JPH0440203Y2 - - Google Patents

Description

[Detailed Description of the Invention] (Industrial Application Field) The present invention relates to an electrophotographic apparatus using a two-component developer containing a mixture of a magnetic carrier and a non-magnetic toner.

(Prior art) In the development method using the above-mentioned apparatus, an image is exposed to light on the surface of a photoreceptor charged with an electrostatic charge to form an electrostatic latent image, and at the same time, an electrostatic latent image is formed on a portion of the electrostatic charge that has not been irradiated with light. , a normal image form in which non-magnetic toner in a two-component developer is electrostatically attracted, and an electrostatic latent image is formed on the surface of the photoreceptor in the same manner as above, and an electrostatic charge remains on the photoreceptor. A bias voltage is applied so that the surface potential of the portion and the surface potential of the developing sleeve are approximately the same potential, and the electric field generated by the bias voltage is applied to the portion of the photoreceptor surface where no static charge remains. There is a form of reversal development in which magnetic toner is attached.

(Problem that the invention aims to solve) By the way, in the case of normal development, toner is attached to the surface of the photoreceptor by electrostatic attraction due to opposite polar charges, and although the adhesion is strong, it still acts on the toner. Due to centrifugal force, gravity, and even air currents generated near the surface of the photoreceptor, toner may be detached from the surface of the photoreceptor, albeit slightly.

On the other hand, in the case of reversal development, toner is attached to the surface of the photoreceptor by an electric field caused by a bias voltage applied to the developing sleeve and the photoreceptor.
This electric field only acts in the developing area and does not act on the post-development path.Therefore, an electric field is generated around the electrostatic latent image due to the so-called edge effect. Although the toner does not separate from the surface of the photoconductor, the adhesion force of the toner in areas away from the boundaries of the latent image becomes extremely weak, making it easy for the toner to separate from the surface of the photoreceptor due to the effects of centrifugal force, gravity, etc. In other words, this is particularly noticeable in the case of reversal development, but regardless of whether it is normal development or reversal development, toner is likely to scatter on the path to the transfer device, leading to deterioration in image quality and dirt inside the machine. are doing.

Furthermore, during normal development, magnetic carriers may adhere to areas where no static charge remains due to the application of a bias voltage to prevent fogging, and conversely, in the case of reverse development, magnetic carriers may adhere to areas where static charges remain. Although the amount of magnetic carrier adhering is small, it also causes deterioration of image quality and staining of the inside of the machine.

Furthermore, in the developing section, the magnetic brush collides with the surface of the photoreceptor while rotating, and the magnetic carrier can also be scattered due to the impact force at this time and the centrifugal force caused by the rotation of the magnetic brush. It is causing pollution.

The present invention aims to solve these inconveniences extremely simply and rationally.

(Means for Solving the Problems) In the present invention, between a developing device using a two-component developer containing a magnetic carrier and a non-magnetic toner and a transfer device, the charge polarity of the magnetic carrier is Electrodes to which a bias voltage of opposite polarity is applied are arranged opposite to each other along the surface of the photoreceptor so that the distance from the photoreceptor surface increases sequentially toward the downstream side in the rotational direction of the photoreceptor, and Thus, a collection tray for magnetic carriers is formed, and the carriers attracted to the electrodes are collected by cutting off the bias power supply to the electrodes.

(Function) When a bias voltage is applied to the electrode, the electrode generates an electric field that is charged with the same polarity as the toner, and the toner receives a repulsive force due to the same polar charge and is repulsed from the surface of the photoreceptor. Secession is deterred.

Since the above-mentioned electrode has a polarity opposite to that of the carrier, the carrier attached to the surface of the photoreceptor and the carrier mechanically scattered in the developing section are attracted to the electrode by the attraction force caused by the opposite polarity charge. By being able to capture the carrier and cutting off the bias voltage applied to the electrode, the captured carrier can be collected in the tray that the electrode also serves as.

(Example) Hereinafter, an example of the present invention will be described based on the drawings regarding reversal development using a two-component developer.
FIG. 1 shows a detailed cross section of the vicinity of the developing section, and FIG. 2 shows an outline of an electrostatographic copying machine as an example of an electrophotographic apparatus.

The electrophotographic copying machine has a photosensitive drum 2 having a photosensitive member 1 on its outer peripheral surface mounted horizontally on a copying machine main body 3, and
Around the photoreceptor 1, a charging device 4, an exposure device 5 with a moving optical system, a developing device 6, a charger type transfer device 7, a copy paper separation device 8, and a cleaning device 9 are installed around the photoreceptor 1. They are arranged in this order in the rotational direction (indicated by arrow R), and the paper feed section 10
A paper feed conveyance means 11 from the transfer device 7 to the transfer device 7
and from the copy paper separating device 8 to the fixing device 1
In addition to disposing paper discharge conveying means 13 over two sections, a pair of paper discharge rollers 15 and a paper discharge tray 16 are also provided.

As shown in FIG. 1, the developing device 6 includes a developing sleeve 17 that rotates in the opposite direction to the photoreceptor 1.
A magnetic brush forming mechanism 19 including a magnet 18 fixedly provided inside the brush forming mechanism 19 is provided in a case 21 containing a two-component developer 20 containing a mixture of non-magnetic toner a and magnetic carrier b. At the same time, non-magnetic toner a is supplied via the toner supply roller 22...
A hopper 23 for replenishing the storage case 21 is connected to the storage case 21, and a stirring rotor 24 rotates in the same direction (or in the opposite direction) as the sleeve 17; A conveyance rotor 25 that rotates in the opposite direction is built into the developer storage case 21, a spike plate 26 that cuts the spikes of the two-component developer 20, and a toner supply roller 22 that detects the toner concentration. A toner concentration control sensor 27 for controlling the rotation of the developer storage case 21 is provided in the developer storage case 21.

As shown in FIG. 4, the surface potential of the portion where static charges remain on the base 2a of the photosensitive drum 2 having the photosensitive member 1 on its surface (for example, made of metal such as aluminum) and the developing sleeve 17 A DC power supply 28 is connected across the base 2a and the developing sleeve 17 to apply a bias voltage so that the surface potentials of the photoreceptors 1 and 17 are approximately the same. An electric field is generated in the developing section A by the developing sleeve 17.

Therefore, similar to the conventional form described at the beginning,
Due to the electric field generated by the bias voltage, the non-magnetic toner a...
An inversion phenomenon is carried out that causes the adhesion of .

Now, the electric field caused by the above bias voltage acts near the developing section A and does not extend to the path leading to the transfer device 7. In this path, the toner a adhering to the photoreceptor surface S is moved by centrifugal force. As described above, the magnetic carrier b is likely to be mechanically detached due to, for example, the electrostatic charge remaining portion 1a in the developing section A.

Therefore, an electrode 29 is provided in the path from the developing device 6 to the transfer device 7 to apply a bias voltage having the same polarity as the charge polarity of the toner a.
Efforts are being made to prevent carrier b from leaving and recover carrier b.

As shown in FIG. 8, the electrode 29 has a box structure made of conductive metal, and includes an upper plate 30 and a lower plate 31 having a curved surface with a radius approximately equal to the radius of the photoreceptor 1. It consists of a circumferential side plate 32 that connects the upper and lower plates 30 and 31 with an interval between the upper and lower sides, and the upper plate 30 has a plurality of openings c along the direction of the rotational axis of the photoreceptor 1. It is formed by cutting and bending the plate part.

This electrode 29 is connected to the developing device 6 and the transfer device 7.
and facing the surface of the photoreceptor 1, and the spacing between the counter electrode 29 and the photoreceptor surface S is set so as to increase sequentially toward the downstream side in the rotational direction of the photoreceptor 1. And, as shown in Figure 4,
A DC power supply 33 to which a bias voltage having the same polarity as the charge polarity of the toner a is applied is connected to the counter electrode 29, thereby creating an electric field between the photoreceptor 1 and the counter electrode 29. Therefore, in the portion facing the electrode 29, a repulsive force due to the same polar charge can be applied to the toner a adhering to the photoreceptor surface S, and thereby the photoreceptor surface S
This makes it possible to prevent toner a from leaving the toner a.

Moreover, since the electrodes 29 are arranged so that the distance becomes larger toward the downstream side in the rotational direction of the photoreceptor 1, the toner a is allowed to escape from the electric field region while gradually weakening the repulsive force acting on the toner a. Therefore, for example, if the toner a is allowed to escape from the electric field region while applying a certain repulsive force, there is a possibility that the toner a will be detached from the photoreceptor surface S due to the shock caused by the sudden release of the repulsive force. , it becomes easier to avoid such a situation.

Moreover, since the electrode 29 has a polarity opposite to that of the carrier b, the carrier b attached to the surface of the photoreceptor and the carrier b mechanically scattered in the developing section A are attracted by the attraction force due to the opposite polarity charge. If the bias power supply 33 is cut off at the end of printing to eliminate the attraction of the carrier b, the carrier b will roll off the upper surface of the top plate 30. , this can be collected through the opening c... into a carrier collection tray which also serves as the lower part of the electrode.

The case of reversal development has been explained above, but in the form of a regular image using a two-component developer, by providing an electrode with the same polarity as the charged polarity of the toner, the separation of the toner is caused by the repulsive force caused by the same polar charge. It will be understood that this can be prevented and that the carrier can be recovered using the attraction force caused by the opposite polarity charge.

Another embodiment of the counter electrode 29 is shown in FIG. In this device, the counter electrode 29 is arranged in steps so that the distance between the counter electrode 29 and the surface S of the photoreceptor becomes larger toward the downstream side in the rotational direction of the photoreceptor 1. is configured to double as a carrier collection tray.

In addition, in each of the above-mentioned embodiments, the counter electrode 29
Although it is provided over almost the entire range from the developing device 6 to the transfer device 7, a configuration in which it is provided in a narrower range can still be sufficiently effective.

(Effects of the invention) As explained above, in the invention, between the developing device and the transfer device, which use a two-component developer in which a magnetic carrier and a non-magnetic toner are mixed, the charge polarity of the magnetic carrier and the Electrodes to which a bias voltage of opposite polarity is applied are arranged facing each other along the surface of the photoreceptor so that the distance from the surface of the photoreceptor increases sequentially toward the downstream side in the direction of rotation of the photoreceptor, and A collection tray for the magnetic carriers is formed by the above-mentioned electrodes, and the carriers attracted to the electrodes are collected by cutting off the bias power supply to the electrodes. While it is possible to prevent toner from detaching from the photoconductor surface due to force or gravity, the attraction force caused by the opposite polarity charge can prevent magnetic carriers from adhering to the photoconductor surface or being mechanically scattered. Can be captured by suction.

In particular, in the present invention, an electrode to which a bias voltage with a polarity opposite to that of the magnetic carrier is applied is placed along the photoreceptor surface, and the distance from the photoreceptor surface increases toward the downstream side in the rotational direction of the photoreceptor. Since they are arranged facing each other so as to increase in size sequentially, it is possible to gradually weaken the repulsive force against the toner and allow the toner to escape from the electric field area created by the electrodes, thereby reducing the shock caused by the sudden release of the repulsive force. The more the toner can be prevented from detaching from the surface of the photoreceptor.

As described above, according to the present invention, it is possible to prevent toner from leaving the surface of the photoreceptor in both normal image and reversal development, and
Capable of capturing and collecting magnetic carriers that adhere to the surface of the photoconductor and magnetic carriers that are mechanically scattered in the developing section. By simultaneously preventing toner separation and collecting magnetic carriers, it is effective in reducing internal contamination and image quality deterioration. It has become possible to prevent this from happening.

In the present invention, the electrodes form a collection tray for magnetic carriers, and the magnetic carriers attracted to the electrodes are collected by cutting off the bias power to the electrodes. This method has the advantage that it is simple, can prevent cost increases, and does not require time and effort to recover the magnetic carrier.

[Brief explanation of the drawing]

The drawings show an embodiment of the present invention, in which FIG. 1 is a detailed sectional view of the vicinity of the developing section, FIG. 2 is a schematic longitudinal sectional view of an electrostatographic copying machine, FIG. The figure shows the form of reversal development using a two-component developer.
FIG. 5 is a side view of a counter electrode according to another embodiment. DESCRIPTION OF SYMBOLS 1... Photoreceptor, 6... Developing device, 7... Transfer device, 20... Two-component developer, 29... Electrode, 3
3...Bias power supply, S...Photoconductor surface, a...
Toner, b...magnetic carrier.

Claims (1)

[Scope of utility model registration request] An electrode to which a bias voltage having a polarity opposite to that of the magnetic carrier is applied is connected between the developing device and the transfer device, which use a two-component developer containing a magnetic carrier and a non-magnetic toner, on the surface of the photoreceptor. The electrodes are arranged facing each other so that the distance from the surface of the photoreceptor increases gradually toward the downstream side in the rotational direction of the photoreceptor, and the electrode forms a collection tray for magnetic carriers, and 1. An electrophotographic apparatus characterized in that the carrier attracted to the electrode is collected by cutting off the bias power supply.