JP4072666B2 - Image forming apparatus - Google Patents

Description

【００２５】
形状係数ＭＬ²／Ａは、トナーの投影面積と、それに外接する円の面積との比で表しており、真球の場合１００となり、形状が崩れるにつれ増加する。形状係数は、トナー粒子複数個に対して計算され、その平均値を代表値とする。本実施の形態では、形状係数１２５以下の略球形なトナーを用いた。
また、離型性を高めるため、該トナーに、平均粒径１０〜１５０ｎｍのシリカ及び酸化チタン（チタニア）等の無機微粒子を外添剤として適宜量外添し、平均粒径３５μｍのフェライトビーズからなるキャリアと混合し現像剤とした。
尚、トナーとしては、本製造法により作成したトナー以外にも、懸濁重合法、溶解懸濁法、乳化重合法、混練粉砕法等により形成された球形トナーあるいは非球形トナーを使用してもよく、また、上述したようなトナーとキャリアとを混在させた二成分系現像剤でも、トナーのみの一成分系現像剤でも構わないことは勿論である。
【００２６】
図３には、本実施の形態に係るベルトクリーナ６０の拡大断面図を示す。
同図において、ベルトクリーナ６０は、前記中間転写ベルト２０の像担持面側に配設されるスクレーパ６１と、当該スクレーパ６１が収容されるクリーナハウジング６２とを有している。
本実施の形態においては、スクレーパ６１は、例えば厚さ０．１５ｍｍのステンレス板（ＳＵＳ３０４）で構成されている。このスクレーパ６１は、一端側がブロック６３に固定されており、このブロック６３は、軸６４ａを中心に揺動するホルダ６４に取り付けられるようになっている。
【００２７】
また、前記ホルダ６４の下端側に設けられた凹部６４ｂと、クリーナハウジング６２下部に設けられた膨出部６２ａとの間には、前記スクレーパ６１を前記中間転写ベルト２０に向けて付勢するばね６５が取り付けられている。更に、前記ホルダ６４は、図示しないカムにより前記ばね６５の付勢方向とは逆方向に付勢されるようになっており、これによりスクレーパ６１が中間転写ベルト２０に対して接離できるようになっている。
【００２８】
尚、符号６６は、スクレーパ６１からみて中間転写ベルト２０の移動方向Ｂ上流側に設けられ除去された残留物の外部への飛び散りを防止するためのフィルムシール、符号６７は、前記クリーナハウジング６２に前記フィルムシール６６を固定するＬ字状プレートである。このフィルムシール６６は前記スクレーパ６１にリンクして移動するようになっており、クリーニング動作時以外は中間転写ベルト２０から離間するようになっている。
また、前記スクレーパ６１には、正極性の電圧を印加する電源４２が接続されている。
【００２９】
次に、本実施の形態に係るカラー画像形成装置の作像プロセスについて説明する。
今、図示外のスタートスイッチがオンされると、所定の作像プロセスが実行される。
まず、感光体ドラム１１上に静電潜像の書き込みが行われ、この静電潜像に対応した現像器によって現像される。
これは、例えば感光体ドラム１１上に書き込まれた静電潜像がイエロの画像情報に対応したものであれば、この静電潜像はイエロのトナーを内包する現像器１５で現像され、感光体ドラム１１上にはイエロのトナー像Ｔが形成される。
そして、感光体ドラム１１上に形成されたトナー像Ｔは、感光体ドラム１１と中間転写ベルト２０とが接する一次転写位置で感光体ドラム１１から中間転写ベルト２０の表面に転写される。一方、一次転写後に感光体ドラム１１上に残留したトナーはドラムクリーナ１９によって除去される。
【００３０】
このとき、単色画像を形成する場合には、中間転写ベルト２０に一次転写されたトナー像Ｔを直ちに用紙３０に二次転写するのであるが、複数色のトナー像Ｔを重ね合わせたカラー画像を形成する場合には、感光体ドラム１１上でのトナー像Ｔ形成並びにこのトナー像Ｔの一次転写の工程が色数分だけ繰り返される。
例えば、４色のトナー像を重ね合わせたフルカラー画像を形成する場合には、感光体ドラム１１上にはその一回転毎にイエロ、マゼンタ、シアン及びブラックのトナー像Ｔが形成され、これらトナー像Ｔは順次中間転写ベルト２０に一次転写される。一方、中間転写ベルト２０は最初に一次転写されたトナー像Ｔを保持したまま感光体ドラム１１と同一周期で回動し、中間転写ベルト２０上にはその一回転毎にマゼンタ、シアン及びブラックのトナー像Ｔが転写される。
【００３１】
このようにして中間転写ベルト２０に一次転写されたトナー像Ｔは、中間転写ベルト２０の回動に伴って二次転写位置へと搬送される。
一方、用紙３０はレジストロール５２にて所定のタイミングで二次転写位置へと供給され、バックアップロール２６に対して二次転写ロール２８が用紙３０をニップする。
すると、二次転写位置では、二次転写装置４０である二次転写ロール２８とバックアップロール２６との間に形成される転写電界の作用で、中間転写ベルト２０に担持されたトナー像Ｔが二次転写位置において用紙３０に静電転写される。その後、二次転写された用紙３０は、搬送ベルト５３を経て定着器５４へと搬送されて用紙３０上のトナー像Ｔが定着され、一方、二次転写位置を通過した中間転写ベルト２０の像担持面側は、ベルトクリーナ６０によってクリーニングされる。
【００３２】
ここで、二次転写装置４０による二次転写プロセス及びベルトクリーナ６０による中間転写ベルト２０のクリーニングプロセスは次の通りである。尚、図４は、二次転写バイアス及びスクレーパ印加バイアスのタイミングチャートを示している。
図３及び図４において、中間転写ベルト２０上の画像領域Ｄ（トナー像Ｔが形成される領域）が二次転写装置４０を通過する間、バックアップロール２６には転写電源４１より例えば−２ｋＶの転写バイアスが印加され、中間転写ベルト２０上のトナー像Ｔは用紙３０に転写される。また、前記画像領域Ｄの先端部が二次転写装置４０を通過すると、これに対応してスクレーパ６１及びフィルムシール６６が中間転写ベルト２０に圧接される。
【００３３】
そして、前記画像領域Ｄが前記スクレーパ６１との対向部を通過する間、前記スクレーパ６１には前記電源４２により＋２００Ｖのバイアスが印加される。本実施の形態では、二次転写装置４０のニップ部と中間転写ベルト２０及びスクレーパ６１の当接部との間の距離が７０ｍｍであり、また、中間転写ベルト２０の速度が上述の通り２２０ｍｍ／ｓであることから、二次転写バイアスの印加開始、印加停止タイミングより夫々Ｔ1＝７０ｍｍ／２２０ｍｍ／ｓ＝３１８ｍｓだけ遅らせるようになっている。
この間、中間転写ベルト２０の画像領域Ｄに付着した残留物Ｒ（転写後の残留トナーや用紙３０から転移した紙粉等）は、スクレーパ６１により掻き取られ、クリーニングされる。
【００３４】
そして、画像領域Ｄがスクレーパ６１との対向部を通過すると、当該スクレーパ６１及びフィルムシール６６が中間転写ベルト２０から離間され、一連のプロセスを終了する。
【００３５】
本実施の形態において、スクレーパ６１に上述したようなバイアスを印加しているのは、次の理由による。
本発明者は、金属製のスクレーパ６１を用いた場合に発生するクリーニング不良の原因を究明するため、以下の実験を行った。
まず、スクレーパ６１の先端近傍に表面電位計プローブを設置し、中間転写ベルト２０の表面電位を測定した。
その結果、二次転写バイアスの印加開始時間から中間転写ベルト２０が二次転写装置４０のニップ部からスクレーパ６１との対向部まで移動する移動時間だけ遅れて、二次転写バイアスの約１／１０の大きさの表面電位が測定された。通常環境下では二次転写バイアスが−２ｋＶに設定されているので、この実験においては、約３２０ｍｓ後から＋２００Ｖの表面電位が測定された。二次転写バイアスの印加が停止された後も、同じ時間遅れをもって表面電位は＋２００Ｖから０Ｖになった。このことは、中間転写ベルト２０は所謂半導電性の材質で構成されるものであるが、二次転写バイアスよって帯電され、その電荷がある程度残存した状態でスクレーパ６１との対向部まで到達することが示唆された。
【００３６】
次に、スクレーパ６１先端部に溜まった紙粉の挙動を観察した。中間転写ベルト２０にスクレーパ６１先端が接した状態から離れる状態へと移行するとき、紙粉は金属スクレーパ６１先端に保持されているが、逆に離れた状態から接触した状態に移行するときの紙粉は、二次転写バイアスの有無で異なる挙動を示した。
すなわち、二次転写バイアスが印加されているときには、スクレーパ６１先端の紙粉は中間転写ベルト２０側に倒れ込み、スクレーパ６１と中間転写ベルト２０との間に挟み込まれた。一方、二次転写バイアスが印加されていないときには、上述したような紙粉の倒れ込みは見られず、挟み込みも見られなかった。
【００３７】
以上の観察結果から、本発明者は、紙粉によるクリーニング不良の発生メカニズムを以下のように推定した。これを図５（ａ）〜（ｅ）に示す模式図を用いて説明する。尚、同図において、符号Ｐは紙粉を示している。
（ａ）図２及び図３に示すように、用紙３０が搬送ロール（例えばフィードロール５１、レジストロール５２等）と摺擦されて発生した紙粉Ｐが、用紙３０から中間転写ベルトに転移し、その後スクレーパ６１によって掻き取られその先端に堆積する。
（ｂ）二次転写バイアスの印加により帯電した中間転写ベルト２０（図中帯電電荷を「＋」で示す）がスクレーパ６１との対向部まで到達し、堆積した紙粉Ｐが電荷（負極性）を帯びる。
（ｃ）クリーニング終了によりスクレーパ６１が一旦中間転写ベルト２０から離れる。
（ｄ）次のクリーニング開始のためスクレーパ６１が中間転写ベルト２０と再び接触する直前に、電荷を帯びた紙粉Ｐが中間転写ベルト側に静電的に引き寄せられ、紙粉Ｐが中間転写ベルト２０側に倒れ込む。
（ｅ）スクレーパ６１と中間転写ベルト２０とで倒れ込んだ紙粉Ｐを挟み込んでしまい、スクレーパ６１とベルト間に間隙が生じクリーニング不良が発生する。
【００３８】
次に、本発明者は、スクレーパ６１に種々の大きさのバイアスを印加し、クリーニング不良が発生するか否か実験を行った。そして、中間転写ベルト２０の帯電領域（画像領域Ｄ）に対向している間のみバイアスを印加した場合と、常時バイアスを印加した場合との比較も行った。
前者の実験結果を図６（ａ）に、後者の実験結果を図６（ｂ）に示す。
前者の結果より、中間転写ベルト２０及びスクレーパ６１の電位差が１００Ｖ以下であればクリーニング不良の防止に効果があり、５０Ｖ以下であればクリーニング不良は発生しないことが確認された。
一方、後者の場合は、画像領域Ｄに関しては中間転写ベルト２０及びスクレーパ６１が略同電位となるものの、画像領域Ｄ以外の領域では両者の電位差が大きくなるので、クリーニング不良が発生することがわかった。
【００３９】
従って、上述したようなメカニズムで紙粉Ｐを原因とするクリーニング不良が発生していることが明らかとなったため、本実施の形態では、紙粉Ｐに電荷を帯びさせないようにすること、具体的には中間転写ベルト２０とスクレーパ６１間の電位差を著しく小さくするように構成した。
これにより、紙粉Ｐの挟み込みに伴うクリーニング不良を防止することができる。
【００４０】
尚、本実施の形態では、実験結果に基づいてスクレーパ６１に印加するバイアスを＋２００Ｖ一定にしていたが、これに限られるものではなく、例えば図７に示すように、二次転写装置４０とベルトクリーナ６０との間の中間転写ベルト２０に対向して表面電位検知センサ７１を配置し、この検知結果に基づいてスクレーパ６１に印加するバイアスを可変するようにしてもよい。
【００４１】
【発明の効果】
以上説明したように、本発明によれば、非変形クリーニング部材が像担持体の画像を担持搬送する画像領域に対向している間、非変形クリーニング部材の対向部における像担持体の表面電位と同電位を非変形クリーニング部材に印加するようにしたので、非変形クリーニング部材に付着した紙粉等の異物の帯電を防止することができ、もって、像担持体と非変形クリーニング部材との間に紙粉等の異物が挟み込まれることによって生じるクリーニング不良を防止することができる。
【図面の簡単な説明】
【図１】 本発明に係る画像形成装置の概要図である。
【図２】 本発明が適用された画像形成装置の実施の一形態の説明図である。
【図３】 二次転写装置及びベルトクリーナの拡大図である。
【図４】 二次転写バイアス及びスクレーパ印加バイアスのタイミングチャートである。
【図５】 （ａ）〜（ｅ）はクリーニング不良発生のメカニズムを示す模式図である。
【図６】 （ａ）は画像領域に対向する間のみバイアスを印加したときの実験結果、（ｂ）は常時バイアスを印加したときの実験結果を示す図表である。
【図７】 変形の形態を示す説明図である。
【符号の説明】
１…像担持体，２…転写材，３…転写手段，４…非変形クリーニング部材，５…電位設定手段，Ｇ…画像，Ｒ…残留物[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a cleaning device for cleaning an image carrier used in an image forming apparatus such as an electrophotographic copying machine or a printer, and more particularly to an improvement of a cleaning device of a type provided so as to be able to come in contact with and separate from an image carrier. .
[0002]
[Prior art]
As a conventional intermediate transfer type image forming apparatus, for example, a developing device for each color component of yellow (Y), magenta (M), cyan (C), and black (Bk) is provided around the photosensitive drum, and the photosensitive drum is used. For example, a belt-like intermediate transfer member (intermediate transfer belt) is disposed opposite to the photosensitive drum, and the toner images of the respective color components formed on the photosensitive drum for each rotation of the photosensitive drum are sequentially applied to the intermediate transfer belt. It is known that after the primary transfer, the composite primary transfer image superimposed on the intermediate transfer belt is batch-transferred (secondarily transferred) to a sheet to form a desired color image on the sheet.
[0003]
In this type of image forming apparatus, if the residual toner remaining on the intermediate transfer belt after the secondary transfer is left as it is, the next image formed on the intermediate transfer belt will be stained. A cleaning device (belt cleaner) for removing residual toner on the intermediate transfer belt after the transfer is provided.
[0004]
Such a belt cleaner is made of, for example, a cleaner housing having an opening at a portion facing the intermediate transfer belt and, for example, urethane rubber disposed at a location facing the opening of the cleaner housing. A device provided with a cleaning blade is known.
In the image forming apparatus described above, when the primary transfer of each color component toner image from the photosensitive drum to the intermediate transfer belt is performed, the cleaning blade is separated from the surface of the intermediate transfer belt, and the sheet is transferred from the intermediate transfer belt to the sheet. After the secondary transfer of the toner image to the toner image, the cleaning blade is pressed against the intermediate transfer belt.
[0005]
Incidentally, in recent years, there has been a rapid increase in demand for higher image quality for this type of image forming apparatus. As one direction toward such high image quality, a reduction in the particle size of toner used as a developer is being promoted. As a method for reducing the particle size of such toner, a number of methods for producing a toner by polymerization have been studied. According to this method, the toner can be efficiently reduced in particle size and advantageous in terms of cost. Is possible. In addition, the fluidity of the toner decreases as the particle size of the toner decreases, and image quality defects such as a lack of a part of the image pattern may occur. Therefore, the surface shape is made smooth to improve fluidity. Then, it is made into a spherical shape.
[0006]
However, when the polymerized toner having a small particle diameter manufactured in this way is used, there is a problem that the cleaning blade is easily slipped through, and as a result, the cleaning performance is deteriorated.
[0007]
Therefore, in order to solve such problems, the present applicant has previously proposed using a metal scraper as a cleaning device (see Japanese Patent Application No. 2000-278014).
[0008]
[Problems to be solved by the invention]
However, since the metal scraper is less elastic than the urethane rubber cleaning blade, when a large residue such as paper dust is sandwiched between the metal scraper and the intermediate transfer belt for some reason during pressure contact, There was a technical problem that a large gap was generated between the two, and residual toner slipped through the gap, resulting in poor cleaning.
[0009]
The present invention has been made in order to solve the above technical problem, and it has been found that a defective cleaning caused by foreign matter such as paper dust being sandwiched between an image carrier and a cleaning member such as a metal scraper. An image forming apparatus capable of preventing the above is provided.
[0010]
[Means for Solving the Problems]
That is, according to the present invention, as shown in FIG. 1, an image carrier 1 on which an image G is carried and conveyed, a transfer means 3 for electrostatically transferring the image G to a transfer material 2 by applying a transfer bias, and the image A conductive plate-like member that is disposed so as to be in contact with and away from the carrier 1 and removes the residue R on the image carrier 1, and the shape of the contact portion stops movement of the image carrier 1. a non-deformable cleaning member 4 is kept in the non-deformed state regardless, and a potential setting means 5 for setting the potential and application timing for applying said to non-deformable cleaning member 4, said potential setting means 5, the non While the deformation cleaning member 4 faces the image area for carrying and conveying the image G of the image carrier 1, the same potential as the surface potential of the image carrier 1 at the opposite portion of the non-deformation cleaning member 4 is set to the non-deformation member. Deformable cleaning member And applying to the.
[0011]
In such a technical means, the image carrier 1 may be an image carrier such as a photosensitive member or a dielectric member on which the image G is formed and carried as long as the image G is carried and conveyed. Further, it may be an intermediate transfer member on which the image G formed on the image forming carrier is intermediately supported.
The image G is composed of other charged particles as well as a toner image formed of toner as long as it can be electrostatically transferred from the image carrier 1 to the transfer material 2. May be.
Further, the transfer means 3 may be a contact transfer type or a non-contact transfer type as long as the image G is electrostatically transferred to the transfer material 2 by applying a transfer bias.
[0012]
The non-deformable cleaning member 4 can typically be a metal scraper such as SUS, but is not necessarily made of metal, and is made of non-metal such as ceramics or hard resin. There is no problem.
For the non-deformable cleaning member 4, for example, all those in which the shape of the contact portion is maintained in the non-deformed state regardless of the movement or stop of the image carrier 1 under the contact pressure condition pressed against the image carrier 1 are included. It is.
For this reason, if the non-deformable cleaning member 4 is, for example, a metal scraper, when the tip is brought into contact with the image carrier 1, the entire metal scraper is naturally elastically deformed in the plate pressure direction. Such a mode of elastic bending deformation also falls within the concept of the non-deformable cleaning member 4.
[0013]
Further, the potential setting means 5 sets the potential of the non-deformable cleaning member 4 corresponding to the surface potential of the image carrier 1 at the facing portion of the non-deformable cleaning member 4 and the image carrier 1. .
Here, the non-deformable cleaning member 4 potential, it is rather preferable to set the surface potential and the same potential of the image bearing member 1, the undeformed residue adhering to the cleaning member 4 R is the image bearing member However, in the present invention, a method of setting the same potential as the surface potential of the image carrier 1 is adopted.
[0014]
In the present invention, considering that the image carrier 1 is charged by the transfer operation of the transfer unit 3, the potential setting unit 5 has a transfer bias applied by the transfer unit 3 of the image carrier 1. A method is adopted in which a voltage is applied to the non-deformable cleaning member 4 while the applied site passes through the portion facing the non-deformable cleaning member 4 .
Here, the image carrier 1 includes an image forming carrier on which the image G is carried and conveyed, and an intermediate transfer member on which a composite image in which the image G on the image forming carrier is superimposed is carried and conveyed. In an embodiment in which the non-deformable cleaning member 4 is disposed opposite to the intermediate transfer member, the non-deformable cleaning member 4 is in pressure contact when the composite image passes through the transfer means 3, A portion of the intermediate transfer member to which a transfer bias is applied by the transfer unit 3 may be separated after passing through a portion facing the non-deformable cleaning member 4.
[0015]
Note that there is a prior art in which a voltage is applied to the cleaning blade in the image forming apparatus, but this is irrelevant to the present invention and will be supplementarily described for the sake of safety.
That is, Japanese Patent Application Laid-Open No. 8-123287 discloses a technique in which a conductive rubber blade is grounded via a direct current, an alternating current, or a bias power source in which these are superimposed.
These are for controlling the strength of the cleaning effect of the residual toner, and merely disclose a technique for improving the cleaning performance of the residual toner on the image carrier. Further, this prior art does not describe anything about the magnitude of the bias applied to the cleaning blade. Further, this prior art only describes the use of rubber blades, and therefore the technical problem of the present invention, that is, the remaining of paper dust or the like when using non-deformable cleaning members such as metal scrapers. There is no description or even suggestion that the cleaning failure occurs due to the pinching of the object.
Therefore, even if the above prior art is known, it is practically impossible to assume the features of the present invention.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, the present invention will be described in detail based on embodiments shown in the accompanying drawings.
FIG. 2 shows a schematic configuration of an embodiment of a color image forming apparatus (a color electrophotographic copying machine in the present embodiment) to which a cleaning device according to the present invention is applied.
In the figure, reference numeral 11 denotes a photosensitive drum (latent image carrier), and a charging device 12 and an exposure device 13 (exposure beam is indicated by reference symbol Bm in the figure) on the surface thereof in accordance with the rotation in the direction of arrow A. An electrostatic latent image corresponding to image information is formed by a known electrophotographic process such as the above.
Around the photosensitive drum 11, a developing unit 14 including developing units 15 to 18 corresponding to the respective colors of yellow (Y), magenta (M), cyan (C), and black (Bk) is disposed. The electrostatic latent image formed on the photosensitive drum 11 is developed by any of the developing devices to form a toner image T.
In this embodiment, the photosensitive drum 11 is configured to be negatively charged, and development is performed by a reversal development method. Therefore, all the toners used are of a negatively charged type.
[0017]
Reference numeral 20 denotes an intermediate transfer belt disposed so as to be in contact with the surface of the photosensitive drum 11, and is stretched around a plurality of (six in the present embodiment) rolls 21 to 26 and is indicated by an arrow B It is designed to rotate in the direction.
Here, in this embodiment, reference numerals 21 and 25 are driven rolls, 22 is a metal idler roll (Idler roll) used for positioning of the intermediate transfer belt 20 and formation of a flat primary transfer surface, and 23 is an intermediate. A tension roll for controlling the tension of the transfer belt 20 to be constant, 24 is a drive roll for the intermediate transfer belt 20, and 26 is a counter roll (backup roll) for secondary transfer.
[0018]
Further, in the present embodiment, as the intermediate transfer belt 20, an appropriate amount of carbon black is contained as an antistatic agent in a resin such as polyimide, polycarbonate, polyester, polypropylene, polyethylene terephthalate, acrylic, vinyl chloride, or various rubbers. The surface resistivity is 10 ¹¹ Ω / □, the volume resistivity is 10 ¹¹ Ωcm, and the thickness is 150 μm.
[0019]
Further, a primary transfer device (primary transfer roll in the present embodiment) 27 is disposed on the back side of the intermediate transfer belt 20 at a portion (primary transfer position) facing the photosensitive drum 11 of the intermediate transfer belt 20. The toner image T on the photosensitive drum 11 is transferred to the intermediate transfer belt 20 by applying a primary transfer bias to the primary transfer roll 27 with a polarity opposite to the charging polarity of the toner (positive polarity in this embodiment). Electrostatic attraction.
Reference numeral 19 denotes a drum cleaner for removing the toner remaining on the photosensitive drum 11 after the primary transfer.
[0020]
Further, a secondary transfer device 40 is disposed at the secondary transfer position of the intermediate transfer belt 20 facing the conveyance path of the sheet 30 as a transfer material. In this embodiment, the toner transfer of the intermediate transfer belt 20 is carried out. A secondary transfer roll 28 is disposed in pressure contact with the surface side, and a counter roll (backup roll) 26 that is disposed on the back side of the intermediate transfer belt 20 and forms a counter electrode of the secondary transfer roll 28.
In this embodiment, the secondary transfer roll 28 is grounded, and a secondary transfer bias having the same polarity as the toner charging polarity is stabilized on the backup roll 26 by the transfer power supply 41 (see FIG. 3). Applied.
[0021]
Further, a belt cleaner 60 for removing toner remaining on the intermediate transfer belt 20 after the secondary transfer is provided on the downstream side of the secondary transfer device 40.
The secondary transfer roll 28 and the belt cleaner 60 are disposed so as to be able to come into contact with and separate from the intermediate transfer belt 20. These are separated from the intermediate transfer belt 20 until T passes through the secondary transfer roll 28 and the belt cleaner 60. Details of the belt cleaner 60 will be described later.
[0022]
In the present embodiment, the paper transport system feeds the paper 30 from the paper tray 50 by the feed roll 51, temporarily stops the positioning by the registration roll (registration roll) 52, and then performs secondary transfer at a predetermined timing. Further, the sheet 30 is fed to the position, and the sheet 30 after the secondary transfer is guided to the conveyance belt 53 through a sheet conveyance guide (not shown), and the conveyance belt 53 leads to the fixing device 54. It is designed to be transported.
Reference numeral 29 denotes a sheet metal member disposed opposite to the belt cleaner 60 with the intermediate transfer belt 20 interposed therebetween, and reference numeral 55 denotes a paper transport guide for guiding the paper 30 to the secondary transfer device 40.
[0023]
In this embodiment, as each color component toner, styrene acrylic resin fine particles and yellow, magenta, cyan, and black pigment fine particles are aggregated and united to prepare a volume average particle diameter of about 3 to 7 μm. The toner produced by the emulsion aggregation and coalescence method (EA method) was used. The particle size distribution index (GSD) was 1.23. The average particle diameter is a value of a volume average particle diameter measured with a Coulter counter (manufactured by Coulter). Then, the heating time and the heating temperature during the polymerization were adjusted, and four types (four colors) of toners having substantially the same average particle size and particle size distribution were prepared.
The shape of the toner is represented by a shape factor ML ² / A. An enlarged photograph of the toner obtained with an optical microscope (Microphoto FXA; manufactured by Nikon Corporation) is subjected to image analysis with an image analyzer Luzex3 (manufactured by NIRECO) and the following. This is a value calculated by using Equation (1).
[0024]
[Expression 1]

[0025]
The shape factor ML ² / A is expressed as a ratio of the projected area of the toner and the area of the circle circumscribing the toner, and is 100 for a true sphere, and increases as the shape collapses. The shape factor is calculated for a plurality of toner particles, and the average value is used as a representative value. In the present embodiment, a substantially spherical toner having a shape factor of 125 or less is used.
In addition, in order to improve the releasability, an appropriate amount of inorganic fine particles such as silica and titanium oxide (titania) having an average particle diameter of 10 to 150 nm is externally added to the toner as an external additive, and ferrite toner having an average particle diameter of 35 μm is used. A developer was mixed with the carrier.
In addition to the toner prepared by this production method, a spherical toner or a non-spherical toner formed by a suspension polymerization method, a dissolution suspension method, an emulsion polymerization method, a kneading pulverization method, or the like may be used as the toner. Of course, a two-component developer in which the toner and the carrier are mixed as described above or a one-component developer containing only the toner may be used.
[0026]
In FIG. 3, the expanded sectional view of the belt cleaner 60 which concerns on this Embodiment is shown.
In the figure, a belt cleaner 60 has a scraper 61 disposed on the image carrying surface side of the intermediate transfer belt 20 and a cleaner housing 62 in which the scraper 61 is accommodated.
In the present embodiment, the scraper 61 is made of, for example, a stainless steel plate (SUS304) having a thickness of 0.15 mm. One end of the scraper 61 is fixed to a block 63, and the block 63 is attached to a holder 64 that swings about a shaft 64a.
[0027]
A spring that biases the scraper 61 toward the intermediate transfer belt 20 between a concave portion 64b provided on the lower end side of the holder 64 and a bulging portion 62a provided at a lower portion of the cleaner housing 62. 65 is attached. Further, the holder 64 is urged in a direction opposite to the urging direction of the spring 65 by a cam (not shown) so that the scraper 61 can contact and separate from the intermediate transfer belt 20. It has become.
[0028]
Reference numeral 66 denotes a film seal provided on the upstream side in the moving direction B of the intermediate transfer belt 20 as viewed from the scraper 61 to prevent the removed residue from scattering to the outside, and reference numeral 67 denotes the cleaner housing 62. It is an L-shaped plate for fixing the film seal 66. The film seal 66 moves so as to be linked to the scraper 61 and is separated from the intermediate transfer belt 20 except during the cleaning operation.
The scraper 61 is connected to a power source 42 for applying a positive voltage.
[0029]
Next, an image forming process of the color image forming apparatus according to the present embodiment will be described.
Now, when a start switch (not shown) is turned on, a predetermined image forming process is executed.
First, an electrostatic latent image is written on the photosensitive drum 11 and developed by a developing device corresponding to the electrostatic latent image.
For example, if the electrostatic latent image written on the photosensitive drum 11 corresponds to yellow image information, the electrostatic latent image is developed by the developing device 15 containing yellow toner, and is exposed to light. A yellow toner image T is formed on the body drum 11.
The toner image T formed on the photosensitive drum 11 is transferred from the photosensitive drum 11 to the surface of the intermediate transfer belt 20 at a primary transfer position where the photosensitive drum 11 and the intermediate transfer belt 20 are in contact with each other. On the other hand, the toner remaining on the photosensitive drum 11 after the primary transfer is removed by the drum cleaner 19.
[0030]
At this time, when forming a single-color image, the toner image T primarily transferred to the intermediate transfer belt 20 is immediately secondary-transferred to the paper 30. However, a color image obtained by superimposing a plurality of color toner images T is used. In the case of forming, the toner image T formation on the photosensitive drum 11 and the primary transfer process of the toner image T are repeated for the number of colors.
For example, when a full color image is formed by superimposing four color toner images, a yellow, magenta, cyan, and black toner image T is formed on the photosensitive drum 11 for each rotation. T is sequentially primary-transferred onto the intermediate transfer belt 20. On the other hand, the intermediate transfer belt 20 is rotated at the same cycle as that of the photosensitive drum 11 while holding the toner image T that has been primarily transferred first, and magenta, cyan, and black are transferred on the intermediate transfer belt 20 for each rotation. The toner image T is transferred.
[0031]
The toner image T primarily transferred to the intermediate transfer belt 20 in this way is conveyed to the secondary transfer position as the intermediate transfer belt 20 rotates.
On the other hand, the sheet 30 is supplied to the secondary transfer position by the registration roll 52 at a predetermined timing, and the secondary transfer roll 28 nips the sheet 30 with respect to the backup roll 26.
Then, at the secondary transfer position, the toner image T carried on the intermediate transfer belt 20 is secondly transferred by the action of a transfer electric field formed between the secondary transfer roll 28 and the backup roll 26 which are the secondary transfer device 40. It is electrostatically transferred to the paper 30 at the next transfer position. Thereafter, the sheet 30 that has been secondarily transferred is conveyed to the fixing device 54 via the conveyance belt 53 and the toner image T on the sheet 30 is fixed, while the image of the intermediate transfer belt 20 that has passed the secondary transfer position. The carrying surface side is cleaned by the belt cleaner 60.
[0032]
Here, the secondary transfer process by the secondary transfer device 40 and the cleaning process of the intermediate transfer belt 20 by the belt cleaner 60 are as follows. FIG. 4 shows a timing chart of the secondary transfer bias and the scraper application bias.
3 and 4, while the image region D (region where the toner image T is formed) on the intermediate transfer belt 20 passes through the secondary transfer device 40, the backup roll 26 receives a transfer power supply 41 of −2 kV, for example. A transfer bias is applied, and the toner image T on the intermediate transfer belt 20 is transferred to the paper 30. When the leading end of the image area D passes through the secondary transfer device 40, the scraper 61 and the film seal 66 are pressed against the intermediate transfer belt 20 correspondingly.
[0033]
A bias of +200 V is applied to the scraper 61 by the power source 42 while the image area D passes through the portion facing the scraper 61. In the present embodiment, the distance between the nip portion of the secondary transfer device 40 and the contact portions of the intermediate transfer belt 20 and the scraper 61 is 70 mm, and the speed of the intermediate transfer belt 20 is 220 mm / second as described above. Since s, the application of the secondary transfer bias is delayed by T1 = 70 mm / 220 mm / s = 318 ms from the application stop timing.
During this time, the residue R (residual toner after transfer, paper dust transferred from the paper 30) adhering to the image area D of the intermediate transfer belt 20 is scraped off and cleaned by the scraper 61.
[0034]
Then, when the image area D passes through the portion facing the scraper 61, the scraper 61 and the film seal 66 are separated from the intermediate transfer belt 20, and the series of processes is completed.
[0035]
In the present embodiment, the bias as described above is applied to the scraper 61 for the following reason.
The present inventor conducted the following experiment in order to investigate the cause of the cleaning failure that occurs when the metal scraper 61 is used.
First, a surface potential meter probe was installed near the tip of the scraper 61 and the surface potential of the intermediate transfer belt 20 was measured.
As a result, the intermediate transfer belt 20 is delayed from the nip portion of the secondary transfer device 40 to the portion facing the scraper 61 with a delay of about 1/10 of the secondary transfer bias from the application start time of the secondary transfer bias. A surface potential of magnitude was measured. Since the secondary transfer bias is set to −2 kV under a normal environment, a surface potential of +200 V was measured after about 320 ms in this experiment. Even after the application of the secondary transfer bias was stopped, the surface potential changed from +200 V to 0 V with the same time delay. This is because the intermediate transfer belt 20 is made of a so-called semiconductive material, but is charged by the secondary transfer bias, and reaches the portion facing the scraper 61 with the charge remaining to some extent. Was suggested.
[0036]
Next, the behavior of the paper dust accumulated at the tip of the scraper 61 was observed. When shifting from the state where the tip of the scraper 61 is in contact with the intermediate transfer belt 20 to a state where the scraper 61 is separated, the paper dust is held at the tip of the metal scraper 61, but conversely, the paper when shifting from a state where the scraper 61 is in contact to the state The powders behaved differently with and without secondary transfer bias.
That is, when the secondary transfer bias is applied, the paper dust at the tip of the scraper 61 falls to the intermediate transfer belt 20 side and is sandwiched between the scraper 61 and the intermediate transfer belt 20. On the other hand, when the secondary transfer bias was not applied, the paper powder did not fall as described above, and no pinching was observed.
[0037]
From the above observation results, the present inventor estimated the occurrence mechanism of cleaning failure due to paper dust as follows. This will be described with reference to schematic diagrams shown in FIGS. In the figure, the symbol P indicates paper dust.
(A) As shown in FIGS. 2 and 3, the paper dust P generated when the paper 30 is rubbed against a transport roll (for example, the feed roll 51 and the resist roll 52) is transferred from the paper 30 to the intermediate transfer belt. Then, it is scraped off by the scraper 61 and deposited on the tip thereof.
(B) The intermediate transfer belt 20 (charged charge is indicated by “+” in the figure) charged by the application of the secondary transfer bias reaches the portion facing the scraper 61, and the accumulated paper dust P is charged (negative polarity). Take on.
(C) The scraper 61 once separates from the intermediate transfer belt 20 upon completion of cleaning.
(D) Immediately before the scraper 61 comes into contact with the intermediate transfer belt 20 again to start the next cleaning, the charged paper dust P is electrostatically attracted to the intermediate transfer belt, and the paper dust P is transferred to the intermediate transfer belt. It falls to the 20 side.
(E) The fallen paper powder P is sandwiched between the scraper 61 and the intermediate transfer belt 20, and a gap is generated between the scraper 61 and the belt, resulting in poor cleaning.
[0038]
Next, the present inventor applied biases of various sizes to the scraper 61 and conducted an experiment to determine whether or not a cleaning failure occurred. A comparison was also made between the case where the bias was applied only while facing the charging area (image area D) of the intermediate transfer belt 20 and the case where the bias was always applied.
The former experimental result is shown in FIG. 6 (a), and the latter experimental result is shown in FIG. 6 (b).
From the former results, it was confirmed that if the potential difference between the intermediate transfer belt 20 and the scraper 61 is 100 V or less, it is effective in preventing cleaning failure, and if it is 50 V or less, no cleaning failure occurs.
On the other hand, in the latter case, regarding the image area D, the intermediate transfer belt 20 and the scraper 61 have substantially the same potential, but the potential difference between the two becomes large in the area other than the image area D, and it is understood that a cleaning failure occurs. It was.
[0039]
Therefore, since it became clear that the cleaning failure caused by the paper dust P occurs due to the mechanism as described above, in the present embodiment, it is possible to prevent the paper dust P from being charged. In the configuration, the potential difference between the intermediate transfer belt 20 and the scraper 61 is remarkably reduced.
As a result, it is possible to prevent a cleaning failure associated with the paper powder P being caught.
[0040]
In the present embodiment, the bias applied to the scraper 61 is fixed at +200 V based on the experimental results. However, the present invention is not limited to this. For example, as shown in FIG. A surface potential detection sensor 71 may be disposed opposite the intermediate transfer belt 20 between the cleaner 60 and the bias applied to the scraper 61 based on the detection result.
[0041]
【The invention's effect】
As described above, according to the present invention, while the non-deformable cleaning member faces the image area for carrying and conveying the image on the image carrier, the surface potential of the image carrier at the facing portion of the non-deformable cleaning member Since the same potential is applied to the non-deformable cleaning member, it is possible to prevent charging of foreign matters such as paper dust adhering to the non-deformable cleaning member, and thus, between the image carrier and the non-deformable cleaning member. It is possible to prevent a cleaning failure caused by foreign matter such as paper dust being caught.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of an image forming apparatus according to the present invention.
FIG. 2 is an explanatory diagram of an embodiment of an image forming apparatus to which the present invention is applied.
FIG. 3 is an enlarged view of a secondary transfer device and a belt cleaner.
FIG. 4 is a timing chart of a secondary transfer bias and a scraper application bias.
FIGS. 5A to 5E are schematic views showing a mechanism of occurrence of defective cleaning.
6A is a chart showing experimental results when a bias is applied only while facing an image region, and FIG. 6B is a chart showing experimental results when a bias is always applied.
FIG. 7 is an explanatory view showing a modified embodiment.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Transfer material, 3 ... Transfer means, 4 ... Non-deformable cleaning member, 5 ... Potential setting means, G ... Image, R ... Residue

Claims (2)

An image carrier on which an image is carried and conveyed;
A transfer means for electrostatically transferring the image to a transfer material by applying a transfer bias;
A conductive plate-like member that is disposed so as to be in contact with and away from the image carrier and removes residues on the image carrier, and the shape of the contact portion is irrespective of the stoppage of movement of the image carrier. A non-deformable cleaning member that is maintained in an undeformed state;
A potential setting means for setting a potential applied to the non-deformable cleaning member and a timing for applying the potential.
The potential setting means has the same potential as the surface potential of the image carrier at the facing portion of the non-deformable cleaning member while the non-deformable cleaning member faces the image area for carrying and conveying the image of the image carrier. Is applied to the non-deformable cleaning member. The image forming apparatus according to claim 1 .
The image carrier includes an image forming carrier on which an image is carried and conveyed, and an intermediate transfer member on which a composite image in which images on the image forming carrier are superimposed is carried, and the non-deformable cleaning member includes It is arranged opposite to the intermediate transfer member,
The non-deformable cleaning member is brought into pressure contact when the composite image passes through the transfer unit, and a portion of the intermediate transfer body to which a transfer bias is applied by the transfer unit forms a portion facing the non-deformable cleaning member. An image forming apparatus that separates after passing.

Images