JP4154106B2 - Toner particle manufacturing method, magnetic toner, and image forming method - Google Patents

Description

［式中、Ｒはアルコオキシ基を示し、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。］で示されるものである。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、γ−メタクリルオ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、メチルトリエトキシシラン、イソブチルトリメトキシシラン、ジメチルジメトキシシラン、ジメチルジエトキシシラン、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、フェニル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。
【００６７】
特に、下記一般式（II）
【００６８】
【化２】

［式中、ｐは２〜２０の整数を示し、ｑは１〜３の整数を示す］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使用して水系媒体中で磁性粉体を疎水化処理するのが良い。
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を抑制するのが難しくなる。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、画像にカブリが生じたり、転写材への転写性が悪化する等の傾向が見られる。
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。その使用量は磁性粉体１００質量部に対して、０.０５〜２０質量部、好ましくは０.１〜１０質量部とするのが良い。カップリング剤の使用量が０.０５質量部よりも少ないと、磁性粉体の表面疎水化処理が十分に行われないことがあり、２０質量部よりも多いと、余剰のカップリング剤が無駄になる、又は磁性粉体の表面疎水化処理に悪影響を及ぼすことがある。
【００６９】
ここで、疎水化処理における前記水系媒体とは、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等、が挙げられる。界面活性剤としては、例えば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。また、界面活性剤の添加量は、使用される界面活性剤の種類等によって異なるが、概ね水に対して０．１〜５ｗｔ％であることが好ましい。ｐＨ調整剤としては、前記疎水化処理に悪影響を及ぼさないｐＨ調整剤であれば特に限定されないが、例えば塩酸の如き無機酸が挙げられる。
【００７０】
水系媒体中での磁性粉体の表面疎水化処理における撹拌は、例えば撹拌羽根を有する混合機（具体的には、アトライター、ＴＫホモミキサーの如き高剪断力混合装置）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おこなうのが良い。
【００７１】
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、トナー粒子用の材料として用いた場合、トナー粒子中への分散性が非常に良好である。しかもトナー粒子表面からの露出が無く、ほぼ球形に近いトナー粒子を得ることも可能になる。従って、こういった磁性粉体を用いることにより、最終的に得られる磁性トナーの平均円形度が０.９７０以上、モード円形度が０.９９０以上となり転写性が向上し、電子写真プロセスへの適合性が良好なものとなる。
【００７２】
本発明で使用される磁性粉体は、結着樹脂１００質量部に対して、１０質量部乃至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質量部未満では現像剤の着色力が乏しく、カブリの抑制も困難になることがある。一方、２００質量部を越えると、画像形成時に現像剤担持体（例えば前記回転スリーブ等）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。
【００７３】
また、本発明において用いられる磁性粉体の平均粒径が０.１〜０.３μｍであることが好ましい。
平均粒径が０.１μｍ未満の磁性粉体を用いた磁性トナーから画像を得ると、画像の色味が赤味にシフトし、画像の黒色度が不足したり、ハーフトーン画像ではより赤味が強く感じられる傾向が強くなることなどがあり、好ましいものではない。また、このような磁性トナーをカラー画像に用いた場合には、色再現性が得られにくくなったり、色空間の形状がいびつになる傾向があるため好ましくない。さらに、磁性粉体の表面積が増大するために分散性が悪化し、トナー粒子の製造時により強力な撹拌を必要とするなど、製造時に要するエネルギーが増大し、効率的ではない。また、磁性粉体の添加量から得られるべき画像の濃度が不足することもあり好ましいものではない。
【００７４】
一方、磁性粉体の平均粒径が０.３μｍを越えると、磁性粉体一粒子あたりの質量が大きくなるため、トナー粒子の製造時にバインダー（結着樹脂）との比重差の影響でトナー粒子表面に磁性粉体が露出する確率が高まったり、製造装置の摩耗などが著しくなる可能性が高まったり、分散物の沈降安定性等が低下することなどがあり好ましくない。
【００７５】
磁性粉体の粒度の測定方法としては、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付けて０.０４〜２０００μｍの測定範囲で測定したり、レ−ザ−回折式粒径分布測定機（ハイアック／ロイコ社製：ナイコンプ モデル３７０）で０.４５μｍ以下の粒子を測定し求める方法や、あるいは、磁性粉体そのものを分離可能な場合は磁性粉体を、トナー粒子中または磁性トナー中においてはこれらを、樹脂中に包埋したのちに薄片とし透過型電子顕微鏡（ＴＥＭ）にて視野中の１００個の磁性粉体の粒子径を測定して求める方法などが挙げられる。本発明においては、透過型電子顕微鏡にて測定するのが好適である。
【００７６】
前述のＴＥＭによる具体的な観察方法としては、常温硬化性のエポキシ樹脂中へ観察すべき粒子（磁性粉体又はトナー粒子等）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状のサンプルとして観察する方法が例示される。
また、磁性粉体の粒度の他の測定方法としては、例えば、画像解析装置により平均粒径を算出する方法であっても良い。
【００７７】
本発明のトナー粒子の製造方法で使用される磁性粉体としては、例えば、マグネタイト、マグヘマイト、フェライト等の磁性酸化鉄、鉄、コバルト、ニッケル等の金属、或いはこれらの金属とアルミニウム、コバルト、銅、鉛、マグネシウム、錫、亜鉛、アンチモン、ベリリウム、ビスマス、カドミウム、カルシウム、マンガン、セレン、チタン、タングステン、バナジウム等の金属の合金、及びその混合物、リン、マグネシウム、ケイ素等の元素をさらに含む合金又は混合物等が挙げられる。これら例示された磁性体を１種または２種以上併用して用いられる。これら磁性粉体は、モース硬度が５〜７のものが一般に好ましい。
【００７８】
これらの磁性粉体の磁気特性としては、磁場７９５.８ｋＡ／ｍ下で飽和磁化が１０〜２００Ａｍ²／ｋｇ、残留磁化が１〜１００Ａｍ²／ｋｇ、抗磁力が１〜３０ｋＡ／ｍであるものが用いられる。このような磁性粉体の中でもマグネタイトを主とするものが特に好ましい。
【００７９】
本発明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。
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の如きアルカリを加え、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ｐＨ８〜１０）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、磁性酸化鉄粒子の芯となる種晶をまず生成する。
【００８０】
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６〜１０に維持しながら空気を吹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粒子を成長させる。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。
【００８１】
酸化反応の終期に液のｐＨを調製し、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磁性酸化鉄粒子が得られる。あるいは、酸化反応終了後、洗浄、濾過して得られた酸化鉄粒子を、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を調製し、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。いずれにせよ、酸化反応終了後に乾燥工程を経ずに表面処理を行うことが肝要であり、本発明のトナー粒子の製造方法における重要なポイントである。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。
【００８２】
前述した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で用いられる。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。
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トナー粒子を含む磁性トナーを使用することにより、感光体の削れ及びトナー融着が発生せず、画像形成時における高画質及び高安定性が可能となる。
【００８３】
本発明のトナー粒子の製造方法においては、ポリエステル樹脂は必要不可欠な成分である。前述したように、帯電性が均一で、電子写真プロセスにおける静電潜像の現像時において良好な現像性を示すトナー粒子を得るためには、環境に左右されにくく、安定、且つ均一な帯電性能が必要であることから、粒度分布がシャープで、かつ形状が球形でその分布も均一であり、さらに表面状態及び表面組成が極めて均一でなければならない。そのためには、金属塩コロイドの調製方法および疎水化処理された磁性粉体が必要であることは述べてきたが、それに加えて金属塩コロイドの前記液滴粒子に対する保護作用がより効率的に発現されるように、さらには疎水化された磁性粉体が液滴粒子から遊離したり、表面に多量に付着したりすることを抑制するためには、本発明のトナー粒子の製造方法において、ポリエステル樹脂が必須となる。
【００８４】
このポリエステル樹脂は、比較的高い極性を示すエステル結合を数多く含むために樹脂の極性が高くなる。一方、本発明によるトナー粒子を構成する結着樹脂としては、重合性単量体を重合することにより生成するスチレン系樹脂が好ましい形態とされている。この２種の樹脂を比較すると、通常、ポリエステル樹脂の方が極性が高く、その極性により液滴粒子中で水系分散媒側に偏在化する傾向が強くなる。界面化学的にはこの状態の方がポテンシャル的に安定であり、この状態を保ちつつ重合が進行しトナー粒子が得られる。このトナー粒子が得られる過程では、このポリエステル樹脂による安定化効果と前述の金属塩コロイドの存在が相まって機能し、トナー粒子の粒度分布がシャープなものとなると発明者らは考えている。
【００８５】
一方、得られるトナー粒子は、表面にポリエステル樹脂が偏在化することで表面状態や表面組成が均一なものとなり、その結果、帯電性が均一となり環境に左右されにくいものとなる。ここで、極性の極端に高い官能基が重合性単量体組成物中に含まれると、リークサイトとなったり、水分の吸着によって高温高湿下での帯電性が極端に低下することがあるため、導入する官能基数を適切に制限する必要がある。このような事実から、適度な極性を有する官能基を数多く有するポリエステル樹脂を用いることは、本発明の目的からしても非常に好ましいものである。
【００８６】
即ち、今まで述べてきたように本発明では、ポリエステル樹脂、疎水化処理された磁性粉体、金属塩コロイドの調製方法の３つは相互作用しつつ、トナー粒子の特性を決定づけているため、何れも必要不可欠なものである。
【００８７】
本発明に使用されるポリエステル樹脂は、例えばトナー粒子から得られる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及び不飽和ポリエステル樹脂のいずれか一方又は両方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を構成するアルコール成分と酸成分を以下に例示する。
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、また下記一般式（III）で表されるビスフェノール誘導体、
【００８８】
【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。］、あるいは一般式（III）の化合物の水添物
また、下記一般式（IV）で示されるジオール、
【００８９】
【化４】

あるいは式（IV）の化合物の水添物のジオール、さらには、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等、が挙げられる。
【００９０】
２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、さらには、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の如き多価カルボン酸やその無水物など、が挙げられる。
【００９１】
該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の場合が好ましく使用される。この化合物の場合には、定着性や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。また、該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。前記範囲から大きく離れると、トナー粒子の良好な表面組成を損なう場合がある。
【００９２】
該ポリエステル樹脂は、本発明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未満だとトナー粒子表面での存在量が絶対的に不足することがあり、５０ｍｇＫＯＨ／樹脂１ｇを越えるとトナー粒子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。
【００９３】
該ポリエステル樹脂は、重合性単量体１００質量部に対して０.５〜３５質量部用いられることが好ましく、５〜２０質量部がさらに好ましい。０.５質量部未満だと均一な帯電性が得られないことがあり、３５質量部を越えると重合性単量体組成物の粘度が高くなり、得られるトナー粒子の粒度分布がシャープにならないことがあるため好ましくない。
【００９４】
また、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２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するなどして、物性を調整したポリエステル樹脂を単独で使用、又は併用しても良い。また、ポリエステル樹脂は、前述した重合性単量体と同様に、磁性トナーとしたときの安定性や定着性を考慮して、理論ガラス転移温度が４０〜７０℃を示すように用いられることが好ましい。
【００９５】
本発明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なうと、分子量１万〜１０万の間に極大を有する重合体を得、トナー粒子に望ましい強度と適当な溶融特性を与えることが出来る。重合開始剤の半減期及び添加量は、前記範囲を大きく逸脱すると、重合性単量体の重合が不十分となったり、又は重合した結着樹脂の良好な物性が損なわれることがある。
【００９６】
重合開始剤の添加は、重合性単量体の重合前であれば、任意の段階で添加することができる。例えば、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と同時に加えても良いし、水系分散媒中に重合性単量体組成物を懸濁する直前に混合しても良い。又、造粒直後、重合反応を開始する前に重合性単量体あるいは溶媒に溶解した重合開始剤を加える事も出来る。
【００９７】
重合開始剤例としては、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のアゾ系またはジアゾ系重合開始剤、ベンゾイルパーオキサイド、メチルエチルケトンパーオキサイド、ジイソプロピルパーオキシカーボネート、クメンヒドロパーオキサイド、２,４−ジクロロベンゾイルパーオキサイド、ラウロイルパーオキサイド、ｔ−ブチルパーオキシ−２−エチルヘキサノエート等の過酸化物系重合開始剤が挙げられる。
【００９８】
本発明では、架橋剤を添加しても良く、好ましい添加量としては、重合性単量体１００質量部に対して０.００１〜１５質量％である。ここで架橋剤としては、主として２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２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３個以上のビニル基を有する化合物等、が単独もしくは混合物として用いられる。架橋剤の添加量が前記範囲よりも少ないと十分な効果が発揮されないことがあり、前記範囲よりも多すぎると結着樹脂の物性に悪影響を及ぼすことがある。
【００９９】
本発明のトナー粒子の製造方法では、トナー粒子に離型剤が含まれることも好ましい形態の一つである。
転写材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。
このとき小径のトナー粒子を用いれば非常に高精細な画像を得ることができるが、粒径の小さなトナー粒子は紙等の転写材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、本発明において、離型剤として適正量のワックスを使用することにより、高解像性と耐オフセット性を両立させつつ画像形成装置における感光体の削れを防止することが可能なトナー粒子を製造することができる。
【０１００】
本発明に離型剤として使用可能なワックスとしては、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、あるいはその化合物、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。
【０１０１】
これらのワックス成分の内でも、示差走差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、４５〜９０℃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。該最大吸熱ピークが４０℃未満であるとワックス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ことがある。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することがあり好ましくない。さらに、該最大吸熱ピーク温度が高いと水系分散媒中での造粒中にワックス成分が析出する等の問題を生じることがあり好ましくない。
【０１０２】
ワックス成分の最大吸熱ピーク温度の測定は、例えば「ＡＳＴＭ Ｄ ３４１８−８」に準じて行うことが好ましい。一例を挙げるならば、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、昇温速度１０℃／ｍｉｎで測定を行う。
【０１０３】
離型剤としてのこれらのワックス成分の含有量としては、得られるトナー粒子から磁性トナーを製造したときに、磁性トナー全体に対して０.１〜２０質量％の範囲が好ましい。含有量が０.１質量％未満では低温オフセット抑制効果が十分に得られないことがあり、２０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、他の材料の分散性が悪くなることがあり、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。
【０１０４】
また、本発明のトナー粒子の製造方法においては、重合性単量体組成物に前記結着樹脂及び前記ポリエステル樹脂以外の樹脂を添加して重合しても良い。例えば、重合性単量体に導入するとその水溶性により水系分散媒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、スルフォン酸基、グリシジル基、ニトリル基等親水性官能基含有の単量体成分をトナー粒子中に導入したい時には、これらとスチレンあるい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、あるいはグラフト共重合体等、共重合体の形にすることにより、あるいはポリエステル、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にすることにより使用が可能となる。
【０１０５】
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、前記離型材を使用した場合に前述のワックス成分（前記離型剤）を相分離させ、より内包化が強力となり、耐オフセット性、耐ブロッキング性、低温定着性の良好な磁性トナーを得ることができる。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５０００以上が好ましく用いられる。５０００以下、特に４０００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場合がある。
【０１０６】
また、材料の分散性や定着性、あるい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さらに添加しても良く、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、テルペン樹脂、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挙げられ、これらの樹脂は、単独或いは混合して使用できる。
【０１０７】
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十分に得られないことがあり、一方２０質量部以上添加するとトナー粒子の種々の物性設計が難しくなることがある。また、重合性単量体を重合して得られる結着樹脂等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トナー粒子を得ることが出来る。
【０１０８】
本発明では、トナー粒子の荷電特性を安定化するために荷電制御剤を使用しても良い。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、荷電制御剤は、重合阻害性が低く、水系分散媒への可溶化物が実質的にない荷電制御剤であることが特に好ましい。
【０１０９】
具体的な荷電制御剤としては、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、アゾ染料あるい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。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。
【０１１０】
該荷電制御剤は重合性単量体１００質量部に対し０.５〜１０質量部使用することが好ましい。しかしながら、本発明では、荷電制御剤の使用は必須ではなく、画像形成装置の現像装置における磁性トナーの層圧規制部材や現像剤担持体（前記回転スリーブ等）との摩擦帯電を積極的に利用することで、帯電量や帯電スピードを制御することができる。荷電制御剤を添加する場合では、得られるトナー粒子の使用形態等を考慮して添加量を決めることが好ましい。
【０１１１】
さらに、本発明のトナー粒子の製造方法では、磁性粉体以外に他の着色剤を併用しても良い。併用し得る着色材料としては、磁性あるい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、磁性粉体と同様に表面を疎水処理して用いても良い。
【０１１２】
本発明では、分散安定剤として公知の無機分散剤を併用しても良い。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粒子に悪影響を与え難いので、好ましく使用できる。
【０１１３】
こうした無機分散剤の例としては、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。これらの無機分散剤は、重合性単量体組成物１００質量部に対して、０.２〜２０質量部を単独で、又は複数種類を混合して使用しても良い。無機分散剤の使用量が前記範囲よりも少ないと、添加による効果が十分に得られないことがあり、前記範囲よりも多すぎると、前記分散安定剤に干渉して重合性単量体組成物の分散に悪影響を及ぼすことがある。
【０１１４】
また、前記無機分散剤を使用する場合では、そのまま使用しても良いが、前述したリン酸カルシウム塩類と同様に、水溶液を混合させて所望の無機分散剤を水系分散媒中に生成すると、より細かい無機分散剤の粒子を得ることができ好ましい。また、水系分散媒中に水溶性塩が副生すると、重合性単量体の水への溶解が抑制されるため、例えば乳化重合で見られるようなトナー粒子の超微粒子化を抑制する上で好都合である。無機分散剤は、重合反応終期に残存重合性単量体を除去する時には障害となることから、水系媒体を交換するか、イオン交換樹脂で脱塩したほうが良い。無機分散剤は、重合終了後酸あるい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。
【０１１５】
本発明で得られるトナー粒子は重量平均粒径で３〜１０μｍの粒径を有していることが好ましく、高画質化のためには４〜９μｍの粒径を有していることがより好ましい。さらに得られたトナー粒子に於いては重量平均粒径（Ｄ４）と数平均粒径（Ｄ１）の比Ｄ４／Ｄ１が１.４未満である粒度分布を持つことが好ましい。特に重合法でトナー粒子を製造する際に、トナー粒子表面に磁性粉体が露出しているとトナー粒子の粒度分布を悪化させる傾向にある。
【０１１６】
次に本発明の磁性トナーについて説明する。
本発明の磁性トナーにおいて平均円形度は０.９７０以上でなければならず、モード円形度が０.９９０以上であることが好ましい。その理由については、以下のとおりである。
平均円形度が０.９７０以上の磁性トナー（トナー粒子と無機微粉体とで構成される粉体）は転写性に非常に優れている。これはトナー粒子と感光体（像担持体）との接触面積が小さく、鏡像力やファンデルワールス力等に起因するトナー粒子の感光体への付着力が低下するためと考えられる。
【０１１７】
さらに、平均円形度が０.９７０以上の磁性トナーのトナー粒子は表面のエッジ部がほとんど無いため、転写部材と感光体との圧接部が存在する接触転写方法において感光体表面を引っ掻くことが無いことから、感光体表面の削れが抑制されることも挙げられる。平均円形度が０.９７０よりも小さいと、磁性トナーの形状に起因するこれらの効果が発揮されないことがある。これらの効果は、転写中抜けの発生しやすい先述の接触転写工程を含む画像形成方法においては、より顕著となって現れる。平均円形度が高くとも主として存在する粒子の円形度が低いと効果が不十分であり、特にはモード円形度が０.９９０以上であることによって、円形度が０.９９０以上の粒子が主として存在することから、上記の効果が顕著に現れることから好ましい。
【０１１８】
次に、Ｘ線光電子分光分析により測定されるトナー粒子の表面に存在する炭素元素の含有量（Ａ）に対する鉄元素の含有量（Ｂ）の比（Ｂ／Ａ）が、０.００１未満である場合が必須構成要素である点について説明する。
【０１１９】
先述したように、接触帯電工程を含む画像形成方法において、上述の如き（Ｂ／Ａ）が０.００１未満である、すなわち磁性粉体が表面にほとんど露出していない磁性トナーを用いれば、転写部材などにより磁性トナーが感光体表面に圧接されても感光体表面が削れることはほとんど無く、感光体の削れやトナー融着を著しく低減させることが可能となる。一方で、Ｂ／Ａが０.００１以上である場合には、磁性トナー表面に磁性粉体が露出し、露出した磁性粉体による感光体の削れがより顕著となって現れることがある。本発明のように磁性粉体が表面にほとんど露出していない磁性トナーでは、接触転写工程を組み合わせた画像形成方法においてもその効果は絶大であり、非常に高精細な画像を長期に亘って得ることが可能である。
【０１２０】
なお、トナー粒子内部の特定の部分のみに磁性粉体が含有されている特殊な磁性トナーは、特開平７−２０９９０４号公報においても既に開示されている。しかしながら、特開平７−２０９９０４号公報においては、開示されている磁性トナーの円形度に関する言及がなされていない。本発明の画像形成方法においては、特定の平均円形度を有する磁性トナーの使用が必須要素であり、特開平７−２０９９０４号公報に記載されているような磁性トナーを本発明のような使用形態で用いても同じような効果が発現するかどうかは不明である。
【０１２１】
本発明において、該磁性トナーの投影面積円相当径をＣとし、透過型電子顕微鏡（ＴＥＭ）を用いた該磁性トナーの断面観察における磁性粉体表面とトナー粒子との距離の最小値をＤとしたときに、Ｄ／Ｃ≦０.０２以下の関係を満たすトナー粒子数が５０％以上であることが好ましく、６５％以上がより好ましく、７５％以上がさらに好ましい。
その理由は以下のとおりである。
【０１２２】
前記条件を満たさない場合には、トナー粒子において少なくともＤ／Ｃ＝０.０２境界線よりも外側には磁性粉体が全く存在しないことになる。仮に前述のような粒子を球形として想定すると、一つのトナー粒子を全空間とした場合に磁性粉体が存在しない空間は、トナー粒子の表面に少なくとも１１.５％は存在することになる。実際には、最近接位置に磁性粉体が均一に整列してトナー粒子内部に内壁を作るように存在するわけではないので、トナー粒子内に磁性粉体が存在しない空間は、１２％以上になることは明らかである。
【０１２３】
一粒子あたりこれだけの空間に磁性粉体が存在しないと、
＜１＞トナー粒子内部に磁性粉体が偏り、磁性粉体の凝集が起こる可能性が極めて高くなる。その結果として着色力の低下を招く。
＜２＞磁性粉体の含有量に応じてトナー粒子の比重が高くなるものの、トナー粒子表面は結着樹脂やワックス成分が偏在する。そのため、仮に何らかの手段で最表面に表面層をトナー粒子表面に設けても、トナー粒子や、磁性トナーの製造時にトナー粒子にかかる応力などがかかる場合、融着や変形が起こりやすくなり、製造時での扱いが複雑になったり、変形により得られるトナー粒子の粉体特性に分布が生じ、電子写真特性に悪影響を及ぼしたり、磁性トナーの貯蔵時でのブロッキング性が悪化する可能性が高まる。
＜３＞トナー粒子表面が結着樹脂及びワックスのみで、内部には磁性粉体が偏在する粒子構造では、トナー粒子外部が軟らかく内部が硬い構造となるために、該添剤の埋め込みが非常に起こりやすく、磁性トナーの耐久性が悪化する。
などといった弊害を招くおそれが高まる。
Ｄ／Ｃ≦０.０２となるトナー粒子数が５０％未満であると前述のような着色力の低下、ブロッキング性の悪化及び耐久性の悪化などの弊害は顕著になる傾向にある。
そのため、本発明ではＤ／Ｃ≦０.０２を満足するトナー粒子の個数が５０％以上であることが好ましいものである。
【０１２４】
ＴＥＭによる具体的な観察方法としては、常温硬化性のエポキシ樹脂中へ観察すべき粒子を十分に分散させた後に温度４０℃の雰囲気中で二日間硬化させ得られた硬化物を、そのまま、あるいは凍結してミクロトームにより薄片状のサンプルとして観察する方法が好ましい。
該当する粒子数の割合の具体的な決定方法については、以下のとおりである。
【０１２５】
ＴＥＭにてＤ／Ｃを決定するための粒子は、顕微鏡写真での断面積から円相当径を求め、その値が数平均粒径の±１０％の幅に含まれるものを該当粒子とし、その該当粒子について、磁性粉体表面と該トナー粒子表面との距離の最小値（Ｄ）を計測し、Ｄ／Ｃを計算する。こうして計算されたＤ／Ｃ値が０.０２以下の粒子の割合を下記式１により求めるものと定義する。このときの顕微鏡写真は精度の高い測定を行うために、１万〜２万倍の倍率が好適である。本発明では、透過型電子顕微鏡（日立製Ｈ−６００型）を装置として用い、加速電圧１００ｋＶで観察し、拡大倍率が１万倍の顕微鏡写真を用いて観察、測定した。
【０１２６】
【式１】

該磁性トナーの数平均粒径は、後述するコールターカウンターにて決定するのが良い。
【０１２７】
さらに、特開平７−２０９９０４号公報においては特殊な構造の磁性トナーそのものが提案されているだけであり、その具体的な使用形態に関しては検討の余地が残されている。本発明者等は、特開平７−２０９９０４号公報において開示されている技術思想とは異なる発想にて得られた特殊な磁性トナーを、特定の画像形成方法と組み合わせることにより、感光体の耐久性において著しい改良効果が発現することを見出し、本発明に至ったものである。
【０１２８】
本発明の磁性トナーにおいて、高画質化のため、前述したとおり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粒径が４μｍ〜９μｍであることが好ましい。重量平均粒径が４μｍ未満の磁性トナーに於いては、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が十分に抑制されないことがある。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、個々の磁性トナーを均一に帯電させることが困難となることからカブリが生じるなど、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、本発明の磁性トナーには好ましくない。また、磁性トナーの重量平均粒径が９μｍ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、高解像度の画像が得られないことがある。さらには、磁性トナーの重量平均粒径は、４μｍよりも大きく、８μｍ未満がより好ましい。
【０１２９】
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型あるい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、電解液は１級塩化ナトリウムを用いて１％ＮａＣｌ水溶液を調製することによる測定が可能である。このような測定方法では、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。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フォン酸塩を０．１〜５ｍＬ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分間分散処理を行な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以上の磁性トナーの体積、個数を測定して体積分布と個数分布とを算出し、それから、本発明に係わる所の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数平均粒径（Ｄ１）を求めることができる。
【０１３０】
また、本発明では磁性トナーの重量平均粒径（Ｄ４）で４μｍ以下の粒子が２０個数％以下であることが、安定して良質な画像を得る上で必要である。４μｍ以下の粒子が２０個数％よりも多いと、前述したように、粒径の小さな磁性トナーによる転写残トナーが多くなりやすく、この転写残トナーによる一次帯電不良に起因する帯電不良（感光体の帯電ムラの発生）よって、得られる画像の画質が低下することがある。
【０１３１】
また、本発明においては、磁性トナーの磁場７９.６ｋＡ／ｍ（１０００エルステッド）における磁化の強さが１０〜５０Ａｍ²／ｋｇ（ｅｍｕ／ｇ）であることが必要である。現像装置内に磁気力発生手段を設けることで、磁性トナーではトナーの漏れを防止でき、磁性トナーの搬送性或いは攪拌性を高められるばかりでなく、前記回転スリーブ等の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磁性トナーの飛散を防止することが容易となる。
【０１３２】
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、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、及び転写残トナーの回収不良に起因する画像不良等を生じることがある。また、磁性トナーの磁場７９.６ｋＡ／ｍにおける磁化の強さが１０Ａｍ²／ｋｇ（ｅｍｕ／ｇ）よりも小さいと磁気力による磁性トナーの搬送を行うことが困難となり、トナー担持体上による磁性トナーの担持の均一性が損なわれることがある。
【０１３３】
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た場合に磁気凝集により磁性トナーの流動性が著しく低下し、転写性が低下することで転写残トナーが増加することがある。また、磁場７９.６ｋＡ／ｍにおける磁化の強さが５０Ａｍ²／ｋｇ（ｅｍｕ／ｇ）よりも大きいとトナー粒子に含まれる磁性体量が多いために、転写材へ十分に定着しないことがある。
なお、穂立ちについて言及するならば、本発明の磁性トナーのように０.９７０以上の円形度、０.９９０以上のモード円形度を有することによって、トナー担持体上での磁性トナーの穂立ちが細く密になることによって、帯電が均一化され更にカブリが大幅に減少する。
【０１３４】
本発明において磁場７９.６ｋＡ／ｍにおける磁化の強さを規定する理由は、磁性粉体の磁気特性を表わす量としては、磁気飽和における磁化の強さ（飽和磁化）が用いられるが、本発明においては画像形成装置内で実際に磁性トナーに作用する磁場における磁性トナーの磁化の強さが重要であるためである。画像形成装置に磁性トナーが適用される場合、磁性トナーに作用する磁場は、画像形成装置外への磁場の漏洩を大きくしないため、或いは磁場発生源のコストを低く抑えるために、市販されている多くの画像形成装置において数十から百数十ｋＡ／ｍであり、画像形成装置内で実際に磁性トナーに作用する磁場の代表的な値として磁場７９.６ｋＡ／ｍ（１０００エルステッド）を選択し、磁場７９.６ｋＡ／ｍにおける磁化の強さを規定した。
【０１３５】
また、本発明において磁性トナーの磁化の強さは、振動型磁力計ＶＳＭＰ−１−１０（東英工業社製）を用いて、２５℃の室温にて外部磁場７９.６ｋＡ／ｍで測定することにより求めることができる。また、磁性粉体の磁気特性は、２５℃の室温にて外部磁場７９６ｋＡ／ｍで測定することにより求めることができる。
【０１３６】
本発明の磁性トナーは、トナー粒子と無機微粉体とによって構成される。この磁性トナーを構成するトナー粒子は、前述したトナー粒子の製造方法によって製造することが可能であり、前述したように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前述した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）等を均一に溶解または分散せしめて前記重合性単量体組成物とした後、この重合性単量体組成物を分散安定剤を含有する連続層（例えば前記水系分散媒等の水相）中に適当な撹拌機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。この懸濁重合法で得られるトナー粒子は、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、特にはモード円形度が０.９９０以上という物性要件を満たす磁性トナーが得られやすく、さらに円形度の高い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。
【０１３７】
また、先のトナー粒子の製造方法で述べたように、表面が疎水化処理された磁性粉体を使用し、かつ前記結着樹脂に比して極性の高いポリエステル樹脂等の極性樹脂を使用することが、磁性粉体が表面に露出しないトナー粒子を製造する上で重要であるが、このような極性樹脂として、前述したポリエステル樹脂はもちろんのこと、例えば前記スチレン系樹脂にも、極性の高い官能基、例えば、カルボキシル基やヒドロキシル基等、を導入することで極性を高くし、トナー粒子の表面組成に反映させることが可能である。このとき導入される官能基は、極性の高い官能基がトナー粒子表面に多く存在することによるリークサイトの発生や、水分を吸着することによる高温高湿下での帯電性の極端な低下等が生じない範囲の官能基数であることが好ましい。また、トナー粒子の所望の物性を得られるような官能基を選択して前記ポリエステル樹脂等の前記極性樹脂に導入することも可能である。
【０１３８】
本発明の磁性トナーは、流動化剤として平均１次粒子径４〜８０ｎｍの無機微粉体が添加されることも重要である。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トナー粒子の帯電量の調整、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。
【０１３９】
無機微粉体の平均１次粒子径が８０ｎｍよりも大きい場合、或いは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になることがある。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が生じることがある。無機微粉体の平均一次粒径が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、前記感光体或いは前記トナー担持体等を傷つけるなどによる画像欠陥を生じることがある。磁性トナーの帯電分布をより均一とするためには無機微粉体の平均一次粒径は６〜３５ｎｍであることがより良い。
【０１４０】
本発明において、無機微粉体の平均１次粒子径は、例えば、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或いは遊離して存在している無機微粉体の１次粒子を１００個以上測定し、個数平均径を求めることで測定する。
【０１４１】
本発明で用いられる無機微粉体としては、例えばシリカ等のケイ酸微粉体、アルミナ、チタニアなどが使用できる。
より詳しくは、例えば、ケイ酸微粉体としては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、前記無機微粉体はそれらも包含するものである。
【０１４２】
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に発揮されないことがあり、３.０質量％以上では定着性が悪くなることがある。
【０１４３】
無機微粉体は、表面が疎水化処理されていることが高温高湿環境下での特性から好ましい。磁性トナー中の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。
【０１４４】
無機微粉体の疎水化処理の処理剤としては、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、シランカッブリング剤、その他有機硅素化合物、有機チタン化合物等の如き処理剤の１種又は２種以上の混合物が挙げられる。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、無機微粉体を疎水化処理すると同時に、或いは処理した後に、シリコーンオイルにより処理することが高湿環境下でも磁性トナーの帯電量を高く維持し、トナー飛散を防止する上でよい。
【０１４５】
無機微粉体の処理条件としては、例えば第一段反応としてシリル化反応を行な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ことができる。上記シリコーンオイルは、２５℃における粘度が１０〜２０００００ｍｍ²／ｓのものが、さらには３，０００〜８００００ｍｍ²／ｓのものが好ましい。１０ｍｍ²／ｓ未満では、無機微粉体上における疎水化処理層の安定性が小さく、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。２０００００ｍｍ²／ｓを超える場合は、均一な処理が困難になる傾向がある。
【０１４６】
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。
シリコーンオイルの処理の方法としては、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。あるいは適当な溶剤にシリコーンオイルを溶解あるいは分散せしめた後、シリカ等の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。
【０１４７】
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１〜２３質量部、好ましくは５〜２０質量部が良い。前記範囲に比して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ないことがあり、多すぎるとカブリ発生等の不具合を生じることがある。
【０１４８】
本発明で用いられる平均一次粒径が８０ｎｍ以下の無機微粉体は、ＢＥＴ法で測定される窒素吸着で比表面積が２０〜２５０ｍ²／ｇの範囲内のものが好ましく、より好ましくは４０〜２００ｍ²／ｇのものが更に良い。前記範囲よりも比表面積が小さすぎると所望の流動性を得られにくくなる場合があり、大きすぎると磁性トナーの帯電安定性に悪影響を与える場合がある。
【０１４９】
ＢＥＴ比表面積は、湯浅アイオニクス（株）製、全自動ガス吸着量測定装置：オートソーブ１を使用し、吸着ガスに窒素を用い、ＢＥＴ多点法により求めることができる。なお、サンプルの前処理としては、温度５０℃で１０時間の脱気を行うことが好ましい。
【０１５０】
また、転写後における感光体の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。
【０１５１】
本発明の磁性トナーには、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の如き滑剤粉末、あるい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、あるい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、あるいは例えばカーボンブラック粉末、酸化亜鉛粉末、酸化スズ粉末等の導電性付与剤、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。
【０１５２】
次に、本発明の画像形成装置の一例を図に沿って具体的に説明する。
図１に於いて、１００は感光ドラム（像担自体）で、その周囲に感光ドラム１００に当接して感光ドラム１００を帯電する一次帯電ローラ１１７、帯電した感光ドラム１００にレーザーを照射して感光ドラム１００に静電潜像を形成するレーザー発生装置（露光装置）１２１、内部に現像剤を収容するとともに静電潜像が形成された感光ドラム１００に現像剤を供給する現像器（現像装置）１４０、現像剤によって顕像化されたトナー画像を転写材（普通紙等）に転写する転写帯電ローラ１１４、転写後の感光ドラム１００上に残留する現像剤を除去するクリーナ１１６、感光ドラム１００と転写帯電ローラ１１４の間に転写材を搬送するレジスタローラ１２４、トナー画像が転写された転写材を次段に搬送する搬送ベルト１２５、及び転写材に転写されたトナー画像を転写材に定着させる定着器１２６、等が設けられている。なお、感光ドラム１００、現像器１４０、一次帯電ローラ１１７、及びクリーナ１１４は、図示しない保持部材によって一体的に、かつ画像形成装置本体に着脱自在に保持されてなるプロセスカートリッジとして画像形成装置に配設されている。
【０１５３】
現像器１４０は、図２に示されるように、感光ドラム１００に面して開口しており、開口部分には、感光ドラム１００に近接してアルミニウム、ステンレス等非磁性金属で作られた円筒状の現像剤担持体（現像スリーブ）１０２が設けられている。現像スリーブ１０２は円筒状であり、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。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は現像剤コート量規制、Ｓ２は現像剤の取り込み／搬送、Ｎ２は現像剤の吹き出し防止に影響している。また、現像器１４０には、現像スリーブ１０２上に付着する現像剤の付着量を規制する弾性ブレード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現像剤量が制御される。また、現像器１４０内部には、収容された現像剤を撹拌する撹拌部材１４１が設けられており、現像器１４０内には、後述する実施例の磁性トナーが現像剤として収容されている。感光体１００と現像スリーブ１０２との間隙は前記保持部材等により約３００μｍに維持されている。
【０１５４】
転写帯電ローラ１１４は、図３に示されるように、導電性の芯金３４ａと、芯金３４ａの周面を被覆する弾性層３４ｂとを有しており、芯金３４ａには転写バイアスを芯金３４ａに印加する転写帯電装置３５が接続されている。
【０１５５】
上記構成の画像形成装置を使用して、本発明の画像形成方法の一例を以下に説明する。
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、直流電圧−７００Ｖｄｃ）そして、レーザー発生装置１２１によりレーザー光１２３を感光体１００に照射する事によって感光ドラム１００が露光され静電潜像が形成される。
一方、現像器１４０では、磁性トナーは、マグネットローラ１０４の磁力によって現像スリーブ１０２上に付着し、弾性ブレード１０３によって付着量が規制されるとともに、現像スリーブ１０２上に均一に付着する。磁性トナーは、現像スリーブ１０２上に均一に付着するまでに、撹拌部材１４１の撹拌による磁性トナー同士の摩擦や、弾性ブレード１０３との摩擦等によって帯電している。
感光体１００と現像スリーブ１０２との間には、図示しない現像バイアス印加手段から直流電圧及び交流電圧を有する現像バイアス電圧が現像スリーブ１０２に印加されることにより、現像バイアス電界が形成され、現像スリーブ１０２上の磁性トナーは静電潜像に応じて感光体１００上に飛翔し、静電潜像を顕像化する。
磁性トナーによって顕像化された静電潜像（トナー画像）は、転写材を介して感光体１００に対向し転写帯電装置３５によって転写バイアスが印加されている転写帯電ローラ１１４により転写材上へ転写される。トナー画像が転写された転写材は搬送ベルト１２５等により定着器１２６へ運ばれ転写材上に定着される。また、一部感光体上に残された磁性トナーはクリーニング手段１１６によりクリーニングされる。
【０１５６】
前記磁性トナーは、その粒径と平均円形度を規定している。そのため、磁性トナー中での磁性粉体が均一な分布となり磁性トナーの有する磁性が揃い、磁性トナーの形状も一定の分布内に収まることから、前記画像形成方法において、静電潜像をより細かく顕像化でき、かつより細かく顕像化したトナー像をそのまま転写材に転写できる。従って、前記磁性トナーを使用した画像形成方法では、良好な現像性を示し、画像品質も高い画像を得ることができる。
また、前記磁性トナーは、その形状が球形であり、磁性粉体が表面に露出していないことから流動性が良く、磁性トナー同士又は磁性トナーと各部材等との摩擦により劣化することがなく、かつ各部材等を摩擦によって損傷することもないので、高品質の画像を安定して形成することができる。
また、前記磁性トナーは、現像同時クリーニング画像形成方法あるいはクリーナレス画像形成方法にも好ましく適用される。
【０１５７】
また、前述した磁性トナーにおけるトナー粒子は、粒度分布がシャープであり、さらに磁性トナーの状態・組成も均一である。これらのことからトナー粒子の帯電速度、帯電量分布が揃い、転写残トナーも少ない。
また、前述したトナー粒子の製造方法により、前記トナー粒子を効率良く製造することが可能である。
【０１５８】
本発明に係わる各種物性データの測定法を以下に詳述する。
（１）磁性トナーの平均円形度とモード円形度
本発明における平均円形度及びモード円形度とは、粒子の形状を定量的に表現する簡便な方法として用いたものであり、本発明では東亜医用電子製フロー式粒子像分析装置ＦＰＩＡ−１０００を用いて測定を行い、３μｍ以上の粒径のトナー粒子群について測定された粒子の円形度を下記式２より求め、さらに下記式３で示されるように、測定された全粒子の円形度の総和を全粒子数（ｍ）で除した値を平均円形度（Ｅ_mean）と定義する。
【０１５９】
【式２】
円形度Ｅ＝Ｌ₀／Ｌ
（式中、Ｌ₀は粒子像と同じ投影面積をもつ円の周囲長を示し、Ｌは粒子の投影像の周囲長を示す。）
【０１６０】
【式３】

また、モード円形度とは、円形度を０.４０から１.００までを０.０１毎に６１分割し、測定した磁性トナーの円形度を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。
【０１６１】
なお、前記分析装置である「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あたって、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。
【０１６２】
具体的な測定方法としては、界面活性剤を約０.１ｍｇ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整し、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以上の粒径のトナー粒子群の平均円形度及びモード円形度を求める。
【０１６３】
本発明における平均円形度とは、現像剤の凹凸の度合いの指標であり、現像剤が完全な球形の場合１．０００を示し、現像剤の表面形状が複雑になるほど平均円形度は小さな値となる。
なお、本測定において３μｍ以上の粒径のトナー粒子群についてのみ円形度を測定する理由は、３μｍ未満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等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のみについての円形度が正確に見積もれない場合があることによる。
【０１６４】
（２）トナー粒子表面に存在する炭素元素の含有量（Ａ）に対する鉄元素の含有量（Ｂ）の比（Ｂ／Ａ）
本発明に係わる、トナー粒子表面に存在する炭素元素の含有量（Ａ）に対する鉄元素の含有量（Ｂ）の比（Ｂ／Ａ）は、ＥＳＣＡ（Ｘ線光電子分光分析）により表面組成分析を行い算出する。この際、測定される磁性トナーを超音波洗浄し、トナー粒子表面に付着している付着物等を除去した後、洗浄されたトナー粒子を磁気力で分離し、乾燥した後に測定することが好ましい。
本発明では、ＥＳＣＡの装置および測定条件は、下記の通りである。
使用装置：ＰＨＩ社製 １６００Ｓ型 Ｘ線光電子分光装置

本発明では、測定された各元素のピーク強度から、ＰＨＩ社提供の相対感度因子を用いて表面原子濃度を算出する。本測定は磁性トナーを超音波洗浄し、磁性トナー表面に付着している無機微粉体等の外添剤を除去したのち、磁気力にて分離し、乾燥し測定する。前記外添剤を除去しにくい場合は、イソプロパノール等、磁性トナーが溶解しない有機溶剤中にて超音波洗浄を行う。
【０１６５】
（３）定着画像のカブリの測定方法
カブリの測定は、東京電色社製のＲＥＦＬＥＣＴＭＥＴＥＲ ＭＯＤＥＬ ＴＣ−６ＤＳを使用して測定する。
フィルターとしてはグリーンフィルターを用い、下記式４より算出した。数値が小さい程、カブリが少ない。
【０１６６】
【式４】
カブリ（反射率）（％）＝
標準紙上の反射率（％）−サンプル非画像部の反射率（％）
【０１６７】
（４）酸価の測定方法
本発明におけるポリエステル樹脂の酸価は以下の方法で求められる。
ポリエステル樹脂２〜１０ｇを２００ｍＬの三角フラスコに秤量して入れ、さらにこの中にメタノール：トルエン＝３０：７０の混合溶媒約５０ｍＬを加えて磁性トナー又はトナー粒子を溶解させる。そして、０.１％のブロムチモールブルーとフェノールレッドの混合試薬と用い、予め標亭された．１Ｍ−水酸化カリウム／エタノール溶液に滴定し、水酸化カリウム／エタノール溶液の消費量から下記式５より酸価を求める。
【０１６８】
【式５】

（上記式中ｆは、０.１Ｍ−水酸化カリウム／エタノール溶液のファクターである。）
【０１６９】
【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。
【０１７０】
まず磁性体（磁性粉体）の製造例について以下に説明する。
（表面処理磁性体の製造例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及び珪酸ソーダを混合し、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。
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に維持して、空気を吹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に調製し、十分攪拌しながらシランカップリング剤（ｎ−Ｃ₁₀Ｈ₂₁Ｓｉ（ＯＣＨ₃）₃）を磁性酸化鉄に対し１.２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、表面処理磁性体１を得た。
【０１７１】
（磁性体の製造例１）
表面処理磁性体の製造例１と同様に酸化反応を進め、酸化反応後に生成した磁性酸化鉄粒子を洗浄、濾過後、表面処理を行わずに、乾燥し、凝集している粒子を解砕処理し、磁性体１を得た。
【０１７２】
（表面処理磁性体の製造例２）
磁性体の製造例１で得られた磁性体１を、別の水系媒体中に再分散させた後、再分散液のｐＨを約６に調製し、十分攪拌しながらシランカップリング剤（ｎ−Ｃ₁₀Ｈ₂₁Ｓｉ（ＯＣＨ₃）₃）を磁性酸化鉄に対し１.２質量部添加し、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、次いで凝集している粒子を解砕処理して、表面処理磁性体２を得た。
【０１７３】
（表面処理磁性体の製造例３）
表面処理磁性体の製造例１に於いてシランカップリング剤を
（ｎ−Ｃ₆Ｈ₁₁Ｓｉ（ＯＣＨ₃）₃）とする以外は同様にして表面処理磁性体３を得た。
【０１７４】
（表面処理磁性体の製造例４）
磁性体の製造例１で得られた磁性体１を、磁性体１に対し１.２質量部のシランカップリング剤（ｎ−Ｃ₁₀Ｈ₂₁Ｓｉ（ＯＣＨ₃ ）₃）で気相中にて表面処理することにより、表面処理磁性体４を得た。
前述した製造例により得られた磁性体の平均粒径を表１に示す。
【０１７５】
【表１】

【０１７６】
次に、ポリエステル樹脂の製造例について以下に説明する。
（ポリエステル樹脂の製造例１）
温度計、攪拌機、冷却器および窒素導入管の付いた反応槽中にビスフェノールＡのＥＯ付加物（水酸基価３２０）４０３質量部、ビスフェノールＡのＰＯ付加物（水酸基価３００）２８７質量部、テレフタル酸３１２質量部およびジブチルチンオキサイド３質量部を入れて、窒素気流中で２３０℃で反応させた。反応物に透明感がでた時点で減圧下でポリエステル化反応を進め、酸価が１０になった時点で反応を停止しポリエステル樹脂１を得た。この樹脂のＴｇは５８℃、数平均分子量は５２００であった。
【０１７７】
（ポリエステル樹脂の製造例２）
温度計、攪拌機、冷却器および窒素導入管の付いた反応槽中にビスフェノールＡのＰＯ付加物（水酸基価３１６）６８１質量部、フマル酸２１８質量部およびジブチルチンオキサイド２.８質量部を入れて、窒素気流中で２３０℃で反応させた。反応物に透明感がでた時点で減圧下でポリエステル化反応を進め、酸価が１０になった時点で反応を停止しポリエステル樹脂２を得た。この樹脂のＴｇは５７℃、数平均分子量は５１００であった。
【０１７８】
（ポリエステル樹脂の製造例３）
ポリエステル樹脂の製造例１と同様の操作を行い、酸価２０になった時点で下記一般式（V）に示されるＳＦ８４１３（東レダウコーニング社製）を５０質量部添加しさらに反応を続け、酸価が１０になった時点で反応を停止しポリエステル樹脂３を得た。この樹脂のＴｇは５５℃、数平均分子量は５５００であった。＜ＳＦ８４１３の構造＞
【０１７９】
【化５】

【０１８０】
次に、前述した磁性体、及びポリエステル樹脂を用いたトナー粒子の製造例について、以下に説明する。
（トナー粒子の製造例１）
イオン交換水７２０質量部に０.１Ｍ−Ｎａ₃ＰＯ₄水溶液４５０質量部を投入し６０℃に加温した後、塩化カルシウム水溶液添加後のｐＨが５.１となるように１Ｎ塩酸を２１ｍＬ投入し、１.０Ｍ−ＣａＣｌ₂水溶液６７.７質量部を徐々に添加してリン酸カルシウム塩を含むｐＨ＝５.１の水系分散媒を得た。
スチレン ８０質量部
ｎ−ブチルアクリレート ２０質量部
ポリエステル樹脂１ ５質量部
負荷電性制御剤（モノアゾ染料系のＦｅ化合物） １質量部
表面処理磁性体１ １００質量部
上記処方をＴＫホモミキサー（特殊機化工業（株））を用いて均一に分散混合した。
この重合性単量体組成物を６０℃に加温し、そこにベヘニン酸ベヘニルを主体とするエステルワックス（ＤＳＣにおける吸熱ピークの極大値７２℃）１０質量部を添加混合溶解し、これに重合開始剤２,２'−アゾビス（２,４−ジメチルバレロニトリル）４質量部を溶解した。
前記水系分散媒中に上記重合性単量体系を投入し、６０℃、窒素雰囲気下においてＴＫ式ホモミキサー（特殊機化工業（株））にて１００００ｒｐｍ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６時間反応させた。その後液温を８０℃とし更に４時間撹拌を続けた。反応終了後、８０℃で更に２時間蒸留を行い、その後、懸濁液を冷却し、塩酸を加えてリン酸カルシウム塩を溶解し、濾過、水洗、乾燥して重量平均粒径６.８μｍ、数平均粒径６.１μｍのトナー粒子Ａを得た。
【０１８１】
（トナー粒子の製造例２）
トナー粒子の製造例１において、塩化カルシウム水溶液添加後のｐＨが６.０となるように投入する１Ｎ塩酸を１８ｍＬに変える以外は製造例１と同様に製造し、トナー粒子Ｂを得た。
【０１８２】
（トナー粒子の製造例３）
トナー粒子の製造例１において、塩化カルシウム水溶液添加後のｐＨが７.０となるように投入する１Ｎ塩酸を１３.５ｍＬに変える以外は製造例１と同様に製造し、トナー粒子Ｃを得た。
【０１８３】
（トナー粒子の製造例４）
トナー粒子の製造例１において、塩化カルシウム水溶液添加後のｐＨが８.５となるように投入する１Ｎ塩酸を９ｍＬに変える以外は製造例１と同様に製造し、トナー粒子Ｄを得た。
【０１８４】
（トナー粒子の製造例５）
トナー粒子の製造例１において、塩化カルシウム水溶液添加後のｐＨが４.５となるように投入する１Ｎ塩酸を３２ｍＬに変える以外は製造例１と同様に製造し、トナー粒子Ｅを得た。
【０１８５】
（トナー粒子の製造例６）
トナー粒子の製造例１において、塩化カルシウム水溶液を添加した後にｐＨが５.１となるように１Ｎ塩酸２１.５ｍＬを添加する以外は製造例１と同様に製造し、トナー粒子Ｆを得た。
【０１８６】
（トナー粒子の製造例７）
トナー粒子の製造例１において、塩化カルシウム水溶液に代えて塩化マグネシウムを使用する以外は製造例１と同様に製造し、トナー粒子Ｇを得た。
【０１８７】
（トナー粒子の製造例８）
トナー粒子の製造例１において、塩化カルシウム水溶液添加後のｐＨが６.０となるように投入する無機酸を１Ｎ塩酸に代えて１Ｎ硫酸を使用する以外は製造例１と同様に製造し、トナー粒子Ｈを得た。
【０１８８】
（トナー粒子の製造例９）
トナー粒子の製造例１において、塩化カルシウム水溶液添加後のｐＨが７.０となるように投入する無機酸を１Ｎ塩酸に代えて１Ｎ硝酸を使用し、重合開始剤を２,２'−アゾビス（２,４−ジメチルバレロニトリル）に代えてｔ−ブチルパーオキシ−２−エチルヘキサノエートを使用する以外は製造例１と同様に製造し、トナー粒子Ｉを得た。
【０１８９】
（トナー粒子の製造例１０）
トナー粒子の製造例１において、表面処理磁性体１に代えて表面処理磁性体２を使用する以外は製造例１と同様に製造し、トナー粒子Ｊを得た。
【０１９０】
（トナー粒子の製造例１１）
トナー粒子の製造例１において、表面処理磁性体１に代えて表面処理磁性体３を使用する以外は製造例１と同様に製造し、トナー粒子Ｋを得た。
【０１９１】
（トナー粒子の製造例１２）
トナー粒子の製造例１において、表面処理磁性体１に代えて表面処理磁性体４を使用する以外は製造例１と同様に製造し、トナー粒子Ｌを得た。
【０１９２】
（トナー粒子の製造例１３）
トナー粒子の製造例１において、ポリエステル樹脂１を５質量部使用することに代えてポリエステル樹脂２を２質量部使用する以外は製造例１と同様に製造し、トナー粒子Ｍを得た。
【０１９３】
（トナー粒子の製造例１４）
トナー粒子の製造例１において、ポリエステル樹脂１を５質量部使用することに代えてポリエステル樹脂１を９質量部とポリエステル樹脂２を１質量部使用する以外は製造例１と同様に製造し、トナー粒子Ｎを得た。
【０１９４】
（トナー粒子の製造例１５）
トナー粒子の製造例１において、ポリエステル樹脂１を５質量部使用することに代えてポリエステル樹脂３を２０質量部使用する以外は製造例１と同様に製造し、トナー粒子Ｏを得た。
【０１９５】
（トナー粒子の比較製造例１）
トナー粒子の製造例１において、塩化カルシウム水溶液添加後のｐＨが４.２となるように投入する１Ｎ塩酸を４０ｍＬに変える以外は製造例１と同様に製造し、トナー粒子Ｐを得た。
【０１９６】
（トナー粒子の比較製造例２）
トナー粒子の製造例１において、塩化カルシウム水溶液添加後のｐＨが８.７となるように投入する１Ｎ塩酸を７.５ｍＬに変える以外は製造例１と同様に製造し、トナー粒子Ｑを得た。
【０１９７】
（トナー粒子の比較製造例３）
トナー粒子の製造例１において、表面処理磁性体１に代えて磁性体１を使用する以外は製造例１と同様に製造し、トナー粒子Ｒを得た。
【０１９８】
（トナー粒子の比較製造例４）
トナー粒子の製造例１において、ポリエステル樹脂を使用しない以外は製造例１と同様に製造し、トナー粒子Ｓを得た。
【０１９９】
（トナー粒子の製造例１６）
トナー粒子の製造例１においてリン酸カルシウム塩を含むｐＨ＝５.１の水系分散媒を、０.５Ｍ−Ｎａ₃ＰＯ₄水溶液９０質量部を投入し６０℃に加温した後、塩化カルシウム水溶液添加後のｐＨが５.１となるように１Ｎ塩酸を２１ｍＬ投入し、１.０Ｍ−ＣａＣｌ₂水溶液６７.７質量部を徐々に添加して調製し、ドデシルベンゼンスルホン酸ナトリウム０.００５質量部を添加する以外は製造例１と同様に製造し、トナー粒子Ｔを得た。
【０２００】
（トナー粒子の比較製造例５）
トナー粒子の製造例１において、水系分散媒の調製方法を、イオン交換水５００部に塩化マグネシウム１９部を溶解した水溶液に、イオン交換水１００部に水酸化ナトリウム１１.６部を溶解した水溶液を攪拌下で徐々に添加して、水酸化マグネシウムコロイドを含むｐＨ＝１３.０の水系分散媒を得る以外は製造例１と同様に製造し、トナー粒子Ｕを得た。
【０２０１】
次に、前述したトナー粒子を用いた磁性トナーの製造例について、以下に説明する。
磁性トナーは、前記トナー粒子Ａ〜Ｕを１００質量部と、一次粒径１２ｎｍのシリカにヘキサメチルジシラザン処理した後シリコーンオイルで処理し、処理後のＢＥＴ値が１４０ｍ² ／ｇの疎水性シリカ微粉体１．２質量部とをヘンシェルミキサー（三井三池化工機（株））で混合して、トナー１〜２１を調製した。
得られた磁性トナーの磁場７９.６ｋＡ／ｍにおける磁化の強さは、いずれも２６〜３０Ａｍ²／ｋｇであった。
得られたトナー粒子の製造条件を表２及び表３に、磁性トナーの物性を表４及び表５にそれぞれ示す。なお、表２におけるｐＨ（１）は、金属塩コロイドを含み無機酸によってｐＨ調整された状態の水系分散媒のｐＨであり、表２におけるｐＨ（２）は、金属塩コロイドの素となる水溶液を混合して得られる水溶液のｐＨである。
【０２０２】
【表２】

【０２０３】
【表３】

【０２０４】
【表４】

【０２０５】
【表５】

【０２０６】
次に、前述したトナー１〜２１を用いて電子写真方式の画像形成装置による画像を異なる環境下で形成し、これらのトナーによって得られる画像の画質を評価した。
【０２０７】
（実施例１）
画像形成装置には、前記実施の形態において図１に示した画像形成装置に準ずる画像形成装置（ＬＢＰ−１７６０）を用いた。
像坦持体（感光体）としては有機感光体（ＯＰＣ）ドラムを用いた。この感光体に、一次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されたゴムローラ帯電器を当接させ（当接圧６０ｇ／ｃｍ）、直流電圧−７００Ｖｄｃ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。一次帯電に次いで、レーザー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＝−７００Ｖ、明部電位ＶＬ＝−１８０Ｖとした。
感光ドラムと現像スリーブとの間隙は２９０μｍとし、トナー担持体として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、表面をブラストした直径１６φのアルミニウム円筒上に形成した現像スリーブを使用し、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１.０ｍｍのシリコーンゴム製ブレードを２４.５Ｎ／ｍ（２５ｇ／ｃｍ）の線圧で当接させた。
フェノール樹脂 １００部
グラファイト（粒径約７μｍ） ９０部
カーボンブラック １０部
次いで、現像バイアスとして直流バイアス成分Ｖｄｃ＝−５００Ｖ、重畳する交流バイアス成分Ｖｐ−ｐ＝１７００Ｖ、ｆ＝２０００Ｈｚを用いた。また、現像スリーブの周速は感光体周速（９４ｍｍ／ｓｅｃ）に対して順方向に１１０％のスピード（１０３ｍｍ／ｓｅｃ）とした。
また、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。
定着方法としてはＬＢＰ−１７６０のオイル塗布機能のない、フィルムを介してヒーターにより加熱加圧定着する方式の定着装置を用いた。この時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であった。また、定着温度は１８５℃、ニップ幅を７ｍｍに設定した。
まず、現像剤としてトナー１を使用し、常温常湿（２５℃、６０％ＲＨ）、高温高湿（３０℃、８０％ＲＨ）、及び低温低湿（１５℃、１０％ＲＨ）環境下において画出し試験を行った。転写材としては７５ｇ／ｍ²の紙を使用した。その結果、初期において高い転写性を示し、文字やラインの転写中抜けもなく、非画像部へのカブリのない良好な画像が得られた。
【０２０８】
次に、印字面積比率４％の横ラインからなる格子画像パターンで耐久性の評価を行った。
画像評価は以下のように行った。
感光体の削れ及びトナー融着の評価は、画像不良が現れやすいハーフトーン画像上に、削れあるいはトナー融着による画像不良、即ち黒点あるいは白抜けが発生した耐久枚数で判断した。発生するまでの耐久枚数が多い程、画像形成方法の耐久性が良好なことを意味する。加えて、転写残トナーによる一次帯電不良に起因する画像不良、即ち帯電ムラもハーフトーン画像上で評価した。これらの画像不良が発生しない場合は印字枚数５０００枚まで耐久試験を続けた。
本実施例においては、連続モード（すなわち、連続して通紙することでトナーの消費を促進させるモード）で５０００枚のプリントアウト試験を行なった。
【０２０９】
画像評価は以下のように行った。
（１）画像濃度
通常の複写機用普通紙（７５ｇ／ｍ²）に５０００枚プリントアウト終了時の画像濃度維持により評価した。尚、画像濃度は「マクベス反射濃度計 ＲＤ９１８」（マクベス社製）を用いて、原稿濃度が０.００の白地部分のプリントアウト画像に対する相対濃度を測定した。
Ａ（優） ：１.４０以上
Ｂ（良） ：１.３５以上、１.４０未満
Ｃ（可） ：１.００以上、１.３５未満
Ｄ（不可）：１.００未満
【０２１０】
（２）画像カブリ
「ＲＥＦＬＥＣＴＭＥＴＥＲ ＭＯＤＥＬ ＴＣ−６ＤＳ」（東京電色社製）により測定したプリントアウト画像の白地部分の白色度と転写紙の白色度の差から、カブリ濃度（％）を算出し、画像カブリを評価した。フィルターは、グリーンフィルターを用いた。
Ａ：非常に良好（１.５％未満）
Ｂ：良好 （１.５％以上乃至２.５％未満）
Ｃ：普通 （２.５％以上乃至４.０％未満）
Ｄ：悪い （４％以上）
【０２１１】
（３）転写性
転写性はベタ黒画像形成時の感光体上の転写残トナーを、マイラーテープによりテーピングしてはぎ取り、はぎ取ったマイラーテープを紙上に貼ったもののマクベス濃度から、マイラーテープのみを紙上に貼ったもののマクベス濃度を差し引いた数値で評価した。
Ａ：非常に良好（０.０５未満）
Ｂ：良好（０.０５以上乃至０.１未満）
Ｃ：普通（０.１以上乃至０.２未満）
Ｄ：悪い（０.２以上）
初期濃度は初期から２０枚目の画像濃度とした。
【０２１２】
（４）ハーフトーン画像の均一性
画質の判断基準は以下の通りである。
Ａ：非常に良好。
Ｂ：わずかにがさついているものの、良好な画像。
Ｃ：がさついているものの、実用上問題の無いレベル。
Ｄ：がさつきがひどく、実用不可。
得られた結果を表６〜表８に示す。
【０２１３】
（実施例２）
現像剤としてトナー２を使用し、実施例１と同様に評価したところ、表６〜表８に示す様に非常に良好な結果が得られた。
【０２１４】
（実施例３〜１６）
現像剤としてトナー３、４、５、６、７、８、９、１０、１１、１２、１３、１４、１５、２０を使用し、実施例１と同様に評価した。その結果、表６〜表８に示す様に実用的に問題の無い結果が得られた。
【０２１５】
（比較例１）
現像剤としてトナー１６を使用し、実施例１と同様に評価した。その結果、転写性が悪く、飛び散りが多く鮮鋭性の低い画像となった。結果を表６〜表８に示す。
【０２１６】
（比較例２）
現像剤としてトナー１７を使用し、実施例１と同様に評価した。その結果、カブリが多くガサつきの多い画像となった。結果を表６〜表８に示す。
【０２１７】
（比較例３）
現像剤としてトナー１８を使用し、実施例１と同様に評価した。その結果、初期からやや画像濃度が低く、転写残、カブリも多く、耐久試験を最後まで継続することが不可能であった。結果を表６〜表８に示す。
【０２１８】
（比較例４）
現像剤としてトナー１９を使用し、実施例１と同様に評価した。その結果、初期から画像濃度が極端に低く、転写残、カブリも多いため、試験を実施することが不可能であった。結果を表６〜表８に示す。
【０２１９】
（比較例５）
現像剤としてトナー２１を使用し、実施例１と同様に評価した。その結果、初期から画像濃度が低く、転写残、カブリも多く、画像の品質が低いものであった。結果を表６〜表８に示す。
【０２２０】
【表６】

【０２２１】
【表７】

【０２２２】
【表８】

【０２２３】
【発明の効果】
本発明によれば、円形度が０.９７０以上であり、トナー粒子表面における炭素元素含有量に対する鉄元素含有量の比である鉄元素含有量／炭素元素含有量が０.００１未満であり、かつ磁場７９.６ｋＡ／ｍにおける磁化の強さが１０〜５０Ａｍ²／ｋｇである特殊な磁性トナーを用いることにより、環境安定性に優れ、環境の差に依らず、高品位で解像性の高い画像が長期間安定して得られる。
さらには、本発明のトナー粒子の製造方法によれば、前述のように高品質な画像を出力可能な磁性トナーを効率良く提供することが可能である。
【図面の簡単な説明】
【図１】本発明の画像形成装置における一実施の形態を示す図である。
【図２】図１の感光ドラム及び現像器周辺を拡大して示す図である。
【図３】図１の感光ドラム及び転写帯電ローラ周辺を拡大して示す図である。
【符号の説明】
３４ａ 芯金
３４ｂ 弾性層
３５ 転写帯電装置
１００ 感光ドラム（像担持体）
１０２ 現像スリーブ（現像剤担持体）
１０３ 弾性ブレード
１０４ マグネットローラ
１１４ 転写帯電ローラ
１１６ クリーナ
１１７ 一次帯電ローラ
１２１ レーザー発生装置（露光装置）
１２３ レーザー光
１２４ レジスタローラ
１２５ 搬送ベルト
１２６ 定着器
１４０ 現像器（現像装置）
１４１ 攪拌部材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic toner for use in a recording method such as an electrophotographic method, an electrostatic recording method, a magnetic recording method, and a toner jet method, a method for producing toner particles constituting the magnetic toner, and image formation using the magnetic toner. The present invention relates to a method and an image forming apparatus used in the image forming method.
[0002]
[Prior art]
Electrophotographic image forming apparatuses such as printers and copiers are required to have a higher resolution and higher definition image forming capability. For example, LED and LBP printers have become mainstream in the recent market for printer devices, and higher resolutions in the direction of technology, that is, conventional 300 and 600 dpi have become 1200 and 2400 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. This digitalization mainly involves forming a latent electrostatic image with a laser, so it is also progressing in the direction of high resolution. Here, as with printers, high resolution and high definition development methods are required. ing.
[0003]
As an electrophotographic technique used in the image forming apparatus, there are many methods as described in US Pat. No. 2,297,691, Japanese Patent Publication No. 42-23910 and Japanese Patent Publication No. 43-24748. It has been known. In general, a photoconductive substance is used to form an electrostatic latent image on a photoconductor by various means, and then the electrostatic latent image is developed with toner, and transferred to paper or film as necessary. After the toner image is transferred to the material, it is fixed by heating, pressure, heating and pressurization or solvent vapor to obtain a toner image.
[0004]
As the developing method, there are known a one-component developing method using only toner as a developer and a two-component developing method using a two-component developer in which a toner and a carrier are mixed at a constant ratio. As a two-component development method, a cascade development method, a magnetic brush development method, a pressure development method, and the like are known. Further, there is a method in which a rotating sleeve having a magnetic pole at the center is used and a toner having a magnetic material is used. The toner is attached to the rotating sleeve by a magnetic force, and the toner is ejected from the rotating sleeve onto the photosensitive member by an electric field. It is used.
[0005]
In the two-component development method, since it is necessary to keep the toner concentration in the carrier constant, a device for detecting the toner concentration and supplying a necessary amount of toner is required, and the developing device becomes large and heavy. In contrast, the one-component development method does not require a carrier such as glass beads or iron powder as in the two-component development method, and therefore does not require a device for controlling the toner concentration. There is an advantage that can be made small and light.
[0006]
Further, as the developing method, a developing method using a conductive magnetic toner having conductivity and a developing method using a high-resistance insulating magnetic toner are known. As a developing method using a conductive magnetic toner, for example, a developing method proposed in US Pat. No. 3,909,258 is known. In this method, conductive magnetic toner is deposited on a cylindrical conductive rotating sleeve having magnetism inside, and this is brought into contact with an electrostatic latent image for development. At this time, in the developing unit, a conductive path is formed by toner particles between the surface of the photoreceptor on which the electrostatic latent image is formed and the surface of the rotating sleeve, and electric charges are guided to the toner particles from the rotating sleeve through this conductive path. The toner particles adhere to the image portion by the Coulomb force between the surface of the photoreceptor on which the electrostatic latent image is formed and the electrostatic latent image is developed.
[0007]
The developing method using the conductive magnetic toner is an excellent method that avoids the problems associated with the conventional two-component developing method. However, since the toner is conductive, the developed image is usually removed from the photoreceptor. There is a problem that it is difficult to electrostatically transfer to a final transfer material such as paper.
[0008]
On the other hand, the developing method using the insulating magnetic toner is superior to the developing method using the conductive magnetic toner in that it can be electrostatically transferred to the final transfer material. As a developing method using an insulating magnetic toner, for example, there is a developing method using dielectric polarization of toner particles. However, this method has problems such as a slow development speed or insufficient density of a developed image, and is difficult in practical use.
[0009]
As another development method using an insulating magnetic toner, there is known a method in which toner particles are frictionally charged by friction between toner particles, friction between toner particles and a rotating sleeve, and the like, and then contact the photosensitive member for development. It has been. However, in this method, the number of contact between the toner particles and the friction member is small, and the magnetic toner used has a lot of magnetic material exposed on the surface of the toner particles. There were problems such as.
[0010]
Further, as another developing method using an insulating magnetic toner, a jumping developing method is proposed in Japanese Patent Application Laid-Open No. 55-18656. In this method, a magnetic toner is applied very thinly on a rotating sleeve, and this is triboelectrically charged. Then, the toner is ejected in close proximity to the surface of the photoreceptor and developed. This method is excellent in that the magnetic toner is thinly applied on the rotating sleeve, thereby increasing the chance of contact between the rotating sleeve and the toner and enabling sufficient frictional charging.
[0011]
However, the developing method using the insulating magnetic toner has unstable elements related to the insulating magnetic toner to be used. That is, a considerable amount of fine powdery magnetic powder is mixed and dispersed in the insulating magnetic toner, and the dispersion state of the magnetic powder in the toner particles affects the flowability and triboelectric charging property of the magnetic toner, As a result, it may cause fluctuation or deterioration of various characteristics required for the magnetic toner such as development characteristics and durability of the magnetic toner.
[0012]
It is considered that the above-mentioned problem occurs in the developing method using the insulating magnetic toner because the magnetic powder is exposed on the surface of the magnetic toner. That is, a magnetic powder having a relatively low resistance compared to the resin constituting the toner particles is exposed on the surface of the magnetic toner, so that the toner charging performance is lowered, the toner fluidity is lowered, and the toner is deteriorated. Is caused. The deterioration of the toner is caused by peeling of the magnetic powder by rubbing between toners or a regulating member that regulates the amount of toner adhering to the surface of the rotating sleeve in long-term use. It is known to cause unevenness.
[0013]
On the other hand, in order to achieve high resolution and high definition of an image obtained by the development method described above, it is required to reduce the toner particle size. However, when the toner particle size is reduced, the variation in the physical properties of the toner particles tends to increase. Therefore, it is important to produce toner particles having a small particle size and stable physical properties in order to stably achieve a high-resolution and high-definition developing method. Proposals have been made.
[0014]
As a toner manufacturing method, for example, a pulverization method is known. This pulverization method is a method in which a binder resin, a colorant and the like are melt-mixed and uniformly dispersed, then pulverized by a fine pulverizer and classified by a classifier to obtain a toner having a desired particle size. In the pulverization method, the selection range of materials is limited. For example, in the pulverization method, the resin colorant dispersion must be sufficiently brittle and can be 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 ( There arises a problem that excessively pulverized particles) are included therein. Further, such highly brittle materials are often further pulverized or powdered when used as developing toners in copying machines and the like.
[0015]
Also, in the pulverization method, it is difficult to completely and uniformly disperse solid fine particles such as magnetic powder or colorant in the resin, and depending on the degree of dispersion, it may cause an increase in fog and a decrease in image density. Become. Furthermore, the pulverization method inherently exposes the magnetic powder on the surface of the toner, so that problems still remain in the fluidity of the toner and the charging stability in a harsh environment.
[0016]
That is, in the pulverization method, it is difficult to produce toner particles having a substantially constant particle diameter, and it is difficult to control the distribution state of the magnetic powder in the toner particles. For this reason, the charging uniformity and fluidity of the toner are remarkably attenuated, a good toner cannot be obtained, and it is difficult to produce toner particles required for high definition and high image quality.
[0017]
As a method for overcoming the problems of the toner by the pulverization method as described above, a toner production method by a suspension polymerization method has been proposed.
In the suspension polymerization method, a water-insoluble polymerizable monomer and a polymerization initiator are dispersed in an aqueous dispersion medium to form droplets of the polymerizable monomer composition, and in the droplet state, a polymerizable monomer is used. This is a method of polymerizing a monomer. The toner by suspension polymerization (hereinafter referred to as “polymerized toner”) can be easily made into fine particles of toner, and further, since the shape of the obtained toner is spherical, it has excellent fluidity and is advantageous for high image quality. It becomes.
[0018]
However, in the case of producing magnetic toner particles by the suspension polymerization method, if the polymerizable monomer composition contains a magnetic powder, the fluidity and charging characteristics of the obtained magnetic toner are significantly reduced. This is because the magnetic powder is generally hydrophilic and thus tends to be present on the surface of the toner particles during polymerization, and the magnetic powder is exposed on the surface of the obtained magnetic toner. In order to solve this problem, it is important to modify the surface characteristics of the magnetic powder.
[0019]
Many proposals have been made regarding surface modification for improving the dispersibility of magnetic powder in polymerized toner. 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 these treatments improve the dispersibility of the magnetic powder in the toner, there is a problem in that the chargeability, charging stability and uniformity of the toner are not necessarily controlled. That is, in the polymerized toner, the suspension granulation / polymerization stability of the polymerized toner is not only a productive factor, but also has an extremely important influence on the toner physical properties. The polymerization conditions cause particle coalescence / aggregation, significantly impairing the particle size distribution, particle shape / surface state, and lowering the triboelectric chargeability.
[0021]
For this reason, many proposals have been made on toner particle production methods aimed at the stability of suspension granulation, the prevention of coalescence of particles during polymerization, and the sharpening of the particle size distribution of the produced particles. For example, the method of controlling the particle size distribution by using a dispersant and an anionic surfactant in JP-A-57-42052, JP-A-57-41649, JP-B-1-55643, JP-A-7-165847, etc. Many methods for adjusting the particle size by adding an aqueous phase polymerization inhibitor are proposed.
[0022]
However, the former has disadvantages such as residual surface activity, the triboelectric charging property of the toner particles becomes unstable, and the development characteristics of the toner particles are remarkably deteriorated. The latter has advantages such as the removal of by-product emulsion polymerized fine particles. However, the problem is that microsuspension particles that are problematic as fine particles are generated, and the particle size distribution of the toner particles is significantly impaired. Clogging and frictional charging non-uniformity are easily induced.
[0023]
On the other hand, many proposals have been made to improve the particle size distribution of the polymerized toner by improving the dispersion stabilizer that stabilizes the dispersion state of the droplets of the polymerizable monomer composition during suspension polymerization. For example, as typified by JP-A-9-54457, JP-A-7-49586, etc., the produced dispersion stabilizer is once solubilized with an acid and then reprecipitated with an alkali (pH 7 to 12). There are proposals such as a method of obtaining a desired dispersion stabilizer under an alkali and using this to obtain polymerized toner particles having a sharp particle size distribution. However, at present, the control including the toner particle shape, the charging property of the toner, the surface property, etc. is required. This proposal is not sufficient and cannot satisfy all the required physical properties.
[0024]
Japanese Patent Application Laid-Open No. 7-301949 describes a method of directly producing calcium phosphate as a dispersion stabilizer in an aqueous dispersion medium by mixing an aqueous sodium phosphate solution and an aqueous calcium chloride solution. This method is an excellent method for adjusting the particle shape of the toner particles, but when an aqueous dispersion medium is produced with the composition described in the publication and applied to a toner containing magnetic powder, A large amount of fine powder is generated, and the particle size distribution of the toner is not necessarily sharp, which adversely affects the chargeability in general.
[0025]
Further, JP-A-10-198067 describes a method of using a poorly water-soluble compound as a dispersion stabilizer in the range of pH 5.5 to 8.5. This method is an excellent method for adjusting the particle shape and particle size distribution of toner particles. However, as it is, a large amount of magnetic powder is present on the surface of the toner particles, and the charging required for development under high temperature and high humidity. I can't get the amount.
[0026]
As described above, in order to overcome various problems in the magnetic toner, in addition to controlling the particle shape and particle size distribution of the toner particles, it is necessary to suppress the exposure of the magnetic powder to the toner particle surface. It becomes. Specific means includes surface modification of the magnetic material, which is as described above.
[0027]
Furthermore, it is also known to add a polar resin when producing a polymerized toner (JP-A-8-286416). This method is an excellent method for suppressing the exposure of the magnetic powder on the surface of the toner particles, but this alone does not result in a sharp toner particle size distribution. I was never satisfied with sex.
[0028]
In addition, when the toner is produced by suspension polymerization, the concentration ratio of the dispersoid and the dispersion medium is also known to be involved in the particle size distribution of the obtained toner particles. In addition, there is no known proposal that states that charging performance is improved thereby.
[0029]
As described above, the actual condition is that sufficient study has not been made on an efficient toner manufacturing method that makes the toner particle size distribution sharp and satisfies charging stability and charging uniformity. .
[0030]
[Problems to be solved by the invention]
One object of the present invention is that it is less influenced by the environment, has a stable and uniform charging performance, has no fog, has a high image density even during long-term use, has a good transferability, and has an image reproducibility. It is an object of the present invention to provide an excellent magnetic toner and a method for efficiently producing toner particles constituting the magnetic toner.
Another object of the present invention is to provide a higher quality and higher resolution image regardless of environmental differences in an electrophotographic system or the like.
[0031]
[Means for Solving the Problems]
  The present invention relates to a method for producing toner particles having at least a binder resin, a magnetic powder whose surface is hydrophobized, and a polyester resin, and an aqueous dispersion medium comprising a hardly water-soluble metal salt colloid as a dispersion stabilizer The polymerizable monomer comprising at least a polymerizable monomer that forms the binder resin by polymerization, a magnetic powder having a hydrophobic surface, and a polyester resin. The monomer composition is dispersed in the pH-adjusted aqueous dispersion medium, droplet particles of the polymerizable monomer composition are generated in the aqueous dispersion medium, and the polymerizable monomer in the droplet particles is dispersed. Polymerization in the presence of a polymerization initiatorThe magnetic powder whose surface is hydrophobized is hydrophobized in an aqueous medium without drying the magnetic iron oxide particles generated from ferrous hydroxide. Magnetic iron oxide particlesThis is a method for producing toner particles.
[0034]
DETAILED DESCRIPTION OF THE INVENTION
In the method for producing toner particles of the present invention, at least a polymerizable monomer is contained in an aqueous dispersion medium containing a hardly water-soluble metal salt colloid as a dispersion stabilizer and having a pH adjusted to 4.5 to 8.5. A polymerizable monomer composition containing a hydrophobized magnetic powder and a polyester resin is dispersed to form droplet particles of the polymerizable monomer composition, and a polymerization initiator at an arbitrary stage before polymerization. Is added to the system to polymerize the polymerizable monomer component contained in the droplet particles, the particle size distribution is sharp, the shape is spherical, and the distribution is uniform. Toner particles having an extremely uniform surface composition can be obtained. In addition, since the surface state and shape of the obtained toner particles are uniform, the chargeability is also uniform. For example, good developability is exhibited even when developing an electrostatic latent image in an electrophotographic process. Furthermore, the resulting toner particles are similarly charged under high temperature and high humidity and low temperature and low humidity due to the surface condition and surface composition, and exhibit good developability regardless of the environment.
[0035]
In the method for producing toner particles of the present invention, a normal method for producing toner particles using a polymerization reaction can be used as long as the production method of the present invention described above is established. As the method for producing the toner particles of the present invention, for example, an emulsion polymerization method, an emulsion association polymerization method, a suspension polymerization method, a dispersion polymerization method, and the like can be used. Among them, the suspension polymerization method is preferably used in the present invention. It is efficient and preferable in obtaining toner particles having a diameter and a preferable average circularity. In addition, the polymerizable monomer composition includes generally usable toner compositions such as a release agent, a plasticizer, a charge control agent, a cross-linking agent, and a colorant as the case may be. Additives, for example, an organic solvent, a high molecular weight polymer, a dispersing agent and the like which are added in order to reduce the viscosity of the polymer produced by the polymerization reaction may be appropriately added.
[0036]
In the method for producing toner particles of the present invention, when the polymerizable monomer composition is dispersed in the aqueous dispersion medium, it is uniformly dissolved by a dispersing machine such as a homogenizer, a ball mill, a colloid mill, a dissolver, or an ultrasonic dispersing machine. Alternatively, the dispersed polymerizable monomer composition is suspended in an aqueous medium containing a dispersion stabilizer. At this time, it is preferable to use a high-speed disperser such as a high-speed stirrer or an ultrasonic disperser at a stretch to obtain a desired toner particle size in order to sharpen the particle size distribution of the obtained toner particles. After granulation in which the polymerizable monomer composition becomes droplet particles, stirring may be performed to such an extent that the particle state of the droplet particles is maintained and the droplet particles are prevented from floating and settling.
[0037]
In the polymerization reaction in the method for producing toner particles of the present invention, the reaction temperature of the polymerization reaction is determined by the physical properties of the compound contained in the polymerizable monomer composition, the physical properties of the polymerization initiator used, and the like. As described above, the polymerization is generally performed at a temperature of 50 to 90 ° C. When the polymerization is carried out in this temperature range, for example, when the above-mentioned release agent is contained in the polymerizable monomer composition, the release agent or wax to be sealed inside is precipitated by phase separation and contained. Will become more complete. Further, 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.
[0038]
After the polymerization, the toner particles produced by the polymerization are filtered, washed and dried by a known method, and the inorganic fine powder is mixed and adhered to the surface to obtain a magnetic toner. For example, since the toner particles produced in the present invention are in a state in which a slightly water-soluble metal salt colloid is adhered to the surface as it is, the pH of the aqueous dispersion medium containing the produced toner particles is adjusted to 0.8 to 3.0. The toner particles can be obtained by adjusting to a certain degree, completely dissolving the metal salt colloid, taking out the toner particles by a method such as filtration, repeatedly washing with water and drying.
In addition, it is also a desirable form of the present invention that a classification step is included in the toner particle production process to cut coarse powder and fine powder.
Hereinafter, the method for producing toner particles of the present invention will be described in detail.
[0039]
For the dispersion stabilizer in the present invention, a hardly water-soluble metal salt colloid is used. The metal salt colloid adheres so as to cover the surface of the droplet particles of the polymerizable monomer composition produced in the aqueous dispersion medium, and suppresses the fragmentation and coalescence of the particles. The mechanism is not completely elucidated, but can be inferred from general facts as follows.
[0040]
The colloid particle diameter is several nanometers to several hundred nanometers, which is very small compared to the droplet particles, and has a stable electric double layer, so that the droplet particle surface is coated after adhering to the droplet particle surface. In this way, a stable electric double layer is formed, an electric repulsive force is generated, and a colloidal particle adheres to form a protective layer to suppress the breakage of the droplet particle or the droplet particle due to steric repulsion. It is thought that deterrence of union.
[0041]
The metal atom constituting the metal salt colloid is not particularly limited as long as it is a poorly water-soluble salt. Among them, alkaline earth metals such as magnesium and calcium are preferable, and calcium is more preferable. As the metal salt colloid, a phosphate metal salt colloid of these metal atoms and phosphoric acid is preferable. Further, the metal salt colloid varies depending on the type of metal salt colloid, colloid particle size, colloid particle concentration, etc., but when dispersing the polymerizable monomer composition, it is based on 100 parts by mass of the polymerizable monomer composition. 0.1 to 5 parts by mass are preferably present in the aqueous dispersion medium. If the amount of the metal salt colloid is too small than the above range, the amount of the protective colloid may be insufficient and stable droplet particles may not be obtained. If the amount is too large, the viscosity of the dispersion medium increases. The particle size distribution of the obtained toner particles may be extremely broad.
[0042]
The phosphate metal salt colloid has a large intramolecular polarization due to its molecular skeleton and a large number of atoms as adsorption points. Furthermore, since the phosphorus atom, which is one of the adsorption points, has a relatively large atomic radius among the atoms having an electron-accepting adsorption point, it becomes a soft base in the HSAB rule and has an affinity for the droplets mainly composed of organic compounds Is relatively high compared to other atoms. Therefore, the interaction between the droplet particles and the organic compound is moderate, and the droplet particles are efficiently protected. Furthermore, since it is a colloidal particle, the surface area is large with respect to the mass of the particle, and the ability to form a protective layer is also high.
[0043]
Specific examples of the dispersion stabilizer include magnesium phosphate, magnesium hydrogen phosphate, magnesium dihydrogen phosphate, aluminum phosphate, zinc phosphate, calcium phosphate, calcium hydrogen phosphate, calcium dihydrogen phosphate, hydroxy Examples thereof include apatite and the like, and a mixture of the above-mentioned compounds, preferably calcium phosphate salts containing phosphoric acid and calcium. In consideration of effects such as the crystal size of these salts, the particle size of crystal aggregates, and the solubility in acids, a mixture of the above compounds containing hydroxyapatite and calcium phosphate is preferable. Furthermore, hydroxyapatite or a mixture of hydroxyapatite and calcium phosphate is more preferable.
[0044]
The means for dispersing the calcium phosphates in the aqueous dispersion medium is not particularly limited, but a method of using the calcium phosphate salts in the aqueous dispersion medium by mixing the aqueous phosphate solution and the aqueous calcium salt solution is used as an aggregate. Therefore, it is most effective when used as a dispersion stabilizer for the droplet particles, and is preferable because a stable suspended state of the droplet particles can be obtained. When powdered calcium phosphate salts are used as they are, they tend to form strong agglomerates as powder, so that the colloidal particle size becomes non-uniform and dispersion in an aqueous dispersion medium is quite difficult. Furthermore, as an advantage of the method of producing calcium phosphate salts in an aqueous medium, water-soluble neutral salts that are by-produced simultaneously with the calcium phosphate salts are effective in preventing the dissolution of the polymerizable monomer composition in water and the aqueous dispersion medium. And having an effect of increasing the specific gravity.
[0045]
The phosphate aqueous solution and the calcium salt aqueous solution to be used are not particularly limited, but the phosphate aqueous solution is preferably a sodium phosphate aqueous solution, and the calcium salt aqueous solution is preferably a calcium chloride aqueous solution. Moreover, it is preferable that pH of the aqueous dispersion medium in the stage which mixed phosphate aqueous solution and calcium salt aqueous solution is 7-14, and it is more preferable that it is 9-14.
[0046]
Here, the pH adjustment of the aqueous dispersion medium during the production of the metal salt colloid and the pH adjustment of the aqueous dispersion medium before the dispersion of the polymerizable monomer composition will be described.
The aqueous dispersion medium can control the size, particle concentration, crystal structure, etc. of the metal salt colloid by adjusting the pH during the production of the metal salt colloid, and before the dispersion of the polymerizable monomer composition. It has been clarified by the present inventors that the stability of the droplet particles is increased by adjusting the pH to 4.5 to 8.5. These reasons have not been fully elucidated so far, but the present inventors consider as follows.
[0047]
Hereinafter, an apatite (apatite) will be described as an example.
Apatite is produced by first producing tricalcium phosphate and then crystallizing it. At that time, it is known that the transition is remarkably around pH 9 to 10, and the apatite crystals are easy to grow. Here, by shifting the pH to the acidic side, the transition state of tricalcium phosphate to apatite changes, or the transition rate is slowed to increase the abundance ratio of tricalcium phosphate. That is, by controlling the pH in this way, the crystal structure and crystal size of the metal salt colloid change, thereby changing the potential and thickness of the electric double layer surrounding the droplet particles. As a result, since the interaction between the metal salt colloid and the droplet particles of the polymerizable monomer composition becomes moderate, it is considered that the stabilization effect of the droplet particles is increased.
[0048]
In addition, as described above, since apatite crystal growth is remarkable at a pH of around 9 to 10 when producing apatite, it is expected that the crystal is difficult to grow when the pH is changed to the acidic side. That is, when the same amount of apatite as the alkali side is generated on the acidic side, the particle size of the obtained apatite becomes small, and the number of particles increases. As a result, the droplet particles of the polymerizable monomer composition are uniformly coated with finer metal salt colloids to increase the stabilization effect of the droplet particles, or the number of particles per unit mass of the metal salt colloid is increased. The advantage that the total amount of the metal salt colloidal particles required for the large amount is small is also obtained.
For the reasons described above, in the present invention, the pH of the aqueous dispersion medium at the stage of mixing the aqueous phosphate solution and the aqueous calcium salt solution is 7.0 or more and 14.0 or less, particularly 9.0 or more and 14.0 or less. It may be preferable to increase the stabilizing effect of the droplet particles. In the case of other metal salt colloids, crystals are formed by almost the same mechanism, and the same effect is expected.
[0049]
Further, if the pH of the aqueous dispersion medium before dispersion of the polymerizable monomer composition is too low than 4.5, dissolution of calcium phosphate salts in water may start to occur rapidly, and the polymerizable monomer composition The effect of sufficiently stabilizing the droplet particles of the object cannot be obtained.
On the other hand, if the pH is too higher than 8.5, the transfer rate of tricalcium phosphate to apatite may increase, and the effect of stabilizing the droplet particles obtained by this metal salt colloid becomes small. Therefore, it is not preferable.
For the reasons described above, in the present invention, the pH of the aqueous dispersion medium containing the hardly water-soluble metal salt colloid as a dispersion stabilizer is set to 4.5 to 8.5 before the dispersion of the polymerizable monomer composition. It needs to be adjusted. Since the droplet particles granulated in this pH range are stably dispersed in water until the end of the polymerization reaction, the shape of the toner particles produced is almost spherical, which can be obtained stably and with good reproducibility. It is done. In the present invention, it is more preferable that the pH of the aqueous dispersion medium is 5.0 or more and 7.0 or less because the effect of stabilizing droplet particles is further enhanced.
[0050]
The compound used for adjusting the pH of the aqueous dispersion medium is not particularly limited as long as it does not affect the polymerization reaction, but is generally preferably an inorganic compound, and requires a water-soluble inorganic base or a water-soluble inorganic acid. Can be used according to. Among these, the water-soluble inorganic acid is preferably a water-soluble inorganic acid selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid. These water-soluble inorganic acids may be diluted to a predetermined concentration with water as necessary.
[0051]
A predetermined amount of the water-soluble inorganic acid may be added to the aqueous dispersion medium in advance so that the pH of the aqueous dispersion medium after the formation of the phosphate metal salt is 4.5 to 8.5, or phosphoric acid. A predetermined amount may be added so that the pH becomes 4.5 to 8.5 after the stable formation of the metal salt, but by adding a predetermined amount of a water-soluble inorganic acid in advance, It is preferable to adjust the pH.
[0052]
A preferable addition amount of the water-soluble inorganic acid is 0.2 to 0.9 molar equivalent with respect to the phosphate in the aqueous phosphate solution. For example, when a monovalent water-soluble inorganic acid is used. , And 0.2 to 0.9 mole per mole of phosphate in the aqueous phosphate solution, and when a divalent water-soluble inorganic acid is used, the amount of phosphate is 0.1 per mole of phosphate in the aqueous phosphate solution. 1 to 0.45 mol, and when using a trivalent water-soluble inorganic acid, it is 0.067 to 0.3 mol per mol of phosphate in an aqueous phosphate solution.
[0053]
Further, a known surfactant as a dispersion stabilizer may be added to the aqueous dispersion medium. The addition of the surfactant is preferable for producing toner particles having an average particle size of 5 μm or less, and the addition amount is 0.001 to 0.1 parts by mass with respect to 100 parts by mass of the polymerizable monomer composition. It is preferable that If the addition amount of the surfactant is less than the above range, the effect of the addition may be hardly obtained. If the addition amount of the surfactant is too much, the surface state of the toner particles obtained may be changed. May be exacerbated. Examples of the surfactant include sodium dodecylbenzene sulfate, sodium tetradecyl sulfate, sodium pentadecyl sulfate, sodium octyl sulfate, sodium oleate, sodium laurate, sodium stearate, potassium stearate and the like.
[0054]
In the method for producing toner particles according to the present invention, in order to sharpen the particle size distribution of the obtained toner particles, the polymerizable single amount with respect to the total mass of the aqueous dispersion medium and the polymerizable monomer composition. The body composition preferably has a mass fraction of 10 to 65%. Droplet particles serving as toner particles are generated while droplets generated at an early stage are repeatedly divided and united in an aqueous dispersion medium. Here, if the mass fraction is less than 10% or exceeds 65%, there may be cases where only the initial droplet breakup or coalescence occurs preferentially, making it difficult to control the particle size distribution. This is not preferable because the particle size distribution of the obtained toner particles is widened. For the same reason, the mass fraction is more preferably 15% to 50%.
[0055]
The polymerizable monomer composition in the method for producing toner particles of the present invention includes at least a polymerizable monomer that forms a binder resin by polymerization, a magnetic powder whose surface has been subjected to a hydrophobic treatment, and a polyester resin. It is.
The binder resin only needs to have physical properties such as appropriate thermal stability as a toner. The polymerizable monomer may be a monomer having an appropriate polarity that forms a binder resin by polymerization and uniformly disperses the magnetic powder whose surface has been hydrophobized in the droplet particles. The polymerizable monomer is preferably a compound having a vinyl group, for example. Among these, more preferable polymerizable monomers include, for example, a styrene monomer, an acrylate monomer, and methacrylic acid. An ester monomer etc. can be illustrated.
[0056]
Specific examples of the polymerizable monomer include the following.
Examples of the styrene monomer include styrene, o-methyl styrene, m-methyl styrene, p-methyl styrene, p-methoxy styrene, and p-ethyl styrene.
Examples of the acrylic acid ester monomer include methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, n-propyl acrylate, n-octyl acrylate, dodecyl acrylate, 2-acrylic acid 2- Examples include ethylhexyl, stearyl acrylate, 2-chloroethyl acrylate, and phenyl acrylate.
Moreover, as a methacrylic acid ester monomer, methyl methacrylate, ethyl methacrylate, n-propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, dodecyl methacrylate, methacrylic acid 2 -Ethylhexyl, stearyl methacrylate, phenyl methacrylate and the like.
Examples of other polymerizable monomers include monomers such as dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate, and other acrylonitrile, methacrylonitrile, and acrylamide.
[0057]
These polymerizable monomers can be used alone or in combination, but among the polymerizable monomers described above, a styrene monomer is used alone, or a styrene monomer and an acrylic monomer are used. Use of two or more monomers selected from acid ester monomers and methacrylic acid ester monomers and development characteristics and durability during development It is preferable for obtaining good toner particles.
[0058]
The polymerizable monomer generally has a theoretical glass transition temperature (Tg) of 40 to 75 ° C. described in Publication Polymer Handbook 2nd edition III-p139-192 (manufactured by John Wiley & Sons). In addition, they are used alone or in appropriate mixture. When the theoretical glass transition temperature is less than 40 ° C., problems may occur in terms of storage stability and durability stability of the toner, while when it exceeds 75 ° C., the toner fixing point may be increased. . In particular, in the case of a color toner for forming a full-color image, the color mixing property at the time of fixing each color toner is lowered, the color reproducibility is poor, and the transparency of the OHP image is further lowered.
[0059]
The magnetic powder used in the present invention must have a hydrophobic surface. The reason for this is that if it is not hydrophobized, it is released into the aqueous dispersion medium during the production of the toner particles due to the interaction with the aqueous dispersion medium due to the hydrophilicity of the surface of the magnetic powder. For example, it may be unevenly attached to the surface. When the magnetic powder is released into the aqueous dispersion medium, there is a gap between the addition amount and the content, and there is a high possibility that the coloring power and magnetic force necessary for the toner cannot be obtained.
[0060]
In general, magnetic powder has a low resistance and, on the other hand, has a property of easily adsorbing moisture. For this reason, if it adheres unevenly to the toner particle surface, it becomes a leak site due to low resistance, and there is a high possibility that the chargeability of the toner will be impaired. Is unfavorable, and the difference in chargeability between environments becomes large.
[0061]
Furthermore, it is conceivable that the magnetic powder moves randomly when the aqueous dispersion medium is stirred, and the surface of the droplet particles composed of a polymerizable monomer or the like is dragged, and the shape is distorted and is not easily rounded. In order to solve these problems, it is important to modify the surface characteristics of the magnetic powder particles.
[0062]
The method for hydrophobizing the surface of the magnetic powder used in the method for producing toner particles of the present invention is not particularly limited, but the magnetic powder is preferably surface-treated with a coupling agent, and more preferably an aqueous medium. Among them, it is more preferable that the surface treatment is performed by hydrolyzing the coupling agent while dispersing the magnetic powder so as to be primary particles. Compared with the method of treating the surface of the magnetic powder in the gas phase, this hydrophobic treatment method is less likely to cause coalescence between the magnetic powders, and the repulsive action between the magnetic powders due to the hydrophobic treatment works. The magnetic powder is surface-treated in the form of primary particles.
[0063]
In addition, the hydrophobization method involving hydrolysis does not require the use of a coupling agent that generates gas, such as chlorosilanes and silazanes. It is possible to use a high-viscosity coupling agent that is easy to unite and difficult to process well.
[0064]
Many proposals have been made regarding the surface modification of magnetic powder applicable to the present invention. 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. JP-A-63-250660 discloses a technique for treating silicon element-containing magnetic particles with a silane coupling agent. By using these treatment techniques, a preferable magnetic powder is obtained. Obtainable.
[0065]
Examples of the coupling agent include a silane coupling agent and a titanium coupling agent. More preferably used is a silane coupling agent, which has the following general formula (I)
[0066]
[Chemical 1]

[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. ]. For example, vinyltrimethoxysilane, vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, vinyltriacetoxysilane, methyltrimethoxysilane, methyltriethoxysilane, isobutyltrimethoxysilane, dimethyldimethoxysilane, dimethyldiethoxysilane, trimethyl Examples include methoxysilane, hydroxypropyltrimethoxysilane, phenyltrimethoxysilane, n-hexadecyltrimethoxysilane, and n-octadecyltrimethoxysilane.
[0067]
In particular, the following general formula (II)
[0068]
[Chemical 2]

[Wherein p represents an integer of 2 to 20, q represents an integer of 1 to 3], and the magnetic powder is hydrophobized in an aqueous medium using an alkyltrialkoxysilane coupling agent represented by Is good.
When p in the above formula is smaller than 2, the hydrophobization treatment is easy, but it is difficult to sufficiently impart hydrophobicity, and it becomes difficult to suppress the exposure of the magnetic powder from the toner particles. On the other hand, when p is larger than 20, hydrophobicity is sufficient, but the coalescence between the magnetic powders increases, making it difficult to sufficiently disperse the magnetic powders in the toner particles, and fogging occurs in the image. There is a tendency that transferability to a transfer material deteriorates.
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. The amount to be used is 0.05 to 20 parts by mass, preferably 0.1 to 10 parts by mass with respect to 100 parts by mass of the magnetic powder. If the amount of coupling agent used is less than 0.05 parts by mass, the surface of the magnetic powder may not be sufficiently hydrophobized. If it exceeds 20 parts by mass, excess coupling agent is wasted. Or may adversely affect the surface hydrophobization treatment of the magnetic powder.
[0069]
  Here, the aqueous medium in the hydrophobic treatment is a medium containing water as a main component. Specifically, water itself as an aqueous medium, water with a small amount of surfactant added, pH adjustment in waterAdjustmentAnd the like, and those obtained by adding an organic solvent to water. As the surfactant, for example, a nonionic surfactant such as polyvinyl alcohol is preferable. Moreover, although the addition amount of surfactant changes with kinds etc. of surfactant to be used, it is preferable that it is generally 0.1-5 wt% with respect to water. The pH adjuster is not particularly limited as long as it is a pH adjuster that does not adversely affect the hydrophobizing treatment, and examples thereof include inorganic acids such as hydrochloric acid.
[0070]
The stirring in the surface hydrophobization treatment of the magnetic powder in the aqueous medium is performed by, for example, a mixer having a stirring blade (specifically, a high shear force mixing device such as an attritor or a TK homomixer). It is good to carry out sufficiently so that it may become a primary particle in an aqueous medium.
[0071]
In the magnetic powder thus obtained, no particle aggregation is observed, and the surface of each particle is uniformly hydrophobized. Therefore, when used as a material for toner particles, the dispersibility in the toner particles is extremely high. It is good. Moreover, there is no exposure from the surface of the toner particles, and it is possible to obtain toner particles that are almost spherical. Therefore, by using such a magnetic powder, the finally obtained magnetic toner has an average circularity of 0.970 or more and a mode circularity of 0.990 or more, thereby improving transferability and improving the electrophotographic process. Good compatibility.
[0072]
The magnetic powder used in 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 developer is poor, and it may be difficult to suppress fogging. On the other hand, if the amount exceeds 200 parts by mass, the retention force due to the magnetic force on the developer carrying member (for example, the rotating sleeve) is increased during image formation, and developability is reduced. In addition to difficulty in dispersion, the fixability may be reduced.
[0073]
Moreover, it is preferable that the average particle diameter of the magnetic powder used in the present invention is 0.1 to 0.3 μm.
When an image is obtained from a magnetic toner using a magnetic powder having an average particle size of less than 0.1 μm, the color of the image shifts to red, and the blackness of the image is insufficient. This is not preferable because there is a tendency to feel strongly. In addition, when such a magnetic toner is used for a color image, it is not preferable because color reproducibility becomes difficult to obtain or the shape of the color space tends to be distorted. Further, since the surface area of the magnetic powder is increased, the dispersibility is deteriorated, and the energy required for the production is increased, such as the need for stronger stirring during the production of the toner particles. Further, the density of an image to be obtained from the amount of magnetic powder added is insufficient, which is not preferable.
[0074]
On the other hand, if the average particle size of the magnetic powder exceeds 0.3 μm, the mass per magnetic powder particle increases, and therefore the toner particles are affected by the difference in specific gravity with the binder (binder resin) during the production of the toner particles. This is not preferable because the probability that the magnetic powder is exposed on the surface increases, the possibility of significant wear of the manufacturing apparatus increases, and the sedimentation stability of the dispersion decreases.
[0075]
As a method for measuring the particle size of the magnetic powder, for example, a liquid module is attached to an LS-230 type laser diffraction particle size distribution measuring device manufactured by Coulter, Inc., and measurement is performed in a measurement range of 0.04 to 2000 μm, or laser. A method for measuring and obtaining particles of 0.45 μm or less with a diffraction type particle size distribution analyzer (manufactured by Hiac / Leuco Co., Ltd .: Nikon model 370), or if the magnetic powder itself can be separated, In toner particles or magnetic toners, these are embedded in a resin and then sliced to determine the particle diameter of 100 magnetic powders in the field of view with a transmission electron microscope (TEM). Is mentioned. In the present invention, it is preferable to measure with a transmission electron microscope.
[0076]
As a specific observation method using the above-mentioned TEM, particles to be observed (magnetic powder, toner particles, etc.) are sufficiently dispersed in a room temperature curable epoxy resin and then cured in an atmosphere at a temperature of 40 ° C. for 2 days. A method of observing the cured product obtained as a flaky sample with a microtome is exemplified.
Further, as another method for measuring the particle size of the magnetic powder, for example, a method of calculating an average particle size using an image analysis device may be used.
[0077]
Examples of the magnetic powder used in the method for producing toner particles of the present invention include magnetic iron oxides such as magnetite, maghemite and ferrite, metals such as iron, cobalt and nickel, or these metals and aluminum, cobalt and copper. Alloys of metals such as lead, magnesium, tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, vanadium, and mixtures thereof, alloys further including elements such as phosphorus, magnesium, silicon Or a mixture etc. are mentioned. These exemplified magnetic materials are used alone or in combination of two or more. These magnetic powders generally have a Mohs hardness of 5-7.
[0078]
As magnetic properties of these magnetic powders, the saturation magnetization is 10 to 200 Am under a magnetic field of 795.8 kA / m.²/ Kg, residual magnetization 1-100Am²/ Kg and a coercive force of 1 to 30 kA / m are used. Among such magnetic powders, those mainly composed of magnetite are particularly preferable.
[0079]
For example, in the case of magnetite, the magnetic powder used in the present invention is produced by the following method.
An aqueous solution containing ferrous hydroxide is prepared by adding an alkali such as sodium hydroxide in an amount equivalent to or higher than the iron component to the ferrous salt aqueous solution. Air was blown in while maintaining the pH of the prepared aqueous solution at pH 7 or higher (preferably pH 8 to 10), the ferrous hydroxide oxidation reaction was performed while heating the aqueous solution to 70 ° C. or higher, and the core of magnetic iron oxide particles First, a seed crystal is formed.
[0080]
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 liquid at 6 to 10, the reaction of ferrous hydroxide is promoted while blowing air, and magnetic iron oxide particles are grown with the seed crystal as the core. 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.
[0081]
Adjust the pH of the solution 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 disintegrate By doing so, hydrophobic treated magnetic iron oxide particles can be obtained. Alternatively, after completion of the oxidation reaction, the iron oxide particles obtained by washing and filtering are redispersed in another aqueous medium without drying, and then the pH of the redispersion is adjusted and the silane is stirred well. A coupling agent may be added to perform the coupling treatment. In any case, it is important to perform the surface treatment after the oxidation reaction without passing through the drying step, which is an important point in the toner particle production method of the present invention. 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.
[0082]
The above-described method for producing magnetic iron oxide by the aqueous solution method is generally used at an iron concentration of 0.5 to 2 mol / L 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. Further, in the reaction, the larger the amount of air and the lower the reaction temperature, the easier the atomization.
By using a magnetic toner containing toner particles made of the hydrophobic magnetic powder produced in this way, the photoconductor is not scraped and the toner is not fused, and high image quality and high stability during image formation are achieved. Sexuality is possible.
[0083]
In the method for producing toner particles of the present invention, a polyester resin is an indispensable component. As described above, in order to obtain toner particles with uniform chargeability and good developability when developing an electrostatic latent image in an electrophotographic process, stable and uniform charging performance is hardly affected by the environment. Therefore, the particle size distribution must be sharp, the shape is spherical, the distribution is uniform, and the surface state and surface composition must be extremely uniform. To that end, it has been stated that a metal salt colloid preparation method and a hydrophobized magnetic powder are necessary, but in addition to that, the protective effect of the metal salt colloid on the droplet particles is more efficiently expressed. As described above, in order to prevent the hydrophobic magnetic powder from being released from the droplet particles or adhering to the surface in a large amount, in the method for producing toner particles of the present invention, polyester is used. Resin is essential.
[0084]
Since this polyester resin contains many ester bonds having a relatively high polarity, the polarity of the resin is increased. On the other hand, the binder resin constituting the toner particles according to the present invention is preferably a styrene resin produced by polymerizing a polymerizable monomer. When comparing these two types of resins, the polyester resin is usually more polar, and the polarity tends to be unevenly distributed on the aqueous dispersion medium side in the droplet particles. In terms of surface chemistry, this state is more stable in terms of potential, and while this state is maintained, polymerization proceeds and toner particles are obtained. In the process of obtaining the toner particles, the inventors believe that the stabilization effect of the polyester resin and the presence of the above-described metal salt colloid function and the toner particle size distribution becomes sharp.
[0085]
On the other hand, the obtained toner particles have a uniform surface state and surface composition due to the uneven distribution of the polyester resin on the surface, and as a result, the chargeability is uniform and hardly affected by the environment. Here, if a functional group having extremely high polarity is included in the polymerizable monomer composition, it may become a leak site or the chargeability under high temperature and high humidity may be extremely reduced due to moisture adsorption. For this reason, it is necessary to appropriately limit the number of functional groups to be introduced. From such a fact, it is very preferable from the object of the present invention to use a polyester resin having a large number of functional groups having an appropriate polarity.
[0086]
That is, as described above, in the present invention, the polyester resin, the hydrophobized magnetic powder, and the preparation method of the metal salt colloid determine the characteristics of the toner particles while interacting with each other. Both are indispensable.
[0087]
The polyester resin used in the present invention is, for example, one or both of a saturated polyester resin and an unsaturated polyester resin in controlling physical properties such as charging property, durability, and fixing property of a magnetic toner obtained from toner particles. Can be appropriately selected and used.
The alcohol component and acid component which comprise the polyester resin used for this invention are illustrated below.
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 the following general formula (III):
[0088]
[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. Or hydrogenated compounds of the general formula (III)
In addition, a diol represented by the following general formula (IV),
[0089]
[Formula 4]

Or the diol of the hydrogenated compound of the compound of the formula (IV), and polyhydric alcohol such as glycerin, pentaerythritol, sorbit, sorbitan, oxyalkylene ether of novolak type phenol resin, and the like.
[0090]
As the divalent carboxylic acid, benzene dicarboxylic acid such as phthalic acid, terephthalic acid, isophthalic acid, phthalic anhydride or its anhydride, alkyl dicarboxylic acid such as succinic acid, adipic acid, sebacic acid, azelaic acid or its anhydride, Furthermore, succinic acid substituted with an alkyl or alkenyl group having 6 to 18 carbon atoms or anhydride thereof, unsaturated dicarboxylic acid such as fumaric acid, maleic acid, citraconic acid, itaconic acid or anhydride thereof, and further trimellit Acid, pyromellitic acid, polyvalent carboxylic acid such as 1,2,3,4-butanetetracarboxylic acid, benzophenonetetracarboxylic acid, and anhydrides thereof.
[0091]
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 in terms of fixability and toner durability. Moreover, it is preferable that 45-55 mol% of this polyester resin is an alcohol component, and 55-45 mol% is an acid component in all the components. If it is far from the above range, the good surface composition of the toner particles may be impaired.
[0092]
The polyester resin is present on the surface of the toner particles in the production method of the present invention, and the obtained toner particles have an acid value of 0.1 to 50 mgKOH / 1 g of resin in order to develop stable chargeability. It is preferable. If the amount is less than 0.1 mg KOH / resin 1 g, the amount existing on the surface of the toner particles may be absolutely insufficient. If the amount exceeds 50 mg KOH / resin 1 g, the chargeability of the toner particles 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.
[0093]
The polyester resin is preferably used in an amount of 0.5 to 35 parts by weight, more preferably 5 to 20 parts by weight, based on 100 parts by weight of the polymerizable monomer. If the amount is less than 0.5 parts by mass, uniform chargeability may not be obtained. If the amount exceeds 35 parts by mass, the viscosity of the polymerizable monomer composition increases and the particle size distribution of the resulting toner particles does not become sharp. This is not preferable because there are some cases.
[0094]
In the present invention, the physical properties were adjusted by using two or more kinds of polyester resins in combination as long as the physical properties of the obtained toner particles are not adversely affected, or by modification with, for example, silicone or a fluoroalkyl group-containing compound. Polyester resins may be used alone or in combination. Further, like the polymerizable monomer described above, the polyester resin may be used so that the theoretical glass transition temperature is 40 to 70 ° C. in consideration of stability and fixability when the toner is used as a magnetic toner. preferable.
[0095]
As a polymerization initiator used in the present invention, a polymerization initiator having a half-life of 0.5 to 30 hours at the time of the polymerization reaction is carried out with an addition amount of 0.5 to 20 parts by mass with respect to the polymerizable monomer. Thus, a polymer having a maximum between 10,000 and 100,000 in molecular weight can be obtained, and the toner particles can be provided with desirable strength and suitable melting characteristics. If the half-life and addition amount of the polymerization initiator greatly deviate from the above ranges, polymerization of the polymerizable monomer may be insufficient, or good physical properties of the polymerized binder resin may be impaired.
[0096]
The polymerization initiator can be added at any stage as long as it is before the polymerization of the polymerizable monomer. For example, the polymerization initiator may be added at the same time as other additives are added to the polymerizable monomer, or immediately before the polymerizable monomer composition is suspended in the aqueous dispersion medium. You may mix. Further, a polymerization initiator dissolved in a polymerizable monomer or a solvent can be added immediately after granulation and before starting the polymerization reaction.
[0097]
Examples of polymerization initiators are 2,2′-azobis- (2,4-dimethylvaleronitrile), 2,2′-azobisisobutyronitrile, 1,1′-azobis (cyclohexane-1-carbonitrile) Azo or diazo polymerization initiators such as 2,2′-azobis-4-methoxy-2,4-dimethylvaleronitrile, azobisisobutyronitrile, benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, Examples thereof include peroxide type polymerization initiators such as cumene hydroperoxide, 2,4-dichlorobenzoyl peroxide, lauroyl peroxide, and t-butylperoxy-2-ethylhexanoate.
[0098]
In the present invention, a crosslinking agent may be added, and a preferable addition amount is 0.001 to 15% by mass with respect to 100 parts by mass of the polymerizable monomer. Here, as the crosslinking agent, compounds having two or more polymerizable double bonds are mainly used. For example, aromatic divinyl compounds such as divinylbenzene and divinylnaphthalene, such as ethylene glycol diacrylate and ethylene glycol diacrylate. Carboxylic acid ester having two double bonds such as methacrylate, 1,3-butanediol dimethacrylate, divinyl compounds such as divinylaniline, divinyl ether, divinyl sulfide, divinyl sulfone, and three or more vinyl groups A compound etc. are used individually or as a mixture. If the addition amount of the crosslinking agent is less than the above range, a sufficient effect may not be exhibited, and if it is more than the above range, the physical properties of the binder resin may be adversely affected.
[0099]
In the method for producing toner particles of the present invention, it is one of preferred modes that the toner particles contain a release agent.
The toner image transferred onto the transfer material is then fixed on the transfer material with energy such as heat and pressure to obtain a semi-permanent image. At this time, heat roll type fixing is generally used.
At this time, if a toner particle having a small diameter is used, a very high-definition image can be obtained. However, when a transfer material such as paper is used, the toner particle having a small particle diameter enters a gap between paper fibers and is used for heat fixing. Heat reception from the roller becomes insufficient, and low temperature offset is likely to occur. However, in the present invention, toner particles capable of preventing the photoconductor from being scraped in the image forming apparatus while achieving both high resolution and offset resistance by using an appropriate amount of wax as a release agent. Can be manufactured.
[0100]
Examples of waxes that can be used as a release agent in the present invention include petroleum waxes such as paraffin wax, microcrystalline wax, petrolactam and derivatives thereof, montan wax and derivatives thereof, hydrocarbon waxes and derivatives thereof according to the Fischer-Tropsch method, and polyethylene. Representative polyolefin waxes and derivatives thereof, natural waxes such as carnauba wax and candelilla wax and derivatives thereof, 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.
[0101]
Among these wax components, those having a maximum endothermic peak in the region of 40 to 110 ° C. at the time of temperature rise in the DSC curve measured by a differential differential calorimeter are preferable, and those in the region of 45 to 90 ° C. 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. When the maximum endothermic peak is less than 40 ° C., the self-aggregation force of the wax component becomes weak, and as a result, the high temperature offset resistance may be deteriorated. On the other hand, if the maximum endothermic peak exceeds 110 ° C., the fixing temperature becomes high and low temperature offset may occur, which is not preferable. Furthermore, if the maximum endothermic peak temperature is high, problems such as precipitation of a wax component during granulation in an aqueous dispersion medium may occur, which is not preferable.
[0102]
The maximum endothermic peak temperature of the wax component is preferably measured according to, for example, “ASTM D 3418-8”. For example, DSC-7 manufactured by Perkin Elmer is used for the measurement. 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, an empty pan is set as a control, and measurement is performed at a heating rate of 10 ° C./min.
[0103]
The content of these wax components as a release agent is preferably in the range of 0.1 to 20% by mass with respect to the entire magnetic toner when a magnetic toner is produced from the obtained toner particles. When the content is less than 0.1% by mass, the effect of suppressing the low temperature offset may not be sufficiently obtained. When the content exceeds 20% by mass, the long-term storage stability is deteriorated and the dispersibility of other materials is poor. This may lead to deterioration of fluidity of magnetic toner and deterioration of image characteristics.
[0104]
In the method for producing toner particles of the present invention, the polymerizable monomer composition may be polymerized by adding a resin other than the binder resin and the polyester resin. For example, when introduced into a polymerizable monomer, it cannot be used because it dissolves in an aqueous dispersion medium due to its water solubility and causes emulsion polymerization. Hydrophilic properties such as amino groups, carboxylic acid groups, hydroxyl groups, sulfonic acid groups, glycidyl groups, and nitrile groups When it is desired to introduce functional group-containing monomer components into toner particles, random copolymers, block copolymers, or graft copolymers of these with vinyl compounds such as styrene or ethylene are used to form a copolymer. It can be used by forming a polycondensate such as polyester or polyamide, or a polyaddition polymer such as polyether or polyimine.
[0105]
When such a polymer containing a polar functional group is allowed to coexist in the toner particles, the wax component (the release agent) described above is phase-separated when the release agent is used, and the encapsulation becomes stronger and the resistance to resistance is increased. A magnetic toner having good offset, blocking resistance, and low-temperature fixability can be obtained. When using such a high molecular polymer containing a polar functional group, the average molecular weight is preferably 5000 or more. When the molecular weight is 5000 or less, particularly 4000 or less, the present polymer tends to concentrate near the surface, so that adverse effects on developability, blocking resistance and the like are likely to occur, which may be undesirable.
[0106]
In addition, a resin other than the above may be further 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 polystyrene and polyvinyltoluene. Styrene and substituted homopolymers, 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-dimethyl methacrylate Noethyl 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 copolymer such as styrene-maleic ester copolymer, polymethyl methacrylate, polybutyl methacrylate, polyvinyl acetate, polyethylene, polypropylene, polyvinyl butyral, silicone resin, polyester resin, polyamide resin, epoxy resin Polyacrylic acid resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, and the like, and these resins can be used alone or in combination.
[0107]
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 may not be sufficiently obtained. On the other hand, if it is added by 20 parts by mass or more, it may be difficult to design various physical properties of the toner particles. In addition, if a polymer having a molecular weight different from the molecular weight range such as a binder resin obtained by polymerizing a polymerizable monomer is dissolved in the monomer and polymerized, the molecular weight distribution is wide and the offset resistance is high. Toner particles can be obtained.
[0108]
In the present invention, a charge control agent may be used to stabilize the charge characteristics of the toner particles. 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. Furthermore, the charge control agent is particularly preferably a charge control agent that has low polymerization inhibitory properties and is substantially free from solubilized products in an aqueous dispersion medium.
[0109]
Specific examples of charge control agents include negative charge control agents such as 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. And polymeric compounds having a sulfonic acid or carboxylic acid group in the side chain, boron compounds, urea compounds, silicon compounds, calixarene, and the like. 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.
[0110]
The charge control agent is preferably used in an amount of 0.5 to 10 parts by mass with respect to 100 parts by mass of the polymerizable monomer. However, in the present invention, the use of a charge control agent is not indispensable, and the frictional charging of the magnetic toner layer pressure regulating member and the developer carrier (such as the rotating sleeve) in the developing device of the image forming apparatus is actively utilized. By doing so, the charge amount and charging speed can be controlled. In the case of adding the charge control agent, it is preferable to determine the addition amount in consideration of the usage form of the obtained toner particles.
[0111]
Furthermore, in the method for producing toner particles of the present invention, other colorants may be used in addition to the magnetic powder. Examples of coloring materials that can be used in combination include magnetic or nonmagnetic inorganic compounds, and 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 hydrophobic treatment of the surface in the same manner as the magnetic powder.
[0112]
In the present invention, a known inorganic dispersant may be used in combination as a dispersion stabilizer. Inorganic dispersants are unlikely 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 cleaning is easy and does not adversely affect toner particles. Can be preferably used.
[0113]
Examples of such inorganic dispersants include carbonates such as calcium carbonate and magnesium carbonate, inorganic salts such as calcium metasuccinate, calcium sulfate, and barium sulfate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, silica, bentonite, Examples thereof include inorganic oxides such as alumina. These inorganic dispersants may be used in an amount of 0.2 to 20 parts by mass with respect to 100 parts by mass of the polymerizable monomer composition, or a mixture of plural kinds thereof. If the amount of the inorganic dispersant used is less than the above range, the effect due to the addition may not be sufficiently obtained. If the amount is more than the above range, the dispersion stabilizer interferes with the polymerizable monomer composition. May adversely affect the distribution of
[0114]
Further, in the case of using the inorganic dispersant, it may be used as it is. However, as in the case of the calcium phosphate salts described above, when a desired inorganic dispersant is produced in an aqueous dispersion medium by mixing an aqueous solution, finer inorganic Dispersant particles can be obtained, which is preferable. Further, when a water-soluble salt is by-produced in the aqueous dispersion medium, the dissolution of the polymerizable monomer in water is suppressed. For example, in order to suppress the ultrafine particle formation of toner particles as seen in emulsion polymerization, for example. Convenient. Since the inorganic dispersant becomes an obstacle when removing the remaining polymerizable monomer at the end of the polymerization reaction, it is better to replace the aqueous medium or desalinate with an ion exchange resin. The inorganic dispersant can be almost completely removed by dissolving with an acid or alkali after completion of the polymerization.
[0115]
The toner particles obtained in the present invention preferably have a weight average particle diameter of 3 to 10 μm, and more preferably 4 to 9 μm for high image quality. . Further, the obtained toner particles preferably have a particle size distribution in which the ratio D4 / D1 of the weight average particle diameter (D4) to the number average particle diameter (D1) is less than 1.4. Particularly when toner particles are produced by a polymerization method, if the magnetic powder is exposed on the surface of the toner particles, the particle size distribution of the toner particles tends to be deteriorated.
[0116]
Next, the magnetic toner of the present invention will be described.
In the magnetic toner of the present invention, the average circularity must be 0.970 or more, and the mode circularity is preferably 0.990 or more. The reason is as follows.
Magnetic toner (powder composed of toner particles and inorganic fine powder) having an average circularity of 0.970 or more is very excellent in transferability. This is presumably because the contact area between the toner particles and the photosensitive member (image carrier) is small, and the adhesion force of the toner particles to the photosensitive member due to mirror image force, van der Waals force, or the like is reduced.
[0117]
Further, since the toner particles of the magnetic toner having an average circularity of 0.970 or more have almost no edge portion on the surface, the surface of the photoreceptor is not scratched in the contact transfer method in which the pressure contact portion between the transfer member and the photoreceptor exists. For this reason, the surface of the photoconductor can be prevented from being scraped. If the average circularity is less than 0.970, these effects due to the shape of the magnetic toner may not be exhibited. These effects are more prominent in the image forming method including the above-described contact transfer process in which transfer loss is likely to occur. Even if the average circularity is high, the effect is insufficient when the circularity of the particles that are mainly present is low, especially when the mode circularity is 0.990 or more, and particles with a circularity of 0.990 or more are mainly present. Therefore, it is preferable because the above-described effect appears remarkably.
[0118]
Next, the ratio (B / A) of the content (B) of the iron element to the content (A) of the carbon element present on the surface of the toner particles measured by X-ray photoelectron spectroscopy is less than 0.001. The point that a certain case is an essential component will be described.
[0119]
As described above, in the image forming method including the contact charging step, if the magnetic toner having (B / A) as described above is less than 0.001, that is, the magnetic powder is hardly exposed on the surface, the transfer is performed. Even when the magnetic toner is pressed against the surface of the photoreceptor by a member or the like, the surface of the photoreceptor is hardly scraped, and the scraping of the photoreceptor or toner fusion can be remarkably reduced. On the other hand, when B / A is 0.001 or more, the magnetic powder is exposed on the surface of the magnetic toner, and the abrasion of the photoreceptor due to the exposed magnetic powder may be more noticeable. The magnetic toner in which the magnetic powder is hardly exposed on the surface as in the present invention is very effective in the image forming method combined with the contact transfer process, and a very high-definition image can be obtained over a long period of time. It is possible.
[0120]
A special magnetic toner in which a magnetic powder is contained only in a specific portion inside the toner particles has already been disclosed in Japanese Patent Application Laid-Open No. 7-209904. However, Japanese Patent Laid-Open No. 7-209904 does not mention the circularity of the magnetic toner disclosed. In the image forming method of the present invention, the use of a magnetic toner having a specific average circularity is an essential element. A magnetic toner as described in JP-A-7-209904 is used as in the present invention. It is unclear whether similar effects will be manifested when used in
[0121]
In the present invention, the projected area equivalent circle diameter of the magnetic toner is C, and the minimum value of the distance between the magnetic powder surface and the toner particles in the cross-sectional observation of the magnetic toner using a transmission electron microscope (TEM) is D. The number of toner particles satisfying the relationship of D / C ≦ 0.02 is preferably 50% or more, more preferably 65% or more, and even more preferably 75% or more.
The reason is as follows.
[0122]
If the above conditions are not satisfied, the magnetic particles do not exist at least outside the boundary line of D / C = 0.02 in the toner particles. Assuming that the particles as described above are spherical, when one toner particle is the entire space, at least 11.5% of the space in which no magnetic powder exists is present on the surface of the toner particle. Actually, the magnetic powder does not exist uniformly at the closest position so as to form an inner wall inside the toner particle, so the space where the magnetic powder does not exist in the toner particle is 12% or more. Obviously.
[0123]
If there is no magnetic powder in such a space per particle,
<1> The magnetic powder is biased inside the toner particles, and the possibility of aggregation of the magnetic powder becomes extremely high. As a result, the coloring power is reduced.
<2> Although the specific gravity of the toner particles increases according to the content of the magnetic powder, the binder resin and the wax component are unevenly distributed on the surface of the toner particles. For this reason, even if a surface layer is provided on the surface of the toner particles by some means, if the toner particles or stress applied to the toner particles during production of the magnetic toner is applied, fusion or deformation is likely to occur. The handling of the toner becomes complicated, the distribution of the powder characteristics of the toner particles obtained by deformation occurs, adversely affects the electrophotographic characteristics, and the possibility that the blocking property during storage of the magnetic toner deteriorates increases.
<3> In the particle structure in which the toner particle surface is only the binder resin and the wax, and the magnetic powder is unevenly distributed inside, the toner particle exterior is soft and the interior is hard. It tends to occur and the durability of the magnetic toner deteriorates.
The risk of causing harmful effects such as
If the number of toner particles satisfying D / C ≦ 0.02 is less than 50%, the above-mentioned adverse effects such as a decrease in coloring power, a deterioration in blocking property, and a deterioration in durability tend to become remarkable.
Therefore, in the present invention, the number of toner particles satisfying D / C ≦ 0.02 is preferably 50% or more.
[0124]
As a specific observation method by TEM, a cured product obtained by sufficiently dispersing particles to be observed in a room temperature curable epoxy resin and then curing for 2 days in an atmosphere at a temperature of 40 ° C. A method of freezing and observing as a flaky sample with a microtome is preferred.
A specific method for determining the ratio of the number of corresponding particles is as follows.
[0125]
Particles for determining D / C by TEM are obtained by calculating the equivalent circle diameter from the cross-sectional area in the micrograph, and the value included in the width of ± 10% of the number average particle diameter is the corresponding particle. For the relevant particle, the minimum value (D) of the distance between the magnetic powder surface and the toner particle surface is measured, and D / C is calculated. It is defined that the ratio of particles having a D / C value calculated in this way of 0.02 or less is obtained by the following formula 1. In this case, a magnification of 10,000 to 20,000 times is suitable for the microphotograph to perform measurement with high accuracy. In the present invention, a transmission electron microscope (Hitachi model H-600) was used as an apparatus, observed at an accelerating voltage of 100 kV, and observed and measured using a photomicrograph with a magnification of 10,000.
[0126]
[Formula 1]

The number average particle diameter of the magnetic toner is preferably determined by a Coulter counter described later.
[0127]
Furthermore, Japanese Patent Application Laid-Open No. 7-209904 only proposes a magnetic toner having a special structure, and there is still room for study regarding its specific usage. The inventors of the present invention have combined the use of a special magnetic toner obtained with an idea different from the technical idea disclosed in Japanese Patent Laid-Open No. 7-209904 with a specific image forming method, thereby improving the durability of the photoreceptor. The present inventors have found that a significant improvement effect is exhibited in the present invention and have led to the present invention.
[0128]
In the magnetic toner of the present invention, the magnetic toner preferably has a weight average particle diameter of 4 μm to 9 μm in order to develop finer latent image dots faithfully as described above in order to improve image quality. For magnetic toners with a weight average particle size of less than 4 μm, the transfer residual toner on the photoconductor increases due to a decrease in transfer efficiency, and the photoconductor shaving and toner fusion in the contact charging process are not sufficiently suppressed. There is. Furthermore, in addition to an increase in the overall surface area of the magnetic toner, the fluidity and agitation as a powder are reduced, and it becomes difficult to uniformly charge individual magnetic toners. Since it tends to deteriorate and tends to cause non-uniform image unevenness other than scraping and fusion, it is not preferable for the magnetic toner of the present invention. When the weight average particle diameter of the magnetic toner exceeds 9 μm, characters and line images are likely to be scattered and a high resolution image may not be obtained. Further, the weight average particle size of the magnetic toner is preferably larger than 4 μm and smaller than 8 μm.
[0129]
  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 (manufactured by Coulter Co., Ltd.). ) To connect the interface (manufactured by Nikka) and PC9801 personal computer (manufactured by NEC) that output the number distribution and volume distribution, and prepare 1% NaCl aqueous solution using 1st grade sodium chloride as the electrolyte.MadeIt is possible to measure by doing. In such a measuring method, for example, ISOTON R-II (manufactured by Coulter Scientific Japan) can be used. As a measuring method, 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 electrolyte solution in which the sample is suspended is dispersed for about 1 to 3 minutes with an ultrasonic disperser, and the volume distribution is measured by measuring the volume and number of magnetic toners of 2 μm or more using the 100 μm aperture as the aperture by the Coulter Multisizer. And the number distribution, and then the volume-based weight average particle diameter (D4) determined from the volume distribution of the present invention and the number-based number average particle diameter (D1) determined from the number distribution. Can do.
[0130]
In the present invention, it is necessary to obtain 20% by number or less of particles having a weight average particle diameter (D4) of 4 μm or less of the magnetic toner in an amount of 20% by number or less. When the number of particles of 4 μm or less is more than 20% by number, as described above, the transfer residual toner due to the magnetic toner having a small particle diameter tends to increase, and the charging failure (photosensitive member of the photoreceptor) due to the primary charging failure due to this transfer residual toner. Due to the occurrence of charging unevenness, the image quality of the obtained image may deteriorate.
[0131]
In the present invention, the magnetic toner has a magnetization intensity of 10 to 50 Am at a magnetic field of 79.6 kA / m (1000 oersted).²/ Kg (emu / g). By providing a magnetic force generating means in the developing device, magnetic toner can prevent leakage of the toner, and not only can the magnetic toner be conveyed or stirred, but also magnetic force can be generated on the toner carrier such as the rotating sleeve. By providing the magnetic force generating means so as to act, it is possible to further improve the recoverability of the transfer residual toner and to easily prevent the magnetic toner from scattering because the magnetic toner forms spikes.
[0132]
However, the magnetic toner has a magnetization intensity of 10 Am at a magnetic field of 79.6 kA / m.²When the amount is less than / kg, the above effect cannot be obtained, and when magnetic force is applied to the toner carrier, the rising of the magnetic toner becomes unstable, and fogging due to the fact that charging to the magnetic toner cannot be performed uniformly, Image density unevenness and image failure due to poor collection of residual toner may occur. The magnetic toner has a magnetization intensity of 10 Am at a magnetic field of 79.6 kA / m.²If it is less than / kg (emu / g), it becomes difficult to carry the magnetic toner by magnetic force, and the uniformity of the magnetic toner carrying on the toner carrying member may be impaired.
[0133]
Magnetic toner has a magnetic strength of 50 Am at a magnetic field of 79.6 kA / m.²If it is greater than / kg, when magnetic force is applied to the magnetic toner, the fluidity of the magnetic toner is remarkably reduced due to magnetic aggregation, and the transfer residual toner may increase due to a decrease in transferability. Further, the strength of magnetization at a magnetic field of 79.6 kA / m is 50 Am.²If it is greater than / kg (emu / g), the amount of magnetic material contained in the toner particles is large, and therefore, the toner particles may not be sufficiently fixed to the transfer material.
In addition, if mention is made of spikes, the magnetic toners on the toner carrier can be spiked by having a circularity of 0.970 or more and a mode circularity of 0.990 or more like the magnetic toner of the present invention. As a result, the charging becomes uniform and fogging is greatly reduced.
[0134]
In the present invention, the reason why the strength of magnetization at a magnetic field of 79.6 kA / m is defined is that the amount of magnetization (saturation magnetization) in magnetic saturation is used as the quantity representing the magnetic characteristics of the magnetic powder. This is because the strength of magnetization of the magnetic toner in the magnetic field that actually acts on the magnetic toner in the image forming apparatus is important. When magnetic toner is applied to the image forming apparatus, the magnetic field acting on the magnetic toner is commercially available in order not to increase leakage of the magnetic field outside the image forming apparatus or to keep the cost of the magnetic field generation source low. In many image forming apparatuses, a magnetic field of 79.6 kA / m (1000 oersted) is selected as a representative value of the magnetic field actually acting on the magnetic toner in the image forming apparatus. The strength of magnetization in a magnetic field of 79.6 kA / m was defined.
[0135]
In the present invention, the magnetization strength of the magnetic toner is measured using a vibration magnetometer VSMP-1-10 (manufactured by Toei Kogyo Co., Ltd.) at a room temperature of 25 ° C. and an external magnetic field of 79.6 kA / m. Can be obtained. The magnetic properties of the magnetic powder can be determined by measuring at an external magnetic field of 796 kA / m at a room temperature of 25 ° C.
[0136]
The magnetic toner of the present invention is composed of toner particles and inorganic fine powder. The toner particles constituting the magnetic toner can be manufactured by the above-described toner particle manufacturing method, and are preferably manufactured by the suspension polymerization method as described above. In this suspension polymerization method, the above-described polymerization monomer and colorant (further, if necessary, a polymerization initiator, a crosslinking agent, a charge control agent, other additives) and the like are uniformly dissolved or dispersed in the polymerization. After making the polymerizable monomer composition, the polymerizable monomer composition is dispersed in a continuous layer containing a dispersion stabilizer (for example, an aqueous phase such as the aqueous dispersion medium) using an appropriate stirrer and simultaneously A polymerization reaction is performed to obtain toner particles having a desired particle size. The toner particles obtained by this suspension polymerization method have the physical property requirement that the average circularity is 0.970 or more, especially the mode circularity is 0.990 or more because the individual toner particle shapes are almost spherical. Magnetic toner can be easily obtained, and magnetic toner having a high degree of circularity has high transferability because the distribution of charge amount is relatively uniform.
[0137]
Further, as described in the previous method for producing toner particles, magnetic powder whose surface has been hydrophobized is used, and a polar resin such as a polyester resin having a higher polarity than the binder resin is used. This is important in producing toner particles in which the magnetic powder is not exposed on the surface. As such a polar resin, not only the polyester resin described above, but also the styrene resin has a high polarity. By introducing a functional group such as a carboxyl group or a hydroxyl group, the polarity can be increased and reflected in the surface composition of the toner particles. The functional groups introduced at this time include the occurrence of leak sites due to the presence of many highly polar functional groups on the surface of the toner particles, and extremely low chargeability under high temperature and high humidity due to adsorption of moisture. The number of functional groups is preferably within a range that does not occur. It is also possible to select a functional group capable of obtaining the desired physical properties of the toner particles and introduce it into the polar resin such as the polyester resin.
[0138]
In the magnetic toner of the present invention, it is also important that an inorganic fine powder having an average primary particle size of 4 to 80 nm is added as a fluidizing agent. The inorganic fine powder is added to improve the flowability of the magnetic toner and to make the toner particles uniformly charged. However, the inorganic fine powder can be subjected to a treatment such as a hydrophobic treatment to adjust the charge amount of the toner particles and improve the environmental stability. It is also a preferable form to provide functions such as improvement.
[0139]
When the average primary particle diameter of the inorganic fine powder is larger than 80 nm, or when no inorganic fine powder of 80 nm or less is added, it becomes easy to adhere to the charging member when the transfer residual toner adheres to the charging member. Therefore, it may be difficult to stably obtain good charging characteristics. In addition, good fluidity of the magnetic toner cannot be obtained, 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 occur. When the average primary particle size of the inorganic fine powder is smaller than 4 nm, the agglomeration property of the inorganic fine powder is increased, and the aggregate is not a primary particle but an aggregate having a wide particle size distribution having a strong agglomeration property that is difficult to break even by crushing treatment It tends to behave and may cause image defects due to development of aggregates, damage to the photoreceptor or the toner carrier, and the like. In order to make the charge distribution of the magnetic toner more uniform, the average primary particle size of the inorganic fine powder is preferably 6 to 35 nm.
[0140]
In the present invention, the average primary particle diameter of the inorganic fine powder is, for example, a photograph of a magnetic toner magnified by a scanning electron microscope, and further by an elemental analysis means such as XMA attached to the scanning electron microscope. The number average diameter is determined by measuring 100 or more primary particles of inorganic fine powder adhering to or freeing from the toner particle surface while comparing photographs of magnetic toner mapped with elements contained in Measure with
[0141]
As the inorganic fine powder used in the present invention, for example, silica fine powder such as silica, alumina, titania and the like can be used.
More specifically, for example, as the fine silicate powder, 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, but 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 a composite fine powder 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, The inorganic fine powder includes them.
[0142]
The addition amount of the inorganic fine powder having an 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. It may not be sufficiently exhibited, and if it is 3.0% by mass or more, the fixability may be deteriorated.
[0143]
The surface of the inorganic fine powder is preferably hydrophobized in view of characteristics in a high temperature and high humidity environment. When the inorganic fine powder in the magnetic toner absorbs moisture, the charge amount of the toner particles is remarkably reduced, and the toner is easily scattered.
[0144]
Treatment agents for hydrophobizing inorganic fine powder include silicone varnish, various modified silicone varnishes, silicone oil, various modified silicone oils, silane compounds, silane coupling agents, other organic silicon compounds, organic titanium compounds, etc. Or a mixture of two or more thereof. Among them, those treated with silicone oil are preferred, and more preferably, treatment with silicone oil at the same time as or after hydrophobizing inorganic fine powder increases the charge amount of the magnetic toner even in a high humidity environment. It is good for maintaining and preventing toner scattering.
[0145]
As the processing conditions for the inorganic fine powder, for example, a silylation reaction is carried out as a first stage reaction and silanol groups are eliminated by chemical bonding, and then a hydrophobic thin film is formed on the surface with silicone oil as a second stage reaction. it can. The silicone oil has a viscosity at 25 ° C. of 10 to 200,000 mm.²/ S, moreover, 3,000-80000mm²/ S is preferred. 10mm²If it is less than / s, the stability of the hydrophobized layer on the inorganic fine powder is small, and the image quality tends to deteriorate due to heat and mechanical stress. 200000mm²If it exceeds / s, uniform processing tends to be difficult.
[0146]
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.
As a method for treating the 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 silicone oil is sprayed onto the inorganic fine powder. A method may be used. Alternatively, after dissolving or dispersing silicone oil in an appropriate solvent, an inorganic fine powder such as silica 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.
[0147]
The treatment amount of the silicone oil is 1 to 23 parts by mass, preferably 5 to 20 parts by mass with respect to 100 parts by mass of the inorganic fine powder. If the amount of silicone oil is too small compared to the above range, good hydrophobicity may not be obtained, and if it is too large, problems such as fogging may occur.
[0148]
The inorganic fine powder having an average primary particle size of 80 nm or less used in the present invention has a specific surface area of 20 to 250 m by nitrogen adsorption measured by the BET method.²/ G is preferred, more preferably 40-200m²/ G is even better. If the specific surface area is smaller than the above range, it may be difficult to obtain desired fluidity, and if it is too large, the charging stability of the magnetic toner may be adversely affected.
[0149]
The BET specific surface area can be obtained by the BET multipoint method using a fully automatic gas adsorption amount measuring device: Autosorb 1 manufactured by Yuasa Ionics Co., Ltd., using nitrogen as the adsorption gas. In addition, as pre-processing of a sample, it is preferable to deaerate for 10 hours at the temperature of 50 degreeC.
[0150]
Further, for the purpose of improving the cleaning property of the photosensitive member after transfer, the primary particle size exceeds 30 nm (preferably the specific surface area is 50 m).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.
[0151]
The magnetic toner of the present invention may further contain other additives within a range that does not substantially adversely affect, for example, a lubricant powder such as Teflon powder, zinc stearate powder, polyvinylidene fluoride powder, cerium oxide powder, silicon carbide powder. An abrasive such as strontium titanate powder, or a fluidity imparting agent such as titanium oxide powder or aluminum oxide powder, an anti-caking agent, or a conductivity imparting agent such as carbon black powder, zinc oxide powder or tin oxide powder, In addition, organic fine particles having opposite polarity and inorganic fine particles can be used in a small amount as a developability improver. These additives can also be used after hydrophobizing the surface.
[0152]
Next, an example of the image forming apparatus of the present invention will be specifically described with reference to the drawings.
In FIG. 1, reference numeral 100 denotes a photosensitive drum (image carrier itself). A primary charging roller 117 that abuts the photosensitive drum 100 around the photosensitive drum 100 to charge the photosensitive drum 100, and a laser beam is applied to the charged photosensitive drum 100 to sensitize the photosensitive drum 100. A laser generator (exposure device) 121 that forms an electrostatic latent image on the drum 100, and a developer (development device) that stores the developer inside and supplies the developer to the photosensitive drum 100 on which the electrostatic latent image is formed. 140, a transfer charging roller 114 for transferring a toner image visualized by the developer onto a transfer material (plain paper or the like), a cleaner 116 for removing the developer remaining on the photosensitive drum 100 after the transfer, and the photosensitive drum 100. A register roller 124 that conveys the transfer material between the transfer charging roller 114, a conveyance belt 125 that conveys the transfer material onto which the toner image has been transferred to the next stage, and a transfer Fixer 126 for fixing the toner image on the transfer material, etc. is provided that has been transferred to. The photosensitive drum 100, the developing device 140, the primary charging roller 117, and the cleaner 114 are arranged in the image forming apparatus as a process cartridge that is integrally and detachably held by a holding member (not shown). It is installed.
[0153]
As shown in FIG. 2, the developing device 140 is open facing the photosensitive drum 100, and the opening is close to the photosensitive drum 100 and is made of a nonmagnetic metal such as aluminum or stainless steel. The developer carrying member (developing sleeve) 102 is provided. The developing sleeve 102 has a cylindrical shape, and 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. The magnet roller 104 is provided with a plurality of magnetic poles as shown in the figure, where S1 affects the development, N1 controls the developer coating amount, S2 takes in / conveys the developer, and N2 affects the prevention of the developer from blowing out. . In addition, the developing device 140 is provided with an elastic blade 103 that regulates the amount of developer adhering to the developing sleeve 102, and the development conveyed to the developing region by the contact pressure of the elastic blade 103 against the developing sleeve 102. The dosage is controlled. Further, an agitating member 141 for agitating the contained developer is provided inside the developing device 140, and in the developing device 140, magnetic toner of an embodiment described later is accommodated as a developer. The gap between the photoconductor 100 and the developing sleeve 102 is maintained at about 300 μm by the holding member or the like.
[0154]
As shown in FIG. 3, the transfer charging roller 114 has a conductive metal core 34a and an elastic layer 34b covering the peripheral surface of the metal core 34a. A transfer charging device 35 to be applied to the gold 34a is connected.
[0155]
An example of the image forming method of the present invention using the image forming apparatus having the above configuration will be described below.
The photoreceptor 100 is charged to −700 V by the primary charging roller 117. (Applied voltage is AC voltage -2.0 kVpp, DC voltage -700 Vdc) Then, the photosensitive drum 100 is exposed by irradiating the photosensitive member 100 with the laser beam 123 by the laser generator 121 to form an electrostatic latent image.
On the other hand, in the developing device 140, the magnetic toner adheres to the developing sleeve 102 by the magnetic force of the magnet roller 104, the amount of adhesion is regulated by the elastic blade 103, and uniformly adheres to the developing sleeve 102. The magnetic toner is charged by the friction between the magnetic toners by the stirring of the stirring member 141, the friction with the elastic blade 103, or the like until it uniformly adheres to the developing sleeve 102.
A developing bias electric field is formed between the photosensitive member 100 and the developing sleeve 102 by applying a developing bias voltage having a DC voltage and an AC voltage from a developing bias applying means (not shown) to the developing sleeve 102, thereby forming the developing sleeve. The magnetic toner on 102 flies onto the photoconductor 100 according to the electrostatic latent image, and visualizes the electrostatic latent image.
The electrostatic latent image (toner image) visualized by the magnetic toner is transferred onto the transfer material by the transfer charging roller 114 to which the transfer bias is applied by the transfer charging device 35 while facing the photoreceptor 100 via the transfer material. Transcribed. The transfer material onto which the toner image has been transferred is conveyed to the fixing device 126 by the conveyance belt 125 and fixed on the transfer material. Further, the magnetic toner remaining on a part of the photoreceptor is cleaned by the cleaning unit 116.
[0156]
The magnetic toner defines its particle size and average circularity. Therefore, the magnetic powder in the magnetic toner has a uniform distribution, the magnetism of the magnetic toner is uniform, and the shape of the magnetic toner is within a certain distribution. Therefore, in the image forming method, the electrostatic latent image is finer. A toner image that can be visualized and finely visualized can be directly transferred to a transfer material. Therefore, in the image forming method using the magnetic toner, an image showing good developability and high image quality can be obtained.
In addition, the magnetic toner has a spherical shape and the magnetic powder is not exposed on the surface, so it has good fluidity and does not deteriorate due to friction between the magnetic toners or between the magnetic toner and each member. In addition, since each member or the like is not damaged by friction, a high-quality image can be stably formed.
The magnetic toner is also preferably applied to a simultaneous development cleaning image forming method or a cleanerless image forming method.
[0157]
Further, the toner particles in the magnetic toner described above have a sharp particle size distribution, and the state and composition of the magnetic toner are uniform. For these reasons, the charging speed and charge amount distribution of the toner particles are uniform, and there is little transfer residual toner.
Further, the toner particles can be efficiently manufactured by the above-described toner particle manufacturing method.
[0158]
A method for measuring various physical property data according to the present invention will be described in detail below.
(1) Average circularity and mode circularity of magnetic toner
The average circularity and the mode circularity in the present invention are used as a simple method for quantitatively expressing the shape of the particles. In the present invention, flow type particle image analyzer FPIA-1000 manufactured by Toa Medical Electronics is used. The circularity of the particles measured for a toner particle group having a particle diameter of 3 μm or more is obtained from the following formula 2, and the total roundness of all the measured particles is calculated as shown in the following formula 3. The value obtained by dividing the total number of particles (m) by the average circularity (E_mean).
[0159]
[Formula 2]
Circularity E = L₀/ L
(Where L₀Indicates the perimeter of a circle having the same projected area as the particle image, and L indicates the perimeter of the projected image of the particle. )
[0160]
[Formula 3]

In addition, the mode circularity is obtained by dividing the circularity from 0.40 to 1.00 into 61 divisions every 0.01, and assigning the measured magnetic toner circularity to each division range according to the circularity. This is the circularity of the peak having the maximum frequency value in the frequency distribution.
[0161]
In addition, “FPIA-1000” as the analysis apparatus calculates the circularity of each particle, and then calculates the average circularity and the mode circularity according to the circularity obtained from the particles. A calculation method is used in which 0.000 is divided into 61 classes, and the average circularity and 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.
[0162]
As a specific measurement method, about 5 mg of magnetic toner is dispersed in 10 mL of water in which about 0.1 mg of a surfactant is dissolved to prepare a dispersion, and ultrasonic waves (20 KHz, 50 W) are applied to the dispersion for 5 minutes. Irradiation is performed, the dispersion concentration is set to 5000 to 20,000 / μL, and measurement is performed by the above-described apparatus to determine the average circularity and mode circularity of the toner particle group having a particle diameter of 3 μm or more.
[0163]
The average circularity in the present invention is an index of the degree of unevenness of the developer, and is 1.000 when the developer is a perfect sphere, and the average circularity becomes smaller as the developer surface shape becomes more complex. Become.
The reason for measuring the circularity only for the toner particle group having a particle diameter of 3 μm or more in this measurement is that the particle group of less than 3 μm includes many particle groups such as external additives that exist independently of the toner particles. For this reason, the circularity of only the toner particle group may not be accurately estimated due to the influence.
[0164]
(2) Ratio of iron element content (B) to carbon element content (A) present on the toner particle surface (B / A)
The ratio (B / A) of the content of iron element (B) to the content of carbon element (A) present on the toner particle surface according to the present invention (B / A) is determined by ESCA (X-ray photoelectron spectroscopy). And calculate. At this time, it is preferable to measure after the magnetic toner to be measured is ultrasonically cleaned to remove deposits and the like adhering to the surface of the toner particles, and then the washed toner particles are separated by magnetic force and dried. .
In the present invention, the ESCA apparatus and measurement conditions are as follows.
Equipment used: 1600S type X-ray photoelectron spectrometer manufactured by PHI

In the present invention, the surface atomic concentration is calculated from the measured peak intensity of each element using a relative sensitivity factor provided by PHI. In this measurement, the magnetic toner is ultrasonically cleaned, and external additives such as inorganic fine powder adhering to the surface of the magnetic toner are removed, and then separated by magnetic force, dried and measured. When it is difficult to remove the external additive, ultrasonic cleaning is performed in an organic solvent that does not dissolve the magnetic toner, such as isopropanol.
[0165]
(3) Method for measuring fog of fixed image
The fog is measured using a REFECTMETER MODEL TC-6DS manufactured by Tokyo Denshoku.
As a filter, a green filter was used and calculated from the following formula 4. The smaller the value, the less fog.
[0166]
[Formula 4]
Fog (reflectance) (%) =
Reflectivity on standard paper (%)-Reflectance of sample non-image area (%)
[0167]
(4) Acid value measurement method
The acid value of the polyester resin in the present invention is determined by the following method.
2-10 g of polyester resin is weighed into a 200 mL Erlenmeyer flask, and about 50 mL of a mixed solvent of methanol: toluene = 30: 70 is further added to dissolve the magnetic toner or toner particles. It was pre-labeled with 0.1% bromthymol blue and phenol red mixed reagent. Titration to a 1M potassium hydroxide / ethanol solution and the acid value is determined from the following formula 5 from the consumption of the potassium hydroxide / ethanol solution.
[0168]
[Formula 5]

(In the above formula, f is a factor of a 0.1M potassium hydroxide / ethanol solution.)
[0169]
【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.
[0170]
First, an example of manufacturing a magnetic material (magnetic powder) will be described below.
(Production Example 1 of Surface-treated Magnetic Material)
An aqueous solution containing ferrous hydroxide was prepared by mixing 1.0 to 1.1 equivalents of a caustic soda solution and sodium silicate 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 and an oxidation reaction was performed at 80 to 90 ° C. to prepare a slurry liquid for generating seed crystals.
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 pH 8, and air is supplied. The oxidation reaction was promoted while blowing, and the magnetic iron oxide particles produced after the oxidation reaction were washed, filtered, and taken out once. 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_TenH_{twenty one}Si (OCH_Three)_Three) Was added to magnetic iron oxide in an amount of 1.2 parts by mass (the amount of magnetic iron oxide was calculated as a value obtained by subtracting the water content from the water-containing sample) and subjected to a coupling treatment. The produced hydrophobic iron oxide particles were washed, filtered and dried by a conventional method, and then the slightly agglomerated particles were crushed to obtain a surface-treated magnetic body 1.
[0171]
(Production Example 1 of magnetic material)
In the same manner as in Production Example 1 of the surface-treated magnetic material, the magnetic iron oxide particles generated after the oxidation reaction are washed, filtered, dried without surface treatment, and the aggregated particles are crushed. As a result, magnetic body 1 was obtained.
[0172]
(Production Example 2 of Surface-treated Magnetic Material)
After re-dispersing the magnetic substance 1 obtained in Production Example 1 of the magnetic substance in another aqueous medium, the pH of the re-dispersed liquid was adjusted to about 6, and the silane coupling agent (n- C_TenH_{twenty one}Si (OCH_Three)_Three) Was added to 1.2 parts by mass with respect to magnetic iron oxide, and a coupling treatment was performed. The produced hydrophobic iron oxide particles were washed, filtered and dried by a conventional method, and then the agglomerated particles were pulverized to obtain a surface-treated magnetic body 2.
[0173]
(Production Example 3 of Surface-treated Magnetic Material)
In Production Example 1 of the surface-treated magnetic material, a silane coupling agent was used.
(N-C₆H₁₁Si (OCH_Three)_ThreeThe surface-treated magnetic body 3 was obtained in the same manner except that.
[0174]
(Production Example 4 of Surface-treated Magnetic Material)
The magnetic body 1 obtained in Production Example 1 of the magnetic body is obtained by adding 1.2 parts by mass of a silane coupling agent (nC_TenH_{twenty one}Si (OCH_Three)_ThreeThe surface-treated magnetic body 4 was obtained by performing surface treatment in the gas phase.
Table 1 shows the average particle diameters of the magnetic materials obtained by the above-described production examples.
[0175]
[Table 1]

[0176]
Next, production examples of the polyester resin will be described below.
(Production Example 1 of Polyester Resin)
403 parts by mass of EO addition product of bisphenol A (hydroxyl value 320), 287 parts by mass of PO adduct of bisphenol A (hydroxyl value 300) in a reaction vessel equipped with a thermometer, stirrer, cooler and nitrogen introduction tube, terephthalic acid 312 parts by mass and 3 parts by mass of dibutyltin oxide were added and reacted at 230 ° C. in a nitrogen stream. When the reaction product became transparent, the polyesterification reaction proceeded under reduced pressure, and when the acid value reached 10, the reaction was stopped to obtain polyester resin 1. The resin had a Tg of 58 ° C. and a number average molecular weight of 5,200.
[0177]
(Production Example 2 of Polyester Resin)
In a reaction vessel equipped with a thermometer, a stirrer, a cooler and a nitrogen introduction tube, 681 parts by mass of PO adduct of bisphenol A (hydroxyl value 316), 218 parts by mass of fumaric acid and 2.8 parts by mass of dibutyltin oxide were placed. The reaction was conducted at 230 ° C. in a nitrogen stream. When the reaction product became transparent, the polyesterification reaction proceeded under reduced pressure, and when the acid value reached 10, the reaction was stopped to obtain polyester resin 2. The resin had a Tg of 57 ° C. and a number average molecular weight of 5100.
[0178]
(Production Example 3 of Polyester Resin)
The same operation as in Production Example 1 for polyester resin was performed, and when the acid value reached 20, 50 parts by mass of SF8413 (manufactured by Toray Dow Corning) shown in the following general formula (V) was added, and the reaction was continued. When the value reached 10, the reaction was stopped to obtain polyester resin 3. The resin had a Tg of 55 ° C. and a number average molecular weight of 5,500. <Structure of SF8413>
[0179]
[Chemical formula 5]

[0180]
Next, production examples of toner particles using the above-described magnetic material and polyester resin will be described below.
(Production Example 1 of Toner Particles)
0.1M-Na in 720 parts by mass of ion-exchanged water_ThreePO_FourAfter 450 parts by mass of the aqueous solution was added and heated to 60 ° C., 21 mL of 1N hydrochloric acid was added so that the pH after addition of the aqueous calcium chloride solution was 5.1, and 1.0 M-CaCl was added.₂67.7 parts by mass of the aqueous solution was gradually added to obtain an aqueous dispersion medium having a pH of 5.1 containing calcium phosphate.
80 parts by mass of styrene
20 parts by mass of n-butyl acrylate
5 parts by mass of polyester resin 1
Negative charge control agent (monoazo dye-based Fe compound) 1 part by mass
Surface treatment magnetic material 1 100 parts by mass
The above formulation was uniformly dispersed and mixed using a TK homomixer (Special Machine Industries Co., Ltd.).
This polymerizable monomer composition is heated to 60 ° C., and 10 parts by mass of ester wax (the maximum value of endothermic peak in DSC at 72 ° C.) mainly composed of behenyl behenate is added, mixed, dissolved, and polymerized therein. 4 parts by mass of initiator 2,2′-azobis (2,4-dimethylvaleronitrile) was dissolved.
The polymerizable monomer system was charged into the aqueous dispersion medium and granulated by stirring at 10000 rpm for 15 minutes in a TK homomixer (Special Machine Industries Co., Ltd.) in a nitrogen atmosphere at 60 ° C. Thereafter, the mixture was reacted at 60 ° C. for 6 hours while stirring with a paddle stirring blade. Thereafter, the liquid temperature was raised to 80 ° C., and stirring was further continued for 4 hours. After completion of the reaction, distillation was further performed at 80 ° C. for 2 hours, after which the suspension was cooled, hydrochloric acid was added to dissolve the calcium phosphate salt, filtered, washed with water, and dried to have a weight average particle diameter of 6.8 μm, number average Toner particles A having a particle size of 6.1 μm were obtained.
[0181]
(Toner particle production example 2)
In toner particle production example 1, toner particles B were obtained in the same manner as in production example 1 except that 1N hydrochloric acid was added to 18 mL so that the pH after addition of the calcium chloride aqueous solution was 6.0.
[0182]
(Toner particle production example 3)
In toner particle production example 1, toner particles C were obtained in the same manner as in production example 1 except that 1N hydrochloric acid was added to 13.5 mL so that the pH after addition of the calcium chloride aqueous solution was 7.0. .
[0183]
(Toner particle production example 4)
In toner particle production example 1, toner particles D were obtained in the same manner as in production example 1 except that 1N hydrochloric acid was added to 9 mL so that the pH after addition of the calcium chloride aqueous solution was 8.5.
[0184]
(Toner particle production example 5)
In toner particle production example 1, toner particles E were obtained in the same manner as in production example 1 except that 1N hydrochloric acid was added to 32 mL so that the pH after addition of the calcium chloride aqueous solution was 4.5.
[0185]
(Toner Particle Production Example 6)
Toner particles F were obtained in the same manner as in Production Example 1 except that 21.5 mL of 1N hydrochloric acid was added so that the pH was 5.1 after adding the calcium chloride aqueous solution.
[0186]
(Toner particle production example 7)
Toner particles G were obtained in the same manner as in Production Example 1 except that magnesium chloride was used instead of the calcium chloride aqueous solution in Toner Particle Production Example 1.
[0187]
(Toner Particle Production Example 8)
In Toner Particle Production Example 1, toner was produced in the same manner as in Production Example 1 except that 1N sulfuric acid was used instead of 1N hydrochloric acid so that the pH after addition of calcium chloride aqueous solution was 6.0. Particle H was obtained.
[0188]
(Toner particle production example 9)
In the toner particle production example 1, 1N nitric acid is used instead of the 1N hydrochloric acid instead of the 1N hydrochloric acid so that the pH after adding the calcium chloride aqueous solution becomes 7.0, and the polymerization initiator is 2,2′-azobis ( Toner particles I were obtained in the same manner as in Production Example 1 except that t-butylperoxy-2-ethylhexanoate was used instead of 2,4-dimethylvaleronitrile).
[0189]
(Toner particle production example 10)
In toner particle production example 1, toner particles J were obtained in the same manner as in production example 1 except that surface treated magnetic body 2 was used instead of surface treated magnetic body 1.
[0190]
(Production Example 11 of Toner Particles)
In toner particle production example 1, toner particles K were obtained in the same manner as in production example 1 except that surface-treated magnetic body 3 was used instead of surface-treated magnetic body 1.
[0191]
(Toner Particle Production Example 12)
A toner particle L was obtained in the same manner as in Production Example 1 except that the surface-treated magnetic body 4 was used instead of the surface-treated magnetic body 1 in the toner particle production example 1.
[0192]
(Toner Particle Production Example 13)
In toner particle production example 1, toner particles M were obtained in the same manner as in production example 1 except that 5 parts by mass of polyester resin 1 was used and 2 parts by mass of polyester resin 2 was used.
[0193]
(Toner Particle Production Example 14)
In Toner Particle Production Example 1, toner was produced in the same manner as in Production Example 1 except that 5 parts by mass of polyester resin 1 was used and 9 parts by mass of polyester resin 1 and 1 part by mass of polyester resin 2 were used. Particle N was obtained.
[0194]
(Toner Particle Production Example 15)
Toner particle O was obtained in the same manner as in Production Example 1 except that, in toner particle production example 1, instead of using 5 parts by mass of polyester resin 1, 20 parts by mass of polyester resin 3 was used.
[0195]
(Comparative Production Example 1 of Toner Particles)
In toner particle production example 1, toner particles P were obtained in the same manner as in production example 1 except that 1N hydrochloric acid was added to 40 mL so that the pH after addition of the calcium chloride aqueous solution was 4.2.
[0196]
(Comparative Production Example 2 of Toner Particles)
In toner particle production example 1, toner particles Q were obtained in the same manner as in production example 1 except that 1N hydrochloric acid was added to 7.5 mL so that the pH after addition of the aqueous calcium chloride solution was 8.7. .
[0197]
(Comparative Production Example 3 of Toner Particles)
In toner particle production example 1, toner particles R were obtained in the same manner as in production example 1 except that magnetic material 1 was used instead of surface-treated magnetic material 1.
[0198]
(Comparative Production Example 4 of Toner Particles)
In Toner Particle Production Example 1, toner particles S were obtained in the same manner as in Production Example 1 except that no polyester resin was used.
[0199]
(Toner Particle Production Example 16)
In Production Example 1 of toner particles, an aqueous dispersion medium containing calcium phosphate and having a pH of 5.1 is used as 0.5 M Na._ThreePO_FourAfter 90 parts by mass of the aqueous solution was added and heated to 60 ° C., 21 mL of 1N hydrochloric acid was added so that the pH after addition of the aqueous calcium chloride solution was 5.1, and 1.0 M-CaCl was added.₂A toner particle T was obtained in the same manner as in Production Example 1 except that 67.7 parts by mass of an aqueous solution was gradually added and 0.005 part by mass of sodium dodecylbenzenesulfonate was added.
[0200]
(Comparative Production Example 5 of Toner Particles)
In Production Example 1 of toner particles, an aqueous dispersion medium was prepared by dissolving an aqueous solution in which 19 parts of magnesium chloride was dissolved in 500 parts of ion-exchanged water, and an aqueous solution in which 11.6 parts of sodium hydroxide was dissolved in 100 parts of ion-exchanged water. Toner particles U were produced in the same manner as in Production Example 1 except that the mixture was gradually added under stirring to obtain an aqueous dispersion medium having a pH = 13.0 containing magnesium hydroxide colloid.
[0201]
Next, an example of manufacturing a magnetic toner using the above-described toner particles will be described below.
The magnetic toner is obtained by treating the toner particles A to U with 100 parts by mass and silica having a primary particle diameter of 12 nm with hexamethyldisilazane and then treating with silicone oil, and the BET value after treatment is 140 m.²Toners 1 to 21 were prepared by mixing 1.2 parts by mass of / g hydrophobic silica fine powder with a Henschel mixer (Mitsui Miike Chemical Co., Ltd.).
The strength of magnetization of the obtained magnetic toner at a magnetic field of 79.6 kA / m is 26 to 30 Am.²/ Kg.
The production conditions of the obtained toner particles are shown in Tables 2 and 3, and the physical properties of the magnetic toner are shown in Tables 4 and 5, respectively. The pH (1) in Table 2 is the pH of the aqueous dispersion medium containing the metal salt colloid and adjusted with an inorganic acid, and the pH (2) in Table 2 is an aqueous solution that is the base of the metal salt colloid. Is the pH of the aqueous solution obtained by mixing.
[0202]
[Table 2]

[0203]
[Table 3]

[0204]
[Table 4]

[0205]
[Table 5]

[0206]
Next, an image formed by an electrophotographic image forming apparatus was formed in different environments using the toners 1 to 21 described above, and the image quality of images obtained with these toners was evaluated.
[0207]
Example 1
As the image forming apparatus, the image forming apparatus (LBP-1760) according to the image forming apparatus shown in FIG.
An organic photoreceptor (OPC) drum was used as the image carrier (photoreceptor). A rubber roller charger in which conductive carbon is dispersed as a primary charging member and coated with nylon resin is brought into contact with this photoreceptor (contact pressure 60 g / cm), and an AC voltage of 2.0 kVpp is superimposed on a DC voltage of −700 Vdc. A bias is applied to uniformly charge the photosensitive member. Subsequent to primary charging, an electrostatic latent image is formed by exposing the image portion with laser light. At this time, the dark portion potential Vd = −700 V and the bright portion potential VL = −180 V.
The gap between the photosensitive drum and the developing sleeve is 290 μm, and the toner carrier has a resin layer with a layer thickness of about 7 μm and a JIS centerline average roughness (Ra) of 1.0 μm as described below. Using a developing sleeve formed on a cylinder, a developing magnetic pole of 85 mT (850 gauss), a toner regulating member having a thickness of 1.0 mm and a free length of 1.0 mm of a silicone rubber blade of 24.5 N / m (25 g / cm). The contact was made with linear pressure.
100 parts of phenolic resin
90 parts of graphite (particle size approx. 7μm)
10 parts of carbon black
Next, a DC bias component Vdc = −500 V, an overlapping AC bias component Vp−p = 1700 V, and f = 2000 Hz were used as the developing bias. The peripheral speed of the developing sleeve was 110% (103 mm / sec) in the forward direction with respect to the peripheral speed of the photosensitive member (94 mm / sec).
Also, a transfer roller (made of ethylene-propylene rubber in which conductive carbon is dispersed, volume resistance value of conductive elastic layer 108 Ωcm, surface rubber hardness 24 °, diameter 20 mm, contact pressure 59 N / m (60 g / cm)) is illustrated. 3 at a constant speed relative to the circumferential speed of the photoreceptor (94 mm / sec) in the A direction, and the transfer bias was 1.5 kV DC.
As a fixing method, there was used a fixing device of LBP-1760 which does not have an oil application function and which is fixed by heating and pressing with a heater through a film. At this time, a pressure roller having a fluororesin surface layer was used, and the diameter of the roller was 30 mm. The fixing temperature was set to 185 ° C. and the nip width was set to 7 mm.
First, toner 1 is used as a developer, and the image is printed under normal temperature and humidity (25 ° C., 60% RH), high temperature and high humidity (30 ° C., 80% RH), and low temperature and low humidity (15 ° C., 10% RH) environment. A dispensing test was conducted. 75g / m as transfer material²Paper was used. As a result, a high transfer property was exhibited at the initial stage, no transfer of characters or lines was lost during transfer, and a good image free from fogging on non-image areas was obtained.
[0208]
Next, durability was evaluated using a grid image pattern composed of horizontal lines with a printing area ratio of 4%.
Image evaluation was performed as follows.
The evaluation of the photoconductor scraping and toner fusion was judged by the number of durable sheets in which image defects due to scraping or toner fusion, that is, black spots or white spots, occurred on a halftone image in which image defects tend to appear. It means that the durability of the image forming method is better as the number of the durable sheets is increased. In addition, image defects due to primary charging failure due to transfer residual toner, that is, charging unevenness were also evaluated on the halftone image. When these image defects did not occur, the durability test was continued up to 5000 printed sheets.
In this embodiment, a printout test of 5000 sheets was performed in a continuous mode (that is, a mode in which toner consumption is promoted by continuously passing paper).
[0209]
Image evaluation was performed as follows.
(1) Image density
Ordinary paper for ordinary copying machines (75 g / m²) Was evaluated by maintaining the image density at the end of printing out 5000 sheets. The image density was measured by using “Macbeth reflection densitometer RD918” (manufactured by Macbeth Co., Ltd.) to measure the relative density with respect to the printout image of the white background portion where the document density is 0.00.
A (excellent): 1.40 or more
B (good): 1.35 or more, less than 1.40
C (possible): 1.00 or more, less than 1.35
D (No): Less than 1.00
[0210]
(2) Image fog
The fog density (%) was calculated from the difference between the whiteness of the white background portion of the printout image and the whiteness of the transfer paper measured by “REFLECTMETER MODEL TC-6DS” (manufactured by Tokyo Denshoku Co., Ltd.), and the image fogging was evaluated. . A green filter was used as the filter.
A: Very good (less than 1.5%)
B: Good (1.5% or more to less than 2.5%)
C: Normal (2.5% or more to less than 4.0%)
D: Poor (4% or more)
[0211]
(3) Transferability
The transferability is determined by removing the transfer residual toner on the photoconductor by tape with Mylar tape when solid black image is formed, and Macbeth with only Mylar tape on the paper, based on the Macbeth density of the stripped Mylar tape on the paper. Evaluation was made by subtracting the concentration.
A: Very good (less than 0.05)
B: Good (0.05 or more to less than 0.1)
C: Normal (more than 0.1 and less than 0.2)
D: Bad (over 0.2)
The initial density was the image density of the 20th sheet from the beginning.
[0212]
(4) Halftone image uniformity
The criteria for determining the image quality are as follows.
A: Very good.
B: Good image although slightly distorted.
C: A level where there is no problem in practical use although it is cluttered.
D: The roughness is severe and impractical.
The obtained results are shown in Tables 6 to 8.
[0213]
(Example 2)
When toner 2 was used as the developer and evaluated in the same manner as in Example 1, very good results were obtained as shown in Tables 6 to 8.
[0214]
(Examples 3 to 16)
Toners 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, and 20 were used as developers, and evaluation was performed in the same manner as in Example 1. As a result, practically satisfactory results were obtained as shown in Tables 6 to 8.
[0215]
(Comparative Example 1)
Evaluation was performed in the same manner as in Example 1 using toner 16 as a developer. As a result, the transferability was poor, and an image with many scattering and low sharpness was obtained. The results are shown in Tables 6-8.
[0216]
(Comparative Example 2)
Evaluation was performed in the same manner as in Example 1 using toner 17 as a developer. As a result, the image has a lot of fog and a lot of roughness. The results are shown in Tables 6-8.
[0217]
(Comparative Example 3)
Evaluation was performed in the same manner as in Example 1 using toner 18 as a developer. As a result, the image density was slightly low from the beginning, and there were many transfer residues and fogging, making it impossible to continue the durability test to the end. The results are shown in Tables 6-8.
[0218]
(Comparative Example 4)
Toner 19 was used as a developer, and evaluation was performed in the same manner as in Example 1. As a result, since the image density was extremely low from the beginning, and there were many transfer residues and fog, it was impossible to carry out the test. The results are shown in Tables 6-8.
[0219]
(Comparative Example 5)
Evaluation was performed in the same manner as in Example 1 using toner 21 as a developer. As a result, the image density was low from the beginning, there were many transfer residues and fogging, and the image quality was low. The results are shown in Tables 6-8.
[0220]
[Table 6]

[0221]
[Table 7]

[0222]
[Table 8]

[0223]
【The invention's effect】
According to the present invention, the circularity is 0.970 or more, and the ratio of the iron element content to the carbon element content on the toner particle surface is an iron element content / carbon element content of less than 0.001. And the strength of magnetization at a magnetic field of 79.6 kA / m is 10 to 50 Am.²By using a special magnetic toner of / kg, it is excellent in environmental stability, and high-quality and high-resolution images can be stably obtained for a long period of time regardless of environmental differences.
Furthermore, according to the method for producing toner particles of the present invention, it is possible to efficiently provide a magnetic toner capable of outputting a high-quality image as described above.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is an enlarged view showing the periphery of the photosensitive drum and the developing device in FIG. 1;
FIG. 3 is an enlarged view showing the periphery of the photosensitive drum and the transfer charging roller in FIG. 1;
[Explanation of symbols]
34a cored bar
34b Elastic layer
35 Transfer charging device
100 Photosensitive drum (image carrier)
102 Development sleeve (developer carrier)
103 Elastic blade
104 Magnet roller
114 Transfer charging roller
116 Cleaner
117 Primary charging roller
121 Laser generator (exposure equipment)
123 Laser light
124 register roller
125 Conveyor belt
126 Fixing device
140 Developer (Developer)
141 Stirring member

Claims (23)

A method for producing toner particles having at least a binder resin, a magnetic powder whose surface is hydrophobized, and a polyester resin,
The pH of an aqueous dispersion medium containing a hardly water-soluble metal salt colloid as a dispersion stabilizer is adjusted to 4.5 to 8.5, and at least the polymerizable monomer that forms the binder resin by polymerization, the surface is hydrophobic The polymerizable monomer composition containing the treated magnetic powder and the polyester resin is dispersed in the aqueous dispersion medium adjusted in pH, and droplet particles of the polymerizable monomer composition are dispersed in the aqueous dispersion medium. And producing a toner particle by polymerizing the polymerizable monomer in the droplet particles in the presence of a polymerization initiator ,
The toner surface is hydrophobized magnetic powder, characterized in that the magnetic iron oxide particles produced from the ferrous hydroxide is magnetic iron oxide particles treated hydrophobic in an aqueous medium without drying Particle production method.   2. The toner particle manufacturing method according to claim 1, wherein the toner particle manufacturing method is a suspension polymerization method.   2. The method for producing toner particles according to claim 1, wherein the metal salt colloid is a phosphate metal salt colloid.   4. The method for producing toner particles according to claim 3, wherein the phosphate metal salt colloid is a calcium phosphate salt obtained by mixing a phosphate aqueous solution and a calcium salt aqueous solution. The method for producing toner particles according to claim 1, wherein the magnetic powder is magnetic iron oxide particles hydrophobized with a coupling agent. 6. The method for producing toner particles according to claim 5, wherein the magnetic powder is magnetic iron oxide particles hydrophobized by hydrolyzing a silane coupling agent in an aqueous medium. The aqueous dispersion medium is adjusted to pH 4.5 to 8.5 by adding a calcium salt aqueous solution after dropping a water-soluble inorganic acid into a phosphate aqueous solution. The manufacturing method of the toner particle of description.   The pH of the aqueous dispersion medium is adjusted to 4.5 to 8.5 by mixing a phosphate aqueous solution and a calcium salt aqueous solution and then adding a water-soluble inorganic acid dropwise. 2. The method for producing toner particles according to 1.   The method for producing toner particles according to claim 7 or 8, wherein the pH of the aqueous dispersion medium is adjusted to 5.0 or more and 7.0 or less.   9. The toner particles according to claim 7, wherein the addition amount of the water-soluble inorganic acid is 0.2 to 0.9 molar equivalent with respect to 1 mol of phosphate in the aqueous phosphate solution. Manufacturing method.   The method for producing toner particles according to claim 10, wherein the water-soluble inorganic acid is a water-soluble inorganic acid selected from the group consisting of hydrochloric acid, sulfuric acid, nitric acid, and phosphoric acid.   The method for producing toner particles according to claim 4 or 8, wherein the pH of the aqueous solution obtained by mixing the aqueous phosphate solution and the aqueous calcium salt solution is 7.0 or more and 14.0 or less.   The method for producing toner particles according to claim 12, wherein the pH of the aqueous solution obtained by mixing the aqueous phosphate solution and the aqueous calcium salt solution is 9.0 or more and 14.0 or less.   The method for producing toner particles according to claim 4, wherein the calcium phosphate salt contains hydroxyapatite.   2. The mass fraction of the polymerizable monomer composition with respect to the total mass of the aqueous dispersion medium and the polymerizable monomer composition is 10 or more and 65% or less. The manufacturing method of the toner particle of description.   The method for producing toner particles according to claim 1, wherein the polymerizable monomer contains at least a styrene monomer.   The polymerizable monomer includes two or more of a styrene monomer and at least one monomer selected from an acrylate ester monomer and a methacrylic ester monomer. The method for producing toner particles according to claim 16, wherein a monomer is contained.   The method for producing toner particles according to claim 1, wherein the polyester resin is one or both of a saturated polyester and an unsaturated polyester.   The method for producing toner particles according to claim 1, wherein an alkylene oxide adduct of bisphenol A (average added mole number: 2 to 10) is contained as a component constituting the polyester resin.   20. The method for producing toner particles according to claim 18, wherein the polyester resin has an acid value of 0.1 to 50 mg KOH / resin 1 g.   The method for producing toner particles according to claim 20, wherein the polyester resin is used in an amount of 0.5 to 35 parts by mass with respect to 100 parts by mass of the polymerizable monomer.   The method for producing toner particles according to claim 1, wherein a surfactant is added to the aqueous dispersion medium.   By adding the polymerization initiator to the polymerizable monomer composition or an aqueous dispersion medium in which the polymerizable monomer composition is dispersed, the polymerization monomer in the droplet particles is started to be polymerized. The method for producing toner particles according to claim 1, wherein the polymerization is performed in the presence of an agent.

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