JPH0611941A - Image forming device - Google Patents

Abstract

PURPOSE:To provide a high-quality color image having no defect by preventing the developing portion of a one-component jumping developing unit from being adversely affected by a carrier entering the one-component developing unit from other two-component developing units, and allowing development by the one-component developing unit to be performed well as by the other two- component developing units. CONSTITUTION:A one-component jumping developing unit 40 for use as the black developing unit of the fourth station of an image forming device has a magnet roller 42 in a developing sleeve 41 with the cut pole N1 of the roller 42 tilted upstream of the direction of rotation of the sleeve 41 and relative to a magnetic blade 43. A carrier 48 put in the developing unit 40 is thereby held in an area where thin layers of a magnetic toner 44 are formed by the blade 43 and the cut pole N1, and so can be prevented from leaking out to a developing portion.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus, and more particularly to an image forming apparatus having a plurality of developing devices such as a full color copying machine.

[0002]

2. Description of the Related Art Conventionally, a full-color copying machine utilizing an electrophotographic system produces an electrostatic latent image sequentially formed in accordance with an exposure signal of color-separated image information, and outputs an electrostatic latent image of a color corresponding to the latent image. A full-color image is obtained by sequentially developing with a developing device to form toner images of magenta, cyan, yellow, black, and the like.

In such a developing device, a two-component developer in which color toner and carrier are mixed is used as a developer.
A two-component magnetic brush development method is often used in which a magnetic brush of the developer is formed and development is performed.

However, in this two-component developing system,
There is a problem of toner concentration detection and toner replenishment for keeping the mixing ratio of the developer toner and carrier (toner concentration of the developer) constant, and the carrier is covered with the binder resin component of the toner due to the use of the developer. There was a problem such as carrier deterioration.

When the toner density fluctuates, the density of the image obtained by the development fluctuates. When the carrier deteriorates, problems such as an increase in image fogging and a decrease in density occur. Further, image defects such as so-called carrier marks and burrs are generated by rubbing the image with the carrier.

[0006]

In order to solve the drawback of using a carrier in the two-component developing method, a magnetic toner containing magnetic particles such as ferrite powder is used as a developer without using a carrier. There is a one-component magnetic development method. As one of such developing methods, a developing method called a so-called jumping developing method is known.

In this developing method, a magnetic toner of a one-component developer is carried on a non-magnetic developing sleeve having a magnet roller installed immovably, and the toner is formed into a thin layer by a magnetic blade. By the rotation of the developing sleeve, the developing sleeve is conveyed to a developing portion facing the photosensitive drum and is faced in a non-contact manner, and an alternating bias is applied between the photosensitive drum and the developing sleeve to perform development.

The developing device using such a jumping developing method solves the drawbacks of the two-component developing method and has a simple device construction. Therefore, it is used in various copying machines.

However, in the above jumping developing device, when the carrier used therein enters from the two-component developing device, the invading carrier adversely affects the jumping development in the developing portion to which the developing bias is applied. Therefore, there is a problem that the obtained image causes image deterioration.

An object of the present invention is to prevent carriers from entering from a developer of another two-component developing device into a one-component developing device by a jumping development method using a one-component magnetic developer.
Preventing the development section of the one-component developing device from being adversely affected and allowing the development in the one-component developing device to be performed as well as other two-component developing devices, a high-quality color image without image defects can be obtained. An object of the present invention is to provide an image forming apparatus capable of obtaining the image.

[0011]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is an image forming apparatus for developing a latent image of each color formed on an image carrier with a plurality of developing devices of corresponding colors to form a color image composed of toner images of each color, At least one of the plurality of developing devices is a one-component developing device using a one-component magnetic developer, and the remaining developing devices are two-component developing devices using a two-component developer. In the one-component developing device, the developer regulating pole of the magnetic field generating means installed in the developer carrying member is located on the upstream side in the rotation direction of the developer carrying member with respect to the developer restricting member installed on the developer carrying member. The image forming apparatus is characterized in that it is inclined to.

By pre-loading the magnetic particles in the developing container containing the developer of the one-component developing device, the magnetic particles can be retained in the vicinity of the regulating member of the developer carrying member.

[0013]

【Example】

First Embodiment FIG. 1 is a schematic configuration diagram showing an embodiment of the image forming apparatus of the present invention. In this embodiment, a digital image forming apparatus will be described.

In this image forming apparatus, the color original 10 placed on the original table is illuminated by the illumination lamp 11, read by the CCD color line sensor 12, and passed through the color signal processing circuit 13 and the cable 14. , And is digitally processed by the first image processing circuit 15. Then, one page of the full-color image signal is temporarily stored in the memory device 16. As described below, in this type of apparatus, a plurality of image forming units are arranged in parallel, and in order to form images of a plurality of colors at the same time, at least image signals corresponding to the distance between the adjacent image forming units are formed. This is because it is necessary to store

The image forming section is provided with image forming stations for each component, that is, image forming stations for magenta, cyan, yellow and black.
1b, 1c, 1d and their surroundings, primary chargers 2a, 2
b, 2c, 2d, developing devices 3a, 3b, 3c, 3d, transfer charging devices 4a, 4b, 4c, 4d, cleaners 5a, 5b,
5c and 5d, and the photosensitive drums 1a, 1b, 1
A common sheet conveyance belt 33 is horizontally provided below the c and 1d. Transfer chargers 4a, 4b, 4c, 4d
Inside the conveyor belt 33, each photosensitive drum 1
It is arranged to face a, 1b, 1c, and 1d.

Paper is fed from the cassette 31 toward the conveyor belt 33, and the leading end of the paper is a detector (ITOP sensor).
When detected at 32, a timing circuit (not shown) reads the image signal for each color component already stored in the memory device 16 in synchronization with the leading edge detection signal. The second image processing circuit 17 processes the signal, and the semiconductor lasers 18, 19, 2
0 and 21 are driven to generate an optical signal of each color image in which light is modulated according to image information. An interface face 26 for inputting image information from an external image device is connected to the memory device 16.

The optical signal of the magenta image generated in this way is reflected by the polygon mirror 27 and the reflection mirrors 22a, 22a.
The latent image of the magenta image is formed on the photosensitive drum 1a by being reflected by b and 22c and irradiated on the photosensitive drum 1a. This latent image is developed by the magenta developing device 3a to form a magenta toner image, and is transferred onto the paper by the transfer charger 4a at the timing when the paper is conveyed below the photosensitive drum 1a.

Subsequently, the same procedure is carried out at the cyan, yellow and black image forming stations, and the optical signals of the cyan, yellow and black images are respectively reflected by the reflection mirrors 23a-23.
c, 24a to 24c, 25a to 25c, and irradiates the photosensitive drums 1b, 1c, and 1d to form a latent image, and the latent image is formed by the cyan developing device 3b, the yellow developing device 3c, and the black developing device 3d. By developing, a cyan toner image, a yellow toner image, and a black toner image are formed, and these toner images are sequentially superposed and transferred onto the sheet on which the conveyed magenta toner image has been transferred.

The paper on which the four-color toner images have been transferred is then separated from the conveyor belt 33 and separated by the conveyor means 35.
It is sent between the pair of fixing rollers 34a and 34b, where
Color toner images are mixed and fixed, thus 1
The full-color copy of the sheet is completed, and the copy is ejected out of the image forming apparatus.

In the present invention, the above magenta developing device 3a,
The cyan developing device 3b and the yellow developing device 3c are two-component developing devices that use a two-component developer in which at least a carrier such as iron powder or ferrite is mixed with toner, and the black developing device 3d is a single component made of magnetic toner. This is a one-component developing device that performs so-called jumping development using a magnetic developer.

In this image forming apparatus, since the image forming stations for the respective colors are horizontally arranged as described above,
There is no possibility that carriers may be mixed depending on the arrangement positions of the developing devices 3a to 3d. The problem with this image forming device is
The toner images formed by the four image forming stations are superposed on the sheet with high accuracy.

Therefore, a standard pattern serving as a reference for each station is formed on the conveyor belt 33 with toner, and the position of this pattern is read by an optical means such as CCD by reflection from the toner, and each color is read from the position of the read pattern. The method of controlling the formation timing of the toner image to secure the overlay accuracy is adopted.

In this case, the magnetic toner of the black toner used in the black developing device 3d for performing the jumping development is a magnetic substance dispersed in the toner and absorbs light in all wavelength regions, so that other toners are used. A black standard pattern must be formed on it against the background. Therefore, the image forming station using the black developing device 3d needs to be the second color or later, and in this embodiment, it is the station of the fourth color of the final color.

FIG. 2 shows a jumper developing type one-component developing device used as the black developing device 3d in this embodiment. As shown in FIG. 2, the jumping developing device 40 includes a toner carrying member 45 containing a magnetic toner black toner 44 as a one-component developer in a developing container 50.
A developing sleeve 41 having a built-in magnet roller 42 is rotatably provided.
Is being opposed to. A magnetic blade 43 is installed above the developing sleeve 41, and the cut pole N ₁ of the magnet roller 42 is opposed to the magnetic blade 43. A thin layer of toner 44 is formed on the developing sleeve 41 by the action of the magnetic field between the cut pole N ₁ and the magnetic blade 43.

The developing sleeve 41 is made of non-magnetic stainless steel, aluminum or the like, and is subjected to surface treatment such as blasting or carbon coating in order to stabilize the charge application to the toner 44 and to convey the toner 44. . 200 to 50 between the magnetic blade 43 and the developing sleeve 41.
0 μm, the magnetic field strength of the cut pole N ₁ is 500 to 1200
Gauss, the thickness of the toner layer is then 30 to 10
0 μm is obtained. At the time of this thinning, the toner 44 is charged by friction with the surface of the developing sleeve 41. The charge amount is 5 to 20 μC / g.

Toner 44 thinned by the cut pole N _1.
The magnet roller 4 at a position facing the photosensitive drum 1.
The second developing pole S ₁ is conveyed to the developing section. In the developing section, the toner 44 becomes a cologne-like (brush-like) aggregate due to the action of the developing pole S ₁ .

The electrostatic latent image carried to the developing section is developed in units of this cologne. For this reason, the image of Cologne is microscopically reflected in the image. A full-color image forming apparatus requires a mechanism for reducing the size of the cologne-like aggregates, especially in the case of a model requiring high image quality. One is to reduce the addition amount of magnetic powder such as ferrite powder for imparting magnetism to the toner 44 as much as possible. The addition amount of the magnetic powder is preferably 40 parts by weight or less. Alternatively, in order to destroy the cologne formed on the photosensitive drum 1 after development, a metal electrode is provided facing the photosensitive drum 1, and an AC bias is applied to this. Either method may be adopted.

The developing magnetic pole S _{1 has} a size of 800 to ₁
It is 200 gauss. If it is too small, fog will increase, and if it is too large, the degree of scattering around the image will worsen. At the time of development, the high voltage power source 4 connected to the developing sleeve 41 in the developing section
By 6, the AC bias that superimposes the DC component is applied,
The latent image on the photosensitive drum 1 is developed and visualized. The DC component is applied to the bright portion of the latent image on the photosensitive drum 1 with a value such that toner does not adhere, the magnitude of AC determines the density of the dark portion, and its frequency determines the gamma characteristic (γ characteristic) of the developing characteristic. decide. Usually, the potential difference between the DC component and the dark portion is about 50 to 200 V, the AC peak-peak value is 1 kV to 3 kV, and the frequency is 0.5 kHz to 300 kHz.

FIG. 3 shows the magnetic blade 43 and the cut pole N _1.
6 is a graph showing the coating amount of the magnetic toner 44 on the developing sleeve 41 and the leakage amount of the carrier mixed in the developing device from the blade 43 when the angle θ formed by and is changed.

Regarding the coating amount of the toner 44, it can be seen that there is a range in which a stable coating amount can be obtained depending on the position (angle θ) of the cut pole N ₁ with respect to the blade 43. Within this range, the developing sleeve 4 is better than the magnetic blade 43.
There is a region where carrier leakage does not occur at a position upstream of 1 in the rotation direction. That is, with respect to the magnetic blade 43, the cut pole N
By arranging ₁ in the upstream, the thin layer of the toner 44 can be made uniform and the carrier leakage can be prevented. In the case of this example, the angle θ of the cutting pole N ₁ with respect to the blade was 5 ° to 25 °.

The position of θ = 0 ° of the magnet roller 42 can be naturally determined if there is no means for regulating the angle θ because of the force due to the concentration of the magnetic force on the magnetic blade 43. The magnet roller 42 is rotated and positioned by a set angle from this naturally determined point,
Just fix it. The method of determining the position of the magnet roller is
In addition to this, there is a method of using a jig in which a magnetic plate is provided at a position deviated from the position of the magnetic blade 43 by a set angle and fixing the magnetic plate at a naturally determined magnetic pole position.

According to the present invention, the cut pole N ₁ of the magnet roller 42 and the magnetic blade 44 for forming the toner thin layer are thus developed in such a manner that the position of the cut pole N ₁ is higher than the position of the magnetic blade 44 facing each other. Since the sleeve 41 is set on the upstream side in the rotation direction, as shown in FIG. 2, even if the carrier 48 is mixed into the jumping developing device 50 from another two-component developing device, its cutting pole N ₁ and magnetic blade Four
The carrier 48 can be prevented from leaking to the developing unit by staying the carrier 48 between the four positions, and the toner 44 can be prevented from adhering to the photosensitive drum 1 because the leaked carrier 48 adheres to the photosensitive drum 1. There is no such thing.

As described above, the one-component jumping developing device 40 is used as the black developing device 3d of the image forming apparatus of FIG. 1, and the position of the cut pole N ₁ of the magnet roller 42 in the developing sleeve 41 with respect to the magnetic blade 43 thereof. To
Since it is set on the upstream side in the rotation direction of the developing sleeve 41, it is possible to stably obtain a high-quality image without image defects even when the carrier is mixed in the black developing device 3d which is a jumping developing device.

Embodiment 2 FIG. 4 is a block diagram showing another embodiment of the image forming apparatus of the present invention. In the image forming apparatus of this embodiment, two developing devices 53 and 54 are arranged around the photosensitive drum 1 so that two-color image formation can be performed.

A primary charger 5 is provided around the photosensitive drum 1.
1, an exposure light source 52, the above-mentioned developing devices 53 and 54, a transfer charger 55, and a cleaning device 56 are provided, and a latent image of the first color is formed on the photosensitive drum 1 by the exposure by the exposing means 52. The developing device 53 develops the toner image of the first color, and the exposing device 52 exposes the toner image of the first color again to form the latent image of the second color. The developing device 54 develops the latent image. To form a second color toner image on the first color toner image. The two-color toner images thus obtained are transferred to the sheet fed from the sheet feeding cassette 57 through the registration rollers 58 to the transfer charger 55.
Is transferred by. The sheet on which the toner image is transferred is fixed by the fixing device 59.

In the present embodiment, the developing device 53 on the upstream side in the rotation direction of the photosensitive drum 1 is a color developing device other than black, and is a two-component developing device using a two-component developer in which colored toner and carrier are mixed. The downstream developing device 54 is a black developing device and is a one-component developing device of a jumping developing device that uses black toner of magnetic toner as a one-component magnetic developer.

Black developing device 54 of jumping developing device
Is disposed downstream, the development in the jumping developing device does not contact the photosensitive drum 1 and therefore does not disturb the color toner image obtained by the development in the two-component developing device 53. If this is configured by a two-component developing device up to the black developing device 54, so-called spike cutting for removing the developer in the developing portion of the developing sleeve 61 is required, or the developing device 54 is separated from the photosensitive drum 1. However, since the black developing device 54 is a jumping developing device, these are unnecessary. However, the carrier from the developer of the two-component developing device 53 easily mixes into the black developing device 54.

Therefore, also in this embodiment, the cut pole of a magnet roller (not shown) in the developing sleeve 61 of the black developing device 54 of the jumping developing device is located upstream of the magnetic blade 63 in the rotational direction of the developing sleeve 61. Located in. As a result, even if the carrier of the developer from the two-component developing device 53 is mixed into the black developing device 54, the mixed carrier can be prevented from leaking out from the blade 63 and being conveyed to the developing portion, and an image defect can be prevented. It is now possible to get images without.

Embodiment 3 FIG. 5 is a sectional view showing a one-component developing device in still another embodiment of the present image forming apparatus. In this embodiment, in the developing container 50 of the one-component jumping developing device 40 of FIG. 2 used as the black developing device 3d of the fourth station of the image forming apparatus described with reference to FIG. 1, as shown in FIG. , The magnetic particles 48A are charged from the beginning, and the cut pole N ₁ of the magnet roller 42 in the developing sleeve 41 and the magnetic blade 4 are inserted.
Magnetic particles 48A in the toner thin layer forming region formed by
The feature is that they are positively retained. As a result, the carrier 48 mixed from the other two-component developing units 3a to 3c in FIG. 1 is prevented from leaking to the developing section, and the toner is formed into a thin layer and the charge applied to the toner is stabilized. It is intended. The other structure of this embodiment is the same as that of the first embodiment, and the same reference numerals as those in FIG. 2 denote the same members in FIG.

As described above, when the magnetic particles 48A are positively retained in the toner thin layer forming region, the carrier 48 mixed with the magnetic particles 48A forming the lump is taken in and strongly regulated, and the carrier 48 is Since it can be stably prevented from leaking to the developing portion through the blade 43, image defects due to the adhesion of the carrier 48 to the photosensitive drum 1 in the developing portion can be stably eliminated. Further, since the toner can be appropriately pressed against the surface of the developing sleeve 41, the opportunity of the contact frictional charging can be controlled, and the highly charged toner strongly adhered to the surface of the developing sleeve 41 can be mechanically. It also has a scraping action.

If the amount of the magnetic particles 48A retained is further increased, the limit amount at which the magnetic particles 48A start to circulate in the developing unit is good. If this amount is large, the regulated capacity of the regulating unit is exceeded, and the mixed carrier 48 leaks to the developing unit.

The magnetic particles 48A to be retained are loaded in the developing container 50 in advance when the developing device 40 is installed. The magnetic particles 48A used here may be the same as the carrier 48 used in another two-component developing device, but those having a particle size larger than the gap between the blade 43 and the developing sleeve 41 or having a magnetic permeability. Higher ones have a smaller probability of leaking to the developing section, and therefore these are preferable.

In this embodiment, as described above, the cut pole N ₁ of the magnet roller 42 and the magnetic blade 44 for forming the thin toner layer are arranged such that the position of the cut pole N ₁ is higher than the position of the magnetic blade 44 facing each other. The magnetic particles 48A are set so as to be located on the upstream side in the rotation direction of the developing sleeve 41, and the magnetic particles 48A are loaded into the developing container 50 from the beginning.
The toner particles are positively retained in the toner thin layer forming region by the magnetic blade 44 and the cut pole N _1. Therefore, even if the carrier 48 is mixed into the jumping developing device 40 from another two-component developing device, the retained magnetic particles The carrier 48 mixed by the lump of 48 A can be taken in, and the carrier 48 can be stably prevented from leaking to the developing section, and therefore the toner 44 can be prevented from adhering to the photosensitive drum 1 due to the leakage of the carrier 48. Disappears.

Fourth Embodiment In this embodiment, in the image forming apparatus of the second embodiment described with reference to FIG. 4, the black developing device 54 is used in the third embodiment.
Same as.

That is, also in this embodiment, the magnetic blade 63 on the developing sleeve 61 of the black developing device 54 on the downstream side in FIG. 4 and the developing sleeve 61 inclined to the upstream side in the rotational direction of the developing sleeve 61 with respect to this. As in the case of Example 3, by pre-charging and retaining the magnetic particles in the toner thin layer forming region formed with the cut pole of the inner magnet roller, the two components upstream due to the agglomeration of the magnetic particles. The carrier mixed in from the developing device can be captured, the mixed carrier can be prevented from leaking out from the blade 63 and conveyed to the developing section, and can be prevented from adhering to the photosensitive drum 1. It is now possible to obtain defect-free images.

[0046]

As described above, according to the image forming apparatus of the present invention, the one-component developing device by the jumping developing method using the one-component magnetic developer is loaded into the one-component developing device from the developer of the other two-component developing device. Even if the carrier invades, the developing section of the one-component developing unit is prevented from being adversely affected, and the development in the one-component developing unit is performed in the same manner as other two-component developing units, resulting in image defects. It is possible to obtain a high-quality color image with no color.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus of the present invention.

2 is a cross-sectional view showing a one-component jumping developing device used as a black developing device of a fourth station of the image forming apparatus of FIG.

FIG. 3 is a graph showing changes in the amount of carrier leakage and the amount of toner coating depending on the angle between the regulation blade of the developing device and the cut pole of the magnet roller in the developing sleeve of FIG.

FIG. 4 is a schematic configuration diagram showing another embodiment of the image forming apparatus of the present invention.

FIG. 5 is a fourth example of still another embodiment of the image forming apparatus according to the invention.
It is sectional drawing which shows the one-component jumping developing device used as the black developing device of a station.

[Explanation of symbols]

 1 Photosensitive drum 3d, 54 Black developing device 40 One-component jumping developing device 41, 61 Developing sleeve 42 Magnet roller 43, 63 Magnetic blade 44 Magnetic toner 50 Developing container 48 Carrier 48A Magnetic particle

Claims (2)

[Claims] 1. An image forming apparatus for forming a color image composed of toner images of respective colors by developing latent images of respective colors formed on an image carrier with a plurality of developing devices of corresponding colors,
At least one of the plurality of developing devices is a one-component developing device using a one-component magnetic developer, and the remaining developing devices are two-component developing devices using a two-component developer. In the one-component developing device, the developer regulating pole of the magnetic field generating means installed in the developer carrying member is located on the upstream side in the rotation direction of the developer carrying member with respect to the developer restricting member installed on the developer carrying member. An image forming apparatus characterized by being inclined to. 2. The magnetic particles are preliminarily charged in a developing container containing a developer of the one-component developing device to retain the magnetic particles in the vicinity of the regulating member of the developer carrier. 1. The image forming apparatus of 1.