JP2668228B2 - Color image forming equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color image forming apparatus such as a color printer or a color copying machine, and more particularly, to a method in which toner is not transferred to an image portion during non-development, and The present invention relates to a color image forming apparatus that prevents toner from entering the body. [Prior Art] An electrophotographic image forming apparatus exposes a photosensitive member surface charged in advance with image light to change the potential of the exposed portion, thereby forming an electrostatic latent image. A toner having a predetermined charge is electrostatically attracted to form a toner image, which is electrostatically transferred to a transfer material. In order to form a color image, the above process is repeated for each color to form a plurality of color toner images on the photoreceptor surface and transfer them all at once to the transfer material, or to rotate a single color toner image several times. Either of the methods of transferring to the copying material is adopted. By the way, in such a color image forming apparatus, while the function of the unused developing device is not stopped while the image forming area on the photoconductor surface passes, unnecessary scattering or mixing of toner occurs. Therefore, in the past, Japanese Patent Laid-Open Nos. 56-14266 and 55
As disclosed in JP-A-137546, there is a device in which a toner is prevented from flying by applying a potential for preventing the toner from flying to a developing sleeve of an unused developing device. Further, as disclosed in Japanese Patent Application Laid-Open No. 55-137546, a separating member is inserted between a developing sleeve and a photoreceptor surface to remove toner on the developing sleeve surface. [Problems to be Solved by the Invention] However, the former method is a method of adsorbing and holding the toner on the developing sleeve, and therefore, in a color image forming apparatus, a toner image of another color is already formed on the front of the developing sleeve. When the exposed photosensitive surface passes, another color toner of the different color toner image may be mixed into the developing sleeve side, and the toner color may become turbid. The latter method has a problem that the mechanism is complicated because the separating member is inserted and removed. SUMMARY OF THE INVENTION The present invention has been made in view of the foregoing, and an object of the present invention is to provide a color image forming apparatus which achieves prevention of toner scattering and prevention of toner mixing with an extremely simple configuration. [Means for Solving the Problems] For this purpose, the present invention has a charging unit, an exposing unit, and a plurality of rotatable developer carriers, and an image bearing member charged by the charging unit. The latent image formed by the exposing means is subjected to non-contact reversal development with toner on a predetermined developer carrier selected from a plurality of developer carriers, and a plurality of toner images are superimposed on the image carrier. In a color image forming apparatus for forming a color image, a developer carrier driving unit for stopping rotation of the developer carrier in a non-development state and rotating the developer carrier in a development state, and the developer carrier in the development state. A voltage in which a first DC voltage and an AC voltage are superimposed on each other to transfer toner from the developer carrier to the image area of the image carrier. In the non-development state, the first DC Second greater than voltage Applying a voltage obtained by superimposing a DC voltage and an AC voltage identical to the developing state to transfer the toner from the developer carrier to the non-image area charged by the charging means of the image carrier, and And a developing bias control means for suppressing transfer of toner from the toner image formed on the image area of the image carrier to the developer carrier by development. Examples Examples of the present invention will be described below. First, 1A
FIG. 1 shows a schematic configuration of a main part of an electrophotographic color image forming apparatus to which the present invention is applied. Reference numeral 1 denotes a photosensitive drum (image carrier) provided with a photoconductive layer (photosensitive surface) on the surface of a conductive drum base maintained at a ground potential, and the photosensitive surface is stripped while rotating in the direction of arrow a. The electrode 2 is charged with a high voltage, and then is exposed to exposure light carrying a yellow color-separated image (a yellow-separated image light or a laser beam modulated by yellow image data of light exposing a document). And exposure is performed, whereby a potential contrast is generated on the photosensitive surface and an electrostatic latent image of a yellow separated image is formed. This electrostatic latent image portion is developed by the developing device 3Y having yellow toner. Then, in a cycle in which the photosensitive drum 1 rotates once, an electrostatic latent image of a magenta color separation image is similarly formed, and the latent image is developed by a developing unit 3M having magenta toner. Further, in the next one rotation cycle, an electrostatic latent image of a cyan color separation image is formed, and the latent image is developed by a developing device 3C having cyan toner. Further, in the next one rotation cycle, an electrostatic latent image of a black color separation image is formed, and the black toner is developed by the developing unit 3B. After the four color toner images are formed on the photosensitive surface of the photosensitive drum 1 in this way, the color toner images are transferred by the transfer pole 4 to the transfer paper fed in the direction of arrow b. The transfer paper on which the transfer has been performed is separated from the photosensitive drum 1 by the next separation pole 5, and the color toner image is fixed by the fixing unit 6 and is discharged. The toner remaining on the photosensitive surface of the photosensitive drum 1 after the transfer is cleaned by the cleaner 7. In addition,
The cleaner 7 is separated so as not to affect the toner image on the photosensitive drum 1 until the transfer is completed. As described above, the color image forming apparatus shown in FIG. 1A performs the toner development of four colors by rotating the drum 1 four times, and performs the operation of transferring the toner image to the transfer paper in one transfer. FIG. 1B shows a similar one-time transfer type color image forming apparatus in which four colors of toner are developed while the drum 1 makes one rotation. For this reason, here, four combinations of the band electrode, the developing device, and the exposing section are arranged around the photosensitive drum 1. 2Y, 2M, 2C and 2B are band electrodes for each color. FIG. 1C also shows a single transfer type color image forming apparatus similar to that shown in FIG. 1C, except that toner development of four colors is performed while the drum 1 rotates twice. 2YC is a band electrode for yellow and cyan, 2MB is a band electrode for magenta and black,
Is the first exposure light, and is the second exposure light. FIG. 2 is a diagram showing in detail the portion of the developing device 3 (3Y to 3B). The developing sleeve 31 (developer carrier) rotates in the direction of the arrow d opposite to the internal magnetic roll 32 so that the toner generated in the form of a magnetic brush on its surface faces the photosensitive surface of the photosensitive drum 1 in a non-contact manner. . The rotation direction of the developing sleeve and the magnetic roll is not particularly limited to the illustrated example, and the developing sleeve and the magnetic roll may be rotated in the opposite direction or stopped in the case of the magnetic roll. As these driving means, a combination of conventionally known motors and a clutch or the like as necessary is used, and it is required that the driving means can be arbitrarily driven / stopped. A different bias voltage V1 or V2 is applied to the developing sleeve 31 by the switching means 33. FIG. 3 is a diagram showing a circuit for generating the developing bias voltages V1 and V2. After the alternating voltage oscillated by the oscillator circuit 10 is boosted to a predetermined voltage by the booster circuit 11,
Voltages output from different output terminals are smoothed by the smoothing circuits 12 and 13 and output as DC components Va and Vb (<Va). The AC voltage oscillated by another oscillation circuit 14 is also boosted by the booster circuit 15, and the AC voltage Vac output therefrom is superimposed on the DC voltages Va and Vb described above. Therefore, the output voltage V
1, V2 is as follows. V1 = Va + Vac V2 = Vb + Vac In the present invention, the bias of the developing sleeve 31 is controlled by using at most these two types of voltages to prevent toner scattering and toner mixing therefrom. FIG. 4A shows a process for forming a three-color image by the single transfer method shown in FIG. 1A (however, the black developing device 3B is not used) using the developing devices 3Y, 3M and 3C. It is a timing chart. Here, reversal development (negative charge toner) in which the potential of the photoreceptor surface is -800v is adopted, rotation is stopped except for the developing sleeve that is currently performing the developing operation, and the stopped developing sleeve is
A voltage (-1000v) larger than the DC bias voltage (-600v) applied to the developing sleeve during development is applied. AC bias is a constant 700v (effective value). Therefore, a larger potential difference occurs between the stopped developing sleeve and the charged and unexposed photoconductor surface than in the case of normal development. A strong electric force acts in the direction, so that most of the toner on the photoconductor surface side of the developing sleeve whose rotation has stopped is transferred to the photoconductor side. Therefore, the toner on the side of the stopped developing sleeve facing the photoconductor is almost completely consumed, and the surface continues to be free of toner, so that toner scattering does not occur. When the already developed portion (image forming area) passes in front of the developing device after the toner transfer has occurred, the toner image of another color on the surface of the photoreceptor is stopped. Since the toner is electrostatically pressed from the side, there is no danger that the toner of the other color will migrate to the stopped developing sleeve side, and no toner is mixed. For the same reason, impurities floating in the apparatus and having charges of the same polarity as the toner are not attracted to the developing sleeve. In FIG. 4B, patch exposure P is performed on the portion after the image exposure portion, and the DC bias of the developing sleeve in a stopped state is -1200 V higher than that during rotation, and the AC bias is 800 V. FIG. 4C is a timing chart when the one-time transfer method shown in FIG. 1C is adopted. Here, first, the latent image formed by the first exposure light is developed by the developing device 3Y, and the latent image formed by the next exposure light is developed by the developing device 3M. The formed latent image is developed by the developing device 3C, and the latent image formed by the next exposure light is developed by the developing device 3B. The stopped developing sleeve other than during the developing is set to a DC bias (−1200 v) higher than the DC bias (−600 v) of the developing sleeve. [Effects of the Invention] As described above, according to the present invention, the developer carrier is stopped except during the developing operation, and an electric field for transferring the toner to the image carrier side during the stop is formed. The toner on the portion of the body facing the image bearing member disappears, and thereafter, the toner does not migrate from the sleeve to the image bearing member side. Therefore, the toner is lost for the two-component developer, and only the carrier remains on the image carrier side of the developer carrier, and for the one-component developer, the developer itself is eliminated. Therefore, the toner does not spill out from the developer carrier, so that toner contamination can be prevented when the apparatus itself is moved, when the drum or the developing device is pulled out, and the image quality is prevented from deteriorating due to contamination of the optical system. it can. Further, since the amount of toner that is exposed to the outside is small, the moisture resistance is improved. Furthermore, toner consumption outside the image area is reduced. Further, in the case of the two-component developer, the carrier is less attached to the photosensitive surface. Also, since the developing bias during non-development is an electric field that does not always attract the toner to the developing sleeve side, even if a different color toner image on the image carrier passes in front of the developer carrier, the different color is used. No toner is mixed in, and there is no fear of color turbidity. For the same reason, there is no possibility that impurities and the like floating in the apparatus and having the same charge as the toner are mixed into the developer carrier. Furthermore, in the present invention, no special mechanical part for removing the toner is used, and the developing bias only switches the DC voltage superimposed on the AC voltage. By increasing the amplitude of the AC voltage of the developing device in the developing state, the toner image already formed on the photoconductor is not disturbed.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. 1A to 1C are schematic structural views of an image forming apparatus to which the present invention can be applied, FIG. 2 is a sectional view of a developing device, FIG. 3 is a circuit diagram of a developing bias circuit, 4A to 4C are timing charts of the image forming process. 1 ... Photoconductor drum, 3Y, 3M, 3C, 3B ... Developer, 31 ...
... Developing sleeve.

   ────────────────────────────────────────────────── ─── Continuation of front page                   (56) References JP-A-62-71970 (JP, A)                 JP-A-61-254959 (JP, A)                 JP-A-62-71969 (JP, A)                 JP-A-61-250665 (JP, A)                 JP-A-58-187962 (JP, A)                 JP-A-61-277977 (JP, A)                 JP-A-57-97551 (JP, A)                 JP-A-61-254960 (JP, A)

Claims (1)

(57) [Claims] A charging unit, an exposing unit, and a plurality of rotatable developer carriers, and a latent image formed by the exposing unit on the image carrier charged by the charging unit is transferred from the plurality of developer carriers. In a color image forming apparatus which performs non-contact reversal development with toner on a selected predetermined developer carrier and forms a color image by superimposing a plurality of toner images on the image carrier, A developer carrier driving unit that stops rotation in a non-development state and rotates in a development state; and applies a voltage in which a first DC voltage and an AC voltage are superimposed on the developer carrier in the development state. And transferring the toner from the developer carrier to the image area of the image carrier. In the non-development state, a second DC voltage larger than the first DC voltage and the same AC as in the development state Superimposed voltage Pressure to transfer the toner from the developer carrier to the non-image area of the image carrier charged by the charging means, and the toner formed in the image area of the image carrier by the preceding development A developing bias control unit configured to suppress transfer of toner from an image to the developer carrying member.