JP2009008833A - 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 developing device of a touch-down developing system, in which stable image density can be obtained even in long-term printing by controlling a toner thin layer on a toner carrier to a predetermined thickness. <P>SOLUTION: A toner layer on a toner carrier 2 is controlled to a predetermined thickness by measuring a toner charge amount on the toner carrier 2 by a charge detecting means 29 and changing a conveyance bias between the toner carrier 2 and a two-component developer carrier 1 based on a charge amount of toner firmly adhering to the toner carrier 2 and not contributing to development. <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, an image forming method using a conventional contact developing method and an image forming method using a so-called touch-down developing (also referred to as hybrid developing) using a non-contact developing method are known. In the conventional developing system, a two-component developer is conveyed by a mag roller, and the photosensitive member is developed by a developing bias. In this method, the amount of toner supplied to the photoreceptor is determined by the developing bias. This is because a developer having a constant toner concentration is always conveyed onto the mag roller, and a large amount of developer is supplied compared to the amount conveyed to the mag roller.

On the other hand, in the touch-down development method, toner is conveyed from a magnetic roller carrying a two-component developer via a magnetic brush formed on the surface thereof, and a thin toner layer is formed on the developing roller. Then, toner is ejected from the toner thin layer to develop and visualize the electrostatic latent image on the photoreceptor. Therefore, in this method, the toner supply amount to the photoconductor is highly dependent on the toner thin layer (toner amount) on the developing roller. In addition to the developing bias on the developing roller, there is a voltage (toner layer voltage) generated from the amount of charge charged by the toner. If this toner layer voltage is large, that is, if the toner layer thickness is large, the developing performance Becomes higher. From this, it can be said that in the touchdown development, the developing performance is determined by the toner layer thickness rather than the developing bias voltage applied to the developing roller. Therefore, when the toner thin layer on the developing roller fluctuates, the development amount on the photosensitive member fluctuates, and as a result, the image quality is affected. For example, when the toner amount of the toner thin layer is small, an image density defect or the like occurs. There was a problem.
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

On the other hand, toner that is not easily affected by the electric field generated between the developing roller and the photosensitive drum is present in the toner thin layer on the developing roller. Such toner has very strong adhesion to the developing roller, and the recovery is hindered not only when developing on the photosensitive drum but also when recovering to the developer present on the magnetic roller during non-printing. become. In particular, when a document with a low printing rate is frequently output or when it is output in a high temperature environment, the presence of such highly adherent toner tends to gradually increase. Furthermore, since this toner has a strong charge and there is a voltage formed from the strong charge in addition to the development bias of the developing roller, the amount of toner that should be developed on the photosensitive drum is reduced, resulting in poor image density. There was a problem that image loss occurred.
An object of the present invention is to control a 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, so that a stable image density can be obtained even in long-term printing. An object of the present invention is to provide an image forming method that can be maintained.

  As a result of intensive research to solve the above problems, the present inventor measured the amount of toner charge on the toner carrier using charge amount detection means, and the toner thin layer on the toner carrier was developed into a two-component development. By measuring the charge amount on the surface of the toner carrier after being collected on the agent carrier, the charge amount of the toner that adheres strongly to the toner carrier and does not contribute to development can be considered. By changing the transport bias between the toner carrier and the two-component developer carrier based on the toner charge amount excluding the toner charge amount that does not contribute to development, the toner layer thickness on the toner carrier is set to a predetermined value. The present inventors have found a new fact that the thickness can be controlled and a stable image density can be maintained even during long-term printing, 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, and causing the toner to fly from the toner thin layer on the toner carrier, thereby forming an electrostatic latent image carrier An image forming method for developing an electrostatic latent image formed on the surface of the toner and recovering a thin toner layer on the toner carrier after development to a two-component developer carrier, using a charge amount detection means In the initial state, the toner carrier -The first step of measuring the amount of charge on the surface of the toner carrier without a thin layer, and the toner thin layer on the toner carrier is collected on the two-component developer carrier at a predetermined timing. A second step of measuring the amount of charge on the surface of the toner carrier after being formed, a third step of measuring the amount of charge on the surface of the toner carrier with a thin toner layer formed thereon, A fourth step of determining the transport bias based on a difference in charge amount obtained in the second and third steps.
(2) The image forming method according to (1), wherein the charge amount detection means is a surface potential sensor.
(3) The charge amount detecting means includes a capacitor provided between the toner carrier and a grounding point, and supplies a bias voltage connected to the toner carrier when measuring the charge amount on the surface of the toner carrier. The image forming method according to (1), wherein the power source is disconnected, the toner carrier is connected to the capacitor, and the charge amount of the toner carrier is measured.

  According to the present invention, toner charge amount detection information in which the amount of toner charge on the toner carrying member is detected using the charge amount detection means and the charge amount of the toner that adheres strongly to the surface of the toner carrier and does not contribute to development is taken into account. Therefore, since the transport bias between the toner carrier and the two-component developer carrier is changed, the toner thin layer on the toner carrier can be maintained at an appropriate thickness. As a result, a stable image density can be maintained even during long-term printing.

  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 type 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 charge amount detection means 29 for detecting the toner charge amount 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 developing 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 moves to the developing roller 2 via the conveyed magnetic brush 6 to form a thin toner layer 9. Then, by applying a developing bias between the photosensitive member 3 and the developing roller 2, the toner 5 is caused to fly from the toner thin layer 9 on the developing roller 2 to develop the electrostatic latent image on the photosensitive member 3.

  After the development, the developing roller 2 having the residual toner layer is closest to the magnetic roller 1 having the magnetic brush 6 at the facing position, and the developing roller 2 is mechanically applied by the magnetic brush 6 at the facing position. The upper toner thin 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 in accordance with the transport bias applied between the magnetic roller 1 and the developing roller 2 to form a new thin toner layer 9. Will be.

  The thin toner layer 9 on the developing roller 2 may be recovered by the magnetic brush 6 by changing the DC bias (Vdc2) 11b while applying the AC bias 12a at the end of development. 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 time for peeling and forming the toner thin layer 9 on the developing roller 2 in a certain period by adjusting the sheet interval. 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.

  In the present invention, the bias voltage 11 applied to the magnetic roller 1 and / or the bias applied to the developing roller 2 using the charge amount detecting means 29 in order to make the toner layer thickness on the developing roller 2 a predetermined thickness. The voltage 12 is controlled to change the potential difference between the developing roller 2 and the magnetic roller 1, that is, the transport bias. In other words, the bias voltages 11 and 12 are controlled by detecting the toner charge amount of the toner thin layer 9 formed on the developing roller 2 by the charge amount detecting means 29, and the magnetic amount according to the toner charge amount. The conveyance bias ΔV between the roller 1 and the developing roller 2 is controlled. In particular, as will be described later, the amount of charge after the toner thin layer 9 on the developing roller 2 is collected by the magnetic roller 1 is measured to take into account the toner firmly adhered to the surface of the developing roller 2. Can do. That is, the toner layer thickness that actually contributes to development can be evaluated by subtracting the charge amount of the toner fixed to the developing roller 2 from the total charge amount.

  As the charge amount detection means 29, for example, a surface potential sensor can be used. The surface potential 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 photoreceptor 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. The amount of charge is determined from the potential of the surface of the developing roller 2 measured by the surface potential sensor 29 and the electrostatic capacity of the developing roller 2 that is known in advance. Then, based on the relationship between the preset charge amount and the transport bias ΔV, the transport bias ΔV corrected to be a predetermined charge amount corresponding to the measured charge amount is determined.

  FIG. 4 is a flowchart showing an example of the control of the transport bias ΔV when the bias voltage applied to the magnetic roller 1 is changed. First, in the initial state after the power is turned on, the surface potential sensor 29 measures the potential on the surface of the developing roller 2 without forming the toner thin layer 9 on the developing roller 2, and the charge amount (1 ) Is obtained (first step). Next, when printing starts and reaches a predetermined condition, it is determined whether it is necessary to control the thickness of the toner layer on the developing roller 2 by comparing with a setting condition such as the number of printed sheets or a printing rate. When it is necessary to control the toner layer thickness, the toner thin layer 9 on the developing roller 2 is collected by the magnetic roller 1 via the magnetic brush 6 and the toner thin layer 9 on the surface is peeled off during non-printing such as between papers. In this state, the potential on the surface of the developing roller 2 is measured, and the charge amount (2) at that time is obtained (second step). By measuring the charge amount (2), it is possible to know the charge amount of the toner adhering to the developing roller 2 without being collected even after the toner thin layer 9 is peeled and collected. Next, the potential on the surface of the developing roller 2 is measured in a state after the toner thin layer 9 is formed, and the charge amount (3) at that time is obtained (third step). If there is a difference between the obtained charge amount difference [(3)-(2)-(1)] and a preset charge amount, the DC bias Vdc2 of the developing roller 2 is fixed and the magnetic The conveyance bias ΔV between the developing roller 2 and the magnetic roller 1 is corrected by changing the DC bias Vdc1 of the roller 1 (fourth step). Thus, the toner layer thickness on the developing roller 2 that actually contributes to the development is appropriately adjusted.

  The conveyance bias ΔV is corrected by fixing the DC bias Vdc1 of the magnetic roller 1 and changing the DC bias Vdc2 of the developing roller 2, or by simultaneously changing the DC bias Vdc1 of the magnetic roller 1 and the DC bias Vdc2 of the developing roller 2. It may be changed. Further, the correction of the transport bias ΔV is preferably performed when the predetermined number of printed sheets is reached, and the predetermined number is preferably 50 to 200.

  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.

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, and 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. Therefore, 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.

(Other embodiments)
Instead of the surface potential sensor 29 as the charge amount detection means in the embodiment, a charge amount detection means 29 ′ including a capacitor may be used. That is, as shown in FIG. 2, the charge amount detecting means 29 ′ is provided with a capacitor C between the developing roller 2 and the grounding point, and when the potential of the developing roller 2 is measured, a bias voltage is applied to the developing roller 2. The power supply 12 to be supplied is disconnected from the developing roller 2, and the developing roller 2 is connected to the capacitor C. The charge amount of the developing roller 2 is obtained from the potential of the capacitor C to be charged and the capacitance of the capacitor C.

  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
As the charge amount detection means 29, a surface potential sensor manufactured by Trek or a capacitor C having a capacitance of 1 μF was used.

Using the image forming apparatus produced above, an image performance confirmation test in a continuous printing operation 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): 35 μm
Distance between magnetic roller and developing roller: 350 μm
Developing roller applied voltage: Vdc2 = 100 V, V _PP = 1.6 kV, frequency f = 3.7 kHz, Duty ratio = 30%
Magnetic roller applied voltage: Vdc1 = 300V (variable width ± 50V at the time of layer thickness control), V _PP = 300V in the same period and opposite phase as the developing roller, frequency f = 3.7 kHz, Duty ratio = 70%

In the confirmation test described above, Example 1 is a case where the surface potential sensor 29 is provided at a position 1 to 4 mm away from the surface of the developing roller 2 and the voltage generated from the toner thin layer 9 on the developing roller 2 is measured. In the second embodiment, the capacitor C is provided between the developing roller 2 and the grounding point, and the DC bias power supply 12b applied to the developing roller 2 is opened during the correction operation of the transport bias ΔV. The voltage applied to C was measured. In both Examples 1 and 2, the conveyance bias ΔV was corrected every predetermined number (100 sheets). As a comparative example, the conditions were the same as in the example except that the charge amount detection means was not used. The results are shown in Table 1.
The image density was measured using a spectrophotometer SpectroEye manufactured by Gretag Macbeth.

  As shown in Table 1, Examples 1 and 2 in which the toner layer thickness was controlled using the charge amount detection means 29 and 29 ′ showed good image density even after printing 5000 sheets and after printing 20,000 sheets. The result was that the image density stabilized over time printing. On the other hand, in Comparative Example 1 in which the charge amount detection means was not used, a good image density could be maintained after printing 5000 sheets, but after 20,000 sheets printing, the image density was greatly reduced and image density was poor. .

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. 6 is a flowchart illustrating an example of a control method for controlling the thickness of a toner layer on a developing roller.

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 Means 9 Toner Thin Layer 11a AC Power Supply 11b DC Power Supply 12a AC Power Supply 12b DC Power Supply 16 Exposure Means 22 Primary Transfer Means 24 Cleaning Means 25 Secondary Transfer Means 26 Fixing Means 29, 29 'Charge detection means C Capacitor

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 the electrostatic latent image, and collecting a thin toner layer on the toner carrier after development on the two-component developer carrier,
A first step of measuring a charge amount on the surface of the toner carrying member in a state where a toner thin layer is not formed on the toner carrying member in an initial state using a charge amount detecting unit; and the toner at a predetermined timing A second step of measuring a charge amount on the surface of the toner carrier after the toner thin layer on the carrier is collected on the two-component developer carrier; and the toner carrier in a state where a toner thin layer is formed An image forming method comprising: a third step of measuring a charge amount on the body surface; and a fourth step of determining the transport bias based on a difference between the charge amounts obtained in the first, second and third steps. .   2. The image forming method according to claim 1, wherein the charge amount detection means is a surface potential sensor.   The charge amount detection means includes a capacitor provided between the toner carrier and a grounding point, and a power source for supplying a bias voltage connected to the toner carrier when measuring the charge amount on the surface of the toner carrier. 2. The image forming method according to claim 1, wherein the toner carrying member is disconnected and the charge amount of the toner carrying member is measured by connecting the toner carrying member to the capacitor.

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