JPS61188548A - Electrostatic charge image developing carrier - Google Patents

Abstract

PURPOSE:To obtain a carrier good in durability by forming a ferrite film specified in composition on the surface of particles composed essentially of iron. CONSTITUTION:The carrier for developing an electrostatic charge image is obtained by forming a ferrite film having a composition of MO.Fe2O3, M being a divalent metal atom, such as Fe, Ni, Co, Mn, Zn, Cu, Sn, or Pb, or an optional plural combination of then on the surfaces of particles composed essentially of iron. The 0.1-10 mum thick ferrite film 2 is formed on the surfaces of the core particles 1 of 10-300 mum particle diameter composed essentially of iron to form the carrier, thus parmitting the carrier to be prevented from scattering and attaching and improved in development performance.

Description

[Detailed description of the invention] B. Industrial application fields The present invention relates to a carrier for developing electrostatic images.

BACKGROUND OF THE INVENTION Cascade development and magnetic brush development are well known as two-component development methods for electrophotographic copying.

That is, a visible image is formed by attaching toner particles using a carrier to an electrostatic charge image or an electrostatic latent image created on a photoreceptor by charging and exposure, and this is transferred to paper or other support. , is a method that will become established.

Carriers for magnetic brush development include conductive carriers based on iron powder and insulating carriers in which an insulating resin film is formed on the surface of iron powder. The shape of the iron powder carrier is often amorphous because it provides a large surface area. Since a resin coated carrier becomes an insulating carrier, it is necessary to obtain an electric field required for developing an electrostatic charge image.

Furthermore, the resulting image also has a significant edge effect.

When an iron powder-based conductive carrier is subjected to a long copying process, the surface becomes contaminated with toner or becomes oxidized, increasing the carrier's own electrical resistance and changing from conductive to insulating. (As a result, the developing characteristics vary greatly, resulting in deterioration of the resulting copied image. Generally, poor developing performance causes a decrease in density and non-uniformity of solid black images. In order to reduce changes in surface properties as much as possible, amorphous iron powders with a larger surface area than spherical ones are used.However, for the reasons mentioned above, the lifespan of conductive iron powder carriers is at most 10,000~ 20.0
The number of copies is 00.

On the other hand, a so-called coated carrier whose surface is coated with a resin has a high electrical resistance and becomes an insulating carrier, resulting in a reproduced image that is black in developability and has a strong edge effect. In order to improve this, it is necessary to design an apparatus that minimizes the gap between the developing device and the photoreceptor or electrostatic recording medium and increases the developing electric field. Therefore, it is necessary to maintain the assembly accuracy of the device, which makes the device complicated. Furthermore, since the resin is coated, the core of the carrier, iron powder or other magnetic powder, must be spherical. Therefore, the surface area to which toner can be attached is reduced, and developability is also impaired in this respect.

Furthermore, there is a ferrite carrier, but this ferrite carrier has a smaller magnetization (saturation magnetization σ5 = 50 to 80 emu/g) than a conductive iron powder carrier, so it cannot be bound by the magnet placed in the developing device. Since the force is weak, there is a high possibility of so-called carrier scattering. Further, since the magnetic binding force of the carrier to the developing sleeve is weak, the carrier is developed together with the toner, and the carrier adheres to the recording medium.

C. OBJECT OF THE INVENTION An object of the present invention is to provide a carrier that has good developability and durability even after long-term use, and does not cause carrier scattering or carrier adhesion.

2. Structure of the invention and its effects, that is, the present invention provides MO on the surface of particles whose main component is iron.
-Fe203 (However, M is one or more types of divalent metal atoms.) The present invention relates to a carrier for developing an electrostatic image formed with a ferrite film represented by -Fe203 (M is one or more types of divalent metal atoms).

The carrier according to the present invention has the following excellent features.

■Magnetic powder mainly composed of iron with high saturation magnetization as the carrier core (especially σ current 100 to 200 emu/g)
Since carrier is used, carrier scattering and carrier adhesion do not occur.

(2) The surface electrical resistance is higher than that of iron powder, but lower than that of the resin coating film, so the developability is good.

(2) The resistance change due to toner contamination is smaller than that of a conductive carrier, so it is durable (the carrier life is, for example, 30.
000-60. □ooo copy).

(2) The shape is determined by the core material used, so it can be spherical or irregular. In the case of an amorphous shape, the surface area becomes large, which is advantageous in terms of development characteristics and durability.

(2) Since the resistance of the ferrite film can be changed by changing the metal element M of the ferrite film deposited on the surface, carriers with a resistance value matching the developing process used can be obtained.
The resistance value is small in the case of Fe, and thick (becomes large) in the case of other atoms.Since the core material particle surface and the ferrite layer are similar in composition and structure, the adhesion of the ferrite film is good. No peeling of the film occurs due to mechanical stress.

In the carrier according to the present invention, the above M is F
e, Ni, Co, cr, Mn, Zn, Cu, Sn poor”P
It is preferable to use one or more types selected from the group such as b.

In the case of multiple types, a state occurs in which different M of type 1 are mixed.

Further, the carrier of the present invention preferably has a Mo-Fe2O3 film (ferrite film) with a thickness of 0.1 to 10 μm formed on the surface of core material particles (mainly composed of iron) with a particle size of 10 to 300 μm. . That is, when the particle size of the core material falls outside of the above range, the magnetic binding force acting on the carrier becomes weaker, and carrier scattering and adhesion to the photoreceptor tend to occur. Furthermore, when the particle size of the core material becomes larger, the shape of the magnetic brush becomes rougher, the friction force against the photoreceptor increases, and once developed toner is easily scraped off, which tends to cause deterioration in image quality and decrease in image density. In addition, if the thickness of the ferrite film is less than 0.1 μm, it will be too thin and its effect will be poor, and if it exceeds 10 μm, the ferrite content will increase and the carrier magnetization will tend to be small. It is preferable to set the thickness to 5 μm.

When the carrier of the present invention is illustrated in FIGS. 1 and 2, FIG. 1 shows a spherical shape, and FIG. 2 shows an amorphous one, and both of them have
It consists of a core material 1 and a ferrite film 2. Core material 1
is made of iron powder (particle size 10 to 300 μm), and examples of the iron powder include pure iron powder such as reduced iron powder, atomized iron powder, and electrolytic iron powder, or those whose surfaces have been oxidized. The ferrite film 2 is formed to a thickness of 0.1 to 10 μm by the method described below, and the divalent metal (M) contained is Fe2
+, Co", Ni", Zn", Mn", Cu"+, etc. are applicable.

FIG. 3 shows an example of a process for manufacturing the carrier of the present invention. This will be explained later.

E, Example Examples of the present invention will be described below along with comparative examples.

11 ■ According to the process flow shown in Figure 3, the average particle size is 15.
1000 g of amorphous reduced iron powder with a particle size range of 70 to 240 μm and 1 mol/l cobalt sulfate aqueous solution IJ
The mixture was poured into a stainless steel beater containing a mol/l aqueous solution of ferric sulfate 1z, and stirred and dispersed using a propeller.

Then, 100,100 O of a separately prepared 1 mol/1 sodium hydroxide solution was added to the beaker at an addition rate of 10 m/min while stirring.

The surface was coated.

The iron powder dispersion was filtered, washed with water, and then heated at 110°C for 12 hours.
Drying was performed for a period of time to obtain an iron powder carrier coated with a cobalt ferrite film.

The obtained carrier resistance value was measured under the electric field condition of E = 10 V/we, and it was found to be 7 × 10 ° 1 Ω - (However,
The iron powder before treatment is 3×10”Ω−1).

The obtained carrier was mixed with a toner consisting of 100 parts of polyester resin and 10 parts of carbon black and having an average particle size of 10 μm to prepare a two-component developer in which the amount of toner was 3% by weight of the total amount of developer. The amount of charge at this time was 17 μc/g.

Using this developer, electrophotographic copying machine U-Bix 1
600 (manufactured by Konishiroku Photo Industry Co., Ltd.) for a copying test. As a result, 60,000 copies of images with a resolution of 8 lines/-1 and no image roughness, sweeping marks, or fog were obtained.

A developer was prepared by using the reduced iron powder in the above example as a carrier as it was. The amount of toner in the developer was 4% by weight, and the amount of charge at that time was 19 μc/g.

This developer was transferred to an electrophotographic copying machine U-Bix 1600.
(manufactured by Konishiroku Photo Industry Co., Ltd.) and a copying test was conducted.

The initial image was good, but after 15,000 copies, the carrier surface became contaminated with toner, the resistance changed, and the ability to control the charge on the toner deteriorated, resulting in fogging on the image.

Comparison 1: 15 g of styrene-methacrylate resin polymerized at a weight ratio of 70:30 was added to 200 g of methyl ethyl ketone.
A coating solution for forming a coating layer of the carrier was prepared by melting the solution in ml. This coating liquid was sprayed onto 1 kg of reduced iron powder in the above example using a fluidization vent device,
It was further dried at a temperature of 70° C. to obtain a carrier having a resin coating layer with a thickness of 1.5 μm.

This carrier was mixed with a toner consisting of 100 parts of polyester resin and 10 parts of carbon black having an average particle diameter of 10 μm to prepare a two-component developer containing 3% by weight of toner based on the total amount of developer. The charge amount of this developer is 18μc/g
Met.

Using this developer, electrophotographic copying machine U-Bix 1
600 (manufactured by Konishiroku Photo Industry Co., Ltd.), a copying test was conducted. The initial image was good, but after 25,000 copies, the toner charge amount decreased to 8 μc/g.
Ground fog occurred. Also, the image density is 1.3 to 0.
It dropped to 7.

[Brief explanation of the drawing]

The drawings show examples of the present invention, and FIGS. 1 and 2 are enlarged cross-sectional views of carrier particles, respectively, and FIG. 3 is a process flow diagram for manufacturing the carrier. In addition, in the reference numerals shown in the drawings, 1... Core material (iron powder) 2... Ferrite film.

Claims (1)

[Claims] 1. MO・Fe_2O on the surface of particles whose main component is iron
A carrier for developing an electrostatic image formed with a ferrite film represented by _3 (where M is one or more types of divalent metal atoms).