JP2009008834A - Image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming method using an image forming apparatus equipped with a touchdown developing device, wherein high image quality is maintained and also productivity in image output is secured by controlling a toner thin layer on a toner carrier to have prescribed thickness. <P>SOLUTION: When forming the toner thin layer on the surface of the toner carrier, the thickness of the toner layer on the toner carrier is detected by a toner layer thickness detection means, and conveyance bias is changed from information on the detected thickness of the toner layer, to control the toner thin layer on the toner carrier to have the prescribed layer thickness. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method using 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. An image in which a developer is used, a magnetic brush is formed, a toner thin layer is formed on the developing roller by the magnetic brush, and the toner of the toner thin layer is ejected onto the electrostatic latent image to develop the latent image. It relates to a forming method.

Conventionally, in an electrophotographic image forming apparatus, as a developing method using a dry toner, a one-component developing method and a two-component developing method are known.
Since the one-component developing method does not include a carrier, the electrostatic latent image on the photosensitive member is not disturbed by the magnetic brush formed from the carrier and the toner, and is suitable for high 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, full-color image forming apparatuses often employ a two-component development system that uses a carrier as a medium for charging and transporting toner.

  As an image forming method using the two-component developing method, a toner thin layer is formed on a toner carrier with a magnetic brush formed on a developer carrier carrying a two-component developer, and the toner on the toner carrier There is known an image forming method by so-called touch-down development (also referred to as hybrid development) in which an electrostatic latent image on an electrostatic latent image carrier is developed and visualized by a thin layer. However, in this development method, when the toner thin layer on the toner carrier fluctuates, the development amount on the electrostatic latent image carrier fluctuates and as a result affects the image quality. For example, when the toner amount of the toner thin layer is small Has a problem that an image density defect occurs.

For this reason, for example, in Patent Document 1, the density patch is developed on the surface of the photosensitive drum or on the transfer belt so that the development amount on the photosensitive drum becomes an appropriate development amount, and the density of the density patch is determined by the ID sensor. For example, it is proposed to control the toner layer thickness on the developing roller by adjusting the potential difference between the developing roller and the magnetic roller according to the density.
JP 2005-55841 A

  However, in this method, since the toner layer thickness needs to be controlled at a timing other than the time of image formation, such as after the image forming apparatus is turned on or between sheets at the time of image output, the image forming apparatus can output. It takes a long time to complete the process, or it is necessary to take a long space between the sheets, so that there is a disadvantage that the number of print processes is reduced and the productivity of image output is affected. Further, since the toner is developed on the photosensitive drum and the toner density is measured, there is a problem that wasteful toner is consumed.

  SUMMARY OF THE INVENTION An object of the present invention is to control the toner layer thickness on a toner carrier to a predetermined thickness in an image forming method using an image forming apparatus of a touch-down development method, thereby maintaining high image quality and producing image output. An object of the present invention is to provide an image forming method capable of securing the property.

  As a result of intensive studies to solve the above problems, the present inventor has determined the toner layer thickness on the toner carrier using a toner layer thickness detection means when forming a toner thin layer on the surface of the toner carrier. By measuring and changing the transport bias between the toner carrier and the two-component developer carrier based on the toner layer thickness and controlling the toner layer thickness on the toner carrier to a predetermined layer thickness, The present inventors have found a new fact that image quality can be maintained and productivity of image output can be secured, and the present invention has been completed.

That is, the image forming method of the present invention has the following configuration.
(1) Using a two-component developer carrying member carrying a carrier and a toner developer, and having a magnetic brush formed on the surface, and a toner carrying member arranged close to the two-component developer carrying member. Then, a transfer bias is applied between the two-component developer carrier and the toner carrier, and the toner is transferred via the magnetic brush of the two-component developer carrier, so that the toner is transferred onto the surface of the toner carrier. Forming a thin layer, applying a developing bias to the toner carrier and / or the two-component developer carrier, causing the toner to fly from the toner thin layer on the toner carrier, and An image forming method for developing an electrostatic latent image formed on a surface, wherein when forming a toner thin layer on the surface of the toner carrying member, a toner layer thickness detecting unit detects a toner layer thickness on the toner carrying member. And the detected toner layer thickness Image forming method characterized in that by changing the transport bias from the information, to control the toner thin layer on the toner carrying member to a predetermined thickness.
(2) Using a two-component developer carrying body carrying a developer composed of a carrier and a toner and forming a magnetic brush on the surface, and a toner carrying body arranged close to the two-component developer carrying body Then, a transfer bias is applied between the two-component developer carrier and the toner carrier, and the toner is transferred via the magnetic brush of the two-component developer carrier, so that the toner is transferred onto the surface of the toner carrier. Forming a thin layer, applying a developing bias to the toner carrier and / or the two-component developer carrier, causing the toner to fly from the toner thin layer on the toner carrier, and An image forming method for developing an electrostatic latent image formed on a surface, wherein when forming a toner thin layer on the surface of the toner carrying member, a toner layer thickness detecting unit detects a toner layer thickness on the toner carrying member. And the detected toner layer thickness And the toner carrying member and / or by changing the rotational speed of the two-component developer carrier from the information, the image forming method characterized by controlling the toner thin layer on the toner carrying member to a predetermined thickness.
(3) The image forming method according to (1) or (2), wherein the toner layer thickness detecting means is a toner density sensor or a surface potential sensor.

  According to the present invention, when the toner thin layer is formed on the surface of the toner carrier, the toner layer thickness on the toner carrier is detected using the toner layer thickness detecting means, and the toner carrier is detected based on the detection information. Since the transport bias applied to the two-component developer carrier is changed, the toner layer thickness on the toner carrier can be maintained at a predetermined layer thickness, and as a result, high image quality can be maintained. Further, since the toner layer thickness can be directly detected by the toner layer thickness detecting means, the toner layer thickness can be quickly controlled, and the productivity of image output can be ensured.

  Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is an explanatory diagram showing a schematic configuration of an image forming apparatus of a touchdown development system according to an embodiment of the present invention. FIG. 2 is a schematic configuration diagram showing a part of the developing means of FIG. FIG. 3 is a schematic configuration diagram showing an example of a tandem type color image forming apparatus using the developing unit shown in FIG.

(Image forming device)
The image forming apparatus of the present invention forms a toner thin layer 9 on the developing roller 2 with the two-component developer carried on the magnetic roller 1 using the two-component developer composed of the magnetic carrier 4 and the toner 5, and the toner. This is an image forming apparatus based on a so-called touch-down developing method in which the toner 5 is ejected from the thin layer 9 to develop the electrostatic latent image formed on the photoreceptor 3 (electrostatic latent image carrier). As shown in FIG. 1, the image forming apparatus includes the photoreceptor 3, and around the photoreceptor 3, a charging unit 8, an exposing unit 16, a developing unit 18, a primary transfer unit 22, and a secondary transfer unit 25. The fixing unit 26, the cleaning unit 24, and the like are disposed.

  Image formation by the image forming apparatus is performed as follows. That is, the surface of the photosensitive member 3 is uniformly charged by the charging unit 8, and the charged surface is exposed by the exposure unit 16 to form an electrostatic latent image. The obtained electrostatic latent image is developed as a toner image by attaching the toner 5 from the developing means 18. This toner image is transferred from the photoreceptor 3 onto an intermediate transfer member (intermediate transfer belt) 20 by a primary transfer roller 22 as a primary transfer unit. After the toner images of a plurality of colors are transferred onto the intermediate transfer body 20 in an overlapping manner, the secondary transfer roller 25 as a secondary transfer unit transfers the toner image to the transfer target conveyed from the paper feed cassette 27 to the secondary transfer position. Transfer the toner image. This transferred body is conveyed to a fixing roller 26 as a fixing unit, and after the toner image is fixed on the transferred body, it is discharged to, for example, a discharge tray (not shown). Undeveloped toner remaining on the surface of the photoreceptor 3 after the transfer is removed by the cleaning means 24.

  Examples of the photoreceptor 3 include inorganic photoreceptors such as selenium and amorphous silicon, and organic photoreceptors in which a single-layer or multilayer photosensitive layer containing a charge generating agent, a charge transport agent, a binder resin, and the like is formed on a conductive substrate. (OPC) and the like. Examples of the charging unit 8 include a scorotron system, a charging roller, and a charging brush. As for the exposure means 16, LED or a semiconductor laser is mentioned as exposure light. Moreover, as the cleaning means 24, for example, a doctor blade method or the like can be used, and known ones can be used.

  The developing means 18 has a plurality of magnetic members fixed therein, a sleeve-like magnetic roller 1 (two-component developer carrier) rotating around the outer periphery of the magnetic member, and the magnetic roller 1 inside. A magnetic member having a different polarity from the magnetic member is fixed, and a sleeve-like developing roller 2 (toner carrier) that rotates on the outer peripheral portion of the magnetic member, and different magnetic poles of the magnetic roller 1 and the developing roller 2 are provided. A magnetic field is formed by this magnetic force, and a restriction blade 7 for keeping the height of the magnetic brush 6 formed on the magnetic roller 1 constant by this magnetic field is constituted. Further, a bias power source 11 including an alternating current (AC) bias power source 11a and a direct current (DC: Vdc1) bias power source 11b applied to the magnetic roller 1, and an alternating current (AC) bias power source 12a and a direct current (DC: DC) applied to the developing roller 2. Vdc2) a bias power source 12 including a bias power source 12b. Further, a toner layer thickness detecting means 29 for detecting the toner layer thickness on the developing roller 2 according to the present invention is provided.

  The image forming apparatus of the present invention also includes a toner container (not shown) in which the toner 5 is stored and the toner 5 supplied from the toner container to the two-component developer storage unit 45 that stores the two-component developer. The two-component developer supplied to the stirring screw 44 from the stirring screw 40 through both ends of the partition plate 42 is communicated at both ends of the partition plate 42 and stirred with the carrier 4 to be charged. Supplied to the magnetic roller 1, the stirring screw 44 circulates the two-component developer from the other end side to the stirring screw 40 side, and the magnetic roller 1, the developing roller 2, the stirring screw 40, and the stirring screw 44. And a housing 46 in which is stored.

  As shown in FIG. 3, the image forming apparatus of the present invention is a tandem (indirect transfer tandem type) color image forming apparatus in which four photoconductors 3A, 3B, 3C, and 3D are arranged on an intermediate transfer body 20. It can be used suitably. In this case, using the developing means 18 described above, the developing devices 18A, 18B, 18C, and 18D containing magenta, cyan, yellow, and black toners are electrostatically charged on the photoreceptors 3A, 3B, 3C, and 3D, respectively. The latent image is visualized and a toner image is formed. The toner images visualized on the photoreceptors 3A, 3B, 3C, 3D are sequentially transferred onto the surface of the intermediate transfer member 20 from the upstream photoreceptor 3A. The full-color image transferred onto the intermediate transfer member 20 is transferred to the transfer member conveyed from the paper feed cassette 27 by the secondary transfer roller 25 and then fixed by the fixing roller 26, and then the transfer member. Is discharged.

(Development method)
FIG. 2 schematically shows a part of the developing means according to the present invention, and the developing method will be described with reference thereto.
A magnetic brush 6 comprising a carrier 4 (magnetic particles) that is magnetically constrained by a fixed magnet contained in the magnetic roller 1 and a toner 5 that is charged and held on the surface of the carrier 4 is attached to the surface of the magnetic roller 1. It is rotated and conveyed to the developing roller 2. The surface of the magnetic roller 1 can be conveyed more smoothly by using a blasted or grooved surface.

  As shown in FIG. 2, a developing bias voltage 12 in which an alternating voltage (AC) 12a is superimposed on a direct current voltage (DC: Vdc2) 12b is applied to the developing roller 2, and a direct current voltage (DC: Vdc1) is applied to the magnetic roller 1. ) 11b is applied with a bias voltage 11 in which an alternating voltage (AC) 11a is superimposed. The magnetic brush 6 is formed on the magnetic roller 1. The magnetic brush 6 on the magnetic roller 1 is layer-regulated by a regulating blade 7, and a potential difference (conveying bias) between the magnetic roller 1 and the developing roller 2. Due to ΔV (= | Vdc1−Vdc2 |), the toner 5 of the conveyed magnetic brush 6 moves to the developing roller 2 to form a thin toner layer 9. For example, when ΔV is increased, the toner thin layer 9 on the developing roller 2 is thickened, and when ΔV is decreased, the toner thin layer 9 is thinned. Then, in accordance with the potential difference between the photosensitive member 3 and the developing roller 2, the toner jumps from the toner thin layer 9 on the developing roller 2 to the electrostatic latent image formed on the photosensitive member 3 for development.

  In the present invention, the direct current voltage (DC: Vdc1) 11b applied to the magnetic roller 1 using the toner layer thickness detection means 29 and / or development in order to make the toner layer thickness on the developing roller 2 a predetermined thickness. A direct current voltage (DC: Vdc2) 12b applied to the roller 2 is controlled to change the transport bias ΔV between the developing roller 2 and the magnetic roller 1. That is, the control of the DC voltages 11b and 12b is performed by detecting the layer thickness of the toner thin layer 9 formed on the developing roller 2 by the toner layer thickness detecting means 29, and the magnetic layer thickness according to the toner layer thickness. Since the transport bias ΔV between the roller 1 and the developing roller 2 is controlled, proper control of the toner thin layer 9 can be quickly performed, thereby shortening the time until development is possible, or shortening the paper interval. Therefore, productivity of image output can be improved.

As the toner layer thickness detecting means 29 for detecting the toner layer thickness on the developing roller 2, for example, a reflection type density sensor can be used. The reflection type density sensor is provided at a position facing the developing roller 2 on the upstream side or the downstream side in the rotation direction of the developing roller 2 from the closest position of the photoconductor 3 and the developing roller 2. Preferably, it is arranged on the upstream side in the rotation direction of the developing roller 2. Thereby, the layer thickness after the toner thin layer 9 is formed can always be detected.
FIG. 4 shows a schematic diagram of a reflection type density sensor. The reflection type density sensor uses a near-infrared LED as a light emitting element and a photodiode as a light receiving element, and detects the density from regular reflection light and irregular reflection light obtained from toner on the developing roller 2. The method will be described below.

このようにして検出したセンサ出力を予め設定されたトナー量とセンサ出力の関係からトナー量として検知する。 The reflection type density sensor includes an LED as a light emitting unit, PDs (Photo Detector) 1, 2 and 3 as light receiving units, and BS (Beam Splitter) 1 and 2. The light emitted from the LED is separated by the BS 1 into a component that vibrates in a direction perpendicular to the incident surface (s-wave light) and a component that vibrates in a direction parallel to the incident surface (p-wave light). The s-wave light is applied to the PD1 near the LED, and the p-wave light is applied to the toner surface. The p-wave light incident on a non-image area such as the photosensitive member 3 and the intermediate transfer member 20, in this embodiment, the surface that becomes the ground when detecting the toner density on the developing roller 2, is substantially specularly reflected and becomes specularly reflected light. It passes through BS2 as a p-wave and enters PD2. The p-wave light applied to the toner surface is irregularly reflected, and part of it becomes an s-wave, which is divided into a p-wave and an s-wave.
Passing through BS2, the p-wave enters PD2 as regular reflected light, and the s-wave enters PD3 and is detected as irregularly reflected light. Therefore, PD2 functions as a regular reflection light amount detection unit, and PD3 functions as a diffuse reflection light amount detection unit. Actually, it is considered that the irregular reflection component is also incident on PD2. Therefore, a true regular reflection output can be obtained by subtracting the product of the s-wave output from PD3 multiplied by the correction coefficient from the p-wave output from PD2, that is, the following equation (1). The correction coefficient is often a predetermined fixed value.

The sensor output detected in this way is detected as the toner amount from the relationship between the preset toner amount and the sensor output.

  In the present invention, according to the flowchart shown in FIG. 5, the toner amount on the developing roller 2 is detected by the density sensor 29 to control the toner layer thickness. That is, first, in step 1, the power is turned on, and in step 2, it is determined whether or not the toner layer thickness on the developing roller 2 needs to be controlled by comparing with setting conditions such as the number of printed sheets or the printing rate. If the number of printed sheets is small and does not satisfy the set condition, the control of the layer thickness is unnecessary and the process proceeds to Step 7. When the set condition is reached, the layer thickness needs to be controlled, and the process proceeds to Step 3.

  In step 3, as described above, the toner is ejected from the toner thin layer 9 on the developing roller 2 to the electrostatic latent image formed on the photoreceptor 3, and development is performed. The density sensor 29 detects the toner amount at a predetermined position on the surface of the toner thin layer 9 formed on the developing roller 2. The density sensor 29 is preferably provided at a position opposite to the developing roller 2 on the upstream side in the rotation direction of the developing roller 2 from the closest position of the photosensitive member 3 and the developing roller 2, thereby detecting the toner layer thickness earlier. And the development timing can be accelerated. The toner amount may be detected at 2 to 60 positions at equal intervals in the circumferential direction, and the average value may be used as the toner amount.

In step 4, it is determined whether or not the toner layer thickness is appropriate based on the output signal from the density sensor 29. If it is appropriate, the process proceeds to step 7, and if not, the process proceeds to step 5.
In step 5, the value of the direct current voltage (DC: Vdc1) 11a applied to the magnetic roller 1 is adjusted so that the thickness of the toner thin layer 9 on the developing roller 2 becomes an appropriate (predetermined) layer thickness, thereby conveying bias. ΔV is set. Then, the process proceeds to step 6 and the layer thickness is adjusted by the set transport bias ΔV. After this layer thickness adjustment, the process returns to step 3 and is detected by the density sensor 29 to determine whether or not a predetermined layer thickness has been reached. If the predetermined layer thickness cannot be obtained, the process proceeds to step 5 again, and the layer thickness is adjusted by changing the transport bias ΔV. Note that the timing of the density sensor detection by the density sensor and the application of the transport bias in the series of steps is controlled by a control device (not shown).

  By controlling the toner layer thickness on the developing roller 2 in this way, a constant print density can be obtained whenever the print density is controlled, and a development enable signal is output in the next step 7 and the process ends. To do. As shown in step 2, this control is preferably performed when the integrated value of the number of printed sheets and the printing rate, that is, when a certain printing rate is reached.

  The conveyance bias ΔV may be adjusted by changing either the direct current voltage (DC: Vdc2) 12b applied to the developing roller 2 or the direct current voltage (DC: Vdc1) 11b applied to the magnetic roller 1. You may carry out by making it change simultaneously.

  The electrostatic latent image on the photoreceptor 3 can be formed by using the exposure unit 16 on the surface of the photoreceptor 3 charged to +250 to 800 V by the charging unit 8. When an OPC photoconductor is used, +70 to 220 V is obtained in all exposures, and an amorphous silicon photoconductor provides a post-exposure potential of 10 to 50 V. For the exposure, either a semiconductor laser or an LED can be used.

  At the time of development, for example, when a regular positively charged toner is used as the toner, +300 to 500 V is applied to the magnetic roller 1 and +100 V is applied to the developing roller 2 as a developing bias condition. The potential difference for forming the thin layer is appropriately 200 to 400 V, and may be adjusted according to the balance with the charge amount of the toner 5.

The AC conditions are as follows: the magnetic roller 1 has the same frequency as the developing roller 2, the same period and the opposite phase of V _PP (peak AC bias) = 0.1-2.0 kV, frequency = 2-4 kHz, DUTY ratio = 60-80% In the developing roller 2, it is preferable that V _PP = 1.0 to 2.0 kV, frequency = 2 to 4 kHz, and DUTY ratio = 20 to 40%. When V _PP is increased, the thin layer is formed more instantly, but on the other hand, the leak resistance is weakened, which causes noise. With respect to these points, it is preferable to increase the insulation by anodizing the surface of the magnetic roller 1 or the developing roller 2 because the margin is widened. The frequency may be adjusted by the charge amount of the toner 5.

  After the development, the developing roller 2 having the residual toner layer is closest to the magnetic roller 1 having the developer layer at the opposed position, and the developing roller 2 is mechanically applied by the magnetic brush 6 at the opposed position. The upper toner layer 9 is scraped off and collected. At the same time, the toner 5 is supplied from the developer layer on the magnetic roller 1 to the developing roller 2 side according to the potential difference ΔV formed between the magnetic roller 1 and the developing roller 2.

  At the end of development, while the AC voltage 12a is applied to the developing roller 2, the DC voltage (Vdc1) 11b applied to the magnetic roller 1 may be changed to recover the toner thin layer 9 on the developing roller 2 to the magnetic brush 6. . In this case, the toner 5 cannot be supplied from the developer layer on the magnetic roller 1 to the developing roller 2 side during collection. When the toner 5 is peeled off from the developing roller 2 every time the development is completed, the toner 5 is always refreshed. However, it takes time to form the stable toner thin layer 9 again, and a sufficient printing speed cannot be achieved. In order to maintain a good printing speed, it is only necessary to adjust the sheet interval and adjust the time for the toner thin layer 9 on and off the developing roller 2 to be taken in and out in a certain period. In order to supply sufficient toner to the latent image on the photoconductive drum 3 without increasing the paper interval, the peripheral speed of the developing roller 2 is set to 1.5 times or more with respect to the photoconductive drum 3 for a short time. The toner can be taken in and out. Further, when the magnetic roller 1 is set to a speed exceeding 1 and 2 times that of the developing roller 2, the replacement of the toner thin layer 9 is promoted. At this time, it is preferable that the rotating direction of the magnetic roller 1 is opposite to the developing roller 2.

As the toner 5, both positively charged toner and negatively charged toner can be used. The volume average particle diameter of the toner 5 is preferably 4.0 to 7.5 μm. If the thickness is less than 4.0 μm, the influence of non-electrostatic adhesion increases, and developability and recoverability deteriorate. If the thickness is greater than 7.5 μm, it is difficult to obtain a high-quality image such as smooth image quality. The charge amount of the toner 5 is preferably about 6 to 30 μC / g. If the charge amount is lower than this, the toner 5 will fly from the magnetic brush 6 and stain the periphery, and if it is higher than this, the thin layer formation will be weakened.
The toner volume average particle diameter can be measured using Multisizer III (manufactured by Beckman Coulter, Inc.) with an aperture diameter of 100 μm (measurement range: 2.0 to 60 μm).
The toner charge amount can be measured with a QM meter (manufactured by TREK, MODEL 210HS).

As the carrier 4, a known carrier can be used. Preferably, a carrier whose surface is coated with a resin using a ferrite core is preferably used. The coating resin may be a known one such as silicone, fluorine epoxy, fluorine silicone, polyamide, polyamideimide. Moreover, it is preferable to use a carrier particle diameter (weight average particle diameter) of 25-50 micrometers. If it is less than 25 μm, the holding force due to the magnetic force is weakened, so that carrier jumping or the like that causes the carrier 4 to move to the developing roller 2 occurs, and if it exceeds 50 μm, the magnetic brush 6 is not dense enough and the toner is thin. The formation of the layer 9 is not smooth and the specific surface area is small, so that the recoverability of the toner 5 is also lowered. Further, the saturation magnetization of the carrier 4 is preferably 35 to 90 emu / g. When the saturation magnetization is lower than 35 emu / g, the carrier jump is remarkably deteriorated. When the saturation magnetization is higher than 90 emu / g, the magnetic brush 6 becomes sparse and a uniform thin layer cannot be formed.
The saturation magnetization of the carrier 4 can be measured with a magnetic field of 79.6 kA / m (1 kOe) using “VSM-P7” manufactured by TOEI.

  The gap between the magnetic roller 1 and the developing roller 2 is 200 to 600 μm, preferably 300 to 400 μm. The gap is the most effective factor for instantly forming a thin layer. If the width is wide, the efficiency is lowered, and problems such as development ghosts occur. On the other hand, if it is narrow, the magnetic brush 6 that passes through the blade gap cannot pass through the gap and the toner thin layer 9 is disturbed.

  In the present invention, a surface potential sensor may be used as the toner layer thickness detecting means 29. Using the surface potential sensor, the surface potential of the developing roller 2 is measured, and the toner charge amount on the developing roller 2 is obtained from the known electrostatic capacity of the developing roller 2. Then, the transport bias ΔV is determined so as to be a predetermined charge amount (that is, a predetermined toner layer thickness) from the relationship between the preset charge amount and the transport bias ΔV.

(Other embodiments)
In order to maintain the toner layer thickness on the developing roller 2 at a predetermined layer thickness, the developing roller 2 and the magnetic roller are replaced with the control by the transport bias ΔV between the developing roller 2 and the magnetic roller 1 in the embodiment. The rotation number (rotational speed) of 1 may be controlled. That is, the toner layer thickness detecting means 29 detects the toner layer thickness of the toner thin layer 9 formed on the developing roller 2 and the toner layer thickness and the developing roller prepared in advance according to the toner layer thickness are detected. 2 and a data table showing the relationship between the rotational speeds of the magnetic roller 1, and a control for keeping the toner layer thickness constant by adjusting the rotational speed. This control is performed by correcting the rotation speed of the developing roller 2 with the rotation speed of the magnetic roller 1 being constant, correcting the rotation speed of the magnetic roller 1 with the rotation speed of the developing roller 2 being fixed, or the magnetic roller 1 and the development. For example, the number of rotations of the roller 2 can be corrected. For example, when the rotation speed of the developing roller 2 is controlled to be relatively higher than the rotation speed of the magnetic roller 1, the amount of toner on the developing roller 2 conveyed from the magnetic roller 1 decreases and the toner thin layer 9 On the contrary, when the rotation speed of the developing roller 2 is decreased, the toner thin layer 9 becomes thicker.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated in detail, this invention is not limited only to a following example.

The image forming apparatus of the present invention shown in FIG. 1 was produced according to the following specifications. The dimensions of the sleeves of the photosensitive member 3, the developing roller 2, and the magnetic roller 1 are as follows.
Photoconductor 3: outer diameter 30 mm
Developing roller 2: 20 mm outer diameter
Magnetic roller 1: outer diameter 25mm
Amorphous silicon is used for the photoconductor 3 drum, and aluminum is used for the sleeve of each roller. The peripheral speed of each drum is as follows. Photoconductor 3: 300 mm / sec
Developing roller 2: 450 mm / sec
Magnetic roller 1: 675mm / sec
Examples of the toner density detecting means 29 include density sensors manufactured by Omron, Nichicon, and Stanley. In this embodiment, a density sensor manufactured by Stanley was used. A graph showing the relationship between the output value (output conversion value) of the density sensor and the toner amount (layer thickness) on the developing roller 2 and a graph showing the relationship between the toner amount (layer thickness) and the transport bias ΔV are shown in FIG. Shown in (a) and (b).

Using the image forming apparatus produced above, continuous image output was performed under the following image forming conditions.
Photoconductor surface potential: + 310V
Q / m of toner in developer: 20 μC / g
Toner particle size (volume average particle size): 6.7 μm
Carrier particle size (weight average particle size): 45 μm
Distance between magnetic roller and developing roller: 350 μm
Developing roller applied voltage: Vdc2 = 100 V, V _PP = 1.6 kV, frequency f = 2.7 kHz, Duty ratio = 30%
Magnetic roller applied voltage: Vdc1 = 250 V (variable width ± 50 V when controlling the layer thickness), V _PP = 300 V in the same cycle as the developing roller, opposite phase, frequency f = 2.7 kHz, Duty ratio = 70%

  As described above, by changing the transport bias between the toner carrier and the two-component developer carrier using the toner layer thickness detection means, and controlling the toner thin layer on the toner carrier to a predetermined layer thickness, A high-quality image was obtained and productivity of image output was ensured.

1 is an explanatory diagram showing a schematic configuration of an image forming apparatus of a touchdown development system according to an embodiment of the present invention. It is a schematic block diagram which shows a part of developing means of FIG. FIG. 2 is a schematic configuration diagram illustrating an example of a tandem color image forming apparatus using the developing unit illustrated in FIG. 1. FIG. 6 is a diagram illustrating an example of a method for detecting a toner density by a toner density detecting unit according to an embodiment of the present invention. 6 is a flowchart illustrating an example of a control method for controlling the thickness of a toner layer on a developing roller. 4A is a graph showing a relationship between an output converted value of a density sensor and a toner amount, and FIG. 4B is a graph showing a relationship between the toner amount and a transport bias ΔV.

Explanation of symbols

1 Two-component developer carrier (magnetic roller)
2 Toner carrier (developing roller)
3 Electrostatic latent image carrier (photoreceptor)
4 Carrier 5 Toner 6 Magnetic Brush 7 Regulating Blade 8 Charging Unit 9 Toner Thin Layer 11a AC Power Supply 11b DC Power Supply 12a AC Power Supply 12b DC Power Supply 16 Exposure Unit 22 Primary Transfer Unit 24 Cleaning Unit 25 Secondary Transfer Unit 26 Fixing Unit 29 Toner Layer Thickness detection means

Claims (3)

Using a two-component developer carrying member carrying a developer composed of a carrier and a toner and forming a magnetic brush on the surface, and a toner carrying member arranged close to the two-component developer carrying member, A transport bias is applied between the two-component developer carrier and the toner carrier, and the toner is transferred via the magnetic brush of the two-component developer carrier to form a thin toner layer on the surface of the toner carrier. And forming a bias on the toner carrier and / or the two-component developer carrier and causing the toner to fly from the toner thin layer on the toner carrier to form on the surface of the electrostatic latent image carrier. An image forming method for developing an electrostatic latent image, comprising:
When forming a toner thin layer on the surface of the toner carrying member, the toner layer thickness on the toner carrying member is detected by a toner layer thickness detecting means, and the transport bias is changed based on the detected toner layer thickness information. An image forming method comprising controlling a toner thin layer on the toner carrier to a predetermined layer thickness. Using a two-component developer carrying member carrying a developer composed of a carrier and a toner and forming a magnetic brush on the surface, and a toner carrying member arranged close to the two-component developer carrying member, A transport bias is applied between the two-component developer carrier and the toner carrier, and the toner is transferred through the magnetic brush of the two-component developer carrier to form a toner thin layer on the surface of the toner carrier. Then, a developing bias is applied to the toner carrier and / or the two-component developer carrier, and the toner is ejected from the toner thin layer on the toner carrier to form on the surface of the electrostatic latent image carrier. An image forming method for developing an electrostatic latent image, comprising:
When forming a toner thin layer on the surface of the toner carrier, a toner layer thickness on the toner carrier is detected by a toner layer thickness detecting means, and the toner carrier and / or the information on the detected toner layer thickness is detected. An image forming method comprising: controlling a thin toner layer on the toner carrier to a predetermined layer thickness by changing a rotation speed of the two-component developer carrier.   3. The image forming method according to claim 1, wherein the toner layer thickness detecting means is a toner density sensor or a surface potential sensor.

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