JP3747823B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a facsimile, a printer, and the like, particularly sheets such as copying paper, transfer paper, copying paper, and recording paper that are conveyed in a predetermined conveying direction by a conveying belt (hereinafter simply referred to as “sheet”). The present invention relates to an image forming apparatus that causes toner to fly on the sheet, directly forms a toner image on the sheet, and fixes the toner image on the sheet.
[0002]
[Prior art]
As an image forming method using toner, a jumping method and a projection method are most widely used. In this type of image forming method, an electrostatic latent image corresponding to an image is formed on a photosensitive member, and toner as an image forming agent is attached to the electrostatic latent image on the photosensitive member from a toner carrier such as a developing roller. After the toner image is obtained, the toner image is transferred to a sheet. However, these image forming methods require a process (photosensitive process) for forming an electrostatic latent image on the surface of the photosensitive member, which includes problems that the apparatus configuration is complicated, and the apparatus cost and running cost are high. Yes. Therefore, in recent years, as described in US Pat. Nos. 3,689,935, 5,036,341 and JP-T-2001-505146, toner is transported in a predetermined transport direction by the action of an electric field. An image forming apparatus of a so-called “toner jet (registered trademark)” type, in which a toner image is directly formed on a sheet by flying on the sheet, has been attracting attention.
[0003]
Here, as a method of transporting a sheet in a predetermined transport direction, for example, many sheet transport units using a transport belt for transporting a sheet have been used. In this sheet conveying unit, a sheet is conveyed by running a conveying belt around a plurality of rollers and running the conveying belt in a predetermined conveying direction while holding the sheet on the surface of the conveying belt. Then, after the toner image is formed by the toner jet method during the sheet conveyance, the sheet is peeled off from the conveyance belt, and further conveyed to the fixing unit to fix the toner image on the sheet.
[0004]
[Problems to be solved by the invention]
Incidentally, as described above, in the toner jet type image forming apparatus, the sheet conveying unit for conveying the sheet and the fixing unit are configured as separate units, which increases the size and cost of the apparatus. It was one of the main factors of the increase.
[0005]
The present invention has been made in view of the above problems, and has a structure in which a toner image is formed by flying and adhering toner to the sheet while the sheet is conveyed using a conveyance belt, and then the toner image is fixed to the sheet. An object of the present invention is to reduce the size and cost of the image forming apparatus.
[0006]
In order to achieve the above-mentioned object, the present invention achieves the above-described object by holding the sheet on the surface of the conveyor belt by passing the conveyor belt around the first and second rollers and running the conveyor belt in a predetermined conveyance direction. Sheet conveying means for conveying from one roller to the second roller, and arranged in a line along the conveying direction at a position above the conveying belt, the toner is caused to fly from above to the sheet being conveyed being conveyed by the sheet conveying means. A plurality of developing units that form toner images of different colors on the sheet being conveyed, a back electrode disposed on each opposite side of the plurality of developing units across the sheet being conveyed, and facing the second roller Each of the plurality of developing devices is disposed between the toner carrier that carries the charged toner and the toner carrier and the sheet being conveyed. A control electrode provided on the base so as to surround a toner passage hole formed through the base from the toner carrier toward the back electrode, and a semiconductive layer provided on the surface of the base. And a toner flying control means for forming a toner image on the sheet during conveyance by controlling toner flying from the toner carrier to the back electrode while preventing the substrate from being charged by the semiconductive layer, and heating the second roller The roller is configured to press the third roller as a pressure roller toward the heating roller to fix the toner image formed on the sheet by the developing unit to the sheet, and the heating roller includes a toner image on the sheet. Simultaneously with the fixing, the conveying belt is heated, and the semiconductive layer is warmed by the heat radiated from the conveying belt.
[0007]
In the invention configured as above, the semiconductive layer can be warmed by the heat radiated from the conveyor belt warmed by the heating roller. Therefore, it is not necessary to provide a heater for each semiconductive layer in order to optimize the resistance value of the semiconductive layer. Therefore, the apparatus configuration is simplified, and the apparatus can be downsized and the apparatus cost can be reduced. Further, by pressing the pressure roller toward the heating roller, the heating roller functions as one component of the sheet conveying unit, and also functions as a fixing unit in cooperation with the pressure roller. That is, the sheet is conveyed in a predetermined direction to form a toner image, and the toner image is fixed to the sheet at the conveyance destination (between the heating roller and the pressure roller) at the same time. As a result, the apparatus configuration is simplified as compared with the case where the sheet conveying unit and the fixing unit are provided separately, and the apparatus can be downsized and the apparatus cost can be reduced.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1 is a view showing an embodiment of an image forming apparatus according to the present invention. FIG. 2 is an enlarged view of a developing device constituting the image forming apparatus of FIG. FIG. 3 is a block diagram showing an electrical configuration of the image forming apparatus shown in FIG. In this image forming apparatus, when an image signal is given to the main controller 101 of the control unit 100 from an external device such as a host computer, the engine controller 102 has four developers 1Y, 1M, By controlling each part of 1C and 1K, the toner is ejected and adhered to the sheet S conveyed in the predetermined conveying direction Y by the sheet conveying unit 2 to form a toner image corresponding to the image signal.
[0009]
In the sheet conveying unit 2, a conveying belt 23 is stretched between a first roller 21 and a second roller 22, and the conveying belt 23 travels in the conveying direction Y by a driving force applied from a driving motor that is omitted from the drawing. To do. The conveyance belt 23 conveys the sheet S from the first roller 21 to the second roller 22 while holding the sheet S such as copy paper, transfer paper, recording paper, and OHP transparent sheet taken out from the cassette 7. In this specification, in order to clarify the technical matters of the present invention, a sheet conveyed from the first roller 21 to the second roller 22 by the conveyance belt 23 is referred to as a “sheet being conveyed” and will be described later. The sheet on which the toner image is formed is referred to as a “toner image formed sheet”, and the sheet before the toner image is formed is referred to as a “toner image non-formed sheet”.
[0010]
Further, in this image forming apparatus, four types of developing devices 1Y, 1M, 1C, and 1K of yellow (Y), magenta (M), cyan (C), and black (K) are used to form a color image. 23, each developing unit 1Y, 1M, 1C, 1K forms a toner image on the sheet S being conveyed, and finally superimposes four color toner images. To form a full color image. Note that these developing units 1Y, 1M, 1C, and 1K basically have the same configuration except that the toner colors that fly and adhere to the sheet S during conveyance are different from each other. The common configuration and operation of 1 (1Y, 1M, 1C, 1K) will be described with reference to FIGS.
[0011]
In each developing device 1, toner T as a developer is stored in a housing 11, and a developing roller 12, a supply roller 13, and a regulating blade 14 are accommodated. The developing roller 12 carries charged toner (that is, charged particles for image formation) T, and rotates at a predetermined peripheral speed in the arrow direction D of FIG. The toner carrying member conveyed to the flight start position (J). The developing roller 12 is formed in a cylindrical shape from a metal or alloy such as aluminum or iron, and a DC voltage is applied from a developing roller bias generator 103 provided in the engine controller 102.
[0012]
The supply roller 13 is in contact with the outer peripheral surface of the developing roller 12 and rotates in the opposite direction to the developing roller 12 to supply the toner T to the developing roller 12 and to drop excess toner T from the developing roller 12. Is. The supply roller 13 is made of, for example, a synthetic rubber such as urethane sponge wound around a metal core, and has a function of charging the toner T to a predetermined polarity by frictional contact with the developing roller 12. In the present embodiment, the following description will be made assuming that the toner T is negatively charged.
[0013]
The regulating blade 14 is applied to the outer peripheral surface of the developing roller 12 on the downstream side of the supply roller 13 in the rotation direction D of the developing roller 12, and negatively charges the toner T due to friction with the developing roller 12. The amount of the toner T carried on the toner 12 is regulated. For example, the toner is regulated so as to be carried on about 1 to 3 layers. The regulating blade 14 is configured by attaching an elastic member 142 to the other end portion of the plate-shaped metal piece 141 having one end fixed to the housing 11, and the elastic member 142 abuts on the outer peripheral surface of the developing roller 12, T is regulated.
[0014]
A back electrode 3 is disposed opposite to the developing roller 12. More specifically, as shown in FIG. 2, the back electrode 3 is disposed on the opposite side of the developing roller 12 with the sheet S being conveyed being conveyed in the conveyance direction Y by the conveyance belt 23. A DC voltage higher than the voltage applied to the developing roller 12 is applied from the back bias generation unit 104 provided in the engine controller 102, and the charged toner T is applied between the developing roller 12 and the back electrode 3. A transfer electrostatic field for transfer toward the back electrode 3 is formed. For this reason, this charged electrostatic field causes the charged toner T to fly from the developing roller 12 toward the back electrode 3 at the toner flying start position J and land on and adhere to the surface of the sheet S being conveyed.
[0015]
In this embodiment, a flexible printed circuit board (hereinafter referred to as FPC) 4 is disposed between the developing roller 12 and the sheet S being conveyed in order to control the flying of the charged toner T to the sheet S being conveyed. ing. Hereinafter, the configuration and operation of the FPC 4 will be described with reference to FIGS. 4 and 5.
[0016]
FIG. 4 is a diagram showing a partially enlarged cross section of a flexible printed circuit board and a flying model of charged toner. FIG. 5 is a diagram showing control electrodes and deflection electrodes formed on the flexible printed circuit board. In this FPC 4, a toner passage hole 41 for guiding the charged toner T from the developing roller 12 to the back electrode 3 is formed in a base 42 made of an electrically insulating material such as polyimide. In FIG. 4, only one toner passage hole 41 is shown, but in this embodiment, a plurality of toner passage holes 41 are provided in a line at equal intervals in the vertical direction X of the paper surface of FIG. The charged toner T can pass toward the back electrode 3 through each toner passage hole 41. In this embodiment, the toner passage holes 41 are arranged in one row, but may be provided in a plurality of rows. The shape of the toner passage hole 41 may be circular as in this embodiment, or may be oval or polygonal.
[0017]
A control electrode 43 is formed in a ring shape on the developing roller 12 side of the base 42 so as to surround each toner passage hole 41. A lead wire 44 extends from each control electrode 43 in a direction perpendicular to the arrangement direction of the toner passage holes 41. Note that the shape of the control electrode 43 is not limited to a circular shape, and is arbitrary. For example, the control electrode 43 may be an elliptical shape or a polygonal shape. .
[0018]
Further, on the back electrode 3 side of the base 42, a pair of deflection electrodes 45L and 45R is provided for each toner passage hole 41 in the conveyance direction of the sheet S being conveyed (direction orthogonal to the toner passage hole row) as shown in FIG. The lead wires 46L and 46R extend from the deflection electrodes 45L and 45R, respectively, so as to be diagonally opposed to Y.
[0019]
Although not shown in FIGS. 4 and 5, the base 42 is provided with a control bias generator 47 (FIG. 3), an L deflection bias generator 48L (FIG. 3), and an R deflection composed of a high voltage driver IC or the like. A bias generator 48R (FIG. 3) is provided. Among these, the control bias generator 47 is electrically connected to each control electrode 43, and an appropriate voltage is selectively applied according to an open / close control signal from the CPU 105 of the engine controller 102, whereby the toner is The passage hole 41 is electrostatically opened and closed. That is, for each control electrode 43, the toner between the developing roller 12 and the back electrode 3 so that the charged toner T jumps out of the developing roller 12, passes through the toner passage hole 41 and flies toward the back electrode 3. The transfer electrostatic field passing through the passage hole 41 is exposed, and the exposure is limited.
[0020]
Further, the L deflection bias generator 48L is electrically connected to the deflection electrode 45L, and the R deflection bias generator 48R is electrically connected to the deflection electrode 45R, and corresponds to the deflection control signal from the engine controller 102. Thus, by appropriately applying appropriate voltages to the deflection electrodes 45L and 45R, the flying direction of the charged toner T is switched to the following three directions.
[0021]
(1) No deflection: arrow P1 in FIG.
When the same voltage is applied to both the deflection electrodes 45L and 45R, the charged toner T passes straight through the toner passage hole 41 as shown by an arrow P1 in FIG. Fly to a position corresponding to the hole 41.
[0022]
(2) Left deflection: arrow P2 in FIG.
A voltage that is relatively higher than the deflection electrode 45R disposed on the right side is applied to the deflection electrode 45L disposed on the left side of the toner passage hole 41 with respect to the conveyance direction Y of the sheet S being conveyed as a reference among the deflection electrodes 45L and 45R. In this case, the negatively charged charged toner T is deflected to the left side by a deflecting electrostatic field generated between the electrodes 45L and 45R, as indicated by an arrow P2 in FIG.
[0023]
(3) Right deflection: arrow P3 in FIG.
A voltage higher than the deflection electrode 45L arranged on the left side is applied to the deflection electrode 45R arranged on the right side of the toner passage hole 41 with respect to the conveyance direction Y of the sheet S being conveyed among the deflection electrodes 45L and 45R. In this case, the negatively charged charged toner T is deflected to the right side by a deflecting electrostatic field generated between the electrodes 45L and 45R, as indicated by an arrow P3 in FIG.
[0024]
As described above, in this embodiment, while the flying direction of the charged toner T is switched to three directions, the charged toner T is landed on the sheet S being conveyed at the landing position PI of the sheet S being conveyed including the deflection range. .
[0025]
However, as described above, the deflection electrodes 45L and 45R are disposed in an oblique direction with respect to the conveyance direction Y of the sheet S being conveyed, so that (1) no deflection, (2) left deflection, and (3) right deflection. With these three modes, when the sheet S during conveyance is stopped, three dots arranged linearly obliquely with respect to the conveyance direction Y of the sheet S during conveyance are formed on the sheet S during conveyance. In this case, by determining the conveyance speed so that the sheet S being conveyed is conveyed by the shift amount (distance) of adjacent dots in the period (time) of hitting the dots, the three dots of the sheet S being conveyed are determined. They can be arranged linearly in a direction orthogonal to the transport direction Y. Therefore, three dots can be formed by one toner passage hole 41, and the density of the dots can be increased.
[0026]
In the base 42 of the FPC 4, an antistatic semiconductive layer 49 is formed on the surface 421 on the developing roller 12 side and the surface 422 on the back electrode 3 side, and a ground potential is applied. These semiconductive layers 49 exhibit an optimum resistance value at a preset temperature (initial setting temperature), and friction charges generated when the charged toner T flying as described above comes into contact with the FPC 4 are generated from the FPC 4. It is configured to escape and effectively prevent the FPC 4 from being charged, and to suppress the influence on the transfer electrostatic field and the deflection electric field. That is, it is possible to ensure good print quality while the temperature of the semiconductive layer 49 is maintained within the initial set temperature or the allowable temperature range.
[0027]
Further, on the upstream side of the toner flying start position J in the rotation direction D of the developing roller 12, the longitudinal direction of the developing roller 12 (the direction perpendicular to the paper surface in FIG. 4) is between the FPC 4 configured as described above and the developing roller 12. ) The spacer 5 extending over the entire length of X is inserted in front of the toner passing hole 41 of the FPC 4 in the rotational direction D, so that the distance between the developing roller 12 and the toner passing hole 41 of the FPC 4 becomes a constant value. It is regulated.
[0028]
Next, returning to FIG. 1, the description of the overall configuration and operation of the image forming apparatus will be continued. In this image forming apparatus, four color toner images are superimposed on the sheet S being conveyed by the four developing units 1Y, 1M, 1C, and 1K configured as described above, and a color toner image is formed on the sheet S. . The toner image-formed sheet S is further conveyed to the second roller 22, and a third roller 24 is disposed so as to face the second roller 22, and the toner image-formed sheet S is sandwiched between them. While peeling this from the conveyance belt 23, it conveys toward the discharge tray which abbreviate | omits illustration.
[0029]
Here, in this embodiment, the second roller 22 is constituted by a heating roller, while the third roller 24 is pressed against the second roller (heating roller) 22 as a pressure roller. The second roller 22 is electrically connected to a heater driving unit 106 provided in the engine controller 102, and the heater driving unit 106 receives a second heating control signal from the CPU 105 of the engine controller 102. The heater built in the roller 22 is turned ON / OFF to fix the toner image on the toner image formed sheet S to the sheet S. As described above, in this embodiment, the second roller 22 and the third roller 24 perform the same function as the conventional fixing unit.
[0030]
As described above, according to this embodiment, the second roller 22 is a component of the sheet conveying unit 2 that conveys the sheet S, and at the same time, is configured of a heating roller, and is a third pressure roller. It also functions as a heating roller for the fixing unit in cooperation with the roller 24. That is, the sheet S is conveyed in a predetermined conveyance direction Y in order to form a toner image, and the toner image on the toner image-formed sheet S at the conveyance destination (between the second roller 22 and the third roller 24). Since the fixing is performed at the same time, the apparatus configuration can be simplified compared to the case where the sheet conveying unit and the fixing unit are provided separately, and the apparatus can be downsized and the apparatus cost can be reduced. Can be achieved.
[0031]
In this embodiment, since the conveyor belt 23 is heated by the second roller (heating roller) 22, the following two functions and effects can be further obtained.
[0032]
(1) When the semiconductive layer 49 is formed on the FPC 4 as in the above embodiment, it is necessary to optimize the resistance value of the semiconductive layer 49. This is because, in order to prevent the FPC 4 from being charged, it is necessary to efficiently release the charged triboelectric charge from the FPC 4, and it is desirable to set the resistance value of the semiconductive layer 49 low. If the value is too low, the following problems occur and the print quality is degraded.
[0033]
In other words, the reduction in resistance of the semiconductive layer 49 shields the electric field generated by the voltage application to the control electrode 43 and the deflection electrodes 45L and 45R by the semiconductive layer 49, and the toner flying property and the toner deflection amount. Will fall. As a result, the shape, size, blackness, resolution, etc. of the dots formed on the sheet S being conveyed may be affected, leading to a decrease in print quality. Therefore, when the semiconductive layer 49 is provided on the FPC 4, the optimum resistance value of the semiconductive layer 49 is balanced so as to balance the effect of preventing charging and the effect of suppressing the influence on the electric field. In order to execute good printing, it is necessary to always maintain the resistance value within a predetermined appropriate range.
[0034]
However, since the semiconductive material has a relatively large temperature dependency as conventionally known, when the temperature of the semiconductive layer 49 fluctuates, the resistance value is in an appropriate range along with the temperature fluctuation. The print quality may be greatly deteriorated.
[0035]
On the other hand, in the present embodiment, the heater built in the second roller (heating roller) 22 is configured to be appropriately ON / OFF controlled, so that the toner image is fixed to the sheet S and conveyed at the same time. The belt 23 is heated, and the temperature of the semiconductive layer 49 is held at a temperature stored in advance in the memory 107 by the heat radiated from the conveyor belt 23 to suppress temperature fluctuation, that is, to stabilize the temperature. be able to. Therefore, fluctuations in the resistance value of the semiconductive layer 49 can be suppressed, and high-quality printing can be executed regardless of fluctuations in the internal temperature, ambient temperature, etc. of the image forming apparatus, for example.
[0036]
(2) In the toner jet type image forming apparatus, as described above, the charged toner T is caused to fly to the sheet S being conveyed by the transfer electrostatic field, so that the charged toner T collides with the sheet S at a high speed. The toner T may bounce on the sheet S, or the toner T already adhered on the sheet S may be scattered. As a result, there may be a problem that toner scattering occurs, or the scattered toner adheres to the FPC 4 to deteriorate the printing quality.
[0037]
On the other hand, in the above embodiment, the toner image is fixed on the toner image formed sheet S by the second roller (heating roller) 22 and the third roller (pressure roller) 23 functioning as a fixing unit. The conveyance belt 23 is heated by the second roller (heating roller) 22, and the toner image non-formed sheet S conveyed by the conveyance belt 23 is preheated by the conveyance belt 23 in a high temperature state. As a result, almost or all of the landing toner T melts almost simultaneously with the toner landing on the preheated conveying sheet S, and the landing toner T can be reliably attached to the landing position PI of the conveying sheet S. As a result, the occurrence of toner scattering and toner scattering from the sheet S can be suppressed, and printing can be performed with excellent quality.
[0038]
Here, in order to surely dissolve a part or all of the toner T almost simultaneously with the landing of the toner on the sheet S during conveyance, the surface temperature of the developing roller 12 by applying heat from the conveyance belt 23 to the sheet S, That is, it is desirable to preheat the sheet S to a temperature higher than the temperature of the flying toner T. In order to melt the landing toner T more reliably, it is more preferable to preheat the landing position PI of the sheet S during conveyance to a temperature higher than the glass transition temperature of the toner T.
[0039]
The present invention is not limited to the above-described embodiment, and various modifications other than those described above can be made without departing from the spirit of the present invention. For example, in the above embodiment, the second roller 22 is a heating roller and the third roller 24 is a pressure roller, but these relationships may be interchanged. That is, one of the second roller 22 and the third roller 23 may be a heating roller and the other may be a pressure roller.
[0040]
In the above embodiment, the present invention is applied to the image forming apparatus in which the semiconductive layer 49 is provided to prevent the FPC 4 from being charged. However, the scope of application of the present invention is not limited to this. Instead, the present invention can also be applied to an image forming apparatus that does not have an antistatic semiconductive layer.
[0041]
In the above embodiment, the present invention is applied to an image forming apparatus in which the flying direction of the charged toner T can be switched to the three directions P1, P2, and P3 by the deflection electrodes 45L and 45R. The object is not limited to this, and the present invention can also be applied to an image forming apparatus in which the flying direction of the charged toner T is fixed.
[0042]
In the above embodiment, a predetermined DC voltage is applied to the developing roller 12 from the developing roller bias generator 103. However, the developing roller 12 may be configured to be grounded or an AC voltage.
[0043]
Furthermore, in the above-described embodiment, the present invention is applied to a color image forming apparatus that forms a color image with the four developing devices 1Y, 1M, 1C, and 1K, but an image is formed with one developing device 1. The present invention can also be applied to an image forming apparatus that performs so-called monochromatic printing. That is, the present invention relates to an image forming apparatus having a structure in which a toner image is formed by flying and adhering toner to the sheet while the sheet is conveyed using a conveying belt, and then the toner image is fixed to the sheet. It is applicable to this.
[0044]
【The invention's effect】
As described above, according to the present invention, the semiconductive layer can be warmed by the heat radiated from the transport belt warmed by the heating roller. Therefore, it is not necessary to provide a heater for each semiconductive layer in order to optimize the resistance value of the semiconductive layer. Therefore, the apparatus configuration is simplified, and the apparatus can be downsized and the apparatus cost can be reduced. Further, by pressing the pressure roller toward the heating roller, the heating roller functions as one component of the sheet conveying unit, and also functions as a fixing unit in cooperation with the pressure roller. As a result, the apparatus configuration is simplified as compared with the case where the sheet conveying unit and the fixing unit are provided separately, and the apparatus can be downsized and the apparatus cost can be reduced.
[Brief description of the drawings]
FIG. 1 is a diagram showing an embodiment of an image forming apparatus according to the present invention.
FIG. 2 is an enlarged view of a developing device constituting the image forming apparatus of FIG.
3 is a block diagram showing an electrical configuration of the image forming apparatus of FIG. 1;
4 is a diagram showing a partially enlarged cross section of a flexible printed circuit board used in the image forming apparatus of FIG. 1 and a flying model of charged toner.
FIG. 5 is a diagram showing control electrodes and deflection electrodes formed on a flexible printed circuit board.
[Explanation of symbols]
1, 1Y, 1M, 1C, 1K ... developer 2 ... sheet transport unit 3 ... back electrode 4 ... FPC (toner flight control means)
12: Developing roller (toner carrier)
21 ... 1st roller 22 ... 2nd roller (heating roller, pressure roller)
23 ... Conveying belt 24 ... Third roller (pressure roller, heating roller)
41 ... Toner passage hole 42 ... Base 43 ... Control electrode 47 ... Control bias generator 106 ... Heater driver PI ... Landing position S ... Sheet T ... Charged toner Y ... Conveying direction

Claims (1)

A conveyor belt is stretched between the first and second rollers, and the conveyor belt travels in a predetermined conveyor direction, so that the sheet is held on the surface of the conveyor belt while the sheet is held from the first roller to the second roller. Sheet conveying means for conveying;
In the upper position of the conveying belt, arranged in a line along the conveying direction, the toners fly from the upper side to the conveying sheets being conveyed by the sheet conveying means, and are different from each other on the conveying sheets. A plurality of developing units for forming a color toner image;
A back electrode disposed on the opposite side of each of the plurality of developing units across the sheet during conveyance;
A third roller disposed opposite to the second roller,
Each of the plurality of developing devices includes a toner carrier that carries charged toner, a base disposed between the toner carrier and the sheet being conveyed, and the toner carrier toward the back electrode. A control electrode provided on the substrate so as to surround a toner passage hole formed through the substrate; and a semiconductive layer provided on the surface of the substrate; and charging of the substrate by the semiconductive layer. Toner flying control means for forming a toner image on the sheet during conveyance by controlling toner flying from the toner carrier to the back electrode while preventing
The second roller is constituted by a heating roller, the third roller is pressed against the heating roller as a pressure roller, and the toner image formed on the sheet by the developing device is fixed on the sheet, The image forming apparatus , wherein the heating roller heats the conveying belt simultaneously with fixing of the toner image on the sheet and warms the semiconductive layer by heat radiated from the conveying belt .

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