JP2006284948A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To suppress the transfer of deposits originated in transfer material from a transfer material transporting member to an image carrier for carrying a toner image. <P>SOLUTION: This image forming apparatus 100 is provided with: an image carrier 1; a transfer material transporting member 11; a transfer means 12; a transfer bias output means 31 which outputs a bias for transferring the toner image to the transfer means 12; an attraction means B for attracting a transfer material P to the transfer material transporting member 11 in an attraction part M on the upstream side in the transporting direction of the transfer material P, of a transfer part N; and an attraction bias output means 32 which outputs the bias to the attraction means B. The image forming apparatus 100 is constituted to provide a first image forming mode in which the attraction bias output means 32 outputs a bias of a first polarity, while the transfer material P to which the toner image is transferred passes through the attraction part M and a second image forming mode in which the attraction bias output means 32 outputs a bias of a second polarity opposite to the first polarity, while the transfer material P to which the toner image is transferred passes through the attraction part M, or does not output the bias. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a copying machine for transferring an image formed on an image carrier using an electrophotographic system, an electrostatic recording system, etc., to a transfer material carried and conveyed on a transfer material conveyance member, The present invention relates to an image forming apparatus such as a printer and a facsimile.

  Conventionally, for example, an image formed on a transfer material (paper, OHT sheet, gloss film, etc.) using an electrophotographic method, a printer (eg, laser beam printer, LED printer, etc.), a copying machine, a facsimile machine, etc. Forming devices are widely used.

  In an electrophotographic image forming apparatus, an electrostatic image (latent image) is formed on an image carrier that is generally a cylindrical electrophotographic photosensitive member (photosensitive drum), and this electrostatic image is used as a developer. Development is performed with toner particles made of resin or the like. An image (toner image) of toner particles is transferred onto a transfer material such as paper using electrostatic force. Thereafter, the toner image is melt-fixed (fixed) on the transfer material by heat and pressure applied by the fixing device to form an output image.

  In recent years, color image forming apparatuses using an electrophotographic system have become widespread. The color image forming apparatus is divided into various types. Among them, a transfer material having a plurality of different color image forming means (image forming stations) and conveyed by a transfer material conveying member (transfer material carrier). An in-line method for transferring toner onto (for example, paper) is excellent in terms of high-speed printing. In addition, the vertical in-line method in which the image forming stations are arranged in the vertical direction can reduce the installation area and is excellent in terms of space saving. As the transfer material conveying member, a belt which is stretched around a plurality of rollers and moves endlessly, that is, a conveying belt is widely used.

  In an in-line type image forming apparatus, for example, a rotatable drum-shaped electrophotographic photosensitive member, that is, a photosensitive drum, is arranged as a plurality of image carriers along the conveying direction of the conveying belt. Each photosensitive drum is charged by a charging means such as a charging roller and then exposed in accordance with an image information signal, and an electrostatic image (latent image) is formed thereon. This latent image is then developed as a toner image with toner by a developing device. A toner image is formed on each photoconductive drum with different types of toner (for example, magenta, cyan, yellow, and black toners). The toner images are sequentially superimposed and transferred from the photosensitive drums onto a transfer material on the conveyance belt. Thereafter, the transfer material is separated from the conveying belt, and after the toner image is fused and fixed thereon by the fixing device, it is discharged out of the device. On the other hand, toner remaining on the photosensitive drum without being transferred to the transfer material (transfer residual toner) is removed from the photosensitive drum by a cleaning unit including a cleaning member such as a cleaning blade.

  Generally, a toner image on a photosensitive drum is electrostatically transferred to a transfer material. That is, transfer means such as a transfer roller is disposed at a position facing the photosensitive drum via the conveyance belt, and a transfer portion (transfer nip) where the photosensitive drum and the conveyance belt come into contact is formed. A transfer bias having a polarity opposite to the normal charging polarity of the toner is applied to the transfer roller, whereby the toner image is transferred from the photosensitive drum onto the transfer material at the transfer portion.

  In order to stably convey the transfer material, there is a method of electrostatically adsorbing the transfer material on the conveyance belt. That is, as an adsorbing member for electrostatically adsorbing the transfer material to the conveying belt, an adsorbing roller or the like that presses against the conveying belt is provided, and an adsorbing bias is applied to the adsorbing roller (see, for example, Patent Document 1).

Incidentally, paper is mainly used as a transfer material in the image forming apparatus. There are various types of paper used as a transfer material, and there is paper containing calcium carbonate (CaCO ₃ ) as a filler. Some paper containing calcium carbonate contaminates the inside of the image forming apparatus as paper dust.

  In particular, in the case of an in-line image forming apparatus using a conveyance belt, the transfer material such as paper is electrostatically adsorbed to the conveyance belt by an adsorption member such as an adsorption roller. And charged to the opposite polarity.

  On the other hand, in each image forming station, a voltage having a polarity opposite to the normal charging polarity of the toner is applied to a transfer member such as a transfer roller in order to transfer the toner to a transfer material. As a result, the toner charged with a predetermined polarity is transferred from the photosensitive drum onto the transfer material.

  At this time, since the calcium carbonate in the transfer material is charged with the opposite polarity to the photosensitive drum, it is transferred to the photosensitive drum when passing through the image forming station. The calcium carbonate transferred onto the photosensitive drum is difficult to scrape off with the cleaning blade, and easily slips through the contact portion between the cleaning blade and the photosensitive drum. The calcium carbonate reaches the charging roller after passing through the cleaning blade and adheres to the charging roller to contaminate it.

  When the charging roller is further contaminated, a portion where the photosensitive drum cannot be charged satisfactorily occurs, and due to poor charging, image defects such as “vertical stripes” that are image defects in which the image density partially changes occur. There is.

The same problem occurs when paper containing talc as a filler is used as a transfer material.
Japanese Patent Laid-Open No. 11-84812

  In general, an object of the present invention is to provide an image forming apparatus capable of suppressing transfer of deposits derived from a transfer material from a transfer material conveying member to an image carrier that carries a toner image. is there.

  One of the more detailed objects of the present invention is to prevent calcium carbonate and talc in the transfer material from being transferred to the image carrier, and to prevent contamination of the charging means for charging the image carrier that carries the toner image. Thus, an image forming apparatus capable of suppressing the occurrence of image defects due to paper dust is provided.

  The above object is achieved by the image forming apparatus according to the present invention. In summary, the present invention relates to an image carrier that carries a toner image, a transfer material conveyance member that carries a transfer material and conveys it between the image carrier, and a toner image on the image carrier. A transfer means for transferring to a transfer material carried on a transfer material conveying member; a transfer bias output means for outputting a bias for transferring a toner image to the transfer means; and In an image forming apparatus having an adsorption unit for adsorbing a transfer material to the transfer material conveyance member at an adsorption unit upstream in the conveyance direction and an adsorption bias output unit for outputting a bias to the adsorption unit, a toner image is transferred A first image forming mode in which the suction bias output means outputs a bias having a first polarity while the transfer material to be transferred passes through the suction portion; and a transfer material to which a toner image is transferred is the suction portion. Pass through The suction bias output means outputs a bias having a second polarity opposite to the first polarity or a second image forming mode in which no bias is output. The image forming apparatus.

  According to another aspect of the present invention, first and second image carriers that carry toner images, and first and second transfer portions are formed in contact with the first and second image carriers, respectively. A transfer material conveying member that carries the transfer material and conveys it between the first and second image carriers, and a toner image on the first and second image carriers, respectively. First and second transfer means for transferring to a transfer material carried on a member; and transfer bias output means for outputting a bias for transferring a toner image to the first and second transfer means; An adsorbing unit for adsorbing the transfer material to the transfer material conveying member at an adsorbing unit upstream of the first and second transfer units in the conveying direction of the transfer material, and an adsorbing bias for outputting a bias to the adsorbing unit The relative position of the output means, the first image carrier and the transfer material conveying member is moved. A first mode in which the transfer material on the transfer material conveying member is conveyed in contact with the first image carrier, and the transfer material on the transfer material conveying member is In the image forming apparatus having the second mode transported without contacting the first image carrier, the output of the suction bias output means has a reverse polarity in the first mode and the second mode. An image forming apparatus is provided.

  According to still another aspect of the present invention, the first and second image carriers that carry a toner image, and the first and second transfer units that are in contact with the first and second image carriers, respectively. A transfer material conveying member formed and carried between the first and second image carriers, and a toner image on the first and second image carriers, respectively. First and second transfer means for transferring to a transfer material carried on a conveying member, and transfer bias output means for outputting a bias for transferring a toner image to the first and second transfer means An adsorbing means for adsorbing the transfer material to the transfer material conveying member at an adsorbing portion upstream of the first and second transfer portions in the conveying direction of the transfer material, and an adsorption for outputting a bias to the adsorbing means Bias output means, relative positions of the first image carrier and the transfer material conveying member A first mode in which the transfer material on the transfer material conveying member is conveyed in contact with the first image carrier, and a transfer material on the transfer material conveying member In the image forming apparatus having the second mode conveyed without contacting the first image carrier, the output of the suction bias output means is not output in the first mode, and the second mode An image forming apparatus is provided that is output in the mode.

  According to the present invention, it is possible to suppress the transfer material-derived deposits from being transferred from the transfer material transport member to the image carrier that carries the toner image. Further, as one of the operational effects obtained by the present invention, it becomes possible to suppress contamination of the charging means that occurs when a transfer material such as paper powder, especially paper containing calcium carbonate or talc is used. It is possible to suppress the occurrence of image defects due to defects.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

Example 1
[Overall Configuration and Operation of Image Forming Apparatus]
First, the overall configuration and operation of the image forming apparatus of this embodiment will be described. FIG. 1 is a schematic longitudinal sectional view of an image forming apparatus 100 of the present embodiment. The image forming apparatus 100 according to the present exemplary embodiment is configured to perform electrophotography in response to an image information signal from an external device such as a personal computer, a document reading device, or a digital camera connected to the image forming apparatus main body (apparatus main body) A. This is a laser beam printer adopting an in-line method that can form a four-color full-color image on a transfer material (recording paper, plastic film, cloth, etc.) using this method. The image forming apparatus according to the present invention may be an electrophotographic laser beam printer, an electrophotographic copying machine, a facsimile, or the like, and an electrostatic recording printer, copying machine, facsimile, or the like. It may be.

  The image forming apparatus 100 includes first, second, third, and fourth image forming stations Sa, Sb, Sc, and Sd as a plurality of image forming units inside the apparatus main body A. The four image forming stations Sa, Sb, Sc, Sd are arranged in series in the vertical direction (substantially vertical direction) along the conveying direction of the transfer material P in this order. The four image forming stations Sa, Sb, Sc, and Sd form cyan, yellow, magenta, and black toner images in this order. Each image forming station Sa, Sb, Sc, Sd is provided with process cartridges 7a, 7b, 7c, 7d that can be attached to and detached from the apparatus main body A, and each process cartridge 7a, 7b, 7c, 7d is provided. Toner images are formed on the provided image carriers 1a, 1b, 1c, and 1d. The toner image formed on each image carrier 1a, 1b, 1c, 1d is carried and conveyed by a conveyance belt (electrostatic adsorption conveyance belt) 11 as a transfer material conveyance member (transfer material carrier). Transferred to the material P.

  In this embodiment, the basic configuration and operation of each image forming station are substantially the same except that the type of toner is different. Accordingly, in the following, when there is no particular need to distinguish, the subscripts a, b, c, and d given to the reference numerals to indicate that they are elements provided for any color are omitted and are generally described. To do.

  Further details will be described with reference to FIG. FIG. 2 is an enlarged longitudinal sectional view of the process cartridge 7. The image forming station S includes a drum-shaped electrophotographic photosensitive member, that is, a photosensitive drum 1 as an image carrier. Around the photosensitive drum 1, there are a charging roller 2 as a charging means (primary charging means), an exposure device 3 as an exposure means (image writing means), a developing device 4 as a developing means, and a cleaning device 6 as a cleaning means. Etc. are arranged. Further, the transfer device 5 includes a transport belt 11 as a transfer material transport member that can move in contact with each of the photoconductor drums 1a, 1b, 1c, and 1d, facing the photoconductor drums 1a, 1b, 1c, and 1d. Is arranged. A transfer roller 12 serving as a transfer unit is disposed at a position facing the photosensitive drum 1 with the conveyance belt 11 interposed therebetween.

  The charging device 2 charges the surface of the photosensitive drum 1 substantially uniformly. The exposure device (scanner unit) 3 forms an electrostatic image (latent image) by irradiating the surface of the photosensitive drum 1 after the charging process with a laser beam based on image information. The developing device 4 develops a toner image by attaching toner to the electrostatic image formed on the photosensitive drum 1 by the exposure device 3. The transfer roller 12 transfers the toner image formed on the photosensitive drum 1 to a transfer material carried on the transport belt 11. The cleaning device 6a removes toner (residual toner) remaining on the surface of the photosensitive drum 1 after the transfer process.

  In this embodiment, the photosensitive drum 1, the charging roller 2, the developing device 4, and the cleaning device 6 are integrally formed as a cartridge and can be attached to and detached from the apparatus main body A. Is configured. As shown in FIG. 2, the process cartridge 7 is further divided into a photosensitive drum unit 50 and a developing unit 45. The photosensitive drum unit 50 includes a photosensitive drum 1, a charging roller 2, and a cleaning device 6. On the other hand, the developing unit 45 includes a developing device 4. The process cartridge 7 is detachably mounted on the apparatus main body A via mounting means (not shown) such as a mounting guide and a positioning member.

  Next, each element of the image forming apparatus 100 will be described in more detail.

  The photosensitive drum 1 is configured by coating an organic optical semiconductor layer (OPC photosensitive layer) on an outer peripheral surface of an aluminum cylinder having a diameter of 30 mm, for example. The photosensitive drum 1 is rotatably supported at both ends in the longitudinal direction (rotation axis direction) by a support member (not shown). The photosensitive drum 1 is counterclockwise in FIG. 1 when a driving force from a driving motor (not shown) provided in the apparatus main body A is transmitted to one end in the longitudinal direction. Driven by rotation.

  As the charging means, a charging roller 2 formed in a roller shape is used. The charging roller 2 is connected to a charging bias application power source (not shown) as charging bias output means provided in the apparatus main body A. The charging roller 2 is brought into contact with the surface of the photosensitive drum 1 and a predetermined charging bias is applied to the charging roller 2 by a charging bias application power source, whereby the surface of the photosensitive drum 1 is substantially set to a predetermined polarity and potential. Charge uniformly (uniformly). In this embodiment, the surface of the photosensitive drum 1 is charged almost uniformly negatively by the charging roller 2.

  The exposure device 3 is arranged on the left side of each photosensitive drum 1 in FIG. In the exposure apparatus 3, image light corresponding to the image signal is emitted by a laser diode (not shown). This image light is applied to the polygon mirror 9 that is rotated at a high speed by a scanner motor (not shown). The image light reflected by the polygon mirror 9 is applied to the surface of the charged photosensitive drum 1 through the imaging lens 10. As a result, the surface of the photosensitive drum 1 that is charged substantially uniformly can be selectively exposed to form an electrostatic image. In this embodiment, the charge of the portion irradiated with the image light is removed, and the image portion of the electrostatic image is formed.

  The developing device 4 includes a container (developing device main body) 41 that stores a non-magnetic one-component developer, that is, toner, as a developer. The toner 41 of each color of cyan, yellow, magenta, and black is accommodated in the container 41 of each developing device 4a, 4b, 4c, 4d of each image forming station Sa, Sb, Sc, Sd. The developing device 4 carries the toner and supplies the toner to the developing roller 40 as a developer carrying member that conveys the toner to a portion facing the photosensitive drum 1 (development region), and supplies the toner from the developing roller 40 to the toner. A toner supply roller 43 as a developer supplying and peeling member, a developing blade 44 as a developer regulating member for regulating the toner on the developing roller 40, and a toner feeding mechanism for conveying the toner toward the toner supply roller 43 42. The toner in the container 41 is fed in the direction of the toner supply roller 43 by the toner feeding mechanism 42, and the toner supply roller 43 rotating in the clockwise direction (arrow Z direction) in FIG. The blade 44 applies toner to the outer peripheral surface of the developing roller 40 that rotates clockwise (in the arrow Y direction) in FIG. At the same time, a charge is applied to the toner applied to the outer peripheral surface of the developing roller 40.

  In this embodiment, the developing roller 40 is in contact with the photosensitive drum 1 at a portion facing the photosensitive drum 1. Then, an electrostatic image formed on the photosensitive drum 1 is applied by applying an image bias to the current developing roller 40 by a developing bias applying power source (not shown) as a developing bias output means provided in the apparatus main body A. A negatively charged toner is attached to the toner image and developed as a toner image. In this embodiment, the toner is attached to the portion (exposed portion) where the potential is attenuated by exposure on the photosensitive drum 1 charged to the same polarity as the normal charging polarity (negative polarity in this embodiment) of the toner (reversal). Development method).

A transfer device 5 is disposed on the right side of the process cartridge 7 in FIG. The transfer device 5 has a conveyor belt 11 that circulates (rotates) so as to be in contact with and face the photosensitive drum 1. The conveyor belt 11 is formed of a film-like member having a volume resistivity of 10 ⁸ to 10 ¹³ Ω · cm and a thickness of 50 to 300 μm. In the present embodiment, the conveyance belt 11 is made of PVdF (polyvinylidene fluoride). The conveyor belt 11 is wound around four rollers arranged in parallel with each other as a plurality of rollers, that is, the driving roller 13 and the driven rollers 14, 15 and 16, and as a whole in the vertical direction. It is arranged. When the driving force is transmitted to the driving roller 13, the conveying belt 11 rotates in the direction indicated by the arrow R in FIG. 1 (clockwise). The conveyance belt 11 rotates in a state where the transfer material P is electrostatically adsorbed on the outer peripheral surface at a portion located between the driving roller 13 and one driven roller (adsorption counter roller) 14. In the present embodiment, the transport belt 11 transports the transfer material P in the vertical direction, that is, in a direction intersecting the horizontal direction (in the present embodiment, substantially upward in the vertical direction). For example, at the time of forming a color image, the transfer material P is carried on the transport belt 11 and sequentially transported to the transfer section of each image forming station S, and the toner images on the respective photosensitive drums 1 are sequentially transferred. .

  On the inner peripheral surface side of the conveyor belt 11, four transfer rollers 12a, 12b are arranged at positions corresponding to the respective photosensitive drums 1a, 1b, 1c, 1d of the image forming stations Sa, Sb, Sc, Sd. , 12c, 12d are disposed. These transfer rollers 12a, 12b, 12c, and 12d are in contact with the back side of the conveyor belt 11, and sandwich the conveyor belt 11 between the photosensitive drums 1a, 1b, 1c, and 1d. Accordingly, the first, second, third, and fourth transfer portions (transfer nips) Na, Nb, Nc, and Nd are provided between the photosensitive drums 1a, 1b, 1c, and 1d and the conveyor belt 11, respectively. It is formed. In this embodiment, the interval between the transfer portions N is 75 mm. In this embodiment, the transfer roller 12 of each image forming station S is connected to a transfer bias application power source 31 (FIG. 8) as transfer bias output means provided in the apparatus main body A. Then, a positive transfer bias having a polarity opposite to the normal charging polarity of the toner is applied to the transfer roller 12 by the transfer bias applying power source 31. As a result, the negatively charged toner on the photosensitive drum 1 is transferred onto the transfer material P on the transport belt 11 at the transfer portion N. That is, the transfer roller 12 is supplied with a bias having a polarity opposite to the normal charging polarity (negative polarity in the present embodiment) of the toner output from the transfer bias applying power source 31, so that the transfer portion N has a normal polarity. An electric field is formed in a direction in which the toner charged to the polarity of the toner is directed from the photosensitive drum 1 to the transfer material P on the transport belt 11.

  The cleaning device 6 removes the toner (residual toner) remaining on the photosensitive drum 1 without being transferred to the transfer material P when the toner image is transferred. As shown in FIG. 2, the cleaning device 6 has a cleaning blade 60 as a cleaning member that contacts the surface of the photosensitive drum 1 and removes residual toner on the surface of the photosensitive drum 1. The residual toner removed from the surface of the photosensitive drum 1 by the cleaning blade 60 is sequentially sent to a waste toner chamber 53 provided behind the cleaning frame 51 by the toner feeding mechanism 52.

  A detachable transfer material storage cassette 17 is disposed below the apparatus main body A in FIG. In the transfer material storage cassette 17, a plurality of transfer materials (for example, plain paper, envelope, transparent film) P are stored in a stacked state. At the time of image formation, the transfer material P in the transfer material storage cassette 17 is separated and fed one by one by the rotation of the transfer material supply roller 18 (half moon roller). Next, the transfer material P is temporarily stopped when its leading end abuts against the registration roller pair 19 to form a loop. Thereafter, the transfer material P is supplied to the conveyance belt 11 by the registration roller pair 19 in synchronization with the rotation of the conveyance belt 11 and the image writing position on the photosensitive drums 1a, 1b, 1c, and 1d.

  An adsorption unit for adsorbing the transfer material P to the conveyance belt 11 in the adsorption unit M further upstream than the first transfer unit Na of the first image forming station Sa on the most upstream side in the conveyance direction of the transfer material P. B is disposed. In the present embodiment, the suction unit B uses the suction roller 20 disposed on the photosensitive drum 1 side with respect to the transport belt 11 as a suction member to which a bias for attracting the transfer material P to the transport belt 11 is applied. Have. In this embodiment, the suction roller 20 that contacts the transfer material P is disposed to face one driven roller (suction counter roller) 14 among a plurality of rollers on which the transport belt 11 is stretched. The conveyance belt 11 is sandwiched between the suction facing roller 14 as a member. In other words, in this embodiment, the adsorbing means B is opposite to the first member contacting the transfer material carrying surface of the transport belt 11 and the transfer material carrying surface of the transport belt 11 facing the first member. And a second member in contact with the side surface.

  As will be described in detail later, in the normal image forming mode, the suction bias application power source 32 (FIG. 8) as the suction bias output means provided in the apparatus main body A causes the suction roller 20 to have the same polarity as the transfer bias (that is, A positive polarity adsorption bias having a polarity opposite to the normal charging polarity of the toner is applied. At this time, a bias having the same polarity as the transfer bias output from the suction bias application power source 32 is applied to the suction roller 20, whereby the direction of the electric field formed in the suction portion M and the transfer portion N by the transfer bias. The direction of the electric field formed is the same direction. The electrostatic polarization between the transfer material P and the transport belt 11 is promoted by the electric field and the charge supply due to the suction bias, and the transfer material P is attracted to the surface of the transport belt 11. In this way, the transfer material P supplied toward the transport belt 11 by the registration roller pair 19 is electrostatically attracted to the transport belt 11 by the suction portion M. The distance between the suction portion (suction nip) M where the suction roller 20 and the transport belt 11 are in contact with the first transfer portion Na is 45 mm.

The suction roller 20 is a two-layer roller having a rubber layer with an adjusted electrical resistance value on a core metal having a diameter of 6 mm and a coating layer having releasability. The rubber layer is provided to give elasticity, and has a diameter of 12 mm in which carbon black is dispersed in EPDM rubber for adjusting electric resistance. The electric resistance value of the rubber layer is adjusted to 1 × 10 ⁵ Ω when a metal foil having a width of 1 cm is wound around the outer periphery of the roller and a voltage of 500 V is applied between the metal core and the metal core. On the rubber layer, a fluorine coating having a releasability and an adjusted electric resistance is applied. The thickness of the release layer is 100 μm, and a metal oxide is added to the fluororesin, and the electric resistance value as the final suction roller 20 is adjusted to 1 × 10 ⁶ Ω by the above-described measurement method. Yes.

  A fixing device 21 as a fixing unit is disposed further downstream (upward in FIG. 1) than the fourth image forming station Sd on the most downstream side in the conveyance direction of the transfer material P. The fixing device 21 fixes the toner image transferred to the transfer material P. In this embodiment, the fixing device 21 includes a rotating fixing roller (heating roller) 22 and a pressure roller 23 that is pressed against the fixing roller 22 and applies heat and pressure to the transfer material P. For example, when forming a color image, the transfer material P transferred so that the toner images of the respective colors are sequentially overlapped is nipped and conveyed by the fixing roller 22 and the pressure roller 23 when passing through the fixing device 21 and heated. Pressurized. As a result, the toner images of a plurality of colors are melted and mixed on the surface of the transfer material P and fixed.

(Color image formation operation in normal image formation mode)
Next, a color image forming operation in the normal image forming mode in the image forming apparatus 100 of the present embodiment will be described.

Referring to FIG. 1, the photosensitive drums 1a, 1b, 1c, and 1d in the process cartridges 7a, 7b, 7c, and 7d are rotationally driven in accordance with the image forming timing. The rotating photosensitive drums 1a, 1b, 1c, and 1d are uniformly charged negatively by the charging rollers 2a, 2b, 2c, and 2d. The charged surfaces of the photosensitive drums 1a, 1b, 1c, and 1d are exposed according to image signals (image information) by the exposure devices 3a, 3b, 3c, and 3d, and electrostatic images are formed. At this time, a portion that is not exposed becomes a dark portion (high potential portion), and the potential (dark portion potential) is set to V _D. On the other hand, the exposed portion becomes a bright portion (low potential portion), and the potential (bright portion potential) is set to _VL . Next, the developing devices 4a, 4b, 4c, and 4d attach the toner to the bright portions of the electrostatic images formed on the photosensitive drums 1a, 1b, 1c, and 1d, and the photosensitive drums 1a and 1b. Cyan, yellow, magenta, and black toner images are formed on 1c and 1d, respectively.

  On the other hand, the transfer material P supplied from the transfer material storage cassette 17 to the conveyance belt 11 by the transfer material supply roller 18, the registration roller pair 19, etc. is sandwiched between the suction roller 20 and the conveyance belt 11. By being in pressure contact with the surface (outer peripheral surface) and applying a voltage between the conveyance belt 11 and the suction roller 20, electrostatic adsorption is performed on the surface of the conveyance belt 11. At this time, a positive voltage is applied from the suction roller 20 side, and the suction counter roller 14 is grounded. More specifically, in this embodiment, a bias of +1500 V output from the suction bias application power source 32 is applied to the suction roller 20.

  The transfer material P adsorbed on the surface of the transport belt 11 in this way is rotated by the transport belt 11 in the direction of the arrow R in FIG. 1, and the first image forming stations Sa, Sb, Sc, Sd of the first to fourth image forming stations Sa, Sd. To the fourth transfer portions Na, Nb, Nc, and Nd. Then, the photosensitive drums 1a, 1b, 1c, and 1d are generated by an electric field (transfer electric field) formed between the photosensitive drums 1a, 1b, 1c, and 1d and the transfer rollers 12a, 12b, 12c, and 12d. The upper toner image is sequentially transferred onto the transfer material P.

  The transfer material P onto which the four color toner images have been transferred is separated (curvature separation) from the conveying belt 11 by the curvature of the driving roller 13 and is carried into the fixing device 21. The transfer material P is heated and pressed by the fixing roller 22 and the pressure roller 23 in the fixing device 21, and a four-color toner image is fixed on the surface. Thereafter, the transfer material P is discharged onto the discharge tray 25 formed on the upper surface of the apparatus main body A by the discharge roller pair 24 with the image surface facing downward.

  On the other hand, residual toner remaining on the surfaces of the photosensitive drums 1a, 1b, 1c, and 1d after the toner image is transferred to the transfer material P is removed by the cleaning devices 6a, 6b, 6c, and 6d, and the photosensitive drums 1a, 1a, 1b, 1c and 1d are used for the next image formation. Thus, the four-color full-color image formation is completed.

(Monochrome image forming operation in normal image forming mode)
Next, a monochrome image forming operation in the normal image forming mode in the image forming apparatus 100 of the present embodiment will be described.

  FIG. 3 is a schematic vertical sectional view showing the main part of the inside of the apparatus main body A during the monochrome image forming operation. In this embodiment, during the monochrome image forming operation, the photosensitive drum 1 of the process cartridge 7 is separated from the conveying belt 11 so as not to operate the process cartridge 7 for the color on which image formation is not performed.

  More specifically, in this embodiment, the fourth image forming station Sd, which is the most downstream in the transport direction of the transfer material P, is used as a black image forming station, and a monochrome image forming operation is performed as a monochrome image forming operation. Is possible. In this monochrome image forming operation, the photosensitive drum 1d of the fourth image forming station Sd for black is brought into contact with the transport belt 11, and the image forming station in which image formation is not performed, that is, transport of the transfer material P is performed. The photosensitive drums 1a, 1b, and 1c in the first to third image forming stations Sa, Sb, and Sc on the upstream side in the direction are separated from the conveyance belt 11. That is, the image forming apparatus 100 according to the present exemplary embodiment includes a separation unit that moves the relative positions of the photosensitive drums 1a, 1b, and 1c of the first to third image forming stations Sa, Sb, and Sc and the conveyance belt 11. The transfer material P on the transport belt 11 is transported in contact with the photosensitive drums 1a, 1b, 1c of the first to third image forming stations Sa, Sb, Sc, and the transport belt 11. The upper transfer material P has a second mode in which the transfer material P is conveyed without contacting the photosensitive drums 1a, 1b, and 1c of the first to third image forming stations Sa, Sb, and Sc.

  As the separating means for separating the photosensitive drum 1 and the transport belt 11 from the image forming station S where image formation is not performed, the transfer device 5 (of the transport belt 11 and the transport belt 11 is centered on the driving roller 13 as a rotation center). The driven rollers 14, 15, 16, the transfer roller 5, the suction roller 20, etc. disposed on the peripheral surface side are swung as a whole, or the pressing of the transfer roller 12 toward the photosensitive drum 1 is released. A contact / separation mechanism can be used. In the present embodiment, as shown in FIG. 3, the contact / separation mechanisms 36a, 36b, which can press the transfer rollers 12a, 12b, 12c against the photosensitive drums 1a, 1b, 1c and can release the press. 36c was used.

  Further, in this embodiment, during the monochrome image forming operation, in the first to third image forming stations Sa, Sb, and Sc in which image formation is not performed, the image of the photosensitive drum 1 is rotated, the transfer bias is applied, and the like. The forming operation is stopped.

  As described above, since unnecessary operation / rotation is not performed during the monochrome image forming operation, deterioration of the process cartridge 7 can be reduced.

  During the monochrome image forming operation, the photosensitive drum 1d of the fourth image forming station Sd that forms the black toner image is driven to rotate in accordance with the image forming timing, and in the same manner as in the color image forming operation, A black toner image is formed on the body drum 1d.

  The transfer material P is supplied to the conveyor belt 11 in the same manner as in the color image forming operation. At this time, as in the color image forming operation in the normal image forming mode described above, in the suction portion M, a positive voltage is applied from the suction roller 20 side, and the suction counter roller 14 is grounded. More specifically, in this embodiment, a bias of +1500 V output from the suction bias application power source 32 is applied to the suction roller 20.

  As a result, the transfer material P is attracted to the transport belt 11 and transported to the fourth transfer portion Nd of the fourth image forming station Sd, which is the most downstream in the transport direction of the transfer material P. That is, the transfer material P adsorbed on the surface of the conveyor belt 11 is in the first to third states in which the photosensitive drum 1 is separated from the conveyor belt 11 by the rotation of the conveyor belt 11 in the direction of arrow R in the figure. The first through third transfer portions Na, Nb, and Nc of the image forming stations Sa, Sb, and Sc are sequentially passed to the fourth transfer portion Nd of the fourth image forming station Sd. The toner image on the photosensitive drum 1d is transferred onto the transfer material by the electric field formed between the photosensitive drum 1d and the transfer roller 12d in the fourth image forming station Sd.

  Thereafter, in the same manner as in the color image forming operation, the transfer material P is discharged out of the apparatus after the toner image is fixed. Further, the residual toner remaining on the surface of the photosensitive drum 1d after the toner image is transferred to the transfer material P is removed by the cleaning device 6d as in the color image forming operation, and the photosensitive drum 1d is moved to the next image. Served for formation. The normal monochrome image formation is thus completed.

[Suction bias]
In this embodiment, the suction bias is set to positive polarity +1500 V having the same polarity as the transfer bias (that is, opposite to the normal charging polarity of the toner) in the image forming operation in the normal image forming mode. This is because the adsorption bias has functions of “electrostatic adsorption of the transfer material P to the conveyance belt 11” and “transfer assist by applying electric charge”. That is, the transfer material P is electrostatically attracted to the transport belt 11 by the suction bias, and the transfer material P is peeled off from the transport belt 11 to prevent jamming (paper jam). In addition, since the four color toners are transferred to the transfer material P during the color image forming operation, the potential of the transfer material P rises every time it passes through the transfer portion N. Therefore, it is necessary to increase the absolute value of the transfer bias as it goes to the downstream image forming station S in the transfer direction of the transfer material P. Therefore, by charging the surface of the transfer material P to the positive polarity in advance by the adsorption portion M, the negative toner can be transferred with a transfer bias having a lower absolute value.

  However, as described above, the suction bias may cause a problem due to transfer of deposits derived from the transfer material onto the photosensitive drum 1.

That is, there are various types of paper mainly used as the transfer material P in the image forming apparatus, and among them, there is paper containing calcium carbonate (CaCO ₃ ) as a filler. Some calcium carbonate-containing papers contaminate the image forming apparatus as paper dust.

  In particular, in the inline type image forming apparatus 100 using the conveyance belt 11 as in the present embodiment, if the calcium carbonate-containing paper continues to be passed, the following problems may be caused.

  In the color image forming operation in the normal image forming mode and the monochrome image forming operation in the normal image forming mode, the transfer material P is electrostatically adsorbed to the transport belt 11 by the adsorbing roller 20 to which a positive adsorbing bias is applied. The calcium carbonate is charged with a polarity (positive polarity) opposite to that of the surface of the photosensitive drum 1.

  On the other hand, in each image forming station S, in order to transfer the toner to the transfer material P, a bias having a polarity (positive polarity) opposite to that of the toner or the surface of the photosensitive drum 1 is applied to the transfer roller 12. As a result, the negatively charged toner is transferred from the photosensitive drum 1 onto the transfer material P.

  At this time, when the calcium carbonate charged with the opposite polarity (positive polarity) to the surface of the photosensitive drum 1 passes through the image forming station S, the calcium carbonate is charged with the opposite polarity to the surface of the photosensitive drum 1. Then, it is transferred to the photosensitive drum 1. Since the calcium carbonate transferred onto the photosensitive drum 1 is electrostatically tied, scraping with the cleaning blade 60 becomes difficult, and the contact portion between the cleaning blade 60 and the photosensitive drum 1 tends to slip through. Then, after passing through the cleaning blade 60, the calcium carbonate reaches the charging roller 2 and adheres to the charging roller 2 to contaminate it.

  In FIG. 4, during an image forming operation in the normal image forming mode, calcium carbonate α from the calcium carbonate-containing paper as the transfer material P is charged positively by the suction roller 20 and then transferred to the photosensitive drum 1. FIG. 2 schematically shows a state where the charging roller 2 is contaminated.

  When contamination of the charging roller 2 progresses, a portion where the photosensitive drum 1 cannot be charged satisfactorily occurs, and image defects such as “vertical stripes” may occur due to charging failure. Therefore, there is a problem that the life of the process cartridge 7 may be shortened.

[Adhesion reduction image formation mode]
Next, a method for suppressing the transfer material-derived deposit, which is the most characteristic feature of this embodiment, from being transferred to the photosensitive drum 1 will be described.

  The image forming apparatus 100 of the present embodiment has an adhesion reduction image forming mode in addition to the normal image forming mode in order to prevent the occurrence of the above-described problems. For example, an apparatus user who frequently uses calcium carbonate-containing paper can take measures against calcium carbonate-containing paper by performing a color image forming operation or a monochrome image forming operation in the adhesion reduction image forming mode. .

  In other words, in the image forming apparatus 100, a first image forming mode in which the suction bias applying power source 32 outputs a bias having the first polarity while the transfer material P to which the toner image is transferred passes through the suction portion M (see FIG. In the normal image forming mode), while the transfer material P onto which the toner image is transferred passes through the suction portion M, the suction bias application power source 32 applies a bias having a second polarity that is opposite to the first polarity. A second image forming mode that outputs or does not output a bias (adhesion reduction image forming mode). The first polarity is typically the same polarity as the transfer bias (that is, the polarity opposite to the charging polarity of the toner). The second polarity is typically the same polarity as the charging polarity of the photosensitive drum 1.

  FIG. 8 shows a schematic control mode of this embodiment. As shown in FIG. 8, in this embodiment, the controller unit 33 as a control unit provided in the apparatus main body A controls the suction bias, the transfer bias, and other operations of the image forming apparatus 100. To do. The controller unit 33 controls the bias output start / stop by the suction bias application power source 32 and also has a function of a suction bias switching means for controlling the bias polarity and output value.

  The controller unit 33 is connected to an operation unit 34 provided in the apparatus main body A and an external device 200 such as a personal computer. An image formation mode selection signal is input to the controller unit 33 together with an image formation start instruction via the operation unit 34 of the apparatus main body A or the operation unit of the external device 200. When the selection signal for the image forming mode indicates the normal image forming mode, the controller unit 33 causes the color image forming operation or the monochrome image forming operation to be executed in the normal image forming mode as described above. On the other hand, when the image mode selection signal indicates the adhesion reduction image formation mode, the color image formation operation or the monochrome image formation operation is executed in the adhesion reduction image formation mode described in more detail below.

(Color image formation operation in adhesion reduction image formation mode)
First, a color image forming operation in the adhesion reduction image forming mode will be described.

  In this embodiment, in particular, since the transfer material P is transported in the vertical direction, it is necessary to prevent the transfer material P from being peeled off from the transport belt 11 during transport. However, even if the transfer material P is not electrostatically attracted to the transport belt 11 by the suction portion M, it can be transported to the first transfer portion Na by the stiffness of the transfer material P. Further, when transferring the toner at the first transfer portion Na, the transfer material P is charged and adsorbed by the action of the transfer bias. Therefore, the transfer material P can be transported relatively stably without charging the transfer material P at the suction portion M.

  Therefore, at the time of color image forming operation in the adhesion reduction image forming mode, the suction bias is nonpolar, that is, 0V. That is, the suction bias application power source 32 does not output a bias to the suction roller 20 during the color image forming operation in the adhesion reduction image forming mode. At this time, both the suction roller 20 and the suction counter roller 14 are grounded.

  FIG. 5 schematically shows the behavior of calcium carbonate α from the calcium carbonate-containing paper when the adsorption bias is made nonpolar during color image forming operation in the adhesion reduction image forming mode.

  Since the transfer material P is not charged at the adsorption portion M, the calcium carbonate existing in the transfer material P reaches the first transfer portion Na without being charged. In the first transfer portion Na, toner is transferred from the photosensitive drum 1a onto the transfer material P, and the surface of the transfer material P becomes negative. Since the calcium carbonate existing in the transfer material P is also negatively charged, the calcium carbonate is transferred onto the photosensitive drum 1 when passing through the second to fourth transfer portions Nb, Nc, Nd on the downstream side. Can be suppressed.

  As described above, during the color image forming operation in the adhesion reduction image forming mode, calcium carbonate is transferred to the photosensitive drum 1 without causing jam (paper jam) by making the suction bias nonpolar. Image defects due to contamination of the charging roller 2 with calcium carbonate can be suppressed.

(Monochrome image forming operation in adhesion reduction image forming mode)
Next, a monochrome image forming operation in the adhesion reduction image forming mode will be described.

  During the monochrome image forming operation, as described above, the first to third image forming stations Sa, Sb, and Sc that do not perform image formation are prevented from deteriorating in the process cartridges 7a, 7b, and 7c. In the third image forming stations Sa, Sb, and Sc, the photosensitive drums 1a, 1b, and 1c are separated from the transport belt 11, and the image forming operation such as rotation of the photosensitive drum 1 and application of a transfer bias is stopped.

  Here, in this embodiment, in particular, since the transfer material P is transported in the vertical direction, the photosensitive drum 1 is transported by the transport belt 11 in the first to third image forming stations Sa, Sb, Sc during the monochrome image forming operation. Even in a state of being separated from the transfer material P, it is necessary to prevent the transfer material P from being peeled off from the transport belt 11 during the transport.

  That is, in the first to third image forming stations Sa, Sb, and Sc, the photosensitive drum 1 is separated from the conveyance belt 11 and its rotation is stopped. Unless it is electrostatically attracted to the transfer material P, it is difficult to stably convey the transfer material P to the fourth transfer portion Nd. Therefore, there is a possibility that the transfer material P peels off during conveyance and a jam (paper jam) occurs.

  Therefore, during the monochrome image forming operation in the adhesion reduction image forming mode, the suction roller 20 has a negative polarity (that is, the same polarity as the charging polarity of the photosensitive drum 1) having the opposite polarity to that of the normal image forming mode. Bias) is applied. That is, at the time of monochrome image forming operation in the adhesion reduction image forming mode, the suction bias application power source 32 outputs a negative polarity bias to the suction roller 20. More specifically, in this embodiment, a bias of −1500 V output from the suction bias application power source 32 is applied to the suction roller 20. At this time, the suction opposing roller 14 is grounded. At this time, the suction roller 20 is formed in the suction portion M by applying a reverse polarity to the normal image forming mode, that is, a reverse bias to the transfer bias, which is output from the suction bias application power source 32. The direction of the electric field is opposite to the direction of the electric field formed in the transfer portion N by the transfer bias.

  FIG. 6 schematically shows the behavior of calcium carbonate α from the calcium carbonate-containing paper when the adsorption bias is negative (−1500 V) during monochrome image formation in the adhesion reduction image formation mode (first Only the vicinity of the transfer portion Na and the fourth transfer portion Nd is shown).

  Since the calcium carbonate present in the transfer material P at the adsorbing portion M is also negatively charged, the calcium carbonate has the same polarity as the surface of the photosensitive drum 1 and is suppressed from being transferred to the surface of the photosensitive drum 1. can do.

  Further, a bias is applied to the transfer material P by the suction portion M, and the transfer material P is electrostatically attracted to the transport belt 11, so that the photosensitive drums 1a, 1b, and 1c are formed at the first to third image forming stations Sa, Sb, and Sc. Even if 1b and 1c are separated from the transport belt 11, the transfer material P is transported to the fourth transfer section Nd, which is the farthest from the suction section M in the transport direction, without causing a jam (paper jam). can do. In addition, since the calcium carbonate in the transfer material P is negatively charged, it can be suppressed from being transferred to the photosensitive drum 1 at the fourth transfer portion Nd.

  Furthermore, since the transfer of the toner from the photosensitive drum 1 to the transfer material P is performed only once at the fourth transfer portion Nd, there is no problem even if the transfer material P is charged negatively by the suction portion M.

  As described above, the image forming apparatus 100 according to the present exemplary embodiment is configured such that (i) the photosensitive drums 1a, 1b, 1c, and 1d of all the image forming stations Sa, Sb, Sc, and Sd are in contact with the conveyance belt 11, or The photosensitive drums 1a, 1b, and 1c of the first to third image forming stations Sa, Sb, and Sc are separated from the transport belt 11, and the photosensitive drum 1d of the fourth image forming station Sd is in contact with the transport belt 11. In this state, a first image forming mode (normal image forming mode) in which the suction bias applying power source 32 outputs a bias having the first polarity while the transfer material P on which the toner image is transferred passes through the suction portion M. Color image forming operation and monochrome image forming operation), (ii) the photosensitive drums 1a, 1b, 1c, 1d of all the image forming stations Sa, Sb, Sc, Sd are transported bells. In the second image forming mode (in the adhesion reducing image forming mode), the suction bias applying power source 32 does not output a bias while the transfer material P to which the toner image is transferred passes through the suction portion M. Color image forming operation), (iii) The photosensitive drums 1a, 1b, 1c of the first to third image forming stations Sa, Sb, Sc are separated from the transport belt 11 and the photosensitive drum of the fourth image forming station Sd. While the body drum 1d is in contact with the transport belt 11, the suction bias application power source 32 has a polarity opposite to the first polarity while the transfer material P onto which the toner image is transferred passes through the suction portion M. And a third image forming mode for outputting a bias having a polarity of 2 (monochrome image forming operation in the adhesion reduction image forming mode).

  In other words, as described above, the image forming apparatus 100 according to the present embodiment is configured such that the transfer material P on the transport belt 11 is the photosensitive drum 1a of the first to third image forming stations Sa, Sb, and Sc. The first mode conveyed in contact with 1b, 1c, and the transfer material P on the conveyor belt 11 contact the photosensitive drums 1a, 1b, 1c of the first to third image forming stations Sa, Sb, Sc. In some cases, the output of the suction bias application power source 32 has a reverse polarity in the first mode and the second mode. That is, the output of the suction bias application power source 32 has a reverse polarity between the color image forming operation in the normal image forming mode and the monochrome image forming operation in the adhesion reducing image forming mode. Further, in the image forming apparatus 100 of the present embodiment, the output of the suction bias application power source 32 may not be output in the first mode but may be output in the second mode. That is, the bias from the suction bias application power source 32 is not output during the color image forming operation in the adhesion reducing image forming mode, but is output when the monochrome image is formed in the normal image forming mode (and the adhesion reducing image forming mode).

(Experimental example)
Using calcium carbonate-containing paper as the transfer material P, durability tests were performed in the normal image formation mode and the adhesion reduction image formation mode. Here, in a low-temperature and low-humidity environment of 15 ° C./10% RH, a paper of calcium carbonate-containing paper, which is calcium carbonate-containing paper, weighing 80 g / cm ² , which is a calcium carbonate-containing paper, is passed through, and the adsorption bias in the normal image forming mode (+ 1500V) was compared with an image when the suction bias in the adhesion reduction image forming mode (color image forming operation: 0 V, monochrome image forming: −1500 V).

  When the normal image forming mode is set, an image defect (vertical stripe) may occur at 8000 sheets. In some cases, the level of contamination of the charging roller 2 by calcium carbonate may be very poor. On the other hand, in the setting of the adhesion reduction image forming mode (adsorption bias is nonpolar or negative polarity), the contamination of the charging roller 2 due to calcium carbonate is greatly improved in an endurance test up to 16000 sheets, resulting in an image defect. There was no outbreak.

  As described above, according to the present embodiment, contamination of the charging roller 2 due to adhesion of calcium carbonate can be suppressed and occurrence of charging failure can be suppressed. When the calcium carbonate-containing paper is used, the life of the process cartridge 7 can be increased. In this example, the same effect can be obtained for talc-containing paper that causes the same problem as calcium carbonate-containing paper.

  Note that not all the calcium carbonate-containing papers cause problems as described in this embodiment. When a problem such as charging failure due to contamination of the charging roller 2 due to adhesion of calcium carbonate occurs, the user of the apparatus reduces the adhesion forming image forming mode described in this embodiment in order to prevent calcium carbonate adhesion. Can be done with. Paper (transfer material) P having a high calcium carbonate content tends to adhere to various places in the apparatus as calcium dust. As an example, whether or not the image defect is caused by calcium carbonate can be determined by whether or not calcium carbonate is adhered and whitened on the conveyance belt 11.

Example 2
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the first embodiment. Accordingly, elements having substantially the same or corresponding functions and configurations as those of the image forming apparatus 100 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  The present embodiment is different from the first embodiment in that the photosensitive drum is not separated from the transport belt 11 even in an image forming station that is not used during the monochrome image forming operation. By not providing the contact / separation mechanism, the cost of the image forming apparatus can be reduced.

  In the present embodiment, the color image forming operation is substantially the same as that in the first embodiment in both the normal image forming mode and the adhesion reducing image forming mode, and the description thereof is omitted here.

(Monochrome image forming operation in normal image forming mode)
First, a monochrome image forming operation in the normal image forming mode will be described. During the monochrome image forming operation, as in the first embodiment, only the black image is formed by the fourth image forming station Sd. At this time, in this embodiment, the photosensitive drums 1a, 1b, 1c, and 1d are brought into contact with the conveyor belt 11 in all of the first to fourth image forming stations Sa, Sb, Sc, and Sd (that is, The photosensitive drums 1a, 1b, and 1c are not separated from the conveyor belt 11 in the first to third image forming stations Sa, Sb, and Sc that do not perform image formation. In the monochrome image forming operation, the photosensitive drums 1a, 1b, 1c, and 1d rotate in all of the first to fourth image forming stations Sa, Sb, Sc, and Sd. In the first to third image forming stations Sa, Sb, and Sc that do not perform image formation, transfer bias application to the transfer rollers 12a, 12b, and 12c is turned off. Other image forming operations are the same as the monochrome image forming operation in the normal image forming mode described in the first embodiment.

  In the suction portion M, a positive voltage is applied from the suction roller 20 side, and the suction counter roller 14 is grounded. More specifically, in this embodiment, a bias of +1500 V outputted from the suction bias application power source 32 is applied to the suction roller 20.

  As a result, the transfer material P is adsorbed to the transport belt 11, passes through the first to third transfer portions Na, Nb, and Nc and is transported to the fourth transfer portion Nd. That is, the transfer material P adsorbed on the surface of the conveyor belt 11 is in the first to third states in which the photosensitive drum 1 is in contact with the conveyor belt 11 due to the rotation of the conveyor belt 11 in the direction of arrow R in the drawing. The image forming stations Sa, Sb, and Sc sequentially pass through the first to third transfer portions Na, Nb, and Nc, and are conveyed to the fourth transfer portion of the fourth image forming station Sd. The toner image on the photosensitive drum 1d is transferred onto the transfer material by the electric field formed between the photosensitive drum 1d and the transfer roller 12d in the fourth image forming station Sd.

(Monochrome image forming operation in adhesion reduction image forming mode)
Next, a monochrome image forming operation in the adhesion reduction image forming mode will be described.

  In this embodiment, even in the adhesion reduction image forming mode, the photosensitive drums 1a, 1b, 1c, and 1d are in all of the first to fourth image forming stations Sa, Sb, Sc, and Sd during the monochrome image forming operation. It is in contact with the conveyor belt 11. In the monochrome image forming operation, the photosensitive drums 1a, 1b, 1c, and 1d rotate in all of the first to fourth image forming stations Sa, Sb, Sc, and Sd. On the other hand, in the first to third image forming stations Sa, Sb, and Sc that do not perform image formation, the application of the transfer bias to the transfer rollers 12a, 12b, and 12c is turned off.

  Here, for example, when a lot of calcium carbonate-containing paper is used as the transfer material P, when a positive voltage is applied from the suction roller 20 side, the calcium carbonate in the transfer material P is charged to the positive polarity, This is not preferable because it is transferred to the photosensitive drum 1.

  Therefore, in this embodiment, the suction bias is nonpolar, that is, 0 V during the monochrome image forming operation in the adhesion reduction image forming mode. That is, at the time of monochrome image forming operation in the adhesion reduction image forming mode, the suction bias application power source 32 does not output a bias to the suction roller 20. At this time, both the suction roller 20 and the suction counter roller 14 are grounded.

  FIG. 7 schematically shows the behavior of calcium carbonate α from the calcium carbonate-containing paper when the adsorption bias is made nonpolar during the monochrome image forming operation in the adhesion reduction image forming mode.

  Although the transfer material P is not electrostatically attracted to the conveyance belt 11 in the adsorption portion M, the first to third transfer portions Na, Nb, and Nc are in contact with the conveyance belt 11, so that a jam (paper jam) occurs. The transfer material P can be conveyed to the fourth transfer portion Nd without any problem.

  Then, the toner image on the photosensitive drum 1d is transferred onto the transfer material P by the electric field formed between the photosensitive drum 1d and the transfer roller 12d in the fourth image forming station Sd. At this time, since calcium carbonate is not positively charged, it is difficult to transfer it onto the surface of the photosensitive drum 1d.

  As described above, according to the present embodiment, contamination of the charging roller 2 due to adhesion of calcium carbonate can be suppressed and occurrence of charging failure can be suppressed. According to the present embodiment, it is possible to take measures against calcium carbonate-containing paper even in an image forming apparatus that omits a mechanism for contacting and separating the photosensitive drum 1 from the transport belt 11 for cost reduction or the like. In this example, the same effect can be obtained for talc-containing paper that causes the same problem as calcium carbonate-containing paper.

Example 3
Next, another embodiment of the present invention will be described. The basic configuration and operation of the image forming apparatus of the present embodiment are the same as those of the first embodiment. Accordingly, elements having substantially the same or corresponding functions and configurations as those of the image forming apparatus 100 of the first embodiment are denoted by the same reference numerals, and detailed description thereof is omitted.

  In this embodiment, the apparatus main body A is provided with an environmental sensor 35 (FIG. 9) as detection means capable of detecting at least humidity information, and image forming operation is performed in the adhesion reduction image forming mode according to the humidity of the apparatus environment. No is determined. This will be described in more detail below.

  For example, the phenomenon of contamination of the charging roller 2 by calcium carbonate when calcium carbonate-containing paper is used as the transfer material P is likely to occur in a low humidity environment. This is because the moisture in the transfer material P is dried and the calcium carbonate is easily charged, and the charge of the calcium carbonate once charged is difficult to attenuate.

  Therefore, in this embodiment, when the implementation of the adhesion reduction image forming mode is permitted, the adhesion reduction image described in the embodiment 1 is detected only when the environment sensor 35 detects the humidity and the environment is a low humidity environment. An image forming operation is performed in the forming mode. More specifically, in this embodiment, when the humidity is detected by the environmental sensor 35 and the humidity falls below 30% RH, the image forming operation is performed in the adhesion reduction image forming mode described in the first embodiment. .

  FIG. 9 shows a schematic control mode of this embodiment. As shown in FIG. 9, in this embodiment, an environmental sensor 35 is connected to the controller unit 33. Then, the detection result of the temperature and humidity by the environment sensor 35 is input to the controller unit 33 at a predetermined timing. Similarly to the first embodiment, an image formation mode selection signal is input to the controller unit 33 together with an image formation start instruction via the operation unit 34 of the apparatus main body A or the operation unit of the external device 200.

  As shown in FIG. 10, in this embodiment, when the image formation start instruction is input, the controller unit 33 determines whether or not the adhesion reduction image formation mode is selected (that is, the adhesion reduction image formation mode is permitted). (Step 1). When it is determined that the adhesion reduction image forming mode is selected, the controller 33 reads the detection result of the environment sensor 35 (step 2) and determines whether the humidity is less than 30% RH (step 2). 3). When the humidity is less than 30% RH, the controller unit 33 executes a color image forming operation or a monochrome image forming operation in the adhesion reduction image forming mode (step 4).

  On the other hand, if the controller unit 33 determines in step 1 that the adhesion reduction image forming mode is not selected, or if it determines in step 3 that the humidity is 30% RH or higher, the normal image forming mode is selected. A color image forming operation or a monochrome image forming operation is executed at (Step 5).

(Experimental example)
The state of occurrence of image defects due to the calcium carbonate contamination of the charging roller 2 for each temperature and humidity by the image forming operation in the normal image forming mode was examined. Here, as the transfer material P, 8000 sheets of paper weighing 80 g / cm ² manufactured by Occeley, which is calcium carbonate-containing paper, were passed. The results were as follows.
30 ° C / 80% RH No image defect 23 ° C / 60% RH No image defect 15 ° C / 10% RH "Vertical streak" Image defect occurred

  Image defects did not occur at 30 ° C./80% RH or 23 ° C./60% RH. This is because the calcium carbonate is difficult to be charged due to high humidity, or even if the calcium carbonate adheres to the photosensitive drum 1, the electrostatic adhesion to the photosensitive drum 1 is weak, so the cleaning blade 60. This is considered to be because of being scraped off by the toner and easily collected in the waste toner chamber 53.

  Therefore, as described above, in this embodiment, when the humidity is detected by the environmental sensor 35 and the humidity falls below 30% RH, the image forming operation is performed in the adhesion reduction image forming mode described in the first embodiment. carry out. When the humidity is 30% RH or higher, there is no problem even if the image forming operation is performed in the normal image forming mode described in the first embodiment because calcium carbonate hardly adheres to the photosensitive drum 1.

  As described above, according to the present embodiment, by detecting the humidity with the environment sensor 35, the image forming operation is executed in the normal image forming mode which is advantageous in terms of the transportability and transferability of the transfer material P as much as possible. Therefore, it is possible to adopt the adhesion reduction image forming mode.

  In the present embodiment, the adhesion reduction image forming mode described in the first embodiment has been described as an example, but naturally, in the adhesion reduction image forming mode described in the second embodiment according to the detection result of the environment sensor 35. An image forming operation can also be performed.

  As mentioned above, although this invention was demonstrated according to the specific Example, it should be understood that this invention is not limited to each said Example. For example, the charging polarity of the toner is not limited to negative polarity but may be positive. In that case, the polarities of the transfer bias and the suction bias having the polarities in the above embodiments are opposite.

  In each of the above embodiments, the suction means has been described as having a suction roller as a suction member. However, the present invention is not limited to this, and a brush shape, a blade shape, or a sheet shape that contacts the conveyance belt. Etc. can be used.

  In each of the above embodiments, the suction bias applying power source as the suction bias output means outputs the suction bias to the suction roller as the suction member in the suction means. However, the present invention is not limited to this, and is attracted to one of the rollers (adsorption opposed roller) that stretches the conveyor belt that functions as a facing member (counter electrode) in each of the above embodiments. A bias may be output. That is, the functions of the suction roller and the suction counter roller in each of the above embodiments are reversed, and a bias is applied to the roller that contacts the inner peripheral surface side of the transport belt, so that the roller that contacts the outer peripheral surface side of the transport belt faces the roller. You may make it function as a member (counter electrode). In this case, the direction of the electric field formed on the transfer material P on the transport belt (transfer material transport member) in the suction portion is opposite to that in the above embodiments.

1 is a schematic cross-sectional view of an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a cross-sectional view of a process cartridge mounted on the image forming apparatus in FIG. 1. FIG. 2 is a schematic cross-sectional view of a main part showing a relationship between a photosensitive drum and a conveyor belt during a monochrome image forming operation in the image forming apparatus of FIG. It is a schematic diagram for demonstrating the behavior of the calcium carbonate from the calcium carbonate containing paper in normal image formation mode. It is a schematic diagram for demonstrating the behavior of the calcium carbonate from the calcium carbonate containing paper at the time of the color image formation operation | movement in one Example of the adhesion reduction image formation mode according to this invention. It is a schematic diagram for demonstrating the behavior of the calcium carbonate from the calcium carbonate containing paper at the time of the monochrome image formation operation | movement in one Example of the adhesion reduction image formation mode according to this invention. It is a schematic diagram for demonstrating the behavior of the calcium carbonate from the calcium carbonate containing paper at the time of the monochrome image formation operation | movement in the other Example of the adhesion reduction image formation mode according to this invention. It is a block diagram for demonstrating the control aspect in one Example of this invention. It is a block diagram for demonstrating the control aspect in the other Example of this invention. It is a flowchart for demonstrating one Example of the control which judges adoption of the adhesion reduction image formation mode according to this invention.

Explanation of symbols

1 Photosensitive drum (image carrier)
2 Charging roller (charging means)
3 Exposure equipment (exposure means)
4 Developing device (Developing means)
5 Transfer device 6 Cleaning device (cleaning means)
12 Transfer roller (transfer means)
14 Adsorption opposite roller 20 Adsorption roller 31 Transfer bias application power supply (transfer bias output means)
32 Suction bias application power supply (Suction bias output means)
DESCRIPTION OF SYMBOLS 100 Image forming apparatus A Apparatus main body B Adsorption means

Claims (13)

An image carrier that carries a toner image, a transfer material conveyance member that carries a transfer material and conveys it between the image carrier, and a toner image on the image carrier is carried by the transfer material conveyance member A transfer means for transferring to the transfer material, a transfer bias output means for outputting a bias for transferring the toner image to the transfer means, and an adsorption portion upstream of the transfer portion in the transport direction of the transfer material In an image forming apparatus comprising: an adsorption unit for adsorbing a transfer material to the transfer material conveyance member; and an adsorption bias output unit for outputting a bias to the adsorption unit.
A first image forming mode in which the suction bias output means outputs a bias having a first polarity while a transfer material onto which a toner image is transferred passes through the suction portion;
While the transfer material onto which the toner image is transferred passes through the suction portion, the suction bias output means outputs a bias having a second polarity opposite to the first polarity or outputs a bias. A second image forming mode that does not,
An image forming apparatus comprising: First and second image carriers that carry toner images, and first and second transfer portions that are in contact with the first and second image carriers, respectively. A transfer material conveying member conveyed between the first and second image carriers, and a toner image on the first and second image carriers are transferred to a transfer material carried on the transfer material conveying member, respectively. First and second transfer means, transfer bias output means for outputting a bias for transferring a toner image to the first and second transfer means, and the first and second transfer An adsorbing means for adsorbing the transfer material to the transfer material conveying member at an adsorbing portion upstream of the transfer material in the conveying direction, an adsorbing bias output means for outputting a bias to the adsorbing means, and the first image Separating means for moving the relative position of the carrier and the transfer material conveying member, A first mode in which the transfer material on the transfer material transport member is transported in contact with the first image carrier; and a transfer material on the transfer material transport member is in contact with the first image carrier. In an image forming apparatus having a second mode conveyed without
The image forming apparatus according to claim 1, wherein the output of the suction bias output means has a reverse polarity in the first mode and the second mode. First and second image carriers that carry toner images, and first and second transfer portions that are in contact with the first and second image carriers, respectively. A transfer material conveying member conveyed between the first and second image carriers, and a toner image on the first and second image carriers are transferred to a transfer material carried on the transfer material conveying member, respectively. First and second transfer means, transfer bias output means for outputting a bias for transferring a toner image to the first and second transfer means, and the first and second transfer An adsorbing means for adsorbing the transfer material to the transfer material conveying member at an adsorbing portion upstream of the transfer material in the conveying direction, an adsorbing bias output means for outputting a bias to the adsorbing means, and the first image Separating means for moving the relative position of the carrier and the transfer material conveying member, A first mode in which the transfer material on the transfer material transport member is transported in contact with the first image carrier; and a transfer material on the transfer material transport member is in contact with the first image carrier. In an image forming apparatus having a second mode conveyed without
The image forming apparatus is characterized in that the output of the suction bias output means is not output in the first mode but output in the second mode.   The image forming apparatus according to claim 1, wherein the suction unit is disposed on the image carrier side with respect to the transfer material conveying member.   5. The image forming apparatus according to claim 1, wherein the first polarity is the same as a polarity of a bias output by the transfer bias output unit for transferring a toner image.   The image forming apparatus according to claim 1, wherein the second polarity is the same polarity as a charging polarity of the image carrier.   The image forming apparatus according to claim 1, wherein the suction unit is grounded when no bias is applied by the suction bias output unit.   The adsorbing means is in contact with a transfer material carrying surface of the transfer material carrying member and a side opposite to the transfer material carrying surface of the transfer material carrying member facing the first member. 8. The apparatus according to claim 1, wherein the attraction bias output means outputs a bias to the first member or the second member. The image forming apparatus described in the item.   The image forming apparatus according to claim 8, wherein the first and second members are grounded when a bias is not applied by the suction bias output unit.   The image forming apparatus according to claim 1, wherein the transfer material conveying member conveys a transfer material in a direction intersecting a horizontal direction.   11. The image forming mode is changed according to an instruction from an operation unit of the image forming apparatus main body or an external device connected to the image forming apparatus main body so as to be communicable. The image forming apparatus according to one item.   12. The apparatus according to claim 1, further comprising a detection unit that detects environmental information of the apparatus including at least humidity information, wherein the image forming mode is changed according to a detection result of the detection unit. The image forming apparatus described in the item.   The image forming mode in which the suction bias output means outputs the bias of the second polarity or the bias is not output while the transfer material onto which the toner image is transferred passes through the suction portion is humidity in the apparatus environment. The image forming apparatus according to claim 1, wherein the image forming apparatus is performed when the value is less than a predetermined value.

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