JPH06130819A - Developing device for multicolor image forming device - Google Patents

Abstract

PURPOSE:To prevent the hysteresis of developing at a preceding stage by increasing the toner carrying ability of a developing roll. CONSTITUTION:This developing device is provided with the developing roll 28a arranged to be opposed to an electrostatic latent image carrier 3 at a specified distance and holding a toner layer on its surface so that an electrostatic latent image formed on the electrostatic latent image carrier may be developed, and a magnetic roll 65 arranged near the developing roll so as to be opposed to the developing roll in a state where it holds two-component developer consisting of at least carrier and toner on its surface and supplying the toner to the developing roll. The magnetic roll is constituted of a non-magnetic rotating sleeve 65b carrying a developer layer and a magnetic pole 65a disposed in the rotating sleeve. As for the magnetic pole N1 inside the magnetic roll at the opposed position of the developing roll and the magnetic roll, the falling amount GL of magnetic force in the center part of the magnetic pole is set so that peak values GH on both sides of the center part may not show repulsive magnetic poles.

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 such as a color electrophotographic copying machine, a facsimile or a laser printer, and more particularly to a developing apparatus therefor.

[0002]

2. Description of the Related Art There are various types of multi-color image forming apparatuses utilizing electrophotography, one of which is to form a toner image on a photoconductor for each color and to form the toner image of each color on a recording paper. There is a method of forming a multicolor image by sequentially superimposing and transferring. In this case, a charging unit, an exposing unit, a plurality of developing units corresponding to respective colors, a transfer unit and a cleaning device are arranged around the drum-shaped photosensitive member, and charging, developing, transferring, and By repeating the cleaning process, the toner images of the respective colors are sequentially superposed on the recording paper and transferred to form a multicolor image for each rotation of the photosensitive member.

Further, there is also a multicolor image forming apparatus by a single transfer method in which toner images of respective colors are superposed on a drum-shaped photoconductor for each rotation and a multicolor image is formed on a recording paper by one transfer. Are known. In this method, since the photoconductor must be rotated by the number of necessary colors, there is a problem that it takes a long time to obtain a final multicolor image.

In order to solve this problem, Japanese Patent Laid-Open No. 63-
As disclosed in Japanese Patent No. 273883, a plurality of image recording portions are sequentially arranged along the surface of the photoconductor, and one rotation of the photoconductor repeats the charging, exposing and developing processes a plurality of times to obtain a plurality of different images. A multicolor image forming apparatus has been proposed in which a color image is formed and then transferred onto a recording sheet at once.

These methods for forming a multicolor image are desirable because they can be used in a wider range of use because they can add color information as compared with information obtained by a black and white image. To summarize the problems, it is necessary to transfer the image to the transfer portion for each rotation when the development of each color is completed, which increases the size of the machine and the time required for image formation.

It is necessary to ensure accuracy by causing a color shift and a position shift of each toner image by repeatedly repeating and sequentially overlapping.

Forming a plurality of toner images on the photoreceptor,
If you want to complete the transfer process only once, if you repeat the development multiple times on the photoconductor on which the toner image has already been formed, the toner image already formed on the photoconductor will be disturbed or the toner will not be developed during the subsequent development. Adhering to and mixing with the roll, color mixing occurs.

Therefore, in order to solve the problem of color mixing and mixing, various apparatuses have been proposed in which a toner layer is formed on a donor roll and the electrostatic latent image on the photoconductor is developed by the toner layer. This method has been conventionally used in non-magnetic one-component toner development. In the method of developing the electrostatic latent image on the photoreceptor by the toner layer formed on the donor roll, the toner on the donor roll and the photosensitive material are not in contact with each other, so that the developed image is less disturbed and high image quality can be obtained. In addition, there are advantages such as the possibility that toners of a plurality of colors can be overlaid and developed on a photosensitive material in a color electrophotographic apparatus.

In such a non-contact one-component developing method, the toner applied to the donor roll is peeled off from the donor roll by the Coulomb force generated by the developing electric field formed between the donor roll and the photoconductor. It is necessary to move it to the body side. However, the adhesion force of the toner to the donor roll is considerably larger than the Coulomb force due to the developing electric field formed between the donor roll and the photoconductor, and it is difficult to separate the toner from the donor roll and move it to the photoconductor side. .

Therefore, in reality, for example, Japanese Patent Publication Sho 63
As described in Japanese Patent Laid-Open No. 31776, a method of applying an AC electric field between a donor roll and a photoconductor to facilitate development is adopted. In addition, JP-A-56-116060
In the method disclosed in the publication, a porous electrode is arranged between a donor roll and a photoconductor, and an AC electric field generated between the donor roll and the porous electrode separates toner from the donor roll to form a toner cloud. Has been proposed, whereby a toner is developed on the photoconductor. With this method, even if the toner charge amount is relatively high, the toner is separated from the donor roll and a relatively low AC electric field can be used, so there is little danger of being disturbed by the AC electric field, and the toner is developed on the photosensitive material before that. Since there is little risk of disturbing the toner with an alternating electric field, there is a possibility that toner of multiple colors can be developed in succession. However, the setting of the porous electrode is difficult, or the image is deteriorated due to the foreign matter adhering to the porous electrode, so that there is a problem in reliability.

Further, JP-A-59-121077 discloses a method of forming a toner layer by advancing a two-component developer onto a donor roll using a magnetic roll and transferring the toner onto the donor roll. Has been done. According to this method, it is possible to stably form and convey the toner layer on the donor roll, but the charge amount of the toner becomes relatively high, and it becomes difficult to separate the toner from the donor roll in the developing process, which is strong. There is no choice but to apply an AC electric field between the donor roll and the photoconductor, and the toner that has been developed on the photosensitive material before that is disturbed by the AC electric field. There wasn't. Therefore, a method has been proposed in which an auxiliary electrode made of a wire is provided between the donor roll and the photoconductor, and a weak AC electric field is applied to the auxiliary electrode so as not to disturb the developed toner.

In the conventional one-component developing method using a donor roll, for example, the charge amount of the toner is low, there is a problem in the long-term maintenance of the image quality, and a slight change in the characteristics of the toner causes a change in the donor roll. There is a phenomenon that the transportability changes or the blade member for controlling the toner layer on the donor roll and charging the toner and partially clogging the toner on the donor roll causes an image defect, which is not always reliable. I couldn't say.

Therefore, an apparatus has been proposed in which the advantages of the one-component developing method using a donor roll and the advantages of the conventional two-component developing are successfully combined to obtain desirable characteristics of both. For example, the Society for Photographic Scientists and Engineers held on November 8, 1984 in Washington, DC, USA.
s) "The 2nd International Congress on Advances i"
n Non-impact Printing), Toshiba explained a device for forming a toner layer by advancing a two-component developer onto a donor roll using a magnetic roll and transferring the toner onto the donor roll.

Also, in US Pat. No. 3,929,098 and Japanese Patent Laid-Open No. 59-121077, a two-component developer is advanced to a donor roll using a magnetic roll, and the toner is deposited on the donor roll. An apparatus for transferring a toner to form a toner layer is shown.

[0015]

However, a two-component developer is actually advanced to a donor roll by using a magnetic roll, and the toner is transferred onto the donor roll to form a toner layer on the photosensitive material. When the electrostatic latent image of No. 1 was developed, it has the advantage of one-component development and the advantage of conventional two-component development, but on the other hand, the toner is developed and the toner is removed from the donor roll, and the toner is developed. If the toner remains on the donor roll as it is, the developing property may differ during the next rotation of the donor roll, resulting in a density difference on the print, a so-called history phenomenon may occur as a new problem. found.

This hysteresis phenomenon is caused by the fact that when the toner is transferred from the two-component developer onto the donor roll again by the magnetic roll and applied, the toner is developed and the toner is removed from the donor roll, and the toner is not developed. This is because it is difficult to make uniform the toner layer on the part where the toner on the donor roll remains as it is.

The present invention solves the above-mentioned problems, and by increasing the toner transporting ability to the developing roll, the development of the multicolor image forming apparatus capable of preventing the history phenomenon of the development in the previous stage. The purpose is to provide a device.

[0018]

To this end, the developing device of the multicolor image forming apparatus of the present invention is arranged so as to face the electrostatic latent image carrier at a predetermined interval and holds a toner layer on its surface. And a developing roll for developing the electrostatic latent image formed on the electrostatic latent image carrier and a two-component developer composed of at least a carrier and toner held on the surface in the vicinity of the developing roll. A developing device having a magnetic roll for supplying toner onto the developing roll, wherein the magnetic roll comprises a non-magnetic rotating sleeve for carrying a developer layer, and a magnetic pole arranged in the rotating sleeve. The magnetic pole inside the magnetic roll at the position where the developing roll and the magnetic roll face each other is set so that the amount of magnetic force drop at the central portion of the magnetic roll is set so that the peak values on both sides do not become repulsive magnetic poles. To.

As an example, when the magnetic force drop amount at the center of the magnetic pole inside the magnetic roll is G _L and the magnetic forces of the peak values on both sides thereof are G _H , 10 ≦ (G _L / G _H ) × 10
0 ≦ 25 is satisfied, and when the angle between the peak values is θ, 30 ° ≦ θ ≦ 50 ° is satisfied.

[0020]

In the present invention, the magnetic pole inside the magnetic roll facing the developing roll has a small magnetic force drop portion formed in the central portion thereof, and the magnetic roll surface can be ears at peak positions on both sides of the magnetic force drop portion. It contacts the developing roll relatively softly, and the degree of filling of the developer increases in the sloping part, and it comes into contact with the developing roll at a high pressure. There is no retention or movement of the developer as seen in
Therefore, it is possible to maintain a good conveyance state even when the magnetic roll rotates at a high speed.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a configuration diagram showing an example of a multicolor image forming apparatus to which the present invention is applied.

The multicolor image forming apparatus includes an upper image forming section 1
And the lower sheet feeding section 2. Image forming unit 1
In, the translucent belt-shaped photoconductor 3 is driven by the drive roller 4
a, the idler rollers 4b, 4c, 4d, 4e and the like are vertically arranged, and are driven to rotate in the direction of arrow A by the drive roller 4a. Around the belt-shaped photoconductor 3,
The image recording unit 5, the second image recording unit 6, the third image recording unit 7,
Fourth image recording unit 8, registration adjustment optical sensor 10a, pre-transfer charger 9, developing density sensor 10b, light guiding unit 11, transfer unit 12, pre-cleaning corotron 13, cleaning device 14, and ground strip 15.
Are arranged. The components constituting each of these image recording units are arranged along a substantially vertical surface of the belt-shaped photosensitive member 3,
Further, inside the lower end portion of the belt-shaped photoreceptor 3, the transfer portion 1
Before and after 2, the static elimination lamps 16 for irradiating the belt-shaped photoconductor 3 from inside are arranged.

The transfer section 12 is a transfer corotron 12a.
Further, the peeling corotron 12b is provided, and is arranged at the lowermost end portion of the vertically long belt-shaped photosensitive member 3 such that the sheet conveying direction is substantially horizontal. In addition, the transfer unit 12
A sheet conveying device 17 and a conveying roller 18 are provided adjacent to the sheet feeding side, and a conveying belt 20 that conveys the recording sheet after transfer to the fixing device 19 is provided on the sheet discharging side.

The first image recording section 5 includes the first charger 2
1, a laser light source (not shown), a rotary polygon mirror 22a irradiated with the laser light source, a motor 22b for rotationally driving the rotary polygon mirror 22a, lenses 22c, 22d, mirrors 22e, 2
It is provided with a first exposure device 22, a first potential sensor 23, a first developing device 24, etc. that are configured by 2f and the like. In addition, the second image recording unit 6 includes a second charger 25, a second exposure device 26 including a light emitting diode array, a second potential sensor 27, and a second potential sensor 27.
The developing device 28 and the like are provided. Further, the third and fourth image recording units 7 and 8 similarly have the third and fourth chargers 29 and
33, third and fourth exposure devices 30, 34 each comprising a light emitting diode array, third and fourth potential sensors 31, 3
5, third and fourth developing devices 32, 36, etc. are provided.

The first, second, third and fourth image recording units 5, 6, 7 and 8 are, for example, black, red and red, respectively.
An image of each color is formed on the belt-shaped photoconductor 3 by using toners of each color of green and blue. In addition, each potential sensor 2
3, 27, 31, 35 are the image recording units 5, 6, 7, 8 respectively.
The surface potential of the belt-shaped photoconductor 3 is detected, and each charger 21, 25, 29, 33 is controlled by a control circuit (not shown) so as to reach the set predetermined potential. Also,
The final developing density is detected by the developing density sensor 10b, and each image recording section 5, 6 is provided so that an appropriate density is obtained.
The development conditions in 7 and 8 are adjusted. The developing density sensor 10b is configured by arranging color sensor elements corresponding to respective colors in a direction perpendicular to the moving direction of the photoconductor 3.

The developing units 24, 28, 32 and 36 are
The developing rolls 24a, 28a, 32a, 36a and the backup rolls 24b, 28b, 32b, 36b are provided, respectively. Second, third and fourth developing units 28, 32, 3
No. 6 should not disturb the toner image formed on the photoconductor 3 by the preceding developing device, so a non-contact type developing device is adopted. The details will be described later.

The sheet feeding section 2 includes an intermediate tray 41 having sheet feeding devices 37, 38, 39 and 40, sheet feeding trays 42 and 43, a large capacity tray 44, and a sheet reversing section 4.
5 etc. are arranged. The intermediate tray 41 is provided with a switching claw device 46 having a plurality of switching claws 46a, 46b, 46c. Incidentally, 47 and 48 are conveying rollers, and 49 is a reversing roller.

Next, the control circuit for forming an image in the multicolor image forming apparatus will be described with reference to FIG.

Image signals from the image input device 51, the computer 52, and the communication device 54 that communicates via the communication line 53 are input to the multicolor image forming device 50 through the image processing device 55. It The image signal input to the image processing device 55 is separated by the color separation circuit 56 into first to fourth color component signals, for example, four color component signals of black, red, green and blue, and the first color component signal is The second to fourth color component signals are supplied to the first exposure device 22 of the first recording unit 5 without being substantially delayed, and the first to third delay circuits 5 respectively.
7 to 59, the 2nd to 4th of the 2nd to 4th recording units 6 to 8
It is supplied to the exposure devices 26, 30, and 34. In addition, first to
The delay time in the third delay circuits 57 to 59 corresponds to the distance from the exposure position of the on-belt photoreceptor 3 by the first exposure device 22 to the exposure position of the second to fourth exposure devices 26, 30, 34. .

Further, the first to fourth chargers 21, 25, 29, 33 of the recording sections 5 to 8 and the first to fourth exposure devices 22, 2 are arranged.
6, 30, 34, first to fourth developing devices 24, 28, 32,
The operation of 36 is controlled by the control circuit 61 that operates based on an instruction from the control panel 60.

Next, referring to FIGS. 1, 2 and 3, the outline of the operation of the multicolor image forming apparatus having the above structure will be described by taking the case of forming two color images of black and red as an example. In this case, based on the instruction from the control panel 60, only the first and second image recording units 5 and 6 are enabled by the control circuit 61, and the third and fourth image recording units 7 and 8 are disabled. To be done. This switching between operation and non-operation is performed by, for example, the first and second chargers 21 and 25, the first and second exposure devices 2.
2, 26, and the first and second developing devices 24, 28 are applied by applying a predetermined operating voltage or bias voltage.

The belt-shaped photosensitive member 3, which is rotationally driven in the direction of arrow A by the driving roller 4a, firstly includes the first image recording section 5
In FIG. 3, the first charger 21 uniformly charges the surface of the photoconductor 3 as shown in FIG. 3A, so that the surface potential of the photoconductor 3 becomes, for example, V _P (where V _P is a negative value). Next, the surface of the photoconductor 3 is exposed by the laser light L _K modulated by the signal corresponding to the black of the image in the first exposure device 22, and the potential of the exposed portion becomes as shown in FIG. 3B. for example V _R (where V _R is a negative value) decreases to. Next, this exposed portion proceeds to the first developing device 24, where the black toner T
_After being developed by _K , as shown in FIG. 3C, the surface potential of the black image portion is still reduced after this development.

Next, the black developing portion advances to the second image recording portion 6 and is charged again by the second charger 25. As shown in FIG. 3D, the surface potential of the photoconductor 3 is near V _P. Rise to. Next, in the second exposure device 26, as shown in FIG. 3E, the photoconductor 3 is irradiated with the light L _R from the light emitting diode array modulated by the signal corresponding to the red color of the image.
Is exposed, and the potential of the exposed portion drops to V _R. Next, this exposed portion proceeds to the second developing device 28 and is developed with red toner, and as shown in FIG. 3F, the surface potential of the red image portion remains reduced after this development.

The belt-shaped photosensitive member 3 further passes through the third and fourth image recording portions 7 and 8, but since these image recording portions are inoperative, the toner image of each color is affected. Absent. Then, the charge of the toner image is adjusted by the pre-transfer charger 9 and the charge eliminating lamp 16 to bring the toner image into a state suitable for transfer. When the toner images of the respective colors reach the transfer unit 12, in synchronization therewith, the recording paper is fed along the conveyance path B from any of the trays 41 to 44 of the paper feeding unit 2 by any of the paper feeding devices 37 to 40. The sheet is fed to the image forming unit 1 side, and is further brought into contact with the surface of the photoconductor 3 by the sheet conveying device 17 and the conveying roller 18.

In the transfer section 12, the toner image of each color is transferred from the surface of the photoconductor 3 to the recording paper by the electric field from the transfer corotron 12a. The recording paper after transfer is peeled from the surface of the photoconductor 3 by the peeling corotron 12b, and is transported to the fixing device 19 by the transport belt 20 to fix the toner image on the recording paper. The recording paper after fixing advances in the direction of arrow C, for example, and is directly ejected outside the apparatus by the conveying roller 47 with the image surface facing upward. In the case of discharging with the image surface facing down, the sheet is once conveyed by the conveying rollers 48 and 49 in the directions of arrows D and E, then the rotations of the conveying rollers 48 and 49 are reversed, and the conveying roller 47 is used. Discharge to the outside.

The toner remaining on the photoconductor 3 after the transfer is removed by the cleaning device 14 after the charge state is adjusted by the charge eliminating lamp 16 and the pre-cleaning corotron 13, and the charge remaining on the photoconductor 3 is removed. ,
Discharged through the ground strip 15 in preparation for the next imaging cycle.

In the case of double-sided copying, the recording paper after fixing advances in the direction of arrow D, is fed to the paper reversing unit 45 of the paper feeding unit 2 by the conveying roller 48, and is temporarily moved in the direction of arrow E by the reversing roller 49. After being conveyed, the rotation of the reversing roller 49 is reversed and the conveying direction of the recording paper is reversed in the arrow F direction, and the recording paper is stored in the intermediate tray 41 with the image surface facing upward. At this time, by changing the postures of the switching claws 46a, 46b, 46c of the switching claw device 46 according to the size of the recording paper,
The recording paper is stored in the intermediate tray 41 from an appropriate position. The recording paper is again sent to the transfer unit 12 of the image forming unit 1 by the paper feeding device 37, and an image is formed on the back surface of the recording paper this time. In the case of double-sided printing, it goes without saying that a toner image is formed by the image forming unit 1 on each side. Further, in the case of making two copies by superposing on one side, the recording paper is directly conveyed from the conveyance roller 48 into the intermediate tray 41.

Next, the developing device according to the present invention will be described. In the multi-color image forming apparatus, the first developing device 24 is a contact-type developing device such as a magnetic brush method which has been conventionally used in order to repeat the development a plurality of times on the photoconductor on which the toner image is already formed. However, the second, third, and fourth developing units 28, 32, and 36 in the latter stage may be arranged so as not to disturb the toner image formed on the photoconductor 3 by the preceding developing unit. A non-contact type developing device that does not bring the above toner into contact with the photoconductor is adopted. This is the second
The developing device 28 will be described as an example with reference to FIG. Figure 4 (A)
Is a sectional view showing one embodiment of a developing device according to the present invention, and FIG. 4 (B) is an enlarged sectional view of FIG. 4 (A).

The developing device 28 has a housing 62 for storing a predetermined supply amount of the developer, and in the housing 62, a wire 63 as an auxiliary electrode, a donor roll, that is, a developing roller is provided from the belt photosensitive member 3 side. The roll 28a, the magnetic roll 65, and the auger 66 are sequentially arranged. The developing roll 28a and the belt-shaped photoconductor 3 have a predetermined distance (200
.About.500 .mu.m), and the developing roll 28a can rotate in either the same direction or the opposite direction to the moving direction of the photoconductor 3. The magnetic roll 65 has a magnet 65a fixed inside and a rotating sleeve 65b rotated around the outer circumference of the magnet 65a. The rotating sleeve 65b is
By changing the arrangement position of the layer thickness regulating member 67, the developing roll 28a can be rotated in either the same direction or the opposite direction with respect to the rotation direction. A two-component developer including a carrier and toner is stored in the housing 62, and an auger 66 for mixing and stirring the developer is rotatably arranged. The developer is attracted to the surface of the rotating sleeve 65b by the magnetic force of the magnet 65a fixed inside the magnetic roll 65, and is conveyed toward the developing roll 28a by the rotation of the rotating sleeve 65b.

The magnetic roll 65 has an AC power source 69 (2 to 20 kHz, 100 to 600) via a changeover switch 68.
V) and a DC power supply 70 (-200 to -600V), and a DC power supply 71 (-
200--350V) is connected, and further wire 63
DC power supply 71 and AC power supply 72 (2 to 12 kH)
z, 500-1500V) is connected.

The operation of the present invention having the above structure will be described. A bias voltage in which the DC component from the DC power supply 70 is superimposed on the AC component from the AC power supply 69 is applied to the magnetic roll 65, and a part of the developer adheres to the magnetic roll 65. The developer adhered to the magnetic roll 65 is conveyed downward by the rotation of the sleeve 65b and is controlled to an optimum amount by the regulating member 67, and the developer is conveyed to a position where the magnetic roll 65 and the developing roll 28a face each other. To be done. Here, only the toner particles in the developer are applied to the developing roll 28a according to the voltage applied to the developing roll 28a and the magnetic roll 65.

The toner layer applied to the developing roll 28a is conveyed by the rotation of the developing roll 28a, and the toner is conveyed to the position where the developing roll 28a and the belt-shaped photoreceptor 3 face each other. Since the bias voltage in which the direct current component from the direct current power source 71 is superimposed on the alternating current component from the alternating current power source 72 is applied to the wire 63, the toner applied to the developing roll 28a forms a toner cloud, Toner particles separated from the layers are attracted to the latent image recorded on the photoreceptor 3 to develop the electrostatic latent image. Developing roll 28
New toner is again supplied from the magnetic roll 65 to the portion where the toner a has been developed and has disappeared from the developing roll.

Next, the magnet 65a inside the magnetic roll 65, which is a feature of the present invention, will be described with reference to FIG. A magnet 65a is magnetized in the magnetic roll 65 so as to have five magnetic poles of a main pole N1, a trimming pole N2, a carrier pole S1, a pickup pole S2, and a pickoff pole S3. ) Is shown. The main pole N1 facing the developing roll 28a has a small magnetic force drop portion G _L formed in the central portion thereof, and at the peak positions P on both sides of the magnetic force drop portion, the surface of the magnetic roll 65 can be erected, which is relatively soft. It contacts the developing roll 28a. Further, in the magnetic force drop portion, the filling degree of the developer becomes high, and the developer roll 28a comes into contact with the developer roll 28a at a high pressure. In addition, since the amount of magnetic force drop is small and the contact pressure is high, the retention and movement of the developer as seen in a normal repulsive magnetic pole (relationship between the S3 pole and the S2 pole) is not seen, and therefore the high speed of the magnetic roll 28a. A good transport state can be maintained even during rotation.

FIG. 5 shows the experimental results in the present invention. FIG. 5 shows the relationship between the ratio of the amount of toner applied on the developing roll and the amount of toner saturated in one rotation, that is, the relationship between the toner application capability and the angle θ between the peak positions on both sides of the magnetic force drop portion of the N1 pole. Shows. However, the value C at angle 0 is
This is the case where the magnetic pole does not fall on the N1 pole. And
Assuming that the magnetic force drop amount at the central portion of the magnetic pole N1 is G _L and the magnetic forces at the peak positions on both sides thereof are G _H , the curve A is 10 ≦.
The case of ( _GL / _GH ) * 100≤25 is shown, and the curve B shows the case of ( _GL / _GH ) * 100> 25.

According to this, it can be seen that when the magnetic force has a small drop as shown by the curve A, the toner coating capability is increased. Further, it can be seen that there is a considerable difference in coating ability when the angle θ between the peak values is between 25 ° and 30 °. Further, even if the angle between the peak values is the same, the magnetic force of which is greatly decreased, the coating ability is considerably low, and the developer is spilled, so that the good conveyance state cannot be maintained.

When the magnetic roll 65 applies the two-component developer again onto the developing roll 28a by transferring the toner, the toner is developed and the toner is removed from the developing roll, and the developing roll without developing the toner. The history phenomenon that occurs because the toner layer in the portion where the above toner remains as it is is not uniform occurs when the toner is developed in this developing device and the lost portion does not recover to 80% or more in one rotation.
In order to solve the hysteresis phenomenon, the angle θ between the peak values is
Must be set between 30 ° and 50 °. In other words, 200 Gauss (peak value 8
The hysteresis phenomenon can be solved by forming a magnetic force drop portion within 100 Gauss) and setting the angle θ between the peak values of the magnetic force on both sides thereof to 30 ≦ θ ≦ 50.

The present invention is not limited to the above embodiments, and various modifications can be made by those having ordinary knowledge in the technical field to which the present invention belongs. For example, in the above embodiment, the belt photosensitive member is described as an example, but the present invention is also applicable to a drum photosensitive member. In this case, a member corresponding to the backup roll is provided at the end of the drum.

[0048]

As is apparent from the above description, according to the present invention, the electrostatic latent image bearing member is arranged to face the electrostatic latent image bearing member at a predetermined interval and holds the toner layer on the surface thereof. A developing roll for developing the electrostatic latent image formed on the image carrier,
In a developing device provided with a magnetic roll for supplying the toner onto the developing roll, the developing roll is provided in the vicinity of the developing roll so as to face each other while holding a two-component developer composed of at least a carrier and a toner on the surface. The roll is composed of a non-magnetic rotating sleeve that conveys the developer layer and a magnetic pole disposed inside the rotating sleeve. The magnetic pole inside the magnetic roll at the position where the developing roll and the magnetic roll face each other is located at the center of the magnetic pole. Since the amount of magnetic force drop is set so that the peak values on both sides do not become repulsive magnetic poles,
By increasing the toner transporting ability to the developing roll, it is possible to prevent the hysteresis phenomenon of the previous stage of development.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram showing an example of a multicolor image forming apparatus to which the present invention is applied.

FIG. 2 is a configuration diagram of a control circuit in FIG.

FIG. 3 is a diagram for explaining the developing process of FIG.

4A is a sectional view showing one embodiment of a developing device according to the present invention, and FIG. 4B is an enlarged sectional view of FIG. 4A.

FIG. 5 is a diagram for explaining an experimental result in the present invention.

[Explanation of symbols]

3 ... Electrostatic latent image carrier, 28 ... Developing device, 28a ... Developing roll, 62 ... Housing 65 ... Magnetic roll, 65a ... Magnet, 65b ... Rotating sleeve 69, 72 ... AC power supply, 70, 71 ... DC power supply G _L … Depression, G _H … Peak value

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yoshikazu Takahashi 2274 Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Takashi Fuchiwaki 2274, Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor Miho Ikeda 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. An electrostatic latent image formed on the electrostatic latent image carrier is developed while being opposed to the electrostatic latent image carrier at a predetermined interval and holding a toner layer on the surface thereof. And a magnetic roll for supplying toner onto the developing roll, the developing roll facing the developing roll and a two-component developer composed of at least a carrier and toner held on the surface in the vicinity of the developing roll. In the apparatus, the magnetic roll is composed of a non-magnetic rotating sleeve that conveys the developer layer and a magnetic pole arranged inside the rotating sleeve. The magnetic pole inside the magnetic roll at the position where the developing roll and the magnetic roll face each other is A developing device for a multicolor image forming apparatus, wherein the amount of magnetic force drop in the central portion of the magnetic pole is set so that the peak values on both sides thereof do not become repulsive magnetic poles. 2. When G _{L is} the amount of magnetic force drop in the central portion of the magnetic pole inside the magnetic roll and G _H is the magnetic force of the peak values on both sides of the magnetic roll, 10 ≦ (G _L / G _H ) × 100 ≦ 25 is satisfied. The developing device of the multicolor image forming apparatus according to claim 1, wherein 3. The developing device for a multicolor image forming apparatus according to claim 1, wherein when the angle between the peak values is θ, 30 ° ≦ θ ≦ 50 ° is satisfied. .