JP2003021968A - Developing device - Google Patents

Abstract

(57) [Summary] [Problem] To prevent developer leakage at a screw end. SOLUTION: A ring magnet for a magnetic seal provided for preventing leakage of a developer is set so that a repulsive magnetic field is generated.
Are arranged facing each other.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is characterized by an electrophotographic type or electrostatic recording type image forming apparatus such as a copying machine or a printer, and in particular, a developing apparatus.

[0002]

2. Description of the Related Art A rotatable developer carrying member carrying and transporting a developer carries a developer at a developer layer thickness regulating portion provided at a container outlet position for carrying the developer from the container toward a developing portion. A developing device in which a magnetic material (hereinafter referred to as a regulation blade) is arranged along the longitudinal direction of the member is general. This magnetic material is arranged in the magnetic field of the magnet arranged inside the developer carrying member, and also contributes to regulating the developer to a proper layer thickness.

By the way, a technique for preventing the developer from leaking out of the container from the longitudinal end of the developer carrying member has already been applied for in Japanese Patent Application No. 1-82849.

In the technique described in this prior application, a ferromagnetic material member such as iron is arranged opposite to the end portion of the developer carrying member, and the ferromagnetic material member and a magnet arranged inside the developer carrying member are disposed. A magnetic brush of developer is formed by the magnetic field formed between the two, and the magnetic brush prevents the developer from leaking from the end portion of the developer carrying member.

On the other hand, in the container containing the developer,
In addition to the developer carrying member, like a screw or a shaft with fins, the developer is stirred by rotating,
A rotary member that conveys in the longitudinal direction of the developer carrying member is provided, and such a rotary member is supported by bearings provided on the side wall of the container. Therefore, a method of sealing the rotating shaft of the rotating member and the developer near the bearing, which has been conventionally used, is shown below.

First, the conventional example using the elastic seal member (oil seal) shown in FIG. 9a is excellent in the developer sealing effect, but in order to obtain the sealing effect, the rotary shaft 20 contacting the elastic sealing member is used. The accuracy of the surface property must be improved, and the processing cost increases and the rotating shaft 20
As the sliding friction with the above is repeated, the contact portion is worn and damaged, and the contact pressure is deformed due to the circulating pressure of the developer, and the sealing effect becomes weak.

If the close contact between the end seal member and the rotary shaft is increased in order to prevent the above problems, a large force is applied to the screw rotary shaft, and the load on the screw drive motor increases. In any case, the toner rubs against the rubbing portion between the seal and the shaft, and fine agglomerates of the toner are generated.

When the toner agglomerates are large, the developer is not coated on the developer carrying member by being restrained by the regulating blade portion, which may cause white streaks on the image. . If the aggregates are small, they are developed together with the developer, and especially in the case of a solid image, transfer voids occur around the developed aggregates.

In particular, in recent years, colorization has progressed in printers, copying machines and the like, and higher image quality is required.
Therefore, a toner having an average particle diameter of 8 μm or less is often used, or a polyester resin having a sharp melting property suitable for a full-color image is often used as a binder. However, since the above toners generally tend to aggregate,
At present, it is easy to generate the above-mentioned micro-aggregates.

[0010]

The generation of aggregates in the above example is caused by the contact between the end seal member and the rotary shaft. Therefore, recently, a magnetic brush is formed between the rotary shaft and the fixed magnet ring by non-contactly fixedly disposing the magnet ring facing the rotary shaft 20 made of a magnetic material as shown in FIG. 9b. A developing device has been proposed in which the leakage of the developer is prevented by a brush.

However, in the above construction, it is still difficult to obtain a satisfactory sealability of the developer, and the developer, which once lost the restraining force by the magnetic brush, is fixed to the ball bearing constituting the bearing portion. Accumulated in the magnet, the load on the screw drive motor increased, and the leaked developer mixed in the ball bearing, which sometimes caused ball bearing lock.

Therefore, an object of the present invention is to prevent the developer from leaking from the longitudinal end of the rotating member easily without increasing the driving load of the member rotating in contact with the developer in the container. It is to provide a device.

[0013]

The above object can be achieved by an image forming apparatus according to the present invention. In summary, the present invention provides a container for accommodating a developer containing magnetic particles, a rotating member that is supported by a bearing portion and is rotatable in contact with the developer in the accommodating container, and close to the bearing portion. And a non-rotating magnet member surrounding the rotating member at a position inside the container with respect to the bearing portion, the rotating shaft of the rotating member includes a ferromagnetic material magnetized by the magnet member, The magnet member is a developing device in which two magnet members are opposed to each other so that a repulsive magnetic field is formed between the magnets, and a predetermined space is provided between the magnets.

According to one embodiment of the present invention, the surface magnetic flux density of the repulsive magnetic field forming magnet can be changed by the magnet close to the bearing portion and the magnet close to the container side.

According to another embodiment of the present invention, in the repulsive magnetic field forming magnet, the magnet provided on the container side can be arranged with a predetermined gap outside the container wall.

According to another embodiment of the present invention, the developer comprises toner particles and carrier particles, and the magnetic particles are the carrier particles. The toner particles may have an average particle diameter of 4 to 10 μm, and the carrier particles may have an average particle diameter of 30 to 80 μm.

According to another embodiment of the present invention, the amount of magnetization of the carrier particles can be set to 60 Am2 / Kg or less.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of an image forming apparatus according to the present invention will be described below in detail with reference to the drawings.

(Embodiment 1) As an example of an image forming apparatus to which the present invention can be applied, an overall schematic configuration of a full-color electrophotographic copying machine is shown in FIG. In FIG. 2, a photosensitive drum 1, which is an image carrier, is rotatably supported in a direction of an arrow, and an image forming unit described below is arranged around the shaft.

Around the photosensitive drum 1, primary chargers 2 and 2 are provided.
Component developing device yellow developing device 4Y, magenta developing device 4
M, a cyan developing device 4C, and a black developing device 4K are detachably arranged, and further, a transfer drum 7, a cleaning device 1
0 is arranged, a transfer material conveying roller 6 is provided between the black developing device 4K and the transfer drum 7, and a transfer charger 8 is provided inside the transfer drum 7 of the image transfer portion facing the photosensitive drum 1.
Further, at a position apart from the upper portion of the transfer drum 7, the fixing device 12
Are arranged respectively. Developing devices 4Y, 4M, 4C,
4K is a developing sleeve 5 as a developer carrying member.
It has Y, 5M, 5C and 5K.

The operation of the above image forming apparatus will be described below.
First, the primary charger 2 uniformly charges the surface of the photosensitive drum 1. Then, a yellow electrostatic latent image is formed on the photosensitive drum 1 by irradiating the laser light L in accordance with a digital signal from a reader (original reading device) (not shown) or a controller. This electrostatic latent image is brought into contact with a yellow developing device 4Y containing a two-component developer of a non-magnetic toner and a magnetic carrier, which are negatively charged, at a developing position, and is subjected to reversal development on the photosensitive drum 1 to thereby make a yellow color. Form a toner image.

On the other hand, in synchronism with the image, the transfer roller P supplies the transfer material P to the area where the photosensitive drum 1 and the transfer drum 7 contact each other by the conveying roller 6, and makes the transfer material P carried on the transfer drum 7. The yellow toner image on the photosensitive drum 1 is transferred onto the transfer material by the action of the transfer charger 9 by being conveyed to the image transfer portion facing the photosensitive drum 1 by rotation. After the transfer of the yellow toner image is completed, the residual toner on the surface of the photosensitive drum 1 is cleaned by the cleaning device 10, the pre-exposure device 11 removes the charge, and the photosensitive drum 1 is used again in the image forming process.

Thereafter, the same operation as described above is repeated for magenta, cyan and black in this order to obtain a color image in which four color toner images of yellow, magenta, cyan and black are superposed and transferred on the transfer material. The transfer material on which the four color toner images have been transferred is next transferred onto the transfer drum 7.
The toner image is separated and sent to the fixing device 12, where the toner image is fixed on the transfer material and mixed to form a full-color permanent image, and then discharged to the outside of the image forming apparatus.

FIG. 3 is a sectional view of one developing device shown in FIG. This developing device has a developing container 40 containing a two-component developer D. In the developing container 40, a developing sleeve 46 that carries and conveys the developer D to the developing portion 101 facing the photosensitive drum 1 in order to develop the latent image on the photosensitive drum 1 is provided with an opening portion of the developing container 40. Is rotatably provided in the direction of arrow b.

The developing sleeve 46 is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (for example, SUS316). A roller-shaped magnet is fixedly arranged inside the sleeve 46. In addition, the container 4 above the developing sleeve 46
At the developer outlet from 0, a regulating blade 4 as a developer layer regulating member for regulating the amount of the developer on the developing sleeve 46.
7 is attached to the container with a predetermined gap from the sleeve.

The regulating blade 47 is made of a non-magnetic material such as aluminum or non-magnetic stainless steel (for example, SUS316), or a ferromagnetic material such as iron, nickel, cobalt, or an alloy thereof, and is provided between the regulating blade 47 and the developing sleeve 46. The amount of developer that is conveyed to the developing section due to the size of the gap
Specifically, the thickness of the developer on the developing sleeve 46 is regulated. Therefore, in this embodiment, the developer including the non-magnetic toner and the magnetic carrier particles is applied to the developing sleeve 46 between the tip of the regulating blade 47 and the surface of the developing sleeve 46.
The toner is carried on the sheet, passes through, and is sent to the developing section 101.

With this structure, as in the conventional case, the developer drawn up by the N2 pole by the rotation of the developing sleeve 46 is conveyed from the S2 pole to the N1 pole, and is regulated by the regulation member 47 in the middle thereof, so that the developer is thin. Form the layers. The S1 pole is a developing magnetic pole, and the developer that stands up in the magnetic field of the magnetic pole develops the electrostatic latent image on the image carrier 1. After that, the developer on the developing sleeve 46 falls into the developing container 40 due to the repulsive magnetic field between the N3 pole and the N2 pole.

An AC voltage on which a DC voltage is superimposed is applied to the developing sleeve 46 as a bias voltage from the power source 41, whereby an alternating electric field whose direction changes alternately is formed in the developing section 101. During this alternating electrolysis, the toner and the carrier violently vibrate, and the toner sticks to the drum 1 corresponding to the latent image by shaking off the restraining force on the developing sleeve and the carrier. In the container, a first rotating screw 42 and a second rotating screw 43 as stirring members for stirring the developer in the developing container 40 and supplying the developer to the developing sleeve 46 are substantially in the longitudinal direction of the sleeve 46, respectively. Are arranged in parallel.

The screw 42 returns to the inside of the container 40 after passing through the developing portion 101, receives the developer separated from the sleeve 46 by the repulsive magnetic field between the N2 pole and the N3 pole, and agitates the developer, so that the longitudinal direction of the sleeve. Transport to.

The screw 43 stirs the fresh toner and the developer supplied from the hopper (not shown), and the screw 4
By 2 the developer is conveyed in the opposite direction. There is a partition wall 44 between the screws 42 and 43. The partition wall 44 is provided with openings (not shown) in the vicinity of both ends in the longitudinal direction of the screw. The developer is transferred to and from the screws 43 to 42. That is, the developer circulates in the container 40. The developer agitated by the screws 42 and 43 is
Sleeve 4 from near the screw 42 by the magnetic force of N2 pole
Pumped up to 6. During the stirring, the toner in the developer is triboelectrically charged to a polarity that develops the latent image by friction with the carrier.

The developer D is a two-component developer composed of an insulating non-magnetic toner and magnetic particles (carriers). The non-magnetic toner preferably has a weight average particle size of 4 μm or more and 10 μm or less. . In this embodiment, a toner for a color copying machine having a weight average particle diameter of 8 μm and a weight average particle diameter of 50 are used.
A μm carrier was used.

FIG. 1 shows a rotary member and its bearing portion, which are the characteristic parts of the present invention. In this embodiment, both ends of the rotating shaft 20 of the first screw 42 and the second screw 43, which are rotating members, are rotatably supported by the side wall 40a of the developing container 40 via ball bearings 24, which are bearing members. The stop ring 25 restricts the movement of the rotary shaft 20 in the axial direction. The bearing member 24 is fixed to the container side wall 40a which is a non-magnetic material such as synthetic resin. Incidentally, FIG.
Shows only one end side of the shaft 20, but the other end side is also configured in the same manner. This also applies to other drawings.

With respect to the longitudinal direction of the shaft 20, two cylindrical magnet rings 22 and 23, which are characteristic of the present embodiment, are provided inside the container rather than the ball bearing 24. Is fixed to the container side wall 40a. Further, the inner peripheral surfaces of the magnet rings 22 and 23 are opposed to the shaft 20 with a gap. In this embodiment, the magnet ring is magnetized in the thickness direction of the shaft 20, and in FIG. 1, the magnet ring 22 is magnetized on the surface facing the inside of the container in order from N pole to S pole, and the magnet ring is also magnetized. 23 is the south pole,
By arranging the magnets so that the N poles are magnetized in this order, a repulsive magnetic field is generated in the magnet rings 22 and 23. Of course, the magnet ring 22 may be magnetized to the S pole and N pole from the surface facing the inside of the container, and the magnet ring 23 may be magnetized to the N pole and S pole.

With this structure, the ferromagnetic rotation shaft 20 is magnetized by the magnetic force of the magnet rings 22 and 23, and the magnet ring 2
A magnetic circuit is formed between the magnetic rotating shafts 20 and 23 and the magnetic rotating shaft 20, and a repulsive magnetic field is generated by the magnet rings 22 and 23 facing each other with the same poles (S poles in this embodiment). Can easily stand toward the shaft 20. However, due to the repulsive magnetic field between the magnet rings 22 and 23, the developer D
Cannot enter the magnet ring 23 side, and as a result, as shown in FIG.
As indicated by b, the dense magnetic brush M made of the developer is formed only in the gap between the magnet ring 22 and the ferromagnetic rotary shaft 20.

Further, as shown in FIG. 1, in the present invention, the repulsive magnetic field generating magnet rings 22 and 23 are arranged at a predetermined interval. This is because if the two magnets are adhered, the lines of magnetic force concentrate on the outer peripheral end surface of the magnet ring as shown in FIG. 5, so the developer sealing property can be improved, but the magnetic brush width W (indicated by W in the figure). There is a problem that there is less. Therefore, there arises a problem that the magnetic brush is apt to be cut by the rotation of the rotary shaft and the pressing force of the developer.

In this example, a magnetic carrier having a carrier particle size of 40 μm and a magnetization amount of 58 Am2 / Kg was used. It has been found that under the above conditions, the sealability can be secured by providing the magnetic brush width W at least twice the magnet ring thickness.

Therefore, in the present embodiment, magnet rings having a thickness of 2 mm are installed at a predetermined interval (2 mm in the present embodiment), and the inner diameter of the spacer ring used for making the predetermined interval is made wider than the inner diameter of the magnet ring (the present In the example, the inner diameter of the magnet ring was 6φ, the outer diameter was 12φ, the spacer ring inner diameter was 10φ, and the outer diameter was 12φ with respect to the rotation axis of 4φ.

By adopting this structure, it is possible to secure a sufficient magnetic brush width W while improving the magnetic sealing property due to the repulsive magnetic field, and it is possible to achieve a very strong sealing property as compared with the conventional example. This is based on the carrier particle size, the amount of magnetization used, and the surface magnetic flux density of the magnet ring (45 m in this embodiment).
Needless to say, this can be achieved by appropriately setting the optimum interval according to T) and forming a good magnetic brush width.

According to the results of the experiments conducted by the present inventors, the developer leaked to the magnet ring 23 adhered to the magnet ring 23, although the amount was very small, when the images were continuously printed on 500,000 sheets. This is due to the developer breaking the restraint of the magnetic brush by the magnet ring 22. However, with 500,000 sheets, problems such as generation of a melt and stopping of rotation of the ball bearing 24 did not occur.

(Embodiment 2) In this embodiment, based on the results of Embodiment 1, the surface magnetic flux densities of the magnet rings 22 and 23 used are changed in order to achieve higher sealing performance. In particular, the magnet ring 23 close to the ball bearing 24
The surface magnetic flux density of was set to be larger than the surface magnetic flux density of the magnet ring 22 near the container side. Specifically, the surface magnetic flux density is 45
A magnet ring having a surface magnetic flux density of 23 mT and a surface magnetic flux density of 60 mT was used.

FIG. 6 shows changes in the direction of magnetic force lines according to this embodiment. As is clear from the figure, the magnetic lines of force further extend toward the inside of the container, and the effect of sealing is improved.

According to the results of experiments conducted by the present inventors, the magnet ring 2 is completely used even when images are continuously displayed on 500,000 sheets.
No developer adhered to No.3.

Recently, as a technique for extending the life of the developer, studies using a low-magnetization carrier, which can be lightly loaded, have been advanced. However, when a low-magnetization carrier is used, the magnetic brush seal has a problem that the magnetic binding force is small and the sealing force becomes weak.

FIG. 7 shows the result of the sealing force of the above-mentioned embodiment due to the difference in the amount of magnetization of the magnetic carrier. ◎ in the figure is 50
In the case where there is no magnetic brush on the magnet ring 23 even after the endurance of 10,000 sheets, ◯ indicates that the developer is slightly attached to the magnet ring 23, and ◯ Δ indicates that the magnetic brush is formed. From the above, it was found that this structure has a sufficient sealing force even if a low-magnetization carrier is used.

(Embodiment 3) In the above Embodiment 2, the magnetic lines of force extend toward the inside of the container, so that the sealing property is increased. However, as a result, strong rubbing occurs between the developer conveying screw end portion 26 attached to the rotating shaft (usually a return member is provided so that the developer does not enter the end seal) and the magnetic brush, In some cases, the temperature was raised at the end of the screw, the toner was melted, and screw lock occurred.

Therefore, in this embodiment, in order to provide a gap between the magnet ring 22 and the screw end portion 26 as shown in FIG. 8, the magnet ring 22 is displaced toward the bearing side by 3 mm. As a result, the rubbing between the magnetic brush and the end of the screw was weakened, and the screw lock was not generated. Of course, since the magnetic seal due to the repulsive magnetic field is high, the developer does not leak to the bearing portion.

[0047]

As is apparent from the above description, the image forming apparatus according to the present invention includes a container for accommodating a two-component developer containing magnetic particles, and a bearing portion for supporting the developer in the container. In a developing device having a rotating member that is rotatable in contact with the rotating member and a non-rotating magnet member that surrounds the rotating member in a position closer to the bearing portion and inside the storage container than the bearing portion, The rotating shaft is provided with a ferromagnetic material magnetized by the magnet member, and the magnet member faces two magnet members so that a repulsive magnetic field is formed by the magnets, and a predetermined space is provided between the magnets. With the developing device provided and arranged, it is possible to easily prevent the developer from leaking from the end portion in the longitudinal direction of the rotating member, without significantly increasing the driving load of the rotating member.

Further, the sealing property can be improved by changing the surface magnetic flux density of the repulsive magnetic field forming magnet between the magnet close to the bearing portion and the magnet close to the container side.

Further, when the average particle size of the toner particles in the two-component developer is 4 to 10 μm and the average particle size of the carrier particles is 30 to 80 μm, a better sealing property is maintained.

Even if a low-magnetization carrier of 60 Am2 / Kg or less is used, good sealing property can be maintained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an end portion of a rotary shaft of a rotary member of a developing device according to the present invention.

FIG. 2 is a schematic configuration diagram of a color electrophotographic copying machine to which the present invention can be applied.

FIG. 3 is a cross-sectional view of a developing device showing an embodiment of the present invention.

4A and 4B are explanatory views showing lines of magnetic force by a repulsive magnetic field generating magnet applied in the first embodiment.

FIG. 5 is an explanatory diagram showing a magnetic brush width.

FIG. 6 is an explanatory view showing lines of magnetic force by a repulsive magnetic field generating magnet applied in the second embodiment.

FIG. 7 is an explanatory diagram showing sealing performance when a low magnetization carrier is used in the second embodiment.

FIG. 8 is a sectional view showing an end portion of a rotary shaft of a rotary member applied in the third embodiment.

9A and 9B are cross-sectional views showing a rotary shaft end portion of a rotary member of a conventional developing device.

[Explanation of symbols]

1 Photosensitive drum (image carrier) 4 developing device 20 rotation axis 22,23 Magnet ring 24 ball bearings 26 Screw end 40 developer container 42,43 screw D developer P transfer material

Claims (5)

[Claims] 1. An accommodating container for accommodating a two-component developer containing magnetic particles, a rotating member supported by a bearing portion and rotatable in contact with the developer in the accommodating container, and in proximity to the bearing portion. And a non-rotating magnet member surrounding the rotating member at a position inside the container with respect to the bearing portion, the rotating shaft of the rotating member includes a ferromagnetic material magnetized by the magnet member, In the developing device, two magnet members are opposed to each other so that a repulsive magnetic field is formed between the magnet members, and a predetermined space is provided between the magnet members. 2. The developing device according to claim 1, wherein the surface magnetic flux density of the repulsive magnetic field forming magnet is changed by a magnet close to the bearing portion and a magnet close to the container side. 3. The developing device according to claim 1, wherein in the repulsive magnetic field forming magnet, the magnet provided on the container side is arranged with a predetermined gap outside the container wall. 4. The two-component developer comprises toner particles and carrier particles, and the average particle diameter of the toner particles is 4 to 10.
μm, and the average particle size of the carrier particles is 30 to 80.
The developing device according to claim 1, wherein the developing device has a thickness of μm. 5. The magnetization amount of the carrier particles is 60 Am2.
5. The developing device according to claim 4, wherein the developing device is less than or equal to / Kg.