JP3652331B2 - Image forming apparatus - Google Patents

Description

〔比較例１〕
比較例１は、帯電部材として帯電ローラを用い、該帯電ローラを感光体に従動する構成とした。また現像剤４ｄに帯電促進粒子ｍを配合しない構成とした。即ち帯電促進粒子ｍを用いない装置である。
【０１２２】
〔比較例２〕
比較例２は、比較例１の構成において、予め帯電促進粒子を塗布した帯電ローラを用いた。
【０１２３】
〔評 価〕
各々の例において帯電性の評価は印刷速度の異なる画像記録装置を用いゴースト画像の優劣で評価した。
【０１２４】
本例は反転現像系で行っているので、ここで意味するゴーストとは、感光体の１周目において画像露光した部分（トナー画像部である）が、感光体２周目で帯電不足を起こすため、感光体上の前回の画像パターンのところがより強く現像され、ゴースト画像が発生することを言う。
【０１２５】
ここでは、その画像評価を以下の基準で行った。
【０１２６】
×：ベタ黒後の白地部においてゴーストが見られる。
【０１２７】
○：ベタ黒後の白地部においてゴーストが見られないが、中間調部において若干ゴーストパターンが見られる。
【０１２８】
◎：ベタ黒後の白地部及び中間調部の何れにおいてゴーストが見られない。
【０１２９】
また、評価は印字初期と１０００枚（Ａ４縦方向）の印字を行った後に行った。表中のスラッシュ線（斜線）上段は初期、下段は印字後の評価結果を表わしている。
【０１３０】
表から明らかなように、比較例１では初期において既に、何れの速度でも帯電性を満足することがなかった。つまり、これは帯電部材（帯電ローラ）が感光体に充分接触できないため直接帯電が不可能であることを表わしている。
【０１３１】
また、比較例２は、帯電促進粒子を塗布した初期はゴーストは見られないが、印字を続けると急速に帯電ローラの汚れが進むと同時に、帯電促進粒子が脱落し画像は大幅に劣化した。
【０１３２】
実施形態例１では、現像剤４ｄに帯電促進粒子ｍを混合し感光体を経由し該粒子を帯電部材へ安定して供給することが可能であるため、感光体に対し充分な接触性が得られ帯電性を満足し、かつそれを維持することができる。更に、感光ドラムと帯電部材の速度をともに増加した場合にも良好な帯電性を示すが、帯電部材の速度が低下すると若干の帯電不足が生じる。従って、帯電部材と感光体は速度差を設けた方がより効率良く帯電が行うことができる。
【０１３３】
また、実施形態例２においては、感光体表層の抵抗を静電潜像を維持できる範囲で低めに設定することにより、接触状態としては同じであってもより効率良く電荷の授受を行える。それは、よりプロセスが高速で実行される場合に効果があり、表中の感光体速度が１００ｍｍ／ｓｅｃ、帯電部材速度５０ｍｍ／ｓｅｃの評価を満足できることから明確である。
【０１３４】
〈その他〉
１）接触帯電部材としての帯電ローラ２は実施形態例の帯電ローラに限られるものではない。
【０１３５】
また可撓性の接触帯電部材は弾性帯電ローラの他に、ファーブラシ、フェルト、布などの材質・形状のものも使用可能である。また、これらを積層し、より適切な弾性と導電性を得ることも可能である。
【０１３６】
２）接触帯電部材２や現像スリーブ４ａに対する印加帯電バイアスあるいは印加現像バイアスは直流電圧に交番電圧（交流電圧）を重畳してもよい。
【０１３７】
交番電圧の波形としては、正弦波、矩形波、三角波等適宜使用可能である。また、直流電源を周期的にオン／オフすることによって形成された矩形波であっても良い。このように交番電圧の波形としては周期的にその電圧値が変化するようなバイアスが使用できる。
【０１３８】
３）静電潜像形成のための画像露光手段としては、実施形態例の様にディジタル的な潜像を形成するレーザー走査露光手段に限定されるものではなく、通常のアナログ的な画像露光やＬＥＤなどの他の発光素子でも構わないし、蛍光燈等の発光素子と液晶シャッター等の組み合わせによるものなど、画像情報に対応した静電潜像を形成できるものであるなら構わない。
【０１３９】
像担持体は静電記録誘電体等であっても良い。この場合は、該誘電体面を所定の極性・電位に一様に一次帯電した後、除電針ヘッド、電子銃等の除電手段で選択的に除電して目的の静電潜像を書き込み形成する。
【０１４０】
４）現像手段４は実施形態例では一成分磁性トナーによる現像装置を例に説明したが現像装置構成について特に限定するものではない。
【０１４１】
５）像担持体からトナー画像の転写を受ける記録媒体は転写ドラム等の中間転写体であってもよい。
【０１４２】
６）トナー粒度の測定方法の１例を述べる。測定装置としては、コールターカウンターＴＡ−２型（コールター社製）を用い、個数平均分布、体積平均分布を出力するインターフェイス（日科機製）及びＣＸ−１パーソナルコンピュータ（キヤノン製）を接続し、電解液は一級塩化ナトリウムを用いて１％ＮａＣｌ水溶液を調製する。
【０１４３】
測定法としては、前記電解水溶液１００〜１５０ｍｌ中に分散剤として界面活性剤、好ましくは、アルキルベンゼンスルホン酸塩０．１〜５ｍｌ加え、更に測定試料を０．５〜５０ｍｇ加える。
【０１４４】
試料を懸濁した電解液は、超音波分散器で約１〜３分間分散処理を行い、前記コールターカウンターＴＡ−２型により、アパーチャーとして１００μアパーチャーを用いて２〜４０μｍの粒子の粒度分布を測定して、体積平均分布を求める。これらの求めた体積平均分布より体積平均粒径を得る。
【０１４５】
【発明の効果】
以上述べたように本発明は、接触帯電方式、転写方式、トナーリサイクルプロセス（クリーナーレスシステム）の画像形成装置において、接触帯電部材として帯電ローラやファーブラシ等の簡易な部材を用い、現像手段の現像剤に帯電促進粒子を混合することで、トナーをリサイクルすると同時に接触帯電部材の像担持体への接触密度の向上を図り直接注入帯電を長期に渡り維持することを可能にした。本構成では、絶縁体であるところのトナーが接触帯電部材に混入した場合においても、同時に導電性粒子である帯電促進粒子を安定して供給することにより接触帯電部材と像担持体間に介在させて接触帯電部材の像担持体への接触性を向上させることで直接注入帯電を持続することができた。
【０１４６】
また、像担持体と接触帯電部材は速度差をもって接触させる。より好ましくは逆方向に移動するよう回転させて帯電することにより、像担持体と接触帯電部材の接触性と接触機会を一層増加させるとともに、転写残トナーの影響を抑え良好な帯電を維持することが可能である。
【０１４７】
さらに、像担持体表面の抵抗を調節することで、更に高速帯電にも適した帯電装置を構成することが可能になった。高速の記録装置においては、部材の長寿命が要求されるため帯電部材の速度を下げて、感光体など各部材の削れを低減することが望ましい。その意味では、像担持体の表層の抵抗調整をすることにより帯電効率を向上することで、帯電部材が低速度で駆動されているときも十分な帯電性能を得て、それを長期に渡り維持することが可能になった。
【０１４８】
このように本発明は、接触帯電方式、転写方式、トナーリサイクルプロセスの画像形成装置において、接触帯電部材として帯電ローラやファーブラシ等の簡易な部材を用いて、しかも該接触帯電部材の転写残トナーによる汚染にかかわらず、低印加電圧でオゾンレスの直接注入帯電を長期に渡り安定に維持させて実現する、即ち帯電ローラやファーブラシ等の接触帯電部材を用いた簡易な構成で、直接注入帯電と、トナーリサイクルプロセスを実現することができ初期の目的がよく達成された。
【図面の簡単な説明】
【図１】実施形態例１における画像形成装置の概略構成図
【図２】実施形態例２における、表面に電荷注入層を設けた感光体の層構成模型図
【図３】帯電特性グラフ
【符号の説明】
１ 感光体（像担持体、被帯電体）
２ 帯電ローラ（接触帯電部材）
３ レーザービームスキャナ（露光器）
４ 現像装置
４ａ 現像スリーブ
４ｄ 現像剤（トナーｔ＋帯電促進粒子ｍ）
５ 転写ローラ
６ 定着装置
Ｐ 転写材[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming method and an image forming apparatus such as a copying machine or a printer.
[0002]
More specifically, the present invention relates to an image forming apparatus using a contact charging method, a transfer method, and a toner recycling process.
[0003]
[Prior art]
Conventionally, for example, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an image bearing member such as an electrophotographic photosensitive member or an electrostatic recording dielectric is uniformly charged to a required polarity and potential (also a charge eliminating process). A corona charger (corona discharger) has often been used as a charging device.
[0004]
The corona charger is a non-contact type charging device, and includes a discharge electrode such as a wire electrode and a shield electrode surrounding the discharge electrode, and is disposed in a non-contact manner with the discharge opening facing the image carrier that is a charged body. The image carrier surface is charged to a predetermined level by exposing the image carrier surface to a discharge current (corona shower) generated by applying a high voltage to the discharge electrode and the shield electrode.
[0005]
Recently, in medium and low speed image forming apparatuses, contact charging devices have advantages such as low ozone and low power compared to corona chargers as charging devices for charged objects such as image carriers. Have been proposed and put to practical use.
[0006]
The contact charging device contacts a charged object such as an image carrier with a conductive charging member (contact charging member / contact charger) such as a roller type (charging roller), a fur brush type, a magnetic brush type, or a blade type. Then, a predetermined charging bias is applied to the contact charging member to charge the charged body surface to a predetermined polarity and potential.
[0007]
There are two types of contact charging mechanisms (charging mechanism, charging principle): (1) discharge charging mechanism and (2) direct injection charging mechanism, depending on which is dominant. The characteristic of appears.
[0008]
(1). Discharge charging mechanism
This is a mechanism for charging the surface of the member to be charged by a discharge phenomenon that occurs in a minute gap between the contact charging member and the member to be charged.
[0009]
Since the discharge charging mechanism has a constant discharge threshold value for the contact charging member and the member to be charged, it is necessary to apply a voltage larger than the charging potential to the contact charging member. Further, although the generation amount is remarkably smaller than that of the corona charger, it is unavoidable that a discharge product is generated in principle, and thus harmful effects due to active ions such as ozone are unavoidable.
[0010]
(2). Direct injection charging mechanism
In this system, the surface of the charged body is charged by directly injecting the charge from the contact charging member to the charged body. It is also called direct charging, injection charging, or charge injection charging. More specifically, a medium-resistance contact charging member comes into contact with the surface of the member to be charged, and charge is directly injected into the surface of the member to be charged without going through a discharge phenomenon, that is, basically using no discharge. Therefore, even if the applied voltage to the contact charging member is an applied voltage that is equal to or lower than the discharge threshold, the object to be charged can be charged to a potential corresponding to the applied voltage.
[0011]
Since this charging system is not accompanied by the generation of ions, there is no adverse effect caused by the discharge products. However, since direct injection charging is used, the contact property of the contact charging member to the member to be charged greatly affects the charging property. Therefore, the contact charging member needs to be configured more densely, have a large speed difference from the object to be charged, and must be configured to contact the object to be charged more frequently.
[0012]
A) Roller charging
In the contact charging device, a roller charging method using a conductive roller (charging roller) as a contact charging member is preferable in terms of charging stability and is widely used.
[0013]
The roller charging is mainly performed by the discharge charging mechanism (1).
[0014]
The charging roller is made of a conductive or medium resistance rubber material or foam. In addition, there are those obtained by laminating these to obtain desired characteristics.
[0015]
The charging roller has elasticity in order to obtain a certain contact state with a member to be charged (hereinafter referred to as a photosensitive member), but has a large frictional resistance, and is often driven by the photosensitive member or at a slight speed. Driven with a difference. Therefore, even if direct injection charging is attempted, a decrease in absolute charging ability, lack of contactability, roller-shaped unevenness, and charging unevenness due to adhering material on the photosensitive member cannot be avoided. The charging mechanism is dominant.
[0016]
FIG. 3 is a graph showing an example of charging efficiency in contact charging. The horizontal axis represents the bias applied to the contact charging member, and the vertical axis represents the photosensitive member charging potential obtained at that time. The charging characteristic in the case of roller charging is represented by A. That is, charging starts after the discharge threshold of about −500V. Therefore, when charging to -500 V, apply a DC voltage of -1000 V, or in addition to a charging voltage of -500 V DC, apply an AC voltage with a peak-to-peak voltage of 1200 V so as to always have a potential difference greater than the discharge threshold. Thus, a method of converging the photoreceptor potential to the charging potential is common.
[0017]
More specifically, when the charging roller is brought into pressure contact with an OPC photoconductor having a thickness of 25 μm, the surface potential of the photoconductor starts to rise when a voltage of about 640 V or more is applied. Thereafter, the photosensitive member surface potential increases linearly with a slope of 1 with respect to the applied voltage. This threshold voltage is defined as the charging start voltage Vth.
[0018]
That is, in order to obtain the photoreceptor surface potential Vd required for electrophotography, the charging roller requires a DC voltage higher than that required, that is, Vd + Vth. A method of charging by applying only the DC voltage to the contact charging member in this way is referred to as a “DC charging method”.
[0019]
However, in DC charging, the resistance value of the contact charging member fluctuates due to environmental fluctuations, and Vth fluctuates when the film thickness changes due to the photoconductor being scraped. It was difficult.
[0020]
Therefore, an AC component having a peak-to-peak voltage of 2 × Vth or more is added to a DC voltage corresponding to a desired Vd, as disclosed in Japanese Patent Laid-Open No. 63-149669, in order to further uniform charge. An “AC charging method” is used in which the superimposed voltage is applied to the contact charging member. This is for the purpose of smoothing the potential due to AC, and the potential of the charged body converges to Vd, which is the center of the peak of the AC voltage, and is not affected by disturbances such as the environment.
[0021]
However, even in such a contact charging device, the essential charging mechanism uses a discharge phenomenon from the contact charging member to the photosensitive member, so that the voltage applied to the contact charging member is photosensitive as described above. A value higher than the body surface potential is required, and a trace amount of ozone is generated.
[0022]
Further, when AC charging is performed for uniform charging, further generation of ozone, generation of vibration noise (AC charging sound) between the contact charging member and the photosensitive member due to an AC voltage electric field, and surface of the photosensitive member due to discharge As a result, the deterioration and the like became remarkable, which was a new problem.
[0023]
B) Fur brush charging
Fur brush charging uses a member (fur brush charger) having a conductive fiber brush portion as a contact charging member, and the conductive fiber brush portion is brought into contact with a photosensitive member as a member to be charged, and a predetermined charging bias is applied. This is applied to charge the photoreceptor surface to a predetermined polarity and potential.
[0024]
The charge charging mechanism of the fur brush charging is dominated by the discharge charging mechanism (1).
[0025]
Fur brush chargers are available in fixed and roll types. A fixed type is a medium-resistance fiber folded into a base fabric and bonded to an electrode. The roll type is formed by winding a pile around a metal core. The fiber density is 100 / mm ² However, the contact is still insufficient to achieve sufficiently uniform charging by direct injection charging. As a configuration, it is necessary to have a speed difference that is difficult, which is not realistic.
[0026]
The charging characteristics of the fur brush charged when a DC voltage is applied are the characteristics shown in FIG. Accordingly, in the case of fur brush charging, both the fixed type and the roll type are charged using a discharge phenomenon by applying a high charging bias.
[0027]
C) Magnetic brush charging
Magnetic brush charging uses a member (magnetic brush charger) having a magnetic brush portion formed in a brush shape by magnetically constraining conductive magnetic particles with a magnet roll or the like as a contact charging member, and the magnetic brush portion is to be charged. And a predetermined charging bias is applied to charge the surface of the photosensitive member to a predetermined polarity and potential.
[0028]
In the case of this magnetic brush charging, the direct injection charging mechanism (2) is dominant as the charging mechanism.
[0029]
By using conductive magnetic particles constituting the magnetic brush portion having a particle diameter of 5 to 50 μm and providing a sufficient speed difference from the photoreceptor, uniform direct injection charging is possible.
[0030]
As indicated by C in the charging characteristic graph of FIG. 3, it is possible to obtain a charging potential substantially proportional to the applied bias.
[0031]
However, there are other disadvantages such as a complicated apparatus configuration and conductive magnetic particles constituting the magnetic brush portion falling off and adhering to the photoreceptor.
[0032]
Japanese Patent Laid-Open No. 6-3921 proposes a method of injecting charges into a charge holding member such as a trap level on the surface of a photoreceptor or a conductive particle of a charge injection layer to perform contact injection charging. Since the discharge phenomenon is not used, the voltage required for charging is only the desired photoreceptor surface potential, and ozone is not generated. Furthermore, since no AC voltage is applied, no charging noise is generated, and this is an excellent charging system that is ozone-free and has low power compared to the roller charging system.
[0033]
D) Toner recycling process (cleanerless system)
In the transfer type image forming apparatus, the transfer residual toner remaining on the photoconductor (image carrier) after the transfer is removed from the photoconductor surface by a cleaner (cleaning device) and becomes waste toner. It is desirable not to come out from the aspect. Therefore, the image forming apparatus of the toner recycling process is configured such that the cleaner is eliminated, and the transfer residual toner on the photosensitive member after transfer is removed from the photosensitive member by “development simultaneous cleaning” by the developing device and collected and reused in the developing device. Has also appeared.
[0034]
Simultaneous development cleaning refers to the toner remaining on the photoconductor after the transfer, during the subsequent development, that is, the photoconductor is subsequently charged and exposed to form a latent image, and a fog removal bias ( This is a method of recovery by a fog removal potential difference Vback, which is a potential difference between the DC voltage applied to the developing device and the surface potential of the photoreceptor. According to this method, since the transfer residual toner is collected by the developing device and reused after the next step, waste toner can be eliminated, and troublesome maintenance can be reduced. Further, the cleaner-less has a great space advantage, and the image forming apparatus can be greatly downsized.
[0035]
E) Powder application to contact charging member
Japanese Patent Publication No. 7-99442 discloses a configuration in which powder is applied to a contact surface of a contact charging member with a surface of an object to be charged in order to prevent uneven charging and perform stable uniform charging. Although the contact charging member (charging roller) is driven to rotate (without speed difference driving), the generation of ozone products is much less than that of corona chargers such as Scorotron. The charging principle is mainly based on the discharge charging mechanism as in the case of the roller charging described above. In particular, in order to obtain more stable charging uniformity, a voltage obtained by superimposing an AC voltage on a DC voltage is applied, and therefore, more ozone products are generated due to discharge. Therefore, when the apparatus is used for a long time or when the cleaner-less image forming apparatus is used for a long time, adverse effects such as image flow due to ozone products tend to appear.
[0036]
Japanese Patent Application Laid-Open No. 5-150539 discloses that in an image forming method using contact charging, charging inhibition due to toner particles and silica fine particles adhering to the surface of the charging means during repeated image formation for a long time is prevented. Therefore, it is disclosed that the developer contains at least visible particles and conductive particles having an average particle size smaller than the visible particles. However, this contact charging is based on the discharge charging mechanism, not the direct injection charging mechanism, and has the above-described problems due to discharge charging.
[0037]
[Problems to be solved by the invention]
1) As described in the section of the prior art, in the contact charging, the surface of the contact charging member is rough for direct injection charging with a simple configuration using a charging roller or a fur brush as the contact charging member. Thus, intimate contact with the image bearing member as the charged member is not ensured, and direct injection charging is impossible.
[0038]
Therefore, in contact charging, even when a simple member such as a charging roller or a fur brush is used as a contact charging member, direct injection charging that is more excellent in charging uniformity and stable over a long period of time is realized. Therefore, it is expected to realize ozone-less direct injection charging with a simple configuration.
[0039]
2) Further, in the image forming apparatus of the toner recycling process, when a contact charging device is adopted as a charging means for the image carrier, a cleaner that removes residual transfer residual toner on the surface of the image carrier after transfer is not used. The residual toner remaining on the surface of the image carrier after the transfer is carried as it is by the movement of the image carrier surface to the charging portion which is the contact portion between the image carrier and the contact charging member, and the contact charging member is contaminated with toner. The direct injection charging from the contact charging member to the image bearing member is also inhibited. In addition, when charging failure occurs, toner mixture into the contact charger further increases, and charging failure is intensified.
[0040]
Accordingly, the present invention provides a contact charging method, a transfer method, and a toner recycling process (cleanerless system) image forming apparatus using a simple member such as a charging roller or a fur brush as the contact charging member. Regardless of contamination due to transfer residual toner, ozone-less direct injection charging is stably maintained over a long period of time with a low applied voltage, that is, with a simple configuration using a contact charging member such as a charging roller or a fur brush. The purpose is to realize injection charging and toner recycling process.
[0041]
[Means for Solving the Problems]
The present invention is an image forming apparatus having the following configuration.
[0042]
(1) Photoconductor When, The photoreceptor Charging means for charging Exposure means for exposing the photoconductor to form an electrostatic latent image on the photoconductor, and the photoconductor Formed in Said A developing unit that visualizes the electrostatic latent image as a toner image with toner, and a transfer unit that transfers the toner image to a recording medium; after the developing unit transfers the toner image to the recording medium; Photoconductor In the image forming apparatus capable of collecting the toner remaining on the top,
The charging means is a charging member to which a voltage is applied, The photoreceptor And a flexible charging member that forms a nip portion, Said In advance on the surface of the charging member Non-magnetic Loading conductive particles in the nip Non-magnetic Interposing conductive particles,
The developer of the developing means is toner and Non-magnetic Containing conductive particles, Non-magnetic Conductive particles from the developing means The photoreceptor An image forming apparatus, wherein the image forming apparatus is supplied to the nip portion.
[0043]
(2) The surface of the charging member is Non-magnetic With conductive particles Photoconductor The image forming apparatus according to (1), wherein the image forming apparatus moves with a speed difference with respect to the surface of the photosensitive member so as to rub the surface.
[0044]
(3) The above Non-magnetic Conductive particles have a resistance of 10 ¹² The image forming apparatus according to (1) or (2), wherein the image forming apparatus has an Ω · cm or less and a particle size of 50 μm or less.
[0045]
(4) The above Non-magnetic Conductive particles have a resistance of 10 ¹⁰ The image forming apparatus according to claim 1, wherein the image forming apparatus has an Ω · cm or less and a particle size of 50 μm or less.
[0046]
(5) The charging member and the Photoconductor The image forming apparatus according to any one of (1) to (4), wherein the nip portions move in opposite directions to each other at the nip portion.
[0047]
(6) The image forming apparatus according to any one of (1) to (5), wherein the charging member is an elastic conductive roller.
[0048]
(7) The image forming apparatus according to any one of (1) to (6), wherein the charging member includes a foam on a surface thereof.
[0049]
(8) The charging member is disposed in the nip portion. Non-magnetic The image forming apparatus according to any one of (1) to (7), wherein the conductive particles are carried and conveyed.
[0050]
(9) The above Photoconductor The volume resistance of the outermost surface layer is 1 × 10 ⁹ (Ω · cm) or more 1 × 10 ¹⁴ The image forming apparatus according to any one of (1) to (8), wherein the image forming apparatus is (Ω · cm) or less.
[0053]
(10) The developing means simultaneously develops the electrostatic latent image on the photoreceptor with toner. Photoconductor The toner remaining in the toner can be collected. (9) The image forming apparatus according to any one of the above.
[0054]
<Operation>
a) Conductive charge accelerating particles contained in the developer of the developing means (Nonmagnetic conductive particles) Is an image carrier by the developing means. (Photoconductor) When the toner of the side electrostatic latent image is developed, an appropriate amount is transferred to the image carrier side together with the toner.
[0055]
The toner image on the image carrier is attracted and actively transferred to the recording medium side due to the effect of the transfer bias in the transfer unit. Does not actively transfer and remains substantially adhered and held on the image carrier.
[0056]
Since the image forming apparatus of the toner recycling process does not use a cleaner, the transfer residual toner remaining on the surface of the image carrier after transfer and the above-described residual charge accelerating particles are placed on the nip portion between the image carrier and the contact charging member. It is carried as it is by moving and adheres to and mixes with the contact charging member.
[0057]
Therefore, contact charging of the image carrier is performed in a state where the charge accelerating particles are present in the nip portion between the image carrier and the contact charging member.
[0058]
Due to the presence of the charge accelerating particles, even when toner adheres to or mixes with the contact charging member, the contact charging member can maintain a close contact property and contact resistance with the image carrier. It is a simple member such as a brush, and it is possible to perform direct injection charging of the image carrier with the contact charging member regardless of contamination of the contact charging member with residual toner.
[0059]
That is, the contact charging member comes into close contact with the image carrier via the charge accelerating particles, and the charge accelerating particles existing in the nip portion between the contact charging member and the image carrier rub against the surface of the image carrier without gaps. Therefore, the charging of the image carrier by the contact charging member is dominated by stable and safe direct injection charging that does not use the discharge phenomenon due to the presence of the charge accelerating particles, and high charging efficiency not obtained by conventional roller charging or the like is obtained. Thus, a potential substantially equal to the voltage applied to the contact charging member can be applied to the image carrier.
[0060]
Further, the transfer residual toner adhering to and mixed in the contact charging member is gradually discharged from the contact charging member onto the image carrier, reaches the developing unit along with the movement of the image carrier surface, and is simultaneously cleaned (collected) by the developing means (development). Toner recycling process).
[0061]
Even if the charge accelerating particles fall off from the contact charging member, the image forming apparatus is operated so that the charge accelerating particles contained in the developer of the developing means are transferred to the surface of the image carrier at the developing portion. As the surface moves, it is carried to the charging unit via the transfer unit and continuously supplied to the contact charging member, so that good chargeability due to the presence of the charge accelerating particles is stably maintained.
[0062]
Thus, in an image forming apparatus using a contact charging method, a transfer method, or a toner recycling process, a simple member such as a charging roller or a fur brush is used as a contact charging member, and regardless of contamination of the contact charging member due to transfer residual toner. , Ozone-less direct injection charging can be stably maintained over a long period of time with a low applied voltage, uniform chargeability can be given, and there is no obstruction due to ozone products, no obstruction due to poor charging, etc., A low-cost image forming apparatus can be obtained.
[0063]
b) By interposing the charge accelerating particles in the nip portion between the contact charging member and the image carrier, the effect of lubrication (friction reducing effect) of the charge accelerating particles is easily achieved between the contact charging member and the image carrier. Thus, it is possible to provide a speed difference.
[0064]
By providing a speed difference between the contact charging member and the image carrier, the chance of the charge accelerating particles contacting the image carrier at the nip portion between the contact charging member and the image carrier is greatly increased, and high contactability is achieved. Which can be easily obtained and allows direct injection charging.
[0065]
As a configuration for providing the speed difference, the contact charging member is rotationally driven to provide a speed difference between the image carrier and the contact charging member. Preferably, in order to temporarily collect and level the transfer residual toner on the image carrier carried by the charging unit on the contact charging member, the contact charging member is driven to rotate. It is desirable to configure to rotate in the direction opposite to the moving direction. That is, it is possible to perform direct injection charging preferentially by once separating the transfer residual toner on the image carrier by reverse rotation and performing charging.
[0066]
Although it is possible to move the charging member in the same direction as the moving direction of the image carrier surface to give a speed difference, the charging property of direct injection charging is the ratio of the peripheral speed of the image carrier to the peripheral speed of the charging member. Therefore, in order to obtain the same peripheral speed ratio as in the reverse direction, the rotation speed of the charging member is larger in the forward direction than in the reverse direction. Therefore, it is advantageous in terms of the rotation speed to move the charging member in the reverse direction. It is. The peripheral speed ratio described here is
Peripheral speed ratio (%) = (charging member peripheral speed−image carrier peripheral speed) / image carrier peripheral speed × 100
(The charging member peripheral speed is a positive value when the surface of the charging member moves in the same direction as the surface of the image carrier at the nip portion).
[0067]
c) By using an elastic conductive roller or a brush made of conductive fibers as the contact charging member, the transfer residual toner on the image carrier is temporarily collected and the charge accelerating particles are supported so that direct injection charging is superior. To run.
[0068]
d) The volume resistance of the outermost surface layer of the image carrier is 1 × 10 ⁹ (Ω · cm) or more 1 × 10 ¹⁴ By setting it to (Ω · cm) or less, it is possible to maintain an electrostatic latent image and to provide sufficient chargeability even in an apparatus having a high process speed, and to realize direct injection charging.
[0069]
DETAILED DESCRIPTION OF THE INVENTION
<Embodiment Example 1> (FIG. 1)
FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus according to the present invention.
[0070]
The image forming apparatus of this example is a laser printer (recording apparatus) using a transfer type electrophotographic process, a direct injection charging system, and a toner recycling process (cleanerless system).
[0071]
(1) Overall schematic configuration of this example printer
Reference numeral 1 denotes a φ30 mm rotating drum type OPC photosensitive member (negative photosensitive member) as an image bearing member, which is rotationally driven in a clockwise direction indicated by an arrow at a peripheral speed (process speed) of 50 mm / sec.
[0072]
Reference numeral 2 denotes a conductive elastic roller (hereinafter referred to as a charging roller) as a contact charging member.
[0073]
The charging roller 2 is formed by forming a rubber or foam medium resistance layer 2b as a flexible member on a cored bar 2a. The middle resistance layer 2b is formulated with a resin (for example, urethane), conductive particles (for example, carbon black), a sulfurizing agent, a foaming agent, and the like, and is formed in a roller shape on the core metal 2a. Thereafter, the surface was polished as necessary to prepare a charging roller 2 which is a conductive elastic roller having a diameter of 12 mm and a longitudinal length of 250 mm.
[0074]
The roller resistance of the charging roller 2 of this example was measured and found to be 100 kΩ. The roller resistance is measured by applying 100 V between the core metal 2a and the aluminum drum in a state where the charging roller 2 is pressure-bonded to an aluminum drum having a diameter of 30 mm so that the core metal 2a of the charging roller 2 is loaded with a total pressure of 1 kg. did.
[0075]
Here, it is important that the charging roller 2 which is a conductive elastic roller functions as an electrode. In other words, it is necessary to provide a sufficient contact state with the member to be charged by providing elasticity, and at the same time to have a sufficiently low resistance to charge the moving member to be charged. On the other hand, it is necessary to prevent voltage leakage in the case where a defect site such as a pinhole exists in the member to be charged. When an electrophotographic photosensitive member is used as the member to be charged, 10 is necessary to obtain sufficient chargeability and leakage resistance. ⁴ -10 ⁷ A resistance of Ω is desirable.
[0076]
If the hardness of the charging roller 2 is too low, the shape is not stable, so that the contact property with the member to be charged is deteriorated. If the hardness is too high, the charging nip portion cannot be secured between the member and the member to be charged. Since the micro-contact property to the surface of the charged body is deteriorated, the preferred range of Asker C hardness is 25 to 50 degrees.
[0077]
The material of the charging roller 2 is not limited to the elastic foam, and the material of the elastic body may be EPDM, urethane, NBR, silicone rubber, or the like such as carbon black or metal oxide for resistance adjustment to IR or the like. Examples thereof include a rubber material in which a conductive material is dispersed and a foamed material of these materials. It is also possible to adjust the resistance using an ion conductive material without dispersing the conductive substance.
[0078]
The charging roller 2 is disposed in pressure contact with a photosensitive member 1 as a member to be charged with a predetermined pressing force against elasticity. n is a charging nip portion which is a nip portion between the photosensitive member 1 and the charging roller 2 The charging nip width is 3 mm. In this example, the charging roller 2 is rotationally driven in the clockwise direction of the arrow at about 80 rpm so that the charging roller surface and the photosensitive member surface move in the opposite directions to each other at a constant speed in the charging nip portion n. That is, the surface of the charging roller 2 as the contact charging member has a speed difference with respect to the surface of the photosensitive member 1 as the member to be charged.
[0079]
Further, a DC voltage of −700 V is applied as a charging bias to the cored bar 2a of the charging roller 2 from the charging bias application power source S1. In this example, the surface of the photoreceptor 1 is uniformly charged by a direct injection charging method at a potential (−680 V) substantially equal to the voltage applied to the charging roller 2. This will be described later.
[0080]
A laser beam scanner (exposure device) 3 includes a laser diode, a polygon mirror, and the like. This laser beam scanner outputs a laser beam whose intensity is modulated in accordance with the time-series electric digital pixel signal of the target image information, and scans and exposes the uniformly charged surface of the rotating photoreceptor 1 with the laser beam. By this scanning exposure L, an electrostatic latent image corresponding to target image information is formed on the surface of the rotary photosensitive member 1.
[0081]
Reference numeral 4 denotes a developing device. The electrostatic latent image on the surface of the rotating photoreceptor 1 is developed as a toner image by this developing device. The developing device of this example is a reversal developing device using magnetic one-component insulating toner (negative toner). Reference numeral 4a denotes a non-magnetic rotary developing sleeve as a developer carrying member enclosing a magnet roll 4b. The rotating developer sleeve 4a is coated with a developer 4d in a thin layer by a regulating blade 4c. The toner of the developer 4d is regulated in layer thickness with respect to the rotary developing sleeve 4a by the regulating blade 4c, and is charged. The developer coated on the rotating developing sleeve 4a is transported to the developing portion (developing region portion) a which is a facing portion between the photoreceptor 1 and the sleeve 4a by the rotation of the sleeve 4a. A developing bias voltage is applied to the sleeve 4a from a developing bias applying power source S2. The developing bias voltage used was a superposition of a DC voltage of −500 V and a rectangular AC voltage with a frequency of 1800 Hz and a peak-to-peak voltage of 1600 V. As a result, the electrostatic latent image on the photoreceptor 1 side is developed with toner.
[0082]
Developer 4d is a mixture of toner t and charge accelerating particles (charging auxiliary particles) m. Toner t is prepared by mixing binder resin, magnetic particles and charge control agent, and kneading, pulverizing, and classifying. In addition, the charge promoting particles m and a fluidizing agent are added as external additives. The weight average particle diameter (D4) of the toner t was 7 μm. In this example, conductive zinc oxide particles having a particle size of 3 μm were used as the charge accelerating particles m. In this example, 2 parts by weight of the charge accelerating particles m are externally added to 100 parts by weight of the toner t.
[0083]
In this example, the electrification promoting particle m having conductivity has a specific resistance of 10 ⁶ Although conductive zinc oxide particles having an average particle size of 3 μm including Ω · cm and secondary agglomerates were used, as the material of the charge accelerating particles m, conductive inorganic particles such as other metal oxides and organic substances can be used. Various conductive particles such as a mixture can be used.
[0084]
The particle resistance is 10 to 10 because the specific resistance is exchanged through particles. ¹² Ω · cm or less is required, preferably 10 ¹⁰ Ω · cm or less is desirable.
[0085]
The resistance was measured by the tablet method and normalized. That is, the bottom area 2.26cm ² Approximately 0.5 g of a powder sample was placed in the cylinder, and 15 kg of pressure was applied to the upper and lower electrodes. At the same time, a voltage of 100 V was applied to measure the resistance value, and then normalized to calculate the specific resistance.
[0086]
The particle size is desirably 50 μm or less in order to obtain good charging uniformity. The lower limit of the particle size is 10 nm, as long as particles can be stably obtained.
[0087]
In the present invention, the particle size when the particles are constituted as an aggregate is defined as an average particle size as the aggregate.
[0088]
For the measurement of the particle size, 100 or more samples were extracted from observation with an optical or electron microscope, the volume particle size distribution was calculated with the maximum horizontal chord length, and the 50% average particle size was determined.
[0089]
As described above, there is no problem that the charge promoting particles m exist not only in the state of primary particles but also in the state of aggregation of secondary particles. In any aggregate state, the form is not important as long as the function as the charge promoting particles can be realized as the aggregate.
[0090]
In particular, when the charge promoting particles m are used for charging the photosensitive member 1, colorless or nearly white particles are suitable so as not to disturb the latent image exposure. Further, when performing color recording, it is desirable that the charge accelerating particles m be transferred to the recording material P from the photoreceptor to be colorless or nearly white. Also, in order to prevent light scattering by the charge promoting particles during image exposure, the particles are desirably smaller than the constituent pixel size.
[0091]
In addition, the charge promoting particles m are preferably non-magnetic so as not to hinder exposure.
[0092]
Reference numeral 5 denotes a medium resistance transfer roller as a contact transfer means, which is brought into pressure contact with the photoreceptor 1 to form a transfer nip portion b. A transfer material P as a recording medium is fed to the transfer nip b from a paper feed unit (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 5 from a transfer bias application power source S3. Thus, the toner image on the photosensitive member 1 side is sequentially transferred onto the surface of the transfer material P fed to the transfer nip portion b. In this example, the roller resistance value is 5 × 10. ⁸ The transfer was carried out by applying a DC voltage of +2000 V using an Ω. That is, the transfer material P introduced into the transfer nip portion b is nipped and conveyed by the transfer nip portion b, and the toner images formed and supported on the surface of the rotary photosensitive member 1 are sequentially pressed against the surface by the electrostatic force and the pressing force. Transferred by pressure.
[0093]
Reference numeral 6 denotes a fixing device such as a heat fixing method. The transfer material P that has been fed to the transfer nip portion b and has received the transfer of the toner image on the photoconductor 1 side is separated from the surface of the rotary photoconductor 1 and is introduced into the fixing device 6 to receive the fixing of the toner image. It is discharged out of the apparatus as an image formed product (print, copy).
[0094]
The printer of this example is cleaner-less, and residual transfer residual toner remaining on the surface of the rotating photosensitive member 1 after the transfer of the toner image to the transfer material P is not removed by the cleaner. Then, it reaches the developing section a and is simultaneously cleaned (collected) by the developing device 4 (toner recycling process).
[0095]
(2) Direct injection charging of the photoreceptor 1
a) An appropriate amount of the charge accelerating particles m having conductivity contained in the developer 4d of the developing device 4 together with the toner when the developing device 4 develops the toner of the electrostatic latent image on the photoconductor 1 side is placed on the photoconductor 1 side. Transition.
[0096]
The toner image on the photoconductor 1 is attracted to the transfer material P side and actively transferred at the transfer nip b due to the effect of the transfer bias. However, the charge promoting particles m on the photoconductor 1 are transferred due to their conductivity. The material P is not positively transferred to the material P side, and remains substantially adhered and held on the photoreceptor 1. In addition, the presence of the charge accelerating particles m that are substantially adhered and held on the surface of the photosensitive member 1 can also improve the transfer efficiency of the toner image from the photosensitive member 1 side to the transfer agent P side.
[0097]
Since the image forming apparatus of the toner recycling process does not use a cleaner, the residual toner remaining on the surface of the photoreceptor 1 after transfer and the above-described residual charge accelerating particles m are transferred to the photoreceptor 1 and the charging roller 2 which is a contact charging member. The photosensitive member 1 is carried as it is to the charging nip portion n by being rotated, and adheres to and mixes with the charging roller 2.
[0098]
Therefore, contact charging of the photosensitive member 1 is performed in a state in which the charge accelerating particles m exist in the nip portion n between the photosensitive member 1 and the charging roller 2. In the initial stage of printing, since the charge accelerating particles are not supplied to the surface of the charging roller and cannot be charged, it is possible to apply the charge accelerating particles to the surface of the charging roller in advance.
[0099]
Due to the presence of the charge accelerating particles m, even when toner adheres to or mixes with the charging roller 2, the contact property of the charging roller 2 to the photosensitive member 1 and the contact resistance can be maintained. Such a simple member, and the charging roller 2 can perform direct injection charging of the photosensitive member 1 regardless of contamination of the charging roller due to transfer residual toner.
[0100]
That is, the charging roller 2 comes into close contact with the photosensitive member via the charging accelerating particles m, and the charging accelerating particles m existing in the nip portion between the charging roller 2 and the photosensitive member 1 rub against the surface of the photosensitive member 1 without a gap. Thus, the charging of the photoreceptor 1 by the charging roller 2 is dominated by stable and safe direct injection charging without using a discharge phenomenon due to the presence of the charge accelerating particles m, and high charging efficiency that cannot be obtained by conventional roller charging or the like. And a potential substantially equal to the voltage applied to the charging roller 2 can be applied to the photoreceptor 1.
[0101]
Further, the transfer residual toner adhering to and mixed in the charging roller 2 is gradually discharged from the charging roller 2 onto the photosensitive member 1 to reach the developing portion a along with the movement of the surface of the photosensitive member 1, and in the developing device 4 simultaneous cleaning (collection) of development. (Toner recycling process)
[0102]
As described above, the simultaneous development cleaning is performed in the image forming process in which the toner remaining on the photoreceptor 1 after the transfer is continued, that is, the photoreceptor is continuously charged and exposed to form a latent image, and the latent image is developed. At this time, the image is recovered by the fog removal bias of the developing device, that is, the fog removal potential difference Vback which is the potential difference between the DC voltage applied to the developing device and the surface potential of the photosensitive member. In the case of reversal development as in the printer in this embodiment, this simultaneous development cleaning is performed by attaching toner from the dark portion potential of the photosensitive member to the developing sleeve and from the developing sleeve to the bright portion potential of the photosensitive member. This is done by the action of an electric field.
[0103]
Even if the charge accelerating particles m fall off from the charging roller 2, the image forming apparatus is operated, so that the charge accelerating particles m contained in the developer 4d of the developing device 4 are transferred to the surface of the photoreceptor 1 at the developing portion a. Since the rotation of the photosensitive member 1 is carried to the charging portion n through the transfer nip portion b by the rotation of the photosensitive member 1 and continuously supplied to the charging roller 2, the good charging property due to the presence of the charge accelerating particles m is stabilized. Maintained.
[0104]
Thus, in an image forming apparatus using a contact charging method, a transfer method, and a toner recycling process, a charging roller is used as a contact charging member, and ozoneless direct operation is possible with a low applied voltage regardless of contamination of the charging roller 2 due to residual transfer toner. Injection charging can be maintained stably over a long period of time, uniform chargeability can be imparted, and a simple configuration and low-cost image forming apparatus free from failures due to ozone products, failures due to poor charging, etc. are obtained. be able to.
[0105]
b) By interposing the charge accelerating particles m in the nip portion n between the charging roller 2 and the photosensitive member 1, the lubricating effect (friction reducing effect) of the charging accelerating particles m is provided between the charging roller 2 and the photosensitive member 1. It is possible to easily and effectively provide a speed difference.
[0106]
By providing a speed difference between the charging roller 2 and the photoreceptor 1, the chance of the charge accelerating particles m to contact the photoreceptor 1 at the nip n between the charging roller 2 and the photoreceptor 1 is greatly increased, and high contact is achieved. And can be directly charged by direct injection.
[0107]
As a configuration for providing a speed difference, preferably, the charging roller 2 is rotationally driven in order to temporarily collect and level the transfer residual toner on the photosensitive member 1 carried to the charging unit n by the charging roller 2, It is desirable that the rotation direction is configured to rotate in the direction opposite to the moving direction of the surface of the photoreceptor 1. That is, it is possible to preferentially perform direct injection charging by once separating the transfer residual toner on the photosensitive member 1 by reverse rotation and performing charging.
[0108]
If the amount of the charge accelerating particles m in the nip n between the photosensitive member 1 as the image carrier and the charging roller 2 as the contact charging member is too small, the lubricating effect by the particles cannot be obtained sufficiently, and the charging roller The friction between the photosensitive member 1 and the photosensitive member 1 is large, and it is difficult to rotationally drive the charging roller 2 to the photosensitive member 1 with a speed difference. That is, the driving torque becomes excessive, and the surface of the charging roller 2 and the photosensitive member 1 is scraped if it is forcibly rotated. Furthermore, the effect of increasing the contact opportunity by the particles may not be obtained, and sufficient charging performance cannot be obtained. On the other hand, when the amount of the inclusion is too large, dropping of the charge accelerating particles from the charging roller 2 is remarkably increased, which adversely affects image formation.
[0109]
According to experiments, the amount of intervention is 10 ³ Piece / mm ² The above is desirable. 10 ³ Piece / mm ² If it is lower, a sufficient lubrication effect and an effect of increasing the contact opportunity cannot be obtained, resulting in a decrease in charging performance.
[0110]
More desirably 10 ³ ~ 5x10 ⁵ Piece / mm ² This amount of inclusion is preferred. 5 × 10 ⁵ Piece / mm ² Exceeding this causes the particles to drop off to the photoconductor 1 significantly, resulting in insufficient exposure of the photoconductor 1 regardless of the light transmittance of the particles themselves. 5 × 10 ⁵ Piece / mm ² In the following, the amount of dropped particles can be kept low, and the adverse effect can be improved. When the abundance of particles dropped on the photoreceptor 1 in the intervening amount range is measured, 10 is obtained. ² -10 ⁵ Piece / mm ² Therefore, the abundance that is not harmful to image formation is 10 ⁵ Piece / mm ² The following is desired:
[0111]
A method for measuring the intervening amount and the existing amount on the photoreceptor 1 will be described. It is desirable to directly measure the contact surface portion between the charging roller 2 and the photosensitive member 1. However, most of the particles existing on the photosensitive member 1 before contacting the charging roller 2 are moved in the opposite direction and contact with each other. Since it is peeled off by the roller 2, in the present invention, the amount of particles on the surface of the charging roller 2 immediately before reaching the contact surface portion is used as the amount of interposition. Specifically, rotation of the photosensitive drum 1 and the charging roller 2 is stopped in a state where no charging bias is applied, and the surfaces of the photosensitive member 1 and the charging roller 2 are video microscope (OLYMPUS OVM1000N) and a digital still recorder (manufactured by DELTAS). SR-3100). The charging roller 2 is in contact with the slide glass under the same conditions as the case where the charging roller 2 is in contact with the photosensitive drum 1, and the contact surface of the charging roller 2 is 10 or more with a 1000 × objective lens from the back surface of the slide glass. I took a picture. In order to separate individual particles from the obtained digital image, binarization processing was performed with a certain threshold value, and the number of regions where particles exist was measured using desired image processing software. Further, the abundance on the photoconductor 1 was measured by photographing the photoconductor 1 with the same video microscope and performing the same processing.
[0112]
The amount of intervening was adjusted by setting the blending amount of the charge accelerating particles m in the developer 4d of the developing device 4. Generally, the charge promoting particles m are 0.01 to 20 parts by weight with respect to 100 parts by weight of the developer (toner).
[0113]
<Embodiment 2> (FIG. 2)
In this example, in the image forming apparatus of Embodiment 1 described above, the surface resistance of the photoreceptor 1 as an image carrier is adjusted to perform charging more stably and uniformly.
[0114]
In other words, even when the transfer residual toner is mixed in the contact charging member and the contact area with the photoreceptor 1 is reduced, the interposition of the charge accelerating particles and the surface resistance on the photoreceptor side are set low in the region where the latent image can be formed. Thus, charge transfer is performed more efficiently.
[0115]
In this example, a charge injection layer is provided on the surface of the photoreceptor 1 to adjust the resistance of the surface of the photoreceptor. FIG. 2 is a layer configuration model diagram of the photoreceptor 1 used in this example and provided with a charge injection layer on the surface. That is, the photosensitive member 1 is generally coated on an aluminum drum substrate (Al drum substrate) 11 in the order of an undercoat layer 12, a positive charge injection preventing layer 13, a charge generation layer 14, and a charge transport layer 15. By applying the charge injection layer 16 to the organic photoreceptor drum, the charging performance is improved.
[0116]
The charge injection layer 16 is made of SnO as conductive particles (conductive filler) on a photo-curable acrylic resin as a binder. ₂ Ultrafine particles 16a (diameter is about 0.03 μm), a lubricant such as tetrafluoroethylene resin (trade name: Teflon), a polymerization initiator, and the like are mixed and dispersed, and after coating, a film is formed by a photocuring method.
[0117]
An important point as the charge injection layer 16 is the resistance of the surface layer. In the charging method by direct injection of charges, charges can be exchanged more efficiently by reducing the resistance on the charged object side. On the other hand, since the electrostatic latent image needs to be held for a certain time when used as a photoconductor, the volume resistance value of the charge injection layer 16 is 1 × 10 6. ⁹ ~ 1x10 ¹⁴ A range of (Ω · cm) is appropriate.
[0118]
Even when the charge injection layer 16 is not used as in this configuration, for example, when the charge transport layer 15 is in the resistance range, the same effect can be obtained.
[0119]
Furthermore, the volume resistance of the surface layer is about 10 ¹³ The same effect can be obtained by using an amorphous silicon photoconductor having an Ωcm.
[0120]
<Evaluation of Example Embodiment>
Table 1 summarizes the advantages of the present invention along with the comparative examples.
[0121]
[Table 1]

[Comparative Example 1]
In Comparative Example 1, a charging roller was used as the charging member, and the charging roller was driven by the photoreceptor. The developer 4d is not mixed with the charge accelerating particles m. That is, the apparatus does not use the charge accelerating particles m.
[0122]
[Comparative Example 2]
In Comparative Example 2, a charging roller in which the charge accelerating particles were previously applied in the configuration of Comparative Example 1 was used.
[0123]
[Evaluation]
In each example, the chargeability was evaluated based on the superiority or inferiority of the ghost image using image recording apparatuses having different printing speeds.
[0124]
In this example, since the reversal development system is used, ghost as used herein means that a portion exposed to an image (a toner image portion) on the first round of the photoconductor causes insufficient charging on the second round of the photoconductor. Therefore, it means that the previous image pattern on the photoconductor is more strongly developed and a ghost image is generated.
[0125]
Here, the image evaluation was performed according to the following criteria.
[0126]
X: A ghost is seen in the white background after solid black.
[0127]
○: A ghost pattern is not observed in the white background portion after the solid black, but a slight ghost pattern is observed in the halftone portion.
[0128]
(Double-circle): A ghost is not seen in the white background part and halftone part after a solid black.
[0129]
The evaluation was performed after the initial printing and printing of 1000 sheets (A4 lengthwise direction). The upper part of the slash line (hatched line) in the table indicates the initial stage, and the lower part indicates the evaluation result after printing.
[0130]
As is apparent from the table, in Comparative Example 1, the chargeability was not satisfied at any speed already in the initial stage. In other words, this indicates that the charging member (charging roller) cannot sufficiently contact the photoconductor, and thus cannot be directly charged.
[0131]
In Comparative Example 2, no ghost was observed at the initial stage of application of the charge accelerating particles, but when the printing was continued, the charging roller was rapidly stained, and at the same time, the charge accelerating particles dropped and the image was greatly deteriorated.
[0132]
In Embodiment 1, the charge promoting particles m can be mixed with the developer 4d, and the particles can be stably supplied to the charging member via the photosensitive member, so that sufficient contact with the photosensitive member can be obtained. The charging property is satisfied and can be maintained. Further, good chargeability is exhibited even when the speeds of the photosensitive drum and the charging member are both increased. However, when the speed of the charging member is decreased, a slight charge shortage occurs. Therefore, charging can be performed more efficiently if a speed difference is provided between the charging member and the photosensitive member.
[0133]
Further, in the second embodiment, by setting the resistance of the photoreceptor surface layer to be low within a range in which the electrostatic latent image can be maintained, even if the contact state is the same, charge can be exchanged more efficiently. This is effective when the process is executed at a higher speed, and is clear because the photosensitive member speed in the table satisfies the evaluation of 100 mm / sec and the charging member speed of 50 mm / sec.
[0134]
<Others>
1) The charging roller 2 as the contact charging member is not limited to the charging roller of the embodiment.
[0135]
In addition to the elastic charging roller, the flexible contact charging member can be made of a material / shape such as a fur brush, felt, or cloth. Moreover, these can be laminated | stacked and it can also obtain more suitable elasticity and electroconductivity.
[0136]
2) The applied charging bias or the applied developing bias applied to the contact charging member 2 and the developing sleeve 4a may be superimposed with an alternating voltage (AC voltage) on a DC voltage.
[0137]
As the waveform of the alternating voltage, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Further, it may be a rectangular wave formed by periodically turning on / off a DC power source. In this way, a bias that changes the voltage value periodically can be used as the waveform of the alternating voltage.
[0138]
3) The image exposure means for forming the electrostatic latent image is not limited to the laser scanning exposure means for forming a digital latent image as in the embodiment, but a normal analog image exposure or Other light emitting elements such as LEDs may be used, and any combination of a light emitting element such as a fluorescent lamp and a liquid crystal shutter may be used as long as it can form an electrostatic latent image corresponding to image information.
[0139]
The image carrier may be an electrostatic recording dielectric or the like. In this case, the dielectric surface is uniformly primary-charged to a predetermined polarity and potential, and then selectively neutralized by a neutralizing means such as a static elimination needle head or an electron gun to write and form a target electrostatic latent image.
[0140]
4) In the embodiment, the developing unit 4 has been described by taking a developing device using a single component magnetic toner as an example, but the configuration of the developing device is not particularly limited.
[0141]
5) The recording medium that receives the transfer of the toner image from the image carrier may be an intermediate transfer member such as a transfer drum.
[0142]
6) An example of a toner particle size measuring method will be described. As a measuring device, a Coulter counter TA-2 type (manufactured by Coulter Inc.) was used, and an interface (manufactured by Nikka) and a CX-1 personal computer (manufactured by Canon) that output number average distribution and volume average distribution were connected, and electrolysis was performed. Prepare 1% NaCl aqueous solution using primary sodium chloride.
[0143]
As a measuring method, a surfactant, preferably 0.1 to 5 ml of alkylbenzene sulfonate, is added to 100 to 150 ml of the electrolytic aqueous solution, and 0.5 to 50 mg of a measurement sample is further added.
[0144]
The electrolyte in which the sample is suspended is subjected to a dispersion treatment for about 1 to 3 minutes with an ultrasonic disperser, and the particle size distribution of 2 to 40 μm particles is measured using the 100 μ aperture as the aperture by the Coulter Counter TA-2 type. Then, the volume average distribution is obtained. The volume average particle diameter is obtained from the obtained volume average distribution.
[0145]
【The invention's effect】
As described above, the present invention uses a simple member such as a charging roller or a fur brush as a contact charging member in a contact charging method, a transfer method, and a toner recycling process (cleanerless system) image forming apparatus. By mixing the charge accelerating particles with the developer, the toner can be recycled, and at the same time, the contact density of the contact charging member to the image carrier can be improved, and the direct injection charging can be maintained for a long time. In this configuration, even when the toner as the insulator is mixed into the contact charging member, the charge promoting particles as the conductive particles are simultaneously stably supplied to interpose between the contact charging member and the image carrier. Thus, direct injection charging could be maintained by improving the contact property of the contact charging member to the image carrier.
[0146]
Further, the image carrier and the contact charging member are brought into contact with each other with a speed difference. More preferably, by rotating and charging so as to move in the opposite direction, the contact property and contact opportunity between the image carrier and the contact charging member can be further increased, and the influence of residual toner can be suppressed and good charging can be maintained. Is possible.
[0147]
Furthermore, by adjusting the resistance of the surface of the image carrier, it is possible to configure a charging device that is more suitable for high-speed charging. In a high-speed recording apparatus, since a long life of the member is required, it is desirable to reduce the speed of the charging member to reduce the abrasion of each member such as the photoconductor. In that sense, the charging efficiency is improved by adjusting the resistance of the surface layer of the image bearing member, so that sufficient charging performance can be obtained even when the charging member is driven at a low speed and maintained for a long period of time. It became possible to do.
[0148]
As described above, the present invention uses a simple member such as a charging roller or a fur brush as a contact charging member in an image forming apparatus using a contact charging method, a transfer method, or a toner recycling process, and the transfer residual toner of the contact charging member. Regardless of contamination due to, the ozone-less direct injection charging can be stably maintained over a long period of time with a low applied voltage, that is, with a simple configuration using a contact charging member such as a charging roller or a fur brush, The toner recycling process can be realized and the initial purpose is well achieved.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first exemplary embodiment.
FIG. 2 is a layer configuration model diagram of a photoreceptor having a charge injection layer provided on the surface in Embodiment 2.
Fig. 3 Charging characteristic graph
[Explanation of symbols]
1 Photoconductor (image carrier, charged body)
2 Charging roller (contact charging member)
3 Laser beam scanner (exposure device)
4 Development device
4a Development sleeve
4d Developer (toner t + charge-promoting particle m)
5 Transfer roller
6 Fixing device
P transfer material

Claims (10)

A photosensitive member, the charging means for charging the photosensitive member, an exposure means for exposing said photosensitive member to form an electrostatic latent image on the photosensitive member, the electrostatic latent image formed on the photosensitive member A developing unit that visualizes the toner image with toner; and a transfer unit that transfers the toner image to a recording medium. The developing unit collects the toner remaining on the photoreceptor after the toner image is transferred to the recording medium. In an image forming apparatus capable of
Said charging means is a charging member to which a voltage is applied, the comprises a flexible charging member to form a photosensitive member and the nip, the carrying the previously non-magnetic conductive particles to the surface of the charging member Non-magnetic conductive particles are interposed in the nip,
The image forming apparatus according to claim 1, wherein the developer of the developing unit includes toner and nonmagnetic conductive particles, and the nonmagnetic conductive particles are applied from the developing unit to the photoreceptor and replenished to the nip portion. The charging member surface, the image forming apparatus according to claim 1, characterized in that to move with a speed difference relative to the photoreceptor surface to rub the photosensitive member surface in the non-magnetic conductive particles. The image forming apparatus according to claim 1, wherein the nonmagnetic conductive particles have a resistance of 10 ¹² Ω · cm or less and a particle size of 50 μm or less. The image forming apparatus according to claim 1, wherein the nonmagnetic conductive particles have a resistance of 10 ¹⁰ Ω · cm or less and a particle size of 50 μm or less. 5. The image forming apparatus according to claim 1, wherein the charging member and the photosensitive member move in directions opposite to each other at the nip portion.   6. The image forming apparatus according to claim 1, wherein the charging member is an elastic conductive roller.   The image forming apparatus according to claim 1, wherein the charging member includes a foam on a surface thereof. The image forming apparatus according to claim 1, wherein the charging member carries and transports the nonmagnetic conductive particles to the nip portion. 9. The volume resistance of the outermost surface layer of the photoconductor is 1 × 10 ⁹ (Ω · cm) or more and 1 × 10 ¹⁴ (Ω · cm) or less. 9. Image forming apparatus. The developing unit is according to any one of claims 1, wherein 9 that it is possible to recover the toner remaining an electrostatic latent image on the photoconductor at the same time the photosensitive member is developed with toner Image forming apparatus.

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