JPH083680B2 - Development device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device arranged corresponding to a photosensitive drum of an image forming apparatus, and in particular, in a developing device using a two-component developer, carrier recovery. The present invention relates to a device configured so as to reliably perform the above.

(Prior Art) In a copying machine configured to develop a latent electrostatic image by using a two-component developer to form a toner image, the two-component developer is provided inside a McNet roller. The magnetic force of a magnet causes the developer to adhere to the surface of the developing sleeve, and the developer is formed as a brush-like toner brush. Then, when applying the two-component magnetic brush developing method of developing by rubbing the electrostatic latent image with the toner brush,
It is known that the image characteristics greatly change depending on the electrical properties of the carrier.

Further, when a conductive carrier is used, the developing electric field between the electrostatic latent image and the developing electrode increases, which is advantageous for reproducing solid black areas, but tends to result in poor reproducibility of line images. Further, the use of an insulating carrier is advantageous for reproducing a line image due to the peripheral effect, but is disadvantageous for reproducing a solid black portion because the developing electric field is small.

Therefore, in order to improve the reproducibility of the solid black portion with the two-component developer using the insulating carrier, it is necessary to reduce the gap between the photosensitive drum and the developing sleeve and increase the electric field of the solid black portion. However, in the case of such a configuration, the rubbing force of the developer on the photosensitive drum becomes large, and the toner image once developed on the photosensitive drum and the photosensitive drum is strongly rubbed with the toner brush. In addition, there is a possibility of scratching them and degrading the image quality.

In order to solve the above-mentioned problems, it is conceivable to use a system as disclosed in, for example, JP-A-60-48060 or JP-A-60-98473. In the above-mentioned conventional example, in a device that performs development using a two-component developer, a carrier recovery plate is provided in the space between the photosensitive drum and the development sleeve at the end of the development area, and A device is shown which is adapted to apply charge from a bias power supply to recover carriers.

(Problems to be Solved by the Invention) As described above, in the general two-component developing device, when the two-component magnetic brush developing method is used, the toner brush (magnetic brush) for the photosensitive drum or the toner image is used. To reduce the rubbing force, the magnetic permeability of the carrier may be reduced, a soft toner brush may be formed, and development may be performed using the toner brush. However, when such a method is used, the attraction force from the developing sleeve with respect to the carrier becomes small, and a phenomenon occurs in which the carrier adheres to the photoconductor drum side due to residual charges remaining after the toner is lost. Sometimes. This phenomenon poses a serious problem in relation to the image quality of the toner image, particularly when considering the speeding up of development accompanying the speeding up of the copying machine.

It is also possible to install a carrier recovery plate,
When such a means is provided, even if a voltage is applied to the recovery plate from a bias power source to recover the carrier transferred to the toner image side, the carrier once transferred to the recovery plate is While moving on the surface of the plate, transfer to the toner image side of the photoconductor is assumed again, and there are many problems that need to be solved in order to fully carry out the action of collecting the carrier. It exists.

(Object of the Invention) The present invention provides a conventional developing device as described above,
Separation of carrier that occurs when using a two-component developer
The problem of collection is solved, and the electrode member arranged between the photoconductor drum and the developing roller makes it possible to easily collect the carrier and prevent the carrier from adhering to the photoconductor drum. It is intended to provide a developing device.

(Means and Actions for Solving Problems) The present invention uses a developer composed of toner and a magnetic carrier, and is provided with a plurality of magnetic poles fixed inside and a developing sleeve rotatably around the magnetic poles. The present invention relates to a developing device. In the present invention, at least the magnetic pole is composed of a main developing pole in a developing area including a photoconductor and a developing sleeve, and a second magnetic pole downstream of the main developing pole in the rotational direction of the developing sleeve. Within the range of the magnetic field created,
Apply a voltage opposite to the photoconductor and opposite in polarity to the carrier,
An electrode member for recovering a carrier made of a non-magnetic material is provided, and a space for returning the carrier attached to the electrode member to the developing sleeve is formed in the electrode member.

Therefore, in the developing device of the present invention, when the electrostatic latent image is rubbed with the toner brush, the carrier transferred to the electrostatic latent image is surely returned to the electrode member and the space portion provided in the electrode member is provided. It is possible to collect the particles without moving them to the photoconductor. Then, after moving the carrier along the surface of the electrode member, the magnetic force of the second magnetic pole causes the carrier to move from the void portion toward the developing sleeve, and the carrier can be collected in the developing device. .

(Example) The configuration of the developing device of the present invention will be described with reference to the illustrated example. As shown in FIG. 1, in the developing device,
The exposed portion of the developing sleeve 5 of the magnet roller is provided corresponding to the developing area 2 of the photosensitive drum 1, and the gap between both rollers is set to a constant value in the developing area. The magnet roller is provided in a predetermined portion of the developing device (not shown), and the developing main pole 6 and the second magnetic pole 7 are provided at fixed positions with respect to the magnet holding member fixed to the shaft. And are arranged. A developing sleeve 5 is rotatably provided around the magnet, and the two-component developer accommodated in the developing device is adsorbed around the developing sleeve 5 to be conveyed, and Electric charges are supplied from the developing bias power source 8 to the developing sleeve 5 to transfer the toner.

In the developing device of the present invention, the developing main pole 6 and the second
The non-magnetic electrode member in the magnetic field generated by the magnetic pole 7 of
10 is provided, and an electrode bias member is provided for the electrode member 10.
A voltage having a polarity opposite to that of the residual charge of the carrier is applied from 16 so that the carrier transferred to the electrostatic latent image is returned to the electrode member 10. The electrode member 10 has a constant width 1 as shown in FIG. 2, and when viewed from the moving direction of the photosensitive drum 1, the upstream side is P1 and the downstream side is P2.
P2 is set at a position affected by the second magnetic pole 7.

Then, in the electrode member 10, the electrode member 10
Regardless of where the carrier is present on the surface of the photoconductor drum between the upstream and downstream ends P1 and P2 (hereinafter referred to as the surface of the electrode member), the carrier 4 does not contact the second magnetic pole 7. The force Fm received by the magnetic force is FmH in the relationship between the component force FmH parallel to the surface of the electrode member and the component force FmV perpendicular to it.
Is always directed to the P2 side, and is collected from the end of the electrode member 10 toward the developing sleeve 5.

A specific example of the present invention will be described with reference to FIGS. 3 and 4. As shown in FIG. 3, the exposed portion of the developing sleeve 5 is formed so as to face the developing area 2 of the photoconductor drum 1, and the developing bias power source 8 supplies electric charge to fly the toner in the exposed area. In the developing device for developing the electrostatic latent image on the surface of the photoconductor drum to form a toner image, the electrode member 10 is provided so as to project at the end of the developing device bottom plate 17 on the photoconductor drum side. A predetermined charge can be supplied to the member 10 from the electrode bias power supply 16.

As shown in FIG. 4, the electrode member 10 is formed in a substantially wedge shape, and is entirely made of non-magnetic stainless steel. Then, the electrode function part 11 is formed at the tip end thereof, the width thereof is set to about 4 mm, and the through hole 12 as a space part is provided below the electrode function part 11. The lower part of the through hole 12 is configured as a member that acts to support the electrode member 10.

The developer 3 used in the examples of the present invention has a magnetic permeability of about 40 emu / g and a particle size of about 130 μm as its carrier.
The resin coating is an insulating material.
Further, in the image forming apparatus, when a selenium (Se) -based member is used as the surface material of the photosensitive drum 1, the toner is negatively charged and the carrier is positively charged. Further, the photosensitive drum 1 is rotated at a peripheral speed of 256 mm / sec, the developing sleeve 5 is rotated at about 2.3 times that speed, and the photosensitive drum 1 and the developing sleeve 5 in this case are rotated.
The gap between and was set in the range of 0.8 to 1.7 mm. In the developing device configured as described above, the surface of the electrode member 10 is provided substantially parallel to the surface of the photoconductor in the vicinity of the outlet of the developing area. Then, the developer that has entered the developing area 2 is deprived of the toner by the electrostatic latent image on the photosensitive drum 1, and the carrier has a (+) residual charge.

A detailed explanation of the above-mentioned state is the fifth.
It is a model figure shown by a figure. In FIG. 5,
The movement of the toner of the developer and the carrier 5 between the developing sleeve 5 and the photosensitive drum 1 is shown. These members are moved from the left side to the right side in FIG. It is described that the action of the flight of the toner is performed. The developer that has adhered to the surface of the electrode member 10 and has entered the developing area has a carrier residual charge 4a when a so-called peripheral electric field Ef is exerted in the vicinity of the carrier in the developing area A.
Becomes (+), which causes a force to move the carrier 4 toward the (-) of the photosensitive drum 1. Therefore, when the force for moving the carrier exceeds the attraction force of the developing main pole 6 provided in the developing sleeve 5, the carrier is attached to the photosensitive drum 1 in the carrier attaching area B.

The carrier attached to the photosensitive drum moves to the carrier recovery area C set in a state where it is affected by the electrode member 10 applied to the (-) side as the photosensitive drum moves. The electric field in the carrier recovery region C acts in such a direction as to move the carrier 4 toward the electrode member 10, so that the carrier 4 is moved to the electrode member 10 and almost no carrier is present on the photosensitive drum 1. It will not remain. On the other hand, the carrier 4 adsorbed on the electrode member 10 in the carrier recovery area C is pushed to the downstream side by the adsorbed carriers one after another after being accumulated on the surface of the electrode member to some extent, and then downstream of the electrode member 10. It is returned to the developing sleeve 5 by the attraction force of the second magnetic pole 7 at the through hole portion of the side end portion.

In the device shown in FIG. 3, the carrier 4 is formed on the surface of the electrode member 10 by adopting the above structure.
Even when the toner was accumulated, there was no change in the effect of adsorption on the carrier, and the carrier remaining on the toner image could be completely eliminated. Further, in the above-mentioned state, about 10,000 sheets were copied, but the carrier was completely recovered from the photosensitive drum, and the image quality of the image was not affected.

In the above-mentioned embodiment, a non-magnetic member is used as the electrode member 10. However, when a magnetic material is used as the electrode member 10, as shown in FIG. Then, a magnetic field induced by the main developing pole 6 and the second magnetic pole 7 is generated. In this state, when the developing sleeve 5 is rotated, magnetic lines of force may be connected between the upstream point P1 of the electrode member 10 and the main developing pole 6, and the developer may form a bridge. Riding on the surface, the behavior of the developer in the developing area is greatly affected. Therefore, not only the effect of the electrode member adsorbing the carrier disappears, but also the carrier is mixed in the toner image formed on the photosensitive member, which may cause a drawback that the image quality of the copy is greatly affected. .

Therefore, the problem as described above is that a non-magnetic member is used as the electrode member, and further, the distance between the photosensitive drum 1 and the electrode member 10 and the necessary minimum applied voltage are set as shown in FIG. It turned out to be solved by setting. Further, in the embodiment of the present invention, when the distance between the photoconductor drum 1 and the electrode member 10 is set to be small, it is unnecessary to apply a voltage to the electrode member 10, and it is sufficient to simply connect the electrode member to the ground. It is also possible to demonstrate.

FIG. 8 shows another embodiment of the present invention in which a conductive carrier is used as the carrier. The state in which the carrier is attached to the photosensitive drum when this conductive carrier is used is as shown in FIG. In this model diagram, unlike the case where the insulating carrier shown in FIG. 5 is used, the toner flies in the developing area A due to the attraction of the electrostatic latent image, but the toner on the photoconductor drum 1 The carrier 4 approaching the electrostatic latent image receives the charge injection from the developing sleeve 5 side, and the carrier 4 holds the electric charge of the polarity opposed to the electrostatic latent image.

Therefore, in the carrier attachment area B, an attractive force is generated between the electrostatic latent image and the carrier, which causes the carrier 4 to be attached to the photosensitive drum 1. That is, in this case, if the electrostatic latent image is (+), the carrier holds the (-) charge, and the carrier-holding charge 4a is transferred to the photoconductor drum 1 in the carrier attachment area B. Will be.

This phenomenon is the opposite of the case of using an insulating carrier, so in order to recover the carrier in this case,
When the voltage applied to the electrode member 10 also has the (+) polarity, the function can be exhibited. However,
In this embodiment, when the carrier is adsorbed on the electrode member 10 and accumulates to some extent, a leak occurs between the electrode member 10 and the photosensitive drum 1 because the carrier has conductivity. . In order to prevent this leakage, as shown in FIG.
It is necessary to provide an insulating layer 15 on the surface of the conductive layer 14 forming the 11 to insulate the same.

Further, the embodiment shown in FIG. 10 shows another embodiment of the present invention, in which the electrode member 10 is one in which a conductive layer 14 is provided on the surface of a permanent magnet 13. As shown in the case of FIG. 6, the permanent magnet electrode member can strongly attract the carrier without applying a voltage.
In this example, the carrier strongly attracted to the electrode member has the effect of strengthening the electric field for collecting the carrier generated between the photosensitive drum and the electrode member, and therefore, compared with the case without a permanent magnet, It is possible to set a wide gap between the photosensitive drum and the electrode member.

As described above, FIG. 11 shows the relationship between the distance between the photosensitive drum and the electrode member and the minimum applied voltage at which the effect can be exhibited when the permanent magnet electrode member is used. In this figure, the curve indicated by the solid line shows the case where the permanent magnet electrode member is used, and the curve indicated by the chain line shows the example when the electrode member is simply used. Further, as described above, when the permanent magnet electrode member is used, it is necessary to set the polarity of the permanent magnet to the N-S relationship as shown in FIG. When the setting is reversed, magnetic lines of force are formed as in the case of using a magnetic body as the electrode member in FIG. 6, and it becomes impossible to exert a sufficient effect.

As described above, the developing device of the present invention is a developer comprising a magnetic roller having a magnetic field forming means fixed inside and a developing sleeve rotatably provided around the magnetic roller, and a toner and a carrier. The toner brush formed on the surface of the developing sleeve is used to rub the electrostatic latent image formed on the photoconductor drum to perform development, and the electrode member is within the magnetic field of the magnetic field forming means. Is provided and the electrode member is formed as a relatively short one, and a voltage is applied to the electrode member from a bias power source so that the carrier can be effectively recovered.

(Effects of the Invention) Since the developing device of the present invention has the above-described configuration, even if the carrier is once transferred to the photosensitive drum in the developing area, it is moved toward the electrode member thereafter. You can Then, the carrier transferred to the electrode member is recovered toward the developing sleeve from a through hole as a space provided at the end of the electrode member,
The carrier is reliably prevented from remaining on the toner image formed on the photoconductor. Therefore, the problem that the carrier generated when the two-component developer is used is mixed in the toner image of the photoconductor is provided with the electrode member within the range of the magnetic field formed by the second magnetic pole in the developing area. This can be easily solved by providing the member with a space and providing a means for moving the carrier toward the developing sleeve.

Further, in the apparatus of the present invention, it becomes possible to use the electrode member having the most effective function according to the property of the developer, thereby improving the effect of carrier recovery. Become. Further, in the apparatus of the present invention, even if the degree to which the photoconductor drum is rubbed by the toner brush is set to be weak, the formation of the toner image is not affected, and a clear copy can be obtained.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a basic structure of the present invention, FIG. 2 is an explanatory view of a mounting position of an electrode member, and FIG. 3 is a first view of the present invention.
FIG. 4 is a perspective view of the electrode member used in FIG. 3, FIG. 5 is a model diagram showing the behavior of the carrier in the case of FIG. 3, and FIG. 6 is a magnetic substance in the electrode member. FIG. 7 is an explanatory view showing the state of the magnetic force lines when using, FIG. 7 is a graph showing the relationship between the distance between the photosensitive drum and the electrode member and the applied voltage in the case of the example shown in FIG. 6, and FIG. FIG. 9 is an explanatory view showing the constitution of another embodiment of the invention, FIG. 9 is a perspective view showing the constitution of the electrode member used in that example, and FIG. 10 is a perspective view of the electrode member used in another embodiment of the present invention. FIG. 11 is a graph showing the relationship between the distance between the photosensitive drum and the electrode member and the applied voltage in the example of FIG. 10, and FIG. 12 is a model diagram showing the behavior of the carrier in the apparatus shown in FIG. Is. Reference numeral 1 in the figure: 1 photosensitive drum, 2 development area, 3 developer,
4 ... Carrier, 5 ... Development sleeve, 6 ... Development main pole, 7 ... Second magnetic pole, 8 ... Development bias power supply, 10 ...
… Electrode member, 11 …… Electrode functional part, 12 …… Through hole,
13 ... Permanent magnet, 14 ... Conductive layer, 15 ... Insulating layer, 16 ...
Electrode bias power supply, 17 ... Developer bottom plate.

Claims (1)

[Claims] 1. A developing device using a developer comprising toner and a magnetic carrier, wherein a plurality of magnetic poles fixed inside and a developing sleeve rotatably provided around the magnetic pole are provided, wherein at least the magnetic pole is a photosensitive member. A developing main pole in a developing area including a developing sleeve and a second magnetic pole downstream of the developing main pole in a rotation direction of the developing sleeve, and the photoconductor is within a range of a magnetic field formed by the two magnetic poles. A carrier collecting electrode member made of a non-magnetic material, which is applied with a voltage having a polarity opposite to that of the carrier, and has a space for returning the carrier attached to the electrode member to the developing sleeve. A developing device formed on a member.