JP2005156776A - Color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent damage to an intermediate transfer belt and photoreceptor drums during monochrome printing and restrain deterioration of toner which results from the rotations of the rollers in the development device, in a color image forming apparatus with development devices arranged in tandem manner. <P>SOLUTION: In a monochrome print mode, the photoreceptor drums for yellow, magenta, and cyan which are not used for an image are separated from the intermediate transfer belt. As a method for separation, primary transfer rollers (for yellow, magenta, and cyan) pressed against the respective photoreceptor drums are retracted. In addition, the separation stops the rotations of the photoreceptor drums and stirring of developer in the development devices as well. Accordingly, deterioration of the developer can be restrained. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a color image forming apparatus using an electrophotographic method, such as a printer for a computer or a copying machine.

Some image forming apparatuses perform image formation using an electrophotographic technique in which a developer made of fine powder is electrostatically controlled and adsorbed. For example, an electrostatic latent image is formed on the surface of a photosensitive drum or a photosensitive belt as an image carrier, and the electrostatic latent image on the image carrier is developed with a toner or the like as a developer to be visualized. The developed image is transferred onto a transfer material by a transfer device to carry the image, and a toner image on the transfer material is fixed onto the transfer material by a fixing device using pressure or heat. An image is formed by sequentially performing these steps. Further application of this technique to obtain a multi-color image (so-called color image) is possible by using a multi-color developer. In principle, if yellow, magenta, and cyan developers are used, a full-color image can be obtained by mixing colors. (In some cases, a black developer is used in addition to the above three types.)
As a configuration of a color image forming apparatus, a developing device for storing the developer is provided for each color, and the plurality of developing devices are arranged on a straight line or a curve to develop an electrostatic latent image corresponding to the developer of each color. There is. There are a direct transfer method and an intermediate transfer method as a method of superimposing a plurality of color images in a color image forming apparatus until a final image is obtained on a transfer material such as paper or a plastic sheet.

  The former direct transfer method is a case where a transfer material is a partner to which a developed image on an image carrier adjacent (or included) with a developing device is transferred in the next step. When the transfer material is brought into contact with the image carrier or passed through a small gap, an electric bias is formed so that the developer on the image carrier is attracted to the transfer material, and the image is directly transferred from the image carrier to the transfer material. Let In a color image forming apparatus having a plurality of developing devices and a plurality of image carriers, a transfer material is moved to an image carrier corresponding to each color, and a developed image corresponding to each color is sequentially transferred to the transfer material.

  On the other hand, in the latter intermediate transfer system, there is a second image carrier that holds all the developed images of the respective colors during the process of transferring the image from the image carrier to the transfer material. From the image carrier corresponding to each color, all the developed images are once held on the second image carrier, and the second image carrier and the transfer material downstream from the transfer position between the first and second image carriers. And an electric bias is formed at the contact point and the image is transferred from the second image carrier to the transfer material. This second image carrier is sometimes called an intermediate transfer member.

  The color image forming apparatus using the intermediate transfer method is more advantageous in terms of the stability of the formed image than the direct transfer method. When a single color developed image on the image carrier corresponding to each color is transferred in the next step, the developer must be superimposed. In the direct transfer method, since the developer is transferred from the image carrier to the transfer material, the transfer environment differs depending on the physical properties, thickness, stiffness, and the like of the transfer material, and the image becomes unstable upon overlay. The transferability of the transfer material also affects the image. Depending on the attraction force of the transfer material, the developer that has already been transferred to the transfer material may be reversely transferred to the downstream image carrier. On the other hand, in the intermediate transfer method, since the transfer target in the overlaying process is always the same object, a stable overlay image can be obtained. Since the image is transferred from the intermediate transfer member to the transfer material in a lump, the transfer conditions may be set for the worst-case transfer material.

  In a direct transfer type color image forming apparatus, since each single color image carrier is directly transferred to a transfer material, the image carrier must also serve as a transfer material conveyance function. For example, in the transfer material conveyance path, a transfer material that is short in the conveyance direction with respect to the distance between the conveyance units (such as conveyance rollers) immediately before and after the image carrier transfer unit cannot be conveyed only by these conveyance units. That is, it is necessary for the image carrier to rotate and transport the transfer material.

  When all the image carriers are rotating and there is an image carrier that does not need to adsorb the developer by the image, the image carrier deterioration is promoted by the cleaning means for the image carrier. For example, as a cleaning means, there is a method of pressing a blade-shaped rubber against the image carrier. The developer is scraped off by rubbing rubber on the surface of the image carrier. If a small amount of developer remains on the image carrier, the frictional force between the image carrier and the rubber blade is reduced. When almost no developer remains, the frictional force increases, and image carrier scraping and blade turning are likely to occur.

  The same can be said for an intermediate transfer type color image forming apparatus. In the intermediate transfer system, as described above, the transfer material transport function by the image carrier is not necessary. However, when the image carrier and the intermediate transfer member are always in contact with each other, if the rotation of the image carrier on which the developer is not adsorbed depending on the image form is stopped, the image carrier and the intermediate transfer member slide with each other. become. This rubbing surface may cause the image carrier or the intermediate transfer member to be scraped off and the image on the intermediate transfer member to be rubbed.

  According to the present invention, the problem can be solved by separating the image bearing member and the intermediate transfer member of the developing device not involved in the image from each other at the transfer position.

  The intermediate transfer member may move away from the image carrier that does not move, or the image carrier may move relative to the intermediate transfer member that does not move. Sometimes both move.

  The image carrier and the intermediate transfer member which are selectively separated from each other are not in contact with each other, and the members are less likely to be scraped or worn. In addition, an image formed by a developing device that is not separated is transferred to the intermediate transfer member, and is not rubbed against a downstream image carrier that is not involved in the image.

  In this way, a good image can be obtained even if the life of the image forming apparatus is extended.

  As described above, the following effects can be obtained in the color image forming apparatus having the intermediate transfer member.

  At a location where image transfer from the image carrier to the intermediate transfer member is performed, the image carrier and the intermediate transfer member are selectively separated relative to each other in accordance with the image. Thereby, damage due to rubbing between the image carrier and the intermediate transfer member can be prevented in advance. Further, by stopping the rotation of the image carrier that is not used, the image carrier and the cleaning means (rubber blade, etc.) are not slid, and they are not damaged.

  Further, when the rotation of the image carrier is stopped, the developer need not be stirred. As the developer is agitated, deterioration of image formation is promoted. Without rotation or agitation, deterioration of the developer quality can be suppressed.

  Therefore, as an effect of the present invention, the life of the intermediate transfer member, the image carrier and its cleaning means can be extended. It can also be expected to suppress the deterioration of the developer quality.

  The separation between the image carrier and the intermediate transfer member can be realized by moving a primary transfer unit that presses the intermediate transfer member. When the entire intermediate transfer member is swung or moved, the belt drive coupling needs to be linked to the swing, or the position where the developed image on the intermediate transfer member is collectively transferred to the transfer material must be linked. Disappear. On the other hand, in the present invention, as viewed from the intermediate transfer body, the relative position of the transfer position to the image carrier or transfer material involved in image formation is not accompanied, so that the image formation reliability is increased.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.

  FIG. 1 shows a schematic configuration of a color image forming apparatus using an electrophotographic system according to the present invention. The color image forming apparatus A as an example is a laser beam printer that can form a four-color full-color image.

  The color image forming apparatus A, which forms an image through a process of fixing an image visualized with a developer (for example, toner) to a transfer material by heat or the like, is a drum-type electrophotography as a first image carrier. Photosensitive drums 1Y, 1M, 1C, and 1BK are provided as photosensitive members. The photosensitive drum 1 (when these symbols are common to Y, M, C, and BK, these symbols are omitted) is driven to rotate, for example, counterclockwise by driving means (not shown).

  A charging device 2 (Y, M, C, BK) that uniformly charges the surface of the photosensitive drum 1 and a light source (for example, laser light or LED light) blinking on the basis of image information, and electrostatic latent image on the photosensitive drum 1 The exposure device 3 for forming an image, the developing device 4 (Y, M, C, BK) for developing the toner by attaching the toner to the electrostatic latent image on the photosensitive drum 1, and the toner image on the photosensitive drum 1 being transferred. An intermediate transfer unit 5 or the like is installed as a second image carrier. The intermediate transfer member 5b in this case has a belt shape and rotates clockwise.

The developing device 4 including the photosensitive drum 1 is fixedly disposed in parallel to the intermediate transfer unit 5. The developing device 4 that develops the electrostatic latent image on the photosensitive drum 1 has four developer accommodating portions that accommodate four color toners. Each developer container is provided with a developer carrying roller 4a that carries toner as a developer on the surface and that faces the photosensitive drum 1 when the developer container faces the photosensitive drum 1. The electrostatic latent image on the photosensitive drum 1 can be developed by the developer carrying roller 4a.
By sequentially transferring and superimposing the developed image on the photosensitive drum 1 to one intermediate transfer body unit 5 facing each other, a single full-color developed image electrostatically adsorbed on the intermediate transfer body 5b is formed. In order to transfer the toner from the photosensitive drum 1 to the intermediate transfer belt 5b, transfer means 5d (Y, M, C, BK) for generating an electric bias with respect to the photosensitive drum is placed on the opposite side of the photosensitive drum across the belt. On the side.

  After one developed image is formed on the intermediate transfer member 5b, the intermediate transfer member 5b further rotates to a location E where the developed image is transferred to the transfer material. The transfer material in the transfer material storage box 6 is supplied to the transfer location E by the feeding / conveying device 7 at a predetermined timing. At this transfer location E, transfer means 5e for generating an electric bias with respect to the transfer belt 5b is provided on the opposite side of the transfer belt 5b with the transfer material interposed therebetween.

  In this way, the toner image is transferred to the transfer material by using the electrostatic attraction force. Further, in order to fix the toner image to the transfer material, the transfer material is conveyed to a fixing device. In the fixing device, heat and pressure are used to melt and fix the toner on the transfer material.

  The transfer material that has passed through the fixing device 8 is discharged to the paper discharge tray 10 by the transport unit 9. A curve 20 indicates a transfer material conveyance path.

  Among conventional color image forming apparatuses, there is a type that directly transfers to a transfer material as shown in the schematic sectional view of FIG. From the upper side of the apparatus, a fixing device 58, an exposure device 53, a developing device, a photosensitive drum 51 as a first image carrier, an electrostatic belt 55 for electrostatically attracting and conveying a transfer material, and a transfer material storage unit 56 are arranged in this order. ing.

  An electrostatic latent image is formed on the image carrier 51 by irradiation light from the exposure device 53 corresponding to the image. The latent image is developed by a developer from a developing device adjacent to the rotation. At the same time, one transfer material is taken out by the pickup roller 56c of the transfer material storage unit 56, and supplied to the electrostatic belt unit 55 through the conveying means 56a. At the timing when the transfer material passes through each image carrier 51, the development on the image carrier 51 is transferred to the transfer material. In this case, the developed image on the image carrier is moved to the transfer material by a high voltage or pressure. The transfer material carrying the developed image passes through the fixing device 58, whereby the developer is fixed to the transfer material by heat and pressure. The development-fixed transfer material is conveyed to the discharged paper storage unit 60 and obtained as a developed image.

  In this conventional example, in the path for transferring an image to a transfer material, the transfer material is conveyed so that the transfer material is sandwiched between the image carrier 51 and the electrostatic belt 55. An image carrier that does not carry a developed image, that is, an image carrier that does not carry a developer, must also come into contact with a transfer material or an electrostatic belt in order to transport the transfer material.

  Therefore, the image carrier that does not carry the developer is always rubbed, and the image carrier and the electrostatic belt are easily damaged.

  9 and 10 schematically show the state of the developer. The transfer target from the image carrier is the same for both the transfer material and the intermediate transfer member.To remove the developer that cannot be transferred from the image carrier, the blade-shaped rubber 59 is pressed against the image carrier and cleaned. Yes. As shown in FIG. 9, if any developer remains on the image carrier, the frictional force between the image carrier 51 and the rubber blade 59 is small. However, as shown in FIG. 10, when the rubber blade is pressed with almost no developer on the image carrier, the frictional force between them increases. As a result, surface scraping of the image carrier and scratching of the rubber blade are promoted, and there is a risk that a formed image will be defective.

  According to the present invention, in a color image forming apparatus using an intermediate transfer system, it is possible to obtain a good image without promoting damage to the image forming unit.

  2 and 3 are schematic views of the present invention.

  In FIG. 2, all of the plurality of developing devices and the image carrier are in the state of forming an image. The primary transfer member 5d presses the intermediate transfer belt 5b against the image carrier 1 (Y, M, C, BK) corresponding to each color. Using this contact and the high voltage bias, the developed image on the image carrier 1 is transferred to the intermediate transfer member 5b.

  FIG. 3 shows a case where the full-color image forming apparatus is operated to form, for example, a black color image only. For the unused colors, yellow, magenta, and cyan, the primary transfer member 5d is moved to separate the image carrier 1 and the intermediate transfer member 5b from each other. By adopting this configuration, the image carriers 1Y, 1M, and 1C that are not used and the intermediate transfer belt 5b are not rubbed and are not damaged.

  Further, if the rotation of the image carrier that is not used is stopped, the rubber blade (not shown in these drawings) will not be able to rotate and slide on the image carrier. The image carrier and the rubber blade are not damaged.

  In the present invention, it is suitable to employ a charging roller as the transfer means 5d for transferring the image from the image carrier to the intermediate transfer member. For example, when corona charging is used for image transfer, residual ions may exist in a space between the image carrier and the intermediate transfer member. Therefore, even if they are separated from each other, the developer may be attracted by a high voltage and transferred. On the other hand, the charging roller has almost no residual ions in the space and will not transfer unless it is in contact.

(First embodiment)
A first embodiment of the present invention is shown in FIGS.

  As shown in FIG. 4, the primary transfer members 5dY, 5dM, and 5dC are supported by the swing holder 21. 5dBK is a primary transfer member for black. The swing holder 21 can rotate around a fulcrum 26 and is restricted by a connecting shaft 22a. In FIG. 4, all the primary transfer members press the intermediate transfer belt 5b against the image carrier corresponding to each color while all the developing devices are in operation.

  FIG. 5 shows a state in which only a black color (BK) image is formed. When the connecting member 22 moves the connecting shaft 22a by rotation or the like, the swing holder 21 is rotated about the fulcrum 26.

  At the same time, the primary transfer members 5dY, 5dM, and 5dC supported by the swing holder 21 are not pressed toward the image carrier, and the intermediate transfer belt 5b is relatively separated from the image carrier.

  In this way, damage to the image carrier or intermediate transfer member can be prevented.

(Second embodiment)
6 and 7 show a second embodiment of the present invention. As shown in FIG. 6, the primary transfer members 5dY, 5dM, and 5dC are supported by transfer holders 25Y, 25M, and 25C, respectively. These transfer holders are always urged toward the image carrier, for example (the urging means is not shown). The transfer holders 25Y, 25M, and 25C are moved in the horizontal direction by the vertical movement of the cam slider 23. In FIG. 6, all the primary transfer members press the intermediate transfer belt 5b against the image carrier corresponding to each color while all the developing devices are in operation.

  FIG. 7 shows a state in which an image of only black color is formed. The cam slider 23 moves upward and moves the transfer holders 25Y, 25M, and 25C to the right. As a result, the transfer holders 25Y, 25M, and 25C do not press the image carrier, and the image carriers 1Y, 1M, and 1C and the intermediate transfer belt 5b are relatively separated from each other.

1 is a schematic cross-sectional view of a color image forming apparatus according to the present invention. 1 is a schematic view of the present invention showing a state in which all developing devices are operating. FIG. In the schematic of this invention, the state which the developing device is working selectively is shown. The first embodiment of the present invention shows a state in which all the developing devices are operating. The first embodiment of the present invention shows a state where the developing device is selectively operated. The second embodiment of the present invention shows a state in which all the developing devices are operating. The second embodiment of the present invention shows a state where the developing device is selectively operated. 1 is a schematic cross-sectional view of a conventional color image forming apparatus. The development process with a developing agent and the transfer process of a prior art example are shown. The development process and transfer process without a developer of a prior art example are shown.

Explanation of symbols

1 Photosensitive drum (image carrier)
4 Developing Device 5 Intermediate Transfer Unit 5b Intermediate Transfer Belt 5d Primary Transfer Means 21 Swing Holder 23 Cam Slider

Claims (5)

There are an image carrier that carries an electrostatic latent image, an exposure device for forming an electrostatic latent image on the image carrier, and a developing device that develops the electrostatic latent image of the image carrier. In the process of transferring a plurality of developments on the image carrier to a transfer material, there are endless belt-like intermediate transfer members for simultaneously carrying a plurality of images and transferring the images to the transfer material at once. And a color image forming apparatus having transfer means opposed to the developing device on the opposite side of the image carrier as viewed from the intermediate transfer member for transferring an image from the plurality of developing devices to the intermediate transfer member. ,
The plurality of transfer units are pressed against the intermediate transfer member, and the image carrier and the intermediate transfer member are transferred while maintaining a minute gap or contact, and selected from a plurality of the developing devices. In this case, for a developing device that is not used, a color image characterized in that the intermediate transfer member is separated from the image carrier to a position where the image cannot be transferred by reducing or eliminating the pressing force of the transfer unit. Forming equipment.   2. The color image forming apparatus according to claim 1, wherein the plurality of transfer units are held on one support frame, and the support frame is swung with respect to one fulcrum.   3. The color image forming apparatus according to claim 2, wherein a roller or the like that stretches the intermediate transfer member is not interlocked with the separating operation of the transfer unit.   4. The color image forming apparatus according to claim 3, wherein the intermediate transfer member and the image carrier are contacted / separated and separated selectively by full-color printing and mono-color printing. 2. The color image forming apparatus according to claim 1, wherein the transfer unit includes a member using roller charging.

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