JPH0697350B2 - Electrophotographic development method - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dry two-component electrophotographic developing method suitable for a copying system using a photoconductor having a photoconductive layer containing amorphous silicon as a main component. .

[Description of Prior Art]

The method of developing an electrostatic latent image formed by electrophotography can be roughly classified into a dry developing method using colored fine powder called toner and a wet developing method using a liquid developer.

In the former dry development method, charged toner particles are attracted by electrostatic attraction and adhered to an electrostatic latent image having the opposite polarity to the toner to visualize the electrostatic latent image. Various methods are known until now. One of such known methods is a magnetic brush development method, which uses a two-component developer of toner and iron powder carrier, and mixes and stirs the toner and carrier to cause mutual friction. The content is such that the toner is charged by charging. The carrier used in the magnetic brush method is preferably one having a large specific surface area which is a surface area per unit weight, that is, one having a small particle size, but the iron powder carrier generally used is difficult to be miniaturized. However, if the size is reduced, the carrier becomes oxidized and becomes a carrier with deteriorated magnetism, which often causes the carrier to adhere to the charge holding member during development, resulting in poor quality of the developed image.

As a dry two-component developer which does not have such a problem, one using a ferrite carrier is reported in Japanese Patent Application No. 52-56536. And, ferrite carrier is easy to miniaturize due to the manufacturing method, the chemical composition is stable, and the magnetic characteristics are different from the case of iron powder carrier,
Since it is homogeneous up to the center of the tissue, the frictional electrification effect with the toner can be effectively maintained, the attracting force to the magnetic developing roller can be enhanced, and further, the adhesion of the carrier to the charge holding member can be prevented and the long-term It enables stable image development.

On the other hand, various types of electrophotographic photoconductors such as zinc oxide type and selenium type have been known, but recently, high sensitivity, high SN ratio (photocurrent / dark current) and photoresponsiveness have been obtained. Due to advantages such as speed and no pollution at the time of use, a photoconductor having a photoconductive layer composed of amorphous silicon (a-Si) is disclosed, for example, in German Patent Publication Nos. 2,746,967 and 2,855,715. It is proposed by the specification etc.

By the way, although the ferrite carrier has various advantages as described above, when it is used in a copying system using such an a-Si-based photoconductor, it is considered that the surface of the photoconductor drum is caused by friction with the carrier. As a result of research conducted by the present inventors, it has been found that there is a problem in that the scratches are generated in a relatively short period of time and white streaks are generated during copying to deteriorate the developed image quality.

[Object of the Invention]

An object of the present invention is to provide a dry two-component developing method using a ferrite carrier which can solve the above-mentioned problems.

That is, an object of the present invention is to provide a dry two-component developing method suitable for a copying system using an a-Si type photoreceptor.

Another object of the present invention is to provide a dry two-component developer that can provide excellent development image quality without "white streaks" in a copying system using an a-Si photoconductor.

[Structure of Invention]

In order to achieve the above-mentioned object, the inventors of the present invention have conducted extensive studies on the dry two-component developing method, and as a result, the ferrite carrier used in the dry two-component developing method is efficiently treated by the specific treatment. I got the knowledge that it can be achieved.

That is, the present invention relates to a copying system using a photoconductor having a photoconductive layer containing amorphous silicon as a main component,
The electrostatic latent image formed on the photoreceptor is developed with a two-component developer having a spherical ferrite carrier having a particle size of 30 to 100 μm, which is obtained by coating a spherical ferrite core material with a condensation-crosslinking type silicone resin, and a toner. And a dry two-component electrophotographic developing method.

In the present invention, the ferrite carrier used is represented by the general formula: MO · Fe ₂ O ₃ [wherein M is a divalent metal ion, for example, Mn ²⁺ , Fe ⁺ , Co ²⁺ , Ni ²⁺ , Cu ²⁺ , Zn ^2+, etc. ] The core material is a ferromagnetic ferrite having a composition represented by the following.

And as a typical example of the ferromagnetic ferrite,
For example, magnetite Fe ₃ O ₄ can be mentioned. Such a ferromagnetic ferrite that can be the core material preferably has a spherical shape regardless of whether or not it has irregularities on the surface.
The resin for coating the ferromagnetic ferrite core material is preferably a condensation-crosslinking type silicone resin in terms of adhesion to the magnetic ferrite spherical particles as the core material, strength of the coating, and frictional chargeability of the coating. Since the photoreceptor composed of amorphous silicon and the condensation-crosslinking silicone resin are charged to the same polarity, they repel electrostatically, and the spherical ferrite carrier coated with the condensation-crosslinking silicone resin adheres to the photoreceptor. It is difficult to do so, and because the material has silicon atoms as its constituent atoms and has good affinity, it is difficult to get scratches even when it is rubbed hard with the magnetic spikes of the carrier.

For the production of the resin-coated carrier used in the present invention,
Although all methods conventionally known as surface coating methods (coating methods) can be used, from the viewpoint of manufacturing efficiency Wurster
A type of circulating fluidized bed process is preferred. The production of the resin-coated carrier of the present invention by this method is an outline, under the condition of 85 to 90 ° C., the ferrite particles to be the core material are placed on a rotating disk, and a gas flow is generated from below the mesh in the peripheral part of the disk. Is introduced to float the ferrite particles and fluidize them in a gas flow, and the coating resin liquid is sprayed from the upper portion through a spray nozzle to coat and dry. The thickness of the film formed on the core material by coating the core material in the resin coating step is an important factor for obtaining the intended carrier suitable for the purpose of the present invention. , Usually 0.
Although it is set to 1 to 2.0 μ, it is desirable to set it to 0.5 to 1.0 μ.

〔Example〕

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples, but the present invention is not limited thereto.

Example A spherical ferrite powder with an average particle size of 100μ (made by TDK) was used as a core material, and a condensation-crosslinking type silicone resin (trade name SR
-2411 Toray Silicone Co., Ltd.) was used to obtain a coated carrier with a resin coating having an average film thickness of 0.8 μm by the Wurster type fluidized bed method.

On the other hand, 100 parts by weight of St-acrylic resin (product side SBM-700, manufactured by Sanyo Kasei Co., Ltd.) 2 parts by weight of charge control agent (product name: Spiron Black TRH, Hodogaya Chemical Co., Ltd.) 10 parts by weight of carbon (# 44 manufactured by Mitsubishi Kasei) The above materials were kneaded, pulverized and classified to obtain a classified product (toner) having an average particle size of 9μ. Hydrophobic silica (trade name: R-972, manufactured by Nippon Aerosil Co., Ltd.) was externally added to the classified product in an amount of 0.5% by weight to obtain a silica externally added toner.

Next, the coated carrier and the toner were mixed at a toner concentration of 3% by weight to prepare a two-component developer.

Using this developer, a copying system experimental machine equipped with an a-Si photosensitive drum was used, and the developer was replaced every 20,000 sheets to make 300,000 copies.

Even after 300,000 sheets, the copied image was good and white streaks did not occur. No scratch was observed on the surface of the photosensitive drum.

Furthermore, copying was performed up to 400,000 sheets, but the copied image was good, no white streaks occurred, and no scratches were observed on the surface of the photosensitive drum.

Comparative Example 1 A copy test was conducted in the same manner as in Example except that the core material used in Example was used as a carrier, but white stripes appeared on the copied image from about 100,000 sheets. Scratch-like scratches were observed in the form of strips on the photosensitive drum.

Comparative Example 2 A copy test was conducted in the same manner as in Example except that spherical carrier iron powder (trade name: Micro Shot 100, manufactured by Shinto Plater Co., Ltd.) having an average particle size of 100 μ was used as a carrier. White streaks occurred on the copied image. A band of scratches was observed on the drum.

Comparative Example 3 Carrier-specific irregular iron powder with an average particle size of 70μ (trade name TEFV
A copy test was conducted in the same manner as in the example except that (200/300 Nippon Steel Powder Co., Ltd.) was used, and white streaks appeared on the copied image from about 80,000 sheets. A band of scratches was observed on the drum.

Comparative Example 4 Wurster fluidization using spherical ferrite powder with an average particle size of 70μ (trade name CB-100DM Stuart Co., Ltd.) as a core material and a methyl methacrylate resin (trade name BR-85 Mitsubishi Rayon Co., Ltd.) as a coating material. The average film thickness of the resin coating by the bed method
I got a 0.8μ copy carrier.

Using this carrier and the same toner as used in the examples, a developer was prepared, and then 300,000 copies were made in the same manner as the examples. No white streak, which is thought to be due to abrasion of the photoconductor drum, was generated. However, when copying was continued up to 400,000 sheets, several white lines appeared on the copied image from about 350,000 sheets.
Band-shaped scratches were formed on the surface of the photoconductor drum up to 400,000 sheets.

Comparative Example 5 Other than using a selenium photosensitive drum as the photosensitive drum,
When a copy test was conducted in the same manner as in the example, scratches were generated on the surface of the selenium photosensitive drum at the number of copies of about 10,000 sheets, and scratches spread in a band shape at the number of copies of about 30,000 sheets. A large white streak was observed at.

Comparative Example 6 A copying test was conducted in the same manner as in the example except that an OPC photosensitive drum was used as the photosensitive drum. As a result, scratches occurred on the surface of the OPC photosensitive drum at about 20,000 copies, resulting in about 3 At the number of copies, the toner particles were fused to the scratches on the surface of the OPC photosensitive drum, and black streaks were observed on the copied image.

[Outline of Effects of Invention]

The present invention relates to a dry two-component development method using a spherical ferrite carrier coated with a condensation-crosslinking type silicone resin in a copying system using a photoreceptor having a photoconductive layer containing amorphous silicon (a-Si) as a main component. By carrying out development with, it is possible to obtain an excellent copy image with no occurrence of "white spots" even if a large number of copies are made.
In addition, the surface of the photoconductor has a remarkable effect such that it can be stably held at all times without any damage.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-59-222847 (JP, A) JP-A-58-150960 (JP, A) JP-A-58-121046 (JP, A) JP-A 52- 56536 (JP, A) JP 59-27904 (JP, B2)

Claims (1)

[Claims] 1. A particle size obtained by coating a spherical ferrite core material with a condensation crosslinking silicone resin in a copying system using a photoconductor having a photoconductive layer containing amorphous silicon as a main component.
A dry two-component electrophotographic developing method, which comprises developing the electrostatic latent image formed on the photoreceptor with a two-component developer having a spherical ferrite carrier of 30 to 100 μm and a toner.