JP2001194864A - Electrifying device and image recorder using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a contact type electrifying device whose stability in durability is improved by preventing a contact electrifying member from getting to a state where it is excessively soiled because of long service, and to provide an image recorder using the contact type electrifying device by which a high- quality image is maintained over a long term by preventing the contact electrifying member from getting to the state where it is excessively soiled by toner because of the long service or even in the case of performing the consecutive printing of a high printing rate image in a cleaner-less system and which can be rapidly restored from an image defect occurring state even when the contact electrifying member is excessively soiled by the toner because of the consecutive printing of the high printing rate image in the cleaner-less system or the occurrence of jamming. SOLUTION: This electrifying device is equipped with a magnetic field forming means 8a forming magnetic field from the back surface side of a body to be electrified (image carrier) 1 toward a contact part (n) between the electrifying member 2 and the body to be electrified 1. Furthermore, the device is provided with a nip forming member 9 forming a nip (c) by coming in contact with the member 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a charging device for charging an object to be charged. More specifically, the present invention relates to a contact-type charging device that contacts a member to be charged and charges the surface of the member.

[0002] The present invention also relates to an image recording apparatus (image forming apparatus) such as a copying machine or a printer using the charging device as a charging means for an image carrier.

[0003]

2. Description of the Related Art Conventionally, for example, in an image recording apparatus such as an electrophotographic apparatus or an electrostatic recording apparatus, an image carrier (a member to be charged) such as an electrophotographic photosensitive member or an electrostatic recording dielectric has a required polarity and potential. A corona charger (a corona discharger) has often been used as a charging device for uniformly performing a charging process (including a static elimination process).

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

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

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

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

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

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

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

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

A) Roller Charging In the contact charging device, a roller charging method using a conductive roller (charging roller) as a contact charging member is preferable in terms of charging stability, and is widely used.

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

The charging roller is made of a conductive or medium-resistance rubber or foam. In some cases, these are laminated to obtain desired characteristics.

The charging roller has elasticity in order to obtain a certain contact state with a member to be charged (hereinafter, referred to as a photosensitive member). Therefore, frictional resistance is large, and in many cases, the charging roller is driven by the photosensitive member. It is driven with a slight speed difference. Therefore, even if an attempt is made to charge directly, the reduction mechanism of the absolute charging ability, the lack of contact, the unevenness of the roller shape, and the unevenness of charging due to the adhesion of the photoreceptor cannot be avoided. The mechanism is dominant.

FIG. 8 is a graph showing an example of charging efficiency in contact charging. DC applied to the contact charging member on the horizontal axis
The bias and the vertical axis represent the photosensitive member charging potential (drum potential) obtained at that time.

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

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

That is, in order to obtain the photosensitive member surface potential Vd required for electrophotography, the charging roller needs Vd + Vth
Therefore, a DC voltage higher than required is required. A method of applying only a DC voltage to the contact charging member to perform charging in this manner is referred to as a “DC charging method”.

However, in DC charging, since the resistance value of the contact charging member fluctuates due to environmental fluctuations and the like, and Vth fluctuates when the film thickness changes due to shaving of the photoreceptor, the potential of the photoreceptor changes to a desired value. It was difficult to value.

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

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

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

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

In the fur brush charging, the charging mechanism is dominated by the discharge charging mechanism.

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

The charging characteristics of the fur brush charging when a DC voltage is applied are as shown in FIG. 8B. Therefore, also in the case of the fur brush charging, in both the fixed type and the roll type, charging is performed by applying a high charging bias and using a discharge phenomenon.

C) Magnetic Brush Charging The magnetic brush charging uses a member (magnetic brush charger) having a magnetic brush portion formed by brushing conductive magnetic particles magnetically with a magnet roll or the like as a contact charging member. The magnetic brush portion is brought into contact with a photosensitive member as a member to be charged, and a predetermined charging bias is applied to charge the surface of the photosensitive member to a predetermined polarity and potential.

In the case of this magnetic brush charging, the charging mechanism is dominated by the direct injection charging mechanism.

The use of conductive magnetic particles having a particle size of 5 to 50 μm as a constituent of the magnetic brush portion and providing a sufficient speed difference from the photosensitive member enables uniform direct charging.

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

However, there are other adverse effects, such as the complexity of the device configuration, and the fact that the conductive magnetic particles constituting the magnetic brush portion fall off and adhere to the photoreceptor.

Japanese Patent Application Laid-Open No. Hei 6-3921 proposes a method in which charge is injected into a charge holding member such as a trap level on the surface of a photoreceptor or conductive particles in a charge injection layer to perform contact injection charging. . Since the discharge phenomenon is not used, the voltage required for charging is only the desired surface potential of the photoconductor, and no ozone is generated. Furthermore, since no AC voltage is applied, no charging noise is generated, and the charging method is excellent in ozone-less and low-power compared to the roller charging method.

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

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

In the toner recycling system, the transfer residual toner is not removed from the photosensitive member surface by a dedicated cleaner as described above, but is transferred to a developing device via a charging unit and reused in the developing process. Therefore, when contact charging is used as a charging means for the photoconductor, how to charge the photoconductor in a state where an insulating toner is interposed in a contact portion between the photoconductor and the contact charging member has become an issue. ing. In the above-described roller charging and fur brush charging, transfer residual toner on a photoreceptor is diffused to form a non-pattern, and a large bias is applied and discharge charging is often used. In magnetic brush charging, powder is used as a contact charging member, so there is an advantage that the magnetic brush portion of the conductive magnetic particles as the powder can flexibly contact the photoconductor and charge the photoconductor, but the equipment configuration is complicated. In addition, there is a large adverse effect due to the drop of the conductive magnetic particles constituting the magnetic brush portion.

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

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

From such a background, a charging device using charging promoting particles has been devised and disclosed in Japanese Patent Application Laid-Open No. 10-307455. In this method, direct injection charging is performed via fine particles having a resistance value of 10 ¹² Ω · cm or less, which are referred to as charge promoting particles, between a charging member and a member to be charged.

One of the roles of the charge promoting particles is to reduce the frictional force between the charging member and the surface of the member to be charged. A charging member such as the above-described charging roller having a large frictional force with the member to be charged cannot provide a peripheral speed difference between the charging member and the member to be charged, so that a sufficient contact opportunity cannot be obtained. However, the interposition of the charge promoting particles makes it possible to reduce the frictional force between the above-described charging roller and the member to be charged, thereby providing a peripheral speed difference. Second, the charge-promoting particles fill the irregularities of the charging member and improve the contact with the member to be charged.

The charge-promoting particles adhere to the member to be charged with the charging operation, and the amount of the charge-promoting particles present on the charging member decreases and eventually disappears. Therefore, it is necessary to supply the charge accelerating particles around the charger in some way.

As a method, there are a method of applying and supplying the charge accelerating particles to the charging member, and a method of applying the particles to the photosensitive drum and supplying the particles to the charging member. There is a method of mixing particles as a part of a developer. In this method, the charge promotion particles are developed together with the toner on the photosensitive drum through the development process, and the charge promotion particles are supplied from the photoreceptor to the charging member. Has the advantage of being able to

[0043]

By the way, in a contact-type charging device, a charging member in contact with a member to be charged picks up contaminants from the surface of the member to be charged and accumulates and contaminates the particles due to durability. Excessive contamination of the contact charging member lowers the charging performance of the device, resulting in a reduction in the charging potential of the member to be charged and poor charging such as uneven charging.

In the image recording apparatus, the charging member in contact with the image carrier easily picks up toner from the surface of the image carrier and easily contaminates the toner. Particularly, in the cleanerless system, the transfer residual toner adheres to the contact charging member by being carried to the contact portion between the contact charging member and the image carrier. When the image with a high printing ratio is continuously printed, the amount of the transfer residual toner increases, the chargeability decreases, and image defects such as fogging of the image occur. Further, after an abnormal stop of the apparatus due to a paper conveyance failure (JAM), a large amount of toner of the non-transferred toner image remaining on the surface of the image carrier is carried to the contact portion between the contact charging member and the image carrier. The charging member is temporarily excessively contaminated with the toner at one time, causing image defects.

Accordingly, an object of the present invention is to improve the durability stability of a contact-type charging device by preventing a contact charging member from being excessively contaminated by durability.

Further, with respect to an image recording apparatus using a contact-type charging device, even when continuous printing of a high printing rate image is performed in a durable manner or in a cleanerless system, the contact charging member may be excessively contaminated with toner. To prevent the contact charging member from being excessively contaminated with toner due to continuous printing of a high printing rate image or occurrence of JAM in a cleanerless system. An object of the present invention is to make it possible to quickly recover from an image defect occurrence state even when it occurs.

[0047]

SUMMARY OF THE INVENTION The present invention is a charging device and an image recording device having the following constitutions.

(1) A charging device which has a flexible charging member which is driven or rotated or driven in contact with the charged object, and charges the surface of the charged object, wherein the charging member and the charged object are charged. A magnetic field forming means for forming a magnetic field from the back side of the member to be charged toward a contact portion with the charging device.

(2) There is a flexible charging member for forming a nip portion with the member to be charged, and at least a nip portion between the charging member and the member to be charged is interposed with charge-promoting particles, which are conductive particles. The surface of the charging member is a charging device that moves at a speed difference with respect to the surface of the member to be charged, and charges the surface of the member to be charged. A charging device comprising a magnetic field forming means for forming a magnetic field from the back side.

(3) A flexible charging member for forming a nip portion with the charged object is provided, and at least a nip portion between the charged member and the charged member has a volume resistance of 10 ¹² Ω · cm or less. The charging device is a charging device in which charge-promoting particles are interposed and the surface of the charging member moves with a speed difference with respect to the surface of the member to be charged to charge the surface of the member to be charged. A magnetic field forming means for forming a magnetic field from the back side of the member to be charged.

(4) The charging device according to any one of (1) to (3), wherein the magnetic field forming means is constituted by a permanent magnet.

(5) The charging device according to any one of (1) to (3), wherein the magnetic field forming means is constituted by an electromagnet.

(6) The charging device according to any one of (1) to (5), further including a nip forming member that contacts the charging member to form a nip.

(7) In an image recording apparatus for performing image formation by applying an image forming process including a step of charging the image carrier to the image carrier, the means for charging the image carrier is (1)
An image recording apparatus, which is the charging device according to any one of (1) to (6).

(8) An electrophotographic image comprising an image bearing member, a charging device, an image exposing device, a developing device, a transfer device, and a fixing device for fixing an image on a recording medium disposed around the image bearing member. In the recording apparatus, the charging device is any one of the charging devices described in (1) to (6).

(9) An electrophotographic image comprising an image carrier, and a charging device, an image exposing device, a developing device, a transfer device, and a fixing device for fixing an image on a recording medium disposed around the image carrier. In a recording apparatus, an image recording apparatus of an image carrier cleaner-less configuration that temporarily carries at least a charging device with a developer remaining on the surface of the image carrier after a transfer process, and recovers the developer again through the image carrier. An image recording apparatus, wherein the developer of the developing device is a magnetic toner, and the charging device is any one of the charging devices described in (1) to (6).

<Operation> a. That is, for the contact-type charging device, the contact charging member is provided with a magnetic field forming means for forming a magnetic field from the back side of the member to be charged, toward the contact portion between the contact charging member and the member to be charged. The contaminants (magnetism) picked up and adhered from the surface are quickly discharged from the contact charging member onto the member to be charged by the magnetic field (magnetic force), so that the contact charging member is excessively contaminated due to durability. Is prevented, and the durability stability of the device is improved.

By forming the magnetic field forming means by an electromagnet, it is possible to discharge contaminants from the contact charging member by controlling the strength of the magnetic field in accordance with the contamination state of the contact charging member.

By providing a nip forming member that contacts the contact charging member to form a nip, the polarity of the contaminant discharged from the contact charging member onto the member to be charged is normalized, and then the contaminant is discharged onto the member to be charged. The removal efficiency in the case of removal from the wastewater by the removal means can be increased.

B. In an image recording apparatus using a contact-type charging device as a charging unit for an image carrier, a magnetic field is formed from the back side of the image carrier toward a contact portion between a contact charging member and an image carrier as a member to be charged. Due to the configuration including the magnetic field forming means, the toner as contaminants picked up and adhered to the contact charging member from the image carrier is quickly discharged from the contact charging member onto the image carrier by the magnetic field (magnetic force). Even when continuous printing of a high printing rate image is performed by durability or in a cleanerless system, the contact charging member is prevented from being excessively contaminated with toner, and a high-quality image can be maintained for a long time. The durability stability of is improved.

In a cleanerless system, even when the contact charging member is significantly contaminated with toner due to continuous printing of a high printing rate image or the occurrence of JAM, the toner is quickly discharged from the contact charging member. It is possible to quickly recover from an image defect occurrence state.

By forming the magnetic field forming means by an electromagnet, it is possible to discharge the toner from the contact charging member by controlling the strength of the magnetic field in accordance with the toner contamination state of the contact charging member.

By providing a nip forming member which is in contact with the contact charging member to form a nip, the polarity of the toner discharged from the contact charging member onto the image carrier is normalized, and the toner is removed by simultaneous cleaning with the developing means in the developing means. Recovery efficiency can be increased.

Further, since the magnetic field forming means has an effect of attracting the toner scattered in the vicinity of the contact charging member to the image carrier, the magnetic field forming means is also advantageous in preventing the toner scatter.

[0065]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiment 1 (FIGS. 1 and 2) FIG. 1 is a schematic structural view of an image recording apparatus using a charging device according to the present invention.

The image recording apparatus of this embodiment is a laser printer (recording apparatus) using a transfer type electrophotographic process, a direct injection charging method using charge-promoting particles, and a toner recycling process (cleanerless system).

(1) Overall Schematic Configuration of Printer 1 is an image carrier, which in this embodiment is a rotary drum type negative OPC photosensitive member having a diameter of 30 mm (a negative photosensitive member, hereinafter referred to as a photosensitive drum). The photosensitive drum 1 has a peripheral speed of 50 mm / sec (= process speed P
(S, printing speed).

Reference numeral 2 denotes a conductive elastic roller (hereinafter, referred to as a charging roller) as a contact charging member. As shown in FIG. 2, the charging roller 2 has both ends of a cored bar 2a rotatably supported by roller shaft support members (bearing members) 2d. The charging roller 2 is brought into contact with the photosensitive drum 1 with a predetermined pressing force by urging the roller shaft supporting members 2d and 2d toward the photosensitive drum 1 with the pressure springs 2e and 2e. .

Reference symbol n denotes a nip portion between the photosensitive drum 1 and the charging roller 2 (charging nip portion). The charging roller 2 holds (supports) conductive charge-promoting particles m (conductive particles for the purpose of promoting charge) on its outer peripheral surface, and a charge nip n between the photosensitive drum 1 and the charge roller 2. Is interposed with the charge accelerating particles m.

The charging roller 2 is rotationally driven by a driving system (not shown) in the charging nip n in a direction (counter) opposite to the rotation direction of the photosensitive drum 1, and contacts the surface of the photosensitive drum 1 with a speed difference. . Further, at the time of image recording by the printer, a predetermined charging bias, that is, a DC voltage of -700 V in this embodiment, is applied to the charging roller 2 from a charging bias applying power source S1. As a result, the peripheral surface of the rotary photosensitive drum 1 is uniformly contact-charged to a predetermined polarity and potential by the direct injection charging method.

A magnetic field 8a is applied from the back side of the photosensitive drum 1 to a charging nip n which is a contact portion between the charging roller 2 as a contact charging member and the photosensitive drum 1 as an image carrier (charged body). It is a magnet (permanent magnet) as a magnetic field forming means (magnetic material) to be formed. In this embodiment, the magnet 8a is inserted into the inner space of the photosensitive drum 1 so that the magnetic pole position is fixed and supported toward the downstream side of the charging nip n in the photosensitive drum rotation direction. The magnet 8a promotes the discharge of the magnetic toner from the charging roller 2.

The charging roller 2, magnet 8a, charge accelerating particles m, and direct injection charging will be described in detail in another section.

Reference numeral 4 denotes a laser beam scanner (exposure device) including a laser diode, a polygon mirror, and the like. The laser beam scanner 4 outputs a laser beam L intensity-modulated according to a time-series digital image signal of target image information, and scans and exposes the uniformly charged surface of the rotary photosensitive drum 1 with the laser beam L. . By this scanning exposure, an electrostatic latent image corresponding to the target image information is formed on the surface of the rotating photosensitive drum 1.

Reference numeral 5 denotes a developing device (developing device). The electrostatic latent image on the surface of the rotating photosensitive drum 1 is developed as a toner image at the developing site a by the developing device 5. The developing device 5 includes a mixture (pre-development mixture) t + m obtained by adding the charge accelerating particles m to the developer (toner) t.

Reference numeral 6 denotes a transfer roller of medium resistance as a contact transfer means, which is brought into pressure contact with the photosensitive drum 1 at a predetermined pressure to form a transfer nip portion b. A transfer material P as a recording medium is supplied to the transfer nip b from a paper supply unit (not shown) at a predetermined timing, and a predetermined transfer bias voltage is applied to the transfer roller 6 from a transfer bias application power source S3. As a result, the toner image on the photosensitive drum 1 side is sequentially transferred onto the surface of the transfer material P fed to the transfer nip portion b.

The transfer roller 6 used in the present embodiment is
a having a medium resistance foam layer 6b formed thereon, a roller resistance value of 5 × 1
It is of 0 ⁸ Omega, was performed transfer by applying a voltage of + 2.0 kV to the metal core. The transfer material P introduced into the transfer nip portion b is conveyed by nipping the transfer nip portion b, and the toner image formed and carried on the surface of the rotary photosensitive drum 1 on its surface side is sequentially reduced by electrostatic force and pressing force. Is transcribed.

Reference numeral 7 denotes a fixing device such as a heat fixing system. The transfer material P fed to the transfer nip portion b and receiving the transfer of the toner image on the photosensitive drum 1 side is separated from the surface of the rotary photosensitive drum 1 and is introduced into the fixing device 7, where the toner image is fixed. It is discharged out of the apparatus as an image formed product (print, copy).

The printer of this embodiment is cleaner-less, and the transfer residual toner remaining on the surface of the rotating photosensitive drum 1 after the transfer of the toner image onto the transfer material P is not removed by a dedicated cleaner (cleaning device). With the rotation of 1, the toner reaches the developing site a via the charging nip n, and is collected and reused by the developing device 4 by simultaneous cleaning with development.

(2) Charging Roller 2 The charging roller 2 as a contact charging member in this embodiment is formed by forming a medium resistance layer 2b of rubber or foam on a cored bar 2a.

The medium resistance layer 2b is made of resin (for example, urethane),
It was formulated with conductive particles (for example, carbon black), a sulfide agent, a foaming agent, and the like, and was formed in a roller shape on the cored bar 2a. Thereafter, the surface was polished as needed. Finally, a core metal 2a having a diameter of 6 mm and a length of 240 mm has a layer thickness of 3 m.
m of the sponge layer 2b was formed, and the charging roller 2 as a conductive elastic roller having an outer diameter of 12 mm and a sponge layer longitudinal length of 220 mm was prepared.

When the roller resistance of the charging roller 2 of this embodiment was measured, it was 100 kΩ. The roller resistance is such that a total pressure of 1 kg (9.80665N) is applied to the core metal 2a of the charging roller 2.
100 V was applied between the cored bar 2a and the aluminum drum while the charging roller 2 was pressed against an aluminum drum having an outer diameter of 30 mm so as to apply a load, and measurement was performed.

Here, the charging roller 2 as a contact charging member
Is important to function as an electrode. That is, it is necessary to obtain a sufficient contact state with the member to be charged by providing elasticity, and at the same time, it is necessary to have a resistance low enough to charge the moving member to be charged. On the other hand, it is necessary to prevent voltage leakage when a charged body has a pressure-resistant defect site such as a pinhole. In the case where an electrophotographic photosensitive member is used as a member to be charged, 10 ⁴ -10
^{A 7} Ω resistor is desirable.

It is desirable that the surface of the charging roller 2 has micro unevenness so as to hold the charging promoting particles m.

If the hardness of the charging roller 2 is too low, the shape is not stable and the contact with the member to be charged is deteriorated. If the hardness is too high, the charging nip n cannot be secured between the charging roller 2 and the member to be charged. In addition, the microscopic contact with the surface of the member to be charged is deteriorated, so that the Asker C hardness is preferably 25 to 50 degrees. In the present embodiment, the Asker C hardness is 3
A 0 degree roller was used.

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

The charging roller 2 is disposed so as to be pressed against the photosensitive drum 1 as an object to be charged with a predetermined pressing force against elasticity. In this embodiment, a charging nip n having a width of several mm is formed. It is.

FIG. 2 shows the relationship between the charging roller 2 and the photosensitive drum 1 in detail. Core 2a at end of charging roller
There is a rotating body (spacer roller) 2c that regulates the distance between the cored bar 2a and the surface of the photosensitive drum 1. The radius of the rotating body 2c is 5.7 mm, and there is a difference of 0.3 mm from the charging roller radius of 6.0 mm. This difference is the amount of penetration of the charging roller 2 into the photosensitive drum 1.

In this embodiment, the charging roller 2 is rotated at approximately 80 rpm clockwise as indicated by an arrow so that the surface of the charging roller and the surface of the photoreceptor move in opposite directions at a constant speed in the charging nip n. . That is, the surface of the charging roller 2 as the contact charging member has a speed difference from the surface of the photosensitive drum 1 as the member to be charged.

(3) Magnet 8a The magnet 8a provided in the inner space of the photosensitive drum 1 is freely attached to the inner space of the photosensitive drum 1 and is fixed in relation to the charging roller 2. So fixed. The magnetic pole position of the magnet 8a is directed to a charging nip n which is a contact portion between the charging roller 1 and the photosensitive drum 1. Further, preferably, the magnetic toner is directed downstream in the rotation direction of the photosensitive drum to promote discharge of the magnetic toner on the charging roller 2. Further, the magnet 8a is set at a sufficient distance so as not to adversely affect the developing section a. Alternatively, a magnetic circuit such as a magnetic shield was provided.

(4) Developing Device 5 The developing device 5 of this embodiment is a reversal developing device using a one-component magnetic toner (negative toner) as the developer t. The developing device is provided with a developer (toner) t and a pre-development mixture t + m of the charge accelerating particles m.

Reference numeral 5a denotes a non-magnetic rotary developing sleeve as a developer carrying member which contains a magnet roll 5b, and a pre-development developer t + m provided in a developing container 5d.
The toner t inside is subjected to layer thickness regulation and charge application by the regulation blade 5c in the process of being conveyed on the rotary developing sleeve 5a.

The pre-development mixture t + m coated on the rotary developing sleeve 5a is conveyed to the developing site (developing area) a where the photosensitive drum 1 and the developing sleeve 5a are opposed by the rotation of the developing sleeve 5a. The developing sleeve 5a
Is applied with a developing bias voltage from a developing bias applying power source S2.

In this embodiment, the developing bias voltage is as follows: DC voltage = −500 V AC voltage = peak-to-peak voltage 1600 V, frequency 1.8 kHz
z, a rectangular wave DC / AC superimposed voltage.

Thus, the electrostatic latent image on the photosensitive drum 1 is reversely developed with the toner t.

A) Toner t: A one-component magnetic toner t, which is a developer, is prepared by mixing a binder resin, magnetic particles, and a charge controlling agent, and kneading, pulverizing, and classifying the toner. m and a fluidizer are added as external additives. The average particle size (D4) of the toner was 7 μm.

B) Charge-promoting particles m: In this embodiment, the charge-promoting particles have a specific resistance of 10 ⁶ Ω · cm and an average particle size of 3
μm conductive zinc oxide was used. Then, 1 part by weight of zinc oxide as the charge accelerating particles m was added to 100 parts by weight of the classified toner t, uniformly dispersed by a mixer, and housed in a developing device.

As the material of the charge accelerating particles m, various kinds of conductive particles such as a mixture with conductive inorganic particles such as other metal oxides or an organic substance, or a surface-treated mixture thereof can be used.

The particle resistance requires a specific resistance of 10 ¹² Ω · cm or less in order to transfer charges via the particles.
Preferably, it is 10 ¹⁰ Ω · cm or less.

The resistance was measured by the tablet method and normalized. That is, in a cylinder having a base area of 2.26 cm ² , 0.5 g of a sample of the accelerating particles before being granulated is put, and a pressure of 15 V (147.9975 N) is applied to the upper and lower electrodes, and at the same time, a voltage of 100 V is applied to the upper and lower electrodes. Was measured and then normalized to calculate the specific resistance.

The particle size is 50 in order to obtain good charging uniformity.
μm or less is desirable. In the present invention, the particle size of the field where the particles constitute the aggregate is defined as the average particle size of the aggregate. For the measurement of the particle size, 100 or more samples were extracted from observation by an optical or electron microscope, the volume particle size distribution was calculated with the maximum chord length in the horizontal direction, and the 50% average particle size was determined.

There is no problem that the charge accelerating particles exist not only in the form of primary particles but also in the form of aggregated secondary particles. Regardless of the state of aggregation, the form is not important as long as the function as the charge promotion particles can be realized as an aggregate.

It is desirable that the charge-promoting particles be white or nearly transparent so as not to hinder the exposure of the latent image, particularly when used for charging the photosensitive member. Further, considering that the charge accelerating particles are partially transferred from the photoreceptor to the recording medium P, it is desirable that the color recording be colorless or white. Further, in order to prevent light scattering by particles during image exposure, the particle diameter is desirably equal to or smaller than the constituent pixel size. The lower limit of the particle size is considered to be 10 nm as a limit so that the particles can be stably obtained.

The charge accelerating particles are preferably non-magnetic so as not to hinder the exposure.

(5) Amount of Charge-Promoting Particles The amount of the charge-promoting particles m in the nip n between the photosensitive drum 1 as the image carrier and the charging roller 2 as the contact charging member may be too small. A sufficient lubrication effect cannot be obtained, and the friction between the charging roller 2 and the photosensitive drum 1 is large, so that it is difficult to rotationally drive the charging roller 2 with a difference in speed between the photosensitive drums 1. That is, the driving torque becomes excessively large, and the surface of the charging roller 2 and the photosensitive drum 1 is scraped when the forcible rotation is performed. Further, the effect of increasing the chance of contact by the particles may not be obtained, so that sufficient charging performance cannot be obtained. On the other hand, if the intervening amount is too large, the drop of the charge accelerating particles m from the charging roller 2 increases remarkably, which adversely affects image formation.

According to experiments, it is desirable that the intervening amount between the charging member and the photosensitive member is not less than 10 ³ / mm ² . 10 ³ / mm
^If it is lower than ² , a sufficient lubricating effect and an effect of increasing the chance of contact cannot be obtained, resulting in a decrease in charging performance.

More preferably, 10^Three ~ 5 × 10^Five Pieces / m
m^Two Is preferred. 5 × 10 ^Five Pieces / mm^Two Beyond
Then, the drop of the particles to the photoreceptor increases remarkably, and the particles themselves
Irrespective of the light transmittance of the photoconductor, an insufficient amount of exposure to the photoconductor occurs.
5 × 10^Five Pieces / mm^Two In the following, the amount of particles falling off is also low
The effect can be improved.

When the abundance of the particles dropped on the photoreceptor after charging was measured and found to be 10 ² to 10 ⁵ / mm ² , the abundance without adverse effect on image formation was 10 ⁵ / M
m ² or less is desired.

A method for measuring the intervening amount and the amount present on the photoreceptor will be described. It is desirable to directly measure the interposed amount at the contact surface between the charging roller and the photoreceptor. Therefore, in the present invention, the amount of particles on the surface of the charging roller immediately before reaching the contact surface portion is defined as the intervening amount. Specifically, the rotation of the photoconductor and the charging roller is stopped in a state where the charging bias is not applied, and the surfaces of the photoconductor and the charging roller are cleaned with a video microscope (OVM1000N manufactured by OLYMPUS) and a digital still recorder (SR-3100 manufactured by DELTAS).
Taken in. For the charging roller, the charging roller contacts the slide glass under the same conditions as the contacting of the photoconductor,
The contact surface was photographed with a 1000 × objective lens from behind the slide glass using a video microscope. In order to separate individual particles from the obtained digital image, binarization processing was performed with a certain threshold value, and the number of regions where particles exist was measured using desired image processing software. The amount of the abundance on the photoreceptor was measured by photographing the same on the photoreceptor with the same video microscope and performing the same processing.

The adjustment of the interposition amount is performed by the developer 4 of the developing device 4.
The measurement was performed by setting the amount of the charge promotion particles m in d. Generally, the amount of the charge accelerating material m is 0.01 to 20 parts by weight based on 100 parts by weight of the developer (toner) t.

(6) Direct Injection Charging In the developing device 5, an appropriate amount of the charge promoting particles m of the pre-development mixture t + m together with the toner t during the toner development of the electrostatic latent image on the photosensitive drum 1 by the developing sleeve 5 a. Move to

The toner image on the photosensitive drum 1 is attracted to the transfer material P by the influence of the transfer bias in the transfer nip portion b and moves positively. However, the charge promoting particles m on the photosensitive drum 1 are conductive. As a result, the toner does not actively move to the transfer material P side, but remains substantially adhered and held on the photosensitive drum 1. Further, the transfer efficiency of the toner image from the photosensitive drum 1 side to the transfer material P side is improved by the presence of the charge promoting particles m substantially adhered and held on the surface of the photosensitive drum 1.

Since the image forming apparatus in the toner recycling process does not use a cleaner, the transfer residual toner remaining on the surface of the photosensitive drum 1 after the transfer and the remaining charge promoting particles m are charged with the photosensitive drum 1 and the contact charging member. Roller 2
Is carried as it is by the rotation of the photosensitive drum 1 to the charging nip n, and adheres to the charging roller 2.

Therefore, contact charging of the photosensitive drum 1 is performed in a state where the charge promoting particles m are present in the nip portion n between the photosensitive drum 1 and the charging roller 2. In the initial stage of printing, since the charge accelerating particles are not supplied to the surface of the charging roller and charging cannot be performed, it is possible to apply the charge accelerating particles on the surface of the charging roller in advance.

Even if toner adheres to and mixes with the charging roller 2 due to the presence of the charge accelerating particles m, the contact property and the contact resistance of the charging roller 2 to the photosensitive drum 1 can be maintained. The charging roller 2 can directly inject and charge the photosensitive drum 1 irrespective of contamination of the charging roller by transfer residual toner.

That is, the charging roller 2 comes into close contact with the photosensitive drum 1 via the charging promoting particles m, and the charging promoting particles m existing in the nip portion n of the charging roller 2 and the photosensitive drum 1 cover the surface of the photosensitive drum 1. By rubbing without gaps, the charging of the photosensitive drum 1 by the charging roller 2 becomes stable and safe by direct injection charging without using a discharge phenomenon due to the presence of the charge promoting particles m. High charging efficiency, which cannot be obtained by charging or the like, is obtained, and a potential substantially equal to the voltage applied to the charging roller 2 can be applied to the photosensitive drum.

The transfer residual toner adhering to and entering the charging roller 2 is discharged from the charging roller 2 onto the photosensitive drum 1 and moves to the photosensitive drum 1 to reach the developing section a. Collected) (toner recycling process).

The discharging of the toner from the charging roller 2 onto the photosensitive drum 1 is performed electrostatically, and in the present embodiment, the toner is discharged toward a charging nip n which is a contact portion between the charging roller 2 and the photosensitive drum 1. The toner (magnetic toner) picked up from the photosensitive drum 1 and adhered to the charging roller 2 by the magnet 8a as a magnetic field forming means for forming a magnetic field from the back side (inside of the drum) of the photosensitive drum 1 8a Due to the magnetic field (magnetic force), the toner is rapidly discharged from the charging roller 2 onto the photosensitive drum 1 so that the charging roller 2 is excessively contaminated with toner due to durability or even when continuous printing of a high printing rate image is performed in a cleanerless system. Is prevented from being reached. Further, even in a case where the charging roller 2 is significantly contaminated with toner due to continuous printing of a high printing rate image or occurrence of JAM in the cleanerless system, the toner is quickly discharged from the charging roller 2 to cause an image defect. It is possible to quickly recover from the occurrence state.

A magnet 8a as a magnetic field generating means
Indicates the toner scattered in the vicinity of the charging roller 2
Therefore, the configuration is advantageous in scattering toner.

As described above, the simultaneous cleaning for development is as follows.
The toner remaining on the photosensitive drum 1 after the transfer is developed in a subsequent image forming process, that is, the photosensitive member is continuously charged and exposed to form a latent image. That is, the toner is collected by a fog removing potential difference Vback which is a potential difference between a DC voltage applied to the developing device and a photosensitive member surface potential sense. In the case of the reversal development as in the printer in this embodiment, the simultaneous cleaning for development includes the electric field for collecting the toner from the dark portion potential of the photoconductor to the developing sleeve and the electric field for attaching the toner from the developing sleeve to the bright portion potential of the photoconductor. Made by the action of

Further, even if the charge promoting particles m fall off from the charging roller 2, the image forming apparatus is operated, and as described above, the charge promoting particles m mixed with the toner t of the developing device 5 are developed. To move to the surface of the photosensitive drum 1
Is carried to the charging nip n via the transfer nip b by the rotation of, and is continuously supplied to the charging roller 2 sequentially.
Good chargeability due to the presence of the charge promoting particles m is stably maintained.

Thus, in the image forming apparatus of the direct injection charging method, the transfer method, and the toner recycling process using the charge promoting particles, the charging roller 2 is used as the contact charging member, and the transfer residual toner of the charging roller 2 is used. Despite contamination, the ozone-less direct injection charging can be stably maintained at a low applied voltage for a long period of time at a low applied voltage, and uniform charging properties can be provided in the longitudinal direction. A simple, low-cost image forming apparatus can be obtained.

By interposing the charge promoting particles m in the nip portion n between the charging roller 2 and the photosensitive drum 1, the lubricating effect (friction reducing effect) of the charge promoting particles m causes the gap between the charging roller 2 and the photosensitive drum 1 to change. It is possible to easily and effectively provide a speed difference.

By providing a speed difference between the charging roller 2 and the photosensitive drum 1, the chance that the charge promoting particles m contact the photosensitive drum 1 at the nip n of the charging roller 2 and the photosensitive drum 1 is greatly increased. , A high contact property can be obtained, and direct injection charging can be easily performed.

As a configuration for providing a speed difference, preferably, the charging roller 2 is driven to rotate so that the transfer residual toner on the photosensitive drum 1 carried to the nip portion n is temporarily collected by the charging roller 2. In addition, it is preferable that the rotation direction is configured to rotate in a direction opposite to the moving direction of the surface of the photosensitive drum 1. That is, by directly separating the transfer residual toner on the photosensitive drum 1 by the reverse rotation and performing the charging, the direct injection charging can be predominantly performed.

<Embodiment 2> (FIG. 3) In the present embodiment, a nip forming member 9 for forming a contact nip c with the charging roller 2 in the image recording apparatus of the above-described Embodiment 1 (FIG. 1) is newly added. It is arranged.

In this embodiment, the nip forming member 9 is
A sheet in which a 50 μm polyimide film is adhered to a 00 μm PET sheet.
The charging roller 2 was brought into contact with the charging roller 2 at a roller entrance amount of 0.5 mm, and was fixedly supported by the support member 9a.

The other components of the image recording apparatus are basically the same as those of the first embodiment.

By providing the nip forming member 9 that contacts the charging roller 2 and forms a nip in this manner, the photosensitive member is exposed from the charging roller 2 by frictional charging of the nip forming member 9 and the toner on the charging roller 2 at the nip c. The polarity of the toner discharged on the drum 1 is normalized. In this embodiment, the polarity is made uniform to the negative polarity, and the efficiency of removing and collecting the toner by the simultaneous development cleaning in the developing device 5 is improved.

Accordingly, the nip forming member preferably has a positive frictional charging polarity with respect to the toner, and preferably has a positive polarity in a general charging line such as nylon in addition to the polyimide film of the present embodiment. Conversely, when the toner has a positive polarity, a material having a negative triboelectric charge polarity with respect to the toner is preferable, and a material having a negative polarity, for example, Teflon or polypropylene is preferable in a general charging sequence.

<Embodiment 3> (FIG. 4) In the present embodiment, a magnet (permanent magnet) 8 as a magnetic field forming means in the image recording apparatus of the above-described Embodiment 2 (FIG. 2) is used.
a is changed to an electromagnet (excitation magnet, coil) 8b,
The discharge of the toner from the charging roller 2 to the photosensitive drum 1 was promoted by the electromagnet 8b. The electromagnet 8b can be controlled from outside the photosensitive drum. The magnetic force at each time is controlled by controlling the timing of energizing the coil and the amount of current.

The other components of the image recording apparatus are basically the same as those of the first and second embodiments.

Comparative Example 1 The image recording apparatus of the first embodiment (FIG. 1) does not include the magnet 8a as the magnetic field forming means.

<Evaluation Results> Table 1 shows the evaluation results of the image recording apparatuses of Examples 1 to 3 and the image recording apparatus of Comparative Example 1, and describes the effectiveness of Examples 1 to 3.

A) Recovery during JAM In each of the image recording apparatuses of Examples 1 to 3 and Comparative Example 1,
The photosensitive drum was forcibly stopped during printing of a solid black image, then a solid white image was output, and a comparison was made as to how many image outputs were required until fog fell below 3%.

B) Durability stability The printing was repeated 3000 times, and the change in the charged potential before and after the printing was measured.

Table 1 summarizes the above evaluation results.

[0137]

[Table 1]

The superiority of the present invention will be described from Table 1 above.

The comparison between Comparative Example 1 and Example 1 shows that Example 1
By installing the magnet 8a as described above, the number of sheets required for recovery during JAM is reduced. That is, it means that the toner contaminating the charging roller 2 is discharged in a short time and can be quickly recovered.

Next, in the second embodiment, the nip forming member 9 is attached to the charging roller 2 so that the polarity of the toner discharged from the charging roller 2 is returned to normal, so that the toner is easily collected by development.

Since the magnetic force generated by the magnets 9a and 9b acts on the magnetic toner, it is easy to discharge even the toner that is not sufficiently frictionally charged and exists on the charging roller 2.
By making the charge of the toner on the charging roller 2 to have a regular polarity, the recoverability in the development is improved and the JAM is more efficiently performed.
It is possible to recover from time.

Further, in the third embodiment, the magnetic field generating means is constituted by an electromagnet (coil), and the timing and intensity of toner discharge from the charging roller 2 to the photosensitive drum 1 by the magnetic field generating means can be externally controlled. It is.

The control was performed when the photosensitive drum was rotating during non-image recording. That is, as shown in the operation sequence of FIG. 5, the operation is performed at the time of multiple rotations before printing, at the time of rotation after printing, and also at the time of continuous paper passing. As a result, repeated printing
The effect of suppressing the decrease in the charged potential was obtained.

A. Multi-rotation process before: A start operation period (start operation period, warming period) of the printer. When the main power switch is turned on, the main motor of the apparatus is driven to rotate the photosensitive drum 1, and a preparation operation of a predetermined process device is executed.

B. Pre-rotation step: a period during which a pre-print operation is performed. This pre-rotation step is executed subsequent to the pre-multi-rotation step when a print signal is input during the pre-multi-rotation step.

When there is no input of a print signal, the drive of the main motor is temporarily stopped after the completion of the previous multi-rotation step, the rotation of the photosensitive drum 1 is stopped, and the printer is in a standby state until a print signal is input. Is kept.

When a print signal is input, a pre-rotation step is executed.

C. Printing process (image forming process, image forming process): When a predetermined pre-rotation process is completed, an image forming process is subsequently performed on the rotating photosensitive drum, and the toner image formed on the rotating photosensitive drum surface is transferred to a recording material. The fixing process of the toner image by the fixing unit is performed, and the image formed matter is printed out.

In the case of the continuous printing (continuous printing) mode, the above printing process is repeatedly executed for a predetermined set number of prints n.

D. Paper interval process: In continuous printing mode,
The non-sheet passing state of the recording material at the transfer nip b after the rear end of one recording material has passed through the transfer nip b and before the leading end of the next recording material reaches the transfer nip b Period.

E. Post-rotation step: This is a period in which the main motor continues to be driven for a while after the last recording material printing step is completed to rotate and drive the photosensitive drum 1 to execute a predetermined post-operation.

F. Standby: When the post-rotation process is completed, the drive of the main motor is stopped and the photosensitive drum 1
Is stopped, and the printer is kept in a standby state until the next print start signal is input.

In the case of printing only one sheet, after the printing is completed, the printer goes into a standby state through a post-rotation process.

In the standby state, when a print start signal is input, the printer shifts to a pre-rotation step.

<Others> 1) In the present embodiment, the recoverability at the time of JAM was evaluated by outputting a solid white image at the time of the recovery operation. However, when a system such as a printer is actually constructed, it is necessary to pass paper. Instead, the recovery operation is performed by sequentially performing the cleaning mode of the charging roller and the cleaning mode of the transfer roller. Here, the cleaning of the transfer roller and the charging roller was performed by superimposing and applying an AC voltage to a DC voltage of, for example, a transfer bias of 0 V and a charging bias of -700 V, moving the negative toner of the transfer roller to the drum, and further moving on the charging roller. The toner is further moved downstream of the drum rotation by the AC voltage. Then, the discharged toner is collected in the developing device by a bias in which a DC voltage and an AC voltage that are higher in the positive direction than the charging potential are superimposed. Even in such a case, the recovery operation can be efficiently performed in a shorter time by adopting this configuration.

2) In the third embodiment using the electromagnet (coil) 8b as the magnetic field generating means, the charging capability of the charging roller 2 is monitored by a charging current or surface potential sensor and the like. It is also effective to control the magnetic force to control the discharge of the toner from the charging roller 2.

3) In the present invention, it is preferable to use a charge injection layer provided on the surface of the photosensitive drum 1 to adjust the resistance of the photosensitive member surface.

FIG. 6 is a schematic view of the layer structure of the photosensitive drum 1 having a charge injection layer on the surface. That is, the photosensitive drum 1 has an undercoat layer 1 on an aluminum drum base (Al drum base) 11.
2. The charge performance is improved by applying the charge injection layer 16 to a general organic photoreceptor drum, which is coated in order of the positive charge injection prevention layer 13, the charge generation layer 14, and the charge transport layer 15. It is.

The charge injection layer 16 is formed by adding a photo-curable acrylic resin as a binder to conductive particles (conductive filler).
Ultrafine particles 16a of SnO ₂ (having a diameter of about 0.03 μm)
m), a polymerization initiator and the like are mixed and dispersed, and after coating, a film is formed by a photocuring method.

In addition, by incorporating a lubricant such as tetrafluoroethylene resin (trade name: Teflon), the effect of suppressing the surface energy of the drum surface and generally preventing the adhesion of the charge accelerating particles is obtained.

An important point for the charge injection layer 16 is the resistance of the surface layer. In the charging method by direct injection of electric charges, the electric charges can be transferred more efficiently by lowering the resistance of the object to be charged. On the other hand, when used as a photoconductor, it is necessary to hold the electrostatic latent image for a certain time,
The volume resistance value of the charge injection layer 16 is 1 × 10 ⁹ to 1 ×.
A range of 10 ¹⁴ (Ω · cm) is appropriate.

Even when the charge injection layer 16 is not used, the same effect can be obtained, for example, when the charge transport layer 15 is in the above resistance range. Furthermore, the volume resistance of the surface layer is about 1
The same effect can be obtained by using an amorphous silicon photosensitive member having a resistance of 0 ¹³ Ωcm.

4) In the embodiment, the configuration using the cleaner-less system is shown. However, as shown in FIG.
The present invention is also effective in an apparatus configuration in which a cleaning device using a rubber blade 10a is provided, for example, and a device 20 for directly applying the charge accelerating particles m to the charging roller 2 is provided.

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

6) For the applied charging bias or the applied developing bias to the contact charging member 2 and the developing sleeve 5a, an alternating voltage (AC voltage) may be superimposed on a DC voltage.

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

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

The image carrier may be an electrostatic recording dielectric or the like. In this case, the dielectric surface is uniformly charged to a predetermined polarity / potential, and then selectively neutralized by a static elimination means such as a static elimination needle head or an electron gun to write and form a target electrostatic latent image.

8) In the embodiment, the developing device 5 has been described as an example of a developing device using a one-component magnetic toner. However, the structure of the developing device is not particularly limited, and is arbitrary. Regular development may be used.

In general, a method of developing an electrostatic latent image is such that non-magnetic toner is coated on a developer carrier by a blade or the like, and magnetic toner is coated on the developer carrier by a magnetic force and transported to carry the image. A method of developing in a non-contact state with a body (one-component non-contact development), a method of developing in a contact state (one-component contact development), and a method in which a magnetic carrier is mixed with toner particles as a developer Using a magnetic force to coat and transport the developer on a developer carrier and developing the image carrier in contact with the image carrier (two-component contact development), and a method of developing in a non-contact state (two-component non-contact development) )).

9) The transfer means 6 is not limited to roller transfer, but may be any type such as belt transfer or corona discharge transfer. An image recording apparatus that forms not only a single-color image but also a multi-color or full-color image by multiple transfer or the like using an intermediate transfer member such as a transfer drum or a transfer belt may be used.

10) An image recording apparatus of a direct system instead of a transfer system may be used. There is also an image display device (display device) in which a toner image corresponding to required image information is formed and held on an image carrier, and the toner image forming unit is positioned in a reading and displaying unit to display an image. The image recording device of the present invention includes such an image display device.

[0173]

As described above in detail, according to the present invention, a contact-type charging device using charge-promoting particles is prevented by preventing the contact charging member from being excessively contaminated by durability. Endurance stability can be improved.

Further, with respect to an image recording apparatus using the charging device as a charging means for an image bearing member, even when continuous printing of a high printing rate image is performed due to durability or in a cleanerless system, the contact charging is performed. It is possible to prevent the member from being excessively contaminated with toner, to enhance the durability stability, and to maintain a high-quality image for a long time. In a cleanerless system, even when the contact charging member is excessively contaminated with toner due to continuous printing of a high printing rate image or occurrence of JAM, it is possible to quickly recover from an image defect occurrence state. Further, the scattering of the toner near the contact charging member is effectively prevented.

[Brief description of the drawings]

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

FIG. 2 is an explanatory view of an arrangement structure of a charging roller.

FIG. 3 is a schematic diagram of an image recording apparatus according to a second embodiment.

FIG. 4 is a schematic diagram of an image recording apparatus according to a third embodiment.

FIG. 5 is an operation stroke diagram of the apparatus.

FIG. 6 is a schematic diagram of a layer configuration of an example of a photoconductor having a charge injection layer.

FIG. 7 is a schematic diagram of an image recording apparatus according to another embodiment.

Fig. 8 Charging efficiency graph

[Explanation of symbols]

Reference Signs List 1 photoreceptor (image carrier), 2 charging roller (contact charging member), m charging promotion particles, 4 laser scanner, 5 developing device, 5a ... Developing sleeve, 5b: magnet roller, 5c: development regulating blade, t: one-component magnetic toner, 6: transfer charger, P: recording medium, 7: fixing device, 8a ・ 8
b: magnetic field generating means (magnetic material, permanent magnet, electromagnet),
9: Nip forming member, 10: Cleaning device (cleaner), 20: Charging promoting particle supply / coating device

Claims (9)

[Claims] 1. A charging device which has a flexible charging member which is driven or rotated and driven in contact with a member to be charged, and charges the surface of the member to be charged. A magnetic field forming means for forming a magnetic field from the back side of the member to be charged toward the contact portion of the charging device. And a flexible charging member forming a nip portion with the member to be charged, wherein at least a nip portion between the charging member and the member to be charged is interposed with charge-promoting particles as conductive particles. The surface of the member is a charging device that moves at a speed difference with respect to the surface of the member to be charged, and charges the surface of the member to be charged. A charging device comprising a magnetic field forming means for forming a magnetic field from a side. 3. A charging member having a flexible charging member forming a nip portion with a member to be charged, wherein at least a nip portion between the charging member and the member to be charged has a volume resistance of 10 ¹² Ω · cm or less. The accelerating particles are interposed, and the surface of the charging member is a charging device that moves with a speed difference with respect to the surface of the member to be charged and charges the surface of the member to be charged. A charging device, comprising: a magnetic field forming unit that forms a magnetic field from the back side of a member to be charged. 4. The charging device according to claim 1, wherein said magnetic field forming means is constituted by a permanent magnet. 5. The charging device according to claim 1, wherein said magnetic field forming means is constituted by an electromagnet. 6. The charging device according to claim 1, further comprising a nip forming member that contacts the charging member to form a nip. 7. An image recording apparatus for executing image formation by applying an image forming process including a step of charging the image carrier to the image carrier, wherein the means for charging the image carrier is described in any one of claims 1 to 6. An image recording apparatus, comprising: the charging device according to any one of the preceding claims. 8. An electrophotographic image recording system comprising an image carrier, and a charging device, an image exposure device, a developing device, a transfer device, and a fixing device for fixing an image on a recording medium, which are arranged around the image carrier. 7. An image recording apparatus, wherein the charging device is any one of claims 1 to 6. 9. An electrophotographic image recording system comprising an image carrier, a charging device, an image exposing device, a developing device, a transfer device, and a fixing device for fixing an image on a recording medium, which are arranged around the image carrier. An image recording apparatus having an image carrier cleaner-less configuration in which the developer remaining on the surface of the image carrier after the transfer process is temporarily carried at least by a charging device, and is collected by the developing device again through the image carrier. 7. An image recording apparatus, wherein the developer of the developing device is a magnetic toner, and the charging device is any one of the charging devices according to claim 1.