JP4378051B2 - Magnetic toner and image forming method using the magnetic toner - Google Patents

Description

【数２】

【００８２】
本発明における平均円形度は、例えば東亞医用電子製フロー式粒子像分析装置「ＦＰＩＡ−１０００」を用いて測定することができる。
【００８３】
また、モード円形度は、円形度を０．４０から１．００までを０．０１毎に６１分割し、測定した粒子の円形度をそれぞれの円形度に応じて各分割範囲に割り振り、円形度頻度分布において頻度値が最大となるピークの円形度である。
【００８４】
なお、上記測定装置である「ＦＰＩＡ−１０００」は、各粒子の円形度を算出後、平均円形度及びモード円形度の算出に当たって、粒子を得られた円形度によって、円形度０．４０〜１．００を６１分割したクラスに分け、分割点の中心値と頻度を用いて平均円形度及びモード円形度の算出を行う算出法を用いている。しかしながら、この算出法で算出される平均円形度及びモード円形度の各値と、上述した各粒子の円形度を直接用いる算出式によって算出される平均円形度及びモード円形度の各値との誤差は、非常に少なく、実質的には無視出来る程度のものであり、本発明においては、算出時間の短絡化や算出演算式の簡略化の如きデータの取り扱い上の理由で、上述した各粒子の円形度を直接用いる算出式の概念を利用し、一部変更したこのような算出法を用いても良い。
【００８５】
平均円形度及びモード円形度の測定手順の具体例としては、以下の通りである。
界面活性剤約０．１ｍｇを溶解している水１０ｍＬに、磁性トナー約５ｍｇを分散させて分散液を調製し、超音波（２０ＫＨｚ、５０Ｗ）を分散液に５分間照射し、分散液濃度を５０００〜２万個／μＬとして、前記装置により測定を行い、３μｍ以上の円相当径の粒子群の平均円形度及びモード円形度を求める。
【００８６】
なお、本発明において３μｍ以上の円相当径の粒子群についてのみ円形度を測定する理由は、３μｍ未満の円相当径の粒子群にはトナー粒子とは独立して存在する外部添加剤の粒子群も多数含まれるため、その影響によりトナー粒子群についての円形度が正確に見積もれないからである。
【００８７】
本発明の磁性トナーは、鉄及び鉄化合物の遊離率が０.０５〜３.００％であることを特徴とする。この遊離率は好ましくは０.０５〜２．００％、より好ましくは０．０５〜１．５０％、更に好ましくは０．０５〜１.００％である。前述したように、本発明の磁性トナーは、磁性粉体を含有している。従って、本発明において、鉄及び鉄化合物の遊離率とは、具体的にはトナー粒子から遊離している磁性粉体の個数の割合を示すものである。
【００８８】
鉄及び鉄化合物の遊離率は、例えば磁性トナーをプラズマへ導入し、このときの発光スペクトルから測定することができる。この場合では遊離率とは、結着樹脂の構成元素である炭素原子の発光と、鉄原子の発光の同時性から次式により定義される値である。
【００８９】
【数３】

【００９０】
ここで、「同時に発光」とは、炭素原子の発光から２．６ｍｓｅｃ以内に発光した鉄原子の発光を同時発光とし、それ以降の鉄原子の発光は鉄原子のみの発光とする。
【００９１】
本発明では磁性粉体を多く含有している為、炭素原子と鉄原子が同時発光するという事は、トナー粒子が磁性粉体を含有している事を意味し、鉄原子のみの発光は、磁性粉体がトナー粒子から遊離している事を意味すると言い換えることも可能である。
【００９２】
上記の鉄及び鉄化合物の遊離率は、Ｊａｐａｎ Ｈａｒｄｃｏｐｙ９７論文集の６５−６８ページに記載の原理に基づいて測定することができ、このような測定を行う場合では、例えばパーティクルアナライザー（ＰＴ１０００：横河電機（株）製）が好ましくは用いられる。具体的には、該装置はトナー等の微粒子を一個ずつプラズマへ導入し、微粒子の発光スペクトルから発光物の元素、粒子数、粒子の粒径を知る事が出来る。
【００９３】
上記測定装置を用いる具体的な測定方法は以下の通りである。０．１％酸素含有のヘリウムガスを用い、２３℃で湿度６０％の環境にて測定を行い、トナーサンプルは同環境下にて１晩放置し、調湿したものを測定に用いる。また、チャンネル１で炭素原子（測定波長２４７．８６０ｎｍ、Ｋファクターは推奨値を使用）、チャンネル２で鉄原子（測定波長２３９．５６ｎｍ、Ｋファクターは３．３７６４を使用）を測定し、一回のスキャンで炭素原子の発光数が１０００〜１４００個となるようにサンプリングを行い、炭素原子の発光数が総数で１００００以上となるまでスキャンを繰り返し、発光数を積算する。この時、炭素元素の発光個数を縦軸に、炭素元素の三乗根電圧を横軸にとった分布において、該分布が極大を一つ有し、更に、谷が存在しない分布となるようにサンプリングし、測定を行う。そして、このデータを元に、全元素のノイズカットレベルを１．５０Ｖとし、上記計算式を用い、鉄及び鉄化合物の遊離率を算出する。後述の実施例においても同様に測定した。
【００９４】
又、荷電制御剤であるアゾ系の鉄化合物等といった、鉄原子を含有する無機化合物以外の材料もトナー粒子中に含まれている場合があるが、こういった化合物は鉄原子と同時に有機化合物中の炭素も同時に発光するため、遊離の鉄原子としてはカウントされない。
【００９５】
本発明者らが検討を行ったところ、鉄及び鉄化合物の遊離率とトナー粒子表面への露出量には深い関連があり、遊離の磁性粉体量が３．００％以下であれば、おおむね磁性粉体のトナー粒子表面への露出が抑制されるとともに、高い帯電量を有する事が判明した。鉄及び鉄化合物の遊離率は磁性粉体の疎水化度、樹脂とのなじみ性、粒度分布、処理の均一性等に依存するものであるが、一例として、磁性粉体の表面処理が不均一である場合、表面処理が充分に施されていない（親水性が強い）磁性粉体はトナー粒子表層に存在しやすくなると共に、その一部または全てが遊離してしまう。この為、鉄及び鉄化合物の遊離率が低い程磁性トナーの帯電量は高い傾向を示す。
【００９６】
一方、遊離率が上記範囲より大きいと、チャージのリーク点が多くなりすぎてしまい、トナーの帯電量が低下してしまうことがある。この傾向は高温高湿下で特に顕著なものとなる。また、帯電量の低いトナーはカブリの増加を招くと共に、転写効率が低くなり好ましくない。また、このような鉄及び鉄化合物の遊離率が大きなトナーは定着性がやや劣るものとなる。これは、比熱の大きな磁性粉体がトナー表面に存在、または、トナーから遊離して存在するため、定着時にトナーに十分熱が伝わらない為であると考えられる。
【００９７】
一方、鉄及び鉄化合物の遊離率が０．０５％より少ないと、実質的に磁性粉体はトナー粒子から遊離していない事を意味する。このように鉄及び鉄化合物の遊離率が低い磁性トナーは高い帯電量を有するものの、多数枚画出し、特に低温低湿下における多数枚画出しにおいて、磁性トナーのチャージアップに起因する画像濃度の低下、及び、画像のがさつきが生じてしまう。
これは、次の様な理由であると考えている。
【００９８】
一般的に、磁性トナー担持体上の磁性トナーは感光体上へ全て現像される事は無く、現像直後においても磁性トナー担持体上には磁性トナーは存在する。特に磁性トナーを用いたジャンピング現像においてはその傾向が強く、現像効率はさほど高くない。さらに円形度の高い磁性トナーは前述の通り、現像部において、均一な細い穂を形成しており、穂の先端部に存在する磁性トナーから現像されてしまい、磁性トナー担持体付近の磁性トナーはなかなか現像されないものと考えられる。
【００９９】
そのため、磁性トナー担持体付近の磁性トナーは繰り返し帯電部材による摩擦帯電を受け、チャージアップしてしまい、さらに現像されにくくなるという悪循環に陥ってしまう。また、この様な状態では、磁性トナーの帯電均一性は損なわれ、画像のがさつきを生じてしまう。
【０１００】
ここで、鉄及び鉄化合物の遊離率が０．０５％以上のトナーを用いた場合、遊離の磁性粉体またはトナー粒子表面にわずかに存在している磁性粉体により磁性トナーのチャージアップが抑制されると共に、磁性トナーの帯電量の均一性が促され、がさつきは抑制される。
【０１０１】
これらの理由により、高い帯電量を安定して得る為には、鉄及び鉄化合物の遊離率が０．０５％から３．００％であることが必要である。
【０１０２】
また、本発明の磁性トナーのように、平均円形度が高く、鉄及び鉄化合物の遊離率が低い磁性トナーであること、磁性トナーの形状がそろっていること、そして、磁性トナーの帯電量が均一に高い事、による相乗効果により、転写効率は非常に高くなると共に、カブリも非常に少なくなる。また、磁性トナーの飛び散りも低減され、画質も向上する。さらに、このような磁性トナーは長期使用においても選択現像が起こりにくく、使用前後でトナー物性の差が起きにくいことから、耐久性も向上する。
【０１０３】
一方、特開平５−１５０５３９号公報、特開平８−２２１９１号公報に開示されている様に、不定形のトナー表面にマグネタイトを外部添加する事で、チャージアップの抑制は可能ではある。しかしながら、本発明の如き平均円形度が０．９７０以上の磁性トナーにマグネタイトを外部添加した場合、カブリの増加を招くと共に、特に、高温高湿下での帯電性が劣るものとなる。この理由は定かではないが、マグネタイトの如き低抵抗のものがトナー粒子表面に多量に存在する事、また、平均円形度が０．９７０以上というトナー表面が比較的なめらかな磁性トナーを用いた場合、マグネタイト混合時にシェアが十分にかからず、マグネタイトが均一にトナー粒子表面に付着せず、トナー粒子間で、付着量の差が生じてしまうためであると考えている。
【０１０４】
本発明の画像形成方法において、更に高画質化のため、より微小な潜像ドットを忠実に現像するためには、磁性トナーの重量平均径は３〜２０μｍが好ましく、更には４〜９μｍであることがより好ましい。重量平均粒径が３μｍ未満のトナーにおいては、転写効率の低下から感光体上の転写残トナーが多くなり、接触帯電工程での感光体の削れやトナー融着の抑制が難しくなる。さらに、磁性トナー全体の表面積が増えることに加え、粉体としての流動性及び攪拌性が低下し、個々のトナー粒子を均一に帯電させることが困難となることからカブリや転写性が悪化傾向となり、削れや融着以外にも画像の不均一ムラの原因となりやすいため、本発明で使用する磁性トナーには好ましくない。
【０１０５】
また、磁性トナーの重量平均粒径が２０μｍを越える場合には、文字やライン画像に飛び散りが生じやすく、高解像度が得られにくい。さらに装置が高解像度になっていくと２０μｍ以上のトナーは１ドットの再現が悪化する傾向にある。
【０１０６】
また、本発明の磁性トナーは、個数平均粒径に対する重量平均粒径の比、すなわち重量平均粒径／個数平均粒径の比（Ｄ４／Ｄ１）が１．４０以下であることが重要で有り、より好ましくは１．３５以下である。
【０１０７】
重量平均粒径／個数平均粒径の比が１．４０より大きいという事は、磁性トナー中に微粉、粗粒が多数存在することを意味し、選択現像が生じ易くなると共に、帯電量分布も広くなり好ましくない。
【０１０８】
一方、重量平均粒径／個数平均粒径の比が１．４０以下、特に、１．３５以下の磁性トナーでは、磁性トナーの平均円形度が０．９７０以上であるという磁性トナーの形状因子に合せ、粒径もそろっているという粒度分布の相乗効果により、現像部での穂立ちが非常に均一になり、ドット再現性に非常に優れる画像を得ることが出来る。
【０１０９】
ここで、磁性トナーの平均粒径及び粒度分布は、コールターカウンターＴＡ−ＩＩ型またはコールターマルチサイザー（コールター社製）等種々の方法で測定可能であるが、本発明においてはコールターマルチサイザー（コールター社製）を用い、個数分布、体積分布を出力するインターフェイス（日科機製）及びＰＣ９８０１パーソナルコンピューター（ＮＥＣ製）を接続して測定することが好ましい。上記の測定では、電解液は１級塩化ナトリウムを用いて１％ＮａＣｌ水溶液を調整する。電解液には、たとえば、ＩＳＯＴＯＮ Ｒ−ＩＩ（コールターサイエンティフィックジャパン社製）が使用できる。
【０１１０】
上記測定の具体的な測定法としては、前記電解水溶液１００〜１５０ｍＬ中に分散剤として界面活性剤、好ましくはアルキルベンゼンスルホン酸塩を０．１〜５ｍＬを加え、更に測定試料を２〜２０ｍｇ加える。試料を懸濁した電解液は超音波分散器で約１〜３分間分散処理を行い、前記コールターマルチサイザーによりアパーチャーとして１００μｍアパーチャーを用いて、２μｍ以上のトナー粒子の体積、個数を測定して体積分布と個数分布とを算出する。それから、体積分布から求めた体積基準の重量平均粒径（Ｄ４）、個数分布から求めた個数基準の長さ平均粒径、即ち個数平均粒径（Ｄ１）を求める。後述の実施例においても同様に測定した。
【０１１１】
また、本発明の磁性トナーは、フローテスター測定での粘度が１．０×１０⁵Ｐａ・ｓとなる温度が８０〜１２０℃であり、かつ１．０×１０⁴Ｐａ・ｓとなる温度が１００〜１５０℃であることを特徴とする。更には、１．０×１０⁵Ｐａ・ｓとなる温度が８０〜１１０℃であり、１．０×１０⁴Ｐａ・ｓとなる温度が１００〜１４０℃であることが好ましい。
【０１１２】
粘度が１．０×１０⁵Ｐａ・ｓとなる温度が８０℃に満たない場合や、１．０×１０⁴Ｐａ・ｓとなる温度が１００℃に満たない場合は、低温定着性は優れたものとなるが、このように低粘度の磁性トナーは、トナー粒子表面近傍の磁性粉体が露出、更には脱落してしまうことがある。また、外添剤が埋め込まれてしまう等の原因で、耐久により遊離率が変動してしまう。その結果、磁性トナーの流動性や帯電性が変化し、現像性や転写性が損なわれてしまうことがある。
【０１１３】
特に、本発明のような流動性や転写性の優れた、円形度の高い磁性トナーの場合、現像器内や、帯電部材などとの接触面積が大きくなるため、上記の現象がより発生しやすくなってしまう。さらに、１．０×１０⁴Ｐａ・ｓとなる温度が１００℃に満たない場合は、耐オフセット性も損なわれてしまうことがある。
【０１１４】
逆に、粘度が１．０×１０⁵Ｐａ・ｓとなる温度が１２０℃を超える場合や、１．０×１０⁴Ｐａ・ｓとなる温度が１５０℃を超える場合は、遊離率の変動は抑えられるが、低温定着性が損なわれてしまい好ましくない。すなわち、本発明は、磁性トナーの円形度、鉄及び鉄化合物の遊離率、温度で規定される粘度、更に、重量平均粒径／個数平均粒径の比のバランスをとることで、低温定着性を損なうことなく、帯電性が安定しているため、現像/転写性が耐久により変化しない高画質の画像が安定して得られるものである。
【０１１５】
帯電性の変化とは、たとえば、帯電量分布のブロード化である。帯電量分布がブロード化することによって、低帯電量の磁性トナーばかりか、逆極性に帯電したトナー粒子も増加する。この磁性トナーは転写材に転写されず、画像上では確認できないが、トナー消費量の点で好ましくない。更には、本発明の一つであるクリーナーレス画像形成方法の場合は、帯電部材への負荷が大きくなることから好ましくない。
【０１１６】
本発明の磁性トナーのフローテスター測定での粘度は、以下の手段により測定することができる。
高架式フローテスター（例えば島津フローテスターＣＦＴ−５００Ｄ）を用い、先ず加圧成形器を用いて成形した約１．５ｇの磁性トナーを一定温度下でプランジャーにより１０ｋｇｆ（＝９８Ｎ）の荷重をかけ直径１ｍｍ、長さ１ｍｍのノズルより押し出すようにし、これによりフローテスターのプランジャー降下量（流出速度）を測定する。この流出速度を各温度（６０℃〜１８０℃の温度範囲を５℃間隔）で測定し、この値より粘度η′を次式により求める。
【０１１７】
【数４】

【０１１８】
本発明の磁性トナーは、粉砕法によっても製造することができ、粉砕法により製造する場合は、公知の方法が用いられるが、例えば、結着樹脂、磁性粉体、離型剤、場合によって荷電制御剤、着色剤等の磁性トナーとして必要な成分及びその他の添加剤等を、ヘンシェルミキサー、ボールミル等の混合器により十分混合してから加熱ロール、ニーダー、エクストルーダーの如き熱混練機を用いて熔融混練し、樹脂類をお互いに相熔させた中に磁性粉体等の他の磁性トナー材料を分散又は溶解させ、冷却固化、粉砕後、分級、必要に応じて表面処理を行ってトナー粒子を得ることが出来る。分級及び表面処理の順序はどちらが先でもよい。分級工程においては生産効率上、多分割分級機を用いることが好ましい。
【０１１９】
粉砕工程は、機械衝撃式、ジェット式等の公知の粉砕装置を用いた方法により行うことができる。本発明に係わる特定の円形度を有する磁性トナーを得るためには、さらに熱をかけて粉砕したり、または補助的に機械的衝撃を加える処理をすることが好ましい。また、微粉砕（必要に応じて分級）されたトナー粒子を熱水中に分散させる湯浴法、熱気流中を通過させる方法などを用いても良い。
【０１２０】
機械的衝撃力を加える手段としては、例えば川崎重工社製のクリプトロンシステムやターボ工業社製のターボミル等の機械衝撃式粉砕機を用いる方法、また、ホソカワミクロン社製のメカノフージョンシステムや奈良機械製作所製のハイブリダイゼーションシステム等の装置のように、高速回転する羽根によりトナー粒子をケーシングの内側に遠心力により押しつけ、圧縮力、摩擦力等の力によりトナー粒子に機械的衝撃力を加える方法が挙げられる。
【０１２１】
機械的衝撃法を用いる場合においては、処理温度をトナー粒子のガラス転移点Ｔｇ付近の温度（Ｔｇ±１０℃）を加える熱機械的衝撃が、凝集防止、生産性の観点から好ましい。さらに好ましくは、トナー粒子のガラス転移点Ｔｇ±５℃の範囲の温度で行うことが、転写効率を向上させるのに特に有効である。
【０１２２】
本発明に関わる磁性トナーを粉砕法により製造する場合の結着樹脂としては、ポリスチレン、ポリビニルトルエンなどのスチレン及びその置換体の単重合体；スチレン−プロピレン共重合体、スチレン−ビニルトルエン共重合体、スチレン−ビニルナフタリン共重合体、スチレン−アクリル酸メチル共重合体、スチレン−アクリル酸エチル共重合体、スチレン−アクリル酸ブチル共重合体、スチレン−アクリル酸オクチル共重合体、スチレン−アクリル酸ジメチルアミノエチル共重合体、スチレン−メタアクリル酸メチル共重合体、スチレン−メタアクリル酸エチル共重合体、スチレン−メタアクリル酸ブチル共重合体、スチレン−メタクリル酸ジメチルアミノエチル共重合体、スチレン−ビニルメチルエーテル共重合体、スチレン−ビニルエチルエーテル共重合体、スチレン−ビニルメチルケトン共重合体、スチレン−ブタジエン共重合体、スチレン−イソプレン共重合体、スチレン−マレイン酸共重合体、スチレン−マレイン酸エステル共重合体などのスチレン系共重合体；ポリメチルメタクリレート、ポリブチルメタクリレート、ポリ酢酸ビニル、ポリエチレン、ポリプロピレン、ポリビニルブチラール、シリコン樹脂、ポリエステル樹脂、ポリアミド樹脂、エポキシ樹脂、ポリアクリル酸樹脂、ロジン、変性ロジン、テンペル樹脂、フェノール樹脂、脂肪族または脂環族炭化水素樹脂、芳香族系石油樹脂、パラフィンワックス、カルナバワックスなどが単独または混合して使用できる。特に、スチレン系共重合体及びポリエステル樹脂が現像特性、定着性等の点で好ましい。
【０１２３】
磁性トナーのガラス転移点温度（Ｔｇ）は、４０〜８０℃であることが好ましく、より好ましくは４５℃〜７０℃である。Ｔｇが４０℃よりも低いと磁性トナーの保存性が低下する傾向にあり、８０℃よりも高いと定着性に劣ることがある。磁性トナーのガラス転移点は、例えばパーキンエルマー社製ＤＳＣ−７の様な高精度の内熱式入力補償型の示差走査熱量計を用いて測定することができる。このときの測定方法は、ＡＳＴＭＤ３４１８−８に準じて行う。本発明においては、試料を１回昇温させ前履歴をとった後、急冷し、再度昇温速度１０℃／ｍｉｎ、温度３０〜２００℃の範囲で昇温させた時に測定されるＤＳＣ曲線を用いる。
【０１２４】
また、本発明に係わる磁性トナーは、特公昭５６−１３９４５号公報等に記載のディスク又は多流体ノズルを用い溶融混合物を空気中に霧化し球状トナーを得る方法や、単量体には可溶で得られる重合体が不溶な水系有機溶剤を用い直接トナーを生成する分散重合方法又は水溶性極性重合開始剤存在下で直接重合しトナーを生成するソープフリー重合方法に代表される乳化重合方法等を用いトナーを製造する方法でも製造が可能である。
【０１２５】
本発明の磁性トナーは、上述のように粉砕法によって製造することも可能であるが、この粉砕法で得られるトナー粒子は一般に不定形のものであり、本発明に係わる磁性トナーの必須要件である平均円形度が０．９７０以上という物性を得る為には、機械的・熱的または何らかの特殊な処理を行う事が必要となり、生産性が劣るものとなる。
【０１２６】
そこで、本発明においては、トナー粒子を重合法、特には懸濁重合法により製造することが好ましい。この懸濁重合法においては重合性単量体および着色剤（更に必要に応じて重合開始剤、架橋剤、荷電制御剤、その他の添加剤）を均一に溶解または分散させて重合性単量体系とした後、この重合性単量体系を分散安定剤を含有する連続層（例えば水相）中に適当な撹拌器を用いて分散し同時に重合反応を行わせ、所望の粒径を有するトナー粒子を得るものである。
【０１２７】
この懸濁重合法で得られるトナー（以後重合トナー）は、個々のトナー粒子形状がほぼ球形に揃っているため、平均円形度が０．９７０以上、モード円形度が０．９９以上という本発明に必須な物性要件を満たす磁性トナーが得られやすく、さらにこういった磁性トナーは帯電量の分布も比較的均一となるため高い転写性を有している。
【０１２８】
しかしながら、重合トナー中に通常の磁性粉体を含有させても、トナー粒子表面に磁性粉体が多数存在し、トナー粒子の帯電特性が著しく低下する。さらに、懸濁重合トナーの製造時に磁性粉体と水との相互作用が強いことにより、円形度が０．９７０以上の磁性トナーが得られ難く、さらに、磁性トナーの粒度分布が広いものとなる。
【０１２９】
これは、（１）磁性粉体は一般的に親水性であるためにトナー粒子表面に存在しやすいこと、（２）水溶媒撹拌時に磁性粉体が乱雑に動き、それに単量体から成る懸濁粒子表面が引きずられ、形状が歪んで円形になりにくいこと等が原因と考えられる。こういった問題を解決するためには磁性粉体の有する表面特性の改質が重要である。
【０１３０】
重合トナーに使用される磁性粉体の表面改質に関しては、数多く提案されている。前述したように、特開昭５９−２００２５４号公報、特開昭５９−２００２５６号公報、特開昭５９−２００２５７号公報、特開昭５９−２２４１０２号公報等に磁性粉体の各種シランカップリング剤処理技術が提案されており、特開昭６３−２５０６６０号公報では、ケイ素元素含有磁性粒子をシランカップリング剤で処理する技術が開示されている。
【０１３１】
しかしながら、これらの処理により磁性粉体の遊離はある程度抑制されるものの、磁性粉体表面の疎水化を均一に行うことが困難であるという問題があり、したがって、磁性粉体同士の合一や疎水化されていない磁性粉体の発生を避けることができず、磁性粉体の分散性は十分では無く、粒度分布も広いものとなってしまう。
【０１３２】
また、疎水化磁性酸化鉄を用いる例として特開昭５４−８４７３１号公報にアルキルトリアルコキシシランで処理した磁性酸化鉄を含有するトナーが提案されている。この磁性酸化鉄の添加により、確かに磁性トナーの電子写真諸特性は向上しているものの、磁性酸化鉄の表面活性は元来小さく、処理の段階で合一粒子が生じたり、疎水化が不均一であったりで、必ずしも満足のいくものではない。
【０１３３】
また、小粒径の磁性粉体を用いた場合、均一な処理がより困難なものとなり、本発明に適用するにはさらなる改良が必要である。さらに、磁性粉体の内包性向上の為、処理剤等を多量に使用したり、高粘性の処理剤等を使用した場合、疎水化度は確かに上がるものの、粒子同士の合一等が生じて分散性は逆に悪化してしまう。
【０１３４】
このような磁性粉体を用いて製造された磁性トナーは、摩擦帯電性が不均一であり、それに起因してカブリや転写性が良くないものとなる。
【０１３５】
このように、従来の表面処理磁性粉体を用いた重合トナーでは、疎水性と分散性の両立は必ずしも達成されておらず、このような重合トナーを本発明の接触帯電工程を含む画像形成方法に適用しても、高精細な画像を安定して得ることは難しい。
【０１３６】
そこで、本発明の磁性トナーに使用される磁性粉体は、カップリング剤で均一に疎水化処理されていることが好ましい。磁性粉体表面を疎水化する際、水系媒体中で、磁性粉体を一次粒径となるよう分散しつつカップリング剤を加水分解させながら表面処理する方法を用いることが非常に好ましい。この疎水化処理方法は気相中で処理するより、磁性粉体同士の合一が生じにくく、また疎水化処理による磁性粉体間の帯電反発作用が働き、磁性粉体はほぼ一次粒子の状態で表面処理される。
【０１３７】
カップリング剤を水系媒体中で加水分解させながら磁性粉体表面を処理する方法は、クロロシラン類やシラザン類のようにガスを発生するようなカップリング剤を使用する必要もなく、さらに、これまで気相中では磁性粉体同士が合一しやすくて、良好な処理が困難であった高粘性のカップリング剤も使用できるようになり、疎水化の効果は絶大である。
【０１３８】
本発明に用いられる磁性粉体の表面処理において使用できるカップリング剤としては、例えば、シランカップリング剤、チタンカップリング剤等が挙げられる。より好ましく用いられるのはシランカップリング剤であり、一般式（Ｉ）で示されるものである。
【化１】
Ｒ_mＳｉＹ_n （Ｉ）
［式中、Ｒはアルコキシ基を示し、ｍは１〜３の整数を示し、Ｙはアルキル基、ビニル基、グリシドキシ基、メタクリル基の如き炭化水素基を示し、ｎは１〜３の整数を示す。ただし、ｍ＋ｎ＝４である。］
【０１３９】
一般式（Ｉ）で示されるシランカップリング剤としては、例えば、ビニルトリメトキシシラン、ビニルトリエトキシシラン、ビニルトリス（β−メトキシエトキシ）シラン、β−（３、４エポキシシクロヘキシル）エチルトリメトキシシラン、γ−グリシドキシプロピルトリメトキシシラン、γ−グリシドキシプロピルメチルジエトキシシラン、γ−アミノプロピルトリエトキシシラン、N−フェニル−γ−アミノプロピルトリメトキシシラン、γ−メタクリロキシプロピルトリメトキシシラン、ビニルトリアセトキシシラン、メチルトリメトキシシラン、ジメチルジメトキシシラン、フェニルトリメトキシシラン、ジフェニルジメトキシシラン、メチルトリエトキシシラン、ジメチルジエトキシシラン、フェニルトリエトキシシラン、ジフェニルジエトキシシラン、ｎ−ブチルトリメトキシシラン、イソブチルトリメトキシシラン、トリメチルメトキシシラン、ヒドロキシプロピリトリメトキシシラン、ｎ−ヘキサデシルトリメトキシシラン、ｎ−オクタデシルトリメトキシシラン等を挙げることができる。
【０１４０】
この中で特に下記一般式（II）で示されるアルキルトリアルコキシシランカップリング剤を併用する事がより好ましい。
【化２】
Ｃ_pＨ_2p+1−Ｓｉ−（ＯＣ_qＨ_2q+1）₃ （II）
［式中、ｐは２〜２０の整数を示し、ｑは１〜３の整数を示す。］
【０１４１】
上記式におけるｐが２より小さいと、疎水化処理は容易となるが、疎水性を十分に付与することが困難であり、トナー粒子からの磁性粉体の露出、または遊離を抑制する事が難しくなる。またｐが２０より大きいと、疎水性は十分になるが、磁性粉体同士の合一が多くなり、トナー粒子中へ磁性粉体を十分に分散させることが困難になり、カブリや転写性が悪化傾向となる。
【０１４２】
また、ｑが、３より大きいとシランカップリング剤の反応性が低下して疎水化が十分に行われにくくなる。特に、式中のｐが２〜２０の整数（より好ましくは、３〜１５の整数）を示し、ｑが１〜３の整数（より好ましくは、１又は２の整数）を示すアルキルトリアルコキシシランカップリング剤を使用するのが良い。
【０１４３】
前述したこれらのカップリング剤の処理量は、磁性粉体１００質量部に対して、シランカップリング剤の総量が０．０５〜２０質量部、好ましくは０．１〜１０質量部であり、磁性粉体の表面積、カップリング剤の反応性等に応じて処理剤の量を調整することが好ましい。
【０１４４】
磁性粉体の表面処理として水系媒体中でカップリング剤で処理するには、水系媒体中で適量の磁性粉体およびカップリング剤を撹拌する方法が挙げられる。撹拌は、例えば撹拌羽根を有する混合機で、磁性粉体が水系媒体中で、一次粒子になるように充分に行うのが良い。
【０１４５】
ここで、水系媒体とは、水を主要成分としている媒体である。具体的には、水系媒体として水そのもの、水に少量の界面活性剤を添加したもの、水にｐＨ調整剤を添加したもの、水に有機溶剤を添加したものが上げられる。界面活性剤としては、ポリビニルアルコールの如きノンイオン系界面活性剤が好ましい。界面活性剤は、水に対して０．１〜５質量％添加するのが良い。ｐＨ調整剤としては、塩酸等無機酸が挙げられる。有機溶剤としてはアルコール類等が挙げられる。
【０１４６】
こうして得られる磁性粉体は粒子の凝集が見られず、個々の粒子表面が均一に疎水化処理されているため、重合トナー用の材料として用いた場合、トナー粒子の均一性が良好なものとなる。
【０１４７】
また、本発明の磁性トナーに用いられる磁性粉体は、リン、コバルト、ニッケル、銅、マグネシウム、マンガン、アルミニウム、珪素などの元素を含んでもよい四三酸化鉄、γ-酸化鉄等、酸化鉄を主成分とするものであり、これらを一種または二種以上併用して用いられる。これら磁性粉体は、窒素吸着法によるＢＥＴ比表面積が２〜３０ｍ²／ｇが好ましく、特に３〜２８ｍ²／ｇがより好ましい。また、モース硬度が５〜７のものが好ましい。
【０１４８】
磁性粉体の形状としては、多面体、８面体、６面体、球形、針状、燐片状などがあるが、多面体、８面体、６面体、球形等の異方性の少ないものが画像濃度を高める上で好ましい。こういった磁性粉体の形状はＳＥＭなどによって確認することができる。
【０１４９】
磁性粉体の体積平均粒径としては０．０５〜０．４０μｍが好ましく、より好ましくは０．１０〜０．３０μｍである。体積平均径が０．０５μｍ未満の場合、黒色度の低下が顕著となり、白黒用トナーの着色剤としては着色力が不十分となるうえに、複合酸化物粒子どうしの凝集が強くなるため、分散性が悪化する傾向となる。また、磁性粉体の均一な表面処理が困難となり、鉄及び鉄化合物の遊離率が大きくなってしまう。さらに、磁性粉体の粒径が０．０５μｍよりも小さいと、磁性粉体自体が赤味の強いものとなってしまい、得られる画像も赤味の黒になる傾向にあり、画像品位が落ちるものとなる。
【０１５０】
一方、磁性粉体の体積平均粒径が０．４０μｍを越えてしまうと、一般の着色剤と同様に着色力が不足するようになる。加えて、特に小粒径トナー用の着色剤として使用する場合、個々のトナー粒子に均一に磁性粉体を分散させることが確率的に困難となり、分散性が悪化しやすくなり、トナーの耐久性が劣る場合もあり好ましくない。
【０１５１】
なお、磁性粉体の体積平均粒径は、透過型電子顕微鏡を用いて測定できる。具体的には、エポキシ樹脂中へ観察すべきトナー粒子を十分に分散させた後、温度４０℃の雰囲気中で２日間硬化させ得られた硬化物を、ミクロトームにより薄片上のサンプルとして、透過型電子顕微鏡（ＴＥＭ）において１万倍ないしは４万倍の拡大倍率の写真で視野中の１００個の磁性粉体粒子径を測定する。そして、磁性粉体の投影面積に等しい円の相当径をもとに、体積平均粒径を算出する。後述の実施例においても同様に測定した。
【０１５２】
本発明では、磁性粉体以外に他の着色剤を併用しても良い。併用し得る着色剤としては、磁性または非磁性無機化合物、公知の染料及び顔料が挙げられる。具体的には、例えば、コバルト、ニッケルなどの強磁性金属粒子、またはこれらにクロム、マンガン、銅、亜鉛、アルミニウム、希土類元素などを加えた合金、ヘマタイトなどの粒子、チタンブラック、ニグロシン染料／顔料、カーボンブラック、フタロシアニン等が挙げられる。これらもまた、表面を処理して用いても良い。
【０１５３】
また、本発明に用いられる磁性粉体は、体積平均変動係数が３５以下であることが好ましい。磁性粉体の体積平均変動係数は磁性粉体の粒度分布の広さを表す指標であり、体積平均変動係数が３５より大きいと言う事は磁性粉体の粒度分布が広い事を意味する。このような磁性粉体を使用すると、前述の磁性粉体の処理の均一性が劣るとともに、トナー中での分散性が悪化する傾向がある。さらには、造粒時にトナー粒子一粒一粒に磁性粉体が均一に入りにくくなり、トナー粒子間で磁性粉体の含有量に大きな差が生じ易くなり、好ましくない。なお、本発明において、体積平均変動係数は次式により求めるものと定義する。
【０１５４】
【数５】

【０１５５】
本発明に用いる磁性粉体の疎水化度は３５〜９５％であることが好ましく、より好ましくは４０〜９５％である。疎水化度は磁性粉体表面の処理剤の種類、及び量により任意に変える事が可能である。疎水化度とは磁性粉体の疎水性を示しており、疎水化度が低いものは親水性が高い事を意味する。
【０１５６】
そのため、疎水化度が低い磁性粉体を用いた場合、本発明の磁性トナーを製造する際に好適に用いられる懸濁重合法では、造粒中に磁性粉体が水系に移行してしまい、粒度分布がブロードになると共に、トナー粒子の平均円形度が低くなる。これは、疎水化処理が不十分である磁性粉体がトナー粒子表面に露出しやすくなるために起こる。また、疎水化度が低いものは鉄及び鉄化合物の遊離率が高くなり好ましくない。一方、疎水化度を９５％よりも大きくするためには磁性粉体表面の処理材を多量に使用しなければならず、この様な状態では磁性粉体の合一が生じ易く、処理の均一性が損なわれてしまうことがある。
【０１５７】
なお、本発明における疎水化度とは以下の方法により測定されたものである。磁性粉体の疎水化度の測定は、メタノール滴定試験により行う。メタノール滴定試験は、疎水化された表面を有する磁性粉体の疎水化度を確認する実験的試験である。
【０１５８】
メタノールを用いた疎水化度測定は次のように行う。磁性粉体０．１ｇを容量２５０ｍＬのビーカーの水５０ｍＬに添加する。その後メタノールを液中に徐々に添加し滴定を行う。この際メタノールは液底部より供給し、緩やかに攪拌しながら行う。磁性粉体の沈降終了は、液面に磁性粉体の浮遊物が確認されなくなった時点とし、疎水化度は、沈降終了時点に達した際のメタノール及び水混合液中のメタノールの体積百分率としてあらわされる。後述の実施例においても同様に測定した。
【０１５９】
本発明の磁性トナーに用いられる磁性粉体は、結着樹脂１００質量部に対して、１０〜２００質量部を用いることが好ましい。さらに好ましくは２０〜１８０質量部を用いることが良い。１０質量部未満では磁性トナーの着色力が乏しく、カブリの抑制も困難である。一方、２００質量部を越えると、磁性トナー担持体への磁力による保持力が強まり現像性が低下したり、個々のトナー粒子への磁性粉体の均一な分散が難しくなるだけでなく、定着性が低下してしまうことがある。
【０１６０】
なお、トナー粒子中の磁性粉体の含有量の測定は、例えばパーキンエルマー社製熱分析装置、ＴＧＡ７を用いて測定することができる。測定方法は、窒素雰囲気下において昇温速度２５℃／分で常温から９００℃まで、磁性トナーを加熱し、１００℃から７５０℃まで間の減量質量を、トナー粒子から磁性粉体を除いた成分の質量とし、残存質量を磁性粉体量とする。
【０１６１】
本発明の磁性トナーに用いられる磁性粉体は、例えばマグネタイトの場合、下記方法で製造される。
【０１６２】
第一鉄塩水溶液に、鉄成分に対して当量または当量以上の水酸化ナトリウム等のアルカリを加え、水酸化第一鉄を含む水溶液を調製する。調製した水溶液のｐＨをｐＨ７以上（好ましくはｐＨ８〜１４）に維持しながら空気を吹き込み、水溶液を７０℃以上に加温しながら水酸化第一鉄の酸化反応をおこない、磁性酸化鉄粉体の芯となる種晶をまず生成する。
【０１６３】
次に、種晶を含むスラリー状の液に前に加えたアルカリの添加量を基準として約１当量の硫酸第一鉄を含む水溶液を加える。液のｐＨを６〜１４に維持しながら空気を吹き込みながら水酸化第一鉄の反応をすすめ種晶を芯にして磁性酸化鉄粉体を成長させる。酸化反応がすすむにつれて液のｐＨは酸性側に移行していくが、液のｐＨは６未満にしない方が好ましい。酸化反応の終期に液のｐＨを調整し、磁性酸化鉄が一次粒子になるよう十分に攪拌し、カップリング剤を添加して十分に混合攪拌し、攪拌後に濾過し、乾燥し、軽く解砕することで疎水性処理された磁性酸化鉄粉体が得られる。または、酸化反応終了後、洗浄、濾過して得られた酸化鉄粉体を、乾燥せずに別の水系媒体中に再分散させた後、再分散液のｐＨを調整し、十分攪拌しながらシランカップリング剤を添加し、カップリング処理を行っても良い。
【０１６４】
第一鉄塩としては、一般的に硫酸法チタン製造に副生する硫酸鉄、鋼板の表面洗浄に伴って副生する硫酸鉄の利用が可能であり、更に塩化鉄等が可能である。
【０１６５】
水溶液法による磁性酸化鉄の製造方法は一般に反応時の粘度の上昇を防ぐこと、及び、硫酸鉄の溶解度から鉄濃度０．５〜２ｍｏｌ／Ｌが用いられる。硫酸鉄の濃度は一般に薄いほど製品の粒度が細かくなる傾向を有する。又、反応に際しては、空気量が多い程、そして反応温度が低いほど微粒化しやすい
【０１６６】
このようにして製造された疎水性磁性粉体を材料とした磁性トナーを使用することにより、安定したトナーの帯電性が得られ、転写効率が高く、高画質及び高安定性が可能となる。
【０１６７】
本発明の磁性トナーは、磁場７９．６ｋＡ／ｍ（１０００エルステッド）におけるトナーの飽和磁化が１０〜５０Ａｍ²／ｋｇ（ｅｍｕ／ｇ）である磁性トナーであることが必要である。これは、現像装置内に磁気力発生手段を設けることで磁性トナーの漏れを防止でき、磁性トナーの搬送性または攪拌性を高められるばかりでなく、磁性トナー担持体上に磁力が作用するように磁気力発生手段を設けることで、転写残トナーの回収性が更に向上し、又磁性トナーが穂立ちを形成するためにトナーの飛散を防止することが容易となる。
【０１６８】
しかし、磁性トナーの磁場７９．６ｋＡ／ｍにおける磁化の強さが１０Ａｍ²／ｋｇ未満であると、上記の効果が得られず、磁性トナー担持体上に磁力を作用させると磁性トナーの穂立ちが不安定となり、磁性トナーへの帯電付与が均一に行えないことによるカブリ、画像濃度ムラ、転写残トナーの回収不良等の画像不良を生じる易くなる。
【０１６９】
一方、磁性トナーの磁場７９．６ｋＡ／ｍにおける磁化の強さが５０Ａｍ²／ｋｇよりも大きいと、磁性トナーに磁力を作用させると磁気凝集により磁性トナーの流動性が著しく低下し、現像性が低下し、磁性トナーがダメージを受けやすくなり、トナー劣化が著しくなる。また、磁性トナーの磁気凝集により、特に、高温高湿下での耐久性が劣るものとなる。さらに、転写性も低下することで転写残トナーが増加し好ましくない。
【０１７０】
また、現像兼クリーニング工程、または、クリーナーレスシステムの画像形成方法に使用する場合、磁性トナーの磁場７９．６ｋＡ／ｍ（１０００エルステッド）におけるトナーの残留磁化が０．５〜６Ａｍ²／ｋｇ（ｅｍｕ／ｇ）である磁性トナーであることが好ましい。残留磁化が６Ａｍ²／ｋｇを超えた場合、転写残トナー同士が磁気凝集してしまいトナーの凝集体としてふるまいやすく、帯電部材と感光体との間で摺擦されることで感光体表面を傷つけることがあり好ましくない。一方、残留磁化が０．５Ａｍ²／ｋｇに満たない場合は、転写残トナーが粒子一個一個に散らばった状態で存在しやすく、帯電部材で捕捉されにくく、その結果として正規に帯電されにくくなってしまうことがあり好ましくない。すなわち、磁性トナーが好ましい残留磁化を持つことで、転写残トナーが適度に凝集した状態で存在することにより、感光体を傷つけることなく、適正にされるのである。
【０１７１】
磁性トナーの磁化の強さ（飽和磁化、残留磁化）は、含有する磁性粉体の量、磁性粉体の飽和磁化、残留磁化により任意に変えることが可能である。
【０１７２】
また、磁性粉体の飽和磁化は磁場７９６ｋＡ／ｍにおいて３０から１２０Ａｍ²／ｋｇであることが好ましい。
【０１７３】
本発明において磁性トナーの飽和磁化及び残留磁化の強さは、例えば振動型磁力計ＶＳＭ Ｐ−１−１０（東英工業社製）を用いて測定することができる。上記装置を使用する場合では、２５℃の室温にて外部磁場７９．６ｋＡ／ｍで測定する。また、磁性粉体の磁気特性についても、振動型磁力計ＶＳＭ Ｐ−１−１０（東英工業社製）を用いて、２５℃の室温にて外部磁場７９６ｋＡ／ｍで測定することができる。
【０１７４】
本発明の磁性トナーは定着性向上のために離型剤を含有しているが、本発明の磁性トナーは、離型剤を結着樹脂に対し総量で１〜３０質量％含有することが好ましい。より好ましくは、３〜２５質量％である。離型剤の含有量が１質量％未満では離型剤の添加効果が十分ではなく、さらに、オフセット抑制効果も不十分である。一方、３０質量％を超えてしまうと長期間の保存性が悪化すると共に、離型剤、磁性粉体等の磁性トナー材料の分散性が悪くなり、磁性トナーの流動性の悪化や画像特性の低下につながる。また、離型剤成分のしみ出しも起こり、高温高湿下での耐久性が劣るものとなりやすくなる。さらに、多量のワックスを内包するために、磁性トナーの形状がいびつになりやすくなる。
【０１７５】
一般に、記録媒体上に転写されたトナー像はその後、熱・圧力等のエネルギーにより転写材上に定着され、半永久的画像が得られる。この際、熱ロール式定着が一般に良く用いられる。先述したように、重量平均粒径が２０μｍ以下の磁性トナーを用いれば非常に高精細な画像を得ることができるが、粒径の細かいトナー粒子は紙等の記録媒体を使用した場合に紙の繊維の隙間に入り込み、熱定着用ローラからの熱の受け取りが不十分となり、低温オフセットが発生しやすい。しかしながら、本発明の磁性トナーにおいて、適正量の離型剤を含有せしめ、且つ、鉄及び鉄化合物の遊離率を前述の如きに制御することにより、高画質と定着性を両立させることが可能となる。
【０１７６】
本発明の磁性トナーに使用可能な離型剤としては、パラフィンワックス、マイクロクリスタリンワックス、ペトロラクタム等の石油系ワックス及びその誘導体、モンタンワックス及びその誘導体、フィッシャートロプシュ法による炭化水素ワックス及びその誘導体、ポリエチレンに代表されるポリオレフィンワックス及びその誘導体、カルナバワックス、キャンデリラワックス等天然ワックス及びその誘導体などで、誘導体には酸化物や、ビニル系モノマーとのブロック共重合物、グラフト変性物を含む。さらには、高級脂肪族アルコール、ステアリン酸、パルミチン酸等の脂肪酸、またはその化合物、酸アミドワックス、エステルワックス、ケトン、硬化ヒマシ油及びその誘導体、植物系ワックス、動物性ワックスなども使用できる。
【０１７７】
これらの離型剤成分の内でも、示差走査熱量分析による吸熱ピークが４０〜１１０℃のもの、即ち、示差走査熱量計により測定されるＤＳＣ曲線において昇温時に４０〜１１０℃の領域に最大吸熱ピークを有するものが好ましく、さらには５０〜１００℃の領域に有するものがより好ましい。上記温度領域に最大吸熱ピークを有することにより、低温定着に大きく貢献しつつ、離型性をも効果的に発現する。
【０１７８】
最大吸熱ピークが４０℃未満であると離型剤成分の自己凝集力が弱くなり、結果として耐高温オフセット性が悪化する傾向にある。また、離型剤のしみだしが生じ易くなり、トナーの帯電量が低下すると共に、高温高湿下での耐久性が低下する傾向にある。一方、該最大吸熱ピークが１１０℃を越えると定着温度が高くなり低温オフセットが発生しやすくなり好ましくない。さらに、水系媒体中で造粒／重合を行い重合方法により直接トナーを得る場合、該最大吸熱ピーク温度が高いと、主に造粒中に離型剤成分が析出する等の問題を生じ、離型剤の分散性が悪化し好ましくない。
【０１７９】
離型剤の吸熱量ならびに最大吸熱ピーク温度の測定は、「ＡＳＴＭ Ｄ ３４１８−８」に準じて行う。測定には、例えばパーキンエルマー社製ＤＳＣ−７を用いる。装置検出部の温度補正はインジウムと亜鉛の融点を用い、熱量の補正についてはインジウムの融解熱を用いる。測定サンプルにはアルミニウム製のパンを用い、対照用に空パンをセットし、試料を一回２００℃まで昇温させ熱履歴を除いた後、急冷し、再度、昇温速度１０℃／ｍｉｎにて温度３０〜２００℃の範囲で昇温させた時に測定されるＤＳＣ曲線を用いる。後述の実施例においても同様に測定した。
【０１８０】
本発明の磁性トナーは、磁性トナーのＴＨＦ可溶分のゲルパーミュエーションクロマトグラフィー（ＧＰＣ）により測定した分子量分布において、分子量５０００〜５００００の範囲にメインピークのピークトップがあることが好ましく、より好ましくは８０００〜４００００の範囲である。ピークトップが５０００未満であると、トナーの耐保存安定性に問題が生じたり、多数枚のプリントアウトを行った際にトナーの劣化が著しくなる傾向にある。逆に、ピークトップが５００００を超える場合には、低温定着性に問題が生じるとともに、重合中の液滴粘度の急激な上昇により、トナーの平均円形度を０．９７０以上とすることが困難になることがある。
【０１８１】
尚、ＧＰＣによるＴＨＦに可溶な樹脂成分の分子量の測定は、以下の様にして行えばよい。
本発明の磁性トナーをＴＨＦに室温で２４時間静置して溶解した溶液を、ポア径が０．２μｍの耐溶剤性メンブランフィルターで濾過してサンプル溶液とし、以下の条件で測定する。尚、サンプル調製は、ＴＨＦに可溶な成分の濃度が０．４〜０．６質量％になるようにＴＨＦの量を調整する。
装置 ： 高速ＧＰＣ ＨＬＣ８１２０ ＧＰＣ（東ソー社製）
カラム： Ｓｈｏｄｅｘ ＫＦ−８０１、８０２、８０３、８０４、８０５、８０６、８０７の７連（昭和電工社製）
溶離液： ＴＨＦ
流速 ： １．０ｍｌ／ｍｉｎ
オーブン温度： ４０．０℃
試料注入量 ： ０．１０ｍｌ
【０１８２】
また、試料の分子量の算出にあたっては、標準ポリスチレン樹脂（東ソー社製ＴＳＫ スタンダード ポリスチレン Ｆ−８５０、Ｆ−４５０、Ｆ−２８８、Ｆ−１２８、Ｆ−８０、Ｆ−４０、Ｆ−２０、Ｆ−１０、Ｆ−４、Ｆ−２、Ｆ−１、Ａ−５０００、Ａ−２５００、Ａ−１０００、Ａ−５００）により作成した分子量校正曲線を使用する。
【０１８３】
磁性トナーの分子量は、粉砕法において磁性トナーを製造する場合、用いる結着樹脂と混練状況により任意に変える事が出来る。また、重合法においては、用いる開始剤、架橋剤の種類、量等の組み合わせにより、任意に変えることが可能である。また、連鎖移動剤等を使用しても調整可能である。
【０１８４】
本発明の磁性トナーには、荷電特性を安定化するために荷電制御剤を配合しても良い。荷電制御剤としては、公知のものが利用でき、特に帯電スピードが速く、かつ、一定の帯電量を安定して維持できる荷電制御剤が好ましい。さらに、磁性トナーを直接重合法を用いて製造する場合には、重合阻害性が低く、水系分散媒体への可溶化物が実質的にない荷電制御剤が特に好ましい。
【０１８５】
具体的な化合物としては、ネガ系荷電制御剤としてサリチル酸、アルキルサリチル酸、ジアルキルサリチル酸、ナフトエ酸、ダイカルボン酸の如き芳香族カルボン酸の金属化合物、アゾ染料またはアゾ顔料の金属塩または金属錯体、スルホン酸又はカルボン酸基を側鎖に持つ高分子型化合物、ホウ素化合物、尿素化合物、ケイ素化合物、カリックスアレーン等が挙げられる。また、ポジ系荷電制御剤として四級アンモニウム塩、該四級アンモニウム塩を側鎖に有する高分子型化合物、グアニジン化合物、ニグロシン系化合物、イミダゾール化合物等が挙げられる。
【０１８６】
荷電制御剤をトナーに含有させる方法としては、トナー粒子内部に添加する方法とトナー粒子に外添する方法がある。これらの荷電制御剤の使用量としては、結着樹脂の種類、他の添加剤の有無、分散方法を含めた磁性トナーの製造方法によって決定されるもので、一義的に限定されるものではないが、内部添加する場合は、好ましくは結着樹脂１００質量部に対して０．１〜１０質量部、より好ましくは０．１〜５質量部の範囲で用いられる。また、外部添加する場合、トナー粒子１００質量部に対し、好ましくは０．００５〜１．０質量部、より好ましくは０．０１〜０．３質量部である。
【０１８７】
しかしながら、本発明の磁性トナーは、荷電制御剤の添加は必須ではなく、トナーの層圧規制部材や磁性トナー担持体との摩擦帯電など、画像形成プロセスにおける帯電プロセスを積極的に利用することで磁性トナー中に必ずしも荷電制御剤を含む必要はない。
【０１８８】
次に本発明に関わる重合トナーの懸濁重合法による製造方法を説明する。本発明に係わる重合トナーは、一般にトナー組成物、すなわち結着樹脂となる重合性単量体中に、磁性粉体、離型剤、可塑剤、荷電制御剤、架橋剤、場合によって着色剤等トナーとして必要な成分及びその他の添加剤、例えば、高分子重合体、分散剤等を適宜加えて、分散機等に依って均一に溶解または分散させた重合性単量体系を、分散安定剤を含有する水系媒体中に懸濁して製造できる。
【０１８９】
本発明に関わる重合トナーの製造において、重合性単量体系を構成する重合性単量体としては以下のものが挙げられる。
【０１９０】
重合性単量体としては、スチレン、ｏ−メチルスチレン、ｍ−メチルスチレン、ｐ−メチルスチレン、ｐ−メトキシスチレン、ｐ−エチルスチレン等のスチレン系単量体、アクリル酸メチル、アクリル酸エチル、アクリル酸ｎ−ブチル、アクリル酸イソブチル、アクリル酸ｎ−プロピル、アクリル酸ｎ−オクチル、アクリル酸ドデシル、アクリル酸２−エチルヘキシル、アクリル酸ステアリル、アクリル酸２−クロルエチル、アクリル酸フェニル等のアクリル酸エステル類、メタクリル酸メチル、メタクリル酸エチル、メタクリル酸ｎ−プロピル、メタクリル酸ｎ−ブチル、メタクリル酸イソブチル、メタクリル酸ｎ−オクチル、メタクリル酸ドデシル、メタクリル酸２−エチルヘキシル、メタクリル酸ステアリル、メタクリル酸フェニル、メタクリル酸ジメチルアミノエチル、メタクリル酸ジエチルアミノエチル等のメタクリル酸エステル類その他のアクリロニトリル、メタクリロニトリル、アクリルアミド等の単量体が挙げられる。これらの単量体は単独、または混合して使用し得る。上述の単量体の中でも、スチレンまたはスチレン誘導体を単独で、または他の単量体と混合して使用する事がトナーの現像特性及び耐久性の点から好ましい。
【０１９１】
本発明に係わる重合トナーの製造においては、重合性単量体系に樹脂を添加して重合しても良い。例えば、単量体では水溶性のため水性懸濁液中では溶解して乳化重合を起こすため使用できないアミノ基、カルボン酸基、水酸基、スルホン酸基、グリシジル基、ニトリル基等親水性官能基含有の重合性単量体成分をトナー粒子中に導入したい時には、これらとスチレンまたはエチレン等ビニル化合物とのランダム共重合体、ブロック共重合体、またはグラフト共重合体等、共重合体の形にして、またはポリエステル、ポリアミド等の重縮合体、ポリエーテル、ポリイミン等重付加重合体の形で使用が可能となる。こうした極性官能基を含む高分子重合体をトナー粒子中に共存させると、前述のワックス成分を相分離させ、より内包化が強力となり、耐ブロッキング性、現像性の良好な磁性トナーを得ることができる。
【０１９２】
これらの樹脂の中でも特にポリエステル樹脂を含有する事により、その効果は大きな物となる。これは次に述べる理由からと考えている。ポリエステル樹脂は比較的極性の高い官能基であるエステル結合を数多く含む為、樹脂自身の極性が高くなる。その極性の為、水系分散媒中では液滴表面にポリエステルが偏在する傾向が強くなり、その状態を保ちながら重合が進行し、トナー粒子となる。この為、トナー粒子表面にポリエステル樹脂が偏在する事で表面状態や、表面組成が均一な物となり、その結果帯電性が均一になると共に、離型剤の内包性が良好な事との相乗効果により非常に良好な現像性を得る事が出来る。
【０１９３】
本発明に使用されるポリエステル樹脂は、例えば磁性トナーの帯電性、耐久性および定着性などの物性をコントロールする上で、飽和ポリエステル樹脂、不飽和ポリエステル樹脂、またはその両者を適宜選択して使用することが可能である。本発明に使用されるポリエステル樹脂は、アルコール成分と酸成分から構成される通常のものが使用でき、両成分については以下に例示する。
【０１９４】
アルコール成分としては、エチレングリコール、プロピレングリコール、１，３−ブタンジオール、１，４−ブタンジオール、２，３−ブタンジオール、ジエチレングリコール、トリエチレングリコール、１，５−ペンタンジオール、１，６−ヘキサンジオール、ネオペンチルグリコール、２−エチル−１，３−ヘキサンジオール、シクロヘキサンジメタノール、ブテンジオール、オクテンジオール、シクロヘキセンジメタノール、水素化ビスフェノールＡ、また式（Ｉ）で表されるビスフェノール誘導体；または式（Ｉ）の化合物の水添物、式（II）で示されるジオール；または式（II）の化合物の水添物のジオールが挙げられる。
【０１９５】
【化３】

［式中、Ｒはエチレンまたはプロピレン基であり、ｘ，ｙはそれぞれ１以上の整数であり、かつｘ＋ｙの平均値は２〜１０である。］
【化４】

【０１９６】
二価のカルボン酸としてはフタル酸、テレフタル酸、イソフタル酸、無水フタル酸の如きベンゼンジカルボン酸またはその無水物；コハク酸、アジピン酸、セバシン酸、アゼライン酸の如きアルキルジカルボン酸またはその無水物、またさらに炭素数６〜１８のアルキルまたはアルケニル基で置換されたコハク酸もしくはその無水物；フマル酸、マレイン酸、シトラコン酸、イタコン酸の如き不飽和ジカルボン酸またはその無水物などが挙げられる。
【０１９７】
さらに、アルコール成分としてグリセリン、ペンタエリスリトール、ソルビット、ソルビタン、ノボラック型フェノール樹脂のオキシアルキレンエーテルの如き多価アルコールが挙げられ、酸成分としてトリメリット酸、ピロメリット酸、１，２，３，４−ブタンテトラカルボン酸、ベンゾフェノンテトラカルボン酸やその無水物等の多価カルボン酸が挙げられる。
【０１９８】
上記ポリエステル樹脂の中では、帯電特性、環境安定性が優れておりその他の電子写真特性においてバランスのとれた前記のビスフェノールＡのアルキレンオキサイド付加物が好ましく使用される。この化合物の場合には、定着性や磁性トナーの耐久性の点においてアルキレンオキサイドの平均付加モル数は２〜１０が好ましい。
【０１９９】
本発明に用いられるポリエステル樹脂は全成分中４５〜５５モル％がアルコール成分であり、５５〜４５モル％が酸成分であることが好ましい。
【０２００】
ポリエステル樹脂は、本発明の磁性トナーの製造方法においてトナー粒子表面に存在し、得られるトナー粒子が安定した帯電性を発現するためには、０．１〜５０ｍｇＫＯＨ／樹脂１ｇの酸価を有していることが好ましい。０．１ｍｇＫＯＨ／樹脂１ｇ未満だとトナー表面への存在量が絶対的に不足する傾向にあり、５０ｍｇＫＯＨ／樹脂１ｇを越えるとトナーの帯電性に悪影響を及ぼすことがある。さらに本発明では、５〜３５ｍｇＫＯＨ／樹脂１ｇの酸価の範囲がより好ましい。
【０２０１】
本発明においては、得られるトナー粒子の物性に悪影響を及ぼさない限り二種以上のポリエステル樹脂を併用したり、例えば、シリコーンやフルオロアルキル基含有化合物により変性したりして物性を調製することも好適に行われる。
【０２０２】
また、このような極性官能基を含む高分子重合体を使用する場合、その平均分子量は５，０００以上が好ましく用いられる。５，０００以下、特に４，０００以下では、本重合体が表面付近に集中し易い事から、現像性、耐ブロッキング性等に悪い影響が起こり易くなり好ましくない。
【０２０３】
また、材料の分散性や定着性、または画像特性の改良等を目的として上記以外の樹脂を単量体系中に添加しても良く、用いられる樹脂としては、例えば、ポリスチレン、ポリビニルトルエンなどのスチレン及びその置換体の単重合体；スチレン−プロピレン共重合体、スチレン−ビニルトルエン共重合体、スチレン−ビニルナフタリン共重合体、スチレン−アクリル酸メチル共重合体、スチレン−アクリル酸エチル共重合体、スチレン−アクリル酸ブチル共重合体、スチレン−アクリル酸オクチル共重合体、スチレン−アクリル酸ジメチルアミノエチル共重合体、スチレン−メタアクリル酸メチル共重合体、スチレン−メタアクリル酸エチル共重合体、スチレン−メタアクリル酸ブチル共重合体、スチレン−メタクリル酸ジメチルアミノエチル共重合体、スチレン−ビニルメチルエーテル共重合体、スチレン−ビニルエチルエーテル共重合体、スチレン−ビニルメチルケトン共重合体、スチレン−ブタジエン共重合体、スチレン−イソプレン共重合体、スチレン−マレイン酸共重合体、スチレン−マレイン酸エステル共重合体などのスチレン系共重合体；ポリメチルメタクリレート、ポリブチルメタクリレート、ポリ酢酸ビニル、ポリエチレン、ポリプロピレン、ポリビニルブチラール、シリコン樹脂、ポリエステル樹脂、ポリアミド樹脂、エポキシ樹脂、ポリアクリル酸樹脂、ロジン、変性ロジン、テンペル樹脂、フェノール樹脂、脂肪族または脂環族炭化水素樹脂、芳香族系石油樹脂などが単独または混合して使用できる。これら樹脂の添加量としては、重合性単量体１００質量部に対し１〜２０質量部が好ましい。１質量部未満では添加効果が小さく、一方２０質量部以上添加すると重合トナーの種々の物性設計が難しくなる。
【０２０４】
さらに、重合性単量体を重合して得られるトナー粒子の分子量範囲とは異なる分子量の重合体を単量体中に溶解して重合すれば、分子量分布の広い、耐オフセット性の高い磁性トナーを得ることが出来る。
【０２０５】
本発明の磁性トナーに関わる重合トナーの製造において使用される重合開始剤としては、重合反応時に半減期０．５〜３０時間であるものを、重合性単量体に対し０．５〜２０質量部の添加量で重合反応を行うと、ＧＰＣにおいてメインピークのピークトップが分子量５０００〜５００００の間に存在する重合体を得ることが出来る。
【０２０６】
本発明で使用される重合開始剤としては、従来公知のアゾ系重合開始剤、過酸化物系重合開始剤などがあり、アゾ系重合開始剤としては、２，２'−アゾビス−（２，４−ジメチルバレロニトリル）、２，２'−アゾビスイソブチロニトリル、１，１'−アゾビス（シクロヘキサン−１−カルボニトリル）、２，２'−アゾビス−４−メトキシ−２，４−ジメチルバレロニトリル、アゾビスイソブチロニトリル等が例示され、過酸化物系重合開始剤としてはｔ−ブチルパーオキシアセテート、ｔ−ブチルパーオキシラウレート、ｔ−ブチルパーオキシピバレート、ｔ−ブチルパーオキシ−２−エチルヘキサノエート、ｔ−ブチルパーオキシイソブチレート、ｔ−ブチルパーオキシネオデカノエート、ｔ−ヘキシルパーオキシアセテート、ｔ−ヘキシルパーオキシラウレート、ｔ−ヘキシルパーオキシピバレート、ｔ−ヘキシルパーオキシ−２−エチルヘキサノエート、ｔ−ヘキシルパーオキシイソブチレート、ｔ−ヘキシルパーオキシネオデカノエート、ｔ−ブチルパーオキシベンゾエート、α，α'−ビス（ネオデカノイルパーオキシ）ジイソプロピルベンゼン、クミルパーオキシネオデカノエート、１，１，３，３−テトラメチルブチルパーオキシ−２−エチルヘキサノエート、１，１，３，３−テトラメチルブチルパーオキシネオデカノエート、１−シクロヘキシル−１−メチルエチルパーオキシネオデカノエート、２，５−ジメチル−２，５−ビス（２−エチルヘキサノイルパーオキシ）ヘキサン、１−シクロヘキシル−１−メチルエチルパーオキシ−２−エチルヘキサノエート、ｔ−ヘキシルパーオキシイソプロピルモノカーボネート、ｔ−ブチルパーオキシイソプロピルモノカーボネート、ｔ−ブチルパーオキシ２−エチルヘキシルモノカーボネート、ｔ−ヘキシルパーオキシベンゾエート、２，５−ジメチル−２，５−ビス（ベンゾイルパーオキシ）ヘキサン、ｔ−ブチルパーオキシ−ｍ−トルオイルベンゾエート、ビス（ｔ−ブチルパーオキシ）イソフタレート、ｔ−ブチルパーオキシマレイックアシッド、ｔ−ブチルパーオキシ−３，５，５−トリメチルヘキサノエート、２，５−ジメチル−２，５−ビス（ｍ−トルオイルパーオキシ）ヘキサンなどのパーオキシエステル、ベンゾイルパーオキサイド、ラウロイルパーオキサイド、イソブチリルパーオキサイドなどのジアシルパーオキサイド、ジイソプロピルパーオキシジカーボネート、 ビス（４−ｔ−ブチルシクロヘキシル）パーオキシジカーボネートなどのパーオキシジカーボネート、１，１−ジ−ｔ−ブチルパーオキシシクロヘキサン、１，１−ジ−ｔ−ヘキシルパーオキシシクロヘキサン、１，１−ジ−ｔ−ブチルパーオキシ−３，３，５−トリメチルシクロヘキサン、２，２−ジ−ｔ−ブチルパーオキシブタンなどのパーオキシケタール、ジ−ｔ−ブチルパーオキサイド、ジクミルパーオキサイド、ｔ−ブチルクミルパーオキサイドなどのジアルキルパーオキサイド、その他としてｔ−ブチルパーオキシアリルモノカーボネート等が挙げられ、必要に応じてこれらの開始剤を二種以上用いることもできる。
【０２０７】
本発明の磁性トナーを重合法で製造する際は、目的の溶融粘度を得るために、上記開始剤とともに、架橋剤を添加し、溶融粘度を調整することが重要である。本発明で使用される架橋剤としては、主として二個以上の重合可能な二重結合を有する化合物が用いられ、例えば、ジビニルベンゼン、ジビニルナフタレン等のような芳香族ジビニル化合物；例えばエチレングリコールジアクリレート、エチレングリコールジメタクリレート、１，３−ブタンジオールジメタクリレート等のような二重結合を二個有するカルボン酸エステル；ジビニルアニリン、ジビニルエーテル、ジビニルスルフィド、ジビニルスルホン等のジビニル化合物；及び三個以上のビニル基を有する化合物；が単独もしくは混合物として用いられる。添加量としては、使用する開始剤、架橋剤の種類、反応条件で調整が必要であるが、おおむね、重合性単量体に対して、０．０１〜５質量部が適当である。
【０２０８】
本発明の磁性トナーを重合法で製造する方法では、一般に上述の磁性粉体、重合性単量体、離型剤等のトナー組成物等を適宜加えて、ホモジナイザー、ボールミル、コロイドミル、超音波分散機等の分散機に依って均一に溶解または分散させた重合性単量体系を、分散安定剤を含有する水系媒体中に懸濁する。この時、高速撹拌機もしくは超音波分散機のような高速分散機を使用して一気に所望のトナー粒子のサイズとするほうが、得られるトナー粒子の粒径がシャープになる。重合開始剤添加の時期としては、重合性単量体中に他の添加剤を添加する時同時に加えても良いし、水系媒体中に懸濁する直前に混合しても良い。又、造粒中または、造粒直後に、重合反応を開始する前に重合性単量体または溶媒に溶解した重合開始剤を加える事も出来る。
【０２０９】
造粒後は、通常の撹拌機を用いて、粒子状態が維持され且つ粒子の浮遊・沈降が防止される程度の撹拌を行えば良い。
【０２１０】
本発明の磁性トナーを重合法で製造する場合には、分散安定剤として公知の界面活性剤や有機分散剤・無機分散剤が使用できる。中でも無機分散剤は、有害な超微粉を生じ難く、その立体障害性により分散安定性を得ているので反応温度を変化させても安定性が崩れ難く、洗浄も容易でトナーに悪影響を与え難いので、好ましく使用できる。こうした無機分散剤の例としては、燐酸カルシウム、燐酸マグネシウム、燐酸アルミニウム、燐酸亜鉛等の燐酸多価金属塩、炭酸カルシウム、炭酸マグネシウム等の炭酸塩、メタ硅酸カルシウム、硫酸カルシウム、硫酸バリウム等の無機塩、水酸化カルシウム、水酸化マグネシウム、水酸化アルミニウム、シリカ、ベントナイト、アルミナ等の無機酸化物が挙げられる。
【０２１１】
これら無機分散剤を用いる場合には、そのまま使用しても良いが、より細かい粒子を得るため、水系媒体中にて該無機分散剤粒子を生成させて用いることが好ましい。例えば、燐酸カルシウムの場合、高速撹拌下、燐酸ナトリウム水溶液と塩化カルシウム水溶液とを混合して、水不溶性の燐酸カルシウムを生成させることが出来、より均一で細かな分散が可能となる。この時、同時に水溶性の塩化ナトリウム塩が副生するが、水系媒体中に水溶性塩が存在すると、重合性単量体の水への溶解が抑制されて、乳化重合に依る超微粒トナーが発生し難くなるので、より好都合である。無機分散剤は、重合終了後酸またはアルカリで溶解して、ほぼ完全に取り除くことが出来る。
【０２１２】
また、これらの無機分散剤は、重合性単量体１００質量部に対して、０．２〜２０質量部を単独で使用する事が望ましいが、超微粒子を発生し難いもののトナーの微粒化についてはやや不十分なこともあるので、０．００１〜０．１質量部の界面活性剤を併用しても良い。
【０２１３】
上記界面活性剤としては、例えばドデシルベンゼン硫酸ナトリウム、テトラデシル硫酸ナトリウム、ペンタデシル硫酸ナトリウム、オクチル硫酸ナトリウム、オレイン酸ナトリウム、ラウリル酸ナトリウム、ステアリン酸ナトリウム、ステアリン酸カリウム等が挙げられる。
【０２１４】
前記重合工程においては、重合温度は４０℃以上、一般には５０〜９０℃の温度に設定して重合を行う。この温度範囲で重合を行うと、内部に封じられるべき離型剤やワックスの類が、相分離により析出して内包化がより完全となる。残存する重合性単量体を消費するために、重合反応終期ならば、反応温度を９０〜１５０℃にまで上げる事は可能である。
【０２１５】
重合トナー粒子は重合終了後、公知の方法によって濾過、洗浄、乾燥を行い、必要により無機微粉体を混合し表面に付着させることで、本発明の磁性トナーを得ることができる。また、製造工程に分級工程を入れ、粗粉や微粉をカットすることも、本発明の望ましい形態の一つである。
【０２１６】
本発明において磁性トナーは、流動化剤として個数平均一次粒径４〜８０ｎｍの無機微粉体が添加されることも好ましい形態である。無機微粉体は、磁性トナーの流動性改良及びトナー粒子の帯電均一化のために添加されるが、無機微粉体を疎水化処理するなどの処理によって磁性トナーの帯電量の調整、環境安定性の向上等の機能を付与することも好ましい形態である。
【０２１７】
無機微粉体の個数平均一次粒径が８０ｎｍよりも大きい場合、または８０ｎｍ以下の無機微粉体が添加されていない場合には、転写残トナーが帯電部材へ付着した際に帯電部材に固着し易くなり、安定して良好な帯電特性を得ることが困難である。また、良好な磁性トナーの流動性が得られず、トナー粒子への帯電付与が不均一になり易く、カブリの増大、画像濃度の低下、トナー飛散等の問題を避けられないことがある。無機微粉体の個数平均一次粒径が４ｎｍよりも小さい場合には、無機微粉体の凝集性が強まり、一次粒子ではなく解砕処理によっても解れ難い強固な凝集性を持つ粒度分布の広い凝集体として挙動し易く、凝集体の現像、像担持体または磁性トナー担持体等を傷つけるなどによる画像欠陥を生じ易くなる。トナー粒子の帯電分布をより均一とするためには無機微粉体の個数平均一次粒径は６〜３５ｎｍであることがより良い。
【０２１８】
本発明において、無機微粉体の個数平均一次粒径の測定法は、走査型電子顕微鏡により拡大撮影した磁性トナーの写真で、更に走査型電子顕微鏡に付属させたＸＭＡ等の元素分析手段によって無機微粉体の含有する元素でマッピングされた磁性トナーの写真を対照しつつ、トナー粒子表面に付着または遊離して存在している無機微粉体の一次粒子を１００個以上測定し、個数基準の平均一次粒径、個数平均一次粒径を求めることで測定することが出来る。
【０２１９】
本発明で用いられる無機微粉体としては、シリカ、酸化チタン、アルミナなどが使用でき、単独で用いても、複数種組み合わせて用いても良い。シリカとしては、例えば、ケイ素ハロゲン化物の蒸気相酸化により生成されたいわゆる乾式法又はヒュームドシリカと称される乾式シリカ、及び水ガラス等から製造されるいわゆる湿式シリカの両者が使用可能であるが、表面及びシリカ微粉体の内部にあるシラノール基が少なく、またＮａ₂Ｏ、ＳＯ₃ ^2-等の製造残滓の少ない乾式シリカの方が好ましい。また乾式シリカにおいては、製造工程において例えば、塩化アルミニウム、塩化チタン等他の金属ハロゲン化合物をケイ素ハロゲン化合物と共に用いることによって、シリカと他の金属酸化物の複合微粉体を得ることも可能でありそれらも包含する。
【０２２０】
個数平均一次粒径が４〜８０ｎｍの無機微粉体の添加量は、トナー粒子に対して０．１〜３．０質量％であることが好ましく、添加量が０．１質量％未満ではその効果が十分ではなく、３．０質量％以上では定着性が悪くなる傾向にある。
【０２２１】
なお、無機微粉体の含有量は、蛍光Ｘ線分析を用い、標準試料から作成した検量線を用いて定量できる。
【０２２２】
また本発明において無機微粉体は、疎水化処理された物であることが高温高湿環境下での特性から好ましい。磁性トナーに添加された無機微粉体が吸湿すると、トナー粒子の帯電量が著しく低下し、トナー飛散が起こり易くなる。
【０２２３】
疎水化処理に用いる処理剤としては、シリコーンワニス、各種変性シリコーンワニス、シリコーンオイル、各種変性シリコーンオイル、シラン化合物、シランカップリング剤、その他有機硅素化合物、有機チタン化合物等の処理剤を単独でまたは併用して処理しても良い。
【０２２４】
その中でも、シリコーンオイルにより処理したものが好ましく、より好ましくは、無機微粉体をシラン化合物で疎水化処理すると同時、または処理した後にシリコーンオイルにより処理したものが、高湿環境下でもトナー粒子の帯電量を高く維持し、トナー飛散を防止する上でよい。
【０２２５】
そのような無機微粉体の処理方法としては、例えば第一段反応として、シラン化合物でシリル化反応を行いシラノール基を化学結合により消失させた後、第二段反応としてシリコーンオイルにより表面に疎水性の薄膜を形成する処理方法を例示することができる。
【０２２６】
上記シリコーンオイルは、２５℃における粘度が１０〜２００，０００ｍｍ²／ｓのものが、さらには３，０００〜８０，０００ｍｍ²／ｓのものが好ましい。１０ｍｍ²／ｓ未満では、無機微粉体に安定性が無く、熱および機械的な応力により、画質が劣化する傾向がある。２００，０００ｍｍ²／ｓを超える場合は、均一な処理が困難になる傾向がある。
【０２２７】
使用されるシリコーンオイルとしては、例えばジメチルシリコーンオイル、メチルフェニルシリコーンオイル、α−メチルスチレン変性シリコーンオイル、クロルフェニルシリコーンオイル、フッ素変性シリコーンオイル等が特に好ましい。
【０２２８】
無機微粉体をシリコーンオイルで処理する方法としては、例えば、シラン化合物で処理された無機微粉体とシリコーンオイルとをヘンシェルミキサー等の混合機を用いて直接混合してもよいし、無機微粉体にシリコーンオイルを噴霧する方法を用いてもよい。または適当な溶剤にシリコーンオイルを溶解または分散させた後、無機微粉体を加え混合し溶剤を除去する方法でもよい。無機微粉体の凝集体の生成が比較的少ない点で噴霧機を用いる方法がより好ましい。
【０２２９】
シリコーンオイルの処理量は、無機微粉体１００質量部に対し１〜４０質量部、好ましくは３〜３５質量部が良い。シリコーンオイルの量が少なすぎると良好な疎水性が得られず、多すぎるとカブリ発生等の不具合が生ずる傾向がある。
【０２３０】
本発明で用いられる無機微粉体は、磁性トナーに良好な流動性を付与させる為にシリカ、アルミナ、酸化チタンが好ましく、その中でも特にシリカであることが好ましい。更に、窒素吸着によるＢＥＴ法で測定したシリカの比表面積が２０〜３５０ｍ²／ｇ範囲内のものが好ましく、より好ましくは２５〜３００ｍ²／ｇのものが更に良い。
【０２３１】
無機微粉体の比表面積は、ＢＥＴ法に従って、例えば比表面積測定装置オートソーブ１（湯浅アイオニクス社製）を用いて試料表面に窒素ガスを吸着させ、ＢＥＴ多点法を用いて測定し、算出することができる。
【０２３２】
本発明において、無機微粉体としてシリカを用いる場合、シリカの遊離率は０．１％から２．０％であることが好ましく、より好ましくは０．１％から１．５０％である。シリカの遊離率は前述のパーティクルアナライザーにより測定することができ、次式によりシリカの遊離率を求められる。
【数６】

【０２３３】
具体的な測定方法としては、チャンネル１で炭素原子、チャンネル２でケイ素原子（測定波長２８８．１６０ｎｍ、Ｋファクターは推奨値を使用）を測定すれば良い。
【０２３４】
本発明者らが検討を行ったところ、シリカの遊離率が０．１％より少ないと多数枚画出し試験の後半、特に高温高湿下でカブリの増大、がさつきが生じやすい。一般に、高温環境下では規制部材等のストレスにより外添材の埋め込みが起こりやすく、多数枚印刷後では磁性トナーの流動性は初期に比べ劣るものとなってしまい、上記の問題が生じてしまうと考えられる。しかしながら、シリカの遊離率が０．１％以上であるとこのような問題は生じにくい。これは、ある程度シリカが遊離した状態で存在すると、トナーの流動性が良好となる為に、耐久による埋め込みが生じにくくなると共に、ストレスによりトナー粒子に付着しているシリカの埋め込みが生じても、遊離のシリカがトナー粒子表面に付着する事により磁性トナーの流動性の低下が少なくなる為であると考えている。
【０２３５】
一方、シリカの遊離率が２．００％より多いと遊離のシリカが帯電規制部材を汚染し、カブリの増大を生じ好ましくない。また、このような状態では磁性トナーの帯電均一性も損なわれ、転写効率も低下する。このため、シリカの遊離率は０．１％から２．０％であることが重要である。
【０２３６】
また、本発明の磁性トナーは、磁性トナーの重量平均粒径よりも小さい体積平均粒径を有する導電性微粉体をさらに有する事が好ましく、さらに上記無機微粉体の個数平均一次粒径よりも大きく、且つ、磁性トナーの重量平均粒径よりも小さい体積平均粒径を有する導電性微粉体を有する事がより好ましい。これは、導電性微粉体を有する事により磁性トナーの現像性が向上し、高い画像濃度を得る事が出来るからである。また、導電性微粉体の遊離率が５．０％〜５０．０％であるとその効果は顕著なものとなる。
【０２３７】
この理由は定かではないが、遊離の磁性粉体と共に、遊離の導電性微粉体が存在する事で、磁性トナーのチャージアップが抑制されると共に、トナー粒子の帯電がより均一になる事で現像性が向上すると考えている。さらには、トナー粒子に付着している導電性微粉体がマイクロキャリアの如き挙動をする為に現像性が向上するものと考えている。この為、導電性微粉体の遊離率は５．０％より少ないとこの効果が充分には得られない。一方、導電性微粉体の遊離率が５０．０％より多いと、トナー粒子への導電性微粒子の付着の均一性が劣るものとなり好ましくない。
【０２３８】
なお、導電性微粉体の遊離率は前述のパーティクルアナライザーにより測定することができ、次式により求められる。
【数７】

【０２３９】
具体的な測定方法としては、チャンネル１で炭素原子を測定し、チャンネル３で導電性微粉体が有する金属元素（測定波長は金属元素の種類により異なる。例えば、導電性微粒子として酸化亜鉛を用いた場合、測定波長は３３４．５００ｎｍ、Ｋファクターは推奨値を使用）を測定すれば良い。
【０２４０】
また、本発明の磁性トナーを現像兼クリーニングを利用した画像形成方法に適用する場合には、導電性微粉体は重要な役割を果たす。
【０２４１】
ここで、トナー粒子に導電性微粉体を外部添加した場合の画像形成プロセス中でのトナー粒子及び導電性微粉体の挙動を説明する。
【０２４２】
磁性トナーに含有させた導電性微粉体は、現像工程における像担持体側の静電潜像の現像時にトナー粒子とともに適当量が像担持体側に移行する。像担持体上のトナー像は転写工程において記録媒体側に転移する。像担持体上の導電性微粉体も一部は記録媒体側に付着するが残りは像担持体上に付着保持されて残留する。磁性トナーと逆極性の転写バイアスを印加して転写を行う場合には、磁性トナーは記録媒体側に引かれて積極的に転移するが、像担持体上の導電性微粉体は導電性であることで記録媒体側には積極的には転移せず、一部は記録媒体側に付着するものの残りは像担持体上に付着保持されて残留する。
【０２４３】
クリーナを用いない画像形成方法では、転写後の像担持体面に残存の転写残トナーおよび上記の残存導電性微粉体は、像担持体と接触帯電部材の当接部である帯電部に像担持体面の移動でそのまま持ち運ばれて接触帯電部材に付着・混入する。従って、像担持体と接触帯電部材との当接部に導電性微粉体が介在した状態で像担持体の接触帯電が行われる。
【０２４４】
この導電性微粉体の存在により、接触帯電部材への転写残トナーが少ない場合、転写残トナーの付着・混入による汚染にかかわらず、接触帯電部材の像担持体への緻密な接触性と接触抵抗を維持できるため、該接触帯電部材による像担持体の帯電を良好に行わせることができる。
【０２４５】
また、接触帯電部材に付着・混入した転写残トナーは、帯電部材から像担持体へ印加される帯電バイアスによって、帯電バイアスと同極性に帯電を揃えられて接触帯電部材から徐々に像担持体上に吐き出され、像担持体面の移動とともに現像部に至り、現像工程において現像兼クリーニング（回収）される。
【０２４６】
更に、画像形成が繰り返されることで、磁性トナーに含有させてある導電性微粉体が、現像部で像担持体面に移行し該像担持面の移動により転写部を経て帯電部に持ち運ばれて帯電部に逐次に導電性微粉体が供給され続けるため、帯電部において導電性微粉体が脱落等で減少したり、劣化するなどしても、帯電性の低下が生じることが防止されて良好な帯電性が安定して維持される。
【０２４７】
このため、導電性微粉体の遊離率は５.０％から５０.０％であることが好ましい。導電性微粉体の遊離率が５.０％より少ないと、像担持体上に保持される導電性微粉体が少なくなり、良好な帯電性が得られない。また、導電性微粉体の遊離率が５０.０％より多いと、現像兼クリーニングによって回収される導電性微粉体の量が多くなり、現像器内での導電性微粉体の蓄積が起こりやすくなり、磁性トナーの帯電性、現像性の低下を生じ好ましくない。
【０２４８】
また、このように磁性トナーの帯電量の均一性を促す為に、導電性微粉体の抵抗は、１×１０⁹Ωｃｍ以下が好ましい。導電性微粉体の抵抗が、１×１０⁹Ωｃｍよりも大きいと導電性微粉体を帯電部材と像担持体との当接部及びその近傍の帯電領域に介在させ、接触帯電部材の導電性微粉体を介しての像担持体への緻密な接触性を維持させても、良好な帯電性を得るための帯電促進効果が得られにくい。導電性微粉体の帯電促進効果を十分に引き出し、良好な帯電性を安定して得るためには、導電性微粉体の抵抗が、接触帯電部材の表面部または像担持体との接触部の抵抗よりも小さいことが好ましい。
【０２４９】
更に、導電性微粉体の抵抗が、１×１０⁸Ωｃｍ以下であることが、接触帯電部材への絶縁性の転写残トナーへの付着・混入による帯電阻害に打ち勝って像担持体の帯電をより良好に行わせる上で好ましく良い。
【０２５０】
本発明においては導電性微粉体の磁性トナー全体に対する含有量は、０．５〜１０質量％であることが好ましい。導電性微粉体の磁性トナー全体に対する含有量が０．５質量％よりも少ないと、接触帯電部材への絶縁性の転写残トナーへの付着・混入による帯電阻害に打ち勝って像担持体の帯電を良好に行わせるのに十分な量の導電性微粉体を、帯電部材と像担持体との当接部またはその近傍の帯電領域に介在させることができず、帯電性が低下し帯電不良を生じることがある。また、含有量が１０質量％よりも多い場合では、現像兼クリーニングによって回収される導電性微粉体が多くなりすぎることによる現像部での磁性トナーの帯電能、現像性を低下させ、画像濃度低下やトナー飛散を生ずる傾向がある。導電性微粉体の磁性トナー全体に対する含有量は、０．５〜５質量％であることが好ましく良い。
【０２５１】
導電性微粉体の粒径として具体的には、体積平均粒径が０．１μｍ以上であり、磁性トナーの重量平均粒径よりも小さいことが好ましい。導電性微粉体の体積平均粒径が小さいと、現像性の低下を防ぐために導電性微粉体の磁性トナー全体に対する含有量を小さく設定しなければならない。導電性微粉体の体積平均粒径が０．１μｍ未満では、導電性微粉体の有効量を確保できず、帯電工程において、接触帯電部材への絶縁性の転写残トナーへの付着・混入による帯電阻害に打ち勝って像担持体の帯電を良好に行わせるのに十分な量の導電性微粉体を帯電部材と像担持体との当接部及びその近傍の帯電領域に介在させることができず、帯電不良を生じ易くなる。
【０２５２】
また、導電性微粉体の体積平均粒径が磁性トナーの重量平均粒径よりも大きいと、帯電部材から脱落した導電性微粉体は静電潜像を書き込む露光を遮光または拡散し、静電潜像の欠陥を生じ画像品位を低下させることがある。更に、導電性微粉体の体積平均粒径が大きいと、単位重量当たりの粒子数が減少するため、帯電部材からの導電性微粉体の脱落等による減少、劣化を考慮して導電性微粉体を帯電部材と像担持体との当接部またはその近傍の帯電領域に逐次に導電性微粉体が供給し続け介在させるために、また、接触帯電部材が導電性微粉体を介して像担持体への緻密な接触性を維持し良好な帯電性を安定して得るためには、導電性微粉体の磁性トナー全体に対する含有量を大きくしなければならない。しかし、導電性微粉体の含有量を大きくしすぎると、特に高湿環境下での磁性トナー全体としての帯電能、現像性を低下させ、画像濃度低下やトナー飛散を生ずる。このような観点から、導電性微粉体の体積平均粒径は好ましくは５μｍ以下が良い。
【０２５３】
また、導電性微粉体は、透明、白色または淡色の導電性微粉体であることが、記録媒体上に転写される導電性微粉体がカブリとして目立たないため好ましく良い。静電潜像形成工程における露光の妨げとならない意味でも導電性微粉体は、透明、白色または淡色の導電性微粉体であることがよく、より好ましくは、導電性微粉体は、露光に対する透過率が３０％以上であることが良い。
【０２５４】
本発明においては、導電性微粉体の光透過性については以下の手順で測定することができる。片面に接着層を有する透明のフィルムの導電性微粉体を一層分固定した状態で透過率を測定する。光はシートの鉛直方向から照射しフィルム背面に透過した光を集光し光量を測定する。フィルムのみと導電性微粉体を付着したときの光量から正味の光量として導電性微粉体の透過率を算出する。実際にはＸ−Ｒｉｔｅ社製３１０Ｔ透過型濃度計を用いて測定することができる。
【０２５５】
本発明における導電性微粉体の体積平均粒径及び粒度分布の測定には、例えばコールター社製、ＬＳ−２３０型レーザー回折式粒度分布測定装置にリキッドモジュールを取り付けたものを用いることが出来、測定条件としては０．０４〜２０００μｍの測定範囲が良い。測定法としては、純水１０ｍＬに微量の界面活性剤を添加し、これに導電性微粉体の試料１０ｍｇを加え、超音波分散機（超音波ホモジナイザー ）にて１０分間分散した後、測定時間９０秒、測定回数１回で測定する方法を例示することができる。
【０２５６】
本発明において、導電性微粉体の粒度及び粒度分布の調整方法としては、導電性微粉体の一次粒子が製造時において所望の粒度及び粒度分布が得られるように製造法、製造条件を設定する方法以外にも、一次粒子の小さな粒子を凝集させる方法、一次粒子の大きな粒子を粉砕する方法または分級による方法等が可能であり、更には、所望の粒度及び粒度分布の基材粒子（導電性微粉体を調製するにあたり、導電性材料を付着または固定化する際に母体となる粒子）の表面の一部もしくは全部に導電性微粉体を付着または固定化する方法、所望の粒度及び粒度分布の粒子に導電性成分が分散された形態を有する導電性微粉体を用いる方法等も可能であり、これらの方法を組み合わせて導電性微粉体の粒度及び粒度分布を調整することも可能である。
【０２５７】
導電性微粉体の粒子が凝集体として構成されている場合の粒径は、その凝集体としての平均粒径として定義される。導電性微粉体は、一次粒子の状態で存在するばかりでなく二次粒子の凝集した状態で存在することも問題はない。どのような凝集状態であれ、凝集体として帯電部材と像担持体との当接部またはその近傍の帯電領域に介在し、帯電補助または促進の機能が実現できればその形態は問わない。
【０２５８】
本発明において、導電性微粉体の抵抗測定は、いわゆる錠剤法により測定し正規化して求めることができる。より具体的には、底面積２．２６ｃｍ²の円筒内に凡そ０．５ｇの粉体試料を入れ上下電極に１５ｋｇの加圧を行うと同時に１００Ｖの電圧を印加し抵抗値を計測、その後正規化して比抵抗を算出する。
【０２５９】
本発明における導電性微粉体としては、例えばカーボンブラック、グラファイトなどの炭素微粉体；銅、金、銀、アルミニウム、ニッケルなどの金属微粉体；酸化亜鉛、酸化チタン、酸化すず、酸化アルミニウム、酸化インジウム、酸化珪素、酸化マグネシウム、酸化バリウム、酸化モリブデン、酸化タングステンなどの金属酸化物；硫化モリブデン、硫化カドミウム、チタン酸カリなどの金属化合物、またはこれらの複合酸化物などが必要に応じて粒度及び粒度分布を調整することで使用できる。これらの中でも導電性微粉体は非磁性であることが好ましく、酸化亜鉛、酸化すず、酸化チタン等の無機酸化物微粉体が特に好ましい。
【０２６０】
また、導電性無機酸化物の抵抗値を制御する等の目的で、アンチモン、アルミニウムなどの元素をドープした金属酸化物、導電性材料を表面に有する微粉体なども使用できる。例えば酸化スズ・アンチモンで表面処理された酸化チタン微粉体、アンチモンでドープされた酸化第二スズ微粉体、または酸化第二スズ微粉体などである。
【０２６１】
市販の酸化スズ・アンチモン処理された導電性酸化チタン微粉体としては、例えばＥＣ−３００（チタン工業株式会社）、ＥＴ−３００、ＨＪ−１、ＨＩ−２（以上、石原産業株式会社）、Ｗ−Ｐ（三菱マテリアル株式会社）などが挙げられる。
【０２６２】
市販のアンチモンドープの導電性酸化スズとしては、例えばＴ−１（三菱マテリアル株式会社）やＳＮ−１００Ｐ（石原産業株式会社）などが、また市販の酸化第二スズとしては、ＳＨ−Ｓ（日本化学産業株式会社）などが挙げられる。
【０２６３】
また、本発明の磁性トナーは、クリーニング性向上等の目的で、さらに一次粒径３０ｎｍを超える（好ましくは比表面積が５０ｍ²／ｇ未満）、より好ましくは一次粒径５０ｎｍ以上（好ましくは比表面積が３０ｍ²／ｇ未満）の無機又は有機の球状に近い微粒子をさらに添加することも好ましい形態のひとつである。例えば球状シリカ粒子、球状ポリメチルシルセスキオキサン粒子、球状樹脂粒子等が好ましく用いられる。
【０２６４】
本発明に用いられる磁性トナーには、実質的な悪影響を与えない範囲内で更に他の添加剤、例えばテフロン粉末、ステアリン酸亜鉛粉末、ポリフッ化ビニリデン粉末等の滑剤粉末、または酸化セリウム粉末、炭化硅素粉末、チタン酸ストロンチウム粉末などの研磨剤、または例えば酸化チタン粉末、酸化アルミニウム粉末などの流動性付与剤、ケーキング防止剤、また、逆極性の有機微粒子、及び無機微粒子を現像性向上剤として少量用いる事もできる。これらの添加剤も表面を疎水化処理して用いることも可能である。
【０２６５】
上記微粉末を磁性トナーに外添する方法としては磁性粒子（トナー粒子または磁性トナー）と微粉末を混合、攪拌する事により行う。具体的にはメカノフュージョン、Ｉ式ミル、ハイブリタイザー、ターボミル、ヘンシェルミキサー等が挙げられ、粗粒の発生を防ぐという観点からヘンシェルミキサーを用いる事が特に好ましい。
【０２６６】
また、微粒子の遊離率を調整する為、外添時の温度、外添強度、外添時間等を調整する事が好ましい。一例としてヘンシェルミキサーを用いた場合、外添時の槽内温度は５０℃以下であることが好ましい。これ以上の温度であると、熱により外添剤の埋め込みが急激に起こると共に粗粒が発生し、好ましくない。また、ヘンシェルミキサーの羽根の周速としては外添剤の遊離率を調整するという観点から１０から８０ｍ／ｓｅｃであることが好ましい。なお、上記の遊離率の調整は、前述した無機微粉体及び導電性微粉体の遊離率の調整にも適用できる。
【０２６７】
本発明の磁性トナーは、耐久性に優れ、カブリが少なく、転写性が高いために、接触帯電工程を用いる画像形成方法に好適に用いられ、さらにはクリーナレス画像形成方法にも用いる事が出来、これらの使用形態もまた本発明の一部である。
【０２６８】
接触帯電工程から構成される画像形成方法においては、転写されずに帯電工程に移行する磁性トナー、即ち転写残トナーとカブリトナーの低減がキー技術であるが、本発明の磁性トナーの如き、前述したような性能を備えた本発明の磁性トナーを用いることにより、環境安定性に優れ、長期に渡り優れた画像が得ることが可能となる。
【０２６９】
また、クリーナレスの画像形成方法においては、転写残トナーが帯電工程をすり抜けて現像工程で現像器内に回収されるが、このような転写性の悪いトナーは帯電性の劣るものが多いため、耐久と共に現像器内に蓄積されて画像特性が悪化しやすい。また、転写性が悪いトナーは、転写残トナーが多くなる事から、帯電工程において均一な帯電を阻害し、良好な画像を得る事が困難となる。特に、耐久性に劣るトナーではこの傾向が強く、好ましくない。
【０２７０】
しかしながら本発明の磁性トナーは良好な画像特性、耐久性を有するため、クリーナレスの画像形成方法に用いても長期に渡って高画質を安定に維持できることから、この磁性トナーを用いることにより本発明の画像形成方法が達成される。
以下に本発明の画像形成方法について説明する。
【０２７１】
本発明の画像形成方法は、帯電工程と、静電潜像形成工程と、現像工程と、転写工程とを含むものであり、現像工程における磁性トナーに本発明の磁性トナーを用い、さらに帯電工程は、像担持体と当接部を形成して接触する帯電部材に電圧を印加することにより像担持体を帯電させる工程であることを特徴とする。
次に、本発明の画像形成方法の実施形態を図に沿って詳細に説明するが、本発明はこれらに限定されない。
【０２７２】
本発明の画像形成方法を実現する画像形成装置の一例を図１に示す。
図１において、像担持体としての感光体１００の周囲に、帯電部材である一次帯電ローラ１１７、現像器１４０、転写ローラ１１４、クリーナ１１６、レジスタローラ１２４等が設けられている。
【０２７３】
感光体１００は、一次帯電ローラ１１７によって−７００Ｖに帯電される（印加電圧は交流電圧−２．０ｋＶｐｐ（Ｖｐｐ：ピーク間電位）、直流電圧−７００Ｖｄｃ）。
【０２７４】
そして、レーザビームスキャナ１２１によりレーザ光１２３が感光体１００に照射され、感光体１００は露光され、感光体１００に静電潜像が形成される。
【０２７５】
感光体１００上の静電潜像は現像器１４０によって一成分磁性トナーで現像され、記録媒体を介して感光体に当接された転写ローラ１１４により記録媒体上へ転写される。
【０２７６】
トナー像をのせた記録媒体Ｐは、搬送ベルト１２５等により定着装置１２６へ運ばれ記録媒体Ｐ上に定着される。また、一部感光体上に残されたトナーはクリーナ１１６によりクリーニングされる。
【０２７７】
現像器１４０は、図２に示すように感光体１００に近接して、アルミニウムやステンレス等の非磁性金属で作られた円筒状の磁性トナー担持体１０２（以下、「現像スリーブ」ともいう）が配設され、感光体１００と現像スリーブ１０２との間隙は、図示されないスリーブ／感光体間隙保持部材等により約２３０μｍに維持されている。この間隙は、必要により替えることは可能である。現像スリーブ１０２内にはマグネットローラ１０４が、現像スリーブ１０２と同心的に固定、配設されている。但し、現像スリーブ１０２は回転可能である。
【０２７８】
マグネットローラ１０４には図示の如く複数の磁極が具備されており、Ｓ１は現像、Ｎ１は磁性トナーのコート量規制、Ｓ２は磁性トナーの取り込み／搬送、Ｎ２は磁性トナーの吹き出し防止に影響している。現像スリーブ１０２に付着して搬送される磁性トナー量を規制する部材として、弾性ブレード１０３が配設され、弾性ブレード１０３の現像スリーブ１０２に対する当接圧により現像領域に搬送される磁性トナー量が制御される。現像領域では、感光体１００と現像スリーブ１０２との間に直流電圧及び交流電圧の現像バイアスが印加され、現像スリーブ１０２上のトナーは静電潜像に応じて感光体１００上に飛翔し可視像となる。
【０２７９】
本発明の画像形成方法において、現像工程は、トナー像を転写材上に転写した後に感光体に残留した磁性トナーを回収するクリーニング工程を兼ねる現像兼クリーニング工程またはクリーナレス工程を有する画像形成方法であっても好ましい画像形成が可能である。
【０２８０】
本発明の画像形成方法では、帯電工程において、帯電部材と像担持体の当接部及びその近傍の少なくともいずれかに導電性微粉体が介在していることが好ましい。本発明の画像形成方法において、上記当接部及びその近傍に導電性微粉体を介在させる手段としては、例えば本発明の画像形成方法に用いられる帯電手段に、導電性微粉体を帯電部材に供給するホッパー等の導電性微粉体供給手段を例示することができる。
【０２８１】
さらに、本発明では、上記当接部及びその近傍に導電性微粉体を介在させるには、本発明の磁性トナーに含まれる導電性微粉体を利用することができる。すなわち磁性トナー中に含まれる導電性微粉体が現像工程で像担持体に付着し、転写工程の後も像担持体上に残留することで、上記当接部及びその近傍に運ばれる。このような導電性微粉体の供給方法は、現像兼クリーニング画像形成方法またはクリーナレス画像形成方法において特に有効であり、本発明で好ましく用いられる。
【０２８２】
本発明における帯電工程では、像担持体と接触帯電部材との当接部における導電性微粉体の介在量は、少なすぎると該微粉体による潤滑効果が十分に得られず、像担持体と帯電部材との摩擦が大きくて帯電部材を像担持体に対して速度差を持って回転駆動させることが困難である。つまり、駆動トルクが過大となるし、無理に回転させると帯電部材や像担持体の表面が削れてしまう。更に導電性微粉体による接触機会増加の効果が得られないこともあり十分な帯電性能が得られない。一方、介在量が多過ぎると、導電性微粉体の帯電部材からの脱落が著しく増加し作像上に悪影響が出ることがある。
【０２８３】
また本発明における帯電工程は、帯電部材と像担持体との当接部に１×１０³個／ｍｍ²以上の導電性微粉体が介在した状態で該像担持体を帯電することが好ましい。より好ましくは１０⁴個／ｍｍ²以上が良い。１０³個／ｍｍ²より低いと上記のように十分な潤滑効果と接触機会増加の効果が得られず帯電性能の低下が生じる傾向がある。また１０⁴個／ｍｍ²より低いと転写残トナーが多い場合に帯電性能の低下が生じる可能性がある。
【０２８４】
当接部での導電性微粉体の介在量及び潜像形成工程での像担持体上の導電性微粉体の介在量は、帯電部材と像担持体の接触面部を直接測ることが望ましいが、当接部を形成する帯電部材の表面と像担持体の表面には速度差を設けている場合、帯電部材に接触する前に像担持体上に存在した粒子の多くは逆方向に移動しながら接触する帯電部材に剥ぎ取られることから、本発明では接触面部に到達する直前の帯電部材表面の粒子量をもって介在量とする。
【０２８５】
具体的には、帯電バイアスを印加しない状態で像担持体及び帯電部材（例えばローラ部材）の回転を停止し、像担持体及びローラ部材の表面をビデオマイクロスコープ（例えばＯＬＹＭＰＵＳ製ＯＶＭ１０００Ｎ）及びデジタルスチルレコーダ（例えばＤＥＬＴＩＳ製ＳＲ−３１００）で撮影する。ローラ部材については、ローラ部材を像担持体に当接するのと同じ条件でスライドガラスに当接し、スライドガラスの背面からビデオマイクロスコープにて接触面を１０００倍の対物レンズで１０箇所以上撮影する。得られたデジタル画像から個々の粒子を領域分離するため、ある閾値を持って２値化処理し、粒子の存在する領域の数を所望の画像処理ソフトを用いて計測する。また、像担持体上の存在量についても像担持体上を同様のビデオマイクロスコープにて撮影し同様の処理を行い計測する。
【０２８６】
また、本発明の画像形成方法、特にクリーナレス画像形成方法においては、帯電部材が、帯電部材と像担持体との間に導電性微粉体を介在させる当接部を設ける上で弾性を有することが好ましく、帯電部材に電圧を印加することにより像担持体を帯電するために導電性であることが好ましい。従って、帯電部材は導電性弾性ローラであるローラ部材、磁性粒子を磁気拘束させた磁気ブラシ部を有し該磁気ブラシ部を感光体に接触させた磁気ブラシ帯電部材、または導電性繊維から構成されるブラシ部材であることが好ましく良い。
【０２８７】
また、本発明の画像形成方法では、帯電部材が可撓性を有していることが、帯電部材と像担持体の当接部において導電性微粉体が像担持体に接触する機会を増加させ、高い接触性を得ることができ、直接注入帯電性を向上させる点で好ましく良い。
【０２８８】
つまり、帯電部材が導電性微粉体を介して密に像担持体に接触して、帯電部材と像担持体の当接部に存在する導電性微粉体が像担持体表面を隙間なく摺擦することで、帯電部材による像担持体の帯電は導電性微粉体の存在により放電現象を用いない安定かつ安全な直接注入帯電が支配的となり、従来のローラ帯電等では得られない高い帯電効率が得られ、帯電部材に印加した電圧とほぼ同等の電位を像担持体に与えることができる。
【０２８９】
更に、本発明の画像形成方法では、帯電工程は、当接部を形成する帯電部材の表面と像担持体の表面とが、相対速度差を有して移動しつつ像担持体を帯電する工程であることが好ましい。このような帯電工程によれば、上記当接部において導電性微粉体が像担持体に接触する機会を格段に増加させることができ、より高い接触性を得ることができ、直接注入帯電性を向上させる点で好ましく良い。
【０２９０】
また、帯電部材と像担持体との当接部に導電性微粉体を介在させることにより、導電性微粉体の潤滑効果（摩擦低減効果）により、帯電部材と像担持体との間に大幅なトルクの増大及び帯電部材及び像担持体表面の顕著な削れ等を伴うことなく速度差を設けることが可能となる。
【０２９１】
また、前記当接部に持ち運ばれる像担持体上の転写残トナーを帯電部材に一時的に回収し均すために、本発明における帯電工程は、帯電部材の表面と像担持体の表面が互いに逆方向に移動しつつ像担持体を帯電させる工程であることが好ましい。例えば、帯電部材を回転駆動し、さらに、その回転方向は、当接部において像担持体表面の移動方向とは逆方向に回転するように構成することが望ましい。即ち、逆方向回転で像担持体上の転写残トナーを一旦引き離し帯電を行うことにより、優位に直接注入帯電を行うことが可能である。
【０２９２】
帯電部材を像担持体表面の移動方向と同じ方向に移動させて速度差をもたせることも可能であるが、直接注入帯電の帯電性は像担持体の周速と帯電部材の周速の比に依存するため、逆方向と同じ周速比を得るには順方向では帯電部材の回転数が逆方向の時に比べて大きくなるので、帯電部材を逆方向に移動させる方が回転数の点で有利である。
【０２９３】
速度差を設ける構成としては、帯電部材を回転駆動させ像担持体と該帯電部材に速度差を設けることができる。ここで記述した周速比は、下式で表せる。
【数８】
周速比（％）＝（帯電部材周速／像担持体周速）×１００
【０２９４】
像担持体上の転写残トナーを帯電部材に一時的に回収するとともに導電性微粉体を担持し直接注入帯電を優位に実行する上でも、帯電部材が可撓性を有することが好ましく、回動自在であることがより好ましい。このような帯電部材としては、前述したように、導電性及び弾性を有するローラ部材や導電性のブラシ部材等を好ましくは例示することができる。
【０２９５】
本発明において、帯電部材として用いるローラ部材の硬度は、アスカーＣ硬度が５０度以下であることが好ましい。硬度が低すぎると形状が安定しないために像担持体との接触性が悪くなり、更に、帯電部材と像担持体との当接部に導電性微粉体を介在させることでローラ部材表層を削り、または傷つけ、安定した帯電性が得られない傾向にある。また、硬度が高すぎると像担持体との間に帯電当接部を確保できないだけでなく、像担持体表面へのミクロな接触性が悪くなりやすい。さらには、アスカーＣ硬度で２５〜５０度が好ましい範囲である。
【０２９６】
本発明に用いられるローラ部材は、例えば、芯金上に可撓性部材としてのゴムまたは発泡体の中抵抗層を形成することにより作製され得る。中抵抗層は樹脂（例えばウレタン）、導電性粒子（例えばカーボンブラック）、硫化剤、発泡剤等により処方され、芯金の上にローラ状に形成する。その後必要に応じて切削、表面を研磨して形状を整えローラ部材を作製することができる。
【０２９７】
また、本発明では、ローラ部材は、球形換算での平均セル径が５〜３００μｍである窪みを少なくとも表面に有しており、この窪みを空隙部としたローラ部材の表面の空隙率が１５〜９０％であることが、該ローラ部材表面に導電性微粉体を介在させる上で好ましい。
【０２９８】
ローラ部材の表面の平均セル径が５μｍより小さい場合は、導電性微粉体の供給が不足し、３００μｍを越える場合は、導電性微粉体の供給が過剰となり、いずれも像担持体の帯電電位が不均一となり好ましくない。また、空隙率が１５％より少ないと、導電性微粉体の供給が不足し、９０％を越えると導電性微粉体の供給が過剰となり、いずれも像担持体の帯電電位が不均一となることから好ましくない。
【０２９９】
ローラ部材は、弾性を持たせて被帯電体との十分な接触状態を得ると同時に、移動する被帯電体を充電するに十分低い抵抗を有する電極として機能することが重要である。一方では被帯電体にピンホールなどの欠陥部位が存在した場合に電圧のリークを防止する必要がある。像担持体として感光体を用いた場合、十分な帯電性と耐リークを得るには、本発明における帯電工程で用いられる帯電部材は、体積抵抗値が１×１０³〜１×１０⁸Ωｃｍの抵抗であることが良く、より好ましくは体積抵抗値が１×１０⁴〜１×１０⁷Ωｃｍであることが良い。
【０３００】
ローラ部材の体積抵抗値は、ローラの芯金に総圧１ｋｇの加重がかかるよう直径３０ｍｍの円筒状アルミドラムにローラを圧着した状態で、芯金とアルミドラムとの間に１００Ｖを印加し、計測することにより測定できる。
【０３０１】
ローラ部材の材質としては、弾性発泡体に限定するものでは無く、弾性体の材料として、エチレン−プロピレン−ジエンポリエチレン、ウレタン、ブタジエンアクリロニトリルゴム、シリコーンゴムや、イソプレンゴム等に抵抗調整のためにカーボンブラックや金属酸化物等の導電性物質を分散したゴム材や、またこれらを発泡させたものがあげられる。また、導電性粒子を分散せずに、または導電性粒子と併用してイオン導電性の材料を用いて抵抗調整をすることも可能である。
【０３０２】
また、ローラ部材に用いられる芯金としては、アルミニウム、ＳＵＳ等が挙げられる。
【０３０３】
ローラ部材は、像担持体としての被帯電体に対して弾性に抗して所定の押圧力で圧接させて配設し、ローラ部材と像担持体の当接部を形成させる。この当接部の幅は特に制限されるものではないが、ローラ部材と像担持体の安定して密な密着性を得るため１ｍｍ以上、より好ましくは２ｍｍ以上が良い。
【０３０４】
また、本発明における帯電工程では、導電性を有するブラシ部材を上記帯電部材として好適に用いることが出来る。帯電部材としてのブラシ部材としては、一般に用いられている繊維に導電材を分散させて抵抗調整された帯電ブラシが挙げられる。
【０３０５】
繊維としては、一般に知られている繊維が使用可能であり、例えばナイロン、アクリル、レーヨン、ポリカーボネート、ポリエステル等が挙げられる。導電材としては、一般に知られている導電材が使用可能であり、例えば、ニッケル、鉄、アルミニウム、金、銀等の導電性金属または酸化鉄、酸化亜鉛、酸化スズ、酸化アンチモン、酸化チタン等の導電性金属の酸化物、更にはカーボンブラック等の導電粉が挙げられる。なおこれら導電材は必要に応じ疎水化、抵抗調整の目的で表面処理が施されていてもよい。使用に際しては、繊維との分散性や生産性を考慮して選択して用いる。
【０３０６】
帯電部材としてブラシ部材を用いる場合には、固定型と回動可能なロール状のものがある。ロール状帯電ブラシとしては、例えば、導電性繊維をパイル地にしたテープを金属製の芯金にスパイラル状に巻き付けてロール状のブラシ部材とすることができる。導電性繊維は、繊維の太さが１〜２０デニール（繊維径１０〜５００μｍ程度）、ブラシの繊維の長さは１〜１５ｍｍ、ブラシ密度は１平方インチ当たり１万〜３０万本（１平方メートル当たり１．５×１０⁷〜４．５×１０⁸本程度）のものが好ましく用いられる。
【０３０７】
ブラシ部材は、極力ブラシ密度の高い物を使用することが好ましく、１本の繊維を数本〜数百本の微細な繊維から作ることも好ましく良い。例えば、３００デニール／５０フィラメントのように３００デニールの微細な繊維を５０本束ねて１本の繊維として植毛することも可能である。しかしながら、本発明においては、直接注入帯電の帯電ポイントを決定しているのは、主には帯電部材と像担持体との当接部及びその近傍の導電性微粉体の介在密度に依存しているため、帯電部材の選択の範囲は広められている。
【０３０８】
ブラシ部材に用いられる芯金としては、前記ローラ部材に用いられるものと同様のものが挙げられる。
【０３０９】
ブラシ部材の材質としては、例えばユニチカ（株）製の導電性レーヨン繊維ＲＥＣ−Ｂ、ＲＥＣ−Ｃ、ＲＥＣ−Ｍ１、ＲＥＣ−Ｍ１０、東レ（株）製のＳＡ−７、日本蚕毛（株）製のサンダーロン、カネボウ製のベルトロン、クラレ（株）製のクラカーボ、レーヨンにカーボンを分散したもの、三菱レーヨン（株）製のローバル等があるが、環境安定性の点でＲＥＣ−Ｂ、ＲＥＣ−Ｃ、ＲＥＣ−Ｍ１、ＲＥＣ−Ｍ１０が特に好ましく挙げられる。
【０３１０】
本発明の画像形成方法における帯電工程は、被帯電体であり像担持体でもある感光体に、図１における上記一次帯電ローラであるローラ型（帯電ローラ）の他に、ファーブラシ型、磁気ブラシ型、ブレード型（帯電ブレード）等の導電性の帯電部材（接触帯電部材・接触帯電器）と当接部を形成して接触させ、この接触帯電部材に所定の帯電バイアスを印加して感光体面を所定の極性・電位に帯電させる接触帯電装置を用いることができる。これらの接触帯電部材を用いる帯電工程には、高電圧が不要になったり、オゾンの発生が低減するといった効果がある。
【０３１１】
上記図１のように帯電ローラを用いたときの好ましいプロセス条件として、ローラ部材の当接圧が４．９〜４９０Ｎ／ｍ（５〜５００ｇ／ｃｍ）で、直流電圧または直流電圧に交流電圧を重畳したものが用いられる。直流電圧に交流電圧を重畳したものを用いる場合は、交流電圧＝０．５〜５ｋＶｐｐ、交流周波数＝５０〜５ｋＨｚ、直流電圧＝±０．２〜±５ｋＶが好ましい。
【０３１２】
このように交流電圧を用いる場合では、本発明における帯電工程は、前記帯電部材に、２×Ｖｔｈ（Ｖｔｈ：直流電圧印加における放電開始電圧）（Ｖ）未満のピーク間電圧を有する交流電圧を直流電圧に重畳した電圧を印加する工程であることが好ましい。
【０３１３】
直流電圧に印加される交流電圧のピーク電圧が、２×Ｖｔｈ未満でないと、像担持体上の電位が不安定となることがあり好ましくない。直流電圧に交流電圧を重畳されたバイアスを印加する際の交流電圧として、より好ましくはＶｔｈ未満のピーク電圧を有するものである。それにより、実質的な放電現象を伴うことなく、像担持体を帯電させることができる。
【０３１４】
帯電工程において用いられる交流電圧の波形としては、正弦波、矩形波、三角波等適宜使用可能である。また、直流電源を周期的にオン／オフすることによって形成されたパルス波であっても良い。このように交流電圧の波形としては周期的にその電圧値が変化するようなバイアスが使用できる。
【０３１５】
次に本発明の画像形成方法において、上記帯電工程で帯電される被帯電体である像担持体について説明する。
【０３１６】
本発明の画像形成方法において、像担持体は光導電性物質を利用した感光体であることが好ましく、表面層を有するものであることが好ましい。
【０３１７】
本発明に用いられる像担持体のさらに好ましい態様のひとつを以下に説明する。
本発明において、像担持体の最表面層の体積抵抗値は１×１０⁹〜１×１０¹⁴Ωｃｍであることが、より良好な帯電性を像担持体に与える上で好ましい。電荷の直接注入による帯電方式においては、被帯電体である像担持体側の抵抗を下げることでより効率良く電荷の授受が行えるようになる。このためには、像担持体の最表面層の体積抵抗値としては１×１０¹⁴Ωｃｍ以下であることが好ましく良い。一方、像担持体として静電潜像を一定時間保持する必要するためには、最表面層の体積抵抗値としては１×１０⁹Ωｃｍ以上であることが好ましく良い。
【０３１８】
更に、像担持体の最表面層の体積抵抗値が１×１０⁹〜１×１０¹⁴Ωｃｍであることにより、プロセススピードの速い装置においても、十分な帯電性を与えることができより好ましい。
【０３１９】
なお、本発明における像担持体の最表面層の体積抵抗値の測定方法は、表面に金を蒸着させたポリエチレンテレフタレート（ＰＥＴ）フィルム上に像担持体の最表面層と同様の組成からなる層を作製し、これを体積抵抗測定装置（例えばヒューレットパッカード社製４１４０Ｂ ｐＡ ＭＡＴＥＲ）にて、２３℃、６５％の環境で１００Ｖの電圧を印加して測定する方法が挙げられる。
【０３２０】
また、本発明では、像担持体の最表面層における体積抵抗値を調整するために、上記最表面層は、少なくとも金属酸化物からなる導電粒子が分散された樹脂層であることが好ましい。
【０３２１】
上記導電粒子の例としては、金属、金属酸化物等が挙げられ、好ましくは、酸化亜鉛、酸化チタン、酸化スズ、酸化アンチモン、酸化インジウム、酸化ビスマス、酸化スズ被膜酸化チタン、スズ被膜酸化インジウム、アンチモン被膜酸化スズ、酸化ジルコニウム等の超微粒子がある。これらは単独で用いても二種以上を混合して用いても良い。
【０３２２】
一般的に最表面層に導電粒子を分散させる場合、分散粒子による入射光の散乱を防ぐために入射光の波長よりも粒子の粒径の方が小さいことが必要であり、上記最表面層に分散される導電粒子の粒径としては０．５μｍ以下であることが好ましい。また、最表面層中での導電粒子の含有量は、最表面層総重量に対して２〜９０質量％が好ましく、５〜８０質量％がより好ましい。また最表面層の膜厚は、０．１〜１０μｍが好ましく、１〜７μｍがより好ましい。
【０３２３】
本発明の画像形成方法では、種々の像担持体を好適に用いることが出来、例えば、セレン、アモルファスシリコンなどの無機感光体の上に樹脂を主体とした保護膜を設ける場合、又は機能分離型有機像担持体の電荷輸送層として、電荷輸送物質と樹脂からなる表面層をもつ場合、さらにその上に保護層を設けて最表面層とする場合等がある。
【０３２４】
像担持体の最表面層には離型性を付与することが、磁性トナーの転写性及び像担持体の耐久性をより一層向上させる上で好ましく、このような観点から本発明で用いられる像担持体の表面の水に対する接触角が８５度以上であることが好ましい。より好ましくは上記接触角が９０度以上である。
【０３２５】
なお、後述する手段によって感光体表面の水に対する接触角を８５度以上とすることができ、トナーの転写性及び感光体の耐久性を一層向上させることができる。好ましくは水に対する接触角は９０度以上がよい。
【０３２６】
上記接触角の測定は、滴下式の接触角計（例えば、協和界面科学（株）の接触角計ＣＡ−Ｘ型）を用いて水の自由表面が像担持体に接する場所で、液面と像担持体表面のなす角（液の内部にある角）で定義する。
【０３２７】
なお、上記測定は室温（約２５℃）で行われるものとする。後述の実施例においても同様に測定した。
【０３２８】
像担持体表面に上記のような離型性を付与する手段としては、
（１）膜を構成する樹脂自体に表面エネルギーの低いものを用いる、
（２）撥水、親油性を付与するような添加剤を加える、
（３）高い離型性を有する材料を粉体状にして分散する、
などが挙げられる。
【０３２９】
（１）の例としては、樹脂の構造中にフッ素含有基、シリコーン含有基等を導入することにより達成する。（２）としては、界面活性剤等を添加剤とすればよい。（３）としては、フッ素原子を含む化合物、すなわちポリ４フッ化エチレン、ポリフッ化ビニリデン、フッ化カーボン等が挙げられる。
【０３３０】
これらの手段の中でも、（３）の手段がより好ましい。すなわち、像担持体の最表面層は、フッ素系樹脂粒子、シリコーン系樹脂粒子、及びポリオレフィン系樹脂粒子から選ばれる少なくとも一種以上の滑剤微粒子が分散された樹脂層であることが、本発明の画像形成方法において一つの好ましい形態である。上記の滑剤微粒子の中でも、含フッ素樹脂などのフッ素系樹脂粒子の離型性粉体を最表面層への分散させる方法が好適であり、特にポリ４フッ化エチレンを用いることが好適である。
【０３３１】
上記滑剤微粒子を像担持体の表面に含有させるためには、バインダー樹脂中に該微粒子を分散させた層を像担持体最表面に設けるか、または、元々樹脂を主体として構成されている有機感光体などの像担持体であれば、新たに表面層を設けなくても、最上層に該粉体を分散させれば良い。添加量は、表面層総重量に対して、１〜６０質量％、さらには、２〜５０質量％が好ましい。１質量％より少ないと磁性トナーの転写性及び像担持体の耐久性改善の効果が不十分であり、６０質量％を越えると膜の強度が低下したり、像担持体への入射光量が著しく低下したりするため、好ましくない。
【０３３２】
本発明の画像形成方法は、帯電手段が帯電部材を像担持体に当接させる直接帯電法であり、オゾンの発生が少ない点で好ましいが、 帯電手段が像担持体に接することのないコロナ放電等による方法にくらべて像担持体表面に対する負荷が大きいので、上記の構成は像担持体寿命という点で改善効果が顕著であり、好ましい適用形態のひとつである。
【０３３３】
本発明で用いられる像担持体には、前述したように、従来より知られている種々の像担持体を利用することができ、導電性基体と、導電性基体上に形成される感光層とを有する像担持体が用いられる。該感光層には、電荷発生層、電荷輸送層、及び像担持体の表面を保護するための表面層（保護層）など、種々の機能を有する複数の層を積層してなる感光層を用いることが出来る。
【０３３４】
導電性基体としては、アルミニウム、ステンレス等の金属、アルミニウム合金、酸化インジウム−酸化錫合金等による被膜層を有するプラスチック、導電性粒子を含侵させた紙、プラスチック、導電性ポリマーを有するプラスチック等の円筒状シリンダー及びフィルムが用いられる。
【０３３５】
これら導電性基体上には、感光層の接着性向上・塗工性改良・基体の保護・基体上に欠陥の被覆・基体からの電荷注入性改良・感光層の電気的破壊に対する保護等を目的として下引き層を設けても良い。下引き層は、ポリビニルアルコール、ポリ−Ｎ−ビニルイミダゾール、ポリエチレンオキシド、エチルセルロース、メチルセルロース、ニトロセルロース、エチレン−アクリル酸コポリマー、ポリビニルブチラール、フェノール樹脂、カゼイン、ポリアミド、共重合ナイロン、ニカワ、ゼラチン、ポリウレタン、酸化アルミニウム等の材料によって形成される。その膜圧は通常０．１〜１０μｍ、好ましくは０．１〜３μｍ程度である。
【０３３６】
電荷発生層は、アゾ系顔料、フタロシアニン系顔料、インジゴ系顔料、ペリレン系顔料、多環キノン系顔料、スクワリリウム色素、ピリリウム塩類、チオピリリウム塩類、トリフェニルメタン系色素、セレン、非晶質シリコン等の無機物質などの電荷発生物質を適当な結着剤に分散し塗工するまたは蒸着等により形成される。結着剤としては、広範囲な結着性樹脂から選択でき、例えば、ポリカーボネート樹脂、ポリエステル樹脂、ポリビニルブチラール樹脂、ポリスチレン樹脂、アクリル樹脂、メタクリル樹脂、フェノール樹脂、シリコン樹脂、エポキシ樹脂、酢酸ビニル樹脂等が挙げられる。電荷発生層中に含有される結着剤の量は８０質量％以下、好ましくは０〜４０質量％である。また、電荷発生層の膜圧は５μｍ以下、特には０．０５〜２μｍが好ましい。
【０３３７】
電荷輸送層は、電界の存在下で電荷発生層から電荷キャリアを受け取り、これを輸送する機能を有している。電荷輸送層は電荷輸送物質を必要に応じて結着樹脂と共に溶剤中に溶解し、塗工することによって形成され、その膜圧は一般的には５〜４０μｍである。電荷輸送物質としては、主鎖または側鎖にビフェニレン、アントラセン、ピレン、フェナントレンなどの構造を有する多環芳香族化合物、インドール、カルバゾール、オキサジアゾール、ピラゾリンなどの含窒素環式化合物、ヒドラゾン化合物、スチリル化合物、セレン、セレン−テルル、非晶質シリコン、硫化カドニウム等が挙げられる。
【０３３８】
また、これら電荷輸送物質を分散させる結着樹脂としては、ポリカーボネート樹脂、ポリエステル樹脂、ポリメタクリル酸エステル、ポリスチレン樹脂、アクリル樹脂、ポリアミド樹脂等の樹脂、ポリ−Ｎ−ビニルカルバゾール、ポリビニルアントラセン等の有機光導電性ポリマー等が挙げられる。
【０３３９】
また表面層として、保護層を設けてもよい。保護層の樹脂としては、ポリエステル、ポリカーボネート、アクリル樹脂、エポキシ樹脂、フェノール樹脂、またはこれらの樹脂の硬化剤等が単独または二種以上組み合わされて用いられる。
【０３４０】
表面層等の塗工は、樹脂分散液をスプレーコーティング、ビームコーティングまたは浸透（ディッピング）コーティングすることによって行うことができる。
【０３４１】
本発明においては、像担持体の帯電面に静電潜像を形成する静電潜像形成工程が、像露光手段により行われることが好ましい。静電潜像形成のための画像露光手段としては、デジタル的な潜像を形成するレーザ走査露光手段に限定されるものではなく、通常のアナログ的な画像露光やＬＥＤなどの他の発光素子でも構わないし、蛍光燈等の発光素子と液晶シャッター等の組み合わせによるものなど、画像情報に対応した静電潜像を形成できるものであるなら構わない。
【０３４２】
また本発明の画像形成方法においては、カブリの無い高画質を得るために磁性トナー担持体上に磁性トナー担持体−感光体の最近接距離（Ｓ−Ｄ間）よりも小さい層厚で、磁性トナーを塗布し、交流電圧を印加して現像を行う現像工程で現像される。すなわち、磁性トナー担持体上の磁性トナーを規制する層圧規制部材によって磁性トナー担持体上のトナー層厚よりも感光体と磁性トナー担持体の最近接間隙が広くなるように設定して用いるが、磁性トナー担持体上の磁性トナーを規制する層圧規制部材が磁性トナーを介して磁性トナー担持体に当接されている弾性部材によって規制される事が、磁性トナーを均一帯電させる観点から特に好ましい。
【０３４３】
上記のことから、本発明の画像形成方法における現像工程では、磁性トナー担持体上に５〜５０ｇ／ｍ²のトナー層を形成することが好ましく良い。磁性トナー担持体上のトナー量が５ｇ／ｍ²よりも小さいと、十分な画像濃度が得られにくく、トナーの帯電が過剰になることによるトナー層のムラを生じることがある。磁性トナー担持体上のトナー量が５０ｇ／ｍ²よりも多くなると、トナー飛散を生じ易くなる。
【０３４４】
また、磁性トナー担持体は像担持体に対して１００〜１０００μｍの間隔を有して対向して設置されることが好ましく良い。磁性トナー担持体の像担持体に対する間隔が１００μｍよりも小さいと、間隔の振れに対する磁性トナーの現像特性の変化が大きくなるため、安定した画像性を満足する画像形成装置を量産することが困難となる。磁性トナー担持体の像担持体に対する間隔が１０００μｍよりも大きいと、像担持体上の潜像に対する磁性トナーの追従性が低下するために、解像性の低下、画像濃度の低下等の画質低下を招く傾向がある。好ましくは１２０〜５００μｍが良い。
【０３４５】
本発明の画像形成方法において、現像工程は磁性トナー担持体に対して交番電界を現像バイアスとして印加して、像担持体の静電潜像にトナーを転移させてトナー像を形成する工程であることが好ましく、印加現像バイアスは直流電圧に交番電界を重畳した電圧でもよい。
【０３４６】
交番電界の波形としては、正弦波、矩形波、三角波等適宜使用可能である。また、直流電源を周期的にオン／オフすることによって形成されたパルス波であっても良い。このように交番電界の波形としては周期的にその電圧値が変化するようなバイアスが使用できる。
【０３４７】
本発明における現像工程では、トナーを担持をする磁性トナー担持体と像担持体との間に、少なくともピークトゥーピークの電界強度で３×１０⁶〜１０×１０⁶Ｖ／ｍ、周波数５００〜５０００Ｈｚの交番電界を現像バイアスとして印加することが好ましく良い。
【０３４８】
現像バイアスによる電界強度が３×１０⁶Ｖ／ｍよりも小さいと、現像兼クリーニング方式における現像工程での転写残トナーの回収性が低下し、回収不良によるカブリを生じやすくなる。また、現像バイアスによる電界強度が１０×１０⁶Ｖ／ｍよりも大きいと、現像力が大きすぎることによる、細線の潰れによる解像性の低下、カブリの増大による画質低下等を生じやすく、現像バイアスの像担持体へのリークによる画像欠陥を生じやすくなる。
【０３４９】
また、上記周波数が５００Ｈｚよりも小さいと、潜像に対する磁性トナーの脱着頻度が少なくなり、現像工程での転写残トナーの回収性が低下し易く、画像品質も低下しやすい。また、上記周波数が５０００Ｈｚよりも大きいと、電界の変化に追従できる磁性トナーが少なくなるため、転写残トナーの回収性が低下し、現像性が低下しやすい。
【０３５０】
本発明に使用される磁性トナー担持体は、アルミニウム、ステンレススチール等の金属又は合金で形成された導電性円筒（現像ローラ）が好ましく使用される。充分な機械的強度及び導電性を有する樹脂組成物で導電性円筒が形成されていても良く、導電性のゴムローラを用いても良い。また、上記のような円筒状に限られず、回転駆動する無端ベルトの形態をしても良い。
【０３５１】
また、本発明に使用される磁性トナー担持体の表面粗さはＪＩＳ中心線平均粗さ（Ｒａ）で０．２〜３．５μｍの範囲にあることが好ましい。Ｒａが０．２μｍ未満では磁性トナー担持体上の帯電量が高くなり、現像性が不充分となる傾向がある。Ｒａが３．５μｍを超えると、磁性トナー担持体上のトナーコート層にむらが生じ、画像上で濃度むらとなる傾向がある。さらに好ましくは、０．５〜３．０μｍの範囲にあることが好ましい。
【０３５２】
本発明において、磁性トナー担持体の表面粗度Ｒａは、ＪＩＳ表面粗さ「ＪＩＳ Ｂ ０６０１」に基づき測定され、表面粗さ測定器（例えばサーフコーダＳＥ−３０Ｈ、株式会社小坂研究所社製）を用いて測定される中心線平均粗さに相当する。具体的には、粗さ曲線からその中心線の方向に測定長さａとして２．５ｍｍの部分を抜き取り、この抜き取り部分の中心線をＸ軸、縦倍率の方向をＹ軸、粗さ曲線をｙ＝ｆ（ｘ）で表したとき、下式によって求められる値をミクロメートル（μｍ）で表したものを言う。
【数９】

【０３５３】
本発明における磁性トナー担持体の表面粗度（Ｒａ）を上記範囲にするには、例えば、磁性トナー担持体の表層の研磨状態を変える、または球状炭素粒子、カーボン微粒子、グラファイト等を添加するなどの手法により可能となる。
【０３５４】
さらに、本発明の磁性トナーは高い帯電能力を有するために、現像に際しては磁性トナーの総帯電量をコントロールすることが望ましく、本発明に係わる磁性トナー担持体の表面は導電性微粒子及び／又は滑剤を分散した樹脂層で被覆されていることが好ましい。
【０３５５】
磁性トナー担持体の被覆層に含まれる導電性微粒子は、１１．７Ｍｐａ（１２０ｋｇ／ｃｍ²）で加圧した後の抵抗値が０．５Ωｃｍ以下であるものが好ましい。導電性微粒子としては、カーボン微粒子、カーボン微粒子と結晶性グラファイトとの混合物、または結晶性グラファイトが好ましい。導電性微粒子は、粒径０．００５〜１０μｍを有するものが好ましい。
【０３５６】
上記の樹脂層に用いる樹脂としては、例えば、スチレン系樹脂、ビニル系樹脂、ポリエーテルスルホン樹脂、ポリカーボネート樹脂、ポリフェニレンオキサイド樹脂、ポリアミド樹脂、フッ素樹脂、繊維素系樹脂、アクリル系樹脂の如き熱可塑性樹脂；エポキシ樹脂、ポリエステル樹脂、アルキッド樹脂、フェノール樹脂、メラミン樹脂、ポリウレタン樹脂、尿素樹脂、シリコーン樹脂、ポリイミド樹脂の如き熱硬化性樹脂または光硬化性樹脂を使用することができる。
【０３５７】
中でもシリコーン樹脂、フッ素樹脂等のような離型性のあるもの、またはポリエーテルスルホン、ポリカーボネート、ポリフェニレンオキサイド、ポリアミド、フェノール樹脂、ポリエステル、ポリウレタン、スチレン系樹脂のような機械的性質に優れたものがより好ましい。特に、フェノール樹脂が好ましい。
【０３５８】
導電性微粒子は、樹脂成分１０質量部当たり３〜２０質量部使用するのが、好適な導電性を付与する上で好ましい。
【０３５９】
カーボン微粒子とグラファイト粒子を組み合わせて使用する場合は、グラファイト１０質量部当たり、カーボン微粒子１〜５０質量部を使用するのが好ましい。導電性微粒子が分散されてる磁性トナー担持体の樹脂層の体積抵抗率は１０^-6〜１０⁶Ωｃｍが好ましい
【０３６０】
また本発明においては、磁性トナーを担持する磁性トナー担持体表面は、像担持体表面の移動方向と同方向に移動していてもよいし、逆方向に移動していてもよい。その移動方向が同方向である場合像担持体の移動速度に対して、比で１００％以上であることが望ましい。１００％未満であると、画像品質が悪くなりやすい。移動速度比が高まれば高まるほど、現像部位に供給されるトナーの量は多く、潜像に対しトナーの脱着頻度が多くなり、不要な部分は掻き落とされ必要な部分には付与されるという繰り返しにより、潜像に忠実な画像が得られる。具体的には、磁性トナー担持体表面の移動速度が像担持体表面の移動速度に対し、１．０５〜３．０倍の速度であることが好ましい。
【０３６１】
次に、本発明の画像形成方法において好ましく適用される接触転写工程について具体的に説明する。本発明において、像担持体からトナー像の転写を受ける記録媒体は転写ドラム等の中間転写体であってもよい。記録媒体を中間転写体とする場合、中間転写体から紙などの転写材に再度転写することでトナー像が得られる。
【０３６２】
接触転写工程とは、像担持体が記録媒体を介して転写部材と当接しながらトナー像を記録媒体に静電転写するものであるが、転写部材の当接圧力としては線圧２．９Ｎ／ｍ（３ｇ／ｃｍ）以上であることが好ましく、より好ましくは１９．６Ｎ／ｍ（２０ｇ／ｃｍ）以上である。当接圧力としての線圧が２．９Ｎ／ｍ（３ｇ／ｃｍ）未満であると、記録媒体の搬送ずれや転写不良の発生が起こりやすくなるため好ましくない。
【０３６３】
また、接触転写工程における転写部材としては、転写ローラまたは転写ベルト等が使用される。図３に転写ローラの構成の一例を示す。転写ローラ３４は少なくとも芯金３４ａと導電性弾性層３４ｂからなり、導電性弾性層３４ｂはカーボン等の導電材を分散させたウレタンやエピクロルヒドリンゴム等の、体積抵抗１０⁶〜１０¹⁰Ωｃｍ程度の弾性体で作られており、転写バイアス電源３５により転写バイアスが印加されている。
【０３６４】
本発明における接触転写方法は、像担持体の表面が有機化合物である画像形成装置において特に有効である。即ち、有機化合物が像担持体の表面層を形成している場合には、無機材料を用いた他の像担持体よりもトナー粒子に含まれる結着樹脂との接着性が強く、転写性がより低下する傾向にあるためである。
【０３６５】
また、本発明における接触転写方法を適用する場合、有機化合物として使用される像担持体の表面物質としては、たとえばシリコーン樹脂、塩化ビニリデン、エチレン−塩化ビニル、スチレン−アクリロニトリル、スチレン−メチルメタクリレート、スチレン、ポリエチレンテレフタレートおよびポリカーボネート等が挙げられるが、これらに限定されることはなく他のモノマーまたは前述の結着樹脂間での共重合体およびブレンド体等も使用することができる。
【０３６６】
また、接触転写方法を適用した本発明の画像形成方法は、直径が５０ｍｍ以下の小径の像担持体を有する画像形成装置に対し特に有効に用いられる。即ち、小径感光体の場合には、同一の線圧に対する曲率が大きく、当接部における圧力の集中が起こりやすいためである。ベルト状像担持体でも同一の現象があると考えられるが、本発明は、転写部での曲率半径が２５ｍｍ以下の画像形成装置に対しても有効である。
【０３６７】
また、本発明の画像形成方法では、上記の工程の他にも、記録媒体上のトナー像を定着させる定着工程や、転写後の像担持体における潜像記録を消去する前露光工程など、種々の工程を必要に応じて用いることが出来る。
【０３６８】
また、本発明の画像形成方法を実現する画像形成装置については、その構成について前述した工程等を実現する構成であれば特に限定されることはなく、従来より知られている種々の構成を利用することができる。例えば、本発明では磁性トナーが用いられることから、像担持体、現像工程を実現する現像手段等を一体的に構成し、かつ画像形成装置本体に着脱自在に構成したプロセスカートリッジを用いることも、本発明を好適に実施するための好ましい構成の一つである。
【０３６９】
【実施例】
以下、本発明を製造例及び実施例により具体的に説明するが、これは本発明をなんら限定するものではない。尚、以下の配合における部数は全て質量部である。
【０３７０】
（表面処理磁性粉体の製造例１）
硫酸第一鉄水溶液中に、鉄イオンに対して１．０〜１．１当量の苛性ソーダ溶液を混合し、水酸化第一鉄を含む水溶液を調製した。
水溶液のｐＨを9前後に維持しながら、空気を吹き込み、８０〜９０℃で酸化反応を行い、種晶を生成させるスラリー液を調製した。
【０３７１】
次いで、このスラリー液に当初のアルカリ量（苛性ソーダのナトリウム成分）に対し０．９〜１．２当量となるよう硫酸第一鉄水溶液を加えた後、スラリー液をｐＨ８前後に維持して、空気を吹き込みながら酸化反応をすすめ、酸化反応後に生成した磁性酸化鉄粒子を洗浄、濾過して一旦取り出した。この時、含水サンプルを少量採取し、含水量を計っておいた。次に、この含水サンプルを乾燥せずに別の水系媒体中に再分散させた後、再分散液のｐＨを約６に調整し、充分攪拌しながらシランカップリング剤（ｎ−Ｃ₄Ｈ₁₃Ｓｉ（ＯＣＨ₃）₃）を磁性酸化鉄１００質量部に対し３．０質量部（磁性酸化鉄の量は含水サンプルから含水量を引いた値として計算した）添加し、カップリング処理を行った。生成した疎水性酸化鉄粒子を常法により洗浄、濾過、乾燥し、次いで若干凝集している粒子を解砕処理して、表面処理磁性粉体１を得た。物性を表１に示す。
【０３７２】
（表面処理磁性粉体の製造例２〜６）
表面処理磁性粉体の製造例１においてシランカップリング剤の処理量を調整した以外は同様にして表面処理磁性粉体２〜６を得た。物性を表１に示す。
【０３７３】
（表面処理磁性粉体の製造例７及び８）
表面処理磁性粉体の製造例１において、シランカップリング剤の処理量、及び、添加する苛性ソーダ溶液の量及び反応条件を変更した以外は、表面処理磁性粉体の製造例１と同様とし、表面処理磁性粉体７および８を得た。物性を表１に示す。
（表面処理磁性粉体の製造例９）
表面処理磁性粉体の製造例１において、原材料として硫酸第一鉄以外に、硫酸亜鉛も使用した以外は表面処理磁性粉体の製造例１と同様とし、表面処理磁性粉体９を得た。物性を表１に示す。
（表面処理磁性粉体の製造例１０）
表面処理磁性粉体の製造例１において、原材料として硫酸第一鉄以外に、硫酸バリウムも使用した以外は表面処理磁性粉体の製造例１と同様とし、表面処理磁性粉体１０を得た。物性を表１に示す。
【０３７４】
【表１】

【０３７５】
（導電性微粉体１）
微粒子酸化亜鉛を風力分級し、体積平均粒径２．９μｍ、粒度分布における０．５μｍ以下が３．２体積％、５μｍ以上が０個数％の白色微粒子酸化亜鉛（抵抗１３００Ω・ｃｍ）を得た。これを導電性微粉体１とする。
【０３７６】
この導電性微粉体１は、走査型電子顕微鏡にて３０００倍及び３万倍で観察したところ、０．１〜０．３μｍの酸化亜鉛一次粒子と１〜５μｍの凝集体からなっていた。
【０３７７】
実施例の画像形成装置で画像露光に用いられるレーザービームスキャナの露光光波長７４０ｎｍにあわせて、波長７４０ｎｍの光源を用いて、この波長域における透過率をＸ−Ｒｉｔｅ社製３１０Ｔ透過型濃度計を用い測定したところ、この導電性微粉体１の透過率はおよそ３３％であった。
【０３７８】
（導電性微粉体２）
酸化スズ・アンチモンで表面処理されたホウ酸アルミニウムを風力分級によって粗粒子を除いた後に、水系に分散しての濾過を繰り返し行うことで微粒子を除き、体積平均粒径３．０μｍ、粒度分布における０．５μｍ以下が０．５体積％、５μｍ以上が１個数％の灰白色の導電性粒子を得た（抵抗５０Ω・ｃｍ）。これを導電性微粉体２とする。
【０３７９】
（磁性トナー１の製造）
イオン交換水７０９ｇに０．１Ｍ−Ｎａ₃ＰＯ₄水溶液４５１ｇを投入し６０℃に加温した後、１．０Ｍ−ＣａＣｌ₂水溶液６７．７ｇを添加してＣａ₃（ＰＯ₄）₂を含む水系媒体を得た。
【０３８０】
スチレン ９０部
２−エチルヘキシルアクリレート １０部
架橋剤：トリエチレングリコールジメタクリレート １．０部
飽和ポリエステル樹脂 ５部
負荷電性制御剤（サリチル酸系金属化合物） １部
表面処理磁性粉体１ ８５部
上記処方をアトライター（三井三池化工機（株））を用いて均一に分散混合した。この単量体組成物を６０℃に加温し、そこにエステルワックス（ＤＳＣにおける吸熱ピークの極大値８０℃）１２部を添加混合溶解し、これに重合開始剤２，２'−アゾビスイソブチロニトリル５質量部を溶解した。
【０３８１】
前記水系媒体中に上記重合性単量体系を投入し、６０℃、Ｎ₂ 雰囲気下においてＴＫ式ホモミキサー（特殊機化工業（株））にて１０，０００ｒｐｍで１５分間撹拌し、造粒した。その後パドル撹拌翼で撹拌しつつ、６０℃で１時間反応させた。その後液温を８０℃とし更に９時間撹拌を続けた。反応終了後、蒸留を行い、その後、懸濁液を冷却し、塩酸を加えて分散剤を溶解し、濾過，水洗，乾燥して重量平均粒径６．９μｍの黒色粒子１を得た。
【０３８２】
この黒色粒子１００部と、一次粒径 ９ｎｍのシリカにヘキサメチルジシラザンで処理をした後シリコーンオイルで処理し、処理後のＢＥＴ値が２００ｍ²／ｇの疎水性シリカ微粉体１．２部、導電性微粉体１を１．２部とをヘンシェルミキサー（三井三池化工機（株））を用い、攪拌羽根の周速を４０ｍ／ｓｅｃとして３分間混合し、磁性トナー１を調製した。
磁性トナー１の物性を表２に示す。
【０３８３】
（磁性トナー２の製造）
重合開始剤を４質量部に変更した以外は、磁性トナー１の製造例と同様にして磁性トナー２を得た。磁性トナー２の物性を表２に示す。
【０３８４】
（磁性トナー３の製造）
重合開始剤を４質量部、架橋剤を１．５質量部に変更した以外は、磁性トナー１の製造例と同様にして磁性トナー３を得た。磁性トナー３の物性を表２に示す。
【０３８５】
（磁性トナー４の製造）
重合開始剤を１０質量部、架橋剤を０．１質量部に変更した以外は、磁性トナー１の製造例と同様にして磁性トナー４を得た。磁性トナー４の物性を表２に示す。
【０３８６】
（磁性トナー５の製造）
重合開始剤を３質量部、架橋剤を１．５質量部に変更し、反応中に昇温しなかった以外は、磁性トナー１の製造例と同様にして磁性トナー５を得た。磁性トナー５の物性を表２に示す。
【０３８７】
（磁性トナー６の製造）
重合開始剤を９質量部、架橋剤を０．０７質量部に変更した以外は、磁性トナー１の製造例と同様にして磁性トナー６を得た。磁性トナー６の物性を表２に示す。
【０３８８】
（磁性トナー７の製造）
重合開始剤を３．５質量部、架橋剤を１．７質量部に変更し、反応中に昇温しなかった以外は、磁性トナー１の製造例と同様にして磁性トナー７を得た。磁性トナー７の物性を表２に示す。
【０３８９】
（磁性トナー８の製造）
表面処理磁性粉体２を用い、かつ導電性微粉体１を用いなかった以外は磁性トナー１の製造例と同様にして磁性トナー８を得た。磁性トナー８の物性を表２に示す。
【０３９０】
（磁性トナー９の製造）
表面処理磁性粉体３を用い、かつ導電性微粉体１を用いなかった以外は磁性トナー１の製造例と同様にして磁性トナー９を得た。磁性トナー９の物性を表２に示す。
【０３９１】
（磁性トナー１０の製造）
表面処理磁性粉体４を用い、かつ導電性微粉体１を用いなかった以外は磁性トナー１の製造例と同様にして磁性トナー１０を得た。磁性トナー１０の物性を表２に示す。
【０３９２】
（磁性トナー１１の製造）
表面処理磁性粉体５を用い、かつ導電性微粉体１を用いなかった以外は磁性トナー１の製造例と同様にして磁性トナー１１を得た。磁性トナー１１の物性を表２に示す。
【０３９３】
（磁性トナー１２の製造）
表面処理磁性粉体７を用い、かつ導電性微粉体１を用いなかった以外は磁性トナー１の製造例と同様にして磁性トナー１２を得た。磁性トナー１２の物性を表２に示す。
【０３９４】
（磁性トナー１３の製造）
表面処理磁性粉体８を用い、かつ導電性微粉体１を用いなかった以外は磁性トナー１の製造例と同様にして磁性トナー１３を得た。磁性トナー１３の物性を表２に示す。
【０３９５】
（磁性トナー１４の製造）
表面処理磁性粉体６を用い、かつ導電性微粉体１を用いなかった以外は磁性トナー１の製造例と同様にして磁性トナー１４を得た。磁性トナー１４の物性を表２に示す。
【０３９６】
（磁性トナー１５の製造）
イオン交換水７０９ｇに０．１Ｍ−Ｎａ₃ＰＯ₄水溶液４５１ｇを投入し６０℃に加温した後、１．０Ｍ−ＣａＣｌ₂水溶液６７．７ｇを添加してＣａ₃（ＰＯ₄）₂を含む水系媒体を得た。
【０３９７】
スチレン ８５部
ｎ−ブチルアクリレート １５部
架橋剤：ジビニルナフタレン ０．５部
飽和ポリエステル樹脂 ２０部
負荷電性制御剤（ホウ素金属化合物） １部
表面処理磁性粉体１ ８０部
上記処方をアトライター（三井三池化工機（株））を用いて均一に分散混合した。この単量体組成物を６０℃に加温し、そこにパラフィンワックス（ＤＳＣにおける吸熱ピークの極大値６０℃）５部を添加混合溶解し、これに重合開始剤２，２'−アゾビスイソブチロニトリル５質量部を溶解した。
【０３９８】
前記水系媒体中に上記重合性単量体系を投入し、６０℃、Ｎ₂雰囲気下においてＴＫ式ホモミキサー（特殊機化工業（株））にて１０，０００ｒｐｍで１５分間撹拌し、造粒した。その後パドル撹拌翼で撹拌しつつ、６０℃で５時間反応させた。
【０３９９】
次に、スチレン２０．０質量部、２，２'−アゾビスイソブチロニトリル０．４質量部、ラウリル硫酸ナトリウム０．０３質量部を水８０質量部に投入し、超音波ホモジナイザーを用い分散させ、水乳濁液を得た。
【０４００】
これを、前記磁性トナー粒子分散液中に滴下し、粒子に付着させた。その後、窒素雰囲気下にて攪拌を行い、８５℃で１０時間反応を行った。反応終了後、蒸留を行い、その後、懸濁液を冷却し、塩酸を加えて分散剤を溶解し、濾過、水洗、乾燥して重量平均粒径７．３μｍの黒色粒子を得た。
【０４０１】
この黒色粒子１００部と、一次粒径９ｎｍのシリカにヘキサメチルジシラザンで処理をした後シリコーンオイルで処理し、処理後のＢＥＴ値が２００ｍ²／ｇの疎水性シリカ微粉体１．２部をヘンシェルミキサー（三井三池化工機（株））を用い、攪拌羽根の周速を４０ｍ／ｓｅｃとして３分間混合し、磁性トナー１５を調製した。磁性トナー１５の物性を表２に示す。
【０４０２】
（磁性トナー１６の製造）
水系媒体の調製で、イオン交換水１２００ｇに炭酸カルシウム塩１０ｇを微分散させ、かつ導電性微粉体１を用いなかった以外は磁性トナー１の製造例と同様にして磁性トナー１６を得た。磁性トナー１６の物性を表２に示す。
【０４０３】
（磁性トナー１７の製造）
表面処理磁性粉体９を用いた以外は磁性トナー１の製造例と同様にして磁性トナー１７を得た。磁性トナー１７の物性を表２に示す。
【０４０４】
（磁性トナー１８の製造）
表面処理磁性粉体１０を用いた以外は磁性トナー１の製造例と同様にして磁性トナー１８を得た。磁性トナー１８の物性を表２に示す。
【０４０５】
【表２】

【０４０６】
なお、上記各磁性トナーの磁場７９．６ｋＡ／ｍにおける飽和磁化強さは、いずれも２４〜２６Ａｍ²／ｋｇであった。また、磁性トナー１から１６の磁場７９．６ｋＡ／ｍにおける残留磁化は、２〜４Ａｍ²／ｋｇであり、磁性トナー１７の残留磁化は、０．４Ａｍ²／ｋｇ、磁性トナー１８の残留磁化は、７Ａｍ²／ｋｇであった。
【０４０７】
［実施例１］
＜感光体１の製造＞
感光体としては直径３０ｍｍのＡｌシリンダーを基体とした。これに、図４及び下記に示すような構成の層を順次浸漬塗布により積層して、感光体１を作製した。
（１）導電性被覆層：酸化錫及び酸化チタンの粉末をフェノール樹脂に分散したものを主体とする。膜厚１５μｍ。
（２）下引き層：変性ナイロン及び共重合ナイロンを主体とする。膜厚０．６μｍ。
（３）電荷発生層：長波長域に吸収を持つアゾ顔料をブチラール樹脂に分散したものを主体とする。膜厚０．６μｍ。
（４）電荷輸送層：ホール搬送性トリフェニルアミン化合物をポリカーボネート樹脂（オストワルド粘度法による分子量２万）に８：１０の質量比で溶解したものを主体とし、さらにポリ４フッ化エチレン粉体（粒径０．２μｍ）を総固形分に対して１０質量％添加し、均一に分散した。膜厚２５μｍ。水に対する接触角は９５度であった。
なお、接触角の測定には純水を用い、装置は協和界面科学（株）の接触角計ＣＡ−Ｘ型を用いた。
【０４０８】
＜画像形成装置＞
画像形成装置として、ＬＢＰ−１７６０を改造して、上記実施の形態で示した図１と同様のものを用いた。像担持体としての感光体１００には、上記の感光体１を用いた。
【０４０９】
この感光体に、帯電部材として導電性カーボンを分散しナイロン樹脂で被覆した一次帯電ローラ（ゴムローラ帯電器）１１７を当接させ（当接圧６０ｇ／ｃｍ）、直流電圧−６８０Ｖｄｃに交流電圧２．０ｋＶｐｐを重畳したバイアスを印加して、感光体上を一様に帯電する。帯電に次いで、レーザ光で画像部分を露光することにより静電潜像を形成する。この時、暗部電位Ｖｄ＝−６８０Ｖ、明部電位ＶＬ＝−１５０Ｖとした。
【０４１０】
感光ドラムと現像スリーブとの間隙は２３０μｍとし、磁性トナー担持体として、表面をブラストした直径１６ｍｍのアルミニウム円筒上に、下記の構成の層厚約７μｍ、ＪＩＳ中心線平均粗さ（Ｒａ）１．０μｍの樹脂層を形成した現像スリーブ１０２を使用し、現像磁極８５ｍＴ（８５０ガウス）、トナー規制部材として厚み１．０ｍｍ、自由長０．５ｍｍのウレタン製ブレードを３４．３Ｎ／ｍ（３５ｇ／ｃｍ）の線圧で当接させた。
・フェノール樹脂 １００質量部
・グラファイト（粒径約７μｍ） ９０質量部
・カーボンブラック １０質量部
【０４１１】
次いで、現像バイアスとして直流電圧Ｖｄｃ＝−４５０Ｖ、重畳する交番電界として５．２２×１０⁶Ｖ／ｍ、周波数２４００Ｈｚのものを用いた。また、現像スリーブの周速は感光体周速（１９８ｍｍ／ｓｅｃ）に対して順方向に１１０％のスピード（２１８ｍｍ／ｓｅｃ）とした。
【０４１２】
また、転写ローラ１１４としては、図３のような転写ローラ（導電性カーボンを分散したエチレン−プロピレンゴム製、導電性弾性層の体積抵抗値１０⁸Ωｃｍ、表面ゴム硬度２４°、直径２０ｍｍ、当接圧５９Ｎ／ｍ（６０ｇ／ｃｍ））を図３中Ａ方向の感光体周速（９４ｍｍ／ｓｅｃ）に対して等速とし、転写バイアスは直流１．５ｋＶとした。
【０４１３】
定着方法としては、表層がフッ素系樹脂である定着ローラ、及び加圧ローラである、定着装置１２６を用いた。ローラの直径は３０ｍｍであり、定着温度は２２０℃、ニップ幅を８ｍｍに設定した。
【０４１４】
磁性トナー１を使用し、常温常湿環境下（２５℃、６０％ＲＨ）において、印字率２％の縦線のみからなる画像パターンで５０００枚の画出し試験を行った。なお、記録媒体としては８０ｇ／ｍ²の紙を使用した。また、初期の画出し後、１０５ｇ紙を用い、ハーフトーン画像を得て、定着性の評価も行った。その結果、磁性トナー１では、初期において高い転写性を示し、転写中抜け、ゴーストもなく、良好な画像が得られた。定着性についても良好であり、オフセットも発生しなかった。評価結果を表３に示す。
【０４１５】
本発明の実施例並びに比較例に記載の評価項目とその判断基準について以下に述べる。
【０４１６】
＜現像スリーブ上のトナーの摩擦帯電量の測定＞
現像スリーブ上のトナーの摩擦帯電量は、吸引式ファラデーゲージ法を使用して求める。
この吸引式ファラデーゲージ法は、その外筒を現像スリーブ表面に押しつけて現像スリーブ上の一定面積上のトナーを吸引し、内筒のフィルターに採取してフィルターの重量増加分より、吸引したトナーの重量を計算することができる。それと同時に外部から静電的にシールドされてた内筒に蓄積された電荷量を測定することによって、現像スリーブ上のトナーの摩擦帯電量を求めることができる方法である。
【０４１７】
＜画像濃度＞
画像濃度はベタ画像部を形成し、このベタ画像をマクベス反射濃度計（マクベス社製）にて測定を行った。
【０４１８】
＜画質＞
画質の判断基準は、画像の均一性、細線再現性を総合的に評価したものである。なお、画像の均一性はべた黒画像、ならびに、ハーフトーン画像の均一性で判断を行う。
Ａ：細線再現性、画像の均一性に優れ、鮮明な画像。
Ｂ：細線再現性、画像の均一性が若干劣るものの、良好な画像。
Ｃ：実用的には問題の無い画質。
Ｄ：細線再現性、画像の均一性が悪く、実用上好ましくない画像。
【０４１９】
＜感光体上のカブリ＞
感光体上のカブリの測定は、東京電色社製のREFLECTMETER MODEL TC-6DSを使用して測定した。フィルターは、グリーンフィルターを用い、感光体上のカブリは下式より算出した。
【数１０】

【０４２０】
なお、感光体上のカブリの判断基準は以下の通りである。
Ａ：非常に良好（２．０％未満）
Ｂ：良好（２．０％以上、４．０％未満）
Ｃ：普通（４．０％以上、６．０％未満）
Ｄ：悪い（６．０％以上）
【０４２１】
＜定着性＞
定着性は５０ｇ／ｃｍ²の荷重をかけ、柔和な薄紙により定着画像を５往復摺擦し、摺擦前後での画像濃度の低下率（％）で評価した。
Ａ：１０％未満
Ｂ：１０％以上２０％未満
Ｃ：２０％以上３０％未満
Ｄ：３０％以上
【０４２２】
＜耐オフセット性＞
耐オフセット性は、耐久試験後の画像上及び紙裏の汚れの程度により評価した。
Ａ：汚れは未発生。
Ｂ：かすかに汚れが見られる。
Ｃ：若干の汚れが見られる。
Ｄ：顕著な汚れが発生。
【０４２３】
［実施例２〜９］
トナーとして、磁性トナー２、３及び８〜１３を使用し、実施例１と同様の条件で画出し試験及び耐久性評価を行った。その結果、初期の画像特性も問題無く、５０００枚までいずれも大きな問題の無い結果が得られた。結果を表３に示す。
【０４２４】
［比較例１］
トナーとして、磁性トナー４を使用し、実施例１と同様の画像形成方法で画出し試験及び耐久性評価を行った。その結果、画像濃度、帯電性、感光体カブリの悪化が生じた。これは、トナーの溶融粘度が低いために、鉄及び鉄化合物の遊離率が耐久により変化したためと考えられる。また、耐オフセット性も悪化した。結果を表３に示す。
【０４２５】
［比較例２］
トナーとして、磁性トナー５を使用し、実施例１と同様の画像形成方法で画出し試験及び耐久性評価を行った。その結果、画像濃度、帯電性、感光体カブリには問題は発生しなかったが、定着性が悪化した。これは、トナーの溶融粘度が高いためと考えられる。結果を表３に示す。
【０４２６】
［比較例３］
トナーとして、磁性トナー６を使用し、実施例１と同様の画像形成方法で画出し試験及び耐久性評価を行った。その結果、画像濃度、帯電性、感光体カブリの悪化が生じた。これは、トナーの溶融粘度が低いために、鉄及び鉄化合物の遊離率が耐久により変化したためと考えられる。また、耐オフセット性も著しく悪化した。結果を表３に示す。
【０４２７】
［比較例４］
トナーとして、磁性トナー７を使用し、実施例１と同様の画像形成方法で画出し試験及び耐久性評価を行った。その結果、画像濃度、帯電性、感光体カブリには問題は発生しなかったが、定着性と耐オフセット性が悪化した。これは、トナーの溶融粘度が高いため、トナー中のワックスが十分機能できなかったためと考えられる。結果を表３に示す。
【０４２８】
［比較例５］
トナーとして、磁性トナー１４を使用し、実施例１と同様の画像形成方法で画出し試験及び耐久性評価を行った。その結果、初期より画質、帯電性、感光体カブリが悪かった。これは、鉄及び鉄化合物の遊離率が高いためと考えられる。また、定着性もやや悪化した。結果を表３に示す。
【０４２９】
［比較例６］
トナーとして、磁性トナー１５を使用し、実施例１と同様の画像形成方法で画出し試験及び耐久性評価を行った。その結果、初期から画質、感光体カブリがやや悪く。耐久でチャージアップによる画質の低下が発生した。これは、トナーの鉄及び鉄化合物の遊離率が低いためと考えられる。また、定着性もやや悪化した。結果を表３に示す。
【０４３０】
［比較例７］
トナーとして、磁性トナー１６を使用し、実施例１と同様の画像形成方法で画出し試験及び耐久性評価を行った。その結果、初期より画質、感光体カブリが悪かった。これは、トナーの円形度が低い、重量平均粒径／個数平均粒径が高いためと考えられる。結果を表３に示す。
【０４３１】
［実施例１０］
また、本発明の磁性トナーは、クリーナレス画像形成方法または現像兼クリーニング（回収）画像形成方法にも適用可能である。以下、具体的実施例によって本発明の画像形成方法を説明するが本発明はなんらこれに限定されるものではない。
【０４３２】
＜感光体２の製造＞
感光体は負帯電用の有機光導電性物質を用いた感光体であり、直径３０ｍｍのアルミニウム製のシリンダーを基体とした。これに、図５及び下記に示すような構成の層を順次浸漬塗布により積層して、感光体２を作製した。
（１）第１層は導電層であり、アルミニウム基体の欠陥等をならすため、またレーザ露光の反射によるモアレの発生を防止するために設けられている厚さ約２０μｍの導電性粒子分散樹脂層（酸化錫及び酸化チタンの粉末をフェノール樹脂に分散したものを主体とする）である。
（２）第２層は正電荷注入防止層（下引き層）であり、アルミニウム支持体から注入された正電荷が感光体表面に帯電された負電荷を打ち消すのを防止する役割を果たし、メトキシメチル化ナイロンによって１０⁶Ωｃｍ程度に抵抗調整された厚さ約１μｍの中抵抗層である。
（３）第３層は電荷発生層であり、ジスアゾ系の顔料をブチラール樹脂に分散した厚さ約０．３μｍの層であり、レーザ露光を受けることによって正負の電荷対を発生する。
（４）第４層は電荷輸送層であり、ポリカーボネート樹脂にヒドラゾン化合物を分散した厚さ約２５μｍの層であり、Ｐ型半導体である。従って、感光体表面に帯電された負電荷はこの層を移動することはできず、電荷発生層で発生した正電荷のみを感光体表面に輸送することができる。
（５）第５層は電荷注入層であり、光硬化性のアクリル樹脂に導電性酸化スズ超微粒子及び粒径約０．２５μｍの四フッ化エチレン樹脂粒子を分散したものである。具体的には、アンチモンをドーピングし低抵抗化した粒径約０．０３μｍの酸化スズ粒子（導電粒子）を樹脂に対して１００質量％、更に四フッ化エチレン樹脂粒子を２０質量％、分散剤を１．２質量％分散したものである。このようにして調製した塗工液をスプレー塗工法にて厚さ約２．５μｍに塗工し、光照射により硬化させて電荷注入層とした。
得られた感光体の表面の抵抗は５×１０¹²Ωｃｍ、感光体表面の水に対する接触角は１０２度であった。
【０４３３】
＜帯電部材の製造＞
直径６ｍｍ、長さ２６４ｍｍのＳＵＳローラを芯金とし、芯金上にウレタン樹脂、導電性粒子としてのカーボンブラック、硫化剤、発泡剤等を処方した中抵抗の発泡ウレタン層をローラ状に形成し、さらに切削研磨し形状及び表面性を整え、可撓性部材である、直径１２ｍｍ、長さ２３４ｍｍの帯電ローラを作製した。
得られた帯電ローラは、抵抗が１０⁵Ωｃｍであり、硬度は、アスカーＣ硬度で３０度であった。また、この帯電ローラ表面を走査型電子顕微鏡で観察したところ、平均セル径は約１００μｍで、空隙率は６０％であった。
【０４３４】
＜画像形成装置＞
図６は本発明に従う画像形成装置の一例の概略構成模型図である。
実施例１０で用いる画像形成装置は、転写式電子写真プロセスを利用した現像兼クリーニングプロセス（クリーナーレスシステム）のレーザプリンタ（記録装置）である。クリーニングブレード等のクリーニング部材を有するクリーニングユニットを除去したプロセスカードリッジを有し、磁性トナーとしては磁性トナー１を使用し、磁性トナー担持体上のトナー層と像担持体が非接触となるよう配置される非接触現像の例である。定着方法としては、フィルムを介してヒータにより加熱加圧定着する方式の定着装置２６を用いた。加圧ローラはフッ素系樹脂の表面層を有するものを使用し、ローラの直径は３０ｍｍである。また、定着温度は２３０℃、ニップ幅を６ｍｍに設定した。
【０４３５】
（１）本実施例プリンタの全体的な概略構成
像担持体としての、上記感光体２を用いた回転ドラム型ＯＰＣ感光体２１は、矢印のＸ方向に１９８ｍｍ／ｓｅｃの周速度（プロセススピード）をもって回転駆動される。
【０４３６】
接触帯電部材としての上記帯電部材である帯電ローラ２２は、感光体２１に対して弾性に抗して所定の押圧力で圧接させて配設してある。ｎは感光体２１と帯電ローラ２２の当接部である。本例では、帯電ローラ２２は感光体２１との接触面である当接部ｎにおいて対向方向（矢印Ｙ方向）に１００％の周速で回転駆動されている。即ち接触帯電部材としての帯電ローラ２２の表面は感光体２１の表面に対して速度差を持たせた。また、帯電ローラ２２の表面には、塗布量がおよそ１×１０⁴個／ｍｍ²で均一になるように前記導電性微粉体１を塗布した。
【０４３７】
また帯電ローラ２２の芯金２２ａには帯電バイアス印加電源から−７００Ｖの直流電圧を帯電バイアスとして印加するようにした。本例では感光体２１の表面は帯電ローラ２２に対する印加電圧とほぼ等しい電位（−６８０Ｖ）に直接注入帯電方式にて一様に帯電処理される。これについては後述する。
【０４３８】
２３はレーザダイオード・ポリゴンミラー等を含むレーザビームスキャナ（露光器）である。このレーザビームスキャナは目的の画像情報の時系列電気ディジタル画素信号に対応して強度変調されたレーザ光を出力し、該レーザ光で上記感光体２１の一様帯電面を走査露光Ｌする。この走査露光Ｌにより回転感光体２１の面に目的の画像情報に対応した静電潜像が形成される。
【０４３９】
２４は現像器である。感光体２１の表面の静電潜像はこの現像器によりトナー像として現像される。本例の現像器２４においては、磁性トナーとして実施例１で使用した磁性トナー１を用いた、非接触型の反転現像装置である。磁性トナー１には導電性微粉体１が外添添加されている。
【０４４０】
感光ドラム２１と現像スリーブ２４ａとの間隙は２３０μｍとし、磁性トナー担持体２４ａとして、表面をブラストした直径１６ｍｍのアルミニウム円筒上に、下記の構成のＪＩＳ中心線平均粗さ（Ｒａ）１．０μｍの樹脂層（層厚約７μｍ）を形成した現像スリーブを使用し、現像磁極８５ｍＴ（８５０ガウス）のマグネットロールを内包し、磁性トナー層規制部材である弾性ブレード２４ｃとして厚み１．０ｍｍ、自由長０．５ｍｍのウレタン製ブレードを３４．３Ｎ／ｍ（３５ｇ／ｃｍ）の線圧で当接させた。
・フェノール樹脂 １００質量部
・グラファイト（粒径約７μｍ） ９０質量部
・カーボンブラック １０質量部
【０４４１】
また、感光体２１との対向部である現像部ａ（現像領域部）にて感光体２１の回転方向と順方向（矢印Ｗ方向）に感光体２１の周速の１２０％の周速で回転させる。この現像スリーブ２４ａに弾性ブレード２４ｃにより磁性トナーが薄層にコートされる。磁性トナーは弾性ブレード２４ｃで現像スリーブ２４ａに対する層厚が規制され、また電荷が付与される。この時、現像スリーブ２４ａにコートされた磁性トナー量は１５ｇ／ｍ²であった。
【０４４２】
現像スリーブ２４ａにコートされた磁性トナーは現像スリーブ２４ａの回転により、感光体２１と現像スリーブ２４ａの対向部である現像部ａに搬送される。また、現像スリーブ２４ａには現像バイアス印加電源より現像バイアス電圧が印加される。現像バイアス電圧は、−４５０Ｖの直流電圧と、周波数１８００Ｈｚ、５．２２×１０⁶Ｖ／ｍの交番電界を重畳したものを用い、現像スリーブ２４ａと感光体２１の間ａで一成分ジャンピング現像を行わせた。
【０４４３】
接触転写手段としての中抵抗の転写ローラ２５は、感光体２１に９８Ｎ／ｍ（１００ｇ／ｃｍ）の線圧で圧接させて転写ニップｂを形成させてある。この転写ニップ部ｂに不図示の給紙部から所定のタイミングで記録媒体としての転写材Ｐが給紙され、かつ転写ローラ２５に転写バイアス印加電源から所定の転写バイアス電圧が印加されることで、感光体２１側のトナー像が転写ニップ部ｂに給紙された転写材Ｐの面に順次に転写されていく。
【０４４４】
本例ではローラ抵抗値は５×１０⁸Ωｃｍのものを用い、＋３０００Ｖの直流電圧を印加して転写を行った。即ち、転写ニップ部ｂに導入された転写材（記録媒体）Ｐはこの転写ニップ部ｂを挟持搬送されて、その表面側に感光体２１の表面に形成担持されているトナー像が順次に静電気力と押圧力によって転写されていく。
【０４４５】
２６は熱定着方式等の定着装置である。転写ニップ部ｂに給紙されて感光体２１側のトナー像の転写を受けた転写材Ｐは感光体１の表面から分離されてこの定着装置２６に導入され、トナー像の定着を受けて画像形成物（プリント、コピー）として装置外へ排出される。
【０４４６】
本例のプリンタはクリーニングユニットを除去しており、転写材Ｐに対するトナー像転写後の感光体２１の表面に残留の転写残トナーはクリーナで除去されることなく、感光体２１の回転にともない帯電部ｎを経由して現像部ａに至り、現像器２４において現像兼クリーニング（回収）される。
【０４４７】
２７はプリンタ本体に対して着脱自在のプロセスカートリッジである。本例のプリンタは、感光体２１、帯電ローラ２２、現像器２４の３つのプロセス機器を一括してプリンター本体に対して着脱自在のプロセスカートリッジとして構成してある。プロセスカートリッジ化するプロセス機器の組み合わせ等は上記に限られるものではなく任意である。２８はプロセスカートリッジの着脱案内・保持部材である。
【０４４８】
（２）本実施例における導電性微粉体の挙動について
現像器２４中の磁性トナーに混入させた導電性微粉体は、現像器２４による感光体２１側の静電潜像のトナー現像時にトナーとともに適当量が感光体２１側に移行する。
【０４４９】
感光体２１上のトナー像は転写部ｂにおいて転写バイアスの影響で記録媒体である転写材Ｐ側に引かれて積極的に転移するが、感光体２１上の導電性微粉体は導電性であることで転写材Ｐ側には積極的には転移せず、感光体２１上に実質的に付着保持されて残留する。
【０４５０】
本例においては、画像形成装置はクリーニング工程を有さないため、転写後の感光体２１の表面に残存の転写残トナーおよび上記の残存導電性微粉体は感光体２１と接触帯電部材である帯電ローラ２２の当接部である帯電部ｎに感光体２１面の移動でそのまま持ち運ばれて、帯電ローラ２２に付着または混入する。したがって、感光体２１と帯電ローラ２２との当接部ｎにこの導電性微粉体が存在した状態で感光体２１の直接注入帯電が行われる。
【０４５１】
この導電性微粉体の存在により、帯電ローラ２２にトナーが付着・混入した場合でも、帯電ローラ２２の感光体２１への緻密な接触性と接触抵抗を維持できるため、該帯電ローラ２２による感光体２１の直接注入帯電を行わせることができる。
【０４５２】
つまり、帯電ローラ２２が導電性微粉体を介して密に感光体２１に接触して、帯電ローラ２２と感光体２１の相互接触面に存在する導電性微粉体が感光体２１表面を隙間なく摺擦することで、帯電ローラ２２による感光体２１の帯電は導電性微粉体の存在により放電現象を用いない安定かつ安全な直接注入帯電が支配的となり、従来のローラ帯電等では得られなかった高い帯電効率が得られ、帯電ローラ２２に印加した電圧とほぼ同等の電位を感光体２１に与えることができる。
【０４５３】
また帯電ローラ２２に付着または混入した転写残トナーは帯電ローラ２２から徐々に感光体２１上に吐き出されて感光体２１面の移動とともに現像部に至り、現像手段において現像兼クリーニング（回収）される。
【０４５４】
現像兼クリーニングは、転写後に感光体２１上に残留したトナーを、引き続く画像形成工程の現像時、即ち引き続き感光体を帯電し、露光して潜像を形成し、該潜像の現像時において、現像装置のかぶり取りバイアス、即ち現像器に印加する直流電圧と感光体の表面電位間の電位差であるかぶり取り電位差Ｖｂａｃｋによって回収するものである。本実施例におけるプリンタのように反転現像の場合では、この現像兼クリーニングは、現像バイアスによる感光体の暗部電位から現像スリーブにトナーを回収する電界と、現像スリーブから感光体の明部電位へトナーを付着させる電界の作用でなされる。
【０４５５】
また、画像形成装置が稼働されることで、現像器２４の磁性トナー中に混入させてある導電性微粉体が現像部ａで感光体２１面に移行し該像担持面の移動により転写部ｂを経て帯電部ｎに持ち運ばれて帯電部ｎに新しい導電性微粉体が逐次に供給され続けるため、帯電部ｎにおいて導電性微粉体が脱落等で減少したり、該粉体が劣化するなどしても、帯電性の低下が生じることが防止されて良好な帯電性が安定して維持される。
【０４５６】
かくして、接触帯電方式、転写方式、トナーリサイクルプロセスの画像形成装置において、接触帯電部材として簡易な帯電ローラ２２を用いて、しかも該帯電ローラ２２の転写残トナーによる汚染にかかわらず、低印加電圧でオゾンレスの直接注入帯電を長期に渡り安定に維持させることができ、均一な帯電性を与えることが出来、オゾン生成物による障害、帯電不良による障害等のない、簡易な構成、低コストな画像形成装置を得ることができる。
【０４５７】
また、前述のように導電性微粉体は帯電性を損なわないために、電気抵抗値が１×１０⁹Ωｃｍ以下である必要がある。そのため、現像部ａにおいて磁性トナーが直接感光体２１に接触する接触現像器を用いた場合には、現像像剤中の導電性微粉体を通じて、現像バイアスにより感光体２１に電荷注入され、画像かぶりが発生してしまう。
【０４５８】
しかし、本例では現像器は非接触型現像器であるので、現像バイアスが感光体２１に注入されることがなく、良好な画像を得ることが出来る。また、現像部ａにおいて感光体２１への電荷注入が生じないため、ＡＣのバイアスなど現像スリーブ２４ａと感光体２１間に高電位差を持たせることが可能であり、導電性微粉体が均等に現像されやすく、均一に導電性微粉体を感光体２１表面に塗布し、帯電部で均一な接触を行い、良好な帯電性を得ることが出来き、良好な画像を得ることが可能となる。
【０４５９】
帯電ローラ２２と感光体２１との接触面ｎに導電性微粉体を介在させることにより、該導電性微粉体の潤滑効果（摩擦低減効果）により帯電ローラ２２と感光体２１との間に容易に効果的に速度差を設けることが可能となる。
【０４６０】
帯電ローラ２２と感光体２１との間に速度差を設けることにより、帯電ローラ２２と感光体２１の相互接触面部ｎにおいて導電性微粉体が感光体２１に接触する機会を格段に増加させ、高い接触性を得ることができ、良好な直接注入帯電を可能としている。
【０４６１】
本実施例では、帯電ローラ２２を回転駆動し、その回転方向は感光体２１表面の移動方向とは逆方向に回転するように構成することで、帯電部ｎに持ち運ばれる感光体２１上の転写残トナーを帯電ローラ２２に一時的に回収し均す効果を得ている。即ち、逆方向回転で感光体２１上の転写残トナーを一旦引き離し、帯電を行うことにより優位に直接注入帯電を行うことが可能である。
【０４６２】
更に、本実施例では像担持体としての感光ドラム２１と接触帯電部材としての帯電ローラ２２との当接部ｎにおける適当な量の導電性微粉体の介在によって、導電性微粉体による潤滑効果により帯電ローラ２２と感光ドラム２１との摩擦を低減し、帯電ローラ２２を感光ドラム２１に速度差を持って回転駆動させることが容易である。つまり、駆動トルクが低減し、帯電ローラ２２や感光ドラム２１の表面の削れまたは傷を防止できる。更に該粒子による接触機会増加により十分な帯電性能が得られる。また、導電性微粉体の帯電ローラ２２からの脱落よる作像上に悪影響もない。
【０４６３】
（３）評価
本実施例では、磁性トナー１を使用し、常温常湿環境下（２５℃、６０％ＲＨ）において、画出し試験を行った。感光体としては最表面層の体積抵抗が５×１０¹²Ωｃｍの上述の感光体２を用い、転写材としては８０ｇ／ｍ²の紙を使用した。初期画像特性においては、帯電不良に起因するカブリは見られず、解像性の高い良好な画像濃度が得られた。この時、直接注入帯電後感光体電位は、印加帯電バイアス−７００Ｖに対して−６８０Ｖであった。次に、印字率２％の縦線のみからなる画像パターンで耐久性の評価を行った。その結果、５０００枚のプリント後まで帯電不良に起因する画像欠陥を生じず、良好な直接注入帯電性が得られた。
【０４６４】
また、５０００枚のプリント後の直接注入帯電後感光体電位は、印加帯電バイアス−７００Ｖに対して−６５５Ｖであり、初期からの帯電性の低下は２５Ｖと軽微であり、帯電性の低下による画像品質の低下は認められなかった。得られた結果を表３に示す。なお、評価項目及び、評価基準は実施例1と同様である。
また、像担持体と接触帯電部材との当接部における導電性微粉体の存在量は前述の方法で測定したところ、２×１０⁵個であった。
【０４６５】
［実施例１１］
実施例１０において、磁性トナー１７を使用して同様の評価を行ったところ、初期画像特性においては、帯電不良に起因するカブリは見られず、解像性の高い良好な画像濃度が得られた。この時、直接注入帯電後感光体電位は、印加帯電バイアス−７００Ｖに対して−６８０Ｖであった。次に、印字率２％の縦線のみからなる画像パターンで耐久性の評価を行った。その結果、５０００枚のプリント後に若干のカブリが発生した。また、像担持体と接触帯電部材との当接部における導電性微粉体の存在量は前述の方法で測定したところ、２×１０⁵個であった。
【０４６６】
［実施例１２］
実施例１０において、磁性トナー１８を使用して同様の評価を行ったところ、初期画像特性においては、帯電不良に起因するカブリは見られず、解像性の高い良好な画像濃度が得られた。この時、直接注入帯電後感光体電位は、印加帯電バイアス−７００Ｖに対して−６８０Ｖであった。次に、印字率２％の縦線のみからなる画像パターンで耐久性の評価を行った。その結果、５０００枚のプリント後に、実用上問題ないレベルであるものの、感光体の傷に起因する画像欠陥が生じた。また、像担持体と接触帯電部材との当接部における導電性微粉体の存在量は前述の方法で測定したところ、２×１０⁵個であった。
【０４６７】
【表３】

【０４６８】
【発明の効果】
本発明の磁性トナーは、少なくとも結着樹脂、離型剤、及び磁性粉体を有するトナー粒子を含み、重量平均粒径が３〜２０μｍであり、磁場７９．６ｋＡ／ｍにおける磁化の強さが１０〜５０Ａｍ²／ｋｇである磁性トナーにおいて、平均円形度が０．９７０以上であり、個数平均粒径に対する重量平均粒径の比が１．４０以下であり、鉄及び鉄化合物の遊離率が０．０５％から３．００％であり、フローテスター測定での粘度が１．０×１０⁵Ｐａ・ｓとなる温度が８０〜１２０℃であり、かつ１．０×１０⁴Ｐａ・ｓとなる温度が１００〜１５０℃であることから、良好な定着性を有し、帯電安定性に優れ、長期の使用においても画像濃度が高く、高精細な画像を得ることが出来る。
【０４６９】
さらに本発明の磁性トナーは、フローテスター測定での粘度が１．０×１０⁵Ｐａ・ｓとなる温度が８０〜１１０℃であること、さらには粘度が１．０×１０⁴Ｐａ・ｓとなる温度が１００〜１４０℃であることとすると、定着性と帯電性の良好なバランスをとる上でより一層効果的である。
【０４７０】
さらに本発明の磁性トナーは、モード円形度が０．９９以上であること、及び個数平均粒径に対する重量平均粒径の比が１．３５以下であることとすると、再現性に優れ、高画質の画像を得る上でより一層効果的である。
【０４７１】
さらに本発明の磁性トナーは、鉄及び鉄化合物の遊離率が０．０５％から２．００％、より好ましくは０．０５％から１．５０％、さらに好ましくは０．０５％から１．００％であることとすると、磁性トナーの帯電均一性を向上させ、画像のがさつきを抑制する上でより一層効果的である。
【０４７２】
さらに本発明の磁性トナーは、離型剤を結着樹脂に対し総量で１〜３０質量％含有することとすると、高画質の画像形成と定着性とを両立させる上でより効果的である。
【０４７３】
さらに本発明の磁性トナーは、離型剤の示差走査熱量分析による吸熱ピークが４０〜１１０℃、より好ましくは５０〜１００℃であることとすると、定着性のバランスをとる上でより一層効果的である。
【０４７４】
さらに本発明の磁性トナーは、磁性トナーのＴＨＦ可溶分のゲルパーミュエーションクロマトグラフィーにより測定した分子量分布において、分子量５０００〜５００００の範囲にメインピークのピークトップが存在することとすると、磁性トナーの安定性や定着性、トナー粒子の形状や粒度分布の均一性などを向上させる上でより一層効果的である。
【０４７５】
さらに本発明の磁性トナーは、トナー粒子表面に無機微粉体を有し、該無機微粉体の個数平均一次粒径が４〜８０ｎｍであることとし、無機微粉体がシリカ、酸化チタン、アルミナから選ばれる少なくとも一種以上、特にシリカであることと、磁性トナーの流動性を良好にする上でより一層効果的である。
【０４７６】
さらに本発明の磁性トナーは、無機微粉体が疎水化処理されていること、より好ましくは少なくともシリコーンオイルで処理されていること、さらに好ましくは少なくともシラン化合物で処理すると同時に、またはその後にシリコーンオイルで処理されていることとすると、高湿環境下でのトナー粒子の帯電性を維持する上でより一層効果的である。
【０４７７】
さらに本発明の磁性トナーは、無機微粉体がシリカであり、該シリカの遊離率が０．１〜２．０％、より好ましくは０．１〜１．５％であることとすると、磁性トナーの良好な流動性を維持する上でより効果的である。
【０４７８】
さらに本発明の磁性トナーは、トナー粒子の表面に磁性トナーの重量平均粒径よりも小さい体積平均粒径の導電性微粉体を有すると、磁性トナーの現像性を向上させ、画像濃度が高い画像を得る上でより一層効果的である。
【０４７９】
さらに本発明の磁性トナーは、導電性微粉体の抵抗が１×１０⁹Ωｃｍ以下、より好ましくは１×１０⁸Ωｃｍ以下であることとすると、像担持体と帯電部材の接触部における接触性を向上させ、かつ良好な帯電を実現させる上でより一層効果的である。
【０４８０】
さらに本発明の磁性トナーは、導電性微粉体が非磁性であることとすると、上記の接触部へ搬送性を向上させる上でより一層効果的である。
【０４８１】
さらに本発明の磁性トナーは、導電性微粉体の遊離率が５．０〜５０．０％であることとすると、磁性トナーの現像性を向上させ、画像濃度が高い画像を得る上でより一層効果的である。
【０４８２】
さらに本発明の磁性トナーは、磁性粉体の体積平均粒径が０．０５〜０．４０μｍであることとすると、トナー粒子中の磁性粉体を良好に分散させる上でより効果的である。
【０４８３】
さらに本発明の磁性トナーは、磁性粉体の粒度分布において、体積平均変動係数が３５以下であることとすると、トナー粒子間における磁性粉体の含有量を均一化する上でより一層効果的である。
【０４８４】
さらに本発明の磁性トナーは、磁性粉体がカップリング剤で疎水化処理されていること、より好ましくは水系媒体中でカップリング剤を加水分解することにより表面処理されることとすると、トナー粒子における所期の形状や表面状態を得る上でより一層効果的である。
【０４８５】
また、本発明の画像形成方法は、本発明の磁性トナーを用いた接触帯電方法として、磁性一成分現像方式、接触帯電方式、当接転写方式、及びトナーリサイクルプロセスを用いる画像形成方法においても、磁性トナーの性能劣化が無いため、繰り返し使用においても良好な画像を長期間安定して得ることができる。
【図面の簡単な説明】
【図１】本発明の画像形成方法を実施する画像形成装置の一例を示す図である。
【図２】図１に示す画像形成装置に用いられる一成分現像用現像器の一例を示す図である。
【図３】本発明の画像形成方法を実施するための画像形成装置に用いられる接触転写部材の一例を示す図である。
【図４】本発明の画像形成方法に用いられる像担持体の一例を示す図である。
【図５】本発明の画像形成方法に用いられる像担持体の層構成の一例を示す図である。
【図６】本発明の画像形成方法を実施する画像形成装置の他の例を示す図である。
【符号の説明】
１１ アルミニウム基体
１２ 導電層
１３ 正電荷注入防止層
１４ 電荷発生層
１５ 電荷輸送層
１６ 電荷注入層
１６ａ 導電粒子（導電フィラー）
２１、１００ 感光体（像担持体）
２２ 帯電ローラ（帯電部材）
２２ａ、３４ａ 芯金
２３、１２１ レーザービームスキャナ
２４、１４０ 現像器
２４ａ、１０２ 現像スリーブ（磁性トナー担持体）
２４ｂ、１４１ 攪拌部材
２４ｃ、１０３ 弾性ブレード
２５、３４、１１４ 転写ローラ
２６、１２６ 定着装置
２６ａ ヒータ
２６ｂ 定着フィルム
２６ｃ 加圧ローラ
２７ プロセスカートリッジ
２８ カートリッジ保持部材
３４ｂ 導電性弾性層
３５ 転写バイアス電源
１０４ マグネットローラ
１１６ クリーナ
１１７ 一次帯電ローラ（帯電部材）
１２３ レーザ光
１２４ レジスタローラ
１２５ 搬送ベルト
Ｐ 記録媒体[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a toner for developing an electrostatic latent image in an image forming method such as an electrophotographic method, an electrostatic recording method, a magnetic recording method, and a toner jet method, and an image forming method using the toner.
[0002]
[Prior art]
Many methods are known as electrophotographic methods. Generally, an electrostatic latent image is formed on an electrostatic charge image carrier (hereinafter also referred to as a “photosensitive member”) by using a photoconductive substance by various means. Then, the latent image is developed with toner to form a visible image. If necessary, the toner image is transferred to a recording medium such as paper, and then the toner image is fixed on the recording medium by heat or pressure. To obtain a copy. Examples of such an image forming apparatus include a copying machine and a printer.
[0003]
In recent years, LED printers and LBP printers have become mainstream in the recent market, and the direction of technology is higher resolution, that is, what was conventionally 240, 300 dpi has become 600, 800, 1200 dpi. Accordingly, the development method is also required to have higher definition. In addition, copiers are also becoming more sophisticated, and therefore are moving toward digitalization. Since this method is mainly a method of forming an electrostatic charge image with a laser, it is also proceeding in the direction of high resolution. In addition to the improvement in image quality, there is a great demand for higher speed and longer life.
[0004]
In the developing method used in such printers and copiers, the toner image formed on the photoconductor in the developing process is transferred to the recording medium in the transfer process, but the image portion remaining on the photoconductor is not transferred. The transfer residual toner and the fog toner in the non-image area are cleaned in the cleaning process, and the toner is stored in the waste toner container. For this cleaning process, conventional blade cleaning, fur brush cleaning, roller cleaning, and the like are used. From the standpoint of the apparatus, the apparatus becomes inevitably large in order to have such a cleaning apparatus, which is a bottleneck when aiming to make the apparatus compact. Furthermore, from the viewpoint of ecology, a system with little waste toner is desired in the sense of effective use of toner, and a toner having high transfer efficiency and low fog is demanded.
[0005]
Also, from the viewpoint of making the apparatus compact, the one-component development method is preferable because carrier particles such as glass beads and iron powder are not required unlike the two-component method, and the development device itself can be reduced in size and weight. Furthermore, since the two-component development method needs to keep the toner concentration in the magnetic toner constant, a device for detecting the toner concentration and supplying a necessary amount of toner is necessary, and the developing device becomes large and heavy. On the other hand, the one-component development method is preferable because such an apparatus is not necessary and can be reduced in size and weight.
[0006]
The magnetic toner used in such an image forming process contains a binder resin and a colorant as main components, and also contains additives such as a charge control agent and a release agent for extracting the necessary properties as a toner. It is common. As magnetic toner colorant, magnetic powder is used as colorant as it is, or carbon black or non-magnetic inorganic compound, organic pigment, dye, etc. are used together with magnetic powder, and as release agent, low molecular weight polyethylene is used. A material that is not compatible with the binder resin such as low molecular weight polypropylene is used.
[0007]
However, the developing method using the insulating magnetic toner has unstable elements related to the insulating magnetic toner to be used. This is because a considerable amount of fine powdery magnetic material is mixed and dispersed in the insulating magnetic toner, and a part of the magnetic material is exposed on the surface of the toner particles. As a result, it causes fluctuation or deterioration of various characteristics required for the magnetic toner such as development characteristics and durability of the magnetic toner. This is considered to be caused by the presence of magnetic fine particles having a relatively low resistance compared to the resin constituting the toner on the surface of the magnetic toner. Further, the chargeability of toner has a great influence on development and transfer, and is closely related to image quality. Therefore, a toner capable of stably obtaining a high charge amount is desired.
[0008]
On the other hand, proposals regarding magnetic iron oxide contained in the magnetic toner have been made, but there are still points to be improved.
[0009]
For example, JP-A-62-279352 proposes a magnetic toner containing magnetic iron oxide containing silicon element. Such magnetic iron oxide intentionally has silicon element present inside the magnetic iron oxide, but still has a point to be improved in the fluidity of the magnetic toner containing the magnetic iron oxide.
[0010]
In Japanese Examined Patent Publication No. 3-9045, a proposal is made to control the shape of magnetic iron oxide to be spherical by adding silicate. The magnetic iron oxide obtained by this method uses silicate to control the particle shape, so that a large amount of silicon element is distributed inside the magnetic iron oxide, and the amount of silicon element present on the magnetic iron oxide surface is small. Since the smoothness of the magnetic iron oxide is high, the fluidity of the magnetic toner is improved to some extent, but the adhesion between the binder resin constituting the magnetic toner and the magnetic iron oxide is insufficient.
[0011]
Japanese Patent Application Laid-Open No. 61-34070 proposes a method for producing iron tetroxide by adding a hydrosilosilicate solution during the oxidation reaction to iron tetroxide. Although the iron tetroxide by this method has Si element near the surface, the Si element exists in a layer near the iron tetroxide surface, and the surface is weak against mechanical impact such as friction. Has a point.
[0012]
On the other hand, the toner is manufactured as a toner having a desired particle size by melting and mixing a binder resin, a colorant, and the like, uniformly dispersing, pulverizing with a fine pulverizer, and classifying with a classifier (pulverization method). However, there is a limit to the range of materials that can be used to reduce the toner particle size. For example, the resin colorant dispersion must be sufficiently brittle and capable of being finely pulverized by an economically usable production apparatus. From this requirement, in order to make the resin colorant dispersion brittle, when the resin colorant dispersion is actually finely pulverized at a high speed, particles having a wide particle size range are easily formed, and in particular, a relatively large proportion of fine particles ( A large amount of excessively pulverized particles) are produced, and the magnetic powder is easily detached from the resin during pulverization. Further, such highly brittle materials are often further pulverized or powdered when used as developing toners in copying machines and the like.
[0013]
On the other hand, JP-A-2-256604 discloses a toner production method in which free magnetic powder is removed by classification after pulverization in the production of pulverized toner. However, in the pulverization method, magnetic iron oxide particles are essentially exposed on the surface of the toner, so that problems remain in the fluidity of the toner and the charging stability in a harsh environment, and the transferability is inferior. There is room for further improvement.
[0014]
Also, in the pulverization method, it is difficult to completely disperse solid fine particles such as magnetic powder or colorant into the resin, and depending on the degree of dispersion, it may cause an increase in fog and a decrease in image density. .
[0015]
That is, in the pulverization method, there is a limit to the finer toner particles required for high definition and high image quality, and accordingly, the powder characteristics, particularly the uniform chargeability and fluidity of the toner are remarkably attenuated.
[0016]
In order to overcome the problems of the toner by the pulverization method as described above, and further to satisfy the above-described requirements, a toner production method by a suspension polymerization method has been proposed.
[0017]
The toner by suspension polymerization (hereinafter referred to as polymerized toner) can easily make the toner fine particles, and further, since the shape of the obtained toner is spherical, it has excellent fluidity and is advantageous for high image quality.
[0018]
However, by including a magnetic substance in the polymerized toner, its fluidity and charging characteristics are remarkably lowered and the developability cannot be satisfied. This is because the magnetic particles are generally hydrophilic and thus tend to exist on the toner surface. In addition, in the granulation step when producing the polymerized toner, the hydrophilic magnetic material is partially transferred to an aqueous system and exists as a free magnetic material detached from the toner. In order to solve this problem, it is important to modify the surface characteristics of the magnetic material.
[0019]
In order to improve the dispersibility and inclusion of the magnetic substance in the polymerized toner, many proposals have been made regarding the surface modification of the magnetic substance. For example, various silane coupling agent treatment techniques for magnetic materials are disclosed in Japanese Patent Application Laid-Open Nos. 59-200254, 59-2000025, 59-200277, and 59-224102. Japanese Laid-Open Patent Publication No. 63-250660 discloses a technique for treating silicon element-containing magnetic particles with a silane coupling agent.
[0020]
However, although the dispersibility in the toner is improved to some extent by these treatments, it is difficult to make the surface of the magnetic material hydrophobic, and the exposure of the magnetic material to the toner surface is not suppressed. The solution is not enough.
[0021]
On the other hand, regarding the amount of magnetic material on the toner surface, Japanese Patent Application Laid-Open No. 7-209904 proposes a toner having a special structure in which magnetic fine particles are not present on the toner surface layer. This toner is excellent in that the magnetic powder has an excellent encapsulating property and the magnetic powder on the toner surface is not exposed.
[0022]
However, when the embodiment is carried out, the toner production method is complicated and production on a production scale is difficult, and repeated use over a long period of time under low humidity causes deterioration in image quality due to toner charge-up, Further improvements in toner charging stability were required.
[0023]
Furthermore, many techniques have been disclosed, including Japanese Patent Application Laid-Open No. 1-112253, for reducing the toner particle size in order to improve image quality. However, the toner having a small particle diameter has a more difficult uniform dispersibility and inclusion property of the magnetic powder, and the various problems described above have not been sufficiently solved.
[0024]
Also, a method of adding inorganic fine powder as an external additive to toner particles has been proposed and widely used for the purpose of improving toner flow characteristics, charging characteristics, and the like.
[0025]
For example, an inorganic fine powder that has been hydrophobized in JP-A-5-66608, JP-A-4-9860 or the like, or an inorganic fine powder that has been hydrophobized and then treated with silicone oil or the like, or JP-A-61-249059, JP-A-4-264453, and JP-A-5-346682 disclose a method of adding a hydrophobized inorganic fine powder and a silicone oil-treated inorganic fine powder in combination.
[0026]
Many methods of adding conductive fine particles as an external additive have been proposed. For example, carbon black as conductive fine particles is used to adhere to or adhere to the toner surface for the purpose of imparting conductivity to the toner, or to suppress excessive charging of the toner and to make the tribo distribution uniform. It is widely known to use as an external additive. In JP-A-57-151952, JP-A-59-168458, and JP-A-60-69660, conductive fine particles of tin oxide, zinc oxide, and titanium oxide are respectively added to the high-resistance magnetic toner. The addition is disclosed. In JP-A-61-275864, JP-A-62-258472, JP-A-61-141452, and JP-A-02-120865, the toner includes graphite, magnetite, polypyrrole conductive particles, polyaniline. In addition to the disclosure of adding conductive particles, it is known to add a wide variety of conductive fine particles to the toner.
[0027]
However, these proposals also have room for further improvement in the above-described problems when toner particles having a smaller particle diameter are used in order to increase the resolution.
[0028]
In recent years, space saving, cost reduction, and low power consumption due to downsizing of copiers and printers have become very important issues, and the fixing device needs to be downsized, simplified and low power consumption. It has been said that. Along with this, the toner reduces the viscosity of the toner at the time of melting, increases the adhesion area with the fixing substrate, or contains a release agent so that sufficient fixability can be exhibited with a low heat quantity and low pressure. There is a need for improved fixing properties. For this reason, it is requested | required that Tg and molecular weight of binder resin to be used should be made low. However, toners mainly composed of soft components are difficult to achieve both high-temperature offset resistance, and further have problems such as low developability during long-term use and easy adhesion to the photoreceptor.
[0029]
On the other hand, with regard to improvement in fixability, for example, in Japanese Patent Laid-Open No. 6-282098, a melt viscosity measured by a flow tester of a binder resin of magnetic toner is specified, and a toner having excellent fixability is proposed. Yes. In this publication, a magnetic material to be used is surface-treated with inorganic fine particles and combined with a binder resin having a low melt viscosity to achieve both fixability, offset resistance and developability. However, in the case of toner with excellent transferability and high circularity, compatibility with developability is insufficient.
[0030]
Japanese Patent Laid-Open No. 8-137262 proposes a low-melting-point toner that defines a softening point temperature measured by a flow tester. This publication proposes a photoconductor scraping means as a means for suppressing toner filming on a photoconductor that is likely to occur by using a low-melting toner, and developability and durability of the toner itself. Is not a solution.
[0031]
Furthermore, Japanese Patent Application Laid-Open No. 2000-284534 proposes a toner having excellent fixability containing a resin that defines a softening point temperature measured by a flow tester. This publication specifically describes a non-magnetic toner, and when applied to a magnetic toner, a sufficient effect cannot be obtained.
[0032]
On the other hand, as a conventional image forming method, many methods such as an electrostatic recording method, a magnetic recording method, and a toner jet method are known. For example, in electrophotography, it is generally possible to form an electrostatic latent image on a photoreceptor using a photoconductive material as an image carrier by various means, and then develop the latent image with toner. As a visual image, a toner image is transferred to a recording medium such as paper as necessary, and then the toner image is fixed on the recording medium by heat, pressure, or the like to obtain an image.
[0033]
As a method for visualizing an electrostatic latent image, a cascade development method, a magnetic brush development method, a pressure development method, and the like are known. Further, there is also used a method in which a magnetic toner is used and a rotating sleeve having a magnetic pole at the center is used to fly between the photosensitive member and the sleeve by an electric field.
[0034]
For example, in Japanese Patent Application Laid-Open No. 54-43027, a magnetic toner is thinly applied on a magnetic toner carrier, and this is triboelectrically charged, and then is brought very close to an electrostatic latent image under the action of a magnetic field, and There is disclosed a method of developing without facing each other and developing. According to this method, the magnetic toner is sufficiently applied to the magnetic toner carrier by thinly coating the magnetic toner, so that sufficient magnetic charging of the magnetic toner is possible, and development can be performed without contacting the electrostatic latent image while supporting the magnetic toner by magnetic force. Therefore, the transfer of the magnetic toner to the non-image portion, so-called fogging, is suppressed, and a high-definition image can be obtained.
[0035]
As for the transfer efficiency, generally, when a toner having a high and uniform charge amount distribution is used, the transfer efficiency becomes high. However, as described above, the magnetic toner still needs to be improved with respect to such a toner. have.
[0036]
Also, spherical toner is said to have high transfer efficiency due to its shape. In this regard, Japanese Patent Application Laid-Open No. 61-279864 proposes to define the shape factors SF1 and SF2, and Japanese Patent Application Laid-Open No. 63-235953 proposes a magnetic toner that is spheroidized by a mechanical impact force. ing. However, the transfer efficiency of these toners is still insufficient and further improvement is required.
[0037]
On the other hand, such a spherical toner has an advantage that the transfer efficiency is higher than that of the pulverized toner, but has a property that it is difficult to be cleaned because of the spherical shape. Further, as described above, the toner particle diameter is directed toward the smaller particle diameter, and it is more difficult to completely clean the transfer residual toner. However, through the improvement of the cleaning device or the like, it is possible to suppress the toner slipping to a level that does not cause a big problem. In the image forming method having the conventional corona charging method, an image having no practical problem can be formed. Is possible.
[0038]
However, in recent years, from the viewpoint of environmental protection, primary charging using a corona discharge, which has been used in the past, and primary transfer (contact charging) using a photoreceptor contact member that has great advantages such as low ozone and low power. ) And transfer processes (contact transfer) are becoming mainstream.
[0039]
For example, Japanese Patent Laid-Open Nos. 63-149669 and 2-123385 have been proposed. These relate to a contact charging method and a contact transfer method, a conductive elastic roller is brought into contact with the photosensitive member, and the surface of the photosensitive member is uniformly charged while applying a voltage to the conductive roller. After obtaining a toner image by the development process, the transfer material is passed while pressing another conductive roller to which a voltage is applied to the photoconductor, and the toner image on the photoconductor is transferred to the transfer material. A copy image is obtained through a fixing process.
[0040]
However, it has been found that the contact charging method or the contact transfer method has an alarming problem, unlike the case of using corona discharge.
[0041]
Specifically, first, in the case of the contact charging method, the charging member is pressed against the surface of the photoreceptor with a pressing pressure. For this reason, the presence of untransferred residual toner, ie, transfer residual toner, makes it difficult to maintain sufficient contact between the contact charging member and the photosensitive member, and the chargeability deteriorates. Toner transfer, i.e., fog, is likely to occur. Further, since toner accumulates on the charging member, the photosensitive member cannot be uniformly charged, resulting in a decrease in image density and a harshness. Further, since the charging member is pressed against the toner, toner fusing is likely to occur, and these tendencies become more pronounced as the amount of toner remaining after transfer increases.
[0042]
Next, in the case of the contact transfer method, the transfer member is brought into contact with the photoconductor through the transfer member at the time of transfer, so that the toner image is pressed against the transfer material when the toner image formed on the photoconductor is transferred to the transfer material. In other words, a problem of partial transfer failure called so-called transfer omission occurs. In addition, as a recent technology direction, there has been a demand for higher resolution and higher definition development methods, and in order to respond to these demands, progress is being made toward reducing the particle size of toner. Thus, the smaller the toner particle size, the greater the adhesion force (mirror power, van der Waals force, etc.) of the toner particles to the photoreceptor as compared to the Coulomb force applied to the toner particles in the transfer process, resulting in transfer. The residual toner increases, and the transfer failure tends to be further deteriorated.
[0043]
As described above, in an image forming method using a contact charging method and a contact transfer method that are very preferable in consideration of the environment, a magnetic toner having high transferability, excellent charging stability, and hardly causing toner fusion, and an image forming method Development is desired.
[0044]
On the other hand, for the toner having high transfer efficiency as described above, a technique called development / cleaning or cleanerless has been proposed as a system without waste toner.
[0045]
However, the conventional technology relating to development / cleaning or cleanerless mainly focuses on positive memory, negative memory, and the like due to the influence of residual toner on the image as disclosed in Japanese Patent Laid-Open No. 5-2287. is there. However, with the progress of the use of electrophotography, there is a need to transfer toner images to various recording media. In this sense, it is not satisfactory for various recording media.
[0046]
JP-A-59-133573, JP-A-62-203182, JP-A-63-133179, JP-A-64-20587 are disclosed in which technologies related to cleanerless are disclosed. There are JP-A-2-302277, JP-A-5-2289, JP-A-5-53482, JP-A-5-61383, etc., but a desirable image forming method is not described, and the toner configuration Is not mentioned.
[0047]
As a development method preferably applied to development / cleaning or cleaner-less, conventionally, in development / cleaning that essentially does not have a cleaning device, a configuration in which the surface of the image carrier is rubbed with toner and a toner carrier has been essential. Many contact development methods in which toner or toner contacts an image carrier have been studied. This is because it is considered that a configuration in which the toner or toner comes into contact with the image carrier and rubs in order to collect the transfer residual toner in the developing unit is considered advantageous. However, the development / cleaning or cleaner-less process using the contact development method causes toner deterioration, toner carrier surface deterioration, photoreceptor surface deterioration or wear, etc. due to long-term use, and a sufficient solution to durability characteristics has been made. Not. Therefore, a development and cleaning method using a non-contact development method is desired.
[0048]
Here, consider the case where the contact charging method is applied to a developing and cleaning method and a cleanerless image forming method. In the developing and cleaning method and the cleanerless image forming method, since there is no cleaning member, the transfer residual toner remaining on the photosensitive member directly contacts the contact charging member and is attached or mixed. Further, in the case of a charging method in which the discharge charging mechanism is dominant, adhesion to the charging member is also deteriorated due to toner deterioration due to discharge energy. When generally used insulating toner adheres to or mixes with the contact charging member, the chargeability is reduced.
[0049]
In the charging method in which the discharge charging mechanism is dominant, the charging property of the member to be charged is abruptly generated since the toner layer attached to the surface of the contact charging member becomes a resistance that inhibits the discharge voltage. On the other hand, in the charging method in which the direct injection charging mechanism is dominant, the transfer residual toner adhering or mixed reduces the contact probability between the surface of the contact charging member and the object to be charged, thereby charging the object to be charged. Sex is reduced.
[0050]
This decrease in the uniform chargeability of the object to be charged results in a decrease in the contrast and uniformity of the electrostatic latent image after image exposure, thereby decreasing the image density or increasing the fog.
[0051]
In the development and cleaning method and the cleanerless image forming method, the charge polarity and charge amount of the transfer residual toner on the photoreceptor are controlled, and the transfer residual toner is stably recovered in the development process. The important point is not to deteriorate the charge, and the charging polarity and the charge amount of the transfer residual toner are controlled by the charging member.
[0052]
This will be specifically described by taking a general laser printer as an example. In the case of reversal development using a charging member to which a negative polarity voltage is applied, a negatively chargeable photoreceptor and a negatively charged toner, the image visualized by the positive polarity transfer member is transferred to a recording medium in the transfer process. However, depending on the relationship between the type of recording medium (difference in thickness, resistance, dielectric constant, etc.) and the image area, the charging polarity of the residual toner varies from positive to negative. However, due to the negative polarity charging member when charging the negatively chargeable photoconductor, even the toner remaining on the transfer surface as well as the remaining toner on the transfer surface is uniformly negative even if it is shifted to the positive polarity in the transfer process. Charge polarity can be made uniform.
[0053]
Therefore, when reversal development is used as the developing method, the toner remaining in the transfer is left negatively charged in the bright portion potential portion where the toner is to be developed, and the dark portion potential where the toner is not to be developed is Due to the development electric field, the toner is attracted toward the toner carrying member, and the transfer residual toner is collected without remaining on the photosensitive member having the dark portion potential. That is, by controlling the charging polarity of the toner remaining on the transfer simultaneously with the charging of the photosensitive member by the charging member, the developing / cleaning and cleanerless image forming method is established.
[0054]
However, if the transfer residual toner adheres to or mixes with the contact charging member in excess of the control capability of the toner charging polarity of the contact charging member, the charging polarity of the transfer residual toner cannot be made uniform, and the toner is collected by the developing member. Difficult to do. Even if the toner carrier is recovered by mechanical force such as rubbing, if the charge of the residual toner is not uniform, the chargeability of the toner on the toner carrier will be adversely affected, and the development characteristics Reduce.
[0055]
That is, in the development and cleaning and cleanerless image forming methods, the charge control characteristics of the transfer residual toner when passing through the charging member and the adhesion / mixing characteristics to the charging member are closely related to the durability characteristics and the image quality characteristics.
[0056]
Japanese Patent Publication No. 7-99442 also discloses a configuration in which powder is applied to a contact surface of a contact charging member with a surface to be charged in order to prevent charging unevenness and perform stable uniform charging. However, the contact charging member (charging roller) is driven and rotated (without speed difference driving) by the member to be charged (photosensitive member), and generation of ozone products is remarkably reduced as compared with a corona charger such as Scorotron. However, the charging principle is still mainly the discharge charging mechanism as in the case of the roller charging described above. In particular, in order to obtain more stable charging uniformity, a voltage obtained by superimposing an AC voltage on a DC voltage is applied, and therefore, more ozone products are generated due to discharge. Therefore, when the apparatus is used for a long time, adverse effects such as image flow due to ozone products tend to appear. Further, when applied to a cleanerless image forming apparatus, it becomes difficult for the applied powder to uniformly adhere to the charging member due to the mixing of the transfer residual toner, and the effect of uniform charging is reduced.
[0057]
Japanese Patent Laid-Open No. 5-150539 discloses that in an image forming method using contact charging, toner particles and silica fine particles that could not be cleaned by a cleaning means such as a blade while repeating image formation for a long time are used as charging means. In order to prevent charging inhibition due to adhesion and accumulation on the surface, it is disclosed that the toner contains at least visible particles and conductive fine particles having an average particle size smaller than the visible particles. However, the contact charging or proximity charging used here is based on the discharge charging mechanism, and not the direct injection charging mechanism, but has the above-described problems due to discharge charging.
[0058]
In addition, when applied to a cleanerless image forming apparatus, compared to the case where the cleaning mechanism is provided, the large amount of conductive fine particles and transfer residual toner have an influence on the charging property due to passing through the charging step. No consideration is given to the recoverability of the conductive fine particles and transfer residual toner in the development process, and the influence of the collected conductive fine particles and transfer residual toner on the development characteristics of the toner. Further, when the direct injection charging mechanism is applied to the contact charging, a necessary amount of conductive fine particles is not supplied to the contact charging member, and charging failure occurs due to the influence of the transfer residual toner.
[0059]
Also, with proximity charging, it is difficult to uniformly charge the photoconductor with a large amount of conductive fine particles and transfer residual toner, and the effect of leveling the pattern of residual transfer toner cannot be obtained. A pattern ghost for shading is generated. Further, when the power supply is interrupted or a paper jam occurs during image formation, the contamination inside the machine due to toner becomes significant.
[0060]
Japanese Patent Laid-Open No. 11-15206 discloses that a development and cleaning image forming method improves the development and cleaning performance by improving the charge control characteristics when the transfer residual toner passes through a charging member. An image forming method using a toner having toner particles containing a specific azo-based iron compound and inorganic fine powder has been proposed. Further, in the development / cleaning image forming method, it has also been proposed to improve the development / cleaning performance by reducing the amount of residual transfer toner with a toner having excellent transfer efficiency that defines the shape factor of the toner.
[0061]
However, the contact charging used here is also due to the discharge charging mechanism, and not the direct injection charging mechanism, but has the above-mentioned problems due to discharge charging. Furthermore, even though these proposals have the effect of suppressing the chargeability deterioration due to the transfer residual toner of the contact charging member, the effect of positively increasing the chargeability cannot be expected.
[0062]
Further, among commercially available electrophotographic printers, a developing and cleaning image forming apparatus that uses a roller member that abuts on the photoreceptor between the transfer process and the charging process to assist or control the transfer residual toner recovery in development. There is also. Such an image forming apparatus exhibits good developing and cleaning properties and can greatly reduce the amount of waste toner, but the cost is increased and the advantages of developing and cleaning are impaired in terms of miniaturization.
[0063]
On the other hand, in Japanese Patent Application Laid-Open No. 10-307456, a developing and cleaning image forming method using a direct injection charging mechanism for a toner containing electrically conductive charge accelerating particles having a particle size of 1/2 or less of the toner particle size An image forming apparatus applied to the above is disclosed. According to this proposal, it is possible to significantly reduce the amount of waste toner without generating a discharge product, and to obtain a developing and cleaning image forming apparatus that is advantageous for downsizing at low cost. Alternatively, a good image that does not cause diffusion can be obtained.
[0064]
In Japanese Patent Application Laid-Open No. 10-307421, a toner containing conductive particles having a particle size of 1/50 to 1/2 of the toner particle size is applied to a developing and cleaning image forming method using a direct injection charging mechanism. An image forming apparatus in which conductive particles have a transfer promoting effect is disclosed.
[0065]
Furthermore, in Japanese Patent Application Laid-Open No. 10-307455, the particle size of the conductive fine powder is set to 10 nm in order to make the particle size of the conductive fine powder smaller than the size of one pixel of the constituent pixels and to obtain better charging uniformity. It is described that it is set to ˜50 μm.
[0066]
In Japanese Patent Laid-Open No. 10-307457, in consideration of human visual characteristics, the conductive particles are made to be about 5 μm or less, preferably 20 nm to 5 μm in order to make it difficult to visually recognize the influence on the image of the poorly charged portion. It is described to do.
[0067]
Further, according to Japanese Patent Laid-Open No. 10-307458, the particle size of the conductive fine powder is set to be equal to or smaller than the toner particle size, so that the development of the toner is inhibited during development, or the development bias is passed through the conductive fine powder. It is possible to prevent leakage and eliminate image defects, and by setting the particle size of the conductive fine powder to be larger than 0.1 μm, the conductive fine powder is embedded in the image carrier to block exposure. In other words, a developing and cleaning image forming method using a direct injection charging mechanism that realizes an excellent image recording is described.
[0068]
According to Japanese Patent Laid-Open No. 10-307456, conductive fine powder is externally added to the toner, and at least the conductive fine powder contained in the toner at the contact portion between the flexible contact charging member and the image carrier. However, it adheres to the image carrier in the development step and remains on the image carrier after the transfer step and is carried and intervened, so that a good image that does not cause poor charging and light shielding of image exposure can be obtained. A developing and cleaning image forming apparatus is disclosed.
[0069]
However, these proposals also have room for further improvement in performance when toner particles having a smaller particle diameter are used in order to improve stable performance and resolution in repeated use over a long period of time.
[0070]
[Problems to be solved by the invention]
An object of the present invention is to provide a magnetic toner and an image forming method that solve the above-described problems of the prior art.
[0071]
That is, an object of the present invention is to provide a magnetic toner and an image forming method that have good fixability, excellent charging stability, high image density even in long-term use, and capable of obtaining a high-definition image. It is in.
[0072]
An object of the present invention is to provide an image forming method capable of forming a good developing and cleaning image.
[0073]
Another object of the present invention is to provide an image forming method capable of forming a cleaner-less image which can stably obtain good chargeability.
[0074]
[Means for Solving the Problems]
The present invention includes toner particles having at least a binder resin, a release agent, and magnetic powder, has a weight average particle diameter of 3 to 20 μm, and a magnetization strength of 10 to 50 Am at a magnetic field of 79.6 kA / m.²/ Kg of the magnetic toner, the average circularity of the magnetic toner is 0.970 or more, and the ratio of the weight average particle diameter to the number average particle diameter of the magnetic toner is 1.40 or less. The liberation rate of iron and iron compound is 0.05% to 3.00%, and the viscosity of the magnetic toner measured by a flow tester is 1.0 × 10^FiveThe temperature at which Pa.s is 80 to 120 ° C. and 1.0 × 10^FourThe present invention relates to a magnetic toner characterized in that the temperature at which Pa · s is 100 to 150 ° C.
[0075]
The present invention also includes a charging step for charging the image carrier, an electrostatic latent image forming step for writing image information as an electrostatic latent image on the charged image carrier, and an image carrier for holding the electrostatic latent image on the surface. The developing unit is formed by arranging the body and the magnetic toner carrier carrying the magnetic toner on the surface with a certain distance, and the magnetic toner is coated on the surface of the magnetic toner carrier to a thickness thinner than the above-mentioned distance. A developing step of transferring magnetic toner to an electrostatic latent image to form a toner image in a developing portion to which an alternating electric field is applied, and a transfer step of transferring the toner image to a recording medium. In the image forming method in which image formation is repeatedly performed, the magnetic toner includes toner particles having at least a binder resin, a release agent, and magnetic powder, has a weight average particle diameter of 3 to 10 μm, and a magnetic field 79. .6 kA / m The strength of the reduction is 10~50Am²Magnetic toner having an average circularity of 0.970 or more, a ratio of a weight average particle diameter to a number average particle diameter of 1.40 or less, and a liberation ratio of iron and an iron compound of 0. 05 to 3.00%, viscosity measured by flow tester is 1.0 × 10^FiveThe temperature at which Pa.s is 80 to 120 ° C. and 1.0 × 10^FourThe magnetic toner is characterized in that the temperature at which Pa · s is 100 to 150 ° C. The charging step forms an image by applying a voltage to a charging member that forms a contact portion with the image carrier and contacts it. The present invention relates to an image forming method, which is a step of charging a carrier.
[0076]
DETAILED DESCRIPTION OF THE INVENTION
First, the magnetic toner of the present invention will be described.
As a result of intensive studies by the present inventors, it has been found that when the average circularity of the magnetic toner is 0.970 or more, the transfer property of the magnetic toner is very good. This is presumably because the contact area between the toner particles and the photoconductor is small, and the adhesion force of the toner particles to the photoconductor due to the mirroring force, van der Waals force, or the like is reduced. Further, since the circularity of the toner is as high as 0.970 or more, the magnetic toner can form uniform thin spikes at the developing portion and can be developed faithfully to the latent image, and an improvement in image quality can be expected.
[0077]
The magnetic toner of the present invention preferably has a mode circularity of 0.99 or more in the circularity distribution of the magnetic toner. A mode circularity of 0.99 or more means that most of the toner particles have a shape close to a true sphere, and the above action becomes more remarkable, which is preferable.
[0078]
Therefore, if such a magnetic toner is used, the transfer efficiency is high and the residual toner is reduced, so that the amount of toner at the pressure contact portion between the charging member and the photosensitive member is very small, stable charging is performed and toner fusion is performed. Is prevented, and image defects are considered to be significantly suppressed.
[0079]
These effects are more prominent in an image forming method including a contact transfer process in which transfer loss is likely to occur.
[0080]
The average circularity in the present invention is used as a simple method for quantitatively expressing the shape of the particles, and is an index of the degree of unevenness of the magnetic toner. In the present invention, the degree of circularity (Ci) of each particle measured for a particle group having a circle-equivalent diameter of 3 μm or more is obtained by the following equation (1), and further measured as shown by the following equation (2): The value obtained by dividing the sum of the circularity by the total number of particles (m) is defined as the average circularity (C). The average circularity in the present invention is 1.000 when the magnetic toner is a perfect sphere, and the average circularity becomes smaller as the surface shape of the magnetic toner becomes more complicated.
[0081]
[Expression 1]

[Expression 2]

[0082]
The average circularity in the present invention can be measured by using, for example, a flow type particle image analyzer “FPIA-1000” manufactured by Toago Medical Electronics.
[0083]
In addition, the mode circularity is obtained by dividing the circularity from 0.40 to 1.00 into 61 units every 0.01, and assigning the measured particle circularity to each divided range according to each circularity. This is the circularity of the peak having the maximum frequency value in the frequency distribution.
[0084]
In addition, after calculating the circularity of each particle, “FPIA-1000”, which is the measurement apparatus, calculates the average circularity and the mode circularity, and the circularity is 0.40 to 1 depending on the circularity obtained. .00 is divided into 61 classes, and a calculation method is used in which the average circularity and the mode circularity are calculated using the center value and frequency of the dividing points. However, an error between each value of the average circularity and the mode circularity calculated by this calculation method and each value of the average circularity and the mode circularity calculated by the calculation formula that directly uses the circularity of each particle described above. Is very small and substantially negligible, and in the present invention, for the reasons of data handling such as short calculation time and simplified calculation formula, Such a calculation method that is partially changed by using the concept of a calculation formula that directly uses the circularity may be used.
[0085]
Specific examples of the procedure for measuring the average circularity and the mode circularity are as follows.
A dispersion is prepared by dispersing about 5 mg of magnetic toner in 10 mL of water in which about 0.1 mg of a surfactant is dissolved, and the dispersion is irradiated with ultrasonic waves (20 KHz, 50 W) for 5 minutes. The measurement is performed with the above apparatus at 5000 to 20,000 / μL, and the average circularity and mode circularity of a particle group having a circle-equivalent diameter of 3 μm or more are obtained.
[0086]
In the present invention, the reason why the circularity is measured only for the particle group having an equivalent circle diameter of 3 μm or more is that the particle group of the external additive existing independently of the toner particles in the particle group having an equivalent circle diameter of less than 3 μm. This is because the circularity of the toner particle group cannot be accurately estimated due to the influence of such a large amount.
[0087]
The magnetic toner of the present invention is characterized in that the liberation rate of iron and iron compound is 0.05 to 3.00%. This liberation rate is preferably 0.05 to 2.00%, more preferably 0.05 to 1.50%, and still more preferably 0.05 to 1.00%. As described above, the magnetic toner of the present invention contains magnetic powder. Therefore, in the present invention, the liberation rate of iron and iron compound specifically indicates the ratio of the number of magnetic powders liberated from the toner particles.
[0088]
The liberation rate of iron and iron compounds can be measured, for example, by introducing a magnetic toner into plasma and measuring the emission spectrum at this time. In this case, the liberation rate is a value defined by the following equation based on the simultaneous emission of carbon atoms that are constituent elements of the binder resin and light emission of iron atoms.
[0089]
[Equation 3]

[0090]
Here, “simultaneous light emission” means that light emission of iron atoms emitted within 2.6 msec from light emission of carbon atoms is simultaneous light emission, and light emission of iron atoms thereafter is light emission of only iron atoms.
[0091]
In the present invention, since a large amount of magnetic powder is contained, the fact that carbon atoms and iron atoms emit light simultaneously means that the toner particles contain magnetic powder. In other words, it means that the magnetic powder is free from the toner particles.
[0092]
The liberation rate of the iron and the iron compound can be measured based on the principle described on pages 65-68 of the Japan Hardcopy 97 collection of papers. In such a measurement, for example, a particle analyzer (PT1000: Yokogawa) (Electric Co., Ltd.) is preferably used. Specifically, the apparatus introduces fine particles such as toner into the plasma one by one and can know the element of the luminescent material, the number of particles, and the particle size of the particles from the emission spectrum of the fine particles.
[0093]
A specific measuring method using the measuring apparatus is as follows. Measurement is performed using a helium gas containing 0.1% oxygen at 23 ° C. in an environment of 60% humidity, and the toner sample is left to stand overnight in the same environment and used for measurement. Also, channel 1 measures carbon atoms (measurement wavelength 247.860 nm, K factor uses recommended value), and channel 2 measures iron atoms (measurement wavelength 239.56 nm, K factor uses 3.3964). In this scan, sampling is performed so that the number of light emission of carbon atoms is 1000 to 1400, and the scan is repeated until the total number of light emission of carbon atoms reaches 10,000 or more, and the number of light emission is integrated. At this time, in the distribution in which the number of light emission of the carbon element is taken on the vertical axis and the cube root voltage of the carbon element is taken on the horizontal axis, the distribution has one maximum and further has a valley. Sampling and measurement. Based on this data, the noise cut level of all elements is set to 1.50 V, and the liberation rate of iron and iron compounds is calculated using the above formula. The same measurement was performed in the examples described later.
[0094]
In addition, toner particles may contain materials other than inorganic compounds containing iron atoms, such as azo-based iron compounds that are charge control agents. These compounds are organic compounds simultaneously with iron atoms. Since the carbon inside also emits light simultaneously, it is not counted as a free iron atom.
[0095]
As a result of investigations by the present inventors, there is a deep relationship between the liberation rate of iron and iron compounds and the exposure amount on the toner particle surface, and if the amount of free magnetic powder is 3.00% or less, it is almost the case. It has been found that exposure of the magnetic powder to the toner particle surface is suppressed and that the charge amount is high. The liberation rate of iron and iron compounds depends on the degree of hydrophobicity of the magnetic powder, compatibility with the resin, particle size distribution, uniformity of treatment, etc. As an example, the surface treatment of the magnetic powder is non-uniform In this case, the magnetic powder not sufficiently surface-treated (strongly hydrophilic) is likely to be present on the surface layer of the toner particles and part or all of the magnetic powder is released. For this reason, the lower the liberation rate of iron and iron compounds, the higher the charge amount of the magnetic toner tends to be.
[0096]
On the other hand, if the liberation rate is larger than the above range, the charge leakage point becomes excessive, and the charge amount of the toner may be reduced. This tendency becomes particularly remarkable under high temperature and high humidity. In addition, a toner with a low charge amount is not preferable because it causes an increase in fog and lowers transfer efficiency. In addition, such a toner having a large liberation rate of iron and iron compound is slightly inferior in fixability. This is presumably because the magnetic powder having a large specific heat exists on the toner surface or is separated from the toner, so that the heat is not sufficiently transferred to the toner during fixing.
[0097]
On the other hand, if the liberation rate of iron and iron compound is less than 0.05%, it means that the magnetic powder is not substantially liberated from the toner particles. In this way, although the magnetic toner having a low liberation rate of iron and iron compound has a high charge amount, the image density caused by the charge-up of the magnetic toner in the printing of a large number of sheets, especially in the printing of a large number of sheets under low temperature and low humidity Reduction and image roughness.
This is considered to be the following reason.
[0098]
In general, the magnetic toner on the magnetic toner carrier is not completely developed on the photoconductor, and the magnetic toner exists on the magnetic toner carrier even immediately after development. This tendency is particularly strong in jumping development using magnetic toner, and the development efficiency is not so high. Further, as described above, the magnetic toner having a high degree of circularity forms uniform thin spikes at the developing portion, and is developed from the magnetic toner present at the tip of the spike, and the magnetic toner near the magnetic toner carrier is It is thought that it is difficult to develop.
[0099]
Therefore, the magnetic toner in the vicinity of the magnetic toner carrier is repeatedly subjected to frictional charging by the charging member, is charged up, and falls into a vicious circle where it becomes difficult to develop. Further, in such a state, the charging uniformity of the magnetic toner is impaired and the image becomes rough.
[0100]
Here, when a toner having a liberation ratio of iron and iron compound of 0.05% or more is used, the charge up of the magnetic toner is suppressed by the free magnetic powder or the magnetic powder slightly present on the toner particle surface. At the same time, the uniformity of the charge amount of the magnetic toner is promoted, and the roughness is suppressed.
[0101]
For these reasons, in order to stably obtain a high charge amount, the liberation rate of iron and iron compounds needs to be 0.05% to 3.00%.
[0102]
Further, like the magnetic toner of the present invention, the magnetic toner has a high average circularity and a low liberation rate of iron and iron compounds, the magnetic toner has a uniform shape, and the charge amount of the magnetic toner is Due to the synergistic effect of being uniformly high, the transfer efficiency is very high and fog is also very low. Further, the scattering of magnetic toner is reduced, and the image quality is improved. Further, such a magnetic toner is less likely to undergo selective development even during long-term use, and the difference in toner physical properties is less likely to occur before and after use, thereby improving durability.
[0103]
On the other hand, as disclosed in JP-A-5-150539 and JP-A-8-22191, charge-up can be suppressed by externally adding magnetite to the surface of an irregular toner. However, when magnetite is externally added to a magnetic toner having an average circularity of 0.970 or more as in the present invention, fogging is increased and chargeability under high temperature and high humidity is particularly poor. The reason for this is not clear, but low resistance materials such as magnetite are present on the surface of the toner particles in a large amount, and when the toner surface having an average circularity of 0.970 or more is used with a relatively smooth magnetic toner. This is considered to be because the shear is not sufficiently applied when magnetite is mixed, and magnetite does not uniformly adhere to the toner particle surface, resulting in a difference in the amount of adhesion between toner particles.
[0104]
In the image forming method of the present invention, the magnetic toner preferably has a weight average diameter of 3 to 20 [mu] m, more preferably 4 to 9 [mu] m, in order to develop finer latent image dots faithfully for higher image quality. It is more preferable. In a toner having a weight average particle size of less than 3 μm, the transfer residual toner on the photoconductor increases due to a decrease in transfer efficiency, and it becomes difficult to suppress the photoconductor scraping and toner fusion in the contact charging step. Furthermore, in addition to an increase in the surface area of the magnetic toner as a whole, the fluidity and stirrability as a powder decrease, and it becomes difficult to uniformly charge individual toner particles, so fog and transferability tend to deteriorate. This is not preferable for the magnetic toner used in the present invention because it tends to cause non-uniform image unevenness other than scraping and fusion.
[0105]
Further, when the weight average particle diameter of the magnetic toner exceeds 20 μm, the characters and line images are likely to be scattered and high resolution is difficult to obtain. Further, as the apparatus becomes higher in resolution, toner of 20 μm or more tends to deteriorate the reproduction of one dot.
[0106]
In the magnetic toner of the present invention, it is important that the ratio of the weight average particle diameter to the number average particle diameter, that is, the ratio of the weight average particle diameter / number average particle diameter (D4 / D1) is 1.40 or less. More preferably, it is 1.35 or less.
[0107]
The ratio of the weight average particle diameter / number average particle diameter being larger than 1.40 means that there are a large number of fine powders and coarse particles in the magnetic toner. It is not preferable because it becomes wide.
[0108]
On the other hand, in the magnetic toner having a weight average particle diameter / number average particle diameter ratio of 1.40 or less, particularly 1.35 or less, the magnetic toner has an average circularity of 0.970 or more. In addition, due to the synergistic effect of the particle size distribution that the particle diameters are uniform, the heading at the developing portion becomes very uniform, and an image with excellent dot reproducibility can be obtained.
[0109]
Here, the average particle size and particle size distribution of the magnetic toner can be measured by various methods such as Coulter Counter TA-II type or Coulter Multisizer (manufactured by Coulter Co.). In the present invention, Coulter Multisizer (Coulter Co., Ltd.) can be used. It is preferable to perform measurement by connecting an interface (manufactured by Nikka) and a PC 9801 personal computer (manufactured by NEC) that output the number distribution and volume distribution. In the above measurement, a 1% NaCl aqueous solution is prepared using first grade sodium chloride as the electrolyte. As the electrolytic solution, for example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used.
[0110]
As a specific measurement method for the above measurement, 0.1 to 5 mL of a surfactant, preferably alkylbenzene sulfonate, is added as a dispersant to 100 to 150 mL of the electrolytic aqueous solution, and 2 to 20 mg of a measurement sample is further added. The electrolytic solution in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the volume and number of toner particles of 2 μm or more are measured using the 100 μm aperture as the aperture by the Coulter Multisizer. Distribution and number distribution are calculated. Then, the volume-based weight average particle diameter (D4) obtained from the volume distribution and the number-based length average particle diameter obtained from the number distribution, that is, the number average particle diameter (D1) are obtained. The same measurement was performed in the examples described later.
[0111]
Further, the magnetic toner of the present invention has a viscosity of 1.0 × 10 5 as measured by a flow tester.^FiveThe temperature at which Pa.s is 80 to 120 ° C. and 1.0 × 10^FourThe temperature at which Pa · s is obtained is 100 to 150 ° C. Furthermore, 1.0 × 10^FiveThe temperature at which Pa · s is 80 to 110 ° C., 1.0 × 10^FourThe temperature at which Pa · s is obtained is preferably 100 to 140 ° C.
[0112]
Viscosity is 1.0 × 10^FiveWhen the temperature at which Pa · s is less than 80 ° C., or 1.0 × 10^FourWhen the temperature at which Pa · s is less than 100 ° C., the low-temperature fixability is excellent. However, in such a low-viscosity magnetic toner, the magnetic powder in the vicinity of the toner particle surface is exposed and further dropped off. May end up. In addition, the liberation rate fluctuates due to durability, for example, because the external additive is embedded. As a result, the flowability and chargeability of the magnetic toner may change, and developability and transferability may be impaired.
[0113]
In particular, in the case of a magnetic toner having excellent fluidity and transferability, such as the present invention and having a high degree of circularity, the contact area with the developing unit or the charging member becomes large, so the above phenomenon is more likely to occur. turn into. Furthermore, 1.0 × 10^FourIf the temperature at which Pa · s is less than 100 ° C., the offset resistance may be impaired.
[0114]
Conversely, the viscosity is 1.0 × 10^FiveWhen the temperature for Pa · s exceeds 120 ° C, or 1.0 × 10^FourIf the temperature at which Pa · s exceeds 150 ° C., the fluctuation of the liberation rate can be suppressed, but the low-temperature fixability is impaired, which is not preferable. That is, the present invention provides low temperature fixability by balancing the circularity of the magnetic toner, the liberation rate of iron and iron compounds, the viscosity defined by temperature, and the ratio of weight average particle diameter / number average particle diameter. Since the chargeability is stable without impairing the image quality, a high-quality image whose development / transferability does not change due to durability can be stably obtained.
[0115]
The change in chargeability is, for example, broadening of the charge amount distribution. By broadening the charge amount distribution, not only a low charge amount magnetic toner but also toner particles charged in the opposite polarity are increased. This magnetic toner is not transferred to the transfer material and cannot be confirmed on the image, but is not preferable in terms of toner consumption. Furthermore, the cleanerless image forming method according to the present invention is not preferable because the load on the charging member is increased.
[0116]
The viscosity of the magnetic toner of the present invention as measured by a flow tester can be measured by the following means.
Using an elevated flow tester (for example, Shimadzu flow tester CFT-500D), first, apply a load of 10 kgf (= 98N) to a magnetic toner of about 1.5 g formed using a pressure molding device with a plunger at a constant temperature. The nozzle is pushed out from a nozzle having a diameter of 1 mm and a length of 1 mm, thereby measuring the plunger descending amount (outflow speed) of the flow tester. This outflow rate is measured at each temperature (temperature range of 60 ° C. to 180 ° C. at intervals of 5 ° C.), and the viscosity η ′ is obtained from this value by the following equation.
[0117]
[Expression 4]

[0118]
The magnetic toner of the present invention can also be manufactured by a pulverization method. When the pulverization method is used, a known method is used. For example, a binder resin, a magnetic powder, a release agent, and a charge may be charged depending on the case. Using a heat kneader such as a heating roll, kneader, or extruder after thoroughly mixing the components necessary for the magnetic toner, such as a control agent and colorant, and other additives by a mixer such as a Henschel mixer and a ball mill. Toner particles that are melt-kneaded and other magnetic toner materials such as magnetic powder are dispersed or dissolved in resins that are mutually melted, cooled, solidified, pulverized, classified, and surface-treated as necessary. Can be obtained. Either the classification or the surface treatment may be performed first. In the classification step, it is preferable to use a multi-division classifier in terms of production efficiency.
[0119]
The pulverization step can be performed by a method using a known pulverizer such as a mechanical impact type or a jet type. In order to obtain a magnetic toner having a specific circularity according to the present invention, it is preferable to further heat and pulverize or to supplementarily apply a mechanical impact. Further, a hot water bath method in which finely pulverized (classified as necessary) toner particles are dispersed in hot water, a method of passing in a hot air stream, or the like may be used.
[0120]
Examples of means for applying mechanical impact force include a method using a mechanical impact type pulverizer such as a kryptron system manufactured by Kawasaki Heavy Industries, Ltd. and a turbo mill manufactured by Turbo Industry Co. A method of applying mechanical impact force to the toner particles by a force such as a compressive force or a frictional force by pressing the toner particles against the inside of the casing by a centrifugal force with a blade rotating at high speed, such as a device such as a hybridization system made by the manufacturer. It is done.
[0121]
In the case of using the mechanical impact method, a thermomechanical impact in which the processing temperature is a temperature in the vicinity of the glass transition point Tg (Tg ± 10 ° C.) of the toner particles is preferable from the viewpoint of preventing aggregation and productivity. More preferably, it is particularly effective to improve the transfer efficiency to carry out at a temperature in the range of the glass transition point Tg ± 5 ° C. of the toner particles.
[0122]
The binder resin used in the production of the magnetic toner according to the present invention by a pulverization method includes styrene such as polystyrene and polyvinyltoluene, and a homopolymer of a substituted product thereof; styrene-propylene copolymer, styrene-vinyltoluene copolymer Styrene-vinyl naphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-dimethyl acrylate Aminoethyl copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-dimethylaminoethyl methacrylate copolymer, styrene-vinyl Methyl ether copolymer, styrene-vinyl Styrene copolymers such as tilether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-maleic acid copolymer, styrene-maleic acid ester copolymer Combined; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, silicone resin, polyester resin, polyamide resin, epoxy resin, polyacrylic acid resin, rosin, modified rosin, temper resin, phenol resin, fat Aromatic or alicyclic hydrocarbon resins, aromatic petroleum resins, paraffin wax, carnauba wax and the like can be used alone or in combination. In particular, a styrene copolymer and a polyester resin are preferable in terms of development characteristics, fixing properties, and the like.
[0123]
The glass transition temperature (Tg) of the magnetic toner is preferably 40-80 ° C, more preferably 45 ° C-70 ° C. If the Tg is lower than 40 ° C., the storage stability of the magnetic toner tends to be lowered, and if it is higher than 80 ° C., the fixability may be inferior. The glass transition point of the magnetic toner can be measured using a high-precision internal heat input compensation type differential scanning calorimeter such as DSC-7 manufactured by PerkinElmer. The measurement method at this time is performed according to ASTM D3418-8. In the present invention, the DSC curve measured when the sample is heated once and then the previous history is taken, rapidly cooled, and heated again at a temperature rising rate of 10 ° C./min and a temperature of 30 to 200 ° C. is used. .
[0124]
In addition, the magnetic toner according to the present invention is a method for obtaining a spherical toner by atomizing a molten mixture into air using a disk or a multi-fluid nozzle described in JP-B-56-13945, etc. The emulsion polymerization method represented by the dispersion polymerization method for directly producing a toner using an aqueous organic solvent in which the polymer obtained in 1 is insoluble or the soap-free polymerization method for producing the toner by directly polymerizing in the presence of a water-soluble polar polymerization initiator, etc. The toner can also be manufactured by a method of manufacturing toner.
[0125]
The magnetic toner of the present invention can also be produced by the pulverization method as described above. However, the toner particles obtained by this pulverization method are generally indefinite shape, which is an essential requirement for the magnetic toner according to the present invention. In order to obtain a physical property of an average circularity of 0.970 or more, it is necessary to perform mechanical / thermal or some special treatment, resulting in poor productivity.
[0126]
Therefore, in the present invention, the toner particles are preferably produced by a polymerization method, particularly a suspension polymerization method. In this suspension polymerization method, a polymerizable monomer and a colorant (in addition, a polymerization initiator, a crosslinking agent, a charge control agent, and other additives as necessary) are uniformly dissolved or dispersed to form a polymerizable monomer system. After that, this polymerizable monomer system is dispersed in a continuous layer (for example, an aqueous phase) containing a dispersion stabilizer by using a suitable stirrer, and a polymerization reaction is simultaneously performed, whereby toner particles having a desired particle size are obtained. Is what you get.
[0127]
The toner obtained by this suspension polymerization method (hereinafter referred to as polymerized toner) has an average circularity of 0.970 or more and a mode circularity of 0.99 or more because individual toner particle shapes are almost spherical. In addition, it is easy to obtain a magnetic toner satisfying the essential physical property requirements, and the magnetic toner has a high transferability because the distribution of charge amount is relatively uniform.
[0128]
However, even if a normal magnetic powder is contained in the polymerized toner, a large number of magnetic powders are present on the surface of the toner particles, and the charging characteristics of the toner particles are remarkably deteriorated. Furthermore, due to the strong interaction between the magnetic powder and water during the production of the suspension polymerization toner, it is difficult to obtain a magnetic toner having a circularity of 0.970 or more, and the magnetic toner has a wide particle size distribution. .
[0129]
This is because (1) the magnetic powder is generally hydrophilic and thus tends to be present on the surface of the toner particles, and (2) the magnetic powder moves randomly when the aqueous solvent is stirred, and the magnetic powder is suspended from the monomer. It is considered that the turbid particle surface is dragged, the shape is distorted, and it is difficult to form a circle. In order to solve these problems, it is important to modify the surface characteristics of the magnetic powder.
[0130]
Many proposals have been made regarding the surface modification of magnetic powders used in polymerized toners. As described above, various silane couplings of magnetic powder are disclosed in Japanese Patent Application Laid-Open Nos. 59-200254, 59-2000025, 59-200277, 59-224102, etc. An agent treatment technique has been proposed, and Japanese Patent Application Laid-Open No. 63-250660 discloses a technique for treating silicon element-containing magnetic particles with a silane coupling agent.
[0131]
However, although the release of the magnetic powder is suppressed to some extent by these treatments, there is a problem that it is difficult to make the surface of the magnetic powder hydrophobic uniformly. It is impossible to avoid the generation of magnetic powder that is not formed, and the dispersibility of the magnetic powder is not sufficient and the particle size distribution becomes wide.
[0132]
As an example of using hydrophobic magnetic iron oxide, Japanese Patent Application Laid-Open No. 54-84731 proposes a toner containing magnetic iron oxide treated with alkyltrialkoxysilane. Although the addition of this magnetic iron oxide has certainly improved the electrophotographic characteristics of the magnetic toner, the surface activity of the magnetic iron oxide is originally small, and coalesced particles are formed at the processing stage, and hydrophobicity is not improved. It is uniform and not always satisfactory.
[0133]
Further, when a magnetic powder having a small particle diameter is used, uniform processing becomes more difficult, and further improvement is required to apply to the present invention. Furthermore, in order to improve the inclusion of magnetic powder, when a large amount of treatment agent is used, or when a highly viscous treatment agent is used, the degree of hydrophobicity will surely increase, but the particles will coalesce. On the contrary, dispersibility deteriorates.
[0134]
A magnetic toner manufactured using such a magnetic powder has non-uniform frictional chargeability, resulting in poor fog and transferability.
[0135]
As described above, the conventional polymerized toner using the surface-treated magnetic powder does not always achieve both hydrophobicity and dispersibility, and the image forming method including the contact charging step of the present invention is performed on such polymerized toner. It is difficult to stably obtain a high-definition image even if applied to the above.
[0136]
Therefore, it is preferable that the magnetic powder used in the magnetic toner of the present invention is uniformly hydrophobized with a coupling agent. When hydrophobizing the surface of the magnetic powder, it is very preferable to use a method in which the surface treatment is performed while hydrolyzing the coupling agent while dispersing the magnetic powder to have a primary particle size in an aqueous medium. This hydrophobic treatment method is less likely to cause coalescence between the magnetic powders than in the gas phase, and the repulsive action between the magnetic powders due to the hydrophobic treatment works, and the magnetic powder is almost in the form of primary particles. Surface treatment with.
[0137]
The method of treating the surface of the magnetic powder while hydrolyzing the coupling agent in an aqueous medium does not require the use of a coupling agent that generates gas such as chlorosilanes and silazanes. In the gas phase, the magnetic powders can be easily combined with each other, and a highly viscous coupling agent that has been difficult to be treated can be used, so that the hydrophobizing effect is great.
[0138]
Examples of the coupling agent that can be used in the surface treatment of the magnetic powder used in the present invention include a silane coupling agent and a titanium coupling agent. More preferably used is a silane coupling agent, which is represented by the general formula (I).
[Chemical 1]
R_mSiY_n  (I)
[Wherein, R represents an alkoxy group, m represents an integer of 1 to 3, Y represents a hydrocarbon group such as an alkyl group, a vinyl group, a glycidoxy group, or a methacryl group, and n represents an integer of 1 to 3. Show. However, m + n = 4. ]
[0139]
Examples of the silane coupling agent represented by the general formula (I) include vinyltrimethoxysilane, vinyltriethoxysilane, vinyltris (β-methoxyethoxy) silane, β- (3,4 epoxy cyclohexyl) ethyltrimethoxysilane, γ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropylmethyldiethoxysilane, γ-aminopropyltriethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane, γ-methacryloxypropyltrimethoxysilane, Vinyltriacetoxysilane, methyltrimethoxysilane, dimethyldimethoxysilane, phenyltrimethoxysilane, diphenyldimethoxysilane, methyltriethoxysilane, dimethyldiethoxysilane, phenyltriethoxysilane, diphenyl Silane, n- butyl trimethoxysilane, isobutyl trimethoxysilane, trimethyl methoxysilane, hydroxypropyl Ritori silane, n- hexadecyl trimethoxy silane, can be mentioned n- octadecyl trimethoxysilane.
[0140]
Among these, it is more preferable to use an alkyltrialkoxysilane coupling agent represented by the following general formula (II) in combination.
[Chemical formula 2]
C_pH_{2p + 1}-Si- (OC_qH_{2q + 1})_Three  (II)
[In formula, p shows the integer of 2-20, q shows the integer of 1-3. ]
[0141]
When p in the above formula is smaller than 2, the hydrophobic treatment is easy, but it is difficult to sufficiently impart hydrophobicity, and it is difficult to suppress the exposure or release of the magnetic powder from the toner particles. Become. On the other hand, when p is larger than 20, the hydrophobicity is sufficient, but the coalescence between the magnetic powders increases, and it becomes difficult to sufficiently disperse the magnetic powders in the toner particles. Deteriorating.
[0142]
On the other hand, when q is larger than 3, the reactivity of the silane coupling agent is lowered and the hydrophobicity is not sufficiently performed. In particular, p in the formula represents an integer of 2 to 20 (more preferably an integer of 3 to 15), and q represents an integer of 1 to 3 (more preferably an integer of 1 or 2). A coupling agent should be used.
[0143]
The processing amount of these coupling agents described above is such that the total amount of the silane coupling agent is 0.05 to 20 parts by weight, preferably 0.1 to 10 parts by weight with respect to 100 parts by weight of the magnetic powder. It is preferable to adjust the amount of the treatment agent according to the surface area of the powder, the reactivity of the coupling agent, and the like.
[0144]
In order to treat the surface of the magnetic powder with a coupling agent in an aqueous medium, a method of stirring an appropriate amount of the magnetic powder and the coupling agent in the aqueous medium can be mentioned. Stirring is preferably performed sufficiently, for example, with a mixer having stirring blades so that the magnetic powder becomes primary particles in the aqueous medium.
[0145]
Here, the aqueous medium is a medium containing water as a main component. Specifically, water itself, water added with a small amount of a surfactant, water added with a pH adjusting agent, water added with an organic solvent can be raised as an aqueous medium. As the surfactant, a nonionic surfactant such as polyvinyl alcohol is preferable. The surfactant is preferably added in an amount of 0.1 to 5% by mass with respect to water. Examples of the pH adjuster include inorganic acids such as hydrochloric acid. Examples of the organic solvent include alcohols.
[0146]
In the magnetic powder thus obtained, no particle aggregation is observed, and the surface of each particle is uniformly hydrophobized, so that when used as a material for polymerized toner, the uniformity of the toner particles is good. Become.
[0147]
Further, the magnetic powder used in the magnetic toner of the present invention may contain elements such as phosphorus, cobalt, nickel, copper, magnesium, manganese, aluminum, silicon, etc., iron trioxide, γ-iron oxide, etc., iron oxide Is used as a main component, and these are used alone or in combination of two or more. These magnetic powders have a BET specific surface area of 2 to 30 m by nitrogen adsorption method.²/ G is preferred, especially 3 to 28 m²/ G is more preferable. Further, those having a Mohs hardness of 5 to 7 are preferred.
[0148]
The shape of the magnetic powder includes polyhedron, octahedron, hexahedron, spherical shape, needle shape, flake shape, etc., but those having less anisotropy such as polyhedron, octahedron, hexahedron, spherical shape and the like have an image density. It is preferable in terms of enhancement. The shape of such magnetic powder can be confirmed by SEM or the like.
[0149]
The volume average particle size of the magnetic powder is preferably 0.05 to 0.40 μm, more preferably 0.10 to 0.30 μm. When the volume average diameter is less than 0.05 μm, the decrease in blackness becomes remarkable, the coloring power is insufficient as a colorant for black and white toner, and the aggregation between the composite oxide particles becomes strong, so that the dispersion Tend to deteriorate. In addition, uniform surface treatment of the magnetic powder becomes difficult, and the liberation rate of iron and iron compounds increases. Furthermore, when the particle size of the magnetic powder is smaller than 0.05 μm, the magnetic powder itself is strongly reddish, and the resulting image also tends to be reddish black, resulting in poor image quality. It will be a thing.
[0150]
On the other hand, when the volume average particle size of the magnetic powder exceeds 0.40 μm, the coloring power becomes insufficient as in the case of a general colorant. In addition, especially when used as a colorant for small particle size toners, it is stochastically difficult to uniformly disperse magnetic powder in individual toner particles, dispersibility tends to deteriorate, and toner durability May be inferior.
[0151]
The volume average particle size of the magnetic powder can be measured using a transmission electron microscope. Specifically, after sufficiently dispersing toner particles to be observed in an epoxy resin, a cured product obtained by curing for 2 days in an atmosphere at a temperature of 40 ° C. is used as a sample on a thin piece by a microtome. In an electron microscope (TEM), 100 magnetic powder particle diameters in the field of view are measured with a photograph with an enlargement magnification of 10,000 to 40,000 times. Then, the volume average particle diameter is calculated based on the equivalent diameter of a circle equal to the projected area of the magnetic powder. The same measurement was performed in the examples described later.
[0152]
In the present invention, other colorants may be used in combination with the magnetic powder. Examples of colorants that can be used in combination include magnetic or nonmagnetic inorganic compounds, known dyes and pigments. Specifically, for example, ferromagnetic metal particles such as cobalt and nickel, or alloys obtained by adding chromium, manganese, copper, zinc, aluminum and rare earth elements to these, particles such as hematite, titanium black, nigrosine dye / pigment , Carbon black, phthalocyanine and the like. These may also be used after treating the surface.
[0153]
The magnetic powder used in the present invention preferably has a volume average variation coefficient of 35 or less. The volume average variation coefficient of the magnetic powder is an index representing the breadth of the particle size distribution of the magnetic powder, and a volume average variation coefficient larger than 35 means that the particle size distribution of the magnetic powder is wide. When such a magnetic powder is used, the uniformity of the processing of the magnetic powder described above tends to be inferior and the dispersibility in the toner tends to deteriorate. Furthermore, it is difficult to make the magnetic powder uniformly enter each toner particle at the time of granulation, and a large difference in the content of the magnetic powder among the toner particles tends to occur. In the present invention, the volume average variation coefficient is defined to be obtained by the following equation.
[0154]
[Equation 5]

[0155]
The degree of hydrophobicity of the magnetic powder used in the present invention is preferably 35 to 95%, more preferably 40 to 95%. The degree of hydrophobicity can be arbitrarily changed depending on the type and amount of the treatment agent on the surface of the magnetic powder. The degree of hydrophobicity indicates the hydrophobicity of the magnetic powder, and those having a low degree of hydrophobicity mean that the hydrophilicity is high.
[0156]
Therefore, when using a magnetic powder having a low degree of hydrophobicity, in the suspension polymerization method suitably used for producing the magnetic toner of the present invention, the magnetic powder moves to an aqueous system during granulation, As the particle size distribution becomes broader, the average circularity of the toner particles becomes lower. This occurs because the magnetic powder that is insufficiently hydrophobized is likely to be exposed on the surface of the toner particles. Also, those having a low degree of hydrophobicity are not preferable because the liberation rate of iron and iron compounds is high. On the other hand, in order to make the degree of hydrophobicity greater than 95%, it is necessary to use a large amount of the treatment material on the surface of the magnetic powder. In such a state, the magnetic powder tends to coalesce and the treatment is uniform. May be impaired.
[0157]
The degree of hydrophobicity in the present invention is measured by the following method. The degree of hydrophobicity of the magnetic powder is measured by a methanol titration test. The methanol titration test is an experimental test for confirming the degree of hydrophobicity of a magnetic powder having a hydrophobic surface.
[0158]
Hydrophobization degree measurement using methanol is performed as follows. Add 0.1 g of magnetic powder to 50 mL of water in a 250 mL beaker. Thereafter, methanol is gradually added to the liquid and titration is performed. At this time, methanol is supplied from the bottom of the liquid and is gently stirred. The end of sedimentation of the magnetic powder is when the suspended matter of the magnetic powder is no longer confirmed on the liquid surface, and the degree of hydrophobicity is the volume percentage of methanol in the methanol and water mixture when the end of sedimentation is reached. Appears. The same measurement was performed in the examples described later.
[0159]
The magnetic powder used in the magnetic toner of the present invention is preferably used in an amount of 10 to 200 parts by mass with respect to 100 parts by mass of the binder resin. More preferably, 20 to 180 parts by mass are used. If it is less than 10 parts by mass, the coloring power of the magnetic toner is poor, and it is difficult to suppress fogging. On the other hand, when the amount exceeds 200 parts by mass, not only the retention force by the magnetic force on the magnetic toner carrier is increased and the developability is lowered, but it is difficult not only to uniformly disperse the magnetic powder into individual toner particles, but also the fixability. May fall.
[0160]
The content of the magnetic powder in the toner particles can be measured using, for example, a thermal analysis device manufactured by Perkin Elmer, TGA7. The measurement method is as follows: a magnetic toner is heated from room temperature to 900 ° C. at a temperature rising rate of 25 ° C./min in a nitrogen atmosphere, and the weight loss between 100 ° C. and 750 ° C. is obtained by removing the magnetic powder from the toner particles. The remaining mass is the amount of magnetic powder.
[0161]
For example, in the case of magnetite, the magnetic powder used in the magnetic toner of the present invention is produced by the following method.
[0162]
An aqueous solution containing ferrous hydroxide is prepared by adding an alkali such as sodium hydroxide to the ferrous salt aqueous solution in an amount equivalent to or greater than the iron component. While maintaining the pH of the prepared aqueous solution at pH 7 or higher (preferably pH 8-14), air was blown in, and the aqueous ferrous hydroxide was oxidized while heating the aqueous solution to 70 ° C. or higher. First, a seed crystal to be a core is generated.
[0163]
Next, an aqueous solution containing about 1 equivalent of ferrous sulfate is added to the slurry-like liquid containing seed crystals based on the amount of alkali added previously. While maintaining the pH of the solution at 6 to 14, the reaction of ferrous hydroxide is promoted while blowing air, and the magnetic iron oxide powder is grown around the seed crystal. As the oxidation reaction proceeds, the pH of the liquid shifts to the acidic side, but the pH of the liquid is preferably not less than 6. Adjust the pH of the liquid at the end of the oxidation reaction, stir well so that the magnetic iron oxide becomes primary particles, add the coupling agent, stir well, stir, filter, dry, and lightly crush after stirring By doing so, a magnetically treated iron oxide powder can be obtained. Alternatively, after the oxidation reaction is completed, the iron oxide powder obtained by washing and filtering is redispersed in another aqueous medium without drying, and then the pH of the redispersion is adjusted and sufficiently stirred A silane coupling agent may be added to perform the coupling treatment.
[0164]
As the ferrous salt, iron sulfate generally produced as a by-product in the production of sulfuric acid titanium, iron sulfate produced as a by-product with the surface cleaning of the steel sheet can be used, and iron chloride or the like can be used.
[0165]
In the method for producing magnetic iron oxide by the aqueous solution method, an iron concentration of 0.5 to 2 mol / L is generally used from the viewpoint of preventing an increase in viscosity during the reaction and the solubility of iron sulfate. Generally, the lower the iron sulfate concentration, the finer the particle size of the product. Also, during the reaction, the larger the amount of air and the lower the reaction temperature, the easier it is to atomize.
[0166]
By using the magnetic toner made of the hydrophobic magnetic powder produced as described above, stable toner charging property can be obtained, transfer efficiency is high, and high image quality and high stability are possible.
[0167]
The magnetic toner of the present invention has a saturation magnetization of 10 to 50 Am at a magnetic field of 79.6 kA / m (1000 oersted).²It is necessary that the magnetic toner be / kg (emu / g). This is because the magnetic toner can be prevented from leaking by providing a magnetic force generating means in the developing device, so that the magnetic toner can be transported or stirred, and the magnetic force acts on the magnetic toner carrier. By providing the magnetic force generating means, the recoverability of the transfer residual toner is further improved, and it becomes easy to prevent toner scattering because the magnetic toner forms spikes.
[0168]
However, the magnetic toner has a magnetization intensity of 10 Am at a magnetic field of 79.6 kA / m.²If the amount is less than / kg, the above effect cannot be obtained, and if magnetic force is applied to the magnetic toner carrier, the rise of the magnetic toner becomes unstable, and fogging due to inability to uniformly charge the magnetic toner. In addition, image defects such as image density unevenness and poor transfer residual toner are likely to occur.
[0169]
On the other hand, the magnetic toner has a magnetization intensity of 50 Am at a magnetic field of 79.6 kA / m.²If it is greater than / kg, when a magnetic force is applied to the magnetic toner, the fluidity of the magnetic toner is remarkably reduced due to magnetic aggregation, the developability is lowered, the magnetic toner is easily damaged, and toner deterioration becomes remarkable. Further, due to the magnetic aggregation of the magnetic toner, the durability under high temperature and high humidity is inferior. Further, transferability is lowered, and untransferred toner increases.
[0170]
Further, when used in an image forming method of a development and cleaning process or a cleaner-less system, the residual magnetization of the toner in a magnetic toner magnetic field of 79.6 kA / m (1000 oersted) is 0.5 to 6 Am.²The magnetic toner is preferably / kg (emu / g). Residual magnetization is 6 Am²/ Kg exceeds the untransferred toner, magnetically agglomerates and tends to behave as an aggregate of toner, and the surface of the photoconductor may be damaged by rubbing between the charging member and the photoconductor. . On the other hand, the residual magnetization is 0.5 Am²If it is less than / kg, the transfer residual toner tends to be present in a state of being dispersed in each particle, and it is difficult to be captured by the charging member, and as a result, it is difficult to be properly charged. In other words, since the magnetic toner has a preferable residual magnetization, the transfer residual toner exists in an appropriately aggregated state, so that it is made appropriate without damaging the photoreceptor.
[0171]
The magnetization intensity (saturation magnetization, residual magnetization) of the magnetic toner can be arbitrarily changed by the amount of magnetic powder contained, the saturation magnetization of the magnetic powder, and the residual magnetization.
[0172]
The saturation magnetization of the magnetic powder is 30 to 120 Am at a magnetic field of 796 kA / m.²/ Kg is preferred.
[0173]
In the present invention, the strength of saturation magnetization and residual magnetization of the magnetic toner can be measured using, for example, a vibration magnetometer VSM P-1-10 (manufactured by Toei Kogyo Co., Ltd.). In the case of using the above apparatus, the measurement is performed at a room temperature of 25 ° C. with an external magnetic field of 79.6 kA / m. Also, the magnetic properties of the magnetic powder can be measured using a vibration magnetometer VSM P-1-10 (manufactured by Toei Kogyo Co., Ltd.) at a room temperature of 25 ° C. and an external magnetic field of 796 kA / m.
[0174]
The magnetic toner of the present invention contains a release agent for improving the fixability, but the magnetic toner of the present invention preferably contains 1 to 30 mass% of the release agent in a total amount with respect to the binder resin. . More preferably, it is 3 to 25% by mass. When the content of the release agent is less than 1% by mass, the effect of adding the release agent is not sufficient, and further, the offset suppressing effect is also insufficient. On the other hand, if it exceeds 30% by mass, the long-term storage stability is deteriorated, and the dispersibility of the magnetic toner material such as the release agent and the magnetic powder is deteriorated. Leading to a decline. In addition, the release agent component oozes out and tends to be inferior in durability under high temperature and high humidity. Furthermore, since a large amount of wax is included, the shape of the magnetic toner tends to be distorted.
[0175]
In general, a toner image transferred onto a recording medium is then fixed on a transfer material by energy such as heat and pressure, and a semi-permanent image is obtained. At this time, heat roll type fixing is generally used. As described above, a very high-definition image can be obtained by using a magnetic toner having a weight average particle diameter of 20 μm or less. However, a toner particle having a small particle diameter can be obtained when a recording medium such as paper is used. It enters into the gap between the fibers, and heat reception from the heat fixing roller becomes insufficient, and low temperature offset tends to occur. However, in the magnetic toner of the present invention, it is possible to achieve both high image quality and fixability by containing an appropriate amount of a release agent and controlling the liberation rate of iron and iron compounds as described above. Become.
[0176]
As the release agent usable in the magnetic toner of the present invention, petroleum wax such as paraffin wax, microcrystalline wax, petrolactam and derivatives thereof, montan wax and derivatives thereof, hydrocarbon wax and derivatives thereof by Fischer-Tropsch method, Polyolefin waxes typified by polyethylene and derivatives thereof, natural waxes and derivatives thereof such as carnauba wax and candelilla wax, and the derivatives include oxides, block copolymers with vinyl monomers, and graft modified products. Furthermore, fatty acids such as higher aliphatic alcohols, stearic acid and palmitic acid, or compounds thereof, acid amide waxes, ester waxes, ketones, hydrogenated castor oil and derivatives thereof, plant waxes, animal waxes and the like can also be used.
[0177]
Among these release agent components,Differential scanning calorimetryEndothermic peak due to 40-110 ° C., ie, differentialscanningIn the DSC curve measured by a calorimeter, those having a maximum endothermic peak in the region of 40 to 110 ° C. at the time of temperature rise are preferred, and those having in the region of 50 to 100 ° C. are more preferred. By having the maximum endothermic peak in the above temperature range, the mold releasability is effectively expressed while greatly contributing to low-temperature fixing.
[0178]
When the maximum endothermic peak is less than 40 ° C., the self-aggregating force of the release agent component becomes weak, and as a result, the high temperature offset resistance tends to deteriorate. In addition, bleeding of the release agent tends to occur, and the charge amount of the toner tends to decrease, and the durability under high temperature and high humidity tends to decrease. On the other hand, if the maximum endothermic peak exceeds 110 ° C., the fixing temperature becomes high and low temperature offset is likely to occur, which is not preferable. Further, when granulation / polymerization is performed in an aqueous medium and a toner is obtained directly by the polymerization method, if the maximum endothermic peak temperature is high, a problem such as precipitation of a release agent component mainly occurs during granulation. Dispersibility of the mold is deteriorated, which is not preferable.
[0179]
The endothermic amount of the release agent and the maximum endothermic peak temperature are measured according to “ASTM D 3418-8”. For the measurement, for example, DSC-7 manufactured by PerkinElmer is used. The temperature correction of the device detection unit uses the melting points of indium and zinc, and the correction of heat uses the heat of fusion of indium. An aluminum pan is used as a measurement sample, and an empty pan is set as a control. The sample is heated up to 200 ° C. once to remove the heat history, then rapidly cooled, and again at a heating rate of 10 ° C./min DSC curve measured when the temperature is raised in the range of 30 to 200 ° C. is used. The same measurement was performed in the examples described later.
[0180]
The magnetic toner of the present invention preferably has a peak top of the main peak in the molecular weight range of 5000 to 50000 in the molecular weight distribution measured by gel permeation chromatography (GPC) of the THF soluble content of the magnetic toner. Preferably it is the range of 8000-40000. When the peak top is less than 5,000, there is a problem in the storage stability of the toner, or the toner tends to be significantly deteriorated when a large number of sheets are printed out. On the other hand, when the peak top exceeds 50000, there is a problem in low-temperature fixability, and it becomes difficult to make the average circularity of the toner not less than 0.970 due to a rapid increase in droplet viscosity during polymerization. May be.
[0181]
In addition, what is necessary is just to perform the measurement of the molecular weight of the resin component soluble in THF by GPC as follows.
A solution obtained by allowing the magnetic toner of the present invention to stand still in THF at room temperature for 24 hours is filtered through a solvent-resistant membrane filter having a pore diameter of 0.2 μm to obtain a sample solution, which is measured under the following conditions. In addition, sample preparation adjusts the quantity of THF so that the density | concentration of the component soluble in THF may be 0.4-0.6 mass%.
Apparatus: High-speed GPC HLC8120 GPC (manufactured by Tosoh Corporation)
Column: Seven series of Shodex KF-801, 802, 803, 804, 805, 806, 807 (manufactured by Showa Denko KK)
Eluent: THF
Flow rate: 1.0 ml / min
Oven temperature: 40.0 ° C
Sample injection amount: 0.10 ml
[0182]
In calculating the molecular weight of the sample, standard polystyrene resin (TSO standard polystyrene F-850, F-450, F-288, F-128, F-80, F-40, F-20, F- manufactured by Tosoh Corporation) was used. 10, F-4, F-2, F-1, A-5000, A-2500, A-1000, A-500).
[0183]
The molecular weight of the magnetic toner can be arbitrarily changed depending on the binder resin to be used and the kneading condition when the magnetic toner is produced by the pulverization method. Further, in the polymerization method, it can be arbitrarily changed depending on the combination of the initiator used, the type and amount of the crosslinking agent, and the like. It can also be adjusted by using a chain transfer agent or the like.
[0184]
The magnetic toner of the present invention may contain a charge control agent in order to stabilize the charge characteristics. As the charge control agent, a known one can be used, and a charge control agent that has a high charging speed and can stably maintain a constant charge amount is particularly preferable. Further, when the magnetic toner is produced using a direct polymerization method, a charge control agent having a low polymerization inhibitory property and substantially free from a solubilized product in an aqueous dispersion medium is particularly preferable.
[0185]
Specific compounds include, as negative charge control agents, metal compounds of aromatic carboxylic acids such as salicylic acid, alkylsalicylic acid, dialkylsalicylic acid, naphthoic acid and dicarboxylic acid, metal salts or metal complexes of azo dyes or azo pigments, sulfones Examples thereof include a polymer compound having an acid or carboxylic acid group in the side chain, a boron compound, a urea compound, a silicon compound, and a calixarene. Further, examples of the positive charge control agent include a quaternary ammonium salt, a polymer compound having the quaternary ammonium salt in the side chain, a guanidine compound, a nigrosine compound, and an imidazole compound.
[0186]
As a method of adding a charge control agent to the toner, there are a method of adding it inside the toner particles and a method of adding it externally to the toner particles. The amount of these charge control agents used is determined by the method of manufacturing the magnetic toner including the type of binder resin, the presence or absence of other additives, and the dispersion method, and is not limited uniquely. However, when added internally, it is preferably used in the range of 0.1 to 10 parts by mass, more preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the binder resin. Further, when externally added, the amount is preferably 0.005 to 1.0 part by mass, more preferably 0.01 to 0.3 part by mass with respect to 100 parts by mass of the toner particles.
[0187]
However, in the magnetic toner of the present invention, it is not essential to add a charge control agent. By actively using a charging process in an image forming process such as frictional charging with a toner layer pressure regulating member or a magnetic toner carrier. It is not always necessary to include a charge control agent in the magnetic toner.
[0188]
Next, a method for producing a polymerized toner according to the present invention by suspension polymerization will be described. The polymerized toner according to the present invention is generally a toner composition, that is, a polymerizable monomer that becomes a binder resin, a magnetic powder, a release agent, a plasticizer, a charge control agent, a crosslinking agent, and a colorant depending on the case. Components necessary for the toner and other additives such as a polymer, a dispersant, etc. are appropriately added, and a polymerizable monomer system uniformly dissolved or dispersed by a disperser is used as a dispersion stabilizer. It can be produced by suspending in an aqueous medium containing it.
[0189]
In the production of the polymerized toner according to the present invention, examples of the polymerizable monomer constituting the polymerizable monomer system include the following.
[0190]
Examples of the polymerizable monomer include styrene monomers such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, p-methoxystyrene, p-ethylstyrene, methyl acrylate, ethyl acrylate, Acrylate esters such as n-butyl acrylate, isobutyl acrylate, n-propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, 2-chloroethyl acrylate, and phenyl acrylate , Methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, Methacrylic acid dimethyl aminoethyl, methacrylic acid esters other acrylonitrile such as diethylaminoethyl methacrylate, methacrylonitrile, and the like monomers acrylamide. These monomers can be used alone or in combination. Among the above-mentioned monomers, styrene or a styrene derivative is preferably used alone or mixed with other monomers from the viewpoint of developing characteristics and durability of the toner.
[0191]
In the production of the polymerized toner according to the present invention, the polymerization may be performed by adding a resin to the polymerizable monomer system. For example, it contains hydrophilic functional groups such as amino groups, carboxylic acid groups, hydroxyl groups, sulfonic acid groups, glycidyl groups, and nitrile groups that cannot be used because monomers are water-soluble and dissolve in aqueous suspension to cause emulsion polymerization. When it is desired to introduce the polymerizable monomer component into the toner particles, a random copolymer of these and a vinyl compound such as styrene or ethylene, a block copolymer, or a graft copolymer is used. Or a polycondensate such as polyester or polyamide, or a polyaddition polymer such as polyether or polyimine. When such a high molecular polymer containing a polar functional group is allowed to coexist in the toner particles, the above wax component is phase-separated, the encapsulation becomes stronger, and a magnetic toner having good blocking resistance and developability can be obtained. it can.
[0192]
Among these resins, the effect is greatly increased by containing a polyester resin. I think this is because of the following reasons. Since the polyester resin contains many ester bonds which are functional groups having relatively high polarity, the polarity of the resin itself is increased. Due to its polarity, the tendency of the polyester to be unevenly distributed on the surface of the droplets in the aqueous dispersion medium becomes strong, and polymerization proceeds while maintaining this state, resulting in toner particles. For this reason, the polyester resin is unevenly distributed on the surface of the toner particles, so that the surface state and surface composition become uniform. As a result, the chargeability becomes uniform and the inclusion of the release agent is good. Therefore, very good developability can be obtained.
[0193]
As the polyester resin used in the present invention, for example, a saturated polyester resin, an unsaturated polyester resin, or both are appropriately selected and used for controlling physical properties such as charging property, durability, and fixing property of the magnetic toner. It is possible. As the polyester resin used in the present invention, a normal resin composed of an alcohol component and an acid component can be used, and both components are exemplified below.
[0194]
As alcohol components, ethylene glycol, propylene glycol, 1,3-butanediol, 1,4-butanediol, 2,3-butanediol, diethylene glycol, triethylene glycol, 1,5-pentanediol, 1,6-hexane Diol, neopentyl glycol, 2-ethyl-1,3-hexanediol, cyclohexanedimethanol, butenediol, octenediol, cyclohexenedimethanol, hydrogenated bisphenol A, and bisphenol derivatives represented by formula (I); Hydrogenated compounds of (I), diols of formula (II); or diols of hydrogenated compounds of formula (II).
[0195]
[Chemical 3]

[Wherein, R is an ethylene or propylene group, x and y are each an integer of 1 or more, and the average value of x + y is 2 to 10. ]
[Formula 4]

[0196]
As the divalent carboxylic acid, benzene dicarboxylic acid such as phthalic acid, terephthalic acid, isophthalic acid, phthalic anhydride or the anhydride thereof; alkyl dicarboxylic acid such as succinic acid, adipic acid, sebacic acid, azelaic acid or the anhydride, Furthermore, succinic acid substituted with an alkyl or alkenyl group having 6 to 18 carbon atoms or an anhydride thereof; unsaturated dicarboxylic acid such as fumaric acid, maleic acid, citraconic acid, itaconic acid or the anhydride thereof may be used.
[0197]
In addition, polyhydric alcohols such as glycerin, pentaerythritol, sorbit, sorbitan, and oxyalkylene ethers of novolac type phenol resins can be cited as the alcohol component, and trimellitic acid, pyromellitic acid, 1,2,3,4- Examples thereof include polyvalent carboxylic acids such as butanetetracarboxylic acid, benzophenonetetracarboxylic acid and anhydrides thereof.
[0198]
Among the polyester resins, the alkylene oxide adduct of bisphenol A, which is excellent in charging characteristics and environmental stability and balanced in other electrophotographic characteristics, is preferably used. In the case of this compound, the average number of added moles of alkylene oxide is preferably 2 to 10 from the viewpoint of fixability and durability of the magnetic toner.
[0199]
It is preferable that 45-55 mol% of the polyester resin used in the present invention is an alcohol component, and 55-45 mol% is an acid component.
[0200]
The polyester resin is present on the surface of the toner particles in the magnetic toner production method of the present invention, and the obtained toner particles have an acid value of 0.1 to 50 mg KOH / resin 1 g in order to develop stable chargeability. It is preferable. If the amount is less than 0.1 mgKOH / resin 1 g, the amount existing on the toner surface tends to be absolutely insufficient. If the amount exceeds 50 mgKOH / resin 1 g, the chargeability of the toner may be adversely affected. Furthermore, in the present invention, the acid value range of 5 to 35 mg KOH / resin 1 g is more preferable.
[0201]
In the present invention, as long as the physical properties of the obtained toner particles are not adversely affected, it is also suitable to prepare physical properties by using two or more kinds of polyester resins together, for example, by modifying with silicone or a fluoroalkyl group-containing compound. To be done.
[0202]
Moreover, when using the high molecular polymer containing such a polar functional group, the average molecular weight is preferably 5,000 or more. If it is 5,000 or less, particularly 4,000 or less, the present polymer is likely to concentrate near the surface, and this tends to adversely affect developability, blocking resistance, etc., which is not preferred.
[0203]
In addition, resins other than those described above may be added to the monomer system for the purpose of improving the dispersibility and fixing properties of the material or image characteristics. Examples of the resin used include styrene such as polystyrene and polyvinyltoluene. And styrene-propylene copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, Styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-dimethylaminoethyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene -Butyl methacrylate copolymer, Styrene-Dimethylaminoethyl methacrylate Copolymer, Styrene-vinyl methyl ether copolymer, Styrene-vinyl ethyl ether copolymer, Styrene-vinyl methyl ketone copolymer, Styrene-butadiene copolymer, Styrene-isoprene copolymer, Styrene-maleic acid copolymer Styrene copolymers such as polymers, styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, silicone resin, polyester resin, polyamide resin, epoxy resin, Polyacrylic acid resin, rosin, modified rosin, temper resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin and the like can be used alone or in combination. As addition amount of these resin, 1-20 mass parts is preferable with respect to 100 mass parts of polymerizable monomers. If it is less than 1 part by mass, the effect of addition is small, while if it is added in an amount of 20 parts by mass or more, it becomes difficult to design various physical properties of the polymerized toner.
[0204]
Further, if a polymer having a molecular weight different from the molecular weight range of the toner particles obtained by polymerizing the polymerizable monomer is dissolved in the monomer and polymerized, the magnetic toner has a wide molecular weight distribution and high offset resistance. Can be obtained.
[0205]
The polymerization initiator used in the production of the polymerized toner related to the magnetic toner of the present invention has a half-life of 0.5 to 30 hours during the polymerization reaction, and 0.5 to 20 mass relative to the polymerizable monomer. When the polymerization reaction is carried out with a part addition amount, a polymer in which the peak top of the main peak exists in the molecular weight between 5000 and 50000 in GPC can be obtained.
[0206]
Examples of the polymerization initiator used in the present invention include conventionally known azo polymerization initiators and peroxide polymerization initiators. As the azo polymerization initiator, 2,2′-azobis- (2, 4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis-4-methoxy-2,4-dimethyl Examples include valeronitrile, azobisisobutyronitrile, and peroxide polymerization initiators include t-butyl peroxyacetate, t-butyl peroxylaurate, t-butyl peroxypivalate, t-butyl peroxy Oxy-2-ethylhexanoate, t-butylperoxyisobutyrate, t-butylperoxyneodecanoate, t-hexylperoxyacetate, t-hexyl Ruperoxylaurate, t-hexylperoxypivalate, t-hexylperoxy-2-ethylhexanoate, t-hexylperoxyisobutyrate, t-hexylperoxyneodecanoate, t-butylperoxy Benzoate, α, α′-bis (neodecanoylperoxy) diisopropylbenzene, cumylperoxyneodecanoate, 1,1,3,3-tetramethylbutylperoxy-2-ethylhexanoate, 1,1 , 3,3-tetramethylbutylperoxyneodecanoate, 1-cyclohexyl-1-methylethylperoxyneodecanoate, 2,5-dimethyl-2,5-bis (2-ethylhexanoylperoxy) Hexane, 1-cyclohexyl-1-methylethylperoxy-2-ethylhexanoate, -Hexylperoxyisopropyl monocarbonate, t-butylperoxyisopropyl monocarbonate, t-butylperoxy 2-ethylhexyl monocarbonate, t-hexylperoxybenzoate, 2,5-dimethyl-2,5-bis (benzoylperoxy) ) Hexane, t-butylperoxy-m-toluoyl benzoate, bis (t-butylperoxy) isophthalate, t-butylperoxymaleic acid, t-butylperoxy-3,5,5-trimethylhexano , Peroxyesters such as 2,5-dimethyl-2,5-bis (m-toluoylperoxy) hexane, diacyl peroxides such as benzoyl peroxide, lauroyl peroxide, isobutyryl peroxide, diisopropyl peroxide -Oxydicarbonate, peroxydicarbonate such as bis (4-t-butylcyclohexyl) peroxydicarbonate, 1,1-di-t-butylperoxycyclohexane, 1,1-di-t-hexylperoxycyclohexane Peroxyketals such as 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, 2,2-di-t-butylperoxybutane, di-t-butyl peroxide, dicumyl Dialkyl peroxides such as peroxide and t-butylcumyl peroxide, and others include t-butylperoxyallyl monocarbonate, and two or more of these initiators can be used as necessary.
[0207]
When the magnetic toner of the present invention is produced by a polymerization method, it is important to adjust the melt viscosity by adding a crosslinking agent together with the above initiator in order to obtain the target melt viscosity. As the crosslinking agent used in the present invention, compounds having two or more polymerizable double bonds are mainly used. For example, aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene; for example, ethylene glycol diacrylate Carboxylic acid esters having two double bonds such as ethylene glycol dimethacrylate, 1,3-butanediol dimethacrylate, etc .; divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide, divinyl sulfone; and three or more A compound having a vinyl group is used alone or as a mixture. The addition amount needs to be adjusted depending on the initiator to be used, the type of the crosslinking agent, and the reaction conditions, but is generally 0.01 to 5 parts by mass with respect to the polymerizable monomer.
[0208]
In the method for producing the magnetic toner of the present invention by a polymerization method, a toner composition such as the above-mentioned magnetic powder, polymerizable monomer, release agent, etc. is generally added as appropriate, and a homogenizer, ball mill, colloid mill, ultrasonic wave is added. A polymerizable monomer system uniformly dissolved or dispersed by a dispersing machine such as a dispersing machine is suspended in an aqueous medium containing a dispersion stabilizer. At this time, the particle size of the obtained toner particles becomes sharper by using a high-speed disperser such as a high-speed stirrer or an ultrasonic disperser to obtain a desired toner particle size at a stretch. The polymerization initiator may be added at the same time when other additives are added to the polymerizable monomer, or may be mixed immediately before being suspended in the aqueous medium. Further, a polymerization initiator dissolved in a polymerizable monomer or a solvent can be added during granulation or immediately after granulation, before starting the polymerization reaction.
[0209]
After granulation, stirring may be performed using a normal stirrer to such an extent that the particle state is maintained and the particles are prevented from floating and settling.
[0210]
When the magnetic toner of the present invention is produced by a polymerization method, a known surfactant, organic dispersant or inorganic dispersant can be used as a dispersion stabilizer. In particular, inorganic dispersants are less likely to produce harmful ultrafine powders, and because of their steric hindrance, dispersion stability is obtained, so even if the reaction temperature is changed, stability is not easily lost, and washing is easy and does not adversely affect the toner. Therefore, it can be preferably used. Examples of such inorganic dispersants include polyvalent metal phosphates such as calcium phosphate, magnesium phosphate, aluminum phosphate and zinc phosphate, carbonates such as calcium carbonate and magnesium carbonate, calcium metasuccinate, calcium sulfate and barium sulfate. Inorganic oxides such as inorganic salts, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, silica, bentonite and alumina can be mentioned.
[0211]
When these inorganic dispersants are used, they may be used as they are, but in order to obtain finer particles, it is preferable to generate and use the inorganic dispersant particles in an aqueous medium. For example, in the case of calcium phosphate, a sodium phosphate aqueous solution and a calcium chloride aqueous solution can be mixed with high-speed stirring to produce water-insoluble calcium phosphate, which enables more uniform and fine dispersion. At the same time, a water-soluble sodium chloride salt is produced as a by-product. However, if a water-soluble salt is present in the aqueous medium, dissolution of the polymerizable monomer in water is suppressed, and an ultrafine toner based on emulsion polymerization is produced. Since it becomes difficult to generate | occur | produce, it is more convenient. The inorganic dispersant can be almost completely removed by dissolving with an acid or alkali after completion of the polymerization.
[0212]
These inorganic dispersants are preferably used alone in an amount of 0.2 to 20 parts by mass with respect to 100 parts by mass of the polymerizable monomer. Since it may be somewhat insufficient, 0.001 to 0.1 parts by mass of a surfactant may be used in combination.
[0213]
Examples of the surfactant include sodium dodecylbenzene sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, sodium oleate, sodium laurate, sodium stearate, and potassium stearate.
[0214]
In the polymerization step, the polymerization is performed at a polymerization temperature of 40 ° C. or higher, generally 50 to 90 ° C. When the polymerization is carried out in this temperature range, the release agent or wax to be sealed inside is precipitated by phase separation, and the encapsulation becomes more complete. In order to consume the remaining polymerizable monomer, it is possible to raise the reaction temperature to 90 to 150 ° C. at the end of the polymerization reaction.
[0215]
The polymerized toner particles are filtered, washed and dried by a known method after the polymerization is completed, and the magnetic toner of the present invention can be obtained by mixing inorganic fine powders if necessary and adhering them to the surface. Moreover, it is one of the desirable forms of this invention to put a classification process in a manufacturing process and to cut coarse powder and fine powder.
[0216]
In the present invention, the magnetic toner is preferably added with an inorganic fine powder having a number average primary particle size of 4 to 80 nm as a fluidizing agent. The inorganic fine powder is added to improve the fluidity of the magnetic toner and to make the charge of the toner particles uniform. However, the inorganic fine powder can be treated to adjust the charge amount of the magnetic toner and improve the environmental stability. It is also a preferable form to provide functions such as improvement.
[0217]
When the number average primary particle size of the inorganic fine powder is larger than 80 nm, or when the inorganic fine powder of 80 nm or less is not added, it becomes easy to adhere to the charging member when the transfer residual toner adheres to the charging member. It is difficult to stably obtain good charging characteristics. In addition, good fluidity of the magnetic toner cannot be obtained, and charging to the toner particles is likely to be uneven, and problems such as an increase in fog, a decrease in image density, and toner scattering may be unavoidable. When the number average primary particle size of the inorganic fine powder is smaller than 4 nm, the agglomeration of the inorganic fine powder is strengthened, and the aggregate is not a primary particle but an aggregate with a wide particle size distribution having a strong agglomeration property that is difficult to break even by crushing treatment. Image defects due to development of the aggregate, damage to the image carrier or magnetic toner carrier, and the like. In order to make the charge distribution of the toner particles more uniform, the number average primary particle size of the inorganic fine powder is preferably 6 to 35 nm.
[0218]
In the present invention, the method of measuring the number average primary particle size of the inorganic fine powder is a photograph of the magnetic toner magnified by a scanning electron microscope, and further by an elemental analysis means such as XMA attached to the scanning electron microscope. While comparing photographs of magnetic toner mapped with the elements contained in the body, 100 or more primary particles of inorganic fine powder that are attached to or released from the surface of the toner particles are measured, and the number-based average primary particles It can be measured by determining the diameter and number average primary particle size.
[0219]
As the inorganic fine powder used in the present invention, silica, titanium oxide, alumina, and the like can be used, and they may be used alone or in combination. As the silica, for example, both a so-called dry method produced by vapor phase oxidation of silicon halide or dry silica called fumed silica, and so-called wet silica produced from water glass or the like can be used. There are few silanol groups on the surface and inside the silica fine powder, and Na₂O, SO_Three ^2-For example, dry silica with less production residue is preferred. In dry silica, it is also possible to obtain composite fine powders of silica and other metal oxides by using other metal halogen compounds such as aluminum chloride and titanium chloride together with silicon halogen compounds in the production process. Is also included.
[0220]
The addition amount of the inorganic fine powder having a number average primary particle size of 4 to 80 nm is preferably 0.1 to 3.0% by mass with respect to the toner particles, and the effect is obtained when the addition amount is less than 0.1% by mass. However, when the content is 3.0% by mass or more, the fixability tends to deteriorate.
[0221]
The content of the inorganic fine powder can be quantified using a calibration curve prepared from a standard sample using fluorescent X-ray analysis.
[0222]
In the present invention, the inorganic fine powder is preferably a hydrophobized product in view of characteristics in a high temperature and high humidity environment. When the inorganic fine powder added to the magnetic toner absorbs moisture, the charge amount of the toner particles is remarkably reduced, and the toner is likely to scatter.
[0223]
As the treatment agent used for the hydrophobization treatment, treatment agents such as silicone varnish, various modified silicone varnishes, silicone oil, various modified silicone oils, silane compounds, silane coupling agents, other organic silicon compounds, and organic titanium compounds may be used alone or You may process together.
[0224]
Of these, those treated with silicone oil are preferred, and more preferably, the inorganic fine powder treated with silicone oil at the same time as or after hydrophobizing with a silane compound is charged with toner particles even in a high humidity environment. It is good for keeping the amount high and preventing toner scattering.
[0225]
As a method for treating such inorganic fine powder, for example, as a first-stage reaction, a silanization reaction is performed with a silane compound and silanol groups are eliminated by chemical bonds, and then a hydrophobic reaction is performed on the surface with a silicone oil as a second-stage reaction. A processing method for forming the thin film can be exemplified.
[0226]
The silicone oil has a viscosity at 25 ° C. of 10 to 200,000 mm.²/ S, even 3,000-80,000mm²/ S is preferred. 10mm²If it is less than / s, the inorganic fine powder is not stable and the image quality tends to deteriorate due to heat and mechanical stress. 200,000mm²If it exceeds / s, uniform processing tends to be difficult.
[0227]
As the silicone oil used, for example, dimethyl silicone oil, methylphenyl silicone oil, α-methylstyrene modified silicone oil, chlorophenyl silicone oil, fluorine modified silicone oil and the like are particularly preferable.
[0228]
As a method for treating the inorganic fine powder with silicone oil, for example, the inorganic fine powder treated with the silane compound and the silicone oil may be directly mixed using a mixer such as a Henschel mixer, or the inorganic fine powder may be mixed with the inorganic fine powder. A method of spraying silicone oil may be used. Or after dissolving or dispersing silicone oil in a suitable solvent, an inorganic fine powder may be added and mixed to remove the solvent. A method using a sprayer is more preferable in that the formation of inorganic fine powder aggregates is relatively small.
[0229]
The treatment amount of the silicone oil is 1 to 40 parts by mass, preferably 3 to 35 parts by mass with respect to 100 parts by mass of the inorganic fine powder. If the amount of silicone oil is too small, good hydrophobicity cannot be obtained, and if it is too large, problems such as fogging tend to occur.
[0230]
The inorganic fine powder used in the present invention is preferably silica, alumina, or titanium oxide in order to impart good fluidity to the magnetic toner, and among them, silica is particularly preferable. Furthermore, the specific surface area of silica measured by the BET method by nitrogen adsorption is 20 to 350 m.²/ G is preferable, more preferably 25-300m²/ G is even better.
[0231]
The specific surface area of the inorganic fine powder is calculated according to the BET method, for example, by adsorbing nitrogen gas to the sample surface using a specific surface area measuring device Autosorb 1 (manufactured by Yuasa Ionics), using the BET multipoint method. be able to.
[0232]
In the present invention, when silica is used as the inorganic fine powder, the liberation rate of silica is preferably 0.1% to 2.0%, more preferably 0.1% to 1.50%. The liberation rate of silica can be measured by the particle analyzer described above, and the liberation rate of silica can be obtained by the following formula.
[Formula 6]

[0233]
As a specific measuring method, a carbon atom in channel 1 and a silicon atom in channel 2 (measuring wavelength 288.160 nm, K factor using recommended value) may be measured.
[0234]
As a result of investigations by the present inventors, if the liberation rate of silica is less than 0.1%, fogging tends to occur in the latter half of the multi-image printing test, particularly under high temperature and high humidity. Generally, under high temperature environment, the external additive is easily embedded due to stress of the regulating member, etc., and after the printing of a large number of sheets, the fluidity of the magnetic toner is inferior to the initial value, and the above problem occurs. Conceivable. However, such a problem hardly occurs when the liberation rate of silica is 0.1% or more. This is because if the silica is present in a state where it is liberated to some extent, the fluidity of the toner becomes good, so that embedding due to durability becomes difficult to occur, and even if the silica adhering to the toner particles is embedded due to stress, This is considered to be because the decrease in fluidity of the magnetic toner is reduced by the free silica adhering to the surface of the toner particles.
[0235]
On the other hand, if the liberation rate of the silica is more than 2.00%, the free silica contaminates the charge regulating member, resulting in an increase in fog. In such a state, the charging uniformity of the magnetic toner is also impaired, and the transfer efficiency is also lowered. For this reason, it is important that the liberation rate of silica is 0.1% to 2.0%.
[0236]
The magnetic toner of the present invention preferably further comprises a conductive fine powder having a volume average particle size smaller than the weight average particle size of the magnetic toner, and is larger than the number average primary particle size of the inorganic fine powder. It is more preferable to have conductive fine powder having a volume average particle size smaller than the weight average particle size of the magnetic toner. This is because by having the conductive fine powder, the developability of the magnetic toner is improved and a high image density can be obtained. Moreover, the effect will become remarkable if the isolation | separation rate of electroconductive fine powder is 5.0%-50.0%.
[0237]
The reason for this is not clear, but the presence of free conductive fine powder together with free magnetic powder suppresses the charge-up of magnetic toner, and the toner particles are more uniformly charged. I think that it will improve. Further, it is considered that the developability is improved because the conductive fine powder adhering to the toner particles behaves like a microcarrier. For this reason, if the release rate of the conductive fine powder is less than 5.0%, this effect cannot be sufficiently obtained. On the other hand, if the release rate of the conductive fine powder is more than 50.0%, the uniformity of the adhesion of the conductive fine particles to the toner particles is inferior, which is not preferable.
[0238]
The liberation rate of the conductive fine powder can be measured by the particle analyzer described above, and is determined by the following equation.
[Expression 7]

[0239]
As a specific measurement method, carbon atoms are measured in channel 1 and metal element contained in conductive fine powder in channel 3 (measurement wavelength varies depending on the type of metal element. For example, zinc oxide is used as conductive fine particles. In this case, the measurement wavelength is 334.500 nm, and the K factor is a recommended value).
[0240]
When the magnetic toner of the present invention is applied to an image forming method using development and cleaning, the conductive fine powder plays an important role.
[0241]
Here, the behavior of the toner particles and the conductive fine powder during the image forming process when the conductive fine powder is externally added to the toner particles will be described.
[0242]
An appropriate amount of the conductive fine powder contained in the magnetic toner is transferred to the image carrier side together with the toner particles during development of the electrostatic latent image on the image carrier side in the development process. The toner image on the image carrier is transferred to the recording medium side in the transfer process. Part of the conductive fine powder on the image carrier also adheres to the recording medium side, but the rest remains attached and held on the image carrier. When transfer is performed by applying a transfer bias having a polarity opposite to that of the magnetic toner, the magnetic toner is attracted to the recording medium and actively transferred, but the conductive fine powder on the image carrier is conductive. As a result, it does not actively move to the recording medium side, and a part of the material adhering to the recording medium side remains attached and held on the image carrier.
[0243]
In an image forming method that does not use a cleaner, the residual transfer toner remaining on the image carrier surface after transfer and the above-mentioned residual conductive fine powder are transferred to the image carrier surface on the charging portion that is the contact portion between the image carrier and the contact charging member. It is carried as it is and adheres to and mixes with the contact charging member. Accordingly, contact charging of the image carrier is performed in a state where the conductive fine powder is interposed in the contact portion between the image carrier and the contact charging member.
[0244]
Due to the presence of the conductive fine powder, when there is little transfer residual toner on the contact charging member, the contact charging member is closely contacted with the image carrier and the contact resistance regardless of contamination due to adhesion or mixing of the transfer residual toner. Therefore, it is possible to satisfactorily charge the image carrier with the contact charging member.
[0245]
Further, the transfer residual toner adhering to and mixed in the contact charging member is uniformly charged with the same polarity as the charging bias by the charging bias applied from the charging member to the image carrier, and gradually moves from the contact charging member onto the image carrier. As the image carrier surface moves, it reaches the developing section and is developed and cleaned (collected) in the developing process.
[0246]
Further, by repeating the image formation, the conductive fine powder contained in the magnetic toner is transferred to the surface of the image carrier at the developing portion, and is carried to the charging portion through the transfer portion by the movement of the image bearing surface. Since the conductive fine powder is continuously supplied to the charging unit sequentially, even if the conductive fine powder decreases or deteriorates due to dropout or the like in the charging unit, it is possible to prevent a decrease in charging property, which is good. Chargeability is stably maintained.
[0247]
For this reason, the liberation rate of the conductive fine powder is preferably 5.0% to 50.0%. If the liberation rate of the conductive fine powder is less than 5.0%, the conductive fine powder held on the image carrier is reduced and good chargeability cannot be obtained. Further, if the release rate of the conductive fine powder is more than 50.0%, the amount of the conductive fine powder recovered by the development and cleaning increases, and the accumulation of the conductive fine powder in the developing device tends to occur. This is not preferable because the chargeability and developability of the magnetic toner are lowered.
[0248]
In order to promote the uniformity of the charge amount of the magnetic toner in this way, the resistance of the conductive fine powder is 1 × 10.⁹Ωcm or less is preferable. Resistance of conductive fine powder is 1 × 10⁹If it is larger than Ωcm, the conductive fine powder is interposed in the contact portion between the charging member and the image carrier and the charging area in the vicinity thereof, and the fineness to the image carrier through the conductive fine powder of the contact charging member is dense. Even if the contact property is maintained, it is difficult to obtain a charge promoting effect for obtaining good chargeability. In order to sufficiently extract the charge-promoting effect of the conductive fine powder and stably obtain good chargeability, the resistance of the conductive fine powder is the resistance of the surface portion of the contact charging member or the contact portion with the image carrier. Is preferably smaller.
[0249]
Furthermore, the resistance of the conductive fine powder is 1 × 10⁸It is preferable that the resistance is not more than Ωcm in order to overcome charging inhibition caused by adhesion / mixing of the insulating transfer residual toner to the contact charging member and to charge the image carrier more favorably.
[0250]
In the present invention, the content of the conductive fine powder with respect to the entire magnetic toner is preferably 0.5 to 10% by mass. If the content of the conductive fine powder with respect to the entire magnetic toner is less than 0.5% by mass, charging of the image carrier is overcome by overcoming charging inhibition due to adhesion / mixing of insulating transfer residual toner to the contact charging member. A sufficient amount of conductive fine powder for good performance cannot be interposed in the contact area between the charging member and the image bearing member or in the vicinity of the charged area, resulting in a decrease in chargeability and poor charging. Sometimes. In addition, when the content is more than 10% by mass, too much conductive fine powder is recovered by developing and cleaning, thereby reducing the chargeability and developability of the magnetic toner in the developing portion, thereby reducing the image density. Or toner scattering. The content of the conductive fine powder with respect to the entire magnetic toner is preferably 0.5 to 5% by mass.
[0251]
Specifically, the conductive fine powder preferably has a volume average particle size of 0.1 μm or more and smaller than the weight average particle size of the magnetic toner. If the volume average particle size of the conductive fine powder is small, the content of the conductive fine powder with respect to the entire magnetic toner must be set small in order to prevent a decrease in developability. When the volume average particle size of the conductive fine powder is less than 0.1 μm, an effective amount of the conductive fine powder cannot be secured, and charging due to adhesion / mixing of the insulating transfer residual toner to the contact charging member in the charging process. A sufficient amount of conductive fine powder to overcome the hindrance and to charge the image carrier satisfactorily cannot be interposed in the contact portion between the charging member and the image carrier and the charging area in the vicinity thereof. It becomes easy to cause charging failure.
[0252]
If the volume average particle diameter of the conductive fine powder is larger than the weight average particle diameter of the magnetic toner, the conductive fine powder dropped from the charging member shields or diffuses the exposure for writing the electrostatic latent image, thereby This may cause image defects and reduce image quality. Furthermore, since the number of particles per unit weight decreases when the volume average particle size of the conductive fine powder is large, the conductive fine powder is reduced in consideration of reduction or deterioration due to dropping of the conductive fine powder from the charging member. In order to continuously supply and intervene the conductive fine powder in the contact area between the charging member and the image carrier or in the vicinity of the charged region, and the contact charging member passes through the conductive fine powder to the image carrier. In order to maintain the fine contact property and stably obtain good chargeability, the content of the conductive fine powder with respect to the entire magnetic toner must be increased. However, if the content of the conductive fine powder is excessively increased, the charging ability and developability of the magnetic toner as a whole, particularly in a high humidity environment, are reduced, resulting in a decrease in image density and toner scattering. From such a viewpoint, the volume average particle diameter of the conductive fine powder is preferably 5 μm or less.
[0253]
Further, it is preferable that the conductive fine powder is a transparent, white or light-colored conductive fine powder because the conductive fine powder transferred onto the recording medium is not noticeable as fog. The conductive fine powder is preferably a transparent, white or light-colored conductive fine powder from the viewpoint of not hindering exposure in the electrostatic latent image forming step, and more preferably, the conductive fine powder has a transmittance with respect to exposure. Is preferably 30% or more.
[0254]
In the present invention, the light transmittance of the conductive fine powder can be measured by the following procedure. The transmittance is measured in a state where the conductive fine powder of a transparent film having an adhesive layer on one side is fixed for one layer. The light is irradiated from the vertical direction of the sheet, and the light transmitted through the back of the film is collected and the amount of light is measured. The transmittance of the conductive fine powder is calculated as a net light amount from the light amount when only the film and the conductive fine powder are attached. Actually, it can be measured using a 310T transmission densitometer manufactured by X-Rite.
[0255]
For the measurement of the volume average particle size and particle size distribution of the conductive fine powder in the present invention, for example, a product obtained by attaching a liquid module to a LS-230 type laser diffraction particle size distribution measuring device manufactured by Coulter, Inc. can be used. As a condition, a measurement range of 0.04 to 2000 μm is preferable. As a measuring method, a trace amount of surfactant is added to 10 mL of pure water, 10 mg of a conductive fine powder sample is added thereto, and the mixture is dispersed for 10 minutes with an ultrasonic disperser (ultrasonic homogenizer), and then measured for 90 hours. An example is a method in which measurement is performed in seconds and the number of times of measurement once.
[0256]
In the present invention, as a method for adjusting the particle size and particle size distribution of the conductive fine powder, a method for setting the production method and production conditions so that the primary particle of the conductive fine powder can obtain a desired particle size and particle size distribution at the time of production. Besides, a method of agglomerating small particles of primary particles, a method of pulverizing particles of large primary particles or a method by classification, etc. are possible, and further, substrate particles having a desired particle size and particle size distribution (conductive fine powder) In preparing a body, a method of attaching or immobilizing a conductive fine powder on a part or all of the surface of a particle that is a base material when adhering or immobilizing a conductive material, particles having a desired particle size and particle size distribution It is also possible to use a method using a conductive fine powder having a form in which a conductive component is dispersed in the particle, and the particle size and particle size distribution of the conductive fine powder can be adjusted by combining these methods. .
[0257]
The particle diameter in the case where the conductive fine powder particles are formed as an aggregate is defined as an average particle diameter of the aggregate. There is no problem that the conductive fine powder exists not only in the state of primary particles but also in the state of aggregation of secondary particles. In any aggregated state, any form can be used as long as the aggregate is interposed in the contact portion between the charging member and the image carrier or a charged region in the vicinity thereof and can realize a charge assisting or promoting function.
[0258]
In the present invention, the resistance of the conductive fine powder can be determined by measuring and normalizing by a so-called tablet method. More specifically, the bottom area is 2.26 cm.²A powder sample of about 0.5 g is placed in the cylinder, and 15 kg of pressure is applied to the upper and lower electrodes. At the same time, a voltage of 100 V is applied to measure the resistance value, and then normalized to calculate the specific resistance.
[0259]
Examples of the conductive fine powder in the present invention include carbon fine powder such as carbon black and graphite; metal fine powder such as copper, gold, silver, aluminum and nickel; zinc oxide, titanium oxide, tin oxide, aluminum oxide and indium oxide. Metal oxides such as silicon oxide, magnesium oxide, barium oxide, molybdenum oxide, and tungsten oxide; metal compounds such as molybdenum sulfide, cadmium sulfide, and potassium titanate, or composite oxides of these may be used as required. It can be used by adjusting the distribution. Among these, the conductive fine powder is preferably non-magnetic, and inorganic oxide fine powders such as zinc oxide, tin oxide, and titanium oxide are particularly preferable.
[0260]
Further, for the purpose of controlling the resistance value of the conductive inorganic oxide, a metal oxide doped with an element such as antimony or aluminum, a fine powder having a conductive material on its surface, or the like can be used. For example, a fine powder of titanium oxide surface-treated with tin oxide / antimony, a fine powder of stannic oxide doped with antimony, or a fine powder of stannic oxide.
[0261]
Examples of commercially available tin oxide / antimony-treated conductive titanium oxide fine powders include EC-300 (Titanium Industry Co., Ltd.), ET-300, HJ-1, HI-2 (above, Ishihara Sangyo Co., Ltd.), W -P (Mitsubishi Materials Corporation).
[0262]
Examples of commercially available antimony-doped conductive tin oxide include T-1 (Mitsubishi Materials Corporation) and SN-100P (Ishihara Sangyo Co., Ltd.), and examples of commercially available stannic oxide include SH-S (Japan). Chemical Industry Co., Ltd.).
[0263]
The magnetic toner of the present invention further exceeds the primary particle size of 30 nm (preferably having a specific surface area of 50 m for the purpose of improving the cleaning property).²/ G), more preferably the primary particle size is 50 nm or more (preferably the specific surface area is 30 m).²It is also one of preferable modes to add inorganic or organic fine particles close to spherical shape (less than / g). For example, spherical silica particles, spherical polymethylsilsesquioxane particles, spherical resin particles and the like are preferably used.
[0264]
The magnetic toner used in the present invention may further contain other additives such as Teflon powder, zinc stearate powder, polyvinylidene fluoride powder, or cerium oxide powder, A small amount of abrasives such as silicon powder and strontium titanate powder, or fluidity-imparting agents such as titanium oxide powder and aluminum oxide powder, anti-caking agents, and organic fine particles having opposite polarity and inorganic fine particles as a developing property improver. It can also be used. These additives can also be used after hydrophobizing the surface.
[0265]
The fine powder is externally added to the magnetic toner by mixing and stirring magnetic particles (toner particles or magnetic toner) and fine powder. Specific examples include mechano-fusion, I-type mill, hybridizer, turbo mill, Henschel mixer and the like, and it is particularly preferable to use a Henschel mixer from the viewpoint of preventing the generation of coarse particles.
[0266]
Further, in order to adjust the liberation rate of the fine particles, it is preferable to adjust the temperature at the time of external addition, the external addition strength, the external addition time, and the like. As an example, when a Henschel mixer is used, the temperature in the tank at the time of external addition is preferably 50 ° C. or less. If the temperature is higher than this, embedding of the external additive is abruptly caused by heat and coarse particles are generated, which is not preferable. The peripheral speed of the Henschel mixer blades is preferably 10 to 80 m / sec from the viewpoint of adjusting the liberation rate of the external additive. Note that the adjustment of the liberation rate can be applied to the adjustment of the liberation rate of the inorganic fine powder and the conductive fine powder.
[0267]
Since the magnetic toner of the present invention has excellent durability, low fog, and high transferability, it can be suitably used in an image forming method using a contact charging process, and can also be used in a cleanerless image forming method. These forms of use are also part of the present invention.
[0268]
In the image forming method including the contact charging process, the key technology is to reduce the magnetic toner that is transferred to the charging process without being transferred, that is, the transfer residual toner and the fog toner. By using the magnetic toner of the present invention having such performance, it is possible to obtain an excellent image for a long period of time with excellent environmental stability.
[0269]
Further, in the cleanerless image forming method, the transfer residual toner passes through the charging process and is collected in the developing unit in the development process.Such toner with poor transferability is inferior in chargeability. It is accumulated in the developing unit with durability and image characteristics are likely to deteriorate. In addition, since toner with poor transferability increases the amount of untransferred toner, uniform charging is inhibited in the charging step, making it difficult to obtain a good image. In particular, this tendency is strong with a toner having poor durability, which is not preferable.
[0270]
However, since the magnetic toner of the present invention has good image characteristics and durability, high image quality can be stably maintained over a long period of time even when used in a cleanerless image forming method. The image forming method is achieved.
The image forming method of the present invention will be described below.
[0271]
The image forming method of the present invention includes a charging step, an electrostatic latent image forming step, a developing step, and a transferring step. The magnetic toner of the present invention is used as the magnetic toner in the developing step, and the charging step is further performed. Is a step of charging the image carrier by applying a voltage to a charging member that is in contact with the image carrier to form a contact portion.
Next, embodiments of the image forming method of the present invention will be described in detail with reference to the drawings, but the present invention is not limited thereto.
[0272]
An example of an image forming apparatus for realizing the image forming method of the present invention is shown in FIG.
In FIG. 1, a primary charging roller 117 as a charging member, a developing device 140, a transfer roller 114, a cleaner 116, a register roller 124, and the like are provided around a photoconductor 100 as an image carrier.
[0273]
The photoreceptor 100 is charged to −700 V by the primary charging roller 117 (applied voltage is AC voltage −2.0 kVpp (Vpp: peak-to-peak potential), DC voltage −700 Vdc).
[0274]
Then, the laser beam 123 is irradiated onto the photoconductor 100 by the laser beam scanner 121, the photoconductor 100 is exposed, and an electrostatic latent image is formed on the photoconductor 100.
[0275]
The electrostatic latent image on the photoreceptor 100 is developed with a one-component magnetic toner by the developing device 140, and is transferred onto the recording medium by the transfer roller 114 in contact with the photoreceptor via the recording medium.
[0276]
The recording medium P on which the toner image is placed is conveyed to the fixing device 126 by the conveyance belt 125 or the like and fixed on the recording medium P. Further, the toner remaining on a part of the photoconductor is cleaned by the cleaner 116.
[0277]
As shown in FIG. 2, the developing device 140 has a cylindrical magnetic toner carrier 102 (hereinafter also referred to as “developing sleeve”) made of a nonmagnetic metal such as aluminum or stainless steel in the vicinity of the photoreceptor 100. The gap between the photosensitive member 100 and the developing sleeve 102 is maintained at about 230 μm by a sleeve / photosensitive member gap holding member (not shown) or the like. This gap can be changed if necessary. A magnet roller 104 is fixed and disposed concentrically with the developing sleeve 102 in the developing sleeve 102. However, the developing sleeve 102 is rotatable.
[0278]
The magnet roller 104 is provided with a plurality of magnetic poles as shown in the figure, S1 is development, N1 is magnetic toner coating amount regulation, S2 is magnetic toner intake / conveyance, and N2 is magnetic toner blowing prevention. Yes. An elastic blade 103 is provided as a member for regulating the amount of magnetic toner that adheres to the developing sleeve 102 and is conveyed, and the amount of magnetic toner conveyed to the developing region is controlled by the contact pressure of the elastic blade 103 against the developing sleeve 102. Is done. In the developing area, a developing bias of a DC voltage and an AC voltage is applied between the photosensitive member 100 and the developing sleeve 102, and the toner on the developing sleeve 102 flies on the photosensitive member 100 according to the electrostatic latent image and is visible. Become a statue.
[0279]
In the image forming method of the present invention, the developing step is an image forming method having a developing and cleaning step or a cleaner-less step that also serves as a cleaning step for collecting the magnetic toner remaining on the photoreceptor after the toner image is transferred onto the transfer material. Even if it exists, preferable image formation is possible.
[0280]
In the image forming method of the present invention, it is preferable that in the charging step, conductive fine powder is present at least in the contact portion between the charging member and the image carrier and in the vicinity thereof. In the image forming method of the present invention, as the means for interposing the conductive fine powder in the contact portion and the vicinity thereof, for example, the conductive fine powder is supplied to the charging member in the charging means used in the image forming method of the present invention. A conductive fine powder supply means such as a hopper can be exemplified.
[0281]
Furthermore, in the present invention, the conductive fine powder contained in the magnetic toner of the present invention can be used to interpose the conductive fine powder in the contact portion and the vicinity thereof. That is, the conductive fine powder contained in the magnetic toner adheres to the image carrier in the development process and remains on the image carrier after the transfer process, thereby being carried to the contact portion and the vicinity thereof. Such a supply method of the conductive fine powder is particularly effective in the development and cleaning image forming method or the cleanerless image forming method, and is preferably used in the present invention.
[0282]
In the charging step of the present invention, if the amount of conductive fine powder intervened at the contact portion between the image carrier and the contact charging member is too small, a sufficient lubricating effect by the fine powder cannot be obtained, and the image carrier and the charging member are charged. It is difficult to rotate the charging member with a speed difference with respect to the image carrier due to a large friction with the member. That is, the driving torque becomes excessive, and if it is rotated forcibly, the surface of the charging member or the image carrier is scraped. Furthermore, the effect of increasing the contact opportunity due to the conductive fine powder may not be obtained, and sufficient charging performance cannot be obtained. On the other hand, if the amount of intervening is too large, dropping of the conductive fine powder from the charging member is remarkably increased, which may adversely affect image formation.
[0283]
In the charging process according to the present invention, the contact portion between the charging member and the image carrier is 1 × 10 6.^ThreePiece / mm²It is preferable to charge the image bearing member with the above conductive fine powder interposed. More preferably 10^FourPiece / mm²The above is good. 10^ThreePiece / mm²If it is lower, the sufficient lubricating effect and the effect of increasing the contact opportunity cannot be obtained as described above, and the charging performance tends to be lowered. Also 10^FourPiece / mm²If it is lower, there is a possibility that the charging performance is lowered when there is a large amount of residual toner.
[0284]
The amount of conductive fine powder intervened in the contact portion and the amount of conductive fine powder intervened on the image carrier in the latent image forming step are preferably measured directly on the contact surface portion of the charging member and the image carrier. When there is a speed difference between the surface of the charging member forming the contact portion and the surface of the image carrier, many of the particles present on the image carrier before contacting the charging member move in the opposite direction. In the present invention, the amount of particles on the surface of the charging member immediately before reaching the contact surface portion is used as the intervening amount because the charging member is peeled off.
[0285]
Specifically, the rotation of the image carrier and the charging member (for example, a roller member) is stopped in a state where no charging bias is applied, and the surface of the image carrier and the roller member is placed on a video microscope (for example, OVM1000N manufactured by OLYMPUS) and a digital still. Take a picture with a recorder (for example, SR-3100 manufactured by DELTAS). As for the roller member, the roller member is brought into contact with the slide glass under the same conditions as in contact with the image carrier, and the contact surface is photographed with a video microscope from the back surface of the slide glass at 10 or more positions with a 1000 × objective lens. In order to separate individual particles from the obtained digital image, binarization processing is performed with a certain threshold value, and the number of regions where particles are present is measured using desired image processing software. Also, the abundance on the image carrier is measured by photographing the image carrier with the same video microscope and performing the same processing.
[0286]
In the image forming method of the present invention, particularly the cleanerless image forming method, the charging member has elasticity in providing a contact portion for interposing the conductive fine powder between the charging member and the image carrier. It is preferable that the image bearing member is electrically conductive in order to charge the image bearing member by applying a voltage to the charging member. Accordingly, the charging member is composed of a roller member that is a conductive elastic roller, a magnetic brush charging member that has a magnetic brush portion in which magnetic particles are magnetically constrained, and the magnetic brush portion is in contact with the photosensitive member, or conductive fibers. It is preferable that it is a brush member.
[0287]
Further, in the image forming method of the present invention, the charging member having flexibility increases the chance that the conductive fine powder contacts the image carrier at the contact portion between the charging member and the image carrier. In terms of improving the direct injection chargeability, high contactability can be obtained.
[0288]
That is, the charging member comes into close contact with the image carrier via the conductive fine powder, and the conductive fine powder present at the contact portion between the charging member and the image carrier rubs the surface of the image carrier without any gap. Therefore, the charging of the image carrier by the charging member is dominated by stable and safe direct injection charging without using the discharge phenomenon due to the presence of the conductive fine powder, and high charging efficiency that cannot be obtained by conventional roller charging or the like is obtained. Thus, a potential substantially equal to the voltage applied to the charging member can be applied to the image carrier.
[0289]
Further, in the image forming method of the present invention, the charging step is a step of charging the image carrier while moving the surface of the charging member forming the contact portion and the surface of the image carrier with a relative speed difference. It is preferable that According to such a charging step, the opportunity for the conductive fine powder to contact the image carrier at the contact portion can be greatly increased, higher contact can be obtained, and direct injection charging can be achieved. This is preferable in terms of improvement.
[0290]
In addition, by interposing the conductive fine powder at the contact portion between the charging member and the image carrier, the lubricating effect (friction reduction effect) of the conductive fine powder significantly increases the gap between the charging member and the image carrier. It is possible to provide a speed difference without increasing torque and not causing significant scraping of the charging member and the image carrier surface.
[0291]
Further, in order to temporarily collect and level the transfer residual toner on the image carrier carried to the abutting portion on the charging member, the charging process in the present invention includes the surface of the charging member and the surface of the image carrier. The step of charging the image carrier while moving in opposite directions is preferable. For example, the charging member is preferably driven to rotate, and the rotation direction of the charging member rotates in the direction opposite to the moving direction of the image carrier surface at the contact portion. That is, it is possible to perform direct injection charging predominantly by once separating the transfer residual toner on the image carrier by reverse rotation and performing charging.
[0292]
Although it is possible to move the charging member in the same direction as the moving direction of the image carrier surface to give a speed difference, the charging property of direct injection charging is the ratio of the peripheral speed of the image carrier to the peripheral speed of the charging member. Therefore, in order to obtain the same peripheral speed ratio as in the reverse direction, the rotation speed of the charging member is larger in the forward direction than in the reverse direction. Therefore, it is advantageous in terms of the rotation speed to move the charging member in the reverse direction. It is.
[0293]
As a configuration for providing the speed difference, the charging member can be rotationally driven to provide a speed difference between the image carrier and the charging member. The peripheral speed ratio described here can be expressed by the following equation.
[Equation 8]
Peripheral speed ratio (%) = (charging member peripheral speed / image carrier peripheral speed) × 100
[0294]
In order to temporarily collect the transfer residual toner on the image bearing member on the charging member and to carry the conductive fine powder and to perform direct injection charging, it is preferable that the charging member has flexibility. More preferably, it is free. As such a charging member, as described above, a roller member having conductivity and elasticity, a conductive brush member, and the like can be preferably exemplified.
[0295]
In the present invention, the roller member used as the charging member preferably has an Asker C hardness of 50 degrees or less. If the hardness is too low, the shape will not be stable, resulting in poor contact with the image carrier, and the roller member surface layer will be scraped by interposing a conductive fine powder at the contact portion between the charging member and the image carrier. Or, there is a tendency that stable chargeability cannot be obtained. On the other hand, if the hardness is too high, a charging contact portion cannot be ensured between the image carrier and the micro contact property to the surface of the image carrier tends to deteriorate. Furthermore, 25-50 degree | times is a preferable range by Asker C hardness.
[0296]
The roller member used in the present invention can be produced, for example, by forming a middle resistance layer of rubber or foam as a flexible member on a cored bar. The middle resistance layer is formulated with a resin (for example, urethane), conductive particles (for example, carbon black), a sulfurizing agent, a foaming agent, and the like, and is formed in a roller shape on the core metal. Thereafter, if necessary, the roller member can be prepared by cutting and polishing the surface to adjust the shape.
[0297]
Further, in the present invention, the roller member has at least the surface of a recess having an average cell diameter of 5 to 300 μm in terms of a sphere, and the porosity of the surface of the roller member using the recess as a space portion is 15 to. 90% is preferable for interposing the conductive fine powder on the surface of the roller member.
[0298]
When the average cell diameter on the surface of the roller member is smaller than 5 μm, the supply of the conductive fine powder is insufficient. When the average cell diameter exceeds 300 μm, the supply of the conductive fine powder is excessive, and the charging potential of the image carrier is in any case. This is not preferable because it becomes uneven. Further, when the porosity is less than 15%, the supply of the conductive fine powder is insufficient, and when it exceeds 90%, the supply of the conductive fine powder becomes excessive, and the charging potential of the image carrier becomes nonuniform in all cases. Is not preferable.
[0299]
It is important that the roller member functions as an electrode having a sufficiently low resistance to charge the moving charged object while at the same time obtaining a sufficient contact state with the charged object by giving elasticity. On the other hand, it is necessary to prevent voltage leakage in the case where a defect site such as a pinhole exists in the member to be charged. When a photoreceptor is used as the image bearing member, the charging member used in the charging step of the present invention has a volume resistance value of 1 × 10 6 in order to obtain sufficient chargeability and leakage resistance.^Three~ 1x10⁸The resistance is preferably Ωcm, more preferably a volume resistance of 1 × 10^Four~ 1x10⁷It is good that it is Ωcm.
[0300]
The volume resistance value of the roller member is such that 100 V is applied between the core metal and the aluminum drum in a state where the roller is pressure-bonded to a cylindrical aluminum drum having a diameter of 30 mm so that a total pressure of 1 kg is applied to the core metal of the roller. It can be measured by measuring.
[0301]
The material of the roller member is not limited to the elastic foam. As the material of the elastic body, carbon such as ethylene-propylene-diene polyethylene, urethane, butadiene acrylonitrile rubber, silicone rubber, or isoprene rubber is used for resistance adjustment. Examples thereof include rubber materials in which conductive materials such as black and metal oxides are dispersed, and those obtained by foaming these materials. It is also possible to adjust the resistance using an ion conductive material without dispersing the conductive particles or in combination with the conductive particles.
[0302]
Examples of the core bar used for the roller member include aluminum and SUS.
[0303]
The roller member is disposed in pressure contact with a member to be charged as an image carrier with a predetermined pressing force against elasticity to form a contact portion between the roller member and the image carrier. The width of the contact portion is not particularly limited, but is preferably 1 mm or more, more preferably 2 mm or more in order to obtain a stable and close adhesion between the roller member and the image carrier.
[0304]
In the charging step of the present invention, a conductive brush member can be suitably used as the charging member. Examples of the brush member as the charging member include a charging brush in which resistance is adjusted by dispersing a conductive material in commonly used fibers.
[0305]
As the fiber, generally known fiber can be used, and examples thereof include nylon, acrylic, rayon, polycarbonate, polyester and the like. As the conductive material, generally known conductive materials can be used. For example, conductive metal such as nickel, iron, aluminum, gold, silver or iron oxide, zinc oxide, tin oxide, antimony oxide, titanium oxide, etc. The conductive metal oxides, and further conductive powders such as carbon black. These conductive materials may be subjected to surface treatment for the purpose of hydrophobization and resistance adjustment as necessary. In use, it is selected in consideration of dispersibility with fibers and productivity.
[0306]
When a brush member is used as the charging member, there are a fixed type and a rotatable roll type. As the roll-shaped charging brush, for example, a tape having conductive fibers piled can be spirally wound around a metal core to form a roll-shaped brush member. The conductive fiber has a fiber thickness of 1 to 20 denier (fiber diameter of about 10 to 500 μm), a brush fiber length of 1 to 15 mm, and a brush density of 10,000 to 300,000 per square inch (1 square meter) 1.5 × 10 per⁷~ 4.5 × 10⁸About this) is preferably used.
[0307]
It is preferable to use a brush member having as high a brush density as possible, and it is also preferable to make one fiber from several to several hundreds of fine fibers. For example, it is possible to bundle 50 fine fibers of 300 denier, such as 300 denier / 50 filament, and plant the fibers as one fiber. However, in the present invention, the charging point for direct injection charging is mainly determined by the contact density between the charging member and the image carrier and the density of the conductive fine powder in the vicinity thereof. Therefore, the range of selection of the charging member is widened.
[0308]
Examples of the core bar used for the brush member include the same ones used for the roller member.
[0309]
Examples of the material of the brush member include conductive rayon fibers REC-B, REC-C, REC-M1, and REC-M10 manufactured by Unitika Ltd., SA-7 manufactured by Toray Industries, Inc., Nippon Kashige Co., Ltd. There are Sanderlon made by Kanebo, Beltron made by Kanebo, Kuraray made by Kuraray Co., Ltd., carbon dispersed in rayon, and Roval made by Mitsubishi Rayon Co., Ltd. REC-B, REC in terms of environmental stability. -C, REC-M1, and REC-M10 are particularly preferable.
[0310]
The charging step in the image forming method of the present invention includes a photosensitive member that is a member to be charged and an image carrier, a roller type (charging roller) that is the primary charging roller in FIG. Form a contact portion with a conductive charging member (contact charging member / contact charger) such as a die or blade type (charging blade), and apply a predetermined charging bias to the contact charging member to expose the photoreceptor surface. It is possible to use a contact charging device that charges the battery to a predetermined polarity and potential. The charging process using these contact charging members has an effect of eliminating the need for a high voltage and reducing the generation of ozone.
[0311]
As a preferable process condition when the charging roller is used as shown in FIG. 1, the contact pressure of the roller member is 4.9 to 490 N / m (5 to 500 g / cm), and the AC voltage is applied to the DC voltage or the DC voltage. Superposed ones are used. In the case of using a DC voltage superimposed with an AC voltage, AC voltage = 0.5 to 5 kVpp, AC frequency = 50 to 5 kHz, and DC voltage = ± 0.2 to ± 5 kV are preferable.
[0312]
Thus, in the case of using an AC voltage, the charging step in the present invention is performed by applying an AC voltage having a peak-to-peak voltage less than 2 × Vth (Vth: discharge start voltage when DC voltage is applied) (V) to the charging member. A step of applying a voltage superimposed on the voltage is preferable.
[0313]
If the peak voltage of the AC voltage applied to the DC voltage is not less than 2 × Vth, the potential on the image carrier may become unstable. The AC voltage when applying a bias in which an AC voltage is superimposed on the DC voltage is more preferably a peak voltage less than Vth. As a result, the image carrier can be charged without a substantial discharge phenomenon.
[0314]
As a waveform of the AC voltage used in the charging process, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Further, it may be a pulse wave formed by periodically turning on / off a DC power source. In this way, a bias that periodically changes the voltage value can be used as the waveform of the AC voltage.
[0315]
Next, in the image forming method of the present invention, an image carrier that is a member to be charged in the charging step will be described.
[0316]
In the image forming method of the present invention, the image carrier is preferably a photoconductor using a photoconductive substance, and preferably has a surface layer.
[0317]
One of the more preferable embodiments of the image carrier used in the present invention will be described below.
In the present invention, the volume resistance value of the outermost surface layer of the image carrier is 1 × 10.⁹~ 1x10¹⁴It is preferable that the resistance is Ωcm in order to give better chargeability to the image carrier. In the charging method using direct injection of charges, charges can be exchanged more efficiently by lowering the resistance on the side of the image carrier that is a charged body. For this purpose, the volume resistance value of the outermost surface layer of the image carrier is 1 × 10.¹⁴It is preferable that it is Ωcm or less. On the other hand, in order to hold an electrostatic latent image as an image carrier for a certain time, the volume resistance value of the outermost surface layer is 1 × 10.⁹It is preferable that it is Ωcm or more.
[0318]
Furthermore, the volume resistance value of the outermost surface layer of the image carrier is 1 × 10.⁹~ 1x10¹⁴By being Ωcm, it is more preferable because sufficient chargeability can be imparted even in an apparatus having a high process speed.
[0319]
In the present invention, the volume resistance value of the outermost surface layer of the image bearing member is a layer having the same composition as the outermost surface layer of the image bearing member on a polyethylene terephthalate (PET) film having gold deposited on the surface. And measuring this by applying a voltage of 100 V in an environment of 23 ° C. and 65% with a volume resistance measuring device (for example, 4140B pA MATER manufactured by Hewlett-Packard Company).
[0320]
In the present invention, in order to adjust the volume resistance value in the outermost surface layer of the image carrier, the outermost surface layer is preferably a resin layer in which conductive particles made of at least a metal oxide are dispersed.
[0321]
Examples of the conductive particles include metals, metal oxides, and the like, preferably zinc oxide, titanium oxide, tin oxide, antimony oxide, indium oxide, bismuth oxide, tin oxide-coated titanium oxide, tin-coated indium oxide, There are ultrafine particles such as antimony-coated tin oxide and zirconium oxide. These may be used alone or in combination of two or more.
[0322]
In general, when conductive particles are dispersed in the outermost surface layer, it is necessary that the particle diameter of the particles is smaller than the wavelength of the incident light in order to prevent scattering of incident light by the dispersed particles. The particle size of the conductive particles is preferably 0.5 μm or less. Moreover, 2-90 mass% is preferable with respect to the outermost surface layer total weight, and, as for content of the electrically-conductive particle in an outermost surface layer, 5-80 mass% is more preferable. Moreover, 0.1-10 micrometers is preferable and, as for the film thickness of an outermost surface layer, 1-7 micrometers is more preferable.
[0323]
In the image forming method of the present invention, various image carriers can be suitably used. For example, when a protective film mainly composed of a resin is provided on an inorganic photoreceptor such as selenium or amorphous silicon, or a function separation type When the charge transport layer of the organic image carrier has a surface layer made of a charge transport material and a resin, a protective layer may be further provided on the surface layer to form an outermost surface layer.
[0324]
It is preferable to impart releasability to the outermost surface layer of the image carrier in order to further improve the transferability of the magnetic toner and the durability of the image carrier, and from this viewpoint, the image used in the present invention. It is preferable that the contact angle of water on the surface of the carrier is 85 degrees or more. More preferably, the contact angle is 90 degrees or more.
[0325]
Incidentally, the contact angle of the surface of the photoreceptor with respect to water can be set to 85 degrees or more by means described later, and toner transferability and durability of the photoreceptor can be further improved. Preferably, the contact angle with water is 90 degrees or more.
[0326]
The contact angle is measured by using a drop-type contact angle meter (for example, contact angle meter CA-X type manufactured by Kyowa Interface Science Co., Ltd.) where the free surface of water is in contact with the image carrier. It is defined by the angle formed by the surface of the image carrier (the angle inside the liquid).
[0327]
In addition, the said measurement shall be performed at room temperature (about 25 degreeC). The same measurement was performed in the examples described later.
[0328]
As a means for imparting releasability as described above to the image carrier surface,
(1) A resin having a low surface energy is used as the resin constituting the film.
(2) Add additives that impart water repellency and lipophilicity.
(3) A material having high releasability is dispersed in powder form.
Etc.
[0329]
As an example of (1), it is achieved by introducing a fluorine-containing group, a silicone-containing group or the like into the resin structure. As (2), a surfactant or the like may be used as an additive. Examples of (3) include compounds containing fluorine atoms, that is, polytetrafluoroethylene, polyvinylidene fluoride, carbon fluoride, and the like.
[0330]
Among these means, the means (3) is more preferable. That is, the outermost surface layer of the image carrier is a resin layer in which at least one kind of lubricant fine particles selected from fluorine resin particles, silicone resin particles, and polyolefin resin particles are dispersed. This is one preferred form in the forming method. Among the above-mentioned lubricant fine particles, a method of dispersing a releasable powder of fluorine-based resin particles such as a fluorine-containing resin in the outermost surface layer is preferable, and polytetrafluoroethylene is particularly preferable.
[0331]
In order to contain the lubricant fine particles on the surface of the image carrier, a layer in which the fine particles are dispersed in a binder resin is provided on the outermost surface of the image carrier, or an organic photosensitive material originally composed mainly of a resin. In the case of an image carrier such as a body, the powder may be dispersed in the uppermost layer without newly providing a surface layer. The addition amount is preferably 1 to 60% by mass, and more preferably 2 to 50% by mass with respect to the total weight of the surface layer. If it is less than 1% by mass, the effect of improving the transferability of the magnetic toner and the durability of the image carrier is insufficient, and if it exceeds 60% by mass, the strength of the film is reduced or the amount of incident light on the image carrier is remarkably high. It is not preferable because it decreases.
[0332]
The image forming method of the present invention is a direct charging method in which the charging unit makes the charging member abut on the image carrier, and is preferable in terms of less generation of ozone, but the corona discharge in which the charging unit does not contact the image carrier. Since the load on the surface of the image carrier is large as compared with the method according to the above, the above configuration has a remarkable improvement effect in terms of the life of the image carrier, and is one of the preferable application forms.
[0333]
As described above, various conventionally known image carriers can be used for the image carrier used in the present invention. The conductive substrate, the photosensitive layer formed on the conductive substrate, Is used. As the photosensitive layer, a photosensitive layer formed by laminating a plurality of layers having various functions such as a charge generation layer, a charge transport layer, and a surface layer (protective layer) for protecting the surface of the image carrier is used. I can do it.
[0334]
Examples of conductive substrates include metals such as aluminum and stainless steel, plastics having a coating layer made of aluminum alloy, indium oxide-tin oxide alloy, paper impregnated with conductive particles, plastics, plastics having conductive polymers, etc. Cylindrical cylinders and films are used.
[0335]
On these conductive substrates, the purpose is to improve the adhesion of the photosensitive layer, improve coating properties, protect the substrate, cover defects on the substrate, improve charge injection from the substrate, and protect against electrical breakdown of the photosensitive layer. An undercoat layer may be provided. Undercoat layer is polyvinyl alcohol, poly-N-vinylimidazole, polyethylene oxide, ethyl cellulose, methyl cellulose, nitrocellulose, ethylene-acrylic acid copolymer, polyvinyl butyral, phenol resin, casein, polyamide, copolymer nylon, glue, gelatin, polyurethane It is made of a material such as aluminum oxide. The membrane pressure is usually about 0.1 to 10 μm, preferably about 0.1 to 3 μm.
[0336]
The charge generation layer is composed of azo pigments, phthalocyanine pigments, indigo pigments, perylene pigments, polycyclic quinone pigments, squarylium dyes, pyrylium salts, thiopyrylium salts, triphenylmethane dyes, selenium, amorphous silicon, etc. A charge generating material such as an inorganic material is dispersed in a suitable binder and applied, or vapor deposition is used. The binder can be selected from a wide range of binder resins, such as polycarbonate resin, polyester resin, polyvinyl butyral resin, polystyrene resin, acrylic resin, methacrylic resin, phenol resin, silicon resin, epoxy resin, vinyl acetate resin, etc. Is mentioned. The amount of the binder contained in the charge generation layer is 80% by mass or less, preferably 0 to 40% by mass. Further, the film pressure of the charge generation layer is preferably 5 μm or less, particularly preferably 0.05 to 2 μm.
[0337]
The charge transport layer has a function of receiving charge carriers from the charge generation layer in the presence of an electric field and transporting them. The charge transport layer is formed by dissolving a charge transport material in a solvent together with a binder resin as necessary, and coating, and the film pressure is generally 5 to 40 μm. Examples of the charge transport material include polycyclic aromatic compounds having a structure such as biphenylene, anthracene, pyrene, and phenanthrene in the main chain or side chain, nitrogen-containing cyclic compounds such as indole, carbazole, oxadiazole, and pyrazoline, hydrazone compounds, Examples include styryl compounds, selenium, selenium-tellurium, amorphous silicon, and cadmium sulfide.
[0338]
In addition, as a binder resin for dispersing these charge transport materials, polycarbonate resin, polyester resin, polymethacrylic acid ester, polystyrene resin, acrylic resin, polyamide resin, and other organic materials such as poly-N-vinylcarbazole and polyvinyl anthracene are used. A photoconductive polymer etc. are mentioned.
[0339]
Moreover, you may provide a protective layer as a surface layer. As the resin for the protective layer, polyester, polycarbonate, acrylic resin, epoxy resin, phenol resin, or a curing agent for these resins may be used alone or in combination of two or more.
[0340]
Coating of the surface layer or the like can be performed by spray coating, beam coating, or penetration (dipping) coating of the resin dispersion.
[0341]
In the present invention, it is preferable that an electrostatic latent image forming step for forming an electrostatic latent image on the charging surface of the image carrier is performed by an image exposure unit. The image exposure means for forming the electrostatic latent image is not limited to the laser scanning exposure means for forming a digital latent image, and other light emitting elements such as normal analog image exposure and LEDs may be used. It does not matter as long as it can form an electrostatic latent image corresponding to image information, such as a combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter.
[0342]
In addition, in the image forming method of the present invention, in order to obtain a high image quality without fogging, a magnetic layer having a layer thickness smaller than the closest distance (between S and D) between the magnetic toner carrier and the photoconductor is formed on the magnetic toner carrier. Development is performed in a development process in which toner is applied and development is performed by applying an AC voltage. That is, the layer pressure regulating member that regulates the magnetic toner on the magnetic toner carrier is set and used so that the closest gap between the photoreceptor and the magnetic toner carrier is wider than the toner layer thickness on the magnetic toner carrier. From the viewpoint of uniformly charging the magnetic toner, the layer pressure regulating member that regulates the magnetic toner on the magnetic toner carrier is regulated by the elastic member that is in contact with the magnetic toner carrier via the magnetic toner. preferable.
[0343]
From the above, in the development step in the image forming method of the present invention, 5-50 g / m on the magnetic toner carrier.²It is preferable to form a toner layer. The amount of toner on the magnetic toner carrier is 5 g / m.²If it is smaller than 1, it is difficult to obtain a sufficient image density, and the toner layer may become uneven due to excessive charging of the toner. The amount of toner on the magnetic toner carrier is 50 g / m.²If the amount is larger than that, toner scattering tends to occur.
[0344]
Further, it is preferable that the magnetic toner carrier is placed facing the image carrier with an interval of 100 to 1000 μm. If the interval between the magnetic toner carrier and the image carrier is less than 100 μm, the change in development characteristics of the magnetic toner with respect to the fluctuation of the interval becomes large, making it difficult to mass-produce an image forming apparatus satisfying stable image quality. Become. When the distance between the magnetic toner carrier and the image carrier is larger than 1000 μm, the followability of the magnetic toner to the latent image on the image carrier is lowered, so that the resolution is lowered and the image density is lowered, such as a lower image density. Tend to invite. Preferably 120-500 micrometers is good.
[0345]
In the image forming method of the present invention, the developing step is a step of applying an alternating electric field as a developing bias to the magnetic toner carrier to transfer the toner to the electrostatic latent image on the image carrier to form a toner image. Preferably, the applied developing bias may be a voltage in which an alternating electric field is superimposed on a DC voltage.
[0346]
As the waveform of the alternating electric field, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Further, it may be a pulse wave formed by periodically turning on / off a DC power source. As described above, a bias whose voltage value periodically changes can be used as the waveform of the alternating electric field.
[0347]
In the developing step of the present invention, at least a peak-to-peak electric field strength of 3 × 10 5 is provided between the magnetic toner carrier that carries toner and the image carrier.⁶-10x10⁶It is preferable to apply an alternating electric field of V / m and a frequency of 500 to 5000 Hz as a developing bias.
[0348]
Electric field strength due to development bias is 3 × 10⁶If it is less than V / m, the recoverability of the transfer residual toner in the development process in the development and cleaning system is lowered, and fogging due to poor recovery tends to occur. Further, the electric field strength due to the developing bias is 10 × 10.⁶If V / m is greater than V / m, the developing power is too large, the resolution is likely to deteriorate due to the collapse of fine lines, the image quality is likely to deteriorate due to increased fog, and image defects due to leakage of the developing bias to the image carrier are likely to occur. It tends to occur.
[0349]
On the other hand, when the frequency is lower than 500 Hz, the frequency of desorption of the magnetic toner with respect to the latent image is reduced, the transfer residual toner recoverability in the developing process is liable to be lowered, and the image quality is liable to be lowered. On the other hand, if the frequency is higher than 5000 Hz, the magnetic toner that can follow the change in the electric field is reduced, so that the recoverability of the transfer residual toner is lowered and the developability is liable to be lowered.
[0350]
The magnetic toner carrier used in the present invention is preferably a conductive cylinder (developing roller) formed of a metal or alloy such as aluminum or stainless steel. A conductive cylinder may be formed of a resin composition having sufficient mechanical strength and conductivity, or a conductive rubber roller may be used. Moreover, it is not limited to the cylindrical shape as described above, and may be an endless belt that is rotationally driven.
[0351]
The surface roughness of the magnetic toner carrier used in the present invention is preferably in the range of 0.2 to 3.5 μm in terms of JIS centerline average roughness (Ra). If Ra is less than 0.2 μm, the amount of charge on the magnetic toner bearing member tends to be high, and the developability tends to be insufficient. When Ra exceeds 3.5 μm, unevenness occurs in the toner coat layer on the magnetic toner carrier, and there is a tendency that the density is uneven on the image. More preferably, it is in the range of 0.5 to 3.0 μm.
[0352]
In the present invention, the surface roughness Ra of the magnetic toner carrier is measured based on JIS surface roughness “JIS B 0601”, and a surface roughness measuring instrument (for example, Surfcoder SE-30H, manufactured by Kosaka Laboratory Co., Ltd.). This corresponds to the centerline average roughness measured using. Specifically, a 2.5 mm portion as the measurement length a is extracted from the roughness curve in the direction of the center line, the center line of this extraction portion is the X axis, the direction of the vertical magnification is the Y axis, and the roughness curve is When expressed by y = f (x), the value obtained by the following formula is expressed in micrometers (μm).
[Equation 9]

[0353]
In order to bring the surface roughness (Ra) of the magnetic toner carrier in the present invention into the above range, for example, the polishing state of the surface layer of the magnetic toner carrier is changed, or spherical carbon particles, carbon fine particles, graphite, etc. are added. It is possible by the method of.
[0354]
Further, since the magnetic toner of the present invention has a high charging ability, it is desirable to control the total charge amount of the magnetic toner during development, and the surface of the magnetic toner carrier according to the present invention has conductive fine particles and / or a lubricant. It is preferable to coat with a resin layer in which is dispersed.
[0355]
The conductive fine particles contained in the coating layer of the magnetic toner carrier are 11.7 Mpa (120 kg / cm²) Having a resistance value of 0.5 Ωcm or less after pressurization is preferred. The conductive fine particles are preferably carbon fine particles, a mixture of carbon fine particles and crystalline graphite, or crystalline graphite. The conductive fine particles preferably have a particle size of 0.005 to 10 μm.
[0356]
Examples of the resin used for the resin layer include thermoplastic resins such as styrene resin, vinyl resin, polyethersulfone resin, polycarbonate resin, polyphenylene oxide resin, polyamide resin, fluorine resin, fiber resin, and acrylic resin. Resin; Thermosetting resin or photocurable resin such as epoxy resin, polyester resin, alkyd resin, phenol resin, melamine resin, polyurethane resin, urea resin, silicone resin, polyimide resin can be used.
[0357]
Among them, those having releasability such as silicone resin and fluorine resin, or those having excellent mechanical properties such as polyethersulfone, polycarbonate, polyphenylene oxide, polyamide, phenol resin, polyester, polyurethane, styrene resin, etc. More preferred. In particular, a phenol resin is preferable.
[0358]
The conductive fine particles are preferably used in an amount of 3 to 20 parts by mass per 10 parts by mass of the resin component in order to impart suitable conductivity.
[0359]
When carbon fine particles and graphite particles are used in combination, it is preferable to use 1 to 50 parts by mass of carbon fine particles per 10 parts by mass of graphite. The volume resistivity of the resin layer of the magnetic toner carrier in which conductive fine particles are dispersed is 10^-6-10⁶Ωcm is preferred
[0360]
In the present invention, the surface of the magnetic toner carrier that carries the magnetic toner may move in the same direction as the moving direction of the image carrier surface, or may move in the opposite direction. When the moving direction is the same direction, the ratio is preferably 100% or more with respect to the moving speed of the image carrier. If it is less than 100%, the image quality tends to deteriorate. The higher the moving speed ratio, the more toner is supplied to the development site, the more frequently the toner is desorbed from the latent image, and the unnecessary parts are scraped off and applied to the necessary parts. Thus, an image faithful to the latent image can be obtained. Specifically, the moving speed of the surface of the magnetic toner carrier is preferably 1.05 to 3.0 times the moving speed of the surface of the image carrier.
[0361]
Next, the contact transfer process preferably applied in the image forming method of the present invention will be specifically described. In the present invention, the recording medium that receives the transfer of the toner image from the image carrier may be an intermediate transfer member such as a transfer drum. When the recording medium is an intermediate transfer member, a toner image can be obtained by transferring again from the intermediate transfer member to a transfer material such as paper.
[0362]
In the contact transfer process, the toner image is electrostatically transferred to the recording medium while the image carrier is in contact with the transfer member via the recording medium. The contact pressure of the transfer member is 2.9 N / line pressure. m (3 g / cm) or more is preferable, and 19.6 N / m (20 g / cm) or more is more preferable. If the linear pressure as the contact pressure is less than 2.9 N / m (3 g / cm), it is not preferable because the recording medium is easily transported and a transfer failure is likely to occur.
[0363]
In addition, a transfer roller, a transfer belt, or the like is used as a transfer member in the contact transfer process. FIG. 3 shows an example of the configuration of the transfer roller. The transfer roller 34 includes at least a cored bar 34a and a conductive elastic layer 34b. The conductive elastic layer 34b has a volume resistance 10 such as urethane or epichlorohydrin rubber in which a conductive material such as carbon is dispersed.⁶-10^TenIt is made of an elastic body of about Ωcm, and a transfer bias is applied by a transfer bias power source 35.
[0364]
The contact transfer method of the present invention is particularly effective in an image forming apparatus in which the surface of the image carrier is an organic compound. That is, when the organic compound forms the surface layer of the image carrier, the adhesion with the binder resin contained in the toner particles is stronger than other image carriers using inorganic materials, and the transferability is high. This is because it tends to be lower.
[0365]
When the contact transfer method in the present invention is applied, examples of the surface material of the image carrier used as the organic compound include silicone resin, vinylidene chloride, ethylene-vinyl chloride, styrene-acrylonitrile, styrene-methyl methacrylate, styrene. , Polyethylene terephthalate, polycarbonate, and the like, but are not limited thereto, and other monomers or copolymers and blends between the above-described binder resins can also be used.
[0366]
In addition, the image forming method of the present invention to which the contact transfer method is applied is particularly effective for an image forming apparatus having an image carrier having a small diameter of 50 mm or less. That is, in the case of a small-diameter photoconductor, the curvature with respect to the same linear pressure is large, and pressure concentration tends to occur at the contact portion. The belt-like image carrier is considered to have the same phenomenon, but the present invention is also effective for an image forming apparatus having a radius of curvature of 25 mm or less at the transfer portion.
[0367]
Further, in the image forming method of the present invention, in addition to the above steps, there are various methods such as a fixing step for fixing a toner image on a recording medium and a pre-exposure step for erasing a latent image record on an image carrier after transfer. These steps can be used as necessary.
[0368]
Further, the image forming apparatus that realizes the image forming method of the present invention is not particularly limited as long as it is a configuration that realizes the above-described processes and the like, and various conventionally known configurations are used. can do. For example, since magnetic toner is used in the present invention, it is possible to use a process cartridge in which an image carrier, a developing means for realizing a developing process, and the like are integrally configured and detachably attached to the image forming apparatus main body. It is one of the preferable structures for implementing this invention suitably.
[0369]
【Example】
Hereinafter, the present invention will be specifically described with reference to production examples and examples, but this does not limit the present invention in any way. In addition, all the parts in the following mixing | blending are a mass part.
[0370]
(Surface treatment magnetic powder production example 1)
An aqueous solution containing ferrous hydroxide was prepared by mixing 1.0 to 1.1 equivalents of a caustic soda solution with respect to iron ions in an aqueous ferrous sulfate solution.
While maintaining the pH of the aqueous solution at around 9, air was blown in, and an oxidation reaction was performed at 80 to 90 ° C. to prepare a slurry liquid for generating seed crystals.
[0371]
Subsequently, after adding ferrous sulfate aqueous solution to this slurry liquid so that it may become 0.9-1.2 equivalent with respect to the original alkali amount (sodium component of caustic soda), the slurry liquid is maintained at about pH 8, and air The magnetic iron oxide particles produced after the oxidation reaction were washed, filtered, and once taken out. At this time, a small amount of water-containing sample was collected and the water content was measured. Next, this water-containing sample was re-dispersed in another aqueous medium without drying, and then the pH of the re-dispersed liquid was adjusted to about 6, and the silane coupling agent (n-C_FourH₁₃Si (OCH_Three)_Three) Was added in an amount of 3.0 parts by mass with respect to 100 parts by mass of magnetic iron oxide (the amount of magnetic iron oxide was calculated as a value obtained by subtracting the water content from the water-containing sample), and a coupling treatment was performed. The produced hydrophobic iron oxide particles were washed, filtered and dried by a conventional method, and then the slightly agglomerated particles were pulverized to obtain surface-treated magnetic powder 1. The physical properties are shown in Table 1.
[0372]
(Production Examples 2 to 6 of surface-treated magnetic powder)
Surface-treated magnetic powders 2 to 6 were obtained in the same manner except that the treatment amount of the silane coupling agent was adjusted in Production Example 1 of the surface-treated magnetic powder. The physical properties are shown in Table 1.
[0373]
(Production Examples 7 and 8 of surface-treated magnetic powder)
In the production example 1 of the surface-treated magnetic powder, the surface treatment magnetic powder was produced in the same manner as in the production example 1 of the surface-treated magnetic powder except that the treatment amount of the silane coupling agent, the amount of the caustic soda solution to be added, and the reaction conditions were changed. Treated magnetic powders 7 and 8 were obtained. The physical properties are shown in Table 1.
(Production Example 9 of surface-treated magnetic powder)
In surface-treated magnetic powder production example 1, surface-treated magnetic powder 9 was obtained in the same manner as in surface-treated magnetic powder production example 1 except that zinc sulfate was also used in addition to ferrous sulfate as a raw material. The physical properties are shown in Table 1.
(Production Example 10 of Surface-treated Magnetic Powder)
In the surface-treated magnetic powder production example 1, the surface-treated magnetic powder 10 was obtained in the same manner as in the surface-treated magnetic powder production example 1 except that barium sulfate was used in addition to ferrous sulfate as a raw material. The physical properties are shown in Table 1.
[0374]
[Table 1]

[0375]
(Conductive fine powder 1)
Fine particle zinc oxide was classified by wind to obtain white fine particle zinc oxide (resistance 1300 Ω · cm) having a volume average particle size of 2.9 μm, 0.5 μm or less in the particle size distribution of 3.2% by volume, and 5 μm or more of 0% by number. . This is designated as conductive fine powder 1.
[0376]
When the conductive fine powder 1 was observed with a scanning electron microscope at 3000 times and 30,000 times, it was composed of 0.1 to 0.3 μm zinc oxide primary particles and 1 to 5 μm aggregates.
[0377]
In accordance with the exposure light wavelength of 740 nm of the laser beam scanner used for image exposure in the image forming apparatus of the embodiment, a light source having a wavelength of 740 nm is used to measure the transmittance in this wavelength region by using a 310T transmission densitometer made by X-Rite. When used and measured, the transmittance of the conductive fine powder 1 was approximately 33%.
[0378]
(Conductive fine powder 2)
After removing the coarse particles of the aluminum borate surface-treated with tin oxide / antimony by air classification, fine particles are removed by repeated filtration after being dispersed in an aqueous system, and the volume average particle size is 3.0 μm. Grayish white conductive particles having 0.5% by volume of 0.5 μm or less and 1% by number of 5 μm or more were obtained (resistance of 50 Ω · cm). This is designated as conductive fine powder 2.
[0379]
(Manufacture of magnetic toner 1)
0.1M-Na in 709g of ion-exchanged water_ThreePO_FourAfter adding 451 g of aqueous solution and heating to 60 ° C., 1.0 M-CaCl₂Add 67.7 g of aqueous solution and add Ca_Three(PO_Four)₂An aqueous medium containing was obtained.
[0380]
90 parts of styrene
2-ethylhexyl acrylate 10 parts
Cross-linking agent: 1.0 part of triethylene glycol dimethacrylate
Saturated polyester resin 5 parts
Negative charge control agent (salicylic acid-based metal compound) 1 part
85 parts of surface-treated magnetic powder 1
The above formulation was uniformly dispersed and mixed using an attritor (Mitsui Miike Chemical Co., Ltd.). This monomer composition is heated to 60 ° C., and 12 parts of ester wax (maximum value of endothermic peak in DSC 80 ° C.) is added and dissolved therein, and then the polymerization initiator 2,2′-azobisiso is added thereto. 5 parts by weight of butyronitrile was dissolved.
[0381]
The polymerizable monomer system is charged into the aqueous medium, 60 ° C., N₂ Under an atmosphere, the mixture was stirred and granulated at 10,000 rpm for 15 minutes with a TK homomixer (Special Machine Industries Co., Ltd.). Thereafter, the mixture was reacted at 60 ° C. for 1 hour while stirring with a paddle stirring blade. Thereafter, the liquid temperature was raised to 80 ° C., and stirring was further continued for 9 hours. After completion of the reaction, distillation was performed, and then the suspension was cooled and hydrochloric acid was added to dissolve the dispersant, followed by filtration, washing with water and drying to obtain black particles 1 having a weight average particle diameter of 6.9 μm.
[0382]
100 parts of the black particles and silica having a primary particle size of 9 nm were treated with hexamethyldisilazane and then treated with silicone oil, and the BET value after treatment was 200 m.²/ G of 1.2 parts of hydrophobic silica fine powder and 1.2 parts of conductive fine powder 1 using a Henschel mixer (Mitsui Miike Chemical Co., Ltd.) and a peripheral speed of the stirring blade of 3 m The magnetic toner 1 was prepared by mixing for minutes.
Table 2 shows the physical properties of the magnetic toner 1.
[0383]
(Manufacture of magnetic toner 2)
A magnetic toner 2 was obtained in the same manner as in the production example of the magnetic toner 1 except that the polymerization initiator was changed to 4 parts by mass. Table 2 shows the physical properties of the magnetic toner 2.
[0384]
(Manufacture of magnetic toner 3)
A magnetic toner 3 was obtained in the same manner as in the production example of the magnetic toner 1 except that the polymerization initiator was changed to 4 parts by mass and the crosslinking agent was changed to 1.5 parts by mass. Table 2 shows the physical properties of the magnetic toner 3.
[0385]
(Manufacture of magnetic toner 4)
A magnetic toner 4 was obtained in the same manner as in the production example of the magnetic toner 1 except that the polymerization initiator was changed to 10 parts by mass and the crosslinking agent was changed to 0.1 parts by mass. Table 2 shows the physical properties of the magnetic toner 4.
[0386]
(Manufacture of magnetic toner 5)
A magnetic toner 5 was obtained in the same manner as in the production example of the magnetic toner 1 except that the polymerization initiator was changed to 3 parts by mass and the crosslinking agent was changed to 1.5 parts by mass, and the temperature was not raised during the reaction. Table 2 shows the physical properties of the magnetic toner 5.
[0387]
(Manufacture of magnetic toner 6)
A magnetic toner 6 was obtained in the same manner as in the production example of the magnetic toner 1 except that the polymerization initiator was changed to 9 parts by mass and the crosslinking agent was changed to 0.07 parts by mass. Table 2 shows the physical properties of the magnetic toner 6.
[0388]
(Manufacture of magnetic toner 7)
A magnetic toner 7 was obtained in the same manner as in the production example of the magnetic toner 1 except that the polymerization initiator was changed to 3.5 parts by mass and the crosslinking agent was changed to 1.7 parts by mass, and the temperature was not raised during the reaction. Table 2 shows the physical properties of the magnetic toner 7.
[0389]
(Manufacture of magnetic toner 8)
A magnetic toner 8 was obtained in the same manner as in the production example of the magnetic toner 1 except that the surface-treated magnetic powder 2 was used and the conductive fine powder 1 was not used. Table 2 shows the physical properties of the magnetic toner 8.
[0390]
(Manufacture of magnetic toner 9)
A magnetic toner 9 was obtained in the same manner as in the production example of the magnetic toner 1 except that the surface-treated magnetic powder 3 was used and the conductive fine powder 1 was not used. Table 2 shows the physical properties of the magnetic toner 9.
[0390]
(Manufacture of magnetic toner 10)
A magnetic toner 10 was obtained in the same manner as in the production example of the magnetic toner 1 except that the surface-treated magnetic powder 4 was used and the conductive fine powder 1 was not used. Table 2 shows the physical properties of the magnetic toner 10.
[0392]
(Manufacture of magnetic toner 11)
A magnetic toner 11 was obtained in the same manner as in the production example of the magnetic toner 1 except that the surface-treated magnetic powder 5 was used and the conductive fine powder 1 was not used. Table 2 shows the physical properties of the magnetic toner 11.
[0393]
(Manufacture of magnetic toner 12)
A magnetic toner 12 was obtained in the same manner as in the production example of the magnetic toner 1 except that the surface-treated magnetic powder 7 was used and the conductive fine powder 1 was not used. Table 2 shows the physical properties of the magnetic toner 12.
[0394]
(Manufacture of magnetic toner 13)
A magnetic toner 13 was obtained in the same manner as in the production example of the magnetic toner 1 except that the surface-treated magnetic powder 8 was used and the conductive fine powder 1 was not used. Table 2 shows the physical properties of the magnetic toner 13.
[0395]
(Manufacture of magnetic toner 14)
A magnetic toner 14 was obtained in the same manner as in the production example of the magnetic toner 1 except that the surface-treated magnetic powder 6 was used and the conductive fine powder 1 was not used. Table 2 shows the physical properties of the magnetic toner 14.
[0396]
(Manufacture of magnetic toner 15)
0.1M-Na in 709g of ion-exchanged water_ThreePO_FourAfter adding 451 g of aqueous solution and heating to 60 ° C., 1.0 M-CaCl₂Add 67.7 g of aqueous solution and add Ca_Three(PO_Four)₂An aqueous medium containing was obtained.
[0397]
85 parts of styrene
15 parts of n-butyl acrylate
Cross-linking agent: 0.5 parts of divinylnaphthalene
20 parts of saturated polyester resin
Negative charge control agent (boron metal compound) 1 part
80 parts of surface-treated magnetic powder 1
The above formulation was uniformly dispersed and mixed using an attritor (Mitsui Miike Chemical Co., Ltd.). This monomer composition was heated to 60 ° C., and 5 parts of paraffin wax (maximum endothermic peak value of 60 ° C. in DSC) was added, mixed and dissolved therein, and the polymerization initiator 2,2′-azobisiso was added thereto. 5 parts by weight of butyronitrile was dissolved.
[0398]
The polymerizable monomer system is charged into the aqueous medium, 60 ° C., N₂Under an atmosphere, the mixture was stirred and granulated at 10,000 rpm for 15 minutes with a TK homomixer (Special Machine Industries Co., Ltd.). Thereafter, the mixture was reacted at 60 ° C. for 5 hours while stirring with a paddle stirring blade.
[0399]
Next, 20.0 parts by mass of styrene, 0.4 parts by mass of 2,2′-azobisisobutyronitrile and 0.03 parts by mass of sodium lauryl sulfate are added to 80 parts by mass of water and dispersed using an ultrasonic homogenizer. Water emulsion was obtained.
[0400]
This was dropped into the magnetic toner particle dispersion and adhered to the particles. Then, it stirred in nitrogen atmosphere and reacted for 10 hours at 85 degreeC. After completion of the reaction, distillation was performed, and then the suspension was cooled and hydrochloric acid was added to dissolve the dispersant, followed by filtration, washing with water and drying to obtain black particles having a weight average particle diameter of 7.3 μm.
[0401]
100 parts of the black particles and silica having a primary particle size of 9 nm were treated with hexamethyldisilazane and then treated with silicone oil, and the BET value after treatment was 200 m.²Magnetic toner 15 was prepared by mixing 1.2 parts of / g hydrophobic silica fine powder using a Henschel mixer (Mitsui Miike Chemical Co., Ltd.) for 3 minutes with a peripheral speed of the stirring blade of 40 m / sec. Table 2 shows the physical properties of the magnetic toner 15.
[0402]
(Manufacture of magnetic toner 16)
A magnetic toner 16 was obtained in the same manner as in the production example of the magnetic toner 1 except that 10 g of calcium carbonate salt was finely dispersed in 1200 g of ion-exchanged water and the conductive fine powder 1 was not used. Table 2 shows the physical properties of the magnetic toner 16.
[0403]
(Manufacture of magnetic toner 17)
A magnetic toner 17 was obtained in the same manner as in the production example of the magnetic toner 1 except that the surface-treated magnetic powder 9 was used. Table 2 shows the physical properties of the magnetic toner 17.
[0404]
(Manufacture of magnetic toner 18)
A magnetic toner 18 was obtained in the same manner as in the production example of the magnetic toner 1 except that the surface-treated magnetic powder 10 was used. Table 2 shows the physical properties of the magnetic toner 18.
[0405]
[Table 2]

[0406]
The saturation magnetization strength of each magnetic toner at a magnetic field of 79.6 kA / m is 24 to 26 Am.²/ Kg. The residual magnetization of the magnetic toners 1 to 16 at a magnetic field of 79.6 kA / m is 2 to 4 Am.²/ Kg, and the residual magnetization of the magnetic toner 17 is 0.4 Am²/ Kg, the residual magnetization of the magnetic toner 18 is 7 Am²/ Kg.
[0407]
[Example 1]
<Manufacture of photoreceptor 1>
As the photoreceptor, an Al cylinder having a diameter of 30 mm was used as a base. 4 and the layers having the structure as shown below were sequentially laminated by dip coating to prepare the photoreceptor 1.
(1) Conductive coating layer: Mainly composed of a powder of tin oxide and titanium oxide dispersed in a phenolic resin. Film thickness 15 μm.
(2) Undercoat layer: Mainly composed of modified nylon and copolymer nylon. Film thickness 0.6 μm.
(3) Charge generation layer: Mainly composed of an azo pigment having absorption in a long wavelength region dispersed in a butyral resin. Film thickness 0.6 μm.
(4) Charge transport layer: Mainly composed of a hole-transporting triphenylamine compound dissolved in a polycarbonate resin (molecular weight of 20,000 by the Ostwald viscosity method) at a mass ratio of 8:10, and polytetrafluoroethylene powder ( 10% by weight of the total solid content was added and dispersed uniformly. Film thickness 25 μm. The contact angle with water was 95 degrees.
Note that pure water was used for measuring the contact angle, and a contact angle meter CA-X type manufactured by Kyowa Interface Science Co., Ltd. was used.
[0408]
<Image forming apparatus>
As the image forming apparatus, LBP-1760 was remodeled and the same as that shown in FIG. 1 in the above embodiment was used. The photoreceptor 1 described above was used as the photoreceptor 100 as an image carrier.
[0409]
A primary charging roller (rubber roller charger) 117 in which conductive carbon is dispersed as a charging member and coated with a nylon resin is brought into contact with the photosensitive member (contact pressure 60 g / cm), and an AC voltage of 2.680 Vdc is applied. A bias superimposed with 0 kVpp is applied to uniformly charge the photosensitive member. Subsequent to charging, the electrostatic latent image is formed by exposing the image portion with laser light. At this time, the dark portion potential Vd = −680V and the light portion potential VL = −150V.
[0410]
The gap between the photosensitive drum and the developing sleeve is 230 μm, and a magnetic toner carrier is formed on an aluminum cylinder having a blasted surface with a diameter of 16 mm and a layer thickness of about 7 μm and a JIS centerline average roughness (Ra) of 1. Using a developing sleeve 102 having a 0 μm resin layer formed, a developing magnetic pole 85 mT (850 gauss), a toner regulating member having a thickness of 1.0 mm and a free length 0.5 mm urethane blade 34.3 N / m (35 g / cm) ).
・ Phenolic resin 100 parts by mass
・ Graphite (particle size: about 7μm) 90 parts by mass
・ 10 parts by mass of carbon black
[0411]
Next, a DC voltage Vdc = −450 V as a developing bias, and 5.22 × 10 6 as an overlapping alternating electric field.⁶The thing of V / m and frequency 2400Hz was used. The peripheral speed of the developing sleeve was 110% (218 mm / sec) in the forward direction with respect to the peripheral speed of the photoreceptor (198 mm / sec).
[0412]
Further, as the transfer roller 114, a transfer roller as shown in FIG. 3 (made of ethylene-propylene rubber in which conductive carbon is dispersed, volume resistance value 10 of the conductive elastic layer is used.⁸Ωcm, surface rubber hardness of 24 °, diameter of 20 mm, contact pressure of 59 N / m (60 g / cm)) are set to the constant speed with respect to the peripheral speed of the photosensitive member in the A direction (94 mm / sec) in FIG. The voltage was 1.5 kV.
[0413]
As a fixing method, a fixing roller 126 having a surface layer made of a fluororesin and a pressure roller was used. The roller diameter was 30 mm, the fixing temperature was 220 ° C., and the nip width was 8 mm.
[0414]
Using the magnetic toner 1, in a normal temperature and normal humidity environment (25 ° C., 60% RH), an image printing test of 5000 sheets was performed with an image pattern composed of only vertical lines with a printing rate of 2%. Note that the recording medium is 80 g / m.²Paper was used. Further, after the initial image output, 105 g paper was used to obtain a halftone image, and the fixability was also evaluated. As a result, the magnetic toner 1 showed high transferability in the initial stage, and there was no transfer loss or ghost, and a good image was obtained. The fixability was also good and no offset occurred. The evaluation results are shown in Table 3.
[0415]
The evaluation items described in Examples and Comparative Examples of the present invention and the criteria for the evaluation are described below.
[0416]
<Measurement of triboelectric charge amount of toner on developing sleeve>
The triboelectric charge amount of the toner on the developing sleeve is obtained using a suction type Faraday gauge method.
In this suction type Faraday gauge method, the outer cylinder is pressed against the surface of the developing sleeve, the toner on a certain area on the developing sleeve is sucked, collected on the filter of the inner cylinder, and the suctioned toner is extracted from the weight increase of the filter. The weight can be calculated. At the same time, the amount of triboelectric charge of the toner on the developing sleeve can be obtained by measuring the amount of charge accumulated in the inner cylinder electrostatically shielded from the outside.
[0417]
<Image density>
The image density formed a solid image portion, and this solid image was measured with a Macbeth reflection densitometer (manufactured by Macbeth).
[0418]
<Image quality>
The image quality criterion is a comprehensive evaluation of image uniformity and fine line reproducibility. The uniformity of the image is determined based on the uniformity of the solid black image and the halftone image.
A: A clear image excellent in fine line reproducibility and image uniformity.
B: A good image although the fine line reproducibility and image uniformity are slightly inferior.
C: Image quality with no practical problem.
D: An image unfavorable for practical use due to poor fine line reproducibility and image uniformity.
[0419]
<Fog on photoconductor>
The fog on the photoreceptor was measured using a REFLECTMETER MODEL TC-6DS manufactured by Tokyo Denshoku. The filter used was a green filter, and the fog on the photoreceptor was calculated from the following equation.
[Expression 10]

[0420]
Note that the criteria for determining fog on the photoreceptor are as follows.
A: Very good (less than 2.0%)
B: Good (2.0% or more and less than 4.0%)
C: Normal (4.0% or more and less than 6.0%)
D: Poor (6.0% or more)
[0421]
<Fixability>
Fixability is 50 g / cm²The fixed image was rubbed and reciprocated 5 times with a soft thin paper, and the reduction rate (%) of the image density before and after rubbing was evaluated.
A: Less than 10%
B: 10% or more and less than 20%
C: 20% or more and less than 30%
D: 30% or more
[0422]
<Offset resistance>
The offset resistance was evaluated by the degree of stain on the image after the durability test and on the back of the paper.
A: Dirt is not generated.
B: Dirt is slightly seen.
C: Some dirt is seen.
D: Significant dirt is generated.
[0423]
[Examples 2 to 9]
Magnetic toners 2, 3, and 8 to 13 were used as toners, and an image formation test and durability evaluation were performed under the same conditions as in Example 1. As a result, there was no problem in the initial image characteristics, and no problem was obtained in any of up to 5000 sheets. The results are shown in Table 3.
[0424]
[Comparative Example 1]
The magnetic toner 4 was used as the toner, and an image formation test and durability evaluation were performed by the same image forming method as in Example 1. As a result, image density, chargeability, and photoreceptor fogging deteriorated. This is presumably because the release rate of iron and iron compounds changed due to durability because the melt viscosity of the toner was low. Also, the offset resistance deteriorated. The results are shown in Table 3.
[0425]
[Comparative Example 2]
The magnetic toner 5 was used as the toner, and an image formation test and durability evaluation were performed by the same image forming method as in Example 1. As a result, no problem occurred in image density, chargeability, and photoreceptor fog, but the fixability deteriorated. This is presumably because the toner has a high melt viscosity. The results are shown in Table 3.
[0426]
[Comparative Example 3]
The magnetic toner 6 was used as the toner, and an image formation test and durability evaluation were performed by the same image forming method as in Example 1. As a result, image density, chargeability, and photoreceptor fogging deteriorated. This is presumably because the release rate of iron and iron compounds changed due to durability because the melt viscosity of the toner was low. Also, the offset resistance was significantly deteriorated. The results are shown in Table 3.
[0427]
[Comparative Example 4]
The magnetic toner 7 was used as the toner, and an image formation test and durability evaluation were performed by the same image forming method as in Example 1. As a result, there were no problems with image density, chargeability, and photoreceptor fog, but the fixability and offset resistance deteriorated. This is probably because the wax in the toner could not function sufficiently because the melt viscosity of the toner was high. The results are shown in Table 3.
[0428]
[Comparative Example 5]
The magnetic toner 14 was used as the toner, and an image formation test and durability evaluation were performed by the same image forming method as in Example 1. As a result, the image quality, chargeability and photoreceptor fog were poor from the beginning. This is thought to be due to the high liberation rate of iron and iron compounds. In addition, the fixability was slightly deteriorated. The results are shown in Table 3.
[0429]
[Comparative Example 6]
The magnetic toner 15 was used as the toner, and an image formation test and durability evaluation were performed by the same image forming method as in Example 1. As a result, the image quality and the photoreceptor fog are a little worse from the beginning. Durability and deterioration of image quality due to charge up occurred. This is thought to be due to the low liberation rate of iron and iron compounds in the toner. In addition, the fixability was slightly deteriorated. The results are shown in Table 3.
[0430]
[Comparative Example 7]
The magnetic toner 16 was used as the toner, and an image formation test and durability evaluation were performed by the same image forming method as in Example 1. As a result, the image quality and photoreceptor fog were poor from the beginning. This is presumably because the toner has a low degree of circularity and a high weight average particle diameter / number average particle diameter. The results are shown in Table 3.
[0431]
[Example 10]
The magnetic toner of the present invention can also be applied to a cleanerless image forming method or a development and cleaning (collection) image forming method. Hereinafter, the image forming method of the present invention will be described with reference to specific examples, but the present invention is not limited thereto.
[0432]
<Manufacture of Photoconductor 2>
The photoreceptor is a photoreceptor using an organic photoconductive material for negative charging, and an aluminum cylinder having a diameter of 30 mm was used as a base. 5 and the layers having the structure as shown below were sequentially laminated by dip coating to produce a photoreceptor 2.
(1) The first layer is a conductive layer, and is a conductive particle-dispersed resin layer having a thickness of about 20 μm, which is provided to smooth out defects in the aluminum substrate and to prevent the occurrence of moire due to reflection of laser exposure. (Mainly composed of powders of tin oxide and titanium oxide dispersed in phenol resin).
(2) The second layer is a positive charge injection preventing layer (undercoat layer), which serves to prevent the positive charge injected from the aluminum support from canceling the negative charge charged on the surface of the photoreceptor. 10 with methylated nylon⁶This is a medium resistance layer having a thickness of about 1 μm, the resistance of which is adjusted to about Ωcm.
(3) The third layer is a charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a butyral resin, and generates positive and negative charge pairs upon receiving laser exposure.
(4) The fourth layer is a charge transport layer, which is a layer having a thickness of about 25 μm in which a hydrazone compound is dispersed in a polycarbonate resin, and is a P-type semiconductor. Accordingly, negative charges charged on the surface of the photoreceptor cannot move through this layer, and only positive charges generated in the charge generation layer can be transported to the surface of the photoreceptor.
(5) The fifth layer is a charge injection layer in which conductive tin oxide ultrafine particles and ethylene tetrafluoride resin particles having a particle size of about 0.25 μm are dispersed in a photocurable acrylic resin. Specifically, tin oxide particles (conductive particles) having a particle size of about 0.03 μm doped with antimony to reduce the resistance are 100% by mass with respect to the resin, and further 20% by mass of ethylene tetrafluoride resin particles. Is 1.2 mass% dispersed. The coating solution thus prepared was applied to a thickness of about 2.5 μm by spray coating, and cured by light irradiation to form a charge injection layer.
The resistance of the surface of the obtained photoreceptor is 5 × 10¹²The contact angle with respect to water on the surface of the photoreceptor was 102 degrees.
[0433]
<Manufacture of charging member>
A SUS roller having a diameter of 6 mm and a length of 264 mm is used as a core, and a medium-resistance foamed urethane layer is formed on the core as a roller, in which urethane resin, carbon black as a conductive particle, sulfurizing agent, foaming agent, etc. Further, the shape and surface properties were adjusted by cutting and polishing to produce a charging roller having a diameter of 12 mm and a length of 234 mm, which is a flexible member.
The resulting charging roller has a resistance of 10^FiveThe hardness was 30 degrees in terms of Asker C hardness. When the surface of the charging roller was observed with a scanning electron microscope, the average cell diameter was about 100 μm and the porosity was 60%.
[0434]
<Image forming apparatus>
FIG. 6 is a schematic structural model diagram of an example of an image forming apparatus according to the present invention.
The image forming apparatus used in Example 10 is a laser printer (recording apparatus) of a development and cleaning process (cleanerless system) using a transfer type electrophotographic process. It has a process cartridge from which a cleaning unit having a cleaning member such as a cleaning blade is removed, uses magnetic toner 1 as magnetic toner, and is arranged so that the toner layer on the magnetic toner carrier and the image carrier are not in contact with each other. This is an example of non-contact development. As a fixing method, a fixing device 26 of a type in which heat and pressure are fixed by a heater through a film was used. A pressure roller having a fluororesin surface layer is used, and the roller has a diameter of 30 mm. The fixing temperature was set to 230 ° C. and the nip width was set to 6 mm.
[0435]
(1) Overall schematic configuration of the printer of this embodiment
A rotating drum type OPC photosensitive member 21 using the photosensitive member 2 as an image bearing member is driven to rotate at a peripheral speed (process speed) of 198 mm / sec in the X direction of an arrow.
[0436]
The charging roller 22 serving as the charging member as the contact charging member is disposed in pressure contact with the photoreceptor 21 with a predetermined pressing force against elasticity. n is a contact portion between the photosensitive member 21 and the charging roller 22. In this example, the charging roller 22 is rotationally driven at a peripheral speed of 100% in the facing direction (arrow Y direction) at the contact portion n that is a contact surface with the photoreceptor 21. That is, the surface of the charging roller 22 as a contact charging member has a speed difference with respect to the surface of the photoreceptor 21. In addition, the amount of coating on the surface of the charging roller 22 is approximately 1 × 10^FourPiece / mm²The conductive fine powder 1 was applied so as to be uniform.
[0437]
Further, a DC voltage of -700 V was applied as a charging bias to the cored bar 22a of the charging roller 22 from a charging bias application power source. In this example, the surface of the photosensitive member 21 is uniformly charged by a direct injection charging method at a potential (−680 V) substantially equal to the voltage applied to the charging roller 22. This will be described later.
[0438]
Reference numeral 23 denotes a laser beam scanner (exposure device) including a laser diode and a polygon mirror. This laser beam scanner outputs a laser beam whose intensity is modulated in accordance with the time-series electric digital pixel signal of the target image information, and scans and exposes the uniformly charged surface of the photosensitive member 21 with the laser beam. By this scanning exposure L, an electrostatic latent image corresponding to target image information is formed on the surface of the rotary photosensitive member 21.
[0439]
Reference numeral 24 denotes a developing device. The electrostatic latent image on the surface of the photoreceptor 21 is developed as a toner image by the developing device. The developing device 24 of this example is a non-contact type reversal developing device using the magnetic toner 1 used in Example 1 as the magnetic toner. A conductive fine powder 1 is externally added to the magnetic toner 1.
[0440]
The gap between the photosensitive drum 21 and the developing sleeve 24a is 230 μm, and the magnetic toner carrier 24a is formed on a 16 mm diameter aluminum cylinder blasted on the surface with a JIS centerline average roughness (Ra) of 1.0 μm having the following configuration. A developing sleeve having a resin layer (layer thickness of about 7 μm) is used, and a magnet roll having a developing magnetic pole of 85 mT (850 gauss) is included, and the elastic blade 24c as a magnetic toner layer regulating member has a thickness of 1.0 mm and a free length of 0 A 5 mm urethane blade was brought into contact with a linear pressure of 34.3 N / m (35 g / cm).
・ Phenolic resin 100 parts by mass
・ Graphite (particle size: about 7μm) 90 parts by mass
・ 10 parts by mass of carbon black
[0441]
In addition, the developing unit a (developing region) that is opposed to the photoconductor 21 rotates at a peripheral speed of 120% of the peripheral speed of the photoconductor 21 in the forward direction (arrow W direction) of the photoconductor 21. Let The developing sleeve 24a is coated with a magnetic toner in a thin layer by an elastic blade 24c. In the magnetic toner, the layer thickness with respect to the developing sleeve 24a is regulated by the elastic blade 24c, and an electric charge is applied. At this time, the amount of magnetic toner coated on the developing sleeve 24a is 15 g / m.²Met.
[0442]
The magnetic toner coated on the developing sleeve 24a is conveyed to the developing portion a, which is a facing portion between the photosensitive member 21 and the developing sleeve 24a, by the rotation of the developing sleeve 24a. A developing bias voltage is applied to the developing sleeve 24a from a developing bias applying power source. The development bias voltage is a DC voltage of −450 V, a frequency of 1800 Hz, and 5.22 × 10.⁶One-component jumping development was performed between the developing sleeve 24a and the photosensitive member 21 using a superposed alternating electric field of V / m.
[0443]
A medium-resistance transfer roller 25 as a contact transfer unit is brought into pressure contact with the photosensitive member 21 with a linear pressure of 98 N / m (100 g / cm) to form a transfer nip b. A transfer material P as a recording medium is fed to the transfer nip b from a paper feed unit (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 25 from a transfer bias application power source. Then, the toner image on the photosensitive member 21 side is sequentially transferred onto the surface of the transfer material P fed to the transfer nip portion b.
[0444]
In this example, the roller resistance value is 5 × 10.⁸Transferring was performed by applying a DC voltage of +3000 V using an Ωcm one. That is, the transfer material (recording medium) P introduced into the transfer nip portion b is nipped and conveyed through the transfer nip portion b, and the toner images formed and supported on the surface of the photoreceptor 21 are sequentially electrostatically charged on the surface side. It is transferred by force and pressure.
[0445]
Reference numeral 26 denotes a fixing device such as a heat fixing method. The transfer material P that has been fed to the transfer nip b and has received the transfer of the toner image on the side of the photoconductor 21 is separated from the surface of the photoconductor 1 and introduced into the fixing device 26. It is discharged out of the apparatus as a formed product (print, copy).
[0446]
In the printer of this example, the cleaning unit is removed, and residual toner remaining on the surface of the photoconductor 21 after the transfer of the toner image onto the transfer material P is not removed by the cleaner, and is charged as the photoconductor 21 rotates. The developing unit a is reached via the part n and developed and cleaned (collected) in the developing unit 24.
[0447]
A process cartridge 27 is detachable from the printer body. In the printer of this example, the three process devices of the photosensitive member 21, the charging roller 22, and the developing device 24 are collectively configured as a process cartridge that is detachable from the printer body. The combination of process devices to be processed into a process cartridge is not limited to the above, and is arbitrary. Reference numeral 28 denotes a process cartridge attachment / detachment guide / holding member.
[0448]
(2) Behavior of conductive fine powder in this example
An appropriate amount of the conductive fine powder mixed in the magnetic toner in the developing device 24 is transferred to the photoconductor 21 side together with the toner when the developing device 24 develops the electrostatic latent image on the photoconductor 21 side.
[0449]
The toner image on the photoconductor 21 is attracted and actively transferred to the transfer material P, which is a recording medium, under the influence of the transfer bias at the transfer portion b, but the conductive fine powder on the photoconductor 21 is conductive. As a result, the transfer material P is not positively transferred and remains substantially adhered and held on the photoreceptor 21.
[0450]
In this example, since the image forming apparatus does not have a cleaning process, the residual toner remaining on the surface of the photoconductor 21 after transfer and the above-mentioned residual conductive fine powder are charged by the photoconductor 21 and a contact charging member. It is carried as it is by the movement of the surface of the photosensitive member 21 to the charging portion n which is the contact portion of the roller 22, and is attached or mixed into the charging roller 22. Accordingly, direct injection charging of the photosensitive member 21 is performed in a state where the conductive fine powder exists in the contact portion n between the photosensitive member 21 and the charging roller 22.
[0451]
Due to the presence of the conductive fine powder, even when the toner adheres to and mixes with the charging roller 22, the contact property and contact resistance of the charging roller 22 to the photosensitive member 21 can be maintained. 21 direct injection charging can be performed.
[0452]
That is, the charging roller 22 is in close contact with the photosensitive member 21 via the conductive fine powder, and the conductive fine powder existing on the mutual contact surface between the charging roller 22 and the photosensitive member 21 slides on the surface of the photosensitive member 21 without a gap. By rubbing, the charging of the photosensitive member 21 by the charging roller 22 is dominated by stable and safe direct injection charging without using a discharge phenomenon due to the presence of the conductive fine powder, which was not obtained by conventional roller charging or the like. Charging efficiency is obtained, and a potential almost equal to the voltage applied to the charging roller 22 can be applied to the photoconductor 21.
[0453]
Further, the transfer residual toner adhering to or mixed in the charging roller 22 is gradually discharged from the charging roller 22 onto the photosensitive member 21, reaches the developing unit along with the movement of the surface of the photosensitive member 21, and is developed and cleaned (collected) by the developing unit. .
[0454]
In the development and cleaning, the toner remaining on the photosensitive member 21 after the transfer is developed in the subsequent image forming process, that is, the photosensitive member is continuously charged and exposed to form a latent image, and the latent image is developed. It is recovered by the fog removal bias of the developing device, that is, the fog removal potential difference Vback which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photoreceptor. In the case of reversal development as in the printer in this embodiment, this development and cleaning is performed by the electric field for collecting toner from the dark portion potential of the photosensitive member to the developing sleeve by the developing bias and the toner from the developing sleeve to the bright portion potential of the photosensitive member. It is made by the action of an electric field that adheres.
[0455]
In addition, when the image forming apparatus is operated, the conductive fine powder mixed in the magnetic toner of the developing device 24 is transferred to the surface of the photosensitive member 21 at the developing portion a, and the transfer portion b is moved by the movement of the image carrying surface. Since the conductive fine powder is carried to the charging part n and supplied continuously to the charging part n sequentially, the conductive fine powder is decreased in the charging part n due to dropping or the powder is deteriorated. Even so, it is prevented that the chargeability is lowered, and good chargeability is stably maintained.
[0456]
Thus, in the image forming apparatus of the contact charging system, the transfer system, and the toner recycling process, the simple charging roller 22 is used as the contact charging member, and the applied roller 22 can be applied with a low applied voltage regardless of contamination of the transfer roller with the transfer residual toner. Ozone-less direct injection charging can be maintained stably over a long period of time, uniform chargeability can be imparted, and there is no obstruction caused by ozone products, no obstruction due to poor charging, etc. Simple configuration, low-cost image formation A device can be obtained.
[0457]
Further, as described above, since the conductive fine powder does not impair the charging property, the electric resistance value is 1 × 10.⁹Must be Ωcm or less. Therefore, when a contact developing device in which the magnetic toner directly contacts the photosensitive member 21 is used in the developing portion a, charge is injected into the photosensitive member 21 by the developing bias through the conductive fine powder in the developed image agent, and the image fogging is performed. Will occur.
[0458]
However, in this example, since the developing device is a non-contact type developing device, a developing bias is not injected into the photosensitive member 21, and a good image can be obtained. Further, since no charge injection into the photosensitive member 21 occurs in the developing portion a, it is possible to give a high potential difference between the developing sleeve 24a and the photosensitive member 21 such as an AC bias, and the conductive fine powder is uniformly developed. Therefore, the conductive fine powder is uniformly applied to the surface of the photoreceptor 21 and uniform contact is made at the charging portion, so that good chargeability can be obtained and a good image can be obtained.
[0459]
By interposing the conductive fine powder on the contact surface n between the charging roller 22 and the photosensitive member 21, the lubricating effect (friction reducing effect) of the conductive fine powder makes it easy between the charging roller 22 and the photosensitive member 21. It is possible to effectively provide a speed difference.
[0460]
By providing a speed difference between the charging roller 22 and the photosensitive member 21, the chance of the conductive fine powder contacting the photosensitive member 21 at the mutual contact surface portion n between the charging roller 22 and the photosensitive member 21 is remarkably increased. Contactability can be obtained and good direct injection charging is possible.
[0461]
In this embodiment, the charging roller 22 is driven to rotate, and the rotation direction of the charging roller 22 rotates in the direction opposite to the moving direction of the surface of the photosensitive member 21, so that the charging roller n is carried on the photosensitive member 21. The transfer residual toner is temporarily collected on the charging roller 22 and leveled. That is, it is possible to preferentially perform direct injection charging by once separating the transfer residual toner on the photoconductor 21 by reverse rotation and performing charging.
[0462]
Further, in this embodiment, due to the lubrication effect by the conductive fine powder, an appropriate amount of the conductive fine powder is interposed in the contact portion n between the photosensitive drum 21 as the image carrier and the charging roller 22 as the contact charging member. It is easy to reduce the friction between the charging roller 22 and the photosensitive drum 21 and to rotate the charging roller 22 with respect to the photosensitive drum 21 with a speed difference. That is, the driving torque is reduced and the surface of the charging roller 22 and the photosensitive drum 21 can be prevented from being scraped or scratched. Furthermore, sufficient charging performance can be obtained by increasing the contact opportunity with the particles. Further, there is no adverse effect on the image formation due to the removal of the conductive fine powder from the charging roller 22.
[0463]
(3) Evaluation
In this example, the magnetic toner 1 was used, and an image printing test was performed in a normal temperature and humidity environment (25 ° C., 60% RH). For the photoreceptor, the volume resistance of the outermost layer is 5 × 10¹²Using the above-mentioned photoreceptor 2 of Ωcm, the transfer material is 80 g / m.²Paper was used. In the initial image characteristics, fog due to poor charging was not observed, and a good image density with high resolution was obtained. At this time, the photoreceptor potential after direct injection charging was -680V with respect to the applied charging bias of -700V. Next, durability was evaluated with an image pattern composed of only vertical lines with a printing rate of 2%. As a result, image defects due to poor charging did not occur until after printing 5000 sheets, and good direct injection charging properties were obtained.
[0464]
Further, the photoconductor potential after direct injection charging after printing 5000 sheets is -655 V with respect to the applied charging bias of -700 V, and the decrease in chargeability from the initial stage is as small as 25 V. No deterioration in quality was observed. The obtained results are shown in Table 3. The evaluation items and evaluation criteria are the same as those in Example 1.
Further, the amount of the conductive fine powder in the contact portion between the image carrier and the contact charging member was measured by the above-described method, and was 2 × 10.^FiveIt was a piece.
[0465]
[Example 11]
In Example 10, the same evaluation was performed using the magnetic toner 17. As a result, in the initial image characteristics, fog due to charging failure was not observed, and a good image density with high resolution was obtained. . At this time, the photoreceptor potential after direct injection charging was -680V with respect to the applied charging bias of -700V. Next, durability was evaluated with an image pattern composed of only vertical lines with a printing rate of 2%. As a result, slight fogging occurred after printing 5000 sheets. Further, the amount of the conductive fine powder in the contact portion between the image carrier and the contact charging member was measured by the above-described method, and was 2 × 10.^FiveIt was a piece.
[0466]
[Example 12]
In Example 10, the same evaluation was performed using the magnetic toner 18. As a result, in the initial image characteristics, fog due to charging failure was not observed, and a good image density with high resolution was obtained. . At this time, the photoreceptor potential after direct injection charging was -680V with respect to the applied charging bias of -700V. Next, durability was evaluated with an image pattern composed of only vertical lines with a printing rate of 2%. As a result, image defects caused by scratches on the photoconductor occurred after printing 5000 sheets, although the level was not problematic for practical use. Further, the amount of the conductive fine powder in the contact portion between the image carrier and the contact charging member was measured by the above-described method, and was 2 × 10.^FiveIt was a piece.
[0467]
[Table 3]

[0468]
【The invention's effect】
The magnetic toner of the present invention includes toner particles having at least a binder resin, a release agent, and a magnetic powder, has a weight average particle diameter of 3 to 20 μm, and has a magnetization strength at a magnetic field of 79.6 kA / m. 10-50Am²/ Kg of magnetic toner, the average circularity is 0.970 or more, the ratio of the weight average particle diameter to the number average particle diameter is 1.40 or less, and the liberation rate of iron and iron compound is 0.05%. To 3.00%, and the viscosity as measured by a flow tester is 1.0 × 10^FiveThe temperature at which Pa.s is 80 to 120 ° C. and 1.0 × 10^FourSince the temperature at which Pa · s is 100 to 150 ° C., it has good fixability, excellent charging stability, high image density even in long-term use, and high-definition images can be obtained.
[0469]
Furthermore, the magnetic toner of the present invention has a viscosity of 1.0 × 10 5 as measured by a flow tester.^FiveThe temperature at which Pa · s is 80 to 110 ° C., and the viscosity is 1.0 × 10^FourIf the temperature at which Pa · s is 100 to 140 ° C., it is more effective in achieving a good balance between fixability and chargeability.
[0470]
Further, the magnetic toner of the present invention has excellent reproducibility and high image quality when the mode circularity is 0.99 or more and the ratio of the weight average particle diameter to the number average particle diameter is 1.35 or less. It is much more effective in obtaining the image.
[0471]
Furthermore, in the magnetic toner of the present invention, the liberation rate of iron and iron compound is 0.05% to 2.00%, more preferably 0.05% to 1.50%, and still more preferably 0.05% to 1.00. % Is more effective in improving the charging uniformity of the magnetic toner and suppressing image roughness.
[0472]
Furthermore, the magnetic toner of the present invention is more effective in achieving both high-quality image formation and fixability when the release agent is contained in a total amount of 1 to 30% by mass with respect to the binder resin.
[0473]
Further, the magnetic toner of the present invention is a release agent.Differential scanning calorimetryIf the endothermic peak due to is 40 to 110 ° C., more preferably 50 to 100 ° C., it is more effective in balancing the fixing properties.
[0474]
Further, in the magnetic toner of the present invention, when the molecular weight distribution measured by gel permeation chromatography of the THF soluble content of the magnetic toner has a peak top of the main peak in the molecular weight range of 5000 to 50000, the magnetic toner This is more effective in improving the stability and fixability of the toner, the shape of the toner particles and the uniformity of the particle size distribution, and the like.
[0475]
Further, the magnetic toner of the present invention has an inorganic fine powder on the surface of the toner particles, the number average primary particle size of the inorganic fine powder is 4 to 80 nm, and the inorganic fine powder is selected from silica, titanium oxide, and alumina. At least one or more of them, particularly silica, is more effective in improving the fluidity of the magnetic toner.
[0476]
Further, in the magnetic toner of the present invention, the inorganic fine powder is hydrophobized, more preferably at least treated with silicone oil, and more preferably at least simultaneously with or after treatment with the silane compound. If it is treated, it is even more effective in maintaining the chargeability of the toner particles in a high humidity environment.
[0477]
Furthermore, in the magnetic toner of the present invention, the inorganic fine powder is silica, and the release rate of the silica is 0.1 to 2.0%, more preferably 0.1 to 1.5%. It is more effective in maintaining good fluidity.
[0478]
Furthermore, when the magnetic toner of the present invention has conductive fine powder having a volume average particle size smaller than the weight average particle size of the magnetic toner on the surface of the toner particles, the developability of the magnetic toner is improved and an image having a high image density is obtained. It is much more effective in obtaining.
[0479]
Further, in the magnetic toner of the present invention, the resistance of the conductive fine powder is 1 × 10.⁹Ωcm or less, more preferably 1 × 10⁸If it is Ωcm or less, it is more effective in improving the contact property at the contact portion between the image carrier and the charging member and realizing good charging.
[0480]
Further, the magnetic toner of the present invention is more effective in improving the transportability to the contact portion when the conductive fine powder is non-magnetic.
[0481]
Further, in the magnetic toner of the present invention, when the release rate of the conductive fine powder is 5.0 to 50.0%, the developability of the magnetic toner is improved, and an image with a high image density is obtained. It is effective.
[0482]
Further, the magnetic toner of the present invention is more effective in favorably dispersing the magnetic powder in the toner particles when the volume average particle size of the magnetic powder is 0.05 to 0.40 μm.
[0483]
Further, in the magnetic toner of the present invention, when the volume average variation coefficient is 35 or less in the particle size distribution of the magnetic powder, the magnetic toner is more effective in uniforming the content of the magnetic powder among the toner particles. is there.
[0484]
Further, in the magnetic toner of the present invention, it is assumed that the magnetic powder is hydrophobized with a coupling agent, more preferably, the surface is treated by hydrolyzing the coupling agent in an aqueous medium. This is more effective in obtaining the desired shape and surface condition.
[0485]
In addition, the image forming method of the present invention includes a magnetic one-component developing method, a contact charging method, a contact transfer method, and an image forming method using a toner recycling process as a contact charging method using the magnetic toner of the present invention. Since there is no deterioration in the performance of the magnetic toner, a good image can be stably obtained for a long time even in repeated use.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an example of an image forming apparatus that performs an image forming method of the present invention.
2 is a diagram showing an example of a one-component developing device used in the image forming apparatus shown in FIG.
FIG. 3 is a view showing an example of a contact transfer member used in an image forming apparatus for carrying out the image forming method of the present invention.
FIG. 4 is a diagram showing an example of an image carrier used in the image forming method of the present invention.
FIG. 5 is a diagram showing an example of a layer structure of an image carrier used in the image forming method of the present invention.
FIG. 6 is a diagram illustrating another example of an image forming apparatus that performs the image forming method of the present invention.
[Explanation of symbols]
11 Aluminum base
12 Conductive layer
13 Positive charge injection prevention layer
14 Charge generation layer
15 Charge transport layer
16 Charge injection layer
16a Conductive particles (conductive filler)
21, 100 photoconductor (image carrier)
22 Charging roller (charging member)
22a, 34a Core metal
23, 121 Laser beam scanner
24, 140 Developer
24a, 102 Developing sleeve (magnetic toner carrier)
24b, 141 stirring member
24c, 103 elastic blade
25, 34, 114 Transfer roller
26, 126 Fixing device
26a heater
26b fixing film
26c Pressure roller
27 Process cartridge
28 Cartridge holding member
34b Conductive elastic layer
35 Transfer bias power supply
104 Magnet roller
116 Cleaner
117 Primary charging roller (charging member)
123 Laser light
124 register roller
125 Conveyor belt
P Recording medium

Claims (19)

It contains toner particles having at least a binder resin, a release agent, and magnetic powder, has a weight average particle diameter of 3 to 20 μm, and a magnetization strength of 10 to 50 Am ² / kg at a magnetic field of 79.6 kA / m. In a certain magnetic toner, the average circularity of the magnetic toner is 0.970 or more, the ratio of the weight average particle diameter to the number average particle diameter of the magnetic toner is 1.40 or less, and the magnetic toner is introduced into the plasma. The release rate of iron and iron compounds derived from the magnetic powder defined by the following formula is 0.05% to 3.00%, and the viscosity of the magnetic toner measured by a flow tester is measured. The magnetic toner is characterized in that the temperature at which the toner becomes 1.0 × 10 ⁵ Pa · s is 80 to 120 ° C. and the temperature at which the toner becomes 1.0 × 10 ⁴ Pa · s is 100 to 150 ° C.

("Simultaneous light emission" means that light emission of iron atoms emitted within 2.6 msec from light emission of carbon atoms is simultaneous light emission, and light emission of iron atoms thereafter is light emission of iron atoms only.) 2. The magnetic toner according to claim 1, wherein a temperature at which the viscosity of the magnetic toner measured by a flow tester is 1.0 × 10 ⁵ Pa · s is 80 to 110 ° C. 3. 2. The magnetic toner according to claim 1, wherein a temperature at which the viscosity of the magnetic toner measured by a flow tester is 1.0 × 10 ⁴ Pa · s is 100 to 140 ° C. 3.  The magnetic toner according to claim 1, wherein a liberation rate of iron and an iron compound of the magnetic toner is 0.05% to 1.50%.  The magnetic toner according to claim 1, wherein a liberation rate of iron and an iron compound of the magnetic toner is 0.05% to 1.00%. The magnetic toner has an inorganic fine powder on the toner particle surfaces are the inorganic fine powder silica, the emission spectrum which was introduced magnetic toner to the plasma was measured, the free silica is defined by the following formula The magnetic toner according to claim 1, wherein the percentage is 0.1 to 2.0%.

The magnetic toner has an inorganic fine powder on the toner particle surfaces are the inorganic fine powder silica, the emission spectrum which was introduced magnetic toner to the plasma was measured, the free silica is defined by the following formula The magnetic toner according to claim 1, wherein the percentage is 0.1 to 1.5%.

The magnetic toner has a conductive fine powder having a volume average particle size smaller than the weight average particle size of the magnetic toner on the surface of the toner particles, and measures an emission spectrum when the magnetic toner is introduced into plasma. The magnetic toner according to claim 1, wherein the release rate of the conductive fine powder defined by the formula is 5.0 to 50.0%.

 The magnetic toner according to claim 1, wherein the magnetic powder is surface-treated by hydrolyzing a coupling agent in an aqueous medium. The magnetic toner according to claim 1, wherein the magnetic toner has a residual magnetization strength of 0.5 to 6 Am ² / kg in a magnetic field of 79.6 kA / m. A charging step for charging the image carrier, an electrostatic latent image forming step for writing image information as an electrostatic latent image on the charged image carrier, an image carrier for holding the electrostatic latent image on the surface, and magnetic toner A developing portion is formed by disposing a magnetic toner carrier carrying the surface of the magnetic toner on the surface at a predetermined interval, and the magnetic toner is coated on the surface of the magnetic toner carrier to a thickness smaller than the interval, An image carrier having a developing step of transferring the magnetic toner to the electrostatic latent image to form a toner image and a transfer step of transferring the toner image to a recording medium. In the image forming method in which image formation is performed repeatedly, the magnetic toner includes toner particles having at least a binder resin, a release agent, and magnetic powder, and has a weight average particle diameter of 3 to 20 μm, Magnetic field 79.6k / Intensity of magnetization in m is the magnetic toner as a 10~50Am ² / kg, and an average circularity of 0.970 or more, the ratio of the weight average particle diameter to the number average particle diameter of 1.40 or less The emission spectrum when the magnetic toner was introduced into the plasma was measured, and the liberation rate of iron and iron compound derived from the magnetic powder defined by the following formula was 0.05 to 3.00%. The temperature at which the measured viscosity is 1.0 × 10 ⁵ Pa · s is 80 to 120 ° C., and the temperature at which the viscosity becomes 1.0 × 10 ⁴ Pa · s is 100 to 150 ° C. An image forming method, wherein the charging step is a step of charging the image carrier by applying a voltage to a charging member that forms a contact portion with the image carrier and contacts the magnetic carrier. .

("Simultaneous light emission" means that light emission of iron atoms emitted within 2.6 msec from light emission of carbon atoms is simultaneous light emission, and light emission of iron atoms thereafter is light emission of iron atoms only.)  The image forming method according to claim 11, wherein the developing step also serves as a cleaning step of collecting toner remaining on the image carrier after the toner image is transferred onto a recording medium.  The image forming method according to claim 11 or 12, wherein the magnetic toner used in the developing step is the magnetic toner according to any one of claims 2 to 10.  The conductive fine powder is interposed in at least one of the contact portion of the charging member and the image carrier and the vicinity thereof in the charging step. Image forming method. In the charging step, the image carrying is performed in a state where conductive fine powder of 1 × 10 ³ pieces / mm ² or more and 2 × 10 ⁵ pieces / mm ² or less is interposed in a contact portion between the charging member and the image carrier. The image forming method according to claim 11, wherein the image forming method is a step of charging a body. 16. The charging process according to claim 11, wherein the charging step is a step of charging the image carrier by applying a voltage to a roller member having an Asker C hardness of 25 to 50 degrees . Image forming method.  The charging step is a step of charging the image carrier by applying a voltage to the roller member, and the roller member has at least a depression having an average cell diameter in a spherical form of 5 to 300 μm on the surface. The image forming method according to any one of claims 11 to 16, wherein a porosity of the surface of the roller member having the depression as a gap portion is 15 to 90%.  16. The charging process according to claim 11, wherein the charging step is a step of charging the image carrier by applying a voltage to a conductive brush member as the charging member. Image forming method. The developing step is a step of forming a toner layer of 5 to 50 g / m ^{2 on} a magnetic toner carrier, and transferring a magnetic toner from the toner layer to an image carrier to form a toner image. Item 19. The image forming method according to any one of Items 11 to 18.

Images