JP3232472B2 - Contact charging member, charging device, image forming apparatus, and process cartridge - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a contact charging member, a charging device, an image forming device (image recording device, image display device), and a process cartridge.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus such as an electrophotographic apparatus (copier, printer, facsimile, etc.), an electrostatic recording apparatus, etc., an electrophotographic photosensitive member, an electrostatic recording dielectric, a transfer material, and other charged objects have been used. Charges body (including static elimination)
As a means for performing this, a “corona charging method” using a corona charger has been used.

[0003] In recent years, charging devices of the "contact charging type" have been put into practical use.

[0004] An 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 opposite to a charged object in a non-contact manner, and the charged object is exposed to a corona emitted from the corona charger to bring the surface of the charged object to a predetermined polarity / potential. It is 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 a member to be charged, and a voltage is applied to the charging member to charge the surface of the member. The purpose is to achieve low ozone and low electric power. In particular, the roller charging method using a conductive roller as the charging member has stable charging, and furthermore, the amount of generated ozone is about one thousandth of that of the corona charger. In particular, it has been widely used in recent years.

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

More specifically, since charging is performed by discharging from the charging member to the member to be charged, the charging is started by applying a voltage higher than a certain threshold voltage. As an example, an electrophotographic OPC having a thickness of 25 μm as a member to be charged is described.
When the charging roller is pressed against the photoconductor,
When a voltage of about 640 V or more is applied, the surface potential of the photoconductor starts to increase, and thereafter, the surface potential of the photoconductor increases linearly with a slope of 1 with respect to the applied voltage. 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 to have Vd + Vth
Therefore, a DC voltage (DC voltage) higher than the required surface potential Vd is required. The method of charging by applying only the DC voltage to the contact charging member in this manner is called a DC bias application method (DC charging method).

However, in the DC bias application method, charging starts when the film thickness changes due to the resistance value of the contact charging member fluctuating due to environmental fluctuations, etc. Since the voltage Vth fluctuated, it was difficult to set the charging potential of the photoconductor to a desired value.

Therefore, as disclosed in Japanese Patent Application Laid-Open No. 63-149669, a DC voltage corresponding to a desired surface potential Vd of a member to be charged is set to 2 × Vth or more as disclosed in JP-A-63-149669. AC bias application method (AC charging method) in which an oscillating voltage (a voltage whose voltage value changes periodically with time) on which an AC component (AC voltage component) having a peak-to-peak voltage is superimposed is applied to a contact charging member to perform charging. Is used. This is for the purpose of a leveling effect of the potential caused by the AC component. The potential of the member to be charged converges to Vd, which is the center of the peak of the AC voltage, and is not affected by disturbances such as the environment. .

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

C) Contact Injection Charging Method As a new charging method, Japanese Unexamined Patent Publication No. Hei 6-3921 discloses a charging method by directly injecting electric charge to a member to be charged (photosensitive member).

In this contact injection charging system, a member having a charge injection layer on its surface is used as a member to be charged, and a voltage is applied to a contact charging member such as a charging roller, a charging brush, a charging magnetic brush, and the like. This is a method of injecting charges into conductive particles of a charge injection layer on the surface of the photoreceptor to perform charging.

FIG. 7 shows a schematic configuration of an example of the charging device 2 of the contact injection charging system. (A) is a cross-sectional model diagram,
(B) is a vertical cross-sectional model diagram omitting an intermediate portion, and (c) is a graph of a photosensitive member charging potential distribution along the longitudinal direction of the charging nip.

Reference numeral 1 denotes a rotating drum type electrophotographic photosensitive member as a member to be charged, which is driven to rotate at a predetermined peripheral speed in a clockwise direction indicated by an arrow. This photoreceptor 1 has a charge injection layer on the surface.

A contact charging member 20 is a roller type magnetic brush in this embodiment. This magnetic brush 20 is
1a, a cylindrical magnet 21 fixed and supported concentrically on the mandrel, and a non-magnetic electrode sleeve (feeding portion) 22 fitted concentrically on the mandrel 21a so as to rotate freely around the mandrel 21a;
A magnetic brush layer (magnetic brush portion) 23 of a magnetic carrier (magnetic particles) formed on the outer peripheral surface of the electrode sleeve by being attracted and held by the magnetic force of the magnet 21 inside the sleeve.

The magnetic brush 20 as the contact charging member
Is substantially parallel to the photoconductor 1 and the magnetic brush layer 23 is
A charging nip N having a predetermined width is formed on the surface and is arranged so as to be in contact with the surface. The electrode sleeve 22 is rotationally driven in the charging nip N in the direction indicated by the arrow (counter direction) opposite to the rotational direction of the photoconductor 1, and the magnetic brush layer 23 is accordingly driven.
Also rotate in the same direction to rub the surface of the photoconductor 1.

A predetermined charging bias is applied to the electrode sleeve 22 of the magnetic brush 20 from a charging bias application power supply S1, and the surface of the photoconductor 1 is charged to a predetermined surface potential by a contact injection charging method.

In this contact injection charging system, since no discharge phenomenon is used, the voltage required for charging is only the desired photoconductor surface potential Vd, and the amount of generated ozone is also B).
Of the contact charging method, which is 1/10 or less of the roller charging method.

In the case of this contact injection charging system, a DC bias application system in which only a DC voltage is applied to the contact charging member to perform charging, and an AC bias in which charging is performed by applying a voltage having an AC component to the contact charging member. There is an application method. In this case, since the AC bias application method shows more stable charging performance even when the contact charging member is deteriorated in durability or changes in the environment than the DC bias application method, recently, especially the contact injection charging method and the AC bias application method. Research on a method (AC injection charging) is underway.

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

The reason for this is that, in the case where there is always a gap where a discharge is likely to occur between a round solid charging roller and a member to be charged as in the roller charging method, the magnetic brush of the magnetic carrier is particularly used for the contact charging member. When a DC or AC bias is applied, the charged and fluid magnetic carrier constituting the magnetic brush is attracted to the opposite charge injected into the member to be charged and moves in a large amount when a DC or AC bias is applied. This is probably because the magnetic brush and the member to be charged are completely in close contact with each other, and there is no gap that discharges, because a larger contact area is formed than in the roller charging method.

[0024]

However, when the magnetic brush 20 is used as the contact charging member as in the above example, the magnetic carrier at the longitudinal end of the magnetic brush layer 23 is
In the contact portion between the magnetic brush and the photoreceptor to be charged, that is, in the charging nip, the magnetic brush is pushed out in the longitudinal direction (region D in FIG. 7B) (direction of arrow A).

In the region D, since the magnetic brush layer 23 is not in contact with the photosensitive member 1, the surface of the photosensitive member is not charged, and the surface potential of the photosensitive member is considerably lower than the charged potential. However, since a voltage corresponding to the charged potential (eg, -700 V) is applied to the magnetic brush, a potential difference is generated between the magnetic brush and the surface of the photoreceptor, and the magnetic carrier constituting the magnetic brush layer 23 is applied to the magnetic carrier. Since a force (in the direction of arrow B) generated by the injection of the electric charge from the electrode sleeve 22 as the power supply portion acts, the magnetic carrier adheres to the photoreceptor surface.

Since this occurs at a place where a sharp potential gradient (part E in FIG. 7C) exists, such as near the end of the charging member, a DC bias is applied to make the potential gradient gentle. As a countermeasure in the case of the system, it has been proposed that the longitudinal end of the power supply portion to the magnetic brush be formed of a member electrically insulated from the power supply portion, but AC bias application where current flows even in the insulator. It was found that the effect was small in the case of the method.

This phenomenon is particularly conspicuous in injection charging performed by a magnetic brush composed of a medium-resistance magnetic carrier. This does not occur when the brush is rubbed with a high-resistance magnetic brush or simply a magnetic brush.

In the case of a magnetic brush such as two-component development, the development contrast (the difference between the development potential and the photoconductor surface potential) is usually smaller than the charging contrast (the difference between the charging potential and the photoconductor surface potential). The adhesion of a magnetic carrier to a photosensitive member as a member to be charged is not so remarkable as when a magnetic brush is used for charging. Further, when a magnetic brush is used for development, toner is present in the magnetic brush, and the toner adheres to the photoconductor before the magnetic carrier. This is because the toner is lighter than the magnetic carrier and has a higher resistance because of its higher resistance. Therefore, the toner easily adheres to the photoconductor by electric force. Therefore, the magnetic carrier rarely adheres to the photoconductor.

In the magnetic brush charging, when the magnetic carrier adheres to the photoreceptor, the magnetic carrier of the magnetic brush serving as a charging member gradually decreases, and an image failure due to a charging failure or the like occurs gradually. There was a disadvantage that it could not be used.

Therefore, the present invention relates to a charging process using a magnetic brush as a contact charging member, and a contact injection charging method.
Even in the case of the C bias application method, the magnetic carrier (magnetic particles), which is extruded outward in the longitudinal direction by the charging nip and constitutes the magnetic brush, is substantially prevented from adhering to the member to be charged and being carried away. It is another object of the present invention to prevent a decrease in chargeability due to a decrease in magnetic carriers of a magnetic brush over a long period of time.

[0031]

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

[0032] (1) the surface is brought into contact with the charge-receiving member having a charge injection layer, by applying an AC voltage or AC voltage component is a contact charging member for charging the member to be charged, said contact charging member is a magnetic A magnetic brush portion composed of particles,
A power supply unit for supplying power to the magnetic brush unit;
Provided at the longitudinal end and between the magnetic brush part and the power supply part.
A charge potential attenuating function section,
Contact charging member function unit, characterized in <br/> Rukoto attenuates gradually charge potential of the member to be charged after charging by said magnetic brush portion in the longitudinal end direction of the magnetic brush portion.

[0033] (2) the charging potential attenuation function portion in the dielectric
Contact charging member according to (1) that there is.

(3) The capacitance of the dielectric is:
(2) The contact charging member according to (2), wherein the contact charging member decreases in size in the direction of the longitudinal end.

(4) The contact charging member according to (2), wherein the thickness of the dielectric increases as it approaches the longitudinal end.

(5) The contact charging member according to (2), wherein the magnitude of the dielectric constant of the dielectric material decreases in the direction of the longitudinal end.

[0037] (6) the dielectric is a foam fleshy material, the contact charging member according to foaming rate toward the longitudinal end direction, characterized in that the increase (2).

[0038] (7) the magnitude of the capacitance of said magnetic brush portion constituting the longitudinal edges near the magnetic brush is constituted that the charging potential attenuation function portion so as to become smaller toward the longitudinal end direction The contact charging member according to (1), wherein

(8) The contact charging member according to (7), wherein the magnitude of the dielectric constant of the magnetic particles constituting the vicinity of the longitudinal end of the magnetic brush decreases in the direction of the longitudinal end.

[0040] (9), wherein the charging potential charge potential attenuation in the longitudinal edge near the front Symbol magnetic brush portion Ru good attenuation function portion to the longitudinal end direction is less attenuation gradient 1 kV / mm The contact charging member according to any one of (1) to (8).

(10) In a charging device which performs charging by bringing a contact charging member, to which an AC voltage or a voltage including an AC voltage component is applied, into contact with a member to be charged having a charge injection layer on the surface thereof, the contact charging member comprises ( A charging device comprising the contact charging member according to any one of 1) to 9).

[0042] (11) by applying the image forming process comprising charging the image bearing member surface to an image bearing member having a charge injection layer on the surface is an image forming apparatus for executing image formation, before
An image forming apparatus wherein the process means for charging the serial image bearing member is a charging device according to the (10).

[0043] (12) a photoreceptor the image bearing member has a charge injection layer on the surface, the effective width of the magnetic brush portion,
The image forming apparatus according to (11), wherein the width is shorter than a coating width of a photosensitive layer of the photoconductor.

[0044] (13) a process cartridge is detachably attached to the image forming apparatus main body, (1)乃
A process cartridge accommodating the contact charging member according to any one of ( 1 ) to (9) and at least one of an image carrier, a developing device, and a cleaning device.

[0045] (14) the image bearing member is a photosensitive member having a charge injection layer on the surface, the effective width of the magnetic brush portion is pre
A process cartridge according to serial and being shorter than the coating width of the photoconductor of the photosensitive layer (13). <Operation> The present invention relates to a charging device provided between a magnetic brush portion and a power supply portion.
The attenuating function of the charged object after charging by the magnetic brush
The charge potential is gradually attenuated toward the longitudinal end of the magnetic brush.
The invention is characterized in that
Prevents reduction of charging property due to reduction of magnetic particles in brush section
Can be That is, in a charging process using a magnetic brush as a contact charging member, a magnetic brush (magnetic brush) is used.
A) a charging potential attenuating function section is provided at a longitudinal end of the magnetic brush to gradually attenuate the charging potential of the charged body after being charged by the magnetic brush toward the longitudinal end near the longitudinal end of the magnetic brush. As a result, the potential of the end of the magnetic brush and the potential of the surface of the member to be charged contacting the position become equal, so that the magnetic brush was pushed out of the longitudinal direction by the charging nip which is the contact portion between the magnetic brush and the member to be charged. Even when the magnetic particles (magnetic carrier) are of the contact injection charging type and the AC bias application type,
The magnetic brush does not remarkably adhere to the surface of the member to be charged, and a decrease in chargeability due to a decrease in magnetic particles of the magnetic brush can be prevented for a long time. That is, even when the magnetic brush is used for a long time, the magnetic particles of the magnetic brush do not decrease, so that a stable charging property is secured and maintained.

A good effect was obtained when the attenuation gradient of the charging potential in the vicinity of the longitudinal end of the magnetic brush in the direction of the longitudinal end was 1 kV / mm or less.

Specific means of a charging potential attenuating function unit for gradually attenuating the charging potential of the member to be charged after charging by the magnetic brush in the direction of the longitudinal end near the longitudinal end of the magnetic brush. As a configuration, as described in the above items (2) to (8),. At the longitudinal end of the magnetic brush, a dielectric is disposed between the magnetic brush portion and a power supply portion for the magnetic brush portion, and the thickness of the dielectric is increased in the longitudinal end direction. By reducing the magnitude of the dielectric constant in the longitudinal end direction, or by increasing the foaming degree of the dielectric material to a foamed material and increasing in the longitudinal end direction, etc. .. The magnitude of the capacitance of the dielectric material decreases in the direction of the longitudinal end (the charging potential decreases as the capacitance decreases); The magnitude of the capacitance of the magnetic brush forming the vicinity of the longitudinal end of the magnetic brush is reduced by reducing the magnitude of the dielectric constant of the magnetic particles constituting the vicinity of the longitudinal end of the magnetic brush in the direction of the longitudinal end. Means and configuration such as reducing the size in the longitudinal end direction can be adopted.

[0048]

BEST MODE FOR CARRYING OUT THE INVENTION

<Embodiment 1> (FIGS. 1 to 3) (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 embodiment is a laser beam printer using a transfer type electrophotographic process, a contact injection charging type / AC bias applying type, and a process cartridge attaching / detaching type.

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

Reference numeral 20 denotes a conductive magnetic brush as a contact charging member brought into contact with the photosensitive member 1, and S1 denotes a power supply for applying a charging bias to the magnetic brush. This magnetic brush 20,
The charging device 2 is constituted by the charging bias application power supply S1 and the like. The details of the magnetic brush 20 will be described later in section (3).

In the course of rotation, the photosensitive member 1 is subjected to a uniform primary charging process of a predetermined polarity and potential by a conductive magnetic brush 20 to which a voltage is applied, by a contact injection charging system and an AC bias application system, and then the image exposure means In the case of this example, scanning by a laser beam intensity-modulated according 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 the exposure L, an electrostatic latent image corresponding to the target image information is formed on the peripheral surface of the rotating photoconductor 1.

The electrostatic latent image is developed by the developing device 3 as a toner image. In this embodiment, the developing device 3 is a reversal developing device using a magnetic-component insulating toner (negative toner).
Reference numeral 3a denotes a non-magnetic developing sleeve having a diameter of 16 mm and containing a magnet 3b. The developing sleeve 3a is coated with the above-described negative toner, and the distance from the surface of the photoconductor 1 is set to 300 μm.
m, the photosensitive member 1 is rotated at a constant speed, and a developing bias voltage is applied to the sleeve 3a from a developing bias power source S2. A voltage obtained by superimposing 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 is used, and jumping development is performed between the sleeve 3a and the photosensitive member 1.

On the other hand, a transfer material P as a recording material (recording medium) is supplied from a paper supply unit (not shown),
At a predetermined timing into a pressure contact nip portion (transfer portion) T with a transfer roller 4 having a medium resistance, which is a contact transfer means contacted with a predetermined pressing force. A predetermined transfer bias voltage is applied to the transfer roller 4 from a transfer bias application power source S3. The transfer material P introduced into the transfer portion T is conveyed by sandwiching the transfer portion T, and the toner image formed and carried on the surface of the rotary photoreceptor 1 is sequentially transferred by electrostatic force and pressing force. Will be done. In this embodiment, a transfer roller 4 having a resistance value of 5 × 10 ⁸ Ω is used,
Transfer was performed by applying a DC voltage of 0V.

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

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

In the image forming apparatus of this embodiment, the four process devices of the photosensitive member 1, the contact charging member 20, the developing device 3, and the cleaning device 6 are contained in the cartridge 30 and are collectively attached to and detached from the main body of the image forming device. It is an exchangeable cartridge type device. Reference numerals 31 denote positioning support members for positioning the process cartridge 30 in the printer main body. The combination of the process devices included in the process cartridge 30 is not limited to the above.

(2) Photoreceptor 1 The photoreceptor 1 of the present example as a member to be charged has a surface in which the following first to fifth functional layers are provided in order from the bottom on an aluminum drum base. 30 mm diameter with charge injection layer
, And is rotatably driven at a process speed (peripheral speed) of 100 mm / sec.

First layer: an undercoat layer, which is a conductive layer having a thickness of about 20 μm and provided for smoothing defects of the aluminum drum base and for preventing the occurrence of moire due to reflection by laser exposure. is there.

Second layer: a positive charge injection preventing layer, which serves to prevent positive charges injected from the aluminum drum base from canceling out negative charges charged on the surface of the photoreceptor. This is a medium resistance layer having a thickness of about 1 μm, the resistance of which 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 positive and negative charge pairs by being exposed to a laser.

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

Fifth layer: 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 of a material in which antimony-doped SnO ₂ particles having a particle diameter of about 0.03 μm and having a reduced resistance are dispersed in a resin by 70% by weight.
The coating solution thus prepared was applied to a thickness of about 2 μm by a dipping coating method to form a charge injection layer.

In the structural model diagram of the photoconductor 1 and the conductive magnetic brush 20 shown in FIG. 2A, 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 this charge. The conductive particles (S
nO ₂ ). The undercoat layer, the positive charge injection preventing layer, and the charge generation layer are omitted in the figure.

(3) Contact Charging Member 20 As shown in the structural model diagram of FIG. 2, the magnetic brush 20 as a contact charging member is provided with a magnet 21 fixedly supported on a mandrel 21a and a rotatable outer fitting on the magnet 21. Also, a non-magnetic electrode sleeve 22 having a diameter of 16 mm as a power supply portion, and a charging potential attenuating function provided at the longitudinal end of the electrode sleeve (more precisely, in the vicinity corresponding to the longitudinal end of the magnet 21, the same applies hereinafter). A magnetic brush layer (magnetic brush portion) 23 of a magnetic carrier (magnetic particles) adhered and held by the magnetic force of the magnet 21 on the outer peripheral surface of the electrode sleeve 22 including a part of the charged potential attenuation function unit 24. Do it. The magnetic flux density by the magnet 21 on the electrode sleeve 22 is 800 ×
10-4T (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 photosensitive member 1. In this example, the magnetic carrier amount of the magnetic brush layer 23 is about 10 g, and the gap at the charging nip N between the electrode sleeve 22 and the photoconductor 1 is 500 μm. Electrode sleeve 22
Is rotated in the direction indicated by the arrow in the opposite direction (counter direction) of the rotation of the photoconductor 1 at the charging nip N, and the rotation of the electrode sleeve 22 causes the rotation of the magnetic brush layer 23 to slide the surface of the photoconductor 1. Rub.

The electrode sleeve 22 of the magnetic brush 20 has a DC voltage of -700 V from the charging bias application power source S1.
_PP = 800 V, and the charging bias V _DC + V _AC to AC voltage of a frequency 1kHz is superimposed is applied, the outer peripheral surface of the rotating photosensitive member 1 at uniform contact injection charging method · AC bias method substantially -700V Be charged.

Here, the peripheral speed ratio between the magnetic brush 20 and the photosensitive member 1 is defined by the following equation.

Circumferential speed ratio% = (magnetic brush peripheral speed−photosensitive member peripheral speed) / photosensitive member peripheral speed × 100 * The peripheral speed of the magnetic brush 20 is a negative value in the case of counter rotation.

Since the magnetic brush is stopped when the peripheral speed ratio is -100%, the shape of the magnetic brush stopped on the surface of the photoreceptor directly becomes a charging failure and appears on an image. In the forward rotation, the rotational speed of the magnetic brush is increased if an attempt is made to obtain the same peripheral speed ratio as in the counter direction. When the magnetic brush contacts the photoconductor at a slow speed in a forward rotation, the magnetic carrier of the magnetic brush 20 tends to adhere to the photoconductor 1. Therefore, the peripheral speed ratio is preferably -100% or less, and in this example, it was -150%.

A) Magnetic Carrier As the magnetic carrier constituting the magnetic brush layer 23, the following can be used.

[0071] A resin and magnetic powder such as magnetite are kneaded to form particles, or mixed with conductive carbon or the like to adjust the resistance value. Sintered magnetite, ferrite, or those whose resistance has been adjusted by reducing or oxidizing them. The above magnetic particles are coated with a coating material (such as a phenol resin in which carbon is dispersed) having a resistance adjusted or plated with a metal such as Ni to have an appropriate resistance value. If it is too high, the charge cannot be uniformly injected into the photoreceptor, resulting in a fog image due to minute charging failure. If the temperature is too low, when there is a pinhole on the surface of the photoreceptor, current concentrates on the pinhole and the charging voltage drops, so that the surface of the photoreceptor cannot be charged, resulting in charging nip-shaped charging failure.

Therefore, the resistance value of the magnetic carrier is 1
× 10 ⁴ to 1 × 10 ⁷ Ω is desirable.

As for the magnetic characteristics of the magnetic carrier, it is better to increase the magnetic binding force in order to prevent the magnetic carrier from adhering to the photoreceptor, and the saturation magnetization is desirably 50 (A · m ² / kg) or more.

Actually, the magnetic carrier 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 58 (A · m ² / kg).

In this example, the method of measuring the resistance value, the method of measuring the particle size, the method of calculating the average particle size, and the method of measuring the saturation magnetization of the magnetic carrier are as follows.

Measurement method of resistance value: The resistance value of the magnetic carrier is determined by applying a voltage to a metal cell (bottom area: 228 mm ² ).
2 g of the magnetic carrier is added thereto and then weighted, and the voltage is increased to 1 to 10
The measurement was performed by applying 00V.

The average particle size of the magnetic carrier is indicated by the maximum chord length in the horizontal direction.
00 or more were randomly selected, the diameter was actually measured, and the arithmetic average was taken to obtain the magnetic carrier particle diameter in the present invention.

For the measurement of the magnetic characteristics of the magnetic carrier, a DC magnetization BH characteristic automatic recording apparatus BHH-5 manufactured by Riken Denshi Co., Ltd. was used.
0 can be used. At this time, the diameter (inner diameter) is 6.5.
A cylindrical carrier having a height of 10 mm and a height of 10 mm is filled with a magnetic carrier at a load of about 2 g weight, and the saturation magnetization is measured from the BH curve of the magnetic carrier while the magnetic carrier does not move in the container.

B) Principle of Charging The charge injection charging is a medium-resistance contact charging member for injecting charges onto the surface of a member to be charged having a medium resistance surface resistance. In this embodiment, a photosensitive member as a member to be charged is used. Instead of injecting charge into the trapping potential of the surface material described above, the charge is charged by charging the conductive particles 13a of the charge injection layer 13.

More specifically, as shown in the equivalent circuit diagram of FIG. 3, the charge transport layer 12 is made of a dielectric material, the aluminum drum base 11 and the conductive particles (SnO ₂ ) 13 in the charge injection layer 13.
This is based on the theory that a small capacitor having a as both electrode plates is charged with electric charge by the contact charging member 2.

At this time, the conductive particles 13a are electrically independent of each other and form a kind of minute float electrode. Therefore, macroscopically, the photoreceptor surface appears to be charged and charged to a uniform potential, but in reality, the countless minute charged conductive particles 13a cover the photoreceptor surface. It 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 an electrostatic latent image can be held.

C) Charge Potential Attenuation Function 24 The charge potential attenuator 24 provided at the longitudinal end of the electrode sleeve 22 (near the longitudinal end of the magnet 21), which is the power supply part of the magnetic brush 20, The magnetic nip N, which is a contact portion between the brush 20 and the photoreceptor 1 as a member to be charged, functions to prevent the magnetic carrier extruded to the outside of its length from adhering and transferring to the photoreceptor 1.

In this embodiment, the charge potential attenuating function section 24 is provided with a dielectric member layer between the magnetic brush layer 23 and the electrode sleeve 22 serving as a power supply section for the magnetic brush layer at the longitudinal end of the magnetic brush. By increasing the thickness of the dielectric member layer in the longitudinal end direction, the capacitance of the dielectric member layer is decreased in the longitudinal end direction. is there.

More specifically, the dielectric constant 3 as a dielectric member
A polyethylene terephthalate tape (trade name, Mylar) is wound around the outer peripheral surface of the longitudinal end of the electrode sleeve 22 in an annular shape such that the thickness increases from 0 mm to 1 mm in a tapered cross-section in the longitudinal end direction. It was done.

The outer peripheral surface of the electrode sleeve 22 (a length range substantially corresponding to the length of the magnet 21) including a part of the dielectric member layer 24 serving as the charge potential attenuating function section is provided. The magnetic brush layer 23 is formed by attaching and holding the magnetic carrier by the magnetic force.

The longitudinal (width) range of the dielectric member layer 24 serving as the charge potential attenuating function section is set from the inside of the magnetic brush layer 23 with a certain margin beyond the longitudinal end of the magnetic brush layer 23, and the magnetic brush layer 23 It is sufficient if the magnetic carrier is extruded. In this embodiment, the dielectric member layer 24 has a width of 20 mm from the inside of 5 mm from the longitudinal end of the magnetic brush layer 23, but these are also due to the resistance value of the magnetic carrier and the dielectric constant of the dielectric member 24. The value should not be limited to this value, but should be adjusted so that the photoconductor potential near the longitudinal end of the magnet 21 is gradually attenuated in the direction of the longitudinal end so that the magnetic carrier does not adhere. A favorable effect was obtained when the attenuation gradient of the charging potential in the direction of the longitudinal end near the longitudinal end of the magnetic brush was 1 kV / mm or less.

Conventionally, in the charging nip N, the magnetic carrier that has been pushed out to the outside of the longitudinal direction (D region) where the surface of the photoreceptor is not at the charging potential is changed to an electric force by the electric charge injected into the magnetic carrier. Although it adhered to one surface, by adopting this configuration, the conductive path between the magnetic carrier and the electrode sleeve 22 as a power supply portion was gradually cut off in the longitudinal end direction, and the photoconductor charged after being charged by the magnetic brush Potential
As shown in the graph of the measurement result of the charged potential of the photoreceptor after charging shown in FIG. 2C, the magnetic brush gradually attenuates in the direction of the longitudinal end in the vicinity of the longitudinal end of the magnetic brush. Since the potential of the photoreceptor surface in contact with that position becomes equal, no charge is injected into the magnetic carrier,
Even in the case of the contact injection charging system and the AC bias application system, the magnetic carrier does not significantly adhere to the surface of the photoreceptor 1 from the magnetic brush, so that a decrease in chargeability due to a decrease in the magnetic carrier of the magnetic brush can be prevented. In addition, stable chargeability was secured and maintained even when used for a long time.

In the measurement of the charged potential of the photoreceptor after charging shown in FIG. 2C, the probe of the Trek surface voltmeter Model 344 is disposed at a position about 2 mm away from the photoreceptor surface instead of the developing device at the developing position. I went in.

In this embodiment, the dielectric member layer 24 as the charge potential attenuating function portion is made of polyethylene terephthalate, but need not be limited to this, and may be made of a dielectric material such as polyester tape, Teflon or phenol. There was an effect even if it was constituted by applying a resin.

In this embodiment, the effective width of the magnetic brush (the effective length range of the magnetic brush layer 23) is shorter than the application width of the photosensitive layer of the photosensitive member. Due to this dimensional relationship, a portion where the charging potential changes abruptly does not exist on the surface on the side to be charged, so that extra magnetic carrier adhesion can be prevented.

<Embodiment 2> (FIG. 4) Similarly, in this embodiment, the charging potential attenuating function unit 24 is provided at the longitudinal end of the magnetic brush by the magnetic brush layer 23 and the electrode sleeve serving as a power supply unit for the magnetic brush layer. In this embodiment, the dielectric member layer 24 is formed by disposing the dielectric member layer 24 between the dielectric member layers 22 as shown in the model diagrams of FIGS. Four dielectric materials 24a and 24 having different rates
By arranging b · 24c · 24d side by side so that the dielectric constant becomes smaller from the largest in the longitudinal end direction, the magnitude of the capacitance in the whole dielectric member layer 24 is increased in the longitudinal end direction. It becomes smaller as it goes.

In this example, a phenol resin (dielectric constant 5) as the dielectric material 24a, polyethylene terephthalate (dielectric constant 3) as 24b, polyethylene (dielectric constant 2) as 24c, and polytetrafluoroethylene (Teflon) as 24d. , Dielectric constant 2).

As a whole, in the present embodiment, the dielectric member layer 24 has a width of 20 mm from the inside of 5 mm from the longitudinal end of the magnetic brush layer 23 and a thickness of 200 μm, but is not limited to this value.

By adopting this configuration, the conductive path between the magnetic carrier and the electrode sleeve 22 as the power supply portion is gradually cut off toward the longitudinal end, as in the case of the first embodiment. As shown in the graph of FIG. 4B, the charged potential of the photoconductor after charging is gradually attenuated near the longitudinal end of the magnetic brush in the direction of the longitudinal end (attenuation). When the gradient is 1 kV / mm or less), the potential of the end of the magnetic brush and the surface of the photoreceptor in contact with the position become equal, so that no electric charge is injected into the magnetic carrier. Even in the case of the bias application method, the magnetic carrier does not significantly adhere to the surface of the photoreceptor 1 from the magnetic brush, thereby preventing a decrease in chargeability due to a decrease in the magnetic carrier of the magnetic brush. , Stable charging property even when used for long-term is ensured and maintained.

As in the present embodiment, even when the photoconductor potential near the longitudinal end of the magnetic brush (corresponding to the longitudinal end of the magnet 21) gradually attenuates stepwise toward the longitudinal end, the present invention can be applied. The effect is obtained.

<Embodiment 3> (FIG. 5) In this embodiment, similarly, the charging potential attenuating function unit 24 is provided at the longitudinal end of the magnetic brush by the magnetic brush layer 23 and the electrode sleeve serving as a power supply unit for the magnetic brush layer. In this embodiment, the dielectric member layer 24 has a longitudinal shape as shown in the model diagrams of FIGS. 5A and 5C. foaming rate as it goes in the end direction is gradually increased by gradually such foamed resin (the total air quantity ratio of the bubble contained in per unit body volume) (such as expanded polystyrene) is constructed by winding in a ring.

The charge potential attenuating function section (dielectric member layer)
In the foamed resin layer 24, the degree of foaming gradually increases in the longitudinal end direction (for example, the degree of foaming is 0.1 → 0.4), so that the magnitude of the dielectric constant decreases as it goes in the longitudinal end direction. As a result, the magnitude of the capacitance of the entire dielectric member layer 24 decreases as it goes toward the longitudinal end.

In this embodiment, the dielectric member layer 24 has a width of 20 mm from the inside of 5 mm from the longitudinal end of the magnetic brush. However, the present invention is not limited to this value. It is necessary to adjust the dielectric constant and foaming degree of the magnet 21 so that the potential of the photoconductor near the longitudinal end of the magnet 21 is gradually attenuated in the direction of the longitudinal end so as not to adhere to the magnetic carrier. Is an important point.

With this configuration, as in the first embodiment, the conductive path between the magnetic carrier and the electrode sleeve 22 as the power supply portion is gradually cut off toward the longitudinal end, and the magnetic brush is used. As shown in the graph of FIG. 5B, the charged potential of the photoconductor after charging is gradually attenuated near the longitudinal end of the magnetic brush in the direction of the longitudinal end (attenuation). When the gradient is 1 kV / mm or less), the potential of the end of the magnetic brush and the surface of the photoreceptor in contact with that position become equal, so that no charge is injected into the magnetic carrier. Even in the case of the bias application method, the magnetic carrier does not significantly adhere to the surface of the photoreceptor 1 from the magnetic brush, thereby preventing a decrease in chargeability due to a decrease in the magnetic carrier of the magnetic brush. , Stable charging property even when used for long-term is ensured and maintained.

In the present embodiment, the foamed resin material constituting the charge potential attenuating function section (dielectric member layer) 24 and whose foaming degree gradually decreases toward the longitudinal end portion is, for example, a foaming agent. Can be produced by controlling and changing the dispersion state.

<Other Embodiments> 1) The charged potential of the member to be charged after being charged by the magnetic brush,
The means and configuration of the charged potential attenuating function unit for making the magnetic brush gently attenuate in the direction of the longitudinal end near the longitudinal end of the magnetic brush besides using a dielectric member as in the first to third embodiments. Can also be variously configured. For example, the capacitance of the magnetic brush forming the vicinity of the longitudinal end of the magnetic brush is reduced by reducing the magnitude of the dielectric constant of the magnetic carrier constituting the vicinity of the longitudinal end of the magnetic brush layer 23 toward the longitudinal end. And the like may be adopted such that the size is reduced as going toward the longitudinal end.

As the magnetic carrier, for example, those having various dielectric constants can be prepared by containing and dispersing a magnetic substance in various resins having different dielectric constants.

The dielectric constant of the magnetic carrier was used based on the measured value (or characteristic value) of the resin alone.

2) Magnetic brush 20 as contact charging member
Is a sleeve rotating type in the embodiment, but may be a magnet rotating type in which conductive magnetic particles are magnetically attracted and held as a magnetic brush layer directly on a rotating magnet roller or via a conductive coating layer. .

3) The magnetic brush as the contact charging member may be a non-rotating magnetic brush. FIG. 6 (a)
And (b) show such examples, respectively.

(A) A magnetic brush 20 as a contact charging member is composed of a pair of low carbon steel horizontal yokes by sandwiching the magnet on both longitudinal sides of a horizontal rectangular magnet 21 extending in the direction perpendicular to the drawing. The magnetic carriers are attracted and held as magnetic brush portions 23 by the magnetic force between the gaps at the opposing gaps (gap) of the two yoke members 22. The magnetic brush portion 23 is fixedly arranged by forming a magnetic nip N having a predetermined width on the surface of the photoreceptor 1 as a member to be charged. A charging bias is applied to the magnetic brush unit 23 from the power supply S1 via the yoke material 22.

(B) shows the two yoke members 22.2
The magnetic carrier 23 is provided with a magnetic carrier at the tip of
The magnetic brush portions 23 are attracted and held as 23.
23, a charging nip NN having a predetermined width is formed on the surface of the photoreceptor 1 as a member to be charged and brought into contact with the magnetic brush 2.
0 is fixedly arranged. A charging bias is applied to the magnetic brush parts 23 from the power source S1 via the yoke members 22.

The non-rotating magnetic brush 20 is provided with a charge potential attenuating function at the longitudinal end of the magnetic brush in the same manner as in the first to third embodiments, and the present invention is also applied to the present invention. Of course, it can be applied.

4) As a waveform of the AC voltage or the AC voltage component, a sine wave, a rectangular wave, a triangular wave, or the like can be used as appropriate. Further, the AC bias naturally includes, for example, a rectangular wave voltage formed by periodically turning on and off the DC power supply. At this time, controlling the AC bias means controlling the peak-to-peak voltage. As described above, a bias whose voltage value periodically changes can be used as the AC bias.

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

6) In the image forming apparatus of the present invention, the image portion formed on the surface of the member to be charged, such as a rotating belt type, is positioned on the display section for reading, and then the image is transferred to a recording medium. Without performing cleaning and removal from the surface of the member to be charged, the member to be charged is repeatedly used for forming a display image, an image forming display device, and a direct type image forming device,
That is, an apparatus or the like that applies an image forming process including a charging step to a member to be charged such as photosensitive paper or electrostatic recording paper and executes image formation without a transfer step may be used.

[0112]

As described above, according to the present invention, in the charging process using the magnetic brush as the contact charging member, even in the case of the contact injection charging system and the AC bias application system, the charging nip extends outward in the longitudinal direction. The extruded magnetic carriers (magnetic particles) constituting the magnetic brush are substantially prevented from adhering to and being carried away from the member to be charged, and a reduction in the chargeability due to a decrease in the magnetic carriers of the magnetic brush for a long period of time. Can be prevented.

Therefore, in an image forming apparatus or a process cartridge provided with a charging device using a magnetic brush as a contact charging member, good image quality free from a decrease in chargeability due to a reduction in magnetic carrier of the magnetic brush is obtained. An image of high quality can be formed stably over a long period of time.

[Brief description of the drawings]

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

FIG. 2 is a configuration explanatory view of a magnetic brush as a contact charging member.

FIG. 3 is a diagram illustrating the principle of contact injection charging.

FIG. 4 is a configuration explanatory view of a magnetic brush as a contact charging member according to a second embodiment.

FIG. 5 is an explanatory diagram of a configuration of a magnetic brush as a contact charging member according to a third embodiment.

FIGS. 6 (a) and (b) are model views of a configuration example of a non-rotating magnetic brush, respectively.

FIG. 7 is a diagram illustrating a configuration of a magnetic brush as a conventional contact charging member.

DESCRIPTION OF SYMBOLS 1. Photoreceptor as an object to be charged, 11: Aluminum drum base, 12: Charge transport layer, 13, Charge injection layer, 13a, conductive particles, 2, charging device, 20 ..Magnetic brushes as contact charging members, 21.magnets
22 ... electrode sleeve or yoke material, 23 ... magnetic brush layer or magnetic brush part, 24 ... charge potential attenuating part,
S1 ··· Charging bias application power supply, N ·· Charging nip, 3
..Developing device, 4..Transfer roller, 5..Fixing device, 6
..Cleaning devices and 30 process cartridges

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 15/02 G03G 15/09

Claims (14)

(57) [Claims] 1. A surface is brought into contact with the charge-receiving member having a charge injection layer, by applying an AC voltage or AC voltage component is a contact charging member for charging the member to be charged, said contact charging member is a magnetic particle Magnetic brush part composed of
A power supply unit for supplying power to the magnetic brush unit;
At the longitudinal end of the brush and between the magnetic brush and the power supply
And a charging potential attenuating function unit provided in the
Contact charging member potential decay function unit, characterized in Rukoto attenuates gradually charge potential of the member to be charged after charging by said magnetic brush portion in the longitudinal end direction of the magnetic brush portion. 2. The contact charging member according to claim 1, wherein the charge potential attenuating function part is a dielectric . 3. The contact charging member according to claim 2, wherein the magnitude of the capacitance of the dielectric material decreases as it goes toward the longitudinal end. 4. The contact charging member according to claim 2, wherein the thickness of the dielectric increases as it approaches the longitudinal end. 5. The contact charging member according to claim 2, wherein the magnitude of the dielectric constant of the dielectric material decreases as it goes toward the longitudinal end. Wherein said dielectric is a foam fleshy material, the contact charging member according to claim 2, characterized in that the foaming degree is increased toward the longitudinal end direction. 7. is the charging potential attenuation function portion magnitude of the capacitance of the magnetic brush portion is made to be smaller toward the longitudinal end portion direction which constitutes the vicinity of the longitudinal ends configuration of the magnetic brush portion The contact charging member according to claim 1, wherein: 8. The contact charging member according to claim 7, wherein the magnitude of the dielectric constant of the magnetic particles constituting the vicinity of the longitudinal end of the magnetic brush decreases as the direction of the longitudinal end increases. 9. claims, wherein the charge potential attenuation of the longitudinal end direction in the longitudinal end portion vicinity of the charging potential decay function prior Symbol magnetic brush portion Ru good in part is less attenuation gradient 1 kV / mm A contact charging member according to any one of claims 1 to 8. 10. A charging device that performs charging by bringing a contact charging member, to which an AC voltage or a voltage including an AC voltage component is applied, into contact with a member to be charged having a charge injection layer on a surface thereof, wherein the contact charging member is charged. Any one of claims 1 to 9
A charging device, comprising: 11. A surface on an image bearing member having a charge injection layer
An image forming apparatus that performs image formation by applying an image forming process including a step of charging an image carrier surface, wherein the step of charging the image carrier is the charging device according to claim 10. Image forming apparatus. 12. a photoreceptor having a charge injection layer on the image bearing member surface, and wherein the effective width of the magnetic brush portion is shorter than the coating width of the photosensitive layer of the <br/> photoreceptor The image forming apparatus according to claim 11, wherein: 13. A process cartridge which is detachably attached to the image forming apparatus main body, the contact charging member and the image bearing member according to any one of claims 1 to 9, the developing device, A process cartridge accommodating at least one of the cleaning devices. 14. a photoreceptor having a charge injection layer on the image bearing member surface, and wherein the effective width of the magnetic brush portion is shorter than the coating width of the light-sensitive layer of the sensitive <br/> optical body The process cartridge according to claim 13, wherein: