JP2007264477A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing image quality from being changed caused by the sticking of an externally added agent to an intermediate body during refreshing of a developer. <P>SOLUTION: The image forming apparatus primarily transfers a visible image, formed on a photoreceptor by supplying the externally added agent and the developer comprising toner, by a primary transfer means, and secondarily transferring the primary transfer image to a recording member by a secondary transfer means, and cleans off the developer on the intermediate body by an intermediate transfer body cleaning means. This image forming apparatus is provided with a control means that applies a transfer bias by the primary transfer means when the developer is refreshed. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus including an intermediate transfer member.

  In general, an image forming apparatus such as a copying machine or a printer has a charging process for uniformly charging a photosensitive drum, an exposure process for irradiating the charged photosensitive drum to form a latent image, and a toner on the latent image. A series of a development process for forming a visible image by adhering, a transfer process for transferring the visible image to the paper between the photosensitive drum and the transfer body, and a fixing process for melting and fixing the developed visible image on the paper. Through this process, image formation is performed. In order to prepare for the next image formation, the toner remaining on the photosensitive drum is generally removed by a cleaning mechanism such as a cleaning blade or a cleaning roller that rubs against the photosensitive drum.

  In this way, the image forming process is repeated, but the toner in the developing device is not consumed due to a low printing rate, that is, a case where the number of printing dots in a single image continues. In addition, the charge amount of toner (the charge amount per unit weight) may vary. In such a case, there is a problem in that the toner adhesion amount of the toner image formed on the photosensitive drum varies, and the image density of the output image is not stable or background stains occur.

  Therefore, in order to solve such a phenomenon, a method of refreshing the developer by replacing the deteriorated toner in the developing device with a new toner is used. In this case, at the time of non-image formation, a predetermined amount of toner in the developing device is ejected by discharging it to the photosensitive drum, and the deteriorated toner is forcibly consumed by removing it from the photosensitive drum with a cleaning blade. Such refresh processing is a well-known technique, and various cleaning means have been proposed as disclosed in, for example, Japanese Patent Application Laid-Open No. 2005-134776.

  On the other hand, it is known that a phenomenon called image flow often occurs due to an ion product or the like generated in the charging process. When image formation is performed in a high-humidity environment, the ion product absorbs moisture, so that the electrical resistance of the portion where the ion product adheres on the photosensitive drum is reduced, and this reduction in electrical resistance is caused by exposure. This is because it adversely affects the formation of the latent image.

Therefore, a so-called refresh process is known in which a toner containing an external additive is attached to a photosensitive drum during non-image formation, and the surface of the photosensitive drum is polished and rubbed with a cleaning blade or the like. When a cleaning blade or the like is used, the surface of the photosensitive drum is scraped along with the rotation of the photosensitive drum by bringing the edge portion into contact with the photosensitive drum surface, and residual toner, ion products, Paper dust etc. are scraped off.
2005-134776

  However, in an image forming apparatus in which a visible image formed on a photosensitive drum is transferred to an intermediate transfer body and then transferred to a sheet, a large amount of toner may be discharged in the developer refresh process. Before the large amount of toner is scraped off by the photoconductor cleaning blade, a toner external treatment agent adheres to the intermediate transfer member to some extent. For this reason, in the cleaning of the intermediate transfer member, the attached external additive cannot be completely removed, and the toner is transferred to the paper at the portion where the external additive that cannot be removed during image formation is attached. The intensity of the electric field may change and affect the image quality. In addition, when an elastic body is used as the material of the intermediate transfer body, the surface smoothness is deteriorated, which becomes particularly remarkable.

  The present invention has been proposed to solve the above-described conventional problems, and an object thereof is to provide an image forming apparatus that prevents a change in image quality due to adhesion of an external additive to an intermediate transfer member.

  The image forming apparatus of the present invention primarily transfers a visible image formed on a photoreceptor by supplying a developer having an external additive and a toner to an intermediate transfer member by a primary transfer unit, and by a secondary transfer unit. It is assumed that the primary transfer image is secondarily transferred to a recording member to form an image, and the developer on the intermediate transfer member is cleaned by an intermediate transfer member cleaning unit.

  The image forming apparatus according to the present invention includes a control unit that applies a transfer bias by the primary transfer unit when the developer is refreshed to refresh the developer. As a result, the toner moves and adheres from the photosensitive drum to the intermediate transfer member, so that the residual external additive is adhered to the toner and removed together with the toner by moving and attaching the toner from the photosensitive member to the intermediate transfer member. can do.

  In the present invention, the surface of the intermediate transfer member can be made of an elastic material. In this case, the external additive is likely to adhere to the intermediate transfer member, but the residual external additive adheres to the toner and is removed together with the toner by moving and attaching the toner from the photosensitive member to the intermediate transfer member. can do.

  Further, the image forming apparatus of the present invention collects the toner removed by the first transfer means for collecting the toner removed by the photoreceptor cleaning means for cleaning the photoreceptor, and the toner removed by the intermediate transfer body cleaning means. A second recovery means can be provided separately. By doing so, it is possible to prevent the collecting means from being filled with toner immediately.

  By adopting the configuration as described above, in the present invention, it is possible to prevent a change in image quality due to the adhesion of the external additive to the intermediate transfer member when the developer is refreshed.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. In this embodiment, the present invention is embodied as a digital copying machine.

  FIG. 1 is a conceptual diagram showing the overall configuration of the copying machine 101 according to the present embodiment. Light emitted from the light source 109 is reflected by the document placed on the document table 104 and guided to the image sensor 113 by the mirrors 110, 111, and 112. The image sensor 113 photoelectrically converts the received light to generate document image data.

  The user places a document on the document table 104 or sets the document on the document tray 116. Documents set on the document tray 116 are sent one by one to the conveyance path 117 by the pickup roller 114. The document sent to the conveyance path 117 is conveyed to the document discharge tray 118 via the image reading position 119 in the middle of the conveyance path 117, and is read by the image reading unit 102 when passing the image reading position 119. Read. Further, the image reading unit 102 can read not only the document conveyed by the document feeder 115 but also the document placed on the document table 104.

  The surface of the photosensitive drum 120 in the image forming unit 103 is made of an amorphous silicon thin film, and rotates in a predetermined direction at a constant speed. Around the photosensitive drum 120, a charger 121, an exposure unit 122, a developing unit 123, an intermediate transfer unit 124, a photosensitive member cleaning unit 125, and the like are arranged in this order from the upstream side in the rotation direction. The charger 121 uniformly charges the surface of the photosensitive drum 120. The exposure device 122 irradiates light according to image data, and forms an electrostatic latent image on the photosensitive drum 120. The developing unit 123 attaches toner to the electrostatic latent image formed by the exposure device 122 to form a toner image on the photosensitive drum 120. The intermediate transfer unit 124 transfers the toner image on the photosensitive drum 120 to a sheet. The photoconductor cleaning unit 125 cleans the surface of the photoconductor drum 120. A series of these processes is performed by rotating the photosensitive drum 120.

  When performing printing, the image forming unit 103 draws one sheet from the sheet feeding tray 127 to the conveyance path 130 using the pickup roller 128. The paper drawn out to the conveyance path 130 is sent to the intermediate transfer unit 124 by the registration roller 131, and the visible image is transferred. Thereafter, in order to fix the visible image, the sheet is sent to the fixing device 132 through the conveyance path. In the fixing device 132, when the paper passes between the heating roller 133 and the pressure roller 134, the visible image is fixed on the paper by heat and pressing force on the paper. The image forming unit 103 discharges the sheet that has passed through the fixing device 132 to the discharge tray 135.

  FIG. 2 is an enlarged view of a main part of the image forming unit 103 in the present embodiment. The developing unit 123 includes four color developing cartridges 123Y (yellow), 123C (cyan), 123M (magenta), and 123K (black). When the developing unit 123 rotates, the developing cartridges 123Y, 123C, 123M, 123K can be arranged at a position facing the photosensitive drum 120. Each developing cartridge sequentially forms a toner image on the photosensitive drum 120 for each color.

  A toner image formed on the photosensitive drum 120 is transferred to an intermediate transfer unit 124 described later, and a photosensitive member cleaning unit 125 is provided to remove the remaining developer that cannot be transferred. The photoconductor cleaning unit 125 is adjacent to the photoconductor drum 120 and includes a blade 208 that cleans the surface of the photoconductor drum 120. The blade 208 is made of, for example, an elastic material such as polyurethane, and the edge portion 208 a is in contact with the surface of the photosensitive drum 120. The edge portion 208a grinds and rubs the photosensitive drum 120, so that the developer remaining on the photosensitive drum 120 is removed.

  The photoconductor cleaning unit 125 is provided with a collection container 211 via a toner conveyance tube 210, and the toner removed from the photoconductor drum 120 is collected into the collection container 211 through the toner conveyance tube 210. .

  The intermediate transfer unit 124, a primary transfer roller 202 that primarily transfers the toner image on the photosensitive drum 120 to the intermediate transfer belt 201, and a secondary transfer that primarily transfers the primary transfer image of the intermediate transfer belt 201 to a sheet. A next transfer roller 203 and a transfer body cleaning unit 204 for cleaning the intermediate transfer belt 201 are provided.

  The intermediate transfer belt 201 is stretched over support rollers 205, 206 and a primary transfer roller 202, and the intermediate transfer belt 201 can be rotated by stretching and driving these rollers 202, 205, 206. The intermediate transfer belt 201 is made of, for example, an elastic material such as silicon rubber and urethane rubber. While the cleaning property can be ensured and the amount of wear of the blade 209, which will be described later, can be reduced, the external additive as fine particles remains. The structure is easy to do.

  The primary transfer roller 202 and the photosensitive drum 120 are pressed against each other with the intermediate transfer belt 201 interposed therebetween, and a nip portion 202 a serving as a primary transfer position is formed between the photosensitive drum 120 and the intermediate transfer belt 201. The primary transfer roller 202 includes a primary transfer applying unit (not shown) that applies a primary transfer bias. When the primary transfer bias is applied, the color toner image formed on the surface of the photosensitive drum 120 is temporarily temporarily transferred onto the intermediate transfer belt 201 that has passed through the nip portion 202a. This operation is repeated four times for each color of yellow (Y), cyan (C), magenta (M), and black (K), so that four color toner images are superimposed on the intermediate transfer belt 201.

  The secondary transfer roller 203 presses the support roller 206 with the intermediate transfer belt 201 sandwiched therebetween, thereby forming a nip portion 203a serving as a secondary transfer position between the secondary transfer roller 203 and the intermediate transfer belt 201. A secondary transfer bias can also be applied to the secondary transfer roller 203 by a secondary transfer application unit (not shown). When the secondary transfer bias is applied, the four-color toner images primarily transferred to the intermediate transfer belt 201 are conveyed from the conveyance path when passing through the nip portion 203a between the intermediate transfer belt 201 and the secondary transfer roller 203. Secondary transfer is performed on the sheet.

  A transfer body cleaning unit 204 is provided in order to remove a part of the developer remaining on the intermediate transfer belt 201 without being completely transferred onto the paper in the secondary transfer. The transfer body cleaning unit 204 is provided adjacent to the intermediate transfer belt 201 and includes a blade 209 that cleans the surface of the intermediate transfer belt 201. Similarly to the photosensitive member blade 208, the transfer member blade 209 is made of an elastic material, and the edge portion 209a abuts against the intermediate transfer belt 201 to remove residual toner on the intermediate transfer belt 201. be able to.

  Further, the transfer body cleaning unit 204 is provided with a collection container 213 via a toner conveyance tube 212, and the toner removed from the intermediate transfer belt 201 passes through the toner conveyance tube 212 to the collection container 213. And recovered.

  FIG. 3 is a diagram for explaining the refresh of the developer in the present embodiment. The refresh of the developer is performed when the printing rate is low, that is, when the number of print dots in one image continues and the developer deteriorates.

  The image forming apparatus is provided with a printing rate measuring unit 303 that measures the printing rate. The printing rate measuring unit 303 can count the cumulative number of dots of an image formed on the photosensitive drum 120 and measure the average printing rate based on the cumulative number of dots and the number of printed pages. If the printing rate measuring unit 303 determines that the average printing rate is still low, a refresh signal is transmitted to the refresh control unit 304.

  When the refresh control unit 304 receives a refresh signal from the printing rate measurement unit 303, first, the photosensitive drum 120 is uniformly charged by the charger 121, and the entire surface is exposed by the exposure unit 122. By discharging the developer onto the photosensitive drum 120 and discharging it, the deteriorated developer can be forcibly consumed.

  The refresh controller 304 controls the primary transfer roller 202 to apply a predetermined primary transfer bias voltage in response to the refresh signal. When the primary transfer bias voltage is applied, the charged toner 301 on the photosensitive drum 120 moves and adheres to the intermediate transfer belt 201, but a part of the external additive 302 remains on the photosensitive drum 120. .

  The external additive 302 remaining on the photosensitive drum 120 moves to the rubbing position of the blade 208 in accordance with the rotation of the photosensitive drum 120 while adhering to the photosensitive drum 120. Thereafter, as the edge 208 a of the blade 208 rubs against the surface of the photosensitive drum 120, the external additive 302 is also removed, and is collected in the collection container 211 through the toner conveyance tube 210.

  In this case, since the toner 301 does not adhere to the photosensitive drum 120, it is possible to prevent the collection container 211 from becoming full immediately.

  On the other hand, the toner 301 and a part of the external additive 302 that have moved and adhered from the photosensitive drum 120 onto the intermediate transfer belt 201 are removed by the blade 209 and then conveyed to the collection container 213 through the toner conveyance tube 212. . Here, as described above, the external additive 302 is likely to remain on the intermediate transfer belt 201 made of an elastic material, but it is difficult to remove the external additive 302 because it is a fine particle. In this embodiment, since the toner 301 moves and adheres on the intermediate transfer belt 201, the external additive 302 adheres to the toner 301, and the external additive 302 is scraped off together with the toner 301, thereby reliably adding the external additive. The processing agent 302 can be removed.

  FIG. 4 is a diagram for explaining the refreshing of the photosensitive drum 120. The refreshing of the photosensitive drum 120 is performed, for example, when a high-temperature and high-humidity environment continues or when the potential of the photosensitive drum 120 is lowered. This is because, when an ion product or the like adheres to the photosensitive drum 120 in a high temperature and high humidity environment, the ion product absorbs moisture, and thus image flow is likely to occur. In addition, since a large amount of ion products adhere to the photosensitive drum 120, the charge distribution on the surface of the photosensitive drum 120 is disturbed. This causes the potential of the photosensitive drum 120 to decrease.

  Therefore, the image forming apparatus is provided with a temperature / humidity sensor 403 that detects whether the environment is in a high temperature and high humidity environment and a potential sensor 404 that detects the potential of the surface of the photosensitive drum 120. The temperature / humidity sensor 403 detects the temperature and humidity of the surface of the photoconductor drum 120, and transmits a refresh signal to the photoconductor refresh controller 405 when detecting that the temperature exceeds the preset predetermined temperature or humidity. The potential sensor 404 detects the potential of the photosensitive drum 120, and transmits a refresh signal to the photosensitive member refresh control unit 405 when detecting that the potential does not reach the predetermined potential.

  When receiving the refresh signal from the temperature / humidity sensor 403 or the potential sensor 404, the photoconductor refresh controller 405 first uniformly charges the photoconductor drum 120 with the charger 121 and exposes the entire surface with the exposure unit 122. As a result, the toner 301 containing the external additive 302 such as silica or titanium oxide is ejected from the developing unit 123 to form a visible image on the entire surface of the photosensitive drum 120.

  The photoreceptor refresh control unit 305 receives the refresh signal and controls a primary transfer bias unit (not shown) not to apply a predetermined bias voltage to the primary transfer roller 202. Since no bias voltage is applied, the charged toner 301 on the photosensitive drum 120 does not move and adhere to the intermediate transfer belt 201, and the toner 301 and the external additive 302 remain on the photosensitive drum 120.

  The toner 301 and the external processing agent 302 remaining on the photosensitive drum 120 move to the rubbing position of the blade 208 in accordance with the rotation of the photosensitive drum 120 while being attached to the photosensitive drum 120. Thereafter, as the blade 208 scrapes the surface of the photosensitive drum 120, the toner 301 and the external additive 302 are also scraped off and are collected in the collection container 211 through the toner conveyance tube 210.

  Therefore, a recovery container 211 for the photosensitive drum 120 that collects the toner 301 and the external additive 302 on the surface of the photosensitive drum 120, and a recovery container 213 for the intermediate transfer belt 201 that recovers the toner 301 on the surface of the intermediate transfer belt 201. Are separately provided, so that it is possible to prevent the toner 301 from being filled immediately compared to the case where there is only one collection container.

  The above-described embodiment is an example embodying the present invention, and is not intended to limit the technical scope of the present invention.

  According to the image forming apparatus of the present invention, it is possible to prevent a change in image quality due to adhesion of an external processing agent to the intermediate transfer member when the developer is refreshed. Useful for various devices.

The figure for demonstrating schematic structure of the copying machine in this Embodiment The main part enlarged view of the image formation part in this Embodiment The figure for demonstrating refresh of the developer of this Embodiment The figure for demonstrating the refresh of the photosensitive drum of this Embodiment

Explanation of symbols

DESCRIPTION OF SYMBOLS 101 Image forming apparatus 120 Photoconductor drum 124 Intermediate transfer unit 125 Photoconductor cleaning unit 201 Intermediate transfer belt 202 Primary transfer roller 203 Secondary transfer roller 204 Transfer body cleaning unit

Claims (3)

A visible image formed on the photosensitive member by supplying a developer having an external additive and a toner is primarily transferred to an intermediate transfer member by a primary transfer unit, and the primary transfer image is transferred to a recording member by a secondary transfer unit. In an image forming apparatus for forming an image by secondary transfer and cleaning the developer on the intermediate transfer member by an intermediate transfer member cleaning unit,
An image forming apparatus comprising: a control unit that applies a transfer bias by the primary transfer unit when the developer is refreshed to refresh the developer of the developing unit.   The image forming apparatus according to claim 1, wherein the intermediate transfer member is made of an elastic material. A first recovery means for recovering the developer removed by the photosensitive member cleaning means for cleaning the photosensitive member;
A second recovery means for recovering the developer removed by the intermediate transfer member cleaning means;
The image forming apparatus according to claim 1, further comprising:

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