JP2006221048A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce transfer of toner from a photoreceptor drum to an electrostatic conveyance belt. <P>SOLUTION: The image forming apparatus includes: the photoreceptor drum 1 on which an electrostatic latent image is formed; a charging device 2 for charging the photoreceptor drum 1; a scanner 3 for forming an electrostatic latent image by exposing the charged photoreceptor drum 1 ; a developing device 4 for developing the electrostatic latent image as a toner image; and the electrostatic conveyance belt 9 for transferring the toner image onto a transfer material and conveying the transfer material. The scanner 3 exposes a non-image area of the photoreceptor drum 1. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electrophotographic image forming apparatus such as a copying machine or a printer using an electrophotographic system.

  In an electrophotographic image forming apparatus, an electrostatic latent image formed on an image carrier is visualized as a toner image by a developing device.

  As such a developing device, for example, a developing device of a non-magnetic one-component contact method, a magnetic one-component non-contact method, a magnetic two-component method, etc. has been proposed and put into practical use. In the developing device, a phenomenon called fogging may occur as the use continues. The term “fogging” generally indicates a phenomenon in which a toner having low chargeability is transferred from a developing roller to a charged potential on a photosensitive drum.

  Therefore, when fog occurs in the image forming apparatus having the developing device, fog toner on the photosensitive drum transports a white background portion of a transfer material (for example, paper or an OHP sheet) or a transfer member (for example, a transfer material). (Transfer belt). In particular, when an image is formed on a narrow transfer material, for example, an envelope or a postcard, since the photosensitive drum and the transport belt are in direct contact, the fog toner is directly transferred to the transport belt.

  Therefore, if the conveyor belt in which dirt due to fog toner is accumulated is used as it is, for example, when a wide A4 shaped paper is passed immediately after forming a narrow envelope as described above, In some cases, the stain due to fog toner may stain the back surface of the A4 standard paper that contacts the conveyor belt.

  Therefore, a configuration is known in which belt cleaning means for removing fog toner on the transport belt is provided.

Japanese Patent Application Laid-Open No. H10-228561 discloses a configuration in which unnecessary toner on the conveyor belt is collected by a cleaning unit that is in contact with the photosensitive drum via the photosensitive drum by applying a cleaning bias. Then, such a belt cleaning sequence is performed every time the size of the transfer material is different or periodically for a predetermined number of sheets to remove fog toner on the conveyance belt.
JP 2000-338821 A

  However, in the case of the configuration using the belt cleaning means, a waste toner box that accommodates the fog toner removed from the conveying belt is necessary, and when the waste toner box becomes full of toner, the user replaces the waste toner box. And waste toner boxes need to be discarded.

  On the other hand, since the belt cleaning sequence takes a predetermined time, the throughput (the number of images formed per unit time) of the image forming apparatus decreases when the belt cleaning sequence is periodically executed for a predetermined number of sheets to be passed. In addition, even when the sequence is executed every time the transfer material size is different, a waiting time occurs.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus capable of reducing the transfer of toner from an image carrier to a conveyance member.

  Another object of the present invention is to provide an image forming apparatus capable of reducing the occurrence of fog toner in a non-image area of an image carrier.

In order to achieve the above object, the present invention provides:
An image carrier on which an electrostatic latent image is formed;
Charging means for charging the image carrier;
Exposure means for exposing the charged image carrier to form an electrostatic latent image; and
Developing means for developing the electrostatic latent image as a toner image;
A transfer member that transfers and conveys the toner image onto a transfer material,
The exposure means exposes a non-image area of the image carrier.

In another aspect of the present invention,
An image carrier on which an electrostatic latent image is formed;
Charging means for charging the image carrier;
Exposure means for exposing the charged image carrier to form an electrostatic latent image; and
Developing means for developing the electrostatic latent image as a toner image;
A transfer member that transfers and conveys the toner image onto a transfer material,
The exposure means exposes an area outside the longitudinal direction of the image carrier from an area where the image carrier is in contact with the transfer material.

In another aspect of the present invention,
An image carrier on which an electrostatic latent image is formed;
Charging means for charging the image carrier;
Exposure means for exposing the charged image carrier to form an electrostatic latent image; and
Developing means for developing the electrostatic latent image as a toner image;
A transfer member that transfers and conveys the toner image onto a transfer material,
The exposure means exposes an area of the image carrier that comes into contact with the conveying member when a toner image is transferred onto the transfer material.

  As described above, according to the present invention, it is possible to reduce the transfer of toner from the image carrier to the conveying member. In addition, it is possible to reduce the occurrence of fog toner in the non-image area of the image carrier.

  The best mode for carrying out the present invention will be exemplarily described in detail below with reference to the drawings and embodiments. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. . Further, the materials, shapes, etc. of the members once described in the following description are the same as those in the first description unless otherwise described.

(Schematic configuration of image forming apparatus)
FIG. 1 is a schematic sectional view of the image forming apparatus according to the first embodiment. The image forming apparatus according to the present embodiment is a printer capable of forming a four-color full-color image.

  An image forming apparatus A shown in FIG. 1 includes photosensitive drums 1 (1A, 1B, 1C, 1D) as four image carriers arranged side by side in the vertical direction. The photosensitive drum 1 is rotationally driven by a driving unit (not shown) in the direction of the arrow (clockwise). In order to uniformly charge the surface of the photosensitive drum 1 in order according to the rotation direction, the periphery of the photosensitive drum 1 is irradiated with a laser based on the charging device 2 (2A, 2B, 2C, 2D) and image information. , A scanner 3 (3A, 3B, 3C, 3D) as exposure means for forming an electrostatic latent image on the photosensitive drum 1, and a developing device 4 (4A, 4B, 4C, 4D) for developing the electrostatic latent image as a toner image ), An electrostatic conveyance transfer device 6 for transferring and conveying the toner image on the photosensitive drum 1 to the transfer material 5, and a cleaner 7 (7A, 7B, 7) for removing residual transfer toner remaining on the surface of the photosensitive drum 1 after the transfer. 7C, 7D) and the like are provided.

  In this embodiment, the photosensitive drum 1, the charging device 2, the developing device 4, and the cleaner 7 are integrally formed into a cartridge to form a process cartridge 8 (8A, 8B, 8C, 8D). It is removable.

  In this embodiment, the process cartridges 8A, 8B, 8C, and 8D all have the same shape, and the toners contained therein are cyan, yellow, magenta, and black, respectively.

  An electrostatic conveyance belt 9 is disposed as a conveyance member that circulates and moves so as to face and contact all the photosensitive drums 1A, 1B, 1C, and 1D. The thickness of the electrostatic conveyance belt 9 is 50 to 200 μm, the volume resistivity is about 10E8 to 10E14 Ω · cm, the resin film such as PvdF, ETFE, polyamide, polyimide, PET, polycarbonate, and the thickness is about 0.5 to 2 mm. The thing using the resin layer on the base layer of rubber | gum can be used.

  Here, the volume resistivity is a value obtained by standardizing a measured value obtained by applying 100 V to a high resistance meter R8340 manufactured by ADVANTEST, using a measurement probe according to JIS method K6911, by the thickness of the electrostatic conveyance belt. is there.

  A transfer roller 10 (10A, 10B, 10C, 10D) as a transfer member is arranged in parallel in contact with the inside of the electrostatic conveyance belt 9 and corresponding to the four photosensitive drums 1A, 1B, 1C, 1D. Yes.

  These transfer rollers 10 face the photosensitive drum 1 and form a transfer portion. A positive charge is applied from the transfer roller 10 to the transfer material 5 via the electrostatic conveyance belt 9, and the transfer material 5 contacting the photosensitive drum 1 is applied to the transfer material 5 by the electric field due to the charge. The negative polarity toner is transferred. In this embodiment, Vtr = + 1200 V is applied to the transfer rollers 10A, 10B, 10C, and 10D as the transfer bias Vtr.

  The fixing device 11 fixes a plurality of toner images transferred to the transfer material 5. When the transfer material 5 onto which the toner image on the photosensitive drum 1 has been transferred passes through the fixing device 11, heat and pressure are applied. As a result, the toner images of a plurality of colors are permanently fixed on the surface of the transfer material 5.

(Schematic configuration of process cartridge)
FIG. 2 is a schematic cross-sectional view of the process cartridge according to the first embodiment.

  The photosensitive drum 1 is a rigid body formed by applying a photosensitive layer to the outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, and is driven to rotate in the direction of arrow R1 in the figure.

The charging device 2 is a conductive roller formed in a roller shape. By applying a charging bias by bringing the roller into contact with the photosensitive drum 1, the surface of the photosensitive drum 1 is charged with a charging potential (dark portion potential) Vd. = Charge to -700V. Then, the laser beam corresponding to the image signal of each color is irradiated from the scanner 3 onto the uniformly charged photosensitive drum 1. The photosensitive drum 1 irradiated with the laser light is selectively exposed, and the exposed portion becomes an exposure potential (bright portion potential) Vl = -100 V, and an electrostatic latent image is formed.

  Next, the developing device 4 (4A, 4B, 4C, 4D) will be described.

  The developing container 21 contains a negatively charged nonmagnetic toner 22 as a one-component developer. The developing device 4 is located in an opening extending in the longitudinal direction in the developing container 21, and includes a developing roller 23 as a developer carrying member arranged to face the photosensitive drum 1. The electrostatic latent image is developed with toner and visualized.

  The negatively chargeable non-magnetic toner 22 in this embodiment is a substantially spherical toner having 1.0 wt% of hydrophobic silica externally added and excellent in particle size distribution.

  The developing roller 23 having elasticity has a diameter of 16 mm, and is disposed with the substantially half right circumference shown in the figure protruding into the developing container 21 and the left half circumferential surface exposed from the developing container 21 at the opening. . The surface exposed from the developing container 21 is opposed to the photosensitive drum 1 positioned on the left side of the developing device 4 so as to be pressed and brought into contact with the photosensitive drum 1 by a predetermined amount. In this embodiment, the developing roller 23 enters 50 μm and comes into contact with the photosensitive drum 1.

  The developing roller 23 is rotationally driven in the direction of arrow R2. The surface has moderate unevenness in order to enhance the establishment of friction with the toner 22 and to carry the toner 22 well. The developing roller 23 in this embodiment has a two-layer structure in which silicon rubber is used as a base layer and acrylic / urethane rubber is coated on the surface, and has a roughness of Rz = 10 μm and a resistance of 10E4 to 10E6Ω. In this embodiment, a DC voltage of Vdc = −400 V is applied to the developing roller 23 as the developing bias Vdc.

  An elastic roller 24 is abutted below the developing roller 23 and is rotatably supported. The elastic roller 24 preferably employs a sponge structure or a fur brush structure in which fibers such as rayon or nylon are planted on a core metal from the viewpoint of supplying toner to the developing roller 23 and stripping off undeveloped toner. In this embodiment, it is a urethane sponge roller having a diameter of 14 mm, and is driven to rotate in the same direction as the developing roller 23.

  Above the developing roller 23, an elastic developing blade 25 is supported by a support metal 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 23 in surface contact. As the abutting direction, the free end side of the abutting portion is a counter direction located upstream in the rotation direction of the developing roller 23. In this embodiment, a thin metal plate made of phosphor bronze having a thickness of 100 μm is used.

  When the toner carried on the developing roller 23 by rubbing against the elastic roller 24 passes through the contact portion with the developing blade 25, the toner is charged by frictional charging and restricted to a thin layer.

  The cleaner 7 removes transfer residual toner remaining on the photosensitive drum 1 without being transferred after the toner developed on the photosensitive drum 1 by the developing device 4 is transferred to the transfer material 5.

(Cabritoner)
Next, fog toner will be described. In order to develop the electrostatic latent image formed on the photosensitive drum 1, the developing roller 23 and the elastic roller 24 provided in the developing device 4 are repeatedly driven to rotate. As a result, the negatively chargeable non-magnetic toner 22 deteriorates due to repeated rubbing between the developing roller 23 and the elastic roller 24 or between the developing roller 23 and the developing blade 25. There is a case where the toner is extremely reduced and transformed into a toner having no charging property.

  Such a deteriorated toner is not usually the exposure potential (in this embodiment, Vl = -100 V) of the electrostatic latent image formed on the photosensitive drum 1 to which the negatively chargeable toner is to be transferred, but a charged potential (this In the embodiment, Vd = −700 V).

  Here, FIG. 4 shows a change in the amount of fog toner transferred onto the photosensitive drum when the developing bias Vdc = −400 V in this embodiment is fixed and the charging potential Vd is changed.

  As can be seen from FIG. 4, the amount of fog is reduced by increasing the charging potential (decreasing the difference from the developing bias Vdc). In this embodiment, the occurrence of fog can be suppressed by setting the charging potential to Vd = −550V. That is, by setting the development bias Vdc = −400 V and the difference between the charging potentials to 150 V, the transfer of fog toner onto the drum can be suppressed.

  Further, as one of means for increasing the charging potential, in the present embodiment, a method using laser light from the scanner 3 as exposure means will be described. In addition to this, other exposure means may be provided as means for increasing the charging potential.

  FIG. 5 shows charging when the surface of the photosensitive drum 1 is charged to Vd = −700 V by applying a charging bias, and the amount of laser light per unit area for exposing the surface of the photosensitive drum 1 is changed. The change in the potential Vd is shown.

The horizontal axis represents the laser light amount (μJ / cm ² ) per unit area on the drum. In this embodiment, the exposure potential (Vl = −100 V) for forming the electrostatic latent image is 0.5 μJ / cm ² as the laser light amount. It is shown that. Further, in this embodiment, after applying a charging bias and charging to Vd = −700 V, exposure with laser light is performed, and in order to obtain a charging potential Vd = −550 V, the laser light quantity is 0.1 μJ / cm ^2. It turns out that it is necessary.

(Image forming operation)
An image forming operation using the process cartridge and the image forming apparatus in the configuration of the present embodiment described above will be described, particularly, an image forming operation of a small size envelope, a postcard or the like.

  The image forming apparatus A is connected to a host 14 (see FIG. 1) such as a personal computer, receives a print request signal from the host 14, and receives image data. The image data is developed into color data of cyan, yellow, magenta, and black by a controller unit (not shown).

  The transfer material 5 such as an envelope or a postcard is separated and fed from the feeding unit 15 and temporarily stops at the registration roller 16. Then, after the scanner 3 is started up and the potential of the photosensitive drum 1 is stabilized by the charging device 2, the recording position of the transfer material 5 and the image formation timings of the four color toner images are synchronized, and the electrostatic conveyance transfer device 6. It is conveyed by.

  In this embodiment, the first color cyan image is formed first.

The photosensitive drum 1A is uniformly charged to Vd = −700 V by the charging device 2A. The scanner 3A performs laser exposure on the image area based on cyan image data, and the non-image area is weakly exposed with a laser light amount of 0.1 μJ / cm ² . The weakly exposed non-image area is uniformly charged to Vd = −550V. As described above, the non-image area of the photosensitive drum 1 is exposed by the scanner 3 to increase the charging potential of the non-image area, and the difference between the charging potential and the developing bias potential is reduced, so that the fog toner is generated. It becomes difficult to transfer to a non-image area. Therefore, the transfer of fog toner from the photosensitive drum 1 to the electrostatic conveyance belt 9 can be reduced, and contamination on the back surface of the transfer material can be prevented or reduced.

  FIG. 3 is a diagram schematically illustrating the surface potential of the photosensitive drum during the image forming operation according to the first embodiment. Normally, the length of the developer carrying area in the longitudinal direction of the developing roller 23A is longer than the size of the maximum transfer material (medium) that can be used in the image forming apparatus, and the effective charging area length in the longitudinal direction of the charging device 2A is The length of the developer carrying area of the developing roller 23A is longer. Therefore, the non-image area to be weakly exposed is an area outside the width direction of the transfer material (direction perpendicular to the transport direction), and is outside the length of the developer carrying area in the longitudinal direction of the developing roller, The area is the same as or shorter than the effective charging area length of the charging device 2A.

  On the developing roller 23A of the developing device 4A incorporating cyan toner, the cyan toner is carried by sliding with the elastic roller 24A. When the developing roller 23 is rotationally driven, the carried cyan toner passes through a contact portion with the developing blade 25A. At this time, electric charge is imparted by frictional charging, and the uniform thin layer is regulated. Further, the cyan toner layer formed as a thin layer on the developing roller 23A is conveyed to a contact portion (developing portion) with the photosensitive drum 1A. A DC voltage of Vdc = −400V is applied as a developing bias to the developing roller 23A. In this developing unit, the cyan toner layer develops the electrostatic latent image on the photosensitive drum 1A with a developing bias and visualizes it as a cyan toner image.

  The visualized cyan toner image on the photosensitive drum 1A is conveyed to a transfer portion with the opposing transfer roller 10A by the rotational drive of the photosensitive drum 1A. At the same time, the transfer material 5 is transported to the transfer section by the electrostatic transport belt 9. A transfer bias Vtr = 1200 V is applied to the transfer roller 10A. As a result, the cyan toner image on the photosensitive drum 1A is transferred to the transfer material 5 in contact with the photosensitive drum 1A.

  Next, yellow image formation, which is the second color in this embodiment, is performed.

The photosensitive drum 1B is uniformly charged to Vd = −700 V by the charging device 2B. By the scanner 3B, the image area is subjected to laser exposure based on yellow image data, and the non-image area is subjected to weak exposure of 0.1 μJ / cm ² as the laser light quantity. The weakly exposed non-image area is uniformly charged to Vd = −550V.

  The electrostatic latent image on the photosensitive drum 1B is developed by a process similar to that for the first color, visualized as a yellow toner image, and conveyed to a transfer portion with the opposing transfer roller 10B by rotational driving of the photosensitive drum 1B. The

  At the same time, the transfer material 5 onto which the cyan toner image has been transferred is transported to the transfer portion by the electrostatic transport belt 9. The yellow toner image is transferred so as to overlap the cyan toner image.

  Next, magenta image formation, which is the third color in this embodiment, is performed.

The photosensitive drum 1C is uniformly charged to Vd = −700 V by the charging device 2C. The scanner 3C performs laser exposure on the image area based on magenta image data, and the non-image area is weakly exposed with a laser light amount of 0.1 μJ / cm ² . The weakly exposed non-image area is uniformly charged to Vd = −550V.

  The electrostatic latent image on the photosensitive drum 1C is developed by a process similar to that for the first and second colors, visualized as a magenta toner image, and transferred to the opposing transfer roller 10C by rotating the photosensitive drum 1C. It is conveyed to.

  Simultaneously, the transfer material 5 onto which the cyan toner image and the yellow toner image are transferred is conveyed to the transfer unit by the electrostatic conveyance belt 9.

  The magenta toner image is transferred by superimposing the cyan toner image and the yellow toner image.

  Finally, black image formation, which is the fourth color in this embodiment, is performed.

The photosensitive drum 1D is uniformly charged to Vd = −700 V by the charging device 2D. By the scanner 3D, the image area is subjected to laser exposure based on the black image data, and the non-image area is subjected to weak exposure of 0.1 μJ / cm ² as a laser light amount. The weakly exposed non-image area is uniformly charged to Vd = −550V.

  The electrostatic latent image on the photosensitive drum 1D is developed by the same process as described above, visualized as a black toner image, and conveyed to a transfer portion with the opposing transfer roller 10D by the rotational driving of the photosensitive drum 1D.

  At the same time, the transfer material 5 onto which the cyan toner image, the yellow toner image, and the magenta toner image are transferred by the electrostatic transfer belt 9 is transferred to the transfer portion.

  The black toner image is transferred by superimposing the toner image superimposed on the cyan toner image, the yellow toner image, and the magenta toner image.

  In this manner, the cyan toner image, the yellow toner image, the magenta toner image, and the black toner image are sequentially transferred while the transfer material 5 is conveyed to the electrostatic conveyance belt 9.

  The transfer material 5 onto which the four color toner images have been transferred is separated from the electrostatic conveyance belt 9, permanently fixed by the fixing device 11, and discharged outside the apparatus.

  By performing image formation in the image forming apparatus, the occurrence of fog can be suppressed by setting the potential of the non-image area of the photosensitive drum to an appropriate value, and toner transfer from the image carrier to the conveying member is reduced. It becomes possible. As a result, contamination of the electrostatic conveyance belt with fog toner can be prevented or reduced. In particular, even when a postcard or envelope having a narrow size is passed, the electrostatic conveyance belt can be prevented or reduced from being contaminated with fog toner. For this reason, it is possible to prevent or reduce the contamination of the back surface of a postcard or envelope having a small width immediately after forming an image on a postcard or envelope having a wide width even if the A4 shaped paper having a large width is passed through.

  Here, the non-image area can also be referred to as a portion where the photosensitive drum 1 and the electrostatic conveyance belt 9 are in contact with each other. Further, an area outside the longitudinal direction of the photosensitive drum 1 from an area where the photosensitive drum 1 is in contact with the transfer material 5 may be exposed. Further, the area of the photosensitive drum 1 where the photosensitive drum 1 and the electrostatic conveyance belt 9 are in contact with each other when the toner image is transferred onto the transfer material 5 may be exposed.

  As a result, the occurrence of fog can be suppressed by exposing the photosensitive drum 1 corresponding to the region where the photosensitive drum 1 and the electrostatic conveyance belt 9 are in direct contact with the scanner 3 serving as an exposure unit.

  Further, there is no need to provide belt cleaning means to separately collect fog on the conveying belt, and an image forming apparatus having a simple configuration can be provided. In addition, it is possible to provide an image forming apparatus that is preferable in terms of usability without a decrease in productivity due to the belt cleaning sequence.

  An image forming apparatus according to Embodiment 2 of the present invention will be described below. FIG. 6 is a schematic cross-sectional view of the image forming apparatus according to the second embodiment. A description of the same configuration and operation as those of the image forming apparatus described in the first embodiment will be omitted.

  The image forming apparatus B according to the second embodiment is largely different from the image forming apparatus A according to the first embodiment in that a humidity sensor 40 is provided as a humidity detecting unit that detects humidity information.

  As described in the first exemplary embodiment, fog toner deteriorates due to repeated rubbing between the developing roller 23 and the elastic roller 24, or between the developing roller 23 and the developing blade 25, and is negatively charged. It is a toner with extremely low chargeability and difficult to have chargeability. Furthermore, the chargeability of the toner strongly depends on the surrounding environment.

  Accordingly, FIG. 7 shows a change in fog amount transferred onto the drum when the developing bias (Vdc = −400 V) is fixed and the charging potential Vd is changed for each humidity in the surrounding environment of the image forming apparatus.

  As can be seen from FIG. 7, first, the amount of fog is reduced by increasing the charging potential at each relative humidity (decreasing the difference from the developing bias). Secondly, at a relative humidity of 80% RH, the charging potential Vd = −500V, that is, the difference between the developing bias Vdc = −400V and the charging potential Vd is set to 100V, thereby the fog toner drum. It is possible to suppress the upward transition. At a relative humidity of 50% RH, when the charging potential Vd = −550V, that is, the difference between the development bias Vdc = −400V and the charging potential Vd is 150V, the fog toner is transferred onto the drum. Can be suppressed. At a relative humidity of 10% RH, by setting the charging potential Vd = −650 V, that is, by setting the difference between the development bias Vdc = −400 V and the charging potential Vd to 250 V, the fog toner is transferred onto the drum. Can be suppressed.

  Thus, it can be seen that the charging potential that can suppress the occurrence of fogging changes depending on the ambient environment of the image forming apparatus, particularly relative humidity.

  Therefore, also in the present embodiment, as one means for increasing the charging potential, a method using laser light from the scanner 3 which is an exposure means is used.

  Then, the amount of laser light is controlled to change based on humidity information detected by the humidity sensor 40 provided in the image forming apparatus B. In this embodiment, as shown in FIGS. 8 and 9, the laser light quantity is changed so that the drum surface light quantity is changed by a linear expression with respect to the relative humidity, and a desired charging potential can be obtained at each relative humidity. . Therefore, the occurrence of fogging can be suppressed under each relative humidity environment.

  Since the image forming operation using the process cartridge and the image forming apparatus in the configuration of the present embodiment described above is mainly the same as that of the first embodiment, differences from the first embodiment will be particularly described.

Prior to the image forming operation described in the first embodiment, the image forming apparatus B detects the humidity information of the surrounding environment by the humidity sensor 40 provided in the image forming apparatus. Based on the humidity information, a control means (not shown) provided in the image forming apparatus B calculates the laser light amount in the non-image area and controls the exposure amount. In this embodiment, when the humidity detection result of the surrounding environment is 50%, the laser light quantity is calculated as 0.1 μJ / cm ² from FIGS.

  First, in this embodiment, an image of cyan, which is the first color, is formed.

  The photosensitive drum 1A is uniformly charged to Vd = −700 V by the charging device 2A. The image area is subjected to laser exposure based on cyan image data by the scanner 3A, and the non-image area is subjected to predetermined weak exposure of 0.1 μJ / cm 2 as a laser light amount based on the detection result. The weakly exposed non-image area is uniformly charged to Vd = −550V.

  As in the first embodiment, the cyan toner is carried on the developing roller 23A of the developing device 4A incorporating the cyan toner by rubbing against the elastic roller 24A. When the developing roller 23 is rotationally driven, the carried cyan toner passes through a contact portion with the developing blade 25A. At this time, electric charge is imparted by frictional charging, and the uniform thin layer is regulated. Further, the cyan toner layer formed as a thin layer on the developing roller 23A is conveyed to a contact portion (developing portion) with the photosensitive drum 1A. A DC voltage of Vdc = −400V is applied as a developing bias to the developing roller 23A. In this developing unit, the cyan toner layer develops the electrostatic latent image on the photosensitive drum 1A with a developing bias and visualizes it as a cyan toner image.

  The visualized cyan toner image on the photosensitive drum 1A is conveyed to a transfer portion with the opposing transfer roller 10A by the rotational drive of the photosensitive drum 1A. At the same time, the transfer material 5 is transported to the transfer section by the electrostatic transport belt 9. A transfer bias Vtr = 1200 V is applied to the transfer roller 10A. As a result, the cyan toner image on the photosensitive drum 1A is transferred to the transfer material 5 in contact with the photosensitive drum 1A.

  Thereafter, image formation is performed for each of the colors yellow, magenta, and black as in the first embodiment. At that time, the non-image areas of the respective photosensitive drums 1B, 1C, and 1D are subjected to predetermined weak exposure of 0.1 μJ / cm 2 as a laser light amount based on the detection result by the humidity sensor 40. The weakly exposed non-image area is uniformly charged to Vd = −550V.

  The transfer material 5 onto which the four color toner images have been transferred is separated from the electrostatic conveyance belt 9, fixed by the fixing device 11, and discharged outside the apparatus.

  By forming an image in the image forming apparatus B, the occurrence of fog can be suppressed by setting the potential of the non-image area of the photosensitive drum to an appropriate value even when the ambient environment of the image forming apparatus changes. The transfer of toner from the image carrier to the conveying member can be reduced. As a result, contamination of the electrostatic conveyance belt with fog toner can be prevented or reduced. In particular, even when a postcard or envelope having a narrow size is passed, the electrostatic conveyance belt can be prevented or reduced from being contaminated with fog toner. For this reason, it is possible to prevent or reduce the contamination of the back surface of a postcard or envelope having a small width immediately after forming an image on a postcard or envelope having a wide width even if the A4 shaped paper having a large width is passed through.

  Further, there is no need to provide belt cleaning means to separately collect fog on the conveying belt, and an image forming apparatus having a simple configuration can be provided. In addition, it is possible to provide an image forming apparatus that is preferable in terms of usability without a decrease in productivity due to the belt cleaning sequence.

  An image forming apparatus according to Embodiment 3 of the present invention will be described below. FIG. 10 is a schematic cross-sectional view of the image forming apparatus according to the third embodiment. A description of the same configuration and operation as those of the image forming apparatus described in the first and second embodiments is omitted.

  The image forming apparatus C according to the present embodiment is largely different in that the storage unit 50 is provided in the image forming apparatus A according to the first embodiment.

  In the process cartridges 8A, 8B, 8C, and 8D of this embodiment shown in the figure, storage means 50 indicated by 50A, 50B, 50C, and 50D are provided in the vicinity of the developing devices 4A, 4B, 4C, and 4D, respectively. A non-volatile memory was used as the storage means 50 mounted on the process cartridge 8.

  Since the image forming apparatus C is a non-contact type memory that can communicate with the main body of the image forming apparatus C and the storage means 50 without being mechanically connected, a writing / reading means 51 ( 51A, 51B, 51C, 51D) are provided. In addition, a volatile memory equipped with a power source can be used as the storage means. As the capacity of the storage means 50 provided in the process cartridge, an appropriate capacity can be selected according to the amount of information to be stored. The storage unit 50 may be a contact type.

  In the storage unit 50 disposed in the process cartridge 8 according to the present embodiment, as the life information associated with the life of the developing unit, the number of image formations of the image forming apparatus C, the number of sheets of the transfer material 5 passed, the developing roller 23 Among these rotation speeds or rotation times, the developing roller rotation time is detected and stored.

  As described in the first and second embodiments, the fog toner is developed between the developing roller 23 and the elastic roller 24 or developed in order to develop the electrostatic latent image formed on the photosensitive drum 1. The toner is deteriorated due to repeated rubbing between the roller 23 and the developing blade 25, and the negative chargeability is extremely reduced.

  Therefore, as the rotation time of the developing roller 23, which is life information of the developing means, increases, that is, the rubbing occurs between the developing roller 23 and the elastic roller 24 or between the developing roller 23 and the developing blade 25. As the repeated time becomes longer, fog toner tends to be generated.

  Thus, FIG. 11 shows the change in fog amount transferred onto the drum when the developing bias (Vdc = −400 V) is fixed and the charging potential Vd is changed for each rotation time of the developing roller.

  As can be seen from FIG. 11, first, the amount of fog is reduced by increasing the charging potential (decreasing the difference from the developing bias) during each developing roller rotation time. Second, when the developing roller rotation time is 10000 sec, the charging potential is set to Vd = −650V, that is, the difference between the developing bias Vdc = −400V and the charging potential Vd is set to 250V. Thus, generation of fog can be suppressed, and transfer of fog toner onto the drum can be suppressed. When the rotation time of the developing roller is 50000 sec, fog is generated by setting the charging potential to Vd = −600V, that is, by setting the difference between the developing bias Vdc = −400V and the charging potential Vd to 200V. This can suppress the transfer of fog toner onto the drum. In the case where the rotation time of the developing roller is 100000 sec, fogging is generated by setting the charging potential to Vd = −550V, that is, by setting the difference between the developing bias Vdc = −400V and the charging potential Vd to 150V. This can suppress the transfer of fog toner onto the drum.

  Thus, it can be seen that the charging potential at which fogging can be suppressed changes depending on the rotation time of the developing roller, which is an index of the life of the developing means.

  The developing roller rotation time can be easily calculated from the driving time of the image forming apparatus side drive motor (not shown), and can be calculated for each process cartridge. The calculated developing roller rotation time is written in the storage unit 50 by the writing / reading unit 51 on the image forming apparatus side at a predetermined timing.

  The image forming apparatus C reads the developing roller rotation time written in the storage unit 50 provided in the process cartridge 8 by the writing / reading unit 51. Then, a control unit (not shown) provided in the image forming apparatus C sets the exposure amount by the laser light from each scanner 3 based on the read developing roller rotation time, and controls the charged potential of the non-image area. FIG. 12 is a graph illustrating the relationship between the exposure amount and the developing roller rotation time in the image forming apparatus according to the third embodiment.

  By providing the storage means 50 in the process cartridge 8, it is possible to easily know the life of the developing means provided in each process cartridge individually. Therefore, an appropriate charging potential can be controlled even when the process cartridge is replaced.

  Since the image forming operation using the process cartridge and the image forming apparatus in the configuration of the present embodiment described above is mainly the same as that of the first embodiment, differences from the first embodiment will be particularly described.

  Prior to the image forming operation described in the first embodiment, the image forming apparatus C reads the developing roller rotation time of each process cartridge stored in the storage unit 50 provided in the process cartridge by the writing / reading unit 51. The image forming apparatus C calculates the laser light amount of the non-image area in each process cartridge based on the read information on the developing roller rotation time.

  First, in this embodiment, an image of cyan, which is the first color, is formed. Hereinafter, a case where the rotation time of the cyan developing roller 23A is stored in the storage unit 50A as 10000 s will be described.

The photosensitive drum 1A is uniformly charged to Vd = −700 V by the charging device 2A. The scanner 3A performs laser exposure on the image area based on cyan image data, and the non-image area is a predetermined 0.025 μJ / cm calculated from the graph shown in FIG. 12 as the laser light quantity based on the detection result. Weak exposure is performed with a light quantity of ² . The weakly exposed non-image area is Vd
= Uniformly charged to -650V.

  As in the first embodiment, the cyan toner is carried on the developing roller 23A of the developing device 4A incorporating the cyan toner by rubbing against the elastic roller 24A. When the developing roller 23 is rotationally driven, the carried cyan toner passes through a contact portion with the developing blade 25A. At this time, electric charge is imparted by frictional charging, and the uniform thin layer is regulated. Further, the cyan toner layer formed as a thin layer on the developing roller 23A is conveyed to a contact portion (developing portion) with the photosensitive drum 1A. A DC voltage of Vdc = −400V is applied as a developing bias to the developing roller 23A. In this developing unit, the cyan toner layer develops the electrostatic latent image on the photosensitive drum 1A with a developing bias and visualizes it as a cyan toner image.

The visualized cyan toner image on the photosensitive drum 1A is conveyed to a transfer portion with the opposing transfer roller 10A by the rotational drive of the photosensitive drum 1A. At the same time, the transfer material 5 is transported to the transfer section by the electrostatic transport belt 9. A transfer bias Vtr = 1200 V is applied to the transfer roller 10A. As a result, the cyan toner image on the photosensitive drum 1A is transferred to the transfer material 5 in contact with the photosensitive drum 1A.

  Next, yellow image formation, which is the second color in this embodiment, is performed. Hereinafter, a case where the rotation time of the yellow developing roller 23B is stored in the storage unit 50B as 10000 s will be described.

The photosensitive drum 1B is uniformly charged to Vd = −700 V by the charging device 2B. The image area is subjected to laser exposure based on the yellow image data by the scanner 3B, and the non-image area is determined to be a predetermined 0.025 μJ / cm calculated from the graph shown in FIG. 12 as the laser light quantity based on the detection result. Weak exposure is performed with a light quantity of ² . Weakly exposed non-image areas are V
d = −650V is uniformly charged.

  The electrostatic latent image on the photosensitive drum 1B is developed by the same process as that for the first color, visualized as a yellow toner image, and conveyed to the transfer portion with the opposing transfer roller 10B by the rotational driving of the photosensitive drum 1B. The At the same time, the transfer material 5 onto which the cyan toner image has been transferred is transported to the transfer portion by the electrostatic transport belt 9. A transfer bias Vtr = 1200 V is applied to the transfer roller 10B. Thus, the yellow toner image is transferred so as to be superimposed on the cyan toner image on the transfer material 5 in contact with the photosensitive drum 1B.

  Next, magenta image formation, which is the third color in this embodiment, is performed. The case where the rotation time of the magenta developing roller 23C is stored in the storage unit 50C as 50000 s will be described below.

The photosensitive drum 1C is uniformly charged to Vd = −700 V by the charging device 2C. The image area is subjected to laser exposure based on magenta image data by the scanner 3C, and the non-image area is determined to be a predetermined 0.05 μJ / cm calculated from the graph shown in FIG. 12 as the laser light quantity based on the detection result. Weak exposure is performed with a light quantity of ² . The weakly exposed non-image area is Vd
= Uniformly charged to -600V.

  The electrostatic latent image on the photosensitive drum 1C is developed by a process similar to that for the first and second colors, visualized as a magenta toner image, and transferred to the opposing transfer roller 10C by rotating the photosensitive drum 1C. It is conveyed to. At the same time, the transfer material 5 onto which the cyan toner image and the yellow toner image have been transferred is transported to the transfer portion by the electrostatic transport belt 9. A transfer bias Vtr = 1200 V is applied to the transfer roller 10C. Thus, the magenta toner image is transferred so as to be superimposed on the cyan toner and the yellow toner on the transfer material 5 in contact with the photosensitive drum 1C.

  Finally, in this embodiment, black image formation, which is the fourth color, is performed. Hereinafter, a case where the rotation time of the black developing roller 23D is stored in the storage unit 50D as 100000 s will be described.

The photosensitive drum 1D is uniformly charged to Vd = −700 V by the charging device 2D. The image area is laser-exposed based on cyan image data by the scanner 3D, and the non-image area is a predetermined 0.1 μJ / cm calculated from the graph shown in FIG. 12 as a laser light quantity based on the detection result. Weak exposure is performed with a light quantity of ² . The weakly exposed non-image area is uniformly charged to Vd = −550V.

The electrostatic latent image on the photosensitive drum 1D is developed by the same process as described above, visualized as a black toner image, and conveyed to a transfer portion with the opposing transfer roller 10D by the rotational driving of the photosensitive drum 1D. At the same time, the transfer material 5 onto which the cyan toner image, the yellow toner image, and the magenta toner image are transferred by the electrostatic transfer belt 9 is transferred to the transfer portion. A transfer bias Vtr = 1200 V is applied to the transfer roller 10D. As a result, the black toner image is transferred by superimposing the cyan toner, the yellow toner, and the magenta toner on the transfer material 5 in contact with the photosensitive drum 1C on each other.

  The transfer material 5 onto which the four color toner images have been transferred is separated from the electrostatic conveyance belt 9, fixed by the fixing device 11, and discharged outside the apparatus.

  In the image forming apparatus C, even when the detachable process cartridge included in the image forming apparatus is replaced, information on the life of the developing unit is read from the storage unit provided in the process cartridge, thereby Even if the exposure conditions in the case of fluctuating, it is possible to suppress the occurrence of fog by setting the potential of the non-image area to an appropriate value, and to reduce the transfer of toner from the image carrier to the conveying member. Become. As a result, contamination of the electrostatic conveyance belt with fog toner can be prevented or reduced. In particular, even when a postcard or envelope having a narrow size is passed, the electrostatic conveyance belt can be prevented or reduced from being contaminated with fog toner. For this reason, it is possible to prevent or reduce the contamination of the back surface of a postcard or envelope having a small width immediately after forming an image on a postcard or envelope having a wide width even if the A4 shaped paper having a large width is passed through.

  Further, there is no need to provide belt cleaning means to separately collect fog on the conveying belt, and an image forming apparatus having a simple configuration can be provided. In addition, it is possible to provide an image forming apparatus that is preferable in terms of usability without a decrease in productivity due to the belt cleaning sequence.

  As described above, the present invention has been described with reference to each of the above-described embodiments. However, the present invention is not limited to each of the above-described embodiments, and may be modified and combined as much as possible. Needless to say.

  In each of the embodiments, an image forming apparatus that includes a plurality of sets of an image carrier, a charging unit, an exposure unit, and a developing unit and forms a multicolor image by sequentially superimposing toner images on a transfer material has been described. The present invention can also be applied to an image forming apparatus that forms a monochrome image having only one set of an image carrier, a charging unit, an exposure unit, and a developing unit.

  In each of the embodiments, the nonmagnetic one-component contact development method has been described. However, the present invention can be applied to other development methods such as a magnetic one-component development method and a magnetic two-component development method. Needless to say, the present invention can be applied to not only a multi-color image forming apparatus but also a monochrome image forming apparatus.

1 is a schematic sectional view of an image forming apparatus according to Embodiment 1. FIG. 1 is a schematic sectional view of a developing device according to Embodiment 1. FIG. FIG. 3 is a diagram schematically illustrating the surface potential of the photosensitive drum during the image forming operation according to the first exemplary embodiment. 6 is a graph showing a relationship between a charging potential on the surface of a photosensitive drum and a fog toner amount in the image forming apparatus according to the first embodiment. 6 is a graph showing the relationship between the exposure amount and the charged potential amount on the surface of the photosensitive drum in the image forming apparatus according to Example 1; 6 is a schematic cross-sectional view of an image forming apparatus according to Embodiment 2. FIG. 6 is a graph showing the relationship between the charging potential on the surface of the photosensitive drum and the amount of fog toner at each relative humidity of the image forming apparatus according to Example 2. 6 is a graph showing a relationship between an exposure amount and a charged potential amount on the surface of a photosensitive drum in an image forming apparatus according to Example 2. 6 is a graph illustrating a relationship between an exposure amount and relative humidity in the image forming apparatus according to the second embodiment. 6 is a schematic cross-sectional view of an image forming apparatus according to Embodiment 3. FIG. 10 is a graph showing the relationship between the charging potential on the surface of the photosensitive drum and the amount of fog toner at each number of rotations of the developing roller included in the image forming apparatus according to Example 3. 10 is a graph showing a relationship between an exposure amount and a developing roller rotation time in an image forming apparatus according to Example 3.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging device (charging means)
3 Scanner (exposure means)
4 Developing device (Developing means)
5 Transfer material 6 Electrostatic transfer device 8 Process cartridge 9 Electrostatic transfer belt (transport member)
DESCRIPTION OF SYMBOLS 10 Transfer roller 11 Fixing device 21 Developing container 22 Toner 23 Developing roller 40 Humidity sensor 50 Storage means 51 Reading means A, B, C Image forming apparatus

Claims (12)

An image carrier on which an electrostatic latent image is formed;
Charging means for charging the image carrier;
Exposure means for exposing the charged image carrier to form an electrostatic latent image; and
Developing means for developing the electrostatic latent image as a toner image;
A transfer member that transfers and conveys the toner image onto a transfer material,
The image forming apparatus, wherein the exposure unit exposes a non-image area of the image carrier.   The image forming apparatus according to claim 1, wherein the non-image area is a portion where the image carrier and the transport member are in contact with each other. An image carrier on which an electrostatic latent image is formed;
Charging means for charging the image carrier;
Exposure means for exposing the charged image carrier to form an electrostatic latent image; and
Developing means for developing the electrostatic latent image as a toner image;
A transfer member that transfers and conveys the toner image onto a transfer material,
The image forming apparatus according to claim 1, wherein the exposure unit exposes a region on the outer side in the longitudinal direction of the image carrier from a region where the image carrier is in contact with the transfer material. An image carrier on which an electrostatic latent image is formed;
Charging means for charging the image carrier;
Exposure means for exposing the charged image carrier to form an electrostatic latent image; and
Developing means for developing the electrostatic latent image as a toner image;
A transfer member that transfers and conveys the toner image onto a transfer material,
The image forming apparatus according to claim 1, wherein the exposure unit exposes a region of the image carrier that contacts the conveying member when a toner image is transferred onto the transfer material.   The image forming apparatus according to claim 4, wherein the contact area is outside in a longitudinal direction with respect to a developable width of the developing unit. Humidity detection means for detecting humidity information;
Control means for controlling the exposure amount of the exposure means based on the humidity information;
The image forming apparatus according to claim 1, further comprising:   7. The image forming apparatus according to claim 1, wherein life information associated with a life of the developing unit is detected, and an exposure amount of the exposure unit is controlled based on the life information.   8. The lifetime information is at least one of a rotation time of a developer carrying member included in the developing unit, the number of times of image formation of the image forming apparatus, and the number of sheets of the transfer material passed. Image forming apparatus.   The image forming apparatus according to claim 7, wherein the developing unit includes a storage unit that stores the life information.   The image forming apparatus according to claim 9, wherein the storage unit is a contact-type or non-contact-type nonvolatile memory.   11. The image forming apparatus according to claim 1, wherein a process cartridge having the developing unit is detachable.   12. A plurality of sets of the image carrier, the charging unit, the exposure unit, and the developing unit, and a multicolor image is formed by sequentially superposing toner images on the transfer material. The image forming apparatus according to any one of the above.

Images