JPH08220882A - Developing device - Google Patents

Abstract

PURPOSE: To provide a developing device capable of preventing the scattering of a developer caused by the increase of internal pressure in a developing tank, various kinds of factors generated in the lower side of a developing region, etc. CONSTITUTION: A developer carrier 110 is arranged to face an image carrier 11 and a latent image formed on the image carrier 11 is actualized by a magnetic brush with the developer carried on the developer carrier 110. A vent 184 is formed along the bottom wall of the developing tank 180 housing the developer carrier 110 and a developing suction fan 188 sucking air from a duct 185 formed in the vent 184 with a toner filter 187 is provided. The speed of the wind generated by the developing suction fan 188 is set 0.2-2.0m/s.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device adopting an electrophotographic method, and more particularly to a developing device capable of preventing scattering of a developer.

[0002]

2. Description of the Related Art A developing device used in an image forming apparatus such as a copying machine is provided with a developing sleeve provided with a magnet inside and facing the image bearing member, and a height of the developer on the developing sleeve. It consists of a regulating blade that regulates the developing sleeve and a developing tank that encloses the lower and side portions of the developing sleeve, forms a brush of the developer as a magnetic brush, and rotates the developing sleeve or the relative rotation of the developing sleeve and the magnet body. It is well known that the developer is conveyed while being stirred, and in the developing area, the developer approaches or contacts the surface of the image carrier to develop the electrostatic latent image carried on the surface of the image carrier.

[0003]

However, in such a developing device, since the developer bristles rotate as a magnetic brush, it acts as a kind of fan and sucks air from the gap between the image carrier and the developing device. Cause a phenomenon. As the amount of intake of the internal pressure in the developing device increases, the internal pressure in the developing tank rises, and at that time, the developer in the developing tank scatters together with air from the seal part between the developing tank and the image carrier. Will be done. If the developer scatters outside the developing tank, it may stain the inside of the copying machine or stain the optical sensor or the like, causing malfunction. In order to avoid such an increase in internal pressure in the developing tank,
It is disclosed in Japanese Patent Laid-Open No. 60-39861 that a pressure relief hole is provided to close the pressure relief hole in a filter that allows passage of air.

Further, according to the above construction, there is a problem in that the developer is scattered right under the developing area and its periphery to stain them. This problem occurs due to the following reasons. That is, the developer is held on the developing sleeve by the magnetic attractive force of the magnet body, but in the developing area, an electric field is generated due to the potential difference between the developing sleeve and the image carrier, so that electrostatic force of the image carrier is generated. The attractive force acts on the developer. Therefore, in the developer located nearer to the image bearing member, the attraction force to the image bearing member exceeds the attractive force of the magnet member to the developing sleeve, so that the developer is attracted to the surface of the image bearing member to develop. Be seen.

On the other hand, since the attractive force of the magnet body on the developing sleeve is greater than that of the developer located closer to the surface of the developing sleeve, the developer passes through the developing area while being retained on the developing sleeve. However, there is always a place somewhere in the gap between the surface of the image bearing member and the surface of the developing sleeve where the attractive force from the image bearing member and the attractive force from the magnet member are in balance, so that the developer located in the vicinity is not It is in a stable state.

Further, various forces such as the influence of the rotation of the developing sleeve and the self-weight of the developer act on it. These act intricately and a part of the developer existing in the developing area is scattered under the developing area and its periphery.

In view of the above technical problems, the present invention is to provide a developing device capable of preventing the developer from scattering due to various factors such as an increase in the internal pressure in the developing tank and a phenomenon below the developing area. .

[0008]

Means for achieving the above object can be achieved by the following constitution.

(1) Development in which a developer carrying member is arranged so as to face the image carrying member, and the latent image formed on the image carrying member is visualized with a magnetic brush from the developer carried on the developer carrying member. In the apparatus, a vent is formed along a bottom wall of a developing tank that accommodates the developer carrier, and a suction unit that sucks air from a duct formed in the vent through a toner filter is provided. And developing device.

(2) The wind speed generated by the suction means is set to 0.
The developing device of (1), characterized in that it is set to 2 to 2.0 m / s.

[0011]

With the above-mentioned structure, scattering from the developing area,
The developer that jumps off the image carrier can be captured in the toner filter by being carried on the air flow flowing through the image carrier and the ventilation hole formed along the bottom wall of the developing tank.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described based on the embodiments shown in the drawings.

Prior to the description, an outline of a laser printer as an example of an image forming apparatus will be described as shown in FIG.
FIG. 1 is a schematic diagram showing an outline of a laser printer.

The original 1 is placed on the contact glass 2, and the reflected light from the original 1 is converted into a photoelectric conversion element 7, for example C by an optical system having a mirror 4, a lens 5 and another mirror 6.
It is projected on a CD. The image light read by the CCD 7 is electrically processed by the image processing circuit 8, and the processed electric signal is sent to the laser scanner 9.

The image carrier 11 is charged by the charger 12 while rotating in the direction of the arrow shown, and the image information of the original 1 processed by the image processing circuit 8 is exposed on the image carrier 11 by the laser scanner 9. To form an electrostatic latent image. The electrostatic latent image formed on the image carrier 11 is visualized by the developing device 100. The visible image is transferred onto the transfer material under the action of the transfer electric field by the transfer corona discharger 15. After the transfer, the recording paper is transferred to the image carrier 11 by the action of the separation corona discharger 16.
And is fixed by a fixing device (not shown). The residual toner on the image carrier 11 after the transfer is removed by the cleaning device 17, and the image forming process from the charging by the charger 12 is repeated.

The image carrier 11 is formed by forming a photosensitive layer on the surface of a conductive base material made of, for example, aluminum. The photosensitive layer has a film thickness of 15 to 30 μm, a dielectric constant of 2.0 to 5.0, the conductive base material is grounded, and rotates in the direction of the arrow at a predetermined linear velocity.
Is a drum-shaped photoconductor, and an encoder EK (not shown) for detecting a phase is provided on the rotation axis of the image carrier 11. The encoder EK electronically outputs a phase signal indicating the phase of the image carrier 11. It is sent to the photographic process control unit (not shown).

Next, the structure of the developing device of this embodiment will be described with reference to FIGS.

FIG. 2 is a sectional view showing an embodiment of the developing device of the present invention.

The developing device 100 includes an image carrier 11 in a developing tank 180.
And a developer carrier 110 that keeps a predetermined gap between the image carrier 1 and
The latent image on 1 is visualized by a non-contact reversal development method, and at the time of development, the image carrier 11 grounded to a predetermined reference potential as the developer carrier 110 rotates and a DC power source (not shown). No.) and an AC power supply (not shown) apply a voltage obtained by superimposing AC on DC through a protective resistance (not shown). In addition, stirring screws 140, 150, regulating blade 120 and magnetic carrier particles A magnetic brush of the two-component developer D is formed on the surface of the developing sleeve 111 which is composed of a two-component developer D mixed with toner particles and is rotatably supported, and is formed from a non-magnetic material. By rotating the developing sleeve 111 in contact with the body 11,
The developer D is conveyed to the developing area and the latent image formed on the image carrier 11 is visualized with toner particles under a predetermined developing bias. A developing device adopting this developing method is abbreviated as a so-called two-component contact developing device.

The developing tank 180 is composed of a developing tank 180 formed of an upper wall 181a, a lower wall 181b and a side wall 181c (not shown), and a supporting wall 182 for accommodating and supporting the developing tank 180. A vent 184 is formed between the support wall 182 and the lower wall 181b forming the developing tank 180.

The position where the opening of the developing tank 180 is formed and which corresponds to both ends of the developing sleeve 111 is at the tip of the lower wall 181b.
Since 183 is arranged close to the developing sleeve 111, it comes into contact with the magnetic brush carried on the developing sleeve 111 to perform a sealing action. A part of the magnetic brush carried by the developing sleeve 111 is exposed at the opening of the developing tank 180. Development tank 180
When the tip end portion 183 of the lower wall 181b in the opening of the image contacting the image carrier 11 at the edge of the image carrier 11 on the output side in the rotation direction, the toner image on the image carrier 11 is disturbed. Image carrier 11
It should be as close as possible to the image carrier 11 so as not to come into contact with the image carrier 11. With such a structure, a gap is formed between the image carrier 11 and the tip portion 183 of the lower wall 181b forming the developing tank 180.

Since a gap is generated between the tip portion 183 and the image carrier 11, the developing sleeve 111 rotates, and the magnetic brush formed on the surface of the developing sleeve 111 rotates together. It acts as a kind of fan, the developing tank 180 side is depressurized, and air flows into the developing tank 180 through the gap. In this way, since the air is sucked through the gap between the tip portion 183 and the image carrier 11, the toner is prevented from scattering to the outside.

Since the upper wall 181a forming the opening of the developing tank 180 has a space formed between the upper wall 181a and the developing sleeve 111, when the air is sucked through the space by the rotation of the magnetic brush as described above, the upper wall 181a. Air is blown from the gap between the developing sleeve 111 and the developing sleeve 111 in the directions of arrows a and b, and at that time, the toner is also blown out. If the rotation speed of the developing sleeve 111 is reduced, the amount of intake air also gradually decreases, and the toner scattering prevention effect in this portion also decreases.

Since the tip of the support wall 182 extends to the downstream of the gap between the image carrier 11 and the developing sleeve 111, for example, the image carrier 1 in the gap between the image carrier 11 and the developing sleeve 111.
Toner that falls by gravity due to its own weight is collected from a place where the balance between the attractive force from 1 and the attractive force from the magnet body 112 is balanced. Further, an optical reflection type density sensor PS is arranged at the tip portion 182b of the support wall 182. An optical system such as an optical system including a laser scanner 9 (not shown) exposes a pattern called a toner mark to the outside of the printing area of the image carrier 11 each time the recording paper changes, and the developing device 100 can develop the pattern. The toner density of the visual image is measured by the optical reflection density sensor PS, and when the measured value becomes lower than a certain reference value, a certain amount of toner is replenished to the developing tank 180 so that the toner density is controlled to an optimum value. The optical density sensor PS is a bracket 18
The detection surface is fixed to 2a and faces the center of the image carrier 11. The bracket 182a is fixed so that the distance between the optical density sensor detection surface and the measurement surface (drum surface) is appropriate.

The supporting wall 182 is a lower wall 181 forming the developing tank 180.
A ventilation duct 184 formed between the duct 185 and b forms a rectangular duct 185, and a toner suction filter 187f for sucking toner is provided in the duct 185 via a ventilation pipe 186 and a developing suction fan 188. As a result, the air inside the vent 184 is sucked and exhausted to the outside of the device, and the toner accumulated on the tip portion 182b of the support wall 182 can be adsorbed to the toner filter 187f and collected by the airflow generated at this time. . Since a predetermined wind speed is required to prevent the toner that is scattered by the air flow of the arrow a, it will be described later with reference to FIG.

The toner filter 187f has, for example, a mesh capable of adsorbing toner particles, and is attached to the toner filter case 187.

The developing suction fan 188 sucks the air accumulated in the vent 184 and is composed of a propeller type brushless DC motor (manufactured by Nidec: D06T-24TG 1).
3BH5) is provided at a position facing the outside of the device.

The developer D is generally composed of magnetic carrier particles having an average particle diameter of 60 μm and non-magnetic toner particles having an average particle diameter of 8.5 μm. Since the toner particles and the carrier particles are fine, delicate lines, dots, or density difference. Has the advantage that it can be reproduced with high image quality.

However, when the toner particles and the carrier particles are made into fine particles, a clear image cannot be obtained due to the conspicuous side effects such as the aggregation phenomenon of the toner particles and the adhesion of the carrier particles. Therefore, the toner particles and the carrier particles are made into fine particles. Things are really difficult. Specifically, if the toner particles have an average particle size of 20 μm or less, especially 10 μm or less, the influence of the Van der Waals force appears relatively to the Coulomb force during development, and the background portion of the image background appears. In other words, so-called fogging in which toner particles adhere is generated, and it becomes difficult to prevent fogging even by applying a DC bias voltage to the developing sleeve. Further, it becomes difficult to control the triboelectric charging of the toner particles, and aggregation easily occurs. On the other hand, when the carrier particles are made finer, the carrier particles also adhere to the electrostatic image portion of the image carrier. Further, when the bias voltage increases, carrier particles also adhere to the ground portion of the image background. The cause of this is that the magnetic force is reduced and the carrier particles together with the toner particles become the image carrier 11.
It is thought that it was because it adhered to the side. In this embodiment,
The carrier preferably has an insulating property, specifically, a specific resistance of 10 ⁸ ΩcmS or more. Furthermore, the toner and carrier particle sizes are 0.
It is preferably in the range of 1 to 100 μm.

The developing sleeve 111 is formed in a cylindrical shape from a non-magnetic material such as 40 mmφ stainless steel or aluminum, and is rotatable with respect to the magnet body 112 contained therein. Magnet body 112
Has a plurality of N and S magnetic poles on its surface in the circumferential direction. Further, the developing sleeve 111 rotates in the leftward direction shown by the arrow. Further, the N and S magnetic poles of the magnet body 112 of the developing section are normally 500
It is magnetized to a magnetic flux density of 1,500 gauss, and the magnetic force forms a layer of the developer D composed of toner particles and carrier particles, that is, a magnetic brush on the surface of the developing sleeve 111. The magnetic brush moves in the same direction as the rotation of the developing sleeve 111 by the rotation of the developing sleeve 111, and is conveyed to the developing area. The magnetic brush formed on the developing sleeve 111 is in a state of a nap by the N and S magnetic poles arranged in the vicinity of the developing device, and the developing sleeve 111 and the regulating blade are arranged so as to softly contact the surface of the image carrier 11. The gap 120 and the gap D _sd between the developing sleeve 111 and the image carrier 11 (hereinafter, also abbreviated as D _sd ) are adjusted.
In this embodiment, D _sd is preferably 1 mm or less.

The stirring screws 140 and 150 circulate and stir the developer D before and after in the figure to make the components uniform.

The regulation blade 120 is molded from a non-magnetic material or a magnetic material provided to regulate the height and amount of the magnetic brush.

When the surface of the photosensitive layer of the image carrier 11 is charged to -750 (V), the DC power supply outputs a voltage of -600 V to prevent fog during reversal development, and the AC power supply supplies a frequency. It is an AC power source that outputs an AC voltage of 200 to 4000 V _pp at 500 Hz to 20 KHz, and these voltages are arranged in series and applied to the developing sleeve 111.

The AC component supplied from the AC power supply is not limited to a sine wave, but may be a rectangular wave, a triangular wave, or the like. Although the frequency is also related, the higher the voltage value is, the more the magnetic brush of the developer is vibrated, which facilitates the separation and flight of the toner particles from the carrier particles, but on the other hand, the phenomenon of fog or lightning strike occurs. Dielectric breakdown easily occurs. The generation of fogging is prevented by a direct current component, and the dielectric breakdown is caused by coating the surface of the developing sleeve 111 with an insulating or semi-insulating material such as a resin or an oxide film, or by coating the carrier particles of the developer with spherical insulating carrier particles. It can be prevented by using it.

Next, the developing operation will be described from the operation of the toner particles by the AC component of the oscillating electric field in addition to the developer conveying operation.

As shown in FIG. 1, it has a developing tank 180 in which a developer carrier 110 is arranged, and a toner hopper 190. The toner T in the toner hopper 190 is replenished by a replenishing roller 191.
The supply roller 191 is rotated by the motor 22.

The toner T in the toner hopper 190 is agitated by an agitator (not shown) and is replenished into the developing tank 180 through a stirring blade or the like (not shown) by the rotation of the replenishing roller 191. The toner supplied into the developing tank 180 is sufficiently agitated with the developer D by the agitating screws 140 and 150, and then agitated by the paddle wheel 130 and pumped up to the developing sleeve 111.

The developing sleeve 111 is exposed at the developing opening provided in the developing tank 180 and faces the image carrier 11.

On the peripheral surface of the developing sleeve 111, ears of a developer composed of a carrier and toner are formed, and are conveyed to a developing area to develop the electrostatic latent image formed on the surface of the image carrier 11 to be developed. Visualize.

Specifically, the image carrier 11 is charged with the surface potential V _s of the photosensitive layer to, for example, -750 (V), and the developing sleeve 111 has a DC component of -600 (V) and a frequency of 50 Hz to 20 KHz. ,
If an AC component of 200 to 4000 V _pp is applied preferably at 500 Hz to 20 KHz, an oscillating electric field on the image carrier 11 is formed between the image carrier 11 and the developing sleeve 111. This is an oscillating oscillating electric field that contributes to visualize the latent image formed on the photosensitive layer which is the image carrier 11. During development, the developing sleeve 111 carries a magnetic brush composed of toner particles and carriers. The toner particles formed by the magnetic brush move alternately between the image carrier 11 and the developing sleeve 111 by the oscillating electric field, and are assisted in the flight toward the latent image on the image carrier 11 to be visualized as a uniform toner image. To do.

The developer on the surface of the developing sleeve 111 is regulated to a constant amount by the regulating blade 120. The developer removed by the regulation blade 120 is returned to the inside of the developing tank 180, but a part of the developer is sent laterally by the stirring screws 140 and 150 to be stirred.

During the above-described developing operation, the developing suction fan 188 operates while the developing sleeve 111 rotates in the direction of the arrow to perform the developing operation, and the air in the vent 184 is exhausted. There is. Therefore, the outside air is always sucked through the ventilation port 184 formed by the surface of the image carrier 11 and the support wall 182. During the developing operation, as described above, the toner is generated to drop downward from the developing area, and this toner is trapped by the airflow entering from the vent 184. Further, when the toner adheres to the surface of the image carrier 11 in the developing area and then approaches the tip portion 182b of the support wall 182 by the rotation of the image carrier 11, the developing tank 18
The toner that jumps to the front end portion 183 of the lower wall 181b forming 0 is also captured by the air flow passing through the ventilation port 184. Thus, it is possible to prevent the toner that is scattered to the outside through the space between the tip portion 183 of the lower wall 181b forming the developing tank 180 and the image carrier 11.

FIG. 3 is a graph showing the relationship between the wind speed of the vent and the toner scattering.

In the graph, the vertical axis represents the amount of toner scattering per 10 cm ² (mg / 10KC), and the horizontal axis represents the ventilation port 18.
The wind speed of 4 is the wind speed (m / s) at an arbitrary position b of the ventilation hose 186. Wind speed at position b (m /
s) is an anemometer (product name: Anemomaster MODEL6611)
It was measured in. The maximum value of the developing sleeve rotation speed is 375.0 (rpm) as a parameter. □ is B shown in FIG.
The toner scattering amount (mg / 10KC) in the vicinity of the point is shown, and the circle indicates the toner scattering amount in the vicinity of the point A shown in FIG.

What can be read from such a graph is the wind speed.
When it is 0.2 (m / s), it is possible to suppress the toner scattering due to the blowout flow A. It can be seen that the scattering by the blowout flow C increases from around the wind speed of 2.0 (m / s). Therefore, in the developing device of this embodiment, it is preferable that the wind speed at the arbitrary point b is 0.2 to 2.0 (m / s).

In the developing device 100 which employs the magnetic brush developing method described above, the magnetic brush of the two-component developer is brought into contact with the image carrier 11 to generate flying toner by the oscillating electric field, and the image carrier 11 is produced. It was possible to separate and fly to toner to visualize with a high-quality toner image, and the above-mentioned toner scattering was not observed.

The constitution using the magnetic brush developing method can be applied to the one-component non-magnetic developer and the one-component magnetic developer. In this embodiment, the developing device 100 has been described as a device that visualizes a latent image, but the invention is not limited to this.
For example, it is obvious that a magnetic latent image can also be visualized.

[0048]

As described above, the present invention provides a developing device which is capable of preventing the scattering of the developer due to the increase of the internal pressure in the developing tank and various factors which occur below the developing area. I was able to.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an outline of a laser printer.

FIG. 2 is a sectional view showing an embodiment of the developing device of the present invention.

FIG. 3 is a graph showing a relationship between a wind speed of a vent and toner scattering.

[Explanation of symbols]

 11 Image carrier 100 Development device 111 Development sleeve 112 Magnet 180 Development tank 181a Upper wall 181b Lower wall 181 Support wall 183 Tip part 184 Vent hole 186 Vent pipe 187 Toner filter case 188 Development suction fan

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Nishida 2970 Ishikawa-cho, Hachioji City, Tokyo Konica Stock Company

Claims (2)

[Claims] 1. A developing device in which a developer carrying member is arranged so as to face the image carrying member, and the latent image formed on the image carrying member is visualized from the developer carried on the developer carrying member by a magnetic brush. In the above, the air vent is formed along the bottom wall of the developing tank for accommodating the developer carrying member, and the suction means for sucking air from the duct formed in the air vent through the toner filter is provided. Developing device. 2. The wind speed generated by the suction means is 0.2 to 2.0.
The developing device according to claim 1, wherein the developing device has a speed of m / s.