JP3087936B2 - Charging device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Conventionally, respective process means of exposure, development, transfer, cleaning (removal of residual toner), charge elimination 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 photoconductive drum is formed by laminating a light-transmitting conductive layer and a photoconductive layer on a cylindrical light-transmitting support, and a light output corresponding to image information is formed in the drum. Exposure means (for example, an LED head) to be generated is interpolated, and the light output of the exposure means is exposed on a photosensitive drum charged on the photosensitive drum using a predetermined charging means through a converging lens, or simultaneously or immediately after the exposure. An image forming apparatus configured to form the latent image into a toner image (development) via a developing sleeve facing the photosensitive drum and transfer the toner image to recording paper via a transfer roller or other transfer means; Apparatuses (JP-A-58-153957 and others) are also known.

The charging means used in this type of apparatus is generally a corotron type in which a high voltage is applied to a thin tungsten wire to perform corona discharge, or a charging means in which a voltage of several hundred volts is applied to a conductive roller to contact and charge a photosensitive drum. In addition, there is a type in which a voltage is applied to a conductive brush while being brought into contact with a photosensitive drum to charge the conductive brush. However, the corotron method uses high voltage and generates ozone for safety reasons.
Many environmental problems. Further, the charging roller is unstable in charging because the contact with the photosensitive drum is a line contact. Further, in the brush charging method, the charging of the brush is likely to occur because the drum and the brush are in contact with each other to perform charging.

In order to eliminate such a defect, 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 is a so-called particle charging method in which a magnetic particle group 104 is adhered to the brush 3 and a brush-shaped magnetic spike is rubbed against the photosensitive drum 101 to apply a charging bias 108 to the magnetic particle group 104 via a sleeve 103 to perform charging. Has been proposed.
(JP-A-59-133569, JP-A-63-18726)
7 others)

In such a charging method, when a magnetic spike 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. The magnetic coercive force of the magnetic particles located is the weakest. On the other hand, the magnetic particle group 104 slidably rubs between particles or with the photosensitive drum 1 in the charged area, and is charged to have a charge. Therefore, when the photosensitive drum 101 is rotated in this state, a centrifugal force acts on the drum surface, and the magnetic particles 4 electrostatically adhered to the photosensitive drum 101 cause the magnetic coercive force ( magnetic field)
A force acts in the direction away from the magnetic chain, that is, the charged region, and the particles 104a attached to the photosensitive drum adversely affect the exposure and development in the next step.

There is also a method of rotating the magnet assembly. However, such a method requires a complicated drive system structure,
Since the magnetic pole moves at high speed, not only leakage but also scattering of magnetic particles is further increased. For this reason, the prior art is configured to collect the magnetic particles by arranging the blade 105 on the downstream side of the charging area in the photoconductor moving direction. The blade 10
A mechanism for collecting the magnetic particles 104a attached to the surface 5 is required, and the configuration becomes complicated.

In view of the drawbacks of the prior art, the present invention can effectively prevent the magnetic particles from leaking and scattering outside the charged area with a simple structure, and can further reduce the size of the photosensitive drum. Still another object of the present invention is to provide a charging device capable of stably charging even if an assembly error of a charging sleeve or the like occurs.

[0009]

SUMMARY OF THE INVENTION In order to achieve the above technical object, a photoreceptor is structured such that the photoreceptor can be charged by magnetic force via magnetic particles held on a charged area of the photoreceptor. The first feature of the apparatus is that one or a plurality of magnets (hereinafter, referred to as a first magnet) are arranged on the back side of the photoreceptor and cooperate with the magnet or another magnet. The point is that the magnetic particles are magnetically supported on the charged area on the surface of the photoreceptor by operation. That is, more specifically, as shown in the examples described later, a plurality of magnetic poles having opposite polarities are arranged on the back side of the photoreceptor to form a horizontal magnetic field, and the horizontal magnetic field adheres the magnetic particles on the surface of the photoreceptor. The magnetic field may be formed by arranging a plurality of magnetic poles having opposite polarities on the back side and both sides of the photoconductor with the photoconductor interposed therebetween, and the magnetic field carries the magnetic particles on the photoconductor surface. May be charged,
In any case, it is assumed that at least one magnetic pole exists on the back surface of the photoconductor.

As a result, the magnet body for holding the magnetic particles magnetically is arranged not only in the charging sleeve on the surface of the photoreceptor but on the back side of the photoreceptor. By comparison, the magnetic field of the charged area on the photoreceptor surface can be increased, thereby preventing the scattering of magnetic particles on the charged area and the like.As a result, even if there is some assembly error of the charging gap, etc. Even if the gap tolerance is set large, it is possible to maintain a stable magnetic coercive force of the magnetic particles without considering the eccentricity of the photosensitive drum 1 and the non-magnetic sleeve. The fact that the assembly tolerance and the eccentricity can be set roughly leads to a reduction in the number of assembly steps and manufacturing costs. Even when the diameter of the photosensitive drum is reduced, a charging magnetic field can be effectively secured.

A second feature of the present invention is that a second magnet body having the same polarity as the magnet body is formed on the back surface or the surface of the photosensitive body downstream in the movement direction of the photosensitive body. And a magnetic shield of a group of magnetic particles at the lower end side of the charged area using a repulsive magnetic field formed between the magnet body of the first magnet body and one of the first magnet bodies located on the downstream side of the photoconductor charged area. I have done it. That is, specifically, the second magnet body may be provided on the back side of the photoconductor adjacent to the magnet body located on the downstream side of the photoconductor charging area, or may be provided on the downstream side of the photoconductor charging area. The second magnet body may be provided so as to extend in a direction orthogonal to the photosensitive body moving direction on the surface side of the photosensitive body so as to be substantially opposed to the magnet body to be sandwiched by the photosensitive body.

Thus, a repulsive magnetic field consisting of a pair of adjacent magnetic poles having the same polarity forms a non-magnetic force band at the downstream end of the charged area on the photoreceptor, and the non-magnetic force band prevents leakage of magnetic particles to the photoreceptor drum. In addition, since particles can be maintained on the charged area side, leakage from the charged area can be effectively prevented without using a blade or the like. In this case, preferably, a first magnet body is provided on the downstream side of the charged area on the back side of the photoconductor, and a third magnet body having a polarity opposite to that of the first magnet body is provided on the back side of the non-magnetic sleeve opposed to the first magnet body. A second magnet body having the same polarity as that of the first magnet body is disposed on the back surface or the surface of the photosensitive body on the downstream side in the movement direction of the photosensitive body, and the second magnet body is disposed on the surface of the photosensitive body of the first magnet body. The magnetic force density of the second magnet body is set higher than the magnetic force density. As a result, the magnetic particles that have been prevented from leaking out of the charged area on the surface of the photoreceptor drum by the non-magnetic force band formed at the downstream end of the charged area on the photoreceptor due to the repulsive magnetic field are caused by the magnetic force difference. That is, it is possible to circulate in the charging region toward the non-magnetic sleeve. In this case, by arranging the non-magnetic sleeve so as to be rotatable against the moving direction of the photoconductor, it is easier to circulate the magnetic particles to the upstream side of the charging area.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention; However, unless otherwise specified, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention, but are merely illustrative examples. Not just. FIG.
The configuration of the charging device according to the first embodiment of the present invention will be described based on (A) and (B). As described above, the charging device is opposite to the photosensitive drum 1 at the charging area position via the charging gap (0.5 mm) with respect to the photosensitive drum 1 rotating rightward in the drawing, that is, in the opposite direction (see FIG. The non-magnetic sleeve 3 is rotatably provided in the upper left direction, and when viewed from the rotation axis, the rotation direction is the same. In addition, the non-magnetic sleeve 3 is fixed and disposed on the back side of the non-magnetic sleeve 3 downstream of the charging area. The fixed magnet body 2A is disposed in the magnet assembly 2 thus formed. Reference numeral 8 denotes a bias power supply for applying a developing bias to the conductive magnetic particle group 4 via a conductive blade or a non-magnetic sleeve 3 (not shown).

On the other hand, on the back side of the photosensitive drum 1, a first magnet body 5A is substantially opposed to the fixed magnet body 2A located on the downstream side of the charging area, and is adjacent to the first magnet body 5A. The horizontal magnetic field forming magnet 5B is disposed adjacent to the charging area upstream side, the first magnet 5A is set to the S pole having the opposite polarity to the fixed magnet 2A, and the horizontal magnetic field forming magnet 5B is The first magnetic body 5A is set to have an N pole having a polarity opposite to that of the first magnet body 5A, and a horizontal magnetic field is formed on the photosensitive drum 1 between the two magnet bodies 5A and 5B.

That is, specifically, the first opposedly arranged first
5A and the fixed magnet 2 are disposed downstream of the charged area in the rotation direction of the photosensitive drum 1, and the magnetic particles 4 are magnetically held by a vertical magnetic field 6A between the two magnets 2A and 5A. The forming magnet body 5B is the first magnet body 5
A, and the magnetic particle group 4 is closely attached to the photosensitive drum 1 by a horizontal magnetic field mainly formed between the first magnet body 5A and the horizontal magnetic field forming magnet body 5B. Let it.

The non-magnetic sleeve 3 and the photosensitive drum 1
The conductive magnet particles 4 are interposed on the charged area between the fixed magnet body 2A and the first magnet body 5A in an air space slightly downstream of the downstream end of the developing area in the moving direction of the photosensitive drum 1. An S-pole or substantially trapezoidal S-pole magnet body 5C is disposed at an opposing position.

The magnetic particles 4 are not particularly limited as long as they are conductive. However, the magnetic particles 4 may be made of conductive magnetic particles coated with a conductive resin on the surface of a magnetic core such as ferrite, iron powder, magnetite or the like. Mixed particle group 4 of magnetic particles
May be configured. For example, a mixture of a magnetic particle base material having an average particle size of about 30 μm and a conductive particle material having an average particle size of about 15 μm may be used. In this example, the average particle diameter was 20 to 35 μm, and the resistivity was 10 ³ to 10 μm.
Use is made of ferrite core particles of 10 ⁶ Ω · cm with magnetic properties set to 60 to 70 emu / g (1 k Oe).

The magnetic force of each of the magnet bodies is 800 to 1000 gauss on the sleeve 3 facing the photosensitive drum 1 in the fixed magnet body 2A, and the first magnet body 5A is The magnetic force density is set so that a magnetic force of about 300 to 400 Gauss can be obtained on the surface of the photosensitive drum 1 on the magnet body 5A, and the magnetic force of the horizontal magnetic field forming magnet body 5B is set to be equal to that of the first magnet body 5A. By setting them substantially equal, a magnetic force of about 300 to 400 gauss can be obtained on the surface of the photosensitive drum 1, and the magnetic body 5C of the S pole has a magnetic force on the photosensitive drum surface of the first magnet 5A. The magnetic force density is set higher than the density, for example, about 600 to 800 Gauss.

Although the surface magnetic force of the photoreceptor of the first and second magnet bodies 5A and 5B should be as large as possible for uniform charging and improvement of adhesion, the photoreceptor drum 1 side on a vertical magnetic field 6A is preferable. In order to smoothly move particles from the photosensitive drum 1 to the non-magnetic sleeve 3 side, it is necessary to increase the magnetic force on the sleeve 3 side with respect to the photosensitive drum 1 side. Therefore, the limit value is the position just above each magnet body on the surface of the photosensitive drum 1 and the first magnet body 5A
And the horizontal magnetic field forming magnet 5B are preferably set to 1000 gauss or less, and the magnetic force density on the sleeve of the fixed magnet 2A and the repulsion magnet 2B are preferably set to 1200 gauss or less.

The S-pole magnet body 5C is composed of a fixed magnet body 2A that is prevented from moving outside the charged area by the repulsive magnetic field formed between the first magnet body and the S-pole magnet body 5C.
In order to make it possible to smoothly attract to the side, the magnetic body 5C of the S pole is preferably set to a magnetic force density larger than the magnetic force density on the surface of the photosensitive drum 1 of the first magnet body 5A.

According to this embodiment, the magnetic particle group 4 adhered to the charged area is composed of both N-pole and S-pole magnet bodies 5A,
On the vertical magnetic field 6B downstream from the horizontal magnetic field 6A on the charged area, which adheres closely to the photosensitive drum on the horizontal magnetic field 6A between 5B, and coarsely in the normal direction of the photosensitive drum 1 It is attached to stand. In this state, the photosensitive drum 1
Rotates, the photosensitive drum is charged on the horizontal magnetic field 6A while moving from the vertical magnetic field 6B to the vertical magnetic field 6B, and the magnetic particles 4 are repelled by the repulsive magnetic field between the S magnetic pole and the magnet body 5C. The vertical magnetic field 6B is not transferred to the downstream side by the non-magnetic force zone 6D formed by the photosensitive drum 1.
Escapes in the vertical direction.

The magnetic particle group 4 oriented in the vertical direction is
This time, on the contrary, the magnetic field adheres to the sleeve 3 side by the attractive force of the S-pole magnet body 5C and the fixed magnet body, and thereafter, is returned to the horizontal magnetic field 6A side on the upstream side of the charging area according to the rotation of the sleeve 3, and thereafter the circulation is repeated. Do. Therefore, according to this embodiment, the smooth charging is performed without the magnetic particles 4 leaking to the downstream side of the charging area.

The S-pole magnet body 5C may be arranged on the back side of the developing sleeve 3, as shown in FIG. In this embodiment, as shown in FIG. 1 and FIG. 1A, repulsion having the same polarity as the fixed magnet body 2A is provided in the upstream direction of the charging area of the fixed magnet body 2A, in other words, in the downstream side of the sleeve rotation direction. The magnet body 2B is provided. And the fixed magnet body 2A
The repulsion magnet body 2B, which is set to have the same polarity as the N pole, is laid out such that the non-magnetic force zone due to the repulsion magnetic field formed between the two is located on the upstream side of the charging area, and is thereby carried on the non-magnetic sleeve 3. Then, the magnetic particles 4C conveyed to the upstream side of the charging area from the position of the vertical magnetic field 4A are magnetically released, fall to the photosensitive drum 1 side, and the circulation and leakage prevention of the magnetic particles are performed more smoothly.

FIG. 3 shows an embodiment in which the charging sleeve and the fixed magnet assembly are not arranged on the photosensitive drum but opposed to each other, and are arranged only on the rear surface of the photosensitive drum. Reference numeral 1 denotes a photosensitive drum which rotates clockwise. On the back side of the drum corresponding to the charged region, an N-pole horizontal magnetic field forming magnet body 5B and a downstream are arranged on the upstream side so as to substantially divide the charged region into two. The first magnet body 5A of the S pole having the opposite polarity is disposed adjacent to the first magnet body 5A.
A horizontal magnetic field 6A is formed on the photosensitive drum 1 between A and 5B. At a position adjacent to the first magnet body 5A and beyond the downstream end of the charging area in the rotation direction of the photosensitive drum 1, a repulsion magnet body 5C having the same polarity as the first magnet body 5A and having the S pole is arranged. And a non-magnetic force zone 6D formed by the repulsive magnetic field 6C formed therebetween is located at the downstream end of the charging area.

In order to more smoothly prevent the leakage of the magnetic particles, the non-magnetic conductive thin film 7a is exposed from the conductive support member 7b so that the free end side contacts the photosensitive drum 1 at the entrance end of the non-magnetic force zone. Droop in the body drum normal direction,
Further, a bias power source 8 is connected via the support member 7b. FIG. 4 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 FIG. 4, a vertical magnetic field 6B is formed immediately above each magnetic pole, and N Pole and S pole first and second
A strong horizontal magnetic field 6A between the magnet bodies 5A and 5B
A repulsive magnetic field 6C, in which two horizontal magnetic fields 6A are separated, is formed between the first pole 5A and the repulsive magnet 5C of the S pole on the lower end side of the charged area, and as a result, the two magnetic poles 5A, 5A
A nonmagnetic zone 6D is formed between C. As a result, the magnetic field moves from the horizontal magnetic field 6A to the vertical magnetic field 6B, and the magnetic particles move in the vertical direction by the vertical magnetic field 6B without being transported downstream by the non-magnetic force zone 6D formed by the repulsive magnet 5C. However, while the bias power 8 is applied by the thin film 7a, the leakage is further mechanically prevented, and the circulation of the magnetic particles is smoothly performed.

[0026]

As described above, according to the present invention, it is possible to smoothly prevent magnetic particles from leaking out of the charged area and smoothly circulate in the charged area with a simple configuration in which a plurality of magnetic poles are opposed to each other.
Further, according to the present invention, even when the size of the photosensitive drum is reduced, charging can be stably performed even if an assembly error of the charging sleeve or the like occurs. And so on.

[Brief description of the drawings]

FIG. 1 is a schematic view of a charging device according to a first embodiment of the present invention, showing a printing state (A) and a non-printing state (B), respectively.

FIG. 2 is a schematic diagram showing a modification of FIG.

FIG. 3 is a schematic diagram showing an embodiment of the present invention in which a magnet body is arranged only on the back side of the photosensitive drum.

FIG. 4 is an operation diagram of the magnetic field lines of FIG. 3;

FIG. 5 is an overall schematic diagram of a charging device according to the related art.

[Explanation of symbols]

 Reference Signs List 1 photoconductor drum 2A fixed magnet body (third magnet body) 5A first magnet body 5C S pole magnet body (second magnet body) 5B horizontal magnetic field forming magnet body 4 conductive magnetic particle group

Continuation of the front page (72) Inventor Yasuo Nishiguchi 2-14-9 Tamagawadai, Setagaya-ku, Tokyo Kyocera Corporation Tokyo Yoga Office (56) References JP-A-5-181347 (JP, A) JP-A Sho-59 -228675 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/02 101 G03G 15/09

Claims (6)

(57) [Claims] 1. A charging device for a photoreceptor configured to be capable of charging a photoreceptor via a group of magnetic particles held on a charging area of the photoreceptor by a magnetic force, wherein one or a plurality of magnets are provided on the back side of the photoreceptor. (Hereinafter, referred to as a first magnet body), magnetic particles are magnetically supported on a charged area on the surface of the photoconductor by cooperating with the magnet body or another magnet body, and the moving direction of the photoconductor is changed. A second magnet body having the same polarity as the magnet body is formed on the back surface or the surface of the downstream photosensitive body, and the second magnet body and the first magnet body, and the downstream side of the photosensitive body charging area. A charging device characterized by using a repulsive magnetic field formed by a single magnet body positioned at the lower end to magnetically shield a group of magnetic particles at the lower end of the charging area. 2. The charging device according to claim 1, wherein the second magnet is disposed on the back side of the photoconductor adjacent to a magnet located downstream of the photoconductor charging area. A second magnet extending in a direction orthogonal to a moving direction of the photosensitive member on a surface of the photosensitive member so as to be substantially opposed to the magnet member located on the downstream side of the photosensitive member charging area with the photosensitive member interposed therebetween;
The charging device according to claim 1, wherein the magnet body is disposed. 4. A charging device in which a magnetic particle group is carried between a non-magnetic sleeve facing a photoreceptor and the photoreceptor can be charged via the particle group. A first magnet body, the first magnet body;
A third magnet body having a polarity opposite to that of the first magnet body on the back side of the non-magnetic sleeve opposite to the magnet body, and a same polarity as the first magnet body on the downstream side in the photoconductor moving direction slightly out of the charged area. Second
Charging device characterized in that each magnet body is disposed. 5. The charging device according to claim 4, wherein the magnetic force density of the second magnet body is set to be larger than the magnetic force density of the first magnet body on the photoreceptor surface. 6. The charging device according to claim 4, wherein said non-magnetic sleeve is configured to be rotatable against the moving direction of the photosensitive member.