JPH0850379A - Image forming device - Google Patents

Abstract

PURPOSE:To enhance solid black image developing ability by reducing the saturation magnetization of a carrier and making the average particle diameter small. CONSTITUTION:Ferrite particles having such characteristics as <=40emu/g saturation magnetization and >=10<9>OMEGAcm resistivity in an electric field of 1kV/cm and 1-30mum average particle diameter are used as a carrier and mixed with a toner. A magnetic brush is formed using the resultant developer and an electrostatic latent image formed on a photoconductive insulator is developed with the magnetic brush and fixed on recording paper to obtain a toner image.

Description

Detailed Description of the Invention

[0001]

[Outline] It is possible to increase the solid black developing ability by lowering the saturation magnetization value and decreasing the average particle diameter of the carrier, thereby increasing the resistance of the carrier and avoiding the characteristic deterioration due to toner filming.

[0002]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus using a long-life developer for developing a magnetic brush for electrophotography.

[0003]

BACKGROUND OF THE INVENTION Electrophotographic processes employed in copiers, laser printers and the like generally provide a uniform electrostatic charge on a photoconductive insulating layer and irradiate a light image on the insulating layer. By doing so, the electrostatic charge is partially removed to form an electrostatic latent image, and a fine powder called toner is attached to the remaining electrostatic charge to form a toner image that visualizes the latent image (called development). The toner image is fixed to recording paper (referred to as fixing) to obtain a printed matter.

The toner is a fine powder in which a colorant and a charge control agent are dispersed in a binder resin made of a natural or synthetic polymer substance, and is usually crushed to about 1 to 30 μm, such as iron powder and ferrite. It is mixed with a carrier substance (carrier) composed of magnetic particles to form a developer and is used for development. Although various materials have been used as carrier particles, iron powder, ferrite powder, and the like are most often used. These magnetic particles, as a developer mixed with toner, form a magnetic brush on a cylindrical sleeve in which a magnet is arranged, and electrostatically in contact with a photoconductive insulator, so-called photocon. Develop the latent image.

In this magnetic brush development, the electric resistance of the magnetic particles forming the developer is a very important factor in the development characteristics. When the resistance is low, the tips of the magnetic brush of the developer serve as the development electrode, and this development is performed. Due to the electrode effect, it has the ability to uniformly develop an electrostatic latent image having a large area. On the contrary, when the electric resistance is high, it is difficult to develop a large area, but it has a feature that it is excellent in line drawing, that is, line copy characteristics. Therefore, generally, the electrical resistance of the magnetic particles of the developer, that is, the carrier is lowered to some extent (for example, 10
⁴ to 10 ⁶ Ωcm) Used so that a large area electrostatic latent image can be uniformly developed.

[0006]

However, if the electric resistance of the carrier is too low, a problem of so-called carrier over, in which the carrier adheres to the photocon, occurs, so that the electric resistance cannot be lowered so much. Further, since the carrier is constantly mixed and stirred in the toner and the developing device, the toner filming development in which the toner is fused on the surface of the carrier occurs. Therefore, the solid black development characteristic depends only on the low electric resistance of the carrier. In the process described above, there is a problem that the black solid characteristics change with time due to the high resistance of the carrier due to the toner filming, and the life of the carrier becomes short.

Therefore, an object of the present invention is to eliminate the drawbacks of these conventional electrophotographic developers and to provide a developer composition having excellent black solid development characteristics and long life.

[0008]

In order to achieve the above object, the image forming apparatus of the present invention has an electric resistivity of 10 ⁹ Ωcm or more in an electric field of 1 kV / cm and a saturation magnetic susceptibility of 40 emu / g.
A magnetic brush is formed by using a developer mixed with toner with ferrite particles having the following characteristics and an average particle size of 1 to 30 μm as a carrier, and the magnetic brush forms a photoconductive insulator. The electrostatic latent image is developed to obtain a toner image to be fixed on the recording paper.

According to the present invention, when the solid black developing property of the developer depends on the low resistance of the carrier, the electric resistance changes due to toner filming, and the developing property deteriorates when used for a long time. In order to avoid it, the carrier has a high resistance and an excellent black solid development characteristic is achieved. That is, the solid black printing characteristics of the carrier of the developer according to the present invention (which has a high resistance) are not obtained by the developing electrode effect in the low resistance carrier, but ferrite having a small saturation magnetization and a small grain size is used for the carrier, By increasing the density of the tips of the magnetic brush and softly contacting them with the photo controller, the developing ability of the toner is enhanced and realized. Furthermore, in the developer of the present invention, by using a micro toner having a small particle diameter as the toner, it is possible to perform high-quality printing with excellent resolution.

In the present invention, the electric resistivity of the ferrite core is set to 10 ⁹ Ω · cm or more at an electric field strength of 1 kV / cm in order to avoid image change due to toner filming which is a problem when the resistance is low. And especially 1 kV
The resistance value under the condition of high electric field strength in / cm is important.
This is because the developing bias voltage is 100 V to 200 V between the sleeve and the photoconductive drum in the normal developing process.
Since about V is applied, considering the distance between the sleeve and the photocondrum (usually 1 to 2 mm), the electric resistance of the developer must be expressed as a resistance value at an electric field strength of about 1 kV / cm. is there.

The saturation magnetization value of ferrite is 40 emu.
The reason for this is that if the saturation magnetization is high, especially in the case of iron powder having a value of 200 to 300 emu / g, the tip of the magnetic brush is hard and soft touch development cannot be performed. In addition, even with ferrite of several tens of emu / g, depending on the magnetization and arrangement of the magnet in the sleeve, even if the developer is cut with the same blade gap, the height of the spike becomes abnormally high (swelling), resulting in a dense spike. Because you cannot get it. FIG.
Shows the relationship between the saturation magnetization value and the head height of the magnetic brush.
As described above, the developer 2 is supplied to the magnet roller 1, and the gap between the spike cutting blade 3 and the sleeve is G _B (0.9 mm,
FIG. 6 is a diagram showing the height h of the spike at the developing position as a function of the saturation magnetization value of the carrier when the tip of the developer is cut to 1.1 mm, 1.3 mm, and 1.5 mm). 1, if the saturation magnetization value is less 40 emu / g, Hotaka h is not throat no changes interval G _B and殆the doctor blade and the sleeve also in the developing position, indicating that the magnetic brush is closely There is.

Further, the particle size of the carrier is important because it is a major factor in determining the density of the magnetic brush and is also related to the toner replenishing ability for filling the electrostatic latent image with the toner. It exhibits excellent solid black printing characteristics, and in particular, in order to extend the life of the printing characteristics, the carrier particle size is 30μ.
m or less. Toner is usually 5-25μ
The particle size of m is used, but it is preferable to reduce the particle size of the toner as the particle size of the carrier is reduced. In particular, the particle size of substantially 1 to 10 μm is suitable in order to exhibit good resolution and good triboelectrification ability with the carrier. The toner having a particle size of substantially 1 to 10 μm as used herein refers to a toner that passes through a sieve having a mesh size of 10 μm and remains on the 1 μm sieve. Is not excluded.

The ferrite used in the present invention is generally represented by the general formula MFe as a magnetic oxide containing iron as a main metal.
It is represented by O ₂ or MFe ₂ O ₄ . Here, M represents a monovalent or divalent metal, and iron has a +3 oxidation state. M is nickel, manganese, magnesium, zinc,
One or more of iron and barium are included. The saturation magnetization value and electric resistance value of the ferrite particles can be adjusted by appropriately selecting the type and proportion of the metal M or changing the firing conditions.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION A ferrite carrier having the characteristics shown in Table 1 was used to prepare a developer in which a positively chargeable micro toner (particle size 1 to 10 μm) and an average particle size 5.8 μm) were combined. Then, as a result of performing a printing test with a laser printer adopting an electrophotographic method, a black solid printing characteristic with an optical density (OD) of 1.2 or more was obtained,
Moreover, even after printing 200,000 sheets, the resolution of 10 lines / mm or more, the O. D. It was confirmed that the solid black printability of 1.1 or more was maintained, and the background part had less background stain.

Table 1 Ferrite composition Magnesium Zinc ferrite (MgZnFe ₄ O ₈ ) Electrical resistivity 5 × 10 ⁹ Ω · cm (electric field strength 1 kV / cm) Saturation magnetization 38 emu / g Particle size 1 to 25 μm

[0016]

As is clear from the above description, the present invention provides an image forming apparatus which exhibits excellent effects such as a developer having excellent black solid development characteristics and a long carrier life.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between carrier saturation magnetization and spike height.

FIG. 2 is a schematic diagram for explaining the measurement of the spike height of FIG.

[Explanation of symbols]

1 ... Magnet roller 2 ... Developer 3 ... Ear-cutting blade G _B ... Distance between the ear-cutting blade and sleeve h ... Ear height at developing position

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tsuneo Watanuki 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Toshiaki Naruzawa, 1015, Kamikodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited

Claims (1)

[Claims] 1. A carrier of ferrite particles having an electric resistivity of 10 ⁹ Ωcm or more in an electric field of 1 kV / cm, a saturation magnetization value of 40 emu / g or less, and an average particle size of 1 to 30 μm. To form a magnetic brush using a developer mixed with toner, develop the electrostatic latent image formed on the photoconductive insulator with the magnetic brush, and obtain a toner image to be fixed on the recording paper. An image forming apparatus characterized by.