JPH01163758A - Ferrite carrier to be used for electrophotographic developing agent - Google Patents

Abstract

PURPOSE:To reduce a fluctuation of quantity of electric charge of a ferrite carrier for electrophotographic developing agent and to make the developer durable for the use for a long time by specifying a compsn. of the ferrite. CONSTITUTION:A ferrite consisting of a compsn. expressed by formula I, satisfying also formula II, III, and IV is used in a ferrite carrier. In the formulas, when X exceeds a value defined by the formula, or a value of Z is out of a range defined by the formula, the value of resistivity exceeds a desired value. When the value of Y is below a value defined by the formula, calcination becomes difficult due to severe melt-sticking, and when the value of Y exceeds a value defined by the formula, saturation magnetization becomes smaller than a desired value. The ferrite of this invention is produced by crushing a mixture of each specified amt. of CuO, MnO, ZnO and Fe2O3 to a slurry, granulating thereafter by adding a binder thereto, then calcining and classifying.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Field of Application> The present invention relates to a carrier for a two-component magnetic brush developer for electrophotography.

<Prior art> Carriers for two-component magnetic brush developers for electrophotography include
Conventionally, iron powder has been used, but such iron powder does not have a specific resistance of 10'Ω at the opening, which is required to prevent the leakage of developing bias voltage and electrostatic latent image charge. ,
It cannot be used as is, and in actual use, the surface is oxidized or coated with resin to give it a high specific resistance.

However, carriers with such a surface layer,
The high-resistance layer on the surface is likely to wear out or peel off due to friction and impact caused by stirring during use as a developer (it cannot withstand long-term use, and such iron powder carriers have a saturation magnetization of 150~ Since it is large at 200 esu/g, the strength of the magnetic brush becomes excessive, which has the disadvantage of causing scratches called brush marks on copied images.In addition, the bulk density is large at approximately 5 g/cd, so the stirring torque of the developing machine must be increased. As the stress to which the image forming agent is subjected increases, some of the toner particles are destroyed, and the destroyed toner particles cover the surface of the carrier, making it easy to produce so-called spent toner in which chargeability deteriorates. From this point of view, it could not withstand long-term use.

In order to overcome these drawbacks of iron powder carriers, ferrite raw material ria has recently been proposed in Japanese Patent Publication No. 56-52305 and other publications. Such ferrite carriers can have a specific resistance of 10'Ω·1 or more by appropriately selecting the components and firing conditions, so they can be used without surface oxidation or resin coating to increase the specific resistance. , there is no deterioration in characteristics due to surface wear or peeling, and the saturation magnetization is less than 100 esu/g, so it does not cause brush marks.In addition, the bulk density is approximately 2.5 g/g.
Since it is small in size (CD), it has the advantage of being less likely to produce spent toner.

The ferrite used as a carrier includes Ni-Zn
There are ferrite, Cu-Zn ferrite, Mn-Zn ferrite, etc., but Cu--Zn ferrite is the most widely used because it is inexpensive and easy to manufacture.

For example, Cu-Zn ferrite is disclosed in Japanese Patent Application Laid-Open No. 60-9034.
As described in Publication No. 5, (Cub) o, + s-a, a (ZnO) 6
+@II z (FezOs) o, h, o, ? A ferrite raw material having a composition represented by the chemical formula is granulated to obtain 10
It is manufactured by a method such as firing at a temperature of 00 to 1500°C.

However, although the Cu--Zn ferrite carrier has such excellent properties and is widely used, it has the disadvantage that the amount of recovered toner is large due to large variations in the amount of charge.

<Problems to be solved by the invention> The present invention effectively solves the above problems.
- A ferrite carrier is provided in which the variation in the amount of charge of the -Zn ferrite carrier is improved and the amount of collected toner is reduced.

Means for Solving the Problem> The present invention provides the following problems:
[FezO+] The amount of recovered toner is characterized by satisfying 0.10≦X≦0.40, 0.1≦Y≦0.7, 1.0≦2≦1.2 in the composition of ferrite represented by z. It is a ferrite carrier for use in electrophotographic developers, and if necessary, 50% or less of Mn is replaced by Ni, Mg, or both in terms of molar ratio.

<Function> As a carrier for electrophotographic developer, the saturation magnetization is 30
~10100e/g-specific resistance is 10h~101oΩ・1
Desirably, the saturation magnetization is in the range of 30 emu/
If it is less than 10100e/
If it exceeds g, the strength of the magnetic brush becomes excessive, and
Brush marks appear on the copied image. Specific resistance is 106
If there is no Ω・1 groove, the developing bias voltage and electrostatic latent image charge will leak, causing white spots on the copied image, and the 1011Ω・
If it exceeds 1, the developing electrode effect will be insufficient and the gradation will deteriorate.

As a result of intensive research, the present inventors have found a composition ratio of ferrite that satisfies the above-mentioned conditions as a carrier, has small variations in band IT amount, and has a small amount of collected toner.

That is, the reasons for limiting the numerical values in the compositional formula of the present invention are as follows.

When X>0.40 or Z<1.0 or Z>1.2, the specific resistance exceeds 1010Ω·0.

If Y<0.1, the fusion will be significant and firing will be difficult,
When Y>0.7, the saturation magnetization is 30 emu/g or less.

Further, in the case of X<0.10, the variation in the amount of charge is not sufficiently improved. FIG. 1 shows the variation in the variation in the amount of charge when X is changed. It can be seen that the variation in charge amount is improved when X≧0.10.

The amount of charge on each toner particle was determined by measuring the movement of toner particles in an electric field using the laser Doppler method.

The reason why the band MM variation is improved is not clear, but Mn has the effect of promoting the spinelization reaction, and Cu
It is believed that this is effective in controlling the precipitation of unreacted residual groups or non-spinel phases existing on the -Zn ferrite carrier surface, and as a result, the carrier surface becomes homogeneous and the variation in charge amount is improved.

When a part of Mn is replaced with old or Mg or both, it is preferable that the molar ratio is 50% or less of Mn.

When it exceeds 50%, the effect of improving the variation in the amount of charge is almost eliminated.

Therefore, according to the present invention, a ferrite carrier that does not cause carrier scattering, has good gradation, and has small variations in the amount of charge, resulting in a small amount of recovered toner can be obtained.

Next, an example of the method for manufacturing the carrier of the present invention will be described.

Formula [(Cu+-XMnx)+-yZnyoko! -2
[Fetus] Oxide or fired ferrite raw material blended into a composition such that 0.10≦X≦0.40 0.1≦Y≦0.7 1.0≦2≦1.2 in z Salt having the above composition is mixed with attritor from 1 to
It is possible to omit this calcination step, in which the resulting slurry is dried and ground for 10 hours in a wet state, and then calcined at 700 to 1000°C using an alumina container.

After calcination, the slurry was crushed to about 0.1 to IIIll with a crusher, and further wet-pulverized with an attritor.
Pellets are granulated to a predetermined particle size using a spray dryer using ~1% Pv^ as a binder. The granulated calcined product or ferrite raw material is heated at 1100 to 1400°C using an alumina container.
After baking for 1 to 10 hours, the mutually attached particles are crushed and classified to a predetermined particle size, for example, 63 to 105 μm to obtain a carrier.The carrier of the present invention can be manufactured by the above steps. , but is not limited to this manufacturing process.

<Example> Example 1 Formula [(Cu+-11Mnx)+-yZnvo] t-z
[In FezO31z, CuO+MnO,
The raw material blended with ZnO* Pe5os was wet mixed and pulverized for 2 hours using an attritor to form a slurry with a concentration of 50%. Add 0.2% PVA as a binder to this slurry.
In addition, it was granulated to an average particle size of 100 μm using a spray dryer. These granules were heated at 1000 to 1300°C for 3
After baking for a period of time, the carrier was classified to 63 to 105 μm to obtain a carrier. Table 1 also shows the specific resistance, saturation magnetization, and standard deviation of the charge amount of the obtained carrier, and the amount of recovered toner measured by adding 4% toner to the carrier and using a commercially available copying machine as a developer.

Example 2 Formula [(C+++-XMnX)1-yZnyo]
[In FezO31z, x, y, z are each second
Cub, MnO, ZnO, Fe
The raw materials blended with tus were wet mixed and pulverized for 2 hours using an attritor to form a slurry with a concentration of 50%. To this slurry, 0.2% PVA was added as a binder, and the slurry was granulated to an average particle size of 100 μm using a spray dryer. After firing each of these granules for 3 hours at the temperature shown in Table 2,
A carrier was obtained by classifying into 5 μm particles. Table 2 shows the specific resistance and saturation magnetization of the obtained carrier. Table 2 shows the results of measuring the amount of toner collected by adding 4% toner to this carrier and binding it with developer using a commercially available copier. I am getting a good career.

Example 3 In the composition of sample No. 5 of Table 2, Cub, MnO, ZnO was substituted with Ni or/and Mg in various molar ratios shown in Table 3 with respect to the total amount of Mn.

A raw material containing Nip, MgO, Fe, and O was wet-mixed and pulverized for 2 hours using an attritor to form a slurry with a concentration of 50%. Add 0.2% PVA as a binder to this slurry, and use a spray dryer to obtain an average particle size of 100 μm.
It was granulated. 20 The granulated material was fired for 3 hours at the temperature shown in Table 3, and then classified to 63 to 105 μm to obtain a carrier. Table 3 also shows the specific resistance and saturation magnetization of the obtained carrier, and the results of measuring the amount of recovered toner by adding 4% toner to this carrier and using it as a developer using a commercially available copying machine.

<Effects of the Invention> According to the present invention, the drawbacks of the ferrite carrier, which had excellent properties but had a problem in terms of the amount of recovered toner, can be improved, and a carrier with excellent economic efficiency can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the standard deviation of the amount of charge of individual toner particles measured by the laser Doppler method with respect to the value of X. Patent applicant: Kawasaki Steel Corporation

Claims (1)

[Claims] 1. Formula [(Cu_1_-_XMn_X)_1_-_YZ
The composition of the ferrite represented by n_YO]_2_-_Z[Fe_2O_3]_2 satisfies 0.10≦X≦0.40 0.1≦Y≦0.7 1.0≦Z≦1.2 A ferrite carrier for electrophotographic developers that collects only a small amount of toner. 2. A ferrite for an electrophotographic developer with a small amount of recovered toner according to claim 1, which has a composition in which 50% or less of Mn is replaced by Ni, Mg, or both in terms of molar ratio. career.