JP2003307916A - Developing device and image forming apparatus having the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a developing device which prevents a fogged image in a latent image non-existent part of the surface of a latent image carrier and low density of a developer image in a latent image present part and ensures satisfactory image formation over a long period of time and to provide an image forming apparatus having the developing device. <P>SOLUTION: In a development bias power source 20, an electric field intensity for the latent image present part of a photosensitive drum 1 in a second electric field is equal to or higher than 0.25 V/μm and equal to or lower than 5.0 V/μm in the direction in which the developer is caused to fly from a developing sleeve 6 to the photosensitive drum 1. Also, the absolute value of electric field intensity for the latent image non-existent part of the drum 1 in the second electric field is greater than the absolute value of electric field intensity for the latent image non-existent part of the drum 1 in a first electric field. Herein, in the second electric field, the developer is caused to fly from the developing sleeve 6 to only the latent image existent part of the latent image formation area of the surface of the drum 1 and developer is caused to fly to the developing sleeve 6 from only the latent image non-existent part of the latent image formation area. Meanwhile, in the first electric field, the developer is caused to fly from the developing sleeve 6 to the entire latent image formation area. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device used in an image forming apparatus such as a printer or a copying machine which employs an electrophotographic system or an electrostatic recording system, and an image forming apparatus including the developing device.

[0002]

2. Description of the Related Art In an image forming apparatus such as an electrophotographic copying machine or a printer, a document image or an input multi-valued image signal is formed on the surface of a latent image carrier uniformly charged by a charging means. By the image exposure corresponding to
An electrostatic latent image is formed, the electrostatic latent image is developed as a developer image by a developing device, the developer image is transferred to a recording material by a transfer means, and the developer image on the recording material is fixed by a fixing means. Is fixed on the recording material and output.

Various devices have been proposed for a developing device for carrying out dry one-component development, but as one of the most general methods, a developer carrier rotates while carrying a developer, The developer on the developer carrying member is frictionally charged to a predetermined potential when passing between the developer carrying member and a developer regulating member arranged in contact with or close to the developer carrying member. Along with this, an alternating electric field composed of an AC component and a DC component is formed between the developer carrying member and the latent image carrying member arranged in the vicinity of the developer carrying member so as to be a thin layer which is regulated to a predetermined layer thickness. There is a method in which the developing bias is applied and the potential difference between the developer carrying member and the latent image carrying member causes the developer to fly from the developer carrying member to the latent image carrying member for development.

However, in a developing device in which a thin layer of developer is formed on a developer carrying member and at the same time charged to a predetermined potential, it is difficult to uniformly charge the developer on the developer carrying member, so that the developer is locally charged. There is a problem on the image due to insufficient charging of the developer or excessive charging.

Therefore, in recent years, by forming a film of a resin containing particles having an effect of stabilizing the charge of the developer on the developer carrier, the charge of the developer on the developer carrier is made uniform. There is known a developing device that achieves high quality and performs good development.

As an example of this developing device, a latent image carrier and the surface of the developer carrier are subjected to reversal development in which a bright portion of the latent image carrier is used as a latent image portion to develop using a negatively charged developer. A case where the distance between the two is set to 200 μm will be described.

The developer carrying member has a resin layer containing particles having an effect of stabilizing the charging of the developer on the surface layer, and the developer on the developer carrying member is charged extremely uniformly.

The latent image carrier has a potential as shown in FIG. The vertical axis of FIG. 4 represents the magnitude of the potential.

First, the surface of the latent image carrier is uniformly charged to -700 V by the charging means (dark portion). A latent image is formed by irradiating the document image or image exposure corresponding to the input multi-valued image signal (light portion). The latent image potential in this example is -200V.

The developer carrying member near the latent image carrying member is
DC component -500V, AC component amplitude 800V, frequency 1
000 Hz is applied, and the surface potential of the developer carrying member is 1000 Hz between −900V and −100V.
It changes in the cycle. At this time, since the developer on the surface of the developer carrier is negatively charged, the force of flying and adhering to the side having a more positive potential acts.

In the shaded area in FIG. 4, the potential difference between the latent image carrier and the surface of the developer carrier (latent image carrier surface potential-developer carrier surface potential) is +700 V in the bright part and + in the dark part.
The electric field strength is ((potential difference between latent image bearing member and developer bearing member surface) / (distance between latent image bearing member and developer bearing member)), and +700/200 in the bright portion.
= + 3.5V / μm, + 200/200 = + in the dark area
It becomes 1.0 V / μm. Due to the force of the electric field, the developer on the developer carrier flies toward and adheres to the latent image carrier. At this time, a large amount of the developer adheres to the bright part where the electric field strength is stronger, but the developer also adheres to the dark part. Adhesion of a large amount of the developer to the dark portion is the adhesion of the developer to the white background portion (non-latent image portion) on the image, which causes a fog phenomenon.

Next, in the shaded area in the figure, the potential difference between the latent image carrier and the surface of the developer carrier (latent image carrier surface potential-developer carrier surface potential) is -100 V in the bright portion, The electric field strength is ((potential difference between the latent image bearing member and the surface of the developer bearing member) / (distance between the latent image bearing member and the surface of the developer bearing member)) in the dark portion, and in the bright portion. -100/2
00 = −0.5 V / μm, −600 / 200 = in the dark area
It becomes −3.0 V / μm. By the force of the electric field, the developer flies from the latent image carrier to the developer carrier and adheres thereto. As a result, the developer adhering to the dark portion at the shaded portion is pulled back to the developer carrier. At this time, a large amount of the developer is pulled back in the dark part where the electric field strength is strong, but a slight amount of the developer is also pulled back in the bright part.

By repeating the state with diagonal lines,
The developer adheres to the bright part (latent image part) and the developer does not adhere to the dark part (white background part), and a good image without fog is formed.

Generally, the greater the absolute value of the electric field strength, the more the developer is caused to fly, and the higher the electric field strength in the direction in which the developer is made to fly from the developer carrying member to the latent image carrying member, the density at the black portion is increased. If the electric field strength in the direction in which the developer flies from the latent image bearing member toward the developer bearing member is increased, the development can be performed without fog in the white background.

[0015]

However, in the developer carrier having a resin layer coated on the surface thereof, the developer in the developer layer formed on the surface is uniformly charged, while the charge of the developer is changed. Since the developer becomes lower overall and the developer is less likely to fly due to the electric field, the electric field strength for flying the developer from the developer carrying member toward the latent image carrying member must be relatively large. As a general means for increasing the electric field strength, it is effective to increase the AC component of the bias voltage applied to the developer carrying member.
When the C component is increased, the electric field strength that causes the developer to fly from the developer carrier in the bright portion toward the latent image carrier in the first electric field increases, and at the same time, from the latent image carrier in the bright portion in the second electric field. The intensity of the electric field that causes the developer to fly toward the developer carrying member also increases, and the developer that has adhered to the latent image on the latent image carrying member in the first electric field moves on the developer carrying member in the second electric field. However, there is a problem in that the density of the image is reduced as a result.

This phenomenon becomes more remarkable when the developing device is used for a long period of time and the developer is deteriorated to some extent.

Therefore, the present invention prevents a defective image of a fog image in the non-latent image portion of the latent image bearing member and a low density of the developer image in the latent image portion of the latent image bearing member, thereby providing a good image. An object of the present invention is to provide a developing device that can be provided for a long period of time and an image forming apparatus including the same.

[0018]

SUMMARY OF THE INVENTION According to the present application, the above object is to provide a developer carrier which is disposed in the vicinity of a latent image carrier which carries a latent image and which carries a developer, and the developer carrier. A latent image bearing member, and a voltage applying unit for applying an alternating voltage between the latent image bearing member and the latent image bearing member. By applying a developer from the developer bearing member to the latent image bearing member, the latent image is formed into a developer image. In the developing device visualized as above, the developer carrying member has a resin layer adhered to the surface thereof, and the voltage applying means is arranged alternately between the developer carrying member and the latent image carrying member. By applying a voltage, the first electric field and the second electric field are alternately and periodically generated between the developer carrier and the latent image carrier, and the first electric field is The developer is caused to fly from the developer carrier to the entire latent image formable region on the latent image carrier. The second electric field causes the developer to fly from the developer bearing member only to the latent image portion of the latent image formable region, and the developer from only the non-latent image portion of the latent image formable region. In the developing device configured to fly the developer toward the carrier, the voltage applying means has a field intensity with respect to the latent image portion of the latent image carrier in the second electric field from the developer carrier to the latent image carrier. 0.25 V / μm or more and 5.0 V / μm or less in the direction in which the developer flies to
In addition, the absolute value of the electric field strength with respect to the non-latent image portion of the latent image carrier in the second electric field is larger than the absolute value of the electric field strength with respect to the non-latent image portion of the latent image carrier in the first electric field. Achieved by the invention.

According to the present application, the above object can also be achieved by the second invention in which the image agent is an insulating one-component developer in the first invention.

Further, according to the present application, the above object is also achieved by the third invention in which the weight average particle diameter of the developer is 8 μm or less in the first invention or the second invention.

According to the present invention, the above-mentioned object is that in any one of the first to third inventions, the distance between the developer carrying member and the latent image carrying member is 230 μm or less. It is also achieved by the fourth invention.

Further, according to the present application, the above-mentioned object is an image forming apparatus for recording an image formed by a series of image forming processes on a recording material, which is one of the first to fourth inventions. It is also achieved by the fifth invention including the developing device.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the accompanying drawings.

(First Embodiment) First, a first embodiment of the present invention will be described with reference to FIGS.

FIG. 1 is a sectional view of an essential part of the image forming apparatus according to this embodiment.

As shown in FIG. 1, the image forming apparatus of the present embodiment comprises a photosensitive drum 1 which is a latent image carrier, around which a primary charger 2, an exposure device 10, a developing device 3 and a transfer device are provided. 4, a cleaning device 5 and the like are arranged.

Here, a series of image forming processes in the image forming apparatus will be briefly described.

The photosensitive drum 1 is rotating in the direction of arrow A, and its surface is uniformly charged to -700V by the primary charger 2. Thereafter, the exposure device 10 irradiates the original image or the image exposure corresponding to the image signal, so that the potential of the surface exposed to the image exposure becomes −200 V and an electrostatic latent image is formed. Then, after the electrostatic latent image is developed as a toner image by the developing device 3, it is transferred to a recording material (not shown) by the transfer device 4 and fixed on the recording material by a fixing device (not shown), and then an output image Is discharged as. on the other hand,
The cleaning device 5 removes residual toner adhering to the surface of the photosensitive drum 1 from the photosensitive drum 1 that has passed through the transfer device.

Next, regarding the developing device 3 of the present embodiment,
explain in detail.

The developing device 3 includes a developing sleeve 6 which is a developer carrier, a developer regulating member 7, a developer chamber 9 which contains the developer 8, a developing bias power source which is a voltage applying means including a DC power source section and an AC power source section. It is configured to have 20 or the like.

The developing device 3 configured as described above is activated and the developing sleeve 6 rotates in the direction of arrow B, so that in the developer chamber 9, the developers 8 or the developers 8 and the surface of the developing sleeve 6 are separated from each other. The electric charge is given to the developer 8 by the contact friction of the above and is applied to the surface of the developing sleeve 6.

Since the surface of the developing sleeve 6 is coated with a resin containing particles having the effect of stabilizing the charging of the developing agent, the developing agent applied onto the developing sleeve 6 is charged extremely uniformly. After that, the developer is applied to the developing sleeve 6
Thus, the toner is conveyed to the developing area formed between the photosensitive drum 1 and the developing sleeve 6. Then, in this developing area, the developer flies due to the action of the magnetic field by the magnet fixedly arranged in the developing sleeve 6 and the electric field due to the application of the developing bias voltage from the developing bias power source 20, and the electrostatic charge on the photosensitive drum 1 is caused. The latent image is developed and visualized.

In this embodiment, reversal development using a negatively charged one-component developer is used, and the distance d between the developer carrier and the latent image carrier is 200 μm.

The photosensitive drum 1 has a potential as shown in FIG. The vertical axis of FIG. 2 represents the magnitude of the potential.

First, the surface of the photosensitive drum 1 is uniformly charged to -700 V by the primary charger 2 (dark portion).
A latent image is formed by performing image exposure corresponding to the original image or the input multi-valued image signal here (bright portion). The latent image potential here is −100V. Between the photosensitive drum 1 and the developing sleeve 6, a DC component of -50
A bias voltage of 0 V, AC component amplitude 600 V, Duty 50%, frequency 1000 Hz is applied, and the surface potential of the developing sleeve 6 changes from −800 V to −200 V at a cycle of 1000 Hz. At this time, since the developer on the surface of the developing sleeve 6 is negatively charged, the force of flying and adhering to the side having a more positive potential acts. Here, the surface potential of the developing sleeve 6 is -8.
The state of 00V is the first electric field, and the state of the surface of the developing sleeve 6 is -200V is the second electric field.

In the first electric field, the potential difference between the photosensitive drum 1 and the surface of the developing sleeve 6 (photosensitive drum 1 surface potential-developing sleeve 6 surface potential) is +700 V in the light portion and + in the dark portion.
100 V, and the electric field strength ((the potential difference between the photosensitive drum 1 and the surface of the developing sleeve 6) / (the distance between the photosensitive drum 1 and the surface of the developing sleeve 6)) is +700/20 in the bright portion.
0 = + 3.5 V / μm, + 100/200 = + in the dark area
It becomes 0.5 V / μm. At this time, the developer flying from the developing sleeve 6 adheres to the bright portion, which is the black portion of the image, with sufficient electric field strength to be developed. On the other hand, even in a dark area which is a white background portion of the image, the developer flying from the developing sleeve 6 adheres due to the electric field strength of +0.5 V / μm.

In the second electric field, the potential difference between the photosensitive drum 1 and the surface of the developing sleeve 6 (photosensitive drum 1 surface potential-developing sleeve 6 surface potential) is +100 V in the light portion, and -in the dark portion.
It is 500 V, and the electric field strength ((potential difference between the photosensitive drum 1 and the surface of the developing sleeve 6) / (distance between the photosensitive drum 1 and the surface of the developing sleeve 6)) is +100/20 in the bright portion.
0 = + 0.5 V / μm, −500 / 200 = − in the dark area
It becomes 2.5 V / μm. At this time, the electric field strength in the bright portion, which is the black portion of the image, is the direction in which the developer flies from the developing sleeve 6 to the photosensitive drum 1, and its value is +0.2.
It is well above 5 V / μm. Therefore, the developer attached to the bright portion of the photosensitive drum 1 by the first electric field does not return to the developing sleeve 6 again, and further, the developer flies and adheres from the developing sleeve 6 toward the photosensitive drum 1, The development density in the bright area, which is the black area, increases.

The electric field strength in the dark area, which is the white background of the image, is the direction in which the developer flies from the photosensitive drum 1 toward the developing sleeve 6, and its value is sufficiently larger than when the first electric field is applied. . Therefore, the developer that has adhered to the dark portion, which is the white background portion of the image, in the first electric field is sufficiently developed.
Then, the development without fog is performed.

With the above settings, when an image was output, a good image having a high density could be output for a long period of time, and there was no image defect such as fog or reduction in density.

(Second Embodiment) Next, a second embodiment of the present invention will be described with reference to FIG. The description of the same configuration as the first embodiment described above will be omitted.

The structure of the developing device of this embodiment is the same as that of the first embodiment.

This embodiment also uses reversal development using a negatively charged one-component developer, and the distance between the developer carrier and the latent image carrier is 200 μm.

The surface of the latent image carrier is uniformly charged to -700 V by the charging means (dark portion). A latent image is formed by performing image exposure corresponding to the original image or the input multi-valued image signal here (bright portion). The latent image potential here is −100V. A bias voltage of DC component -500V, AC component amplitude 800V, Duty 35%, frequency 1000Hz is applied between the latent image carrier and the developer carrier, and the surface potential of the developer carrier is -1020V. From -220V is changing at a cycle of 1000Hz. At this time, since the developer on the surface of the developer carrier is negatively charged, the force of flying and adhering to the side having a more positive potential acts. here,
The state where the surface potential of the developer carrier is -1020V is the first electric field, and the state where the surface of the developer carrier is -220V is the second electric field.

In the first electric field, the potential difference between the latent image carrier and the surface of the developer carrier (latent image carrier surface potential-developer carrier surface potential) is +920 V in the light portion and +320 V in the dark portion.
And the electric field strength ((potential difference between the latent image carrier and the surface of the developer carrier) / (distance between the latent image carrier and the surface of the developer carrier)) is + 920/200 = + 4 in the bright portion. .6V /
μm, and + 320/200 = + 1.6 V / μm in the dark area. At this time, the developer flying from the developer carrier adheres to the bright portion, which is the black portion of the image, with sufficient electric field strength to be developed. On the other hand, even in a dark area which is a white background portion of the image, the developer flying from the developer carrier adheres due to the electric field strength of +1.6 V / μm.

Next, in the second electric field, the potential difference between the latent image carrier and the surface of the developer carrier (latent image carrier surface potential-developer carrier surface potential) is +120 V in the bright part and -4 in the dark part.
80 V, and the electric field strength ((potential difference between the latent image carrier and the surface of the developer carrier) / (distance between the latent image carrier and the surface of the developer carrier)) is + 120/200 = in the bright part. +0.
6V / μm, -480 / 200 = -2.4V / in the dark area
μm. At this time, the electric field strength in the bright portion, which is the black portion of the image, is the direction in which the developer flies from the developer carrying member to the latent image carrying member, and the value thereof is sufficiently above +0.25 V / μm. Therefore, the developer adhered to the bright portion of the latent image carrier by the first electric field does not return to the developer carrier again, and further, the developer flies from the developer carrier to the latent image carrier. Then, the development density of the bright portion, which is the black portion, increases.

The electric field strength in the dark area, which is the white background of the image, is the direction in which the developer flies from the latent image carrier to the developer carrier, and its value should be set when the first electric field is applied. Big enough. Therefore, the developer attached to the dark portion, which is the white background portion of the image, by the first electric field is sufficiently pulled back to the developer carrying member, and the development without fog is performed.

With the above settings, when an image is output, as in the first embodiment, a good image having a high density can be output for a long period of time, and an image defect such as a fog or a decrease in density does not occur. .

In the first and second embodiments described above, the distance between the developer carrier and the latent image carrier is 2
Although it is set to 00 μm, it can be set arbitrarily according to the characteristics of the developing device, and is preferably 230 μm or less.

[0049]

As described above, according to the first invention of the present application, the voltage applying means develops from the developer carrier to the entire latent image formable region on the latent image carrier. The first electric field that causes the developer to fly, and the developer that flies from the developer carrying member only toward the latent image portion of the latent image formable area, and only the non-latent image portion of the latent image formable area. Therefore, a voltage is applied between the latent image carrier and the developer carrier so that the second electric field for flying the developer toward the developer carrier is optimized and generated. It is possible to prevent a defective image of a fog image in the non-latent image portion of the latent image bearing member and a low density of the developer image in the latent image portion of the latent image bearing member, and provide a good image for a long period of time. it can.

According to the second invention of the present application,
The voltage applying unit includes a first electric field that causes the developer to fly from the developer carrier to the entire latent image formable region on the latent image carrier, and a latent image formable region from the developer carrier. Of the second electric field that causes the developer to fly only toward the latent image portion of the developer and that flies the developer toward the developer carrier from only the non-latent image portion of the latent image formable region. Since a voltage is applied between the latent image bearing member and the developer bearing member so as to generate, a defective image of a fog image in the non-latent image portion of the latent image bearing member or the latent image bearing member is generated. It is possible to prevent the density of the developer image in the latent image area of 1) from being reduced and to provide a good image for a long time.

Further, according to the third invention of the present application, the voltage applying means causes the developer to fly from the developer carrier to the entire latent image formable region on the latent image carrier. The developer is caused to fly from the developer carrier to only the latent image portion of the latent image formable region, and the developer carrier is formed only from the non-latent image portion of the latent image formable region. A voltage is applied between the latent image carrier and the developer carrier so that the second electric field that causes the developer to fly toward and is optimized is generated. It is possible to prevent a defective image of a fog image in the non-latent image portion and a low density of the developer image in the latent image portion of the latent image carrier, and provide a good image for a long period of time.

According to the fourth invention of the present application,
The voltage applying unit includes a first electric field that causes the developer to fly from the developer carrier to the entire latent image formable region on the latent image carrier, and a latent image formable region from the developer carrier. Of the second electric field that causes the developer to fly only toward the latent image portion of the developer and that flies the developer toward the developer carrier from only the non-latent image portion of the latent image formable region. Since a voltage is applied between the latent image bearing member and the developer bearing member so as to generate, a defective image of a fog image in the non-latent image portion of the latent image bearing member or the latent image bearing member is generated. It is possible to prevent the density of the developer image in the latent image area of 1) from being reduced and to provide a good image for a long time.

Further, according to the fifth invention of the present application, the voltage applying means causes the developer to fly from the developer carrier to the entire latent image formable region on the latent image carrier. The developer is caused to fly from the developer carrier to only the latent image portion of the latent image formable region, and the developer carrier is formed only from the non-latent image portion of the latent image formable region. A voltage is applied between the latent image carrier and the developer carrier so that the second electric field that causes the developer to fly toward and is optimized is generated. It is possible to prevent a defective image of a fog image in the non-latent image portion and a low density of the developer image in the latent image portion of the latent image carrier, and provide a good image for a long period of time.

[Brief description of drawings]

FIG. 1 is a schematic sectional view showing a schematic configuration of an image forming apparatus according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining the relationship between the potential of the latent image carrier and the potential of the developer carrier in the first embodiment of the present invention.

FIG. 3 is a diagram for explaining the relationship between the potential of the latent image carrier and the potential of the developer carrier in the second embodiment of the present invention.

FIG. 4 is a diagram for explaining a relationship between a potential of a latent image carrier and a potential of a developer carrier in the related art.

[Explanation of symbols]

1 Photosensitive drum (latent image carrier) 3 developing device 6 Development sleeve (developer carrier) 8 developer 20 Development bias power supply (voltage application means)

Claims (5)

[Claims] 1. A developer carrier for carrying a developer, which is disposed in the vicinity of a latent image carrier carrying a latent image, and an alternating voltage is applied between the developer carrier and the latent image carrier. A developing device, comprising: a voltage applying unit for applying a voltage, which visualizes the latent image as a developer image by applying a developer to the latent image carrier from the developer carrier. Is
With a resin layer deposited on the surface, the voltage applying means,
By applying an alternating voltage between the developer bearing member and the latent image bearing member, a first electric field and a second electric field are alternately and periodically applied between the developer bearing member and the latent image bearing member. The first electric field causes the developer to fly from the developer carrier to the entire latent image formable region on the latent image carrier, and the second electric field causes the developer to fly. The developer is caused to fly only from the developer bearing member to only the latent image portion of the latent image formable area, and is developed from only the non-latent image portion of the latent image formable area to the developer bearing body. In the developing device configured to fly the developer, the voltage application unit has a field strength with respect to the latent image portion of the latent image carrier in the second electric field, and a direction in which the developer flies from the developer carrier to the latent image carrier. Is 0.25 V / μm or more and 5.0 V / μm or less, and The developing device is characterized in that the absolute value of the electric field strength with respect to the non-latent image portion of the latent image carrier in the field is larger than the absolute value of the electric field strength with respect to the non-latent image portion of the latent image carrier in the first electric field. 2. The developing device according to claim 1, wherein the developer is an insulating one-component developer. 3. The developing device according to claim 1, wherein the weight average particle diameter of the developer is 8 μm or less. 4. The developing device according to claim 1, wherein the distance between the developer carrier and the latent image carrier is 230 μm or less. 5. An image forming apparatus for recording an image formed by a series of image forming processes on a recording material, comprising the developing device according to any one of claims 1 to 4. Image forming apparatus.