JP2015079059A - Development device and image formation device provided therewith - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress unevenness in image density which could occur in an alternating voltage development system in which a toner is reciprocated within a development area.SOLUTION: Provided is a development device for applying an alternating voltage to a developer carrier in order to form, in the development area, an alternating magnetic field for reciprocating a toner in a developer and moving it from a developer carrier side to a latent image carrier side, wherein a voltage with a waveform of the alternating voltage in which a narrow width waveform, which is at least one of a development narrow width waveform C1 with a development-direction polarity having a voltage value larger in absolute value than, and a time width narrower than, a development waveform section C2 of the alternating voltage and a non-development narrow width waveform D1 with a non-development-direction polarity having a voltage value larger in absolute value than, and a time width narrower than, a non-development waveform section D2 of the alternating voltage, so that its relative position against the waveform of the alternating voltage will change in time, is applied to the developer carrier.

Description

  The present invention relates to a developing device that performs development processing by forming an alternating electric field that moves toner from a developer carrier side to a latent image carrier side while reciprocating toner, and an image forming apparatus including the developing device.

  In image forming apparatuses such as copying machines and printers that employ an electrophotographic method, the surface of the latent image carrier is uniformly charged by a charging device, and then the surface of the latent image carrier is irradiated with image light to electrostatically charge the surface. Development is performed by forming a latent image and forming a toner image on the electrostatic latent image. This toner image is transferred onto a recording medium such as paper or an intermediate transfer member by a transfer device, and further transferred onto the paper surface. Up to now, various methods have been studied for the development method. Specifically, there are a DC voltage developing method and an alternating voltage developing method, and the aim has been to achieve high image quality by utilizing the difference in developer characteristics exhibited by each of DC and AC. There are also one component and two components in the type of developer used, and there is a difference in whether the developer is brought into contact with the surface of the latent image carrier or not in the development region. In addition, the latent image carrier and developer carrier are characterized, new development methods are developed, and the characteristics of copiers and printers are satisfied by combining these developer characteristics and development methods. It has been given a function. In particular, the following techniques are known for an alternating voltage developing method that has been used as a developing method.

  In Patent Document 1, the frequency f of the alternating voltage used for the developing bias and the peak-to-peak voltage Vpp are increased to maintain the merit of the alternating voltage developing method, while the image is rough and the two-component developer is scattered on the drum. An image forming apparatus that suppresses such disadvantages is disclosed. In this image forming apparatus, the frequency of the alternating voltage applied to the developing sleeve is set to any value in the range of 4 [kHz] to 7 [kHz], and the peak-to-peak voltage of this alternating voltage is 1.5 [kV]. It is disclosed that any value in the range of 2.5 kV [kV] is used.

  Further, in Patent Document 2, a voltage waveform is periodically applied such that the vibration amplitude Vpp (kV) of the AC component of the developing bias whose frequency f is 5 [kHz] <f <15 [kHz] gradually decreases. Thus, there is disclosed an image forming apparatus for the purpose of suppressing the occurrence of background contamination and rear end omission. In this patent document 2, in an experiment for confirming the effect, background stain, trailing edge omission, and graininess when the frequency f of the AC component of the developing bias is swung in the range of 0 [kHz] ≦ f ≦ 20 [kHz]. The evaluation results are disclosed. According to the disclosed content, it is shown that the evaluation result is improved as the frequency f increases toward 20 [kHz] with respect to the background stain, but the frequency f is related to the rear end omission and graininess. It is shown that the evaluation results worsen as it increases toward 20 [kHz].

  In an image forming apparatus employing such an alternating voltage developing method, the developer carrying member and the latent image carrying member provided in the developing device in the image forming apparatus are slightly deviated within an error range during manufacturing. The distance between the axes of the developer carrier and the latent image carrier may fluctuate. The change in the inter-axis distance changes the developing electric field due to the alternating voltage applied in the developing area, thereby changing the toner behavior and causing image density unevenness. Specifically, an image portion that is developed by receiving a relatively large amount of a waveform portion (development waveform portion) in the developing direction that moves toner from the developer carrier side to the latent image carrier side, and the toner carrying the latent image There is an image portion that is developed by receiving a relatively large amount of the action of the waveform portion in the non-development direction (non-development waveform portion) that is moved from the body side to the developer carrier side. At this time, an image portion developed by receiving a relatively large amount of the development waveform portion has a high image density, and conversely, an image portion developed by receiving a relatively large amount of the non-development waveform portion has an image density. Lower. If such an image portion having a high image density and an image portion having a low image density are repeatedly generated at a frequency that is easily perceivable by humans, a problem of uneven image density occurs.

  The present invention has been made in view of this problem, and an object of the present invention is to provide a developing device capable of suppressing image density unevenness that may occur in an alternating voltage developing method in which toner reciprocates in a developing region. An image forming apparatus is provided.

  In order to achieve the above object, the present invention comprises a developer carrying member that carries a developer on the surface and is disposed to face the latent image carrying member, and the latent image carrying member and the developer carrying member. In order to form an alternating electric field that moves the toner in the developer from the developer carrier side to the latent image carrier side while reciprocating the toner in the developer in the opposite development area, an alternating voltage is applied to the developer carrier. The alternating voltage applying means has a polarity in the developing direction for moving the toner from the developer carrying body side to the latent image carrying body side, and has an absolute value greater than the waveform portion of the alternating voltage in the developing direction. Has a large voltage value and a narrow time width, and has a non-developing direction polarity for moving toner from the latent image carrier side to the developer carrier side, and the waveform in the non-developing direction at the above alternating voltage Part A narrow waveform that is at least one of non-development narrow waveforms having a large absolute value and a narrow time width is applied to the alternating voltage so that the relative position with respect to the waveform of the alternating voltage changes over time. A voltage included in the waveform is applied to the developer carrier.

  As described above, according to the present invention, it is possible to obtain an excellent effect that image density unevenness that can occur in the alternating voltage developing method in which the toner is reciprocated in the developing region can be suppressed.

1 is a schematic configuration diagram of a copier according to an embodiment. FIG. 2 is a schematic diagram illustrating a schematic configuration of a developing device of the copier. FIG. 3 is a perspective view showing the developing device and a power supply unit provided in the copying machine main body. FIG. 4 is an enlarged view in which a connection portion between a developing device and a power supply unit indicated by a symbol A in FIG. 3 is enlarged. It is a graph which shows an example of the voltage waveform in a certain time when the relative position of the non-narrow waveform with respect to the waveform of an alternating voltage is changed with time. It is a graph which shows an example of the voltage waveform in another time when the relative position of the non-narrow waveform with respect to the waveform of an alternating voltage is changed with time. It is a graph which shows the example of the voltage waveform in which the development narrow width waveform is contained in the head location of the development waveform part of an alternating voltage. It is a graph which shows the example of the voltage waveform in which the non-development narrow waveform is included in the head part of the non-development waveform part of an alternating voltage. It is explanatory drawing which shows the power supply part of the apparatus example 2 used in Experimental example 1. FIG. It is explanatory drawing which shows the power supply part of the apparatus example 3 used in Experimental example 1. FIG. It is explanatory drawing which shows the power supply part of the apparatus example 4 used in Experimental example 1. FIG. It is a schematic diagram which shows the outline | summary of the experimental apparatus used in Experimental example 1. FIG. 10 is a graph showing an experimental result of Experimental Example 2. 10 is a graph showing evaluation results of image density unevenness in Experimental Example 3. It is a graph which shows the evaluation result of background dirt in example 3 of an experiment.

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 schematic diagram showing a schematic configuration of the developing device 4 of the present embodiment, and is a cross-sectional view as viewed from the back side of the paper surface in FIG.
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.
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.
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. In this embodiment, a two-component developer composed of toner and carrier is used as the developer 43 accommodated in the developing case 41. However, 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.

  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 alternating voltage are connected to the power supply output terminal 512 via a power supply cable 513.

  The waveform of the alternating voltage applied by the DC power source 514 and the AC power source 515 includes a developing waveform portion having a polarity in the developing direction for moving the toner from the developing roller 42A, 42B side to the photosensitive member 2 side, and the toner on the photosensitive member 2 side. The non-developing waveform portions having the polarity in the non-developing direction that move from the developing rollers 42A and 42B to the developing rollers 42A and 42B alternately exist according to the frequency of the alternating voltage. In this embodiment, toner having a normal charging polarity of negative polarity is used, and therefore, a waveform portion having a negative polarity (a portion surrounded by a solid line in FIG. 5) is a non-development waveform portion, and a waveform portion having a positive polarity (FIG. 5). 5 is a development waveform portion.

  Further, in the present embodiment, the development narrowness having a voltage value having a larger absolute value than the development waveform portion in the alternating voltage applied by the DC power source 514 and the AC power source 515 and having a polarity in the development direction with a narrow time width. The width waveform and the narrow width of at least one of the non-development narrow-width waveforms having a voltage value having a larger absolute value than the non-development waveform portion at the same alternating voltage and having a narrow time width in the non-development direction A pulse power source 517 is included for including the waveform in the waveform of the alternating voltage.

  In the present embodiment, a control box 516 is connected to the pulse power source 517. The waveform of the narrow waveform voltage output from the pulse power supply 517 can be changed by the control signal output from the control box 516. Specifically, the position of the development narrow waveform or the non-development narrow waveform included in the alternating voltage waveform (relative position with respect to the alternating voltage waveform) is changed over time by the narrow waveform voltage output from the pulse power supply 517. A control signal is output from the control box 516. In this embodiment, the DC power supply 514, the AC power supply 515, the pulse power supply 517, and the control box 516 constitute an alternating voltage application unit. The same developing voltage is applied to the two developing rollers 42A and 42B.

FIG. 5 is a graph illustrating an example of a voltage waveform output from the power supply unit 510 in the present embodiment.
In the voltage waveform example shown in FIG. 5, as shown in the portion surrounded by the broken line in FIG. 5, the development waveform portion has a head portion that is more absolute than the remaining portion of the development waveform portion (the development waveform portion of the alternating voltage) C2. There is a narrow-width waveform portion (development narrow-width waveform) C1 having a large voltage value. The development narrow waveform C1 is included in the development waveform portion of the alternating voltage by the narrow waveform voltage applied by the pulse power source 517. Further, in the present embodiment, as shown in a portion surrounded by a solid line in FIG. 5, the head portion of the non-development waveform portion is more than the remaining portion of the non-development waveform portion (non-development waveform portion of alternating voltage) D2. There is a narrow waveform portion (non-development narrow waveform) D1 in which the absolute value is a large voltage value. The non-development narrow waveform D1 is included in the non-development waveform portion of the alternating voltage by the narrow waveform voltage applied by the pulse power source 517.

Specific contents of the waveform example shown in FIG. 5 are as follows.
The frequency of the alternating voltage applied by the DC power source 514 and the AC power source 515 is 20.1 [kHz]. First, between 0.000048 seconds and 0.0000544 seconds, a non-development narrow waveform having a narrow waveform voltage by the pulse power supply 517 exists, and a positive polarity voltage of +2 [kV] is applied. Thereafter, the voltage value returns to the voltage value of the non-development waveform portion (+500 [V]) of the alternating voltage, and during the period from 0.0000729 seconds to 0.0000799 seconds, the development narrow waveform of the narrow waveform voltage by the pulse power source 517 is obtained. And a negative polarity voltage of -2 [kV] is applied. Thereafter, the voltage value returns to the development waveform portion (−1 [kV]) of the alternating voltage.

  Here, when the waveform of the alternating voltage does not include a narrow waveform by the pulse power source 517, that is, when only the alternating voltage by the DC power source 514 and the AC power source 515 is applied, the same voltage is used in the cycle of the alternating voltage. The waveform is repeatedly applied. In this case, the image portion developed by receiving a relatively large amount of the development waveform portion (including the development narrow waveform voltage) and the non-development waveform portion (including the non-development narrow waveform voltage) relatively. Image portions developed and received in large numbers are likely to occur periodically. If this period corresponds to a frequency that is easily perceived by humans, an image portion having a high image density and an image portion having a low image density are repeatedly generated at the frequency, thereby causing uneven image density. The same applies to the case where a voltage that always includes a narrow waveform at the same position with respect to the waveform of the alternating voltage is applied.

  Therefore, in the present embodiment, as described above, the positions of the development narrow waveform and the non-development narrow waveform included in the alternating voltage waveform (relative positions with respect to the alternating voltage waveform) are changed over time. In this embodiment, as an example, the position of the non-development narrow waveform D1 included in the waveform of the alternating voltage is changed over time, and the position of the development narrow waveform C1 is a voltage fixed at the beginning of the development waveform portion of the alternating voltage. Apply. Such a voltage shows a waveform in which the non-development narrow waveform D1 is located at the beginning of the non-development waveform portion of the alternating voltage at a certain time as shown in FIG. As shown in FIG. 6, the non-development narrow waveform D1 indicates a waveform located near the rear end of the alternating waveform development waveform portion (near the non-development waveform portion).

  By applying such a voltage, a situation in which a voltage having the same waveform is repeatedly applied in an alternating voltage cycle does not occur. Therefore, the effects of the development waveform portion (including the development narrow waveform voltage) are relatively large and the image portion developed and the non-development waveform portion (including the non-development narrow waveform voltage) relatively A situation in which a large amount of the developed and developed image portion occurs periodically is less likely to occur. As a result, image density unevenness is suppressed.

  Note that the narrow waveform that changes the relative position with respect to the waveform of the alternating voltage over time may be a non-development narrow waveform because it is only necessary that the same waveform voltage be repeatedly applied in the alternating voltage cycle. The development waveform may be narrow or both.

  In addition, when applying a voltage that includes a narrow waveform in the waveform of the alternating voltage as in this embodiment, compared to the case of applying only the alternating voltage that does not include such a narrow waveform voltage, It is possible to improve the development efficiency and reduce background contamination. The function of the narrow waveform that produces such an effect will be described below. Since the development narrow waveform and the non-development narrow waveform have different functions, these narrow waveforms will be described separately.

FIG. 7 is a graph showing an example of a voltage waveform in which a development narrow waveform is included at the beginning of the development waveform portion of the alternating voltage. This voltage waveform does not include a non-development narrow waveform.
In the waveform portion surrounded by the broken line in FIG. 7, the voltage value applied to the developing rollers 42A and 42B is on the negative polarity side with respect to the latent image portion potential Vl (= −60 [V]). A developing electric field having a corresponding strength is formed in the developing area. If the development narrow waveform C1 is present at the beginning of the development waveform portion of the alternating voltage, the development narrow waveform C1 has a larger potential difference from the latent image portion potential Vl than the development waveform portion C2 of the alternating voltage. Become. Therefore, the developing electric field when such a developing narrow waveform C1 is applied is stronger than the developing electric field when the alternating waveform developing waveform portion C2 is applied, so that more toner is transferred to the photoreceptor 2 side. Can be moved. Therefore, the development efficiency can be improved by setting so that the development narrow waveform is applied at the timing of overlapping the development waveform portion of the alternating voltage.

  Here, if the voltage value of the entire development waveform portion of the alternating voltage is set to the same voltage value (−2 [kV]) as the development narrow waveform C1, the development efficiency is improved, but the background on the photoreceptor 2 is improved. The amount of toner adhering to the area also increases, and the background stains worsen. In addition, since the discharge easily occurs in the development area, charging abnormality occurs in the toner, and the evaluation of solid filling, luminance, edge reproducibility, and the like is deteriorated, and the photoreceptor 2 is deteriorated. Therefore, the time width of the development narrow waveform C1 is preferably set to be 50% or less of the time width (application time) of the development waveform portion (C1 + C2) of the alternating voltage.

  In order to improve the development efficiency, it is effective to set the development narrow waveform C1 so as to partially exist at the development waveform portion of the alternating voltage, particularly at the head portion of the development waveform portion. Such improvement in development efficiency has the effect of improving the above-described three evaluations, that is, solid filling, brightness, and edge reproducibility. Therefore, it is possible to further enhance these three evaluations by applying a voltage such that the development narrow waveform C1 is positioned at the beginning of the development waveform portion of the alternating voltage. In addition, although it is preferable that the effect by having development narrow waveform C1 exists in the frequency range whose alternating voltage is 20 [kHz] or more and 60 [kHz] or less, it is not restricted to this frequency range.

FIG. 8 is a graph showing an example of a voltage waveform in which a non-development narrow-width waveform is included at the beginning of the non-development waveform portion of the alternating voltage. This voltage waveform does not include a development narrow waveform.
In the non-development waveform portion surrounded by the solid line in FIG. 8, the voltage value applied to the developing rollers 42A and 42B with respect to the latent image portion potential Vl (= −60 [V]) is on the positive polarity side. A non-developing electric field having an intensity corresponding to the potential difference (an electric field for returning the toner from the photosensitive member side to the developing roller side) is formed in the developing region. If the non-development narrow waveform D1 is present at the beginning of the non-development waveform portion of the alternating voltage, the non-development narrow waveform D1 has a potential difference from the latent image portion potential Vl as compared to the non-development waveform portion D2 of the alternating voltage. Is a big one. Therefore, the non-development electric field when such a non-development narrow-width waveform D1 is applied is stronger than the non-development electric field when the non-development waveform portion D2 of the alternating voltage is applied. It can be returned from the body 2 side to the developing rollers 42A and 42B side. Therefore, by setting so that the non-development narrow waveform is applied at a timing at which the non-development narrow waveform is superimposed on the non-development waveform portion of the alternating voltage, more toner attached to the background portion can be collected to the developing roller side. Dirt can be improved.

  Here, if the voltage value of the entire non-development waveform portion of the alternating voltage is set to the same voltage value (+2 [kV]) as that of the non-development narrow waveform D1, the background stain is improved, but the discharge is generated in the development area. As a result, charging abnormalities occur in the toner, and evaluations such as solid filling, brightness, and edge reproducibility are deteriorated, and the photoreceptor 2 is deteriorated. Accordingly, the time width of the non-development narrow waveform D1 is preferably set to be 50% or less of the time width (application time) of the non-development waveform portion (D1 + D2) of the alternating voltage. .

  It is effective to set such that the non-development narrow waveform D1 is partially present at the non-development waveform portion of the alternating voltage, particularly at the head portion of the non-development waveform portion. Such an improvement of the background contamination is preferably in a frequency range where the alternating voltage is 20 [kHz] or more and 60 [kHz] or less, but is not limited to this frequency range.

[Experimental Example 1]
Here, an experimental example (hereinafter, this experimental example will be referred to as “experimental example 1”) for confirming the effect of suppressing unevenness in image density and background contamination in the alternating voltage developing method will be described.
In this Experimental Example 1, the image density unevenness and the background stain were evaluated for four device examples having different configurations of the power supply unit 510.

  The apparatus example 1 used in this experiment example 1 is shown in FIG. Specifically, the control box 516 applies a voltage including a development narrow waveform and a non-development narrow waveform whose positions change with respect to the waveform of the alternating voltage to the developing roller.

  Further, the apparatus example 2 used in this experimental example 1 is shown in FIG. Specifically, the control box 516 applies the voltage including the development narrow waveform and the non-development narrow waveform whose positions change with respect to the waveform of the alternating voltage to the developing roller, as in the apparatus example 1. . However, the apparatus example 1 is different in that control for changing the peak voltage of the development narrow waveform and the non-development narrow waveform according to the toner concentration in the developer in the developing device by the toner density sensor 49 is added. Is different. In this control, when the toner concentration is high, the peak voltage of the development narrow waveform and the non-development narrow waveform is lowered, and when the toner concentration is low, the peak voltage of the development narrow waveform and the non-development narrow waveform is increased. Control to do. Specifically, when the toner density is higher than a predetermined threshold, the peak voltage of the development narrow waveform and the non-development narrow waveform is set to 1.5 [kV], and when the toner density is lower than the predetermined threshold The peak voltage of the development narrow waveform and the non-development narrow waveform is controlled to 2.0 [kV].

  Further, the device example 3 used in the experimental example 1 is shown in FIG. Specifically, after the DC power supply 514 is removed from the power supply unit of the apparatus example 1, a voltage including a development narrow waveform and a non-development narrow waveform whose positions change with respect to the waveform of the alternating voltage is applied to the developing roller. To do.

  Further, the apparatus example 4 used in the experimental example 1 is shown in FIG. Specifically, after the AC power source 515 is removed from the power supply unit of the apparatus example 1, a voltage including a development narrow waveform and a non-development narrow waveform whose positions change with respect to the waveform of the alternating voltage is applied to the developing roller. To do.

FIG. 12 is a schematic diagram showing an outline of the experimental apparatus 600 used in the first experimental example.
The experimental apparatus 600 includes a pseudo photoconductor 601 configured to form a pseudo latent image by depositing ITO (Indium Tin Oxide) 601b, which is a transparent electrode, on a transparent glass substrate 601a, and a voltage across the ITO 601b. Are composed of an electrode 602, a high-speed camera 603, a developing unit 604, and the like. The developing device 4 of the present embodiment is configured to include two developing rollers 42A and 42B, and the developing unit 604 of the experimental device 600 is configured to include a single developing roller 642. The configuration is similar. The developing unit 604 is fixedly disposed on the fixing base 605 so that the developing roller 642 is disposed to face the pseudo photoconductor 601.

  The pseudo-photosensitive member 601 and the high-speed camera 603 are supported by the moving table 606. The moving table 606 is configured to be slidable in the vertical direction in the drawing so that the surface of the pseudo photoconductor 601 on which the ITO 601b is deposited passes through a position facing the developing roller 642. The high-speed camera 603 is disposed at a position where the toner attached to the pseudo latent image portion is imaged from the back surface of the pseudo photoconductor 601 (the surface opposite to the surface on which the ITO 601b is deposited).

  In this experiment, first, the moving table 606 that supports the pseudo photoreceptor 601 and the high-speed camera 603 is moved downward in the drawing. Further, a -60 V DC voltage was applied to the pseudo latent image portion of the pseudo photoconductor 601 so that the pseudo latent image portion potential Vl was set to -100V. Thereafter, a voltage similar to that of the present embodiment is applied to the developing roller 642 to operate the developing unit 604, and the moving table 606 is slid upward. The slide moving speed at this time is set to the same speed as the linear speed (surface moving speed) of the photosensitive member 2 of the present embodiment. Then, after the pseudo latent image and the pseudo background portion on the pseudo photoconductor 601 passed through the area facing the developing roller 642 (developing area), the developing state was observed with the high-speed camera 603.

In Experimental Example 1, each of the apparatus examples 1 to 4 was used to evaluate the image density unevenness from the toner adhesion state when the solid image was developed. Image density unevenness is an index for determining how much the developed toner amount is biased. In the evaluation of the image density unevenness, the unevenness of the surface portion of 12 [mm] × 28 [mm] (= 336 [mm ² ]) in the developed solid image portion is measured with a laser microscope. Specifically, a difference in height from the background portion was taken for each portion where the toner adhered, and a portion having an average height value or less was defined as a recess, and the total area of the recess was measured. The smaller the total area of the recesses, the better the image density unevenness. In the evaluation method, since the total area of the recesses was 50 [mm ² ] in 336 [mm ² ] when developed with a development voltage consisting only of DC voltage, this was set to rank 2.5, and the total area of the recesses was Normalization was performed so that the rank of zero was 5.0, the highest rank, and rank evaluation of image density unevenness under each condition was performed.

  Further, in Experimental Example 1, background stains were evaluated from the toner adhesion state when a solid image was developed using each of the device examples 1 to 4. For evaluation of the background stain, the potential of the background portion is set to −350 [V], and after the solid image is developed using each of the apparatus examples 1 to 4, the number of toners attached to the background portion is determined. Measured. The smaller the number of toners, the better the background stain. In the evaluation method, the number of toner adhering to the background portion when developed with a developing voltage consisting only of a direct current voltage is ranked 3.8, and the rank in which the number of toner adhering to the background portion is zero is the highest rank. Normalization was performed so as to be 0, and the rank evaluation of background stains in each of the device examples 1 to 4 was performed.

The experimental results of Experimental Example 1 are as shown in Table 1 below.
As shown in Table 1, in any of the apparatus examples 1 to 4, the image density unevenness and the background stain are improved as compared with the case where the development is performed with the development voltage including only the DC voltage (DC development). However, in the apparatus example 3 and the apparatus example 4, the rank of the image density unevenness is lower than the rank 4.0 which can be said to be a level that causes no practical problem.

[Experimental example 2]
Next, an experimental example (hereinafter, this experimental example will be referred to as “experimental example 2”) for confirming conditions that can suppress image density unevenness in the alternating voltage developing method will be described.

  In this experimental example 2, the same experimental apparatus as in the above experimental example 1 (the above-mentioned apparatus example 1 was used for the power supply unit) was used, and the development narrow waveform and the non-development narrow waveform output from the pulse power source 517 were applied. Only the period (frequency) was changed, and each image density unevenness was evaluated. The main experimental conditions in Experimental Example 2 are as shown in Table 2 below. The latent image potential Vl is −100 [V].

FIG. 13 is a graph showing the experimental results of the second experimental example.
In this graph, the horizontal axis represents the application period (frequency) of the development narrow waveform and the non-development narrow waveform output from the pulse power source 517, and the vertical axis represents the evaluation rank for image density unevenness. As can be seen from this graph, when the frequency of the narrow waveform is 50 [kHz], the rank is 4.6, when the frequency of the narrow waveform is 60 [kHz], the rank is 4.2, and the frequency of the narrow waveform is 70 [kHz]. ] Ranked 3.0. If the rank of the image density unevenness is 4.0 or more, it can be said that the image density unevenness is at a level that does not cause a problem in practice, and therefore the frequency of the narrow waveform is preferably 60 [kHz] or less.

[Experimental Example 3]
Next, an experimental example (hereinafter, this experimental example will be referred to as “experimental example 3”) for confirming conditions for suppressing image density unevenness and background smearing in the alternating voltage developing method will be described.
In this experimental example 3, the same experimental apparatus as in the above experimental example 1 (the above-mentioned apparatus example 1 was used for the power supply unit) and the duty width of the developing narrow waveform and the non-developing narrow waveform output from the pulse power source 517 were used. Only the ratio was changed, and each image density unevenness and background stain were evaluated. The duty ratio here is the ratio of the application time (time width) of the development narrow waveform C1 to the application time (time width) of the development waveform portion of the alternating voltage, and the application time of the non-development waveform portion of the alternating voltage (time width). It means the ratio of the application time (time width) of the non-development narrow waveform D1 to (time width). The main experimental conditions in Experimental Example 3 are as shown in Table 3 below. The latent image potential Vl is −100 [V].

FIG. 14 is a graph showing evaluation results of image density unevenness in Experimental Example 3.
In this graph, the horizontal axis represents the duty ratio of the development narrow waveform and the non-development narrow waveform output from the pulse power source 517, and the vertical axis represents the evaluation rank for the image density unevenness. As can be seen from this graph, with respect to the image density unevenness, if the duty ratio of the narrow waveform is 50 [%] or less, a rank of 4.0 or more can be obtained, which can be regarded as a practically no problem level.

FIG. 15 is a graph showing the evaluation result of background stains in Experimental Example 3.
In this graph, the horizontal axis represents the duty ratio of the development narrow waveform and the non-development narrow waveform output from the pulse power source 517, and the vertical axis represents the evaluation rank for background contamination. As can be seen from this graph, with respect to background dirt, if the duty ratio of the narrow waveform is 50 [%] or less, a rank of 4.0 or more can be obtained, which can be said to be a practically no problem level.

Next, the carrier used in this embodiment will be described.
The carrier having a volume resistivity value of 1.0 × 10 ¹⁹ [Ω · cm] is within the range of 1.0 × 10 ⁸ [Ω · cm] to 1.0 × 10 ¹⁰ [Ω · cm]. It has been confirmed that the number of toners to be removed from the carrier increases by 30% when changed to the above. This is a result of visualizing and observing the number of toners detached from the carrier per unit time with a high-speed camera. Therefore, higher development efficiency can be obtained by using a carrier having a volume resistivity within a range of 1.0 × 10 ⁸ [Ω · cm] to 1.0 × 10 ¹⁰ [Ω · cm]. it can.

Next, the toner used in this embodiment will be described.
When using a toner having a particle diameter (volume average particle diameter) of 4 [μm] or more and 7 [μm] or less, using a toner having a particle diameter of less than 4 [μm], or 7 [μm]. When the larger toner was used, the area ratio and toner scattering amount of the toner (background toner) adhering to the background portion were compared. When the particle size of the toner is within the range of 5 [μm] ± 1 [μm], the evaluation of solid filling and brightness is 5% compared to the case where the toner particle size is less than 4 [μm]. However, the evaluation of background stain and toner scattering amount decreased by 30%. Further, compared to the case of using a toner having a toner particle size larger than 7 [μm], the evaluation of the background contamination and the toner scattering amount increased by 5%, and the evaluation of the solid filling and the luminance was improved by 20%. In this embodiment, a toner having a particle size in the range of 5 [μm] ± 1 [μm] is used.

Next, the amplitude of the toner that reciprocates within the development area will be described.
When the electric field formed in the developing area by the alternating voltage is Eo, the frequency of the alternating voltage is f, and the charge amount of the toner is q, the apparent amplitude D of the toner reciprocating in the developing area is It can be calculated from equation (1).
D = q × Eo / (2πf) ² (1)

The electric field Eo in the developing area is obtained from the relational expression shown in the following formula (2) using the distance d between the developing rollers 42A and 42B and the photosensitive member 2 and the peak-to-peak voltage Vpp of the alternating voltage. be able to.
Eo = V / d (2)

The toner charge amount q is a mass m (= V × ρ) obtained from the apparent volume V obtained from the toner radius r and the toner density ρ, and a total charge q ′ of the toner charge amount in 1 g. Can be obtained from the relational expression shown in the following expression (3).
q = q ′ / m (3)

  The toner amplitude D thus obtained is inversely proportional to the square of the frequency f of the alternating voltage from the above equation (1). Therefore, the higher the frequency f of the alternating voltage, the higher the toner amplitude. D is significantly reduced. Under the conditions of the experimental example described above, when the frequency of the alternating voltage is 2 [kHz], the amplitude D of the toner is larger than 300 [μm], and it is confirmed that the amplitude D gradually decreases as the frequency increases. did. However, since the non-development electric field formed in the development region is smaller than the development electric field under the conditions of the experimental example described above, the observed toner is larger than the value of the amplitude D of the toner calculated from the above formula (1). The amplitude D of was smaller. Further, when the magnetic brush is in the vicinity of the photoconductor surface, the amplitude when the toner vibrates becomes large. The particularly excellent result regarding the solid filling was obtained when the toner amplitude D was in the range of 0.3 [μm] to 30 [μm].

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A developer carrier such as developing rollers 42A and 42B, which carries a developer such as a two-component developer including toner and carrier on the surface, and is disposed opposite to a latent image carrier such as the photosensitive member 2; In order to form an alternating electric field that moves the toner in the developer from the developer carrier side to the latent image carrier side while reciprocating the toner in the developer in the development area where the latent image carrier and the developer carrier face each other. In the developing device 4 having an alternating voltage applying unit such as a power supply unit 510 for applying an alternating voltage to the agent carrier, the alternating voltage applying unit moves the toner from the developer carrier side to the latent image carrier side. A development narrow waveform C1 having a polarity, a voltage value having a larger absolute value than the waveform portion C2 in the development direction at the alternating voltage and a narrow time width, and toner from the latent image carrier side to the developer carrier side Move to A narrow width having a polarity in the non-development direction and having a voltage value that is larger than the waveform portion D2 in the non-development direction in the alternating voltage and has a narrow time width. A voltage included in the waveform of the alternating voltage is applied to the developer carrier so that the relative position of the waveform with respect to the waveform of the alternating voltage changes with time.
When the alternating voltage waveform does not include a narrow waveform, or when a voltage that always includes the narrow waveform at the same position as the alternating voltage waveform is applied, the same voltage waveform is displayed in the alternating voltage cycle. It is repeatedly applied. In this case, an image portion developed by receiving a relatively large amount of the action of the development waveform portion of the alternating voltage, and an image portion developed by receiving a relatively large amount of the action of the non-development waveform portion of the alternating voltage are cycled. It is easy to generate. If this period corresponds to a frequency that is easily perceived by humans, an image portion having a high image density and an image portion having a low image density are repeatedly generated at the frequency, thereby causing uneven image density.
In this aspect, the position of the narrow waveform included in the waveform of the alternating voltage (relative position with respect to the waveform of the alternating voltage) changes over time, so that the voltage of the same waveform is repeatedly applied in the period of the alternating voltage. No longer occurs. Therefore, a situation occurs in which an image portion developed by receiving a relatively large amount of the development waveform portion and an image portion developed by receiving a relatively large amount of the non-development waveform portion are periodically generated. It becomes difficult. As a result, image density unevenness is suppressed.

(Aspect B)
In the aspect A, the alternating voltage applying means periodically applies the narrow waveform at a frequency different from the frequency of the alternating voltage (for example, 40 [kHz]) within a predetermined frequency range (for example, 50 [kHz] or less). A voltage included in the alternating voltage is applied to the developer carrying member.
According to this, image density unevenness can be more stably suppressed.

(Aspect C)
In the aspect A or B, the time width of the narrow waveform is 50% or less of the time width of the waveform portion in the development direction or the waveform portion in the non-development direction in the alternating voltage.
According to this, it is possible to suppress image density unevenness and background stain more stably.

(Aspect D)
In any one of the above aspects A to C, the toner has a volume average particle diameter of 4 [μm] or more and 7 [μm] or less.
According to this, the background toner and the toner scattering amount can be reduced.

(Aspect E)
In any one of the above embodiments A to D, the volume resistivity value of the carrier is 1.0 × 10 ⁸ [Ω · cm] or more and 1.0 × 10 ¹⁰ [Ω · cm] or less. To do.
According to this, the development efficiency can be further improved.

(Aspect F)
In any one of the above embodiments A to E, the alternating voltage is set so as to reciprocate the toner with an amplitude of 0.3 [μm] or more and 30 [μm] or less in the development region. Features.
According to this, as described above, solid filling or the like can be improved more stably.

(Aspect G)
A latent image carrier such as the photosensitive member 2; a latent image forming unit such as an exposure device 6 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. And a developing means for performing the transfer, and finally transferring the toner image formed on the latent image carrier by the developing process onto a recording material such as a recording paper P to form an image on the recording material. In the image forming apparatus, the developing device 4 according to any one of the above aspects A to F is used as the developing unit.
According to this, it is possible to form a good image in which image density unevenness is bathed and ranked fourth.

DESCRIPTION OF SYMBOLS 1 Process cartridge 2 Photoconductor 3 Charging member 4 Developing device 5 Photoconductor cleaning device 6 Exposure device 7 Intermediate transfer belt 8 Primary transfer roller 9 Secondary transfer roller 12 Fixing device 41 Developing case 42A, 42B, 642 Developing roller 43 Developer 44A , 44B Power input terminal 100 Printer unit 200 Paper supply unit 300 Scanner unit 400 Toner bottle 500 Copier 510 Power source unit 511A, 511B Terminal hole 512 Power output terminal 513 Power cable 514 DC power source 515 AC power source 516 Control box 517 Pulse power source 600 Experiment Device 601 Pseudo-photosensitive member 603 High-speed camera 604 Development unit 605 Fixed base 606 Moving base

Japanese Patent Laid-Open No. 2003-287961 JP 2000-347507 A

Claims (7)

A developer carrier that carries the developer on the surface and is disposed opposite to the latent image carrier;
In order to form an alternating electric field for moving the toner in the developer from the developer carrier side to the latent image carrier side in a development area where the latent image carrier and the developer carrier are opposed to each other, In a developing device having an alternating voltage applying means for applying an alternating voltage to the developer carrier,
The alternating voltage applying means has a polarity in the developing direction for moving the toner from the developer carrier side to the latent image carrier side, and has a voltage value whose absolute value is larger than the waveform portion in the developing direction in the alternating voltage and A narrow development width waveform with a narrow time width and a non-development direction polarity for moving toner from the latent image carrier side to the developer carrier side, and a voltage whose absolute value is larger than the waveform portion of the alternating voltage in the non-development direction A voltage having a narrow waveform that is at least one of the non-development narrow waveforms having a value and a narrow time width included in the waveform of the alternating voltage so that the relative position with respect to the waveform of the alternating voltage changes over time Is applied to the developer carrying member. The developing device according to claim 1.
The alternating voltage applying means applies to the developer carrier a voltage in which the narrow waveform is periodically included in the alternating voltage at a frequency different from the frequency of the alternating voltage within a predetermined frequency range. A developing device. The developing device according to claim 1 or 2,
2. The developing device according to claim 1, wherein the time width of the narrow waveform is 50% or less of the time width of the waveform portion in the developing direction or the waveform portion in the non-developing direction in the alternating voltage. The developing device according to any one of claims 1 to 3,
The developing device according to claim 1, wherein the toner has a volume average particle diameter of 4 [μm] to 7 [μm]. The developing device according to any one of claims 1 to 4,
A developing device, wherein the carrier has a volume resistivity of 1.0 × 10 ⁸ [Ω · cm] or more and 1.0 × 10 ¹⁰ [Ω · cm] or less. The developing device according to any one of claims 1 to 5,
The developing device according to claim 1, wherein the alternating voltage is set so that the toner reciprocates with an amplitude of 0.3 [μm] or more and 30 [μm] or less in the developing region. 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.

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