JP3636590B2 - Development device - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a developing device using a two-component developer in an image forming apparatus using an electrostatic latent image.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, developing devices that perform development using a two-component developer magnetic brush generally have an average particle size of 50 μm to 80 μm, saturation magnetization of 60 emu / g to 70 emu / g, and volume resistance of about 10 ⁷ to 10 ⁸ Ωcm. In many cases, a two-component developer composed of a carrier and a non-magnetic toner is used and a developing device as shown in FIG. 4 is used.
[0003]
This developing device includes a developing container 2, and developer conveying screws 4 and 6 are disposed in the developing container 2. The two-component developer accommodated in the developing container 2 is reciprocated in the developing container 2 by the screws 4 and 6 described above. Further, the developing device rotates in the direction of arrow b so that the developer in the developing container 2 faces the photosensitive drum 100 in order to develop the latent image on the photosensitive drum 100 as an image carrier that rotates in the direction of arrow a. The developer carrying member 10 is conveyed toward the developed portion. Usually, the developer carrying member 10 is a cylindrical developing sleeve 10, and a magnet roller 11 magnetized as magnetic field generating means 11 is provided inside the developing sleeve 10 so as not to rotate with respect to the rotation of the developing sleeve 10. The developer in the developing container 2 is pumped onto the developing sleeve 10 by the N2 pole of the magnet roller 11 and is conveyed on the magnet roller 11 in the order of S2 pole → N3 pole → S1 pole as the developing sleeve 10 rotates. During the transport, the developer is regulated in layer thickness by a regulating blade 30 that is disposed in contact with the developing sleeve 10 in the vicinity of the S2 pole portion in a non-contact manner, and a thin layer of developer is formed on the developing sleeve 10. . The S1 pole located in the developing portion of the magnet roller 11 is a development main pole, and the developer spiked by the S1 pole develops the latent image formed on the photosensitive drum 100, and the developer is then the N1 pole and N2 The developer is removed from the developing sleeve 10 by the repulsive magnetic field of the pole, and the developer falls back into the developing container 2.
[0004]
[Problems to be solved by the invention]
However, in such a conventional developing device, a large amount of the developer remaining regulated by the regulating blade 30 is held near the upstream side in the rotation direction of the developing sleeve 10 of the regulating blade 30 by the magnetic force of the S2 pole and the N2 pole. Further, the developer is successively conveyed by the rotation of the developing sleeve 10 and is retained on the inner surface of the regulating blade 30, so that a large pressure is applied thereto.
[0005]
Therefore, a large pressure is applied between the magnetic carrier and the resin toner on the developer collected in the vicinity of the regulation blade 30, and fine powder particles such as SiO ₂ added to the resin toner are embedded in the resin toner. Phenomenon occurs. Further, the shape of the resin toner itself is rounded due to the collision with the magnetic carrier. Further, when used for a long time, a so-called spent phenomenon occurs in which the resin toner adheres to the surface of the magnetic carrier and cannot be removed.
[0006]
When such a phenomenon occurs, the charge amount of the resin toner, so-called tribo changes with use time, the image density changes, the mechanical adhesion of the resin toner to the magnetic carrier or the photosensitive drum 100 increases, and the electric field is increased. Corresponding development and transfer are difficult to perform, and so-called unevenness, which is a partial omission of development toner, occurs. That is, with use, the image was very poor in comparison with the initial image.
[0007]
Accordingly, an object of the present invention is to reduce the amount of the two-component developer that accumulates on the upstream side of the regulating blade of the developer container, and to prevent the developer that is successively conveyed from being subjected to a large pressure. It is an object of the present invention to provide a developing device capable of preventing the deterioration of the toner and stably obtaining an image having a sufficient density as in the case of the initial image over a long period of time.
[0008]
[Means for Solving the Problems]
The above object is achieved by the developing device according to the present invention.
That is, according to the present invention, a two-component developer composed of a magnetic carrier and a non-magnetic toner housed in a developer container is carried on a developer carrier having a built-in magnetic field generating means, and the developer carrier is loaded with the developer carrier. The developer regulating means placed in the vicinity controls the thickness of the developer while transporting it to the developing unit facing the image carrier, and the developing unit transfers the latent image formed on the image carrier by the developer. in the developing device for developing, the magnetic carrier has an average particle size of 60μm or less, the saturation magnetization is not more than 50 emu / g, the magnetic field generating means, and at the downstream side in the rotational direction of said developer carrying member than said developing unit a first magnetic field generating means provided in said developer container, is provided downstream in the rotation direction of the developer carrier of the magnetic field generating means of the first, the first magnetic field generating means of the same polarity as the Two magnetic field generating means and the first magnetic field Between the second magnetic field generating means and the raw device, the magnetic flux density in the vertical direction of the developer carrying member surface is not more than 80G, and the magnetic flux density in the horizontal direction and a repulsion pole region is less than 80G , the screw for conveying the repelling poles falling from the area developer is provided, said developer regulating means has a magnetic plate for regulating the developer by magnetic binding force, the second of said developer carrying member It is arrange | positioned in the vicinity of the opposing position of the magnetic field generation means.
[0009]
With such a configuration, the amount of developer pool formed on the upstream side of the developer regulating means is limited to the amount carried only by the second magnetic field generating means. The amount of accumulation is greatly reduced. Further, on the upstream side in the rotation direction of the second magnetic field generating means, the developer is dropped and removed in the above-described region where the magnetic field is small, so that the developer conveyed one after another is not pushed by a large pressure.
[0010]
Further, when a carrier having an average particle size of 60 μm or less and a saturation magnetization of 50 emu / g or less is used as the magnetic carrier, the force attracted to the magnetic field generating means is weak, and a greater pressure is not applied to the developer. . That is, a developing device that does not deteriorate the developer over a long period of time becomes possible.
[0011]
The amount of magnetization of the magnetic carrier is obtained by obtaining the strength of magnetization of the carrier packed in a cylindrical shape in an external magnetic field of 1 kilo-Oersted by an oscillating magnetic field type automatic magnetic recording device manufactured by Riken Denshi Co., Ltd. .
[0012]
However, as in the present invention, when the developer is regulated in a state where the developer pool is small, the desired layer thickness (about 45 mg / cm) is required unless the distance between the regulating blade and the developer carrier is reduced to 200 μm to 400 μm. ² ) Cannot be regulated. However, when the distance between the regulating blade and the developer carrying member is 400 μm or less and image formation is performed over a long period of time, white streaks due to developer blockage in the regulating portion may occur.
[0013]
Therefore, according to the present invention, the second magnetic field generating means has a vertical maximum magnetic flux density of 500 gauss or more on the surface of the developer carrying member, and a range of 80% or more of the vertical maximum magnetic flux density is 20 degrees or more. Is. By disposing the regulating blade as the developer regulating means at the opposite portion of the magnetic field generating means, the regulating blade is easily magnetized and the magnetic restraining force is increased. Therefore, even if the distance between the regulating blade and the developer carrying member is 400 μm or more, the desired layer thickness can be regulated.
[0014]
However, simply widening the width of the second magnetic field generating means narrows the small magnetic field region between the first magnetic field generating means and the second magnetic field generating means, and the developer can be completely dropped and removed. There is a case in which a so-called ghost phenomenon occurs because the dropped developer is pumped up again by the second magnetic field generating means before being stirred with the developer in the screw.
[0015]
As a method for preventing this, in the present invention, the second magnetic field generating means has a vertical maximum magnetic flux density of 500 gauss or more on the surface of the developer carrying member, and a range of an area of 80% or more of the vertical maximum magnetic flux density. The range of 20 ° or more and 50% or more of the maximum magnetic flux density in the vertical direction is set to 45 ° or less.
[0016]
Further, the configuration of the present invention can make the developer pool small, but if the developer pool is made too small, the thickness of the developer layer may be uneven. As a method for preventing this, it is preferable to dispose the developer regulating means slightly downstream in the rotational direction from the magnetic flux density peak position of the second magnetic field generating means, and the developer is located in a region where the magnetic binding force is large. It is preferable to arrange a regulating means.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 1 is a longitudinal sectional view of the developing device according to the first embodiment of the present invention.
[0018]
The developing device of the present embodiment includes a developing container 2 containing a two-component developer composed of a magnetic carrier having an average particle diameter of 40 μm, a saturation magnetization of 60 emu / g, and a volume resistance of 10 ⁷ Ωcm, and a nonmagnetic resin toner. A developing sleeve 10 is provided in the developing container 2 so as to face the photosensitive drum 100 rotating in the direction of arrow a.
[0019]
The developing sleeve 10 as a developer carrying member is made of a nonmagnetic material such as SUS316 and is rotated in the direction of arrow b. A magnet roller 11 having five magnetic poles (S 1, S 2, N 1, N 2, N 3) is provided as a magnetic field generating means 11 in the developing sleeve 10 so as not to rotate.
[0020]
The developer in the developer container 2 is transported from the back side to the near side while being stirred by the developer transport screw 6 provided in the developer container 2. At this time, a part of the developer is N3 of the magnet roller 11. Pumped by the pole. Here, the maximum magnetic flux density in the vertical direction on the surface of the developer carrier of N3 pole is 600 gauss, and the range of 80% or more of the maximum magnetic flux density in the vertical direction is 25 degrees, and the area of 50% or more is 40 degrees. It is.
[0021]
The developer pumped up is regulated to a layer thickness of about 45 mg / cm ² by the regulating blade 30 arranged so that the nearest contact point is located at a distance of 550 μm from the developing sleeve 10 5 degrees downstream of the N3 pole. Is done. The regulating blade 30 is obtained by adhering a magnetic plate 30b having a thickness of 0.3 mm to the inner wall surface of the nonmagnetic blade 30a, and the developer is regulated by a magnetic field formed between the N3 pole and the magnetic plate 30b.
[0022]
The developer whose layer thickness is regulated is conveyed from the S2 pole to the N1 pole, and the latent image on the photosensitive drum 100 is developed in the vicinity of the S1 pole which is the development pole. The developer that has passed through the developing unit is conveyed to the N2 pole, and the vertical magnetic field strength Br on the developing sleeve 10 between the N2 and N3 poles is 50 G or less and the horizontal magnetic field strength is 50 G. In the following area, it falls from the developing sleeve 10, is transported to the back side by the screw 7 provided below the developing sleeve 10, and is delivered to the screw 6.
[0023]
According to the present embodiment, the regulating blade 30 regulates the developer in the vicinity of the facing position of the N3 pole located downstream in the rotation direction of the developing sleeve 10 among the two magnetic field generating means of the same polarity (N2, N3). Thus, among the remaining developer that is not applied on the developing sleeve 10 due to the restriction by the restriction blade 30, the developer that cannot be held by the N3 pole quickly falls onto the screw 6. A large reservoir of developer does not occur near the downstream side of the sleeve 10 in the rotational direction.
[0024]
Further, since the developer is dropped and removed between the N2 and N3 electrodes, the developer is conveyed one after another as in the prior art, and a large pressure is not applied to the developer. Thereby, it is possible to prevent the deterioration of the magnetic carrier and the non-magnetic toner.
[0025]
Further, according to the experimental results, the developer developing level determined from the idling time of the developing device and the obtained image quality is the same as that of this embodiment in the conventional developing device shown in FIG. In comparison, in the developing device of the present embodiment, almost the same developer deterioration occurred in the idling time about 6 times that in the conventional developing device.
[0026]
Further, when an experiment was performed using a magnet roller 11 having a different N3 pole magnetic flux density distribution as shown in FIGS. 2 and 5, an area of 80% or more of the maximum vertical magnetic flux density on the developing sleeve surface of the N3 pole was obtained. If the range is not 20 degrees or more, the distance between the developing sleeve 10 and the regulating blade 30 for regulating the developer to 45 mg / cm ² , which is a layer thickness suitable for this apparatus, could not be 400 μm or more.
[0027]
Further, it has been confirmed that a ghost image is generated unless a region of 50% or more of the maximum magnetic flux density in the vertical direction on the surface of the developing sleeve 10 of the N3 pole is set to 45 degrees or less. These phenomena are considered to occur for the reasons described above.
[0028]
(Second Embodiment)
As shown in FIG. 3, the present embodiment is a developing device using a developing sleeve 10 that rotates in the counter direction in the developing unit with respect to the photosensitive drum 100 that rotates in the direction of arrow a.
[0029]
In the developing device having such a configuration, the regulating blade 30 can be disposed in the vicinity of the lowest point in the vertical direction of the developing sleeve 10, and it is not necessary to pump up the developer against the gravity from the screw 6a. Even a developer using a magnetic carrier having a diameter of 60 μm or less and a saturation magnetization of 50 emu / g or less and a small saturation magnetization can be pumped stably.
[0030]
When such a carrier having a small magnetization amount is used, the pressure applied to the developer is further reduced, and the deterioration of the toner is further reduced.
[0031]
The N3 pole of the magnet roller 11 used in the present embodiment has a maximum vertical magnetic flux density of 600 gauss (G) on the surface of the developer carrying member, as in the first embodiment, and the vertical direction The region of 80% or more of the maximum magnetic flux density is 25 degrees, and the region of 50% or more is 40 degrees. The regulating blade 30 is downstream of the developing sleeve 10 in the rotation direction from the vertical maximum magnetic flux density position of the N3 pole. It is arranged at a position of 10 degrees.
[0032]
Further, according to the experimental result, even when the magnetic field generating means having a range of 80% or more of the maximum magnetic flux density in the vertical direction is 20 degrees or more, the developing sleeve 10 within the range of the 80% or more region is used. The distance between the developing sleeve 10 and the regulating blade 30 could not be 400 μm or more unless the regulating blade 30 was disposed at the opposing position.
[0033]
Further, if the regulating blade 30 is disposed from the maximum magnetic flux density position of the N3 pole on the upstream side in the rotation direction of the developer carrying member, the developer accumulation is excessively reduced, resulting in uneven thickness of the regulated developer layer. In some cases, it may be arranged downstream of the maximum magnetic flux density position.
[0034]
【The invention's effect】
According to the first aspect of the present invention, since the amount of the developer pool formed on the upstream side of the developer regulating means is limited to the amount carried only by the second magnetic field generating means, development is conventionally performed. The amount of agent pool is greatly reduced. Further, on the upstream side in the rotation direction of the second magnetic field generating means, the developer is dropped and removed in the region where the magnetic field is small, so that the developer conveyed one after another does not give a large pressure. That is, a developing device that does not deteriorate the developer over a long period of time becomes possible.
Further, since the magnetic carrier has a small amount of magnetization, the force attracted to the magnetic field generating means is weaker than before, and the pressure applied to the developer is further reduced. That is, a developing device that does not deteriorate the developer over a long period of time becomes possible.
[0035]
According to the second and third aspects of the invention, image defects such as white stripes and ghosts can be prevented.
[0036]
According to the fourth aspect of the invention, even if the developer pool is small, the thickness of the developer layer is not uneven.
[0037]
According to the fifth aspect of the present invention, since the two-component developer comprising the magnetic carrier and the non-magnetic toner having the average particle diameter of 60 μm or less and the saturation magnetization of 50 emu / g or less is used, upstream of the developer regulating means. The amount of developer pool formed on the side is further reduced.
[Brief description of the drawings]
FIG. 1 is a configuration diagram showing a developing device according to a first embodiment of the present invention. FIG. 2 shows a result of magnetic flux density distribution at the N3 pole of a magnet roller in an experiment of the first embodiment according to the present invention. FIG. 3 is a block diagram showing a developing device according to a second embodiment of the present invention. FIG. 4 is a block diagram showing a conventional developing device. FIG. 5 is a diagram showing the first and second embodiments of the present invention. The figure which shows the experimental result of embodiment of [Description of code]
2 ... developing containers 6, 7 ... screw 10 ... developing sleeve (developer carrier)
11: Magnet roller (magnetic field generating means)
30 ... Regulating blade (developer regulating means)
30a ... Non-magnetic blade (developer regulating means)
30b ... Magnetic plate (developer regulating means)
100: Photosensitive drum (image carrier)

Claims (4)

A two-component developer composed of a magnetic carrier and a non-magnetic toner contained in a developer container is carried on a developer carrier having a built-in magnetic field generating means, and is installed in the vicinity of the developer carrier. In a developing device that transports to a developing unit facing an image carrier while regulating the thickness of the developer by a developer regulating unit, and develops a latent image formed on the image carrier by the developer at the developing unit. the magnetic carrier has an average particle size of 60μm or less, the saturation magnetization is not more than 50 emu / g, the magnetic field generating means, a downstream side in the rotational direction of the developer carrying member than said developing unit and said developer container a first magnetic field generating means provided, provided downstream in the rotation direction of the developer carrier of the magnetic field generating means of the first and second magnetic field generating means of said first magnetic field generating means and the same polarity , The first magnetic field generating means and the second magnetic field generating means Between the field generating means, the magnetic flux density in the vertical direction of the developer carrying member surface is not more than 80G, and the magnetic flux density in the horizontal direction and a repulsion pole region is less than 80G, dropped from the repelling electrode area provided screw for conveying the developer is the developer regulating means comprises a magnetic plate for regulating the developer by the magnetic binding force, a position facing the second magnetic field generating means of the developer carrier A developing device arranged in the vicinity. Said second magnetic field generating means in the developer ranges vertical maximum magnetic flux density of 80% or more of the magnetic flux density of the maximum magnetic flux density is 500 gauss or more regions on the carrier surface is 20 degrees or more, 50% or more The developing device according to claim 1, wherein the area is 45 degrees or less. Said developer regulating means, according to claim 1, characterized in that it is arranged in a position facing the surface of the developer carrying member of the region of 80% or more of the vertical maximum magnetic flux density of the second magnetic field generating means or 2. The developing device according to 2. Said developer regulating means, at the downstream side in the rotational direction of the developer carrier from the opposing position of maximum magnetic flux density position of the second magnetic field generating means, a position facing region of 80% or more of maximum vertical magnetic flux density 4. The developing device according to claim 1, wherein the developing device is arranged.

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