JPH0352623B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a ferrite carrier for electrophotography. Development methods for electrophotography include cascade development, magnetic brush development, and other methods.
The characteristics required of the toner carrier used in these development methods are that it has appropriate triboelectric charging properties and attracts toner particles, that it is dense and has sufficient particle strength so that it does not break, and that it has good particle fluidity. that the particles are uniform, that the surface condition does not change due to temperature, etc., and that various properties are stable;
It must have tensile/compressive strength, etc., and appropriate saturation magnetization, magnetic permeability, or coercive force. Although various materials have been used as toner carrier particles, iron powder is the most commonly used material. This is made by appropriately treating the surface of iron powder, but when used for a long time, the surface of the particles changes physically or chemically, causing toner to adhere to it, or causing the particles to become unusable. The drawback is that it has a short lifespan because it becomes sensitive to environmental humidity and the sharpness of the image may fade. It is also known to use ferrite, which is an oxide magnetic material, as a toner carrier (for example, Japanese Patent Laid-Open No. 52-56536, etc.), but conventional ferrite carriers for electrophotography have poor image characteristics or service life. It is not always satisfactory in this respect. An object of the present invention is to eliminate these drawbacks of conventional toner carriers for electrophotography and to provide a new ferrite carrier for electrophotography that has excellent image characteristics and has a long life. In order to achieve the above object, the present invention provides CuO5~
30 mol%, ZnO mol 0.1-30 mol%, _{Fe2O3 45-70}
It contains 0.01 to 5% by weight as CaO, has an electrical resistivity of 10 ³ to 10 ¹² Ωcm, and has a saturation magnetization value of 10 3 to 10 12 Ωcm.
It has the characteristics of 10~80emu/g, and the average particle size is 5μm~
It is characterized by being made of spherical ferrite with a diameter of 500 μm. In the present invention, the coercive force Hc of the ferrite is
When is 10 Oe or less, more favorable effects can be obtained. Further, in the ferrite carrier for electrophotography of the present invention, the electrical resistivity is 10 ³ to 10 ¹² Ω.
It is preferable that the amount is in the range of cm. Outside this range, it is difficult to control the amount of triboelectric charge to an appropriate value, and it becomes susceptible to the effects of humidity, etc., making it difficult to obtain the desired clear image. Further, the appropriate value of saturation magnetization is in the range of 10 to 80 emu/g, and if the value is smaller than this value, the adhesion force with the magnetic roll decreases, making it difficult to obtain the desired clear image. Moreover, if it is larger than 80 emu/g, the rotational torque becomes large and more force than necessary is required for rotation. Furthermore, if Hc is 10 Oe or more, the particles themselves have magnetic properties and tend to adhere to various parts, making it impossible to obtain good images. Furthermore, if the magnetic permeability μ is less than 10, the response to the magnetic roll will be poor and the image quality will be affected. Hereinafter, the present invention will be explained in detail with reference to Examples. Example 1 In terms of molar ratio, CuO20%, ZnO30%, Fe ₂ O ₃ 50%,
Further, the mixture was weighed and mixed so that the CaO content was 1.0% by weight. As a mixer, a ball mill, a vibration mill, a mixer, etc. were used. The mixed powder was calcined at 800-1200°C. The calcined sample was pulverized using a pulverizer such as a ball mill, vibration mill, or attritor. The particle size of the pulverizer was measured using an air permeation method, and the average particle size was 0.3 to 2.0 μm. The crushed sample was processed using a spray dryer, kneader, etc. using an aqueous solution of PVA (polyvinyl alcohol) as a binder.
The mixture was granulated using a granulator such as a mixer. Next, the granulated powder was fired at 1100-1400°C. As a firing method, granulated powder may be placed in a container such as alumina and fired, but if a large amount is placed in a container and fired, the grains may grow during firing and the grains may join together. Therefore, in this example, the sample was fired while rotating in a rotary kiln or the like. As a result of compositional analysis of the obtained powder, it was found that the composition was almost as desired. Further, various properties of the obtained ferrite are shown in Table 1.

[Table] As a result of electronic copying using this spherical ferrite as a toner carrier, the number of copies was about 10,000 with a conventional iron powder carrier, and about 50,000 with a normal ferrite carrier for electrophotography, whereas the number of copies made with the present invention's electronic By using a photographic ferrite carrier, it was possible to make 70,000 to 100,000 clear copies. Example 2 25 mol% of CuO, 25 mol% of ZnO, 50 mol% of Fe ₂ O ₃ and 3.0% by weight of CaO were added to prepare a sample in the same manner as in Example 1, and various properties were measured.
The results are shown in Table 2 as sample a. Also,
CuO12 mol%, ZnO 18 mol%, _{Fe2O3 70} mol%
A sample was prepared in the same manner with 1.0% by weight of CaO added. The results are shown in Table 2 as sample b.

[Table] As a result of a copying test using these spherical ferrites as a toner carrier, the same copying performance as in Example 1 was obtained. Reference example 1 Molar ratio: NiO15%, ZnO30.5%, CuO1.5%,
Spherical ferrite was produced in the same manner as in Example 1 by weighing so that MnO was 3% and Fe ₂ O ₃ was 50%.
The properties of the obtained ferrite are shown in Table 3.

[Table] Next, using the ferrite carrier of the present invention of Examples 1 and 2 and the ferrite carrier of Reference Example 1, a developer was prepared at a toner concentration of 3%, and a developer was prepared using a commercially available electrophotographic copying machine (Konishi Rokusha Manufactured by U-BIX3000
The image was created using a machine). As a result, images obtained using the ferrite carrier of the present invention were clearer than images obtained using the ferrite carrier of the comparative example. This is because the magnetic brush formed by the ferrite carrier of the present invention has no unevenness and is formed uniformly compared to the reference example, and is essentially a composition system that can obtain high image quality. It is thought to be a ferrite carrier. Further, it is thought that the addition of CaO improves the sinterability, reduces the number of pores, and improves the saturation magnetization value, which also brings about more favorable effects. As described above, it is clear that the ferrite carrier of the present invention has a longer lifespan than the conventionally used iron powder carrier, exhibits outstanding effects as a developer for electrophotography, and has great industrial value. be.

Claims (1)

[Claims] 1 The basic composition is 5 to 30% CuO, 0.1 to 30% ZnO, and 45 to 70% Fe ₂ O ₃ in molar ratio, and further contains 0.01 to 0.01 to 70% CaO in weight ratio. 5%, electrical resistivity 10 ³ ~ 10 ¹² Ωcm, saturation magnetization value 10 ~
It has the characteristics of 80emu/g and the average particle size is 5-500μm.
A ferrite carrier for electrophotography, which is characterized by: 2. In what is stated in claim 1,
A ferrite carrier for electrophotography characterized by a coercive force Hc of 100e or less. 3. A ferrite carrier for electrophotography according to claim 1 or 2, characterized in that the magnetic permeability μ is 10 or more. 4. In the product according to any one of claims 1 to 3, the Curie temperature Tc is 50°C.
A ferrite carrier for electrophotography characterized by the above. 5. A ferrite carrier for electrophotography according to any one of claims 1 to 4, characterized in that the ferrite particles are spherical. 6. A ferrite carrier for electrophotography according to any one of claims 1 to 5, characterized in that the surface of the ferrite particles is oxidized. 7. A ferrite carrier for electrophotography according to any one of claims 1 to 6, characterized in that the surface of the ferrite particles is coated with a resin or the like.