JPH08234557A - Developing device - Google Patents

Abstract

PURPOSE: To provide an improved developing device capable of obtaining a sufficient image density and maintaining stable image quality with less surface staining, afterimages, etc. CONSTITUTION: This developing device is provided with a developing roller 10 arranged to face a latent image carrier 2 and supplying toner to the latent image carrier in the facing part, a conductive toner supplying roller 12 which is arranged in contact with the periphery of the developing roller 10 and whose periphery is relatively moved int he contact part with the developing roller 10 and a power source 18 for applying a bias voltage between these rollers. Then, the toner excessively supplied from the toner supplying roller 12 to the developing roller 10 with electric force generated by the bias voltage is turned into a thin layer on the roller 10 by a triboelectrifying means 14 and the thin layer toner is uniformly electrified. In other words, a member for regulating the quantity of the toner on the toner supplying roller 12 is not provided in a part nearer to the upstream side in the rotational direction of the roller 12 than the contact part.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developing device,
More specifically, the present invention relates to a developing device applicable to a developing device using a one-component developer in an electrophotographic device, a printer, or the like.

[0002]

2. Description of the Related Art Conventionally, in a developing device such as an electrophotographic device, a developing roller for supplying a toner as a thin-layered one-component developer to a latent image carrier, and an independent rotating roller facing the developing roller There is a configuration having a toner replenishing roller for

In such a conventional developing device, a high resistance elastic member such as sponge (volume resistance 10 ¹⁰ Ωcm or more) is used as the material of the toner replenishing roller, but this is the function of the toner replenishing roller. The residual toner on the surface of the developing roller is not sufficiently scraped off efficiently, and if you try to improve the function by forcibly increasing the rotation speed of the developing roller, you will see an increase in drive torque and the occurrence of afterimages. Causes the problem of.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to sufficiently control the charge amount and adhesion amount of toner having an uneven charging polarity, which is excessively supplied to a developing roller by a toner replenishing roller to which a voltage is applied. It is an object of the present invention to provide an improved developing device capable of obtaining a high image density and maintaining stable image quality with less background stain and afterimage.

[0005]

In order to achieve the above object, the present invention is arranged so as to face a latent image carrier on which an electrostatic latent image is formed, and the latent image carrier is disposed at the facing portion. A developing roller that supplies toner to the developing roller; and a conductive toner replenishing roller that is disposed in contact with the peripheral surface of the developing roller and that moves relatively in the peripheral surface at the contact portion with the developing roller.
A power supply for applying a voltage between the developing roller and the toner replenishing roller, where the voltage of the developing roller is VB and the voltage of the toner replenishing roller is VR,
When the toner is positively charged, VB <VR is set. When the toner is negatively charged, VB> VR is set, and in the rotation direction of the developing roller, the power is set to be higher than that of the toner replenishing roller. It is arranged on the downstream side between the facing portion and the toner replenishing roller, and
The toner excessively supplied from the toner replenishing roller to the developing roller is thinned on the developing roller by an electric force generated by the potential difference between the toner and VR, and the thinned toner is evenly charged. A toner is supplied to the peripheral surface of the toner replenishing roller at a position upstream of the contact portion between the toner replenishing roller and the developing roller in the rotational direction of the toner replenishing roller, the frictional charging unit being provided. The developing device is not provided with a member for regulating the amount of toner on the toner replenishing roller between the toner supplying portion and the contact portion.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION An example of the present invention will be specifically described below.

In FIG. 1, reference numeral 2 indicates, for example, a photosensitive drum as a latent image carrier.

The photosensitive drum 2 is, for example, a photosensitive drum as a latent image carrier.

The photosensitive drum 2 is driven to rotate in a clockwise direction, passes through the developing device 4 while carrying an electrostatic latent image, and the electrostatic latent image is generated when passing through the developing device 4. The image is visualized.

The developing device 4 includes a toner hopper 6, an agitator 8 which is rotationally driven in the direction of an arrow, a developing roller 10 which is rotationally driven counterclockwise and is closely opposed to the photosensitive drum 2, and a developing roller 10. The toner replenishing roller 12 is in contact with and is driven to rotate counterclockwise. It should be noted that the static elimination brush 1 is provided on the peripheral surface of the developing roller 10.
6 and a thin layer regulation member 14 as a frictional charging means.

The developing roller 10 has the structure shown in FIG. 2, and the so-called rubber mug layer 10 is provided around the core material 101.
2, and the N pole and the S pole are alternately magnetized in this rubber mag layer. Further, a float electrode 104 in which carbon particles are dispersed in copper particles or epoxy resin is provided on the outer periphery of the rubber mug layer 102 via an adhesive layer 103 so as to appear in stripes on the surface.

On the other hand, the toner replenishing roller 12 is made of a conductive elastic material such as Bridgestone Polyurethane Foam, Everlight TS, Everlight Scott HR-5.
0, Everlight SX impregnated with conductive carbon such as Ketjen black, or dispersed and molded in a base material is used.

A power source 18 is connected between the developing roller 10 and the toner replenishing roller 12. The voltage applied to each roller by the power source 18 is set so as to comply with the following conditions according to the charging characteristics of the toner used.

That is, when the toner used is positively charged, VB <VR (where VB is the developing roller voltage, V
R is the toner supply roller voltage. ), And in the case of negative charging, VB> VR.

The operation state of the developing device thus constructed is as follows.

The one-component toner (magnetic toner or non-magnetic toner) stored in the toner hopper 6 is conveyed to a toner replenishing roller 12 by an agitator 8 as a developer conveying means, and is further conveyed by rotation of the toner replenishing roller 12. Then, the toner is charged by friction with the surface of the developing roller 10. Then, it adheres to the float electrode 104.

Next, the toner is regulated to a substantially single layer by the thinning regulating member 14 while rotating together with the developing roller 10, and the toner particles are not formed between the developing roller 10 and the thinning regulating member 14. Triboelectrically charged float electrode 10
4 is attached to the surface of the photosensitive drum 4 and is carried to the developing area in the vicinity of the photosensitive drum 2.

The toner layer thus conveyed to the developing area is
A part of the toner adheres to the electrostatic latent image and is carried away and removed from the developing roller 10. However, the remaining toner layer remains attached to the developing roller 10, and the charge is removed to remove the residual charge on the surface of the developing roller. After passing through the brush 16, the charge is removed and the original toner replenishing roller 12 is returned. Here, the charge removal brush 16 also has a function of removing the counter charge generated on the developing roller side due to the development of the charged toner attached to the float electrode 104.

In this way, the toner on the float electrode 104 which has returned to the toner replenishing roller 12 is stripped off by the toner replenishing roller 12 rotating in the direction opposite to the developing roller 10 and regulated in a thin layer. As a result, the surface of the developing roller 10 returns to the initial state.

Next, new toner is charged by the triboelectric charging between the developing roller 10 and the toner replenishing roller 12 and the float electrode 10
4 is attached and is conveyed toward the developing area, and the developing operation is carried out by repeating the above-described process.

Here, the relationship between the voltage VB to the developing roller 10 and the voltage VR to the toner replenishing roller 12 is changed by changing the polarity and voltage of the power source 18 variously.
Further, regarding the toner used, various developing characteristics were examined for each of the positively chargeable toner and the negatively chargeable toner.

1. Development characteristics when positively charged toner is used (a) When the toner replenishment property is replaced with the image density and evaluated in 1 to 5 ranks, as shown in FIG. 3, VB <V
It is considered that this is because the electric field between the toner replenishing roller and the developing roller under the condition of R accelerates the movement of the toner from the toner replenishing roller to the developing roller. Note that FIG. 3 shows the difference between the voltage VR and the voltage VB, that is, V
It is shown that the case where R-VB is approximately 200 V or higher is more preferable.

(B) An image pattern corresponding to the electrostatic latent image on the photosensitive drum is formed on the surface of the developing roller immediately after the development, and this image pattern is formed as an afterimage on the photosensitive drum at the next development. There is a phenomenon that it is transferred.

When the level of presence or absence of the afterimage was evaluated in the ranks of 1 to 5, it was found that the afterimage was hard to occur under the condition of VB <VR as shown in FIG. This is VB <V
Due to the electric field between the toner replenishing roller and the developing roller under the condition R, the toner is excessively supplied from the toner replenishing roller to the developing roller, and the image pattern on the developing roller that causes an afterimage immediately after development is eliminated. It is thought that this is due to the result. Note that FIG. 4 shows that it is more preferable if the difference between the voltage VR and the voltage VB, that is, VR-VB is approximately 300V.

(C) At the time of development, so-called background stains in which toner adheres to the background such as a character portion may occur. The presence or absence of this background stain is evaluated by ranks 1 to 5, and as shown in FIG. It was found that scumming is less likely to occur under the condition of VB <VR. This is because the toner excessively supplied from the toner replenishing roller to the developing roller by the electric field between the toner replenishing roller and the developing roller under the condition of VB <VR is developed on the developing roller by the frictional charging means and the toner replenishing roller and the developing roller. It is considered that this is because the insufficient triboelectric charging of the toner due to the roller is compensated for, and a toner having a sufficient charge amount and having a thin layer is obtained. Note that FIG. 5 shows that it is more preferable if the difference between the voltage VR and the voltage VB, that is, VR-VB is approximately 100 volts or more.

2. Development characteristics when negatively charged toner is used Toner replenishability (see FIG. 6), afterimage (see FIG. 7), and background stain (see FIG. 8) in the same manner as when positively charged toner is used
As a result of examining the above, it was found that good results were obtained under the condition of VB <VR. Thus, the developing performance can be improved by selecting the applied voltage and the polarity according to the charging characteristics of the toner used.

[0027]

According to the present invention, the toner replenishment property to the developing roller is improved, and the charge amount of the thinned toner that contributes to the development is improved to improve the image density and suppress the occurrence of afterimages. This is convenient because it can improve the soiling of the background.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a developing device according to the present invention.

FIG. 2 is a sectional view of a developing roller according to the present invention.

FIG. 3 is a graph showing development characteristics according to an embodiment of the present invention.

FIG. 4 is a graph showing development characteristics according to an embodiment of the present invention.

FIG. 5 is a graph showing development characteristics according to an embodiment of the present invention.

FIG. 6 is a graph showing development characteristics according to an embodiment of the present invention.

FIG. 7 is a graph showing development characteristics according to an embodiment of the present invention.

FIG. 8 is a graph showing development characteristics according to an embodiment of the present invention.

[Explanation of symbols]

 2 latent image carrier 4 developing device 10 developing roller 12 toner replenishing roller 14 friction charging means 18 power supply

Claims (1)

[Claims] 1. A developing roller which is arranged so as to face a latent image carrier on which an electrostatic latent image is formed, and which supplies toner to the latent image carrier at the facing portion, and a peripheral surface of the developing roller. For applying a voltage between the developing roller and the toner replenishing roller, and a conductive toner replenishing roller which is disposed in contact with the developing roller and whose peripheral surface relatively moves at the contact portion with the developing roller. Of the power source, the voltage of the developing roller is VB, and the voltage of the toner replenishing roller is VR,
When the toner is positively charged, VB <VR is set. When the toner is negatively charged, VB> VR is set, and in the rotation direction of the developing roller, the power is set to be higher than that of the toner supply roller. Toner excessively supplied from the toner replenishing roller to the developing roller by an electric force generated on the downstream side between the facing portion and the toner replenishing roller and generated by a potential difference between VB and VR. And a triboelectric charging means for uniformizing the charging of the thinned toner, and the toner replenishing roller rather than the contact portion between the toner replenishing roller and the developing roller. Of the toner replenishing roller upstream of the toner replenishing roller from the toner replenishing portion where the toner is replenished to the peripheral surface of the toner replenishing roller to the contact portion. A developing device not provided with members for restricting the amount of toner.