JPS63157176A - Developing method for electrophotography - Google Patents

Abstract

PURPOSE:To deteriorate no image density, and also, to obtain an image having smooth and high picture quality by developing an electrostatic latent image on an image carrying body by separate developing devices using developers different in toner grain size distribution and having the same color. CONSTITUTION:A developing device 4 has a first developing part 4a and a second developing part 4b, and in the first developing part 4a, a toner whose grain size distribution is a small diameter is contained, and in the second developing part 4b, a toner whose grain size distribution is a large diameter is contained. The same latent image of a photosensitive drum 1 is developed by the first developing part 4a first and transferred, and subsequently, developed by the second developing part 4b, and can be superposed and transferred to the same transfer paper, as well, and on the other hand, development by both developing parts is superposed on the same latent image, and thereafter, can be transferred to the transfer paper, as well. In case when the transfer is repeated with regard to each developer, it is desirable that the development by small grain size toner is executed first, and thereafter, the development by large grain size toner is executed. By the large grain size toner, the image density is secured, and by the small grain size toner, a smooth image is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic developing method, and more particularly to a dry developing method.

In conventional dry electrophotography, the range of toner particle diameters that contribute to development is limited by the developing device used. When the toner particle size that contributes to development is large, as shown by curve A in FIG. 2, high image density can be obtained in high density areas, as shown by curve A in FIG. 3, but halftone development is difficult. It becomes difficult 3
1 tonality cannot be obtained.

When the toner particle size is small as shown by curve B in FIG.
The developability of intermediate tones is improved, the gradation is improved, the resolution is increased, and a smooth image can be obtained, but as shown by curve B in FIG. 3, high image density cannot be obtained.

It is an object of the present invention to provide a developing method which eliminates the above-mentioned conventional problems, does not reduce image density, and can obtain smooth Takako Prize images.

In order to achieve the above object, the present invention is characterized in that an electrostatic latent image on an image carrier is developed using developers of the same color having different toner particle size distributions using separate developing devices.

The structure and operation of the present invention will be explained in detail based on the embodiment shown in the drawings.

In FIG. 1, an image carrier 1, for example a photosensitive drum, is charged by a charger 2 and then exposed to light by an exposure device 3 to form an electrostatic latent image. The charged latent image is developed by a developing device! 4.

The developing device 4 has a first developing section 4a and a second developing section 4b, each containing a developer having the same color but different particle size distribution. 1 developing roller 5a, the second developing section 4b is connected to the second developing roller 5.
Developed by b.

The developed image is transferred to transfer paper.

It is also possible to first develop and transfer the same latent image on the photosensitive drum I in the first developing section 4a, and then develop it in the second developing section 4b and transfer it onto the same transfer paper in an overlapping manner. It is also possible to perform the development by the first developing section 4a and the developing by the second developing section 4b in an overlapping manner, and then transfer the image to the transfer paper.

When the first developing section 4a and the second developing section 4b perform overlapping development and post-transfer, the toner with a large particle size is easily cleaned, and when the toner with a small particle size is used as a developer before development, the toner with a large particle size becomes large. The toner image is cleaned and the image density decreases. Therefore, in this case, the curve B in FIG. 2 is applied to the first developing section 4a.
The second developing section 4b accommodates toner having a small diameter particle size distribution shown by curve A in FIG. 2, and the toner having a large particle size distribution shown by curve A in FIG. In FIG. 2, the horizontal axis represents the particle size, and the vertical axis represents the amount of toner. - For example, the first developing section 4a accommodates developing toner having a particle size of 7 microns, and the second developing section 4b contains developing toner having a particle size of 15 microns.

As the toner, it is preferable to use a one-component non-magnetic toner.

Even when the transfer is repeated for each developer, the smaller the toner particle size, the worse the transfer rate. Therefore, it is preferable to perform development with the small particle size toner first, and then perform development with the large particle size toner.

Image density is ensured by the large particle diameter toner, and a smooth image is obtained by the small particle diameter toner.

The result of development using a mixture of both developers is as shown by curve C in FIG. 3, and a well-balanced image can be obtained.

In FIG. 3, the horizontal axis represents original density, and the vertical axis represents image density.

The first developing section 4a and the second developing section 4b also have developing rollers 5a and 5.
It is preferable to control the developed toner layer by using a blade or the like so that it becomes a single layer. It is not necessary to greatly change the developing bias voltage in both the first developing section 4a and the second developing section 4b.

The present invention can also be applied to full-color development, in which case each color is developed repeatedly with a developer having a different particle size.

According to the present invention, it has become possible to obtain smooth images with high density and intermediate gradation.

[Brief explanation of the drawing]

FIG. 1 is a schematic explanatory diagram of the main parts of a copying machine according to the present invention, and FIG.
The figure is a diagram explaining the toner particle size distribution, and FIG. 3 is a diagram showing the relationship between document density and image density depending on the toner particle size.

Claims (1)

[Claims] 1. An electrophotographic developing method comprising developing an electrostatic latent image on an image bearing member using separate developing devices with developers of the same color having different toner particle size distributions.