JPS61254959A - Image forming device - Google Patents

Abstract

PURPOSE:To prevent color mixture and to obtain a copy of high quality by scattering part or the whole of a developer to a no-image area on a latent image carrier and removing said part or whole of the developer from the surface of its developing roller. CONSTITUTION:A bias voltage of hundreds - thousands volts which has the same polarity with toner put in each developing unit is applied to a developing roll 5a in a rotation stop state before an electrostatic latent image on the surface of the photosensitive body begins to be developed and developing rolls 4a and 6a which are also in the rotation stop state and positioned on the upstream and downstream sides of said developing roll 5a. Therefore, the no-image area on the surface of the photosensitive drum is developed forcibly by the respective developing rollers 4a, 5a, and 6a. Mixed color toner on the developing roll 5a which is selected by said forcible development is carried to the no-image area on the photosensitive body before the electrostatic latent image on the surface of the photosensitive body reaches the developing rolls, thus preventing an image area from being developed with the mixed color toner.

Description

[Detailed description of the invention]

TECHNICAL FIELD The present invention generally relates to an electrophotographic image forming apparatus, and particularly to an image forming apparatus using two or more monochrome colors,
The present invention relates to an image forming apparatus such as a so-called multi-color electrophotographic copying device, a full-color electrophotographic copying device, or a color recording device of a computer output section. In the following explanation. Although the present invention will be described in connection with a copying apparatus, the present invention is not limited thereto.

[Suetate]Recently, the demand for color copying has increased rapidly not only in specialized fields but also in the general office field, and there is a desire for improved quality of color copied images and low-cost copying devices. One of the important problems that must be solved in order to meet such demands is the development process that visualizes the electrostatic latent images of each color formed on the developing object, that is, the photoreceptor, in full-color and multi-color color copying devices. The problem lies in how the device is configured. In particular, there is an increasing demand for full-color and multi-color color copying bags for single-color copies of two or more colors, so-called multi-color copies. In addition, in a color copying machine having a multi-mode, in which the transfer material that has been copied is stored in an intermediate tray within the machine and can be copied again, multicolor composite copying can be easily performed, and there are many uses for this purpose. Several methods have been proposed as developing methods for obtaining such monochrome copies. One method is to prepare a plurality of developing units each containing a developer of a different color, and to sequentially install the desired developing units in the developing section of the main body of the copying machine. The second method is to arrange a plurality of developing units having developer of each color in parallel along the surface of the photoreceptor, and select one developing unit to perform development. It's strange. The first method is extremely complicated to operate. According to the second method, since a plurality of developing units are arranged around the photoreceptor, the developer may be scattered from the developing roll of the selected developing unit, and the developer powder image on the surface of the developed photoreceptor may be prevented. The surfaces of the developing rolls of other developing units will be contaminated by scattering from the developer. When the next developing operation is performed using a developing roll contaminated with other colors, the quality of the copies is significantly deteriorated. Furthermore, according to the second method, the developer on the developing roll of each developing unit is transferred to the surface of the photoreceptor by an electric field between the photoreceptor and each developing roll, which is generated by an electrostatic latent image formed on the surface of the photoreceptor. This caused a problem as a so-called mixed color development phenomenon occurred. In order to solve this problem, measures have been proposed in the past, such as installing a shutter between the developing roll and the photoreceptor, or moving unselected development units away from the surface of the photoreceptor. This method is complicated, making it difficult to miniaturize the developing device and copying device, and increasing the cost of the copying machine. OBJECTS OF THE INVENTION Accordingly, the main objects of the present invention are to prevent color mixture on a developing roll due to developer scattering without requiring any special equipment, and to prevent color mixture development on an electrostatic latent image on a photoreceptor surface by unselected developing units. An object of the present invention is to provide an image forming apparatus that can achieve the following. Another object of the present invention is to provide an image forming apparatus equipped with a plurality of developing units that has a simple structure and can always produce high-quality color copies. Still another object of the present invention is to provide an image forming apparatus such as a color copying apparatus and a color printing press that is small and inexpensive. 4. The above objectives are fully achieved by the present invention. To summarize, the present invention provides an image forming apparatus in which one or more developing units are arranged along a latent image carrier, and any one developing unit is selected to develop an electrostatic latent image on the surface of the latent image carrier. At least a bias bias pressure is applied to the developing roller of the selected developing unit, and part or all of the developer located on the side of the developing roller facing the latent image carrier is transferred to a non-image area of the latent image carrier. The image forming apparatus is characterized in that part or all of the developer is removed from the surface of the developing roller. FIG. 1 is a schematic diagram partially showing a latent image carrier 1 and a developing roller 4a of a developing unit 4 for explaining the present invention in detail. An electrostatic latent image is formed on the surface of the latent image carrier l by a conventional image forming process. On the other hand, a thin layer of developer, that is, toner T, is formed on the surface of the developing roller 4a, and during the developing process, the toner T on the developing roller 4a flies to the electrostatic latent image on the latent image carrier 1 and performs development. However, as described above, toner t of other colors scattered from other developing units is attached to the surface of the developing roller 4a before the developing operation, and if development is continued as is, color mixing will occur. According to the present invention, the developing roller 4a is rotated as shown in FIG. 2 when the rotation is stopped before the developing operation.
A bias voltage is applied to the latent image carrier l of the developing roller.
A part or all of the toner T located on the side facing the is made to fly to the latent image carrier l, a part or all of the toner T is removed from the surface of the developing roller 4a, and at the same time, a portion of the mixed toner is also developed. It is removed from the roller 4a before the developing process. As a result, a portion of the mixed color toner is removed from the surface of the developing roller 4a, and mixed color development will not occur during subsequent development operations. The timing for applying a bias voltage to the developing roller 4a to cause a portion of the mixed color toner to fly to the latent image carrier is, for example, immediately after the start of the latent image forming process and when the image area on the latent image carrier is on the developing roller 4a. Preferably, the period is before passing through 4a, or until the latent image developing step is completed and the latent image carrier stops moving. In addition, in order to efficiently fly a portion of the mixed color toner to the latent image carrier, an electrostatic latent image is formed in a non-image area prior to the image area of the latent image carrier, and the non-image latent image area is used as a portion of the mixed color toner. Child,
It is effective to develop the film at t. Further, the bias voltage applied to the developing roller 4a will be of the same polarity as the toner T or approximately OV.A more detailed explanation will be given later. Next, the image forming apparatus according to the present invention will be described in more detail based on embodiments. Embodiment 1 As described above, the image forming apparatus according to the present invention can be suitably realized by an image forming apparatus such as a multi-color or full-color electrophotographic copying apparatus, or a color recording apparatus of a computer output section. However, in this embodiment, for example, black and red are used. The present apparatus will be described as being applied to a color electrophotographic copying apparatus for obtaining a three-color image such as blue. Further, such a color electrophotographic copying apparatus employs various electrostatic latent image forming processes, such as the so-called NP process or primary charging-color separation process, which includes the steps of primary charging, secondary charging, seven-color separation exposure, and full-surface exposure. The so-called Carlson process, which includes various steps of decomposition exposure, and others may be used, but in this embodiment, an electrophotographic copying apparatus to which the Carlson process is applied will be described. FIG. 3 is a schematic cross-sectional view of a color electrophotographic copying apparatus for obtaining three-color images of black, red, and blue, which is one embodiment of the image forming apparatus according to the present invention. First, the overall configuration of a color electrophotographic copying apparatus will be described. A photosensitive drum 1 having an electrophotographic photosensitive layer formed on its surface is disposed approximately in the center of the copying apparatus. The photosensitive drum 1 is rotatably and removably attached to a rotation support shaft (not shown) having a rotation center O in a well-known manner. In this embodiment, it is assumed that the photosensitive drum 1 rotates in the direction of arrow X, that is, clockwise in FIG. A primary charger 2 is located approximately directly above the photosensitive drum 1, and a multicolor developing device 3 is located on the right side of the photosensitive drum 1 in FIG. A transfer discharger 9 is disposed approximately directly below the photosensitive drum 1, and a cleaning device 10 is disposed on the left side of the photosensitive drum 1 in FIG. Further, an optical system 11 is arranged in the upper part of the electrophotographic copying apparatus, and an optical system 11 is arranged in the upper part of the electrophotographic copying apparatus, and the original image is transferred onto the photosensitive drum l at an exposure section E located between the primary charger 2 and the multicolor developing device 3. configured to project. Optical system 11 can use any optical system. Further, a potential sensor S for measuring the surface potential of the photosensitive drum l is provided between the exposure position E and the developing device M3, and a potential sensor S for measuring the surface potential of the photosensitive drum l is provided between the primary charger 2 and the cleaning device 10. a light source 12 for erasing the residual charge of
will be provided. Since the color copying apparatus described here is a color electrophotographic copying apparatus for obtaining three-color images of black, red, and blue as described above, the multicolor developing bag R3 has three developing units 4.5 and 6. Although it has a developing unit, the present invention is not limited to this configuration, and it is also possible to have two or more developing units. Of course, the apparatus may have one developing unit. The operation of the color electrophotographic copying apparatus configured as described above will be briefly explained. The photosensitive drum 1 begins to rotate in the direction of arrow X at the start of operation, and is charged by the primary charger 2 . The charged photosensitive drum 1 further rotates, and a light image is slit-exposed at the exposure section E by the action of the optical system 11, so that electrostatic latent images of each color are formed on the photosensitive drum 1. At this time, the surface potential of the photosensitive drum 1 is measured by the potential sensor S. The latent image on the photosensitive drum 1 is then brought to a development area where a multicolor development device 3 is arranged by rotation of the photosensitive drum 1. In the developing area, the electrostatic latent image on the photosensitive drum 1 is developed as a toner image by a selected developing unit in the multicolor developing bag M3. Although each developing unit 4.5.6 may have various structures as long as it is a developing unit having developing rolls 4a, 5a, 6a, in this specification, each developing unit 4.5.6 is used for simplicity of explanation. Reference numerals 6 and 6 are development units of a jumping development type, such as those described in Japanese Patent Publication No. 58-32375 or No. 58-32377, each of which has basically the same structure and houses a monochrome developer. The toner image on the photosensitive drum is transferred to a transfer material 7 fed from a paper feeding device (not shown) in a timely manner by registration rollers 8 in a transfer area Tr where a transfer discharger 9 is arranged. Ru. The transfer material 7 carrying the toner image is then conveyed to a chamber mounting M (not shown) and fixed thereon. After the photosensitive drum 1 is subjected to the action of the cleaning device M10 and the light source 12, the next image forming process is performed again. Next, the operation of the multicolor developing device 3, that is, the developing unit 4.5.6 will be explained. Referring to FIG. 4, the developer unit 4.5.6 has a developer supply container 20 with open sides. Developing rolls 4a, 5a, and 6a are arranged in the openings. The developing rolls 4a and 5a are composed of a fixed magnet 24 and a developing sleeve 26 surrounding the magnet 24 and rotatably attached to the developing container 20. Developing sleeve 26
is made of a non-magnetic material such as aluminum or stainless steel, and rotates as shown by the arrow 28 in the figure. A black, red, or blue toner 30 containing magnetite is stored in the developer container 20 . The color toner 30 is attracted to the surface of the developing sleeve 26 by the magnetic field of the magnet 24 fixed within the developing sleeve 26, and is conveyed from the inside of the developing container to the outside of the developing container toward the photosensitive drum 1 by rotation of the developing sleeve 26. However, the toner 30 is prevented from moving out of the developer container by a blade 32 provided at the opening of the developer container, and is formed into a thin layer on the developer sleeve 26 and charged to the opposite polarity to the electrostatic latent image. The magnetic toner 30 is transferred to the outside of the developer container. Now, it is assumed that among the developing units 4.5.6, the developing unit 5 on the upstream side in the rotational direction of the photosensitive drum 1 is selected and the above-described copying process is started. The developing roll 4a of the developing unit 4, 5.6 having the above configuration,
5a and 6a are held in a stopped state before starting the development of the electrostatic latent image on the surface of the photoreceptor drum. According to the present invention, rotation before starting the development of the electrostatic latent image on the surface of the photoreceptor drum is maintained. The developing roll 5a in a stopped state and the developing rolls 4a and 6a located upstream and downstream of the developing roll 5a, which is also in a stopped state, have the same polarity as the number of toners stored in each developing unit. A bias voltage of 100 volts to several kilovolts is applied. The bias voltage may be adjusted in various ways depending on the amount of charge of the latent image on the photoreceptor drum l, for example as follows. If the surface potential of the non-image area on the photosensitive drum is a bright area potential of about +50V, a bias of about -500V may be used, and if the dark area potential is about +500V, a bias of approximately OV may be used. Such a bias voltage of the same polarity is applied to the developing roll 5a until the latent image in the image area of the photoreceptor drum passes near the developing unit 4 as the photoreceptor drum 1 rotates. Until the developing roll 5a starts rotating, the powder image on the surface of the photoreceptor drum developed by the developing roll 5a is transferred to the developing unit 6 as the photoreceptor drum 1 rotates. It is applied continuously or in pulses (intermittent) until it passes near the area. A bias voltage of several hundred ports to several kilovolts having the same polarity as the toner is sequentially applied from the upstream side. Therefore, the non-image area on the surface of the photoreceptor drum is
a, 6a forcibly develops. By such forced development, the mixed color toner on the selected developing roll 5a is transferred to the non-image area of the photoreceptor before the electrostatic latent image on the surface of the photoreceptor reaches the position of the developing roll, and is transferred to the image area. Development by mixed color toner is prevented. Furthermore, color mixture development on the latent image on the surface of the photoreceptor drum or the developed toner powder image by the unselected developing rolls 4a and 6a is also performed before the latent image reaches the developing roll 4a. This can be prevented by forcibly developing the mixed color toners on the developing rolls 4a and 6a into the non-image area before the image reaches the position of the developing roll 6a. Further, the bias applied to the image area of the unselected developing units 4 and 6 may be a bias of the same polarity as that of the float or toner, or a bias of a different polarity. The voltage may be arbitrarily selected within the range of 0-1000V.
．． 6, a method was adopted in which a bias voltage of several hundred ports having a polarity different from that of the toner contained in the developing unit was applied to forcefully mix colors on the developing roll and prevent mixed color development from occurring on the photoreceptor drum. In this case, it is necessary to remove the mixed toner on the developing roll by applying a bias of the same polarity or approximately OV using the above method before use. In addition, as described above, in the non-image area, a bias of the same polarity as the stored toner is applied to each developing roll to forcibly perform development sequentially from the upstream side, and the mixed color toner on the developing roll is removed. A configuration that switches to apply a bias having a polarity different from that of the stored toner to the developing roll that is not selected for the image area in the next step so as to prevent the development of the electrostatic latent ft (or visible image) on the surface of the photoreceptor drum. If so, it is possible to lower the applied bias voltage. In some cases, it can be left floating. Example 2゜Selected developing unit in the same configuration as Example 1)
Developing roll 4 of developing unit 4 located upstream of 5a
Unlike the first embodiment, a bias voltage of several hundred ports to several thousand ports is applied to a, which has a polarity different from that of the toner contained in the developing unit 4. In this case, the developing roll 4
Although the toner on the photoreceptor drum 1 is not removed, the latent image in the image area of the latent image carrier is prevented from being developed with mixed color toner. In this embodiment, the bias applied to the developing roll 4a can be of a polarity different from that of the toner always stored, but the bias is of a different polarity only for the non-image area of the latent image carrier, and the bias is applied to the image area by a float. This is effective in preventing color mixing due to floating toner on the developing roll. At this time, it would be more preferable if the unselected developing rolls could be moved even slightly away from the photoreceptor. l Mitate A] The image forming apparatus according to the present invention configured as described above has the following features:
A bias voltage is applied to at least the developing roller of the selected developing unit, and part or all of the developer located on the side of the developing roller facing the latent image carrier is transferred to a non-image area of the latent image carrier. By causing the developer to fly and removing part or all of the developer from the surface of the developing roller, mixed color development can be prevented and high-quality copies can be obtained. Furthermore, according to the present invention, a multi-color developing device having a simple structure and small size and equipped with a plurality of developing units is achieved, which in turn enables compact and inexpensive image forming apparatuses such as color copying machines and color printing machines. can be provided.

[Brief explanation of drawings]

1 and 2 are partial schematic cross-sectional views of a latent image carrier and a developing roller, illustrating the principle of preventing color mixture in an image forming apparatus according to the present invention. FIG. 3 is a schematic sectional view of a color copying apparatus showing an embodiment of the multicolor developing device according to the present invention. FIG. 4 is a schematic cross-sectional view showing one embodiment of a developing unit that can be used in the image forming apparatus according to the present invention. 2: Latent image carrier 3: Multicolor developing device 4.5.6: Developing units 4a, 5a, 6a: Developing roll

Claims (1)

[Claims] 1) An image in which one or more developing units are arranged along a latent image carrier, and any one developing unit is selected to develop an electrostatic latent image on the surface of the latent image carrier. In the forming apparatus, a bias voltage is applied to at least the developing roller of the selected developing unit, and part or all of the developer located on the side of the developing roller facing the latent image carrier is transferred to the non-latent image carrier. An image forming apparatus characterized in that part or all of the developer is removed from the surface of the developing roller by causing the developer to fly to an image area. 2) The apparatus according to claim 1, wherein the bias voltage is applied when the rotation of the developing roll is stopped. 3) The apparatus according to claim 2, wherein the bias voltage has the same polarity as the developer contained in the development unit. 4) The device according to claim 2, wherein the bias voltage is approximately OV. 5) A bias voltage having a polarity different from that of the developer stored in each developing unit is applied to the developing roll of each developing unit located upstream of the selected developing unit in the rotation direction of the latent image carrier, and a bias voltage having a polarity different from that of the developer stored in each developing unit is applied. A bias voltage of the same polarity as the developer of each developing unit is applied to the developing roll of each developing unit located upstream of the developing unit in the rotational direction of the latent image carrier in a non-image area preceding the image area of the latent image carrier. An apparatus according to claim 2, wherein the apparatus is adapted to perform the following steps. 6) In the image area of the latent image carrier, a bias voltage having a polarity different from that of the toner contained in each developing unit is applied to the developing roll of the unselected developing unit, or the developing roll is placed in a floating state. The device according to any one of Items 3 to 5.