JP2003015379A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an excellent image forming apparatus in which a color mixture of toner is avoided by preventing the adhesion of an unnecessary developer to an image carrier, waste of toner hardly occurs, the change of a main body structure is restrained maximally. SOLUTION: The image forming apparatus has a first developing device and a second developing device which develop a latent image on the image carrier by using a developer and which form a developed image on the image carrier by applying a bias voltage between the image carrier and the device, and a bias power unit which is connected to the first developing device and which can change the applied bias voltage. The second developing device makes a plurality of developing units rotate in which developers each having different color are housed, bring them close to the image carrier successively, and carries out the development operations of the latent image corresponding to the color of each developer. The bias voltage applied while the image is not formed in the first developing device is changed when the image is formed in the second developing device so as to be different from that in the case of forming the image in the first developing device. The bias voltage is changed so as to make the latent image formed on the image carrier have a predetermined potential difference.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus having a developing means for developing a latent image formed on an image carrier in a copying apparatus, an image forming / recording apparatus, a printer, a facsimile, etc., and more particularly to a color apparatus. The present invention relates to an image forming apparatus.

[0002]

2. Description of the Related Art In an image forming apparatus for forming a color image by superposing developed images (toner images) of a plurality of colors, a conventional color image having no color shift is shown in FIG. An image forming apparatus using such an intermediate transfer member has been proposed.

This image processing apparatus is a copying machine or a laser beam printer using an electrophotographic process. The configuration and operation of the image processing apparatus shown in FIG. 7 will be described below.

Inside the main body of the apparatus (hereinafter referred to as "inside the aircraft")
A rotary drum type electrophotographic photosensitive member (hereinafter referred to as “photosensitive drum”) 1 as an image bearing member is disposed in the printer 1. Here, an amorphous silicon photoconductor is used, and its schematic diagram is shown in FIG.

FIG. 8 is a partial sectional view showing the photosensitive drum 1 in the axial direction and one side from the central axis. In FIG. 8, the direction from the bottom to the top is the direction from the center of the photosensitive drum 1 to the surface layer. , Al, etc. are used as the core metal. As shown in FIG. 8, a long-wavelength light absorption layer 105 for preventing reflection from the conductive support 101 is provided on the conductive support 101 from the inside to the surface layer. A charge injection blocking layer 104 for blocking the injection of electric charges, a photoconductive layer 102 which is made of at least an amorphous silicon-based material and exhibits photoconductivity, and a photoconductive layer 102 which is formed on the photoconductive layer 102 as an outermost layer. The surface protection layer 103 for protecting the photoconductive layer 102 is provided to configure the photosensitive drum 1.

The photosensitive drum 1 is rotationally driven in the direction of arrow R1 at a predetermined peripheral speed (process speed), and each image forming process described later is repeatedly performed on the surface thereof.

The photosensitive drum 1 is charged to have a predetermined polarity and a predetermined surface potential by a charging device 2 such as a corona discharger in the course of rotation in the direction of arrow R1. A color image of interest by receiving an image exposure L from an image forming exposure optical system based on decomposition or a scanning exposure optical system based on a laser scanner that outputs a laser beam modulated corresponding to a time-series digital pixel signal of image information. An electrostatic latent image corresponding to the color component image of is formed. Since this image forming apparatus uses four color developers (toners) of yellow Y, magenta M, cyan C, and black Bk, an electrostatic latent image is formed for any of these colors.

As a developing device which is a developing means, a first developing device and a second developing device are provided, and each of them faces the photosensitive drum 1 at one location.

As the first developing device, a black (Bk) developing device (hereinafter referred to as "Bk developing device") is fixedly arranged on the upstream side in the rotation direction of the photosensitive drum 1 (direction of arrow R1). .) 401 is provided. Further, as the second developing device, in the present embodiment, the rotary developing device 4b having the other three color developing devices rotatably arranged on the downstream side is provided.

The fixed developing device 4 which is the first developing device.
a is a fixed developing device 4a which is a first developing device, and a fixed developing device 4a is provided between the upstream exposing unit 3 and the downstream rotary developing device 4b.
It is fixedly arranged in that position so as to divide them.

A rotary developing device 4 which is a second developing device.
Reference numeral b denotes a rotating body that rotates in the direction of arrow R4b and three developing devices mounted on the rotating body, that is, toners of magenta (M), cyan (C), and yellow (Y), respectively. Developing devices 402, 404, 403 (hereinafter, “M developing device 402, C developing device 404, Y developing device 40
3 ”. ).

The rotary developing device 4b is indicated by an arrow R4b.
By rotating in the direction, the developing device for development (M developing device 402 in FIG. 7) is arranged at the developing position facing the surface of the photosensitive drum 1. The rotation direction R4b of the rotary developing device 4b is the same as the rotation direction R1 of the photosensitive drum 1, and the rotation direction of the intermediate transfer belt 5 (arrow R5).
Direction) is the opposite direction.

The rotation direction of the rotary developing device 4b is indicated by an arrow R.
4b, and the development order of the four colors is, for example, M, C,
If it is performed in the order of Y, the M developing device 4 of the rotary developing device 4b.
02, the C developing device 404, and the Y developing device 403 are arranged such that the M developing device 402, the Y developing device 403, and the C developing device 404 are arranged along the rotation direction R4b of the rotary developing device 4b as shown in FIG.
Will be in order.

In the present embodiment, the toner images formed by the developing devices for the respective colors are primarily transferred to the intermediate transfer member. The intermediate transfer belt 5 is used as the intermediate transfer member. The intermediate transfer belt 5 is suspended between one conductive roller 6 and four turn rollers 7a, 7b, 7c, and 7d, that is, a total of five rollers. The conductive roller 6 that constitutes the primary transfer means holds the intermediate transfer belt 5 in a state of being pressed against the photosensitive drum 1 with a predetermined pressing force. The intermediate transfer belt 5 is rotationally driven in the direction of arrow R5 at the same peripheral speed as the photosensitive drum 1 so that the portion facing the photosensitive drum 1 advances in the same direction as the photosensitive drum 1. Is applied with a transfer bias having a polarity (plus) opposite to the toner charging polarity (minus in this embodiment) of the toner image on the photosensitive drum 1.

The intermediate transfer belt 5 is, for example, a dielectric film of polyester, polyethylene or the like, or a composite layer type dielectric film of which the back surface (inner surface side) is made of a medium resistance rubber or the like and is lined with a conductor. The first-color magenta toner image formed and carried on the surface of the photosensitive drum 1 passes through the transfer section by the electric field formed by the application of the transfer bias to the conductive roller 6, and in the process of passing through the intermediate transfer belt 5. Of the toner image of the other two colors are sequentially transferred, as described below.

The image forming operation in the image processing apparatus of this embodiment shown in FIG. 7 will be described below by dividing it into processes (1) to (5). Note that FIG. 7 shows a state in which the M developing device 402 among the three developing devices in the rotary developing device 4b is on standby at the current position.

(1) First, a latent image of an M color image, which is the first color, is formed on the photosensitive drum 1 and development is performed. The M toner image visualized with the M toner by the developing device 402 is
The photosensitive drum 1 is carried, moves along with the rotation in the arrow R1 direction (counterclockwise in FIG. 7), is conveyed to the intermediate transfer belt 5, and is primarily transferred (intermediate transfer) to the outer peripheral surface of the intermediate transfer belt 5. It Then, the surface of the photosensitive drum 1 that has finished transferring the M toner image of the first color to the intermediate transfer belt 5 is cleaned by the cleaning device 8.

(2) Subsequently, the second drum is placed on the photosensitive drum 1.
A latent image of a C color image is formed, and the rotary developing device 4b
Rotates in the direction of arrow R4b (counterclockwise) to perform C toner development, and the C developing device 404 is conveyed to the developing position facing the photosensitive drum 1.

(3) Then, similarly, the photosensitive drum 1
The C toner image is formed on the upper surface by developing with the C toner, the C toner image is intermediately transferred to the intermediate transfer belt 5, and the surface of the photosensitive drum 1 is cleaned by the cleaning device 8.

(4) And like (2) to (3),
The rotary developing device 4b is rotated, the Y developing device 403 is opposed to the photosensitive drum 1, and development with Y toner is performed. The Y toner development on the photosensitive drum 1, the intermediate transfer of the Y toner image onto the intermediate transfer belt 5, and the cleaning of the surface of the photosensitive drum 1 by the cleaning device 8 are performed.

(5) Next, a latent image corresponding to the fourth Bk component image is formed on the photosensitive drum 1 by the exposure L, and the latent image is formed by the Bk toner of the Bk developing device 401 included in the fixed developing device 4a. After being developed, the Bk toner image is intermediately transferred to the intermediate transfer belt 5, and the surface of the photosensitive drum 1 is cleaned by the cleaning device 8.

By sequentially performing the above processes (1) to (5), the above-described toner images of magenta, cyan, yellow, and black are superposed and transferred onto the outer surface of the intermediate transfer belt 5, and the desired toner images are transferred. A composite color toner image (mirror image) corresponding to the color image is formed.

Next, from the paper feed cassette 9 to the paper feed roller 1
One transfer material (for example, plain paper) P is separated and conveyed by 0, passes through the registration roller pair 11 and the transfer guide 12, and then is transferred to the secondary transfer device 13 (corona charger) and the secondary transfer device. The sheet is fed to the secondary transfer portion formed by the turn roller 13a in the transfer device 13 at a predetermined timing.

The conductive roller 6 is applied with 0 V or a bias (negative in this example) having the same charging polarity as that of the toner, which is the reverse of the transfer process, from the bias power source. Further, on the transfer material P fed at a predetermined timing, when the toner image is transferred, a secondary transfer bias power source supplies a secondary charge of the toner charging polarity (negative in this example) and a reverse polarity (plus). A transfer bias is applied to the turn roller 13a in the secondary transfer device 13.

By repeating the above-described series of image forming processes, the transferred composite color images are sequentially intermediate-transferred (primary transfer) onto the intermediate transfer belt 5, and the intermediate-transferred color toner images are transferred to the transfer unit 13. The final transfer (secondary transfer) is performed on the subsequent transfer material P that is successively sent.

When the transfer process is completed, 0V or a transfer bias (minus in this example) having the same polarity as the toner charging polarity (minus) is applied to the intermediate transfer belt 5 from the turn roller 13a or the transfer roller 6. .

The transfer material P on which the toner image on the intermediate transfer belt 5 has been transferred through the secondary transfer device 13 is introduced into the fixing device 15 via the conveying guide 14 and is heated and regulated to a predetermined value. The toner image is fixed by being heated and pressed by the roller 15a and the pressure roller 15b,
The final color image formed product is output.

On the other hand, the intermediate belt 5 after the toner image transfer is
It is cleaned by the belt cleaning device 16. The belt cleaning device 16 is a cleaning device for the intermediate transfer belt 5, and is normally kept inactive with respect to the intermediate transfer belt. However, when the transfer of the toner image onto the transfer material P is finished, the intermediate transfer belt 16 is transferred. The cleaning device 16 operates on the outer surface of the belt 5 to clean the outer surface of the intermediate transfer belt 5.

Depending on the outer peripheral length of the transfer belt 5, it is also possible to carry two or more transfer materials P at one time and form two images at once by one rotation.

[0030]

However, as described above, the first developing device 4a having the Bk developing device is installed at the exposure position and the M, C, Y developing devices (402, 404, 40).
3) and the rotary developing device 4b.
When the image-exposed latent image portion on the photosensitive drum 1, which is an electrophotographic photosensitive member, passes the Bk toner developing position during the development with the M, C, and Y toners, the latent image portion precedes the M, C, and Y toners. In addition, the Bk toner may be transferred to the image-exposed portion to cause color mixing.

Even if the Bk developing device 401 is supported in a non-contact manner with respect to the photosensitive drum 1, the amount of Bk toner is a little,
It may be transferred to the photosensitive drum 1. For example, Y
At the time of development by the toner developing unit 404, the color mixture of Bk toner is conspicuous on the image due to the high brightness of the Y toner, and especially in the highlight part (the part where the density is low), the amount of the Bk toner is small. The color mixture of is very conspicuous and impairs the image quality.

When the Bk developing device 401 is located downstream of the other developing device, color mixing with the toner image from the upstream thereof occurs, but this problem often occurs mainly when it is located upstream.

However, in order not to move the Bk developing device 401 to another position or to attach a small amount of Bk toner to the photosensitive drum 1 during image formation for another color, the Bk developing device 401 and the photosensitive drum 1 are not attached. If an attempt is made to provide a separating mechanism, the device becomes complicated and the provision of inexpensive products is hindered.

Therefore, an object of the present invention is to prevent unnecessary developer from adhering to the image bearing member, prevent color mixture of toner, reduce toner waste, and suppress changes in main body structure as much as possible. An object is to provide an image forming apparatus capable of providing an image.

[0035]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention is
By applying a bias between the image carrier, an exposing unit that exposes the surface of the image carrier based on image information to form a latent image, and a bias is applied between the image carrier and the image carrier. A first developing device and a second developing device for developing the latent image with a developer to form a developed image on the image carrier, and an applied voltage of the bias, which is connected to the first developing device. A bias power supply device capable of varying
In the developing device, a plurality of developing devices each containing a developer having a different color are rotated to sequentially approach the image carrier,
In the image forming apparatus for performing the developing operation of the latent image corresponding to the color of each developer on the image carrier,
The bias voltage applied during non-image formation of the second developing device is changed so as to be different during image formation by the second developing device as compared with that during image formation by the first developing device. An image forming apparatus is provided.

According to one embodiment of the present invention, the bias voltage applied when the first developing device is not forming an image is equal to the bias voltage when the second developing device is forming an image.
The potential of the latent image portion formed on the image carrier is changed so as to have a predetermined potential difference.

[0037]

BEST MODE FOR CARRYING OUT THE INVENTION An image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. However, the dimensions, materials, shapes of the components described in this embodiment,
The relative arrangement, etc., unless otherwise specified,
The scope of the present invention is not limited thereto.

Embodiment 1 Since the main body structure of the image forming apparatus in this embodiment is the same as the main body structure of the image forming apparatus shown in FIG. 7 described in the conventional example, a detailed description of the main body structure will be omitted and the present invention will be described. Fixed developing device 4a which is the first developing device which is the characteristic part
This will be described with reference to FIG.

As described in the conventional example, the fixed developing device 4a is provided with the Bk developing device 401 so that the exposing device 3 on the upstream side and the rotary developing device 4b on the downstream side can be separated from each other. It is fixedly placed at that position. In this embodiment, the Bk developing device 401 is fixed in the fixed developing device 4a, but as another example described in detail in the third embodiment, the Bk developing device 401 can be separated from the photosensitive drum 1. It may be installed.

The state of the Bk developing device 401 is shown in FIG. B
The Bk toner 45, which is the developer used in the k developing device 401, is housed in the developing container 40 that constitutes the Bk developing device 401, and the developing container 40 is arranged in the longitudinal direction of the container 40 (the direction perpendicular to the paper surface of FIG. 7). ) Is provided with a developing sleeve 41 which is a developer carrier and which conveys the toner 45 from the developing container 40 to the photosensitive drum 1.

In this embodiment, the toner 45 contained in the fixed developing device 4a is a one-component magnetic toner.

The developing sleeve 41 of the developer carrying member is made of a material such as aluminum or SUS, and in FIG. 4, the left substantially half peripheral surface of the opening H is projected into the container 40, and the right substantially half peripheral surface is formed. It is rotatably installed so as to be exposed to the outside of the container 40 and face the photosensitive drum 1. There is a slight gap S-Dg between the developing sleeve 41 and the photosensitive drum 1.
ap is provided, and the developing sleeve 41 is rotationally driven in the direction of arrow R4a, which is a direction that follows the rotational direction R1 of the photosensitive drum 1.

A magnet 42 is provided as a magnetic field generating means in the developing sleeve 41. In this embodiment, a magnet 42 is provided.
The magnet 42 is a permanent magnet. The magnet 42 is non-rotatably arranged in the developing sleeve 41 so as to generate a fixed magnetic field regardless of the rotation of the developing sleeve 41. In the vicinity of the developing sleeve 41 in the developing sleeve 41, a plate-shaped magnetic blade 43 is provided as a developer regulating member, the fixed end of which is supported by the opening of the developing container and the free end of which faces the developing sleeve 41. The magnetic blade 43 is arranged so that one pole of the magnetic pole of the magnet 42 substantially opposes.

The magnetic toner 45 carried on the developing sleeve 41 by the stirring member 44 is transferred to the developing sleeve 4 thereafter.
1 rotation, the developing sleeve 41 of the magnetic blade 43
It is transported to the facing part. Then, the layer thickness S-Bgap is regulated by the magnetic regulation formed in the gap between the magnetic blade 43 and the developing sleeve 41 to form a thin layer on the developing sleeve 41, and then the regulating portion S-Bgap is removed. And a small gap S-Dgap with respect to the photosensitive drum 1 is opened, and the photosensitive drum 1 is conveyed to the opposing developing area.

Then, in the developing area, the developing sleeve 4
1 and the photosensitive drum 1, a bias power supply device 46 capable of varying an applied voltage applies an alternating voltage as a developing bias in which a direct current and an alternating current are superposed, so that the toner 45 on the developing sleeve 41 is transferred onto the photosensitive drum 1. The electrostatic latent image is visualized and developed as a toner image.

On the other hand, the Y, M, and C toner developing devices 4 provided in the rotary developing device 4b, which is the second developing device, respectively.
The configurations of 03, 402, and 404 include a developing container 40 installed in the rotary developing device 4b and a developing sleeve 41 having the same configuration as the Bk developing device 401. The toner used in the developing units 402, 403 and 404 is a two-component developer using non-magnetic toner composed of respective color components. The Y, M and C toners may be other non-magnetic one-component toners or magnetic one-component toners.

In the present embodiment, in the rotary developing device 4b, the developing sleeve 41 of the developing device 402 which is in contact with the photosensitive drum 1 is supplied to the developing sleeve 41 from a power source 48 different from the bias power source device 46 of the fixed developing device 4a. A developing bias is applied, the toner moves from the developing sleeve 41 to the photosensitive drum 1, and each color is developed (FIG. 7).

Next, the image formation by the Bk developing device 401 in the present embodiment will be described with reference to the diagram showing the order relation of the potentials established between the photosensitive drum 1 and the developing sleeve 41 in FIG. 3A. To do.

First, the surface of the photosensitive drum 1 in FIG. 7 is charged by the primary charger 2 to the drum surface potential Vd = + 400.
It is uniformly charged to V. Next, exposure L by PWM is performed at 600 dpi by a semiconductor laser having a wavelength of 680 μm to form an electrostatic latent image on the photosensitive drum 1. The laser power at this time is set so that the electrostatic latent image becomes Vl = + 50V.

Subsequently, S-Bgap: 250 μm, S-
Development is performed by a Bk developing device 401 having a Dgap of 250 μm to visualize the toner image. Although a color image may be formed by reversal development, regular development is adopted here.

The developer used in this embodiment is a negative magnetic one-component toner, and the developing bias Vdc is +200 V DC voltage of 2700 Hz, 1500 Vpp, 50% Duty.
By superimposing the AC voltage of, jumping development is realized. This is because, as shown in FIG. 3A, the Bk development contrast Vcont = 200V and the fog removal bias Vback = 150V in the normal development are set.

On the other hand, M in the rotary developing device 4b,
Color image formation in the C, Y developing devices (402, 403, 404) is performed for all three colors as shown in the order of potentials established between the photosensitive drum 1 and the developing sleeve 41 in FIG. 3B. Vd = + 400V and Vl = + 50V are set. Also, Vcont = + 150V, Vback =
Since + 200V is required, Vdc = 250V (20
00 Hz, 2000 Vpp, 50% duty superimposition).

That is, similar latent images are formed in M, C, and Y with respect to Bk. Therefore, even the color latent image is developed by the Bk developing device 401 in the fixed developing device 4a.

Therefore, in the present embodiment, as shown in FIG. 1, the bias applied to the Bk developing device 401 during non-image formation as the developing bias of the Bk image during the development of the M, C and Y images. Is changed to Vdc = + 600V. This makes it possible to prevent the transfer of Bk toner to the image-exposed portion by maintaining Vback = 200 V or more in absolute value with respect to the electrostatic latent image in color in any case.

FIG. 2 shows the case of forming a color image by reversal development. In this case, the photosensitive drum 1 is -400V
And the developing bias is applied in the negative direction. Therefore, in the color image formation in the M, C, and Y developing devices (402, 404, 403) in the rotary developing device 4b, Vd = -400 for all three colors, as shown in FIG.
V and Vl = -50V are set. Also, Vc in absolute value
Since ont = 150V and Vback = 200V in absolute value are required, Vdc = −200V (2000 Hz, 2
000 Vpp, 50% duty superimposition).

Also at this time, the Bk developing device 40 at the time of non-image formation
1, the bias applied as the developing bias of the Bk image during the M, C, and Y development was Vdc = + 150V.
Change to. As a result, with respect to the electrostatic latent image in color, the absolute value of Vback =
By maintaining the voltage of 200 V or more, it is possible to prevent the Bk toner from transferring to the image exposure portion.

That is, in both normal development and reversal development, the bias voltage applied during non-image formation in the first developing device is changed during image formation in the second developing device, and in particular, the photosensitive voltage is changed. The potential difference of any latent image portion formed on the drum is changed to a predetermined potential difference, here, Vback = 200 V in absolute value, so that when the non-image formation of the first developing device is performed, The toner included in the toner does not transfer to the photosensitive drum.

Further, since the Bk developing device adopts the jumping developing system, it is supported without contact with the drum,
There is almost no influence on the drum when the developing bias is changed, for example, transfer of attachment of magnetic particles to the photosensitive drum in two-component development.

As described above, without changing the main body configuration, Bk
Color mixing of Bk toner is prevented only by making the developing bias variable when the developing device 401 is not created.

The bias voltage applied to the fixed developing device 4a during non-image formation is after the completion of the Bk toner image developing process, and the post-rotation process in the fixed developing device 4a is performed.
This can be performed in the pre-rotation step or between transfer materials when images are continuously formed on a plurality of transfer materials, and when the image is not formed with respect to the Bk toner, and the second developing device is a rotary developing device. This is performed during image formation in the device 4b.

In the first embodiment, M, C, Y and B are actually used.
When a 1-million-sheet durability test was conducted in the formation of a full-color image with the k toner, no image defect due to color mixing of the Bk toner occurred, and a good image could be formed.

Embodiment 2 In this embodiment, the Bk developing device 4 is used for the purpose of further improving the image quality.
No. 01 non-imaging developing bias is proposed to be only DC voltage, which will be described below.

The developing bias structure of the Bk developing device 401 has been described with reference to FIG. 3A in the previous embodiment. However, in reality, the bias power supply device 46 to which the Bk developing device 401 is connected has an AC voltage (3700 Hz, 1500 V) for realizing jumping development as shown in FIG.
pp, 50% overlap). By this, Bk
The development contrast is not always Vcont = 200V, and the maximum contrast is Vcmax (= Vcont + 1
/ 2Vpp) = 950V.

Therefore, as shown in FIG.
The developing bias power source 46 of No. 01 can be switched to the bias power source 47 of only DC voltage, and when not imaged, by switching to the DC power source 47 by the control means (not shown), the electric field strength is further reduced, and Bk to the drum 1 is increased. Toner can be reduced.

Third Embodiment In addition to the first and second embodiments, this embodiment further proposes that the developing bias of the Bk developing device 401 is made variable at the time of non-image formation and is separated from the drum at the time of image formation. , As described below.

As described above, the Bk developing device 401 has the SD:
The thickness is set to 250 μm in order to achieve a reflection density of 1.50 in a solid image. Therefore, FIG.
As shown in, the Bk developing device installed in the fixed developing device 4a is parallel to the photosensitive drum 1 (direction of arrow R4c).
By controlling the pressure applied to the S-Dgap
Separate. As a result, the electric field strength between the photosensitive drum 1 and the developing sleeve 41 is reduced, and the transfer of Bk toner onto the photosensitive drum due to electrostatic force can be prevented.

Conventionally, the developing sleeve 4 of the Bk developing device 401
Even when 1 is not in contact with the photosensitive drum 1, the Bk toner is transferred to the photosensitive drum 1 to mix colors during Y, M, and C toner image formation by the rotary developing device 4b that is the second developing device. However, as described in the first and second embodiments, the bias voltage is switched to the Bk developing device 401 during non-image formation, and the Bk developing device 401 is further changed as in the present embodiment.
Is separated from the image carrier, the transfer of Bk toner to the photosensitive drum 1 can be prevented reliably.

In the first to third embodiments, the second developing device has been described as a rotary developing device. However, the configuration of the second developing device is not limited to this. It may be arranged so as to sequentially face the image bearing member by movement, and the number of developing devices and the types of colors are not limited to this.

Although the image forming apparatus using the intermediate transfer member has been described in the first to third embodiments, the transfer material may be carried on the transfer material carrying member and transferred directly from the image carrying member to the transfer material. .

Needless to say, the magnitude of various biases in the image forming process is not limited to this.

[0071]

As described above, the image forming apparatus of the present invention develops an image by developing a latent image on the image carrier by applying a bias between the image carrier and the image carrier. A first developing device and a second developing device for forming a developed image on a carrier; and a bias power supply device connected to the first developing device and capable of varying a bias applied voltage. In the developing device, a plurality of developing devices containing developers of different colors are rotated and sequentially brought close to the image carrier to perform a developing operation of a latent image corresponding to each developer color. The bias voltage applied during non-image formation of the developing device of
When the image is formed in the second developing device, it is changed so as to be different from that when the image is formed in the first developing device, and in particular, the potential of the latent image portion formed on the image carrier is
Since the toner is changed so as to have a predetermined potential difference, it is possible to reduce waste of toner, suppress changes in the main body structure as much as possible, prevent toner color mixing, and provide a good image.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing an example of a potential relationship established between a photosensitive drum and a developing sleeve during image formation in a fixed developing device and a rotary developing device according to the present invention.

FIG. 2 is an explanatory diagram showing another example of the order relation of the potentials established between the photosensitive drum and the developing sleeve during image formation in the fixed developing device and the rotary developing device according to the present invention.

FIG. 3A is a sequence of potentials established between a photosensitive drum and a developing sleeve in a developing operation during image formation of a fixed developing device and FIG. 3B is a rotating developing device. It is explanatory drawing which shows a relationship.

FIG. 4 is a schematic configuration diagram showing an example of a Bk developing device according to the present invention.

FIG. 5 is a schematic configuration diagram showing another example of the Bk developing device according to the present invention.

FIG. 6 is a schematic configuration diagram showing another example of the Bk developing device according to the present invention.

FIG. 7 is a schematic configuration diagram showing an example of a configuration of an image forming apparatus of the present invention.

FIG. 8 is a partial sectional view of a photosensitive drum according to the present invention.

FIG. 9 is an explanatory diagram showing the order relation of the potentials established between the photosensitive drum and the developing sleeve during image formation in the conventional rotary developing device.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Photosensitive drum (image bearing member) 3 Exposure means 4a Fixed developing device (first developing device) 4b Rotating developing device (second developing device) 5 Intermediate transfer belt 6 Turn roller (primary transfer means) 8 Photosensitive drum cleaner 40 Developing container 41 Developing sleeve (developer carrier) 42 Magnet (magnet) 43 Developing blade (developer regulating member) 44 Stirring member 45 Magnetic one-component toner (magnetic one-component developer) 46 Bias power supply device 47 DC bias power supply device 401 Bk developing device 402 M developing device 403 Y developing device 404 C developing device

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/14 G03G 21/00 372 F term (reference) 2H027 DA02 DA03 DA04 EA05 EA15 EB04 ED09 EE01 EF07 EF11 EF12 2H030 AA04 AD17 AD19 BB01 BB22 BB33 BB34 BB42 BB46 BB63 BB71 2H073 AA01 AA05 BA04 BA09 BA13 BA23 BA41 CA02 CA22 2H077 AD02 AD06 AD13 AD17 AD24 AD36 BA09 DB08 DB14 DB18 EA13 EA16 FA19 GA13 GA17

Claims (13)

[Claims] 1. A bias is applied between an image carrier, an exposing unit that exposes the surface of the image carrier based on image information to form a latent image, and a bias is applied between the image carrier.
A first developing device and a second developing device that develop the latent image on the image carrier with a developer to form a developed image on the image carrier, and are connected to the first developing device. And a bias power supply device capable of varying the applied voltage of the bias, and the second developing device rotates a plurality of developing devices containing developer of different colors, and sequentially applies the image to the image carrier. In an image forming apparatus that performs a developing operation of the latent image corresponding to the color of each developer on the image carrier in close proximity, the bias voltage applied during non-image formation of the first developing apparatus is The image forming apparatus is characterized in that when the image is formed in the second developing device, it is changed so as to be different from that when the image is formed in the first developing device. 2. The bias voltage applied at the time of non-image formation of the first developing device is the bias voltage of the latent image portion formed on the image carrier at the time of image formation of the second developing device. The image forming apparatus according to claim 1, wherein the image forming apparatus is changed to have a predetermined potential difference with respect to the potential. 3. The image forming apparatus according to claim 1, wherein the first developing device is arranged between the second developer device and the exposing unit. 4. The bias power source for applying the bias to the first developing device outputs a bias in which an AC voltage is superimposed on a DC voltage.
Two or three image forming apparatuses. 5. The developing bias power source for applying a bias to the first developing device outputs a bias of only a DC voltage during non-image formation.
The image forming apparatus according to any one of items 1 to 4. 6. The first developing device has a developing device, and the developing device includes a developing container for accommodating a developer, and a developer carrying member for carrying the developer from the developing container to the image carrier. And the developer carrying member is in non-contact with the image carrying member,
The magnetic field generating means is provided inside, and the layer thickness of the developer layer on the developer carrier is thinner than the distance between the developer carrier and the image carrier in the developing section. 1
The image forming apparatus according to any one of items 1 to 5. 7. A developer regulating member for regulating the layer pressure of the developer layer of the developer carrying member included in the first developing device,
The image forming apparatus according to claim 6, wherein the image forming apparatus is a magnetic material. 8. The image forming apparatus according to claim 1, wherein the developer used in the first developing device is a one-component developer containing a magnetic material. . 9. The image forming apparatus according to claim 1, wherein the image bearing member is an electrophotographic photosensitive member having a surface layer containing amorphous silicon. 10. The developing process by the first developing device or the second developing device is reversal development for the latent image formation, according to any one of claims 1 to 9. Image forming device. 11. The bias voltage applied to the first developing device during non-image formation is after the completion of the developing process of the first developing device. The image forming apparatus according to item. 12. The bias voltage applied to the first developing device during non-image formation is a post-rotation step or a pre-rotation step, or when images are continuously formed on a plurality of transfer materials. The image forming apparatus according to any one of claims 1 to 10, wherein the time is between transfer materials. 13. The first developing device has a developing device that can be separated from the image carrier, and separates the developing device from the image carrier during non-image formation.
The image forming apparatus according to any one of 1 to 12.