JP2007298816A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus in which a speed difference is provided between an image carrier and an intermediate transfer belt, and in which the removal of discharge products arising from contact charging is securely performed without depending on the size of constituting apparatus or the like, thus the abrasion of the image carrier and the occurrence of an image defect can be prevented. <P>SOLUTION: The image forming apparatus includes: image carriers 21 on the surface of which toner images of respective colors are formed; contact type charging rolls 22 contacted with the image carriers 21 to charge the surfaces of the image carriers 21 to a prescribed potential; and an intermediate transfer belt 30 abutted against image carriers 21, and to which the toner images of respective colors formed at respective image carriers 21 are transferred, and a prescribed speed difference is provided between image carriers 21 and the intermediate transfer belt 30, the apparatus is characterized in that it is equipped with a discharge product removal mode where, in such a state that the contact areas between image carriers 21 and the intermediate transfer belt 30 are increased, the image carriers 21 and the intermediate transfer belt 30 are driven at a prescribed speed difference to remove discharge products. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic image forming apparatus having a contact type charging roll, and in particular, removal of discharge products accompanying contact charging in an image forming apparatus in which a speed difference is provided between an image carrier and an intermediate transfer belt. It is about technology.

Japanese Patent Laid-Open No. 08-2111755 JP 2004-77651 A

  In recent years, contact charging systems have been used in image forming apparatuses such as copiers. In such contact charging systems, a roll-shaped charging member to which a charging voltage is applied is applied to an image carrier such as a photosensitive drum. The charged surface of the photosensitive drum is charged to a predetermined potential by causing a discharge between the photosensitive drum and the charging member.

  In such a roll-shaped charging member (hereinafter also referred to as a charging roll), the photosensitive drum is charged to a predetermined potential by using discharge in a minute gap around the photosensitive drum contact surface. Discharge products such as ozone and nitrogen oxides are generated due to the influence of discharge in the vicinity, and the discharge products adhere to the surface of the photosensitive drum, degrading the quality of the toner image transferred to the intermediate transfer member. Have the problem of letting

  In addition, the adhesion of discharge products due to the discharge between the photosensitive drum and the charging member and the deterioration due to the discharge of the surface layer of the photosensitive drum make the photosensitive drum easy to scrape, thereby shortening the life of the photosensitive member. It was a factor. When the discharge product and the surface layer of the photoconductor can be cut together with a cleaning blade, such a problem of the discharge product does not occur, but when a photoconductor drum having a hard surface is used, Since the effect of scraping the surface of the photosensitive member by the cleaning blade becomes small, removal of the discharge product becomes a significant problem.

  Therefore, prior arts for removing such discharge products and preventing image defects have been proposed (see, for example, Patent Documents 1 and 2).

  Here, in Patent Document 1, a predetermined linear velocity difference is provided between the photosensitive drum and the intermediate transfer belt, and both the mechanical force and the force due to the transfer electric field are applied to the transfer nip portion, thereby transferring the transfer property. An image forming apparatus that is improved and prevents image defects such as image omission is disclosed.

  In Patent Document 2, a predetermined speed difference is provided between the photosensitive drum and the intermediate transfer belt in order to prevent unevenness of the photosensitive drum, unevenness of image density (hereinafter also referred to as banding), and the like. An image forming apparatus that improves image quality is disclosed.

  However, all of the prior arts disclosed in the above-mentioned patent documents have the following problems.

  For example, in the prior arts disclosed in Patent Documents 1 and 2, the effect of removing discharge products adhering to the photosensitive drum due to the speed difference provided between the photosensitive drum and the intermediate transfer belt. However, if such a speed difference is set to a large value, image defects such as banding occur, and slippage occurs between the photosensitive drum and the intermediate transfer belt, resulting in poor adhesion between the two. In return, the removal effect is reduced, and the discharge product cannot be sufficiently removed. On the other hand, when such a speed difference is small, the transferability is not improved, image defects such as image omission occur, or a rubbing effect cannot be obtained between the photosensitive drum and the intermediate transfer belt, There has been a problem that discharge products cannot be sufficiently removed.

  Therefore, the speed difference between the photosensitive drum and the intermediate transfer belt is inevitably within a predetermined range (for example, 1%) from the viewpoint of maintaining and improving the image quality and promoting the effect of removing the discharge products by maintaining the adhesion. About 10% to 10%).

  Under such circumstances, in recent years, components have also been downsized based on requests for downsizing of the apparatus. For example, when a small-diameter photosensitive drum is used, the contact area with the intermediate transfer belt is reduced. In addition, the contact pressure is inevitably reduced, and there has been a problem that a sufficient removal effect of the discharge product cannot be obtained within a predetermined speed difference range that does not cause image defects or slippage. That is, there has been a problem in that the discharge product removal effect cannot be sufficiently obtained only by a predetermined speed difference depending on the device configuration, the size of the constituent devices, and the like.

  Accordingly, the present invention has been made in view of the above-described problems of the prior art, and in an image forming apparatus in which a speed difference is provided between the image carrier and the intermediate transfer belt, the size of the constituent devices is determined. It is an object of the present invention to provide an image forming apparatus capable of reliably removing discharge products associated with contact charging, thereby preventing the wear of an image carrier and the occurrence of image defects.

  In order to achieve the above object, an image forming apparatus according to the present invention has an image carrier on which a toner image of each color is formed on the surface thereof, and contacts the image carrier with the surface of the image carrier at a predetermined potential. A contact-type charging roll that is electrically charged, and an intermediate transfer belt that is in contact with the image carrier and onto which the toner images of the respective colors formed on the image carrier are transferred. In an image forming apparatus in which a predetermined speed difference is provided between the image carrier and the intermediate transfer belt, the image carrier and the intermediate transfer belt are driven at a predetermined speed difference in a state where a contact area between the image carrier and the intermediate transfer belt is increased. And a discharge product removal mode for removing the discharge product.

  Here, the state where the contact area is increased means a state where the contact area is increased more than a predetermined contact area (nip area) between the image carrier and the intermediate transfer belt during normal image formation (image formation mode). is there.

  In general, in an image forming apparatus using a contact-type charging roll, an AC voltage is applied and discharged in order to charge the image carrier to a predetermined potential by discharging at a small gap between the charging roll and the image carrier. Is generated to uniformly charge a predetermined voltage. For this reason, the discharge product due to the alternating current component increases and is likely to adhere to the image carrier, and this discharge product causes an image defect and promotes the wear of the photosensitive drum.

  In order to remove such discharge products, a predetermined speed difference is provided between the image carrier and the intermediate transfer belt, and the discharge generated by the rubbing force generated by the speed difference adheres to the image carrier. A method for removing an object is known.

  However, since such a speed difference can only be set within a predetermined range, the discharge product may not be sufficiently removed only by the rubbing force due to the speed difference.

  Therefore, the image forming apparatus according to the present invention configured as described above includes an image carrier, a contact-type charging roll, and an intermediate transfer belt, and a predetermined speed difference is provided between the image carrier and the intermediate transfer belt. In the image forming apparatus provided with the discharge, the discharge is removed by driving the image carrier and the intermediate transfer belt at a predetermined speed difference in a state where the contact area between the image carrier and the intermediate transfer belt is increased. Since the product removal mode is provided, the discharge product generated by the contact-type charging roll can be surely removed regardless of the size of the constituent devices, and the occurrence of image defects can be prevented.

  The discharge product removal mode may be executed during standby for image formation.

  Here, the standby time for image formation is a predetermined standby time that enables the rated operation of the image forming apparatus, such as a standby operation until the fixing roll reaches a predetermined temperature or an initial check operation of the control program. It means the time of operation, and includes not only waiting for image formation immediately after power-on, but also waiting for image formation when a predetermined time has elapsed after completion of a series of image formations. .

  In general, when the discharge product adhered on the image bearing member is left in a stand-by state such as a standby state for a long time, it absorbs moisture with time and becomes a hygroscopic state. It is known that the discharge product that has become in a hygroscopic state is more easily removed by being in close contact with toner, external additives, and the like.

  Therefore, in such a configuration, since the discharge product removal mode is executed during standby for image formation, the discharge products that have become moisture-absorbed over time can be more affected without affecting the image forming operation. It can be reliably removed easily.

  Further, the increase in the contact area in the discharge product removal mode is caused by moving a moving roll disposed inside the intermediate transfer belt and in the vicinity of a nip portion between the image carrier and the intermediate transfer belt to the image carrier. And the intermediate transfer belt may be moved so as to increase the contact area.

  In such a configuration, the discharge roll removal mode is located inside the intermediate transfer belt and near the nip portion between the image carrier and the intermediate transfer belt. Since the contact area with the belt is increased so that the contact area increases, the increase in the contact area between the image carrier and the intermediate transfer belt depends on the size of the image carrier without damaging the image carrier. It can be realized easily.

  Furthermore, the predetermined contact area during the image formation between the image carrier and the intermediate transfer belt may be smaller than the contact area necessary for removing the discharge products formed on the image carrier. Good.

  In such a configuration, the discharge product formed on the image carrier has a predetermined contact area during image formation between the image carrier and the intermediate transfer belt, which makes removal of the discharge product particularly difficult. For example, a more suitable image forming apparatus can be provided for an apparatus configuration having a photosensitive drum having a small diameter smaller than the contact area necessary for removing the toner.

  According to the present invention, in the image forming apparatus in which a speed difference is provided between the image carrier and the intermediate transfer belt, the discharge product accompanying contact charging is reliably removed regardless of the size of the constituent device, etc. As a result, the wear of the image carrier and the occurrence of image defects can be prevented in advance.

<First embodiment>

  Embodiments according to the present invention will be described below with reference to the drawings.

  First, a schematic configuration of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is an overall configuration diagram of a tandem type color image forming apparatus according to the present invention.

  In FIG. 1, an image forming apparatus and a document reading device 10 that reads a document 12 on a platen 11 and four color components (for example, yellow, magenta, cyan, and black) images (toner images) by, for example, electrophotography. An image forming unit 20 to be formed (in this embodiment, a yellow image forming unit: 20a, a magenta image forming unit: 20b, a cyan image forming unit: 20c, a black image forming unit: 20d) and each image forming unit 20 An intermediate transfer belt 30 that sequentially transfers (primary transfer) the formed color component images, and a secondary transfer device 50 that collectively transfers (secondary transfer) the superimposed images transferred on the intermediate transfer belt 30 to the recording paper 100. A fixing device 70 for fixing the batch-transferred image on the recording paper 100, and the recording paper 10 at the batch transfer portion. It is obtained by a paper transportation system 80 for supplying a.

  In the present embodiment, the document reading apparatus 10 includes, for example, a light source 13 that is disposed below the platen 11 and irradiates light on the surface of the document 12, and a CCD that converts reflected light from the surface of the document 12 into an electrical signal. The photoelectric conversion element 14, an appropriate number of mirrors 15 that form a path for guiding the reflected light from the surface of the document 12 to the photoelectric conversion element 14, and the reflected light from the surface of the document 12 are coupled on the imaging surface of the photoelectric conversion element 14. And an imaging lens 16 for imaging.

  The image forming units 20a to 20d have photosensitive drums 21a to 21d, and charging devices 22a to 22d for charging the photosensitive drums 21a to 21d are disposed around the photosensitive drums 21a to 21d. An electrostatic latent image (an electrostatic latent image based mainly on image data read by the photoelectric conversion element 14 or image data taken from another recording medium) is written on the charged photosensitive drums 21a to 21d. Exposure devices 23a to 23d such as laser scanning devices, developing devices 24a to 24d in which electrostatic latent images written on the photosensitive drums 21a to 21d are developed with respective color component toners, and toners on the photosensitive drums 21a to 21d Residual toner on the primary transfer devices 25a to 25d and the photosensitive drums 21a to 21d such as a transfer roll for transferring the image to the intermediate transfer belt 30 is removed. Ram cleaner 26a~26d are disposed respectively.

  Here, the image forming units 20a to 20d have the same configuration, and these components (for example, the photosensitive drums 21a to 21d) have the same structure. Notation (for example, photosensitive drum 21) is used.

  The photosensitive drum 21 in the present embodiment is a small-diameter drum-like member having an outer diameter of φ30 mm. For example, an organic photosensitive material, an amorphous selenium photosensitive material, A photosensitive layer made of a crosslinked resin having a charge transporting property such as an amorphous silicon photosensitive material is formed into a film, and the charging roll 22 comes into contact with the surface of the corresponding photosensitive drum 21, and the DC voltage / current is changed to AC voltage / current. The photosensitive layer is configured to be charged to a predetermined potential by a bias with superimposed current. The charging roll 22 is in contact with the photosensitive drum 21 with a constant load and a biting amount, and is rotated at the same speed as the photosensitive drum 21 by the rotation of the photosensitive drum 21 by the frictional force of the contact portion. It is like that.

  The charging roll 22 according to the present embodiment is a surface of a roll-shaped member configured by covering a surface of a metal core made of metal such as stainless steel with a conductive elastic layer made of conductive synthetic resin or synthetic rubber. Further, a resistance control layer whose resistance value is adjusted to a predetermined value is laminated, and a release layer is further formed on the surface of the resistance control layer as necessary. A gap discharge is generated in a minute gap between the charging roll 22 and the photosensitive drum 21 by applying, for example, an alternating voltage on which a direct current voltage is superimposed on the core metal, and the photosensitive drum 21 is generated by the discharge. The surface of the battery is charged.

  The intermediate transfer belt 30 is an intermediate transfer body to which toner images of respective colors sequentially formed by these image forming units 20 a to 20 d are transferred in a state of being superimposed on each other, and corresponds to each image forming unit 20. It is inserted between each of the primary transfer rolls 25 arranged to face each of the photosensitive drums 21, and is passed over a plurality of support rolls 31 to 34, etc., so as to be able to circulate in the direction of the arrow. . In this embodiment, the support roll 31 is used as a drive roll driven by a belt drive motor (not shown), the support roll 32 is used as a driven roll, and the support roll 33 is used as the intermediate transfer belt 30. Used as a correction roll for controlling meandering in a direction substantially perpendicular to the moving direction (steering roll: provided so as to be tiltable with one end in the axial direction as a fulcrum), and further, a support roll 34 constitutes a secondary transfer device 50. It is used as a backup roll for the transfer roll 51.

  Further, a belt cleaner 35 for removing residual toner on the intermediate transfer belt 30 after the secondary transfer is provided on the surface side of the intermediate transfer belt 30 facing the support roll 31 so as to be retractable with respect to the intermediate transfer belt 30. In addition, a conveyance belt 53 and a fixing device 70 are disposed on the downstream side of the secondary transfer device 50 in the sheet conveyance direction.

The intermediate transfer belt 30 in the present embodiment is, for example, a film-like endless belt having a volume resistivity of about 10 ⁹ to 10 ¹² Ω · cm, in which conductive carbon black is kneaded with flexible polyimide resin. It is formed as.

  In this embodiment, the speed difference between the intermediate transfer belt 30 and the photosensitive drum 21 is increased from the viewpoint of promoting the effect of removing the discharge products, forming a stable nip, and preventing banding and smearing. 3% (linear velocity of the intermediate transfer belt 30 / linear velocity of the photosensitive drum 21 = 1.03).

Further, in the present embodiment, a moving roll Rm ₁ is provided inside the intermediate transfer belt 30 between the yellow image forming unit 20a and the magenta image forming unit 20b, and the cyan image forming unit 20c and the black image forming unit 20d. Moving rolls Rm ₂ are disposed inside the intermediate transfer belt 30 therebetween. The operation of these moving rolls Rm ₁ and Rm ₂ will be described later.

  Next, a basic image formation process during normal image formation (image formation mode) of the image forming apparatus according to the present embodiment will be described.

  First, the surface (photosensitive layer) of the photosensitive drum 21 is uniformly charged by applying a bias voltage / current obtained by superimposing an AC voltage / current to a predetermined DC voltage / current to the charging roll 22. The Next, for example, when the image data of each color component image (black, yellow, magenta, cyan) read by the document reading device 10 is sent to the exposure device 23 of each image forming unit 20 (20a to 20d), An electrostatic latent image for each color component is formed on the photoconductive drum 21 of each image forming unit 20, and an unfixed toner image for each color is formed by the developing device 24 containing the corresponding color toner.

  The unfixed toner images of the respective color components are charged with the polarity of the toner charged with respect to the base material of the intermediate transfer belt 30 by the primary transfer roll 25 at the primary transfer portion where the respective photosensitive drums 21 and the intermediate transfer belt 30 are pressed. By applying a reverse polarity voltage, primary transfer is performed by sequentially superimposing on the surface of the intermediate transfer belt 30 by a pressure contact force and an electrostatic attraction force. The unfixed toner image primarily transferred to the intermediate transfer belt 30 in this way is conveyed to a secondary transfer portion facing the conveyance path of the recording paper 100 as a recording material as the intermediate transfer belt 30 rotates. The

  At the secondary transfer site, the secondary transfer roll 51 is pressed by the backup roll 34 disposed in the space in the intermediate transfer belt 30 via the intermediate transfer belt 30 and fed from the paper feed tray 82 (paper transport system 80). The recording paper 100 unloaded at a predetermined timing by 81 (paper transport system 80) is inserted between the secondary transfer roll 51 and the intermediate transfer belt 30 through a predetermined number of transport rollers 83 (paper transport system 80). .

  The unfixed toner images held on the intermediate transfer belt 30 are collectively transferred to the recording paper 100 at the secondary transfer site by a transfer electric field formed between the backup roll 34 and the secondary transfer roll 51. Electrotransfer is performed.

  Thereafter, the recording paper 100 onto which the unfixed toner image has been transferred is sent to the fixing device 70 via the conveyance belt 53, and the fixing device 70 fixes the unfixed toner image on the recording paper 100 with heat and pressure. The The residual toner is removed by the belt cleaner 35 from the intermediate transfer belt 30 after the transfer of the unfixed toner image to the recording paper 100 is completed.

  Incidentally, as described above, when a contact-type charging roll is used as the charging device 22 for the photosensitive drum 21, a discharge product is generated due to discharge at a minute gap between the photosensitive drum 21 and the charging roll 22. There is a possibility that the discharge product adheres to the photosensitive drum 21 and an image defect or the like is generated by the discharge product. Therefore, it is necessary to remove the discharge products adhering to the photosensitive drum 21.

  Therefore, in the image forming apparatus according to the present embodiment, in order to remove such discharge products adhering to the surface of the photosensitive drum 21, a predetermined speed is provided between the photosensitive drum 21 and the intermediate transfer belt 30. A difference (for example, about 3%) is provided, and the discharge product is removed by the rubbing force of the intermediate transfer belt 30 against the surface of the photosensitive drum 21 caused by the speed difference.

  However, setting an excessively large speed difference between the photosensitive drum 21 and the intermediate transfer belt 30 causes image defects such as banding, and slippage occurs between the photosensitive drum 21 and the intermediate transfer belt 30. Since it is difficult to remove the discharge product due to the rubbing force, a very large speed difference cannot be set.

  In order to compensate for the rubbing force due to such a speed difference, the contact area between the photosensitive drum 21 and the intermediate transfer belt 30 is increased by increasing the pressure contact force between the photosensitive drum 21 and the intermediate transfer belt 30. Although it is conceivable to remove the discharge products, such an increase in the contact area due to the increase in the pressure contact force cannot provide a substantial effect for the following reason.

  In general, in order to ensure a stable contact state between the intermediate transfer belt 30 and the photosensitive drum 21 and to ensure a stable rotation of the intermediate transfer belt 30, the undulation or bias of the intermediate transfer belt 30 is ensured. Therefore, the accuracy and strength of the primary transfer roll 25 are not required.

  For example, when the hard primary transfer roll 25 is used, when a hard foreign matter (such as a carrier piece) is mixed into the primary transfer region (the contact region between the photosensitive drum 21 and the intermediate transfer belt 30), the foreign matter portion is moved to. As a result, the concentration of stress increases, and the photosensitive drum 21 is damaged. Further, even if the pressure contact force (transfer nip pressure) is increased by using the hard primary transfer roll 25, the gap between the intermediate transfer belt 30 and the photosensitive drum 21 around the foreign matter portion cannot be reduced, and image omission etc. This is a cause of image failure. Therefore, in order to prevent damage to the photosensitive drum 21 and form a stable primary transfer region, a soft elastic roll is required.

  Therefore, generally, in the primary transfer portion, a foamed elastic roll (Asker C hardness of about 10 to 40 degrees) is used as the primary transfer roll 25 for securing a stable transfer nip.

  On the other hand, since the intermediate transfer belt 30 is stretched with a tension of about 4 to 8 kg / 340 mm, even if the pushing force to the intermediate transfer belt 30 is increased using such a foamed elastic roll 25, the foamed elastic roll Therefore, it is practically difficult to increase the nip width (contact width) between the intermediate transfer belt 30 and the photosensitive drum 21 by increasing the pressure contact force of the primary transfer roll 25. Therefore, it is difficult to remove discharge products.

  Therefore, in the image forming apparatus according to the present embodiment, in addition to an image forming mode for performing normal image formation, a discharge product removal mode described below is provided, so that the photosensitive drum 21 and the intermediate transfer belt 30 are provided. The image quality can be improved and the discharge products can be sufficiently removed while maintaining a stable primary transfer area while maintaining the difference in speed with a predetermined range.

  Specifically, in the discharge product removal mode according to the present embodiment, the contact area between the intermediate transfer belt 30 and the photosensitive drum 21 is set to an intermediate value during image formation when the image is not formed, such as during image formation standby. The photosensitive drum 21 and the intermediate transfer belt 30 are driven at a predetermined speed difference in a state where the transfer belt 30 and the photosensitive drum 21 are larger than a predetermined contact area, and discharge generated on the photosensitive drum 21 is generated. Things are to be removed.

  Next, the contents of the discharge product removal mode in the present embodiment will be further described with reference to FIG. Here, FIG. 2A is a diagram schematically showing a contact state between the photosensitive drum 21 and the intermediate transfer belt 30 in the normal image forming mode, and FIG. 2B is a photosensitivity in the discharge product removal mode. 3 is a diagram schematically showing a contact state between the body drum 21 and the intermediate transfer belt 30. FIG.

In the present embodiment, as schematically shown in FIG. 2, the downstream side of the primary transfer region formed by the photosensitive drum 21a and the primary transfer roll 25a constituting the yellow image forming unit 20a, Inside the intermediate transfer belt 30 upstream of the primary transfer region formed by the photosensitive drum 21b and the primary transfer roll 25b constituting the magenta image forming unit 20b (on the primary transfer roll 25 side of the intermediate transfer belt 30). Is provided with a moving roll Rm ₁ formed so as to be able to contact with and separate from the intermediate transfer belt 30, and a primary transfer formed by a photosensitive drum 21 c and a primary transfer roll 25 c constituting the cyan image forming unit 20 c. Formed by the photosensitive drum 21d and the primary transfer roll 25d constituting the black image forming unit 20d on the downstream side of the area. Inside the intermediate transfer belt 30 upstream of the primary transfer area (primary transfer roll 25 side of the intermediate transfer belt 30) is, the intermediate transfer belt 30 so as to be separable therefrom formed moved roll Rm ₂ are distribution It is installed. The arrangement position and the number of arrangement of the moving rolls Rm are not limited to the above example, and the contact area of the intermediate transfer belt 30 with respect to the photosensitive drum 21 can be changed to a desired value. For example, the arrangement position and the number of arrangements can be arbitrarily selected.

In the normal image forming mode, the moving rolls Rm ₁ and Rm ₂ are arranged at positions separated from the intermediate transfer belt 30 so as not to prevent smooth rotation of the intermediate transfer belt 30 during image formation. ing.

On the other hand, in the discharge product removal mode, as shown in FIG. 2B, the contact area between the intermediate transfer belt 30 and the photosensitive drum 21 is equal to the intermediate transfer belt 30 and the photosensitive drum 21 in the image forming mode. The photosensitive drum 21 and the intermediate transfer belt 30 are driven in a state in which the moving rolls Rm ₁ and Rm ₂ are moved (in this example, moved upward) so as to be larger than a predetermined contact area (nip area). .

  In such a configuration, the discharge product can be reliably removed by executing the discharge product removal mode without affecting the normal image forming mode.

  Further, the contact area between the photosensitive drum 21 and the intermediate transfer belt 30 is made larger than the contact area at the time of image formation, and the toner is present at the interface of the contact area by driving both at a predetermined speed difference. The distance and time at which the discharge product is rubbed with the toner increases, so that the discharge product in close contact with the intervening toner can be more easily removed and the removal effect can be improved.

Further, the contact area between the photosensitive drum 21 and the intermediate transfer belt 30 is increased by the moving rolls Rm ₁ and Rm ₂ provided in the vicinity of the nip region between the primary transfer roll 25 and the intermediate transfer belt 30, thereby performing the primary transfer. Compared to a configuration in which the hardness of the roll 25 is increased to increase the pressure contact force, it is possible to contribute to the formation of a stable primary transfer region without damaging the photosensitive drum 21.

  The discharge product removal mode is preferably executed when no image is formed, for example, when waiting for image formation after the power is turned on, or when waiting for image formation when a predetermined period of time has elapsed.

  By executing the discharge product removal mode at the time of image formation standby with the passage of a predetermined time from such a stopped state, the discharge product becomes a moisture absorption state, and the removal thereof becomes easier. Further, when the contact area (nip area) is increased during image formation, the contact frictional force between the photosensitive drum 21 and the intermediate transfer belt 30 increases, and image defects such as color misregistration and banding occur. On the other hand, by increasing the contact area when no image is formed, it is possible to remove the discharge product without affecting the image forming operation and to improve the image quality based on a predetermined speed difference during image formation. Improvements can be realized.

  The discharge product removal mode according to the present embodiment is naturally applicable to a normal image forming apparatus, but is more preferably used in an image forming apparatus having a smaller-sized photosensitive drum 21 with a smaller size. Applicable.

  Specifically, a predetermined contact area (nip area) between the photosensitive drum 21 and the intermediate transfer belt 30 in the image forming mode is smaller than a predetermined contact area necessary for removing the discharge product (for example, φ30 mm). The image forming apparatus having the photoconductive drum 21 of about a degree) can be more suitably applied. In the image forming apparatus having such a configuration, it is more difficult to remove the discharge product within a predetermined speed difference (eg, about 3%) in which no image defect or slip occurs.

In addition, regarding the moving amount of the moving rolls Rm ₁ and Rm ₂ in the discharge product removal mode, the speed difference between the photosensitive drum 21 and the intermediate transfer belt 30 is maintained within a predetermined range, while being on the photosensitive drum 21. It can select suitably so that the contact area which can fully remove the discharge product which adhered can be implement | achieved.

  Using the image forming apparatus configured as described above, the result of measuring the relationship between the transfer nip width (contact width) and the discharge product removal effect when the speed difference between the photosensitive drum 21 and the intermediate transfer belt 30 is 3% is shown. As shown in FIG. In this embodiment, since the photosensitive drum 21 having a small diameter of 30 mm is used, the transfer nip between the photosensitive drum 21 and the intermediate transfer belt 30 in the primary transfer area during normal image formation (image formation mode). The width is set to 1.5 to 2.0 mm.

  As can be seen from FIG. 3, when the transfer nip width is less than 3 mm, the discharge product removal effect is abruptly reduced.

Accordingly, the photosensitive drum 21 having a small diameter is set such that the speed difference between the photosensitive drum 21 and the intermediate transfer belt 30 is set to 3% and the transfer nip width in the image forming mode is 1.5 to 2.0 mm. Even in such a case, it is understood that if the transfer nip width in the discharge product removal mode is set to 3 mm or more, sufficient removal of the discharge product and improvement in image quality based on a predetermined speed difference can be achieved. Specifically, in the discharge product removal mode, the moving rolls Rm ₁ and Rm ₂ are moved upward to push up the intermediate transfer belt 30 so that the transfer nip width between the photosensitive drum 21 and the intermediate transfer belt 30 is a predetermined value. Thus, it is possible to achieve both improvement in image quality and reliable removal of discharge products even in an apparatus configuration in which the constituent devices are miniaturized.
<Second Embodiment>

  Next, a second embodiment of the image forming apparatus according to the present invention will be described with reference to FIG. FIG. 4 is a diagram schematically illustrating members around the photosensitive drum and the intermediate transfer belt of the image forming apparatus according to the second embodiment.

  The image forming apparatus according to the present embodiment is a four-cycle type image forming apparatus using a so-called rotary developing device having a different arrangement configuration of the components from the image forming apparatus according to the previous embodiment. Members having the same functions as those of the tandem image forming apparatus in the previous embodiment are denoted by the same reference numerals, and description thereof is omitted.

  In FIG. 4, the image forming apparatus according to the present embodiment, unlike the image forming apparatus according to the previous embodiment, has one photosensitive drum 21 and an intermediate transfer belt 30 disposed in contact with the photosensitive drum 21. A plurality of developing units (yellow developing unit 24Ry, magenta developing unit 24Rm, cyan developing unit 24Rc, black developing unit 24Rk) in which toner of each color component is accommodated are mounted around the photosensitive drum 21 and intermittently. In particular, a rotary type developing device 24R that is arranged to face the photoconductive drum 21 and visualizes the electrostatic latent image formed on the photoconductive drum 21 with each corresponding color toner, and the photoconductive drum 21 on the photoconductive drum 21. A primary transfer device 25 such as a transfer roll for transferring each color component toner image to the intermediate transfer belt 30 is provided. Further, around the photosensitive drum 21, as in the previous embodiment, a contact charging device (not shown), an exposure device (not shown) for writing an electrostatic latent image for each color component, and on the photosensitive drum 21. A drum cleaner (not shown) or the like for removing residual toner is provided.

  Further, in the image forming apparatus according to the present embodiment, in the vicinity of the transfer nip region between the photosensitive drum 21 and the primary transfer roll 25 (in this example, on the downstream side of the nip region), A moving roll Rm ′ is disposed on the inner side. Note that the arrangement position and the number of arrangement of the moving rolls Rm ′ in the present embodiment can also be appropriately selected as in the previous embodiment.

  In the image forming apparatus according to the present embodiment configured as described above, the toner image formed on the photosensitive drum 21 is a toner image of each color at the primary transfer position every time the intermediate transfer belt 30 makes one round. The images are sequentially superimposed on the intermediate transfer belt 30. Thereafter, when the entire unfixed toner image superimposed on the intermediate transfer belt 30 passes the secondary transfer position, the secondary transfer roll 51 is pressed against the backup roll 34 via the intermediate transfer belt 30, and the intermediate transfer belt 30. The unfixed toner image formed thereon is secondarily transferred onto the recording paper 100 at once.

Also in the image forming apparatus according to the present embodiment, similarly to the image forming apparatus according to the previous embodiment, a discharge product removal mode is provided, and the moving roll Rm _{1 is used} during standby for image formation. _' Is moved from the separation position (in the image forming mode) shown in FIG. 4A to the push-up position shown in FIG. 4B to increase the contact area between the photosensitive drum 21 and the intermediate transfer belt 30. In this state, the photosensitive drum 21 and the intermediate transfer belt 30 are driven at a predetermined speed difference (for example, 3%), so that an image can be obtained even in a downsized component device as in the previous embodiment. Both improvement in quality and sufficient removal of discharge products can be achieved.

  As described above, according to the image forming apparatus of the present invention, the image quality is improved by the predetermined speed difference provided between the photosensitive drum 21 and the intermediate transfer belt 30, and the photosensitive product is removed by the discharge product removal mode. Without damaging components such as body drum 21 and without depending on the device configuration and component size such as tandem type and rotary type, discharge products accompanying contact charging are surely removed, and photosensitivity by discharge products is achieved. It is possible to effectively prevent body drum wear and image defects.

1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention. It is a schematic diagram explaining the discharge product removal mode in the image forming apparatus according to an embodiment of the present invention. It is a figure which shows the contact width at the time of implementing the discharge product removal mode which concerns on this invention, and the discharge product removal effect. It is a schematic diagram explaining a discharge product removal mode in an image forming apparatus according to another embodiment of the present invention.

Explanation of symbols

  20a-20d: image forming unit, 21a-21d: photosensitive drum, 22a-22d: charging device, 23a-23d: exposure device, 24a-24d: developing device, 24R: rotary developing device, 25a-25d: primary transfer 26a-26d: drum cleaner, 25: primary transfer roll, 30: intermediate transfer belt, 35: belt cleaner, 50: secondary transfer device, 51: secondary transfer roll, 53: transport belt, 70: fixing device, 80: paper transport system, 100: recording paper, Rm, Rm ′: moving roll

Claims (4)

An image carrier on which a toner image of each color is formed on the surface, a contact-type charging roll that comes into contact with the image carrier and charges the surface of the image carrier to a predetermined potential, and abuts the image carrier. And an intermediate transfer belt to which toner images of respective colors formed on the image carrier are transferred, and an image forming apparatus in which a predetermined speed difference is provided between the image carrier and the intermediate transfer belt.
A discharge product removal mode for removing the discharge products by driving the image carrier and the intermediate transfer belt at a predetermined speed difference in a state where a contact area between the image carrier and the intermediate transfer belt is increased; An image forming apparatus.   The image forming apparatus according to claim 1, wherein the discharge product removal mode is executed during standby for image formation.   In the discharge product removal mode, the contact area is increased by moving a moving roll disposed between the image carrier and the intermediate transfer belt inside the intermediate transfer belt and between the image carrier and the intermediate transfer belt. The image forming apparatus according to claim 1, wherein the image forming apparatus is executed by moving the contact area so as to increase a contact area with the transfer belt.   A predetermined contact area at the time of image formation between the image carrier and the intermediate transfer belt is smaller than a contact area necessary for removing discharge products formed on the image carrier. The image forming apparatus according to claim 1.

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