JP2006330437A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of performing high definition secondary transfer by appropriately neutralizing toner on a transfer belt. <P>SOLUTION: The image forming apparatus has the transfer belt 10 on the surface of which a toner image is transferred and which performs the secondary transfer of the transferred toner image to a recorded material, a plurality of image carriers 1, 2, 3, 4 arranged in series so as to transfer the toner image formed on the surface to the transfer belt 10 in order, a neutralizer 18 which is opposite to a linear stretched part of the transfer belt 10 and which neutralizes the toner image on the transfer belt 10, and an opposite electrode 19 which is opposite to the neutralizer 18 with the transfer belt 10 therebetween and which contacts the rear surface of the transfer belt 10. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image with toner.

  Conventionally, toner images formed on a plurality of image carriers are primarily transferred so as to be sequentially superimposed on a transfer belt, and the toner images transferred on the transfer belt are secondarily transferred to a recording material such as recording paper. In the image forming apparatus, there is a problem that the toner that has been primarily transferred first is charged by the subsequent primary transfer and obstructs the secondary transfer.

For this reason, the image forming apparatus described in Patent Documents 1 to 5 includes a charge eliminator facing the transfer belt (a charger that removes a charge having a polarity opposite to the original polarity of the toner or imparts a charge having the original polarity of the toner). Thus, the toner on the transfer belt is discharged (or charged).
JP-A-7-225522 JP-A-8-63003 JP 2000-181237 A JP-A-10-274892 Japanese Patent Laid-Open No. 11-305566

  In the image forming apparatuses disclosed in Patent Documents 1 to 3, the static eliminator is provided so as to face the linear stretch portion between the rollers that guide the transfer belt. In this case, the electric charge discharged from the toner becomes a current that flows through the transfer belt and is grounded via a roller that guides the transfer belt. Such a resistance of the ground path prevents the toner from being neutralized, and the secondary transfer defect may not be sufficiently improved.

  In the image forming apparatuses disclosed in Patent Documents 4 and 5, the static eliminator is provided so as to face the bent portion of the transfer belt that is folded back along the roller. In this case, since the electric charge discharged from the toner penetrates the transfer belt in the thickness direction and is grounded via the roller immediately below, the ground resistance is small. However, since the transfer belt is bent, an appropriate distance between the charge eliminator and the transfer belt can be ensured only with a short length in the moving direction of the transfer belt, and the charge removal of the toner becomes insufficient. was there.

  In addition, since corotrons and scorotrons used in the static eliminator generate ozone, the image forming apparatuses described in Patent Documents 1 to 5 have a problem that an exhaust fan is required to remove the ozone generated in the static eliminator. there were.

  Further, when the charge on the transfer belt is large and an attempt is made to neutralize the charge to an appropriate charge amount by the static eliminator, the toner is excessively discharged at a portion where the adhesion amount is small, and the toner adhesion amount is small (thin). There was a problem that the image could not be transferred sufficiently.

  In view of the above-described problems, an object of the present invention is to provide an image forming apparatus capable of performing high-quality secondary transfer by appropriately discharging the toner on the transfer belt.

  In order to solve the above problems, an image forming apparatus according to the present invention is formed on a surface with a transfer belt on which a toner image is primarily transferred onto a surface and the transferred toner image is secondarily transferred onto a recording material. A plurality of image carriers arranged in series so as to sequentially transfer the toner images to the transfer belt; a static eliminator that faces the transfer belt and neutralizes the toner image on the transfer belt; and the transfer belt. It has a counter electrode which is opposed to the static eliminator and is in contact with the back surface of the transfer belt.

  According to this configuration, even when the static eliminator is provided opposite to the linear stretch portion of the transfer belt, the ground resistance of the transfer belt at the portion where the static eliminator is opposed is low, and the toner on the transfer belt is neutralized. The static elimination current of is easy to flow. For this reason, the toner can be reliably discharged and stable secondary transfer is possible.

  Further, in the image forming apparatus of the present invention, if the counter electrode is a conductive flat plate grounded, the contact area with the transfer belt is wide and the grounding resistance of the static elimination current is small. Further, the portion of the transfer belt facing the static eliminator is flattened, and the distance between the static eliminator and the transfer belt can be appropriately maintained over a sufficient length in the moving direction of the transfer belt. it can.

  Further, in the image forming apparatus of the present invention, if the counter electrode is a conductive brush grounded, stable grounding can be performed regardless of the unevenness of the back surface of the transfer belt and the conveyance state.

  Further, in the image forming apparatus of the present invention, the static eliminator may become excessively charged when the toner adhesion amount is small. However, if the static eliminator is disposed between the image carriers, the static eliminator is excessive. Since the toner thus formed is charged again in the primary transfer by the downstream image carrier, an image having a low toner density can be appropriately secondary-transferred. If the static eliminator is disposed on the upstream side of the image carrier, which is the most downstream in the transfer belt traveling direction, the toner image on the transfer belt is neutralized once by the static eliminator. Secondary transfer is performed through the next transfer step. For this reason, the toner image on the transfer belt is charged to the same extent as the toner image that is primarily transferred by one image carrier, so that optimal secondary transfer can be performed.

  Further, in the image forming apparatus of the present invention, the image carrier includes at least a carrier charger for charging the image carrier and a developing unit integrated with a developer for supplying toner to the image carrier. If configured and the static eliminator is incorporated in any of the developing units, the image forming apparatus does not increase in size.

  In the image forming apparatus of the present invention, if the static eliminator is connected to an exhaust fan of a charger that charges any of the image carriers, an exhaust fan may not be added for the static eliminator. In particular, if the static eliminator is connected to an exhaust fan of the charger incorporated in the same unit, the efficiency of the exhaust fan does not decrease because the distance between the charger and the static eliminator is short.

  As described above, according to the present invention, since the static eliminator and the counter electrode are provided so as to sandwich the transfer belt, the ground resistance is low, and the toner on the transfer belt can be stably discharged. For this reason, there is no defect in secondary transfer and a high-quality image can be formed.

Embodiments of the present invention will now be described with reference to the drawings.
FIG. 1 shows a configuration of a main part of the image forming apparatus according to the first embodiment of the present invention. The image forming apparatus according to the present embodiment includes four developing units 1, 2, 3, and 4 that form yellow, magenta, cyan, and black toner images, respectively. A rotatable photoconductor (image carrier) 5, a charger 6 for charging the photoconductor 5, an exposure device 7 for exposing the charged photoconductor 5 to form an electrostatic latent image, and an electrostatic latent image It has a developing device 8 that forms a toner image by attaching toner, and a cleaner 9 that cleans the surface of the photoreceptor 5. The transfer belt 10 is sandwiched between the photoreceptor 5 and the primary transfer roller 11, and the toner image formed on the photoreceptor 5 is transferred by the electrostatic force of the primary transfer roller 11 (primary transfer). The charger 6 is connected to an exhaust fan 12 provided outside the developing units 1, 2, 3, and 4, and the air inside is forcibly exhausted. The transfer belt 10 is stretched between the drive roller 13 and the free roller 14, is given a predetermined tension by the tension roller 15, and rotates in the arrow direction by the rotation of the drive roller 13. The developing units 1, 2, 3, and 4 are arranged in series on a stretched portion of the transfer belt 10 that is linearly stretched between the free roller 14 and the driving roller 13. The secondary transfer roller 16 sandwiches the transfer belt 10 and a recording material such as recording paper between the driving roller 13 and transfers the toner image on the transfer belt 10 to the recording material by electrostatic force (secondary transfer). . A belt cleaner 17 abuts on the transfer belt 10 on the free roller 14 and scrapes off toner remaining on the surface. Further, the most downstream developing unit 4 is provided with a static eliminator 18 facing the transfer belt 10 on the downstream side of the photoreceptor 5. The static eliminator 18 is connected to the same exhaust fan 12 as the charger 6, and the internal air is forcibly exhausted. A counter electrode 19 made of a metal (conductive) flat plate is provided so as to face the static eliminator 18 across the transfer belt 10.

  FIG. 2 shows a detailed configuration of the static eliminator 18 and the counter electrode 19. In the static eliminator 18, a wire (band electrode) 21 is stretched over the frame 20 in the width direction of the transfer belt 10, and a grid electrode 22 is provided so as to face the surface of the transfer belt 10 on which an image of toner T is formed. A scorotron charger. The counter electrode 19 is a flat metal that contacts the back surface of the transfer belt 10. The wire 21 of the static eliminator 18 is applied with a 3 to 10 kV band electrode applied voltage having a polarity opposite to that of the toner T (plus when the toner T is negative), and the grid electrode 22 has the same polarity as the toner T ( A negative voltage of 30 to 200 V is applied when the toner T has a negative polarity, and the counter electrode 19 is grounded to the ground line.

Subsequently, the operation of the imaging apparatus of the present embodiment will be described.
The primary transfer roll 11 is charged with a polarity opposite to that of the toner T, and transfers the toner image to the transfer belt 10 by attracting the toner T on the photoreceptor 5 by electrostatic force. At this time, the toner T is charged to the reverse polarity by the primary transfer roll 11 after contacting the transfer belt 10. The yellow toner T transferred from the developing unit 1 to the transfer belt 10 is further charged to a reverse polarity by the primary transfer roller that transfers the magenta toner T in the developing unit 2. In this way, the toner T transferred by the upstream developing unit is charged to a polarity opposite to the original polarity every time it passes through the downstream developing unit.

  However, the developing unit 4 is provided with a charge eliminator 18 to which a voltage having a polarity opposite to the original polarity of the toner T is applied. The charge eliminator 18 transfers the charge charged to the toner T to the transfer belt 10 and the opposite side. The toner T is discharged by being pushed through the electrode 19 to the ground line. As a result, the toner T returns to its original polarity and is reliably transferred to the recording material by the electrostatic force of the secondary transfer roller 16 charged to the opposite polarity.

In the present embodiment, the transfer belt 10 preferably has a thickness of 30 μm to 500 μm and a volume resistivity of 10 ³ to 10 ⁹ Ωcm. Thickness insufficient 30μm smaller than strength, 500 [mu] m larger than the resistance irregularity in the thickness direction is liable to occur, the volume resistivity is difficult to adjust the 10 ³ [Omega] cm less than the transfer current, 10 ⁹ [Omega] cm greater than the residual This is because there is a risk of image defects due to electric charges. Examples of the material of the transfer belt 10 include nylon, polyester, polycarbonate, fluorine resin, silicon resin, polyurethane, polyimide, and the like. For example, an electronic conductive material such as carbon black, an ionic polymer, a surfactant, and the like. The ion-introducing material is added and used.

  It is preferable that the static eliminator 18 has a length of 5 mm or more in the traveling direction of the transfer belt 10 and a distance from the transfer belt 10 is 3 mm or less. There may be a plurality of wires 21 or a wire-like band electrode. Further, by adjusting the voltage applied to the grid electrode 22, it is possible to suppress the neutralizing effect of the toner T.

  Further, by providing the static eliminator 18 within a distance of 100 mm from the charger 6, the ozone generated inside the static eliminator 18 and the charger 6 can be discharged to the outside without reducing the efficiency of the exhaust fan 12. Can do.

  Since the transfer belt 10 is semiconductive, in order to remove the toner T efficiently, it is necessary to shorten the distance that the electricity removal current flows in the transfer belt 10 as much as possible. For this reason, it is preferable that the counter electrode 19 covers the entire range where the toner T is discharged so that the discharging current flows only in the thickness direction of the transfer belt 10. The counter electrode 19 may be fixed, or may be biased toward the transfer belt 10 by a spring or the like.

  As shown in FIG. 2, when a hard member such as metal is used for the counter electrode 19, the entire surface of the counter electrode 19 is uniformly in contact with the back surface of the transfer belt 10 depending on the unevenness of the back surface of the transfer belt 10 and the conveyance state of the transfer belt 10. It is difficult to let Therefore, as shown in FIG. 3, if the counter electrode made of the conductive brush 23 is used instead of the counter electrode 19 made of a metal flat plate, the back surface of the transfer belt 10 is always applied regardless of the state of the transfer belt 10. It is possible to make a uniform contact with the ground line and reliably ground the charge removed from the toner T.

  FIG. 4 shows the configuration of the main part of the image forming apparatus according to the second embodiment of the present invention. The same components as those in the first embodiment are denoted by the same reference numerals and description thereof is omitted. In the image forming apparatus of the present embodiment, a static eliminator 18 is provided on the upstream side of the photoreceptor 5 of the most downstream developing unit 4. The toner T transferred by the upstream developing unit is charged to the opposite polarity to the original polarity every time it passes through the downstream developing unit. However, the toner T that forms a thin image is easily discharged, so It tends to be excessive. If the charge is excessive, secondary transfer cannot be performed well, and the reproducibility of a thin image may deteriorate. However, since the black toner image formed by the developing unit 4 is further transferred onto the toner neutralized by the static eliminator 18 by the corresponding primary transfer roller 11, the yellow, magenta, The cyan toner T and the black toner T transferred from the photoreceptor 5 are charged by the last primary transfer roller 11. For this reason, the toner T that has been over-charged is slightly charged again and an appropriate charge amount is obtained, so that it is appropriately transferred to the recording material by the secondary transfer roller 16.

  Further, as in the third embodiment of the present invention shown in FIG. 5, the static eliminator 18 is provided on the downstream side of the photoconductor 5 of the developing unit 3 that forms the second (forms a cyan toner image) from the downstream side. It may be. In this case, the static eliminator 18 may be connected to the exhaust fan 12 that exhausts the air of the charger 6 of the developing unit 3. Naturally, the counter electrode 19 also needs to be provided at a position facing the static eliminator 18.

(Comparative experiment)
Next, FIG. 6 shows the results of a comparative experiment that verified the effects of the present invention. This comparative experiment was carried out at an environmental temperature of 10 ° C. and a relative humidity of 15%. The static eliminator is arranged “after” the most downstream photoconductor 5 as shown in FIG. 1 or the most downstream as shown in FIG. Is provided in front of the photosensitive member 5. The solid transfer efficiency is the ratio of the amount of toner transferred to the recording material to the amount of toner transferred onto the transfer belt 10, and the voltage of the secondary transfer roll 16 was measured at 1700V. As a guideline, the solid transfer efficiency only needs to exceed 90%, and less than 80% is not suitable. Also, halftone dot transferability means that a 15-tone image with a different toner adhesion amount is formed and a thin image with the smallest toner adhesion amount is reproduced as “「 ”, and images other than the thinnest image are reproduced. This is the result of evaluating all the reproduced images as “◯” and the others as “×”, and the evaluation becomes worse when a thin image is not transferred due to too much charge removal of the toner T.

  Comparative Example 1 described below the table is a configuration of an image forming apparatus without the charge eliminator 18, and since the charge removal of the toner T is not sufficient, the solid transfer efficiency is only 72%, which is insufficient. I understand. Comparative Example 2 is a configuration of a conventional image forming apparatus that includes the static eliminator 18 but is not provided with the counter electrode 19. In Comparative Example 2, the effect of the static eliminator 18 is not sufficiently exhibited, and the neutralization of the toner T is not sufficient. Therefore, the solid transfer efficiency is only 72%, and no improvement is seen in comparison with Comparative Example 1. However, in each of Experimental Examples 1 to 6 in which the counter electrode 19 (or the conductive brush 23 or the conductive sponge roller) is arranged, the solid transfer efficiency is improved. In particular, when the length of the counter electrode 19 in the conveyance direction of the transfer belt 10 is 10 mm or more, the solid transfer efficiency is 90% or more, and a preferable result is obtained.

  In view of the halftone dot transferability, when the static eliminator 18 and the counter electrode 19 are arranged “behind (downstream side)” of the most downstream photoreceptor 5, the thinnest image cannot be reproduced, and excessive static elimination is performed. It turns out that it is. On the other hand, when the static eliminator 18 and the counter electrode 19 are arranged “front (upstream side)” of the most downstream photoreceptor 5 as shown in FIG. 4, the thinnest image can be properly reproduced. .

  As described above, the toner T on the transfer belt 10 can be reliably discharged by the counter electrode 19, and if the charge eliminator 18 and the counter electrode 19 are arranged in front of the most downstream photoconductor 5, the problem of excessive charge removal is eliminated. High-quality preferable secondary transfer is possible.

1 is a configuration diagram showing a main part of an image forming apparatus according to a first embodiment of the present invention. FIG. 2 is a configuration diagram illustrating in detail a static eliminator and a counter electrode of the image forming apparatus in FIG. 1. The block diagram which shows the counter electrode and static eliminator of the alternative of FIG. 2 in detail. FIG. 6 is a configuration diagram illustrating a main part of an image forming apparatus according to a second embodiment of the present invention. FIG. 10 is a configuration diagram illustrating a main part of an image forming apparatus according to a third embodiment of the present invention. 6 is a table showing experimental results of the image forming apparatus of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Developing unit 2 Developing unit 3 Developing unit 4 Developing unit 5 Photoconductor (image carrier)
6 Charging Device 10 Transfer Belt 11 Primary Transfer Roller 12 Exhaust Fan 16 Secondary Transfer Roller 18 Charger 19 Counter Electrode 23 Conductive Brush (Counter Electrode)

Claims (7)

A transfer belt on which a toner image is primarily transferred onto a surface, and the transferred toner image is secondarily transferred to a recording material;
A plurality of image carriers arranged in series to sequentially transfer toner images formed on the surface to the transfer belt;
A static eliminator that opposes the transfer belt and neutralizes the toner image on the transfer belt;
An image forming apparatus comprising: a counter electrode facing the charge eliminator across the transfer belt and contacting the back surface of the transfer belt.   The image forming apparatus according to claim 1, wherein the counter electrode is a grounded conductive flat plate.   The image forming apparatus according to claim 1, wherein the counter electrode is a grounded conductive brush.   The image forming apparatus according to claim 1, wherein the static eliminator is disposed between the image carriers.   The image forming apparatus according to claim 4, wherein the static eliminator is disposed on the upstream side of the image carrier that is most downstream in the moving direction of the transfer belt. The image carrier comprises a developing unit integrated with at least a charger for charging the image carrier and a developer for supplying toner to the image carrier,
The image forming apparatus according to claim 1, wherein the static eliminator is incorporated in any one of the developing units.   The image forming apparatus according to claim 1, wherein the static eliminator is connected to an exhaust fan of a charger that charges any one of the image carriers.

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