JPH028859A - Ferrite carrier for electrophotographic developer - Google Patents

Abstract

PURPOSE:To allow the control of an electrostatic charge quantity without coating spinel type ferrite with a high-polymer resin by using said ferrite as a base material and adding CaO thereto. CONSTITUTION:The CaO is incorporated at 0.1-10wt.% into the ferrite material having the compsn. consisting of 40-60mol% Fe2O3, 20-40mol% MgO, 5-20% ZnO, and 0.5-15mol% CuO. Saturation magnetization does not increase and the surface smoothness is impaired if the contents of the Fe2O3 and MgO are below the prescribed ratios. The adequate saturation magnetization is not obtainable and the Curie temp. falls if the content of the ZnO is beyond the prescribed mol%. The effect of improving the surface characteristic is not obtd. if the content of the CuO is below 0.5mol% and the fusion of the carrier particles to each other arises if the ratio exceeds 15mol%. There is substantially no effect to the electrostatic charge quantity of a toner if the amt. of the CaO to be added is below 0.1wt.% and the saturation magnetization decreases drastically if the ratio exceeds 10wt.%. The electrostatic charge quantity is freely controlled in this way without requiring the resin coating.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application> The present invention relates to a ferrite carrier for electrophotographic developer.

<Prior Art> The most widely used developing method for electrophotography at present is a dry two-component developing method called a magnetic brush developing method. The characteristics required of the carrier material used here are the amount of toner charge.

Electrical and magnetic properties such as saturation magnetization, magnetic permeability, specific resistance, and dielectric constant, as well as particle size, crystal grain size, particle size distribution, fluidity,
Powder properties such as bulk density are being studied from various angles.

Traditionally, two types of carrier materials are mainly used: iron powder carriers and ferrite carriers. Compared to iron powder carriers, ferrite carriers are chemically stable and long-lasting because they are metal oxides. It has a long service life, has a small apparent specific gravity and can be used as a lightweight developer, and has lower saturation magnetization than iron powder-based carriers and can form a soft magnetic brush, preventing damage to the photosensitive drum. This has advantages such as being able to avoid the generation of brush marks. Further, the ferrite carrier has the advantage that by changing the composition, saturation & fl and specific resistance can be freely set according to the requirements of the copying machine. Therefore, ferrite carriers have become an indispensable material for electrophotographic developers.

However, in conventional ferrite carriers, the change in charge amount with respect to composition is not clear, and it has been difficult to control it. The toner is mixed and stirred with the carrier, adheres to the surface of the carrier, is carried to the photosensitive drum, and is transferred to the latent image area. At this time, if the amount of frictional charge between the toner and the carrier is small, the binding force between the carrier and the toner is weak, and phenomena such as toner scattering and fogging occur. On the other hand, if the amount of charge is too high, the binding force between the carrier and the toner is strong, making it difficult for the toner to move to the latent image area, resulting in a decrease in image density. The amount of charge induced by the friction between the carrier and toner must be suitable for the copying machine being used.The amount of charge on the toner of the developer used in currently available copying machines varies depending on the model in the range of 5 to 80 pc/g. In conventional ferrite carriers, the amount of charge induced by friction is controlled by coating the carrier surface with a polymer resin such as styrene-acrylic resin, but in this case, the amount of charge induced by friction is controlled. There are various problems such as adhesion, toner filming due to close contact between the toner and the coating resin, and early fogging due to insufficient control of the amount of charge, resulting in a decrease in the amount of charge. Also 4M
Since the fat coating step is involved in the carrier manufacturing process, it not only increases costs, but also uses an organic solvent, which is unfavorable from a safety standpoint.

<Problems to be Solved by the Invention> An object of the present invention is to provide a developer carrier used for clear development of electrostatic latent images in electrophotographic machines and electrostatic recording methods.

Another object of the present invention is to provide a ferrite carrier whose charge amount can be freely controlled.

Another object of the present invention is to provide a ferrite that does not require resin coating.

As a result of intensive research into a method for controlling the 4+F charge by 1νj without coating ferrite with a polymer resin, the present inventors have found that this can be achieved by optimizing the carrier composition and adding additives. This discovery led to the present invention.

That is, the present invention provides Fe, 0. 40-60 mol%,
M, 020-40 mol%, ZnO 5-20% mol%, C
This is a ferrite carrier for an electrophotographic developer, characterized in that 0.1-10 mol% of CaO is contained in a ferrite material having a composition of 0.5-15 mol% uO.

<For production> The present invention will be explained in detail below.

The present invention uses spinel type ferrite as a base material and adds CaO to it to form a band. The feature is that it controls the itm. As a ferrite base material, a carrier having a saturation magnetization of 30 emu/8 or more is desirable as a carrier for an electrophotographic developer using a magnetic brush development method, and the optimum composition range for this was determined.

In addition, it is necessary to select an appropriate composition range from the viewpoints of carrier surface properties, Curie temperature, and specific resistance.

Fe, 0. If it is less than 40 mol%, the amount of spinel ferrite produced is small and no increase in saturation magnetization can be expected.
The same problem occurs when the amount exceeds 60 mol %, and the smoothness of the surface deteriorates.

Regarding MgO, if the content is less than 20 mol%, the amount of magnesium ferrite produced is small and the saturation magnetization does not increase, and if it exceeds 40 mol%, MgO is a high melting point substance, so the smoothness of the carrier surface is deteriorated, especially Specific resistance increases.

Regarding ZnO, since zinc ferrite is non-magnetic when it is less than 5 mol% or exceeds 20 mol%, it is necessary to
1 cannot be obtained, and in particular, the Curie temperature decreases.

Moreover, CuO particularly affects the surface properties. If the amount is less than 0.5 mol %, the effect of improving the surface quality will not be exhibited. 1
When it exceeds 5 mol%, fusion of carrier particles occurs,
There are many manufacturing problems.

As described above, in order to obtain optimal characteristics in terms of saturation magnetization, resistivity 1 surface texture, Curie temperature, etc., it is necessary to appropriately select the ferrite composition, and the composition range of the ferrite base material of the present invention is F et Oy 40 to 60. Mol%, MgO20
~40 mol%, ZnO 5~20 mol%.

CuO0.5 to 15 mol% is determined as 1 (v).

However, the ferrite carrier used as the base material has the disadvantage that the amount of toner charge is too large for a developer, and the toner is difficult to move to the latent image area of the photosensitive drum, making it impossible to obtain high image density. The inventors have discovered that by incorporating CaO into the base material, the toner charge amount can be reduced to an appropriate range.

The amount of CaO added is 0 to the above ferrite base material.
．． 1-10% by weight. When the amount was less than 0.1% by weight, almost no effect on the toner charge amount was observed. 10 more
If it exceeds % by weight, the saturation IF will be significantly reduced, the surface of the carrier particles will become a glassy layer, and the resistivity will increase, which is not suitable.

Further, as a result of extensive research, it has been found that when the amount of CaO added is within the above range, the toner band ml can be controlled within the range of 5 to 80 pc/h. This can be considered as follows. Charged development due to friction between carrier particles and toner is caused by carrier physical properties,
In particular, it is closely related to surface texture. The amount of charge on carrier particles largely depends on the crystal grain size. When the crystal grain size is small, the number of grain boundaries and grain surfaces increases, and the number of contact points with the toner increases. It is thought that when the crystal grain size is large, the number of points of contact with the toner decreases, and there are also fewer grain boundaries, so that the charges existing on the surface of the carrier particle become easier to move.

The addition of CaO causes CaO to react with the carrier matrix composition,
It promotes liquid phase sintering, densifies particles, and forms grain boundaries. This grain boundary is a compound of CaO and a ferrite base material, and functions as a high-resistance layer that prevents the movement of charges existing on the surface of the carrier particles. In this way C
The amount of electrification due to friction can be controlled by adding aO to prevent the movement of charges, and by controlling the size of the crystal grains.

On the other hand, if the toner charge amount is less than 5 μc/g, toner scattering and fogging occur during development, which is not preferable. 8 again
If it exceeds 0 pc/g, the toner does not move sufficiently from the magnetic brush to the photosensitive drum during development, resulting in a decrease in image density and an edge effect, which is undesirable.
The amount of toner charge is controlled by adding the carrier particles to an appropriate crystal grain size. A detailed explanation will be given below according to examples.

<Example> The base material composition of ferrite is Feg0. somol%.

A raw material mixed powder was prepared with a constant composition of 33 mol% MgO, 15 mol% ZnO, and 2 mol% CuO, and the amount of CaO added was varied as shown in Table 1. The manufacture of the carrier is as follows. The mixed powder of the above composition is made into a high viscosity slurry using a wet pulverizer such as 0-order Attrike, which is made into a slurry by grinding the slurry concentration to 50% by weight in a mixing standard equipped with a stirring blade, and then
Add a binder such as A (polyvinyl alcohol) and dry the granules to obtain spherical granules. This granule is 1
After heat treatment by holding at 250°C for 5 hours,
A carrier having a particle size of 60 to 150 μm was obtained by classification. Table 1 shows the obtained characteristics of the carrier and the results of the live-action test.
It is also shown in . The toner charge amount in the table was determined using a commercially available toner using blow-off. Image density was measured using a copying machine manufactured by Sanda Kogyo, model DC-112. CaO
The relationship between the amount added and the amount of toner charge is shown in Figure 1.

*Hinakagi Table-1 From Table-1, the carrier according to the present invention has a high image density.
However, in the comparative example 11.12, the image 4 degree was low,
In particular, Comparative Example 12 is Tonashi tF? IJ was low and fog was high at 4 degrees. Furthermore, it has been revealed that the carrier according to the present invention has a long lifespan and shows a high image density of 1.3 or more even after copying 50,000 copies, and is also excellent in durability.

<Effects of the Invention> As described above, the carrier according to the present invention has a charge amount suitable for providing a high image density as a carrier for an electrophotographic developer without impairing the characteristics such as saturation magnetization.

Furthermore, it is a safe and economical carrier because it can be fired in the atmosphere and can be manufactured from inexpensive raw materials without going through processes such as resin corrugation.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the influence of the CaO addition surface on the toner charge amount. Patent applicant: Kawasaki Steel Corporation Addition amount of C (wt%)

Claims (1)

[Claims] For a ferrite material having a composition of Fe_2O_340-60 mol%, MgO 20-40 mol%, ZnO 5-20% mol%, CuO 0.5-15 mol%, CaO was added to 0.1%.
A ferrite carrier for an electrophotographic developer, characterized in that it contains up to 10% by weight.