JPH0527546A - Multicolor image forming device - Google Patents

Abstract

PURPOSE:To provide a multicolor image forming device capable of preventing color mixture with magnetic toner developed on an image carrier. CONSTITUTION:In the multicolor image forming device where at least one of plural developing units fixedly arranged around the image carrier 1 uses the magnetic toner and a developing unit 4M on which a magnet roller 41 is disposed and non-magnetic developer carrier 5M is provided is arranged further downstream than the developing unit in the direction in which the image carrier rotates, a magnetic field generating means 11 is provided in the image carrier 1 in the position where a development part in which the developing unit 4M positioned downstream faces the image carrier 1 is situated. Thus, color mixture with the magnetic toner is prevented and an image is prevented from being darkened.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multicolor image forming apparatus in an electrophotographic apparatus used in a copying machine or a facsimile.

[0002]

2. Description of the Related Art Conventionally, as a multi-color image forming apparatus, a two-component developing device for magenta, cyan, yellow and black is fixedly arranged around a photosensitive drum which is an image carrier, and is located upstream in the rotational direction of the photosensitive drum. In order to develop the electrostatic latent image formed on the photosensitive drum in order from the developing device and not to develop the other three developing devices that are not involved in the development, the developing device is attached or detached, and the developing sleeve that is the developer carrying member. The developer above can be removed by bringing the blade cutting blade into contact with the developing sleeve or by rotating the developing sleeve in the reverse direction using the repulsive pole of the magnet roller in the developing sleeve. A type of so-called ear cutting that causes the adhering portion to face the photosensitive drum has been devised and implemented.

Further, as a black of a multicolor image forming apparatus, a developing system using magnetic toner instead of the two-component developing system,
In particular, a device using a jumping development method using magnetic one-component toner has been devised.

FIG. 6 shows an example in which a developing device using a jumping developing method using magnetic one-component toner, which is one of those conventional techniques, is located at the most upstream position in the photosensitive drum rotation direction.

In FIG. 6, 1 is a photosensitive drum which rotates in the direction of arrow A, 2 is a primary charger, 3 is laser light, 4
K, 4M, 4C and 4Y are a jumping developing device using black magnetic one-component toner and a two-component developing device of magenta, cyan and yellow, which are 5K, 5M, 5C and 5Y, respectively.
Y indicates the developing sleeve. 6 is a transfer material (paper)
A transport unit, 7 is a transfer drum that rotates in the direction of arrow B, 8 is a transfer charger, 9 is a cleaning device, and 10 is a fixing device.

Next, the operation will be described. The primary charger 2
On the photosensitive drum 1 uniformly charged to -700V, a black latent image is formed by the laser beam 3 in accordance with a digital signal from a reader (document reading device) (not shown), and the latent image is formed. Develop with black developer 4K. At this time, the other two-component developing device is cutting the head.

On the other hand, the transfer material guided to the area where the photosensitive drum 1 and the transfer drum 7 are in contact with each other by the transfer material conveying section 6 in synchronism with the image is transferred with a black toner image by the transfer charger 8. It After the transfer is completed, the residual toner on the surface of the photosensitive drum 1 is cleaned by the cleaning device 9, and is then subjected to the image forming process again.

Thereafter, this operation is repeated in the order of magenta, cyan, and yellow to form an image. further,
The transfer material that has completed the transfer process is conveyed to the fixing device 10 and provided as an image.

The operation of the developing device during normal development will be described with reference to FIG. 7, and the operation of the developing device during cutting will be described with reference to FIG.

In FIGS. 7 and 8, 41 is a magnet roller, 42 and 43 are screws as a developer carrying member, and 44 is a developer layer regulating blade.

The operation during development will be described with reference to FIG.
The developer 45 composed of the magnetic carrier and the non-magnetic toner is rotated forward in the longitudinal direction by the rotation of the screw 42 in the arrow D direction.
By rotating the screw 43 in the direction of arrow E, it is leveled inward in the longitudinal direction while circulating between the screws 42 and 43.

The developer 45 at the position of the screw 43 is N of the magnet roller 41 in the developing sleeve 5M.
_It is pumped up to the surface of the developing sleeve 5M by the _two poles, and S
₂ , is conveyed by the rotation of the developing sleeve 5M in the direction of arrow C by the N ₁ pole, is coated in a thin layer by the developer layer regulating blade 44, and is further conveyed to the developing portion which is the closest portion to the photosensitive drum 1. , The developer 45 on the developing sleeve 5M is developed by a contact two-component developing method in which the developer 45 is brought into contact with the photosensitive drum 1.

The developed developer 45 is conveyed by the N ₃ pole, the developer falls by gravity from the developing sleeve 5M to the center of the N ₃ and N ₂ poles which are repulsive poles, and is collected in the developing unit. .

The operation at the time of cutting the head will be described with reference to FIG. After the development, the rotation of the arrow F direction of the developing sleeve 5M (during development and reverse) during development, N ₃ of the developer magnet roller 41 present near the developing unit, S _1, N
_1, is conveyed by S _2-pole, further developer with developer drawn up by N ₂ pole forms a repulsive pole N _2, N
Gravity falls from the developing sleeve 5M to the center of the ₃ poles,
It is collected in the developing device.

On the other hand, when the non-adhesive portion of the developer which starts from the center of the repelling electrode reaches the S ₂ pole by the rotation of the developing sleeve 5M in the direction of arrow F, the rotation of the developing sleeve 5M may be stopped (or not stopped). ), The surface of the developing sleeve 5M is exposed to prevent development.

[0016]

However, in the above-mentioned conventional example, when the image output durability is increased, the black toner is mixed in the two-component developing device located downstream,
There was a problem that the image became dark.

As a result of investigating how this development takes place, in FIG. 6, the magnetic one-component toner developed on the photosensitive drum 1 from the black developing device 4K is detected on the photosensitive drum 1 and the developing sleeve. Gap is 500 μm
When passing through each of the two-component developing devices 4M, 4C and 4Y for magenta, cyan and yellow, which have been cut off, the magnetic poles of the developing poles of the developing sleeves 5M, 5C and 5Y cause magnetic poles in the developing portion of the developing sleeve. It was found that the cause was that they were attracted to nearby areas.

The present invention is intended to solve the above problems. That is, the present invention is capable of preventing color mixing with magnetic toner developed on an image carrier such as a photosensitive drum, so that an image does not become dark. It is intended to provide.

[0019]

In order to achieve the above object, according to the present invention, a plurality of developing devices are fixedly arranged around an image carrier as a fixed developing device which is not detachable, and at least one developing device is provided. The developing device uses magnetic toner, and at least one developing device provided with a non-magnetic developer carrying member having a magnet roller inside is disposed downstream of the developing device in the rotational direction of the image carrying member. In a multicolor image forming apparatus,
It is assumed that the magnetic field generating means is provided in the image carrier of the developing unit, which is a position where the developing unit located downstream of the developing unit using the magnetic toner in the rotation direction of the image carrier faces the image carrier. .

[0020]

According to the present invention, at least one of the plurality of developing units fixedly arranged around the image carrier as the stationary developing unit uses the magnetic toner, and is downstream of the developing unit in the rotational direction of the image carrier. When one or more developing devices each having a non-magnetic developer bearing member having a magnet roller disposed therein are disposed in the developing unit, the developing unit of the developing unit located downstream is opposed to the image bearing member. Since the magnetic field generating means is provided in the image bearing body at a certain position, color mixture with the magnetic toner is prevented by the magnetic action of the magnetic field generating means.

[0021]

1 is a sectional view showing a two-component developing device of a multicolor image forming apparatus according to a first embodiment of the present invention.

In FIG. 1, a magnetic field generating means 11 is provided inside the photosensitive drum 1, and in this embodiment,
It is a permanent magnet.

That is, in FIG. 1, after the cutting ends,
At the time of developing the magnetic one-component toner, the magnetic field generating means 11 moves to the position shown in the figure to attract the magnetic one-component toner developed on the photosensitive drum 1 onto the photosensitive drum 1 without causing color mixing. . At this time, the magnetic field generating means 11 (permanent magnet) has different poles facing each other.

FIG. 2 is a sectional view showing a part of FIG. 1 in an enlarged manner, and is for explaining the effect of the present invention in detail.

In FIG. 2, the surface 12 equidistant from the end of the magnet roller 41 on the side of the photosensitive drum 1 and the end of the magnetic field generating means 11 on the side of the developing sleeve 5M is the uppermost layer of the toner image on the photosensitive drum 1 ( Unless it is located closer to the magnet roller 41 than the developing sleeve side), the magnetic field generating means 11 provided cannot keep the magnetic toner on the photosensitive drum 1 and cannot prevent color mixing.

FIG. 3 is a sectional view showing a two-component developing device of a multicolor image forming apparatus according to the second embodiment of the present invention.

In this second embodiment as well, a permanent magnet is used as the magnetic field generating means 11, but the same poles face each other.

In FIG. 3, in the developing section, the S ₁ pole which is the developing pole of the magnet roller 41 and the S ₃ pole of the magnetic field generating means 11 are used.
The appearance of the magnetic field lines emerging from each other of the poles is simply illustrated.

As can be seen from FIG. 3, the magnetic lines of force repel each other, so that the lines of magnetic force of the magnet roller 41 did not reach the toner image on the photosensitive drum 1 and color mixing could be prevented.

4 and 5 are sectional views showing a two-component developing device of a multicolor image forming apparatus according to a third embodiment of the present invention.
Shows one state and FIG. 5 shows the other state.

In the third embodiment, the photosensitive drum 1 and the magnetic field generating means 11 composed of a permanent magnet are located in the photosensitive drum 1 of the developing sleeve 5M facing the photosensitive drum 1 and in the opposing photosensitive drum 1. A magnetic shield plate such as the magnetic plate 20 is provided between them.

In FIG. 4, the magnetic plate 20 is at the position shown, except during the development of the magnetic toner, and the magnetic field generating means 11 is used.
Of the magnetic field, the magnetic field generating means 11 is moved in the first and second embodiments described above by moving in the direction of arrow G and stopping at the position shown in FIG. 5 when developing the magnetic toner. The same action and effect as those of the above are obtained.

Further, by doing so, the developing device 4
During M, the carrier can be prevented from being attracted onto the drum surface by the magnetic force of the magnetic field generating means 11.

Next, as a fourth embodiment of the present invention, there is a magnetic field generating means 11 using an electromagnet.

In each of the above embodiments, the case of full color has been described, but the case of mono color can be cited as the fifth embodiment of the present invention.

[0036]

As described above, according to the present invention,
As a fixed developing device, at least one of a plurality of developing devices fixedly arranged around the image carrier uses magnetic toner, and a magnet roller is provided inside the developing device at a position downstream of the developing device in the rotational direction of the image carrier. When at least one developing device having a non-magnetic developer bearing member is disposed, a magnetic field is generated in the image bearing member at a position where the developing unit is a portion facing the image bearing member of the developing unit positioned downstream. Since the generating unit is provided, color mixture with the magnetic toner is prevented by the magnetic action of the magnetic field generating unit. Therefore, the image does not become dark.

[Brief description of drawings]

FIG. 1 is a sectional view showing a two-component developing device of a multicolor image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a sectional view showing a part of FIG. 1 in an enlarged manner.

FIG. 3 is a sectional view showing a two-component developing device of a multicolor image forming apparatus according to a second embodiment of the present invention.

FIG. 4 is a sectional view showing one state of a two-component developing device of a multicolor image forming apparatus according to a third embodiment of the present invention.

FIG. 5 is a cross-sectional view showing another state of the same.

FIG. 6 is an explanatory diagram showing an example of a conventional technique.

FIG. 7 is a sectional view showing a state of the developing device of FIG. 6 during normal development.

FIG. 8 is a cross-sectional view showing a state of cutting the ear.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 4M ... Magenta developing device 5M ... Magenta developing sleeve 11 ... Magnetic field generating means 41 ... Magnet roller 45 ... Developer

Claims (6)

[Claims] 1. A plurality of developing devices are fixedly arranged around the image carrier as a fixed developing device which is not attached and detached, and at least one of the developing devices uses magnetic toner, and the image carrier is more than the developing device. In a multi-color image forming apparatus in which one or more developing devices each including a non-magnetic developer carrier having a magnet roller disposed therein are arranged downstream in the rotation direction,
The magnetic field generating means is provided in the image carrier of the developing section, which is a position where the developing device located downstream of the developing device using the magnetic toner in the rotation direction of the image carrier faces the image carrier. And a multicolor image forming apparatus. 2. The multicolor image forming apparatus according to claim 1, wherein the magnetic field generating means in the image carrier comprises a permanent magnet. 3. The multicolor image forming apparatus according to claim 1, wherein the magnetic field generating means in the image carrier comprises an electromagnet. 4. The multicolor according to claim 1, wherein the magnetic pole in the developing section of the magnetic field generating means in the image carrier is different from the magnetic pole in the developing section of the magnet roller in the developer carrier. Image forming apparatus. 5. The multicolor according to claim 1, wherein the magnetic pole in the developing section of the magnetic field generating means in the image carrier is the same as the magnetic pole in the developing section of the magnet roller in the developer carrier. Image forming apparatus. 6. The developer of the magnetic field generating means in the image carrier is the uppermost layer of the developer layer developed on the image carrier, rather than the tip of the magnet roller of the developer carrier on the image carrier side. 2. The end portion on the carrier side is closer to the front end portion.
The multicolor image forming apparatus described in 2, 3, 4 or 5.