JPS6244752A - Developer composition - Google Patents

Abstract

PURPOSE:To improve a black solid development characteristic and to extend the life of the titled compsn. by using ferrite particles having the characteristics of >=10<9>OMEGAcm electric resistivity in 1kV/cm electric field and <=40emu/g satd. magnetization rate as a carrier and a microtoner having substantially 1-10mum grain size as a toner. CONSTITUTION:The ferrite particles having the characteristics of >=10<9>OMEGAcm electric resistivity in 1kV/cm electric field and <=40emu/g satd. magnetization value and <=30mum average grain size are used as the carrier and the grain size of the toner is made substantially 1-10mum. The reason for specifying the electric resistivity of the ferrite core to >=10<9>OMEGAcm at 1kV/cm electric field intensity is to avert the image change by toner filming which is of a problem when the resistance is low. The grain size of the carrier is the significant factor to determine the density of a magnetic brush and is important as the grain size thereof relates also to the toner replenishing power to embed an electrostatic latent image with the toner. The adequate grain size is substantially 1-10mum in order to exhibit the excellent black solid printing characteristic and to extend the life of an imaging characteristic in particular.

Description

[Detailed description of the invention] [Summary] By lowering the saturation magnetization value of the carrier and reducing the average particle size, the black solid development ability is increased, thereby increasing the resistance of the carrier and avoiding characteristic deterioration due to toner filming. make it possible.

C. INDUSTRIAL APPLICATION FIELD OF THE INVENTION The present invention relates to a developer composition, and more particularly to a long-life developer composition for electrophotographic magnetic brush development.

[Conventional technology]

Electrophotography, which is used in copiers, laser printers, etc., generally applies a uniform static charge on a photoconductive insulating layer, and then irradiates a light image onto the insulating layer to remove the static charge. An electrostatic latent image is formed by partially removing it, and a fine powder called toner is attached to the remaining part of the electrostatic charge to form a toner image that visualizes the latent image (referred to as development). Printed matter is obtained by fixing (called fixing) on recording paper.

Toner is a fine powder obtained by dispersing a coloring agent, a charge control agent, etc. in a binder resin made of natural or synthetic polymeric material, and is usually ground to a size of about 1 to 30 μm, and is composed of magnetic particles such as iron powder and ferrite. A carrier substance (carrier) consisting of
is mixed with the toner to form a developer, which is used for development.

Various materials have been used as carrier particles, but the most commonly used ones include iron powder and ferrite powder. These magnetic particles, as a developer mixed with toner, form a magnetic brush on a cylindrical sleeve in which a magnet is placed, which, when in contact with a photoconductive insulator, the so-called photocon, generates an electrostatic charge. Develop the latent image.

In this magnetic brush development, the electrical resistance of the magnetic particles forming the developer is a very important factor in the development characteristics. When the resistance is low, the tip of the magnetic brush of the developer becomes the development electrode, and this development electrode effect , has the ability to uniformly develop electrostatic latent images with large areas. On the other hand, when the electrical resistance is high, it is difficult to develop a large area, but it has excellent line drawing, that is, line copying characteristics. Therefore, in general, the electrical resistance of the magnetic particles of the developer, that is, the carrier, is lowered to some extent (for example, 104 to 106 Ωc).
m) So that a large area electrostatic latent image can be developed uniformly)
I am using it as.

[Problem that the invention seeks to solve]

However, if the electrical resistance of the carrier is too low, a so-called carrier over problem occurs in which the carrier adheres to the photocon, so the electrical resistance cannot be made very low. Furthermore, since the carrier is constantly mixed and stirred with the toner in the developing device, a toner filming phenomenon occurs in which the toner fuses onto the surface of the carrier. In processes that depend on this, there is a problem in that black solid characteristics change over time due to the high resistance of the carrier due to toner filming, and the life of the carrier is shortened.

SUMMARY OF THE INVENTION An object of the present invention is to eliminate these drawbacks of conventional electrophotographic developers and to provide a developer composition with excellent black solid development properties and a long life.

[Means for solving problems]

In order to achieve the above object, the present invention has the characteristics that the electrical resistivity in an electric field of 1 kV/mouth is 109 Ωcm or more, the saturation magnetic susceptibility is 40 emu/g or less, and the average particle size is 30
The present invention is characterized in that ferrite particles of .mu.m or less are used as a carrier, and micro toner having a particle size of substantially 1 to 10 .mu.m is used as a toner.

The present invention is intended to avoid the problem that when the black solid development characteristics of the developer depend on the low resistance of the carrier, the electrical resistance changes due to toner filming and the development characteristics deteriorate when used for a long time. This is a high-resistance carrier that achieves excellent black solid development characteristics. That is, the black solid printing characteristics of the developer carrier (which has high resistance) according to the present invention are not obtained by the development electrode effect in a low resistance carrier, but by using ferrite with small saturation magnetization and small particle size as the carrier.
This is achieved by increasing the density of the magnetic brush tip and bringing it into soft contact with the photocon to improve the developing ability of the toner. Furthermore, in the developer of the present invention, by using micro toner with a small particle size as the toner,
Enables high-quality printing with excellent resolution.

In the present invention, the electrical resistivity of the ferrite core is l
The reason why the electric field strength of kV/cm is set to I09Ω...(2) or more is to avoid image changes due to toner filming, which is a problem when the resistance is low.
The resistance value under conditions of high electric field strength (/cm) is important. This means that in a normal development process, the development bias voltage between the sleeve and the photocon drum is 100V to 20V.
Since approximately 0 V is applied, considering the distance between the sleeve and the photocon drum (usually 1 to 2 m), the electrical resistance of the developer must be expressed as a resistance value at an electric field strength of approximately lkV/cm. It is.

In addition, the reason why the saturation magnetization value of ferrite is set to 40 emu/g is because the saturation magnetization value is high, especially when it is 200 to 3 emu/g like iron powder.
If it has a value of 00 emu/g, the tip of the magnetic brush will be hard (this is because soft-touch development is not possible. Also, even if the ferrite is about several tens of emu/g, the same blade may be used depending on the magnetization and arrangement of the magnet in the sleeve. Even if I cut the developer in the gap, the height of the developer becomes abnormally high (
This is because dense tips cannot be obtained. FIG. 1 shows the relationship between the saturation magnetization value and the height of the magnetic brush. As shown in FIG. FIG. 3 is a diagram showing the height of the developer at the development position as a function of the saturation magnetization value of the carrier when the tip of the developer is cut at the tip of the developer.

Figure 1 shows that if the saturation magnetization value is 40 emu/g or less,
Even at the development position, the height of the ears hardly changes with the distance Gg between the ear cutting blade and the sleeve, indicating that the magnetic brush is dense.

Further, the particle size of the carrier is important because it is a major factor determining the density of the magnetic brush and is also related to the toner replenishment ability to fill the electrostatic latent image with toner. In order to exhibit excellent black solid printing characteristics and, in particular, to extend the life of printing characteristics, it is preferable that the particle size of the carrier is 30 μm or less.

Toner particles having a particle size of 5 to 25 .mu.m are normally used, but as the particle size of the carrier becomes smaller, it is preferable to reduce the particle size of the toner as well. In particular, in order to exhibit good resolution and good triboelectric charging ability with the carrier, the particle size is substantially 1 to 10.
μm is appropriate. The particle size here is substantially 1 to 10
The term "μm toner" refers to toner that passes through a sieve with a sieve mesh interval of 10 μm and remains on the 1 μm sieve.1. ~
It is not excluded that some amount of toner outside the 10 μm range is present.

The ferrite used in the present invention generally has the general formula MFeOz or MFeOz as a magnetic oxide containing iron as the main metal.
It is represented by Fe20a. Here, M represents a monovalent or divalent metal, and iron is in the +3 oxidation state. M includes one or more of nickel, manganese, magnesium, lead, iron, barium, etc. The saturation magnetization value and electrical resistance value of the ferrite particles can be adjusted by appropriately selecting the type and proportion of the metal M or by changing the firing conditions.

Example C] Using a ferrite carrier having the characteristics shown in Table 1, a positively chargeable micro toner (particle size 1 to 10 μm) was used as a toner.
As a result of a printing test using a laser printer that uses an electrophotographic method, we adjusted the developer in combination with 5.8 μm (average particle size: 5.8 μm) and found that black with an optical density (0, D, Solid printing characteristics are obtained, and even after printing 200,000 sheets, the resolution is 10 lines/I11 or more, 0. D, is 1.
It was confirmed that the black solid printability of 1 or more was maintained, and there was also little background staining in the background area.

Table 1 Ferrite composition Magnesium Zinc ferrite (Mg
ZnFetOa> Electrical resistivity: 5 x 109 Ω (electric field strength: 1 kV/cm) Saturation magnetization: 38 emu/g Particle size: 1 to 25 μm [Effects of the Invention] As is clear from the above description, the present invention improves the black solid development characteristics and resolution. A developer composition having excellent image properties and a long carrier life is provided.

[Brief explanation of drawings]

FIG. 1 is a graph showing the relationship between the saturation magnetization value of the carrier and the height of the ears, and FIG. 2 is a schematic diagram illustrating the measurement of the height of the ears shown in FIG. 1... Magnet roller, 2... Developer, 3...
...ear cutting blade, GB...distance between ear cutting blade and sleeve, h...
・Hotaka at the development position.

Claims (1)

[Claims] 1. Electrical resistivity in an electric field of 1 kV/cm is 10^
Ferrite particles having a characteristic of 9 Ωcm or more, a saturation magnetization value of 40 emu/g or less, and an average particle size of 30 μm or less are used as carriers, and the toner particle size is substantially 1 to 1
A developer composition characterized in that the particle size is 0 μm.