JPH10171223A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a multicolor image of high quality by simply and inexpensively preventing irregularities in an image caused by a color mixture and magnetic carriers, when a latent image on an image carrier is developed by plural two-component contact developing units arranged around the image carrier. SOLUTION: At the time of preliminary rotation in an image forming process, a bias obtained by superimposing an alternating current on a direct current is applied to the developing sleeve 60 of a developing unit except the first color, that is, from the second color, out of plural developing unit, without rotating the developing sleeve 60, so that a developer 62 on the developing sleeve 60 is reciprocated between it and a photoreceptor drum 1, to eliminate the developer 62 from the inside of a developing nip G. After that, an image of the first color is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using electrophotography, such as a copying apparatus, an image recording apparatus, a printer, and a facsimile, and more particularly, to an image forming apparatus in which color mixing during development is eliminated.

[0002]

2. Description of the Related Art FIG. 4 is a schematic diagram of a digital full-color copying machine. The copier has a photosensitive drum 1 as an image carrier, and has four developing units 4Y, 4Y near its periphery.
A developing device 4 having C, 4M, and 4K is arranged.
The developing units 4Y, 4C, 4M, and 4K are yellow,
The contact type two-component developing method is used for each color of cyan, magenta, and black and uses a two-component developer in which a non-magnetic toner and a magnetic carrier are mixed.

[0005] First, a copying machine converts a document image 30 into a CCD 4 image.
1, the analog image signal obtained is amplified to a predetermined level by an amplifier 42, and is converted into an 8-bit digital image signal (0 to 256 gradations) by an A / D converter 43. Next, this digital image signal is converted to a gamma converter (256
Γ-corrected by a conversion unit 45 composed of a byte RAM and performing a digital conversion by a lookup system, and then input to a D / A converter 46. The image signal converted into an analog signal again by the D / A converter 46 is compared with a signal of a predetermined cycle generated from a triangular wave generation circuit 49 by a comparator 47 and pulse width modulated.

The binarized image signal subjected to the pulse width modulation is directly input to a laser drive circuit 50 and used as an on / off control signal for light emission of a laser diode 51. The laser light emitted from the laser diode 51 is scanned in the main scanning direction by a well-known polygon mirror 3a, and passes through an f / θ lens 3b and a reflection mirror 3c.
Irradiation is performed on the photosensitive drum 1 rotating in the direction of the arrow R1, and an electrostatic latent image is formed on the surface of the photosensitive drum 1.

[0005] The photosensitive drum 1 is first uniformly discharged by the exposure device 11 and then uniformly charged negatively by the charger 2. Thereafter, an electrostatic latent image corresponding to the image signal is formed on the surface by receiving the laser light. The developing devices 4Y to 4K for the respective colors of the developing device 4 develop the electrostatic latent image on the photosensitive drum 1 by a well-known reversal developing method, that is, the portion on the photosensitive drum 1 which has been subjected to the charge removal by the laser beam is negatively charged. The developed toner is adhered and developed to be visualized as a toner image. FIG. 5 shows the relationship between the surface potential of the photosensitive drum 1 and the development contrast in such reversal development.

In FIG. 5, Vd is the surface potential of the photosensitive drum 1 negatively charged by the charger 2. V00 is A
The laser is driven by the image signal of 00H (0 level) digitized by the / D converter 43 and the surface potential of the photosensitive drum irradiated with the laser beam, and Vff is similarly FF
This is the surface potential of the photosensitive drum when irradiating laser light in the case of an image signal of H (256 levels). At the time of development, each developing device 4Y-4
A DC voltage of Vdev and an AC voltage (for example, frequency 2 kHz, peak-to-peak voltage 2 kVp
p) is applied, and | Vdev−V
Development corresponding to the development contrast indicated by xx | is performed.

Therefore, assuming that | Vdev-Vff | shown in FIG. 5 is an appropriate contrast potential Vcont and a developing density developed by Vcont is Dmax, generally, 1.2 to 1.8.
It can be seen that the value of Vcont should be set to an appropriate value in order to obtain a desirable image density. In addition,
The fog removal potential Vback in FIG. 5 is for completely removing the fog on the white background portion of the image irradiated with the light amount of 00H.

As shown in FIG. 4, the toner image formed by the negative toner formed on the photosensitive drum 1 by the above development is transferred onto a transfer material (generally paper) P carried on a transfer drum 5a by a transfer charger. Transcribed by the action of 5b.
After the transfer, the photosensitive drum 1 is subjected to the above-described image forming process again after the residual toner remaining on the surface is scraped off by the cleaner 6. By repeating this image forming process for each color, a full-color image in which four color toner images are superimposed and transferred on the transfer material P is formed.

[0009]

However, in the conventional image forming apparatus shown in FIG. 4, since the developing units 4Y to 4K employ a developing system in which the developer on the developing sleeve is brought into contact with the photosensitive drum 1, the photosensitive drum is not used. When the first color, for example, the yellow toner image of the first color passes through the developing devices 4C to 4K for the second and subsequent colors, the developers on the developing sleeves of the developing devices 4C to 4K come into contact with the yellow toner image, and There is a fear that cyan, magenta and black toners of the second and subsequent colors adhere to the toner image, or yellow toner adheres from the photosensitive drum 1 to the developing sleeves of the developing devices 4C to 4K, so that a so-called color mixing phenomenon occurs. Was. The reason will be described with reference to the potential model of FIG.

FIG. 6 schematically shows the surface potentials of the photosensitive drum 1 during the image forming process for the first color and the developing sleeves of the developing units 4C, 4M, and 4K used for the image forming processes for the second and subsequent colors. FIG. The surface potential of the photosensitive drum 1 is changed from V00 to Vff by the exposure of the first color.
Developing devices 4C to 4K used in the image forming process for the second and subsequent colors
The surface potential of the developing sleeve becomes Vss induced by the surface potential of the photosensitive drum.

For this reason, when the image portion of the first color on the surface of the photosensitive drum 1 passes through the developing devices 4C to 4K for the second and subsequent colors, the portion of the image portion on the surface of the photosensitive drum 1 which has a higher potential than Vss. Then, toner adheres from the developer on the developing sleeves of the developing devices 4C to 4K, and color mixing occurs in the first color toner image on the photosensitive drum 1. In addition, the toner of the first color in a portion having a potential lower than Vss in the image portion on the surface of the photosensitive drum 1 adheres to the developing sleeves of the developing devices 4C to 4K, and the toner of the developing devices 4C to 4K is mixed.

Further, when the toner image of the first color on the photosensitive drum 1 passes through the locations of the developing devices 4C to 4K for the second and subsequent colors, the toner image is rubbed by the developer on the developing sleeves of the developing devices 4C to 4K. There is also a problem that the image is disturbed and streaky traces are generated on the first color toner image and consequently on the multicolor image.
When the second and subsequent developing units, for example, the second developing unit 4C are the first-color developing units, the first-color electrostatic latent image formed on the photosensitive drum 1 is used as the first developing unit. When passing through the portion 4Y, the first color electrostatic latent image is disturbed by the rubbing of the developer on the developing sleeve of the developing device 4Y.
The problem of image streaks occurs.

As a method for solving the above problem, developing units 4Y to 4K are detachably mounted on the photosensitive drum 1 so that
There is a method of separating a developing sleeve of a developing device from a photosensitive drum other than the developing sleeve used for developing a color image.

However, this method has a problem that the apparatus configuration is complicated and the cost is increased, and the image is disturbed due to a shock at the time of attaching / detaching the developing unit.

An object of the present invention is to provide a method for developing a latent image formed on an image carrier by a plurality of two-component contact developing devices arranged in the vicinity of the periphery of the image carrier. It is an object of the present invention to provide an image forming apparatus capable of obtaining a high-quality multi-color image by preventing image disturbance due to simplicity and low cost.

[0016]

The above object is achieved by an image forming apparatus according to the present invention. In summary, in the present invention, a plurality of developers are arranged in the vicinity of the image carrier along the rotation direction, and each developer has a different color developer composed of a magnetic carrier and a non-magnetic toner. A two-component contact developing device for developing a developer by contacting the image bearing member, forming a latent image on the image bearing member every one rotation of the image bearing member, and forming the latent image on a plurality of developing devices. Develop with the corresponding color developer,
An image forming step of transferring the obtained toner image onto a transfer material is repeated for a plurality of colors during a plurality of rotations of the image carrier, and a multi-color image obtained by superimposing a plurality of color toner images on the transfer material is obtained. In the image forming apparatus for obtaining an image, when the image carrier is pre-rotated before the first color image forming process is performed, the developer carrier of the developing device other than the developing device used for the first color image formation is not rotated. An image forming apparatus is characterized in that a bias obtained by superimposing an AC voltage on a DC voltage is applied thereto.

According to the present invention, further, during the first color image forming step, the developer carrier of the developing device other than the developing device used for forming the first color image is not rotated, and the toner is charged on the developer carrier. A DC voltage having the same polarity as the polarity can be applied, and the DC voltage is higher in absolute value than the surface potential of the image carrier. Furthermore, at the time of post-rotation of the image carrier after performing the image forming process of the final color, a predetermined electrostatic latent image is formed on the image carrier, and the developing device other than the developing device used in the image formation of the first color is developed. Without rotating the developer carrier of the developing device, a bias in which an AC voltage was superimposed on a DC voltage was applied to the developing device, and the developer adhered to the developing device other than the developing device used in the first color image formation. The toner can be returned to the image carrier.

Further, according to the present invention, the charge polarity of the toner is negatively charged. The first developing device among the plurality of developing devices arranged in the rotation direction of the image carrier performs the first color development, and the second and subsequent developing devices can perform the second color development and thereafter. Further, of the plurality of developing devices arranged in the rotation direction of the image carrier, any one of the second and subsequent developing devices develops the first color, and the other developing devices develop the second color and thereafter. be able to. The image carrier may be a rotatable cylindrical drum having a photosensitive layer on the surface, or a rotatable endless belt.

[0019]

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

Embodiment 1 FIG. 1 is a sectional view showing a schematic configuration of an embodiment of an image forming apparatus according to the present invention, and shows a color image forming apparatus. The present image forming apparatus has a digital color image reader unit at the top and a digital color image printer unit at the bottom.

In the reader section, the original 30 is placed on an original platen glass 31 and exposed and scanned by an exposure lamp 32 so that a reflected light image from the original 30 is condensed on a full color sensor 34 by a lens 33 and color separation is performed. Obtain an image signal. The color separation image signal is supplied to an amplifier (not shown).
Are processed by a video processing unit (not shown) and sent to a printer unit.

In the printer section, a photosensitive drum 1, which is an image carrier, is rotatably supported in the direction of an arrow. Around the photosensitive drum 1, a pre-exposure lamp 11, a corona charger 2, a laser exposure optical system 3, a potential sensor 12, four developing units 4Y, 4C, 4M, and 4K of different colors, an on-drum light amount detecting unit 13, a transfer device 5, and a cleaning unit 6 are arranged.

In the laser exposure optical system 3, an image signal from a reader unit is converted into an optical signal by a laser output unit (not shown), and the converted laser light is reflected by a polygon mirror 3a, and is converted into a lens 3b and a mirror. 3c, and is projected on the surface of the photosensitive drum 1.

The printer unit includes a photosensitive drum 1 for forming an image.
Is rotated in the direction of the arrow, and the photosensitive drum 1 after the charge is removed by the pre-exposure lamp 11 is uniformly charged by the charger 2 to irradiate a light image E for each separation color. Form a latent image.

Next, a predetermined developing device is operated to develop the latent image on the photosensitive drum 1 by the well-known reversal development to form an image using a resin-based toner on the photosensitive drum 1, ie, a toner image. I do. On the other hand, the recording material is conveyed from the recording material cassette 7 to the image transfer unit facing the photosensitive drum 1 via the conveyance system and the transfer device 5, and the toner image formed on the photosensitive drum 1 is recorded in the image transfer unit. Is transferred onto the material.

In the present embodiment, the transfer device 5 includes a transfer drum 5a.
And a transfer charger 5b and an adsorption charger 5c around the transfer charger 5b.
And an attraction roller 5g, an inner charger 5d, an outer charger 5e, and the like opposed thereto. The transfer drum 5a is supported so as to be driven to rotate, and a recording material carrying sheet 5f is integrally extended in a cylindrical shape in a peripheral opening area. As the recording material supporting sheet 5f, a dielectric sheet such as a polycarbonate film is used. The recording material is an adsorption charger 5
Due to the action of c and the suction roller 5g, the sheet is electrostatically adsorbed on the surface of the recording material carrying sheet 5f, and is repeatedly rotated through the image transfer section according to the rotation of the transfer drum 5a.

The toner image on the photosensitive drum 1 is moved to the image transfer section as the photosensitive drum 1 rotates,
The toner image is transferred onto the recording material passing through the image transfer portion by the transfer of the transfer member a by the operation of the transfer charger 5b. In this manner, a desired number of color toner images, in this example, four color toner images are superimposedly transferred onto the recording material on the transfer drum 5a, and a full-color image is formed.

In the case of forming a full-color image on one side, after the transfer of the four-color toner image onto the recording material is completed, the separation claw 8
a, the recording material is separated from the transfer drum 5a by the action of the separation push-up roller 8b and the separation charger 5h, and the separated recording material is sent to the heat roller fixing device 9 to be fixed, thereby completing the image formation, and the one-sided full-color image Is discharged onto the tray 10. After the transfer, the photosensitive drum 1 is cleaned by a cleaning device 6 to remove the residual toner on the surface, and then subjected to the image forming process again.

When a full-color image is to be formed on both sides of the recording material, the conveyance path switching guide 19 is driven immediately after the recording material exits the fixing device 9, and the recording material is reversed through the conveyance vertical path 20. 21a. Thereafter, by the reverse rotation of the reversing roller 21b, the recording material is retreated in a direction opposite to the direction in which the recording material is fed, with the rear end when fed in as the head,
It is stored in the intermediate tray 22. Thereafter, the recording material is sent from the intermediate tray 22 to the transfer drum 5a, and a full-color image is formed on the other surface of the recording material again by the above-described image forming process, thereby obtaining a recording material of a double-sided full-color image.

In order to prevent powder from adhering to the recording material carrying sheet 5f of the transfer drum 5a and to prevent oil from adhering to the recording material, the fur brush 14 opposed to the recording material carrying sheet with the fur brush 14 interposed therebetween. By the operation of the backup brush 15, the oil removing roller 16 and the backup brush 17, the recording material carrying sheet 5f is cleaned. Such cleaning is performed before or after image formation, and is performed at any time when a jam (paper jam) occurs.

In this embodiment, the gap between the recording material carrying sheet 5f and the photosensitive drum 1 is reduced by operating the eccentric cam 25 at a desired timing and operating the cam follower 5i integrated with the transfer drum 5a. The configuration can be set arbitrarily. For example, during standby or when the power is off, the interval between the transfer drum 5a and the photosensitive drum 1 is increased.

In the present invention, a special developing process is performed during the pre-rotation of the photosensitive drum 1 before performing the above-described four-color image forming process, that is, before performing the first-color image forming process, thereby performing color mixing of images. And so on. Hereinafter, the developing process during the pre-rotation will be described.

During the pre-rotation of the photosensitive drum 1, a plurality of developing devices 4
Developing devices for the second and subsequent colors other than the developing devices used for developing the first color image formation of Y to 4K, for example, the second, third, and fourth cyan and magenta other than the first yellow developing device 4Y , Black developing units 4C, 4M, and 4K
A bias in which the developing sleeve is not rotated and DC is superimposed on DC is applied to the developing sleeve. In this example, −
Apply 350V DC + 2kHz, 2kVpp AC. The surface of the photosensitive drum 1 is uniformly maintained at a predetermined potential, in this example, -470V.

Due to the AC electric field of the superimposed bias, FIG.
As shown in (a), the developer 62 on the developing sleeve 60 of the developing device for the second and subsequent colors, together with the toner and the magnetic carrier, is located between the photosensitive drum 1 and the developing sleeve 60 (SD).
). At this time, since both the photosensitive drum 1 and the developing sleeve 60 have a convex curved surface at the opposing portion, as shown in FIG.
Is almost linear in the vicinity of the development nip G, but curves outwardly convex toward the outside between S and D.

In the region where the electric field lines h are curved, FIG.
As shown in (b), the developer located at the point a1 on the line of electric force h1 has a vector velocity V1 in the tangential direction of the line of electric force h1 at the point a1. At the next moment, when the developer moves to the point a2 on the line of electric force h2, it has a vector velocity V2 in the tangential direction of the line of electric force h2 at the point a2. Then, the developer moves from the point a2 in the direction of V1 + V2 obtained by combining the velocities V1 and V2 in a vector manner, that is, in the direction outside the vector V2.

As described above, when the developer moves from the developing sleeve 60 to the photosensitive drum 1, the developer always moves outward from the center of the developing nip G. Similarly, when returning from the photosensitive drum 1 to the developing sleeve 60, it always moves away from the center of the developing nip G to the outside. For this reason, while the developer 62 on the developing sleeve 60 repeats the reciprocating movement, it spreads from the inside of the developing nip G to both sides in the circumferential direction of the developing sleeve 60, and when the pre-rotation is completed, FIG.
As shown in (2), the developer 62 that comes into contact with the photosensitive drum 1 almost disappears in the developing nip (the area where the photosensitive drum 1 can be developed with the toner) G between SD.

According to the present invention, the developing devices 4C to 4C for the second and subsequent colors are thus obtained until the pre-rotation of the photosensitive drum 1 is completed.
The developer 62 on the K developing sleeve 60 is removed from the developing nip G, and thereafter, image formation of the first color is started. Therefore, when the first color image is formed, even if the first color toner image formed on the photosensitive drum 1 passes through the location of the developing unit for the second and subsequent colors, the photosensitive drum using the developer on the developing sleeve 60 for the second and subsequent colors A mixed color of the first color toner image on
It is possible to prevent the occurrence of image disturbance due to the mixed color of the developers of the second and subsequent developing units by the toner of the second color and the rubbing of the first color toner image by the magnetic carriers of the second and subsequent developing agents. it can.

Further, for example, the second developing device 4C
Is the first color developing device, the first developing device 4Y
Similarly, the developer 62 on the developing sleeve 60
In the developing nip G, the first-color electrostatic latent image formed on the photosensitive drum 1 is not disturbed by the magnetic carrier of the developer when passing through the location of the developing device 4Y. The resulting image can also be prevented from being disturbed.

Therefore, according to the present invention, high-quality images can be stably obtained over a long period of time by preventing color mixing and disturbance of images easily and at low cost.

Embodiment 2 In Embodiment 1, during the pre-rotation of the photosensitive drum 1, the developing units for the second and subsequent colors (for example, except for the first yellow developing unit 4Y) other than the developing units used for developing the first color image formation. While the developing sleeves of the second, third, and fourth cyan, magenta, and black developing units 4C, 4M, and 4K) were not rotated, an AC voltage was applied to the developing sleeves.

In the present embodiment, subsequently, during the formation of the first color image, while the developing sleeves of the developing units for the second and subsequent colors are not rotated, the charging polarity of the first color toner is the same as that of the first color toner. A DC voltage having an absolute value larger than the surface potential of the photosensitive drum 1 during image formation was applied. When the charge polarity of the toner is negative, for example, the DC voltage is -300 V with respect to the surface potential of the image portion of the photosensitive drum 1 of -100 V.

In this manner, even if the toner scatters from the toner image formed on the photosensitive drum 1 during the formation of the first color image and floats near the developing sleeves of the developing units for the second and subsequent colors, It is possible to prevent the toner from mixing in the second and subsequent color developing devices via the developing sleeve, and to more effectively prevent the color mixing.

Embodiment 3 In this embodiment, a predetermined potential is applied to the photosensitive drum 1 at the time of post-rotation of the photosensitive drum 1 after one image forming step (ie, an image forming step of four colors) is completed. Then, an electrostatic latent image of -150 V is formed. Then, without rotating the developing sleeves of the developing units other than the developing unit used for forming the first color image, a developing bias in which an AC voltage is superimposed on a DC voltage is applied thereto, in this example, -350 V DC + 2 kHz, 2 kVpp AC is applied. I did it.

According to this, even if a situation occurs where the first color toner cannot be prevented from adhering to the developing sleeves of the developing devices for the second and subsequent colors due to the prevention of color mixing in the first and second embodiments, the adhered toner is Is transferred onto the photosensitive drum 1 by development, and color mixing of the second and subsequent developing units is prevented again, so that color mixing can be more effectively prevented.

Since the first color toner transferred onto the photosensitive drum 1 is cleaned and removed by the cleaning device 6, there is no problem in forming an image on the next recording material.

Therefore, according to the present embodiment, the effect of preventing color mixture and image disturbance of images can be stably obtained for a longer period.

In each of the above embodiments, the first developing unit 4Y of the plurality of developing units 4Y to 4K arranged in the rotation direction of the photosensitive drum 1 performs the development of the first color, and the second to fourth units. The second developing devices 4C to 4K perform development of the second to fourth colors, but any one of the second and subsequent developing devices performs development of the first color, and the other developing devices perform development of the second and subsequent colors. Development up to the fourth color of the final color can be performed.

Although the photosensitive drum 1, that is, a cylindrical drum having a photosensitive layer on the surface, is used as the image carrier, a rotatable endless belt having a photosensitive layer on the surface may be used.

[0049]

As described above, according to the present invention,
A plurality of two-component contact developing devices are arranged along the vicinity of the image carrier, and form a latent image, develop by the developing device, and transfer the obtained toner image onto a transfer material every rotation of the image carrier. The image forming step is repeated a plurality of times during a plurality of rotations of the image carrier, when forming images of a plurality of colors on the transfer material,
At the time of pre-rotation of the image carrier before performing the first color image forming step, the developer carrier of the developing device other than the developing device used for the first color image formation is not rotated, and the DC voltage is applied to this.
The bias on which the voltage C was superimposed was applied to remove the developer on the developer carrier of the developing device other than the first color from the inside of the development nip and brought into non-contact with the image carrier. , And disturbance of the image due to the magnetic carrier can be easily and inexpensively prevented, and a high-quality multicolor image can be stably obtained over a long period of time.

Further, during the image formation of the first color following the pre-rotation of the image carrier, the developer carriers of the developing units other than the first color have the same polarity as the charge polarity of the toner and the potential of the surface of the image carrier. Since the DC voltage having a large absolute value is applied, it is possible to more reliably prevent color mixing of the image and disturbance of the image when forming the first color image. Further, at the time of post-rotation of the image carrier after performing the image forming process of the final color, a predetermined electrostatic latent image is formed on the image carrier without rotating the developer carriers of the developing units other than the first color. Without rotating the developer carrying members of the developing devices other than the developing device used for the first color image formation,
A bias in which an AC voltage is superimposed on the C voltage is applied to return the toner adhered to the developer carrier of the developing device other than the developing device used for the first color image formation to the image carrier. Prevention can be further achieved.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an embodiment of an image forming apparatus according to the present invention.

FIG. 2 is an explanatory diagram showing that a developer is removed from a developing nip by applying a bias to a developing sleeve in a developing process performed during pre-rotation in the present invention.

FIG. 3 is an explanatory view showing a mechanism of removing from a developing nip by a bias to a developing sleeve in FIG. 3;

FIG. 4 is an explanatory diagram illustrating a schematic configuration of a conventional image forming apparatus.

FIG. 5 is a potential model diagram illustrating development in the image forming apparatus of FIG. 4;

FIG. 6 is a potential model diagram for explaining the reason of the color mixing phenomenon occurring in the development of FIG. 5;

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 photosensitive drum 2 corona charger 3 laser exposure optical system 4Y to 4K developing device 5a transfer drum 60 developing sleeve 62 developer

Claims (9)

[Claims] A plurality of developing devices are arranged in the vicinity of an image carrier along a rotation direction thereof, and each developing device has a developer of a different color composed of a magnetic carrier and a non-magnetic toner. A two-component contact developing device that contacts and develops an image carrier, forms a latent image on the image carrier for each rotation of the image carrier, and develops the latent image into a corresponding color of a plurality of developing devices. The image forming step of developing the toner image on the transfer material and developing the toner image on the transfer material is repeated for a plurality of colors during a plurality of rotations of the image carrier, so that a plurality of color toners are formed on the transfer material. In an image forming apparatus that obtains a multicolor image in which images are superimposed on each other, when the image carrier is pre-rotated before the first color image forming process is performed,
An image forming apparatus, wherein a bias in which an AC voltage is superimposed on a DC voltage is applied to a developer carrying member of a developing device other than a developing device used for forming a color image without rotating the developer carrying member. 2. During a first color image forming process, a developer carrying member of a developing device other than the developing device used for the first color image forming is not rotated, and a DC having the same polarity as the charged polarity of the toner is applied thereto.
The image forming apparatus according to claim 1, wherein a voltage is applied. 3. The image forming apparatus according to claim 2, wherein the DC voltage is higher in absolute value than the surface potential of the image carrier. 4. A developing device other than a developing device used for forming a first color image, wherein a predetermined electrostatic latent image is formed on the image carrier during post-rotation of the image carrier after performing a final color image forming step. Without rotating the developer carrying member of the developing device of FIG.
4. A toner according to claim 1, wherein a bias on which the voltage C is superimposed is applied to return the toner adhered to the developer carrier of the developing device other than the developing device used in the first color image formation to the image carrier. An image forming apparatus according to claim 1. 5. The image forming apparatus according to claim 1, wherein the charge polarity of the toner is negative. 6. A plurality of developing devices arranged in the direction of rotation of the image carrier, wherein a first developing device develops a first color, and a second developing device develops a second color and thereafter. The image forming apparatus according to claim 1. 7. An arbitrary one of a plurality of developing units arranged in the rotation direction of the image carrier after the second one develops the first color, and the other developing units develop the second and subsequent colors. The image forming apparatus according to claim 1, wherein the developing is performed. 8. The image forming apparatus according to claim 1, wherein the image carrier is a rotatable cylindrical drum having a photosensitive layer on a surface. 9. The image forming apparatus according to claim 1, wherein the image carrier is a rotatable endless belt having a photosensitive layer on a surface.