JPH06175472A - Charging device, process unit and image forming device - Google Patents

Abstract

PURPOSE:To prevent the radiation of the radiation noise, which is to be generated at the time of contact-charge, outside a device main body. CONSTITUTION:A charging roller 2 is made to be in contact with a photosensitive drum 1 to form a contact-nip part (n) between the photosensitive drum 1 and the charging roller 2. A voltage, which is obtained by overlapping the alternating current with the direct current, is applied from a power source 5 to the charging roller 2 to charge the photosensitive drum 1. At this stage, the radiation (electrostatic) noise on the basis of the charge is generated from a part near the contact nip part (n). The contact nip part (n) is surrounded by a shield member 20 made of a conductive member, and furthermore, the shield member 20 is grounded. The radiation noise leaked outside the shield member 20 is thereby reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device, a process unit and an image forming apparatus of a type in which a charging member is brought into contact with an object to be charged.

[0002]

2. Description of the Related Art Conventionally, a corona charger is often used as a charging device for an electrophotographic image forming apparatus such as a copying machine or a laser beam printer. The corona charger is formed with a wire electrode facing a photosensitive drum (image bearing member) as a member to be charged and a U-shaped cross section, and a shield that surrounds the wire electrode on three sides with the opening facing the photosensitive drum. An electrode is provided, and the surface of the photosensitive drum is charged by applying a voltage to a wire electrode that is not in contact with the photosensitive drum. The corona charger has advantages that it is easy to uniformly charge the photosensitive drum to a predetermined potential.

On the other hand, the disadvantages of using the corona charger are that the voltage applied to the wire electrode is as high as 4 kV to 8 kV, and the current applied by the voltage is almost not the wire electrode, and it is surrounded by this. Since the current flows to the shield electrode side, the charging efficiency is poor, ozone is often generated during corona discharge, and discharge unevenness is generated due to dirt on the wire electrode.

As a means for solving the drawbacks of such a non-contact type corona charger, a so-called contact type charging means for charging the photosensitive drum by using a charging member in contact with the photosensitive drum has been proposed by the present applicant. Proposed.

FIG. 4 is a schematic view showing an example of an image forming apparatus using a contact type charging device. A charging roller (charging member) 2 is provided with a compression spring S with respect to a photosensitive drum (image carrier) 1 as a member to be charged which is rotatably supported in the direction of arrow R1.
A contact nip portion n is formed between the photosensitive drum 1 and the charging roller 2 by being pressed by. A voltage obtained by superimposing an AC voltage on a DC voltage is applied to the charging roller 2 by the power supply 5, and the photosensitive drum 1 is charged in the vicinity of the contact nip portion n. An electrostatic latent image is formed by the exposure device 6 on the surface of the photosensitive drum 1 that is uniformly charged, and the electrostatic latent image is visualized with toner attached by the developing device 7. Becomes The toner image on the photosensitive drum 1 is transferred onto the transfer material P by the transfer device 11. The toner image on the transfer material P is then permanently fixed by a fixing device (not shown).

On the other hand, the residual toner remaining on the surface of the photosensitive drum 1 is removed by the cleaner device 15 to prepare for the next image formation.

FIG. 5 shows the photosensitive drum 1, the charging member (in FIG. 5, not the charging roller but the charging blade) 2, the developing device 7 and the cleaner device 1 shown in FIG.
5 and the like are integrally housed in a box-shaped cartridge body Pc to form a process unit Pu as a whole, and the process unit Pu is detachably attached to the image forming apparatus body. is there.

[0008]

However, according to the above-mentioned conventional technique, there is a problem that radiation (electrostatic) noise due to charging is emitted to the outside of the main body of the image forming apparatus. That is, when charging is performed in the vicinity of the contact nip portion n shown in FIG. 4, radiation noise due to the charging is generated from this vicinity. This radiation noise is radiated above the photosensitive drum 1 and leaks to the outside of the main body. The leaked radiation noise causes malfunction of nearby electronic devices. Therefore, it is essential to reduce such radiation noise when using the image forming apparatus. In the conventional image forming apparatus shown in FIG. 4, the radiation noise emitted to the outside of the apparatus body sometimes reaches 45 dB (μV / m).

Therefore, according to the present invention, an object to be charged (photosensitive drum) and a charging member (charging roller) which are sources of radiation noise are generated.
An object of the present invention is to provide a charging device, a process unit, and an image forming apparatus in which a radiation noise radiated to the outside of the image forming apparatus main body is reduced by covering a contact nip portion with the shield member with a shield member. .

[0010]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and a charging device includes a charging member arranged so as to contact a member to be charged, the charging member and the member to be charged. In a charging device including a power source for charging the charged body via the charging member by applying a voltage between the charging body and the charging body, the charging device is formed by a grounded conductive member and A shield member surrounding a contact nip portion formed between the member to be charged is provided.

The process unit accommodates a body to be charged and a charging member arranged so as to contact the body to be charged in the cartridge body, is detachably mounted to the body of the image forming apparatus, and is mounted at the time of mounting. In a process unit in which a voltage is applied between the charging member and a member to be charged by a power source on the side of the image forming apparatus main body and the member to be charged is charged via the charging member, grounding is performed in the cartridge body. And a shield member surrounding the contact nip formed between the charging member and the body to be charged.

The image forming apparatus includes a member to be charged, the above-described charging device, an exposure device that forms an electrostatic latent image on the member to be charged, and a toner image by attaching toner to the electrostatic latent image. A developing device for forming the toner image and a transfer device for transferring the toner image onto a transfer material are provided.

The image forming apparatus may be detachably equipped with the above-mentioned process unit.

An image forming apparatus characterized by the above.

When the shield member is disposed between the bias member having the bias and the non-grounded conductor,
While separating the distance from the bias member by 6 mm or more,
It is preferable that the conductor is separated from the conductor by 1 mm or more for a voltage of 1 kV at which the conductor is charged up.

[0016]

According to the above-mentioned structure, the shield member surrounds the contact nip portion between the charged member and the charging member, which is the source of the radiation noise, to reduce the radiation noise radiated to the outside of the main body of the image forming apparatus. be able to.

[0017]

Embodiments of the present invention will be described below with reference to the drawings. <Embodiment 1> FIG. 1 is a schematic sectional view of an image forming apparatus of Embodiment 1. In this embodiment, a charging roller 2, a developing device (developing device) 7, a cleaner device 15, which will be described later,
The shield member 20 and the like are integrally housed in the cartridge body Pc, and constitute an integrated process unit Pu as a whole.

In this image forming apparatus, a photosensitive drum 1 serving as an image bearing member, which is a member to be charged, is arranged at substantially the center. In the photosensitive drum 1, a photosensitive layer 1a is provided on a conductive base 1b made of aluminum, iron or the like, and the conductive base 1b is grounded. Charging roller 2 which is a charging member
Contacts the surface of the photosensitive drum 1 and forms a contact nip portion n with the photosensitive drum 1. A power source 5 for applying a voltage to the photosensitive drum 1 is connected to the charging roller 2 via a control power source 3.

When the photosensitive drum 1 is rotated in the direction of arrow R1, the photosensitive drum 1 is primarily charged by the charging roller 2 which is driven and rotated by the photosensitive drum 1. Then, an electrostatic latent image is formed on the surface of the photosensitive drum 1 by laser exposure (exposure device) 6 from a laser scanning device (not shown). This electrostatic latent image is developed on the developing sleeve 7a, which is a carrier for carrying the toner (developer) of the developing device 7, with the toner whose layer thickness is regulated by the developing blade 7b which is a regulating member for regulating the toner. ,
The toner image is visualized. The toner image formed on the photosensitive drum 1 in this way is transferred onto a transfer material P such as paper which is fed by a paper feed roller 9 and is conveyed with a timing adjusted by a pair of registration rollers 10 (transfer device).
11 is transferred. The transfer material P on which the toner image is transferred is fixed by a fixing device including a fixing roller 12 and a pressure roller 13. The toner remaining on the photosensitive drum 1 after the toner image is fixed is cleaned and removed by the cleaner device 15.

The power source 5 has a vibration component (voltage between peaks 1500 V) whose voltage value changes periodically and a DC component (700 V).
V) is applied to the core metal of the charging roller 2. This peak-to-peak voltage of the vibration component is 2 times the charging start voltage of the photosensitive drum (non-charged body) 1 as shown in Japanese Patent Application Laid-Open No. 63-149668 filed by the present applicant.
More than double. As a result, the charging of the photosensitive drum 1 becomes uniform. As the waveform of the vibration component, a sine wave, a rectangular wave, a triangular wave, or the like can be used. The oscillating voltage may be formed by turning on and off a DC power supply. Further, the vibration component supplied to the charging roller 2 is controlled by the control means 20 so as to have a constant current (560 μA). The constant current control of the vibration component forms a constant alternating electric field between the photosensitive drum 1 and the charging roller 2 even if the ambient environment of the apparatus such as temperature and humidity changes. The photosensitive drum 1 can always be uniformly charged regardless of the environment. Here, it is desirable that the constant current control be performed so that the peak-to-peak voltage of the oscillating voltage for making the charging uniform regardless of the environment becomes equal to or more than twice the charging start voltage value of the photosensitive drum 1. The current value at this time was 560 μA.

Now, at the time of this charging, radiation (charging) noise is generated and radiated from the contact nip portion n between the photosensitive drum 1 and the charging roller 2. In order to reduce this radiation noise. Then, as shown in FIG. 1, the shield member 20 is arranged so as to surround the contact nip portion n. A higher shielding effect can be obtained by setting the disposition position as close to the contact nip portion n as possible. This is because the radiation noise generated in the contact nip portion n diffuses radially around the contact nip portion n, so that the shield member 20 should be placed closer to the source of the radiation noise to shield the noise. Is improved. Further, as an effect when the shield members 20 are brought close to each other, it is possible to reduce the size of the shield member 20 as a whole.

Therefore, in this embodiment, as shown in FIG. 1, the shield member 20 is attached to the support member 21 that rotatably supports the charging roller 2 so as to surround the support member 21 immediately outside thereof.

By the way, the cleaner device 15 in this embodiment is provided with a cleaning blade 15a, and the cleaning blade 15a has an elastic rubber tip 15b arranged at the tip and a holder portion 15c for supporting the rubber tip 15b. The holder portion 15c is an electrically floating body, that is, a non-grounded conductor. Further, the holder 15c is electrostatically charged due to the friction between the rubber chip 15b and the photosensitive drum 1, and the voltage thereof is up to about -1000V in the operating state of the image forming apparatus according to the measurement by the applicant. It has become clear that Therefore, in the case of the configuration of this embodiment, the distance between the shield member 20 and the holder portion 15c of the cleaning blade 15a is 1.2 mm.
It is known that if not done above, the electric charge charged up in the holder portion 15c will spark to the shield member 20 and generate new noise, and the shield effect will be lost. Generally, the shield member 20
The distance between the holder and the holder 15c (non-grounded conductor) is
1k of absolute value of voltage to charge up this conductor
It is preferable to secure at least 1 mm per V.

Further, the shield member 20 must naturally be grounded in order to obtain its shield effect. Then, the alternating current flowing through the charging roller 2 as the bias member also flows through the shield member 20.
At this time, the current flowing through the shield member 20 (leakage current)
Is greatly affected by the distance between the charging roller 2 and the shield member 20. For example, if the distance between the surface of the charging roller 2 and the shield member 20 is set to 3.2 mm, the leakage current will be 39.8 μA, and the charging current of the charging roller 2 will not be sufficiently large. Image defects may occur due to charging failure. Actually, the leak current that does not adversely affect the image is 10 μA or less, and in order to satisfy this condition, the distance between the charging roller 2 and the shield member 20 needs to be 6 mm or more.

With the above configuration, radiation noise can be shielded in the upward and leftward directions shown in FIG. The radiation noise from the contact nip portion n toward the photosensitive drum 1 side is excellently suppressed because the base of the photosensitive drum 1 is grounded by a conductor such as aluminum.

In this embodiment, the radiation noise has an electromagnetic field strength of less than 30 dB, and an electromagnetic field strength of 45 dB when a non-conductive resin material is used as the holder 20.
Radiation noise can be reduced significantly compared to.

A preferred example of the structure of the charging roller 2 in the above embodiment is shown in FIG. The conductive elastic layer 2b is provided on the core metal 2a, and the high resistance elastic layer 2 is provided thereon.
c, and has a protective film 2d on the surface. Conductive elastic layer 2
b is composed of EPDM (ethylene propylene diene terpolymer) in which carbon is dispersed.
It serves to guide the bias voltage supplied to a. The high resistance elastic layer 2c is made of urethane rubber or the like, and contains, as an example, a minute amount of conductive fine powder (for example, carbon). Even when 2 are opposed to each other, the leak current to the photosensitive drum 1 is limited to prevent the sudden drop of the bias voltage. The surface protective film 2d is made of N-methylmethoxylated nylon, and the composition material of the conductive elastic layer 2b and the high resistance elastic layer 2c may touch the photosensitive drum 1 to alter the surface of the photosensitive drum 1. It acts as a protection so that it does not exist.

Further, in the above embodiments, the volume resistance value of the shield member (conductive member) 20 in order to reduce the radiation noise is preferably 10 ³ Ω · cm or less.

In order to uniformly and stably charge, for example, when an oscillating voltage is applied to the charging roller 2 to form an alternating electric field between the charging roller 2 and the photosensitive drum 1, a DC voltage is applied to the charging roller 2. Since the radiation noise tends to be larger than that when only the voltage is applied, it is particularly effective to provide the shield member 20 as described above.

Further, in the above embodiments, the charging of the photosensitive drum 1 is not limited to the case where the potential of the photosensitive drum 1 is raised, but it goes without saying that the potential of the photosensitive drum 1 is lowered and so-called static elimination is included. .

Generally, the ground includes a signal ground in the circuit and a frame ground grounded to the ground. Here, in this embodiment, the shield member 20 is
It is directly connected to the frame ground. This is because even if it is directly connected to the signal ground, it is effective in preventing the radiation noise, but if it is dropped to the frame ground via the signal ground on the circuit in the image forming apparatus, the radiation generated in the contact nip portion n is generated. This is because noise may enter the circuit and cause the image forming apparatus main body to malfunction. For this reason, it is more preferable to connect directly to the frame ground.

Further, in the contact charging type charging device,
When the charging member such as the charging roller 2 primarily charges the photosensitive drum 1, radiation noise is generated to some extent. Therefore, the present invention is effective in preventing the radiation noise of the contact charging device, but in particular, as in the above-mentioned embodiment, the current value having the vibration component applied to the charging member maintains the charging uniformity regardless of the environment. Constant current control (560 μ in this embodiment)
In the case of A), the generated radiation noise is relatively large and easily leaks out of the device.
It is particularly effective to provide. <Second Embodiment> FIG. 3 shows a second embodiment. A feature of this embodiment is that the charging roller 2 is arranged not in the cartridge body Pc of the process unit Pu but in the upper frame 30 which is opened and closed when the process unit Pu is attached to and detached from the image forming apparatus body. Since the charging roller 2 has high durability as a part in the process unit Pu, it does not need to be replaced every time the process unit Pu is replaced. Therefore,
When the charging roller 2 is provided in the cartridge body Pc, the cost of the entire process unit Pu is reduced, and the running cost of the image forming apparatus can be significantly reduced.
At this time, the shield member 20 naturally has a high shield efficiency, that is, the contact nip portion n in the main body of the image forming apparatus.
It is arranged so as to be close to. Shield member 20
Is not a consumable member, so its function continues as long as the life of the image forming apparatus main body continues.

Further, also in the present embodiment, in order to obtain the downsizing of the shield member 20, the structure is as shown in FIG. 3, and as shown in the above-mentioned Embodiment 1, the holder of the cleaning blade 15a. The condition is to be separated from the portion 15c by 1.2 mm or more and from the charging roller 2 by 6 mm or more.

[0034]

As described above, according to the present invention,
When the charging member is brought into contact with the member to be charged and the member to be charged is charged, conventionally, radiation noise is generated from the vicinity of the contact nip portion formed between the two members, which tends to leak to the outside of the image forming apparatus main body. By surrounding the contact nip portion with the shield member formed of a grounded conductive member, it is possible to effectively prevent radiation noise from being radiated to the outside of the apparatus main body. As a result, it is possible to prevent the electronic device placed near the apparatus body from malfunctioning due to radiation noise.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically illustrating a state in which a charging device according to a first exemplary embodiment of the present invention is housed in a process unit and the process unit is attached to an image forming apparatus.

FIG. 2 is a cross-sectional view showing the structure of a charging roller.

FIG. 3 is a cross-sectional view schematically showing a charging device and a process unit according to the second embodiment.

FIG. 4 is a cross-sectional view schematically showing the vicinity of an image forming unit of a conventional image forming apparatus.

FIG. 5 is a cross-sectional view schematically showing an image forming apparatus in which a conventional process cartridge is mounted.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Charged object (photosensitive drum) 2 Charging member (charging roller, charging device, bias member) 5 Power supply 6 Exposure device 7 Developing device 11 Transfer device 15c Non-grounded conductor (holder part) 20 Shield member n Contact nip part P Transfer material Pc Cartridge body Pu process unit

Claims (5)

[Claims] 1. A charging member, which is arranged so as to contact the charged body, and a voltage is applied between the charging member and the charged body to charge the charged body through the charging member. And a shield member that is formed of a conductive member that is grounded and that surrounds a contact nip portion that is formed between the charging member and the body to be charged. And charging device. 2. A cartridge main body contains a member to be charged and a charging member arranged so as to contact the member to be charged, and the cartridge is detachably mounted to the main body of the image forming apparatus, and the image at the time of mounting. In a process unit in which a voltage is applied between the charging member and a body to be charged by a power source on the main body side of the forming apparatus, and the body to be charged is charged via the charging member, the process unit is grounded in the cartridge body. A process unit comprising a shield member formed of a conductive member and surrounding a contact nip portion formed between the charging member and a body to be charged. 3. A charged body, the charging device according to claim 1, and an exposure device for forming an electrostatic latent image on the charged body.
An image forming apparatus comprising: a developing device that adheres toner to the electrostatic latent image to form a toner image; and a transfer device that transfers the toner image onto a transfer material. 4. An image forming apparatus, wherein the process unit according to claim 2 is removably mounted. 5. The shield member, when arranged between a bias member having a bias and a non-grounded conductor, separates the distance from the bias member by 6 mm or more and the distance from the conductor. The image forming apparatus according to claim 3, wherein the conductors are separated by 1 mm or more for each 1 kV of charge-up voltage.