JPH08112932A - Image forming apparatus - Google Patents

Abstract

PURPOSE: To carry out the printing of high quality by constituting a rear electrode element so as to reduce the difference in the intensity of the electric field to an image recording medium between the aperture part and non-aperture part of an electrode array. CONSTITUTION: The difference between the distance from the place of a control electrode to the outer peripheral surface of the recessed annular part 2b opposed to an aperture part 12 and the distance from the place of the control electrode to the outer peripheral surface of the protruding annular part 2a opposed to a non-aperture part 14 is eliminated or reduced. Therefore, the difference in the intensity of the electric field formed between an image recording medium 3 and an electrode array 1 is reduced between the region opposed to the aperture part 12 and the region opposed to the non-aperture part 14. The accumulation amt. of toner on the surface of the image recording medium 3 of the region opposed to the aperture part 12 and that of toner on the surface of the image recording medium 3 of the region opposed to the non-aperture part 14 become almost equal and the diffusion rate of the toner to the surfaces of the image recording medium 3 of the regions opposed to the aperture part 12 and the non-aperture part 14 adjacent thereto is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a structure of an image forming apparatus which can be used in a copying machine, a facsimile machine, a printer, etc., and more specifically, an image forming apparatus for forming an image by flying charged toner by an electric field. It is about.

[0002]

2. Description of the Related Art Heretofore, as an image forming apparatus of this type, the applicant of the present invention has previously disclosed that a thin film-like electric insulating sheet is provided with a plurality of openings in a line in JP-A-6-155798. A control electrode is provided for each opening in the electrode array, and an image recording medium such as a sheet of paper and a back electrode body are provided on the opposite side of the toner carrying roller in the toner case containing toner from the electrode array. An image forming apparatus for forming an image on the image recording medium by controlling the passage of the charged toner through an opening by a control voltage applied to each of the control electrodes. It has been proposed that a DC power source is connected between the body and the body, and that a voltage of 0 V is applied to the toner carrying roller and a voltage of +1 kV is applied to the back electrode body.

According to this structure, the negatively charged toner is carried on the surface of the toner carrying roller and conveyed to the vicinity of the opening of the electrode array, and the control electrode of the opening corresponding to the image forming portion is controlled to + 50V or the like. When a voltage is applied,
Due to the potential difference between the control electrode and the toner carrying roller, the negatively charged toner receives an electrostatic force in the direction of the control electrode having a high potential and is pulled out toward the opening.

The toner thus drawn out from the opening flies toward the surface of the image recording medium due to an electric field formed between the back electrode body and the image recording medium, to which a voltage of +1 kV is applied. Toner can be accumulated on the surface of the image recording medium to form visible pixels.

[0005]

However, according to the above configuration, the control electrode is provided so as to surround the openings arranged in a row at a constant interval in the electrode array. However, a portion between the adjacent openings is provided. Since the control electrode does not exist in the non-opening portion (hereinafter referred to as the non-opening portion), no electric field is formed between the non-opening portion and the back electrode body facing the non-opening portion, or even if the electric field is formed, the non-opening portion faces the non-opening portion. Since the strength of the electric field in the portion to be opened is extremely smaller than the strength of the electric field in the portion facing the opening, even if the electric field control is performed by the control electrode in the opening, the image recording medium corresponding to the non-opening Toner does not fly toward the surface of the.

[0006] Therefore, although a large amount of toner is accumulated on the surface of the image recording medium facing the opening, there is little or no toner accumulation on the surface of the image recording medium facing the non-opening. , The density difference of the image such as continuous straight lines parallel to the opening row can be large,
It was not possible to form a high quality image. In order to solve this inconvenience, it is conceivable to reduce the interval between the openings arranged in rows, but the electrode array is a thin film, and the electrode array should not be wrinkled and the electrode array Since the vicinity of the lower surface of each opening is pressed against the surface of the toner carrying roller with a substantially uniform contact pressure, it is necessary to apply an appropriate pulling force. A fatal defect occurs in which a crack is generated such that the openings are continuous with each other.

Further, there is a problem in that the space between the openings cannot be reduced to a certain value or less due to the physical limitation of the size of the openings and the width of the control electrode surrounding the outer circumference. The present invention has been made to solve these technical problems, and an object of the present invention is to provide an image forming apparatus that can obtain high-quality printing.

[0008]

In order to achieve the above object, the image forming apparatus of the invention according to claim 1 is a film-shaped electrode in which a plurality of openings are formed and each opening has a control electrode. An array, a toner supply means for supplying toner to the openings of the electrode array, an image recording medium and a back electrode body arranged on the opposite side of the electrode array from the toner supply means, and each of the electrode arrays. An image forming apparatus comprising: a control unit that independently controls a control electrode to selectively fly the toner from a toner supply unit onto the image recording medium through an opening by an electric field;
Openings are formed in a row in the electrode array in a direction intersecting with the moving direction of the image recording medium, and the back electrode body is formed by the openings and non-openings in the electrode array. It is configured to reduce the difference in the strength of the electric field with respect to.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the surface of the back electrode body is brought closer to the image recording medium at a portion facing the non-opening portion and faces the opening portion. It is configured so as to be separated from the image recording medium at the portion to be opened. According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the rear electrode body is formed in a roller shape, and the outer peripheral surface of the rear electrode body faces the non-opening portion. Is formed in the concavo-convex annular portion so as to approach the image recording medium and separate from the image recording medium at the portion facing the opening.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, electrodes are provided on the surface of the back electrode body at a portion facing the opening and a portion facing the non-opening, respectively. And a voltage applied to the electrode portion facing the non-opening portion is higher than a voltage applied to the electrode portion facing the opening portion.

[0011]

Next, an embodiment of the present invention will be described. FIG. 1 shows an outline of an image forming apparatus of the present invention, which is about 1 mm from the surface of an electrode array 1 as toner flow control means.
In the first embodiment, the metal-roller-shaped rear electrode body 2 rotating in the direction of the arrow A has a frame (not shown).
Supported by.

An image recording medium 3 such as a printing paper, which is inserted in a gap between the electrode array 1 and the back electrode body 2, can be conveyed in the direction of arrow B by a paper feeding device 4 composed of a roller pair. On the downstream side in the transport direction of the image recording medium 3,
A fixing device 5 including a heating roller 6 and a pressing roller 7 for fixing an image is arranged. Next, the respective components will be described in detail. A toner supply device 8 as a toner supply unit includes a toner case 9 that also serves as a housing.
The toner 18 contained in the toner case 9, the supply roller 15, the conductive toner carrying roller 16 made of a metal cylinder such as copper or aluminum, and the like. A toner carrying roller 16 and a supply roller 15 having a rotating shaft in a direction orthogonal to the direction in which the image recording medium 3 is conveyed.
Have substantially the same length and are rotated in the directions of arrows D and C in FIG. 1 by a rotation driving device (not shown).

The back surface of the insulating sheet 11 is arranged so that the rows of openings 12 of the electrode array 1 described later are along the axis of the toner carrying roller 16 and the openings 12 are in contact with part of the outer peripheral surface of the toner carrying roller 16. Has been done. The base end of a regulation blade 19 for regulating the toner layer thickness, which is in pressure contact with the peripheral surface of the toner carrying roller 16 on the upstream side of rotation, is fixed to the toner case 9, and the toner 18 supplied by the supply roller 15 is supplied.
Is slidably contacted with the outer peripheral surface of the toner carrying roller 16 by the regulation blade 19 to regulate the layer thickness of the toner 18 to a predetermined uniform thickness and to charge the toner 18.

The electrode array 1, as shown in FIG.
A plurality of openings 12 having a diameter of about 100 μm are formed in a row in a direction orthogonal to the moving direction of the image recording medium 3 on an insulating sheet 11 made of polyimide as an electrically insulating base material having a thickness of 5 μm. Control electrodes 13 are formed on the side facing the image recording medium 3 so as to be divided into the openings 12.

If the insulating sheet 11 is made too thin,
A polyimide resin having a thickness of 25 μm is suitable because it becomes difficult to form the control electrode 13 and handle the electrode array 1 itself. As shown in FIG. 2, for each opening 12 such as a round hole formed by penetrating the insulating sheet 11, an annular electrode portion is provided on the upper side of the insulating sheet 11 along the circumferential edge of each opening 12. A control electrode 13 composed of 13a and a lead portion 13b for connecting each electrode portion 13a to the control voltage applying circuit 21 is formed of a metal such as copper or gold having a thickness of about 1 μm.

In the embodiment shown in FIGS. 1 and 2, the lead portion 13b of the control electrode with respect to the openings 12 arranged in a line extends along the moving direction of the image recording medium 3 and the outer peripheral portion of the electrode array 1 is covered with the toner. It is fixed to the upper flange of the case 9. As a result, the back surface of the sheet 11 in the stretched electrode array 1 contacts the upper surface of the toner carrying roller 16. In this state, the position of the row of the openings 12 is kept pushed upward by the outer peripheral upper surface of the toner carrying roller 16, so in other words, the toner carrying roller 16 is held.
On the other hand, the sheet 11 is bent at substantially the same angle upstream and downstream in the moving direction of the image recording medium 3 with the row of the openings 12 as the center, and the rows 12 of the openings 12 form the toner carrying roller 16.
Is uniformly pressed against the outer peripheral surface of the toner carrying roller 16 and has a tension force component in a direction in which the contact area with the outer peripheral surface of the toner carrying roller 16 increases.

Next, the structure of the back electrode body 2 will be described. The back electrode body 2 is defined by the openings 1 in the electrode array 1.
2 and the non-opening portion 14 (a portion between the adjacent opening portions 12 and 12, the same applies hereinafter) reduces the difference in the electric field strength with respect to the image recording medium 3. For example, the strength of the electric field in the non-opening portion 14 and the strength of the electric field in the opening portion 12 are made substantially equal to each other, or the strength of the electric field in the non-opening portion 14 is brought close to the strength of the electric field in the opening portion 12 (the difference is reduced. ) Is configured as follows. The strength of the electric field in the non-opening portion 14 may be made substantially equal to the strength of the electric field in the opening portion 12, or the strength of the electric field in the non-opening portion 14 may be made stronger.

In the first embodiment shown in FIGS. 3 and 4, the back electrode body 2 is formed of a conductive metal into a roller shape, and the openings 12 are formed on the outer peripheral surface of the back electrode body 2. The concave annular portions 2b and the convex annular portions 2a are alternately formed so as to be spaced apart from the image recording medium 3 at a portion facing the image recording medium 3 and approach the image recording medium 3 at a portion facing the non-opening portion 14. To do.

Therefore, the back surface of the image recording medium 3 is in contact with the outer peripheral surface of the convex annular portion 2a having a large diameter, but the back surface of the image recording medium 3 is not in contact with the outer peripheral surface of the concave annular portion 2b having a small diameter. (See FIGS. 3 and 4). A DC power supply 20 is connected between the back electrode body 2 and the toner carrying roller 16 so that a high voltage of about +1 kV is applied to the back electrode body 2.
And the control voltage applying circuit 21 are connected to each other, and the control electrode 1 is controlled based on an image forming signal from a data control circuit (not shown).
3 is applied with a voltage of 0V or + 50V.

The toner 18 is an electrically insulating toner having an electrically insulating property, and is supplied to the surface of the toner carrying roller 16 by the supply roller 15. Conductive toner carrying roller 1
Including the surface 6 and the toner 18 attached thereto, the potential becomes the same as a whole. Next, the recording operation (printing operation) of the image forming apparatus thus configured will be described.

First, the toner carrying roller 16 and the toner supply roller 15 having substantially the same length as the toner carrying roller 16 rotate in the directions of arrows D and C shown in FIG. The insulating toner 18 sent from the supply roller 15 is rubbed against the surface of the toner carrying roller 16 and is charged to a large negative value.

Next, the blade 1 for regulating the toner layer thickness
At 9, the layer thickness of the toner 18 is thinned to a predetermined value, and the toner 18 carried on the surface of the toner carrying roller 16 is rubbed against the back surface of the sheet 11 of the electrode array 1 by the rotation of the toner carrying roller 16. It is conveyed toward the opening 12. Here, when there is an image, the control voltage application circuit 21 is driven based on the image signal from the data control circuit, and the voltage of +50 V is applied to the control electrode 13 corresponding to the image portion. As a result, the opening 1 corresponding to the image portion
In the vicinity of 2, the ring-shaped control electrode portion 13a is formed due to the potential difference between the control electrode 13 and the conductive toner carrying roller 16.
The lines of electric force E are further formed toward the toner carrying roller 16. The strength of the line of electric force E at this time is proportional to the potential difference and inversely proportional to the distance between the control electrode 13 and the surface of the toner carrying roller 16.

Then, the negatively charged toner 18
Is subjected to an electrostatic force in the direction of higher potential by the line of electric force from the control electrode 13 toward the toner carrying roller 16, and is drawn out so as to pass through the opening 12. The toner 18 thus extracted is further subjected to the voltage (+1 kV) applied to the back electrode body 2 so that the image recording medium 3
The electric field formed between the electrode array 1 and the electrode array 1 causes the toner 18 to fly toward the image recording medium 3, and the toner 18 is deposited on the surface of the image recording medium 3 to form a visible pixel.

In this case, the image recording medium 3 and the electrode array 1
The strength of the electric field formed between the electrode array 1 and the outer peripheral surface of the back electrode body 2 on the side where the back surface of the image recording medium 3 faces.
Is inversely proportional to the distance to the control electrode 13 at, and is proportional to the potential difference. Therefore, as in the present embodiment, the distance from the position of the control electrode 13 to the outer peripheral surface of the concave annular portion 2b facing the opening 12 and the distance to the outer peripheral surface of the convex annular portion 2a facing the non-opening portion 14. And the difference between them becomes smaller or smaller, so that the strength of the electric field formed between the image recording medium 3 and the electrode array 1 depends on the area facing the opening 12 and the non-opening area 14. The amount of toner accumulated on the surface of the image recording medium 3 in the area facing the opening 12 and the toner on the surface of the image recording medium 3 in the area facing the non-opening 14 are reduced. Of the image recording medium 3 in the area facing the opening 12 and the non-opening 14 adjacent to the opening 12 are almost equal (or the difference is small).
The diffusivity of the toner 18 to the surface of the toner can be increased, and, for example, it is possible to prevent uneven density of the toner in an image such as a continuous straight line parallel to the row of the openings 12.

In addition, from the location of the control electrode 13 to the opening 12
By setting the distance to the outer peripheral surface of the concave annular portion 2b facing to the non-opening portion 14 longer than the distance to the outer peripheral surface of the convex annular portion 2a facing the non-opening portion 14, the electric field at the portion facing the opening portion 12 is made smaller. The electric field at the portion facing the opening 14 may be strengthened. In the case of non-image operation, the control voltage application circuit 21 is driven according to the signal from the data control circuit to apply a voltage of 0 V to the control electrode 13 for the non-image portion. As a result, since no electric field is formed between the toner carrying roller 16 and the control electrode 13, the toner 18 on the toner carrying roller 16 is not subjected to electrostatic force, and these toners 18 do not pass through the opening 12. Absent.

Further, the opening 1 is formed on the surface of the image recording medium 3.
While one row of toner 18 is formed by the two rows, the image recording medium 3 is conveyed by one pixel in the direction perpendicular to the row of the openings 12 (direction of arrow B in FIG. 1). By repeating such an operation, a predetermined image is formed by the toner 18 on the surface of the image recording medium 3. After that, the toner image is heated and fixed on the image recording medium 3 at the position of the fixing device 5.

In the image forming apparatus constructed as described above, when the insulating toner 18 is used, the conductive toner carrying roller 16 and the control electrode 1 in the electrode array 1 are used.
The electrical insulation between 3 and 3 is maintained. In the second embodiment shown in FIG. 5, one side of the flat plate 22a of the plate-like back electrode body 22 made of a metal having conductivity (the side facing the electrode array 1).
In addition, a strip-shaped ridge 23 made of a conductive metal or the like is formed so as to face the non-opening portions 14 and extend in the moving direction of the image recording medium 3. Therefore, according to this embodiment, the image recording medium 3 moves in the direction of the arrow B with the back surface of the image recording medium 3 in contact with the front surface of the protrusion 23, and the image recording medium 3 is located at the portion facing the opening 12. Since the back surface of No. 3 and the front surface of the flat plate 22a of the back electrode body 22 are separated from each other, the same operation and effect as those of the first embodiment can be obtained.

As a modification of the second embodiment, instead of the protrusion 23, a convex portion having a circular shape in plan view is formed near each non-opening portion 14, and the image recording medium 3 is formed on each convex portion. The back surface of the image recording medium 3 may be in contact with the back surface of the image recording medium 3, but may not be in contact with the back surface of the image recording medium 3. FIG.
In the third embodiment shown in FIG. 8, a strip 25 of conductive metal or the like is provided on one surface (a side facing the electrode array 1) of a non-conductive plate-shaped support plate 24 such as ceramics. It is formed in a comb-like shape in plan view so as to face each of the non-opening portions 14 and extend in the moving direction of the image recording medium 3. Similarly, on one surface of the support plate 24, the space between the protrusions 25 is formed. In addition, a strip-shaped protrusion 26 made of a conductive metal or the like is formed in a comb-like shape in plan view so as to face each opening 12 and extend in the moving direction of the image recording medium 3. The back electrode body 27 is configured (see FIGS. 6 and 7).

In this case, the protrusion 25 and the continuous lead portion 25a thereof and the protrusion 26 and the continuous lead portion 26a formed on one surface of the support plate 24 may be formed by a printing technique or the like.
Then, a low voltage (for example, +1 k
V) is applied and the ridge 25 is connected to the DC power source 20 so as to apply a higher voltage (for example, +1010 V) than that applied to the ridge 26. Since the other structure is the same as that of the first embodiment, the same members are designated by the same reference numerals and detailed description thereof is omitted.

According to the configuration of this embodiment, the image recording medium 3
Although the distance between the front surface of the back electrode body 27 and the control electrode 13 in the electrode array 1 on the side where the back surface of the control electrode 13 faces is the same, the protrusion 25 facing the non-opening portion 14 from the position of the control electrode 13
Potential difference from the position of the control electrode 13 to the opening 12
Is higher than the potential difference in the ridge 26 facing the image recording medium, the distance from the electrode array 1 to the image recording medium 3 on the non-aperture portion 14 side away from the opening portion 12 becomes large, The strength of the electric field formed between the electrode 3 and the electrode array 1 can be set to be approximately the same in the region facing the opening 12 and the region facing the non-opening 14.

Therefore, the amount of toner deposited on the surface of the image recording medium 3 at the portion facing the opening 12 and the non-opening 14
The amount of toner deposited on the surface of the image recording medium 3 in a portion facing to the surface of the image recording medium 3 becomes almost equal, and the diffusion rate of the toner 18 to the surface of the image recording medium 3 in a portion facing to the opening 12 and the non-opening 14 adjacent thereto. Therefore, for example, it is possible to prevent uneven density of toner in an image such as a continuous straight line parallel to the row of the openings 12.

The strength of the electric field formed between the image recording medium 3 and the electrode array 1 at the portion facing the non-opening portion 14 is higher than that at the portion facing the opening portion 12. In order to increase the strength of the electric field, the potential difference in the ridge 25 facing the non-opening portion 14 can be made higher than the potential difference in the ridge 26 facing the opening 12 from the location of the control electrode 13. In this case, the toner 18 is sufficiently ejected to the surface of the image recording medium 3 at a portion facing the non-opening portion 14 which is located away from the opening portion 1.
It is possible to further eliminate the uneven density of toner in an image such as a continuous straight line parallel to the row of the openings 12.

In the non-image operation, the control voltage applying circuit 21 is driven according to the signal from the data control circuit so that a negative voltage such as -10V is applied to the control electrode 13 for the non-image portion. May be. In this case,
An electric field opposite to the electric field with respect to the image forming portion is formed between the toner carrying roller 16 and the control electrode 13, so that the flying of the toner 18 on the toner carrying roller 16 can be further suppressed, and fogging is reduced. An image can be formed.

According to the above-described process, the control electric field in the electrode array 1 is formed between the control electrode 13 and the surface of the toner carrying roller 16 as one electrode facing the opening 12. The electric field for control can be directly applied to the toner 18 conveyed by the toner carrying roller 16 to the vicinity of the opening 12, and the toner control efficiency is excellent.

Since the toner carrying roller 16 which is one of the electrodes and the electrode array 1 having the control electrode 13 are extremely close to each other with the toner 18 being conveyed therebetween, the applied voltage for control is applied. Even if it is lowered, the strength of the electric field can be increased, and the flying force of the toner 18 can be increased. Therefore, an integrated circuit element for low voltage can be used as a control voltage application circuit for driving the control electrode 13. Therefore, the manufacturing cost of the image forming apparatus becomes low.

If the electrically insulating sheet 11 in the electrode array 1 is brought into contact with the outer peripheral surface of the toner carrying roller 16 as one of the electrodes, even if the toner 18 is not carried on the toner carrying roller 16, it will be electrically charged. There is no short circuit. An integrated circuit chip (IC) for applying a control voltage may be mounted on both sides or one side of the array of openings 12 on the surface of the electrode array 1.

[0037]

As described above, claim 1
The image forming apparatus according to the invention described in 1), a plurality of openings are formed, each opening has a film-like electrode array each having a control electrode, a toner supply unit for supplying toner to the openings of the electrode array, The image recording medium and the back electrode body, which are arranged on the side opposite to the toner supply unit with respect to the electrode array, and each control electrode of the electrode array are independently controlled to open the toner from the toner supply unit by an electric field. An image forming apparatus comprising control means for selectively flying onto the image recording medium through a section, wherein the electrode array has openings formed in rows in a direction intersecting with a moving direction of the image recording medium. While forming a part, the back electrode body is configured so that the difference in the strength of the electric field with respect to the image recording medium between the opening and the non-opening in the electrode array is reduced.

As described above, the toner flying from the openings in the electrode array adheres to the front surface side of the image recording medium according to the strength of the electric field between the rear electrode body disposed on the rear surface side of the image recording medium. However, in the present invention, the back electrode body is configured to reduce the difference in electric field strength with respect to the image recording medium between the opening and the non-opening in the electrode array. The difference between the amount of toner on the surface of the image recording medium at the portion facing the opening and the amount of toner on the surface of the image recording medium at the portion facing the non-opening is reduced. Therefore, it is possible to realize image formation in which the toner adhesion amount at the portion facing the opening portion and the non-opening portion does not vary and the toner density is less uneven, and high-quality image formation can be performed.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the surface of the back electrode body is brought closer to the image recording medium at a portion facing the non-opening portion and faces the opening portion. It is configured so as to be separated from the image recording medium at the portion to be opened. Therefore, it is possible to eliminate a large difference in the distance from the surface of the back electrode body to the electrode array for forming the electric field between the portion facing the opening and the portion facing the non-opening. Therefore, at the time of image formation, a large difference does not occur in the strength of the electric field with respect to the image recording medium between the part facing the opening and the part facing the non-opening adjacent thereto, and the part facing the non-opening does not appear. In addition, the toner can fly sufficiently and the toner density does not become uneven during the image forming operation, such as a continuous straight line parallel to the row of the openings, and high quality image formation can be performed.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the back electrode body is formed in a roller shape, and the outer peripheral surface of the back electrode body is formed in the non-opening portion. The concavo-convex annular portion is formed so as to approach the image recording medium at the facing portion and separate from the image recording medium at the facing portion. Therefore, also in this invention, the same action and effect as the invention according to claim 2 can be achieved.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first aspect, electrodes are provided on the surface of the back electrode body at a portion facing the opening and a portion facing the non-opening, respectively. And a voltage applied to the electrode portion facing the non-opening portion is higher than a voltage applied to the electrode portion facing the opening portion. According to this configuration, the distance between the surface of the back electrode body and the electrode array is short at the portion facing the opening and long at the portion facing the non-opening, but conversely, the portion facing the non-opening is better. Since the applied voltage is higher than the portion facing the opening, the strength of the electric field to the image recording medium is large between the portion facing the opening and the portion facing the non-opening adjacent to the opening during image formation. No disparity occurs, the toner uniformly flies to the image recording medium, and the toner density is not uneven during image forming operation such as a continuous straight line parallel to the row of openings,
An effect that high-quality image formation can be performed is achieved.

[Brief description of drawings]

FIG. 1 is a schematic side sectional view of an image forming apparatus according to a first embodiment.

FIG. 2 is a perspective view of a main part of an electrode array.

FIG. 3 is a partially cutaway sectional view showing an arrangement state of a back electrode body and an electrode array in the first embodiment.

FIG. 4 is an operation explanatory view showing a cross section of a main part of the first embodiment.

FIG. 5 is a partially cutaway perspective view showing an arrangement state of a back electrode body and an electrode array according to a second embodiment.

FIG. 6 is a plan view of a back electrode body according to a third embodiment.

7 is a cross-sectional view of a main part shown in the line VII-VII of FIG.

FIG. 8 is an operation explanatory view showing a cross section of the main part of the third embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 electrode array 2, 22, 27 back electrode body 2a convex annular portion 2b concave annular portion 3 image recording medium 8 toner supply device 9 toner case 11 insulating sheet 12 opening 13 control electrode 14 non-opening portion 16 toner carrying roller 21 control voltage Application circuit 23, 25, 26 Projection 24 Support plate

Claims (4)

[Claims] 1. A film-shaped electrode array having a plurality of openings, each opening having a control electrode, a toner supply unit for supplying toner to the openings of the electrode array, and an electrode array for the electrode array. The image recording medium and the back electrode body arranged on the opposite side of the toner supply means, and the respective control electrodes of the electrode array are independently controlled, and the toner is supplied from the toner supply means through the opening by an electric field. In the image forming apparatus including a control unit for selectively flying on the image recording medium, the electrode array has openings formed in a row in a direction intersecting with a moving direction of the image recording medium. An image forming apparatus characterized in that the back electrode body is configured to reduce a difference in electric field strength with respect to an image recording medium between an opening portion and a non-opening portion in an electrode array. 2. The surface of the back electrode body is configured to approach the image recording medium at a portion facing the non-opening portion and be separated from the image recording medium at a portion facing the opening portion. The image forming apparatus according to claim 1, wherein: 3. The back electrode body is formed in a roller shape, and the outer peripheral surface of the back electrode body approaches the image recording medium at a portion facing the non-opening portion and at a portion facing the opening portion. The image forming apparatus according to claim 1 or 2, wherein the uneven annular portion is formed so as to be separated from the image recording medium. 4. An electrode portion is provided on a surface of the back electrode body at a portion facing the opening and a portion facing the non-opening portion, and is applied to the electrode portion facing the non-opening portion. The image forming apparatus according to claim 1, wherein the voltage is configured to be higher than the voltage applied to the electrode portion facing the opening.