JPH11219023A - Developing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a ghost from being generated by electrostatically discharging a toner, by moving the toner on a toner carrier reciprocally between the toner carrier and a conductive member and by applying an AC voltage between the toner carrier and the conductive member. SOLUTION: This device is equipped with a conductive member 15 opposite to a toner roll 11. Then, a vibration voltage power source 16 applies the conductive member 15 with a vibration voltage containing an AC voltage component and a DC voltage component canceling a developing bias voltage to form an AC electric field between the conductive member 15 and the toner roll 11. Then, even highly electrostatically charged toner 12 of small particle size which is not peeled off from the toner roll 11 with a developing electric field is peeled off from the toner roll 11 with the AC electric field which is formed by such a way to move reciprocally between the conductive member 15 and the toner roll 11 and the electric charges of the toner 12 are taken and discharged by the conductive member 15 through being brought into contact with the conductive member 15.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for an electrophotographic image forming apparatus such as a copying machine or a printer.
The present invention relates to a developing device for visualizing an electrostatic latent image.

[0002]

2. Description of the Related Art Conventionally, an image bearing member carrying an electrostatic latent image is opposed in a predetermined developing area, carries charged toner on its surface, and circulates along a path passing through the developing area. 2. Description of the Related Art There is known a developing device that includes a toner carrying member that adheres toner to an electrostatic latent image in a development area to visualize the electrostatic latent image. As a method of charging the toner in such a developing device, generally, the fact that the toner is agitated or conveyed in the developing device is utilized, and the toner is frictionally applied with the toner in a conveying path or the like. A method has been used in which a substance that easily generates triboelectric charging is arranged, and the toner is charged by friction between the substance and the toner. There is a certain amount of charge distribution in the charge amount of the toner charged by friction, and the toner has a low charge amount with a small charge amount or a charge polarity opposite to the charge polarity of the entire toner. In many cases. The low-charged toner easily becomes a so-called toner cloud floating in the image forming apparatus apart from the toner carrier, and this toner cloud causes a failure of the image forming apparatus. Further, the opposite polarity toner is attracted to a background portion of the electrostatic latent image on the image carrier where toner is not originally attached, and causes so-called fog, which is a uniform stain on the background portion.

In order to prevent the occurrence of toner cloud or fogging, a charging device for releasing charge and positively applying charge to the toner has conventionally been added. Techniques for increasing the number of occupants have been proposed. FIG. 12 is a graph showing the distribution of the charge amount of the toner. The curves 101 and 102 shown in this figure show the charge amount distribution of the toner. The vertical axis of the graph is the number of toners, and the horizontal axis is the charge amount. However, the region where the charge amount is negative indicates the distribution of the opposite polarity toner.

[0004] The charge amount distribution of the toner before the charge is applied and the charge amount is increased is represented by a curve 101 on the left side of FIG. 12, and the toner is distributed on the left side of the vertical axis y. And a large amount of low-charge toner having a charge amount equal to or less than the charge amount indicated by a line l parallel to the vertical axis y. For this reason, toner cloud and fogging are likely to occur.

[0005] The distribution of the charge amount of the toner after the charge is applied by the charging device is represented by a curve 102 on the right side of FIG. 12. It becomes the distribution of the shape which moved. As a result, the inverse characteristic toner is eliminated, and the amount of low-charged toner is reduced, so that the occurrence of toner cloud and fogging is prevented.

[0006]

By the way, toner is
It has a certain particle size distribution, and small particle size toner
If the charge amount is equal to or more than a certain charge amount indicated by a line m parallel to the vertical axis y shown in FIG. 12, it becomes difficult to separate from the toner carrier, and the toner is not separated from the toner carrier surface in the developing area. As a countermeasure against fogging, charge is given to the toner,
When the charge distribution shown by the curve 101 shown in FIG. 12 shifts to the charge distribution shown by the curve 102, the ratio of the toner having the charge amount equal to or more than the charge amount shown by the line m parallel to the vertical axis y becomes The ratio of the toner having a small particle size and a high charge also increases.

When the proportion of the small-particle-size and highly-charged toner increases, the small-particle-size and highly-charged toner having the same shape as the image formed by the electrostatic latent image is formed on the surface of the toner carrier after passing through the developing area. Afterimages due to the toner are easily generated. Such an afterimage reaches the developing area again as the toner carrier circulates. As a result, a so-called ghost occurs in which an image having the same shape as that of the previously developed electrostatic latent image appears again on the image carrier.

The present invention has been made in view of the above circumstances, and has as its object to provide a developing device capable of preventing occurrence of a ghost.

[0009]

A developing device according to the present invention for achieving the above object is arranged so as to face an image carrier which carries an electrostatic latent image and moves in a predetermined direction in a predetermined developing area. A toner carrier that carries the charged toner on its surface and circulates in a predetermined moving direction along a transport path passing through the developing area, and transfers the toner on the toner carrier to the electrostatic carrier on the image carrier. A developing device for moving to a latent image and developing the electrostatic latent image, comprising: a conductive member disposed to face a surface of the toner carrier in the moving direction ahead of the developing area; And a static eliminator for neutralizing the toner by reciprocating the toner on the toner carrier between the toner carrier and the conductive member by applying a predetermined alternating voltage between the toner carrier and the conductive member. Features.

[0010]

Embodiments of the present invention will be described below. FIG. 1 is a view showing a first embodiment of the developing device of the present invention. The developing device 10 is provided with a toner roll 11 corresponding to a toner carrier according to the present invention. The toner roll 11 carries a toner 12 on the surface thereof, and is directed in the direction of an arrow a shown in FIG. Rotate to move. This toner roll 11 faces the surface of an image carrier 20 composed of a rotating roll that carries a positively charged electrostatic latent image on its surface and rotates and moves in the direction of arrow b (clockwise) in the figure on the left side in the figure. I do.

The toner 12 carried on the surface of the toner roll 11 is formed on the toner layer by the layer forming member 13 and is negatively charged by friction with the layer forming member 13. Further, in this embodiment, a constant voltage developing bias voltage is applied to the toner roll 11 by a constant voltage power supply 14. Then, a developing electric field is formed between the toner roll 11 and the image carrier 20, and the toner 12 on the toner roll 11 moves and adheres to the electrostatic latent image by the developing electric field, and the electrostatic latent image is developed. Is done.

The developing device 10 is provided with a flat conductive member 15 facing the toner roll 11 at a lower position in the figure, and an oscillating voltage power supply 16 is connected to the conductive member 15. Have been. The surface of the conductive member 15 facing the toner roll 11 is mirror-finished. An oscillating voltage including an AC voltage component and a DC voltage component for canceling the developing bias voltage is applied to the conductive member 15 by the oscillating voltage power supply 16, and an AC electric field is applied between the conductive member 15 and the toner roll 11. Is formed. Further, the distance between the conductive member 15 and the toner roll 11 and the strength of the AC voltage component are adjusted so that the maximum value of the strength of the AC electric field is greater than the strength of the developing electric field. . For this reason, even if the toner 12 has a small particle size and a high charge, which is not separated from the toner roll 11 by the developing electric field, the conductive member 15 and the toner roll 11
And an AC electric field formed between the toner roll 11 and
, Reciprocatingly move between the conductive member 15 and the toner roll 11, and by contacting the conductive member 15, the charge is deprived by the conductive member 15 and the charge is removed. Also,
The AC electric field formed between the conductive member 15 and the toner roll 11 causes a part of the toner 12 on the toner roll 11 to reciprocate. The collision produces an action of loosening the toner 12, so to speak. By these actions, as described later, when the toner 12 is scraped off from the toner roll 11, the toner 12 is sufficiently scraped off. Since the DC component of the vibration voltage applied to the conductive member 15 and the developing bias voltage cancel each other, an AC voltage is applied between the conductive member 15 and the toner roll 11. It will be. As a result, the toner 11 is applied to the conductive member 15.
The toner 12 can be efficiently reciprocated while preventing the toner 12 from adhering.

Further, in the developing device 10, a supply scraping roll 17 is provided ahead of the conductive member 15 in the rotational movement direction of the toner roll 11. The supply scraping roll 17 abuts on the toner roll 11 and rotates in the direction of the arrow c in the figure (counterclockwise), and at the contact position where the supply scraping roll 17 and the toner roll 11 abut, the supply scraping roll 17 is removed. Toner Roll 1 by Roll 17
The toner 12 carried on the surface of the toner roll 11 is scraped down to the lower side in the figure, and a new toner is applied to the surface of the toner roll 11 by the supply scraping roll 17 immediately downstream of the contacting position in the rotational movement direction of the toner roll 11. 12 are supplied. The toner 12 that is easily peeled off from the surface of the toner roll 11 due to the reciprocating motion between the conductive member 15 and the toner roll 11 is sufficiently scraped off from the surface of the toner roll 11 by the supply scraping roll 17. ,
Ghost generation is prevented.

Further, the toner 12 scraped off from the surface of the toner roll 11 by the supply scraping roll 17 is used.
However, if the toner drifts near the conductive member 15, the charge removal of the toner 12 on the toner roll 11 is hindered. For this reason, the developing device 10 is provided with a seal member 18 between the conductive member 15 and the supply scraping roll 17,
The seal member 18 prevents the toner 12 scraped off from the surface of the toner roll 11 by the supply scraping roll 17 from floating near the conductive member 15.

In the present embodiment, a type having a flat surface is adopted. However, the conductive member according to the present invention has a flat surface and a convex surface facing the toner carrier in order to prevent discharge from the end. Any material may be used as long as it has one of the surfaces. The type having a convex surface will be described later. FIG.
FIG. 4 is a view showing a second embodiment of the developing device of the present invention.

The developing device 30 is similar to the developing device 10 shown in FIG. 1 except that a charger 31 is provided so as to face the toner roll 11 in the upper part of FIG. Can be prevented. Charger 3
As described below with reference to FIG. 3, charge is applied to the toner to increase the charge amount, thereby preventing the occurrence of toner cloud and fogging.

After all, the developing device 30 shown in FIG. 2 can prevent any of toner cloud, fogging and ghost. FIG. 3 is a detailed view showing the charger. The charging device 31 includes a supply electrode 311 and a discharge electrode 312.
, A control electrode 313 having a mesh shape, the supply electrode 311 and the control electrode 313 are conductors, and the discharge electrode 312 is a resistor. In addition, the discharge electrode 312 includes
A supply voltage 314 is applied via the supply electrode 311, and a control voltage 315 is applied to the control electrode 313. An electric field is formed between the discharge electrode 312 and the limiting electrode 313 by a voltage difference between the supply voltage 314 and the control voltage 315, and electrons are emitted from the discharge electrode 312 by this electric field. The emitted electrons pass through the mesh of the control electrode 313 and move downward in the figure, hit the toner 12 carried on the toner roll 11, and the charge amount of the toner 12 increases. As a result, the opposite polarity toner and the low charge toner are eliminated, and the toner cloud and the fog are prevented.

The charger 31 includes a current controller 3
16 are provided, and are controlled so that the current from the supply electrode 311 is constant. As a result, the amount of charge released from the charger 31 becomes constant, and the toner 12
And the effect of preventing fogging and ghosting is stabilized. FIG. 4 is a view showing a third embodiment of the developing device of the present invention.

In the developing device 40, the conductive member 15
As described below, the rotation shaft 111 of the toner roll 11 is
The developing device 30 is the same as the developing device 30 shown in FIG. 2 except that the distance is fixed so as to keep the distance to the developing device 30 constant. The developing device 40 includes an insulating support member 41. The support member 41 is fixed to the conductive member 15 and rotatably holds the rotation shaft 111 of the toner roll 11. The distance between rotation shaft 111 and conductive member 15 is kept constant. By keeping the distance between the rotating shaft 111 and the conductive member 15 constant, the distance between the surface of the toner roll 11 and the surface of the conductive member 15 facing the surface is substantially constant. Is kept. as a result,
The intensity of the electric field formed between the toner roll 11 and the conductive member 15 is stabilized, and the toner is stably discharged.

FIG. 5 is a view showing a fourth embodiment of the developing device of the present invention. Of the components constituting the developing device 50, the same components as those constituting the developing device 30 shown in FIG. However, the illustration of the layer forming member is omitted in FIG. The developing device 50 includes a conductive roller 51 corresponding to the conductive member according to the present invention, which is an example of a conductive member having a convex surface facing the toner roll 11, and includes a holding member 52 and a spring. 53 are provided. The holding member 52 is an insulating member that holds the conductive roll 51 and abuts against the surface of the toner roll 11 to maintain a constant distance between the conductive roll 51 and the surface of the toner roll 11. It is provided at two places, a near side and a far side. Further, the spring 53 urges the rotating shaft 511 of the conductive roll 51 toward the toner roll 11. As the toner roll 11 rotates, the holding member 52 and the conductive roll 51 rotate in the direction of arrow d (clockwise) shown in FIG.

Further, the developing device 50 is provided with a toner removing member 54 in front of the supply scraping roll 17 in the rotational movement direction of the toner roll 11. The toner removing members 54 are provided at two positions on the near side and the far side in the figure corresponding to the holding members 52, and remove the toner supplied to the surface of the toner roll 11. FIG. 6 shows FIG.
The toner roll 11 and the conductive roll 51 shown in FIG.
FIG.

The holding member 52 is provided at an end of the conductive roll 51, and is in contact with a contact area 112 existing on the end of the toner roll 11 on the surface of the toner roll 11. The toner is removed from the contact area 112 by the toner removing member 54 shown in FIG. 5, so that the holding member 52 directly contacts the toner roll 11,
The distance between the toner roll 11 and the conductive roll 51 is kept constant. As a result, similarly to the case of the developing device 40 shown in FIG. 4, the intensity of the electric field formed between the toner roll 11 and the conductive roll 51 is stabilized, and the toner is stably discharged.

FIG. 7 is a view showing a developing device according to a fifth embodiment of the present invention. The developing device 60 includes the conductive roll 5
1. A scraping member 61 for scraping off the toner attached to 1.
And a developing device 50 shown in FIG. 5 except that a toner reservoir 62 for storing the scraped toner is provided. However, the vibration voltage power supply, the holding member, the spring, and the toner removing member are not shown in FIG.

The toner is rejected by reciprocating motion between the toner roll 11 and the conductive roll 51, but a part of the toner adheres to the surface of the conductive roll 51 and causes a reduction in the charge removing effect. . The scraping member 61 comes into contact with the surface of the conductive roll 51 at the bottom of FIG. 7 to scrape off the toner attached to the surface of the conductive roll 51 and maintain the charge eliminating effect.

FIG. 8 is a view showing a sixth embodiment of the developing device of the present invention. Of the components constituting the developing device 70, the same components as the components constituting the developing device 10 shown in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. The developing device is provided with a conductive roll 71 corresponding to the conductive member according to the present invention. The conductive roll 71 is dispersedly arranged on the peripheral surface of the conductive roll 71, abuts on the toner roll 11, and is carried on the toner roll 11 surface. A plurality of insulating protrusions 72 are provided to scrape off the toner and keep the gap between the conductive surface of the conductive roll 71 and the surface of the toner roll 11 constant.

The conductive roll 71 rotates in the direction of the arrow e (counterclockwise) shown in FIG. 8, and immediately downstream of the rotation direction of the toner roll 11 at the position where the insulating protrusion 72 contacts the toner roll 11. New toner is supplied to the surface of the toner roll 11. Further, at the position where the insulating protrusion 72 abuts on the toner roll, the toner reciprocates between the toner roll 11 and the conductive roll 71 to remove electricity, and is sufficiently scraped off by the insulating protrusion 72. As a result, generation of a ghost is prevented.

FIG. 9 is a view of the toner roll 11 and the conductive roll 71 shown in FIG. 8 as viewed from the lower side of FIG.
The insulating protrusions 72 are arranged in a zigzag pattern on the peripheral surface of the conductive roll 71, so that the toner can be efficiently scraped off from the surface of the toner roll 11. An insulating cap 73 is provided at an end of the conductive roll 71 to prevent discharge from the end of the conductive roll 71.

In each of the embodiments described above, a constant voltage is applied as a developing bias voltage, and an oscillating voltage is applied to a conductive member or the like. However, in the developing device of the present invention, an oscillating voltage is applied as a developing bias voltage. A constant voltage may be applied to the conductive member and the conductive roll. In each of the embodiments described above, the toner is negatively charged. However, in the developing device of the present invention, the toner may be positively charged.

In each of the embodiments described above, the supply and scraping of the toner is performed by a supply scraping roll or the like. The developing device of the present invention may further include a carrier surface scraping member that scrapes the toner carried on the toner carrier surface ahead of the conductive member in the moving direction of the toner carrier. What is necessary is just to have.

In each of the embodiments described above, the toner is carried on the toner roll by electrostatic force. However, in the developing device of the present invention, a magnetic toner is used and the toner is carried on the toner carrier by magnetic force. May be carried.

[0031]

The results of an experiment conducted using an apparatus similar to the developing apparatus shown in FIG. 7 will be described below. However, in the following experiment, an oscillating voltage was applied as the developing bias voltage,
A constant voltage was applied to the conductive roll. The experimental conditions are as follows.

The toner roll is made of aluminum which has been subjected to a surface sandblast treatment (Rz = 2.5 μm) and has a diameter of 3
0 mm and rotated at a peripheral speed of 130 mm / sec. As a developing bias voltage, an oscillating voltage having an AC component having a frequency of 2.0 kHz and an amplitude of 2.0 kV and a DC component of -350 V was applied. The supply scraping roll was made of urethane foam, had a diameter of 16 mm, and was rotated at a peripheral speed of 80 mm / sec.

The image carrier had a diameter of 80 mm, the surface of which was coated with an organic photoreceptor, and was rotated at a peripheral speed of 80 mm / sec. Further, the distance between the toner roll and the image carrier is 0.1 mm.
5 mm, the potential of the electrostatic latent image portion was -200 V, and the potential of the background portion was -500 V. The conductive roll was made of mirror-finished aluminum and had a diameter of 10 mm. The scraping member and the toner removing member are made of a polyester film.

The layer forming member was made of a SUS plate having a thickness of 0.2 mm, and urethane rubber having a thickness of 0.5 mm was adhered to a portion in contact with the toner. The charger is formed by applying a semiconductive glass on a ceramic substrate to form a discharge electrode, and securing a space between the discharge electrode and 75 μm thick polyimide so that a hole having a diameter of 100 μm has an aperture ratio of about 15%. A SUS control electrode having a thickness of 20 μm was used. The distance between the charger and the toner roll is 3mm
And

As the toner, a polyester toner having an average particle diameter of about 7 μm was used, and was negatively charged. In each of the following experiments, an experiment was performed by incorporating the developing device into a copying machine, and an image developed by the developing device was fixed on copy paper. Printing was performed using a printing pattern in which a halftone character "H" followed by a uniform solid image. Unless otherwise specified, the experiment was performed by removing the scraping member and removing the current control unit of the charger.

First, as a first comparative example, printing was performed without applying a voltage to the charger and removing the conductive member.
FIG. 10 is a diagram schematically showing a printing result. In this figure, an image fixed on the copy paper 80 is shown.
An arrow f direction shown in the figure is a direction corresponding to the rotation direction of the image carrier. A ghost 83, which has the same shape as the character 81 and has a faint image, is generated on the solid image 82 one rotation of the toner roll behind the halftone character 81. Further, fogging occurred in the background portion 84.

When the toner immediately after passing through the layer forming member was analyzed, the average charge amount was 6.1 μC / g, the reverse polarity toner was present at 7 wt%, and the average particle size of the toner was 7.2 μm. there were. Further, an image of the halftone character "H" is clearly left on the toner roll after passing through the developing area. When the toner forming this image is analyzed, the average charge amount is 10. The average particle diameter was 1 μC / g, and the average particle diameter was 6.5 μm.

Next, as a first embodiment, the distance between the toner roll and the conductive roll is set to 0.45 m by the holding member.
Attach a conductive roll as m, and add -3 to the conductive roll.
When printing was performed by applying a voltage of 50 V, fog occurred, but no ghost occurred. It was found that the image of the character "H" formed on the toner roll was blurred when passing between the conductive roll and the toner roll, and the toner was loosened.

As a second comparative example, the supply electrode of the charger was
A voltage of -500 V was applied to the control electrode at 1.5 kV, the potential of the background was changed from -500 V to -550 V, and the DC component of the developing bias voltage was-
When printing was performed by changing the voltage from 350 V to -400 V and removing the conductive roll, strong ghosts occurred but no fog occurred. When the toner immediately after passing between the charger and the toner roll was analyzed, the average charge amount was 10.5 μC / g, which shifted to a higher charge side than in the first comparative example and the first embodiment. I knew it was there. The reverse polarity toner was reduced to 0.7 wt%.
The average particle size of the toner was 7.3 μm. Further, an image of the halftone character "H" is clearly left on the toner roll after passing through the developing area. When the toner forming this image is analyzed, the average charge amount is 15. 7 μC / g, the average particle diameter was 5.9 μm, and the ratio of the small-particle-size and highly-charged toner was the same as in the first comparative example and the first comparative example.
It turned out that it is more than the case of an Example.

As a second embodiment, a conductive roll was attached to the second comparative example with the distance between the toner roll and the conductive roll set to 0.45 mm by a holding member, and a voltage of -400 V was applied to the conductive roll. As a result, no fogging occurred and the ghost became thin. As in the case of the first embodiment, the image of the character "H" formed on the toner roll has a blurred outline when passing between the conductive roll and the toner roll, indicating that the toner is loosened. Was.

In the experimental conditions of the second embodiment, the distance between the toner roll and the conductive roll was 0.45 mm to 0.4 mm.
When printing was carried out using the third embodiment changed to 4 mm, neither ghost nor fogging occurred. It can be seen that the image of the letter "H" formed on the toner roll has no contour when passing between the conductive roll and the toner roll, and the toner is loosened better than in the second embodiment. Was. The charge amount of the toner immediately after passing between the conductive roll and the toner roll was measured.
It was found that the charge was removed to μC / g. from this result,
It has been found that when the gap between the conductive roll and the toner roll is narrowed and the electric field formed between the conductive roll and the toner roll is increased, the ghost annihilation effect increases.

Printing was performed using the fourth embodiment in which the diameter of the supply scraping roll was changed from 16 mm to 15 mm and the fifth embodiment in which the diameter of the supply scraping roll was changed to 17 mm among the experimental conditions of the second embodiment. In the fourth embodiment, the ghost became dark, and in the fifth embodiment, the ghost disappeared. From this result, it was found that the ghost eliminating effect was enhanced by sufficiently scraping off the toner with the supply scraping roll.

Next, when a printing experiment was performed on 1,000 sheets using the fifth embodiment, no fogging and no ghost occurred until the end. In the experimental conditions of the fifth embodiment, the voltage applied to the conductive roll was changed from -400 V to -3.
A printing experiment was performed on 1,000 sheets of the sixth embodiment in which the voltage was changed to 00 V. When one or two sheets were printed, toner adhered to the conductive roll to cover the conductive roll, and the static elimination effect was reduced. As a result, No fogging occurred, but the ghost annihilation effect was weakened. Also,
Among the experimental conditions of the fifth embodiment, when a printing experiment was performed on 1,000 sheets for the seventh embodiment in which the voltage applied to the conductive roll was changed from -400 V to -500 V, the ghost annihilation effect gradually attenuated. After 1000 sheets, the sixth
It became equivalent to the case of the embodiment. This is probably because the opposite polarity toner gradually adhered to the conductive roll and gradually covered the conductive roll. From the results of these printing experiments, between the conductive roll and the toner roll,
It has been found that it is desirable to apply only an AC voltage having no DC component.

Next, using the fifth embodiment, a high-temperature, high-humidity environment (28 ° C., 85% RH) and a low-temperature, low-humidity environment (10 ° C., 30% RH) were used.
% RH) and a normal temperature and normal humidity environment (22 ° C. 55% RH), and a printing experiment was performed on 10,000 sheets while switching the operating environment every 2,000 sheets in this order. Fog was generated depending on the operating environment. Or a ghost has occurred. No ghost occurred when fogging occurred, and no fogging occurred when ghosting occurred. This is probably because the resistance of the resistor used in the charger changed according to the operating environment, and as a result, the amount of the opposite polarity toner and the level of the highly charged toner changed. Then, when a current control section was attached to the charger of the fifth embodiment and a printing experiment similar to the above was performed, the toner charge amount was stable, and no fogging or ghost was generated until the end. Further, when a scraping member was attached to the conductive roll of the fifth embodiment and a printing experiment similar to the above was performed,
No fogging or ghosting occurred until the end. This eliminates the toner from covering the conductive roll surface,
It is considered that the static elimination effect was maintained to the end.

In the above description, an experimental result using a print pattern in which a uniform solid image follows a halftone character "H" has been described. An experiment using a print pattern followed by a tone image was also performed. FIG. 11 is a diagram schematically illustrating a ghost generated in this case. 11 as well as FIG.
An image fixed on the copy paper 80 is shown, and the direction of arrow f shown in the figure is a direction corresponding to the rotation direction of the image carrier. A ghost 93 having the same shape as that of the character 91 and darkening the image occurs on the halftone image 92 one rotation of the toner roll behind the solid character 91. Further, as a result of the experiment, the same ghost annihilation effect as described above was observed.

The results of an experiment performed using an apparatus similar to the developing apparatus shown in FIG. 8 will be described below. The experimental conditions are as follows. The toner roll is made of aluminum that has been subjected to surface sand blasting (Rz = 2.5 μm),
The diameter was 30 mm, and it was rotated at a peripheral speed of 130 mm / sec. The frequency is 2.0 k as the developing bias voltage.
An AC component having an amplitude of 2.0 kV in Hz and -350 V
An oscillating voltage having a DC component of was applied.

As the conductive roll, a SUS thin plate was adhered to the surface of urethane foam, and the diameter was 16 mm.
And rotated at a peripheral speed of 80 mm / sec. The insulating protrusion is made of polyimide, has a diameter of 0.5 mm and a height of 0.5 mm.
2 mm and arranged at a pitch of 1 mm. The image carrier has a diameter of 80 mm, an organic photoreceptor is applied on the surface, and the peripheral speed is 80 mm.
It was rotated at mm / sec. The distance between the toner roll and the image carrier was 0.5 mm, the potential of the electrostatic latent image portion was -200 V, and the potential of the background portion was -500 V.

The layer forming member was made of a SUS plate having a thickness of 0.2 mm, and urethane rubber having a thickness of 0.5 mm was adhered to a portion in contact with the toner. The charger is formed by applying a semiconductive glass on a ceramic substrate to form a discharge electrode, and securing a space between the discharge electrode and 75 μm thick polyimide so that a hole having a diameter of 100 μm has an aperture ratio of about 15%. A SUS control electrode having a thickness of 20 μm was used. The distance between the charger and the toner roll is 3mm
And

The toner used was a polyester toner having an average particle size of about 7 μm, and was negatively charged. In the following experiments, printing was performed using a print pattern in which a uniform solid image followed by a halftone character "H" and a print pattern in which a uniform halftone image followed by a solid character "H" Was done. Unless otherwise specified, the experiment was performed with the current control unit of the charger removed.

First, as a third comparative example, when printing was performed by applying the same voltage as that of the toner roll to the conductive roll without applying a voltage to the charger, the solid color following the halftone character was printed. A weak ghost appeared on the image, and a strong ghost appeared on the halftone image following the solid character. As a fourth comparative example, a voltage of -1.5 kV was applied to the supply electrode of the charger, and a voltage of -500 V was applied to the control electrode.
V to -550 V, the DC component of the developing bias voltage was changed from -350 V to -400 V, and the same voltage as that of the toner roll was applied to the conductive roll to perform printing. On the solid image that follows,
Strong ghosts occurred on the halftone image following the solid characters.

Next, as an eighth example, when printing was performed by applying a voltage of -400 V to the conductive roll, no fog occurred and the ghost became inconspicuous. At this time, the supply of the toner onto the toner roll was stopped, the toner passing between the conductive roll and the toner roll was collected, and the charge amount was measured. As a result, it was found that the charge was removed to 1.9 μC / g. I understood.

Next, when a print test was performed on 1,000 sheets using the eighth embodiment, no fogging and no ghost occurred until the end. In the experimental conditions of the eighth embodiment, the voltage applied to the conductive roll was changed from -400 V to-
A printing experiment was performed on 1,000 sheets for the ninth embodiment in which the voltage was changed to 300 V and the tenth embodiment in which the voltage applied to the conductive roll was changed from -400 V to -500 V among the experimental conditions of the eighth embodiment. Experimental results similar to the experimental results in the sixth and seventh embodiments described above were obtained.

Further, using the eighth embodiment, a high-temperature and high-humidity environment (28 ° C., 85% RH) and a low-temperature, low-humidity environment (10 ° C.
0% RH) and normal temperature and normal humidity environment (22 ° C, 55% RH)
Under each of these conditions, a printing experiment was performed on 10,000 sheets while switching the operating environment for every 2,000 sheets in this order. As a result, fogging or ghosting occurred depending on the operating environment. A similar printing experiment was performed by attaching a current controller to the charger of the eighth embodiment. As a result, the toner charge amount was stabilized, and no fogging or ghost occurred until the end.

[0054]

As described above, according to the developing device of the present invention, ghost can be prevented.

[Brief description of the drawings]

FIG. 1 is a diagram showing a first embodiment of a developing device of the present invention.

FIG. 2 is a view showing a second embodiment of the developing device of the present invention.

FIG. 3 is a detailed view showing a charger.

FIG. 4 is a view showing a third embodiment of the developing device of the present invention.

FIG. 5 is a view showing a fourth embodiment of the developing device of the present invention.

6 is a view of the toner roll and the conductive roll shown in FIG. 5 as viewed from the left side of FIG.

FIG. 7 is a view showing a fifth embodiment of the developing device of the present invention.

FIG. 8 is a view showing a sixth embodiment of the developing device of the present invention.

9 is a view of the toner roll and the conductive roll shown in FIG. 8 as viewed from the lower side of FIG.

FIG. 10 is a schematic diagram illustrating a ghost that occurs on a solid image following a halftone character “H”.

FIG. 11 is a schematic diagram showing a ghost that occurs on a halftone image following a solid character “H”.

FIG. 12 is a graph showing a distribution of a charge amount of toner.

[Explanation of symbols]

 Reference Signs List 10, 30, 40, 50, 60, 70 Developing device 11 Toner roll 12 Toner 15 Conductive member 17 Supply scraping roll 18 Seal member 20 Image carrier 31 Charger 41 Support member 51 Conductive roll 52 Holding member 61 Scrapping Member 71 Conductive roll 72 Insulating protrusion

Claims (7)

[Claims] 1. An image bearing member, which carries an electrostatic latent image and moves in a predetermined direction, is disposed so as to face a predetermined developing region, and carries charged toner on the surface and passes through the developing region. A developing device that includes a toner carrier that circulates in a predetermined moving direction along a transport path, and moves the toner on the toner carrier to an electrostatic latent image on the image carrier to develop the electrostatic latent image The apparatus, further comprising: a conductive member disposed to face the toner carrier surface in the movement direction ahead of the developing region, wherein a predetermined AC voltage is applied between the toner carrier and the conductive member. A charge removing means for removing the toner by reciprocating the toner on the toner carrier between the toner carrier and the conductive member by applying the voltage. 2. A holding member that holds the conductive member and abuts on the surface of the toner carrier to maintain a distance between the conductive member and the surface of the toner carrier at a constant distance. The developing device according to claim 1. 3. The image forming apparatus according to claim 1, wherein the toner carrier is a rotating roll, and the conductive member is fixed so as to keep a constant distance from a rotating shaft of the rotating roll. Developing device. 4. The conductive member comprises a rotating roll,
2. The developing device according to claim 1, further comprising a member for scraping off the toner adhered to the rotating roll. 5. The developing device according to claim 1, wherein the conductive member has one of a flat surface and a convex surface facing the toner carrier. 6. The developing device according to claim 1, further comprising a carrier surface scraping member for scraping off the toner carried on the toner carrier surface, ahead of the conductive member in the movement direction. apparatus. 7. The conductive member comprises a rotating roll,
The rotating roll is dispersedly arranged on the peripheral surface of the rotating roll, abuts on the toner carrier surface, scrapes off the toner carried on the toner carrier surface, and removes the conductive surface of the rotating roll and the toner carrier. 2. The developing device according to claim 1, further comprising a plurality of insulating protrusions for maintaining a constant gap with the surface.