JP2013171282A - Image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image formation apparatus having high transfer performance due to a second transfer unit.SOLUTION: The image formation apparatus includes: a first transfer unit for transferring a toner image from an image holding body surface onto a transferred body at a first transfer position; a second transfer unit for transferring the toner image from the transferred body onto a recording medium at a second transfer position; a conveyance unit having a belt-like conveyance member moving through the second transfer position and for adsorbing the recording medium to the conveyance member to convey it to the second transfer unit; and an electric charge supply unit for supplying electric charges whose polarity has a reverse polarity to the charge polarity of the toner, with respect to the recording medium conveyed toward the second transfer unit by the conveyance unit.

Description

  The present invention relates to an image forming apparatus.

  Regarding image forming apparatuses represented by printers, copiers, facsimile machines, etc., for example, Patent Document 1 adopts an intermediate transfer method in electrophotographic technology, and applies a charge of the same polarity as toner to a sheet before secondary transfer. The technique of doing is proposed.

  Further, for example, Patent Document 2 proposes a technique in which a direct transfer method is adopted in electrophotographic technology and a charge having the same polarity as that of toner is applied to a sheet before transfer.

  Further, for example, Patent Document 3 proposes a technique in which an intermediate transfer method is adopted in electrophotographic technology, and a charge having a polarity opposite to that of toner is applied to a sheet before secondary transfer.

JP 2008-262085 A JP 2009-300909 A JP 2008-185890 A

  An object of the present invention is to provide an image forming apparatus having high transfer performance by a second transfer device.

An image forming apparatus according to claim 1 is provided.
An image carrier that forms an image on the surface and holds the image;
An image forming device that forms an image with charged toner on the image carrier;
A first transfer unit that transfers the toner image from the surface of the image carrier onto the transfer target at a first transfer position;
A second transfer device for transferring the toner image from the transfer medium onto a recording medium at a second transfer position;
A belt-shaped conveyance member that moves via the second transfer position, a conveyance device that adsorbs the recording medium to the conveyance member and conveys the recording medium to the second transfer device;
A charge imparting device that imparts a charge having a polarity opposite to the charge polarity of the toner to a recording medium that is transported toward the second transfer device by the transport device;
A fixing device for fixing the toner image on the recording medium onto the recording medium;
It is provided with.

An image forming apparatus according to claim 2
The charge applicator has a brush electrode in contact with the surface of the recording medium, and applies charge to the recording medium through the brush electrode.

An image forming apparatus according to claim 3
The transporter includes a transport member having a volume resistivity of 9 LogΩ · cm or more as the transport member.

  According to the image forming apparatus of the first aspect, the transfer performance of the second transfer unit is higher than that in the case where the transporter and the charge applying unit are not provided.

  According to the image forming apparatus of the second aspect, there is less transfer unevenness compared to the case where no brush electrode is provided.

  According to the image forming apparatus of the third aspect, the transfer by the second transfer device is more stable than when the volume resistivity is other than the above-described volume resistivity.

1 is a schematic configuration diagram of an image forming apparatus as an embodiment of the present invention. FIG. 6 is a diagram schematically showing a structure near a secondary transfer position. It is a graph showing the electric potential state in the recessed part of a paper. FIG. 6 is a diagram schematically showing a structure near a secondary transfer position in another embodiment. It is the graph showing the electric potential in a paper recessed part about several types of conveyance belts from which volume resistivity differs. FIG. 6 is a diagram illustrating a relationship between a residual potential of a conveyance belt and image quality in the next transfer. It is a graph showing the relationship between the residual potential of a conveyance belt and volume resistivity.

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

  FIG. 1 is a schematic configuration diagram of an image forming apparatus as an embodiment of the present invention.

  The image forming apparatus 100 is a tandem type color printer. The image forming apparatus 100 includes a sheet feed table 10 at a lower portion, and the sheet P is stored in a stacked state on the sheet feed table 10. When forming an image, one sheet P is sent out from the paper feed tray 10 by the pick-up roll 11 and is transported on the transport path 121 in the direction of arrow A by the transport roll 12. Then, the paper P is further conveyed by the standby roll 13 with the subsequent conveyance timing adjusted. The conveyance after the standby roll 13 will be described later.

  The image forming apparatus 100 is provided with four image forming engines 20Y, 20M, 20C, and 20K. Each of the image forming engines 20Y, 20M, 20C, and 20K uses yellow (Y) toner, magenta (M) toner, cyan (C) toner, and black (K) toner, respectively. An engine that forms a toner image. These four image forming engines 20Y, 20M, 20C, and 20K have the same configuration except that the toners used are different. Here, the four image forming engines 20Y, 20M, 20C, and 20K will be representatively described, and the configuration of the image forming engine 20Y will be described.

  The image forming engine 20Y includes a photoreceptor 21Y, and a charger 22Y, an exposure unit 23Y, a developing unit 24Y, a transfer unit 25Y, a charge removal lamp 26Y, and a cleaner 27Y are disposed around the photoreceptor 21Y. Here, the transfer unit 25Y is disposed at a position where an intermediate transfer belt 31 described later is sandwiched between the transfer unit 25Y and the photoreceptor 21Y.

  The photoreceptor 21 </ b> Y has a cylindrical shape, and is charged on the surface of the photoconductor 21 </ b> Y while being rotated in the direction of the arrow B to be exposed to form an electrostatic latent image. This photoreceptor 21Y corresponds to an example of the image carrier in the present invention.

  The charger 22Y includes a contact charging roll 22Y_1 that charges the photoconductor 21Y while rotating while being in contact with the photoconductor 21Y. The contact charging roll 22Y_1 is charged with the potential bias of −1000 V from the power supply 60 and charges the photoreceptor 21Y. Further, the charger 22Y has a charger cleaner 22Y_2 that removes dirt such as toner and external additives attached to the contact charging roll 22Y_1.

  Further, at the time of this charging, the static elimination lamp 26Y located upstream of the charger 22Y in the rotation direction of the photosensitive member 21Y is in a lighting state. The light from the charge removal lamp 26Y serves to bring the surface potential of the photoreceptor 21Y closer to the ground potential. The surface potential of the photosensitive member 21 charged by the contact charging roll 22Y_1 that has been applied with a potential bias of −1000 V becomes −400 V in combination with the action of light from the charge eliminating lamp 26Y.

  Image data is input to the exposure unit 23Y from a control unit 50 described later, and exposure light 231Y modulated according to the input image data is output from the exposure unit 23Y. The photoreceptor 21Y is irradiated with the exposure light 231Y from the exposure unit 23Y after being charged by the charger 22Y. The potential of the irradiated portion slightly approaches the ground potential and becomes approximately −200V. As a result, an electrostatic latent image is formed on the surface of the photoreceptor 21Y in which a portion having a potential of -400V and a portion having a potential of -200V are distributed according to the image data.

  The photoreceptor 21Y is irradiated with the exposure light 231Y to form an electrostatic latent image on the surface, and then developed by the developing device 24Y, so that a toner image is formed on the surface of the photoreceptor 21Y.

  The developing device 24Y includes two augers 242 that stir the developer in a case 241 that contains a developer composed of toner and a magnetic carrier, and a developing roll that carries the developer to a position facing the photoreceptor 21Y. 243. In the accommodated case 241, the toner is frictionally charged with the magnetic carrier by the stirring of the two augers 242. Due to this triboelectric charge, the toner is negatively charged and the magnetic carrier is positively charged. The developing roll 243 is magnetized, and the magnetic carrier in which toner is electrostatically attached by frictional charging is held on the developing roll 243 by the magnetic force of the developing roll 243.

  In developing the electrostatic latent image formed on the photoreceptor 21Y, a potential bias of −300 V is applied to the developing roll 243. By the action of the potential bias, the toner in the developer adheres to a portion having a potential of −200 V in the electrostatic latent image formed on the photoreceptor 21Y, and a toner image is formed.

  A combination of the charger 22Y, the exposure unit 23Y, and the developing unit 24Y corresponds to an example of the image forming unit referred to in the present invention.

  The toner image formed on the photoreceptor 21Y by development by the developing device 24Y is transferred onto the intermediate transfer belt 31 by the transfer device 25Y. In transferring the toner image, a potential bias is applied from the power supply 60 to the transfer device 25Y. The transfer device 25Y corresponds to an example of the first transfer device according to the present invention.

  The surface of the photoreceptor 21Y after the transfer of the toner image is brought close to the ground potential uniformly by the action of light from the charge eliminating lamp 26Y. Thereby, the history of the electrostatic latent image is erased from the surface of the photoreceptor 21Y after the transfer. Subsequently, residual toner or the like remaining on the photoreceptor 21Y is removed from the photoreceptor 21Y by the cleaner 27Y.

  The intermediate transfer belt 31 is an endless belt that circulates in the direction of arrow C and is wound around a drive roll 32 and other plural rolls 33. The intermediate transfer belt 31 corresponds to an example of a transfer target according to the present invention.

  The toner images formed by the image forming engines 20Y, 20M, 20C, and 20K with the Y, M, C, and K toners are sequentially overlapped with the toner images formed by the image forming engine 20Y as the lowest layer. Thus, the toner image is transferred onto the intermediate transfer belt 31. Then, it is conveyed to a secondary transfer position where the secondary transfer unit 34 is disposed. In synchronization with this, the sheet that has been conveyed to the standby roll 13 is conveyed to the secondary transfer position, and the toner image on the intermediate transfer belt 31 is transferred onto the conveyed sheet by the secondary transfer unit 34. Transcribed. The secondary transfer unit 34 corresponds to an example of the second transfer unit referred to in the present invention.

  Although details of toner image transfer at the secondary transfer position will be described later, a conveyance belt 71 and a charge applying brush 72 are provided in the vicinity of the secondary transfer position. The sheet is conveyed to the secondary transfer position by the conveyance belt 71, and a positive charge is applied to the sheet by the charge applying brush 72. The positive charge applied by the charge applying brush 72 assists the transfer of the toner image by the secondary transfer unit 34.

  The sheet on which the toner image has been transferred is further conveyed on the conveying belt 14 in the direction of arrow D, and the toner image on the sheet is fixed on the sheet by pressurization and heating by the fixing device 40. As a result, an image composed of the fixed toner image is formed on the paper. The fixing device 40 corresponds to an example of a fixing device according to the present invention.

  The sheet on which the image is formed is transported in the direction of arrow E by the transport belt 15 and discharged outside the image forming apparatus 100.

  The intermediate transfer belt 31 after the toner image is transferred onto the paper by the secondary transfer unit 34 further circulates and the toner remaining on the surface thereof is removed from the intermediate transfer belt 31 by the cleaner 35.

  Further, the image forming apparatus 100 includes a control unit 50, an operation / display unit 501, and a power source 60. Image data Cin is input to the control unit 50. Then, the control unit 50 processes the image data Cin according to the control data input together with the image data Cin or according to an instruction from the operation / display unit 501. Thereby, the image data Cin is converted into image data suitable for irradiation of the exposure light 231Y, 231M, 231C, 231K in each of the exposure devices 23Y, 23M, 23C, 23K. The converted image data is transmitted to the exposure units 23Y, 23M, 23C, and 23K. Each of the exposure units 23Y, 23M, 23C, and 23K irradiates each of the photoconductors 21Y, 21M, 21C, and 21K with the exposure light according to the input image data corresponding to each color of Y, M, C, and K.

  The operation / display unit 501 displays various messages regarding the image forming apparatus 100 to the user, and displays various operation buttons to accept operations such as instructions regarding image formation from the user. It is.

  The output level of the power supply 60 is controlled by the control unit 50, and the voltage of the controlled output level is applied to each element of the image forming apparatus 100.

  Details of the toner image transfer at the secondary transfer position will be described below.

  FIG. 2 is a diagram schematically showing the structure near the secondary transfer position.

  As described above, the secondary transfer unit 34 is disposed at the secondary transfer position, and the conveyance belt 71 and the charge applying brush 72 are provided in the vicinity of the secondary transfer position. Further, a driving roll 73 that drives the conveyor belt 71 is provided at a position facing the charge applying brush 72 with the conveyor belt 71 interposed therebetween. The conveyor belt 71 is wound around the drive roll 73 and the secondary transfer device 34, and is circulated and moved in the direction of arrow F when driven by the drive roll 73. The charge applying brush 72 is in contact with the conveyor belt 71 and is rotated in the direction of arrow G by being driven by a motor (not shown).

  One of the rolls 33 around which the intermediate transfer belt 31 is wound is disposed at the secondary transfer position so as to face the secondary transfer unit 34 with the intermediate transfer belt 31 interposed therebetween. The transfer of the toner image by the secondary transfer unit 34 is realized by a potential bias. However, the secondary transfer unit 34 itself has a ground potential, and a power source 60 (see FIG. 5) is supplied to the roll 33 facing the secondary transfer unit 34. 1), a potential bias of −2000 V is applied.

  Further, a potential bias of +2000 V is applied to the charge applying brush 72 by the power supply 60, and the driving roll 73 facing the charge applying brush 72 is at the ground potential. The charge application brush 72 functions as a brush electrode by such a potential bias. Further, the charge applying brush 72 contacts the surface of the conveyed paper P while rotating in the direction of arrow G, and applies a positive charge having a polarity opposite to the charging polarity of the toner to the paper P. The charge applying brush 72 follows the surface of the paper P even if the paper P has irregularities on the surface, such as embossed paper. The surface of the paper P is uniformly charged.

  The charge applied to the paper P causes the paper P to be attracted to the transport belt 71. The conveyance belt 71 conveys the paper P to the secondary transfer position by being driven by the drive roll 73 while adsorbing the paper P.

  A combination of the charge application brush 72 and the power source 60 corresponds to an example of a charge applicator according to the present invention, and the charge application brush 72 corresponds to an example of a brush electrode according to the present invention. A combination of the conveyance belt 71 and the drive roll 73 corresponds to an example of a conveyance device according to the present invention, and the conveyance belt 71 corresponds to an example of a conveyance member according to the present invention. In addition to the one having a brush electrode, as the charge applicator referred to in the present invention, one having a wire electrode extending along the surface of the paper, one having a needle electrode protruding toward the surface of the paper, An apparatus having a roll electrode whose peripheral surface is in contact with the surface of the paper may be employed.

  At the secondary transfer position, the toner image on the intermediate transfer belt 31 is transferred to the surface of the paper P by the potential bias. At this time, the positive charge applied to the paper P electrostatically assists the transfer by the potential bias. As a result, even if the paper P has irregularities such as embossed paper, transfer defects in the recesses are avoided and high transfer performance is obtained.

  FIG. 3 is a graph showing a potential state in the concave portion of the paper.

  The vertical axis of the graph shown in FIG. 3 indicates the potential at the concave portion of the paper, and the horizontal axis indicates the elapsed time after the charge is applied. This graph shows the potential change in the concave portion of the paper sheet after the electric charge is applied to the paper sheet P by the electric potential bias of 2000 V, and the graph curve with the square mark is provided with the conveying belt as in this embodiment. The graph curve with a triangle mark represents the potential change when the conveyance belt is not provided.

  As shown in the graph, when the conveyance belt is not provided, the potential in the concave portion of the paper is rapidly decreased. For example, if it is assumed that the process speed is 250 mm / s and the distance from the charge applying brush 72 to the secondary transfer position is about 50 mm, it takes 0.2 seconds to reach the secondary transfer position after the charge is applied. However, if the conveyance belt is not provided, the potential at the concave portion becomes about one-fourth before reaching the secondary transfer position. When the potential of the concave portion is reduced in this way, the electric field for transferring the toner image may be insufficient in the concave portion of the paper with the potential bias at the secondary transfer position.

  On the other hand, when the transport belt is provided, the potential tends to stop decreasing as shown in the graph, and the potential due to the applied charge even after about 1 second has elapsed since the charge was applied. Has kept more than three quarters. By maintaining the potential in the concave portion in this way, the toner image is properly transferred even in the concave portion of the paper P in the transfer at the secondary transfer position. That is, when the conveyance belt is provided, the transfer performance is higher than when the conveyance belt is not provided.

In the following, an example in which paper having a surface with unevenness (Rezac 66) is used as paper will be described. The conditions for image formation are as follows: the process speed is 250 mm / s, the distance from the charge applying brush 72 to the secondary transfer position is 50 mm, the nip width in the secondary transfer unit 34 is 6 mm, and the rotational axis direction of the secondary transfer unit 34 is The nip length was 350 mm, the thickness of the conveyor belt 71 was 450 μm, and the conveyor belt 71 was made of chloroprene containing conductive carbon black and had a volume resistivity of 13.6 LogΩ · cm. Further, as the charge application brush 72, a brush having a diameter of 26 mm, a hair length of 7 mm, and a hair density of 1800 / inch ² was used, and a potential bias of +2000 V was applied. As a ^{result, 150g / m 2, 203g /} m 2, 250g / m 2 did not occur even transfer failure for any thickness of paper that good transfer image is obtained.

  Such a high transfer performance can be obtained regardless of the type of the charge applicator referred to in the present invention. However, the type having the brush electrode as in this embodiment has a high followability to the paper surface. It is particularly preferable that the charge is uniformly applied to the P surface because there is little transfer unevenness.

  Here, another embodiment of the present invention will be described. This other embodiment is the same as the above-described embodiment except for the point that the structure of the transporter according to the present invention is different. Therefore, the duplicate description will be omitted and only the difference will be described.

  FIG. 4 is a diagram schematically showing a structure near the secondary transfer position in another embodiment.

  In this other embodiment, a longer conveyor belt 74 is employed instead of the conveyor belt 71 shown in FIG. The transport belt 74 is looped around the drive roll 73 and the secondary transfer unit 34, and is also looped around a roll 75 disposed at a position beyond the secondary transfer position. For this reason, the conveyance belt 74 shown in FIG. 3 conveys the paper P to the secondary transfer position and guides the secondary transfer position forward. In this way, the paper P is guided to the secondary transfer position and from the secondary transfer position to the front by the same conveying belt 74, so that the movement of the paper P at the secondary transfer position is stabilized, and as a result, Transfer by the secondary transfer unit 34 is stabilized.

  The physical property values of the conveyor belt suitable as the conveyor belts 71 and 74 employed in each of the embodiments described above will be discussed below.

  FIG. 5 is a graph showing the potential in the paper recess for a plurality of types of transport belts having different volume resistivity.

  The vertical axis of the graph shown in FIG. 5 indicates the potential in the concave portion of the paper, and the horizontal axis indicates the volume resistivity (Log Ω · cm) of the conveyor belt. This graph represents the potential in the concave portion of the sheet when 0.2 seconds elapses after the charge is applied with the potential bias of 2000V. As shown in the graph, the higher the volume resistivity of the conveyance belt, the higher the potential in the concave portion of the paper. However, when the volume resistivity of the conveyance belt is 9 LogΩ · cm or more, the potential tends to reach a peak. Further, if the potential at the concave portion of the paper is less than 1500 V, there may be a case where a transfer failure in the concave portion of the paper occurs. Therefore, the volume resistivity of the conveyor belt is desirably 9 LogΩ · cm or more.

  On the other hand, when the volume resistivity of the transport belt is too high, the charge applied to the transport belt is excessively small due to the transfer of the toner image by the secondary transfer unit 34, and the transport belt is circulated by the circulation movement. When returning to the next transfer position, the next transfer is affected.

  FIG. 6 is a diagram illustrating the relationship between the residual potential of the conveyor belt and the image quality in the next transfer.

  When the potential bias for transfer by the secondary transfer unit 34 is 2000V, the image quality in the next transfer is particularly good when the residual potential is 200V or less when the conveying belt returns to the secondary transfer position. There is no effect. However, when the residual potential exceeds 200 V, the image quality in the next transfer is affected.

  FIG. 7 is a graph showing the relationship between the residual potential of the conveyor belt and the volume resistivity.

  The vertical axis of the graph in FIG. 7 indicates the residual potential of the conveyor belt, and the horizontal axis indicates the elapsed time from the transfer by the secondary transfer unit 34. This graph shows the graph curves of each of the four types of transport belts having different volume resistivity. In any graph curve, the static elimination proceeds only in a short time from the transfer by the next transfer device 34. Thereafter, the residual potential becomes almost constant. It can be seen that the volume resistivity of the conveying belt is desirably 13 LogΩ · cm or less in order to suppress the residual potential to 200 V or less.

  However, the residual potential shown in the graph of FIG. 7 is a residual potential that does not consider the charge application by the charge application brush 72, and the charge application by the charge application brush 72 works in the direction of promoting the charge removal of the transport belt. Therefore, in each of the above embodiments, the upper limit of the volume resistivity in the conveyor belts 71 and 74 is higher than 13 LogΩ · cm. In the case of the potential bias described with reference to FIG. 3, the volume resistivity is 15 LogΩ · cm. Even for the conveyor belt, the residual potential does not affect the image quality in the next transfer. Although the residual potential of the conveyor belt is not determined only by the volume resistivity, there is no doubt that the upper limit of the volume resistivity is increased by the charge application by the charge application brush 72. On the other hand, for various other reasons, the upper limit of the volume resistivity of the conveyor belt is said to be at most about 16 LogΩ · cm. Therefore, the configuration shown in FIGS. 3 and 4 has a special upper limit for the volume resistivity of the conveyor belt. It can be said that no value is produced.

  In each of the above-described embodiments, a printer is illustrated as an example of an image forming apparatus. However, the image forming apparatus of the present invention may be a facsimile, a copier, or a multifunction machine.

  In each of the above-described embodiments, the image forming device according to the present invention is exemplified by a toner image formed by a so-called electrophotographic method. However, the image forming device according to the present invention has a latent image on an image carrier. A toner image can be formed by directly attaching toner without forming an image.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 20Y Image forming engine 21Y Photoconductor 22Y Charger 23Y Exposure device 24Y Developing device 25Y Transfer device 31 Intermediate transfer belt 34 Secondary transfer device 60 Power supply 71, 74 Conveying belt 72 Charge application brush 73 Drive roll 75 Roll

Claims (3)

An image carrier that holds an image on which an image is formed;
An image forming device for forming an image with charged toner on the image carrier;
A first transfer unit that transfers the toner image from the surface of the image carrier onto the transfer target at a first transfer position;
A second transfer device for transferring the toner image from the transfer medium onto a recording medium at a second transfer position;
A belt-shaped conveyance member that moves via the second transfer position, and a conveyance device that adsorbs the recording medium to the conveyance member and conveys the recording medium to the second transfer device;
A charge imparting device that imparts a charge having a polarity opposite to the charge polarity of the toner to a recording medium that is transported toward the second transfer device by the transport device;
A fixing device for fixing the toner image on the recording medium onto the recording medium;
An image forming apparatus comprising:   2. The image forming apparatus according to claim 1, wherein the charge applicator has a brush electrode that contacts the surface of the recording medium, and applies charge to the recording medium through the brush electrode. .   The image forming apparatus according to claim 1, wherein the transporter has a transport member having a volume resistivity of 9 LogΩ · cm or more as the transport member.

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