JP3772928B2 - Color image forming apparatus - Google Patents

Description

【００８４】
上記に示す一成分系現像剤１０及び現像装置１１を用いて、１８０（ｍｍ／ｓｅｃ）のプロセス速度で解像度６００（ｄｐｉ）の点画像と線画像と面画像とを含むＡ４サイズの印字パターンをＸｅｒｏｘ４０２４紙上に画像形成したところ、現像剤Ｂ、現像剤Ｃ、現像剤Ｄを用いた場合には粒状性及び鮮鋭度に優れた高精細な画像を形成することができた。特に、粒状性については従来の粉砕法トナーを使用して形成した画像が示す粒状性評価値Ｔｋｓ＝０．１０〜０．１２に対して、上記の現像剤１０を使用して形成した画像はＴｋｓ＝０．０７〜０．０８という優れた数値を示した。しかし、現像剤Ａを用いた場合には、画素を構成する微小な線画像（万線スクリーン）が不均一になって粒状性の低下した（Ｔｋｓ＝０．１０）ザラツキ感のある画像が形成された。また、現像剤Ｅを用いた場合には、ベタ画像の形成過程において中間転写媒体からＸｅｒｏｘ４０２４紙上に画像を転写する工程でベタ画像の一部に転写の中抜け現象を生じて微小な濃度むらのある画像になった。
【００８５】
ここで画像の粒状性の程度を表す粒状性評価値Ｔｋｓは次式で示され、Ｔｋｓが大きな値を示す画像ほど視覚的なザラツキ感が大きくなり、特に０．１２以上の値を示す画像は著しいザラツキ感を有するものになる。
【００８６】
・Tks＝〔∫WS（λ）^1/2・VTF（λ）・dλ〕／（REF明度−SAM明度）^1/3
ＷＳ（λ） ：Ｗｉｅｎｅｒスペクトル
ＶＴＦ（λ）：視覚系のＭＴＦ
ＲＥＦ明度：Xerox４０２４紙上の白地背景部の平均明度
ＳＡＭ明度：Xerox４０２４紙上に形成した万線スクリーン画像の平均明度
ただし、ＶＴＦ（λ）は次式を採用する。
【００８７】

ｆ：空間周波数（ｃｙｃｌｅ／ｍｍ）
本実施例において粒状性評価値Ｔｋｓは、解像度６００（ｄｐｉ）の１ｄｏｔ線画像を等間隔で形成した２００（Ｌｉｎｅ／ｉｎｃｈ）の万線スクリーンを画素としたサンプル画像において濃度分布Ｄ（ｉ）を求めて算出する。マイクロデンシトメータで求めた濃度分布Ｄ（ｉ）は、次式により明度分布Ｌ（ｉ）に変換して、明度コントラストＬＣ（ｉ）を求める。
【００８８】
・Ｌ（ｉ）＝１１６・〔１０^-D(i)〕^1/3−１６
・ＬＣ（ｉ）＝平均明度−Ｌ（ｉ）
次に、上記の明度コントラストＬＣ（ｉ）を周波数変換してＷｉｅｎｅｒスペクトルＷＳ（λ）を算出する。
【００８９】
〔実施例２〕
＜トナーの緩み見掛密度＞
実施例１と同様な条件のもとで、１８０（ｍｍ／ｓｅｃ）のプロセス速度で解像度６００（ｄｐｉ）の点画像と線画像と面画像とを含むＡ４サイズの印字パターンをＸｅｒｏｘ４０２４紙上に画像形成した。ただし、現像剤１０は、実施例１で用いた現像剤Ｂのトナー粒子を母粒子として用いることとし、前記母粒子に外添する外添剤の添加量を変更することによって、表２に示すように緩み見掛密度の異なる５種類の一成分系現像剤１０をそれぞれ現像剤Ｆ〜現像剤Ｊとして作成した。
【００９０】
【表２】

【００９１】
上記の現像剤Ｇ、現像剤Ｈ、現像剤Ｉを用いて画像形成すると、潜像担持体１上の潜像が忠実に再現されて粒状性及び鮮鋭度に優れた高精細な画像をＸｅｒｏｘ４０２４紙上に形成することができた。しかし、現像剤Ｆを用いて画像形成すると、現像装置１１内におけるトナーの流動が滞ったためトナー層の形成が不均一になり、ベタ画像の後端が部分的にかすれる画像濃度の低下現象を生じた。また、現像剤Ｊを用いて画像形成すると、トナー層の積層過程でトナー層が広がるように流動したため画素を構成する微小な線画像（万線スクリーン）に太りや滲みが発生し、Ｘｅｒｏｘ４０２４紙上には鮮鋭度の低い画像が形成された。
【００９２】
〔実施例３〕
＜ワーデルの実用球形化度＞
実施例１と同様な条件のもとで、１８０（ｍｍ／ｓｅｃ）のプロセス速度で解像度６００（ｄｐｉ）の点画像と線画像と面画像とを含むＡ４サイズの印字パターンをＸｅｒｏｘ４０２４紙上に画像形成した。ただし、現像剤１０は、実施例１で用いた現像剤Ｂのトナー粒子をジェット粉砕機にて異形化処理を行ったものであり、体積平均粒径５〜６（μｍ）でワーデルの実用球形化度が異なるトナー母粒子を４種類作成した。これに表面を疎水化処理したシリカ微粉末（日本アエロジル製Ｒ８１２）を３（ｗｔ％）外添してそれぞれを１成分系現像剤とし、以下に示すように現像剤Ｋ〜現像剤Ｎとして作成した。
【００９３】
・現像剤Ｋ：ワーデルの実用球形化度 １．００
・現像剤Ｌ：ワーデルの実用球形化度 ０．９９
・現像剤Ｍ：ワーデルの実用球形化度 ０．９１
・現像剤Ｎ：ワーデルの実用球形化度 ０．８３
上記の現像剤Ｋ、現像剤Ｌ、現像剤Ｍを用いて画像形成すると、潜像担持体１上の潜像が忠実に再現されて粒状性及び鮮鋭度に優れた高精細な画像をＸｅｒｏｘ４０２４紙上に形成することができた。しかし、現像剤Ｎを用いて画像形成すると、中間転写媒体７上から記録媒体８上への転写動作時に画素を構成する微小な線画像（万線スクリーン）が部分的に発散して隣接する線画像の一部と合体し、Ｘｅｒｏｘ４０２４紙上には粒状性の劣る画像（Ｔｋｓ＝１．０）が形成された。
【００９４】
〔実施例４〕
＜トナー表面の起伏＞
実施例１と同様な条件のもとで、１８０（ｍｍ／ｓｅｃ）のプロセス速度で解像度６００（ｄｐｉ）の点画像と線画像と面画像とを含むＡ４サイズの多色印字パターンをＸｅｒｏｘ４０２４紙上に画像形成した。ただし、現像剤１０は、体積平均粒径６〜７（μｍ）のトナー表面に設けた凹凸状起伏の凹部開口径を所定値に設定したものとし、シアン、マゼンタ、イエローの各色についてトナー母粒子をそれぞれ２種類作成した。これに表面を疎水化処理したシリカ微粉末（日本アエロジル製Ｒ９７２：直径約２０ｎｍ）を２（ｗｔ％）外添して前記３色のカラートナーで構成した１成分系現像剤１０をそれぞれ現像剤Ｏ、現像剤Ｑとした。このとき、前記トナー母粒子は、Ｄｎ５０／Ｄｎ２５＝１．２５〜１．３５、ワーデルの実用球形化度０．９８〜０．９９を示し、さらに外添処理後の現像剤１０は、緩み見掛密度０．３５〜０．３９（ｍｇ／ｃｍ³）、トナー付着量０．４（ｍｇ／ｃｍ²）時の最大画像濃度が１．２〜１．３であった。
【００９５】
・現像剤Ｏ：トナー表面の凹部開口径 ０．１０〜０．１５μｍ
・現像剤Ｐ：トナー表面の凹部開口径 ０．０１μｍ未満
上記の現像剤Ｏを用いて多色画像を形成すると、複数色のトナーを積層化したときに生じ易い画像の太りや滲みが抑制されて、Ｘｅｒｏｘ４０２４紙上には鮮鋭度の高い多色画像を形成することができた。しかし、現像剤Ｑを用いて画像形成すると、画素を構成する微小な線画像（万線スクリーン）に太り及び滲みを生じてボケた印象を与える鮮鋭度の低い多色画像になった。
【００９６】
〔実施例５〕
＜トナー付着量と画像濃度＞
実施例１と同様な条件のもとで、１８０（ｍｍ／ｓｅｃ）のプロセス速度で解像度６００（ｄｐｉ）の点画像と線画像と面画像とを含むＡ４サイズの多色印字パターンをＸｅｒｏｘ４０２４紙上に画像形成した。ただし、現像剤は、体積平均粒径６〜７（μｍ）のトナーに色濃度を以下の様に設定し、シアン、マゼンタ、イエローの各色毎にトナー母粒子をそれぞれ２種類作成した。これに表面を疎水化処理したシリカ微粉末（日本アエロジル製Ｒ８１２：直径１０ｎｍ以下）を２（ｗｔ％）外添して、前記３色のカラートナーで構成した１成分系現像剤をそれぞれ現像剤Ｑ〜現像剤Ｓとした。このとき、前記トナー母粒子はＤｎ５０／Ｄｎ２５＝１．２５〜１．３５、ワーデルの実用球形化度０．９８〜０．９９を示した。さらに外添処理後の現像剤は、緩み見掛密度０．３７〜０．４０（ｍｇ／ｃｍ³）を示した。
【００９７】
【表３】

【００９８】
上記の現像剤Ｑ、現像剤Ｒを用いて記録媒体上への単色トナー当りの最大トナー付着量を０．４（ｍｇ／ｃｍ²）に設定して多色画像を形成すると、複数色のトナーを積層化したときに生じ易い画像の太りや滲みが抑制されて、Ｘｅｒｏｘ４０２４紙上には鮮鋭度の高い多色画像を形成することができた。さらに、記録媒体８として所謂ラフ紙であるニーナ・ボンド紙を用いた場合にも、微小画像の太りや滲みが抑制されて鮮鋭度の高い多色画像を形成することができた。しかし、現像剤Ｓを用いて画像形成すると、各トナーの色濃度が低いために画像濃度が低くなり、全体が白っぽくて発色の悪い画像になった。さらに、十分な画像濃度を得るために単色トナー当りの最大トナー付着量を０．７（ｍｇ／ｃｍ²）に設定して多色画像を形成したところ、画像の発色は良好になったものの画素を構成する微小な線画像（万線スクリーン）に太り及び滲みが生じて、ボケた印象を与える鮮鋭度の低い多色画像になった。
【００９９】
〔実施例６〕
＜トナーの電気抵抗率＞
実施例１と同様な条件のもとで、１８０（ｍｍ／ｓｅｃ）のプロセス速度で解像度６００（ｄｐｉ）の点画像と線画像と面画像とを含むＡ４サイズの多色印字パターンをＸｅｒｏｘ４０２４紙上に画像形成した。ただし、現像剤は、体積平均粒径７（μｍ）の黒トナーに対して帯電制御剤ａまたは帯電制御剤ｂ、体積平均粒径６〜７（μｍ）のカラートナー各色に対して帯電制御剤ｂをそれぞれ２重量部含有させたものをトナーの母粒子として、さらに表面を疎水化処理したシリカ微粉末（日本アエロジル製Ｒ８１２：直径１０ｎｍ以下）を２（ｗｔ％）外添して１成分系現像剤１０とした。このとき、前記トナー母粒子は、Ｄｎ５０／Ｄｎ２５＝１．２８〜１．３０、ワーデルの実用球形化度０．９８〜０．９９を示し、さらに外添処理後の現像剤１０は、緩み見掛密度０．３８〜０．４０（ｍｇ／ｃｍ³）、トナー付着量０．４（ｍｇ／ｃｍ²）時の最大画像濃度が１．２〜１．３であった。表４に示すように、帯電制御剤ａを含有した黒トナーＡは、帯電制御剤ｂを含有した黒トナーＢよりも高い電気抵抗率を示した。また、黒トナーＡは、シアン、マゼンタ、イエローの各カラートナーの中で最も低い電気抵抗率を有するマゼンタトナーよりも高い電気抵抗率を示した。
【０１００】
【表４】

【０１０１】
上記の黒トナーＡを用いて黒ベタ画像を形成すると、ミクロ的な転写の中抜け現象が防止されて、Ｘｅｒｏｘ４０２４紙上にはトナー付着量０．５（ｍｇ／ｃｍ²）で均一な黒ベタ画像を形成することができた。しかし、黒トナーＢを用いて画像形成すると、トナー付着量０．５（ｍｇ／ｃｍ²）では転写の中抜け現象が発生して、微小な濃度むらを有する黒ベタ画像が形成された。さらに、転写の中抜け現象を防止するためにトナー付着量を０．７（ｍｇ／ｃｍ²）に設定して画像形成したところ、黒ベタ画像は濃度むらのない均一な画像になったものの画素を構成する微小な線画像（万線スクリーン）に太り及び滲みが生じて、ボケた印象を与える鮮鋭度の低い画像になった。
【０１０２】
【発明の効果】
以上に述べたように本発明のカラー画像形成装置によれば、点画像や線画像等の画素を構成する微小潜像の細部を充填密度の高いトナー層で再現できるようになり、前記トナー層を潜像担持体上あるいは中間転写媒体上から記録媒体上への転写動作時に転写電界の乱れで発散することなく移行させることが可能になる。さらに、トナー層の積層過程で崩落現象による二次元の面方向へのトナー層の広がりが生ずるのを抑制し、さらに記録媒体上にトナー層を移行させる際に転写部材の支持体による与圧で生じるトナー層の流動を抑制することもできる。
【０１０３】
したがって、画素を構成する微小画像は、ミクロ的に不均一になることなく再現されると共に、太りや滲みにより画像全体がボケる現象が防止されるので、粒状性に優れると共に鮮鋭度の高い画像を形成することが可能なカラー画像形成装置を得ることができる。
【０１０４】
また、黒トナーが有する電気抵抗率を、イエロー、マゼンタおよびシアンの３色のカラートナーが有する電気抵抗率のうち、最低の電気抵抗率より大きくしたことによって、黒トナーによる画像形成時に顕著に発生するミクロ的な転写の中抜け現象が防止され、少ないトナー付着量で濃度むらのない均一な黒ベタ画像を形成することが可能なカラー画像形成装置を得ることができる。
【０１０５】
したがって、本発明のカラー画像形成装置によれば、粒状性及び鮮鋭度に優れると共にラフ紙上に高精細な多色画像を形成することが可能なカラー画像形成装置を提供することができる。
【０１０６】
特に、請求項２の発明によれば、トナー粒子が稠密充填することによってトナーの粒子間相互に粒子間力が作用し易くなるように充填され、潜像担持体上あるいは中間転写媒体上から記録媒体上への転写動作時に転写電界の乱れで発散することなく移行させることができる。さらに、トナー粒子の表面に凹凸状の起伏を設けることによって、トナー粒子を多層化して積層したときに表層のトナー粒子が転がり落ちる現象を抑制することもできる。したがって、トナー層の積層過程で崩落現象による二次元の面方向へのトナー層の広がりが生ずる現象を抑制する効果が高まると共に、微小画像はミクロ的不均一化あるいは太りや滲みが生じることなく再現されるので、複数色のトナーを積層化したときに生じ易い画像の太りや滲みによる多色画像の鮮鋭度が低下する現象をより一層低減すると共に、より粒状性の優れた画像を形成することが可能なカラー画像形成装置とすることができる。
【図面の簡単な説明】
【図１】本発明の一実施例を示す画像形成装置の模式図。
【図２】本発明の一実施例を示す現像装置の模式図。
【図３】本発明の一実施例を示すトナー表面の起伏を表す模式図。
【符号の説明】
１ 潜像担持体
７ 中間転写媒体
８ 記録媒体
１０ 現像剤
１１ 現像装置
２０ 現像剤担持体
２３ 規制部材
２４ 供給部材[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a recording apparatus used for electrophotography, and more specifically, an electrostatic latent image formed on a latent image carrier is composed of black toner and yellow, magenta, and cyan color toners. The present invention relates to a color image forming apparatus in which a visible image is formed by a developer of four colors and an image of the visible image is formed on an intermediate transfer medium.
[0002]
[Prior art]
Conventionally, various image forming apparatuses that use a two-component developer composed of toner and carrier or a one-component developer composed only of toner have been proposed for image forming apparatuses that form images on a recording medium. These image forming apparatuses are further improved in the definition of electrostatic latent images in response to the demand for higher image quality, and the characteristics of the developer that adheres to the recording medium in order to faithfully reproduce the high-definition latent images. Need to be controlled with high accuracy. With regard to the developer whose characteristics have been controlled so far, a technique for obtaining a high-quality image by controlling the average particle diameter or particle size distribution of the toner, the coloring power of the toner, and the like has been proposed.
[0003]
For example, a conventional technique as disclosed in Japanese Patent Application Laid-Open No. 1-15859 specifies that the toner particle size distribution is sharp from the relationship between the number average particle size and the volume average particle size of the color toner. An attempt was made to prevent image quality deterioration associated with image formation. Further, the conventional technique as disclosed in Japanese Patent Laid-Open No. 7-146589 has a ratio of a large particle size component in a particle size distribution of a color toner having a small particle size, a toner adhesion amount before fixing, and an image density after fixing. The toner coloring power is defined from the relationship with (OD), and the toner with a predetermined coloring power is formed with a predetermined adhesion amount to improve highlight reproducibility and solid image uniformity. Met.
[0004]
However, color toners manufactured by the melt-kneading-pulverization method, which is a conventional toner manufacturing method, are difficult to reduce the toner particle size or to control the toner particle size distribution. It wasn't. That is, the toner produced by the melt kneading-pulverization method (pulverization method toner) has a small production amount per unit time that can be reduced by pulverization, and therefore the toner production cost increases as the toner particle size decreases. The smaller the toner particle size, the higher the cohesion force after pulverization, and it becomes difficult to control the classification to a desired particle size distribution, so there is a practical limit to reducing the particle size. Further, in the pulverized toner, as the pigment addition amount is increased, it is necessary to increase the kneading strength of the resin in order to maintain the high dispersibility of the pigment in the resin, and as a result, the melt viscosity of the resin is decreased. In addition, it has been difficult to achieve both toner color development and offset resistance during heat roll fixing.
[0005]
In recent years, a so-called polymerization toner obtained by directly synthesizing toner particles by a suspension polymerization method or the like with respect to a conventional pulverization toner has been proposed, and is composed of a small particle toner having a volume average particle diameter of 7 (μm) or less. It has become easier to produce a one-component developer. For example, a polymerization method toner is a continuous liquid after a colorant, a charge control agent, a polymerization initiator, a dispersing agent or a crosslinking agent is added to a polymerizable monomer and uniformly dispersed or dissolved to form a monomer composition. To a particulate composite obtained by dropping into a medium composed of a phase (for example, an aqueous phase medium) and suspending the monomer composition into fine droplets by a disperser and proceeding with polymerization. A fine powder for external addition is added. The toner produced by the polymerization method can achieve both high color development and offset resistance, can easily reduce the particle size of the toner, and can make the toner particle size distribution sharper than the pulverized toner. The toner has a characteristic of being a pseudo-spherical shape having a smooth surface.
[0006]
[Problems to be solved by the invention]
However, in the conventional image forming apparatus, the microscopic non-uniformity of the pixels reduces noise that causes a rough feeling on the entire image, and the multilayered toner layer spreads in a dual surface direction. Degradation of sharpness that causes image blurring, microscopic density unevenness that occurs when the image does not follow the unevenness of the paper surface in so-called rough paper such as bond paper and low-pressure paper, and especially with multiple color toners When multi-color images are formed using multiple layers, these are the main factors that deteriorate image quality.
[0007]
In particular, when the polymerization method toner as described above is used as a one-component developer, a toner is developed by a developing device into a minute latent image forming a pixel such as a high-definition point image or line image formed on a latent image carrier. When an image is formed on a recording medium by applying a layer, the fine latent image is better than the case of using a conventional pulverized toner, but has a problem that it is not always reproduced faithfully. The outline of the minute latent image becomes minute sawtooth unevenness formed by irregularly arranging toner particles of almost the same size, and this serrated unevenness further expands when transferred onto a recording medium. As a result, a phenomenon occurs in which the toner layer is connected to a part of the toner layer of an adjacent pixel or a part of the pixel becomes unclear because the toner layer diverges in all directions. The microscopic nonuniformity of these pixels directly causes a decrease in graininess, which is one of the factors that determine the image quality of a multicolor image.
[0008]
Further, when the polymerization toner as described above is used as a one-component developer, it is better than the case of using a conventional pulverization toner, but on a latent image carrier, an intermediate transfer medium, or a recording medium. When a plurality of color toners are laminated, the toner layer flows and spreads in a two-dimensional surface direction in the lamination process, resulting in the fattening and bleeding of the minute images constituting the pixels such as point images and line images, There was a problem that the entire image was blurred. These pixel fatness and blurring directly reduce the resolution of thin lines and the like, and directly reduce sharpness, which is one of the factors that determine the image quality of multicolor images.
[0009]
Further, when a surface image having the same color as or similar to that of the toner is formed using the above-described polymerization toner as a one-component developer, if so-called rough paper such as bond paper or low-pressure paper is used as a recording medium, There is a problem in that the fibers are partly exposed without being completely hidden by the toner layer, and fine white spots and roughness are easily generated on the surface image. In particular, when the toner color density is set high and the image density is obtained with the minimum necessary toner adhesion amount, the toner layer may completely hide the unevenness of the paper surface formed by paper fibers and fillers. Since it becomes difficult, the phenomenon of producing minute density unevenness and roughness in the surface image becomes remarkable.
[0010]
  The present invention solves such a conventional problem, and an object of the present invention is to form a high-definition image having excellent graininess and high sharpness on a recording medium, and with a small toner adhesion amount. An object of the present invention is to provide a color image forming apparatus capable of forming a uniform black solid image without unevenness.
[0011]
[Means for Solving the Problems]
  In order to solve the above-described problem, the color image forming apparatus of the invention of claim 1 uses an image carrier on which an electrostatic latent image is formed, and black toner and three color toners of yellow, magenta and cyan. Four developing devices each using black toner and each color toner for developing a latent color image by developing an electrostatic latent image on the image carrier, and a color image of the visible image on the image carrier In the color image forming apparatus provided with at least an intermediate transfer medium on which is formed, Dn25 having a cumulative number of 25% and Dn50 having a cumulative number of 50% are 1.25 ≦ Dn50 / Dn25 ≦ 1. .50, and the loose apparent density of the developer is 0.30 to 0.45 (g / cm^Three), And the electrical resistivity of the black toner is larger than the lowest electrical resistivity among the electrical resistivity of the three color toners.
[0012]
  Therefore, a minute image constituting a pixel such as a point image or a line image is reproduced without becoming microscopically non-uniform, and a phenomenon in which the entire image is blurred due to fattening or bleeding is prevented. An image with excellent sharpness can be formed.
[0013]
  In addition, the micro-transfer dropout phenomenon that occurs at the time of solid image formation with black toner is prevented, and a uniform black solid image with no density unevenness can be formed with a small toner adhesion amount.
[0014]
  According to a second aspect of the present invention, there is provided the color image forming apparatus according to the second aspect of the present invention, wherein the practical spherical degree of the Wadel of the developer is set to 0.9 to 1, and the concave and convex concave opening diameter provided on the developer surface is further developed. The diameter is larger than the diameter of the external additive particles externally added to the surface of the additive. Therefore, it is possible to further reduce the phenomenon that the sharpness of a multicolor image is lowered due to the thickening or bleeding of an image that is likely to occur when a plurality of color toners are stacked, and it is possible to form an image with more excellent graininess. .
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention, and the configuration of the entire image forming apparatus will be described below.
[0016]
The latent image carrier 1 is obtained by forming a photosensitive layer made of an organic or inorganic photoconductive material on a conductive support. The photosensitive layer is charged using a charger 4 such as a charging roller, and then light emitted from a light source 5 such as a laser or LED is selectively irradiated through an imaging optical system 6 to generate a potential contrast. A desired electrostatic latent image pattern having is formed on the photosensitive layer. The developing device 11 visualizes the electrostatic latent image on the latent image carrier 1, and attaches the developer 10 onto the latent image carrier 1 in accordance with the electrostatic latent image. The developer 10 adhering to the latent image carrier 1 is transferred onto the recording paper 8 and then fixed on the recording medium 8 by applying heat or pressure to form a desired image.
[0017]
The developer carrying body 20 provided in the developing device 11 moves while carrying the developer 10 as shown in FIG. 2, and is a state in which the developer 10 charged to a predetermined polarity is thinned. Then, the developer 10 is transferred onto the latent image carrier 1 at a position opposed to (or in contact with) the latent image carrier 1. The regulating member 23 is a blade-like member that comes into contact with the developer carrier 20 via the developer 10 and is made thin by pressing the developer 10 and is triboelectrically charged to a predetermined polarity. The developer 10 is uniformly supported on the developer carrier 20. Further, the supply member 24 supplies the developer 10 accommodated in the developing device onto the developer carrier 20, and the developer is moved while moving the developer 10 captured on the surface of the supply member 24. The developer 10 is supplied to the carrier 20 and the developer 10 in the vicinity of the supply member 24 is encouraged to flow, whereby the developer 10 can be continuously supplied to the developer carrier 20.
[0018]
The developing device 11 is located at a position where the developer carrying member 20 and the latent image carrying member 1 face each other when the developer carrying member 20 provided in the developing device 11 is brought close to (or in contact with) the latent image carrying member 1. The potential contrast of the latent image carrier 1 and the development electric field by the bias applying means 26 applied between the latent image carrier 1 and the developer carrier 20 (or between the latent image carrier 1 and the regulating member 23). The electrostatic latent image is visualized by selectively depositing the charged developer 10 on the latent image carrier 1 in accordance with the developing electric field.
[0019]
FIG. 2 is a schematic diagram of the developing device 11 according to an embodiment of the present invention, and the configuration and operation relating to the developing device 11 will be described below.
[0020]
The developer carrier 20 is made of a solid member such as rubber, elastomer, metal or the like having a film thickness of several (mm) on the outer periphery of a shaft made of metal or resin, and has a surface roughness Ra (JIS-B-0601, It is formed so as to be about 0.1 to 2 (μm) in terms of (centerline average roughness). For solid members, aluminum is used in this embodiment, but similarly, rubber materials such as natural rubber, silicon, butadiene, chloroprene, neoprene, EPDM, NBR, styrene, vinyl chloride, polyurethane, polyethylene, methacryl, etc. It is possible to use metal materials such as elastomer, SUS, titanium, phosphor bronze. Further, by forming a flexible layer on the surface of the solid member, it is possible to reduce the frictional load and to stabilize the chargeability and transportability of the developer. Further, when rubber or elastomer is used for the solid member, the surface of the solid member can be hardened using heat treatment or chemical treatment to reduce the frictional load and increase the durability of the solid member surface.
[0021]
The surface of the developer carrying member 20 preferably has conductivity in order to realize high resolution printing due to the developing electrode effect. The width of the development nip formed at the position where the developer carrier 20 and the latent image carrier 1 are opposed to each other is a few (mm) or less. Therefore, in order to realize a high printing speed, the development current is applied in a short development time. A sufficiently small time constant that can flow is required, and the surface of the developer carrier 20 is 10⁹The electrical resistance is preferably (Ω) or less.
[0022]
The regulating member 23 is a thin plate made of a metal material having a plate thickness of about several hundred (μm), a plate made of an organic material made of rubber or elastomer having a thickness of about several (mm), and a plate thickness of several hundred (μm). It is possible to use a thin plate material made of about a metal material and a solid member such as rubber or elastomer provided on the free end side with a few (mm) as a support. Since the restricting member 23 is easily elastically deformed, it is preferable that one of the restricting members 23 is clamped and fixed by a fixing plate with one end as a fixed end, and the other end is a free end and the developer carrier 20 is pressed through the developer near the tip.
[0023]
A development bias voltage is applied to at least two of the developer carrying member 20, the regulating member 23, and the supply member 24, and the charge of reverse polarity generated by frictional charging between the member and the developer 10 is released to a power source or the like. As a result, the formation of a reverse potential layer caused by the accumulation of charges on the member can be prevented, and a stable development state can be maintained over time.
[0024]
As shown in FIG. 3, the developer 10 is composed of at least toner particles obtained by directly synthesizing by a polymerization method, and can be a one-component developer composed only of toner, or composed of a carrier and toner. A two-component developer can also be used. The polymerization toner is prepared by adding a colorant, a charge control agent, a polymerization initiator, a dispersing agent or a crosslinking agent to a polymerizable monomer, and uniformly dispersing or dissolving it to obtain a monomer composition. The volume average particle size obtained by dropping the polymer composition into a medium (for example, an aqueous medium) and suspending the monomer composition into fine droplets with a disperser and advancing the polymerization is 1 to 10 (μm) particulate composite.
[0025]
Examples of the polymerizable monomer include styrene monomers such as styrene, o (m, p) -methylstyrene, m (p) -ethylstyrene, methyl (meth) acrylate, ethyl (meth) acrylate, ( Meth) propyl acrylate, butyl (meth) acrylate, octyl (meth) acrylate, dodecyl (meth) acrylate, stearyl (meth) acrylate, behenyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, Acrylic ester monomers such as dimethylaminoethyl (meth) acrylate and dimethylaminoethyl (meth) acrylate, and ene monomers such as butadiene, isoprene, cyclohexane, acrylonitrile, and acrylamide can be used. . In addition, particles obtained by polymerizing these polymerizable monomers are used as inner core particles, and a resin layer such as styrene- (meth) acryl copolymer, polyester, epoxy, styrene-butadiene copolymer is formed on the outer shell. You can also.
[0026]
Coloring agents include black dyes or pigments such as carbon black, graphite, black titanium oxide, iron trioxide, spirit black, nigrosine, phthalocyanine, rhodamine B lake, solar pure yellow 8G, quinacridone, polytungstophosphoric acid, indus Non-black dyes or pigments such as Ren blue and sulfonamide derivatives can be used.
[0027]
As the charge control agent, metal complex salt dyes such as Cr complex salt, Zn complex salt, Fe complex salt, Al complex salt, quaternary ammonium salt, nigrosine dye and the like can be used.
[0028]
As polymerization initiators, 2 · 2′-azobis (2,4-dimethylvaleronitrile), 2 · 2′-azobisisobutyronitrile, 1 · 1′-azobis (cyclohexane-1-carbonitrile), 2 -Azo or diazo polymerization initiators such as 2'-azobis-4-methoxy-2, 4-dimethylvaleronitrile, azobisisobutyronitrile, benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxycarbonate, cumene hydroperoxide, 2 A peroxide polymerization initiator such as 4-dichlorobenzoyl peroxide or lauroyl peroxide can be used.
[0029]
Dispersants include tricalcium phosphate, magnesium phosphate, aluminum phosphate, zinc phosphate, calcium carbonate, magnesium carbonate, calcium hydroxide, magnesium hydroxide, aluminum hydroxide, calcium metasilicate, calcium sulfate, barium sulfate, Inorganic dispersants such as bentonite, silica, and alumina, and organic dispersants such as polyvinyl alcohol, gelatin, methylcellulose, methylhydroxypropylcellulose, ethylcellulose, and sodium salt of carboxymethylcellulose can be used.
[0030]
In addition, the magnetic toner can be directly synthesized by adding magnetic powder to the polymerizable monomer. Magnetic powders include iron, cobalt, nickel, chromium, manganese metals, chromium dioxide, iron sesquioxide, iron sesquioxide, ferrite and other metal oxides, alloys that show ferromagnetism by heat treatment, such as alloys containing manganese and copper. Or the like can be used.
[0031]
An external additive having a primary particle diameter of about 1 to 100 (nm) is attached to the surface of the toner particles at a ratio of 0.1 to 5 (wt%) with respect to the weight of the toner. Examples of external additives include silicon oxide, aluminum oxide, titanium oxide, strontium titanate, cerium oxide, aluminum oxide, magnesium oxide, chromium oxide, metal oxide fine powder, silicon nitride fine powder, silicon carbide, etc. Fine powder of carbide, fine powder of metal salt such as calcium sulfate, barium sulfate, calcium carbonate, fine powder of fatty acid metal salt such as zinc stearate, calcium stearate, fine powder of resin such as PMMA, vinylidene fluoride, polytetrafluoroethylene, Carbon black or fine powder of carbon fluoride can be used. The surface of the fine powder is preferably hydrophobized in advance with a silane, titanate or aluminate coupling agent, silicon or fluorine oil, or the like.
[0032]
<Toner particle size distribution>
It is assumed that the toner directly synthesized by the polymerization method satisfies the relationship of 1.25 ≦ Dn50 / Dn25 ≦ 1.50 for Dn25 having a cumulative number of 25% and Dn50 having a cumulative number of 50%. When an image is formed by laminating toner on the carrier 1 or the intermediate transfer medium 7, the toner having a moderately small particle size distribution component than the one having an excessively narrow particle size distribution and uniform particle size. However, it is easy to fill the gaps between adjacent toner particles with a toner having a small particle diameter, and the details of the minute latent image constituting the pixel can be reproduced with a toner layer having a high filling density. The toner particle size is Dn50 / Dn25 <1.50 because the cohesive force of the toner layer increases when the presence frequency of the small particle size toner is excessive, and the latent image carrier 1 or the intermediate transfer medium 7 This is because when a high-duty image such as a solid image is transferred onto the recording medium 8, a so-called transfer dropout phenomenon that causes a region that cannot be partially transferred easily occurs. In addition, the toner particle size is Dn50 / Dn25> 1.25 because the voids between the particles cannot be filled when the existence frequency of the small particle size toner is excessively low. This is because the packing density does not increase. By controlling the particle size distribution of the toner in this way, the toner particles are filled so that the interparticle force can easily act between the toner particles, and the toner layer is transferred from the latent image carrier 1 or the intermediate transfer medium 7 to the recording medium. 8 can be transferred without divergence due to the disturbance of the transfer electric field at the time of transfer operation. Therefore, since the micro image is faithfully reproduced without being microscopically nonuniform, an image with excellent graininess can be formed.
[0033]
In the present invention, the particle size of the toner was measured using a Coulter counter (MODEL-TAII type manufactured by Coulter Electronics) in the following manner.
[0034]
{Circle around (1)} A predetermined amount of measurement toner is added to ISOTON-II (commercially available NaCl solution), and a small amount of surfactant is added.
[0035]
{Circle around (2)} The toner charged using an ultrasonic cleaner is uniformly dispersed in ISOTON-II.
[0036]
(3) A few drops of the toner dispersion are dropped into a beaker in which an aperture tube is immersed in ISOTON-II, and the toner is gently dispersed with an attached stirrer.
[0037]
(4) Take an appropriate amount of the toner dispersed in the beaker through the aperture tube, and sequentially count the particle diameter of the toner with a counter.
[0038]
(5) The data counted by the attached dedicated software is processed to determine the particle size distribution of the captured toner.
[0039]
(6) Dn25 having a cumulative number of 25% and Dn50 having a cumulative number of 50% are obtained from the above particle size distribution data, and Dn50 / Dn25 is calculated.
[0040]
<Toner loose apparent density>
The toner is loosened and the apparent density is 0.30 to 0.45 (g / cm^Three) Is defined by controlling the loose apparent density, which is an index of the filling property of toner under non-high pressure, to a predetermined range, so that the sharpness of the image and a high-density surface image (so-called solid image) over a wide area. This is to achieve both uniformity of density). In order to reproduce the entire area of a solid image with a large area at a uniform density, a new layer of toner is continuously supplied to the developer carrier 20 that has consumed toner by the developing operation, and a constant layer thickness is formed on the latent image carrier 1. It is necessary to deposit the toner layer uniformly. The apparent density of loose toner is 0.30 (g / cm^ThreeIn this way, the toner in the developing device 11 proceeds without being delayed by the supply member 24, and the latent image carrier 1 can carry the toner layer regulated to a constant layer thickness. Therefore, a toner layer having a constant layer thickness is formed on the latent image of the solid image on the latent image carrier 1, and the solid image is reproduced uniformly without causing density unevenness over the entire area. On the other hand, in order to reproduce an image with high sharpness, it is necessary to prevent the toner layer from flowing and spreading in a two-dimensional surface direction during the lamination process when a plurality of color toners are laminated on a recording medium. is there. The apparent density of loose toner is 0.45 (g / cm^Three) By the following, it is possible to suppress the spread of the toner layer in the two-dimensional surface direction due to the collapse phenomenon in the lamination process of the toner layer, and when transferring the toner layer onto the recording medium 8, The flow of the toner layer caused by the pressurization by the support can be suppressed. Therefore, a phenomenon in which the entire image is blurred due to the occurrence of fatness or blurring in a minute image constituting a pixel such as a point image or a line image is prevented, and an image with high sharpness is formed.
[0041]
In the present invention, the apparent loose density of the toner was measured using a powder tester (PT-E manufactured by Hosokawa Micron Corporation) as follows.
[0042]
(1) Set the following parts on the shaking table.
[0043]
-Funnel (tip opening diameter: 5mm)
・ Fluy (mesh opening diameter: 710μm)
・ Fluid holding
(2) Gently place an appropriate amount of toner for measurement on a sieve.
[0044]
(3) The amplitude of the shaking table is set to about 1 mm and the shaking table is vibrated.
[0045]
{Circle around (4)} Toner flows out into the cup through the funnel and fills the cup until it reaches a heap.
[0046]
{Circle around (5)} The toner filled in the cup is scraped off along the opening of the cup, and the excess part of the pile is removed outside the cup.
[0047]
(6) Obtain the weight of the toner filled in the cup and the internal volume of the cup.
[0048]
(7) The toner loose apparent density is calculated by the following formula.
[0049]
・ Loose apparent density (g / cm^Three) = Weight of developer (g) / inner volume of cup (cm^Three)
<Wadel's practical sphericity>
Further, setting the toner to a Wadel practical sphericity of 0.9 to 1 is suitable for faithfully visualizing a minute latent image constituting a pixel on the latent image carrier 1. It is. When the toner is attached to the latent image carrier 1 by a developing operation by changing the shape of the toner into a pseudo sphere with a Wadel's practical sphericity of 0.9 to 1, the toner is It becomes easy to form a densely packed toner layer. The densely packed toner layer is effective to faithfully and clearly reproduce the image outline of the minute latent image details, and further, the toner particles are densely packed, so that the interparticle force easily acts between the toner particles. In the transfer operation from the latent image carrier 1 or the intermediate transfer medium 7 to the recording medium 8, the transfer can be performed without divergence due to the disturbance of the transfer electric field. Therefore, since the micro image is faithfully reproduced without causing micro unevenness, an image having further excellent graininess is formed.
[0050]
In the present invention, the practical sphericity of the toner Wadel is expressed by the ratio of the diameter of a circle having a volume equal to the projected area of the particle in the enlarged projected image of the toner particle to the diameter of the smallest circle circumscribing the projected image of the particle. It is a numerical value. The practical sphericity of Wardel was measured in the following manner using an image processing apparatus (manufactured by Avionics) equipped with an optical microscope.
[0051]
{Circle around (1)} A two-dimensional projection image of a developer is obtained by enlarging a small amount of toner dispersed on a glass plate with an optical microscope so that toner particles do not overlap.
[0052]
{Circle around (2)} For example, the projection image magnified 500 times is binarized by an image processing apparatus, and its area is measured.
[0053]
{Circle around (3)} A circle having an area equal to the area of the projected image is derived and its diameter is obtained.
[0054]
(4) The smallest circle circumscribing the projected image is derived and its diameter is obtained.
[0055]
{Circle around (5)} The diameter ratio of 100 developer particles arbitrarily extracted by such a method is obtained, and the average value is taken as the practical sphericity of Wadel.
[0056]
<Toner surface relief>
Further, the concave / convex concave / convex opening diameter provided on the toner surface is larger than the diameter of the external additive particles externally added to the toner surface because the external additive is caused by stress applied from the constituent members of the developing device 11. This is because it is effective to suppress the phenomenon of separation from the toner surface and the flow of the toner layer caused by the pressure applied by the support of the transfer member when the toner layer is transferred onto the recording medium 8. Since the conventional polymer toner has a quasi-spherical shape having a smooth surface, the externally added external additive is easily detached from the surface due to the stress applied to the toner surface, and the constituent members of the developing device 11, the latent image carrier, and the cleaning are removed. There was a problem of contaminating members and the like. However, by providing a recess having an opening diameter larger than the diameter of the external additive to be externally added to the surface of the polymerized toner, when the external additive is added, the external additive particles are trapped by the uneven undulations on the toner surface. Further, it is possible to make it difficult for the external additive to be detached from the toner surface. When attaching a plurality of types of external additives having different diameters to the toner surface, it is preferable to set the recess opening diameter based on the diameter of the external additive particle having the smallest particle diameter, and similarly, the opening of the uneven undulation The depth of the recess is preferably set to about half of the opening diameter of the recess. Further, by providing unevenness on the surface of the toner particles, it is possible to suppress the phenomenon that the toner particles on the surface layer roll down when the toner particles are laminated in layers. Therefore, the effect of suppressing the phenomenon in which the toner layer spreads in the two-dimensional surface direction due to the collapse phenomenon in the lamination process of the toner layer is enhanced, so that image thickening and bleeding that are likely to occur when a plurality of color toners are laminated. It is possible to further reduce the phenomenon that the sharpness of a multicolor image is reduced.
[0057]
In the present invention, the recess opening diameter on the toner surface was measured using a scanning electron microscope (SEM) as follows.
[0058]
(1) A small amount of a toner base particle sample for measurement is put into an epoxy resin-based sealant to completely cure the sealant.
[0059]
(2) The toner base particle sample fixed with the sealant is cut using a microtome so that the cross section can be observed.
[0060]
{Circle around (3)} The cut surface of the sample is made an SEM enlarged image of about 10,000 times using SEM. At this time, it is preferable that the outer diameter contour of the toner base particles is set so that it can be observed as a cross-sectional curve of the particles, and a photograph is taken.
[0061]
(4) As shown in FIG. 3, in the cross-sectional curve obtained from the photograph of the enlarged SEM image, the average peak interval Sm is obtained assuming the average line of the cross-sectional curve. Sm is the average value of the distance from the point from the peak to the valley of the cross-sectional curve to the crossing point from the next peak to the valley.
[0062]
(5) The concave opening diameter R on the toner surface is calculated from the following equation.
[0063]
-Concave opening diameter: R = Sm / 2
<Toner adhesion amount and image density>
In addition, the maximum weight per unit area of the toner single color adhered on the recording medium 8 is 0.6 (mg / cm²) And the weight per unit area of the toner single color adhered on the recording medium 8 is 0.4 (mg / cm²When the maximum image density is 1.0 or more, the amount of toner adhering to the recording medium 8 is set to the minimum necessary amount, and the toner color density is set high. This is because it is effective to prevent image thickening and blurring that are likely to occur when a multi-color image is formed by stacking layers.
[0064]
When forming a monochromatic solid image on the recording medium 8, the necessary minimum weight per unit area of toner adhering to the recording medium 8 is, for example, toner particles having a volume average particle diameter of 7 (μm) used in this embodiment. At a minimum toner weight of 0.4 (mg / cm) when arranged so as to completely cover the recording medium surface.²) In general, in an image forming apparatus based on electrophotography, the amount of toner adhering to a recording medium can easily fluctuate due to the operating environment of the apparatus and the deterioration of the developer, so a solid image is formed. It is preferable to set a numerical value slightly higher than the necessary minimum amount. However, the toner adhesion amount when forming a solid image is 0.6 (mg / cm²) When set to a larger value, two or more toner layers on the recording medium are arranged so as to overlap each other. In particular, the toner layer forming the contour portion of the image spreads in the two-dimensional plane direction and is likely to be blurred. Therefore, it is inappropriate to set the toner adhesion amount per single color larger than this. On the other hand, the weight per unit area of the toner single color adhered on the recording medium 8 is 0.4 (mg / cm²When the maximum image density is set to 1.0 or more, sufficient color developability can be obtained even if the toner layer on the recording medium 8 is thinned to form a solid image. Therefore, even when a multi-color image is formed using a plurality of color toners, a micro-image that constitutes a pixel while maintaining color reproducibility by forming multiple layers while setting a small amount of adhesion per toner color. It is possible to obtain a multicolor image having excellent sharpness by suppressing the fatness and bleeding. In particular, when so-called rough paper having a low surface smoothness is used as the recording medium 8, the effect of suppressing the phenomenon of causing fattening or bleeding in a minute image is further exhibited, and the sharpness is excellent even on the rough paper. Multicolor images can be formed.
[0065]
In the present invention, the weight per unit area of the developer 10 deposited on the recording medium 8 was measured as follows.
[0066]
(1) A monochromatic solid image formed on a smooth paper as an example of a recording medium through a transfer process is obtained. At this time, the solid image is held on the smooth paper in an unfixed state without passing through the fixing step.
[0067]
(2) The toner layer forming the solid image is sucked under reduced pressure using a suction nozzle having a membrane filter (Millipore) set. The toner layer on the recording medium is preferably electrostatically removed in advance before suctioning under reduced pressure.
[0068]
(3) The area of the sucked solid image and the weight of the toner are obtained, and the weight per unit area of the developer adhered on the recording medium is calculated.
[0069]
<Electric resistivity of toner>
Furthermore, the image forming apparatus includes a plurality of developing devices including a developing device 11b that uses black toner as the developer 10 and a developing device 11c that uses color toner as the developer 10, and the electric power that the black toner has The reason why the resistivity is higher than the electrical resistivity of the color toner is that when the solid layer is formed by thinning the toner layer on the recording medium 8, the recording medium 8 is formed when the solid image is formed with the color toner. This is to prevent minute density unevenness caused by the low degree of concealment of black toner when a solid image is formed with black toner as compared with the degree of concealment of color toner. As a method for preventing the minute density unevenness of the black solid image without reducing the sharpness of the image, the toner adhesion amount on the recording medium 8 is set to the minimum necessary amount, and the minute transfer skipping phenomenon is prevented. The black toner is made to transfer uniformly so that the electrical resistivity of the black toner is greater than the electrical resistivity of the color toner. It is possible to form a uniform black solid image with no density unevenness. When a plurality of color toners are used as color toners in a plurality of developing devices 11, the black toner has a higher electrical resistivity than that of the color toner having the lowest electrical resistivity. It is preferable to set.
[0070]
As a method for making the electrical resistivity of the black toner larger than the electrical resistivity of the color toner, it is possible to prevent the electrical resistivity of the black toner itself from decreasing, and to add externally to the black toner base particle. It is effective to increase the surface resistance of the black toner by the external additive. Since black toner generally contains carbon black or the like as a colorant, the electric resistivity of the mother particle itself tends to be lower than that of color toner. Therefore, when a conductive material such as a charge control agent is added in addition to carbon black, the electrical resistivity of the black toner mother particles itself is more likely to be lowered. It is preferable to use a material having low conductivity and to reduce the amount of the internal additive as much as possible. On the other hand, it is also possible to increase the electrical resistivity of the toner by coating the surface of the black toner base particles with a highly insulating material. For example, the external addition process is performed so that the toner surface is completely covered with silica fine particles. By doing so, the electrical resistivity of the toner can be increased.
[0071]
In the present invention, the electrical resistivity of the toner was measured in the following manner using a microammeter.
[0072]
(1) A toner for measurement is molded into a tablet using a tablet molding machine.
[0073]
{Circle around (2)} The electrode is pressed with a predetermined load so that the electrode can be in uniform contact with the back and front of the tablet.
[0074]
(3) The measurement system is sufficiently aged in an environment of 23 ° C. and 65% RH.
[0075]
(4) A constant voltage V = 10 (v) is applied between the electrodes, and the current I flowing between the electrodes is measured with a microammeter.
[0076]
(5) The electrical resistivity ρ is calculated from the following equation.
[0077]
・ Ρ = V / I ・ S / t
V: Applied voltage (v)
I: Current direct reading (Ω)
S: Tablet area (cm²)
t: tablet thickness (cm)
Detailed examples of the embodiment of the invention described above will be described below.
[0078]
[Example 1]
<Toner particle size distribution>
The developing device 11 is configured by using the developer carrier 20, the regulating member 23, the supply member 24, and the developer 10 as shown in the following items (1) to (4), and image formation including the developing device 11 is performed. An image was formed on the recording medium 8 by the apparatus.
[0079]
(1) Developer carrier
A flange having a φ6 (mm) aluminum shaft was bonded to the end of a φ20 (mm) aluminum pipe to form an exterior of the developer carrier. Further, a blasting treatment with glass beads is performed on a developer thin layer forming region excluding an end portion on the surface of the aluminum pipe, and this is treated with a developer carrying member having a surface roughness of Ra = 0.7 (μm); did.
[0080]
(2) Restriction member
A solid member made of urethane rubber and having a thickness of 2 (mm) was integrally formed on one end of a metal plate having a thickness of 2 (mm) to form a regulating member. The edge portion of the solid member has an R of 50 (μm) and faces the developer carrier, and presses the developer carrier through the developer with a contact pressure of 20 (g / cm). Arranged. Further, the regulating member was set to have the same potential as the developer carrying member.
[0081]
(3) Supply material
A supply member was formed by forming a polyurethane foam having a thickness of 3.5 (mm) around a SUS shaft having a diameter of 5 mm and conducting it with an impregnating agent containing carbon black. The supply member was arranged so that the outer periphery of the supply member was rotated in the opposite direction at the opposing portion while being pressed with a contact pressure of 10 (g / cm) against the developer carrying member. The supply member was set to have the same potential as the developer carrying member.
[0082]
(4) Developer
・ Styrene monomer: 85 parts by weight
・ Butyl acrylate monomer: 15 parts by weight
・ Carbon black: 5 parts by weight
Charge control agent a: 2 parts by weight
・ Polymerization initiator: 5 parts by weight
・ Crosslinking agent: 5 parts by weight
・ Dispersant: 1 part by weight
A monomer composition for polymerization comprising the above was directly synthesized by suspension polymerization to obtain five types of toner particles having different particle size distributions. The five types of toner particles have a Wadel's practical sphericity of 0.98 to 0.99, and 2 (wt%) externally added silica fine powder (R812 manufactured by Nippon Aerosil Co., Ltd.) hydrophobized on the surface. Is a loose apparent density of 0.37 to 0.41 (mg / cm^Three)showed that. Also, the toner adhesion amount 0.4 (mg / cm²) Was 1.3. The particle size distribution is shown in Table 1 as developer A to developer E each of the one-component developer 10 composed of the above five types of toners.
[0083]
[Table 1]

[0084]
Using the one-component developer 10 and the developing device 11 described above, an A4 size printing pattern including a point image, a line image, and a plane image with a resolution of 600 (dpi) at a process speed of 180 (mm / sec). When an image was formed on Xerox 4024 paper, when Developer B, Developer C, and Developer D were used, a high-definition image excellent in graininess and sharpness could be formed. In particular, with respect to graininess, an image formed using the developer 10 described above with respect to the graininess evaluation value Tks = 0.10 to 0.12 indicated by an image formed using a conventional pulverized toner is An excellent numerical value of Tks = 0.07 to 0.08 was shown. However, when developer A is used, a fine line image (line screen) constituting pixels becomes non-uniform and graininess is lowered (Tks = 0.10). It was done. In addition, when the developer E is used, in the process of forming a solid image, the transfer of the image from the intermediate transfer medium onto the Xerox 4024 paper causes a transfer void in a part of the solid image, thereby causing minute density unevenness. It became an image.
[0085]
Here, the graininess evaluation value Tks representing the degree of graininess of the image is expressed by the following equation. An image having a larger value of Tks has a greater visual roughness, and particularly an image having a value of 0.12 or more. It becomes a thing with remarkably rough feeling.
[0086]
・ Tks = [∫WS (λ)^1/2・ VTF (λ) ・ dλ] / (REF brightness-SAM brightness)^1/3
WS (λ): Wiener spectrum
VTF (λ): MTF of the visual system
REF brightness: Average brightness of white background on Xerox 4024 paper
SAM brightness: Average brightness of line screen images formed on Xerox 4024 paper
However, VTF (λ) adopts the following equation.
[0087]

f: Spatial frequency (cycle / mm)
In this embodiment, the graininess evaluation value Tks is a density distribution D (i) in a sample image using pixels of a 200 (Line / inch) line screen that is formed from 1 dot line images with a resolution of 600 (dpi) at equal intervals. Find and calculate. The density distribution D (i) obtained by the microdensitometer is converted into the lightness distribution L (i) by the following equation to obtain the lightness contrast LC (i).
[0088]
L (i) = 116. [10^{-D (i)}]^1/3-16
LC (i) = average brightness−L (i)
Next, the brightness contrast LC (i) is frequency-converted to calculate the Wiener spectrum WS (λ).
[0089]
[Example 2]
<Toner loose apparent density>
An A4 size print pattern including a point image, a line image, and a plane image with a resolution of 600 (dpi) at a process speed of 180 (mm / sec) is formed on Xerox 4024 paper under the same conditions as in the first embodiment. did. However, as developer 10, toner particles of developer B used in Example 1 are used as mother particles, and the amount of external additive added externally to the mother particles is changed as shown in Table 2. Thus, five types of one-component developers 10 having different loose apparent densities were prepared as Developer F to Developer J, respectively.
[0090]
[Table 2]

[0091]
When an image is formed using the developer G, the developer H, and the developer I, the latent image on the latent image carrier 1 is faithfully reproduced, and a high-definition image having excellent graininess and sharpness is printed on Xerox 4024 paper. Could be formed. However, when an image is formed using the developer F, the toner flow is stagnated in the developing device 11 and the formation of the toner layer becomes non-uniform, causing a phenomenon in which the rear end of the solid image is partially faded. It was. Further, when an image is formed using the developer J, the toner layer flows in the process of laminating the toner layer, so that a fine line image (line screen) constituting the pixel is overweighted and blurred, and is formed on the Xerox 4024 paper. An image with low sharpness was formed.
[0092]
Example 3
<Wadel's practical sphericity>
An A4 size print pattern including a point image, a line image, and a plane image with a resolution of 600 (dpi) at a process speed of 180 (mm / sec) is formed on Xerox 4024 paper under the same conditions as in the first embodiment. did. However, developer 10 is obtained by subjecting the toner particles of developer B used in Example 1 to a deforming process with a jet pulverizer, and has a volume average particle diameter of 5 to 6 (μm) and a practical spherical shape of Wardel. Four types of toner base particles having different degrees of conversion were prepared. 3 (wt%) of silica fine powder (Nippon Aerosil R812) whose surface was hydrophobized to this was added externally to make each one-component developer, and created as Developer K to Developer N as shown below did.
[0093]
Developer K: Wardel's practical sphericity 1.00
Developer L: Wardel's practical sphericity 0.99
Developer M: Wardel's practical sphericity 0.91
Developer N: Wardel's practical sphericity 0.83
When an image is formed using the developer K, the developer L, and the developer M, the latent image on the latent image carrier 1 is faithfully reproduced, and a high-definition image having excellent graininess and sharpness is obtained on Xerox 4024 paper. Could be formed. However, when an image is formed using the developer N, a fine line image (line screen) constituting pixels is partially diverged during the transfer operation from the intermediate transfer medium 7 to the recording medium 8 and adjacent lines are formed. A part of the image was merged, and an image with poor graininess (Tks = 1.0) was formed on Xerox 4024 paper.
[0094]
Example 4
<Toner surface relief>
Under the same conditions as in the first embodiment, an A4 size multicolor print pattern including a point image, a line image, and a plane image with a resolution of 600 (dpi) at a process speed of 180 (mm / sec) is printed on Xerox 4024 paper. An image was formed. However, the developer 10 has a concave / convex concave / convex opening diameter provided on the toner surface having a volume average particle diameter of 6 to 7 (μm) set to a predetermined value, and toner base particles for cyan, magenta, and yellow colors. Two types of each were created. To this, 2 parts (wt%) of silica fine powder whose surface is hydrophobized (R972 manufactured by Nippon Aerosil Co., Ltd., diameter: about 20 nm) is externally added, and each one-component developer 10 composed of the above three color toners is developed. O and developer Q. At this time, the toner base particles showed Dn50 / Dn25 = 1.25 to 1.35, a Wadel's practical sphericity of 0.98 to 0.99, and the developer 10 after the external addition treatment was loose. Hanging density 0.35 to 0.39 (mg / cm^Three), Toner adhesion amount 0.4 (mg / cm²) At the maximum image density of 1.2 to 1.3.
[0095]
Developer O: Toner surface recess opening diameter 0.10 to 0.15 μm
Developer P: Concave opening diameter of toner surface less than 0.01 μm
When a multicolor image is formed using the developer O described above, thickening and blurring of an image that is likely to occur when a plurality of color toners are stacked are suppressed, and a multicolor image with high sharpness is formed on Xerox 4024 paper. We were able to. However, when an image was formed using the developer Q, a multi-color image with low sharpness that gives a blurred impression due to fattening and blurring of a minute line image (line screen) constituting a pixel was obtained.
[0096]
Example 5
<Toner adhesion amount and image density>
Under the same conditions as in the first embodiment, an A4 size multicolor print pattern including a point image, a line image, and a plane image with a resolution of 600 (dpi) at a process speed of 180 (mm / sec) is printed on Xerox 4024 paper. An image was formed. However, as the developer, the color density of the toner having a volume average particle diameter of 6 to 7 (μm) was set as follows, and two types of toner base particles were prepared for each color of cyan, magenta, and yellow. 2 parts (wt%) of silica fine powder (Nippon Aerosil R812: diameter 10 nm or less) externally added to the surface is added to this, and each one-component developer composed of the above three color toners is developed. Q to developer S. At this time, the toner base particles exhibited Dn50 / Dn25 = 1.25 to 1.35, and Wadel's practical sphericity of 0.98 to 0.99. Further, the developer after the external addition treatment has a loose apparent density of 0.37 to 0.40 (mg / cm^Three)showed that.
[0097]
[Table 3]

[0098]
Using the developer Q and developer R described above, the maximum toner adhesion amount per monochrome toner on the recording medium is 0.4 (mg / cm²) To form a multicolor image, the image thickening and bleeding that are likely to occur when multiple color toners are stacked are suppressed, and a multicolor image with high sharpness can be formed on Xerox 4024 paper. did it. Further, even when Nina Bond paper, which is so-called rough paper, is used as the recording medium 8, it is possible to form a multicolor image with high sharpness by suppressing the thickening and blurring of the micro image. However, when an image was formed using the developer S, the image density was low because the color density of each toner was low, and the whole image was whitish and poorly colored. Further, in order to obtain a sufficient image density, the maximum toner adhesion amount per monochromatic toner is 0.7 (mg / cm²), A multicolor image was formed, but although the color of the image was improved, the minute line image (line screen) constituting the pixel was overweight and blurred, giving a sharp impression It became a low multicolor image.
[0099]
Example 6
<Electric resistivity of toner>
Under the same conditions as in the first embodiment, an A4 size multicolor print pattern including a point image, a line image, and a plane image with a resolution of 600 (dpi) at a process speed of 180 (mm / sec) is printed on Xerox 4024 paper. An image was formed. However, the developer is a charge control agent a or a charge control agent b for black toner having a volume average particle diameter of 7 (μm), and a charge control agent for each color toner having a volume average particle diameter of 6 to 7 (μm). 1 part system by externally adding 2 wt% of silica fine powder (R812 manufactured by Nippon Aerosil Co., Ltd., diameter: 10 nm or less) whose surface has been hydrophobized as toner base particles each containing 2 parts by weight of b Developer 10 was obtained. At this time, the toner base particles showed Dn50 / Dn25 = 1.28 to 1.30, a Wadel's practical sphericity of 0.98 to 0.99, and the developer 10 after the external addition treatment was loose. Hanging density 0.38-0.40 (mg / cm^Three), Toner adhesion amount 0.4 (mg / cm²) At the maximum image density of 1.2 to 1.3. As shown in Table 4, the black toner A containing the charge control agent a showed higher electrical resistivity than the black toner B containing the charge control agent b. Further, the black toner A exhibited a higher electrical resistivity than the magenta toner having the lowest electrical resistivity among the cyan, magenta, and yellow color toners.
[0100]
[Table 4]

[0101]
When a black solid image is formed using the above-described black toner A, a microscopic transfer drop-out phenomenon is prevented, and the toner adhesion amount on the Xerox 4024 paper is 0.5 mg / cm.²), A uniform black solid image could be formed. However, when an image is formed using the black toner B, the toner adhesion amount 0.5 (mg / cm²), A transfer dropout phenomenon occurred, and a black solid image having minute density unevenness was formed. Further, the toner adhesion amount is set to 0.7 (mg / cm 2) in order to prevent the transfer dropout phenomenon.²), The black solid image is a uniform image with no density unevenness, but the fine line images (line screens) that make up the pixels are fattened and blurred, creating a blurred impression The resulting image has low sharpness.
[0102]
【The invention's effect】
  As described above, according to the color image forming apparatus of the present invention, it becomes possible to reproduce details of a minute latent image constituting a pixel such as a dot image or a line image with a toner layer having a high packing density. Can be transferred without divergence due to the disturbance of the transfer electric field during the transfer operation from the latent image carrier or the intermediate transfer medium onto the recording medium. Furthermore, the toner layer is prevented from spreading in the two-dimensional surface direction due to the collapse phenomenon during the lamination process of the toner layer, and further, when the toner layer is transferred onto the recording medium, the pressure applied by the transfer member support It is also possible to suppress the toner layer flow that occurs.
[0103]
  Therefore, the micro-images that make up the pixels are reproduced without becoming microscopically nonuniform, and the phenomenon of blurring of the entire image due to fattening or bleeding is prevented, so that the image has excellent graininess and high sharpness. A color image forming apparatus capable of forming the image can be obtained.
[0104]
  In addition, the electrical resistivity of black toner is made larger than the lowest electrical resistivity of the three color toners of yellow, magenta, and cyan. Therefore, it is possible to obtain a color image forming apparatus capable of preventing a microscopic drop-out phenomenon and forming a uniform black solid image without uneven density with a small toner adhesion amount.
[0105]
  Therefore, according to the color image forming apparatus of the present invention, it is possible to provide a color image forming apparatus that is excellent in graininess and sharpness and can form a high-definition multicolor image on rough paper.
[0106]
  In particular, according to the second aspect of the present invention, the toner particles are densely packed so that the interparticle force is easily applied between the toner particles, and recording is performed from the latent image carrier or the intermediate transfer medium. The transfer can be performed without divergence due to the disturbance of the transfer electric field during the transfer operation onto the medium. Further, by providing unevenness on the surface of the toner particles, it is possible to suppress the phenomenon that the toner particles on the surface layer roll down when the toner particles are laminated in layers. Therefore, the effect of suppressing the phenomenon in which the toner layer spreads in the two-dimensional surface direction due to the collapse phenomenon in the toner layer lamination process is enhanced, and the micro image is reproduced without causing micro unevenness or thickening or bleeding. Therefore, it is possible to further reduce the phenomenon that the sharpness of a multi-color image is lowered due to image thickening or bleeding, which is likely to occur when a plurality of color toners are laminated, and to form an image with more excellent graininess. Therefore, a color image forming apparatus capable of achieving the above can be obtained.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic diagram of a developing device showing an embodiment of the present invention.
FIG. 3 is a schematic diagram showing undulations on a toner surface according to an exemplary embodiment of the present invention.
[Explanation of symbols]
1 Latent image carrier
7 Intermediate transfer media
8 Recording media
10 Developer
11 Development device
20 Developer carrier
23 Restriction member
24 Supply member

Claims (2)

The electrostatic latent image on the image carrier is developed using an image carrier on which an electrostatic latent image is formed and a developer composed of black toner and three color toners of yellow, magenta, and cyan. A color image forming apparatus comprising at least four developing devices each using a black toner and a color toner for forming a visible image, and an intermediate transfer medium on which a color image of the visible image on the image carrier is formed ,
Dn25 having a cumulative number of 25% and Dn50 having a cumulative number of 50% satisfy the relationship of 1.25 ≦ Dn50 / Dn25 ≦ 1.50, and the loose apparent density of the developer is reduced to 0. .30 to 0.45 (g / cm ³ )
A color image forming apparatus, wherein the black toner has an electrical resistivity greater than a minimum electrical resistivity among the electrical resistivities of the three color toners . The practical sphericity of the Wader of the developer is set to 0.9 to 1, and the diameter of the concave and convex concave portions provided on the developer surface is larger than the diameter of the external additive particles externally added to the developer surface. 2. The color image forming apparatus according to claim 1 , wherein the color image forming apparatus is enlarged.

Images