JP3769762B2 - Electrostatic image developer - Google Patents

Description

【００２４】
また、本発明のキャリアは、コア材である球形磁性粒子表面を樹脂被覆することが必要である。表面を樹脂被覆しない磁性粒子をキャリアとした場合は、その表面エネルギーが高いために、現像器内の撹拌ストレスによりトナーがキャリア表面へ融着しやすく、その結果、長期使用するにつれキャリアの帯電付与能力が低下し、かぶりや画像荒れの原因となる。
【００２５】
本発明のキャリアの被覆に用いることのできる樹脂としては、必要な帯電性を付与できる公知の材料を使用できるが、具体的には、スチレン系樹脂、アクリル系樹脂、スチレン／アクリル系樹脂、エステル系樹脂、ウレタン系樹脂、オレフィン系樹脂、フェノール系樹脂、カーボネート樹脂、ケトン系樹脂、フッ素系樹脂、シリコン系樹脂またはその変性体等、もしくはこれらのうちの２種以上の共重合体や混合体からなる樹脂を用いることができる。
【００２６】
樹脂の製造方法としては具体的に、溶液重合法、懸濁重合法、乳化重合法、塊状重合法、in-situ重合法等を用いることができる。
【００２７】
本発明においては上記樹脂の内の１種、必要に応じてこれらの樹脂の内の２種類以上を併用しても良い。
【００２８】
キャリアの被覆層の体積固有抵抗は、１×10¹⁰〜１×10¹⁴Ωcmの範囲のものが良好な結果を与える。この値が１×10¹⁰Ωcm以下の場合は、トナーへの帯電付与能力が低く、かぶりやトナー飛散の原因となり、実用上の問題が大きい。
【００２９】
また、１×10¹⁴Ωcm以上の場合は十分な現像性が得られず、画像濃度が不足する。被覆層の体積固有抵抗の測定法は、基本的にはコア材の場合と同様であるが、測定試料は成型機にてペレット化したものを使用する。成型にあたっては被覆層を構成する材料約0.2ｇを成型機に投入し、面圧500kgf／cm²にて30秒間圧縮成型し、断面積１cm²のペレットを作成する。こうして得られたペレットを、コア材と同様の条件にて体積固有抵抗を測定した。
【００３０】
本発明のキャリアの被覆に用いることのできる樹脂の好ましい被覆量は樹脂の比重によっても多少変更する必要があるが、多くの場合、コア材に対して好ましくは0.5〜5.0wt％、さらに好ましくは1.0〜3.0wt％のものが良好な結果を与える。樹脂被覆量が0.5wt％以下の場合は、長期使用した場合にコア材表面が露出しやすく、樹脂を被覆しない場合と同様の問題が発生する。また、樹脂被覆量が5.0wt％以上の場合は、キャリアの流動性が低くなるために現像器内にて現像剤の混合ムラが生じやすく、トナー帯電量が不安定となり、かぶりやトナー飛散の原因となる。
【００３１】
本発明のキャリアのコア材表面への樹脂被覆の方法としては、公知の方法を使用できるが、具体的には、前述の方法で得られた樹脂の分散溶液を該コア材表面へ噴霧する方法、分散溶液中へ該コア材を浸漬させる方法等の湿式コーティング方法や、微粒子化した被覆用樹脂をキャリアのコア材表面に静電気的に付着させ、その後、該コア材表面に熱と機械的応力のどちらか一方もしくは両方を加えることにより、該キャリアのコア材表面に樹脂層を付着し、固定化させる乾式コーティング方法を用いることができる。
【００３２】
また、上記の方法により樹脂被覆したキャリアの磁化は、10kOeの磁場を印加した際に磁化が70〜120emu／ｇ、好ましくは80〜100emu／ｇであるものを使用できる。磁化が120emu／ｇより高いと磁気ブラシが硬くなり、現像性が不足気味となる。その結果、出力画像上では、濃度低下、濃度ムラ、掃き目等の画像不良が発生する。逆に、磁化が70emu／ｇより低いと、現像領域へ搬送される現像剤量が不足するため、現像性低下を引き起こし、出力画像の濃度低下が発生する。さらに、上記の方法により樹脂被覆したキャリアの残留磁気は、10kOeの磁場を印加した後に、残留磁気が30〜240Gauss、好ましくは50〜120Gaussであるものを使用できる。残留磁気が240Gaussより高いと、現像器内での現像剤が凝集気味となり、撹拌によって現像剤に与えるストレスが過大となり現像剤の耐久性が低下する。逆に残留磁気が30Gaussより低いと、補給されたトナーと現像剤との混合性が不足し、多くの場合、不十分な帯電量のトナーが発生する。その帯電不良トナーは現像器周りへ飛散したり、かぶり等の画像不良の原因となる。
【００３３】
本発明の樹脂被覆したキャリアの磁化、残留磁気の測定には、直流磁化特性自動記録装置3257-35型（横河電機(株)製）を使用して求めることができる。測定条件を以下に示す。
【００３４】
測定するキャリアは、あらかじめ室温20℃、相対湿度50％の環境にて２時間調湿しておいたものを使用する。高さ20mm、内径15.8mmのアクリル製円筒にキャリアを充填し、試料重量Ｗ［ｇ］を求める。その後、キャリアを充填したアクリル円筒を上記直流磁化特性自動記録装置にセットし、10kOeの磁場をかけて、ｙ軸が磁束密度Ｂ(Gauss)、ｘ軸が磁界の強さＨ（Oe）の磁気ヒステリシス曲線を得る。
【００３５】
磁気ヒステリシス曲線の例を図１に示す。
【００３６】
ｘ軸上に10kOeの磁場をかけた時、（0.0）から徐々に上昇してｙ軸の磁束密度がBmに達した時点をａとし、次に磁界を弱めると磁界が０になっても磁束密度は０にならず、ｂという磁束が残る。ｙ軸の磁束密度Ｂにおけるｂの磁気を０に戻すために、逆方向に磁界を強めて行けばｃの点で磁束密度は０となる。さらに磁界を強めればｄの点で飽和する。そこから、また磁界を弱め、ｅの点で磁界が０になるとOeの残留磁束が残り、なお正方向に磁界を強めて行けばｆの点で磁束は０となる。
【００３７】
磁化は10kOeの磁場の印加時の磁束密度Ｂmを用いて、以下の変換式により算出される。
【００３８】
磁化＝Ｂm／(４π・Ｗ)
Ｗ：測定キャリア重量（ｇ）
また、残留磁気は10kOeの磁場の印加後の磁束密度Ｂの値（図における（０ｂ＋０ｅ）／２）として得られる。
【００３９】
本発明に必要な磁気特性を持つ、樹脂被覆したキャリアに用いるコア材を製造するには、以下の方法を用いることができる。
【００４０】
原料となるα-Fe₂O₃を粉砕した後、水素などの還元雰囲気下にて500〜700℃の温度で数時間加熱還元し、得られた鉄酸化物を水に混合してスラリーとする。
【００４１】
このスラリーをスプレードライヤーにて噴霧、造粒した後、焼結を行う。この場合、焼結工程の雰囲気として窒素などの不活性ガスまたは還元性ガス雰囲気を選択し、その焼結温度を1050〜1250℃、焼結時間を２〜６時間の範囲内の条件とすることが好ましい。その後、解砕、分級の工程を経て本発明に用いるコア材が得られる。磁気特性の制御にあたっては、飽和磁化については原料純度、還元工程、焼結工程の条件により、また、残留磁気については、焼結工程の雰囲気、温度、時間の制御により適正な範囲に収めることができる。
【００４２】
また、本発明に用いられるトナーは公知のものを使用できる。具体的には、少なくとも結着樹脂、着色剤からなるトナーであり、さらに必要に応じて離型剤、荷電制御剤、磁性体、流動化剤等を添加したものを使用できる。構成される材料には公知のものが用いられる。
【００４３】
上記本発明に用いられるトナーの製造方法は、公知の方法を使用できる。具体的には、構成される材料を混合し、溶融混練した後、冷却工程を経て、粉砕、分級を行いトナーを得る方法、また、乳化重合、懸濁重合等を用いてトナーを得る重合法等を挙げることができる。
【００４４】
上記トナーの体積平均粒径としては、好ましくは、キャリアの体積平均粒径に対して１／30〜１／２のもの、さらに好ましくは１／20〜１／５の範囲のものを使用すると、良好な結果を与える。なお、トナーの体積平均粒径の測定はキャリアの場合と同様に、レーザー回折式粒度測定機「ＨＥＬＯＳ」（日本電子製）を使用して求めることができる。
【００４５】
本発明のキャリアに対するトナーの体積平均粒径が１／30以下の場合は、該キャリアがトナーに比べ大き過ぎ、現像器内の現像剤の撹拌による該キャリアによりトナーが圧縮変形されたり、該キャリア表面へトナーが融着しやすくなるため、長期間使用する場合に、帯電付与能力の低下がみられ、また、かぶりや画像荒れの原因となる。
【００４６】
また、本発明のキャリアに対するトナーの体積平均粒径が１／２以上の場合は、現像器内の現像剤の撹拌によって該キャリアがトナーに十分な帯電量を付与することができず、トナーの帯電量が不安定となり、かぶりやトナー飛散の原因となる。
【００４７】
なお、二成分現像剤として使用するためには、あらかじめ、キャリアとトナーを混合しておく必要がある。
【００４８】
本発明のキャリアとトナーの混合比率は、該キャリアやトナーの比重や粒径によって多少変更する必要があるが、多くの場合、該キャリアに対して、トナーは2.0〜10.0wt％の範囲に設定するのが好ましい。トナーの混合比率が2.0wt％以下の場合は現像領域に搬送されるトナー量が不十分であり、出力画像濃度が不足する。また、トナーの混合比率が10.0wt％以上の場合は、キャリアに対しトナーの量が過剰となり、トナーが十分にキャリアと接触できず、トナー帯電量が不安定となり、かぶりやトナー飛散の原因となる。
【００４９】
本発明のキャリアとトナーの混合に際しては、従来より公知の混合機を用いることができるが、その際に現像剤に加わるストレスが小さいものの方が好ましい。具体的には、Ｖ型混合機、Ｗコーン混合機、ロッキングミキサー等の自転型の混合機等を挙げることができ、ヘンシェルミキサー等の撹拌型よりも良好な結果が得られる。
【００５０】
本発明に用いられる現像剤に適用する現像器には、現像剤の撹拌混合部と、現像剤を現像領域へ搬送する現像剤搬送部、トナー補給部から構成されるものを使用できる。上記現像剤の撹拌混合部の構成としては、公知の現像器に用いられている撹拌混合方式を用いることができる。
【００５１】
上記現像剤の搬送部の構成としては、固定された磁気ロールを内包し、その磁気力を利用して外周の非磁性スリーブが回転することにより現像剤を現像領域へ搬送する構成のものを使用できる。
【００５２】
本発明に用いられる現像剤搬送部の非磁性スリーブの材質としてはアルミニウム、ステンレス等が使用可能である。また、上記現像剤を現像領域へ安定して搬送するためには非磁性スリーブ表面に溶射処理、サンドブラスト処理などの粗面化処理を加えたものを使用することが有効である。
【００５３】
また、本発明に用いられる現像剤搬送部の内部に固定された磁気ロールは、現像剤の搬送、現像を目的とした複数の磁極により構成される。
【００５４】
現像のために作用する磁極は１個、もしくは複数で構成され、その磁束密度は600〜1400Gauss、好ましくは800〜1200Gaussのものを用いると良好な結果を得られる。
【００５５】
さらに、現像のための磁極の位置は、現像スリーブと感光体が最接近する位置を中心とし、現像スリーブの回転軸に対し±30°の範囲が適切であるが、好ましくは±15°の範囲に設定するとより良好な結果が得られる。
【００５６】
搬送のために作用する磁極には、磁束密度が400〜800Gaussのものを用いるのが好ましい。
【００５７】
また、搬送のための磁極の総数は少なくとも３個、好ましくは４〜８個で構成されると、現像剤の搬送性が非常に安定する。
【００５８】
【実施例】
以下、実施例を挙げて本発明を詳細に説明するが、本発明の態様はこれらに限定されない。
【００５９】
−キャリアの作成−
本発明の実施にあたり、表１の様に７種のキャリアを作成して用いた。なお、被覆用樹脂には、メチルメタクリレート／ブチルメタクリレート＝７／３共重合樹脂（体積固有抵抗2.5×10¹³Ωcm）を使用した。また、樹脂の被覆方法は、コア材を流動化させて樹脂溶液をスプレーにより噴霧する方法を用いた。
【００６０】
キャリア一覧
【００６１】
【表１】

【００６２】
−トナーの作成−
本発明を実施するにあたって使用したトナーは、以下の方法で作成した。しかし、本発明に使用されるトナーは、この作成法に限定されない。
【００６３】
ポリエステル樹脂に対し、離型剤としてカルナバワックス２wt％、着色剤としてカーボンブラック12wt％を混合し、２軸混練機にて溶融混練を行なった。
【００６４】
その後冷却、粗砕工程を経て、微粉砕、風力分級を行い、体積平均粒径が8.0μmの着色粒子を得た。さらにその後、流動化剤として、着色粒子に対し疎水性シリカ微粒子を0.5wt％外添混合し、本発明の実施例に用いるトナーとした。
【００６５】
−現像剤の調製−
表１に示した７種のキャリア各々1692ｇ、および該キャリアに対してそれぞれトナー108ｇをＶ型混合機に投入し、10分間混合してトナー濃度6.0wt％の現像剤を調製した。
【００６６】
実施例１
表１のキャリアNo.１を用いて調製した現像剤１をU-Bix5076（Konica製）改造機に投入し、連続５万枚複写を行うことにより該現像剤１の性能評価を行った。
【００６７】
なお、図２は本実施例で使用した複写機の現像器の現像スリーブの磁極配置を模式的に示す断面図である。図２において、現像磁極３の位置は現像スリーブ６と感光体９の最接近部を中心とし、現像スリーブ６の磁極固定軸７に対し現像剤の搬送上流側＋５°の位置に設置されている。
【００６８】
また、本発明においては上記現像磁極３は、幅10mm、磁束密度は1000Gaussのものを使用した。搬送磁極１，２，４，５については図２に示した通り現像スリーブ６内に設置し、磁束密度はそれぞれ搬送磁極１から順に700，750，750，600Gaussであるものを使用した。
【００６９】
実施例１の結果を表２に示す。
【００７０】
実施例２、３、４
現像剤１をキャリアNo.２，３，４からなる現像剤２，３，４にそれぞれ換えた以外は実施例１と同様に連続５万枚複写を行い、各々現像剤２，３，４の性能評価を行った。結果を以下の表２に示す。
【００７１】
比較例１
上記現像剤をキャリアNo.５からなる現像剤５に換えた以外は実施例１と同様に連続５万枚複写を行い、該現像剤５の性能評価を行った。結果を以下の表２に示す。
【００７２】
比較例２
上記現像剤をキャリアNo.６からなる現像剤６に換えた以外は実施例１と同様に連続５万枚複写を行い、該現像剤６の性能評価を行った。結果を以下の表２に示す。
【００７３】
比較例３
上記現像剤をキャリアNo.７からなる現像剤７に換えた以外は実施例１と同様に連続５万枚複写を行い、該現像剤７の性能評価を行った。結果を以下の表２に示す。
【００７４】
−評価−
現像剤の性能を以下の方法および基準で評価した。
【００７５】
（画像濃度）
原稿濃度1.30のベタ画像を複写し、その出力画像の白紙に対する相対反射濃度を測定した。なお、濃度測定にはマクベス濃度計を使用し、画像濃度1.30以上は良好であると判断した。また、評価は複写１枚目（複写初期ともいう）と５万枚目について行った。
【００７６】
（解像度）
細線画像を複写し、その出力画像の１mm幅当たりに再現された細線の本数を評価した。なお、再現細線本数が多いほど解像度が高く、良好な画像であると判断した。また、評価は複写５万枚目の画像について行った。
【００７７】
（掃き目）
複写５万枚を行った後、原稿濃度1.00のベタ画像を複写し、その出力画像を目視観察することにより判断した。紙送り方向に擦過状の画像乱れが未発生の場合は良好であり「○」、発生が見られる場合は不良であり「×」とした。
【００７８】
（かぶり）
複写５万枚を行った後、白紙原稿を複写し、その出力画像の白紙に対する相対反射濃度を測定した。なお、濃度測定にはマクベス濃度計を使用し、画像濃度0.005以下は良好であると判断した。
【００７９】
（濃度ムラ）
複写５万枚を行った後、原稿濃度1.00のベタ画像を連続10枚複写し、その出力画像の白紙に対する相対反射濃度を10枚すべてについて、各々測定した。その10枚の各濃度データの最大値と最小値の差が0.02以下の場合は良好であり「○」、それを超えるものを「×」とし不良であると判断した。
【００８０】
（キャリア付着）
複写１枚目から10枚目までの出力画像の目視観察により判断した。キャリア付着が未発生で問題のないものは「○」、キャリア付着が確認され不良であるものは「×」とした。
【００８１】
以下、上記結果を表２に示す。
【００８２】
【表２】

【００８３】
実施例１〜４
表２のデータから明らかな様に、本発明の現像剤を用いた実施例１〜４は、複写初期から高い画像濃度と解像力を維持し、掃き目、かぶり濃度、濃度ムラ及びキャリア付着のない高品位な画像を終始得ることができた。
【００８４】
特に、残留磁気が50〜120Gaussの範囲にある現像剤を用いた実施例１および２においては、複写初期の画像濃度が他に比して一段と良好であり、また、複写５万枚目でも複写初期の画像濃度とほとんど差がなく、画像濃度の劣化が著しく少ないことがわかる。さらに、前記実施例１および２の解像力およびかぶり濃度についても、他に比して良好であり、その効果が顕著に優れていることがわかる。比較例１
表２のデータから明らかな如く、複写初期から画像が低く、また、解像度も不十分であった。さらに、キャリア付着も発生し、実用上の問題があった。
【００８５】
比較例２
表２のデータから明らかな如く、５万枚複写を行ったところ、ベタ部に掃き目が目立ち、また、かぶり濃度が著しく高く、そのためかぶりが発生していることがわかる。又、濃度ムラも発生しており、高品位な画像を得ることが出来なかった。
【００８６】
比較例３
表２のデータから明らかな如く、複写初期から画像濃度がやや低めであり、解像度も不十分であった。また、５万枚複写を行ったところ、ベタ部に掃き目が目立ち、濃度ムラも発生した。
【００８７】
【発明の効果】
本発明の二成分現像剤である静電荷像現像用キャリア並びに該キャリアを用いた電子写真方法を用いれば、キャリア付着や、画像背景部へのかぶり、ベタ部分の掃き目がなく、濃度が高く均質で、かつ高い解像度をもつ出力画像を長期に渡り得ることができる。
【図面の簡単な説明】
【図１】本発明における磁気ヒステリシス曲線の一例を模式的に示す図である。
【図２】本発明で使用される感光体と現像スリーブの一例を模式的に示す断面図である。
【符号の説明】
１、２、４、５ 搬送磁極
３ 現像磁極
６ 現像スリーブ
７ 磁極固定軸
８ 厚さ規制部材
９ 感光体[0001]
[Industrial application fields]
The present invention relates to an electrostatic charge image developing carrier used for electrophotography, electrostatic photography, electrostatic printing or the like.
[0002]
[Prior art]
The two-component developer applied to the magnetic brush development method is composed of a toner and a carrier for developing an electrostatic image (hereinafter referred to as a carrier). In many cases, iron powder or ferrite particles are used as the carrier. .
[0003]
However, iron powder has a large specific gravity of the particles themselves, and when applied to a carrier used by mixing with toner, the stress applied to the toner and carrier particles is increased by mixing and stirring in the developing device. When the mechanical load applied to the developer is large, the performance of the toner and the carrier is deteriorated at an early stage, and the output image is rough and the background is fogged. In addition, iron powder has extremely high magnetization, and the magnetic brush ears become hard. When applied to the magnetic brush development method, the developed toner layer is disturbed, which adversely affects the output image. It has become.
[0004]
In order to avoid the above problem, ferrite particles are often used in conventional two-component developers. Ferrite particles have a lower specific gravity and magnetization than iron powder, and the above-described problems are unlikely to occur. On the other hand, since the volume resistivity is high, the developability is low and the output image density is low. In order to solve the problem, the toner concentration is increased or conductive fine particles are added to the carrier coating resin. Currently, no performance is available.
[0005]
Further, in order to obtain high image quality, it has been conventionally performed to reduce the particle size of the toner. However, in the case of a two-component developer, it is necessary to reduce the carrier particle size in accordance with the toner particle size in order to secure a charging site. However, when the ferrite carrier used conventionally is made smaller in size, the ears of the magnetic brush become dense and the ears become harder. As a result, the scratching force of the magnetic brush becomes larger, and the magnetic particles per one The above-mentioned problems appear more prominently, such as a decrease in magnetization and carrier adhesion.
[0006]
[Problems to be solved by the invention]
The object of the present invention is to obtain an output image having a high density, a uniform density, and a high resolution without carrier adhesion, fogging on the background of the image, and no solid portion sweep even when the carrier has a small particle size. it is to provide an electrophotographic image forming method using the career for developing electrostatic images capable.
[0007]
[Means for Solving the Problems]
Result of intensive studies to solve the above problems, and found that it is effective to control the residual magnetism impact the mixing characteristics with magnetization of the magnetic carrier used in two-component developer.
[0008]
Therefore, the above object of the present invention has been achieved by the following constitution.
[0009]
An electrostatic charge image developing carrier having a volume average particle size of 30 to 70 μm and substantially spherical magnetite particles as a core material coated with a resin, and a magnetic field of 10 kOe applied to the resin coated electrostatic charge image developing carrier Is a developer using an electrostatic charge image developing carrier having a magnetization of 70 to 120 emu / g and a residual magnetic Br of 60 to 110 Gauss after applying a magnetic field of 10 kOe, and is further included in the developer An electrostatic charge image developer, wherein the toner is a non-magnetic toner and the volume average particle diameter thereof is 1/20 to 1/5 of the volume average particle diameter of the carrier.
[0010]
The present invention will be described in more detail below.
[0011]
Magnetization (hereinafter referred to as magnetization when a magnetic field of 10 kOe is applied) affects the mixing characteristics on the magnetic sleeve, that is, the ability to replace the developer in the development area and the hardness of the head of the magnetic brush.
[0012]
When the saturation magnetization is high, the magnetic brush is too hard, and in the development area, the toner present on the side close to the magnetic sleeve remains taken into the magnetic brush and is difficult to be developed. Further, since the magnetic brush is hard, the rubbing force in the developing area increases, and the toner once developed is scraped off. Accordingly, the developability tends to be insufficient, and image defects such as density reduction, density unevenness, and sweeping occur on the output image. On the other hand, if the saturation magnetization is low, the ears of the magnetic brush are lowered, the developer carrying ability of the magnetic sleeve is also lowered, and the amount of developer carried to the developing area is insufficient. Accordingly, the developability is lowered and the density of the output image is lowered.
[0013]
In addition to the mixing characteristics on the magnetic sleeve , the residual magnetism (hereinafter referred to as the residual magnetic Br after applying a magnetic field of 10 kOe ) is the developer agitation and mixing characteristics in the developer, that is, the developer and replenishment toner. Affects mixability.
[0014]
When the residual magnetism is high, the developer in the developing device tends to agglomerate, and as the mixing and stirring torque increases, the stress applied to the developer becomes excessive and the durability of the developer decreases. This is because image defects such as a decrease in image density and fogging on the background occur as the number of copies increases.
[0015]
On the other hand, if the residual magnetism is low, the cohesive force of the developer is insufficient, so that carrier adhesion occurs in the development region, causing image defects. Further, in the stirring and mixing region, for the same reason, it is not possible to give an appropriate stress to the developer by stirring, and the mixing property between the replenished toner and the developer becomes insufficient. As a result, in many cases, the toner is introduced into the development area before a sufficient charge amount can be imparted to the toner. Insufficiently charged toner scatters around the developing device or adheres to the photoconductor regardless of the latent image, causing image defects such as contamination of the output image and fogging on the background.
[0016]
In order to improve the mixing characteristics of the two-component developer, it is important to use a magnetite carrier made of hematite and wustite as a carrier and keep the residual magnetism in an appropriate range together with the saturation magnetization.
[0017]
When the developer comprising the carrier of the present invention is used, even when the particle size of the carrier is reduced, high developability can be secured while suppressing carrier adhesion, and a high-quality output image can be obtained.
[0018]
As the core material used in the carrier of the present invention, substantially spherical magnetic particles are used. The term “substantially spherical” as used herein means that the core material particles have a minor axis / major axis ratio of 0.7 to 1.0. Measurement can be easily performed with an electron micrograph. Specifically, the minor axis / major axis ratio was determined for any 300 of the photographed carriers, and the average value was calculated. When the minor diameter / major diameter ratio of the core material particles is 0.7 or less, uneven mixing of the developer is likely to occur in the developing machine, so that the toner charge amount becomes unstable and causes fogging or toner scattering.
[0019]
The volume average particle size of the core material is preferably 20 to 150 μm, more preferably 30 to 80 μm.
[0020]
The volume average particle diameter can be measured using a laser diffraction particle size measuring instrument “HELOS” (manufactured by JEOL Ltd.). When the volume average particle size is 20 μm or less, carrier adhesion is likely to occur, which causes a practical problem. On the other hand, when the volume average particle diameter is larger than 150 μm, the uniformity of the magnetic brush is insufficient, image density unevenness is likely to occur, and the reproducibility of fine lines is also poor.
[0021]
The core material preferably has a volume resistivity of 1 × 10 ⁴ to 1 × 10 ¹² Ωcm, more preferably 1 × 10 ⁵ to 1 × 10 ¹⁰ Ωcm. . When this value is 1 × 10 ⁴ Ωcm or less, carrier adhesion to the photoconductor occurs, which is a practical problem. When the density is 1 × 10 ¹² Ωcm or more, sufficient developability cannot be obtained, and the image density is insufficient.
[0022]
Specifically, the volume resistivity of the core material is measured by filling an insulating cylindrical container having a cross-sectional area of 1.0 cm ² with about 1 g of core material in an environment of room temperature of 20 degrees and relative humidity of 50%. After obtaining the sample height under load, an electric field of DC 100 V is applied to measure the current value. From the obtained sample height and current value, the volume resistivity was calculated by the following formula.
[0023]
[Expression 1]

[0024]
In addition, the carrier of the present invention needs to be resin-coated on the surface of the spherical magnetic particles as the core material. When magnetic particles that do not have a resin-coated surface are used as the carrier, the surface energy is high, so the toner is easily fused to the carrier surface due to agitation stress in the developing unit. As a result, the carrier is imparted with long-term use. The ability is reduced, causing fogging and image roughness.
[0025]
As the resin that can be used for coating the carrier of the present invention, known materials that can impart the necessary chargeability can be used. Specifically, styrene resins, acrylic resins, styrene / acrylic resins, esters Resin, urethane resin, olefin resin, phenol resin, carbonate resin, ketone resin, fluorine resin, silicon resin or a modified product thereof, or a copolymer or mixture of two or more of them A resin made of can be used.
[0026]
Specifically, a solution polymerization method, a suspension polymerization method, an emulsion polymerization method, a bulk polymerization method, an in-situ polymerization method, or the like can be used as the resin production method.
[0027]
In the present invention, one of the above resins, and two or more of these resins may be used in combination as required.
[0028]
The volume resistivity of the carrier coating layer in the range of 1 × 10 ¹⁰ to 1 × 10 ¹⁴ Ωcm gives good results. When this value is 1 × 10 ¹⁰ Ωcm or less, the ability to impart charge to the toner is low, causing fogging and toner scattering, which is a practical problem.
[0029]
When the density is 1 × 10 ¹⁴ Ωcm or more, sufficient developability cannot be obtained, and the image density is insufficient. The method for measuring the volume resistivity of the coating layer is basically the same as in the case of the core material, but the measurement sample is pelletized with a molding machine. In molding, about 0.2 g of the material constituting the coating layer is charged into a molding machine and compression molded at a surface pressure of 500 kgf / cm ^{2 for} 30 seconds to produce a pellet having a cross-sectional area of 1 cm ² . Volume specific resistance of the pellets thus obtained was measured under the same conditions as the core material.
[0030]
The preferred coating amount of the resin that can be used for coating the carrier of the present invention needs to be changed somewhat depending on the specific gravity of the resin, but in many cases, it is preferably 0.5 to 5.0 wt%, more preferably based on the core material. 1.0-3.0 wt% gives good results. When the resin coating amount is 0.5 wt% or less, the core material surface is easily exposed when used for a long period of time, and the same problem as when the resin is not coated occurs. In addition, when the resin coating amount is 5.0 wt% or more, the carrier fluidity is low, and therefore, the developer is likely to be unevenly mixed in the developing device, the toner charge amount becomes unstable, and fog and toner scattering occur. Cause.
[0031]
As a method of coating the surface of the core material of the carrier of the present invention with a resin, a known method can be used. Specifically, a method of spraying the resin dispersion obtained by the above-described method onto the surface of the core material. A wet coating method such as a method of immersing the core material in a dispersion solution, or a finely divided coating resin is electrostatically attached to the surface of the core material of the carrier, and then heat and mechanical stress are applied to the surface of the core material. By adding either or both of these, a dry coating method can be used in which a resin layer is attached to the surface of the core material of the carrier and immobilized.
[0032]
Moreover, the magnetization of the carrier coated with the resin by the above-described method can be one having a magnetization of 70 to 120 emu / g, preferably 80 to 100 emu / g, when a magnetic field of 10 kOe is applied . Magnetization becomes hard high magnetic brush than 120 emu / g, the developing property becomes scant. As a result, on the output image, image defects such as density reduction, density unevenness, and sweeping occur. Conversely, when the magnetization is less than 70 emu / g, due to the lack of amount of the developer conveyed to the developing area causes the developability decreases, the concentration decrease of an output image is generated. Further, the residual magnetic carriers coated with resin by the above method, after applying a magnetic field of 10 kOe, remanence 30～240Gauss, preferably using those which are 50～120Gauss. When the residual magnetism is higher than 240 Gauss, the developer in the developing device tends to agglomerate, and the stress applied to the developer by agitation becomes excessive, and the durability of the developer is lowered. On the other hand, if the residual magnetism is lower than 30 Gauss, the miscibility between the replenished toner and the developer is insufficient, and in many cases, an insufficiently charged toner is generated. The poorly charged toner scatters around the developing device and causes image defects such as fogging.
[0033]
Magnetization of the resin-coated carrier of the present invention, the measurement of residual magnetism can be determined using the DC magnetization properties logger 3257-35 (manufactured by Yokogawa Electric Corporation). The measurement conditions are shown below.
[0034]
The carrier to be measured is one that has been conditioned for 2 hours in an environment of room temperature 20 ° C. and relative humidity 50%. An acrylic cylinder having a height of 20 mm and an inner diameter of 15.8 mm is filled with a carrier, and a sample weight W [g] is obtained. Then, the acrylic cylinder filled with the carrier is set in the above-mentioned DC magnetization characteristic automatic recording device, a magnetic field of 10 kOe is applied, the magnetic axis of magnetic flux density B (Gauss) on the y axis and the magnetic field strength H (Oe) on the x axis. Obtain a hysteresis curve.
[0035]
An example of a magnetic hysteresis curve is shown in FIG.
[0036]
When a magnetic field of 10 kOe is applied on the x-axis, when the magnetic flux density on the y-axis gradually increases from (0.0) and the y-axis magnetic flux density reaches Bm, a is assumed. The density does not become zero, and the magnetic flux b remains. If the magnetic field is increased in the opposite direction to return the b magnetism at the y-axis magnetic flux density B to 0, the magnetic flux density becomes 0 at point c. If the magnetic field is further strengthened, it is saturated at the point d. From there, if the magnetic field is weakened and the magnetic field becomes zero at the point e, the residual magnetic flux of Oe remains, and if the magnetic field is strengthened in the positive direction, the magnetic flux becomes zero at the point f.
[0037]
Magnetization by using a magnetic flux density Bm of time of application of a magnetic field of 10 kOe, is calculated by the following conversion equation.
[0038]
Magnetization = Bm / (4π · W)
W: Measurement carrier weight (g)
Further, the residual magnetic is obtained as ((0b + 0e) / 2 in FIG. 1) the value of the magnetic flux density B after application of a magnetic field of 10 kOe.
[0039]
The following method can be used to produce a core material used for a resin-coated carrier having the magnetic properties required for the present invention.
[0040]
After crushing α-Fe ₂ O ₃ as a raw material, it is heated and reduced for several hours at a temperature of 500 to 700 ° C. in a reducing atmosphere such as hydrogen, and the resulting iron oxide is mixed with water to form a slurry. .
[0041]
The slurry is sprayed and granulated with a spray dryer, and then sintered. In this case, an inert gas atmosphere such as nitrogen or a reducing gas atmosphere is selected as an atmosphere for the sintering process, and the sintering temperature is set to 1050 to 1250 ° C., and the sintering time is set to a range of 2 to 6 hours. Is preferred. Then, the core material used for this invention is obtained through the process of crushing and classification. When controlling magnetic properties, saturation magnetization can be kept within the proper range by controlling the purity of the raw material, reduction process, and sintering process, and residual magnetism by controlling the atmosphere, temperature, and time of the sintering process. it can.
[0042]
Further, known toners can be used for the present invention. Specifically, it is a toner composed of at least a binder resin and a colorant, and a toner added with a release agent, a charge control agent, a magnetic material, a fluidizing agent and the like can be used as necessary. Known materials are used as the constituent materials.
[0043]
As a method for producing the toner used in the present invention, a known method can be used. Specifically, a method in which the constituent materials are mixed, melted and kneaded, and then subjected to a cooling step, followed by pulverization and classification to obtain a toner, and a polymerization method in which the toner is obtained using emulsion polymerization, suspension polymerization, etc. Etc.
[0044]
The volume average particle size of the toner is preferably 1/30 to 1/2 of the volume average particle size of the carrier, more preferably 1/20 to 1/5. Give good results. The volume average particle diameter of the toner can be measured using a laser diffraction particle size measuring instrument “HELOS” (manufactured by JEOL Ltd.) as in the case of the carrier.
[0045]
When the volume average particle diameter of the toner relative to the carrier of the present invention is 1/30 or less, the carrier is too large compared to the toner, and the toner is compressed and deformed by the carrier due to the stirring of the developer in the developing device. Since the toner easily adheres to the surface, when used for a long period of time, the charge imparting ability is reduced, and fogging and image roughness are caused.
[0046]
Further, when the volume average particle diameter of the toner with respect to the carrier of the present invention is ½ or more, the carrier cannot impart a sufficient charge amount to the toner by stirring of the developer in the developing device, and the toner The amount of charge becomes unstable, causing fogging and toner scattering.
[0047]
In order to use as a two-component developer, it is necessary to mix a carrier and a toner in advance.
[0048]
The mixing ratio of the carrier and the toner of the present invention needs to be slightly changed depending on the specific gravity and particle size of the carrier and the toner. In many cases, the toner is set in the range of 2.0 to 10.0 wt% with respect to the carrier. It is preferable to do this. When the toner mixing ratio is 2.0 wt% or less, the amount of toner conveyed to the development area is insufficient and the output image density is insufficient. Also, if the toner mixing ratio is 10.0 wt% or more, the amount of toner will be excessive with respect to the carrier, the toner will not be able to contact the carrier sufficiently, the toner charge amount will become unstable, and this may cause fogging or toner scattering. Become.
[0049]
In mixing the carrier and the toner of the present invention, a conventionally known mixer can be used, but it is preferable that the stress applied to the developer is small at that time. Specifically, a rotating mixer such as a V-type mixer, a W-corn mixer, or a rocking mixer can be used, and a better result can be obtained than a stirring type such as a Henschel mixer.
[0050]
As a developing device applied to the developer used in the present invention, a developing device including a developer agitation and mixing unit, a developer conveying unit that conveys the developer to the developing region, and a toner replenishing unit can be used. As a configuration of the developer stirring and mixing unit, a stirring and mixing method used in a known developing device can be used.
[0051]
As the configuration of the developer transport unit, a configuration in which a fixed magnetic roll is contained and the developer is transported to the development area by rotating the outer non-magnetic sleeve using the magnetic force is used. it can.
[0052]
Aluminum, stainless steel, etc. can be used as the material of the non-magnetic sleeve of the developer conveying section used in the present invention. In order to stably transport the developer to the development area, it is effective to use a non-magnetic sleeve surface that has been subjected to a surface roughening process such as a thermal spraying process or a sandblasting process.
[0053]
Further, the magnetic roll fixed inside the developer transport unit used in the present invention is composed of a plurality of magnetic poles for the purpose of transporting and developing the developer.
[0054]
A magnetic pole acting for development is composed of one or a plurality of magnetic flux densities of 600 to 1400 Gauss, preferably 800 to 1200 Gauss, and good results can be obtained.
[0055]
Furthermore, the position of the magnetic pole for development is centered on the position where the developing sleeve and the photosensitive member are closest to each other, and a range of ± 30 ° with respect to the rotation axis of the developing sleeve is appropriate, but preferably a range of ± 15 °. If set to, better results are obtained.
[0056]
It is preferable to use a magnetic pole having a magnetic flux density of 400 to 800 Gauss as a magnetic pole acting for conveyance.
[0057]
Further, when the total number of magnetic poles for transport is at least 3, preferably 4 to 8, the transportability of the developer is very stable.
[0058]
【Example】
EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, the aspect of this invention is not limited to these.
[0059]
−Career creation−
In carrying out the present invention, seven types of carriers were prepared and used as shown in Table 1. As the coating resin, methyl methacrylate / butyl methacrylate = 7/3 copolymer resin (volume resistivity 2.5 × 10 ¹³ Ωcm) was used. The resin coating method used was a method of fluidizing the core material and spraying the resin solution by spraying.
[0060]
Carrier list [0061]
[Table 1]

[0062]
-Toner creation-
The toner used in carrying out the present invention was prepared by the following method. However, the toner used in the present invention is not limited to this production method.
[0063]
To the polyester resin, 2% by weight of carnauba wax as a release agent and 12% by weight of carbon black as a colorant were mixed and melt-kneaded in a biaxial kneader.
[0064]
Thereafter, through cooling and coarse crushing steps, fine pulverization and air classification were performed to obtain colored particles having a volume average particle diameter of 8.0 μm. Further, as a fluidizing agent, 0.5 wt% of hydrophobic silica fine particles were externally added to the colored particles to obtain a toner used in the examples of the present invention.
[0065]
-Preparation of developer-
Each of the six types of carriers shown in Table 1 (1692 g) and 108 g of toner for each of the carriers were put into a V-type mixer and mixed for 10 minutes to prepare a developer having a toner concentration of 6.0 wt%.
[0066]
Example 1
Developer 1 prepared using carrier No. 1 in Table 1 was put into a modified U-Bix5076 (manufactured by Konica), and the performance of developer 1 was evaluated by continuously copying 50,000 sheets.
[0067]
FIG. 2 is a sectional view schematically showing the magnetic pole arrangement of the developing sleeve of the developing device of the copying machine used in this embodiment. In FIG. 2, the position of the developing magnetic pole 3 is set at a position of + 5 ° upstream of the developer conveyance with respect to the magnetic pole fixing shaft 7 of the developing sleeve 6 with the developing sleeve 6 and the photosensitive member 9 as the center. .
[0068]
In the present invention, the developing magnetic pole 3 having a width of 10 mm and a magnetic flux density of 1000 Gauss is used. Conveying magnetic poles 1, 2, 4, and 5 were installed in the developing sleeve 6 as shown in FIG. 2, and magnetic flux densities of 700, 750, 750, and 600 Gauss were sequentially used from the conveying magnetic pole 1, respectively.
[0069]
The results of Example 1 are shown in Table 2.
[0070]
Examples 2, 3, 4
50,000 continuous copies were made in the same manner as in Example 1 except that Developer 1 was replaced with Developers 2, 3, and 4 comprising Carrier Nos. 2, 3, and 4, respectively. Performance evaluation was performed. The results are shown in Table 2 below.
[0071]
Comparative Example 1
50,000 continuous copies were made in the same manner as in Example 1 except that the developer was changed to the developer 5 composed of carrier No. 5, and the performance of the developer 5 was evaluated. The results are shown in Table 2 below.
[0072]
Comparative Example 2
50,000 continuous copies were made in the same manner as in Example 1 except that the developer was changed to the developer 6 composed of carrier No. 6, and the performance of the developer 6 was evaluated. The results are shown in Table 2 below.
[0073]
Comparative Example 3
50,000 continuous copies were made in the same manner as in Example 1 except that the developer was changed to the developer 7 composed of carrier No. 7, and the performance of the developer 7 was evaluated. The results are shown in Table 2 below.
[0074]
-Evaluation-
The performance of the developer was evaluated by the following method and criteria.
[0075]
(Image density)
A solid image with a document density of 1.30 was copied, and the relative reflection density of the output image with respect to white paper was measured. For density measurement, a Macbeth densitometer was used, and an image density of 1.30 or higher was judged to be good. The evaluation was made on the first copy (also called the initial copy) and the 50,000th copy.
[0076]
(resolution)
Fine line images were copied and the number of fine lines reproduced per 1 mm width of the output image was evaluated. It was determined that the larger the number of reproduced thin lines, the higher the resolution and the better the image. The evaluation was made on the 50,000th copy image.
[0077]
(Sweeping eye)
After making 50,000 copies, a solid image with a document density of 1.00 was copied, and the output image was visually observed to make a judgment. When no flawed image disturbance occurred in the paper feeding direction, it was judged as “good”, and when it occurred, it was judged as “poor”.
[0078]
(Cover)
After making 50,000 copies, a blank original was copied, and the relative reflection density of the output image with respect to the blank was measured. A Macbeth densitometer was used for density measurement, and an image density of 0.005 or less was judged to be good.
[0079]
(Uneven density)
After making 50,000 copies, ten continuous images with a document density of 1.00 were copied continuously, and the relative reflection density of the output image with respect to white paper was measured for all ten sheets. When the difference between the maximum value and the minimum value of each of the 10 sheets of density data was 0.02 or less, it was judged as “good”, and when it exceeded that, it was judged as “bad”.
[0080]
(Carrier adhesion)
Judgment was made by visual observation of the output images from the first copy to the tenth copy. The case where carrier adhesion did not occur and no problem was indicated as “◯”, and the case where carrier adhesion was confirmed and defective was indicated as “x”.
[0081]
The results are shown in Table 2 below.
[0082]
[Table 2]

[0083]
Examples 1-4
As is apparent from the data in Table 2, Examples 1 to 4 using the developer of the present invention maintain high image density and resolving power from the beginning of copying, and have no sweeping, fog density, density unevenness, and carrier adhesion. We were able to obtain high quality images from start to finish.
[0084]
In particular, in Examples 1 and 2 using a developer whose residual magnetism is in the range of 50 to 120 Gauss, the image density at the initial stage of copying is much better than others, and copying is possible even at the 50,000th copy. It can be seen that there is almost no difference from the initial image density, and the deterioration of the image density is extremely small. Furthermore, it can be seen that the resolving power and fog density of Examples 1 and 2 are also better than others, and the effect is remarkably excellent. Comparative Example 1
As is apparent from the data in Table 2, the image was low from the initial stage of copying and the resolution was insufficient. Furthermore, carrier adhesion also occurred, causing a practical problem.
[0085]
Comparative Example 2
As is apparent from the data in Table 2, when 50,000 copies were made, it was found that sweeping was conspicuous in the solid portion and the fog density was extremely high, so that fog was generated. In addition, density unevenness occurred, and a high-quality image could not be obtained.
[0086]
Comparative Example 3
As is apparent from the data in Table 2, the image density was slightly lower from the initial stage of copying and the resolution was insufficient. Further, when 50,000 sheets were copied, sweeping was conspicuous in the solid portion and density unevenness occurred.
[0087]
【The invention's effect】
By using the electrostatic image developing carrier which is the two-component developer of the present invention and the electrophotographic method using the carrier, there is no carrier adhesion, fogging on the background of the image, no solid portion sweeping, and a high density. An output image that is homogeneous and has a high resolution can be obtained over a long period of time.
[Brief description of the drawings]
FIG. 1 is a diagram schematically showing an example of a magnetic hysteresis curve in the present invention.
FIG. 2 is a cross-sectional view schematically showing an example of a photoreceptor and a developing sleeve used in the present invention.
[Explanation of symbols]
1, 2, 4, 5 Conveying magnetic pole 3 Developing magnetic pole 6 Developing sleeve 7 Magnetic pole fixing shaft 8 Thickness regulating member 9 Photoconductor

Claims (1)

An electrostatic charge image developing carrier having a volume average particle size of 30 to 70 μm and substantially spherical magnetite particles as a core material coated with a resin, and a magnetic field of 10 kOe applied to the resin coated electrostatic charge image developing carrier Is a developer using an electrostatic charge image developing carrier having a magnetization of 70 to 120 emu / g and a residual magnetic Br of 60 to 110 Gauss after applying a magnetic field of 10 kOe, and is further included in the developer An electrostatic charge image developer, wherein the toner is a non-magnetic toner and the volume average particle diameter thereof is 1/20 to 1/5 of the volume average particle diameter of the carrier.

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