JP2007086693A - Color image forming apparatus and electrostatic developing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a small and inexpensive image forming apparatus that can form superposed toner images by an image-on-image system in a developing process without disturbance to obtain a color image of high picture quality and that has excellent maintenance property. <P>SOLUTION: The image forming apparatus includes a developing device for a first color which first forms a toner image on an image carrier and other developing devises of second and succeeding colors, wherein the developing device of the first color develops an image with a black toner by a contact system while the developing devices of second and succeeding colors are electrostatic developing devices (EH electrostatic hopping or, for short, EH developing devices). The electrostatic developing device is equipped with a toner electrostatic conveying device having a large number of electrodes each running in a direction approximately orthogonal to the conveying direction of the toner and arranged along the conveying direction of the toner at a minute interval, and the developing device applies a voltage to each electrode so as to generate a forward wave electric field to electrostatically convey the toner and to generate a developing electric field to electrostatically transfer the toner onto an electrostatic latent image formed on a photoreceptor belt. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus and an electrostatic developing apparatus using an electrophotographic process such as a copying machine, a facsimile machine, and a printer, and more particularly to a color on one image carrier using a plurality of charging apparatuses, exposure apparatuses, and developing apparatuses. In particular, the present invention relates to a color image forming apparatus and a developing apparatus that form an image by superimposing and forming a toner image having a different color by using an image-on-image color image formation, and transferring the superimposed toner image to a recording medium.

  2. Description of the Related Art Conventionally, an image forming apparatus configured as a copying machine, a printer, a facsimile, or a complex machine thereof is known (for example, see Patent Document 1). This type of color image forming apparatus is configured to directly superimpose toner images of different colors on a single photoreceptor belt and transfer the superimposed toner image to a recording medium. Therefore, the configuration of the apparatus can be simplified, which is advantageous for downsizing and cost reduction, and it is possible to form a high-quality color image. Such a color image forming apparatus is also called an image-on-image type color image forming apparatus. However, this type of conventional color image forming apparatus has the following serious drawbacks.

  If the developing device that first forms a toner image on the photosensitive belt is the developing device for the first color, and the other developing devices are called the developing devices for the second and subsequent colors, the developing devices for the second and subsequent colors are already toners. A toner image having a color different from that of the toner image is formed on the photoreceptor belt on which the image is formed. Therefore, development for the second and subsequent colors must be performed in a non-contact manner. As a conventional non-contact developing device, a developer is carried and conveyed on a developing sleeve, and an electric field in the developing direction and an electric field in the reverse developing direction are alternately formed between the developing sleeve and the photosensitive belt (AC An electric field is applied to make the electrostatic latent image visible while moving the toner between the developing sleeve and the photosensitive belt.

  However, when such a developing device is employed in a second or subsequent color developing device in an image-on-image type color image forming device, the toner already formed on the photosensitive belt when an electric field in the reverse developing direction is formed. A part of the toner in the image is transferred to the developer on the developing sleeve, and the color of the developer is different from the original color. If a toner image is formed on the photosensitive belt by such a developing device, the image quality is significantly deteriorated. Further, it is necessary to remove toner (hereinafter referred to as transfer residual toner) remaining on the photosensitive belt after transfer, and disposal of the transfer residual toner is a big problem in terms of maintenance of the image forming apparatus. In particular, in the superposition method on the photoconductor, there is a tendency that the toner remaining after transfer tends to increase. A general method is to temporarily store the toner collected by cleaning in a container for disposal and then discard it together. However, it takes time and effort, which is not preferable from the viewpoint of reducing waste. Moreover, the space of a container is required.

  Thus, several methods have been proposed as a method for reusing the collected toner to eliminate the waste toner. First, an apparatus has been proposed in which toner collected by a cleaning device is transported to a developing device and reused (see, for example, Patent Document 2). However, when this method is used, extra parts are required, which is counterproductive for the purpose of downsizing and cost reduction.

  There is also known an apparatus in which a collected toner is reused for development as it is by providing a developing device with a cleaning function (see, for example, Patent Document 3). However, in such an image apparatus, since multiple color toners are superimposed on the intermediate transfer member, the purpose of miniaturization and cost reduction cannot be achieved, and cleaning and disposal of untransferred toner on the intermediate transfer member cannot be achieved. The problem is neglected.

In addition to a normal developing device, there has been proposed a system in which a developing device for toner collecting means and test printing is installed (see, for example, Patent Document 4). However, this system requires one more developing device, which is not suitable for downsizing and cost reduction. Further, there is a problem that the black image quality is deteriorated in the method of collecting multi-color toner for black toner development. This includes a problem that can be solved by adjusting the black toner amount of the developing device. Furthermore, although the case where it uses for an image-on-image system is also proposed (for example, refer patent document 4), the problem of the developing apparatus after the 2nd color mentioned above is not touched at all.
JP-A-8-339110 JP 60-156081 A JP-A-5-249796 Japanese Patent Laid-Open No. 9-80845

  However, as described above, in the conventional color development method, there is an unfavorable image disturbance at the time of development to superimpose other colors, and the disposal of the cleaned toner is a problem, and a lot of toner that is not transferred is collected. Although it is considered that a general method is to temporarily put the toner in a waste container and discard it together, it takes time and labor, which is not preferable from the viewpoint of reducing waste. Further, a space for the container is necessary, and there are problems on the apparatus that are contrary to miniaturization and cost reduction.

  The present invention has been made in view of such circumstances, and on the premise of solving such a problem, the first color of development is contact development of black using the image-on-image method, and the second and subsequent colors are developed. By using color non-contact development, a superimposed toner image can be formed without being disturbed during development to form a high-quality color image, and a small and low-cost image forming apparatus having excellent maintainability can be realized. For the purpose.

  In order to solve the above problems, the invention described in claim 1 is a color image forming apparatus having a plurality of different color developing devices, wherein the first developing device performs black toner development by a contact method. The plurality of second developing devices include a plurality of electrode groups each composed of a plurality of electrode rows in which microelectrodes are arranged in a direction perpendicular to the toner conveyance direction with a minute interval in the toner conveyance direction. An electrostatic conveying means for electrostatically conveying the toner by an electric field formed by the multiple electrode group, and a developing electric field for electrostatically transferring the toner to an electrostatic latent image formed on the photosensitive belt. And a toner electrostatic transfer means for applying a voltage to the electrodes of the multiple electrode group so as to be formed.

  According to a second aspect of the present invention, in the color image forming apparatus according to the first aspect, the first developing device includes a recovery unit that recovers toner on the image carrier. .

  According to a third aspect of the present invention, in the color image forming apparatus according to the second aspect, the first developing device has a black toner developing function and a function of collecting the toner on the image carrier. It is characterized by exhibiting.

  According to a fourth aspect of the present invention, in the color image forming apparatus according to any one of the first to third aspects, a cleaning device that collects toner on the image carrier is provided, and the cleaning device provides the cleaning device. The toner collected from the image carrier is supplied to the first developing device and reused.

  According to a fifth aspect of the present invention, in the color image forming apparatus according to any one of the first to fourth aspects, the charging potential of the image carrier by the first charging device includes a plurality of second potentials. The charging potential of the image carrier is higher than that of the image bearing member.

  According to a sixth aspect of the present invention, in the color image forming apparatus according to any one of the first to fifth aspects, the charging potential by the first charging device and the charging potential by the second charging device. Are substantially equal to each other, and the exposure amount by the first exposure apparatus is changed from the exposure amounts by the plurality of second exposure apparatuses so that the exposure portion potentials are different.

  According to a seventh aspect of the present invention, in the color image forming apparatus according to any one of the first to sixth aspects, the toner of the first developing device is a charge of the toner of the second developing device. It is characterized by being less than the amount.

  In addition, according to an eighth aspect of the present invention, in the color image forming apparatus according to any one of the first to seventh aspects, the toner particle size of the first developing device is a plurality of the second developments. It is characterized by being smaller than the particle size of the toner of the apparatus.

  According to a ninth aspect of the present invention, in the color image forming apparatus according to any one of the first to eighth aspects, the plurality of electrodes of the electrostatic toner conveying means are arranged in a ring shape. And

  According to a tenth aspect of the present invention, in the color image forming apparatus according to any one of the first to ninth aspects, the second developing device supplies toner to the electrostatic toner transport device. And the toner supply device includes developer transport means for transporting the magnetic carrier and the developer having toner while being magnetically supported, and the toner transported by the developer transport device is the magnetic carrier. And electrostatically supplied to the toner electrostatic transfer device.

  According to an eleventh aspect of the present invention, in the color image forming apparatus according to the tenth aspect, the second developing device includes a toner replenishing device for replenishing toner to a developer conveying device, and the toner replenishing device. The apparatus is characterized in that the toner consumed for the visualization is automatically supplied to the developer conveying device.

  In the invention according to claim 12, a multi-electrode group is formed which includes a plurality of electrode arrays in which micro-electrodes are arranged in the direction perpendicular to the toner transport direction with a minute interval in the toner transport direction. The multiple electrodes are formed so that toner is electrostatically conveyed by the electric field formed by the multiple electrode group, and a developing electric field is formed to electrostatically transfer the toner to the electrostatic latent image formed on the photosensitive belt. An electrostatic developing device comprising electrostatic toner transporting means for applying a voltage to a group of electrodes.

  Further, the invention described in claim 13 is the electrostatic developing device according to claim 12, wherein the electrostatic developing device includes a toner supply device for supplying toner to a toner electrostatic transfer device, and the toner supply The apparatus includes a developer transport device that transports a developer having a magnetic carrier and toner while supporting the developer by magnetic force, and the toner transported by the developer transport device is charged by friction with the magnetic carrier and statically. The toner is electrically supplied to the toner electrostatic transfer device.

  According to a fourteenth aspect of the present invention, in the electrostatic developing device according to the thirteenth aspect, the electrostatic developing device includes a toner replenishing device that replenishes a developer conveying device, and the toner replenishing device. Is characterized in that the toner consumed for the visualization is automatically supplied to the developer conveying device.

  According to the present invention, it is possible to eliminate the above-described drawbacks of the image-on-image method, and to realize an image forming apparatus with high image quality and a small size and low cost.

  Hereinafter, an image forming apparatus and a developing apparatus according to an embodiment of the present invention will be described in detail with reference to the drawings. The embodiments described below are preferred embodiments of the present invention, and therefore technically preferable various kinds of limitations are given. However, the scope of the present invention is not limited to the following description. As long as there is no description which limits, it is not restricted to these aspects.

  An image forming apparatus according to an embodiment of the present invention uses a plurality of charging devices, an exposure device, and a developing device to superimpose and form toner images of different colors on one image carrier, and the superimposed toner images are formed. A color image forming apparatus (image-on-image system) that obtains an image by transferring it to a recording medium by a transfer device. Further, the first developing device that forms a toner image on the image carrier is the first developing device, the other developing devices are the second and subsequent developing devices, and the first developing device is contacted with black toner. As a developing device for developing, the developing devices for the second and subsequent colors have a large number of electrodes extending in a direction substantially perpendicular to the toner transport direction and arranged at a minute interval in the toner transport direction. A voltage is applied to each electrode so that a traveling wave electric field that electrostatically conveys the toner is formed and a developing electric field that electrostatically transfers toner to the electrostatic latent image formed on the photosensitive belt is formed. An electrostatic developing device (EH developing device) including a toner electrostatic transfer device is used.

  FIG. 1 is a diagram showing a schematic configuration of a color image forming apparatus according to an embodiment of the present invention. The color image forming apparatus shown here has an endless photoreceptor belt 4 wound around a plurality of support rollers 1, 2, and 3, and around the photoreceptor belt 4, the photoreceptor belt 4 is provided. First to fourth charging devices 5BK, 5M, 5C, 5Y, first to fourth developing devices 6BK, 7M, 7C, 7Y that are spaced apart from the surface of the photosensitive member, and a photoreceptor belt. A transfer device 8 composed of a transfer roller in contact with the surface of 4 is disposed.

  In the present embodiment, the developing devices 6BK, 7M, 7C, and 7Y can form a black toner image, a magenta toner image, a cyan toner image, and a yellow toner image on the photoreceptor belt 4, respectively. The developing device 6BK is of a contact type and has a function of forming a black toner image on the photosensitive belt 4 and collecting a transfer residual toner adhering to the photosensitive belt. A non-contact method is used for the developing devices 7M, 7C, and 7Y. The features of the present invention reside in these developing devices 6BK, 7M, 7C and 7Y, which will be described in detail later. Further, the charging devices 5BK to 5Y shown as an example in the figure are composed of scorotron chargers. Further, backup rollers 9BK, 9M, and 9C are arranged at positions facing the developing devices 6BK to 6C with the photosensitive belt 4 interposed therebetween. The photoreceptor belt 4 has a photosensitive layer formed on the surface of a substrate belt, and has a well-known configuration.

  All the elements described above are arranged in the image forming apparatus main body 10, and an exposure device 11, a paper feeding device 12, a fixing device 13, and the like are further provided in the image forming apparatus main body 10.

  When an image forming operation is started by such an image forming apparatus, the photosensitive belt 4 is driven in a direction indicated by an arrow A in FIG. At this time, the first charging device 5BK charges the photosensitive belt 4 to a predetermined polarity (minus polarity in the illustrated example), and light-modulated writing light (in the illustrated example) emitted from the exposure device 11 on the charging surface. Laser light L) is irradiated, thereby forming a first electrostatic latent image on the photoreceptor belt. The first electrostatic latent image is visualized as a black toner image by the first developing device 6BK.

  Subsequently, the photosensitive belt 4 on which the black toner image is formed is charged to a negative polarity by the second charging device 5M, and the light-modulated laser light L emitted from the exposure device 11 is irradiated on the charging surface. . As a result, a second electrostatic latent image is formed on the photosensitive belt 4, and the electrostatic latent image is visualized as a magenta toner image by the second developing device 7M. Similarly, the photosensitive belt 4 (on which the black toner image and the magenta toner image are formed) is charged to a negative polarity by the third charging device 5C, and the charged surface is exposed by the exposure device 11 to be third. Electrostatic latent image is formed. The latent image is visualized as a cyan toner image by the third developing device 7C, and a yellow toner image is formed by the fourth charging device 5Y, the exposure device 11, and the fourth developing device 7Y. In this manner, four color toner images are sequentially superimposed on the photosensitive belt 4 and formed.

  On the other hand, a recording medium P made of transfer paper or a resin sheet is accommodated in the paper feeding cassette 14 of the paper feeding device 12, and the uppermost recording medium P is fed in the direction of arrow B by the rotation of the paper feeding roller 15. Then, it is sent to a transfer portion between the photosensitive belt 4 and the transfer device 7 at a predetermined timing. At this time, a predetermined transfer voltage is applied to the transfer device 7, whereby the superimposed toner image on the photosensitive belt 4 is transferred to the recording medium P. The recording medium to which the toner image has been transferred passes through the fixing device 13, and at this time, heat and pressure are applied, and the transferred toner image is fixed to the recording medium P. Subsequently, the recording medium is discharged to a paper discharge unit 16 at the top of the image forming apparatus main body 10 as indicated by an arrow C. The transfer residual toner adhering to the photosensitive belt 4 after the toner image transfer is provided with a cleaning function in the developing device 6BK, and is collected by the developing device 6BK simultaneously with the black toner development.

  As described above, in the color image forming apparatus according to this embodiment, the photosensitive belt is charged by the charging device, the charged surface is exposed by the exposure device, and an electrostatic latent image is formed on the photosensitive belt. By repeating the process of visualizing the electrostatic latent image as a toner image by a developing device a plurality of times, toner images of different colors are superimposed on the photosensitive belt, and the superimposed toner image is recorded on the recording medium by the transfer device. And a recorded image is obtained. Such an image forming apparatus is an image-on-image type color image forming apparatus. Since the photoreceptor belt 4 is used as the photoreceptor, a plurality of developing devices 6BK, 7M, 7C, and 7Y and charging devices 5BK, 5M, 5C, and 5Y are disposed around the photoreceptor belt 4 with a margin. Can do.

  Assuming that a photosensitive drum is used as the photosensitive member, it is necessary to make the diameter of the photosensitive drum very large in order to arrange a plurality of developing devices and charging devices around the photosensitive drum. Although the overall structure is enlarged, the use of the photoreceptor belt 4 does not cause such a defect.

  Here, the first developing device 6BK that first starts to form a toner image on the photosensitive belt 4 is referred to as a first color developing device, and the other second to fourth developing devices 7M, 7C, and 7Y are referred to as two. This is referred to as a developing device after the color. It is a feature of the present invention to employ different types of developing devices for the first color and developing devices for the second and subsequent colors.

  First, the developing devices 7M, 7C, and 7Y for the second and subsequent colors form toner images on the photosensitive belt 4 on which toner images of different colors have already been formed. Therefore, in order not to disturb the toner images already formed on the photosensitive belt 4 by the second and subsequent color developing devices, the second and subsequent color developing devices 7M, 7C, and 7Y are non-contact developing type developing devices. It is necessary to use it. In addition, it is necessary to prevent the toner of the toner image already formed on the photosensitive belt 4 from entering the developing devices 7M, 7C, and 7Y for the second and subsequent colors.

  Therefore, in the present invention, an electrostatic developing device including a toner electrostatic transfer device is used. This electrostatic developing device is of a non-contact type and is configured so that the toner on the photosensitive belt is not returned to the developing device side. The first color developing device is not limited as described above. In the present embodiment, the developing device 6BK for the first color is a contact-type developing device having a function of collecting the transfer residual toner on the photosensitive belt 4 simultaneously with the development of the black toner. Since the collected toner is mixed with the black toner and used, waste toner can be eliminated or at least reduced. Further, it is not necessary to install a cleaning device alone. Here, the developing device 6BK for the first color is black so that there is no problem even if toners of other colors are mixed.

  However, when the other color toner collected in the developing device 6BK is developed and does not come out, there is a problem that the other color toner accumulates in the developing device 6BK and the color changes from the original black. Therefore, the charge amount of the 7M, 7C, and 7Y toners of the developing device is set to be smaller than that of the black toner of the developing device 6BK.

  For example, in the case of the two-component developing method, the original black toner of the developing device 6BK is set to −30 μC / g and the toners of the other developing devices 7M to 7Y are set to −20 μC / g with respect to the same carrier. . Accordingly, when the other color toners of the developing devices 7M to 7Y are collected in the developing device 6BK, the other color toners of the developing devices 7M, 7C, and 7Y are more easily developed than the black toner, and thus the developing device 6BK. In addition, it is possible to prevent a problem that toners of other colors accumulate.

  The toner charge amount can be controlled by adjusting the charge control agent or external additive of the toner component. Further, even if the particle size of the black toner of the developing device 6BK is reduced to, for example, about 6 μm and the particle size of the toners of the other developing devices 7M to 7Y is increased to, for example, about 10 μm, the difference in charge amount as described above can be obtained. You can turn it on. The toner particle size generally increases when manufactured by a pulverization method and decreases when manufactured by a polymerization method. Therefore, the manufacturing method of the toner of the developing device 6BK and the toner of the developing devices 7M to 7Y is appropriately adjusted. Can also be manufactured.

  Hereinafter, the specific configuration of the developing device 6BK for the first color will be described first, and the specific configuration of the developing devices 7M to 7Y for the second and subsequent colors will be described in detail.

  The developing device 6BK will be described. In this embodiment, since there is usually no cleaning device installed, the surface of the photosensitive drum 4 is charged to, for example, −700 V by the charging device 5BK while the transfer residual toner is attached on the photosensitive drum 4. To do. At this time, the transfer residual toner is simultaneously negatively recharged. Next, the photosensitive drum 4 is exposed by the laser light L from the exposure device 11, and the potential of the exposed portion is attenuated to, for example, −50 V (residual potential). Although exposure is hindered by the transfer residual toner, the transfer residual toner is not so much, so that the surface potential can be set to -50V except for the charging of the photosensitive drum 4 by irradiating light of sufficient intensity.

  FIG. 2 schematically shows the space between the developing device 6BK and the photosensitive belt 4. Since FIG. 2 is a schematic diagram, the developing device 6BK and the photosensitive belt 4 are not in contact with each other, but a contact method is adopted in order to provide sufficient cleaning capability. For example, when the developing potential is −400 V, the exposed portion has a potential of −50 V, so that the black toner is developed on the exposed portion of the photosensitive belt 4. Since the amount of transfer residual toner is small, it can be covered by developing a sufficient amount of black toner. Further, since the potential of the unexposed portion is −700 V, the untransferred toner moves to the developing device 6BK on the contrary in the unexposed portion. Therefore, the developing device 6BK simultaneously develops the black toner and collects the transfer residual toner. Accordingly, the transfer residual toner that is inevitably collected is mixed with the black toner and reused. It is black toner that other colors are mixed in, so there is not much influence. Accordingly, waste toner can be eliminated or at least reduced, and the work of discarding waste toner can be reduced, which is very effective from the viewpoint of maintenance. In addition, the space for the waste toner collecting container can be reduced, which can contribute to the downsizing of the image forming apparatus. Further, there is an advantage that an independent cleaning device can be omitted.

  In addition, when the transfer residual toner is not so clean by the developing device 6BK, an operation mode in which only the transfer residual toner is collected may be activated at any time. After charging the surface of the photosensitive belt 4 by the charging device 5BK, the transfer residual toner can be collected on the entire surface of the photosensitive belt 4 if no exposure is performed.

  Further, a method of alternately performing cleaning of the transfer residual toner, development of black toner, and development of toner for the second and subsequent colors can be employed. This means that for each image output, the photosensitive belt 4 is rotated once for cleaning. Therefore, in order to output one image, the photosensitive belt 4 needs to be rotated twice, and there is a disadvantage that the output speed becomes slow. Another disadvantage is that the size of the photosensitive belt 4 is determined by the size of the output paper. When the development of the black toner and the collection of the transfer residual toner are performed at the same time, there is an advantage that the size of the photosensitive belt 4 can be determined irrespective of the output paper.

  Next, the second and subsequent developing devices 7M to 7Y according to the embodiment of the present invention will be described. The configurations of the electrostatic developing devices 7M to 7Y having the toner electrostatic transfer device are substantially the same, so only one developing device 7M needs to be described. An outline of the electrostatic toner transport device will be described below.

  As shown in FIG. 3, the electrostatic toner transport device 20 of the developing device 7 </ b> M is disposed with a predetermined interval with respect to the photosensitive belt 4. As shown in FIG. 4, the electrostatic toner transport device 20 has a support 21 made of an insulator formed in a columnar shape, and a plurality of electrodes 22 fixedly disposed along the outer peripheral surface of the support 21. An insulating layer 23 is laminated on the outer surfaces of the electrodes 22 and the support 21.

  In FIG. 4, only some of the electrodes 22 are shown. However, in practice, the electrodes 22 are arranged over the entire circumference of the support 21 as schematically shown in FIG. As will be described later, the powdery toner T is conveyed in the circumferential direction of the support 21 as indicated by an arrow E in FIGS. 3 and 4, and each electrode 22 is substantially in the toner conveying direction E. It is formed by extending in an orthogonal direction, and extends over the entire width of the image forming area of the photoreceptor belt 4. The electrodes 22 are arranged in an annular shape with a minute interval in the toner transport direction E. As shown in FIG. 5, the width W of each electrode 22 is, for example, 30 μm, and the pitch PT thereof is, for example, about 60 μm. In FIGS. 3 and 4, the toner T is represented by dots, and a carrier CA described later is represented by a small circle. In FIG. 5, each electrode is hatched.

  Here, on each electrode 22, a traveling wave electric field for electrostatically transporting the toner T and an electrostatic latent image formed on the photosensitive belt 4 along the outer peripheral surface of the toner electrostatic transport device described above are provided. Voltages are respectively applied by the three-phase pulse power source 19 shown in FIG. 4 so that a developing electric field for electrostatically moving the toner T is formed. One example will be described below.

  A large number of the electrodes 22 constitute one set, and a voltage is applied to each of the three electrodes of each set while shifting the phase. FIG. 6 is a view showing the first and second sets I and II composed of three electrodes 22A to 22C side by side. Here, as shown in FIG. 6A, it is assumed that the negatively charged toner T is present on the first set I of electrodes 22B, and at this time, the I and II electrodes 22A to 22A of each set. It is assumed that voltages of −130 V, −130 V, and −40 V are sequentially applied to C. At this time, due to the formed electric field, the toner T is electrostatically transferred to the electrode 22C adjacent to the electrode 22B of the first set I (for example, I in FIG. 6A → B in FIG. 6). See I). Next, as shown in FIG. 6B, voltages of −40V, −130V, and −130V are applied to the electrodes 22A to 22C of the sets I and II, respectively. For this reason, the negative toner T on the first set I electrode 22C is electrostatically transferred onto the second set II electrode 22A. Next, as shown in FIG. 6C, voltages of −130 V, −40 V, and −130 V are sequentially applied to the first and second sets of electrodes 22 </ b> A to 22 </ b> C, respectively. The toner T that was on the electrode 22A of the set II moves to the adjacent electrode 22B, and in exactly the same manner, as shown in FIG. 6 (d), the toner T is applied to the second set of electrodes 22C. Move electrostatically. In this way, the toner T is conveyed in the direction of arrow E.

  The voltage change of the electrode due to the voltage application as described above is an example of a traveling wave electric field, and the electric field is formed so that the toner is supplied from the toner supply device 24 shown in FIGS. 3 and 4 to the electrostatic toner transport device 20. The negative polarity toner T thus conveyed is conveyed in the direction of arrow E while hopping the peripheral surface of the toner electrostatic conveyance device 20, and the photosensitive belt 4 and the toner electrostatic conveyance device 20 are conveyed to a developing region close to each other. It is. At this time, an electrostatic latent image is formed on the photosensitive belt 4 as described above. The electrostatic latent image is formed by charging the photosensitive belt 4 by the charging device 5M shown in FIG. 1 and then selectively irradiating the laser beam L emitted from the exposure device 11. Here, as an example, it is assumed that the photosensitive belt 4 is charged to −150 V by the charging device 5M, and as shown in FIG. 4, the surface potential of the electrostatic latent image F formed by irradiating the laser beam is − The surface potential of the ground portion G that is 50 V and is not irradiated with the laser light is maintained at −150 V.

  On the other hand, as can be seen from FIG. 6, the average value of the voltages applied to the electrodes 22A to 22C of each set I and II is −100V. For this reason, the negative toner T on the electrostatic toner transport device 20 transported to the development area is electrostatically transferred only to the electrostatic latent image F on the photosensitive belt 4, and becomes the electrostatic latent image F. Adhere to. In this way, by applying the voltage exemplified above to each electrode, a developing electric field for electrostatically transferring toner to the electrostatic latent image formed on the photoreceptor belt 4 can be formed. The toner that has passed through the developing region without being transferred to the photosensitive belt 4 is further transported in the direction indicated by the arrow H in FIG. Carried to the 24 side.

  The developing devices 7C and 7Y according to the present embodiment shown in FIG. As described above, the electrostatic developing device having the electrostatic toner transport device performs the developing operation on the photosensitive belt 4 in a non-contact manner, so that the developing devices 7M to 7Y for the second and subsequent colors are already in the photosensitive belt. The toner image formed on 4 is not disturbed. In addition, since the developing electric field is always in one direction and the direction is not reversed, the toner of the toner image already formed on the photosensitive belt 4 is not mixed in the developing devices 7M to 7Y. . For this reason, toner mixing cannot occur in any of the developing devices, and a high-quality color image can be formed over a long period of time. Further, contaminants such as paper dust attached on the photosensitive belt 4 can be prevented from flowing into the developing devices 7M to 7Y. The toner used in each developing device may be a magnetic toner or a non-magnetic toner. Further, as shown in FIGS. 3 and 4, the multiple electrodes 22 of the toner electrostatic conveyance device 20 of this example are arranged in an annular shape, so that the toner that has not been developed can be used as it is in the toner supply device 24. Can be transported to the side. Further, since the toner on the photosensitive belt 4 does not enter the developing devices 7M to 7Y, the transfer residual toner is reduced by increasing the efficiency with which the toner image on the photosensitive belt 4 is transferred to the recording medium P. Accordingly, the collection of the transfer residual toner by the above-described first color developing device 6BK becomes effective.

  Next, the toner supply device 24 according to the embodiment of the present invention shown in FIG. 3 will be described. The toner supply device 24 shown here has a developer conveying device 27 including a sleeve 25 and a magnet roller 26 disposed inside the sleeve 25, and the circumferential surface of the magnet roller 26 has a circumferential direction thereof. S poles and N poles are alternately magnetized. The sleeve 25 is made of a non-magnetic material, and a dry developer D having a magnetic carrier CA and a toner T is carried on the peripheral surface thereof by a magnetic force. In this state, the magnet roller 26 is fixed without rotating, and the sleeve 25 is driven to rotate counterclockwise in FIG. As a result, the developer D is conveyed counterclockwise, and the toner T is charged to a negative polarity by friction with the carrier CA. When the carrier CA moves between the magnetic poles of the magnet roller 26, the carrier CA performs a fine motion as if the mag brush (magnet brush) rolls, thereby increasing the stirring motion of the toner T and the carrier CA. The developer D is transported to a region where the sleeve 25 and the toner electrostatic transport device 20 face each other. At this time, each electrode 22 of the toner electrostatic transport device 20 is applied with the voltage as described above. Since a voltage of −600 V, for example, is applied to the sleeve 25, the toner in the developer D is electrostatically transferred to the electrode 22 of the electrostatic toner transport device 20 and supplied to the electrostatic toner transport device 20. The

  In some cases, abnormal toner that is not sufficiently charged may be present in the toner carried on the sleeve 25. However, even if such abnormal toner is not supplied to the toner electrostatic transfer device 20, it is abnormal. Since the electrostatic conveyance force with respect to the toner is extremely low, the abnormal toner is not conveyed to the development area. In this way, only normal charged toner is carried to the development area, so that it is possible to prevent toner scattering and background contamination.

  It is also possible to transport the developer D on the sleeve 25 by fixing the sleeve 25 shown in FIG. 3 and rotating the magnet roller 26. According to this configuration, the sleeve 25 can be integrated with the casing 28 of the developing device 7M. It is also possible to convey the developer D on the sleeve 25 by rotating the sleeve 25 and the magnet roller 26 in opposite directions. Furthermore, the sleeve 25 can be omitted, the developer D can be carried directly on the magnet roller 26, and the developer D can be conveyed by driving the magnet roller 26 to rotate. According to such a developer transport device, the configuration can be greatly simplified.

  In any of the developer conveying devices described above, a doctor blade (not shown) is disposed facing the sleeve 25 or the magnet roller 26, and is carried on the sleeve 25 or the magnet roller 26 by the doctor blade. If the developer to be conveyed is agitated, the triboelectric charging ability for the toner can be enhanced. Further, by configuring such a doctor blade not to be provided, it is possible to prevent excessive stress from being applied to the toner and the carrier, and to reduce the wear on the carrier surface.

  As described above, the toner supply device 24 includes the developer transport device 27 that transports the developer D having the magnetic carrier CA and the toner T while being carried by the magnetic force, and is transported by the developer transport device 27. The toner T is charged by friction with the carrier CA, and the charged toner T is electrostatically supplied to the electrostatic toner transport device 20.

  Further, as shown in FIG. 3, the electrostatic developing device 7 </ b> M according to the present embodiment is provided with a toner replenishing device 29 that replenishes the developer conveying device 27 with toner. The toner replenishing device 29 includes a toner container 30 constituted by a part of the casing 28 of the developing device 7M, and a rotating blade 31. The rotating blade 31 rotates in the counterclockwise direction in FIG. The powdery toner T in the toner container 30 is pumped up and replenished to the developer transport device 27. At that time, the toner pumped up by the rotary blades 31 is temporarily stored in the inlet portion space 32 of the developer conveying device 27 and is consumed for visualization of the electrostatic latent image. Is supplied to the developer conveying device 27 from the entrance space 32. The replenished toner is replenished to the entrance space by the rotary blade 31. As described above, the toner replenishing device 29 according to the present embodiment automatically replenishes the developer conveying device 27 with the toner consumed for making the electrostatic latent image visible. According to such a configuration, a device for adjusting the toner density of the developer D conveyed by the developer conveying device 27 is not required, and the configuration of the developing device can be simplified or further downsized (miniaturized).

  Conventionally, in the developing method employed in this type of color image forming apparatus, as described in the developing device 6BK, the photosensitive belt is charged to, for example, −700 V, and the charged surface is exposed to expose the electrostatic latent image. After the surface potential of the electrostatic latent image was set to about −50 V, for example, the toner was electrostatically attached thereto. However, in this configuration, the surface potential of the photosensitive belt needs to be greatly reduced from −700 V to −50 V, and thus it is necessary to irradiate a large amount of light on the charged surface. At that time, in the second and subsequent processes, an electrostatic latent image is formed on the photosensitive belt on which the toner image has already been formed. However, the already formed toner image prevents the light from traveling, and thus the photosensitive belt. The surface cannot be irradiated with a large amount of light. For this reason, in the conventional color image forming apparatus of the image-on-image method, the photosensitive belt is configured to be transparent, and an exposure device is disposed on the back side of the photosensitive belt, and light is irradiated from the back side of the photosensitive belt. As a result, an electrostatic latent image was formed. In this way, even if a toner image has already been formed on the photoreceptor belt, an electrostatic latent image can be formed by irradiating the photoreceptor belt with a large amount of light. In order to do so, the range of material selection for the photoreceptor belt has been narrowed. In addition, when the back surface of the transparent photosensitive belt becomes dirty or scratched, it is impossible to irradiate the photosensitive belt with a large amount of light. Further, when the exposure device is disposed on the back side of the endless photoconductor belt, the entire exposure device and the photoconductor belt are extremely large.

  In contrast, in the present invention, since the electrostatic developing device described above is used as the developing device for the second and subsequent colors, even if the difference between the charged potential of the photosensitive belt 4 and the potential of the exposed portion electrostatic latent image is small. A visible image can be reliably obtained. For this reason, it is only necessary to irradiate the charging surface of the developing device with a small amount of light. Therefore, the exposure apparatus 11, such as the image forming apparatus shown in FIG. 1, is configured to irradiate the outer peripheral surface of the photosensitive belt 4 with light to form an electrostatic latent image on the photosensitive belt 4. Even if the apparatus is used, it is possible to reliably form an electrostatic latent image by irradiating the surface of the photosensitive belt 4 on which the toner image is already formed on the photosensitive belt 4 with laser light.

  As described above, in the present embodiment, since the exposure device 11 is disposed not on the inside of the photoreceptor belt 4 but on the outside thereof, the enlargement of the photoreceptor belt 4 can be prevented. Further, the photoconductor belt 4 is prevented from light fatigue (breakage of molecular chains in the belt constituent material due to photolysis, fatigue due to preservation of internal stress due to heat generated from a light source, etc.) Long life can be achieved.

  It has been described that the photosensitive belt 4 is charged to −150V and the potential of the exposed portion electrostatic latent image is −50V. This has the problems described below. In this embodiment, a normal developing device 6BK is used as the developing device for the first color. In the first color, since the toner image is not yet formed on the photosensitive belt, the above-described problem does not occur. However, when the first color charging device charges the photosensitive belt 4 to -700 V, and the second and subsequent charging devices charge the photosensitive belt 4 at -150 V, it is necessary to remove the charge after developing the first color. . For this reason, it is necessary to install a static eliminator, which is an obstacle to miniaturization and cost reduction. In the present embodiment, instead of neutralizing, the charging devices for the second and subsequent colors are also charged so that the photosensitive belt 4 is charged at the same charging potential as that of the charging device for the first color, for example, 700V. For example, the exposure is performed so that the potential of the electrostatic latent image on the exposed portion of the photosensitive belt 4 becomes −600 V with the exposure device for the second and subsequent colors. In accordance with this, the voltage values of the electrodes 22A to 22C of the electrostatic developing device 7 described above are adjusted to be, for example, -650V on average. In this way, a large amount of light is not required for the exposure apparatuses for the second and subsequent colors. For this reason, it is possible to prevent the photosensitive belt 4 from becoming extremely large by installing the exposure device 11 so as to irradiate the outer peripheral surface of the photosensitive belt 4 with light. Further, it is possible to extend the life of the photosensitive belt 4 by suppressing the light fatigue of the photosensitive belt 4.

  When the EH development method is used for the second and subsequent colors, the following effects are obtained. In this method, since the developing operation is performed in a non-contact manner, the toner image already formed on the image carrier is not disturbed. Further, since the developing electric field is always in one direction and the direction is not reversed, the toner of the toner image already formed on the image carrier is not mixed in the developing devices for the second and subsequent colors.

  Further, the development device that develops the black toner by the contact method for the first color has the following two effects. First, waste toner can be eliminated by collecting and mixing untransferred toner in the first color developing device using the method described below, thereby achieving further downsizing and excellent maintainability. By setting the first color to black, the influence can be minimized even when toner of other colors is mixed. Secondly, by using black toner development of the first color as a contact method, a frequently used black image can have high resolution.

  Since the developing device for the first color is a normal contact system, a large background potential (difference between the charging potential and the exposure portion potential) is required. Recovery of the transfer residual toner is more effective as the background potential increases. Further, since the developing devices for the second and subsequent colors use the EH developing device, development at a low potential is possible and the charging potential may be small. This has the effect of reducing electrostatic stress on the photoreceptor. Furthermore, since the exposure amount by the exposure apparatus for the second and subsequent colors can be reduced, there is also an effect of suppressing light fatigue of the photoreceptor.

  FIG. 7 is a schematic view of an image forming apparatus according to another embodiment of the present invention. In the present embodiment, a cleaning device 17 and a collected toner conveyance path 18 are further provided in the embodiment shown in FIG. In the embodiment shown in FIG. 1, the transfer residual toner is also collected by the developing device 6BK, but the configuration of this embodiment (FIG. 7) is particularly preferable when the amount of the transfer residual toner is large. That is, the cleaning device 17 is added, and the transfer residual toner collected thereby is supplied to the developing device 6BK through the collected toner conveyance path 18. Although this configuration is somewhat complicated, waste toner can be reliably eliminated.

  As mentioned above, the invention made by the present inventor has been specifically described based on the preferred embodiments. However, the present invention is not limited to the above, and various modifications can be made without departing from the scope of the invention. Needless to say.

1 is a schematic cross-sectional view illustrating an overall configuration of a color image forming apparatus according to an embodiment of the present invention. FIG. 4 is an explanatory diagram schematically illustrating the principle of simultaneously developing black toner and collecting transfer residual toner by the developing device according to the embodiment of the present invention. 1 is an enlarged sectional view of an electrostatic developing device according to an embodiment of the present invention. FIG. 3 is an explanatory cross-sectional view showing the principle of the electrostatic toner transport device according to the embodiment of the present invention. FIG. 6 is a plan view showing an arrangement state of electrode portions of the electrostatic toner transport apparatus according to the embodiment of the present invention. FIG. 4 is an explanatory diagram illustrating a principle of transporting toner by a toner electrostatic transport device according to an embodiment of the present invention. It is a schematic sectional drawing which shows the other structural example of the color image forming apparatus which concerns on embodiment of this invention.

Explanation of symbols

1, 2, 3 Support roller 4 Photosensitive belt 5BK, 5M, 5C, 5Y Charging device 6BK Contact developing device 7M, 7C, 7Y Electrostatic developing device 8 Transfer device 9BK, 9M, 9C Backup roller 10 Image forming apparatus main body DESCRIPTION OF SYMBOLS 11 Exposure apparatus 12 Paper feed apparatus 13 Fixing apparatus 14 Paper feed cassette 15 Paper feed roller 16 Paper discharge part 17 Cleaning apparatus 18 Collected toner conveyance path 20 Toner electrostatic conveyance apparatus 21 Support body 22,22A, 22B, 22C Electrode 23 Insulating layer 24 Toner supply device 25 Sleeve 26 Magnet roller 27 Developer transport device 28 Casing 29 Toner supply device 30 Toner container 31 Rotating blade 32 Entrance space L Laser light P Recording medium CA Carrier T Toner D Developer

Claims (14)

A color image forming apparatus having a plurality of different color developing devices,
The first developing device is a developing device that performs black toner development by a contact method,
The plurality of second developing devices are
A multi-electrode group is formed of a multi-electrode array in which micro-electrodes are arranged in the direction perpendicular to the toner transport direction with a small interval in the toner transport direction, and an electric field formed by the multi-electrode group is formed. Electrostatic conveying means for electrostatically conveying toner;
Electrostatic toner conveying means for applying a voltage to the electrodes of the multiple electrode group so as to form a developing electric field for electrostatically transferring the toner to the electrostatic latent image formed on the photosensitive belt. A color image forming apparatus.   The color image forming apparatus according to claim 1, wherein the first developing device includes a collecting unit that collects toner on the image carrier.   The color image forming apparatus according to claim 2, wherein the first developing device exhibits a black toner developing function together with a function of collecting toner on the image carrier.   A cleaning device for collecting toner on the image carrier is provided, and the toner collected from the image carrier by the cleaning device is supplied to the first developing device and reused. Item 4. The color image forming apparatus according to any one of Items 1 to 3.   The charging potential of the image carrier by the first charging device is higher than the charging potential of the image carrier by a plurality of second charging devices. Color image forming apparatus.   The charging potential by the first charging device is substantially equal to the charging potential by the second charging device, and the exposure amount by the first exposure device is changed by changing the exposure amounts by the plurality of second exposure devices. 6. A color image forming apparatus according to claim 1, wherein the partial potentials are different.   7. The color image forming apparatus according to claim 1, wherein the toner of the first developing device is less than the charge amount of the toner of the second developing device.   8. The color image formation according to claim 1, wherein a particle diameter of toner of the first developing device is smaller than a particle diameter of toner of the plurality of second developing devices. apparatus.   The color image forming apparatus according to claim 1, wherein a large number of electrodes of the electrostatic toner conveying unit are arranged in a ring shape. The second developing device includes a toner supply device that supplies toner to the electrostatic toner transport device,
The toner supply device has developer transport means for transporting a magnetic carrier and a developer having toner while being carried by a magnetic force,
10. The toner according to claim 1, wherein the toner conveyed by the developer conveying device is charged by friction with the magnetic carrier and electrostatically supplied to the toner electrostatic conveying device. The color image forming apparatus according to Item. The second developing device includes a toner replenishing device that replenishes the developer conveying device with toner,
The color image forming apparatus according to claim 10, wherein the toner replenishing device automatically replenishes toner consumed for visualization into a developer conveying device.   A multi-electrode group is formed of a multi-electrode array in which micro-electrodes are arranged in the direction perpendicular to the toner transport direction with a small interval in the toner transport direction, and an electric field formed by the multi-electrode group is formed. Toner electrostatically applies a voltage to the electrodes of the multiple electrode group so as to form a developing electric field that electrostatically transfers the toner to an electrostatic latent image formed on the photoreceptor belt. An electrostatic developing apparatus comprising a conveying unit. The electrostatic developing device includes a toner supply device that supplies toner to a toner electrostatic conveyance device;
The toner supply device has a developer conveying device that conveys a magnetic carrier and a developer having toner while being carried by a magnetic force,
13. The electrostatic development according to claim 12, wherein the toner conveyed by the developer conveying device is charged by friction with the magnetic carrier and electrostatically supplied to the toner electrostatic conveying device. apparatus. The electrostatic developing device includes a toner replenishing device that replenishes the developer conveying device with toner,
The electrostatic developing device according to claim 13, wherein the toner replenishing device automatically replenishes toner consumed for visualization into a developer conveying device.

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