JPH0559423B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a developer for electrophotography, and particularly to a ferrite carrier in a two-component developer composed of a toner and a carrier. Development methods for electrophotography include cascade development, magnetic brush development, and other methods. The characteristics required of the 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 to prevent particle breakage, and that the particles are fluid. The particles must be highly elastic, the particles must be uniform, the surface condition must be stable regardless of humidity, etc., the tensile and compressive strengths must be high, and the particles must have appropriate saturation magnetization, magnetic permeability, or It has coercive force, etc. Conventionally, various materials have been used as toner carrier particles, but iron powder has been the most commonly used. Iron powder is used after its surface has been appropriately treated, but when used for a long time, the surface of the particles changes physically or chemically, causing toner to adhere to it, or due to the temperature of the usage environment. The drawbacks are that the image becomes sensitive to light and the clarity of the image fades, and that it has a short lifespan. Furthermore, the use of ferrite, which is an oxide magnetic material, as a carrier is known, for example, in
Although reported in Japanese Patent No. 56536, etc., conventional ferrite carriers are not necessarily satisfactory in terms of image characteristics or lifespan. The present invention eliminates these drawbacks of conventional electrophotographic toner carriers and provides a carrier with excellent image characteristics and long life. In order to achieve the above object, the present invention uses MgO 1% to 50%, ZnO 1% to 30%, and Fe ₂ O ₃ 45% in molar ratio.
60%, has an electrical resistivity of 10 ³ cm to 10 ¹² Ωcm, a saturation magnetization value of 15 to 80 emu/g, and a spherical ferrite carrier with an average particle size of 5 μm to 500 μm. It is something to do. In the present invention, Fe ₂ O ₃ is an essential component that imparts magnetism, and in order to function as a carrier, the amount is preferably within the above range. In addition, MgO and ZnO improve the squareness and lower Hc due to their synergistic effect, but if their content is small, the saturation magnetization value σs does not increase and Hc increases.
If the content of these is too large, the squareness ratio will deteriorate, so it is desirable that the content of MgO and ZnO is within the above range. In the present invention, the electrical resistivity is preferably 10 ³ to ^{10 12} Ωcm; outside this range, the amount of triboelectric charge cannot be controlled to an appropriate value, and it is easily affected by humidity, etc., making it difficult to obtain the desired clear image. That is difficult. The saturation magnetization value is preferably in the range of 15 to 80 emu/g, and if it is smaller than this value, the attraction force with the magnetic roll decreases and it is difficult to obtain the desired clear image. Furthermore, if Hc exceeds 10 Oe, the particles themselves have magnetic properties and 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 adversely affected. Hereinafter, the present invention will be explained in more detail based on examples. Example 1 MgO26%, ZnO14%, and Fe ₂ O ₃ 60 in molar ratio
% and mixed. As a mixer, a ball mill, a vibration mill, a mixer, etc. were used. The mixed powder was calcined at 800 to 1200°C. The calcined sample was pulverized using a pulverizer such as a ball mill, vibration mill, or attritor. The particle size after pulverization was measured using an air permeation method, and the average particle size was 0.3 to 2.0μ. The pulverized sample was granulated using a granulator such as a spray dryer, kneader, or mixer using an aqueous solution of PVA (polyvinyl alcohol) (PVA amount: 0.05 to 50 wt%) as a binder. Next, the granulated powder was fired at 1100 to 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, grains may grow during firing and the grains may join together. The sample may be fired while rotating in a rotor kiln or the like. The properties of the ferrite thus obtained are shown in Table 1.

[Table] As a result of using this spherical ferrite as a toner carrier and copying, the conventional iron powder carrier is approximately
10,000 sheets and 50,000 sheets for ferrite carriers, by using the carrier of the present invention.
It was possible to make 70,000 to 100,000 clear copies. Example 2 MgO, ZnO, and Fe ₂ O ₃ were weighed to have the composition shown in Table 2, and a sample was prepared in the same manner as in Example 1.
In addition, the weighing unit in the table is mol%.

[Table] Next, the characteristics of the samples were measured, and the results were as shown in Table 3.

[Table] Next, a copy test was conducted using Sample A as a toner carrier. As a result, the carrier of the present invention was able to produce 70,000 to 100,000 clear copies, compared to the lifespan of about 10,000 copies for conventional iron powder carriers and about 50,000 copies for ordinary ferrite carriers. In addition, it was possible to obtain a device that does not depend on the moisture content of the atmosphere in which the device is placed. 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%.
Table 3 shows the properties of the obtained ferrite.

[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, an image with higher density was obtained using the ferrite carrier of the present invention than an image using the ferrite carrier of the comparative example. That is, since the ferrite carrier according to the present invention can essentially obtain images with higher density than conventional ferrite carriers, it is possible to ease the developing conditions by increasing the distance between the magnetic brush and the photoreceptor, for example. It also has effects. As described above, the ferrite carrier according to the present invention makes it easy to obtain clear images, and has extremely little dependence on the external atmosphere, making the invention of great significance.

Claims (1)

[Claims] 1 MgO 1% to 50%, ZnO 1% to 30%, in molar ratio
Fe ₂ O ₃ 45% ~ 60%, electrical resistivity 10 ³ Ωcm ~
Saturation magnetization value is 15emu/g to 80emu/g at 10 ¹² Ωcm
A spherical ferrite carrier for electrophotographic development having the following characteristics and an average particle size of 5 μm to 500 μm. 2. In what is stated in claim 1,
A ferrite carrier for electrophotographic development, characterized by a holding force Hc of 10 Oe or less. 3 In what is stated in claim 1,
A ferrite carrier for electrophotographic development, characterized by a magnetic permeability μ of 10 or more. 4 In what is stated in claim 1,
A ferrite carrier for electrophotographic development, characterized by a Kyrie temperature Tc of 50°C or higher. 5. A ferrite carrier for electrophotographic development according to any one of claims 1 to 4, characterized in that the surface of the particles is oxidized. 6. A ferrite carrier for electrophotographic development according to any one of claims 1 to 4, characterized in that the surface of the particles is coated with a resin or the like.