JPH08171282A - Developing device and image forming device - Google Patents

Abstract

PURPOSE: To stably prevent the scattering of toner by pushing back the toner scattered from the developing sleeve of a developing device toward the developing sleeve. CONSTITUTION: An electrode 16 for a conductive member is provided to face the developing sleeve 3 in the lower part of the opening part of a developing unit 8 in which the developing sleeve 3 is arranged and a DC voltage having the same polarity as that of the charge of the toner is applied to the electrode 16 between it and the developing sleeve 3 to which a developing bias is applied. Then, an electric field E (V/m) formed by the DC voltage and the DC component of the developing bias and the charge quantity q (C/kg) of the toner scattered from the developing sleeve 3 are set so as to satisfy 6×10<2> (N)<=|qE|<1.1×10<3> (N). Thus, pushing back force can be exerted on the toner scattered from the developing sleeve 3 by the electric field, so that the electric breakdown of the sleeve 3 never occurs.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as an electrophotographic copying machine or an electronic printer and a developing apparatus used therein.

[0002]

2. Description of the Related Art FIG. 8 shows an example of a developing device used in a conventional image forming apparatus. The main developing device 9 includes a developing container 8, a developing sleeve 3 as a developer carrying member, a developer returning member 1 for restricting the developer reservoir 5, and a blade 2 as a developer spike height restricting member. And is arranged to face the photosensitive drum 4, which is an image carrier.

The inside of the developing container 8 is divided into a developing chamber (first chamber) 13 and a stirring chamber (second chamber) 14 by a partition wall 6 extending in the direction perpendicular to the plane of the drawing, and an upper part of the partition wall 6 is formed. Is open. In this example, the developing chamber 13 and the agitating chamber 14 contain a two-component developer containing a non-magnetic toner and a magnetic carrier, and the excess developer in the developing chamber 13 is collected on the agitating chamber 14 side. It

In the developing chamber 13 and the agitating chamber 14, first and second agitating screws 11 and 12 are arranged as developer agitating / conveying means, respectively. The first stirring screw 11 stirs and conveys the developer in the developing chamber 13, and the second stirring screw 12 is controlled from a toner replenishing tank (not shown) under the control of the developer concentration controller. The toner supplied to the upstream side of the stirring screw 12 and the developer already in the stirring chamber 14 are stirred and conveyed,
Make the toner density uniform. The partition wall 6 is provided with a developer passage (not shown) that allows the developing chamber 13 and the stirring chamber 14 to communicate with each other at the front and rear ends in FIG. The developer in the developing chamber 13 whose density has been lowered due to the stirring is mixed with the stirring screws 11 and 12.
It is configured to move from one passage of the partition wall 6 into the stirring chamber 14 by the transporting force of.

The developing chamber 13 of the developing device 9 includes the photosensitive drum 4
Is open at a location facing the surface, and the developing sleeve 3 is rotatably arranged so that the developing sleeve 3 is partially exposed at the opening. The developing sleeve 3 is made of a non-magnetic material, and rotates in the arrow direction in the drawing during the developing operation. Development sleeve 3
A magnet (magnet roller) 10, which is a magnetic field generating means, is fixed inside.

The developer in the developing chamber 13 is supplied to the surface of the developing sleeve 3 by the stirring screw 11 and carried by the magnetic force of the magnet roller 10 on the surface of the developing sleeve 3 in the state of a magnetic brush. The developer carried on the developing sleeve 3 is conveyed to the developing area facing the photosensitive drum 4 by the rotation of the developing sleeve 3. During the transportation, the developer on the developing sleeve 3 is regulated by the developer returning member 1 and the blade 2, and the amount of the developer transported to the developing area is appropriately maintained.

The developer conveyed to the developing area is used for developing the latent image formed on the photosensitive drum 4. Development efficiency,
That is, in order to improve the toner application rate to the latent image,
The developing sleeve 3 is applied with a developing bias voltage, which is obtained by superimposing an AC voltage on a DC voltage, for example, from a power supply 15.

To explain further, the magnet roller 10 in the developing sleeve 3 has a five-pole structure, and the magnetic force of the conveying magnetic pole (pumping pole) S2 causes the stirring screw 1 to move.
The developer supplied by No. 1 is restrained on the surface of the developing sleeve 3, held and carried, and conveyed to the developer reservoir 5 by the rotation of the developing sleeve 3. The amount of the developer is regulated by the developer return member 1, and the carrying magnetic pole (cut pole) N2 having a magnetic flux density higher than a certain level necessary for stable restraint
The developer is sufficiently restrained on the surface of the developing sleeve 3 to form a magnetic brush. Then, the magnetic brush is cut off by the blade 2 to further regulate the amount of the developer to make it an appropriate amount, and the developer is conveyed by the conveying magnetic pole S1 toward the developing area.

Next, in the developing area, a DC voltage and / or an alternating voltage obtained by superimposing an AC voltage on this is applied as a developing bias from the bias power source 15 to the developing sleeve 3 while the magnetic brush of the developer is formed by the developing pole N1. Then, the toner in the magnetic brush is transferred onto the photosensitive drum 4,
Toner is attached to the latent image on the photosensitive drum 4 to develop it, and the latent image is visualized as a toner image.

At this time, in order to obtain a high quality image, it is necessary to stabilize the triboelectric charge amount of the toner. Therefore, when a two-component developer is used, the stirring screw 1
The toner charge amount is stabilized by rubbing the carrier and the toner in the developer reservoirs 1 and 12 and the toner in the developer reservoir 5 is used when the toner of the one-component developer is used. By rubbing against the developing sleeve 3 and the blade 2, the charge amount of the toner is stabilized.

[0011]

By the way, in the developing device, a part of the toner or the developer is scattered with the rotation of the developing sleeve 3, and the obtained image is contaminated with the toner, or the other image is nearby. Toner may adhere to the device and cause various harmful effects.

In order to prevent such toner scattering,
Conventionally, various measures have been taken. For example, it is known that a magnetic plate 23 is arranged near the transport magnetic pole S3 (take-in pole) and a magnetic curtain is applied by a developer to prevent toner scattering. In addition, as disclosed in Japanese Patent Publication No. 4-6949, an electric field curtain which electrically insulates a conductive member adjacent to a photosensitive drum and which is provided at a developer supply port of a developing device to suppress toner scattering is disclosed. There are also those that form.

However, in the magnetic curtain method, when the magnetic flux density of the transport magnetic pole S3 is not sufficiently high, a sufficient magnetic curtain is not formed to prevent toner scattering, and the magnetic pole S3 is closer to the developing pole N1. The effect was small for the scattered toner that occurred.

Further, in the electric field curtain method, since an electric field (electric field) is formed between the conductive member and the photosensitive drum, fog toner adheres to the surface of the photosensitive drum to cause image contamination. Further, there is a drawback that scattered toner adheres to the conductive member and the electric field decreases.

When the toner scattering prevention method of these methods is applied to a developing device for a plurality of colors of a color image forming apparatus, the difference in conditions depending on the kind of the developer is not taken into consideration. The prevention effect was even lower.

It is an object of the present invention to provide a developing device capable of stably preventing the toner from scattering by pushing back the toner scattered from the developing sleeve toward the developing sleeve.

Another object of the present invention is to provide an image forming apparatus capable of preventing toner scattering under the most suitable condition for each developer of each color developing device.

[0018]

The above object is achieved by the developing device and the image forming apparatus according to the present invention. In summary, the present invention is configured such that the developer is carried on the rotating developer carrier in which the magnetic field generating means is immovably installed, and the developing pole is opposed to the image carrier of the magnetic field generating means. Is conveyed to a developing area, and in the developing area, a developing bias in which an alternating voltage is superimposed on a direct voltage is applied to the developer carrier,
In a developing device for developing an electrostatic latent image formed on an image bearing member with a developer, a magnetic pole is formed downstream of the developing area with respect to the rotational direction of the developer bearing member of the magnetic field generating means. Within the range up to the magnetic field, at least one electrode facing the developer carrying member is arranged, and a DC voltage having the same polarity as the charge polarity of the developer is applied to the electrode. The electric field E (V / m) formed by the DC component of the bias and the charge amount q (C / kg) of the toner scattered from within the range up to the magnetic field are 6 × 10 ² (N) ≦ | qE The developing device is characterized by satisfying | <1.1 × 10 ³ (N).

According to another aspect of the present invention, a developer is carried on a rotating developer carrier in which magnetic field generating means is immovably installed, and a developing electrode facing the image carrier of the magnetic field generating means. To a developing area mainly composed of the developer, and in the developing area, under application of a developing bias in which a DC voltage and an AC voltage are superposed on the developer carrying member, an electrostatic charge formed on the image carrying member by the developer is applied. In an image forming apparatus having a plurality of developing devices for developing a latent image, a magnetic field formed by magnetic poles arranged on the downstream side with respect to the rotating direction of the developer carrier of the magnetic field generating means extends from the developing area of each developing device. In the range up to, at least one electrode facing the developer carrying member is provided, and a DC voltage having the same polarity as the charging polarity of the developer is applied to the electrode, and the DC voltage is equal to the developing bias voltage. One potential difference from the DC component Be different from the other developing units in the developing device is an image forming apparatus according to claim.

[0020]

【Example】

Embodiment 1 FIG. 1 is a sectional view showing a developing device according to an embodiment of the present invention. The present invention is characterized in that the electrode 16 is provided in the concealing portion of the developing sleeve 3 of the developing device 9, and a DC voltage is applied between the electrode 16 and the developing sleeve 3 to generate a toner scattering inhibiting force. Other structures of the present invention are basically the same as those of the conventional developing device shown in FIG.
The same members as those in (1) are assigned the same reference numerals and explanations thereof are omitted.

In the developing device 9 of this embodiment, the developer carried on the developing sleeve 3 arranged in the developing chamber 13 of the developing container 8 passes through the blade 2 as the developing sleeve 3 rotates, and the photosensitive drum After coming out of the developing chamber 13 from the upper part of the opening of the developing container 8 facing the developer container 4, the toner is conveyed from the conveying magnetic pole S1 of the magnet roller 10 to the developing pole N1.
Then, the developer develops the latent image formed on the photosensitive drum 4 while passing through the developing area where the developing pole N1 is located, and then, from the lower portion of the opening portion to the inside of the developing chamber 13 by the transport magnetic pole S3. It is captured.

In the process of transporting the developer as described above, during the transport of the developer from the developing pole N1 to the transport magnetic pole S3 and at the time of taking the developer into the transport magnetic pole S3, the developer is mainly used. Toner with low charge is scattered. Furthermore, the developer is quickly scraped off by the repulsive magnetic field composed of the transport magnetic pole S3 and the scooping magnetic pole S2, but it causes scattering.

In view of this, in this embodiment, the concealing portion of the developing sleeve 3, that is, from the point where the developer, which has finished development at the developing pole N1, begins to enter the developing container 8,
As described above, the electrode 16 is provided in a portion until it is collected in No. 3, that is, a portion below the opening of the developing device 8 in this example. The electrode 16 is formed of a flat plate of a conductive member such as a conductive metal, and is provided so that the flat plate of the electrode 16 faces the peripheral surface of the developing sleeve 3. That is, the electrode 16 is connected to the developing sleeve 3
It was provided so as to be on a plane perpendicular to the normal line of the peripheral surface.

In the non-magnetic toner of the two-component developer used in this embodiment, 80 to 90 wt% of the polyester resin is mixed with 5 to 15 wt% of the coloring pigment, and further, the alkyl-substituted salicylic acid as the negative charge control agent is added. A toner containing a metal complex and having an average particle size of 4 to 11 μm was used by externally adding 0.2 to ₂ wt% of titanium oxide (TiO ₂ ). As the external additive, silica or the like can be used in addition to titanium oxide.

As the magnetic carrier of the two-component developer, any ferrite carrier, especially sintered ferrite particles, is used. That is, Zn-based ferrite, Ni-based ferrite, Cu-based ferrite, Mn-Mg-based ferrite, Cu-Zn-based ferrite, Ni-Zn-based ferrite, and the like are used as the core material, and triboelectrification, environmental stability, and durability are used. For the purpose of improving the
A carrier having an average particle size of 30 to 60 μm coated with wt% was used.

The non-magnetic toner of this developer has a charge amount q = -2000 C / kg due to frictional charging with a magnetic carrier.
Charged with negative electricity.

At the time of development, a DC voltage of -300 V and an alternating voltage of 1000 V peak-to-peak voltage were applied as a developing bias to the developing sleeve 3 by the power supply device 15. Further, -1200 V was applied to the electrode 16 from the power supply device 17 as a DC voltage having the same polarity as the toner charging polarity.
As a result, an electric field E is generated between the electrode 16 and the facing portion of the developing sleeve 3 and in the vicinity thereof.

This electric field E is applied to the electrode 16 and the developing sleeve 3.
It is determined from the distance t between them and the potential difference ΔE between them.
In the present embodiment, the distance t = 3 × 10 ⁻³ m, and the potential difference ΔE = −1200V − (− 300V) =
Since it is −900V, the electric field E = −900 / 3 × 10 ⁻³ = −3 × 10 ⁻⁵ (V / m).

The electric field E changes its direction depending on the alternating voltage of the developing bias applied to the developing sleeve 3, but as a whole, a force is exerted on the toner in the direction of directing the scattered toner toward the developing sleeve 3, F = qE = −2 × 10 ⁻³ (C / kg) × (−3 × 10 ⁵ ) (V / m) = 6 × 10 ² (N). The scattered toner is pushed back onto the developing sleeve 3 by the force F received from the electric field, that is, the scattering suppressing force. As a result, toner scattering could be suppressed.

According to experiments by the present inventors, F = 6 × 10
By adding a scattering suppression force F of ² N or more, the charge amount q
Although the toner scattering of −2000 C / kg could be suppressed, if the electric field E becomes too large and exceeds a certain value, a leak due to dielectric breakdown occurs between the developing sleeve 3 and the electrode 16, and the obtained image Has deteriorated.

That is, the voltage applied to the electrode 16 is -20
When the voltage was set to 00V, a sudden change in the voltage applied to the developing sleeve 3 caused a change in the electric field between the photosensitive drum and the photosensitive drum, causing a leak due to dielectric breakdown. At this time, the potential difference ΔE = −2000 − (− 300) = − 1700V, the electric field E = ΔE / t = −1700 / 3 × 10 ⁻³ = −5.7 × 10 ⁵ (V / m), and the scattering suppression force F = QE = -2 * 10 < ^-3 > (C / kg) * (-5.7 * 10 < ⁵ >) (V / m) = 1.1 * 10 < ³ > (N). Therefore, F needs to be less than 1.1 × 10 × 10 ³ N.

Therefore, the scattering suppression force F = qE is generally 6 × 10 ² (N) ≦ | F | = | qE | <1.1 × 10 ³ (N) in consideration of the polarity of the positively chargeable toner. It is effective in the range of N), and in the present invention, F = qE is defined in this range.

Embodiment 2 Another embodiment of the present invention is shown in FIG. In this embodiment, a plurality of electrodes insulated from each other are provided along the rotation direction of the developing sleeve 3 in the portion of the developing container 8 located under the opening in order to generate the toner scattering inhibiting force. It is an example. This example is an example in which two electrodes 16a and 16b that are insulated from each other are provided. Along with this, the electrode 16
Power supplies 17a and 17a for a and 16b are provided.

At this time, in order to guide the scattered toner into the developing container 8 more effectively, the electrode 16a on the outer side of the container 8 is used.
, V1 applied to the inner side electrode 16b, and DC voltage V3 of the developing bias applied to the developing sleeve 3 are | V1 |> | V2 |. Naturally, | V2 |> | V3 |. Then, the electric field generated by the electrode 16a of the electrodes 16a and 16b goes from the electrode 16a toward the inside of the developing container 8 rather than the normal line direction of the developing sleeve 3 as shown in FIG. It can be effectively collected in the container 8.

Example 3 In the above examples, the flat electrode 16 (or the electrode 1) is used.
6a and 16b) are provided so as to face the peripheral surface of the developing sleeve 3. When the flat plate electrode 16 is arranged on such a curved surface as the peripheral surface, the distance between the end of the electrode 16 and the developing sleeve 3 is larger than that at the central portion. The electric lines of force of the electric field generated by applying the voltage are shown in FIG.
As shown in, the electrode 16 bulges outward at the end. For this reason, there is a drawback that the electric field becomes small at the end portion of the electrode 16 and the toner scattering suppressing force becomes weak.

Therefore, in this embodiment, as shown in FIG. 4A, the electrode 16 is formed as a curved plate having the same curvature as the peripheral surface of the developing sleeve 3, and the electrode 16 is formed on the peripheral surface of the developing sleeve 3. They were arranged parallel to each other along the bend. According to this, the distance from the developing sleeve 3 is the same over the entire surface of the electrode 16, and the generated electric field is suppressed from expanding outward at the end of the electrode 16, so that the electric field at the end of the electrode 16 is reduced. To prevent the reduction of the toner scattering inhibiting force. Therefore, according to this embodiment, the toner scattering prevention effect can be further improved.

As described above, in Examples 1 to 3,
An electrode facing the developing sleeve 3 is provided in the portion of the developing container 8 below the opening where the developing sleeve 3 is arranged, and a DC voltage having the same polarity as the charging polarity of the toner is applied to the electrode.
Due to the electric field formed by the DC voltage and the DC component of the developing bias, 6 × 1 is applied to the toner having the charge amount q (C / kg).
0 ² (N) ≦ | F | = | qE | <1.1 × 10 ³ (N)
Since such a scattering suppressing force F is generated between the electrode and the developing sleeve 3, it is possible to push back the scattered toner toward the developing sleeve 3 and stably prevent the toner from scattering.

Embodiment 4 FIG. 5 is a schematic block diagram showing an image forming apparatus according to still another embodiment of the present invention. In this embodiment, the case of a 4-drum type color electrophotographic apparatus is shown, but the invention is not limited to this.

As shown in FIG. 5, the image forming apparatus has four image forming sections arranged in series, and the image forming sections A, B, C and D have photosensitive drums 4a as image bearing members, respectively.
4b, 4c and 4d. This photosensitive drum 4
Around each of a, 4b, 4c and 4d, primary chargers 22a, 22b, 22c and 22d for uniformly charging their respective surfaces are provided, and the uniformly charged photosensitive drum 4 is provided.
Each of a, 4b, 4c and 4d is exposed with image information 23a, 23 from a light emitting element such as a laser.
b, 23c and 23d, the photosensitive drum 4a,
An electrostatic latent image of each color is formed on the surfaces of 4b, 4c and 4d. A developing device for developing those latent images with a developer of a corresponding color, for example, a yellow developing device 9a, a magenta developing device 9
b, a cyan developing device 9c and a black developing device 9d are provided, and by this development, toner images of yellow, magenta, cyan and black colors are formed on the photosensitive drums 4a, 4b, 4c and 4d.

The toner images of the respective colors obtained in this way are transferred onto the transfer paper 26 conveyed by the transfer conveyer belt 25 in order by the transfer chargers 27a, 27b, 27c and 27d. The transfer paper 26 that has been transferred is conveyed to a fixing device 28, where the toner images of four colors are mixed and fixed by fixing, and a full-color permanent image is formed into a print image. After the transfer of the toner image, the photosensitive drums 4a, 4b, 4c and 4d are
The cleaning device 29 removes the transfer residual toner on the surface.
a, 29b, 29c and 29d.

In this image forming apparatus, the developing device 9 shown in FIG. 1 shown in the first embodiment is added to each of the developing devices 9a, 9b, 9c and 9d for yellow, magenta, cyan and black. Using. That is, each developing device 9d
9d, in the lower part of the opening of the developing container 8 of FIG.
An electrode 16 for preventing toner scattering is arranged. Each toner of the developer of each color of the developing devices 9d to 9d has a negative charging property. To prevent the toner from scattering, a DC voltage of about -500V to -1000V having the same polarity as the charging polarity of the toner is applied to the electrodes 16 of the developing devices 9d to 9d by the power supply devices 17 and 17 '. Those developing devices 9a to 9d
To the developing sleeve of FIG. 9, that is, the developing sleeve 3 of FIG. 9, a DC voltage of −300 V and an alternating voltage of peak-to-peak voltage of 1000 V were applied as a developing bias by the power supply device 15 common to each color.

In this embodiment, the toner of each color has a polyester resin as a main component, and yellow, magenta, cyan and black pigments are mixed with this to obtain a negatively chargeable toner of each color of yellow, magenta, cyan and black. Was prepared.

Due to the difference in the pigment, the triboelectric charging characteristics between the toners of the respective colors are changed. In particular, the black toner using carbon as a pigment has a smaller average triboelectric charge amount than the toners of the other three colors. That is, in the black toner, the proportion of the toner having a small charge amount and easily scattered increases. Therefore, when the DC voltage applied to the electrode 16 is the minimum voltage required to suppress the scattering of the black toner, the applied voltage is already sufficient for the toners of the other three colors to prevent the scattering. Voltage.

Generally, the DC voltage applied to the electrode 16 is
The larger the potential difference from the direct current component of the developing bias applied to the developing sleeve 3, the higher the effect of suppressing toner scattering. However, if the electric field between the electrode 16 and the developing sleeve 3 is too strong,
In the meantime, dielectric breakdown occurs, which not only adversely affects the image but also may cause an accident such as a fire. For this reason, the voltage applied to the electrode 16 must be large enough to prevent toner scattering and yet large enough not to cause dielectric breakdown.

In consideration of the above points, the present embodiment is specifically as follows. That is, as shown in FIG. 5, the above-mentioned power supply device 17 'is provided exclusively for the electrode 16 of the black developing device 9d, and the power supply device 17 is provided for the developing devices 9 of the other three colors.
a to 9c are commonly provided. A relatively large DC voltage of -900V is applied to the electrode 16 of the black developing device 9d, which has a small amount of electrification and an increased proportion of toner that easily scatters, in order to enhance the scattering prevention effect in a range where dielectric breakdown does not occur. Is applied by the power supply device 17 ′, and a DC voltage of −700 V, which is smaller than this, is applied by the power supply device 17 to each electrode 16 of the developing devices 9 a to 9 d in which the toner is less likely to scatter than the black toner.

As described above, in the present embodiment, the voltage for preventing toner scattering is appropriately applied to the electrodes 16 of the developing devices 9a to 9d for the respective colors according to the characteristics of the respective developing agents. Toner scattering can be suppressed well, and dielectric breakdown does not occur. Therefore, a high quality color image can be obtained.

Embodiment 5 FIG. 6 is a constitutional view showing still another embodiment of the present invention. The image forming apparatus according to the present exemplary embodiment has four image forming units A, B, C, and D as in the fourth exemplary embodiment. In this embodiment, a black pigment prepared by mixing yellow, magenta, and cyan pigments with the black toner of the developer used in the black developing device 4d of the image forming section D is used.

In this embodiment, as described above, yellow,
From the relationship of mixing magenta and cyan pigments to prepare a black pigment, the yellow toner used for this has a characteristic that density can be easily obtained as compared with toners of other three colors. Considering this, the toner concentration in the developer is set to 4.5% for yellow and 5% for the other three colors.

As described above, in this embodiment, since the yellow toner concentration is lowered, it is advantageous to reduce the scattering of the yellow toner. Further, since the amount of yellow toner scattered is smaller than that of the other three colors, the yellow developing device 9
The DC voltage applied to the electrode 16a of the
It can be lower than in the case of 9d.

That is, according to this embodiment, if the toner has the same triboelectrification polarity, the voltage applied to the electrode 16 can be lowered by lowering the toner concentration. As a result, the power supply cost can be reduced, the dielectric breakdown latitude can be expanded, toner scattering can be suppressed, and dielectric breakdown can be prevented. The electrodes 16 of the developing devices 9a to 9d are each provided with a dedicated power supply device 17.

In this embodiment, specifically, a DC voltage of -600C was applied to the electrode 16 of the yellow developing device 9a, and a DC voltage of -700V was applied to the developing devices 9b to 9d of the other colors. The developing bias applied to the developing devices 9a to 9d was the same as that in the fourth embodiment. By this, the developing device 9
The above effects could be achieved in any of a to 9d.

Example 6 This example is an example in which the yellow toner concentration is made lower than that in the case of multiple colors and carbon black is used as the black pigment, and corresponds to an extension of Examples 4 and 5.
In this embodiment, the DC voltage applied to the electrode 16 of each developing device is -600V for the yellow developing device 9a, -700V for the magenta developing device 9b and cyan developing device 9c, and -900V for the black developing device 9d.

As a result, toner scattering can be suppressed in each of the developing devices 9a to 9d, and dielectric breakdown does not occur.

Embodiment 7 In this embodiment, as shown in FIG. 7, the developing devices 9a to 9d are used.
Is characterized in that two electrodes 16a and 16b are provided. That is, the developing device 9 shown in FIG. 2 of the second embodiment is used for each of the developing devices 9a to 9d. The components of the toner of each color, the toner concentration in the developer, the voltage applied to the developing sleeve, etc. were in accordance with Example 4.

A common power supply unit 17a is used for each electrode 16a of the yellow, magenta, and cyan developing units 9a, 9b, and 9c, and a common power supply unit 1 is used for each electrode 16b.
7b is provided. Electrodes 16a and 16 of the black developing device 9d
Power supply devices 17a 'and 17b' for exclusive use are respectively provided in b.

The potential difference between the electrodes 16a and 16b of the developing devices 9a to 9d is set to about 200 V, and the potential of the electrode 16a is larger than the potential of the electrode 16b with respect to the DC component of the developing bias. And these electrodes 16a,
By applying a DC voltage to 16b, as shown in FIG. 3, the direction of the electric field force (scattering inhibiting force) applied to the scattered toner can be bent to the direction taken into the developing container 8, which is more effective. In addition, it is possible to prevent toner from scattering.

Therefore, the electromotive force of the power supply device is changed to the power supply device 1
7a is 800V, power supply 17b is 600V, power supply 17a 'is 1000V, and power supply 17b' is 800V. Then, -80 is applied to the electrodes 16a of the developing devices 9a to 9c.
0 V, a DC voltage of -600 V is applied to the electrode 16b, and the developing device 9
-1000V to the electrode 16a 'of d and -8 to the electrode 16b'
A DC voltage of 00V was applied. As a result, it is possible to effectively and safely prevent the toner scattering of the developing devices 9a to 9d of each color in a form corresponding to the characteristics of the developer.

As described above, according to Examples 4 to 7, it is possible to effectively and safely prevent the toner scattering of the developer of each color developing device under the most appropriate conditions for each color developer. it can.

[0059]

As described above, in the developing device of the present invention, the electrode of the conductive member is provided on the peripheral surface of the developing sleeve at the concealing portion of the developing sleeve, that is, the lower portion of the opening of the developing device where the developing sleeve is arranged. The DC voltage of the same polarity as the charging polarity of the toner is applied to the electrode between the developing sleeve and the developing sleeve by the electric field generated by the DC voltage of the developing bias and the developer bias of the developing sleeve. Since a force is applied to the scattered toner to push it back toward the developing sleeve, it is possible to stably prevent the toner from scattering.

Further, in the image forming apparatus of the present invention, since the above-mentioned developing device is used for the developing device of each color, it is possible to effectively and safely prevent toner scattering under the most suitable conditions for each developer. it can.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram showing a developing device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram showing another embodiment of the present invention.

FIG. 3 is an explanatory diagram showing an electric field between an electrode and a developing sleeve in the embodiment of FIG.

4 is an explanatory view showing an electric field between an electrode and a developing sleeve in still another embodiment of the present invention and the embodiment of FIG. 1. FIG.

FIG. 5 is a schematic configuration diagram showing an image forming apparatus according to still another embodiment of the present invention.

FIG. 6 is a schematic configuration diagram showing still another embodiment of the present invention.

FIG. 7 is a schematic configuration diagram showing still another embodiment of the present invention.

FIG. 8 is a schematic configuration diagram showing a conventional developing device.

[Explanation of symbols]

 3 Development Sleeve 4 Photosensitive Drum 8 Development Container 9 Development Device 10 Magnet Roller 16 Electrode 17 Power Supply Device

Claims (3)

[Claims] 1. A developer pole is supported on a rotating developer bearing body in which magnetic field generating means is fixedly installed, and a developing pole facing the image bearing body of the magnetic field generating means is formed as a center. Development in which the electrostatic latent image formed on the image bearing member is developed by the developer while being conveyed to the developing region and applying a developing bias in which the alternating voltage is superimposed on the DC voltage to the developer bearing member in the developing region. In the apparatus, within a range from the developing area to a magnetic field formed by a magnetic pole arranged on the downstream side in the rotation direction of the developer carrier of the magnetic field generating means,
An electric field formed by disposing at least one electrode facing the developer carrying member, applying a DC voltage having the same polarity as the charging polarity of the developer to the electrode, and forming a DC voltage of the DC voltage and a DC component of the developing bias. E (V / m), and the amount of charge q (C / kg) of the toner scattered from within the range up to the magnetic field
The developing device is characterized by satisfying the following condition: 6 × 10 ² (N) ≦ | qE | <1.1 × 10 ³ (N). 2. A developing electrode is carried on a rotating developer carrier in which magnetic field generating means is immovably installed, and a developing pole facing the image carrier of the magnetic field generating means is formed as a center. Development in which the electrostatic latent image formed on the image bearing member is developed by the developer while being conveyed to the developing region and applying a developing bias in which the alternating voltage is superimposed on the DC voltage to the developer bearing member in the developing region. In an image forming apparatus having a plurality of developing devices, within the range from the developing area of each developing device to the magnetic field formed by the magnetic poles arranged on the downstream side with respect to the rotating direction of the developer carrier of the magnetic field generating means, At least one electrode facing the developer carrying member is disposed, and a DC voltage having the same polarity as the charging polarity of the developer is applied to the electrode, and the DC voltage has a potential difference from the DC component of the developing bias. In one developer An image forming apparatus, which is different from a developing device. 3. The image forming apparatus according to claim 2, wherein a magnetic pole having the same pole as the magnetic pole is arranged further downstream of the magnetic pole arranged on the downstream side.