JP3402878B2 - Charging device, image forming device, and process cartridge - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device, an image forming device, and a process cartridge.

[0002]

2. Description of the Related Art Conventionally, in image forming apparatuses such as electrophotographic devices (copiers, printers, facsimiles, etc.) and electrostatic recording devices, electrophotographic photosensitive members, electrostatic recording dielectrics, transfer materials, and other materials to be charged. Charging the body (including static elimination)
A "corona charging method" using a corona charger has been used as a means for doing so. In recent years, a “contact charging type” charging device has been put into practical use. A ozone-less, low-power “contact injection charging (charge injection charging) type” charging device has also been developed.

A) Corona charging method A corona charger is disposed in a non-contact manner opposite to a body to be charged, and the body to be charged is exposed to the corona discharged from the corona charger so that the surface of the body to be charged has a predetermined polarity and potential. It is to be charged.

B) Contact charging method: A charging member such as a roller type, a blade type, a brush type, or a magnetic brush is brought into contact with an object to be charged, and a voltage is applied to the charging member to charge the surface of the object to be charged. It is aimed at low ozone and low power consumption. Above all, the roller charging method using a conductive roller as a charging member has stable charging, and the amount of ozone generated is about 1/1000 of that of a corona charger, which is an office environment. Since it is also preferred, it has been widely used in recent years.

In roller charging, a conductive elastic roller (charging roller) is brought into pressure contact with an object to be charged, and a voltage is applied to the object to charge the object.

Specifically, since the charging is performed by discharging from the charging member to the body to be charged, the charging is started by applying a voltage equal to or higher than a certain threshold voltage. As an example, an electrophotographic OPC having a thickness of 25 μm as a member to be charged
When the charging roller is pressed against the photoconductor,
When a voltage of about 640 V or higher is applied, the surface potential of the photoconductor starts to rise, and thereafter, the surface potential of the photoconductor linearly increases with an inclination of 1 with respect to the applied voltage. This threshold voltage is defined as the charging start voltage Vth.

That is, in order to obtain the photoreceptor surface potential Vd required for electrophotography, Vd + Vth is applied to the charging roller.
That is, a DC voltage (DC voltage) higher than the required surface potential Vd is required. A method of applying only the DC voltage to the contact charging member in this way to perform charging is called a DC bias method (DC charging method).

However, in the DC bias method, the resistance value of the contact charging member fluctuates due to environmental fluctuations and the like.
Further, when the photosensitive member as the member to be charged is repeatedly worn away and the film thickness is changed, the charging start voltage V
Since th varies, it is difficult to set the charging potential of the photoconductor to a desired value.

Therefore, as disclosed in Japanese Patent Laid-Open No. 63-149669, in order to further homogenize charging, the DC voltage corresponding to the desired surface potential Vd of the member to be charged is 2 × Vth or more. There is an AC bias method (AC charging method) in which an oscillating voltage (a voltage whose voltage value periodically changes with time) superposed with an AC component (AC voltage component) having a peak-to-peak voltage is applied to a contact charging member to perform charging. Used. This is for the purpose of leveling the potential by the AC component, and the potential of the charged body converges on Vd which is the center of the peak of the AC voltage, and is not affected by disturbance such as the environment. .

However, in the above-mentioned contact charging system, DC
In both the bias method and the AC bias method, the essential charging mechanism uses the discharge phenomenon from the charging member to the charged member. Therefore, as described above, the voltage applied to the charging member is the desired voltage of the charged member. The surface potential Vd is required to be equal to or higher than the surface potential Vd, and a minute amount of ozone is generated. Further, when the AC bias system is used for uniform charging, further ozone is generated, vibration noise (AC charging sound) of the charging member and the charged body due to the electric field of the AC voltage is generated, and the charged body is caused by discharge. Deterioration of the surface became remarkable and became a new problem.

C) Contact injection charging system Then, as a new charging system, Japanese Patent Laid-Open No. 6-3921 discloses a charging system by directly injecting an electric charge to an object to be charged (photoconductor).

In this contact injection charging system, a voltage is applied to a contact charging member such as a charging roller, a charging brush, a charging magnetic brush, etc., and charges are injected into the conductive particles in the charge injection layer on the surface of the photosensitive member as the member to be charged. Is a method of charging.

In this charging method, since the discharge phenomenon is not used, the voltage required for charging is only the desired photoconductor surface potential Vd, and the amount of ozone generated is the roller charging in the contact charging method of the above B). It is excellent as less than 1/10 of the method.

Also in the case of this contact injection charging method, a DC bias method in which only a DC voltage is applied to the contact charging member to perform charging, and an AC bias method in which a voltage having an AC component is applied to the contact charging member to perform charging. There is. In this case, compared with the DC bias method, the AC bias method exhibits stable charging performance even when the contact charging member is deteriorated in durability or changes in the environment. Therefore, the contact injection charging method / AC bias method (AC Injection charging) is under study.

In the contact injection charging method, even if an AC bias is applied to the contact charging member, the amount of ozone generated is significantly increased as compared with the DC bias method like the roller charging method of the contact charging method in the above B). It is known that there is no.

The reason is that a magnetic brush of a magnetic carrier (magnetic particles) is used especially in the case where there is always a gap in which discharge easily occurs between a round solid charging roller and an object to be charged as in a roller charging system. In the contact injection charging method in which is used as a contact charging member, when a DC or AC bias is applied, the charged and flowable magnetic carrier forming the magnetic brush is attracted to the opposite charge injected into the body to be charged. It is considered that this is because there is no air gap that moves a large amount and forms a contact area larger than that of the roller charging method, and the magnetic brush and the member to be charged are in complete contact and discharge.

The contact injection charging system and the AC bias system are disclosed in Japanese Patent Laid-Open Nos. 4-21873 and 4-11666.
Japanese Laid-Open Patent Publication No. 74 proposes a magnetic brush charging method in which an AC bias voltage containing a DC component is applied to the magnetic brush to charge the image forming body.

[0018] However, in the method of charging according to the publication, is not set voltage Vp over p between appropriate peaks when the temperature becomes lower low humidity during environmental changes increases the resistance of the magnetic particles, the magnetic particles adhere to the image forming body However, there is a problem in that charging is not sufficiently performed and uneven charging occurs. Also,
There is a problem that the resistance of the magnetic particles becomes low at high temperature and high humidity, causing breakdown.

To solve this, Japanese Patent Laid-Open No. 6-314
In the 016 publication, the DC component of the AC bias voltage is
A method in which the charging potential is changed by adjusting the voltage of the AC component or changing the voltage value of the DC component supplied from a constant voltage source at that time and the current value of the DC component is also disclosed.
In Japanese Patent No. 138753, a method of strictly controlling the alternating current I _AC of the applied bias and the contact width formed by the magnetic brush and the image carrier is proposed.

[0020]

However, the above-mentioned JP-A-6-314016 and JP-A-6-138753.
When several devices were actually created and actually tested in consideration of the method described in the publication, it was found that there was a large difference in actual charging performance.

That is, even if the current value of the DC component is controlled as in the method described in JP-A-6-314016, the AC current I _AC and the AC current I _{AC in} the method described in JP-A-6-138753 are also used. Even if the contact width (charging portion width) formed by the magnetic brush and the image forming body is strictly controlled, the level of the output image varies.

Therefore, in the present invention, the contact injection charging method AC
With respect to a bias type charging device and an apparatus using the charging device, it is possible to eliminate the individual difference in the ability of the charging performance, which was the drawback of the above-mentioned conventional technology, and to perform stable charging even in various environments even after a long time has passed from the initial stage. The purpose is to obtain performance.

[0023]

SUMMARY OF THE INVENTION The present invention is a charging device, an image forming apparatus, and a process cartridge characterized by the following configurations.

(1) In a charging device for charging an object to be charged having a charge injection layer on its surface by contacting a contact charging member to which a voltage in which an AC voltage and a DC voltage are superimposed , is contacted, By monitoring the alternating current supplied to the charged body and variably adjusting the maximum value of the positive component and the maximum value of the absolute value of the negative component within one cycle of the waveform of the alternating current, the charged body after charging A charging device, characterized in that the charging potential of is set to a desired value.

[0025]

(2) The relationship between the maximum value Imax + of the positive component and the maximum value Imax- of the absolute value of the negative component within one cycle of the AC current waveform is 0.7 ≦ Imax + / Imax− ≦ 1.4. The charging device according to (1) . (3) The charging device according to (1) or (2) , wherein a magnetic brush composed of magnetic particles is used as the contact charging member.

(4) The charging device according to (1) or (2) , characterized in that brush fibers are used as the contact charging member.

(5) An image forming apparatus for performing image formation by applying an image forming process including a step of charging the surface of the image carrier to the image carrier, wherein the image carrier has a charge injection layer on its surface. An image forming apparatus, wherein the step means for charging the image carrier is the charging device according to any one of (1) to (4) .

(6) A process cartridge that is detachably attached to the main body of the image forming apparatus.
A process cartridge containing at least a contact charging member of the charging device according to any one of (4) and at least one of an image carrier, a developing device, and a cleaning device.

<Operation> That is, as a result of detailed investigation of the individual difference phenomenon of the charging performance, which was a drawback of the above-mentioned conventional technique, a slight individual difference in the AC bias voltage waveform is large in the AC current waveform at that time. It was found that the difference between the solids produced and this difference appeared as a difference in charging performance. That is, it is essential to control the AC current waveform for stable charging performance.

Therefore, in the present invention, a contact injection charging method or an AC bias method in which a contact charging member to which a voltage obtained by superimposing an AC voltage and a DC voltage is applied is brought into contact with an object to be charged having a charge injection layer on its surface to perform charging. In the charging device and the device using the charging device, the AC current waveform is controlled. More specifically, the AC current supplied from the contact charging member to the member to be charged is monitored, and one cycle of the waveform of the AC current is controlled. By variably adjusting the maximum value of the positive component and the maximum value of the absolute value of the negative component in the above, the individual difference in the ability of the charging performance, which was the drawback of the conventional technology, is eliminated, and even in various environments,
It became possible to obtain stable charging performance even after a long time had passed from the beginning.

[0032]

DETAILED DESCRIPTION OF THE INVENTION

<Embodiment 1> (FIGS. 1 to 4) (1) Example of image forming apparatus FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus. The image forming apparatus of this example is a laser beam printer using a transfer type electrophotographic process, a contact injection charging type / AC bias type, and a process cartridge attaching / detaching type.

Reference numeral 1 is a rotary drum type electrophotographic photosensitive member (photosensitive drum) as an image bearing member (charged member). This example is an OPC photoreceptor having a charge injection layer on the surface,
It is rotationally driven in the clockwise direction indicated by an arrow at a predetermined process speed (peripheral speed).

Reference numeral 2 denotes a conductive magnetic brush as a contact charging member which is brought into contact with the photosensitive member 1, and S1 is a power source for applying a charging bias to this magnetic brush.

In the rotating process, the photosensitive member 1 is subjected to a uniform primary charging process of a predetermined polarity and potential by a conductive magnetic brush 2 to which a voltage is applied by a contact injection charging system / AC bias system, and then as an image exposing means. In the case of this example, scanning exposure is performed by a laser beam whose intensity is modulated corresponding to a time-series electric digital pixel signal of target image information output from a laser beam scanner (not shown) including a laser diode, a polygon mirror, and the like. By receiving L,
An electrostatic latent image corresponding to desired image information is formed on the peripheral surface of the rotating photoconductor 1.

The electrostatic latent image is developed as a toner image by the developing device 3. The developing device 3 is a reversal developing device using a magnetic component insulating toner (negative toner) in this example.
Reference numeral 3a denotes a non-magnetic developing sleeve having a diameter of 16 mm, which contains a magnet 3b. The developing sleeve 3a is coated with the above negative toner so that the distance from the surface of the photoconductor 1 is 300 μm.
In the state of being fixed to m, the photoconductor 1 is rotated at the same speed, and a development bias voltage is applied to the sleeve 3a from the development bias power source S2. As the voltage, a DC voltage of -500 V and a rectangular AC voltage having a frequency of 1800 Hz and a peak-to-peak voltage of 1600 V are superimposed, and jumping development is performed between the sleeve 3 a and the photoconductor 1.

On the other hand, a transfer material P as a recording material is supplied from a paper feeding section (not shown), and the rotary photosensitive member 1 is brought into contact with the transfer material P with a predetermined pressing force. Is introduced into the pressure contact nip portion (transfer portion) T with the transfer roller 4 at a predetermined timing. A predetermined transfer bias voltage is applied to the transfer roller 4 from the transfer bias applying power source S3. The transfer material P introduced into the transfer portion T is nipped and conveyed through the transfer portion T, and the toner images formed and carried on the surface of the rotary photosensitive member 1 are sequentially transferred onto the surface side thereof by electrostatic force and pressing force. Will be done. In this example, a transfer roller 4 having a resistance value of 5 × 10 ⁸ Ω was used, and a DC voltage of +2000 V was applied to transfer.

The transfer material P on which the toner image has been transferred is separated from the surface of the photoconductor 1 and is introduced into a fixing device 5 such as a heat fixing system to receive the toner image fixing, and an image-formed product (print, copy). Is discharged outside the device.

The surface of the photosensitive member after the transfer of the toner image onto the transfer material P is cleaned by the cleaning device 6 to remove adhered contaminants such as residual toner, and is repeatedly used for image formation.

In the image forming apparatus of this embodiment, four process equipments of the photosensitive member 1, the contact charging member 2, the developing device 3 and the cleaning device 6 are included in the cartridge 30 and are collectively attached to and detached from the main body of the image forming apparatus. It is a replaceable cartridge type device. Reference numerals 31 and 31 are positioning support members of the process cartridge 30 in the printer body.
The combination of process equipment included in the process cartridge 30 is not limited to the above.

(2) Photoreceptor 1 In the photoreceptor 1 of the present example, the following first to fifth functional layers are provided in order from the bottom on an aluminum drum substrate, and a charge injection layer is formed on the surface. Negatively charged OPC with a diameter of 30 mm
It is a photoconductor and is rotationally driven at a process speed (peripheral speed) of 150 mm / sec.

First layer: an undercoat layer, which is a conductive layer having a thickness of about 20 μm, which is provided to smooth defects such as the aluminum drum substrate and to prevent moire due to reflection of laser exposure. is there.

Second layer: a positive charge injection preventing layer, which plays a role of preventing the positive charges injected from the aluminum drum substrate from canceling out the negative charges charged on the surface of the photoconductor, and the amylan resin and methoxymethylation. It is a medium resistance layer having a thickness of about 1 μm, whose resistance is adjusted to about 10 ⁶ Ωcm by nylon.

Third layer: a charge generation layer, which is a layer having a thickness of about 0.3 μm dispersed in a disazo pigment resin, and generates a positive and negative charge pair upon exposure to laser.

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

Fifth layer: a charge injection layer, which is a coating layer of a material in which fine particles of SnO ₂ are dispersed in a photocurable acrylic resin. Specifically, it is a coating layer made of a material in which antimony-doped SnO ₂ particles having a low resistance and a particle size of about 0.03 μm are dispersed in a resin in an amount of 70% by weight.
The coating solution thus prepared was applied by dipping to a thickness of about 2 μm to form a charge injection layer.

In the structural model diagram of the photoconductor 1 and the conductive magnetic brush 2 of FIG. 2, 11 is an aluminum drum substrate of the photoconductor 1, 12 is a charge transport layer, 13 is a charge injection layer, and 13a is in this charge injection layer. The dispersed conductive particles (SnO ₂ ). The undercoat layer, the positive charge injection prevention layer, and the charge generation layer are omitted in the figure.

(3) Contact charging member 2 The magnetic brush 2 as a contact charging member is a magnet 21 fixedly supported by a mandrel 21a as shown in the structural model diagram of FIG.
And a non-magnetic electrode sleeve 22 having a diameter of 16 mm, which is rotatably fitted on the electrode sleeve 22, and a magnetic brush layer of magnetic particles (magnetic carrier) attached and held by the magnetic force of the magnet 21 on the outer peripheral surface of the electrode sleeve 22. It consists of 23. The magnetic flux density by the magnet 21 on the electrode sleeve 22 is 8
It is 00 × 10 ⁻⁴ T (Tesla).

The magnetic brush layer 23 is coated with a thickness of 1 mm to form a charging nip N having a width of about 5 mm with the photoconductor 1. In this example, the amount of magnetic particles in the magnetic brush layer 23 is about 1
At 0 g, the gap at the charging nip N between the electrode sleeve 22 and the photoconductor 1 is 500 μm. The electrode sleeve 22 is rotationally driven in the charging nip N in a direction (counter direction) opposite to the rotation direction of the photoconductor 1, and the magnetic brush layer 23 is also rotated by the rotation of the electrode sleeve 22 and the photoconductor 1 is rotated. Rub the surface.

The electrode sleeve 22 of the magnetic brush 2 is applied with a DC voltage of -700V from the charging bias applying power source S1.
A charging bias V _DC + V _AC on which a rectangular wave AC having a frequency of 1 kHz and _PP = 800 V is superimposed is applied, and the outer peripheral surface of the rotating photoconductor 1 is uniformly set to approximately -700 V by the contact injection charging method / AC bias method. Is charged with.

Here, the peripheral speed ratio between the magnetic brush 2 and the photosensitive member 1 is defined by the following equation.

Peripheral speed ratio% = (magnetic brush peripheral speed-photosensitive body peripheral speed) / photosensitive body peripheral speed × 100 * The peripheral speed of the magnetic brush 2 is a negative value in the case of counter rotation.

Since the magnetic brush is in a stopped state at a peripheral speed ratio of -100%, the stopped shape of the magnetic brush on the surface of the photoconductor becomes defective as it is and appears in the image. Further, in the forward rotation, if an attempt is made to obtain the same peripheral speed ratio as in the counter direction, the rotational speed of the magnetic brush will increase. When the magnetic brush comes into contact with the photoconductor at a slow speed in the forward rotation, the magnetic particles of the magnetic brush easily adhere to the photoconductor. Therefore, the peripheral speed ratio is preferably −100% or less, and in this example, set to −150%.

The following can be used as the magnetic particles forming the magnetic brush layer 23.

A) Resin and magnetic powder such as magnetite are kneaded and molded into particles, or are mixed with conductive carbon or the like to adjust the resistance value. B) Sintered magnetite, ferrite, or these. C) whose resistance value has been adjusted by reducing or oxidizing c) The above magnetic particles are coated with a resistance-adjusted coating material (such as phenol resin in which carbon is dispersed) or plated with a metal such as Ni for resistance. If the resistance value of these magnetic particles is too high, electric charges cannot be evenly injected into the photoconductor, resulting in a fog image due to minute charging failure. If it is too low, when there are pinholes on the surface of the photoconductor, current concentrates on the pinholes, the charging voltage drops, and the surface of the photoconductor cannot be charged, resulting in a charging nip-like charging failure. Therefore, the resistance value of the magnetic particles is preferably 1 × 10 ⁴ to 1 × 10 ⁷ Ω. The resistance value of the magnetic particles depends on the metal cell (bottom area 228
2g of magnetic particles are put in mm ² ) and then weighted, and the voltage is 1 to
It was measured by applying 1000 V.

Regarding the magnetic characteristics of the magnetic particles, it is better to increase the magnetic restraining force in order to prevent the magnetic particles from adhering to the photosensitive member, and the saturation magnetization is preferably 50 (A · m ² / kg) or more.

In practice, the magnetic particles used in this example had an average particle size of 30 μm, a resistance value of 1 × 10 ⁶ Ω, and a saturation magnetization of 5.
It was 8 (A · m ² / kg).

(4) Principle of Charge Injection Charging Charge injection charging is a contact charging member having a medium resistance and performs charge injection on the surface of a charged body having a medium resistance surface resistance. In this example, the charged body is charged. No charge is injected into the trapping potential of the surface material of the photoconductor as described above, but the conductive particles 13a of the charge injection layer 13 are charged with electric charge for charging.

Specifically, as shown in the equivalent circuit model diagram of FIG. 3, the charge transport layer 12 is a dielectric, the aluminum drum substrate 11 and the conductive particles (SnO ₂ ) 13 in the charge injection layer 13 are formed.
This is based on the theory that the contact charging member 2 charges a minute capacitor having a as both electrode plates.

At this time, the conductive particles 13a are electrically independent of each other and form a kind of minute float electrode. For this reason, the surface of the photoconductor seems to be charged and charged to a uniform potential on a macroscopic scale, but in reality, countless minute charged conductive particles 13a cover the photoconductor surface. Has become. For this reason, even if the image exposure L is performed by the laser, the respective conductive particles 13a are electrically independent, so that the electrostatic latent image can be held.

(5) Adjustment of AC Current Waveform supplied from Contact Charging Member to Charged Member FIG. 2 shows the shape of AC current waveform supplied from the magnetic brush 2 as a contact charging member to the photoreceptor 1 as a charged member. A block diagram of a control system in which the charge potential of the photosensitive member after charging is adjusted to a desired value by adjustment is shown.

That is, the positive component and the negative component of the AC current are separated by the diode d, and they are connected to the AC through the resistor R.
Monitor current. 71 and 72 are voltmeters. The AC current value is converted into a digital value by the A / D converters 81 and 82 and then input to the CPU 84. This AC
The maximum value Imax value in the current data is read and compared with the target value Imax in FIG. 4B stored in the ROM 85 by the CPU 84 as data, and the power source S1
A new waveform obtained by changing the AC voltage waveform output from the first AC voltage waveform by changing the inclination in the direction b from the one in FIG. 4A is used as a control signal.
It is output from U84. This control signal is the D / A converter 8
3 is converted into an analog value and sent to the power source S1 to output a new AC voltage waveform.

The above control is appropriately repeated, resulting in A
The I current of the C current waveform is adjusted so that both positive and negative become the I max target value. By controlling the AC current waveform in this way, the solid difference in the performance of the charging performance, which was a drawback of the conventional technology, is eliminated, and stable charging performance can be obtained in various environments even after a long time has passed from the initial stage. It became so.

<Embodiment 2> (FIGS. 5 and 6) In this embodiment, various types of A
Using the C voltage waveform, creating a variety of AC current waveform, similar to Imax values as in the first embodiment, this embodiment direct the AC current I _AC is the temporal average value instead of in FIG resistor R An ammeter was placed to measure positive and negative I _{AC +} and I _AC- , respectively. Further, as an index of the charging performance at that time, the rising speed of charging of the photoconductor (photosensitive drum) is set to the saturation potential −1.
The value of the peripheral potential (Fig. 5) was measured. It is considered that the smaller this value is, the better the charging ability is.

By considering the above results, it is possible to know what characteristics the AC current waveform has, which is suitable for charging the photosensitive member.

Of the results, the negative component is shown in FIG. From this, it is understood that the Imax value is more closely related to the charging performance than the AC current I _AC which is the temporal average value. Therefore, it can be seen that it is difficult to maintain the charging performance at the I _AC value as in Japanese Patent Laid-Open No. 6-138753.

In other words, it is necessary to have an electrical / physical structure in which an AC current waveform having a maximum Imax value is obtained.
It leads to p.

<Embodiment 3> (FIG. 7) Similar to Embodiment 2, positive and negative I _{AC +} and I _AC- are measured for AC voltage waveforms such as (1) to (3) in FIG. . Looking at FIG. 7, in the cases of (1) and (2), positive and negative asymmetric characteristics of Imax are shown.
This is in contrast to the property (3). When the waveform as shown in (3) is used, generally when charging the photoreceptor, it tends to converge to a potential near the value of the DC component of the voltage. However, when a photoconductor for direct charge injection such as that used in the present invention with waveforms such as (1) and (2) is used, the potential near the value of the DC component of the voltage is applied when the photoconductor is charged. It does not converge. Even if the DC component of the voltage is adjusted so as to converge to a desired potential under a certain condition, if the condition changes even a little, not only the potential does not converge to the desired potential, but control becomes impossible. As a result of our detailed experiments, it was found that the reason is the asymmetrical characteristic of Imax in FIG.

As described above, the characteristic that Imax is substantially symmetric with respect to positive and negative (when it is completely symmetrical, charging is difficult, and the balance is 0.7 ≦ Imax + / Imax− ≦ 1.4 is appropriate). By providing the toner, stable charging performance can be obtained both in the initial stage of copying and after a lapse of time. <Others> 1) The magnetic brush 2 as the contact charging member is a sleeve rotating type in the embodiment, but the conductive magnetic particles are magnetically attracted as the magnetic brush layer to the rotating magnet roller directly or through the conductive coat layer. It is also possible to use a magnet rotating type that is held by holding it. It may be a non-rotating magnetic brush body.

Instead of the magnetic brush, the contact charging member of other forms such as a conductive fur brush, a conductive roller, a conductive blade, etc. can be used.

In FIG. 8, in the image forming apparatus of the embodiment, a fur brush 2A made of a conductive fiber brush is used instead of the magnetic brush 2 as the contact charging member. The rest of the device configuration is the same as that of the embodiment, and thus the repetitive description is omitted. In the fur brush 2A of this example, the outer diameter of the core metal roller 24 having an outer diameter of 10 mm is 3 mm, the bristle length is 3 mm, the flocking density is 100,000 / inch ² , and the resistance value is 1 × 10 ⁶ Ω. It has a total outer diameter of 16 mm in which fibers 25 are planted in a brush shape.

This fur brush 2A is arranged with the conductive fiber brush portion 25 in contact with the surface of the photosensitive member 1. The width of the electrically conductive fiber brush portion 25 and the charging nip N of the photoconductor 1 is 7 mm.
And The fur brush 2A is configured to rotate in the counter direction with respect to the photoconductor 1.

Then, by applying a predetermined charging bias from the charging bias applying power source S1 to the fur brush 2A to rotate the fur brush 2A, the surface of the rotating photoconductor 1 is rubbed by the conductive fiber brush 25 to which the charging voltage is applied. The photoconductor 1 is uniformly charged to a desired potential by the injection charging method.

2) The image bearing member as the member to be charged is not limited to the electrophotographic photosensitive member, but may be a dielectric member or the like in electrostatic recording. The member to be charged is not limited to the image carrier.

3) In the present invention, the image forming apparatus positions the image portion formed on the surface of the member to be charged on the display unit for reading, and thereafter transfers the image to the recording medium without transferring the image. The surface of the charged body is cleaned and removed, and the body to be charged is repeatedly used to form a display image.An image forming display device or a direct type image forming apparatus, that is, a body to be charged such as photosensitive paper or electrostatic recording paper is charged. It may be an apparatus or the like that applies an image forming process including steps to execute image formation without a transfer step.

[0076]

As described above, according to the present invention, an AC voltage and a DC voltage are applied to a member to be charged having a charge injection layer on its surface.
A charging device for charging by contacting a contact charging member to which a superimposed voltage is applied, and an AC current waveform is controlled in a device including the charging device, that is, an alternating current supplied from the contact charging member to a body to be charged. Is monitored and the maximum value of the positive component and the maximum value of the absolute value of the negative component in one cycle of the waveform of the alternating current are variably adjusted, thereby reducing the charging performance, which is a drawback of the above-mentioned conventional technology. There is no individual difference, and stable charging performance can be obtained in various environments even after a long time has passed from the initial stage.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an example of an image forming apparatus.

FIG. 2 is a structural model diagram of a photoconductor and a conductive magnetic brush.

FIG. 3 Equivalent circuit diagram model diagram of injection charging mechanism

FIG. 4 is an explanatory diagram of current waveform adjustment.

FIG. 5 is a diagram showing the potential of the first round of the photoreceptor and the saturation potential of the photoreceptor.

FIG. 6 is an explanatory diagram of a relationship between a control parameter Imax and charging performance.

FIG. 7 is a diagram for explaining the importance of positive / negative balance of the control parameter Imax.

FIG. 8 is a schematic view when the contact charging member is a fur brush.

[Explanation of symbols]

1 ... Charged member (electrophotographic photoreceptor), 2. Contact charging member (magnetic brush), 3. Developing device, 4. Transfer roller, 5. Fixing device, 6. Cleaning device, 30.
· Process cartridge, S1 to S3 · · Bias applying power source, P · · Recording material (transfer material), 11 · · Aluminum drum substrate, 12 · · Charge transport layer, 13 · · Charge injection layer, 13a · · Conductive particles (SnO ₂ ), 71 ・ 72 ・ ・
Voltmeter, 81-83 ... A / D or D / A converter, 84
..CPU, 85..ROM

Claims (6)

(57) [Claims] 1. A charging device for charging an object to be charged having a charge injection layer on its surface by contacting a contact charging member to which a voltage obtained by superposing an AC voltage and a DC voltage is applied, the charging device comprising: By monitoring the AC current supplied to the charged body and variably adjusting the maximum value of the positive component and the maximum value of the absolute value of the negative component within one cycle of the waveform of this AC current, the charged body of the charged body is charged. A charging device characterized by setting a charging potential to a desired value. 2. The relationship between the maximum value Imax + of the positive component and the maximum value Imax- of the negative component absolute value within one cycle of the AC current waveform is 0.7 ≦ Imax + / Imax− ≦ 1.4. The charging device according to claim 1. 3. The charging device according to claim 1, wherein a magnetic brush composed of magnetic particles is used as the contact charging member. 4. The charging device according to claim 1, wherein brush fibers are used as the contact charging member. 5. An image forming apparatus for performing image formation by applying an image forming process including a step of charging the surface of the image carrier to the image carrier, the image carrier having a charge injection layer on the surface. An image forming apparatus, wherein the step means for charging the image carrier is the charging device according to any one of claims 1 to 4. 6. A process cartridge detachably attached to the main body of the image forming apparatus, wherein at least the contact charging member of the charging device according to claim 1, an image carrier, and a developing unit. A process cartridge containing at least one of a device and a cleaning device.