the toner, a conventional external additive can be used, and inorganic fine particles or organic fine particles, or a mixture thereof can be used. These external additives have a specific surface area of 100 m by the BET method.²/ G or more. Specific surface area is 100m²If it is less than / g, the fluidity of the toner is lost, and the transferability of the toner cannot be sufficiently improved.
[0085]
Further, in the image forming method of the present invention, the developer carrying member has a surface shape.
0.2 μm ≦ center line average roughness (Ra) ≦ 5.0 μm
10 μm ≦ average interval of unevenness (Sm) ≦ 80 μm
0.05 ≦ Ra / Sm ≦ 0.5
It is preferable to satisfy the above conditions.
[0086]
Ra and Sm are values defined by JIS-B0601 and ISO468, which define the average roughness of the center line and the average interval of the unevenness, and are obtained by the following formulas.
[0087]
(Equation 1)

[0088]
When Ra is less than 0.2 μm, the developer transportability is insufficient, so that image unevenness and image density unevenness due to durability are likely to occur. When Ra exceeds 5 μm, although the developer transportability is excellent, the regulating force in the developer transporting amount regulating section such as a blade becomes too large, so that the external additives are deteriorated by rubbing and the image quality at the endurance is deteriorated. Decreases.
[0089]
If Sm is larger than 80 μm, it becomes difficult to hold the developer on the developer carrying member, so that the image density is lowered. Although the cause of this Sm is unknown in detail, since the sliding with the developer carrier occurs at the transport amount regulating portion of the developer carrier, the developer becomes dense when the distance between the irregularities is too large. It is considered that the force acts as a mass packed in the developer, and the force exceeds the holding force between the developer carrier and the developer. When Sm is less than 10 μm, many of the irregularities on the surface of the carrier become smaller than the average particle diameter of the developer, so that the particle size selectivity of the developer entering the concave portion is generated, and fusion by the developer fine powder component is easily caused. . It is also difficult in terms of manufacturing.
[0090]
Further, from the above viewpoint, the slope of the convex / concave (Δf (Ra / Sm)) obtained from the height of the convex portion on the developer carrier and the interval between the concave and convex portions is an important cause in the present invention. In the present invention
0.05 ≦ Ra / Sm ≦ 0.5
And more preferably 0.07 or more and 0.3 or less.
[0091]
If Ra / Sm is less than 0.05, the developer holding force on the developer carrying member is weak, so that the developer is not easily held on the developer carrying member. As a result, image unevenness occurs. When Ra / Sm is more than 0.5, the developer that has entered the concave portion on the surface of the developer carrying member becomes difficult to circulate with other developers, so that the developer is fused.
[0092]
By further processing several grooves (so-called knurls) in the length direction of the developer carrying member, it becomes easy to uniformly coat the developer carrying member with even more excellent developer.
[0093]
The measurement of Ra and Sm in the present invention was performed using a contact type surface roughness measuring instrument SE-3300 (manufactured by Kosaka Laboratories) in accordance with JIS-B0601.
[0094]
As a method for producing the developer carrier having a predetermined surface roughness of the present invention, for example, a sand blast method using irregular and regular particles as abrasive grains, sand paper to form irregularities in the sleeve circumferential direction. A sandpaper method of rubbing the sleeve surface in the axial direction, a method of chemical treatment, a method of forming a resin convex portion after coating with an elastic resin, and the like can be used.
[0095]
Hereinafter, the measurement method used in the present invention will be described.
[0096]
The particle size of the toner particles used in the present invention is measured within a range of 0.4 μm to 60 μm using a laser scan type particle size distribution analyzer (CIS-100 GALAI). A sample was prepared by adding 0.5 ml of a toner to a solution obtained by adding 0.2 ml of a surfactant (alkylbenzenesulfonate) to 100 ml of water, dispersing the mixture with an ultrasonic disperser for 2 minutes, and then placing the mixture in a cubic cell containing a magnetic stirrer. Add about 80% of water, and add one or two drops of the sample ultrasonically dispersed therein with a pipette. The weight average particle diameter, number average particle diameter Dn, and S.P. D. Based on (standard deviation), the weight average particle diameter and the coefficient of variation are determined.
[0097]
Coefficient of variation (%) = S. D. / Dn × 100
[0098]
Regarding the particle size of the magnetic carrier, 300 or more magnetic carrier particles having a particle size of 0.1 μm or more were randomly extracted by a scanning electron microscope (100 to 5,000 times), and an image processing analyzer manufactured by Nireco Co., Ltd. The analysis was performed using Luze × 3, and the number average horizontal Feret diameter was defined as the number average particle diameter of the carrier.
[0099]
The magnetic characteristics of the magnetic carrier were measured using an oscillating magnetic field type magnetic characteristics automatic recording device BHV-30 manufactured by Riken Denshi Co., Ltd. The magnetic characteristic value of the carrier powder was determined by creating an external magnetic field of 10 kOe, and determining the saturation magnetization and the residual magnetization when returning to 0 Oe therefrom. The measurement sample of the magnetic carrier is prepared in a state of being packed in a cylindrical plastic container so as to be sufficiently dense. In this state, the magnetization moment is measured, and the actual weight of the sample filled above is measured to determine the magnetization intensity (emu / g). Next, the true specific gravity of the carrier particles is determined by a dry automatic densimeter Acupic 1330 (manufactured by Shimadzu Corporation), and the magnetization intensity (emu / g) is multiplied by the true specific gravity to obtain a unit defined in the present invention. Magnetization intensity per volume (emu / cm³).
[0100]
In the measurement of the specific resistance of the magnetic carrier in the present invention, in the present invention, the Fe (II) content with respect to the concentration of the dissolved iron element on the surface of the magnetic carrier particles can be determined by the following method.
[0101]
Pour 31 deionized water into beaker 51 and warm to a water temperature of 45-50 ° C. 400 ml of deionized water and 25 g of magnetic carrier particles are mixed to form a slurry, and all are added to a 51 beaker while being washed with 805 ml of deionized water. Next, while maintaining the solution temperature in the first 51 beaker at 50 ° C. and the stirring speed at 200 rpm, 695 ml of special grade sulfuric acid is added into the first 51 beaker to start dissolution. One hour after the start of dissolution, 20 ml of the solution is sampled and filtered through a 0.1 μm membrane filter to collect the filtrate.
[0102]
10 ml of the filtrate is weighed, and the dissolved concentration of elemental iron is quantified by plasma emission spectroscopy (ICP).
[0103]
On the other hand, 100 ml of ion-exchanged water is added to 10 ml of the filtrate of the solution, and titration is performed using a 0.1 N aqueous solution of KMnO4. In parallel, a blank test is performed, and the Fe (II) content with respect to the concentration of the eluted iron element on the surface of the magnetic carrier particles can be determined by the following equation.
[0104]
(Equation 2)

[0105]
The method for measuring the triboelectric charge used in the present invention is described below. The toner and the carrier are mixed so as to have a predetermined mixing ratio, and mixed for 120 seconds with a evening bra mixer. This developer is placed in a metal container equipped with a 635-mesh conductive screen at the bottom, and is suctioned by a suction machine. The amount of frictional charge is determined based on the weight difference before and after suction and the potential accumulated in a condenser connected to the container. Ask. At this time, the suction pressure is set to 250 mmHg. With this method, the triboelectric charge amount is calculated using the following equation.
Q (μC / g) = (C × V) × (W₁-W₂)^-1
(W in the formula₁Is the weight before suction and W₂Is the weight after suction, C is the capacity of the condenser, and V is the potential stored in the condenser. )
[0106]
A method for measuring the surface resistance of the electrostatic latent image carrier used in the present invention will be described. A comb-shaped electrode having an effective electrode length of 2 cm and an inter-electrode distance of 120 μm is gold-deposited on the surface of the latent image carrier, and is measured by applying a voltage of 100 V with a resistance measuring device (4140BpAMATER manufactured by Hewlett-Packard Company).
[0107]
【Example】
Hereinafter, examples of the present invention will be specifically described, but the present invention is not limited thereto.
[0108]
(Manufacture of toner)
[Toner 1]
Propoxylated bisphenol and fumaric acid
100 parts by mass of polyester resin obtained by condensation
C. I. Pigment Blue 15:35 5 parts by mass
Chromium complex salt of di-tert-butylsalicylic acid 4 parts by mass
These were mixed by a fixed tank type dry mixer, and melt kneading was performed by a twin screw extruder while connecting the vent port to a suction pump and sucking.
[0109]
The melt-kneaded product was crushed by a hammer mill to obtain a crushed toner composition having a 1 mm mesh pass. Further, after crushing the coarsely crushed product by a mechanical crusher to a weight average diameter of 20 to 30 μm, crushing by a jet mill utilizing collision between particles in a swirling flow, and then by a multi-stage classifier. Classification was performed to obtain cyan colored particles.
[0110]
The specific surface area by the BET method was 200 m with respect to 100 parts by mass of the toner composition.²/ G of hydrophobic titanium oxide was externally added by 1.8 parts by mass to obtain a toner 1. The obtained particles had a weight average particle size of 4.8 μm. The coefficient of variation of the number distribution was 28%.
[0111]
[Toner 2]
0.1M-Na in 710 parts by mass of ion-exchanged water₃PO₄After 450 parts by mass of the aqueous solution was charged and heated to 60 ° C., the mixture was stirred at 12,000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo). 1.0M-CaCl₂75 parts by mass of an aqueous solution is gradually added, and Ca in a uniformly and finely dispersed state is₃(PO₄)₂An aqueous medium containing was prepared.
[0112]
Styrene 160 parts by mass
35 parts by mass of n-butyl acrylate
C. I. Pigment Blue 15: 3 15 parts by mass
Aluminum complex salt of di-tert-butylsalicylic acid 15 parts by mass
Saturated polyester (acid value 14, peak molecular weight; 8000) 10 parts by mass
Ester wax (melting point 70 ° C) 50 parts by mass
[0113]
On the other hand, the above materials were mixed and heated to 60 ° C., and were uniformly dissolved and dispersed at 12,000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo). In this, 10 parts by mass of a polymerization initiator 2,2'-azobis (2,4-dimethylvaleronitrile) was dissolved to prepare a composition containing a polymerizable monomer.
[0114]
Next, the composition containing the obtained polymerizable monomer is put into the aqueous medium prepared in advance as described above, and the mixture is mixed with a TK homomixer at 10,000 rpm for 10 minutes under an N2 atmosphere at 60 ° C. With stirring, the composition was granulated. Thereafter, while stirring with a paddle stirring blade, the temperature was raised to 80 ° C., and the reaction was performed for 10 hours. After the completion of the polymerization reaction, the remaining monomers were distilled off under reduced pressure. After cooling, hydrochloric acid was added to dissolve the calcium phosphate, followed by filtration, washing with water and drying to obtain cyan colored suspension particles.
[0115]
Thereafter, classification was performed twice using a multi-stage classifier. The specific surface area by the BET method is 200 m with respect to 100 parts by mass of the colored particles.²/ G of hydrophobic titanium oxide was externally added by 3.5 parts by mass to obtain a toner 2 produced by a polymerization method. The obtained particles had a weight average particle size of 3.1 μm. The coefficient of variation of the number distribution was 18%.
[0116]
[Toner 3]
Cyan colored particles were produced in the same manner as in Toner 1 except that the classification condition of Toner 1 by a multi-segment classifier was changed. The specific surface area by the BET method is 200 m with respect to 100 parts by mass of the cyan colored particles.²/ G of hydrophobic titanium oxide was externally added to obtain a toner 3 manufactured by a pulverization method. The weight average particle size of the obtained particles was 5.2 μm. The coefficient of variation of the number distribution was 37%.
[0117]
(Manufacture of carrier)
[Carrier 1]
First, 4.8% by mass of a silane-based cup with respect to a magnetite powder having a number average particle diameter of 0.25 μm, a barium ferrite powder having a number average particle diameter of 0.25 μm, and a hematite powder having a number average particle diameter of 0.40 μm. A ring agent (3- (2-aminoethylaminopropyl) dimethoxysilane) was added, and the mixture was mixed and stirred at a high speed of 1000 ° C. or higher in a container to perform lipophilic treatment of the metal oxide fine particles.
・ Phenol 10 parts by mass
・ Formaldehyde solution 6 parts by mass
(Formaldehyde 40%, methanol 10%, water 50%)
・ 72 parts by weight of lipophilic magnetite
・ 18 parts by weight of lipophilic barium ferrite
・ Lipophilicized hematite 10 parts by mass
The above-mentioned material, 5 parts by mass of 28% ammonia water and 10 parts by mass of water were put into a flask, heated to 85 ° C. for 30 minutes while stirring and mixing, and polymerized for 3 hours to cure.
[0118]
Further, as described above, 1.5 parts by mass of a hematite powder having a number average particle diameter of 0.20 μm, lipophilic treatment with (3- (2-aminoethylaminopropyl) dimethoxysilane), 1.5 parts by mass of phenol, and a formaldehyde solution Was added, and a polymerization reaction was further performed for 3 hours.
[0119]
Thereafter, the mixture was cooled to 30 ° C., water was further added, the supernatant was removed, and the precipitate was washed with water and air-dried. Next, this was dried at a temperature of 50 to 60 ° C. under reduced pressure (5 mmHg or less) to obtain spherical particles.
[0120]
Further, the surface of the particles obtained above was coated with a thermosetting silicone resin by the following method. At that time, a 10% by mass carrier code solution was prepared using toluene as a solvent so that the amount of the coating resin on the surface of the carrier core particles was 1.5% by mass. The solvent was volatilized at 70 ° C. while continuously applying shear stress to the coating solution to coat the carrier core surface. The coated magnetic carrier particles were heat-treated with stirring at 200 ° C. for 3 hours, cooled, crushed, and classified with a 200-mesh sieve to obtain Carrier 1.
[0121]
The number average particle diameter of the obtained carrier 1 was 22.0 μm. Further, a magnetic field of 10 kOe was applied to the obtained carrier, and its magnetic properties were measured. The saturation magnetization at 10 kOe is 248 emu / cm³And the residual magnetization is 24.8 emu / cm.³Met. The true specific gravity of the carrier 1 was 3.55 g / cm3. Further, the content of Fe (II) with respect to the concentration of the eluted iron element on the surface of the carrier particles was 2.1% by mass.
[0122]
[Carrier 2]
First, 4.8% by mass of a silane-based cup with respect to a magnetite powder having a number average particle size of 0.25 μm, a strontium ferrite powder having a number average particle size of 0.27 μm, and a hematite powder having a number average particle size of 0.40 μm. A ring agent (3- (2-aminoethylaminopropyl) dimethoxysilane) was added, and the mixture was mixed and stirred at a high speed of 100 ° C. or higher in a container to perform lipophilic treatment of the metal oxide fine particles in the same manner as the carrier 1.
・ Phenol 12 parts by mass
・ Formaldehyde solution 7 parts by mass
(Formaldehyde 40%, methanol 10%, water 50%)
・ 42 parts by mass of lipophilic magnetite
・ 28 parts by mass of strontium ferrite subjected to lipophilic treatment
・ 30 parts by mass of lipophilic hematite
The above materials, 6 parts by mass of 28% aqueous ammonia, and 12 parts by mass of water were placed in a flask, and the temperature was raised to and maintained at 85 ° C. for 30 minutes while stirring and mixing, followed by a polymerization reaction for 3 hours to cure.
[0123]
Further, 1.5 parts by mass of a hematite powder having a number average particle size of 0.20 μm subjected to lipophilic treatment in the same manner as the carrier 1, 1 part by mass of phenol, and 0.4 parts by mass of a formaldehyde solution are added, and a polymerization reaction is further performed for 3 hours. Was.
[0124]
Thereafter, spherical particles were obtained in the same manner as in Carrier 1.
[0125]
Further, the surface of the particles obtained above was coated with a thermosetting silicone resin in the same manner as in the case of the carrier 1, whereby a carrier 2 was obtained.
[0126]
The number average particle diameter of the obtained carrier 2 was 29.3 μm. The saturation magnetization at 10 kOe is 181 emu / cm³And the residual magnetization is 30.1 emu / cm.³Met. The true specific gravity of the carrier 1 is 3.60 g / cm.³Met. Further, the Fe (II) content based on the concentration of the eluted iron element on the surface of the carrier particles was 1.2% by mass.
[0127]
[Carrier 3]
Polymerization was performed using the lipophilic magnetite and barium ferrite used in Carrier 1 according to the following formulation.
・ Phenol 10 parts by mass
・ Formaldehyde solution 6 parts by mass
(Formaldehyde 40%, methanol 10%, water 50%)
・ 90 parts by weight of lipophilic magnetite
・ Lipophilic barium ferrite 10 parts by mass
The above materials, 4 parts by mass of 28% ammonia water, and 8 parts by mass of water were placed in a flask, and the temperature was raised to and maintained at 85 ° C. for 30 minutes while stirring and mixing, followed by a polymerization reaction for 3 hours to cure. Further, 1.5 parts by mass of a hematite powder having a number average particle size of 0.28 μm subjected to lipophilic treatment in the same manner as the carrier 1, 1 part by mass of phenol, and 0.4 parts by mass of a formaldehyde solution are added, and a polymerization reaction is further performed for 3 hours. Was.
[0128]
Thereafter, spherical particles were obtained in the same manner as in Carrier 1.
[0129]
Further, the surface of the particles obtained above was coated with a thermosetting silicone resin in the same manner as in the case of the carrier 1 to obtain a carrier 3.
[0130]
The number average particle diameter of the obtained carrier 3 was 15.7 μm. The saturation magnetization at 10 kiloeld ted is 281 emu / cm³And the residual magnetization is 19.5 emu / cm³Met. The true specific gravity of the carrier 1 is 3.58 g / cm.³Met. The Fe (II) content with respect to the concentration of the eluted iron element on the surface of the carrier particles was 4.4% by mass.
[0131]
[Carrier 4]
3.8 mass% silane coupling to copper zinc ferrite powder having a number average particle size of 0.25 μm, barium ferrite powder having a number average particle size of 0.25 μm, and hematite powder having a number average particle size of 0.40 μm. The agent (3- (2-aminoethylaminopropyl) dimethoxysilane) was added, and the mixture was stirred at high speed at 100 ° C. or higher in a container to perform lipophilic treatment of the metal oxide fine particles.
・ Phenol 12 parts by mass
・ Formaldehyde solution 7 parts by mass
(Formaldehyde 40%, methanol 10%, water 50%)
・ Lipophilized copper zinc ferrite 24 parts by mass
・ Lipophilic barium ferrite 56 parts by mass
・ 20 parts by weight of lipophilic hematite
The above materials, 6 parts by mass of 28% ammonia water, and 12 parts by mass of water were placed in a flask, and the temperature was raised and maintained at 85 ° C. in 30 minutes while stirring and mixing, followed by reaction and curing in 3 hours.
[0132]
Further, 1.0 part by mass of the hematite powder used in the carrier 1, 1 part by mass of phenol, and 0.4 part by mass of the formaldehyde solution were added, and the polymerization reaction was further performed for 3 hours.
[0133]
Thereafter, spherical particles were obtained in the same manner as in Carrier 1.
[0134]
Further, the surface of the particles obtained above was coated with a thermosetting silicone resin in the same manner as the carrier 1 to obtain a carrier 4.
[0135]
The number average particle diameter of the obtained carrier 4 was 28.1 μm. The saturation magnetization at 10 kOe is 182 emu / cm³And the residual magnetization is 52.1 emu / cm.³Met. The true specific gravity of the carrier 1 is 3.53 g / cm.³Met. Further, the Fe (II) content based on the concentration of the eluted iron element on the surface of the carrier particles was 0.2% by mass.
[0136]
[Carrier 5]
First, a silane coupling agent (3- (2-aminoethylamino) having a mass average particle size of 0.40 μm and a barium ferrite powder having a number average particle size of 0.41 μm were added in an amount of 3.0% by mass. Propyl) dimethoxysilane) was added, and high-speed mixing and stirring was performed at 100 ° C. or higher in a container in the same manner as in the case of Carrier 1 to carry out lipophilic treatment of metal oxide fine particles.
・ Phenol 10 parts by mass
・ Formaldehyde solution 6 parts by mass
(Formaldehyde 40%, methanol 10%, water 50%)
・ Lipophilized magnetite 60 parts by mass
・ 40 parts by mass of lipophilic barium ferrite
The above-mentioned material, 5 parts by mass of 28% ammonia water and 10 parts by mass of water were put into a flask, heated to 85 ° C. for 30 minutes while stirring and mixing, and polymerized for 3 hours to cure.
[0137]
Thereafter, the mixture was cooled to 30 ° C., water was further added, the supernatant was removed, and the precipitate was washed with water and air-dried. Next, this was dried at a temperature of 50 to 60 ° C. under reduced pressure (5 mmHg or less) to obtain spherical particles.
[0138]
Further, the surface of the particles obtained above was coated with a thermosetting silicone resin in the same manner as in the case of the carrier 1, whereby a carrier 5 was obtained.
[0139]
The number average particle diameter of the obtained carrier 4 was 20.3 μm. The saturation magnetization at 10 kOe is 255 emu / cm³And the residual magnetization is 45.9 emu / cm.³Met. The true specific gravity of the carrier 1 is 3.58 g / cm.³Met. Further, the Fe (II) content with respect to the concentration of the eluted iron element on the surface of the carrier particles was 8.8% by mass.
[0140]
[Carrier 6]
In molar ratio, Fe₂O₃= 50 mol%, CuO = 27 mol%, ZnO = 23 mol%, and mixed using a ball mill. After calcining this, it was pulverized by a ball mill and further granulated by a spray drier. This was sintered and further classified to obtain carrier core particles.
[0141]
Further, the surface of the particles obtained above was coated with a thermosetting silicone resin in the same manner as in the case of the carrier 1, whereby a carrier 5 was obtained.
[0142]
The number average particle diameter of the obtained carrier 4 was 38.1 μm. The saturation magnetization at 10 kOe is 325 emu / cm³And the residual magnetization is 0.4 emu / cm³Met. The true specific gravity of the carrier 1 is 5.02 g / cm.³Met. Further, the Fe (II) content based on the concentration of the eluted iron element on the surface of the carrier particles was 0.1% by mass.
[0143]
<Magnetic particles for contact charging magnetic brush>
(Core particles) Hydrogen-reduced Zn-Cu ferrite 200 parts by mass
(Number average particle size 48.0 μm, specific resistance 5 × 10⁶Ωcm)
(Coat resin solution)
Polycarbonate 1.0 parts by mass
Epoxy-modified silicone resin 1.0 parts by mass
4.0 parts by mass of conductive titanium oxide
0.2 parts by mass of tetrafluoroethylene resin particles (0.25 μm)
Xylene solution 14.0 parts by mass
Each formulation of the above coating resin solution was dispersed for 2 hours with a paint shaker containing glass beads to prepare a coating resin solution. This was coated on the above-mentioned core particles using the above-mentioned spira coater, and dried at 150 ° C. for 1 hour. The specific resistance of the obtained magnetic particles for contact charging magnetic brush is 8.9 × 10⁶Ωcm and the number average particle size was 48.3 μm. Magnetization intensity at 1 kOe = 262.1 emu / cm³(The true specific gravity of the magnetic particles was 5.02 g / cm.³).
[0144]
The specific resistance and the number average particle size of the magnetic particles for the contact charging magnetic brush used here were determined by the above-described method for measuring the characteristics of the magnetic carrier for development.
[0145]
<Example 1>
The carrier 1 was magnetized with a magnetic field of 10 kOe, and the toner 1 and the carrier 1 were mixed so as to have a toner concentration of 8% to prepare a two-component developer. At this time, the charge amount of the toner was −35.1 μC / g.
[0146]
Using this two-component developer, an image output test was carried out using a modified full-color copying machine CLC500 manufactured by Canon Inc. FIG. 1 is a schematic view showing the periphery of the developing section, and the description will be made with reference to FIG. In the figure, 11 is a photosensitive drum, 12 is a developing sleeve, 13 is a magnet roller rotatably arranged in the developing sleeve 12, and 14 is a regulation for supplying the developing agent to the developing sleeve 12 to a constant thickness. A blade 15 is a peeling blade arranged to peel off the developer from the developing sleeve 12, a stirring screw 16 and a hopper 17 for supplying toner.
[0147]
The developing sleeve 12 is disposed so that the re-approaching distance to the photosensitive drum 11 is 550 μm, and is configured so that the developer can be developed in a state where the developer contacts the photosensitive drum 11. The developing sleeve 12 has an outer diameter of 32 mm, and the internal magnet roller 13 has eight poles with a multipole magnetic force of 1000 Gauss and is arranged at substantially equal positions. The photosensitive drum 11 rotates at 160 mm / sec in the direction of the arrow. In addition, the magnet roller 13 has a 2,500 r.p. p. m at high speed. Further, the developing sleeve 12 rotates at 100 mm / sec in the direction of the arrow opposite to the magnet roller 13, and the two-component developer including the toner 1 and the carrier 1 rolls on the developing sleeve 12 while rotating on the developing sleeve 12. Conveyed in the direction.
[0148]
The developing sleeve 12 was sand-blasted on the surface of a developing sleeve (material: SUS, manufactured by Hitachi Metals, 32φ) used in the developing device of the CLC500 using a pneumatic plaster (manufactured by Fuji Seisakusho), and Ra = A blast sleeve (Ra / Sm = 0.07) of 2.1 μm and Sm: 29.7 μm was used.
[0149]
A DC voltage and an AC voltage are superimposed and applied to the developing sleeve 12. In this embodiment, the developing bias is obtained by superimposing an AC voltage Vpp = 2,000 V and a frequency Vf = 2,200 Hz on a DC voltage Vdc = −450 V. In addition, Vcont was set to 350 V and fogging bias Vback was set to 80 V as a development contrast.
[0150]
As the voltage applied to the contact charging member 21, a DC bias of -560V was used.
[0151]
As the photosensitive drum, an OPC photosensitive member having five layers of the following functional layers on a φ80 aluminum drum was used.
[0152]
The first layer is an undercoat layer, the second layer is a positive charge injection preventing layer, the third layer is a charge generation layer, the fourth layer is a charge transport layer, and the fifth layer is a charge injection layer in order from the aluminum base layer side. . This charge injection layer is made of a photocurable acrylic resin made of SnO.₂Ultrafine particles, and dispersion particles of ethylene tetrafluoride resin for uniform charging by increasing the contact time between the contact charging member and the photosensitive member. Specifically, SnO doped with antimony and reduced in resistance has a particle diameter of about 0.03 μm.₂The particles are 70% by mass with respect to the resin, 20% by mass of tetrafluoroethylene resin particles having a particle size of 0.25 μm, and 1.2% by mass of a dispersant. The surface resistance of this photosensitive drum is 1 × 10¹²Ω.
[0153]
An image was formed under the above development conditions. As a result, an excellent image having very good halftone reproducibility and a high solid image density was obtained. Further, no image disturbance or toner fogging in the image area and the non-image area due to carrier adhesion was observed.
[0154]
The toner transfer efficiency when the solid black image was transferred from the photosensitive drum to the paper was 99.4%, which was a level sufficient for a cleaner-less process. Actually, when the cleaner was removed and 10,000 images were printed, the chargeability of the charged magnetic brush did not change at all, and no charged ghost or the like was observed.
[0155]
Table 2 shows the results of this example. Table 2 also shows the results of the following Examples and Comparative Examples.
[0156]
<Example 2>
The carrier 2 was magnetized with a magnetic field of 10 kOe, and mixed with the toner 1 and the carrier 2 so as to have a toner concentration of 5% in the same manner as in Example 1 to prepare a two-component developer. The charge amount of the toner was -35.7 μC / g.
[0157]
An image output test was performed under the same conditions as in Example 1. As in Example 1, there was no image contamination due to carrier adhesion or fog, and there was no problem with halftone reproducibility, and good image density was obtained. was gotten. The toner transfer efficiency was as good as 97.6%.
[0158]
<Example 3>
The carrier 3 was magnetized with a magnetic field of 10 kOe, and mixed with the toner 2 and the carrier 3 so as to have a toner concentration of 5% in the same manner as in Example 1 to prepare a two-component developer. The charge amount of the toner was -41.0 μC / g.
[0159]
When an image output test was performed under the same conditions as in Example 1, good results were obtained in the same manner as in Example 1, with no image contamination such as image density, carrier adhesion, and fog. In particular, the halftone reproducibility was excellent. Further, the result of the image output durability test was also good. The transfer efficiency was 99.7%.
[0160]
When the image was taken out of 10,000 sheets to remove the cleaner, durability was good as in Example 1.
[0161]
<Example 4>
The carrier 4 was magnetized with a magnetic field of 10 kOe, and mixed with the toner 1 and the carrier 4 so as to have a toner concentration of 5% in the same manner as in Example 2 to prepare a two-component developer. The charge amount of the toner was -31.8 μC / g.
[0162]
When an image output test was performed under the same conditions as in Example 1, as in Example 1, good results were obtained in which the carrier adhesion and fog were good and the image density was sufficient. The transfer efficiency was 98.8%. Further, the result of the image output durability test was also good.
[0163]
<Comparative Example 1>
The carrier 5 was magnetized with a magnetic field of 10 kOe, and a two-component developer was prepared in the same manner as in Example 1 using the toner 1 and the carrier 5. The charge amount of the toner was -32.5 μC / g.
[0164]
When an image output test was performed under the same conditions as in Example 1, the image density was at a sufficient level, but some fogging occurred and stains due to carrier adhesion occurred. The transfer efficiency was 93.1%. In addition, as a result of the image output durability test, poor charging of the photoreceptor due to fog toner occurred and was stopped halfway.
[0165]
<Comparative Example 2>
Using the toner 1 and the carrier 6, a two-component developer was prepared in the same manner as in Example 1. The charge amount of the toner was -32.9 μC / g.
[0166]
When an image output test was performed under the same conditions as in Example 1, carrier adhesion was observed, fogging occurred, and only an image having a low image density was obtained. Observation of the developing portion revealed that the fluidity of the developer was poor. The transfer efficiency was 90.4%. Further, as a result of the image output durability test, poor charging of the photoreceptor due to fog toner occurred and was stopped halfway.
[0167]
The physical properties of the toner and the magnetic carrier used in the examples and comparative examples are shown in Table 1 below.
[0168]
[Table 1]

[0169]
[Evaluation]
Evaluation of an image formation test performed using a two-component developer composed of a toner and a magnetic carrier having physical properties shown in Table 1 used in Examples and Comparative Examples was performed according to the following method and the following criteria. .
[0170]
(1) Carrier adhesion:
A solid white image is imaged, the portion on the photosensitive drum between the developing section and the cleaner section is sampled by closely attaching a transparent adhesive tape, and the magnetic carrier adhered to the photosensitive drum of 5 cm × 5 cm. Count the number of particles, 1mm²Per carrier was calculated.
◎: 0.1 pieces / mm²Less than
：: 0.1 to 0.5 pieces / mm²Less than
Δ: 0.5 to 2.0 pieces / mm²Less than
×: 2.0 pieces / mm²that's all
[0171]
(2) Image density:
The image density was measured as a relative density of a solid image formed on plain paper using a Macbeth color checker RD-1255 manufactured by Macbeth equipped with an SPI filter.
A: 1.6 or more
：: 1.5 to less than 1.6
Δ: 1.4 to less than 1.5
×: less than 1.4
[0172]
(3) Fog:
The average reflectance Dr (%) of plain paper before image formation was measured by a densitometer TC-6MC manufactured by Tokyo Denshoku Co., Ltd. On the other hand, a solid self-portrait was imaged on plain paper, and then the reflectance Ds (%) of the solid self-portrait was measured. Fog (%) was calculated from the measured values by the following formula and evaluated according to the following criteria.
fog (%) = Dr (%)-Ds (%)
◎: less than 1.0%
：: 1.0 to less than 1.5
Δ: 1.5 to less than 2.0
×: 2.0 or more
[0173]
(4) Halftone dot reproducibility:
The dots developed on the photosensitive drum of the halftone portion of the image (latent image spot diameter 15 μm) were captured as image data on a personal computer using a stereo microscope (× 100) equipped with a CCD. Next, the pixel area of this dot was calculated, and 100 were added to calculate the average value a and the standard deviation S. The value S / a obtained by dividing the standard deviation S of the pixel area of the dot by the average value was used as an evaluation value of the dot reproducibility, and evaluated according to the following criteria.
◎: less than 0.05
: 0.05 to less than 0.1
Δ: 0.1 to less than 0.15
Δ ×: less than 0.15 to 0.2
×: 0.2 or more
[0174]
The evaluation results are shown in Table 2 below.
[0175]
[Table 2]

[0176]
【The invention's effect】
As described above, according to the present invention, in a method for forming an image having a contact charging device for charging a latent image carrier by bringing a charging member into contact therewith, a magnetic carrier having a very high resistance and unique magnetic properties Performs contact two-component AC development using an image forming method to effectively prevent the occurrence of carrier adhesion, fog-free, excellent halftone reproducibility, and obtain high image density. A method is provided.
[Brief description of the drawings]
FIG. 1 is a schematic view used to describe a two-component developing device used in an embodiment of the present invention.
[Explanation of symbols]
11. Photosensitive drum
12. Developing sleeve
13. Magnet roller
14． Regulation blade
15. Peeling blade
16. Stirring screw
17. hopper
21. Contact charging member
22. Exposure equipment

Claims (6)

A charging step of charging an electrostatic latent image carrier having a charge injection layer having a surface resistance of 1 × 10 ¹⁰ to 1 × 10 ¹⁶ Ω with a magnetic brush composed of magnetic particles; A latent image forming step of forming an electrostatic latent image on the electrostatic latent image carrier by exposure to light; and a two-component image forming apparatus including a magnetic carrier and a toner, the electrostatic latent image formed on the electrostatic latent image carrier having the charge injection layer. A developing step of developing with the toner of a system developer;
In the image forming method having
The magnetic carrier contains at least a binder resin and magnetic metal oxide particles,
The specific resistance of the magnetic carrier particles is 5.0 × 10 ¹³ Ω · cm or more when a voltage of 25 V to 500 V is applied,
The saturation magnetization of the magnetic carrier particles at 10 kOe is 100 to 300 emu / cm ³ , the residual magnetization is 25 to 150 emu / cm ³ ,
The true specific gravity of the magnetic carrier particles is 3.0 to 4.9 g / cm ³ ,
The Fe (II) content relative to the concentration of the eluted iron element on the surface of the magnetic carrier particles is 0.001 to 5.0% by mass,
An image forming method characterized by satisfying the following expression.

R: Number average particle size of magnetic carrier particles (μm)
M: saturation magnetization of magnetic carrier particles (emu / cm ³ ) In the developing step, a magnetic brush of a two-component developer having a magnetic carrier and a toner carried on a developer carrier disposed opposite to the electrostatic latent image carrier having the charge injection layer is applied to the charge injection layer. An electrostatic latent image carrier having the charge injection layer by applying a developing bias voltage in which a DC bias is superimposed on a continuous or discontinuous AC bias to the developer carrier. 2. The image forming method according to claim 1, wherein the electrostatic latent image formed in the image is developed with the toner. The magnetic carrier is characterized in that the magnetic metal oxide contains at least one of magnetite or soft ferrite having a lipophilic surface, and one of barium ferrite or strontium ferrite having a lipophilic surface. The image forming method according to claim 1. The magnetic carrier contains nonmagnetic metal oxide particles in the vicinity of the surface, and the Fe (II) content is 0.001 to 5.0% by mass based on the concentration of the eluted iron element on the surface of the magnetic carrier particles. The image forming method according to claim 1, wherein: 5. The image forming method according to claim 1, wherein the magnetic carrier is surface-coated with a silicone resin. In the developing step, the two-component developer is carried on a developer carrier and transported to a developing section, where a magnetic brush of the two-component developer is formed on the developer carrier in the developing section. In the step of developing the electrostatic latent image formed on the latent image carrier by bringing the magnetic brush into contact with the latent image carrier, the developer carrier comprises a cylindrical non-magnetic sleeve and the non-magnetic sleeve. The image forming method according to any one of claims 1 to 5, further comprising a magnet included in the image forming apparatus, and configured to rotate the magnet.

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