JP2003307912A - Electrifier, process cartridge, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrifier in which electrification performance is further improved by a direct injection electrifying mechanism and to provide a process cartridge and an image forming apparatus. <P>SOLUTION: An electrifying member 2 which electrifies a rotary body 1 to be electrified defines a contact area n between the body 1 and itself. The electrifying member 2 is rotatable so that the surface thereof moves in a direction opposite to the direction of the rotation of the body 1 in the contact area n. In the electrifier 2A in which conductive particles m are transported to the contact area n while it is held on the body 1, when a horizontal line passing through the center of the rotation of the body 1 is assumed to be an X-axis and a vertical line passing through the center of the rotation of the body 1 is assumed to be a Y-axis, the entrance s of the contact area n in the direction of the rotation of the body 1 is disposed in the first quadrant of an XY coordinate plane, as viewed from the direction where the rotary direction of the body 1 is clockwise. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device for charging a body to be charged, and more specifically, a contact type charging device (contact charging device) for charging a surface of the body to be charged by bringing a charging member into contact with the body to be charged. ) Is related to. The present invention also provides
The present invention relates to an image forming apparatus such as a copying machine or a printer, which uses the above charging device as a charging processing means for an image carrier.

The present invention can be suitably applied to a process cartridge detachably mountable to an electrophotographic image forming apparatus and an electrophotographic image forming apparatus. Here, the electrophotographic image forming apparatus is an apparatus that forms an image on a recording medium using an electrophotographic image forming method. Examples of the electrophotographic image forming apparatus include, for example, an electrophotographic copying machine, an electrophotographic printer (for example, laser printer, LED printer, etc.), a facsimile machine, a word processor, and a multifunction machine (multifunction printer, etc.) of these. Further, the process cartridge is an integrally formed cartridge of an electrophotographic photosensitive member and at least a charging unit as a process unit that acts on the electrophotographic photosensitive member, and the cartridge can be attached to and detached from the main body of the electrophotographic image forming apparatus. It is a thing. Alternatively, the process cartridge is a cartridge in which the electrophotographic photosensitive member, the charging unit, and at least one of the developing unit and the cleaning unit are integrally made into a cartridge and can be attached to and detached from the main body of the electrophotographic image forming apparatus.

[0003]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic image forming apparatus or an electrostatic recording apparatus, an image carrier such as an electrophotographic photosensitive member or an electrostatic recording dielectric has a uniform polarity and potential. A corona charger (corona discharger) has been often used as a charging device that performs the charging process (including the charge removing process).

The corona charger is a non-contact type charging device, and is provided with a discharge electrode such as a wire electrode and a shield electrode surrounding the discharge electrode, and a discharge opening is made to face an image carrier, which is a member to be charged. The surface of the image carrier is charged by exposing the surface of the image carrier to a discharge electrode (corona shower) generated by applying a high voltage to the discharge electrode and the shield electrode, which are arranged in a non-contact manner.

In recent years, a contact charging device has been proposed as a charging device for a charged member such as an image carrier because it has advantages such as low ozone and low power compared to a corona charger.
It has also been put to practical use.

(A) Contact charging The contact charging device is a conductive charging member (contact charging) such as a roller type (charging roller), a fur brush type, a magnetic brush type, or a blade type, which is attached to a member to be charged such as an image carrier. (Member / contact charger), and a predetermined charging bias is applied to the contact charging member to charge the surface of the body to be charged to a predetermined polarity and potential.

Contact charging devices differ greatly from one another in terms of their charging mechanism (charging mechanism, charging principle). The contact charging mechanism includes (1) a discharge charging mechanism and (2) a direct injection charging mechanism. The characteristics of the charging device are determined depending on which charging mechanism is used for the charging device.

(1) Discharge Charging Mechanism This is a mechanism in which the surface of the member to be charged is charged with a discharge product due to a discharge phenomenon that occurs in the gap between the contact charging member and the member to be charged.

Since the discharge charging system has a constant discharge threshold value between the contact charging member and the member to be charged, as shown in A (conventional roller charging device) of FIG. It is necessary to apply it to the contact charging member. Further, compared with the corona charger, the generated amount is remarkably small, but in principle, discharge products are generated.

A charging method (roller charging device) using a conductive roller (charging roller for discharging) as a contact charging member by discharge is preferable from the viewpoint of discharge stability and is widely used. This discharge charging roller is formed by forming a conductive or medium-resistance rubber material or foam as a base layer into a roller shape, and covering the surface with a high resistance layer. In this configuration, the discharge phenomenon occurs in a gap of several tens of μm, which is slightly apart from the contact portion between the discharge charging roller and the member to be charged. Therefore, in order to stabilize the discharge phenomenon, the surface layer of the discharge charging roller is flat and has an average surface roughness Ra of sub-μm or less,
It has a high hardness surface.

Further, in the roller charging by electric discharge, the applied voltage is high, and if there is a pinhole (exposure of the substrate due to damage of the film to be charged), a voltage drop will occur even around the pinhole and defective charging will occur. Therefore, the surface resistance of the surface layer is set to 10 ¹¹ Ω / □ or more to prevent the voltage drop.

(2) Direct Injection Charging Mechanism The direct injection charging is to charge (charge) the surface of an object to be charged by directly giving and receiving an electric charge by contact between the contact charging member and the object to be charged at the molecular level. It is a charging mechanism that does. It is also called direct charging or injection charging.

In this charging mechanism, the potential difference between the contact charging member and the body to be charged is about several volts to several tens of volts. The charging characteristics are shown in B (magnetic brush charging device) of FIG. The charging potential is almost equal to the applied voltage, and there is no voltage difference that causes discharge. In addition, the voltage required for charging can be kept low. The direct injection charging system does not cause the generation of ions as a charging mechanism, and therefore does not cause a harmful effect due to discharge products. That is, the charging method is excellent in environmental safety, member deterioration, and low power consumption.

In the direct injection charging mechanism, the important factor that determines the charging performance is the contact between the contact charging member and the member to be charged. The term "contact property" as used herein means the ability of the contact charging member to make microscopic contact with many surfaces while the body to be charged passes through the charging device. For this reason, the contact charging member is required to have a surface having both a dense surface structure and elasticity capable of flexibly contacting.

As a form of the contact charging member used in the direct injection charging device, an attempt has been made to use a discharge charging roller or the like, but direct injection charging cannot be performed with the discharge charging roller. With the high hardness and smooth surface structure as described above, it looks like it is in close contact with the body to be charged, but in the sense of the microscopic contact property at the molecular level necessary for charge injection, there is almost no contact. is there.

At present, as a direct injection charging method which has been proposed, there is particle charging using a magnetic brush.

(B) Particle Charging (Magnetic Brush Type) Considering the improvement of contact density, a charging method using conductive particles (particle charging) is advantageous. Examples of the conductive particles include conductive magnetic particles, and an example in which a magnetic brush charging member is formed by a magnet has been proposed.

The magnetic brush charging device is, for example, a fixedly supported magnet roll, a non-magnetic / conductive charging sleeve concentrically and rotatably fitted around the outer circumference of the magnet roll, and an outer periphery of the charging sleeve. A magnetic brush charging member having a magnetic brush layer of conductive magnetic particles formed by being attracted and held by a magnetic force of a magnet roll inside the charging sleeve is provided on the surface. This magnetic brush charging member is assembled in a casing, and an appropriate amount of conductive magnetic particles is contained and stored in the casing. Then, a magnetic brush charging member is arranged so that the magnetic brush layer is brought into contact with a member to be charged such as an image carrier with a predetermined width. Since it is necessary to use a rigid body as the charging sleeve, it is necessary to provide the magnetic brush layer of the conductive magnetic particles with flexibility as a contact charging member. Therefore, the magnetic brush layer requires a certain thickness and the amount of conductive magnetic particles supported.

(C) Process Cartridge Conventionally, in an electrophotographic image forming apparatus using an electrophotographic image forming process, an electrophotographic photosensitive member and a charging means, a developing means, as a process means acting on the electrophotographic photosensitive member, At least one of the cleaning means is integrally formed into a cartridge, and a process cartridge system is adopted in which the cartridge can be attached to and detached from the main body of the electrophotographic image forming apparatus. According to this process cartridge system, the maintenance of the apparatus can be performed by the user himself without resorting to a serviceman, so that the operability can be markedly improved. Therefore, this process cartridge system is widely used in electrophotographic image forming apparatuses.

(D) Toner Recycle Process (Cleanerless System) In the transfer type image forming apparatus, the transfer residual developer (transfer residual toner) remaining on the image carrier after transfer is imaged by a cleaning device (cleaner). Although the waste toner is removed from the surface of the carrier to become waste toner, it is desirable that this waste toner does not appear from the viewpoint of environmental protection. Therefore, the toner recycling process is designed to eliminate the cleaner, remove residual toner on the image bearing member after transfer from the image bearing member by "developing simultaneous cleaning" by the developing device, and collect and reuse it in the developing device. Image forming apparatuses (toner recycling system, cleanerless system) have also appeared.

The "simultaneous development cleaning" means that the toner remaining on the image carrier after the transfer is charged during the subsequent development process, that is, in the electrophotographic system, the image carrier is continuously charged and exposed to form a latent image. When the latent image is formed and developed, a fog removing bias (a fog removing potential difference Vb, which is a potential difference between the DC voltage applied to the developing device and the surface potential of the image bearing member).
It is a method of collecting by ack). According to this method, the transfer residual toner is collected by the developing device and reused after the next step, so that it is possible to eliminate the waste toner and reduce the troublesome maintenance. Further, since the cleaner is not used, there is a great space advantage, and the image forming apparatus or the process cartridge can be significantly downsized.

In the toner recycling process, the transfer residual toner is once taken into the contact charging member and is returned to the developing device via the image carrier so that it can be reused (original toner charge amount) to be used again for development. Or, if unnecessary, collect it. This enables toner recycling. The charging device used here needs to collect the transfer residual toner and recharge the toner in addition to charging the image carrier.

(E) Particle charging (powder coating type) Particle charging is suitable for a toner recycling system. In the magnetic brush charging using the conductive magnetic particles, the magnetic brush itself is composed of particles, can move with a degree of freedom, and has a large specific surface area. Therefore, in the magnetic brush, it is possible to advantageously realize the functions that are indispensable for toner recycling, such as collecting the transfer residual toner from the image bearing member and making the charge of the taken-in toner proper.

As described above, the magnetic brush charging device is an excellent charging device, but further improvement in charging performance and toner recycling performance is required. Therefore, it is desired to reduce the particle size of the conductive particles, and it is ideal to form a more dense and flexible contact charging member.

However, in particle charging by the conventional magnetic brush, if the size of the conductive magnetic particles, which are conductive particles, is simply reduced (10 μm or less), the magnetic coercive force of the conductive magnetic particles decreases, so that the conductive magnetism from the magnetic brush is reduced. The problem of particles falling off can occur. In a magnetic brush charging member that requires a certain amount of carried particles, if the problem of dropping of the magnetic particles, which are charged particles, occurs, the adverse effect is great. Further, the magnetic particles that have fallen off the magnetic brush and adhered to the image bearing member cause leakage of the developing bias and defective development, and are further transferred to a recording material (recording paper etc.) to cause fog, which causes various image defects. There is a possibility that it may not be solved by simply supplying magnetic particles. Further, the magnetic brush charging device has a relatively complicated device configuration.

As described above, it is considered that there is a limit to the improvement of the contact density in the conventional magnetic brush charging using the conductive magnetic particles.

On the other hand, in the state where non-magnetic conductive particles are present in the charging contact portion formed by the image carrier and the contact charging member, the charging device for charging the image carrier by direct injection charging (powder coating type direct An injection charging device) has been proposed. Next, a conventional charging device of this type will be described with reference to FIG.

The image forming apparatus shown in FIG. 12 is a laser beam printer of a direct injection charging type and a toner recycling process (cleanerless system) which utilizes a transfer type electrophotographic process.

The image forming apparatus 200 has a rotary drum type electrophotographic photosensitive member (hereinafter referred to as "photosensitive drum") 1 as an image bearing member. The photosensitive drum is rotationally driven in the clockwise direction indicated by the arrow in the figure at a predetermined peripheral speed (process speed).

The image forming apparatus 200 includes a conductive elastic roller (hereinafter simply referred to as "charging roller") 2 as a contact charging member, and a charging bias power source S1 for applying a charging bias voltage to the charging roller 2. It has a charging device 2A including. The charging roller 2 is manufactured by forming a rubber or foam medium resistance layer 2b as a flexible member on the cored bar 2a. The charging roller 2 is arranged so as to be pressed against the photosensitive drum 1 as a member to be charged with a predetermined pressing force against the elasticity. As a result, a charging contact portion n having a predetermined width is formed between the photosensitive drum 1 and the charging roller 2. In this example, the charging roller 2 is rotationally driven in the clockwise direction indicated by an arrow in the figure so that the surface of the charging roller 2 and the surface of the photosensitive drum 1 at the charging contact portion n move in opposite directions at a constant speed. It

On the surface of the photosensitive drum 1 uniformly charged by the charging roller 2 to which a charging bias voltage is applied from the charging bias applying power source S1, the exposure device (optical system) 3 emits a laser beam according to the image information signal. An electrostatic latent image is formed by scanning exposure with L.

The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed as a toner image by the developing device 4 with a developer (toner). The developing device 4 of this example is a reversal developing device using magnetic one-component insulating toner (negative toner). The developing device 4 includes a developing roller 4a, which is a non-magnetic rotating sleeve that contains a magnet roll 4a as a developer carrying member.
Have. The layer thickness of the developer is regulated by the developing blade 4c, which is a developer layer thickness regulating member, and an electric charge is applied, so that the developing roller 4a is coated with a thin layer. The developer coated on the developing roller 4a is conveyed to the developing section (developing area) a, which is the facing portion between the photosensitive drum 1 and the developing roller 4a, by the rotation of the developing roller 4a. A developing bias voltage is applied to the developing roller 4a from a developing bias applying power source S2. As the developing bias voltage, a voltage in which a DC voltage and an AC voltage are superposed is usually used.

In this example, the developing device 4 uses a developer as a developer.
It contains a mixture (mixture) t + m of toner t and charged particles (conductive particles) m. In this example, the conductive particles m
Conductive zinc oxide particles are used as
2 parts by weight of the conductive particles m are externally added to the parts by weight.

Further, around the photosensitive drum 1, there is provided a medium resistance transfer roller 6 as a contact transfer means.
The transfer roller 6 is pressed against the photosensitive drum 1 with a predetermined pressing force to form a transfer nip portion b. A transfer material P as a recording medium is fed to the transfer nip portion b from a paper feed portion (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 6 from a transfer bias applying power source S3. By doing so, the toner image formed on the photosensitive drum 1 is sequentially transferred to the surface of the transfer material P fed to the transfer nip portion b. After that, the transfer material P is subjected to fixing of the toner image by a fixing device 7 such as a heat fixing system, and is discharged outside the device as an image forming unit (print, copy).

The image forming apparatus 200 of this embodiment employs a cleanerless system, and the transfer residual toner t remaining on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P is performed.
Is not removed by the cleaner, reaches the developing portion a through the charging contact portion n as the photosensitive drum 1 rotates, and is simultaneously cleaned (recovered) by the developing device 4 during development. The transfer residual toner t that reaches the charging contact portion n by the rotation of the photosensitive drum 1 and adheres to and is mixed with the charging roller 2 is gradually discharged from the charging roller 2 onto the photosensitive drum 7, and as the surface of the photosensitive drum 1 moves. It reaches the developing section a and is simultaneously cleaned (collected) by the developing device 4 during development.

The conductive particles m contained in the developer of the developing device 4 are transferred to the photosensitive drum 1 together with the toner t at the time of developing the electrostatic latent image. The toner image on the photosensitive drum 1 is attracted and actively transferred to the transfer material P side under the influence of the transfer bias in the transfer nip portion b, but the conductive particles m on the photosensitive drum 1 are conductive. It is not positively transferred to the transfer material P side, and is substantially adhered and held on the photosensitive drum 1 and remains. Then, the conductive particles m remaining on the surface of the photosensitive drum 1 after the transfer of the toner image onto the transfer material P are directly carried to the charging contact portion n by the rotation of the photosensitive drum 1 together with the transfer residual toner t.

In this way, the contact charging of the photosensitive drum 7 is performed in the state where the conductive particles m are present in the charging contact portion n.

Since the presence of the conductive particles m makes it possible to maintain the close contact property and contact resistance of the charging roller 2 to the photosensitive drum 1, the direct injection charging of the photosensitive drum 1 by the charging roller 2 can be performed. That is, the charging roller 2 is in close contact with the photosensitive drum 1 via the conductive particles m, and
Since the conductive particles m existing in the charging contact portion n rub the surface of the photosensitive drum 1 without any gap, high charging efficiency can be obtained by stable and safe direct injection charging without using a discharge phenomenon, and the charging roller 2 can be applied with the charging efficiency. It is possible to apply a potential almost equal to the applied voltage to the photosensitive drum 1.

[0039]

[Problems to be Solved by the Invention]
No consideration has been given to the arrangement of the entrance of the charging contact portion n formed by the contact charging member and the charged body such as the image carrier in the moving direction of the charged body.

Referring to FIG. 12, conventionally, an entrance of the charging contact portion n formed by the charging roller 2 and the photosensitive drum 1 in the rotation direction of the photosensitive drum 1 (hereinafter, simply referred to as "contact portion entrance"). .) S is not considered in any way. For example, as shown in the drawing, a wedge-shaped space formed by the surface of the charging roller 2 and the surface of the photosensitive drum 1 (hereinafter referred to as “contact portion entrance area”). It was supposed that r was open vertically downward.

Although direct injection charging can be performed by such a structure, the present inventors have obtained a better charging property in a stable manner through a lot of experimental studies, and therefore, a better toner recycling. It has been found that the arrangement of the inlet s of the contact portion is important for obtaining the property.

For example, when the contact portion entrance region r is opened vertically downward as shown in FIG. 12, the amount of the conductive particles m accumulated in the contact portion entrance region r is small or the conductive particles m are in contact with each other. It was sometimes dropped from the entrance area r.

In the direct injection charging mechanism, the contact property of the contact charging member to the member to be charged affects the charging property, and it is important to improve the contact uniformity and the denseness of the contact charging member to the member to be charged. . Further, in order to enhance the charging ability of particle charging, it is important to properly maintain the particle size and the resistance value of the conductive particles m, their carrying amount on the charging roller 2, and the coverage rate.

However, as described above, if the amount of the conductive particles m accumulated in the contact area entrance region r is small or if the conductive particles m fall off from the contact area entrance region r, the charging performance by the direct injection charging mechanism deteriorates. In some cases, the proper carrying amount and coverage cannot be obtained, and the charging performance may become unstable.

Further, the transfer residual toner t and the conductive particles m fall off from the contact portion entrance region r, and the inside of the image forming apparatus is soiled. Then, in this way, the contact portion entrance region r
Falling off from the core leads to consumption of the conductive particles m. When the developing device 4 is used as a means for supplying the conductive particles m and the conductive particles m are mixed in the developer, it is impossible to mix the conductive particles m more than necessary in the developing device 4 from the viewpoint of developing property. However, simply increasing the amount of conductive particles m for supply does not solve the problem. Further, when the toner recycling process is adopted, the toner may fall off from the contact portion entrance region r, which may deteriorate the toner recycling property.

Therefore, an object of the present invention is generally to provide a charging device having a charging performance further improved by a direct injection charging mechanism,
An object of the present invention is to provide a process cartridge and an image forming apparatus including the same.

Another object of the present invention is to provide a charging device capable of maintaining a proper amount of conductive particles to be carried on a charging member and a coverage rate, and constantly exhibiting good charging performance, a process cartridge equipped with the charging device, and an image. A forming device is provided.

Another object of the present invention is to prevent particles from coming off from the entrance of the contact portion formed by the charging member and the body to be charged in the moving direction of the body to be charged, and to contaminate inside the machine and to consume the conductive particles. It is an object of the present invention to provide a charging device capable of preventing such problems, a process cartridge including the charging device, and an image forming apparatus.

Another object of the present invention is, in an image forming apparatus employing a toner recycling system, to prevent toner from falling off from an entrance of a contact portion formed by a charging member and an image carrier in the moving direction of the image carrier. It is an object of the present invention to provide a charging device, a process cartridge, and an image forming apparatus that can prevent the toner and improve the toner recycling property.

[0050]

The above object can be achieved by a charging device, a process cartridge and an image forming apparatus according to the present invention. In summary, the first aspect of the present invention is a charging member for charging a rotatable charged body, wherein a contact portion is formed with the charged body, and the rotation direction and the surface of the charged body are formed at the contact portion. Has a rotatable charging member so as to move in the opposite direction, and in a charging device in which conductive particles are carried by the charged body and conveyed to the contact portion, a horizontal line passing through the rotation center of the charged body Assuming that the X axis is a vertical line passing through the rotation center of the charged body and the Y axis is the entrance to the contact portion in the rotation direction of the charged body, the rotation direction of the charged body is from the clockwise direction. As seen, the charging device is provided in the first quadrant of the XY coordinates. According to one embodiment of the present invention, it has a supply means for supplying conductive particles to the body to be charged. In one embodiment, the member to be charged is an image carrier, the supply unit is a developing unit that develops the electrostatic image formed on the image carrier with a developer, and the developer is toner. And the conductive particles. Further, in one embodiment, the developing unit can collect the toner remaining on the charged body.

According to a second aspect of the present invention, there is provided a process cartridge characterized in that the charging device of the first aspect of the present invention can be attached to and detached from the main body of the image forming apparatus together with the image bearing member which is the member to be charged. To be done.

According to a third aspect of the present invention, the charging device according to the first aspect of the present invention includes an image carrier which is a member to be charged and a developing means for developing an electrostatic image formed on the image carrier with a developer. A process cartridge is also provided, which is removable from the main body of the image forming apparatus.

According to the fourth aspect of the present invention, the rotatable image bearing member, which is the charged member, and the contact portion with the image bearing member are formed.
The image carrier is provided with a charging member rotatable in the contact portion so that the surface of the image carrier rotates in the opposite direction to the rotation direction of the image carrier, and a supply unit for supplying conductive particles to the image carrier. In the image forming apparatus in which the carried conductive particles are conveyed to the contact portion, a horizontal line passing through the rotation center of the image carrier is an X axis, and a vertical line passing through the rotation center of the image carrier is a Y axis. The image forming apparatus is characterized in that the entrance to the contact portion in the rotation direction of the image carrier is provided in the first quadrant of XY coordinates when viewed from the direction in which the rotation direction of the charged body is clockwise. Will be provided. According to an embodiment of the present invention, the supplying unit is a developing unit that develops the electrostatic image formed on the image carrier with a developer, and the developer includes toner and the conductive particles. or,
In one embodiment, the image forming apparatus charges the image carrier by the charging member, and exposes the charged surface of the image carrier by an image exposure device to form an electrostatic image, An image is formed by an image forming process including the steps of developing the electrostatic image on the body with a developer by the developing means, and then transferring the developer image on the image carrier to the transfer target, and after the transfer step The developer remaining on the surface of the image carrier can be temporarily carried on at least the charging member, transferred to the surface of the image carrier again, and collected by the developing means. The charging member may be attachable to and detachable from the main body of the image forming apparatus together with the image carrier. Further, the charging member is the image carrier,
It may be detachable from the main body of the image forming apparatus together with the developing means.

According to each of the embodiments of the present invention described above, the angle formed by the X axis and the straight line connecting the rotation center of the body to be charged and the entrance to the contact portion within the first quadrant. Is 15 to 75 degrees.

In each of the above inventions, according to one embodiment, the conductive particles have a particle size of 10 nm to 10 μm, and the resistance of the conductive particles carried on the charging member is 10 ⁻¹ to 10 ¹²
Ω · cm, and a value obtained by dividing the amount of conductive particles carried on the charging member by the surface roughness Raμm of the charging member is 0.05.
˜1 mg / cm ² / μm. According to another embodiment, when the ratio of the conductive particles coating the charging member is Rc, 0.2 ≦ Rc ≦ 1. According to another embodiment, the surface resistance of the charging member is 10 ⁴ to.
It is 10 ¹⁰ Ω / □. According to another embodiment, the charging member is an elastic body having a porous body surface.

[0056]

BEST MODE FOR CARRYING OUT THE INVENTION The charging device, process cartridge and image forming apparatus according to the present invention will now be described in more detail with reference to the drawings.

Example 1 FIG. 1 shows a schematic structure of an image forming apparatus using a charging device according to the present invention. The image forming apparatus 100 is a laser beam printer of a direct injection charging type and a toner recycling process (cleanerless system) using a transfer type electrophotographic process.

(1) Overall Structure of Image Forming Apparatus 100 The image forming apparatus 100 includes a rotating drum type negative OPC photosensitive member (negative photosensitive member;
Called "photosensitive drum". ) Has 1. The photosensitive drum 1 is rotationally driven in the clockwise direction indicated by the arrow in the figure at a constant peripheral speed of 47 mm / sec (= process speed PS, printing speed). The photosensitive drum 1 will be described in detail in another section.

The image forming apparatus 100 includes a charging device 2A having a charging roller 2 which is a particle charging type (powder coating type) contact charging member according to the present invention and a charging bias applying power source S1 for the charging roller 2. Have

The charging roller 2 includes a core metal 2a and the core metal 2a.
A rubber or foam elastic / medium resistance layer (hereinafter referred to as “elastic layer”) formed concentrically and in a roller shape on the outer periphery of a. 2
b, and conductive particles m are supported on the outer peripheral surface of the elastic layer 2b. The charging roller 2 is pressed and brought into contact with the photosensitive drum 1 with a predetermined amount of intrusion to form a charging portion (charging contact portion or nip portion) n having a predetermined width. The conductive particles m carried on the charging roller 2 come into contact with the surface of the photosensitive drum 1 at the charging contact portion n.

The charging roller 2 is driven to rotate in the same clockwise direction as the arrow of the photosensitive drum 1 in the figure, and rotates in the charging contact portion n in the opposite direction (counter) to the rotating direction of the photosensitive drum 1 so that the conductive particles m. And contact the surface of the photosensitive drum 1 with a speed difference. In this embodiment, the photosensitive drum 1 and the charging roller 2 are rotationally driven in the charging contact portion n in opposite directions at a constant speed (peripheral speed). The charging roller 2 and the photosensitive drum 1 are, for example, the photosensitive drum 1
The peripheral speed may be 100%, and the charging roller 2 may be rotated at a peripheral speed of 80%.

Since the charging property of the direct injection charging depends on the ratio between the peripheral speed of the photosensitive drum 1 and the peripheral speed of the charging roller 2, the charging roller 2 is moved in the same direction as the photosensitive drum 1 (the opposite direction at the charging contact portion). Rotational driving is more advantageous in terms of the number of rotations than rotationally driving in different directions (the same direction in the charging contact portion) with a peripheral speed difference, and in terms of particle retention, this structure is also adopted. Is preferred.

At the time of image formation by the image forming apparatus 100, a predetermined charging bias voltage is applied to the core metal 2a of the charging roller 2 from the charging bias applying power source S1. As a result, the peripheral surface of the photosensitive drum 1 is of a direct injection charging type and has a predetermined polarity.
Contact charging is applied uniformly to the electric potential. In this embodiment, a charging bias applying power source S1 to -6 is applied to the core metal 2a of the charging roller 2.
A charging bias of 10 V is applied to the surface of the photosensitive drum 1 so that the charging potential (-600) is almost the same as the applied charging bias.
V) was obtained.

The conductive particles m applied to the outer peripheral surface of the charging roller 2 adhere to the surface of the photosensitive drum 1 as the charging roller 2 charges the photosensitive drum 1 and are carried away. Then, a part is transferred to the transfer material P. Therefore, a means for supplying conductive particles to the charging roller 2 is required to compensate for this. As will be described later, in this embodiment, the developing device 4
Function as a means for supplying the conductive particles m.

According to the present invention, the charging roller 2 and the photosensitive drum 1 have a horizontal line passing through the rotation center of the photosensitive drum 1 as the X axis and a vertical line passing through the rotation center of the photosensitive drum 1 as the Y axis. Of the charging contact portion n formed by
The entrance (contact part entrance) s in the rotation direction of the photosensitive drum 1 is provided so as to be located in the first quadrant of the XY coordinates when viewed from the direction in which the rotation direction of the photosensitive drum 1 is clockwise. Particularly, in this embodiment, the X axis and the straight line connecting the rotation center of the photosensitive drum 1 and the contact portion entrance s are arranged so that the angle α formed in the first quadrant is 45 degrees. As described later, the angle α is preferably 15 degrees to 75 degrees,
It is more preferably 30 to 60 degrees. The direct injection charging by the charging roller 2 and the arrangement of the charging roller 2 will be described in detail in another section.

The image forming apparatus 100 has a laser beam scanner 2 having a laser diode, a polygon mirror, etc. as an exposure device (optical system) for performing image exposure. The laser beam scanner 3 outputs a laser beam L 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 photosensitive drum 1 with the laser beam L. . By this scanning exposure, an electrostatic latent image corresponding to target image information is formed on the surface of the photosensitive drum 1.

The electrostatic latent image formed on the photosensitive drum 1 is
Then, it is developed by the developing device 4. In this embodiment,
The developing device 4 is a reversal developing device using a negatively-charged one-component magnetic developer (negative toner). In the developing container (developing device main body) 4e of the developing device 4, as will be described later in detail, a mixture t of a toner t as a developer and a conductive particle m.
It houses + m. The electrostatic latent image formed on the surface of the photosensitive drum 1 is developed by the developing device 4 at a developing portion (developing area) a.
Is developed as a toner image at.

That is, the developing device 4 has a developing roller 4a as a developer carrying member, which is a non-magnetic rotary developing sleeve in which a magnet roll 4b is contained. The toner t in the mixture t + m provided in the developing container 4e is subjected to the layer thickness regulation and the charge application by the developing blade 4c which is the developer layer thickness regulating member in the process of being conveyed on the developing roller 4a. Further, the developing device 4 has a stirring member 4d that circulates the mixed agent t + m in the developing container 4e and sequentially conveys the mixed agent t + m around the developing roller 4a.

Toner t coated on the developing roller 4a
Is conveyed to a developing portion (developing area) a, which is an opposing portion of the photosensitive drum 1 and the developing roller 4a, by rotation of the developing roller 4a. A developing bias voltage is applied to the developing roller 4a from a developing bias applying power source S2. In this embodiment, the developing bias voltage is a superimposed voltage of DC voltage and AC voltage. As a result, the electrostatic latent image formed on the photosensitive drum 1 is reversely developed by the toner t.

Here, the one-component magnetic developer (toner) t, which is a developer, is prepared by mixing a binder resin, magnetic particles and a charge control agent, and kneading, pulverizing and classifying, It is produced by adding charged particles m, a fluidizing agent and the like as external additives. The average particle diameter (D4) of the toner was 7 μm in this example.

Further, in this embodiment, the conductive particles m were added (externally added) in an amount of 2 parts by weight with respect to 100 parts by weight of the toner t.

The toner image formed on the photosensitive drum 1 is then transferred onto a transfer material P as a recording material by a medium resistance transfer roller 6 as a contact transfer means. Transfer roller 6
Has a transfer nip portion b formed by pressing it against the photosensitive drum 1 with a predetermined pressing force. The transfer material P is fed to the transfer nip portion b from a paper feeding portion (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 6 from the transfer bias applying power source S3. The toner images formed on the photosensitive drum 1 are sequentially transferred to the surface of the transfer material P fed to the transfer nip portion b.

The transfer roller 6 used in the present embodiment has a roller resistance value of 5 ×, in which a medium resistance foaming layer 6b is formed on a core metal 6a.
10 ⁸ Ω, +2.0 kV voltage is applied to the core metal 6a
Was applied to transfer. The transfer material P introduced into the transfer nip portion b is nipped and conveyed through the transfer nip portion b, and the toner image formed and carried on the surface of the photosensitive drum 1 on the surface side thereof is sequentially subjected to electrostatic force and pressing force. Will be transcribed.

The photosensitive drum 1 is fed to the transfer nip portion b.
The transfer material P that has received the transfer of the toner image from the photosensitive drum 1
After being separated from the surface of the sheet, the sheet is introduced into a fixing device 7, which is a thermal fixing system in the present embodiment, and the toner image is fixed and discharged as an image-formed product (print, copy) to the outside of the device. Then, the photosensitive drum 1 is charged again by the charging roller 2 and is repeatedly used for image formation.

In this embodiment, the conductive particles m are added to the toner t of the developing device 4, and adhere to the surface of the photosensitive drum 1 together with the toner t during the development of the electrostatic latent image on the photosensitive drum 1.
When the photosensitive drum 1 rotates, it is carried to the charging contact portion n. That is, the conductive particles m are supplied to the charging roller 2 via the photosensitive drum 1.

That is, the image forming apparatus 100 of this embodiment adopts the toner recycling process, and the transfer residual toner t remaining on the surface of the photosensitive drum 1 after the image transfer is removed by a dedicated cleaning device (cleaner). Instead, it is carried to the charging contact portion n as the photosensitive drum 1 rotates and is temporarily collected by the charging roller 2 that counter-rotates with respect to the rotation of the photosensitive drum 1 at the charging contact portion n. Then, as the toner t goes around the outer periphery of the charging roller 2, the inverted toner charge is normalized (in the present embodiment, has a negative polarity) and is sequentially discharged to the photosensitive drum 1. Then, the toner t reaches the developing portion a as the photosensitive drum 1 rotates, and is collected and reused by the developing device 4 in the simultaneous cleaning of development. That is, at the time of development after the next step, that is, when the photosensitive drum 1 is continuously charged by the charging roller 2 and exposed to form a latent image, and the latent image is developed, the fog removing bias (DC applied to the developing device is applied). It is recovered by the fog-removal potential difference Vback) which is the potential difference between the voltage and the surface potential of the photoconductor. In the case of the reversal development method as in the present embodiment, this simultaneous development cleaning is performed by an electric field for collecting toner from the dark portion potential of the photosensitive drum 1 to the developing roller 4a and a toner from the developing roller 4a to the light portion potential of the photosensitive drum 1. It is made by the action of an electric field that adheres.

(2) Photosensitive Drum 1 The photosensitive drum 1 will be described in more detail. FIG. 7 is a schematic diagram of the layer structure of the photosensitive drum 7. FIG. 7A is a schematic diagram of the layer structure of the photosensitive drum 1a with a charge injection layer, and FIG. 7B is a layer configuration of the photosensitive drum 1b without a charge injection layer.

The photosensitive drum 1b having no charge injection layer shown in FIG. 7B is an aluminum drum base (Al drum base) 11
On top, an undercoat layer 12, a charge generation layer 13, a charge transport layer 14
It is a general organic photoconductor drum coated in the order of.

The photosensitive drum 1a with a charge injection layer shown in FIG. 7B is the same as the photosensitive drum 1b shown in FIG. 7B.
In addition, the charge injection layer 15 is further applied to improve the charging performance.

The charge injection layer 15 is made of a photo-curing acrylic resin as a binder and conductive particles (conductive filler).
SnO ₂ ultrafine particles 15a (diameter of about 0.03μ
m), a polymerization initiator and the like are mixed and dispersed, and after coating, a film is formed by a photo-curing method.

In addition, by additionally including a lubricant such as tetrafluoroethylene resin, the surface energy of the surface of the photosensitive drum 1 is suppressed, and the adhesion of the conductive particles m is generally suppressed. The surface energy is preferably 85 degrees or more, and more preferably 90 degrees or more when expressed by the contact angle of water.

The resistance of the surface layer is important from the viewpoint of charging performance.
It becomes a factor. In the direct injection charging method,
One injection point by reducing the resistance on the charged body side
Around the (contact point), the surface of the body to be charged that can be charged
The product will be widened. Therefore, the charging roller 2 is the same.
Even if they are in the same contact state, if the resistance of the surface to be charged is low.
In this case, it is possible to efficiently transfer charges. On the other hand, image carrier
As a result, it is necessary to hold the electrostatic latent image for a certain time.
Therefore, the volume resistance value of the charge injection layer 15 is 1 × 10.⁹~
1 x 10¹⁴The range of (Ω · cm) is appropriate. Also, FIG.
Photosensitive drum not using the charge injection layer 15 shown in (b)
Even in the case of 1b, for example, the charge transport layer 14 has the above resistance range.
In case of, the same effect can be obtained. Furthermore, the body of the superficial layer
Product resistance is about 10 ¹³Amorphous silicon with Ω · cm
The same effect can be obtained by using a photoconductor or the like.

According to the image forming apparatus 100 of this embodiment,
Either the photosensitive drum 1a shown in FIG. 7 (a) having a surface layer resistance of 10 ¹² Ω · cm or more and the photosensitive drum 1b shown in FIG. 7 (b) having surface layers facing each other of 10 ¹⁴ Ω · cm or more are used. Even if it was, it could be charged well.

(3) Charging Roller 2 The charging roller 2 used as the contact charging member in this embodiment will be described in more detail. As described above, the charging roller 2 is composed of the cored bar 2a and the elastic layer 2b of rubber or foam as a charged particle carrier formed in a roller shape so as to be concentrically integrated with the outer periphery of the cored bar 2a. The conductive particles m are carried on the outer peripheral surface of the elastic layer 2b of the charging roller 2.

In this embodiment, the elastic layer 2b is made of a resin (for example, urethane), conductive particles (for example, carbon black), a sulfurizing agent, a foaming agent and the like, and is formed in a roller shape on the core metal 2a. Then, the surface was polished.

The charging roller 2 used in this embodiment is different from the discharging charging roller generally used conventionally in the following points. i) Surface structure and roughness characteristics for supporting high-density charged particles m on the surface layer ii) Resistance characteristics required for direct injection charging (volume resistance, surface resistance)

(3) -1 Surface Structure and Roughness Characteristics The surface of the conventional charging roller for discharge is flat, the average surface roughness Ra is sub-μm or less, and the roller hardness is high. In charging using discharge, the discharge phenomenon occurs in a gap of several tens of μm, which is slightly apart from the contact portion between the discharge charging roller and the body to be charged. When unevenness exists on the surface of the discharging charging roller and the surface of the member to be charged, the electric field strength is partially different and the discharging phenomenon becomes unstable, resulting in uneven charging. Therefore, the conventional discharge charging roller requires a flat and hard surface.

However, in the surface structure of the discharge charging roller as described above, it seems that the surface is in close contact with the photosensitive drum, but in terms of the microscopic contact property at the molecular level necessary for charge injection, it is almost the same. Not in contact. Therefore, direct injection charging cannot be performed with the discharging charging roller.

On the other hand, the charging roller 2 used as the contact charging member in this embodiment is required to have a certain degree of roughness because it is necessary to carry the conductive particles m at a high density. The average roughness Ra is preferably 1 μm to 500 μm.

When the average roughness Ra is less than 1 μm, the surface area for supporting the conductive particles m is insufficient, and when an insulating material (for example, toner) or the like adheres to the surface of the charging roller 2, the surrounding area becomes small. The photosensitive drum 1 cannot be contacted, and the charging performance deteriorates. Further, in consideration of the particle retaining ability, it is preferable that the roughness be larger than the particle diameter of the conductive particles m used.

On the contrary, when the average roughness Ra is larger than 500 μm, the unevenness of the surface of the charging roller 2 reduces the charging uniformity on the surface of the body to be charged.

In this example, the average roughness Ra of the surface of the charging roller 2 was 50 μm.

Incidentally, the surface roughness measuring microscopes VF-7500 and VF7510 manufactured by Keyence Corporation were used for measuring the average roughness Ra.
The objective lens was used from 250 times to 1250 times.
The shape and Ra of the surface of the charging roller 2 are contactlessly
Was measured.

(3) -2 Resistance Characteristics In the conventional charging roller for discharge, after a low resistance base layer is formed on a core metal, the surface is covered with a high resistance layer. The roller charging due to discharge has a high applied voltage, and if there is a pinhole (exposure of the substrate due to damage to the film), the voltage drops to the periphery thereof and charging failure occurs. Therefore, its surface resistance is 10 ¹¹ Ω /
□ Need to be above.

On the other hand, in the direct injection charging method, since charging at a low voltage is possible, it is not necessary to make the surface layer of the contact charging member have high resistance, and the charging roller 2 can be composed of a single layer. Rather, the surface resistance of the charging roller 2 in direct injection charging needs to be 10 ⁴ to 10 ¹⁰ Ω / □.

When the surface resistance is larger than 10 ¹⁰ Ω / □, a large potential difference is generated on the surface of the charging roller 2,
Expulsion bias acts on the conductive particles to facilitate expulsion. Further, the uniformity on the charging surface is reduced, and the charging roller 2
The unevenness due to rubbing appears as streaks in the halftone image,
The image quality is degraded.

On the other hand, when the surface resistance is smaller than 10 ⁴ Ω / □, the peripheral voltage drop occurs due to the pinhole of the photosensitive drum 1 even by the injection charging.

Further, regarding the volume resistance, 10 ⁴ to 10 ⁷
It is preferably in the range of Ω. If it is smaller than 10 ⁴ Ω, the voltage drop of the power source is likely to occur due to the pinhole leak. On the other hand, when it is larger than 10 ⁷ Ω, the current required for charging cannot be secured, and the charging voltage is lowered.

The surface resistance and volume resistance of the charging roller 2 used in this example were 10 ⁷ Ω / □ and 10 ⁶ Ω.

The resistance of the charging roller 2 was measured by the following procedure. FIG. 8 shows a schematic diagram of the configuration at the time of measurement. The resistance of the charging roller 2 is such that the total pressure of the core metal 2a of the charging roller 2 is 9.
24mm outer diameter so that a load of 8N (1kgf) is applied
An electrode was applied to the insulating drum 93 of No. 1 and measured. As for the electrodes, a guard electrode 91 is arranged around the main electrode 92, and as shown in FIG.
The measurement was performed with the wiring diagram shown in (b). The distance between the main electrode 92 and the guard electrode 91 was adjusted to about the thickness of the elastic layer 2b of the charging roller 2, and the main electrode 92 had a sufficient width with respect to the guard electrode 91. The measurement was performed by applying +100 V from the power source S4 to the main electrode 92, measuring the currents flowing through the ammeters Av and As, and measuring the volume resistance and the surface resistance, respectively.

(3) -3 Other roller characteristics In the direct injection charging system, it is important that the contact charging member functions as a flexible electrode. In the present embodiment, this is achieved by adjusting the elastic characteristics of the elastic layer 2b of the charging roller 2. The Asker C hardness is preferably in the range of 15 to 50 degrees. More preferably, it is 20 to 40 degrees.

If the hardness is too high, the required amount of penetration cannot be obtained and the charging contact portion n cannot be secured between the charged body and the charged body, so that the charging performance is deteriorated. Further, since the molecular level contact property of the substance cannot be obtained, contact with the periphery thereof is hindered by the inclusion of foreign matter.

On the other hand, if the hardness is too low, the shape is not stable, so that the contact pressure with the member to be charged becomes uneven, resulting in uneven charging. Alternatively, charging failure occurs due to permanent distortion of the charging roller 2 due to long-term standing.

In this embodiment, the charging roller 2 having an Asker C hardness of 22 degrees was used. Further, the charging roller 2 is arranged with an intrusion amount of 0.3 mm with respect to the photosensitive drum 1, and has a contact width of about 2 mm.
A charging contact portion n of mm is formed.

(3) -4 Material, Structure, and Size of Charging Roller The material of the elastic layer 2b of the charging roller 2 is EPDM,
Examples thereof include urethane, NBR, silicone rubber, and rubber materials in which a conductive substance such as carbon black or metal oxide for resistance adjustment is dispersed in IR or the like. It is also possible to adjust the resistance by using an ion conductive material without dispersing the conductive substance. Then adjust the surface roughness if necessary,
Mold by polishing. Further, a structure having a plurality of layers with separated functions is also possible.

However, as the form of the elastic layer 2b of the charging roller 2, a porous structure is more preferable. It is also advantageous in manufacturing in that the above-mentioned surface roughness can be obtained at the same time when the roller is molded. The cell diameter of the foam is 1 to 500 μm
Is appropriate. After foam molding, the surface of the porous body is exposed by polishing the surface, and the surface structure having the aforementioned roughness can be produced.

Finally, the diameter is 6 mm and the longitudinal length is 2
Layer thickness 3 mm with porous body surface on 40 mm core metal 2a
The elastic layer 2b was formed, and a charging roller 2 having an outer diameter of 12 mm and a longitudinal length of the elastic layer 2b of 220 mm was produced.

(4) Conductive Particle m In this example, the specific resistance of the conductive particle m was 10 ⁶ Ω.
A conductive zinc oxide having a cm and an average particle diameter of 3 μm was used. The conductive particles m are contained in the developing device 4 in this embodiment.

As the material for the conductive particles m, various conductive particles such as conductive inorganic particles such as other metal oxides, a mixture with an organic substance, or those subjected to surface treatment can be used. Further, since the conductive particles m do not need to be magnetically restrained, they need not have magnetism. For example, titanium oxide particles doped with alumina powder or tin oxide can be preferably used.

The resistance of the conductive particles m is required to be 10 ¹² Ω · cm or less, preferably 10 ¹⁰ Ω · cm or less, in order to transfer charges through the particles. Further, the resistance of the conductive particles m is set to be 10 ⁻¹ Ω · cm or more in terms of resistivity in consideration of the leak of the developing bias during development.

The resistance was measured by the tablet method and normalized. That is, approximately 0.5 g of conductive particles m are put in a cylinder having a bottom area of 2.26 cm ² , and 147 N is put on the upper and lower electrodes.
Simultaneously with the pressurization of (15 kgf), a voltage of 100 V was applied to measure the resistance value, and then normalized to calculate the specific resistance.

As a result of examining variously changing the resistance of the conductive particles m, when the resistance of the conductive particles m was larger than 10 ¹² Ω · cm, charge transfer could not be performed and the charging performance was insufficient (defective). . On the other hand, when the resistance of the conductive particles m is smaller than 10 ⁻¹ Ω · cm, leak of the developing bias occurs during development and the image defect is remarkable.

Further, the particle diameter of the conductive particles m is preferably 10 μm or less in order to obtain high charging efficiency exceeding the magnetic brush charging device and charging uniformity. Here, the particle size in the case where the particles form an aggregate is defined as the average particle size of the aggregate. To measure the particle size, 100 or more particles were extracted from the observation with an electron microscope, the volume particle size distribution was calculated with the maximum extension in the horizontal direction, and the 50% average particle size was determined.

There is no problem that the conductive particles m exist not only in the state of primary particles but also in the state of agglomeration of secondary particles. Whatever the aggregated state, the form is not important as long as the aggregate can realize the function of the conductive particles m.

It is desirable that the conductive particles m are close to white or transparent so as not to interfere with latent image exposure when used for charging the photosensitive drum 1. Further, considering that the conductive particles m are partially transferred from the photosensitive drum 1 to the transfer material P, colorless or white particles are desirable in color image formation. Further, in order to prevent light scattering due to the conductive particles m at the time of image exposure, it is desirable that the particle size is equal to or smaller than the constituent pixel size and further equal to or smaller than the particle size of the toner t.

The lower limit of the particle size is considered to be 10 nm as a particle which can be stably obtained as particles. That is, the particle size of the conductive particles m is preferably in the range of 10 nm to 10 μm. Furthermore, considering the fog characteristics on the transfer material P,
0.1 to 5 μm is a particularly preferable range.

As a result of studying variously changing the particle diameter of the conductive particles m, when zinc oxide particles having a particle diameter of 0.01 μm, which is a general conductive particle m, are used, there is a slight disadvantage in terms of poor development and fogging. However, the charging performance was sufficient. On the other hand, when zinc oxide particles having a particle size of more than 10 μm are used, the particle size is large, which is disadvantageous in terms of contact density and the charging performance is insufficient (defective). Furthermore, particle size 30μ
When the zinc oxide particles of m were used, the particle size was large and the force of adhering to the charging roller 2 was weak, so many particles fell off, resulting in poor development and fog.

(5) Conductive Particle Carrying Amount Although the charging performance is improved by reducing the particle size of the conductive particles m in the particle charging, the photosensitive particles 1 of the conductive particles m are improved.
The dropout to Since the force capable of holding the conductive particles m on the charging roller 2 is a weak adhesive force, it is difficult to restrain the particles even if a large number of particles are supplied. In the developing process and the transfer process onto the transfer material P, the image defect is affected. Therefore, ideally, it is desirable that the surface layer of the charging roller 2 is evenly coated. However, in actuality, by adjusting the carried amount, it becomes possible to secure the chargeability and reduce the particles to be attached to a level that does not have a harmful effect.

The amount of the conductive particles m to be carried needs to be appropriately maintained by the average roughness Ra of the surface of the charging roller 2. That is, the value obtained by dividing the supported amount by the average roughness Ra (hereinafter, simply referred to as “supported amount / Ra”) is 1 mg / cm ² / μm or less,
It is more preferably 0.3 mg / cm ² / μm or less.

In this example, the amount of the conductive particles m supported was about 3 mg / cm ² , and Ra was 50 μm.
a was 0.06 mg / cm ² / μm.

The carrying amount of the conductive magnetic particles used in the conventional magnetic brush charging device is about 167 mg / c in carrying amount / Ra.
m ² / μm (200 mg / cm ² , Ra on the surface of the charging sleeve = 1.2 μm), whereas in the present invention, the supported amount of the non-magnetic conductive particles m is 1 in the supported amount / Ra.
mg / cm ² / μm (for example, 50 mg / cm ² , Ra =
50 μm) or less, more preferably 0.3 mg / cm ²
/ Μm (for example, 15 mg / cm ² , Ra = 50 μm)
Good results can be obtained by setting the following.

On the other hand, since it is necessary to secure the charging performance, the minimum carrying amount is the same as the carrying amount / Ra of 0.05 mg / cm ² /
μm (eg, 0.25 mg / cm ² , Ra = 50 μm
m) or more, more preferably 0.02 mg / cm ² / μ
m (for example, 1 mg / cm ² , Ra = 50 μm) or more.

That is, the carrying amount of the conductive particles m on the charging roller 2 is 0.005 to 1 mg / cm ² / carrying amount / Ra.
μm, more preferably 0.02-0.3 mg / cm ²
/ Μm.

Charging roller 2 having a surface roughness Ra of 50 μm
Then, the conductive particles m have a particle size of 3 μm and a resistance of 10 ⁴ (Ω · c
m) using zinc oxide particles, the loading amount is 0.05,
0.25, 1, 5, 15, 50, 100 mg / cm ² and the charging roller 2 having a surface roughness Ra of 10 μm.
Then, the supported amount of the particles is 0.01, 0.05, 0.2,
Examinations were made for cases of 1, ^{3, 10,} and 50 mg / cm ² .

As a result, the same loading amount of 0.05 mg / cm
^{Even in} the case of 2, the surface roughness Ra of the charging roller 2 is 1
When it is 0 μm, the loaded amount / Ra is 0.005 mg / c
m ² / μm and 0.0 when Ra is 50 μm
Compared to 01 mg / cm ² / μm, the number was large, and the charging property was excellent.

When the carried amount is 100 mg / cm ² and the surface roughness Ra of the charging roller 2 is 50 μm, the charging performance is sufficient, but the carried amount is too large and the charging roller 2 can be sufficiently held. Instead, it dropped onto the photosensitive drum 1 and caused defective development and fogging. This loading amount is 50 mg / cm
² (Ra = 50 μm), carried amount / Ra is 1 mg /
By lowering the value to cm ² / μm, the amount carried on the charging roller 2 became appropriate, and the development failure and fog could be improved.

On the other hand, even if the carrying amount is 50 mg / cm ² , the surface roughness Ra of the charging roller 2 is 10 μm and the carrying amount / Ra is 5 mg / cm ² / μm. On the other hand, since the carried amount was too large, the occurrence of defective development became remarkable.

As described above, there is an appropriate carrying amount according to the surface roughness Ra of the charging roller 2. Therefore, a good correlation with the image can be obtained by using the carried amount / Ra normalized by Ra as an index. Carrying amount / Ra 0.00
5 to 1 mg / cm ² / μm, preferably 0.02 to 0.
By adjusting to 3 mg / cm ² / μm, the chargeability,
It is possible to set conditions with excellent developability.

In the present embodiment, the image forming apparatus 1
Since 00 uses a toner recycling system,
Compared to the case where a cleaning device is installed separately,
-Contaminates the surface of the charging roller 2. Toner t is a friction band
The resistance value is 10 in order to maintain the electric charge on the surface.
¹³Has a resistance of Ω · cm or more. Therefore, the charging roller 2
When the toner is contaminated with the toner t, the toner is carried on the charging roller 2.
Particles (in addition to conductive particles m, toner t, paper powder, etc.
(Including contaminants) will increase and the charging performance will decrease.
It Even if the resistance of the conductive particles m is low,
When mixed, the resistance of the powder carried on the charging roller 2 is
There is a possibility that the temperature rises and the charging property is impaired. Therefore conductive
The supported amount of particles is in the above range, that is, the supported amount / Ra is 0.0
05-1mg / cm²/ Μm, more preferably 0.02
~ 0.3 mg / cm²Even if it is / μm,
Since a large amount of toner t may be contained, the chargeability is low.
There is a risk of falling. In this case, it was carried on the charging roller 2.
Particles (conductive particles m as well as contaminants such as toner t and paper powder)
(Including also) will increase, so grasp the situation
You can That is, in the actual use state, the charging roller 2
Particles carried by the toner (conductive particles m, toner t, paper
(Including powders and other contaminants)
Anti-measurement is performed and the value is 10^-1-10¹²Ω · cm, more
Preferably 10 ^-1-10^TenMust be Ω · cm
Becomes

(6) Coverage of Conductive Particles Further, in order to grasp the effective amount of the conductive particles m in charging, it is more important to adjust the coverage of the conductive particles m. For example, when conductive zinc oxide is used as the conductive particles m, since the conductive particles m are white, they can be distinguished from the color of the toner (black of the magnetic toner in this embodiment).
In the observation with a microscope, a white area is obtained as an area ratio. If the coverage is 0.1 or less, the charging performance is insufficient even if the peripheral speed of the charging roller 2 is increased. Therefore, the coverage of the conductive particles m should be kept in the range of 0.2 to 1. It becomes important.

As a result of various changes in the coverage of the conductive particles m, when the charging was performed without mixing the conductive particles m into the developing device 4 and without using the conductive particles m (coverage 0), In the case of using a developer in which 0.3 parts by weight of conductive particles m (coverage of 0.1) is added (externally added) to 100 parts by weight of toner t, the amount of particles carried on the charging roller 2 is the same. However, since the particle resistance of the toner was as high as 10 ¹⁴ Ω · cm, the charging was insufficient (defective).

On the other hand, in the case of using the developer added (externally added) with 0.5 parts by weight (coverage of 0.2) and 2 parts by weight (coverage of 0.5) to 100 parts by weight of the toner t, respectively, Both the particle resistance and the supported amount were within the above-mentioned appropriate ranges, and although the coverage was a little low, sufficient chargeability, development and fog characteristics were exhibited. Therefore, the coverage is preferably in the range of 0.2 to 1.

The amount of the carried particles can be adjusted basically by adjusting the amount of the conductive particles m added to the toner t.
If necessary, an elastic blade as a carrying amount adjusting member may be brought into contact with a part of the outer circumference of the charging roller 2 for adjustment. By bringing the carrying amount adjusting member into contact with the toner, there is an effect of normalizing the triboelectrification polarity of the toner, and the amount of particles carried on the charging roller 2 can be adjusted.

(7) A method for measuring the amount of carried particles and the resistance,
Charging Performance and Image Evaluation Method Here, the particle carrying amount and the resistance measuring method, the charging performance and the image evaluation method mentioned above will be described.

(A) Measurement of amount of particles carried and resistance The particles carried on the charging roller 2 were washed, and the weight and resistance of the particles were measured. A cleaning liquid composed of ethanol and water (1: 2) was prepared in the ultrasonic cleaning machine, and the charging roller 2 was dipped in the cleaning liquid for cleaning. Removal of deposits on the charging roller 2 by confirming the surface of the charging roller 2 with an optical microscope or the like, and repeating the cleaning while rubbing the surface of the charging roller 2 with a blade or the like as necessary. You can

The obtained washing solution is allowed to stand for 1 to 2 hours, and when it can be clearly separated from the supernatant, the supernatant is removed. Then, the material carried on the charging roller 2 was extracted by sufficiently drying at 105 ° C.

The particle resistance is measured according to the above-mentioned tablet method.

The carrying amount is obtained as a carrying amount per unit area from the total weight of the obtained particles and the surface area of the charging roller 8 (calculated from the longitudinal length and outer diameter of the charging roller 8).

When referring to the amount of the magnetic brush carried, the measurement is made by directly collecting the magnetic particles on the surface of the charging sleeve after coating and measuring the coating amount.

(B) Measurement of Coverage Regarding the measurement of the coverage, the area covered with the conductive particles m was measured by observing with a microscope under a condition close to the contact condition of the charging roller 2. Specifically, the rotation of the photosensitive drum 1 and the charging roller 2 is stopped without applying the charging bias, and the surfaces of the photosensitive drum 1 and the charging roller 2 are covered with a video microscope (OVM1000N made by OLYMPUS) and a digital still recorder (made by DELTS). It was photographed with SR-3100). Regarding the charging roller 2, the charging roller 2 was brought into contact with the slide glass under the same conditions as when the charging roller 2 was brought into contact with the photosensitive drum 1, and the contact surface of the charging roller 2 was photographed from the back surface of the sliding glass with a video microscope using a 1000 × objective lens. . After that, the region covered with the particles was separated based on the color or the brightness of the conductive particles m measured in advance, and the area ratio was calculated and used as the coverage. Further, when it was difficult to discriminate by color, the substance on the outermost surface of the charging roller 2 was measured by a fluorescent X-ray analyzer SYSTEM3080 (manufactured by Rigaku Denki Kogyo Co., Ltd.). First, between the charging roller 2 covered with the conductive particles m in the initial state and the photosensitive drum 1, the adhesive surface of a polyester tape (Nichiban No. 550 (# 25)) is inserted toward the charging roller 2 to expose it to light. The drum 1 and the charging roller 2 are driven to rotate so that the charging contact portion n between the charging roller 2 and the photosensitive drum 1 passes once. At this time, particles on the outermost surface of the charging roller 2 are further sampled on the tape surface. On the other hand, the charging roller 2 that has completed the printing test is also sampled in the same manner. The coverage can be obtained by quantifying the content of a specific element contained in the conductive particles m. That is, with the tape sample of the charging roller 2 carrying only the conductive particles m as 1, the ratio of the sample after the printing test can be calculated and the coverage can be obtained.

(C) Evaluation of Charging Performance Here, the evaluation of charging property was performed by ghost. In this embodiment, since image recording is performed by the reversal developing system, a ghost here means that a portion (toner image portion) image-exposed in the first round of the photosensitive drum 1 is the second round of the photosensitive drum. It means that the previous image pattern on the photosensitive drum 1 is more strongly developed due to insufficient charging, and a ghost image is generated. The evaluation standard is bad when a ghost is seen in the white background after solid black, and is good when no ghost is seen in the white background after solid black but a slight ghost pattern is seen in the halftone area. When no ghost was observed in both the white background portion and the intermediate top portion, it was considered excellent. The print rate of the image pattern was 5%, and the print test was conducted using a pattern having no difference in print rate in the longitudinal direction.

(D) Image evaluation Image evaluation was performed by outputting a halftone image and evaluating the number of defects in the image. An image was recorded using a 600 dpi laser scanner as the exposure device 3. In this evaluation,
The halftone image means a striped pattern in which one line in the main scanning direction is recorded and then two lines are not recorded, and represents the density of halftone as a whole.

Here, since image recording is carried out by the reversal developing system, when image exposure is blocked or leak occurs during development, white spots appear on the image. The number of these defect sites was evaluated. In particular, the uniformity of the halftone image was emphasized and defects of 0.3 mm or more were evaluated. The evaluation standard is 5 white dots with a diameter of 0.3 mm or more in the halftone image.
When there were more than 0 pieces, it was judged as bad, when there were 5 to 50 pieces, it was judged as good, and when there were less than 5 pieces, it was judged as excellent.

(E) Fog Evaluation Fog is an image defect in which white areas (unexposed areas) that are not originally printed are slightly developed and appear like background stains. The amount of fog is measured by an optical reflectometer (TC-
6DS), the optical reflectance by a green filter was measured, and the reflectance amount of fog was subtracted from the reflectance of only the recording paper to evaluate the fog amount. The fog amount was obtained by measuring 10 or more points on the recording paper and averaging the measured values. The evaluation standard is that if the fog amount exceeds 10%, it is judged as defective.
When it was -10%, it was evaluated as good, and when it was less than 2%, it was evaluated as excellent.

(8) Arrangement of Charging Roller 2 Next, the most characteristic arrangement of the charging roller 2 in the present invention will be described. In the present invention, the arrangement of the inlet (contact portion inlet) s of the charging contact portion n formed by the charging roller 2 and the photosensitive drum 1 in the moving direction of the photosensitive drum 1 is defined.

In the present invention, as shown in FIG. 3, when the horizontal line passing through the center of rotation of the photosensitive drum 1 is the X axis and the vertical line passing through the center of rotation of the photosensitive drum 1 is the Y axis, the contact portion entrance s
Is provided so as to be located in the first quadrant of the XY coordinates when viewed from the direction in which the photosensitive drum 1 rotates in the clockwise direction.

In the present specification, when referring to the quadrant of the XY coordinates, it refers to a case where the rotating charged body is viewed from the clockwise direction. Further, the contact portion inlet s is the upstream end of the charging contact portion n in the rotation direction of the photosensitive drum 1. Further, a wedge-shaped space formed by the surface of the charging roller 2 and the surface of the photosensitive drum 1 near the front side of the contact portion entrance s in the rotation direction of the photosensitive drum 1 is defined as a contact portion entrance region r.

First, referring to FIG. 2, the state of the charging contact portion n when the image forming apparatus of this embodiment is in operation will be described in more detail.

In the following description, for ease of understanding, it is assumed that the image forming operation is started from the state where the electrically conductive particles m are not carried on the charging roller 2. However, when the conductive particles m are not supplied to the surface of the charging roller 2 at the beginning of use of the charging roller 2, the photosensitive drum 1 cannot be charged, so the conductive particles m are applied to the surface of the charging roller 2 in advance. You can keep it.

(Step 1) As shown in FIG.
The photosensitive drum 1 is rotating at a predetermined peripheral speed, and the surface of the photosensitive drum 1 is moving in the arrow direction in the figure. The charging roller 2 is rotationally driven at a predetermined speed so that the surface facing the contact portion n with the photosensitive drum 1 moves in the direction opposite to the photosensitive drum 1. The toner (transfer residual toner) t remaining on the photosensitive drum 1 after the transfer process and the conductive particles m are
Due to electrostatic force (Coulomb force), intermolecular force, frictional force, or other adhesion force, the charging contact portion n is approached while being attached to the surface of the photosensitive drum 1.

(Step 2) As shown in FIG.
When the transfer residual toner t and the conductive particles m on the photosensitive drum 1 reach the contact portion entrance region r, the transfer residual toner t and the conductive particles m accumulate in the contact portion entrance region r, and the mechanical force of the charging roller 2 acts. Then, it is gradually carried to the surface of the charging roller 2.

(Step 3) As shown in FIG.
The charging roller 2 rotates while mechanically gradually conveying the transfer residual toner t and the conductive particles m accumulated in the contact portion entrance area r. At this time, a predetermined charging bias voltage (-610V in this embodiment) is applied to the charging roller 2 from the charging bias applying power source S1, and the conductive particles m carried to the charging contact portion n by the rotation of the charging roller 2 are transferred. The surface of the photosensitive drum 1 is charged to a predetermined potential (in this embodiment, -600 V) by direct injection charging. In the figure, the charged portion on the photosensitive drum 1 is schematically shown by the shaded portion.

The charging roller 2 slidably rotates the surface of the photosensitive drum 1 with the conductive particles m, which are fine powder, and the transfer residual toner t applied to the elastic layer 2b, and the lubricity with the photosensitive drum 1 is maintained. It also maintains contact and chargeability. At the time of charging, an electric field and a current are generated between the charging roller 2 and the photosensitive drum 1 due to the potential difference.

In this way, the transfer residual toner t is temporarily collected by the charging roller 2, and the conductive particles m are supplied and applied to the charging roller 2.

Here, in the force applied to the particles on the surface of the charging roller 2, the force for holding the surface of the charging roller 2 is the frictional force between the surface of the charging roller 2 and the particles,
There is a mechanical holding force due to the surface shape of the charging roller 2. On the other hand, examples of the force in the direction of moving the surface of the photosensitive drum 1 include an electric field, a Coulomb force, and a frictional force based on the potential difference between the charging roller 2 and the photosensitive drum 1. The conductive particles m gradually transfer to the surface side of the photosensitive drum 1 as the photosensitive drum 1 is charged, and are carried away as the photosensitive drum 1 rotates. Then, a part is transferred to the transfer material P.

(Step 4) As shown in FIG.
The transfer residual toner t adhering to and mixing with the charging roller 2 is normalized by reversing the toner charge due to the charging bias voltage applied to the charging roller 2 or the frictional charging as it goes around the outer circumference of the charging roller 2. In the embodiment, the surface potential of the photosensitive drum 1 which is negatively charged and is charged by injection charging and the potential difference between the charging roller 2 are sequentially transferred to the photosensitive drum 1. That is, it is discharged onto the photosensitive drum 1. Then, the toner t reaches the developing portion a as the surface of the photosensitive drum 1 moves, and is collected and reused by the developing device 4 in the simultaneous cleaning of development.

As described above, the photosensitive drum 1 is charged by the direct injection charging mechanism by the charging roller 2 coated with the conductive particles m supplied from the developing device 4, and the transfer residual toner t is charged by the developing device 4. Be recovered.

As described above, in the direct injection charging mechanism by the particle charging (powder coating type), the contact property of the contact charging member to the member to be charged affects the charging property, and the contact charging member to the member to be charged is affected. It is important to improve contact uniformity and denseness. Further, in order to obtain good chargeability, it is necessary to maintain the amount of conductive particles carried on the contact charging member and the coverage thereof so as to be within proper preset ranges.

The present inventors have conducted many experimental studies from this viewpoint, and as described above, by disposing the contact part inlet s in the first quadrant, the charging performance is further improved and the development failure ( Image defects) and fogging are prevented,
It has been found that a good image can be formed more stably.
It has also been found that by disposing the charging roller 2 in this way, the toner recyclability can also be improved.

That is, the contact part entrance s is defined as XY defined above.
By arranging in the first quadrant of the coordinates, as shown in FIG. 3, the contact portion entrance region r becomes an arrangement that is open in the vertically upward direction. As a result, (1a) the transfer residual toner t reaching the contact portion entrance area r
3 and the conductive particles m are subjected to a gravitational force in the direction toward the charging contact portion n and the direction toward the photosensitive drum 1.
As indicated by the middle arrow G1, the transfer residual toner t and the conductive particles m are likely to accumulate in the contact portion entrance region r. As a result, the transfer residual toner t and the conductive particles m do not drop off from the contact portion entrance area r, the inside of the apparatus is not polluted, and the conductive particles m
It is less consumed due to falling off, and the toner recyclability is also improved. (2a) Since the conductive particles m are accumulated in the inlet region r of the contact portion, the contact uniformity and the denseness are good, and the charging property by the direct injection charging is improved. Further, the transfer residual toner t and the conductive particles m accumulated in the contact portion entrance region r are mechanically carried little by little by the charging roller 2. As a result, the amounts of the transfer residual toner t and the conductive particles m carried on the charging roller 2 are made uniform, and the conductive particles m to the charging roller 2 set in advance are set.
It is possible to maintain the supported amount and the coverage rate of P in an appropriate state. (3a) Further, the transfer residual toner t is not discharged onto the photosensitive drum 1 at one time, and the latent image exposure by the exposure device 3 is not hindered. Such an effect can be obtained.

On the other hand, when the contact part entrance s is in the second, third and fourth quadrants, all of them are contacted in terms of dropout of particles from the contact part entrance region r, charging property, image defect and the like. It is inferior to the case where the entrance s is in the first quadrant.

First, as shown in FIG. 4, when the contact portion entrance region r is in the second quadrant of the XY coordinates defined above, the contact portion entrance region r is opened vertically downward. In such an arrangement, (1b) transfer residual toner t reaching the contact portion entrance region r
Since the conductive particles m are arranged so that gravity acts on the conductive particles m in a direction away from the charging contact part n and vertically downward, as shown by an arrow G2 in FIG. The transfer residual toner t and the conductive particles m easily fall off. This may pollute the inside of the device, and the conductive particles m
May be consumed, and the toner recyclability may be deteriorated. (2b) Since it is difficult for the conductive particles m to collect in the contact portion entrance region r, the contact uniformity and the density are likely to be deteriorated, and the charging property by direct injection charging is poor. Further, when the transfer residual toner t and the conductive particles m fall off from the contact portion entrance area r,
In some cases, the amounts of the transfer residual toner t and the conductive particles m carried on the charging roller 2 become non-uniform, and the preset carrying amount and coverage of the conductive particles m on the charging roller 2 cannot be maintained in an appropriate state. is there. (3b) Further, the transfer residual toner t collected in a large amount at one time is discharged onto the photosensitive drum 1, which may hinder (shield) latent image exposure by the exposure device 3. Such problems may occur.

Next, as shown in FIG. 5, the contact part entrance s
Is in the third quadrant of the XY coordinates defined above,
As indicated by the middle arrow G3, the transfer residual toner t and the conductive particles m are more likely to fall off from the contact portion entrance region r, and the contact portion entrance s is in the second quadrant.
b), (2b), and (3b) become more prominent. Particularly in (1b), since the gravity of the particles in the contact portion entrance region r acts in the direction of moving away from the contact portion n to the maximum, and also acts directly on the charging roller 2, the particles are carried by the charging roller 2. , The amount of particles in the contact area r is reduced.

On the other hand, as shown in FIG. 6, the contact part entrance s
Is in the fourth quadrant of the XY coordinates defined above, (1c) in the rotational direction of the photosensitive drum 1, the contact portion outlet area e facing the contact portion inlet area r with the charging contact portion n interposed therebetween is vertically downward. Because of the open arrangement, the transfer residual toner and the conductive particles m are easily dropped from here, as shown by an arrow G5 in FIG. Therefore, the inside of the apparatus may be polluted, the conductive particles m may be consumed, and the toner recyclability may be deteriorated. (2c) The contact portion entrance area r is opened vertically upward, but gravity acts on the transfer residual toner t and the conductive particles m reaching the contact portion entrance area r in the direction toward the charging roller 2. As indicated by an arrow G4 in FIG. 6, the transfer residual toner t and the conductive particles m are more likely to be carried to the charging roller 2 immediately rather than being accumulated in the contact portion entrance region r. As a result, the conductive particles m are less likely to be accumulated in the contact portion entrance region r, the contact uniformity and the denseness are likely to be deteriorated, and the charging property by the direct injection charging is deteriorated. Further, when the amounts of the transfer residual toner t and the conductive particles m carried on the charging roller 2 become unstable, and the preset carrying amount of the conductive particles m on the charging roller 2 and the preset coverage cannot be maintained in an appropriate state. There is. (3c) Further, a large amount of conductive particles m and transfer residual toner t are carried on the charging roller 2 and discharged to the photosensitive drum 1, thereby hindering the exposure of the latent image by the exposure device 3 (blocking light). )Sometimes. Such problems may occur.

According to a study made by the present inventors, the reason for the phenomenon that a large amount of transfer residual toner t is discharged to the photosensitive drum 1 at a time (the above (3b) and (3c)) is as follows. Conceivable.

In this embodiment, a force in the direction toward the photosensitive drum 1 due to the potential difference between the charging roller 2 and the photosensitive drum 1 acts on the negative particles in the contact portion entrance region r. That is, in this embodiment, the charging roller 2 has a voltage of −610V.
Is applied to the photosensitive drum 1 so that
Although it is charged to 600 V, the potential is attenuated by the influence of the bias application of the reverse polarity by the transfer roller 6 or the like until the photosensitive drum 1 makes one round from the charging contact portion n and reaches the charging contact portion n again.

In the non-exposed area, the surface potential of the photosensitive drum 1 when entering the charging contact area n is usually -400 to -50.
The surface potential is about 0V. Therefore, in the contact portion entrance region r, the negative particles have a potential difference between the charging roller 2 and the photosensitive drum 1 ((-610V)-(-400 to -5).
00V)) is pressed toward the photosensitive drum 1. On the other hand, in the exposed portion, the surface potential of the photosensitive drum 1 when entering the charging contact portion n is usually a surface potential of −0 to −100V. Therefore, when the exposed portion on the photosensitive drum 1 passes through the contact portion entrance region r, the negative polarity particles (transfer residual toner and conductive particles) are pushed toward the photosensitive drum 1 more strongly than the non-exposed portion. Has been done.

In this way, when the potential step due to the exposed portion and the non-exposed portion is formed on the photosensitive drum 1, when the potential step passes through the contact portion entrance region r in the order of the exposed portion and the non-exposed portion. Moreover, the force of pushing the negative-polarity particles in the contact portion entrance region r toward the photosensitive drum 1 suddenly weakens. As a result, the negative-polarity particles in the contact portion entrance region r are easily transferred to the charging roller 2 side.

At this time, according to the present invention, the contact part entrance s
Is in the first quadrant of the XY coordinates defined above, the particles in the contact portion entrance region r are subjected to gravity in the direction toward the charging contact portion n and remain in the contact portion entrance region r. The power to try increases. Further, the particles accumulated in the contact portion inlet region r are mechanically carried little by little by the charging roller 2 because part of gravity acts on the particles accumulated in the contact region entrance region r in the direction of the charging roller 2 as well. It is considered that it is unlikely to be affected by the potential step.

On the other hand, when the contact portion entrance s is in the second quadrant of the XY coordinates defined above, the particles in the contact portion entrance area r are gravitationally acted in the direction away from the area, and thus the contact area Since the force that tries to stay in the part entrance region r becomes weak, it is expected that the potential step is easily affected. In fact, when the contact part entrance s is in the second quadrant of the XY coordinates defined above, a large amount of particles collected at one time from the contact part entrance area r are carried by the charging roller 2 and transferred to the photosensitive drum 1. In some cases, a streak image, which is considered to be formed by blocking the image exposure, is recorded.

When the contact part entrance s is in the third quadrant and the fourth quadrant, an image defect obstructing the latent image exposure is seen, but the characteristic is slightly different from that seen in the second quadrant, and the ghost is different. It may appear as an image. The ghost is a phenomenon in which an image previously recorded on the photosensitive drum 1 appears again at a certain distance, but when the time is taken, the distance is one rotation of the photosensitive drum 1 and one rotation of the charging roller 2. Equivalent to. That is, the transfer residual toner t of the image pattern goes around the outer circumference of the charging roller 2, and again moves to the photosensitive drum 1 from the downstream side of the charging contact portion n in the rotational direction of the photosensitive drum 1, and then the photosensitive drum 1 It is presumed that this transfer residual toner t that has moved upward is generated by blocking the latent image exposure. In the third and fourth quadrants, gravity acts in the direction of the charging roller 2,
Most of the transfer residual toner t and the charged particles m are transferred to the charging roller 2 as they are and cause an image defect as a ghost image.

From this, it can also be proved that the accumulation of particles in the contact portion entrance region r plays an important role in the first and second quadrants, particularly in the first quadrant. It can be understood that the particles accumulated in the contact portion entrance region r have an action of leveling the transfer-untransferred image pattern in the longitudinal direction of the charging roller 2 by accumulating in the region.

Even when the contact portion entrance s is at the boundary between the first quadrant and the second quadrant (that is, on the Y axis), the above-mentioned inconvenience (1) when the contact portion entrance s is in the second quadrant
b), (2b) and (3b) are improved. Similarly, when the contact part entrance s is at the boundary between the first quadrant and the fourth quadrant (that is, on the X axis), the above-mentioned problem (1c) when the contact part entrance s is in the fourth quadrant, (2c) and (3
c) is improved. Therefore, the contact portion entrance s may be arranged at the boundary between the first quadrant and the second quadrant, or at the boundary between the first quadrant and the second quadrant.

However, according to the studies by the present inventors, in order to obtain higher charging performance and higher halftone image uniformity, from the positive X axis of the X axis defined above, the rotation center of the photosensitive drum 1 is determined. The angle α (Fig. 3) to the straight line connecting the
It is preferable that the angle is 15 degrees or more and 75 degrees or less. More preferably, it is 30 degrees or more and 60 degrees or less.

Next, the inventors of the present invention conducted the following tests.
According to the present invention, the superiority of the arrangement in which the contact part entrance s is provided in the first quadrant was confirmed.

(Evaluation Items) A print test of 2000 sheets was carried out in each arrangement (specific examples (present invention) 1 to 7 and comparative examples 1 to 7) shown in the following evaluation result table, and (1) at that time
In-machine contamination, (2) charging performance evaluation, and (3) halftone image uniformity evaluation were performed by the following methods.

(Evaluation Method) (1) In-apparatus Contamination Toner t and in-apparatus contamination state due to charged particles m were compared for each constitution. Since it was difficult to quantify, the in-flight contamination state in each configuration was classified into 3 stages (A: 5 cases, B: 5 cases, C4 cases) and relatively evaluated.

(2) Evaluation of charging property Here, the charging property was evaluated more strictly by the following new evaluation method. As an index of charging performance, evaluation of a ghost image due to insufficient charging and charging uniformity were used.

In the evaluation, after drawing an image pattern in which a black square of 5 mm to 25 mm square is arranged at the tip, the above-mentioned halftone image, that is, one line in the main scanning direction is recorded, and then two lines are not recorded. It was performed based on an evaluation image in which an image having a striped pattern and expressing a halftone density as a whole is arranged. When the charging performance is low, the square exposure pattern cannot be uniformly charged on the charging roller 2,
In the halftone image area, a light square pattern is observed. The presence or absence of this pattern was used as an index of charging performance. Further, in order to catch a slight change in charging performance, attention was paid to the uniformity of the halftone image. When the charging performance deteriorates, the rubbing traces of the charging roller 2 appear as black short lines. In particular, the presence or absence of the streak in the halftone image was used as another index of the charging performance.

Since the toner filling amount in the developing device 4 varies depending on the image forming apparatus embodying the present invention, its life is not constant. Further, according to the study by the present inventors, in particular, an image defect becomes remarkable just before the end of the toner. Therefore, this evaluation was also performed on the printed images at the toner end and 200 sheets before that.

[0181] A: No ghosts or streaks B: No ghost can be seen, but a slight streak is confirmed. C: Minor ghost and streak are confirmed D: Clear ghost and streak are confirmed

(3) Halftone Uniformity (Evaluation of Image Defects) Here, the evaluation including the halftone ghost image defects was carried out by the following evaluation method. For the image evaluation, a halftone image was output and the number of defects in the image was evaluated. Image recording was performed using a 600 dpi laser scanner in the printer of each example.

The evaluation was also carried out for the evaluation of the charging property.
After drawing an image pattern in which five black squares of 5 mm square were arranged, it was performed based on the evaluation image in which the halftone image was arranged. Also in this evaluation, the halftone image is 1 in the main scanning direction.
It means a striped pattern in which a line is recorded and then two lines are not recorded, and a halftone density is expressed as a whole.

Since the printers of the respective examples carry out image recording by the reversal developing system, when image exposure is blocked, they appear as white spots on the image. In particular, in the present invention, importance is attached to the uniformity of the halftone image, and the number of these defective portions is evaluated according to the following criteria. In the image defect evaluation, white dots were evaluated by counting points of 0.3 mm or more as defective parts.

A: There are 0 to less than 5 image defects B: There are 5 to less than 50 image defects C: There are 50 to less than 100 image defects D: There are more than 100 image defects, and also white Counting was performed in the same way when the dots appeared on a straight line and when they appeared on the ghost of all images.

(Evaluation result)

[Table 1]

As described above, according to this embodiment, the amount of the conductive particles m carried on the charging roller 2 and the coverage thereof can be appropriately maintained, and good charging performance can always be exhibited. Further, it is possible to prevent the conductive particles m and the toner t from coming off from the entrance s of the charging contact portion n in the rotation direction of the photosensitive drum 1, and to prevent the inside of the machine from being consumed and the consumption of the conductive particles m. Recyclability can also be improved. Then, it is possible to obtain a high charge density by using the conductive particles m having a small particle diameter, to reduce the dropping of the conductive particles, and to enhance the charging ability. Therefore, the charging performance of the direct injection charging mechanism by particle charging (powder coating type) can be further improved.

Embodiment 2 Next, an embodiment in which the present invention is embodied in an electrophotographic image forming apparatus in which a process cartridge is detachable will be described. FIG. 9 is a schematic explanatory view of the configuration of the electrophotographic image forming apparatus in which the process cartridge is mounted, and FIG. 10 is a schematic schematic illustration of the configuration of the process cartridge.

The basic construction of the electrophotographic image forming apparatus 100, which is the laser beam printer shown in FIG. 9, is the same as that described with reference to FIG. Method, toner recycling process (cleanerless system).

The image forming apparatus 100 has a drum-shaped electrophotographic photosensitive member (photosensitive drum) 1 as an image bearing member. Information light based on image information is emitted from the optical system 3 to the photosensitive drum 1 to form a latent image on the photosensitive drum 1, and the latent image is developed with a developer (toner) to form a toner image.

In synchronism with the formation of the toner image on the photosensitive drum 1, the sheet feeding cassette 8a containing the transfer material P as a recording medium is separated and fed one by one by the pickup roller 8b and the pressure contact member 8c in pressure contact with the pickup roller 8b. And transporting means 8
Transport by e.

Then, the toner image formed on the photosensitive drum 1 which has been made into the process cartridge B is transferred to the transfer material P by applying a voltage to the transfer roller 6 as the transfer means, and the transfer material P is conveyed. 8
It is conveyed to the fixing means 7 by f.

The fixing means 7 comprises a driving roller 7a and a heater 7
and a fixing rotator 7d that is a cylindrical sheet that is rotatably supported by a support 7c.
Heat and pressure are applied to the passing transfer material P to fix the transferred toner image. Then, the transfer material P is ejected by a pair of discharge rollers 8d.
And then discharged to the discharge unit 9 through the reverse conveyance route.

As shown in FIG. 10, the process cartridge B of this embodiment rotates the photosensitive drum 1 which is an electrophotographic photosensitive member having a photosensitive layer, and the charging roller 2 which is a charging means.
Voltage is applied to uniformly charge the surface of the photosensitive drum 1, and the charged photosensitive drum 1 is exposed to an optical image from the optical system 3 through the exposure opening 10a to form a latent image. The latent image is developed by the developing device 4, which is a developing unit.

The developing device 4 is a rotatable toner feeding member (stirring member) 4d, which is a toner feeding means in the developer accommodating portion 4e1 of the developing container 4e formed by the toner accommodating frame 10f1 and the lid member 10f2. Allows the developer storage section 4e
1 to the developing chamber 4e2 through the opening 10k to rotate the developing roller 4a, which is a developing rotary member (developer carrying member) having the fixed magnet 4b built therein, and the developing blade 4a.
A toner layer to which a triboelectric charge has been applied by c is formed on the surface of the developing roller 4a, and the toner is transferred to the photosensitive drum 1 according to the latent image on the photosensitive drum 1 to form a toner image and a visible image. It will be transformed.

Then, a voltage having a polarity opposite to that of the toner image is applied to the transfer roller 6 to transfer the toner image to the transfer material P. The transfer residual toner remaining on the photosensitive drum 1 is developed by the developing device 4 at the time of the subsequent development process. Collect by.

The process cartridge B is different from the cartridge mounting means 10b provided in the main body A of the image forming apparatus,
It is removably mounted by using guide portions (not shown) provided at both ends of the cartridge.

The process cartridge B is a drum frame unit C that holds the photosensitive drum 1 and the charging roller 2.
And the developing unit D constituting the developing device 4 are integrally assembled.

Except that the image forming apparatus is of a process cartridge detachable type, in the present embodiment, the configuration and arrangement of the photosensitive drum 1 and the charging roller 2, which are the members to be charged, the toner t, the conductive particles m, etc. The details of are all based on the above-mentioned embodiment. Regarding the arrangement of the charging roller 2, the angle α was set to 45 °. Therefore, the duplicated description will be omitted here, and the entire description of the above-described embodiment will be cited.

According to the present embodiment, by applying the particle charging (powder coating type) according to the present invention to the image forming apparatus of the process cartridge detachable type, the charging performance in the direct injection charging mechanism is further improved, and moreover, By adopting the cleanerless system and supplying the conductive particles m from the developing device, the process cartridge and the apparatus main body can be remarkably downsized and the cost can be reduced.

(Other Embodiments) (1) In the above embodiments, a laser beam printer was illustrated as an image forming apparatus, but the present invention is not limited to this, and an electrophotographic copying machine, a facsimile machine, a word processor. Of course, it can be applied to other image forming apparatuses.

(2) In the case of the electrostatic recording device, the image bearing member as the member to be charged is an electrostatic recording dielectric.

(3) The image bearing member is not limited to the drum type, and may be an endless type, a belt type having an end, a sheet type or the like. However, the definition of the angle α at this time is as follows. Assuming a contact portion n between the image bearing member and the charging member and a virtual circle corresponding to the contact portion entrance area r, which is approximately close to the outer peripheral portion of the image bearing member, and the center of this circle is the photosensitive drum in the above-described embodiment. By fitting it to the center of 1, the angle α is similarly obtained.

(4) The contact charging member is not limited to the roller type, but may be an endless type or an endless belt type.

(5) The charging device according to the present invention is not limited to the charging device for the image bearing member (electrophotographic photosensitive member, electrostatic recording dielectric member, etc.) of the image forming apparatus, and is widely used as a charging processing means for charged members ( Of course, it is effective when used as a static elimination process).

(6) As the developing method, various known developing methods such as a two-component magnetic brush developing method, a cascade developing method, a touchdown developing method and a cloud developing method can be used.

(7) The electrophotographic photosensitive member is not limited to the photosensitive drum, but includes, for example, the following. First, a photoconductor is used as the photoconductor, and examples of the photoconductor include amorphous silicon, amorphous selenium, zinc oxide, titanium oxide, and organic photoconductor (OP).
C) etc. are included. The shape on which the photosensitive member is mounted includes, for example, a drum-shaped or belt-shaped rotating body and a sheet-shaped member. Generally, a drum-shaped or belt-shaped one is used. For example, in the case of a drum type photoconductor, a photoconductor is vapor-deposited or coated on a cylinder of aluminum alloy or the like. Is.

(8) In each of the above-described embodiments, the conductive particles are described as being supplied to the charging member via the image bearing member, which is the member to be charged, at the same time as the developing device as the supplying unit. It is not limited to this. A dedicated supply unit for supplying the conductive particles to the charging member via the member to be charged may be provided upstream of the charging member in the moving direction of the surface of the member to be charged.

(9) Furthermore, in each of the above-mentioned embodiments, the image forming apparatus is described as adopting the cleanerless process. However, the present invention is not limited to this, and the image forming apparatus is a member to be charged. The present invention can be applied to the case where a conventionally known cleaner (cleaning device) for cleaning the surface of the image carrier (photosensitive drum or the like) is provided. In this case, a supply means for supplying the conductive particles to the charging member via the image carrier, for example, downstream of the cleaner in the moving direction of the image carrier surface, and
It can be provided upstream of the charging member. However, the effect of applying the present invention to a cleanerless process is greater, and in the sense that a cleanerless process having advantages such as not producing waste toner, reducing the size of the apparatus, and reducing the cost can be realized. Is also superior.

(10) The transferred material which receives the transfer of the toner image from the image carrier may be an intermediate transfer material such as a transfer drum or a transfer belt.

[0211]

As described above, according to the present invention,
It is possible to further improve the charging performance in the direct injection charging mechanism by particle charging (powder coating type). Further, according to the present invention, it is possible to properly maintain the amount of conductive particles carried on the charging member and the coverage thereof, and always exhibit good charging performance.
In addition, the toner recycle system is adopted to prevent particles from dropping from the entrance of the contact part formed by the charging member and the body to be charged from the entrance in the moving direction of the body to be charged, and to prevent dirt inside the machine and consumption of conductive particles. In the image forming apparatus, the toner recyclability can be improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a schematic configuration of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic diagram showing a state of a charging contact portion when the image forming apparatus is in operation.

FIG. 3 is a schematic view showing an arrangement mode of charging contact portions according to the present invention.

FIG. 4 is a schematic view showing an arrangement mode of charging contact portions not according to the present invention.

FIG. 5 is a schematic view showing an arrangement mode of charging contact portions not according to the present invention.

FIG. 6 is a schematic view showing an arrangement mode of charging contact portions not according to the present invention.

FIG. 7 is a layer configuration model diagram of a photosensitive drum.

FIG. 8 is an explanatory diagram of a method of measuring the charging roller facing each other.

FIG. 9 is a schematic sectional view of another embodiment of the image forming apparatus according to the present invention.

10 is a schematic cross-sectional view of a process cartridge that can be attached to and detached from the image forming apparatus of FIG.

FIG. 11 is a graph for explaining charging characteristics by a charging method.

FIG. 12 is a schematic sectional view showing a schematic configuration of an example of a conventional image forming apparatus.

[Explanation of symbols]

1 Photosensitive Drum (Image Bearing Member, Charged Member, Electrophotographic Photosensitive Member) 2 Charging Roller (Charging Member) 3 Exposure Device (Optical System) 4 Developing Device 6 Transfer Roller (Transfer Member) 7 Fixing Device 100 Image Forming Device A Image Forming device B Process cartridge

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 15/08 507 G03G 15/08 507B (72) Inventor Takeshi Kawamura 3-30-2 Shimomaruko, Ota-ku, Tokyo No. Canon Inc. (72) Inventor Koichi Okuda 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Keiji Okano 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. In-house F-term (reference) 2H005 AA08 CB07 DA07 DA09 EA01 EA05 2H077 AD00 2H200 FA16 GA23 GA44 GB37 HA03 HA21 HA29 HB12 HB22 HB23 HB46 HB47 LA23 MB05 MC01 3J103 AA02 AA14 AA5 FA14 GA18 BA52 FA18 BA43 FA43 FA18 FA18 FA43 FA43 FA05 HA03 HA04 HA12 HA18 HA20 HA52 HA53 HA60

Claims (21)

[Claims] 1. A charging member for charging a rotatable member to be charged, the member being in contact with the member to be charged, and the surface of the member to be moved is opposite to the rotation direction of the member in the contact portion. In such a charging device having a rotatable charging member, in which conductive particles are carried on the charged body and conveyed to the contact portion, a horizontal line passing through the rotation center of the charged body is indicated by X.
Assuming that the axis is a vertical line passing through the rotation center of the body to be charged, and the Y axis is the axis, the entrance to the contact portion in the rotation direction of the body to be charged is viewed from the direction in which the rotation direction of the body to be charged is clockwise. And a charging device provided in the first quadrant of XY coordinates. 2. The angle formed by the X axis and a straight line connecting the center of rotation of the body to be charged and the entrance to the contact portion in the first quadrant is 15 degrees to 75 degrees. The charging device according to claim 1, wherein: 3. The conductive particles have a particle size of 10 nm to 10 nm.
μm, the resistance of the conductive particles carried on the charging member is 10
⁻¹ to 10 ¹² Ω · cm, and a value obtained by dividing the amount of conductive particles carried on the charging member by the surface roughness Raμm of the charging member is 0.05 to 1 mg / cm ² / μm. The charging device according to claim 1 or 2. 4. The charging device according to claim 1, wherein the ratio Rc of the conductive particles coating the charging member is 0.2 ≦ Rc ≦ 1. . 5. The surface resistance of the charging member is 10 ⁴ to 1
The charging device according to claim 1, wherein the charging device has a resistance of 0 ¹⁰ Ω / □. 6. The charging device according to claim 1, wherein the charging member is an elastic body having a surface of a porous body. 7. The charging device according to claim 1, further comprising a supply unit that supplies conductive particles to the body to be charged. 8. The member to be charged is an image carrier, the supply unit is a developing unit for developing an electrostatic image formed on the image carrier with a developer, and the developer is toner and the toner. The charging device according to claim 7, further comprising conductive particles. 9. The charging device according to claim 8, wherein the developing unit is capable of collecting the toner remaining on the member to be charged. 10. A process cartridge, wherein the charging device according to any one of claims 1 to 7 can be attached to and detached from a main body of an image forming apparatus together with an image bearing member which is a member to be charged. 11. The main body of the image forming apparatus, wherein the charging device according to claim 8 or 9 is provided with an image carrier that is a member to be charged and a developing unit that develops an electrostatic image formed on the image carrier with a developer. A process cartridge that is removable. 12. A rotatable image carrier and a charging member which forms a contact portion with the image carrier and is rotatable so that a surface of the image carrier moves in a direction opposite to the rotation direction of the image carrier at the contact portion. And a supply means for supplying conductive particles to the image carrier, wherein the conductive particles carried by the image carrier are conveyed to the contact portion, the center of rotation of the image carrier When a horizontal line passing through is the X axis and a vertical line passing through the rotation center of the image carrier is the Y axis, the entrance to the contact portion in the rotation direction of the image carrier has a clockwise rotation direction of the charged body. The image forming apparatus is provided in the first quadrant of XY coordinates when viewed from the direction. 13. The angle formed by the X axis and a straight line connecting the center of rotation of the image carrier and the entrance to the contact portion in the first quadrant is 15 to 75 degrees. The image forming apparatus according to claim 12, wherein. 14. The conductive particles have a particle size of 10 nm to 1
0 μm, the resistance of the conductive particles carried on the charging member is 1
0 ⁻¹ to 10 ¹² Ω · cm, and a value obtained by dividing the amount of conductive particles carried on the charging member by the surface roughness Raμm of the charging member is 0.05 to 1 mg / cm ² / μm. The image forming apparatus according to claim 12, wherein the image forming apparatus is an image forming apparatus. 15. The image formation according to claim 12, 13 or 14, wherein when the ratio of the conductive particles coating the charging member is Rc, 0.2 ≦ Rc ≦ 1. apparatus. 16. The surface resistance of the charging member is from 10 ⁴ to
It is 10 ¹⁰ Ω / □ and it is characterized by being 12-15.
The image forming apparatus according to any one of 1. 17. The image forming apparatus according to claim 12, wherein the charging member is an elastic body having a porous body surface. 18. The supplying means is a developing means for developing the electrostatic image formed on the image bearing member with a developer, and the developer comprises toner and the conductive particles. The image forming apparatus according to any one of Items 12 to 17. 19. The image forming apparatus charges the image carrier by the charging member, and exposes a charged surface of the image carrier by an image exposing device to form an electrostatic image, An image is formed by an image forming process including the steps of developing the electrostatic image on the body with a developer by the developing means, and then transferring the developer image on the image carrier to the transfer target, and after the transfer step 19. The image forming apparatus according to claim 18, wherein the developer remaining on the surface of the image carrier is temporarily carried by at least the charging member, transferred to the surface of the image carrier again, and collected by the developing means. . 20. The image forming apparatus according to claim 12, wherein the charging member is attachable to and detachable from the main body of the image forming apparatus together with the image carrier. 21. The image forming apparatus according to claim 18, wherein the charging member is attachable to and detachable from the main body of the image forming apparatus together with the image carrier and the developing unit.