JP2005140945A - Charging roller, method for manufacturing charging roller and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent toner fogging which occurs immediately after start of use and to stably produce high-quality good images, in a toner recycling configuration using an ozoneless injection charging system at low applied voltage. <P>SOLUTION: In a charging roller obtained by forming a layer of an electrically conductive elastic foam having a porous surface on at least a core metal, the circumferential surface of the charging roller which comes in contact with a member to be charged is coated with movable electrically conductive particles whose bulk density is ρ g/cm<SP>3</SP>by means of a coating roller at a density of ≥4×10<SP>-3</SP>×ρ g/cm<SP>3</SP>. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a charging roller in contact charging, a contact charging method and apparatus, an image forming apparatus such as a copying machine or a copying machine using contact charging, and a process cartridge.

  Conventionally, for example, in an image forming apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an electrophotographic photosensitive member / an electrostatic recording dielectric body such as an electrophotographic photosensitive member (charged body) is uniformly charged to a required polarity and potential. A corona charger (corona discharger) is often used as a charging device for processing (including charge removal processing).

  A corona charger is a non-contact type charging device. For example, a corona charger is provided with a discharge electrode such as a wire electrode and a shield electrode surrounding the discharge electrode, and a discharge opening is opposed to an image carrier as 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.

  Recently, since there are advantages such as low ozone and low power compared to the corona charger, as described above, the contact method of charging the charged object by contacting the charged roller to which the voltage is applied to the charged object The charging device (contact charging device) has been put into practical use.

  The contact charging device contacts a charged object such as an image carrier with a conductive charging member such as a roller type (charging roller), a fur brush type, a magnetic brush type, or a blade type, and the charging member (contact charging member). A predetermined charging bias is applied to a contact charger (hereinafter referred to as a contact charging member) to charge the charged object surface to a predetermined polarity and potential.

  There are two types of contact charging mechanism (charging mechanism, charging principle): (1) discharge charging mechanism and (2) direct injection charging mechanism, depending on which is dominant. The characteristic of appears. Fig. 1 shows typical charging characteristics of each.

(1) Discharge Charging Mechanism This is a mechanism for charging the surface of a member to be charged by a corona discharge phenomenon that occurs in a minute gap between the contact charging member and the member to be charged.

  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.

(2) Injection charging mechanism This is a system in which 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. Since this direct charging system does not involve the generation of ions, no adverse effects caused by the discharge products occur.

  However, since it is directly charged, 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 larger peripheral speed difference from the object to be charged, and must be configured to contact the object to be charged more frequently.

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.

  The charging mechanism of the roller charging is dominated by the discharge charging system (1).

  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.

  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 in many cases is driven by the photosensitive member or has a slight circumference. It is driven with a speed difference. Therefore, even if direct charging is attempted, a decrease in absolute charging ability, lack of contactability, unevenness on the roller, and uneven charging due to the adherence of the photosensitive member cannot be avoided. The system is dominant.

  FIG. 1 is a graph showing an example of charging efficiency in contact charging. The horizontal axis represents the bias applied to the contact charging roller, and the vertical axis represents the photosensitive member charging potential obtained at that time.

  The charging characteristic in the case of conventional 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.

  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.

  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”.

  However, in DC charging, the resistance value of the contact charging member fluctuates due to environmental fluctuations, etc., and Vth fluctuates when the film thickness changes due to the photoconductor being scraped, so that the potential of the photoconductor is set to a desired value. It was difficult.

  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.

  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.

  Further, when AC charging is performed for uniform charging, generation of further ozone, generation of vibration noise (AC charging sound) between the contact charging member and the photosensitive member due to the electric field of the AC voltage, and surface of the photosensitive member due to discharge As a result, the deterioration and the like became remarkable, which was a new problem.

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 photoreceptor as a charged body, A predetermined charging bias is applied to charge the photoreceptor surface to a predetermined polarity and potential.

  The charging mechanism of the fur brush charging is dominated by the discharge charging system (1).

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. A fiber density of about 100 fibers / mm ² can be obtained relatively easily. However, the contact is still insufficient for sufficiently uniform charging by direct charging, and sufficiently uniform charging is performed by direct charging. However, it is necessary for the photosensitive member to have a peripheral speed difference that is difficult as a mechanical configuration, which is not practical.

  The charging characteristics of the fur brush charged when a DC voltage is applied take the characteristics shown in FIG. Accordingly, in the case of fur brush charging, both the fixed type and the roll type are charged by applying a high charging bias and using a discharge phenomenon.

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. The portion is brought into contact with a photosensitive member as a member to be charged, and a predetermined charging bias is applied to charge the surface of the photosensitive member to a predetermined polarity and potential.

  In the case of this magnetic brush charging, the direct charging system (2) is dominant in the charging mechanism.

  By using conductive magnetic particles constituting the magnetic brush portion having a particle diameter of 5 to 50 μm and providing a sufficient peripheral speed difference from the photoreceptor, uniform direct charging is possible.

  As indicated by C in the charging characteristic graph of FIG. 1, it is possible to obtain a charging potential that is substantially proportional to the applied bias.

  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.

  Japanese Patent Laid-Open No. 6-3921 proposes a method of performing contact injection charging by injecting charges into a charge holding member such as a trap level on the surface of a photoreceptor or conductive particles in a charge injection layer. 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.

D) Toner recycling system (cleanerless)
In the transfer type image recording apparatus, the developer (toner) remaining on the photoconductor (image carrier) after transfer is removed from the photoconductor surface by a cleaner (cleaning device) to become waste toner. It is desirable that waste toner does not come out from the viewpoint of environmental protection. Therefore, the toner recycling system (or toner recycling system) is configured to eliminate the cleaner and remove the transfer residual toner on the photoconductor after transfer from the photoconductor by “development simultaneous cleaning” and collect and reuse it in the developing device. Process) image recording devices have also appeared.

  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. In addition, the cleanerless has a great space advantage, and the image recording apparatus can be greatly downsized.

  Since the toner recycling system does not remove the transfer residual toner from the surface of the photosensitive member by a dedicated cleaner as described above, it reaches the developing device via the charging unit and is used again in the development process. When contact charging is used as the charging means for the photosensitive member, how to charge the photosensitive member with an insulating toner interposed in the contact portion between the photosensitive member and the contact charging member is a problem. . In the above-described roller charging or fur brush charging, the transfer residual toner on the photosensitive member is diffused and non-patterned, and charging by discharging by applying a large ba ice is often used. In magnetic brush charging, powder is used as the contact charging member, so there is an advantage that the magnetic brush portion of the conductive magnetic particles, which is the powder, can flexibly contact the photoconductor to charge the photoconductor, but the device configuration is complicated. That is, the harmful effect caused by dropping off of the conductive magnetic particles constituting the magnetic brush portion is great.

E) (Sponge + conductive particles) Direct injection charging Direct injection charging uses the direct charge transfer from the contact charging member to the part to be charged. The charging roller as the contact charging member needs to be in sufficient contact with the surface of the member to be charged, and the driven rotation is insufficient.

  In order to sufficiently bring the charging roller into contact with the surface of the member to be charged, it is necessary to rotate the charging roller with a difference in peripheral speed with respect to the member to be charged, like the magnetic brush charger described above. However, the contact charging roller formed of an elastic body cannot be rotated with a speed difference between the charged body and the charged body because the frictional force between the contact charging roller and the charged body is large. In addition, if it is rotated forcibly, there is a problem that the surface of the contact charging roller or the object to be charged is scraped off.

  The speed difference between the charging roller and the member to be charged is, specifically, a speed difference is provided between the charging roller and the member to be charged by moving and driving the surface of the charging roller. Preferably, the charging roller is driven to rotate, and the rotation direction thereof is configured to rotate in the direction opposite to the moving direction of the surface of the charged body.

Although it is possible to move the charging roller surface in the same direction as the movement direction of the surface of the object to be charged, a difference in speed is possible, but the chargeability of direct injection charging is the ratio of the peripheral speed of the object to be charged and the peripheral speed of the charging roller. Therefore, in order to obtain the same peripheral speed ratio as in the reverse direction, the rotation speed of the charging roller in the forward direction is larger than that in the reverse direction. Therefore, it is more efficient to move the charging roller in the reverse direction. It is advantageous. The peripheral speed ratio described here is: peripheral speed ratio (%) = (peripheral speed of charging roller−peripheral speed of charged body) / peripheral speed of charged body × 100
(The charging roller peripheral speed is a positive value when the surface of the charging roller moves in the same direction as the surface of the member to be charged in the nip portion).

  Thus, even when a charging roller or the like is used as a contact charging roller, the applied bias necessary for charging the contact charging roller is sufficient as a voltage corresponding to the potential required for the object to be charged. A stable and safe charging method that does not use the phenomenon can be realized.

  In other words, in a contact charging device, even when a simple member such as a charging roller is used as a contact charging roller, direct injection charging that is more excellent in charging uniformity and stable over a long period of time is realized. Can be realized with a simple configuration.

  Accordingly, uniform chargeability can be provided, and an image forming apparatus and a process cartridge with a simple configuration and low cost that are free from troubles due to ozone products, troubles due to poor charging, and the like can be obtained.

  As means for reducing the frictional force between the contact charging roller and the member to be charged, at least the powder is present in the nip portion between the contact charging roller and the member to be charged, thereby providing a lubricating effect (friction reducing effect) by the powder. The frictional force between the contact charging roller and the member to be charged can be effectively reduced. Further, by providing a low friction layer on the surface of the contact charging roller, the frictional force between the contact charging roller and the member to be charged can be effectively reduced.

  By causing the powder to exist at least in the nip portion between the contact charging roller and the member to be charged, friction can be reduced in the nip portion between the member to be charged and the contact charging roller, and the torque of the contact charging roller can be reduced. At the same time, it can contact the charged body with a speed difference, and at the same time, it contacts the charged body densely and uniformly through the powder, that is, the powder existing in the nip portion between the contact charging roller and the charged body touches the surface of the charged body. By rubbing without gaps, the charge can be directly injected into the member to be charged. That is, direct injection charging is dominant in charging the object to be charged by the contact charging roller due to the presence of the powder.

  Therefore, high charging efficiency can be obtained, and a potential substantially equal to the voltage applied to the contact charging roller can be applied to the member to be charged. When the surface of the contact charging roller using an elastic body is brought into contact with the object to be charged while moving the object to be charged with a speed difference, contact charging is achieved by reducing the frictional force between the contact charging roller and the object to be charged. The initial drive torque of the roller is reduced so that the surface of the contact charging roller can be moved stably, and a uniform direct contact state is obtained at the charging nip portion of the contact charging roller and the object to be charged, enabling uniform direct injection charging. It is what.

F) (Sponge + conductive particles) Wear of the surface protection layer of the photoconductor in direct injection charging (Sponge + conductive particles) In the direct injection charging, a conductive elastic member that rotates at a relative speed with respect to the photoconductor Since a voltage is applied to the surface of the elastic member and charging is performed through conductive particles attached to the surface of the elastic member, the surface protective layer constituting the photoreceptor is easily worn by friction with the elastic member and the conductive particles. Wear of the surface protective layer leads to a reduction in the life of the photoreceptor, and is liable to cause image quality deterioration such as vertical stripes.

  Therefore, it is preferable that the surface protective layer constituting the photoconductor is less likely to be worn by friction with the elastic member and the conductive particles, or a sufficient thickness of the surface protective layer is ensured even if wear occurs. .

  Specifically, it is preferable to provide a high-quality image over a long period of time by forming the surface protective layer with a material having high hardness such as amorphous silicon carbide (a-SiC) or amorphous carbon (a-C). .

  As a result of intensive studies by the inventors using an image forming apparatus in which the Canon copier GP405 is modified to a negative charging method by contact injection charging, and by using a-C, a surface protective layer having a higher hardness can be obtained. In the image forming apparatus in which the Canon copier GP405 was modified to the negative charging method by contact charging, a high-quality image could be stably supplied even after printing 500,000 sheets. Further, the a-Si photosensitive member used in the present invention requires a sufficient surface layer thickness to stably supply a high-quality image over a long period of time. As a result of intensive studies by the present inventors, by forming the surface protective layer with a-C having a layer thickness of 500 to 5000 mm, a sufficient surface protective layer thickness can be secured even if wear occurs. High-quality images could be supplied stably even after printing 10,000 sheets.

  Therefore, in order to achieve the object of the present invention to provide an image forming apparatus and an image forming method capable of stably supplying a high-quality image over a long period of time, the surface is made of a high hardness material such as a-SiC or a-C. It is preferable to constitute a protective layer. More preferably, it is desirable to use a photoreceptor having a surface protective layer made of aC on the resurface.

  In the case of direct injection charging using the above-mentioned conductive particles, if the conductive particles slide off from the charging roller, the conductive particles present at the contact portion between the charging roller and the object to be charged cannot rub the surface of the object to be charged without any gap. Therefore, uniform direct injection charging cannot be performed on the member to be charged. Therefore, a configuration for supplying conductive particles to the charging roller is required.

  In the case of a cleanerless device, conductive particles are mixed with a developer, and the conductive particles are supplied to the surface of the image carrier from the developing unit together with the toner in the developing unit, and only the toner is transferred to the transfer material mainly in the transfer unit. Is done. The conductive particles are supplied to the contact portion between the charging roller and the image carrier without being removed by the cleaner due to the cleaner-less configuration. As a result, even if the conductive particles slide off from the charging roller, the image forming apparatus is operated, so that uniform charging is maintained.

  However, in the image forming apparatus configured as described above, when a charging roller to which conductive particles are applied in advance with a brush or brush is used, when the transfer residual toner adheres to the charging roller in the initial state of the apparatus, the transfer residual toner is Friction with the conductive particles on the charging roller is not sufficient, so that the transfer residual toner whose charge is reversed has almost no regular charge, and is discharged onto the drum and is not collected by the developing device, and is not transferred. Toner adheres to the transfer member and fog occurs.

  This is because a charging roller in which conductive particles are applied using a brush or a brush has a small amount of conductive particles on the outer peripheral surface or unevenness.

  In order to solve such problems, the present invention is a charging roller, a method for manufacturing the charging roller, and an image forming apparatus having the following configuration.

1. A charging roller in which a layer of a conductive elastic foam having a porous surface is formed on a core metal, and 4 × 10 4 of movable conductive particles are placed on the outer peripheral surface of the charging roller that comes into contact with the member to be charged. ^-3 × ρ g / cm ³ (where ρ is the bulk density of conductive particles measured according to JIS K 5101 ρ g / cm ³ ) or higher.
2. The charging roller according to 1, wherein the cell structure of the elastic foam of the charging roller is an open cell or a semi-independent semi-open cell
3. A charging roller having a step of contacting a charging roller and a coating roller for supplying and applying conductive particles and rotating the rollers with a difference in peripheral speed in order to apply a necessary amount of conductive particles to the charging roller in advance. Manufacturing method
4. The method for producing a charging roller according to 3, wherein the surface of the coating roller is smooth
5. The method for producing a charging roller according to 3, wherein the application roller is a fur brush roller
6. A rotating image carrier, a charging means for charging the image carrier, an image information writing means for forming an electrostatic latent image on the charging surface of the image carrier, and the electrostatic latent image is visualized with toner An image forming apparatus comprising a developing unit and a transfer unit that transfers the toner image to a recording medium, and having no unit for removing toner from the image carrier between the transfer unit and the charging unit, An image forming apparatus comprising a one-component developer containing 0.5% or more and 5% or less of a toner weight, wherein a charging roller is brought into contact with a member to be charged and driven with a peripheral speed difference with respect to the image carrier.
7. The image carrier is composed of a photoconductive layer composed of a non-single crystal material based on silicon atoms and a surface layer composed of a non-single crystalline hydrogenated carbon film on a conductive substrate. The image forming apparatus according to 6
8. The image carrier is an organic photoconductive (OPC) photoreceptor, and has a charge injection layer made of a material of 10 ⁹ to 10 ¹⁴ (Ω · cm) on the surface of the image carrier, 6. The image forming apparatus according to 6, wherein the image forming apparatus comprises a light transmissive and insulating binder, a lubricant powder, and conductive particles.

(Function)
4 × moveable conductive particles with a bulk density of ρ g / cm ^{3 on} the outer peripheral surface of the charging roller in contact with the object to be charged on the charging roller whose elastic foam structure is open cell or semi-independent semi-open cell. When a charging roller uniformly coated with a density of 10 ⁻³ × ρ g / cm ³ or more is used, the toner and the conductive material are in contact with the toner when the reversal component transfer residual toner adheres to the charging roller even immediately after the start of use of the apparatus. Friction with the particles is sufficient, and the toner of the reversal component becomes a normal charge and is discharged onto the drum and collected by the developer. Therefore, toner fog does not occur even immediately after the start of use of the image forming apparatus.

  As a method for manufacturing such a charging roller, the conductive particles are charged by contacting the charging roller with a coating roller for supplying and applying conductive particles to the charging roller and rotating the rollers with a difference in peripheral speed. Supply to the roller. By using this method, a sufficient amount of conductive particles can be uniformly applied to the charging roller.

  In addition, by using a charging roller in which the cell structure of the elastic foam of the charging roller is an open cell or semi-independent semi-open cell, it is possible to fill the inside of the charging roller with the conductive particles, so that the charging roller is sufficient An amount of conductive particles can be retained.

As described above, in a cleanerless image forming apparatus using a conductive elastic foam charging roller and an a-Si photosensitive member, a conductive material having a bulk density of ρ g / cm ³ is previously formed on the outer peripheral surface of the charging roller. Even when printing from the initial stage for a long period of time, it is possible to stably produce high-quality and good images without toner fogging by uniformly applying the photosensitive particles at a density of 4 × 10 ⁻³ × ρ g / cm ³ or more. Can output.
<Others>
1) The charging bias applied to the elastic member may include an alternating voltage component (AC component, voltage whose voltage value periodically changes). As a waveform of the alternating voltage component, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. It may be a rectangular wave formed by periodically turning on / off a DC power supply.

  2) In the case of the image forming apparatus, the image exposure means as the information writing means for the charging surface of the photosensitive member as the image carrier is not limited to the laser scanning means in the embodiment, but a solid light emitting element array such as an LED. The digital exposure means used may be used. An analog image exposure unit using a halogen lamp or a fluorescent lamp as a document illumination light source may be used. In short, any device capable of forming an electrostatic latent image corresponding to image information may be used.

  3) In the case of the image forming apparatus, the electrostatic latent image toner developing method and means are arbitrary. A regular development system or a reversal development system may be used.

(Example 1)
This example is an example of an image forming apparatus provided with a charging roller or a contact charging device according to the present invention. FIG. 2 is a schematic configuration model diagram thereof.

  The image forming apparatus of the present example is a transfer type electrophotographic process use, process cartridge attaching / detaching type, contact charging type copying machine (recording apparatus).

(1) Overall schematic configuration of copier (Fig. 2)
Reference numeral 1 denotes an object to be charged (image carrier). This embodiment is a rotating drum type negative a-Si photosensitive member (negative photosensitive member, hereinafter referred to as a photosensitive drum) having a diameter of 30 mm. The photosensitive drum 1 is rotationally driven in a clockwise direction indicated by an arrow with a peripheral speed of 210 mm / sec (= process speed PS, printing speed).

The charging roller 2 is a conductive elastic roller (hereinafter referred to as a charging roller) as a contact charging roller (contact charger) disposed in contact with the photosensitive drum 1 with a predetermined pressing force. A is a charging nip portion that is a nip portion between the photosensitive drum 1 and the charging roller 2. Advance on the surface of the charging roller 2 using the conductive particle coating apparatus shown in FIG. 3, the charging roller bulk density 0.4 g / cm ³ movable conductive particles on the outer circumferential surface of which is in contact with the member to be charged 3 It is applied at a density of mg / cm ³ . The charging roller 2 and the conductive particles M1 and M2 will be described later.

  The charging roller 2 is rotationally driven in a reverse direction (counter) with respect to the rotation direction of the photosensitive drum 1 in a charging nip portion A, which is a nip portion with the photosensitive drum 1, and contacts the surface of the photosensitive drum 1 with a peripheral speed difference. . A predetermined charging bias is applied from the charging bias application power source S1.

  As a result, the peripheral surface of the rotating photosensitive drum 1 is uniformly contact-charged to a predetermined polarity / potential by the direct injection charging method. This will be described later.

  A laser beam scanner (exposure apparatus) 3 includes a laser diode, a polygon mirror, and the like. The laser beam scanner 3 outputs a laser beam whose intensity is modulated in accordance with a time-series electric digital pixel signal of target image information, and scans and exposes the uniformly charged surface of the rotating photosensitive drum 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 drum 1.

  Reference numeral 4 denotes a developing device. Conductive particles M1 are added to the developer t. The electrostatic latent image on the surface of the rotating photosensitive drum 1 is developed as a toner image by the developing unit 4 at the developing unit a. The developing device 4 and the conductive particles M1 will be described later.

Reference numeral 5 denotes a medium resistance transfer roller as a contact transfer means, which is brought into pressure contact with the photosensitive drum 1 to form a transfer nip portion b. A transfer material P as a recording material 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 drum 1 side is sequentially transferred onto the surface of the transfer material P fed to the transfer nip b. In this embodiment, a roller resistance value of 5 × 10 ⁸ Ω was used, and transfer was performed by applying a DC voltage of + 2000V. 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 drum 1 on the surface side thereof are sequentially pressed by electrostatic force and pressure. Transferred by pressure.

  6 is a main charge eliminating light, and after the toner image on the photosensitive drum is transferred to the transfer material, the surface of the photosensitive drum is uniformly exposed to eliminate the charge.

  Reference numeral 7 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 photosensitive drum 1 side is separated from the surface of the rotating photosensitive drum 1 and is introduced into the fixing device 7 to receive the fixing of the toner image. It is discharged out of the apparatus as an image formed product (print, copy).

  The copying machine of this embodiment is cleanerless, and residual toner remaining on the surface of the rotating photosensitive drum 1 after the transfer of the toner image onto the transfer material P is not removed by a dedicated cleaner (cleaning device), and the photosensitive drum 1 is removed. With the rotation of the toner, the toner reaches the developing portion via the charging nip portion A and is collected by the developing device 4 by the simultaneous development cleaning (toner recycling process).

(2) Conductive particle coating apparatus FIG. 3 shows a conductive particle coating jig in this example. The application roller is a fur brush roller. The charging roller is disposed so as to contact the application roller. A sufficient amount of conductive particles are uniformly held on the application roller, and the charging roller and the application roller rotate in the counter direction, whereby a sufficient amount of conductive particles are uniformly supplied and applied to the charging roller.

  The application roller is not limited to the fur brush roller, and an elastic foam roller (EPDM, urethane, NBR, silicone rubber, etc.) may be used.

(3) Charging roller 2
In this embodiment, the charging roller 2 as a contact charging roller has a medium resistance elastic foam layer in which carbon is dispersed in urethane as a flexible member on a cored bar. The cell structure of the elastic foam of the charging roller is open cells. In advance, the conductive particles (M2) that can be moved are uniformly applied to the charging roller at a density of ³ mg / cm ³ by using the conductive particle coating device shown in FIG.

  The medium resistance layer was formulated with urethane, conductive particles (for example, carbon black), a sulfurizing agent, a foaming agent, and the like, and formed in a roller shape on the core metal. Thereafter, if necessary, the surface was polished to prepare a charging roller 2 which is a conductive elastic roller having a diameter of 16 mm and a longitudinal length of 300 mm.

  The roller resistance of the charging roller 2 of this example was measured and found to be 100 kΩ. The roller resistance was measured by applying 100 V between the cored bar and the aluminum drum in a state where the charging roller 2 was pressure-bonded to an aluminum drum having a diameter of 30 mm so that the cored bar of the charging roller 2 was loaded with a total pressure of 1 kg.

Here, it is important that the charging roller 2 which is a contact charging 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 when a low-voltage defect site such as a pinhole is present in the member to be charged. When an electrophotographic photoreceptor is used as the member to be charged, a resistance of 10 ⁴ to 10 ⁷ Ω is desirable in order to obtain sufficient chargeability and leakage resistance.

  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.

  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.

  The charging roller 2 is disposed in pressure contact with the photosensitive drum 1 as a member to be charged against elasticity with a predetermined pressing force, and in this embodiment, a charging nip portion having a width of 3 mm is formed.

  In this embodiment, the charging roller 2 is driven to rotate in the clockwise direction indicated by the arrow at about 100 rpm so that the surface of the charging roller and the surface of the photosensitive member move in the opposite directions in the charging nip portion A at a constant speed. That is, the surface of the charging roller 2 as a contact charging roller has a peripheral speed difference with respect to the surface of the photosensitive drum 1 as a member to be charged.

  A DC voltage of −440 V is applied as a charging bias from the charging bias application power source S1 to the core 2a of the charging roller 2.

(4) Developer 4
The developing device 4 of this embodiment is a reversal developing device 4 using a one-component magnetic toner (negative toner) as the developer t.

  Reference numeral 4b denotes a non-magnetic rotating developing sleeve as a developer carrying member enclosing a magnet roll 4C (50 to 100 mT). The developer t is formed into a thin layer by a magnetic blade 4a facing the rotating developing sleeve 4b in a non-contact manner. Coated.

  The layer thickness of the developer t with respect to the rotating developing sleeve 4b is regulated by the magnetic blade 4a. At this time, the developer t is given an electric charge by frictional charging with the sleeve.

  The developer coated on the rotating developing sleeve 4b is conveyed to a developing portion (developing region portion) which is a portion facing the photosensitive drum 1 and the sleeve 4b by the rotation of the sleeve 4b. A developing bias voltage is applied to the sleeve 4b from a developing bias applying power source. The development bias voltage used was a superposition of a DC voltage of −230 V and a rectangular AC voltage with a frequency of 1800 Hz and a peak-to-peak voltage of 800 V. As a result, the electrostatic latent image on the photosensitive drum 1 side is developed with toner.

  Developer t, that is, one-component magnetic toner, is prepared by mixing binder resin, magnetic particles, and charge control agent, and kneading, pulverizing, and classifying, and adding a fluidizing agent or the like as an external additive. It was created. The weight average particle diameter (D4) of the toner was 7 μm.

  In this embodiment, 2% by weight of conductive particles M1 as conductive particles are added to 100 parts by weight of the developer t.

(5) Migration between developer t and conductive particles M1 The conductive particles M1, which are conductive particles added by 2% by weight to the developer t of the developing device 4, are electrostatically charged on the photosensitive drum 1 side by the developing device 4. When developing the toner of the latent image, an appropriate amount is transferred to the photosensitive drum 1 side together with the toner in the developing section a.

  The toner image on the photosensitive drum 1 is attracted and actively transferred to the recording material P side due to the influence of the transfer bias at the transfer nip b, but the conductive particles M1 on the photosensitive drum 1 are conductive particles. The recording material P is not positively transferred to the recording material P side, and remains substantially adhered and held on the photosensitive drum 1.

  Since the copying machine is cleanerless, the conductive particles M1 remaining on the surface of the photosensitive drum 1 after transfer are transferred to the charging nip portion A, which is the nip portion between the photosensitive drum 1 and the charging roller 2, on the surface of the photosensitive drum 1. As it moves, it is carried as it is, adheres to the charging roller 2, and is supplied to the charging roller 2.

  That is, even if the conductive particles fall off from the charging roller 2, the copying machine is operated, so that the conductive particles M <b> 1 that are conductive particles contained in the developer t of the developing device 4 are formed in the developing portion a. The surface of the photosensitive drum 1 moves to the surface of the photosensitive drum 1 and is moved to the charging nip A via the transfer nip portion by the movement of the surface of the photosensitive drum 1 and sequentially supplied to the charging roller 2.

  The conductive particles dropped from the charging roller 2 are collected by the developing device 4 and mixed with the developer t for circulation.

  Since the copying machine is cleanerless, the residual toner remaining on the surface of the photosensitive drum 1 after transfer is held as it is by moving the surface of the photosensitive drum 1 to the charging nip A where the photosensitive drum 1 and the charging roller 2 are in contact with each other. It is carried and adheres to and mixes with the charging roller 2. Even if the transfer residual toner adheres to and mixes with the charging roller 2 in this way, the conductive particles M1 and M2 are present in the charging nip portion A, which is the nip portion between the photosensitive drum 1 and the charging roller 2, whereby the charging roller. 2 can maintain the close contact property and contact resistance to the photosensitive drum 1, so that the ozone-less direct injection charging can be stably maintained over a long period of time at a low applied voltage regardless of the contamination of the transfer roller 2 with the transfer roller toner. And uniform chargeability can be provided.

  Since the charging roller 2 is in contact with the photosensitive drum 1 with a peripheral speed difference, the transfer residual toner from the transfer nip portion to the charging nip portion A is disturbed due to the pattern being disturbed. The previous image pattern portion does not appear as a ghost.

  The transfer residual toner adhering to and mixed in the charging roller 2 is gradually discharged from the charging roller 2 onto the photosensitive drum 1, reaches the developing portion along with the movement of the surface of the photosensitive drum 1, and is simultaneously cleaned (collected) by the developing means.

  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 copying machine in the present 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 light portion potential of the photosensitive member. This is done by the action of the electric field.

(6) Conductive Particles In this embodiment, the conductive particles M2 previously applied to the charging roller are conductive zinc oxide particles having a specific resistance of 10 ⁶ Ω · cm, an average particle size of 3 μm, and a bulk density of 0.4 g / cm ^3. Was used. The bulk density of the conductive particles was measured according to JIS K5101. (The name of the conductive zinc oxide particles used this time is 23-K (C), manufactured by Hakusui Tech Co., Ltd.)
In order to obtain uniform chargeability, the conductive particles preferably have a particle size of 10 μm or less and finer.

Further, the particle resistance is preferably 10 ¹² Ω · cm or less, more preferably 10 ¹⁰ Ω · cm or less as the specific resistance is to transfer charges through particles.

  There is no problem that the conductive particles exist not only in the state of primary particles but also in the state of aggregation of secondary particles.

  In this embodiment, the conductive particles M1 mixed with the developer were equivalent to the conductive particles M2 previously applied to the charging roller.

  If the particle size of the conductive particles is too small, the low-resistance particles cover the surface of the toner, and the toner cannot be sufficiently frictionally charged, thereby deteriorating the development characteristics. On the other hand, if the particle size is too large, the particles are shielded from light at the time of exposure, or after development, the particles become noticeable in the toner, resulting in image unevenness and the like, thereby deteriorating the image. Therefore, the particle size of the conductive particles added to the developer is desirably 0.1 μm or more and not more than the toner particle size.

  The conductive particles are present in the charging nip portion A which is the nip portion between the photosensitive drum 1 which is a member to be charged and the charging roller 2 which is a contact charging roller. Even if the charging roller has a large resistance and is difficult to be brought into contact with the photosensitive drum 1 with a peripheral speed difference as it is, it can be easily and effectively applied to the surface of the photosensitive drum 1 without difficulty. It becomes possible to make the contact state with a peripheral speed difference.

  By providing a peripheral speed difference between the charging roller 2 and the photosensitive drum 1, the chance of the conductive particles contacting the photosensitive drum 1 at the nip portion between the charging roller 2 and the photosensitive drum 1 is remarkably increased, and high contactability is achieved. The conductive particles existing in the nip portion between the charging roller 2 and the photosensitive drum 1 can rub the surface of the photosensitive drum 1 without any gap so that the charge can be directly injected into the photosensitive drum 1. In the contact charging of the photosensitive drum 1 by 2, direct injection charging is dominant due to the presence of conductive particles.

(7) Photoconductor 1
The image carrier used in this example is a rotating drum type electrophotographic photosensitive member. The copying machine of this embodiment uses reversal development, and the photosensitive member is a negative a-Si photosensitive member having a diameter of 30 mm and is driven to rotate in the direction of the arrow at a peripheral speed of 210 mm / sec.
A schematic cross-sectional view of the image carrier is shown in FIG.

  The image carrier used in this example is a single-layer type light receiving member composed of a single layer in which the photoconductive layer is not functionally separated. The a-Si photoreceptive member shown in FIG. 4 includes a conductive substrate 101 such as aluminum, a charge injection blocking layer 102, a photoconductive layer 103, a buffer layer 104, and a surface layer 105 sequentially stacked on the surface of the conductive substrate 101. Consists of. Here, the charge injection blocking layer 102 blocks the injection of charges from the conductive substrate 101 to the photoconductive layer 103, and is provided as necessary. The photoconductive layer 103 is made of an amorphous material containing at least silicon atoms and exhibits photoconductivity. Further, the surface layer 105 is made of an aC: H film containing carbon atoms and hydrogen atoms, and has the ability to maintain a visible image in an electrophotographic apparatus.

  In the following description, it is assumed that the charge injection blocking layer 102 is present unless the effect varies depending on the presence or absence of the charge injection blocking layer 102.

As the film forming gas for the surface layer 105, gases such as CH ₄ , C ₂ H ₆ , C ₃ H ₈ , C ₄ H ₁₀ , and hydrocarbons that can be gasified can be effectively used. Further, these raw material gases for supplying carbon may be diluted with a gas such as H2, He, Ar, Ne or the like as necessary.

  Using a plasma CVD apparatus with VHF, the lower blocking layer, photoconductive layer, buffer layer, and surface layer are sequentially laminated on the cylindrical AL substrate under the conditions shown in Table 1, and a light receiving member used for negative charging is completed. I let you.

(Example 2)
In this embodiment, in the copying machine of the first embodiment, conductive particles (M2) that can be moved to the charging roller are applied in advance by a conductive particle applying apparatus using an application roller having a smooth surface. On the outer peripheral surface of the initial charging roller, conductive particles are present at a density of 5 mg / cm ³ .

  The rest is the same as the copying machine of the first embodiment.

(Example 3)
In this embodiment, an organic photoconductive (OPC) photoreceptor is used in the copying machine of the first embodiment. A charge injection layer was provided on the surface of the photoconductor 1 for the purpose of reducing the frictional force between the conductive particles and the surface of the photoconductor and adjusting the resistance of the photoconductor surface to further stably and uniformly charge. .

  FIG. 5 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.

The charge injection layer 16 is composed of a photo-curing acrylic resin as a binder, SnO ₂ ultrafine particles 16a (diameter of about 0.03 μm) as conductive particles (conductive filler), tetrafluoroethylene resin (trade name Teflon ( (Registered trademark))), a polymerization initiator, and the like are mixed and dispersed, and after coating, a film is formed by a photocuring method.

The important points as the charge injection layer 16 are the resistance and surface energy of the surface layer. In the charging method using direct injection of charges, charges can be exchanged more efficiently by reducing the resistance on the charged object side. Meanwhile, it is necessary for a predetermined time holding the electrostatic latent image in the case of using as an image bearing member (photosensitive ^{member), 1 × 10 9 ~1 ×} 10 14 as the volume resistivity of the charge injection layer 16 (Omega · cm) is suitable.

  Further, since the charge injection layer contains the lubricant, the surface energy of the member to be charged is reduced. For this reason, the toner easily moves to the transfer material, and the paper dust does not easily adhere to the charged body. Therefore, the contact charging member is less contaminated with the toner and paper dust, and the charging ability of the charging roller is maintained over a long period of time. Furthermore, since the frictional force between the accelerating particles and the member to be charged becomes small, the wear of the member to be charged is greatly reduced.

On the outer peripheral surface of the initial charging roller, conductive particles are present at a density of 3 mg / cm ³ .
The rest is the same as the copying machine of the first embodiment.

(Comparative Example 1)
In this comparative example, in the copying machine of Example 1, conductive particles (M2) that can be moved to the charging roller were previously applied using a brush, and 1.5 mg of the conductive particles were formed on the outer peripheral surface of the initial charging roller. It exists at a density of / cm ³ .

  The rest is the same as the copying machine of the first embodiment.

(Comparative Example 2)
In this comparative example, in the copying machine of Example 3, conductive particles (M2) that can be moved to the charging roller are applied in advance using a brush, and 1.5 mg of the conductive particles are formed on the outer peripheral surface of the initial charging roller. It exists at a density of / cm ³ .

Others are the same as those of the copying machine of the fourth embodiment.
[Evaluation]
Evaluation of Solid White Toner Fog The solid white toner fog was evaluated in the above Examples and Comparative Examples. The results are summarized in a table.

  For the evaluation, A4 paper was used, and a solid white image was printed in the middle of printing a character pattern (A4 vertical direction) with a printing rate of 20%, and the solid white image was evaluated.

  The solid white image was evaluated using a reflection densitometer, measuring 10 points of the reflectance of the paper as it was not passed through the copier and 10 points of the reflectance of the paper on which the solid white was recorded, The value with the smallest reflectance was obtained and evaluated by the difference between the two reflectances. The original paper and the paper before recording solid white have almost the same reflectance.

The evaluation results of the examples and comparative examples are shown in the following table. In the following table, the vertical axis represents the difference between the reflectance of the paper as it is and the reflectance of the paper printed with solid white, and the horizontal axis represents the number of printed character patterns with a printing rate of 20%.
1. Results of Examples and Comparative Examples using a-Si photoconductors are shown below.

  In Example 1 and Example 2, from the initial printing up to 100,000 sheets, the solid white image had a reflectance difference of 1.2% or less, and there was almost no toner fog.

This is a density of bulk density on the outer peripheral surface of the initial charging roller 0.4 g / cm ³ of the conductive particles in Example 1, ³ mg / cm 3, uniformly at a density of Example 2, 5 mg / cm ³ The density value of the conductive particles applied to this charging roller is 4 × 10 ⁻³ × ρ g / cm ³ (where ρ is the bulk density of the conductive particles measured by JIS K 5101 ρ g / cm ³ ) or more. Therefore, in the embodiment, since a sufficient amount of conductive particles are held on the charging roller from the beginning of the number of printed sheets, even when the reversal component transfer residual toner adheres to the charging roller even in the initial state, the toner and conductive particles The toner of the reversal component becomes a regular charge and is discharged onto the drum and collected by the developing device. As a result, toner fog hardly occurs in printing 100,000 sheets from the initial state of the apparatus.

  In addition, the toner fog of the second embodiment is better than that of the first embodiment. The reason is that the conductive particle coating apparatus using a coating roller having a smooth surface is easier to fill a charging roller with a sufficient amount of conductive particles than the conductive particle coating apparatus using a fur brush. This is because the larger amount of conductive particles was held in this charging roller than in the charging roller of Example 1.

  In the comparative example, there was a difference in reflectance of 2% or more in the initial stage, and toner fogging occurred.

It need not only be applied at a density of conductive particles having a bulk density of 0.4 g / ^{cm @ 3} is 1.6 mg / cm ³ on the outer peripheral surface of the charging roller, the value of the density of the conductive particles is coated on the charging roller 4 × 10 ⁻³ × ρ g / cm ³ (where ρ is the bulk density of conductive particles measured by JIS K 5101 ρ g / cm ³ ) or less. For this reason, in the comparative example, a sufficient amount of conductive particles are not held on the charging roller. Therefore, when the reversal component transfer residual toner adheres to the charging roller at the initial number of printed sheets, the toner and the conductive particles The toner of the reversal component is discharged on the drum without having a regular charge, and is not collected by the developing device, but is attached to the transfer member and fogging occurs.

  However, as the number of printed sheets increased, the toner fog gradually decreased, and the toner fog of the comparative example became almost the same as the toner fog of the example after the number of printed sheets of 60,000. This is because as the number of printed sheets increases, the amount of conductive particles supplied from the developing unit to the charging roller increases, which is almost the same as the amount of conductive particles held by the charging roller of the embodiment. .

  2. Next, the results of Examples and Comparative Examples using organic photoconductive (OPC) photoreceptors are shown below.

  In Example 3, there was almost no toner fog, with a solid white image having a reflectance difference of 1.0% or less from the initial printing to 10,000 printing.

This is because conductive particles with a bulk density of 0.4 g / cm ³ are uniformly applied at a density of 3 mg / cm ³ on the outer peripheral surface of the initial charging roller, and the density of the conductive particles applied to this charging roller Is 4 × 10 ⁻³ × ρ g / cm ³ (where ρ is the bulk density of conductive particles ρ g / cm ³ measured according to JIS K 5101). Therefore, in the embodiment, since a sufficient amount of conductive particles are held on the charging roller from the beginning of the number of printed sheets, even when the reversal component transfer residual toner adheres to the charging roller even in the initial state, the toner and conductive particles The toner of the reversal component becomes a regular charge and is discharged onto the drum and collected by the developing device. As a result, toner fog hardly occurs in printing 10,000 sheets from the initial state of the apparatus.

In Comparative Example 2, the difference in reflectance was 1% or more in the initial stage, and toner fogging occurred. This is because conductive particles with a bulk density of 0.4 g / cm ³ are only applied at a density of 1.6 mg / cm ³ on the outer peripheral surface of the charging roller, and the density value of the conductive particles applied to this charging roller is 4 × 10 ⁻³ × ρ g / cm ³ (where ρ is the bulk density of conductive particles ρ g / cm ³ measured by JIS K 5101) or less. For this reason, in the comparative example, a sufficient amount of conductive particles are not held on the charging roller. Therefore, when the reversal component transfer residual toner adheres to the charging roller at the initial number of printed sheets, the toner and the conductive particles The toner of the reversal component is discharged on the drum without having a regular charge, and is not collected by the developing device, but is attached to the transfer member and fogging occurs.

Charging characteristic graph Schematic configuration diagram of image forming apparatus of embodiment Schematic configuration diagram of the conductive particle coating apparatus of the embodiment Schematic cross section of a-Si photoconductor used in the examples Schematic cross section of organic photoconductive (OPC) photoconductor used in the examples

Explanation of symbols

1 Photoconductor (image carrier, charged body)
2 Charging roller 3 Laser beam scanner (exposure device)
4 Developing container 4a Magnetic blade 4b Developing sleeve 4c Magnet 4d Stirring bar 5 Transfer roller 6 Main charge eliminating light 7 Fixing roller C Process cartridge P Transfer material t Developer (toner)
M1, M2 conductive particles 101 conductive substrate 102 charge injection preventing layer 103 photoconductive layer 104 buffer layer 105 surface layer

Claims (8)

A charging roller in which a layer of a conductive elastic foam having a porous surface is formed on a cored bar, and 4 × 10 ⁻³ movable conductive particles are placed on the outer peripheral surface of the charging roller in contact with the member to be charged. A charging roller characterized in that it is applied at a density equal to or higher than × ρ g / cm ³ (where ρ is the bulk density of conductive particles measured by JIS K 5101 ρ g / cm ³ ).   2. The charging roller according to claim 1, wherein the cell structure of the elastic foam of the charging roller is an open cell or a semi-independent semi-open cell.   In order to apply a necessary amount of conductive particles to the charging roller in advance, a charging roller having a step of contacting the charging roller with a coating roller for supplying and applying the conductive particles and rotating the rollers with a difference in peripheral speed. Production method.   4. The method for manufacturing a charging roller according to claim 3, wherein the surface of the application roller is smooth.   4. The method for manufacturing a charging roller according to claim 3, wherein the application roller is a fur brush roller.   Rotating image carrier, charging means for charging the image carrier, image information writing means for forming an electrostatic latent image on the charging surface of the image carrier, and developing means for visualizing the electrostatic latent image with toner And a transfer means for transferring the toner image to a recording medium, wherein there is no means for removing the toner from the image carrier between the transfer means and the charging means, and the conductive particles are added to the toner weight. An image forming apparatus comprising: a one-component developer containing 0.5% to 5% of the toner, wherein a charging roller is brought into contact with a member to be charged and driven with a peripheral speed difference with respect to the image carrier.   The image carrier comprises a photoconductive layer made of a non-single crystal material based on silicon atoms and a surface layer made of a non-single crystalline hydrogenated carbon film on a conductive substrate. 7. The image forming apparatus according to claim 6. The image carrier is an organic photoconductive (OPC) photoreceptor,
A charge injection layer made of a material of 10 ⁹ to 10 ¹⁴ (Ω · cm) is provided on the surface of the image carrier, and the charge injection layer contains a light-transmitting insulating binder, a lubricant powder, and conductive particles. 7. The image forming apparatus according to claim 6, wherein

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