JP3982162B2 - Image forming method and image forming apparatus - Google Patents

Description

測定する元素は炭素（Ｃ１ｓ）、窒素（Ｎ１ｓ）、酸素（Ｏ１ｓ）及びケイ素（Ｓｉ２ｐ）を基本に、他の外添剤を添加した場合、それに起因する元素を含めて測定する。測定した元素の面積強度から元素比率を算出する。
【００２７】
添加率は以下のようにして算出する。予め、疎水性シリカ微粉末を所定の添加率で着色粒子に添加した標準サンプルを作製する。その標準サンプルを用い、蛍光Ｘ線分析装置（３２７０型、理学電機工業株式会社製）にて疎水性シリカ微粉末とシリカ元素のＸ線強度の検量線を作成する。次いで同様にして未知サンプルのシリカ元素のＸ線強度を測定し、検量線から未知サンプルの疎水性シリカ微粉末の添加率を算出する。
【００２８】
《疎水性シリカ微粉末》
シリカ微粉末は−Ｓｉ−Ｏ−Ｓｉ−結合を有する２酸化ケイ素の微粒子が好ましく、乾式法或いは湿式法で製造したものいずれでも良いが、好ましくは乾式法で製造したもので、より好ましくはケイ素ハロゲン化合物の蒸気相酸化により製造した微粒子である。
【００２９】
又、シリカ微粉末としては２酸化ケイ素の他に、ケイ酸アルミニウム、ケイ酸ナトリウム、ケイ酸カルシウム、ケイ酸カリウム或いはケイ酸マグネシウム等のケイ酸の塩を有する微粒子を含んでいてもよいが、２酸化ケイ素を８５質量％以上含むものがより好ましい。
【００３０】
本発明に用いられるシリカ微粉末の数平均一次粒径は１０〜５００ｎｍのものが好ましい。この数平均一次粒径は電子顕微鏡で画像を撮影し、その画像を解析して得られた数値を示す。
【００３１】
シリカ微粉末は疎水化処理剤で処理して、適度な疎水性を示すようにしたものが好ましい。疎水性はメタノールに対する濡れ性の尺度（メタノールウェッタビリティ）で示される疎水化度で３０〜７０％の範囲になるようにすることが好ましい。疎水化度が３０％未満であるとシリカ微粉末の耐水性が十分でなく、環境変動により帯電性が変化しやすくなる。又、疎水化度が７０％を越えるとシリカ微粉末と着色粒子との密着性が低下し、長期にわたり帯電性を安定に制御することが出来なくなる。
【００３２】
シリカ微粉末の疎水化処理は、シリカ微粉末を撹拌等によりクラウド状に分散させたものに、アルコール等で溶解した疎水化処理剤溶液を噴霧するか或いは気化した疎水化処理剤を接触させて付着させる乾式処理、又は、シリカ微粉末を溶液中に分散させ、その中に疎水化処理剤を滴下して付着させる湿式処理等の従来公知の方法で行うことが出来る。
【００３３】
疎水化処理剤としては、公知の化合物を用いることが出来、具体例を下記に挙げる。又、これらの化合物は組み合わせて使用しても良い。
【００３４】
チタンカップリング剤としてはテトラブチルチタネート、テトラオクチルチタネート、イソプロピルトリイソステアロイルチタネート、イソプロピルトリデシルベンゼンスルフォニルチタネート及びビス（ジオクチルパイロフォスフェート）オキシアセテートチタネート等が挙げられる。
【００３５】
シランカップリング剤としてはγ−（２−アミノエチル）アミノプロピルトリメトキシシラン、γ−（２−アミノエチル）アミノプロピルメチルジメトキシシラン、γ−メタクリロキシプロピルトリメトキシシラン、Ｎ−β−ビニルベンジルアミノエチル−Ｎ−γ−アミノプロピルトリメトキシシラン塩酸塩、ヘキサメチルジシラザン、メチルトリメトキシシラン、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、ヘキシルトリメトキシシラン、オクチルトリメトキシシラン、デシルトリメトキシシラン、ドデシルトリメトキシシラン、フェニルトリメトキシシラン、ｏ−メチルフェニルトリメトキシシラン及びｐ−メチルフェニルトリメトキシシラン等が挙げられる。
【００３６】
脂肪酸及びその金属塩としては、脂肪酸としてウンデシル酸、ラウリン酸、トリデシル酸、ミリスチン酸、ドデシル酸、パルミチン酸、ペンタデシル酸、ステアリン酸、ヘプタデシル酸、アラキン酸、モンタン酸、オレイン酸、リノール酸及びアラキドン酸等の長鎖脂肪酸が挙げられ、その金属塩として亜鉛、鉄、マグネシウム、アルミニウム、カルシウム、ナトリウム及びリチウム等の金属との塩が挙げられる。
【００３７】
シリコーンオイルとしては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及びアミノ変性シリコーンオイル等が挙げられる。その他の化合物としてはアンモニウム塩を官能基として有するポリシロキサンが挙げられる。
【００３８】
これらの疎水化処理剤は、シリカ微粉末に対して１〜４０質量％添加して被覆することが好ましく、３〜３０質量％がより好ましい。
【００３９】
疎水化度を表すメタノールウェッタビリティとは、メタノールに対するシリカ微粉末の濡れ性を評価するものである。濡れ性の測定は以下の方法で行う。内容量２５０ｍｌのビーカーに入れた蒸留水５０ｍｌに、測定対象のシリカ微粉末を０．２ｇ添加して撹拌する。次にメタノールを先端が液体中に浸漬されているビュレットからゆっくり撹拌した状態でシリカ微粉末の全体が濡れるまでゆっくり滴下する。このシリカ微粉末を完全に濡らすために必要なメタノールの量をａ（ｍｌ）とした時、下記式（２）により疎水化度を算出する。
【００４０】
式（２） 疎水化度＝ａ／（ａ＋５０）×１００
《疎水性シリカ微粉末等の外添剤を着色粒子へ混合》
疎水性シリカ微粉末等の外添剤を着色粒子へ混合する際の混合メカニズムは以下のように推定している。
【００４１】
混合装置内で、疎水性シリカ微粉末はその凝集状態から解砕されるプロセスと、着色粒子表面に付着し固定化されるプロセスがほぼ同時進行している。この２つのプロセスを混合装置及び混合条件でコントロールすることにより前記式（１）を満足する疎水性シリカ微粉末の存在状態を作製することことが出来る。
【００４２】
疎水性シリカ微粉末等の外添剤と着色粒子を混合し、前記式（１）を満足するような疎水性シリカ微粉末の存在状態を得る混合装置としては、ガラスビーズ等のメディアを使用する装置或いは高速撹拌混合機を使用する装置等が挙げられる。メディアを使用する装置の具体例としては、タービュラーミキサー（Ｗｉｌｌｙ Ａ．Ｂａｃｈｏｆｅｎ，Ｂａｓｅｌ，Ｓｗｉｔｚｅｒｌａｎｄ製）及びバイブロミル（安川商事社製）等を挙げることを出来る。高速撹拌混合機を用いる装置の具体例としては、ヘンシェルミキサー（三井金属製）及びナウターミキサ（パウダーテック社製）等を挙げることが出来る。
【００４３】
又、疎水性シリカ微粉末は混合装置で混合する前に別途解砕して用いても良い。解砕装置としては通常市販されている解砕機（粉砕機）、例えばターボミル、サンプルミル、エジェクター及びラボジェット等が挙げられる。
【００４４】
疎水性シリカ微粉末等の外添剤を着色粒子へ混合する混合条件は混合装置により異なるが、基本的には疎水性シリカ微粉末及び着色粒子へ加える機械的ストレス及び熱量を管理することにより、疎水性シリカ微粉末の存在状態（（Ｓｉ／Ｃ）／Ｘ）を要望範囲に入るようコントロールすることが出来る。
【００４５】
疎水性シリカ微粉末等の外添剤の添加量は、着色粒子に対して０．０５〜５．０質量％が好ましく、より好ましくは０．２〜３．０質量％である。
【００４６】
クリーニング性の付与や現像性等をのコントロールする目的で無機微粒子、有機微粒子或いは滑剤粒子等の添加剤を外添剤として併用してもよい。無機微粒子としては、マグネシウム、亜鉛、チタン、アルミニウム、セリウム、コバルト、鉄、ジルコニウム、クロム、マンガン、ストロンチウム、錫或いはアンチモン等の金属の酸化物、チタン酸カルシウム、チタン酸バリウム、チタン酸マグネシウム或いはチタン酸ストロンチウム等の複合金属の酸化物、炭酸カルシウム、炭酸マグネシウム或いは炭酸アルミニウム等の金属塩、カオリン等の粘土鉱物、アパタイト等のリン酸化合物、炭化ケイ素或いは窒化ケイ素等のケイ素化合物、カーボンブラック或いはグラファイト等の炭素粉末が挙げられるが、好ましくは酸化チタン、酸化アルミニウム、酸化セリウム、チタン酸ストロンチウム及びチタン酸バリウムである。
【００４７】
有機微粒子としては、ビニル系、エポキシ系及びフェノール系樹脂微粉末が
挙げられる。
【００４８】
滑剤粒子としては、テフロン、ポリフッ化ビニリデン等のフッ素系樹脂或いはフッ化カーボン等のフッ素系化合物、ステアリン酸亜鉛或いはステアリン酸カルシウム等の脂肪酸の金属塩、脂肪酸或いは脂肪酸エステル等の脂肪酸の誘導体、硫化モリブデン及びアミノ酸或いはアミノ酸誘導体等が挙げられ、好ましくはステアリン酸亜鉛等の脂肪酸の金属塩である。
【００４９】
《着色粒子》
本発明に用いられる着色粒子は特に限定は無く、通常良く用いられている着色粒子を適用することが出来る。上記着色粒子は樹脂と着色剤を含有し、必要に応じて添加剤を添加しても良く、その平均粒径は体積平均粒径で通常３〜１５μｍ、好ましくは４〜１０μｍである。この体積平均粒径は「コールターカウンターＴＡ−２型」或いは「コールターマルチサイザー」（コールター株式会社製）で、アパーチャー径＝１００μｍを用い、２．０〜４０．０μｍの範囲の粒径分布から求めたものである。
【００５０】
前記樹脂としては、特に限定は無く、従来公知の種々の樹脂が用いられる。具体例としてスチレン系樹脂、アクリル系樹脂、スチレン−アクリル系樹脂及びポリエステル系樹脂等が挙げられる。
【００５１】
スチレン系樹脂、アクリル系樹脂及びスチレン−アクリル系樹脂を構成する化合物としては、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、α−メチルスチレン、ｐ−クロロスチレン、３，４−ジクロロスチレン、ｐ−フェニルスチレン、ｐ−エチルスチレン、２，４−ジメチルスチレン、ｐ−ｔ−ブチルスチレン、ｐ−ヘキシルスチレン、ｐ−オクチルスチレン、ｐ−ノニルスチレン、ｐ−デシルスチレン、ｐ−ドデシルスチレンの如きスチレン或いはスチレン誘導体、メタクリル酸メチル、メタクリル酸エチル、メタクリル酸−ブチル、メタクリル酸イソプロピル、メタクリル酸イソブチル、メタクリル酸ｔ−ブチル、メタクリル酸オクチル、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、メタクリル酸ラウリル、メタクリル酸フェニル、メタクリル酸ジエチルアミノエチル、メタクリル酸ジメチルアミノエチル等のメタクリル酸エステル誘導体、アクリル酸メチル、アクリル酸エチル、アクリル酸イソプロピル、アクリル酸ブチル、アクリル酸ｔ−ブチル、アクリル酸イソブチル、アクリル酸オクチル、アクリル酸２−エチルヘキシル、アクリル酸ステアリル、アクリル酸ラウリル、アクリル酸フェニル、アクリル酸ジメチルアミノエチル及びアクリル酸ジエチルアミノエチル等のアクリル酸エステル誘導体等が挙げられ、これらは単独あるいは組み合わせて使用することが出来る。
【００５２】
ポリエステル樹脂は、２価以上のカルボン酸と２価以上のアルコール成分を縮合重合させて得られる樹脂である。
【００５３】
２価以上のカルボン酸の例としてはマレイン酸、フマール酸、シトラコン酸、イタコン酸、グルタコン酸、フタル酸、イソフタル酸、テレフタル酸、コハク酸、アジピン酸、セバシン酸、アゼライン酸、マロン酸、ｎ−ドデシルコハク酸、ｎ−ドデセニルコハク酸、イソドデシルコハク酸、イソドデセニルコハク酸、ｎ−オクチルコハク酸及びｎ−オクテニルコハク酸等が挙げられ、これらの酸無水物も使用することが出来る。
【００５４】
２価以上のアルコール成分の例としてはポリオキシプロピレン（２．２）−２，２−ビス（４−ヒドロキシフェニル）プロパン、ポリオキシプロピレン（３．３）−２，２−ビス（４−ヒドロキシフェニル）プロパン、ポリオキシエチレン（２．０）−２，２−ビス（４−ヒドロキシフェニル）プロパン、ポリオキシプロピレン（２．０）−ポリオキシエチレン（２．０）−２，２−ビス（４−ヒドロキシフェニル）プロパン、ポリオキシプロピレン（６）−２，２−ビス（４−ヒドロキシフェニル）プロパン等のエーテル化ビスフェノール、エチレングリコール、ジエチレングリコール、トリエチレングリコール、１，２−プロピレングリコール、１，３−プロピレングリコール、１，４−ブタンジオール、１，４，ブテンジオール、ネオペンチルグリコール、１，５−ペンタングリコール、１，６−ヘキサングリコール、１，４−シクロヘキサンジメタノール、ジプロピレングリコール、ポリエチレングリコール、ポリプロピレングリコール、ポリテトラメチレングリコール、ビスフェノールＡ、ビスフェノールＺ及び水素添加ビスフェノールＡ等を挙げることが出来る。
【００５５】
前記着色剤としては、特に限定されず、従来公知の種々の着色剤が使用出来る。具体例としてカーボンブラック、ニグロシン染料、アニリンブルー、カルコインブルー、クロムイエロー、ウルトラマリンブルー、デュポンオイルレッド、キノリンイエロー、メチレンブルークロライド、フタロシアニンブルー、マラカイトグリーンオクサレート及びローズベンガル等を挙げることが出来る。
【００５６】
又、前記着色粒子には、樹脂及び着色剤以外に種々の機能を付与することの出来る添加剤を加えてもよい。具体例として離型剤及び荷電制御剤等を挙げることが出来る。
【００５７】
前記離型剤としては、特に限定されず、従来公知の種々の離型剤を使用することが出来る。具体例としてポリプロピレン或いはポリエチレン等のオレフィン系ワックスやこれらの変性物、カルナウバワックス或いはライスワックス等の天然ワックス及び脂肪酸ビスアミド等のアミド系ワックスを挙げることが出来る。
【００５８】
前記荷電制御剤としては、特に限定されず、従来公知の種々の電荷制御剤を使用することが出来る。具体例としてニグロシン系染料、ナフテン酸或いは高級脂肪酸の金属塩、アルコキシル化アミン、第４級アンモニウム塩化合物、アゾ系金属錯体及びサリチル酸金属塩及びその金属錯体等を挙げることが出来る。
【００５９】
《キャリア》
本発明に用いられるキャリアは磁性キャリアコアをシリコーン樹脂で被覆されたものが好ましい。
【００６０】
シリコーン樹脂で被覆されたキャリアの芯材となる磁性キャリアコアは、従来公知の種々の磁性キャリアコアを使用することが出来る。
【００６１】
芯材となる磁性キャリアコアの具体例としては鉄粉、マグネタイト及び各種フェライト等を挙げることが出来る。好ましくは各種フェライトである。フェライトとしては銅、亜鉛、ニッケル或いはマンガン等の重金属を含有する重金属フェライト、アルカリ金属及びアルカリ土類金属を含有する軽金属フェライトが好ましく、より好ましくはアルカリ金属及びアルカリ土類金属を含有する軽金属フェライトである。
【００６２】
又、樹脂中に前記磁性キャリアコアの微粉を分散して作製したキャリアを用いても良い。
【００６３】
キャリアの大きさは、トナーとの摩擦帯電及び感光体へのキャリア付着を考慮すると、体積平均粒径で１０〜２００μｍのものが好ましい。
【００６４】
シリコーン樹脂被覆用のシリコーン樹脂は、下記一般式（Ｉ）及び（II）で表されるセグメントの集合体が好ましい。
【００６５】
【化１】

【００６６】
一般式（Ｉ）及び（II）で表わされるセグメント中、Ｒ⁵〜Ｒ⁸はそれぞれメチル基、エチル基、フェニル基又はビニル基から選ばれる炭化水素基を表わす。接着性及び強度の観点からメチル基のものが好ましい。又、アルキッド変性、アクリル変性、ポリエステル変性、フェノール変性、メラミン変性及びウレタン変性等の変性シリコーン樹脂を使用しても良い。
【００６７】
一般式（Ｉ）及び（II）の質量比は（Ｉ）／（II）＝０／１００〜７０／３０が好ましく、０／１００〜５０／５０がより好ましい。
【００６８】
（Ｉ）／（II）＞７０／３０であると直鎖成分が多くなるために硬度が低下し、十分な耐久性が得られず好ましくない。
【００６９】
キャリアの帯電付与能力を高めるためにアミノシランカップリング剤を添加しても良い。使用されるカップリング剤は、特に限定されるものでは無く、２種以上のアミノシランカップリング剤を混合して使用しても良い。具体的な化合物としてはγ−アミノプロピルトリメトキシシラン、γ−アミノプロピルトリエトキシシラン、γ−アミノエチル−アミノプロピルトリメトキシシラン、メチル−γ−アミノプロピルジメトキシシラン、メチル−γ−アミノエチルアミノプロピルジメトキシシラン、γ−ジメチルアミノ−プロピルトリメトキシシラン、γ−アニリノプロピルトリメトキシシラン、γ−モルホリノプロピルトリメトキシシラン、Ｎ，Ｎ′−ビス（３−トリメトキシシリル）エチレンジアミン及びこれらの部分縮合物を挙げることが出来る。
【００７０】
上記アミノシランカップリング剤の添加量はシリコーン樹脂固形分１００質量部に対して０．０１〜６０質量部が好ましく、より好ましくは０．１〜４０質量部である。０．０１質量部未満であるとキャリアの帯電付与能力を高めることが出来ず、一方、６０質量部を越える場合はシリコーン樹脂の膜強度が低下し、キャリアの耐久性が低下し好ましくない。
【００７１】
又、シリコーン樹脂被覆時に架橋剤、硬化触媒等の添加物を添加しても良い。前記架橋剤としては、一般に知られている脱アルコール型、脱酢酸型、脱オキシム型、脱アミド型、脱アミノキシ型及び脱アセトン型等の低分子シラン化合物を使用することが出来る。
【００７２】
前記硬化触媒としては、亜鉛、錫、鉄、鉛、コバルト、ニッケル或いはアルミニウム等の金属石鹸、キレート化合物、蟻酸或いは酢酸等の有機酸及びアミン等の塩基を使用することが出来る。
【００７３】
これらの添加物の添加量はシリコーン樹脂固形分１００質量部に対して０．０１〜１０質量部が好ましく、０．１〜５質量部がより好ましい。
【００７４】
磁性キャリアコアのシリコーン樹脂による被覆量は、磁性キャリアコアに対して０．０１〜１０質量％が好ましく、０．５〜５質量％がより好ましい。シリコーン樹脂による被覆量が０．０１質量％未満であると磁性キャリアコア表面に均一な被覆層を形成することが出来ず、一方、１０質量％を越える場合は磁性キャリアコア粒子同士の造粒が生じて流動性が低下し、トナーとの混合性が悪くなり好ましくない。
【００７５】
磁性キャリアコアにシリコーン樹脂の被覆層（コーティング層）を形成する方法としては特に限定されないが、具体例としてシリコーン樹脂を溶剤に溶解させた後、溶解液を浸漬法或いはスプレードライ法等によりコア表面に塗布し、乾燥により溶剤を除去し、その後焼き付けを行う方法を挙げることが出来る。焼き付け温度としては、１５０〜３００℃が好ましく、より好ましくは１７０〜２８０℃である。焼き付け温度が１５０℃未満であるとシリコーン樹脂の架橋反応が十分進行せず、硬度が不十分になり、一方、３００℃を越える場合はシリコーン樹脂の一部やアミノシランカップリング剤の一部が分解し、均一な樹脂被覆層が得られなくなり好ましくない。
【００７６】
スプレードライ法による塗布は回転円筒型流動層粒子コーティング装置を用いて行うことが出来る。
【００７７】
塗布（コーティング）に用いられる好ましい溶剤としては、トルエン、キシレン、メチルエチルケトン及びメチルイソブチルケトンを挙げることが出来る。
【００７８】
《トナーリサイクルシステム》
本発明に係る画像形成装置は、トナーリサイクルシステムを搭載した画像形成装置である。
【００７９】
トナーリサイクルシステムとは、転写されずに感光体表面に残留した転写残トナーをクリーニング部で回収し、この回収トナーを再び現像器或いはトナー補給ボックスに戻し再利用するシステムである。
【００８０】
トナーリサイクルシステムは回収トナーを再利用するため、廃棄トナーが発生せず環境保護の点で優れたシステムである。
【００８１】
図１はトナーリサイクルシステムの一例を示す概略図である。
図１中、１は現像器、２は現像剤搬送スリーブ、３は現像剤搬送スクリュー、４は感光体、５はクリーナー部、６はクリーニング部材（弾性ブレード）、７はリサイクルトナー回収スクリュー、８はリサイクルトナー搬送スクリューを示す。
【００８２】
図１に於いて、クリーニング部材６により掻き取られた転写残トナーは、リサイクルトナー回収スクリュー７によりクリーナー部５に集められ、リサイクルトナー搬送スクリュー８により再び現像器１に供給される。
【００８３】
【実施例】
以下に、実施例を挙げて本発明を具体的に説明するが、本発明の実施態様はこれらに限定されるものではない。
【００８４】
《トナー作製》
「トナー１」の作製
ポリエステル樹脂１００部、カーボンブラック７．５部及び低分子量ポリプロピレン３部を混合後、溶融混練を行い、粉砕分級して体積平均粒径９．０μｍの着色粒子を作製した。
【００８５】
得られた着色粒子１００部にヘキサメチルジシラザンで疎水化処理（疎水化度６０）した数平均一次粒径１２ｎｍの疎水性シリカ微粉末０．８部を添加し、着色粒子の温度を４０℃に制御したヘンシェルミキサーで周速３０ｍ／ｓｅｃの条件にて１０分間混合し、疎水性シリカ微粉末が外部添加された「トナー１」を作製した。
【００８６】
トナー１の外添剤存在状態（（Ｓｉ／Ｃ）／Ｘ）は０．２９であった。
「トナー２〜５」の作製
スチレン／ｎ−ブチルアクリレート／メチルメタアクリレート共重合体（共重合比＝８６／１０／４）１００部、カーボンブラック１２部、低分子量ポリプロピレン５部及び荷電制御剤（アゾ系金属錯体）１．０部を混合後、溶融混練を行い、粉砕分級して体積平均粒径７．５μｍの着色粒子を作製した。
【００８７】
得られた着色粒子１００部にテトラオクチルチタネートで疎水化処理した数平均一次粒径１５ｎｍの疎水性チタニア微粉末０．７５部とオクチルトリメトキシシランで疎水化処理（疎水化度５５）した数平均一次粒径１２ｎｍの疎水性シリカ微粉末１．０部を下記表１に示した条件にてヘンシェルミキサーで混合し、疎水化チタニア微粉末及び疎水性シリカ微粉末が外部添加された「トナー２〜５」を作製した。
【００８８】
このトナー２〜５の外添剤存在状態（（Ｓｉ／Ｃ）／Ｘ）、ヘンシェルミキサーの周速、混合時間及び着色粒子の温度を下記表１に示す。
【００８９】
【表１】

【００９０】
「トナー６」の作製
スチレン／ｎ−ブチルアクリレート／メチルメタアクリレート共重合体（共重合比＝８６／１０／４）１００部、カーボンブラック１２部、低分子量ポリプロピレン５部及び荷電制御剤（アゾ系金属錯体）１．０部を混合後、溶融混練を行い、粉砕分級して体積平均粒径７．５μｍの着色粒子を得た。
【００９１】
得られた着色粒子１００部にオクチルトリメトキシシランで疎水化処理（疎水化度４０）し、予めエジェクター解砕機により解砕した数平均一次粒径１２ｎｍの疎水性シリカ微粉末１．０部を添加し、着色粒子の温度を３５℃に制御したヘンシェルミキサーで周速３０ｍ／ｓｅｃの条件にて１０分間混合し、疎水性シリカ微粉末が外部添加された「トナー６」を作製した。
【００９２】
トナー６の外添剤存在状態（（Ｓｉ／Ｃ）／Ｘ）は０．４８であった。
《シリコーン樹脂被覆キャリアの作製》
シリコーン樹脂液（シリコーンＳＲ２４０６、東レ株式会社製、固形分濃度２０質量％）１００部とγ−アミノエチル−アミノプロピルトリメトキシシラン５部をトルエン３００部に溶解した被覆用樹脂液を作製した。次いで回転円筒型流動層粒子コーティング装置に体積平均粒径６０μｍのフェライトキャリア１０００部を入れ、流動させながら上記被覆用樹脂液を７０℃に加熱条件下でスプレーコーティングした。その後１８０℃で３時間熱処理を行い、解砕、分級して「シリコーン樹脂被覆キャリア」を作製した。
【００９３】
《現像剤の作製》
前記「トナー１〜６」と前記「シリコーン樹脂被覆キャリア」を下記表２に示した配合比で混合し、「現像剤１〜６」を作製した。
【００９４】
【表２】

【００９５】
《評価》
上記にて作製したトナーと現像剤を用い、トナーリサイクルシステムを搭載したＫｏｎｉｃａ Ｓｉｔｉｏｓ７０７５（コニカ株式会社製）複写機により常温常湿（２０℃、５０％ＲＨ）下で１０万枚のコピーテストを行い、帯電量、外添剤存在状態、地カブリ、トナー飛散を評価した。
【００９６】
〈帯電量〉
現像器から現像剤測定サンプルを約１ｇ取り、ステンレス製のメッシュを張ったセルに入れ、窒素ガス（ガス圧０．２ｋｇ／ｃｍ²）で６秒間ブローしてトナーを飛ばし、残ったキャリアの電荷（Ｑ）を測定した。現像剤の帯電量は下記式（３）により算出した。
【００９７】
式（３） 帯電量（μＣ／ｇ）＝Ｑ／（Ｍ₁−Ｍ₂）
Ｑ：キャリアの電荷（μＣ）
Ｍ₁：ブロー前のサンプル質量（ｇ）
Ｍ₂：ブロー後のサンプル質量（ｇ）
〈１０万枚コピー時の外添剤存在状態（（Ｓｉ／Ｃ）／Ｘ）〉
１０万枚コピー終了後、ベタ黒原稿に対応した潜像を現像し、ＯＨＰシートに転写させ、定着工程を通過する前に取り出し、ＯＨＰシートからトナーを掻き取り外添剤存在状態測定のサンプルとした。サンプルをＥＳＣＡにてＳｉ及びＣを測定して外添剤存在状態（（Ｓｉ／Ｃ）／Ｘ）を求めた。
【００９８】
〈地カブリ〉
サクラデンシトメーター（コニカ株式会社製）により転写紙の白地部分（反射濃度０．０００）に対応するコピー画像の白地部分の相対濃度を測定した。
【００９９】
〈トナー飛散〉
前記複写機の現像領域の下に白紙を置き、飛散するトナーを付着させ、その白紙を前記複写機の定着器を通して定着し、サクラデンシトメーターで相対濃度を測定した。
【０１００】

評価結果を下記表３に示す。
【０１０１】
【表３】

【０１０２】
疎水性シリカ微粉末が前記式（１）を満足する存在状態にあるトナーを用いた実施例１〜４は、１０万枚コピーまで外添剤存在状態の変化が少ないため、帯電量の低下が少なく安定していた。画像的にも地カブリの無い高品質の画像が得られ、トナー飛散による機内汚れも問題ないレベルであった。
【０１０３】
一方、比較例１は、疎水性シリカ微粉末がトナー中に分散している状態のトナーを用いたため、コピーの進行とともに現像器内、クリーニング部材及びリサイクルトナー搬送部材等で受けるストレスにより、疎水性シリカ微粉末がトナー内部に埋没し、帯電量の低下を招いた。１０万枚コピーの時点では地カブリの多い画像となり、更にトナー飛散により顕著な機内汚れが発生した。
【０１０４】
比較例２は、疎水性シリカ微粉末がスタートより埋没した状態のトナーを用いたため、５万枚コピー時点で地カブリの発生が認められ、１０万枚コピーの時点では地カブリの多い画像となり、更にトナー飛散により顕著な機内汚れも発生した。
【０１０５】
【発明の効果】
実施例で実証した如く、トナーリサイクルシステムを搭載した画像形成装置で繰り返しコピーをしても、地カブリ及びトナー飛散が無く安定して高品質の画像が得られる優れたトナー、現像剤及び画像形成装置を提供することが出来た。
【図面の簡単な説明】
【図１】トナーリサイクルシステムの一例を示す概略図。
【符号の説明】
１ 現像器
２ 現像剤搬送スリーブ
３ 現像剤搬送スクリュー
４ 感光体
５ クリーナー部
６ クリーニング部材
７ リサイクルトナー回収スクリュー
８ リサイクルトナー搬送スクリュー[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming method and an image forming apparatus capable of stably obtaining a high-quality image without causing background fog and toner scattering even when repeated copying is performed by an image forming apparatus equipped with a toner recycling system.
[0002]
[Prior art]
Conventionally, the electrophotographic method used for image formation of a copying machine is to apply a uniform electrostatic charge to a photoconductor containing a photoconductive material, and then to expose the original on the surface of the photoconductor by image exposure. The electrostatic latent image is formed, and the electrostatic latent image is developed with an electrophotographic toner (hereinafter simply referred to as toner) and an electrophotographic developer having a carrier (hereinafter also simply referred to as developer). In this image forming apparatus, an image is formed, the toner image is further transferred onto a transfer paper, and the transfer paper is separated and fixed.
[0003]
Such a developer is required to have many functions in terms of developability and fixability. In particular, in toner, electrostatic properties, thermal properties, strength properties, or powder properties such as fluidity and blocking are problems, and in order to cope with these problematic properties, the shape, composition and manufacturing method of colored particles. In addition, various external additives are added to the colored particles to form a toner. In particular, in order to ensure the transportability and charging characteristics of toner particles, appropriate fluidity is required, and for this purpose, a technique of adding hydrophobic silica fine powder is employed.
[0004]
However, in this method, when a document with a low printing rate is repeatedly copied, the toner particles are repeatedly subjected to mechanical stress through the carrier from the stirring blades in the developing device, and the hydrophobic silica fine powder on the toner particle surface is buried inside. Occurs. When the embedding of the hydrophobic silica fine powder occurs, the effect of ensuring the transportability and the charging characteristics imparted by the hydrophobic silica fine powder disappears, and many problems occur as the toner.
[0005]
For example, when the hydrophobic silica fine powder is responsible for securing the charging characteristics, the toner charge amount is reduced by repeatedly performing copying, resulting in background fogging or in-machine contamination due to toner scattering.
[0006]
Even if the fluidity of the toner is lowered, the mixing property of the toner and the carrier is lowered, so that the toner is transported to the development area and developed without obtaining a sufficient charge amount. As a result, background fogging occurs or internal contamination occurs due to toner scattering.
[0007]
In order to solve these problems, Japanese Patent Publication No. 2-45188 discloses a toner (1) in which a 0.15-5.0 μm large particle size inorganic oxide is added together with silica fine powder. A toner (2) in which silica fine powder is fixed on the surface is proposed as a toner (3) in which Japanese Patent Application Laid-Open No. 2-289859 adheres silica fine powder in a partially aggregated state.
[0008]
However, since the toner (1) has a large particle size inorganic oxide having a weak adhesion to the toner particles, the toner (2) is separated from the toner particle surface by repeated copying, and the toner (2) is silica on the toner particle surface. The fixing of the fine powder instead promotes its embedding, and in the toner (3), the silica aggregate is disintegrated by the mechanical stress in the developing device, dispersed to the primary particles, and buried in the toner particles. Will be lost.
[0009]
On the other hand, recently, from the viewpoint of environmental protection, disposal of recovered toner generated by removing (cleaning) transfer residual toner remaining on the surface of the photoreceptor after transfer has been regarded as a problem. As a means for solving this toner disposal problem, it is conceivable to collect and reuse the transfer residual toner removed from the surface of the photosensitive member, and return the transfer residual toner to the developing device or the toner supply hopper for use as a specific means. An image forming apparatus equipped with a toner recycling system has been proposed.
[0010]
In an image forming apparatus equipped with such a toner recycling system, the reused toner is more likely to be stressed by a cleaning member, a recycled toner conveying member, and the like, and therefore image degradation caused by the embedding of silica fine powder. This problem is more serious, and it has been difficult for conventional toners to withstand the toner recycling system.
[0011]
[Problems to be solved by the invention]
The present invention has been proposed in view of the above problems, and the object of the present invention is to embed hydrophobic silica fine powder in toner particles even after repeated copying with an image forming apparatus equipped with a toner recycling system. It is an object of the present invention to provide an excellent image forming method and an image forming apparatus which can obtain a stable and high quality image with little fogging and no background fog and toner scattering.
[0012]
[Means for Solving the Problems]
The problems of the present invention are solved by adopting the following configuration.
[0013]
1. In the image forming method in which the transfer residual electrophotographic toner is collected from the cleaning unit, and the collected toner is returned to the developing device or the toner replenishing box and used for development, the electrophotographic toner contains a resin and a colorant. A method for forming an image, characterized in that hydrophobic silica fine powder is present on the surface so as to satisfy the following formula (1) .
Formula (1) 0.20 <(Si / C) / X <= 0.50
However, Si and C are the ratio of silicon atoms and carbon atoms present on the surface of the toner particles as measured by ESCA, and X is the addition ratio (% by mass) of the hydrophobic silica fine powder to the colored particles.
[0014]
2. 2. The image forming method according to claim 1, wherein the electrophotographic developer used in the image forming method comprises a carrier having a magnetic carrier core coated with a silicone resin.
[0015]
3. An image forming apparatus using the image forming method described in 1 above .
[0016]
That is, the present inventors presume that the embedding of the hydrophobic silica fine powder existing on the toner particle surface inside the toner particles is caused by applying a direct stress to the hydrophobic silica fine powder. Stress is caused by stirring of the developer in the developing device and passing through the spike control plate portion. In an image forming apparatus equipped with a toner recycling system, a cleaning member (cleaning blade, brush, etc.) and a recycled toner conveying member are further provided. It is estimated that the embedding of the hydrophobic silica fine powder inside the toner particles proceeds.
[0017]
The present inventors have considered that it is important to create a dispersion state of hydrophobic silica fine powder that is difficult to be embedded in the toner particles against the above stress.
[0018]
By allowing the hydrophobic silica fine powder to be present so as to satisfy the above formula (1), the hydrophobic silica fine powder is hardly embedded in the toner particles even after repeated copying. I found it on the surface. As a result, the inventors have found that toner transportability and chargeability are maintained, and that high-quality images free from background fog and toner scattering can be obtained by repeated copying.
[0019]
In addition, the method of mixing the hydrophobic silica fine powder with the colored particles is performed by various mixing apparatuses, and the mixing mechanism is estimated as follows.
[0020]
In the mixing apparatus, the process in which the hydrophobic silica fine powder is crushed from the aggregated state and the process in which the fine particles are attached to the surface of the colored particles and immobilized are proceeding almost simultaneously.
[0021]
That is, the present inventors can produce the desired state of the fine hydrophobic silica powder by controlling the mixing device and the mixing conditions for crushing the fine hydrophobic silica powder and fixing it to the colored particle surface. As a result, the present invention has been completed.
[0022]
Hereinafter, the present invention will be described in more detail.
First, the characteristics of the existing state of the hydrophobic silica fine powder used in the present invention will be described.
[0023]
The presence of the hydrophobic silica fine powder on the surface of the colored particles containing the resin and the colorant (hereinafter also referred to as the external additive presence state) is shown ((Si / C) / X) is 0.20 <(Si / C ) /X≦0.50, the hydrophobic silica fine powder is difficult to embed inside the toner particles and is not easily detached from the toner particles, which is good because no fog and toner scattering occur.
[0024]
However, when the external additive is in the state of (Si / C) /X≦0.2, the hydrophobic silica fine powder is embedded in the toner particles and received by the developing unit, the cleaning member, the recycled toner conveying member, and the like. The embedding further proceeds due to the stress, and a sufficient charge amount cannot be obtained due to a decrease in the charge amount of the toner itself or a miscibility with the carrier, leading to generation of background fogging and internal contamination due to toner scattering. When the external additive is (Si / C) / X> 0.5, the hydrophobic silica fine powder is crushed and finely dispersed on the surface of the toner particles. Due to the stress applied to the recycled toner conveying member, etc., the toner particles are buried in the interior of the toner particles, and the charge amount of the toner itself is reduced or a sufficient charge amount cannot be obtained due to the mixing property with the carrier. This leads to in-flight contamination.
[0025]
In the above formula (1), Si and C are the silicon atom ratio and carbon atom ratio present on the surface of the toner particles as measured by ESCA, and X is the addition ratio (% by mass) of the hydrophobic silica fine powder to the colored particles. Examples of specific measurement conditions and elements to be measured are shown below.
[0026]

The elements to be measured are based on carbon (C1s), nitrogen (N1s), oxygen (O1s) and silicon (Si2p). When other external additives are added, the elements including the elements are measured. The element ratio is calculated from the measured area intensity of the element.
[0027]
The addition rate is calculated as follows. A standard sample is prepared in advance by adding hydrophobic silica fine powder to colored particles at a predetermined addition rate. Using the standard sample, a calibration curve of the X-ray intensity of the hydrophobic silica fine powder and the silica element is prepared with a fluorescent X-ray analyzer (type 3270, manufactured by Rigaku Corporation). Subsequently, the X-ray intensity of the silica element of the unknown sample is measured in the same manner, and the addition rate of the hydrophobic silica fine powder of the unknown sample is calculated from the calibration curve.
[0028]
<< Hydrophobic silica powder >>
The silica fine powder is preferably silicon dioxide fine particles having a —Si—O—Si— bond, which may be either a dry method or a wet method, but is preferably a dry method, more preferably silicon. Fine particles produced by vapor phase oxidation of halogen compounds.
[0029]
In addition to silicon dioxide, the silica fine powder may contain fine particles having a silicate salt such as aluminum silicate, sodium silicate, calcium silicate, potassium silicate or magnesium silicate, Those containing 85% by mass or more of silicon dioxide are more preferable.
[0030]
The number average primary particle size of the silica fine powder used in the present invention is preferably 10 to 500 nm. The number average primary particle size is a numerical value obtained by taking an image with an electron microscope and analyzing the image.
[0031]
The silica fine powder is preferably treated with a hydrophobizing agent so as to exhibit appropriate hydrophobicity. The hydrophobicity is preferably in the range of 30 to 70% in terms of the degree of hydrophobicity indicated by the wettability scale for methanol (methanol wettability). When the degree of hydrophobicity is less than 30%, the water resistance of the silica fine powder is not sufficient, and the chargeability tends to change due to environmental fluctuations. On the other hand, if the degree of hydrophobicity exceeds 70%, the adhesion between the fine silica powder and the colored particles is lowered, and the chargeability cannot be stably controlled over a long period of time.
[0032]
Hydrophobic treatment of silica fine powder is carried out by spraying a hydrophobizing agent solution dissolved with alcohol or the like into a cloud-like dispersion of silica fine powder dispersed by stirring or the like, or contacting a vaporized hydrophobizing agent. It can be performed by a conventionally known method such as a dry process for adhesion or a wet process in which silica fine powder is dispersed in a solution and a hydrophobizing agent is dropped and adhered therein.
[0033]
As the hydrophobizing agent, known compounds can be used, and specific examples are given below. These compounds may be used in combination.
[0034]
Examples of the titanium coupling agent include tetrabutyl titanate, tetraoctyl titanate, isopropyl triisostearoyl titanate, isopropyl tridecylbenzenesulfonyl titanate, and bis (dioctylpyrophosphate) oxyacetate titanate.
[0035]
Silane coupling agents include γ- (2-aminoethyl) aminopropyltrimethoxysilane, γ- (2-aminoethyl) aminopropylmethyldimethoxysilane, γ-methacryloxypropyltrimethoxysilane, N-β-vinylbenzylamino. Ethyl-N-γ-aminopropyltrimethoxysilane hydrochloride, hexamethyldisilazane, methyltrimethoxysilane, butyltrimethoxysilane, isobutyltrimethoxysilane, hexyltrimethoxysilane, octyltrimethoxysilane, decyltrimethoxysilane, dodecyl Examples include trimethoxysilane, phenyltrimethoxysilane, o-methylphenyltrimethoxysilane, and p-methylphenyltrimethoxysilane.
[0036]
Examples of fatty acids and their metal salts include undecyl acid, lauric acid, tridecylic acid, myristic acid, dodecylic acid, palmitic acid, pentadecylic acid, stearic acid, heptadecylic acid, arachidic acid, montanic acid, oleic acid, linoleic acid and arachidone. Examples include long chain fatty acids such as acids, and metal salts thereof include salts with metals such as zinc, iron, magnesium, aluminum, calcium, sodium and lithium.
[0037]
Examples of the silicone oil include dimethyl silicone oil, methylphenyl silicone oil, and amino-modified silicone oil. Examples of the other compound include polysiloxane having an ammonium salt as a functional group.
[0038]
These hydrophobizing agents are preferably coated by adding 1 to 40% by mass with respect to the silica fine powder, and more preferably 3 to 30% by mass.
[0039]
Methanol wettability representing the degree of hydrophobicity is an evaluation of wettability of silica fine powder to methanol. The wettability is measured by the following method. 0.2 g of silica fine powder to be measured is added to 50 ml of distilled water in a beaker having an inner volume of 250 ml and stirred. Next, methanol is slowly added dropwise from a burette whose tip is immersed in the liquid until the entire silica fine powder is wetted while being slowly stirred. When the amount of methanol necessary to completely wet the silica fine powder is a (ml), the degree of hydrophobicity is calculated by the following formula (2).
[0040]
Formula (2) Hydrophobicity = a / (a + 50) × 100
<Mixing external additives such as hydrophobic silica fine powder into colored particles>
The mixing mechanism when mixing external additives such as hydrophobic silica fine powder into the colored particles is estimated as follows.
[0041]
In the mixing apparatus, the process of pulverizing the hydrophobic silica fine powder from its aggregated state and the process of adhering and fixing to the surface of the colored particles are proceeding almost simultaneously. By controlling these two processes with a mixing apparatus and mixing conditions, it is possible to produce an existing state of the hydrophobic silica fine powder that satisfies the above formula (1).
[0042]
Media such as glass beads are used as a mixing device for mixing an external additive such as hydrophobic silica fine powder and colored particles to obtain the presence state of the hydrophobic silica fine powder satisfying the formula (1). Examples thereof include an apparatus or an apparatus using a high-speed stirring mixer. Specific examples of the apparatus using the media include a turbuler mixer (manufactured by Willy A. Bachofen, Basel, Switzerland), a vibro mill (manufactured by Yaskawa Corporation), and the like. Specific examples of the apparatus using a high-speed stirring mixer include a Henschel mixer (made by Mitsui Kinzoku) and a Nauter mixer (made by Powdertech).
[0043]
Further, the fine hydrophobic silica powder may be separately pulverized before being mixed in the mixing apparatus. Examples of the crusher include a commercially available crusher (pulverizer) such as a turbo mill, a sample mill, an ejector, and a lab jet.
[0044]
The mixing conditions for mixing the external additive such as hydrophobic silica fine powder into the colored particles differ depending on the mixing apparatus, but basically, by controlling the mechanical stress and heat applied to the hydrophobic silica fine powder and the colored particles, The presence state ((Si / C) / X) of the hydrophobic silica fine powder can be controlled to fall within the desired range.
[0045]
The amount of external additives such as hydrophobic silica fine powder added is preferably 0.05 to 5.0 mass%, more preferably 0.2 to 3.0 mass%, based on the colored particles.
[0046]
Additives such as inorganic fine particles, organic fine particles, or lubricant particles may be used in combination as external additives for the purpose of imparting cleaning properties and controlling developability. Inorganic fine particles include magnesium, zinc, titanium, aluminum, cerium, cobalt, iron, zirconium, chromium, manganese, strontium, tin, antimony and other metal oxides, calcium titanate, barium titanate, magnesium titanate or titanium. Complex metal oxides such as strontium acid, metal salts such as calcium carbonate, magnesium carbonate or aluminum carbonate, clay minerals such as kaolin, phosphate compounds such as apatite, silicon compounds such as silicon carbide or silicon nitride, carbon black or graphite Examples of the carbon powder include titanium oxide, aluminum oxide, cerium oxide, strontium titanate, and barium titanate.
[0047]
Examples of the organic fine particles include vinyl-based, epoxy-based, and phenol-based resin fine powders.
[0048]
Examples of the lubricant particles include fluorine resins such as Teflon and polyvinylidene fluoride, fluorine compounds such as carbon fluoride, metal salts of fatty acids such as zinc stearate and calcium stearate, fatty acid derivatives such as fatty acids and fatty acid esters, molybdenum sulfide. And an amino acid or an amino acid derivative, preferably a metal salt of a fatty acid such as zinc stearate.
[0049]
<Colored particles>
The colored particles used in the present invention are not particularly limited, and commonly used colored particles can be applied. The colored particles contain a resin and a colorant, and additives may be added as necessary. The average particle size is usually 3 to 15 μm, preferably 4 to 10 μm in terms of volume average particle size. This volume average particle size is “Coulter Counter TA-2” or “Coulter Multisizer” (manufactured by Coulter Co., Ltd.), using an aperture diameter = 100 μm, and a particle size distribution in the range of 2.0 to 40.0 μm. It is a thing.
[0050]
The resin is not particularly limited, and various conventionally known resins are used. Specific examples include styrene resins, acrylic resins, styrene-acrylic resins, and polyester resins.
[0051]
Examples of the compound constituting the styrene resin, acrylic resin, and styrene-acrylic resin include styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-chlorostyrene, 3,4 -Dichlorostyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, pt-butylstyrene, p-hexylstyrene, p-octylstyrene, p-nonylstyrene, p-decylstyrene, p- Styrene or styrene derivatives such as dodecylstyrene, methyl methacrylate, ethyl methacrylate, butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, octyl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, Methacrylic acid ester derivatives such as lauryl tacrylate, phenyl methacrylate, diethylaminoethyl methacrylate, dimethylaminoethyl methacrylate, methyl acrylate, ethyl acrylate, isopropyl acrylate, butyl acrylate, t-butyl acrylate, isobutyl acrylate Acrylate derivatives such as octyl acrylate, 2-ethylhexyl acrylate, stearyl acrylate, lauryl acrylate, phenyl acrylate, dimethylaminoethyl acrylate and diethylaminoethyl acrylate, and the like. Can be used.
[0052]
The polyester resin is a resin obtained by condensation polymerization of a divalent or higher carboxylic acid and a divalent or higher alcohol component.
[0053]
Examples of divalent or higher carboxylic acids include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, n -Dodecyl succinic acid, n-dodecenyl succinic acid, isododecyl succinic acid, isododecenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid, etc. are mentioned, These acid anhydrides can also be used.
[0054]
Examples of dihydric or higher alcohol components include polyoxypropylene (2.2) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene (3.3) -2,2-bis (4-hydroxy). Phenyl) propane, polyoxyethylene (2.0) -2,2-bis (4-hydroxyphenyl) propane, polyoxypropylene (2.0) -polyoxyethylene (2.0) -2,2-bis ( 4-hydroxyphenyl) propane, etherified bisphenol such as polyoxypropylene (6) -2,2-bis (4-hydroxyphenyl) propane, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1, 3-propylene glycol, 1,4-butanediol, 1,4, butenediol, neo Ntile glycol, 1,5-pentane glycol, 1,6-hexane glycol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol, bisphenol A, bisphenol Z and hydrogenated bisphenol A etc. can be mentioned.
[0055]
The colorant is not particularly limited, and various conventionally known colorants can be used. Specific examples include carbon black, nigrosine dye, aniline blue, calcoin blue, chrome yellow, ultramarine blue, dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate and rose bengal.
[0056]
In addition to the resin and the colorant, an additive capable of imparting various functions may be added to the colored particles. Specific examples include release agents and charge control agents.
[0057]
The release agent is not particularly limited, and various conventionally known release agents can be used. Specific examples include olefinic waxes such as polypropylene and polyethylene, modified products thereof, natural waxes such as carnauba wax and rice wax, and amide waxes such as fatty acid bisamides.
[0058]
The charge control agent is not particularly limited, and various conventionally known charge control agents can be used. Specific examples include nigrosine dyes, naphthenic acid or higher fatty acid metal salts, alkoxylated amines, quaternary ammonium salt compounds, azo metal complexes and salicylic acid metal salts and metal complexes thereof.
[0059]
《Career》
The carrier used in the present invention is preferably one in which a magnetic carrier core is coated with a silicone resin.
[0060]
Various conventionally known magnetic carrier cores can be used as the magnetic carrier core as the core material of the carrier coated with the silicone resin.
[0061]
Specific examples of the magnetic carrier core as the core material include iron powder, magnetite, and various ferrites. Various ferrites are preferable. As the ferrite, a heavy metal ferrite containing a heavy metal such as copper, zinc, nickel or manganese, a light metal ferrite containing an alkali metal and an alkaline earth metal is preferable, and a light metal ferrite containing an alkali metal and an alkaline earth metal is more preferable. is there.
[0062]
A carrier prepared by dispersing the fine powder of the magnetic carrier core in a resin may be used.
[0063]
The size of the carrier is preferably 10 to 200 μm in volume average particle size in consideration of frictional charging with the toner and carrier adhesion to the photoreceptor.
[0064]
The silicone resin for coating the silicone resin is preferably an assembly of segments represented by the following general formulas (I) and (II).
[0065]
[Chemical 1]

[0066]
In the segments represented by the general formulas (I) and (II), R ^{5 to} R ⁸ each represents a hydrocarbon group selected from a methyl group, an ethyl group, a phenyl group, or a vinyl group. A methyl group is preferable from the viewpoint of adhesiveness and strength. Further, modified silicone resins such as alkyd modified, acrylic modified, polyester modified, phenol modified, melamine modified and urethane modified may be used.
[0067]
The mass ratio of the general formulas (I) and (II) is preferably (I) / (II) = 0/100 to 70/30, more preferably 0/100 to 50/50.
[0068]
When (I) / (II)> 70/30, the linear component increases, the hardness decreases, and sufficient durability cannot be obtained.
[0069]
An aminosilane coupling agent may be added to increase the charge imparting ability of the carrier. The coupling agent to be used is not particularly limited, and two or more aminosilane coupling agents may be mixed and used. Specific compounds include γ-aminopropyltrimethoxysilane, γ-aminopropyltriethoxysilane, γ-aminoethyl-aminopropyltrimethoxysilane, methyl-γ-aminopropyldimethoxysilane, methyl-γ-aminoethylaminopropyl. Dimethoxysilane, γ-dimethylamino-propyltrimethoxysilane, γ-anilinopropyltrimethoxysilane, γ-morpholinopropyltrimethoxysilane, N, N′-bis (3-trimethoxysilyl) ethylenediamine and partial condensates thereof Can be mentioned.
[0070]
The addition amount of the aminosilane coupling agent is preferably 0.01 to 60 parts by mass, more preferably 0.1 to 40 parts by mass with respect to 100 parts by mass of the solid content of the silicone resin. If the amount is less than 0.01 parts by mass, the charge imparting ability of the carrier cannot be increased. On the other hand, if it exceeds 60 parts by mass, the film strength of the silicone resin is lowered, and the durability of the carrier is lowered.
[0071]
Moreover, you may add additives, such as a crosslinking agent and a curing catalyst, at the time of silicone resin coating. As the cross-linking agent, generally known low-molecular-weight silane compounds such as dealcohol-type, deacetate-type, deoxime-type, deamid-type, deaminoxy-type, and deacetone-type can be used.
[0072]
As the curing catalyst, metal soap such as zinc, tin, iron, lead, cobalt, nickel or aluminum, chelate compound, organic acid such as formic acid or acetic acid, and base such as amine can be used.
[0073]
The addition amount of these additives is preferably 0.01 to 10 parts by mass and more preferably 0.1 to 5 parts by mass with respect to 100 parts by mass of the silicone resin solid content.
[0074]
0.01-10 mass% is preferable with respect to a magnetic carrier core, and, as for the coating amount with the silicone resin of a magnetic carrier core, 0.5-5 mass% is more preferable. When the coating amount by the silicone resin is less than 0.01% by mass, a uniform coating layer cannot be formed on the surface of the magnetic carrier core. On the other hand, when the coating amount exceeds 10% by mass, the granulation of the magnetic carrier core particles is not possible. As a result, the fluidity is lowered, and the mixing property with the toner is deteriorated.
[0075]
The method for forming the silicone resin coating layer (coating layer) on the magnetic carrier core is not particularly limited, but as a specific example, after dissolving the silicone resin in a solvent, the solution is immersed in the core by spraying or spraying. A method of removing the solvent by drying and then baking is applied. As baking temperature, 150-300 degreeC is preferable, More preferably, it is 170-280 degreeC. If the baking temperature is less than 150 ° C, the crosslinking reaction of the silicone resin does not proceed sufficiently and the hardness becomes insufficient. However, a uniform resin coating layer cannot be obtained, which is not preferable.
[0076]
Application by spray drying can be performed using a rotating cylindrical fluidized bed particle coating apparatus.
[0077]
Preferable solvents used for coating (coating) include toluene, xylene, methyl ethyl ketone and methyl isobutyl ketone.
[0078]
<Toner recycling system>
The image forming apparatus according to the present invention is an image forming apparatus equipped with a toner recycling system.
[0079]
The toner recycling system is a system in which a transfer residual toner that is not transferred and remains on the surface of the photosensitive member is collected by a cleaning unit, and the collected toner is returned to the developing unit or the toner supply box for reuse.
[0080]
Since the toner recycling system reuses the collected toner, it is an excellent system in terms of environmental protection because no waste toner is generated.
[0081]
FIG. 1 is a schematic diagram illustrating an example of a toner recycling system.
In FIG. 1, 1 is a developing device, 2 is a developer conveying sleeve, 3 is a developer conveying screw, 4 is a photosensitive member, 5 is a cleaner, 6 is a cleaning member (elastic blade), 7 is a recycled toner collecting screw, 8 Indicates a recycled toner conveying screw.
[0082]
In FIG. 1, the untransferred toner scraped off by the cleaning member 6 is collected in the cleaner unit 5 by the recycled toner collecting screw 7 and supplied again to the developing device 1 by the recycled toner conveying screw 8.
[0083]
【Example】
EXAMPLES The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited to these examples.
[0084]
<Toner preparation>
Preparation of “Toner 1” 100 parts of a polyester resin, 7.5 parts of carbon black, and 3 parts of low molecular weight polypropylene were mixed and then melt-kneaded and pulverized to prepare colored particles having a volume average particle diameter of 9.0 μm.
[0085]
To 100 parts of the obtained colored particles, 0.8 part of hydrophobic silica fine powder having a number average primary particle size of 12 nm hydrophobized with hexamethyldisilazane (hydrophobic degree 60) is added, and the temperature of the colored particles is 40 ° C. Was mixed with a Henschel mixer controlled at a peripheral speed of 30 m / sec for 10 minutes to prepare “Toner 1” to which hydrophobic silica fine powder was externally added.
[0086]
The external additive presence state ((Si / C) / X) of the toner 1 was 0.29.
Preparation of “Toners 2 to 5” 100 parts of styrene / n-butyl acrylate / methyl methacrylate copolymer (copolymerization ratio = 86/10/4), 12 parts of carbon black, 5 parts of low molecular weight polypropylene and a charge control agent ( After mixing 1.0 part of azo-based metal complex), melt-kneading was performed and pulverization classification was performed to produce colored particles having a volume average particle diameter of 7.5 μm.
[0087]
Number average of 100 parts of the resulting colored particles hydrophobized with tetraoctyl titanate and 0.75 parts of hydrophobic titania fine powder having a primary average particle size of 15 nm and octyltrimethoxysilane (hydrophobic degree 55). 1.0 part of a hydrophobic silica fine powder having a primary particle size of 12 nm was mixed with a Henschel mixer under the conditions shown in Table 1 below, and the hydrophobic titania fine powder and the hydrophobic silica fine powder were externally added to “Toner 2”. 5 "was produced.
[0088]
The external additive presence state ((Si / C) / X) of toners 2 to 5, the peripheral speed of the Henschel mixer, the mixing time, and the temperature of the colored particles are shown in Table 1 below.
[0089]
[Table 1]

[0090]
Preparation of “Toner 6” 100 parts of styrene / n-butyl acrylate / methyl methacrylate copolymer (copolymerization ratio = 86/10/4), 12 parts of carbon black, 5 parts of low molecular weight polypropylene and charge control agent (azo type) After mixing 1.0 part of the metal complex), melt kneading was performed, and pulverization classification was performed to obtain colored particles having a volume average particle diameter of 7.5 μm.
[0091]
Hydrophobic treatment with octyltrimethoxysilane (hydrophobic degree 40) was performed on 100 parts of the obtained colored particles, and 1.0 part of hydrophobic silica fine powder having a number average primary particle size of 12 nm previously pulverized by an ejector pulverizer was added. Then, the toner was mixed for 10 minutes with a Henschel mixer in which the temperature of the colored particles was controlled at 35 ° C. under the condition of a peripheral speed of 30 m / sec, to prepare “Toner 6” to which hydrophobic silica fine powder was externally added.
[0092]
The external additive presence state ((Si / C) / X) of the toner 6 was 0.48.
<< Production of silicone resin-coated carrier >>
A coating resin solution was prepared by dissolving 100 parts of a silicone resin liquid (silicone SR2406, manufactured by Toray Industries, Inc., solid content concentration 20 mass%) and 5 parts of γ-aminoethyl-aminopropyltrimethoxysilane in 300 parts of toluene. Next, 1000 parts of a ferrite carrier having a volume average particle diameter of 60 μm was placed in a rotating cylindrical fluidized bed particle coating apparatus, and the coating resin solution was spray-coated at 70 ° C. under heating conditions while flowing. Thereafter, a heat treatment was performed at 180 ° C. for 3 hours, and pulverization and classification were performed to produce a “silicone resin-coated carrier”.
[0093]
<Production of developer>
The “toners 1 to 6” and the “silicone resin-coated carrier” were mixed at a blending ratio shown in Table 2 below to produce “developers 1 to 6”.
[0094]
[Table 2]

[0095]
<Evaluation>
Using the toner and developer produced above, a copy test of 100,000 sheets was performed at room temperature and normal humidity (20 ° C., 50% RH) using a Konica Sitios 7075 (manufactured by Konica Corporation) copier equipped with a toner recycling system. The amount of charge, the presence of external additives, background fogging, and toner scattering were evaluated.
[0096]
<Charge amount>
About 1g of developer measurement sample is taken from the developing device, put into a cell with a stainless steel mesh, blown with nitrogen gas (gas pressure 0.2kg / cm ² ) for 6 seconds to blow off the toner, and the remaining carrier charge (Q) was measured. The charge amount of the developer was calculated by the following formula (3).
[0097]
Formula (3) Charge amount (μC / g) = Q / (M ₁ −M ₂ )
Q: Charge of carrier (μC)
M ₁ : Sample mass before blowing (g)
M ₂ : Mass of sample after blow (g)
<External additive presence state when copying 100,000 sheets ((Si / C) / X)>
After copying 100,000 sheets, the latent image corresponding to the solid black original is developed, transferred to the OHP sheet, taken out before passing through the fixing step, scraped off the toner from the OHP sheet, did. The sample was measured for Si and C by ESCA to determine the external additive presence state ((Si / C) / X).
[0098]
<Ground fog>
The relative density of the white portion of the copy image corresponding to the white portion (reflection density of 0.000) of the transfer paper was measured with a Sakura Densitometer (manufactured by Konica Corporation).
[0099]
<Toner scattering>
A white paper was placed under the developing area of the copying machine, the scattered toner was adhered, the white paper was fixed through the fixing device of the copying machine, and the relative density was measured with a cherry densitometer.
[0100]

The evaluation results are shown in Table 3 below.
[0101]
[Table 3]

[0102]
In Examples 1 to 4 using the toner in which the hydrophobic silica fine powder is in the presence state satisfying the above formula (1), the change in the external additive presence state is small up to 100,000 copies, so the charge amount is reduced. It was a little stable. In terms of image quality, a high-quality image free of background fogging was obtained, and the contamination inside the machine due to toner scattering was at a level with no problem.
[0103]
On the other hand, in Comparative Example 1, since the toner in which the hydrophobic silica fine powder is dispersed in the toner is used, the hydrophobicity is caused by the stress received in the developing unit, the cleaning member, the recycled toner conveying member, and the like as copying progresses. Silica fine powder was buried inside the toner, resulting in a decrease in charge amount. At the time of copying 100,000 sheets, an image with a lot of background fogging was formed, and remarkable internal contamination occurred due to toner scattering.
[0104]
In Comparative Example 2, since the toner in which the hydrophobic silica fine powder was embedded from the start was used, generation of background fogging was observed at the time of 50,000 copies, and an image with much background fogging was obtained at the time of 100,000 copies. Further, remarkable in-machine contamination occurred due to toner scattering.
[0105]
【The invention's effect】
As demonstrated in the examples, excellent toner, developer, and image formation that can stably obtain a high-quality image without causing background fog and toner scattering even when repeated copying is performed by an image forming apparatus equipped with a toner recycling system. We were able to provide a device.
[Brief description of the drawings]
FIG. 1 is a schematic diagram illustrating an example of a toner recycling system.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Developing device 2 Developer conveyance sleeve 3 Developer conveyance screw 4 Photoconductor 5 Cleaner part 6 Cleaning member 7 Recycled toner collection screw 8 Recycled toner conveyance screw

Claims (3)

In the image forming method in which the transfer residual electrophotographic toner is collected from the cleaning unit, and the collected toner is returned to the developing device or the toner supply box and used for development, the electrophotographic toner contains colored resin and resin A method for forming an image, characterized in that hydrophobic silica fine powder is present on the surface so as to satisfy the following formula (1) .
Formula (1) 0.20 <(Si / C) / X <= 0.50
However, Si and C are the ratio of silicon atoms and carbon atoms present on the surface of the toner particles as measured by ESCA, and X is the addition rate (% by mass) of the hydrophobic silica fine powder to the colored particles. The image forming method according to claim 1, wherein the electrophotographic developer used in the image forming method has a carrier in which a magnetic carrier core is coated with a silicone resin. An image forming apparatus using the image forming method according to claim 1.

Images