JP3791834B2 - Control method in tandem type image forming apparatus - Google Patents

Control method in tandem type image forming apparatus Download PDF

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Publication number
JP3791834B2
JP3791834B2 JP2001202996A JP2001202996A JP3791834B2 JP 3791834 B2 JP3791834 B2 JP 3791834B2 JP 2001202996 A JP2001202996 A JP 2001202996A JP 2001202996 A JP2001202996 A JP 2001202996A JP 3791834 B2 JP3791834 B2 JP 3791834B2
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Japan
Prior art keywords
toner
image
roll
image forming
developing
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JP2003015380A (en
Inventor
昌一 坂田
義夫 小沢
英司 落合
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京セラ株式会社
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Priority to JP2001202996A priority Critical patent/JP3791834B2/en
Priority claimed from DE2002125182 external-priority patent/DE10225182A1/en
Priority claimed from CN 02123228 external-priority patent/CN1280682C/en
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Description

[0001]
BACKGROUND OF THE INVENTION
BACKGROUND OF THE INVENTION 1. Field 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 method, and more particularly, to a recording medium using a process unit having a plurality of photoconductors corresponding to each color toner. In a tandem type image forming apparatus that forms a color image in synchronism with the feeding of a transfer member and performs color superposition on the recording medium or the transfer member, two components for charging non-magnetic toner using a magnetic carrier A non-contact developing method that uses a developer, holds only the charged toner on the developing roll, and flies to the electrostatic latent image on the electrostatic latent image carrier (photoconductor) to develop the latent image. The present invention relates to a control method in a tandem type image forming apparatus to be provided.
[0002]
[Prior art]
Conventionally, a two-component developer that uses a magnetic carrier to charge non-magnetic toner is used, and only the charged toner is held on the developing roll to hold the electrostatic latent image on the electrostatic latent image carrier (photoconductor). The non-contact development method for developing the latent image by flying it to an image has been studied as a non-contact one-component development means. It has also been studied for a one-drum color superimposing method for sequentially forming a plurality of color images on a body (photoconductor). In this method, it is possible to form a color image with little color misregistration by accurately superimposing toner on an electrostatic latent image carrier (photosensitive member), and it is attracting attention as a technique for improving color quality. Yes.
[0003]
As a prior art related to such a technique, US Pat. No. 3,866,574 discloses a non-magnetic material on a donor roll (developing roll) placed in non-contact with an electrostatic latent image carrier (photosensitive member). There has been proposed a method in which a thin layer is formed with toner and the toner is caused to fly to a latent image on an electrostatic latent image carrier (photoconductor) by an alternating electric field. U.S. Pat. No. 3,929,098 discloses a developing device that uses a magnetic roll to advance a developer to a donor roll and transfers toner onto the donor roll to form a toner layer. .
[0004]
However, in these proposals, it is possible to form a thin layer on the donor roll using a two-component developer, but when the charge of the toner becomes high, it becomes difficult to separate the toner on the donor roll, and a strong AC An electric field is required. Since this electric field disturbs the toner layer on the electrostatic latent image carrier (photoconductor), there is a problem with color superposition and the like. For this reason, JP-A-3-113474 discloses a toner developed by providing an auxiliary electrode made of a wire between a donor roll and an electrostatic latent image carrier (photoconductor), and applying a weak alternating electric field to the auxiliary electrode. A so-called powder cloud development method has been proposed which does not disturb the image.
[0005]
Furthermore, in this type of technology, when a toner consumption area and a non-consumption area are generated on the developing roll, a variation in the toner adhesion state on the roll and the toner potential difference occurs. A phenomenon in which a part appears as an afterimage (ghost) at the next development, that is, a so-called hysteresis phenomenon occurs, but a complicated mechanism is required to prevent this phenomenon, and it has not been put to practical use in a small electrophotographic process. In order to prevent this, Japanese Patent Application Laid-Open No. 11-231652 proposes a member for scraping off the development residual toner on the developing roll and a collecting device for the scraped toner. Japanese Patent Application Laid-Open No. 7-72733 (US Pat. No. 5,420,375) discloses that toner on a developing roll is collected in a magnetic roll by a potential difference between copies and between papers to charge the toner. In addition, as a countermeasure against the hysteresis phenomenon using a magnetic brush, Japanese Patent Laid-Open No. 7-128983 discloses a method of setting a wide half-value width region of the magnetic flux density of the magnetic roll, thereby providing a toner on the developing roll. Proposals have been made to collect and supply waste.
[0006]
In terms of theory, a report on the formation of a toner layer on a developing roll using a two-component developer was made by Toshiba Corp. in Journal of Electrophotographic Society, Vol. 19, No. 2 (1981). No.-121077 has a patent application. Further, as a method for reliably collecting the toner on the developing roll, Japanese Patent Application Laid-Open No. 2000-81788 proposes using a dedicated collecting roll.
[0007]
In recent years, for speeding up, a tandem method that uses a plurality of photoconductors corresponding to the color of toner, forms a color image in synchronization with the feeding of the transfer member, and superimposes the color on the transfer member has attracted attention. ing. Although this method has the advantage of being excellent in high-speed performance, it has the disadvantage of increasing the size because the electrophotographic process members of 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 interval between the photoconductors is narrowed and a downsized image forming unit is arranged.
[0008]
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 method, in the case of the method in which the developing devices are arranged vertically as described above, the reflux of the developer, that is, the supply from the developer stirring unit to the developing member close to the photosensitive member becomes complicated, There is a problem in that there is a limit to downsizing of the apparatus, and carrier adhesion to the photoreceptor and toner scattering are unavoidable.
[0009]
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 with a charge roll and the layer thickness on the developing roll is regulated with an elastic regulation blade, so that the toner additive adheres to the charge roll and is charged. Or the toner adheres to the regulating blade and the layer formation becomes non-uniform, resulting in image defects.
[0010]
Japanese Patent Laid-Open No. 63-249164 discloses a method for controlling a tandem developing device by stopping the operation of the developing device in an image forming unit other than the image forming unit performing the transfer process, thereby preventing the deterioration of the developer. An application has been filed to prevent this.
[0011]
In general, in a one-component developing device, a toner having a small particle diameter adheres to the surface of the developing roll due to a high charging amount due to repeated image formation, and other toner particles are in contact with the developing roll. The frictional charging is hindered, and the toner is conveyed to the electrostatic latent image portion without being uniformly charged on the developing roll, which may cause problems such as a decrease in image density and fogging.
[0012]
Such a phenomenon is promoted because toner particles tend to remain on the developing roll because less toner flies from the developing roll to the electrostatic latent image portion (photoreceptor), particularly when the document printing rate on the image is low. , Image density reduction and fogging occur. In such a case, it is alleviated by consuming a large amount of toner from the developing roll to the photosensitive member side by a pattern having a high original printing ratio such as solid black, and transferring the toner to a recording medium to consume the toner. Although it is possible, if the solid black pattern is not printed after leaving the toner unconsumed for a long time, the toner particles may be fixed on the surface of the developing roll due to the influence of humidity or the like and may not recover. . And as an environmental condition, it tends to appear especially in a low-humidity environment.
[0013]
Therefore, when the printing rate is low, that is, when the number of printed dots is small on a single screen, the developing electric field is applied to the developing roll so that the toner of the developing roll is consumed after image formation, whereby the development is performed. The roll surface is refreshed and image deterioration can be prevented.
[0014]
However, if a large amount of toner adheres to the developing roll and is left for a long period of time, it will peel off from the surface layer in order to peel off from the developing roll. There are drawbacks, high toner consumption, inefficiency and uneconomical.
[0015]
Further, when such a developing roll is refreshed, an alternating electric field for refreshing is applied to the developing roll and the electrostatic latent image carrier (photosensitive member). For this reason, even when a normal bias is applied, In some cases, the reverse polarity charge toner generated in the developing device that is not provided adheres to the transfer portion without being transferred to the recording medium or the toner image carrier, and the back of the printing paper may be contaminated. In a high-humidity environment where the charging voltage is lowered, reversely charged toner may be mixed in the normally charged toner, but this also causes the same problem.
[0016]
[Problems to be solved by the invention]
However, the powder cloud development method described in Japanese Patent Application Laid-Open No. 3-113474 is not a very general method because the wires of the auxiliary electrode are very easily soiled and image deterioration due to vibration occurs. Not. Further, JP-A-11-231652, JP-A-7-72733 (USP 5,420,375), JP-A-7-128983, JP-A-59-121077, JP-A-2000-81788. In the devices shown in the above, the toner stress increases due to the toner scraping device or the application of a special recovery bias, which causes deterioration of the durability of the toner. In addition, during long-term use, the chargeability of the toner changes due to deterioration of the durability of the carrier, the charging characteristics of the toner on the developing roll change significantly, and the charge distribution of the replenishment toner and the recovered toner becomes wider. It was a cause of scattering and fogging. In addition, there is a troublesome carrier exchange that has deteriorated, and the actual situation is that it has not been put into practical use.
[0017]
Further, in the prior art, since the toner polarity is negatively charged, especially in a low-temperature and low-humidity environment, the toner charge potential difference between the developing part and the non-developing part tends to increase, and the development afterimage (ghost) tends to become noticeable. there were. This is because the toner material generally tends to be negatively charged, and the potential of the toner layer on the developing roll rises when repeatedly exposed to a high electric field.
[0018]
As a technique for preventing fogging, there is a technique introduced in Japanese Patent Laid-Open No. 6-186811, etc., which is exposed from the support side of a photoconductor provided with a photoconductive layer on a transparent conductive support. In an image forming apparatus for forming an image, a photosensitive roller is charged by a charging roller, and a developer is composed of a high-resistance carrier, a low-resistance carrier, and an insulating magnetic toner to form a magnetic brush. Injects charge into the photoconductive layer of the body, charges the high-resistance carrier with a polarity opposite to that of the toner to improve toner retention and developability, and reduces the charge attenuation with an insulating magnetic toner for high efficiency. There is shown an image forming apparatus in which transfer can be performed and toner remaining at the time of transfer is charged by a charging roller and collected by a developing device, thereby improving transferability and developability.
[0019]
However, the apparatus disclosed in Japanese Patent Application Laid-Open No. 6-186811 is an image forming apparatus in which exposure is performed from the back side of an electrostatic latent image carrier (photosensitive member), and the photoconductive layer of the photosensitive member is formed with a low resistance carrier. The purpose of this is to reduce the fog phenomenon by injecting the electric charge, which requires a complicated mechanism for exposure from the back side and cannot be used in a tandem type image forming apparatus.
[0020]
Further, the control method described in Japanese Patent Laid-Open No. 63-249164 requires complicated control to stop the operation of the developing device in the image forming unit other than the image forming unit performing the transfer process. Although it is a tandem type, it is a conventional type in which developing devices are arranged beside the photosensitive member, and there is a drawback that it is difficult to reduce the size.
[0021]
In view of the above circumstances, the present invention prevents the occurrence of afterimages during continuous development without complicating the developing device, and reliably supplies charged toner to the developing roll, so that stable image quality can be obtained over a long period of time. It is an object to provide a control method in a tandem type image forming apparatus that can constitute a small process unit, and thereby to make the tandem image forming apparatus small.
[0022]
In addition, when continuously printing an image with an extremely low printing rate or printing only a specific color, the charge of the developer may increase and the toner development amount may change. It is also an object to discharge the deteriorated toner from the process unit before causing a change so that a stable color image can always be obtained.
[0023]
[Means for Solving the Problems]
In order to solve the above problems, the invention described in claim 1 is a method invention,
In order to develop the latent image formed on the photoconductor by electrophotographic development, a thin layer is obtained by supplying toner from a developing roll disposed facing the photoconductor and a magnetic brush formed of a two-component developer on the developing roll. Control method in a tandem type image forming apparatus that has a plurality of process units each having a magnetic roll for forming the image, and forms an image by transferring an image of each color from each process unit to a recording medium or an intermediate transfer member In
In the non-image forming period in each process unit, or before the start of image formation, the developing roll and the magnetic roll are rotated to make the potential between the two rolls equal to each other, and in the equipotential state, on the developing roll Residual toner was collected with the magnetic brush, and the toner consumption was estimated from the dot amount of the image data to be printed, and the value of the toner permeability sensor showed a value less than a certain value with respect to the toner consumption. When the toner charge amount increases, the toner is forcibly discharged from the process unit to the recording medium or the intermediate transfer member. It is characterized by that.
[0024]
In this way, the magnetic brush formed on the magnetic roll is brought into an equipotential state in which the potential between the two rolls is made equal while the developing roll and the magnetic roll are rotated before the image formation starts or before the image formation starts. All the toner on the developing roll is collected and the development history on the developing roll is eliminated to prevent the occurrence of afterimages and fogging, so that the charged toner can be reliably supplied to the developing roll, and stable image quality can be obtained over a long period of time. In addition, the process unit can be configured in a small size, whereby the tandem image forming apparatus itself can be configured in a small size.
[0026]
The present invention also provides the above-mentioned When the amount of toner consumed in each process unit is less than the specified amount, the toner is forcibly discharged from the process unit to the recording medium or intermediate transfer body, and images with extremely low printing rates are continuously printed or specified. In the case of printing only one color, the developer charge is prevented from increasing and the toner development amount is prevented from changing, and the deteriorated toner is discharged from the process unit before changing the image, so that a stable color image is always obtained. Thus, stable image quality can be obtained over a long period of time, and the process unit can be configured in a small size, whereby the tandem image forming apparatus itself can be configured in a small size.
[0028]
The present invention also provides the above-mentioned Thus, when continuously printing an image with an extremely low printing rate or printing only a specific color, the charge of the toner (hereinafter referred to as Q / M) increases, and the surface of the carrier 4 becomes tight. The developer magnetic permeability output value by the toner density (T / C) sensor decreases and is estimated to be less than the actual amount of toner used, preventing the toner from being replenished and stable over a long period of time. The image quality can be obtained and the process unit can be configured in a small size, whereby the tandem image forming apparatus itself can be configured in a small size.
[0029]
And these controls are claimed. 2 and 3 As described above, the toner amount discharged to the recording medium or the intermediate transfer member is measured for each color by the developing amount detecting means. Further, when there are a plurality of process units that are less than the predetermined toner consumption amount, the transfer is performed in a state of being overlaid on the same part of the non-sheet passing portion on the recording medium or the intermediate transfer member.
[0030]
In this way, the amount of discharged toner can always be grasped, and this control can be performed in a short time even when toner is discharged from a plurality of process units.
[0031]
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.
[0032]
FIG. 1 is a view for explaining a developing device in a process unit used in a tandem type image forming apparatus according to the present invention, and FIG. 2 is a-Si of an electrostatic latent image carrier (photosensitive member) used in the present invention. FIG. 3 is a diagram for explaining an appropriate development region of a bias voltage applied to the developing device in the image forming apparatus according to the present invention, and FIG. 4 is a diagram showing a high resistance carrier and a low resistance layer. FIG. 5 and FIG. 6 are diagrams illustrating an example of a tandem type image forming apparatus that implements the control method according to the present invention. When the toner image formed on the electrostatic latent image carrier (photoreceptor) is directly transferred to a recording medium, FIG. 6 shows the toner image formed on the electrostatic latent image carrier (photoreceptor) once as an intermediate transfer member. After transferring, the structure for transferring to a recording medium It is an example.
[0033]
In FIG. 1, reference numeral 1 denotes a magnetic roll that generates a magnetic brush 10 by a carrier 4 contained in a developer by a magnet disposed therein, and 2 denotes a toner thin layer 6 by toner 5 supplied from the magnetic brush 10. Development roller for developing the electrostatic latent image on the electrostatic latent image carrier 3, 4 is a toner carrier, 4-1 is a low resistance carrier, 4-2 is a high resistance carrier, 5 is toner, 6 Is a toner thin layer on the developing roll 2, 7 is a developing bias power source for applying a developing bias between the electrostatic latent image carrier (photoconductor) 3 and the developing roll 2, and 7a is a direct current (DC) bias (V dc1 ) Power supply, 7b is an alternating current (AC) bias power supply, and 8 is a direct current (DC) bias (V) of the magnetic roll 1. dc2 ) A power source 9 is a regulating blade for regulating the thickness of the magnetic brush 10 on the magnetic roll 1.
[0034]
In FIG. 2, 20 is a base material in the electrostatic latent image carrier (photoconductor) 3, 21 is a blocking layer, 22 is a photosensitive layer made of a-Si, and 23 is a surface protective layer. In the following description, when expressed as “thickness” of the a-Si electrostatic latent image carrier (photoconductor) 3, the surface of the substrate 20 in the electrostatic latent image carrier (photoconductor) 3. To the surface of the electrostatic latent image carrier (photoconductor) 3 opposite to the substrate. Therefore, as shown in FIG. 2, when the electrostatic latent image carrier (photoconductor) 3 is composed of a blocking layer 21, a photosensitive layer 22, and a surface protective layer 23, the thickness of the photosensitive layer is This is the sum of the thickness of each layer.
[0035]
5 and 6, 50 is a developer container, 51 is a magnetic roll shown by 1 in FIG. 1, 52 is a developing roll shown by 2 in FIG. 1, 53 is a paper feed cassette containing a recording medium, 54 Is a conveyance belt for the recording medium, 55 is an electrostatic latent image carrier (hereinafter abbreviated as a photoconductor) indicated by 3 in FIG. 1, 56 is a charger for charging the photoconductor, and 57 is a photoconductor 55. An exposure device 58 for exposing the toner image to the recording medium 58, a transfer device for applying a transfer bias for transferring the toner image on the photoreceptor 55 to the recording medium, and a fixing device 59 for fixing the toner image transferred to the recording medium. 6, reference numeral 60 denotes an intermediate transfer member for transferring the toner images formed on the respective photosensitive members 55 in an overlapping manner, 61 denotes a transfer roller for transferring the toner image on the photosensitive member 55 to the intermediate transfer member 60, and 62 denotes an intermediate transfer member. 60 Transfers the toner image on the recording medium. A secondary transfer roller 63, an intermediate transfer member cleaner 64, and a development amount detecting means 64, among which a photosensitive unit 55, a developing roller 52, a magnetic roller 51, a charger 56, an exposure device 57, etc. Is configured.
[0036]
First, the operation of these tandem type image forming apparatuses will be described. In the tandem type image forming apparatus of the type that directly transfers the toner image formed on the photosensitive member 55 shown in FIG. Container 50 (50 4 ~ 50 1 ), A magnetic roll 51 (51) by a developer composed of a toner and a carrier corresponding to each color such as yellow, cyan, magenta, and black. 4 ~ 51 1 ) On the developing roll 52 (52). 4 ~ 52 1 ) A thin layer of toner is formed thereon. When a print start signal is received from a control circuit (not shown), the recording medium is sent out from the paper feed cassette 53 and sent to the conveyor belt 54. The recording medium is a photosensitive member 55 (55 for each color). 4 ~ 55 1 ) To meet the timing of reaching the charging device 56 (56). 4 ~ 56 1 ) Photoconductor 55 (55) 4 ~ 55 1 ) Charging, exposure device 57 (57 4 ~ 57 1 ) By the image signal sent to the photosensitive member 55 (55). 4 ~ 55 1 ) Exposure and latent image formation, developing roll 52 (52) 4 ~ 52 1 ) To develop the latent image, and the recording medium is a photosensitive member 55 (55). 4 ~ 55 1 ), The transfer device 58 (58 4 ~ 58 1 ) Is applied to transfer the toner image onto the recording medium. This process is performed by each photoconductor 55. 4 ~ 55 1 The images of each color are sequentially transferred onto the recording medium, fixed by the fixing device 59, and discharged.
[0037]
In the tandem type image forming apparatus in which the toner image formed on the photosensitive member 55 shown in FIG. 6 is once transferred to the intermediate transfer member 60 and then transferred to the recording medium, the developer container is the same as in FIG. 50 (50 1 ~ 50 4 ), A magnetic roll 51 (51) by a developer composed of a toner and a carrier corresponding to each color such as yellow, cyan, magenta, and black. 1 ~ 51 4 ) On the developing roll 52 (52). 1 ~ 52 2 ) A thin layer of toner is formed thereon. When a print start signal is received from a control circuit (not shown), each photosensitive member 55 is placed on the intermediate transfer member 60 constituted by an intermediate transfer belt or the like. 1 From55 4 The charger 56 (56 so that the toner images formed thereon overlap. 4 ~ 56 1 ) Photoconductor 55 (55) 1 ~ 55 4 ) Charging, exposure device 57 (57 1 ~ 57 4 ) By the image signal sent to the photosensitive member 55 (55). 1 ~ 55 4 ) Exposure and latent image formation, developing roll 52 (52) 1 ~ 50 4 ) Development of the latent image with the toner on the transfer roller 61 (61 1 ~ 61 4 ) Is transferred to the intermediate transfer body 60, and when all the toner images are transferred to the intermediate transfer body 60, the recording medium is sent out from the paper feed cassette 53 and is secondary to the intermediate transfer body 60. The toner image is transferred to the transfer position and a transfer bias is applied to the secondary transfer roller 62 to transfer the toner image to the recording medium. Then, the image is fixed by the fixing device 59 and discharged.
[0038]
In the process unit of the tandem type image forming apparatus according to the present invention configured as described above, the toner 5 is supplied from the developer container (not shown) to the magnetic roll 1, and the toner 5, the low resistance carrier 4-1, The two-component developer composed of the high-resistance carrier 4-2 forms the magnetic brush 10 to positively charge the toner 5 by stirring, and the layer thickness is regulated by the regulating blade 9. Then, the charged toner 5 moves to the developing roll 2 side due to the potential difference between the magnetic roll 1 and the developing roll 2 to form a thin layer 6 only of toner on the developing roll 2, and the toner of the toner thin layer 6 is further formed. Reference numeral 5 denotes a direct current (DC) bias 7a (V) applied to the electrostatic latent image carrier (photoconductor) 3. dc1 ), An electrostatic latent image formed on the electrostatic latent image carrier (photoconductor) 3 is caused to fly and developed by a bias superimposed with an alternating current (AC) bias 7b. The toner 5 of the toner thin layer 6 remaining on the developing roll 2 after the development has only the brush effect due to the difference in peripheral speed between the rolls when the magnetic brush 10 on the magnetic roll 1 comes into contact with the toner thin layer 6 on the developing roll 2. Thus, it is possible to easily collect and replace the toner without providing a special device such as a scraping blade.
[0039]
The low-resistance carrier 4-1 is for collecting the residual toner remaining on the developing roll 2, and in the present invention, the volume resistivity is 10 6 A ferrite carrier with Ωcm, saturation magnetization of 70 emu / g, and average particle size of 35 μm was used. That is, in order to collect the toner remaining after development from the developing roll, 10 8 It is necessary to use a low resistance carrier of ΩCm or less, and to peel off the toner firmly and electrostatically attached at the nip between the developing roll and the magnetic roll with a magnetic brush. In order to improve the peelability by the electrode effect of the magnetic brush formed in the nip between the developing roll and the magnetic roll, it is effective to set the saturation magnetization of the low resistance carrier to a high magnetic force of 67 emu / g or more. . When the saturation magnetization of the low-resistance carrier is less than 67 emu / g, the electrode effect at the time of recovery and the scraping effect by the magnetic brush are lowered, and a sufficient effect cannot be obtained. At this time, in order to increase the contact point 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 of the carrier. Examples of high magnetic force and low resistance carriers include magnetite carriers, Mn ferrites, Mn-Mg ferrites, etc. These carriers may be used as they are, but they may be used after being surface-treated within a range where resistance is not increased. Is possible.
[0040]
The high resistance carrier 4-2 is for holding the negatively charged positively charged toner 5. In the present invention, the ferrite surface is covered with a high molecular weight polyethylene surface polymer and treated with a resistance adjusting agent. The coating material is used so that it has a tough surface performance with respect to problems such as toner adhesion and coating peeling, and the coating agent is not peeled off until the mechanical life of the developing device is exhausted. In general, in the case of a surface-coated carrier, when the surface coating agent is peeled off by 20% or more, the charging performance to the toner changes, and in the case of the developing method of the present invention, an image due to toner scattering due to poor charging at 5 μC / g or less. Contamination occurs, and if it is 20 μC / g or more, the development performance deteriorates and selective development or the like is likely to occur.
[0041]
The high-resistance carrier 4-2 is particularly important for charging the toner 5 and is effective in suppressing toner scattering from the developing roll 2 when alternating current (AC) is applied at the same time as charging the toner 5. There is. That is, the low-resistance carrier 4-1, which places importance on recovery, is effective as a countermeasure for development afterimage (ghost), but it is difficult to maintain development without causing fogging by applying accurate charging to the toner 5. In addition, since toner 5 scatters from the surface of the developing roll 2 when it is operated for a longer period of time and causes a problem of contaminating the charger and the exposure unit, a high resistance carrier 4-2 having charging performance should be used in combination. Is essential.
[0042]
This high-resistance carrier 4-2 has an average particle diameter of 50 μm or more, holds a polymerization catalyst on the surface of a ferrite magnetic carrier having a saturation magnetization of 60 to 200 emu / g, introduces ethylene gas, and grows by polymerization. A surface coating is formed with a high molecular weight polyethylene having a weight average molecular weight Mw of 50,000 or more so that the coating amount is 1 to 5 Wt% in terms of polyethylene amount, and the surface is made of 10 by conductive particles. 9 -10 12 An electrostatic latent image developing carrier whose resistance is controlled to Ωcm is preferable. Resistance value is 10 8 If it is less than Ωcm, carrier development and fog may occur. 12 If it exceeds Ωcm, there is a risk of image quality deterioration such as a decrease in image density. The resistance value displayed here is an electrode area of 5 cm. 2 In addition, a carrier layer having a thickness of 0.5 cm is provided for a load of 1 kg, a voltage of 1 to 500 V is applied to the upper and lower electrodes, and a current value flowing therethrough is measured and converted.
[0043]
For such a high resistance carrier, for example, as proposed by the present applicant in Japanese Patent Laid-Open No. 10-142843, a carrier core material having magnetism and a high molecular weight polyethylene resin covering the surface of the carrier core material are used. And a coating layer made of a high molecular weight polyethylene resin containing at least an outermost shell layer containing a charge adjusting agent, a resistance adjusting agent, a fluidity adjusting agent, etc. By setting various external additives on the surface of the high molecular weight polyethylene, durability and charge control can be achieved. As the high resistance carrier, a carrier treated with a treatment agent having high resistance can be used as long as high durability performance is confirmed in addition to the above carrier.
[0044]
The mixing ratio of the high-resistance carrier 4-2 and the low-resistance carrier 4-1 is such that the low-resistance carrier 4-4-1 in all the carriers 4 is collected from the viewpoint of the recovery performance of the toner 5 remaining on the developing roll 2 and the charging of the toner 5. It is appropriate that the ratio of 1 is about 50% to 80%. If it is 50% or less, the toner 5 cannot be sufficiently collected, and an afterimage (ghost) is observed, and if it is 80% or more, scattering of the toner 5 cannot be prevented.
[0045]
The mixing ratio of the toner 5 in the present invention is 2 to 40% by weight, preferably 3 to 30% by weight, more preferably 4 to 25% by weight of the toner 5 with respect to the total amount of the carrier 4 and the toner 5. . That is, if the mixing ratio of the toner is less than 2% by weight, the charge amount of the toner 5 becomes high and a sufficient image density cannot be obtained, and if it exceeds 40% by weight, a sufficient charge amount cannot be obtained. Are scattered from the developing unit, contaminating the inside of the image forming apparatus and causing toner fog on the image.
[0046]
Thus, by combining both carriers at a fixed ratio, it is possible to collect the toner 5 of the toner thin layer 6 on the developing roll and to recharge the charged toner 5 to the developing roll 2 again while collecting it. Become. The toner 5 is controlled to 5 to 20 μC / g, prevents toner scattering and fogging, and develops with a low electric field, leaving no development history phenomenon on the developing roll 2 and excellent toner 5 recoverability. A developing method in the image forming apparatus can be provided.
[0047]
The surface potential (charging potential) of the electrostatic latent image bearing member (photoconductor) 3 is set to 250 V or less and the post-exposure potential is set to 100 V or less, thereby reducing the potential applied to the developing roll 2. Sufficient image density can be obtained. As the electrostatic latent image carrier (photoconductor) 3 used in the image forming apparatus, a positively charged organic photoconductor (OPC) has been conventionally known. When a photoconductor (OPC) is used, it is important to set the film thickness of the photosensitive layer to 25 μm or more and increase the amount of charge generation material added in order to make the residual potential 100 V or less. In particular, an organic photoreceptor (OPC) having a single layer structure is advantageous because a charge generating material is added to the photosensitive layer.
[0048]
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 and excellent durability and function retention (maintenance-free) compared to an OPC photosensitive member. 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 in this way, manufacturing time and manufacturing cost are required, which is economically disadvantageous. Therefore, the present applicant has proposed an a-Si photosensitive member in which the thickness of the photosensitive layer is set to less than 25 μm in Japanese Patent Application Laid-Open No. 7-175276.
[0049]
When an a-Si photosensitive member is used as the photosensitive material for the electrostatic latent image carrier (photosensitive member) 3, the post-exposure potential on the surface has a very low characteristic of 10 V or less. If the thickness is reduced, the saturation charging potential is lowered, and the withstand voltage leading to dielectric breakdown is lowered. On the other hand, the charge density on the surface of the electrostatic latent image carrier (photoconductor) 3 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 for an a-Si photoreceptor having a dielectric constant of about 10 or less, more preferably 20 μm or less.
[0050]
However, when the thickness of the photosensitive layer 22 is less than 10 μm, it is difficult to adjust the potential of the electrostatic latent image carrier (photoconductor) 3 and so-called black spots and fog are likely to occur. On the other hand, when the thickness of the photosensitive layer 22 is less than 10 μm, the saturation charging potential is lowered, and there is a tendency that a necessary charging potential cannot be secured. On the other hand, if the thickness of the photosensitive layer 22 exceeds 25 μm, low-potential development becomes difficult, and ozone tends to be generated, or the manufacturing time of the photosensitive layer tends to be long, which tends to be economically disadvantageous. Furthermore, since the time required for the holes generated in the charge generation layer in the photosensitive layer 22 to move to the surface of the photosensitive layer becomes long, it becomes difficult to adjust the potential of the electrostatic latent image carrier (photosensitive member) 3, so-called fogging. And problems such as low image density are likely to occur. Therefore, the thickness of the photosensitive layer 22 in the electrostatic latent image carrier (photosensitive member) 3 is from the viewpoint of better balance between adjustment of the potential of the electrostatic latent image carrier (photosensitive member) 3 and economy. The thickness is more preferably set to a value in the range of 11 to 25 μm, and further preferably set to a value in the range of 12 to 18 μm.
[0051]
Further, as a more preferable state of the photosensitive layer 22, the thickness of the surface protective layer 23 is preferably set to a value of 0.3 μm or more and 5 μm or less. That is, when the thickness of the surface protective layer 23 is less than 0.3 μm, the characteristics such as the saturated charging potential, wear resistance, and environmental resistance of the photosensitive layer 22 tend to deteriorate, whereas the surface protective layer If the thickness of 23 exceeds 5 μm, it causes deterioration in image quality, and the manufacturing time becomes longer, which is economically disadvantageous. Therefore, it is more preferable to set the thickness of the surface protective layer 23 to a value within the range of 0.3 to 3 μm from the viewpoint of a better balance between the saturation charging potential of the photosensitive layer 22 and the manufacturing time.
[0052]
The material constituting the photosensitive layer 22 is not particularly limited as long as it is amorphous silicon (a-Si). Preferred materials include inorganic materials such as a-Si, a-SiC, a-SiO, and a-SiON. Materials can be exemplified. Further, as the surface protective layer 23, a-SiC has a particularly high resistance, and is more suitable as a photosensitive layer material in the present embodiment because it can provide a more excellent saturated charging potential, abrasion resistance, and environmental resistance. is there. Moreover, it is preferable to use a specific ratio of Si and C (carbon) among a-SiC. As such a-SiC, a-SiC may be used. (1-X) C x (0.3 ≦ X ≦ 1.0), more preferably a-Si (1-X) C x (0.5 ≦ X ≦ 0.95). This is because such a-SiC is 10 12 -10 13 This is because it has a particularly high resistance of Ωcm, and an excellent saturation charging potential, wear resistance, and environmental resistance (moisture resistance) can be obtained.
[0053]
The bias between the developing roll 2 and the electrostatic latent image carrier (photoconductor) 3 is a DC bias power source 7a (V dc1 ), Which is determined by the AC bias power source 7b, but in order to efficiently collect the undeveloped toner with the magnetic roll 1, the bias 8 (V dc2 ) Is preferably 500 V or less. DC bias power supply 7a (V dc1 If a voltage of 150 V or more is applied at (1), the electrostatic force with which the toner adheres to the developing roll 2 increases, making it difficult to collect with a magnetic brush. Further, by using an alternating electric field with the AC bias power supply 7b, the development onto the electrostatic latent image carrier (photoconductor) 3 can be performed accurately, and the development residual toner on the magnetic roll 1 can be easily collected. There are benefits.
[0054]
FIG. 3 shows an excellent development DC bias potential 7a (V) in which no development afterimage (ghost) or fog occurs in the developing device of the present invention. dc1 ) And 8 (V dc2 ). Horizontal axis is potential difference | V dc2 -V dc1 Represents the bias potential (V dc1 ). As shown in FIG. 3, the bias potential (V dc1 ) Is higher than 150V, a ghost occurs and the potential difference | V dc2 -V dc1 Even if | becomes less than 100V, a ghost is generated. Therefore, the DC bias potential 7a (V dc1 ) Is 150 V or less, and the DC bias potential of the magnetic roll 1 is 8 (V dc2 ) And DC bias potential 7a (V dc1 ) | V dc2 -V dc1 If | is in the range of 100 V to 350 V, it can be seen that high quality image quality can be obtained. As an alternating current (AC) bias power supply 7 b applied to the developing roll 2, the peak-to-peak voltage (V p-p ) Is set to be in the range of 500 to 2000 V and the frequency in the range of 1 to 3 kHz.
[0055]
Setting the developing bias low in this way suppresses the dielectric breakdown of the a-Si thin film of the electrostatic latent image carrier (photosensitive member) 3 and prevents the toner 5 from being excessively charged. It is effective in suppressing the occurrence. Further, a thin toner layer 6 having a thickness of 10 to 100 μm, preferably 30 to 70 μm, is formed on the developing roll 2, and a gap between the developing roll 2 and the electrostatic latent image carrier (photoconductor) 3 is 150 to 400 μm, preferably A clear image can be obtained by setting the toner to 200 to 300 μm and causing the toner to fly on the electrostatic latent image carrier (photoconductor) 3 by a direct current and an alternating electric field.
[0056]
The gap between the regulating blade 9 and the magnetic roll 2 is 0.3 to 1.5 mm, and the gap between the magnetic roll 1 and the developing roll 2 is similarly about 0.3 to 1.5 mm. By doing so, the toner thin layer 6 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 the toner 5 when the average particle size of the toner 5 is 7 μm. The gap between the developing roll 2 and the electrostatic latent image carrier (photoconductor) 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 5 to fly to the electrostatic latent image carrier (photoconductor) 3, and a sufficient image density cannot be obtained. Further, it becomes a factor that causes selective development.
[0057]
In the present invention, the non-image forming period from the development of one image when continuously forming a plurality of images of each process unit to the start of the development of the next image, or before the start of image formation, An equipotential state in which the potentials between the two rolls are made equal while the developing roll 2 and the magnetic roll 1 are rotated is generated, and in this equipotential state, the residual image toner of the toner thin layer 6 on the developing roll 2 is transferred to the magnetic brush 10. Collect with.
[0058]
Note that the non-image forming period may be detected based on, for example, print image data sent to the exposure device 57, or may be detected based on the leading edge or the trailing edge of the recording medium in the paper feeding cassette 53, for example. .
[0059]
The electrostatic latent image carrier (photoconductor) 3 is made of a-Si having a layer thickness of 15 μm, the surface potential is set to 230 V, and the DC bias 7a (V dc1 ) Is 50V, and the AC (AC) bias 7b is the peak-to-peak voltage (V p-p ) 1.1 kV, frequency 3.0 kHz, DC bias 8 to magnetic roll 1 (V dc2 ) Is set to 200 V, and the surface potential of the developing roll 2 (that is, the DC bias 7a (V dc1 )) And the surface potential of the magnetic roll 1 (ie, DC bias 8 (V dc2 )) Were set to 0 V, and an equipotential state was generated. Then, as shown in FIG. 4, an image is formed with an image pattern arranged so as to continuously develop a solid image composed of rectangular solid black and a halftone image wider than this solid image. We evaluated whether afterimages of solid solid images appeared. Here, although the density of the halftone image is set to 25% of the density of the solid image, this is because an afterimage is relatively likely to appear.
[0060]
As a comparative example, the equipotential state is not set even in the non-image forming period. First, as the comparative example 1, the same bias voltage as that in the image forming period, that is, the DC bias 7a (V dc1 ) Is 50V, and the AC (AC) bias 7b is the peak-to-peak voltage (V p-p ) 1.1 kV, frequency 3.0 kHz, DC bias 8 to magnetic roll 1 (V dc2 ) Is 200 V, and in Comparative Example 2, the bias to the developing roll 2 and the magnetic roll 1 is reversed during the non-image forming period, that is, the DC bias 7a (V dc1 ) 200V, no AC (AC) bias 7b applied, DC bias 8 (V dc2 ) Was set to 50 V, and the initial state, density at the three stages of the 100th sheet and the 1000th sheet, afterimages, and occurrence of fogging were confirmed. The results are shown in Table 1.
[0061]
[Table 1]
[0062]
In Table 1, “◯” in the density column indicates that no blur is observed in the formed image, and “△” indicates that after slight blur is observed, the afterimage and fog column. “○”, “Δ”, “X” marks in FIG. 4 indicate that the image pattern shown in FIG. 4 is printed, and an afterimage or a ghost image cannot be seen on the half image as shown in FIG. As shown in (b), Δ was given when a slight afterimage or ghost image was found on the half image, and x was given when it was clearly recognized.
[0063]
As can be seen from Table 1, in the first embodiment, there is no blurring in the density at any stage of the first, 100th and 1000th sheets, no afterimage and fogging are observed, and good image formation is possible. I understand. On the other hand, in Comparative Example 1, since the same bias was applied during the non-image forming period as during the image forming period, afterimages were gradually accumulated. As a result, afterimages were slightly recognized at the 100th sheet, Furthermore, afterimages were clearly recognized at the 1000th stage. In Comparative Example 2, since a bias in which the potential difference during the non-image forming period was reversed was applied, the occurrence of an afterimage could be suppressed, but the toner charge changed and fogging occurred. A slight amount of fog is observed, and in the 1000th stage, fog is clearly recognized. Therefore, it can be seen from the results shown in Table 1 that by setting the equipotential state during the non-image forming period, the generation of afterimages is suppressed while the occurrence of fogging is avoided, and a clear image is formed.
[0064]
In the above description of the embodiment, the non-image formation period when the present invention forms a plurality of images continuously is set to be equipotential. However, this is also possible even if the non-image formation period before starting image formation is set to be equipotential. The potential of the developing roll 2 and the magnetic roll 1 that is equipotential is set to 0 V. However, it is sufficient that both surface potentials are equal to each other, for example, 50 V may be set for each. Further, this equipotential state may be realized by controlling both surface potentials of the developing roll 2 and the magnetic roll 1 or may be controlled so that the surface potential on one side is matched with the other. Instead of setting the entire period to the equipotential state, only a part may be set to the equipotential state.
[0065]
In addition, when continuously printing an image with an extremely low printing rate or printing only a specific color, the charge of the developer may increase and the toner development amount may change. Before the change occurs, the deteriorated toner is discharged from the process unit so that a stable color image can always be obtained.
[0066]
That is, image data is measured as the number of dots by a CPU (not shown) in the tandem image forming apparatus main body, and the document density a on the image n The original density a for each surface of the measured storage medium is measured. 1 , A 2 , A 3 , ..., a n When the average document density A is less than 3%, the image forming is stopped and the non-image forming state is stopped, and the toner on the developing roll 2 is ejected to the photosensitive member 3 side and consumed. Next, a refresh process for applying an alternating electric field is performed. In the present embodiment, the case where the image formation is immediately stopped has been described. However, when continuous printing is being performed, the image forming may be performed after the end of continuous printing.
[0067]
The developing roll 2 has a surface subjected to blasting treatment with regular or irregular particles, and as an alternating electric field, an AC component of a rectangular wave, a triangular wave, or a sine wave is superimposed on a DC voltage. The image print density is calculated for each print, and an average print rate of a certain number of sheets (for example, 1 to 500 sheets) is calculated. When no image is formed on the photosensitive member 3 according to the print density (non-image formation) Or after the driving of the photoreceptor 3 and the developing roll 2 is stopped, the toner is ejected from the developing roll 2 to consume the toner. The toner adhering to the photosensitive member 3 during the non-image formation by this refresh process is shown in FIG. 6 from the photosensitive member 3 to the recording medium in the tandem type image forming apparatus not using the intermediate transfer member shown in FIG. In the tandem type image forming apparatus using the intermediate transfer member 60, the intermediate transfer member 60 is swept out and discarded by the intermediate transfer member cleaner 63.
[0068]
That is, after calculating the average printing rate, the alternating bias is controlled so that the toner can be consumed when the photosensitive member 3 and the developing roll 2 are in a driving state. It has been experimentally confirmed that toner charge-up is likely to occur when the average printing rate is 3% or less. Further, when the average printing rate is lowered, the amount of residual toner on the developing roll 2 increases, the application time of the alternating bias for peeling the residual toner is lengthened, and the developing roll is rotated a plurality of times to transfer the toner to the photosensitive drum. It is necessary to increase the amount of flying. Therefore, the toner consumption amount in the non-image portion is equivalent to a minimum of 3% original printing, but is set so as to be able to cope with the situation (use environment, etc.) by providing several types of refresh modes. It is desirable. Further, in the refresh step, the refreshing alternating electric field has a higher effective value than the alternating electric field at the time of image formation, so that toner can be easily consumed.
[0069]
In this case, the toner transferred onto the intermediate transfer body 60 in the refresh step is measured by the development amount detection means 64 to determine that the toner amount determined for each color is developed, and the forced consumption toner By measuring the development amount, it is possible to simultaneously detect the deterioration state of the toner. In addition, when toner is transferred onto the intermediate transfer member 60 for refreshing, if there are a plurality of process units that do not satisfy the predetermined development amount, the color is applied to the same portion of the non-sheet passing portion on the intermediate transfer member. By performing the transfer in an overlapped state, this refresh can be performed at high speed.
[0070]
In addition, as described above, when an image with an extremely low printing rate is continuously printed or only a specific color is printed, the toner charge may increase and the toner development amount may change. When the toner (hereinafter referred to as Q / M) rises, the toner adheres tightly to the surface of the carrier 4 and is described in detail in JP-A Nos. 2000-112220 and 2000-112221. The magnetic permeability output value of the developer by the toner density (T / C) sensor decreases, and when Q / M decreases, the toner easily peels off from the carrier surface, and thus the magnetic permeability increases.
[0071]
That is, the magnetic permeability sensor for measuring the toner concentration disclosed in JP 2000-112220 A, JP 2000-112221 A, and the like is provided around a rotation shaft rotatably mounted in a developer container. A screw-type stirrer in which a screw is fixed in a spiral shape, or a stirrer (single-vibration type stirrer) in which a large number of blades inclined in parallel to the axial direction are connected to such a rotating shaft. Since the developer amount on the magnetic permeability sensor changes with each rotation of the stirring device, it pulsates as indicated by 70 in FIG. 7, but when the Q / M of the toner increases, as described above Since the toner adheres tightly to the surface of the carrier 4, the magnetic permeability of the magnetic permeability sensor decreases, and when Q / M decreases, the toner easily peels off and floats from the carrier surface. Permeability is increased.
[0072]
However, in the hybrid development as described above, since the toner is continuously applied with a bias while being rubbed by the magnetic brush 10 particularly during continuous printing, the toner Q / M in the toner thin layer 6 formed on the developing roller 2 is maintained. Is easy to rise. The toner replenishment is performed when the value of the toner density sensor increases and the toner density becomes low. However, as the toner Q / M increases, the magnetic permeability output of the toner density sensor decreases as described above. Although the toner is consumed by printing, the magnetic permeability is low and the toner concentration (T / C) is estimated to be higher than the actual value, so that the toner may not be replenished for a while.
[0073]
Therefore, in the present invention, as described above, the printing rate is read by measuring the number of dots by the CPU (not shown) in the main body of the tandem type image forming apparatus, and the consumed toner amount is estimated by calculation, and the actual toner density is estimated. When a low toner concentration is detected, the refresh process is performed to sweep out the toner.
[0074]
Now, C is obtained by calculating the amount of consumed toner per predetermined number of sheets with the printing rate calculated by the measured number of dots, and the average value of the toner density sensor analog output during the mixer period is Tave (Q / M is The initial average value is defined as Tini. then,
ΔT = Tini-Tave (1)
The consumed toner amount D with respect to the total carrier amount in the developer is
D = C / (total carrier amount in developer) * 100 (%) (2)
When D> 1 (%),
(I) ΔT ≧ 0.2V
In this case, as described above, the developing roll 2 and the magnetic roll 1 are set to an equipotential, for example, a mode in which a solid image is developed on the photosensitive member 3 and the toner is positively swept to the intermediate transfer member.
(Ii) 0V <ΔT <0.2V
In this case, as a mode for sweeping out a little toner, for example, a half image or a line image is developed on the photosensitive member 3, and
(Iii) ΔT ≦ 0V
In this case, it is assumed that the toner container is replaced because the toner has deteriorated.
[0075]
The coefficient of the number of dots in this control is performed by a CPU (not shown) in the tandem type image forming apparatus body when the toner replenishment motor drive is stopped, and the toner replenishment motor drive is performed to replenish the toner. When the toner concentration sensor (permeability sensor) senses this replenishment, it resets the Tini value, C value, and D value, and then repeats the same process.
[0076]
By controlling the toner Q / M in this way, a remarkable difference was observed in the Q / M transition as shown in FIG. That is, in FIG. 8, the X-axis is the number of printed sheets, the Y-axis is the toner Q / M (μC / g), and 80 is the toner charge (Q / M) when the control as described above is performed. The amount 81 is the toner charge (Q / M) amount when such control is not performed. When the control is not performed, the toner charge (Q / M) amount is increased. Clearly has a toner charge (Q / M) amount within a certain range.
[0077]
【The invention's effect】
As described above, according to the first aspect of the present invention, the potential between the two rolls is set to the equipotential state while the developing roll and the magnetic roll are rotated before the image formation period or before the image formation starts. Therefore, the magnetic brush formed on the magnetic roll collects all the toner on the developing roll, eliminates the development history on the developing roll, and suppresses the occurrence of afterimages and fogging. It can be supplied to the developing roll, stable image quality can be obtained over a long period of time, and the process unit can be made compact, whereby the tandem image forming apparatus itself can be made compact.
[0078]
So Book According to the invention, when the toner consumption amount in each process unit is lower than a predetermined amount, the toner is forcibly discharged from the process unit to the recording medium or the intermediate transfer member, so that an image with an extremely low printing rate is continuously displayed. When printing or printing only specific colors, the developer charge is prevented from increasing and the toner development amount is prevented from changing, and the deteriorated toner is discharged from the process unit before changing the image. A stable color image can be obtained, stable image quality can be obtained over a long period of time, and the process unit can be configured in a small size, whereby the tandem image forming apparatus itself can be configured in a small size.
[0079]
More According to the present invention, when an image with an extremely low printing rate is continuously printed or when only a specific color is printed, the charge (Q / M) of the toner is increased and the electrostatic adhesion of the carrier 4 to the surface of the carrier 4 is tight. However, the magnetic permeability output value of the developer by the toner density (T / C) sensor decreases and is estimated to be higher than the actual amount of toner used, preventing the toner from being replenished, and stable image quality can be obtained over a long period of time. In addition, the process unit can be configured in a small size, whereby the tandem image forming apparatus itself can be configured in a small size.
[0080]
And claims 2, 3 According to the present invention described above, the amount of discharged toner can always be grasped, and this control can be performed in a short time even when toner is discharged from a plurality of process units.
[0081]
As described above, according to the present invention, it is possible to prevent the occurrence of an afterimage during continuous development without complicating the developing device, and to supply a reliably charged toner to the developing roll so that the image quality is stable over a long period of time. In addition, a small process unit can be configured, and even when an image with an extremely low printing rate is continuously printed or when only a specific color is printed, the charge of the developer is increased and the toner development amount is reduced. It is possible to prevent the toner from changing, and to discharge the deteriorated toner from the process unit before causing an image change, so that a stable color image can be always obtained.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a developing device in a process unit used in a tandem type image forming apparatus according to the present invention.
FIG. 2 shows a basic layer configuration model of a-Si of an electrostatic latent image carrier (photoconductor) used in the present invention.
FIG. 3 is a diagram for explaining a developing region in which a bias voltage to be applied to the developing device in the image forming apparatus according to the present invention is appropriate.
FIG. 4 is a diagram for explaining the generation of an afterimage that occurs at the content ratio of a high-resistance carrier and a low-resistance carrier.
FIG. 5 is an example of a tandem type image forming apparatus that implements a control method according to the present invention.
FIG. 6 is an example of a tandem type image forming apparatus that implements the control method according to the present invention.
FIG. 7 is a graph showing fluctuations in the output value of the magnetic permeability sensor depending on the toner charge amount (Q / M).
FIG. 8 is a graph showing a difference in toner charge amount (Q / M) between when the control according to the present invention is performed and when the control is not performed.
[Explanation of symbols]
50 Developer container
51 Magnetic roll
52 Development Roll
53 Paper cassette
54 Conveyor belt
55 Electrostatic latent image carrier (photoconductor)
56 Charger
57 Exposure unit
58 Transfer device
59 Fixing device
60 Intermediate transfer member
61 Transfer roller
62 Secondary transfer roller
63 Cleaner for intermediate transfer member
64 Development amount detection means

Claims (3)

  1. In order to develop the latent image formed on the photoconductor by electrophotographic development, a thin layer is obtained by supplying toner from a developing roll disposed facing the photoconductor and a magnetic brush formed of a two-component developer on the developing roll. Control method in a tandem type image forming apparatus that has a plurality of process units each having a magnetic roll for forming the image, and forms an image by transferring an image of each color from each process unit to a recording medium or an intermediate transfer member In
    In the non-image forming period in each process unit, or before the start of image formation, the developing roll and the magnetic roll are rotated to make the potential between the two rolls equal to each other, and in the equipotential state, on the developing roll Residual toner was collected with the magnetic brush, and the toner consumption was estimated from the dot amount of the image data to be printed, and the value of the toner permeability sensor showed a value less than a certain value with respect to the toner consumption. A control method in a tandem type image forming apparatus, wherein toner is forcibly discharged from a process unit to a recording medium or an intermediate transfer member even if the toner charge amount is increased.
  2. 2. A control method in a tandem type image forming apparatus according to claim 1 , wherein the toner amount discharged to the recording medium or the intermediate transfer member is measured for each color by a developing amount detecting means.
  3. Claim 1, wherein the process unit below the predetermined toner consumption amount is as if the plurality there is transferred in a state where color superimposition was the same parts of the non-sheet passing portion on the recording medium or an intermediate transfer member, Or a control method in the tandem type image forming apparatus described in 2 .
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DE2002125182 DE10225182A1 (en) 2001-06-13 2002-06-06 Electrographic image generator has thin toner coating formation area in axial direction on development roller smaller than magnetic brush formation area in axial direction on magnetic roller
CN 02123228 CN1280682C (en) 2001-06-13 2002-06-13 Image forming apparatus
US10/173,416 US6917780B2 (en) 2001-06-13 2002-06-13 Image forming apparatus that prevents attachment of toner to lateral sides of the developing roll

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JP2006091314A (en) * 2004-09-22 2006-04-06 Canon Inc Image forming apparatus
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JP2007086694A (en) * 2005-09-26 2007-04-05 Ricoh Co Ltd Developing device, image forming process unit, and image forming apparatus
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JP2007249109A (en) * 2006-03-20 2007-09-27 Kyocera Mita Corp Method for adjusting developing device
JP2007293068A (en) * 2006-04-26 2007-11-08 Kyocera Mita Corp Image forming apparatus
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JP5699534B2 (en) * 2010-10-25 2015-04-15 富士ゼロックス株式会社 Image forming apparatus
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