JP2007156335A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image forming apparatus where a photoreceptor drum 1 is charged by a developing roller 2, without an independent charging device, thereby, only one polarity of bias is applied to the developing roller 2 to simplify the apparatus. <P>SOLUTION: In the image forming apparatus, the photoreceptor drum 1 whose peripheral length is larger than the size of maximum recording material is used, and the developing roller 2 charges the photoreceptor drum 1 in contact with the photoreceptor drum 1 before a latent image is formed while it carries developer, and develops the latent image. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus using an electrophotographic system, an electrostatic recording system, or the like.

  2. Description of the Related Art Conventionally, an electrophotographic apparatus that forms an image by a predetermined electrophotographic process by disposing exposure, development, transfer, cleaning (residual toner removal), charge removal, and charging process means on the outer peripheral surface of a photosensitive drum. It is well known. According to such an apparatus, the process means must be provided independently on the outer peripheral surface of the photosensitive drum, and a high voltage is required not only for charging but also for the developing bias. The configuration becomes complicated.

In order to eliminate such drawbacks, for example, an exposure unit that generates a light output corresponding to image information in a photosensitive drum formed by laminating a translucent conductive layer and a photoconductive layer on a translucent support. What is to be interpolated is known. The exposure means converges the light output and forms a latent image on the photoconductor layer. At the same time or immediately after that, the latent image is visualized through a developing sleeve placed facing the photosensitive drum. (Toner image). Thereafter, the toner image can be transferred onto plain paper via a transfer roller or other transfer means. In this type of image forming apparatus, the configuration can be further simplified, ozone generation and the like can be prevented, and further, ground cover can be prevented. That is, a conductive magnetic toner is carried on a developing sleeve that is disposed opposite to the photosensitive drum without providing an independent charger, and a so-called magnetic brush-like toner is utilized by using a fixed magnet contained in the sleeve. A rubbing area is provided near the development position. Then, charging is performed by injecting electric charge into the photoconductive layer of the drum through the rubbing area using the developing bias applied to the developing sleeve side while rubbing the surface of the photosensitive drum by the rubbing area. . Immediately after the charging, the developing is performed almost simultaneously with the exposure while performing exposure using the exposure means contained in the drum. (For example, see Patent Document 1)
In order to achieve higher image quality than the above-described apparatus, there is provided an apparatus provided with a charging device that faces the surface of the photoreceptor and is disposed at least on the downstream side of the image formation and on the non-contact area side of the developer. It has been proposed (see, for example, Patent Document 2). This means that the photosensitive member is reversely rotated until the surface of the photosensitive member charged by the charging device by the reverse rotation means prior to image formation reaches at least the contact area of the developer, and the charging device transfers the image. It is the structure which serves as.
Japanese Patent Laid-Open No. 5-94068 JP-A-5-273820

  In Patent Document 1, without providing an independent charger, a conductive magnetic toner is carried on a developing sleeve, and a magnetic brush-like toner is provided using a magnetic force contained in the sleeve. Such a configuration in which charge is injected by injecting a charge into the photoconductive layer of the photosensitive drum using a developing bias is difficult when a one-component toner is used.

  Further, Patent Document 2 proposes a configuration in which the charging device also serves as a means for transferring an image. In this configuration, when the reversal development method is employed, the bias used for charging and transferring requires two polarities.

  Accordingly, an object of the present invention is to apply an image to the developer carrier without providing an independent charging device by charging the image carrier while the developer carrier carrying the one-component developer carries the developer. The bias to be made can be of one polarity, which is to simplify the device.

  In order to achieve the above object, the present invention comprises a rotatable image carrier having a circumference larger than the maximum recording material size, a latent image forming unit for forming a latent image on the image carrier, and a one-component developer. In the image forming apparatus for forming the image on the recording material by performing reversal development, the developer carrying body carries the developer, and the latent image is formed on the developer carrying body. Before the image forming apparatus, the image bearing member is brought into contact with the image bearing member to charge the image bearing member and develop the latent image.

  The image forming apparatus of the present invention charges the image carrier in a state where the developer carrier carrying the one-component developer carries the developer, so that an independent charging device is not provided and the developer carrier is attached to the developer carrier. The applied bias can have a single polarity, and the device can be simplified.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings. The examples described below illustrate the present invention by way of example, and the dimensions, materials, shapes, relative arrangements, etc. of the components described below are not particularly specified unless otherwise specified. However, the scope of the present invention is not limited thereto.

Example 1
FIG. 1 is a schematic cross-sectional view showing the configuration of the image forming apparatus of the present invention. An image forming process according to the reversal development method of the present invention will be briefly described with reference to FIG. First, the photosensitive drum 1 as an image carrier is uniformly charged to a negative polarity by a developing roller 2 as a developer carrier in a state of holding a one-component developer. The developing roller 2 is provided in contact with the photosensitive drum 1 and includes an elastic layer. Next, the photosensitive drum 1 rotates in the direction of the arrow, and a bias is not applied to the transfer roller 6 serving as a transfer unit, and the scanner 8 serving as a latent image forming unit is exposed to laser light according to image information. An electrostatic latent image is formed thereon. Next, in the second rotation of the photosensitive drum 1, the electrostatic latent image is developed on the photosensitive drum 1 in contact with the developing roller 2 using the negative developer supplied by the developing device 7. Even during development, the developing roller 2 remains in contact with the photosensitive drum 1. Thereafter, the toner image on the photosensitive drum 1 is transferred onto the recording material by applying a positive bias to the transfer roller 6. The unfixed toner image on the recording material is permanently fixed to the recording material by heat and pressure by a fixing device (not shown). In the present image forming apparatus, since the developing roller 2 performs charging and development, the photosensitive drum 1 needs to rotate twice for each image formation. This operation is repeated for a continuous job (a job for continuously forming a plurality of images). Further, in this embodiment, simultaneous development cleaning is performed (details will be described later), and an independent cleaner for cleaning the transfer residual toner is not provided. Reference numeral 9 denotes a changeover switch for switching a power supply for applying a voltage to the developing roller 2. The charging switch is switched to a charging-side power supply when the developing roller 2 charges the photosensitive drum 1, and a developing-side power supply is used for development. The charging-side power supply and the developing-side power supply have the same negative polarity, but the charging-side power supply voltage has a larger absolute value than the developing-side power supply voltage. Further, in this embodiment, after the transfer process and before charging, exposure is performed by the scanner 8 to remove the charge of the photosensitive drum 1 so that the surface potential of the photosensitive drum 1 is made uniform.

  Next, the configuration of main components used in the image forming apparatus according to the embodiment of the present invention will be described. The maximum recording material size of the image forming apparatus in this embodiment is A4 size. Therefore, according to the image forming process described above, the photosensitive drum 1 moves to the start of the developing operation in the second rotation after the circumference of the maximum recording material size has been charged in the first rotation. Perimeter is required for A4 size. Accordingly, the diameter of the photosensitive drum 1 in this embodiment is set to 96 mm so that the circumferential length of the photosensitive drum is larger than the A4 size. The photosensitive drum 1 employs a polycarbonate organic photoconductor (OPC) drum. The developing device 7 has a negatively charged nonmagnetic toner (toner) 4 as a one-component developer. In this embodiment, the toner 4 is a substantially spherical toner having a good volumetric particle size of about 6 μm and excellent viscoelasticity during high-speed printing.

  A part of the developing container 7 facing the photosensitive drum 1 is opened over substantially the entire longitudinal direction of the photosensitive drum 1, and the developing roller 2 which is a roller-shaped developer carrier (developing means) is provided in the opening. Is arranged. The developing roller 2 is pressed and brought into contact with the photosensitive drum 1 located on the upper left side of the developing device 7 in the drawing so as to have a predetermined penetration amount, and is driven to rotate in the direction of arrow R2 in the drawing. The developing roller 2 used was an Asker C hardness of 50 ° and an MD-1 hardness (measured with a micro rubber hardness meter manufactured by Kobunshi Keiki Co., Ltd.) of 40 °.

  An elastic roller 5 is in contact with the developing roller 2 as a means for supplying a developer to the developing roller 2 and stripping off the undeveloped toner from the developing roller 2 at the lower right in the drawing. The elastic roller 5 is rotatably supported by the developing container 7. The elastic roller 5 is a rubber sponge roller from the viewpoint of supplying toner to the developing roller 2 and stripping off undeveloped toner, and is driven to rotate in the direction of arrow D in the figure, which is the same rotation direction as the developing roller 2.

  Further, the developing device 4 includes a developing blade 3 as a developer layer thickness regulating member that regulates the amount of toner carried on the developing roller 2. The developing blade 3 is made of an elastic phosphor bronze metal thin plate, and is provided so that the vicinity of the free end side is in contact with the outer peripheral surface of the developing roller 2 in surface contact. The toner carried on the developing roller 2 by rubbing against the elastic roller 5 is given a negative charge by frictional charging when passing through the contact portion with the developing blade 3, and is restricted to a thin layer. .

  A charging method using the developing roller 2 and a simultaneous development cleaning method using the developing roller 2 in a state where toner is held in the image forming apparatus according to the present exemplary embodiment will be described.

First, a charging method for the photosensitive drum 1 by the developing roller holding toner will be described. The discharge breakdown voltage Vb with respect to the gap g by a normal charging roller is Vb = 312 + 6.2 g (1)
The discharge start voltage Vin from the charging roller to the photosensitive drum 1 when the electrostatic capacitance between the photosensitive drum 1 and the gap is C and the dielectric constant of the gap is ε is Vin = VbεC / g (2)
It becomes. Then, the photosensitive drum surface potential Vd by the charging bias V is Vd = V−Vin (3)
It is represented by From the formulas (1), (2), and (3), for example, when the charging bias is fixed to −3000 V or less, the discharge is not performed if the gap g is increased. In this embodiment, since charging is performed by the developing roller 2, toner is present between the photosensitive drum 1, and if the toner layer becomes thick and the gap g becomes large, discharging cannot be performed. However, in this embodiment, the toner layer thickness is 20 μm or less and uniformly coated, and as shown in FIG. 2, there is no difference in the relationship between the charging drum surface potential and the charging bias with and without toner coating. As shown in FIG. 2, in this example, the discharge start voltage for the photosensitive drum 1 (the voltage applied to the developing roller when the discharge starts) is 500V. Therefore, in this embodiment, a voltage of −1000 V is applied to the developing roller 2 as a charging bias, and the surface potential of the photosensitive drum is set to −500 V. Furthermore, in this embodiment, the developing roller 2 is rotated at a constant speed with respect to the photosensitive drum 1 during charging in order to reduce the load on the toner due to the friction between the toner and the photosensitive drum 1. At the time of development, the peripheral speed of the developing roller 2 is preferably set to be larger than the peripheral speed of the photosensitive drum 1, for example, 130 to 160% so that the image density does not decrease.

  Next, the simultaneous development cleaning in this embodiment will be described. First, details of development will be described. In this embodiment, the toner coat amount on the photosensitive drum at 100% development is set to 0.6 (mg / cm 2), so the toner coat amount on the developing roller is set to 0.4 (mg / cm 2). The roller 2 rotates with respect to the photosensitive drum 1 at a peripheral speed of 1.5 times. The developing bias applied to the developing roller 2 is set to −330V with respect to the photosensitive drum surface potential (dark portion potential) of −500V. As shown in FIG. 2, the developing bias is a voltage lower than the discharge start voltage of the photosensitive drum 1.

Next, the details of the simultaneous development cleaning will be described. In this embodiment, after the transfer process is completed, a little transfer residual toner is left on the photosensitive drum 1. At this time, as a small amount of untransferred toner on the photosensitive drum 1, positive and negative polarity are mixed due to discharge, but the polarity is made negative in the next charging step. In this embodiment, the developing bias applied to the developing roller 2 is −330 V between the dark portion potential and the light portion potential of the photosensitive drum 1. Accordingly, in the portion where the electrostatic latent image is not formed on the surface of the photosensitive drum 1 during development (dark portion), the transfer residual toner is collected to the developing roller 2 and the portion where the electrostatic latent image is formed (bright portion). Then it is visualized. That is, an electric field for cleaning the toner from the dark part of the photosensitive drum 1 to the developing roller 2 and an electric field for developing the toner from the developing roller 2 to the bright part of the photosensitive drum 1 are formed, so that simultaneous development cleaning can be performed. Note that the transfer residual toner may be present at the exposure position after charging, but in this embodiment, if the toner coat amount on the drum is 0.3 (mg / cm ² ) or less, there is no influence on the latent image formation. In this embodiment, the transfer residual toner is 0.1 (mg / cm ² ) or less, so the transfer residual toner has no influence on the latent image formation.

  In this embodiment, as described above, charging and development are performed by the developing roller in a state where the one-component developer is held, so that an independent charging device is not provided, and the bias applied to the developing roller has one polarity. Thus, the apparatus can be simplified.

  In this embodiment, the developing roller 2 is rotated at a constant speed with respect to the photosensitive drum 1 at the time of charging. An effect can be obtained.

  In this embodiment, the exposure position by the scanner 8 is the downstream side of the transfer roller 6 and the upstream side of the developing roller 2, but the downstream side of the developing roller 2 and the upstream side of the transfer roller 6 is exposed by the scanner 8 after the transfer process. It is also possible to omit the step of aligning the surface potential of the drum 1.

  In this embodiment, when the developing roller 2 is charged, a DC bias equal to or higher than the discharge start voltage is applied to the developing roller 2, but a superimposed voltage of the DC bias and the AC bias may be applied. That is, for example, an AC bias (development bias (AC)) having a peak-to-peak voltage of 1600 VPP and a frequency of 2200 Hz and a DC bias (development bias (DC)) of −500 V can be applied to the developing roller 2 in an overlapping manner. At this time, the surface potential of the photosensitive drum 1 can be set to −500V. In this case, since the surface potential of the developing roller 2 and the photosensitive drum 1 becomes the same potential and the toner adheres to the surface of the photosensitive drum 1, a cleaning member is provided on the downstream side of the transfer roller 6 and the upstream side of the scanner 8. And more effective. The cleaning member is separated from the photosensitive drum 1 at the first rotation of the photosensitive drum 1 (when charged by the developing roller) and is brought into contact with the photosensitive drum 1 at the second rotation of the photosensitive drum 1 (when developing by the developing roller) for cleaning. Is good.

Example 2
Next, another embodiment of the image forming apparatus according to the present invention will be described.

  The present embodiment is characterized in that, in the image forming apparatus described in the first embodiment, the developing method is jumping development as shown in FIG. In this embodiment, the image forming process, the charging method using the developing roller 2 while holding the toner, and the developing simultaneous cleaning method using the developing roller 2 are the same as those in the first embodiment.

  In this embodiment, unlike the first embodiment, the photosensitive drum 1 and the developing roller 2 can be contacted and separated so that the developing roller 2 is separated from the photosensitive drum 1 during development. That is, the photosensitive drum 1 and the developing roller 2 are separated by 100 μm only at the time of development, and the development bias is applied by superimposing an AC bias with a peak-to-peak voltage of 1600 VPP and a DC bias of −330 V. At the time of development, the toner carried on the developing roller 2 and the photosensitive drum 1 are separated from each other, and the developer flies to the photosensitive drum 1 for development. As a result, the load on the toner due to the friction between the toner and the photosensitive drum can be further reduced, so that toner deterioration can be reduced.

  In this embodiment, as described above, charging and development are performed by the developing roller in a state where the one-component developer is held, so that an independent charging device is not provided, and the DC component of the bias applied to the developing roller is One polarity can be obtained, and the apparatus can be simplified.

  In this embodiment, the developing roller 2 is rotated at a constant speed with respect to the photosensitive drum 1 at the time of charging. An effect can be obtained.

  In this embodiment, the exposure position by the scanner 8 is on the downstream side of the transfer roller 6 and on the upstream side of the developing roller 2, but may be on the downstream side of the developing roller 2 and the upstream side of the transfer roller 6. Thereby, the step of aligning the surface potential of the photosensitive drum 1 by the scanner 8 after the transfer step can be omitted.

In this embodiment, a DC bias that is equal to or higher than the discharge start voltage is applied during charging by the developing roller 2, but a superimposed voltage of a DC bias and an AC bias may be applied. That is, for example, an AC bias (development bias (AC)) having a peak-to-peak voltage of 1600 VPP and a frequency of 2200 Hz and a DC bias (development bias (DC)) of −500 V can be applied to the developing roller 2 in an overlapping manner. At this time, the surface potential of the photosensitive drum 1 can be set to −500 V. In this case, the surface potentials of the developing roller 2 and the photosensitive drum 1 become the same potential, and the toner adheres to the surface of the photosensitive drum 1. It is more effective to provide a cleaning member downstream of the transfer roller 6 and upstream of the scanner 8.

  The cleaning member is separated from the photosensitive drum 1 at the first rotation of the photosensitive drum 1 (when charged by the developing roller) and is brought into contact with the photosensitive drum 1 at the second rotation of the photosensitive drum 1 (when developing by the developing roller) for cleaning. Is good.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. It is a figure which shows the relationship between the photosensitive drum surface potential and a charging bias in a present Example. 1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention using a jumping development system.

Explanation of symbols

1 Photosensitive drum (electrophotographic photosensitive member, image carrier)
2 Elastic roller 3 Developing blade 4 Developer (toner)
5 Toner Supply Roller 6 Transfer Roller 7 Developing Device 8 Scanner (Exposure Device)
9 Changeover switch

Claims (6)

A rotatable image carrier having a circumference larger than the maximum recording material size, a latent image forming means for forming a latent image on the image carrier, and a developer carrier for carrying a one-component developer, In an image forming apparatus that performs reversal development and forms an image on a recording material,
The developer carrying member, in a state where a developer is carried, contacts the image carrying member before the latent image is formed, charges the image carrying member, and develops the latent image. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the developer carrying member is in contact with the image carrying member to develop the latent image.   2. The image forming apparatus according to claim 1, wherein the developer carrying member develops the latent image in a state where the developer carried on the developer carrying member is separated from the image carrying member.   The developer carrier is charged with a voltage equal to or higher than a discharge start voltage for the image carrier when charging the image carrier, and is less than a discharge start voltage for the image carrier when developing the latent image. The image forming apparatus according to claim 1, wherein the voltage is applied.   5. The image forming apparatus according to claim 1, wherein the developer carrying member has different peripheral speeds when charging the image carrying member and when developing the latent image. .   6. The image forming apparatus according to claim 5, wherein the developer carrying member has a peripheral speed equal to a peripheral speed of the image carrier when charging the image carrier.

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