JP2004226451A - Magnetic carrier and two-component system developer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a magnetic carrier and a two-component system developer which does not cause carrier sticking, can obtain a high grade picture which has an adequate picture density and has an excellent half-tone reproducibility and, moreover, can maintain the characteristic durably. <P>SOLUTION: Magnetic carriers contain at least binder resin and magnetic metal oxide particles and satisfy inequations (1): -6.0 R+300≤M≤ -3.0 R+350, 5≤R≤30. In the inequations (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）
【００１１】
【発明の実施の形態】
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。
【００１２】
本発明者らは、上記した従来技術の課題について鋭意検討の結果、磁性キャリアにおいて、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磁性キャリアが得られることを知見して本発明に至った。
【００１３】
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。以下、これらについて更に詳細に説明する。
【００１４】
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又は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。
【００１５】
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又は３００ｅｍｕ／ｃｍ^３であり、残留磁化が１５又は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又は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。
【００１６】

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）
【００１７】
−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。
【００１８】
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。
【００１９】
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又は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。
【００２０】
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、熱硬化一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。
【００２１】
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。
【００２２】
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。
【００２３】
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。
【００２４】
さらに、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。
【００２５】
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％であることが必須である。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ｇ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必要である。
【００２６】
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必要である。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。
【００２７】
以下、本発明の現像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。
【００２８】
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。式申の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。
【００２９】
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、Ａ１、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。
【００３０】
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。
【００３１】
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ワエ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。
【００３２】
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。
【００３３】
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。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、パーフロロカーボン樹脂、溶剤可溶性パ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。
【００３４】
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、メラミンーグアテミン樹脂、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。
【００３５】
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。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。
【００３６】
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。
【００３７】
以下に、本発明で用いる測定方法について述べる。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又は２ｍｇを加え、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。
【００３８】
変動係数（％）＝Ｓ．Ｄ．／Ｄｎ×１００
【００３９】
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Ｌｕｚｅｘ３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。
【００４０】
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。
【００４１】
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。
【００４２】
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℃、携幹スピードを２００ｒｐｍに保ちながら、特級硫酸６９５ｍｌを前期５１ビーカー中に加え、溶解を開始す孔溶解開始から１時問後に溶解液を２０ｍけンプリングして、０．１μｍメンブランフィルターで濾過して濾液を採取する。
【００４３】
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。
【００４４】
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ＫＭｎ０４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。
【００４５】
【数１】

【００４６】
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トナー重量が５質量％となるように混合し、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）×（Ｗ１−Ｗ２）^−１
（式中Ｗ１は吸引前の重量でありＷ２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。）
【００４７】
【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。
【００４８】
（トナーの製造）
［トナー１］
プロボ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。
【００４９】
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。
【００５０】
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。
【００５１】
［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。
【００５２】
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
一方、上記材料を混合して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’−アソビス（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。
【００５３】
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Ｎ_２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。
【００５４】
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。
【００５５】
［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。
【００５６】
（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。
【００５７】
・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。
【００５８】
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。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。
【００５９】
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％のキャリアコート溶液を作製した。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。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３，５５９／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、２．１質量％であった。
【００６０】
［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重量郡
・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。
【００６１】
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。その後キャリア１と同様にして球状の粒子を得た。
【００６２】
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。
【００６３】
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。
【００６４】
［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。その後キャリア１と同様にして球状の粒子を得た。
【００６５】
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。得られたキャリア３の個数平均粒径は１５．７μｍであった。１０キロエルス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、キャリナ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。
【００６６】
［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、高速混合挽幹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。
【００６７】
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、を加え、さらに３時間重合反応させた。その後キャリア１と同様にして球状の粒子を得た。
【００６８】
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。
【００６９】
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。
【００７０】
［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。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。
【００７１】
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。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。
【００７２】
［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梓を行った。これを焼結し、さらに分級してキャリアコア粒子を得た。
【００７３】
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。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。
【００７４】
＜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−３４．８μＣ／ｇであった。
【００７５】
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。図１に、本実施例で用いた現像装置の概略図を示す。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。
【００７６】
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５００μｍ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。
【００７７】
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＝１，８００Ｈｚ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１００Ｖとして、画出し試験を行なった。
【００７８】
画像出し試験の結果、キャリア付着やカブリ等の画像汚れがなく、ハーフトーン再現性に優れ、画像濃度が充分である良好な結果が得られた。更に、１万枚の画像出し耐久試験を行なったが、性能の変化は見られなかった。
【００７９】
＜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−３８．２μＣ／ｇであった。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の画像汚れがなく、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。又、画像出し耐久試験の結果も良好なものであった。
【００８０】
＜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−４７．１μＣ／ｇであった。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に比較して少し画像濃度が薄かったが充分な濃さであり、実施例１と同様に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。
【００８１】
＜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−３５．７μＣ／ｇであった。
【００８２】
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、キャリア付着も良好であり、実施例１と同様にカブリもなく画像濃度が充分である良好な結果が得られた。又、画像出し耐久試験の結果も良好なものであった。
【００８３】
＜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−３３．６μＣ／ｇであった。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、カブリが発生し、画像濃度は充分なレベルであったが、初期から非画像部にキャリア付着による汚れが発生した。
【００８４】
＜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−３４．８μＣ／ｇであった。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、キャリア付着はなかったもののカブリが発生し、また極度に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、現像剤がうまく搬送されておらず、現像部に充分な量が供給されていなかった。
【００８５】
＜比較例３＞
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３とキャリア１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−３７．１μＣ／ｇであった。
【００８６】
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、キャリア付着はなかったもののカブリが発生し、画像濃度が低くなった。耐久によりさらに画像濃度低下が起こった。
【００８７】
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。
【００８８】
【表１】

【００８９】
［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。
【００９０】
（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
【００９１】
（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ベ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
【００９２】
（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
【００９３】
（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
【００９４】
評価結果は、下記の表２にまとめて示した。
【００９５】
【表２】

【００９６】
【発明の効果】
以上、説明したように、本発明によれば、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ることで、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でき、上記した優れた性能を耐久維持することが可能な磁性キャリアが提供される。また、小粒径でシャープな粒度分布を有するトナーと用いることでより高画質が達成できる二成分系現像剤を提供できる。
【図面の簡単な説明】
【図１】図１は現像装置の概略図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a magnetic carrier and a two-component developer that can be widely used in a copying machine, a printer, a facsimile, a plate making system, and the like using an electrophotographic method.
[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. 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.
[0003]
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.
[0004]
However, when the particle size of the toner is small, the charge amount becomes large, and the adhesion to the carrier by van der Waalska increases, so that the toner hardly separates from the carrier at the time of development. This causes a problem that the thickness becomes thinner.
[0005]
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.
[0006]
As the magnetic carrier used here, those made of a single hard magnetic material such as barium ferrite and strontium ferrite have been used, but when used alone, the specific resistance of carrier particles is low, and in contact development, the It is used after being coated with a resin so as not to leak the bias applied from the agent carrier. This causes inconvenience when the coating material comes off.
[0007]
In addition, due to a demand for a reduction in particle size, a magnetic material-dispersed resin carrier has been developed as disclosed in, for example, Japanese Patent Publication No. 59-224416. Further, as disclosed in Japanese Patent Application Laid-Open No. 10-268575, spherical composite particles have been proposed in which the magnetic properties can be freely controlled and the resistance can be increased.
[0008]
However, when the toner is small and the carrier particles are small, the image density is high, and the specific resistance is still insufficient to sufficiently prevent the carrier from adhering. No system developer was obtained.
[0009]
[Problems to be solved by the invention]
Accordingly, it is an object of the present invention to provide a magnetic carrier and a two-component magnetic recording medium that can provide a high-quality image having sufficient image density and excellent halftone reproducibility without causing carrier adhesion, and capable of maintaining the characteristics thereof. Another object of the present invention is to provide a system developer.
[0010]
[Means for Solving the Problems]
The above object is achieved by the present invention described below. That is, the present invention relates to a magnetic carrier particle containing at least a binder resin and magnetic metal oxide particles, wherein 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, saturation magnetization at 10 kOe particles are 100~300emu / cm ^3, the residual magnetization is 25~150emu / cm ^3, the true specific gravity of the magnetic carrier particles are 3.0~4.9g / cm ^3, 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, and the carrier can be achieved 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 )
[0011]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in more detail by way of preferred embodiments of the present invention.
[0012]
The present inventors have conducted intensive studies on the above-mentioned problems of the prior art, and found that a magnetic carrier having a specific magnetic characteristic as a carrier was used as the carrier, and the specific resistance was sufficiently high, and the elution of the magnetic carrier particle surface was performed. By using magnetic carrier particles in which the Fe (II) content is controlled with respect to the iron element concentration, a sufficient image density can be obtained, a magnetic carrier which does not cause carrier adhesion, and which can maintain its characteristics durably can be obtained. The knowledge has led to the present invention.
[0013]
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 has different magnetic characteristics. It has also been found that it is effective to use a combination of two or more magnetic metal oxides and use a magnetic substance-dispersed resin carrier in which these are dispersed. Hereinafter, these will be described in more detail.
[0014]
As a result of a detailed study of the magnetic carrier by the present inventors, it is preferable to use a magnetic carrier having a number average particle size of 5 to 30 μm when the toner particle size is reduced to 1 or 10 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.
[0015]
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, it is important that the saturation magnetization in a magnetic field of 10 kOe is 100 or 300 emu / cm ³ , and the residual magnetization is 15 or 150 emu / cm ^3. It has also been found that the magnetic carrier particle size and the saturation magnetization of the carrier are closely related. When the particle size of the magnetic carrier is 5 or 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.
[0016]

R: Number average particle size of magnetic carrier particles (μm)
M: saturation magnetization of magnetic carrier particles (emu / cm ³ )
[0017]
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.
[0018]
When the residual magnetization of the magnetic carrier to be used is lower than 15 emu / cm ³ , the two-component developer cannot roll well on the developer carrier, which is the intended object of the present invention. If the image density cannot be improved and the residual magnetization of the magnetic carrier is higher than 150 emu / cm ³ , the aggregation of the carriers by the magnetization of the carriers is large even at a distance from the magnetic field of the developer carrier. Therefore, deterioration of the toner is inevitable, and the durability is deteriorated.
[0019]
In the magnetic carrier of the present invention, the specific resistance of the carrier particles is important together with the magnetic characteristics. That is, it has been found that it is essential to have a high specific resistance of 5.0 × 10 ¹³ Ω · cm or more when 25 or 500 V is applied. In any carrier, a carrier exhibiting a specific resistance lower than 5.0 × 10 ¹³ Ω · cm at the time of applying a voltage causes the developing bias to lower the latent image potential via the carrier, causing deterioration of an image, fogging, or the like. Further, carriers may be attached due to injection of electric charges into the carriers themselves.
[0020]
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. Is a so-called magnetic substance dispersion type resin carrier in which magnetic metal oxide particles containing at least a magnetic substance are dispersed in a binder resin. It has been found that it is effective to use at least one or more magnetic metal oxides and produce them by a polymerization method.
[0021]
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.
[0022]
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.
[0023]
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. .
[0024]
Furthermore, by using a magnetic carrier coated with a silicone-based resin layer, the magnetic carrier can be more excellent in fluidity, excellent in chargeability, and further enhanced in strength.
[0025]
It is essential that the toner that can be suitably used in the present invention has a weight average particle diameter of 1 to 10 μm and a coefficient of variation on a number basis of 0 to 35%. 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 of 0.2 μm or less g, or a mixture thereof. is necessary.
[0026]
Further, in the toner, it is necessary that the whole or a part of the particles be formed by a polymerization method, and that the shape factor SF-1 of the toner is 100 to 130 in order to further enhance fluidity and achieve high image quality. is there. 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.
[0027]
Hereinafter, the magnetic carrier of the above-described embodiment which can be suitably used in the developing method of the present invention will be described.
[0028]
The metal oxides which can be used in this case, as the soft magnetic particles, for example, represented by the general formula MO · Fe ₂ O ₃ or MFe ₂ O _4, magnetite, are preferably used soft ferrite it can. M in the formula corresponds to a divalent or monovalent metal ion, for example, Mn, Fe, Ni, Co, Cu, Mg, Zn, Cd, Li, etc. Further, M is a single or a plurality of metals. 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.
[0029]
Examples of the hard magnetic metal oxide particles used together with the above soft magnetic metal oxide particles include barium ferrite and strontium ferrite represented by BaFe ₁₂ O ₁₉ and SrFe ₁₂ O ₁₉ . Further, in order to adjust magnetic properties, electric resistance, etc., in addition to the above metal oxides, Mg, A1, 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.
[0030]
The soft ferrite mentioned above is a soft magnetic ferrite having a coercive force Hc of 100 Oe or less.
[0031]
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, vinyl monomers which are thermosetting resin raw materials such as the phenol resin and melamine resin mentioned above, for example, in the case of phenol resin, phenols and aldehydes, and in the case of urea resin Urea and aldehydes, melamine and aldehydes in the case of melamine resin, and biswaenols and epichlorohydrin, which are other starting materials for epoxy resin, 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.
[0032]
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.
[0033]
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. 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, perfluorocarbon resin, solvent-soluble perfluorocarbon 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.
[0034]
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-guatemine resin, acetoguanamine resin, gliptal resin, furan resin, silicone resin, polyimide, polyamide Examples include imide resin, polyetherimide resin, and polyurethane resin.
[0035]
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. 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.
[0036]
Further, the magnetic carrier of the present invention can be suitably used when the true specific gravity is 3.0 to 4.9 g / cm ³ . That is, a magnetic carrier having a true specific gravity of less than 3.0 g / cm ³ substantially means a carrier having a high resin content such that the ratio of the resin to the carrier weight is 50% or more. In some cases. On the other hand, when the true specific gravity is larger than 4.9 g / cm ³ , the share given to the toner in the developing device tends to be large, depending on the magnetic properties of the carrier, and there is a possibility that the toner may be deteriorated during the durability. In some cases, the binder component becomes insufficient and the strength may decrease.
[0037]
Hereinafter, the measurement method used in the present invention will be described. 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 or 2 mg of toner to a solution obtained by adding 0.2 ml of a surfactant (alkylbenzene sulfonate) to 100 ml of water, dispersing the mixture with an ultrasonic disperser for 2 minutes, and 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.
[0038]
Coefficient of variation (%) = S. D. / Dn × 100
[0039]
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. Analysis was performed using Luzex3, and the number average horizontal Feret diameter was used as the number average particle diameter of the carrier.
[0040]
The magnetic properties of the magnetic carrier were measured using an oscillating magnetic field type magnetic property automatic recording device BHV-30 manufactured by Riken Denshi Co., Ltd. The magnetic properties of the carrier powder were determined by creating an external magnetic field of 10 kOe, and determining the saturation magnetization and the residual magnetization when returning to 0 Oe. 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 densitometer 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. The intensity of magnetization per volume (emu / cm ³ ) is determined.
[0041]
In the present invention, 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 method.
[0042]
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. Then, while maintaining the temperature of the solution in the first beaker at 50 ° C. and the speed of the carrier at 200 rpm, 695 ml of special grade sulfuric acid was added to the first beaker and the solution was removed 20 m after 1 hour from the start of the hole dissolution to start dissolution. The sample is filtered and filtered through a 0.1 μm membrane filter to collect a filtrate.
[0043]
10 ml of the filtrate is weighed, and the dissolved concentration of elemental iron is quantified by plasma emission spectroscopy (ICP).
[0044]
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 KMn04. 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.
[0045]
(Equation 1)

[0046]
The method for measuring the triboelectric charge used in the present invention is described below. The toner and the carrier are mixed so that the weight of the toner is 5% by mass, and mixed for 120 seconds with an 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
(Where W1 is the weight before suction, W2 is the weight after suction, C is the capacity of the capacitor, and V is the potential stored in the capacitor.)
[0047]
【Example】
Hereinafter, examples of the present invention will be specifically described, but the present invention is not limited thereto.
[0048]
(Manufacture of toner)
[Toner 1]
100 parts by mass of a polyester resin obtained by condensing a propoxylated bisphenol with fumaric acid I. Pigment Blue 15:35 5 parts by mass Di-tert-butylsalicylic acid chromium complex 4 parts by mass These are mixed by a fixed-tank type dry mixer, and connected to a suction pump at a vent port, while suctioning, and using a twin screw extruder. Melt kneading was performed.
[0049]
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.
[0050]
Further, 1.8 parts by mass of hydrophobic titanium oxide having a specific surface area of 200 m ² / g by the BET method was externally added to 100 parts by mass of the toner composition to obtain 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%.
[0051]
[Toner 2]
450 parts by mass of an aqueous 0.1 M Na ₃ PO ₄ solution was added to 710 parts by mass of ion-exchanged water, heated to 60 ° C., and then 12.000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo). And stirred. To this, 75 parts by mass of a 1.0 M CaCl ₂ aqueous solution was gradually added to prepare an aqueous medium containing Ca ₃ (PO ₄ ) ₂ in a uniformly and finely dispersed state.
[0052]
160 parts by mass of styrene 35 parts by mass of n-butyl acrylate 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 The mixture was heated to 60 ° C., and was uniformly dissolved and dispersed at 12,000 rpm using a TK homomixer (manufactured by Tokushu Kika Kogyo). Into 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.
[0053]
Next, the composition containing the obtained polymerizable monomer was charged into the aqueous medium prepared in advance as described above, and the mixture was heated at 10,000 rpm with a TK homomixer at 60 ° C. in an N ₂ atmosphere. The composition was granulated by stirring for minutes. 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.
[0054]
Thereafter, classification was performed twice using a multi-stage classifier. To 100 parts by mass of the colored particles, 3.5 parts by mass of hydrophobic titanium oxide having a specific surface area of 200 m ² / g by the BET method was externally added 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%.
[0055]
[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. 1.8 parts by mass of hydrophobic titanium oxide having a specific surface area of 200 m ² / g by the BET method was externally added to 100 parts by mass of the cyan colored particles 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%.
[0056]
(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 stirred at high speed at 100 ° C. or higher in a container to perform lipophilic treatment of the metal oxide fine particles.
[0057]
・ Phenol 10 parts by mass ・ Formaldehyde solution 6 parts by mass (formaldehyde 40%, methanol 10%, water 50%)
・ 72 parts by mass of magnetite subjected to lipophilic treatment ・ 18 parts by mass of barium ferrite subjected to lipophilic treatment ・ 10 parts by mass of hematite subjected to lipophilic treatment 5 parts by mass of 28% ammonia water and 10 parts by mass of water in a flask The temperature was raised to 85 ° C. over 30 minutes while stirring and mixing, and the mixture was polymerized and cured for 3 hours.
[0058]
Further, as described above, 1.5 parts by mass of a hematite powder having a number average particle size of 0.20 μm, which was lipophilized 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. 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.
[0059]
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 coat solution was prepared using toluene as a solvent so that the amount of the coat 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. 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 was 248 emu / cm ³ , and the residual magnetization was 24.8 emu / cm ³ . The true specific gravity of the carrier 1 was 3,559 / cm ³ . Further, the content of Fe (II) with respect to the concentration of the dissolved iron element on the surface of the carrier particles was 2.1% by mass.
[0060]
[Carrier 2]
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 strontium ferrite powder having a number average particle diameter of 0.27 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 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% by weight of lipophilic magnetite 28% by weight of strontium ferrite subjected to lipophilic treatment 30% by weight of hematite subjected to lipophilic treatment 6% by weight of 28% ammonia water and 12% by weight of water in a flask The temperature was raised to 85 ° C. over 30 minutes while stirring and mixing, and the mixture was polymerized and cured for 3 hours.
[0061]
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. Thereafter, spherical particles were obtained in the same manner as in Carrier 1.
[0062]
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.
[0063]
The number average particle diameter of the obtained carrier 2 was 29.3 μm. The saturation magnetization at 10 kOe was 181 emu / cm ³ , and the residual magnetization was 30.1 emu / cm ³ . The true specific gravity of the carrier 1 was 3.60 g / cm ³ . 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.
[0064]
[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 mass of magnetite subjected to lipophilic treatment 10 parts by mass of barium ferrite subjected to lipophilic treatment The above material, 4 parts by mass of 28% ammonia water and 8 parts by mass of water are placed in a flask, and stirred and mixed for 30 minutes. The temperature was raised to and maintained at 85 ° C., and a polymerization reaction was performed 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. Thereafter, spherical particles were obtained in the same manner as in Carrier 1.
[0065]
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. The number average particle diameter of the obtained carrier 3 was 15.7 μm. The saturation magnetization at 10 kOe was 281 emu / cm ³ , and the remanence was 19.5 emu / cm ³ . The true specific gravity of Carina 1 was 3.58 g / cm ³ . Further, 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.
[0066]
[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 subjected to high-speed mixing and grinding 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%)
24 parts by mass of copper-zinc ferrite subjected to lipophilic treatment 56 parts by mass of barium ferrite subjected to lipophilic treatment 20 parts by mass of hematite subjected to lipophilic treatment 20 parts by mass of 28% ammonia water and 12 parts by mass of water The mixture was placed in a flask, heated and maintained at 85 ° C. in 30 minutes while stirring and mixing, and reacted and cured in 3 hours.
[0067]
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. Thereafter, spherical particles were obtained in the same manner as in Carrier 1.
[0068]
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.
[0069]
The number average particle diameter of the obtained carrier 4 was 28.1 μm. The saturation magnetization at 10 kOe was 182 emu / cm ³ and the residual magnetization was 52.1 emu / cm ³ . The true specific gravity of Carrier 1 was 3.53 g / cm ³ . 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.
[0070]
[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%)
60 parts by mass of magnetite subjected to lipophilic treatment 40 parts by mass of barium ferrite subjected to lipophilic treatment The above material, 5 parts by mass of 28% ammonia water, and 10 parts by mass of water are placed in a flask, and stirred and mixed for 30 minutes. The temperature was raised to and maintained at 85 ° C., and a polymerization reaction was performed for 3 hours to cure. 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.
[0071]
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. The number average particle diameter of the obtained carrier 4 was 20.3 μm. The saturation magnetization at 10 kOe was 255 emu / cm ³ and the residual magnetization was 45.9 emu / cm ³ . The true specific gravity of the carrier 1 was 3.58 g / cm ³ . 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.
[0072]
[Carrier 6]
They were weighed so that the molar ratios of Fe ₂ O ₃ = 50 mol% · CuO = 27 mol% and ZnO = 23 mol% were mixed using a ball mill. After calcining this, it was pulverized by a ball mill, and further prepared by a spray drier. This was sintered and further classified to obtain carrier core particles.
[0073]
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. The number average particle diameter of the obtained carrier 4 was 38.1 μm. The saturation magnetization at 10 kOe was 325 emu / cm ³ and the residual magnetization was 0.4 emu / cm ³ . The true specific gravity of the carrier 1 was 5.02 g / cm ³ . The Fe (II) content with respect to the concentration of the eluted iron element on the surface of the carrier particles was 0.1% by mass.
[0074]
<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 -34.8 μC / g.
[0075]
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 diagram of a developing device used in this embodiment. 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.
[0076]
The developing sleeve 12 is arranged so that the re-approaching distance to the photosensitive drum 11 is 500 μm, and is configured so that the developing can be performed 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.
[0077]
A DC voltage and an AC voltage are superimposed and applied to the developing sleeve 12. In the present embodiment, the developing bias is obtained by superimposing an AC voltage Vpp = 2,000 V and a frequency Vf = 1,800 Hz on a DC voltage Vdc = −450 V. Further, an image output test was carried out with Vcont as a developing contrast of 350 V and a fog removing bias Vback of 100 V.
[0078]
As a result of the image output test, good results were obtained in which there was no image stain such as carrier adhesion or fog, excellent halftone reproducibility, and sufficient image density. Further, an image output durability test was performed on 10,000 sheets, but no change in performance was observed.
[0079]
<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 produce a two-component developer. The charge amount of the toner was -38.2 μC / g. When an image output test was performed under the same conditions as in Example 1, as in Example 1, there was no image contamination such as carrier adhesion or fogging, there was no problem with halftone reproducibility, and good image density was sufficient. was gotten. Further, the result of the image output durability test was also good.
[0080]
<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 -47.1 μC / g. When an image output test was performed under the same conditions as in Example 1, the image density was slightly lower than that of Example 1, but the density was sufficient. As in Example 1, images such as carrier adhesion and fogging were observed. Good results without stains were obtained. In particular, the halftone reproducibility was excellent. Further, the result of the image output durability test was also good.
[0081]
<Example 4>
The carrier 4 was magnetized with a magnetic field of 10 kOe, and the toner 1 and the carrier 4 were mixed in the same manner as in Example 2 so as to have a toner concentration of 5% to prepare a two-component developer. The charge amount of the toner was -35.7 μC / g.
[0082]
An image output test was performed under the same conditions as in Example 1. As a result, good results were obtained in which the carrier adhesion was good and the image density was sufficient without fogging as in Example 1. Further, the result of the image output durability test was also good.
[0083]
<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 -33.6 μC / g. An image output test was performed under the same conditions as in Example 1. As a result, fogging occurred and the image density was at a sufficient level.
[0084]
<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 -34.8 μC / g. An image output test was performed under the same conditions as in Example 1. As a result, although no carrier was adhered, fogging occurred, and only an image having an extremely low image density was obtained. When the developer was observed, the developer was not conveyed well, and a sufficient amount was not supplied to the developer.
[0085]
<Comparative Example 3>
The carrier 1 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 3 and the carrier 1. The charge amount of the toner was -37.1 μC / g.
[0086]
An image output test was performed under the same conditions as in Example 1. As a result, although no carrier was attached, fogging occurred and the image density was low. The image density further decreased due to the durability.
[0087]
The physical properties of the toner and the magnetic carrier used in the examples and comparative examples are shown in Table 1 below.
[0088]
[Table 1]

[0089]
[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. .
[0090]
(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. The number of particles was counted, and the number of adhered carriers per 1 mm ² was calculated.
◎: less than 0.1 pieces / mm ² ：: 0.1 to less than 0.5 pieces / mm ² △: 0.5 to less than 2.0 pieces / mm ² ×: 2.0 pieces / mm ² or more ]
(2) Image density:
The image density was measured as a relative density of a solid image formed on plain paper using Macbeth color checker RD-1255 manufactured by Macbeth equipped with an SPI filter.
◎: 1.6 or more ：: 1.5 to less than 1.6 Δ: 1.4 to less than 1.5 ×: less than 1.4
(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% ：: less than 1.0 to 1.5 △: 1.5 to less than 2.0 x: 2.0 or more
(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 △: 0.1 to less than 0.15 △: 0.15 to less than 0.2 x: 0.2 or more
The evaluation results are shown in Table 2 below.
[0095]
[Table 2]

[0096]
【The invention's effect】
As described above, according to the present invention, by using a magnetic carrier having a very high resistance and unique magnetic characteristics, the occurrence of carrier adhesion can be effectively prevented, and the halftone without fog can be obtained. There is provided a magnetic carrier which is excellent in reproducibility, can obtain a high image density, and can maintain the excellent performance described above. Further, by using a toner having a small particle size and a sharp particle size distribution, a two-component developer capable of achieving higher image quality can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a developing device.

Claims (9)

In magnetic carrier particles containing 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,
A carrier characterized by satisfying the following formula.

R: Number average particle size of magnetic carrier particles (μm)
M: saturation magnetization of magnetic carrier particles (emu / cm ³ ) 2. The magnetic metal oxide according to claim 1, wherein at least the surface is lipophilized, either magnetite or soft ferrite, and the surface is lipophilized, barium ferrite or strontium ferrite. The magnetic carrier according to any one of the preceding claims. 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 magnetic carrier according to claim 1 or 2, wherein 4. The magnetic carrier according to claim 1, wherein the surface of the magnetic carrier is coated with a silicone resin. In a two-component developer containing at least a toner and a magnetic carrier, the toner has a weight-average particle diameter of 1 to 10 μm, a coefficient of variation on a number basis of 0 to 35%, and a number-average particle diameter of 0.1 to 0.1%. The magnetic carrier contains inorganic fine particles of 2 μm or less, organic fine particles of 0.2 μm or less, or a mixture thereof. The magnetic carrier contains at least a binder resin and magnetic metal oxide particles, and the magnetic carrier particles have a specific resistance of 25 V to 500 V applied. Sometimes 5.0 × 10 ¹³ Ω · cm or more, and 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 , and Fe (II) with respect to the concentration of the eluted iron element on the surface of the magnetic carrier particles. A two-component developer having a content of 0.001 to 5.0% by mass and satisfying the following formula.

R: Number average particle size of magnetic carrier particles (μm)
M: saturation magnetization of magnetic carrier particles (emu / cm ³ ) 6. The two-component developer according to claim 5, wherein the whole or a part of the toner is formed by a polymerization method, and the toner has a shape factor SF-1 of 100 to 130. 7. The carrier contains a magnetic metal oxide, and the magnetic metal oxide has at least a lipophilic surface, either magnetite or soft ferrite, and a barium ferrite or a strontium ferrite having a lipophilic surface. The two-component developer according to claim 5, further comprising a heel. 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 two-component developer according to claim 5, wherein 9. The two-component developer according to claim 5, wherein the magnetic carrier is surface-coated with a silicone resin.

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