JPH06332320A - Developing device - Google Patents

Abstract

PURPOSE:To provide a developing device capable of reducing degradation due to the use of a developer, sufficiently electrifying developer and obtaining a high quality image. CONSTITUTION:In a magnet roller 13 in a developing sleeve 3, the densities of the magnetic fluxes of magnetic poles for carrying S2 and n2 corresponding to a carrying area from a position where the developer is supplied onto the developing sleeve 3 and carried to a bristle cutting position, are made low into 10-49% of that of a developing pole N1 and an auxiliary electrifying screw 18 is provided. Therefore, the densities of the magnetic fluxes of the magnetic poles S2 and N2 are made low so that the density on the retaining part 5 of the developer magnetically restricted on the sleeve 3 is set low to reduce compressing force, the degradation of the developer is lessened and moreover, the deficient electrification of the developer because of the densities are made low is auxiliary electrified, so that the developer is sufficiently electrified.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus such as a copying machine or a printer such as an electrophotographic system or an electrostatic recording system which visualizes a latent image formed on an image carrier by attaching a developer thereto. The present invention relates to a developing device used.

[0002]

2. Description of the Related Art In an image forming apparatus using an electrophotographic system, a latent image formed on an image carrier is developed with a developer and visualized as a toner image. FIG. 7 shows an example of a conventional developing device used for such development.

As shown in FIG. 7, the developing device 9 includes a developing container 9a containing a developer, and a developing sleeve 3 at the opening of the container 9a facing the photosensitive drum 4. The partition wall 6 is provided at a substantially bottom portion of the developing container 9a to form the developing chamber 1
6 and the stirring chamber 17, and in the developing chamber 16 and the stirring chamber 17, conveying screws 11 and 12 for stirring and conveying the developer are installed.

The developer contained in the developing container 9a is supplied to the developing sleeve 3 by the conveying screws 11 and 12, and the surface of the developing sleeve 3 is in the state of a magnetic brush due to the magnetic force of the magnet roller 13 installed therein. Is carried by. Then, as the developing sleeve 3 rotates, the developing sleeve 3 is conveyed to a developing area facing the photosensitive drum 4. On the way of transportation,
The amount of developer on the developing sleeve 3 is regulated by the developer returning member 1 in the upper portion of the developing container 9a, and the magnetic brush is further trimmed by the spike-cutting member (spike height regulating member) 2 and conveyed to the developing area. The amount of developer is properly maintained.

More specifically, the magnet roller 13 of the conventional developing device has a five-pole structure, and the developing chamber 1
The developer agitated by the carrying screw 11 of 6 is carried by being restrained on the surface of the developing sleeve 3 while forming a magnetic brush by the magnetic force of the scooping pole S2, and carried to the developer reservoir 5 by the rotation of the developing sleeve 3. To be done. The amount of the developer conveyed to the reservoir 5 is first regulated by the return member 1 and then sufficiently increased by the cut pole N2 having a magnetic flux density of a certain level or more to obtain a stable restraining force. Restrain,
The magnetic brush is conveyed in a state where it is formed, the magnetic brush is cut by the brush cutting member 2, and the amount of developer is regulated to an appropriate amount.
Then, it is transported to the developing area by the transport pole S1.

In the developing area, the magnet roller 1
By the magnetic force of the developing pole N1 of No. 3 and the developing bias in which the direct current and / or the alternating electric field applied to the developing sleeve 3 from the bias power source 15 provided on the image forming apparatus main body are superimposed, the developer is a two-component developer. In this case, the toner from the developer on the developing sleeve 3 is transferred to the electrostatic latent image on the photosensitive drum 4, and when the developer is a one-component developer, the toner that is the one-component developer remains as it is. 4 is transferred to the electrostatic latent image, and the latent image is visualized as a toner image.

In forming a high quality image, it is essential to stabilize the charge amount of the toner. Therefore, in the two-component developer, the packing density of the developer is increased in the developer reservoir portion 5 so that the toner and the carrier rub against each other, and in the one-component developer, the toner is developed in the developer reservoir portion 5 by the developing sleeve. By rubbing with 3 and the brush cutting member 2, the amount of charge of the toner is stabilized.

[0008]

As described above, in the conventional developing device, the charge is imparted to the developer only by the developer reservoir 5.

As a countermeasure against the deterioration due to the use of the developer, the absolute value of the magnetic flux density of the scooping pole S2 and the cut pole N2 of the magnet roller 13 may be lowered to lower the magnetic binding force in the developer pool 5. In such a case, the charge imparting ability to the developer in the reservoir portion 5 is weakened, and the developer cannot be sufficiently charged, which may cause fog or scattering of the developer particularly in a high temperature and high humidity environment. There were many

An object of the present invention is to provide a developing device which is less deteriorated by the use of the developer and which is capable of giving sufficient charge to the developer and capable of obtaining a high quality image. Is.

Another object of the present invention is to provide a developing device which is less likely to deteriorate due to the use of a developer, can prevent image deterioration for a long period of time, and can obtain a uniform image without sleeve ghost.

Still another object of the present invention is to provide a developing device capable of maintaining a high quality image with less deterioration due to the use of a developer, a stable output characteristic of a toner concentration sensor. is there.

[0013]

The above object can be achieved by the developing device according to the present invention. In summary, the present invention relates to a rotatable developer carrier that carries a developer and conveys the developer to a developing area facing the image carrier, and a stirring / conveying mechanism that agitates and supplies the developer to the developer carrier. Means, a magnet non-rotatably arranged in the developer carrying member, a regulating mechanism for applying a charge to the developer carried on the developer carrying member and for regulating the carried amount, and the developer. In a developing device having a spike-cutting member for cutting the spikes of the magnetic brush of the developer carried on a carrier to a predetermined height, a carrying position of the magnet on the developer carrier. The carrying magnetic pole corresponding to the carrying area from the brush cutting position has a magnetic flux density of 10 to 49% of that of the developing pole of the magnet corresponding to the developing area, and is provided with the regulating mechanism in the developing container. another,
In the developing device, a charging giving auxiliary means for giving a charging charge to the developer carried on the developer carrying body is provided.

According to the present invention, the charge imparting assisting means can be a developer stirring / conveying screw provided separately from the stirring / conveying means, and can be brought into contact with the developer carrying member. Elastic blades.

According to another aspect of the present invention, a rotatable developer carrier that carries a two-component developer and conveys the developer to a developing area facing the image carrier, and is non-rotatably disposed in the developer carrier. Magnet, a regulating mechanism for imparting a charging charge to the developer carried on the developer carrying body and regulating the carrying amount thereof, and a magnetic brush of the developer carried on the developer carrying body. In a developing device equipped with a spike-cutting member that cuts the spikes into a predetermined spike height, for transport corresponding to a transport region from the carrying position of the developer of the magnet on the developer carrier to the spike-cutting position. The magnetic pole has a magnetic flux density of 10 to 49% of that of the developing pole corresponding to the developing area of the magnet, and a coating film containing crystalline graphite is formed on the surface of the developer carrier. It is a developing device.

Still another aspect of the present invention is a detection means for detecting the toner concentration of a two-component developer, and a rotatable developer carrier for carrying the developer and transporting the developer to a developing area facing the image carrier. Body, a magnet non-rotatably arranged in the developer carrying body, a regulating mechanism for applying a charge to the developer carried on the developer carrying body and for regulating the carried amount, and the developing unit. In a developing device including a spike-cutting member that cuts the spikes of the magnetic brush of the developer carried on the developer carrier to a predetermined spike height, carrying the developer of the magnet on the developer carrier. The carrying magnetic pole corresponding to the carrying area from the position to the spike cutting position has a magnetic flux density of 10 to 49% of that of the developing pole of the magnet corresponding to the developing area, and the detecting means has a magnetic flux density of the carrying pole. Developing device characterized by being located in the vicinity A.

[0017]

【Example】

First Embodiment FIG. 1 is a schematic configuration diagram showing an image forming apparatus including a developing device according to an embodiment of the present invention. This image forming apparatus is
4 illustrates a four-station laser beam printer which is an example of a laser beam printer having a plurality of image forming stations.

In this four-station printer, image forming stations having image forming means around the photosensitive drum are provided corresponding to four colors of magenta, cyan, yellow, and black, and at each station. The formed toner image on the photosensitive drum is transferred onto a transfer material that is conveyed by a transfer belt that moves in opposition to the photosensitive drum.

That is, the photosensitive drums 4M, 4C, 4Y, and 4K are arranged in the magenta, cyan, yellow, and black image forming stations Pm, Pc, Py, and Pk, respectively, and rotated in the arrow direction (clockwise direction) in the figure. It Around the photosensitive drums 4M, 4C, 4Y and 4K, corona chargers 46M, 46C, 46Y and 46K, scanning optical devices 47M, 47C, 47Y and 47K as optical scanning means, and developing devices 9M, 9C and 9Y. , 9K, cleaning device 48
M, 48C, 48Y and 48K are arranged.

Further, the transfer portion which constitutes a part of the image forming means includes a transfer belt 49a which is commonly used by the image forming stations Pm to Pk and transfer chargers 49M, 49C, 49Y and 49K for the photosensitive drums. The full-color image formation has a transfer material P formed on the transfer belt 49a.
This is realized by sequentially transferring the toner images formed on the photosensitive drums 4M to 4K on top.

The transfer material P is supplied from the paper feed cassette 50 onto the transfer belt 49a, separated from the transfer belt 49a when the transfer process is completed, and passed through the fixing device 51 and the tray 52.
Is discharged to.

The scanning optical devices 47M, 47C, 47
Reference numerals Y and 47K denote a laser light source (not shown), a rotating polygon mirror for scanning the laser light from the laser light source, an fθ lens for condensing the scanning beam on the generatrix of the surface of the photosensitive drum, and a reflecting mirror for deflecting the light beam. And a beam detector for detecting a specific position of the scanning beam.

Developing device 9 installed in the image forming apparatus
M to 9K are configured like the developing device shown in FIG. In the present embodiment, the developing device 9 includes a developing container 9a containing a two-component developer containing a non-magnetic toner and a magnetic carrier, and a developing sleeve 3 as a developer carrying member and a developer reservoir 5. Return member 1 and developing sleeve 3
It has a brush cutting member 2 for controlling the brush of the developer carried thereon. A substantially lower half of the developing container 9a is divided into a developing chamber (first chamber) 16 and a stirring chamber (second chamber) 17 by a partition wall 6 extending in a direction perpendicular to the plane of the drawing. The above developer is contained in the developing chamber 16 and the stirring chamber 17. Partition 6
The upper portion of the developing chamber is open, and the developer that has become excessive in the developing chamber 16 is collected by the stirring chamber 17 side.

The developing chamber 16 and the stirring chamber 17 are provided with first and second conveying screws 11 and 12, respectively, as developer stirring / conveying means. The first conveying screw 11 conveys the developer in the developing chamber 16 while agitating it, and the second conveying screw 12 controls the toner concentration from the toner replenishing layer (not shown) under the control of the developer concentration controller.
The toner supplied to the upstream side of the second conveying screw 12 in 7 and the developer already in the stirring chamber 17 are conveyed while being stirred, and the toner concentration of the developer is made uniform.

A developing chamber 7 and a stirring chamber 8 are provided at both ends of the partition wall 6.
A developer passage (not shown) is formed to make the developer and the developer communicate with each other. Thus, the toner is moved into the stirring chamber 17 through one of the developer passages.

According to the present invention, the developer reservoir 5 is provided with a screw 18, which is a stirring / conveying means, as a means for assisting in imparting a charge to the developer. Reference numeral 18 stirs the developer in the developer reservoir 5 to assist the charging of the developer in order to compensate for the insufficient charge of the developer conveyed to the developing area via the regulation blade 2.

The developing chamber 16 of the developing device 9 has an opening at a position corresponding to the developing area facing the photosensitive drum 4, and the developing sleeve 3 has the opening in the opening.
It is rotatably arranged so as to be partially exposed in the direction. The developing sleeve 3 is made of a non-magnetic material, and a magnet roller 13 which is a magnetic field generating means is installed inside the developing sleeve 3 so as not to rotate. In this embodiment, the magnet roller 13 includes a developing pole N1 and magnetic poles S1 and N2 that convey the developer.
It has S2 and S3.

The developing sleeve 3 rotates in the direction of the arrow shown in the drawing at the time of development, and carries the two-component developer whose developer amount (layer thickness) is regulated by the brush cutting of the magnetic brush by the above-mentioned brush cutting member 2. It is transported to the development area facing the drum 4,
A developer is supplied to the latent image formed on the photosensitive drum 4 to develop the latent image. In order to improve the developing efficiency, that is, the toner application rate to the latent image, the developing sleeve 3 has a power supply 15
Is applied with a developing bias voltage in which a DC voltage and an AC voltage are superposed.

The bristle-cutting member 2 is made of a non-magnetic material such as aluminum and has a developing sleeve 3 rather than the photosensitive drum 4.
Is disposed on the upstream side in the rotation direction of. This ear cutting member 2
Both the non-magnetic toner of the developer and the magnetic carrier pass between the tip of the developing roller and the developing sleeve 3 and are sent to the developing area. By adjusting the gap between the brush cutting member 2 and the surface of the developing sleeve 3, the brush cutting amount of the developer magnetic brush carried on the developing sleeve 3 is regulated, and the amount of developer conveyed to the developing area is adjusted. To be done.

The first conveying screw 11 is arranged substantially parallel to the bottom of the developing chamber 16 along the axial direction of the developing sleeve 3 (developing width direction). It has a screw structure in which the blade member is provided in a spiral shape, and rotates to convey the developer in the developing chamber 17 in one direction along the axial direction of the developing sleeve 3 at the bottom of the developing chamber 16. Similarly to the first conveying screw 11, the second conveying screw 12 has a screw structure in which a blade member is provided in a spiral shape around the rotating shaft in a direction opposite to that of the first screw 11, and inside the stirring chamber 17. Is arranged substantially parallel to the first screw 11 at the bottom of the first screw 11 and rotates in the same direction as the first screw 11 to convey the lower developer in the stirring chamber 17 in the opposite direction to the first screw 11. Thus, the developer is circulated between the developing chamber 16 and the stirring chamber 17 through the openings at both ends of the partition wall 6 by the conveyance by the rotation of the first and second screws 11 and 12.

Further, the screw 18 as an auxiliary charging means
Has a structure similar to that of the first screw 11, and is composed of a screw in which a blade member is spirally provided around the rotating shaft in the same direction as that of the first screw 11, and the developer reservoir 5 Is arranged in parallel with the developing sleeve 3 and rotates in the same direction as the first screw 11 to collect in the reservoir portion 5.
The developer is conveyed in the same direction as the first screw 11.
Thus, the rotation of the screw 18 further charges the developer and assists the charging of the developer, thereby eliminating the insufficient charge of the developer.

After being carried on the developing sleeve 3 and conveyed to the developing area and subjected to the developing operation, the developer remaining undeveloped in the developing area remains in the developing chamber 16 as the developing sleeve 3 rotates. It is returned to the inside, is scraped off from the developing sleeve 3 by the repelling magnetic poles S3 and S2 of the magnet roller 13, and is collected in the developing chamber 16.

On the other hand, the developer conveyed by the rotation of the first screw 11 is pumped up onto the developing sleeve 3 by the one magnetic pole S2 of the repulsion magnetic pole in an amount of the developer proportional to the absolute value of the magnetic flux density. The amount of the developer drawn up is determined by the magnetic restraining force acting in the central direction of the developing sleeve 3 formed by the magnetic field from the magnetic pole S2 and the conveying force acting in the rotating direction of the developing sleeve 3.

At this time, the developer on the surface of the developing sleeve of the developing layer on the developing sleeve 3 or a developer in the lowermost layer near the surface of the developing sleeve 3 has a strong compressive force due to the magnetic binding force from the surface of the developing sleeve 3 and the developer below the uppermost layer. Receive. Further, when an image is formed for a long period of time under the influence of a rubbing force generated by a conveying force acting in the rotation direction of the developing sleeve 3, the image quality is deteriorated due to the deterioration of the developer.

Therefore, in the present invention, in order to prevent this, the magnetic flux density of the magnetic pole S2 is optimized. Magnetic pole S2
The magnetic flux density is optimized by securing the minimum required magnetic binding force for pumping up the developer to the magnetic pole S2 while reducing the magnetic binding force of the magnetic pole S2 in order to suppress the deterioration of the developer. Is determined from.

The developer drawn up by the magnetic pole S2 then acts on the developing sleeve 3 formed by the magnetic field from the next magnetic pole N2, as in the case of the magnetic pole S2, and the developer return member. The magnetic binding force determined according to the amount of the developer regulated by 1 and the conveying force acting in the rotation direction of the developing sleeve 3 conveys the toner to the location of the bristle cutting member 2.

At this time, as in the case of the magnetic pole S2, when the developer forms an image for a long period of time due to the influence of the compressive force between the developers and the rubbing force between the developer and the surface of the developing sleeve 3, Since the image quality is deteriorated due to the deterioration of the developer, the magnetic flux density of the magnetic pole N2 is optimized in the present invention in order to prevent this.

That is, since the above magnetic flux density is a factor relating to the magnetic restraining force of the developer by the magnetic pole N2, in the present invention, as in the conventional developing device shown in FIG. 7, as shown in FIG. A magnetic probe sensor 7 including a Hall element is provided at a position where the magnetic pole N2 and the return member 1 are arranged to detect the compression state of the developer in the developer reservoir 5 and the magnetic flux density from the magnetic pole N2. As a result, the magnetic restraining force in the reservoir 5 is optimized.

The magnetic probe sensor 7 has a developer pool 5
The magnetic flux density from the magnetic pole N2 that restrains the developer is detected. According to such a magnetic probe sensor 7, a magnetic roller 13 is provided between the developing sleeve 3 and the sensor 7. When the packing density of the existing developer layer is constant, a constant value is output, and when the density of the developer layer changes, the output changes according to the change.

Therefore, if the output change of the magnetic probe sensor 7 is large, the packing density change of the developer layer in the reservoir 5 formed by the magnetic pole N2 and the return member 1 is large, and the change of the compression force is large, so that the developer is deteriorated. Is big. On the contrary, if the output change of the sensor 7 is small and the packing density change of the developer layer is small, the change of the compression force is small and the developer deterioration is small.

In this embodiment, the magnet roller 13
As the magnetic poles of nine types (magnetic pole types a to i) having different magnetic flux densities of the developing pole N1, the transport magnetic poles N2 and S2, the developing roller N1 is used in the developing device 9 of FIG. After being incorporated and developed, an A4 size image having an image density of 10% duty (10% duty) was formed up to 100,000 sheets.

Then, the transportability of the developer in the developing device 9 at that time, the occurrence state of image deterioration, and the change of the magnetic flux density by the magnetic probe sensor 7 were examined. The detection by the sensor 7 is a change in the magnetic flux density of the developer on the surface of the return member 1 at the closest distance 3.0 mm between the developing sleeve 3 and the return member 1. The measurement results are shown in Table 1.

The image deterioration was evaluated by the roughness of the highlight portion of the image, the maximum density, the stability of the density, and the like.

[0044]

[Table 1]

The non-magnetic toner used in the present embodiment has a polyester resin of 80 to 90 wt% and a coloring pigment of 5 to 15 w.
t%, and a toner having an average particle size of 5 to 11 μm in which a metal complex of an alkyl-substituted salicylic acid is dispersed as a negative charge control agent is used, and titanium oxide (TiO ₂ ) is added in an amount of 0.2 to ₂ w.
t% was used as an external additive. Other than the above, silica may be used as the external additive of the toner.

As the magnetic carrier, any ferrite carrier can be used, but sintered ferrite particles can be preferably used. That is, as the core material, Zn-based ferrite, N
i-type ferrite, Cu-type ferrite, Mn-Zn-type ferrite, Mn-Mg-type ferrite, Cu-Zn-type ferrite, Ni-Zn-type ferrite, etc. are used for the purpose of improving triboelectricity, environmental stability and durability. As coated with 0.5 to 2 wt% of acrylic resin, the average particle size is 30
A carrier of -60 μm was used. Other than the above, polyester resin, fluororesin, silicone resin and the like can be appropriately selected and used as the carrier coating material.

From the above results, the developing sleeve 3 for the developer is
It is effective for image deterioration that the magnetic flux density of the transport magnetic poles N2 and S2 corresponding to the transport region from the supply position to the cutting position to the carrying position is 10 to 49% of the magnetic flux density of the developing pole N1. there were. More specifically, it has been found that it is better if the change in the magnetic flux density in the developer returning member 1 is 8 gauss or less.

In this way, the magnetic flux density of the transport magnetic poles N2 and S2 is set as low as 10 to 49% of that of the developing pole N1 (see Table 1 in the past).
50 to 100%) as in the magnetic pole type a) is effective against image deterioration, but on the other hand, since the magnetic binding force in the developer reservoir 5 is low, the compressive force between the developers is reduced. This weakens and causes a problem that the amount of charge imparted to the developer becomes insufficient. FIG. 3 shows the result of measuring the phenomenon in which the amount of charge imparted is insufficient.

FIG. 3 shows the result of examining the rise of the triboelectric charge amount from the state where the developer was left standing by idling the developing device. The horizontal axis of the figure is the idle rotation time (second),
The vertical axis represents the average triboelectric charge amount Q / M (μC / g) of the developer on the developing sleeve 3.

When the magnetic flux densities of the transport magnetic poles N2 and S2 are not lowered as in the conventional case, the triboelectric charge amount of the developer rises as shown by a curve a. On the contrary, when the magnetic flux densities of the transport magnetic poles N2 and S2 are lowered, the rise of the triboelectric charge amount becomes like the curve b, and the rise of the triboelectric charge amount becomes weaker than in the conventional case. On the other hand, in the present invention, since the screw 18 is provided to assist the charging of the developer, the rise of the triboelectric charge amount of the developer is as shown by the dotted curve c, which is similar to the conventional rise. Thus, the problem of insufficient charge application due to the lower magnetic flux density of the transport magnetic poles S2 and N2 was solved.

As described above, according to the present invention, it is possible to obtain a high-quality image in which the deterioration of the developer is small and the developer can be favorably charged, and there is no adverse effect such as fogging or scattering due to insufficient charge of the developer. You can

Embodiment 2 FIG. 4 is a sectional view showing another embodiment of the developing device of the invention. In the developing device of Embodiment 1 shown in FIG. 2, the screw 18 is installed in the developer reservoir 5 as a charge imparting assisting means, but in the present embodiment, as shown in FIG. 3 is characterized in that an elastic blade 19 which is in contact with 3 is provided, and this is used as a charging giving auxiliary means.

In this embodiment, the elastic blade and 19 are made of urethane rubber whose surface is coated with nylon. According to the charge imparting assisting means using the elastic blade 19 as described above, the average triboelectric charge amount of the developer can be changed by making the surface material of the elastic blade 19 different in the charging series. There is an advantage that the average triboelectric charge amount of the agent can be easily controlled.

Embodiment 3 FIG. 5 is a sectional view showing still another embodiment of the developing device of the present invention. In this embodiment, instead of installing the first conveying screw for stirring and conveying the developer in the developing chamber 16,
A kneading type screw 20 as shown in FIG. 6 is installed, and the kneading type screw 20 stirs the developer.
The feature is that it is carried and assisted in its charging.

The above-mentioned kneading type screw 20 includes two screws 20 which overlap each other at a portion A along the axial direction.
a and the two screws 20a are both shown in FIG.
Since they rotate in the direction of the arrow and move toward each other in the overlapping portion A in the counter direction, the developer is rubbed well in this overlapping portion A and charging is imparted.

Therefore, according to the kneading type screw 20 as described above, the charging of the developer can be favorably assisted, and the stirring efficiency of the developer is increased, so that the developer is more uniformly charged. Therefore, the image quality of the image obtained by development can be further improved.

As described above, in the developing devices of Examples 1 to 3, the developer is supplied to the developing sleeve, and the magnetic flux density of the carrying magnetic poles of the magnet roller corresponding to the carrying region from the carrying position to the cutting edge position. Is 10 to 49% of the developing pole,
In addition, since a charging charge assisting means is installed to give a charging charge to the developer on the developing sleeve to assist the charging of the developer, it is possible to prevent image deterioration due to long-term use, and to prevent insufficient charging of the developer. It is possible to eliminate the harmful effects such as fog and scattering.

Embodiment 4 FIG. 9 is a sectional view showing still another embodiment of the developing device of the invention. In the developing device of this embodiment, the developer charging section 5 on the developing sleeve 3 in the developing chamber 16 is not provided with a developer charging assisting means, and crystalline graphite is provided on the surface of the developing sleeve 3. The developing device of Example 1 shown in FIG. 2 differs from the developing device in that the contained coating layer 3a is formed. The other structure of the present embodiment is basically the same as that of the first embodiment, and also in this embodiment, the magnetic flux density of the magnetic pole S2 and the magnetic pole N2 of the magnet roller 13 is optimized to be 10 to 49% of the developing pole N1. Planned. In FIG. 9, the same reference numerals as those shown in FIG. 2 indicate the same members.

First, the problem to be solved in this embodiment will be described. In the conventional developing device 9 shown in FIG. 7, the two-component developer is placed on the developing sleeve 3 and the magnet roller 1 thereof.
3 is drawn up and carried by the magnetic binding force from the drawing-up pole S2 of 3, but the developer is deteriorated in the developer pool 5 formed by the return member 1 and the cut pole N2, and is developed for a long period of time. However, there is a problem that the image quality is significantly deteriorated.

As shown in FIG. 12, this is the lowermost layer of the developer layers magnetically constrained by the scooping pole S2 and the cut pole N2 of the magnet roller 13, that is, the development constrained on the surface of the developing sleeve 3. The force of the developer acting in the direction normal to the developing sleeve 3, that is, the developer layer thickness and the magnet roller 13
Force fr acting in the direction of the center of the developing sleeve 3 depending on the absolute value of the magnetic flux density (magnetic pole S2: fr ₁ , magnetic pole N2:
fr ₂ ) and fθ (magnetic pole S2: fθ ₁ and magnetic pole N2: fθ ₂ ) acting in the rotation direction of the developing sleeve 3 strongly rubs against the developing sleeve 3.

Therefore, carrier deterioration of the two-component developer, in which toner resin is fused (spent formation),
In order to improve the fluidity of the toner, external additives such as silica and titanium oxide that are externally added to the toner may be buried in the toner, which results in stable charging of the developer. However, there are drawbacks such that the developer cannot be carried out, the developer scatters or is fogged, and the image quality of the entire image is significantly deteriorated.

In order to eliminate these defects, a method is proposed in which the magnetic force of the cut pole N2 in the vicinity of the developer return member 1 is weakened to reduce the rubbing force applied to the developer to prolong the life of the developer. Has been done. By this method, it is possible to extend the life of the developer, but since the sliding force of the lowermost developer on the developing sleeve 3 on the surface of the developing sleeve 3 by the return member 1 is weakened, a high density is obtained. Of the developing sleeve 3 used for forming the image portion of the developing sleeve 3 and the portion of the developing sleeve 3 not used for forming the image.
The adhered state of the above toner is different. In the portion of the developing sleeve 3 used for forming the high-density image portion, the amount of toner is small, whereas in the portion of the developing sleeve 3 not used for image formation, a large amount of toner is present. For this reason, for example, even if an attempt is made to obtain a uniform halftone image portion, the density of the developing sleeve 3 after being used for forming the high density image portion becomes low, and the portion of the developing sleeve 3 not used for image formation is In this case, the density becomes high, and density unevenness, that is, so-called sleeve ghost occurs on the image.

As described above, in the conventional developing device, when the method of weakening the magnetic force of the magnetic pole in the vicinity of the developer returning member is used, the deterioration of the developer can be prevented, but the amount of toner in the developer on the developing sleeve 3 is reduced. A sleeve ghost was generated due to the difference, and it became difficult to obtain a uniform halftone image. This has been a serious problem especially in the developing method using a thin two-component developer in which the amount of the developer carried on the developing sleeve is reduced.

The present embodiment shown in FIG. 9 is intended to solve the above problems.

As described above, in the developer layer carried on the developing sleeve 3 by being drawn up by the drawing-up pole S2 of the magnet roller 13, the developing agent on the surface of the developing sleeve or the lowermost developer close thereto is the surface of the developing sleeve 3. And a strong compressive force due to a magnetic binding force from the developer below the uppermost layer, and a sliding frictional force generated by a conveying force acting in the rotation direction of the developing sleeve 3 influences image formation for a long period of time. If it is carried out, the image quality will deteriorate due to the deterioration of the developer. Therefore, in the present embodiment as well, in order to prevent this, the magnetic flux density of the magnetic pole S2 is optimized.

The developer drawn up by the magnetic pole S2 has a magnetic restraining force acting in the central direction of the developing sleeve 3 formed by the magnetic field from the next magnetic pole N2 and a conveying force acting in the rotating direction of the developing sleeve 3. By this, the developer is conveyed to the location of the bristle cutting member 2, but at this time, due to the compression force between the developers and the rubbing force between the developer and the surface of the developing sleeve 3, the developer is formed over a long period of time. If done, the image quality will be deteriorated due to the deterioration of the developer. Therefore, similarly in this embodiment,
In order to prevent this, the magnetic flux density of the magnetic pole N2 is optimized. However, in addition to the magnetic flux density as a factor related to the magnetic pole N2, there is also the developer amount of the reservoir 5 regulated by the return member 1, so the magnetic probe sensor 7 is used. Thus, in addition to the magnetic flux density of the developer in the reservoir 5, the amount of developer is optimized.

As described above, the magnetic probe sensor 7
Is configured to detect the magnetic flux density from the magnetic pole N2 that restrains the developer in the developer reservoir 5, and if the output change of the sensor 7 is large, the reservoir formed by the magnetic pole N2 and the return member 1 The change in the packing density of the developer layer in part 5 is large, the change in the compression force is large, and the deterioration of the developer is large. On the contrary, if the output change of the sensor 7 is small and the packing density change of the developer layer is small, the change of the compression force is small and the developer deterioration is small.

In the present embodiment, as in the case of the first embodiment, as the magnet roller 13, nine kinds of magnet rollers having different magnetic flux densities of the developing pole N1, the transport magnetic poles N2 and S2 are prepared. The developing device 9 of No. 9 was incorporated into an image forming apparatus to develop the image, and an A4 size image having a duty of image density of 10% was formed up to 100,000 sheets.

Table 2 shows the results of examining the developer transportability in the developing device 9 at that time, the occurrence of image deterioration, and the change in the density of the developer by the magnetic probe sensor 7 (change in magnetic flux density). Shown in.

The image deterioration was evaluated by the roughness of the highlight portion of the image, the maximum density, the stability of the density, and the like.

[0071]

[Table 2]

Further, in this embodiment, in order to prevent the sleeve ghost from occurring even when the magnetic force of the cut pole N2 is reduced, as described above, the coating layer containing at least crystalline graphite on the surface of the developing sleeve 3. 3a was formed, especially the coating layer 3a was formed so that the crystal plane of graphite was exposed on the surface thereof.

The method of forming the coating layer 3a on the surface of the developing sleeve 3 will be described below. The crystalline graphite used was csp (average particle size: 10 μm) manufactured by Nippon Graphite. In addition, co-produced by Columbia Carbon Co. as amorphous conductive carbon
nductex SC was used. The binding resin was phenol resin (J-325) manufactured by Dainippon Ink. The solvent is a mixed solvent of methanol, methyl cellocerve and butanol (1:
1: 1) was used.

Crystalline graphite: 8 parts by weight, amorphous conductive carbon: 2 parts by weight, phenol resin: 10 parts by weight, solvent: 80 parts by weight, mixed with glass beads and dispersed in a paint shaker for 24 hours. After that, it was filtered through a nylon mesh (300 μm) to form a paint.

The obtained coating material was uniformly applied to the aluminum cylinder of the sleeve substrate with a thickness of 10 μm by the air spray method, and the coating film was dried at 170 ° C. for 30 minutes to form a coating layer on the surface of the aluminum cylinder. This was used as a developing sleeve.

In order to form the coating layer 3a with the crystalline graphite exposed on its surface, the following procedure may be performed. As a general method for forming a film, there are a dipping method, a spray method, a roll coating method, a curtain coating method, a sputtering method and the like.
The dipping method and spray method are suitable.

Specifically, in the dipping method, the solid content of the coating material is adjusted to 5 to 30%, and the pulling rate of the aluminum cylinder is set to 50 to 200 mm / minute, whereby the film thickness of the obtained coating layer is 0. The thickness was adjusted to 0.5 to 20 μm, and a coating layer was obtained with the crystalline graphite particles exposed on the surface.

[0078] In the spray method, it employs air spray method, using a gun of Binks Co. No. 601, a coating pressure 0.1 to 5 kg / cm ^2, the air pressure pattern adjustment 5 kg / cm ² or less, fog Chemical air pressure is 0.5 to
The coating layer was adjusted to 4 kg / cm ² and spray-coated on an aluminum cylinder to obtain a coating layer having a film thickness of 0.5 to 20 μm. Similarly, particles of crystalline graphite were exposed on the surface of the coating layer.

Various types of crystalline graphite were examined. For crystalline graphite, graphite (natural) made by Nippon Graphite: USSP (average particle size 0.5 μ)
m), CSPE (average particle size 4.5 μm), CSP (average particle size 5.0 μm), CP (average particle size 7.0 μm), CP
B (average particle size 7.0 μm); Graphite (manufactured by Showa Denko): UFG-5 (average particle size 1 μm), UFG-
10 (average particle size 2.0 μm), UFG-30 (average particle size 4.0 μm); Tokai Carbon (manufactured): Tokai Material Graphite (average particle size 7.0 μm).

In the present invention, these crystalline graphites can be used regardless of whether they are natural or artificial. Both were effective in eliminating the sleeve ghost, and the effects of the present invention were obtained. The average particle size of graphite is 0.5-1
The thickness is preferably 0 μm, more preferably 1 to 10 μm.

It is considered as follows that the sleeve ghost can be eliminated by forming the coating layer 3a containing crystalline graphite on the surface of the developing sleeve 3. Crystalline graphite is an allotrope of carbon and has a layered structure with its crystal surface exposed at the surface layer, and the crystal fragments are easily sheared and separated, preventing the adhesion of fine powder and binder resin powder contained in the toner. It is believed that they are working to Since the exfoliation amount of this graphite is very small, the graphite will not be consumed by long-term use.
For the reasons described above, the developing sleeve 3 of the present embodiment has an effect of always stably fixing the toner and eliminating the occurrence of the sleeve ghost.

In the conventional developing sleeve that remains the metal cylinder, the toner consumption state on the developing sleeve varies depending on the image after the development, and the toner consumption portion of the development sleeve is different from the toner consumption portion. A difference in charge amount occurred in the carried toners, resulting in a density difference in the halftone portion of the image. In the case of the present invention, however, the conveyance poles of the magnet roller 13 (suction pole S2, cut pole N2). Even if the magnetic flux density of the toner is weakened, the toner and the fine powder contained in the toner do not adhere to the developing sleeve 3. Therefore, the toner on the developing sleeve 3 is always developed in the same state, and the halftone image portion However, it became possible to always form a uniform density without sleeve ghost.

The developers usable in the present invention will be described below. In this example, a two-component developer having a carrier and a toner was used. The carrier used in the present invention preferably has a smaller average particle size and a sharper particle size distribution than conventional general carriers. Due to the small particle size, the number of contact between the carrier and the toner is increased, the charging of the toner rises faster, and the uncharged toner is not developed even if the replenishment amount is increased. Further, since the rise of the charging speed becomes faster, it is possible to prevent the scattering and the increase of the fog due to the uncharged toner under high humidity. Therefore, in combination with the toner described below, a developer that does not scatter or fog even when continuous copying of an original having a large image area is tolerant to humidity (in the present invention, magenta, yellow, cyan, and black are used). Each developer) is obtained.

By sharpening the particle size distribution,
This solves the phenomenon that a fine powder carrier sometimes accompanies the toner and adheres to the photosensitive drum at the time of development, which is sometimes caused by a small particle size carrier, and prevents deterioration of image quality due to poor charging due to the coarse powder carrier.

The ultrafine powder of 400 mesh or less is 20% by weight or less, preferably 13% by weight or less. 20% by weight
In the above, the carrier is attached to the photosensitive drum, smooth frictional charging with the toner is disturbed, and the edge effect is promoted. Fine powder of 350 mesh or less is 30% by weight or less,
Preferably 25% by weight or less, more preferably 20% by weight
It is the following. When the amount is 30% by weight or more, the rise of the charging of the toner is significantly deteriorated and the edge effect is increased.

Further, the amount of coarse powder of 250 mesh or more closely correlates with the sharpness of the image, and when it is 10% by weight or more, the scattering of the toner to the non-image area increases and the resolution of the image decreases. It is easy to cause rustiness. Therefore 250
The mesh or more is 10% by weight or less, preferably 7% by weight
Or less, more preferably 5% by weight or less.

The average particle size of the carrier is preferably 20 to 60 μm, more preferably 30 to 56 μm. 20
If the average particle size is less than or equal to μm, the image density will decrease due to toner charge-up and carrier adhesion to the photosensitive drum will increase. If the average particle size is greater than or equal to 60 μm, the reproducibility of fine lines in copying will be deteriorated.

The magnetic characteristics of the carrier have a great influence on the developing characteristics and the transportation of the developer, and the uniformity and gradation of the image are important.

When the saturation magnetization is 75 emu / g (for an applied magnetic field of 3000 oersteds) or more, at the time of development, the toner is composed of the carrier and toner on the developing sleeve facing the electrostatic latent image on the photosensitive drum. The ears of the magnetic brush are tightly tightened, and the reproduction of gradation and halftone becomes poor. When it is less than 55 emu / g, it becomes difficult to hold the toner and carrier on the developing sleeve,
There is a drawback that fog and toner scattering are worsened. Further, if the residual magnetization and coercive force of the carrier are too high, the conveyance of the developer in the developing device is deteriorated, and image blurring and uneven density in a solid image are likely to occur. Therefore, the remanent magnetization and the coercive force should be 10 emu / g or less and 10 oersted or less (for an applied magnetic field of 3000 oersted), preferably 5 emu / g or less and 6.0 oersted or less.

As the binder resin applied to the toner, all known binder resins can be used. For example, polystyrene,
Poly-p-chlorostyrene, homopolymers of styrene such as polyvinyltoluene and its substitution products, styrene-p-chlorostyrene copolymers, styrene-propylene copolymers, styrene-vinyltoluene copolymers, styrene-vinylnaphthalene Copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene -Ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether Copolymer, styrene-vinyl methyl Styrene-based copolymers such as ketone copolymers, styrene-butadiene copolymers, styrene-isoprene copolymers, styrene-acrylonitrile-indene copolymers, styrene-maleic acid copolymers, styrene-maleic acid ester copolymers Coalesce, polymethylmethacrylate, polybutylmethacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene,
Polyester, polyurethane, polyamide, epoxy resin, polyvinyl butyral, polyamide, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, Paraffin wax and the like can be used alone or as a mixture.

If necessary, a charge control agent may be added to the toner. Taking magenta toner as an example, in the case of a negatively chargeable toner, a dye having an anthraquinone-based magenta color, or a metal chelate of alkylsalicylic acid, or a positively chargeable toner, a magenta basic dye, Alternatively, those lake pigments and the like can be used.

Further, with respect to the developer in which the toner is used, a charge control agent such as colloidal silica and a fluidity modifier are used in an amount of 0.01 to 5% by weight (preferably 0.1 to 2). It is preferable to add about 10% by weight).

The average particle size of the toner used in this embodiment is preferably 3 to 15 μm, more preferably 5 to 5.
12 μm is preferable.

The carrier used in this embodiment is as follows.
Known materials can be used, for example, surface-oxidized or unoxidized iron, nickel, copper, zinc, cobalt, manganese,
Metals such as chromium and rare earths, their alloys or oxides, and ferrites are preferable, and ferrites selected from metals such as zinc, copper, nickel, and cobalt can be preferably used. Further, there is no particular limitation as a manufacturing method thereof.

It is also possible to coat the surface of the carrier with a resin or the like. As the method, any conventionally known method such as a method of dissolving or suspending a coating material such as a resin in a solvent and applying the coating material and attaching it to a carrier, or a method of simply mixing with a powder can be applied.

The substance adhered to the surface of the carrier varies depending on the toner material. For example, polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, metal complex of di-t-butylsalicylic acid, Styrene resin,
Acrylic resin, polyamide, polyvinyl butyral,
It is suitable to use nigrosine, amino acrylate resin, basic dye and its lake, fine silica powder, fine alumina powder, etc. alone or in combination, but not limited thereto.

The treatment amount of the above compounds may be appropriately determined so that the carrier satisfies the above conditions, but generally, the total amount is 0.1 to 30% by weight (preferably 0.5 to 20% by weight) based on the carrier. ) Is desirable.

In a particularly preferred embodiment which can be used in this embodiment, Cu-Zn-Fe ternary ferrite is used, and the surface thereof is a combination of a resin such as a fluorine resin and a styrene resin, for example, polyfluoride. Vinylidene and styrene-methylmethacrylate resin, polytetrafluoroethylene and styrene-methylmethacrylate resin,
Fluorine-based copolymer and styrene-based copolymer 90: 1
A mixed ferrite carrier having a ratio of 0 to 20:80, preferably 70:30 to 30:70, which is a coated ferrite carrier of 0.01 to 5% by weight, preferably 0.1 to 1% by weight. Can be mentioned. Examples of the fluorine-based copolymer include vinylidene fluoride-tetrafluoroethylene copolymer (10:90 to 90:10), and examples of the styrene-based copolymer include styrene-acrylic acid-2-
Examples are ethylhexyl (20:80 to 80:20) and styrene-acrylic acid-2-ethylhexyl-methyl methacrylate (20 to 60: 5 to 30:10 to 50).

The method of measuring the particle size distribution of the carrier in this example is as follows. 1. Approximately 100 g of sample is weighed to the nearest 0.1 g. 2. As the sieve, a standard sieve of 100 mesh to 400 mesh (hereinafter simply referred to as “sieve”) is used, and 100 to 1 from the top.
45, 200, 250, 350, 400 are stacked in order, a saucer is placed on the bottom, and the sample is put on the top sieve and covered. 3. This is 285 ± 6 per minute with horizontal vibration
Shake for 15 minutes at 150 ± 10 times per minute. 4. After sieving, the iron powder in each sieve and the pan is weighed to the nearest 0.1 g. 5. Calculated to the second decimal place in weight percentage, and JIS-Z8
Round up to the first decimal place by 401.

At this time, the size of the frame of the sieve is such that the inner diameter above the sieve surface is 200 mm and the depth from the upper surface to the sieve surface is 45 mm.
mm, and the total weight of the iron powder in each part must not be less than 99% of the mass of the sample initially taken.

Further, the average particle size is determined from the above-mentioned fixed value on the particle size distribution side. Average particle size (μ) = 1/100 × {(remaining amount of 100 mesh sieve) × 140 + (remaining amount of 145 mesh sieve) × 122 + (Remaining amount of 200 mesh sieve) × 90 + (Remaining amount of 250 mesh sieve) × 68 + (Remaining amount of 350 mesh sieve) × 52 + (Remaining amount of 400 mesh sieve) × 38 + (Total passing amount) X14}.

As a device for measuring the magnetic characteristics of the carrier,
A BHU-60 type magnetism measuring device (manufactured by Riken Seisakusho) is used.

About 1.0 g of the measurement sample was weighed and the inner diameter was 7 m.
The cells are packed in a cell having a height of 10 mm and a height of 10 mm and set in the above apparatus.

In the measurement, first, the applied magnetic field is gradually added and changed up to 3000 Oersted. Next, the applied magnetic field is reduced, and finally the hysteresis curve of the sample is obtained on the recording paper. From this, the saturation magnetization, remanent magnetization, and coercive force are obtained.

The developer used in this embodiment will be described in detail below.

Carriers A, B and C shown in Table 3 and toners a, b and c shown below were prepared.

[0107]

[Table 3]

Toner a: Styrene-n-butylmethacrylate copolymer 100 parts by weight Charge control agent 4.0 parts by weight Quinacridone pigment (CI Pigment Red 122) 4.0 parts by weight Methine pigment (CI Basic Red 12) 1 Toner b: Unsaturated polyester resin 100 parts by weight Charge control agent 4.0 parts by weight Quinacridone pigment (CI Pigment Red 202) 3.5 parts by weight Methine pigment (CI Basic Red 14) 0.5 parts by weight Toner c: Styrene resin 100 parts by weight Charge control agent 4.0 parts by weight Quinacridone pigment (CI Pigment Red 122) 4.0 parts by weight

The above formulations of the toners a to c were melt-kneaded by a roll mill, cooled, and then finely pulverized and classified by a jet mill to obtain a toner classified product having an average particle diameter of 8 to 15 μm.
0.5 wt% of hydrophobic silica (trade name R-972, manufactured by Nippon Aerosil Co., Ltd.) was externally added to this toner classified product with a modified shell mixer to obtain a toner used in this example. Then, the toners a to c and the above carriers A to C are used as a carrier A + toner a, a carrier C + toner a, and a carrier B +.
Toner b and carrier A + toner c were combined and mixed, and used as a two-component developer having a toner concentration of 6%.

In the above combinations, when two-component developers of carrier A + toner a, carrier B + toner b and carrier A + toner c are used, the results of the magnetic pole types a to i shown in Table 2 above are obtained. On the other hand, in the case of the two-component developer of the combination of carrier C + toner a, the comprehensive evaluation was poor (x) under all the same conditions as the magnetic pole types a to i.

From the above results, the developing sleeve 3 for the developer is
The magnetic flux density of the conveying magnetic poles S2, N2 of the magnet roller 13 corresponding to the feeding area from the carrying position to the cutting edge position is in the range of 10 to 49% of the developing pole N1 against the image deterioration. It was effective. By forming the coating layer 3a containing crystalline graphite on the surface of the developing sleeve 3, a uniform image without sleeve ghost was obtained. More specifically, it has been found that it is better if the change in the magnetic flux density in the developer returning member 1 is 8 gauss or less.

In addition to the closest distance between the developer return member 1 and the developing sleeve 3 being 3.0 mm, 2.0, 4.0, 5.
As a result of performing the positional relationship inclined with 0 mm, when it was 5.0 mm, the result was even worse than the result in Table 2 above.

Embodiment 5 FIG. 10 is a sectional view showing still another embodiment of the developing device of the invention. In this embodiment, in order to further enhance the effect of the fourth embodiment, the developer return member 1 is characterized as shown in FIG.

That is, in order to reduce the magnetic compressive force acting on the developer from the time when the developer is scooped up onto the developing sleeve 3 by the scooping magnetic pole S2 of the magnet roller 13 to the time when the scooping member 2 scoops it. The return member 1 was formed in a shape that kept the distance of the return member 1 to the developing sleeve 3 constant. In other words, at two points of the return member 1 facing the developing sleeve 3, the distance between the return member 1 and the developing sleeve 3 is made one turn more than the developing sleeve 3 so that the distances r1 and r2 therebetween are r1 = r2. The curved surface has a large curvature.

The above r1 = r2 = 1, 2, 3, 4, 5,
As a result of conducting an experiment as shown in Table 2 of Example 4 under the conditions of 6, 7 and 8 mm, the image deterioration similar to that in Table 2 was observed when r1 = r2 = 8 mm or more. Also r1
= R2 = 1 mm or less, the developer transporting property and the developing property were significantly deteriorated. When r1 = r2 = 2 to 7 mm, the change in the density of the developer was reduced as compared with the return member 1 in Example 4, and the image deterioration was reduced, and the effect of the present invention was further improved.

As described above, since the coating layer 3a containing crystalline graphite is formed on the surface of the developing sleeve 3, sleeve ghost is generated even when the compression of the developer is reduced as compared with that in the fourth embodiment. Instead, uniform images can always be obtained stably.

Embodiment 6 FIG. 11 is a sectional view showing still another embodiment of the developing device of the invention. In the present embodiment, it will be described that the present invention can be applied to a developing device different from the developing devices of the fourth to fifth embodiments.

As shown in FIG. 11, the rotating direction of the developing sleeve 3 facing the photosensitive drum 4 is the opposite direction (counter direction). The developer return member 1 is provided below the developing sleeve 3 of the developing container 9a. The developer scooping pole of the magnet roller 13 in the developing sleeve 3 is the magnetic pole S2, and the transporting pole for transporting the developer scooped up on the developing sleeve 3 to the position of the spike-cutting member 2 by the magnetic binding force is the magnetic pole N2, and this point is the same. However, the developing pole located in the developing area facing the photosensitive drum 4 is the S1 pole.

In this embodiment, as a result of the experiment as shown in Table 2 of the fourth embodiment, as a result, in the developing device in which the rotating direction of the developing sleeve 3 and the magnetic pole arrangement of the magnet roller 13 are different as in the present embodiment. Even if the developer is supplied to the developing sleeve 3, the magnetic flux density of the carrying magnetic poles S2, N2 of the magnet roller 13 corresponding to the carrying area from the carrying position to the cutting edge position is 10 to 49% of the developing pole S1. By doing so, it was confirmed that the same effect as in Example 4 was obtained.

Also in this embodiment, of course, it is important to form the coating layer 3a containing crystalline graphite on the surface of the developing sleeve 3 so that a uniform image without sleeve ghost can be obtained. It was

As described above, in the developing devices of Examples 4 to 6, the developer is supplied to the developing sleeve, and the magnetic flux density of the carrying magnetic poles of the magnet roller corresponding to the carrying area from the carrying position to the cutting edge position. Is 10 to 49% of the developing pole,
Moreover, since the coating layer containing crystalline graphite is formed on the surface of the developing sleeve, image deterioration can be prevented for a long period of time, and a uniform image without sleeve ghost can be obtained.

Embodiment 7 FIG. 13 is a sectional view showing still another embodiment of the developing device of the invention. The developing device of this embodiment is characterized in that the developer returning member 1 in the developing container 9a is provided with the toner concentration sensor 27.

First, the problem to be solved by this embodiment will be described. Conventionally, in a color image forming apparatus that forms a full-color or multi-color image such as an electrophotographic color laser beam printer or a copying machine, a two-component developer including a non-magnetic toner and a magnetic carrier is used from the viewpoint of the tint of the image. A developing device using is often used. Further, for the purpose of improving the reproducibility of the highlight part of the image and improving the image quality, an external additive such as titanium oxide or silica is added to the toner surface to improve the fluidity of the toner and improve the image quality. Is being pursued.

As is well known, the toner concentration of the two-component developer (that is, the ratio of the toner weight to the total weight of the carrier and the toner) is an extremely important factor in stabilizing the image quality. The toner of the developer is consumed at the time of development, and the toner density is reduced. For this reason, the developer concentration control device (ATR) is used to accurately detect the toner concentration of the developer at a proper time, and the toner is replenished in accordance with the decrease in the toner concentration to constantly control the toner concentration. Image quality should be preserved.

FIG. 16 shows an example of a conventional developing device equipped with the above developer concentration control device. The basic structure of the developing device itself is the same as that of the conventional developing device shown in FIG. 7. In the developing device 9 shown in FIG. 16, the developing chamber 1 is provided at the bottom of the developing container 9a.
A developer toner concentration sensor 27 of the developer concentration control device is installed at a position below the first conveying screw 11 in the unit 6.

The control device employs the inductance ATR method in which the toner concentration sensor 27 detects a change in the toner concentration of the developer as an apparent change in magnetic permeability due to a change in the mixing ratio of the non-magnetic toner and the magnetic carrier.

However, since the fluidity of the toner is improved in order to improve the image quality, its bulk density changes as the developer is stirred. Specifically, the developer, which was initially in a dense state by the stirring of the developer, is loosened and becomes a coarse state. For this reason, when the toner is scattered or the toner consuming operation is performed due to continuous stirring, as shown in FIG. 17, in the normal developer, the toner concentration (T
/ T + C ratio. (T: toner weight, C: carrier weight) decreases, the inductance ATR output becomes a straight line a.
However, with a developer with a large change in bulk density,
The effect of reducing the number of carriers in the unit volume is more effective, and as a result, the output of the inductance ATR decreases as indicated by the straight line b. When such an ATR output decrease occurs, the stability of the toner density cannot be maintained, and there is a drawback that causes deterioration of image quality.

The present embodiment shown in FIG. 13 is intended to solve the above problems.

As described above, the scooping amount of the developer onto the developing sleeve 3 depends on the magnetic restraining force which is formed by the magnetic field from the magnetic pole S2 in the central direction of the developing sleeve 3 and the rotational direction of the developing sleeve 3. It depends on the transport force that acts.

Therefore, the magnitude (absolute value) of the magnetic flux density of the magnetic pole S2 is the minimum magnetic flux density for stably pumping the developer, and the maximum magnetic flux density which does not cause the packing density change due to the strong magnetic binding force. Determined between

The developer drawn up by the magnetic pole S2 is
The developer return member 1 having the toner concentration sensor 27 and the developing sleeve 3 are compressed by the magnetic binding force from the magnetic pole N2.
Is conveyed to the location of the ear cutting member 2 by the conveying force that acts in the rotation direction of. The toner concentration sensor 27 is preferably located at a stable position where the developer is compressed, and is preferably located near the magnetic pole N2. At this time, the sensor 27 adopts a method of detecting an apparent magnetic permeability due to a change in the mixing ratio of the non-magnetic toner and the magnetic carrier in the developer. Therefore, when the density of the developer changes, the malfunction occurs even though the toner concentration does not change.

Therefore, in this embodiment, the absolute value of the magnetic flux density of the magnetic pole N2 and the distance between the developing sleeve 3 and the return member 1 are optimized to minimize the change in the density of the developer in the developer reservoir 5. Is to take. Toner density sensor 27
In order to determine the conditions for the stable behavior such as the straight line a in FIG. 17, a magnetic probe sensor using a Hall element at the position of the sensor 27 at a position along the longitudinal direction of the developing sleeve 3 of the return member 1. 7 was installed, and the developer reservoir 5 was optimized by the magnetic sensor 7.

In this embodiment, the magnet roller 13
As the magnetic poles, nine types of magnet rollers having different magnetic flux densities of the developing pole N1, the transport magnetic poles N2 and S2 were prepared, and these were used in the developing device 9 of FIG. .

At that time, it is investigated whether or not the developer transportability in the developing device 9 and the output value of the toner concentration sensor 27 show a stable output characteristic as shown by the straight line a in FIG. Table 4 shows the results of examining changes in the density of the developer (changes in magnetic density) by the sensor 7.

[0135]

[Table 4]

As a result, when the magnetic flux density of the magnetic poles N1, N2 and S2 is configured so that the change in the magnetic flux density of the developer can be suppressed to 5 gauss or less, the toner density sensor 27
A stable output characteristic was obtained.

The two-component developer usable in this embodiment is
The same as described in Example 4 can be used.

In this example, the toners a, b, and c used in Example 4 and the carriers A, B, and C shown in Table 3 of Example 4 were similarly prepared as carrier A + toner a,
Carrier C + toner a, carrier B + toner b, carrier A + toner c were combined and mixed to be used as a two-component developer having a toner concentration of 6%.

In the above combination, when two-component developers of carrier A + toner a, carrier B + toner b and carrier A + toner c are used, the results of the magnetic pole types a to i shown in Table 4 above are obtained. On the other hand, in the case of the two-component developer of the combination of carrier C + toner a, the output evaluation was poor (x) under all the same conditions as the magnetic pole types a to i.

From the above results, the developing sleeve 3 for the developer is
The magnetic flux density of the conveying magnetic poles S2, N2 of the magnet roller 13 corresponding to the feeding area from the carrying position to the cutting edge position is in the range of 10 to 49% of the developing pole N1 against the image deterioration. It was effective.

Further, the closest distance between the developer returning member 1 and the developing sleeve 3 is 3.0 mm, 2.0, 4.0, 5.
As a result of performing the positional relationship inclined with 0 mm, when it was 5.0 mm, the result was even worse than the result in Table 4 above.

Embodiment 8 FIG. 14 is a sectional view showing still another embodiment of the developing device of the invention. In this embodiment, in order to further enhance the effect of the seventh embodiment, the developer return member 1 is characterized as shown in FIG.

That is, in order to reduce the magnetic compression force acting on the developer from the time when the developer is scooped up onto the developing sleeve 3 by the scooping magnetic pole S2 of the magnet roller 13 to the time when the scooping member 2 scoops the scissors. The return member 1 was formed in a shape that kept the distance of the return member 1 to the developing sleeve 3 constant. In other words, at two points of the return member 1 facing the developing sleeve 3, the distance between the return member 1 and the developing sleeve 3 is made one turn more than the developing sleeve 3 so that the distances r1 and r2 therebetween are r1 = r2. The curved surface has a large curvature.

The above r1 = r2 = 1, 2, 3, 4, 5,
As a result of conducting an experiment as shown in Table 4 of Example 7 under conditions of 6, 7, and 8 mm, the density change of the developer (flux density change) is large when r1 = r2 = 8 mm or more, and the toner concentration sensor The output characteristics of No. 27 were the same as those in Table 4, and the output characteristics were not stable. When r1 = r2 = 1 mm or less,
The developer transporting property and the developing property were remarkably deteriorated. r1 = r
When 2 = 2 to 7 mm, the density change of the developer was reduced as compared with the return member 1 in Example 4, and the output characteristics of the sensor 27 were stabilized, and the effect of the present invention was further improved.

Embodiment 9 FIG. 15 is a sectional view showing still another embodiment of the developing device of the invention. In the present embodiment, it will be described that the present invention can be applied to a developing device different from the developing devices of the seventh to eighth embodiments.

The basic structure of the developing device 9 of the present embodiment shown in FIG. 15 is the same as that of the developing device 9 of the embodiment 6 shown in FIG. 11, and the rotation direction of the developing sleeve 3 facing the photosensitive drum 4 is opposite (counter). Direction), and the developer return member 1 is provided below the developing sleeve 3 of the developing container 9a. The developer scooping pole of the magnet roller 13 in the developing sleeve 3 is the magnetic pole S2, and the magnetic pole N2 is a conveying pole for conveying the developer scooped up on the developing sleeve 3 to the position of the spike-cutting member 2 by the magnetic binding force. The developing pole located in the developing area opposite to is the S1 pole. In this embodiment, the toner concentration sensor 27 is further installed on the return member 1.

In this embodiment, as a result of conducting an experiment as shown in Table 4 of the seventh embodiment, as a result, a developing device in which the rotating direction of the developing sleeve 3 and the magnetic pole arrangement of the magnet roller 13 are different as in the present embodiment. It was confirmed that even if there was, the same effect as in Example 7 could be obtained.

As described above, in the developing devices of Embodiments 7 to 9, the developer is supplied to the developing sleeve, and the magnetic flux density of the carrying magnetic poles of the magnet roller corresponding to the carrying area from the carrying position to the cutting edge position. Is 10 to 49% of the developing pole,
In addition, the toner concentration sensor for the developer is placed near the magnetic poles for conveyance, so there is little deterioration due to the use of the developer, the output characteristics of the toner concentration sensor are stable, and good development is performed to maintain high-quality images. can do.

[0149]

As described above, according to the developing device of the present invention, the developer is supplied to the developer carrying member, and the magnetic flux of the carrying magnetic pole of the magnet corresponding to the carrying region from the carrying position to the cutting edge position is provided. Since the density is set to 10% to 49% of the developing pole, and a charge imparting assisting means is installed to impart a charge to the developer on the developer carrying member to assist the charge of the developer, long-term use is possible. The image deterioration can be prevented, and the insufficient charge of the developer can be eliminated to eliminate the adverse effects such as fog and scattering.

According to another aspect of the present invention, the magnetic flux density of the feeding magnetic pole of the magnet corresponding to the feeding area of the developer to the developer carrying member and the carrying area from the carrying position to the cutting edge position is set to 1 of the developing pole.
Since a coating layer containing crystalline graphite is formed on the surface of the developer carrier in an amount of 0 to 49%, deterioration due to use of the developer is small, image deterioration can be prevented for a long time, and sleeve ghost No uniform image is obtained.

According to still another aspect of the present invention, the developer is supplied to the developer carrying member, and the magnetic flux density of the carrying magnetic pole of the magnet corresponding to the carrying area from the carrying position to the cutting edge position is set to the developing pole. 10% to 49%, and the toner concentration sensor for the developer is arranged in the vicinity of the magnetic pole for conveyance, so that there is little deterioration due to the use of the developer, the output characteristics of the toner concentration sensor are stable, and good development is performed. A high quality image can be maintained.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus including a developing device according to an exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a developing device provided in the image forming apparatus of FIG.

FIG. 3 is a graph showing the results of examining the rise of the triboelectric charge amount from the state where the developer is left standing by idling the developing device of FIG. 2 in comparison with the results of the conventional developing device.

FIG. 4 is a sectional view showing another embodiment of the developing device of the invention.

FIG. 5 is a sectional view showing still another embodiment of the developing device of the present invention.

FIG. 6 is a perspective view showing a kneading type screw provided in the developing device of FIG.

FIG. 7 is a cross-sectional view showing a conventional developing device.

8 is a cross-sectional view showing that a magnetic probe sensor is installed in the developing device of FIG.

FIG. 9 is a sectional view showing still another embodiment of the developing device of the present invention.

FIG. 10 is a sectional view showing still another embodiment of the developing device of the invention.

FIG. 11 is a sectional view showing still another embodiment of the developing device of the present invention.

FIG. 11 is a sectional view showing still another example of the developing device of the present invention.

FIG. 12 is an explanatory diagram schematically showing a force acting near the surface of a developer carrier of a conventional developing device.

FIG. 13 is a cross-sectional view showing still another example of the developing device of the present invention.

FIG. 14 is a sectional view showing still another example of the developing device of the present invention.

FIG. 15 is a cross-sectional view showing still another example of the developing device of the present invention.

FIG. 16 is a sectional view showing another example of a conventional developing device.

FIG. 17 is a sectional view showing still another example of a conventional developing device.

[Explanation of symbols]

 1 developer returning member 2 spike-cutting member 3 developing sleeve 4 photosensitive drum 7 magnetic probe sensor 9 developing device 13 magnet roller 27 toner concentration sensor

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[Procedure amendment]

[Submission date] March 29, 1994

[Procedure Amendment 1]

[Document name to be amended] Statement

[Name of item to be corrected] Brief description of the drawing

[Correction method] Change

[Correction content]

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram illustrating an image forming apparatus including a developing device according to an exemplary embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a developing device provided in the image forming apparatus of FIG.

FIG. 3 is a graph showing the results of examining the rise of the triboelectric charge amount from the state where the developer is left standing by idling the developing device of FIG. 2 in comparison with the results of the conventional developing device.

FIG. 4 is a sectional view showing another embodiment of the developing device of the invention.

FIG. 5 is a sectional view showing still another embodiment of the developing device of the present invention.

FIG. 6 is a perspective view showing a kneading type screw provided in the developing device of FIG.

FIG. 7 is a cross-sectional view showing a conventional developing device.

8 is a cross-sectional view showing that a magnetic probe sensor is installed in the developing device of FIG.

FIG. 9 is a sectional view showing still another embodiment of the developing device of the present invention.

FIG. 10 is a sectional view showing still another embodiment of the developing device of the invention.

FIG. 11 is a sectional view showing still another embodiment of the developing device of the present invention.

FIG. 12 is an explanatory diagram schematically showing a force acting near the surface of a developer carrier of a conventional developing device.

FIG. 13 is a cross-sectional view showing still another example of the developing device of the present invention.

FIG. 14 is a sectional view showing still another example of the developing device of the present invention.

FIG. 15 is a cross-sectional view showing still another example of the developing device of the present invention.

FIG. 16 is a sectional view showing another example of a conventional developing device.

FIG. 17 is a sectional view showing still another example of a conventional developing device.

[Explanation of reference numerals] 1 developer returning member 2 bristle cutting member 3 developing sleeve 4 photosensitive drum 7 magnetic probe sensor 9 developing device 13 magnet roller 27 toner concentration sensor

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Claims (5)

[Claims] 1. A rotatable developer carrier that carries a developer and conveys the developer to a developing area facing the image carrier; and an agitating / conveying unit that agitates and supplies the developer to the developer carrier. A non-rotatably arranged magnet in the developer carrier, a regulation mechanism for imparting a charge to the developer carried on the developer carrier and regulating the amount of the carrier carried, and the developer carrier In a developing device having a brush cutting member that cuts the brush of the magnetic brush of the developer carried on the developer carrying body from the carrying position of the developer of the developer on the developer carrying body. The carrying magnetic pole corresponding to the carrying area up to the cutting position has a magnetic flux density of 10 to 49% of that of the developing pole of the magnet corresponding to the developing area, and is different from the regulating mechanism in the developing container. , The developer carried on the developer carrier is charged with an electric charge. A developing device provided with a charging assisting means for applying. 2. The developing device according to claim 1, wherein the charge imparting assisting means is a developer stirring / transporting screw provided separately from the stirring / transporting means. 3. The developing device according to claim 1, wherein the charge imparting assisting means is an elastic blade that is in contact with the developer carrying member. 4. A rotatable developer carrier that carries a two-component developer and conveys it to a developing area facing the image carrier, a magnet that is non-rotatably disposed in the developer carrier, and A regulating mechanism that applies a charge to the developer carried on the developer carrying body and regulates the carried amount thereof, and a brush of the magnetic brush of the developer carried on the developer carrying body to a predetermined height. In a developing device having a spike-cutting member that cuts the spikes, the magnetic poles for transport corresponding to the transport region from the carrying position of the developer on the developer carrier to the spike-cutting position of the magnet are the magnets. One of the developing poles corresponding to the developing area
A developing device having a magnetic flux density of 0 to 49% and having a film containing crystalline graphite formed on the surface of the developer carrying member. 5. A detection unit for detecting the toner concentration of a two-component developer, a rotatable developer carrier for carrying the developer and transporting the developer to a developing area facing the image carrier, and the developer carrier. A magnet that is non-rotatably arranged in the body, a regulation mechanism that applies a charging charge to the developer carried on the developer carrying body and regulates the carried amount, and a carrying mechanism carried on the developer carrying body. In a developing device having a spike-cutting member that cuts the spikes of the magnetic brush of the developer into a predetermined spike height, from the carrying position of the magnet of the developer on the developer carrying member to the spike-cutting position. The carrying magnetic poles corresponding to the carrying area are the developing poles of the magnet corresponding to the developing area.
A developing device having a magnetic flux density of 49% and wherein the detecting means is located near the carrying magnetic pole.