JP2016090713A - Developing device and image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to sufficiently suppress a white void.SOLUTION: There is provided a developing device having developer carriers, such as developing rollers 42A and 42B that are arranged opposite to a latent image carrier, such as a photoreceptor 2 and carry a developer on their surface, and AC voltage application means, such as a power source part 510 that applies, to the developer carriers, an AC voltage in which an AC component is superposed on a DC component, two AC components having frequencies different from each other can be selectively used as the AC component, and one of the two AC components having a higher frequency is used in a process in a development step where a toner is moved from the latent image carrier to the developer carriers, and the other AC component is used in a process of the development step where a toner is moved from the developer carriers to the latent image carrier.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a developing device that performs a developing process by applying an alternating voltage, and an image forming apparatus including the developing device.

  In an image forming apparatus such as a copying machine or a printer that employs an electrophotographic method, the surface of the latent image carrier is uniformly charged, and then the surface of the latent image carrier is irradiated with image light to form an electrostatic latent image. A developing process is performed to form a toner image on the electrostatic latent image. As a developing method in the above developing device, there is known a method in which an alternating electric field is formed in a developing region by an alternating voltage in which an alternating current component is superimposed on a direct current component, and the toner is moved from the developer carrier side to the latent image carrier side while reciprocating. Has been.

  In Patent Document 1, the frequency range of the alternating current component of the alternating voltage applied in the developing device is set to 2.0 to 8.0 [kHz], so that white spots in the halftone image portion adjacent to the solid image portion are not white. A technique for suppressing the occurrence is described.

  However, as a result of diligent research by the present inventors, it has been found that the technique of Patent Document 1 may not sufficiently suppress the occurrence of white spots in a halftone image portion adjacent to a solid image.

  In order to solve the above-described problems, the present invention provides a developer carrying body that is disposed opposite to a latent image carrying body and carries a developer on the surface, and an alternating voltage that superimposes an AC component on a DC component. In a developing device having an alternating voltage applying means for applying to a carrier, two alternating current components having different frequencies are selectively used as the alternating current component, and one of the two alternating current components having a higher frequency. In the process where the toner moves from the latent image carrier to the development carrier in the development process, the other AC component moves in the development process from the developer carrier to the latent image carrier. It is characterized by being used in the above.

  According to the present invention, white spots can be sufficiently suppressed.

1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. FIG. 2 is a schematic configuration diagram of a developing device in the image forming apparatus. The perspective view of the power supply part of the developing device. The enlarged view of the contact location of the developing device and the power supply unit. FIG. 4 is a diagram illustrating an example of a waveform of an alternating voltage applied to the developing device. The figure which shows the example of the waveform of the alternating voltage applied in the developing device of the conventional image forming apparatus which applied only one type of alternating current component to the direct current component. Explanatory drawing about the criteria in the sensitivity evaluation of graininess.

Hereinafter, an embodiment in which the present invention is applied to a copying machine as an image forming apparatus will be described.
FIG. 1 is a schematic configuration diagram of a copying machine 500 according to the present embodiment.
The copying machine 500 includes a copying apparatus main body (hereinafter referred to as “printer unit”) 100, a paper feed table (hereinafter referred to as “paper feed unit”) 200, and a scanner mounted on the printer unit 100 (hereinafter referred to as “scanner unit”). 300.

  The printer unit 100 includes process cartridges 1Y, 1M, 1C, and 1K as four process units, and an intermediate transfer belt 7 as an intermediate transfer member that is stretched by a plurality of stretching rollers and moves in the direction of arrow A in FIG. , An exposure device 6 as exposure means, a fixing device 12 as fixing means, and the like. The suffixes Y, M, C, and K attached to the four process cartridges 1 indicate that the specifications are for yellow, magenta, cyan, and black. The four process cartridges 1Y, 1M, 1C, and 1K have substantially the same configuration except that the colors of the toners to be used are different from each other. Therefore, the subscripts K, Y, M, and C are omitted in the following description. .

  The process cartridge 1 is a unit that integrally supports a photosensitive member 2 as a latent image carrier, a charging member 3 as a charging unit, a developing device 4 as a developing unit, and a photosensitive member cleaning device 5 as a cleaning unit. The configuration is shaped like Each process cartridge 1 can be attached to and detached from the copying machine 500 main body by releasing a stopper (not shown).

  The photoconductor 2 rotates in the clockwise direction in the figure as indicated by the arrow in the figure. The charging member 3 is a roller-shaped charging roller, is in pressure contact with the surface of the photoconductor 2, and is rotated by the rotation of the photoconductor 2. At the time of image formation, a predetermined bias is applied to the charging member 3 by a high voltage power source (not shown) to charge the surface of the photoreceptor 2. In the process cartridge 1 of the present embodiment, the roller-shaped charging member 3 that contacts the surface of the photoreceptor 2 is used as the charging unit, but the charging unit is not limited to this, and non-contact such as corona charging. A charging method may be used.

  The exposure device 6 functions as a latent image forming unit, and exposes the surface of the photoreceptor 2 based on image information of an original image read by the scanner unit 300 or image information input from an external device such as a personal computer. Then, an electrostatic latent image is formed on the surface of the photoreceptor 2. The exposure device 6 provided in the printer unit 100 uses a laser beam scanner system using a laser diode, but may have other configurations such as an exposure unit using an LED array. The photoconductor cleaning device 5 cleans the transfer residual toner remaining on the surface of the photoconductor 2 that has passed the position facing the intermediate transfer belt 7.

  The four process cartridges 1 form yellow, cyan, magenta, and black toner images on the photoreceptor 2, respectively. The four process cartridges 1 are arranged in parallel in the surface movement direction of the intermediate transfer belt 7, and transfer the toner images formed on the respective photoreceptors 2 in order to be superimposed on the intermediate transfer belt 7 in order. A visible image is formed on the belt 7.

  In FIG. 1, a primary transfer roller 8 serving as a primary transfer unit is disposed at a position facing each photoconductor 2 across the intermediate transfer belt 7. A primary transfer bias is applied to the primary transfer roller 8 by a high voltage power source (not shown) to form a primary transfer electric field with the photosensitive member 2. By forming a primary transfer electric field between the photosensitive member 2 and the primary transfer roller 8, the toner image formed on the surface of the photosensitive member 2 is transferred to the surface of the intermediate transfer belt 7. One of a plurality of stretching rollers that stretch the intermediate transfer belt 7 is rotated by a drive motor (not shown), so that the intermediate transfer belt 7 moves in the direction of arrow A in the drawing. A full color image is formed on the surface of the intermediate transfer belt 7 by sequentially transferring the toner images of the respective colors on the surface of the intermediate transfer belt 7 moving on the surface.

  With respect to the position where the four process cartridges 1 face the intermediate transfer belt 7, intermediate transfer is performed on the downstream side in the surface movement direction of the intermediate transfer belt 7 with respect to the secondary transfer counter roller 9 a that is one of the stretching rollers. A secondary transfer roller 9 is disposed at a position opposed to the belt 7 and forms a secondary transfer nip with the intermediate transfer belt 7. A predetermined voltage is applied between the secondary transfer roller 9 and the secondary transfer counter roller 9a to form a secondary transfer electric field. A full color formed on the surface of the intermediate transfer belt 7 when the recording paper P, which is a recording material fed from the paper supply unit 200 and conveyed in the direction of arrow S in FIG. 1, passes through the secondary transfer nip. The image is transferred onto the recording paper P by a secondary transfer electric field formed between the secondary transfer roller 9 and the secondary transfer counter roller 9a.

  A fixing device 12 is disposed downstream of the secondary transfer nip in the conveyance direction of the recording paper P. The recording paper P that has passed through the secondary transfer nip reaches the fixing device 12, the full color image transferred onto the recording paper P is fixed by heating and pressurization in the fixing device 12, and the recording paper P on which the image is fixed is The data is output outside the copying machine 500. On the other hand, the toner remaining on the surface of the intermediate transfer belt 7 without being transferred to the recording paper P at the secondary transfer nip is collected by the transfer belt cleaning device 11.

  As shown in FIG. 1, above the intermediate transfer belt 7, toner bottles 400Y, 400M, 400C, and 400K that store toners of various colors are detachably disposed on the copying machine 500 main body. The toner stored in each color toner bottle 400 is supplied to each color developing device 4 by a toner replenishing device (not shown) corresponding to each color.

FIG. 2 is a diagram showing a schematic configuration of the developing device 4 of the present embodiment, and is a cross-sectional view seen from the back side of the paper in FIG.
As shown in FIG. 2, the developing device 4 is provided with two developing rollers 42A and 42B as developer carriers, a doctor blade 45, a stirring paddle 46, a conveying screw 48, a toner concentration sensor 49, and the like. . The developing case 41 that accommodates these components has an opening at a position facing the photoreceptor 2 so that the surface of the photoreceptor 2 and the two developing rollers 42A and 42B face each other through the opening. It is configured. As the developer 43 accommodated in the developing case 41, a two-component developer composed of toner and carrier is used, but a one-component developer composed of toner may be used. The developer 43 in the developing case 41 is stirred by the stirring paddle 46 and the conveying screw 48.

  The developer 43 in the developing case 41 is carried on the surface by the magnetic force of a magnet roller serving as a magnetic field generating means installed inside the developing rollers 42A and 42B, and each developing roller 42A and 42B is driven to rotate to develop each developer. The roller and the photosensitive member 2 face each other and are conveyed to respective development areas where development processing is performed. The developer 43 on the first developing roller 42A is regulated to a predetermined amount by the doctor blade 45 and then transported to the first developing area and used for the developing process. Thereafter, the developer 43 on the first developing roller 42A that has passed through the developing area is delivered to the second developing roller 42B side at a location where the first developing roller 42A and the second developing roller 42B face each other. Then, it is transported to the second development area by the rotational drive of the second development roller 42B, and is used again for development processing.

FIG. 3 is a perspective view showing the developing device 4 and the power supply unit 510 provided in the copying machine 500 main body.
As shown in FIG. 3, a DC power supply 514 for applying a DC component is connected to the power supply unit 510 via a power cable 513. A first AC power supply 515 and a second AC power supply 516 for applying an AC component are connected to the DC power supply 514, and a changeover switch 517 is provided midway between the two AC power supplies and the power supply unit 510. When the control unit 518 controls the switching of the switch 517, either the AC component formed by the first AC power source 515 or the AC component formed by the second AC power source 516 is a DC component. Is superimposed on the screen. The switching control by the switch 517 will be described later.

  The first AC power supply 515 and the second AC power supply 516 are each equipped with a function generator capable of generating an AC voltage signal having an arbitrary frequency and waveform. Also, the duty ratio can be changed by the function generator. The same alternating voltage is applied to the two developing rollers 42A and 42B.

FIG. 4 is an enlarged view in which a connecting portion between the developing device 4 and the power supply unit 510 indicated by a symbol A in FIG. 3 is enlarged.
As the process cartridge 1 is attached to the copying machine 500 main body, the power input terminals 44A and 44B of the developing device 4 in the process cartridge 1 are inserted into the terminal holes 511A and 511B of the power supply unit 510 in the copying machine 500 main body. The As a result, the power input terminals 44A and 44B of the developing device 4 are in contact with and electrically connected to the power output terminal 512 of the power supply unit 510 of the copying machine 500 main body. A DC power supply 514 for applying a DC voltage and an AC power supply 515 for applying an AC voltage are connected to the power output terminal 512 via a power cable 513.

  Here, the waveform of the alternating voltage applied to the developing device 4 in this embodiment and the switching control by the switch 517 will be described with reference to FIG. In the following description, FIG. 3 will be referred to as appropriate.

FIG. 5 is a diagram illustrating an example of a waveform of an alternating voltage applied to the developing device 4 in the present embodiment.
FIG. 5B shows the waveform of the alternating voltage when the AC component (first AC component) generated by the first AC power source 515 is superimposed on the DC component. FIG. 5C shows the waveform of the alternating voltage when the AC component (second AC component) generated by the second AC power supply 516 is superimposed on the DC component. The first AC component is the AC component with the lower frequency, and the second AC component is the AC component with the higher frequency. The frequency of the second AC component is set to be four times higher than the frequency of the first AC component. In the figure, the changeover switch 517 (see FIG. 3) is controlled so that the alternating voltage shown in FIG. 5B is applied in the period indicated by T1 and the alternating voltage shown in FIG. 5C is applied in the period indicated by T2. As a result, the waveform of the alternating voltage shown in FIG.

  In FIG. 5A, the offset voltage Vb indicates a voltage applied by the DC power supply 514. The feed potential peak value Vt is the absolute value (| Vd−Vl |) of the difference between the charging potential Vd and the latent image portion potential Vl. The return potential peak value Vr is the return potential Ve and the latent image portion potential Vl. The absolute value (| Ve−Vl |) of the difference between the two is shown. At the alternating voltage, Vt is made larger than Vr (Vt> Vr).

  5A, T1 in the figure indicates a period in which the first AC component is superimposed, and T2 in the figure indicates a period in which the second AC component is superimposed. The period in which the first AC component is superimposed mainly relates to a process (hereinafter referred to as “feed process”) in which the toner moves from the developing roller toward the photosensitive member in the developing process. Further, the period in which the second AC component is superimposed mainly relates to a process in which the toner moves from the photoconductor toward the developing roller in the developing process (hereinafter referred to as “returning process”). The first AC power supply 515 and the power supply unit 510 are energized during the period in which the first AC component is superimposed, and the second AC power supply 516 and the power supply unit 510 are in the period during which the second AC component is superimposed. The changeover switch 517 is switched so that and are energized. When the second AC component is selected as the AC component, the alternating voltage is applied for at least two cycles.

Here, the cause of occurrence of white spots and the method for suppressing them will be described.
The main factors that are considered to cause white spots are “suction” and “relocation”.
The solid image portion has a higher absolute value than the halftone image portion. Therefore, in the feeding process, the toner particles flying from the developing roller toward the photoconductor are bent during the flight and are attracted toward the solid image portion having a higher potential. This is inhalation.
In the returning process, the toner particles near the boundary between the solid image portion and the halftone image portion are detached when the polarity of the AC component is reversed. The detached toner particles move in the air to a position immediately above the center of the solid image portion or the halftone image portion. Then, when the polarity of the AC component is reversed next, the toner particles are attracted onto the photoconductor while maintaining the position (position just above the center of the solid image portion or the halftone image portion). Adhere to. This is rearrangement.

  When suction or rearrangement occurs, the dots of the halftone image portion in the vicinity of the solid image portion become narrower than usual in the sub-scanning direction of the photosensitive member, and become longer than usual in the main scanning direction. That is, the dots of the halftone image portion in the vicinity of the solid image portion are elongated in the sub-scanning direction. In the vicinity of the solid image portion, there is a space corresponding to the narrowing in the sub-scanning direction, but this space appears to be white.

In order to suppress the occurrence of rearrangement, it is necessary to reduce the amount of movement of the toner particles separated from the photoreceptor in the return process. The toner particles vibrate due to the influence of the AC component of the applied alternating voltage. The movement amount D ′ of the toner particles can be obtained by calculating the amplitude in the vibration of the toner particles. The amplitude of the toner particles is expressed by the amplitude | D | = b / {ω · (a ² + ω ² ) ^0.5 }. Here, a is the air resistance, ω is the angular frequency, and b is the force of the electric field applied to the toner. The air resistance a is represented by a = 6πηR / m, where η is the viscosity resistance of air, R is the radius of the toner particles, and m is the mass of the toner particles. The angular frequency ω is represented by ω = 2πf, where f is the frequency of the AC component. The electric field force b is expressed as b = qE ₀ / m, where q is the charge amount of the toner, E ₀ is the maximum electric field strength, and m is the mass of the toner particles. The movement amount D ′ of the toner particles is obtained by multiplying the amplitude D by one half. Table 1 shows the result of calculating the movement amount D ′ for each frequency.

  From Table 1, it can be seen that the amount of movement of the toner particles decreases as the frequency of the AC component increases. That is, the rearrangement can be suppressed by increasing the frequency of the AC component in the return process and reducing the amount of toner that moves from the photosensitive member to the developing device.

  On the other hand, in order to suppress the occurrence of suction, it is necessary to sufficiently increase the amount of movement of toner particles flying from the developing roller toward the photosensitive member during the feeding process. If the movement amount of the toner particles becomes sufficiently large, the toner particles flying toward the target position on the photoreceptor corresponding to the halftone image portion are not attracted toward the solid image portion on the way, and the above This is because the position can be reached. Table 2 shows the result of measuring the number of toner particles that arrived at the dots in the halftone image area near the solid image area when the frequency of the AC component was varied.

  From Table 2, when the frequency of the AC component is lowered to 20 [Hz], the toner particle movement amount D ′ exceeds 2 [μm], and the toner particles that have arrived at the dots in the halftone image portion in the vicinity of the solid image portion The number of becomes 0 or more. When the frequency of the AC component is further lowered from 20 [Hz], the number of toner particles that have reached the dots in the halftone image portion near the solid image portion increases dramatically. That is, when the frequency of the AC component is further lowered from 20 [Hz], the number of toner particles attracted toward the solid image portion during flight can be reduced. Thereby, inhalation can be suppressed.

  In order to reduce the white spot in the halftone image portion adjacent to the solid image portion to a level where it cannot be visually determined, it is necessary to suppress both the rearrangement and the suction described above. In order to suppress both rearrangement and suction, it is necessary to make the frequency of the AC component related to the return process higher than the frequency of the AC component related to the feeding process.

  As described above, in the present embodiment, in the alternating voltage applied to the developing device, the first AC component that is mainly superimposed on the alternating voltage related to the feeding process and the alternating voltage that is mainly related to the returning process are superimposed. Two AC components, the second AC component, are used. When the frequency of the second AC component was made higher than the frequency of the first AC component, it was confirmed that white spots in the halftone image portion adjacent to the solid image portion could be reduced to a level that cannot be visually determined.

[Experimental example]
In the alternating voltage applied to the developing device, evaluation was performed to confirm the effect of reducing white spots due to the use of two alternating current components, the first alternating current component and the second alternating current component. In this evaluation, the size of the white spots was determined based on the “white gap width”. The white space is a value obtained by measuring the width of a white region when a halftone image portion near the solid image portion is observed. In addition, the graininess was also evaluated. Examples of experiments conducted to evaluate these will be described below.

  The apparatus of FIG. 3 was used for the experiment. In the alternating voltage applied to the developing device, the peak-to-peak voltage was set to 800 [V], and the offset voltage was set to -182 [V]. The duty ratio of the second AC component is set to 50 [%]. In the experiment, a solid image part of 15 [mm] square (a state where toner is attached to the entire surface) and a halftone image part of 15 [mm] square (a state where 25 [%] of toner is attached to the solid part). , 42 [μm] square dots are arranged at intervals of 42 [μm], and a pattern in which the dots are alternately arranged was developed, and the blank width was measured for the development result. Here, the solid image portion means a state in which toner adheres to the entire surface. The halftone image portion is a state in which 25% toner is attached to the solid image portion (42 [μm] square dots are arranged at 42 [μm] intervals).

  For measurement of the whiteout width, a microscope having a magnification of 100 times was used at the boundary between the solid image portion and the halftone image portion. When the blank width is converted into dots in the halftone image portion, 2.0 [mm] is equivalent to about 25 rows of 42 [μm] square dots, and 0.2 [mm] is equivalent to about 3 rows of dots. In other words, when the blank width is 2.0 [mm], a blank corresponding to approximately 25 rows of 42 [μm] square dots is formed, so that the discrimination can be made visually. In order to prevent the white spots from being visually recognized, it is necessary to make the white width smaller than 2.0 [mm]. It is more desirable that the whiteout width is 0.2 mm or less.

The sensitivity evaluation of the graininess was judged by an image obtained by photographing the development result with a microscope having a magnification of 100 times. Judgment criteria were ranks 5-5.
FIG. 7 is a diagram for explaining determination criteria in graininess sensitivity evaluation.
The image shown in FIG. 7A is an example in which the granularity sensitivity evaluation is determined to be rank 5. As shown in FIG. 7A, both the solid image and the halftone image are prepared. Further, the image shown in FIG. 7B is an example in which the determination of the granularity sensitivity evaluation is rank 1. As shown in FIG. 7B, there is a large disturbance in the solid image and the halftone image. Ranks 4 and 2 were judged as intermediate. If the granularity sensitivity evaluation is rank 4 or higher, it is considered that there is no practical problem.

  First, a table comparing results of applying an alternating voltage in which AC components of two different frequencies are alternately superimposed on a DC component and applying an alternating voltage in which an AC component of one frequency is superimposed on the DC component is shown. 3 shows.

  In Example 1-1, the frequency of the first AC component was 0.5 [kHz], and the frequency of the second AC component was 10 [kHz]. In Example 1-2, the frequency of the first AC component was 10 [kHz], and the frequency of the second AC component was 50 [kHz]. In Example 1-3, the frequency of the first AC component was 20 [kHz], and the frequency of the second AC component was 80 [kHz]. In any of the embodiments, the frequency of the second component is set to be four times or more the frequency of the first component.

In Comparative Examples 1-1 to 1-3, an alternating voltage in which only one type of AC component was applied to the DC component was applied to the developing device. The frequency of the alternating current component was 0.5 [kHz] in Comparative Example 1-1, 10 kHz in Comparative Example 1-2, and 20 kHz in Comparative Example 1-3.
FIG. 6 is a diagram illustrating a waveform of an alternating voltage in the comparative example.
FIG. 6A shows an AC component having a frequency of 0.5 [kHz], and FIG. 6B shows an AC component having a frequency of 20 [kHz].

  The blank width of the development result in each example was 0.2 [mm] in all of Examples 1-1, 1-2, and 1-3. On the other hand, the blank width of the development result in each comparative example is 0.5 [mm] in Comparative Example 1-1, 2.0 [mm] in Comparative Example 1-2, and 2. It became 0 [mm]. That is, in any of the comparative examples, the blank width is larger than 0.2 mm.

  Next, Table 4 shows a result of comparison between the case where the frequency of the second AC component is four times or more the frequency of the first AC component and the case where the frequency is made smaller than four times.

  In Example 2-1, the frequency of the first AC component was 0.5 [kHz], and the frequency of the second AC component was 2.0 [kHz]. In Example 2-2, the frequency of the first AC component was 10 [kHz], and the frequency of the second AC component was 40 [kHz]. In Example 2-3, the frequency of the first AC component was 20 [kHz], and the frequency of the second AC component was 80 [kHz]. In any of the examples, the frequency of the second component was set to be four times the frequency of the first component.

  In Comparative Example 2-1, the frequency of the first AC component was 0.5 [kHz], and the frequency of the second AC component was 1.0 [kHz]. In Comparative Example 2-2, the frequency of the first AC component was 10 [kHz], and the frequency of the second AC component was 20 [kHz]. In Comparative Example 2-3, the frequency of the first AC component was 20 [kHz], and the frequency of the second AC component was 40 [kHz]. In any of the comparative examples, the frequency of the second component was set to be twice the frequency of the first component.

  The blank width of the development result in each example is 0.01 [mm] in Example 2-1, 0.1 [mm] in Example 2-2, and 0.2 [mm] in Example 2-3. Became. On the other hand, the blank width of the development result in each comparative example is 0.5 [mm] in Comparative Example 2-1, 2.0 [mm] in Comparative Example 2-2, and 2.2 in Comparative Example 2-3. It became 0 [mm]. That is, in any of the comparative examples, the blank width is larger than 0.2 mm.

  As described above, in order to further reduce the whiteout width, it is preferable that the frequency of the second AC component is four times or more higher than the frequency of the first AC component. Note that the whiteout width is affected by the linear speed ratio between the photoconductor and the developing roller, and strictly speaking, the frequency of the second AC component is set to the first AC in consideration of the linear speed ratio between the photoconductor and the developing roller. It is desirable to determine how high the frequency of the component should be. However, in the case of an image forming apparatus having a general configuration, white spots can be sufficiently suppressed if the frequency of the second AC component is four times higher than the frequency of the first AC component.

  Next, it shows in Table 5 about the evaluation result which shook the frequency of the 1st alternating current component in the range of 0.4-30 [kHz].

  The frequencies of the first AC component and the second AC component in Examples 2-1 to 2-3 are as described above. In Comparative Example 3-1, the frequency of the first AC component was 0.4 [kHz], and the frequency of the second AC component was 1, 6 [kHz]. In Comparative Example 3-2, the frequency of the first AC component was 30 [kHz], and the frequency of the second AC component was 120 [kHz]. In any of the examples and comparative examples listed in Table 5, the frequency of the second component is set to be four times the frequency of the first component.

  As described with reference to Table 4, the blank width of the development result in each example is 0.01 [mm] in Example 2-1, 0.1 [mm] in Example 2-2, and Example 2 -3 was 0.2 [mm]. That is, in any of the examples, the blank width is 0.2 mm or less. On the other hand, the blank width of the development result in each comparative example was 2.0 [mm] in comparative example 3-1, and 2.0 [mm] in comparative example 3-2. That is, in any of the comparative examples, the blank width is larger than 0.2 mm.

Judgment of the sensitivity evaluation of the granularity of the development results in each example was rank 5 in example 2-1, and ranks 4 in example 2-2 and example 2-3. In other words, it can be said that any of the examples has a level of practically no problem with respect to graininess. On the other hand, in Comparative Example 3-1, Rank 1 and Comparative Example 3-2 were Rank 2, both of which were practically problematic.
From the above, it is preferable that the frequency range of the first AC component is 0.5 [kHz] or more and 20 [kHz] or less from the viewpoints of the blank width and graininess.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect 1)
A developer carrying member such as developing rollers 42A and 42B that is disposed opposite to a latent image carrying member such as the photosensitive member 2 and carries the developer on the surface, and an alternating voltage that superimposes the alternating current component on the direct current component. In a developing device having an alternating voltage application unit such as a power supply unit 510 to be applied to the body, two alternating current components having different frequencies are selectively used as the alternating current component, and of the two alternating current components, The AC component having the higher frequency is in the process of moving the toner from the latent image carrier to the development carrier in the development step, and the other AC component is the toner in the development step from the developer carrier to the latent image carrier. Used in the process of moving.
There are two main causes of white spots, “suction” and “relocation”.
The potential of the solid image portion is higher (the absolute value is larger) than the potential of the halftone image portion. For this reason, in the process in which the toner moves from the developer carrier to the latent image carrier in the development process (feeding process), the toner particles that flew from the developer carrier to the latent image carrier are bent during the flight. And attracted toward a solid image portion having a higher potential. This is inhalation. In the feeding process, the amount of movement of the flying toner particles depends on the frequency of the AC component superimposed on the DC component. Specifically, as the frequency of the alternating current component superimposed on the direct current component is lowered, the amount of movement of the flying toner particles increases. It was confirmed by experiments that the number of toner particles attracted toward the solid image portion during the flight decreases as the moving amount of the flying toner particles increases. Suction can be suppressed by reducing the number of toner particles.
In the process of the toner moving from the latent image carrier to the development carrier in the development process (return process), the polarity of the AC component of the toner particles near the boundary between the solid image portion and the halftone image portion is reversed. Leave by. The detached toner particles move in the air to a position immediately above the center of the solid image portion or the halftone image portion. Then, when the polarity of the AC component is reversed next, the toner particles are attracted onto the latent image carrier while maintaining the position (position just above the center of the solid image portion or the halftone image portion). It adheres on the carrier. This is rearrangement. In the returning process, the amount of movement of the flying toner particles depends on the frequency of the AC component superimposed on the DC component. Specifically, as the frequency of the AC component superimposed on the DC component is increased, the amount of movement of the flying toner particles decreases. If the moving distance of the flying toner particles becomes small, the distance that the separated toner particles move to the position immediately above the center of the solid image portion or the halftone image portion in the air also becomes small. Relocation can be suppressed by reducing the moving distance.
As the AC component superimposed on the DC component, the higher frequency AC component is used in the return process, and the other AC component is used in the feed process, so that suction and rearrangement are performed as described above. Both of these can be suppressed. As a result, it is possible to reduce the white spot to a level where it cannot be visually determined.

(Aspect 2)
In the aspect 1, the frequency of the AC component having the higher frequency is a frequency that is four times or more higher than the frequency of the other AC component, and the AC component having the higher frequency is used as the AC component. An alternating voltage was applied for at least two cycles.
When the AC component having the higher frequency is used in the return process, white spots can be further reduced.

(Aspect 3)
In any one of aspects 1 and 2, the frequency of the first AC component is 0.5 [kHz] or more and 20 [kHz] or less.
It has been confirmed by experiments that the granularity can be brought to a level having no practical problem by setting the frequency of the first AC component in the range of 0.5 [kHz] to 20 [kHz].

(Aspect 4)
A latent image carrier such as the photosensitive member 2; a latent image forming unit such as a charging member 3 that forms a latent image on the latent image carrier; and a development process for attaching toner to the latent image on the latent image carrier. A developing device such as a developing device 4 that performs the image forming process, and the toner image formed on the latent image carrier by the developing process is finally transferred to a recording material to form an image on the recording material. In the image forming apparatus, the developing device according to any one of Embodiments 1 to 3 is used as the developing unit.

2 Photoconductors 42A and 42B Developing roller 510 Power supply unit

JP 2005-173378 A

Claims (4)

A developer carrier that is disposed opposite to the latent image carrier and carries the developer on its surface;
In a developing device having an alternating voltage applying means for applying an alternating voltage that superimposes an alternating current component on a direct current component to the developer carrier,
Two alternating current components having different frequencies are selectively used as the alternating current component, and the higher alternating frequency component of the two alternating current components is changed from the latent image carrier to the development carrier in the development process. A developing device characterized in that the other AC component is used in the process of moving the toner toward the latent image carrier in the developing process, while the other AC component is used in the developing process. The developing device according to claim 1,
The frequency of the AC component with the higher frequency is a frequency that is at least four times higher than the frequency of the other AC component, and when the AC component with the higher frequency is used as the AC component, the alternating voltage is at least A developing device characterized in that two cycles are applied. In the developing device according to claim 1 or 2,
The developing device, wherein the frequency of the first AC component is 0.5 [kHz] or more and 20 [kHz] or less. A latent image carrier, a latent image forming unit for forming a latent image on the latent image carrier, and a developing unit for performing a development process for attaching toner to the latent image on the latent image carrier, In an image forming apparatus for finally transferring a toner image formed on the latent image carrier by development processing to a recording material and forming an image on the recording material,
An image forming apparatus using the developing device according to claim 1 as the developing unit.