JP2004151638A - Electrostatic charge image developing color toner - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide electrostatic charge image developing color toner which is excellent in low-temperature fixability, hardly gives rise to hot offset, is therefore wide in a fixing margin and is excellent in shelf stability. <P>SOLUTION: The electrostatic charge image developing color toner contains at least a binder resin, a coloring agent and an electrostatic charge controlling agent. In the dynamic viscoelastic characteristics measured under the conditions of a frequency 10 Hz and strain 1% of the electrostatic charge image developing color toner, the storage modulus (G'<SB>80</SB>) at 80°C is 5x10<SP>6</SP>to 5x10<SP>8</SP>Pa; the storage modulus (G'<SB>160</SB>) at 160°C is 1x10<SP>2</SP>to 1x10<SP>4</SP>Pa; the maximal value 1.2 to 2.5 of tangent loss (tanδ) exists at 80 to 100°C; the minimal value 1 to 2 of tanδ exists at 95 to 125°C; and also, a volume average grain size (Dv) is 2 to 11 μm and the ratio (Dv/Dp) of the volume average grain size (Dv) and the number average grain size (Dp) is specified to ≤1.3. <P>COPYRIGHT: (C)2004,JPO

Description

【数２】

【００２６】
また、本発明の静電荷像現像用カラートナーの融解エンタルピーΔＨは、１〜１０ｍＪ／ｍｇが好ましく、２〜６ｍＪ／ｍｇがより好ましく、３〜５ｍＪ／ｍｇが特に好ましい。融解エンタルピーがこの範囲にあると定着性が優れる。ΔＨが高すぎるとトナーの溶融に多大な熱量を必要とし、カラー画像の如く、多色、多層での画像形成の際、低エネルギー定着（低温定着）が達成できない。また、ΔＨが低すぎると定着性が劣る場合や、十分な離型効果が得られない場合がある。なお、ΔＨは示差走査熱量計（ＤＳＣ）曲線のピークトップを吸熱ピークとし、融点から高温側のベースラインより融点に向けてベースラインを延長し、吸熱ピークのラインとの交点とピークに囲まれた範囲より算出する。
【００２７】
上記特性を有する本発明の静電荷像現像用カラートナーの製造は重合法によるのが好ましい。重合法としては、公知の懸濁重合法、乳化重合法、バルク重合法などを適用することができる。これらの中でも、懸濁重合法が帯電性の制御に影響する乳化剤を使用せず、着色剤や帯電制御剤を均一に粒子内に取り込めることができるので好ましく、特に、コア（粒子核部）に低温定着性を担う易溶融性重合体を、シェル（粒子外郭部）にオフセット防止を担う難溶融性重合体を配置したコア・シェル構造の粒子を製造できる二段懸濁重合法がより好ましい。
コア・シェル粒子のコアとシェルとの重量比率は特に限定されないが、通常、８０／２０〜９９．９／０．１、好ましくは８５／１５〜９９／１である。シェルの割合が過度に小さいと保存性が悪くなり、逆に、過度に大きいと低温で定着し難くなることがある。
【００２８】
結着樹脂を得るための重合性単量体として、モノビニル単量体、架橋性単量体、マクロモノマー等を挙げることができる。この重合性単量体が重合して結着樹脂成分となる。
モノビニル単量体としては、具体的にはスチレン、ビニルトルエン、α−メチルスチレン等の芳香族ビニル単量体；（メタ）アクリル酸；（メタ）アクリル酸メチル、（メタ）アクリル酸エチル、（メタ）アクリル酸プロピル、（メタ）アクリル酸ブチル、（メタ）アクリル酸２−エチルヘキシル、（メタ）アクリル酸シクロヘキシル、（メタ）アクリル酸イソボニル、（メタ）アクリル酸ジメチルアミノエチル、（メタ）アクリルアミド等の（メタ）アクリル酸の誘導体；エチレン、プロピレン、ブチレン等のモノオレフィン単量体；等が挙げられる。
モノビニル単量体は、単独で用いても、複数の単量体を組み合わせて用いても良い。これらモノビニル単量体のうち、芳香族ビニル単量体単独、芳香族ビニル単量体と（メタ）アクリル酸の誘導体との併用などが好適に用いられる。
【００２９】
モノビニル単量体と共に、架橋性単量体及び重合体を用いるとホットオフセットが有効に改善される。架橋性単量体は、２個以上のビニル基を有する単量体である。具体的には、ジビニルベンゼン、ジビニルナフタレン、エチレングリコールジメタクリレート、ペンタエリスリトールトリアリルエーテルやトリメチロールプロパントリアクリレート等を挙げることができる。架橋性重合体は、重合体中に２個以上のビニル基を有する重合体のことであり、具体的には、分子内に２個以上の水酸基を有する重合体と、アクリル酸やメタクリル酸等の不飽和カルボン酸単量体を縮合反応することにより得られるエステルを挙げることができる。これらの架橋性単量体または架橋性重合体は、それぞれ単独で、あるいは２種以上組み合わせて用いることができる。架橋性単量体または架橋性重合体の使用量は、モノビニル単量体１００重量部当たり、通常、１０重量部以下、好ましくは、０．０５〜２重量部、更に好ましくは、０．１〜０．５重量部である。
【００３０】
また、モノビニル単量体と共に、マクロモノマーを用いると、保存性と低温定着性とのバランスが良好になるので好ましい。マクロモノマーは、分子鎖の末端に重合可能な炭素−炭素不飽和二重結合を有するもので、数平均分子量が、通常、１，０００〜３０，０００のオリゴマーまたはポリマーである。数平均分子量が上記範囲にあると、マクロモノマーの溶融性を損なうことなく、定着性および保存性が維持できるので好ましい。
【００３１】
マクロモノマーは、前記重合性単量体を重合して得られる重合体のガラス転移温度よりも高いガラス転移温度を与えるものが好ましい。
マクロモノマーの具体例としては、スチレン、スチレン誘導体、メタクリル酸エステル、アクリル酸エステル、アクリロニトリル、メタクリロニトリル等を単独でまたは２種以上を重合して得られる重合体、ポリシロキサン骨格を有するマクロモノマーなどを挙げることができる。これらの中でも、親水性のもの、特にメタクリル酸エステルまたはアクリル酸エステルを単独でまたはこれらを組み合わせて重合して得られる重合体が好ましい。
マクロモノマーを使用する場合、その量は、モノビニル単量体１００重量部に対して、通常、０．０１〜１０重量部、好適には０．０３〜５重量部、さらに好適には０．０５〜１重量部である。マクロモノマーの使用量が上記範囲にあると、保存性を維持したままで、定着性が低下することがないので好ましい。
【００３２】
以下、二段懸濁重合法による本発明の静電荷像現像用トナーの製造方法について説明する。
先ず、ホモミキサー、ホモジナイザー、高剪断攪拌機などの強攪拌装置を備えた容器中に分散安定剤を含有する水系分散媒に、少なくとも重合性単量体、着色剤および帯電制御剤を含有する、コア形成用原料となる重合性単量体組成物を分散させる。
重合性単量体組成物中には、さらに、離型剤、油溶性重合開始剤、低温定着性と保存性の改善に有効な連鎖移動剤（分子量調整剤）を添加することが好ましく、必要に応じて磁性材料などを添加してもよい。
コア形成のための重合性単量体は、生成する重合体のガラス転移温度が、通常６０℃以下、好ましくは４０〜６０℃となるように選定することが望ましい。コアのガラス転移温度が高すぎるとトナーの定着温度が高くなるおそれがあり、逆に低すぎると保存性が低下することがある。
水系分散媒の使用量は、通常、全単量体の１００〜４００重量％である。
【００３３】
油溶性重合開始剤は特に限定されず、ジ−ｔ−ブチルパーオキシド、ジクミルパーオキシド、ラウロイルパーオキシドなどのジアシルパーオキシド類；ｔ−ブチルパーオキシ−２−エチルヘキサノエート、ｔ−ブチルパーオキシネオデカノエートなどのパーエステル類；ジ−イソプロピルパーオキシジカーボネート、ジ−２−エチルヘキシルパーオキシジカーボネートなどのパーカーボネート類；クメンヒドロパーオキシドなどのヒドロパーオキシド類；等の過酸化物や、２，２’−アゾビス−〔２−メチル−（Ｎ−１，１−ビス（ヒドロキシメチル）−２−ヒドロキシエチル）プロピオアミド〕、２，２’−アゾビヒス（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等のアゾ化合物が挙げられる。また、上記過酸化物と重亜硫酸水素ナトリウム、アスコルビン酸などの還元剤との組み合わせによるレドックス系開始剤を用いることもできる。
油溶性重合開始剤の使用量は、コア用重合性単量体１００重量部に対して、通常、０．０１〜１０重量部である。
【００３４】
連鎖移動剤としては、ｔ−ドデシルメルカプタン、ｎ−ヘキサデシルメルカプタン、２，２，４，４，６−ペンタメチルヘプタン−６−チオールなどのメルカプタン；テトラメチルチウラムジスルフィド、テトラエチルチウラムジスルフィドなどのチウラムジスルフィド；２−エチルヘキシルチオグリコレート；テルピノーレン、β−テルピネン、ジペンテン等のテルペン；α−メチルスチレンダイマー；などが挙げられる。これらは１種単独で、または２種以上併せて使用することができる。連鎖移動剤は、重合性単量体１００重量部に対して、通常、０．０１〜１０重量部、好ましくは０．１〜５重量部の割合で用いられる。この範囲で連鎖移動剤を使用することによって、低温定着性と保存性のバランスを兼備することができる。
上記した連鎖移動剤の中でも、メルカプタンとチウラムジスルフィドを併用すると本発明の動的粘弾性を有するトナーを製造することが容易になるので好ましい。併用するメルカプタンでは、２，２，４，４，６−ペンタメチルヘプタン−６−チオールが好ましく、チウラムジスルフィドでは、テトラエチルチウラムジスルフィドが好ましい。これら併用するメルカプタンの使用量は、通常、０．１〜５重量部、好ましくは１〜３重量部であり、チウラムジスルフィドの使用量は、通常、０．０５〜２重量部であり、好ましくは０．１〜１重量部である。
これらの連鎖移動剤は、重合開始前、あるいは重合途中に添加することができる。
【００３５】
分散安定剤としては、公知の界面活性剤や無機・有機分散剤を使用することができるが、無機分散剤が後処理により取り除くことが容易であるので好ましい。無機分散剤として、例えば、硫酸バリウム、炭酸カルシウム、リン酸カルシウムなどの無機塩；シリカ、酸化アルミニウム、酸化チタン等の無機酸化物；水酸化アルミニウム、水酸化マグネシウム、水酸化第二鉄等の無機水酸化物；等が挙げられる。これらの中でも、特に難水溶性の無機水酸化物のコロイドを含有する分散安定剤は、重合体粒子の粒径分布を狭くすることができ、また分散安定剤の洗浄後の残存性が少なく、画像を鮮明に再現できるので好ましい。
分散安定剤は、重合性単量体１００重量部に対して、通常、０．１〜２０重量部の割合で使用する。この割合が上記範囲にあることで、充分な重合安定性が得られ、重合凝集物の生成が抑制され、所望の粒径のトナーを得ることができるので好ましい。
【００３６】
コアの重合反応は、重合反応器内のコア用単量体組成物水性分散液を攪拌しつつ、温度３０〜８０℃までに昇温して、通常、１〜２０時間その反応温度を制御し、重合率が、通常、９０モル％以上になるまで行う。
【００３７】
コアの重合に引き続き、重合反応器内にシェル形成用重合性単量体およびその単量体に見合う重合開始剤を添加する。
コア粒子に対してシェルの被覆重合が行われるために、シェル形成反応に用いる重合開始剤は、過硫酸カリウム、過硫酸アンモニウム等の過硫酸塩；過酸化水素；４，４’−アゾビス（４−シアノ吉草酸）、２，２’−アゾビス（２−アミジノプロパン）二塩酸塩、２，２’−アゾビス−〔２−メチル−Ｎ−（１，１’−ビス（ヒドロキシメチル）−２−ヒドロキシエチル）プロピオアミド〕などの水溶性アゾ化合物；などの水溶性重合開始剤が水槽層に均一に行き渡るので好都合である。また、前記の油溶性重合開始剤を用いる場合は、分散安定剤を用いてホモミキサーなどで微細な水性分散液にして添加することが好ましい。
シェル形成反応のための単量体および重合開始剤の添加は、好ましくはその後の重合反応の進行に伴って２〜１０回に分割して、より好ましくはプランジャーポンプなどを用いて連続的に添加する。
【００３８】
シェルを構成する重合体（以下、「シェル重合体」と記すことがある。コアについてもこれに倣う。）のガラス転移温度は、コア重合体のガラス転移温度よりも高くなるように設定することが好ましい。シェル重合体のガラス転移温度は、トナーの保存性を向上させるために、通常、５０〜１３０℃、好ましくは６０〜１２０℃、より好ましくは８０〜１１０℃である。
コア重合体とシェル重合体とのガラス転移温度の差は、通常、１０℃以上、好ましくは２０℃以上、より好ましくは３０℃以上である。
【００３９】
コア・シェル粒子のシェル層の平均厚みは、通常０．００１〜１．０μｍ、好ましくは０．００３〜０．５μｍ、より好ましくは０．００５〜０．２μｍである。厚みが過度に大きいと定着性が低下するおそれがあり、過度に小さいと保存性が低下することがある。 コア・シェル粒子のコア粒子径およびシェル層の厚みは、電子顕微鏡により観察できる場合は、その観察写真から無作為に選択した粒子の大きさおよびシェル厚みを直接測ることにより得ることができ、電子顕微鏡でコアとシェルとを観察することが困難な場合は、コア粒子の粒径およびトナー製造時に用いたシェルを形成する単量体の量から算定することができる。
【００４０】
二段懸濁重合反応が終了後、重合体分散液を洗浄し、またはろ過しつつ洗浄し、ろ過後乾燥することにより、コア・シェル構造の結着樹脂、着色剤、帯電制御剤などを包含した本発明の静電荷像現像用カラートナーを得ることができる。
【００４１】
本発明の静電荷像現像用カラートナーのＧ’_８０、Ｇ’_１６０ およびｔａｎδは、使用する重合性単量体や分子量調整剤の種類及びそれらの使用量、更には重合温度、重合時間などが相互に影響し合って決定される。従ってこれらは、上記の重合反応因子を変化させることにより調整することができるが、例えば、重合性単量体としてモノビニル単量体と併用すると好ましい架橋性単量体または架橋性重合体の使用量を少なくし、分子量調整剤としてメルカプタンとチウラムジスルフィド併用することにより比較的容易に達成することができる。
また、本発明のトナーの体積平均粒径（Ｄｖ）、および体積平均粒径と個数平均粒径（Ｄｐ）の比（Ｄｖ／Ｄｐ）は、どの重合方法を採用するかが最大の支配要因であるが、懸濁重合、特に二段懸濁重合を用いることにより比較的容易に目標値にアプローチ可能であり、分散安定剤の種類及び使用量などで調整することができる。
【００４２】
また、本発明のカラートナーは、上記の着色粒子に添加剤（以下、外添剤という）を添加、混合して粒子の表面に外添剤を付着、埋設等させることによって、粒子の帯電性、流動性、保存性などを調整することができる。
【００４３】
本発明で用いる外添剤としては、通常、流動性や帯電性を向上させる目的で使用されている無機粒子や有機樹脂粒子が挙げられる。例えば、無機粒子としては、シリカ、酸化アルミニウム、酸化チタン、酸化亜鉛、酸化錫などが挙げられ、有機樹脂粒子としては、（メタ）アクリル酸エステル重合体粒子、スチレン−（メタ）アクリル酸エステル共重合体粒子などが挙げられる。これらのうち、シリカや酸化チタンが好適であり、粒子表面が疎水化処理され物が好ましく、疎水化処理されたシリカ粒子が特に好ましい。外添剤の量は、特に限定されないが、トナー１００重量部に対して、通常、０．１〜６重量部である。これらの外添剤は２種以上を組み合わせて用いても良い。外添剤を組み合わせて用いる場合には、平均粒子径の異なる無機粒子同士または無機粒子と有機樹脂粒子を組み合わせる方法が好適である。外添剤をトナー粒子に付着させるには、通常、外添剤とトナー粒子とをヘンシェルミキサーなどの混合器に仕込み、撹拌して行う。
【００４４】
本発明の静電荷像現像用カラートナーは、一般的な静電荷像形成装置を用いて画像を形成することができる。すなわち、一様に帯電させた感光体の表面上に露光し、静電荷像を形成し、この静電荷像にトナーを付着させ、現像し、得られたトナー像を転写ロールによって転写材に転写し、この転写材を定着ロールで加熱、圧着させて定着させる。
本発明の静電荷像現像用カラートナーは、低温定着性に優れ、オフセットを起こしにくい。また、本発明の静電荷像現像用カラートナーは、長期に貯蔵してもトナーどうしが凝集しにくく、保存性に優れている。
【００４５】
【実施例】
以下に、実施例および比較例を挙げて、本発明を更に具体的に説明するが、本発明は、これらの実施例のみに限定されるものではない。なお、部および％は、特に断りのない限り重量基準である。
本実施例では、以下の方法で試験し、評価した。
【００４６】
１．トナー特性
（１）体積平均粒径（Ｄｖ）、個数平均粒径（Ｄｐ）およびＤｖ_５０／Ｄｐ_５０Ｄｖ、ＤｐおよびＤｖ／Ｄｐは、マルチサイザー（ベックマン・コールター社製）を用いて測定した。アパーチャー径：１００μｍ、媒体：イソトンＩＩ、濃度１０％、測定粒子個数：１００，０００個の条件で行った。
（２）平均円形度
容器中に予めイオン交換水１０ｍｌを用意し、その中に分散剤として界面活性剤、好ましくはアルキルベンゼンスルホン酸塩を加えた後、更にトナー０．０２ｇを加え、超音波分散機６０ｗ、３分間分散処理して均一に分散させた。この分散液を、測定時のトナー濃度が３０００〜１００００個／μｌとなるよう調整して、フロー式粒子像分析装置（ＦＰＩＡ−１０００；東亞医用電子株式会社製）を用いて、トナーの粒子数を１０００から１００００個の間で計測した。このデータを用いて平均円形度を求めた。
【００４７】
（３）損失弾性率（Ｇ”）、貯蔵弾性率（Ｇ’）および正接損失（ｔａｎδ）
粘弾性測定装置（ＶＡＲ−１００型、レオロジカ社製）で、測定治具として直径２０ｍｍのパラレルプレートを使用し、印加周波数１０Ｈｚ、歪１％、オートテンションとして、データは積算回数５回の平均値として、７０℃〜１８０℃まで昇温工程（昇温速度５℃／分）における動的粘弾性率の温度依存性の測定を行った。 ８０℃における貯蔵弾性率（Ｇ’_８０）、１６０℃における貯蔵弾性率（Ｇ’_１６０ ）と記す。
【００４８】
（４）融解エンタルピー
融解エンタルピーは、示差走査熱量計（ＤＳＣ ＳＳＣ５２００、セイコー電子工業社製）を用いて、ＡＳＴＭ Ｄ３４１８−８２に準拠して、昇温速度１０℃／分で測定したＤＳＣ曲線から算出した。即ち、得られたＤＳＣ曲線の吸熱ピークのピークトップとして測定される融点より高温側のあるベースラインから、融点に向けてベースラインを延長し、吸熱ピークのラインとの交点とピークに囲まれた範囲より算出した。
（５）保存性
トナー２０ｇを容器に入れて密閉した後、温度５５℃の恒温水槽の中に沈め、８時間経過した後に取り出して、４２メッシュの篩いの上にできるだけ構造を破壊しないように移し、粉体測定機（ホソカワミクロン社製、商品名「Ｐｏｗｄｅｒ Ｔｅｓｔｅｒ」）で振動の強度を振幅１ｍｍに設定して、３０秒間振動した後、篩い上に残ったトナー、すなわち凝集したトナーの重量を求めた。この凝集したトナー重量の試料の当初重量に対する割合（重量％）が大きいほどトナーの保存性が悪いと判定される。
【００４９】
２．画質評価
（６）定着温度
市販の非磁性一成分現像方式のカラープリンター（マイクロライン３０２０Ｃ、沖データ社製）の定着ロール部の温度を変化できるように改造したプリンターを用いた。先ず、改造プリンターの定着ロールの温度を変化させて、それぞれの温度でのトナーの定着率を測定し、温度−定着率の関係図を求めた。
定着率は、温度を５℃間隔で変化させる度に５分以上、測定温度で維持して定着ロールの温度を安定化させた後、印刷した試験紙の黒ベタ領域における、テープ剥離操作前後の画像濃度の比率から計算した。すなわち、テープ剥離前の画像濃度をＩＤ前、テープ剥離後の画像濃度をＩＤ後とすると、定着率は、次式から算出することができる。
定着率（％）＝（ＩＤ後／ＩＤ前）×１００
ここで、テープ剥離は、試験用紙の測定部分に粘着テープ（スコッチメンディングテープ８１０−３−１８、住友スリーエム社製）を貼り、一定圧力で押圧して付着させた後、試験用紙とテープの剥離方向が１８０°になるように一定速度で剥離する。また、画像濃度は、マクベス式反射濃度計を用いて測定した。
この定着試験において、定着率８０％に該当する定着ロール温度を現像剤の定着温度とした。
【００５０】
（７）ホットオフセット発生温度および定着マージン
上記（６）の定着温度の測定と同様に、定着ロール温度を５℃間隔で変化させて印字し、オフセットが発生する定着ロール温度をホットオフセット発生温度とした。
定着マージンはホットオフセット発生温度と定着温度との差（℃）として求めた。
【００５１】
（実施例１）
スチレン９０部、アクリル酸ｎ−ブチル１０部、ジビニルベンゼン０．２部、ポリメタクリル酸メチルエステルマクロモノマー（東亜合成化学工業社製、商品名「ＡＡ６」）１部、Ｃ．Ｉ．ピグメントレッド１８５を８部、正帯電制御樹脂（ＦＣＡ２０７Ｐ、藤倉化成社製、４級アンモニウム基２％）１部、負帯電制御樹脂（ＦＣＡ６２６Ｎ、藤倉化成社製、スルホン酸基７％）７部、ジペンタエリスリトールヘキサミリステート１０部、２，２，４，６，６−ペンタメチルヘプタン−４−チオール２部およびテトラエチルチウラムジスルフィド０．１部を室温下でビーズミルにて分散させて、コア用重合性単量体組成物を得た。
【００５２】
一方、イオン交換水１８１部に水酸化ナトリウム７．１部を溶解させた水溶液に２５％塩化マグネシウム水溶液（水溶性多価金属塩水溶液）４４．８部を撹拌下で徐々に添加して、水酸化マグネシウムコロイド（Ｄｐ_５０は０．３６μｍ、Ｄｐ_９０は０．８６μｍ）分散液を調製した。上記により得られた水酸化マグネシウムコロイド分散液に、上記コア用重合性単量体組成物を添加し、プロペラ式撹拌機を用いて撹拌混合した。次いでｔ−ブチルパーオキシ−２−エチルヘキサノエート４．５部を投入し、さらに撹拌混合して、単量体組成物懸濁液を得た。次いで、この単量体組成物懸濁液を回転子が回転数２１，０００ｒｐｍで稼働している造粒装置（クレアミックスＣＬＭ−０．８Ｓ、エムテクニック社製）に、ポンプを用いて供給してコア形成用単量体組成物水性分散液を調製した。
この単量体組成物水性分散液を、攪拌翼を装着した重合反応器に移した。単量体組成物水性分散液を加熱し、温度が９０℃になった時点で一定温度となるよう制御した。
重合転化率がほぼ１００％に達したのを確認して、シェル用重合性単量体メタクリル酸メチル１．５部を添加した。 ５分後、水溶性開始剤２，２’−アゾビス−〔２−メチル−（Ｎ−１，１−ビス（ヒドロキシメチル）−２−ヒドロキシエチル）プロピオアミド〕（ＶＡ−０８６、和光純薬社製）０．２部を水２０部に溶解した水溶液を重合反応器に添加し、メタクリル酸メチルを重合させ、コア・シェル構造の重合体粒子を得た。重合体粒子の水性分散液を攪拌しながら、硫酸により系のｐＨを約５．０にして酸洗浄を２５℃にて１０分間行った。次いで、ろ過により脱水し、洗浄水を振りかけて水洗浄を行った。その後、４５℃の熱風循環式乾燥器にて２昼夜乾燥を行い、トナー粒子を得た。
【００５３】
得られたトナー粒子１００部に、ポリシロキサンとヘキサメチルジシラザンで疎水化処理したコロイダルシリカ（クラリアント社製、製品名「Ｈ１３ＴＸ」）１．０部を添加し、ヘンシェルミキサーを用いて混合してトナーを製造した。得られたトナーの特性及び画質評価の結果を表１に示す。
【００５４】
（実施例２〜４）
表１に示すように２，２，４，６，６−ペンタメチルヘプタン−４−チオール及びジビニルベンゼンの使用量を変更した以外は実施例１と同様にしてトナーを製造した。得られたトナーの特性及び画質評価の結果を表１に示す。
【００５５】
（比較例１）
特開平９−６０５１号公報記載の実施例１に従い、下記によりトナーを調製した。
反応器にメタノール２３３部を入れ、攪拌しながら６．７４部の高分子分散剤Ｇａｎｔｒｅｔを少量づつ添加して完全に溶解させた。次いでスチレン５５部、メタクリル酸メチル４５部、ブタンジオールジメタクリレート１．５部およびドデシルメルカプタン０．２６部を添加して溶解させた後、気相を窒素でパージし、１時間放置した。その後攪拌して温度６０℃に維持し、２，２’−アゾビスイソブチロニトリル１．５５部を溶解した５．６６％メタノール溶液を連続的に注入しつつ重合反応を行った。１時間後に、２部のドデシルメルカプタンを２５．９部のメタノールに溶解した液を追添加した。さらに１６時間後スチレン１８．７部を３５分間で注入し、再度２，２’−アゾビスイソブチロニトリル１．５５部を溶解した５．６６％メタノール溶液を連続的に注入し、さらに２４時間反応させ、重合転化率９５％で反応終了した。得られた分散液にイオン交換水２８．５部を加えて遠心分離機にかけ、ウエットケーキにメタノール２５９部を注いで洗浄後、脱液し、次いで２５９部の水３／メタノール７の混合液で洗浄後、脱液し、次いで２５９部の水５／メタノール５の混合液で２回洗浄、脱液を行った後、ケーキを２４時間減圧乾燥して重合体粒子を得た。
一方、メタノール２５９部にオイルブラック８０３（オリエント化学社製）１．３部を加熱溶解した後、冷却し、１μｍフィルターでろ別して染料溶液を作製した。次に、染料溶液に上記の重合体粒子３１部加えて分散させ、５０℃に加熱しつつ、１時間撹拌した。その後、この樹脂粒子分散液を室温まで冷却しろ別してトナー粒子を得た。これを室温で２４時間真空乾燥後、トナー粒子の１％量のシリカを添加、混合してトナーを得た。得られたトナーの特性及び画質評価の結果を表１に示す。
【００５６】
（比較例２〜３）
表１に示すように２，２，４，６，６−ペンタメチルヘプタン−４−チオール及びジビニルベンゼンの使用量を変更した以外は実施例１と同様にしてトナーを製造した。得られたトナーの特性及び画質評価の結果を表１に示す。
【００５７】
【表１】

【００５８】
表１のトナーの評価結果から、以下のことがわかる。
ドデシルメルカプタンのみを使用して得られた、本発明で規定する範囲よりＧ’_８０およびＧ’_１６０ が低く、ｔａｎδの極大値が高く、極小値が低く、そして極大値および極小値の存在温度域が低い比較例１のトナーは、定着温度が高く、保存性も悪かった。
２，２，４，６，６−ペンタメチルヘプタン−４−チオールを大量に用いて重合して得られた、本発明で規定する範囲よりＧ’_８０およびＧ’_１６０ が低く、ｔａｎδの極小値が大きい比較例２のトナーは、定着温度が１２０℃と極度に低いが、オフセットが発生し、保存性も悪かった。
２，２，４，６，６−ペンタメチルヘプタン−４−チオールを実施例４並みに低減し、ジビニルベンゼンを多く添加して重合して得られた、本発明で規定する範囲よりＧ’_１６０ が大きく、ｔａｎδの極小値が無い比較例３のトナーは、定着温度が１６０℃と高くなった。
一方、本発明の要件を満たす実施例１〜４のトナーはいずれも低温定着性に優れ、ホットオフセット発生温度が発生し難くなり、そのために定着マージンが広く、しかも保存性に優れている。
【００５９】
【発明の効果】
本発明により、低温定着性に優れ、ホットオフセットを起こし難く、そのために定着マージンが広く、しかも保存性に優れた静電荷像現像用カラートナーが提供される。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a color toner for developing an electrostatic image for developing an electrostatic image formed by an electrophotographic method, an electrostatic recording method, or the like. In particular, the present invention relates to a color toner for developing electrostatic images, which has good low-temperature fixability, good storage stability, and hardly causes hot offset.
[0002]
[Prior art]
In recent years, the development from white-black copiers to full-color copiers has been rapidly progressing, and digitized full-color copiers have begun to be sold in the market.
[0003]
In color image formation by full-color electrophotography, color reproduction is generally performed using three color toners of three primary colors, yellow, magenta, and cyan, or four colors obtained by adding black to the color toners. It is performed as follows. In color copying (color copying), first, a color original is separated into a large number of pixels and read, and as a digital image signal for each color, light is applied to a charged photoconductor to form an electrostatic latent image. Next, the electrostatic latent image for each color is developed on a photoreceptor with a color toner corresponding to an image signal, and is transferred to a support made of paper, an OHP film, or the like. The development and transfer steps are sequentially repeated for each color after the second color, and the support is overcoated with registration. In color printing (color printing), electrostatic latent images are individually formed based on digital signals of four colors sent directly to a photoreceptor from a computer or the like, developed for each color in the same manner as described above, and then transferred to a support. I do.
After development and transfer of all colors, the support is heated and fixed by a hot roll. Thus, a full-color image is formed by only one fixing.
[0004]
In such full-color image formation by electrophotography, there is now a strong demand for higher speed and lower fixing energy. Therefore, the toner is required to have a low fixing temperature and a wide difference (fixing margin) between the fixing temperature and the offset occurrence temperature. Also, the sharpness of an image formed in a high-speed and low-energy environment has become more important.
Generally, in order to lower the fixing temperature, it is effective to lower the glass transition temperature and the melt viscosity of the toner. However, in these methods, the storability of the toner may be reduced, or hot offset may occur at a low temperature and the fixing margin may be narrowed.
As a method of preventing hot offset, a method of applying silicone oil to a fixing roll has been performed. However, in this method, it is difficult to reduce the size and cost of a fixing device (image forming apparatus), and it is possible to obtain a fixing device. Shininess occurs on printed matter.
On the other hand, it is also required to reduce toner consumption so that printing can be performed for a long time. As a countermeasure, it is conceivable to increase the amount of the colorant in the toner. However, in this method, the melt viscosity increases, and it is difficult to fix the toner at a low temperature.
In response to such a demand for a full-color image forming toner that is excellent in storability while having good low-temperature fixability and hardly causes offset, attention is paid to the behavior of the overcoat toner layer under high-speed printing. There has been a movement to pursue an appropriate viscoelasticity to be provided by the toner.
[0005]
Patent Document 1 proposes a polymerization toner by dispersion polymerization using a chain transfer agent. However, the toner prepared by this method has insufficient fixability, and is prepared by coloring the resin after polymerization with a dye. Was sometimes done.
Patent Document 2 discloses a storage elastic modulus (G ′) at 60 ° C.₆₀Hereinafter, the measurement temperature of the storage elastic modulus G 'is indicated by a subscript. ) And G '₈₀(G '₆₀/ G '₈₀It has been proposed to produce toners having a) of 80 or more by suspension polymerization. However, although this toner has a low softening temperature and is excellent in fixing property, G 'is largely attenuated between 60 and 80 ° C. and is inferior in storability, and filming on a developing member due to mechanical stress during durable printing. Can easily occur.
Patent Literature 3 discloses G ′ by a method of aggregating polymer particles after emulsion polymerization.₉₀And G '₁₆₀Have been proposed. This toner has good fixability but has a problem with hot offset resistance and lacks storability. In addition, the charge stability in a high-temperature and high-humidity environment is poor due to the effect of the residual surfactant derived from the emulsion polymerization.
Patent Document 4 proposes a pulverized polyester-based toner in which the numerical ranges of G ′ and tan δ at 100 ° C. and 180 ° C. are specified. However, the toner obtained by this method has a low softening point and is inferior in storage stability at 50 ° C.
[0006]
On the other hand, in order to sharpen a formed image, toner particles have been reduced in size and made spherical (see, for example, Patent Document 5). However, when the particle size of the toner is reduced, the adsorptivity to the photoreceptor increases, and a problem that the toner remains on the photoreceptor during transfer occurs. Further, if the fine particles are made spherical, the adhesive force increases.
[0007]
[Patent Document 1]
JP-A-9-6051
[Patent Document 2]
JP-A-9-034163
[Patent Document 3]
JP-A-10-69119
[Patent Document 4]
JP-A-2002-162773
[Patent Document 5]
JP-A-62-184469
[0008]
[Problems to be solved by the invention]
SUMMARY OF THE INVENTION An object of the present invention is to provide a color toner for developing an electrostatic image, which is excellent in low-temperature fixability, hardly causes hot offset, has a wide fixing margin, and is excellent in storability.
[0009]
[Means for Solving the Problems]
The present inventor has conducted intensive studies to achieve the above object, and as a result, a toner having a viscoelastic property, a volume average particle diameter, and a ratio of a volume average particle diameter to a number average particle diameter having a specific value has been developed for the purpose. They have found that this can be achieved, and have completed the present invention based on this finding.
Thus, according to the present invention, there is provided a color toner for developing an electrostatic image containing at least a binder resin, a colorant and a charge control agent, wherein the dynamic viscoelastic properties measured at a frequency of 10 Hz and a strain of 1% are as follows: Storage modulus at 80 ° C. (G ′₈₀) Is 5 × 10⁶~ 5 × 10⁸In Pa, the storage modulus at 160 ° C. (G ′₁₆₀) Is 1 × 10²~ 1 × 10⁴Pa, a maximum value of tangent loss (tan δ) of 1.2 to 2.5 exists at 80 to 100 ° C, a minimum value of tan δ of 1 to 2 exists at 95 to 125 ° C, and a volume average particle size. (Dv) is 2 to 11 [mu] m, and a ratio (Dv / Dp) of a volume average particle diameter (Dv) to a number average particle diameter (Dp) is 1.3 or less, characterized in that: A toner is provided.
[0010]
BEST MODE FOR CARRYING OUT THE INVENTION
The color toner for electrostatic image development of the present invention is a color toner for electrostatic image development containing at least a binder resin, a colorant and a charge control agent,
In the dynamic viscoelastic properties measured under the conditions of a frequency of 10 Hz and a strain of 1%, the storage elastic modulus (G ′) at 80 ° C.₈₀) Is 5 × 10⁶~ 5 × 10⁸In Pa, the storage modulus at 160 ° C. (G ′₁₆₀) Is 1 × 10²~ 1 × 10⁴Pa, a maximum value of tangent loss (tan δ) of 1.2 to 2.5 is present at 80 to 100 ° C, a minimum value of tan δ of 1 to 2 is present at 95 to 125 ° C, and
The volume average particle size (Dv) is 2 to 11 μm, and the ratio (Dv / Dp) of the volume average particle size (Dv) to the number average particle size (Dp) is 1.3 or less.
The color toner for developing an electrostatic image of the present invention preferably further contains a release agent, and may contain a magnetic material if necessary.
[0011]
The binder resin used in the present invention is not particularly limited, and specific examples include polystyrene, styrene-acrylic copolymer, polyester, epoxy resin, and other resins that have been widely used in conventional toners.
[0012]
As the colorant used in the present invention, pigments and / or dyes can be used in addition to carbon black, titanium black, magnetic powder, oil black, and titanium white. As the black carbon black, those having a primary particle diameter of 20 to 40 nm are suitably used. When the particle size is in this range, carbon black can be uniformly dispersed in the toner, and fog is reduced, which is preferable.
[0013]
As a colorant for obtaining a full-color toner, a yellow colorant, a magenta colorant and a cyan colorant are usually used.
As the yellow colorant, compounds such as azo pigments and condensed polycyclic pigments are used. Specifically, C.I. I. Pigment Yellow 3, 12, 13, 14, 15, 17, 62, 65, 73, 74, 83, 90, 93, 97, 120, 138, 155, 180 and 181.
As the magenta colorant, compounds such as azo pigments and condensed polycyclic pigments are used. Specifically, C.I. I. Pigment Red 31, 48, 57, 58, 60, 63, 64, 68, 81, 83, 87, 88, 89, 90, 112, 114, 122, 123, 144, 146, 149, 150, 163, 170, 184, 185, 187, 202, 206, 207, 209, 251; I. Pigment Violet 19 and the like.
As the cyan coloring agent, a copper phthalocyanine compound and its derivative, an anthraquinone compound and the like can be used. Specifically, C.I. I. Pigment Blue 2, 3, 6, 15, 15: 1, 15: 2, 15: 3, 15: 4, 16, 17, 60 and the like.
The amount of such a coloring agent to be used is generally 1 to 10 parts by weight based on 100 parts by weight of the binder resin.
[0014]
In the present invention, as the charge control agent, a charge control agent conventionally used for a toner can be used. It is preferable to include a charge control resin among the charge control agents. The reason is that the charge control resin has high compatibility with the binder resin, is colorless, and can provide a toner having stable chargeability even in continuous color printing at high speed. Examples of the charge control resin include quaternary ammonium produced according to the description in JP-A-63-60458, JP-A-3-175456, JP-A-3-243954, JP-A-11-15192 and the like. A (salt) group-containing copolymer or a sulfonic acid (salt) group-containing copolymer produced according to the description in JP-A-1-217464, JP-A-3-15858 and the like can be used.
The amount of the monomer unit having a quaternary ammonium (salt) group or a sulfonic acid (salt) group contained in these copolymers is 0.5 to 15% by weight, preferably 1 to 10% by weight. When the content is within this range, the charge amount of the toner can be easily controlled, and the occurrence of fog can be reduced.
[0015]
The weight average molecular weight of the charge control resin is usually 2,000 to 50,000, preferably 4,000 to 40,000, and more preferably 6,000 to 30,000. When the weight average molecular weight is in this range, the saturation and transparency of the toner can be maintained.
The glass transition temperature of the charge control resin is usually from 40 to 80C, preferably from 45 to 75C, more preferably from 45 to 70C. When the glass transition temperature is in this range, the storability and fixability of the toner can be improved in a well-balanced manner.
The amount of the charge control agent is usually 0.01 to 20 parts by weight, preferably 0.1 to 10 parts by weight, based on 100 parts by weight of the binder resin.
[0016]
In the present invention, examples of the release agent preferably used include polyolefin waxes such as low molecular weight polyethylene, low molecular weight polypropylene and low molecular weight polybutylene; natural plant waxes such as candelilla, carnauba, rice, wood wax, jojoba; paraffin Waxes and modified waxes thereof such as microcrystalline and petrolactam; synthetic waxes such as Fischer-Tropsch wax; polyfunctional ester compounds such as pentaerythritol tetramyristate, pentaerythritol tetrapalmitate and dipentaerythritol hexamyristate; Is mentioned.
These can be used alone or in combination of two or more.
[0017]
Among these release agents, synthetic waxes and polyfunctional ester compounds are preferred. Among these, a polyfunctional polymer having an endothermic peak temperature in a temperature range of 30 to 150 ° C., preferably 40 to 100 ° C., more preferably 50 to 80 ° C. in a DSC curve measured by a differential scanning calorimeter. Ester compounds are preferred. This is because a toner containing such a release agent has a good balance between fixation and releasability during fixing. In particular, those having a molecular weight of 1,000 or more, dissolving at least 5 parts by weight at 25 ° C. with respect to 100 parts by weight of styrene, and having an acid value of 10 mg / KOH or less are more preferable because they have a remarkable effect on lowering the fixing temperature. Endothermic peak temperature is a value measured by ASTM D3418-82.
The amount of the release agent is usually 0.5 to 50 parts by weight, preferably 1 to 20 parts by weight based on 100 parts by weight of the binder resin.
[0018]
Examples of the magnetic material include iron oxides such as magnetite, γ-iron oxide, ferrite, and iron-rich ferrite; iron, cobalt, nickel, and aluminum, cobalt, copper, lead, magnesium, tin, zinc, antimony, and beryllium. , Bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten, alloys with vanadium and mixtures thereof. The magnetic material is used in an amount of usually 10 to 60 parts by weight, preferably 20 to 50 parts by weight, based on 100 parts by weight of the binder resin.
[0019]
In the present invention, the viscoelastic properties of the toner are measured at a temperature of 70 ° C. to 180 ° C. under a stress of 100 to 300 Pa under the conditions of an applied frequency of 10 Hz and a strain of 1%.
The storage elastic modulus (G ′) of the color toner for developing an electrostatic image of the present invention at 80 ° C.₈₀) Is 5 × 10⁶~ 5 × 10⁸Pa, preferably 5 × 10⁶~ 5 × 10⁷Pa, more preferably 5 × 10⁶~ 3 × 10⁷Pa. Further, the storage elastic modulus at 160 ° C. (G ′₁₆₀) Is 1 × 10²~ 1 × 10⁴Pa, preferably 5 × 10²~ 1 × 10⁴Pa, more preferably 5 × 10²~ 5 × 10³Pa. G '₈₀Also G '₁₆₀Is too small, hot offset tends to occur at a low temperature, and the storage stability of the toner may be reduced.₈₀Also G '_{16 0}Is too large, the low-temperature fixability of the toner is inferior. If G 'at a high temperature is excessively high, the toner tends to agglomerate at the time of melting, and irregularities may easily occur on the fixing surface, and gloss may not be obtained.
[0020]
The maximum value of the tangent loss (tan δ), which is the ratio (G ″ / G ′) between the loss elastic modulus (G ″) and the storage elastic modulus (G ′), of the color toner for developing an electrostatic image of the present invention is 80 to 80%. It is present at 100 ° C, preferably at 80-95 ° C, more preferably at 85-95 ° C. If the maximum value is at an excessively low temperature, the storage stability may be reduced, and if it is at an excessively high temperature, the low-temperature fixability may be reduced.
The maximum value of tan δ is 1.2 to 2.5, preferably 1.2 to 2.3, and more preferably 1.5 to 2.0. If the maximum value of tan δ is excessively high, the releasability from the fixing roller is poor, hot offset is likely to occur at low temperatures, and the toner fixing surface is stretched and smoothed by contact with the roller, and the gloss of the image is reduced. May increase. On the other hand, when the maximum value of tan δ is excessively low, the fixability is poor, and the toner particles may aggregate on the fixing surface to make the surface uneven, thereby reducing the gloss of the image.
[0021]
The minimum value of tan δ is between 95 and 125 ° C, preferably between 100 and 120 ° C, more preferably between 105 and 115 ° C. If the minimum value is at an excessively low temperature, hot offset may occur at a low temperature, and if the minimum value is at an excessively high temperature, the low-temperature fixability may decrease.
The minimum value of tan δ is 1 to 2, preferably 1.0 to 1.8, and more preferably 1.0 to 1.5. When the minimum value is excessively high, hot offset easily occurs at a low temperature, the fixing margin is narrowed, and the fixing surface of the toner is stretched and smoothed by contact with a roller, and the gloss of an image may increase. . If the minimum value is excessively small, the toner particles may aggregate on the fixing surface to make the surface uneven, thereby reducing the gloss of the image. When it does not have the minimum value, the fixability is inferior, and the fixation surface may be uneven and gloss may not be obtained.
[0022]
The volume average particle diameter (Dv) of the color toner for developing an electrostatic image of the present invention is 2 to 11 μm, preferably 3 to 10 μm, more preferably 5 to 10 μm. If Dv is excessively small, the fluidity may decrease, or toner may leak from the seal portion and contaminate the inside of the image forming apparatus. Conversely, if Dv is excessively large, high image quality cannot be achieved, or the fixing property is poor. May drop.
[0023]
The ratio (Dv / Dp) of the volume average particle diameter (Dv) to the number average particle diameter (Dp) of the color toner for developing an electrostatic image of the present invention is 1.3 or less, preferably 1.2 or less. If Dv / Dp is excessively large, the toner production yield may decrease.
[0024]
The color toner for developing an electrostatic image of the present invention has an average circularity measured by a flow type particle image analyzer of usually 0.94 to 0.995, preferably 0.95 to 0.99. . When the average circularity is smaller than 0.94, the transferability may be reduced.
The average circularity (Ca) in the present invention is defined as a value obtained by dividing the perimeter of a circle having the same projected area as the particle image by the perimeter of the projected image of the particle. The degree (Ci) is determined for each particle of 0.6 μm or more, and is defined by the following equation (2) as a value obtained by dividing the obtained sum of circularity of all particles by the total number of particles (n). This average circularity is used as a simple method for quantitatively expressing the shape of particles, and is an index indicating the degree of unevenness of the toner. When the toner has a perfect spherical shape, it indicates 1.000. The average circularity becomes smaller as the surface shape becomes more complicated. This average circularity can be measured using a flow-type particle image analyzer “FPIA-1000” or “FPIA-2000” manufactured by Toa Medical Electronics Co., Ltd.
[0025]
(Equation 1)

(Equation 2)

[0026]
Further, the melting enthalpy ΔH of the color toner for developing an electrostatic image of the present invention is preferably 1 to 10 mJ / mg, more preferably 2 to 6 mJ / mg, and particularly preferably 3 to 5 mJ / mg. When the enthalpy of fusion falls within this range, the fixability is excellent. If ΔH is too high, a large amount of heat is required for melting the toner, and low-energy fixing (low-temperature fixing) cannot be achieved when forming a multi-color, multi-layer image such as a color image. On the other hand, if ΔH is too low, the fixability may be poor or a sufficient releasing effect may not be obtained. ΔH is defined as the endothermic peak at the peak of the differential scanning calorimeter (DSC) curve, extending the base line from the melting point to the melting point from the base line on the high-temperature side, and is surrounded by the intersection of the endothermic peak line and the peak. Calculated from the range.
[0027]
The production of the color toner for developing an electrostatic image of the present invention having the above characteristics is preferably carried out by a polymerization method. As the polymerization method, a known suspension polymerization method, emulsion polymerization method, bulk polymerization method, or the like can be applied. Among these, the suspension polymerization method is preferable because the colorant and the charge control agent can be uniformly incorporated into the particles without using an emulsifier that affects the control of the chargeability. A two-stage suspension polymerization method capable of producing particles having a core-shell structure in which an easily meltable polymer having low-temperature fixability and a hardly meltable polymer having offset prevention in a shell (particle outer portion) is disposed is more preferable.
The weight ratio between the core and the shell of the core-shell particles is not particularly limited, but is usually 80/20 to 99.9 / 0.1, preferably 85/15 to 99/1. If the proportion of the shell is too small, the preservability deteriorates. On the other hand, if the proportion is too large, fixing may be difficult at low temperatures.
[0028]
Examples of the polymerizable monomer for obtaining the binder resin include a monovinyl monomer, a crosslinkable monomer, and a macromonomer. This polymerizable monomer is polymerized to form a binder resin component.
Specific examples of the monovinyl monomer include aromatic vinyl monomers such as styrene, vinyltoluene and α-methylstyrene; (meth) acrylic acid; methyl (meth) acrylate, ethyl (meth) acrylate, ( Propyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, cyclohexyl (meth) acrylate, isobonyl (meth) acrylate, dimethylaminoethyl (meth) acrylate, (meth) acrylamide, etc. (Meth) acrylic acid derivatives; monoolefin monomers such as ethylene, propylene, and butylene; and the like.
Monovinyl monomers may be used alone or in combination of a plurality of monomers. Of these monovinyl monomers, an aromatic vinyl monomer alone, or a combination of an aromatic vinyl monomer and a derivative of (meth) acrylic acid is preferably used.
[0029]
When a crosslinkable monomer and a polymer are used together with the monovinyl monomer, hot offset is effectively improved. The crosslinkable monomer is a monomer having two or more vinyl groups. Specific examples include divinylbenzene, divinylnaphthalene, ethylene glycol dimethacrylate, pentaerythritol triallyl ether, and trimethylolpropane triacrylate. The crosslinkable polymer is a polymer having two or more vinyl groups in the polymer, and specifically, a polymer having two or more hydroxyl groups in the molecule, acrylic acid, methacrylic acid, or the like. And an ester obtained by subjecting the unsaturated carboxylic acid monomer to a condensation reaction. These crosslinkable monomers or crosslinkable polymers can be used alone or in combination of two or more. The amount of the crosslinkable monomer or the crosslinkable polymer used is usually 10 parts by weight or less, preferably 0.05 to 2 parts by weight, more preferably 0.1 to 100 parts by weight per 100 parts by weight of the monovinyl monomer. 0.5 parts by weight.
[0030]
It is also preferable to use a macromonomer together with the monovinyl monomer, because the balance between storage stability and low-temperature fixability is improved. The macromonomer has a polymerizable carbon-carbon unsaturated double bond at the terminal of the molecular chain, and is usually an oligomer or polymer having a number average molecular weight of 1,000 to 30,000. When the number average molecular weight is in the above range, the fixability and the storability can be maintained without impairing the meltability of the macromonomer.
[0031]
The macromonomer preferably has a glass transition temperature higher than the glass transition temperature of the polymer obtained by polymerizing the polymerizable monomer.
Specific examples of the macromonomer include styrene, a styrene derivative, a methacrylate, an acrylate, acrylonitrile, a polymer obtained by polymerizing two or more kinds of methacrylonitrile, etc., and a macromonomer having a polysiloxane skeleton. And the like. Among these, a polymer obtained by polymerizing a hydrophilic polymer, particularly a methacrylic acid ester or an acrylic acid ester, alone or in combination thereof is preferable.
When a macromonomer is used, the amount is usually 0.01 to 10 parts by weight, preferably 0.03 to 5 parts by weight, more preferably 0.05 to 100 parts by weight of the monovinyl monomer. １1 part by weight. It is preferable that the amount of the macromonomer be within the above-mentioned range, since the fixability is not deteriorated while maintaining the storage stability.
[0032]
Hereinafter, a method for producing the toner for developing an electrostatic image of the present invention by a two-stage suspension polymerization method will be described.
First, a homomixer, a homogenizer, an aqueous dispersion medium containing a dispersion stabilizer in a container equipped with a strong stirrer such as a high shear stirrer, containing at least a polymerizable monomer, a colorant, and a charge control agent. A polymerizable monomer composition as a forming raw material is dispersed.
In the polymerizable monomer composition, it is preferable to further add a release agent, an oil-soluble polymerization initiator, and a chain transfer agent (molecular weight modifier) effective for improving low-temperature fixability and storage stability. A magnetic material or the like may be added according to the requirements.
The polymerizable monomer for forming the core is desirably selected so that the glass transition temperature of the resulting polymer is usually 60 ° C or lower, preferably 40 to 60 ° C. If the glass transition temperature of the core is too high, the fixing temperature of the toner may increase, and if it is too low, the storability may decrease.
The amount of the aqueous dispersion medium is usually 100 to 400% by weight of the total monomers.
[0033]
The oil-soluble polymerization initiator is not particularly limited, and diacyl peroxides such as di-t-butyl peroxide, dicumyl peroxide and lauroyl peroxide; t-butyl peroxy-2-ethylhexanoate, t-butyl Peresters such as peroxyneodecanoate; percarbonates such as di-isopropylperoxydicarbonate and di-2-ethylhexylperoxydicarbonate; hydroperoxides such as cumene hydroperoxide; And 2,2'-azobis- [2-methyl- (N-1,1-bis (hydroxymethyl) -2-hydroxyethyl) propioamide], 2,2'-azobihis (2,4-dimethylvaleronitrile ) And azo compounds such as 2,2′-azobisisobutyronitrile. Further, a redox initiator obtained by combining the above peroxide with a reducing agent such as sodium bisulfite and ascorbic acid can also be used.
The amount of the oil-soluble polymerization initiator to be used is usually 0.01 to 10 parts by weight based on 100 parts by weight of the core polymerizable monomer.
[0034]
Examples of the chain transfer agent include mercaptans such as t-dodecyl mercaptan, n-hexadecyl mercaptan and 2,2,4,4,6-pentamethylheptane-6-thiol; thiuram disulfides such as tetramethylthiuram disulfide and tetraethylthiuram disulfide 2-ethylhexylthioglycolate; terpenes such as terpinolene, β-terpinene and dipentene; α-methylstyrene dimer; These can be used alone or in combination of two or more. The chain transfer agent is used in an amount of usually 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the polymerizable monomer. By using a chain transfer agent in this range, a balance between low-temperature fixability and storage stability can be achieved.
Among the above-mentioned chain transfer agents, it is preferable to use mercaptan and thiuram disulfide in combination, since it becomes easy to produce the toner having dynamic viscoelasticity of the present invention. For mercaptan used in combination, 2,2,4,4,6-pentamethylheptane-6-thiol is preferable, and for thiuram disulfide, tetraethylthiuram disulfide is preferable. The amount of mercaptan used in combination is usually 0.1 to 5 parts by weight, preferably 1 to 3 parts by weight, and the amount of thiuram disulfide used is usually 0.05 to 2 parts by weight, preferably 0.1 to 1 part by weight.
These chain transfer agents can be added before the start of the polymerization or during the polymerization.
[0035]
As the dispersion stabilizer, known surfactants and inorganic / organic dispersants can be used, but inorganic dispersants are preferable because they can be easily removed by post-treatment. Examples of the inorganic dispersant include inorganic salts such as barium sulfate, calcium carbonate, and calcium phosphate; inorganic oxides such as silica, aluminum oxide, and titanium oxide; and inorganic hydroxides such as aluminum hydroxide, magnesium hydroxide, and ferric hydroxide. Object; and the like. Among these, dispersion stabilizers containing colloids of poorly water-soluble inorganic hydroxides, in particular, can narrow the particle size distribution of the polymer particles, and have less residual properties after washing of the dispersion stabilizer, This is preferable because an image can be clearly reproduced.
The dispersion stabilizer is used usually in a ratio of 0.1 to 20 parts by weight based on 100 parts by weight of the polymerizable monomer. When the ratio is in the above range, sufficient polymerization stability is obtained, the formation of polymerization aggregates is suppressed, and a toner having a desired particle size can be obtained, which is preferable.
[0036]
The core polymerization reaction is carried out by stirring the aqueous dispersion of the core monomer composition in the polymerization reactor and raising the temperature to a temperature of 30 to 80 ° C., usually controlling the reaction temperature for 1 to 20 hours. The polymerization is usually performed until the polymerization rate becomes 90 mol% or more.
[0037]
Subsequent to the polymerization of the core, a polymerizable monomer for forming a shell and a polymerization initiator corresponding to the monomer are added into a polymerization reactor.
In order to perform shell coating polymerization on the core particles, the polymerization initiator used in the shell formation reaction is a persulfate such as potassium persulfate or ammonium persulfate; hydrogen peroxide; 4,4′-azobis (4- Cyanovaleric acid), 2,2′-azobis (2-amidinopropane) dihydrochloride, 2,2′-azobis- [2-methyl-N- (1,1′-bis (hydroxymethyl) -2-hydroxy It is advantageous because a water-soluble polymerization initiator such as a water-soluble azo compound such as [ethyl] propioamide] is uniformly distributed in the water tank layer. When the above-mentioned oil-soluble polymerization initiator is used, it is preferable to use a dispersion stabilizer and make a fine aqueous dispersion with a homomixer or the like and to add it.
The addition of the monomer and the polymerization initiator for the shell-forming reaction is preferably divided into 2 to 10 times with the progress of the subsequent polymerization reaction, and more preferably continuously using a plunger pump or the like. Added.
[0038]
The glass transition temperature of the polymer constituting the shell (hereinafter sometimes referred to as “shell polymer” and the core is also followed) is set to be higher than the glass transition temperature of the core polymer. Is preferred. The glass transition temperature of the shell polymer is generally from 50 to 130C, preferably from 60 to 120C, more preferably from 80 to 110C, in order to improve the storage stability of the toner.
The difference in the glass transition temperature between the core polymer and the shell polymer is usually 10 ° C. or higher, preferably 20 ° C. or higher, more preferably 30 ° C. or higher.
[0039]
The average thickness of the shell layer of the core / shell particles is usually 0.001 to 1.0 μm, preferably 0.003 to 0.5 μm, more preferably 0.005 to 0.2 μm. If the thickness is too large, the fixability may decrease, and if it is too small, the storability may decrease. When the core particle diameter and the shell layer thickness of the core / shell particles can be observed with an electron microscope, the particle size and shell thickness selected at random from the observation photograph can be obtained directly. When it is difficult to observe the core and the shell with a microscope, it can be calculated from the particle size of the core particles and the amount of the monomer forming the shell used in the production of the toner.
[0040]
After the completion of the two-stage suspension polymerization reaction, the polymer dispersion liquid is washed or filtered and washed, and then filtered and dried to include a binder resin having a core-shell structure, a colorant, and a charge control agent. Thus, a color toner for developing an electrostatic image according to the present invention can be obtained.
[0041]
G 'of the color toner for developing electrostatic images of the present invention₈₀, G '₁₆₀And tan δ are determined in such a way that the types of the polymerizable monomer and the molecular weight modifier used and the amounts used thereof, as well as the polymerization temperature, the polymerization time, and the like mutually influence each other. Therefore, these can be adjusted by changing the above polymerization reaction factors, for example, the amount of the crosslinkable monomer or crosslinkable polymer preferably used in combination with a monovinyl monomer as the polymerizable monomer And can be achieved relatively easily by using mercaptan and thiuram disulfide together as molecular weight regulators.
Further, the volume-average particle diameter (Dv) of the toner of the present invention and the ratio (Dv / Dp) of the volume-average particle diameter to the number-average particle diameter (Dp) are the most dominant factors depending on which polymerization method is used. However, the target value can be relatively easily approached by using suspension polymerization, particularly two-stage suspension polymerization, and can be adjusted by the type and amount of the dispersion stabilizer used.
[0042]
In addition, the color toner of the present invention is characterized in that an additive (hereinafter referred to as an external additive) is added to the above-mentioned colored particles, mixed, and the external additive is adhered to the surface of the particles, embedded, and the like. , Fluidity, storage stability and the like can be adjusted.
[0043]
Examples of the external additive used in the present invention include inorganic particles and organic resin particles that are generally used for the purpose of improving fluidity and chargeability. For example, examples of the inorganic particles include silica, aluminum oxide, titanium oxide, zinc oxide, and tin oxide. Examples of the organic resin particles include (meth) acrylate polymer particles and styrene- (meth) acrylate. Polymer particles and the like. Among these, silica and titanium oxide are preferred, those having a particle surface subjected to hydrophobic treatment are preferred, and silica particles subjected to hydrophobic treatment are particularly preferred. The amount of the external additive is not particularly limited, but is usually 0.1 to 6 parts by weight based on 100 parts by weight of the toner. These external additives may be used in combination of two or more kinds. When an external additive is used in combination, a method of combining inorganic particles having different average particle diameters or a combination of inorganic particles and organic resin particles is preferable. In order for the external additive to adhere to the toner particles, the external additive and the toner particles are usually charged into a mixer such as a Henschel mixer and stirred.
[0044]
The color toner for developing an electrostatic image of the present invention can form an image using a general electrostatic image forming apparatus. That is, the surface of the uniformly charged photoreceptor is exposed to light to form an electrostatic image, toner is adhered to the electrostatic image, developed, and the obtained toner image is transferred to a transfer material by a transfer roll. Then, the transfer material is heated and pressed by a fixing roll to fix the transfer material.
The color toner for developing an electrostatic image of the present invention is excellent in low-temperature fixability and hardly causes offset. Further, the color toner for developing an electrostatic image of the present invention is less likely to agglomerate with each other even when stored for a long period of time, and is excellent in storability.
[0045]
【Example】
Hereinafter, the present invention will be described more specifically with reference to Examples and Comparative Examples, but the present invention is not limited to only these Examples. Parts and percentages are by weight unless otherwise specified.
In this example, the test and evaluation were performed by the following methods.
[0046]
1. Toner properties
(1) Volume average particle diameter (Dv), number average particle diameter (Dp) and Dv₅₀/ Dp₅₀Dv, Dp and Dv / Dp were measured using a Multisizer (manufactured by Beckman Coulter). The measurement was performed under the conditions of an aperture diameter: 100 μm, a medium: Isoton II, a concentration of 10%, and the number of measured particles: 100,000.
(2) Average circularity
10 ml of ion-exchanged water is prepared in advance in a container, and a surfactant, preferably an alkylbenzene sulfonate, is added as a dispersant therein, and then 0.02 g of toner is further added. Treated and dispersed uniformly. The dispersion was adjusted so that the toner concentration at the time of measurement was 3000 to 10000 particles / μl, and the number of toner particles was measured using a flow-type particle image analyzer (FPIA-1000; manufactured by Toa Medical Electronics Co., Ltd.). Was measured between 1,000 and 10,000. The average circularity was determined using this data.
[0047]
(3) Loss modulus (G ″), storage modulus (G ′) and tangent loss (tan δ)
Using a viscoelasticity measuring device (VAR-100, manufactured by Rheological), a parallel plate having a diameter of 20 mm was used as a measuring jig, an applied frequency of 10 Hz, a strain of 1%, and an auto-tension. The temperature dependence of the dynamic viscoelastic modulus in the temperature raising step (temperature raising rate 5 ° C./min) from 70 ° C. to 180 ° C. was measured. Storage modulus at 80 ° C. (G ′₈₀), Storage modulus at 160 ° C. (G ′₁₆₀).
[0048]
(4) Enthalpy of melting
The enthalpy of fusion was calculated from a DSC curve measured at a heating rate of 10 ° C./min using a differential scanning calorimeter (DSC SSC5200, manufactured by Seiko Instruments Inc.) in accordance with ASTM D3418-82. That is, from the base line on the higher temperature side than the melting point measured as the peak top of the endothermic peak of the obtained DSC curve, the base line was extended toward the melting point and surrounded by the intersection with the endothermic peak line and the peak. It was calculated from the range.
(5) Storage
After putting 20 g of the toner in a container and sealing it, it is immersed in a constant temperature water bath at a temperature of 55 ° C., taken out after 8 hours, and transferred onto a 42-mesh sieve so as not to destroy the structure as much as possible. (Powder Tester, manufactured by Hosokawa Micron Co., Ltd.), the vibration intensity was set to 1 mm, and after shaking for 30 seconds, the weight of the toner remaining on the sieve, that is, the aggregated toner was determined. It is determined that the larger the ratio (% by weight) of the weight of the aggregated toner to the initial weight of the sample, the poorer the storability of the toner.
[0049]
2. Image quality evaluation
(6) Fixing temperature
A commercially available non-magnetic one-component developing type color printer (Microline 3020C, manufactured by Oki Data Co., Ltd.) was used which was modified so that the temperature of the fixing roll portion could be changed. First, while changing the temperature of the fixing roll of the modified printer, the fixing rate of the toner at each temperature was measured, and the relationship between the temperature and the fixing rate was obtained.
The fixing rate was maintained at the measurement temperature for 5 minutes or more each time the temperature was changed at 5 ° C. intervals to stabilize the temperature of the fixing roll, and then before and after the tape peeling operation in the black solid area of the printed test paper. It was calculated from the ratio of image density. That is, assuming that the image density before tape removal is before ID and the image density after tape removal is after ID, the fixing rate can be calculated from the following equation.
Fixing rate (%) = (after ID / before ID) × 100
Here, the tape peeling is performed by applying an adhesive tape (Scotch Mending Tape 810-3-18, manufactured by Sumitomo 3M Limited) to the measurement portion of the test paper and pressing it with a constant pressure to adhere the test paper and the tape. Peeling is performed at a constant speed so that the peeling direction becomes 180 °. The image density was measured using a Macbeth reflection densitometer.
In this fixing test, the fixing roll temperature corresponding to a fixing rate of 80% was used as the fixing temperature of the developer.
[0050]
(7) Hot offset occurrence temperature and fixing margin
In the same manner as in the measurement of the fixing temperature in the above (6), printing was performed while changing the fixing roll temperature at intervals of 5 ° C., and the fixing roll temperature at which offset occurred was defined as the hot offset occurrence temperature.
The fixing margin was determined as the difference (° C.) between the hot offset occurrence temperature and the fixing temperature.
[0051]
(Example 1)
90 parts of styrene, 10 parts of n-butyl acrylate, 0.2 part of divinylbenzene, 1 part of polymethacrylic acid methyl ester macromonomer (trade name "AA6" manufactured by Toa Gosei Chemical Industry Co., Ltd.), C.I. I. Pigment Red 185, 8 parts of positive charge control resin (FCA207P, Fujikura Kasei Co., quaternary ammonium group 2%) 1 part, negative charge control resin (FCA626N, Fujikura Kasei Co., 7% sulfonic acid group) 7 parts, 10 parts of dipentaerythritol hexamyristate, 2 parts of 2,2,4,6,6-pentamethylheptane-4-thiol and 0.1 part of tetraethylthiuram disulfide were dispersed at room temperature in a bead mill to polymerize the core. A water-soluble monomer composition was obtained.
[0052]
On the other hand, 44.8 parts of a 25% aqueous magnesium chloride solution (water-soluble polyvalent metal salt aqueous solution) was gradually added to an aqueous solution obtained by dissolving 7.1 parts of sodium hydroxide in 181 parts of ion-exchanged water while stirring. Magnesium oxide colloid (Dp₅₀Is 0.36 μm, Dp₉₀Is 0.86 μm) to prepare a dispersion. The polymerizable monomer composition for a core was added to the magnesium hydroxide colloidal dispersion obtained as described above, and the mixture was stirred and mixed using a propeller type stirrer. Next, 4.5 parts of t-butylperoxy-2-ethylhexanoate was added, and the mixture was further stirred and mixed to obtain a monomer composition suspension. Next, this monomer composition suspension was supplied to a granulator (CLEARMIX CLM-0.8S, manufactured by M Technique Co., Ltd.) in which a rotor was operating at a rotation speed of 21,000 rpm using a pump. Thus, an aqueous dispersion of the core-forming monomer composition was prepared.
The aqueous dispersion of the monomer composition was transferred to a polymerization reactor equipped with a stirring blade. The aqueous monomer composition dispersion was heated and controlled to a constant temperature when the temperature reached 90 ° C.
After confirming that the polymerization conversion reached almost 100%, 1.5 parts of a polymerizable monomer for shell methyl methacrylate was added. After 5 minutes, the water-soluble initiator 2,2′-azobis- [2-methyl- (N-1,1-bis (hydroxymethyl) -2-hydroxyethyl) propioamide] (VA-086, manufactured by Wako Pure Chemical Industries, Ltd.) 2.) An aqueous solution in which 0.2 part was dissolved in 20 parts of water was added to a polymerization reactor, and methyl methacrylate was polymerized to obtain polymer particles having a core-shell structure. While the aqueous dispersion of the polymer particles was stirred, the pH of the system was adjusted to about 5.0 with sulfuric acid, and acid washing was performed at 25 ° C. for 10 minutes. Next, the mixture was dehydrated by filtration and washed with water for washing. Thereafter, drying was performed for two days and nights in a hot air circulating dryer at 45 ° C. to obtain toner particles.
[0053]
To 100 parts of the obtained toner particles, 1.0 part of colloidal silica (manufactured by Clariant, product name "H13TX") hydrophobized with polysiloxane and hexamethyldisilazane was added and mixed using a Henschel mixer. A toner was manufactured. Table 1 shows the characteristics of the obtained toner and the results of the image quality evaluation.
[0054]
(Examples 2 to 4)
As shown in Table 1, a toner was produced in the same manner as in Example 1 except that the amounts of 2,2,4,6,6-pentamethylheptane-4-thiol and divinylbenzene were changed. Table 1 shows the characteristics of the obtained toner and the results of the image quality evaluation.
[0055]
(Comparative Example 1)
According to Example 1 described in JP-A-9-6051, a toner was prepared as follows.
233 parts of methanol was put into the reactor, and 6.74 parts of the polymer dispersant Gantret was added little by little while stirring, and completely dissolved. Next, 55 parts of styrene, 45 parts of methyl methacrylate, 1.5 parts of butanediol dimethacrylate and 0.26 parts of dodecyl mercaptan were added and dissolved, and then the gas phase was purged with nitrogen and left for 1 hour. Thereafter, the mixture was stirred and maintained at a temperature of 60 ° C., and a polymerization reaction was carried out while continuously injecting a 5.66% methanol solution in which 1.55 parts of 2,2′-azobisisobutyronitrile was dissolved. One hour later, a solution obtained by dissolving 2 parts of dodecyl mercaptan in 25.9 parts of methanol was added thereto. After a further 16 hours, 18.7 parts of styrene were injected in 35 minutes, and again a 5.66% methanol solution in which 1.55 parts of 2,2'-azobisisobutyronitrile was dissolved was continuously injected. The reaction was continued for an hour, and the reaction was completed at a polymerization conversion of 95%. To the obtained dispersion, 28.5 parts of ion-exchanged water is added, and the mixture is centrifuged. 259 parts of methanol is poured into the wet cake for washing, followed by dewatering. Then, a mixture of 259 parts of water 3 / methanol 7 is used. After washing, the mixture was drained and then washed twice with 259 parts of a mixed solution of water 5 / methanol 5 and subjected to drainage. The cake was dried under reduced pressure for 24 hours to obtain polymer particles.
On the other hand, 1.3 parts of oil black 803 (manufactured by Orient Chemical Co., Ltd.) was dissolved in 259 parts of methanol by heating, cooled, and filtered with a 1 μm filter to prepare a dye solution. Next, 31 parts of the above polymer particles were added to and dispersed in the dye solution, and stirred for 1 hour while heating to 50 ° C. Thereafter, the resin particle dispersion was cooled to room temperature and filtered to obtain toner particles. This was vacuum-dried at room temperature for 24 hours, and 1% silica of toner particles was added and mixed to obtain a toner. Table 1 shows the characteristics of the obtained toner and the results of the image quality evaluation.
[0056]
(Comparative Examples 2-3)
As shown in Table 1, a toner was produced in the same manner as in Example 1 except that the amounts of 2,2,4,6,6-pentamethylheptane-4-thiol and divinylbenzene were changed. Table 1 shows the characteristics of the obtained toner and the results of the image quality evaluation.
[0057]
[Table 1]

[0058]
The following can be seen from the evaluation results of the toners in Table 1.
From the range defined in the present invention, G 'obtained using only dodecyl mercaptan,₈₀And G '₁₆₀, The maximum value of tan δ was high, the minimum value was low, and the temperature range where the maximum value and the minimum value were present was low. The toner of Comparative Example 1 had a high fixing temperature and poor storage stability.
From the range defined by the present invention, G 'was obtained by polymerization using a large amount of 2,2,4,6,6-pentamethylheptane-4-thiol.₈₀And G '₁₆₀The toner of Comparative Example 2, which had a low fixing temperature and a large minimum value of tan δ, had an extremely low fixing temperature of 120 ° C., but had offset and poor storage stability.
From the range defined in the present invention, G 'was obtained by polymerization of 2,2,4,6,6-pentamethylheptane-4-thiol reduced to the same level as in Example 4, and a large amount of divinylbenzene was added.₁₆₀And the toner of Comparative Example 3 having no minimum value of tan δ had a high fixing temperature of 160 ° C.
On the other hand, all of the toners of Examples 1 to 4 satisfying the requirements of the present invention are excellent in low-temperature fixing property, hardly cause hot offset occurrence temperature, and therefore have a wide fixing margin and excellent storage stability.
[0059]
【The invention's effect】
According to the present invention, there is provided a color toner for developing an electrostatic image, which is excellent in low-temperature fixability, hardly causes hot offset, has a wide fixing margin, and is excellent in storability.

Claims (5)

An electrostatic image developing color toner containing at least a binder resin, a colorant and a charge control agent,
In dynamic viscoelastic properties measured at a frequency of 10 Hz and a strain of 1%, the storage elastic modulus at 80 ° C. (G ′ ₈₀ ) is 5 × 10 ^{6 to} 5 × 10 ⁸ Pa, and the storage elastic modulus at 160 ° C. (G ′ ₁₆₀ ) is 1 × 10 ² to 1 × 10 ⁴ Pa, a maximum value of tangent loss (tan δ) of 1.2 to 2.5 exists at 80 to 100 ° C., and a tan δ of 95 to 125 ° C. There are local minimums 1-2,
The volume average particle diameter (Dv) is 2 to 11 μm, and the ratio (Dv / Dp) of the volume average particle diameter (Dv) to the number average particle diameter (Dp) is 1.3 or less;
A color toner for developing an electrostatic image. The color toner for developing electrostatic images according to claim 1, wherein the enthalpy of fusion is 1 to 10 mJ / mg. 3. The color toner for developing electrostatic images according to claim 1, wherein the charge control agent is a copolymer having a quaternary ammonium (salt) group or a sulfonic acid (salt) group. 4. The color toner for developing an electrostatic image according to claim 1, which has a core-shell structure, and wherein the colorant and the charge control agent are contained in the core. 5. The color toner for developing an electrostatic image according to claim 1, wherein a silica treated with a silane coupling agent and / or silicone oil is blended as an external additive.