JPH0623870B2 - Image forming method - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming method. More specifically, it relates to an image forming method using magnetic brush development.

Prior Art and Problems Thereof, it has been proposed to use so-called soft ferrite as carrier particles in magnetic brush development (US Pat. Nos. 3,839,029 and 3,914,181).
No. 3929657, etc.).

Such carrier particles made of ferrite show magnetic characteristics equivalent to those of conventional iron powder carriers, and unlike iron powder carriers, there is no need to provide a coating layer of resin or the like on the surface, and therefore extremely high durability. It is a thing.

In this case, when the composition of the ferrite actually used as the conventional carrier particles is expressed as (MO) _100-X (Fe ₂ O ₃ ) _X (where M is one or more divalent metals), x is It is about 53 mol% or less.

By the way, according to the research results of the present inventors, even if ferrite particles having the same composition are controlled in the atmosphere during firing,
It has been found that the resistance of the particles changes. Then, by changing the resistance of the carrier particles, images having various gradations can be obtained, and various image quality can be selected. Further, by changing the resistance, it is possible to obtain the optimum image characteristics according to various types of copying machines.

Therefore, it can be said that as the ferrite particles, those having a large variation range of the resistance value by changing the firing atmosphere are preferable.

However, in the case of the composition having the Fe ₂ O ₃ content of about 53 mol% or less as described above, the resistance value itself is high and the obtained image density is low. Further, it has been found that the change width of the resistance value is small even when the firing atmosphere is changed, the change rate of the gradation is small, and the image quality cannot be arbitrarily selected.

II Purpose of the invention The main purpose of the present invention is to change the resistance value to a wide range by using ferrite carrier particles whose resistance change width due to the change of the firing atmosphere is significantly wider than the conventional one. Accordingly, it is an object of the present invention to provide an image forming method capable of obtaining a toner image having a required optimum image quality.

The present inventors have completed the present invention as a result of repeating various studies on such an object.

That is, the present invention, when using the same starting material, as the firing atmosphere, when the oxygen partial pressure is changed by changing the mixing ratio of air and nitrogen in the range from air to nitrogen atmosphere,
As a sintered ferrite particle composition having a resistance change ratio of 10 ⁵ or more, a starting material composition ratio corresponding to the composition represented by the following formula [I] is selected by converting it into a divalent metal oxide or a trivalent metal oxide. The starting material is fired under different oxygen partial pressures to obtain a plurality of ferrite particles having different particle resistances. Each of the ferrite particles is mixed with a toner to be used as a developer, and each developer is used. Obtain a toner image with the electrostatic image device of the model used, determine the oxygen partial pressure at the time of firing to obtain the required image density and gradation according to the model, and use the starting material of the selected composition. This is an image forming method in which magnetic carrier particles are baked by the determined oxygen partial pressure and mixed with toner to be a developer, and a toner image is obtained by an electrostatic image device of the above model.

Formula [I] (MO) _100-X (Fe ₂ O ₃ ) _X {In the above formula, M is Mn, Zn, Mn + Zn, M
Represents any of n + Mg, Mn + Mg + Zn, Mn + Mg + Cu and Mn + Mg + Zn + Cu. However,
When M contains one or more elements other than Mn, the atomic ratio of Mn in M is 0.05 or more.

Moreover, when M contains Mg, the atomic ratio of Mg in M is 0.
It is less than 05.

Furthermore, x is greater than 53 mol%. } III Specific Structure of the Invention Hereinafter, the specific structure of the present invention will be described in detail.

In the above formula, M is Mn, Zn, Mn + Zn, Mn
+ Mg, Mn + Mg + Zn, Mn + Mg + Cu and M
It is either n + Mg + Zn + Cu.

On the other hand, the Fe amount x converted to Fe ₂ O ₃ is larger than 53 mol%. When x is 53 mol% or less, the resistance value change width becomes small. And, in particular, x is 54 mol%
When the above is reached, the resistance value variation range becomes extremely large.

On the other hand, the upper limit of x is not particularly limited, and 10
It need only be less than 0 mol%. However, in terms of saturation magnetization, x is preferably 99 mol% or less, more preferably 90 mol% or less. At this time, the saturation magnetization becomes extremely large, and the carrier hardly adheres to the photoconductor or scatters from the magnetic brush.

On the other hand, M is as described above. M is Mn or Zn
It may be composed of only Mn, or may be composed of Mn and one or more kinds of other Zn, Cu, Mg and Co under the above-mentioned restrictions. However, when M contains one or more elements other than Mn, the atomic ratio of Mn in M is 0.0
It is 5 or more.

This is because when the atomic ratio of Mn is less than 0.05, the saturation magnetization decreases, and the carrier adhesion and carrier scattering as described above increase.

Further, the atomic ratio of Mg in M is less than 0.05.

In this case, when the Mn atomic ratio in M is 0.05 to 0.99, particularly 0.1 to 0.7, high saturation magnetization is given and more preferable results are obtained.

When Zn and / or Cu is contained in M, the composition ratio of Zn and Cu can be arbitrary.

Such ferrite particles have a spinel structure.

In ferrite particles having such a composition, in general,
Within the range of 5 mol% of the total, Ca, Ba, Cr, T
Elements such as a, Mo, Si, V, B, Pb, K and Na may be contained in the form of oxides and the like.

Such ferrite particles usually have an average particle size of 1000 μm or less.

Further, generally, a coating layer is not formed on the particle surface, and the magnetic carrier particles are used as they are.

The resistance of the ferrite particles constituting the magnetic carrier as described above is 10 ⁴ to 10 ¹⁴ Ω, especially 10 ⁵ to 10 ¹² when 100 V is applied when the following measurement is performed.
Within the range of Ω.

Then, within such a resistance value range, according to the present invention, the resistance value continuously changes due to a change in firing conditions described later, and the maximum change ratio thereof is 10 ⁵ or more, particularly 10 ⁵ to 10
It is possible to properly select an electrostatic image having an arbitrary image quality as many as ¹⁰ .

The resistance measurement of the ferrite particles is performed as follows, simulating the magnetic brush development method.

That is, the N pole and the S pole are opposed to each other with a gap between magnetic poles of 8 mm. In this case, the surface magnetic flux density of the magnetic pole is 1500 Gaus
The opposing magnetic pole area is 10 × 30 mm. A non-magnetic parallel plate electrode is arranged between the magnetic poles with an interelectrode gap of 8 mm, 200 mg of the test sample is put between the electrodes, and the sample is held between the electrodes by magnetic force. In this way, the resistance may be measured with an insulation resistance meter or an ammeter.

When the resistance measured in this way exceeds 10 ¹⁴ Ω, the image density decreases. On the other hand, when it is less than 10 ⁴ Ω, the carrier is often attached to the photoconductor, the resolution and gradation are deteriorated, and the image quality tends to be high.

Furthermore, the saturation magnetization σm of the ferrite particles in the present invention
Is preferably 35 emu / g or more. At this time,
This is because the so-called carrier pulling in which the carrier adheres to the photoconductor is eliminated, and the carrier does not scatter during repeated development. In this case, a more preferable result is obtained when σm is 40 emu / g or more.

Magnetic carriers composed of such ferrite particles are generally described in U.S. Pat. Nos. 3839029 and 391418,
It is manufactured by a general procedure as described in Japanese Patent No. 3926657.

That is, first, a corresponding metal oxide is prepared.

Next, a solvent, usually water, is added to form a slurry by, for example, a ball mill, and if necessary, a dispersant, a binder and the like are added.

Then, it is granulated and dried by a spray dryer.

After that, firing is performed in a predetermined firing atmosphere and firing temperature profile. Firing follows a conventional method.

In this case, if the equilibrium oxygen partial pressure during firing is reduced, the resistance value is reduced. Then, when the oxygen partial pressure is continuously changed from the air to the nitrogen atmosphere in the firing atmosphere, the resistance value of the particles continuously changes.

After firing, the particles are crushed or dispersed, and then classified to a desired particle size to produce the magnetic carrier particles of the present invention.

The procedure of the image forming method of the present invention is as follows.

First, using the same starting material, when the oxygen partial pressure is changed by changing the mixing ratio of air and nitrogen in the range from air to nitrogen atmosphere as the firing atmosphere, the resistance change ratio is 10 ⁵ or more. As the composition of the calcined ferrite particles, a starting material composition ratio corresponding to the composition represented by the above formula [I] is selected.

Next, this starting material is fired while changing the oxygen partial pressure to obtain a plurality of ferrite particles having different particle resistances. Then, each of the plurality of ferrite particles is mixed with a toner to be used as a developer, and a toner image is obtained by an electrostatic image device of a model using each developer, and an image density required according to the model is obtained. It determines the oxygen partial pressure at the time of firing at which gradation is obtained.

Then, the starting material having the selected composition is fired at the determined oxygen partial pressure to obtain magnetic carrier particles.

The magnetic carrier produced according to the present invention is combined with toner to form a developer. In this case, there is no limitation on the type of toner used and the toner concentration.

Further, in obtaining an electrostatically copied image, there is no particular limitation on the magnetic brush developing method and the photoconductor used, and the electrostatically copied image can be obtained according to a known magnetic brush developing method.

IV Specific Actions and Effects of the Invention In the present invention, magnetic carrier particles having a wide resistance change ratio of 10 ⁵ to ¹⁰ 10 can be obtained by changing the firing atmosphere. Therefore, it is possible to easily obtain carrier particles that give an optimum image according to the model of the copying apparatus. Also, any image quality can be selected.

Further, since it is not necessary to form a film on the surface, the durability of the carrier is good.

Further, the saturation magnetization is 35 emu / g or more, and so-called carrier pulling, in which the carrier adheres to the photosensitive member, and carrier scattering are less likely to occur.

V Specific Examples of the Invention Hereinafter, the present invention will be described in more detail with reference to specific examples.

Example 1. Converted to divalent metal oxides and Fe ₂ O ₃ , the six types of compositions shown in Table 1 below (molar ratio) (Sample No. 1 to No. 1
6) The corresponding metal oxide was prepared.

Next, 1 part by weight of water was added to 1 part by weight of the prepared composition, and the mixture was mixed in a ball mill for 5 hours to form a slurry,
An appropriate amount of dispersant and binder was added.

Then, it was granulated and dried with a spray dryer at a temperature of 150 ° C. or higher.

Each granulated product was fired in a rotary kiln at a maximum temperature of 1350 ° C. under a nitrogen atmosphere containing oxygen and a nitrogen atmosphere, respectively.

After that, crushing and classification are performed to obtain a total of 12 particles having an average particle diameter of 45 μm.
Seed ferrite particles were obtained.

When X-ray analysis and quantitative chemical analysis were carried out on each of the obtained ferrite particles, it was confirmed that each particle had a spinel structure and had a metal composition corresponding to the above mixing ratio.

Then, the saturation magnetization σm (em
u / g) and the resistance (Ω) at the time of applying 100 V were measured.

In this case, the saturation magnetization σm was measured with a vibrating sample type magnetometer.

The resistance is the same as that of the 200 mg sample as described above.
The resistance when 00V was applied was measured with an insulation resistance meter.

Table 1 shows the measured σm in the nitrogen atmosphere, the resistance R _A in the nitrogen atmosphere containing oxygen, the resistance R _N in the nitrogen atmosphere, and the resistance change ratio R _A / R _N for each composition. .

Further, the above ferrite particles are used as they are as magnetic carrier particles at a toner concentration of 11.5% by weight,
Commercially available two-component toner (average particle size 11.5 ± 1.5μ
m) was mixed to obtain a developer.

Magnetic brush development was performed using a commercially available electrostatic copying machine using each developer.

In this case, the surface magnetic flux density of the magnet roller for the magnetic brush is 1000 Gauss, and the rotation speed is 90 rpm. Also,
The gap between the magnet roller photoconductors is 4.0 ± 0.3 mm. Further, a selenium photoconductor was used as the photoconductor, and the maximum surface potential was 800V.

Using gray steel manufactured by Eastman Kodak Company,
Obtain a toner image on plain paper by the above electrostatic copying machine,
The image density (ID) at the original density (OD) of 1.0 was obtained, and the (I
(D) _N and (I of the particles fired in a nitrogen atmosphere containing oxygen)
D) The difference from _A was calculated.

The results are also shown in Table 1.

It should be noted that most of the magnetic carrier particles did not cause the carrier to adhere to the photosensitive member and the carrier did not scatter, but Fe ₂ O ₃ 53 in Sample Nos. 5 and 6 was used.
Σm is 40em for the ones that are less than mol% and fired in air
Below u / g, carrier adhesion and carrier scattering were observed.

From the results shown in Table 1, the magnetic carrier particles of the present invention in which the (Fe ₂ O ₃ ) amount x is larger than 53 mol% have an extremely large resistance change ratio, the gradation of the image changes greatly, and the image quality that can be selected is It turns out that the degree of freedom is extremely large.

In the above, when the firing atmosphere was a mixed gas of oxygen and nitrogen and the mixing ratio was variously changed, it was confirmed that the resistance and the image density continuously changed in the middle of the above values.

Example 2. At compositions shown in Table 2, to create a magnetic carrier according to Example 1, the _{R A, R N, R A} -R N and (I
D) _N- (ID) _A was measured.

The results are shown in Table 2.

From the results shown in Table 2, the effect of the present invention is clear.

In Sample Nos. 9 to 15, σm of 40 emu / g or more was obtained, and there was almost no carrier pulling and carrier scattering. In Nos. 7 and 8, σm was 20 emu / g or less, and carrier pulling and carrier scattering were large.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Katsuhisa Kakizaki 1-13-1, Nihonbashi, Chuo-ku, Tokyo TDC Corporation (72) Inventor Motohiko Makino 1-13-1 Nihonbashi, Chuo-ku, Tokyo TDC Within the corporation (56) References JP-A-55-65406 (JP, A)

Claims (2)

[Claims] 1. A firing atmosphere using the same starting material,
When the oxygen partial pressure is changed by changing the mixing ratio of air and nitrogen in the range from the air to the nitrogen atmosphere, a sintered ferrite particle composition having a resistance change ratio of 10 ⁵ or more,
The starting material composition ratio corresponding to the composition represented by the following formula [I] is selected in terms of a divalent metal oxide or a trivalent metal oxide, and the starting material is fired while changing the oxygen partial pressure to obtain particles. Obtain a plurality of ferrite particles with different resistances, mix each of these ferrite particles with the toner to be used as a developer, and obtain a toner image with the electrostatic image device of the model used with each developer. Then, the oxygen partial pressure at the time of firing to obtain the required image density and gradation is determined, and the starting material having the selected composition is fired at the determined oxygen partial pressure to obtain magnetic carrier particles. An image forming method for obtaining a toner image with the electrostatic image device of the above model by mixing this with a toner to form a developer. Formula [I] (MO) _100-X (Fe ₂ O ₃ ) _X {In the above formula, M is Mn, Zn, Mn + Zn, M
Represents any of n + Mg, Mn + Mg + Zn, Mn + Mg + Cu and Mn + Mg + Zn + Cu. However,
When M contains one or more elements other than Mn, the atomic ratio of Mn in M is 0.05 or more. Moreover, when M contains Mg, the atomic ratio of Mg in M is 0.
It is less than 05. Furthermore, x is greater than 53 mol%. } 2. The image forming method according to claim 1, wherein the oxygen partial pressure for firing the magnetic carrier particles is deviated from the equilibrium oxygen partial pressure of ferrite constituting the particles.