JPH046951B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a developing device using a dry one-component developer.

Conventionally, many developing devices of this type use a developing sleeve. For example, as shown in U.S. Pat. Some conductive dispersion electrodes are constructed by dispersing conductive powder such as powder. In addition, as shown in Japanese Patent Application Laid-open No. 158197/1983 proposed by the present applicant, a conductive split electrode formed by arranging a plurality of conductors in the circumferential direction is provided on the surface of a non-magnetic insulating sleeve. There are some things.

However, with either method, it is difficult to provide a float bias effect that corresponds to the potential of the latent image on the photoreceptor. As a result, even if we try to obtain copies with good uniformity, reproducibility of low-contrast originals, sharpness, and gradation with little background smearing and high image density, there are currently no technical difficulties in maintaining high precision. This has not been realized due to the difficulties involved, lack of weather resistance and reliability over time, etc.

The present invention has been devised in view of these points, and has a simple configuration, and provides good image quality copies with good uniformity, good reproducibility of low-contrast originals, sharpness, and gradation, less background stains, and high density. The object of the present invention is to obtain a developing device capable of obtaining the following.

An embodiment of the present invention will be described based on the drawings.
First, a belt-shaped photoreceptor 1 is connected to a grounded conductive layer 2.
and a photosensitive layer 3 on the front side thereof, and has a support belt 4 made of Mylar or the like as a base, and is supported by rollers 5 and the like and rotates in the direction of the arrow. A developing sleeve 6 is provided on the photoreceptor 1 and is closely opposed to the photoreceptor 1 with a developing gap. The developing sleeve 6 is provided in a hopper 8 containing a high-resistance toner 7 as a dry one-component developer, and by conveying the toner 7 through its rotation, an electrostatic latent image 9 on the photoreceptor 1 is formed. It is developed as a toner image 10. In addition, the hopper 8 has a developing sleeve 6.
A doctor 11 for regulating the thickness of the upper seven toner layers is provided while being connected to the doctor power source _VD , and further,
A stirring blade 12 is provided.

Here, when the specific gravity of the toner 7 is 2 or less, the thin layer toner conveyed on the developing sleeve 6 is preferably 5 mg/cm ² or less per unit surface area of the developing sleeve 6, and the minute developing gap is 0.3 mm. The following are preferred. The means for holding this minute developing gap may be any known means, such as a pressure contact method (in this case, it is preferable that the photoreceptor 1 or the developing sleeve 6 has elasticity), or a spacer roller on both ends of the developing sleeve 6. There are various methods to use.
The method of charging the toner 7 may also be a known method, such as a charging method using friction between the doctor 11 and the toner 7 when the doctor 11 passes through it, a charging method using friction between the toner 7 and the developing sleeve 6, or a charge injection method.

Therefore, the feature of the present invention lies in the developing sleeve 6, which has a three-layer structure consisting of a first layer 13, a second layer 14, and a third layer 15 from the surface side. Here, the volume resistivity of the first layer 13 is
10 ¹⁴ Ωcm or less, and the second layer 14 below is composed of a conductive particle dispersion layer whose volume resistivity is larger than that of the first layer 13. , third layer 1
5 is a conductive layer that supports these, and is connected to a bias power supply _VB . That is, the first layer 13
serves as a float electrode layer, and as shown in FIG. 2, the potential on the surface of the developing sleeve 6 changes in response to the potential of the electrostatic latent image 9 on the photoreceptor 1. Furthermore, although the second layer 14 functions as a dielectric layer, the second layer 14 is not made of a complete insulating layer such as resin alone, but has conductive fine particles having a high volume resistivity dispersed therein. In order to prevent the image density from decreasing due to a decrease in the developing ability due to the dielectric thickness becoming too thick and the developing electric field strength decreasing, the second layer 14 is made to have an appropriate dielectric thickness based on (thickness)/(effective dielectric constant). This is to facilitate manufacturing to such an extent that the unevenness of the dielectric thickness does not significantly cause unevenness of the image. In any case, with such a second layer 14, even if the second layer 14 is relatively thick, such as 100 μm or more,
The first layer 13 can have an appropriate float bias effect, and conversely, this second layer 13 can have an appropriate float bias effect.
4 can be made thicker, so it is easy to reduce the influence of uneven coating on the image.

However, when copying was performed using the developing sleeve 6 with such a three-layer structure, the image density was high, there was little background smearing, and good gradation, sharpness, and reproducibility of low-contrast originals were obtained. This is the image obtained.

By the way, the toner 7 may be either a magnetic toner or a non-magnetic toner, but when using a magnetic toner, if a magnet 16 is provided in the developing sleeve 6 as shown in FIG. 1, toner conveyance will be improved. . At this time, either the developing sleeve 6 or the magnet 16 may be rotated. Further, if at least one of the first layer 13 and the second layer 14 of the developing sleeve 6 is formed as an elastic layer, the developing gap can be maintained as a uniform minute gap by press contact with the photoreceptor 1. And the first
When the average volume determined from the particle size distribution, volume distribution, etc. of the conductive particles dispersed in the layer 13 is ₁ , and the average volume of the conductive particles dispersed in the second layer 14 is ₂ , ₁ > ₂ , then the first
The layer 13 can be easily formed into a fine float electrode having an appropriate size, and the conductive fine particles of the second layer 14 can be uniformly dispersed. Furthermore, if part or all of the conductive particles dispersed in the first layer 13 are made of magnetic material, the synergistic effect of (float bias) + (developing sleeve applied bias) + (magnetic bias) will reduce background stains. can be made smaller.

As described above, the present invention provides at least three predetermined
By using a developing sleeve containing a layered structure,
Even if the second layer is relatively thick, the first layer can have a float bias effect depending on the potential of the latent image on the photoreceptor, which improves uniformity, reproducibility of low-contrast originals, and sharpness. , it is possible to obtain good image quality copies with good gradation, little background smudge, and high density.

[Brief explanation of drawings]

The drawings show one embodiment of the present invention, and FIG. 1 is a schematic longitudinal sectional side view, and FIGS. 2a and 2b are voltage characteristic diagrams. 6...Developing sleeve, 13...First layer, 14...
...Second layer, 15...Third layer.

Claims (1)

[Claims] 1 A first layer consisting of a conductive particle dispersion layer with a volume resistivity of 10 ¹⁴ Ωcm or less, and a volume resistivity of this first layer.
A developing device comprising: a developing sleeve comprising a second layer made of a conductive particle dispersion layer having a larger resistivity than the volume resistivity of the layer, and a third layer made of a conductive layer laminated on the third layer made of the conductive layer.