JPS60227269A - Ferrite carrier material for electrostatic copying - Google Patents

Abstract

PURPOSE:To enhance smoothness of the surface of a carrier by incorporating a specified amt. of one or both of oxides of Ba and Sr in an Mg-Zn type ferrite contg. specified amts. of Fe2O3, MgO, and ZnO. CONSTITUTION:Spherical pellets are formed by incorporating one or both of oxides of Ba and Sr in an Mg-Zn type ferrite compsn. contg. 45-65mol% Fe2O3, 26-32mol% MgO, and 18-22mol% ZnO, further in an amt. of 0.01-5wt%, mixing it with a binder, a dispersing agent, water or an org. solvent, etc., to form a slurry, and spray drying it. In these steps, the specific gravity of the pellet powder can be properly controlled, and a state of dispersion of void holes can be adjusted to a desired form. The obtained spherical particles are burned in a kiln or a furnace and classified by screening to obtain a carrier material having a desired particle size distribution.

Description

DETAILED DESCRIPTION OF THE INVENTION "Field of Industrial Application" The present invention relates to a carrier material used in a two-component developer for electronic copying machines. The present invention relates to a spherical ferrite carrier material for electrostatic copying, which has a composition containing an appropriate amount of an oxide of a part of Group 1 elements of the periodic table, and has a smooth surface and excellent durability and image characteristics.

[Prior Art] There is a dry two-component developing method as one of the developing methods for electrophotography, and the one currently most widely used is the one called the magnetic brush developing method. The characteristics necessary for the carrier material of the system developer include triboelectric charging properties, magnetic properties, fluidity, durability, etc., and studies on these characteristics have been attempted from various aspects.

Ferrite carrier materials are currently widely used as two-component carrier materials. As is well known, ferrite is a metal oxide, so it has a smaller apparent density than iron powder carriers and can be used as a lightweight developer.
Furthermore, compared to iron powder, it has a lower residual magnetic flux density and a smaller coercive force, resulting in a smaller hysteresis loop area, and can always maintain its initial characteristics against magnetization reversal and magnetization history. has. In addition, ferrite is an oxide that is chemically stable and resistant to image deterioration such as developer surface contamination caused by high-speed development and multiple copying.
It has the advantage of being maintenance-free and is suitable for carriers. Furthermore, by changing the composition, the electrical resistance value can be increased from 104 to 101 due to the semiconducting properties of ferrite.
It can be freely varied within a range of about 2 Ω-cm, and image characteristics can be significantly improved by controlling the amount of charge. Because of these excellent properties, the ferrite carrier material has become an indispensable material as a developer in current electronic copying machines.

1. Problems to be Solved by the Invention] However, conventional ferrite carrier materials of this type have the following drawbacks, and there is still room for improvement. The surface of the carrier particles is rough and irregular, and mechanical or impact contact between the particles causes peeling or destruction of the crystal, and the resulting fine ferrite particles adhere to the surface of the photoreceptor through electrostatic development. The purpose of the invention is to eliminate the above-mentioned drawbacks of conventional ferrite carrier materials, to significantly improve the smoothness of the carrier surface, and to improve the smoothness of the carrier surface.
The object of the present invention is to provide an economical ferrite carrier material that can exhibit stable and good electrostatic copying performance.

Means for Solving Problem E] The present invention, which can achieve such objects, has a composition of Fe2O3 of 45 to 65 mol%.

The main component is a magnesium-zinc ferrite material containing 26 to 32 mol% of MgO, 18 to 22 mol% of ZnO, and in some cases 5 mol% or less of MnO. It has a composition containing 0.01 to 5% by weight of one or both oxides, and has a spherical shape with a microscopic particle size, and its surface is extremely smooth due to the growth promotion of primary sintered particles. This is a ferrite carrier material for electrostatic photography.

[Specific structure of the invention] The present invention will be explained in more detail below.

As described above, the present invention uses a magnesium-zinc ferrite as a base material, and contains an appropriate amount of an oxide of a part of the elements of group (I) of the periodic table to have a t-composition. That is, first, the magnesium-zinc ferrite material that becomes the base material is Fe2
O345-65 mol%2Mg026-32 mol%, Zn
018 to 22 mol%. This composition may contain 5 mol% or less of MnO. The ferrite carrier material according to the present invention contains an oxide of one or both of Ba and Sr among group (I) elements of the periodic table in a magnesium-zinc ferrite base material such as B. It has a composition with a weight of %.

The method for producing the ferrite carrier material is almost the same as that in the prior art, and can be produced by a well-known method for producing spherical particles, such as a spray drying method or a fluidized granulation method. For example, fine ferrite particles having the above composition are thoroughly mixed with a binder, a dispersant, water, an organic solvent, etc., and the slurry solution is spray-dried under appropriate conditions to produce spherical pellets. In this step, the specific gravity of the powder can be appropriately controlled, and the state of dispersion of pores can be controlled to a desired shape. After the spherical particles created in this way are fired in a kiln or furnace, they are classified using a sieve to obtain a carrier material having a desired particle size distribution.

The reason why magnesium-zinc ferrite is used in the present invention is that it is cheaper than the conventionally commonly used nickel-zinc ferrite, and is a high-resistance material that falls within the resistance range suitable for carrier materials for electrostatic copying. ! It is from. Since the composition range of each component is almost the same as that normally used for this type of magnesium-zinc ferrite material, explanations of the individual composition ranges will be omitted. The electrical resistivity required for a carrier material for electrostatic copying varies over a fairly wide range depending on the requirements of the copying machine that uses it, but is usually between 104 and 10".
It is about Ω-(7). In the present invention, the electrical resistivity can be adjusted to an appropriate value by mainly changing the amount of zinc oxide in the composition range. Further, as described above, a configuration in which a small amount of manganese oxide is added to this magnesium-zinc ferrite is also included in the present invention. When manganese is added, the resistivity tends to increase, and it can stabilize the resistance value and function as an extender.

In any case, one of the features of the present invention is that a magnesium-saltite ferrite material having such a composition is used as a base material, and an appropriate amount of oxides of one or both of Ba and Sr among the elements of Group 1 of the periodic table is contained therein. There are two major characteristics that allow it to achieve the desired properties. By containing these materials, the wettability of crystal grains is improved during the crystal growth stage during sintering, and together with the promotion of grain growth, the smoothness of the surface of the ferrite carrier material is significantly improved. The shortcomings of the prior art can be improved to a large extent. Here, one or both of Ba and Sr may be added in the form of a simple substance, an oxide, a hydroxide, or a salt. These additives will be contained in the particles in the form of oxides during the sintering process. The amount of the additive ranges from 0.01 to 5% by weight in terms of oxide. The reason why the lower limit is set at 0.01% by weight is that it is necessary to add at least this amount or more in order to improve the surface smoothness. On the other hand, the reason why the upper limit was set at 5% by weight is that even if it is added in an amount exceeding 5% by weight, there will not be a very extreme change in the properties, and adding more than that is completely meaningless.

The smoothness of the surface of the carrier material can be clearly understood especially by observation using an electron microscope. This is done by randomly extracting several electron micrographs of a region containing a large number of carrier materials taken many times at a low magnification of several hundred times, and then selecting a unit 1-grain with a size larger than a window (for example, about 20 μm or larger). By calculating the percentage of spherical cores having (unit grain) relative to the total number of cores, it is possible to numerically understand the large crystallization rate. From these observations using an electron microscope and the calculation of the large crystallinity rate based on the observation, it can be seen that the surface roughness is significantly improved when a small amount of the additive is added, compared to when the additive is not added.

In the present invention, the particle size of the carrier material is preferably about 5 to 200 μm. In order to improve image resolution in a two-component developer, it is better for the carrier particles to be fine, but if the carrier particles are too fine, the fluidity will deteriorate. In other words, in order to mix uniformly with the toner, it must have a certain degree of fluidity, and if it is too fine than 5 μm, the fluidity will be extremely poor, and conversely, if it is too fine than 5 μm, the fluidity will be extremely poor.
If it becomes larger than , the resolution of the image will deteriorate significantly.

Next, examples of the present invention will be described.

[Example 1 Fe2O3 542 mol%, Mg0 26.6 mol%, Z
With respect to the blending ratio of n0182 mol% and Cu0 1.0 mol%, four types with different compositions were prepared, with no BaO (comparative amount) and with 10 to 50% by weight (inventive product). Prepare powders to be used as samples and mix them in a ball mill. In the actual trial production, it was added in the form of BaCO3. After drying, 900
Calculate at ℃ for 1 hour and grind again using a ball mill. A binder is added to the solution of B, granulated into spherical pellets by a spray drying method, and the obtained pellets are fired at 1250 ° C.
After classification, a ferrite carrier material of 60 to 200 μm was obtained.

Table 1 The properties of carrier materials of each of these compositions are shown in Table 1. Tototo [large crystallization rate] means that a photograph containing about 30 carrier cores is taken at 200 to 300 times magnification using an electron microscope, and all carrier cores with unit grains of 20 μm or more are present. This is a calculation of what percentage of the number of carrier cores exists.

As can be seen from Table 1, when BaO is contained at 10% by weight, the large crystallization rate (probability of existence of particles with large unit grains) increases rapidly and becomes saturated at about 5% by weight. Although it is not listed in Table 1, BaO is 0.01
Even when it is contained in a large amount by weight, a considerably large crystallization rate is obtained. In other words, the increase in the large crystallinity ratio means the improvement in the smoothness of the particles, and this can be easily understood from the following diagram that reproduces the image of the electron Ii @ characteristic mirror. It would be possible. If Ba'0 is not included (
(See Figure 2), there are countless sharp and fine irregularities on the surface of the carrier core.

On the other hand, when an appropriate amount of BaO is contained, the smoothness of the surface of the carrier core is significantly improved as shown in FIG.

[Example 2] Fe20347.6 mol%, MgO29.2 mol%,
In the blending ratio of 10 mol% of Zn02 and 2 mol% of MnO2, there is a case where S'0 is not included (comparative amount) and a case where S08-4 is not included (comparative amount).
, 6% by weight (product of the present invention), four types of powders were prepared with different compositions.
A ferrite carrier material of 60 to 200 μm was obtained in the same manner as described above. In addition, in this case as well, strontium is 5
It is added in the form of rCO.

The properties of the carrier materials of each of these compositions are shown in Table 2. Further, the large crystallization rate was calculated by the same method as in Example 1 above.

Although not shown in Table 2, a considerably large crystallization rate was obtained even when SrO was contained in an amount of 0.01% by weight.

In addition, although the above-mentioned example describes only the case where Ba and Sr are added alone, substantially the same effect is produced when these are added in combination, but the description of the example will be omitted.

[Effects of the Invention] Since the present invention is a ferrite carrier material for electrostatic copying configured as described above, the smoothness of the surface of the carrier material can be improved by growing crystal grains in the particles constituting the carrier material. This makes it possible to stabilize image characteristics and improve fluidity. Therefore, even if carrier particles come into mechanical or impact contact with each other, there is almost no peeling or breakage of the crystals, and the surface of the copy paper is improved. The disadvantages of the prior art, such as contamination or wear of the photoreceptor itself, can be completely eliminated. According to the present invention, since the ferrite carrier material itself has a smooth surface, it can be used without coating, and the raw material itself is inexpensive, making it possible to use a low-mounting carrier material. Furthermore, even when coating the surface of the carrier material, the coating thickness can be made uniform, a small amount of coating material is required, and the moisture resistance of the developer can be stabilized. It is possible to achieve many excellent effects.

[Brief explanation of the drawing]

Figure 1 is a reproduction of an electron microscope image of a magnesium-zinc ferrite carrier material according to the present invention, and Figure 2 is a reproduction of an electron microscope image of a magnesium-zinc ferrite carrier material without additives. be. Patent applicant Fuji Electrochemical Co., Ltd. Agent Shigeru Estimates Figure 1 Figure 2

Claims (1)

[Claims] I Magnesium with Fe2O 345-65 mol%, Mg0 26-32 mol%, ZnO 18-22 mol%
The zinc-based ferrite material has a composition containing 0.001 to 5% by weight of oxides of one or both of Ba and Sr among Group II elements of the periodic table, and promotes the growth of sintered particles constituting the spherical carrier. A ferrite carrier material for electrostatic copying characterized by a smooth surface.