JP2003270956A - Electrophotographic device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-quality printed image free from jitter by preventing the vibration of a developing machine caused by magnetic field interference between magnet rolls in an electrophotographic device equipped with a plurality of developing rolls consisting of a plurality of sleeves and a plurality of developing rolls. <P>SOLUTION: By inserting a magnetic shielding plate between a core rotating type developing roll where the sleeve and the magnet roll are rotated and another developing roll adjacent to the developing roll, magnetic field formed by both magnetic rolls is intercepted so as not to interfere with each other, whereby the magnetic field interference between the developing rolls is prevented. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic apparatus for visualizing an image by using colored particles such as toner in printers, facsimiles, copiers and the like.

[0002]

2. Description of the Related Art A conventional developing device and developing method for an electrophotographic apparatus will be described below. An electrophotographic apparatus includes a developing process for making colored particles visible on the surface of a recording material as an image and a fixing step for fixing the visualized colored particle image on the recording material. For the colored particles, a powder called a toner exclusively for electrophotography is used.

The entire surface of the photoconductor is once charged,
Then, by irradiating with light, partial charge discharge is performed. Here, a potential contrast is formed between the charged area and the discharged area on the surface of the photoconductor, and this is called an electrostatic latent image.

In the developing step, first, toner particles, which are colored particles, are charged with a developer. The developer may be a two-component system composed of a mixed powder of toner and carrier beads which are magnetic particles, or a one-component system composed only of the toner. The developer is contained in the developing device and agitated therein. At that time, in the case of the two-component developer, the toner is charged by friction with the carrier beads. In the case of a one-component developer, the toner is charged by friction with a member or the like. The one-component developer includes a method using a magnetic toner and a method using a non-magnetic toner. The developer is conveyed to a developing position facing the electrostatic latent image on the surface of the photoconductor by a rotating roll having a rotating sleeve called a developing roll and a magnet roll. At this time, the developer forms a "magnetic brush" arranged in a brush shape along the lines of magnetic force at a position facing the photoconductor. The developing method using the method of transporting the developer to the electrostatic latent image on the photoconductor by the developing roll is called magnetic brush development.

On the other hand, a method called bias development is often used as a method for visualizing an electrostatic latent image. In bias development, a bias voltage is applied to the developing roll to separate the charged toner particles from the developer on the developing roll surface by the action of an electric field generated between the latent image potential formed on the surface of the photoconductor and the developing roll. Then, the image is formed by moving it to the surface of the photoconductor. As the latent image potential (that is, the potential of the image forming portion of the photoconductor), the above-mentioned charging potential or the discharge potential due to exposure may be used. Generally, a method using a charging potential as a latent image potential is called a normal development method, and a method using a discharge potential is called a reversal development method. Of the charging potential and the discharging potential, the potential not used as the latent image potential is called the background potential. The bias voltage of the developing roll is set to the midpoint between the charging potential and the discharging potential, and the difference between the developing potential and the latent image potential is called the developing potential difference. Similarly, the difference from the background potential is called the background potential difference.
Usually, the development potential difference that affects the development performance itself is set to be larger than the background potential difference. It goes without saying that the larger the development potential difference, the stronger the electric field formed (called the development electric field), and therefore the higher the development performance (toner development amount).

A method of increasing the rotation speed of the developing roller between the developing roller and the photoconductor, a method of narrowing the distance, and a method of decreasing the electric resistance of the developer also have the same effect of strengthening the developing electric field, and toner development The quantity can be higher.

A method of using magnetic brush development as a method of conveying a developer and bias development for developing an electrostatic latent image is a widely and commonly used development method. This developing method is referred to as magnetic brush bias developing in this specification. The relative movement direction of the developing roll and the photoconductor may be the same direction or the opposite direction. Further, one developing machine may use a plurality of developing rolls.

There are developing devices in which a plurality of developing rolls rotate in the same direction, and there are developing devices in which the rotating directions are different. In this case, the rotation directions of the two developing rolls are made different from each other so that the rotation directions of the adjoining developing rolls are directed from the facing positions of the developing rolls to the photoconductor, and the developer is directed like a fountain from the opposing position of the developing rolls. A developing machine that branches and is conveyed toward a photoconductor is also known. Such a developing machine is found, for example, in Japanese Examined Patent Publication No. 54-10869. In this specification, such a developing machine is referred to as a fountain type developing machine. In the magnetic brush bias development, there is a problem that the edge portion of the image is hard to develop in the rotation direction of the developing roll. The cause of this phenomenon is the mechanical factor of the magnetic brush rubbing the surface of the photoconductor, and the potential of the photoconductor in contact with the magnetic brush suddenly changes from the background potential of the non-image area to the development potential of the image area. Therefore, there is an electrical factor in which the electrical characteristics of the developer cannot follow this change. If a fountain type developing machine is used, the two developing rolls have different rotation directions, and the respective rolls complement each other, so that the above problem does not occur.

The developing roll is composed of a core portion, which is a magnet roll made of a magnet, and a metal sleeve that forms the outer shell of the core portion. There are a method of fixing the core portion and rotating the sleeve to convey the developer, and a method of rotating both the core portion and the sleeve. In this specification, the former method is called a sleeve rotation method and the latter method is called a core rotation method.

The core rotation method has a higher effect of disturbing the developer in the developing area of the portion facing the photosensitive member than the sleeve rotation method, so that the toner development amount can be increased. Therefore, a sufficient toner development amount can be obtained even if the rotation speed of the sleeve is reduced. This can reduce scraping of the toner image on the photoconductor due to mechanical rubbing of the developing roll itself, so that the image quality finally printed on the paper can be improved. Examples of the core rotary developing machine include JP-A-58-142358.

Furthermore, if at least one of the developing rolls of the fountain type developing machine, which is characterized in that there is no edge chipping of the image due to electrical factors, is of the core rotation type, the toner image is scraped off due to mechanical factors. It was found that an extremely high-quality image with little disturbance can be obtained because the image is eliminated. In the present specification, the developing machine having the above structure is referred to as a core rotary fountain type developing machine. However, since the two magnet rolls rotate, the magnetic field interference between the magnetic poles of the two magnet rolls causes vibrations in the developing machine, which causes a problem that jitter appears in the image. Further, in the case of two-component development, the strength of the magnetic force is temporally generated in the developing area, and when the magnetic force is weak, the carrier easily adheres to the photosensitive member. The temporal change in magnetic force in the developing area appears as a phenomenon called fog, which deteriorates print quality.

[0012]

In the above-described conventional core rotation type development, the phenomenon of magnetic field interference between the two magnet rolls is not taken into consideration, and vibration occurs and jitter appears in the image. There were challenges.

SUMMARY OF THE INVENTION An object of the present invention is to provide a core rotary developing machine capable of preventing vibration and printing a high quality image without jitter and an electrophotographic apparatus using the same.

[0014]

In order to prevent magnetic field interference between two magnet rolls, a magnetic shield plate is inserted between the magnet rolls to prevent magnetic field interference.

The magnetic shield plate is composed of two or more magnetic plates. The first magnetic plate is arranged so as to cover the first magnet roll and shields the magnetic field generated by the first magnet roll from leaking to the second magnet roll side. Similarly, the second magnetic plate is arranged so as to cover the second magnet roll, and shields the magnetic field. By providing a gap filled with a non-magnetic material between the magnetic material plates, magnetic field interference by the first and second magnet rolls can be sufficiently prevented.

In order to enhance the magnetic shielding effect and reduce the size of the developing machine, the length of the magnetic shielding plate in the longitudinal direction is set to 0.7 to 1.3 times the length of the magnetic roll in the longitudinal direction. If the length of the magnetic shield plate in the longitudinal direction is 1.0 times or more and 1.3 times or less the length in the longitudinal direction of the magnetic roll, an even better magnetic shielding effect can be obtained.

Further, by setting the width of the magnetic shielding plate to be larger than the interval between the developing rolls and not more than the diameter of the developing rolls,
The magnetic shielding effect and the downsizing of the developing machine can be achieved.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described below with reference to FIGS.

FIG. 1 is a schematic diagram of an electrophotographic apparatus. 1
Is a photoconductor drum, 2 is a charger, 3 is toner, 4 is a developing machine, 5 is paper, 6 is a transfer machine, 7 is a fixing machine, 8 is a cleaner, and 9 is an exposure device. An electrostatic latent image is formed on the surface of the photosensitive drum 1 uniformly charged by the charger 2 by a semiconductor laser whose light emission is controlled by exposure control means such as a laser driver and an exposure device 9 including an optical system. . After that, the electrostatic latent image is developed with the toner 3 by the developing device 4. The toner 3 is transferred onto the sheet 5 by the transfer device 6. After that, the transferred toner image is heated and melted by the fixing device 7 and fixed on the paper 5. The toner 3 remaining on the surface of the photosensitive drum 1 without being transferred is collected by the cleaner 8 and the series of processes is completed. The developing method of this embodiment uses magnetic brush bias development with a two-component developer. Further, the discharge potential is used as the latent image potential, and the reversal development is performed.

FIG. 2 is a schematic cross-sectional view showing the details of the developing machine 4, which uses core rotary fountain type development. 40 is a developer, 41 and 42 are developing rolls, 43 is a doctor blade, 44 is a carrier catch roll, 45 is a scraper, 46 is an auger screw, 47 is a developer conveying roll, 48 is a toner concentration sensor, and 49 is a toner hopper. .

Toner is supplied from the toner hopper 49 into the developing device 4. The carrier and the toner are mixed by the auger screw 46 to form the developer 40. The toner is agitated and charged to an appropriate level by friction with the carrier.
The charged toner becomes a part of the developer 40 and reaches the back surface of the doctor blade 43 by the developer carrying roll 47. After that, the doctor blade 43 and the developing roll 4
Through each gap formed by 1 and 42 (referred to as a doctor gap), the flow is divided into a flow conveyed along the developing roll 41 and a flow conveyed along the developing roll 42. The developing device 4 is a fountain type developing device, and the branched developer 40 develops the toner 3 on the photoconductor 1 at a portion facing the photoconductor 1. The developing rolls 41 and 42 are of a core rotation type.

The vicinity of the developing rolls 41 and 42 will be described in detail with reference to FIG. The core rotation method that rotates the sleeve and the magnet roll has a higher effect of disturbing the developer in the development area of the portion facing the photoconductor, as compared with the sleeve rotation method that rotates only the sleeve, so that the toner development amount is increased. be able to. Therefore, a sufficient toner development amount can be obtained even if the rotation speeds of the sleeves 112 and 122 are reduced. As a result, it is possible to reduce scraping of the toner image on the photoconductor 1 due to mechanical rubbing of the developing rolls 41 and 42 themselves, and thus it is possible to improve image quality. When the developing roll of the fountain-type developing machine is characterized by the fact that the edges of the image are not chipped, the toner image is not scraped off due to mechanical factors due to the rotation of the magnet roll, so extremely high quality with less disturbance. Images can be obtained. Magnet roll 11
When driving 1, 121 respectively, there is a problem that the magnetic field of one magnet roll influences the other magnetic field to accelerate or decelerate the rotation. That is, depending on the magnetic pole positions of the magnet rolls 111 and 121, there arises a problem that the magnetic poles repel or attract each other to exert an attractive force or a repulsive force between the shafts, or apply or reduce a torque. As a result, this action vibrates the developing device 4 and causes jitter in the image. This phenomenon occurs even when only the magnet roll 111 is rotated without rotating the magnet roll 121. The arrow in the sleeve and the magnet roll in FIG. 3 indicates the rotation direction of the sleeve and the magnet roll.

FIG. 3 shows an embodiment in which the magnetic shield plate 110 is provided in order to reduce the vibration due to the magnetic field interference.

The magnetic shielding plate 110 sandwiched between the developing rolls 41 and 42 has, for example, a five-layer structure (SU
S) (Fe) (SUS) (Fe) (SUS). (SUS) is the non-magnetic plate 104, (Fe) is the magnetic plate 1
13,123. At this time, as shown in FIG. 3, the magnetic force lines 105 formed by the pair of NS poles of the magnet roll 111 pass through the magnetic material plate 113 on the developing roll 41 side, but hardly leak to the outside (developing roll 42 side). . This is a physical phenomenon generally called magnetic shielding. Similarly, the magnetic force line 105 formed by the magnet roll 121 of the developing roll 42 can be shielded by the magnetic plate 123 on the developing roll 42 side. A similar effect can be obtained by providing a void instead of the non-magnetic plate 104.

Therefore, even when the magnet rolls 111 and 121 rotate, the magnetic force lines 105 can be sufficiently shielded to prevent vibration due to magnetic field interference. Alternatively, it can be sufficiently reduced.

If only one magnetic plate is used in FIG. 3, lines of magnetic force from both magnet rolls 111 and 121 will enter the plate, and the interference cannot be blocked.

If the gap between the developing rolls is sufficient, it is possible to add two more magnetic plates and use four magnetic plates 103 to form a nine-layer structure as shown in FIG. is there. In this case, the magnetic lines of force that leak out without being completely shielded by the two outer magnetic plates can be more sufficiently shielded by the two inner plates.

Further, in the case of the fountain type developing machine, since the developer conveying path is between the two developing rolls, the magnetic shielding plate also serves as a regulating blade. Therefore, if the doctor blade 43 in FIG. 2 is a magnetic shield plate, the developing machine 4 can be downsized. If the developing machine 4 has a margin, a magnetic shield plate may be provided separately from the doctor blade 43.

Further, in order to further enhance the effect as the magnetic shield, the length L in the longitudinal direction of the magnetic shield plate 110 in FIG. 4 is set to 0.7 of the length in the longitudinal direction of the magnet roll.
It is sufficient if it is more than twice and less than 1.3 times. The longitudinal direction of the magnet rolls means the magnet rolls 111 and 121 in FIG.
Is the rotation center axis direction. If the length is 0.7 times or less the length of the magnet roll in the longitudinal direction, it becomes difficult to sufficiently prevent magnetic field interference due to magnetic lines of force that wrap around the edge of the magnetic shield plate 110. If it is 1.3 times or more, downsizing of the developing machine becomes difficult. In order to obtain a further magnetic shielding effect, the length of the magnetic shielding plate 110 in the longitudinal direction may be 1.0 to 1.3 times the length of the magnetic roll in the longitudinal direction.

Further, in order to enhance the effect as a magnetic shield, the width W of the magnetic shield plate 110 in FIG.
It is possible to prevent magnetic lines of force that wrap around the edges of the. Further, the width W of the magnetic shielding plate 110 is set to be equal to or less than the diameter of the developing roll, so that the developing machine can be downsized.

From the above, there is no magnetic field interference between the developing roll 41 and the developing roll 42, and vibration is eliminated. According to the present embodiment described above, since the fountain type core rotary developing machine is used and the vibration due to the magnetic field interference between the magnet rolls can be prevented, a high quality image without jitter can be obtained.

In this embodiment, the core rotary fountain type development is described. Although similar in magnetic field interference to the sleeve rotary developing machine as in the core rotary developing machine, similar magnetic field interference is present, which may adversely affect the flow of the developer. The present invention exerts the effect of reducing magnetic field interference even in such a case.

[0033]

According to the present invention described above, even if a plurality of core rotation type developing rolls are used, the magnetic shielding plate can block the magnetic field interference with the adjacent developing rolls.
Therefore, vibration due to magnetic field interference between the developing rolls can be prevented, and a core rotary developing machine and an electrophotographic apparatus capable of printing a high quality image without jitter can be provided.

[Brief description of drawings]

FIG. 1 is a schematic diagram of an electrophotographic apparatus that is an embodiment of the present invention.

FIG. 2 is a schematic diagram of a developing machine of an electrophotographic apparatus that is an embodiment of the present invention.

FIG. 3 is a schematic view of the vicinity of a developing roll that is an embodiment of the present invention.

FIG. 4 is a schematic view of a magnetic shielding plate that is an embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum, 2 ... Charging device, 3 ... Toner, 4 ... Developing device, 40 ... Developer, 41 ... Developing roll, 42 ... Developing roll, 43 ... Doctor blade, 44 ... Carrier catch roll, 45 ... Scraper, 46 ... Auger screw,
47 ... Developer transport roll, 48 ... Toner concentration sensor, 4
9 ... Toner hopper, 5 ... Paper, 6 ... Transfer machine, 7 ... Fixing machine, 8 ... Cleaner, 9 ... Exposure device, 110 ... Magnetic shield plate, 111, 121 ... Magnet roll, 112, 122 ... Sleeve, 103, 113, 123 ... Magnetic plate, 104 ...
Non-magnetic plate or void, 105 ... Magnetic field lines.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Tsuneaki Kawanishi             Hitachiko, 1060 Takeda, Hitachinaka City, Ibaraki Prefecture             Machine Co., Ltd. (72) Inventor Hisao Okada             Hitachiko, 1060 Takeda, Hitachinaka City, Ibaraki Prefecture             Machine Co., Ltd. (72) Inventor Masayoshi Ishii             Hitachiko, 1060 Takeda, Hitachinaka City, Ibaraki Prefecture             Machine Co., Ltd. (72) Inventor Keisuke Kubota             Hitachiko, 1060 Takeda, Hitachinaka City, Ibaraki Prefecture             Machine Co., Ltd. (72) Inventor Hiroyoshi Matsumoto             Hitachiko, 1060 Takeda, Hitachinaka City, Ibaraki Prefecture             Machine Co., Ltd. F-term (reference) 2H031 AC11 AC23 AC33 AC34 AD03                       AD11 AD13 AD16 BA04 BB01                       EA03 EA05                 2H077 AB02 AB14 AC03 AD02 AD06                       AD13 AD18 AE06 BA03 BA08                       CA01 CA02 DA10 DA42 EA01                       EA21

Claims (4)

[Claims] 1. An electrophotographic apparatus comprising a photoconductor, a developing machine having a plurality of developing rolls each comprising a sleeve and a magnet roll, comprising at least one developing roll having a rotating magnet roll, and a rotating magnet roll. An electrophotographic apparatus, wherein a magnetic shielding plate is provided between another developing roll adjacent to the developing roll, a developing roll having a rotating magnet roll, and the other developing roll. 2. The electrophotographic apparatus according to claim 1, wherein the magnetic shield plate is provided with a plurality of magnetic material plates and a non-magnetic material between the plurality of magnetic material plates. 3. The electrophotographic apparatus according to claim 1, wherein the length of the magnetic shield plate in the longitudinal direction is 0.7 to 1.3 times the length of the magnet roll in the longitudinal direction. . 4. The electrophotographic apparatus according to claim 1, wherein the width of the magnetic shielding plate is not less than the gap between the developing rolls and not more than the diameter of the developing rolls.