JP3997291B2

JP3997291B2 - Electrophotographic development carrier

Info

Publication number: JP3997291B2
Application number: JP2002007742A
Authority: JP
Inventors: 博瀬戸; 智英飯田; 崇後藤; 竜介中尾
Original assignee: Dowa IP Creation Co Ltd
Current assignee: Dowa IP Creation Co Ltd
Priority date: 2002-01-16
Filing date: 2002-01-16
Publication date: 2007-10-24
Anticipated expiration: 2022-01-16
Also published as: JP2003207950A

Description

【０００１】
【産業上の利用分野】
本発明は電子写真現像用キャリヤに関する。
【０００２】
【従来の技術】
静電荷像の現像剤としてトナーとキャリヤからなる二成分系の現像剤が普及しているが，この現像剤に用いられるキャリヤ（静電写真現像用キャリヤ）には様々な特性（磁気特性，摩擦帯電性，耐久性，流動性など）が要求され，芯材の表面に樹脂被覆されたキャリヤにおいては，芯材（粉体）の見掛け密度や流動性，粒度分布，形状，表面性などを目標値に合わせる必要がある。他方，近年フルカラーの複写機やプリンターが開発され，その高画質要求を満たすために，キャリヤ／トナーの小粒子化が図られるようになり，この場合には，キャリヤに含まれる微粉の割合が必然的に多くなる。
【０００３】
【発明が解決しようとする課題】
二成分系の現像方式を用いるマシンでは，感光体（ドラム）へのキャリヤ付着（キャリヤ飛び）等による現像不良が問題となっており，その原因の一つにキャリヤの微粉の存在が挙げられている。この点からすると，キャリヤとしては，平均粒径が小さくて（全体的に小粒径でありながら）且つ微粉量が少ない粒度分布をもつもの（粒度分布が狭いもの）が望ましい。このため，製造の面では，キャリヤの整粒過程において可能な限り微粉側のものを除くように整粒されるのが望ましく，帯電付与のために樹脂被覆する場合も，このように微粉側のものが除かれたうえで，樹脂被覆が施されるのが好ましく，事実，このような考慮がなされている。
【０００４】
しかしながら，樹脂被覆されたキャリヤでは，樹脂コーテイングの種類によってはその被覆層が芯材に対して強いストレスを付与することにもなり，これが原因で，処理中や現像中に機械的な外部応力が加わると，芯材に亀裂や割れが発生して二次微粉を生成させることがある。
【０００５】
したがって，本発明の課題は，このような機械的ストレスが加わっても二次微粉の発生を可能な限り抑制できるようなキャリヤを得ることにある。
【０００６】
【課題を解決するための手段】
本発明によれば，主としてフエライトまたはマグネタイトの粒子からなる電子写真現像用キャリヤ，或いは，フエライトまたはマグネタイトを主成分とする粒子を芯材としこの芯材の表面に樹脂被覆が施された電子写真現像用キャリヤにおいて，該粒子中に０.００１〜０.１重量％のＢ（ホウ素）および０.０１〜０.５重量％のＳｉを含有することを特徴とする電子写真現像用キャリヤを提供する。
ここで，フエライトは，
一般式（ＭＯ)_Xn (Ｆｅ₂Ｏ₃)_Y，・・(1)
〔式中，Ｍ＝Ｍｎ, ＭｇまたはＦｅの１種または２種, ΣXn＝４０〜６０（モル％），Ｙ＝１００−ΣXn（モル％）である〕で表されるフエライトであることができる。
【０００７】
【発明の実施の形態】
本発明で言う「主としてフエライトまたはマグネタイトの粒子からなる電子写真現像用キャリヤ」とは，理想的にはフエライト粒子および／またはマグネタイト粒子からなるものを言うが，ヘマタイト成分等の他の鉄酸化物や他の元素やその化合物等を粒子中に若干含有したものでもよいし，フエライトまたはマグネタイト以外の化合物や酸化物等からなる粒子がフエライト粒子やマグネタイト粒子中に若干量混在したものでもよい。
【０００８】
本発明者らは，このようなキャリヤからの二次微粉発生の原因調査とその抑制手段について種々の試験検討を重ねたが，キャリヤ粒子の表面状態が二次微粉発生に関与していることがわかったが，二次微粉が発生しないような表面状態を有するキャリヤを得ることは，焼結温度などのキャリヤ製造の条件を変えるだけでは至難であった。
【０００９】
一般に，キャリヤの製造には，前記の(1) 式に示されるようなフエライトを例とすると，目標組成となるように原料を調合し，これを仮焼，粉砕，造粒，乾燥，焼成，解砕，分級を経て所望の粒径もしくは粒度分布のフエライト粒子からなる粉体を得る。そのさい，フエライト結晶の成長は，前記の焼成の段階において，表面成長，粒界成長，内部成長，蒸発成長といった機構を経ると考えられが，結晶成長には結晶中の空格子点の量が深く関わっており，この空格子点が移動することで結晶が成長してゆくとされており，この空格子点は結晶中の不純物の量が多いほど多くなることが知られている。
【００１０】
本発明者らはこの点に着目し，目標組成となるように調合された焼結原料中にフエライトの構成成分以外の元素を意図的に有させ，これによってフエライト結晶の成長挙動を制御し，もって二次微粉が発生し難いような結晶粒子を得るべく試験を重ねた。その結果，そのような物質としてＢ化合物とＳｉ化合物が有利な効果を示すことがわかった。すなわち，フエライトの目標組成となるように調合された焼成原料中に例えばＨ₃ＢＯ₃等のホウ素化合物やＳｉＯ₂等のケイ素化合物を適量含有させておくと，耐衝撃性に優れた表面性をもつフエライト結晶が得られることがわかった。
【００１１】
その含有量については，ホウ素化合物についてはＢ元素に換算して０.００１〜０.１重量％，ケイ素化合物についてはＳｉ元素に換算して０.０１〜０.５重量％となる範囲であるのがよい。ホウ素化合物およびケイ素化合物とも，ＢおよびＳｉが前記の含有量となるように焼結前の原料に配合するが，実際には，仮焼し粉砕した原料粉を造粒する段階で添加するのが都合がよい。焼成時にホウ素化合物は分解および酸化してホウ素の酸化物になると考えられ，ＳｉＯ₂以外のケイ素化合物を添加した場合にも焼成時に分解および酸化してケイ素の酸化物になると考えられる。本発明で使用できるホウ素化合物としてはホウ酸，ホウ酸アンモニウム，ホウ酸エステル，ホウ砂等が挙げられ，本発明で使用できるケイ素化合物としては無水シリカ，ホウケイ酸塩，コロイダルシリカ等が挙げられる。
【００１２】
芯材中のＢ含有量が０.００１重量％未満では，Ｓｉ含有量をたとえ本発明で規定する０.０１重量％以上含有させても前記のような二次微粉の発生を抑制することができず，またＳｉ含有量が０.０１重量％未満の場合にも，Ｂ含有量を本発明で規定する０.００１重量％以上含有させても二次微粉の発生を充分に抑制できない。逆に，Ｂ含有量が０.１重量％より多くなると，フエライトやマグネタイトの組成中に含まれる不純物量が多くなり，芯材の磁気的特性に影響を与えるようになることに加え，芯材粒子の表面形状がいびつになって流動性が悪くなるので好ましいことではない。同様にＳｉ含有量も０.５重量％より多くなっても芯材粒子の表面形状がいびつになり，また芯材の磁気的特性を劣化させるので好ましくない。このような理由から，芯材中のＢ含有量は０.００１〜０.１重量％，Ｓｉ含有量は０.０１〜０.５重量％とする。好ましいＢ含有量は０.０１〜０.０６重量％，さらに好ましくは０.０２〜０.０５重量％である。好ましくはＳｉ含有量は０.１〜０.２重量％，さらに好ましくは０.１２〜０.１６重量％である。
【００１３】
本発明に従うキャリヤの製造法について，ＭｎＯ−ＭｇＯ−Ｆｅ₂Ｏ₃系フェライトの製造を例とすると，まず原料中のＭｎ, ＭｇおよびＦｅの組成比が意図するフェライトの組成比に相当するように，炭酸塩，水酸化物または酸化物等の形態の原料を秤量調合し，よく混合したうえ，加熱炉中で６００〜１０００℃の温度に大気雰囲気中で加熱し，１〜５時間保持して仮焼する。これにより，炭酸塩や水酸化物等の形態で調合した原料は実質的に酸化物の形態の塊状物となり，揮発性成分や非金属介在物などは分解・蒸発除去される。得られた仮焼品は，冷却後，粉砕機例えば振動ミルで１μｍ程度まで粉砕する。
【００１４】
この粉砕品に水を加えてスラリーとするが，このスラリーを作成するさいに，前記のホウ素化合物およびケイ素化合物を，フエライト中のＢ含有量およびＳｉ含有量が既述の範囲となるように添加し，スラリー濃度が６０〜７５％程度の粗スラリーとし，これをボールミル等で湿式粉砕する。これにより，微細に粉砕された仮焼粉のスラリーが得られる。この仮焼粉スラリーに，必要に応じてポリカルボン酸等の分散剤を加えたうえ，噴霧乾燥機等で噴霧乾燥するか，或いはペレタイザーで造粒し，１０〜５００μｍの球状ペレットにして乾燥する。
【００１５】
次いで，前記の造粒品を焼成してフェライトとするが，そのさい，窒素ガス中の酸素濃度が０.５〜６容積％範囲内の所定の値となるように調整した雰囲気中の電気炉で１１００〜１３００℃の温度に少なくとも６０分間保持する焼成処理を行う。
【００１６】
焼成された焼成品は解砕機で解砕し，解砕粉を分級または篩分けしてキャリヤとして適正な粒度のものを採取する。これにより例えば平均粒子径が４０μｍ程度の粒子からなるキャリヤ粉を得るが，場合によってはさらに磁場選鉱し，微粒子を排除して粒度分布の狭い平均粒径４０μｍ程度のものを採取する。
【００１７】
樹脂被覆キャリヤを製造する場合には，得られた粉体を芯材として，これに樹脂被覆するが，その被覆量としては芯材総量の１.０〜５.０重量％に調整するのがよい。被覆する樹脂としては種々のものが適用でき，例えばアクリル系樹脂，スチレン系樹脂，スチレン−アクリル系樹脂，オレフイン系樹脂（ポリエチレン，塩素化ポリエチレン，ポリプロピレン等），ポリエステル系樹脂（ポリエチレンテレフタレート，ポリカーボネート等），不飽和ポリエステル系樹脂，塩化ビニル系樹脂，ポリアミド系樹脂，ポリウレタン系樹脂，エポキシ系樹脂，シリコーン系樹脂，フッ素系樹脂（ポリテトラフルオロエチレン，ポリクロロトリフルオロエチレン，ポリ弗化ビニリデン等），フエノール系樹脂，キシレン系樹脂，ジアリルフタレート系樹脂等が挙げられる。
【００１８】
樹脂コーテイングを行うには，前記の樹脂を溶剤に希釈して芯材の表面に被覆するのが一般的である。溶剤としては各樹脂が可溶なものであればよく，有機溶剤に可溶な樹脂の場合の溶剤としては，トルエン，キシレン，メチルエチルケトン，メチルイソブチルケトン，メタノール等を使用することができ，水溶性樹脂またはエマルジョンタイプの樹脂であれば，水を用いる。
【００１９】
芯材の表面に対し溶剤で希釈された樹脂を被覆するには，その液に芯材を浸漬して攪拌する浸漬法，該液を芯材にスプレーするスプレー法，刷毛塗りする刷毛塗り法等が適用でき，該液を塗布後は溶剤を乾燥させる。このようなコーテイング法は湿式法とも言えるが，溶剤を使用しないで乾式法によって芯材表面に樹脂粉末を被着させる方法も採用できる。
【００２０】
いずれにしても，芯材粒子の表面に被覆付着させた樹脂を焼き付けるのが好ましく，固定式または流動式の電気炉，ロータリー式電気炉，バーナー炉などを使用して，外部加熱方式または内部加熱方式で焼き付けることができる。マイクロウエーブによる焼き付けも可能である。焼き付け温度は樹脂によって異なるが，融点以上またはガラス転移点以上の温度が必要である。熱硬化性樹脂または縮合型樹脂では硬化が十分に進む温度まで上げる必要がある。
【００２１】
シリコーン樹脂で芯材の被膜を形成する場合を例として具体的に説明すると，シリコーン樹脂をトルエンで希釈し，この液と芯材を攪拌機の容器に入れて攪拌する。これにより，例えばシリコーン樹脂の割合が３重量％となるように浸漬法で被着させる。そのさい，使用する樹脂種に応じて硬化剤を添加する。攪拌混合が終えたら，溶媒を乾燥除去する（例えば１３０℃×３０分の加熱処理）。ついで加熱攪拌しながら硬化する（例えばオイルバスで加熱し且つ攪拌しながら１９０℃×３０分の加熱処理を行う）。ついでオーブンまたはトンネル炉を用いて樹脂の焼き付け処理を行う（例えば１６０〜２８０℃×３時間）。これにより樹脂被覆キャリヤ成品が得られる。
【００２２】
このようにして得られた樹脂被覆キャリヤは，この状態でトナーと組み合わされて２成分系の電子写真用現像剤となるが，その場合，被覆樹脂がフェライトコア表面に強固に焼き付けられていても，帯電特性や抵抗性さらには耐久性などにおいてさらなる改善を必要とする場合がある。この場合には，この樹脂被覆キャリヤ成品を研磨処理することによって，具体的には，この成品の樹脂コーテイング層に圧縮応力が作用する機械的表面処理を施すことによって，より具体的には，この成品の粒子同士を互いに衝突させる粒子同士の研磨処理によって，該成品の前記の特性を一層良好にすることができる。このような場合にも，本発明に従う芯材は二次微粉の発生が少ないので，微粉によるキャリヤ飛びなどが起きがたいものが得られる。
【００２３】
【実施例】
〔実施例１〕
Ｍｎ源としてＭｎ₃Ｏ₄を_,Ｍｇ源としてＭｇ(ＯＨ)₂を，そしてＦｅ源としてＦｅ₂Ｏ₃を使用し_,焼成後のフエライト組成として，（ＭｎＯ）Ｆｅ₂Ｏ₃ ：（ＭｇＯ）Ｆｅ₂Ｏ₃ ＝７０：３０となる割合でこれらの原料を調合した。
【００２４】
この混合粉を加熱炉で９００℃で３時問大気雰囲気で加熱して仮焼した。得られた仮焼品を冷却後，振動ミルでほぼ１μｍ大に粉砕し，乾燥粉に対して１重量％の割合で分散剤（商品名：サンノプコＳＮデイスパーサント５４６８）を水と共に加えてスラリー濃度が７５％程度の粗スラリーとし，この粗スラリーにホウ酸と無水シリカを添加した。ホウ酸の添加量は，混合粉に対するホウ酸の割合が０.２５重量％となる量（Ｂ換算では，混合粉に対するＢ含有量が０.０４重量％となる量）とし，無水シリカの添加量は，混合粉に対する無水シリカの割合が０.３重量％となる量（Ｓｉ換算では，混合粉に対するＳｉ含有量が０.１４重量％となる量）とした。
【００２５】
次いで，これらの化合物を添加したスラリーを湿式ボールミルに装填して湿式粉砕し，得られた懸濁液をスプレードライヤーに供給し，アトマイザーの回転数を 15000〜18000 rpm 程度で造粒し，５４μｍの篩を用いて平均粒径が４０μｍ程度の乾燥粒子からなる造粒品を得た。
【００２６】
この造粒品を焼成炉に装填し，酸素濃度をほぼ４〜５vol.％に調整した窒素ガス雰囲気中で１１８０℃で３時間焼成した。得られた塊状の焼成品をハンマーミルで粗砕し，さらにパルベライザーで解砕した。この解砕品を風力分級機にかけて微粉を分級除去し，さらに磁場選鉱して非磁性分を分離し，５４μｍの篩を通して平均粒径が３５μｍのキャリヤ粉を得た。このキャリヤ粉について，比表面積をＢＥＴ法で測定したところ０.０３６ｍ²/ｇであり，走査型電子顕微鏡（ＳＥＭ）で表面観察したところ，ほぼ球形の滑らかな表面を有する粒子からなることが確認された。
【００２７】
以降の例と対比するために，本例のキャリヤ粉の組成・Ｂ添加量，Ｓｉ添加量，比表面積，ＳＥＭ観察結果を表１に示した。
【００２８】
さらに，このキャリヤ粉１０ｇを採取し，サンプルミルに投入して１５秒間処理して機械的ストレスを付加し，この処理の前後の粒度分布を日本レーザー株式会社製のＨＥＬＯＳ粒度分布測定器を用いて測定した。その測定結果を表２に示した。表２において，Ｄ１０，Ｄ５０，Ｄ９０の各値は，ヘロス粒度分布測定装置によって粒度分布を計測したときに，粒径（μｍ）を横軸とし，縦軸にその粒径以下の粒子が存在する容積％をとって表わされた累積粒度曲線において，粒径が１０，５０，９０μｍであるときの，縦軸の値を表している。
【００２９】
〔実施例２〕
ホウ酸の添加量を，混合粉に対するホウ酸の割合が０.０１重量％となる量（Ｂ換算では，混合粉に対するＢ含有量が０.００２重量％となる量）とし，無水シリカの添加量を，混合粉に対する無水シリカの割合が０.０３重量％となる量（Ｓｉ換算では，混合粉に対するＳｉ含有量が０.０１重量％となる量）とした以外は，実施例１を繰り返した。本例のキャリヤ粉の組成・Ｂ添加量，Ｓｉ添加量，比表面積，ＳＥＭ観察結果を表１に示すと共に，本例で得られたキャリヤ粉に対して実施例１と同様に機械的ストレスを付与した前後の粒度分布を表２に示した。
【００３０】
〔実施例３〕
ホウ酸の添加量を，混合粉に対するホウ酸の割合が０.６０重量％となる量（Ｂ換算では，混合粉に対するＢ含有量が０.１０重量％となる量）とし，無水シリカの添加量を，混合粉に対する無水シリカの割合が１.０重量％となる量（Ｓｉ換算では，混合粉に対するＳｉ含有量が０.４７重量％となる量）とした以外は，実施例１を繰り返した。本例のキャリヤ粉の組成・Ｂ添加量，Ｓｉ添加量，比表面積，ＳＥＭ観察結果を表１に示すと共に，本例で得られたキャリヤ粉に対して実施例１と同様に機械的ストレスを付与した前後の粒度分布を表２に示した。
【００３１】
〔実施例４〕
原料調合において（ＭｎＯ）Ｆｅ₂Ｏ₃ ：（ＭｇＯ）Ｆｅ₂Ｏ₃ ＝２５：７５に変更し，且つ焼結時の焼成雰囲気を大気雰囲気とした以外は，実施例１を繰り返した。本例のキャリヤ粉の組成・Ｂ添加量，Ｓｉ添加量，比表面積，ＳＥＭ観察結果を表１に示すと共に，本例で得られたキャリヤ粉に対して実施例１と同様に機械的ストレスを付与した前後の粒度分布を表３に示した。
【００３２】
〔実施例５〕
造粒時に用いた篩を５４μｍのものから６３μｍのものに変更した以外は，実施例１を繰り返した。本例のキャリヤ粉の組成・Ｂ添加量，Ｓｉ添加量，比表面積，ＳＥＭ観察結果を表１に示すと共に，本例で得られたキャリヤ粉に対して実施例１と同様に機械的ストレスを付与した前後の粒度分布を表３に示した。
【００３３】
〔比較例１〕
ホウ酸と無水シリカをいずれも無添加とした以外は，実施例１を繰り返した。本例のキャリヤ粉の組成，比表面積，ＳＥＭ観察結果を表１に示すと共に，本例で得られたキャリヤ粉に対して実施例１と同様に機械的ストレスを付与した前後の粒度分布を表４に示した。
【００３４】
〔比較例２〕
ホウ酸を無添加とし，無水シリカの添加量を，混合粉に対する無水シリカの割合が１.３重量％となる量（Ｓｉ換算では，混合粉に対するＳｉ含有量が０.６１重量％となる量）とした以外は，実施例１を繰り返した。本例のキャリヤ粉の組成・Ｓｉ添加量，比表面積，ＳＥＭ観察結果を表１に示すと共に，本例で得られたキャリヤ粉に対して実施例１と同様に機械的ストレスを付与した前後の粒度分布を表４に示した。
【００３５】
〔比較例３〕
無水シリカを無添加とし，ホウ酸の添加量を，混合粉に対するホウ酸の割合が０.８０重量％となる量（Ｂ換算では，混合粉に対するＢ含有量が０.１４重量％となる量）とした以外は，実施例１を繰り返した。本例のキャリヤ粉の組成・Ｂ添加量，比表面積，ＳＥＭ観察結果を表１に示すと共に，本例で得られたキャリヤ粉に対して実施例１と同様に機械的ストレスを付与した前後の粒度分布を表４に示した。
【００３６】
〔比較例４〕
ホウ酸と無水シリカをいずれも無添加とした以外は，実施例４を繰り返した。本例のキャリヤ粉の組成，比表面積，ＳＥＭ観察結果を表１に示すと共に，本例で得られたキャリヤ粉に対して実施例１と同様に機械的ストレスを付与した前後の粒度分布を表４に示した。
【００３７】
【表１】

【００３８】
【表２】

【００３９】
【表３】

【００４０】
【表４】

【００４１】
表１〜４の結果から，実施例１〜５のものは，表面が平滑で球状のキャリヤ粉であり，機械的ストレスを付与した後でも，ストレス付与前の粒度分布を維持し，微粉は発生していないことがわかる。これに対して，比較例１〜２のものは表面に凹凸があり，機械的ストレスを付与した後では微粉が発生した。比較例３のものはホウ酸の添加量が多いためにコア形状かいびつになり，比較例４のものでは脆い表面状態となり，機械的ストレスを付与した後では微粉が発生した。
【００４２】
【発明の効果】
以上説明したように，本発明によると，微量の添加物によってキャリヤ粉の衝撃強度を向上させることができるので，二次微粉の発生の少ない電子写真現像用キャリヤを経済的に得ることができ，微粉が混在することによるキャリヤ飛び等による画像劣化の問題を未然に回避することができる。[0001]
[Industrial application fields]
The present invention relates to a carrier for electrophotographic development.
[0002]
[Prior art]
Two-component developers consisting of toner and carrier are widely used as developers for electrostatic images, but there are various characteristics (magnetic characteristics, friction, etc.) for the carriers used for this developer (carriers for electrophotographic development). (Chargeability, durability, fluidity, etc.) are required, and in the case of a carrier whose core material is resin-coated, the target density, fluidity, particle size distribution, shape, and surface properties of the core material (powder) are targeted. It is necessary to match the value. On the other hand, full-color copiers and printers have been developed in recent years, and in order to meet the high image quality requirements, carrier / toner particles have become smaller. In this case, the proportion of fine powder contained in the carrier is necessarily Increase in number.
[0003]
[Problems to be solved by the invention]
In a machine using a two-component development system, development failure due to carrier adhesion (carrier jumping) to the photoreceptor (drum) is a problem, and one of the causes is the presence of fine carrier powder. Yes. From this point of view, it is desirable that the carrier has a small average particle size (although the particle size is small as a whole) and a small particle size distribution (a narrow particle size distribution). For this reason, it is desirable to adjust the particle size so as to eliminate as much as possible in the particle size adjustment process of the carrier. It is preferable to apply a resin coating after removing the material, and in fact, this is taken into account.
[0004]
However, with a resin-coated carrier, depending on the type of resin coating, the coating layer can also apply a strong stress to the core material, which causes mechanical external stresses during processing and development. If added, cracks and cracks may be generated in the core material to generate secondary fine powder.
[0005]
Accordingly, an object of the present invention is to obtain a carrier that can suppress the generation of secondary fine powder as much as possible even when such mechanical stress is applied.
[0006]
[Means for Solving the Problems]
According to the present invention, an electrophotographic development carrier mainly composed of ferrite or magnetite particles, or an electrophotographic development in which particles mainly composed of ferrite or magnetite are used as a core material and the surface of the core material is coated with a resin. A carrier for electrophotographic development, characterized in that it contains 0.001 to 0.1% by weight of B (boron) and 0.01 to 0.5% by weight of Si in the particles. .
Here, the ferrite is
General formula (MO) _Xn (Fe ₂ O ₃ ) _Y , ... (1)
[Wherein, M = Mn, Mg or Fe, or ΣXn = 40 to 60 (mol%), Y = 100−ΣXn (mol%)). .
[0007]
DETAILED DESCRIPTION OF THE INVENTION
The “carrier for electrophotographic development mainly composed of ferrite or magnetite particles” as referred to in the present invention is ideally composed of ferrite particles and / or magnetite particles, but other iron oxides such as hematite components and the like. The particles may contain a small amount of other elements or their compounds, or may be a mixture of a small amount of particles made of a compound or oxide other than ferrite or magnetite in the ferrite particles or magnetite particles.
[0008]
The present inventors have conducted various examinations on the investigation of the cause of the generation of secondary fine powder from the carrier and the suppression means, but the surface state of the carrier particles is involved in the generation of secondary fine powder. As can be seen, it has been difficult to obtain a carrier having a surface state that does not generate secondary fine powder by simply changing the carrier production conditions such as the sintering temperature.
[0009]
In general, in the manufacture of a carrier, for example, a ferrite as shown in the above formula (1) is used to prepare raw materials so as to have a target composition, which is calcined, pulverized, granulated, dried, fired, A powder composed of ferrite particles having a desired particle size or particle size distribution is obtained through pulverization and classification. At the same time, the growth of ferrite crystals is thought to proceed through the mechanisms of surface growth, grain boundary growth, internal growth, and evaporation growth in the above-mentioned firing stage. It is deeply involved, and it is said that the crystal grows as the vacancies move. It is known that the vacancies increase as the amount of impurities in the crystal increases.
[0010]
The present inventors pay attention to this point, intentionally having elements other than the constituents of ferrite in the sintered raw material prepared to have a target composition, thereby controlling the growth behavior of the ferrite crystal, Thus, tests were repeated to obtain crystal particles that are less likely to generate secondary fine powder. As a result, it was found that B compound and Si compound show advantageous effects as such substances. That is, if an appropriate amount of a boron compound such as H ₃ BO ₃ or a silicon compound such as SiO ₂ is contained in a fired raw material prepared so as to have a target composition of ferrite, surface properties excellent in impact resistance can be obtained. It turned out that the ferrite crystal which has is obtained.
[0011]
Regarding the content, the boron compound is in the range of 0.001 to 0.1% by weight in terms of B element, and the silicon compound in the range of 0.01 to 0.5% by weight in terms of Si element. It is good. Both boron compounds and silicon compounds are blended into the raw material before sintering so that the above-mentioned contents of B and Si are added. In practice, it is added at the stage of granulating the calcined and pulverized raw material powder. convenient. It is considered that the boron compound is decomposed and oxidized at the time of firing to become a boron oxide. Even when a silicon compound other than SiO ₂ is added, it is considered that the boron compound is decomposed and oxidized at the time of firing to become a silicon oxide. Examples of the boron compound that can be used in the present invention include boric acid, ammonium borate, borate ester, and borax. Examples of the silicon compound that can be used in the present invention include anhydrous silica, borosilicate, colloidal silica, and the like.
[0012]
When the B content in the core material is less than 0.001% by weight, the generation of secondary fine powder as described above can be suppressed even if the Si content is not less than 0.01% by weight as defined in the present invention. In addition, even when the Si content is less than 0.01% by weight, the generation of secondary fine powder cannot be sufficiently suppressed even if the B content is not less than 0.001% by weight as defined in the present invention. Conversely, if the B content exceeds 0.1% by weight, the amount of impurities contained in the composition of ferrite and magnetite increases, which affects the magnetic properties of the core material. It is not preferable because the surface shape of the particles becomes distorted and the fluidity is deteriorated. Similarly, even if the Si content is more than 0.5% by weight, the surface shape of the core particles becomes distorted and the magnetic properties of the core material are deteriorated, which is not preferable. For these reasons, the B content in the core material is 0.001 to 0.1% by weight, and the Si content is 0.01 to 0.5% by weight. The B content is preferably 0.01 to 0.06% by weight, more preferably 0.02 to 0.05% by weight. Preferably, the Si content is 0.1 to 0.2% by weight, more preferably 0.12 to 0.16% by weight.
[0013]
In the manufacturing method of the carrier according to the present invention, taking MnO—MgO—Fe ₂ O ₃ ferrite as an example, first, the composition ratio of Mn, Mg and Fe in the raw material corresponds to the intended composition ratio of ferrite. , Weigh and prepare raw materials in the form of carbonate, hydroxide or oxide, etc., mix well, heat in a heating furnace to a temperature of 600-1000 ° C. and hold for 1-5 hours Calcinate. As a result, the raw material prepared in the form of carbonate, hydroxide, or the like becomes a massive substance in the form of oxide, and volatile components and non-metallic inclusions are decomposed and removed by evaporation. The obtained calcined product is cooled and then pulverized to about 1 μm by a pulverizer such as a vibration mill.
[0014]
Water is added to this pulverized product to form a slurry. At the time of preparing this slurry, the above boron compound and silicon compound are added so that the B content and Si content in the ferrite are within the ranges described above. Then, a coarse slurry having a slurry concentration of about 60 to 75% is obtained, and this is wet pulverized by a ball mill or the like. Thereby, a finely pulverized calcined powder slurry is obtained. If necessary, a dispersant such as polycarboxylic acid is added to the calcined powder slurry, and then spray-dried with a spray dryer or the like, or granulated with a pelletizer, and dried into spherical pellets of 10 to 500 μm. .
[0015]
Next, the granulated product is fired to obtain ferrite. At this time, the electric furnace in an atmosphere adjusted so that the oxygen concentration in the nitrogen gas becomes a predetermined value within the range of 0.5 to 6% by volume. And a baking treatment for holding at a temperature of 1100 to 1300 ° C. for at least 60 minutes.
[0016]
The fired fired product is crushed with a crusher, and the crushed powder is classified or sieved to obtain a carrier having an appropriate particle size. Thereby, for example, carrier powder composed of particles having an average particle size of about 40 μm is obtained. However, in some cases, magnetic field beneficiation is performed, and fine particles are excluded to collect particles having an average particle size of about 40 μm having a narrow particle size distribution.
[0017]
In the case of manufacturing a resin-coated carrier, the obtained powder is coated with resin as a core material, and the coating amount is adjusted to 1.0 to 5.0% by weight of the total amount of the core material. Good. Various resins can be used for coating, such as acrylic resins, styrene resins, styrene-acrylic resins, olefin resins (polyethylene, chlorinated polyethylene, polypropylene, etc.), polyester resins (polyethylene terephthalate, polycarbonate, etc.) ), Unsaturated polyester resin, vinyl chloride resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin, fluorine resin (polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, etc.) , Phenol resins, xylene resins, diallyl phthalate resins, and the like.
[0018]
In general, resin coating is performed by diluting the resin in a solvent and coating the surface of the core material. Solvents can be used as long as each resin is soluble. Toluene, xylene, methyl ethyl ketone, methyl isobutyl ketone, methanol, etc. can be used as the solvent in the case of resins soluble in organic solvents. If it is a resin or emulsion type resin, use water.
[0019]
To coat the surface of the core material with resin diluted with a solvent, immersing the core material in the solution and stirring it, spraying the liquid onto the core material, brushing method for brushing, etc. Can be applied, and after applying the liquid, the solvent is dried. Although such a coating method can be said to be a wet method, a method of depositing resin powder on the surface of the core material by a dry method without using a solvent can also be employed.
[0020]
In any case, it is preferable to bake the resin adhered to the surface of the core particles, using a fixed or fluidized electric furnace, rotary electric furnace, burner furnace, etc. Can be baked by the method. Baking with microwaves is also possible. The baking temperature varies depending on the resin, but a temperature higher than the melting point or higher than the glass transition point is required. In the case of a thermosetting resin or a condensation type resin, it is necessary to raise the temperature to a level at which the curing proceeds sufficiently.
[0021]
The case where the core film is formed of silicone resin will be specifically described as an example. The silicone resin is diluted with toluene, and this liquid and the core material are put into a container of a stirrer and stirred. In this way, for example, the silicon resin is deposited by a dipping method so that the ratio is 3% by weight. At that time, a curing agent is added according to the type of resin used. After stirring and mixing, the solvent is removed by drying (for example, heat treatment at 130 ° C. for 30 minutes). Next, the composition is cured while stirring with heating (for example, heating is performed in an oil bath and stirring is performed at 190 ° C. for 30 minutes). Then, a resin baking process is performed using an oven or a tunnel furnace (for example, 160 to 280 ° C. × 3 hours). As a result, a resin-coated carrier product is obtained.
[0022]
The resin-coated carrier thus obtained is combined with the toner in this state to form a two-component electrophotographic developer. In this case, even if the coating resin is firmly baked on the ferrite core surface, In some cases, further improvements in charging characteristics, resistance, and durability are required. In this case, this resin-coated carrier product is polished, more specifically, by applying a mechanical surface treatment in which a compressive stress acts on the resin coating layer of this product. The above-mentioned properties of the product can be further improved by polishing the particles that cause the particles of the product to collide with each other. Even in such a case, since the core material according to the present invention generates little secondary fine powder, it is possible to obtain a carrier that is difficult to cause carrier jump due to the fine powder.
[0023]
【Example】
[Example 1]
The Mn ₃ O ₄ as a Mn _source, the Mg (OH) ₂ as a Mg source, and using an Fe ₂ O ₃ as the Fe _source, as ferrite composition after _{_{firing, (MnO) Fe 2 O 3}} : (MgO) Fe These raw materials were prepared at a ratio of ₂ O ₃ = 70: 30.
[0024]
This mixed powder was calcined by heating in a heating furnace at 900 ° C. for 3 hours in an air atmosphere. The obtained calcined product is cooled, pulverized to approximately 1 μm by a vibration mill, and a dispersant (trade name: San Nopco SN Dispersant 5468) is added together with water at a ratio of 1% by weight to the dry powder. A coarse slurry having a concentration of about 75% was prepared, and boric acid and anhydrous silica were added to the coarse slurry. The amount of boric acid added is such that the ratio of boric acid to the mixed powder is 0.25% by weight (in terms of B, the amount of B content to the mixed powder is 0.04% by weight). The amount was such that the ratio of anhydrous silica to the mixed powder was 0.3% by weight (in terms of Si, the Si content to the mixed powder was 0.14% by weight).
[0025]
Next, the slurry to which these compounds have been added is loaded into a wet ball mill and wet pulverized. The resulting suspension is supplied to a spray dryer, granulated at an atomizer speed of about 15000-18000 rpm, and 54 μm in diameter. Using a sieve, a granulated product composed of dry particles having an average particle size of about 40 μm was obtained.
[0026]
This granulated product was loaded into a firing furnace and fired at 1180 ° C. for 3 hours in a nitrogen gas atmosphere in which the oxygen concentration was adjusted to approximately 4 to 5 vol. The obtained massive fired product was roughly crushed with a hammer mill and further pulverized with a pulverizer. The pulverized product was applied to an air classifier to classify and remove fine powder, and further, magnetic separation was performed to separate the non-magnetic component, and a carrier powder having an average particle size of 35 μm was obtained through a 54 μm sieve. The specific surface area of this carrier powder measured by the BET method was 0.036 m ² / g, and the surface was observed with a scanning electron microscope (SEM), and it was confirmed that it consisted of particles with a substantially spherical smooth surface. It was done.
[0027]
For comparison with the following examples, Table 1 shows the composition / B addition amount, Si addition amount, specific surface area, and SEM observation results of the carrier powder of this example.
[0028]
Further, 10 g of this carrier powder is sampled, put into a sample mill, treated for 15 seconds to apply mechanical stress, and the particle size distribution before and after this treatment is measured using a HELOS particle size distribution measuring instrument manufactured by Nippon Laser Corporation. It was measured. The measurement results are shown in Table 2. In Table 2, each value of D10, D50, and D90 has a particle size (μm) on the horizontal axis when the particle size distribution is measured with a Helos particle size distribution measuring device, and the vertical axis includes particles smaller than the particle size. In the cumulative particle size curve expressed as volume%, the value on the vertical axis when the particle size is 10, 50, 90 μm is shown.
[0029]
[Example 2]
The amount of boric acid added is such that the ratio of boric acid to the mixed powder is 0.01% by weight (in terms of B, the amount of B content to the mixed powder is 0.002% by weight), and the addition of anhydrous silica Example 1 was repeated except that the amount was such that the ratio of anhydrous silica to the mixed powder was 0.03 wt% (in terms of Si, the Si content to the mixed powder was 0.01 wt%). It was. Table 1 shows the composition / B addition amount, Si addition amount, specific surface area, and SEM observation results of the carrier powder of this example, and mechanical stress was applied to the carrier powder obtained in this example in the same manner as in Example 1. The particle size distribution before and after the application is shown in Table 2.
[0030]
Example 3
The amount of boric acid added is such that the ratio of boric acid to the mixed powder is 0.60% by weight (in terms of B, the B content to the mixed powder is 0.10% by weight), and the addition of anhydrous silica Example 1 was repeated except that the amount was such that the ratio of anhydrous silica to the mixed powder was 1.0% by weight (in terms of Si, the Si content to the mixed powder was 0.47% by weight). It was. Table 1 shows the composition / B addition amount, Si addition amount, specific surface area, and SEM observation results of the carrier powder of this example, and mechanical stress was applied to the carrier powder obtained in this example in the same manner as in Example 1. The particle size distribution before and after the application is shown in Table 2.
[0031]
Example 4
Example 1 was repeated except that the raw material preparation was changed to (MnO) Fe ₂ O ₃ : (MgO) Fe ₂ O ₃ = 25: 75 and the firing atmosphere at the time of sintering was changed to an air atmosphere. Table 1 shows the composition / B addition amount, Si addition amount, specific surface area, and SEM observation results of the carrier powder of this example, and mechanical stress was applied to the carrier powder obtained in this example in the same manner as in Example 1. The particle size distribution before and after the application is shown in Table 3.
[0032]
Example 5
Example 1 was repeated except that the sieve used during granulation was changed from 54 μm to 63 μm. Table 1 shows the composition / B addition amount, Si addition amount, specific surface area, and SEM observation results of the carrier powder of this example, and mechanical stress was applied to the carrier powder obtained in this example in the same manner as in Example 1. The particle size distribution before and after the application is shown in Table 3.
[0033]
[Comparative Example 1]
Example 1 was repeated except that neither boric acid nor anhydrous silica was added. The composition, specific surface area, and SEM observation results of the carrier powder of this example are shown in Table 1, and the particle size distribution before and after applying mechanical stress to the carrier powder obtained in this example as in Example 1 is shown. This is shown in FIG.
[0034]
[Comparative Example 2]
No boric acid was added, and the amount of anhydrous silica added was such that the ratio of anhydrous silica to the mixed powder was 1.3% by weight (in terms of Si, the Si content to the mixed powder was 0.61% by weight). Example 1 was repeated except that Table 1 shows the composition, Si addition amount, specific surface area, and SEM observation results of the carrier powder of this example, and before and after applying mechanical stress to the carrier powder obtained in this example in the same manner as in Example 1. The particle size distribution is shown in Table 4.
[0035]
[Comparative Example 3]
No anhydrous silica was added, and the amount of boric acid added was such that the ratio of boric acid to the mixed powder was 0.80% by weight (in terms of B, the B content to the mixed powder was 0.14% by weight). Example 1 was repeated except that Table 1 shows the composition / B addition amount, specific surface area, and SEM observation results of the carrier powder of this example, and before and after mechanical stress was applied to the carrier powder obtained in this example in the same manner as in Example 1. The particle size distribution is shown in Table 4.
[0036]
[Comparative Example 4]
Example 4 was repeated except that neither boric acid nor anhydrous silica was added. The composition, specific surface area, and SEM observation results of the carrier powder of this example are shown in Table 1, and the particle size distribution before and after applying mechanical stress to the carrier powder obtained in this example as in Example 1 is shown. This is shown in FIG.
[0037]
[Table 1]

[0038]
[Table 2]

[0039]
[Table 3]

[0040]
[Table 4]

[0041]
From the results of Tables 1 to 4, Examples 1 to 5 are smooth and spherical carrier powders that maintain the particle size distribution before applying stress even after applying mechanical stress, and fine powder is generated. You can see that they are not. On the other hand, those of Comparative Examples 1 and 2 had irregularities on the surface, and fine powder was generated after applying mechanical stress. In Comparative Example 3, the amount of boric acid added was large, resulting in a core shape, and in Comparative Example 4, a brittle surface state was formed. After mechanical stress was applied, fine powder was generated.
[0042]
【The invention's effect】
As described above, according to the present invention, since the impact strength of the carrier powder can be improved by a small amount of additive, an electrophotographic developing carrier with less generation of secondary fine powder can be obtained economically, It is possible to avoid the problem of image deterioration due to carrier skipping due to the mixture of fine powder.

Claims

In an electrophotographic developing carrier mainly composed of ferrite or magnetite particles, the particles contain 0.001 to 0.1% by weight of B (boron) and 0.01 to 0.5% by weight of Si. A carrier for electrophotographic development.

In a carrier for electrophotographic development in which particles mainly composed of ferrite or magnetite are used as a core and the surface of the core is coated with a resin, 0.001 to 0.1% by weight of B (boron) is contained in the particles. ) And 0.01 to 0.5% by weight of Si.

The ferrite is
Formula (MO) _Xn (Fe ₂ O ₃ ) _Y ,
Where
One or two of M = Mn, Mg or Fe,
ΣXn = 40-60 (mol%),
Y = 100−ΣXn (mol%),
The carrier for electrophotographic development of Claim 1 or 2 represented by these.

An electrophotographic developer comprising the carrier according to claim 1, 2 or 3 and a toner.