JPH0792804A - Developing device - Google Patents

Abstract

PURPOSE:To obtain a developing device of high reliability without a image quality defect by removing toner on a toner carrier with an electric field generated between the toner carrier and a developer carrier in each developing process. CONSTITUTION:It takes about 0.5 second from the completion of a developing process to the next developing process. that is, two cycles or more of the toner carrier 68. The voltage of the developer carrier 66 is switched for the first cycle to obtain -100V. At this time. the potential difference between the toner carrier 68 and the developer carrier 66 is 100V in an absolute value and the electric field between both carriers is opposite to the forming a toner layer to bring the toner on the toner carrier 68 to a magnetic brush on the developer carrier 66. T}men, for preparing for the second developing process, the voltage of the developer carrier 66 is -400V to start the formation of the toner onto the developer carrier 68. After the second developing process is completed, the voltage to the developer carrier 66 is switched again and the toner on the toner carrier 68 is removed to bring completion. Thus, reduction in an image density and a developing history can be prevented without imparting a mechanical stress to the toner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device generally used in an image forming apparatus or the like, and more particularly, it is used as a printer for computers, facsimiles, CAD, etc. The present invention relates to a developing device used in a multicolor electrophotographic copying apparatus in which a visible image of a plurality of colors is formed on an electrostatic latent image carrier repeatedly, and more specifically, to a toner carrier using a magnetic roll. The present invention relates to a developing device that has a control electrode that is attached to a toner carrier and is disposed in the vicinity of a toner carrier and is separated therefrom, thereby forming a toner cloud in a developing region and developing a latent image.

[0002]

2. Description of the Related Art Conventionally, there are various types of multicolor image forming apparatuses using electrophotography. As one of them, toner images of respective colors are sequentially formed on the photoconductor drum, and the toners of respective colors formed on the photoconductor are sequentially transferred onto the recording paper held around the transfer drum. There is a method of forming a multicolor image. In this case, a charging unit, an exposing unit, a plurality of developing units corresponding to respective colors, a transferring unit and a cleaning device are arranged around the photosensitive drum, and charging, exposing and developing are performed for each rotation of the photosensitive drum. Repeat the steps of transfer and cleaning. As a result, a toner image of each color is sequentially superposed and transferred onto the recording paper for each rotation of the photosensitive drum to form a multicolor image.

As another method of the above-mentioned multicolor image forming apparatus, toner images of respective colors are successively formed on the photosensitive drum for each rotation, and the toner images of the respective colors formed on the photosensitive drum are formed. It is also known to form a multicolor image by transferring a toner image onto a recording sheet in a single transfer process.

However, in any of the above-described multicolor image forming apparatuses, a toner image of one color is formed on the photosensitive drum for each rotation, so that a multicolor image is formed. , The photoconductor drum must be rotated by the number of required colors. Therefore, there is a problem that it takes a long time to obtain a final multicolor image, and the image formation cannot be speeded up. In the former method,
A transfer drum for sequentially transferring the toner images formed on the photoconductor drum is required, which causes a problem that the device becomes large. Further, in the former method, the toner images formed on the photoconductor drum are sequentially transferred onto the recording paper held on the transfer drum. There is a problem in that color misregistration and positional misalignment may occur, and it is necessary to ensure accuracy.

Therefore, as a means for solving these problems, as shown in Japanese Patent Laid-Open No. 63-273883,
A plurality of recording units including a charging device, an exposure optical system, and a developing device are arranged around the photosensitive drum, and a toner image of each color is formed on the photosensitive drum while the photosensitive drum makes one rotation.
A multicolor image forming apparatus has also been proposed which transfers the toner images of the respective colors onto a recording sheet in a single transfer process.

However, in the case of the multicolor image forming apparatus according to this proposal, a plurality of toner images are formed on the photoconductor drum during one rotation of the photoconductor drum, and the transfer process is completed only once. , If the development is repeated a plurality of times while the photoconductor drum makes one rotation, the toner image already formed on the photoconductor drum is disturbed at the time of the subsequent development, or the toner adheres to and mixes with the developing roll to cause color mixing. There is a problem.

In order to solve this problem, there are already various types of apparatuses for forming only toner on a donor roll and developing an electrostatic latent image on a photosensitive drum with a toner layer formed on the donor roll. It has been published. This developing method has been conventionally used in the development of non-magnetic one-component toner. In the method of developing the electrostatic latent image on the photoconductor drum by the toner layer formed on the donor roll, the toner on the donor roll and the photoconductor drum are not in contact with each other. Disturbance does not easily occur in the developed toner image, high quality multicolor image can be obtained,
It has advantages such as the possibility of developing toners of a plurality of colors on the photosensitive drum in a superimposed manner.

In such a non-contact one-component developing method, the toner applied to the donor roll is transferred onto the surface of the donor roll by the Coulomb force generated by the developing electric field formed between the donor roll and the photosensitive drum. It is necessary to peel it off and move it to the photoconductor drum side.

However, the adhesion 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 drum, and the toner is separated from the donor roll and moved to the photoconductor drum side. It is difficult to do so.

Therefore, in reality, for example, Japanese Patent Publication Sho 63
As disclosed in Japanese Patent Laid-Open No. 31776, a method has been proposed in which an AC electric field is applied between a donor roll and a photosensitive drum to facilitate separation of toner from the surface of the donor roll and facilitate development. There is. In addition, JP-A-56-116
In the method disclosed in JP-A No. 060, a porous electrode is arranged between the donor roll and the photoconductor drum, and an AC voltage is applied to the porous electrode to separate the toner from the donor roll to separate the toner. A method has also been proposed in which a cloud is generated and the toner is developed on the photosensitive drum.

In these methods, the toner can be separated from the donor roll even if the charge amount of the toner is relatively high. However, in the former method, the distance between the donor roll and the photosensitive drum is relatively large. Since an AC electric field is applied between them, it is necessary to increase the AC electric field, and there is a problem that this AC electric field may disturb the toner image already developed on the photosensitive drum.

On the other hand, in the latter method, the toner can be separated from the donor roll even if the charge amount of the toner is relatively high, and a relatively low AC electric field can be used. In addition, there is little risk of disturbing the toner image that has already been developed, and there is a possibility that toner of a plurality of colors can be overlaid and developed on the photosensitive drum.

However, in the case of the one-component developing method using the above-mentioned donor roll, since the toner is frictionally charged only, the charge amount of the toner is low, and there is a problem in long-term maintenance of image quality. The toner on the donor roll is partially clogged by a blade member for controlling the toner layer on the donor roll and tribocharging the toner while controlling the toner layer on the donor roll by a slight change in the characteristics of the toner. There is a problem that image defects are likely to occur, and it cannot be said that the reliability is necessarily high.

In order to solve these problems, therefore, the advantages of the one-component developing method using a donor roll and the advantages of the conventional two-component developing method are successfully combined to obtain the desired characteristics of both. A device has been proposed.

For example, Washington DC, D.E., November 8, 1984. C. Society of Photographers and Engineers
icScientists and Engineer
s) "The 2nd International Conference on Advances in Non-impact Printing" (The 2nd International)
Congress on Advances in N
In on-inact Printing, Toshiba Corp. explained a device for forming a toner layer by transferring a two-component developer to a donor roll using a magnetic roll and transferring the toner onto the donor roll. . In addition, before that, Toshiba Corp.
Volume 9, No. 2 (1981), describes the formation of a toner layer on a donor roll using a two-component developer.

Further, US Pat. No. 3,929,098 discloses a developing device in which a two-component developer is advanced to a donor roll by using a magnetic roll and the toner is transferred onto the donor roll to form a toner layer. ing.

In the developing method according to this proposal, a toner layer can be stably formed on a donor roll and conveyed, but since a two-component developer is used, frictional charging of the carrier and toner causes Since the charge amount of the toner becomes relatively high, it becomes difficult to separate the toner from the donor roll in the developing process, and a strong AC electric field has to be applied between the donor roll and the photosensitive drum. Therefore, the AC electric field disturbs the toner image developed on the photosensitive drum before that, so that it is not possible to uniformly develop the toners of a plurality of colors.

Therefore, a method has been proposed in which an auxiliary electrode made of a wire is provided between the donor roll and the photosensitive drum, and a weak AC electric field is applied to the auxiliary electrode so as not to disturb the developed toner ( JP-A-3-113474, US Pat. No. 289347).

FIG. 10 is a schematic configuration diagram showing an actual application of the developing device disclosed in Japanese Patent Laid-Open No. 3-113474.

In this developing device, a donor roll 101, which is opposed to the electrostatic latent image carrier 105 in a housing 115 containing a two-component developer, conveys non-magnetic toner on the surface thereof, and the donor roll 101. A developer carrying member 102 which is arranged close to 101 and which conveys a two-component developer while adsorbing the two-component developer on its surface, and a developer carrying member 102 which is arranged substantially parallel to the developer carrying body 102 and conveys the two-component developer while stirring. It has developer stirring members 106 and 107. Further, a control electrode 104 for controlling the flight of the non-magnetic toner is disposed in the vicinity of the donor roll 101 in the gap between the electrostatic latent image carrier 105 and the donor roll 101.

The electrostatic latent image carrier 105 is composed of a photosensitive drum or the like, which is charged uniformly in advance and then an electrostatic latent image is formed by the difference in the charging potential of the surface by irradiation with laser light or the like. Is.

Further, the developer carrying member 102 has a plurality of magnetic poles whose positions are fixed inside, and forms a magnetic brush on the surface of which the magnetic carrier for carrying the non-magnetic toner is formed in a spike shape. It is a thing. The developer agitating members 106 and 107 convey the developer in opposite directions, and convey the developer while agitating the developer in two developer accommodating chambers 109 and 110 which are partitioned by a partition wall 108 and communicate with each other at both ends. However, it circulates in a certain direction.

In such a developing device, the developer is agitated by the developer agitating members 106 and 107, and a predetermined charge is applied to the nonmagnetic toner by frictional charging between the nonmagnetic toner and the magnetic carrier, so that the developer carrying member is carried. Is supplied to 102. The developer forms a magnetic brush on the developer carrier 102, is conveyed by the rotation of the surface of the developer carrier 102, and is rubbed against the surface of the donor roll 101. An oscillating electric field is formed between the developer carrier 102 and the donor roll 101 by the bias power sources 112 and 113.
The toner attached to the magnetic carrier is the donor roll 1
No. 01 is transferred to form a thin layer of toner.

The thin layer of toner formed on the donor roll 101 is conveyed to the developing area in the vicinity of the electrostatic latent image carrier 105 by the rotation of the donor roll 101. The control electrode 104 provided in the vicinity of the donor roll 101 includes
A DC superimposed AC voltage is applied from the bias power source 111, and the toner is clouded by the oscillating electric field generated in the developing area and adheres to the electrostatic latent image for development.

Such a developing device can be used, for example, in a multicolor image forming apparatus using a plurality of developing devices containing toners of different colors.

In particular, it can be said that the electrostatic latent image carrier can be developed without disturbing toner images of a plurality of colors by repeating the steps of charging, exposing and developing a plurality of times during one revolution of the electrostatic latent image carrier. There are advantages.

[0027]

However, the above-mentioned prior art has the following problems. That is, in the case of the developing device according to the above proposal, as shown in FIG. 10, the two-component developer is advanced to the donor roll 101 by using the developer carrying member 102 made of a magnetic roll, and the developer roll 102 is placed on the donor roll 101. It is configured to transfer only toner to form a toner layer, and it has been found that there is a problem that the image density decreases as the number of prints increases. In addition, when the toner consuming portion and the non-consuming portion in the image output several sheets of the pattern as shown in FIG. 11A continuously and then output the pattern as shown in FIG. 11 (c), there is a drawback that unevenness in output density occurs, which is so-called image history, in which the density increases after the toner consuming portion. In particular, this problem of image history appears as color unevenness when a color image is formed, and significantly deteriorates the image quality.

When the density decrease and the development history phenomenon are examined in more detail, when the toner layer is formed on the donor roll 101, the toner on the donor roll 101 is not consumed and the toner on the developer carrying member 102 is repeatedly used. Assuming that the number of times the toner is continuously supplied from the magnetic brush is “toner resupply repetition number”, when the toner resupply repetition number increases, the toner resupply repetition number, the toner charge amount on the donor roll 101, and the particle The relationship of the diameter distribution is described in JP-A-57-79.
When measured with a device and an image analyzer having the same principle as the charge spectrum graph described in Japanese Patent No. 958,
As the number of toner resupply repeats increases, the proportion of toner having a high charge amount and a small particle size increases, but the characteristics of the toner in the two-component developer are stable without correlation with the number of toner resupply repeats. It turned out.

As a simple measurement, the donor roll 101
There is a method of observing how the above toner potential and the toner layer weight per unit area change with respect to the toner supply time. FIG. 12 shows the result of actual measurement. It can be seen that, as the toner supply time increases, the toner potential does not change much, but the toner layer weight per unit decreases sharply. From this, it can be easily inferred that the toner charge amount on the donor roll 101 has increased.

That is, the toner is supplied each time the donor roll 101 and the magnetic brush pass through the contacting portion, but at that time, the toner having a large electrostatic or non-electrostatic adhesion with the donor, that is, the charge amount. The toner having a high particle size and a small particle diameter is selectively transferred onto the donor roll 101, and is replaced with the toner having a small adhesive force. On the other hand, since the force from the electric field for separating from the donor roll 101 and transferring to the electrostatic latent image is constant, the toner having a large adhesive force is hard to separate from the donor roll 101, and as a result, the developing toner amount decreases, Causes a decrease in concentration. If the toner on the donor roll 101 is consumed on the way,
Since the toner supply is newly started, the number of times of resupply of toner is small, and the toner adhesion force on the donor roll 101 is also small, so that the amount of developing toner is increased and the image density is increased.
Therefore, it is considered that the toner on the donor roll 101 has a difference in adhesive force depending on the image pattern, which causes a development history.

Therefore, as an easy means for preventing the development history phenomenon, all the developed toner on the donor roll 101 is mechanically peeled off once with a scraper or the like, and a new toner layer is formed on the donor roll 101. It is also possible to form. However, in this case, a new problem arises that the toner on the donor roll 101 is mechanically stressed.

Therefore, the present invention has been made in order to solve the above-mentioned problems of the prior art, and the purpose thereof is to provide the toner without mechanical stress.
An object of the present invention is to provide a developing device with high image quality and high reliability, which prevents a decrease in image density and so-called development history.

[0033]

In order to achieve the above-mentioned object, in the developing device according to the first aspect of the present invention, a two-component developer having a non-magnetic toner and a magnetic carrier is carried to form a circle. Toner that is disposed so as to closely face the developer carrying member that is conveyed as a magnetic brush in the circumferential direction and the electrostatic latent image carrying member that forms an electrostatic latent image with the developer carrying member at different positions. A carrier, a means for regulating the amount of developer on the developer carrier, and a toner in the developer forming a magnetic brush on the developer carrier electrostatically attached to the toner carrier. In a developing device provided with a means for forming an electric field between a developer carrier and a toner carrier, the DC component of the electric field formed between the developer carrier and the toner carrier forms at least an electrostatic latent image. Other than when visualizing images, In the state where the developer carrier and the toner carrier are rotating, the direction of the reverse electric field is such that the toner moves from the toner carrier to the developer carrier, and the electric field is generated for one cycle or more of the rotation of the toner carrier. It is configured to have a holding means.

In order to achieve the above object, in the developing device according to the second aspect of the present invention, in the state where the developer carrying member and the toner carrying member are rotating,
In order to switch the toner to the opposite electric field direction so that the toner moves from the toner carrier to the developer carrier, the development is performed such that the difference between the DC components of the voltages applied to both carriers is 10 V or more in absolute value. It is configured to change the voltage applied to the agent carrier.

Further, in the developing device according to the third aspect of the present invention, in order to achieve the above-mentioned object, the toner is transferred to the toner while the developer carrier and the toner carrier are rotating. In order to switch to the reverse electric field direction such that the toner carrier moves to the developer carrier, the toner carrier is adjusted so that the difference between the DC components of the voltages applied to the both carriers becomes 10 V or more in absolute value. It is configured to change the applied voltage.

[0036]

As described above, with respect to the density decrease and the development history phenomenon, which are problems in the prior art, the relation between the number of re-feeding of toner, the charge amount of the toner on the toner carrier and the distribution of the particle size was measured. However, when the number of toner re-supply is increased, the proportion of toner having a high charge amount and a small particle size increases,
It has been found that this occurs because the adhesion between the toner and the toner carrier increases or the distribution of the adhesion becomes uneven.

According to the first aspect of the present invention, the electrostatic latent image is visualized from the relationship of the feeding of the transfer member such as the recording sheet even when the image formation is continuously performed. The process utilizes the fact that there is a non-development time that does not interfere with operation for a certain period of time, and during that time, a reverse electric field that causes the toner to move from the toner carrier to the developer carrier is generated, The toner of the carrier is taken into the magnetic brush of the developer carrier so that the toner is removed from the toner carrier. As a result, in the next step of visualizing the electrostatic latent image, the toner supply to the toner carrier starts from a new state, and the increasing toner adhesive force becomes a low value in the initial state. Therefore, it is possible to prevent the decrease in density that has occurred due to the increase in the adhesive force of the toner. Similarly, it is possible to eliminate the uneven distribution of the toner adhesion force and obtain a uniform image.

Further, in the second aspect of the present invention, the voltage is applied to the developer carrier so that the difference between the DC components of the voltages applied to the both carriers is 10 V or more in absolute value. The applied voltage is changed to generate a reverse electric field that causes the toner to move from the toner carrier to the developer carrier, so that the adhesion state between the toner carrier and the toner can be initialized in the same manner as described above. Therefore, it is possible to prevent the decrease in density that has occurred due to the increase in the adhesive force of the toner. Similarly, it is possible to eliminate the uneven distribution of the toner adhesion force and obtain a uniform image.

Further, in the third aspect of the present invention, the voltage is applied to the toner carrier so that the difference between the DC components of the voltages applied to the both carriers is 10 V or more in absolute value. Since the reverse electric field is generated by changing the voltage so that the toner moves from the toner carrier to the developer carrier, it is possible to initialize the adhered state of the toner carrier and the toner in the same manner as described above. Therefore, it is possible to prevent the decrease in density that has occurred due to the increase in the adhesive force of the toner. Similarly, it is possible to eliminate the uneven distribution of the toner adhesion force and obtain a uniform image.

[0040]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to illustrated embodiments.

FIG. 2 shows a multicolor image forming apparatus to which an embodiment of the developing device according to the present invention can be applied.

This multicolor image forming apparatus is roughly composed of an image forming section 1 located at the upper part and a sheet feeding section 2 located at the lower part.

In the image forming section 1, 3 is a translucent belt-shaped photoreceptor, and this translucent belt-shaped photoreceptor 3 is
Drive roller 4a and a plurality of idler rollers 4b to 4e
It is hung around and arranged vertically. The belt-shaped photoreceptor 3 is rotationally driven in the direction of arrow A by the drive roller 4a. Around the belt-shaped photoconductor 3, a first image recording unit 5, a second image recording unit 6, a third image recording unit 7, a fourth image recording unit 8, and an optical sensor 10 for registration adjustment.
a, a pre-transfer corotron 9, a development density sensor 10b, a light guide section 11 for guiding the light of a discharge lamp 16 described later, a transfer section 12, a pre-cleaning corotron 1.
3, a cleaning device 14 and a ground strip 15 are arranged respectively. The components forming each of these image recording units and the like are arranged along the surface of the belt-shaped photoconductor 3 which is held substantially vertically. Further, inside the lower end portion of the belt-shaped photoreceptor 3, the belt-shaped photoreceptor 3 is provided before and after the transfer section 12.
A static elimination lamp 16 for irradiating the inside from the inside is arranged.

The transfer section 12 is a transfer corotron 12a.
Also, the peeling corotron 12b is provided, and is arranged at the lowermost end of the vertically long belt-shaped photosensitive member 3 so that the sheet conveying direction is substantially horizontal. Further, adjacent to the transfer section 12, a sheet conveying device 17 and a conveying roller 18 are provided on the sheet introducing side, and a conveying belt 20 for conveying the recording sheet after transfer to the fixing device 19 is provided on the sheet discharging side. There is.

The first image recording section 5 includes a first charger 21, a laser light source (not shown), a rotary polygon mirror 22a irradiated with laser light, and a motor 22b for rotationally driving the rotary polygon mirror 22a. , Lenses 22c and 22d, mirror 22e,
The first exposure device 22, the first potential sensor 23, the first developing device 24, and the like, which are configured by 22f and the like, are provided. Also, the second
The 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, a second developing device 28, and the like. Similarly, in the third and fourth image recording units 7 and 8, the third and fourth chargers 29 and 33, the third and fourth exposure devices 30 and 34, the third and fourth potential sensors 3 are also included.
1, 35, third and fourth developing machines 32, 36 and the like are provided.

The first, second, third, and fourth image recording units 5, 6, 7, and 8 are formed on the belt-shaped photoconductor 3 by toners of black, red, green, and blue, for example. Each color image is formed. In addition, each potential sensor 23,
Reference numerals 27, 31, 35 detect the surface potential of the belt-shaped photoconductor 3 in each of the image recording units 5, 6, 7, 8 and control each by a control circuit (not shown) so that the surface potential is set to a predetermined potential. The chargers 21, 25, 29, 33 are controlled. Further, the final development density is detected by the development density sensor 10b,
Each image recording unit 5, 6, 7, so that an appropriate density can be obtained.
The developing conditions in No. 8 are adjusted. The development density sensor 10b is configured by arranging color sensor elements corresponding to each color in a direction perpendicular to the moving direction of the photoconductor 3. Each of the developing machines 24, 28, 32, 36 is provided with a developing roll 24a, 28a, 32a, 36a and a backup roll 24b, 28b, 32b, 36b. The second, third, and fourth developing units 28, 32, and 36 must not cause the toner image formed on the photoconductor 3 by the preceding developing unit to be disturbed, and thus the non-contact type developing device. Is adopted.

Further, the paper feeding section 2 has an intermediate tray 41 having paper feeding devices 37, 38, 39 and 40, respectively.
The paper feed trays 42 and 43, the large capacity tray 44, the paper reversing unit 45, and the like are arranged. The intermediate tray 41 has a switching claw device 46 including a plurality of switching claws 46a, 46b, 46c.
Is provided. In addition, 47 and 48 are transport rolls, 4
9 is a reverse roll.

Next, a circuit configuration for forming an image in the above-described multicolor image forming apparatus will be described with reference to FIG.

Image signals from the image input device 51, the computer 52, the communication device 54 and the like communicating via the communication line 53 are supplied to the multicolor image forming device 50 via the image processing device 55. It The image signal supplied 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 supplied to the first exposure device 22 of the first recording section 5 without being substantially delayed, and the second to fourth color components are respectively supplied to the second exposure device 22 via the first to third delay circuits 57 to 59. ~ Second of the fourth recording unit 6, 7, 8
~ Supplied to the fourth exposure device 26, 30, 34. In addition,
Delay time T1 in the first to third delay circuits 57 to 59,
T2 and T3 correspond to the distances of the exposure positions of the belt-shaped photoreceptor 3 by the second to fourth exposure devices 26, 30, and 34 from the exposure position of the first exposure device 22.

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

First, the image forming mode will be described by taking as an example the case of forming a multicolor image such as red and black.

In this case, the control device 61 controls the first and second image recording units 5 based on the instruction from the operation panel 60.
Only 6 is operable, and the third and fourth image recording units 7 and 8 are inoperable. This operation / non-operation switching is performed by, for example, the first and second chargers 21, 25, the first and second exposure devices 22, 26, the first and second developing devices 24,
This is performed by applying a predetermined operating voltage or bias voltage to only 28.

The belt-shaped photosensitive member 3 which is rotationally driven in the direction of the arrow A by the driving roller 4a, firstly includes the first image recording section 5
In FIG. 4, the first charger 21 uniformly charges the toner as shown in FIG. As a result, the surface potential of the photoconductor 3 becomes, for example, Vp of about -400 V (where Vp is a negative value). Next, in the first exposure device 22, the surface of the photoconductor 3 is exposed by the light Lk from the laser that is modulated by the signal corresponding to the black of the image, and the potential of the exposed portion is, for example, VR, about -100V. (However, VR is a negative value) (see (b) in the figure). Next, this exposed portion advances to the first developing portion 24, where it is developed with the black toner Tk (see FIG. 7C). Even after this development, the surface potential of the black image portion remains low. Next, the black developing portion advances to the second image recording portion 6 and is recharged by the second charger 25, and the surface potential of the photoconductor 3 has a VP of about -50.
It rises to near 0 V (see (d) of the same figure). Then the second
In the exposure device 26, by the light LR from the light emitting diode array modulated by the signal corresponding to the red color of the image,
The surface of the photoconductor 3 is exposed, and the potential VR of the exposed portion is about −.
The voltage drops to 100 V (see (e) in the figure). Next, this exposed portion advances to the second developing portion 28 where it is developed with the red toner TR (see FIG. 7F). After this red development, the surface potential of the red image portion remains low.

The belt-shaped photosensitive member 3 further advances to the third and fourth
After passing through the image recording units 7 and 8, the surface potential of the photoconductor 3 is charged to about −550V by the third charger 29, and the image unit is about −140 by the third exposure device 30 as described above.
It is exposed to V and subjected to reversal development by the third developing section 32. Subsequently, the surface of the photoconductor 3 is charged to about −600V by the fourth charger 33, the image portion is exposed to about −180V by the fourth exposure device 34, and the fourth developing portion 36 is exposed.
Reverse development is performed by. Depending on the performance of the charger, the potential of the exposure unit in the previous stage is low.Therefore, in order to make the potential of the photoconductor uniform by recharging, it is necessary to raise the potential in the previous stage. The recharge potential of the photoconductor increases as each process is repeated.

Then, the charge of the toner image is adjusted by the pre-transfer corotron 9 and the charge eliminating lamp 16 to be in a state suitable for transfer.

When the toner image of each color reaches the transfer unit 12, in synchronization with this, the recording paper is conveyed from any one of the trays 41 to 44 of the paper feeding unit 2 by the paper feeding device 37 to 40. The sheet is fed to the image forming unit 1 side along B, is further conveyed by the sheet conveying device 17 and the conveying roller 18, and comes into contact with the surface of the belt-shaped photoreceptor 3.

In the transfer section 12, the toner image of each color is transferred from the surface of the belt-shaped photoconductor 3 to the recording paper by the electric field from the transfer corotron 12a. The recording paper after the transfer is separated from the belt-shaped photoconductor 3 by the separating corotron 12b and is conveyed to the fixing device 19 by the conveying belt 20 to fix the toner image on the recording paper.

The recording paper after fixing advances, for example, in the direction of arrow C, and is directly discharged outside the apparatus by the conveying roller 47 with the image surface facing upward. When the paper is discharged with the image surface facing down, the conveying rollers 48 and 49 are used to temporarily move the arrows D and E.
Then, the conveyance rollers 48 and 49 reverse the rotation of the conveyance rollers 47, and the conveyance rollers 47 eject the sheets to the outside of the machine.

The toner remaining on the belt-shaped photosensitive member 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. Further, the electric charge remaining on the photoconductor 3 is discharged through the ground strip 15 to prepare for the next image forming cycle.

In the case of double-sided copying, the recording paper after fixing advances in the direction of arrow D, is conveyed by the conveying roller 48 to the paper reversing unit 45 of the paper feeding unit 2, and is once in the direction of arrow E by the reversing roller 49. After being conveyed, the rotation of the reversing roller 49 is reversed, the conveying direction of the recording paper is reversed in the direction of arrow F, 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 from the proper position. This recording paper is sent to the transfer unit 12 of the image forming unit 1 again by the paper feeding device 37, and the image on the back surface of the recording paper is formed 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 may be directly conveyed from the conveying roller 48 to the intermediate tray 41.

Next, a developing device according to an embodiment of the present invention will be described.

FIG. 1 shows a configuration example of a non-contact type developing device. This developing device includes the first to fourth developing machines 24,
It is applicable to any of 28, 32, and 36, but in particular, the belt-shaped photoreceptor 3 on which a toner image is already formed.
It is suitable for the second and subsequent developing machines that develop the toner image by superposing on the second developing machine. Here, the second developing device 28 will be described as an example.

As shown in FIG. 1, the second developing device 28 is arranged so as to face the belt-shaped photosensitive member 3 as an electrostatic latent image carrier. The second developing device 28 is a developing device that magnetically attracts the two-component developer 64 into a housing 65 that accommodates the two-component developer 64 including a non-magnetic toner and a magnetic carrier to form a magnetic brush on the surface. The agent carrier 66, the developer regulating member 67 that regulates the amount of the developer adsorbed on the developer carrier 66, and the developer carrier 6
6 and the belt-shaped photoconductor 3 are arranged so as to be close to each other at different positions, and have a cylindrical toner carrier 68 that rotates by adhering only non-magnetic toner. At a position where the toner carrier 68 and the belt-shaped photoconductor 3 face each other, a plurality of control electrodes 69 for controlling the flight of the non-magnetic toner are stretched.

Further, the housing 6 of the second developing machine 28
In FIG. 5, a first developer stirring chamber 70 is provided at a position adjacent to the developer carrying member 66, and a second developer stirring chamber 72 partitioned by the first developer stirring chamber 70 and a partition 71. Is provided. The first developer agitating chamber 70 and the second developer agitating chamber 72 communicate with each other at both ends in the axial direction of the developer carrier 66, and agitate and convey the two-component developer 64, respectively. A first screw auger 73 and a second screw auger 74 for performing the operation are provided. These two screw augers 73,74
Has a rotation direction and a screw direction so as to convey the developer in mutually opposite directions, and the developer 64 circulates in the first developer stirring chamber 70 and the second developer stirring chamber 72. It is like this. As a result, the two-component developer 64
The distribution of the non-magnetic toner in the inside is maintained uniform, and a charge of -5 to -25 μc / g is imparted by frictional charging with the magnetic carrier. The agitated two-component developer 64 is supplied to the developer carrier 66 by the first screw auger 73.

The position of the developer carrying member 66 is fixed.
Place a rotatable cylindrical sleeve around the outer circumference of the magnet.
The two-component developer 64 is magnetized on the surface of the sleeve.
Magnetically adsorbs to form a magnetic brush and sleeve
Can rotate to convey the developer.
The developer carrying member 66 receives a DC load from the bias power supply 75.
Tatami AC voltage (frequency 2-12KHz, V_PP2Kv or more
Below, V_dc-100V to -1000V is preferable)
Has been done. And has a charge on the developer carrier 66.
Toner is transferred to the toner carrier 68 by Coulomb force.
-10 to -30 μc / g on the surface of the toner carrier 68.
A thin layer of toner is formed that has an electrostatic charge of. The above
Of the bias power supply 75 applied to the image carrier 66,
DC voltage V _dcIs toner formed on the toner carrier 68.
Is the main factor controlling the amount of thin layer. In this example,
In consideration of the desired toner amount and toner charge amount, -28
0V was chosen as a suitable value.

As the toner carrier 68, an aluminum cylinder whose surface is anodized, a cylinder made of phenol resin, or a metal surface on which a synthetic resin layer is formed is used. An aluminum roll having a 25 mm surface anodized was used. Further, the toner carrier 68 has a DC power supply 7
6 to -100V to -400V DC voltage is applied. A DC superimposed AC voltage may be applied to the toner carrier 68.

Further, the toner carrier 68 and the belt-shaped photoconductor 3 are arranged so as to face each other while maintaining a distance of 200 μm to 500 μm, and the toner carrier 68 and the belt-shaped photoconductor 3 face each other. The movement of both surfaces in position is
For example, the rotation direction is set to be the opposite direction,
The movements of both surfaces may be set in the same direction.

On the other hand, it is desirable to set the rotation direction of the developer carrier 66 to be opposite to the rotation direction of the toner carrier 68. In this embodiment, the rotation direction of the toner carrier 68 is opposite to that of the belt-shaped photoconductor 3 and the absolute speed is 415
It has a speed of mm / sec. Further, the developer carrying member 66 is moving at an absolute speed of 1245 mm / sec, which is opposite to the moving direction of the toner carrying member 68.

The control electrode 69 has a diameter of 89 μm.
Axial direction of the toner carrier 68
The toner carrier 68 is linearly arranged in a plurality of rows along the direction.
6 provided so that a part of the peripheral surface of the housing is exposed
5 is supported at both ends of the opening of
It is arranged so as to be close to each other. This control electrode 69
Is the DC bias AC voltage (frequency) from the developing bias power supply 77.
Wave number 2-12KHz, V _PP200-1000V or less,
V_dc-100V to -1000V is preferable).
The toner cloud in the electric field.
It This clouded toner flies in the electric field
The electrostatic latent image on the belt-shaped photoreceptor 3 is attached and developed. Na
The control electrode 69 does not consist of a wire,
Open a metal plate with a size larger than the average particle size of multiple toner particles.
It may have a mouth.

By the way, in this embodiment, when the image formation is continuously performed with two sheets of a single color, the change of the direct current component of the voltage power supply 75 to the developer carrier 66 and the voltage power supply 76 to the toner carrier 68 and both carrying. Figure 5 shows the timing chart for body drive.
As shown in.

That is, about 0.2 when the developing process is started.
The driving of both the carriers 66 and 68 is started a few seconds before, the voltage power supply 75 to the developer carrier 66 is set to -400V, the voltage power supply 76 to the toner carrier 68 is set to -200V, and the toner in the magnetic brush is set. Forms a toner layer on the toner carrier 68. About 0.5 from the end of development process to the next development process
There are two seconds, which is more than two cycles of the toner carrier 68. The voltage of the developer carrying member 66 is switched during the first round, and -1
It becomes 00V. At this time, the potential difference between the toner carrier 68 and the developer carrier 66 is 100 V in absolute value, and the electric field between the two carriers is opposite to that at the time of forming the toner layer, and the toner carrier 68 is
The upper toner is taken in by the magnetic brush on the developer carrying member 66. Next, in order to prepare for the second developing step, the voltage of the developer carrier 66 becomes −400 V, and the formation of toner on the toner carrier 68 is started.
After the second developing process is completed, the developer carrying member 6 is again provided.
The voltage to 6 is switched, the toner on the toner carrier 68 is removed, and the process ends. Needless to say, when forming a large number of images, the above steps may be repeated.

When a print test of 1000 sheets was carried out using this developing device, there was no decrease in density and no density unevenness due to development history was observed, as shown in FIG. As a comparative example, FIG. 6 shows the result of a print test when there is no process for removing the toner layer on the toner carrier 68 by switching the voltage to the developer carrier 66 as shown in the timing chart of FIG. From the result of the experiment, it was confirmed that the effect of the present invention is great.

8A and 8B, the developing device according to the above embodiment is taken out from the main body, the toner carrier 68 is grounded, and the same driving and electric field as in FIG. 7 shows the results of examining the change in the potential of the toner layer on the toner carrier 68 measured with a meter and the change in weight per unit area of the toner layer. The toner on the toner carrier 68 is removed by the reverse electric field in each developing process, and even when repeated for a long time, the potential of the toner layer and the weight per unit area of the toner layer do not change when the toner layer is formed. Nonetheless, it can be seen that the present invention is an effect due to the toner layer being sufficiently initialized during each developing step.

Further, at a portion where the toner carrier 68 and the magnetic brush are in contact with each other, there is also a mechanical scraping effect of the magnetic brush, and the toner is taken into the magnetic brush even with a slight reverse electric field, but the minimum condition for exerting the effect is As a result of the investigation, it was found that there is a difference of 10 V or more in the voltage applied between the two carrier members 66 and 68, and it is sufficient to hold the toner carrier member 68 for one rotation or more. The voltage applied between the developer carrying member 66 and the toner carrying member 68 is not a value that can be easily determined because the regulations of the developer are complicated, but even if the potential difference is small, the toner reverse transfer force is not generated. It seems that a difference of 10 V or more is required when using the "conductive carrier" that exhibits the effect, and a potential difference of more than that is required for other developers.

Second Embodiment Next, as a second embodiment, the voltage source 75 for the developer carrying member 66 has the same construction as the above-mentioned embodiment, but in the case where two sheets of images are continuously formed in a single color. FIG. 9 shows a timing chart of the change of the DC component of the voltage power supply 76 to the toner carrier 68 and the driving of both carriers 66 and 68.
The DC component of the voltage power supply 76 of the toner carrier 68 is changed in order to switch to the electric field for removing the toner from the toner carrier 68 to the developer carrier 66. That is, the driving of both the carriers 66 and 68 is started about 0.2 seconds before the development process is started, and the voltage power supply 75 to the developer carrier 66 is-
400V, voltage power supply 76 to toner carrier 68 is -20
The toner in the magnetic brush is set to 0 V and forms a toner layer on the toner carrier 68.

It takes about 0.5 seconds from the end of the developing process to the next developing process, which is two cycles or more of the toner carrier 68. The voltage of the toner carrier 68 is switched during the first round, and becomes -500V. At this time, the potential difference between the toner carrier 68 and the developer carrier 66 is 100 V in absolute value, the electric field between the carrier 66 and 68 is opposite to that when the toner layer is formed, and the toner on the toner carrier 68 is It is adapted to be taken in by the magnetic brush on the developer carrying member 66. Next, in order to prepare for the second developing step, the toner carrier 68
Voltage returns to -400 V, and formation of a toner layer on the toner carrier 68 is started. After the second developing process is completed, the voltage to the toner carrier 68 is switched again, the toner on the toner carrier 68 is removed, and the process is completed. Needless to say, the above steps may be repeated when forming a large number of images.

When a print test was carried out every 1000 times using this developing device, there was no reduction in density and no density unevenness due to the development history was observed. Also in this case, as a result of investigating the minimum condition to exert the effect,
It has been found that there is a difference of 10 V or more in the voltage applied between them, and it is sufficient to hold the toner carrier 68 for one rotation or more.

Further, the same effect can be obtained in the developing device using the AC bias applied to the toner carrier 68 as in the conventionally proposed non-magnetic one-component developing device without using the wire 69.

[0080]

According to the present invention, which has the above-described structure and function, the toner on the toner carrier is developed in each developing step.
By removing by the electric field generated between the developer carrying member, without giving mechanical stress to the toner,
By constantly increasing the adhesive force between the toner on the toner carrier and the toner carrier or preventing unevenness, it is possible to eliminate density reduction and development history, and provide a highly reliable developing device with no image quality defects. can do.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a developing device according to the present invention.

FIG. 2 is a block diagram showing a multicolor image forming apparatus to which an embodiment of the developing device according to the present invention can be applied.

FIG. 3 is a block diagram showing a control circuit of the multicolor image forming apparatus.

4 (a) to 4 (l) are potential explanatory diagrams showing image forming steps, respectively.

FIG. 5 is a timing chart showing the timing of voltage application to the developer carrier and the toner carrier.

FIG. 6 is a graph showing the relationship between the number of prints and the image density.

FIG. 7 is a timing chart showing the timing of voltage application to the developer carrier and the toner carrier.

FIGS. 8A and 8B are graphs showing the relationship between the number of toner layer formations and the toner layer potential, and the relationship between the number of toner layer formations and the toner layer weight, respectively.

FIG. 9 is a timing chart showing the timing of voltage application to the developer carrier and the toner carrier.

FIG. 10 is a block diagram showing a conventional developing device.

FIG. 11A to FIG. 11C are schematic diagrams respectively showing development history phenomena.

FIGS. 12A and 12B are graphs showing the relationship between the toner supply time and the toner layer potential and the relationship between the toner supply time and the toner layer weight, respectively.

[Explanation of symbols]

3 belt-shaped photoreceptor, 28 second developing machine, 64 two-component developer, 65 housing, 66 developer carrier, 68
Toner carrier.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshi Teshigawara, 2274 Hongo, Ebina, Kanagawa Prefecture, Fuji Xerox Co., Ltd. (72) Inventor, Koichiro Shinohara, 2274, Hongo, Ebina, Kanagawa Prefecture (72, Fuji Xerox Co., Ltd. ) Inventor Takahide Inoue 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Haruyuki Namba 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd. (72) Inventor Toshiaki Sagara, Ebina City, Kanagawa Prefecture 2274 Fuji Xerox Co., Ltd. (72) Inventor Takuto Tanaka 2274 Hongo, Ebina City, Kanagawa Prefecture Fuji Xerox Co., Ltd.

Claims (3)

[Claims] 1. A device having a non-magnetic toner and a magnetic carrier.
A developer carrier that carries a component developer and conveys it as a magnetic brush in the circumferential direction and an electrostatic latent image carrier that forms an electrostatic latent image with the developer carrier closely face each other at different positions. The toner carrier arranged as described above, means for regulating the amount of the developer on the developer carrier, and the toner in the developer constituting the magnetic brush on the developer carrier to the toner carrier. A direct current component of an electric field formed between the developer carrying member and the toner carrying member in a developing device provided with means for forming an electric field that electrostatically adheres between the developer carrying member and the toner carrying member. However, the toner may move from the toner carrying body to the developer carrying body while the developer carrying body and the toner carrying body are rotating except at the time of image formation for visualizing the electrostatic latent image. It becomes the direction of the opposite electric field, and the toner carrier Developing apparatus is characterized in that it comprises a means for holding the electric field at least one cycle of rotation. 2. In order to switch the toner to a reverse electric field direction such that toner moves from the toner carrier to the developer carrier while the developer carrier and the toner carrier are rotating, both carrier are carried. 2. The developing device according to claim 1, wherein the voltage applied to the developer carrying member is changed so that the difference between the DC components of the voltage applied to the body is 10 V or more in absolute value. 3. In order to switch the toner to a reverse electric field direction such that toner moves from the toner carrier to the developer carrier while the developer carrier and the toner carrier are rotating, both carrier are carried. 2. The developing device according to claim 1, wherein the voltage applied to the toner carrier is changed so that the difference between the DC components of the voltage applied to the body is 10 V or more in absolute value.