JPH0685094B2 - Ferrite carrier - Google Patents

Description

TECHNICAL FIELD The present invention relates to a carrier for an electrostatic image developer used in electrophotography, electrostatic recording, electrostatic printing, and the like.

[Prior Art] As a developer for visualizing an electrostatic charge image formed on the surface of an image carrier such as zinc oxide, selenium, or an organic photoconductor by a magnetic brush method, a developer including a magnetic carrier and a toner is used. Component developers have been used conventionally. In the magnetic brush method using a two-component developer, the carrier and toner are mixed at a predetermined ratio, both are frictionally charged, and only the toner charged to a predetermined polarity is attached to the image carrier surface for development. .

An iron powder carrier is often used as the magnetic carrier, and in order to prevent the carrier from fatigue and stabilize the triboelectrification characteristics, the surface is usually subjected to an oxidation treatment and further coated with a resin.

Recently, however, a ferrite carrier has advantages such as being chemically more stable than an iron oxide powder carrier, having less resistance change during use, and having an apparent density of about 2/3 that of iron powder. It is receiving attention and is being put to practical use.

This ferrite carrier is composed of a perfect mixture of suitable metal oxides and iron oxides, Ni, Zn, Mn, Mg, Cu, L
It is a sintered body of oxides of i, Ba, V, Cr, Ca and the like and trivalent iron oxides.

Ferrite carriers having various compositions are known, for example, Japanese Patent Publication No. 53-15040 and Japanese Patent Publication No. 56-5.
Ni-Zn type ferrites or Mn-Zn type ferrites as described in Japanese Patent No. 2305 were generally used.

On the other hand, in recent years, improvement in image quality has been desired, so that carriers made of Mg—Zn ferrite are being used from the viewpoint of magnetic characteristics, electric characteristics, and surface state. This ferrite carrier is disclosed, for example, in JP-A-58-145.
No. 621, No. 60-134249, and No. 60-135958.

[Problems to be Solved by the Invention] However, the conventional Mg-Zn ferrite carrier has the following problems, and there is still room for improvement. In the past, if the amount of iron oxide (Fe ₂ O ₃ ) was increased from the viewpoint of magnetic properties, the surface would not be smooth, so CuO or NiO was added to suppress the amount of iron oxide. It was However, even if such an additive is added, the overall characteristics including the image quality are not necessarily satisfactory, and there is a problem in that it is economically disadvantageous.

Therefore, it is an object of the present invention to provide a ferrite carrier having improved image characteristics, magnetic characteristics and surface condition as compared with the conventional ones.

[Means for Solving Problems] The ferrite carrier of the present invention has the following formula (MO) _100- x (Fe ₂ O ₃ ) x [where M is a combination of Mg and Zn, MgO 15 to 25 mol%, ZnO 10
˜20 mol%, MgO is more than ZnO, 60 <x <65 mol%], and the impurity metal oxides other than Mg and Zn are 0.5 mol% or less in total and are substantially spherical. Made of ferrite particles with an electric resistance of 1 × 10 ⁵ ~
It is in the range of 1 × 10 ¹⁰ Ω · cm, and the saturation magnetic flux density is 60 to 70em.
It is characterized in that it is in the range of u / g and the particle size is in the range of 20 to 200 μm.

The ferrite carrier of the present invention has a spinel type structure crystallographically, and a specific composition is Mg and
It consists of Zn oxide and iron oxide (Fe ₂ O ₃ ). In such a composition, the magnetic properties are proportional to the amount of Fe ₂ O ₃ , and when Fe ₂ O ₃ is less than 60 mol%, the saturation magnetization (σs) is 60 emu.
/ g or less. Generally, when σs is less than 60 emu / g, the carrier easily separates from the magnetic brush, which causes the carrier to adhere to the surface of the photoconductor. On the other hand, when Fe ₂ O ₃ exceeds 65 mol%, σs becomes larger than 70 emu / g, the carrying force is too strong and the toner is deformed, and the ears of the magnetic brush become hard.
Reproducibility of halftone is reduced. Therefore, Fe ₂ O ₃ needs to be in the range of more than 60 mol% and less than 65 mol%. Further, since the amounts of MgO and ZnO are related to the magnetic characteristics similarly to Fe ₂ O ₃ , they may be set so that the saturation magnetization is in the above range. Specifically, MgO is 15 to 25 mol% and ZnO is 10 to 25 mol%.
It is desirable that the content of MgO is 20 mol% and the content of MgO is 3 to 5 mol% higher than that of ZnO.

The characteristics required for the ferrite carrier include electric resistance and particle morphology in addition to the above magnetic characteristics.

The range of the electric resistance is determined depending on the usage conditions of the carrier (for example, the type of the photoconductor and the developing speed). Generally, if it is too low, carrier adhesion occurs. 1 because it becomes uniform
It should be in the range of × 10 ⁵ to 1 × 10 ¹⁰ Ω · cm. The resistance of the carrier varies somewhat depending on the resistance of the carrier, but rather greatly changes depending on the manufacturing conditions, so it may be adjusted according to the manufacturing conditions (for example, sintering atmosphere).

Characteristics such as fluidity and charging characteristics change depending on the electric resistance, surface state, particle shape, and particle diameter of carrier particles, which affects image quality. First, the surface condition of the carrier particles is influenced by the composition, but since the carrier of the present invention has the above-mentioned composition, it has a relatively smooth surface, and the problems of adhesion to the photoreceptor and damage to the photoreceptor do not occur. Next, it is necessary that the particles have substantially spherical shapes in terms of fluidity. And the particle size distribution is 20-200
It is necessary to be in the range of μm. The smaller the particle size, the larger the specific surface area, the higher the maximum toner concentration, and the higher the durability. If the content of particles of 20 μm or less increases, carrier adhesion to the surface of the photoconductor occurs.
Particles having a size of μm or less are preferably 30% by weight or less. On the other hand, the particle size is 20
Since the image density decreases if there are many particles larger than 0 μm, it is preferable that the particles larger than 200 μm be 20% by weight or less.

The ferrite carrier of the present invention can be manufactured, for example, by the following method.

First, a predetermined amount of a predetermined metal oxide and a predetermined amount of iron oxide (Fe ₂ O ₃ ) are weighed and mixed. Then the obtained mixture is 800-1000 ℃
It is calcined at a temperature in the range of several hours for several hours, and then pulverized to a particle size of several μm or less. The obtained pulverized powder is granulated by adding a binder, if necessary, and then spray drying in a heating atmosphere. The obtained spherical particles are sintered at a temperature of 1100-1300 ° C, and then crushed and classified to obtain a ferrite carrier.
If sintering is performed in the atmosphere here, the resistance of the carrier is 10 ⁸ to 1
Becomes 0 ¹⁰ Ω · m, and carried out in a nitrogen atmosphere resistance of the carrier is about 10 ⁵ Ω · m. In addition, the resistance of the carrier can be adjusted by performing an appropriate heat treatment.

The ferrite carrier of the present invention is mixed with toner to form a developer. As a toner, a known toner composition (for example, JP-A-58-150957, JP-A-58-150958, JP-A-58-196549) is used.
No. 57-60341 and No. 57-60342), and a magnetic toner may be used.

The volume resistivity of the ferrite carrier of the present invention is obtained by filling a Teflon (trade name) cylinder (inner diameter 3.05 mmφ) with an improved dial gauge with several tens of mg of a sample, and under a load of 1.0 kg and a DC electric field of 200 V / cm. The resistance is measured and calculated.

The magnetic properties of the ferrite carrier of the present invention are values measured using a vibrating sample magnetometer (VSM-3 type manufactured by Toei Industry Co., Ltd.).

Example 1 Each raw material was weighed so that MgO was 21 mol%, ZnO was 18 mol%, and Fe ₂ O _{3 was} 61 mol%, and they were dry-mixed by a ball mill. The obtained mixed powder was calcined at a temperature of 900 ° C. for 2 hours, and then the calcined powder was put into a ball mill and pulverized into particles of 1 μm or less.
A binder is added to the obtained pulverized powder, the mixture is granulated and dried, and then sintered in air at a temperature of 1300 ° C. for 4 hours, further crushed and classified to obtain a ferrite carrier having a particle size of 63 to 125 μm. It was
Σs of this ferrite carrier is 63 emu / g, resistance is 3 × 1
It was 0 ⁹ Ω · cm.

Examples 2 to 5 Four types of ferrite carriers were manufactured under substantially the same conditions as in Example 1 except that the composition ratio of the raw materials was changed.

The characteristics of these ferrite carriers are shown in Table 1.

Comparative columns 1 to 3 Three types of ferrite carriers were manufactured under substantially the same conditions as in Example 1 except that the acid ratio of the raw materials was changed.

The characteristics of these ferrite carriers are also shown in Table 1.

A commercially available electrophotographic copying machine (U manufactured by Konishi Rokusha Co., Ltd.) was prepared by using the above ferrite carrier to prepare a developer with a toner concentration of 3%.
-BIX3000 machine).

Table 2 shows the evaluation results of the obtained images.

From Table 2, when the ferrite carriers of Examples 1 to 5 are used, it is possible to obtain an image having a density of about 1.3 or more, no background fog, a resolution of 6 lines / mm, and a good halftone reproducibility. Recognize. On the other hand, since the ferrite carriers of Comparative Examples 1 and 2 have a low σs, background fog occurs, and the ferrite carrier of Comparative Example 3 has a high σs, so that the magnetic brush is hard and the reproducibility of the halftone is inferior. Recognize.

Comparative Examples 4 to 7 MgO, ZnO and Fe ₂ O _{3 having} different purities were prepared in the same composition as in Example 1 with 21, 18 and 61 mol%, respectively, and the physical properties shown in Table 3 were obtained.

Image evaluation was carried out in the same manner as in the above-mentioned examples using the above carrier, and in the carriers of Comparative Examples 4 to 7, the image density was less than 1.3 and the images had chipping at the tip, and sufficient printing quality was not obtained. could not.

[Advantages of the Invention] As described above, since the ferrite carrier of the present invention has a specific composition and physical properties, it is possible to obtain a higher quality image than the conventional one.

Claims (1)

[Claims] 1. A ferrite carrier made of a ferrite material exhibiting soft magnetism, comprising the following formula (MO) _100- x (Fe ₂ O ₃ ) x [where M is a combination of Mg and Zn, MgO 15 to 25 mol%, ZnO 10
˜20 mol%, MgO is more than ZnO, 60 <x <65 mol%], and the impurity metal oxides other than Mg and Zn are 0.5 mol% or less in total and are substantially spherical. It consists of ferrite particles and has an electric resistance of 1 × 10 ⁵ -1
× 10 ¹⁰ Ω ・ cm, saturation magnetic flux density is 60 ~ 70emu /
Ferrite carrier characterized by being in the range of g and having a particle size in the range of 20 to 200 μm.