JP6808465B2 - Image forming device - Google Patents

Description

The present invention relates to an electrophotographic apparatus such as a copier, a printer, a facsimile, or a developing apparatus of an electrostatic recording apparatus.

Conventionally, an image forming apparatus such as an electrophotographic copying machine, a laser beam printer, or a facsimile is provided with a developing apparatus. In the developing apparatus, a developing roller that is mainly arranged by closing the opening of a developing agent container that stores the developing agent and partially exposed, and a developing agent that abuts on the surface of the developing roller and is conveyed by the developing roller. A developing agent amount controlling blade for quantifying the amount is provided.

When the developer adhering to the surface of the developing roller passes between the developing agent amount regulating blades as the developing roller rotates, the excess is removed from the surface of the developing roller and returned to the developing agent container for development. It is formed as a thin layer on the roller. At the same time, the developer is given a frictional charge (hereinafter referred to as "trivo") by friction with the developer amount regulating blade. Then, the developer is conveyed from a portion exposed from the developer container of the developing roller to a developing region which is a region close to the photoconductor drum which is an image carrier, and is placed on an electrostatic latent image formed on the photoconductor drum. Move to.

Toner that is not used in the developing area and remains on the developing roller (hereinafter referred to as "developed residual toner") is scraped off by mechanical rubbing between the developing roller and the developing agent supply roller. At the same time, the developer is supplied from the developer supply roller to the developing roller. On the other hand, the developer scraped off by the developer supply roller is mixed with the developer inside and around the developer supply roller.

Conventionally, in such a developing apparatus, a phenomenon in which the halftone density of the background color and the halftone density immediately after solid printing differ depending on the printing pattern during image formation (hereinafter referred to as "development ghost") occurs. was there. Development ghosts are generated due to the difference in the tribo of the developer due to the difference in the printing pattern.

Japanese Unexamined Patent Publication No. 2013-228584

Here, the problem that occurs in the developing apparatus is that the toner on the developing roller in the non-printing area (hereinafter referred to as “white after”) is more than the tribo of the toner on the developing roller in the printing unit (hereinafter referred to as “black after”). It was a development ghost (hereinafter referred to as "development positive ghost") in which the tribo (referred to as "development") was relatively higher and the density after black was higher. In Patent Document 1, in order to stabilize the coating of the developer on the developing roller, the developer is urged from the developer amount controlling blade to the developing roller side between the developing roller side and the developing agent amount controlling blade. A potential difference is provided. However, even if such a potential difference is provided, a development positive ghost has occurred because a trivo difference between white and black occurs.

An object of the present invention is to provide a high-quality image forming apparatus that reduces development ghosts generated by a tribo difference between white and black on a developing roller.

In order to achieve the above object, the present invention abuts a rotatable developer carrier that carries a developer, a developer supply member that supplies the developer to the developer carrier, and the developer carrier. A developing apparatus including a regulating member that regulates the amount of the developing agent carried by the developing agent carrier, a first power source that applies a bias to the developing agent carrier, and a first power source that applies a bias to the regulating member. In an image forming apparatus having two power supplies and control means for controlling the first and second power supplies, the control means are the regulating member and the developer carrier from the start of the development operation to the end of the development operation. Control is performed to provide a potential difference between the developer-supporting body and the regulating member so that a force urged from the regulating member to the developing agent-supporting body acts on the developing agent at the contact portion with the developer, and a plurality of When recording is continuously performed on a sheet of recording material, the developer is attached to the developing agent carrier from the restricting member when the developing operation is completed rather than when the developing operation is started on the first recording material. Control is performed to provide the potential difference so that the force exerted is strongly exerted, and in the second and subsequent recording materials, between the developing agent carrier and the regulating member during the period from the start of the developing operation to the end of the developing operation. It is characterized in that the potential difference is controlled to be the same as the potential difference at the end of the developing operation on the first recording material .

According to the present invention, it is possible to reduce the development ghost generated due to the tribo difference between after white and after black on the developer carrier. This makes it possible to provide a high-quality image forming apparatus.

It is a schematic diagram of an image forming apparatus. It is the schematic of the process cartridge. It is a timing chart of the voltage control of the image forming apparatus which concerns on Example 1 compared with Comparative Example 1-1. (A) and (b) are evaluation images of developed positive ghosts. It is a measurement result of the toner charge amount on the developing roller of Example 1 and Comparative Example 1-1. It is a timing chart of voltage control of the image forming apparatus which concerns on Example 2 compared with Example 1. FIG. It is a timing chart of voltage control of the image forming apparatus which concerns on Example 3 compared with Example 1. FIG. It is a block diagram which shows the structure of the control system of an image forming apparatus. It is the schematic of the process cartridge which concerns on Example 4. FIG.

Hereinafter, embodiments for carrying out the present invention will be described in detail exemplarily with reference to the drawings. However, the dimensions, materials, shapes, relative arrangements, etc. of the components described in the following embodiments are intended to limit the scope of the present invention to those, unless otherwise specified. is not.

[Example 1]
(Image forming device)
The overall configuration of an embodiment of the image forming apparatus will be described. FIG. 1 is a cross-sectional view of the image forming apparatus 100 of this embodiment. The image forming apparatus 100 of this embodiment is a full-color laser beam printer (electrophotographic image forming apparatus) that employs an in-line method and an intermediate transfer method. The image forming apparatus 100 can form a full-color image on a recording material (for example, recording paper, plastic sheet, cloth, etc.) according to the image information. The image information is input to the image forming apparatus main body from an image reading device connected to the image forming apparatus main body or a host device such as a personal computer communicably connected to the image forming apparatus main body. The image forming apparatus 100 has image forming units SY, SM, SC, and SK for forming images of each color of yellow (Y), magenta (M), cyan (C), and black (K), respectively. In this embodiment, the image forming portions SY, SM, SC, and SK are arranged in a row in a direction intersecting the vertical direction.

Each image forming unit includes a process cartridge 7 integrally having a photoconductor drum (image carrier) 1 and process means (charging means, developing means, cleaning means) acting on the photoconductor drum (image carrier) 1. The process cartridge 7 in each image forming unit can be attached to and detached from the image forming apparatus 100 via mounting means such as a mounting guide and a positioning member provided in the image forming apparatus main body. In this embodiment, the process cartridges 7 for each color all have the same shape, and the process cartridges 7 for each color contain yellow (Y), magenta (M), cyan (C), and black (K), respectively. ) Toners of each color are stored.

In this embodiment, as will be described later, a process cartridge including a photoconductor unit 13 including a photoconductor drum 1 and the like and a developing unit 3 including a developing roller 4 and the like will be described. However, the present invention is not limited to this, and the developing unit (developing apparatus) 3 may be independently attached to and detached from the image forming apparatus main body.

The photoconductor drum 1 is rotationally driven by the drum driving means M1. A scanner unit (exposure device) 30 is arranged around the photoconductor drum 1. The scanner unit 30 is an exposure means that irradiates a laser based on image information to form an electrostatic image (electrostatic latent image) on the photoconductor drum 1. The laser exposure is written out from a position signal in the polygon scanner called BD for each scanning line in the main scanning direction (direction orthogonal to the conveying direction of the recording material). On the other hand, in the sub-scanning direction (conveying direction of the recording material), the TOP signal starting from the switch (not shown) in the recording material transport path is delayed by a predetermined time. As a result, laser exposure can always be performed on the same position on the photoconductor drum 1 at the four process stations Y, M, C, and K.

An intermediate transfer belt 31 as an intermediate transfer body for transferring the toner image on the photoconductor drum 1 to the recording material 12 is arranged so as to face the four photoconductor drums 1.

The intermediate transfer belt 31 formed of the endless belt as the intermediate transfer body abuts on all the photoconductor drums 1 and circulates (rotates) in the direction of arrow B (counterclockwise) in the drawing.

On the inner peripheral surface side of the intermediate transfer belt 31, four primary transfer rollers 32 as primary transfer means are arranged side by side so as to face each photoconductor drum 1. Then, a bias having a polarity opposite to the normal charging polarity of the toner is applied to the primary transfer roller 32 from a primary transfer bias power supply (high pressure power supply) as a primary transfer bias applying means (not shown). As a result, the toner image on the photoconductor drum 1 is transferred (primary transfer) onto the intermediate transfer belt 31.

Further, a secondary transfer roller 33 as a secondary transfer means is arranged on the outer peripheral surface side of the intermediate transfer belt 31. Then, a bias having a polarity opposite to the normal charging polarity of the toner is applied to the secondary transfer roller 33 from a secondary transfer bias power supply (high pressure power supply) as a secondary transfer bias applying means (not shown). As a result, the toner image on the intermediate transfer belt 31 is transferred (secondary transfer) to the recording material 12. For example, at the time of forming a full-color image, the above-mentioned process is sequentially performed in the image forming units SY, SM, SC, and SK, and the toner images of each color are sequentially superimposed on the intermediate transfer belt 31 and primary transferred. .. After that, the recording material 12 is conveyed to the secondary transfer unit in synchronization with the movement of the intermediate transfer belt 31. Then, the four-color toner images on the intermediate transfer belt 31 are collectively secondarily transferred onto the recording material 12 by the action of the secondary transfer roller 33 that is in contact with the intermediate transfer belt 31 via the recording material 12. Toner.

The recording material 12 on which the toner image is transferred is conveyed to a fixing device 34 as a fixing means. By applying heat and pressure to the recording material 12 in the fixing device 34, the toner image is fixed to the recording material 12.

(Process cartridge configuration)
The overall configuration of the process cartridge mounted on the image forming apparatus of this embodiment will be described.

FIG. 2 is a cross-sectional view of the process cartridge 7 of this embodiment as viewed along the longitudinal direction (rotational axis direction) of the photoconductor drum 1. The configuration and operation of the process cartridge 7 for each color are substantially the same except for the type (color) of the developing agent contained therein.

The process cartridge 7 has a photoconductor unit 13 including a photoconductor drum 1 and the like, and a developing unit 3 including a developing roller 4 and the like.

A photoconductor drum 1 is rotatably attached to the photoconductor unit 13 via a bearing (not shown). The photoconductor drum 1 is rotationally driven in the direction of arrow A in the drawing according to the image forming operation by receiving the driving force of the driving motor as the drum driving means M1.

Further, in the photoconductor unit 13, a charging roller 2 and a cleaning member 6 are arranged so as to come into contact with the peripheral surface of the photoconductor drum 1. A bias sufficient to allow an arbitrary charge to be placed on the photoconductor drum 1 is applied to the charging roller 2 from a charging bias power source (not shown) as a charging bias applying means. In this embodiment, the bias applied so that the potential (charging potential Vd) on the photoconductor drum 1 becomes −500 V is set.

Then, the scanner unit 30 irradiates the laser beam 11 based on the image information to form an electrostatic latent image on the photoconductor drum 1. In this example, the amount of light of the laser beam 11 was set to 0.2 μJ / cm ² at the time of image formation, and the latent image potential was set to −150 V.

On the other hand, the developing unit (developer) 3 has a developing chamber 18a and a developing agent accommodating chamber 18b, and the developing agent accommodating chamber 18b is arranged below the developing chamber 18a. Toner (developer) 10 is housed inside the developer storage chamber 18b. In this embodiment, the normal charging polarity of the toner 10 is negative electrode, and the case where a negatively charged toner is used will be described below. However, this embodiment is not limited to negatively charged toner.

Further, the developer accommodating chamber 18b is provided with a developer conveying member 22 for conveying the toner 10 to the developing chamber 18a, and the toner is conveyed to the developing chamber 18a by rotating in the direction of arrow G. ing.

The developing chamber 18a is provided with a developing roller 4 as a developing agent carrier that rotates in the direction of arrow D in the drawing by coming into contact with the photoconductor drum 1 and receiving a driving force of a driving motor as a developing driving means M2. There is. In this embodiment, the developing roller 4 and the photoconductor drum 1 rotate so that their surfaces move in the same direction at the opposing contact portions. Further, a sufficient bias is applied to the developing roller 4 from a developing bias power source (not shown) as a developing bias applying means to develop and visualize the electrostatic latent image on the photoconductor drum 1 as a toner image.

Further, inside the developing chamber 18a, a supply roller 5 as a developing agent supplying member for supplying the toner conveyed from the developing agent containing chamber 18b to the developing roller 4 is arranged. Further, inside the developing chamber 18a, a toner amount regulating member that regulates the coating amount of toner on the developing roller 4 supplied by the supply roller 5 and applies electric charge (hereinafter, referred to as "regulating blade"). 8 is arranged.

Next, the configurations of the developing roller 4, the supply roller 5, and the regulating member 8 will be described in detail.

The developing roller 4 has a diameter of 15 mm, and a silicone rubber is formed as a base layer on a conductive core metal having a diameter of 6 mm, and urethane rubber is formed as a surface layer on the silicone rubber. As the volume resistance of the developing roller 4, a resistance of 10 ⁴ to 10 ¹² Ω can be used.

The supply roller 5 is a conductive elastic sponge roller having a diameter of 15 mm and having a foam layer formed on the outer periphery of a conductive core metal having a diameter of 6 mm, and has a volume resistance of 10 ⁴ to 10 ⁸ Ω. It can be used. The resistance value of the supply roller 5 used in this example was 4 × 10 ⁶ Ω and the hardness was 200 gf. The hardness of the supply roller 5 in this embodiment is a value obtained by measuring the load when a flat plate having a longitudinal width of 50 mm is penetrated by 1 mm from the surface of the supply roller 5.

The regulating member 8 is a metal SUS sheet metal having a thickness of 0.1 mm, and is arranged in contact with the developing roller 4 so that the free end is on the upstream side in the rotating direction of the developing roller. As the regulating member 8 used in this embodiment, the tip of the SUS sheet metal was cut from the D roller contact surface side. The tip portion of the developing roller is bent in the cutting direction by the cutting process, and the bending amount of the tip corresponding to the radius of curvature R is 0.02 mm.

A development bias is applied to the development roller 4 using a high-voltage power supply (not shown) for the development bias. Further, a supply roller bias is applied to the supply roller 5 using a high-pressure power supply of the supply roller bias (not shown), and a blade bias is applied to the regulating member 8 using a high-pressure power supply of the regulation blade bias (not shown).

At this time, when the value obtained by subtracting the value of the bias applied to the developing roller 4 from the value of the bias applied to the supply roller 5 is the same as the normal charging polarity of the toner, the contact between the supply roller 5 and the developing roller 4 A force in the direction of being urged from the supply roller 5 to the developing roller 4 acts on the toner at the contact portion. Further, when the value obtained by subtracting the value of the bias applied to the developing roller 4 from the value of the bias applied to the supply roller 5 is opposite to the normal charging polarity of the toner, the toner is transferred from the developing roller 4 to the supply roller 5. The force to be urged works.

For example, if the development bias is −300V and the supply roller bias is −400V, the difference is −100V, and the toner is urged from the supply roller 5 to the development roller 4.

The toner supplied to the developing roller 4 by the supply roller 5 penetrates into the contact contact portion between the regulating member 8 and the developing roller 4 by the rotation of the developing roller 4 in the arrow D direction. The toner that has entered the contact contact portion between the regulating member 8 and the developing roller 4 is triboelectrically charged by the rubbing between the surface of the developing roller 4 and the regulating member 8, and the charge is applied and at the same time the layer thickness is regulated. Toner.

At this time, when the value obtained by subtracting the value of the bias applied to the developing roller 4 from the value of the bias applied to the regulating member 8 is the same as the normal charging polarity of the toner, the contact between the regulating member 8 and the developing roller 4 A force in the direction of being urged from the regulating member 8 to the developing roller 4 acts on the toner at the contact portion. Further, when the value obtained by subtracting the value of the bias applied to the developing roller 4 from the value of the bias applied to the regulating member 8 is opposite to the normal charging polarity of the toner, the toner is applied to the developing roller 4 to the regulating member 8. The force in the direction of being urged works.

The stronger the force in the direction of urging the toner from the regulating member 8 to the developing roller 4, the stronger the rubbing force at the contact contact portion between the regulating member 8 and the developing roller 4, and the triboelectric charge is promoted. The amount of charge given to the toner increases.

The toner on the developing roller 4 whose layer thickness is regulated is conveyed to the portion facing the photoconductor drum 1 by the rotation of the developing roller 4, and is developed and visualized as an electrostatic latent image and a toner image on the photoconductor drum 1. ..

The developing residual toner on the developing roller 4 enters the contact contact portion with the supply roller 5 by the rotation of the developing roller 4. A part of the developing residual toner is collected by the supply roller 5 due to mechanical rubbing between the developing roller 4 and the supply roller 5 and the potential difference between the developing roller 4 and the supply roller 5, and the toner in the supply roller 5 and its surroundings. It is mixed with the toner of. On the other hand, the toner that is not collected by the supply roller 5 and remains on the developing roller 4 is charged with the toner that is newly supplied from the supply roller 5 while being charged by rubbing with the supply roller 5.

Each power source that applies a bias to each of the developing roller 4, the supply roller 5, and the regulating member 8 is controlled by the control means. Here, the control system of the image forming apparatus according to the present embodiment will be briefly described with reference to FIG. The control unit 150 as a control means provided in the image forming apparatus 100 includes a CPU 151 as a central element for performing arithmetic processing, a memory 152 such as a ROM and a RAM as a storage element, and the like. The RAM contains sensor detection results, calculation results, and the like, and the ROM stores control programs, data tables obtained in advance, and the like. The control unit 150 is a control means that comprehensively controls the operation of the image forming apparatus 100, controls the transmission and reception of various electrical information signals, the timing of driving, and the like, and controls a predetermined image formation sequence. Control. Each control target in the image forming apparatus 100 is connected to the control unit 150. For example, the control unit 150 includes a first power supply E1 that applies a bias to the developing roller 4, a second power supply E2 that applies a bias to the regulating member 8, a third power supply E3 that applies a bias to the supply roller 5, and a scanner unit ( Exposure means) 30 and the like are connected. For example, the control unit 150 controls each power source to control the potential difference between the developing roller 4 and the supply roller 5 and the potential difference between the developing roller 4 and the regulating member 8. The control by the control unit 150 will be described later with reference to the timing chart shown in FIG.

(Mechanism of developing ghost)
Next, the mechanism of developing ghost generation will be described.

The development ghost is generated by the difference between the charge amount of the toner on the developing roller 4 after black and the charge amount of the toner on the developing roller 4 after white. The difference in the amount of charge of the toner after white and after black is due to the difference in the number of friction rubbing times of each toner. The toner on the developing roller 4 after whitening is charged with frictional rubbing at the contact portion between the developing roller 4 and the regulating member 8 with respect to the development residual toner that has been frictionally charged in advance. On the other hand, the toner on the developing roller 4 after black has a charge amount that is only once rubbed at the contact portion between the developing roller 4 and the regulating member 8. Due to the difference in the number of friction rubbing, the toner charge amount after white tends to be higher than the toner charge amount after black.

The image pattern used to determine the development ghost level in this embodiment is a one-sided halftone in which the density measured by the X-Rite SPECTORDENSITOMETER 500 becomes 0.6 after one round of the development roller of the solid patch image in addition to the solid patch image. It is a pattern printed with the image of. In the present embodiment, the charge amount of the toner on the developing roller is relatively low at the halftone after one round of the developing roller on which the solid patch image in the present image pattern is printed, that is, at the position corresponding to the black after. Therefore, due to the development γ characteristics, the amount of toner developed from the development roller in the halftone portion becomes relatively larger than that after white, and development positive ghost occurs.

Further, the developed positive ghost has a problem that the rear end of the image is worse than the first half of the image. This is because the amount of charge of the toner on the developing roller 4 after whitening is determined by the number of times of friction rubbing, so that the amount of charge of the toner becomes very high if the amount of charge after whitening continues until the latter half of the image. On the other hand, after blackening, the amount of charge is constant regardless of whether the image is in the first half or the second half because frictional rubbing is performed only once. Therefore, as the image moves from the front end to the rear end, the difference in the amount of charge between white and black becomes large, and the development positive ghost deteriorates.

In order to improve such development positive ghost, it is possible to increase the charge amount of the toner on the developing roller 4 after black while suppressing the charge amount of the toner on the developing roller 4 after white. It is possible to improve the development positive ghost by bringing the toner charge amount after and after black closer to each other. Further, if the amount of charge applied to the toner on the developing roller 4 after black can be increased from the front end to the rear end of the image, the development positive ghost can be improved in one surface of the image.

In this embodiment, this is achieved by controlling the potential difference between the developing roller 4 and the regulating member 8. In the following, the details of the control of this embodiment and its effect will be described with reference to comparative examples.

(Regulatory blade bias control)
Bias control of the developing roller 4 and the regulating member 8 in this embodiment will be described with reference to FIG. FIG. 3 is a timing chart showing bias control of the regulation blade bias when one image is printed. The bias control of the developing roller 4 and the regulating member 8 is performed by the control unit 150 described above controlling each unit according to the timing chart described below.

Here, the details of each timing in the timing chart will be described. The “development drive start” timing is a development operation start timing in which the development roller 4 and the supply roller 5 start rotating as the development drive means M2 by receiving the driving force of the drive motor. The "image formation start" timing is the writing timing of the laser exposure in the sub-scanning direction, and the "image formation end" timing is the timing at which the laser exposure in the sub-scanning direction ends. The “development drive stop” timing is a development operation end timing in which the driving force of the drive motor as the development drive means M2 is stopped and the rotation of the development roller 4 and the supply roller 5 is stopped.

However, each timing is not limited to this. For example, the “image formation start” timing may be set ahead of the writing timing of the laser exposure in the sub-scanning direction by a predetermined time. Further, the "image formation end" timing may be set later than the laser exposure end timing by a predetermined time, for example. In this way, it can be changed to be optimum according to the configuration of the developing device and the image forming device.

The bias applied to the developing roller 4 and the supply roller 5 is a constant bias from "development drive start" to "development drive end". In this embodiment, the bias applied to the developing roller 4 is −400 V, and the supply roller 5 The bias applied to is -450V.

Next, the regulation blade bias control in one page of the recording material will be described. Here, between "image formation start" and "image formation end" in the same recording material, the bias applied to the regulating member 8 is tilted, and the toner is attached from the regulating member 8 to the developing roller 4. Bias control is performed to gradually increase the force in the direction of the force.

Such bias control is a control that increases the amount of charge due to frictional rubbing at the contact portion between the developing roller 4 and the regulating member 8 from the front end to the rear end of the image. By this control, the charge amount of the toner on the developing roller 4 after white increases from the front end to the rear end of the image, whereas the charge amount of the toner on the developing roller 4 after black also increases from the front end of the image. It is possible to increase it by hanging it at the rear end. As a result, it is possible to obtain an effect of suppressing the difference in the amount of charge after white and after black from the front end to the rear end of the image, and it is possible to obtain an effect of improving the developed positive ghost. In this embodiment, control was performed to change the amount of change of the bias applied to the regulating member 8 per unit time during image formation as a constant amount.

(Experiment)
Here, an experiment conducted using a comparative example to show the effect of this example will be described. In this experiment, the above-mentioned development positive ghost determination image was printed using LETTER size paper as a recording material in an environment of a temperature of 23 ° C. and a humidity of 50%, and the development positive ghost was evaluated.

To judge the developed positive ghost, the halftone image density after black and the halftone image density after white of the developed positive ghost judgment image are measured using a measuring device, and the ranking is based on the following criteria based on the density difference. went. Here, as a measuring device, a SPECTORDENSITOMETER 500 manufactured by X-Rite was used. Note that FIG. 4A is an example in which a development positive ghost occurs in the determination image (a) in which a solid patch image and a one-sided halftone image are printed on the tip side of the image. FIG. 4A shows an example in which a developed positive ghost having a higher density than the halftone region is generated at a position corresponding to a solid patch image in the one-sided halftone image of the determination image (a). Further, FIG. 4B is an example in which a development positive ghost occurs in the determination image (b) in which a solid patch image and a one-sided halftone image are printed on the rear end side of the image. FIG. 4B shows an example in which a developed positive ghost having a higher density than the halftone region is generated at a position corresponding to a solid patch image in the one-sided halftone image of the determination image (b).

A: Density difference is less than 0.02 in halftone image B: Density difference is less than 0.02 to 0.06 in halftone image C: Density difference is 0.06 or more in halftone image

As an example of comparing the effects of this example, the same experiment was performed for the case where the bias control of Comparative Example 1-1 shown in FIG. 3 was performed, and the development positive ghost was evaluated.

In Comparative Example 1-1, control was performed to apply a constant bias from “development drive start” to “development drive stop”, and the applied bias was set to −500 V. In Table 1, one developed positive ghost determination image was printed and image evaluation was performed.

Further, for each of Example 1 and Comparative Example 1-1, the charge amount μC / g of the coated toner on the developing roller 4 after passing through the regulating member 8 was measured, and the results are shown in FIG. .. The amount of charge is measured by stopping the operation of the developing device while printing the one-sided solid image and the one-sided white image. The measurement positions were 20 mm, 80 mm, 140 mm, 200 mm, and 260 mm from the tip of the image.

Here, the result of FIG. 5 will be described. Comparing the charge amount at a point 20 mm from the tip of the image of Example 1 and Comparative Example 1-1, it can be seen that the charge amount of Example 1 is smaller than that of Comparative Example 1-1 after whitening. On the other hand, it can be seen that there is no difference in the amount of charge between Example 1 and Comparative Example 1-1 after black. Therefore, in Example 1, the difference in the amount of charge after white and after black is smaller than that in Comparative Example 1-1. This is because the regulation blade bias applied to the regulation member 8 at a point 20 mm from the tip of the image is smaller in Example 1 than in Comparative Example 1-1.

Next, the transition of the charge amount from the front end of the image to the rear end of the image is compared. In Comparative Example 1-1, it can be seen that the amount of charge after whitening increases from the front end of the image to the rear end of the image. Further, in Comparative Example 1-1, the amount of charge after black did not change from the front end to the rear end of the image. Therefore, it can be seen that the difference in the amount of charge after white and after black increases from the front end of the image to the rear end of the image. On the other hand, in Example 1, the amount of charge after white increases from the front end of the image toward the rear end of the image as in Comparative Example 1-1, but the amount of charge after black is also different from that of Comparative Example 1-1. It increases from the front edge of the image to the rear edge of the image. Therefore, in the first embodiment, the difference in the amount of charge between the white and the black is maintained from the front end of the image to the rear end of the image without widening. This is because, in Comparative Example 1-1, the regulation blade bias is constant from the image front end to the image rear end, whereas in Example 1, the regulation blade bias is applied from the image front end to the image rear end. This is because it is made larger. That is, in the first embodiment, the rear end of the image is biased so that the toner between the regulating member 8 and the developing roller 4 exerts a stronger force urged by the regulating member 8 to the developing roller 4 than the front end of the image. This is because it is controlling.

Next, the results in Table 1 will be described. When the control of Comparative Example 1-1 is performed, a development positive ghost occurs in the determination image (a) because there is a difference in the amount of charge between white and black from the tip of the image. Further, as described above, at the rear end of the image, the difference in the amount of charge between white and black becomes large, so that the development positive ghost deteriorates in the determination image (b). On the other hand, when the control of Example 1 is performed, the difference in the amount of charge after white and after black at the tip of the image is suppressed as compared with Comparative Example 1-1, so that development positive ghost occurs in the determination image (a). I didn't. Further, since the difference in the amount of charge between white and black can be maintained in a small state from the front end of the image to the rear end of the image, no development positive ghost occurs in the determination image (b).

As described above, according to the present embodiment, from the regulating member 8 to the developing roller 4 in the toner at the contact portion between the regulating member 8 and the developing roller 4 from the tip of the image to the rear edge of the image in one recording material. A potential difference is provided between the developing roller and the regulating member 8 so that the force urged by the developing roller works. In addition, the rear end of the image is controlled to provide the potential difference so that the force for urging the toner from the regulating member 8 to the developing roller 4 acts stronger than the front end of the image. This makes it possible to reduce the development positive ghost that occurs when a developing device in which the surfaces of the developing roller and the supply roller rotate in the same direction is used.

In a developing device (with developing device) in which the surfaces of the developing roller and the photoconductor drum face each other in the same direction, the physical stripping property of the developing agent supply roller is weak. Significant development ghosts may occur. Therefore, in the method of strengthening the mechanical peeling property of the developer supply roller in order to reduce the development ghost, the mechanical rubbing between the developing roller and the developer supply roller increases, so that the toner deterioration is promoted. It had been done. In this way, when toner deterioration, that is, release or burial of the external additive on the surface of the developing agent is promoted, the charging performance is lowered and the degree of cohesion is increased, and the toner is fused to the surface of the developing roller. Problems such as these have occurred, which has hindered the extension of the life of the developing device. However, according to this embodiment, it is possible to provide an image forming apparatus capable of reducing development positive ghosts without strengthening the mechanical stripping property of the developer supply roller, and capable of high image quality and long life. it can.

[Example 2]
Next, the image forming apparatus according to the second embodiment will be described. In the following description, the description of the same parts as those in the above-described embodiment will be omitted.

When continuous printing of a plurality of recording materials is executed, the image forming apparatus performs a forward rotation operation from "start of development drive" to "start of forming the first image" (hereinafter referred to as "forward rotation"). .. During this pre-rotation operation, the developing roller 4 rotates in an undeveloped state, so that the toner on the developing roller 4 is in a white state. The mileage of the developing roller 4 during the forward rotation operation in this embodiment is 456 mm. Further, since the developing roller 4 rotates in an undeveloped state between media (hereinafter referred to as "paper spacing") from "the end of forming the first image" to "the start of forming the second image", the developing roller 4 is the state after white. However, the mileage is often shorter than during the previous rotation. The mileage between the papers in this embodiment is 31 mm.

The developed positive ghost is aggravated by the large difference in the amount of charge after white and after black, and the amount of charge after white increases as the time of rotation in the undeveloped state increases. Therefore, when continuous printing is executed, the level of development positive ghost is different between the first recording material after the front rotation operation and the second and subsequent recording materials after the space between papers, and the second and subsequent recording materials are developed. The positive ghost is better than the first recording material. Therefore, when a plurality of continuous prints are executed, the control of the regulation blade bias is switched from the control of applying the bias to the control of applying the image with the inclination to the control of applying the bias without the inclination in the images of the second and subsequent sheets of the recording material. It becomes possible.

Therefore, in this embodiment, the control of the regulation blade bias when the continuous printing of a plurality of recording materials is executed will be described. FIG. 6 shows a timing chart showing bias control of the regulation blade bias when two recording materials of Example 1 and Example 2 are continuously printed.

In the first embodiment, bias control between "start of first image formation" and "end of formation of first image" and control of bias between "start of formation of second image" and end of formation of second image " Have the same waveform. Specifically, it is reset to (-450V) in the same manner as the regulation blade bias at the time of "start of formation of the first image" (at the start of the development operation) after "the end of the formation of the first image" (after the end of the development operation). In this way, the bias control between "start of image formation" and "end of image formation" in the same recording material for the second and subsequent sheets is from "start of image formation of the first sheet" to "end of formation of the first image". Similar to the bias control between, it is repeated.

On the other hand, in the second embodiment, the bias control between "start of forming the first image" and "end of forming the first image" has an inclination in the bias applied to the regulating member 8 as in the first embodiment. I'm letting you. However, in the second embodiment, the bias control of the regulating member 8 from "the end of forming the first image" to "the end of forming the second image" is controlled to apply a constant bias. At this time, the bias applied constantly is set to −500V.

(Experiment)
Here, an experiment conducted to show the effect of this example will be described. In this experiment, the above-mentioned development positive ghost determination image was printed using LETTER size paper as a recording material in an environment of a temperature of 23 ° C. and a humidity of 50%, and the development positive ghost was evaluated.

In the determination of the developed positive ghost, the halftone image density after black and the halftone image density after white of the developed positive ghost determination images shown in FIGS. 4 (a) and 4 (b) are measured using a measuring device. Based on the difference in concentration, ranking was performed based on the following criteria. Here, as a measuring device, a SPECTORDENSITOMETER 500 manufactured by X-Rite was used.

In Table 2, both images of two continuous prints were evaluated.

Here, the results in Table 2 will be described. Development positive ghost did not occur in both Example 1 and Example 2. In the first embodiment, the development positive ghost is improved by controlling the regulation blade bias as described above, and the effect is obtained on both the first recording material and the second recording material. On the other hand, in the second embodiment, since the control of the regulation blade bias is the same as that of the first embodiment from the "development drive start" to the "first image formation end", the image of the first recording material is developed. No positive ghosts have occurred. Further, from "the end of forming the first image" to "the start of forming the first image", the developing roller 4 rotates in an undeveloped state, but because the time is short, the developing roller 4 after whitening The charge amount of the upper toner is smaller than that of the first recording material. Therefore, it was obtained that the difference in the amount of charge on the developing roller 4 after white and after black became small, and development positive ghost did not occur even if the regulation blade bias was constant.

As described above, according to the second embodiment, it is possible to reduce the development positive ghost even when the continuous printing of a plurality of recording materials is executed.

[Example 3]
Next, the image forming apparatus according to the third embodiment will be described. In the following description, the same parts as those in the first and second embodiments described above will be omitted.

Since the development positive ghost is determined by the difference between the charge amount of the toner on the developing roller 4 after white and the charge amount of the toner on the developing roller 4 after black, it is under low temperature and low humidity conditions (temperature 15 ° C., humidity 10%). ), The development positive ghost deteriorates in an environment where the amount of charge of the toner increases.

As shown in FIG. 8, the image forming apparatus according to this embodiment is an environment as an environment detecting means (temperature / humidity detecting means, a thermometer and a hygrometer) for detecting an environment such as temperature and humidity in which the apparatus is installed. It has a sensor S1. The environmental information (temperature / humidity information) detected by the environment sensor S1 is input to the control unit 150. Based on this environmental information, the control unit 150 performs the following bias control under the environment of low temperature and low humidity conditions.

Example 3 shows an example of improving the developed positive ghost in such an environment of low temperature and low humidity.

In an environment of low temperature and low humidity, the amount of toner charged on the developing roller 4 increases. Therefore, the difference in the amount of charge of the toner on the developing roller 4 after white and after black becomes larger, and the developing positive ghost deteriorates. Therefore, in such an environment, in order to further improve the development positive ghost, the toner on the developing roller 4 is charged by suppressing the amount of charge at the contact portion between the developing roller 4 and the regulating member 8. The amount needs to be controlled. As a means for suppressing the amount of charge at the contact portion, there is a method of reversing the potential relationship between the development bias applied to the developing roller 4 and the regulating blade bias applied to the regulating member 8. That is, the direction of the force for which the toner is urged at the contact portion between the developing roller 4 and the regulating member 8 is changed from the direction from the regulating member 8 toward the developing roller 4 to the direction from the developing roller 4 toward the regulating member 8. This is a method of reversing.

FIG. 7 is a timing chart showing bias control of the regulation blade bias when one image is printed in Examples 1 and 3.

In the first embodiment, the regulation blade bias is set to a constant bias of −450V during the forward rotation, and then the regulation blade bias is increased from −450V to −500V from “start of image formation” to “end of image formation”. On the other hand, in Example 3, the regulation blade bias is set to a constant bias of −300 V from “development drive start” to “development roller 4 one lap later”, and “image formation is completed” from “development roller 4 one lap later”. The regulation blade bias is increased from -300V to -500V.

From this control, in the first embodiment, although the magnitude of the regulation blade bias changes in one recording material, the toner at the contact portion is always urged from the regulation member 8 to the developing roller 4. Power continues to work. On the other hand, in the third embodiment, the regulation blade bias is constant from "start of development drive" to "after one lap of the developing roller 4" in one recording material, and from "after one lap of the developing roller 4". It is controlled so that the polarity changes across 0V until "the end of image formation". As a result, during recording on the same recording material, the toner at the contact portion is urged from the developing roller 4 to the regulating member 8 from the “development drive start” to the “after one round of the developing roller 4”. The force continues to work in the direction. On the other hand, from "after one round of the developing roller 4" to "the end of image formation", the direction in which the toner is urged at the contact portion is reversed from the regulating member 8 toward the developing roller 4.

(Experiment)
Here, in order to show the effect of this example, the same experiment as that described in Example 1 was carried out for each of Example 1 and Example 3. However, the environment in which the experiment is carried out is changed to a temperature of 15 ° C. and a humidity of 10%.

In Table 3, one developed positive ghost determination image (a) and (b) was printed and image evaluation was performed.

Here, the results in Table 3 will be described. In Example 1, since the environment in which the experiment was carried out became a severe condition for the developed positive ghost of 15 ° C. and 10% humidity, the developed positive ghost occurred in the evaluation image. On the other hand, in the third embodiment, the direction in which the force forcing the toner at the contact portion acts is reversed in the direction from the developing roller 4 to the regulating member 8 until the rear end of the image, so that the developing roller 4 The amount of charge on the top decreased, and the developed positive ghost improved.

From the above experiments, by controlling the regulated blade bias of Example 3, it is possible to improve the developed positive ghost even in a low temperature and low humidity environment.

[Example 4]
Next, other examples of the present invention will be described. In the following description, the same description as in Examples 1 to 3 described above will be omitted.

In Examples 1 to 3, an example in which the supply roller 5 and the developing roller 4 rotate so that their surfaces move in the same direction at the contact portions facing each other has been described. However, in this embodiment, as shown in FIG. 9, the supply roller 5 rotates in the direction of arrow E', and the surfaces of the supply roller 5 and the developing roller 4 move in opposite directions at the opposing contact portions. It may be configured to rotate like this. Even when the surfaces of the developing roller and the supply roller rotate in opposite directions, a tribo difference between white and black on the developing roller occurs. Therefore, it is possible to obtain the same effect as in Examples 1 to 3 regardless of the rotation direction of the supply roller, and by adopting the configuration shown in Example 4, it is possible to better reduce the development ghost. ..

[Other Examples]
In the above-described embodiment, control for changing the bias applied to the regulating member 8 has been exemplified as a control for providing a potential difference between the developing roller 4 and the regulating member 8, but the control is not limited to this. If the control is to provide a potential difference between the developing roller 4 and the regulating member 8, even if the control is to change the bias applied to the developing roller, it is the control to change the bias applied to each of the developing roller and the regulating member. You may.

Further, in the above-described embodiment, four process cartridges are used, but the number of process cartridges used is not limited and may be appropriately set as needed.

Further, in the above-described embodiment, as a process cartridge that can be attached to and detached from the image forming apparatus, a process cartridge having a photoconductor drum and a charging means, a developing means, and a cleaning means as process means acting on the photoconductor drum are integrally provided. Was illustrated. However, it is not limited to this. In addition to the photoconductor drum, a process cartridge having any one of a charging means, a developing means, and a cleaning means may be used.

Further, in the above-described embodiment, a process cartridge having a drum unit including a photoconductor drum and a developing unit including a developing roller integrally attached to and detachable from an image forming apparatus has been illustrated, but the present invention is not limited thereto. .. For example, the developing unit including the developing roller and the drum unit including the photoconductor drum may be detachably attached to the image forming apparatus.

Further, in the above-described embodiment, the printer is exemplified as the image forming apparatus, but the present invention is not limited thereto. For example, it may be another image forming apparatus such as a copying machine or a facsimile apparatus, or another image forming apparatus such as a multifunction device combining these functions. Similar effects can be obtained by applying the present invention to these image forming devices.

E1, E2, E3 ... Power supply S1 ... Environmental sensor SY, SM, SC, SK ... Image forming unit 1 ... Photoreceptor drum 4 ... Developing roller 5 ... Supply roller 7 ... Process cartridge 8 ... Regulatory member 30 ... Scanner unit 100 ... Image Forming device 150 ... Control unit

Claims (4)

A rotatable developer carrier that supports the developer, a developer supply member that supplies the developer to the developer carrier, and a developer that comes into contact with the developer carrier and is supported by the developer carrier. A developing device equipped with a regulating member that regulates the amount of
A first power source that applies a bias to the developer carrier,
A second power source that applies a bias to the regulating member,
A control means for controlling the first and second power supplies,
In the image forming apparatus having
From the start of the developing operation to the end of the developing operation , the control means exerts a force urged by the regulating member on the developing agent carrier at the contact portion between the regulating member and the developing agent carrier. When controlling to provide a potential difference between the developer carrier and the regulating member so as to work and continuously recording on a plurality of recording materials.
In the first recording material, the control for providing the potential difference so that the force for urging the developer from the regulating member to the developer carrier acts stronger at the end of the development operation than at the start of the development operation. And
In the second and subsequent recording materials, the potential difference between the developer carrier and the restricting member from the start of the developing operation to the end of the developing operation is the potential difference at the end of the developing operation on the first recording material. An image forming apparatus characterized by performing the same control. A rotatable developer carrier that supports the developer, a developer supply member that supplies the developer to the developer carrier, and a developer that comes into contact with the developer carrier and is supported by the developer carrier. A developing device equipped with a regulating member that regulates the amount of
A first power source that applies a bias to the developer carrier,
A second power source that applies a bias to the regulating member,
A control means for controlling the first and second power supplies,
In the image forming apparatus having
Further comprising an environment information obtaining means for obtaining environmental information,
From the acquisition information of the environmental information acquisition means, the control means can be used in an environment of low temperature and low humidity.
During the period from the start of the developing operation to the end of the developing operation on the same recording material, the developing agent at the contact portion between the regulating member and the developing agent carrier exerts a force urged by the developing agent carrier to the regulating member. Control is performed to provide a potential difference between the developer carrier and the regulating member so as to work.
At the end of the developing operation, control is performed to provide the potential difference so that a force urged by the regulating member to the developing agent carrier acts on the developing agent at the contact portion.
It is characterized in that the end of the development operation is controlled to provide the potential difference so that the force for urging the developer from the regulating member to the developer carrier is stronger than the start of the development operation. Image forming device. The development agent supply member according to claim 1 or 2 , wherein the surface of the developer supply member rotates in a direction of moving in the same direction as the surface of the developer carrier at a contact portion with the developer carrier. Image forming device. The developer-supplied member according to claim 1 or 2 , wherein the surface of the developer-supplied member rotates in a direction opposite to the surface of the developer-supported body at a contact portion with the developer-supporting body. Image forming device.