JP3007479B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention generally relates to an electrophotographic or electrostatic recording type image forming apparatus.
The recording material is electrostatically attracted to and held on a recording material carrier such as a transfer sheet, and an electric field is applied to the recording material, whereby a visible image (toner image) formed on the image carrier is formed. The present invention is suitably embodied in a color image forming apparatus such as a multicolor electrophotographic copying machine or a color printer which obtains a color image by superimposing and transferring the image on a recording material.

[0002]

2. Description of the Related Art FIG. 24 schematically shows a conventional digital full-color electrophotographic copying machine which is an example of a color image forming apparatus. In this example, the image carrier 1 serving as a photosensitive drum rotates in the direction of the arrow shown in the figure, and is uniformly charged by the charger 2. Next, image exposure is performed by a laser beam E modulated by an image signal of a document (not shown), and the photosensitive drum 1 is exposed.
An electrostatic latent image is formed thereon. This latent image is generated by a predetermined developing device fixed at a developing position of the rotary developing device 3 in advance.
Color development is performed to form a toner image. This toner image is fed from a recording material cassette (not shown), and is transferred to a recording material 6 carried and conveyed on a transfer drum 8. The color image is formed on the recording material 6 by repeating such an image forming process a desired number of times.

Referring to FIG. 24, a description will be given of a high-voltage power supply and related members around the transfer drum 8, and an outline of the operation thereof, in such a color copying machine.

Prior to the above-described copying operation, first, the inner static eliminator 15 and the outer static eliminator 14 operate. The high-voltage power supplies HV6 and HV5 connected to the inner static eliminator 15 and the outer static eliminator 14 are both AC power supplies, and a recording material carrier that carries and conveys the recording material 6 wound around the outer circumference of the transfer drum 8.
That is, the transfer sheet 81 is neutralized to approximately 0V.

Next, when the feeding of the recording material 6 is started, the suction charger 10a is operated by the high voltage power supply HV1. In this case, the power supply HV1 has the same polarity as the polarity of the transfer charger 4 described later. At this time, the opposing roller 10b
And the recording material 6 is attracted to the transfer sheet 81.

Next, when the recording material 6 is conveyed to the transfer position, the transfer charger 4 starts discharging by the high voltage power supply HV2 to transfer the first color toner image. Thereafter, when the toner images of the second to fourth colors are transferred with the rotation of the transfer drum 8, the recording material 6 is separated from the transfer drum 8 by the separation claws 18. At this time, the inner static eliminator 15 and the outer static eliminator 14 operate, and the transfer sheet 81 is also neutralized.

In this conventional example, a system in which a bias having a polarity opposite to that of the transfer charger 4 is applied to the adsorption charger 10a has been proposed.

As another prior art, there has been proposed a technique for simultaneously removing electricity from the transfer belt 8 and adsorbing the recording material 6 in a full-color copying machine using a transfer belt as shown in FIG. As shown in FIG. 26, at the suction position,
An AC bias power supply 80 is connected to the corona discharger 59,
Further, an AC bias power supply 81 is
And a DC bias power supply 82 are connected.

[0009]

In the configuration shown in FIG. 24, when a bias having the same polarity as the transfer charger 4 (that is, a polarity opposite to the normal charging polarity of the toner) is applied by the suction charger 10a. In some cases, the transfer sheet 81 may be charged up during multiple transfer, and the transfer of the fourth color may not be performed particularly well. Conversely, if the bias of the polarity opposite to that of the transfer charger 4 (that is, the same polarity as the normal charge polarity of the toner) is applied by the adsorption charger 10a, the problem of the charge-up can be solved, but the transfer of the first color is performed. A new problem that becomes unstable. This is for the following reasons. This will be described with reference to FIG.

Generally, the total amount of current i ₁ discharged from the discharge wire 102 in the corona discharger 100 is
The current i ₂ flows into the current body 04 and the current i ₃ is injected into the member 106 to be charged. That is, i ₁ = i ₂ + i ₃ . Further, ρ = i ₃ / i ₁ and ρ is defined as charging efficiency. However, the value of ρ greatly depends on the environment and the surface potential V _S of the member 106 to be charged. For example, if the high-voltage power source HV has a positive discharge, ₊ a [rho when V _S is positively charged [rho, the [rho when V _S is negatively charged [rho _- becomes that relationship _- to the [rho ₊ <[rho and . In other words, the charging efficiency is higher when the charged member 106 is charged to the polarity opposite to the polarity to be discharged. However, when there is an environmental change or the like, the amount of injected electric charge is originally large, so that the change becomes large.

In the example of the full-color copying machine using the transfer belt 8 shown in FIG. 25, the cost can be reduced by simultaneously performing the charge elimination and the adsorption charge. However, it depends on the polarity of the DC bias to be superimposed. , Charge-up problems and 1
The problem of instability of color transfer has not been solved.

Accordingly, it is an object of the present invention to solve the problem of charge-up of a recording material carrier during transfer, minimize the influence of the potential of the recording material carrier, and perform good and stable transfer. It is an object of the present invention to provide a low-cost image forming apparatus with a simple configuration, which can always obtain a high-quality image.

[0013]

The above object is achieved by an image forming apparatus according to the present invention. In summary, the present invention provides:
An image carrier that carries the toner image, a recording material carrier that carries the recording material, and a recording material of the recording material carrier that is provided on a side of the recording material carrier opposite to a side on which the recording material is carried. Transfer charging means for applying a charge having a polarity opposite to the normal charge polarity of the toner to the area where the toner image is carried, and transferring the toner image on the image carrier to the recording material carried on the recording material carrier. The transfer charging means, and before transferring the toner image by the transfer charging means,
A charging unit for charging the area of the recording material carrier to the same polarity as the charging polarity; and a constant current control for applying a current from the transfer charging unit to the area of the recording material carrier charged by the charging unit. And a control unit for controlling the image forming apparatus.

According to one embodiment of the present invention, the charging means includes an inner charging means and an outer charging means provided so as to face inward and outward with the recording material carrier interposed therebetween. The means charges the side of the recording material carrier opposite to the side on which the recording material is carried to the same polarity as the charging polarity, and the outer charging means comprises a side of the recording material carrier on which the recording material is carried. Or a voltage having the same polarity as the charging polarity is applied to the inner charging means, and a voltage having a polarity opposite to the charging polarity is applied to the outer charging means. You. Further, the inner charging means and the outer charging means can apply a voltage obtained by superimposing a DC voltage and an AC voltage.

According to another embodiment of the present invention, the inner charging means includes a contact member which is in contact with the side of the recording material carrier opposite to the side on which the recording material is carried and is electrically grounded, A voltage having a polarity opposite to the charging polarity is applied to the outer charging means. According to another embodiment of the present invention, the outer charging means includes a contact member which is in contact with a side of the recording material carrier on which the recording material is carried and is electrically grounded, and wherein the inner charging means is provided. Is applied with a voltage having the same polarity as the charging polarity.

According to another embodiment of the present invention, the charging means may include a corona charger. According to another embodiment of the present invention, before the recording material is carried on the recording material carrier, the charging unit charges the area of the recording material carrier. According to another embodiment of the present invention, the charging unit electrostatically attracts a recording material to the recording material carrier. According to another embodiment of the present invention, during transfer of the toner image, the transfer charging unit is in contact with the area of the recording material carrier, and the transfer charging unit may include a brush. According to still another embodiment of the present invention, the transfer charging unit includes a corona charger, and the image forming apparatus includes a detection unit that detects a current flowing through a shield of the corona charger. At the time of transferring the toner image, the control means can control the current flowing through the wire of the corona charger based on the detection result by the detection means.

According to another embodiment of the present invention, the step of transferring the toner image in the form of an image carrier onto a recording material carried on the recording material carrier is repeated, so that a plurality of color toner images are formed on the recording material. Images can be superimposed and formed. Further, a plurality of the image carriers may be provided to carry the toner images of the plurality of colors, respectively.

[0018]

Next, an image forming apparatus according to the present invention will be described in more detail with reference to the drawings.

Embodiment 1 FIG. 1 is a block diagram showing a first embodiment of an image forming apparatus according to the present invention, in which the present invention is applied to a digital full-color electrophotographic copying machine.

The outline of the operation of the copying machine will be described with reference to FIG. 1. An image carrier 1 serving as a photosensitive drum rotates in the direction of the arrow in the figure and is uniformly charged by a charger 2. Next, image exposure is performed by a laser beam E from an exposure device 17 modulated by an image signal of a document (not shown), and an electrostatic latent image is formed on the photosensitive drum 1. This latent image is supplied to a rotary developing device 3 equipped with a yellow developing device 3a, a magenta developing device 3b, a cyan developing device 3c, and a black developing device 3d.
The first color is developed by a predetermined developing device (yellow developing device 3a in FIG. 1) fixed at a developing position in advance to form a toner image.

On the other hand, the recording material 6 fed from the recording material cassette 60 via the paper supply roller 13a and the paper supply guides 13b and 13c is extruded in the direction along the transfer drum 8. At this time, the suction roller 10b is driven by a driving source (not shown).
As a result, a bias having a polarity opposite to that of the later-described transfer, that is, a negative bias in this embodiment, is applied to the attraction charging brush 10a almost simultaneously. Thereby, the recording material 6 is attracted to the transfer drum 8.

The transfer drum 8 rotates in the direction shown by the arrow in synchronization with the photosensitive drum 1, and the toner image developed by the yellow developing unit 3a is transferred to the recording material 6 by the transfer charging brush 4 at the transfer position. Transcribed. The transfer drum 8 continues to rotate, and prepares for transfer of the next color, magenta in this embodiment.

The photosensitive drum 1 includes a cleaning member 5.
And then charged again by the charger 2 and exposed in the same manner as described above by the next magenta image signal. During this time, the developing device 3 rotates and the magenta developing device 3b is fixed at a predetermined developing position to perform a predetermined magenta development, and the magenta toner image is transferred onto the recording material 6 on the transfer drum 8 in an overlapping manner. .

Subsequently, the same process as described above is performed for cyan and black, respectively. When the transfer of four colors to the recording material 6 is completed, the recording material 6 is separated from the transfer drum 8 by the separation claws 18. Then, the sheet is sent to the fixing device 7 by the transport belt, and a series of full-color printing operations is completed, thereby forming a full-color print image.

FIG. 2 is a schematic diagram of a copying machine showing the transfer drum 8, the photosensitive drum 1 and the high-voltage power supply HV related thereto in FIG.

When the recording material 6 is fed along the transfer drum 8, a high-voltage power supply HV1 is supplied to the suction charging brush 10a.
More DC bias is applied. The high-voltage power supply HV1 is a constant-voltage transformer, and its output value is -3 to-in this embodiment.
It was set to 5 KV. When the recording material 6 is fed to the transfer drum 8, the attracting roller 10 b comes into contact with the transfer drum 8, so that a positive charge of the opposite polarity is induced on the surface of the recording material 6. As a result, the recording material 6 is electrostatically attracted to the transfer drum 8. The charge model at this time is shown in FIG. The recording material carrier that supports and conveys the recording material 6, that is, the transfer sheet 81 wound around the transfer drum 8 in this embodiment is a dielectric sheet having a volume resistivity of about 10 ¹⁴ Ωcm or more. In this example, a film in which carbon was dispersed in PC (polycarbonate) and having a thickness of about 150 μm and a volume resistivity of about 3 × 10 ¹⁶ Ωcm was used.

Next, first transfer of Y (yellow) toner of the first color is performed on the recording material 6 carried on the transfer sheet 81. At this time, the transfer charging brush 4 is supplied with DC voltage from the high voltage power supply HV2. A bias is applied. The high voltage power supply HV2 is a constant current transformer, and the output value is set to about 15 μA in this embodiment.

FIG. 3B shows a charge model after the transfer of the first color Y toner image. The Y toner (minus) has been transferred to the surface of the recording material 6, and the recording material 6 is stabilized by receiving charge injection from the atmosphere.

Next, transfer of M (magenta) toner of the second color is performed. At this time, similarly, a DC bias is applied to the transfer charging brush 4 from HV2, but in the present embodiment, the output value was similarly set to about 15 μA. FIG.
(C) is a charge model after transfer of the second color.

Similarly, the toners of the third color C (cyan) and the fourth color Bk (black) are sequentially transferred, and the charge models at this time are shown in FIGS. 3D and 3E, respectively.

Recording material 6 after transfer of four color toner images
Is separated from the transfer drum 8 by the separation claw 18 as described above. On the other hand, at the time of continuous copying, the next recording material 6 is immediately fed, but the operation is repeated as described above. The charge model is also shown in FIG. 3 as (a) → (b) →
The cycle becomes (c) → (d) → (e) → (a).

The present inventors measured the surface potential of the back surface of the transfer sheet 81 at a position downstream of the suction position in the rotation direction. FIG. 4 shows the results. The vertical axis indicates the surface potential of the back surface of the transfer sheet 81, and the horizontal axis indicates time. Immediately after the suction charging, the back surface of the transfer sheet 81 is set to about −4 KV, which is almost equal to the bias value applied to the charging brush 10 a for suction. Further, when the transfer charge is applied for each color, the potential is sequentially increased.

As can be seen from the measurement results, the transfer sheet 81 is charged in the opposite direction to that during the transfer in the adsorption step, so that the transfer sheet 81 does not charge up even in continuous copying, and can be used stably and repeatedly. it can.

In this embodiment, the structure of the attraction charging means is the same as that shown in FIG.
To FIG. 9. That is, instead of the suction roller 10b, a suction charging brush 10b similar to the suction charging brush 10a can be used (FIGS. 6, 7, and 9).
10b is connected to a high voltage power supply HV having a predetermined polarity or grounded.

As described above, in this embodiment, the transfer sheet 81
In addition to reducing the amount of charge-up, the transfer charging brush 4, that is, a contact such as a conductive brush in this embodiment, is used for transfer, which makes it difficult to perform conventional corona transfer. It is now possible to carry out the transfer step.

The conditions of the full-color copying machine used in this embodiment were as follows.

That is, the photosensitive drum 1 is O mm having a diameter of 80 mm.
Using a PC photoreceptor, the transfer drum 8 had a diameter of 160 mm, and the process speed was 160 mm / sec. The developer used was a toner having a negative charge, and an image was formed by reversal development.

Embodiment 2 In the first embodiment, a contact (conductive brush), that is, a charging brush 10a for suction was used to attract the recording material 6 to the transfer drum 8, but a corona discharger was used. The same effect can be obtained by using.

FIG. 10 is a schematic structural view showing a second embodiment of the image forming apparatus according to the present invention.

According to this embodiment, the suction charger 10a
Is connected to a DC bias power supply HV3. The power supply HV3 outputs the power in synchronization with the feeding of the recording material 6. The power supply HV3 may be either a constant current or a constant voltage, but in the case of the present embodiment, a transformer based on constant current control was used. The distance between the charging wire of the adsorption charger 10a and the transfer sheet 81 is approximately 10 mm, and the opening width of the shield plate is approximately 20 mm.
Met. Further, the output was approximately 300 μA.

The structure of the adsorption charging means using a corona discharger is the same as that shown in FIG.
Configurations as shown in FIGS. 11B and 11C are also possible. That is, a corona discharger can be used instead of the suction roller 10b (FIG. 11B), and a charging brush for suction is used instead of the suction charger 10a.
A corona discharger can be used instead of Ob (FIG. 11C).

Embodiment 3 In the first embodiment, a contact (conductive brush), that is, a transfer charging brush 4 was used to transfer the toner image to the recording material 6. A similar effect can be obtained by using a feedback corona discharger capable of controlling the amount of current flowing.

FIG. 12 is a schematic structural view showing a third embodiment of the image forming apparatus according to the present invention.

The transfer corona discharger 41 is connected to a DC bias power supply HV4, and outputs the data in synchronization with the transfer timing. An ammeter is connected to the shield plate so that the current flowing to the shield plate of the corona discharger 41 for transfer can be monitored. Details are shown in FIG.

The purpose of the construction of this embodiment is that the transfer sheet 8
The purpose is to control the current i ₃ flowing in one direction by monitoring the current i ₂ flowing in the shield plate.
In other words, by using the relationship i ₃ = i ₁ −i ₂ and controlling i ₁ via the CPU while measuring i ₂ , i ₃ can be controlled as a result.

In this embodiment, the power supply HV4 uses a transformer controlled by a constant current. The distance between the charging wire and the transfer sheet 81 was 8 mm, and the opening width of the shield plate was approximately 20 mm. Further, the output range of the power supply HV4 is 0 to
9 KV, 0-500 μA.

Table 1 shows an example of the attraction and transfer output for obtaining a proper image. From Table 1, in the multiple transfer, the transfer sheet direction current i ₃ is an important factor for determining the transfer (transfer efficiency), and particularly when the corona discharger is used, the transfer sheet direction current i ₃ is constant. It can be seen that in order to maintain the current i ₃ , the total current i ₁ needs to be gradually increased.

[0048]

[Table 1]

The most significant effect of the first to third embodiments is that the inner static eliminator 15 and the outer static eliminator 14 are not required as shown in the configuration of the conventional apparatus shown in FIG. By using a bias having a polarity opposite to that of the charging (the same polarity as the toner), good multiple transfer can be performed without charging up the transfer sheet 81 even during continuous copying. That is, by simplifying the transfer configuration, it is possible to realize stabilization and cost reduction. Further, by providing a transfer method capable of controlling the amount of transfer current in the transfer sheet direction, that is, a contact transfer using a conductive brush or a corona discharge device using feedback control, stable multiple transfer can be performed.

In each of the above embodiments, a DC power supply has been described as an example of a high-voltage power supply. However, even if charging is performed with AC (AC) + DC (DC), it does not depart from the concept of the present invention. Absent.

Embodiment 4 FIG. 14 shows a fourth embodiment of the image forming apparatus of the present invention, and shows an embodiment in which the present invention is applied to a digital full-color electrophotographic copying machine. The operation of this copying machine is substantially the same as that of the first embodiment shown in FIG. 1, but the method of carrying the recording material 6 on the transfer drum 8 is different. A brief description will be given.

The paper feed roller 13 from the recording material cassette 60
a, the recording material 6 fed via the paper feed guides 13b and 13c is extruded in a direction along the transfer drum 8.

As shown in FIG. 15, the transfer drum 8 is provided with a gripper 82 for gripping the recording material 6, and the recording material 6 fed to the transfer drum 8 is driven by a driving source (not shown). ) Is gripped by the gripper 82 driven by the gripper. As a result, the recording material 6 is carried on the transfer drum 8 and transported to the transfer position.

The recording material 6 carried on the transfer drum 8
After the multi-transfer of four colors is completed by the above-described series of operations, the outside-separation charger 14 and the inside-separation charger 15 operate,
Further, the separation claw 18 is operated to separate the transfer drum 8 from the transfer drum 8, and is sent to the fixing device 7 by a transport belt, thereby completing a series of full-color printing operations and obtaining a full-color print image.

FIG. 16 is a schematic diagram showing the transfer drum 8, the photosensitive drum 1 and the high-voltage power supply HV related thereto in the copying machine shown in FIG.

As described above, the recording material 6 is transferred to the transfer drum 8
The recording material 6 is gripped by the gripper 82 and rotated to the transfer position. A DC bias is applied to the transfer charging brush 4 from the high voltage power supply HV2 in synchronization with the recording material 6 coming to the transfer position. The power supply HV2 is a constant current transformer in this embodiment, and the output value is set to approximately 15 μA.

Further, when the transfer of the second to fourth colors is performed under the same conditions, next, the high voltage power supplies HV5 and HV6 output,
The separation inner charger 15 and the separation outer charger 14 start discharging. The power supply HV6 has a polarity opposite to that of the transfer (the same polarity as the toner). In the case of the present embodiment, the power supply HV6 is a constant current transformer and is set at approximately -300 μA. The power supply HV5 has the same polarity as the transfer (the polarity opposite to that of the toner). In this embodiment, the power supply HV5 is a constant current transformer and is set to approximately 300 μA. Thereafter, the recording material 6 is immediately separated from the transfer drum 8 by the separation claws 18.

In this embodiment, a feedback corona discharger as shown in FIG. 13 may be used instead of the transfer charging brush 4.

In addition, just before the separation position of the recording material, static elimination was performed by using a pair of corona dischargers 14 and 15 provided with an AC power supply. However, as shown in FIG. A negative charge may be injected into the back surface of the transfer sheet 81 using a grounded contact (conductive brush) 15.

As will be understood from the above description, in this embodiment, as described with reference to FIG.
The cycle of the charge model is repeated, and the same operation and effect as in the first embodiment can be obtained. As a result, also in this embodiment,
During continuous copying, it is possible to avoid charge-up of the transfer sheet and perform excellent multiple transfer.

Fifth Embodiment FIG. 18 is a block diagram showing a fifth embodiment of the image forming apparatus according to the present invention, and includes four photosensitive drums similar to those of the full-color electrophotographic copying machine shown in FIG. 1 shows a digital full-color electrophotographic copying machine. Hereinafter, an outline of the operation of the copying machine will be described.

In FIG. 18, first, second, third and fourth image forming units Pa, Pb and Pc are provided in the main body of the copying machine.
And Pd are provided side by side, and images of different colors are formed through processes of latent image, development, and transfer.

The image forming units Pa, Pb, Pc, and Pd each have a dedicated image carrier, that is, the photosensitive drums 1a, 1b,
1c, 1d, and the image forming units Pa, Pb, Pc,
Photosensitive drums 1a, 1b, 1c, 1d formed of Pd
The upper toner image is transferred onto a recording material 6 carried and conveyed on a recording material carrier 8 disposed adjacent to each image forming unit. In this embodiment, the recording material carrier 8 is a transfer belt, and is stretched between the drive roller 12 and the support roller 11. After the transfer, the image on the recording material 6 is heated and pressed by the fixing unit 7 to be fixed.

More specifically, the formation of a toner image on each of the photosensitive drums 1a, 1b, 1c, and 1d by each image forming unit is performed by a charger 2a disposed on the outer periphery of the photosensitive drum.
2b, 2c, 2d, the photosensitive drums 1a, 1b, 1c,
1d is uniformly charged, and the laser beam exposure device 17 scans an image signal to form a latent image. This latent image is stored in a developing device 3 having different color developers.
a, 3b, 3c, and 3d,
A toner image is formed on a, 1b, 1c, and 1d.

On the other hand, the recording material 6 is fed from the recording material cassette 60 to the transfer belt 8 via the registration rollers 13.

The transfer belt 8 is a dielectric resin film such as a polyethylene terephthalate resin film sheet (PET sheet), a polyvinylidene fluoride resin film sheet, or a polyurethane resin film sheet. A belt that is joined and joined to form an endless shape, or a seamless (seamless) belt is used. In the case of a belt having no seams, not only is it difficult to produce a belt having uniform physical properties, but it is not suitable in terms of cost, etc., for mass production such as a belt having a stable circumference and production time. On the other hand, in the case of a belt having a seam, when forming an image on the seam position, changes in physical properties such as unevenness and resistance value of the seam portion are inevitable, and forming an image on the seam disturbs the image. In general, in order to obtain high image quality, a means for detecting a seam position (not shown) is provided, and an image is not formed on the seam.

When the recording material 6 is conveyed from the registration roller 13 onto the transfer belt 8, the attraction charger 10a operates, and the recording material 6 is attracted onto the transfer belt 8.

The toner image on the photosensitive drum 1a is transferred to the recording material 6 under the action of the transfer charging brush 4a. The recording material 6 includes second, third, and fourth image forming units Pb,
Pc and Pd, and each photosensitive drum 1b, 1c,
The toner image on 1d is overlaid and transferred.

The recording material 6 on which an image has been formed by the fourth image forming unit Pd is separated from the transfer belt 8 and is conveyed to the fixing unit 7.

After the transfer, the photosensitive drums 1a, 1b, 1c, 1
The developer remaining on the photosensitive drum cleaning part 5a
It is removed by 5b, 5c and 5d, and is ready for the subsequent latent image formation. The developer remaining on the transfer belt 8 is neutralized by the belt static eliminator 9 to remove the electrostatic attraction force, and is then scraped off by the rotating fur brush 16.

FIG. 19 shows the transfer belt 8 of the copying machine shown in FIG.
FIG. 2 is a schematic configuration diagram showing a high-voltage power supply HV and the like related thereto.

When the recording material 6 is fed onto the transfer belt 8, a DC bias is applied from the high voltage power supply HVe to the adsorption charging corona discharger 10a. In this case, since the DC bias is applied from the outer peripheral surface side of the transfer belt 8, the transfer charge is a positive bias having the same polarity. Corona discharger 10
The output value of a was set to 3 to 5 KV in the case of the present embodiment. As a result, a negative charge (a polarity opposite to that of the transfer) is induced from the grounded belt support roller 11 acting as the counter electrode, and the recording material 6 is electrostatically attracted to the transfer belt 8.

Next, the transfer of the M (magenta) toner of the first color is performed. At this time, a DC bias is applied to the transfer charging brush 4a from the high voltage power supply HVa. The power supply HVa is a constant current transformer, and the output value is set to approximately 10 μA in this embodiment.

In the same manner, when the transfer of two to four colors is completed, the recording material 6 is separated from the transfer belt 8. The charge model of the back surface of the transfer belt 8 and the surface of the recording material 6 in this embodiment is the same as that shown in FIG. 3, but the change in the surface potential of the back surface of the transfer belt 8 was measured by a method different from the above. .

FIG. 20 shows a schematic configuration of a measuring apparatus for this purpose. By this method, aluminum is vapor-deposited on a part of the back surface of the transfer belt 8, and a monitor aluminum plate 201 connected by a metal wire so as to have the same potential as this part is prepared.
On the other hand, a surface voltmeter 202 and a recorder 203 for recording the output from the surface voltmeter 202 are prepared.

Here, the probe 20 of the surface voltmeter 202
4 is brought close to the monitor aluminum plate 201, and the potential is measured. FIG. 21 shows the measurement results during the copying operation.

From the measurement results, it can be seen that the potential becomes negative due to the adsorption charging, but the potential gradually increases as the transfer proceeds. Further, when the transfer belt 8 rotates and receives the adsorption charge, the same cycle is repeated. The potential is rounded because the electric charge on the back surface of the transfer belt 8 and the surface of the recording material 6 is self-decayed (leaked).

As described above, even in the copying machine of the transfer belt type, the back surface of the transfer belt 8 is charged to the opposite polarity to the transfer in the attraction charging, so that the transfer belt 8 is not charged up even in continuous copying. Good multiple transfer becomes possible. Further, by using a contact (a conductive brush in this embodiment) for transfer charging, good transfer can be performed regardless of the potential of the transfer belt 8.

Embodiment 6 FIG. 22 shows a sixth embodiment of the present invention. In the present embodiment, in the digital full-color electrophotographic copying machine having four photosensitive drums according to the fifth embodiment of the image forming apparatus of the present invention described in the fifth embodiment, the The high-pressure generating means is configured differently, and the same effects as in the fifth embodiment can be obtained.

To explain the outline of the operation of this embodiment, the recording material 6 which has been subjected to the multiple transfer of the four colors by the high voltage power supplies HVa to HVd is discharged by the discharging charger 14 connected to the high voltage power supply HVg. In the present embodiment, the high-voltage power supply HVg is a DC transformer, and the static eliminator 1 is output by the DC transformer.
No. 4 causes corona discharge. At the same time, the high-voltage power supply HVf connected to the drive roller 12 of the transfer belt 8 outputs. The power supply HVg is a constant current DC transformer, and is set to approximately 200 μA in this embodiment. Also, the high voltage power supply HVf
Is a constant voltage transformer, which is set to approximately −3 KV.

As a result, the positive charges on the back surface of the transfer belt 8 accumulated by the transfer charging are removed and negatively charged in addition to the negative charges.

When the change in the surface potential at this time was observed by the above-described measuring method, the result shown in FIG. 23 was obtained.

[0083]

As described above, according to the present invention, the image carrier for carrying the toner image, the recording material carrier for carrying the recording material, and the side of the recording material carrier on which the recording material is carried are described. Transfer charging means provided on the opposite side to apply a charge having a polarity opposite to the normal charge polarity of the toner to the area of the recording material carrier on which the recording material is carried, and records the toner image on the image carrier. And a transfer charging unit that transfers the toner image to a recording material carried on a material carrier. In the image forming apparatus, before transferring the toner image by the transfer charging device, the area of the recording material carrier has the same polarity as the charging polarity. Charging means for charging the recording material carrier, and a control means for controlling the constant current supplied from the transfer charging means to the area of the recording material carrier charged by the charging means. Up and charging means It is possible to prevent the current is transferred defective excess or under-produced to impart the transfer charging means to a more area of the recording material bearing member charged in the normal charging polarity of the same polarity as the toner.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a first embodiment of an image forming apparatus according to the present invention.

FIG. 2 is a schematic configuration diagram of an apparatus showing a transfer drum, a photosensitive drum, and a high-voltage power supply related thereto in the apparatus of FIG.

FIGS. 3A to 3E are charge models showing charge states after superimposed transfer. FIG.

FIG. 4 is a diagram illustrating a result of measuring a surface potential of a back surface of a transfer sheet at a position downstream of a suction position in a rotation direction.

FIG. 5 is a diagram showing an embodiment of an adsorption charging unit.

FIG. 6 is a diagram showing another embodiment of the adsorption charging means.

FIG. 7 is a diagram showing another embodiment of the adsorption charging means.

FIG. 8 is a view showing another embodiment of the adsorption charging means.

FIG. 9 is a view showing still another embodiment of the adsorption charging means.

FIG. 10 is a configuration diagram of a second embodiment of the image forming apparatus according to the present invention.

FIGS. 11 (a) to 3 (c) are diagrams showing another embodiment of the adsorption charging means.

FIG. 12 is a schematic diagram illustrating a configuration of a third embodiment of the image forming apparatus according to the present invention.

FIG. 13 is a diagram illustrating a method of controlling a current to a shield plate of a corona discharger for transfer.

FIG. 14 is a configuration diagram showing a fourth embodiment of the image forming apparatus of the present invention.

FIG. 15 is a perspective view of a transfer drum used in the apparatus of FIG.

FIG. 16 is a schematic configuration diagram showing a transfer drum, a photosensitive drum, and a high-voltage power supply related thereto in the apparatus of FIG.

FIG. 17 is a schematic diagram of another embodiment showing a transfer drum, a photosensitive drum, and a high-voltage power supply related thereto in the apparatus of FIG.

FIG. 18 is a configuration diagram showing a fifth embodiment of the image forming apparatus of the present invention.

19 is a schematic diagram showing a configuration of a transfer belt, a photosensitive drum, a high-voltage power supply related thereto, and the like of the apparatus of FIG. 18;

FIG. 20 is a schematic configuration diagram of a measuring device for measuring a change in surface potential on the back surface of the transfer belt in the device of FIG. 18;

FIG. 21 is a diagram illustrating a change in surface potential on the back surface of the transfer belt.

FIG. 22 is a configuration diagram illustrating a sixth embodiment of the image forming apparatus of the present invention.

FIG. 23 is a diagram showing a change in surface potential on the back surface of the transfer belt of the apparatus in FIG. 22;

FIG. 24 is a configuration diagram illustrating a conventional image forming apparatus.

FIG. 25 is a configuration diagram illustrating a conventional image forming apparatus.

FIG. 26 is an enlarged view showing an adsorption charging unit of the apparatus of FIG. 25.

FIG. 27 is a diagram illustrating the operation of a corona discharger.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 image carrier (photosensitive drum) 2 charger 3 developing device 4 transfer charger 5 cleaning device 8, 81 recording material carrier (transfer sheet, transfer belt) 10a, 10b recording material carrier charger (adsorption charger)

Continuation of the front page (72) Inventor Nobuhiko Takekoshi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (56) References JP-A-5-46032 (JP, A) JP-A-2-148075 ( JP, A) JP-A-63-228179 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 15/16 G03G 15/01

Claims (16)

(57) [Claims] An image carrier for carrying a toner image; a recording material carrier for carrying a recording material; and a recording material carrier provided on a side of the recording material carrier opposite to a side on which the recording material is carried. Transfer charging means for applying a charge having a polarity opposite to the normal charge polarity of the toner to an area of the carrier on which the recording material is carried, wherein the toner image on the image carrier is carried on the recording material carrier. And a transfer charging unit that transfers the toner image onto the recording material, wherein the transfer charging unit charges the area of the recording material carrier to the same polarity as the charging polarity before transferring the toner image. An image forming apparatus comprising: a charging unit; and a control unit that controls a current supplied from the transfer charging unit to the area of the recording material carrier charged by the charging unit with a constant current. 2. The image forming apparatus according to claim 1, wherein the charging unit includes an inner charging unit and an outer charging unit that are provided so as to face inward and outward with the recording material carrier interposed therebetween. 3. The inner charging means charges the opposite side of the recording material carrier to the side on which the recording material is carried to the same polarity as the charging polarity, and the outer charging means comprises the recording material carrier. 3. The image forming apparatus according to claim 2, wherein the side on which the recording material is carried is charged to a polarity opposite to the charging polarity. 4. The device according to claim 2, wherein a voltage having the same polarity as the charging polarity is applied to the inner charging means, and a voltage having a polarity opposite to the charging polarity is applied to the outer charging means. 3 is an image forming apparatus. 5. The image forming apparatus according to claim 4, wherein a voltage obtained by superimposing a DC voltage and an AC voltage is applied to the inner charging unit and the outer charging unit. 6. The inner charging means includes a contact member which is in contact with a side of the recording material carrier opposite to a side on which the recording material is carried and which is electrically grounded, and wherein the outer charging means comprises the charging member. 4. The image forming apparatus according to claim 2, wherein a voltage having a polarity opposite to the polarity is applied. 7. The outer charging means includes a contact member that is in contact with the recording material supporting side of the recording material carrier and is electrically grounded, and the inner charging means has the same polarity as the charging polarity. The image forming apparatus according to claim 2, wherein the voltage is applied. 8. The image forming apparatus according to claim 1, wherein the charging unit includes a corona charger. 9. The recording device according to claim 1, wherein the charging unit charges the area of the recording material carrier before the recording material is carried on the recording material carrier. An image forming apparatus according to claim 1. 10. The recording apparatus according to claim 1, wherein said charging means electrostatically attracts a recording material to said recording material carrier.
Item 8. The image forming apparatus according to any one of Items 8. 11. The image forming apparatus according to claim 1, wherein the transfer charging unit contacts the area of the recording material carrier when transferring the toner image. 12. The image forming apparatus according to claim 11, wherein said transfer charging means includes a brush. 13. The image forming apparatus according to claim 1, wherein the transfer charging unit includes a corona charger. 14. The image forming apparatus according to claim 1, further comprising a detecting unit configured to detect a current flowing through a shield of the corona charger, wherein the controller controls the corona charger based on a detection result of the detecting unit when transferring the toner image. 14. The image forming apparatus according to claim 13, wherein a current flowing through the wire is controlled. 15. The method according to claim 15, wherein a step of transferring the toner image on the image carrier to a recording material carried on the recording material carrier is repeated, and a plurality of color toner images are formed on the recording material in a superimposed manner. The image forming apparatus according to claim 1, wherein: 16. The image forming apparatus according to claim 15, wherein a plurality of said image carriers are provided to respectively carry said plurality of color toner images.