JP2009139594A - Method and device for developing in image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method and a device for developing in an image forming apparatus with no occurrence of leaking between a photoreceptor and a developing roller and always obtaining a clear image by preventing generation of a ghost image, attaching of toner to a surface of a developing roller by selective developing and deterioration of image density, etc., even when particle diameters in toner are made smaller by targeting improvement in image quality and the space between the photoreceptor and the development roller is made narrower for improving developing property in a touch down developing device. <P>SOLUTION: Developing is carried out in an image forming apparatus by compensating with a first step and a second step. The first step sets AC developing bias with no occurrence of leaking between the photoreceptor and the developing roller. The second step sets each difference, which are the difference between a peak voltage in the AC developing bias which is varied by the first step and a minimum peak voltage in AC bias for forming toner thin layer and the difference between the minimum peak voltage in the AC developing bias and the peak voltage in the AC bias for forming toner thin layer by setting the AC bias for forming toner thin layer so that the differences are the same or more than the differences before execution of the first step. <P>COPYRIGHT: (C)2009,JPO&amp;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 a developer, only a charged toner is uniformly formed on the developing roller as a thin layer, and then this toner is ejected from the developing roller onto the electrostatic latent image formed on the photosensitive member for development to form an image. 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 include a one-component development method using only toner, and a toner and a carrier. A two-component development method using a two-component developer is known.

  Since the one-component developing method does not use a carrier, the electrostatic latent image on the electrostatic latent image carrier (hereinafter referred to as a photosensitive member) is not disturbed by a magnetic brush formed from the carrier and the toner. Suitable for image quality. However, in the one-component development method, it is difficult to stably maintain the charge amount of the toner. In the case of a color toner, since transparency is required, it must be a non-magnetic toner. For this reason, in a full-color image forming apparatus, a two-component development system using a carrier is often employed as a medium for charging and transporting toner.

  The two-component development method is suitable for extending the life because a stable charge amount can be obtained over a long period of time. However, the two-component development method is disadvantageous in terms of image quality due to the influence of the magnetic brush. Therefore, in order to take advantage of each of these two development methods, the charge area adopts a two-component development system in consideration of extending the service life, and the development area uses a one-component development system to improve image quality. A development method called a development method or a hybrid development method 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) using 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). 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.

  On the other hand, in recent years, color image forming apparatuses are also required to be reduced in price and increased in definition with personalization, and a reduction in toner particle diameter is being studied. However, the reduction in toner particle size results in improved image quality (high-resolution images), but the toner flyability (developability) from the developing roller to the photoreceptor is weak, so that image density is not achieved in the touchdown development method. There are problems such as generation of ghost images and toner adhesion to the surface of the developing roller due to selective development.

  That is, the toner moves from the toner thin layer on the developing roller to the photosensitive member from the toner having a relatively large particle size with a relatively low charge amount per unit volume, and thus the flying property is particularly low. Small particle size toner with high charge is difficult to use for development. When selective development occurs and continuous printing (printing durability) is performed, fine toner adheres to the developing roller and is not easily consumed and has a low developability. There is a problem that the toner increases in the developing device and the image quality deteriorates.

  In addition, the residual toner that has not been used for development on the developing roller in the touch-down development method is peeled off by the magnetic brush of the magnetic roller, and at the same time, new toner is supplied from the magnetic brush to the developing roller. In the case where the removal is insufficient or the toner supply to the developing roller is insufficient, a development ghost (history phenomenon) phenomenon in which an afterimage after the toner has jumped from the developing roller to the photosensitive member appears on the second round occurs.

  For this reason, the gap between the developing roller and the photosensitive member is made narrow so that the toner having a small particle diameter can sufficiently fly to the photosensitive member, or the developing bias applied to the developing roller is set to a high voltage. There is a new problem that a leak occurs between the developing roller and the photosensitive member to degrade the image quality. In order to prevent such leakage, it is one means to treat the developing roller surface with an anodized surface of, for example, about 20 μm and increase the resistance of the developing roller surface. However, the leakage cannot still be completely prevented, Further surface treatment is costly and technically difficult.

  As a prior art for solving such a leakage problem, in Japanese Patent Application Laid-Open No. 2003-228561, a development bias voltage in which a DC voltage and an AC voltage are superimposed is applied between a toner carrier and an image carrier, and development is performed. In the apparatus, a leak generating means for changing a leak detection voltage applied between the image carrier and the toner carrier and generating a leak between the image carrier and the toner carrier, and the image carrier and the toner carrier 1 shows a developing device provided with a leak detecting means for detecting a leak based on the current flowing between the two and detecting a leak voltage so that the leak does not occur.

  However, in the method disclosed in Patent Document 1, there is a problem that a leak voltage is lowered at a detection point once detected as a leak, and the occurrence of the leak becomes undetectable. Document 2 discloses a developing device in which the voltage value Vpp of the leak detection voltage is temporarily reduced to the voltage value Vpp ′ in one detection step.

  Further, even in the method shown in Patent Document 3, since it takes time to detect the leak voltage by changing the voltage stepwise, Patent Document 3 includes an impedance measurement circuit that measures the impedance of the development region, An image forming apparatus including a leak current detection circuit for detecting a leak based on a leak current flowing in the development region 3, and predicting a leak occurrence voltage based on a measurement value obtained by an impedance measurement circuit and determining a development bias voltage It is shown.

Japanese Patent Laid-Open No. 2003-287942 Japanese Patent Application Laid-Open No. 2004-093701 Japanese Patent Laying-Open No. 2005-0778015

  However, all of the developing devices disclosed in Patent Documents 1 to 3 need to separately provide a leak generating unit and a leak detecting unit, which leads to an increase in cost. The developing devices shown in Patent Documents 1 to 3 are developing devices using a one-component developer. By adjusting the peak-peak value of the AC bias voltage applied to the developing roller, the developing device and the photosensitive device are exposed. Although it has been disclosed that leakage does not occur between the body and the body, no mention is made of how to cope with the developability changed thereby and the changed developability.

  That is, in the touch-down development method, as described above, the magnetic brush is formed on the magnetic roller by the two-component developer composed of toner and carrier, and only the toner from the magnetic brush is applied to the surface of the developing roller by the bias voltage applied to the magnetic roller. This is a system in which a thin layer is transported and then developed by causing toner to fly onto the surface of the photosensitive member on which an electrostatic latent image is formed with a developing bias applied to the developing roller. When the peak-to-peak value of the AC bias voltage is simply changed, the potential difference between the developing roller and the photosensitive member and the potential difference between the developing roller and the magnetic roller change.

  When the potential difference between the developing roller and the magnetic roller changes, as described above, the remaining toner that has not been used for development on the developing roller is peeled off by the magnetic brush formed on the magnetic roller, and from the magnetic brush to the developing roller. In some cases, the supply of the toner becomes insufficient, which causes development ghosting. In addition, when the potential difference between the developing roller and the photosensitive member changes, as described above, the movement of the toner from the toner thin layer on the developing roller to the photosensitive member causes a relative charge amount per unit volume. Since it is made from low-relatively large toner particles that are easy to fly, small-particle toners with high charge amount have low flying properties and are difficult to use for development, and selective development occurs, resulting in continuous printing (printing durability). When this is done, there is a problem that fine powder toner adheres to the developing roller, or fine powder toner that is difficult to be consumed and has low developability increases in the developing device, resulting in deterioration of image quality.

  For this reason, in the present invention, even if the toner is made to have a small particle size with the aim of improving the image quality in the touch-down developing device and the interval between the photosensitive member and the developing roller is narrowed in order to improve developability, the photosensitive member and the developing roller are separated. In an image forming apparatus in which leaks are not generated, and ghost images are generated, toner adheres to the surface of a developing roller due to selective development, and image density is reduced, so that a beautiful image is always obtained. It is an object to provide a developing method and apparatus.

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 and applied with a bias for toner thin layer formation in which alternating current is superimposed on direct current. The alternating current is applied to the direct current from the magnetic brush. A developing method in an image forming apparatus in which a toner thin layer is formed on a developing roller to which a superimposed developing bias is applied and then the toner is ejected onto an electrostatic latent image formed on a photosensitive member by electrophotography. In
A first step of setting an AC developing bias that does not cause a leak between the photosensitive member and the developing roller, and a peak voltage in the AC developing bias and a minimum peak in the AC toner thin layer forming bias that are changed by the first step. The AC toner so that the difference between the voltage and the difference between the minimum peak voltage in the AC developing bias and the peak voltage in the AC toner thin layer formation bias is equal to or greater than the difference before the first step is performed. A second step of setting a thin layer forming bias,
The voltage difference between the AC developing bias and the AC toner thin layer forming bias changed in the first step is compensated by changing the AC toner thin layer forming bias in the second step, and development is performed.

The developing device in the image forming apparatus that implements this developing method is:
A magnetic roller that forms a magnetic brush of a two-component developer composed of toner and a carrier by applying a bias for applying a toner thin layer containing a magnet and superposing an alternating current on a direct current, and forming a toner thin layer on which an alternating current is superimposed on a direct current An image having a developing roller for applying a bias to form a toner thin layer with the magnetic brush and developing the electrostatic latent image formed on the photoreceptor by electrophotography with the toner flying from the toner thin layer. In the developing device in the forming device,
A developing roller bias power supply control device for controlling the AC bias peak value in the AC developing bias, a magnetic roller bias power supply control device for controlling the AC bias peak value in the AC toner thin layer formation bias, and the AC developing bias Instructs the developing roller bias power supply controller a peak value that does not cause a leak between the photosensitive member and the developing roller, and also includes a peak voltage in the AC developing bias that does not cause a leak and a minimum peak voltage in the AC toner thin layer forming bias. And the difference between the minimum peak voltage in the AC developing bias that does not cause leakage and the peak voltage in the AC toner thin layer forming bias before changing to the peak value that does not cause leakage in the AC developing bias. At least equivalent to the difference from the peak value The AC thin toner layer forming bias made, the developing device in an image forming apparatus characterized by comprising a controller for instructing the magnetic roller bias power supply control device.

  In this way, an AC developing bias that does not cause a leak between the photosensitive member and the developing roller is set, and the difference between the peak voltage in the AC developing bias and the minimum peak voltage in the AC toner thin layer forming bias changed by the setting, and the AC developing. By setting the AC toner thin layer formation bias so that the difference between the minimum peak voltage in the bias and the peak voltage in the AC toner thin layer formation bias is equal to or greater than the difference before setting the AC development bias that does not cause leakage. Although the peak value of the AC developing bias is small, the difference between the minimum peak voltage in the AC developing bias for forming a thin layer on the developing roller and the peak voltage in the AC toner thin layer forming bias, and the development on the developing roller are used. The toner at the AC developing bias that pulls back the toner that has not been returned to the magnetic roller The difference between the voltage and the minimum peak voltage in the AC toner thin layer formation bias is the same as before setting the AC development bias, thereby preventing the occurrence of ghost images, toner adhesion to the developing roller surface due to selective development, image density reduction, etc. In addition, it is possible to provide a developing method and apparatus in an image forming apparatus that can always obtain a beautiful image.

  In order to set an AC developing bias that does not cause a leak between the photosensitive member and the developing roller, the environmental temperature and the humidity are changed in advance, and the alternating current set in the first step corresponding to each environmental temperature and the humidity is set. The developing bias and the AC toner thin layer forming bias set in the second step corresponding to the AC developing bias are checked and tabulated, and the AC developing bias of the table corresponding to the environmental temperature and humidity at the time of image formation The AC toner thin layer forming bias is read out, and the first and second steps are performed. Therefore, the control device corresponds to each of a plurality of environmental temperatures and humidity and does not cause a leak in the AC developing bias. Table storing peak value and AC toner thin layer forming bias corresponding to the peak value, and environmental temperature and humidity detecting means And reading from the table a peak value that does not cause a leak in the AC developing bias and the AC toner thin layer forming bias corresponding to the peak value based on the detection results of the environmental temperature and humidity detecting means. By controlling the developing roller bias power source control device and the magnetic roller bias power source control device, the difference between the peak voltage in the AC developing bias and the minimum peak voltage in the AC toner thin layer forming bias and AC development with a simple configuration The AC toner thin layer forming bias may be set so that the difference between the minimum peak voltage in the bias and the peak voltage in the AC toner thin layer forming bias is equal to or greater than the difference before setting the AC developing bias that does not cause a leak. it can.

  The image forming apparatus includes a calibration mode for image density adjustment by solid patch printing performed by changing the AC developing bias and the AC toner thin layer forming bias, and the first step includes the calibration step. Therefore, the image forming apparatus performs calibration for image density adjustment by solid patch printing performed by changing the AC developing bias and the AC toner thin layer forming bias. The control device determines a peak value that does not cause a leak due to the AC developing bias changed in the calibration mode, and controls the developing roller bias power supply control device and the magnetic roller bias power supply control device. Calibration This mode has been provided for a long time, so it does not easily leak, prevents the generation of ghost images, toner adhesion to the developing roller surface due to selective development, and reduction in image density. It is possible to provide a developing method and apparatus in an image forming apparatus that can achieve the above.

  As described above, the developing method and apparatus in the image forming apparatus according to the present invention includes the difference between the minimum peak voltage in the AC developing bias for forming a thin layer on the developing roller and the peak voltage in the AC toner thin layer forming bias, and development. The difference between the peak voltage in the AC development bias for returning the toner not used for development on the roller to the magnetic roller and the minimum peak voltage in the AC toner thin layer formation bias is the same as before the change in the AC development bias. It is possible to provide a developing method and apparatus in an image forming apparatus that can prevent generation, toner adhesion to the surface of the developing roller due to selective development, reduction in image density, and the like and always obtain a beautiful 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, referring to FIG. 3, a schematic configuration of a touch-down developing device that performs the developing method in the image forming apparatus according to the present invention will be described. In the figure, reference numeral 10 denotes a photosensitive drum (electrostatic latent image carrier), and an amorphous silicon (a-Si) photosensitive member, an organic photosensitive member (OPC), or the like can be used as a material. 11 is an electrostatic image formed on the photosensitive drum 10 in an electrophotographic manner by a bias voltage applied from a DC developing bias power supply (DC1) 13 and an AC developing bias power supply (AC1) 14 on which a thin layer 12 of toner is formed. A developing roller 15 for developing the toner image by flying toner onto the latent image has a rotatable sleeve formed in a cylindrical shape with a nonmagnetic metal material and having a plurality of fixed magnets disposed therein. And a magnetic brush 18 of a two-component developer composed of a carrier 17 is formed, and a bias voltage applied from a DC toner thin layer forming bias power source (DC2) 19 and an AC toner thin layer forming bias power source (AC2) 20 A magnetic roller for forming a thin layer 12 of toner on the developing roller 11, and a spike cutting blade 21 for keeping the height of the magnetic brush 18 on the magnetic roller 15 constant. A.

  Reference numeral 22 denotes a developing roller bias power source controller for controlling the voltages of the DC developing bias power source (DC1) 13 and the AC developing bias power source (AC1) 14 of the developing roller 11, and 23 denotes a DC toner thin layer forming bias power source (DC2) for the magnetic roller 15. ) 19, a magnetic roller bias power source control device for controlling the AC toner thin layer forming bias power source (AC 2) 20, and 24 for controlling the developing device, instructing a voltage to the developing roller bias power source control device 21 and the magnetic roller bias power source control device 22. Reference numeral 25 denotes a storage device for storing the temperature detected by the temperature / humidity sensor 26, the AC developing bias voltage corresponding to the humidity, and the magnetic roller bias voltage as a table.

  The outermost surface of the developing roller 11 is composed of a sleeve made of uniform conductive aluminum, SUS, conductive resin coating or the like, and in order to prevent leakage, it is preferable to increase the resistance value by, for example, anodizing about 20 μm. A DC developing bias power source (DC 1) 13 and an AC developing bias power source (AC 1) 14 are connected to the shaft portion, and this direct current is connected between the rotating developing roller 11, the photosensitive drum 10, and the magnetic roller 15. A developing bias voltage superimposed with alternating current is applied. The AC component supplied by the AC developing bias power source (AC1) 14 is constituted by, for example, a rectangular wave having a duty ratio of 50% or less.

For the toner 16, for example, a toner having a small particle size of about 6 μm, which is about 6.8 μm at 10 ¹³ to 10 ¹⁴ Ω, is used for high definition of the formed image. In order to avoid the above-described selective developability, it is important to define the particle size distribution. Generally, the spread of the particle size distribution of the toner is measured by a Coulter counter, and the spread of the particle size distribution is expressed as the volume distribution average particle size. Expressed as a ratio of number distribution average particle size. When the distribution is wide, toner having a relatively small particle size is accumulated on the developing roller 11 during continuous printing, and developability is lowered. In the present invention, the case where positively charged toner is used will be described as an example. However, it is obvious that the same configuration can be obtained even when negatively charged toner is used by reversing the relationship with the bias voltage.

As the carrier 17, a magnetite carrier, Mn-based ferrite, Mn—Mg-based ferrite, or the like can be used, and it can also 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 ⁸ Ωcm ³ and a saturation magnetization of 40 emu / g and an average particle size of 35 μm was used. If the average particle size exceeds 50 μm, the carrier stress increases and the toner density cannot be increased, and the amount of toner supplied to the developing roller 11 decreases.

  The mixing ratio of the toner 16 and the carrier 17 is 5 to 20% by weight, preferably 5 to 15% by weight, based on the total amount of the carrier 17 and the toner 16. When the mixing ratio of the toner 16 is less than 5% by weight, the charge amount of the toner becomes high and a sufficient image density cannot be obtained, and when it exceeds 20% by weight, a sufficient charge amount cannot be obtained. 16 scatters from the developing device and contaminates the inside of the image forming apparatus, or toner fog occurs on the image.

  In the developing apparatus configured as described above, when an instruction for image formation is received, the surface of the photosensitive drum 10 is first charged by a charging unit (not shown) (charging process), and then this is also performed by an exposure unit (not shown). The surface of the photosensitive drum 10 is exposed to form an electrostatic latent image (exposure process). On the other hand, a magnetic brush 18 of a two-component developer composed of toner 16 and carrier 17 is formed on the magnetic roller 15 while the height is kept constant by a spike cutting blade 21, and a DC developing bias power supply (DC 1) 13 is formed. Direct current applied to the developing roller 11 by the AC developing bias power source (AC1) 14 and to the magnetic roller 15 by the direct current toner thin layer forming bias power source (DC2) 19 and the alternating toner thin layer forming bias power source (AC2) 20. First, only the toner is transferred from the magnetic brush 18 to the surface of the developing roller 11 by the bias voltage in which an alternating current is superimposed on the surface of the developing roller 11 to form the toner thin layer 12.

  Then, the toner flies from the toner thin layer 12 to the electrostatic latent image on the photosensitive drum 10 by the developing bias voltage applied to the developing roller 11 by the DC developing bias power supply (DC1) 13 and the AC developing bias power supply (AC1) 14. The electrostatic latent image is developed as a toner image (development process). The toner not used for development on the developing roller 11 is peeled off by the magnetic brush 18 formed on the magnetic roller 15 and the bias voltage described above, and a new toner thin layer 12 is formed. Prepare for the next development. Further, the toner image formed on the photosensitive drum 10 is transferred to a sheet conveyed by a paper conveying device (not shown) or an intermediate transfer body (transfer process) and remains on the surface of the photosensitive drum 10. The remaining toner is cleaned by a cleaning unit (not shown) to prepare for the next image formation.

  Next, the outline of the present invention will be briefly described. In the present invention, in the touch-down developing device configured as described above, for example, 6.8 μm and 6 μm levels of toner are used for the purpose of improving the image quality as described above. To reduce the particle size. Then, problems such as a decrease in image density, generation of a ghost image, adhesion of toner to the surface of the developing roller due to selective development due to a decrease in toner flying property (developability) from the developing roller 11 to the photosensitive drum 10, First, the gap between the developing roller 11 and the photosensitive drum 10, which has conventionally been about 240 μm, is narrowed to, for example, 160 μm to increase the electric field between the developing roller 11 and the photosensitive drum 10 to prevent this.

  As a result, as described above, the surface of the developing roller 11 is subjected to an alumite surface treatment of about 20 μm, for example, as a new problem that the image quality deteriorates due to a leak generated between the developing roller 11 and the photosensitive drum 10. It is reduced by increasing the resistance of the surface. However, it is difficult to increase the resistance of the surface of the developing roller 11 in terms of cost and technology, and leakage cannot be completely prevented. Therefore, as in the above-described Patent Documents 1 to 3, the photosensitive drum 10 and the developing roller 11 This is prevented by adjusting the peak-to-peak voltage in the AC developing bias applied between them.

  However, in this case, when the peak-to-peak voltage in the AC developing bias applied between the photosensitive drum 10 and the developing roller 11 is simply adjusted, the AC developing bias voltage applied to the developing roller 11 and the AC toner applied to the magnetic roller 15 are now adjusted. The voltage difference from the thin layer forming bias voltage becomes small, the remaining toner that has not been used for development on the developing roller 11 is insufficiently peeled off by the magnetic brush 18, the toner is not sufficiently supplied from the magnetic brush 18 to the developing roller 11, etc. The development ghost also causes image quality deterioration due to change in developability, such as adhesion of fine powder toner to the developing roller 11 by selective development and increase of fine powder toner having low developability into the developing device.

  Therefore, in this application, the potential difference for peeling off the toner not used for development on the developing roller 11 with the magnetic brush 18 of the magnetic roller 15, that is, the AC developing bias applied to the developing roller 11 from the AC developing bias power source (AC 1) 14. And the minimum value (minimum peak value) of the AC toner thin layer forming bias applied to the magnetic roller 15 from the AC toner thin layer forming bias power source (AC2) 20, and the magnetic brush on the magnetic roller 15 The potential difference for forming the toner thin layer 12 on the developing roller 11 from 18, that is, the minimum value of the AC developing bias applied to the developing roller 11, and the peak value of the AC toner thin layer forming bias applied to the magnetic roller 15 Before and after adjusting the peak-to-peak voltage in the AC developing bias applied to the developing roller 11. , It is desirable to make each the same or higher.

  Since the leakage voltage changes depending on the environmental temperature and humidity, the AC developing bias Vslv (AC) to be applied to the developing roller 11 and the AC toner thin layer forming bias Vmag (to be applied to the magnetic roller 15 in advance). AC), the voltage at which leakage occurs between the developing roller 11 and the photosensitive drum 10 at each temperature and humidity, the voltage that can prevent the occurrence, and the development ghost, fine toner on the developing roller 11 by selective development The voltage or the like that does not cause deterioration in image quality due to the adhesion of the toner and the increase in fine developing toner having low developability into the developing device is examined and stored in the storage device as a table in advance.

  At the time of image formation, the environmental temperature and humidity are checked, and the corresponding AC developing bias Vslv (AC) and AC toner thin layer forming bias Vmag (AC) are read from the table, and an image is formed with the voltage. Further, in the color image forming apparatus, in order to keep the image density constant, which is called a calibration mode, a solid patch is printed by changing the bias voltage applied to the developing roller 11 and the magnetic roller 15, and the density is read and the target is read. In this calibration mode, the AC developing bias Vslv (AC) is changed to detect the voltage at which leakage occurs, and thereby the table is adjusted. Alternatively, the AC developing bias Vslv (AC) and the AC toner thin layer forming bias Vmag (AC) may be read out or calculated and adjusted without using a table.

FIG. 4 shows the amount of toner on the developing roller by the difference ΔV between the DC developing bias Vslv (DC) supplied to the developing roller 11 and the DC toner thin layer forming bias Vmag (DC) supplied to the magnetic roller 15. A is a graph showing how the solid toner amount (B) and the development efficiency (C) on the photosensitive member change. The horizontal axis of each graph in FIG. 4 is the DC developing bias Vslv (DC) supplied from the DC developing bias power source (DC1) 13 to the developing roller 11, and FIG. The amount (mg / cm ² ), (B) is the amount of solid toner (unit: mg / cm ² ) on the vertical axis, and (C) is the vertical axis how much toner is on the developing roller 11. That is, the ratio of the solid toner amount on the photosensitive drum 10 and the toner amount on the developing roller 11 is multiplied by the ratio of the peripheral speed of the developing roller 11 and the peripheral speed of the photosensitive drum 10 to obtain the developing roller. The developing efficiency (%) is expressed as a ratio between the toner amount of the toner thin layer 12 formed on the toner 11 and the toner amount used for developing the electrostatic latent image on the photosensitive drum 10.

  The image forming apparatus used in this investigation is a modified experimental machine using a touch-down development method manufactured by Kyocera Mita. The photosensitive drum 10 used has an outer diameter of 30 mm, a peripheral speed of 168.2 mm / sec, and the developing roller 1 The outer diameter is 16 mm and the peripheral speed is 269.1 mm / sec. The magnetic roller 15 has an outer diameter of 16 mm and the peripheral speed is 419.8 mm / sec. Further, the blade gap between the magnetic roller 15 and the ear cutting blade 21 is 0.35 mm, the M / S gap between the magnetic roller 15 and the developing roller 11 is 0.35 mm, and the D / S between the developing roller 11 and the photosensitive drum 10. The gap is 0.16 mm, the ratio (S / D) between the circumferential speed of the developing roller 11 and the circumferential speed of the photosensitive drum 10 is about 1.6, and the average particle diameter of the developer is black (BK) 6.8 μm. A two-component developer comprising a toner having a reduced particle size and a carrier was used.

  First, the graph shown as “developing roller toner thin layer amount” in FIG. 4A shows the difference ΔV between the developing roller direct current developing bias Vslv (DC) and the magnetic roller direct current toner thin layer forming bias Vmag (DC). , 400 V (♦), 320 V (▲), and 240 V (■). From the graph of FIG. 4A, the toner amount of the toner thin layer 12 formed on the developing roller 11 is in the range of at least about 20 V to 180 V of the DC developing bias Vslv (DC), and the DC developing bias Vslv (DC ) Regardless of the value of the magnetic roller DC toner thin layer forming bias Vmag (DC), the larger the value of the voltage difference ΔV, the larger the value.

  From the graph shown as “solid toner amount on the drum” in FIG. 4B, the solid toner amount on the photosensitive drum 10 is the DC developing bias Vslv (DC), the DC developing bias Vslv (DC), and the DC toner. It shows that the amount of solid toner on the photosensitive drum 10 increases as the voltage difference ΔV with the thin layer forming bias Vmag (DC) increases.

  Then, from the graph shown as “Developing efficiency (Drum toner amount / Slv toner amount × S / D ratio)” in FIG. 4C, in any case of ΔV, it is proportional to the DC developing bias Vslv (DC). Although the voltage rises, the rate of increase when the ΔV is the smallest, 240V, is the largest, and the maximum development efficiency is also greatest when the DC development bias Vslv (DC) is about 180V. Therefore, from the graph of FIG. 4C, the DC developing bias Vslv (DC) is increased, and the voltage difference ΔV between the DC developing bias Vslv (DC) and the DC toner thin layer forming bias Vmag (DC) is decreased. It can be seen that a large development efficiency can be obtained.

  To summarize these results, the toner amount of the toner thin layer 12 on the developing roller 10 is equal to the difference ΔV between the DC developing bias Vslv (DC) for the developing roller and the DC toner thin layer forming bias Vmag (DC) for the magnetic roller. Therefore, if ΔV is constant, the amount of solid toner on the photosensitive drum 10 is proportional to the DC developing bias Vslv (DC) for the developing roller. If ΔV is constant, the developing efficiency is proportional to the developing roller DC developing bias Vslv (DC), and the slope thereof is ΔV240V (■)> ΔV320V (▲)> ΔV400V (◆). By reducing the difference ΔV between the developing bias Vslv (DC) and the direct current toner thin layer forming bias Vmag (DC) for the magnetic roller, the toner amount of the toner thin layer 12 on the developing roller 11 is reduced, and ΔV is reduced ( It can be seen that the development efficiency can be increased by increasing the DC developing bias Vslv (DC) for the developing roller by reducing the toner amount of the toner thin layer 12 on the developing roller 11.

  That is, from these facts, as described above, leakage caused by reducing the interval between the photosensitive drum 10 and the developing roller 11 in order to improve developability using toner having a small particle size in the touchdown developing device. The AC developing bias applied between the photosensitive drum 10 and the developing roller 11 without changing the DC developing bias Vslv (DC) applied to the developing roller 11 and the magnetic roller 15 and the DC toner thin layer forming bias Vmag (DC). And the difference between the peak value of the AC developing bias applied to the developing roller 11 and the minimum value of the AC toner thin layer forming bias applied to the magnetic roller 15, and the developing roller. 11 is the minimum value of the AC developing bias applied to the magnetic roller 15, and the AC toner thin layer forming bar applied to the magnetic roller 15. If the difference from the peak value of the asphalt is equal to or greater than or equal to before and after adjusting the peak-to-peak voltage in the AC developing bias applied between the photosensitive drum 10 and the developing roller 11, It is possible to provide a developing method and apparatus that can maintain a developability and can always obtain a beautiful image without generation of a ghost image, adhesion of toner to the surface of the developing roller 11 by selective development, and reduction in image density. .

  FIG. 1 shows the development bias voltage applied from the DC development bias power source (DC1) 13 and the AC development bias power source (AC1) 14 to the developing roller 11 according to such a concept, and the DC toner thin layer forming bias power source ( FIG. 6 is a diagram schematically showing bias voltages applied from DC 2) 19 and AC toner thin layer forming bias power source (AC 2) 20. In the figure, the horizontal axis represents time, and the vertical axis represents voltage (V). When this result was obtained, the temperature was 25 ° C. and the humidity was 60%.

  Reference numerals 30 and 32 denote AC developing bias Vslv (AC) applied to the developing roller 11 from the AC developing bias power supply (AC1) 14. Reference numerals 31 and 33 denote magnetic toner 15 applied from the AC toner thin layer forming bias power supply (AC2) 20. The AC toner thin layer forming bias Vmag (AC), of which the solid line 30 is the AC developing bias Vslv (AC) in which the peak-to-peak voltage is adjusted to prevent leakage as described in the outline of the present invention, and the broken line 31 is The AC toner thin layer formation bias Vmag (AC) is changed correspondingly. The alternate long and short dash line 32 is the conventional AC developing bias Vslv (AC) before adjusting the peak-to-peak voltage, and the alternate long and two short dashes line 33 is the alternating toner thin layer forming bias Vmag (AC).

  Reference numeral 34 indicated by a thick solid line indicates an exposure potential DrumVL on the photosensitive drum 10, which is 100V. Similarly, a thick broken line 35 is a DC developing bias Vslv (DC) applied to the developing roller 11 from the DC developing bias power supply (DC1) 13, and a thick dashed line 36 is a DC toner thin layer forming bias power supply (DC2) to the magnetic roller 15. ) DC toner thin layer forming bias Vmag (DC) applied from 19.

  2 shows a developing bias voltage applied from the DC developing bias power source (DC1) 13 and the AC developing bias power source (AC1) 14 to the developing roller 11 shown in FIG. 1, and a DC toner thin layer forming bias power source to the magnetic roller 15. (DC2) 19, AC toner thin layer formation bias power supply (AC2) 20 is applied to change the bias voltage in various ways, the occurrence of leakage between the photosensitive drum 10 and the developing roller 11, the occurrence of a ghost image, the toner The results of examining the flight performance are tabulated. The image forming apparatus used in this investigation is a modified experimental machine using the touch-down development method manufactured by Kyocera Mita, and the specifications are the same, and therefore the description thereof is omitted.

  “Vslvdc (35)” in the leftmost column in the table shown in FIG. 2 indicates the DC developing bias Vslv (DC) applied to the developing roller 11 from the DC developing bias power supply (DC1) 13, and “vmagdc (36)”. The DC toner thin layer forming bias Vmag (DC), “vslvpp (30, 32)” applied to the magnetic roller 15 from the DC toner thin layer forming bias power source (DC2) 19 is supplied to the developing roller 11 by the AC developing bias power source (AC1). ) AC development bias Vslv (AC) 30 and 32 applied from 14 is a peak-to-peak voltage, 30 is an example of the present invention, and 32 is a conventional example. “Vmaggpp (31, 33)” is a peak-to-peak voltage in the AC toner thin layer formation bias Vmag (AC) 31, 33 applied to the magnetic roller 15 from the AC toner thin layer formation bias power source (AC2) 20, and 31 is the main voltage. Inventive Example, 33 is a conventional example, “duty” is a duty ratio in AC developing bias Vslv (AC) 30, 32, AC toner thin layer forming bias Vmag (AC) 31, 33, “DrumVL (34)” is This is the exposure potential on the photosensitive drum 10.

  Further, “Vslvppmax (30, 32)” is the maximum value of the AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power supply (AC1) 14, “Vslvppmin (30, 32)” is also the minimum value, “Vmagppmax ( 31, 33) ”is the maximum value of the AC toner thin layer forming bias Vmag applied to the magnetic roller 15 from the AC toner thin layer forming bias power source (AC 2) 20, and“ Vmagppmin (31, 33) ”is also the minimum value, Vslvppmax−Vmagppmin (37) ”is applied from the AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power supply (AC1) 14 and applied to the magnetic roller 15 from the AC toner thin layer forming bias power supply (AC2) 20. AC toner thin The value obtained by subtracting the minimum value of the forming bias Vmag, “Vslvppmin−Vmagppmax (38)”, is also the value obtained by subtracting the maximum value of the AC toner thin layer forming bias Vmag from the minimum value of the AC developing bias Vslv, “Vslvppmax−DrumVL (39 ")" Is a value obtained by subtracting the exposure potential on the photosensitive drum 10 from the maximum value of the AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power supply (AC1) 14.

  Among them, “Vslvppmax−Vmagppmin (37)” is a potential difference for peeling off the toner not used for development on the developing roller 11 with the magnetic brush 18 of the magnetic roller 15, and “Vslvppmin−Vmagppmax (38)”. "Is a potential difference for forming the toner thin layer 12 on the developing roller 11 by the magnetic brush 18 of the magnetic roller 15. Therefore, when these values are reduced, generation of a ghost image, adhesion of toner to the surface of the developing roller 11 due to selective development, reduction in image density, and the like occur. In “Vslvppmax-DrumVL (39)”, the larger the potential difference, the more the leakage between the developing roller 11 and the photosensitive drum 10 occurs, and the toner flying property between the developing roller 11 and the photosensitive drum 10 is improved. Become.

  The “Developer Roller / Photoreceptor Leakage”, “Ghost Image Occurrence”, and “Developer Roller / Photoreceptor Toner Flyability” below are respectively whether or not the above-mentioned leak has occurred. In the column of whether or not toner has occurred and whether or not there is no problem in the flying property of the toner, each symbol is XX is very good, ◯ is good, △ is somewhat problematic, × is problematic, XX Is very problematic.

  In this table, vslvdc (35) is 200V, vmagdc (36) is 400V, "duty" is 27, "DrumVL (34)" is 100V, and all are the same. In the case where the conventional vslvpp32 generated is 1600 V and the vmagpp33 is 400 V, the “Example” uses 1400 V vslvpp30 and 600 Vvmagpp31, in which no leakage or development ghost occurs and the toner flying property is good. In the case of “Comparative Example 1”, no leak occurred but a ghost image occurred, vslvpp30 was 1400V, and vmagpp31 was 400V. “Comparative Example 2” was leaked vslvpp30 was 1500V, and vmagpp31 was 500V. The example used, “Comparative Example 3”, has some problems with the flying properties of the toner. Is vslvpp30 there is a case where 1300V, vmagpp31 was used 700 V.

  First, in the “conventional example”, the AC developing bias Vslv (AC) indicated by 32 in FIG. 1 is 1600V, and the AC toner thin layer forming bias Vmag (AC) indicated by 33 is maggpp33 of 400V. The AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power supply (AC1) 14 has a maximum value Vslvppmax (32) of 1368 V, a minimum value Vslvppmin (32) of −232 V, and the magnetic roller 15 has an AC toner thin layer forming bias power supply. (AC2) The maximum value Vmagppmax (33) of the AC toner thin layer forming bias Vmag applied from 20 is 508V, and the minimum value Vmagppmin (33) is 108V.

  Therefore, from the maximum value of the AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power source (AC1) 14, the AC toner thin layer forming bias applied to the magnetic roller 15 from the AC toner thin layer forming bias power source (AC2) 20. The value obtained by subtracting the minimum value of Vmag, that is, the potential difference Vslvppmax−Vmagppmin (37) for peeling off the toner not used for development on the developing roller 11 with the magnetic brush 18 of the magnetic roller 15 is 1260V, which is also AC development. A value obtained by subtracting the maximum value of the AC toner thin layer forming bias Vmag from the minimum value of the bias Vslv, that is, a potential difference Vslvppmin−Vmagppma for forming the toner thin layer 12 on the developing roller 11 by the magnetic brush 18 of the magnetic roller 15. (38) is -740 V, a value obtained by subtracting the exposure potential DrumVL on the photosensitive drum 10 from the maximum value of the AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power supply (AC1) 14, that is, the developing roller 11 Vslvppmax-DrumVL (39), which is involved in the occurrence of leakage between the photosensitive drums 10 and indicates the toner flying property between the developing roller 11 and the photosensitive drum 10, is 1268V.

  In this conventional example, since Vslvppmax-DrumVL (39) is as large as 1268 V, a large leak occurs between the developing roller 11 and the photosensitive drum 10, but the developing ghost is good and the toner flying property is also good. Very good.

  On the other hand, in the “Example”, the VSLVPP 30 of the AC developing bias Vslv (AC) indicated by 30 in FIG. 1 is 1400 V, which is 200 V lower than the conventional example, and the vmagpp 31 of the AC toner thin layer forming bias Vmag (AC) indicated by 31 is shown. Is 600V, 200V higher than the conventional example. Therefore, the maximum value Vslvppmax (30) of the AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power supply (AC1) 14 is 1222V, the minimum value Vslvppmin (30) is −178V, and the AC toner thin layer is formed on the magnetic roller 15. The maximum value Vmagppmax (31) of the AC toner thin layer forming bias Vmag applied from the bias power supply (AC2) 20 is 562V, and the minimum value Vmagppmin (33) is −38V.

  For this reason, Vslvppmax-DrumVL (39), which is involved in the occurrence of leakage between the developing roller 11 and the photosensitive drum 10, and indicates the flying property of the toner between the developing roller 11 and the photosensitive drum 10, is as low as 1122V. The potential difference Vslvppmax−Vmagppmin (37) for peeling off the toner that has been prevented from developing on the developing roller 11 with the magnetic brush 18 of the magnetic roller 15 is 1260 V, and the magnetic brush 18 of the magnetic roller 15 is prevented. Thus, the potential difference Vslvppmin−Vmagppmax (38) for forming the toner thin layer 12 on the developing roller 11 is −740 V, which is the same as in the conventional example. Accordingly, both the development ghost and the flying property of the toner are good.

  Next, in Comparative Example 1, the AC development bias Vslv (AC) vslvpp is 1400 V, which is the same as Example 30, which is 200 V lower than the conventional example, but the AC toner thin layer forming bias Vmag (AC) vmaggpp is 33. Therefore, the maximum value Vslvppmax of the AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power supply (AC1) 14 and the minimum value Vslvppmin are 1222 V and -178 V, which are the same as those in the example. The maximum value Vmagppmax of the AC toner thin layer forming bias Vmag applied to the magnetic roller 15 from the AC toner thin layer forming bias power source (AC2) 20 is 508 V, and the minimum value Vmagppmin is 108 V, which is the same as the conventional example.

  Therefore, Vslvppmax-DrumVL (39), which is involved in the occurrence of leakage between the developing roller 11 and the photosensitive drum 10 and indicates the flying property of the toner between the developing roller 11 and the photosensitive drum 10, is 1122 V as in the embodiment. As a result, the leakage is prevented and the flying property of the toner is improved. However, the potential difference Vslvppmax−Vmagppmin (37) for peeling off the toner not used for the development on the developing roller 11 with the magnetic brush 18 of the magnetic roller 15 is as low as 1114 V, and the developing roller is driven by the magnetic brush 18 of the magnetic roller 15. Since the potential difference Vslvppmin−Vmagppmax (38) for forming the toner thin layer 12 on 11 is −686 V, which is smaller than the conventional example, a development ghost is generated.

  In Comparative Example 2, the AC developing bias Vslv (AC) vslvpp was 1500 V between the example and the conventional example, which was 100 V lower than the conventional example and 100 V higher than the example, and the AC toner thin layer forming bias Vmag (AC). The vmagpp is 500 V, which is 100 V higher than the conventional example and 100 V lower than the example. Therefore, the maximum value Vslvppmax and the minimum value Vslvppmin of the AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power supply (AC1) 14 are 1295 V and −205 V, which are larger than the example and smaller than the conventional example. The AC toner thin layer forming bias Vmag applied to the magnetic roller 15 from the AC toner thin layer forming bias power source (AC2) 20 has a maximum value Vmagppmmax of 535 V and a minimum value Vmagppmin of 35 V, which is also an intermediate value. Become.

  For this reason, Vslvppmax-DrumVL (39), which is involved in the occurrence of leakage between the developing roller 11 and the photosensitive drum 10, and indicates the flying property of the toner between the developing roller 11 and the photosensitive drum 10, is as high as 1195V. Leakage occurs, and the toner flying property is good. However, the potential difference Vslvppmax−Vmagppmin (37) for peeling off the toner not used for development on the developing roller 11 with the magnetic brush 18 of the magnetic roller 15 is 1260 V, which is the same as that of the example and the conventional example. Since the potential difference Vslvppmin−Vmagppmax (38) for forming the toner thin layer 12 on the developing roller 11 by the 15 magnetic brushes 18 is −740 V, which is the same as in the example and the conventional example, no development ghost is generated.

  In the last comparative example 3, the AC development bias Vslv (AC) vslvpp is 1300 V, which is 100 V lower than that of the example, and the AC toner thin layer formation bias Vmag (AC) is vmgpp of 700 V, which is 100 V higher than that of the example. Therefore, the maximum value Vslvppmax of the AC developing bias Vslv applied to the developing roller 11 from the AC developing bias power supply (AC1) 14 is 1149 V, which is lower than that of the embodiment, and the minimum value Vslvppmin is −151 V, which is lower than that of the embodiment. The maximum value Vmagppmax of the AC toner thin layer formation bias Vmag applied from the toner thin layer formation bias power source (AC2) 20 is 589 V, which is higher than that of the example, and the minimum value Vmagppmin is also −111 V, which is lower than that of the example.

  Therefore, Vslvppmax-DrumVL (39), which is involved in the occurrence of leakage between the developing roller 11 and the photosensitive drum 10, and indicates the toner flying property between the developing roller 11 and the photosensitive drum 10, is as low as 1049V. Leak does not occur, but toner flying performance is somewhat problematic. However, the potential difference Vslvppmax−Vmagppmin (37) for peeling off the toner not used for development on the developing roller 11 with the magnetic brush 18 of the magnetic roller 15 is 1260 V, which is the same as that of the example and the conventional example. Since the potential difference Vslvppmin−Vmagppmax (38) for forming the toner thin layer 12 on the developing roller 11 by the 15 magnetic brushes 18 is −740 V, which is the same as in the example and the conventional example, no development ghost is generated.

  Returning to FIG. 1 again, what has been described above is reconfirmed in FIG. 1. When the conventional AC developing bias Vslv (AC) indicated by 32 has a vslvpp32 of 1600 V, the conventional AC toner thin layer formation indicated by 33 is shown. In the conventional example where the bias Vmag (AC) vmagpp33 is 400 V, Vslvppmax (32) is 1368 V, Vslvppmin (32) is -232 V, Vmagppmax (33) is 508 V, and Vmagppmin (33) is 108 V. The difference between Vslvppmax and DrumVL indicated as Vslvppmax-DrumVL is 1268 V and leakage occurs, but the toner flying property is very good.

  However, the potential difference Vslvppmax−Vmagppmin (37), which is indicated as 37 (subordinate), for peeling off the toner not used for developing on the developing roller 11 with the magnetic brush 18 of the magnetic roller 15 is 1260V, and 38 Since the potential difference Vslvppmin−Vmagppmax (38) for forming the toner thin layer 12 on the developing roller 11 by the magnetic brush 18 of the magnetic roller 15 shown as (subordinate) is 740 V, no development ghost is generated.

  On the other hand, the AC development bias Vslv (AC) vslvpp30 is 1400 V, which is 200 V lower than the conventional example, and the AC toner thin layer forming bias Vmag (AC) vmagpp 31 indicated by 31 is 600 V, which is 200 V higher than the conventional example. In Example, Vslvppmax (30) is 1222V, Vslvppmin (30) is -178V, Vmagppmax (31) is 562V, and Vmagppmin (31) is -38V, so the difference between Vslvppmax and DrumVL shown as 39 (actual). Vslvppmax-DrumVL becomes 1122 V, the occurrence of leakage is suppressed, and the toner flying property is also good.

  Further, the potential difference Vslvppmax−Vmagppmin (37) shown as 37 (actual) for peeling off the toner not used for development on the developing roller 11 with the magnetic brush 18 of the magnetic roller 15 is 1260V, which is the same as the conventional example. The potential difference Vslvppmin−Vmagppmax (38) for forming the toner thin layer 12 on the developing roller 11 by the magnetic brush 18 of the magnetic roller 15 shown as 38 (actual) is 740 V, which is the same as the conventional example. Therefore, development ghost does not occur.

  However, when the vmagpp of the AC toner thin layer forming bias Vmag (AC) is kept at 400 V as in Comparative Example 1, Vslvppmin-Vmagppmax (38) is reduced to -686 V as shown by 40. In this case, Development ghost occurs.

  From the above results, as described in the outline, leakage is prevented by adjusting the peak-to-peak voltage in the AC developing bias applied between the photosensitive drum 10 and the developing roller 11, thereby reducing the voltage on the developing roller 11. The residual toner that has not been used for the development of the toner is insufficiently peeled off by the magnetic brush 18, the toner is not sufficiently supplied from the magnetic brush 18 to the developing roller 11, the development ghost, and the fine powder toner to the developing roller 11 by the selective development. The AC bias peak value applied to the developing roller 11 from the AC developing bias power source (AC1) 14 and the magnetic roller 15 with a thin AC toner are used for the deterioration of image quality due to an increase in the amount of adhering and developing fine powder toner into the developing device. The difference from the minimum value of the AC bias applied from the layer forming bias power source (AC2) 20 and the developing roller 11 The difference between the minimum value of the AC bias applied and the peak value of the AC bias applied to the magnetic roller 15 is determined before and after the peak-to-peak voltage in the AC developing bias applied between the photosensitive drum 10 and the developing roller 11 is adjusted. It can be seen that it can be prevented by setting the same or more.

  Returning to FIG. 3 again, the developing method and apparatus in the image forming apparatus according to the present invention will be described. As described above, the leak generation voltage varies depending on the environmental temperature and humidity. Therefore, as described above, the ambient temperature, humidity, and AC developing bias Vslv (AC) applied to the developing roller 11 are changed in advance, and the temperature between the developing roller 11 and the photosensitive drum 10 is changed at each temperature and humidity. Investigate the voltage at which leakage occurs and the voltage at which it can be prevented. If it is found, the developing roller 11 by developing ghost and selective development is changed by changing the AC toner thin layer forming bias Vmag (AC) applied to the magnetic roller 15 with each AC developing bias Vslv (AC) that does not cause leakage. The voltage which does not cause image quality deterioration due to the adhesion of fine toner to the developing device and the increase in fine developing toner having low developability into the developing device is checked, and each value is stored in the storage device 25 as a table in advance.

  Then, as described above, when an image formation instruction is received, the control device 24 implements the operation shown in FIG. 2 corresponding to the current environmental temperature and humidity from the table stored in the storage device 25 by a signal from the temperature / humidity sensor 26. The AC developing bias Vslv (AC) applied to the developing roller 11 and the AC toner thin layer forming bias Vmag (AC) applied to the magnetic roller 15 as shown as examples are read. The read values are supplied to the developing roller bias power supply control device 22 and the magnetic roller bias power supply control device 23, and are specified by the DC developing bias power supply (DC1) 13 and the AC developing bias power supply (AC1) 14. The bias voltage specified by the DC toner thin layer forming bias power source (DC2) 19 and the AC toner thin layer forming bias power source (AC2) 20 is applied to the developing roller 11 to the magnetic roller 15.

  When an image formation instruction is received as described above, the surface of the photosensitive drum 10 is first charged by a charging unit (not shown) (charging process), and then the photosensitive unit is also exposed by an exposure unit (not shown). The surface of the drum 10 is exposed to form an electrostatic latent image (exposure process). On the other hand, a magnetic brush 18 of a two-component developer composed of toner 16 and carrier 17 is formed on the magnetic roller 15 while the height is kept constant by a spike cutting blade 21, and a DC developing bias power source is supplied to the developing roller 11. (DC1) 13, a bias voltage supplied from an AC developing bias power supply (AC1) 14, and a DC toner thin layer formation bias power supply (DC2) 19 and an AC toner thin layer formation bias power supply (AC2) 20 to the magnetic roller 15. First, only the toner is transferred from the magnetic brush 18 to the surface of the developing roller 11 by the applied bias voltage, and the toner thin layer 12 is formed on the surface of the developing roller 11.

  Further, from the toner thin layer 12, the toner flies to the electrostatic latent image on the photosensitive drum 10 by the developing bias voltage applied to the developing roller 11 and is developed to form a toner image (developing step). The toner not used for development on the developing roller 11 is peeled off by the magnetic brush 18 formed on the magnetic roller 15 and the bias voltage described above, and a new toner thin layer 12 is formed. Prepare for the next development. Further, the toner image formed on the photosensitive drum 10 is transferred to a sheet conveyed by a paper conveying device (not shown) or an intermediate transfer body (transfer process) and remains on the surface of the photosensitive drum 10. The remaining toner is cleaned by a cleaning unit (not shown) to prepare for the next image formation.

  In the above description, the bias voltage that does not cause a leak is examined in advance for each environmental humidity and temperature, and a table is prepared, and the corresponding voltage is read from the table with the actual environmental humidity and temperature. In a color image forming apparatus, in order to keep the image density constant in a calibration mode, a solid patch is printed by changing the bias voltage applied to the developing roller 11 and the magnetic roller 15, and the density is read and set as a target. The bias voltage for producing the image density to be adjusted is adjusted.

  For this reason, the change in the AC developing bias Vslv (AC) in the calibration mode is also used to detect the voltage at which leakage occurs, and a voltage at which leakage does not occur is obtained. At this time, the AC toner thin layer forming bias power source ( AC2) The amount of change in Vslvppmax-Vmagppmin and Vslvppmin-Vmagppmax is calculated based on the change in the peak-to-peak voltage of 20 and the AC toner thin layer forming bias Vmag (AC) is set so that the value is equal to or greater than the value before the change. It is also possible to change and perform development.

  As described above, according to the present invention, even in the case where the toner is reduced in particle size for the purpose of improving the image quality in the touch-down developing device and the interval between the photosensitive member and the developing roller is narrowed in order to improve developability. , No leaks occur between the photoconductor and the developing roller, and the generation of ghost images, toner adhesion to the developing roller surface due to selective development, reduction in image density, etc. are prevented so that a beautiful image can be always obtained. The developing method and apparatus in the image forming apparatus can be provided.

  According to the present invention, the occurrence of leaks and ghost images between the photosensitive member and the developing roller is suppressed, and toner adhesion to the surface of the developing roller due to selective development, reduction in image density, etc. are prevented, so that a clean image is always obtained. The resulting development method and apparatus can be provided.

A developing bias voltage applied from the DC developing bias power supply (DC1) 13 and the AC developing bias power supply (AC1) 14 to the developing roller 11, and a DC toner thin layer forming bias power supply (DC2) 19 and an AC toner thin layer forming to the magnetic roller 15. 6 is a diagram schematically showing a bias voltage applied from a bias power source (AC2) 20. FIG. A developing bias voltage applied from the DC developing bias power supply (DC1) 13 and the AC developing bias power supply (AC1) 14 to the developing roller 11, and a DC toner thin layer forming bias power supply (DC2) 19 and an AC toner thin layer forming to the magnetic roller 15. The bias voltage applied from the bias power source (AC2) 20 was changed in various ways, and the results of examining the occurrence of leakage between the photosensitive drum 10 and the developing roller 11, the occurrence of a ghost image, and the toner flightability were tabulated. Is. 1 is a diagram showing a schematic configuration of a touch-down developing device that performs a developing method in an image forming apparatus according to the present invention. The horizontal axis is the developing bias voltage Vslv supplied from the DC bias power supply for the developing roller to the developing roller, (A) is the vertical axis, the toner amount (mg / cm ² ) on the developing roller, and (B) is the vertical axis. The solid toner amount (unit: mg / cm ² ) on the photoconductor, (C) is the development efficiency (%) of how much toner on the developing roller flew to the photoconductor, and the vertical axis indicates the developing roller DC developing bias voltage Vslv. And the difference between the DC toner thin layer forming bias voltage Vmag supplied to the magnetic roller and ΔV, the toner amount (A) on the developing roller, the solid toner amount (B) on the photosensitive member, and the developing efficiency (C) are respectively It is the graph which investigated how it changed.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Photosensitive drum 11 Developing roller 12 Toner thin layer 13 DC developing bias power supply (DC1)
14 AC development bias power supply (AC1)
15 Magnetic roller 16 Toner 17 Carrier 18 Magnetic brush 19 DC toner thin layer forming bias power source (DC2)
20 AC toner thin layer forming bias power supply (AC2)
21 Bone Cutting Blade 22 Developing Roller Bias Power Supply Control Device 23 Magnetic Roller Bias Power Supply Control Device 24 Control Device 25 Storage Device 26 Temperature / Humidity Sensor

Claims (6)

A magnetic brush of a two-component developer composed of toner and carrier is formed on a magnetic roller containing a magnet and applied with a bias for toner thin layer formation in which alternating current is superimposed on direct current. The alternating current is applied to the direct current from the magnetic brush. A developing method in an image forming apparatus in which a toner thin layer is formed on a developing roller to which a superimposed developing bias is applied and then the toner is ejected onto an electrostatic latent image formed on a photosensitive member by electrophotography. In
A first step of setting an AC developing bias that does not cause a leak between the photosensitive member and the developing roller, and a peak voltage in the AC developing bias and a minimum peak in the AC toner thin layer forming bias that are changed by the first step. The AC toner so that the difference between the voltage and the difference between the minimum peak voltage in the AC developing bias and the peak voltage in the AC toner thin layer formation bias is equal to or greater than the difference before the first step is performed. A second step of setting a thin layer forming bias,
The voltage difference between the AC developing bias and the AC toner thin layer forming bias changed in the first step is compensated by changing the AC toner thin layer forming bias in the second step, and the image is developed. Development method in forming apparatus.   An AC developing bias set in the first step corresponding to each environmental temperature and humidity is changed in advance, and an AC toner set in the second step corresponding to the AC developing bias. The thin layer forming bias is checked and tabulated, and the AC developing bias and AC toner thin layer forming bias of the table corresponding to the environmental temperature and humidity at the time of image formation are read, and the first and second steps are performed. The developing method for an image forming apparatus according to claim 1.   The image forming apparatus has a calibration mode for image density adjustment by solid patch printing performed by changing the AC developing bias and the AC toner thin layer forming bias, and the first step includes the calibration mode. 2. The developing method in the image forming apparatus according to claim 1, wherein the developing method is performed based on the AC developing bias changed in step (1). A magnetic roller that forms a magnetic brush of a two-component developer composed of toner and a carrier by applying a bias for applying a toner thin layer containing a magnet and superposing an alternating current on a direct current, and forming a toner thin layer on which an alternating current is superimposed on a direct current An image having a developing roller for applying a bias to form a toner thin layer with the magnetic brush and developing the electrostatic latent image formed on the photoreceptor by electrophotography with the toner flying from the toner thin layer. In the developing device in the forming device,
A developing roller bias power supply control device for controlling the AC bias peak value in the AC developing bias, a magnetic roller bias power supply control device for controlling the AC bias peak value in the AC toner thin layer formation bias, and the AC developing bias Instructs the developing roller bias power supply controller a peak value that does not cause a leak between the photosensitive member and the developing roller, and also includes a peak voltage in the AC developing bias that does not cause a leak and a minimum peak voltage in the AC toner thin layer forming bias. And the difference between the minimum peak voltage in the AC developing bias that does not cause leakage and the peak voltage in the AC toner thin layer forming bias before changing to the peak value that does not cause leakage in the AC developing bias. At least equivalent to the difference from the peak value The AC thin toner layer forming bias made, the developing device in an image forming apparatus characterized by comprising a controller for instructing the magnetic roller bias power supply control device.   The control device corresponds to each of a plurality of environmental temperatures and humidity, and stores a peak value that does not cause leakage in the AC developing bias, and a table that stores the AC toner thin layer forming bias corresponding to the peak value; An environmental temperature and humidity detecting means, and based on the detection result of the environmental temperature and humidity detecting means, a peak value causing no leakage in the AC developing bias from the table, and the alternating current corresponding to the peak value 5. The developing device in the image forming apparatus according to claim 4, wherein a toner thin layer forming bias is read and the developing roller bias power source controller and the magnetic roller bias power source controller are controlled.   The image forming apparatus has a calibration mode for image density adjustment by solid patch printing performed by changing the AC developing bias and the AC toner thin layer forming bias, and the control apparatus changes in the calibration mode. 5. The development in the image forming apparatus according to claim 4, wherein a peak value that does not cause a leak is determined by the AC developing bias to be controlled, and the developing roller bias power supply control device and the magnetic roller bias power supply control device are controlled. apparatus.

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