JPH0943968A - Developing device and process cartridge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming device and a process cartridge which can form an excellent image even in the case of shortening length in the longitudinal direction. SOLUTION: A magnetizing length in the longitudinal direction of a magnet 18' is made longer than the opening area (c) of a developer container at a pole S2 on the side in contact with an end-part seal member 30 and made shorter than the outside end part of the end-part seal member 30, and the magnetizing length is made longer than the opening area (c) of the developer container at a pole S1 on the side opposite to a latent carrier and also made longer than the magnetizing length of the pole S2 on the side in contact with the end-part seal member 30.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device and a process cartridge of an image forming apparatus using an electrophotographic process such as a copying machine and a laser beam printer.
The present invention relates to a technique for preventing fogging and toner leakage.

[0002]

2. Description of the Related Art Conventionally, in an image forming apparatus using an electrophotographic process, a developing method using a magnetic one-component toner has been known. One example thereof will be described with reference to FIGS. 2 and 3.

In FIG. 2, which is a sectional view of a conventional developing device, a fixed magnet 18 as a magnetic field generating means is included.
A developing sleeve 8, which is a developer carrier that is rotatably arranged in a cylindrical shape and made of a non-magnetic material, carries the one-component magnetic toner 6 contained in a developer container 7. The carried toner 6 is transferred by the developing blade 9 which is a developer regulating member.
The photosensitive drum 2 which is a latent image carrier is conveyed to the developing unit after the layer thickness is regulated to form a thin toner layer having a predetermined thickness.
It is used for developing the electrostatic latent image formed above.

At the time of development, a developing bias in which an AC voltage is superimposed on a DC voltage is applied between the developing sleeve 8 and the photosensitive drum 2. Development is performed by causing the developer to reciprocate between the photosensitive drum 2 and the developing sleeve 8 by the applied AC voltage. The latent image on the photosensitive drum 2 is thereby visualized as a toner image.

Here, each magnetic pole of the magnet 18 has the following functions. The S2 pole attracts the toner in the container and carries it on the developing sleeve 8, and the N1 pole conveys the toner.
Further, the S1 pole is arranged so as to face the photosensitive drum 2 and has a function of pulling back the fog toner adhering to the non-application portion on the photosensitive drum 2, and the N2 pole functions so as to prevent toner leakage from the lower portion of the container.

Next, the longitudinal relationship in the conventional developing device will be described with reference to FIG. In FIG. 3, FIG. 3B is a positional relationship diagram of the magnet 18, the developing sleeve 8 and the like.
(1) is the magnetic flux density distribution in the longitudinal direction generated by the magnet 18 at that time, and FIG. 3 (3) shows A shown in FIG. 3 (2).
It is sectional drawing in -A '.

Generally, the magnet 18 is shown in FIG.
As shown in (3), it has a cylindrical shape and each pole is magnetized to the end. Therefore, all the poles have the same magnetization length.

Further, as shown in FIG. 3C, an end seal member 30 is arranged in contact with the developing sleeve 8 at the open end of the container 7 to prevent toner leakage.

In the developing device as described above, the developer container 7
The opening, the length of the developing sleeve 8, the magnet 18, the position of the end seal member 30, etc. in the longitudinal direction are determined as follows. Hereinafter, description will be made with reference to FIG.

1: Image area b according to the width a of the paper used
Set.

2: The container opening width c is set to be at least the image width b or more. Toner is coated on the developing sleeve 8 for the opening width c to enable development.

3: The length of the S1 pole of the magnet 18 is set so as to obtain a magnetic flux density that does not cause fog on the photosensitive drum 2 over the entire area c of the opening. The other pole of the magnet 18 has the same length as the S1 pole.

4: An end seal member 30 is arranged at the end of the container opening to prevent toner leakage. The width of the seal is set so as to cover at least a portion where the magnetic flux density of the magnet 18 is present.

Further, a roller member (not shown), which has a role of keeping a constant distance between the developing sleeve 8 and the photosensitive drum 2, a driving gear, etc. are arranged outside the end seal member 30.
The position of the outer end e of the end seal member 30 is one of the factors that determine the length in the longitudinal direction.

[0015]

[Problems to be solved by the invention] However, in recent years, as products such as copiers and printers are becoming more and more personalized, there is an increasing need for downsizing, and it is necessary to shorten the lengthwise direction of the device. Despite this, if a magnet is used that is cylindrical and magnetized to the end of each pole as in the conventional case, it is attempted to shorten the opening width, magnet, end seal member, etc. in the longitudinal direction. Then, the following phenomena occurred.

1: If the aperture width is shortened in the longitudinal direction, the aperture width becomes equal to or smaller than the image area width. As a result, a portion of the developing sleeve 8 in the image area where the toner cannot be coated occurs, and the image may not appear at that portion.

2: An example in which the length of the magnet 18 is shortened by cutting the outside of the end portion seal member 30 to shorten the length of the magnet 18 is shown in FIG. 4B, and the magnetic flux density in the lengthwise direction at that time is also shown. The distribution is shown in FIG. 4 (1), and the conventional configuration diagram is shown in FIG. 4 (3) for comparison. In the case of shortening with the configuration as shown in FIG. 4 (2), the sheet passing edge portion a enters the weak magnetic flux density region shown in the magnetic flux density distribution chart of FIG. Fog sometimes occurred.

3: An example in which the width of the end seal member 30 is reduced to shorten the lengthwise direction is shown in FIG. 5 (2).
Fig. 5 shows the magnetic flux density distribution in the longitudinal direction at that time.
FIG. 5 (3) shows a conventional configuration diagram for comparison (1). If the structure shown in FIG. 5 (2) is used for shortening, as can be seen from FIGS. 5 (1) and 5 (2), magnetic flux exists also outside the end seal member. Therefore, as the developing sleeve 8 rotates, the toner is attracted by the magnetic flux in the region outside the end seal member 30 shown in the magnetic flux density distribution diagram of FIG. 5A and gradually moves to the outside of the end seal member 30. However, toner may leak out of the developing device.

Further, if a developing blade regulating member of the type in which the developing blade 9 is brought into contact with the developing sleeve 8 is used,
In some cases, the toner leaks from the end seal member 30 with respect to the longitudinal direction and a small gap between the end of the developing blade 9 and durability.

Therefore, an object of the present invention is to provide an image forming apparatus and a process cartridge which can form an excellent image even when the length in the longitudinal direction is shortened.

Further, the present invention provides an image forming apparatus and a process cartridge in which a toner leak between the developing blade and the end seal member is hard to occur when the developing blade that contacts the developing sleeve is used as the developer regulating member. Is intended.

[0022]

According to the first invention of the present application, the above-mentioned object is to provide a developer container containing at least a developer, a latent image carrier, and a rotatable developer carrier. ,
In the developing device having a magnetic field generating means having a plurality of magnetic poles in the circumferential direction and contained in the developer carrier, and an end seal member arranged in contact with the developer carrier at the opening end of the container, the magnetic field generation is performed. The magnetizing length of the means in the longitudinal direction is longer than the opening of the developer container and shorter than the outer end of the end seal member at the pole on the side in contact with the end seal member. This is achieved by making the magnetizing length of the pole longer than that of the opening of the developer container and longer than the magnetizing length of the pole on the side in contact with the end seal member.

According to the second invention of the present application, the above object is to provide a developer container containing at least a developer,
A rotatable developer carrier, a magnetic field generating unit fixedly arranged in the developer carrier and having a plurality of magnetic poles in the circumferential direction, and a regulation for abutting on the surface of the developer carrier to regulate the layer thickness of the developer. In a developing device having a member and an end seal member arranged in contact with a developer carrying member at the end of the container opening, the magnetizing length of the magnetic field generating means in the longitudinal direction is a pole contacting the end seal member. Of the above, the pole upstream of the regulating member is longer than the opening of the developer container and shorter than the outer end of the end seal member, and the magnetic flux density outside the image region is at least smaller than the inside. Achieved by

Further, according to the third invention of the present application, the above object is to provide a process cartridge which comprises at least a developing device and which is attachable to and detachable from the image forming apparatus main body.
This is achieved by the developing device being the developing device according to the first invention or the second invention.

Therefore, according to the first aspect of the present invention as described above, the magnetizing length of each pole of the magnetic field generating means is set so that the opening of the developer container at the pole on the side in contact with the end seal member. Since the length is made longer, a predetermined magnetic flux density is provided in the image area, and the developer is well coated on the developer carrier. Moreover, by making the length shorter than the outer end of the end seal member, the amount of the developer moving to the gap between the end seal member and the developer carrying member is reduced, and the developer leakage is prevented. Further, by making the magnetizing length of the pole on the side facing the latent image bearing member longer than that of the opening of the developer container and longer than the magnetizing length of the pole on the side in contact with the end seal member, Since it has a magnetic flux density over the opening area, of the latent image carrier surface,
Fogging is suppressed by pulling back the developer in the non-development area to the developer carrier.

Further, according to the second invention of the present application, the magnetic flux density in the vicinity of the regulating member width and the end seal is located upstream of the regulating member in the pole contacting the end seal member. At the pole, it is longer than the opening of the developer container and shorter than the outer end of the end seal member, and the magnetic flux density outside the image area is at least smaller than the inner side.
The magnetic flux density in the gap between the end seal member and the end portion of the developer carrier is reduced to reduce the magnetic attractive force, and the developer coating amount on the surface of the developer carrier corresponding to this portion is suppressed.
This makes it difficult for developer leakage to occur.

Further, according to the third invention of the present application, by shortening the length of the device in the longitudinal direction by configuring the magnetic field generating means as in the first invention or the second invention. And provide a small process cartridge.

[0028]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, the first embodiment of the present invention will be described in detail. In FIG. 6, which is a cross-sectional view of the image forming apparatus, reference numeral 1 denotes a main body of the image forming apparatus, and a cylindrical photosensitive drum 2 as a latent image carrier is rotatably installed in a central portion of the apparatus main body 1. The surface of the photosensitive drum 2 is uniformly charged by a charging device (charging roller) 3, and then an exposure device 4 performs image exposure to form an electrostatic latent image.

At the time of development, a developing bias power source 19 connected to the developing sleeve 8 serving as a developer carrying member applies a developing bias in which an AC voltage is superimposed on a DC voltage between the developing sleeve 8 and the photosensitive drum 2. The applied alternating voltage causes the toner 6 in the developer container 7 to reciprocate between them, and the electrostatic latent image is visualized as a toner image.

The obtained toner image is transferred onto the transfer material 11 by the transfer device (transfer roller) 10. Transfer material 1
1 is fed from the cassette 11a by the feed roller 12,
The registration roller 13 sends the toner image between the photosensitive drum 2 and the contact portion of the transfer roller 10 in synchronization with the toner image on the photosensitive drum 2. The transfer material 11 on which the toner image has been transferred by the transfer roller 10 is conveyed to the fixing device 14, where the toner image is fixed on the transfer material 11 by heat and pressure to form a permanent image, and thereafter, outside the image forming apparatus. Is discharged to.

On the other hand, after the toner remaining on the surface of the photosensitive drum 2 without being transferred is cleaned and removed by the cleaning device 15, the photosensitive drum 2 is charged again by the charging roller 3 and the above image forming process is repeated.

Next, the structure of the magnet according to the first embodiment of the present invention will be described with reference to FIG. FIG.
(2) is a diagram showing a positional relationship in the longitudinal direction of the magnet 18 ′ serving as a magnetic field generating unit, the developing sleeve 8, the end seal member 30, and the vicinity thereof. In addition, Fig. 1 (1)
It is a magnetic flux density distribution figure with respect to the longitudinal direction of S1 and S2 poles. As shown in FIG. 1 (2), the present embodiment is characterized in that the magnetizing length of a plurality of magnet poles in the circumferential direction is changed for each pole by changing the end shape of the magnet.

Of the magnetic poles of the magnet 18 ', the S1 pole facing the photosensitive drum 2 has a function of returning the toner in the non-developing area on the surface of the photosensitive drum 2 to the developing sleeve 8 as described above. Therefore, when developing is performed in a portion where the magnetic flux density is weak, the toner in the non-development area that flies onto the photosensitive drum 2 due to the AC electric field cannot be pulled back to the developing sleeve 8, and as a result, some toner remains on the photosensitive drum 2. However, so-called fog occurs that is transferred to paper.

This fog becomes less noticeable as the magnetic flux density increases. According to the study by the present inventors, it is found that the effect of fog is extremely small if the magnetic flux density of 80% or more of the average magnetic flux density in the vicinity of the center of the magnet 18 'is provided in the opening region. It was

Therefore, in this embodiment, the S1 pole is shown in FIG.
As shown in (1), the magnet 1 is provided over the entire opening area c.
The position and length are set so as to have a magnetic flux density of 80% or more of the average magnetic flux density near the center of 8 '.

The S2 pole, which has a role of contacting the end seal member 30 and carrying toner, has a correlation with toner leakage and low density.

When the magnetic flux density exists outside the end seal member 30, the magnetic flux is attracted by the magnetic flux and gradually ends from a slight gap formed between the developing sleeve 8 and the end seal member 30 when the developing sleeve 8 rotates. The toner moves to the outside of the part seal member. If this gets worse, the developing sleeve 8
Toner leaks from the edges.

Further, when the magnetic flux density at the position of the developing region in the longitudinal direction with the same S2 pole is weak, the force for coating the toner on the developing sleeve 8 is weakened there, and the toner layer formed on the developing sleeve 8 is formed. Since the image becomes thin, the image has a low density.

According to the study made by the present inventors, this thin concentration is 7% of the average magnetic flux density near the center of the magnet 18 '.
It has been found that there is no problem if the magnetic flux density of more than 50% is provided in the image area.

Therefore, in this embodiment, the S2 pole is shown in FIG.
As shown in (1), the magnet 1 is provided over the entire image area b.
The magnetic flux density is 70% or more of the average magnetic flux density near the center of 8 ', and the end seal member 30 is arranged so that the magnetic flux density generated by the S2 pole does not exist outside thereof.

FIG. 7 shows a comparison of the positional relationship between the above structure and the conventional one. FIG. 7B is a configuration diagram of this embodiment.
As can be seen by comparing with the conventional configuration diagram of FIG.
In the present embodiment, the outside of the end seal 30 can be shortened by the amount of shortening the S2 pole. As described above, the position outside the end seal member 30 is a factor that determines the length in the longitudinal direction.
By adopting the configuration shown in this embodiment in which the magnetizing length of each pole of the magnet 18 'is changed according to its function, the length of the entire system with respect to the longitudinal direction is shortened by the amount of shortening the outside of the end seal member 30. It has become possible to make the length shorter than before.

Specifically, the magnet 18 'has a S2 pole at both ends of about 2.0 mm in the longitudinal direction, and N1 and N2.
Both ends of the pole can be made shorter than the S1 pole by about 1.0 mm, and further, the S1 pole outermost end portion is located slightly 2 mm outside the opening end portion. As a result, the end seal member 30 can be shortened by 2.0 mm by shortening the S2 pole, and as a result, the entire system can be shortened by 2 mm at both ends with a total length of 4 m.
It has become possible to shorten the length by about m.

The above description is only for the case where the shape of the magnet 18 'is changed, but the present invention is not limited to this, and the magnetic flux density distribution generated by each pole is changed by changing the magnetizing length for each pole. Needless to say, the same effect can be obtained if it is the same.

(Second Embodiment) Next, a second embodiment will be described with reference to FIG. In FIG.
(2) is a diagram showing a positional relationship in the longitudinal direction of the present embodiment,
FIG. 8A is a magnetic flux density distribution chart in the longitudinal direction of the S1 and S2 poles at that time.

In the second embodiment, as shown in FIG. 8, an elastic blade 9 that contacts the developing sleeve 8 is used as the layer thickness regulating member.

In the magnet 18 "of this embodiment, the S1 pole has a magnetic flux density of 80% or more of the average magnetic flux density in the vicinity of the center of the magnet over the entire opening region c, as in the first embodiment. The position and length are set so that they will have, and the influence of fog does not appear.

The magnetizing width of the S2 pole is the same as that of the first embodiment, but the magnetic flux density outside the image area is set to about 2/3 of the average magnetic flux density in the image area. In this embodiment, the magnetic flux density is reduced by changing the diameter of the magnet in the S2 pole portion.

In the present embodiment, the magnetic attraction is reduced by the structure in which the magnetic flux density in the gap between the end seal member and the developing blade end is reduced, and the toner on the sleeve surface corresponding to this portion is reduced. It is configured to suppress the amount of coat. According to the study by the present inventors, it has been found that if a large amount of toner is coated in the gap, the leakage is likely to occur, and if the toner coating amount is reduced, the leakage is hard to occur. Therefore, in order to reduce leakage, the lower the magnetic flux density in this gap, the better. However, in FIG. 8, the magnetic flux density is set to 2/3 or less of the average magnetic flux density in the image area. In this setting, it was found that the effect of leakage was extremely small.

In the second embodiment, the magnetizing length of the S2 pole is the first.
Since it is similar to the case of the embodiment, the width of the end seal member,
The resulting length of the entire system in the longitudinal direction is the same as in the first embodiment.

The above is the description when the shape of the magnet is changed, but the present invention is not limited to this, and the magnetic flux density between the end seal member and the end of the developing blade is reduced by changing the magnetizing method. It goes without saying that similar effects can be obtained if they exist.

Further, this effect is also effective against vibration and the like which occur when a toner having an average particle diameter smaller than that of a conventional one is used as a developer or when a cartridge is attached or detached.

(Third Embodiment) Next, a third embodiment of the present invention will be described with reference to FIG. In FIG. 9, 7 is a developer container containing the developer 6, and 8 is a developer carrier containing a fixedly arranged magnetic field generating means 18, and the magnetizing length of the magnetic field generating means and the position with respect to the end seal member. The relationship is similar to that described in the first and second embodiments. Further, 9 is a developer regulating member, 2 is a photosensitive drum, 3 is a charging device, and 15 is a toner recovery container. In the present invention, the above is an integrated process cartridge. By making it detachable from the main body of the image forming apparatus, in addition to the effects of the first and second embodiments, it is possible to provide a small-sized image forming apparatus that is easy to maintain.

[0054]

As described above, according to the first invention of the present application, the magnetizing length in the longitudinal direction of the magnetic field generating means having a plurality of poles in the circumferential direction is measured on the side in contact with the end seal member. The pole is at least longer than the opening of the developer container and shorter than the end of the end seal member, and the pole on the side facing the latent image carrier has a magnetized length longer than the opening of the developer container, and ,
By making it longer than the pole on the side in contact with the end seal member, the length in the longitudinal direction of the developing device could be shortened while the end fog and toner leakage remained at a level at which there was no problem.

Further, according to the second invention of the present application, when an elastic blade that abuts against the developer carrying member is used as the developer regulating member, both end fog and toner leakage remain at a level without problems. In addition to shortening the length of the image forming apparatus with respect to the longitudinal direction, by changing the magnetic flux density distribution of the pole on the upstream side of the blade of the elastic body among the poles in contact with the end seal member of the magnetic field generating means. The toner leakage between the elastic blade and the end seal member can be reduced.

Further, in the third invention, the length in the longitudinal direction of the image forming apparatus can be shortened while the end fog and toner leakage remain at a level at which there is no problem, and the developer carrying member is used as a developer regulating member. Even when using an abutting elastic blade, it is possible to reduce the end fog and the toner leakage between the elastic blade and the end seal member. This made it possible to provide a process cartridge that is small and easy to maintain.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a positional relationship in the vicinity of a magnet of the present invention.

FIG. 2 is a cross-sectional view showing a conventional developing device.

FIG. 3 is a cross-sectional view showing a conventional developing device and a magnetic flux density distribution at that time.

FIG. 4 is a first example of a case where the length of the developing device in the longitudinal direction is shortened.

FIG. 5 is a second example in which the length of the developing device in the longitudinal direction is shortened.

FIG. 6 is a sectional view showing a schematic configuration of an image forming apparatus according to an embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a positional relationship of end seal members and the like when the present invention is used.

FIG. 8 is a cross-sectional view showing a second embodiment of the present invention.

FIG. 9 is a sectional view showing an embodiment of the present invention, a process cartridge.

[Explanation of symbols]

 2 photosensitive drum (latent image carrier) 7 developer container 8 developing sleeve (developer carrier) 9 developing blade (developer regulating member) 18 ', 18 "magnet (magnetic field generating means) 30 end seal member

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masashi Ojima 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc. (72) Inquiry Seiji Yamaguchi 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (3)

[Claims] 1. A magnetic field generating means having a developer container containing at least a developer, a latent image carrier, a rotatable developer carrier, and a plurality of magnetic poles circumferentially contained in the developer carrier. In the developing device having an end seal member arranged in contact with the developer carrying member at the container opening end, the magnetic length in the longitudinal direction of the magnetic field generation means is set to a value on the side in contact with the end seal member. The pole is longer than the opening of the developer container and shorter than the outer end of the end seal member, and the magnetizing length is longer than the opening of the developer container at the side facing the latent image carrier.
The developing device is characterized in that it is made longer than the magnetized length of the pole on the side in contact with the end seal member. 2. A developer container containing at least a developer, a rotatable developer carrier, and a magnetic field generating means fixedly arranged in the developer carrier and having a plurality of magnetic poles in the circumferential direction.
In a developing device having a regulating member that is in contact with the surface of the developer carrier to regulate the layer thickness of the developer, and an end seal member that is disposed in contact with the developer carrier at the opening of the container, the magnetic field The magnetizing length in the longitudinal direction of the generating means is set such that, of the poles in contact with the end seal member, the pole upstream of the regulating member is longer than the opening of the developer container and shorter than the outer end of the end seal member. Further, the developing device is characterized in that the magnetic flux density outside the image area is at least smaller than the inside thereof. 3. A process cartridge comprising at least a developing device and detachable from an image forming apparatus main body, wherein the developing device is the developing device according to claim 1 or 2.