JP4026467B2 - Color toner for electrophotography - Google Patents

Description

以上の材料をヘンシェルミキサーに投入し、予備混合を行った後、エクストルーダーにより混練し、次にハンマーミルにて粗粉砕し、さらにジェットミルにて微粉砕し、気流分級機にて分級を行い、体積平均粒径が約８．５μｍのイエロートナーＹ₁ を得る。
なお、この針状酸化チタン（ＦＴ−１０００；石原テクノ製商品名）は、電気抵抗が５Ω・ｃｍで、平均長軸径が２．５μｍでアクペクト比が１１の針状の微粒子である。
【００６６】
次いで、このトナーＹ₁ に対して外添剤として疎水性シリカ微粒子（Ｈ２０００／４；クラリアント社製商品名）を１重量部添加し、ヘンシェルミキサを用いて攪拌して外添処理を行い、イエロートナーＹ₁ の表面に疎水性シリカを付着させた。
【００６７】
この表面改質されたイエロートナーＹ₁ ５重量部とシリコーン樹脂コートマグネタイトキャリア( 関東電化工業製）９５重量部をボールミルで混合することにより、二成分現像剤を得た。
【００６８】
次いで、ブローオフ帯電量測定器（東芝ケミカル製）を用いてこの二成分現像剤の帯電量を測定したところ、−１７．１μＣ／ｇであった。
また、上述Ｆ６７０８Ｂ（富士通社製商品名）を用いてベタ画像を印刷し、その画像を測色した結果、Ｌ^* ＝７８ 、ａ^* ＝−１３、ｂ^* ＝４７であり、電気抵抗は１２ＧΩ・ｃｍであった。
【００６９】
（マゼンタトナーＭ₁ ）
着色剤の種類及び導電性微粒子の添加量を除いては、イエロートナーＹ₁ と同様にトナーを作製する。

【００７０】
（シアントナーＣ₁ ）
着色剤の種類及び導電性微粒子の添加量を除いては、イエロートナーＹ₁ と同様にトナーを作製する。

【００７１】
図３（ａ）参照
図３（ａ）は、以上のマゼンタトナーＭ₁ 及びシアントナーＣ₁ についてのイエロートナーＹ₁ と同様にしてトナーの表面改質を行い、シリコーン樹脂コートマグネタイトキャリア( 関東電化工業製) とボールミルで混合することにより、二成分現像剤を得、得られた現像剤の帯電量と、その印字を測色した結果、および、カラートナーの電気抵抗を測定した結果をイエロートナーＹ₁ とともに纏めて示したものである。
【００７２】
（グレートナーＧ₁ 〜Ｇ₄ ）
着色剤の種類及び導電性微粒子の添加量を除いては、イエロートナーＹ₁ と同様にトナーを作製し、イエロートナーＹ₁ と同様にしてトナーの表面改質を行い、シリコーン樹脂コートマグネタイトキャリア( 関東電化工業製) とボールミルで混合することにより、二成分現像剤を得た。得られた現像剤の帯電量と、その印字を測色した結果、および、カラートナーの電気抵抗を測定した結果を図３（ｂ）に示す。
【００７３】
図３（ｂ）参照

【００７４】
（ホワイトトナーＷ₁ 〜Ｗ₄ ，ブラックトナーＫ₁ ）
着色剤の種類及び導電性微粒子の添加量を除いては、イエロートナーＹ₁ と同様に参考例用のトナーを作製し、イエロートナーＹ₁ と同様にしてトナーの表面改質を行い、シリコーン樹脂コートマグネタイトキャリア( 関東電化工業製) とボールミルで混合することにより、二成分現像剤を得、得られた現像剤の帯電量と、その印字を測色した結果、および、カラートナーの電気抵抗を測定した結果を図３（ｃ）に示す。
【００７５】
図３（ｃ）参照

【００７６】
次に、本発明の作用効果を確認するための比較例となるカラートナーを構成するめに、導電性微粒子を添加しないカラートナー、ホワイトトナー、グレートナーを作成した。
着色剤の添加量及び導電性微粒子を添加しないことを除いては、イエロートナーＹ₁ と同様に参考例用のトナーを作製し、イエロートナーＹ₁ と同様にしてトナーの表面改質を行い、シリコーン樹脂コートマグネタイトキャリア( 関東電化工業製) とボールミルで混合することにより、二成分現像剤を得、得られた現像剤の帯電量と、その印字を測色した結果、および、カラートナーの電気抵抗を測定した結果を有彩色トナー（Ｙ₅ ，Ｍ₅ ，Ｃ₅ ）については図４（ａ）に、また、無彩色トナー（Ｗ₁ ，Ｇ₅ ）については図４（ｂ）に示す。
【００７７】
図４（ａ）及び（ｂ）参照

【００７８】
次いで、以上のトナーＹ₁ 、マゼンタトナーＭ₁ 、或いは、シアントナーＣ₁ とグレートナーＧ₁ 乃至Ｇ₄ を混合して作製した実施例１〜１０、トナーＹ₁ 、マゼンタトナーＭ₁ 、或いは、シアントナーＣ₁ とホワイトトナーＷ₁ 乃至Ｗ₄ 或いはＫ₁ を混合して作製した参考例１〜１６、及び、トナーＹ₅ 、マゼンタトナーＭ₅ 、或いは、シアントナーＣ₅ とホワイトトナーＷ₅ 、グレートナーＧ₅ 、或いは、ブラックトナーＫ₁ のいずれかを混合して作製した比較例１〜３を説明する。
なお、各実施例、各参考例、及び、各比較例についての組成比を図５に纏めて示し、また、Ｒ_H ／Ｒ_L 、印刷前後の色特性、及び、色差ΔＥについての測定結果を図６に纏めて示した。
【００７９】
図５参照
（実施例１）
無彩色トナー（グレートナーＧ₁ ） ５０重量部
有彩色トナー（イエロートナーＹ₁ ） ２５重量部
有彩色トナー（マゼンタトナーＭ₁ ） ２５重量部
の比率でヘンシェルミキサを用いて混合して、茶色のカラートナーを得た。
この茶色のカラートナーにおける、相対的に電気抵抗の高いイエロートナーＹ₁ の電気抵抗と相対的に電気抵抗の低いマゼンタトナーＭ₁ の電気抵抗との比Ｒ_H ／Ｒ_L は、
Ｒ_H ／Ｒ_L ＝１２ＧΩ・ｃｍ／８ＧΩ・ｃｍ＝１．５
である。
【００８０】
この茶色のカラートナー5 重量部とシリコーン系樹脂コートマグネタイトキャリア（関東電化工業製）９５重量部をボールミルで混合したものを使用し、上述のカラーレーザプリンタを使用して１０万枚の印刷試験を行い、印字色の安定性を評価した。
【００８１】
初期の印字を測色すると、Ｌ^* ＝４２、ａ^* ＝１５、ｂ^* ＝２５であり、１０万枚印刷後、印字を測色するとＬ^* ＝４３、ａ^* ＝１４、ｂ^* ＝２７であり、連続印刷前後の印字の色差ΔＥ＝２．４であり、ほとんど印字色の変化は見られず、印字色安定性が高いことがわかった。
なお、色差ΔＥは、印刷前の色座標を（Ｌ^* _A ，ａ^* _A ，ｂ^* _A ）とし、印刷後の色座標を（Ｌ^* _B ，ａ^* _B ，ｂ^* _B ）とすると、
ΔＥ＝｛（Ｌ^* _A −Ｌ^* _B ）² ＋（ａ^* _A −ａ^* _B ）² ＋（ｂ^* _A −ｂ^* _B ）² ｝^1/2
で定義される。
【００８２】
（実施例２〜５）
図５に示すように、無彩色トナーと有彩色トナーの混合比率を９０：１０〜１０：９０の間で変化させた明度の異なる茶色系カラートナーを用いて評価することを除いては、実施例１と同様に印字色安定性を評価した。
【００８３】
図６に示すように、初期の印字と１０万枚印刷後の印字を比べると、印字の色差ΔＥ＝１．４〜２．２であり、ほとんど印字色の変化は見られず、印字色安定性が高いことがわかった。
なお、Ｒ_H ／Ｒ_L は、いずれもＲ_H ／Ｒ_L ＝１．５である。
【００８４】
（実施例６〜８）
図５に示すように、無彩色トナーとしてカーボンブラック添加量の異なるグレートナーＧ₂ 〜Ｇ₄ を用い、茶色系カラートナーを用いて評価することを除いては、実施例１と同様の評価を行った。
【００８５】
図６に示すように、初期の印字と１０万枚印刷後の印字を比べると、印字の色差ΔＥ＝３．２〜４．６であり、ほとんど印字色の変化は見られず、印字色安定性が高いことがわかった。
なお、Ｒ_H ／Ｒ_L は、Ｒ_H ／Ｒ_L ＝１．５〜１．８８である。
【００８６】
（実施例９，１０）
図５に示すように、有彩色トナーとしてイエロートナーＹ₁ 及びシアントナーＣ₁ を用い、緑色系カラートナーについて評価することを除いては、実施例１と同様の評価を行った。
【００８７】
図６に示すように、初期の印字と１０万枚印刷後の印字を比べると、印字の色差ΔＥ＝２．０〜３．７であり、ほとんど印字色の変化は見られず、印字色安定性が高いことがわかった。
なお、Ｒ_H ／Ｒ_L は、いずれもＲ_H ／Ｒ_L ＝１．５である。
【００８８】
（参考例１〜５）
図５に示すように、無彩色トナーとしてブラックトナーＫ₁ を用い、明度の異なるこげ茶色系カラートナーを用いて評価することを除いては、実施例１〜５と同様の評価を行った。
【００８９】
図６に示すように、初期の印字と１０万枚印刷後の印字を比べると、印字の色差ΔＥ＝２．２〜３．７であり、ほとんど印字色の変化は見られず、印字色安定性が高いことがわかった。
なお、Ｒ_H ／Ｒ_L は、いずれもＲ_H ／Ｒ_L ＝１．５である。
【００９０】
（参考例６〜１０）
図５に示すように、無彩色トナーとしてホワイトトナーＷ₁ を用い、明度の異なる薄茶色系カラートナーを用いて評価することを除いては、実施例１〜５と同様の評価を行った。
【００９１】
図６に示すように、初期の印字と１０万枚印刷後の印字を比べると、印字の色差ΔＥ＝２．８〜３．３であり、ほとんど印字色の変化は見られず、印字色安定性が高いことがわかった。
なお、Ｒ_H ／Ｒ_L は、いずれもＲ_H ／Ｒ_L ＝１．５である。
【００９２】
（参考例１１〜１３）
図５に示すように、無彩色トナーとしてホワイト顔料添加量の異なるホワイトトナーＷ₂ 〜Ｗ₄ を用い、薄茶系カラートナーを用いて評価することを除いては、実施例１と同様の評価を行った。
【００９３】
図６に示すように、初期の印字と１０万枚印刷後の印字を比べると、印字の色差ΔＥ＝１．０〜５．０であり、ほとんど印字色の変化は見られず、印字色安定性が高いことがわかった。
なお、Ｒ_H ／Ｒ_L は、Ｒ_H ／Ｒ_L ＝１．２５〜１．８８である。
【００９４】
（参考例１４〜１６）
図５に示すように、有彩色トナーとしてイエロートナーＹ₁ 、マゼンタトナーＭ₁ 、シアントナーＣ₁ を用い、様々な色調のカラートナーについて評価することを除いては、実施例１と同様の評価を行った。
【００９５】
図６に示すように、初期の印字と１０万枚印刷後の印字を比べると、印字の色差ΔＥ＝２．４〜４．９であり、ほとんど印字色の変化は見られず、印字色安定性が高いことがわかった。
なお、Ｒ_H ／Ｒ_L は、Ｒ_H ／Ｒ_L ＝１．６７〜１．８８である。
【００９６】
（比較例1 ）
無彩色トナー（ホワイトトナーＷ₅ ） ５０重量部
有彩色トナー（イエロートナーＹ₅ ） ２５重量部
有彩色トナー（マゼンタトナーＭ₅ ） ２５重量部
以上のトナーを混合し、導電性微粒子を添加せず、トナーの電気抵抗を制御しないことを除いては、実施例１と同様にして、カラートナー（薄茶色）を評価した。
【００９７】
図６に示すように、初期の印字を測色すると、Ｌ^* ＝７２、ａ^* ＝１３、ｂ^* ＝２３であり、１０万枚印刷後、印字を測色するとＬ^* ＝６１、ａ^* ＝１５、ｂ^* ＝２９であり、連続印刷前後の印字の色差ΔＥ＝１２．７となり、印字色の変化が見られ、印字色安定性が低いことがわかった。
なお、Ｒ_H ／Ｒ_L は、Ｒ_H ／Ｒ_L ＝３．３である。
【００９８】
（比較例２）
図５に示すように、無彩色トナーとして導電性微粒子を添加せず、トナーの電気抵抗が制御されていないグレートナーＧ₅ を用いることを除いては、比較例１と同様にして、カラートナー（こげ茶色）を評価した。
【００９９】
図６に示すように、初期の印字と１０万枚印刷後の印字を比べると、印字の色差ΔＥ＝８．８であり、印字色の変化が見られ、印字色安定性が低いことがわかった。
なお、Ｒ_H ／Ｒ_L は、Ｒ_H ／Ｒ_L ＝２．５である。
【０１００】
（比較例３）
図５に示すように、無彩色トナーとしてブラックトナーＫ₁ を用いることを除いては、比較例１と同様にして、評価した。
【０１０１】
図６に示すように、初期の印字と１０万枚印刷後の印字を比べると、印字の色差ΔＥ＝２３．０であり、印字色の変化が見られ、印字色安定性が低いことがわかった。
なお、Ｒ_H ／Ｒ_L は、Ｒ_H ／Ｒ_L ＝１５である。
【０１０２】
以上の評価結果から、実施例１〜１０のトナーは、１０万枚の印刷試験後においても、初期の印字色と変化は見られないが、一方、比較例１〜３のトナーは印刷に伴った印字色の変化が大きく、安定性に欠けることがわかる。
なお、参考のために示した参考例１〜１６のトナーも、１０万枚の印刷試験後においても、初期の印字色と変化は見られず、実施例１〜１０と同様に好適な結果を示した。
【０１０３】
図７参照
図７は、本発明のカラートナーの色再現範囲を模式的に示したものであり、有彩色カラートナーと無彩色トナーの混合により、有彩色カラートナーのみの混合によるＹ−Ｌ−Ａ−Ｂ−Ｍ−Ｄ−Ｅ−Ｆ−Ｃ−Ｉ−Ｈ−Ｊ−Ｙの閉じた曲線とＧ，Ｋを結ぶ２つの曲面にはさまれた空間の全ての色を再現することが可能となる。
なお、図示は省略しているものの、比較例の場合に、特に比較例２の場合にも、本発明と同様の色再現範囲を実現することは可能である。
また、参考例の場合には、Ｙ−Ｌ−Ａ−Ｂ−Ｍ−Ｄ−Ｅ−Ｆ−Ｃ−Ｉ−Ｈ−Ｊ−Ｙの閉じた曲線とＷを結ぶ曲面（図示を省略）にはさまれた空間の全ての色を再現することが可能となる。
【０１０４】
図８参照
図８は、実施例１〜１０と比較例１〜３の印字色の変化量、即ち、色差ΔＥのＲ_H ／Ｒ_L 依存性の説明図であり、電気抵抗の比Ｒ_H ／Ｒ_L が大きいものほど印字色の変化が大きいこと、即ち、トナー電気抵抗が大きく異なるトナーを混合することにより得られるカラートナーは印字色安定性が低いことが理解される。
したがって、電気抵抗の比Ｒ_H ／Ｒ_L を２以下とすることにより、帯電安定化を図ることが可能であり、それによって、印字色の安定化が図れることがわかる。
【０１０５】
なお、この様なトナーの電気抵抗は、導電性微粒子の添加により容易に制御されるものであり、Ｙ₅ ，Ｍ₅ ，Ｃ₅ の有彩色カラートナー、Ｗ₅ ，Ｇ₅ の無彩色トナー、及び、ブラックトナーＫ₁ を比べると、導電性微粒子が添加されていないため、着色剤の影響により、トナーの電気抵抗が１０ＧΩ・ｃｍから１５０ＧΩ・ｃｍと大きく変化しており、色再現範囲については良好な結果が得られるものの、印字色の安定性は得られない。
【０１０６】
これに対して、Ｙ₁ ，Ｍ₁ ，Ｃ₁ の有彩色カラートナー及びＷ₁ 〜Ｗ₄ ，Ｇ₁ 〜Ｇ₄ の無彩色トナーを比べると、着色剤の電気抵抗に応じて導電性微粒子が添加されているため、トナーの電気抵抗が８ＧΩ・ｃｍから１５ＧΩ・ｃｍであり、狭い範囲に制御されている。
【０１０７】
なお、上記の各実施例の説明においては、有彩色カラートナーとしてイエロー、マゼンタ、及び、シアンの３つの色相のトナーを組み合わせて用いているが、これとは異なった色相体系のカラートナーを用いても良いものである。
即ち、例えば、グリーン、ブルー、及び、レッド等の色相のトナーを組み合わせても良いものである。
【０１０８】
ここで、改めて本発明の詳細な特徴を説明する。
（付記１） 少なくとも着色剤と結着樹脂と導電性微粒子からなる電子写真用トナー組成物において、グレートナーと有彩色のカラートナーを混合することにより得られる電子写真用カラートナーであって、前記グレートナーの着色剤として２重量％以下のカーボンブラックを添加するとともに、前記グレートナーに添加する導電性微粒子の電気抵抗が１〜１００Ωｃｍであることを特徴とする電子写真用カラートナー。
（付記２） 上記有彩色のカラートナーの印字色が、Ｌ^* ａ^* ｂ^* 色空間において、（ａ^* ）² ＋（ｂ^* ）² ≧１０であることを特徴とする付記１記載の電子写真用カラートナー。
（付記３） 上記グレートナーの印字色が、Ｌ^* ａ^* ｂ^* 色空間において、（ａ^* ）² ＋（ｂ^* ）² ≦５であることを特徴とする特徴とする付記１または２に記載の電子写真用カラートナー。
（付記４） 上記グレートナーの印字色が、Ｌ^* ａ^* ｂ^* 色空間において、Ｌ^* ≦３５であることを特徴とする付記１乃至３のいずれか１に記載の電子写真用カラートナー。
（付記５） 上記導電性微粒子の添加量が前記有彩色のカラートナーとグレートナーにおいて互いに異なる添加量であることを特徴とする付記１乃至４のいずれか１に記載の電子写真用カラートナー。
（付記６） 上記２種類以上のトナーの内、最も抵抗の高いトナーの抵抗Ｒ_H と、最も抵抗の低いトナーの抵抗Ｒ_L との比Ｒ_H ／Ｒ_L を、２以下とすることを特徴とする付記１乃至５のいずれか１に記載の電子写真用カラートナー。
（付記７） 付記１乃至６のいずれか１に記載の電子写真用カラートナーを収容したトナーカセットを搭載したことを特徴とする画像形成装置。
【０１０９】
【発明の効果】
本発明によれば、少なくとも一種類の有彩色のカラートナーとグレートナーとを混合しているので、比較的低い明度で各種の色調の多彩な印字色を実現することができ、また、混合する各トナーの電気抵抗をほぼ等しくしているので、混合されたトナーが均等に消費され、安定した印刷画像を得ることができ、ひいては、高画質の画像形成装置の普及に寄与するところが大きい。
【図面の簡単な説明】
【図１】本発明の原理的構成の説明図である。
【図２】本発明の実施の形態に用いる画像形成装置の概念的構成図である。
【図３】本発明の実施の形態に用いる各トナーの特性の説明図である。
【図４】比較例に用いる各トナーの特性の説明図である。
【図５】本発明の実施の形態の各種カラートナーの組成比の説明図である。
【図６】本発明の実施の形態の各種カラートナーの特性の説明図である。
【図７】本発明の実施の形態のカラートナーの色再現領域の説明図である。
【図８】本発明の実施の形態のカラートナーの色差ΔＥのＲ_H ／Ｒ_L 依存性の説明図である。
【図９】従来のカラートナーの色再現領域の説明図である。
【符号の説明】
１０ 感光体
２０ 帯電器
３０ 露光手段
４０ 現像手段
４１ 現像剤容器
４３ 現像ローラ
４５ トナーホッパー
５０ 転写器
６０ クリーナ
７０ 除電器
８０ フラッシュ定着器
８１ キセノンフラッシュランプ[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color toner for electrophotography, and in particular, a color toner obtained by mixing at least one chromatic color toner selected from yellow, magenta, cyan and the like and an achromatic gray toner. The present invention relates to an electrophotographic color toner characterized by a constitution for expanding the color reproduction area and stabilizing the developability.
[0002]
[Prior art]
The electrophotographic method is a technique widely used in image forming apparatuses such as copying machines, electrophotographic facsimiles, and electrophotographic printers, and a method using a photoconductive insulator is generally used as an electrophotographic method ( For example, see Patent Document 1.)
[0003]
In this method, an electrostatic latent image is formed by irradiating light such as a laser or LED on a photoconductive insulator charged by corona discharge or a charge supply roller, and then a pigment or dye called a toner. The resin powder colored by is electrostatically attached to the electrostatic latent image and developed to form a visualized toner image, which is then transferred onto a recording medium such as paper or film. Yes.
[0004]
However, since the toner image at this time is a powder image simply placed on the recording medium, it is necessary to fix it on the recording medium.
Therefore, as a final step, the toner is melted on the recording medium by heat, pressure, light, or the like and then solidified to obtain a toner image finally fixed on the recording medium.
[0005]
As described above, toner fixing is to fix a toner, which is a powder mainly composed of a thermoplastic resin (hereinafter referred to as a binder resin), by heat and fixed onto a recording medium. A heat roll method in which a recording medium on which a toner image is formed is directly heated and pressed by a roller, and a flash fixing method in which toner is fixed on the recording medium by flash light irradiation such as a xenon flash lamp are well known.
[0006]
In order to obtain a color image, three color toners of yellow toner, magenta toner, cyan toner, or four color toners of black toner in addition to the three color toners are developed and superimposed. A printing method that performs color printing by superimposing two or more colors of black toner or color toner is known (for example, see Patent Document 2).
[0007]
In the former printing method, the color toners of yellow toner, magenta toner, cyan toner, and black toner are set in a yellow developing device, a magenta developing device, a cyan developing device, and a black developing device, respectively, and a printed image is formed by each development. The
In this case, even if the physical properties of the respective color toners are different, it is possible to make the development characteristics the same by optimizing the development conditions. However, on the other hand, the apparatus structure becomes complicated and the cost is high. It becomes.
[0008]
On the other hand, in the latter printing method, if there is at least one developing unit for developing color toner, color printing can be performed, the apparatus structure is simple, and the apparatus is low-cost.
[0009]
In the latter printing method, a printing apparatus having a fluidized bed for uniformly mixing toners having substantially the same physical properties and different colors at a set ratio is known (for example, Patent Documents). 3).
[0010]
Conventionally, the electrical resistance of the toner is adjusted by a method of adding a conductive additive to the toner. In a two-component developer composed of a toner and a magnetic carrier, the core material of the magnetic carrier combined with the toner or The electrical resistance is controlled by adjusting the conductivity of the coating material.
[0011]
For example, as a method for controlling the electrical resistance of the toner, a method of adding a conductive additive to the toner is known (see, for example, Patent Documents 4 and 5).
In this method, a conductive additive is added to the toner by internal or external addition to change the electrical resistance of the color toner.
[0012]
By mixing two or more kinds of toners selected from yellow toner, magenta toner, cyan toner, black toner, and the like, color toners of various colors can be provided.
[0013]
[Patent Document 1]
US Pat. No. 2,297,691
[Patent Document 2]
JP 61-132959 A
[Patent Document 3]
JP-A-6-348101
[Patent Document 4]
JP-A-5-19525
[Patent Document 5]
JP 11-327192 A
[0014]
[Problems to be solved by the invention]
In order to perform color printing with the latter printing method described above, various color toners are required to match various printing colors. To obtain various color toners, various materials can be used. It is necessary to use a colorant.
[0015]
However, if the colorant material is different, the electrical resistance of the color toner will change according to the electrical resistance of the colorant. Therefore, for use in a developing device under the same conditions, the electrical resistance is precisely controlled for each color toner. However, in order to precisely control the electrical resistance, it is necessary to repeat numerous experiments and evaluations repeatedly, and it is practically impossible to provide color toners of various colors. There is a problem.
[0016]
Also, if various colors of color toner are provided by changing the colorant by the above method, a large number of color toners will be produced, and piping and manufacturing equipment will be produced each time a different color toner is produced. This requires a large amount of demerit in terms of production costs.
[0017]
That is, by mixing two or more kinds of toners selected from yellow toner, magenta toner, and cyan toner, various color toners can be provided. However, a colorant is added to yellow toner, magenta toner, and cyan toner. Therefore, yellow, magenta, and cyan toners having different electrical resistances can be obtained.
[0018]
When color toners obtained by combining and mixing color toners having different electric resistances are printed, the combined color toners are developed unevenly, which causes a problem that the color tone of the printed image becomes unstable.
For this reason, a method for precisely adjusting the electrical resistance of yellow toner, magenta toner, and cyan toner each containing yellow, magenta, and cyan pigments having different electrical resistances is required.
[0019]
Furthermore, the color that can be reproduced with a color toner obtained by mixing yellow toner, magenta toner, and cyan toner is L^*a^*b^*Since the color space is limited to a predetermined range, this situation will be described with reference to FIG.
[0020]
See FIG.
That is, by changing the mixing ratio of these toners, the color on the closed curve of Y-L-A-B-M-D-E-F-C-I-H-J-Y shown in FIG. Can be reproduced, but the color inside the curve and a^*-B^*Lightness axis L perpendicular to the plane^*Different colors cannot be expressed.
[0021]
Therefore, in order to reproduce colors other than those shown on the closed curve of Y-LA-B-M-D-E-F-C-I-H-J-Y, a further toning method is used. It is necessary to improve.
[0022]
Accordingly, an object of the present invention is to provide color toners of various colors that can stably develop a vivid color tone image.
[0023]
[Means for Solving the Problems]
  Here, with reference to FIG. 1, means for solving the problems in the present invention will be described. FIG. 1 is an explanatory diagram of a color reproduction region of a color toner when gray toner is mixed.
  See Figure 1
  In order to achieve the above object, the present invention comprises at least a colorant, a binder resin,Conductive fine particlesAn electrophotographic color toner obtained by mixing a gray toner and a chromatic color toner, wherein the gray toner colorant comprises:2% by weight or less of carbon black is added, and the electrical resistance of the conductive fine particles added to the gray toner is 1 to 100 Ωcm.It is characterized by that.
[0024]
In this way, by adding a gray toner containing carbon black as a colorant to a chromatic color toner, as shown in FIG. 1, Y-LA-B-M-D-E-F-C-I It becomes possible to reproduce all the colors in the space between the closed curve of -HJY and the two curved surfaces connecting G and K.
[0025]
In this case, the print color of the chromatic color toner is L^*a^*b^*In color space, (a^*)²+ (B^*)²≧ 10 is desirable, so that saturation C when mixed with gray toner^*[= (A^{* 2}+ B^{* 2})^1/2] From high to low saturation C^*Various color toners can be obtained up to low color toners.
[0026]
The gray toner print color is L^*a^*b^*In color space, (a^*)²+ (B^*)²≦ 5, so that the saturation C of the chromatic color toner when mixed with the chromatic color toner.^*Can be reduced.
[0027]
The gray toner print color is L^*a^*b^*In color space, L^*It is desirable that ≦ 35, so that brightness L when mixed with chromatic color toner^*Low color toner can be obtained.
[0028]
Further, in order to effectively control the electric resistance of the gray toner, conductive fine particles are used as an additive, and the electric resistance of the conductive fine particles is desirably 1 to 100 Ω · cm. The problem of color change during printing can be improved.
In addition, if it is less than 1 Ω · cm, the chargeability of the toner is lowered and fog occurs, and if it exceeds 100 Ω · cm, sufficient conductivity cannot be obtained.
[0029]
Also, since organic pigments and dyes have the highest resistance and white inorganic pigments have the highest resistance, conductive fine particles as additives are added to chromatic color toners and gray toners that use organic pigments, dyes, and white inorganic pigments. It is preferable to add and control the electric resistance of each toner according to the electric resistance of the colorant.
[0030]
Among the two or more types of toner, the resistance R of the toner having the highest resistance_HAnd the resistance R of the toner with the lowest resistance_LRatio R_H/ R_LIs preferably 2 or less, whereby good stability of color tone can be obtained.
The electric resistance ratio R of the toner to be mixed_H/ R_LIf the value exceeds 2, the mixed toner is developed and consumed non-uniformly, so that the color tone of printing becomes unstable.
[0031]
As the color toners having different hues, it is preferable to use toners having yellow, magenta, and cyan hues, and toners having green, blue, and red hues may be used.
[0032]
Stable image quality can be realized by storing a color toner, which is a mixture of the above-described chromatic color toner and gray toner, in a toner cartridge and setting the toner cartridge in the image forming apparatus.
[0033]
DETAILED DESCRIPTION OF THE INVENTION
Here, a preferred procedure of the embodiment of the present invention will be described.
The color toner of the present invention can be produced by a conventionally known production method. At least a binder resin, a colorant, conductive fine particles, and, if necessary, a charge control agent and a wax are added to obtain a raw material.
[0034]
This raw material is kneaded with a pressure kneader, a roll mill, an extruder, etc., and uniformly dispersed, and then, for example, pulverized and pulverized with a pulverizer, jet mill, etc., and classified with an air classifier, etc. A chromatic basic color toner or an achromatic toner having a distribution, that is, a gray toner is obtained.
[0035]
Next, one or more basic toners selected from the yellow toner, magenta toner, and cyan toner obtained by the above method are mixed as appropriate according to the color tone to be obtained, and the lightness L to be obtained is obtained.^*The color toner for the electrophotography of the present invention can be obtained by mixing the gray toner in an amount corresponding to the color toner, and mixing uniformly with, for example, a Henschel mixer.
The color toner and the gray toner may be mixed in a step of coating the toner surface with inorganic fine particles serving as an external additive.
[0036]
In this case, the print color of the chromatic color toner is L^*a^*b^*In color space, (a^*)²+ (B^*)²≧ 10 and the gray toner print color is L^*a^*b^*In color space, (a^*)²+ (B^*)²≦ 5 and L^*≦ 35.
[0037]
Each color toner in this case is, for example, 75 to 95 parts by weight of the binder resin and 0.1 to 20 parts by weight, preferably 0.5 to 15 parts by weight of the colorant when the total toner is 100 parts by weight. It is desirable that
[0038]
The binder resin used in the present invention is not particularly limited, and thermoplastic resins made of various natural or synthetic polymer substances can be used. For example, epoxy resins, styrene-acrylic resins, polyamide resins, polyester resins Polyvinyl resin, polyurethane resin, polybutadiene resin, etc. are used alone or in combination.
[0039]
Further, the colorant contained in the color toner of the present invention is not particularly limited, and a known colorant can be used.
For example, monoazo red pigments, disazo yellow pigments, quinacridone magenta pigments, anthraquinone dyes, nigrosine dyes, quaternary ammonium salts, monoazo metal complex dyes, and the like can be used. These may be used in combination.
[0040]
More specifically, for example, aniline blue (CI No. 50405), calco oil blue (CI No. Azoic Blue 3), chrome yellow (CI No. 14090), ultramarine blue ( CI No. 77103), DuPont oil red (C.I.No. 26105), quinoline yellow (C.I.No. 47005), methylene blue chloride (C.I.No. 52015), phthalocyanine blue (C No. 74160), Malachite Green Oxalate (CI No. 42000), Edible Red No. 2 (Amaranth, CI No. 16185), Edible Red No. 3 (Erysulosin, CI No. 45430), Food Red 40 (Arla Red AC, CI No. 16035), Food Red 10 No. (New Coxin, CI No. 16255), Edible Red No. 104 (Phloxine, CI No. 45410), Edible Red No. 105 (Rose Bengal, CI No. 45440), Edible Red No. 106 (Acid Red, CI No. 45100), <Yellow> Edible Yellow No. 4 (Tartrazine, CI No. 19140), Edible Yellow No. 5 (Sunset Yellow FCF, CI No. 15985) ), <Green> Edible Green No. 3 (First Green FCF, CI No. 42053), <Blue> Edible Blue No. 1 (Brilliant Blue FCF, CI No. 42090), Edible Blue No. 2 (Indigo) Carmin, CI No. 73015) and the like can be used.
[0041]
Carbon black is used as the colorant used for the achromatic gray toner.
The addition amount of this carbon black is preferably 3% by weight or less, particularly preferably 2% by weight or less, and if it exceeds 3% by weight, a color toner with low saturation is reproduced when producing a color toner with low brightness. Becomes difficult.
[0042]
In order to stabilize the electrostatic properties of the toner, the electrical resistance of the pigment is 1 × 10⁸~ 1x10¹²It is preferable to set to Ω · cm. This is because a pigment having a resistance higher than this range cannot achieve an appropriate toner electric resistance even when resistance control is performed using conductive fine particles described later.
A pigment having a resistance lower than this range is not preferable because the conductivity of the toner increases and it becomes difficult to stabilize the electrostatic characteristics of the toner.
[0043]
Further, as the conductive fine particles to be added for controlling the electric resistance, a colorless or white additive which does not affect the color of the toner is preferable, and the electric resistance of the conductive fine particles is 1 to 100 Ω · cm. More preferably, when it is 1 to 50 Ω · cm, good charging characteristics are obtained, and when white conductive fine particles less than 1 Ω · cm are used, the surface resistance is excessively lowered, so that a toner having a sufficient specific charge can be obtained. Absent.
[0044]
In addition, when white conductive fine particles exceeding 100 Ω · cm are used, the amount of conductive fine particles added must be increased to a high concentration of 20% or more, and the color of the toner becomes cloudy, so that a printed image with high saturation can be obtained. Since it becomes impossible, it is not preferable.
[0045]
The conductive fine particles preferably have an aspect ratio of 10 or more and a major axis diameter of 4 μm or less, and the conductive fine particles are preferably contained in a mixing ratio of 20 wt% or less.
Since the shape of the conductive fine particles is needle-shaped with a high aspect ratio, the number of contact points of the conductive particles increases, so that the effect of lowering the electric resistance of the toner by adding a small amount is great. As a result, since the addition amount can be 20 wt% or less, high saturation can be realized without causing the toner to become clouded.
[0046]
Furthermore, the conductive fine particles are ZnO, TiO.₂, SnO₂, Sb₂O_Three, In₂O_Three, SiO₂, MgO, BaO, MoO_Three, When it is a metal oxide selected from WO, good developability and a vivid image can be realized, because the metal oxide has a color that has little influence on the color of the color toner. Because.
[0047]
Furthermore, the titanium dioxide (TiO₂When the particles having a major axis diameter of 1 μm or more and a minor axis diameter of 0.1 μm or less are 50% by weight or more of the entire titanium dioxide particles, particularly good developability and a vivid image are realized.
[0048]
This is because the amount of needle-like titanium oxide is particularly effective for resistance control in a small amount, and a shape having a major axis diameter of 1 μm or more and a minor axis diameter of 0.1 μm or less is also effective for resistance control.
In other words, the shape of the conductive fine particles is preferably as long and narrow as possible, and the larger the aspect ratio, the lower the amount of addition, which is effective for lowering the electrical resistance of the toner, and the major axis diameter is 1 μm or more. In addition, the effect is particularly exerted when particles having a minor axis diameter of 0.1 μm or less are present in an amount of 50 wt% or more.
[0049]
Further, tin oxide (SnO) is formed on the surface of the titanium dioxide particles.₂) And antimony oxide (Sb)₂O_ThreeIt is desirable to provide a conductive layer made of (a), thereby realizing particularly good developability and a vivid image.
This is because the conductive layer is particularly effective for resistance control, and the amount added can be further suppressed.
[0050]
The amount of antimony oxide is SnO.₂Sb₂O_Three10 to 25% by weight, thereby achieving particularly good developability and vivid images.
This is because the resistance of titanium oxide can be the lowest under the above conditions.
[0051]
In addition, tin oxide (SnO₂) Particles having a major axis diameter of 1 μm or more and a minor axis diameter of 0.1 μm or less is desirably 50% by weight or more of the total tin oxide particles, thereby achieving particularly good developability and vividness. Realize the image.
This is because the amount of acicular tin oxide is particularly effective for resistance control, and the shape having a major axis diameter of 1 μm or more and a minor axis diameter of 0.1 μm or less is also effective for resistance control.
[0052]
Further, antimony oxide (Sb) is formed on the surface of the tin oxide particles.₂O_ThreeIt is desirable to provide a conductive layer made of (a), thereby realizing particularly good developability and a vivid image.
This is because the conductive layer is particularly effective for resistance control, and the amount added can be further suppressed.
[0053]
In this case, the electrical resistance of the yellow toner, magenta toner, cyan toner, gray toner, etc. used for the color toner of the present invention obtained by mixing the toner has the highest toner resistance R_HR, lowest toner resistance_LThen R_H/ R_LIt is desirable to adjust the material and addition amount of the conductive fine particles so as to be 2.0 or less.
[0054]
Next, a method for measuring the electrical resistance of the conductive fine particles will be described.
First, 100 kg / cm of conductive fine particles²To form a cylindrical green compact having a diameter of 20 mm and a thickness of 1 to 5 mm, the DC electric resistance thereof is measured, and the electric resistance of the white conductive fine particles is calculated from the following formula.
Electrical resistance (Ω · cm) = measured value x (cross-sectional area / thickness)
In addition, the electrical resistance in this case was measured using HV-MEASURE UNIT (KEITHLEY237: trade name made by KEITHLEY).
[0055]
In addition, a charge control agent may be added to the color toner of the present invention for the purpose of imparting chargeability or reducing the change in charge amount under different temperature and humidity environments. Those are preferred.
[0056]
As such a charge control agent, for example, known positively chargeable and negatively chargeable charge control agents such as a quaternary ammonium salt compound, a salicylic acid compound, a boron complex, and a carboxylic acid compound can be used.
[0057]
Furthermore, in order to improve the fluidity of the color toner of the present invention, the toner surface may be coated with inorganic fine particles as an external additive. The external additive usable here has a particle diameter of 5 nm to 2 μm, preferably Are particles in the range of 5 nm to 500 nm, and the specific surface area by the BET method is 20 m.²/ G-500m²/ G is preferable.
[0058]
The ratio of the external additive mixed with the color toner of the present invention is 0.1 to 5 parts by weight, preferably 0.1 to 2.0 parts by weight with respect to 100 parts by weight of the toner. Part.
[0059]
Examples of such external additives include silica, alumina, titanium oxide, barium titanate, magnesium titanate, calcium titanate, strontium titanate, zinc oxide, silica sand, clay, mica, wollastonite, and diatomaceous earth. Chromium oxide, cerium oxide, bengara, antimony trioxide, magnesium oxide, zirconium oxide, barium sulfate, barium carbonate, calcium carbonate, silicon carbide, silicon nitride and the like can be used.
Among these, it is particularly preferable to use silica fine particles, and it is preferable to use those external additives whose surfaces have been subjected to a hydrophobic treatment.
[0060]
Next, a method for measuring the electrical resistance of the color toner produced by the above procedure and materials will be described.
First, toner particles are 5000 kg / cm.²To form a cylindrical green compact having a diameter of 13 mm and a thickness of 200 to 500 μm, and measuring the electrical conductivity of the green compact using a dielectric loss measuring device (manufactured by Ando Electric). The electrical resistance was obtained from
Electrical resistance (Ω · cm) = S / (L · d)
However, S is the bottom area of the cylindrical green compact [cm²], D is the thickness of the cylindrical green compact [cm], L is the conductivity of the cylindrical green compact [Ω^-1].
[0061]
Next, a printing test is performed using this color toner.
In this case, a high-speed development type color laser printer with a process speed of 1100 mm / s, for example, F6708B (Fujitsu product name: 50 sheets / minute) is used as the image forming apparatus, and for example, 100,000 sheets or more are printed. The stability of the printing color is evaluated.
[0062]
Here, the conceptual configuration of the image forming apparatus used in the embodiment of the present invention will be described with reference to FIG.
See Figure 2
FIG. 2 is a conceptual configuration diagram of the color laser printer used for the printing test. Around the photosensitive member 10 made of amorphous silicon, a charger 20, an exposure unit 30, a developing unit 40, a transfer unit 50, a cleaner 60, a removal unit. An electric device 70, a flash fixing device 80 having a xenon flash lamp 81, and the like are disposed.
[0063]
The developing means 40 includes a developer container 41, a developing roller 43, a stirring blade (not shown), and the like, and the toner particles TO and the carrier particles CA in the developer container 41 are brought into contact with each other so that a predetermined charge amount is imparted to the toner. It has become.
The color toner of the present invention is set in the toner hopper 45 in advance, and when the toner concentration in the developing container decreases with printing, the color toner is supplied from the toner hopper 45 to the developing container 41.
Further, by changing the color toner set in the toner hopper 45 and the developing container 41, it is possible to print toners of various colors.
Hereinafter, the color toner of the present invention will be described more specifically based on examples.
[0064]
Based on the above matters, specific examples of the present invention and comparative examples for clarifying the effects of the examples of the present invention will be described below. First, each example and each comparative example will be described. A method for producing various basic toners will be described.
A color toner in which white toner and black toner are mixed will be described for reference.
[0065]
(Yellow Toner Y₁)
First, yellow toner Y₁To make

The above materials are put into a Henschel mixer, premixed, kneaded with an extruder, then coarsely pulverized with a hammer mill, further pulverized with a jet mill, and classified with an airflow classifier. Yellow toner Y having a volume average particle diameter of about 8.5 μm₁Get.
This acicular titanium oxide (FT-1000; trade name, manufactured by Ishihara Techno) is acicular fine particles having an electrical resistance of 5 Ω · cm, an average major axis diameter of 2.5 μm, and an aspect ratio of 11.
[0066]
Next, this toner Y₁1 part by weight of hydrophobic silica fine particles (H2000 / 4; trade name, manufactured by Clariant Co., Ltd.) was added as an external additive, and the mixture was stirred using a Henschel mixer for external addition.₁Hydrophobic silica was allowed to adhere to the surface.
[0067]
This surface-modified yellow toner Y₁A two-component developer was obtained by mixing 5 parts by weight and 95 parts by weight of a silicone resin-coated magnetite carrier (manufactured by Kanto Denka Kogyo Co., Ltd.) with a ball mill.
[0068]
Next, the charge amount of this two-component developer was measured using a blow-off charge amount measuring device (manufactured by Toshiba Chemical Co., Ltd.) and found to be −17.1 μC / g.
Also, as a result of printing a solid image using the above-mentioned F6708B (product name manufactured by Fujitsu Ltd.) and measuring the color of the image, L^*= 78, a^*= -13, b^*= 47, and the electrical resistance was 12 GΩ · cm.
[0069]
(Magenta Toner M₁)
Except for the type of colorant and the amount of conductive fine particles added, yellow toner Y₁A toner is prepared in the same manner as described above.

[0070]
(Cyan Toner C₁)
Except for the type of colorant and the amount of conductive fine particles added, yellow toner Y₁A toner is prepared in the same manner as described above.

[0071]
See Fig. 3 (a)
FIG. 3A shows the above magenta toner M.₁And cyan toner C₁About Yellow Toner Y₁The surface of the toner is modified in the same manner as above, and a two-component developer is obtained by mixing with a silicone resin-coated magnetite carrier (manufactured by Kanto Denka Kogyo Co., Ltd.) and a ball mill, and the charge amount of the obtained developer and its printing The result of measuring the color and the result of measuring the electrical resistance of the color toner are shown as yellow toner Y₁It is shown together.
[0072]
(Gray Toner G₁~ G_Four)
Except for the type of colorant and the amount of conductive fine particles added, yellow toner Y₁Toner is prepared in the same manner as in yellow toner Y₁The toner was surface modified in the same manner as described above, and mixed with a silicone resin-coated magnetite carrier (manufactured by Kanto Denka Kogyo Co., Ltd.) with a ball mill to obtain a two-component developer. FIG. 3B shows the charge amount of the obtained developer, the result of measuring the color of the print, and the result of measuring the electric resistance of the color toner.
[0073]
Refer to FIG.

[0074]
(White Toner W₁~ W_Four, Black toner K₁)
Except for the type of colorant and the amount of conductive fine particles added, yellow toner Y₁In the same manner as described above, a toner for reference example was prepared, and yellow toner Y₁The surface of the toner is modified in the same manner as above, and a two-component developer is obtained by mixing with a silicone resin-coated magnetite carrier (manufactured by Kanto Denka Kogyo Co., Ltd.) and a ball mill, and the charge amount of the obtained developer and its printing FIG. 3C shows the result of measuring the color and the result of measuring the electrical resistance of the color toner.
[0075]
Refer to FIG.

[0076]
Next, color toners, white toners, and gray toners to which no conductive fine particles were added were prepared in order to constitute a color toner as a comparative example for confirming the effects of the present invention.
Except for the addition amount of the colorant and the addition of the conductive fine particles, the yellow toner Y₁In the same manner as described above, a toner for reference example was prepared, and yellow toner Y₁The surface of the toner is modified in the same manner as above, and a two-component developer is obtained by mixing with a silicone resin-coated magnetite carrier (manufactured by Kanto Denka Kogyo Co., Ltd.) and a ball mill, and the charge amount of the obtained developer and its printing The result of color measurement and the result of measurement of the electrical resistance of the color toner are the chromatic color toner (Y_Five, M_Five, C_Five) In FIG. 4 (a) and achromatic toner (W₁, G_Five) Is shown in FIG.
[0077]
See FIGS. 4 (a) and 4 (b).

[0078]
Next, the above toner Y₁, Magenta Toner M₁Or cyan toner C₁And Gray Toner G₁Thru G_Four1 to 10 prepared by mixing toner, toner Y₁, Magenta Toner M₁Or cyan toner C₁And white toner W₁Thru W_FourOr K₁Examples 1 to 16 prepared by mixing the toner and toner Y_Five, Magenta Toner M_FiveOr cyan toner C_FiveAnd white toner W_Five, Gray Toner G_FiveOr black toner K₁Comparative Examples 1 to 3 prepared by mixing any of the above will be described.
In addition, the composition ratio about each Example, each reference example, and each comparative example is collectively shown in FIG._H/ R_LFIG. 6 shows the measurement results of the color characteristics before and after printing and the color difference ΔE.
[0079]
See Figure 5
Example 1
Achromatic toner (Gray toner G₁50 parts by weight
Chromatic toner (yellow toner Y₁25 parts by weight
Chromatic toner (magenta toner M₁25 parts by weight
Were mixed using a Henschel mixer to obtain a brown color toner.
Yellow toner Y with relatively high electrical resistance in this brown color toner₁Magenta Toner M with low electrical resistance₁Ratio R to electrical resistance_H/ R_LIs
R_H/ R_L= 12GΩ · cm / 8GΩ · cm = 1.5
It is.
[0080]
Using a brown mill mixed with 5 parts by weight of this brown color toner and 95 parts by weight of a silicone resin coated magnetite carrier (manufactured by Kanto Denka Kogyo Co., Ltd.), the above color laser printer was used to perform a printing test on 100,000 sheets. The stability of the printing color was evaluated.
[0081]
When the color of the initial print is measured, L^*= 42, a^*= 15, b^*= 25. After printing 100,000 sheets, the color of the print is L.^*= 43, a^*= 14, b^*= 27, the color difference ΔE of the print before and after continuous printing was 2.4, and almost no change in the print color was observed, indicating that the print color stability was high.
Note that the color difference ΔE is the color coordinate before printing (L^* _A, A^* _A, B^* _A) And the color coordinates after printing are (L^* _B, A^* _B, B^* _B)
ΔE = {(L^* _A-L^* _B)²+ (A^* _A-A^* _B)²+ (B^* _A-B^* _B)²}^1/2
Defined by
[0082]
(Examples 2 to 5)
As shown in FIG. 5, the evaluation was carried out except that the evaluation was performed using a brown color toner having a different lightness in which the mixing ratio of the achromatic toner and the chromatic toner was changed between 90:10 and 10:90. The printing color stability was evaluated in the same manner as in Example 1.
[0083]
As shown in FIG. 6, when the initial print and the print after printing 100,000 sheets are compared, the print color difference ΔE = 1.4 to 2.2, and almost no change in print color is seen, and the print color is stable. It was found that the nature is high.
R_H/ R_LAre both R_H/ R_L= 1.5.
[0084]
(Examples 6 to 8)
As shown in FIG. 5, gray toners G having different carbon black addition amounts as achromatic toners.₂~ G_FourThe same evaluation as in Example 1 was performed except that evaluation was performed using a brown color toner.
[0085]
As shown in FIG. 6, when the initial print and the print after printing 100,000 sheets are compared, the print color difference ΔE = 3.2 to 4.6, and almost no change in print color is seen, and the print color is stable. It was found that the nature is high.
R_H/ R_LIs R_H/ R_L= 1.5 to 1.88.
[0086]
(Examples 9 and 10)
As shown in FIG. 5, yellow toner Y is used as the chromatic toner.₁And cyan toner C₁The same evaluation as in Example 1 was performed except that the green color toner was evaluated.
[0087]
As shown in FIG. 6, when the initial print and the print after printing 100,000 sheets are compared, the print color difference ΔE = 2.0 to 3.7, showing almost no change in print color and stable print color. It was found that the nature is high.
R_H/ R_LAre both R_H/ R_L= 1.5.
[0088]
(Reference Examples 1-5)
As shown in FIG. 5, black toner K is used as the achromatic toner.₁The evaluation was the same as in Examples 1 to 5 except that the evaluation was performed using a dark brown color toner having different brightness.
[0089]
As shown in FIG. 6, when the initial print and the print after printing 100,000 sheets are compared, the print color difference ΔE = 2.2 to 3.7, showing almost no change in print color and stable print color. It was found that the nature is high.
R_H/ R_LAre both R_H/ R_L= 1.5.
[0090]
(Reference Examples 6 to 10)
As shown in FIG. 5, white toner W is used as the achromatic toner.₁The same evaluation as in Examples 1 to 5 was performed except that the evaluation was performed using a light brown color toner having a different brightness.
[0091]
As shown in FIG. 6, when the initial print and the print after printing 100,000 sheets are compared, the print color difference ΔE = 2.8 to 3.3, and almost no change in print color is seen, and the print color is stable. It was found that the nature is high.
R_H/ R_LAre both R_H/ R_L= 1.5.
[0092]
(Reference Examples 11-13)
As shown in FIG. 5, white toners W having different white pigment addition amounts as achromatic toners.₂~ W_FourThe same evaluation as in Example 1 was performed except that evaluation was performed using a light brown color toner.
[0093]
As shown in FIG. 6, when the initial print and the print after printing 100,000 sheets are compared, the print color difference ΔE = 1.0 to 5.0, and almost no change in print color is seen, and the print color is stable. It was found that the nature is high.
R_H/ R_LIs R_H/ R_L= 1.25 to 1.88.
[0094]
(Reference Examples 14 to 16)
As shown in FIG. 5, yellow toner Y is used as the chromatic toner.₁, Magenta Toner M₁, Cyan Toner C₁The same evaluation as in Example 1 was performed except that color toners having various tones were evaluated.
[0095]
As shown in FIG. 6, when the initial print and the print after printing 100,000 sheets are compared, the print color difference ΔE = 2.4 to 4.9, showing almost no change in print color and stable print color. It was found that the nature is high.
R_H/ R_LIs R_H/ R_L= 1.67 to 1.88.
[0096]
(Comparative Example 1)
Achromatic toner (white toner W_Five50 parts by weight
Chromatic toner (yellow toner Y_Five25 parts by weight
Chromatic toner (magenta toner M_Five25 parts by weight
A color toner (light brown) was evaluated in the same manner as in Example 1 except that the above toner was mixed, no conductive fine particles were added, and the electric resistance of the toner was not controlled.
[0097]
As shown in FIG. 6, when the color of the initial print is measured, L^*= 72, a^*= 13, b^*= 23 and L is measured by color measurement after printing 100,000 sheets.^*= 61, a^*= 15, b^*= 29, and the color difference ΔE = 12.7 of the print before and after continuous printing was found, indicating a change in print color and low print color stability.
R_H/ R_LIs R_H/ R_L= 3.3.
[0098]
(Comparative Example 2)
As shown in FIG. 5, a gray toner G in which conductive fine particles are not added as an achromatic toner and the electrical resistance of the toner is not controlled._FiveA color toner (dark brown) was evaluated in the same manner as in Comparative Example 1 except that was used.
[0099]
As shown in FIG. 6, when comparing the initial printing and the printing after printing 100,000 sheets, the printing color difference ΔE = 8.8 indicates that the printing color changes and the printing color stability is low. It was.
R_H/ R_LIs R_H/ R_L= 2.5.
[0100]
(Comparative Example 3)
As shown in FIG. 5, black toner K is used as the achromatic toner.₁The evaluation was conducted in the same manner as in Comparative Example 1 except that.
[0101]
As shown in FIG. 6, when comparing the initial printing and the printing after printing 100,000 sheets, it is found that the color difference ΔE = 23.0 of the printing, the change of the printing color is seen, and the printing color stability is low. It was.
R_H/ R_LIs R_H/ R_L= 15.
[0102]
From the above evaluation results, the toners of Examples 1 to 10 did not show any change in the initial print color even after the printing test of 100,000 sheets, while the toners of Comparative Examples 1 to 3 were associated with printing. It can be seen that the printed color changes greatly and lacks stability.
It should be noted that the toners of Reference Examples 1 to 16 shown for reference do not show the initial print color and change even after the 100,000-sheet printing test, and show favorable results as in Examples 1 to 10. Indicated.
[0103]
See FIG.
FIG. 7 schematically shows the color reproduction range of the color toner of the present invention. Y-LAB is obtained by mixing only the chromatic color toner by mixing the chromatic color toner and the achromatic color toner. It becomes possible to reproduce all the colors in the space sandwiched between the closed curved line of -M-D-E-F-C-I-H-J-Y and the two curved surfaces connecting G and K.
Although not shown, in the case of the comparative example, particularly in the case of the comparative example 2, it is possible to realize a color reproduction range similar to that of the present invention.
In addition, in the case of the reference example, a curved surface (not shown) connecting the closed curve of Y-LA-B-M-D-E-F-C-I-H-J-Y and W It is possible to reproduce all the colors in the enclosed space.
[0104]
See FIG.
FIG. 8 shows the amount of change in print color in Examples 1 to 10 and Comparative Examples 1 to 3, that is, R of the color difference ΔE._H/ R_LIt is explanatory drawing of dependence, ratio R of electrical resistance_H/ R_LIt is understood that the larger the toner color, the larger the change in print color, that is, the color toner obtained by mixing toners having greatly different toner electrical resistances has low print color stability.
Therefore, the electrical resistance ratio R_H/ R_LIt can be seen that by setting the value to 2 or less, it is possible to stabilize the charging, thereby stabilizing the printing color.
[0105]
Note that the electrical resistance of such toner is easily controlled by the addition of conductive fine particles._Five, M_Five, C_FiveChromatic color toner, W_Five, G_FiveAchromatic toner and black toner K₁In comparison, since the conductive fine particles are not added, the electric resistance of the toner is greatly changed from 10 GΩ · cm to 150 GΩ · cm due to the influence of the colorant, and good results can be obtained for the color reproduction range. However, the printing color stability cannot be obtained.
[0106]
In contrast, Y₁, M₁, C₁Chromatic color toner and W₁~ W_Four, G₁~ G_FourIn comparison with the achromatic toner, since the conductive fine particles are added according to the electric resistance of the colorant, the electric resistance of the toner is 8 GΩ · cm to 15 GΩ · cm, and is controlled in a narrow range.
[0107]
In the description of each of the embodiments described above, toners of three hues of yellow, magenta, and cyan are used in combination as the chromatic color toner, but a color toner having a different hue system is used. It is good.
That is, for example, toners of hues such as green, blue, and red may be combined.
[0108]
  Here, the detailed features of the present invention will be described again.
  (Appendix 1) At least a colorant and a binder resinConductive fine particlesAn electrophotographic color toner obtained by mixing a gray toner and a chromatic color toner, wherein the gray toner colorant comprises:2% by weight or less of carbon black is added, and the electrical resistance of the conductive fine particles added to the gray toner is 1 to 100 Ωcm.A color toner for electrophotography.
  (Supplementary note 2) The print color of the chromatic color toner is L^*a^*b^*In color space, (a^*)²+ (B^*)²The color toner for electrophotography according to appendix 1, wherein ≧ 10.
  (Appendix 3) The gray toner print color is L^*a^*b^*In color space, (a^*)²+ (B^*)²The color toner for electrophotography according to appendix 1 or 2, wherein ≦ 5.
  (Appendix 4) The gray toner print color is L^*a^*b^*In color space, L^*The electrophotographic color toner according to any one of appendices 1 to 3, wherein ≦ 35.
  (Appendix5) the aboveOf conductive fine particlesSupplementary notes 1 to 3, wherein the additive amount is different from each other in the chromatic color toner and the gray toner.4The color toner for electrophotography according to any one of the above.
  (Appendix6) Of the above two or more types of toner, the resistance R of the toner having the highest resistance_HAnd the resistance R of the toner with the lowest resistance_LRatio R_H/ R_LTo 1 or less, additional notes 1 to5The color toner for electrophotography according to any one of the above.
  (Appendix7Appendices 1 to6An image forming apparatus comprising a toner cassette containing the electrophotographic color toner described in any one of the above.
[0109]
【The invention's effect】
According to the present invention, since at least one kind of chromatic color toner and gray toner are mixed, a variety of print colors of various tones can be realized with relatively low brightness, and mixing is also possible. Since the electric resistances of the respective toners are substantially equal, the mixed toners are consumed evenly, and a stable printed image can be obtained, which in turn greatly contributes to the widespread use of high-quality image forming apparatuses.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram of a basic configuration of the present invention.
FIG. 2 is a conceptual configuration diagram of an image forming apparatus used in an embodiment of the present invention.
FIG. 3 is an explanatory diagram of characteristics of each toner used in the embodiment of the present invention.
FIG. 4 is an explanatory diagram of characteristics of each toner used in a comparative example.
FIG. 5 is an explanatory diagram of composition ratios of various color toners according to the embodiment of the present invention.
FIG. 6 is an explanatory diagram of characteristics of various color toners according to the embodiment of the present invention.
FIG. 7 is an explanatory diagram of a color reproduction area of the color toner according to the embodiment of the present invention.
FIG. 8 illustrates an R of color difference ΔE of the color toner according to the embodiment of the present invention._H/ R_LIt is explanatory drawing of dependency.
FIG. 9 is an explanatory diagram of a color reproduction region of a conventional color toner.
[Explanation of symbols]
10 photoconductor
20 Charger
30 Exposure means
40 Development means
41 Developer container
43 Developing roller
45 Toner Hopper
50 Transfer device
60 Cleaner
70 Static eliminator
80 Flash fuser
81 Xenon flash lamp

Claims (5)

An electrophotographic color toner obtained by mixing a gray toner and a chromatic color toner in an electrophotographic toner composition comprising at least a colorant, a binder resin and conductive fine particles , wherein the gray toner is colored. A color toner for electrophotography , wherein 2% by weight or less of carbon black is added as an agent , and the electrical resistance of the conductive fine particles added to the gray toner is 1 to 100 Ωcm . 2. The color for electrophotography according to claim 1, wherein a printing color of the chromatic color toner is (a ^* ) ² + (b ^* ) ² ≧ 10 in an L ^* a ^* b ^* color space. toner. 3. The electron according to claim 1, wherein the print color of the gray toner satisfies (a ^* ) ² + (b ^* ) ² ≦ 5 in the L ^* a ^* b ^* color space. Color toner for photography. 4. The color toner for electrophotography according to claim 1, wherein a printing color of the gray toner is L ^* ≦ 35 in an L ^* a ^* b ^* color space. 5. The electrophotographic color toner according to claim 1, wherein the conductive fine particles are added in different amounts in the chromatic color toner and the gray toner. 6.

Images