JP2005055842A - Image forming method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method and an image forming device capable of always discharging a fixed quantity of toner without making a developing device complicated, without being affected by a variation in printing ratio and a change in temperature, and capable of maintaining a stable image free from density fluctuation over a long period. <P>SOLUTION: When the integral of a toner supply motor driving time for every fixed time is equal to or below a certain fixed quantity, it is judged that deteriorated toner increases in the developing device, and then, the toner is forcibly discharged when developing is not performed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method and apparatus such as a copying machine, a printer, a facsimile, and a composite machine using an electrophotographic method, and more particularly, a two-component developer that charges a nonmagnetic toner using a magnetic carrier. The present invention relates to an image forming method and apparatus in which only a charged toner is held on a developing roller and is allowed to fly to an electrostatic latent image to develop the latent image.

  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 non-magnetic toner using a magnetic carrier, holds only the charged toner on the developing roller, and flies to the electrostatic latent image to develop the latent image There is a hybrid development method.

  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 roller and the charge roller, and the expendables are expensive 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 lowered, and there are problems such as scattering of the toner from the developing device and adhesion of the fine powder toner on the developing roller.

  The hybrid development method has been conventionally studied as a non-contact one-component development means, but in recent years, as a development method capable of high-speed image formation, in particular, a plurality of color images are sequentially formed on a photoconductor 1. It has also been studied for use in drum color superposition. 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.

  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 performance, 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.

  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.

  As another method, a one-component developing method that does not use a carrier has been proposed. However, the method in which the developing roller 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 a charge roll and the layer thickness on the developing roller is regulated by an 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.

  Therefore, as one means for solving these problems, attention has been paid to the above-described hybrid development method in which toner is once charged using a carrier and then the toner is ejected in a non-contact manner with respect to the photoreceptor. That is, in the hybrid developing system, since the developing roller is not in contact with the photoconductor, torque fluctuation does not occur, and a high-speed image forming apparatus that has excellent dot reproducibility and can extend the life can be provided.

  As a conventional technique related to such a technique, a thin layer is formed with a nonmagnetic toner on a donor roll (developing roller) placed in non-contact with a latent image carrier in Patent Document 1, and a latent image is carried by an alternating electric field. Proposals have been made to make the toner fly on a latent image on the body. Further, Patent Document 2 discloses a developing device that uses a supply roller to advance a developer to a donor roll and transfers toner onto the donor roll to form a toner layer.

  However, although these proposals can use a two-component developer to form a thin layer on the donor roll, it becomes difficult to separate the toner on the donor roll when the charge of the toner becomes high, and strong AC An electric field is required. Since this electric field disturbs the toner layer on the latent image carrier, there is a problem with color superposition and the like. Therefore, Patent Document 3 discloses a so-called powder in which an auxiliary electrode made of a wire is provided between a donor roll and a latent image carrier, and a weak alternating electric field is applied to the auxiliary electrode so as not to disturb the developed toner. A cloud development method has been proposed.

  In terms of theory, Non-Patent Document 1 reports the formation of a toner layer on a developing roller using a two-component developer from Toshiba Corporation, and Patent Document 4 has a patent application.

  Further, in the above-described conventional technology, coarse powder of highly developable toner is easily developed on the latent image carrier, and when continuous printing is performed, fine powder of highly chargeable toner accumulates on the developing sleeve. As a result, selective development occurred and the image density tended to decrease. Further, toner charge control is complicated, and it is necessary to apply a high surface potential and a large development electric field to the latent image carrier. Therefore, if a toner consumption area and a non-consumption area are generated on the developing roller, the previous developed image as shown in FIG. There is a problem that a phenomenon that a part of the image appears as an afterimage (ghost) during the next development, that is, a so-called history phenomenon is likely to occur. That is, in FIG. 9, 35 is a solid image composed of rectangular solid black, and 36 and 37 are halftone images wider than the subsequent solid image. As shown in FIG. When the halftone images 36 and 37 are continuously printed, if a toner consumption area and a non-consumption area are generated on the developing roller, an afterimage (ghost) such as 38 in FIG. 9B is generated. Further, when a high-density development pattern is continuously printed, image nonuniformity such as unevenness in image density is likely to occur, which has been a problem in downsizing a developing device.

  In order to prevent this, Patent Document 5 proposes a member for scraping off the development residual toner on the developing roller and a device for collecting the scraped toner, and the toner on the developing roller is surely removed. As a recovery method, Patent Document 6 proposes to use a dedicated recovery roll. However, these methods cause a potential difference between the toner in the developing section and the toner in the non-developing section, and a complicated mechanism is required to prevent the development ghost during continuous printing. It has not been. Further, as a countermeasure against a hysteresis phenomenon using a magnetic brush, Patent Document 7 proposes to collect and supply the toner on the developing roller by setting a wide half-value width region of the magnetic flux density of the supplying roller. Further, as a method for controlling a tandem developing device, Patent Document 8 discloses an application in which the operation of the developing device in the image forming unit other than the image forming unit performing the transfer process is stopped to prevent the deterioration of the developer. Has been made.

  Also, in such a hybrid development system, image density lowering due to selective development, development defects, image deterioration, development ghost, toner scattering, sleeve adhesion, etc. caused by leaving the toner on the developing roller for a long time may occur. Patent Document 9, Patent Document 10 (Patent Document 11), Patent Document 12 and the like disclose a supply roller that forms a magnetic brush using a two-component developer and a donor that carries a thin layer of toner supplied from the supply roller. It has a roll (developing roller) and an electrode provided between the donor roll and the latent image carrier, and a bias comprising DC and AC is supplied to this electrode, and a DC bias is supplied to the developing roller. The roller has a DC bias (Patent Document 10 (Patent Document 11)) that can be switched to a voltage having a different polarity by a switch, An AC bias (Patent Document 9 and Patent Document 12) superimposed on the bias is applied, and the toner on the developing roller is collected to the supply roller by a potential difference using a space between copies or between papers. A hybrid type developing apparatus is disclosed in which charging of toner is stabilized to solve the above problems.

  That is, in the developing devices shown in Patent Document 9 and Patent Document 10, a DC potential difference (Patent Document 10) between the supply roller and the developing roller and an AC bias (Patent Document 9 and Patent Document 12) are formed on the supply roller. A toner thin layer is formed on the developing roller with the magnetic brush, and a toner cloud is formed near the electrode with a bias in which direct current and alternating current applied between the developing roller and the electrode are superimposed. The latent image on the body is developed, and when image formation is completed (Patent Document 10, Patent Document 12) or at regular intervals (Patent Document 9), the switch is switched to remove the toner from the developing roller to the supply roller. Applying a DC bias to collect the toner on the developing roller, and moving the toner on the supply roller to the developing roller by switching the switch during image formation again DC bias is applied to as provided in (Patent Document 10) imaging, in which so as to solve the above problems.

  However, the powder cloud development method described in Patent Document 3 is not a very general method because the wire of the auxiliary electrode is very easily contaminated and image degradation due to vibration occurs. Furthermore, the devices shown in Patent Document 5, Patent Document 6, Patent Document 7 and the like also require the installation of a toner scraping device and a recovery roll, or the stress of toner increases due to the application of a special recovery bias, etc. This may cause a deterioration in the durability performance of the toner, and it takes time to form a layer of the developing roller at the next development timing, thereby impairing the high speed. In addition, during long-term use, the chargeability of the toner changes due to the deterioration of the durability of the carrier, the charging characteristics of the toner on the developing roller change significantly, and the distribution of the charge of the replenishment toner and the recovered toner becomes wider. It was a cause of scattering and fogging. Furthermore, there is a troublesome replacement of a deteriorated carrier, and the actual situation is not practical.

  In addition, the apparatus disclosed in Patent Document 8 as a control method for a tandem developing device stops the operation of the developing device other than the image forming unit performing the transfer process, or is applied between the developing roller and the supply roller. It is necessary to control and switch the high pressure at a high frequency, and it must be expensive, and the developing device has a configuration in which a toner roll, a supply roller, and a stirring member are arranged side by side. There is a drawback that it is difficult. Furthermore, the devices disclosed in Patent Document 9, Patent Document 10 (Patent Document 11), and Patent Document 12 are also the above-described powder cloud developing method, and the wires of the auxiliary electrode are very easily contaminated, and image degradation due to vibrations, etc. Will occur.

  In addition, when a developing device is downsized to continuously print a high density image, the toner cannot be replenished to the developing roller, and the toner charge amount increases but the image density decreases or the printing speed decreases. In order to solve this problem, a scraping device and application of a special recovery bias have been proposed. However, the stress of the toner has increased, which has been a cause of deterioration in durability performance. In addition, during long-term use, the chargeability of the toner changes due to the deterioration of the durability of the carrier, the charging characteristics of the toner on the developing roller change significantly, the charge distribution of the replenishment toner and the collected toner becomes wider, and charging failure Caused toner scattering and fogging.

  In the hybrid developing system, the toner in the developing device goes back and forth between the supply roller and the developing roller by an AC bias, so that the external additive on the toner surface is buried in the toner or is released from the toner. In particular, when printing a document with a low printing rate, toner deterioration is promoted and the image density is lowered.

  Therefore, in order to prevent the occurrence of afterimages during continuous development without supplying a complicated developing device and to supply the charged toner to the developing roller with certainty, Patent Document 13 describes a tandem image forming process in which the development time is not exceeded. Proposed a method that eliminates the potential difference between the supply roller and the developing roller, and collects most of the toner on the developing roller with a magnetic brush, thereby obtaining an image that does not leave a development history at the next development timing. Patent Documents 14 and 15 including Document 13 propose an image forming apparatus that forcibly consumes toner to prevent a decrease in image density when a document having a printing rate of a predetermined value or less is printed. ing.

U.S. Pat. No. 3,866,574 U.S. Pat. No. 3,929,098 JP-A-3-113474 JP 59-121077 JP 11-231652 A JP 2000-81788 A Japanese Patent Laid-Open No. 7-128983 JP 63-249164 A JP-A-6-67546 Japanese Unexamined Patent Publication No. 7-72733 USP 5,420,375 publication JP-A-7-92804 JP 2003-15380 A JP-A-3-271770 JP 2003-15380 A JP-A-3-271770 The Journal of the Electrophotographic Society, Vol. 19, No. 2 (1981), pp. 44-51, “Touchdown Development”, Toshiba Corporation, Ikuo Hosaka, Yoneda, etc.

  However, in the methods disclosed in Patent Documents 13 to 15, the amount of toner to be discharged is determined only by the document printing rate. However, if the image density varies, it is difficult to stabilize the discharging amount only by controlling the printing rate. As a result, it becomes difficult to stabilize the image density at the time of printing a document having a low printing rate. In addition, there is a problem that the progress of the image density decrease also fluctuates due to temperature fluctuation in the developing device.

  In view of the above circumstances, the present invention makes it possible to always discharge a constant toner without affecting the printing rate and temperature change without complicating the developing device, and to produce a stable image with no change in density over a long period of time. An object is to provide an image forming method and apparatus that can be maintained.

In order to solve the above problems, an image forming method of the present invention includes:
A magnetic brush composed of a carrier and toner is formed on the outer periphery of a supply roller that encloses the fixed magnetic pole member while sequentially supplying toner via a toner replenishing motor, and the potential difference between the two rollers is rubbed against the developing roller while sliding the magnetic brush against the developing roller. In an image forming method using a developing device by a developing method in which only a toner is transferred to a developing roller using a toner, and a latent image on a latent image carrier is non-contact developed with a toner thin layer on the developing roller.
When the integrated value of the toner replenishment motor driving time per certain time is less than a certain amount, it is judged that the deteriorated toner is increasing in the developing device, and the toner is forcibly discharged when not developing. .

  In the present invention, the forcible toner discharge amount at the time of non-development is made variable by a combination of the integrated value of the toner replenishment motor driving time every fixed time and the detected temperature in the developing device.

The image forming apparatus according to the present invention is
A magnetic brush composed of a carrier and toner is formed on the outer periphery of a supply roller that encloses the fixed magnetic pole member while sequentially supplying toner via a toner replenishing motor, and the potential difference between the two rollers is rubbed against the developing roller. In an image forming apparatus using a developing device of a hybrid developing system in which only the toner is transferred to the developing roller using a toner, and the latent image on the latent image carrier is non-contact developed with the toner thin layer on the developing roller.
An arithmetic circuit is provided that corrects the forcible discharge amount of deteriorated toner discharged during non-development calculated from the integrated document printing rate based on the integrated value of the toner replenishment motor driving time for a predetermined time.

  In the present invention, a calculation for correcting the forced discharge amount of deteriorated toner discharged during non-development calculated from the integrated document coverage based on the combination of the integrated value of the toner replenishment motor driving time for a predetermined time and the detected temperature in the developing device. It is characterized by comprising a circuit.

The arithmetic circuit calculates a deteriorated toner forced discharge amount based on the following equation.
A (forced toner discharge amount) = (BC) × (D / C) × K
A: Toner forced discharge amount B: Ideal toner replenishment time (ie, ideal toner discharge amount) in a fixed time
C: Total toner replenishment time (actual toner discharge amount) by the toner motor in a fixed time
D: Toner replenishment time calculated from the integrated printing rate over a certain period of time (discharge amount due to printing rate)
K: Correction coefficient (a constant if the correction is 0)

  It is also a feature of the present invention that the correction coefficient K can be varied according to the detected temperature in the developing device based on the above arithmetic expression.

  As described above, when the integrated value of the toner replenishment motor driving time per certain time is equal to or less than a certain amount, it is determined that the deteriorated toner is increasing in the developing device, and the toner is forcibly discharged when not developing. The toner replenishment motor drive time is optimal for grasping the actual toner replenishment amount by carrying out the image forming method of the developing device by the developing method, and the value is an ideal toner usage amount within a fixed time. If it is lower than, it can be judged that the deteriorated toner is increasing in the developing device, so that it becomes possible to always discharge the toner without complicating the developing device and without being influenced by changes in the printing rate. Thus, it is possible to provide an image forming method capable of maintaining a stable image with no density change over a long period of time.

  In the present invention, the amount of forced toner discharge during non-development can be changed even by changing the combination of the integrated value of the toner replenishment motor driving time per fixed time and the detected temperature in the developing device. Therefore, it is possible to provide an image forming method that can always discharge toner at a constant level and can maintain a stable image with no change in density over a long period of time.

  The image forming apparatus according to the present invention further includes an arithmetic circuit that corrects the forced discharge amount of the deteriorated toner that is discharged during non-development calculated from the integrated document coverage based on the integrated value of the toner replenishment motor driving time for a predetermined time. Therefore, it is possible to provide an image forming apparatus that can easily carry out the above-described image forming method.

  The arithmetic circuit corrects the forcibly discharged amount of deteriorated toner discharged during non-development calculated from the integrated document printing rate based on the combination of the integrated value of the toner replenishment motor driving time for a predetermined time and the detected temperature in the developing device. Therefore, the toner discharge amount can be calculated more accurately.

In addition, it is preferable that the arithmetic circuit calculates the deteriorated toner forced discharge amount based on the following equation.
A (forced toner discharge amount) = (BC) × (D / C) × K
A: Toner forced discharge amount B: Ideal toner replenishment time (ie, ideal toner discharge amount) in a fixed time
C: Total toner replenishment time (actual toner discharge amount) by the toner motor in a fixed time
D: Toner replenishment time calculated from the integrated printing rate over a certain period of time (discharge amount due to printing rate)
K: Correction coefficient (a constant if the correction is 0)

  Then, by varying the correction coefficient K according to the detected temperature in the developing device, the toner discharge amount can be accurately calculated even with respect to temperature fluctuations as described above.

  Hereinafter, exemplary embodiments of the present invention will be 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 unless otherwise specified, but are merely illustrative examples. Not too much.

  FIG. 1 is a schematic diagram of an embodiment of an image forming apparatus that performs an image forming method according to the present invention, FIG. 2 is a schematic configuration diagram of a hybrid developing apparatus that performs a developing method according to the present invention, and FIG. FIG. 4 is a cross-sectional view of an example of a hybrid developing device, FIG. 4 is a schematic diagram for explaining the relationship between the photosensitive member of the developing device and the developing device in the image forming apparatus according to the present invention, and FIG. 5 is a control of the image forming apparatus according to the present invention. FIG. 6 is a schematic block diagram of an embodiment of a circuit, FIG. 6 is a graph showing a transition of image density by an image forming method according to the present invention, a conventional printing rate, and deteriorated toner discharge control depending on a driving time of a toner replenishing motor, and FIG. Is a graph showing the required toner discharge amount due to temperature change, FIG. 8 is a graph showing the transition of the deteriorated toner discharge amount and the image density, and FIG. 9 is a diagram for explaining the afterimage generation state in the conventional hybrid developing device. It is a diagram of.

In the figure, reference numeral 1 is a non-magnetic metal material formed in a cylindrical shape, and a plurality of fixed magnets are disposed therein, and a sleeve-like supply roller (magnetic roll) that can rotate around the fixed magnets, and 2 is a supply roller (Magnetic Roll) Developing roller on which a thin layer 6 of toner is formed by a magnetic brush 10 formed on 1, 3 is a photoreceptor (latent image carrier) drum, 4 is a carrier constituting a developer, and 5 is the same. Toner, 6 is a thin toner layer formed on the developing roller 2, 7a is a power source for applying a direct current (DC) bias _Vdc1 to the developing roller 2, and 7b is also applied with an alternating current (AC) bias _Vac to the developing roller 2. 8 is a power source for applying a direct current (DC) bias V _dc2 to the supply roller (magnetic roll) 1, and 9 is for keeping the height of the magnetic brush 10 formed on the supply roller (magnetic roll) 1 constant. No hokiri Blade (layer thickness regulating blade), 11 is exposure by the exposure device 57, 12 is a frame of the developing device, 20 is an image forming device, 21 is a temperature detection sensor for detecting the temperature in the developing device, and 22 is agitating the developer. The paddle mixer 23 supplies to the supply roller 1, 23 is also a stirring mixer that conveys and charges the developer while stirring, 25 is a toner sensor that detects the amount of toner in the developing device 50 </ b> A, and 26 is a partition in the developing device. As is apparent from FIG. 4, the partition plate has both ends in the longitudinal direction shorter than the length of the developing device 50 </ b> A so that the developer can freely pass through the both ends. 5, 40 is an image forming apparatus control circuit, 41 is an image data storage circuit, 42 is an arithmetic circuit, 43 is a developing device 50 control circuit, 44 is a toner motor 51 control circuit, and 50A in FIG. The developing device for black of the apparatus 20, 50B is also a developing device for yellow, 50C is also a developing device for cyan, 50D is also a developing device for magenta, 51 is a toner replenishing motor for replenishing a necessary amount of toner from the toner container, 53 is a paper feed cassette containing recording paper, 54 is an endless belt for transporting the recording paper, 56 is a charger for charging the photosensitive drum 3, and 57 is for exposing the charged photosensitive drum 3. An exposure device for forming a latent image, 58 a transfer device for transferring the developed toner image onto the recording paper, and 59 on the recording paper onto which the toner image has been transferred. A fixing device for fixing the toner image. In the tandem image forming apparatus, as described above, the charger 56, the exposure device 57, the developing device 50, the transfer device 58, the cleaning device, and the like installed around the photosensitive drum (latent image carrier) 3 are compact. In the present invention, the developing device 50 is adjacent to the photosensitive drum 3 and is arranged in a substantially vertical direction.

As the material of the photoconductor 3, an amorphous silicon (a-Si) photoconductor, an organic photoconductor (OPC) or the like can be used. When an a-Si photoconductor is used, the post-exposure potential on the surface thereof is 10 V or less. However, if the film thickness is reduced, the saturation charging potential is lowered and the withstand voltage leading to dielectric breakdown is lowered. On the other hand, when the latent image is formed, the charge density on the surface of the photoreceptor 3 is improved, and the development performance tends to be improved. This characteristic is particularly remarkable when the dielectric constant is as high as about 10 for an a-Si photosensitive member of 25 μm or less, more preferably 20 μm or less. As the developing bias, the output voltage of the direct current (DC) bias V _dc1 power supply 7a is set to 150V or less, more preferably 100V or less, the AC component of the alternating current (AC) bias _Vac power supply 7b is set to Vpp 500 to 2000V, and the frequency is set to 1 to 3 kHz. Development is possible.

Further, as the photoreceptor 3 used in the image forming apparatus, an OPC photoreceptor has been conventionally known. When a positively charged organic photoreceptor (OPC) is used, the residual potential is reduced to 100 V or less, so that the film of the photosensitive layer is used. It is particularly important to set the thickness to 25 μm or more and increase the amount of charge generation material added. In particular, OPC having a single-layer structure is advantageous because the charge generation material is added to the photosensitive layer, so that the sensitivity hardly changes even when the photosensitive layer is reduced. Even in this case, setting the output voltage of the direct current (DC) bias V _dc1 power source 7a as the developing bias to 400 V or less, more preferably 300 V or less is preferable in terms of preventing applying a strong electric field to the toner. 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.

  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 the glow discharge decomposition method or the like, if the photosensitive layer is thick as described above, there is a problem that it takes a manufacturing time and a manufacturing cost and is economically disadvantageous.

  The exposure device 57 can use a semiconductor laser or an LED. When a positively charged organic photoconductor is used, a wavelength around 770 nm is effective, and when an amorphous silicon photoconductor is used, a wavelength around 685 nm is effective. Hereinafter, in the present invention, a case where a positively charged organic photoreceptor is used as the photoreceptor drum 3 and an LED is used as a light source of the exposure device 57 will be described as an example.

The outermost surface of the developing roller 2 is composed of a sleeve made of uniform conductive aluminum, SUS, conductive resin coating, or the like. A direct current (DC) bias (V _dc1 ) 7 a and an alternating current (AC) bias (V _ac ) 7 b are connected to the shaft portion, and between the rotating developing roller 2, the photosensitive drum 3, and the supply roller 1. The bias that superimposes the direct current and the alternating current is applied to. The AC component supplied by the AC bias 7b is a rectangular wave having a duty ratio of 50% or less. In the present invention, as an example, DC bias (V _dc1 ) 7a is 100V, AC bias 7b is Vpp 1.5kV, frequency 3.0kHz, duty (Duty).
The ratio was set to 30%. By directly applying the DC bias (V _dc1 ) 7a and the AC bias 7b to the developing roller 2 in this way, a sharp bias component is applied between the developing roller 2, the photosensitive drum 3, and the supply roller 1 during development. It is possible to improve the reaction of forming the toner layer at the start of development. In addition to the good developability of the latent image on the photosensitive drum 3, the recoverability of the toner thin layer 6 with respect to the supply roller 1 is enhanced, and the stability of continuous printing is improved. As an example, the interval between the photosensitive drum 3 and the developing roller 2 is about 250 μm, and no wire electrode or the like is used between them.

  The gap between the spike cutting blade 9 and the supply roller 1 is about 0.3 to 1.5 mm, and the gap between the supply roller 1 and the developing roller 2 is about 0.3 to 1.5 mm. The toner thin layer 6 on the developing roller 2 is set to a thickness of 6 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 roller 2 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.

  The toner 5 is controlled to 5 to 20 μC / g, prevents toner scattering and fogging, and does not leave a development history phenomenon on the developing roller 2 by developing with a low electric field, and has excellent recoverability of the toner 5 Development system.

As the developer, a carrier 4 having a resistance of 10 ⁶ Ωcm ³ to 10 ⁹ Ωcm ³ having a role of collecting and supplying toner is used, and the developer is strongly and electrostatically provided at the nip between the developing roller 2 and the supply roller 1. The adhered toner is peeled off by the magnetic brush 10 and the toner necessary for development is supplied. At this time, in order to increase the number of contacts with the toner, it is preferable to use a carrier having a small diameter of 40 μm or less and increase the surface area of the carrier. As the carrier 4, a magnetite carrier, a Mn-based ferrite, a Mn-Mg-based ferrite, or the like can be used, and the carrier 4 can be used after being surface-treated within a range that does not increase an appropriate resistance value. In the present invention, as an example, a ferrite carrier having a volume resistivity of 10 ⁷ Ωcm and a saturation magnetization of 70 emu / g and an average particle diameter of 35 μm was used. At 10 ⁶ Ωcm or less, a low-resistance carrier that emphasizes recovery is effective as a countermeasure against development ghosts, but it is difficult to maintain accurate development with no toner fogging and long-term operation. In this case, the toner scatters from the surface of the developing roller 2 and causes a problem that the charger 56 and the exposure device 57 are contaminated. With a resistance of 10 ⁹ Ωcm or more, charging performance can be imparted, but there is a problem that charging tends to increase. By making the resistance value of the carrier 4 appropriate, the toner 5 on the developing roller 2 can be collected and the charged toner 5 can be recharged into the developing roller 2.

  The mixing ratio of the toner 5 and the carrier 4 is 2 to 40% by weight, preferably 3 to 30% by weight, more preferably 4 to 25% by weight of the toner with respect to the total amount of the carrier 4 and the toner 5. If the mixing ratio of the toner 5 is less than 2% by weight, the charge amount of the toner becomes high and a sufficient image density cannot be obtained, and if it exceeds 40% by weight, a sufficient charge amount cannot be obtained. Is scattered from the developing device and contaminates the inside of the image forming apparatus, or toner fog occurs on the image.

The toner thin layer 6 on the developing roller 2 varies depending on the resistance of the developer and the rotational speed difference between the developing roller 2 and the supply roller 1, but a DC bias (V _dc2 ) 8 and DC bias applied to both rollers. It can also be controlled by the potential difference | (V _dc2 ) − (V _dc1 ) | (hereinafter referred to as Δ) of (V _dc1 ) 7 a. When Δ is increased, the toner thin layer 6 on the developing roller 2 becomes thicker, and when Δ is decreased, the toner becomes a thin layer. The range of Δ is generally about 100V to 250V. Then, a toner layer of 10 to 100 μm, preferably 30 to 70 μm, is formed on the developing roller 20, and the gap between the developing roller 20 and the photosensitive member 3 is set to 150 to 400 μm, preferably 200 to 300 μm. A sharp image can be obtained by causing the toner to fly on the photoreceptor 3 by an AC electric field.

For the residual toner, the magnetic brush 10 on the supply roller 1 is in contact with the toner layer 6 on the developing roller 2 without providing a special device such as a scraping blade, and the brush effect due to the peripheral speed difference of each roll, By replacing the developer by stirring the developer of the magnetic brush 10 with a mixer, the toner can be easily collected and replaced. As a method for promoting the replacement of the developer, the rotation speed of the supply roller 1 is set to 1.0 to 2.0 times the speed of the development roller 2, the toner on the development roller 2 is collected, A uniform toner layer can be formed by supplying a developing material having an appropriate toner density to the developing roller. In order to maintain a uniform image density, the potential difference Δ between the developing roller 2 and the supply roller 1 is set to 0 at a time other than the development timing, so that the toner on the developing roller 2 is not burdened. It is effective to collect the water in the supply roller 1. At this time, since the width H ₃ of the magnetic brush 10 of the supply roller 1 is a width for collecting the toner on the developing roller 2, the width H ₁ of the developing roller 2 is shorter than the width H ₃ of the magnetic brush 10 of the supply roller 1. By doing so, the uncollected area can be eliminated without fail. By doing so, there is no toner adhering to the sleeve of the developing roller 2 outside the area of the supply roller 1, and toner scattering at both ends can be eliminated. (See Figure 4)

  As shown in FIGS. 3 and 4, in the developing device 50, the developing roller 2 is disposed in the frame 12 so as to be separated from the photosensitive member 3 by a predetermined distance. Then, the sleeve-like magnetic roll 1 is formed in a cylindrical shape with a nonmagnetic metal material, spaced apart from the developing roller 2 by a predetermined distance, and a plurality of fixed magnets are disposed therein so that the periphery of the fixed magnet can be rotated. Is arranged. Further, an agitation mixer 23 is provided upstream of the magnetic roll 1 with a paddle mixer 22 and a partition plate 26 interposed therebetween. The two-component developer composed of toner and carrier is agitated by the rotation of the agitation mixer 23 and the paddle mixer 22. The mixture is circulated between the agitating mixer 23 and the paddle mixer 22 by a portion that is charged and has no partition at both ends of the partition plate 26. For this reason, a magnetic brush is formed on the surface of the magnetic roll 1 by the two-component developer, and the magnetic brush has a constant layer thickness by the ear-cutting blade 9 and comes into contact with the developing roller 2.

  On the other hand, between the magnetic roll 1 and the developing roller 2, a bias in which an alternating current is superimposed on a direct current by a direct current (DC) power supply 7a and an alternating current (AC) power supply 7b, and a direct current bias by a direct current (DC) power supply 8 are respectively provided. The toner in the magnetic brush on the magnetic roll 1 is applied to the developing roller 2 by the potential difference | DC7a−DC8 | (hereinafter referred to as Δ) of the bias between the direct current (DC) power source 7a and the direct current (DC) power source 8. A thin layer of only toner is formed on the surface. The toner thin layer on the developing roller 2 flies between the photosensitive member 3 with a bias applied to the developing roller 2 by a direct current (DC) power source 7 a and an alternating current (AC) power source 7 b, and is on the photosensitive member 3. The formed latent image is developed. In order to prevent the toner from scattering, the bias from the alternating current (AC) power supply 7b is applied immediately before the development.

  Further, the toner remaining on the developing roller 2 that is not used for development is not provided with a special device such as a scraping blade, and the magnetic brush on the magnetic roll 1 comes into contact with the toner layer on the developing roller 2 and both The developer is collected and replaced by the brush effect due to the difference in peripheral speed of the rolls and the stirring of the magnetic brush by the paddle mixer 22. The toner amount in the developing device is detected by the toner sensor 25. When the toner density becomes low, the toner motor shown as 51 in FIG. 1 is driven, and a necessary amount of toner is supplied from the toner container.

  First, the operation of the image forming apparatus according to the present invention will be briefly described with reference to the schematic diagram of FIG. 1, the schematic configuration diagram of the hybrid developing device of FIG. 2, and the schematic block diagram of the control circuit of FIG. In the forming apparatus 20, an endless belt 54 is arranged so that the recording paper from the paper feed cassette 53 can be conveyed toward the fixing device 59, and the black development is provided above the belt 54 that conveys the recording paper. A device 50A, a yellow developing device 50B, a cyan developing device 50C, and a magenta developing device 50D are provided. These developing devices 50 (A, B, C, D) are respectively developed in close proximity to the supply roller 1 (A, B, C, D) and the supply roller 1 (A, B, C, D). Rollers 2 (A, B, C, D) are arranged, and the photosensitive drum 3 (A, B, C, D) faces the developing roller 2, and further around the photosensitive drum 3, A charger 56 (A, B, C, D) and an exposure device 57 (A, B, C, D) are arranged.

In the tandem type image forming apparatus of the present invention having the hybrid type developing apparatus configured as described above, the two-component developer including the toner 5 and the carrier 4 corresponding to each color such as yellow, cyan, magenta, and black is developed. A magnetic brush 10 is formed on the supply roller 1 shown in FIG. 2 and supplied to each developing device 50 from the agent container, and the toner 5 is charged by stirring. The layer of the magnetic brush 10 on the supply roller 1 is restricted by the restriction blade 9, and the developing device control circuit 43 is added to the supply roller 1 by a signal given from the control circuit 40 of FIG. 5 to the developing device control circuit 43. The potential difference Δ between the direct-current bias (V _dc2 ) 8 and the direct-current bias (V _dc1 ) 7 a applied to the developing roller 2 is controlled to fly on the developing roller 2 and held as a thin layer 6, and the photoreceptor 3. Development is controlled by a bias 7b in which direct current and alternating current are superimposed on each other. In order to prevent toner scattering, alternating current is applied immediately before development.

Then, when a print start signal is given to the control circuit 40 shown in FIG. 5, the control circuit 40 first sets the photosensitive drum 3 composed of a positively charged organic photosensitive member (positive OPC) by the charger 56 to 400 V, for example. Control is performed so as to be charged, and then, for example, a signal is sent to the exposure device 57 using an LED having a wavelength of 770 nm to perform exposure using the image data stored in the image data storage device 41. Then, the post-exposure potential of the photosensitive drum 3 becomes about 70V, and a latent image is formed. This latent image is developed by the developing roller 2 by the DC bias (V _dc1 ) 7a and the AC bias 7b applied to the developing roller 2. The toner is developed with the toner flying from the upper toner thin layer 6 to the photosensitive drum 3 to form a toner image. Then, when the recording paper is sent out from the paper feed cassette 53 by the signal from the control circuit 40 and sent by the belt 54 and reaches the photosensitive drum 3, the transfer is performed by the transfer device 58 (A, B, C, D). A toner image is transferred to the recording paper by applying a bias, and is fixed by the fixing device 59 and discharged. Thereafter, as described above, the control circuit 40 periodically instructs the developing device control circuit 43 based on the print data, and the direct current (DC) bias (V _dc2 ) 8 while applying the alternating current (AC) bias (V _ac ) 7b. And the toner thin layer 6 on the developing roller is collected by the magnetic brush 10.

  In the image forming apparatus configured as described above, according to the present invention, the toner replenishment amount according to the toner replenishment motor driving time of a certain time, that is, the actual amount of toner replenishment, that is, even when the image density fluctuates can be discharged. By calculating the amount of deteriorated toner to be discharged from the replenished toner amount and the value obtained by integrating the document printing rate over a certain period of time, and then discharging the deteriorated toner, the image density when printing low-printed documents can be reduced. It is intended for stability.

That is, in the developing device using the hybrid developing system according to the present invention, the toner 5 in the developing device is transferred between the supply roller 1 and the developing roller 2 by the alternating current (AC) bias V _ac power source 7b. Since the AC bias is applied, the external additive on the surface of the toner 5 is buried in the toner 5 or is released from the toner, and the deterioration of the toner is promoted particularly when a document having a low printing rate is printed. As a result, the image density decreases. Therefore, when the development is not performed between the papers, the development by the developing roller 2 is performed without charging the photosensitive member 3, and the toner is ejected to the photosensitive member 3 and then the photosensitive member 3 is cleaned, thereby discharging the deteriorated toner. To prevent a decrease in image density. However, in general control, the discharge amount of deteriorated toner is determined in consideration of only the original print rate. Therefore, if the image density varies, the discharge amount is stabilized only by the print rate. This makes it difficult to stabilize the image density when printing a document with a low printing rate.

Therefore, in the present invention, when the cumulative driving time of the toner replenishing motor within a certain time is less than a certain amount, it is determined that the toner consumption from the developing device is small (deteriorated toner is increasing in the developing machine), Further, the toner is discharged. This toner discharge amount is calculated from the accumulated toner replenishment time and the accumulated printing rate so that the toner replenishment amount for a certain period of time becomes a certain amount. That is, now, let A be a forced toner discharge amount, and B be the ideal toner replenishment time by the toner motor 51 in a predetermined time (that is, the ideal toner motor 51 drive time, and at the same time the ideal toner time in the fixed time) C is also a cumulative toner replenishment time (actually supplied toner amount, that is, the amount of toner discharged), and D is a constant time. When the toner replenishment time (discharge amount due to the print rate) by the ideal toner motor 51 calculated from the integrated print rate at, and K is a correction coefficient (a constant when the correction is 0), the forced discharge amount of the A toner is It can be calculated by the following equation (1).
A (toner forced discharge amount) = (BC) × (D / C) × K (1)

  In other words, (BC) on the right side of the equation (1) indicates an actual accumulated toner replenishment time (C) by the toner motor at a certain time from an ideal toner replenishment time (B) by the toner motor 51 at a certain time. Is a value obtained by subtracting the toner amount to be forcibly discharged and multiplied by (D / C) is the toner replenishment time (D / C) calculated by the ideal toner motor 51 calculated from the integrated printing rate in a certain time. ) Divided by the cumulative toner replenishment time (C) by the toner motor 51 over a certain period of time, which represents the ratio of how much toner is actually consumed with respect to the printing rate. That is, if the replenishment time by the toner motor 51 is equal to the time calculated from the printing rate, 1 becomes (BC) and the replenishment time by the toner motor 51 is less than the time calculated from the printing rate. For example, it becomes larger than 1 and (B−C) becomes larger, and in the opposite case, it becomes smaller.

  K is a correction coefficient, and a correction amount based on the detected temperature in the developing device is taken into account. For example, as shown in FIG. 7, when the temperature in the developing device rises, the internal humidity is lowered, the toner is easily charged, the toner is deteriorated, and the density is lowered. This is shown in the graph of FIG. 8, which is a measurement of the change in image density by changing the toner discharge amount when a document with a printing rate of 1% is continuously printed in an environment of 32 ° C. . As is apparent from FIG. 7, the discharge amount 150 mg / min is the discharge amount at 25 ° C., 300 mg / min is the discharge amount at 28 ° C., 500 mg / min is the discharge amount at 32 ° C., and 150 mg / min and 300 mg / min. Then, it is apparent that the image density is lowered. Therefore, this K is determined in consideration of the detection result of the temperature detection sensor 21 shown in FIG.

  The equation (1) is calculated by an arithmetic circuit indicated by 42 in FIG. That is, the control circuit 40 of the image forming apparatus 20 calculates and integrates the printing rate by the arithmetic circuit 42 based on the image data stored in the image data storage device 41, and also detects it by the toner sensor 25 shown in FIG. The toner density in the developing device is received, the toner motor control circuit 44 is instructed to replenish the toner, and the toner replenishment time is integrated. Then, when a certain period of time has elapsed or after a certain number of sheets have been printed, a correction coefficient K based on these values and the temperature in the developing device detected by the temperature detection sensor 21 is determined, and data is given to the arithmetic circuit 42. A forced discharge amount A of toner is calculated. Then, as described above, the discharged toner is developed on the photosensitive member 3, cleaned by a cleaning device, and discharged.

  FIG. 6 shows a case where the toner discharge amount is calculated from the printing rate and the driving time of the toner motor 51 based on the equation (1) when a document having a printing rate of 1% is continuously printed in an environment of 25 ° C. 6 is a graph showing image density transition in each case of normal printing in which the toner discharge amount is calculated based on the rate and further no discharge is performed. According to the graph of FIG. 6, it can be seen that the image density continues to decrease during normal printing, and the image density tends to decrease even when the toner discharge amount is controlled only by looking at the printing rate. . This is because, when only the printing rate is controlled, the toner discharge amount decreases when the image density decreases due to an increase in toner charge amount or the like, and the discharge of deteriorated toner cannot catch up. On the other hand, when the control for calculating the discharge amount from the toner replenishment motor driving time and the printing rate is performed, it can be seen that the image density is stable.

  The developing device in the image forming apparatus according to the present invention is as described above. When the integrated value of the toner replenishment motor driving time per certain time is equal to or less than a certain amount, the deteriorated toner is increased in the developing device. When the toner is forcibly discharged during non-development, the toner replenishment motor drive time is optimal for grasping the actual toner replenishment amount. When it is lower, it can be judged that the deteriorated toner is increasing in the developing device, so that it becomes possible to always discharge a constant toner without being influenced by a change in the printing rate without complicating the developing device. It is possible to provide an image forming method capable of maintaining a stable image having no density change over a long period of time.

  In addition, the amount of forced toner discharge during non-development can be changed by the combination of the integrated value of the toner replenishment motor drive time per fixed time and the detected temperature in the developing device, so that it is always constant in response to temperature changes. It is possible to provide an image forming method capable of discharging toner and maintaining a stable image with no change in density over a long period of time.

  The image forming apparatus according to the present invention further includes an arithmetic circuit that corrects the forced discharge amount of the deteriorated toner that is discharged during non-development calculated from the integrated document coverage based on the integrated value of the toner replenishment motor driving time for a predetermined time. Therefore, it is possible to provide an image forming apparatus that can easily carry out the above-described image forming method.

  The arithmetic circuit corrects the forcibly discharged amount of deteriorated toner discharged during non-development calculated from the integrated document printing rate based on the combination of the integrated value of the toner replenishment motor driving time for a predetermined time and the detected temperature in the developing device. Therefore, the toner discharge amount can be calculated more accurately.

  According to the present invention, it is possible to always discharge a constant toner without being influenced by a change in printing rate or temperature without complicating a developing device, and to maintain a stable image with no density change over a long period of time. An image forming method and apparatus can be provided.

It is a schematic diagram of one Example of the image forming apparatus which implements the image forming method which becomes this invention. It is a schematic block diagram of the hybrid type developing apparatus which implements the developing method according to the present invention. It is sectional drawing of an example of the conventional hybrid developing device. It is a schematic diagram explaining the relationship between the photosensitive member of the developing device and the developing device in the image forming apparatus according to the present invention. 1 is a schematic block diagram of an embodiment of a control circuit of an image forming apparatus according to the present invention. 6 is a graph showing a transition of image density by a deteriorated toner discharge control according to an image forming method according to the present invention, a conventional printing rate, and a driving time of a toner supply motor. 6 is a graph showing a required toner discharge amount due to a temperature change. 6 is a graph showing transition of deteriorated toner discharge amount and image density. It is a figure for demonstrating the afterimage generation situation in the conventional hybrid type developing device.

Explanation of symbols

21 Temperature Sensor 25 Toner Sensor 40 Image Forming Apparatus Control Circuit 41 Image Data Storage Device 42 Arithmetic Circuit 43 Developing Device Control Circuit 44 Toner Motor Control Circuit 57 Exposure Device

Claims (6)

A magnetic brush composed of a carrier and toner is formed on the outer periphery of a supply roller that encloses the fixed magnetic pole member while sequentially supplying toner via a toner replenishing motor, and the potential difference between the two rollers is rubbed against the developing roller. In an image forming method using a developing device by a developing method in which only a toner is transferred to a developing roller using a toner, and a latent image on a latent image carrier is non-contact developed with a toner thin layer on the developing roller.
When the integrated value of the toner replenishment motor driving time per certain time is less than a certain amount, it is judged that the deteriorated toner is increasing in the developing device, and the toner is forcibly discharged when not developing. Image forming method.   2. An image forming method according to claim 1, wherein the forcible toner discharge amount during non-development is varied by a combination of the integrated value of the toner replenishment motor driving time per fixed time and the detected temperature in the developing device. A magnetic brush composed of a carrier and toner is formed on the outer periphery of a supply roller that encloses the fixed magnetic pole member while sequentially supplying toner via a toner replenishing motor, and the potential difference between the two rollers is rubbed against the developing roller. In an image forming apparatus using a developing device of a hybrid developing system in which only the toner is transferred to the developing roller using a toner, and the latent image on the latent image carrier is non-contact developed with the toner thin layer on the developing roller.
An image forming apparatus comprising an arithmetic circuit that corrects a forced discharge amount of deteriorated toner discharged during non-development calculated from an integrated document printing rate based on an integrated value of a toner supply motor driving time for a predetermined time.   Provided a calculation circuit that corrects the forced discharge amount of deteriorated toner discharged during non-development calculated from the integrated document coverage based on the combination of the integrated value of the toner replenishment motor drive time for a fixed time and the detected temperature in the developing device. The image forming apparatus according to claim 3. The image forming apparatus according to claim 3, wherein the arithmetic circuit calculates a deteriorated toner forced discharge amount based on the following equation.
A (forced toner discharge amount) = (BC) × (D / C) × K
A: Toner forced discharge amount B: Ideal toner replenishment time (ie, ideal toner discharge amount) in a fixed time
C: Total toner replenishment time (actual toner discharge amount) by the toner motor in a fixed time
D: Toner replenishment time calculated from the integrated printing rate over a certain period of time (discharge amount due to printing rate)
K: Correction coefficient (a constant if the correction is 0)   An image forming apparatus, wherein the correction coefficient K is varied according to a detected temperature in the developing device based on the arithmetic expression according to claim 5.

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