JP2009198898A - Developing method and device in image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide developing method and device in an image forming apparatus, shortening the time required for refresh operation as much as possible and not lowering the toner scrape-off efficiency in performing a refresh operation of scraping off a toner thin layer on a developing roller 2 between paper sheets and then forming a toner thin layer 6 again in the touch-down developing system developing device. <P>SOLUTION: The time required for the refresh operation is shortened by increasing the peripheral speed of the developing roller 2 during the refresh operation more than that during the image formation, and the alternating current peak-to-peak voltage in toner thin layer forming bias applied to the developing roller 2 is made larger than that during the image formation, whereby the refresh operation can be performed without lowering the toner scrape-off efficiency. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing method and apparatus in an image forming apparatus such as a copying machine, a printer, a facsimile, or a composite machine using an electrophotographic method, and more particularly, a two-component that charges a nonmagnetic toner using a magnetic carrier. Using developer, form only a thin layer of charged toner uniformly on the developing roller, and then develop the image by flying toner from the developing roller onto the electrostatic latent image formed on the photosensitive drum. The present invention relates to a developing method and apparatus in an image forming apparatus.

  Development methods using dry toner in image forming apparatuses such as copiers, printers, facsimiles, and composite machines using electrophotography are two-component development methods that use only toner, and toner and carrier. A two-component development system using a component developer is known.

  Of these, the two-component development system is suitable for extending the life because a stable charge amount can be obtained over a long period of time by friction between the toner and the carrier. However, in the two-component development method, development is performed by bringing a magnetic brush formed of the carrier and toner into contact with an electrostatic latent image carrier (hereinafter referred to as a photoconductor), so that the electrostatic latent image can be developed faithfully. Although it is possible, problems such as print smearing (fogging) on non-latent image areas and carrier adhesion problems where the carrier develops with toner or develops on non-latent image areas are likely to occur. There is a drawback that the toner image formed on the photoreceptor is disturbed.

  On the other hand, the one-component developing system that is not in contact with the photoreceptor does not disturb the formed toner image, and can obtain a sharp image with an edge and is advantageous for fogging, and is suitable for high image quality. . However, in this method, the toner is charged by the charge roller, and the layer thickness on the developing roller is regulated by the elastic regulating blade, so that it is difficult to stably maintain the charge amount of the toner. It may adhere to the charge roller and decrease the charging ability, or toner may adhere to the regulating blade, resulting in non-uniform layer formation and image defects, and in the case of color toner, transparency is required. Therefore, it must be a non-magnetic toner.

  Therefore, in a full-color image forming apparatus, a non-magnetic toner is used to develop a one-component development method with the aim of improving the image quality of the development region, and a two-component development method is adopted for the charging region in consideration of extending the service life. A development method called a touch-down development method or a hybrid development method that takes advantage of the respective advantages of these two development methods has attracted attention. In particular, in a full-color image forming apparatus in which high image quality and long life are important, the characteristics of this development method are sufficiently exhibited.

  In this touch-down development method, a magnetic brush is formed on the surface of a developer carrier (hereinafter referred to as a magnetic roller) with a two-component developer containing toner and carrier, and only the toner is transferred from the magnetic brush to a toner carrier (hereinafter referred to as a magnetic carrier). This is a system in which the toner is transferred to the surface of a developing roller to form a thin layer of toner, and then the toner is ejected onto the surface of the photoreceptor on which the electrostatic latent image is formed to develop it as a toner image.

  However, even in this touch-down development method, since a thin layer is formed on the developing roller with a magnetic brush and a bias voltage, there is a problem that toner adheres to the developing roller 2 when an electric field in one direction is continuously applied, A development ghost (history phenomenon) phenomenon in which an afterimage after the toner flies to the photoconductor also appears on the second round occurs. Therefore, it is necessary to remove the thin layer formed on the developing roller and to perform a work called refreshing to form a new thin layer. For example, it is peeled off with a blade, an elastic roller, etc. There is a method in which a bias voltage is applied so as to generate a reverse potential difference between papers.

  Further, for example, in Patent Document 1, when the toner thin layer on the developing roller is peeled off between recording papers and a new toner thin layer is re-formed on the developing roller, the developing roller is used with respect to the peripheral speed of the photoreceptor. The peripheral speed of the developing roller is set to 1.5 times or more, the magnetic roller is rotated at a peripheral speed more than 1.5 times with respect to the developing roller, and the DC bias voltage of the developing roller is set higher than the developing voltage. Thus, there is shown a developing method and apparatus in an image forming apparatus in which a toner thin layer is peeled off and re-formed. When the peripheral speed of the magnetic roller is made faster than that of the developing roller as in Patent Document 1, in order to peel off the toner thin layer for one rotation of the developing roller, the magnetic roller must be rotated one or more times. The stripping by the second round of the magnetic roller is inefficient and cannot be stripped sufficiently. Therefore, when stripping the second round of the magnetic roller, the DC bias voltage for stripping is set higher than that of the first round. ing.

Further, in Patent Document 2, the distance from the layer forming nip that forms a thin toner layer on the developing roller with a magnetic roller to the developing nip where the developing roller and the photosensitive member face each other is d1, and the distance from the layer forming nip to the developing nip is defined as d1. When the distance is d2, d2> d1, so that the developing roller makes one round to peel off the toner thin layer on the developing roller and the developing roller makes two rounds to re-form a new toner thin layer. , The time from the end of the previous development to the start of the next development (between paper),
The next development can be started in a short time of three rotations or less of the developing roller so that the rotation time is two rotations of the developing roller + d1 minutes, and a toner layer thickness detection pattern is formed on the developing roller to form a toner density. 1 shows a developing device in an image forming apparatus which is detected by a sensor and thereby controls the thickness of a toner layer formed on a developing roller by controlling a DC bias voltage for forming a toner layer.

  Further, Patent Document 3 discloses that when the toner roller is rotated by changing the potential difference between the developing roller and the magnetic roller between papers and the toner layer on the developing roller is peeled off, layer unevenness occurs. Image forming apparatus in which the linear velocity of both rollers is controlled so that the other roller has a circumferential length within the time when one roller rotates once and rotates once in excess or deficiency within a range of ± 2 mm or less. The developing method and apparatus are shown in FIG.

  Further, in Patent Document 4, the developing roller and the magnetic roller can be controlled independently from the photosensitive member, the intermediate transfer roller, and the like, and the linear velocity M of the magnetic roller is set as the linear velocity of the developing roller at the time of image formation and toner thin layer re-formation. S is about 1.5 times S, and when the toner layer is peeled off from the developing roller, the linear velocity S of the developing roller is made faster than the linear velocity M of the magnetic roller, and the time difference for one rotation of each roller is reduced. In the image forming apparatus, the toner is reliably collected by peeling off the toner for one circumference of the developing roller within one revolution of the magnetic roller, and the toner collecting time is shortened.

JP 2005-055837 A JP 2005-055839 A JP 2005-055840 A Japanese Patent Laid-Open No. 2006-337587

  However, as shown in these Patent Documents 1 to 4, if the image is peeled off at a non-image timing, such as between papers, the developing roller will be peeled off by one turn and the next printing will be carried out. Therefore, it is necessary to provide a time until the toner thin layer thickness is stabilized, and the printing speed is lowered. Usually, in order to prevent a decrease in printing speed, it is common to compensate for the delay between the papers by increasing the developing linear speed or mechanical linear speed. An image defect occurs in which the line speed ratio increases and the trailing edge of graphics or the like becomes darker, and when the machine linear speed is increased, the fixing performance and transfer performance are impaired.

  Although the method of reducing the linear speed ratio between the magnetic roller and the developing roller as in Patent Document 4 is effective, the passing time of the nip portion between the developing roller and the magnetic roller is shortened, and the toner stripping efficiency is reduced. As a result, there arises a problem that the collection performance when the toner charge amount is increased is weakened.

  Therefore, in the present invention, in the touch-down development type developing device, when performing the refresh operation of peeling off the toner thin layer on the developing roller at a non-image timing such as between papers and then re-forming the toner thin layer, The time required for the refresh operation is shortened as much as possible, and the recovery performance when the toner charge amount is increased is maintained without lowering the toner removal efficiency, and a good refresh operation is performed to always form a high-quality image. An object is to provide a developing method and apparatus in an image forming apparatus configured as described above.

In order to solve the above problems, the developing method in the image forming apparatus according to the present invention is as follows.
A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller containing a magnet, a toner thin layer is formed on the developing roller from the magnetic brush, and an alternating current is applied to the direct current applied to the developing roller. The toner is caused to fly to the electrostatic latent image formed on the photosensitive member by the superimposed developing bias, and the toner thin layer on the developing roller is peeled off between the paper from the end of the image formation to the next image formation to newly In a developing method for performing development by performing a refresh operation for forming a thin toner layer,
In the refresh operation, the peripheral speed of the developing roller is made faster than that at the time of image formation, and the peak-to-peak voltage in the AC bias applied to the developing roller is made larger than that at the time of image formation.

And the developing device for carrying out this developing method is:
A magnetic roller on which a magnetic brush of a two-component developer composed of toner and a carrier is formed, and a thin toner layer is formed by the magnetic brush, and is formed on the photosensitive member by a developing bias in which alternating current is superimposed on applied direct current. A developing roller that develops the toner by flying toner onto the electrostatic latent image, and an independent drive mechanism that changes the rotational speed of the developing roller independently of the photosensitive member and the magnetic roller.
A developing roller bias voltage control device that controls a developing bias voltage applied to the developing roller, and detects a sheet interval from the end of image formation to the next image formation in a continuous image forming state, and develops the developing roller independent drive mechanism. The roller rotation speed is made higher than that at the time of image formation, and the developing roller bias voltage control device is made to increase the peak-to-peak voltage in the AC bias voltage from that at the time of image formation. And a control device for performing a refresh operation for forming a thin layer.

  In this way, an independent drive mechanism that changes the rotation speed of the developing roller independently of the photosensitive member and the magnetic roller is provided to increase the rotation speed of the developing roller between sheets as compared to the time of image formation, and at the AC bias voltage of the developing roller. By making the peak-to-peak voltage larger than when forming an image and performing the refresh operation, the time required for the refresh operation is shortened first, and the toner charge amount is increased by applying an AC bias with a large peak-to-peak voltage. Even in this case, it is possible to provide a developing method and a developing apparatus that can maintain the collection performance and can always form a high-quality image by performing a good refresh operation.

  In addition, when the image density in the image data for the entire circumference of the developing roller on the end side of the formed image is close to the maximum density, most of the toner on the developing roller is used for development, and in this case, there is no need to perform a refresh operation. From the above, the refresh operation is performed except for the case where the image density in the image data for approximately one round of the developing roller on the end side in the formed image is close to the maximum density during the continuous image formation, and thus the control device for performing the refresh operation. Has a function of calculating the image density from the image data of approximately one turn of the developing roller on the end side of the formed image in the continuous image forming state, and is configured to perform the refresh operation corresponding to the calculation result. Therefore, the image forming speed can be increased as compared with the case where the refresh operation is always performed between sheets.

  As described above, according to the present invention, the time required for the refresh operation can be shortened, and the recovery performance can be maintained even when the toner charge amount is increased without lowering the toner removal efficiency. Thus, it is possible to provide a developing method and apparatus in an image forming apparatus that can always form a high-quality image.

  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.

  First, the outline of the present invention will be briefly described. In the present invention, a two-component developer magnetic brush comprising a toner and a carrier is formed on a magnetic roller containing a magnet and applied with a DC bias. Touch that develops after forming a thin toner layer on the developing roller with a magnetic brush and then flying toner onto the electrostatic latent image formed on the photoconductor with a developing bias in which alternating current is superimposed on the direct current applied to the developing roller. In the down-development device, if an electric field in one direction is continuously applied from the magnetic roller to the developing roller during continuous image formation, there is a problem that the toner adheres to the developing roller. Suitable for development methods in which the toner thin layer formed on the developing roller is peeled off to form a new toner thin layer, and a refresh operation is performed for development. It is intended to be.

  In this refresh operation, it takes about one turn of the developing roller to peel off the thin toner layer on the developing roller, and about two turns of the developing roller until the thickness of the new toner thin layer to be formed thereafter is stabilized. As a result, the continuous image forming speed decreases as it is. However, as a countermeasure for this, if measures such as increasing the developing linear speed or increasing the mechanical linear speed are taken, as described above, if the developing linear speed is increased, the linear speed ratio between the photosensitive member and the developing roller increases, and graphics, etc. An image defect occurs in which the trailing edge becomes dark, and when the machine linear speed is increased, a defect such as deterioration of fixing performance or transfer performance is induced.

  For this reason, in the present invention, as in Patent Document 4, an independent drive mechanism is provided so that the developing roller can be driven independently of the photosensitive member and the magnetic roller. Decreasing the image forming speed was reduced by making it faster than the time of formation. However, in this case, there is a problem that the passing time of the nip portion between the developing roller and the magnetic roller is shortened, the efficiency of toner removal is lowered, and the collection performance when the toner charge amount is increased is weakened. For such problems, a method of increasing the DC bias voltage, a method of increasing the frequency of the AC bias voltage, and a peak-to-peak voltage (Vpp: peak to peak) of the AC bias voltage as in Patent Document 1 and Patent Document 2.・ There are methods to increase the peak.

  However, when the charge amount of the toner attached on the developing roller is high, the toner on the upper layer can be peeled off even if the DC bias voltage is increased, but it is difficult to peel off the toner firmly attached on the developing roller. In the method of increasing the frequency of the AC bias voltage, if the frequency is too high, the toner also has a mass and cannot be followed, and effective stripping is still difficult. Therefore, in the present invention, the peak-to-peak voltage of the AC bias applied to the magnetic roller is increased, thereby increasing the toner stripping efficiency.

  When the image to be formed is an image with the maximum density (solid image), most of the toner thin layer on the developing roller is used for development, and toner does not remain to the extent that it needs to be peeled off. For this reason, in addition to the refreshing operation between sheets, the development image data sent to the control unit is referred to approximately one rotation of the developing roller immediately before the sheet interval, and the data is a solid image, that is, the maximum density. The image forming speed was increased by not performing the refresh operation and minimizing the gap between sheets.

  In this way, even when a refresh operation is performed, a decrease in image formation speed can be suppressed as compared to the conventional case, and when the image data for one rotation of the developing roller just before the sheet is a solid image, the refresh operation is not performed. As a result, the image forming speed can be further increased, and the peak-to-peak voltage of the AC bias applied to the magnetic roller is increased, so that the recovery performance is maintained even when the toner charge amount is increased without decreasing the toner stripping efficiency. Therefore, it is possible to provide a developing method and apparatus in an image forming apparatus that can always form a high-quality image by a good refresh operation.

  The above is the outline of the present invention. Next, the schematic cross-sectional view of the image forming apparatus shown in FIG. 5 and the schematic cross-sectional view of the touch-down developing apparatus for performing the developing method according to the present invention shown in FIG. An embodiment of an image forming apparatus and an embodiment of a developing apparatus that use the developing method of the present invention will be briefly described. In the following description, the same components are given the same numbers.

  First, the image forming apparatus 20 shown in FIG. 5 corresponds to each of the colors of black (K), yellow (Y), cyan (C), and magenta (M) that are generally used in a color image forming apparatus. A photosensitive drum for black indicated by 3Y, a photosensitive drum for yellow indicated by 3Y, a photosensitive drum for cyan indicated by 3C, and a photosensitive drum for magenta indicated by 3M. , 56Y, 56C, 56M, exposure devices 57K, 57Y, 57C, 57M, a magnetic roller 1 indicated by 1K, 1Y, 1C, and 1M, and a developing roller 2 indicated by 2K, 2Y, 2C, and 2M. The paper transport direction in the endless belt 54 that transports the paper picked up from the paper feed cassette 53 through the units composed of the developing devices 50K, 50Y, 50C, 50M, etc. Is a tandem type color image forming apparatus having an array.

  58K, 58Y, 58C, and 58M are transfer devices that transfer the toner image formed on the photosensitive drum 3 onto the sheet conveyed by the endless belt 54, and 59 is a toner image of each color thus transferred. A fixing device that heats and pressurizes a sheet to fix a toner image on the sheet. In the following description, the case where the present invention is applied to the tandem type image forming apparatus shown in FIG. 5 will be described as an example. However, the present invention is an image forming apparatus using a touch-down developing device. Obviously, the present invention can be applied to any type of image forming apparatus.

  FIG. 1 is a schematic sectional view of a touch-down developing device 50 in which a photosensitive drum 3, a magnetic roller 1 and a developing roller 2 are arranged in the image forming apparatus shown in FIG. In the figure, reference numeral 1 denotes a magnetic roller having a fixed magnet (not shown) inside a rotating sleeve, which holds a magnetic brush 10 composed of a carrier 4 and a toner 5 and whose layer is regulated by a spike cutting blade 9, and a DC bias ( Vdc2) A DC bias from the power supply 8 is applied. Reference numeral 2 denotes a developing roller in which a toner thin layer 6 is formed by a magnetic brush 10 formed on the magnetic roller 1 and a toner thin layer forming bias applied between the magnetic roller and the developing roller, and a direct current bias (Vdc1). The toner is caused to fly from the toner thin layer 6 to the electrostatic latent image formed on the photosensitive drum 3 by the developing bias in which the alternating current is superimposed on the direct current applied from the power source 7a and the AC bias (Vac1) power source 7b. Develop.

  As described in the outline of the present invention, the developing roller 2 is driven by a motor via a clutch or a speed reduction mechanism so that its peripheral speed can be driven independently of the photosensitive drum 3 and the magnetic roller 1. Can be transmitted or driven by an independent motor. 11 is a developing roller peripheral speed / bias control device for controlling the peripheral speed of the developing roller 2 and the voltage of the DC bias (Vdc1) power source 7a and the AC bias (Vac1) power source 7b. A magnetic roller peripheral speed / bias control device 13 for controlling the peripheral speed of the roller 1 and the DC bias (Vdc2) power supply 8 is a control device for controlling the entire image forming apparatus.

  As described above, the control device 13 controls the entire image forming apparatus and determines whether or not the continuous image formation is performed based on the sent image data. Examine the image density from the image data for approximately one rotation of the developing roller 2, and detect the paper interval from the end of image formation to the next image formation, except when the image density is close to the maximum density (solid image), The developing roller peripheral speed / bias control device 11 is instructed to cause the independent driving mechanism of the developing roller 2 to increase the rotation speed of the developing roller 2 from the time of image formation, and the developing roller peripheral speed / bias control device 11 is connected to the developing roller 2. Refresh that increases the peak-to-peak voltage of the applied AC bias voltage compared to when forming an image and peels off the toner thin layer on the developing roller 2 to form a new toner thin layer. It has a function to perform the work.

  Referring again to FIG. 5, in the tandem type image forming apparatus 20 having the touch-down type developing apparatus configured as described above, two-component development including toner 5 of each color such as yellow, cyan, magenta, and black and carrier 4. The developer is supplied from the developer container to each of the developing devices 50K, 50Y, 50C, and 50M, and the toner 5 is charged to an appropriate level by stirring, and the cutting blade 9 is applied to the surfaces of the magnetic rollers 1K, 1Y, 1C, and 1M. The magnetic brush 10 is formed with a constant layer thickness. Then, the magnetic brush 10 comes into contact with the developing rollers 2K, 2Y, 2C and 2M, and a DC bias (Vdc2) power source 8 applied to the magnetic roller 1 and a DC bias (Vdc1) power source 7a applied to the developing roller 2 are supplied. The toner thin layer 6 is formed on the developing roller 2 by the potential difference of the DC bias and the AC bias from the AC bias (Vac1) power source 7b applied to the developing roller 2.

  When a print start signal is received from the control circuit 13 (see FIG. 1), first, the photosensitive drums 3K, 3Y, 3C, and 3M are charged to, for example, 400V by the charging devices 56K, 56Y, 56C, and 56M. For example, exposure by exposure apparatuses 57K, 57Y, 57C, and 57M using LEDs having a wavelength of 770 nm causes the post-exposure potential of each photosensitive drum 3 to be about 70 V, and a latent image corresponding to each color is formed. Then, this latent image flies from the toner thin layer 6 on the developing roller 2 to the photosensitive drum 3 by the developing bias from the DC bias (Vdc1) power source 7a and the AC bias (Vac1) power source 7b applied to the developing roller 2. The toner is developed to form a toner image.

  During this time, when the paper is fed from the paper feed cassette 53 and fed by the endless belt 54 and reaches the respective photosensitive drums 3K, 3Y, 3C, 3M, the corresponding transfer devices 58K, 58Y, 58C, 58M. A transfer bias is applied to the toner image, and the toner image is transferred to the paper. The toner image is fixed by the fixing device 59 and discharged. When image formation is continuously performed, as described above, the control device 13 examines the image density from the image data for approximately one turn of the developing roller 2 on the end side of the formed image of each color, and the image density is the maximum density. Unless it is close to (solid image), the sheet interval from the end of image formation to the next image formation is detected, and the developing roller peripheral speed / bias controller 11 is instructed to develop to the independent drive mechanism of the developing roller 2 The rotation speed of the roller 2 is made larger than that at the time of image formation, and the peak-to-peak voltage in the AC bias voltage is made larger than that at the time of image formation, and the toner thin layer on the developing roller 2 is peeled off to form a new toner thin layer. A refresh operation is performed.

  As the photosensitive material of the photosensitive drum 3 used here, a positively charged organic photosensitive member (positive OPC) or an amorphous silicon photosensitive member (a-Si) can be used. In the case of positive OPC, ozone or the like is generated. The system is long-life because it has a small amount of electrification and the positive OPC with a single-layer structure, especially when used for a long period of time, even when the film thickness changes, the photosensitivity changes little and the image quality is stable. Ideal for. In this case, it is preferable to set the film thickness of the positive OPC to about 20 μm to 40 μm. When the film thickness is 20 μm or less, when the film decreases to reach about 10 μm, black spots are noticeably generated due to dielectric breakdown. On the other hand, when the film thickness is 40 μm or more, the sensitivity is lowered, which causes a reduction in image density.

The developing roller 2 is a sleeve-like rotating body whose surface is made of conductive aluminum, and is arranged facing the photosensitive drum 3 with a space of about 250 μm. The material of the sleeve may be a uniform conductor, and SUS, conductive resin coating, etc. can be applied. In this conductive sleeve rotating body, a DC voltage and an AC voltage from a DC bias (Vdc1) power source 7a and an AC bias (Vac1) power source 7b are applied to the shaft and transmitted to the conductive sleeve. The DC bias (Vdc1) power source 7a is, for example, 200V DC during printing, and the AC bias (Vac1) power source 7b is, for example, a peak-to-peak voltage Vpp of 1.4 kV, a frequency of 4.0 KHz, Duty.
Supply 30% AC. The AC component waveform is preferably a rectangular wave.

  By applying these superimposed biases to the conductive sleeve, the latent image formed on the photosensitive drum 3 by electrophotography is recovered with a good developability and the toner thin layer 6 by the magnetic roller 1. And the stability of continuous printing is improved. In order to supply sufficient toner to the latent image on the photosensitive drum 3 without increasing the sheet interval in the refresh operation, it is short if the peripheral speed of the developing roller 2 is set to 1.5 times or more with respect to the photosensitive drum 3. The toner can be put in and out on time. Further, when the magnetic roller 1 is set to a peripheral speed that is 1 to 2 times that of the developing roller 2, toner replacement is promoted. At this time, it is preferable that the rotating direction of the magnetic roller 1 is opposite to the developing roller 2.

  The gap between the ear cutting blade 9 and the magnetic roller 1 is 0.3 to 1.5 mm, and the gap between the magnetic roller 1 and the developing roller 2 is similarly 0.3 to 0.5 mm, preferably 0.2 to 0.00 mm. It is about 4 mm. The toner thin layer 6 on the developing roller 2 is set to a thickness of 20 to 90 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 roller 2 and the photosensitive drum 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 photosensitive drum 3, and a sufficient image density cannot be obtained. Further, it becomes a factor that causes selective development.

The saturated toner amount in the toner thin layer 6 on the developing roller 2 is determined from the DC bias (Vdc2) power source 8 applied to the magnetic roller 1 and the DC bias (Vdc1) power source 7a applied to the developing roller 2. Is determined by the potential difference from the DC bias. When Vdc1 (7a) is set to 200 V and the value of Vdc2 (8) is set to 400 V, a toner layer of about 1.0 mg / cm ² is obtained on the second turn of the developing roller. The adjustment of the saturated toner amount can basically be performed by the potential difference of (Vdc2−Vdc1), but the toner charge amount and the magnetic pole strength of the magnetic roller 1 may contribute as factors. If the saturated toner amount is adjusted according to the density of the image to be formed, the uniform image can be obtained. For example, when continuously performing high density printing, it is preferable to set the value of (Vdc2−Vdc1) slightly higher.

When the toner layer is too small, such as 0.5 mg / cm ² or less, when high density images are continuous, the followability of the density is lowered and image unevenness is likely to occur. On the other hand, if it exceeds 1.5 mg / cm ² , development ghost and toner scattering tend to be noticeable. The toner layer thickness also depends on the charge amount of the toner. When the toner charge amount is as low as 10 μC / g or less, particularly 5 μC / g or less, the toner layer thickness increases and scattering increases. On the other hand, when the toner charge amount is 20 μC / g or more, the toner layer thickness becomes thin, the charge increases, and the developability of the toner decreases.

  It is important to define the particle size distribution of the toner 5 used here in order to avoid selective developability. Generally, the particle size distribution of the toner is measured by a Coulter counter, and the spread of the particle size distribution is expressed by the ratio of the volume distribution average diameter to the number distribution average diameter. In order to prevent selective development, it is important to reduce the ratio. When the distribution is wide, toner having a relatively small particle size is deposited on the developing roller 2 in continuous printing, and developability is deteriorated.

As the carrier, a ferrite carrier having a volume resistivity of 10 ⁸ Ωcm and a silicone resin coating, a saturation magnetization of 40 emu / g, and an average particle size of 35 μm was used. In addition to this, this carrier 4 can use a magnetite carrier, and also in the case of a ferrite carrier, Mn type ferrite, Mn-Mg type ferrite, etc. can be used. These carriers may be used as they are, but as described above, they may be used after being surface-treated within a range in which an appropriate resistance is not increased. If the average particle size of the carrier 4 exceeds 50 μm, the carrier stress increases and the toner density cannot be increased, and the amount of toner supplied to the developing roller 2 decreases.

  In the present invention, the mixing ratio of the toner and the carrier is 5 to 20% by weight, preferably 5 to 15% by weight, based on the total amount of the carrier and the toner. When the mixing ratio of the toner is less than 5% by weight, the toner charge amount becomes high and a sufficient image density cannot be obtained, and when it exceeds 20% by weight, the sufficient charge amount cannot be obtained. As a result, the inside of the image forming apparatus is contaminated, and toner fog occurs on the image.

  FIG. 2 is a timing chart comparing the time required for the refresh operation between the developing method of the present invention (A) and the conventional developing method as a comparative example (B) in the developing apparatus configured as described above. The details of the development conditions at that time and the details of the time required for the refresh operation are shown in the table of FIG. 3, and when the toner charge amount during the refresh operation is 10, 15, 20 μC / g, the developing roller 2 FIG. 4 is a table showing the evaluation results of the stripping performance according to the linear velocity and the AC bias peak-to-peak voltage (Vpp).

  First, the table of details of development conditions and time details during the refresh operation in FIG. 3 will be described. The “photosensitive linear velocity” indicates the rotational speed of the photosensitive drums 3K, 3Y, 3C, and 3M. The “developing roller linear speed during printing” is the rotational speed of the developing rollers 2K, 2Y, 2C, and 2M during image formation. These two are the same speed for both the conventional method (comparative example) and the method of the present invention (example). 240 [mm / sec]. The next “inter-paper development roller linear velocity” is the rotation speed of the development rollers 2K, 2Y, 2C, and 2M from the end of image formation to the next image formation, which is 240 [mm / sec] in the conventional method. On the other hand, in the method of the present invention, 500 [mm / sec] is almost doubled.

  The “photoconductor outer diameter”, “developing roller outer diameter”, and “magnetic roller outer diameter” below indicate the respective outer diameters, which are the same in the conventional method and the method of the present invention, and are 30 mm, 16 mm, and 16 mm, respectively. It is. “A4 vertical one sheet printing time” is the A4 vertical one sheet printing time determined by “photosensitive linear velocity”, and the conventional method and the method of the present invention are the same. “Time required for stripping a thin layer on one round” and “Time required for forming a thin layer on two rounds of a developing roller between paper sheets” and “Total” obtained by adding them are 0.21 sec and 0.42 sec in the conventional method. In contrast to 2.61 sec, in the method of the present invention, the total value is 0.10 sec, 0.20 sec, 2.28 sec, and the total value is 0.33 sec faster, so this “Total” and “A4 vertical 1 sheet” “Ppm”, which is calculated by adding up the “printing time” and calculating the number of printed sheets per minute, is 23.0 in the conventional method, but 26.3 in the method of the present invention and 3.3 in one minute. Can print (image formation) on extra sheets

  During the refresh operation, the DC bias applied from the DC bias (Vdc1) power source 7a in the developing roller 2 is 100 V, and the AC bias Vpp applied from the AC bias (Vac1) power source 7b is 1.4 KV without change. The frequency was 9 kHz, the duty was 70%, and the voltage of the DC bias (Vdc2) power supply 8a applied to the magnetic roller 1 was 0V.

  Next, in FIG. 2A, as described above, the control device 13 in FIG. 1 checks the image density from the image data for approximately one turn of the developing roller 2 on the end side of the formed image of each color, and the image density is When it is recognized that a refresh operation is necessary except when the density is close to the maximum density (solid image), the developing roller peripheral speed / bias control device 11 is instructed and the developing rollers 2K, 2Y, 2C, and 2M are instructed. In this case, the peripheral speed of the toner is increased faster than that at the time of image formation, the peak-to-peak voltage of the applied AC bias is increased, and the toner layer 6 is efficiently stripped and re-formed. This is a case where the peripheral speeds of 2K, 2Y, 2C, and 2M are the same as those at the time of image formation, and the peak-to-peak voltage of the AC bias to be applied is also the same as at the time of image formation.

  In this timing chart, the horizontal axis is time, Vdr with M, C, Y, K on the left is the developing bias applied to the developing rollers 2K, 2Y, 2C, 2M of each color, and Vmr is the magnetic rollers 1K, 1Y, A toner thin layer forming bias applied to 1C and 1M, Mdlp represents a driving state of the developing rollers 2K, 2Y, 2C, and 2M in the developing devices 50K, 50Y, 50C, and 50M. When the rotation of the roller 2 is stopped, the level indicated as “normal operation” is the peripheral speed during image formation, and the level indicated as “high speed rotation” is the case where the peripheral speed during the refresh operation is increased. .

Is first time driving the developing device 50M in t _1, by the developing roller 2M at time t _2, the development of an electrostatic latent image on the photosensitive drum 3M magenta is initiated as described above. And so on to, ...... are developing unit 50C is driven at time t _2, but not developing the electrostatic latent image on the photosensitive drum 3 is carried out so on, the magenta photosensitive at time t ₃ When the development of the electrostatic latent image on the body drum 3M is completed and the gap between sheets begins, in the present invention of (A), as described above, the developing roller 2M (Mdlp) in the developing device 50M is set to “high speed rotation”. At the same time, the peak-to-peak voltage of the AC bias applied to the developing roller 2M is increased.

In the present invention therefore (A), whereas a refresh operation between the paper in the developing roller 2M at time t ₄ ends, conventional development methods also "normal rotation" between the developing roller 2M (MDLP) paper in order for the refresh operation is completed is the time t ₅ as shown (B), the the (t 5 _{-t 4)} content only will take a long time for the refresh operation, slow correspondingly image forming speed Become. Therefore, the time t ₈ in the conventional method whereas in the method of the present invention is the time t ₆ the next image formation is completed in the present invention (A), the developing roller 2M (MDLP) is stopped The time is also time t ₇ in the method of the present invention, whereas it is time t _{9 in the} conventional method, and the time required for image formation is increased by the time difference indicated by “Total” in FIG.

  Lastly, FIG. 4 shows that when the toner charge amount is 10, 15, and 20 μC / g, 1000 sheets of print data having a print density of 4% are continuously printed, and the AC bias peak-to-peak voltage (Vpp) is variously changed. It is the table | surface which showed the result of having evaluated how the stripping performance changed by this. In the table, the “toner charge amount” on the left indicates the toner charge amount on the developing roller during the refresh operation, and the “inter-paper linear velocity” indicates the linear velocity between the sheets of the developing roller 2. The upper row shows the case of 240 mm / sec of the conventional method (comparative example), and the lower row shows the case of 500 mm / sec of the method of the present invention (example). “Vpp of developing roller application bias between papers” in the right column is the peak-to-peak voltage of the AC bias applied to the developing roller 2, and when the “toner charge amount” is 10, 15, 20 μC / g, The “development roller applied bias Vpp between papers” is changed from 1.2 kV to 2.0 kV, and the stripping performance at the linear speeds of 240 mm / sec and 500 mm / sec is evaluated.

  In the table, ◯ indicates a state in which no toner adheres to the developing roller 2 as a result of the refresh operation at each linear velocity and peak-to-peak voltage, △ indicates a slight adhesion, and × indicates poor stripping performance. The toner is sufficiently adhered on the developing roller 2.

  When the toner charge amount is 10, 15 μC / g, good stripping can be achieved at 1.6 kV Vpp, which is the same as for normal printing, regardless of whether the linear velocity between papers is 240 mm / sec, which is the same as during printing, or 500 mm / sec. In contrast, when the toner charge amount is 20 μC / g, when the linear velocity between the sheets is 240 mm / sec, which is the same as that during printing, Vpp is 1.6 kV or more, which shows a good result. At 500 mm / sec, good results have not been obtained unless 2.0 kV or more is applied.

  For these reasons, when the linear velocity of the developing roller 2 is increased to 500 mm / sec in order not to decrease the image forming speed by the refresh operation, the toner charge amount is good in all states of 10, 15, and 20 μC / g. It can be seen that in order to perform the refresh operation, the peak-to-peak voltage of the AC bias applied to the developing roller 2 should be 2.0 kV or more.

  As described above, according to the present invention, the independent driving mechanism for changing the rotation speed of the developing roller 2 independently of the photosensitive drum 3 and the magnetic roller 1 is provided, and the rotation speed of the developing roller 2 between the sheets is changed from the time of image formation. In addition to increasing the peak-to-peak voltage in the AC bias voltage applied to the developing roller 2 and causing the refresh operation to be performed, the time required for the refresh operation is shortened first, and a large peak-to-peak voltage Even when the toner charge amount increases due to the AC bias, the recovery performance is maintained, and a developing method and a developing apparatus capable of always forming a high-quality image by performing a good refresh operation can be obtained.

  In addition, when the image density in the image data of approximately one turn of the developing roller 2 on the end side in the formed image is close to the maximum density, the refresh operation is unnecessary, and therefore, when this is omitted, the refresh operation is always performed between sheets. Compared to the above, the image forming speed can be increased.

  According to the present invention, a developing method in an image forming apparatus capable of always forming a high-quality image by performing a good refresh operation without reducing the efficiency of toner removal without reducing the time required for the refresh operation. And an apparatus can be provided.

It is a schematic sectional drawing of one Example of the image forming apparatus which implements the image development method which becomes this invention. 6 is a timing chart comparing the time required for a refresh operation between the developing method (A) of the present invention and a conventional developing method (B) as a comparative example. 7 is a table showing details of development conditions and time required for a refresh operation in the development method of the present invention and a conventional development method as a comparative example. Evaluation results of the stripping performance by the linear velocity of the developing roller 2 and the AC bias peak-to-peak voltage (Vpp) applied to the magnetic roller 1 when the toner charge amount during the refresh operation is 10, 15, 20 μC / g It is the table | surface which showed. It is a schematic block diagram of the hybrid type developing apparatus which implements the developing method according to the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Magnetic roller 2 Developing roller 3 Photoconductor (electrostatic latent image carrier) drum 4 Carrier 5 Toner 6 Toner thin layer 7a DC bias (Vdc1) power supply 7b AC bias (Vac1) power supply 8 DC bias (Vdc2) power supply 9 Ear cutting Blade 10 Magnetic brush 11 Developing roller peripheral speed / bias controller 12 Magnetic roller peripheral speed / bias controller 13 Controller 20 Image forming apparatus

Claims (4)

A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller containing a magnet, a toner thin layer is formed on the developing roller from the magnetic brush, and an alternating current is applied to the direct current applied to the developing roller. The toner is caused to fly to the electrostatic latent image formed on the photosensitive member by the superimposed developing bias, and the toner thin layer on the developing roller is peeled off between the paper from the end of the image formation to the next image formation to newly In a developing method for performing development by performing a refresh operation for forming a thin toner layer,
A developing method in an image forming apparatus, characterized in that the peripheral speed of the developing roller is made faster during the refresh operation than during image formation, and the peak-to-peak voltage in the AC bias applied to the developing roller is made larger than during image formation.   2. The image formation according to claim 1, wherein the refresh operation is performed during continuous image formation, except when the image density in the image data of approximately one turn of the developing roller on the end side of the formed image is close to the maximum density. Development method in the apparatus. A magnetic roller on which a magnetic brush of a two-component developer composed of toner and a carrier is formed, and a thin toner layer is formed by the magnetic brush, and is formed on the photosensitive member by a developing bias in which alternating current is superimposed on applied direct current. A developing roller that develops the toner by flying toner onto the electrostatic latent image, and an independent drive mechanism that changes the rotational speed of the developing roller independently of the photosensitive member and the magnetic roller.
A developing roller bias voltage control device that controls a developing bias voltage applied to the developing roller, and detects a sheet interval from the end of image formation to the next image formation in a continuous image forming state, and develops the developing roller independent drive mechanism. The roller rotation speed is made higher than that at the time of image formation, and the developing roller bias voltage control device is made to increase the peak-to-peak voltage in the AC bias voltage from that at the time of image formation. A developing device in an image forming apparatus, comprising: a control device that performs a refresh operation for forming a thin layer.   The control device that performs the refresh operation has a function of calculating an image density from image data of approximately one rotation of the terminal-side developing roller of the formed image in the continuous image forming state, and performs the refresh operation according to the calculation result. The developing device in the image forming apparatus according to claim 3, wherein the developing device is configured to perform the operation.

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