JPH0421858B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an electrophotographic method in which toner particles collected in a cleaning section are reused.

Conventionally, as an electrophotographic method, U.S. Patent No. 2297691
Specification of No. 42-23910 and Special Publication No. 1973
Various methods are described in Publication No. 24748, etc., but all of these methods apply a uniform charge to the photoconductive layer, and a light image corresponding to the original is irradiated onto the photoconductive layer. As a result, a latent image is formed, and then the latent image is developed with a black powder toner to become a visible image, and if necessary, it is transferred to paper or the like and permanently fixed by heat, pressure, etc.

The toner used in the process of developing a latent image has conventionally been made by dispersing a coloring agent such as carbon black in a binder resin such as polystyrene and pulverizing it into particles of about 1 to 30 μm. Such toner is usually mixed with a carrier such as glass beads, iron powder, or fur and used as a developer.

When copying is performed using a conventional two-component developer, all of the toner developed on the photoreceptor is not transferred to paper, and the remaining toner must be collected in a cleaning section. In some copying machines, the toner collected in the cleaning section is returned to the developing section and reused. However, the particle size distribution of the toner remaining without being transferred to the paper is smaller than that of the toner transferred to the paper, so as the number of copies increases, the toner particle size in the developing device becomes smaller. When such a phenomenon occurs, the amount of triboelectric charge per unit weight of toner increases over time, resulting in a decrease in image density and an increase in the coverage of toner on the carrier. Frictional electrification of the amount of frictional electrification between the toners also occurs, resulting in toner with a small amount of frictional electrification, which has the disadvantage that the toner is likely to adhere to the background.

An object of the present invention is to provide an electrophotographic method that solves the above problems.

A further object of the present invention is to provide an electrophotographic method that reuses toner collected in a cleaning section and that does not reduce image density.

Specifically, the present invention provides carrier particles, toner particles, and magnetic iron oxide particles having a particle size of 0.5 to 1μ.
The latent image on the photoconductor is developed with an electrophotographic developer containing 5wt% (based on toner particles), the toner particle image on the photoconductor is transferred, and the remaining toner particles on the photoconductor are removed from the cleaning section. The present invention relates to an electrophotographic method characterized in that the collected toner particles are collected by a developer, and the collected toner particles are returned to a developing section for reuse.

As a result, even if the triboelectric charge amount of the toner increases, the toner charge leaks through the magnetic material, suppressing the triboelectric charge amount and making it easier to develop the toner, reducing image density and preventing background stains. Ru. Furthermore, the effect of removing toner adhering to the surface of the photoreceptor can also be obtained.

As toner particles and carrier particles in the developer, conventionally known particles can be used.

The present invention will be explained below using examples. Parts are parts by weight.

Example 1 100 parts of polystyrene and 10 parts of carbon black were melt-kneaded in a roll mill for 20 minutes, cooled, coarsely pulverized in a cutter mill, and further finely pulverized in a supersonic jet mill to obtain a toner with an average particle size of 5 to 7μ. Ta.

To this toner, 1.5 wt % of magnetic material (iron oxide with a particle size of 0.1 to 1 μm) was externally added and mixed for 1 minute using a Henschel. Furthermore, apply toner to carrier iron powder by 5
% and prepared as a developer.

This developer was put into a Canon NP-8500 machine, which has a mechanism that returns the toner collected in the cleaning section to the developing section, and the machine prints 100,000 sheets continuously while returning the toner collected in the cleaning section to the developing section. When copying durability was carried out, the image density was stable at approximately 1.0, and the amount of triboelectric charge was also stable.

Comparative Example 1 A continuous copy durability test of 100,000 sheets was conducted under the same conditions as Example 1 except that no magnetic material was added externally.
After about 5,000 sheets, the frictional charge weight increased, and as a result, the initial image density of 1.5 decreased to 0.6, and toner deterioration was observed.

Comparative Example 2 A developer was prepared in the same manner as in Example 1 except that 1.5 wt% of cerium oxide was externally added to the toner.
A multi-sheet durability test was conducted in the same manner as in Example 1. When the number of sheets exceeds 20,000 sheets, the amount of frictional charging of the toner increases compared to the initial state, and the image density decreases.
It dropped to 0.7.

Example 2 A 100,000-sheet continuous copy durability test was carried out under the same conditions as in Example 1 except that the iron oxide content was changed to 4 wt%. As a result, there was little decrease in image density and the amount of triboelectric charge was stable.

Claims (1)

[Claims] 1. Carrier particles, toner particles, and particle size of 0.1 to
The latent image on the photoconductor is developed with an electrophotographic developer containing 0.5 to 5wt% (based on toner particles) of 1μ magnetic iron oxide particles, the toner particle image on the photoconductor is transferred, and the toner particle image on the photoconductor is transferred. An electrophotographic method characterized by collecting toner particles remaining after transfer in a cleaning section and returning the collected toner particles to a developing section for reuse.