JP2016218182A - Development device and image formation apparatus having the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a development device and image formation apparatus which can perform stable image formation in which the density difference hardly occurs with a simple configuration.SOLUTION: A development device comprises: an image carrier on which a latent image is formed; a developer carrier which develops the latent image formed on the image carrier; and a developer supply body which supplies a developer with a specific polarity to the developer carrier, performs reversal development by applying the developing bias with a specific polarity and value to the developer carrier, and also comprises superposition bias supply means which applies a superposition bias obtained by superposing an AC bias on a DC bias to the developer supply body. In accordance with a case where a negative polarity developer and a positive polarity developer are used, the superposition bias supply means restricts the relation (Vp-Vdev) between the maximum peaks value (Vp) of the positive pole and a developing bias value (Vdev) and the relation (Vp-Vdev) between the maximum peak value (Vp) of the negative pole and the developing bias value (Vdev) in the superposition bias applied to the developer supply body within a prescribed voltage range.SELECTED DRAWING: Figure 1

Description

The present invention relates to a developing device and an image forming apparatus using the same, and more particularly to a developing device mounted on a printer, a copier, or the like using electrophotography, and an image forming apparatus using the developing device.
In particular, the present invention relates to a developing device that uses a non-magnetic one-component developer and performs development under application of a specific bias, and an image forming apparatus using the same.

  As one of conventionally known image forming apparatuses, there are image forming apparatuses such as printers and copiers using electrophotography. As one of the main parts of these image forming apparatuses, electrostatic latent images formed electrostatically There is a developing device that visualizes a toner by attaching a magnetic or non-magnetic charged powder (hereinafter referred to as toner or developer) to the toner.

  This developing device, for example, uniformly charges the surface of a drum-shaped image carrier (hereinafter also referred to as a photosensitive drum) having an optical semiconductor layer capable of forming an electrostatic latent image on a surface thereof to a specific polarity, An electrostatic latent image is formed by irradiating optical information with a light irradiation device such as an LED, and then the developer described above is supplied to the surface of the photosensitive drum using a roller or brush-like developer carrier. The developer image formed on the photosensitive drum is transferred onto a transfer material such as paper. In developing, a developing bias as required is applied to the developer carrying member.

  In these configurations, various inventions and developments have been made, and at present, developing devices using a non-magnetic one-component toner as a developer are widely used. In the developing device having this configuration, new toner is appropriately supplied from the supply roller to the developing roller, the developing roller charges the supplied toner to a predetermined potential, and the charged toner is formed on the photosensitive drum. Development is performed by attracting the electrostatic latent image.

  As described above, the supply roller for supplying toner to the developing roller is called a reset roller, and has the role of peeling off the toner on the developing roller after being subjected to development and collecting it in the developing device. It also has the role of resetting the charge of the toner that remains on the developing roller without being squeezed. Ideally, it is desirable that the toner charge amount is charged up and saturated by one rotation of the developing roller, but it is actually difficult. For this reason, other methods, for example, a method such as rapid charge rising of the toner itself and overcharge prevention have been proposed, but they are still not fully satisfactory.

  Therefore, ideally, it is desired that the supply roller once removes all the toner used by rotating the developing roller once to reset it, and supplies new toner to the developing roller almost at the same time. It is difficult to complete the two different roles of recovery and reset at the same time, so that toners with different charge amounts, that is, toner that has passed several times on the developing roller and new toner that has just passed once are replaced. As a result, there is a problem that the image quality of the formed image is deteriorated.

  As a technique for solving this problem, for example, there is a developing device described in Patent Document 1. The developing device described in Patent Document 1 is based on the proposal of the applicant of the present application. A conductive brush is disposed on the outer peripheral surface of the supply roller, and an AC bias is superimposed on a DC bias on the supply roller. The bias is supplied.

JP 2007-147924 A

  In the developing device described in Patent Document 1, some of the conventional problems such as ghost and image density non-uniformity that are likely to occur when a large amount of high-speed printing is repeatedly performed, which was a problem before the application, are described. In particular, when a wide range of solid images such as A0 and A1 sizes are formed continuously in a wide range such as A0, A1 size, etc. In the case of repeatedly printing or copying a solid image with a ghost, it may not be possible to fully eliminate the occurrence of ghosts, etc., depending on the installation environment and usage conditions of the machine. There is a need for a solution.

  As is well known, one of the causes of ghost and image density non-uniformity in the development process is to replace the developing roller with new toner when there is a low density area in the high density area. Is insufficient, and a ghost (afterimage) having a period corresponding to one rotation of the developing roller is generated. Therefore, a more reliable reduction of the ghost is desired.

  The present invention has been made in view of these problems, and an object of the present invention is to provide a developing device capable of performing stable and high-quality image formation in which ghosts and density differences are unlikely to occur with a simple configuration. The object is to provide an image forming apparatus used.

(1) The present invention for solving the above problems includes an image carrier on which a latent image is formed, a developer carrier that develops the latent image formed on the image carrier, and the developer carrier. A developer supply body for supplying a developer having a specific polarity to the developer, and a developing device for performing reversal development by applying a development bias having a specific polarity and value to the developer carrier,
A bias supply means for applying a superimposed bias in which an AC bias is superimposed on a DC bias on the developer supply body;
The superposition bias is
For negative developer,
The relationship between the maximum peak value (Vp ⁺ ) of the positive electrode and the developing bias value (Vdev) is 50 V ≦ Vp ⁺ −Vdev ≦ 250 V
The relationship between the maximum peak value (Vp ⁻ ) of the negative electrode and the developing bias value (Vdev) is −50V ≧ Vp ⁻⁻ Vdev ≧ −450V,
[(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≦ 0V
For positive developer,
The relationship between the maximum peak value (Vp ⁺ ) of the positive electrode and the developing bias value (Vdev) is −50V ≧ Vp ⁻⁻ Vdev ≧ −250V
The relationship between the maximum peak value (Vp ⁻ ) of the negative electrode and the developing bias value (Vdev) is 50V ≦ Vp ⁺ −Vdev ≦ 450V,
[(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≧ 0V
The developing device is characterized by that.

(2) The present invention for solving the above problems includes an image carrier on which a latent image is formed, a developer carrier that develops the latent image formed on the image carrier, and the developer carrier. A developer supply body that supplies a negative developer to the developer supply body, and a superimposed bias applying unit that applies a superimposed bias in which an AC bias is superimposed on a DC bias to the developer supply body,
The relationship between the maximum peak value (Vp ⁺ ) and the maximum peak value (Vp ⁻ ) of the negative electrode and the development bias value (Vdev) of the superimposed bias is 50 V ≦ Vp ⁺ −Vdev ≦ 250 V.
−50V ≧ Vp ⁻ −Vdev ≧ −450V
[(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≦ 0V
The developing device is characterized by that.

(3) The present invention for solving the above problems includes an image carrier on which a latent image is formed, a developer carrier that develops the latent image formed on the image carrier, and the developer carrier. A developer supply body for supplying a positive polarity developer to the developer supply body, and a superimposed bias applying means for applying a superimposed bias obtained by superimposing an alternating current bias on a direct current bias to the developer supply body,
The relationship between the maximum peak value (Vp ⁺ ) and the maximum peak value (Vp ⁻ ) of the negative electrode and the bias value of the development bias value (Vdev) is −50V ≧ Vp ⁻⁻ Vdev ≧ −250V.
50V ≤ Vp ⁺ -Vdev ≤ 450V
[(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≧ 0V
The developing device is characterized by that.

  (4) In the developing device according to (2) or (3), the frequency of the superimposed bias is 50 to 500 Hz, preferably 50 Hz to 300 Hz. is there.

  (5) The present invention for solving the above problem is the developing device according to any one of (2) to (4), wherein the waveform of the AC component of the superimposed bias is a sine wave.

  (6) The present invention for solving the above problems is characterized in that the waveform of the AC component of the superimposed bias is a rectangular wave, a triangular wave, a pulsating current, or a positive / negative asymmetric wave. The developing device described.

(7) The present invention for solving the above problems develops an electrostatic latent image formed on an image carrier by supplying a developer to the image carrier and places the developed image on a transfer material. (1) to (6) in an image forming apparatus for forming an image by transferring
An image forming apparatus comprising any one of the developing devices.

According to the present invention, the superimposed bias supply means supplies a superimposed bias obtained by superimposing a DC bias, preferably an AC bias having a sine waveform, to the developer supply body.
Furthermore, the supply means for the superimposed bias is a superimposed bias,
For negative developer,
Maximum peak value of the positive electrode (Vp ⁺⁾ and the development bias value (Vdev) relationship with the 50 V ≦ Vp ^- relationship between the developing bias value (Vdev) ^- -Vdev ≦ 250V, the maximum peak value of the negative electrode (Vp) There -50V ≧ ^Vp - -Vdev ≧ -450V, ^{[(Vp + + Vp -) /} 2 ] -Vdev ≦ 0V,
In the positive developer, the maximum peak value of the positive electrode (Vp ⁺⁾ and the development bias value (Vdev) relationship between the -50V ≧ ^Vp - -Vdev ≧ -250V, the maximum peak value of the negative electrode (Vp ^- ) relationship between the developing bias value (Vdev) is 50V ≦ ^Vp + -Vdev ≦ 450V, ^{[(Vp + + Vp -) /} 2 ] -Vdev ≦ 0V
It is set as the structure which is.

  As a result, it is possible to improve the performance of collecting the developer from the developer carrying member while preventing the occurrence of beats, so that stable image formation that is less likely to cause ghosts and density differences can be achieved with a simple configuration. The image quality of the output image from the image forming apparatus can be improved.

Further, in the image forming apparatus provided with the developing device, it is possible to further reduce the ghost and further improve the output image quality.
Other effects of the present invention will become apparent from the description of the entire specification.

It is a front view for demonstrating schematic structure of the image development apparatus which is embodiment of this invention. 1 is a cross-sectional view for explaining a schematic configuration of a developing device according to an embodiment of the present invention. It is a figure for demonstrating an example of the superimposing bias at the time of using the negatively charged toner and negatively charged image carrier in embodiment of this invention. FIG. 4 is a diagram for explaining an example of a superimposed bias when a negatively charged toner and a positively charged image carrier are used in an embodiment of the present invention. FIG. 6 is a diagram for explaining an example of a superimposed bias when using a positively charged toner and a positively charged image carrier in an embodiment of the present invention. FIG. 6 is a diagram for explaining an example of a superimposed bias when using a positively charged toner and a negatively charged image carrier in an embodiment of the present invention.

  Embodiments to which the present invention is applied will be described below with reference to the drawings. However, in the following description, the same components are denoted by the same reference numerals, and repeated description is omitted.

  FIG. 1 is a front view for explaining a schematic configuration of a developing device according to an embodiment of the present invention. FIG. 2 is a cross-sectional view for explaining a schematic configuration of a developing device according to an embodiment of the present invention. Based on FIGS. 1 and 2, the overall configuration of the developing device of the present embodiment will be described.

  In the developing device of the present invention, either a one-component negatively charged toner or a positively charged toner can be used as a developer under the appropriate conditions disclosed in the present invention, and the negatively charged toner is used. In the case of the reverse development using a negatively charged photoconductor as the image carrier, the regular development using the positively charged photoconductor with the negatively charged toner, or the case where the positively charged toner is used. Can also be applied to configurations such as reversal development using a positively charged photoreceptor or regular development using a negatively charged photoreceptor.

  The arrows shown in FIG. 2 indicate the rotation directions of the rollers 1 to 3 and 14 to 16 such as the developing roller and the supply roller. In the following description relating to FIG. 1 and FIG. 2, reversal development using a negatively charged toner and a negatively charged photoconductor will be mainly described as an example. It is not limited only to the photoreceptor.

  As shown in FIG. 2, the developing device of the present embodiment includes a well-known cylindrical image carrier (photosensitive drum) 17 having a latent image (electrostatic latent image) formed on the outer peripheral surface thereof, and includes a developing roller (developing). The agent carrier 2 is disposed so as to face the peripheral side surface of the image carrier 17.

  The developing roller 2 is configured to develop the electrostatic latent image formed on the peripheral side surface (outer peripheral surface) of the image carrier 17 in a region facing the image carrier 17. A supply roller (developer supply body) 1 is disposed so as to face the peripheral side surface of the development roller 2. The supply roller 1 scrapes off the old toner that has been charged by the developing roller 2 and has not contributed to the development of the electrostatic latent image from the developing roller 2, and simultaneously resets (removes) the toner. The toner is supplied or re-supplied to the developing roller 2.

  The material of the supply roller 1 may be foamed urethane, foamed silicon, or bristle brush, which is an elastic body. Among these, a bristle brush is preferable, and a bristle brush can be used to carry a large amount of toner between the brushes. Therefore, the toner supply capability to the developing roller is remarkably increased, and a blurred image due to insufficient toner followability in solid printing is extremely unlikely to occur.

  On the other hand, in order to supply the toner on the developing roller 2 to the image carrier 17 with a predetermined layer thickness, the developing roller 2 faces the peripheral side surface thereof and is downstream of the supplying roller 1 in the rotation direction. A well-known regulation roller 3 is also arranged, and the toner supplied to the peripheral side surface of the developing roller 2 is charged with a predetermined value, and the toner layer thickness is made equal to the predetermined layer thickness. At this time, the toner adhering to the regulating roller 3 is scraped off by a known collection blade 13 and collected in the housing of the developing device. At this time, as shown in FIG. 2, the supply roller 1, the developing roller 2, and the regulating roller 3 are formed of roller bodies and are opposite to the rotation direction of the image carrier 17 (counterclockwise in FIG. 2). It is configured to rotate in the direction (clockwise in FIG. 2).

  In this configuration, as shown in FIGS. 1 and 2, the supply roller 1 has a brush-like shape made of conductive nylon or the like on the outer periphery of a conductive rigid body 1b such as stainless steel having a central shaft 4 serving as a rotation center. The toner supply layer 1a is formed. The toner supply layer 1a is preferably in the form of a brush, but is not limited to the form of a brush, and may be in any other form as long as it has a conductive surface layer. Further, the supply roller 1 is connected to a bias power source (superimposed bias power source, superimposing bias supply means) 12 having a central axis 4 composed of a DC bias power source 8 and an AC bias power source 9, and a bias (AC bias superimposed on a DC bias ( (Superimposed bias) is supplied to the supply roller 1.

  The developing roller 2 has a configuration in which, for example, an elastic surface layer 2a is formed on the outer periphery of a conductive rigid body 2b such as stainless steel having a central shaft 5 serving as a rotation center. Further, the developing roller 2 is configured such that the central shaft 5 is connected to a developing bias power source 10 which is a DC bias power source, and a predetermined DC bias is supplied to the developing roller 2 as a developing bias.

  The regulation roller 3 is composed of a conductive rigid roller having a center shaft 6, and the center shaft 6 is connected to a regulation bias power source 11 that is a DC bias power source, and a predetermined DC bias is supplied as a regulation bias. Yes.

  However, the bias applied to the supply roller 1 and the developing roller 2 will be described in detail later. In addition, the supply roller 1 and the developing roller 2 have a known elastic supply layer 1a and elastic surface layer 2a (or the same electronic brush, for example, a conductive nylon brush) around a central axis made of a conductive rigid body. The structure etc. which are formed may be sufficient.

  Further, in the developing device of the present embodiment, toner supply to the supply roller 1 is performed inside the housing (storage container) 7, the transport rollers 14 and 15 arranged in the vertical direction in FIG. 16 is performed. In particular, in the developing device of this embodiment, toner is appropriately transported (supplemented) into the housing 7 according to consumption from the transport roller 14 disposed above the housing 7, and stirred and transported by the transport roller 15. Thereafter, the toner conveyed to the bottom of the casing 7 is stirred by the stirring roller 16.

  The toner stirred by the stirring roller 16 is supplied to the supply roller 1 disposed at the bottom of the housing 7. The conveying roller and the stirring roller may be screw-shaped, blade-shaped, or roller-shaped, and the developer in the housing is sufficiently stirred by the conveying roller and the stirring roller. However, the supply of the toner to the supply roller 1 is not limited to the configuration in which the transport rollers 14 and 15 and the stirring roller 16 are arranged in the vertical direction, and is arranged in the horizontal direction or the oblique direction in FIG. The number of conveyance rollers may also be the number of either the conveyance roller 14 or the conveyance roller 15 or more.

  In the image forming apparatus including the developing device described above, a known eraser for erasing residual charges on the image carrier 17 is disposed around the image carrier 17, and the surface of the image carrier 17 has a specific polarity (this embodiment). A known charger for uniformly charging in the form (negative polarity), optical information is incident on the surface of the charged image carrier 17 (image exposure) to form a latent image on the surface of the image carrier 17. A known exposure device and a known transfer device for transferring the developer image formed on the image carrier 17 onto a transfer material such as paper are arranged, and the transferred developer image is placed on the transfer material. The image forming apparatus is configured with a known fixing device or the like for fixing to the image forming apparatus.

Next, FIG. 3 is a diagram for explaining an example of the superposed bias in the case of performing reversal development using the negatively charged toner and the negatively charged image carrier (negatively charged photoconductor) in the embodiment of the present invention. .
The superimposed bias supplied from the superimposed bias power supply 12 to the supply roller 1 and the developing bias supplied from the developing bias power supply 10 to the developing roller 2 will be described in detail below with reference to FIGS. In the following description, only the bias value supplied to the supply roller 1 and the developing roller 2 will be described, but the bias value supplied to the supply roller 1 and the developing roller 2 is the potential of the image carrier 17 charged by the charger. And a bias value corresponding to the material of the toner and the like as appropriate.

In the example shown in FIG. 3, the development bias voltage value applied to the developing roller 2 is −150 Vdev, the background potential of the image carrier 17 is −500 VD, and the toner development potential is −50 VL. , An AC bias having a sine waveform of 100 Hz is supplied. According to this condition, as shown in the sine waveform of FIG. 3, the maximum peak voltage value (+ peak value, maximum peak value) of the superimposed bias is −50 Vp ⁺ and the minimum peak voltage value of the superimposed bias is It is clear that (−peak value, minimum peak value) is −500 Vp ⁻ , the maximum peak value (Vp ⁺ ) of the positive electrode and the maximum peak value (Vp ⁻ ) of the negative electrode and the development of the superimposed bias. bias value relation between the voltage of (Vdev) ^{is, 50V ≦ Vp + -Vdev ≦ 250V} (a in ^{FIG.), - 50V ≧ Vp - -Vdev} ≧ -450V (b in ^{FIG.), [(Vp + + Vp} -) / 2] −Vdev ≦ 0V (c in the figure).

In addition, the period in which the supply roller 1 collects the toner corresponds to the period a in the figure, and the period in which the toner is supplied corresponds to the period b in the figure.
Thereby, by setting the superimposing bias in the above-described range, it is possible to improve the efficiency of collecting the old toner of the developing roller 2 by the supply roller 1 and the supply of new toner. It has been confirmed that the ghost can be remarkably suppressed in the numerical setting within the above range without causing a problem in the followability after one rotation.

Next, FIG. 4 is a diagram for explaining an example of the superimposed bias when the negatively charged toner and the positively charged image carrier in the embodiment of the present invention are used. FIG. 4 shows a case where negatively charged toner and a positively charged image carrier are used, and normal development was performed with a development bias voltage value of +400 Vdev, a background potential of the image carrier 17 of +50 VD, and a toner development potential of +500 VL. In this case, an AC bias having a sine waveform of 100 Hz is supplied.
Under this condition, it is possible to form a uniform image without occurrence of a beat phenomenon and without a ghost.

In experiment and verification,
When a rectangular wave is used, a beat (beat noise) is generated in the formed image at a frequency of less than 200 Hz, and when a sine wave is used, a beat is generated in the formed image at a frequency of less than 100 Hz. On the other hand, the occurrence of ghost is greatly reduced when the frequency is set to 100 Hz or less regardless of a rectangular wave, a sine wave, or other waveforms. Therefore, the AC bias power supply 9 of the present embodiment is configured to use an AC power supply that outputs an AC bias (sine wave AC bias) having a sine waveform of 100 Hz. As for the frequency, the frequency of the AC component of the superimposed bias is in the range of 50 Hz to 500 Hz, preferably in the range of 50 Hz to 300 Hz, and a sufficient reduction in ghost was confirmed in this range.

Moreover, as a result of repeating sincerity experiments, it was confirmed that the peak value is important, not the effective value of the AC voltage, which was noted in Patent Document 1. In other words, it was found that when the negative polarity toner is used, the + peak value contributes to the toner recovery, and the − peak value greatly contributes to the toner supply.
Similarly, when positive toner is used, it has been found that the −peak value contributes to toner recovery and the + peak value greatly contributes to toner supply. In other words, regardless of the AC voltage waveform of the supply roller bias, even when the sine wave is changed asymmetrically between the positive half-wave and the negative half-wave (: clamped at 0 V if + peak value> 0 V) It was confirmed that if a bias satisfying a predetermined conditional expression is employed, a uniform image without ghost can be obtained.

This result is clear from the figure showing the presence or absence of ghosts and beats when the superimposed bias supplied to the supply roller shown in Table 1 is changed.

Regarding Vp ⁺ -Vdev, which is the relationship between the maximum peak value (Vp ⁺ ) of the positive electrode and the developing bias value (Vdev), No. 1, No. 1 In the case of 50 V indicated by 2 (indicated by a thick frame in the figure), it has been found that the occurrence of beats can be prevented and the occurrence of a ghost at the developing roller pitch can be significantly suppressed. At this time, as is apparent from Table 1, the occurrence of ghost of followability (scratch) can be prevented. Therefore, by setting Vp ⁺ -Vdev to at least 50 V or more, it is possible to sufficiently reduce ghosts and prevent occurrence of beats.
As for Vp ⁺ -Vdev, no. 3 (indicated by a thick frame in the figure) can prevent the occurrence of beats and can significantly suppress the occurrence of follow-up ghosts. In the case of 350 V shown in FIG. 4, it has been found that a ghost of followability (scratch) occurs. At this time, as apparent from Table 1, the occurrence of the ghost of the developing roller pitch can be prevented at both 250V and 350V. Therefore, by setting Vp ⁺ -Vdev to at least 250 V or less, it is possible to sufficiently reduce ghosts and prevent occurrence of beats.
From the above results, by setting the maximum peak value (Vp ⁺ ) and the developing bias value (Vdev) of the positive electrode so as to satisfy 50V ≦ Vp ⁺ −Vdev ≦ 250V, the ghost can be sufficiently reduced and the beat can be reduced. Occurrence can be prevented.

On the other hand, Vp ⁻ −Vdev, which is the relationship between the maximum peak value (Vp ⁻ ) of the negative electrode and the developing bias value (Vdev), is shown in Table 1. -450V (indicated by a thick frame in the figure) shown in FIG. 3 can prevent the occurrence of beats and greatly suppress the occurrence of ghost of follow-up (scratch). In the case of −550 V indicated by 4, it has been found that a ghost of followability (scratch) occurs. At this time, the occurrence of a ghost at the developing roller pitch could be prevented at either −450V or −550V. Therefore, by setting Vp ⁻ −Vdev to at least −450 V or more, it is possible to sufficiently reduce ghosts and prevent occurrence of beats.
As for Vp ⁻⁻ Vdev, No. In the case of −50 V indicated by 5 (indicated by a thick frame in the figure), the occurrence of a ghost of followability (scratch) can be significantly suppressed along with the ghost of the developing roller pitch. Furthermore, occurrence of beats can also be prevented. Therefore, by setting Vp ⁺ -Vdev to be at least -50 V or less, it is possible to sufficiently reduce ghosts and prevent the occurrence of beats.

These results, -50 V ≧ ^Vp - so as to satisfy the -Vdev ≧ -450V, the maximum peak value of the negative electrode (Vp ^-) by setting the the development bias value (Vdev), and sufficient reduction of ghosting The occurrence of beats can be prevented.
However, the above-mentioned conditions are cases where negative polarity toner is used. In order to supply negative polarity toner, the maximum peak value (Vp ⁺ ) of the positive electrode and the maximum peak value (Vp ⁻ ) of the negative electrode are used. And the developing bias value (Vdev) need to satisfy [(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≦ 0V.

In the case of using positive toner, Vp ⁺ -Vdev, which is the relationship between the maximum peak value (Vp ⁺ ) of the positive electrode and the development bias value (Vdev), and the maximum peak value (Vp ⁻ ) of the negative electrode. Vp ⁻ −Vdev, which is the relationship between the development bias value (Vdev) and the negative polarity toner, needs to have the opposite polarity. Therefore, the maximum peak value (Vp ⁺ ) of the positive electrode and the maximum peak value (Vp ⁻ ) of the negative electrode and development so as to satisfy 50V ≦ Vp ⁺ −Vdev ≦ 450V and −50V ≧ Vp ⁻⁻ Vdev ≧ −250V. By adopting a configuration in which the bias value (Vdev) is set, it is possible to sufficiently reduce the ghost and prevent the occurrence of beats. However, in this case, it is necessary to satisfy [(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≧ 0V.

  Based on the case of the developing bias voltage value Vdev = −150V shown in FIG. 3 which is an example of the output of the superposed bias power source 12 satisfying this condition, the direct current bias power source 8 and the alternating current bias constituting the superposed bias power source 12 of the present embodiment. The output operation of the superimposed bias by the power supply 9 will be described.

As shown in FIG. 3, in the case of the development bias voltage value Vdev = −150 V and a = 100 V, Vp ⁺ = Vdev + a = − because of the relationship of a = Vp ⁺ −Vdev (that is, Vp ⁺ = Vdev + a) described above. 150V + 100V = −50V, and the frequency f is supplied to the supply roller 1 as a superimposed bias 18 which is a sine wave AC bias with f = 100 Hz. In this case, in the configuration of the developing device of the present embodiment, the developing bias voltage value Vdev the minimum peak voltage value of the superimposed bias (- the peak value, minimum peak value) Vp ^- difference between That Vdev-Vp ^- is 350V It is. Therefore, the minimum peak voltage value Vp ⁻ = −500. However, in this case, the peak voltage width Vp-p of the superimposed bias is 450V.

In the case of the developing bias voltage value Vdev = −150V shown in FIG. 3, a sinusoidal AC bias with a frequency f = 100 Hz at which the maximum peak voltage value Vp ⁺ = −50 V and the minimum peak voltage value Vp ⁻ = −500 V is superimposed. By supplying the supply roller 1 as the bias 18, it is possible to improve the efficiency of collecting the old toner of the developing roller 2 by the supply roller 1 and the supply of new toner. Image formation can be performed, and the effect of reducing the occurrence of ghost can be obtained even with a solid image or a solid solid image.

Further, in the case of the developing bias voltage value Vdev = −250V and a = 100V, the maximum peak voltage value Vp ⁺ = Vdev + a = −250V + 100V = −150V, and the frequency f is f = 100 Hz. The bias is supplied to the supply roller 1 as a superimposed bias 18 that is a bias. In this case, Vdev-Vp ^- is a 350 V, as a result, the minimum peak voltage value ^Vp - a = -600. Also in this case, the peak voltage width Vp-p of the superimposed bias is 450V.

In the case of the developing bias voltage value Vdev = −250 V shown in FIG. 3B, a sine wave AC having a frequency f = 100 Hz where the maximum peak voltage value Vp ⁺ = −150 V and the minimum peak voltage value Vp ⁻ = −600 V. By supplying the bias to the supply roller 1 as the superimposed bias 18, the efficiency of collecting old toner and supplying new toner on the developing roller 2 can be improved as in the case of the developing bias voltage value Vdev = −150V. With a simple configuration, it is possible to obtain an effect that it is possible to perform stable image formation in which ghosts and density differences hardly occur.

  FIG. 5 illustrates an example of the superimposed bias when the reversal development is performed using the positively charged toner and the positively charged image carrier (positively charged photoconductor) in the embodiment of the present invention, and FIG. 2 illustrates an example of a superimposed bias when normal development is performed using a positively charged toner and a negatively charged image carrier (negatively charged photoconductor) in an embodiment of the invention.

In the example shown in FIG. 5, the development bias voltage applied to the developing roller 2 is +150 Vdev, the background potential of the image carrier 17 is 0 V, and the toner development potential is +50 VL. It supplies an AC bias with a sine waveform. According to this condition, as shown in the sine waveform of FIG. 5, the maximum peak voltage value (+ peak value, maximum peak value) of the superimposed bias is +500 Vp ⁺ , and the minimum peak voltage value of the superimposed bias is , +50 Vp ^−, and the relationship between the negative peak maximum peak value (Vp ⁻ ) and the positive peak maximum peak value (Vp ⁺ ) and the development bias value (Vdev) is −50 V ≧ ^{Vp - -Vdev ≧ -250V, + 50V} ≦ Vp + -Vdev ≦ 450V, [(Vp + + Vp -) by / 2] satisfies: -Vdev ≧ 0V, ghost or density difference occurs hardly stable image formation I was able to confirm that I could do it.

  Similarly, in the example shown in FIG. 6, stable image formation in which ghosts and density differences hardly occur can be performed under the conditions described in the figure.

As described above, in the developing device of this embodiment, the superimposed bias power source 12 including the DC bias power source 8 and the AC bias power source 9 is configured, and the superimposed bias obtained by superimposing the AC bias on the DC bias is supplied to the supply roller 1. when the superimposed bias, in the negative developer, the relationship of the maximum peak value of the positive electrode and (Vp ⁺⁾ and the development bias value (Vdev) ^{is, 50V ≦ Vp - -Vdev ≦ 250V} , negative maximum peak value (Vp ^-) and the developing bias value relation between (Vdev) is ^{-50V ≧ Vp - -Vdev ≧ -450V,} [(Vp + + Vp -) / 2 ] -Vdev ≧ 0V, positive developer In that,
And the developing bias value (Vdev) maximum peak value of the positive electrode (Vp ⁺⁾ and the development bias value (Vdev) relationship between the ^{-50V ≧ Vp - - -Vdev ≧ -250V} , the maximum peak value of the negative electrode (Vp) relationship ^{50V ≦ Vp + -Vdev ≦ 450V,} [- has a structure in which the / 2] ^{-Vdev ≧ 0V (Vp + + Vp} ). Accordingly, the efficiency of collecting old toner and supplying new toner from the developing roller 2 by the supply roller 1 can be improved with a simple configuration, and as a result, stable image formation that hardly causes ghosts and density differences can be performed. The effect of being able to be obtained.
In the above description, a supply roller in which a known brush having conductivity is formed on the outer peripheral surface of the supply roller 1 may be used.

  From the above results, a sine wave AC bias is used as a superimposed bias, and the occurrence of ghost is suppressed by controlling the maximum peak voltage value and the developing bias voltage value Vdev of the superimposed bias within a specific range according to the present invention. However, it has been found that the occurrence of beat and follow-up can be suppressed.

  As mentioned above, the invention made by the present inventor has been specifically described based on the embodiment of the invention. However, the invention is not limited to the embodiment of the invention, and various modifications can be made without departing from the scope of the invention. It can be changed.

1 Supply roller (developer supply body)
1a supply layer 1b rigid body 2 developing roller (developer carrier)
2a Surface layer 2b Rigid body 3 Regulating rollers 4 to 6 Center shaft 7 Housing (storage container)
8 DC bias power supply 9 AC bias power supply 10 Development bias power supply 11 Regulated bias power supply 12 Superposed bias power supply 13 Blade (recovery blade)
14, 15 Conveying roller 16 Stirring roller 17 Photosensitive drum (image carrier)

Claims (7)

An image carrier on which a latent image is formed, a developer carrier that develops the latent image formed on the image carrier, and a developer supplier that supplies a developer having a specific polarity to the developer carrier And a developing device that performs reversal development by applying a developing bias of a specific polarity and value to the developer carrying member,
A bias supply means for applying a superimposed bias in which an AC bias is superimposed on a DC bias on the developer supply body;
The superposition bias is
For negative developer,
The relationship between the maximum peak value (Vp ⁺ ) of the positive electrode and the developing bias value (Vdev) is 50 V ≦ Vp ⁺ −Vdev ≦ 250 V
The relationship between the maximum peak value (Vp ⁻ ) of the negative electrode and the developing bias value (Vdev) is −50V ≧ Vp ⁻⁻ Vdev ≧ −450V,
[(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≦ 0V
For positive developer,
The relationship between the maximum peak value (Vp ⁺ ) of the positive electrode and the developing bias value (Vdev) is −50V ≧ Vp ⁻⁻ Vdev ≧ −250V
The relationship between the maximum peak value (Vp ⁻ ) of the negative electrode and the developing bias value (Vdev) is 50V ≦ Vp ⁺ −Vdev ≦ 450V,
[(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≧ 0V
A developing device characterized by the above. An image carrier on which a latent image is formed; a developer carrier that develops the latent image formed on the image carrier; and a developer supplier that supplies a negative developer to the developer carrier. A developing device comprising a superimposed bias applying means for applying a superimposed bias obtained by superimposing an alternating current bias on a direct current bias to the developer supply body,
The relationship between the maximum peak value (Vp ⁺ ) and the maximum peak value (Vp ⁻ ) of the negative electrode and the development bias value (Vdev) of the superimposed bias is 50 V ≦ Vp ⁺ −Vdev ≦ 250 V.
−50V ≧ Vp ⁻ −Vdev ≧ −450V
[(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≦ 0V
A developing device characterized by the above. An image carrier on which a latent image is formed; a developer carrier that develops the latent image formed on the image carrier; and a developer supplier that supplies a positive developer to the developer carrier. A developing device comprising a superimposed bias applying means for applying a superimposed bias obtained by superimposing an alternating current bias on a direct current bias to the developer supply body,
The relationship between the maximum peak value (Vp ⁺ ) and the maximum peak value (Vp ⁻ ) of the negative electrode and the bias value of the development bias value (Vdev) is −50V ≧ Vp ⁻⁻ Vdev ≧ −250V.
50V ≤ Vp ⁺ -Vdev ≤ 450V
[(Vp ⁺ + Vp ⁻ ) / 2] −Vdev ≧ 0V
A developing device characterized by the above.   The developing device according to claim 2, wherein a frequency of the superimposed bias is 50 to 500 Hz, preferably 50 Hz to 300 Hz.   5. The developing device according to claim 2, wherein the waveform of the AC component of the superimposed bias is a sine wave.   5. The developing device according to claim 2, wherein the waveform of the AC component of the superimposed bias is a rectangular wave, a triangular wave, a pulsating current, or a positive / negative asymmetric wave.   An image forming apparatus that develops an electrostatic latent image formed on an image carrier by supplying a developer to the image carrier and transfers the developed image onto a transfer material to form an image. An image forming apparatus comprising the developing device according to claim 1.

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