JPH08202144A - Developing device - Google Patents

Abstract

PURPOSE: To provide a developing device and an image forming device having a high developing performance and capable of developing with high density and high image quality without generating the fogging of a background part and ueven density at the trailing end of an image solid part even in the case of using toner of small particle size as developer, and also, without generating the mixture of colors at the time of superpose-developing multicolor toner images. CONSTITUTION: As for the developing device provided with a wire electrode 43 in a gap between an image carrier 10 and a developer carrier 41 and for scattering the toner under a vibration field so as to reversal-develop a latent image formed on the image carrier 10, the wire electrode 43 is constituted of one wire, and provided that X1 [mm] denotes the closest distance between the electrode 43 and the developer carrier 41, X2 [mm] denotes the closest distance between the electrode 43 and the image carrier 10, (d)[mm] denotes the diameter of the electrode 43, (h)[mm] denotes the height of a developer layer at the installation position of the electrode 43 before the electrode 43 is installed, X1 <=X2 and the electrode 43 is installed so as to satisfy h/2<=X1 +d, and X1 <=h.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device for developing a latent image on an image carrier by using an electrophotographic method, and more specifically, a developing device for developing a latent image on a gap between the image carrier and a developer carrier. The present invention relates to a developing device that is provided with a circular electrode and causes toner to fly under an oscillating electric field to reversely develop a latent image on the image carrier.

[0002]

2. Description of the Related Art Conventionally, as an image forming apparatus for developing a latent image on an image carrier by using an electrophotographic method to form a multicolor image, charging, exposing, developing and transferring steps are performed a plurality of times. There is an image forming apparatus that repeatedly forms a plurality of toner images on a transfer material to form a multicolor image. In this image forming apparatus, since the toner image is transferred onto the transfer material each time the development of each color is completed, it is necessary to provide a mechanism for holding the transfer material inside the apparatus, and there is a drawback that the apparatus becomes large. It was

On the other hand, the steps of charging, exposing and developing are repeated a plurality of times to superimpose and develop a plurality of toner images on the same image bearing member, and to collectively develop a plurality of toner images on the image bearing member. There is an image forming apparatus that forms a multicolor image by transferring the image onto a transfer material. Since this image forming apparatus employs a so-called overlay development / collective transfer method, there is no need to provide a mechanism for holding the transfer material inside the apparatus, and there is an advantage that the apparatus is downsized.

In such an image forming apparatus, for example, the developer layer on the developer carrier is not in contact with the image carrier, and a superimposed voltage of a direct current component and an alternating voltage is applied to the developer carrier. A developing device that develops a latent image on the image carrier by flying toner under an oscillating electric field is used, and since it is non-contact, the toner of the previous stage already adhered on the image carrier has a different color. It is preferable in that a large amount of toner is not mixed into the developing device that stores the toner in the subsequent stage.

However, in such non-contact development,
The developer layer on the developer carrier and the image carrier are not in contact with each other,
Since the toner is made to fly and the latent image on the image carrier is developed, there is a problem that it is difficult to reproduce delicate lines or dots or the difference in shade, and it is difficult to obtain high image quality.

Generally, in order to obtain a high quality image, it is effective to atomize the toner. However, when trying to atomize the toner in the non-contact development as described above, in order to obtain a sufficient image density. For this reason, it is necessary to increase the AC voltage applied to the developer transport body. On the other hand, when the AC voltage is increased, fog toner adheres to the background portion, and in the non-contact development as described above, the toner is atomized to obtain high image quality. It was difficult to get.

Therefore, for example, in Japanese Patent Laid-Open No. 59-223467, a wire-shaped control electrode for controlling the flying of toner is provided in the gap between the image carrier and the developer layer on the developer transport body, and the control is performed. A developing method is disclosed in which an alternating voltage is applied to at least one of an electrode and a developer transport body to form an oscillating electric field, and toner is ejected to perform development. It is described in the above-mentioned publication that fine particles can be used as the toner of the two-component developer, fogging is prevented, and clear high image quality can be obtained.

[0008]

However, even when the developing method described in the above publication is used, the position of the linear electrode, the height of the developer layer on the developer carrier, the height of the linear electrode, and the wire. Due to the relative diameter, sufficient developability may not be obtained, fogging may occur on the background, image density unevenness may occur at the trailing edge of the solid image, and high image quality may not always be obtained. was there.

Further, when the developing method or the developing device described in the above publication is used in the image forming apparatus adopting the superposition developing / collective transfer system, vibration is caused on the image carrier on which the toner image is already formed. There is also a problem that so-called color mixing occurs in which the toner of the subsequent stage is unnecessarily adhered to the toner image of the previous stage because the toner is caused to fly under the electric field for development.

The object of the present invention is to solve the above-mentioned problems, and even when a toner having a small particle size is used as a developer, the developability is high and fog does not occur even in the background portion, and at the rear end of the solid image portion. It is an object of the present invention to provide a developing device capable of performing good development, in which density unevenness does not occur, and color mixture does not occur even in superimposing development of multicolor toner images.

[0011]

In order to achieve the above object, a linear electrode is provided in a gap between an image carrier and a developer carrier, and toner is caused to fly under an oscillating electric field to cause the toner to fly on the image carrier. As a result of studying a developing device for reversal developing a latent image, the following has been found.

(1) Relative Position of the Linear Electrode and the Developer Layer on the Developer Conveying Body The linear electrode is located away from the surface of the developer layer on the developer conveying body and close to the image carrier. In this case, the developability is low.

When the closest distance between the linear electrode and the developer transport body is approximately equal to or slightly lower than the height of the developer on the developer transport body, that is, the linear electrode is the developer layer on the developer transport body. High developability when in contact with the surface.

When the linear electrode is completely buried inside the developer layer on the developer carrier, the developability is low.

(2) Position of the linear electrode in the moving direction of the developer carrier The developing property gradually decreases as the linear electrode moves away from the closest position of the developer carrier and the image carrier. The developability drops sharply at the point.

The rate of decrease in developability due to the linear electrode moving away from the closest position between the developer carrier and the image carrier is as follows.
The downstream side is slightly larger than the upstream side in the moving direction of the developer transport body from the closest position between the developer transport body and the image carrier.

(3) Regarding the Number of Linear Electrodes When one linear electrode is installed, the developability is greatly improved as compared with the case where no linear electrode is installed.

If a plurality of linear electrodes are provided, the developability will be further improved, but the rate of improvement in the developability will be small, and the developability of the linear electrodes other than the closest position between the developer carrier and the image carrier will be improved. Has a small contribution.

When a plurality of linear electrodes are installed, the image density unevenness at the rear end of the solid image portion is enlarged.

For the above purpose, the number of linear electrodes is one, and the closest distance between the linear electrodes and the developer carrier is X.
₁ [mm], the closest distance between the linear electrode and the image carrier is X ₂ , the diameter of the linear electrode is d [mm], before the linear electrode is installed at the linear electrode installation position. When the height of the developer layer is h [mm], X ₁ ≤X ₂ and h / 2 ≤X ₁ + d
And the linear electrode is installed so as to satisfy X ₁ ≦ h.

Further, for the above purpose, the number of the linear electrodes is one, the closest distance between the image carrier and the developer carrier is X ₀ [mm], and the image carrier and the developer are the same. The radius of curvature of the developer carrier near the closest position of the carrier is r [m
m], a straight line connecting the center of curvature of the developer carrying body near the closest position of the image carrying body and the developer carrying body to the closest position of the image carrying body and the developer carrying body, and the linear electrode The angle formed by the curvature center of the image carrier and the straight line connecting the centers of curvature of the developer carriers near the closest position of the image carrier and the developer carrier is θ [°], and the moving direction of the developer carrier is When the upstream side with respect to +,

[0022]

[Equation 2]

This is achieved by a developing device in which the linear electrodes are installed so as to satisfy the above condition.

[0024]

In the present invention, the number of linear electrodes is one.

That is, by using one linear electrode, the area of the strong oscillating electric field formed by the linear electrode is narrowed, and the area of the toner cloud formed by the oscillating electric field is narrowed. The area where the developing action is performed becomes narrower, and it is possible to prevent the image density unevenness seen at the rear end of the solid image portion.

Further, in the first invention, the closest distance between the linear electrode and the developer carrier is X ₁ [mm], the closest distance between the linear electrode and the image carrier is X ₂ , and the line is When the diameter of the linear electrode is d [mm] and the height of the developer layer before installing the linear electrode at the linear electrode installation position is h [mm], X
_The linear electrodes are installed so as to satisfy ₁ ≦ X ₂ , h / 2 ≦ X ₁ + d, and X ₁ ≦ h. That is, since the linear electrode is located closer to the developer carrying body than the image carrying body, and further located near the surface of the developer layer on the developer carrying body, the strong oscillating electric field generated by the linear electrode is stronger than the image carrying body. Since it is located on the side of the developer transport body and near the surface of the developer layer on the developer transport body, a strong oscillating electric field acts on the toner near the surface of the developer layer, and a stable toner cloud is formed. Sex is obtained.

In the second aspect of the invention, the closest distance between the image carrier and the developer carrier is X ₀ [mm], and the developer carrier near the closest position between the image carrier and the developer carrier. The radius of curvature of the body is r [mm], and the curvature center of the developer carrier near the closest position of the image carrier and the developer carrier and the closest position of the image carrier and the developer carrier. The angle formed by the connecting straight line, the center of curvature of the linear electrode, and the straight line connecting the center of curvature of the developer carrier near the closest position of the image carrier and the developer carrier is θ [°], and When the upstream side is the + direction with respect to the moving direction of the developer transport body,

[0028]

(Equation 3)

The linear electrodes are installed so as to satisfy the above condition.
That is, since the linear electrode is installed in the area where the developing action is performed even when the linear electrode is not provided, the strong oscillating electric field formed by the linear electrode and the toner cloud formed by the oscillating electric field perform the developing action. Formed in the area,
High developability can be obtained.

[0030]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the drawings.

FIG. 1 is a sectional view showing an example of a developing device according to the present invention. In the figure, 41 is a magnet body 42 fixed inside.
A developing roller which is a developer transporting body having 43, a linear electrode 43, a supply roller 45 which is a developer supply member, a control rod 46 which is a developer transporting amount control member, and a developer scraping member 47. A scraper, 48 is a stirring roller which is a developer stirring member, 49 is a casing of the developing device, 50 is a two-component developer composed of toner T and carrier C, 51 and 52 are power supplies as bias applying means, and 10 is conductive. A photosensitive drum, which is an image carrier having a photosensitive layer 12 formed on a substrate 11, X ₀ is the closest distance between the photosensitive drum 10 and the developing roller 41, X
₁ is the closest distance between the linear electrode 43 and the developing roller 41,
X ₂ is the closest distance between the linear electrode 43 and the photosensitive drum 10, d is the diameter of the linear electrode 43, and h is the position of the linear electrode 43 on the developing roller 41 before the linear electrode 43 is installed. Shows the height of the developer layer. The arrows in the figure indicate the rotation directions of the photosensitive drum 10 and the developing roller 41.

The developing roller 41 is made of non-magnetic and conductive metal such as aluminum or stainless steel and has a diameter of 5 to 5.
It is a cylinder of 30 [mm] and is processed so that the surface roughness is 1 to 30 [μm]. Inside the developing roller 41, a columnar magnet having 4 to 12 magnetic poles magnetized to N pole or S pole so that the magnetic field on the surface of the developing roller 41 becomes 500 to 1,200 [Gauss]. A body 42 is fixedly arranged, and the developing roller 41 is rotatable with respect to the magnet body 42.

The linear electrode 43 is made of a conductive metal such as tungsten or stainless steel, and is preferably a wire having an insulating coating on its surface. The photosensitive drum 10 and the developing roller 41 face each other. The developing roller 41 is provided in the gap in a direction perpendicular to the moving direction of the developing roller 41 in parallel with the developing roller 41.

The casing 49 is made of an insulating resin such as acrylic or polycarbonate. Inside the casing 49, a developing roller 41 including the fixed magnet body 42, a supply roller 45, a scraper 47 and a stirring roller 48 are arranged. ,
A restriction rod 46 is arranged at the outlet of the casing 49. Fixing pins are planted on the outer surfaces of both side plates of the casing 49, and one end of the linear electrode 43 is directly attached to the fixing pin and the other end thereof is attached via a tension spring.

A two-component developer 50 composed of toner T and carrier C is stored inside the casing 49. The two-component developer 50 is agitated and mixed by the agitating roller 48, and is supplied by the supply roller 45 and adheres onto the developing roller 41 to form a magnetic brush. The magnetic brush is conveyed while the conveying amount is regulated by the regulating rod 46 as the developing roller 41 rotates.

A superposed voltage of a direct current component and an alternating current component is applied to the developing roller 41 from the power source 51, and a direct current voltage is applied to the linear electrode 43 from the power source 52.
A strong oscillating electric field and a weak oscillating electric field are formed in a gap between the linear electrode 43 and the linear electrode 43 and a gap between the developing roller 41 and the photosensitive drum 10, respectively. The strong oscillating electric field causes the toner T to fly away from the carrier C and generate a toner cloud. The toner cloud is assisted by the weak oscillating electric field to fly toward the latent image on the photoconductor drum 10, and a toner image is formed on the photoconductor drum 10.

FIG. 2 is a block diagram showing an example of the image forming apparatus of the present invention. In the figure, 10 is a photoconductor drum which is an image carrier, 20 is a scorotron charger which is a charging unit, 25 is an image reading unit, 30 is an image writing unit using a laser beam which is an exposing unit, 40A, 40B and 40C. And 40D are the developing devices shown in FIG. 1 containing two-component developers of different colors, and 60 is a first paper feed roller 61 and a second paper feed roller.
A paper feeding unit having 62, a transfer corona charger 70 as a transfer unit, a separation corona charger 75 as a separation unit, a transport unit 80, a fixing unit 85, and a cleaning blade 91. A cleaning device, 95 represents an exposure lamp before charging. The arrow in the figure indicates the direction of rotation of the photosensitive drum 10.

In the basic operation of the multicolor image forming process according to this embodiment, first, a copy start command is sent from an operation unit (not shown) to a control unit (not shown), and the photosensitive drum 10 starts rotating. As the photosensitive drum 10 rotates, its peripheral surface is uniformly charged by the scorotron charger 20. Further, the image reading unit 25 converts the optical information from the document into an electric signal, and the electric signal is subjected to image processing and then input to the image writing unit 30. An image writing unit 30 irradiates a laser beam onto the charged photoconductor drum 10 to form a latent image on the photoconductor drum 10. The latent image on the photosensitive drum 10 is the developing device 40.
A, 40B, 40C, or 40D is used for development to form a toner image on the photosensitive drum 10.

Photoreceptor drum 10 on which the toner image is formed
Is again uniformly charged by the scorotron charger 20 and is irradiated with a laser beam by the image writing unit 30 to form the next latent image. The latent image on the photosensitive drum 10 is developed by any of the developing devices 40A, 40B, 40C or 40D, and the next toner image is superposed on the photosensitive drum 10.

In this embodiment, the latent image forming step as described above,
The developing process is repeated 4 times, and 4 times is applied on the photoconductor drum 10.
The color toner images are overlaid.

A recording sheet, which is a transfer material, is stored in the sheet feeding section 60, and is synchronized with the toner image superimposed on the photosensitive drum 10 by the first sheet feeding roller 61 and the second sheet feeding roller 62. And is delivered to the transfer corona charger 70. The toner images superposed on the photosensitive drum 10 are transferred onto the recording paper by the transfer corona charger 70, and the recording paper is separated from the photosensitive drum 10 by the separating corona charger 75. The recording paper onto which the toner image has been transferred is conveyed to the fixing unit 85 via the conveying unit 80, melted and pressure-fixed, and then discharged to the outside of the apparatus.

On the other hand, the toner remaining on the photosensitive drum 10 without being transferred to the recording paper is scraped off by a cleaning device 90 equipped with a cleaning blade 91 which is pressed onto the photosensitive drum 10 at a timing. After the residual potential is removed by the pre-charge exposure lamp 95, the next image forming process is started.

The requirements of the present invention will now be described.

In the present invention, the number of linear electrodes 43 is one.

By using one linear electrode 43, the area of the strong oscillating electric field formed by the linear electrode 43 is narrowed, and the area of the toner cloud formed by the oscillating electric field is narrowed. The area where the developing action is performed becomes narrower. The image density unevenness seen at the trailing edge of the solid image portion can be prevented by narrowing the area where the developing action is performed. Therefore, by using one linear electrode 43, the image density seen at the trailing edge portion of the image solid portion is reduced. It is possible to prevent unevenness.

When a plurality of linear electrodes 43 are provided, the space in which the toner cloud is formed becomes wider, so that the developability is improved, but the uneven image density seen at the rear end of the solid image portion is prevented. However, the image density unevenness increases in some cases.

Further, in the first invention, the closest distance between the linear electrode 43 and the developing roller 41 is X ₁ [mm], and the closest distance between the linear electrode 43 and the photosensitive drum 10 is X ₂ [mm]. When the diameter of the linear electrode 43 is d [mm] and the height of the developer layer before the linear electrode 43 at the linear electrode 43 installation position is h [mm], X ₁ ≦
The linear electrode 43 is installed so as to satisfy X ₂ and h / 2 ≦ X ₁ + d, and X ₁ ≦ h.

That is, since the linear electrode 43 is located closer to the developing roller 41 than the photosensitive drum 10 and is located near the surface of the developer layer on the developing roller 41, the strong oscillating electric field generated by the linear electrode 43 is also exposed. Since the toner is located closer to the developing roller 41 than the body drum 10 and closer to the surface of the developer layer on the developing roller 41, a strong oscillating electric field acts on the toner near the surface of the developer layer to form a stable toner cloud. And high developability is obtained.

When X ₁ > X ₂ , the strong oscillating electric field generated by the linear electrode 43 acts not on the developer on the developing roller but on the photosensitive drum 10 side, so that the developability is improved. In an image forming apparatus that does not improve and employs a so-called overlay development / collective transfer system, it causes disturbance of the toner image already developed on the photoconductor drum 10, and high image quality cannot be obtained.

When h <X ₁ , the oscillating electric field acting on the surface of the developer layer becomes weak and the formation of the toner cloud becomes insufficient. Therefore, in order to obtain sufficient developability, it is necessary to increase the AC voltage applied to the developing roller 41,
In this case, the fog toner in the image background portion, which has been a problem in the related art, and the color mixture at the time of superposition development of the multicolor toner images increase, so that high image quality cannot be obtained.

If X ₁ + d <h / 2, the linear electrode 43 is completely buried in the developer layer, so that the oscillating electric field generated by the linear electrode 43 is formed between the linear electrode 43 and the developing roller.
Since the oscillating electric field due to the linear electrode 43 does not act on the surface of the developer layer, the toner cloud is insufficiently generated, and sufficient developability cannot be obtained.

In the second invention, the closest distance between the photosensitive drum 10 and the developing roller 41 is X ₀ [mm], the radius of curvature of the developing roller 41 is r [mm], the center of curvature of the developing roller 41 and the photosensitive member. The angle formed by the straight line connecting the center of curvature of the drum 10, the center of curvature of the linear electrode 43, and the line connecting the center of curvature of the developing roller 41 is θ.
[°] and the upstream side with respect to the moving direction of the developing roller 41 is the + direction,

[0053]

[Equation 4]

The linear electrode 43 is installed so as to satisfy the above condition.

Next, description will be made with reference to FIG. FIG. 3 is an explanatory diagram of the development area before the linear electrodes are installed.

In the conventional non-contact magnetic brush developing method in which the linear electrode 43 is not installed, the developing action is largest at the closest position between the photosensitive drum 10 and the developing roller 41, and the developing roller is rotated from the closest position to the developing roller rotation direction. On the other hand, the developing action becomes smaller toward the upstream side and the downstream side, and eventually the developing action is not performed at all. This is the photosensitive drum 10 and the developing roller 41.
This is because the distance between

The developing action is the photoconductor drum 10 and the developing roller 41.
It was decided to measure the range from the closest position to the circumferential direction of the developing roller 41.

The measurement was carried out by the following method.

In the gap between the photoconductor drum 10 and the developing roller 41, a plate-like shield member is installed on the upstream side with respect to the rotation direction of the developing roller 41, which is sufficiently separated from the closest position between the photoconductor drum 10 and the developing roller 41. To do.

Gradually install the shielding member on the photosensitive drum.
10 and the developing roller 41 are moved toward the closest position, and the position and developing property of the shielding member at that time are measured.

The same measurement is performed from the downstream side with respect to the rotating direction of the developing roller 41.

As a result, the following was found.

(1) On the upstream side with respect to the rotation direction of the developing roller 41, when the shielding member is closer to the closest position between the photosensitive drum 10 and the developing roller 41 than the point Q on the developing roller 41 in FIG. Begins to drop.

(2) On the downstream side with respect to the rotation direction of the developing roller 41, when the shielding member is closer to the closest position between the photosensitive drum 10 and the developing roller 41 than the point Q'on the developing roller in FIG. Begins to drop.

The distance from the points Q and Q'to the photosensitive drum 10 and the closest distance X between the photosensitive drum 10 and the developing roller 41.
Examining the relationship of ₀ , it was found to be 1.2 times and 1.1 times, respectively.

Therefore, P is the closest contact point on the developing roller 41 at the closest position between the photosensitive drum 10 and the developing roller 41, and a straight line connecting P and the rotation center of the developing roller 41, and Q and the developing roller 41.
The angle formed by the straight line connecting the center of rotation of .alpha. [. Degree.] And the line formed by the line connecting P and the center of rotation of the developing roller 41 with Q'and the line connecting the center of rotation of developing roller 41 are .alpha. '[. Degree.]. Assuming that the upstream side with respect to the moving direction of the developing roller 41 is the + direction, the radius of the photosensitive drum is sufficiently larger than the radius of the developing roller, and the surface of the photosensitive drum is a flat surface,

[0067]

(Equation 5)

It can be seen that, the developing action is performed in the region represented by this.

In the present invention, since the linear electrode 43 is installed in the area represented by α and α ′, the strong oscillating electric field generated by the linear electrode 43 and the toner cloud formed by the oscillating electric field are set. Can be formed in the area where the developing action is performed, so that high developability can be obtained. When the linear electrodes 43 are provided outside α and α ′, the toner cloud is formed outside the region where the developing action is performed, so that sufficient developability cannot be obtained.

Various combinations of bias voltages applied to the developing roller 41 and the linear electrode 43 are conceivable. For the developing roller 41, a superimposed voltage of a direct current component and an alternating current component is applied to the linear electrode.
It is preferable to apply a DC voltage to 43. For example, when reversal development using a negatively charged photosensitive drum 10 and a developer of negatively charged toner is performed, the photosensitive member is, for example, −80.
Assuming that the developing roller 41 is charged to 0 [V], the developing roller 41 receives a DC bias voltage of -700 [V] and a frequency of 5 to 20 [KH].
z] is applied a superimposed voltage of AC bias voltage of 600-2000 [Vpp] between peaks, and -700 [V] is applied to the linear electrode 43.
(DC bias voltage applied to developing roller 41) to 0
A DC bias voltage of V, preferably 0 [V] is applied.

When the closest distance between the photoconductor drum 10 and the developing roller 41 is 0.2 to 1 [mm], the height h of the developer layer before installing the linear electrode 43 is 0.1 to 0.5 [mm], The closest distance X ₁ between the roller 41 and the linear electrode 43 is 0.05 to 0.35 [mm], and the closest distance X ₂ between the linear electrode 43 and the photosensitive drum 10 is 0.13 to 0.4 [m].
m], and the diameter d of the linear electrode 43 is preferably 0.02 to 0.25 [mm].

Next, other conditions relating to the present invention will be described.

The linear electrode 43 is a wire made of a conductive metal such as tungsten or stainless steel,
In order to prevent electric discharge generated between the linear electrode 43 and the developing roller 41, it is preferable to have a coating layer on the surface made of an insulating resin such as polyurethane or polyamide.

To attach the linear electrode 43 to the developing device, for example, one end is fixed to a fixing pin implanted on the outer surface of the casing 49 of the developing device, and the other end is implanted to the developing device casing via a tension spring. Fixed to the fixed pin. Positioning of the linear electrode 43 is performed by a positioning member fixed to both ends of the rotation shaft of the developing roller 41 so as not to hinder the rotation of the developing roller 41. The relative position of the linear electrode 43 with respect to the closest position of the roller 41 is determined. The erection tension of the linear electrode 43 is set by the tension spring, the size of which is determined by the material and diameter, the allowable load, the amount of deflection, the frequency of the AC voltage applied to the developing roller 41, and the linear electrode 43. It is determined in consideration of the natural frequency relationship of. For example, diameter 0.
02-0.25 [mm] tungsten wire, developing roller
When the length of the portion facing 41 is 200 to 350 [mm], the tension is suitably 200 to 1500 [g].

When the vibration of the linear electrode 43 poses a problem, a vibration damping member is used inside the positioning member. A material having high elasticity is preferable for the vibration isolation member.

The closest distance X ₀ between the photosensitive drum 10 and the developing roller 41 is preferably 0.2 to 1 [mm].
The developer layer on 41 is arranged in non-contact with the photosensitive drum 10.

Next, the toner T will be described.

Generally, when the average particle diameter dt of the toner T becomes large, the roughness of the image becomes noticeable. Normally 10 [book / mm]
In order to obtain the resolution of fine lines arranged at a certain pitch, there is no problem even if the average particle size dt is about 20 [μm], but the resolution is further improved and a clear high quality image faithfully reproducing the difference in shade is obtained. Therefore, it is preferable that the average particle diameter dt of the toner T is small. The average particle diameter dt of the toner T is 10 [μ
m] or less is preferable, and 4 to 6 [μm] is particularly preferable.

The average particle size dt of the toner T was obtained by adding about 1 mg of a sample and a surfactant to about 200 [ml] of an electrolytic aqueous solution and dispersing by an ultrasonic disperser for about 1 minute. Particle size distribution analyzer for suspension "Coulter Counter TA-II"
(Aperture 100 [μm] manufactured by Coulter, Inc.) is used to measure the volume average particle size distribution.

Further, when the average charge amount Qt of the toner T becomes large, it is necessary to increase the electric field required to fly the toner, and discharge easily occurs in the gap between the linear electrode 43 and the developing roller 41. On the other hand, if the average charge amount Qt of the toner T is too small, the toner T easily scatters from the developing device. The average charge amount Qt of the toner T is usually about 5 to 40 [μC / g] in absolute value.

The average charge amount Qt of the toner T is 2 [c
A conductive plate of m × 5 [cm] is made to face a developing roller having a diameter of 20 [mm] at a closest distance of 0.7 [mm], and the developing roller 41
The developer is supplied to the developing roller 41 and rotated at 200 [rpm], and the superposed voltage (for example, V
_{DC = -1000 [V], V} AC = 1500 [V], f AC = 8000 [H
z]) is applied to develop the toner T on the conductive plate,
Next, the conductive plate on which the toner T has been developed is connected to a Faraday cage, the toner T is blown off, and the amount of charge and the weight of the toner T blown off at this time are measured.

The toner T is, for example, a styrene resin,
Vinyl resins, acrylic resins, polyamide resins, silicone resins, polyester resins, fluororesins, epoxy resins, and other resins are mixed with carbon black or coloring components such as color pigments and color dyes and charge control agents, etc. It can be produced by a method similar to the method for producing toner particles. Further, if necessary, a fluidizing agent for increasing the fluidity of particles and a cleaning agent for cleaning the surface of the photosensitive drum 10 can be mixed. As the fluidizing agent, colloidal silica, silicon varnish, metal soap, nonionic surface active agent and the like can be used, and as the cleaning agent, fatty acid metal salt, organic group-substituted silicon, fluorine and other surface active agents can be used. it can.

In addition to the toner T, the two-component developer 50
The carrier C constituting the metal is a metal such as iron, chromium, nickel, cobalt, zinc or copper, or a compound or alloy thereof, for example, a ferromagnetic material such as γ-ferric oxide, chromium dioxide, manganese oxide or ferrite. Or spherical particles of paramagnetic material, or the surface of those magnetic material particles is coated with a resin such as styrene-based resin, vinyl-based resin, ethylene-based resin, acrylic resin, polyamide resin or polyester, or Particles obtained by forming spherical particles of resin or fatty acid wax dispersed and contained are used. The average particle size is 70 [μm] or less, preferably 30 to 50
Those having a size of about [μm] are preferably used.

The examples of the present invention will be described more specifically below.

[Developing device] Full color copying machine "Konica 9
Both side plates of casing 49 of four types of developing devices for accommodating yellow (Y), magenta (M), cyan (C), and black (K) developers for "028" (manufactured by Konica Corporation) are respectively modified. And the linear electrodes are stretched, and the developing devices 40A, 40
B, 40C and 40D.

[Image forming apparatus] Full-color copying machine "Koni
In place of the yellow (Y), magenta (M), cyan (C) and black (K) developing devices of "ca 9028" (manufactured by Konica), the developing devices 40A, 40B, 40C and 40D of the present invention are mounted. An image forming apparatus of the present invention is provided by separately providing a power source for applying a superimposed voltage of a DC component and an AC component to the developing roller of each developing device and a power source for applying a DC voltage to the linear electrodes. The timing for applying the voltage to each linear electrode 43 is the same as the timing for turning on the charger 20, and the timing for applying the voltage to the developing roller 41 is 0 for the charger 20.
When the rotation of the developing roller 41 is N and the rotation is OFF, only the DC component is applied, and when both the charger 20 and the developing roller 41 are ON, the superimposed voltage of the DC component and the AC component is applied.

(Experimental Example 1) The developing device is set to the conditions shown in Table 1, and the image is output in the single color mode while changing the closest distance X ₁ between the developing roller 41 and the linear electrode 43, and corresponds to the solid portion. The weight of the toner attached per unit area on the surface of the photosensitive drum 10 (hereinafter referred to as the primary attachment amount M / A [mg / c
m ² ]) was measured.

M / A satisfying M / A ≧ 0.68 [mg / cm ² ]
Was obtained, it was determined that sufficient developability was obtained.

[0089]

[Table 1]

The results are shown in FIG. FIG. 4 shows developability characteristics when the linear electrode 43 is installed.

H / 2-d = 0.3 / 2-0.096 = 0.054≈0.05 [mm] By installing the linear electrode 43 as described above, it is nearly twice as large as that in the case where the linear electrode 43 is not installed. Developability was obtained.

The developing property changes depending on the relative relationship between the height h of the developer layer on the developing roller 41 and the closest distance between the developing roller 41 and the linear electrode 43, and the surface of the developer layer contacts the linear electrode 43. The degree of being there was good. When X ₁ <h / 2-d and h <X ₁ , sufficient developability was not obtained.

Even when X ₁ <h / 2-d and h <X ₁ , sufficient developing property can be obtained by increasing the AC component applied to the developing roller 41. Fogging occurred and high image quality could not be obtained.

(Experimental Example 2) The experimental apparatus was set under the conditions shown in Table 2 and images were displayed in the monochromatic mode while changing the number of linear electrodes, and the relationship between the number of linear electrodes and M / A, linear The relationship between the number of electrodes and the density unevenness at the trailing edge of the solid image portion was evaluated.

[0095]

[Table 2]

When the number of linear electrodes is two, the center point of each curvature center is set, and when the number of linear electrodes is three, the center of curvature of the central linear electrode is set to θ to determine the base point on the side of the linear electrodes. And
The closest distance between the linear electrodes was set to 0.5 [mm].

With respect to the density unevenness at the trailing edge of the solid image portion, a change in the image density is used to discharge the vicinity of the edge portion of the trailing edge of the image solid portion, which is perpendicular to the sheet discharging direction, by using a printing accuracy evaluation device (manufactured by Yerman). The measurement was performed by scanning in the direction, and the following criteria were used for judgment.

FIGS. 5A and 5B are views for explaining the evaluation standard of the density unevenness at the trailing edge of the solid image portion.

<Measurement Method> Since the density unevenness at the rear end is more likely to occur in the halftone portion, it was decided to measure the halftone portion. 30.5 cm from the trailing edge of the halftone area toward the leading edge of the paper and 1 cm toward the trailing edge of the paper at 50.5
Measured at 100 [μm] intervals over a measurement area of [μm] * 50.5 [μm], and measure 1 [c near the center of the halftone part of the measurement part.
m] was calculated, and the distance from the measurement point to the edge portion where the density increased continuously by 3 points or more near the trailing edge portion of the halftone portion from the average value was defined as the width of the density unevenness at the trailing edge. .

<Evaluation Criteria> ◯: Density unevenness width of 1 [mm] or less Δ: Density unevenness width of 1 to 2 [mm] ×: Density unevenness width of 2 [mm] or more Number of linear electrodes and M The relationship of / A was evaluated by the same method as in Experimental Example 1. The results are shown in FIG. FIG. 6 is a characteristic diagram showing the relationship between the linear electrode and the developability, and Table 3 is a table showing the evaluation of density unevenness.

[0101]

[Table 3]

From FIG. 6, the developability is improved by increasing the number of linear electrodes 43. However, the ratio is not large.

From Table 3, it can be seen that when the number of the linear electrodes 43 is one, the density unevenness at the trailing edge of the solid image portion is the smallest.

(Experimental Example 3) The experimental apparatus was set under the conditions shown in Table 4, and the straight line connecting the center of the photosensitive drum 10 and the center of the developing roller 41 and the straight line connecting the center of the developing roller 41 and the center of the linear electrode 43 were While changing the formed angle θ and the closest distance X ₁ between the linear electrode 43 and the developing roller 41, the image is output in the single color mode,
The relationship between θ, X ₁ and M / A was evaluated.

The evaluation method was the same as in Experimental Example 1. FIG. 7 shows the results. FIG. 7 is a characteristic diagram showing the relationship between the angle θ and the developability.

[0106]

[Table 4]

[0107]

(Equation 6)

As described above, the developing property changes depending on θ,
When θ <−7 ° and 10 ° <θ, sufficient developability was not obtained.

Even in the case of θ <−7 ° and 10 ° <θ, sufficient developability can be obtained by increasing the AC voltage applied to the developing roller, but in that case, fog in the image background portion occurs. Occurred and high image quality was not obtained.

(Experimental Example 4) The experimental apparatus was set under the conditions shown in Table 5 and M / A was changed (M / A was changed by changing the AC voltage applied to the developing roller).
Images were printed in the single-color mode, and the number of toner particles attached per unit area of the surface of the photosensitive drum corresponding to M / A and the background portion (hereinafter referred to as fog toner number N [units / mm ² ]) was measured. The measurement of M / A was the same as in Experimental Example 1.

The number N of fog toner is 20 [units / mm ² ].
Is the allowable value.

[0112]

[Table 5]

The results are shown in FIG. FIG. 8 is a characteristic diagram showing the relationship between M / A and the number of fog toners.

As can be seen from FIG. 8, the same developability (M
/ A), the number N of fog toner is about 1/2, which is smaller when the linear electrode is installed than when the linear electrode is not installed.

[0115]

As described above, according to the developing device and the image forming apparatus of the present invention, the developability is high even when a toner having a small particle size is used as the developer, and the fog in the background portion and the trailing edge of the solid image portion are caused. It is possible to provide a developing device capable of performing good development in which density unevenness does not occur and color mixing does not occur even in superimposing development of multicolor toner images. Further, in a color image forming apparatus of a system in which a multicolor toner image is superposed and developed on a photosensitive drum and then transferred in a batch,
A high-quality multicolor image with high density and no color mixture can be obtained.

[Brief description of drawings]

FIG. 1 is a sectional view showing an example of a developing device according to the present invention.

FIG. 2 is a configuration diagram showing an example of an image forming apparatus of the present invention.

FIG. 3 is an explanatory diagram of a development area before installation of linear electrodes.

FIG. 4 is a developability characteristic diagram when a linear electrode is installed.

FIG. 5 is a diagram illustrating an evaluation standard of density unevenness at a trailing edge of a solid image portion.

FIG. 6 is a characteristic diagram showing the relationship between linear electrodes and developability.

FIG. 7 is a characteristic diagram showing a relationship between an angle θ and developability.

FIG. 8 is a characteristic diagram showing the relationship between M / A and the number of fog toners.

[Explanation of symbols]

 10 Photosensitive drum (image forming body) 11 Conductive substrate 12 Photosensitive layer 20 Scorotron charger 25 Image reading unit 30 Image writing unit 40A, 40B, 40C, 40D Developing device 41 Developing roller (developer carrier) 42 Magnet 43 Linear electrode 45 Supply roller 46 Control rod 47 Scraper 48 Stirring roller 49 Casing 50 Two-component developer 51, 52 Power supply

Claims (2)

[Claims] 1. A developing device in which a linear electrode is provided in a gap between an image carrier and a developer carrier, and toner is ejected under an oscillating electric field to reverse-develop a latent image on the image carrier. The number of the linear electrodes is 1, the closest distance between the linear electrodes and the developer carrier is X ₁ [mm], and the closest distance between the linear electrodes and the image carrier is X ₂ [. mm], the diameter of the linear electrode is d [mm], and the height of the developer layer before installing the linear electrode at the linear electrode installation position is h [mm], X ₁ ≤X _{2. The} developing device, wherein the linear electrode is installed so as to satisfy the condition 2 and h / 2 ≦ X ₁ + d, and the condition X ₁ ≦ h. 2. A developing device in which a linear electrode is provided in a gap between an image carrier and a developer carrier, and toner is ejected under an oscillating electric field to reverse-develop a latent image on the image carrier. The number of the linear electrodes is one, and the closest distance between the image carrier and the developer transport body is X ₀ [mm], near the closest position between the image carrier and the developer transport body. The radius of curvature of the developer carrying body is r [mm], the center of curvature of the developer carrying body near the closest position of the image carrying body and the developer carrying body, the image carrying body and the developer carrying body. A straight line connecting the center of curvature of the image carrier near the closest position, a center of curvature of the linear electrode, and a line connecting the center of curvature of the developer carrier near the closest position between the image carrier and the developer carrier. When the angle formed by and is θ [°] and the upstream side with respect to the moving direction of the developer transport body is the + direction. , [Equation 1] The developing device, wherein the linear electrode is installed so as to satisfy the above condition.