CN1148612C - image forming device - Google Patents

Abstract

The image generating device has an intermediate transmission element (501) which carries a toner image to be transmitted from an image supply element (100). A primary transmission element (507) applies a charge to the intermediate transmission element (501) to transmit the image from the image supply element to the intermediate element. A discharge device (503) applies a discharge charge to the intermediate device to remove a surface potential from the intermediate element. After this a toner image is transmitted from the intermediate element to a final transmission element. The discharge charge is proportional to the surface potential of the intermediate transmission element. Preferably the toner image is superimposed onto the intermediate element by means of several transfer processes. The discharge charge may be varied based on the number of transfer processes.

Description

image forming device

technical field

The present invention relates to image forming apparatuses such as copiers, printers, facsimile machines, and more specifically, to image forming apparatuses using an intermediate transfer body.

Background technique

Conventionally, this type of image forming apparatus is provided with an intermediate transfer body on which an ink image transferred from an image carrier is placed, and an electric charge for transferring an ink image on the image carrier to the intermediate transfer body is applied to the above-mentioned intermediate transfer body by electrostatic force. A primary charge imparting device for an intermediate transfer body, a secondary charge imparting device for imparting charges for transferring an ink image from the intermediate transfer body onto a transfer material to the transfer material or a transfer material carrier by electrostatic force . The above-mentioned image forming apparatus is known as an anti-static device for an intermediate transfer body that de-energizes the surface of the intermediate transfer body that transfers a toner image onto a transfer material. In this image forming apparatus, the surface potential of the intermediate transfer body is uniformized by using the intermediate transfer body de-energizing device to de-charge the surface of the intermediate transfer body after the toner image is transferred to the transfer material, and removes the surface potential of the intermediate transfer body. Residual toner and other attachments on the intermediate transfer body for subsequent primary transfer from the image carrier to the intermediate transfer body.

However, in the above-mentioned conventional image forming apparatus, even if the intermediate transfer body is de-energized by the above-mentioned intermediate transfer body de-energization device, the surface potential of the intermediate transfer body does not become a predetermined potential, and potential unevenness may remain. , If there is such a poor phenomenon of electricity dissipation, it will have a bad influence on the subsequent transfer process from the image carrier to the intermediate transfer body.

The inventors of the present invention have studied the causes of the above-mentioned poor discharge of the intermediate transfer body, and found that the main cause of the above-mentioned failure of the discharge is that the surface potential of the intermediate transfer body before discharge is very discrete.

Especially when carrying out several times of primary transfer, in order to superimpose the ink images of various colors formed on the image carrier on the above-mentioned intermediate transfer body, and then transfer the superimposed ink images on the intermediate transfer body to the image formation of the transfer material. In the case of the device, the surface potential of the intermediate transfer body before de-energization by the above-mentioned intermediate transfer body de-energization device is very discrete, and it is related to the number of ink images superimposed on the intermediate transfer body, that is, the primary transfer of the intermediate transfer body. Depends on the number of prints.

In addition, in the above-mentioned conventional image forming apparatus, since an intermediate transfer body de-energizing device such as a corona discharger for de-charging the surface of the above-mentioned intermediate transfer body and a cleaning device for cleaning the surface of the intermediate transfer body are provided separately, It is difficult to achieve cost reduction.

In the above-mentioned conventional image forming apparatus, the transfer conditions when transferring the toner image of the intermediate transfer body to the transfer material are generally set at the approximate center of the appropriate transfer range in which the transfer efficiency to the transfer material becomes a predetermined value or more. . The set value of the transfer condition corresponds to the difference between the upper and lower limits of the above-mentioned suitable transfer range and the transfer tolerance when the toner image of the intermediate transfer body is transferred to the transfer material. The larger the difference, the larger the transfer tolerance. The larger the limit.

Here, if the toner image after the primary transfer of the toner image from the image carrier to the intermediate transfer body includes portions with different toner adhesion amounts, variations in the charge amount will occur in the toner image on the intermediate transfer body. For example, when the toner image on the intermediate transfer body includes a full-tone portion and a half-tone portion, the charge amount of the full-tone portion is smaller than that of the half-tone portion. In addition, in the case of, for example, a color image forming apparatus, the charged amount of the toner-image overlapping portion on the intermediate transfer body is smaller than that of the portion where only the single-color toner adheres.

The amount of charge in the ink image after passing through the primary transfer part where the ink image is transferred from the image carrier to the intermediate transfer body may vary due to the adjacent downstream side of the above-mentioned primary transfer part in the surface movement direction of the intermediate transfer body. The resulting peeling discharge occurs.

In this way, when the charge amount in the toner image on the intermediate transfer body varies, portions with different transfer characteristics exist in the same toner image. If all parts with different transfer characteristics are transferred on the transfer material under the same transfer conditions, the range of transfer conditions that can transfer the ink image as a whole at a transfer rate above a predetermined value becomes narrow, so for the ink The transfer margin of the entire image is reduced, and the toner image cannot be stably transferred to the transfer material.

Curve a and curve b in FIG. 10 represent the relationship between the transfer current and the transfer rate for the full-tone portion and the half-tone portion, respectively, and schematically show transfer characteristics. The width indicated by symbols A and B in the figure is the range of the transfer current that can transfer each part to the transfer material at a transfer rate of 80% or more, and the transfer margin is relatively large. However, due to the deviation of the two transfer characteristic curves, the range of the transfer current in which the above two parts can transfer at a transfer rate of 80% or more is narrowed, as indicated by symbol C in the figure, and the transfer tolerance is reduced.

Contents of the invention

The present invention is proposed in view of the problems existing in the above-mentioned prior art, and its purpose is to provide a kind of ink image transfer on the transfer printing material that can uniformly dissipate electricity on the intermediate transfer body, so as to prepare for the following from the image carrier. An image forming device that performs toner image transfer.

Another object of the present invention is to provide an image formation that can be realized at a lower cost than the case where the two devices are separately provided by providing a conductive brush member that can also be used as an intermediate transfer body de-energizing device and an intermediate transfer body cleaning device. device.

Still another object of the present invention is to provide a method that can suppress the transfer margin when the toner image is transferred to the transfer material even if the amount of internal charge of the toner image transferred from the image carrier is dispersed. An image forming apparatus capable of stably transferring the toner image onto a transfer material with reduced weight.

In order to achieve the above object, the present invention proposes an image forming apparatus, which includes: an intermediate transfer body carrying an ink image transferred from an image carrier; The primary transfer charge imparting device for imparting the intermediate transfer body; the intermediate transfer body de-energizing device, which imparts the neutralized charge to the intermediate transfer body, so as to transfer the ink image to the above-mentioned intermediate transfer material on the transfer material. The surface of the transfer body undergoes electricity elimination; the feature is that the voltage of the above-mentioned electricity elimination charge is proportional to the surface potential of the intermediate transfer body.

According to the image forming apparatus of the present invention, it is also characterized in that: the ink image formed on the above-mentioned image carrier is superimposed and transferred on the above-mentioned intermediate transfer body several times; The number of times is to switch the voltage of the neutralized charge obtained by the above-mentioned intermediate transfer body neutralizer.

The image forming apparatus according to the present invention is further characterized in that the voltage of the charge applied by the primary transfer charge applying means is switched in accordance with the number of times the toner image is transferred to the intermediate transfer body.

The image forming apparatus according to the present invention is further characterized in that it includes secondary transfer charge applying means for applying charges for transferring an ink image from the intermediate transfer body to the transfer material to the transfer material carrier; The voltage of the neutralized charges obtained from the above-mentioned intermediate transfer body neutralizing means is switched according to whether or not the aforementioned intermediate transfer body faces the aforementioned secondary transfer charge imparting means during the charging operation.

According to the image forming apparatus of the present invention, it is further characterized in that: a moving speed control device is provided to switch the moving speed of the intermediate transfer body according to the thickness of the transfer material; The voltage of the discharged charge obtained by the bulk discharge device.

The image forming apparatus according to the present invention is further characterized in that a corona eliminator is used as the above-mentioned intermediate transfer body eliminator, and a voltage including a DC component and an AC component is applied; The magnitude of the DC component on .

The image forming apparatus according to the present invention is further characterized in that the intermediate transfer body is a belt having at least first and second layers.

The image forming apparatus according to the present invention is further characterized in that it is provided with a conductive brush member which is in contact with the intermediate transfer body on which the toner image is transferred to the transfer material, and eliminates the intermediate body. Electricity and cleaning; a power supply that applies a bias voltage of a polarity opposite to the surface potential of the intermediate transfer body to the above-mentioned conductive brush member.

An image forming apparatus according to the present invention is further characterized in that a rotatable conductive brush roller is used as the conductive brush member.

The image forming apparatus according to the present invention is further characterized by comprising a pre-transfer charging device for charging the ink image on the intermediate transfer body before being transferred to the transfer material.

The image forming apparatus according to the present invention is further characterized in that a control device is provided for controlling the speed of the above-mentioned pre-transfer charging device based on the moving speed of the surface of the intermediate transfer body passing the charging position of the above-mentioned pre-transfer charging device. output.

Effects of the present invention will be described below.

According to the present invention, even if the surface potential of the intermediate transfer body before de-energization is dispersed, the intermediate transfer body can be uniformly de-charged to prepare for subsequent ink image transfer from the image carrier.

According to the present invention, even if the surface potential of the intermediate transfer body before de-energization is scattered due to the difference in the number of transfers to the intermediate transfer body, the intermediate transfer body can be uniformly de-energized to prepare for subsequent transfer from the image carrier. Ink image transfer.

According to the present invention, even if the surface potential of the intermediate transfer body before discharge is dispersed due to whether or not the intermediate transfer body faces the secondary transfer charge application device in the charge application operation, the intermediate transfer body can be charged. Dissipate electricity uniformly for subsequent ink image transfer from the image carrier.

According to the present invention, even if the surface potential of the intermediate transfer body before de-energization is scattered due to the difference in the moving speed of the intermediate transfer body, the intermediate transfer body can be uniformly de-energized to prepare for subsequent ink transfer from the image carrier. like transfer printing.

According to the present invention, the corona eliminator is used as the intermediate transfer body de-energization device, and the intermediate transfer body can be easily de-energized by switching the easily controllable DC component of the voltage applied to the above-mentioned corona eliminator. control.

According to the present invention, the intermediate transfer body can be neutralized and cleaned only by using one conductive brush member in contact with the intermediate transfer body. Realize cost reduction.

According to the present invention, even if the amount of charge in the ink image on the intermediate transfer body transferred from the image carrier varies, the decrease in the transfer margin when the ink image on the intermediate transfer body is transferred to the transfer material can be suppressed. , the ink image can be stably transferred.

According to the present invention, even if the surface moving speed of the intermediate transfer body changes during the charging of the ink image on the intermediate transfer body by the above-mentioned pre-transfer charging device, the entire ink image on the intermediate transfer body can be uniformly charged, A decrease in the transfer margin is surely prevented.

Description of drawings

FIG. 1 is a schematic configuration diagram of a color copying machine according to a first embodiment of the present invention;

Fig. 2 is a cross-sectional view of an intermediate transfer belt used in the above-mentioned color copier;

Fig. 3 is an enlarged view of a primary transfer section of the above-mentioned color copier;

Fig. 4 is the control block diagram of the belt elimination charger of above-mentioned color photocopier;

Figures 5a-c respectively show the change of the surface potential of the intermediate transfer belt, the on/off time of the charger with discharge and the output diagram of the primary transfer bias device;

6 is a schematic configuration diagram of a color copying machine according to a second embodiment of the present invention;

7 is a schematic configuration diagram of a conductive brush member related to a modification;

Fig. 8 is the block diagram of the control system of the charging condition of controlling PTC;

Figures 9a-b respectively show the time charts of the driving motor of the intermediate transfer belt in the thick paper mode and the grid voltage control of the PTC;

FIG. 10 is a schematic diagram showing a transfer characteristic showing a relationship between a transfer current and a transfer rate in a secondary transfer portion.

Detailed ways

Next, an embodiment of the present invention in which the present invention is applied to an electrophotographic color copier (hereinafter simply referred to as "color copier") as an image forming apparatus will be described.

1 is a schematic configuration diagram of an image forming section of a main part of a color copier according to an embodiment of the present invention. In addition to the image forming section shown in FIG. "Color Scanner"), Paper Feed Unit and Control Unit, etc.

The above-mentioned color scanner reads color image information of an original document by optically decomposing it in red, green, and blue (hereinafter abbreviated as "R, G, B") colors, for example, and converts it into an electrical signal of an image. And based on the color decomposition image signal intensity levels of R, G, and B obtained by the color scanner, a color conversion process is performed in an image processing section not shown to obtain black, cyan, magenta, and yellow (respectively hereinafter). Abbreviated as "Bk, C, M, Y) color image data.

The image forming part of FIG. 1 is composed of a photoreceptor drum 100 as an image carrier, a charging charger 200 as a charging device, a photoreceptor cleaning device 300 consisting of a cleaning blade and a brush, and an unillustrated writing optical device as an exposure device. components, a rotary developing unit 400 as a developing device, an intermediate transfer unit 500, a paper transfer unit 600, a fixing unit using a pair of fixing rollers 701, and the like.

The photoreceptor drum 100 rotates in the counterclockwise direction of the arrow, and the charging charger 200, the photoreceptor cleaning device 300, the developer selected by the rotary developing unit 400, and the intermediate transfer unit 500 as an intermediate transfer body are arranged around it. The intermediate transfer belt 501 and so on.

In addition, the writing optical unit converts the color image data from the color scanner into an optical signal, and performs optical writing corresponding to the original image on the surface of the photosensitive drum 100 uniformly charged by the charging charger. An electrostatic latent image is formed on the drum 100 . The writing optical unit is composed of, for example, a semiconductor laser as a light source, a laser emission drive control unit, a polygon mirror and its rotation motor, an f/θ lens, a reflection mirror, and the like.

The above-mentioned rotary developing unit 400 is composed of a Bk developing device 401 using Bk toner, a C developing device 402 using C toner, an M developing device 403 using M toner, a Y developing device 404 using Y toner, and the assembly as a whole. It is composed of a developing rotary drive unit that rotates counterclockwise, etc. Each developing device installed in the rotary developing unit 400 is composed of a developing sleeve, a developer agitator, a developing roller driving part, etc., and the developing sleeve is used as a developer carrier, and the magnetic force of the developer is used to develop an electrostatic latent image. The ear contacts the surface of the photoreceptor drum 100 and rotates, the developer agitator rotates to pick up and stir the developer, and the developing roller drive unit rotates the developing roller in the clockwise direction of the arrow.

In this embodiment, the toner in each developer is negatively charged by agitation with the ferrite carrier, and the AC voltage Vac (AC component) is superimposed by a developing bias power supply (not shown) as a developing bias applying means. A developing bias at a negative DC voltage Vdc (DC component) is applied to each developing sleeve, and the developing sleeve is biased to a predetermined potential with respect to the metal base layer of the photoreceptor drum 100 .

In the standby state of the color copier body, the rotary developing assembly 400 stops at the original position where the Bk developing device 401 is located at the developing position. Once the copying operation starts, the color scanner 1 starts to read the Bk color image data from a predetermined time. Image data is optically written with laser light to form an electrostatic latent image (hereinafter, an electrostatic latent image formed based on Bk image data is referred to as "Bk electrostatic latent image", and the same applies to C, M, and Y). Before the front end of the electrostatic latent image reaches the developing position of Bk, the Bk developing sleeve starts to rotate, and the Bk electrostatic latent image is developed with Bk toner. Thereafter, the developing operation of the Bk electrostatic latent image area continues, and when the rear end of the Bk electrostatic latent image passes the Bk developing position, the rotary developing assembly 400 rotates, and the developing devices of the following colors quickly come to the developing position. This operation is completed at least before the front end of the electrostatic latent image formed based on the following image data arrives.

The above-mentioned intermediate transfer unit 500 is composed of an intermediate transfer belt 501 and the like as an intermediate transfer body, and the intermediate transfer belt is stretched over several rollers. Around the above-mentioned intermediate transfer belt 501, a pre-transfer charger (hereinafter abbreviated as "PTC") 502 as a pre-transfer charging device and a secondary transfer belt as a transfer material carrier of the paper transfer unit 600 are disposed. 601, a secondary transfer bias roller 605 as a secondary transfer charge imparting device, a charging charger 503 as an intermediate transfer body de-energizing device, a belt cleaning blade 504 as an intermediate transfer body cleaning device, The lubricant brush 505 of the lubricant application device, etc.

The intermediate transfer belt 501 is composed of a primary transfer bias roller 507 as a primary transfer charge imparting device, a belt drive roller 508, a belt tension roller 509, a secondary transfer opposing roller 510, a cleaning opposing roller 511, and The belt discharge roller 512 of the discharge device before the primary transfer is erected. Each roller is formed of a conductive material, and each roller other than the primary transfer bias roller 507 is grounded. A primary transfer bias roller 507 is supplied with a transfer bias controlled to a predetermined magnitude of current or voltage according to the number of toner images superimposed by a primary transfer power source 801 controlled by a constant current or constant voltage. In addition, the intermediate transfer belt 501 is driven to rotate in the direction of the arrow by a belt drive roller 508 which is driven to rotate by a drive motor not shown.

As shown in the sectional view of FIG. 2 , the above-mentioned intermediate transfer belt 501 is composed of a multi-layer structural belt material consisting of a surface layer 501a, an intermediate layer 501b, and a base layer 501c. The outer peripheral surface side in contact with the photoreceptor drum 100 is the surface layer 501a, and the inner peripheral surface side is the base layer 501c. There is an adhesive layer 501d between the middle layer 501b and the base layer 501c for bonding the above two layers.

In the transfer section (hereinafter referred to as "primary transfer section") that transfers the toner image on the photoreceptor drum 100 to the intermediate transfer belt 501, the primary transfer bias roller 507 and the belt discharge roller 512 brings the intermediate transfer belt 501 into contact with the photoreceptor drum 100 side to form a nip portion of a predetermined width between the photoreceptor drum 100 and the intermediate transfer belt 501 . A grounded charge neutralizing brush 513 serving as a primary transfer unit neutralizing device is brought into contact with the inner peripheral surface of the intermediate transfer belt 501 at the contact portion.

As shown in FIG. 3 , the contact width Wn of the primary transfer portion and the distance L of the contact portion from the downstream end in the belt rotation direction to the contact position of the charging brush 513 are set so as to obtain predetermined transfer conditions.

The PTC 502 uniformly charges the toner image on the intermediate transfer belt 501 that has been transferred from the photoreceptor drum 100 by the primary transfer unit to copy paper as a transfer material.

A discharger that applies only an AC voltage or an AC+DC voltage is used as the above-mentioned charger with an eraser 503 . In addition, the above-mentioned belt cleaning blade 504 is in reverse contact with the intermediate transfer belt 501 on the part of the cleaning counter roller 511, and can be switched by an unshown take-off mechanism so that the belt cleaning blade is opposite to the intermediate transfer belt 501. The transfer belt 501 is joined or separated.

The above-mentioned charger 503 for removing electricity and the belt cleaning blade 504 control the switch as follows. The belt elimination charger 513 is set at the on position, and the belt cleaning blade 504 is in contact with the intermediate transfer belt 501 . When the full-color image is repeatedly formed, after the secondary transfer is completed, before the front ends of the subsequent ink images respectively reach the de-energizing position and the cleaning position, set the de-energizing charger 503 to the ON position, and the belt-cleaning blade 504 It is in contact with the intermediate transfer belt 501 . When forming a single-color image, after the primary transfer is completed, at least before the intermediate transfer belt 501 runs for a full cycle, the charger 503 is set to the on position, and the belt cleaning blade 504 is connected to the intermediate transfer belt. 501 connected. When repeatedly forming a single-color image, after the first transfer is completed, before the front ends of the subsequent ink images respectively reach the de-energizing position and the cleaning position, the charger with de-energizing charger 503 is set at the ON position, and the belt-cleaning blade 504 and the cleaning blade 504 are connected to each other. The intermediate transfer belts 501 are in contact.

The lubricant coating brush 505 grinds the zinc stearate 506 formed into a plate as a lubricant, and coats the ground fine particles on the intermediate transfer belt 501 . The lubricant application brush 505 is also provided so as to be accessible to and away from the intermediate transfer belt 501 , and is controlled to come into contact with the intermediate transfer belt 501 at a predetermined timing.

The above-mentioned paper transfer unit 600 is composed of a secondary transfer belt 601 and the like. The secondary transfer belt 601 is spanned by three support rollers 602-604. The secondary transfer belt 601 spanned between the support rollers 602 and 603 The intermediate transfer belt 501 on the secondary transfer counter roller 510 is pressure-contactable. One of the three backup rollers 602 to 604 is a driving roller, which is rotated by a driving device not shown, and the secondary transfer belt 601 is driven to run by the driving roller. The intermediate transfer belt 501, the copy paper and the secondary transfer belt 601 are sandwiched between the secondary transfer bias roller 605 and the secondary transfer counter roller 510, and the secondary transfer power supply 802 controlled by a constant current A transfer bias of a given current is applied. In addition, there is a take-off mechanism (not shown) that drives the backup roller 602 and the secondary transfer bias roller 605 such that the secondary transfer belt 601 and the secondary transfer bias roller 605 have The position where the print is pressed against the roller 510 and the position where it is separated. The secondary transfer belt 601 at the above-mentioned leaving position is indicated by a two-dot chain line in FIG. 1 .

On the portion of the secondary transfer belt 601 that is wound around the support roller 603 toward the fixing roller, a copy paper discharge charger 606 as a transfer material discharge device and a belt discharge charger 606 as a transfer material carrier discharge device are arranged opposite to each other. Electric charger 607 . In addition, a portion of the secondary transfer belt 601 that is wound around the backup roller 604 on the lower side in the drawing is in contact with a cleaning blade 608 as a transfer material carrier cleaning device.

The above-mentioned copy paper de-energizing charger 606 enables the copy paper to be well separated from the secondary transfer belt 601 by virtue of the strength of the copy paper itself by de-energizing the charge on the copy paper. The above-mentioned belt discharge charger 607 can discharge the charge applied to the secondary transfer bias roller 605 and remaining on the secondary transfer belt 601 . The above-mentioned cleaning blade 608 removes the deposits adhering to the surface of the secondary transfer belt 601 for cleaning.

In the color copier configured as above, when the image forming cycle starts, the photoreceptor drum 100 rotates counterclockwise as indicated by the arrow by the drive motor (not shown), and the intermediate transfer belt 501 rotates counterclockwise as indicated by the arrow by the drive roller. Turn clockwise as shown. With the rotation of the intermediate transfer belt 501, ink images of Bk, C, M, and Y are formed, which are superimposed on the intermediate transfer belt 501 in the order of Bk, C, M, and Y to finally form an ink image.

The above-mentioned formation of the Bk ink image is performed as follows. The charging charger 200 uniformly negatively charges the photoreceptor drum 100 to a predetermined potential by corona discharge. When raster exposure is performed based on the Bk color image signal by the writing optical unit, the charge of the exposed portion of the photoreceptor drum 100 that was initially uniformly charged is lost in proportion to the amount of exposure light, forming a Bk electrostatic latent image. Subsequently, when the negatively charged Bk toner on the Bk developing roller comes into contact with the Bk electrostatic latent image, the toner does not adhere to the portion of the photoreceptor drum 100 where the charge remains, and the Bk toner is adsorbed to the portion without charge, that is, is absorbed. In the exposed part, a Bk ink image similar to an electrostatic latent image is formed. The Bk ink image formed on the photoreceptor drum 100 is transferred onto the surface of the intermediate transfer belt 501 which is driven at a constant speed in contact with the photoreceptor drum 100 . Hereinafter, the transfer of the toner image from the photoreceptor drum 100 to the intermediate transfer belt 501 is referred to as "belt transfer".

The toner remaining on the surface of the photoreceptor drum 100 after the tape transfer is cleaned by the photoreceptor cleaning device 300 to prepare the photoreceptor drum 100 for reuse.

On the photoreceptor drum 100, after the Bk image forming process, the C image forming process is performed, and the C image data obtained by the color scanner is read at a predetermined time, and laser writing is performed based on the C image data to form a C electrostatic latent picture. Then, after the rear end portion of the preceding Bk electrostatic latent image passes and before the front end portion of the C electrostatic latent image arrives, the rotating action of the rotary developing assembly is performed, the C developing device 402 is set to the developing position, and the C developing unit 402 is used to make the C toner. C electrostatic latent image development. Afterwards, the development of the C electrostatic latent image area is continued, and when the rear end of the C electrostatic latent image passes, as in the case of the previous Bk developing device 401, the rotary action of the rotary developing assembly is performed to move the rear M developing device 403 to the developing area. Location. This operation ends before the front end of the subsequent M electrostatic latent image reaches the developing position.

In the image forming steps of M and Y, the steps of reading color image data, forming an electrostatic latent image, and developing are the same as those of steps Bk and C described above, and their descriptions are omitted.

The ink images of Bk, C, M, and Y sequentially formed on the photoreceptor drum 100 are transferred onto the intermediate transfer belt 501 in alignment on the same surface in sequence. In this way, a four-color superimposed ink image is formed on the intermediate transfer belt 501 . The ink image superimposed on the intermediate transfer belt 501 is uniformly charged by the PTC 502, and then transferred onto the copy paper at one time in the subsequent secondary transfer process.

At the start of the above-mentioned image forming operation, paper is fed from a paper feeding unit such as an unshown copy paper feeding cassette or a bypass tray, and stands by at a contact portion between a pair of unshown resist rollers. Then, in the secondary transfer portion where the contact portion is formed by the secondary transfer counter roller 510 and the secondary transfer bias roller, when the front end of the toner image on the intermediate transfer belt 501 comes, the paper resist roller is driven to complete the transfer process. The copy paper is aligned with the ink image so that the front end of the copier coincides with the front end of the ink image. Then, the copy paper is superimposed on the toner image on the intermediate transfer belt 501 and passes through the secondary transfer section. At this time, the four-color superimposed ink image on the intermediate transfer belt 501 is transferred onto the copy paper at one time by the transfer bias applied to the secondary transfer bias roller. Thereafter, when the secondary transfer belt passes through the opposing part of the copy paper discharge charger 606 arranged downstream of the secondary transfer part along the moving direction of the secondary transfer belt, the copy paper is decharged and the intermediate transfer belt is peeled off. The printing ribbon 501 is delivered to the outside of the device body by a pair of discharge rollers not shown, and stacked on the copy tray not shown with the surface facing up to obtain a full-color copy.

On the other hand, the toner remaining on the surface of the intermediate transfer belt 501 after the toner image is transferred to the copy paper is cleaned by the belt cleaning blade 504, which is pushed by an unillustrated take-off mechanism. onto the intermediate transfer belt 501.

Here, when copying is repeated, the operation of the color scanner and the formation of an image on the photoreceptor drum 100 are followed by the image forming process of the fourth color (Y) of the first sheet, and the first color (Y) of the second sheet is performed at a predetermined time. Bk) image forming process. The intermediate transfer belt 501, after the one-time transfer process of the four-color superimposed ink image of the first sheet to the copy paper, carries out the belting of the Bk ink image of the second sheet on the surface of the area cleaned by the belt cleaning blade 504. transfer printing. After that, the same action as the first one.

The above is the copy mode for obtaining four-color full-color copies. However, in the case of the three-color copy mode and the two-color copy mode, the operation principle is the same as that of the four-color mode. In the case of monochrome copying mode, before the specified number of sheets is completed, only the developing device of the fixed color of the rotary developing unit 400 is set to the developing operation state, and the belt cleaning blade 504 is pressed against the intermediate transfer belt 501 in a continuous state. Copy action.

Next, control of the belt discharge charger 503 for discharging the charge of the intermediate transfer belt 501 after the above-mentioned secondary transfer will be described.

FIG. 4 is a block diagram of a control system including a control unit 900 as a control device for controlling the power erasing conditions of the charger with erasing system 503 described above. In Fig. 4, the control unit 900 is composed of CPU901, ROM902, RAM903, I/O interface 904, etc., the driving motor 508a, the power supply 804 for power elimination, and the mark sensor 905 are connected to the I/O interface 904, and the driving motor 508a and The intermediate transfer belt 501 is connected to the belt drive roller 508 , and the mark sensor 905 is used to detect a mark (not shown) for detecting a rotation position provided on the inner peripheral surface of the intermediate transfer belt 501 .

As the power source 804 for erasing, a device capable of applying a voltage including a DC component and an AC component to the charger with erasing 503 is used. In order to switch the erasing conditions of the charger with erasing 503, at least one of the DC component and the AC component of the applied voltage may be changed. size.

In addition, the ON/OFF timing of the power supply for erasing 804 that applies a voltage to the charger with erasing 503 is set based on the output signal of the mark sensor 905 .

Fig. 5 shows the change of the surface potential of the intermediate transfer belt 501 and the on/off of the charging charger 503 when the full-color copying operation of superimposing the four-color ink image on the intermediate transfer belt 501 is performed continuously for the second time A timing diagram of an example of time. The graph on the upper side of the figure is the surface potential of the intermediate transfer belt 501 measured with a potential sensor at the PTC facing position in FIG. The surface potential of the primary transfer part of the third color and the fourth color. As can be seen from FIG. 5, every time one transfer is performed, a positive charge is applied to the back surface of the intermediate transfer belt 501 from the primary transfer bias roller 507, and the surface potential of the photoreceptor drum side of the intermediate transfer belt 501 faces the direction of negative polarity. get bigger. In particular, when an intermediate transfer belt 501 with a relatively high electrical resistance is used as in this embodiment, temporarily applied charges tend to be held on the intermediate transfer belt 501, and the above-mentioned surface potential rises significantly. In this way, every time a transfer is performed, the surface potential of the intermediate transfer belt 501 becomes larger in the direction of negative polarity. Therefore, it is related to the number of times of one transfer, that is, the number of times the ink images on the intermediate transfer belt 501 are superimposed. The surface potential of 501 is dispersed.

More specifically, as shown in FIG. 5c, the voltage V output from the primary transfer bias roller 507 can be controlled to increase with the number of times the toner image is transferred. According to a specific embodiment of the present invention, when the first toner image, such as a Bk toner image, is transferred from the photoreceptor drum 100 to the intermediate transfer belt 501, the transfer bias of the primary transfer bias roller 507 is controlled by the power supply 801. The voltage output may be 1000 V, and then, when the next toner image in color image formation, for example, a C toner image, is transferred from the photoreceptor drum 100 to the intermediate transfer belt 501, the output from the primary transfer bias roller 507 The printing bias voltage can be increased to 1500V; later, for M and Y ink images, the transfer bias voltage output from the primary transfer bias roller 507 can be increased to 2000V and 2500V respectively. It can be seen that, in the above process of the present invention, the transfer bias voltage output from the primary transfer bias roller 507 can be increased according to the sequence number of the toner image transferred from the photoreceptor drum 100 to the intermediate transfer belt 501 .

Therefore, in this embodiment, the control unit 900 switches the conditions for erasing electricity by the belt erasing charger 503 according to the surface potential of the intermediate transfer belt 501 so that electricity can be uniformly erased. Specifically, the magnitude of the DC component of the output voltage of the power source 803 for power dissipation is controlled and switched according to the number of superimposed ink images on the intermediate transfer belt 501 . When the number of superimposed toner images is large, the above-mentioned direct current component is increased to enhance the power dissipation capability to perform power dissipation. When the number of overlapping toner images is small, the above-mentioned direct current component is reduced to reduce the electricity dissipation capability to eliminate electricity, so that the intermediate transfer belt 501 is not charged with reverse polarity charges.

In addition, when thick paper is used as the copy paper, the thick paper mode is executed, and the drive motor 508a of the belt drive roller 508 is controlled to switch the moving speed of the intermediate transfer belt 501 to about half of that of plain paper. In this way, the moving speed of the intermediate transfer belt 501 becomes slow, and the belt discharge charger 503 is easily discharged. Therefore, in this embodiment, when the travel speed of the intermediate transfer belt 501 is slowed down by implementing the thick paper mode, the DC component of the applied voltage is adjusted to be smaller than that of ordinary paper, and the power dissipation capacity is reduced for power dissipation, so that the power is not lost. The intermediate transfer belt 501 is charged with reverse polarity charges.

As above, according to the present embodiment, even if the transfer times to the intermediate transfer belt 501 are different, causing the surface potential of the intermediate transfer belt 501 before the charge to be discharged to be discrete, it is also possible to switch the charge applied to the intermediate transfer belt according to the transfer times. The magnitude of the voltage (DC component) on the de-energizing charger 503 can uniformly de-energize the intermediate transfer belt 501 . When switching the moving speed of the intermediate transfer belt 501 in the thick paper mode, the surface potential of the intermediate transfer belt 501 before de-energization will be dispersed due to the different moving speeds. In this case, according to the above-mentioned embodiment of the present invention, The intermediate transfer belt 501 can be uniformly decharged. In this way, the above-mentioned uniform electricity removal can be used to transfer the toner image from the photoreceptor drum 100 later.

In the above-described embodiment, the surface potential of the intermediate transfer belt 501 may vary depending on whether the intermediate transfer belt 501 and the secondary transfer charge applying device in the charge applying operation face each other. In this case, it is preferable to switch the magnitude of the voltage (DC component) applied to the belt-discharging charger 503 according to whether the intermediate transfer belt 501 faces the operating secondary transfer charge imparting device, so that the intermediate transfer belt The transfer body is uniformly decharged.

In particular, the secondary transfer belt 601 with high resistance is not used as shown in FIG. 1 , and the secondary transfer bias roller of medium resistance applied with a positive polarity bias is directly sandwiched between the secondary transfer counter roller and the copying process. In the case of paper, the absolute value of the surface potential of the image portion on the intermediate transfer belt 501, that is, the portion facing the secondary transfer bias roller to which a predetermined transfer bias is applied, is lower than that of the non-image portion, and surface potential dispersion tends to occur. . At this time, the magnitude of the voltage (DC component) applied to the charge erasing charger 503 is switched depending on whether the image portion or the non-image portion faces the secondary transfer bias roller to which the transfer bias is applied. For example, when erasing the image portion facing the secondary transfer bias roller to which the transfer bias is applied, the magnitude of the DC component of the voltage applied to the charge erasing charger 503 is switched to be smaller than that of the non-image area. . The switching time can be determined according to the output signal of the above-mentioned mark sensor 905 .

Next, more specific implementation data related to the color copying machine of the above-mentioned embodiment will be described.

An intermediate transfer belt having a thickness of 0.15 mm, a width of 368 mm, and an inner circumference of 565 mm was used as the intermediate transfer belt 501 , and the moving speed of the intermediate transfer belt was set at 200 mm/sec.

The surface layer 501a of the intermediate transfer belt 501 forms an insulating layer with a thickness of about 1 μm, the intermediate layer 501b forms an insulating layer with a thickness of about 75 μm (volume resistivity about 1013 Ωm) made of PVDF (polyvinylidene fluoride), and the base layer 501c A medium-resistance layer (volume resistivity 108-1011Ωcm) made of PVDF (polyvinylidene fluoride) and titanium oxide with a thickness of about 75 μm was formed. The overall volume resistivity of the intermediate transfer belt made of this material was measured to be 107-1012 Ωcm. Each volume resistivity mentioned above was measured by the measuring method described in JISK6911 (Japanese Industrial Standard K6911) by applying a voltage of 100 volts and holding for 10 seconds. In addition, the surface resistivity of the surface layer 501a side of the intermediate transfer belt 501 was measured to be 107-1012 Ω/□ with a resistance measuring device "HighRester IP" manufactured by Yukadenshi. The surface resistivity may be measured by the surface resistivity measuring method described in JIS K6911 other than the above-mentioned resistance measuring device.

A nickel-plated metal roller is used as the primary transfer bias roller 507 , a metal roller is used as the charge dissipating roller 512 , and a metal roller or a conductive resin roller is used as the other rollers. Apply a DC transfer bias of appropriate size to the primary transfer bias roller 507, for example, 1.0 kv is applied to the first color ink image, 1.3-1.4 kv is applied to the second color ink image, and 1.6 kv is applied to the third color ink image. -1.8kv, apply 1.9-2.2kv to the fourth color ink image.

The contact width Wn of the primary transfer portion is set to 10 mm, and the distance L of the contact portion from the downstream end in the belt moving direction to the contact position of the belt discharge brush 513 is set to 7 mm (see FIG. 3 ). A conductive member implanted with carbon-containing resin fibers is used as the above-mentioned neutralizing brush 513 .

A charger with a grid electrode is used as the PTC 502 , and a DC bias voltage having the same charging polarity as that of the toner image on the intermediate transfer belt 501 is applied to the PTC 502 by the PTC power supply 803 . More specifically, a DC voltage controlled to a constant current of -500 μA is applied to the main wire 502 a of the PTC 502 , and a DC voltage set in the range of 0 to 3 kV is applied to the gate electrode 502 b.

The DC component of the voltage applied to the charger 503 with power elimination is set as shown in Table 1 below, the peak-to-peak voltage of the AC component is set to 6KVp-p, and the frequency is 500HZ.

Table 1 Overlap times Applied voltage of charger with discharge (DC component) plain paper thick paper once 300v 220v secondary 400v 280v three times 500v 340v four times 600v 400v

As the secondary transfer bias roller 605, a roller including a surface layer made of conductive sponge or conductive rubber and a core layer made of metal or conductive resin is used, and the constant current is controlled to A transfer bias of 10-20 [mu]A is applied to the roller. As the above-mentioned secondary transfer belt 601 , a belt material formed of PVDF (polyvinylidene fluoride) having a thickness of 100 μm and a volume resistivity of 1013 Ωcm was used.

A discharger that applies only AC voltage or AC+DC voltage from a power source not shown is used as the above-mentioned copy paper discharge charger 606, and a discharger that applies only AC voltage or AC+DC voltage from a power source not shown is used as the above-mentioned Charger 607 with electricity. The cleaning blade 608 is in contact with the secondary transfer belt 601 spanned by the backup roller 604 in an opposite angular direction.

In the above-mentioned embodiment, the use of the photoreceptor drum 100 as an image carrier has been described as an example, but the present invention is also applicable to image carriers of other shapes, for example, it can also be used to stretch between two rollers, endlessly. Moving photoreceptor strips.

In the above-mentioned embodiments, an example of using the intermediate transfer belt 501 as the intermediate transfer body has been described. However, the present invention is also applicable to the use of intermediate transfer bodies of other shapes. In addition, the electrical characteristics (volume resistivity, surface resistivity), thickness, structure (single layer, double layer, ...), material, material, etc. of the above-mentioned intermediate transfer belt 501 can be adjusted according to imaging conditions and the like. One option, use a suitable intermediate transfer belt.

In the above-mentioned embodiment, the description has been made by taking the use of a static elimination brush as an example of the primary transfer section static elimination device in the contact portion of the above primary transfer section, but the present invention is also applicable to the use of other brushes, rollers, etc. The shape member is used as the above-mentioned primary transfer section static elimination device. In addition, the position for eliminating electricity by the above-mentioned electricity eliminating device is not limited to the position shown in the above-mentioned embodiment, and may be located upstream on the primary transfer bias roller 507 in the direction of travel of the intermediate transfer belt. part of the contact part. The static electricity removal position in the contact portion of the transfer portion is not limited to one location, and electricity removal may be at several locations. In this embodiment, the neutralizing brush is grounded, but a bias voltage opposite to the polarity of the transferred charge may be applied within a range that does not affect the transfer charge necessary for the above-mentioned contact portion.

In the above-mentioned embodiments, an example of using the primary transfer bias roller as the primary transfer charge applying device has been described, but the present invention can also be applied to a primary transfer charge applying device having other shapes. In addition, the primary transfer charge may be applied in the contact portion of the primary transfer portion on the downstream side of the discharge position of the primary transfer portion discharge device such as the discharge brush in the moving direction of the intermediate transfer belt.

In the above-mentioned embodiment, the voltage and current of the primary transfer bias applied to the primary transfer charge imparting means such as the above-mentioned primary transfer bias roller 507 are not limited to those described in the above-mentioned embodiment. Appropriate values are set for various imaging conditions.

In the above-mentioned embodiment, an example of using the charge eliminating roller 512 as the pre-primary transfer eliminating device has been described. However, in the present invention, other shaped members such as blades and brushes may be used instead of the roller.

In the above-mentioned embodiments, an example of using the secondary transfer bias roller as the secondary transfer charge imparting device has been described. However, in the present invention, other shaped members such as blades and brushes may be used instead of the roller.

In the above-described embodiment, the secondary transfer belt 601 is used as the transfer material carrier on which the transfer material is placed in the secondary transfer section. However, in the present invention, other shaped members such as cylinders may be used instead of the belt.

In the above-mentioned embodiment, the photoreceptor drum 100 is negatively charged, and the developer using the two-component developer and the reverse development method are used. However, the present invention is not limited to the charging potential of the above-mentioned photoreceptor drum 100 . Furthermore, the same applies to developing devices using a single-component developer and using a normal developing method.

The second embodiment of the present invention will be described below, and the description of the same parts as the first embodiment will be omitted.

As shown in FIG. 6, around the intermediate transfer belt 501, a pre-transfer charger 502 as a pre-transfer charging device and a secondary transfer belt 601 as a transfer material carrier of a paper transfer unit 600 are arranged facing each other. , a secondary transfer bias roller 605 as a secondary transfer charge imparting device, a brush roller 514 as a conductive brush member serving both as an intermediate transfer body de-energizing device and an intermediate transfer body cleaning device, as a lubricant The lubricant coating brush 505 and the like of the coating device.

The conductive brush roller 514 de-energizes and cleans the intermediate transfer belt 501 after the second transfer, and is applied with the same polarity as the surface potential of the intermediate transfer belt 501 after the second transfer by the power source 804 for de-energization. the DC voltage. In order to improve the power dissipation efficiency, the AC voltage can also be superimposed on the DC voltage. In addition, the above-mentioned conductive brush roller 514 can be switched to be in contact with or separated from the intermediate transfer belt 501 by a not-shown take-off mechanism.

Control above-mentioned brush roller 514 to connect or disconnect in the following manner. For example, when forming a full-color image, the brush roller 514 is brought into contact with the intermediate transfer belt 501 after at least one cycle of the intermediate transfer belt 501 after the secondary transfer is completed. When the full-color image is repeatedly formed, after the secondary transfer is completed, the brush roller 514 is brought into contact with the front end of the following toner image before it reaches the discharge cleaning position. When forming a single-color image, the brush roller 514 is brought into contact with the intermediate transfer belt 501 after at least one cycle of the intermediate transfer belt 501 after the primary transfer is completed. When the single-color image is repeatedly formed, after the primary transfer is completed, the brush roller 514 is brought into contact with the front end of the following toner image before reaching the cleaning position of electricity removal.

In this embodiment, after the toner image is transferred to the above-mentioned copy paper, the surface of the above-mentioned intermediate transfer body 501 is de-charged and cleaned by the brush roller 514. pressed against the intermediate transfer belt 501.

When copying is repeated, the operation of the color scanner and the formation of an image on the photoreceptor drum 100 follow the image forming process of the fourth color (Y) of the first sheet, and the first color (Bk) of the second sheet is performed at a predetermined time. Image forming process. After the intermediate transfer step, the second sheet of the Bk ink image is transferred to the belt on the surface of the cleaned area of the brush roller 514 . After that, the same action as the first one.

The above is the copy mode for obtaining four-color full-color copies. However, in the case of the three-color copy mode and the two-color copy mode, the operation principle is the same as that of the four-color mode. In the case of monochrome copying mode, before the specified number of sheets is completed, only the developer of the fixed color of the rotary developing unit 400 is set to the developing operation state, and the copying operation is continuously performed while the brush roller 514 is pressed against the intermediate transfer belt 501 .

According to this embodiment, only one brush roller 514 is brought into contact with the intermediate transfer belt 501, so that the intermediate transfer belt 501 can be deionized and cleaned. In comparison, cost reduction can be realized.

In the past, a corona discharger was used as the neutralization device for the intermediate transfer body. Although the surface potential of the intermediate transfer belt was around 0V immediately after the neutralization, the potential of the polarity before the neutralization appeared after a while, but in this embodiment Among them, if the structure of applying a voltage to the brush roller 514 to eliminate electricity is adopted, the above-mentioned potential of the polarity before electricity elimination will not appear, and a good electricity elimination effect can be obtained.

In this embodiment, the brush roller 514 is used as the conductive brush member for de-energizing and cleaning the intermediate transfer belt 501, but as shown in FIG. Extends in the axial direction of the cleaning counter roller 511 . In such a structure, it is preferable to dispose or bring a metal roller 517 into contact with the brush 516a as shown in FIG. A voltage higher than that of the member 516 is applied to the metal roller 517, and the toner and the like adhering to the brush 516a of the brush member 516 are adsorbed to the surface of the metal roller 517 by electrostatic force, and the adhering matter on the surface of the metal roller 517 is passed through a scraper (not shown) or the like. Recycle.

In the above-mentioned embodiment, the discharge condition of the brush roller 514 may be switched according to the surface potential of the intermediate transfer belt 501 after the secondary transfer, so as to uniformly discharge the charge on the intermediate transfer belt 501 . For example, the magnitude of the DC component of the output voltage of the power source 804 for power dissipation is switched in accordance with the number of superimposed toner images on the intermediate transfer belt 501 .

In the specific example of this embodiment, a brush roller 514 replaces the charger 503 and the belt cleaning blade 504 in the specific example of the first embodiment, and other conditions are the same as the specific example of the first embodiment. The permanent brush fiber is planted on the metal shaft body, and serves as the brush roller 514 for destaticizing and cleaning the intermediate transfer belt 501 after the secondary transfer. Applying a DC voltage (positive voltage) of opposite polarity to the surface potential of the intermediate transfer belt 501 before de-energization, and using a conductive brush roller 514 that applies the predetermined voltage, even if a brush roller 514 including a high resistance In the case of an intermediate transfer belt 501 with a multi-layer structure of the intermediate layer 501b, the phenomenon that the discharged charges will not reappear on the surface will not occur, and the intermediate transfer belt 501 after the secondary transfer can be depleted well. electricity.

Next, a third embodiment of the present invention will be described. Please refer to FIG. 1 for a schematic configuration diagram of an image forming section of a main part of a color copier related to this embodiment.

Next, the PTC502 as a pre-transfer charging device will be described.

The toner image on the intermediate transfer belt 501 transferred from the photoreceptor drum 100 may have a discrete state of charge because it includes halftone parts and full tone parts, or parts with different superimposed amounts of toner. In addition, there is a possibility that the charge amount may vary in the toner image on the intermediate transfer belt 501 after the primary transfer due to the peeling discharge generated in the gap adjacent to the downstream side of the primary transfer portion in the intermediate transfer belt moving direction. Phenomenon. Such dispersion in the amount of charge within the same ink image reduces the transfer margin of the secondary transfer section.

Therefore, in this embodiment, by uniformly charging the ink image before the PTC 502 is transferred to the copy paper, the problem of discrete charge quantity in the same ink image is solved, and the transfer tolerance of the secondary transfer is improved.

As described above, according to this embodiment, by uniformly charging the toner image on the intermediate transfer belt 501 transferred from the photoreceptor drum 100, even if the internal charging of the toner image on the intermediate transfer belt 501 is discrete, The transfer characteristics of each portion of the toner image on the intermediate transfer belt 501 are substantially constant. Therefore, it is possible to stably transfer the toner image while suppressing a decrease in the transfer margin when transferring to copy paper.

In the above-described embodiments, the charge amount charged at the PTC 502 varies according to the moving speed of the intermediate transfer belt 501 to be charged. For example, if the moving speed of the intermediate transfer belt 501 is slow, it takes longer for the same part of the toner image on the intermediate transfer belt 501 to pass through the charging area of the PTC 502 , and the charged amount increases. On the contrary, when the moving speed of the intermediate transfer belt 501 is high, the charge amount of the toner image on the intermediate transfer belt 501 decreases. Therefore, when the moving speed of the intermediate transfer belt 501 changes while the toner image on the intermediate transfer belt 501 passes the charging position of the PTC 502, it is preferable to control the PTC according to the moving speed so that the charging amount of the toner image does not change on the way.

In the above embodiment, in the color image forming apparatus, when thick paper is used for the copy paper, by selecting and executing the thick paper mode, the copying speed (the number of copies per minute) is not reduced as much as possible, and the image forming operation of the entire apparatus is switched. Action speed, so that the secondary transfer to the copy paper and the fixing thereafter are carried out well. Specifically, after the ink image rear end on the photoreceptor drum 100 is transferred on the intermediate transfer belt 501, and the intermediate transfer Before the front end of the ink image on the printing belt 501 reaches the secondary transfer part, switch the moving speed of the intermediate transfer belt 501 to about 1/2. If such a thick paper mode is implemented, the ink image on the intermediate transfer belt 501 passes through During the charging position of the PTC 502, the moving speed on the intermediate transfer belt 501 changes. Therefore, it is preferable to control the PTC according to the moving speed of the intermediate transfer belt 501 so that the charging amount of the ink image does not change on the way.

8 is a block diagram of a control system including a control unit 900 as a control device for controlling the gate voltage of the PTC 502 based on the moving speed of the intermediate transfer belt 501 . In Fig. 8, the control unit 900 is composed of CPU901, ROM902, RAM903, I/O interface 904, etc., the drive motor 508a, PTC power supply 803, mark sensor 905, etc. are connected to the I/O interface 904, and the drive motor 508a is connected to the middle The belt drive roller 508 of the transfer belt 501 is connected, and the mark sensor 905 detects a mark (not shown) for detecting a rotation position provided on the inner peripheral surface of the intermediate transfer belt 501 .

FIG. 9 shows a time chart of the drive motor for the intermediate transfer belt and the gate voltage control of the PTC in the above-mentioned thick paper mode. The copying operation starts at the time indicated by symbol A in the figure, and the front end of the ink image on the intermediate transfer belt 501 reaches the PTC 502. Before the electrified position (symbol B), the electrification performed by PTC502 begins. Based on the result of the mark sensor 905 detecting the mark on the intermediate transfer belt, it is judged whether or not the time before the leading edge of the toner image on the photoreceptor drum 100 reaches the secondary transfer portion (symbol C). At this time, the belt drive motor 508a is controlled to control the moving speed of the intermediate transfer belt 501 to approximately 1/2. At the same time, the PTC power supply 803 is controlled so that the gate voltage applied to the gate 502b of the PTC 502 is approximately 1/2, thereby reducing the chargeability. In this way, the charge amount of the ink image on the intermediate transfer belt 501 charged by the PTC 502 does not change as the moving speed of the intermediate transfer belt decreases. When the trailing end of the toner image on the intermediate transfer belt 501 passes the charged position of the PTC 502 (symbol D), the application of the bias voltage to the PTC 502 is stopped.

As described above, when the above-mentioned thick paper mode or the like is executed, even if the moving speed of the intermediate transfer belt changes while the PTC 502 is charging the toner image on the intermediate transfer belt 501, the entire toner image on the intermediate transfer belt 501 can be charged. Uniform electrification can reliably prevent reduction in transfer margin.

Claims (11)

1. An image forming device comprising: An intermediate transfer body carrying an ink image transferred from an image carrier; a primary transfer charge imparting device for imparting charges for transferring an ink image from an image carrier to an intermediate transfer body to the intermediate transfer body; An intermediate transfer body de-energizing device, which imparts a de-energizing charge to the intermediate transfer body, so as to de-energize the surface of the above-mentioned intermediate transfer body that has transferred the ink image on the transfer material; It is characterized in that the voltage of the above-mentioned dissipated charges is proportional to the surface potential of the intermediate transfer body. 2. The image forming apparatus according to claim 1, wherein: Superimposing and transferring the ink image formed on the above-mentioned image carrier several times on the above-mentioned intermediate transfer body; The voltage of the neutralized charges obtained by the neutralizer for the intermediate transfer body is switched according to the number of transfers of the toner image to the intermediate transfer body. 3. The image forming apparatus according to claim 1, wherein the voltage of the charge applied by the primary transfer charge applying means is switched according to the number of transfers of the ink image to the intermediate transfer body. 4. The image forming apparatus according to claim 1, wherein: A secondary transfer charge imparting device for imparting charges for transferring an ink image from the intermediate transfer body to the transfer material to the transfer material carrier is provided; The voltage of the neutralized charges obtained from the above-mentioned intermediate transfer body neutralizing means is switched according to whether or not the aforementioned intermediate transfer body faces the aforementioned secondary transfer charge imparting means during the charging operation. 5. The image forming apparatus according to claim 1, wherein: Equipped with a moving speed control device to switch the moving speed of the intermediate transfer body according to the thickness of the transfer printing material; The voltage of the neutralized charges obtained from the intermediate transfer body neutralizer is switched according to the moving speed of the intermediate transfer body. 6. The image forming apparatus according to any one of claims 1-5, characterized in that: Using a corona eliminator as the above-mentioned intermediate transfer body eliminator, applying a voltage including a DC component and an AC component; The above-mentioned extinguishing charge changes the size of the DC component applied to the above-mentioned corona eliminator. 7. The image forming apparatus according to claim 1, wherein the intermediate transfer body is a belt having at least first and second layers. 8. The image forming apparatus according to claim 1, wherein: a conductive brush member, the brush member is in contact with the above-mentioned intermediate transfer body after the ink image is transferred to the above-mentioned transfer material, and performs electricity removal and cleaning of the intermediate transfer body; A power source that applies a bias voltage of a polarity opposite to the surface potential of the intermediate transfer body to the conductive brush member. 9. The image forming apparatus according to claim 8, wherein a rotatable conductive brush roller is used as the conductive brush member. 10. The image forming apparatus according to claim 1, further comprising a pre-transfer charging device for charging the ink image on the intermediate transfer body before being transferred to the transfer material. 11. The image forming apparatus according to claim 10 , wherein a control device is provided for controlling said pre-transfer charging device based on a moving speed of the surface of the intermediate transfer body passing through the charging position of said pre-transfer charging device. The output of the transfer charging device.

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