JPH0887159A - Electrifier - Google Patents

Abstract

PURPOSE: To prevent a defect in image quality such as a streak from being generated by preventing potential by electrification from being made uneven with toner and an external addition agent which are stuck to the vicinity of a contact part, in an electrifier for attaining the electrification in such a manner that an electrifying electrode is brought into contact with the surface of a charger acceptor. CONSTITUTION: The electrifier is provided with the electrifying electrode 2 formed in such a manner that a semiconductive film-like member is bent to obtain a loop shape, in the contact position with the charge acceptor, a conductive supporting member 3 supporting the electrode 2 and a DC power source 4 connected to the supporting member 3. Further, a large number of semiconductive fine grains 5 are filled almost uniformly in an axial direction on the upstream side of the contact part of the electrode 2 with the charge acceptor 1, in its moving direction. Thus, even if the toner, etc., are infiltrated into the gap between the acceptor 1 and the electrode 2, a sufficient charge moving path can be obtained by a discharge among the fine grains 5. Moreover, as the electrode, a blade-like member pressed on the surface of the charger acceptor 1 can be used as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device which is used in an image forming apparatus such as a copying machine or a printer to which an electrophotographic method is applied and which uniformly charges the surface of a photoconductor which is a charge acceptor. In particular, the present invention relates to a charging device that charges a charging electrode by contacting it with the surface of a charge receptor.

[0002]

2. Description of the Related Art In an image forming apparatus such as a copying machine or a printer, the surface of a photoconductor, which is a charge receptor, is charged by a charging device, and then an electrostatic latent image is formed on the surface by irradiating an image light. This electrostatic latent image is visualized by the adherence of.
As a charging device used in such an image forming apparatus, conventionally, a device using corona discharge and a device using a contact charging system using a charging roller or the like are known.

In a charging device using corona discharge, a wire is stretched in a shield case so as to be close to and away from the surface of a charge receptor, and a high voltage is applied to the wire to cause a corona discharge to generate a charge receptor. It imparts a predetermined charge to the surface. Although such a charging device is excellent in uniform charging, it has a drawback in that a large amount of discharge products such as ozone is required to be treated, which makes the device larger and more expensive.

Therefore, in recent years, a charging device using a contact charging system has been used in which a charging electrode is charged by directly contacting a charging electrode with a charging electrode. In such a charging device, a conductive member such as an elastic roller or a brush is arranged in contact with the surface of the charge receptor, and a DC voltage, for example, is applied to the conductive member as a charging voltage, and a minute gap near the contact portion is generated. Charging is performed by causing discharge. The charging device of this type does not utilize corona discharge, so the amount of ozone generated is extremely small, and since the conductive member is arranged so as to contact the charge receptor, it is suitable for downsizing and weight reduction of the device. It has the advantage of

However, among the above-mentioned contact type charging devices, the one using a roller-shaped conductive member has a drawback that a supporting device for an elastic roller or the like is required and the structure tends to be complicated. Further, in order to perform uniform charging, it is necessary to improve the adhesiveness between the elastic roller and the charge receptor to form stable microscopic voids, and it is necessary to take measures such as lowering the hardness of rubber. Therefore, it is necessary to contain a large amount of process oil in the rubber, and this process oil is liable to transfer to the charge acceptor and adversely affect the image quality. On the other hand, in order to eliminate such a defect, there is a method of increasing the outer shape accuracy of the roller, but it is very difficult to increase the outer shape accuracy of an elastic body such as rubber, and the yield is reduced, which leads to an increase in cost.

On the other hand, in the case of using a brush-shaped conductive member, it is easier to make uniform contact than in the roller-shaped member, but it takes time and effort to manufacture the brush, and
There is a drawback that the brush sweep tends to appear in the image as uneven charging.

Therefore, as a countermeasure against the above-mentioned drawbacks, an apparatus using a blade-shaped conductive member which is pressed against the surface of a charge receptor as disclosed in JP-A-1-93760 and JP-A-2-282279, JP-A-4-2492
As disclosed in Japanese Unexamined Patent Publication No. 70-70, there has been proposed a device using a film-shaped conductive member and arranging the tip end portion so as to abut the surface of the charge receptor. Such a charging device has an advantage that stable contact can be easily obtained with a simple structure, and the manufacturing cost of the member is lower than that of the elastic roller or the brush.

[0008]

However, in the charging device as described above, since the charging is performed while the tip end of the blade-shaped member or the film-shaped member is pressed against the surface of the charge receptor, the toner that has slipped through the cleaning device is used. And external additives detached from the toner adhere to the contact portion with the charge acceptor. Therefore, when a DC voltage is applied to the charging electrode, so-called creeping discharge occurs along the surface of the insulating toner or the like attached to the contact portion, and the current locally concentrates on the surface of the charge acceptor. Therefore, there is a problem in that a streak-shaped charging defect occurs such that the charging potential is high in the portion where the toner or the like adheres and the charging potential becomes low on both sides thereof, and streak-shaped image quality defects occur on the image.

The present invention has been made in view of the above problems, and an object thereof is to make the charging potential non-uniform due to the toner or the external additive attached to the contact portion between the charging electrode and the charge receptor. It is an object of the present invention to provide a charging device capable of preventing the occurrence of a problem and obtaining a good image without image quality defects.

[0010]

In order to solve the above problems, the invention according to claim 1 is composed of a flexible member having semiconductivity, and the surface thereof is rotatably supported. A charging electrode placed in contact with the charge acceptor,
In a charging device having a power source for applying a voltage to the charging electrode, a semi-conductive and substantially constant particle size is provided upstream of a contact portion between the charging electrode and the charge receptor in a moving direction of the charge receptor. It is assumed that a large number of fine particles are retained.

According to a second aspect of the present invention, in the charging device according to the first aspect, the charging electrode is made of a film-shaped member and approaches the charge receptor from an upstream side in a moving direction of the charge receptor. , Shall be placed in contact with each other.

According to a third aspect of the present invention, in the charging device according to the first aspect, the charging electrode is a blade made of an elastic member, and a cleaning blade for cleaning toner adhering to the charge receptor. Shall also be used.

According to a fourth aspect of the present invention, there is provided the charging device according to the first, second or third aspect, wherein:
The fine particles are rubbed with the charge acceptor or the toner adhering to the surface of the charge acceptor to be charged with a polarity opposite to the DC voltage applied to the charging electrode.

In the invention described in any one of claims 1 to 4, the semiconductive fine particles are substantially spherical particles,
It is desirable that the average particle diameter is about 5 μm to 100 μm. Further, it is desirable that it is formed of a material having a volume resistivity of about 10 ³ to 10 ¹⁰ Ω · cm. The amount of the fine particles held between the charging electrode and the charge acceptor is appropriately set in consideration of stability during discharge. At this time, it is desirable to hold the charge receptor so that the amount thereof is substantially uniform in the axial direction.

In the invention described in claim 1, the flexible member forming the charging electrode can be appropriately selected from, for example, a film member or an elastic member. The shape of the charging electrode can be appropriately set as long as it can hold a large number of fine particles on the upstream side of the contact portion with the charge acceptor. Further, in the invention described in claims 1 to 4, it is desirable that the member forming the charging electrode has a volume resistivity of about 10 ³ to 10 ¹⁰ Ω · cm.

In the invention according to claim 4, the fine particles are those which are positively charged by rubbing with the toner when a negative DC voltage is applied to the charging electrode. A magnetic carrier or the like used as a two-component developer of a copying machine can be used.

[0017]

In the charging device according to the first aspect of the present invention, a large number of semiconductive fine particles having a substantially constant particle size are held upstream of the contact portion with the charging electrode in the moving direction of the charge receptor. Therefore, even if the toner or the external additive having a relatively small particle diameter, which cannot be completely removed by the cleaning device, is mixed in at the position facing the charging electrode, the toner and the external additive enter the voids between the particles in the region where the large number of particles are held. Therefore, when a voltage is applied to the charging electrode, electric discharge is generated in the voids between the fine particles through the plurality of fine particles, and a substantially uniform charge transfer path is maintained in the axial direction of the charge acceptor. Therefore, the surface of the charge receptor is charged to a uniform potential, and the occurrence of streak-shaped image defects due to poor charging is prevented.

In addition to this, in the charging device according to the second aspect of the invention, the charging electrode is made of a film-shaped member,
It is arranged so as to approach and contact the charge receptor from the upstream side in the moving direction of the charge receptor, and a wedge-shaped region is formed on the upstream side of the contact portion between the charging electrode and the charge receptor. When a large number of fine particles are held in this wedge-shaped region, the fine particles are pressed toward the contact portion between the charging electrode and the charge receptor by the movement of the surface of the charge receptor. Therefore, desorption of the fine particles can be prevented, and a large number of the fine particles can be held in the discharge region more reliably, and a sufficient charge transfer path can be obtained. Moreover, since the charging electrode is formed of a film-shaped member, the manufacturing cost can be reduced with a simple configuration.

In the charging device according to the third aspect of the present invention, the charging electrode is a blade made of an elastic member and has a function as a cleaning blade for cleaning the residual toner on the surface of the charge receptor. The manufacturing cost is low and low cost can be realized. Further, space saving can be achieved in an image forming apparatus using this charging device.

In the charging device according to the fourth aspect of the present invention, since the fine particles are rubbed with the charge acceptor or the toner and charged with a polarity opposite to the DC voltage applied to the charging electrode, the fine particles are applied with a voltage. It is attracted to the charging electrode by the electric attraction force at that time. Therefore, it is possible to prevent the fine particles from being detached from the charging electrode, and it is possible to reliably hold a large number of fine particles in the gap between the charging electrode and the charge acceptor.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic configuration diagram showing a charging device which is an embodiment of the invention described in claim 1, claim 2 or claim 4. The charging device 10 is arranged at a position facing the charge acceptor 1 whose surface is rotatably supported, and has a semi-conductive film-like member curved, and its both end edges are overlapped to form a loop. It has a formed charging electrode 2 and a conductive support member 3 that supports the charging electrode 2 and contacts the charge receptor 1 with an appropriate contact pressure. Further, the support member 3 is connected to the DC power source 4, and the charging electrode 2 is connected.
A DC voltage is applied to. The charging electrode 2 is supported so as to come into close contact with the charge receptor 1 from the upstream side in the moving direction of the charge receptor 1, and the upstream side of the contact portion between the charging electrode 2 and the charge receptor 1. A wedge-shaped void is formed. The wedge-shaped void portion is filled with a large number of semiconductive fine particles 5 substantially evenly in the axial direction of the charge receptor 1.

The charge acceptor 1 has a structure in which a photoconductive layer 1b is laminated on, for example, a cylindrical conductor substrate 1a, and the conductor substrate 1a is electrically grounded. The surface of the charge acceptor 1 is charged by discharging in a minute gap near the contact portion with the charging electrode 2.

As the film-like member constituting the charging electrode 2, a semiconductive member having a thickness of about 30 to 150 μm and a volume resistivity of 10 ³ to 10 ¹⁰ Ω · cm is used. The charging electrode 2 is formed by mixing conductive particles such as carbon black into a film such as polyester, polyamide, polyethylene, polycarbonate, polyolefin, polyurethane, polyvinylidene fluoride, and the like. A suitable volume resistivity can be obtained by appropriately setting the amount. Further, considering that the charging electrode 2 is in direct contact with the charge receptor 1, the tensile elastic modulus is 10 to 280 Kg /
It is set to about mm ² .

The semiconductive fine particles 5 are spherical particles having a substantially constant particle diameter, and have a particle diameter of about 5 to 100 μm. The particle size of the fine particles 5 is set so that gaps are formed between adjacent fine particles 5 to the extent that discharge is likely to occur. Further, the amount of the fine particles 5 to be filled is such that even if a toner or an external additive is mixed, a discharge path of the charging current is maintained by the discharge between the fine particles, that is, an appropriate fine void is provided between the large number of fine particles 5. It is set to be formed. In this embodiment, the semiconductive member forming the fine particles 5 is used for electrophotography in which the surface of a spherical member made of Cu—Zn ferrite is coated with a material mixed with a metal oxide such as titanium oxide. A magnetic carrier is used. The fine particles 5 are rubbed with the charge acceptor 1 or the toner adhering to the surface of the charge acceptor 1, and have a polarity opposite to the DC voltage applied to the charging electrode (in this embodiment, the DC voltage is negative, It is supposed to be positively charged. Therefore, the fine particles 5 are attracted to the charging electrode 2 by an electric attraction force when a voltage is applied,
It is retained in the wedge-shaped void. Furthermore, this fine particle 5
Is pressed against the contact portion between the charging electrode 2 and the charge acceptor 1 by the movement of the charge acceptor 1, and is prevented from falling off from the wedge-shaped void portion.

The DC power source 4 is capable of applying a negative DC voltage having a substantially constant voltage to the support member 3. The voltage applied to the DC power supply 4 will be described later. In addition,
As a toner used in an image forming apparatus to which the above charging device is applied, a magnetic toner that is negatively charged is used.

In such a charging device, when a predetermined voltage is applied to the charging electrode 2 from the DC power source 4 through the conductive support member 3, the charging electrode 2 and the charge acceptor 1 are brought into the vicinity of the contact portion. Discharge is generated in the minute gaps between the fine particles through the filled fine particles 5, and the surface of the charge acceptor 1 is charged. At this time, as shown in FIG. 2, the toner 6 which could not be completely removed by the cleaning device (not shown) in the region filled with the fine particles 5.
Even if the external additive 7 is mixed in, the particles are not trapped in the voids between the fine particles 5 and do not hinder the discharge between the fine particles. That is, even if the toner 6 and the external additive 7 are mixed, discharge occurs in the voids between the fine particles, and a uniform charging current conducting path is maintained. Therefore, the charging potential is not locally nonuniform, and stable charging is performed. Further, in the charging device of the present embodiment, the semiconductive member is used for the charging electrode 2 and the fine particles 5, so that discharge with high current density does not occur unlike the case where the conductive member is used, and the gap It is possible to prevent an excessive current from flowing to any part. Therefore, the charge acceptor 1 can be uniformly charged.

Next, the results of the charging test of the above charging device using the charging test device as shown in FIG. 3 will be shown. This charging test apparatus has a surface potential sensor 11 that detects the potential of the surface of the charge receptor 1 and a discharge lamp 13 that discharges the surface of the charge receptor 1 around the charge receptor 1. Is connected to a surface electrometer 12. Further, the charging device 10 of the present embodiment is arranged opposite to the upstream side of the surface potential sensor 11 in the rotation direction of the charge receptor 1, and the charging electrode 2 of the charging device 10 is connected to the charge receptor 1.
It is fixed to the conductive support member 3 so as to contact the surface. Further, the supporting member 3 is connected to a DC power source 14 so that a DC voltage is applied to the charging electrode 2. The DC power supply 14 is capable of arbitrarily changing the voltage, and the surface potential of the charge acceptor 1 which changes accordingly can be measured by the surface electrometer 12.

FIG. 4 shows the relationship between the applied voltage and the surface potential of the charge receptor 1 when a DC voltage is applied to the charging electrode 2 in the charging test using the above charging test apparatus. In this figure, 0 to -10 from the DC power supply 14
It was confirmed that when a DC voltage of 00V was applied, the surface potential of the charge acceptor 1 started to rise sharply from an applied voltage of about -400V and reached about -450V at an applied voltage of -1000V. During this period, no abnormal discharge was generated by the charging device 10.

FIG. 5 is a schematic configuration diagram showing an image forming apparatus to which the charging device 10 is applied. This image forming apparatus includes a photoconductor (charge receptor) 20 on which a latent image is formed by irradiating image light after uniform charging, and the surface of the photoconductor 20 is charged around the photoconductor 20. In addition to the charging device 10 of this embodiment, an exposure device 21, a developing device 22,
It has a transfer roller 25 and a cleaning device 27.
Further, in the apparatus, a paper cassette 2 for storing paper 24 is provided.
3. It has a fixing device 26 for fixing the toner image.

In such an image forming apparatus, the charging device 1
After the photoconductor 20 is charged to a predetermined potential by 0, the exposure device 21 irradiates a laser beam corresponding to image information, and an electrostatic latent image is formed on the surface of the photoconductor 20. This electrostatic latent image is developed by the developing device 22, and a visible image is formed by the adhesion of toner. Further, the paper 24 is conveyed from the paper cassette 23 along the paper guide 28 between the photoconductor 20 and the transfer roller 25, and the transfer roller 25 transfers the toner image onto the paper 24. The transferred toner image is fixed by the fixing device 26, and one copy image is formed. On the other hand, after the transfer process, the toner remaining on the photoconductor 20 is cleaned by the cleaning device 27, and the photoconductor 2
With the rotation of 0, the charging process by the charging device 10 is started again. The voltage applied to the charging device 10 in the above step is a DC voltage of -900V, and the surface potential of the charge receptor 1 is charged to about -350V.

A print image was formed using such an image forming apparatus, and a reliability test of the charging device 10 was conducted. As a result, the charging potential was uniform and there was no image quality defect as shown in FIG. 6B. It was confirmed that a good image was obtained.
On the other hand, in the conventional charging device of the type not filled with fine particles, the charging potential immediately becomes non-uniform due to the toner adhering to the vicinity of the contact portion between the charging electrode and the photosensitive member, as shown in FIG.
As shown in Fig. 5, many black streak-shaped image defects occurred in the printed image.

FIG. 7 is a schematic diagram showing a charging device according to another embodiment of the first or the fourth aspect. In this charging device, instead of the film-shaped charging electrode 2 applied to the charging device 10 shown in FIG. 1, the tip end of the plate-shaped elastic member is pressed toward the downstream side in the moving direction of the charge receptor 31. It has a blade-shaped charging electrode 32 arranged in this manner. Further, a large number of semiconductive fine particles 35 are filled on the upstream side of the contact portion with the blade-shaped charging electrode 32 in the moving direction of the charge receptor 31.

The blade-shaped charging electrode 32 is formed of an elastic member having semiconductivity, and for example, urethane rubber or the like in which an appropriate amount of conductive particles such as carbon black is mixed is used. The blade-shaped charging electrode 32 has a volume resistivity of about 10 ³ to 10 ¹⁰ Ω · cm. Further, the blade-shaped charging electrode 32 is supported by a conductive support member 33 so that the tip end thereof contacts the charge acceptor 31 with an appropriate pressing force. The material of the semiconductive fine particles 35, the material of the support member 33, and the other configurations of the charging device are the same as those of the charging device 10 shown in FIG.

When a copying test was carried out using an image forming apparatus to which such a charging device was applied, the occurrence of black streak-like image quality defects due to poor charging was greatly reduced as in the charging device shown in FIG. It was confirmed that a good copy image was obtained.

FIG. 8 is a schematic configuration diagram showing a charging device which is an embodiment of the invention described in claim 3 or 4.
This charging device corresponds to the charging electrode 3 of the charging device shown in FIG.
Instead of 2, the charging electrode 42 is arranged so as to press the tip end of the blade-shaped elastic member toward the upstream side in the moving direction of the charge receptor 41. This charging electrode 42
In the above, the blade-shaped elastic member is also used as a cleaning blade disposed in the cleaning device, and the tip of the blade-shaped elastic member is pressed against the charge receptor 41, so that the surface of the charge receptor 41 is Residual toner can be cleaned. Furthermore, charge acceptor 4
A large number of semiconductive fine particles 45 are filled on the upstream side of the contact portion between the charging electrode 42 and the charge acceptor 31 in the moving direction of 1.

The charging electrode 42 is made of the same material as that of the charging electrode 32, and is made of a semiconductive material having a volume resistivity of about 10 ³ to 10 ¹⁰ Ω · cm. . The semi-conductive fine particles 45 are also made of the same material as the fine particles 35, and are rubbed with toner or the like to be charged with the opposite polarity to the DC voltage applied to the charging electrode 42. . As a result, the fine particles 45 are electrically adsorbed to the charging electrode 42, and the toner separated from the charge acceptor at the tip of the charging electrode 42 is separated from the charging electrode 42 and is collected in the apparatus. The other structure of this charging device is the same as that of the charging device shown in FIG.

Even with such a charging device, a copying test was carried out using the image forming apparatus. As with the charging device shown in FIG. 7, streak-like image quality defects due to defective charging were prevented, and a good copy image was obtained. was gotten. Further, since the blade-shaped elastic member forming the charging electrode 2 is also used as the cleaning blade, there is an advantage that space can be saved in the image forming apparatus.

In the above charging device, the fine particles 45 are electrically attracted to the charging electrode 42 to prevent detachment from the charging electrode 42. However, the blade-like elastic member is made of a magnetic material and is made of a magnetic material. The particles may be magnetically adsorbed. In this case, by using non-magnetic toner, only the toner can be collected in the apparatus from the tip of the blade-shaped elastic member.

[0039]

In the charging device according to the first aspect of the present invention, even if the toner or the external additive which cannot be removed by the cleaning device is mixed in the position facing the charging electrode, the charging process is performed. Discharge occurs through a plurality of fine particles, and a uniform charging current conducting path is maintained. Therefore, the charge acceptor can be charged to a uniform potential, and an image with good image quality without streaky image quality defects can be obtained.

In addition to this, in the charging device according to the second aspect of the present invention, a wedge-shaped region is formed on the upstream side of the contact portion between the charging electrode and the charge receptor, and the fine particles are on the surface of the charge receptor. Because it is pressed in the downstream direction by the movement,
It is possible to prevent detachment of the fine particles and reliably hold a large number of particles in the discharge region. Further, since the charging electrode is formed of a film-shaped member and has a simple structure, the manufacturing cost can be reduced.

In the charging device according to the third aspect of the present invention, the charging electrode composed of the elastic blade is also used as the cleaning blade for cleaning the residual toner on the surface of the charge receptor to reduce the manufacturing cost. In addition, it is possible to save space in the device.

In the charging device according to the fourth aspect of the present invention, since the fine particles are charged with a polarity opposite to the DC voltage applied to the charging electrode and are attracted to the charging electrode by an electric attraction force, the fine particles are charged. It can be securely held between the electrode and the charge acceptor to prevent it from falling off the charged electrode.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a charging device that is an embodiment of the invention described in claim 1, claim 2, or claim 4.

FIG. 2 is a diagram for explaining the action of the charging device shown in FIG. 1 during charging.

FIG. 3 is a schematic configuration diagram showing a charging test device for performing a charging test of the charging device shown in FIG.

FIG. 4 is a diagram showing the relationship between the DC voltage applied to the charging device and the surface potential of the charged charge receptor in the charging test device.

5 is a schematic configuration diagram showing an image forming apparatus in which the charging device shown in FIG. 1 is used.

6 is a diagram in which an image obtained by using the image forming apparatus shown in FIG. 5 is compared with an image obtained by a conventional charging device.

FIG. 7 is a schematic configuration diagram showing a charging device according to another embodiment of the invention described in claim 1 or claim 4.

FIG. 8 is a schematic configuration diagram showing a charging device that is an embodiment of the invention described in claim 3.

[Explanation of symbols]

 1, 31, 41 Charge receptor 2, 32, 42 Charging electrode 3, 33, 43 Support member 4, 34, 44 DC power source 5, 35, 45 Fine particles 6 Toner 7 External additive 10 Charging device 11 Surface potential sensor 12 Surface Electrometer 13 Static elimination lamp 14 DC power supply 20 Photoconductor 21 Exposure device 22 Developing device 23 Paper cassette 24 Paper 25 Transfer roller 26 Fixing device 27 Cleaning device 28 Paper guide

Claims (4)

[Claims] 1. A charging electrode, which is made of a flexible material having semi-conductivity and is installed so that its surface comes into contact with a charge receptor rotatably supported, and a power source for applying a voltage to the charging electrode. In the charging device having a plurality of semiconductive particles having a substantially constant particle size are held upstream of the contact portion between the charging electrode and the charge receptor in the moving direction of the charge receptor. Characteristic charging device. 2. The charging device according to claim 1, wherein the charging electrode is formed of a film-shaped member, and is arranged so as to approach and contact the charge receptor from an upstream side in a moving direction of the charge receptor. Charging device characterized in that. 3. The charging device according to claim 1, wherein the charging electrode is a blade made of an elastic member and also serves as a cleaning blade for cleaning toner adhering to the charge receptor. Charging device. 4. The charging device according to claim 1, 2, or 3, wherein the fine particles are rubbed with the charge acceptor or a toner adhering to a surface of the charge acceptor, thereby charging the charge. A charging device, which is charged with a polarity opposite to a DC voltage applied to an electrode.