JP2003107909A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a developing device that is small in size, ensures long developer life, prevents nonuniformity and decrease in density, and obtains a uniform image. SOLUTION: The developing device has a developing roll 1 that incorporates a fixed magnet having a plurality of magnetic poles in its inside and rotates in order to hold and transport developer, a stir supply member 3 that rotates in order to stir the developer 2 and supply it to the developing roll 1, and a regulating member 5 that makes the developer 2 supplied to the developing roll 1 homogenious. One of the magnetic poles of the magnet, N3, is disposed between the stir supply member 3 and the regulating member 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as an electrophotographic printer or a copying machine.

[0002]

2. Description of the Related Art Conventionally, as a two-component type developing device used in an electrophotographic image forming apparatus, a fixed magnet having a plurality of magnetic poles is disposed in the vicinity of or in contact with a latent image carrier. A two-component developer consisting of toner and a magnetic carrier is supplied onto a rotatable developing roll having a roller, the developing roll is rotated to convey the developer to a developing region, and the action of a bias voltage applied to the developing roll is exerted. A method of developing an electrostatic latent image on a latent image carrier is generally used.

As a conventional example, a two-component developing device is shown in FIGS. 4 and 5.

The developing roll has a fixed magnet of five poles in which a developing magnetic pole N1, a peeling magnetic pole S1, a scooping magnetic pole S2, a blade magnetic pole N2, and a carrying magnetic pole S3 are arranged in order, and the developing roller rotates in the direction of arrow A to develop. The agent is carried and conveyed. Since the pumping magnetic pole S2 having the same polarity as the peeling magnetic pole S1 is arranged at a certain distance from the peeling magnetic pole S1, and a repulsive magnetic field is formed between the peeling magnetic pole S1 and the pumping magnetic pole S2, the peeling magnetic pole S1 was conveyed onto the developing roll. The developer drops by the peeling magnetic pole S1, and the developer is newly supplied to the developing roll by the scooping magnetic pole S2. The magnetic pole spacing of the fixed magnet in the developing roll is 45
The degree of 70 to 70 degrees is suitable for stably conveying the developer.
However, the spacing between the peeling magnetic pole S1 and the pumping magnetic pole S2 is set to be wider than the other magnetic pole spacing and is often 80 degrees or more in order to improve the peeling property.

As a stirring supply member, a stirring screw having a screw is installed at a position below the horizontal line passing through the center of the developing roll by 45 degrees to convey and stir the developer in the axial direction, and the stirring screw is arranged in parallel with the stirring screw. By the stirring screw that conveys the developer in the opposite direction to the screw,
The developer is circulated and conveyed.

As a regulating member, a blade is installed at a position facing the blade magnetic pole N2 with a predetermined gap from the developing roll to regulate the layer thickness of the developer to a constant amount. The regulation blade is disposed 85 ° above the stirring screw.

The amount of the developer in the stirring screw, that is, the height of the upper surface of the developer is set to such an extent that the stirring screw can be seen and hidden during rotation, that is, to the same height as the upper limit of the outer circumference of the screw. If the amount of the developer increases more than this, there is a problem that stirring is insufficient, uneven toner concentration or uneven charge amount occurs, and the developer is circulated and conveyed slowly. On the other hand, if the amount is small, there is a problem that the amount of pumping to the pumping magnetic pole is insufficient.

The developer is agitated and conveyed by the agitating screw, and the developer is magnetically supplied from the agitating screw to the developing roll by the scooping magnetic pole S2. The layer of the developer supplied to the developing roll is regulated by the regulating blade, and then the developer is developed in the developing area. Then, the developer falls from the developing roll at the peeling pole S1 and is mixed and stirred with the developer not subjected to the development by the stirring screw. It is circulated and conveyed in the stirring screw.
Then, at the scooping pole S2, the developer is newly supplied from the stirring screw to the developing roll by magnetic force.

In the developing area, a bias voltage is applied to the developing roll, and the developing electric field generated causes the charged toner to move to the latent image carrier for development. The electric field generated by the developed toner cancels out the developing electric field, so when the amount of developing toner increases and the electric field balances with the developing electric field, the development ends at that point. Therefore, since a toner having a high charge amount has a large electric field generated by the toner, the amount of developable toner is small and the image density is low. On the contrary, since the toner having a low charge amount has a small electric field generated by the toner, the toner amount that can be developed is large and the image density is high.

The toner charge amount of the developer increases according to the stirring time and is saturated in a certain time, but the developer having a low toner concentration has a high charge amount of the toner, and conversely, the developer having a low toner concentration has a toner charge amount. The electrification amount of 1 tends to be low.

Therefore, keeping the toner concentration of the developer constant,
It is necessary to keep the charge amount constant in order to keep the image density constant. Particularly in a two-component developing device, if the replacement of the developer is not complete in the peeling magnetic pole and the scooping magnetic pole, the developer having a low toner density once developed is used again for the development, and the image density is lowered. Or
Image density unevenness occurs.

[0012]

However, in the conventional structure, the developer after development falls due to gravity at the peeling magnetic pole, and thereafter, at the scooping magnetic pole, the developer is newly sucked up by the magnetic force from the stirring screw, and is regulated on the conveying magnetic pole. Since the layer is regulated by the blade, it is difficult to set the position of the stirring screw, and there is a problem that torque increase and insufficient supply are likely to occur.

That is, when the position of the agitating screw goes up, the height of the upper surface of the developer also rises, so that a large amount of the developer adheres to the pumping pole and the transporting pole, and the torque increases and the deterioration of the developer accelerates. was there. On the contrary, when the position of the stirring screw is lowered, the height of the upper surface of the developer is also lowered, so that there is a problem that the distance from the pumping magnetic pole is increased and the pumping amount is insufficient.

Further, since the regulating blade is placed on the next blade magnetic pole N2, and the regulating blade is arranged at a distance from the stirring screw (85 ° above the stirring screw in the example), the apparatus is large in size. become. Further, since a large amount of the developer adheres to the surface of the developing roll on the scooping magnetic pole S2 and the blade magnetic pole N2, the rotating torque of the developing roll is large, and the compressive force and the breaking force applied to the developer are large. early.

As described above, in the conventional structure, the positions of the stirring screw and the regulating blade are limited, and it is difficult to downsize the apparatus, and moreover, there is a problem that the image density is lowered or the image density is uneven. Not only that, since the regulation blade is on the blade magnetic pole, the amount of developer adhering to the developing roll is large, and as a result, the rotating torque of the developing roll increases,
Moreover, since the load applied to the developer becomes large, the deterioration of the developer is rapid, and there is a problem that it is necessary to replace the developer frequently.

As another means for improving the releasability of the developer, there is a method in which one end is provided with a release plate near or in contact with the developing roll and the developer is mechanically scraped. There was a problem of becoming.

In view of the above circumstances, it is an object of the present invention to provide a developing device which is small in size, has a long life of the developer, and is capable of obtaining a uniform image while preventing density unevenness and density decrease.

[0018]

To achieve the above object, a developing device of the present invention comprises a two-component developer comprising toner and a magnetic carrier, and a fixed magnet having a plurality of magnetic poles inside. , A developing roll that rotates to carry and convey the developer to a developing area that develops the electrostatic latent image on the latent image carrier that faces each other in a non-contact manner, and agitates the developer to supply the developer to the developing roll. It is characterized in that it has a stirring and supplying member and a regulating member for uniformizing the developer supplied to the developing roll, and a single magnetic pole is arranged among the plurality of magnetic poles of the magnet.

Further, according to the present invention, the center of rotation of the stirring and supplying member is arranged within 20 degrees from the horizontal to the center of rotation of the developing roll, and above the stirring and supplying member within 60 degrees of the center of rotation of the stirring and supplying member. You may arrange | position a regulation member to this.

Further, in the present invention, the regulating member may be arranged at a position where the magnetic force formed by the magnet on the surface of the developing roll is minimized.

[0021]

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

FIG. 1 is a schematic configuration diagram of an embodiment of a developing device of the present invention. 2 is a schematic configuration diagram of the stirring screw in the developing device shown in FIG. FIG. 3 is a schematic distribution diagram of the magnetic force distribution on the surface of the developing roll and the developer in the developing device shown in FIG.

The developing roll 1 is internally provided with a developing magnetic pole N1,
The developer 2 is carried and conveyed by rotating in the direction of arrow A, having a fixed magnet in which five magnetic poles of a conveying magnetic pole S1, a peeling magnetic pole N2, a scooping magnetic pole N3, and a conveying magnetic pole S2 are arranged. The separation magnetic pole N2 is separated from the separation magnetic pole N2 by a predetermined distance.
The pumping magnetic pole N3 having the same polarity as that of No. 2 is arranged, and the peeling magnetic pole N3
2 and the pumping magnetic pole N3 have the same polarity, and the sleeve surface between them forms a repulsive magnetic field.

The developing roller 1 has an outer diameter of φ14 and is made of an aluminum sleeve having irregularities of several μm on the surface. The magnetic force of the fixed magnet inside is N1 magnetic pole is 95 mT and other magnetic poles are 60 m.
It is mT.

A stirring screw 3 having a screw is installed as a stirring and supplying member for rotating and transporting and stirring the developer in the axial direction so that its rotation center is located 10 degrees below the horizontal line of the center of the developing roll. There is. The stirring screw 3 is arranged in parallel with the stirring screw 3.
The developer 2 is circulated and conveyed in the stirring screws 3 and 4 by the stirring screw 4 that conveys the developer in the opposite direction.

As a regulating member, the regulating blade 5 has a gap of 0.3 mm from the developing roll 1 between the scooping magnetic pole N3 and the conveying magnetic pole S2 with respect to the center of the developing roll 1.
It is arranged 50 ° above the stirring screw 3 at a position where the magnetic force is minimized between the peeling magnetic pole and the conveying magnetic pole. The regulation blade 5 is made of aluminum having a thickness of 1.5 mm.

As described above, between the regulation member 5 and the stirring screw 3, only one of the pumping magnetic poles N3 among the plurality of magnetic poles of the magnet 1 is arranged.

The amount of the developer 2 is set to such an extent that the height of the upper surface of the developer 2 becomes the same as the height of the outer periphery of the screw, which is visible and hidden when the stirring screw is rotated. The developer is composed of a magnetic carrier and a toner. The magnetic carrier is ferrite coated on the surface and has an average particle diameter of 35 μm. The toner is made of polyester and has an average particle diameter of 7 μm.

The shape of the bottom surface of the developing case 7 is formed so as to follow the line connecting the concentric circles of the developing roll 1 and the stirring screw 3 with a tangent line.

The developer 2 is agitated and conveyed by the agitating screws 3 and 4, and the developer 2 is supplied from the agitating screw 3 to the developing roll 1 by the scooping magnetic pole N3. At this time, since the height of the upper surface of the developer 2 is almost the same as the height of the suction magnet N3, the developer is reliably supplied to the suction magnetic pole without running out.

After that, the layer is regulated by the regulating blade 5 located in front of the conveying magnetic pole S2, and the sheet is conveyed to the developing area. Therefore, unlike the conventional case, the developer does not adhere to the conveying magnetic pole S2, so that the rotation torque of the developing roll 1 is small, and the compressive force and the coercive force applied to the developer are also small, so that the deterioration of the developer is less than that of the conventional case. , The replacement time of the developer becomes longer.

The developer conveyed to the developing area is developed on the electrostatic latent image carrier 6 in the developing area, and then separated from the developing roll 1 by the peeling magnetic pole N2. The peeled developer is the developing roll 1.
Is moved into the stirring screw 3 along the bottom surface of the developing case 7, is mixed and stirred with the developer not used for development by the stirring screw 3, and is conveyed and circulated in the stirring screws 3 and 4. . Then, the developer is newly drawn up and supplied to the developing roll 1 by the magnetic pole.

In this way, since the developer is peeled off, supplied and agitated and carried out stably and reliably, there is no decrease in image density or unevenness, and the compressive force and the uniform force received by the developer are small, so that the developer is small. Has a long life. Also, the size of the device is reduced.

If the agitating screw 3 is arranged 20 degrees or more below the center of the developing roll, not only the apparatus becomes large, but also the distance of the agitating screw 3 becomes far from the scooping magnetic pole N3, and the scooping amount of the developer is insufficient. Further, when the regulating blade 5 is arranged above the stirring screw 3 by 60 degrees or more, the device becomes large and the pumping magnetic pole N3 is also positioned above, so that the pumping amount is also insufficient.

Therefore, it is appropriate that the position of the stirring screw 3 is within 20 degrees with respect to the horizontal, and the regulation blade 5 is within 60 degrees with respect to the stirring screw 3, so that the apparatus can be downsized.

In the present embodiment, the regulation blade 5 is arranged at the minimum magnetic force position, but it is not limited to this, and it may be in the vicinity of the minimum position. Further, the positions of the agitating screw 3 and the regulating blade 5 are also 10 below the horizontal line in this embodiment.
The angle is 50 degrees above the stirring screw 3, but not limited to this, the stirring screw 3 may be within 20 degrees from the horizontal, and the regulating blade 5 may be within 60 degrees from the stirring screw.

Further, in this embodiment, the magnetic pole next to the developing magnetic pole is the peeling magnetic pole, but a carrier magnetic pole may be provided between the developing magnetic pole and the peeling magnetic pole as in the conventional developing device.

In this embodiment, the stirring screw 3 having a screw is used as the stirring member, and the stirring screw 4 is used.
Although the developer is circulated and conveyed together with this, the invention is not limited to this, and a rotating shaft having a plurality of paddles as an agitating member may be used, and one rotating shaft may be used.

[0039]

As described above, according to the developing device of the present invention, of the plurality of magnetic poles of the magnet, the single magnetic pole is arranged between the stirring and supplying member and the regulating member. A decrease in density is prevented and a uniform image is obtained.

Further, according to the developing device described in the embodiment, of the plurality of magnetic poles of the magnet, a single magnetic pole is arranged between the agitating and supplying member and the regulating member, and further at the center of rotation of the developing roll. On the other hand, since the rotation center of the stirring and supplying member is arranged within 20 degrees above and below the horizontal line, and the regulating member is arranged above the stirring and supplying member within 60 degrees from the stirring and supplying member, the developer is separated from the developing roll and supplied. Is performed reliably, a stable and uniform image is obtained, the life of the developer is long, and the size of the apparatus can be reduced.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an embodiment of a developing device of the present invention.

FIG. 2 is a schematic configuration diagram of a stirring screw in the developing device shown in FIG.

FIG. 3 is a schematic distribution diagram of a magnetic force distribution and a developer on the surface of a developing roll in the developing device shown in FIG.

FIG. 4 is a schematic configuration diagram of a conventional developing device.

FIG. 5 is a schematic distribution diagram of magnetic force distribution and developer on the surface of a developing roll of the conventional developing device shown in FIG.

[Explanation of symbols]

1 developing roll 2 developer 3 stirring screw 1 4 stirring screw 2 5 regulation blade 6 Electrostatic latent image carrier 7 Development case 8 partition boards

Claims (3)

[Claims] 1. A two-component developer comprising a toner and a magnetic carrier, and a fixed magnet having a plurality of magnetic poles inside, for developing an electrostatic latent image on a latent image carrier that faces each other in a non-contact manner. A developing roll that rotates to carry and convey the developer to the developing area, a stirring supply member that rotates to stir the developer and supply the developing roll to the developing roll, and a regulating member that uniformizes the developer supplied to the developing roll. And a single magnetic pole among a plurality of magnetic poles of the magnet is arranged between the stirring and supplying member and the regulating member. 2. The center of rotation of the stirring supply member is arranged within 20 degrees above and below the horizontal with respect to the center of rotation of the developing roll,
The developing device according to claim 1, wherein the regulating member is arranged above the stirring and supplying member within 60 degrees from the rotation center of the stirring and supplying member. 3. The regulating member is arranged at a position where the magnetic force formed by a magnet on the surface of the developing roll is minimized.
Or the developing device described in 2.