JPH0736253A - Photosensitive member charging device and charging method - Google Patents

Abstract

(57) [Summary] [Object] The present invention provides a particle charging device capable of effectively ensuring a charging region and a charging density even when the diameter of a photosensitive drum is reduced. Two magnetic field generating means are arranged adjacent to each other on the back side of the charged area of the photoconductor, and the magnetic particle group is brought into close contact with the photoconductor by a horizontal magnetic field mainly formed between the two magnetic field generation means. To be charged. And a repulsive magnetic field composed of a pair of adjacent magnetic poles of the same polarity on the back side of the photoconductor located on the downstream side of the charging region, and the repulsive magnetic field forms a non-magnetic band at the downstream end of the charging region on the photoconductor. It is configured to prevent leakage of magnetic particles.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a charging device in an electrophotographic apparatus for charging a belt-shaped or drum-shaped photosensitive member by particle charging and a charging method therefor.

[0002]

2. Description of the Related Art Conventionally, process means for exposing, developing, transferring, cleaning (removing residual toner), discharging, and charging are arranged on the outer peripheral surface of a photosensitive drum, and an image is formed by a predetermined electrophotographic process. Image forming apparatuses based on the so-called Carlson process are well known.

In recent years, a light-transmitting conductive layer and a photoconductor layer are laminated on a cylindrical light-transmitting support to form a photosensitive drum, and an optical output corresponding to image information is provided in the drum. At the same time as or immediately after the exposure means (for example, an LED head) to be generated is inserted, and the light output of the exposure means is exposed through the focusing lens on the photosensitive drum charged on the photosensitive drum using a predetermined charging means. Image formation in which the latent image is formed into a toner image (developed) through a developing sleeve facing the photosensitive drum, and then the toner image can be transferred onto a recording sheet through a transfer roller or other transfer means. Apparatuses (Japanese Patent Laid-Open No. 58-153957, etc.) are also known.

The charging means used in this type of apparatus is generally a corotron system in which a high voltage is applied to a thin tungsten wire to carry out corona discharge, or a conductive roller is charged with a voltage of several hundreds of volts to contact and charge the photosensitive drum. In addition, there is one in which a voltage is applied to a conductive brush so that the brush is charged while being in contact with the photosensitive drum. However, the corotron method uses a high voltage, and in terms of safety such as generating ozone,
There are many environmental problems. Further, since the charging roller is in line contact with the photosensitive drum, charging is unstable. Further, in the brush charging method, since the drum and the brush contact each other to perform charging, the charging deterioration of the brush is likely to occur.

In order to eliminate such a drawback, as shown in FIG. 5, a non-magnetic sleeve 103 having a photosensitive drum 101 and a magnet assembly 102 inserted therein is used, and a charging bias 108 is applied to the sleeve 103. , The sleeve 10
3, a magnetic particle group 104 is attached to the magnetic particle group 3, the brush-shaped magnetic brush is rubbed against the photosensitive drum 101, and a charging bias 108 is applied to the magnetic particle group 104 via the sleeve 103 to perform charging. Is proposed.
(JP-A-59-133569, JP-A-63-18726
7 and others)

In the charging method, in order to uniformly charge the photosensitive drum 101 with the conductive fine particles, it is necessary to make the contact area and the contact density between the magnetic particle group 104 and the photosensitive drum 101 in the charging region sufficient conditions. But,
The contact area of the magnetic brush is the photosensitive drum 1 and the magnet assembly 10
2 is determined by the outer diameter of the non-magnetic sleeve 103 in which the photosensitive drum 101 and the sleeve 1 are inserted.
The smaller the size of 03, the narrower the contact nip, and the faster the rotation speed of the photosensitive drum 101, the more likely the contact nip becomes unstable. Therefore, in order to ensure the stability of the contact nip, the gap tolerance between the photosensitive drum 101 and the non-magnetic sleeve 103 is set to be strict. However, with this configuration, the number of assembling steps and the like increase, which leads to an increase in cost. In addition, the magnetic force and the magnetic flux density fluctuate due to an assembly error such as eccentricity between the fixed magnet assembly 102 and the non-magnetic sleeve 103 and expansion / contraction due to heat and other environmental factors, so that stable charging cannot be performed.

Next, there is a problem that magnetic particles adhere to the photosensitive drum (particle pulling). Further, in the above-mentioned prior art, when a magnetic ear is formed by the fixed magnet assembly 102, the magnetic field is attenuated in proportion to the square of the distance from the fixed magnet assembly 102, and therefore the position on the surface of the photosensitive drum 101 is reduced. The magnetic coercive force of the magnetic particles is weakest. On the other hand, the magnetic particle group 104
Are in the charging area between the particles or the photosensitive drum 1
It rubs against and becomes charged and has an electric charge. Therefore, when the photosensitive drum 101 is rotated in this state, the drum 101
The centrifugal force acts on the surface, and the magnetic particles 104 electrostatically adhering to the photosensitive drum 101 are separated from the magnetic brush, that is, the charged area against the magnetic coercive force (magnetic field) from the fixed magnet assembly 102. Force acts in the direction of
The particles 104a attached to the surface adversely affect exposure and development in the next process. However, the above-mentioned drawbacks become more serious as the particle size of the magnetic particles is made smaller and the linear velocity of the photosensitive drum 101 is made faster in order to increase the number of printed sheets per hour. For this reason, in the above-mentioned conventional technique, a blade is arranged on the downstream side of the charging region in the moving direction of the photoconductor to collect the magnetic particles. A mechanism for collecting the magnetic particles attached to the blade is required, which complicates the configuration.

Further, in the prior art, since the magnet assembly or the charging sleeve including the assembly is arranged so as to face the photosensitive drum, the charging device portion is largely projected on the photosensitive drum. Therefore, even if the size of the photosensitive drum is reduced, the size of the entire apparatus cannot be reduced.

In view of the above-mentioned drawbacks of the prior art, it is an object of the present invention to provide a charging device capable of effectively ensuring the charging area and the charging density even when the diameter of the photosensitive drum is reduced. Another object of the present invention is to maintain a stable charging ability even when the magnet assembly or the charging sleeve containing the assembly is removed, preferably facing the photoconductor drum, and these can be maintained. An object of the present invention is to provide a charging device capable of maintaining a stable charging ability without being affected by the fluctuation of the charging gap, an assembly error, and the like even when the charging device is opposed to the above. Another object of the present invention is to provide a charging device capable of effectively preventing leakage of magnetic particles to the outside of the charging region with a simple structure.

[0010]

In order to achieve such a technical problem, charging of a photoconductor is configured so that the photoconductor can be charged through a group of magnetic particles held on a charged region of the photoconductor by a magnetic force. In the device, on the back side of the charged area of the photoconductor,
Two magnetic field generating means composed of two magnet bodies having different polarities or a combination of the magnet body and the magnetic body are adjacently arranged along the moving direction of the photoconductor, and a horizontal magnetic field mainly formed between the two magnetic field generating means is used. It is characterized in that the magnetic particles are charged while being brought into close contact with the photoreceptor. As a result, by the horizontal magnetic field, the magnetic particle group can be brought into close contact with the photoconductor only by the two magnetic field generating means arranged on the back side of the photoconductor, irrespective of the fixed magnet body and the like arranged opposite to each other on the photoconductor drum. . Further, even when the diameter of the photosensitive drum is reduced, not only can the charging contact area and the charging density with which the magnetic particle groups come into contact effectively be secured, but also when the magnet assembly or the charging sleeve is removed facing the photosensitive drum. Can maintain a stable charging ability. As a result, the charging device portion does not largely project on the photosensitive drum, and therefore the photosensitive drum can be downsized and the entire device can be easily downsized.

However, in the case of the above configuration, since the magnetic particles are held only by the magnetic force on the back side of the photoconductor, leakage of the magnetic particles from the charging area cannot be avoided.
Therefore, the present invention provides a repulsive magnetic field composed of a pair of adjacent magnetic poles of the same polarity on the back surface side of the photoconductor located on the downstream side of the charging area,
The repulsive magnetic field forms a non-magnetic band at the downstream end of the charged area on the photoconductor, thereby preventing leakage of magnetic particles. Of course, such a configuration is also effective when the magnet assembly or the charging sleeve is provided so as to face the photoconductor drum, but in this case, a vertical magnetic field in which the magnetic force lines extend in the photoconductor normal direction on the downstream side of the photoconductor charging area. It is better to have a structure that forms a. As such a vertical magnetic field forming means, specifically, of the two magnetic field generating means located on the back side of the charging area of the photoconductor, it substantially opposes the first magnetic field generating means located on the downstream side in the moving direction of the photoconductor. This can be achieved by arranging a vertical magnetic field forming means composed of a magnetic body or a magnet body having a polarity opposite to that of the first magnetic field generating means above the photoconductor.

As more preferable magnetic particle leakage prevention means, of the two magnetic field generating means located on the back side of the charging area of the photoconductor, the first magnetic field generating means located on the downstream side in the moving direction of the photoconductor is formed by a magnet body. On the other hand, a second magnet body having a polarity opposite to that of the first magnetic field generating means is disposed above the photoconductor so as to be substantially opposed to the first magnetic field generating means, and
The magnetic substance is further disposed by arranging the magnetic substance adjacent to the magnetic field generating means or the side face on the downstream side in the charging direction of the second magnet substance, and forming a closed circuit of the vertical magnetic field between any of the magnet substances and the magnetic substance. Is effective. The magnetic particle group is composed of conductive magnetic particles or a mixed particle group of conductive particles and magnetic particles, and a charging bias can be applied to the particle group so that the linear velocity of the photoreceptor can be increased. Sufficient charging can be ensured even if the charging area is narrowed due to the reduction in diameter of the photosensitive drum.

[0013]

Embodiments of the present invention will now be illustratively described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative positions and the like of the components described in this embodiment are not intended to limit the scope of the present invention thereto, but are merely examples, unless otherwise specified. Not too much. Figure 1
The configuration of the charging device according to the first exemplary embodiment of the present invention will be described based on FIG. This apparatus shows an embodiment in which a charging sleeve and a fixed magnet assembly are not arranged opposite to each other on the photosensitive drum, but are arranged only on the rear surface side of the photosensitive drum. Reference numeral 1 denotes a photoconductor drum that rotates clockwise. On the drum back side corresponding to the charging area, the first magnet body 5B having an N pole is provided on the upstream side and the downstream side is provided so as to divide the charging area almost in two. And a second magnet body 5A having an S pole of opposite polarity are arranged adjacent to each other,
A horizontal magnetic field 6A is formed on the photosensitive drum 1 between A and 5B. Then, a repulsive magnet body 5C having an S pole having the same polarity as that of the second magnet body 5A is arranged at a position adjacent to the second magnet body 5A and beyond the downstream end of the charging area in the rotation direction of the photosensitive drum 1. The non-magnetic band 6D due to the repulsive magnetic field 6C formed between the two is located at the downstream end of the charging area.

The magnetic forces of the respective magnets are set to 800 gauss at the end faces of the magnetic poles on the side of the photoconductor drum 1 when the magnetic particles described later are used, and the magnets 5A are set.
It is preferable to set the magnetic force of about 300 to 400 gauss on the surface of the photosensitive drum 1 immediately above. The conductive magnetic particles 4 interposed on the charging area are not particularly limited as long as they are conductive, but are composed of conductive magnetic particles such as ferrite, iron powder, magnetite, etc., whose surface is coated with a conductive resin. Alternatively, it may be composed of a mixed particle group 4 of conductive particles and magnetic particles. For example, the average particle size is 30
It is also possible to use a mixture of a magnetic particle base material having a particle size of about μm and a conductive particle material having an average particle size of about 15 μm in an appropriate ratio.
In this embodiment, ferrite core particles having an average particle size of 20 to 35 μm and a resistivity of 10 ³ to 10 ⁶ Ω · cm are used, and magnetic properties of which are set to 60 to 70 emu / g (1 k Oe) are used. . Reference numeral 8 is a bias power source for applying a charging bias to the conductive magnetic particle group 4 via the linear electrode.

FIG. 2 shows the magnetic action of the vertical magnetic field 6B and the horizontal magnetic field 6A in the magnetic pole layout. As can be understood from this figure, the vertical magnetic field 6B is formed directly above each magnetic pole and the charging area is formed. There is a strong horizontal magnetic field 6A between the N and S pole magnet bodies 5A and 5B, and between the S pole and the second magnet body 5A of the S pole on the lower end side of the charging area and the repulsive magnet body 5C. A repulsive magnetic field 6C is formed by dividing the two horizontal magnetic fields 6A, and as a result, a non-magnetic field 6D is formed between the two magnetic poles 5A and 5C.

As a result, the magnetic particle group 4 adhered to the charged area is adhered and adhered onto the photosensitive drum 1 on the horizontal magnetic field 6A between the N and S magnets 5A and 5B. Vertical magnetic field 6B on the downstream side of the charging area deviated from the horizontal magnetic field 6A
In the above, it is attached so as to stand in the normal direction of the photosensitive drum 1 in a rough state. When the photoconductor drum 1 rotates in this state, the photoconductor drum 1 moves from the horizontal magnetic field 6A to the vertical magnetic field 6B while charging the photoconductor drum 1 on the horizontal magnetic field 6A, and the magnetic particle group is formed by the repulsive magnet body 5C. The vertical magnetic field 6 without being transported downstream due to the non-magnetic field 6D
There is no choice but to escape vertically due to B. The magnetic particle group oriented in the vertical direction is composed of the first and second magnet bodies 5A and 5A.
The magnetic field of B is returned to the horizontal magnetic field 6A side, and the circulation is repeated thereafter. Therefore, according to this embodiment, the smooth charging is performed without the magnetic particles leaking to the downstream side of the charging area.

FIG. 3 shows another embodiment in which a fixed magnet is arranged opposite to a photosensitive drum, and the difference from the above embodiment will be mainly described. In this embodiment, a vertical magnetic field 6B for preventing leakage is formed by the rod-shaped fixed magnet body 2 standing upright from the photosensitive drum 1 in the normal direction through a predetermined gap without providing the repulsive magnet body 5C of the above embodiment. In another embodiment, the fixed magnet body 2 has an N pole located on the side facing the photosensitive drum 1, and the second magnet body 5B and the fixed magnet body 2 arranged to face each other are rotated. Placed on the downstream side of the charging area in the direction
The magnetic particle group 4 is magnetically held by a vertical magnetic field 6B between the two magnet bodies 2 and 5B, and the first magnet body 5A is arranged adjacent to the second magnet body 5B on the upstream side of the charging area. The magnetic particle group 4 is brought into close contact with the photosensitive drum 1 by the horizontal magnetic field 6A mainly formed between the second magnet body 5B and the first magnet body 5A.

In such a structure, the magnetic force of each of the magnet bodies is, for example, about 1200 gauss at the end face of the N pole facing the photosensitive drum 1 in the fixed magnet body 2, and the second magnet body 5A is exposed to light. When the end face of the S pole on the body drum 1 side is set to, for example, 800 Gauss, the two magnet bodies 2, 5A
It was confirmed that a magnetic force of about 300 Gauss could be obtained on the surface of the upper photosensitive drum 1, and a sufficient magnetic holding force of the magnetic particle group 4 could be obtained on the surface of the photosensitive drum 1. The first
It was also confirmed that an effective horizontal magnetic field 6A can be obtained by setting the magnetic force of the magnet body 5A of No. 1 to be almost equal to that of the second magnet body 5B. Further, the stirring means 11 is disposed in the magnetic particle group 4 in the charging area so that the particle group 4 is replaced by mechanical stirring, and the charging bias power source 8 is connected to the stirring means.

According to such an embodiment, the fine particle group in which the surface of the photosensitive drum 1 is smoothly charged while the magnetic particle group 4 is closely contacted on the horizontal magnetic field 6A on the photosensitive drum 1 is According to the rotation, it moves to the position of the vertical magnetic field 6B, where the vertical magnetic field 6B magnetically seals the fine particle group 4 to prevent the particles from leaking out of the charging region, and is fixed from the photosensitive drum 1 side by the magnetic force difference. The magnetic particle group 4 is adsorbed on the magnet body side, and is then returned to the horizontal magnetic field 6A side while moving to the charging area upstream side by rotating the stirring means in the arrow direction, and the above operation is repeated.

Therefore, the magnetic particles 4 on the charged area are always circulated even if they are in close contact with each other by the horizontal magnetic field 6A,
There is no room for deterioration of charged particles even after long-term use.
For the replacement or circulation, the second magnet body 5B or the first magnet body 5A is formed of an electromagnet body, and for example, by using the voltage changer 12 of the DC power supply 13 or the like when no printing is performed or predetermined printing is performed. By appropriately changing the polarity or changing the applied voltage for each number of sheets, the first magnet body 5A
Alternatively, the second magnet body 5B may be appropriately swung by a predetermined angle to exchange and circulate the particle group 4. A vertical magnetic field 6B is similarly formed even if a magnetic material is used instead of the fixed magnet body 2, and in this embodiment, the same operation as in the above embodiment can be achieved, and the developing bias power supply 8 is made a magnetic material. You may connect.

FIGS. 4A and 4B show another embodiment of the present invention, focusing on the difference from the embodiment of FIG. 3, in which the charging gap is set with respect to the photosensitive drum 1 rotating in the right direction in the drawing. (0.5
mm), the non-magnetic sleeve 3 is disposed rotatably in the rotation direction of the photoconductor drum 1 and in the against direction (left direction in the drawing), and on the downstream side of the charging area on the back side of the non-magnetic sleeve 3. The N-pole fixed magnet body 2 is arranged to face the second magnet body 5A, and the magnetic body 2a is arranged adjacent to the lower end side of the charging area of the fixed magnet body 2 to form a closed circuit of the vertical magnetic field 6B. . According to such an embodiment, the fine particle group in which the surface of the photosensitive drum 1 is smoothly charged while the magnetic particle group 4 is brought into close contact with the horizontal magnetic field 6A on the photosensitive drum 1 becomes vertical as the photosensitive drum 1 rotates. The magnetic field 6B is moved to a position where the vertical magnetic field 6B magnetically seals the fine particle group 4 to prevent leakage to the outside of the charging area, and due to the magnetic force difference, from the photosensitive drum 1 side to the sleeve 3 side. The directed magnetic particle group 4 is adsorbed, and is moved to the upstream side of the charging area while being held by the sleeve 3 by the against rotation of the non-magnetic sleeve 3, and is dropped to the photosensitive drum 1 side by the magnetic force of the horizontal magnetic field 6A. Then, the above operation is repeated thereafter.

In this case, since the magnetic body is disposed adjacent to the fixed magnet body to form the closed circuit of the vertical magnetic field 6B, the magnetic shield effect is further enhanced. In this case, the same action is achieved even if the magnetic body is arranged adjacent to the downstream side surface of the second magnet body 5A facing the fixed magnet body in the drum rotation direction. Further, in order to promote the circulation of particles from the developing sleeve 3, a scraper 14 may be provided so that the scraper 14 is mechanically separated and drops onto the photosensitive drum 1 side on the horizontal magnetic field 6A.

[0023]

As described above, according to the present invention, the horizontal magnetic field can secure a charging area in a predetermined width range. Therefore, even when the diameter of the photosensitive drum is reduced, the magnet assembly is provided so as to face the photosensitive drum. Stable charging ability can be maintained even when the body or the charging sleeve containing the assembly is removed. Further, even when the charging sleeve and the like are arranged opposite to each other on the photosensitive drum, the stable charging ability can be maintained without being affected by the fluctuation of the charging gap and the assembly error. Further, it is possible to always obtain a uniform magnetic field without being affected by the fluctuation of the charging gap and the assembly error. Further, the present invention can effectively prevent the leakage of magnetic particles to the outside of the charging area with a simple structure by utilizing a vertical magnetic field or a non-magnetic field. It has various remarkable effects.

[Brief description of drawings]

FIG. 1 is a schematic view showing an embodiment of the present invention in which a magnet body is arranged only on the back side of a photosensitive drum.

FIG. 2 is an operation diagram of magnetic force lines in FIG.

FIG. 3 is a schematic diagram according to a second embodiment of the present invention.

FIG. 4A is a schematic diagram according to a third embodiment of the present invention,
(B) is an enlarged view thereof.

FIG. 5 is an overall schematic view of a charging device according to a conventional technique.

[Explanation of symbols]

 1 Photoconductor drum 2 Fixed magnet body 5A First magnet body 5B Second magnet body 5C Repulsive magnet body 2a Magnetic body 4 Conductive magnetic particle group 6B Vertical magnetic field 6A Horizontal magnetic field 6C Repulsive magnetic field 6D Non-magnetic band

Front Page Continuation (72) Inventor Ryushi Imo 2-14-9 Tamagawadai, Setagaya-ku, Tokyo Kyocera Corporation Tokyo Yoga Works (72) Inventor Yasuo Nishiguchi 2-14-9 Tamagawadai, Setagaya-ku, Tokyo No. Kyocera Corporation Tokyo Yoga Works

Claims (8)

[Claims] 1. A charging device for a photoconductor, comprising a magnetic particle group held on the charging region of the photoconductor by a magnetic force so that the photoconductor can be charged. Two magnetic fields having different polarities along the body moving direction, or two magnetic field generating means composed of a combination of a magnet and a magnetic body are arranged adjacent to each other, and a horizontal magnetic field formed mainly between the two magnetic field generating means A charging device for a photoconductor, characterized in that the magnetic particles are charged while being in close contact with the photoconductor. 2. A repulsive magnetic field composed of a pair of adjacent magnetic poles of the same polarity is formed on the back side of the photoconductor located on the downstream side of the charging region, and the repulsive magnetic field forms a non-magnetic band at the downstream end of the charging region on the photoconductor. The charging device for the photoconductor according to claim 1, which is formed. 3. A charging device for a photosensitive member according to claim 1, wherein a vertical magnetic field having magnetic force lines along the photosensitive member normal direction is formed on the downstream side of the photosensitive member charging area. 4. A magnetic body or a magnetic body located above the photoconductor substantially facing the first magnetic field generation means located downstream of the photoconductor moving direction in the two magnetic field generation means located on the back side of the photoconductor charging area. 4. A charging device for a photosensitive member according to claim 3, wherein a vertical magnetic field forming means composed of a magnet body having a polarity opposite to that of the first magnetic field generating means is arranged. 5. Of the two magnetic field generating means located on the back side of the photoconductor charging area, the first magnetic field generating means located on the downstream side in the moving direction of the photoconductor is formed of a magnet body, and the first magnetic field is formed. A second magnet body having a polarity opposite to that of the first magnetic field generating means is arranged at a position above the photoconductor so as to be substantially opposed to the generating means, and
A magnetic body is disposed adjacent to a downstream side surface of the first magnetic field generating means or the second magnet body in the charging direction, and a closed circuit of a vertical magnetic field is formed between any one of the magnet bodies and the magnetic body. 3. The charging device for the photoconductor according to item 3. 6. The magnetic particle group is composed of conductive magnetic particles or a mixed particle group of conductive particles and magnetic particles, and a charging bias can be applied to the particle group. Photoconductor charging device 7. A method of charging a photoconductor by a magnetic force through a group of magnetic particles held on the charged region of the photoconductor by a magnetic force, comprising: a horizontal magnetic field formed mainly in the charged region of the surface of the photoconductor. By this, the magnetic particle group is charged while being brought into close contact with the photoconductor, and a non-magnetic field is formed on the surface of the photoconductor on the downstream end side of the charging region to prevent leakage of the magnetic particles located on the charging region. Charging method for a photoconductor characterized in that 8. A method of charging a photoconductor by magnetic force through a group of magnetic particles held on the charged region of the photoconductor, comprising: a horizontal magnetic field mainly formed in the charged region of the surface of the photoconductor. The magnetic particle group is charged while being brought into close contact with the photoconductor, and a magnetic leakage block region mainly composed of a vertical magnetic field is formed on the surface of the photoconductor on the downstream end side of the charging region by using the block region. A method of charging a photoconductor, characterized in that it acts so as to prevent leakage of magnetic particles located on the charging area.