JP2003094712A - Imaging apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably form a toner image having a good image quality in an imaging apparatus where the gap between a toner carrier and a toner flight control means is regulated by touching a gap regulating means to a toner layer on the toner carrier. SOLUTION: A spacer 51 for regulating the gap GP between a toner layer TL and an FPC 4 is disposed on the downstream side of toner flight starting position J in the carrying direction D of the toner layer TL. Since the toner layer TL regulated to have uniform thickness and charging quantity by a toner regulating blade 14 is carried, as it is, to the toner flight starting position J, a toner image having a good image quality can be formed stably. Since the spacer 51 is a conductor, remaining toner T is neutralized through contact with the spacer 51 and thereby removed easily.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine, a facsimile or a printer, and more particularly to copying paper, transfer paper, copying paper, recording paper by controlling the toner flying from the toner carrier to the back electrode. The present invention relates to an image forming apparatus that forms an image by attaching toner to an image receiving body such as a transfer medium.

[0002]

2. Description of the Related Art As an image forming method using toner,
Conventionally, the jumping type and the projection type have been most widely used. In this type of image forming method, an electrostatic latent image corresponding to an image is formed on a photoconductor, and toner as an image forming agent is adhered to the electrostatic latent image on the photoconductor from a toner carrier such as a developing roller. To obtain a toner image, and then transfer the toner image to copy paper, transfer paper, copy paper,
It is to be transferred onto recording paper. However, these image forming methods require a step (photosensitive process) of forming an electrostatic latent image on the surface of the photoconductor, which involves a problem that the apparatus configuration is complicated and the apparatus cost and running cost are high. There is. Therefore, in recent years, as described in U.S. Pat. Nos. 3,689,935 and 5,036,341 and Japanese Patent Laid-Open No. 2001-505146, toner is copied by a function of an electric field, recording paper or intermediate paper. An image forming apparatus of a so-called "toner jet (registered trademark)" system, which forms an image by flying on an image receiving body such as a transfer belt, has been attracting attention.

In this image forming apparatus, a toner carrying member such as a developing roller for carrying toner in a predetermined moving direction is provided, and a toner regulating blade is provided so as to contact the surface of the toner carrying member. ing. Therefore, the toner on the toner carrier is triboelectrically charged by the toner regulating blade and, after being regulated to a predetermined thickness, is transported to the toner flying start position facing the back electrode.

Further, in this image forming apparatus, a flexible printed circuit board (Flexible Printed Circuit) having a plurality of toner passage holes for passing charged toner is disposed between the toner carrier and the back electrode. At the same time, an image receiver such as a recording paper or a transfer medium is arranged between the flexible printed circuit board and the back electrode. Then, a potential difference is applied between the toner carrier and the back electrode to form a transfer electrostatic field that causes the charged toner to fly from the toner carrier to the back electrode. Also,
In the flexible printed circuit board, control electrodes are arranged around each toner passage hole, and each toner passage hole is electrostatically opened / closed by controlling the voltage applied to each control electrode according to an image signal. Corresponding to the signal, the charged toner is caused to fly from the toner carrier to the back electrode through the toner passage hole and adhere to the image receiver. By doing so, a toner image corresponding to the image signal is formed on the image receiving body.

In this type of image forming apparatus, in order to stably form a toner image, it is necessary to keep the gap between the toner carrier and the flexible printed circuit board constant.
Therefore, as described in, for example, Japanese Patent No. 3045295, Japanese Patent Laid-Open No. 2000-211180, a spacer (gap defining means) is arranged on the upstream side in the moving direction with respect to the toner flying start position. Therefore, a gap management technique for keeping the above gap constant is proposed. That is, as shown in FIG.
In the toner transport direction (arrow direction D1 in the figure), the toner flying start position J is located downstream of the toner regulating blade 140.
1 is arranged so as to come into contact with the toner layer TL1 carried on the toner carrier 120 at a position P upstream of 1,
This defines the gap between the toner carrier 120 and the toner flying control means 40.

[0006]

By the way, in the image forming apparatus configured as described above, the toner layer regulated by the toner regulating blade always comes into contact with the spacer before being conveyed to the toner flying start position. In order to improve the image quality of the toner image, it is necessary to consider the influence of this contact on the toner image. However, in the conventional apparatus that manages the gap by the spacer, the influence of the contact of the spacer with the toner layer is not considered at all, and there is much room for improvement in improving the image quality.

The present invention has been made in view of the above-mentioned problems, and an image forming operation for defining the gap between the toner carrier and the toner flying control means by bringing the gap defining means into contact with the toner layer on the toner carrier. An object is to stably form a toner image with good image quality in the apparatus.

[0008]

In order to achieve the above-mentioned object, an image forming apparatus of the present invention carries a back electrode and toner while moving in a predetermined moving direction to fly a toner flying opposite the back electrode. A toner carrier that conveys the toner to a start position, and a toner carrier that is disposed between the back electrode and the toner carrier and that controls the toner flight from the toner flight start position of the toner carrier to the back electrode. A toner flying control means for forming a toner image by landing toner on an image receiving body conveyed between the back electrode and the back electrode; and a toner flying control means arranged downstream of the toner flying start position in the moving direction. A gap defining means for contacting a toner layer carried on the toner carrying body to define a gap between the toner carrying body and the toner flying control means is provided. That (claim 1).

Conventionally, there has been proposed a technique for defining the gap between the toner carrier and the toner flying control means by bringing the gap defining means into contact with the toner layer carried on the toner carrier. In the image forming apparatus adopting the technology, the toner forming the toner layer is conveyed to the toner flying start position while being in contact with the gap defining means, so that the toner and the gap defining means are frictionally contacted with each other. Charge transfer may occur between the toner and the toner, and the charge state of the toner may change before and after the contact with the gap defining means. If the charging state of the toner changes just before being conveyed to the toner flying start position in this way, the flying property of the toner also changes, and as a result, the quality of the toner image may deteriorate.

On the other hand, in the present invention, the gap defining means is in contact with the toner layer on the toner carrier on the downstream side of the toner flying start position to maintain the gap between the toner carrier and the toner flying control means. ing. Therefore, the toner layer formed on the toner carrier is conveyed to the toner flying start position without contacting the gap defining means. Therefore, there is no change in the charging state of the toner as described above, and the toner image formation can be stably performed. Then, similar to the conventional image forming apparatus in which the gap defining means is arranged on the upstream side of the toner flying start position, the gap can be kept constant and good image formation can be performed.

Here, it is preferable that, in the contact portion where the gap defining means is in contact with the toner layer, the gap defining means is in contact with the toner layer with a flat surface or a smooth curved surface (claim 2). The toner layer on the toner carrier is not always uniform at this contact portion. That is, there are cases where toner is missing partially or in a wide range due to the toner flying at the toner flying start position. When the gap defining means is brought into contact with such a toner layer with a sharp edge, This is because the gap may fluctuate according to the unevenness of the layer to impair the image quality, or the toner scraped off at the edges may scatter in the apparatus and stain the image.

Therefore, according to the second aspect of the present invention, such a problem is solved by bringing the flat surface portion of the gap defining means or the smooth curved surface into contact with the toner layer so that good image quality can be obtained. It is configured.

As an example of such a structure, the distance between the toner carrier and the gap defining means increases in the vicinity of the contact portion toward the upstream side in the moving direction,
Moreover, at the upstream end of the gap defining means, the gap may be equal to or larger than the thickness of the toner layer (claim 3). By doing so, it is possible to avoid the edge of the upstream side end portion of the gap defining means from contacting the toner layer, and make contact with the flat surface or curved surface. In addition,
The shape of the gap defining means may be, for example, a wedge shape that narrows toward the upstream side, or a shape in which the contact surface with the toner layer is a part of the cylindrical surface.

In order to continuously form a uniform toner layer on the toner carrier, it is necessary to scrape off the toner remaining on the toner carrier and then supply new toner again. This is because the toner partially remaining on the toner carrier and the charge thereof prevent the new toner from adhering to the toner layer, which causes unevenness in the thickness of the toner layer and its charge amount.

Therefore, the gap defining means is formed of a conductive material, and a voltage applying means for applying a DC voltage for removing the charge of the toner between the toner carrier and the gap defining means. May be further provided (Claim 4). With this configuration,
When the toner remaining on the toner carrier comes into contact with the gap defining means, the charge accumulated in the toner can be effectively released, so that the toner is easily separated from the toner carrier. Therefore, it becomes easy to remove the toner from the toner carrier on the downstream side of the gap defining means.

Further, in such an image forming apparatus, there is a problem that the charged toner is apt to adhere to the inside of the apparatus, and the toner charge adhered in the vicinity of the toner flying start position hinders the flight of the toner or is extremely large. In this case, the toner passage hole for passing the toner to the image receiving side may be blocked.

Therefore, according to the present invention, an opening on the downstream side in the moving direction of a toner passage hole formed in the toner flying control means for allowing the toner flying from the toner carrier to the back electrode to pass therethrough. The distance from the end to the end of the gap defining means on the upstream side in the moving direction is equal to or larger than the diameter of the toner passage hole (claim 5).

In the invention thus constituted, the shortest distance from the opening of the toner passage hole to the gap defining means as viewed in the moving direction of the toner carrier is defined to be a predetermined value or more. Even if the toner comes off from the toner carrier due to the contact with the gap defining means and is deposited around the end portion of the gap defining means, the toner passage hole is not immediately closed. That is, by setting this distance to be at least the diameter of the toner passage hole, the adhesion of the toner due to the peeling off is not a serious problem over other causes of clogging the toner passage hole, such as insufficient charge amount of the toner. . On the contrary, when this distance is made smaller than the diameter of the toner passage hole, the above-described toner peeling may be a main cause of blocking the toner passage hole, and continuous printing operation may not be possible.

Further, according to the present invention, when the volume average particle size of the toner is R and the standard deviation in the particle size distribution is σ, the toner flies from the toner carrier toward the back electrode. The distance from the opening end portion of the toner passage hole formed in the toner flight control means for allowing the passage of the toner flow control means on the downstream side in the moving direction to the end portion of the gap defining means on the upstream side in the moving direction is ( R +
3σ) or more (claim 6).

From the viewpoint of controllability of toner flight, it is desirable that the particle diameter of the toner is uniform to a certain value, but considerable variations occur depending on the material of the toner and the manufacturing method thereof. In some cases, toner particles having a large particle size of several times or more are mixed. Such large particles come off from the toner carrier,
If the toner particles adhere to the vicinity of the toner passage hole, the toner particles that subsequently fly from the toner carrier collide with the toner particles and agglomerate with each other, forming a large lump and hindering the toner flight. Therefore, if the above-mentioned distance is at least (R + 3σ), even if toner particles slightly contained in the entire toner and having a larger particle diameter than the toner particles come off due to the contact between the toner carrier and the gap defining means, it is immediately Such a problem can be avoided because the toner does not interfere with the passage hole to prevent the toner from flying.

[0021]

1 is a diagram showing an embodiment of an image forming apparatus according to the present invention. 2 is a block diagram showing an electrical configuration of the image forming apparatus of 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 main controller 1
The engine controller 102 controls each part of the developing device 1 in accordance with a signal from 01, so that the two rollers 21,
The toner flies and adheres to the intermediate transfer belt 23 that is stretched around the sheet 22 to form a toner image corresponding to the image signal. Thus, in this embodiment, the intermediate transfer belt 23
Is functioning as an image receiver.

In this developing device 1, in the housing 11,
The toner T as a developer is stored, and the developing roller 12, the supply roller 13, and the regulation blade 14 are housed. The developing roller 12 carries a charged toner (that is, charged particles for image formation) T, and rotates at a predetermined peripheral speed in a direction D of an arrow in FIG. 1 to face a rear electrode 3 described later (toner). Flight start position) J
It is a toner carrier to be transported to. This developing roller 12
Is formed in a cylindrical shape with a metal or alloy such as aluminum or iron, and a DC voltage is applied from the developing roller bias generator 103 provided in the engine controller 102.

The supply roller 13 is brought into contact with the outer peripheral surface of the developing roller 12 and rotates in the opposite direction to the developing roller 12,
The toner T is supplied to the developing roller 12 and the excess toner T is dropped from the developing roller 12. The supply roller 13 is made of, for example, a metal core wrapped with synthetic rubber such as urethane sponge, and also has a function of charging the toner T to a predetermined polarity by frictionally contacting the developing roller 12. In the present embodiment, the toner T will be described below as being negatively charged.

The regulation 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 the toner T is negatively charged by friction with the developing roller 12. The amount of toner T carried on the developing roller 12 is regulated. More specifically, the regulation blade 14 is constituted by a plate-shaped metal piece 141 having one end fixed to the housing 11, and an elastic member 142 attached to the other end of the plate-shaped metal piece 141. Contact the surface, toner T
Are regulated.

The back electrode 3 is opposed to the developing roller 12.
Are arranged. More specifically, the back electrode 3 is shown in FIG.
As shown in FIG. 3, the intermediate transfer belt 23 is sandwiched between the developing roller 12 and the developing roller 12. The back bias generator 104 provided in the engine controller 102
Therefore, a DC voltage higher than the voltage applied to the developing roller 12 is applied, and a transfer electrostatic field for transferring the charged toner T toward the back electrode 3 is applied between the developing roller 12 and the back electrode 3. Has been formed. For this reason, the charged electrostatic toner T at the toner flying start position J is generated by the transfer electrostatic field.
Flies from the developing roller 12 toward the back electrode 3 and is deposited and attached to the surface of the intermediate transfer belt 23 that functions as an image receiver.

In this embodiment, a flexible printed circuit board (hereinafter referred to as FPC) 4 is provided between the developing roller 12 and the back electrode 3 in order to control the flight of the charged toner T onto the intermediate transfer belt 23. It is arranged. Hereinafter, the configuration and operation of the FPC 4 will be described with reference to FIGS. 3 and 4.

FIG. 3 is a diagram showing a partially enlarged cross section of a flexible printed circuit board and a flying model of charged toner. Further, FIG. 4 is a view showing control electrodes and deflection electrodes formed on the flexible printed circuit board. This F
In the PC 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.
Although only one toner passage hole 41 is shown in FIG. 3, in this embodiment, a plurality of toner passage holes 41 are provided in a line in the direction perpendicular to the plane of FIG. The charged toner T can pass through the toner passage holes 41 toward the back electrode 3 side. Although the toner passage holes 41 are arranged in one row in this embodiment, they may be arranged in plural rows. Further, the shape of the toner passage hole 41 may be circular as in this embodiment, or may be elliptical or polygonal.

On the developing roller 12 side of the substrate 42, a control electrode 43 is formed in a ring shape so as to surround each toner passage hole 41. In addition, each control electrode 43
The lead wire 44 extends in the direction orthogonal to the arrangement direction of the toner passage holes 41. The shape of the control electrode 43 is not limited to the circular shape, but may be any shape, and may be, for example, an elliptical shape or a polygonal shape. Further, the control electrode 43 may have a partial cutout instead of a perfect ring. .

On the back electrode 3 side of the base body 42,
A pair of deflection electrodes 45L, 4L is provided for each toner passage hole 41.
As shown in FIG. 4, 5R is provided so as to be diagonally opposed to the conveyance direction Y of the intermediate transfer belt 23 (direction orthogonal to the toner passage hole array), and the deflection electrodes 45L, 4L,
Lead wires 46L and 46R are extended from 5R, respectively.

Although not shown in FIGS. 3 and 4, the base body 42 includes a control bias generator 47 (FIG. 2) and an L deflection bias generator 48L (FIG. 2) which are composed of a high voltage driver IC or the like. And R deflection bias generator 48
R (FIG. 2) is provided. Of these, the control bias generator 47 is electrically connected to each control electrode 43, and an appropriate voltage is selectively applied according to an opening / closing control signal from the CPU 105 of the engine controller 102, whereby the toner is discharged. The passage hole 41 is opened and closed electrostatically. That is, for each control electrode 43, the charged toner T is ejected from the developing roller 12, passes through the toner passage hole 41, and is ejected toward the back electrode 3, so that the toner is between the developing roller 12 and the back electrode 3. It exposes the transfer electrostatic field passing through the passage hole 41 and limits the exposure.

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. The engine controller 102 controls deflection. By appropriately applying an appropriate voltage to each of the deflection electrodes 45L and 45R according to the signal, the charged toner T
The flight direction of is switched to the following three directions.

(1) No deflection: When the same voltage is applied to both the deflection electrodes 45L and 45R of the arrow P1 in FIG. 3, the charged toner T has a toner passage hole 41 as shown by the arrow P1 in FIG. Straight through the intermediate transfer belt 23
And fly to a position corresponding to the toner passage hole 41 on the above.

(2) Left deflection: Among the deflection electrodes 45L and 45R indicated by the arrow P2 in FIG. 3, the deflection electrode 45L disposed on the left side of the toner passage hole 41 on the right side of the deflection electrode 45L arranged on the left side of the intermediate transfer belt 23 as a reference. Deflection electrode 45 arranged
When a voltage relatively higher than R is applied, the charged toner T charged in the negative polarity has a static charge for deflection generated between the electrodes 45L and 45R as shown by an arrow P2 in FIG. It is deflected to the left by the electric field.

(3) Rightward deflection: Among the deflection electrodes 45L and 45R indicated by the arrow P3 in FIG. 3, the deflection electrode 45R disposed on the right side of the toner passage hole 41 on the left side of the deflection electrode 45R disposed on the right side of the conveyance direction Y of the intermediate transfer belt 23 is a reference. Deflection electrode 45 arranged
When a voltage relatively higher than L is applied, the charged toner T, which is negatively charged, is deflected statically between the electrodes 45L and 45R as shown by the arrow P3 in FIG. It is deflected to the right by the electric field.

As described above, in this embodiment, while changing the flying direction of the charged toner T to three directions, the charged toner T is landed on the intermediate transfer belt 23 at the landing position PI of the intermediate transfer belt 23 including the deflection range. I am letting you.

However, as described above, the deflection electrodes 45L, 45
Since R is diagonally opposed to the transport direction Y of the intermediary transfer belt 23, the intermediary transfer belt 23 is formed by the three modes of (1) no deflection, (2) left deflection, and (3) right deflection. When 23 is stopped, the intermediate transfer belt 23
On the intermediate transfer belt 23, three dots lined up obliquely with respect to the transport direction Y of. In this case, the transport speed is determined so that the intermediate transfer belt 23 is transported by the displacement amount (distance) of the adjacent dots in the cycle (time) of hitting the dots, so that the three dots are transferred to the intermediate transfer belt 23. They can be arranged linearly in the direction orthogonal to the transport direction Y. Therefore, three dots can be formed with one toner passage hole 41, and the density of the dots can be increased.

In the base 42 of the FPC 4, the developing roller 12
On the surface 421 on the side and the surface 422 on the side of the back electrode 3, a semiconductive layer 49 for antistatic is formed and a ground potential is given. These semi-conductive layers 4
Reference numeral 9 indicates an optimum resistance value at a preset temperature (initial setting temperature). The frictional charge generated when the charged toner T flying as described above comes into contact with the FPC 4 is indicated by the FPC 4
The FPC 4 can be effectively prevented from being discharged from the above, and the influence on the electrostatic transfer field and the deflection electric field can be suppressed. That is, good print quality can be ensured while the temperature of the semiconductive layer 49 is maintained within the initial set temperature or the allowable temperature range.

Further, on the downstream side of the toner flying start position J in the rotation direction D of the developing roller 12, between the FPC 4 and the developing roller 12 configured as described above, the longitudinal direction of the developing roller 12 (the plane of FIG. 3). The spacer 51 spread over the entire length in the vertical direction) is inserted to the front side of the toner passage hole 41 of the FPC 4, and a part of the spacer 51 is held on the developing roller 12 by the toner layer T.
By making contact with L, the gap GP between the developing roller 12 and the toner passage hole 41 of the FPC 4 is regulated to a constant value. As described above, in this embodiment, the spacer 51 functions as the gap defining means. This spacer 51
The structure and function of will be described in detail later.

In the image forming apparatus configured as described above, when an image signal is given from the external device to the main controller 101 of the control unit 100, the CPU 105 of the engine controller 102 responds to the signal from the main controller 101. Applies a control signal corresponding to the image signal to the control bias generation unit 47, the L deflection bias generation unit 48L and the R deflection bias generation unit 48R to cause the toner T to fly and adhere onto the intermediate transfer belt 23 to correspond to the image signal. The formed toner image is formed. Then, the toner image is transferred onto a sheet S such as a copy sheet, a transfer sheet, and an OHP transparent sheet taken out from the cassette 7 in a predetermined transfer region TR. Further, the sheet S on which the image is thus formed is conveyed to the discharge tray (not shown) via the fixing unit 8.

Next, the structure of the spacer 51 and its action will be described in more detail with reference to FIGS. 3, 5 and 6. FIG. 5 is a sectional view showing a main part of a conventional image forming apparatus. Further, FIG. 6 is a plot of the surface potential before and after the toner layer TL1 passes through the contact position P with the spacer 5 in the axial direction of the developing roller 120.

As shown in FIG. 5, in the conventional image forming apparatus, the spacer 5 is located at a position P downstream of the toner regulating blade 140 in the toner transport direction D1 and upstream of the toner flying start position J1. Developing roller 12
0 and the FPC 40, the toner layer T
It is in contact with L1. That is, the toner T charged by frictional contact with the toner regulating blade 140 inside the housing 110 comes into contact with the spacer 5 at the position P while being conveyed to the toner flying start position J1 by the developing roller 120.

When the influence of the contact between the spacer 5 and the toner layer TL1 on the surface potential of the toner layer TL1 was tested in this way, the results shown in FIG. 6 were obtained. In this experiment, the surface potential of the toner layer TL is measured by a surface potential meter (model number: MODEL344) manufactured by Trek Japan KK As can be seen from the experimental results shown in FIG.
The surface potential (waveform WF1) of the toner layer TL1 before passing through the contact position P was substantially uniform in the axial direction of the developing roller 120, whereas after passing through the contact position P (waveform WF2). It is greatly disturbed in the axial direction. When the toner is caused to fly while the surface potential is disturbed in the axial direction as described above, the disturbance is directly reflected in the toner image on the image receptor as image quality deterioration. The surface potential of the toner layer reflects the charged state of the toner particles forming the toner layer, and the difference in the charged state of the toner depends on the flying amount of toner at the toner flying start position and the electrostatic field for deflection. This is because the difference appears in the amount of deflection.

On the other hand, in the image forming apparatus of this embodiment, as shown in FIG. 3, the spacer 51 is arranged downstream of the toner flying start position J in the toner transport direction D. Therefore, the toner layer T on the developing roller 12
L is conveyed to the toner flying start position J while maintaining the uniform surface potential shown by the waveform WF1 in FIG. Therefore, the flying amount and the deflection amount of the toner T at the toner flying start position J are stabilized, and as a result, a toner image can be stably formed on the intermediate transfer belt 23 with good image quality.

The spacer 51 is formed of a conductive material such as copper or stainless steel, and is in contact with the semiconductive layer 49 formed on the surface 421 of the FPC 4 and supplied with the ground potential. Therefore, the ground potential is also applied to the spacer 51. Therefore, the developing roller 1
When the charged toner T on 2 comes into contact with the spacer 51, the charge of the toner T is released to the ground through the spacer 51, and the charge of the toner T is weakened, that is, the charge is removed. In this way, the toner T that has been discharged in this way weakens its adhesion to the developing roller 12, so that the surface of the developing roller 12 that has returned to the inside of the housing 11 (FIG. 1) comes into contact with the supply roller 13 again, and the old toner is scraped off. The new toner is always supplied to the developing roller 12. In FIG. 3, the charged toner is indicated by a circle with hatching, and the discharged toner is indicated by a circle without hatching.

The spacer 51 is formed in a wedge shape whose thickness decreases toward the left side in FIG. 3, that is, toward the upstream side in the toner conveying direction D, and the inclined surface F thereof is formed.
At the toner layer TL on the developing roller 12. Here, when the spacer 51 is formed in, for example, a flat plate shape having a uniform thickness and is in contact with the toner layer TL at the edge portion thereof, the edge of the spacer 51 hits the discharged toner to cause the developing roller to come into contact. The toner is easily scraped off from 12. The toner scraped off in this manner adheres to the periphery of the contact portion to change the gap GP, and scatters inside the apparatus to stain the toner image.

On the other hand, in this embodiment, as described above, the toner layer TL is formed on the inclined surface F of the spacer 51.
Since the edge portion is in contact with the toner, the edge portion does not hit the toner, and such scraping of the toner is suppressed. Further, since the toner layer TL and the spacer 51 are in contact with each other over a relatively wide area, even if the toner layer TL has irregularities due to the toner flying at the toner flying start position J, the variation in the gap GP due to this is reduced. The gap GP can be kept constant.

Further, the spacer 51 is provided at a position where the distance d from the end of the toner passage hole 41 provided in the FPC 4 satisfies the following relationship: d ≧ R + 3σ
(1) where R is the volume average particle diameter of the toner T, σ
Is the standard deviation of the particle size distribution. The reason for such a configuration will be described with reference to FIGS. 7 and 8.
FIG. 7 is a graph showing an example of the toner particle size distribution,
FIG. 8 is a partial cross-sectional view showing the structure near the toner flying start position J of this image forming apparatus. The toner T used in the image forming apparatus of this embodiment contains particles having various particle sizes, and the particle size distribution can be expressed as a normal distribution centered on R as shown in FIG. 7, for example.

By the way, the toner particles peeled off from the toner layer TL at the contact portion with the spacer 51 are removed by the spacer 5.
It is considered that they adhere to the FPC 4 in the vicinity of the end portion of 1 (the position of symbol E in FIG. 8). Here, when the toner particles attached to the position E in this way have extremely large particle diameters as indicated by reference numeral T1 shown in FIG.
May block part of 1. The presence of such large particles T1 and the charges thereof affects the flying of the toner particles that are going to pass through the toner passing hole 41 by the subsequent flying. That is, the flying toner particles collide with the toner particles attached to the FPC 4, and the flying direction is changed by the electric field generated by the charges of the charged toner particles T1. Then, the toner particles T1
When other toner particles aggregate to form a large lump, the above-mentioned influence is further strengthened, and the flight of the toner is further hindered, and finally the printing operation becomes impossible.

Therefore, in this embodiment, the distance d from the end of the toner passage hole 41 to the end of the spacer 51 is set so as to satisfy the above expression (1). By doing so, the particle size that occupies most of the toner T is (R +
Even if toner particles having a size of 3σ or less adhere to the position E on the FPC 4, they do not immediately affect the toner flight, and the time during which the toner flight is correctly controlled to continuously perform the printing operation is lengthened. It is possible to do.
The particle size of the toner particles T1 is (R + 3σ).
If the particle size distribution of the toner T is, for example, the normal distribution shown in FIG. 7, the mixing ratio of particles exceeding 0.1 is about 0.14%, and the probability that such toner particles adhere and hinder the flight of toner is low. It can be said that it is low enough.

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 spacer 5 is formed in a wedge shape, and the inclined surface F thereof forms the toner layer TL on the developing roller 12.
However, other than this, for example, the inclined surface F
May be further extended to the upstream side so as to be smoothly connected from the FPC 4 at the position E to the end of the spacer 5. Further, for example, the upper surface of the spacer 5 may be formed so as to be a part of a cylindrical surface whose axial direction is the direction perpendicular to the paper surface of FIG. 3, and the curved surface portion may be brought into contact with the toner layer TL. .

Further, for example, in the above-described embodiment, the spacer 5 is brought into contact with the semiconductive layer 421 provided on the surface of the FPC 4 to give the ground potential. Applying bias voltage to toner T
May be neutralized. At this time, as the power supply for applying the bias voltage, the output voltage of the power supply, which is indispensable for giving appropriate potential to each part of the device, may be used, and the bias voltage is applied to the spacer 5. A power supply for this purpose may be separately provided.

When a bias voltage is applied to the spacer 5, the distance d from the toner passage hole 41 to the end of the spacer 5 is set so as not to disturb the transfer electrostatic field near the toner flying start position J. It is desirable to take it larger than the form. The distance d may be equal to or larger than the diameter of the toner passage hole 41, for example. In this way, the electrostatic transfer field is not disturbed by the bias voltage applied to the spacer 5,
Further, even if the toner peeled off from the developing roller 12 due to the contact with the spacer 5 is accumulated around the end portion of the spacer 5, it takes time until the toner reaches the vicinity of the toner passage hole 41 and affects the flight of the toner. Therefore, the printing operation can be continuously performed during that time.

Further, for example, in the above embodiment, after the toner image is formed on the transfer medium such as the intermediate transfer belt 23,
The present invention is applied to an intermediate transfer type image forming apparatus that transfers the toner image on the transfer medium to the sheet S. However, the charged toner T flying from the developing device 1 is directly landed on the sheet S to form an image. The present invention may be applied to an image forming apparatus to be formed.

In the above embodiment, the semiconductive layer 49 is used.
The present invention is applied to an image forming apparatus in which the FPC 4 is provided with antistatic property, but the application target of the present invention is not limited to this, and an antistatic semiconductive layer is provided. The present invention can be applied to an image forming apparatus which is not provided.

In the above embodiment, the deflection electrode 45 is used.
The flying directions of the charged toner T are three directions P by L and 45R.
Although the present invention is applied to an image forming apparatus that can switch between 1, P2, and P3, the application target of the present invention is not limited to this, and an image in which the flight direction of the charged toner T is fixed is used. The present invention can be applied to a forming apparatus.

Further, in the above-described embodiment, the present invention is applied to an image forming apparatus which forms an image with one developing device 1, that is, which executes so-called monochromatic printing. However, for example, in the case of forming a full-color image, In contrast to a so-called tandem type color image forming apparatus in which the same developing devices 1 for four types of toners of yellow, magenta, cyan and black are arranged in a line in the conveyance direction Y of the intermediate transfer belt 23 or the sheet S, However, the present invention can be applied.

[0057]

As described above, according to the present invention, since the gap defining means is arranged on the downstream side in the toner carrying direction with respect to the toner flying start position, the toner on the toner carrier is in its charged state. Is conveyed to the toner flying start position without being disturbed. Therefore, the toner flying amount at the toner flying start position is stable, and as a result, it is possible to stably form a toner image with good image quality.

Further, the charged toner can be discharged by the contact between the gap defining means arranged on the downstream side and the toner layer. In this case, the toner remaining on the toner carrier can be removed. Since the toner layer can be removed and a new toner layer can be constantly supplied to the toner carrier, a more stable toner image can be formed.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an electrical configuration of the image forming apparatus of FIG.

FIG. 3 is a diagram showing a partially enlarged cross section of a flexible printed circuit board and a flying model of charged toner.

FIG. 4 is a diagram showing control electrodes and deflection electrodes formed on a flexible printed circuit board.

FIG. 5 is a sectional view showing a main part of a conventional image forming apparatus.

FIG. 6 is a graph in which surface potentials before and after a toner layer passes a contact position with a spacer are plotted in an axial direction of a developing roller.

FIG. 7 is a graph showing an example of toner particle size distribution.

FIG. 8 is a partial cross-sectional view showing the structure near the toner flying start position of this image forming apparatus.

[Explanation of symbols]

3 ... Back electrode 4 ... FPC 12 ... Developing roller (toner carrier) 14 ... Toner regulation blade 23 ... Intermediate transfer belt (image receptor) 41 ... Toner passage hole 51 ... Spacer (gap defining means) D ... Rotation direction (of the developing roller 12) F ... Inclined surface (of spacer 5) GP ... Gap J: Toner flight start position T ... toner T1 ... Toner particles TL ... toner layer

   ─────────────────────────────────────────────────── ─── Continued front page    F-term (reference) 2C162 AE04 AE25 AE31 AE47 AE89                       AJ03 AJ09 AJ16 AJ23 AJ24                       AJ25 AJ26 CA02 CA12 CA22                 2H029 DB00

Claims (6)

[Claims] 1. A back electrode, a toner carrier that carries a toner, moves in a predetermined moving direction, and conveys the toner to a toner flying start position facing the back electrode, the back electrode and the toner. The toner is landed on the image receiving body which is disposed between the image carrier and the rear electrode by controlling the flight of the toner from the toner flying start position of the toner carrier to the back electrode. Flying control means for forming a toner image by means of a toner layer, and a toner layer arranged on the downstream side in the moving direction with respect to the toner flying start position and in contact with a toner layer carried on the toner carrying body. An image forming apparatus comprising: a gap defining unit that defines a gap with the toner flying control unit. 2. The contact part where the gap defining means is in contact with the toner layer, the gap defining means is in contact with the toner layer with a flat surface or a smooth curved surface. The image forming apparatus according to item 1. 3. The distance between the toner carrier and the gap defining means increases toward the upstream side in the moving direction in the vicinity of the abutting portion, and the gap is defined at the upstream end of the gap defining means. The image forming apparatus according to claim 2, wherein the distance is equal to or larger than the thickness of the toner layer. 4. The gap defining means is formed of a conductive material, and a voltage applying means for applying a DC voltage for removing the charge of the toner between the toner carrier and the gap defining means. The image forming apparatus according to claim 1, further comprising: 5. A toner passage hole formed in the toner flight control means for allowing toner flying from the toner carrier to the back electrode to pass, from an opening end portion on the downstream side in the moving direction, 5. The image forming apparatus according to claim 1, wherein the distance to the end of the gap defining means on the upstream side in the moving direction is equal to or larger than the diameter of the toner passage hole. . 6. The volume average particle diameter of the toner is R,
And when the standard deviation in the particle size distribution is σ,
From the opening end on the downstream side in the moving direction of the toner passing hole formed in the toner flying control means for allowing the toner flying from the toner carrier to the back electrode to pass, the upstream side in the moving direction. The image forming apparatus according to any one of claims 1 to 4, wherein the distance to the end of the gap defining means on the side is (R + 3σ) or more.