JPH0514907B2 - - Google Patents

Description

[Detailed description of the invention]

[Technical Field of the Invention] The present invention relates to an image forming apparatus that serves both as a developing device and a cleaning device. [Prior Art and its Problems] An apparatus has been proposed that serves both as a developing device and a cleaning device, and moreover, performs development and cleaning at the same time. FIG. 1 is a schematic diagram of the configuration of such an image forming apparatus. A charging device 2, an exposure device 3, a developing/cleaning device 4, a transfer device 5, and an eraser lamp 6 are arranged around the photoconductor 1, and image formation is performed sequentially as the photoconductor 1 rotates. The circumference is shorter than the size of the transfer paper 7 used, and image formation on the first sheet continues even after the photoreceptor 1 has rotated once. That is, while the residual toner image after the transfer of the image formed in the first rotation of the photoreceptor 1 remains on the photoreceptor 1, a new electrostatic latent image is formed thereon. Next, the developing/cleaning device 4
In this step, this electrostatic latent image is developed and the residual toner on the photoreceptor 1 is also cleaned at the same time. In this way, image formation over one or more rotations of the photoreceptor 1 is completed. By the way, in an image forming apparatus that serves both as a developing device and a cleaning device, as a cleaning method when cleaning the toner remaining on the photoreceptor after the transfer process is completed, for example, a two-component developing method using non-magnetic toner and a magnetic carrier is used, and a magnetic brush is used. A method that uses the electric charge of the toner and the electrostatic adsorption force of a magnetic brush by applying a bias to the toner, a method that uses a single-component magnetic toner having magnetism as a developer and uses its magnetic force, or a method that uses the above method. A method has been proposed that uses a combination of a magnetic carrier and magnetic toner and uses their electrostatic adsorption force and magnetic force. This proposed cleaning method is sufficiently effective in a so-called conventional two-rotation, one-copy type apparatus in which the developing device and the cleaning device are both used, or in which developing and cleaning are not performed at the same time. However, when the above-mentioned developing device and cleaning device are used together, and the developing and cleaning are performed at the same time, sufficient cleaning performance cannot be obtained, and the residual toner image of the first rotation of the photoreceptor 1 remains uncleaned. Photoreceptor 1-2
This overlaps with the new image of the rotating eye, resulting in a defective image. [Object of the Invention] In view of the above-mentioned drawbacks of the conventional art, it is an object of the present invention to provide an image forming apparatus which uses both a developing device and a cleaning device, and has significantly improved cleaning ability, especially in a system in which cleaning is performed simultaneously with development. [Summary of the Invention] In order to achieve the above object, the present invention combines a developing device for developing an electrostatic latent image on an image carrier with toner and a cleaning device for cleaning untransferred toner on the image carrier. In an image forming apparatus in which the circumferential length of the image carrier is set to be shorter than the length of the paper used, a charger that charges the image carrier to a predetermined polarity, and a charger that irradiates image information to the charged image carrier to static an exposure means for forming an electrostatic latent image, the developing device contains toner having a charge of the same polarity as the predetermined polarity, and has a grounded sleeve holding the toner on the outer periphery; The method is characterized in that the high potential portion of the image carrier is developed by causing electrostatic induction or dielectric polarization in the toner by the high potential portion of the latent image. [Embodiments of the Invention] Examples of the present invention will be described in detail below with reference to the drawings. FIG. 2 is a block diagram of an image forming apparatus showing an embodiment of the present invention. The photoreceptor 8 is rotatably provided in the direction of the arrow shown in the figure, and a power outage device 9, an exposure device 10, a toner agitation member 11, a developing/cleaning device 12, a transfer device 13, and an eraser lamp 14 are sequentially arranged around the photoreceptor 8. In addition, a paper feed device 15 and a special equipment device 1 are arranged.
6, a separating device 17 and a fixing device 18 are respectively arranged at predetermined positions. The photoreceptor 8 has a circumference shorter than the size of the transfer paper used. The toner agitation member 11 is a bristle brush that slides and rotates against the photoreceptor 8 . Further, the developing/cleaning device 12 is rotatably provided on the outer periphery of a fixed magnet roll.
It has a grounded non-magnetic sleeve 12a, and a magnetic brush is formed on the outer peripheral surface of the sleeve 12a by a magnetic carrier and magnetic toner.
This magnetic toner has a characteristic of being charged to the same polarity as the electrostatic latent image formed on the photoreceptor 8 by frictional charging with the magnetic carrier. Next, the operation of the image forming apparatus having the above configuration will be explained. When the original is inserted from the direction of arrow A at the top of the main body, it is conveyed toward the original glass 19. The original transported onto the original glass 19 is exposed to the exposure device 10.
The reflected light is projected onto the photoreceptor 8 via a lens and a mirror. The photoreceptor 8 is uniformly charged in advance to a predetermined polarity by a charging device 9, and an electrostatic latent image corresponding to the original is formed on the photoreceptor 8 by exposure. This formed photoreceptor 8
As the photoreceptor 8 rotates, the upper electrostatic latent image next comes into contact with the toner-disturbing member 11, but at this time, the toner-disturbing member 11 is in a non-operating state and is only rotating as a result of the photoreceptor 8. Therefore, the electrostatic latent image on the photoreceptor 8 is not disturbed. After passing through the rubbing portion with the toner agitating member 11, the electrostatic latent image on the photoreceptor 8 is then visualized by the magnetic toner in a developing/cleaning device 12. As mentioned above, magnetic toner has a triboelectric charge with the same polarity as the charging polarity of the electrostatic latent image, but in the image forming section (low potential area corresponding to the text area of the document), the electrostatic latent image and the magnetic The electrostatic attraction force generated by electrostatic induction or dielectric polarization becomes larger than the electrostatic repulsion force acting between the toner particles, and the magnetic toner adheres to the image area of the electrostatic latent image. Electrostatic dielectricity is a phenomenon in which toner is charged to the opposite polarity to the surface of the photoconductor due to the influence of the potential on the surface of the photoconductor, and dielectric polarization is a phenomenon in which toner is charged internally due to the influence of the potential on the surface of the photoconductor. This is a phenomenon in which polarization occurs between positive and negative polarities. In dielectric polarization, charges with the opposite polarity to the potential on the photoreceptor surface appear in the toner near the photoreceptor,
Charges with the same polarity as the potential on the surface of the photoreceptor appear in areas far from the photoreceptor. On the other hand, in the non-image area (low potential area corresponding to the background area of the document), only a small potential remains on the photoreceptor after exposure, so no electrostatic induction or dielectric polarization occurs. The magnetic toner does not adhere at all due to the slight residual potential, the electrostatic repulsion of the magnetic toner, and the magnetic attraction between the magnetic carrier and the magnetic toner. Here, the magnetic carrier not only imparts a predetermined charge to the magnetic toner, but also serves as a counter electrode for the electrostatic latent image and assists in electrostatic induction or dielectric polarization. Here, the adhesion force of the toner to the photoreceptor due to electrostatic induction or dielectric polarization is weaker than in normal normal development, so cleaning performance is improved. The developed image formed on the photoreceptor 8 in the developing process is then sent to a transfer area as the photoreceptor 8 rotates. On the other hand, the transfer paper fed from the direction of arrow B by the paper feeding device 15 is temporarily stopped at a standby device 16, and is fed again to the transfer area in synchronization with the developed image on the photoreceptor 8. In the transfer area, a transfer device 13 transfers the developed image on the photoconductor 8 onto a transfer paper, and a separation device 17 separates the transfer paper from the photoconductor 8 and conveys it to the next fixing device 18 where it is fixed. On the other hand, the photoreceptor 8 is optically neutralized by an eraser lamp 14 after the transfer process is completed. In the known two-rotation, one-copy system, a cleaning process is next performed, but in this embodiment, since the circumference of the photoreceptor 8 is shorter than the size of the transfer paper, the image forming operation for the first sheet is further continued. The photoreceptor 8 that has passed through the eraser lamp 14 is charged again in a charging device 9. Since magnetic toner originally tends to be charged with the same polarity as the photoconductor 8, the magnetic toner remaining on the photoconductor 8 by passing through the charging device 9 is charged with a polarity opposite to that of the photoconductor 8 caused by electrostatic induction or dielectric polarization. The charge disappears and the photoreceptor 8
charged to the same polarity as. The uniformly charged photoconductor 8 enters the exposure process, where a new electrostatic latent image is formed again by the exposure device 10, and remains by the toner agitation member 11 that slides and rotates against the photoconductor 8 at a predetermined rotation speed. The toner is uniformly agitated and the electrostatic latent image is subsequently developed in a developing and cleaning device 12. At the same time as the electrostatic latent image is developed, the magnetic toner remaining on the photoreceptor 8 is easily magnetized by the attraction force due to the magnetic force of the magnetic brush on the sleeve 12a and the electrostatic repulsion force due to the electric charge of the photoreceptor 8 and the magnetic toner. Collected by brush. The new developed image formed during the second rotation of the photoreceptor 8 is subsequently transferred onto a transfer paper in a transfer process, and the image forming process that spans one or more rotations of the photoreceptor 8 is completed. Next, the photoreceptor 8 enters a dedicated cleaning process and the image forming operation ends. Next, a specific example will be further explained. Photoreceptor 8
When a selenium photoreceptor was used as a photoreceptor and charged and exposed, the potential of the image area after exposure was +800V and the potential of the non-image area was +80V. The developer used was a mixture of 50% by weight of magnetic carrier and 50% by weight of magnetic toner (magnetic material amount: 50%), and various magnetic toners having different amounts of triboelectric charge were used. Rotation speed of photoconductor 8: 50mm/sec
The rotational speed of sleeve 12a is 300mm/sec.
I went there. The magnetic force on the sleeve 12a was about 700 Gauss. When image formation was carried out under the above conditions, the results shown in Table 1 on the next page were obtained. As can be seen from the results shown in Table 1, toner with a high amount of triboelectric charge has a low image density, and when toner that is triboelectrically charged to the opposite polarity to the electrostatic latent image on the photoreceptor 8 is used, non-image areas is dirty, and cleaning performance is poor, making it impossible to obtain satisfactory images.

〔Effect of the invention〕

As described above in detail, the image forming apparatus of the present invention has a significantly improved cleaning ability, and the effect is particularly great in an apparatus that serves both as a developing device and a cleaning device and performs cleaning at the same time as development.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional image forming apparatus, and FIG. 2 is a block diagram of an image forming apparatus showing an embodiment of the present invention. 8... Photoreceptor, 9... Charging device, 10... Exposure device, 11... Toner disturbing member, 12... Developing and cleaning device, 13... Transfer device, 14...
Eraser lamp, 18...fixing device.

Claims (1)

[Scope of Claims] 1. A developing device that develops an electrostatic latent image on an image carrier with toner and a cleaning device that cleans untransferred toner on the image carrier, and the peripheral length of the image carrier is In an image forming apparatus set to be shorter than the length of paper to be used, a charger charges the image carrier to a predetermined polarity, and an exposure unit irradiates the charged image carrier with image information to form an electrostatic latent image. The developing device stores toner having a charge of the same polarity as the predetermined polarity, and has a sleeve that holds the toner on the outer periphery and is grounded, and the toner is removed by the high potential portion of the electrostatic latent image. An image forming apparatus characterized in that a high potential portion of the image carrier is developed by generating electrostatic induction or dielectric polarization.