JP3758272B2 - Image forming apparatus - Google Patents

Description

【００３６】
次に図２に示す現像装置４で用いられる現像剤について説明する。
〈トナー〉
トナーは、例えば次のようにして作成したものを用いることができる。
ポリエステル（数平均分子量：４，３００、重量平均分子量：９，８００、Ｔｇ＝５８℃）９４ｗｔ％、シアニンブルー４９３８（大日精化）６ｗｔ％を混練粉砕し、平均粒径７μｍの着色粒子を得る。この着色粒子に対し、平均粒径４０ｎｍの酸化チタン微粒子をトナー表面積に対する被覆率３０％の割合で外添してサイアントナーとする。このトナーの帯電極性は負極性であり、平均粒径はコールターカウンタ（コールター社製）で測定した値である。
【００３７】
なお、被覆率ｆ（％）は、トナーの平均粒径をdt( ｍ) 、酸化チタン微粒子の平均粒径をda( ｍ) 、トナーの比重をρt 、酸化チタン微粒子の比重をρa 、酸化チタン微粒子重量をＷａ（ｋｇ）、トナー重量をＷｔ（ｋｇ）とすると、次式で与えられる。
【数１】

また、本例のトナーの比重は１．０、酸化チタン微粒子の比重は４．５である。
【００３８】
〈キャリア〉
キャリアは、例えば次のようなものである。
スチレン−アクリル共重合体（数平均分子量：２３，０００、重量平均分子量：９８，０００、Ｔｇ＝７８°Ｃ）３０ｗｔ％、カーボンブラック（塩基性カーボンブラック：ｐＨ＝８．５）３ｗｔ％、粒状マグネタイト（最大磁化８０ｅｍｕ／ｇ、粒径０．５μｍ ）６７ｗｔ％を混練、粉砕、分級して平均粒径を４５μｍとしたものである。このキャリアの帯電極性は正極性で、電気抵抗値は１０¹²Ω・ｃｍであり、比重は２．２である。なお、平均粒径はマイクロトラック（日機装社製）で測定した値である。
【００３９】
〈現像剤〉
上記トナーとキャリアとを混合した現像剤としては、例えば、トナー濃度（ＴＣ：Ｔｏｎｅｒ Ｃｏｎｃｅｎｔｒａｔｉｏｎ）を１５ｗｔ％、現像剤中のトナーの帯電量の値を−２０μＣ／ｇとしたものを用いることができる。ここでＴＣは次式で示される。
【数２】

【００４０】
次に上記のような構成の画像形成装置の動作について説明する。
像担持体１の表面には、予めほぼ一様に扁平状微粒子が付与されている。その際、微粒子と像担持体表面との接触面では鏡像力やファンデルワールス力等の付着力が作用し、この力によって微粒子が付着する。
画像形成プロセスが開始されると、像担持体１は回転駆動され、帯電器２によってほぼ一様に帯電された後、像書き込み装置３によって像光が照射される。像担持体１の感光体層の電荷は露光によって低減され、表面に静電電位の差による潜像が形成される。その後、像担持体１に形成された潜像は現像装置４との対向位置に移動する。この現像装置４が有する現像ロール３１の表面には、磁石ロール４０の磁力によってキャリアの磁気ブラシが形成されており、このキャリアの表面にトナーが付着している。像担持体１と現像装置４との対向位置では、現像電界の作用によって現像ロール３１からトナーが像担持体１に転移され、潜像が可視化されるが、転移されるトナーは扁平状微粒子の上に重ねて付着される。このようにして形成されたトナー像は、転写帯電器６によって記録用紙に転写される。このとき、トナー像は扁平状微粒子を介して像担持体１上に付着しており、ファンデルワールス力などの非静電的な付着力が小さくなる。このため、トナーは転写電界で容易に離脱し、用紙上に転写される。
【００４１】
その後、用紙上に転写されたトナー像は剥離用帯電器６により剥離され、用紙搬送ベルト９により図示しない定着装置に送られ、トナー像が用紙上に定着される。
一方、記録用紙上にトナー像が転写された後、像担持体上には微粒子が残る。この画像形成装置ではクリーニング装置は設けられておらず、微粒子が像担持体１上に維持されたまま次の画像形成工程に入り、再び現像工程で像担持体上の扁平状微粒子に重ねてトナー像が形成される。
【００４２】
このような画像形成装置では、扁平状微粒子を用いることにより、微粒子と像担持体との接触面積が大きくなり、球状の微粒子に比較して、像担持体とのファンデルワールス力および静電的な力が増加する。このため、扁平状微粒子を長期にわたり像担持体上に付着させておくことが可能となり、トナー像の転写効率を良好に維持することができる。
【００４３】
その一方で、扁平状微粒子を用いることによって、微粒子とトナーとの付着力が増加し、トナーと共に微粒子が像担持体から剥離して微粒子の維持性が劣化するか、あるいは微粒子が像担持体に留まりトナーも微粒子から剥離せず、結果的に転写率が低下する等の現象が懸念される。しかし、像担持体／微粒子間の接触面積とトナー／微粒子間の接触面積に着目し、相互の付着力を制御することにより、このような現象を回避することが可能となる。即ち、像担持体はφ８４ｍｍであるのに対し、トナー粒径は５μｍ〜１０μｍでしかも表層は微小な凹凸があるため、トナー表面に比べ像担持体表面はほぼ平坦と見なすことができ、扁平状微粒子は像担持体と十分な接触面積を確保できる。このため、扁平状微粒子は像担持体との付着力が増大することにより長期にわたりその表面に留まることができ、その一方で、トナーと微粒子との接触面積は極端に小さいので、トナーは微粒子から容易に剥離する。また扁平状微粒子の粒径は１００ｎｍ程度であるので、トナー面積である約１０平方μｍに、微粒子が少なくとも１個、好ましくは２個以上存在することになり、トナーと像担持体との距離を空けることができる。このためトナーと像担持体相互間の付着力は低下し、高転写率を維持することができる。
【００４４】
次に、本願発明の実施形態について説明する。
この画像形成装置は、上記図１に示す画像形成装置で用いられる扁平状微粒子に代えて、針状又は紡錘状の微粒子や、多面体型の微粒子、例えば八面体状微粒子を像担持体表面に付着させるものである。
【００４５】
針状又は紡錘状の微粒子としては、例えば長軸方向の寸法（長軸径）をｌ、厚みをｔとしたときの扁平度ｌ／ｔが１０程度で、粒径が約１００ｎｍの軽質炭酸カルシウムが用いられる。この軽質炭酸カルシウムは、石灰乳と炭酸ガスを反応させる炭酸ガス化合法や、塩化カルシウムとソーダ灰を反応させる炭酸塩溶液化合法などにより製造される。また、多面体型の微粒子としては、例えば粒径が５００ｎｍ程度の正八面体構造の酸化インジウムが用いられる。この酸化インジウム微粒子は、インジウムを酸素とアルゴンの混合気体中で加熱燃焼させることにより得られる。
なお、これらの微粒子を像担持体表面に付着させる方法、および画像形成装置の他の構成は図１に示す画像形成装置と同じである。
【００４６】
上記のような非球形の微粒子を用いることにより、像担持体との接触面積を大きくすることができ、球形の微粒子に比較すると、像担持体とのファンデルワールス力および静電的な力が増加する。このため、微粒子と像担持体との付着力が大きくなり、像担持体からの微粒子の剥離を防止することができる。このため、トナー像の転写率を長期にわたって良好に維持することが可能となる。
【００４７】
〈画像形成装置の経時安定性を確認するための実験〉
次に、上記実施形態に記載した画像形成装置の非球形微粒子付与による転写率とその維持性を確認するため、３０，０００枚連続プリントテストと６０，０００枚連続プリントテストを実施した結果を示す。
非球形の微粒子としては、扁平状微粒子、針状又は紡錘状微粒子、多面体状微粒子を用い、それぞれ像担持体表面にダスティングにより付与して実験を行った。扁平微粒子には、最大粒径（長軸径）が４０ｎｍ、１００ｎｍ、５００ｎｍ、１μｍであり、長軸径をｌ、厚みをｔとしたときのｌ／ｔが２〜４の酸化チタンを、針状又は紡錘状微粒子には、最大粒径（長軸径）が４０ｎｍ、１００ｎｍ、５００ｎｍ、１μｍであり、ｌ／ｔが７〜１０の軽質炭酸カルシウムを、多面体微粒子には、粒径が５００ｎｍであり、ｌ／ｔが約２の正八面体構造の酸化インジウム用いた。
【００４８】
また比較のため、球形微粒子を像担持体表面にダスティングにより付与したものと、扁平状微粒子を像担持体上に付与せずに現像剤にのみ添加したものを用い、同様に実験を行った。
球形微粒子には、粒径が４０ｎｍ、１００ｎｍ、５００ｎｍ、１μｍのシリカを用いた。製法は、気相成長や液相成長等種々あるが、本実施形態では液相成長である加水分解法を用いた。具体的には、Ｓｉアルコキシドを水と反応させ、酸化物を沈殿させる。沈殿物をそのまま乾燥させることによりシリカの粉末を得る。加水分解条件により粒径を制御でき、また粒径のそろった球形シリカを形成できる。
また、現像剤のみに外添する扁平状微粒子は酸化チタン微粒子を用い、現像剤中への添加量を増やして実験を行った。このときの被覆率は〜８０％である。
【００４９】
原稿は、Ａ３サイズの白紙に反射濃度が１．６と０．２、サイズが横２９７ｍｍ×縦４０ｍｍのソリッドパッチを貼りつけたものを使用した。また環境は２２°Ｃ／５５％ＲＨ、２８°Ｃ／８５％ＲＨ、１０°Ｃ／３０％ＲＨの３条件で行い、３０，０００枚連続プリントテストでは１０，０００枚毎に環境を変え、６０，０００枚連続プリントテストでは２０，０００枚毎に環境を変えて行った。
【００５０】
さらに、使用時におけるジャム発生を想定して、５００枚毎にソリッド画像の途中で画像形成装置をシャットダウンして、大量の現像トナ−を帯電、現像、転写の各装置と対向する位置に通過させた。評価尺度としては、現像剤劣化に関するものは、画像濃度および背景部のかぶり、黒点・白点、黒筋・白筋、画像抜け等の画質の変化、トナー帯電量の変化で確認した。転写性に関するものは、残留トナーの影響によるプリント上のポジ／ネガ残像の発生度合いの変化、転写率で確認した。尚、転写率は下記の式によって求めたものである。
【数３】

【００５１】
（１）３０，０００枚連続プリントテストの結果
図１に示すような構成の画像形成装置を用い、上記条件及び方法により３０，０００枚連続プリントテストを行った実験の結果を表１に示す。
（以下余白）
【表１】

表１に示すように、非球形微粒子、すなわち扁平状の酸化チタン微粒子、針状又は紡錘状の軽質炭酸カルシウム微粒子、八面体状の酸化インジウム微粒子を像担持体にダスティングにより付与した場合には、いずれも画質劣化、転写率の低下はなく、良好な結果が得られることが確認された。また、表１には記載しなかったが、現像剤の劣化に起因するトナー帯電量の低下は見られなかった。
【００５２】
但し、酸化チタン微粒子と軽質炭酸カルシウム微粒子において、粒径が１μｍの場合は、僅かにかぶりが発生した。粒径が、４０ｎｍ、１００ｎｍ、５００ｎｍのときには、かぶりが発生していないことから、微粒子を同量付与した場合では、粒径が大きいことにより像担持体と微粒子との接触面積が減少したためと考えられる。従って、画質の点で粒径は、５００ｎｍ以下が良いと考えられる。
【００５３】
一方、球形のシリカ微粒子をダスティングにより付与した場合は、テスト開始時は転写率がほぼ１００％であったが、プリントテスト後には、９０％程度まで低下し、維持性がないことが確認された。
また、酸化チタン微粒子において、あらかじめ像担持体へダスティングする方法を行わないで、現像剤中への添加量を増やした場合は、転写率がほぼ１００％を達成する被覆率は８０％であったが、この条件下では、現像剤の劣化により画像濃度が低下した。これは酸化チタン微粒子を増やしたことにより、トナー帯電量が低下（プラス側にシフト）し、像担持体に転写されたトナー重量が減少したことによる。トナー帯電量を所定の値に保つ被覆率の上限は５０％であったが、この条件下では転写率が９０％まで低下した。よって微粒子を現像剤にのみ添加する方法では、画質と転写率との両方を満足する条件は見い出せなかった。
【００５４】
（２）６０，０００枚連続プリントテストの結果
図１に示した画像形成装置を用い、上記条件及び方法により６０，０００枚連続プリントテストを行った実験の結果を表２に示す。
（以下余白）
【表２】

【００５５】
表２に示すように、非球形微粒子を付与した場合には、３０，０００枚連続ランテストとほぼ同様に、転写率および維持性ともに良好な結果が得られることが確認された。但し、八面体微粒子である酸化インジウムを用いた場合では、僅かにかぶりが発生し、転写率も多少低下し、９８％程度となった。これは酸化インジウムが八面体微粒子であるため、他の微粒子の形状に比べ、球型に近い形状をしていることによると考えられる。従って、望ましくは多面体の面数ｎが、小さい方が本願発明の効果をより発揮できると考えられる。
【００５６】
以上のことから、本実施形態の画像形成装置は、現像剤の劣化を防止することができるとともに、高転写効率を実現することができ、また微粒子の形状効果により維持性が非常に優れていることが分かる。
【００５７】
また、扁平状、針状あるいは紡錘状微粒子として、長軸径をｌ、厚みをｔとしたときのｌ／ｔが転写性にどのような影響を与えるかを確認するための実験を行った。
図３は、３０，０００枚の連続ランテスト後における、ｌ／ｔと像担持体上の残留微粒子の面積率および転写率との関係を調べた結果を示すグラフである。
この図に示すように、ｌ／ｔが２以上のときに残留微粒子の面積率が１０％以上で、微粒子の付着量が良好となり、転写率がほぼ１００％となることが分かる。このため、高転写率を得るためには、１／ｔが２以上が好ましいと考えられる。
【００５８】
なお、本実施形態では、接触式の２成分現像についての例を挙げて説明してきたが、本発明は、非接触式の２成分現像、非接触式の磁性１成分現像、非接触式の非磁性１成分現像を行うクリーナレス方式の画像形成装置に適用しても、同様な効果が得られる。
【００５９】
図４は、本願に係る発明の画像形成装置と同様に機能する画像形成装置の他の例を示す概略構成図である。
この装置は、図１に示す装置と同じ、像担持体５１、帯電器５２、像書き込み装置５３、現像装置５４、除電ランプ５７を備え、さらに複数の支持ロール６２によって周回可能に支持された中間転写体６１と、像担持体５１上のトナー像を上記中間転写体６１に転写する転写帯電器５５とを有している。
また、上記中間転写体６１の下流側には転写ロール６３を備え、これと対向する支持ロール６２との間にバイアス電圧が印加されるようになっており、支持ロール６２との間に中間転写体６１を介して記録用紙を挟み込み、トナー像を記録用紙に転写するようになっている。
【００６０】
上記像担持体５１の表面には、図１に示す装置と同様にあらかじめ扁平状の酸化チタン微粒子がダスティングにより付与されている。この微粒子は、扁平度１／ｔが２〜４で、粒径が５００μｍ以下のものである。
【００６１】
上記中間転写体６１は、ポリカーボネート樹脂中にカーボンブラックを分散したものを厚さ１３５μｍの無端状ベルトにしたもので、電気抵抗値は１０⁸ 〜１０⁹ Ω・ｃｍとなっている。この中間転写体６１および像担持体５１は図中に矢印で示す方向に１６０ｍｍ／ｓの周速で駆動され、これらの部材にはクリーニング装置が設けられていない。
なお、この画像形成装置の他の構成は図１に示す画像形成装置と同じである。
【００６２】
このような画像形成装置では、像担持体５１が回転駆動されると、図１に示す装置と同様に、像担持体５１の一様帯電、像露光による潜像の形成、トナーの転移による現像の各工程が行われ、形成されたトナー像は転写帯電器５５により中間転写体６１に転写される。このとき、像担持体５１上のトナー像は、あらかじめ付与された扁平状微粒子の上に形成されているので、高い効率で転写される。
その後、中間転写体６１に転写されたトナー像は転写ロール６３と支持ロール６２との間に導かれ、ここで記録用紙に転写される。
【００６３】
このような画像形成装置では、前述の実施形態に記載した効果と同様に、像担持体上のトナー像を転写する際に高転写効率を実現できるとともに、微粒子の形状効果により優れた維持性を得ることができる。
【００６４】
また、トナー像が形成される前の中間転写体表面にあらかじめ扁平状微粒子を付与しておくことにより、中間転写体から記録用紙へのトナー像の転写率を大幅に向上させることができる。
【００６５】
なお、像担持体や中間転写体に付与する微粒子は、上記例のような扁平状のものに限らず、棒状、俵形、米粒形ものや、針状、紡錘状、あるいは面数ｎが８以下の多面体構造のものも使用可能であり、同様に優れた転写性および維持性を得ることができる。
【００６６】
【発明の効果】
以上説明したように、本願発明に係る画像形成装置では、像担持体の表面に、例えば扁平状、針状、紡錘状、もしくは多面体状等の非球形の微粒子を付着させ、その後、現像工程で像担持体上に該微粒子を介してトナー像を形成するので、トナーと像担持体との付着力を低減することができる。このため、トナー像の転写効率を著しく向上することができ、クリーナレス方式においてもゴーストやかぶりなどの無い良好な画像を得ることができる。
また上記のような非球形の微粒子を用いることにより、微粒子と像担持体との接触面積が増大し、微粒子の付着力が増加するので、像担持体から微粒子が剥離するのを防止することができる。このため、長期にわたり高転写効率を維持することが可能となる。
【図面の簡単な説明】
【図１】本願発明の一実施形態である画像形成装置を示す概略構成図である。
【図２】上記画像形成装置で用いられる現像装置を示す概略構成図である。
【図３】上記画像形成装置で用いられる微粒子の長軸方向の寸法を１、厚みをｔとしたときの１／ｔと、像担持体上の残留微粒子の面積率及び転写率との関係を示す図である。
【図４】本願発明の他の実施形態である画像形成装置を示す概略構成図である。
【図５】像担持体上に微粒子を介してトナーを付着させた時の、像担持体、微粒子、トナー相互間の付着状態を示す図である。
【図６】上記画像形成装置で用いられる微粒子の形状を説明する図である。
【符号の説明】
１、５１ 像担持体（ＯＰＣ感光体）
２、５２ 帯電器
３、５３ 像書き込み装置
４、５４ 現像装置
５、５５ 転写帯電器
６ 剥離用帯電器
７、５７ 除電露光装置
８ ペーパーガイド
９ 搬送ベルト
３１ 現像ロール
３２ 現像剤規制部材
３３ パドル
３４、３５ オーガー
３６、３７ 現像剤撹拌室
３８ ハウジング
３９ スリーブ
４０ 磁石ロール
６１ 中間転写体
６２ 支持ロール
６３ 転写ロール
６４ ペーパーガイド
６５ 搬送ベルト[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus that forms an electrostatic latent image on an image carrier, selectively attaches toner to the image carrier to form a visible image, and transfers the image to a recording sheet or the like. In particular, the present invention relates to an electrophotographic recording apparatus, an electrostatic recording apparatus, ionography, and an image forming apparatus using a magnetic latent image.
[0002]
[Prior art]
In a conventionally known image forming apparatus, a toner image formed on an image carrier is transferred onto a recording paper or the like and fixed to obtain a recorded image. In general, the toner remaining on the image carrier after the transfer is collected and discarded.
For example, in an electrophotographic image forming apparatus, an electrostatic latent image is formed by irradiating a charged image carrier surface with image light, a charging step for uniformly charging an image carrier having a photosensitive layer on the surface. An exposure process, a developing process for forming a toner image by attaching toner to the electrostatic latent image, a transfer process for transferring the toner image to a recording material, a fixing process for fixing the toner image on the recording material, and An image is formed by a cleaning process for removing toner remaining on the image carrier after the transfer process. In this cleaning process, an elastic rubber blade or brush is pressed against the surface of the image carrier to collect the remaining toner, and the collected toner is accumulated in a collection container and periodically discarded. .
[0003]
In such an apparatus, it is necessary to always detect or measure the amount of collected toner accumulated in the collecting container, and to discard the toner or replace the collecting container before the collecting container becomes full.
The collected toner is being reused from the viewpoints of environmental protection and resource consumption reduction, but there are many problems such as sorting problems, energy problems for transportation and recycling, and problems with the collection method and collection location. Includes problems.
[0004]
The following can be considered as means for solving such problems.
(1) The first means improves transfer efficiency when transferring a toner image to a recording material. If the transfer efficiency to the recording material is improved, the residual toner on the image carrier is reduced accordingly, and the amount of toner that must be recovered and processed is also reduced.
(2) From the viewpoint of not generating waste toner, the second means does not provide a cleaning device for cleaning the toner remaining on the image carrier, and collects the residual toner in the developing device at the same time as development. , It is reused for development. By reusing all of the collected toner, it is not necessary to discard the toner.
[0005]
<Conventional technology to improve transfer efficiency>
The following is disclosed as means for improving the transfer efficiency of (1).
(A) The technique described in Japanese Patent Application Laid-Open No. Sho 56-126872 is intended to improve the transfer efficiency by increasing the area where an electric field for transfer is formed.
(B) The techniques described in Japanese Patent Application Laid-Open Nos. 58-88770 and 58-140769 form an alternating electric field at the transfer position. By this alternating electric field, a force that swings the toner on the image carrier is applied to promote separation from the image carrier.
(C) The techniques described in JP-A-2-1870, JP-A-2-81053, JP-A-2-118671, JP-A-2-118672, and JP-A-2-157766 are used as developers. Incorporating releasable fine particles such as silica in the middle so that these fine particles are interposed between the toner and the image carrier, reducing the adhesive force between the toner and the image carrier and increasing the transfer efficiency of the toner It is.
[0006]
All of the means shown in the above (a) and (b) have the effect of improving the transfer efficiency. However, for the purpose of reducing the amount of waste toner, a certain amount of toner remains on the image carrier after transfer. Is not enough.
[0007]
In the technique shown in (c), in order to maintain high transfer efficiency over a long period of time, it is necessary to add a large amount of peelable fine particles to the developer. On the other hand, since the toner releasability is high, toner cloud is likely to occur during development, and secondary troubles such as fogging of printed images and in-machine contamination occur. In addition, the peelable fine particles adhere to the toner surface or the carrier surface over a long period of time, and the chargeability of the developer is reduced, or the loose peelable fine particles aggregate to form a lump, which causes development. The fluidity of the agent may decrease and cause image unevenness. Further, the image density may fluctuate due to the release of fine particles from the developer to change the chargeability of the developer. Further, since the toner to which a large amount of peelable fine particles are added has high fluidity, the toner image is likely to be disturbed when the toner image comes into contact with the recording material in the transfer process, and a phenomenon such as image distortion due to transfer is likely to occur.
[0008]
<Technology for reusing collected toner>
As a technique for reusing the collected toner in (2) above, a technique for collecting residual toner on the image carrier with a developing device without providing a cleaning device is disclosed in, for example, Japanese Patent Laid-Open Nos. 59-133573, It is described in Japanese Patent Publication No. 59-157661.
In these apparatuses, when the next image is developed after the toner image is transferred, the toner remaining in the background portion is transferred to the developing roll within the electric field of the developing area and collected.
[0009]
However, in such a system, when collecting residual toner in the developing device, paper dust and other foreign matters are simultaneously fed into the developing device, which may adversely affect the life of the developer.
If the image carrier after the transfer is not cleaned, there will be a problem of positive ghost in which the residual toner is printed out in the next image forming process and negative ghost due to the light shielding effect of the residual toner. As a countermeasure against such a ghost, Japanese Patent Application Laid-Open No. 3-114063 discloses a transfer residual toner amount of 0.35 mg / cm.² The ghost can be avoided by setting the following, and JP-A-3-172880 describes that the ghost can be avoided by setting the toner transfer efficiency in the transfer process to 80% or more. It is necessary to increase the toner transfer efficiency.
[0010]
[Problems to be solved by the invention]
In general, the toner image formed on the image carrier is attached mainly by electrostatic force generated between the toner and the image carrier. Non-electrostatic adhesion such as van der Waals force is also added. Therefore, even if ordinary electrostatic transfer is performed, it is difficult to achieve 100% transfer. As described above, various approaches have been studied in order to reduce the non-electrostatic adhesion between the toner and the image carrier in such a situation.
[0011]
However, as described above, in the conventional image forming apparatus, in order to reduce the collected / discarded toner as much as possible or to eliminate the need for the disposal / disposal of the toner, any of them has a large secondary failure and is difficult to realize.
Also, in order to eliminate the toner that must be discarded, the transfer efficiency must be improved to the extent that image defects such as ghosts and fog do not occur without cleaning the residual toner after transfer. It was difficult.
[0012]
Examining such conventional methods, in any case, during the so-called development for forming a toner image on the image carrier, or at the same time as transferring the toner image to the intermediate transfer member, between the toner and the image carrier, etc. This is intended to realize a low adhesion state, which makes the allowable range of the technology extremely narrow or makes it difficult to reliably realize the low adhesion state. Furthermore, even if a relatively low adhesion state can be realized temporarily, it is difficult to maintain such a state in long-term use due to stress in processes such as charging, development, and transfer. In particular, maintaining the low adhesion state of the toner is difficult in an image forming apparatus that employs a charging method and a developing method that come into contact with the image carrier, or is hindered by paper passing during transfer.
[0013]
The present invention has been made in view of the above circumstances, and its object is to improve the efficiency at the time of transferring a toner image to a recording material or an intermediate, and to reduce or eliminate the toner to be collected and discarded. In addition to this, it is necessary to simplify the apparatus by eliminating the need for a cleaning apparatus, and to obtain an image having no deterioration in image quality over a long period of time by preventing the above-described deterioration in transferability.
[0014]
[Means for Solving the Problems]
In order to solve the above-described problems, the present invention is a method for reliably reducing the adhesion force between the toner and the image carrier, by interposing fine particles between the toner and the image carrier, thereby substantially reducing the problem. % Transfer is to be realized. Furthermore, the state where the adhesive force is reduced is to be stably maintained over a long period of time by controlling the shape of the fine particles described above.
[0015]
As a way to reliably reduce the adhesion between the toner and the image carrier, the distance between the toner and the image carrier is increased (separated), and the contact area between the toner and the image carrier is reduced. Is mentioned. A means for realizing these is that powder particles having a particle size smaller than that of the toner are attached in advance to the image carrier, and then the toner for visualizing the latent image is transferred onto the particles to form a toner image. Is to form. At this time, the surface of the image carrier is prepared in a state where at least one, preferably two or more fine particles are present in a toner size, that is, about 10 square μm, by fine surface observation. Therefore, since the toner formed in the subsequent development process is surely arranged on the fine particles, the distance between the toner and the image carrier is increased, and the non-electrostatic force acting between them is reduced. . As a result, when an electric field is applied in the transfer process, the toner particles are easily detached from the image carrier and transferred to the recording sheet or intermediate, and high transfer efficiency can be achieved.
[0016]
Next, the approach to maintain fine particles on the image carrier stably over a long period of time against stresses in processes such as contact-type charging and developing systems, and paper passing during transfer is as follows. An idea opposite to the adhesion effect between the supports may be used. That is, the contact area between the fine particles and the image carrier may be increased by controlling the shape of the fine particles. As means for realizing this, non-spherical (indeterminate) fine particles, for example, fine particles having a flat shape with a large contact area with a substantially flat surface are used. Can increase van der Waals and electrostatic forces with the body.
[0017]
On the other hand, the adhesion force between the non-spherical fine particles and the toner increases, and the fine particles are peeled off from the image carrier together with the toner and the maintenance of the fine particles is deteriorated, or the fine particles stay on the image carrier and the toner is peeled off from the fine particles. However, there is a concern that the transfer rate may decrease as a result. These phenomena may be attributed to the physical properties of the outermost layers of the image carrier, fine particles, and toner, or may be attributed to electrical characteristics such as the charge amount and polarity of each. Since these both depend on the contact area between the image carrier, fine particles and toner, the present invention focuses on the contact area between the image carrier and fine particles and the contact area between the toner and fine particles, The mutual adhesive force is controlled.
[0018]
That is, as shown in FIG. 5, the image carrier (for example, a photoreceptor) is usually 20 mmφ to 100 mmφ, whereas the toner particle diameter is 5 μm to 10 μm and the surface layer has minute irregularities, so that the toner surface In comparison, the surface of the image carrier can be regarded as almost flat. At that time, the non-spherical fine particles, for example, the flat fine particles as shown in FIG. 5, can be secured on the image carrier since the sufficient contact area can be secured (the adsorption force F3 is involved). Since the contact area between the toner and the fine particles is extremely small, the toner is easily peeled off from the fine particles (the adsorption force F2 is involved). Further, the particle size of the flat fine particles is made smaller than the toner particle size, ideally, the particle size is reduced to about 500 nm, and as described above, at least one, preferably two, fine particles are about 10 square μm. If it exists in the above state, the distance between the toner and the image carrier can be increased (separated), and the mutual adhesive force is reduced (the attractive force F1 is involved). For this reason, the toner can be easily peeled off from the image carrier by the action of the transfer electric field, and the fine particles can stably adhere to the image carrier and maintain a high transfer rate over a long period of time.
[0019]
Such fine particles are not limited to the flat-shaped fine particles as shown in FIG. 5 and can be used as long as the contact area with the substantially flat surface is large. There are various methods for expressing the shape of the fine particles, which are roughly classified into two. There are a method of expressing a geometric shape numerically or numerically, and a method of using an equivalent diameter replaced with a sphere diameter equivalent to some physical quantity. In the present invention, attention is paid to the shape of the fine particles and the shape effect is intended to improve the maintainability of the adhesion force of the fine particles. Therefore, the shape of the fine particles is defined using the former shape expression method. For example, as shown in FIG. 6, fine particles having such a shape that l / t is approximately 2 or more when the dimension in the long axis direction of the fine particles is l and the thickness is t are used. In addition, as a specific shape of the fine particles, a rod shape, a bowl shape or a rice grain shape, a needle shape or a spindle shape can be used. Furthermore, polyhedral fine particles having a number of faces n of 8 or less, such as a polyhedral type, preferably an octahedron, can also be used.
[0020]
  Regarding the shape of such non-spherical (irregular) fine particles, for example, a flat shape (including flake shape and disk shape), rod shape, needle shape, spindle shape, or polyhedron, depending on the material and manufacturing method of each fine particle. The state can be selected. As for the production method, there are a method of mechanically pulverizing the raw material, a vapor phase or liquid phase growth method in which chemical or physical growth is performed, or a method in which both are combined, and a method suitable for the purpose is selected.For fine particles, as needle-shaped or spindle-shaped fine particles,There is light calcium carbonate. This is a precipitated calcium carbonate produced by a chemical method, and there are a carbon dioxide compound method for reacting lime milk and carbon dioxide and a carbonate solution compound method for reacting calcium chloride and soda ash. The polyhedral fine particles include indium oxide, which can be obtained by heating and burning indium in a mixed gas of oxygen and argon. This is a fine octahedral fine particle having a particle size of about 500 nm.
[0021]
The fine particles preferably have a smaller particle size than the toner and have a maximum dimension of about 500 nm or less. That is, by making the particle size of the fine particles considerably smaller than the toner particle size, it is possible to obtain at least one, preferably two or more fine particles in about 10 square μm as described above. Accordingly, the fine particles can be reliably interposed between the toner and the image carrier, and the distance between the toner and the image carrier can be increased (separated).
[0022]
In addition, the image forming apparatus for attaching the fine particles on the image carrier is a cleaner-less system, so that the fine particles attached on the image carrier can be kept on the image carrier for a long time. The effect of improving transferability can be maintained. In addition, since the fine particles adhered on the image carrier are not strongly pressed onto the image carrier by the cleaner due to the cleaner-less structure, the transferability is reduced due to the deformation of the fine particles, and the fine particles are applied to the image carrier. There is no need to worry about changes in characteristics of the image carrier due to fusing, abrasion or scratches on the image carrier due to fine particles.
[0023]
In this case, the residual toner can be cleaned by the developing device (also used), and more preferably, the developing toner is transferred almost in one direction without collecting the residual toner by the developing device. By doing so, the problem of paper dust and other foreign matters can be solved.
By such means, image defects such as ghosts can be effectively prevented, and generation of toner to be collected and discarded can be eliminated.
[0024]
Further, as means for attaching the fine particles to the image bearing member, a method of mechanically attaching, a method of attaching electrically, a method using both together, and the like are conceivable. Examples of the mechanical attachment method include a method using rubbing, and examples of such a method include a method of rubbing with a roll, brush, felt, web, or brush. Examples of rolls include a rigid roll formed of a rigid body such as a metal or a hard plastic, and an elastic roll using a material having elasticity such as rubber. The elastic roll is easier to use because of its ease of adjustment. Specific examples of the brush-like material include a magnetic brush using magnetism and a fur brush. By applying an electric field in addition to such a mechanical attachment method, the adhesion state of the fine particles can be further stabilized.
[0025]
As a method for electrically attaching, there is a method in which the fine particles are dispersed in a cloud shape and the fine particles are attached to the image carrier by the force of an electric field. Examples of means for dispersing and adhering fine particles in a cloud shape include, for example, a method using mechanical vibration, air, ultrasonic waves, an alternating electric field, and adhering fine particles to a roll shape, a brush shape, a web shape, a brush shape, for example. A method of rotating, vibrating and moving them can be mentioned.
[0026]
The present invention can be applied not only to an electrophotographic recording system based on the Carlson process, but also to an indirect recording system that transfers to recording paper, such as a chargeless system and a back exposure system. On the other hand, it is also effective in the case of directly writing an electrostatic latent image using a dielectric instead of a photoconductor, developing it, and transferring it, such as a so-called electrostatic recording method or ionography method.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, embodiments of the invention according to the present application will be described with reference to the drawings.
  FIG.An image forming apparatus that functions in the same manner as the image forming apparatus according to the present invention.It is a schematic block diagram.
  In this image forming apparatus, an image carrier 1 on which an electrostatic latent image is formed by irradiating image light after uniform charging, and the surface of the image carrier is uniformly provided around the image carrier 1. A charger 2 that charges the image, an image writing device 3 that forms a latent image by irradiating an image carrier with image light based on image data, and a developing device that selectively transfers toner to the electrostatic latent image for visualization. 4, a transfer charger 5 that transfers the toner image on the surface of the image carrier to the paper supplied from the paper guide 8, a peeling charger 6 that peels the transferred paper from the image carrier, and the peeled paper And a static elimination exposure device 7 for neutralizing the image carrier 1 after transfer. Note that this image forming apparatus is a cleaner-less system, and no cleaning device is provided.
[0028]
The charger 2 is a scorotron charger composed of an electrode wire and a grit electrode, and a corona discharge is generated between the image carrier 1 and the surface of the image carrier 1 by applying a high voltage to the electrode wire. Is uniformly charged.
[0029]
The image writing device 3 includes a large number of light emitting elements (LEDs) arranged in the width direction of an image to be formed, and the image carrier 1 is rotationally driven by the light emitting elements blinking based on an image signal. Image exposure is performed.
[0030]
As shown in FIG. 2, the developing device 4 includes a cylindrical developing roll 31 disposed in a housing 38 with a minute gap in a housing 38, and a developing that regulates the amount of developer on the developing roll 31. And an agent regulating member 32.
[0031]
The developing roll 31 includes a magnet roll 40 having a plurality of magnetic poles in the circumferential direction and a non-magnetic hollow cylindrical sleeve 39 supported rotatably around the developing roll 31. The agent can be magnetically adsorbed and transported.
In addition, a paddle 33 for supplying the developer to the developing roll 31 is provided behind the developing roll 31, and a first stirring chamber 36 and a second stirring chamber 37 are further provided behind the paddle 33. The first agitating chamber 36 and the second agitating chamber 37 are provided with a first auger 34 and a second auger 35 that convey the developer in the axial direction of the developing roll while agitating the developer.
[0032]
As the developer used in the developing device 4, a two-component developer in which a magnetic carrier and a toner are mixed is used. Moreover, what added the external additive may be used. This developer will be described in detail later.
In the developing device 4, the developer in the housing 38 is mixed and charged by the augers 34 and 35, and is supplied to the peripheral surface of the sleeve 39 by the rotation of the paddle 33. The developer supplied onto the sleeve 39 is leveled by the developer regulating member 32 to form a developer layer having a predetermined thickness, which is transported to a region facing the image carrier 1 and used for development. It has become.
[0033]
On the other hand, non-spherical fine particles are applied to the surface of the image carrier 1 in advance. As shown in FIG. 6, the particle shape of this fine particle is a flat shape with a large contact area with respect to a substantially flat surface, the major axis direction dimension (major axis diameter) of the fine particle is 1, and the thickness is t. The flatness 1 / t is approximately 2 or more. In the above example, fine titanium oxide particles having a flatness 1 / t of about 3 are used. As described above, the titanium oxide fine particles are obtained by forming a raw ore of titanium oxide (titania) by the sulfuric acid method or the chlorine method, and performing finish pulverization. The maximum particle diameter (major axis diameter) is about 100 nm. It has become.
[0034]
Further, as a method for attaching the fine particles to the surface of the image carrier 1, a simple and effective dusting method was used. Specifically, titanium oxide fine particles are placed in a cotton pouch, and dusting is performed while lightly tapping the image carrier 1 to give the entire surface of the image carrier 1. At this time, the adhesion state of the fine particles is a state where about two or more fine particles are present at about 10 square μm.
[0035]
The data and settings of the main members of the image forming apparatus as described above are as follows.

[0036]
Next, the developer used in the developing device 4 shown in FIG. 2 will be described.
<toner>
For example, toner prepared as follows can be used.
94 wt% of polyester (number average molecular weight: 4,300, weight average molecular weight: 9,800, Tg = 58 ° C.) and 6 wt% of cyanine blue 4938 (Daiichi Seika) are kneaded and pulverized to obtain colored particles having an average particle diameter of 7 μm. . Titanium oxide fine particles having an average particle diameter of 40 nm are externally added to the colored particles at a coverage ratio of 30% with respect to the toner surface area to obtain a cyan toner. The charging polarity of the toner is negative, and the average particle diameter is a value measured with a Coulter counter (manufactured by Coulter).
[0037]
The coverage f (%) is defined as follows: the average particle diameter of the toner is dt (m), the average particle diameter of the titanium oxide fine particles is da (m), the specific gravity of the toner is ρt, the specific gravity of the titanium oxide fine particles is ρa, and the titanium oxide. When the fine particle weight is Wa (kg) and the toner weight is Wt (kg), the following equation is given.
[Expression 1]

The specific gravity of the toner of this example is 1.0, and the specific gravity of the titanium oxide fine particles is 4.5.
[0038]
<Career>
For example, the carrier is as follows.
Styrene-acrylic copolymer (number average molecular weight: 23,000, weight average molecular weight: 98,000, Tg = 78 ° C.) 30 wt%, carbon black (basic carbon black: pH = 8.5) 3 wt%, granular A magnetite (maximum magnetization 80 emu / g, particle size 0.5 μm) 67 wt% was kneaded, pulverized and classified to an average particle size of 45 μm. The carrier has a positive polarity and an electric resistance value of 10¹²The specific gravity is 2.2. The average particle diameter is a value measured with a microtrack (manufactured by Nikkiso Co., Ltd.).
[0039]
<Developer>
As the developer in which the toner and the carrier are mixed, for example, a toner concentration (TC: Toner Concentration) of 15 wt% and a toner charge amount in the developer of −20 μC / g can be used. . Here, TC is expressed by the following equation.
[Expression 2]

[0040]
Next, the operation of the image forming apparatus configured as described above will be described.
On the surface of the image carrier 1, flat particles are applied almost uniformly in advance. At that time, an adhesion force such as a mirror image force or van der Waals force acts on the contact surface between the fine particles and the surface of the image carrier, and the fine particles adhere by this force.
When the image forming process is started, the image carrier 1 is rotationally driven and charged almost uniformly by the charger 2, and then image light is irradiated by the image writing device 3. The charge on the photoreceptor layer of the image carrier 1 is reduced by exposure, and a latent image is formed on the surface due to the difference in electrostatic potential. Thereafter, the latent image formed on the image carrier 1 moves to a position facing the developing device 4. A magnetic brush of a carrier is formed on the surface of the developing roll 31 of the developing device 4 by the magnetic force of the magnet roll 40, and toner adheres to the surface of the carrier. At the position where the image carrier 1 and the developing device 4 are opposed to each other, the toner is transferred from the developing roll 31 to the image carrier 1 by the action of the developing electric field, and the latent image is visualized. It is stuck on top. The toner image formed in this way is transferred to a recording sheet by the transfer charger 6. At this time, the toner image is attached on the image carrier 1 through the flat fine particles, and non-electrostatic adhesion force such as van der Waals force is reduced. For this reason, the toner is easily separated by the transfer electric field and transferred onto the paper.
[0041]
Thereafter, the toner image transferred onto the paper is peeled off by the peeling charger 6 and sent to a fixing device (not shown) by the paper transport belt 9 to fix the toner image on the paper.
On the other hand, after the toner image is transferred onto the recording paper, fine particles remain on the image carrier. This image forming apparatus is not provided with a cleaning device, and enters the next image forming process while the fine particles are maintained on the image carrier 1, and is again superposed on the flat fine particles on the image carrier in the developing process. An image is formed.
[0042]
In such an image forming apparatus, the use of flat microparticles increases the contact area between the microparticles and the image carrier, and the van der Waals force and electrostatic force with the image carrier compared to spherical microparticles. Power increases. For this reason, it is possible to allow the flat fine particles to adhere to the image carrier for a long period of time, and the transfer efficiency of the toner image can be maintained satisfactorily.
[0043]
On the other hand, the use of flat fine particles increases the adhesion between the fine particles and the toner, and the fine particles are peeled off from the image carrier together with the toner, and the maintenance of the fine particles is deteriorated. There is a concern that the remaining toner does not peel off from the fine particles, resulting in a decrease in transfer rate. However, by paying attention to the contact area between the image carrier / fine particles and the contact area between the toner / fine particles and controlling the mutual adhesion force, such a phenomenon can be avoided. In other words, the image carrier has a diameter of 84 mm, the toner particle diameter is 5 μm to 10 μm, and the surface layer has minute irregularities, so that the surface of the image carrier can be considered to be almost flat compared to the toner surface. The fine particles can ensure a sufficient contact area with the image carrier. For this reason, the flat fine particles can remain on the surface for a long time by increasing the adhesion force with the image carrier, while the contact area between the toner and the fine particles is extremely small. Easily peels off. Further, since the particle diameter of the flat fine particles is about 100 nm, at least one, preferably two or more fine particles are present in the toner area of about 10 square μm, and the distance between the toner and the image carrier is increased. Can be vacant. For this reason, the adhesion force between the toner and the image carrier is reduced, and a high transfer rate can be maintained.
[0044]
  next,An embodiment of the present invention will be described.
  This image forming apparatusInstead of the flat particles used in the image forming apparatus shown in FIG.Needle-like or spindle-like fine particles, polyhedral fine particles, for example octahedral fine particlesAdhering to the surface of the image carrierIt is something to be made.
[0045]
Examples of acicular or spindle-shaped fine particles include light calcium carbonate having a flatness l / t of about 10 and a particle size of about 100 nm, where l is the dimension in the major axis direction (major axis diameter) and t is the thickness. Is used. This light calcium carbonate is produced by a carbon dioxide gas compounding method in which lime milk and carbon dioxide are reacted, a carbonate solution compounding method in which calcium chloride and soda ash are reacted, or the like. As the polyhedral fine particles, for example, regular octahedral indium oxide having a particle size of about 500 nm is used. The indium oxide fine particles can be obtained by heating and burning indium in a mixed gas of oxygen and argon.
The method of attaching these fine particles to the surface of the image carrier and the other configuration of the image forming apparatus are the same as those of the image forming apparatus shown in FIG.
[0046]
By using non-spherical fine particles as described above, the contact area with the image carrier can be increased. Compared with spherical fine particles, van der Waals force and electrostatic force with the image carrier are reduced. To increase. For this reason, the adhesion force between the fine particles and the image carrier increases, and separation of the fine particles from the image carrier can be prevented. For this reason, it becomes possible to maintain the transfer rate of the toner image satisfactorily for a long time.
[0047]
<Experiment to confirm the temporal stability of the image forming apparatus>
Next, in order to confirm the transfer rate by the application of the non-spherical fine particles and the maintainability of the image forming apparatus described in the above embodiment, results of performing a 30,000 continuous print test and a 60,000 continuous print test are shown. .
As the non-spherical fine particles, flat fine particles, needle-like or spindle-shaped fine particles, and polyhedral fine particles were used, and the experiment was performed by applying them to the surface of the image carrier by dusting. The flat fine particles are made of titanium oxide having a maximum particle diameter (major axis diameter) of 40 nm, 100 nm, 500 nm, and 1 μm, a major axis diameter of l, and a thickness of t of 1 to 4 of 1 / t. For light- or spindle-shaped fine particles, light calcium carbonate having a maximum particle diameter (major axis diameter) of 40 nm, 100 nm, 500 nm, and 1 μm and 1 / t of 7 to 10 is used, and for polyhedral fine particles, the particle diameter is 500 nm. Indium oxide having a regular octahedral structure with l / t of about 2 was used.
[0048]
For comparison, the same experiment was performed using spherical fine particles applied to the surface of the image carrier by dusting and flat fine particles added only to the developer without being applied on the image carrier. .
As the spherical fine particles, silica having a particle diameter of 40 nm, 100 nm, 500 nm, and 1 μm was used. There are various production methods such as vapor phase growth and liquid phase growth. In this embodiment, a hydrolysis method which is liquid phase growth is used. Specifically, Si alkoxide is reacted with water to precipitate an oxide. By drying the precipitate as it is, a silica powder is obtained. The particle size can be controlled by the hydrolysis conditions, and spherical silica with a uniform particle size can be formed.
Further, the experiment was conducted by using titanium oxide fine particles as the flat fine particles externally added only to the developer and increasing the amount of addition to the developer. The coverage at this time is ˜80%.
[0049]
The original used was an A3 size white paper with a solid density patch having a reflection density of 1.6 and 0.2 and a size of 297 mm wide × 40 mm long. The environment is 22 ° C / 55% RH, 28 ° C / 85% RH, 10 ° C / 30% RH, and the environment is changed every 10,000 sheets in the 30,000 continuous print test. In the 60,000-sheet continuous print test, the environment was changed every 20,000 sheets.
[0050]
Furthermore, assuming jamming during use, the image forming apparatus is shut down in the middle of a solid image every 500 sheets, and a large amount of developing toner is passed to a position facing the charging, developing, and transfer apparatuses. It was. As the evaluation scale, developer deterioration was confirmed by image density and background fogging, black / white spots, black / white streaks, changes in image quality such as missing images, and changes in toner charge amount. The transferability was confirmed by the change in the degree of occurrence of a positive / negative afterimage on the print due to the influence of residual toner and the transfer rate. The transfer rate is obtained by the following formula.
[Equation 3]

[0051]
(1) Results of 30,000 sheets continuous print test
Table 1 shows the results of an experiment in which an image forming apparatus configured as shown in FIG.
(The following margin)
[Table 1]

As shown in Table 1, when non-spherical fine particles, that is, flat titanium oxide fine particles, needle-like or spindle-shaped light calcium carbonate fine particles, and octahedral indium oxide fine particles are applied to the image carrier by dusting. In either case, it was confirmed that there was no deterioration in image quality and transfer rate, and good results were obtained. Further, although not shown in Table 1, no reduction in the toner charge amount due to deterioration of the developer was observed.
[0052]
However, in the titanium oxide fine particles and the light calcium carbonate fine particles, when the particle size was 1 μm, slight fogging occurred. When the particle size was 40 nm, 100 nm, or 500 nm, no fogging occurred. Therefore, when the same amount of fine particles was applied, the contact area between the image carrier and the fine particles decreased due to the large particle size. It is done. Therefore, it is considered that the particle size is preferably 500 nm or less in terms of image quality.
[0053]
On the other hand, when spherical silica fine particles were applied by dusting, the transfer rate was almost 100% at the start of the test, but after the print test it was reduced to about 90% and it was confirmed that there was no maintainability. It was.
In addition, when the amount of titanium oxide fine particles added to the developer is increased without performing the dusting method on the image carrier in advance, the coverage ratio at which the transfer rate is almost 100% is 80%. However, under this condition, the image density decreased due to the deterioration of the developer. This is because the toner charge amount is decreased (shifted to the plus side) by increasing the titanium oxide fine particles, and the weight of the toner transferred to the image carrier is decreased. The upper limit of the coverage ratio for maintaining the toner charge amount at a predetermined value was 50%, but under these conditions, the transfer ratio decreased to 90%. Therefore, in the method in which the fine particles are added only to the developer, a condition that satisfies both the image quality and the transfer rate cannot be found.
[0054]
(2) Results of 60,000 continuous printing test
Table 2 shows the results of an experiment in which a 60,000 continuous print test was performed using the image forming apparatus shown in FIG.
(The following margin)
[Table 2]

[0055]
As shown in Table 2, it was confirmed that when non-spherical fine particles were applied, good results were obtained in both transfer rate and maintainability, as in the 30,000 continuous run test. However, when indium oxide, which is octahedral fine particles, was used, a slight fog was generated, and the transfer rate slightly decreased to about 98%. This is considered to be due to the fact that indium oxide is octahedral fine particles and has a shape close to a spherical shape compared to the shape of other fine particles. Therefore, it is desirable that the effect of the present invention can be exhibited more preferably when the number of faces n of the polyhedron is smaller.
[0056]
From the above, the image forming apparatus according to the present embodiment can prevent deterioration of the developer, can achieve high transfer efficiency, and has excellent maintainability due to the shape effect of the fine particles. I understand that.
[0057]
In addition, an experiment was conducted to confirm the influence of l / t on flatness, needle-like or spindle-shaped fine particles, where l is the major axis diameter and t is the thickness.
FIG. 3 is a graph showing the results of examining the relationship between 1 / t, the area ratio of residual fine particles on the image bearing member, and the transfer rate after 30,000 continuous run tests.
As shown in this figure, it can be seen that when l / t is 2 or more, the area ratio of the residual fine particles is 10% or more, the adhesion amount of the fine particles is good, and the transfer rate is almost 100%. For this reason, in order to obtain a high transfer rate, it is considered that 1 / t is preferably 2 or more.
[0058]
In this embodiment, the contact type two-component development has been described as an example. However, the present invention is not limited to the non-contact type two-component development, the non-contact type magnetic one-component development, and the non-contact type non-contact development. The same effect can be obtained when applied to a cleanerless type image forming apparatus that performs magnetic one-component development.
[0059]
  FIG.It is a schematic block diagram which shows the other example of the image forming apparatus which functions similarly to the image forming apparatus of the invention which concerns on this application.
  This apparatus is the same as the apparatus shown in FIG. 1 and includes an image carrier 51, a charger 52, an image writing device 53, a developing device 54, and a static elimination lamp 57. A transfer member 61 and a transfer charger 55 that transfers the toner image on the image carrier 51 to the intermediate transfer member 61 are provided.
  Further, a transfer roll 63 is provided on the downstream side of the intermediate transfer body 61, and a bias voltage is applied between the transfer roll 63 and the support roll 62 facing the transfer roll 63. The recording paper is sandwiched through the body 61, and the toner image is transferred to the recording paper.
[0060]
The surface of the image carrier 51 is preliminarily provided with flat titanium oxide fine particles by dusting as in the apparatus shown in FIG. The fine particles have a flatness 1 / t of 2 to 4 and a particle size of 500 μm or less.
[0061]
The intermediate transfer member 61 is obtained by dispersing carbon black in a polycarbonate resin into an endless belt having a thickness of 135 μm.⁸ -10⁹ It is Ω · cm. The intermediate transfer member 61 and the image carrier 51 are driven at a peripheral speed of 160 mm / s in a direction indicated by an arrow in the drawing, and these members are not provided with a cleaning device.
The other configuration of the image forming apparatus is the same as that of the image forming apparatus shown in FIG.
[0062]
In such an image forming apparatus, when the image carrier 51 is rotationally driven, as in the apparatus shown in FIG. 1, the image carrier 51 is uniformly charged, a latent image is formed by image exposure, and development is performed by toner transfer. Each of the steps is performed, and the formed toner image is transferred to the intermediate transfer member 61 by the transfer charger 55. At this time, the toner image on the image carrier 51 is formed on the previously applied flat fine particles, and thus is transferred with high efficiency.
Thereafter, the toner image transferred to the intermediate transfer member 61 is guided between the transfer roll 63 and the support roll 62, and is transferred onto the recording paper.
[0063]
In such an image forming apparatus, similar to the effects described in the above-described embodiments, high transfer efficiency can be realized when transferring the toner image on the image carrier, and excellent maintainability is achieved by the shape effect of the fine particles. Obtainable.
[0064]
Further, by applying flat fine particles in advance to the surface of the intermediate transfer member before the toner image is formed, the transfer rate of the toner image from the intermediate transfer member to the recording paper can be greatly improved.
[0065]
The fine particles applied to the image carrier and the intermediate transfer member are not limited to the flat shape as in the above example, but are a rod shape, a bowl shape, a rice grain shape, a needle shape, a spindle shape, or a surface number n of 8. The following polyhedral structures can also be used, and similarly excellent transferability and maintainability can be obtained.
[0066]
【The invention's effect】
As described above, in the image forming apparatus according to the present invention, non-spherical fine particles such as flat, needle, spindle, or polyhedron are attached to the surface of the image carrier, and then in the development process. Since the toner image is formed on the image carrier via the fine particles, the adhesion force between the toner and the image carrier can be reduced. Therefore, the transfer efficiency of the toner image can be remarkably improved, and a good image free from ghosting and fogging can be obtained even in the cleanerless system.
Further, by using non-spherical fine particles as described above, the contact area between the fine particles and the image carrier increases, and the adhesion of the fine particles increases, so that the fine particles can be prevented from peeling off from the image carrier. it can. For this reason, it is possible to maintain high transfer efficiency over a long period of time.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram illustrating a developing device used in the image forming apparatus.
FIG. 3 is a graph showing the relationship between 1 / t when the dimension of the fine axis used in the image forming apparatus is 1 and the thickness is t, and the area ratio and transfer rate of residual fine particles on the image carrier. FIG.
FIG. 4 is a schematic configuration diagram illustrating an image forming apparatus according to another embodiment of the present invention.
FIG. 5 is a diagram illustrating an adhesion state between the image carrier, the fine particles, and the toner when the toner is adhered to the image carrier through the fine particles.
FIG. 6 is a diagram illustrating the shape of fine particles used in the image forming apparatus.
[Explanation of symbols]
1, 51 Image carrier (OPC photoreceptor)
2,52 Charger
3, 53 Image writing device
4, 54 Development device
5, 55 Transfer charger
6 Charger for peeling
7, 57 Static elimination exposure equipment
8 Paper Guide
9 Conveyor belt
31 Developing roll
32 Developer regulating member
33 paddle
34, 35 Auger
36, 37 Developer stirring chamber
38 Housing
39 sleeve
40 magnet roll
61 Intermediate transfer member
62 Support roll
63 Transfer roll
64 Paper Guide
65 Conveyor belt

Claims (3)

An image carrier on which a latent image is formed on the surface;
A developing device that selectively transfers toner to the image carrier to visualize the latent image;
In an image forming apparatus having a transfer device for transferring the toner image to a recording sheet or an intermediate transfer member,
On the surface of the image carrier, fine particles of a powdery material having a smaller particle diameter than the toner are attached almost uniformly,
The image forming apparatus is characterized in that the fine particles are made of either light calcium carbonate or indium oxide . The image forming apparatus according to claim 1.
The fine particles are made of light calcium carbonate,
The fine particles have a needle shape or a spindle shape, and 1 / t is in a range of 7 to 10 when the major axis diameter is 1 and the minor axis diameter is t. Image forming apparatus. The image forming apparatus according to claim 1, wherein:
The maximum size of each fine particle of the powdery body is 500 nm or less.

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