JPH08114979A - Developing device - Google Patents

Abstract

PURPOSE: To provide a developing device capable of stably obtaining high developing efficiency without the occurrence of image stain and stripe irregularity. CONSTITUTION: As for this developing device developing a latent image by carrying two-component developer D to a developing area A by means of a developing sleeve 81 in which a magnetic material 82 is fixed, and scattering toner in a vibrating electric field; an electrode board 85 is fixed on the upstream part of the area A, a first electrode 85a capable of impressing a voltage is disposed on the downstream side leading edge of the board 85, and the angle of the positions of the downstream side leading edge of the board 85, the first electrode 85a, and the magnetic poles 82a and 82b of the magnetic material 82, etc., and the angles of contact/proximity positions to the sleeve 81 of the board 85 are set to satisfy (θ1 +θ2 )/2>ϕ1 , (θ1 +θ2 )/2>ϕ2 , (θ1 +θ2 )/2>ϕ3 , θ1 <0.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combination of magnetic carrier particles and toner particles in an electrophotographic copying machine.
The present invention relates to a developing device that develops an electrostatic latent image or a magnetic latent image using a component developer.

[0002]

2. Description of the Related Art Conventionally, in electrophotographic copying machines and the like,
A magnetic brush developing type developing device using a two-component developer is used. This developing device has a cylindrical developer carrier (developing sleeve) rotatably supported by a magnet roll made of a magnet body having a plurality of magnetic poles inside.
The magnetic carrier having toner particles adhered to the surface of the developing sleeve is held and conveyed to the developing area for developing.
The triboelectric charge control of toner particles is relatively easy, aggregation of toner particles does not easily occur, and the brushing of the magnetic brush is good,
It has excellent features such as excellent friction property on the surface of the image forming body and exhibits sufficient cleaning effect even when it is used in combination with cleaning, and it is often used in spite of the need to control the amount of toner particles with respect to carrier particles. Has been. But,
The developing method in which this magnetic brush is rubbed against the surface of the image forming body to develop is conventionally composed of magnetic carrier particles having an average particle size of several tens μm to several hundreds μm and non-magnetic toner particles having an average particle size of around 10 μm. Since a developer is used and toner particles and further carrier particles are coarse, there is a problem that it is difficult to obtain a high-quality image that reproduces delicate lines, dots, or a difference in shade. Therefore, in order to obtain high image quality in this developing method, conventionally, for example, resin coating of carrier particles, improvement of the magnet body in the developer carrying carrier,
Although a lot of efforts have been made, the present situation is that still stable and sufficiently satisfactory images cannot be obtained. Therefore, it is considered necessary to make the toner particles and the carrier particles finer in order to obtain a high quality image. However, toner particles with an average particle size of 20 μm or less, especially 1
If the particle size is 0 μm or less, the effect of Van der Waals force appears relative to the Coulomb force at the time of development, the adhesion between the image forming body and the toner becomes strong, and toner particles are also formed on the background of the image background. So-called fogging that adheres will occur, and it will be difficult to prevent fogging even by applying a DC bias voltage to the developer transport carrier. It becomes difficult to control the triboelectric charging of the toner particles, and aggregation easily occurs. on the other hand,
When the carrier particles are made finer, the carrier particles also adhere to the electrostatic image portion of the image forming body. It is considered that this is because the magnetic bias force is reduced and the carrier particles adhere to the image forming body side together with the toner particles. Note that when the bias voltage increases, carrier particles also adhere to the ground portion of the image background. Since the above-mentioned side effects are more conspicuous in the atomization and a clear image cannot be obtained, it is difficult to actually atomize the toner particles and the carrier particles for that reason. It was

As a method for solving the above problem, a control electrode, which is a plate-like member for controlling the flight of toner particles, is applied to the developing area, which is applied by the present applicant, and a bias voltage having an AC voltage component is applied to the control electrode. A method of developing under an oscillating electric field (Japanese Patent Laid-Open No. 59-223467) and a regulating member disclosed in Japanese Patent Laid-Open No. 1-94368 for regulating the central portion of the developing region and the layer thickness of the developer layer. Another method has been proposed in which a leveling member, which is another plate-shaped member, is disposed between the two, and a DC voltage having a polarity opposite to the charging polarity of the toner particles is applied as a bias voltage to the leveling member.

Further, a toner cloud developing method using a plate-like electrode body (JP-A-3-131878 and JP-A-3-131879) has been proposed.

[0005]

However, in the above solution, when the average particle diameter of the toner particles is 10 μm or less, the influence of the Van der Waals force becomes large as described above, so that the adhesive force between the carrier and the toner is increased. There is a problem in that the development efficiency increases and the development efficiency decreases extremely.

Further, when the magnetic field formed by the magnetic poles of the magnet body is a horizontal magnetic field in the developing area, the magnetic force becomes weak and carriers are easily scattered, and when the plate-like member is located upstream of the developing area, the plate Since a DC voltage having a polarity opposite to that of the toner is applied to the electrode portion of the plate-shaped member, the toner adheres and the carrier easily moves toward the magnetic pole, so that it is difficult to separate from the plate-shaped member.
Further, in the vertical magnetic field, the magnetic force is strong and the carrier is hard to fly, but since there is only a vertical force, as shown in FIG. 12, once the carrier adheres to the plate member 85, it cannot move in the lateral direction, so that toner or carrier The developer D ₁ is deposited. There is a problem that this comes into contact with the image forming body 1 and stains or uneven streaks occur on the image.

The present invention solves the above problems and provides a developing device capable of stably obtaining a high developing efficiency without causing image stains and uneven streaks even when toner particles or carrier particles having a small particle diameter are used. The purpose is to provide.

[0008]

The above-mentioned object is to carry a two-component developer to a developing area by a developer carrier having a magnet body having a plurality of magnetic poles fixed therein and to fly toner in an oscillating electric field. In a developing device for developing a latent image formed on an image forming body in a non-contact manner, a plate-like member is provided at an upstream portion of the closest position between the image forming body and the developer carrying body, and The developing device characterized in that the setting positions of the plate-shaped member and the magnetic pole are (θ ₁ + θ ₂ ) / 2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ <0 (first invention) ) Is achieved.

Further, the plate-shaped member is a leveling plate or an electrode plate provided with a first electrode capable of applying a voltage on the downstream end thereof, and the set position thereof is (θ ₁ + θ ₂ ) / 2. > Φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₂ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ <0 is a preferred embodiment of the developing device.

(However, the above θ ₁ , θ ₂ , φ ₁ , φ ₂ , φ ₃
Is the angle between each of the following positions and the closest position to the rotation center of the developer transport body. θ ₁ is the angle with respect to the position of the magnetic pole closest to the closest position, θ ₂
Is the angle with respect to the position of the closest magnetic pole on the upstream side of the closest position, φ ₁ is the angle with respect to the downstream end of the plate member, and φ ₂ is the upstream end of the first electrode on the electrode plate. angle, phi ₃ is the angle of the contact position to the developer conveying member of the plate-like member, each angle is the upstream positive, negative downstream from said closest position. ) Further, the above-mentioned object is to carry a two-component developer to a developing area by a developer carrying body in which a magnet body having a plurality of magnetic poles is fixed, and to fly toner in an oscillating electric field to form a non-contact image. In a developing device for developing a latent image formed on a body, a plate-shaped member having two electrodes is provided at an upstream portion of a closest position between the image forming body and the developer transport body,
The plate-shaped member has a first electrode close to the developer transport body and a second electrode arranged between the first electrode and the image forming body, and the plate-shaped member and the magnetic pole are set. It is also achieved by a developing device (second invention) characterized in that the position is (θ ₁ + θ ₂ ) / 2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ <0.

Further, the set position of the plate-shaped member is set to (θ ₁ + θ ₂ ) / 2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₂ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ < The developing device of the second invention is characterized in that 0 φ ₂ ≦ φ ₄ is a preferable embodiment.

(However, the above θ₁, Θ₂, Φ₁, Φ₂, Φ₃
Is θ in the first invention₁, Θ₂, Φ₁, Φ ₂, Φ₃Is the same as
Yes, the above φ_FourIs the upstream end of the second electrode on the electrode plate
And the closest position to the center of rotation of the developer transport body.
Is the angle, and the upstream side from the closest position is positive and the downstream side is
Is negative. )

[0013]

FIG. 3 is a sectional view showing an example of a color image forming apparatus provided with the developing device of the present invention as a suitable developing means.

In FIG. 3, reference numeral 1 denotes a photoconductor belt which is a belt-shaped photoconductor made of a flexible belt coated or vapor-deposited with a photoconductor, and the photoconductor belt 1 is provided between rotating rollers 2 and 3. It is erected on and is conveyed in the clockwise direction by driving the rotating roller 2.

Reference numeral 4 denotes a guide member fixed to the main body of the apparatus so as to be inscribed in the photoconductor belt 1. The photoconductor belt 1 is tensioned by the action of a tension roller 5 so that the inner peripheral surface thereof is the guide member. Rub 4

6 is a scorotron charger which is a charging means, and 7
Is an optical writing device using a laser beam as image exposure means,
Denoted at 8A to 8D are developing devices of the present invention, which are a plurality of developing means each containing a developer of a specific color, and these image forming means are arranged at the portion of the photoconductor belt 1 in contact with the guide member 4. It

Each of the developing devices 8A, 8B, 8C and 8D will be described in detail later. For example, each of the developing devices 8A, 8B, 8C and 8D accommodates developer of yellow, magenta, cyan and black, and has a predetermined gap from the photosensitive belt 1. Keep each developing sleeve
81, and has a function of visualizing the latent image on the photoreceptor belt 1 by a non-contact reversal development method. Unlike the contact development, the non-contact development has an advantage that it does not hinder the movement of the photosensitive belt 1.

A transfer device 12 and a cleaning device 13 are a blade 13a of the cleaning device 13 and a toner discharge roller.
13b is kept at a position apart from the surface of the photoconductor belt 1 during image formation and is pressed against the surface of the photoconductor belt 1 as shown in the figure only during cleaning after image transfer.

The color image forming process by the color image forming apparatus is carried out as follows.

First, data obtained by a color image data input section in which an image sensor scans an original image is subjected to arithmetic processing in an image data processing section, image data temporarily stored in an image memory, or created by a computer. Image data or the like is extracted at the time of recording and is a recording unit, for example, FIG.
Input to the color image forming apparatus. That is, when image data output from an image reading device separate from the color image forming device is input to the optical writing device 7, the optical writing device 7 generates the image data with a semiconductor laser which is a writing light source (not shown). The laser beam (writing light) passes through a collimator lens and a cylindrical lens (not shown), is rotationally scanned by a rotary polygon mirror 74 rotated by a drive motor 71, passes through an fθ lens 75 and a cylindrical lens 76, and has two mirrors 77 therebetween. , 78, the optical path is bent, and the main scanning is performed on the peripheral surface of the photoconductor belt 1 to which uniform charge is applied by the charger 6 of the scorotron, which is a charging means, and main scanning is performed to perform writing.

On the other hand, when scanning is started, the laser beam is detected by an index sensor (not shown), and the first
The laser beam modulated by the color signal of (1) scans the peripheral surface of the photosensitive belt 1. Therefore, a latent image corresponding to the first color is formed on the peripheral surface of the photosensitive belt 1 by the main scanning by the laser beam and the sub-scanning by the conveyance of the photosensitive belt 1. This latent image is developed by the developing device 8A in which yellow (Y) toner (visual medium) is loaded in the developing means, and a toner image is formed on the belt surface. The obtained toner image passes under the blade 13a of the cleaning device 13 and the toner discharge roller 13b as the cleaning means, which is separated from the peripheral surface of the photosensitive belt 1 while being held on the belt surface, and the next image forming cycle is performed. to go into.

That is, the photoconductor belt 1 is recharged by the charger 6, and then the second color signal is input to the optical writing device 7, and the belt is processed in the same manner as in the case of the first color signal described above. Writing is performed on the surface to form a latent image. The latent image is developed by the developing device 8B loaded with magenta (M) toner as the second color.

This magenta (M) toner image is formed in the presence of the previously formed yellow (Y) toner image.

A developing device 8C has a cyan (C) toner, and forms a cyan (C) toner image on the surface of the belt in the same manner as the first and second colors.

Further, 8D is a developing device having a black toner, which forms a black toner image on the surface of the belt by superposing it by the same processing as the above-mentioned color. To each developing sleeve 81 of each of these developing devices 8A, 8B, 8C, and 8D, a developing bias voltage in which a direct current or an alternating current is further superimposed is applied, and non-contact development is performed by a two-component developer that is a developing means. The photosensitive belt 1 whose base is grounded is developed in a non-contact manner.

The color toner image thus formed on the peripheral surface of the photosensitive belt 1 is sent from the paper feeding cassette 14 through the paper feeding guide 15 by applying a high voltage having a polarity opposite to that of the toner at the transfer portion. It is transferred to the transfer material.

That is, the transfer material contained in the paper feed cassette 14 is carried out by the rotation of the paper feed roller 16 and one of the uppermost layers is carried out, and the timing is adjusted with the image formation on the photosensitive belt 1 via the timing roller 17. And is supplied to the transfer device 12.

The transfer material having received the transfer of the toner image is surely separated from the photosensitive belt 1 which suddenly changes its direction along the rotating roller 2 and goes upward, and the toner image is fused by the fixing roller 18. After being fixed, the paper is discharged onto the tray 20 via the paper discharge roller 19.

On the other hand, the photosensitive belt 1 which has been transferred to the transfer material is further conveyed and the blade 13a and the toner discharge roller 13b are brought into pressure contact with each other, and the residual toner is removed by the cleaning device 13 and the operation is completed. Then, the blade 13a is separated again, and a little later, the toner discharge roller 13b is separated, and a new image forming process is started.

As the color image forming apparatus using the developing device of the present invention, a belt-shaped image forming body is described, but an image forming apparatus having a drum-shaped image forming body can be similarly used. .

The developing devices 8A to 8D have the same structure and will be denoted by reference numeral 8.

(Embodiment 1) (First Invention) FIG. 1 is a schematic sectional view showing an embodiment of the developing device of the present invention.
FIG. 2 is an enlarged cross-sectional view of the vicinity of the developing area A in FIG. 1, showing a developing device having a plate-shaped member provided with a voltage-applicable first electrode at the downstream end. In the figure, 81 is made of a non-magnetic material such as aluminum or stainless steel, and the surface is sandblasted to show JIS 10 point average roughness (JIS-B 0610) and roughened to 0.5 to 5.0 μm, and rotatable. A developing sleeve, which is a supported developer carrier, 82 is a magnet body which is fixed inside the developing sleeve 81 and has a plurality of N and S magnetic poles on its surface in the circumferential direction, and 82a is one of the magnetic poles. A magnetic pole 82b is closest to the downstream side of the closest position of 81 and the photosensitive belt 1 (the closest contact 81a on the developing sleeve 81), and a magnetic pole 82b is adjacent to the upstream magnetic pole 82a of the closest position. . The developing sleeve 81 is rotatable in the direction of the arrow in the drawing with respect to the magnet body 82, and the developing sleeve 81 and the magnet body 82 serve to convey the developer.
Further, the magnetic pole 82a of the magnet body 82 and other N and S magnetic poles are magnetized so as to exhibit a magnetic flux density of usually 500 gauss to 1,500 gauss on the surface of the developing sleeve 81, and the magnetic force thereof causes the toner on the surface of the developing sleeve 81. A layer of developer D composed of particles and carrier particles, that is, a magnetic brush is formed. This magnetic brush moves in the same direction as the rotation of the developing sleeve 81 by the rotation of the developing sleeve 81, and is conveyed to the developing area A. The magnetic brush formed on the developing sleeve 81 does not come into contact with the surface of the photoconductor belt 1 so that a gap is maintained between the developing sleeve 81 and the regulating blade 86 and the developing sleeve 81.
And the gap between the photoconductor belt 1 is adjusted.

Reference numeral 85 is a plate-like member having a voltage-applyable first electrode 85a disposed on the downstream end of an insulating member 85b provided on the upstream side of the developing area A in contact with the layer of the developer D. In the electrode plate, the insulating member 85b also serves as a leveling member made of an electrical insulator such as polyester, polyimide, glass epoxy, polyethylene terephthalate, and polyamide imide. The first electrode 85a is a conductive material such as metal. The insulating member 85b is linearly and integrally provided on the tip of the insulating member 85b.
83A and 83B are agitation screws for agitating the developer D to make the components uniform, and 86 is a developer regulating means made of a non-magnetic material or a magnetic material provided to regulate the height and amount of the magnetic brush. A blade, 87 is a cleaning blade for removing the magnetic brush passing through the developing area A from the developing sleeve 81, 88 is a developer reservoir, 89 is a casing, and 89a is provided in the casing 89 for supporting the fixed portion of the insulating member 85b. It is a supporting part. A pressing plate 90 is an example of a fixing member, and 90s is a set screw for fixing the pressing plate 90 to the supporting portion 89a and fixing the electrode plate 85 so as to press the electrode plate 85 toward the developing sleeve 81.

The first electrode 85a is, as shown in FIG.
The insulating member 85 is formed by using a conventionally known printed circuit board manufacturing method.
The first electrode 85a can be formed at the tip of the insulating member 85b by laminating a conductive member such as a copper foil using glass epoxy, polyimide, paper phenol or the like as b, and then performing an etching process. First electrode 85
A may be coated with an insulating resin to prevent unnecessary discharge and to prevent rust. 84b is a terminal portion for applying a bias voltage.

The insulating member 85b of the electrode plate 85 is the developing sleeve 81.
When the developer D is conveyed upward, as shown in FIGS. 10A and 10B, the developer D enters between the insulating member 85b and the developing sleeve 81, so that the developer D is slightly curved and the insulating member 85b is developed. The sleeve 81 faces the sleeve 81 with a slight gap, or has almost no gap, that is, contacts the layer of the developer D and contacts the developer sleeve 81, or faces the developing sleeve 81. . The point on the developing sleeve 81 which is in contact with / close to is called a contact point and is represented by 81b.

The thickness t ₁ of the insulating member 85b and the first electrode 8
The thickness t of the electrode plate 85 including the thickness t ₂ of 5a (FIG. 7 (b))
Is (1 / 10,0) when the closest distance (developing gap) between the photosensitive belt 1 and the developing sleeve 81 in the developing area A is d.
00) d to (2/3) d, particularly (1 / 1,000) d to (1/2) d are preferable. If it is larger than (2/3) d, the gap between the photoconductor belt 1 and the first electrode 85a becomes narrow, so that the first electrode 85a easily comes into contact with the surface of the photoconductor belt 1 and image disturbance easily occurs. . On the other hand, if it is (1 / 10,000) d or less, the current from the developing sleeve 81 is likely to flow in, causing a voltage drop and a decrease in developing efficiency. The insulating member 85b has an upper end portion of the first electrode 85a on the photosensitive belt 1 side of (2/3) d or less,
The one that can support the electrode plate 85 is selected so that the lower end of the developing sleeve 81 side is (1 / 10,000) d or more, but it is 1/100 from the viewpoint of strength, vibration prevention, and contact with the photosensitive belt 1.
Those of d to 3 / 5d are preferable.

The circumferential length (m) of the first electrode 85a
Is increased so as to cover the downstream side and the upstream side of the contact point 81b, an unnecessary toner cloud is generated in the upstream portion of the conveyance. In order to prevent this and obtain a stable conveyance amount, as shown in FIG. 2, the entire first electrode 85a is the closest position of the developing sleeve 81 to the photosensitive belt 1 rather than the contact point 81b. It is preferable to form it so as to be arranged only on the contact 81a side (that is, φ ₂ <φ ₃ ). The width (length m in the circumferential direction) of the first electrode 85a is preferably 0.05 to 5.0 mm, and particularly preferably 0.1 to 1.0 mm, although it depends on the diameter of the developing sleeve 81 and the conveying speed.
If it is less than 0.05 mm, it is not possible to generate a sufficient toner cloud, and if it is more than 5.0 mm, the toner is charged due to vibration and becomes excessively charged, resulting in a decrease in developing efficiency.

Further, the positions of the electrode plate 85 and the magnetic poles 82a and 82b of the magnet body 82 are (θ ₁ + θ ₂ ) / 2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₂ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ <0 is preferably set.

However, the above θ ₁ , θ ₂ , φ ₁ , φ ₂ , φ
₃ is an angle between each of the following positions and the closest contact 81a with respect to the rotation center O of the developing sleeve.

Θ ₁ is the angle about the position of the magnetic pole 82a closest to the closest contact 81a, θ ₂ is the angle about the position of the closest magnetic pole 82b on the upstream side of the closest contact 81a, and φ ₁ is the electrode plate 85.
Of the first electrode 85a on the downstream side (that is, the downstream side tip of the plate-like member), φ ₂ is the first electrode 85a on the electrode plate 85.
Angle of the upstream end of, phi ₃ is the angle about the position of the contact point 81b that is a contact / proximity to the position of the developing sleeve 81 of the electrode plates 85, each angle is upstream of the closest position Is positive and the downstream side is negative.

(Θ ₁ + θ ₂ ) / 2 is the magnetic pole 82a and the magnetic pole 82b.
It is an angle extending from the center of rotation O between the intermediate point of and and the closest point 81a. When the developing sleeve 81 has a diameter of 10 to 20 mm, θ ₁ is −15 ° to −5 °, and (θ ₁ + θ ₂ ) is 20 ° to 70.
It is preferable that the angles φ and φ ₁ are 0 to 10 ° and φ ₂ is 10 to 30 °.

That is, in the electrode plate 85, the downstream end thereof, the upstream end of the first electrode 85a (the entire width of the first electrode 85a) and the contact point 81b are all located at the midpoint between the magnetic pole 82a and the magnetic pole 82b. It is set to be located on the downstream side. With this setting, the vertical (radial direction) component HAr of the magnetic force vector HA at the closest position of the developing area A becomes larger than the horizontal (circumferential direction) component HAθ (see FIG. 6), and the vertical direction of the magnetic force vector Hc near the first electrode 85a. Ratio of component Hcr and horizontal component Hcθ (Hcr
/ Hcθ) is 0.5 <(Hcr / Hcθ) <5. This makes it difficult for the magnetic particles (magnetic toner or magnetic carrier) to move in the horizontal direction (left and right in the figure),
Rather, the force attracted to the developing sleeve 81 works, so the electrode plate
85 Prevents adhesion to the tip. The ratio of the vertical component to the horizontal component of the magnetic force vector is (H
Ar / HAθ)> 1.5, and more preferably (Hcr / Hcθ)> 1 near the first electrode 85a, and by making the magnetic field asymmetric, the magnetic force is balanced and the adhesion amount is reduced, which is preferable.

As described above, inserting the electrode plate 85, which is a plate-like member, into the developing area A prevents uneven development, but has a drawback of reducing developing efficiency. In this embodiment, the electrode plate 85
The developing efficiency is improved by forming the following oscillating electric field between the first electrode 85a and the developing sleeve 81.

That is, a developing bias voltage in which an AC component is superimposed on a DC component is applied to the developing sleeve 81 by the DC bias power source E ₁ and the AC bias power source E _AC through the protective resistor R ₁ . The DC bias power source E is connected to the first electrode 85a.
A bias voltage of only the DC component is applied from ₂ through the protection resistor R ₂ . It is preferable to apply a DC voltage having the same polarity as the toner to the first electrode 85a from the viewpoint of preventing toner adhesion.

In the developing device 8 of the present invention, by applying the above bias voltage, the alternating electric field (which will be referred to as a second oscillating electric field) formed between the photosensitive belt 1 and the developing sleeve 81, and the electrode A first oscillating electric field is generated between the first electrode 85a of the plate 85 and the developing sleeve 81.

In the above-mentioned color image forming apparatus, if the negative development is performed by using an OPC photosensitive member that is negatively charged as the photosensitive member of the photosensitive belt 1, and the photosensitive member is charged to, for example, -800 V, the first electrode A developing bias voltage of -750V + AC voltage component is applied to the developing sleeve 81 at -750V to 85a. The AC component has a frequency of 100 to 20 KHz, preferably 1 to 10 KHz and a peak-to-peak voltage (V _PP ) of 200.
~ 2,000V. In this case, since the first electrode 85a is provided closer to the developing sleeve 81 than the photosensitive belt 1, the strength of the first oscillating electric field is higher than the strength of the second oscillating electric field.

The toner particles of the developer D which have reached the vicinity of the first electrode 85a are vibrated by the first oscillating electric field in the direction perpendicular to the lines of electric force, so that the toner particles are separated and fly from the carrier to cause the cloud haze. It is possible to sufficiently generate a toner cloud in the shape of a circle. This toner cloud is assisted in the flight toward the latent image on the photosensitive belt 1 by the second oscillating electric field, and since the electrode plate 85 is set at an appropriate position, uniform development is performed.

At this time, since the AC component of the developing bias voltage is applied only to the developing sleeve 81, the first oscillating electric field and the second oscillating electric field have the same phase, and the toner particles are separated from the first oscillating electric field. Smooth transition to the second oscillating electric field,
Moreover, even if a strong oscillating electric field is formed, dielectric breakdown does not occur.

The waveform of the above AC component is not limited to a sine wave,
It may be a rectangular wave or a triangular wave. Although the frequency is also related, the higher the voltage value is, the more the magnetic brush of the developer D is vibrated, and the separation and flight of the toner particles from the carrier particles are facilitated. Dielectric breakdown easily occurs. The generation of fog is prevented by a direct current component, and the insulation breakdown is caused by coating the surface of the developing sleeve 81 with a resin, an oxide film, or the like so as to be insulating or semi-insulating, or the carrier particles of the developer D having an insulating property as described later. It can be prevented by using carrier particles.

FIG. 11 shows the results of changing the frequency and the peak-to-peak voltage of the AC component applied to the developing sleeve 81 in the above embodiment. In FIG. 11, the range shaded with horizontal lines is the range where fogging is likely to occur, the range shaded with vertical lines is the range where dielectric breakdown is likely to occur, and the range shaded with diagonal lines is the range where image quality degradation is likely to occur. There is a preferable range in which a stable and clear image can be obtained. As is clear from the figure, the range in which fogging is likely to occur changes according to changes in the AC component. Further, the low frequency region shaded with dots in the figure is a range where uneven development occurs due to the low frequency.

The electrode plate having the first electrode 85a at the downstream end as the plate member has been described above.
In the case of a plate member having no 85a or a leveling plate which is a plate member entirely made of a conductive material, the position of its tip and the position of the magnetic pole 82a of the magnet body 82 are (θ ₁ + θ ₂ ) By setting 1/2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ <0, the magnetic field is made asymmetric as in the case of the electrode plate 85, and toner is applied to the tip of the electrode plate 85 (plate member). It is possible to prevent the adhesion of the carrier and the carrier.

Also in this case, the developing sleeve 81 has a diameter of 10 to
For 20 mm, θ ₁ is -15 ° to -5 °, (θ ₁ + θ ₂ ) is 20
It is preferable that the angle is in the range of 0 to 70 ° and φ ₁ is in the range of 0 to 10 °.

(Embodiment 2) (Second Invention) FIG. 4 is a schematic sectional view showing another embodiment of the present invention, and FIG. 5 is an enlarged sectional view in the vicinity of the developing region A in FIG. In this embodiment,
The developing device includes an electrode plate 185 having a second electrode as a plate-shaped member, in addition to the first electrode. The same parts as those in FIG. 1 and FIG. 2 are denoted by the same reference numerals, and their operation is also the same, and thus detailed description thereof will be omitted.

In the figure, numeral 185 indicates a width 0.05 to 0.5 mm and a thickness made of a conductive material such as metal at the downstream end of an insulating member 85b provided in contact with the layer of the developer D on the upstream side of the developing area A. A linear first electrode 85a having a width of 1 to 100 μm and a linear second electrode having a width of 0.05 to 1.0 mm and a thickness of 1 to 100 μm, which are also made of a conductive material such as metal, are integrally provided with an insulating material sandwiched therebetween. The tip is insulation-coated with an insulating material 85d. In addition,
The width of the second electrode 85c is not limited to the tip portion and may cover the entire area.

FIG. 8 is a diagram showing another configuration example of the electrode plate. FIG. 8A shows a case where the first and second electrodes 185a and 185c are formed on both sides of one insulating member 85b.
(B) shows that the electrodes 185a, 18 are provided on each of the two insulating members 185b.
5c is formed, and the first electrode 185a is attached so as to be closest to the developing sleeve 81. FIG. 8C shows a structure in which the surfaces opposite to those in FIG. 8B are attached to each other to have an inverse structure. In this case, the first electrode 185a faces the developing sleeve 81 via the insulating member 185b. . In FIG. 8D, a step is formed at the front end on the developing sleeve 81 side, and a space for forming a toner cloud is provided. FIG.
8E is a modification of FIG. 8C in which the second electrode 185c on the image forming body side is formed over the entire area.
In this way, the second electrode 185c has a structure similar to that shown in FIGS.
Also in (C) and (D), it may be formed over the entire region as shown in FIG. 8 (E).

The developing sleeve 81 has a DC bias power source E ₁
A developing bias voltage in which an AC component is superposed on a DC component is applied through a protection resistor R ₁ by an AC bias power source E _AC . In addition, a bias voltage of only a DC component is applied to the first electrode 85a from a DC bias power source E ₂ via a protection resistor R ₂ .
The second electrode 85c protected from DC bias power source E ₃ resistor R ₃
A bias voltage of a DC component is applied via each.

The insulating member 85b of the electrode plate 185 is the developing sleeve 8
When the developer D is conveyed to the upper surface of the first embodiment, as shown in FIG. 11, the developer D enters between the insulating member 85b and the developing sleeve 81 as shown in FIG. Then, the insulating member 85b has a slight gap with respect to the developing sleeve 81 and faces the developing sleeve 81 in the contact / proximity state.

Position of electrode plate 185 and magnetic pole 82 of magnet body 82
The positions of a and 82b are the same as in the first embodiment (θ ₁ + θ ₂ ) / 2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₂ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ <0 φ _It is preferable to set so that ₂ ≦ φ ₄ .

However, the above θ ₁ , θ ₂ , φ ₁ , φ ₂ , φ
₃ is the same as the angle described in the first embodiment, and φ ₄ is the angle between the upstream end of the second electrode 85b of the electrode plate 85 centered on the rotation center O and the closest position. Yes, the upstream side of the closest position is positive and the downstream side is negative.

(Θ ₁ + θ ₂ ) / 2 is the magnetic pole 82a and the magnetic pole 82b.
It is an angle extending from the center of rotation O between the intermediate point of and and the closest point 81a. When the developing sleeve 81 has a diameter of 10 to 20 mm, θ ₁ is −15 ° to −5 °, and (θ ₁ + θ ₂ ) is 20 ° to 70.
It is preferable that the angles φ and φ ₁ are 0 to 10 ° and φ ₂ is 10 to 30 °.

That is, in the electrode plate 85, the downstream end thereof, the upstream end of the first electrode 85a (the entire width of the first electrode 85a) and the contact point 81b are all located at the intermediate point between the magnetic pole 82a and the magnetic pole 82b. It is set to be located on the downstream side. With this setting, as in the first embodiment, the vertical (radial direction) component HARr of the magnetic force vector HA at the closest position of the developing area A becomes larger than the horizontal (circumferential direction) component HAθ (see FIG. 6), and the first electrode 85
Vertical component Hcr and horizontal component H of magnetic force vector Hc near a
The ratio with cθ (Hcr / Hcθ) is 0.5 <(Hcr / Hcθ) <5. This makes it difficult for the magnetic particles (magnetic toner or magnetic carrier) to move in the horizontal direction (left and right in the figure),
Rather, the force attracted to the developing sleeve 81 works, so the electrode plate
85 Prevents adhesion to the tip. The ratio of the vertical component to the horizontal component of the magnetic force vector is (H
Ar / HAθ)> 1.5, and more preferably (Hcr / Hcθ)> 1 near the first electrode 85a, and by making the magnetic field asymmetric, the magnetic force is balanced and the adhesion amount is reduced, which is preferable.

Further, the second electrode 85c is provided on the first electrode 85a to form an electric field P ₁ for moving the toner toward the photosensitive belt ₁ and an electric field P ₂ for moving the toner toward the first electrode 85a. , To prevent wraparound in the direction of the second electrode 85c,
It works to move the toner toward the non-image portion of the photosensitive belt 1, and prevents the toner from adhering to the electrode plate 85, especially the electrode of the second electrode 85c. Further, from the toner image already formed on the photosensitive belt 1, the developing sleeve 81 and the electrodes 85a,
Prevents backward flight to 85c.

A strong oscillating electric field is formed between the first electrode 85a and the developing sleeve 81 to generate a toner cloud, but the distance between the second electrode 85c and the developing sleeve 81 is large as described later. The oscillating electric field is weak, and the second electrode
By applying a DC voltage to 85c, an electric field for moving the toner to the developing sleeve 81 side is formed to prevent the toner cloud from adhering to the surface of the electrode plate 85. For this reason, it is preferable that the width of the second electrode 85c is equal to or wider than the width of the first electrode 85a, that is, φ ₂ ≦ φ ₄ .

The electric field formed by the second electrode 85c is called the third electric field. This third electric field is applied to the first electrode 85a.
Field P ₂ formed with, an oscillating electric field formed between the developing sleeve 81, formed of a field P ₁ formed on the photosensitive belt 1. In this device, the photosensitive belt 1 and the developing sleeve
The strength of the first oscillating electric field is higher than that of the second oscillating electric field which is an oscillating electric field formed between the photoconductor and the photosensitive member 81, and the third electric field maintains the generation of the toner cloud. An electric field for moving the toner to the photosensitive belt 1 is formed between the belt 1 and the electrode plate 85.

FIG. 9 is a diagram showing the relationship between the closest distance (developing gap) d between the photosensitive belt 1 and the developing sleeve 81 in the developing area A and the electrode interval. In order to generate a sufficient toner cloud by making the first oscillating electric field larger than the second oscillating electric field, d ₄ ≧ d ₁ + d ₂ is preferable, and more preferably d ₄ ≧ d ₁ + d ₂ + d ₃ And it is preferable that 0.5 ≦ (d ₁ + d ₂ ) / d ₃ ≦ 2.

The size of the space is such that d ₁ is 0.05 to 0.2 m.
m, d ₂ + d ₃ is 0.05 to 0.4 mm, d ₁ + d ₂ + d ₃ is 0.1 to 0.6 m
It is preferable that m and d ₄ are 0.2 to 1 mm and d is 0.3 to 1.5 mm.

When the developing device of this embodiment is applied to the color image forming apparatus shown in FIG. 3, reversal development is performed using an OPC photosensitive member that is negatively charged as the photosensitive member of the photosensitive belt 1, and the photosensitive member is For example, assuming that the first electrode 85a is charged to −800V, the absolute value of the first electrode 85a is smaller than 0.
A voltage (V ₁ ) of −800V and a voltage (V ₂ ) of −800V or higher are applied to the second electrode 85c to move the negatively charged toner to the photosensitive belt 1. For the developing sleeve 81-
A developing bias voltage of 700 V + AC voltage component is applied. AC component has a frequency of 100 to 20 KHz, preferably 1 to 10 KH
The peak-to-peak voltage (V _PP ) at z is 200 to 2,000V. V ₂ can be V ₂ = V ₁ , but it is preferable that V ₂ is set to be lower so that the negatively charged toner can be pulled out from the developer D layer. That is, the developing sleeve 81 and the first electrode 85
The direct current electric field formed between the first and second electrodes 85
It is more preferable to form a condition for moving in the direction of a.

On the other hand, the photosensitive belt 1 is attached to the second electrode 85c.
A voltage higher than the non-image portion potential of is applied. As a result, a voltage whose absolute value is higher than that of the developing sleeve 81 and the first electrode 85a is applied to the second electrode 85c of the electrode plate 85, so that the toner is directed toward the photosensitive belt and the developing sleeve 81 and the first electrode 85a. An electric field for moving to is formed so that the toner does not adhere to the upper part of the electrode plate 85, and the toner image on the photosensitive belt 1 may adhere to the second electrode 85c even in the image forming process of superposing the toner images. Absent.

The first oscillating electric field causes the toner particles to vibrate in the direction of the lines of electric force thereof, so that the toner can be separated from the carrier and fly, and a toner cloud can be sufficiently generated. This toner cloud is assisted in the flight toward the latent image on the photosensitive belt 1 by the second oscillating electric field, and good development is performed. Furthermore, wraparound of the toner to the dirt or the upper direction of the photosensitive belt field P ₁ and the first electrode 85a the direction of the electric field P ₂ is formed the electrode plate 85 in one direction is prevented by the third field.

The waveform of the above AC component is not limited to a sine wave,
It may be a rectangular wave or a triangular wave. Although the frequency is also related, the higher the voltage value is, the more the magnetic brush of the developer D is vibrated, and the separation and flight of the toner particles from the carrier particles are facilitated. Dielectric breakdown easily occurs. The generation of fog is prevented by the direct current component, and the dielectric breakdown is prevented by the first and second electrodes 85a, 85c.
The phenomenon can be prevented by coating the surface of the sleeve 81 with a resin, an oxide film, or the like so as to be insulating or semi-insulating, or by using insulating carrier particles as described below as the carrier particles of the developer D. .

As described above, the developing device of the present invention keeps the magnetic developer D in non-contact with the photosensitive belt 1 which is an image forming body, and generates the toner cloud by the first and second oscillating electric fields. Therefore, the separation and flight to the photosensitive belt 1 are improved, the selective adsorption property to the electrostatic image is improved, and the carrier particles are prevented from adhering to the photosensitive belt 1. Although it is made possible to use a developer, a high-quality image can be developed, and it is preferable to use a developer D composed of the following carrier particles and toner particles.

Generally, when the average particle size of the magnetic carrier particles is large, the state of the ears of the magnetic brush formed on the developing sleeve 81 becomes rough. Therefore, even if the electrostatic latent image is developed while being vibrated by the electric field. However, there is a problem that unevenness is likely to appear in the toner image and the toner density at the ears becomes low, so that high-density development is not performed. To solve this problem, the average particle size of the magnetic carrier particles should be reduced, and as a result of experiments, it was found that the above problems do not occur when the weight average particle size is 50 μm or less. However, if the particle size of the magnetic carrier is too small, the magnetic carrier tends to adhere to the surface of the photoconductor belt 1 together with the toner particles and scatter easily. These phenomena are related to the strength of the magnetic field acting on the carrier and the strength of the magnetization of the carrier due to it, but in general, the above tendency gradually begins to appear when the weight average particle diameter of the magnetic carrier becomes 15 μm or less. It becomes noticeable at 5 μm or less. Therefore, in this developing device, the magnetic carrier of the developer D preferably has a weight average particle diameter of 50 μm or less, particularly preferably 30 μm or less and 5 μm or more. In order to form the magnetic brush low and uniformly, the strength of magnetization is preferably 10 to 50 emu / g. When the magnetic carrier is spherical, the stirring property of the toner particles and the carrier particles and the transport property of the developer D are improved, and the charge controllability of the toner is further improved. It is preferable because it prevents aggregation of particles.

Such a magnetic carrier is a metal such as iron, chromium, nickel, cobalt or the like, or a compound or alloy thereof, such as iron tetroxide or γ-oxidation, which is the same as in a conventional magnetic carrier as a magnetic material. Spherical particles of ferromagnets or paramagnetic materials such as ferric iron, chromium dioxide, manganese oxide, ferrite, and manganese-copper alloys, or the surfaces of these magnetic particles are styrene resin, vinyl resin, Resins such as ethyl resin, rosin-modified resin, acrylic resin, polyamide resin, epoxy resin, polyester resin, silicone resin, etc., are spherically coated with these copolymer resins or fatty acid waxes such as palmitic acid and stearic acid, or The particles obtained by making spherical particles of resin or fatty acid wax containing dispersed magnetic fine particles are Obtained by a particle size selected in the average particle 径選 another means.

The use of spherical carrier particles coated with a resin or the like as described above, in addition to the above-mentioned effects, makes the layer of the developer D formed on the developer carrying carrier uniform, and Also, the effect that a high bias voltage can be applied to the developer carrier is given. That is, the fact that the carrier particles are spherical carrier particles coated with a resin or the like means that (1) in general, the carrier particles are easily magnetized and adsorbed in the long axis direction, but the spheroidization eliminates the directionality thereof, and therefore the developer layer Are uniformly formed to prevent locally low resistance regions and uneven layer thickness.
(2) As the resistance of the carrier particles is increased, the edge portion as seen in the conventional carrier particles is eliminated, and the electric field is not concentrated on the edge portion. As a result, a high bias voltage is applied to the developer carrier. However, the photoconductor belt 1
It is effective in preventing the electrostatic latent image from being disturbed by discharging on the surface and the bias voltage from breaking down. The fact that this high bias voltage can be applied means that the effects as described above in the development under the oscillating electric field of the present invention can be sufficiently exerted. And, the above-mentioned wax is also used for the spheroidizing of the carrier particles having the above effects, but from the viewpoint of the durability of the carrier, it is preferable to coat the above-mentioned spherical magnetic particles with a resin. Further, it is preferable that the carrier particles are formed of magnetic particles having an insulating property in which the resistivity of the carrier particles is 10 ⁸ Ωcm or more, particularly 10 ¹³ Ωcm or more. The resistivity, after tapping putting particles into a container having a cross section of 0.50 cm ^2, 1Kg / on packed particles cm ²
Is obtained by reading the current value when a voltage that generates an electric field of 1,000 V / cm is applied between the load and the bottom electrode. If this resistivity is low, the developer transport carrier When a bias voltage is applied to the carrier particles, charges are injected into the carrier particles, and the carrier particles are likely to adhere to the surface of the photosensitive belt 1 or the breakdown of the bias voltage is likely to occur.

In summary, the magnetic carrier particles are spherical so that the ratio of the major axis to the minor axis is 3 times or less, preferably 2 times or less, and protrusions such as needle-shaped portions and edge portions are formed. And has a resistivity of 10 ⁸ Ωcm or more, preferably 10 ¹³ Ωcm
The above is the proper condition. Further, such magnetic carrier particles are obtained by increasing the resistance of spherical magnetic particles by forming an oxide film or the like. It is produced by subjecting to spheroidizing treatment or obtaining dispersed resin particles by a spray drying method.

Next, the toner particles will be described. Generally, when the average particle size of toner particles is small, the amount of charge qualitatively decreases in proportion to the square of the particle size, and the adhesive force such as the Van der Waals force is relatively large, and the toner particles are easily scattered. While fogging easily occurs, it becomes difficult to separate from the carrier particles of the magnetic brush. In the conventional magnetic brush developing method, such a problem becomes remarkable when the average particle diameter is 10 μm or less. In the developing device of the present invention, this problem is solved by performing the development with the magnetic brush under a double oscillating electric field. That is, the toner particles attached to the ears of the magnetic brush are
The toner is strongly vibrated in the first oscillating electric field and easily separates from the spikes to form a toner cloud.
The inertial force due to the rotation of the sleeve, the centrifugal force due to the oscillating electric field, and the like cause the toner particles to be carried to the immediately adjacent developing area A, and the toner particles are faithfully adsorbed to the electrostatic latent image under the second oscillating electric field. At this time, since the electrode portion 84a is provided only on the downstream side of the most contact point 81b between the insulating member 83 and the developing sleeve 81, no cloud is generated in an unnecessary portion other than the developing area A. Further, the toner particles having a low charge amount hardly move to the image portion or the non-image portion, and the toner does not rub against the photosensitive belt 1, so that the toner particles may adhere to the photosensitive belt 1 by frictional charging. It will be used up to a toner particle size of about 1 μm. The weakening of the bond between the toner particles and the carrier particles by the oscillating electric field reduces the adhesion of the carrier particles accompanying the toner particles to the photoconductor belt 1, and the ears of the magnetic brush are kept in non-contact with the surface of the photoconductor belt 1. However, the toner particles having a large charge amount with respect to the carrier particles are selectively transferred to the electrostatic latent image under the oscillating electric field as described above, so that the adhesion of the carrier particles to the photosensitive belt 1 is significantly increased. Reduce.

As the average particle diameter of the toner becomes large, the roughness of the image becomes noticeable as already mentioned. Usually, for developing with fine lines arranged at a pitch of about 10 lines / mm, a toner with an average particle size of about 20 μm does not cause any problem, but if a finely divided toner with an average particle size of 10 μm or less is used, the resolution will be improved. Is significantly improved, and it gives a clear high-quality image that faithfully reproduces the tone difference. For the above reasons, the average particle size of the toner is 20 μm or less, preferably 10 μm or less. Further, since the toner particles follow the electric field, the absolute value of the charge amount of the toner particles should be larger than 1 μC / g to 3 μC / g (preferably 3 μC / g).
/ G to 100 μC / g) is desirable. Especially when the particle size is small, a high charge amount is required.

Such a toner can be obtained by a method such as a pulverization / granulation method, a suspension polymerization method, an emulsion polymerization method and the like similar to the conventional toner. That is, it is possible to use a toner in which spherical or amorphous non-magnetic or magnetic toner particles in the conventional toner are selected by the average particle size selection means. Further, the toner particles may be magnetic particles containing magnetic fine particles. In this case, the amount of the magnetic fine particles is 60 wt% or less, especially 30%.
Those that do not exceed wt% are preferable. When the toner particles contain magnetic particles, the toner particles are affected by the magnetic force contained in the developer carrying carrier, so that the uniform forming property of the magnetic brush is further improved and the fogging Generation is prevented, and toner particles are less likely to be scattered. However, if the amount of the magnetic substance contained is too large, the magnetic force between the carrier particles becomes too large,
It becomes impossible to obtain a sufficient developing density, and the magnetic fine particles come to appear on the surface of the toner particles.
It may be difficult to control triboelectric charging, or toner particles may be easily damaged.

In summary, in the developing device of the present invention, as the preferable toner particles, the resin as described for the carrier particles and further the fine particles of the magnetic material are used, and the coloring component such as carbon and the electrification as required. It is composed of particles having an average particle size of 20 μm or less, particularly preferably 10 μm or less, which can be produced by a method similar to a conventionally known method for producing toner particles by adding a control agent and the like.

For the developing device of the present invention, a developer in which the spherical carrier particles and the toner particles as described above are mixed in the same proportion as in the conventional two-component developer is preferably used. Further, if necessary, a fluidizing agent for improving the fluidity of particles and a cleaning agent useful for cleaning the surface of the image forming body are mixed. As the fluidizing agent, colloidal silica, silicon varnish, metal soap, nonionic surface active agent or the like can be used, and as the cleaning agent, fatty acid metal salt, organic group-substituted silicon or fluorine surface active agent or the like can be used. You can

In the color image forming apparatus shown in FIG. 3 equipped with such a developing device, an OPC photosensitive member which is negatively charged as a photosensitive member of the photosensitive belt 1, its peripheral speed is 180 mm / sec, and a latent image on the photosensitive belt 1. Maximum potential −800V, Minimum potential −50
V, the outer diameter of the developing sleeve 81 is 15 mm, the rotation speed is 200 rpm, the magnetic flux density is 1200 gauss on the N and S magnetic poles of the magnet body 82, and the magnetic pole position angles θ ₁ and θ ₂ are θ ₁ = −8 ° and θ ₂ = 45 °, first electrode 85
The position angles φ ₁ , φ ₂ , and φ _{3 of a} are φ ₁ = 8 °, φ ₂ = 15 ° φ ₃
= 25 °, development area A when no development bias voltage is applied
The thickness of the developer D layer is 0.25 mm, the gap d between the developing sleeve 81 and the photosensitive belt 1 is 0.95 mm, the developing bias voltage is -700 V DC component, 10 KHz AC component, peak-peak voltage 1,20.
0V, the first electrode 85a was placed 0.3mm away from the developing sleeve 81 and a -500V DC voltage was applied, and the second electrode 85c was placed 0.075mm away from the first electrode 85a and a -1,000V DC voltage was applied. . In this embodiment, the developer D on the developing sleeve 81
Does not contact the surface of the photosensitive belt 1.

After development under the above conditions, transfer to plain paper and fixing through a heat roller fixing device having a surface temperature of 140 °, the obtained recorded image is free from edge effects and fog and has high image density. It was extremely clear, and after recording 50,000 sheets, it was possible to obtain a stable recorded image from the beginning to the end, and almost no toner adhesion to the electrode plate 85 was observed. .

In the above embodiments, since a specific developing device is selectively used, other developing devices not used are
The rotation of the developing sleeve 81 was stopped, and the AC component of the applied developing bias voltage was stopped. That is, to the developing sleeve 81, a bias voltage of -1,000 V, which is higher than the potential of the non-image portion of the photoconductor, is applied in the floating state or the same polarity as the toner. A bias voltage of -1,000 V, which has the same polarity as the toner and is higher than the non-image portion potential of the photoconductor, was applied to the first and second electrodes 85a and 85c. The first and second electrodes 85a,
One or both of 85c may be floating. This prevents the toner from moving from the toner image on the photoconductor to the electrode plate 85. Almost 0V before and after the image area
The potential pattern is formed and conditions for removing the toner on the developing sleeve 81 and the electrode plate 85 that have stopped are set to prevent color mixture of toner in the image area. Also, the electrode plate 85
The structure of FIG. 8 (C) is used as the material, and a glass fiber-containing epoxy plate with a thickness of 75 μm is attached to a thickness of 150 μm.
The first electrode 85a has a thickness of 10 μm and a width of 500 on a thick epoxy plate.
The second electrode 85c was provided with a linear electrode having a thickness of 10 μm and a width of 1,000 μm.

In the description of the present invention, the device for reversal development has been described, but the same applies to a developing device for regular development. The voltage applied to the electrodes of the developing sleeve 81 and the electrode plate 85 at that time may be a voltage that forms an electric field that acts in the same manner as that acting on the toner in the reversal development.

[0085]

According to the developing device of the first and second aspects of the invention as described above, the magnetic fields at the positions of the developing region and the electrodes of the electrode plate are asymmetrical, and the image forming body and the developing sleeve are provided. By forming an oscillating electric field between
It was possible to prevent the developer from adhering to the electrode portion of the electrode plate.

In the developing device of the second aspect of the invention, the second electrode is further provided, and a voltage having an absolute value higher than that of the developer carrying member and the first electrode is applied. It is possible to provide a developing device capable of performing stable and good development without causing stains and uneven streaks.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing an embodiment of a developing device of the first invention.

FIG. 2 is an enlarged cross-sectional view showing the vicinity of the developing area in the embodiment of FIG.

FIG. 3 is a configuration diagram showing an example of a color image forming apparatus including a developing device of the present invention.

FIG. 4 is a schematic sectional view showing an embodiment of the developing device of the second invention.

5 is an enlarged cross-sectional view showing the vicinity of the developing area in the embodiment of FIG.

FIG. 6 is a diagram showing lines of magnetic force of the developing device of the present invention.

FIG. 7 is a perspective view and a cross-sectional view showing an example of an electrode plate.

FIG. 8 is a cross-sectional view showing another configuration example of the electrode plate.

FIG. 9 is a diagram for explaining the relationship between the development gap and the electrode spacing.

FIG. 10 is a diagram showing an installed state of an electrode plate.

FIG. 11 is a graph showing a preferred range of the AC component of the developing bias voltage.

FIG. 12 is a diagram showing a defect of a conventional plate-shaped member.

[Explanation of symbols]

1 photoconductor belt (image forming body) 7 laser writing device 8, 8A, 8B, 8C, 8D developing device 81 developing sleeve (developer carrier) 81a closest contact (closest position) 81b contact (developing sleeve plate 82 magnet body 82a, 82b magnetic pole 85 electrode plate (plate member) 85a first electrode 85b insulating member 85c second electrode 86 regulating blade A developing area D developer E ₁ , E ₂ , E ₃ DC bias power supply E _AC AC bias power supply R ₁ , R ₂ protection resistor

Claims (4)

[Claims] 1. A two-component developer is transported to a developing area by a developer transport body in which a magnet body having a plurality of magnetic poles is fixed, and toner is ejected in an oscillating electric field to form an image forming body in a non-contact manner. In a developing device for developing a formed latent image, a plate-shaped member is arranged upstream of the closest position between the image forming body and the developer transport body, and the plate-shaped member and the magnetic pole are set. A developing device characterized in that the position is (θ ₁ + θ ₂ ) / 2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ <0. However, the above θ ₁ ,
θ ₂ , φ ₁ , and φ ₃ are angles formed by the following positions and the closest position to the rotation center of the developer transport body.
θ ₁ is the angle for the position of the magnetic pole closest to the closest position, θ ₂ is the angle for the position of the closest magnetic pole on the upstream side of the closest position, and φ ₁ is the first electrode of the plate-like member. The angle with respect to the downstream end, φ ₃ is the angle with respect to the contact / proximity position of the plate-shaped member with respect to the developer transport body, and each of the above angles is positive on the upstream side and downstream on the closest position. Negative. 2. The plate-shaped member is a leveling plate or an electrode plate provided with a first electrode to which a voltage can be applied at a downstream end thereof, and its set position is (θ ₁ + θ ₂ ) / The developing device according to claim 1, wherein 2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₂ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ <0. However, the above-mentioned θ ₁ , θ ₂ , φ ₁ , and φ ₃ are θ ₁ , θ ₂ , and
φ ₁ and φ _3, and φ ₂ is the angle between the upstream end of the first electrode on the electrode plate and the closest position to the rotation center of the developer transport body. The upstream side of the contact position is positive and the downstream side is negative. 3. A two-component developer is conveyed to a developing area by a developer conveying body having a magnet body having a plurality of magnetic poles fixed therein, and toner is ejected in an oscillating electric field to form an image forming body in a non-contact manner. In a developing device for developing a formed latent image, a plate-shaped member having two electrodes is disposed upstream of a closest position between the image forming body and the developer transport body, The plate-shaped member has a first electrode in the vicinity of the developer transport body and a second electrode arranged between the first electrode and the image forming body. , (Θ ₁ + θ ₂ ) / 2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ <0. However, the above θ ₁ ,
θ ₂ , φ ₁ , and φ ₃ are the same as θ ₁ , θ ₂ , φ ₁ , and φ _{3 of} claim 1. 4. The set position of the plate-shaped member is set to (θ ₁ + θ ₂ ) / 2> φ ₁ (θ ₁ + θ ₂ ) / 2> φ ₂ (θ ₁ + θ ₂ ) / 2> φ ₃ θ ₁ < _4. The developing device according to claim 3, wherein 0 φ ₂ ≦ φ ₄ is satisfied. However, the _{θ 1, θ 2, φ 1} , φ 2, φ 3 is, theta ₁ of claim 1 and claim _{2, θ 2, φ 1,} φ 2, is identical to phi _3, the phi ₄ is The upstream end of the second electrode on the electrode plate and the closest position are angles formed by the rotation center of the developer transport body, and the upstream side from the closest position is positive and the downstream side is negative. .