JP2004004648A - Carrier for electrophotographic developer, and its manufacturing method - Google Patents
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Abstract
Description
【０００１】
【発明の属する技術分野】
本発明は、電子写真現像剤用キャリア及びその製造方法に関し、詳しくはフルカラー用現像剤に使用したときに、画像特性等に優れ、かつ長寿命化を達成した電子写真現像剤用キャリア及びその製造方法に関する。
【０００２】
【従来の技術及び発明が解決しようとする課題】
電子写真法では、帯電、露光工程で感光体上に静電潜像を形成し、トナーを含む現像剤で静電潜像を現像し、転写、定着工程を経て可視化される。ここで用いられる現像剤は、トナーとキャリアからなる２成分現像剤と、磁性トナー等のように単独で使用される１成分現像剤がある。
【０００３】
この中で、キャリアを用いた２成分現像剤は画質が優れている等の利点によりフルカラー用現像剤、高速機用現像剤等に幅広く使用されている。
【０００４】
近年、急増しているフルカラー用現像剤は、補給されたトナーに素早く帯電を付与し、広い印字面積を連続して現像する能力を要求されている。さらに装置のコンパクト化が進み現像スリーブ径が細く、現像剤の量も少なくなり現像剤用キャリアはさらなる帯電能力の向上、長寿命化、高画質化が求められている。
【０００５】
このような現状において、キャリアに求められる要求性状としては、トナーの保持性、帯電付与能力、磁気ブラシをソフトにするための小粒径化が挙げられる。しかし、小粒径化による弊害としてキャリア飛散の問題が常にクローズアップされ、これらの対策が多く提案されている。
【０００６】
特許文献１では、高速現像においてキャリア付着による画像欠陥が生じないキャリア及び現像剤の提案がなされている。
【０００７】
特許文献１では、キャリア飛散の防止のために原料の一次粒子の大きさを数平均一次粒子径（Ｄｖ）、体積平均一次粒子径（Ｄｎ）で磁化の均一化を図っている。しかしながら、特許文献１に記載のＤｖ／Ｄｎの比１．０〜２．０では平均粒径２０〜４５μｍの小粒径フェライトに対してキャリア飛散を防止することはできなかった。
【０００８】
すなわち、特許文献１の実施例では、平均粒径６５μｍのキャリアコア粒子による試験であり、キャリア飛散が生じやすい平均粒径２０〜４５μｍではそれらの効果が低減されるものと考えられる。さらに、キャリアの平均粒径が小さくなればそれに応じて構成される原料の粒径も小粒径化が必要であることが推定される。
【０００９】
また、磁気ブラシにキャリア粒子を保持するための磁気特性、粒径分布に関しては多くの提案がある。
【００１０】
特許文献２では、キャリアの重量平均粒径が３５〜５５μｍ、２２μｍ未満：０〜１５％、８８μｍ以上：０〜５％であって、特定の樹脂コートを施し、磁場１ＫＯｅにおける磁化７０〜１２０ｅｍｕ／ｇのキャリアが提案されている。確かに磁気特性は高い方がキャリア飛散に関してマージンがあるが、反面磁気ブラシが硬くなり高品位なソフト現像が困難になってくる。
【００１１】
また微粉側の含有量も少ない方がキャリア飛散に関して良好な傾向にあることは多くの報告がなされている。しかしながら、分級技術、歩留まり等の技術面、価格面の課題も多くあり総合的に満足な性能を有しているとは言い難い。
【００１２】
一方、小粒径キャリアに関する提案は多くあるが、従来の平均粒径が６０μｍ以上のフェライトキャリアにおける技術を、その延長線上として平均粒径２０〜４５μｍのフェライトキャリアに適用したとしても、キャリア飛散に関して充分に対応することができなかった。
【００１３】
従って、本発明の目的は、小粒径化が達成され、かつキャリア飛散等の問題が解消され、フルカラー用現像剤に使用したときに、画像特性等に優れる電子写真現像剤用キャリア及びその製造方法を提供することにある。
【００１４】
【特許文献１】
特開平９−１９７７２１号公報
【特許文献２】
特開２００１−２７８２８号公報
【００１５】
【課題を解決するための手段】
本発明者らは、鋭意検討した結果、均一なフェライト化反応を行う工程を採用することによりキャリア粒子間の磁気特性の均一化が可能になり、シャープな磁気特性によりキャリア飛散のマージンを上げた電子写真現像剤用キャリアの設計が可能になった。
【００１６】
すなわち、本発明は、酸化鉄を主成分とし、主にスピネル構造を有した体積平均粒径が２０〜４５μｍのフェライトキャリアであって、下記の特性又は性状を有することを特徴とする電子写真現像剤用キャリアを提供するものである。
（１）磁場１ＫＯｅにおける磁化が６５〜８０ｅｍｕ／ｇ、
（２）キャリアコア材の電流値が５０〜１５０μＡ、
（３）表面平滑均一度が７５％以上、
（４）樹脂被覆が施されており、被覆量がキャリアコア材に対して０．１〜５．０重量％。
【００１７】
また、本発明は、スラリー原料を造粒し、造粒物とした後、焼成した後、解砕、分級し、得られるキャリアコア材に樹脂を被覆する電子写真現像剤用キャリアの製造方法において、
上記スラリー原料の１次粒子径Ｄｓ１０及びＤｓ９０が下記の関係にあることを特徴とする上記電子写真現像剤用キャリアの製造方法を提供するものである。
Ｄｓ９０≦１μｍ
２．０≦Ｄｓ１０／Ｄｓ９０≦１０．０
（構成原料粉砕時の１０％体積粒径：Ｄｓ１０、構成原料粉砕時の９０％体積粒径：Ｄｓ９０）
【００１８】
【発明の実施の形態】
以下、本発明の電子写真現像剤用キャリア及びその製造方法の実施の形態について説明する。
【００１９】
本発明の電子写真現像剤用キャリアは、酸化鉄を主成分とし、主にスピネル構造を有した体積平均粒径が２０〜４５μｍのフェライトキャリアである。この体積平均粒径は、現在要求されているキャリアの小粒径化に対応したものである。体積平均粒径は、日機装株式会社製マイクロトラック粒度分析計（Ｍｏｄｅｌ１９３２０−Ｘ１００）を用いて測定される。
【００２０】
また、本発明の電子写真現像剤用キャリアは、下記の特性又は性状を有することが必要である。
【００２１】
（１）磁場１ＫＯｅにおける磁化が６５〜８０ｅｍｕ／ｇである。磁場１ＫＯｅにおける磁化は、振動型磁力測定機ＶＳＭ−Ｐ７東英工業株式会社製を用いて測定される。磁化が６５ｅｍｕ／ｇより下回るとキャリア粒子がマグネットロールに保持される力が小さくなりキャリア飛散が生じる。磁化が８０ｅｍｕ／ｇを超えると磁気ブラシが硬くなりソフトな現像ができなくなる。
【００２２】
（２）キャリアコア材の電流値が５０〜１５０μＡである。キャリアコア材の電流値は、アルミ素管に対向させた現像機にキャリアコア材を５００ｇセットし、直流電圧を２００Ｖ印加した時の導通電流の値を読みとることにより測定する。電流値が５０μＡを下回ると現像性が低下し、１５０μＡを超えるとリーク等の問題がでてくる。
【００２３】
（３）表面平滑均一度が７５％以上である。ここでいう表面平滑均一度とは、ＳＥＭの倍率２００倍の視野において、視野中の、粒子表面の１／２以上が平滑なコア粒子の個数と、全粒子個数を数え、（粒子表面の１／２以上が平滑なコア粒子の個数）／（全粒子個数）×１００（％）により算出した割合である。表面平滑均一度が７５％未満では、キャリア粒子間のフェライト化反応に差があり、低磁化粒子によるキャリア飛散が発生しやすくなる。
【００２４】
（４）樹脂被覆が施されており、被覆量がキャリアコア材に対して０．１〜５．０重量％である。被覆量が０．１重量％を下回ると被覆樹脂の効果による帯電量制御、抵抗制御の効果が小さくなり、５．０重量％を超えると帯電量の立ち上がり不良、粒子間の付着による歩留まりの低下等の不具合を生じる。
【００２５】
キャリアコア材を被覆する樹脂は、使用するトナーより適宜選択すればよいが、例えば、ポリプロピレン、ポリスチレン、アクリル樹脂、ポリアクリロニトリル樹脂、ストレートシリコーン樹脂及びその変性品、ポリテトラフルオロエチレン、ポリフッ化ビニデン等のフッ素樹脂、ポリカーボネート樹脂、エポキシ樹脂等が挙げられる。これらは単独或いは混合、変性して使用できる。高画質、長寿命等よりトナー汚染に対して優れているシリコーン系樹脂又はフッ素系樹脂を含む樹脂材料が好ましい。
【００２６】
被覆樹脂として絶縁樹脂を用いると高抵抗になるので、必要に応じてカーボンブラック、酸化チタン等の公知の導電剤を樹脂中に分散して使用することができる。
【００２７】
本発明で用いるキャリアコア材は、上記のように表面性が均一なため、被覆工程においても被膜の膜厚が一定に成りやすく、帯電量分布、耐久性等に非常に優れた性能を有した樹脂被覆キャリアとなる。
【００２８】
被覆の方法は、樹脂溶液中にキャリアコア材を浸漬させ乾燥させる方法、キャリアコア材を流動させて樹脂溶液を噴霧する流動床コート、樹脂とキャリアコア材を混合しながら加熱させてキャリアコア材に被覆する乾式方法等を用いることができる。
【００２９】
次に、本発明の電子写真現像剤用キャリアの製造方法について説明する。
本発明では、スラリー原料を造粒し、造粒物とした後、焼成した後、解砕、分級し、得られるキャリアコア材に樹脂を被覆する。
【００３０】
本発明の製造方法では、上記スラリー原料の１次粒子径Ｄｓ１０及びＤｓ９０が下記の関係にあることが必要である。
Ｄｓ９０≦１μｍ
２．０≦Ｄｓ１０／Ｄｓ９０≦１０．０
（構成原料粉砕時の１０％体積粒径：Ｄｓ１０、構成原料粉砕時の９０％体積粒径：Ｄｓ９０）
【００３１】
スラリー原料の１次粒子径の体積粒径であるＤｓ１０は、粒子径の累積分布において、累積１０％の時の粒子径を表す。またＤｓ９０は、粒子径の累積分布において、累積９０％の時の粒子径を表す。キャリアコア材の製造において、Ｄｓ９０とＤｓ１０の比率により造粒物を均一組成の状態に最密充填することが重要であることが判明した。
【００３２】
上述した特許文献１では、体積平均一次粒子径（Ｍｖ）／数平均一次粒子径（Ｍｎ）を１．０〜２．０にすることを提案している。粉砕条件を一般的な水準から強化していくと、表１に示す状態で変化することが判明した。これらは上記マイクロトラック粒度分析計によって測定された値である。
【００３３】
【表１】
表１に示されるように、粉砕条件３レベルでは、従来技術の範疇であるが、さらに粉砕強度を上げていくと粉砕条件４及び５で変化があることが確認された。これらの粉砕状態では、微粉側にもう一つの分布が存在する２ピークの分布を示している。これにより粉砕条件３以下と粉砕条件４及び５（Ｄｓ１０／Ｄｓ９０＝２．０〜１０．０）の状態による造粒物との特性の差が生じたと思われる。
【００３５】
上記粉砕条件別で平均粒径２０〜４５μｍの造粒物を焼成した場合、粉砕条件を強化することにより、キャリアコア材の表面性、球形度が大きく変わることが確認された。粉砕条件４及び５の１次粒子径を用いることによってキャリアコア材の表面性、球形度が著しく向上された。
【００３６】
また、キャリアの飛散物量を測定した結果、粉砕条件４及び５の１次粒子径を用いたキャリアは、粉砕条件１〜３の１次粒子径を用いたキャリアに比べて少ないことが確認された。
【００３７】
これは、粉砕条件１〜３レベルの１次粒子径を用いた場合、従来の平均粒径が８０μｍ付近のキャリアコア材であれば、均一な表面性と球形度が可能であったが、キャリアコア材の平均粒径が小さくなることによって造粒物を構成する１次粒子が従来と同じレベルだと構成原料の偏析、熱履歴の変動が生じてフェライト化反応が不均一になり、磁気特性に関しても低磁化品の発生があり、キャリアの飛散物が多くなったと思われる。
【００３８】
従って、Ｄｓ９０≦１μｍ、２．０≦Ｄｓ１０／Ｄｓ９０≦１０．０であることが必要であり、Ｄｓ９０が１μｍを超えたり、Ｄｓ１０／Ｄｓ９０が２．０未満では、構成粒子が大きくなり、粒子間のフェライト化反応にバラツキが生じ、キャリア飛散が増加する。Ｄｓ１０／Ｄｓ９０が１０．０を超えると、原料粒子の反応性が高くなり、焼成時に粒子間の付着が発生し、形状が悪化してしまう。
【００３９】
さらに、本発明の製造方法では、均一なフェライト化反応を付与するために、以下の工程を採用することが望ましい。
【００４０】
すなわち、上記造粒物を焼成する前に微粉を除去する工程を採用することが望ましい。フェライトの造粒物は粒径が小さい程、熱に対して反応性が高く、これらを含んだ状態で焼成すると粒子間の熱に対する反応性分布が広くなり均一な焼成が困難になる。また、微粉が他の粒子間の空隙に入り込み結果、空隙が小さく密な状態での焼成となり、熱が均一に焼成物に伝わりにくくなり、均一な焼成を阻害する。さらに、微粉は他粒子に付着し、キャリア飛散の原因、形状の悪化（球形度低下）の原因になる。そこで、上記のように微粉を除去することが望ましいが、微粉のみならず、粗粉を除去してもよい。
【００４１】
さらに、微粉除去後、バインダー等の添加物は、焼成時還元性ガスを発生しフェライト化反応のバラ付きの原因となるので、７００〜９００℃で加熱し除去する工程を採ることが望ましい。
【００４２】
次に、焼成工程において、焼成時の酸素濃度を０．０５％以下で焼成することが望ましい。高磁化フェライトの焼成においては、低酸素濃度の不活性な安定した焼成条件により均一な焼成が可能になる。また、焼成温度は１１００〜１３５０℃、最高温度の滞留時間は１〜６時間であることが望ましい。
【００４３】
また、焼成雰囲気の解除は、焼成物の温度が４００℃以下で行うことより不均一な状態を避けることができる。４００℃を超えた温度での解除は、再酸化等により低磁化品の発生に繋がる。
【００４４】
以上の工程又は条件を設定することにより、焼成物の組成、熱履歴、反応性を均一化し、これにより磁気特性、電気抵抗等も必然的に均一になる。この結果、均一な表面性、一定の球形度を有するキャリアコア材を得ることができる。
【００４５】
また、解砕、分級後、大気中で４００〜６００℃でキャリアコア材の表面を均一に熱処理を行い、次にメカノケミカル処理により表面の抵抗をさらに均一化させることが好ましい。
【００４６】
最後に、得られるキャリアコア材に樹脂を被覆し、電子写真現像剤用キャリアとする。
【００４７】
このような本発明の製造方法によって、表面性、磁気特性、抵抗のバラツキが小さく、表面平滑均一度が高く、キャリア飛散のマージンが高い小粒径キャリアを良好な生産性をもって得ることができる。
【００４８】
本発明の電子写真現像剤は、上記キャリアと平均粒径４〜１０μｍのトナーを少なくとも混合してなる。また、必要に応じて平均粒径１．０μｍ以下の無機微粒子を混合する。
【００４９】
本発明で使用される上記トナーは、結着物質と着色剤により構成される。結着物質としては、特に限定されるものではないが、エポキシ系樹脂、ポリエステル系樹脂、スチレン系樹脂、アクリル系樹脂、ポリアミド系樹脂、オレフィン系樹脂、酢酸ビニル重合体、ポリエーテルポリウレタン、パラフィンワックス及びそれらの共重合体等を単独でまたは混合して使用できる。
【００５０】
着色剤としては、カーボンブラック、ニグロシン、アニリンブルー、クロムイエロー、ウルトラマリンブルー、パーマネントレッド、ハンザイエロー等を広く使用することができる。
【００５１】
また、平均粒径１．０μｍ以下の無機微粒子、すなわち流動化剤や帯電量調整剤等も必要に応じて添加することができる。
【００５２】
本発明の電子写真現像方法は、内部にマグネットを有する現像スリーブ上に、上記現像剤で磁気ブラシを形成させ、該磁気ブラシにより静電潜像担持体に担持された静電潜像を顕像化するものである。
【００５３】
【実施例】
以下、実施例等に基づいて本発明を具体的に説明する。
【００５４】
〔実施例１〕
酸化鉄５５ｍｏｌ％、酸化マンガン４０ｍｏｌ％、酸化マグネシウム５ｍｏｌ％及び酸化ストロンチウムを酸化鉄、酸化マンガン及び酸化マグネシウムに対して、０．８ｍｏｌ％添加し、固形分５５％でアトライターにより湿式粉砕を行った。このスラリー中には、バインダー及び分散剤、消泡剤が添加されている。スラリー原料の粉砕分散を行い、表２示すように、マイクロトラック粒度分析計によるＤｓ１０＝２．１４μｍ、Ｄｓ９０＝０．２４μｍ、Ｄｓ１０／Ｄｓ９０＝８．９２であるスラリー１を作製した。また、Ｍｖ、Ｍｎ、Ｍｖ／Ｍｎを表２に示す。
【００５５】
作製したスラリーをスプレードライヤーにより平均粒径３０μｍの球状造粒乾燥物を得た。造粒物の微粉を気流分級により２０μｍ以下を除去した。次にロータリーキルンによりバインダー等の添加物を７００℃で除去した。焼成雰囲気が調整可能な電気炉を用いて、酸素濃度０．０５％以下、焼成温度１３００℃、最高温度の焼成時間５時間、焼成雰囲気を解除する時の焼成物温度３５０℃である条件で焼成した。焼成物を解砕、分級した後、平均粒径３５μｍのキャリア芯材を得た。キャリア芯材を回転式連続炉で内部の酸素濃度２１％、温度５００℃で熱処理し表面処理を行った後、さらに回転式容器で回転しメカノケミカルストレスを与え、キャリア芯材表面の抵抗を上げた。
【００５６】
得られたキャリア芯材の表面平滑均一度は８５％であった。また、各種物性（表面平滑均一度、平均粒径、磁気特性、電流値）を表３に示す。これらの測定方法は、上述した通りである。
【００５７】
流動床コート装置を用いて、シリコーン樹脂（商品名：ＳＲ−２４１１、東レ・ダウコーニング・シリコーン（株）製）をキャリアコア材に対して、２．０重量％被覆した。被覆後、２５０℃で３時間焼き付けを行った後、２５０メッシュで分級し、磁力選鉱を行いキャリア１を製造した。
【００５８】
（トナー作製）
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重量部、フタロシアニン顔料４重量部、ジ−ｔｅｒｔ−ブチルサリチル酸のクロム錯体４重量部を原料とし、これをヘンシェルミキサーにより十分に予備混合を行い、２軸押し出式混練機により溶融混練し、冷却後ハンマーミルを用いて約１．５μｍ程度に粗粉砕し、次にジェットミルにより微粉砕した。さらに微粉砕物を分級して、重量平均粒径が８．２μｍのシアン色の粉体を得た。該粉体１００重量部と平均粒径０．０５μｍの酸化チタン１重量部をヘンシルミキサーで混合しトナー１を得た。
【００５９】
（実機評価）
キャリア１とトナー１をトナー濃度８重量％で混合し、現像剤を作製した。シャープフルカラー複写機ＡＲＣ−２５０改造機を用いて現像剤及びトナーの初期及び１０万枚の画像評価を下記に具体的に示す方法により行った。評価結果を表４に示す。下記評価方法において、△以上が実使用上問題ないレベルである。
【００６０】
▲１▼画像濃度
適正露光条件下でコピーしＩＤの評価を行った。ベタ部の画像濃度をＸ−Ｒｉｔｅ（日本平版機材製）にて測定してランク付けを行った。
◎：非常によい
○：目標画像濃度の範囲である。
△：画像濃度が若干低めであるが使用可能。
×：目標下限を下回っている
××：画像濃度が非常に低く使用不可能。
【００６１】
▲２▼カブリ
◎：０．５未満
○：０．５〜１．０
△：１．０〜１．５
×：１．５〜２．５
××：２．５以上
【００６２】
▲３▼キャリア飛散
画像上のキャリア飛散、白斑のレベルを評価した。
◎：Ａ３用紙１０枚中に白斑が無いこと。
○：Ａ３用紙１０枚中に１〜５個
△：Ａ３用紙１０枚中に６〜１０個
×：Ａ３用紙１０枚中に１１〜２０
××：Ａ３用紙１０枚中に２１個以上
【００６３】
▲４▼トナー飛散
◎：全く見られない
○：ごく微量確認された
△：限界レベル
×：多い
××：非常に多い
【００６４】
▲５▼横細線再現性
◎：非常に良く再現している
○：ほぼ再現している
△：限界レベル
×：切れカスレが目立つ
××：全く再現していない
【００６５】
▲６▼ハーフトーン均一性
◎：非常に均一である
○：均一でムラがない
△：若干ムラが見られるが限界レベル
×：ムラが目立ち不均一
××：ムラが非常に多く不均一
【００６６】
▲７▼トナー濃度安定性
◎：非常に安定している
○：安定している
△：若干不安定
×：変動が見られる
××：変動が非常に大きい
【００６７】
〔実施例２〕
酸化鉄５５ｍｏｌ％、酸化マンガン４０ｍｏｌ％、酸化マグネシウム５ｍｏｌ％及び酸化ストロンチウムを酸化鉄、酸化マンガン及び酸化マグネシウムに対して、０．８ｍｏｌ％添加し、固形分５５％でアトライターにより湿式粉砕を行った。スラりー中には、バインダー及び分散剤、消泡剤が添加されている。スラリー原料の粉砕分散を行い、表２に示すように、マイクロトラック粒度分析計によるＤｓ１０＝２．３６μｍ、Ｄｓ９０＝０．９６μｍ、Ｄｓ１０／Ｄｓ９０＝２．４６であるスラリー２を作製した。また、Ｍｖ、Ｍｎ、Ｍｖ／Ｍｎを表２に示す。
【００６８】
作製したスラリーをスプレードライヤーを用いて球状造粒乾燥物を得た。造粒物の微紛を気流分級により１６μｍ以下を除去し、焼成温度を１２８０℃とした以外は、実施例１と同様な操作によりキャリアコア材の平均粒径が２５μｍで、樹脂被覆したキャリア２を得た。このキャリアコア材の表面平滑均一度は８０％であった。キャリアコア材の物性と現像剤及びトナーの画像評価を実施例１と同様に評価し、その結果を表３及び４に示す。
【００６９】
〔実施例３〕
実施例１と同様の原料を用いて、原料の粉砕分散を行い、表２に示すように、マイクロトラック粒度分析計によるＤｓ１０＝１．７６μｍ、Ｄｓ９０＝０．２６μｍ、Ｄｓ１０／Ｄｓ９０＝６．７７であるスラリー３を作製した。また、Ｍｖ、Ｍｎ、Ｍｖ／Ｍｎを表２に示す。
【００７０】
作製したスラリーをスプレードライヤーを用いて球状造粒乾燥物を得た。造粒物の微粉を気流分級により２４μｍ以下を除去した。次にロータリーキルンによりバインダー等を７００℃で除去した。焼成温度を１３２０℃とする以外は実施例１と同様な操作によりコア材の平均粒径４５μｍで、樹脂被覆したキャリア３を得た。このキャリアコア材の表面平滑均一度は９０％であった。キャリアコア材の物性と現像剤及びトナーの画像評価を実施例１と同様に評価し、その結果を表３及び４に示す。
【００７１】
〔比較例１〕
実施例１と同様な原料を用いて、原料の粉砕分散を行い、表２に示すように、マイクロトラック粒度分析計によるＤｓ１０＝３．５８μｍ、Ｄｓ９０＝２．１０μｍ、Ｄｓ１０／Ｄｓ９０＝１．７０のスラリー４を得た。体積平均径（Ｍｖ）＝２．８０、数平均径（Ｍｎ）＝２．４６７、Ｍｖ／Ｍｎ＝１．１３の１次粒子径であった。
【００７２】
作製したスラリーをスプレードライヤーにより平均粒径３０μｍの球状造粒乾燥物を得た後は、実施例１と同様な操作によってキャリア４を得た。このキャリアコア材の表面平滑均一度は６５％であった。キャリアコア材の物性と現像剤及びトナーの画像評価を実施例１と同様に評価し、その結果を表３及び４に示す。
【００７３】
〔比較例２〕
酸化鉄５０ｍｏｌ％、酸化マンガン４０ｍｏｌ％、酸化マグネシウム１０ｍｏｌ％及び酸化ストロンチウムを酸化鉄、酸化マンガン及び酸化マグネシウムに対して、０．５ｍｏｌ％添加とした以外は実施例１と同様にしてスラリー５を得た。
【００７４】
このスラリーをスプレードライヤーで造粒した後、微粉除去を行わない以外は、実施例１と同様にしてキャリア５を得た。このキャリアコア材の表面平滑均一度は６５％であった。キャリアコア材の物性と現像剤及びトナーの画像評価を実施例１と同様に評価し、その結果を表３及び４に示す。
【００７５】
〔比較例３〕
酸化鉄８０ｍｏｌ％、酸化マンガン２０ｍｏｌ％を用いた以外は、実施例１と同様な操作によりキャリア６を得た。このキャリアコア材の表面平滑均一度は５５％であった。キャリアコア材の物性と現像剤及びトナーの画像評価を実施例１と同様に評価し、その結果を表３及び４に示す。
【００７６】
【表２】
【表３】
【表４】
表３に示されるように、実施例１〜３は、比較例１〜３に比して、高い表面平滑均一度を有し、磁気特性及び電流値も好適な範囲にある。また、表４に示されるように、実施例１〜３は、比較例１〜３に比して、現像剤及びトナーの初期及び１０万枚の画像特性に優れる。
【００８０】
【発明の効果】
本発明の電子写真現像剤用キャリアにより、小粒径化が達成され、かつキャリア飛散等の問題が解消され、フルカラー用現像剤に使用したときに、画像特性等に優れる。また、本発明の製造方法によって、上記キャリアが良好な生産性をもって得られる。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a carrier for an electrophotographic developer and a method for producing the same, and more particularly, to a carrier for an electrophotographic developer which has excellent image characteristics and a long life when used for a full-color developer, and production thereof. About the method.
[0002]
Problems to be solved by the prior art and the invention
In the electrophotographic method, an electrostatic latent image is formed on a photoreceptor in a charging and exposing step, the electrostatic latent image is developed with a developer containing a toner, and visualized through a transfer and fixing step. The developer used here includes a two-component developer composed of a toner and a carrier, and a one-component developer used alone such as a magnetic toner.
[0003]
Among them, a two-component developer using a carrier is widely used for a full-color developer, a developer for a high-speed machine, and the like due to advantages such as excellent image quality.
[0004]
In recent years, a rapidly increasing full-color developer is required to have a capability of quickly charging a replenished toner and continuously developing a wide printing area. Further, as the size of the apparatus has been reduced, the diameter of the developing sleeve has been reduced, and the amount of the developer has been reduced. As a result, the developer carrier has been required to have further improved charging ability, longer life, and higher image quality.
[0005]
Under such circumstances, the required properties of the carrier include toner holding properties, charge-imparting ability, and reduction in particle size for softening the magnetic brush. However, the problem of carrier scattering as a detrimental effect due to the reduction in particle size has always been brought up, and many countermeasures have been proposed.
[0006]
Patent Document 1 proposes a carrier and a developer that do not cause image defects due to carrier adhesion in high-speed development.
[0007]
In Patent Literature 1, in order to prevent carrier scattering, the size of the primary particles of the raw material is set to be a number average primary particle diameter (Dv) and a volume average primary particle diameter (Dn) to achieve uniform magnetization. However, at a Dv / Dn ratio of 1.0 to 2.0 described in Patent Document 1, carrier scattering could not be prevented for ferrite having a small grain size having an average grain size of 20 to 45 μm.
[0008]
That is, in the example of Patent Document 1, the test is performed using carrier core particles having an average particle diameter of 65 μm, and it is considered that those effects are reduced at an average particle diameter of 20 to 45 μm where carrier scattering easily occurs. Further, it is presumed that as the average particle size of the carrier becomes smaller, the particle size of the raw material formed accordingly needs to be reduced.
[0009]
Further, there are many proposals regarding magnetic properties and particle size distribution for holding carrier particles on a magnetic brush.
[0010]
In Patent Document 2, the weight average particle diameter of the carrier is 35 to 55 μm, less than 22 μm: 0 to 15%, and more than 88 μm: 0 to 5%, a specific resin coat is applied, and the magnetization is 70 to 120 emu / in a magnetic field of 1 KOe. g carriers have been proposed. Certainly, higher magnetic properties have a margin for carrier scattering, but on the other hand, the magnetic brush becomes harder, and high-quality soft development becomes difficult.
[0011]
Many reports have also been made that the smaller the content of the fine powder, the better the carrier scattering. However, there are many technical issues such as classification technology, yield, etc., and price issues, so that it cannot be said that they have satisfactory performance in total.
[0012]
On the other hand, although there are many proposals regarding a small particle size carrier, even if the conventional technology for a ferrite carrier having an average particle size of 60 μm or more is applied to a ferrite carrier having an average particle size of 20 to 45 μm as an extension of the conventional technology, the carrier scattering is not improved. I couldn't respond enough.
[0013]
Accordingly, an object of the present invention is to provide a carrier for an electrophotographic developer which is excellent in image characteristics and the like when used in a full-color developer, in which a reduction in particle size is achieved, and problems such as carrier scattering are eliminated. It is to provide a method.
[0014]
[Patent Document 1]
JP-A-9-197721 [Patent Document 2]
JP 2001-27828 A
[Means for Solving the Problems]
The present inventors have conducted intensive studies and as a result, by adopting a step of performing a uniform ferrite-forming reaction, it has become possible to make the magnetic properties uniform among the carrier particles, and the sharp magnetic properties have increased the carrier scattering margin. The design of carriers for electrophotographic developers has become possible.
[0016]
That is, the present invention provides a ferrite carrier containing iron oxide as a main component, mainly having a spinel structure and having a volume average particle diameter of 20 to 45 μm, and having the following characteristics or properties. It is intended to provide an agent carrier.
(1) magnetization at a magnetic field of 1 KOe is 65 to 80 emu / g,
(2) The carrier core material has a current value of 50 to 150 μA,
(3) Surface smoothness uniformity of 75% or more,
(4) Resin coating is applied, and the coating amount is 0.1 to 5.0% by weight based on the carrier core material.
[0017]
Further, the present invention provides a method for producing a carrier for an electrophotographic developer in which a slurry raw material is granulated, formed into a granulated product, fired, then crushed and classified, and the obtained carrier core material is coated with a resin. ,
An object of the present invention is to provide a method for producing the carrier for an electrophotographic developer, wherein the primary particle diameters Ds10 and Ds90 of the slurry raw material have the following relationship.
Ds90 ≦ 1 μm
2.0 ≦ Ds10 / Ds90 ≦ 10.0
(10% volume particle size at the time of pulverizing constituent raw material: Ds10, 90% volume particle size at the time of pulverizing constituent material: Ds90)
[0018]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the carrier for an electrophotographic developer and the method for producing the same according to the present invention will be described.
[0019]
The carrier for an electrophotographic developer of the present invention is a ferrite carrier containing iron oxide as a main component, mainly having a spinel structure and a volume average particle diameter of 20 to 45 μm. This volume average particle size corresponds to the currently required reduction in carrier particle size. The volume average particle size is measured using a Microtrac particle size analyzer (Model 19320-X100) manufactured by Nikkiso Co., Ltd.
[0020]
Further, the carrier for an electrophotographic developer of the present invention needs to have the following properties or properties.
[0021]
(1) The magnetization at a magnetic field of 1 KOe is 65 to 80 emu / g. The magnetization in a magnetic field of 1 KOe is measured using a vibrating magnetometer VSM-P7 manufactured by Toei Kogyo Co., Ltd. When the magnetization is lower than 65 emu / g, the force for holding the carrier particles on the magnet roll becomes small, and carrier scattering occurs. If the magnetization exceeds 80 emu / g, the magnetic brush becomes hard and soft development cannot be performed.
[0022]
(2) The current value of the carrier core material is 50 to 150 μA. The current value of the carrier core material is measured by setting 500 g of the carrier core material in a developing machine opposed to the aluminum tube and reading the value of the conduction current when a DC voltage of 200 V is applied. When the current value is less than 50 μA, the developability is reduced. When the current value exceeds 150 μA, problems such as leaks occur.
[0023]
(3) The surface smoothness uniformity is 75% or more. The term "surface smoothness uniformity" as used herein refers to the number of core particles in which 1/2 or more of the particle surface is smooth and the total number of particles in the visual field of the SEM at a magnification of 200 times. / 2 or more is the ratio calculated by the number of smooth core particles / (the total number of particles) × 100 (%). If the surface smoothness is less than 75%, there is a difference in the ferrite-forming reaction between the carrier particles, and carrier scattering due to low-magnetization particles tends to occur.
[0024]
(4) Resin coating is applied, and the coating amount is 0.1 to 5.0% by weight based on the carrier core material. When the coating amount is less than 0.1% by weight, the effect of the charge amount control and the resistance control by the effect of the coating resin is reduced. When the coating amount is more than 5.0% by weight, the rising of the charge amount is poor, and the yield is reduced due to adhesion between particles. And the like.
[0025]
The resin for coating the carrier core material may be appropriately selected depending on the toner to be used. For example, polypropylene, polystyrene, acrylic resin, polyacrylonitrile resin, straight silicone resin and its modified products, polytetrafluoroethylene, polyvinylidene fluoride, etc. Fluorocarbon resin, polycarbonate resin, epoxy resin and the like. These can be used alone or in combination or modified. A resin material containing a silicone-based resin or a fluorine-based resin which is superior in toner contamination due to high image quality and long life is preferable.
[0026]
If an insulating resin is used as the coating resin, a high resistance is obtained. Therefore, a known conductive agent such as carbon black or titanium oxide can be dispersed in the resin and used as necessary.
[0027]
Since the carrier core material used in the present invention has a uniform surface property as described above, the film thickness of the film tends to be constant even in the coating step, and the charge core distribution has extremely excellent performance such as durability. It becomes a resin-coated carrier.
[0028]
The coating method is a method of dipping and drying a carrier core material in a resin solution, a fluidized bed coat in which the carrier core material is fluidized and a resin solution is sprayed, and a carrier core material which is heated while mixing the resin and the carrier core material. And a dry method of coating.
[0029]
Next, a method for producing the carrier for an electrophotographic developer of the present invention will be described.
In the present invention, the slurry raw material is granulated, granulated, fired, then crushed and classified, and the obtained carrier core material is coated with a resin.
[0030]
In the production method of the present invention, it is necessary that the primary particle diameters Ds10 and Ds90 of the slurry raw material have the following relationship.
Ds90 ≦ 1 μm
2.0 ≦ Ds10 / Ds90 ≦ 10.0
(10% volume particle size at the time of pulverizing constituent raw material: Ds10, 90% volume particle size at the time of pulverizing constituent material: Ds90)
[0031]
Ds10, which is the volume particle diameter of the primary particle diameter of the slurry raw material, represents the particle diameter at a cumulative 10% in the cumulative distribution of the particle diameter. Ds90 represents the particle diameter when the accumulation is 90% in the cumulative distribution of the particle diameter. In the production of the carrier core material, it has been found that it is important to pack the granules in a state of uniform composition by the ratio of Ds90 to Ds10.
[0032]
Patent Document 1 mentioned above proposes that the volume average primary particle diameter (Mv) / number average primary particle diameter (Mn) be 1.0 to 2.0. It was found that when the grinding conditions were strengthened from a general level, the conditions changed as shown in Table 1. These are values measured by the Microtrac particle size analyzer.
[0033]
[Table 1]
As shown in Table 1, it was confirmed that at the level of the pulverization condition 3, which was within the category of the prior art, there was a change in the pulverization conditions 4 and 5 as the pulverization strength was further increased. In these pulverized states, a distribution of two peaks having another distribution on the fine powder side is shown. It seems that this resulted in a difference in characteristics between the granulated product under the conditions of grinding conditions 3 or less and grinding conditions 4 and 5 (Ds10 / Ds90 = 2.0 to 10.0).
[0035]
It was confirmed that when the granulated product having an average particle size of 20 to 45 μm was baked under each of the above pulverization conditions, the surface properties and sphericity of the carrier core material were significantly changed by strengthening the pulverization conditions. By using the primary particle diameters under pulverization conditions 4 and 5, the surface properties and sphericity of the carrier core material were significantly improved.
[0036]
In addition, as a result of measuring the amount of scattered particles of the carrier, it was confirmed that the number of carriers using the primary particle diameter under the crushing conditions 4 and 5 was smaller than the number of carriers using the primary particle diameter under the crushing conditions 1 to 3. .
[0037]
This is because, when primary particle diameters of pulverization conditions 1 to 3 were used, uniform surface properties and sphericity were possible with a conventional carrier core material having an average particle diameter of about 80 μm. If the average particle diameter of the core material becomes smaller and the primary particles constituting the granulated material are at the same level as the conventional one, segregation of the constituent materials and fluctuation of the heat history occur, and the ferrite formation reaction becomes non-uniform and the magnetic properties It is considered that low magnetized products were also generated and that the amount of scattered carriers was increased.
[0038]
Therefore, it is necessary that Ds90 ≦ 1 μm and 2.0 ≦ Ds10 / Ds90 ≦ 10.0. When Ds90 exceeds 1 μm, or when Ds10 / Ds90 is less than 2.0, constituent particles become large, The ferrite conversion reaction varies, and carrier scattering increases. If Ds10 / Ds90 exceeds 10.0, the reactivity of the raw material particles will increase, and adhesion between the particles will occur during firing, resulting in poor shape.
[0039]
Furthermore, in the production method of the present invention, it is desirable to employ the following steps in order to impart a uniform ferrite-forming reaction.
[0040]
That is, it is desirable to employ a step of removing fine powder before firing the granulated product. The smaller the particle size of the ferrite granules, the higher the reactivity to heat, and if fired in a state containing these, the distribution of heat reactivity between the particles becomes wide and uniform firing becomes difficult. In addition, as a result of the fine powder entering the voids between the other particles, firing is performed in a dense state with small voids, making it difficult for heat to be uniformly transmitted to the fired product, impeding uniform firing. Furthermore, the fine powder adheres to other particles, causing carrier scattering and shape deterioration (sphericity reduction). Therefore, it is desirable to remove fine powder as described above, but not only fine powder but also coarse powder may be removed.
[0041]
Further, after the removal of fine powder, additives such as a binder generate a reducing gas at the time of firing and cause a variation in ferrite formation reaction. Therefore, it is desirable to adopt a step of removing by heating at 700 to 900 ° C.
[0042]
Next, in the firing step, it is desirable to fire at an oxygen concentration of 0.05% or less during firing. In the firing of the high magnetization ferrite, uniform firing can be performed under inert and stable firing conditions with a low oxygen concentration. The firing temperature is desirably 1100 to 1350 ° C, and the residence time at the highest temperature is desirably 1 to 6 hours.
[0043]
In addition, when the firing atmosphere is released at a temperature of the fired product of 400 ° C. or lower, an uneven state can be avoided. Release at a temperature exceeding 400 ° C. leads to generation of a low magnetization product due to reoxidation or the like.
[0044]
By setting the above steps or conditions, the composition, heat history, and reactivity of the fired product are made uniform, whereby the magnetic properties, electric resistance, and the like are necessarily made uniform. As a result, a carrier core material having uniform surface properties and a constant sphericity can be obtained.
[0045]
After crushing and classification, it is preferable to uniformly heat-treat the surface of the carrier core material at 400 to 600 ° C. in the air, and then to further uniform the surface resistance by mechanochemical treatment.
[0046]
Finally, the obtained carrier core material is coated with a resin to obtain a carrier for an electrophotographic developer.
[0047]
According to the production method of the present invention, a carrier having a small particle diameter with small variations in surface properties, magnetic properties, and resistance, high surface smoothness uniformity, and a high carrier scattering margin can be obtained with good productivity.
[0048]
The electrophotographic developer of the present invention is obtained by mixing at least the above carrier and a toner having an average particle diameter of 4 to 10 μm. Further, if necessary, inorganic fine particles having an average particle size of 1.0 μm or less are mixed.
[0049]
The toner used in the present invention is composed of a binder and a colorant. Examples of the binder include, but are not particularly limited to, an epoxy resin, a polyester resin, a styrene resin, an acrylic resin, a polyamide resin, an olefin resin, a vinyl acetate polymer, a polyether polyurethane, and a paraffin wax. And their copolymers can be used alone or as a mixture.
[0050]
As the coloring agent, carbon black, nigrosine, aniline blue, chrome yellow, ultramarine blue, permanent red, Hansa yellow and the like can be widely used.
[0051]
In addition, inorganic fine particles having an average particle size of 1.0 μm or less, that is, a fluidizing agent, a charge control agent, and the like can be added as necessary.
[0052]
According to the electrophotographic developing method of the present invention, a magnetic brush is formed with the developer on a developing sleeve having a magnet therein, and the electrostatic latent image carried on the electrostatic latent image carrier is visualized by the magnetic brush. It becomes something.
[0053]
【Example】
Hereinafter, the present invention will be specifically described based on examples and the like.
[0054]
[Example 1]
0.8 mol% of iron oxide, manganese oxide and magnesium oxide was added to 55 mol% of iron oxide, 40 mol% of manganese oxide, 5 mol% of magnesium oxide, and strontium oxide, and wet pulverization was performed by an attritor at a solid content of 55%. . A binder, a dispersant, and an antifoaming agent are added to the slurry. The slurry raw material was pulverized and dispersed, and as shown in Table 2, Slurry 1 in which Ds10 = 2.14 μm, Ds90 = 0.24 μm, and Ds10 / Ds90 = 8.92 was prepared using a Microtrac particle size analyzer. Table 2 shows Mv, Mn, and Mv / Mn.
[0055]
The prepared slurry was dried with a spray dryer to obtain a spherical granulated dried product having an average particle size of 30 μm. Fine particles of the granules were removed by air current classification to remove particles of 20 μm or less. Next, additives such as a binder were removed at 700 ° C. by a rotary kiln. Using an electric furnace whose firing atmosphere can be adjusted, firing is performed under the conditions of an oxygen concentration of 0.05% or less, a firing temperature of 1300 ° C., a firing time of the maximum temperature of 5 hours, and a firing temperature of 350 ° C. when the firing atmosphere is released. did. After crushing and classifying the fired product, a carrier core material having an average particle size of 35 μm was obtained. The carrier core material is heat-treated in a rotary continuous furnace at an internal oxygen concentration of 21% at a temperature of 500 ° C. to perform surface treatment, and then further rotated in a rotary container to apply mechanochemical stress to increase the resistance of the carrier core material surface. Was.
[0056]
The surface smoothness of the obtained carrier core material was 85%. Table 3 shows various physical properties (surface smoothness uniformity, average particle size, magnetic properties, current value). These measuring methods are as described above.
[0057]
Using a fluidized bed coater, 2.0% by weight of a silicone resin (trade name: SR-2411, manufactured by Dow Corning Toray Silicone Co., Ltd.) was coated on the carrier core material. After coating, baking was performed at 250 ° C. for 3 hours, followed by classification with 250 mesh, and magnetic separation to produce Carrier 1.
[0058]
(Toner production)
100 parts by weight of a polyester resin obtained by condensing propoxylated bisphenol and fumaric acid, 4 parts by weight of a phthalocyanine pigment, and 4 parts by weight of a chromium complex of di-tert-butylsalicylic acid were used as raw materials and thoroughly mixed with a Henschel mixer. The mixture was melt-kneaded by a twin-screw extruder, cooled, coarsely ground to about 1.5 μm using a hammer mill, and then finely ground by a jet mill. The finely pulverized product was further classified to obtain a cyan powder having a weight average particle size of 8.2 μm. 100 parts by weight of the powder and 1 part by weight of titanium oxide having an average particle size of 0.05 μm were mixed with a Hensyl mixer to obtain Toner 1.
[0059]
(Actual machine evaluation)
Carrier 1 and toner 1 were mixed at a toner concentration of 8% by weight to prepare a developer. Using a sharp full-color copying machine ARC-250 modified machine, the initial evaluation of the developer and the toner and the image evaluation of 100,000 sheets were carried out according to the methods specifically shown below. Table 4 shows the evaluation results. In the following evaluation methods, “△” or more is a level that does not cause any problem in practical use.
[0060]
{Circle around (1)} An image was copied under an appropriate exposure condition for image density, and the ID was evaluated. The solid image density was measured with an X-Rite (manufactured by Nippon Lithographic Equipment) and ranked.
◎: very good ：: target image density range
Δ: Image density is slightly lower but usable.
X: lower than the target lower limit xx: image density is extremely low and cannot be used.
[0061]
(2) Fog ◎: less than 0.5 ○: 0.5 to 1.0
Δ: 1.0 to 1.5
×: 1.5 to 2.5
XX: 2.5 or more
(3) The level of carrier scattering and white spots on the carrier scattering image was evaluated.
A: No white spots on 10 A3 sheets.
：: 1 to 5 out of 10 A3 sheets Δ: 6 to 10 out of 10 A3 sheets ×: 11 to 20 out of 10 A3 sheets
XX: 21 or more out of 10 A3 sheets.
{Circle around (4)} Toner scattering ：: not seen at all ：: very small amount confirmed △: limit level x: many xx: very large
(5) Horizontal fine line reproducibility ：: Reproducible very well ：: Almost reproduced △: Limit level X: Cut-out is noticeable XX: Not reproduced at all [0065]
{Circle around (6)} Uniformity of halftone 非常: very uniform ：: uniform and non-uniform △: slight unevenness is observed, but limit level X: unevenness is noticeable and non-uniform XX: non-uniformity is very large and non-uniform ]
{Circle around (7)} Toner density stability ：: very stable ：: stable △: slightly unstable x: fluctuation is observed xx: fluctuation is extremely large
[Example 2]
0.8 mol% of iron oxide, manganese oxide and magnesium oxide was added to 55 mol% of iron oxide, 40 mol% of manganese oxide, 5 mol% of magnesium oxide, and strontium oxide, and wet pulverization was performed by an attritor at a solid content of 55%. . In the slurry, a binder, a dispersant and an antifoaming agent are added. The slurry raw material was pulverized and dispersed, and as shown in Table 2, Slurry 2 in which Ds10 = 2.36 μm, Ds90 = 0.96 μm, and Ds10 / Ds90 = 2.46 by a Microtrac particle size analyzer was prepared. Table 2 shows Mv, Mn, and Mv / Mn.
[0068]
The prepared slurry was used to obtain a spherical granulated dried product using a spray dryer. The same procedure as in Example 1 was carried out except that the fine powder of the granulated material was removed to 16 μm or less by airflow classification, and the firing temperature was set to 1280 ° C., and the carrier-coated carrier 2 having an average particle size of 25 μm was used. Got. The surface smoothness uniformity of this carrier core material was 80%. The physical properties of the carrier core material and the image evaluation of the developer and toner were evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.
[0069]
[Example 3]
Using the same raw materials as in Example 1, the raw materials were pulverized and dispersed, and as shown in Table 2, Ds10 = 1.76 μm, Ds90 = 0.26 μm, and Ds10 / Ds90 = 6.77 by a Microtrac particle size analyzer. Was prepared. Table 2 shows Mv, Mn, and Mv / Mn.
[0070]
The prepared slurry was used to obtain a spherical granulated dried product using a spray dryer. Fine particles of the granules were removed by air current classification to remove 24 μm or less. Next, the binder and the like were removed at 700 ° C. by a rotary kiln. Carrier 3 coated with resin having an average core particle size of 45 μm was obtained in the same manner as in Example 1 except that the firing temperature was changed to 1320 ° C. The surface smoothness of the carrier core material was 90%. The physical properties of the carrier core material and the image evaluation of the developer and toner were evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.
[0071]
[Comparative Example 1]
Using the same raw materials as in Example 1, the raw materials were pulverized and dispersed, and as shown in Table 2, Ds10 = 3.58 μm, Ds90 = 2.10 μm, and Ds10 / Ds90 = 1.70 by a Microtrac particle size analyzer. Slurry 4 was obtained. The volume average diameter (Mv) was 2.80, the number average diameter (Mn) was 2.467, and the primary particle diameter was Mv / Mn = 1.13.
[0072]
After a spherical granulated dried product having an average particle size of 30 μm was obtained from the produced slurry by a spray dryer, a carrier 4 was obtained in the same manner as in Example 1. The surface smoothness uniformity of this carrier core material was 65%. The physical properties of the carrier core material and the image evaluation of the developer and toner were evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.
[0073]
[Comparative Example 2]
Slurry 5 was obtained in the same manner as in Example 1, except that iron oxide, manganese oxide and magnesium oxide were added in an amount of 0.5 mol% to iron oxide, manganese oxide and magnesium oxide, respectively. Was.
[0074]
After granulating this slurry with a spray drier, a carrier 5 was obtained in the same manner as in Example 1 except that fine powder was not removed. The surface smoothness uniformity of this carrier core material was 65%. The physical properties of the carrier core material and the image evaluation of the developer and toner were evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.
[0075]
[Comparative Example 3]
Carrier 6 was obtained in the same manner as in Example 1, except that 80 mol% of iron oxide and 20 mol% of manganese oxide were used. The surface smoothness of the carrier core material was 55%. The physical properties of the carrier core material and the image evaluation of the developer and toner were evaluated in the same manner as in Example 1, and the results are shown in Tables 3 and 4.
[0076]
[Table 2]
[Table 3]
[Table 4]
As shown in Table 3, Examples 1 to 3 have higher surface smoothness uniformity than Comparative Examples 1 to 3, and the magnetic properties and the current value are also in suitable ranges. Further, as shown in Table 4, Examples 1 to 3 are superior to Comparative Examples 1 to 3 in the initial properties of the developer and the toner and the image characteristics of 100,000 sheets.
[0080]
【The invention's effect】
The carrier for an electrophotographic developer according to the present invention achieves a reduction in particle size, eliminates problems such as carrier scattering, and has excellent image characteristics when used in a full-color developer. Further, the carrier can be obtained with good productivity by the production method of the present invention.
Claims (6)
（１）磁場１ＫＯｅにおける磁化が６５〜８０ｅｍｕ／ｇ、
（２）キャリアコア材の電流値が５０〜１５０μＡ、
（３）表面平滑均一度が７５％以上、
（４）樹脂被覆が施されており、被覆量がキャリアコア材に対して０．１〜５．０重量％。A ferrite carrier mainly composed of iron oxide, mainly having a spinel structure and having a volume average particle diameter of 20 to 45 μm, and having the following characteristics or properties, and a carrier for an electrophotographic developer.
(1) magnetization at a magnetic field of 1 KOe is 65 to 80 emu / g,
(2) The carrier core material has a current value of 50 to 150 μA,
(3) Surface smoothness uniformity of 75% or more,
(4) Resin coating is applied, and the coating amount is 0.1 to 5.0% by weight based on the carrier core material.
上記スラリー原料の１次粒子径Ｄｓ１０及びＤｓ９０が下記の関係にあることを特徴とする請求項１記載の電子写真現像剤用キャリアの製造方法。
Ｄｓ９０≦１μｍ
２．０≦Ｄｓ１０／Ｄｓ９０≦１０．０
（構成原料粉砕時の１０％体積粒径：Ｄｓ１０、構成原料粉砕時の９０％体積粒径：Ｄｓ９０）After the slurry raw material is granulated and granulated, after firing, crushed, classified, in a method for producing a carrier for an electrophotographic developer, the obtained carrier core material is coated with a resin,
The method for producing a carrier for an electrophotographic developer according to claim 1, wherein the primary particle diameters Ds10 and Ds90 of the slurry raw material have the following relationship.
Ds90 ≦ 1 μm
2.0 ≦ Ds10 / Ds90 ≦ 10.0
(10% volume particle size at the time of pulverizing constituent raw material: Ds10, 90% volume particle size at the time of pulverizing constituent material: Ds90)
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Cited By (7)
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| JP2006201648A (en) * | 2005-01-24 | 2006-08-03 | Sharp Corp | Toner and developer comprising the toner |
| JP2007011295A (en) * | 2005-06-27 | 2007-01-18 | Toshiba Corp | Image forming apparatus and method for forming image |
| JP2012076955A (en) * | 2010-09-30 | 2012-04-19 | Dowa Electronics Materials Co Ltd | Ferrite particle, and electrophotographic developing carrier and electrophotographic developer using the same |
| WO2012105078A1 (en) | 2011-01-31 | 2012-08-09 | パウダーテック株式会社 | Ferrite carrier core material for electrophotographic developers, ferrite carrier, and manufacturing processes for both, and electrophotographic developers using the ferrite carrier |
| JP5898807B1 (en) * | 2015-08-06 | 2016-04-06 | Ｄｏｗａエレクトロニクス株式会社 | Ferrite particles, electrophotographic developer carrier and electrophotographic developer using the same |
| JP2016118646A (en) * | 2014-12-19 | 2016-06-30 | Ｄｏｗａエレクトロニクス株式会社 | Ferrite particles, and carrier for electrophotography and developer for electrophotography using the same |
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| JP2006201648A (en) * | 2005-01-24 | 2006-08-03 | Sharp Corp | Toner and developer comprising the toner |
| JP2007011295A (en) * | 2005-06-27 | 2007-01-18 | Toshiba Corp | Image forming apparatus and method for forming image |
| JP2012076955A (en) * | 2010-09-30 | 2012-04-19 | Dowa Electronics Materials Co Ltd | Ferrite particle, and electrophotographic developing carrier and electrophotographic developer using the same |
| WO2012105078A1 (en) | 2011-01-31 | 2012-08-09 | パウダーテック株式会社 | Ferrite carrier core material for electrophotographic developers, ferrite carrier, and manufacturing processes for both, and electrophotographic developers using the ferrite carrier |
| KR20140001986A (en) | 2011-01-31 | 2014-01-07 | 파우더테크 컴퍼니 리미티드 | Ferrite carrier core material for electrophotographic developers, ferrite carrier, and manufacturing processes for both, and electrophotographic developers using the ferrite carrier |
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