JP2005010290A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent accumulating of small particle toner in developer inside a developing device and to provide an image forming apparatus obtaining a good image without any image deterioration. <P>SOLUTION: Toner particle size distribution is adjusted by a first process of forming a toner layer with a great amount of powder, by periodically applying AC bias voltage having a specified potential difference between a developing roll and a magnetic roll and then rotating for a given period of time and a second process of completing stopping the rotation of the developing roll on which the powder toner layer is formed, having the toner on the developing roll in the position facing a latent image carrier flown to the latent image carrier and completely peeling the toner off the roll. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic system, and particularly uses a two-component developer that charges a nonmagnetic toner using a magnetic carrier. The present invention relates to an image forming apparatus having a developing device in which only a charged toner is held on a developing roll to fly to an electrostatic latent image and the latent image is developed.
[0002]
[Prior art]
Development methods in image forming apparatuses such as copiers, printers, facsimiles, and composite machines using electrophotography are two-component development methods using toner and a magnetic carrier, and one component using insulation toner and conductive toner. Development method, using a two-component developer that charges a non-magnetic toner using a magnetic carrier, holds only the charged toner on the developing roll, and flies to the electrostatic latent image to develop the latent image There is a hybrid development method.
[0003]
The two-component development method has excellent toner chargeability with a carrier, and can have a long lifespan and has the advantage of uniform solid images, but the developing device becomes large and complicated, and toner scattering and carrier pulling occur. However, there is a drawback that the image quality changes depending on the durability of the carrier. In addition, the one-component development system has a compact developing device and excellent dot reproducibility, but has low durability due to deterioration of the developing roll and charge roller, and the cost of consumables is high because the developing device is replaced. There is a disadvantage that selective development occurs. The hybrid development method is a method that has excellent dot reproducibility and can achieve a long life and high-speed image formation. Conventionally, fine powder toner has been added to the developer due to the development ghost and the change in the toner particle size distribution. As a result, the surface of the carrier is contaminated with the fine powder toner, the charge amount is reduced, and there are problems such as scattering of the toner from the developing device and adhesion of the fine powder toner on the developing roll.
[0004]
The hybrid development method has been conventionally studied as a non-contact one-component development means. However, in recent years, as a development method capable of forming a high-speed image, a plurality of color images are formed on a photoconductor (photoconductor). It has also been examined for a one-drum color superposition method that is formed sequentially. In this method, it is possible to form a color image with little color misregistration by accurately superimposing toner on the photoconductor, and has been attracting attention as a technique for improving the color image quality.
[0005]
However, in this one-drum color superposition method, since the developing devices for the number of colors to be used must be arranged around the photoconductor, the photoconductor becomes large, which hinders downsizing of the image forming apparatus. Therefore, a tandem method in which a plurality of electrophotographic process members corresponding to the color of the toner to be used are arranged side by side, a color image is formed in synchronization with the transfer of the transfer member, and the color is superimposed on the transfer member has attracted attention. It was. However, this method has the advantage of being excellent in high speed, but has the disadvantage of increasing the size because the electrophotographic process members for each color must be arranged side by side. As a countermeasure, there has been proposed a small tandem type image forming apparatus in which the intervals between the photosensitive members are narrowed and a downsized image forming unit is arranged.
[0006]
In the small tandem type image forming apparatus configured as described above, it is advantageous to make the developing device a vertical type in order to minimize the size of the image forming unit in the width direction. That is, it is desirable in terms of layout that the developing device is arranged in the upper direction of the photosensitive member. However, in the conventional two-component development system, when the developing device is arranged vertically as described above, the reflux of the developer, that is, the supply from the developer agitating unit to the developing member adjacent to the photosensitive member becomes complicated. There is a problem that there is a limit to downsizing and carrier adhesion to the photosensitive member and toner scattering are unavoidable.
[0007]
As another method, a one-component developing method that does not use a carrier has been proposed, but the method in which the developing roll is in contact with the photosensitive member causes torque fluctuations of the photosensitive member, and promotes color misregistration that is a weak point of the tandem type. There was a drawback. In the non-contact system, the toner is charged by the charge roll, and the layer thickness on the developing roll is regulated by the elastic regulating blade, so that the toner additive adheres to the charge roll and the charging ability is reduced. The toner may adhere to the regulation blade and the layer formation may become non-uniform, resulting in image defects.
[0008]
For this reason, the above-described hybrid development method has attracted attention as one means for solving these problems. In other words, the hybrid developing system can provide a high-speed image forming apparatus that does not cause torque fluctuation because the developing roll is not in contact with the photosensitive member, has excellent dot reproducibility, and can extend the life.
[0009]
However, in this hybrid type developing device, coarse particles of highly developable toner are easily selectively developed on the photoconductor, and selective development occurs and the toner particle size distribution changes as described above. There is a problem in that the amount of fine toner increases and the surface of the carrier is contaminated to reduce the charge amount, causing the toner to scatter from the developing device and the image density to decrease due to the fine toner adhering to the developing roll. Most of the toner on the development roll is collected by the magnetic brush outside the development time, but if a relatively large amount of fine powder in the toner adheres firmly to the surface of the development roll, the fine powder is collected between short images during continuous printing. It cannot be left on the developing roll. The adhering fine powder toner remaining on the developing roll causes a decrease in the bias of the developing roll, resulting in a decrease in density, a potential difference with the magnetic roll increases, causing carrier pulling, and image defects and toner scattering. Cause. In addition, when a toner consumption area and a non-consumption area are generated on the developing roll, a part of the previous developed image is changed to the next development due to a variation in the toner adhesion state and the toner potential difference on the developing roll. There is also a problem that a phenomenon that sometimes appears as an afterimage (ghost), a so-called history phenomenon, is likely to occur.
[0010]
Of these, the hysteresis phenomenon (ghost) eliminates the potential difference between the magnetic roll and the developing roll outside the development time and collects most of the toner on the developing roll with a magnetic brush, leaving a development history at the next development timing. A method has been proposed in which no image is obtained. Also, with respect to the increase in fine powder toner due to selective development, in Patent Document 1, a fixed amount of development is performed in a hybrid developing device in which an electrode is provided between a developing roll and a photoreceptor to make the toner cloud. A first step of forming a toner layer on the developing roll by transferring a DC-only bias different from the developing step to the magnetic roll and the developing roll to transfer the toner containing fine powder from the magnetic roll to the developing roll, The toner of a large particle size that is easily transferred from the toner layer on the developing roll is returned to the magnetic roll under a bias voltage (the DC bias of the magnetic roll is 0) in the reverse direction to the first step, and only the fine powder toner is returned. The second step that remains on the developing roll and the small particles remaining on the developing roll under a DC superimposed AC bias voltage on the electrode between the developing roll and the photoconductor with the surface potential of the photoconductor cut off The toner is provided a third step of transferring to the photoreceptor, the method to keep the particle size distribution in the developing device toner constant by removing a small particle size toner by the cleaning apparatus is shown.
[0011]
Furthermore, Patent Document 2 includes an electrode-embedded developing roll and a magnetic roll, and a brush is provided between the developing roll and the magnetic roll so that a bias in which an alternating current is superimposed on a direct current can be applied to the electrode of the developing roll. In the hybrid type developing device, in order to prevent selective development and carrier adhesion to the developing roll, an electric field that moves from the magnetic roll to the developing roll is changed from an electric field that moves from the developing roll to the magnetic roll. In order to prevent selective development as a large (duty 30%) in a short time, and utilizing the fact that the carrier and the carrier are less responsive to the electric field than the toner due to the inertia of the toner and the carrier being different, A developing device that prevents the carrier from flying is shown.
[0012]
[Patent Document 1]
JP-A-6-295123 (page 4, FIG. 2)
[Patent Document 2]
JP 2000-250294 A (pages 6-7, FIG. 3)
[0013]
[Problems to be solved by the invention]
However, the devices disclosed in Patent Documents 1 and 2 are developing devices in which an auxiliary electrode is provided between the developing roll and the photosensitive member, or the toner is clouded using an electrode-embedded developing roll, A device provided with an auxiliary electrode made of wire causes the image to deteriorate due to vibration because the wire is very dirty, and the device using the electrode-embedded developing roll also needs to embed the electrode in the developing roller, and AC is applied to this electrode. It is a complicated configuration that requires a brush electrode to supply a bias with superimposed DC, and the electrode is intermittent in the circumferential direction, and the toner adheres to the brush electrode due to dirt or vibration for some reason, and development. If it becomes impossible to contact the electrode of the roll, the toner cannot be controlled at all.
[0014]
The developing device disclosed in Patent Document 1 develops under a bias voltage in the first direction in which toner is transferred from a magnetic roll to a developing roll to form a toner layer on the developing roll, and a bias voltage in the direction opposite to the first step. A second step of returning a large particle size toner, which is easily transferred from the toner layer on the roll, to the magnetic roll; and a small particle size toner remaining on the development roller under a bias voltage between the development roller and the photoreceptor. The fine toner is removed in three steps, the third step of transferring to the photoreceptor, and it is necessary to switch the bias voltage each time, and it is complicated. In this third step, the developing roll and the magnetic roll are rotated. However, the fine powder toner component having the smallest particle size is held densely on the developing roll, and the toner having a large particle size is stacked thereon, and the third step is performed while rotating. In this case, since the developing roller is rotating, the development time is short, and only a large particle size may fly to the photoconductor, and there is a possibility that the finest powder that is most likely to fly will not fly. Furthermore, there is a possibility that the toner layer with much fine powder formed on the developing roller may be peeled off by the magnetic brush carried on the magnetic roller.
[0015]
In the developing device disclosed in Patent Document 2, an electric field (duty 30%) larger than the electric field in the direction from the developing roll to the magnetic roll is applied from the magnetic roll to the developing roll in a short time, and the selected developing or developing roll is applied. However, the amount of fine powder toner in the developer increases and the particle size distribution changes, and the fine powder adheres to the carrier and the charge imparting performance of the carrier deteriorates, which is sufficient for the toner in the developer. No charge is applied, scattering in the machine occurs, the paper transport path is soiled with toner, toner adheres to the paper, color tone is disturbed by scattered toner in the color image forming apparatus, and the image density is constant There is no description about the response to the problem that the image quality deteriorates such as not.
[0016]
Therefore, an object of the present invention is to provide an image forming apparatus capable of preventing a toner having a small particle diameter from accumulating in the developer in the developing apparatus and obtaining a good image without deterioration in image quality. .
[0017]
[Means for Solving the Problems]
In order to solve the above problems, in the present invention,
A developing roll that is disposed opposite to a latent image carrier on which an electrostatic latent image is formed, carries toner on its surface and conveys it, adsorbs and conveys a two-component developer containing carrier and toner, A magnetic roll that is supplied to the developing roll, and is used in an image forming apparatus having a developing device for performing a developing process for developing the electrostatic latent image formed on the latent image carrier,
And a developing device capable of carrying out a first step of carrying toner on the developing roll and a second step of flying toner onto the latent image carrier with the developing roll stopped. And
[0018]
In this way, the first step of forming a fine powdery toner layer and the developing roller are completely stopped, and the toner on the developing roller at a position facing the latent image carrier is ejected onto the latent image carrier. In a second step, the second step of completely peeling off the toner, the fine toner can be collected on the developing roll and developed on the photoconductor, and the development time, which is a concern when the developing roll is rotated, is short. Because of the time, it is possible to avoid the phenomenon that only particles having a large particle size fly to the photoconductor, and the fine powder that is most desired to fly does not fly. It is possible to provide a toner particle size adjustment method for discharging to the body and reducing it.
[0019]
By repeating the second step by repeatedly rotating and stopping the developing roll in a stepwise manner, the processing of the fine toner over the entire circumference of the developing roll can be easily performed.
[0020]
Further, the image density can be kept constant over a long period of time by periodically performing the first process and the second process.
[0021]
Further, in the first step, the duty ratio of the AC bias applied between the latent image carrier and the developing roller is different from the AC bias applied between the latent image carrier and the developing roller applied during the developing step. As a result, in the first step, more fine toner can be deposited on the developing roll within the same time, and further, the second step is performed to reliably reduce the fine toner in the developing device. An image forming apparatus having the apparatus can be provided.
[0022]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be exemplarily described in detail with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, and the like of the components described in this embodiment are not intended to limit the scope of the present invention only to those unless otherwise specified. This is just an example.
[0023]
FIG. 1 is a schematic configuration diagram of an embodiment of a tandem type image forming apparatus that performs a toner particle size adjusting method according to the present invention, and FIG. 2 is an outline of a hybrid type developing device for performing a toner particle size adjusting method according to the present invention. FIG. 3 is a diagram showing the AC bias when fine toner is collected on the developing roll by the toner particle size adjusting method according to the present invention, and FIG. 4 is when the duty ratio of the AC bias voltage applied to the developing roll is changed. FIG. 5 is a graph showing a change in the amount of fine powder toner in the image forming apparatus in which the toner particle size adjusting method according to the present invention is performed.
[0024]
In FIG. 1, 1 is a tandem image forming apparatus main body, 2 is a developing device, 3 is a photosensitive member (latent image carrier), 4 is an exposure unit, 5 is a conveyance belt for a recording medium, 6 is a developer container, and 7 is a developer container. A paper feed cassette containing a recording medium, 8 is a charger for charging the photosensitive member 3, 9 is a transfer device for transferring a toner image on the photosensitive member 3 to the recording medium by a transfer bias, and 10 is a recording medium. A fixing device that fixes a transferred toner image. In the tandem image forming apparatus, the charger 8, the exposure unit 4, the developing device 2, the transfer device 9, the cleaning device, and the like installed around the photosensitive member 3 are compact. In the example of the present invention, the developing device 2 is adjacent to the photoreceptor 3 and is arranged in a substantially vertical direction.
[0025]
In FIG. 2, reference numeral 20 denotes a developing roll that carries a toner thin layer and develops an electrostatic latent image on the photosensitive member 3, and 21 denotes a two-component developer magnetic brush generated by a magnet disposed in the developing roll. Magnetic rolls as developer transport bodies for supplying toner to the roll 20, 22 and 23 have spiral blades and are stirred while transporting the developer in the opposite direction to charge the toner and transport it to the magnetic roll 21. A paddle mixer and an agitating mixer, 24 a spike cutting blade for regulating the thickness of the magnetic brush formed on the magnetic roll 21, 25 a toner sensor for detecting the toner concentration in the developing device 2, and 26 The developing device housing, 27 is a first developer stirring chamber, 28 is a second developer stirring chamber, 29 is a partition wall, and 30a is a DC bias power source for applying a direct current (DC) bias to the developing roll 20. 30b is the AC bias power source also applies an AC (AC) bias to the developing roller 20, 31a is a DC bias power source for applying a direct current (DC) bias to the magnetic roll 21.
[0026]
Conventionally, an OPC photoconductor is known as the photoconductor 3 used in the image forming apparatus. However, the OPC photosensitive member has a problem that the surface of the photosensitive layer is soft and the photosensitive layer is easily scraped by rubbing with a cleaning blade. Therefore, an a-Si photosensitive member having a photosensitive layer thickness of 25 μm or more has been used in recent years because it has a hard surface compared to an OPC photosensitive member and is excellent in durability and function retention (maintenance-free). ing. However, since the a-Si photosensitive member is formed using a glow discharge decomposition method or the like, if the photosensitive layer is thick as described above, there is a problem that manufacturing time and manufacturing cost are increased, which is economically disadvantageous. .
[0027]
When an a-Si photosensitive member is used as the photosensitive material of the photosensitive member 3, the surface has a very low post-exposure potential of 10 V or less, but the saturation charging potential decreases when the film thickness is reduced. In addition, the withstand voltage leading to dielectric breakdown is reduced. On the other hand, the surface charge density when the latent image is formed tends to be improved and the development performance tends to be improved. This characteristic is particularly remarkable when the dielectric constant is about 10 or less, more preferably about 25 μm or less, and more preferably 20 μm or less, for an a-Si photoreceptor having a high dielectric constant of about 10. The direct current (DC) bias 30a during development is 150V or less, more preferably 100V or less. _PP It is possible to develop with 500 to 2000 V and a frequency of 1 to 3 kHz.
[0028]
When a positively charged organic photoconductor (OPC) is used as the photosensitive material of the photoconductor 3, the thickness of the photosensitive layer is set to 25 μm or more in order to reduce the residual potential to 100 V or less, and the charge generating material is added. It is particularly important to increase the amount. In particular, OPC having a single-layer structure is advantageous because a charge generating material is added to the photosensitive layer, and therefore the sensitivity change is small even when the photosensitive layer is reduced. Even in this case, the development direct current (DC) bias 30a is preferably set to 400 V or less, more preferably 300 V or less, from the viewpoint of preventing a strong electric field from being applied to the toner.
[0029]
Setting the developing bias to be low in this way is effective for suppressing the dielectric breakdown of the thin film a-Si photosensitive member, preventing excessive charging of the toner, and suppressing the development history phenomenon. Further, a toner layer of 10 to 100 μm, preferably 30 to 70 μm, is formed on the developing roll 20, and the gap between the developing roll 20 and the photoreceptor 3 is 150 to 400 μm, preferably 200 to 300 μm. A clear image can be obtained by causing the toner to fly on the photoreceptor 3 by applying an alternating electric field in a superimposed manner.
[0030]
The developer has a role of supplying and collecting toner, and 10 ⁶ Ωcm to 10 ⁹ Necessary for development by using a carrier having a volume resistivity of Ωcm and peeling off the toner strongly and electrostatically attached to the developing roll at the nip between the developing roll 20 and the magnetic roll 21 with a magnetic brush carried on the magnetic roll. Supply fresh toner. At this time, in order to increase the chance of contact with the toner, it is preferable to use a carrier having a small diameter of 40 μm or less and to increase the surface area per unit volume of the carrier. Carrier resistance emphasizes toner recovery 10 ⁶ A low-resistance carrier having a volume resistivity of Ωcm or less is effective as a countermeasure against development ghosts, but it is difficult to maintain the development in which accurate charging is applied to the toner to suppress the occurrence of fogging, and for a long period of time. When it is operated, toner is scattered from the surface of the developing roll 20, which causes a problem of contaminating the charger 8 and the exposure unit 4. 10 ⁹ A carrier having a volume resistivity of Ωcm or more can give charging performance, but there is a problem that charging tends to increase. By making the resistance value of the carrier appropriate, it is possible to recharge the charged toner to the developing roller 20 while collecting the toner on the developing roller 20. The toner charge amount is controlled to 5 to 20 μC / g to prevent toner scattering and fogging, and by developing at a low electric field, the development history is not left on the developing roll 20 and the toner recoverability is improved. An excellent development system can be provided.
[0031]
Magnetite carrier, Mn-based ferrite, Mn-Mg-based ferrite, etc. can be used as a high-magnetic force and low-resistance carrier. These carriers may be used as they are, but the surface does not excessively increase the resistance value. It is also possible to process and use. In the present invention, as an example, the volume resistivity is 10 ⁷ A ferrite carrier with Ωcm, saturation magnetization of 70 emu / g, and average particle size of 35 μm was used. When the average particle size exceeds 50 μm, the carrier stress increases and the toner concentration cannot be increased, and the amount of toner supplied to the developing roll 20 decreases. By setting the average particle size of the carrier to 50 μm or less, sufficient charge can be imparted even when the toner concentration in the developer is set to 5 to 20%, and stable development can be performed.
[0032]
The mixing ratio of the toner and carrier of the developer used in the present invention is 2 to 40% by weight, preferably 3 to 30% by weight, and more preferably 4 to 25% by weight with respect to the total amount of toner and carrier. If the mixing ratio of the toner is less than 2% by weight, the toner charge amount becomes high and a sufficient image density cannot be obtained, and if it exceeds 40% by weight, a sufficient charge amount cannot be obtained. Scattered and contaminated the inside of the image forming apparatus, or toner fog occurs on the image.
[0033]
In the image forming apparatus for carrying out the present invention, as an example, the diameter of the developing roll 20 is 16.8 mm, the diameter of the magnetic roll 21 is 16.0 mm, the diameter of the photoreceptor 3 is 30.0 mm, the developing roll 20 and the magnetic roll 21. The rotational speed ratio of the magnetic roll 21 is about 1.5 times the rotational speed of the developing roll 20. The gap between the ear cutting blade 24 and the magnetic roll 20 is about 0.3 to 1.5 mm, and the gap between the magnetic roll 21 and the developing roll 20 is about 0.3 to 1.5 mm. The thin layer of toner on the developing roll is set to a thickness of 10 to 100 μm, preferably 30 to 70 μm. This thickness is a value corresponding to about 5 to 10 layers of toner when the average particle size of the toner is 7 μm. The gap between the developing roll 20 and the photoreceptor 3 is 150 to 400 μm, preferably 200 to 300 μm. If it is smaller than 150 μm, it causes fogging. If it is larger than 400 μm, it becomes difficult to cause the toner to fly to the photoreceptor 3, and a sufficient image density cannot be obtained. Further, it becomes a factor that causes selective development. In the embodiment, the gap between the ear cutting blade 24 and the magnetic roll 20 is 0.55 mm, the gap between the magnetic roll 21 and the developing roll 20 is 0.40 mm, and the thin layer of toner on the developing roll is about It is designed to be maintained at 60 μm.
[0034]
First, a normal printing operation of a tandem type image forming apparatus that implements the toner particle size adjustment method according to the present invention will be briefly described. In the following description, a case where positively charged toner is used as an example will be described. However, it is obvious that the present invention can be similarly implemented even when negatively charged toner is used.
[0035]
First, a two-component developer composed of toner and carrier corresponding to each color such as yellow, cyan, magenta, and black is stirred and charged by the stirring mixer 23 and the paddle mixer 22 shown in FIG. Is done. Then, a magnetic brush is formed on the magnetic roll 21, the layer is regulated by the earbrush blade 24, and for example, +400 V by the DC bias power supply 31 a applied to the magnetic roll 21, and by the DC bias power supply 30 a applied to the developing roll 20. For example, a thin layer of only toner is formed on the developing roll 20 by a potential difference from + 100V. The thickness of the toner thin layer on the developing roll 20 varies depending on the resistance of the developer and the rotational speed difference between the developing roll 20 and the magnetic roll 21, but can also be controlled by the above-described potential difference. When the potential difference is increased, the toner layer on the developing roll 20 becomes thicker, and when the potential difference is decreased, the toner layer becomes a thinner layer.
[0036]
When a print start signal is received from a control circuit (not shown), the photosensitive member 3 is first charged to 400 V, for example, by the charger 8, and then the post-exposure potential of the photosensitive member 3 is exposed by the exposure unit 4. The latent image is formed at about 70V. This latent image is obtained by adding + 100V by the DC bias power source 30a applied to the developing roll 20 and V by the AC bias power source 30b superimposed during development. _p-p The toner image is formed by developing with the toner flying from the toner thin layer on the developing roll 20 to the photosensitive member 3 by a rectangular wave having a frequency of 1.6 kV, a frequency of 3.0 kHz, and a duty ratio of 30%. In order to prevent toner scattering, the AC bias 30b is applied immediately before development. When the toner image is formed on the photosensitive member 3 in this way, the recording medium is taken out from the paper feed cassette 7 at the timing when the toner image reaches the transfer position, and is conveyed by the conveyor belt 5. Transfer is applied to the recording medium by applying a transfer bias by the transfer device 9 installed at the transfer position. When the toner images of the respective colors are sequentially transferred to the recording medium and reach the fixing device 10, the toner images are fixed and discharged by the fixing device 10.
When the toner concentration in the developer in the developing device 2 decreases with development, the decrease in the toner concentration is detected by the toner sensor 25, and a necessary amount of toner is supplied based on the detection result (not shown). By means, the developing device 2 is replenished from the developer container 6.
[0037]
The toner remaining on the developing roll is not provided with a special device such as a scraping blade, and the magnetic brush on the magnetic roll 21 comes into contact with the toner layer on the developing roll 20, and the brush due to the peripheral speed difference between the two rolls. Since the developer is replaced by the effect and stirring by the paddle mixer 22 of the magnetic brush, the toner can be easily collected and replaced. As a method for accelerating the replacement of the developer, the rotational speed of the magnetic roll 21 is set to 1.0 to 2.0 times the rotational speed of the developing roll 20, and the toner on the developing roll 20 is collected. By supplying the developer set to an appropriate toner concentration to the developing roll 20, a uniform toner layer can be formed. Further, in order to prevent an afterimage, during the image formation after development, the + 100V DC voltage of the DC bias power supply 30a is set to + 50V, the duty ratio of the AC supplied from the AC bias power supply 30b is set to 50%, and the magnetic roll 21 is supplied. And the toner on the developing roll 20 is returned to the magnetic roll 21.
[0038]
The developing device shown in FIG. 2 is provided opposite to the photosensitive member 3 capable of holding an electrostatic latent image due to a difference in charging potential, and in a housing 26 containing a two-component developer, the two-component developer is provided. A magnetic roll 21 that magnetically attracts the developer to form a magnetic brush on the surface, a pan blade 24 that regulates the amount of developer adsorbed on the magnetic roll 21, the magnetic roll 21, and the photoreceptor 3. And a cylindrical developing roll 20 which is arranged so as to be close to each other at different portions and rotates with the toner attached thereto. Further, a first developer stirring chamber 27 is provided in the housing 26 at a position adjacent to the magnetic roll 21, and further, a second developer stirring chamber partitioned by the first developer stirring chamber 27 and the partition wall 29. A chamber 28 is provided. The first developer agitating chamber 27 and the second developer agitating chamber 28 communicate with each other at both ends in the axial direction of the magnetic roll 21, and respectively agitate the developer and developer in the axial direction. A paddle mixer 22 and a stirring mixer 23 are provided. These two mixers 27 and 28 are set to rotate in a direction opposite to each other so that the developer circulates between the first developer agitating chamber 27 and the second developer agitating chamber 28. It is supposed to be.
[0039]
The magnetic roll 21 has a rotatable cylindrical sleeve arranged on the outer periphery of a magnet supported so that its position is fixed, and a two-component developer containing toner and a magnetic carrier is magnetically applied to the sleeve surface. The magnetic brush of the two-component developer can be formed by suction and the sleeve can be rotated to convey the developer. A DC voltage of +400 V can be applied to the magnetic roll 21 from a direct current (DC) bias power supply 31a for the magnetic roll. The developing roll 20 is made of an aluminum cylinder whose surface is anodized, a cylinder made of phenol resin, or a resin layer formed on the surface of an aluminum cylinder, and a direct current (DC) bias power supply 30a. To +50 to + 200V DC and AC (AC) bias power supply 30b to V _p-p A bias on which an alternating current of 1.6 kV and frequency of 3.0 kHz is superimposed can be applied.
[0040]
The developer is conveyed and agitated in the first developer agitating chamber 27 and the second developer agitating chamber 28, and the distribution of the toner in the developer is kept uniform and the toner and the carrier are mixed. A predetermined charge is imparted to the toner due to frictional charging therebetween. The agitated developer is supplied to the magnetic roll 21 by the paddle mixer 22, and the magnetic roll 21 magnetically attracts the developer to form a developer magnetic brush composed of toner and carrier, and develops by rotation. It is conveyed to a position facing the roll 20.
[0041]
As described above, a + 100V DC voltage from the direct current (DC) bias power supply 30a is applied to the developing roll 20, and a + 400V DC voltage is applied to the magnetic roll 21 from the magnetic roll direct current (DC) bias power supply 31a. Therefore, an electric field is formed between the developing roll 20 and the magnetic roll 21 by these applied voltages, and the positively charged toner is transferred to the developing roll 20, and a toner layer is formed on the surface of the developing roll 20. On the other hand, the carrier remains magnetically attracted to the magnetic roll 21 without being transferred.
[0042]
The toner layer formed on the developing roll 20 is conveyed to the developing area by the rotation of the developing roll 20, and a + 100V DC voltage applied to the developing roll 20 and a V applied during development. _p-p It flies within the electrostatic field between the photosensitive member 3 and the developing roll 20 by a bias superimposed with 1.6 kV, frequency 3.0 kHz, alternating current with a rectangular wave with a duty ratio of 30%, and adheres to the surface of the photosensitive member 3. Development is performed. At this time, the toner having a large particle diameter is more easily peeled off from the developing roll 20 than the toner having a small particle diameter, and is easily transferred to the photoreceptor 3. For this reason, the toner that does not contribute to the development and remains on the developing roll 20 and is returned to the portion facing the magnetic roll 21 again has a small particle size.
[0043]
A method of adjusting the toner particle size in the developing device will be described. After the continuous printing or a predetermined number of printings, the surface potential of the photoreceptor 3 is not applied periodically. The same bias as that shown in FIG. 3A, that is, a DC voltage of + 100V from the direct current (DC) bias power source 30a is applied to the developing roll 20, and the alternating current (AC) bias power source 30b is applied to V. _p-p 1.6 kV, frequency 3.0 kHz, a ratio of T1 and T2, that is, a bias superimposed with a rectangular wave alternating current with a duty ratio of 30%, is applied to the magnetic roll 21 from a direct current (DC) bias power supply 31a to + 400V. While the DC voltage is applied, the first step of forming the toner layer is performed while the developing roll 20 that is normally rotated about 182 times per minute rotates about 45 to 75 times (about 15 to 25 seconds). In this case, since the fine powder toner has a large charge amount per unit volume, the voltage V applied in the direction in which the toner is moved from the magnetic roll 21 to the developing roll 20. _f Thus, the toner is attracted to the developing roll 20 more strongly than the toner having a large particle diameter. The toner having a large particle diameter is supplied with a voltage V to be returned from the developing roll 20 to the magnetic roll 21. _b However, the fine powder toner having a small particle diameter is difficult to collect, and the fine powder toner is deposited on the developing roll 20. Note that the finer toner may be collected on the developing roller by lowering the duty ratio than that during development.
[0044]
Next, the rotation of the photoconductor 3, the developing roll 20, and the magnetic roll 21 is stopped, and as shown in FIG. 3B, the AC bias V by the alternating current (AC) bias power source 30b to the developing roll 20 is obtained. _p-p The direct current voltage applied to the developing roll 20 from the direct current (DC) bias power source 30a is changed from +100 V to +200 V, and the direct current to the magnetic roll 21 (with a rectangular wave of 1.6 kV, frequency 3.0 kHz, duty ratio 30% is left as it is. DC) A second step is performed in which the DC voltage from the bias power source 31a is changed from +400 V to 0 V, and the surface of the photosensitive member 3 is kept off (0 V). Then, the voltage V for causing the toner to fly from the developing roll 20 to the photosensitive member 3. _b The fine toner deposited at the position facing the photoconductor 3 becomes easy to fly to the photoconductor 3 side by the bias applied to the developing roll 20 and is peeled off and moves to the photoconductor 3.
[0045]
Therefore, this state is continued for about 1 second. As described above, for example, the diameter of the developing roller 20 is 16.8 mm, the magnetic roller 21 is 16.0 mm, the photosensitive member 3 is 30.0 mm, and the developing roller 20 and the photosensitive member 3 The gap between them is set to 300 μm, and the developing roll 20 and the photosensitive member 3 are rotated so that the developing roller 20 rotates about 45 degrees, and similarly, the developing roller 20 is deposited at a position facing the photosensitive member 3. The second step of peeling off the fine toner that has been used and causing it to fly to the photoreceptor 3 is repeated. Similarly, the developing roller 20 and the photosensitive member 3 are rotated stepwise to perform the second step at least one round of the developing roller 20 to fly the accumulated toner to the photosensitive member 3, and the toner moved to the photosensitive member 3 is It is not transferred to the conveyor belt, but is cleaned and removed by a cleaning device (not shown) on the photosensitive member 3 side.
[0046]
As described above, the first process of collecting fine toner on the developing roll 20 every time the developing process is performed for a certain period, such as after continuous printing or after a predetermined number of printings, the developing roll 20 and the photosensitive roll. The second step of stopping the rotation of the body 3 and causing the fine toner collected on the developing roll 20 to fly to the photosensitive body 3, the developing roll 20 and the photosensitive body 3 are rotated and stopped in a stepwise manner, and collected on the developing roll 20. The fine powder toner in the developer is processed by repeating the second process in which the fine powder toner is blown to the photosensitive member 3 and the developing roll 20 and the photosensitive member 3 are rotated stepwise. Even when a large amount of toner is consumed, only a small particle size toner is not accumulated in the developing device, and the toner particle size is always kept constant, and a good image without deterioration in image quality can be obtained. It is possible to provide an image forming apparatus that can. In the embodiment, the above process is set to be performed every time 100 sheets are printed. Further, when the 100th sheet is reached during continuous printing, it is performed after the continuous printing is completed. Then, a new count is started after the above process is performed. By carrying out the above steps as described above, the image density is maintained within an appropriate range (1.30 to 1.50), and the paper is not smeared due to toner scattering in the apparatus, so that the image quality can be maintained. It has become possible. Alternatively, it may be performed each time the developing roller rotates reaches a predetermined time, or may be performed each time the toner consumption converted from the printing rate reaches a predetermined value.
[0047]
FIG. 4 shows an amount of fine powder toner of 5 μm or less deposited on the developing roll 20 when only a direct current, an alternating current with a duty ratio of 50%, and an alternating current with a duty ratio of 30% are applied between the developing roll 20 and the magnetic roll 21. It is the graph which showed. In FIG. 4, the horizontal axis represents the rotation time (seconds) of the developing roll 20, and the vertical axis represents the frequency (%) of fine powder toner of 5 μm or less. As is apparent from this graph, when only DC is applied. The amount of fine powder toner hardly increases when an alternating current is applied, but the amount of fine powder toner increases when the duty ratio is 30% as in the first step described above. You can see that they are collecting.
[0048]
Similarly, FIG. 5 shows that (a) toner is discharged after forming a layer by applying an AC voltage between the developing roll 20 and the magnetic roll 21, and (b) toner is discharged after forming a layer by applying a DC voltage. 6 shows the change in the amount of fine powder toner of 5 μm or less in the developer during continuous printing (20K sheet printing durability) when (c) discharging is not performed. The horizontal axis represents the number of printed sheets, and the vertical axis represents the frequency of finely divided toner of 5 μm or less, as in FIG. 4. The toner was discharged every time 25 sheets were printed. As is apparent from this graph, (c) when the discharge is not performed, the amount of fine powder toner exceeds 15% after printing, whereas (b) the toner is discharged after the layer is formed by applying a DC voltage. 12% when applied, (a) When alternating current is applied and toner is discharged after layer formation, 8.5% is the smallest change in the amount of fine toner, and the change in fine toner is suppressed. I understand.
[0049]
【The invention's effect】
As described above, according to the present invention, the first step of forming the toner layer containing a large amount of fine powder, and the developing roller is completely stopped, and the toner on the developing roller at a position facing the latent image carrier is transferred to the latent image carrier. Development that was a concern when fine toner particles can be collected on the developing roll and developed on the photoconductor by a simple process called the second process of flying up and completely peeling off. Because of the short time, it is possible to avoid the phenomenon that only particles with a large particle size will fly to the photoconductor and the fine powder that you want to fly the most will not fly. It is possible to provide a toner particle size adjusting method that collects, discharges to the photoreceptor, and reduces it.
[0050]
Then, after the second step, by repeating the second step by repeatedly rotating and stopping the developing roll in a stepwise manner, the processing of the fine toner over the entire circumference of the developing roll can be easily performed. .
[0051]
Further, the image density can be kept constant over a long period of time by periodically performing the first process and the second process.
[0052]
Further, in the first step, the duty ratio of the AC bias applied between the latent image carrier and the developing roll is different from the AC bias applied between the latent image carrier and the developing roll applied during the development step. Thus, in the first step, more fine toner can be deposited on the developing roll in the same time, and the second step is performed to reliably reduce the fine toner in the developing device. Can be provided.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of a tandem type image forming apparatus that performs a toner particle size adjusting method according to the present invention.
FIG. 2 is a schematic configuration diagram of a hybrid developing device for carrying out a toner particle size adjusting method according to the present invention.
FIG. 3 is a diagram showing an AC bias when fine powder toner is collected on a developing roll by the toner particle size adjusting method according to the present invention.
FIG. 4 is a graph showing a change in the amount of fine powder toner on the developing roll when the duty ratio of the AC bias voltage applied to the developing roll is changed.
FIG. 5 is a graph showing a change in the amount of fine powder toner in the image forming apparatus in which the toner particle size adjusting method according to the present invention is performed.
[Explanation of symbols]
20 Developing roll
21 Magnetic roll
22 paddle mixer
23 Stir mixer
24 Hobiri Blade
25 Toner sensor
26 Housing
27 First developer stirring chamber
28 Second developer stirring chamber
29 Bulkhead
30a Direct Current (DC) Bias Power Supply
30b AC (AC) bias power supply
31a Direct current (DC) bias power supply

Claims (4)

A developing roll that is disposed opposite to a latent image carrier on which an electrostatic latent image is formed, carries toner on its surface and conveys it, adsorbs and conveys a two-component developer containing carrier and toner, A magnetic roll that is supplied to the developing roll, and is used in an image forming apparatus having a developing device for performing a developing process for developing the electrostatic latent image formed on the latent image carrier,
And a developing device capable of carrying out a first step of carrying toner on the developing roll and a second step of flying toner onto the latent image carrier with the developing roll stopped. An image forming apparatus. The image forming apparatus according to claim 1, wherein the second step is repeatedly performed by repeatedly rotating and stopping the developing roll in a stepped manner. The image forming apparatus according to claim 1, wherein the first step and the second step are periodically performed. The duty ratio of the AC bias applied between the latent image carrier and the developing roll in the first step is different from the AC bias applied between the latent image carrier and the developing roll applied during the development step. The image forming apparatus according to claim 1.

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