KR100305164B1 - Image forming apparatus with intermediate transfer member - Google Patents

Abstract

The image forming apparatus uses an intermediate transfer member. A plurality of toner images, for example different colors, can be superimposed on the intermediate transfer member and then transferred to paper. A discharge mechanism is mounted to discharge the electric charge applied to the intermediate transfer subsidiary. Furthermore, the value of the voltage provided to this discharge mechanism and / or the voltage provided for the transfer bias is proportional to the actual surface potential on the intermediate transfer member, which is formed on the intermediate transfer member before the toner image is transferred to the paper. It is proportional to the number of losses. For example, when a full color toner image is formed on the intermediate transfer member, it is caused by four operations for transferring each toner image onto the intermediate transfer member, and the voltage provided by the discharger and / or the transfer bias mechanism. Is higher than that when an image of only a single color is formed on the intermediate transfer member. Furthermore, the image forming apparatus is operable to form an image on thick paper, in which case the driving speed of the mechanisms provided in the image forming apparatus is reduced, and the voltage applied to the example-charger is also appropriately reduced. The image forming apparatus also includes a cleaning mechanism for the intermediate transfer belt, and both of the intermediate transfer member discharge mechanism and the cleaning mechanism are combined in one brush roller.

Description

Image forming apparatus with intermediate transfer member {IMAGE FORMING APPARATUS WITH INTERMEDIATE TRANSFER MEMBER}

The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, and the like, and more particularly, to an image forming apparatus in which an intermediate transfer member is used.

A conventional image forming apparatus includes the following elements: an intermediate transfer member for carrying a toner image transferred from an image bearing member, and an intermediate transfer member for transferring the toner image from the image bearing member. A first transfer charger for applying charge to the intermediate transfer member for transfer to the second transfer member, a second transfer charger for applying charge to the final transfer member, i.e., paper, for transferring a toner image from the intermediate transfer member to the final transfer member, And an intermediate transfer member discharge mechanism for removing electric charges from the surface of the intermediate transfer member that transferred the toner image to the final transfer member. In such an image forming apparatus, the surface potential of the intermediate transfer member is made uniform by removing electric charges from the surface of the intermediate transfer member with the intermediate transfer member discharge mechanism, which is the next one performed from the image bearing member to the intermediate transfer member. Be prepared for vehicle transcription.

However, in the case of the conventional image forming apparatus described above, after the electric charge is removed from the intermediate transfer member as the intermediate transfer member discharge mechanism, the surface potential of the intermediate transfer member is not at a predetermined potential required or an irregular potential remains. . This discharge defect condition worsens a continuous series of transfer processes from the image bearing member to the intermediate transfer member.

As a result of the investigation of the cause of the discharge defect on the intermediate transfer member made by the inventor of the present invention, the main cause of the discharge defect is that the charge of the intermediate transfer member that is not effectively removed by the intermediate transfer member discharge mechanism causes the surface potential to be significantly uneven. It was understood that.

In particular, this nonuniformity is such that the image forming apparatus is configured to be subjected to several times to superimpose toner images of various colors on which the primary transfer operation is formed on the image bearing member, onto the intermediate transfer member, and toner superposed on the intermediate transfer member. Appears in the case of a color image forming apparatus in which an image is transferred to the final transfer member at one time. In this case, the surface potential of the intermediate transfer member whose charge is not removed by the intermediate transfer member discharge mechanism becomes nonuniform. In addition, the degree of nonuniformity depends on the number of toner images superimposed on the intermediate transfer member, that is, the number of times the primary transfer to the intermediate transfer member is performed.

Further, in such a conventional image forming apparatus, a transfer condition for the transfer rate to the final transfer member whose transfer condition for transferring the toner image on the intermediate transfer member to the final transfer member is usually set to a predetermined value or more. It is set at approximately the center of the area. The difference between the set value of the transfer condition and the upper limit value or the lower limit value of the desired transfer area corresponds to the transfer margin for transferring the toner image of the intermediate transfer member to the final transfer member. As this difference increases, the transfer margin becomes larger.

When the toner image passed through the primary transfer portion, i.e., the toner image transferred from the image bearing member to the intermediate transfer member, differs in the amount of toner adhered thereon, non-uniform amount of charge appears in the toner image on the intermediate transfer member. For example, if the toner image on the intermediate transfer member includes a portion having no contrast and a portion of the contrast, the charge amount of the portion having no contrast is less than that of the intermediate contrast. Further, for example, in the case where a color image forming apparatus is used, the charging amount of a portion where a plurality of colors of toners overlap on a toner image on the intermediate transfer member is a portion where only a single color of toner is attached to the intermediate transfer member. It becomes smaller than

In addition, the nonuniform charge amount in the toner image sometimes causes the toner image to pass through the primary transfer portion for transferring the toner image from the image bearing member to the intermediate transfer member in the primary transfer portion relative to the surface moving direction of the intermediate transfer member. It is due to the peeling discharge appearing in the adjacent downstream side.

When there is a nonuniform charge amount in the toner image on the intermediate transfer member in this way, the toner image includes portions having different transfer characteristics. If all of the portions having different transfer characteristics are transferred to the transfer member under the same transfer conditions, the range of transfer conditions for transferring the entire toner image at a transfer rate of a predetermined value or more is narrowed. As a result, the transfer margin for the entire toner image is lowered, and thus the toner image cannot be stably transferred to the final transfer member.

Referring to Fig. 9, it is a transfer characteristic graph showing curves a and b showing the relationship between the transfer current and the transfer rate for the portion with no contrast and the intermediate contrast portion, respectively. The widths shown by A and B in Fig. 9 correspond to a range of transfer currents capable of transferring each part to the final transfer material at a transfer rate of 80% or more, and the transfer margin increases proportionally. However, due to the deviation of the two curves A and B from each other, the range of the transfer current that allows these two portions to be transferred together at a transfer rate of 80% or more is narrow as indicated by the symbol C in FIG. That is, the overlapping portions of curves A and B, which are areas where both the light and dark and dark and light contrast portions are effectively transferred, are narrow, thus reducing the transfer margin.

As another drawback, the conventional image forming apparatus includes an intermediate transfer member discharge mechanism such as a corona discharger for removing electric charges on the surface of the intermediate transfer member, and a cleaning mechanism such as a cleaning blade for removing deposits on the intermediate transfer member surface. It is necessary to arrange them individually, and therefore, it is difficult to reduce the unit cost of the conventional mechanism.

Therefore, one of the objects of the present invention is to use an intermediate transfer member, which can ensure that image transfer to and from the image transfer to the intermediate transfer member can be appropriately achieved, and can achieve a structure in which high efficiency and low cost are achieved. The present invention provides a new image forming apparatus.

A more special object of the present invention is to provide a new image forming apparatus capable of uniformly removing the charge on the intermediate transfer member after the toner image is transferred to the transfer member in preparation for the next image transfer operation made from the image bearing member. have.

Another more particular object of the present invention is to suppress the reduction of the transfer margin for transferring the toner image to the transfer member, so that even when there is an uneven charge amount on the toner image on the intermediate transfer member after being transferred from the image bearing member, A novel image forming apparatus capable of stably transferring a toner image to a transfer member is provided.

Another more specific object of the present invention is to provide a new image forming apparatus that can realize a low cost by including a new conductive brush that works together as an intermediate transfer member discharge mechanism and an intermediate transfer member cleaning mechanism.

1 is a schematic configuration diagram showing a color copying machine according to an embodiment of the present invention.

2 is a cross-sectional view showing an intermediate transfer belt used in the color copying machine of FIG.

FIG. 3 is an enlarged view of the primary transfer part of the color copying machine of FIG.

4 is a control block diagram of a belt discharger equipped with the color copying machine of FIG.

5 (a), 5 (b) and 5 (c) are timing charts showing the surface potential change with respect to the intermediate transfer belt of FIG. 1, the ON / OFF timing of the belt discharger and the output of the primary transfer bias mechanism.

6 (a) and 6 (b) are timing charts showing the correlation between the rotational speed of the drive motor provided in one embodiment of the present invention and the grid voltage applied to the charging unit.

7 is a schematic diagram showing a color copying machine according to another embodiment of the present invention.

8 shows a combination of a discharge mechanism and a cleaner according to another embodiment of the present invention.

9 shows the relationship between the transfer rate and the transfer current in the image forming mechanism.

Explanation of symbols on the main parts of the drawings

100 ... photoconductive drum

500 ... Intermediate Transfer Unit

501 ... intermediate transfer belt

502 ... pre-charger (PTC)

507 ... 1st Transfer Bias Roller

508 ... Belt Drive Rollers

509 ... Belt Tension Roller

510 ... 2nd Warrior Counter Rollers

511 ... cleaning rollers

512 ... belt discharge roller

513 ... belt discharge brush

514 ... Brush Roller

601 ... 2nd transfer belt

602 ~ 604 ... Support Roller

605 ... 2nd Transfer Bias Roller

801 ... Primary transcription power supply

802 ... secondary transfer power

803 ... PTC power supply

804 ... Discharge power supply

900 ... control unit

905 ... Mark sensor

A preferred embodiment of the present invention is described for the case where the present invention is applied to an electrophotographic color copying machine (hereinafter referred to as a color copying machine) as an image forming apparatus. Of course, the present invention can be applied to other image forming apparatuses.

1 is a schematic configuration diagram of an image forming portion which is a main portion of a color copying machine according to an embodiment of the present invention. The color copying apparatus also includes a color image reading unit (hereinafter referred to as a color scanner), a paper feeding unit, and a control unit.

The color scanner reads the color image information of the original into color separation light of red, green, and blue (hereinafter referred to as R, G, and B, respectively), and converts the color image information into an electric image signal. Then, based on the intensity levels of the color separation image signals for R, G and B obtained by the color scanner, a color conversion processing operation is performed in the image processing unit (not shown), and black, cyan, magenta and yellow are performed. Color image data of (hereinafter referred to as Bk, C, M and Y, respectively) is obtained.

The image forming section of Fig. 1 is a photoconductive drum 100 acting as an image bearing member, a charger 200, a photoconductive element sweeper 300 composed of a sweeping belt and a hairbrush, as an exposing mechanism. It includes a fixing unit consisting of a working (not shown) optical writing unit, a revolver type developing unit 400, an intermediate transfer unit 500, a paper transfer unit 600, and a fixing roller pair 701. do.

The photoconductive drum 100 rotates counterclockwise as indicated by the arrow. Located around the photoconductive drum 100, a developing mechanism selected from those provided in the charger 200, the photoconductive element cleaning device 300, the magazine rotating developing unit 400, and the intermediate transfer unit 500 ) Is an intermediate transfer belt 501.

The optical writing unit converts the color image data obtained from the color scanner into an optical signal and optically converts the data corresponding to the original image onto the surface of the photoconductive drum 100 uniformly charged by the charger 200. By writing, an electrostatic latent image is formed in the photoconductive drum 100. The optical writing unit may include, for example, a semiconductor laser (laser diode) as a light source, a laser light emission driving control unit, a polygon mirror and its rotating motor, an f / θ lens, and a reflecting mirror.

The magazine rotation developing unit 400 is a Bk developing sphere 401 stored Bk toner, C developing sphere 402 stored C toner, M developing sphere 403 stored M toner, Y developing sphere stored Y toner ( 404, and a developing revolver driver for rotating the whole unit 400 counterclockwise. Each developer mechanism provided in the magazine rotation developing unit 400 is a developer carrier in which each developer is rotated by contacting the surface of the photoconductive drum 100 so as to develop an electrostatic latent image formed on the photoconductive drum 100. A developer sleeve as a carrier, a developer paddle rotating to stir each developer, and a developer roller driver for rotating the developer roller clockwise.

In this embodiment, the toner in each developing mechanism 401-404 is negatively charged by stirring with a ferrite carrier. Further, a developing bias voltage obtained by superimposing an AC voltage (AC component) Vac with a negative DC voltage (DC component) Vdc is applied to each developing sleeve by a developing bias power supply (not shown). The developing sleeve is biased at a predetermined predetermined potential relative to the metallic substrate layer of the photoconductive drum 100.

In the standby state of the color copying machine, the magazine rotating developing unit 400 is stopped at the home position in which the Bk developing sphere 401 is located at the developing position. When the copy operation starts, the color scanner starts reading the Bk color image data at a predetermined timing, and then the light writing by the laser light and the formation of the electrostatic latent image are started based on this color image data (hereinafter Bk image). An electrostatic latent image based on the data is called a Bk electrostatic latent image; the same applies to the C, M and Y electrostatic latent images. Before the tip portion of the electrostatic latent image reaches the Bk developing position, the Bk toner starts to rotate to form a Bk electrostatic latent image, and the Bk electrostatic latent image is developed from the tip portion. The magazine rotary developing mechanism 400 rotates until the rear end portion of the Bk electrostatic latent image passes rapidly through the Bk developing position until the developing mechanism of the next color reaches the developing position of the Bk electrostatic latent image region. This operation is completed before the tip of the electrostatic latent image based on at least the following image data reaches the developing position.

The intermediate transfer unit 500 composed of the intermediate transfer belt 501 is positioned to be movable around a plurality of rollers. The following components are arranged around the intermediate transfer belt 501: a pre transfer electrification 502 (hereinafter referred to as PTC 502) and a paper transfer unit 600 to transport the transfer member. The second transfer belt 601, the second transfer bias roller 605 for applying the second transfer charge, the belt discharger 503 for discharging the charge on the intermediate transfer belt 501, the intermediate transfer belt 501 The belt cleaning blade 504 for cleaning, and the lubricant application brush 505 for applying the lubricant to the intermediate transfer belt 501, and the like. As shown in Fig. 7 and described in detail below, a brush roller 514 is disposed around the intermediate transfer belt 500, so that the intermediate transfer belt 501 discharge mechanism and the intermediate transfer member cleaning mechanism. Act as.

The intermediate transfer belt 501, the primary transfer bias roller 507, the belt driving roller 508, the belt tension roller 509, the secondary transfer counter roller 510 for operating the primary transfer charging counter It is positioned to be movable around the roller 511 and the belt discharge roller 512 that acts as the primary transfer discharge discharge mechanism. Each roller is made of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded. The transfer bias is applied to the primary transfer bias roller 507, and in a control state by the primary transfer power supply 801 controlled at a constant current or a constant voltage, a predetermined current predetermined according to the number of superimposed toner images or Adjust the voltage The intermediate transfer belt 501 is driven in the direction of the arrow by a belt drive roller 508 that is rotationally driven by a drive motor (not shown).

As shown in cross section in FIG. 2, the intermediate transfer belt 501 may be formed of a belt-shaped member having a surface layer 501a, an intermediate layer 501b, and a base layer 501c. The surface layer 501a is located on the outer circumferential surface side in contact with the photoconductive drum 100, and the base layer 501c is located on the inner circumferential surface. In addition, between the intermediate layer 501b and the base layer 501c, an adhesive layer 501d is provided for adhering these layers.

In the transfer section (hereinafter referred to as the primary transfer section) for transferring the toner image from the photoconductive drum 100 to the intermediate transfer belt 501, the intermediate transfer belt 501 is formed with the primary transfer bias roller 507. The belt discharge roller 512 is pressed toward the photoconductive drum 100 to form a nip portion having a predetermined width between the photoconductive drum 100 and the intermediate transfer belt 501. In addition, a grounded belt discharge brush 513 serving as the primary transfer part discharge mechanism contacts the inner circumferential surface of the intermediate transfer belt 501 at this nip.

Further, as shown in Fig. 3, the contact position between the belt discharge brush 513 and the intermediate transfer belt 501 from the downstream end of the nip width Wn in the primary transfer portion and the belt moving direction in the nip portion. The distance L to may be set to obtain the required transfer conditions.

Referring back to FIG. 1, the PTC 502 applies pre-charges to the photoconductive drum 100 to transfer the toner image transferred from the photoconductive drum 100 of the primary transfer portion before the toner image is transferred to the transfer paper. The intermediate transfer belt 501 is uniformly charged.

The belt discharger 503 applies either an AC voltage or an AC + DC voltage to the intermediate transfer belt 501. In addition, the belt cleaning blade 504 contacts the intermediate transfer belt 501 at a position where the intermediate transfer belt 501 is positioned to be movable around the cleaning counter roller 511. Also, by using a spacing / contacting mechanism (not shown), the belt cleaning blade 504 is in contact with the intermediate transfer belt 501 and is separated from the intermediate transfer belt 501. It becomes possible to switch between.

The belt discharger 503 and the belt cleaning blade 504 are ON / OFF controlled as described later. If one full-color image is formed on one sheet of paper, the belt discharger 503 is turned on after the secondary transfer is finished, and at least the intermediate transfer belt 501 completes one revolution. It remains in the ON state until the belt cleaning blade 504 is in contact with the intermediate transfer belt 501 for one rotation period. If the full color image is repeatedly formed, the belt discharger 503 is turned on after the secondary transfer is completed and remains ON until the leading edge of the next toner image reaches the discharge position and the sweep position, respectively. Thus, the belt cleaning blade 504 is in contact with the intermediate transfer belt 501 during this period. Furthermore, if a monochromatic color image is formed on the paper, the belt discharger 503 is turned on after the first transfer is completed and remains in the ON state until at least the intermediate transfer belt 501 completes one revolution. The sweep blade 504 is in contact with the intermediate transfer belt 501 during this one rotation period. If the monochromatic color image is repeatedly formed, the belt discharger 503 is turned on after the first transfer is completed and is in the ON state until the leading edge of the next toner image reaches the discharge position and the sweep position, respectively. The belt cleaning blade 504 remains in contact with the intermediate transfer belt 501 during this period.

The lubricant coating brush 505 is used to apply the fine particles to the intermediate transfer belt 501, for example, by grinding zinc stearate 506 as a plate-shaped lubricant. The lubricant coating brush 505 is also configured to be foldable with respect to the intermediate transfer belt 501, and the lubricant applying brush 505 can be controlled to contact the intermediate transfer belt 501 at a desired predetermined timing. .

The paper transfer unit 600 includes a secondary transfer belt 601 positioned to be movable around three support rollers 602, 603, 604. The engaging portion of the secondary transfer belt 601 between the support rollers 602 and 603 contacts the intermediate transfer belt 501 in the secondary transfer counter roller 510. One of the three support rollers 602, 603, 604 is a drive roller rotated by a drive mechanism (not shown), and the secondary transfer belt 601 is driven by this drive roller.

The secondary transfer bias roller 605 is, in advance, between the secondary transfer bias roller 605 and the secondary transfer counter roller 501 by a secondary transfer power source 802 controlled to be at a constant current. By applying the transfer bias of the predetermined current, it is arranged to attract the intermediate transfer belt 501, the transfer paper and the secondary transfer belt 601. In addition, the support roller 602 and the secondary transfer bias roller 605 may be positioned so that the secondary transfer belt 601 and the secondary transfer bias roller 605 may be in contact with or separated from the intermediate transfer belt 501. A fold mechanism (not shown) is provided to drive. The secondary transfer belt 601 at the disengagement position is shown by the dashed-dotted line in FIG.

At the position where the secondary transfer belt 601 is moved around the support roller 603 on the fixing roller 701 side, the transfer fat electric machine 606 and the belt discharger 607 are provided to face each other. Further, the cleaning blade 608 is provided to clean the secondary transfer belt 601.

The transfer fat electric field 606 may be separated from the secondary transfer belt 601 by removing the charge remaining in the transfer paper by the stiffness of the transfer paper itself. The belt discharger 607 is generated by the secondary transfer bias roller 605 and removes the electric charge remaining on the secondary transfer belt 601. The cleaning blade 608 is to be cleaned by removing the deposit attached to the surface of the secondary transfer belt 601.

In the color copying machine of the above configuration, when the image forming cycle is started, the photoconductive drum 100 is rotated counterclockwise as indicated by an arrow by a driving motor (not shown), and the intermediate transfer belt 501 is a driving roller. Rotate clockwise as indicated by the arrow. Bk, C, M and Y toner images are formed on the photoconductive drum 100 with the rotation of the intermediate transfer belt 501, and the formed toner images are formed to form a full color toner image on the intermediate transfer belt 501. This is superimposed on the intermediate transfer belt 501 in the order of Bk, C, M and Y.

The Bk toner image is formed as follows. The charger 200 is used to uniformly charge the photoconductive drum 100 with negative charge by corona discharge. Subsequently, an optical writing unit is used to perform raster exposure based on the Bk color image signal. When the raster image is exposed, charges proportional to the amount of light exposed are removed, and thus a Bk electrostatic latent image is formed in the exposed portion of the photoconductive drum 100. Then, the contact between the Bk toner charged negatively on the Bk developing roller and the Bk electrostatic latent image prevents the toner from sticking to the portion of the photoconductive drum 100 where the charge remains, that is, the portion without charge, i.e. The toner adheres to the portion exposed by the Leicester light exposure, thereby forming a Bk toner image similar to the electrostatic latent image. The Bk toner image formed on the photoconductive drum 100 is transferred to the surface of the intermediate transfer belt 501 which is in contact with the photoconductive drum 100 and driven at the same speed.

Residual toner that is not transferred from the photoconductive drum 100 is cleaned by the photoconductive element sweeper 300 in preparation for the next image forming operation on the photoconductive drum 100.

After the Bk image forming process, the C image forming process in which the C image data is read by the color scanner at a predetermined timing is performed, and the C electrostatic latent image is formed by a laser light writing operation based on the C image data. Before the rear end of the Bk electrostatic latent image passes through the developing position and the tip of the C electrostatic latent image reaches the developing position, the magazine rotating developing unit 400 is rotated so that the C developing mechanism 402 is set at the developing position, and the C electrostatic latent image This C toner is developed. Thereafter, the phenomenon of the C electrostatic latent image region continues, and when the tip portion of the C electrostatic latent image passes the developing position, the magazine rotation developing unit 400 is rotated again, and the M developing sphere M is continuously moved to the developing position. do. This rotation operation is also completed before the leading end of the continuous M electrostatic latent image reaches the developing position.

For the M and Y image forming processes, the read operation of the color image data, the formation of the electrostatic latent image, and the development are the same as in the processes of Bk and C above. Therefore, further description is omitted.

In this way, toner images of Bk, C, M, and Y sequentially formed on the photosensitive drum 100 are sequentially transferred to the intermediate transfer belt 501. By this operation, a toner image of up to four colors is formed on the intermediate transfer belt 501. The toner image superimposed on the intermediate transfer belt 501 is uniformly charged by the PTC 502 and transferred to the transfer paper in the next secondary transfer process.

When the image forming operation is started, the transfer sheet is fed from a paper feeder such as a paper cassette (not shown) or a manual tray, and placed in a standby state at a nip between a pair of registration rollers (not shown). Then, when the tip of the toner image on the intermediate transfer belt 501 reaches the secondary transfer portion where the nip is formed by the secondary transfer counter roller 510 and the secondary transfer bias roller 605, the tip of the transfer paper is the intermediate transfer. A registration roller pair, not shown, is driven to coincide with the leading end of the toner image formed on the belt 501, and registration is performed between the transfer paper and this toner image. Then, the transfer paper overlaps the toner image on the intermediate transfer belt 501 and passes through the secondary transfer portion. At this time, the toner images for the four colors on the intermediate transfer belt 501 are transferred to the transfer paper by the transfer bias applied from the secondary transfer bias roller 605.

When the transfer paper passes through the opposing portion with the transfer fat electric machine 606 disposed downstream of the secondary transfer portion in the moving direction of the secondary transfer belt 601, the charge on the transfer paper is removed, and the transfer paper is transferred to the secondary transfer belt 601. It is peeled off) and conveyed toward the fixing roller pair 701. Further, the toner image is welded and fixed at the nip between the fixing roller pair 701, and is sent out of the main body of the apparatus by the discharge roller pair (not shown), and the surface is stacked on the copy tray (not shown). , Get full color copy.

Further, the toner remaining on the surface of the intermediate transfer belt 501 after the toner image is transferred to the transfer paper is transferred by the belt cleaning blade 504 that contacts the intermediate transfer belt 501 by a (not shown) folding mechanism. It is cleaned.

If the copying operation is repeated, in order to operate the color scanner and to form the image on the photoconductive drum 100, the operation is continued for two minutes at a predetermined timing in succession to the image forming process for four colors (Y) per sheet. The image forming process for one color Bk is performed. The Bk toner image for two sheets is applied to the intermediate transfer belt 501 in the area cleaned by the belt cleaning blade 504, following the transfer process of the toner image for four colors per sheet with respect to the intermediate transfer belt 501. This is transferred. And the same operation | movement as one sheet is performed with respect to a next sheet.

The copy mode operation to obtain four-column full color copies has been described. In the copy mode for three or two colors, the same operation is performed in accordance with the number of times for the specified color. In the single color copy mode, only the predetermined color developing mechanism in the magazine rotation developing unit 400 is placed in the developing active state until the copying operation is completed for a predetermined number of sheets of paper, and the belt cleaning blade 504 ) Contacts the intermediate transfer belt 501 while the copying operation is performed continuously.

Next, control of the belt discharger 503 for removing the charge on the intermediate transfer belt 501 after the secondary transfer will be described.

4 is a block diagram of a discharge control system including a control unit 900 for controlling the discharge of the intermediate transfer belt 501 by the discharger 503. In FIG. 4, the control unit 900 is composed of a CPU 901, a ROM 902, a RAM 903, and an I / O interface 904. In the I / O interface 904, the discharge power 804, the drive motor 508a connected to the belt drive roller 508 of the intermediate transfer belt 501, and for detecting the rotational position of the intermediate transfer belt 501 ( A mark sensor 905 mounted on the inner circumferential surface of the intermediate transfer belt 501 is connected to detect a mark (not shown).

The discharge power source 804 applies voltages having DC and AC components to the belt discharger 503. The discharge condition of the belt discharger 503 can be switched by changing by only one of the DC and AC components of the applied voltage; In the present embodiment, the device has a configuration that is switched by the control unit 900 in terms of achieving easy control of the size of the DC component.

The ON / OFF timing of the discharge power source 804 for applying a voltage to the belt discharger 503 is a mark sensor 905 for detecting a mark (not shown) for detecting the rotational position of the intermediate transfer belt 501. Is set based on an output signal of

One of the features of the present invention is that the intermediate transfer belt 501 has a high resistance. Intermediate transfer belts with relatively low resistance may have particular problems in forming magenta and cyan images, which are images in which magenta toner is superimposed on cyan as the magenta toner does not move and remain in the cyan toner image. Because it is not maintained. Increasing the resistance of the intermediate transfer belt 501 can correct this problem. However, if the resistance of the intermediate transfer belt 501 is increased, the intermediate transfer belt 501 will be able to retain all the charges at their surface potentials during the process of forming the multicolor image; The surface potential on the intermediate transfer belt 501 increases for each overlap of the color image and is maintained with a cumulative effect.

More specifically, Figs. 5 (a) and 5 (b) show the intermediate transfer belt (when the full color copying operation of superimposing four color toner images on the intermediate transfer belt 501 is performed twice in succession. A timing chart showing an example of the surface potential change of 501 and the ON / OFF timing of the belt discharger 503. Fig. 5A shows the surface potential Vs of the intermediate transfer belt 501 measured by the potential sensor at a position opposite to the PTC 502 of Fig. 1; The sizes indicated by the symbols ①, ②, ③ and ④ indicate the surface potential of the portion where the primary transfer has been performed for each of the first, second, third and fourth colors. As shown in Fig. 5 (a), each time primary transfer is executed, positive charges are first generated on the back side of the intermediate transfer belt 501 by the primary transfer bias roller 507, and the intermediate transfer belt 501 The photoconductive drum side surface potential of is tended to be negative.

In particular, in the case where the intermediate transfer belt 501 having a relatively high resistance is used in this embodiment, the electric charge once applied is likely to be held on the intermediate transfer belt 501, which is a continuous color image formation as described above. This results in a significant increase in surface potential on the intermediate transfer belt 501. Therefore, the surface potential of the intermediate transfer belt 501 increases to the negative side each time the primary transfer is performed, and depends on the number of times the primary transfer is performed, that is, the number of times the toner image is superimposed on the intermediate transfer belt 501. The surface potential of the intermediate transfer belt 501 becomes nonuniform.

Therefore, in the present embodiment, the control unit 900 is used to switch the discharge condition of the belt discharger 503 in proportion to the surface potential of the intermediate transfer belt 501, the charge can be uniformly removed. In particular, the discharge power source 803 is controlled to switch the DC component size of the output voltage in accordance with the surface potential as shown in Fig. 5 (a) according to the number of times of toner image superimposition on the intermediate transfer belt 501. . If the toner images overlap a considerable number of times, the charge is progressively eliminated by increasing the DC component output magnitude from the discharge power source 803. If the toner image overlaps a small number of times, the charge is removed with lower performance by relatively reducing the size of the DC component in the above state so that the intermediate transfer belt 501 is not negatively charged.

According to a feature of the invention, if a single color image is formed on the intermediate transfer belt 501, the belt discharger 503 discharges the power source 803 so as to correspond to a value as shown by? In Fig. 5 (a). Will receive the discharge voltage. If a full color image is formed on the intermediate transfer belt 501 by superimposing four toner images, the belt discharger 503 discharges a discharge voltage equal to the value shown by? In Fig. 5A. Will be received from the power source 803. In this way, the discharge voltage provided to the belt discharger 503 will be proportional to the substantial surface potential appearing on the intermediate transfer belt 501. In the present invention, this method of determining the substantial surface potential appearing on the intermediate transfer belt 501 relates the voltage provided to the belt discharger 503 to the number of respective toner images superimposed on the intermediate transfer belt 501.

As described above, when the high resistance intermediate transfer belt 501 is used, the intermediate transfer belt 501 has a tendency to retain charge. As a result, it is difficult to transfer different color images from the photoconductive drum 100 to the intermediate transfer belt 501. As a result, another feature of the present invention is to increase the voltage applied from the primary transfer bias roller 507 in accordance with the number of toner images charged from the photoconductive drum 100 to the intermediate transfer belt 501.

More specifically, as shown in Fig. 5C, as another feature of the present invention, the voltage Vout from the primary transfer bias roller 507 is controlled to increase with each successive image transfer operation. do. As a special example of this operation of the present invention, the transfer bias output by the primary transfer bias roller in the control state by the primary transfer power source 801 is such that the first image, for example, the BK image, is intermediate from the photoconductive drum 100. After being charged to the transfer belt 501 may be 1,000V. Next, when the next image in the color image formation, for example, C image, is transferred from the photoconductive drum 100 to the intermediate transfer belt 501, the transfer bias output from the primary transfer bias roller 507 is 1,500V. Can be increased. Next, the transfer bias output from the primary transfer bias roller 507 can be increased to 2,000V and 2500V, respectively, for successive M and Y images. In this manner, in the operation of the present invention, the transfer bias from the primary transfer bias roller 507 during the first image formation corresponds to the number of toner images transferred from the photoconductive drum 100 to the intermediate transfer belt 501. Can increase.

Another problem that will appear in the mechanism of Fig. 1 is that when thick paper is used as the image transfer paper, the thick paper requires a longer fixing time. However, if longer fixing time is required for such thick paper, the output of the PTC 502 must also be reduced to avoid excessive charging on the intermediate transfer belt 501.

In this way, according to another aspect of the present invention, if a carton board or other thick paper, i.e., a postcard, is used as the transfer paper, the thick paper mode is executed to drive the drive motor of the belt drive roller 508. By controlling 508a, the moving speed of the intermediate transfer belt 501 is changed to about half of that of the plain paper. In this mode, if the moving speed of the intermediate transfer belt 501 is lowered, the charge is more easily removed by the belt discharger 503. Therefore, in this embodiment, if the moving speed of the intermediate transfer belt 501 is lowered in the thick paper mode, the intermediate transfer belt 501 is reduced in charge discharging ability in the discharge operation so that the intermediate transfer belt 501 is not charged with reverse polarity. The DC component size of the applied voltage is smaller than that of ordinary paper.

According to another embodiment of the present invention described above, even when the surface potential of the intermediate transfer belt 501 is uneven before the charge is removed by the transfer frequency difference to the intermediate transfer belt 501, the belt discharger 503 Since the magnitude of the applied voltage (DC component) is switched in accordance with the number of times of transfer of the toner image to the intermediate transfer belt 501, it is possible to uniformly remove the electric charge from the intermediate transfer belt 50. In addition, even if the surface potential of the intermediate transfer belt 501 is uneven before the charge is removed in accordance with the difference in the moving speed, such as when the thick paper mode is executed to switch the moving speed of the intermediate transfer belt 501. It is possible to evenly remove the charge from the intermediate transfer belt 501. In this way, it is possible to uniformly remove the charge from the intermediate transfer belt 501 to prepare for the next toner image transfer from the photoconductivity 100.

In the above embodiment, sometimes the surface potential of the intermediate transfer belt 501 may be nonuniform depending on whether the intermediate transfer belt 501 opposes the bias roller 605 in the charging operation. In this case, the intermediate transfer belt 601 is switched by switching the magnitude of the voltage (DC component) applied to the belt discharger 503 by whether or not the intermediate transfer belt 501 is opposed to the bias roller 605 in the charging operation. It is desirable to remove the charge uniformly from

In particular, the apparatus does not use the relatively high resistance secondary transfer belt 601 shown in Fig. 1, and the secondary transfer bias roller 605 of the medium resistance secondary rollers to which the bipolar bias voltage is applied and the secondary transfer facing roller ( In the case where the transfer paper is directly placed between the 510 and the transfer paper, the absolute value for the surface potential of the intermediate transfer belt 501 becomes smaller than that of the non-image portion, so that the nonuniformity of the surface potential is on the intermediate transfer belt 501. An image portion, i.e., a predetermined predetermined transfer bias, tends to appear in a portion facing the secondary transfer bias roller 605 to which it is applied. In this case, the magnitude of the voltage (DC component) applied to the belt discharger 503 is switched depending on whether the secondary transfer bias roller 605 to which the transfer bias is applied is opposed to the image portion or the non-image portion. do. For example, in order to remove the charge from the image portion opposite to the secondary transfer bias roller 605 to which the transfer bias is applied, the DC component size of the voltage applied to the belt discharger 503 is switched to be smaller than the non-image portion. This switching can be performed at a timing based on the output signal of the mark sensor 905.

Next, a more specific embodiment of the color copying machine according to the above embodiment will be described.

As the intermediate transfer belt 501, a belt having a thickness of 0.15 mm, a width of 368 mm, and an inner circumferential length of 565 mm is used, and the moving speed of the intermediate transfer belt 501 is set to 200 kPa.

The surface layer 501a of the intermediate transfer belt 501 is formed of an insulating layer having a thickness of about 1 μm, and the intermediate layer 501b has an insulating layer (volume resistivity) of about 75 μm made of PVDF (Polyvinylidene Fluoride). : About 10 ¹³ Ω㎝), and the base layer 501c is a medium resistance layer (volume resistivity: about 10 ⁸ to 10 ¹¹ Ω㎝) of about 75 μm thick of polyvinylidene fluoride (PVDF) and titanium oxide. Is formed. As a result of measuring the volume efficiency of the entire intermediate transfer belt 501 formed of such a material, a volume efficiency of 10 ⁷ to 10 ¹² Ωcm was obtained. The volumetric efficiency is measured by applying a voltage of 100V for 10 seconds using the measuring method described in JIS K 6911 (Japanese Industrial Standard; K 6911). Further, the surface resistivity of the surface layer (501a) facing surface of the intermediate transfer belt (501), Yuka Denshi (油化電子) of the resistance measuring device, trade name "High Rester IP" as measured by a bar 10 ^{7-10 12} Ω / □. This surface resistivity can be measured by the surface resistance measuring method described in JIS K6911 in addition to the method using the said resistance measuring instrument.

In addition, a nickel plated metal roller is used as the primary transfer bias roller 507, a metal roller is used as the belt discharge roller 512, and a metal roller or a conductive resin roller is used as another roller. For the primary transfer bias roller 507, for example, 1.0 kV for the toner image of the first color, 1.3 to 1.4 kV for the toner image of the second color, 1.6 to 1.8 kV for the toner image of the third color; An appropriate sized DC transfer bias is applied so as to be 1.9 to 2.2 mW for a four-color toner image.

The nip width Wn of the primary transfer portion is set to 10 mm, and the distance L from the downstream end of the belt movement direction of the nip portion to the contact position of the belt discharge brush 513 is set to 7 mm (see Fig. 3). ). As the belt discharge brush 513, a conductive one containing carbon-containing resin fibers is used.

As the PTC 502, a discharger having a grid electrode is used. To the PTC 502, a discharge power source 803 supplies a DC bias voltage that is the same polarity as the counter electrode of the toner image on the intermediate transfer belt 501. More specifically, a DC voltage controlled at a constant current of -500 mA is applied to the main wire 502a of the PTC 502, and the DC voltage is set within the range of 0 to -3 mA for the grid electrode 502b. Is applied.

The DC component of the voltage applied to the belt discharge charger 503 is set as shown in Table 1 below. In addition, the peak-to-peak voltage of the AC component is set to 6 Hz p-p and the frequency is set to 500 Hz.

Apply voltage to belt discharger 503 (DC component) Nested times Plain paper Thick paper 1 time 150 V 110 V Episode 2 200 V 140 V 3rd time 250 V 170 V 4 times 300 V 200 V

As the secondary transfer bias roller 605, using a roller having a surface layer made of conductive sponge or conductive rubber and a core layer made of metal or conductive resin, a transfer bias controlled at a constant current of 10 to 20 mA is applied to the roller. Is authorized. As the secondary transfer belt 601, a belt-shaped member having a thickness of 100 µm and a volume resistivity of 10 ¹³ Ωcm formed of PVDF (Polyvinylidene Fluoride) is used.

As the transfer local electric machine 606, a discharger which applies only AC voltage or AC + DC voltage by a power source (not shown) is used, and as the belt discharger 607, AC by power source (not shown) The discharger which applied only voltage or AC + DC voltage is used. The sweep blade 608 is positioned to contact the second transfer belt 601 at a position where the sweep blade 608 is hung in the counter angle direction by the support roller 604.

As described above with respect to the conventional image forming apparatus, if the image to be transferred includes both the middle contrast portion and the portion without the contrast, the transfer efficiency for transferring all of this type of image is reduced, and the charge amount of the image transfer member is reduced. The nonuniformity will increase. That is, in the apparatus of the present invention described above with reference to Fig. 1, the toner image on the intermediate transfer belt 501 transferred from the photoconductive drum 100 includes a medium contrast portion and a portion without contrast, or Since the superposition amount of contains the part which differs, the charge quantity may be nonuniform. In addition, in some cases, the amount of charge in the toner image on the intermediate transfer belt 501 after the primary transfer is caused by the peeling discharge occurring in the downstream gap adjacent to the primary transfer portion in the moving direction of the intermediate transfer belt 501. Unevenness occurs. This nonuniformity in the single toner image lowers the transfer margin at the secondary transfer portion for transferring the toner image from the intermediate transfer belt 501 to the transfer paper.

According to yet another aspect of the present invention, by uniformly charging the toner image before being transferred to the transfer paper by the PTC 502, the charge quantity nonuniformity in the single toner image is eliminated, and the transfer in the secondary transfer portion is performed. You can improve the margin.

According to this aspect, the toner image on the intermediate transfer belt 501 transferred from the photoconductor 100 is uniformly charged by the PTC 502, and thereby the charge amount in the toner image on the intermediate transfer belt 501 is changed. Even if there is a nonuniformity, it is possible to keep the transfer characteristic in the secondary transfer portion almost constant over the entire toner image portion on the intermediate transfer belt 501. Therefore, the transfer margin at the time of transferring to the transfer paper is suppressed so that the toner image can be transferred stably.

In the above embodiment, the charge amount by the PTC 502 depends on the moving speed of the intermediate transfer belt 501. For example, if the moving speed of the intermediate transfer belt 501 is relatively slow, the same portion of the toner image on the intermediate transfer belt 501 passes through the charging region by the PTC 502 for a long time, and thus the charging amount increases. On the contrary, when the moving speed of the intermediate transfer belt 501 is high, the amount of toner lower image charge on the intermediate transfer belt 501 is small. Therefore, if the moving speed of the intermediate transfer belt 501 changes while the toner image passes through the charging position by the PTC 502, the charging to the toner image depends on the moving speed of the intermediate transfer belt 501. It is preferable to control the PTC 502 so that the amount does not change in the middle.

In the color image forming apparatus of this embodiment, if a thick paper is used as the transfer paper, the thick paper mode is selected and the second transfer to the transfer paper is carried out under the condition that the copy speed (CPM) is not dropped if possible. In order that the subsequent fixing operation can be performed satisfactorily, the operation speed of the entire apparatus is switched during the image forming operation. Specifically, after the toner image rear end on the photoconductive 100 is transferred to the intermediate transfer belt 501, and before the toner image front end on the intermediate transfer belt 501 reaches the secondary transfer unit, a thick paper mode is applied. If so, the moving speed of the intermediate transfer belt 501 is switched to about 1/2. When the thick paper mode is executed, the moving speed of the intermediate transfer belt 501 changes while the toner image on the intermediate transfer belt 501 passes through the charging position by the PTC 502. Therefore, it is preferable to control the PTC 502 according to the moving speed of the intermediate transfer belt 501 so that the charge amount to the toner image does not change in the middle.

6 (a) and 6 (b) are timing charts showing grid voltage control of the intermediate transfer belt drive motor 508a and the PTC 502 in the carton board mode, respectively. 6 (a) and 6 (b), after starting the copying operation at the timing indicated by the symbol A, before the toner image tip on the intermediate transfer belt 501 reaches the charging position by the PTC 502 (Fig. At B (6), charging by the PTC 502 is started. Subsequently, based on the result of detecting the mark on the intermediate transfer belt by the mark sensor 905, after the toner image rear end on the photoconductive drum 100 is transferred to the intermediate transfer belt 501, the intermediate transfer belt ( The timing (symbol C in Fig. 6) before the tip of the toner image on 501 reaches the secondary transfer portion is determined. At this timing, by controlling the belt drive motor 508a, the moving speed of the intermediate transfer belt 501 is reduced to approximately 1/2. Simultaneously with this control, the PTC power supply 803 is controlled to reduce the grid voltage applied to the grid electrode 502b of the PTC 502 to approximately 1/2, thereby lowering the charging capability of the PTC 502. This operation prevents the amount of toner image charging on the intermediate transfer belt 501 charged by the PTC 502 from changing as the intermediate transfer belt moving speed decreases. Then, at the timing when the rear end of the toner image on the intermediate transfer belt 501 equals the charging position of the PTC 502 (symbol D in FIG. 6), application of the bias voltage to the PTC 502 is stopped.

Therefore, as described above, even if the moving speed of the intermediate transfer belt 501 changes while the toner image is charged on the intermediate transfer belt 501 by the PTC 502 as in the case of executing a thick paper mode or the like. The toner image on the intermediate transfer belt 501 can be uniformly charged on the entire surface, and reliably prevents the transfer margin from decreasing.

Further, as described above, one drawback of the mechanism of Fig. 1 is that both the sweep blade 504 and the belt discharger 503 are required to be used. As shown in FIG. 7, another feature of the present invention is to use one conductive brush roller 514 to perform the functions of both the belt discharger 503 and the sweep blade 504. In this regard, the embodiment of FIG. 7 shows that the sweep blade 504 and belt discharger 503 of FIG. 1 are replaced by the conductive brush roller 514 and the discharge power source 84 is connected to the conductive brush roller 514. Except for the same as that of FIG.

The brush roller 514 is used to discharge and clean the intermediate transfer belt 501 after the secondary transfer, and the discharge power source 804 is equal to the surface potential of the intermediate transfer belt 501 after the secondary transfer. A DC voltage having polarity is applied to the brush roller 514. In order to improve the discharge efficiency, the AC voltage may be superimposed on the DC voltage. In addition, the brush roller 514 is separated from and in contact with the intermediate transfer belt 501 by a folding mechanism (not shown). It is possible to use it so that it can be switched between the present state.

The brush roller 514 is ON / OFF controlled as described later. In the case of forming a full color image on the paper, the brush roller 514 is in contact with the intermediate transfer belt 501 until the intermediate transfer belt 501 completes at least one rotation after the secondary transfer is completed. In order to repeatedly form a full color image, the brush roller 514 is in contact with the intermediate transfer belt 501 until the tip portion of the next toner image reaches the discharge position and the sweep position after the secondary transfer is completed. In addition, to form a single color image on the paper, the brush roller 514 contacts the intermediate transfer belt 501 until the intermediate transfer belt 501 completes at least one rotation after the first transfer is completed. It is. In order to form a single color image repeatedly, the brush roller 514 is in contact with the intermediate transfer belt 501 until the leading end portion of the next toner image reaches the discharge position and the sweep position after the first transfer is completed.

In addition, on the surface of the intermediate transfer belt 501 after the toner image is transferred to the transfer member, charge is removed simultaneously with the cleaning by the brush roller 514 which pushes down the intermediate transfer belt 501 by a folding mechanism not shown. do.

According to a feature of the present invention, by removing the charge of the intermediate transfer belt 501 by making one brush roller 514 in contact with the intermediate transfer belt 501, it is possible to clean, which is the intermediate transfer belt Compared with the apparatus for separately installing the discharge mechanism and the cleaning mechanism for the (501), it is possible to achieve a low cost.

If the corona discharger is used as the intermediate transfer discharge mechanism as in the conventional image forming apparatus, the polarity potential set before discharge will start to appear gradually within a short time, but the surface of the intermediate transfer belt 501 will be at approximately 0V immediately after discharge. Will be present. As described in the present embodiment, by using the configuration in which the voltage for static elimination is applied to the brush roller 514, it is possible to prevent the potential of the polarity set before the discharge from appearing, thereby obtaining desirable discharge characteristics.

Although the brush roller 514 is used as the conductive brush member for discharging and cleaning the intermediate transfer belt 501 in the above embodiment, the brush extending in the axial direction of the cleaning counter roller 511 as shown in FIG. It is also possible to use a conductive brush member 516 including 516a). In such a configuration, it is preferable to configure the metal roller 517 to contact the brush 516a in order to effectively recover the toner adhering to the brush 516a of the brush member 516 as shown in FIG. . A voltage higher than that applied to the brush member 516 is applied to the metal roller 517 so that the metal roller 517 absorbs the toner adhering to the brush 516a of the brush member 516 by electrostatic force. do. Attachments attached to the surface of the metal roller 517 may be recovered by using a blade (not shown) or the like.

In this embodiment, as described above for the discharger 503, the intermediate transfer belt 501 by switching the discharge conditions for the brush roller 514 in accordance with the surface potential of the intermediate transfer belt 501 after the second transfer. It is also possible to employ a configuration that can uniformly remove the charge on the phase. In other words, the level of the DC component with respect to the output voltage of the discharge power source 804 is switched in accordance with the number of times of toner image superimposition on the intermediate transfer belt 501.

In addition, as the brush roller 514 for discharging and cleaning the intermediate transfer belt 501 after the second transfer, a roller having conductive fibers installed on the metallic shaft is used. A DC voltage (+ voltage) having a polarity opposite to the surface potential of the intermediate transfer belt 501 is applied to the shaft before discharge. By using the conductive brush roller 514 to which a predetermined predetermined voltage is applied, even when using the intermediate transfer belt 501 having a multilayer structure including the intermediate layer 501b having a relatively high resistance as described above. It is possible to preferably remove the charge from the intermediate transfer belt 501 after the second transfer without causing the phenomenon that the once removed charge starts to appear on the surface again.

Although the photoconductive drum 100 is used as the image bearing member in the description of the embodiment, the present invention is also applicable to an apparatus including the image bearing member having another form. For example, it is also possible to apply to a crawler type photoconductive belt positioned to be movable between two rollers.

Although the intermediate transfer belt 501 is used as the intermediate transfer member in the description of the above embodiment, the present invention is also applicable to an apparatus including the intermediate transfer member having another form. In addition, the electrical characteristics (volume resistivity, surface resistivity, etc.), thickness, structure (single layer, two layers, ...), materials, materials, and the like of the intermediate transfer belt 501 are appropriately based on the image forming conditions. It is possible to choose.

Although the discharge brush 505 is used as the primary transfer portion discharge mechanism in the nip portion of the primary transfer portion in the description of the embodiment, the present invention includes a primary transfer portion discharge mechanism having another form such as a blade or a roller. It is also applicable to a device. The position where the charge is removed by the discharge brush 505 is not limited to the position shown in the above embodiment, but the upstream primary transfer of the primary transfer bias roller 507 in the moving direction of the intermediate transfer belt 501. It is necessary to be in the nip of the part. In addition, the discharge position in the nip of the primary transfer portion is not limited to one, but it is also possible to remove electric charges at a plurality of locations. In addition, although the discharge brush 505 is grounded in this embodiment, it is also possible to apply a bias having a polarity opposite to that of the transfer charges as long as they do not affect the transfer charges required for transfer in the nip.

Although the primary transfer bias roller 507 is used as the primary transfer charger in the description of the above embodiment, the present invention is also applicable to an apparatus including the primary transfer charger having another form. Further, primary transfer charge can be applied at the nip of the primary transfer portion under conditions where the charge is removed downstream from the position where the charge is removed by the primary transfer portion discharge brush 505 in the moving direction of the intermediate transfer belt 501. have.

In the above embodiment, the values of the voltage and current of the primary transfer bias applied to the primary transfer bias roller 507 are not limited to the examples mentioned above, and may be set to appropriate values according to various image forming conditions.

Although the belt discharge roller 512 is used as the primary pre-transmission discharge mechanism in the description of the above embodiment, the present invention is also applicable to an apparatus including a member having another shape in place of this roller.

Although the secondary transfer bias roller 605 is used as the secondary transfer charger in the description of the above embodiment, the present invention is also applicable to an apparatus including a member having another shape such as a blade or a brush in place of the roller. .

Although the secondary transfer belt 601 is used as the transfer member carrier for supporting the transfer member in the secondary transfer portion in the description of the above embodiment, the present invention provides a member having another shape such as a drum instead of the belt. Applicable to the containing device.

Although the discharging potential of the photoconductive drum 100 in the description of the embodiment is provided with a developing mechanism for use in a reverse development method in which a two-component developer is used with a negative polarity, the present invention provides a discharge of the photoconductive drum 100. The present invention is not limited to the potential and can be applied to an apparatus in which a one-component developer is used or a regular development method is employed.

Obviously, additional improvements and modifications of the present invention can be obtained from the above teachings. It is, therefore, to be understood in terms of the appended claims, and the invention may be practiced otherwise than as specifically described herein. This invention is based on Japanese priority documents 9-098064, 9-098065, and 9-098067, The content is described by reference.

According to the present invention as described above, it is ensured that image transfer to and from the image transfer to the intermediate transfer member can be made appropriately, and achieves a structure in which high efficiency and low cost are achieved.

Further, the charge on the intermediate transfer member can be uniformly removed after the toner image is transferred to the transfer member to prepare for the next image transfer operation made from the image bearing member.

Further, by suppressing the reduction in the transfer margin for transferring the toner image to the transfer member, even when there is an uneven charging amount in the toner image on the intermediate transfer member after being transferred from the image bearing member, the toner image is stably transferred to the transfer member. Can be killed.

In addition, by including a new conductive brush that works together as the intermediate transfer member discharge mechanism and the intermediate transfer member cleaning mechanism, low cost can be realized.

Claims (11)

Intermediate transfer means for transporting the toner image transferred from the image bearing means; Primary transfer means for applying electric charges to said intermediate transfer means for transferring a toner image from said image bearing means to said intermediate transfer means; Discharge means for applying a discharge charge proportional to the surface potential of the intermediate transfer means to the intermediate transfer means to remove the surface potential from the intermediate transfer means after the toner image is transferred from the intermediate transfer means to the final transfer means; Image forming apparatus comprising. The method of claim 1, The toner image transferred from the image bearing means is superimposed on the intermediate transfer means by a plurality of transfer operations, And the discharge charge applied from said intermediate transfer means is switched based on the number of operations of transferring a toner image to said intermediate transfer means. The method of claim 1, And the charge applied to the primary transfer means is switched based on the number of operations of transferring the toner image to the intermediate transfer means. The method of claim 1, A second transfer charging means for applying a transfer charge to transfer the toner image from the intermediate transfer means to the final transfer means, And the discharge charge applied from the discharge means is switched based on whether or not the intermediate transfer means is opposite to the second transfer charge means during the charging operation. The method of claim 1, A moving speed adjusting means for switching the moving speed of the intermediate transfer means based on the thickness of the final transfer means, And the discharge charge applied from the discharge means is switched based on the moving speed of the intermediate transfer means. The method of claim 1, The discharging means includes a corona discharger to which voltages having DC and AC components are applied, And the discharge charge switches the level of the DC component applied to the corona discharger. The method of claim 1, And said intermediate transfer means is a belt having at least first and second layers. The method of claim 1, And the discharging means comprises a conductive brush and a power supply for applying a bias voltage negative to the standard potential of the intermediate transfer means to the conductive brush. The method of claim 8, And the conductive brush includes a rotatable conductive brush roller. The method of claim 1, And pre-transfer charging means for charging the intermediate transfer means before transferring the toner image from the image bearing means to the intermediate transfer means. The method of claim 10, And the output of the yes-transcription means is adjusted based on the moving speed of the intermediate transfer means.