JP2861681B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a two-component magnetic brush developing system for developing with a developer containing a magnetic carrier and a toner. The present invention relates to an image forming apparatus having a carrier collecting means for sucking and collecting a magnetic carrier from an image carrier before a transfer process.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus having an electrophotographic process by a two-component magnetic brush developing system, for example, Japanese Patent Application Laid-Open Nos. 58-176661 and 60-1426.
No. 4, JP-A-1-134484, and the like, a magnetic pole magnet is fixed inside a carrier recovery magnetic sleeve, and the magnetic pole magnet is used together with the toner at the time of development by a developing device. The magnetic carrier attached to the surface of the (image carrier) is magnetically attracted and collected.

Conventionally, as a magnetic pole magnet disposed in the carrier recovery magnetic sleeve, a space in the apparatus,
Ferrite-based magnets having a magnetic flux density of about 5 to 600 gauss were sufficient because of restrictions on cost and the like and the relatively low image quality requirement level mainly in the copying machine market.

[0004]

However, in recent years, there has been an increase in the number of functions such as colorization in the copier and printer markets.
Along with the demand for higher image quality, the two-component magnetic brush developing system has also been improved in a wide variety of ways, all of which tend to increase the adhesion of the magnetic carrier to the photosensitive drum described above. In particular, in a copying machine that requires high image quality, a resin binder carrier containing magnetic powder inside than a conventional iron or ferrite carrier is used. The mainstream is to reduce the particle size of the carrier from about 100 μm to 50 μm or less, so that the amount of the carrier adhered to the surface of the photoreceptor drum is large, and the magnetic attraction efficiency is deteriorated. Therefore, conventional magnetic attraction using a ferrite-based magnet alone is not sufficient for carrier recovery, and there has been a problem that a fatal image quality defect such as white spots or black spots is caused. In order to increase the magnetic attraction of the magnetic carrier, it is conceivable to increase the size of the ferrite-based magnet. However, this has a problem that the size of the entire apparatus is increased.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and has as its object to reduce the size of the apparatus and to efficiently remove the magnetic carrier adhered to the image carrier together with the toner during development before the transfer step. An object of the present invention is to provide an image forming apparatus which can be magnetically attracted from an image carrier to prevent image quality defects such as white spots and black spots from occurring.

[0006]

According to the first aspect of the present invention, (a) an image carrier on which an electrostatic latent image is formed on a surface;
(B) has opposing to the developing roll to the surface of the image bearing member, an electrostatic latent image formed on the surface of the Zo担 lifting member with a developer comprising a magnetic carrier and a toner using the developing roll a developing unit that visible image, in (c) a rotatable non-magnetic sleeve, part of which protrudes in the direction of the image bearing member at a high magnetic flux density than the fixed pole magnets and the pole magnets
Together it is constituted by a carrier recovery roll to be buried rare earth magnet to the magnetic pole magnet in the form, in the developing unit, and is disposed on the downstream side of the developing roller along the toner transport direction by Zo担 lifting body cage, rare earth magnet carrier
Arranged closer to the image carrier than the magnetic pole magnet of the recovery roll
And the rare earth magnet pole is adjacent to the carrier recovery roll
The polarity of the magnetic pole is set to be opposite to the polarity of the magnet.
With the toner during visualization by the developing means
A carrier recovery means for the magnetic carrier adhered to the surface of the Zo担 lifting member magnetically sucked and recovered to provided in the image forming apparatus.

Here, the rare earth magnet is preferably one having a high magnetic flux density of 1500 gauss or more, such as samarium cobalt or neodymium iron, and the other magnetic pole magnet having a magnetic flux density of about 5 to 600 gauss conventionally used. A ferrite magnet is used.

In this image forming apparatus, the electrostatic latent image formed on the surface of the image carrier is visualized by the developing roll in the developing means, and the toner image is formed together with the toner at the time of the visualization. Before the transfer process, the magnetic carrier attached to the surface
Similarly, by the rare earth magnet of the carrier collection roll disposed in the developing means, it is magnetically attracted to the carrier collection roll side with high efficiency and collected in the developing means.

According to the second aspect of the present invention, there is provided (A) an image carrier on which an electrostatic latent image is formed on the surface, and (B) a developing roll opposed to the surface of the image carrier. Using this developing roll, a developer containing a magnetic carrier and toner
A developing unit that visualizes the electrostatic latent image formed on the surface of the Zo担 lifting member, a transfer unit for transferring the toner image formed by (iii) developing means to a transfer medium, (d) A magnetic pole magnet fixed in a rotatable non-magnetic sleeve and a part of the magnetic flux with a higher magnetic flux density than the magnetic pole magnet are directed toward the image carrier.
A carrier recovery roll, which is a rare-earth magnet embedded in the magnetic pole magnet in a protruding form, and is located downstream of the developing roll along the toner conveying direction by the image bearing member.
And rare earth magnets are
Rare earth elements located closer to the image carrier than the pole magnets
The magnetic pole of the magnet is
It has magnetic poles and the polarity are set to be opposite, and a carrier recovery means magnetically attracted to recover the magnetic carriers adhering to the surface of the Zo担 lifting body together with the toner during the visible image by the developing means An image forming apparatus is provided.

In this image forming apparatus, since the carrier collecting roll is provided outside the developing means, the magnetic carrier magnetically attracted to the carrier collecting roll with high efficiency by the rare earth magnet of the carrier collecting roll is separately provided. Collected in the carrier collecting means.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 2 shows the overall schematic structure of a copying machine according to an embodiment of the present invention. This copying machine performs, for example, copying in two colors of black and red. In the copying machine, a photosensitive drum 1 for forming an electrostatic latent image is arranged rotatably in the direction of the arrow in the figure. I have. Around the photosensitive drum 1, a charging corotron 2 for uniformly charging the surface of the photosensitive drum 1, a first writing device 3 for writing first image information electrostatically, and a 1
Developing device 4 for visualizing the image information written by the writing device 3 with black toner to obtain a first developed image
And a second writing device 5 for electrostatically writing the second image information to the first developed image, and the image information written by the second writing device 6 having a different polarity from the black toner. A developing device 6 that obtains a second developed image by superimposing and visualizing the image with red toner; a transfer corotron 7 for transferring the toner image obtained by the developing devices 4 and 6 to copy paper 11; A cleaning device 8 for removing the toner transferred by the photoreceptor 7 from the surface of the photoconductor drum 1 and a charge eliminating corotron 9 for neutralizing the charge remaining on the surface of the photoconductor drum 1 are arranged in this order.

The copy paper 11 is sequentially sent out from a paper supply cassette 10 by a paper supply roller 13, conveyed through a conveyance path 12, and then transferred to a transfer corotron 7 and a photosensitive drum 1 via a registration roller 14 at a transfer timing. Sent between. The copy paper 11 onto which the toner image has been transferred is fed by a conveyor belt 15 from a conveyance path 16 between a fixing roller 17a and a pressure roller 17b constituting a fixing device, where the toner image is thermally fixed. The paper is discharged to the outside of the apparatus by a discharge roller which is not used.

In the developing device 6, a developing roll 21 is provided so as to face the surface of the photosensitive drum 1. The developing roll 21 has a magnetic pole magnet fixedly disposed inside a rotatable non-magnetic sleeve. A magnetic brush of a two-component developer 27 composed of a magnetic carrier and toner is formed on the surface by the magnetic force of the magnetic pole magnet. The magnetic brush is rubbed against the electrostatic latent image formed on the surface of the photosensitive drum 1 by the bias voltage applied to the developing roll 21 and the rotation of the non-magnetic sleeve, and is visualized with toner. .

A carrier recovery roll 22 is disposed in the developing device 6 at a position substantially downstream of the developing roll 21 in the rotation direction of the photosensitive drum 1 and substantially facing the photosensitive drum 1. The carrier recovery roll 22 magnetically attracts and recovers the magnetic carrier attached to the surface of the photosensitive drum 1 together with the toner when the electrostatic latent image is visualized by the developing roll 21.

FIG. 1 is an enlarged view of the structure of the carrier collecting roll 22. This carrier collection roll 2
Reference numeral 2 denotes a non-magnetic sleeve 23 rotatable by driving a motor (not shown), and a ferrite-based sintered magnet 24 fixedly arranged together with a shaft 26 in the non-magnetic sleeve 23.
And a rare earth magnet 25 buried in a part thereof at a position substantially opposed to the photosensitive drum 1. As the rare earth magnet 25, a magnet having a high density magnetic flux of 1500 gauss or more, such as samarium cobalt or neodymium iron, is used.

The carrier recovery roll 22 is used together with the toner during development by the developing roll 21 to transfer the photosensitive drum 1 to the photosensitive drum 1.
The magnetic carrier 27a adhered to the surface of the photosensitive drum 1 is magnetically attracted to the non-magnetic sleeve 23 side by the rare earth magnet 25 in the developing section where the gap D between the photosensitive drum 1 and the magnetic flux density is the largest. Here, the rare earth magnet 2
5 has a higher magnetic flux density than the other ferrite-based sintered magnets 24, so that the magnetic carrier 27a can be attracted with higher efficiency than the conventional one. The sucked magnetic carrier 27a is transported downstream in the rotation direction by the rotation of the non-magnetic sleeve 23. This transported magnetic carrier 2
The carrier 7a loses its conveying force between adjacent magnetic poles (N-poles) of the ferrite-based sintered magnet 24 in the carrier recovery roll 22 and falls into the developing device 6 to be recovered.

As described above, in this embodiment, the magnetic carrier 27 attached to the photosensitive drum 1 by the carrier collecting roll 22 in the developing device 6 is magnetically attracted from the photosensitive drum 1 with high efficiency before the transfer portion. As a result, the magnetic carrier 27a hardly remains on the surface of the photosensitive drum 1 in the transfer portion, and as a result, the magnetic carrier 27a
This can prevent transfer defects and image quality defects from occurring. In this embodiment, the magnetic carrier 27a can be collected with high efficiency without increasing the size of the conventionally used ferrite-based sintered magnet 24.
The entire device can be maintained at a conventional size.

In the above embodiment, the carrier collection roll 22
Has been described inside the developing device 6,
The carrier collecting roll 22 may be provided outside the developing device as shown in FIG.

In this embodiment, in the developing device 30, the blenders 31, 32, the paddle wheel 33 and the developing roll 3
The two-component developer 27, which is frictionally charged by the blenders 31 and 32 and has a uniform toner content, is transported by the paddle wheel 33. The transported two-component developer 27 is picked up by the pick-up magnetic poles of the developing rolls 34, and a brush-like spike is formed in accordance with the magnetization pattern of the developing magnetic poles. After the layer thickness is regulated to the optimum thickness by the layer thickness regulating member 35, the electrostatic latent image on the photosensitive drum 1 is visualized by the toner component.

The carrier collection roll 22 is provided with a developing device 30
At a predetermined position on the upstream side of the transfer corotron 7 near the downstream side in the rotation direction of the photosensitive drum 1. The configuration of the carrier recovery roll 22 is the same as that of the above-described embodiment, but as shown in an enlarged view in FIG.
C) A power supply 36 and an alternating current (AC) power supply 37 are respectively applied.

A carrier collection tray 38 is arranged below the carrier collection roll 22. A scraper 39 is integrated with the carrier collection tray 38 to scrape off the magnetic carrier 27a attached to the surface of the carrier collection roll 22 by suction.
It is designed to be dropped inside. Carrier collection tray
An air duct 40 is provided in 38 . A plurality of holes 41 are formed at the lower end of the scraper 39.

In this embodiment, the magnetic carrier 27a magnetically attracted from the surface of the photosensitive drum 1 by the carrier collection roll 22 with high efficiency is dropped into the carrier collection tray 36, and then is moved by an air suction pump (not shown). Is collected outside the apparatus through a plurality of holes 41 provided in the scraper 39 and the air duct 40. Also in the present embodiment, the magnetic carrier 27a can be collected with high efficiency without increasing the size of the entire apparatus, and the occurrence of transfer failure and image quality defect can be prevented, as in the above embodiment. .

The present invention has been described with reference to the embodiments.
The present invention is not limited to the above embodiments, and can be variously modified without changing the gist thereof. For example, in the embodiment of FIG. 3, the carrier collecting roll 22 is provided near the developing device 30. However, the position of the carrier collecting roll 22 is different from that of the developing device 30 and the transfer corotron 7.
It may be any position between the transfer position according to FIG. 1 and FIG.

[0025]

As described above, according to the image forming apparatus of the present invention, a fixed magnetic pole magnet and a rare earth magnet having a higher magnetic flux density than the magnetic pole magnet are arranged in a rotatable non-magnetic sleeve. The rare earth magnet of the carrier recovery roll
It was arranged closer to the image carrier than the magnetic pole magnet and opposed to the image carrier. Therefore, it is possible to form a combination <br/> specific magnetic force distribution of the magnetic pole magnet, transferring the magnetic carrier adhered to the surface of the Zo担 lifting body together with the toner during the visible image by the developing unit step together as possible out to magnetically collected with high efficiency prior to, it is possible to prevent the occurrence of image defects such as white spots and black spots more effectively.

[Brief description of the drawings]

FIG. 1 is a side view illustrating a configuration of a carrier collection roll according to an embodiment of the present invention.

FIG. 2 is a side view of the entire image forming apparatus using the carrier collection roll of FIG.

FIG. 3 is a side view illustrating a configuration of a developing device and a carrier collecting roll according to another embodiment of the present invention.

FIG. 4 is a side view showing the carrier recovery roll shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Photoreceptor drum, 4, 6 ... Developing device, 7 ... Transfer corotron, 21 ... Developing roll, 22 ... Carrier collection roll,
23: Non-magnetic sleeve, 24: Ferrite sintered magnet,
25 ... rare earth magnet, 26 ... shaft, 27 ... two-component developer, 27a ... magnetic carrier

Claims (2)

(57) [Claims] 1. An image bearing member having an electrostatic latent image formed on a surface thereof, and a developing roll opposed to the surface of the image bearing member. agent by an electrostatic latent image formed on the surface of the image bearing member and developing means a visible image, in a rotatable non-magnetic sleeve, a high magnetic flux density than the fixed pole magnets and the pole magnets Part of the image
Embedded in this pole magnet in the form projecting in the direction of the carrier
Along with a carrier recovery roll serving as a rare earth magnet , inside the developing means, and downstream of the developing roll along a toner conveying direction by the image carrier.
And the rare-earth magnet is disposed in the carrier recovery slot.
Closer to the image carrier than the magnetic pole magnets of the
The magnetic pole of the rare earth magnet is adjacent to the carrier recovery roll.
It is set so that the polarity is opposite to the magnetic pole of the magnet,
An image forming apparatus comprising: a carrier collection unit that magnetically attracts and collects a magnetic carrier attached to the surface of the image carrier together with the toner when the developing unit visualizes the image. 2. An image bearing member having an electrostatic latent image formed on a surface thereof, and a developing roll facing the surface of the image bearing member. The developing roll includes a magnetic carrier and toner using the developing roll. Developing means for visualizing an electrostatic latent image formed on the surface of the image carrier with an agent, transfer means for transferring the toner image formed by the developing means to a transfer-receiving medium, A magnetic pole magnet fixed in a magnetic sleeve and a part of the magnetic pole magnet having a higher magnetic flux density than
Embedded in this pole magnet in the form projecting in the direction of the carrier
It is composed of a carrier recovery roll serving as a rare earth magnet, and is arranged along the toner conveying direction by the image carrier .
The rare earth element is disposed downstream of the developing roll.
The magnets carry more images than the magnetic pole magnets on the carrier recovery roll
The magnetic pole of the rare earth magnet is placed close to the body and the carrier
The polarity of the magnetic pole of the magnetic pole magnet adjacent to the collection roll is opposite.
And it is set to so that, in that a carrier recovery means magnetically sucked recovering magnetic carrier adhering to the surface of the image bearing member with the toner in the visible image by the developing unit Characteristic image forming apparatus.