JP3585364B2 - Image forming device - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus, and more particularly, to an electrostatic latent image formed on an image carrier by an electrophotographic process, wherein toner transferred by a screw pump is mixed with a gas at a position away from a developing position. The present invention relates to an image forming apparatus such as a printer, a facsimile machine, a copying machine, or a multifunction machine for forming an image by supplying the image forming apparatus.
[0002]
[Prior art]
In an image forming apparatus such as a printer, a facsimile machine, a copying machine, or a multifunction machine using a dry one-component or two-component dry toner, the toner is transferred onto a photoreceptor but is not transferred onto a transfer member. Is collected by a cleaning unit and then returned to a developing unit to reuse and reuse to form an image by recycling development.
It is known that a toner of a developer is circulated and supplied to a developing section by a pump using a gas flow (see Japanese Patent Publication No. 63-3308).
FIG. 6 is an exploded perspective view showing a configuration of a toner recycling mechanism using a conventional screw pump, and FIG. 7 is a cross-sectional view of a screw pump section. In FIG. 6, an image carrier 101 which is a drum-shaped photosensitive member is shown. In the case where the toner collected by the cleaning blade 106a of the cleaning unit 106 or the toner remaining on the belt-shaped transfer member (not shown) is reused, the toner is discharged from the discharge pipe 106b of the cleaning unit 106. The collected toner is dropped into the horizontal conveying screw case 107a via the connecting means 107, and the rotational driving force of the drive motor 108 is transmitted via the pulley and belt of the rotational driving force transmitting means 108a to the horizontal conveying screw case 107a. Screw 107b is held in holder 109c of screw pump 109. By rotating the rotor 109b integral with the stator 109a that is, the collected toner by the rotation of the transverse conveying screw 107b fed into the stator 109a.
The rotation of the rotor 109b in the stator 109a of the screw pump 109 causes the toner to be pushed out of the stator 109a through the outlet 109d into the air-fuel mixture conveying means 104 connected to the outlet 109d, and air is transferred by the air pump 103. An image is formed by supplying the toner from a position remote from the developing position by feeding the toner from a position apart from the developing position by feeding the mixture into the mixture conveying means 104 as a mixture with air through a tube and feeding the mixture into the mixture conveying means 104 as a mixture with air. I do. This image forming apparatus has been proposed by the inventor of the same applicant.
However, in such a conventional image forming apparatus, when the space is regulated and the driving source is simplified, for example, when the air pump 103 is used as a driving source for another unit, the air pump 103 is positioned at a position lower than the developing device 102 in the vertical direction. If the toner remaining on the inner wall such as the tube tube of the air-fuel mixture conveying means 104 is subjected to vibration or the like after the air pump 103 is stopped, the toner The pipe 103a flows backward and is clogged, and the valve on the discharge side (not shown) of the air pump 103 is blocked or the valve is not closed.
[0003]
[Problems to be solved by the invention]
In the above-described conventional image forming apparatus, when the toner remaining on the inner wall such as the elastic tube of the air-fuel mixture conveying means is subjected to vibration or the like after the air pump is stopped, the toner is vibrated and gravitationally caused by the air pump side. The air pump does not function properly and the quality of the formed image is deteriorated, such as blocking the valve on the discharge side of the air pump or preventing the valve from closing.
Therefore, an object of the present invention is to solve such a problem. In other words, after the air pump is stopped, the toner remaining on the inner wall of the elastic pipe or the like of the air-fuel mixture conveying means is prevented from flowing back to the air pump side even if vibration is applied, so that the air pump functions normally. It is another object of the present invention to provide an image forming apparatus capable of forming a high quality image.
[0004]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, an electrostatic latent image formed on an image carrier is supplied with a toner transferred by a screw pump as a mixture with a gas from a position remote from a developing position. and in an electrophotographic image forming apparatus to form an image, an image carrying member for carrying the formed image, developing means and the electrostatic latent image formed on said image bearing member to form a toner image And an air pump that circulates and supplies a gas for fluidizing the toner to be supplied to the developing unit, and is connected to an inlet and an outlet of the air pump to convey a mixture of toner and gas. An air-fuel mixture conveying means for forming a circulation path for circulating gas; and a backflow preventing member provided on an inner wall of the air-fuel mixture conveying means coupled to the discharge port to prevent a backflow of toner. The members are Characterized in that it is a brush.
According to a second aspect of the present invention, in the image forming apparatus of the first aspect, the backflow prevention member made of a brush is inclined with respect to the toner conveying direction .
According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the backflow prevention member made of a brush is disposed only in a part of the air-fuel mixture conveying means coupled to the discharge port side of the air pump. It is characterized by the following.
[0005]
[Action]
In the image forming apparatus having the above-described configuration, according to the first aspect, the electrostatic latent image formed on the image carrier in the electrophotographic system is supplied by a screw pump to a developing unit that visualizes the electrostatic latent image to form a toner image. An air pump that is connected to the inlet and outlet of an air pump that transports an air-fuel mixture with a gas for fluidizing the toner to be transported, transports the air-fuel mixture of the toner and the gas, and circulates and reuses the gas. A backflow prevention member is provided on the inner wall of the air-fuel mixture conveying means coupled to the discharge port to prevent the toner from flowing backward, so that the discharge port of the air-fuel mixture conveyance means is positioned higher than the air pump, and the air pump is Even after the stoppage, even if vibration or the like is applied to the toner remaining on the inner wall of the elastic pipe or the like of the air-fuel mixture conveying means, the backflow of the toner to the air pump side is prevented, so that the air pump functions normally and the high flow rate is maintained. As to be able to provide an image forming apparatus an image forming quality is performed. Further, a mixture of gas and a gas for fluidizing toner supplied by a screw pump is transferred to a developing unit that visualizes the electrostatic latent image formed on the image carrier in the electrophotographic system to form a toner image. Combined with the inlet and outlet of the air pump to carry the mixture of toner and gas and circulate and reuse the gas Prevent backflow to the inner wall of the mixture carrier coupled to the outlet of the air pump A member brush is provided to prevent the toner from flowing backward, so that the discharge port of the air-fuel mixture conveying means is at a position higher than the air pump, and after the air pump is stopped, the elastic pipe of the air-fuel mixture conveying means is stopped. Even if vibrations are applied to the toner remaining on the inner wall, a large amount of toner is prevented from flowing back to the air pump side, the toner transport resistance is low, and the air pump functions normally and high quality image formation As to be able to provide an image forming apparatus to be performed.
According to another aspect of the present invention, there is provided a developing device for developing a toner image by visualizing an electrostatic latent image formed on an image carrier in an electrophotographic system, and mixing with a gas for fluidizing toner supplied by a screw pump. The air-fuel pump is connected to an inlet and an outlet of an air pump for transferring air and conveys an air-fuel mixture of toner and gas, and circulates and reuses the gas. A backflow prevention member is provided on the inner wall so as to be inclined with respect to the toner conveyance direction to prevent the backflow of the toner, and the discharge port of the air-fuel mixture conveyance means is located at a position higher than the air pump, and the air pump is stopped. Later, even if vibration or the like is applied to the toner remaining on the inner wall of the elastic pipe or the like of the air-fuel mixture conveying means, the backflow of the toner to the air pump side is prevented, the toner conveyance resistance is further reduced, and the air Flop it is to be able to provide an image forming apparatus is performed function and high-quality image forming properly.
According to a third aspect of the present invention, an electrostatic latent image formed on an image carrier in an electrophotographic system is visualized and mixed with a gas for fluidizing toner supplied by a screw pump to developing means for forming a toner image. The air-fuel pump is connected to an inlet and an outlet of an air pump for transferring air and conveys an air-fuel mixture of toner and gas, and circulates and reuses the gas. A backflow preventing member is provided only on a part of the air-fuel mixture conveying means coupled to the discharge port side of the air pump on the inner wall to prevent the toner from flowing backward, so that the discharge port of the air-fuel mixture conveyance means is higher than the air pump. Therefore, even if vibrations or the like are applied to the toner remaining on the inner wall of the air-fuel mixture conveying means after the air pump is stopped, it is possible to prevent the toner from flowing back to the air pump side and reduce cost. Emissions at possible at low cost, an air pump is to be able to provide an image forming apparatus is performed function and high-quality image forming properly.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
Next, embodiments of the present invention will be described in detail with reference to the drawings.
FIG. 1 is an explanatory diagram of a main part of an image forming section of an image forming apparatus to which the present invention is applied, and FIG. 2 is a cross-sectional view showing an example of the structure of an air pump. The body 1 is rotatably supported by a side plate (not shown), and is driven to rotate clockwise in a direction indicated by an arrow A by a driving unit (not shown).
An electrostatic latent image is formed on the image carrier 1 by being uniformly charged by the charger 10 and then subjected to exposure in accordance with an image portion by the exposure unit 11 in an image forming process based on an electrophotographic method. Carry a toner image formed by developing by the developing means 2.
The drum-shaped photoconductor of the image carrier 1 may be an endless belt-shaped photoconductor. Although not shown, the exposing means 11 uses a copier of an analog optical system or a laser scanning optical system having a laser light source and a deflector to light the light onto the image carrier 1 in accordance with an image signal. If the writing method is adopted, the configuration becomes a laser printer, and if a document reading device is further provided, the configuration becomes a digital copying machine or a facsimile device.
The developing unit 2 includes a developing roller 2a that supplies toner (T) to the electrostatic latent image formed and carried on the image carrier 1, a paddle 2b that agitates and transports the toner (T), and a paddle 2c. , A blade 2d for regulating the height of the toner (T) layer, and a container 2e for housing and holding these. By the toner conveying force of the screw pump 9 and the air pressure of the air pump 3, recycled or new toner (T) to be reused is conveyed through the elastic pipe of the air-fuel mixture conveying means 4 and is replenished in the container 2e. You.
Therefore, new toner (T) provided separately from the developing means 2 and appropriately replenished to a developer storing means (not shown) is also stored in the container 2e by the screw pump 9 (not shown) and the air pump 3 (not shown). Is to be replenished.
[0007]
The electrostatic latent image formed and carried on the image carrier 1 can be developed by a dry one-component or dry two-component development method using a magnetic brush development method with the toner (T) supplied from the developing means 2. It is visualized. The toner (T) in the container 2e of the developing means 2 is transported while being stirred by the paddles 2b and 2c, and the toner (T) and the carrier rub against each other, so that the toner adheres to the carrier. Then, the toner (T) forms a magnetic brush on the developing roller 2 a containing a magnet (not shown), and develops the electrostatic latent image on the image carrier 1.
The paper supply section 12 is provided with a plurality of paper supply cassettes containing transfer papers (P) of various sizes.
When the image forming operation is started, the image carrier 1 is charged by the charger 10, and the original image from the exposure unit 11 is exposed to form an electrostatic latent image. This electrostatic latent image is developed by a dry one-component developer of the developing means 2 or a dry two-component toner (T), and a toner image is formed on the image carrier 1.
The toner image on the image carrier 1 is supplied from the paper supply unit 12, and is transferred to a transfer position of a nip portion between the image carrier 1 and the transfer unit 14 via a registration roller 13. P). The transfer paper (P) onto which the toner image has been transferred is conveyed from the transfer means 14 to the fixing unit 15, where the toner image is fixed on the transfer paper (P) by the fixing unit 15, and the transfer paper (P) after fixing is fixed. Is discharged through a discharge roller 16 and stored in a discharge tray or the like.
On the other hand, the residual toner adhering to the image carrier 1 or the toner (T) adhering to the transfer belt 14a after the transfer of the toner image is scraped off by the cleaning blade 6a of the cleaning unit 6 or the transfer cleaning blade 14b. The toner is discharged from the discharge pipe 6b or the discharge pipe 14c and reused as the collected toner (T). The recovered toner is conveyed to the screw pump 9 via the connecting means 7 and becomes a mixture of the screw pump 9 and the air supplied by the air pump 3, and is conveyed in the elastic pipe in the gas mixture conveying means 4. Then, the developer is supplied into the container 2e of the developing means 2.
[0008]
The screw pump 9 is provided with a new toner (Tn) appropriately supplied to a toner storage unit (not shown) provided separately from the developing unit 2 or a collected toner (Tn) supplied through the discharge pipe 6b or the like. ) Is rotated by a driving source 8 or the like via a horizontal transport screw 7b in a horizontal transport screw case 7a to move the rotor 9b in the axial direction, and a passage arranged so as to wrap the rotor 9b. And a holder 9c for holding and fixing the stator 9a in contact with and engagement with the stator 9b.
The air pump 3 is located on the downstream side of the discharge port of the screw pump 9 and, as shown in FIG. 2, holds the suction valve 3c so as to swing in the direction of arrow C shown in FIG. The discharge valve 3d is held so as to be swingable in the direction of the arrow D shown in the figure, facing the discharge port 3b. When the air-fuel mixture of the toner (T) and the gas air is sucked by the operation of the diaphragm 3f in the direction of the arrow E shown in the figure or in the opposite direction by the rotation of the eccentric cam 3e loosely fitted in the hole 3e ', the suction valve is used. 3c opens the inlet 3a and the discharge valve 3d closes the outlet 3b. When discharging the mixture of the toner (T) and gaseous air, the suction valve 3c closes the suction port 3a and the discharge valve 3d opens the discharge port 3b. An air-fuel mixture of the gas for fluidizing the toner (T) is transferred, and the gas for fluidizing the toner (T) is circulated for reuse.
The mixture of the toner (T) moved by the screw pump 9 and the gas air circulated and supplied by the air pump 3 for fluidizing the toner (T) flows into the elastic pipe of the mixture transport means 4. Is transported to a toner supply unit 2f that supplies toner to the container 2e of the developing unit 2. The toner supply section 2f drops the toner (T) of the air-fuel mixture that has been conveyed through the elastic pipe of the air-fuel mixture conveying means 4 and discharged inside by gravity, and appropriately supplies the toner (T) to the container 2e. The gaseous air separated from the toner (T) in the toner supply unit 2f is supplied to the screw pump 9 through a circulation path that forms a circulation path, and is reused.
An inner wall 4a of the elastic tube of the air-fuel mixture conveying means 4 is connected to the outlet 3b of the air pump 3 to prevent the toner (T) from flowing backward in the direction of arrow B shown in the drawing. A plurality of (for example, annular ridges) backflow prevention members 5 are provided.
The protruding backflow prevention members 5 may be partially scattered instead of the entire circumference of the inner wall of the elastic tube. Further, each projection may be spirally continuous or intermittent.
Further, the protrusion may be tilted toward the transport direction of the air-fuel mixture.
Therefore, the gas re-used in the screw pump 9 is moved from the air pump 3, the toner supply unit 2f, and a circulation path forming a circulation path to a position lower than the screw pump 9 and the toner supply unit 2f. When the air pump 3 is circulated in order and is supplied to the toner supply unit 2f, the inner wall 4a of the air-fuel mixture conveying means 4 such as an elastic tube after the air pump 3 stops operating. The backflow preventing member 5 prevents the toner (T) remaining in the backflow preventing member 5 from flowing back to the air pump 3 side due to vibration and gravity even if vibration or the like is applied to the elastic tube or the like. Therefore, it is possible to prevent the discharge valve 3d from being blocked by the toner (T) due to the reverse flow of the toner (T) or from entering the valve seat of the discharge valve 3d and not closing, and the air pump 3 can be normally operated. Function. Therefore, it is possible to provide an image forming apparatus in which high-quality image formation is performed.
[0009]
FIG. 3 is a cross-sectional view of a main part showing another embodiment of the backflow prevention member. The backflow prevention member 5 is a brush 5a, and the brush 5a is an elastic tube such as a vinyl tube of the air-fuel mixture conveying means 4. It is woven into the base cloth 4a1 of the inner wall 4a, and is made of, for example, a material such as polyester or acrylic. Since it is inclined at an angle θ (10 degrees to 60 degrees), the resistance of the toner (T) of the air-fuel mixture to be conveyed is further reduced, and the backflow can be prevented, so that a large amount of toner can be conveyed. This brush may be allowed to extend over the entire circumference of the inner wall of the elastic tube may be intermittently arranged.
[0010]
FIG. 4 is a cross-sectional view of a main part showing another embodiment of the backflow prevention member. The protrusion 5b of the backflow prevention member 5 has a convex shape on the inner wall 4a when the air-fuel mixture conveying means 4 is molded with a rubber material. Are attached to each other to form a tube, and a predetermined angle θ (from 10 degrees to 60 degrees) with respect to the direction of conveyance of the toner (T) of the air-fuel mixture with the air in the direction of arrow F in the drawing. Degree) Since the toner is tilted, the conveyance resistance of the toner (T) of the air-fuel mixture is small, and the backflow is reliably prevented, so that a large amount of toner can be conveyed.
The projection may extend over the entire circumference of the inner wall of the elastic tube, or may be intermittently arranged.
FIG. 5 is a schematic view showing an example of the arrangement of the backflow prevention member. In FIG. 5, the backflow prevention member 5 is located on the way of the air-fuel mixture conveying means 4 connected to the discharge port 3 b side of the air pump 3. However, since the back-flow preventing member 5 is not provided in the air-fuel mixture conveying means 4 connected to the other end thereof, the cost can be reduced and the mixing of gas with air can be performed at low cost. Since the backflow of the toner (T) can be prevented, a large amount of toner can be transported.
[0011]
【The invention's effect】
Since the present invention is configured as described above, according to the first aspect of the invention, a developing method for visualizing an electrostatic latent image formed on an image carrier in an electrophotographic system to form a toner image is provided. The means is connected to the inlet and outlet of an air pump for transferring a mixture of gas and a gas for fluidizing the toner supplied by a screw pump, and conveys the mixture of toner and gas and circulates the gas. A backflow prevention member is provided on the inner wall of the air-fuel mixture conveying means connected to the discharge port side of the air pump to be reused to prevent the toner from flowing backward, so that the outlet of the air-fuel mixture conveyance means is positioned higher than the air pump. In this way, even after the air pump is stopped, even if vibrations or the like are applied to the toner remaining on the inner wall of the elastic pipe or the like of the air-fuel mixture conveying means, the backflow of the toner to the air pump side is prevented, and the air pump is stopped. High quality image formation is now able to provide an image forming apparatus performed functioning properly. In other words, in a toner recycling mechanism and a toner transport mechanism in which a screw pump and an air pump are used in combination to transport toner as an air-fuel mixture, when the air pump is located at a position lower than the outlet of the air-fuel mixture transport means, When vibration is applied after the air pump is stopped, it is possible to prevent a problem that toner remaining on the inner wall of the air-fuel mixture conveying means flows backward to the air pump side to block the flow path.
In addition, an air-fuel mixture with a gas for fluidizing toner supplied by a screw pump is transferred to a developing unit that visualizes an electrostatic latent image formed on an image carrier in an electrophotographic system to form a toner image. Combined with the inlet and outlet of the air pump to carry the mixture of toner and gas and circulate and reuse the gas Prevent backflow to the inner wall of the mixture carrier coupled to the outlet of the air pump Since the member is provided with a brush to prevent the toner from flowing backward, the discharge port of the air-fuel mixture conveying means is at a position higher than the air pump, and after the air pump is stopped, the elastic pipe of the air-fuel mixture conveying means, etc. Even if vibration etc. is applied to the toner remaining on the inner wall of the printer, a large amount of toner is prevented from flowing back to the air pump side, the toner transport resistance is low, and the air pump functions normally and high quality images Adult is now able to provide an image forming apparatus to be performed. Since the brush is used as the backflow prevention member, the remaining toner is reliably captured by the brush, and is retained by the brush even when vibration is applied, so that the air pump is not clogged. When the air pump is driven again, the toner held by the brush is easily transported to the downstream side. The brush may extend, for example, along the entire circumference of the inner wall of the elastic tube, or may be partially scattered.
[0012]
According to the second aspect of the present invention, a gas for fluidizing toner supplied by a screw pump to developing means for forming a toner image by visualizing an electrostatic latent image formed on an image carrier in an electrophotographic system. The air-fuel mixture is connected to the inlet and outlet of an air pump that transports the air-fuel mixture and transports the air-fuel mixture of toner and gas, and circulates and reuses the gas. A backflow prevention member is provided on the inner wall of the conveying means so as to be inclined with respect to the toner conveying direction to prevent the backflow of the toner. After the pump is stopped, even if vibration or the like is applied to the toner remaining on the inner wall such as the elastic tube of the air-fuel mixture conveying means, the backflow of the toner to the air pump side is prevented, and the toner conveying resistance is further reduced. Aponpu is now able to provide an image forming apparatus is performed function and high-quality image forming properly. Each of the above-described backflow prevention members is disposed so as to be inclined toward the transport direction of the air-fuel mixture, so that the movement of the air-fuel mixture to the downstream side is not hindered. Fall can be effectively prevented.
According to the invention of claim 3 , a gas for fluidizing toner supplied by a screw pump to developing means for forming a toner image by visualizing an electrostatic latent image formed on an image carrier in an electrophotographic system. The air-fuel mixture is connected to the inlet and outlet of an air pump that transports the air-fuel mixture and transports the air-fuel mixture of toner and gas, and circulates and reuses the gas. A backflow prevention member is provided only on a part of the air-fuel mixture conveying means connected to the discharge port side of the air pump on the inner wall of the conveyance means to prevent the toner from flowing backward. Even after the air pump is stopped at a position higher than the pump, even if vibration or the like is applied to the toner remaining on the inner wall such as the elastic tube of the air-fuel mixture conveying means, it is possible to prevent the toner from flowing back to the air pump side, Sutodaun with possible low cost, high quality image forming air pump functions properly now able to provide an image forming apparatus to be performed.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram illustrating a main part (an image forming unit, a toner recycling mechanism, and the like) of an image forming apparatus according to an embodiment of the present invention.
FIG. 2 is an explanatory diagram illustrating a main part (air pump) of the image forming apparatus according to the exemplary embodiment of the present invention.
FIG. 3 is an enlarged cross-sectional view illustrating another main part (brush-shaped backflow prevention member) of the image forming apparatus according to the exemplary embodiment of the present invention.
FIG. 4 is an enlarged cross-sectional view illustrating a main part (a protruding backflow prevention member) of an image forming apparatus according to another embodiment of the present invention.
FIG. 5 is an enlarged sectional view illustrating a main part of an image forming apparatus according to another embodiment of the present invention.
FIG. 6 is an enlarged development view illustrating a main part of a conventional image forming apparatus.
FIG. 7 is an enlarged sectional view illustrating another main part of the conventional image forming apparatus.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Image carrier 2 Developing means, 2a developing roller, 2b paddle, 2c paddle, 2d blade, 2e container, 2f toner supply section 3 Air pump, 3a suction port, 3b discharge port, 3c suction valve, 3d discharge valve, 3e cam Reference numeral 3f Diaphragm 4 Mixed-air conveying means, 4a Inner wall, 4a1 Base cloth 5 Backflow prevention member, 5a Brush, 5b Projection 6 Cleaning unit, 6a Cleaning blade, 6b Discharge pipe 7 Connection means, 7a Horizontal transport screw case, 7b Horizontal transport screw Reference Signs List 8 Drive source 9 Screw pump, 9a Stator, 9b rotor, 9c Holder 10 Charger 11 Exposure means 12 Paper feed unit 13 Registration roller 14 Transfer means, 14a Transfer belt, 14b Transfer cleaning blade, 14c Discharge pipe 15 Fixing unit 16 Discharge roller 101 Image carrier 102 Current Device 103 Air pump 104 Air-fuel mixture conveying means 106 Cleaning unit, 106a Cleaning blade, 106b Discharge pipe 107 Connecting means, 107a Horizontal conveying screw case, 107b Horizontal conveying screw 108 Drive motor, 108a Rotary driving force transmitting means 109 Screw pump, 109a Stator , 109b rotor, 109c holder, 109d outlet

Claims (3)

In an electrophotographic image forming apparatus for forming an image by supplying toner transferred by a screw pump to an electrostatic latent image formed on an image carrier as a gaseous mixture with a gas from a position distant from a developing position, An image carrier for carrying an image, developing means for visualizing the electrostatic latent image formed on the image carrier to form a toner image, and a gas for fluidizing the toner supplied to the developing means an air pump for supplying circulating a mixture conveyance means for forming a circulation path for circulating the gas with coupled to inlet and outlet of the air pump for conveying the mixture of the toner and the gas, the A backflow prevention member provided on the inner wall of the air-fuel mixture conveyance means coupled to the discharge port to prevent backflow of the toner,
The image forming apparatus, wherein the backflow prevention member is a brush. 2. The image forming apparatus according to claim 1, wherein the backflow prevention member made of a brush is inclined with respect to the toner conveying direction . 3. The image forming apparatus according to claim 1, wherein the backflow prevention member made of a brush is disposed only in a part of the air-fuel mixture conveying means connected to the discharge port side of the air pump. .

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