JPH08142393A - Image forming apparatus - Google Patents

Abstract

PURPOSE: To effectively prevent the mixing of black toner with other toner. CONSTITUTION: A toner conveying roller 133 for conveying toner 103 is provided in an opening under an aperture electrode 140 having a plurality of openings and a control electrode, and a back surface electrode roller 150 and a permanent magnet 161 arranged in the roller 133 are provided at a predetermined sheet conveying gap above the electrode 140. When an image is formed of color toners 103a to 103c except black, the magnetic field generator 161a of the magnet 161 is opposed to the openings of the electrode 140 to prevent flying of the black 103d of magnet toner.

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 applicable to a copying machine, a printer, a facsimile, a plotter, etc., in which the voltage of control electrodes of a plurality of openings formed in an aperture electrode body is controlled. The present invention relates to an image forming apparatus for recording by adhering toner passing through an opening onto a recording medium, and particularly, for image quality of a color image recorded with a mixed toner in which a plurality of types of toners are mixed for multicolor image or full color image formation. Regarding what can be enhanced.

[0002]

2. Description of the Related Art Conventionally, an insulating sheet is formed with a plurality of openings arranged in a line in a direction orthogonal to the conveying direction of an image recording medium and an electrode array consisting of a plurality of control electrodes located near these openings. An aperture electrode body, a toner supply mechanism that supplies toner to the electrode array of the aperture electrode body, and a back electrode that closely faces the electrode array of the aperture electrode body with a conveyance gap of the image recording medium. A control unit that individually controls the drive voltage applied to the plurality of control electrodes of the electrode array based on the image signal is provided, and the control unit applies the voltage to each control electrode via the electrode drive circuit based on the image signal. The drive voltage is controlled so that the toner on the surface of the toner transport roller passes through the opening through the electric field between the control electrode and the back electrode, and the image recording medium (paper)
Various image forming apparatuses of the electrostatic recording type configured to perform recording have been proposed (for example, JP-A-2-2975).
70 publication). In this type of image forming apparatus,
Usually, the toner is negatively charged, the back electrode is held at a predetermined positive high voltage, and + 30V or -30V is applied to the control electrode depending on the presence or absence of pixel formation.

Further, in Japanese Unexamined Patent Publication No. 5-124248, three sets of image recording units corresponding to toners of three colors of yellow, magenta and cyan are serially arranged at predetermined intervals in the conveying direction of the image recording medium. An image forming apparatus is provided which is arranged so as to form a color image. In some cases, four sets of image recording units corresponding to four color toners of yellow, magenta, cyan, and black are arranged in series at predetermined intervals in the transport direction of the image recording medium. Each of the image recording units is composed of an aperture electrode body and a toner supply mechanism, but as the back electrode, one common to a plurality of image recording units is applied and the back electrode is maintained at a constant high voltage. However, in the image forming apparatus including a plurality of image recording units of this type, the apparatus becomes large and complicated, and it is disadvantageous in terms of manufacturing cost. Therefore, one image recording unit can generate a multi-color or full-color image. It is desirable to put an image forming apparatus capable of recording into practical use.

In view of this, Japanese Patent Laid-Open No. 4-80776 discloses an image forming apparatus similar to the above, in which the reference electrode located on the toner transport roller side and the back electrode side are provided on both sides of the aperture of the aperture electrode body. A control electrode is provided, and an alternating current is applied between the reference electrode and the toner transport roller to float the toner, and the back electrode is grounded, and the first toner is positively charged and the second toner is negatively charged. A multi-color image in which a negative driving voltage is applied to the control electrode to fly the first toner and a positive driving voltage is applied to the control electrode to fly the second toner. An image forming apparatus capable of forming an image is described.

However, an image forming apparatus having a structure in which the reference electrode is omitted and toner is ejected through an electric field generated between the control electrode and the toner transport roller and an electric field generated between the back electrode and the control electrode is provided. By applying a mixed toner that is a mixture of multiple types of toner, making the electrical characteristics of the toner different for each type of toner, and setting the drive voltage applied to the control electrode and the back voltage applied to the back electrode appropriately, It is also possible to record multi-color images and full-color images.

[0006]

When a mixed toner in which a plurality of types of toners are mixed is applied to record a multi-color image or a full-color image, there are the following problems. For example, when a mixed toner in which four types of toners of yellow, magenta, cyan, and black are mixed is applied, recording is performed through the image forming process of four times for recording with each color toner, but the toner is not charged properly. As a result of other toner being mixed in the toner of each color due to the cohesive force between the toner and the toner, each pixel is recorded as a somewhat turbid pixel, and it is difficult to sufficiently improve the image quality. In particular, even if the toners of the other three primary colors are slightly mixed in the toner of the three primary colors, the image quality is hardly deteriorated.
If even a small amount of black toner is mixed with any one of the primary color toners, the hue remarkably deteriorates in the dark color direction, and the image quality seriously deteriorates. At least one object of the present invention is
An object of the present invention is to provide an image forming apparatus capable of reliably preventing a toner of a type from mixing with another toner, and an image forming apparatus capable of reliably preventing a black toner from mixing with another toner.

[0007]

According to another aspect of the present invention, there is provided an image forming apparatus, wherein a plurality of openings are provided in an insulating sheet in a direction orthogonal to a conveying direction of an image recording medium, and a plurality of openings are provided near the openings. Aperture electrode body formed with an electrode array consisting of control electrodes, a toner supply mechanism for supplying toner to the electrode array of the aperture electrode body, and a gap for conveying the image recording medium with respect to the electrode array of the aperture electrode body. In the image forming apparatus, the toner supply mechanism includes a rear electrode that closely faces each other, and an electrode control unit that individually controls a drive voltage applied to a plurality of control electrodes of the electrode array based on an image signal. The toner supply mechanism is configured to supply a mixed toner obtained by mixing a plurality of types of toner including a non-magnetic toner for image formation and a magnetic toner, It is provided with a switchable magnetic field generating means and non-activated condition that does not generate a magnetic field and an activated condition where a magnetic field is generated around.

According to a second aspect of the present invention, in the first aspect of the invention, the magnetic toner contained in the mixed toner is
It is characterized by being black toner.
An image forming apparatus according to a third aspect is the image forming apparatus according to the first or second aspect, wherein the magnetic field generating means includes a permanent magnet and a position switching means for switching the position of the permanent magnet. According to a fourth aspect of the present invention, in the first or second aspect of the invention, the magnetic field generating means includes an electromagnet.

[0009]

In the image forming apparatus according to the present invention, the aperture electrode body is formed by forming a plurality of openings in the insulating sheet and an electrode array consisting of a plurality of control electrodes located in the vicinity of these openings. The back electrode closely faces the electrode array with a conveyance gap of the image recording medium therebetween, toner is supplied to the electrode array by a toner supply mechanism, and the electrode control means causes the plurality of electrodes of the electrode array to be supplied based on the image signal. By individually controlling the drive voltage applied to the control electrode, the toner is caused to fly and an image is recorded through the electric field between the control electrode and the toner supply mechanism and the electric field between the control electrode and the back electrode.

Here, the toner supply mechanism is configured to supply a mixed toner formed by mixing a plurality of types of toner including a non-magnetic toner for forming a color image and a magnetic toner, and the toner supply mechanism is A magnetic field generating means is provided near the electrode array that can switch between a working state in which a magnetic field is generated and a non-operating state in which no magnetic field is generated.Therefore, the magnetic field generating means is switched into a working state to generate a magnetic field near the electrode array. Then, the magnetic toner is restrained by the magnetic field on the side of the toner supply mechanism, so that it is possible to reliably prevent the magnetic toner from mixing with other toner and flying. On the contrary, when the magnetic field generating means is switched to the non-acting state, the magnetic field is not generated in the vicinity of the electrode array, so that the magnetic toner can be released and recording can be performed with the magnetic toner. Therefore, the stability of image formation can be improved and the image quality can be improved.

In the image forming apparatus of the second aspect, the same operation as that of the first aspect is achieved, but since the magnetic toner contained in the mixed toner is the black toner, the black toner is mixed with other toners. Therefore, it is possible to reliably prevent the recording and the deterioration of the hue due to the mixing of the black toner.

In the image forming apparatus of claim 3, the same operation as in claim 1 or 2 is achieved, but the magnetic field generating means includes a permanent magnet and a position switching means for switching the position of the permanent magnet. Therefore, the magnetic field generating means having a simple and inexpensive structure can be provided. In the image forming apparatus according to claim 4, the same operation as in claim 1 or claim 2 is achieved, but since the magnetic field generating means includes the electromagnet, the magnetic field generating means is compact and has a high degree of freedom in design. Can be

[0013]

Embodiments of the present invention will be described below with reference to the drawings. As shown in FIG. 1, the image forming apparatus 100
Is an image recording apparatus applicable to a copying machine, a printer, a facsimile, a plotter, etc. and capable of recording a full-color image. This image forming apparatus 100 has a main body frame 102 in which a paper P (image recording medium) is stored. A paper transport mechanism 110 for transporting, a fixing mechanism 120, a mixed toner 103 in which four types of toners of yellow, magenta, cyan, and black are mixed, a toner supply mechanism 130, and an upper end of a toner case 131 of the toner supply mechanism 130. Aperture electrode body 140 attached to the rear electrode roller 15
0 and a magnetic field generation mechanism 160 are provided.

The paper transport mechanism 110 has a plurality of guide plates 112 to 114 for supporting the paper P to be transported.
A plurality of transport rollers 115 and 116, and a transport roller (not shown) that supports and transports a portion of the paper P in the width direction at both ends between the transport rollers 115 and 116 and the fixing mechanism 120. A sheet feeding roller (not shown) for feeding the sheets in the sheet cassette 111 one by one, a roller driving mechanism (not shown) for driving the sheet conveying mechanism 110, and the like are provided on the front side of the main body frame 102. A paper feed cassette 111 storing a large number of papers P is provided,
On the rear side of the main body frame 102, a paper discharge tray 119 for receiving the paper P discharged after image recording is provided.
The fixing mechanism 120 is configured to heat and pressurize the fixing roller 117 having a halogen lamp therein and the pressing roller 118 to fix the fixing roller 117.

Next, the toner supply mechanism 130 will be described. In the toner case 131 having a width wider than the maximum width of the paper P in the direction orthogonal to the paper conveyance direction (from front to back), the yellow toner 103a and magenta are formed. The toner 103b, the toner 103c for cyan, and the toner 103d for black are mixed to be mixed toner 103. The toners 103a, 103b, 103c are
Non-magnetic toner, but black toner 103d
Is a magnetic toner containing fine magnetic powder in each toner particle. Inside the toner case 131, a toner supply roller 132 and a toner transport roller 133 are horizontally arranged in the left-right direction.
3 are rotatably pivoted respectively. The toner supply roller 132 is made of silicone foam and is used for the toner 10
3 is transferred to the toner transport roller 133 and charged to the toner 103 through frictional contact with the toner 103.

The four types of toners 103a to 103d are
Although they have known compositions, they have different compositions, particle sizes, specific gravities, electric resistance values, charging characteristics, flow characteristics, etc., and in the case of the present embodiment, in the toner supply mechanism 130,
The toner 103a has an average charge amount of −30 μ coulomb /
The toner 103b is charged to −20 μ coulomb / g, the toner 103c is charged to −10 μ coulomb / g, and the toner 103d is charged to +30 μ coulomb / g. The charge amount of the toners 103a to 103d can be basically set based on the average particle size and the characteristics of FIG. 7, but by appropriately setting the composition and addition amount of a known charge control agent, Can be set to the value of.

The toner carrying roller 133 is a synthetic resin insulating coating or semi-conductive coating on the outer peripheral surface of a roller body 133a (see FIG. 2) which is a thin cylinder made of a non-magnetic metallic material (for example, aluminum). The toner 103 adhered to the surface of the toner transport roller 133 by electrostatic force is transported in the direction of arrow A. The toner supply roller 132 and the toner transport roller 133
Is rotationally driven in the arrow B direction and the arrow A direction by a roller driving mechanism (not shown). The toner case 13
1, a toner regulating blade 134 made of an insulating material having a thin plate-like elasticity is attached, and its curved portion is in pressing contact with the toner conveying roller 133, and is layered on the surface of the toner conveying roller 133. The layer thickness of the adhered toner 3 is a predetermined thickness (about
40 to 50 μm).

Next, when the toners 103a to 103c are applied to perform the image forming processing, the black magnetic toner 103d is used for the image formation.
A magnetic field generation mechanism 160 for generating a magnetic field in the vicinity of the electrode array 144 shown in FIG. 6 will be described in order to prevent mixing into 3a to 103c. As shown in FIG. 2 to FIG. 4, the toner transport roller 133 includes the roller body 1
End plates 133b integrally joined to both ends of 33a,
Cylindrical pivot shafts 13 that are concentrically joined to the center of these end plates 133b and concentric with the roller body 133a and project outward.
3c, and these cylindrical pivot shafts 133c are rotatably supported by the wall portion 131a of the toner case 131, and the cylindrical pivot shaft 133c on one end side of the roller body 133a has a gear of a roller driving mechanism. A gear 135 for driving the toner transport roller 133 to rotate is fixed.

The magnetic field generating mechanism 160 has a permanent magnet body 161 disposed in the roller body 133a, and a working position (working state) in which the permanent magnet body 161 generates a vertically upward magnetic field near the electrode array 144. ) And a non-acting position (non-acting state) rotated by 90 degrees from the actuating position, the switching mechanism 162 and the like. Inside the roller body 133a, a permanent magnet body 161 extending over its entire length is incorporated, and a magnetic field generating portion 161a extending in a plate shape over the entire length of the roller body 133a is formed at the tip of this permanent magnet body 161. At the base end portion of the permanent magnet body 161, a substantially cylindrical pivot portion 161b is provided.
As shown in FIG. 3, the magnetic field generation part 161a is formed in the N pole, and the pivotal support part 161b is formed in the S pole.

The roller body 1 is attached to the pivot portion 161b.
33a is a shaft hole 163 concentric with the cylindrical pivot shaft 133c.
A shaft hole 163 having the same diameter as that of the shaft hole 163 is formed over the entire length, and a shaft member 164 is formed in the shaft hole 163 and a pair of cylindrical pivotally supporting portions 133c.
Is inserted and fixed to the permanent magnet body 161 so as not to be relatively rotatable, and is rotatably supported by the pair of cylindrical pivotally supporting portions 133c. The shaft member 164 projects a predetermined length from the cylindrical pivotally supporting portion 133c on the side opposite to the gear 135,
The switching mechanism 162 is connected to the protrusion 164a.

The switching mechanism 162 is a solenoid actuator 16 controlled by a control unit 146 described later.
5 and the connecting member 166 and the like. Connection member 1
66 is orthogonally fitted and fixed to the shaft member 164 and extends from the shaft member 164 by a predetermined length in the radial direction.
6, the tip of the output rod 165a of the solenoid actuator 165 is connected by pin coupling, and the actuator body 165b of the solenoid actuator 165 is pin coupled to the bracket 167 fixed to the body frame 102. It is connected.

In the image forming process for recording an image other than black, the control unit 146 shown in FIG.
The solenoid actuator 165 shown in is energized.
Then, as shown by the dotted line in FIG. 4, the output rod 165a retracts, the permanent magnet body 161 is switched to the operating position,
In the image forming process for recording with the black magnetic toner 103d, the energization of the solenoid actuator 165 is released. Then, the spring inside the actuator 165 causes the output rod 165a to advance as shown by the chain line in FIG.
It is configured so as to rotate 90 degrees in a clockwise direction integrally with 64 to be switched to the non-acting position.

At the upper end of the toner case 131, the layered toner 10 is provided so as to cover the opening at the upper end of the toner case 131 and at the upper end of the toner transport roller 133.
Aperture electrode body 140 that is inclined in a substantially roof shape is attached so as to come in contact with the upper side through 3. The aperture electrode body 140 will be described. As shown in FIGS. 1 and 6, the aperture electrode body 140 is made of synthetic resin (for example,
25 μm thick insulating sheet 141 made of polyimide)
In addition, a large number of minute opening portions 142 and a large number of annular control electrodes 14 located in the vicinity of the large number of opening portions 142, respectively.
3 is an electrode array 144 and a large number of conducting wires 145 extending from the large number of control electrodes 143.

That is, a large number of 65 .mu.m diameters are provided at the position of the insulating sheet 141 substantially in the center in the front-rear direction (paper transport direction).
m openings 142 are formed in a row in the left-right direction and horizontally at intervals of about 127 μm.
An annular control electrode 143 located on the outer peripheral portion of each opening 142 is formed of a copper coating on the surface of the control electrode 143.
A copper-coated conductive wire 145 is extended in one direction.
However, the surface of the insulating sheet 141 on the opposite side of the control electrode 143 and the conducting wire 145 may be covered with an insulating coating made of synthetic resin, and the surface of the insulating coating may be covered with a semiconductive antistatic coating. is there. In addition, for example, when the A4 size sheet is targeted as the maximum size sheet, the opening 142
Is about 1700 (that is, the number of control electrodes 143).

As shown in FIGS. 1 and 5, the aperture electrode body 140 is mounted such that the electrode array 144 closely faces the lowermost end of the back electrode roller 150 with a paper transport gap. . A back electrode roller 150 (corresponding to a back electrode) is arranged immediately above the aperture electrode body 140, and the back electrode roller 150 is rotatably supported by the main body frame 102 via its supporting shaft 150a. ing. The paper P is the back electrode roller 15
The toner 103 is conveyed horizontally in the conveying direction while being in contact with the lower part of 0, and the toner 103 that has flown from the surface of the toner conveying roller 133 and has passed through the opening 142 adheres to the lower surface of the sheet P. The back electrode roller 150 is rotationally driven in the direction of arrow C in synchronization with the conveyance of the recording paper P by a roller driving mechanism (not shown).

Here, when a full-color image is recorded by the image forming apparatus 100 through four image forming processes, only the yellow toner 103a is ejected and recorded in the first image forming process. In the next image forming process, only the magenta toner 103b is made to fly and recorded, in the next image forming process, only the cyan toner 103c is made to fly and recorded, and in the next image forming process, the black toner 103d is made to fly. Only the flight will be recorded.

Next, the control system of the image recording apparatus 100 will be described. As shown in FIG. 5, a control unit 146 for receiving an image signal from the outside and the control unit 146.
An electrode drive circuit 147 that receives a control signal from the control unit 146, and a drive voltage switching circuit 148 that switches the drive voltage supplied to the electrode drive circuit 147 in response to a command from the control unit 146.
The back electrode 150 according to a command from the control unit 146
Back voltage switching circuit 149 for switching back voltage applied to the
Are provided. The toner transport roller 133
Is always grounded.

The drive voltage switching circuit 148 is 10V and -10V, 20V and -20 with respect to the electrode drive circuit 147.
It is configured to selectively supply four drive voltages of V, 30V and -30V, -10V and 10V, and 10 is received when a command for designating yellow is received from the control unit 146.
V and -10V drive voltage is output, 20V and -20V drive voltage is output when receiving the command to specify magenta,
When the command to specify cyan is received, the drive voltage of 30V and -30V is output, and when the command to specify black is received-
It is configured to output a drive voltage of 10V and 10V.

The electrode driving circuit 147 is connected to the conducting wires 145 extending from the large number of control electrodes 143 via the control lines formed of a bundle of a large number of signal lines, respectively.
The numeral 47 has a large number of switching elements corresponding to the large number of control electrodes 143, and individually controls the drive voltage supplied to the large number of control electrodes 143 based on the control signal from the control unit 146. That is, when recording with the toner 103a, 10V is output to the control electrode 143 that records a pixel, and −10V is output to the control electrode 143 that does not record a pixel, and when recording with the toner 103b, the pixel is recorded. 20 V to the control electrode 143 for controlling the pixel and -20 V to the control electrode 143 for not recording pixels, respectively, and the toner 10
When recording with 3c, the control electrode 143 for recording pixels
30V, and -30V to the control electrode 143 that does not record pixels
In addition, when recording with the toner 103d, −10V is output to the control electrode 143 for recording pixels, and 10V is output to the control electrode 143 for not recording pixels.

The back side voltage switching circuit 149, based on a command from the control unit 146, supplies any one of the toners 103a to 103a for image formation in each image forming process.
According to 103d, the back surface voltage applied to the back surface electrode roller 150 is switched as follows.
When recording with toner 103a, back voltage is 900V
When the toner 103b is used for recording, the back voltage is switched to 1000V, when the toner 103c is used for recording, the back voltage is switched to 1100V, and when the toner 103d is used for recording. Back voltage is -9
Switch to 00V. The above-mentioned back surface voltage is
It is set based on the average charge amount of 3a to 103d and the characteristics shown in FIG.

Next, the image forming operation of the image forming apparatus 100 and the operation of the image forming apparatus 100 will be described by taking the case of recording with the yellow toner 103a as an example. As shown in FIG. 5, the mixed toner 103 is transported to the electrode array 144 by the toner transport roller 133, but a drive voltage of 10 V is applied to the control electrode 143 for recording pixels, and the pixels are also recorded. Control electrode 1
43 is set to -10V, and the rear electrode roller 15
900V is applied to 0.

When 10 V is applied to the control electrode 143,
An electric field from the control electrode 143 toward the toner transport roller 133 and an electric field from the back electrode roller 150 toward the control electrode 143 are generated, and the toner 103a receives electrostatic force and flies through the opening 142 toward the control electrode 143. Then, the paper P flies toward the rear electrode roller 150.
Collide with and adhere to. However, the control electrode 143 has a -10
When V is applied, only the electric field in the opposite direction is generated, and the toner 103a does not fly. Here, since the drive voltage of 10 V and the back voltage of 900 V are set so as to match the composition, particle size, specific gravity, electric resistance value, average charge amount, flow characteristics, etc. of the toner 103a, the mixing is performed. Only the toner 103a of the toner 103 flies and the yellow pixel is recorded.

Next, considering the electric field in the opening 142, a predetermined electric field is generated in the vicinity of the control electrode 143 by the driving voltage of 10 V, and the electric field at the center of the opening 142 becomes weaker than the electric field. But the back electrode roller 150
The electric field at the center of the opening 142 is reinforced by the leakage electric field from the. Then, by setting the drive voltage and the back surface voltage of the control electrode 143 so as to match the toner 103a as described above, a uniform electric field capable of causing only the toner 103a to fly can be formed in the opening 142. Only the toner 103a of the mixed toner 103 flies and a yellow pixel is recorded.

This means that the other toners 103b to 103b
The same applies to 03d, and the driving voltage applied to the control electrode 143 and the backside voltage applied to the backside electrode roller 150 so as to match any one kind of toner used for image formation in each image forming process. Is appropriately set as described above, so that only the toner to be used for image formation can be made to fly. In this way, the toner 10
Of the 3a to 103d, a driving voltage for driving the control electrode 143 and a rear electrode roller 15 so as to match one kind of toner used for image formation in each image forming process.
By switching the back voltage to be applied to 0, only the toner to be used for image formation is caused to fly in each image forming process, the recording performance in each image forming process is improved, and a full-color image is recorded. The performance can be remarkably improved.

In particular, non-magnetic toners 103a to 103c
In the image forming process for recording respectively, the control unit 146 energizes the solenoid actuator 165 to hold the permanent magnet body 161 in the operating position, and the electrode array 1
The black magnetic toner 103d is constrained on the surface of the toner transport roller 133 by the magnetic field generated in the vicinity of 44, so that the magnetic toner 103d becomes the toner 103 of the three primary colors.
It does not fly by being mixed with a to 103c. As a result, the hues of the pixels recorded with the toners 103a to 103c do not decrease due to the mixing of the black toner 103d. Therefore, the stability of image formation when recording with the toners 103a to 103c is increased, and The image quality of the image can be significantly improved. However, the magnetic toner 10
In the image forming process for recording in 3d, the solenoid actuator 165 is de-energized and the permanent magnet 16
1 is switched to the non-acting position to release the restriction of the magnetic force on the magnetic toner 103d.
03d can be recorded by flying. Further, since the magnetic field generation mechanism 160 uses the permanent magnet, the structure is relatively simplified and the manufacturing cost is advantageous.

Next, a magnetic field generating mechanism 160 according to another embodiment.
A will be described. However, the same components as those of the magnetic field generation mechanism 160 are designated by the same reference numerals and the description thereof will be omitted. As shown in FIG. 9, the magnetic field generating mechanism 160A includes an electromagnet 171 instead of the permanent magnet body 161, a pipe-shaped shaft member 172, and a connecting member 173 that fixedly connects the shaft member 172 to the main body frame 102. And an energization control unit 174. Although the electromagnet 171 has a plurality of electromagnet blocks arranged in series, it may be formed of one electromagnet block. The electromagnet 171 is disposed in the roller body 133a and is fixed to the shaft member 172.
It is configured such that it can be switched between an operating state in which a vertically upward magnetic field is generated in the vicinity of 44 and a non-operating state in which energization is released and a magnetic field is not generated.

Conductive wire 17 for energizing the electromagnet 171
1 a is led out to the outside through the shaft member 172 and is connected to the energization control unit 174. The energization control unit 174
May be configured integrally with the control unit 146,
The control unit 146 may also be configured to be used in common.
Similar to the magnetic field generation mechanism 160 of the above-described embodiment, in the image forming process of recording with the non-magnetic toners 103a to 103c, the magnetic field generation mechanism 160A is switched to the operation state for generating the magnetic field, and the black magnetic toner 103 is used.
In the image forming process for recording at d, the magnetic field generation mechanism 16
0A is switched to a non-operating state that does not generate a magnetic field.
Therefore, the stability of image formation can be enhanced and the image quality of a color image can be enhanced as in the above-described embodiment. In addition, since the electromagnet 171 is applied to the magnetic field generation mechanism 160A, the magnetic field generation mechanism 160A can be downsized and is advantageous in terms of design flexibility.

A modified example in which the image forming apparatus 100 of the above-described embodiment is partially modified will be described.
The driving voltage applied to the control electrode 143, the backside voltage applied to the backside electrode roller 150, etc. are appropriately changed according to changes in the composition, particle size, specific gravity, electric resistance value, charging characteristic, fluidity, etc. of 3a to 103d. It is possible. Further, the image forming apparatus 100 may be of a type that conveys the paper P in the vertical direction. Toner 1 of the mixed toner 103
03d may be omitted, and instead, any one kind of toner of the three primary colors (for example, cyan toner 103c) may be configured as a magnetic toner.

[0039]

In the image forming apparatus according to the first aspect of the present invention, the toner supply mechanism is configured to supply a mixed toner obtained by mixing a plurality of types of toner including a non-magnetic toner for forming a color image and a magnetic toner. To the toner supply mechanism,
A magnetic field generating means is provided near the electrode array that can switch between a working state in which a magnetic field is generated and a non-operating state in which no magnetic field is generated.Therefore, the magnetic field generating means is switched into a working state to generate a magnetic field near the electrode array. By doing so, the magnetic toner is restrained by the magnetic force of the magnetic field on the toner supply mechanism side, so that it is possible to reliably prevent the magnetic toner from mixing with other toner and flying. On the contrary, when the magnetic field generating means is switched to the non-acting state, the magnetic field is not generated in the vicinity of the electrode array, so that the magnetic toner can be released and recording can be performed with the magnetic toner. Therefore, the stability of image formation can be improved and the image quality can be improved.

In the image forming apparatus of the second aspect, the same effect as that of the first aspect is obtained, but since the magnetic toner contained in the mixed toner is the black toner, the black toner is mixed with the other toner. Therefore, it is possible to reliably prevent the recording and the deterioration of the hue due to the mixing of the black toner.

In the image forming apparatus of the third aspect, the same effect as that of the second aspect is obtained, but the magnetic field generating means is provided with the permanent magnet and the position switching means for switching the position of the permanent magnet. Therefore, it is possible to provide a simple and inexpensive magnetic field generating means. The image forming apparatus according to claim 4 has the same effect as that of claim 2, but since the magnetic field generating means includes an electromagnet, it can be a magnetic field generating means that is compact and has a high degree of freedom in design. it can.

[Brief description of drawings]

FIG. 1 is a partial vertical cross-sectional side view of an image forming apparatus according to an exemplary embodiment of the present invention.

FIG. 2 is a vertical cross section of a toner transport roller and a magnetic field generation mechanism of the image forming apparatus.

3 is a sectional view taken along line III-III in FIG.

FIG. 4 is a side view of a toner conveying roller and a magnetic field generating mechanism of the image forming apparatus.

FIG. 5 is an enlarged cross-sectional view of a main part of the image forming apparatus.

FIG. 6 is a partial perspective view of an aperture electrode body of the image forming apparatus.

FIG. 7 is a correlation characteristic diagram between a toner particle size and an average charge amount.

FIG. 8 is a correlation characteristic diagram between the average charge amount of toner and the back surface voltage.

9 is a view corresponding to FIG. 2 according to another embodiment.

[Explanation of symbols]

 100 image forming apparatus 130 toner supply mechanism 140 aperture electrode body 141 insulating sheet 142 opening 143 control electrode 144 electrode array 146 control unit 150 back electrode roller 160, 160A magnetic field generation mechanism 161 permanent magnet body 162 switching mechanism 171 electromagnet 174 energization control Department

Claims (4)

[Claims] 1. An aperture electrode in which a plurality of openings arranged in a line in a direction orthogonal to a conveyance direction of an image recording medium and an electrode array formed of a plurality of control electrodes near the openings are formed on an insulating sheet. Body, a toner supply mechanism that supplies toner to the electrode array of the aperture electrode body, a back electrode that closely opposes the electrode array of the aperture electrode body across the conveyance gap of the image recording medium, and based on the image signal. In the image forming apparatus including an electrode control unit that individually controls the drive voltage applied to the plurality of control electrodes of the electrode array, the toner supply mechanism is configured to include a non-magnetic toner and a magnetic toner for forming a color image. The toner supply mechanism is configured to supply a mixed toner formed by mixing a plurality of types of toner including the magnetic field in the vicinity of the electrode array and a magnetic field. Image forming apparatus characterized by the provided non-working switchable magnetic field generating means and a state which does not produce. 2. The magnetic toner contained in the mixed toner is black toner.
The image forming apparatus according to item 1. 3. The image forming apparatus according to claim 1, wherein the magnetic field generating unit includes a permanent magnet and a position switching unit that switches the position of the permanent magnet. 4. The image forming apparatus according to claim 1, wherein the magnetic field generating unit includes an electromagnet.