JPH10307459A - Method and device for electrification, image forming device and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize directly injecting electrification which is excellent in uniformity of electrification and which is stable over a long time, that is, to realize the ozoneless directly injecting electrification with a low applied voltage and a simple constitution even in the case that such a simple member having a low cost as an electrifying roller is used as a contact electrifying member in a contact electrifying device. SOLUTION: This electrifying device electrifies the surface of a body 1 to be electrified by a flexible electrifying member 2 forming a nip part (n) and the body to be electrified when a voltage is applied and the contact electrifying member 2 with respect to the body 1 is an elastic body, is made to rotate while having a speed difference with respect to the body 1 so that the static friction coefficient of frictional force working between the member 2 and the body 1 is <=2.5.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method and a device for charging an object to be charged. More specifically, a voltage is applied,
The present invention relates to a charging method and a charging device of a contact charging method for charging a surface of an object to be charged by a flexible charging member forming a nip portion with the object to be charged.

[0002] Further, the present invention relates to an image forming apparatus provided with the charging device as a charging means for an image carrier, and a process cartridge detachable from the image forming apparatus.

[0003]

2. Description of the Related Art Conventionally, for example, an electrophotographic apparatus (copier,
2. Description of the Related Art In image forming apparatuses such as printers and electrostatic recording devices, an image carrier (charged body) such as an electrophotographic photosensitive member or an electrostatic recording dielectric is uniformly charged to a required polarity and potential (static elimination process). A corona charger (a corona discharger) has often been used as a charging device.

[0004] The corona charger is a non-contact type charging device, which includes a discharge electrode such as a wire electrode and a shield electrode surrounding the discharge electrode, and has a discharge opening facing the image carrier as a member to be charged. The surface of the image carrier is charged in a predetermined manner by exposing the surface of the image carrier to a discharge current (corona shower) generated by applying a high voltage to the discharge electrode and the shield electrode.

Recently, medium- and low-speed image forming apparatuses have advantages such as low ozone and low power as compared with corona chargers as a charging device for a member to be charged such as an image carrier. Many contact charging devices have been proposed and put into practical use.

[0006] The contact charging device includes a charging member such as a roller type (charging roller), a fur brush type, a magnetic brush type, a blade type, or the like. ) Is contacted, and a predetermined charging bias is applied to the contact charging member to charge the surface of the member to be charged to a predetermined polarity and potential.

[0007] The contact charging mechanism (charging mechanism,
In the charging principle), there are two types of charging mechanisms, a discharge charging mechanism and a direct injection charging mechanism, and each characteristic appears depending on which one is dominant.

[0008] Discharge Charging Mechanism This is a mechanism in which the surface of the member to be charged is charged by a discharge phenomenon occurring in a minute gap between the contact charging member and the member to be charged.

Since the discharge charging mechanism has a fixed discharge threshold for the contact charging member and the member to be charged, it is necessary to apply a voltage higher than the charging potential to the contact charging member. Further, although the amount of generation is much smaller than that of the corona charger, it is in principle unavoidable to generate a discharge product, so that the harmful effects of active ions such as ozone are inevitable.

[0010] Direct injection charging mechanism This is a system in which the surface of the object to be charged is charged by injecting charge directly from the contact charging member to the object to be charged. It is also called direct charging, injection charging, or charge injection charging. More specifically, a medium-resistance contact charging member is brought into contact with the surface of the member to be charged, and charges are directly injected into the surface of the member without causing a discharge phenomenon, that is, basically without using discharge. Therefore, even when the voltage applied to the contact charging member is equal to or lower than the discharge threshold, the member to be charged can be charged to a potential corresponding to the applied voltage.

Since this charging system does not involve generation of ions, no adverse effects are caused by the discharge products. However, because of direct injection charging, the contact property of the contact charging member to the member to be charged greatly affects the charging property. Therefore, it is necessary to form the contact charging member more densely, have a large speed difference from the member to be charged, and contact the member 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.

In the roller charging, the charging mechanism is dominated by the discharging charging mechanism.

The charging roller is made of a conductive or medium-resistance rubber or foam. In some cases, these are laminated 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). Therefore, frictional resistance is large, and in many cases, the charging roller is driven by the photosensitive member. It is driven with a slight speed difference. Therefore, even if an attempt is made to perform direct injection charging, the charging mechanism is reduced by the conventional roller charging because the absolute charging ability is reduced, the contact is insufficient, the roller is uneven, and the charging is uneven due to the adhesion of the photoconductor. The charging mechanism is dominant.

FIG. 5 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 photoconductor charging potential obtained at that time. The charging characteristic in the case of roller charging is represented by A. That is, charging starts after passing a discharge threshold of about -500V. Therefore, when charged to -500V, -10
00V DC voltage or -500V
In general, in addition to the DC charging voltage, an AC voltage having a peak-to-peak voltage of 1200 V is applied so as to always have a potential difference equal to or larger than the discharge threshold value so that the photoconductor potential converges on the charging potential.

More specifically, when a charging roller is pressed against an OPC photosensitive member having a thickness of 25 μm, the surface potential of the photosensitive member increases when a voltage of about 640 V or more is applied. Start, and after that, slope 1 with applied voltage
, The photoconductor surface potential increases linearly. This threshold voltage is defined as charging start voltage Vth.

That is, in order to obtain the photosensitive member surface potential Vd required for electrophotography, the charging roller needs Vd + Vth
Therefore, a DC voltage higher than required is required. A method of applying only a DC voltage to the contact charging member to perform charging in this manner 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 and the like, and Vth fluctuates when the film thickness changes due to the shaving of the photoreceptor. It was difficult to value.

For this reason, as disclosed in Japanese Patent Application Laid-Open No. 63-149669, a DC voltage corresponding to a desired Vd has a peak-to-peak voltage of 2 × Vth or more, as disclosed in JP-A-63-149669. An “AC charging method” in which a voltage on which an AC component is superimposed is applied to a contact charging member is used. This is for the purpose of effect of leveling the potential by AC, and the potential of the charged body is V V which is the center of the peak of the AC voltage.
It converges to d and is not affected by disturbances such as the environment.

However, even in such a contact charging device, since the essential charging mechanism uses a discharge phenomenon from the contact charging member to the photosensitive member, the charging is applied to the contact charging member as described above. The voltage is required to be higher than the surface potential of the photoreceptor, and a small amount of ozone is generated.

When AC charging is performed for uniform charging, further generation of ozone, generation of vibration noise (AC charging noise) between the contact charging member and the photosensitive member due to the electric field of the AC voltage, and generation of discharge due to discharge. Deterioration of the surface of the photoreceptor becomes remarkable, and this is a new problem.

B) Fur Brush Charging In the fur brush charging, a member having a brush portion of a conductive fiber (fur brush charger) is used as a contact charging member.
The conductive fiber brush portion is brought into contact with a photoreceptor as a member to be charged, and a predetermined charging bias is applied to charge the photoreceptor surface to a predetermined polarity and potential.

In the fur brush charging, the discharging mechanism is dominant in the charging mechanism.

As the fur brush charger, a fixed type and a roll type have been put to practical use. A fixed type is formed by folding a medium-resistance fiber into a base fabric and forming it in a pile shape and bonding it to an electrode. The roll type is formed by winding a pile around a cored bar. A fiber density of about 100 fibers / mm ² can be obtained relatively easily, but the contact property is still insufficient to perform sufficiently uniform charging by direct injection charging.
In order to perform sufficiently uniform charging by direct injection charging, it is necessary to provide a photoconductor with a speed difference that is difficult as a mechanical configuration, which is not practical.

The charging characteristic of the fur brush charging when a DC voltage is applied has the characteristic shown in FIG. 5B. Therefore, also in the case of the fur brush charging, in both the fixed type and the roll type, charging is performed by applying a high charging bias and using a discharge phenomenon.

C) Magnetic Brush Charging In the magnetic brush charging, a member (magnetic brush charger) having a magnetic brush portion in which conductive magnetic particles are magnetically constrained by a magnet roll or the like to form a brush is used as a contact charging member. The magnetic brush 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 the magnetic brush charging, the charging mechanism is dominated by the direct injection charging mechanism.

By using conductive magnetic particles having a particle size of 5 to 50 μm as the magnetic brush portion and providing a sufficient speed difference from the photosensitive member, direct injection charging can be uniformly performed.

As shown in C of the charging characteristic graph of FIG.
It is possible to obtain a charging potential substantially proportional to the applied bias.

However, there are other disadvantages such as a complicated device configuration, and the conductive magnetic particles constituting the magnetic brush portion falling off and adhering to the photoreceptor.

Japanese Patent Application Laid-Open No. Hei 6-3921 proposes a method in which charge is injected into a charge holding member such as a trap level on the surface of a photoreceptor or conductive particles in 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 surface potential of the photoconductor, and no ozone is generated. Furthermore, since no AC voltage is applied, no charging noise is generated, and the charging method is excellent in ozone-less and low-power compared to the roller charging method.

D) Toner Recycling Process (Cleanerless System) In a transfer type image forming apparatus, untransferred toner remaining on a photoconductor (image carrier) after transfer is removed from the photoconductor surface by a cleaner (cleaning device). However, it is desirable that the waste toner does not appear from the viewpoint of environmental protection. Therefore, the image forming apparatus of the toner recycling process is configured to eliminate the cleaner and remove the transfer residual toner on the photoreceptor after transfer from the photoreceptor by "development simultaneous cleaning" by the developing device, and to collect and reuse it in the developing device. Has also appeared.

Simultaneous development and cleaning means that the toner remaining on the photoreceptor after transfer is developed at the next and subsequent steps, that is, the photoreceptor is subsequently charged and exposed to form a latent image. This is a method of recovering by a picking bias (fogging potential difference Vback which is a potential difference between a DC voltage applied to the developing device and a surface potential of the photoconductor). According to this method, the transfer residual toner is collected in the developing device and reused after the next process. Therefore, waste toner can be eliminated and troublesome maintenance can be reduced. In addition, the cleaner-less system has a great advantage in terms of space, and can greatly reduce the size of the image forming apparatus.

E) Powder Coating on Contact Charging Member For the contact charging device, in order to prevent charging unevenness and to perform stable and uniform charging, a configuration in which powder is applied to the contact charging member on the contact surface with the surface of the member to be charged is particularly fair. As disclosed in Japanese Patent Application Laid-Open No. 7-99442, the contact charging member (charging roller) is driven to rotate (no speed difference driving) by the member to be charged (photoreceptor), and generates ozone as compared with a corona charger such as a scorotron. Although the generation of objects is remarkably reduced, the charging principle is mainly based on the discharge charging mechanism as in the case of the above-described roller charging. In particular, since a voltage obtained by superimposing an AC voltage on a DC voltage is applied in order to obtain more stable charging uniformity, generation of ozone products due to discharge is increased. Therefore, when using the device for a long time,
When a cleanerless image forming apparatus is used for a long period of time, adverse effects such as image deletion due to ozone products are likely to appear.

Japanese Patent Application Laid-Open No. 5-150539 discloses that in an image forming method using contact charging, charge inhibition due to toner particles or silica fine particles adhering to the surface of the charging means during repeated image formation for a long time. It is disclosed that the developer contains at least visible particles and conductive particles having an average particle size smaller than the visible particles in order to prevent the development. However, this contact charging is based on the discharge charging mechanism, and has the above-mentioned problem due to the discharge charging, not the direct injection charging mechanism.

[0037]

As described in the section of the prior art described above, in contact charging, it is difficult to perform direct injection charging with a simple configuration using a charging roller or a fur brush as a contact charging member. In an image forming apparatus, image fogging (in the case of reversal development, a white background portion is developed) and uneven charging occur due to absolute charging failure.

On the other hand, a powder is applied to the contact surface of the contact charging member with the surface to be charged, and the contact charging member is driven. When a cleaner-less image forming apparatus is used for a long period of time, an ozone product accumulates, so that image deletion easily occurs.

In a cleaner-less image forming apparatus, the transfer residual toner causes charging failure in the charging section.

Therefore, in the present invention, in contact charging,
Even when a simple and inexpensive member such as a charging roller is used as a contact charging member, it realizes direct injection charging that is more excellent in charging uniformity and stable for a long period of time, that is, ozoneless direct injection charging at a low applied voltage. With a simple configuration.

It is another object of the present invention to provide an image forming apparatus and a process cartridge which have a simple configuration and are inexpensive and free from obstacles due to ozone products and poor charging.

[0042]

According to the present invention, there is provided a charging method, a charging device, an image forming apparatus and a process cartridge having the following constitutions.

(1) A charging method in which a voltage is applied and the surface of a member to be charged is charged by a flexible charging member forming a nip with the member to be charged.
A charging method, which is an elastic body, moves at a speed difference with respect to the member to be charged, and has a static friction coefficient of a frictional force acting between the contact charging member and the member to be charged of 2.5 or less.

(2) The charging method according to (1), wherein the static friction coefficient of the frictional force acting between the contact charging member and the member to be charged is 0.1 or more and 2.5 or less.

(3) A powder is present at least in a nip portion between a contact charging member and a member to be charged (1).
Or the charging method according to (2).

(4) The resistance of the powder is 1 × 10 ¹² (Ω ·
cm) or less.

(5) The resistance of the powder is 1 × 10 ¹⁰ (Ω ·
cm) or less.

(6) The particle size of the powder is 10 nm or more and 50
The charging method according to any one of (3) to (5), which is not more than μm.

(7) The charging method according to any one of (1) to (6), wherein the contact charging member rotates at a counter with respect to the member to be charged.

(8) The charging method according to any one of (1) to (7), wherein the charging member is made of an elastic foam.

(9) The method according to any one of (1) to (8), wherein the volume resistivity of the outermost surface layer of the member to be charged is 1 × 10 ¹⁴ (Ω · cm) or less. Charging method.

(10) The object to be charged is an electrophotographic photosensitive member, and the outermost surface layer of the electrophotographic photosensitive member has a volume resistance of 1 × 1.
The charging method according to any one of (1) to (9), wherein the charging method is not less than 0 ⁹ (Ω · cm) and not more than 1 × 10 ¹⁴ (Ω · cm).

(11) A charging device in which a voltage is applied and the surface of the member to be charged is charged by a flexible charging member forming a nip with the member to be charged. The contact charging member for the member to be charged is an elastic member. And a longitudinal width 10 which moves with a speed difference with respect to the member to be charged and acts between the contact charging member and the member to be charged.
A charging device having a static friction coefficient of friction force per mm of 2.5 or less.

(12) The static friction coefficient of the frictional force per 10 mm of the longitudinal width acting between the contact charging member and the member to be charged is 0.1 or more and 2.5 or less.
3. The charging device according to claim 1.

(13) A powder is present at least on the contact surface between the contact charging member and the member to be charged.
The charging device according to (1) or (12).

(14) The resistance of the powder is 1 × 10 ¹² (Ω)
(Cm) or less.

(15) The resistance of the powder is 1 × 10 ¹⁰ (Ω)
(Cm) or less.

(16) The particle size of the powder is 10 nm or more and 5
(13) to (1)
The charging device according to any one of 5).

(17) The charging device according to any one of (11) to (16), wherein the contact charging member rotates at a counter with respect to the member to be charged.

(18) The charging device according to any one of (11) to (17), wherein the charging member is made of an elastic foam.

(19) The method according to any one of (11) to (18), wherein the volume resistivity of the outermost surface layer of the member to be charged is 1 × 10 ¹⁴ (Ω · cm) or less. Charging device.

(20) The member to be charged is an electrophotographic photosensitive member, and the outermost surface layer of the electrophotographic photosensitive member has a volume resistance of 1 × 1.
The charging device according to any one of (11) to (19), wherein the charging device has a value of from ⁹ (Ω · cm) to 1 × 10 ¹⁴ (Ω · cm).

(21) An image forming apparatus for forming an image by applying an image forming process including a step of charging the image carrier to the image carrier, wherein the step of charging the image carrier is (11). 20. An image forming apparatus, which is the charging device according to any one of (20) to (20).

(22) A process cartridge detachably mountable to an image forming apparatus main body for executing image formation by applying an image forming process including a step of charging the image carrier to the image carrier. And charging means for charging the image bearing member, wherein the charging means includes (11)
20. A process cartridge, which is the charging device according to any one of (20) to (20).

<Operation> As described above, in the case of the conventional roller charging, the charging roller is driven to rotate with respect to the member to be charged, and the charging mechanism is mainly a discharge charging mechanism utilizing a discharge phenomenon. is there.

The direct injection charging, which is the object of the present invention, is based on the fact that the charge is directly transferred from the contact charging member to the portion to be charged. It is necessary that the charging roller as described above sufficiently contacts the surface of the member to be charged, and the driven rotation is insufficient.

In order to bring the charging roller into sufficient contact with the surface of the member to be charged, it is necessary to rotate the charging roller with a peripheral speed difference with respect to the member to be charged, similarly to the magnetic brush charger described above. . However, the contact charging member composed of an elastic body cannot be rotated with a speed difference between the charged member because of a large frictional force between the contact charging member and the charged member. In addition, there has been a problem that when the forcible rotation is performed, the surfaces of the contact charging member and the member to be charged are scraped.

Therefore, in the present invention, when the surface of the contact charging member using the elastic body is brought into contact with the member to be charged while moving the member at a different speed, the contact between the contact charging member and the member to be charged is changed. By reducing the frictional force, the initial drive torque of the contact charging member is reduced, and the surface of the contact charging member can be moved stably, and a uniform direct contact state is obtained at the charging nip between the contact charging member and the charged body. This enables uniform direct injection charging.

Specifically, the speed difference between the charging member and the member to be charged is determined by moving the surface of the charging member to provide a speed difference between the member and the member to be charged. Preferably, the charging member is driven to rotate, and the rotation direction is rotated in a direction opposite to the moving direction of the surface of the charged member.

Although it is possible to move the surface of the charging member in the same direction as the moving direction of the surface of the member to be charged so as to have a speed difference, the charging property of the direct injection charging is different from the peripheral speed of the member to be charged and the peripheral speed of the charging member. In order to obtain the same peripheral speed ratio as that in the reverse direction, the rotation speed of the charging member in the forward direction is larger than that in the reverse direction because it depends on the speed ratio. It is advantageous in the point. The peripheral speed ratio described here is the peripheral speed ratio (%) = (the peripheral speed of the charging member−the peripheral speed of the member to be charged) / the peripheral speed of the member to be charged × 100. It is a positive value when moving in the same direction as the surface of the member to be charged).

Thus, even when a charging roller or the like is used as the contact charging member, the applied bias required for charging the contact charging member is a voltage equivalent to the potential required for the member to be charged. In addition, it is possible to realize a stable and safe charging method without using a discharge phenomenon.

That is, even when a simple member such as a charging roller is used as the contact charging member in the contact charging device, it is possible to realize direct injection charging that is more excellent in charging uniformity and stable for a long period of time. Ozone-less injection charging at a voltage can be realized with a simple configuration.

In addition, it is possible to obtain an image forming apparatus and a process cartridge which can provide uniform chargeability, have no trouble due to ozone products, trouble due to poor charging, and have a simple configuration and a low cost.

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

The presence of the powder at least in the nip portion between the contact charging member and the member to be charged can reduce friction at the nip portion between the member to be charged and the contact charging member, reduce the torque of the contact charging member, and reduce contact charging. The member can contact the member to be charged with a speed difference, and at the same time, contacts the member to be charged densely and uniformly through the powder, that is, the powder present in the nip portion between the contact charging member and the member to be charged is charged. By rubbing the body surface without gaps, charges can be directly injected into the charged body. That is, direct injection charging is dominant in charging the member to be charged by the contact charging member due to the presence of the powder.

Accordingly, a high charging efficiency, which cannot be obtained by conventional roller charging or the like, is obtained, and a potential substantially equal to the voltage applied to the contact charging member can be applied to the member to be charged.

The resistance value of the powder is 1 × 10 ¹² (Ω · cm)
More preferably, by setting it to 1 × 10 ¹⁰ (Ω · cm) or less, even if powder is interposed between the nip portion between the contact charging member and the member to be charged, the charging property is not reduced and the contact is maintained. The frictional force between the charging member and the member to be charged is reduced, the torque of the contact charging member is reduced, the elastic contact charging member can contact the member to be charged uniformly, and uniform and stable direct injection charging is simplified. It can be obtained by any means configuration.

The provision of the means for supplying the powder enables stable charging even when the apparatus is used for a long time.

When the particle size of the powder is 10 nm or more and 50 μm or less, it is possible to provide an image forming apparatus capable of obtaining a good image without hindering exposure.

The volume resistance of the outermost surface layer of the member to be charged is 1 × 10
¹⁴ (Ω · cm) or less, and the member to be charged is an electrophotographic photosensitive member, and the volume resistivity of the outermost surface layer of the electrophotographic photosensitive member is 1 × 10 ⁹ (Ω · cm) or more and 1 × 10 ¹⁴ (Ω · c
m) or less, sufficient chargeability can be provided even in a device having a high process speed.

[0081]

BEST MODE FOR CARRYING OUT THE INVENTION

<First Embodiment> (FIGS. 1 to 3) This embodiment is an example of an image forming apparatus provided with a contact charging device according to the present invention. FIG. 1 is a schematic model diagram of the image forming apparatus.

The image forming apparatus of this embodiment is a laser printer (recording apparatus) using a transfer type electrophotographic process, a process cartridge attaching / detaching type, and a direct injection charging type.

(1) Overall Schematic Configuration of the Printer 1 is a rotary drum type O of φ30 mm as an image carrier.
It is a PC photoreceptor (negative photoreceptor).
It is driven to rotate at a process speed (peripheral speed) of 0 mm / sec.

Reference numeral 2 denotes an elastic charging roller as a contact charging member for the photosensitive member 1. 4 is a powder 3
Is a member for supplying and applying. This charging roller 2 and powder 3
The powder supply coating member 4 and the principle of direct injection charging will be described in detail in section (2) below.

The charging roller 2 is placed on the photosensitive member 1 against the elasticity.
They are arranged in contact with a nip width of mm. n is the nip portion (charging nip portion). The charging roller 2 is driven to rotate at 80 rpm in the charging nip n in a clockwise direction indicated by an arrow opposite to the moving direction of the photoconductor 1. A DC charging bias voltage of -700 V is applied to the charging roller 2 from a charging bias application power source S1, and the outer peripheral surface of the rotary photoreceptor 1 is directly charged, and is substantially the same as the charging bias applied to the charging roller 2. It is uniformly charged to -680V.

Reference numeral 5 denotes a laser beam scanner (exposure device) including a laser diode, a polygon mirror, and the like. This laser beam scanner 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 uniformly exposes the uniformly charged surface of the rotary photoreceptor 1 with the laser beam. By this scanning exposure L, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photoconductor 1.

Reference numeral 6 denotes a developing device, which develops an electrostatic latent image on the surface of the rotating photosensitive member 1 as a toner image. The developing device 6 of this embodiment is a reversal developing device using a magnetic one-component insulating toner (negative toner). Reference numeral 6a denotes a non-magnetic developing sleeve having a diameter of 16 mm and enclosing the magnet 6b. The developing sleeve 6a is coated with the above-mentioned negative toner, and the distance from the surface of the photoconductor 1 is fixed to 300 μm. To apply a developing bias voltage to the sleeve 6a from the developing bias applying power source S2.
Reference symbol a denotes a developing area, which is an opposing part of the photoconductor 1 and the developing sleeve 6a. As a developing bias voltage, a DC voltage of -500 V and a rectangular AC voltage having a frequency of 1800 Hz and a peak-to-peak voltage of 1600 V are superimposed, and jumping development is performed between the sleeve 6 a and the photosensitive member 1.

Reference numeral 7 denotes a transfer roller of medium resistance as a contact transfer means, which is brought into pressure contact with the photoreceptor 1 at a predetermined pressure to form a transfer nip portion b. A transfer material P as a recording medium is supplied to the transfer nip portion b at a predetermined timing from a paper supply unit (not shown).
Is supplied, and a predetermined transfer bias voltage is applied to the transfer roller 7 from the transfer bias application power source S3.
The toner image on the photoconductor 1 side is sequentially transferred to the surface of the transfer material P fed to the transfer nip portion b. In this example, a roller resistance value of 5 × 10 ⁸ Ω is used, and +2000 V DC is used.
Transfer was performed by applying a voltage. That is, the transfer nip b
The transfer material P introduced into the transfer nip b is conveyed by nipping the transfer nip portion b, and the toner image formed and carried on the surface of the rotary photoreceptor 1 is sequentially transferred to the surface side by electrostatic force and pressing force. Go.

Reference numeral 8 denotes a fixing device such as a heat fixing system. The transfer material P fed to the transfer nip portion b and having received the transfer of the toner image on the photoconductor 1 side is separated from the surface of the rotating photoconductor 1 and introduced into the fixing device 8, where the toner image is fixed. The sheet is discharged out of the apparatus as an image formed product (print, copy).

Reference numeral 9 denotes a cleaning device (cleaner) which cleans the surface of the photoreceptor after transfer of the toner image onto the transfer material P by removing the adhered contaminants such as residual toner by the cleaning device, and repeatedly provides an image. You.

The printer of this embodiment includes a cartridge PC including four process devices including a photosensitive member 1, a charging roller member 2 including a powder 3 and a powder supply / application member 4, a developing device 6, and a cleaning device 9. It is a cartridge-type device that can be attached to and detached from the main body at once. The combination of the process devices to be formed into the process cartridge is not limited to the above, and is optional. Reference numerals 10 and 10 denote attachment / detachment / holding members for the process cartridge PC.
In the present invention, the image forming apparatus is not limited to a cartridge type apparatus.

(2) Charging Roller 2, Powder 3, Powder Supply Coating Member 4 FIG. 2 is an enlarged model diagram of the charging roller 2 portion of the printer of FIG. The contact charging device in the present embodiment reduces the friction coefficient between the photoconductor 1 and the charging roller 2 by applying the powder 3 to the charging roller 2 made of an elastic body, so that the charging roller can be uniformly charged. It is designed to be able to contact the surface.

A) Charging Roller 2 The charging roller 2 of this embodiment is a roller-shaped elastic foam roller. As a material of the elastic foam, an EPDM foam (flexible member) in which carbon was dispersed for resistance adjustment was used. 6m diameter
An elastic foam layer 2b made of the above material having a thickness of 3 mm is provided on a metal core 2a having a diameter of 12 mm and an outer diameter of 250 mm.
mm.

The hardness of the charging roller 2 is 30 degrees for Asker C. The surface of the roller is polished to expose the foam.

The charging roller 2 is pressed against one side by 500
It is arranged in contact with the photoreceptor 1 with a nip width of 5 mm with a load of g.

As a result, the surface of the charging roller 2 is uniformly contacted with the surface of the photoreceptor 1 microscopically, thereby enabling direct injection charging.

As described above, a DC voltage of -700 V was applied as a charging bias from the charging bias applying power source S1 to the core metal 2a of the charging roller 2.

In the present charging method, the conventional high hardness solid roller (Asker C hardness 63 degrees) is not preferable because the hardness is high and it is difficult to secure a nip portion, and sufficient time for direct injection charging is insufficient. In conventional contact charging using electric discharge, the surface of the photoreceptor was charged by causing electric discharge in the gaps at both ends of the nip, so there was no problem with a solid roller.However, in direct injection charging, the charging time was insufficient, or In addition, charging becomes uneven.

The resistance value of the charging roller 2 is 1 × 10 ⁶ Ω at an applied voltage of 100 V.
Converted from the value of current flowing when a voltage of 0 V is applied). The resistance value of the charging roller 2 is used to prevent an image defect in which an excessive leakage current flows into this portion and a charging nip portion n becomes poorly charged even when a pinhole or the like is missing on the photoconductor 1. 10 ⁴ Ω or more, and 10 ⁷ Ω or less in order to sufficiently inject electric charges into the surface of the photoreceptor.

If the hardness of the charging roller 2 is too low, the contact becomes poor because the shape is not stable. If the hardness is too high, not only the charging nip cannot be secured, but also the micro contact with the photoreceptor surface becomes poor. It is 25 in Asker C hardness
Degrees to 50 degrees is a preferred range.

The material of the charging roller 2 is not limited to an elastic foam.
M, urethane, NBR, silicone rubber, a rubber material in which a conductive substance such as carbon black or metal oxide is dispersed in IR or the like for resistance adjustment, or a foamed material thereof. Also, without dispersing the conductive material,
It is also possible to adjust the resistance using an ion conductive material.

In this embodiment, since charging is performed by direct charge injection without using discharge, the charging roller 2 and the photosensitive member 1 are charged.
It is necessary to make the contact state with the finer. Thus, the charging roller 2 is driven to rotate at a rotation speed of 80 rpm so as to move in the direction opposite to the moving direction of the surface of the photoconductor 1 (counter rotation). If the conditions such as the thickness of the charging nip portion n of the photoconductor 1 and the process speed (photoconductor rotation peripheral speed) change, the optimum rotation speed of the charging roller also changes.

B) Powder 3 In this example, the powder 3 effectively reduces the friction between the charging roller 2 as the contact charging member and the photoreceptor 1 as the member to be charged (friction reducing effect). ) And a charge assisting effect is obtained. Hereinafter, the powder 3 will be referred to as charging auxiliary particles. It is preferable to use the following materials, particle diameters, characteristics, and the like of the charging auxiliary particles 3.

In this example, conductive zinc oxide particles having a specific resistance of 10 ⁶ Ω · cm and an average particle diameter of 3 μm including secondary aggregates were used.

As the material of the charge assisting particles 3, various conductive particles such as conductive inorganic particles such as other metal oxides and mixtures with organic substances can be used.

If the resistance of the charge assisting particles 3 is too high, the charge injection is impaired at the time of charging, resulting in poor charging. Therefore, the resistance is preferably 10 ¹² Ω · cm or less. More preferably, it is 10 ¹⁰ Ω · cm or less. More preferably, it is 10 ⁸ Ω · cm or less.

The resistance was measured by the tablet method and normalized. That is, about 0.5 g of a powder sample was placed in a cylinder having a bottom area of 2.26 cm ² , and 15 kg of pressure was applied to the upper and lower electrodes, and at the same time, a voltage of 100 V was applied to measure the resistance value. Was calculated.

The particle size is 50 in order to obtain good charging uniformity.
μm or less is desirable. The lower limit of the particle size is limited to 10 nm as long as the particles can be obtained stably.

In the present invention, the particle diameter when the particles are constituted as an aggregate is defined as the average particle diameter of the aggregate.

For the measurement of the particle size, 100 or more particles were extracted from the observation with an optical or electron microscope, the volume particle size distribution was calculated based on the maximum chord length in the horizontal direction, and the 50% average particle size was determined.

As described above, there is no problem that the auxiliary charging particles 3 exist not only in the state of primary particles but also in the state of aggregation of secondary particles. Regardless of the state of aggregation, the form is not important as long as the function as the charge assisting particles can be realized as an aggregate.

The auxiliary charging particles 3 are preferably non-magnetic so as not to hinder exposure.

C) Powder Supply Coating Member 4 In this example, the charging auxiliary particles 3 are interposed in the charging nip n, which is the nip between the photosensitive member 1 as the member to be charged and the charging roller 2 as the contact charging member. For this purpose, a member 4 for supplying and applying the charging auxiliary particles 3 to the surface of the charging roller 2 is provided. The member 4 is a regulating blade. The regulating blade 4 comes into contact with the charging roller 2, and the charging auxiliary particles 3 are stored and held between the charging roller 2 and the regulating blade 4.

With the rotation of the charging roller 2, a fixed amount of the charging auxiliary particles 3 is applied to the surface of the charging roller 2, carried to the charging nip n, and uniformly supplied to the charging nip n. In this state, the charging auxiliary particles 3 are interposed in the charging nip n.

D) Charging of the Photoconductor 1 In this embodiment, the charging nip n, which is the nip between the photoconductor 1 as the member to be charged and the charging roller 2 as the contact charging member, is charged with an auxiliary charge. The contact charging of the photoconductor 1 is performed in a state where the particles 3 are applied.

The presence of the auxiliary charging particles 3 in the charging nip n between the charging roller 2 and the photosensitive member 1 allows the charging roller 2
In the nip portion between the photosensitive member 1 and the photosensitive member 1, the friction can be reduced, the torque of the charging roller 2 can be reduced, and the charging roller 2 can move with a speed difference from the photosensitive member 1 and at the same time, densely and uniformly via the charging auxiliary particles 3. 1, that is, the charge auxiliary particles 3 present in the nip portion between the charging roller 2 and the photoconductor 1 rub the surface of the photoconductor 1 without any gap, so that the charge can be directly injected into the photoconductor 1. That is, the charging of the photoreceptor 1 by the charging roller 2 is dominated by direct injection charging due to the presence of the auxiliary charging particles 3.

Accordingly, a high charging efficiency, which cannot be obtained by the conventional roller charging, is obtained, and a potential (−680 V) substantially equal to the voltage (−700 V) applied to the charging roller 2 can be applied to the photosensitive member 1. .

Thus, even when a charging roller having a relatively simple structure is used as the contact charging member, the applied bias necessary for charging the charging roller is sufficient to be a voltage corresponding to the potential required for the photosensitive member. A stable and safe charging method without using a phenomenon can be realized. In other words, even when a simple member such as a charging roller is used as a contact charging member in the contact charging device, it is possible to realize direct injection charging that is more excellent in charging uniformity and stable for a long period of time. Can be realized with a simple configuration.

In addition, a uniform configuration and low cost of an image forming apparatus and a process cartridge can be obtained, which can provide uniform chargeability and do not have an obstacle due to an ozone product, an obstacle due to poor charging, or the like.

(3) Coefficient of Static Friction Here, the frictional force was measured and the image was evaluated by changing the amount of the auxiliary charging particles 3 applied to the charging roller 2.
Table 1 shows the results.

[0121]

[Table 1] . When the coating amount is 0, the charging roller 2 has a large friction and the photosensitive member 1
Could hardly be rotated with a speed difference.

. It starts to rotate slightly at an application amount of 0.1, but does not rotate uniformly. Further, the charged particles are not uniformly applied to the roller.

[0123] Only when the coating amount exceeds 0.5 does it begin to rotate almost uniformly.

Then, when the static friction coefficient per 10 mm of the longitudinal width of the charging roller 2 and the photoreceptor 1 at that time is measured, if the static friction coefficient is 2.5 or less, almost excellent charging uniformity is obtained. It turned out to be obtained. Further, it was found that when the static friction coefficient was 1.5 or less, better charging uniformity was obtained.

In the conventional roller charging using discharge as a main charging mechanism, the charging roller cannot rotate stably without a certain amount of friction because the charging roller is driven and rotated by the photosensitive member. In the configuration of the present example, since the drive source of the charging roller 2 is obtained from a portion other than the surface of the photoconductor, the charging roller 2 can be stably rubbed against the photoconductor 1 even in a low friction state.

However, in a state where there is not much friction, even though it seems to be in contact with the macro, there are some places where the micro is not in contact, and the contact state may be insufficient. Therefore, a certain degree of static friction is required also in the present invention, and the static friction coefficient is desirably 0.1 or more.

Here, a method of measuring the static friction coefficient will be described. That is, as shown in FIG. 3, the rotation of the charging roller 2 is stopped, and an agent similar to the surface agent of the photoreceptor 1 is applied to a PET (polyethylene terephthalate) sheet.
The tape 21 is covered with a 0 mm tape material 21 for about 1/4 turn. A weight 22 of 100 g is loaded on one of the tape materials 21, and a digital force gauge (manufactured by Shinpo Kogyo KK) 23 is attached to the other of the tape materials 21. When the rotation is started at (80 rpm), the static friction force acting between the charging roller 2 and the tape material 21 indicated by the digital force gauge 23 is divided by the weight of the weight, and is further converted into a value per 10 mm to obtain a photoreceptor. It was calculated as the coefficient of static friction between No. 1 and the charging roller 2.

Conventionally, in an injection charging device having a speed difference, the charging roller may not rotate at all, the surface may be shaved even if the charging roller rotates, or rotation and contact may be uneven. In the present embodiment, the auxiliary charging particles 3 are applied to the charging roller 2 so that the auxiliary charging particles 3 reduce the friction between the charging roller 2 and the photosensitive member 1 and reduce the torque. As a result, uniform chargeability was obtained.

(4) Others The means for applying and supplying the auxiliary charging particles 4 to the charging roller 2 is not limited to the embodiment. For example, a foam or a fur brush containing the auxiliary charging particles 3 may be used as the charging roller. Arbitrary arrangement is possible, such as a configuration of means for contacting and disposing.

Further, between the cleaning device 9 and the charging roller 2, means for supplying and applying the charging auxiliary particles 3 to the surface of the photoreceptor 1 may be provided.

The colorless or nearly white particles are suitable for the auxiliary charging particles 3 so as not to hinder the exposure of the latent image particularly when used for charging the photosensitive member 1. Further, in the case of performing color recording, the charging auxiliary particles 3 move from the photosensitive member onto the recording material P.
Considering the case where the image is transferred to a colorless image, a colorless or nearly white color is desirable. Further, in order to prevent light scattering by the charge assisting particles during image exposure, it is desirable that the particles have a size equal to or smaller than the constituent pixel size.

In the transfer nip portion b, the toner image on the photosensitive member 1 is attracted to the transfer material P by the influence of the transfer bias and is positively transferred, but the charging auxiliary particles 3 on the photosensitive member 1 are electrically conductive. Does not positively transfer to the transfer material P side,
It is substantially adhered and held on the surface of the photoconductor 1. In addition, the transfer efficiency of the toner image from the photoconductor 1 side to the transfer material P side is improved by the presence of the auxiliary charging particles 3 substantially adhered and held on the surface of the photoconductor 1.

As the device is used, the auxiliary charging particles 3 in the charging nip n adhere to the photosensitive member 1 and are scraped off by the cleaning device 9 to be reduced. Therefore, the charging auxiliary particle supply / application means 4 is configured to always apply a fixed amount of charging auxiliary particles to the charging roller 2 or the surface of the photoconductor 1 and supply the charging auxiliary particles to the charging nip n.

In the configuration in which the auxiliary charging particle supply / applying means 4 is provided on the side of the charging roller 2 serving as the contact charging member, the auxiliary charging particles 3 can be applied without increasing the number of devices around the photosensitive member 1 which is the object to be charged. Therefore, it is effective for downsizing the device.

<Second Embodiment> (FIG. 4) In this embodiment, charging is more stably and uniformly performed by adjusting the surface resistance of the member 1 to be charged. In this embodiment, a charge injection layer is provided on the surface of the photoreceptor 1 as a member to be charged, and the resistance value of the outermost layer of the photoreceptor is adjusted to 10 ¹⁴ Ωcm or less, so that even at a higher process speed, the film is stably and uniformly formed. Charging can be performed.

FIG. 4 is a schematic diagram of the layer structure of the photoreceptor 1 used in this example and having a charge injection layer on the surface. That is, the photoreceptor 1 is a negatively charged OPC photoreceptor, in which the following five first to fifth functional layers are provided in order from the bottom on an aluminum drum base (aluminum base) 11 having a diameter of 30 mm. is there.

The first layer 12 is a subbing layer, which is a conductive layer having a thickness of about 20 μm and provided for smoothing defects of the aluminum substrate 11 and for preventing generation of moire due to reflection of laser exposure. is there.

A second layer 13; a positive charge injection preventing layer, which serves to prevent positive charges injected from the aluminum substrate 11 from canceling out negative charges charged on the surface of the photoreceptor; 10 ⁶
This is a medium resistance layer having a thickness of about 1 μm and a resistance adjusted to about Ωcm.

Third layer 14: A charge generation layer, which is a layer having a thickness of about 0.3 μm in which a disazo pigment is dispersed in a resin, and which generates positive and negative charge pairs by being exposed to laser.

Fourth layer 15: a charge transport layer, in which hydrazone is dispersed in a polycarbonate resin, and is a P-type semiconductor. Therefore, the negative charges charged on the photoreceptor surface cannot move through this layer, and only the positive charges generated in the charge generation layer can be transported to the photoreceptor surface.

Fifth layer 16: A charge injection layer, wherein SnO ₂ particles having a particle size of about 0.03 μm and made conductive by antimony doping were added in a weight of 5 with respect to a weight of 2 of the photocurable acrylic resin. The material dispersed in the above ratio is coated on the photoreceptor by a dipping coating method and cured, and the thickness of this layer 16 is about 3 μm. 16a is dispersed SnO ₂ particles (conductive particles, conductive filler).

[0142] The layer 16 is the volume resistivity of about 10 ¹³ [Omega] cm, but the image blur or the like does not occur due to lateral flow of the surface direction of the latent image charges, in the thickness direction is possible transfer of certain charges, the image It is set so that the residual potential due to exposure is minimized.

As a result, the resistance of the surface of the photoreceptor was 1 × 10 ¹⁵ Ωcm compared to 1 × 10 ¹⁵ Ωcm in the case of the charge transport layer alone.
It decreased to 10 ¹¹ Ωcm.

The resistance value of the charge injection layer 16 is 1 × 10
^In the range of ¹⁰ to 1 × 10 ¹⁴ Ωcm, it is possible to perform injection charging. However, in consideration of resistance fluctuation in an environment such as high temperature, high humidity, and low temperature and low humidity, 1 × 10 ¹² to 1 × 10 ¹³ is preferable. Ωc
The range of m is desirable.

The photoreceptor 1 provided with the charge injection layer 16 was mounted on the printer (FIG. 1) of the first embodiment, the process speed of the photoreceptor was set to 200 mm / sec, and the rotation of the charging roller 2 was changed. The number was set to 320 rpm (the ratio of the peripheral speed of the photosensitive member 1 to the charging roller was constant), and other than that, the image was formed by the apparatus shown in the first embodiment.

In some cases, injection charging cannot be performed with the same charging nip as in the case where the process speed is slow because of the high process speed. However, even when the process speed is high, uniform injection can be performed by using a photosensitive member having the above-described resistance value. Charging becomes possible.

In this example, the coefficient of static friction per 10 mm in the longitudinal width between the charging roller 2 and the photosensitive member 1 was 0.9. Therefore, when the process speed is increased and the number of rotations of the charging roller 2 is increased (peripheral speed ratio is constant), uniform contact property in the charging section is maintained, and good charging property without uneven charging is obtained. .

In this example, the charge injection layer was provided on the surface layer of the OPC photosensitive member to achieve uniform injection charging even at a high process speed. However, the structure of the photosensitive member is not limited to this, and the charge injection is not limited to this. Even when the layer 16 is not used, for example, when the charge transport layer 15 is within the above-described resistance range, the same effect can be obtained. In addition, the volume resistance of the surface layer is about 1
The same effect can be obtained by using an amorphous silicon photosensitive member having a resistance of 0 ¹³ Ωcm.

<Third Embodiment> In this embodiment, the surface of the charging roller is subjected to a process for reducing friction.

Specifically, the surface of the foam charging roller 2 described in the first embodiment is coated on the surface of the foamed charging roller 2 with a slippery Teflon (resistance is adjusted with conductive carbon). PTFE) -containing resin was applied unevenly. By non-uniform application, contact properties can be obtained while leaving microscopic irregularities on the surface of the charging roller.

The charging roller was mounted on the printer of the first embodiment (FIG. 1), and the photosensitive member 1 used was one whose surface resistance was controlled as described in the second embodiment. The evaluation was performed using an image forming apparatus having the same configuration as that of the first embodiment except that the auxiliary particles were not applied.

In this example, the surface of the charging roller was subjected to the low friction treatment as described above, so that the charging roller could be rotated with the peripheral speed of the photosensitive member varied, and good charging properties were obtained.

In this example, the longitudinal width 1 between the charging roller and the photosensitive member was 1
The coefficient of static friction per 0 mm was 0.8.

By adopting this configuration, the charging roller can be rotated with a good peripheral speed difference with good contact without applying powder (charging auxiliary particles) to the charging nip portion. can get.

<Others> 1) The charging roller 2 as a flexible contact charging member is not limited to the charging roller of the embodiment. In addition to the charging roller, a material and a shape such as a fur brush, felt, and cloth can be used as the contact charging member. It is also possible to obtain a more appropriate elasticity and conductivity by laminating them.

2) As an applied charging bias or an applied developing bias to the contact charging member 2 and the developing sleeve 6a, an alternating voltage (AC voltage) may be superimposed on a DC voltage.

As the waveform of the alternating voltage, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Alternatively, a rectangular wave formed by periodically turning on / off a DC power supply may be used. As described above, a bias whose voltage value periodically changes can be used as the waveform of the alternating voltage.

3) The image forming apparatus and the process cartridge may be of a cleanerless system having no cleaning device.

4) The image exposing means for forming an electrostatic latent image is not limited to the laser scanning exposing means for forming a digital latent image as in the embodiment, but may be a general analog exposing means. Other light-emitting elements such as an image exposure or LED may be used, and any device that can form an electrostatic latent image corresponding to image information, such as a combination of a light-emitting device such as a fluorescent lamp and a liquid crystal shutter, may be used.

The image carrier may be an electrostatic recording dielectric or the like. In this case, after the dielectric surface is uniformly charged to a predetermined polarity and potential, the charge is selectively removed by a charge removing means such as a charge removing needle head or an electron gun to write and form a desired electrostatic latent image.

5) The recording medium for receiving the transfer of the toner image from the image carrier may be an intermediate transfer member such as a transfer drum.

6) One example of a method for measuring the particle size of the toner will be described. As a measuring device, Coulter Counter TA-2
Interface (manufactured by Nikkaki) and CX that output the number average distribution and volume average distribution using a mold (manufactured by Coulter)
-1 Connect a personal computer (Canon),
As the electrolytic solution, a 1% NaCl aqueous solution is prepared using primary sodium chloride.

The measuring method is as follows.
A surfactant as a dispersant in 150 ml, preferably
0.1 to 5 ml of an alkylbenzene sulfonate is added, and 0.5 to 50 mg of a measurement sample is further added.

The electrolytic solution in which the sample was suspended was subjected to a dispersion treatment for about 1 to 3 minutes by an ultrasonic disperser, and the particle size of 2 to 40 μm was measured with the Coulter Counter TA-2 using a 100 μ aperture as an aperture. The distribution is measured to determine the volume average distribution. The volume average particle size is obtained from the obtained volume average distribution.

[0165]

As described above, according to the present invention, even when an inexpensive elastic member having a simple structure such as a charging roller is used as a contact charging member in a contact charging device, it can be applied to a member to be charged. By reducing the initial driving torque, rotation with a stable peripheral speed difference can be achieved, a uniform contact state can be obtained at the charging nip portion, and excellent uniform charging and stable direct charging over a long period of time can be realized. Ozone-less direct injection charging with an applied voltage can be realized with a simple configuration.

In addition, this makes it possible to obtain an image forming apparatus or a process cartridge which has a simple configuration and is inexpensive, free from troubles due to ozone products and troubles due to poor charging. Achieved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is an enlarged model diagram of a charging roller portion.

FIG. 3 is a diagram illustrating a method of measuring a static friction coefficient.

FIG. 4 is a schematic diagram of a layer structure of a photoreceptor having a charge injection layer on a surface.

FIG. 5 is a graph showing charging characteristics.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photoconductor (image carrier, charged object) 2 charging roller (contact charging member) 3 powder (charging auxiliary particles, conductive particles) 4 regulating blade (particle supply coating means)

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yukio Nagase 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc.

Claims (22)

[Claims] 1. A charging method in which a voltage is applied and a surface of a member to be charged is charged by a flexible charging member forming a nip with the member to be charged, wherein a contact charging member for the member to be charged is an elastic member; A charging method characterized by moving at a speed difference with respect to a member to be charged and having a static friction coefficient of a frictional force acting between the contact charging member and the member to be charged of 2.5 or less. 2. The charging method according to claim 1, wherein a static friction coefficient of a frictional force acting between the contact charging member and the member to be charged is 0.1 or more and 2.5 or less. 3. The charging method according to claim 1, wherein powder is present at least in a nip portion between the contact charging member and the member to be charged. 4. The resistance of the powder is 1 × 10 ¹² (Ω · c).
The charging method according to claim 3, wherein m) or less. 5. The resistance of the powder is 1 × 10 ¹⁰ (Ω · c).
The charging method according to claim 3, wherein m) or less. 6. A powder having a particle size of 10 nm or more and 50 μm or more.
6. The method according to claim 3, wherein:
The charging method described in (1). 7. The charging method according to claim 1, wherein the contact charging member rotates at a counter with respect to the member to be charged. 8. The charging method according to claim 1, wherein the charging member is made of an elastic foam. 9. The volume resistance of the outermost surface layer of the member to be charged is 1
9. The charging method according to claim 1, wherein the charging method is equal to or less than × 10 ¹⁴ (Ω · cm). 10. 10. The object to be charged is an electrophotographic photosensitive member, and the outermost surface layer of the electrophotographic photosensitive member has a volume resistance of 1 × 10
The charging method according to claim 1, wherein the charging method is ⁹ (Ω · cm) or more and 1 × 10 ¹⁴ (Ω · cm) or less. 11. A charging device to which a voltage is applied and which charges a surface of a member to be charged by a flexible charging member forming a nip portion with the member to be charged, wherein a contact charging member for the member to be charged is an elastic member. A charging device which moves at a speed difference with respect to the member to be charged and has a static friction coefficient of a frictional force acting between the contact charging member and the member to be charged of 2.5 or less. 12. The charging device according to claim 11, wherein a static friction coefficient of a frictional force acting between the contact charging member and the member to be charged is 0.1 or more and 2.5 or less. 13. A powder is present at least on a contact surface between a contact charging member and a member to be charged.
Or the charging device according to 12. 14. The resistance of the powder is 1 × 10 ¹² (Ω · c).
The charging device according to claim 13, wherein m) or less. 15. The resistance of the powder is 1 × 10 ¹⁰ (Ω · c).
The charging device according to claim 13, wherein m) or less. 16. The particle size of the powder is 10 nm or more and 50 μm or more.
The charging device according to claim 13, wherein m is equal to or less than m. 17. The charging device according to claim 11, wherein the contact charging member rotates at a counter with respect to the member to be charged. 18. The charging device according to claim 11, wherein the charging member is made of an elastic foam. 19. The charging device according to claim 11, wherein a volume resistance of an outermost surface layer of the member to be charged is 1 × 10 ¹⁴ (Ω · cm) or less. 20. The object to be charged is an electrophotographic photosensitive member, and the outermost surface layer of the electrophotographic photosensitive member has a volume resistance of 1 × 10
The charging device according to any one of claims 11 to 19, wherein the charging amount is ⁹ (Ω · cm) or more and 1 × 10 ¹⁴ (Ω · cm) or less. 21. An image forming apparatus for performing image formation by applying an image forming process including a step of charging the image carrier to the image carrier, wherein the step of charging the image carrier is performed. From 20
An image forming apparatus, which is the charging device according to any one of the above. 22. A process cartridge detachably mountable to an image forming apparatus main body for executing image formation by applying an image forming process including a step of charging the image carrier to the image carrier, and at least the image carrier. 21. A process cartridge, comprising: a charging unit for charging the image carrier; and the charging unit is the charging device according to claim 11.