JPH09292740A - Production of ferrite carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a production method of a Li-Mn ferrite carrier which does not contain harmful elements and can form a high quality image. SOLUTION: After source materials are mixed to obtain a basic composition of 2 to 15mol% Li2 O, 5 to 30mol% MnO and 60 to 90mol% Fe2 O3 , the mixture is calcined, pulverized, granulated and sintered in a N2 gas atmosphere having 0 to 15vol.% O2 concn. Or, after the source materials are mixed to obtain a basic composition of 2 to 15mol% LiO2 , 5 to 30mol% MnO and 60 to 90mol% Fe2 O3 , the mixture is calcined, pulverized, granulated and sintered in air, and then heat treated in a N2 gas atmosphere having 0 to 15vol.% O2 concn.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-component developer used for developing an electrostatic charge image formed on the surface of an image carrier in an image forming apparatus such as a laser beam printer or a dry copying machine. The present invention relates to a method for producing a magnetic carrier, which is particularly capable of improving image quality.
The present invention relates to a method for manufacturing an n-type ferrite carrier.

[0002]

2. Description of the Related Art Conventionally, in a printer, a facsimile or the like to which an electrophotographic method is applied, for example, an electrostatic charge image corresponding to information is formed on a photosensitive drum formed in a cylindrical shape, and provided to face the photosensitive drum. A developing roller having a built-in permanent magnet member sucks and conveys a magnetic developer to form a magnetic brush in a developing area, and rubs an electrostatic image forming surface on the photosensitive drum with the magnetic brush to form a toner image. And visualized as The most common means is to transfer this visualized toner image to recording paper and then fix it by heat.

[0003] As the magnetic developer used in the above-mentioned developing method, a one-component type developer consisting of only a toner,
There is a two-component developer which is a mixed powder of a toner and a magnetic carrier. In a developing method using a two-component developer, a toner and a magnetic carrier are mixed at a predetermined ratio,
Both are frictionally charged, and only the toner charged to a predetermined polarity is attached to the electrostatic charge image formed on the surface of the photosensitive drum to form a visible image.

The above two-component type developer is generally required to have stability and maintainability of image quality in continuous development.
For that purpose, it is necessary to maintain the charge imparting ability of the magnetic carrier to the toner and the developer resistance within appropriate ranges, and it is desirable that the charge imparting ability and the developer resistance at the initial stage of development do not change even after a long time use. .

Next, as the toner, a fine powder obtained by mixing and pulverizing a binder resin with a colorant such as a dye or a pigment and various functional additives such as a magnetic powder, a charge control agent and a wax and pulverizing the mixture are used. ing. On the other hand, iron powder or ferrite powder is frequently used as a magnetic carrier. For the purpose of maintaining the charge imparting ability and resistance of the developer, which is a mixed powder of the toner and the magnetic carrier, in a stable state, a binder resin, a charge control agent, and other additives have conventionally been added to the toner. As the design and selection of agents are considered,
Regarding magnetic carriers, various studies have been made on the oxidation treatment method of iron powder, the constituent material of ferrite, the surface properties of these magnetic powders, the coating material and the treatment method thereof.

[0006]

Among the above magnetic carriers, iron powder carriers are subjected to appropriate treatment (for example, oxidation treatment) on the surface.
When used for a long time, the surface of the particles changes physically or chemically and toner adheres (toner spent), and the charging ability is reduced.
Alternatively, it is sensitive to the humidity of the use environment, and the sharpness of the image may be reduced, and there is a disadvantage that the life is short.

On the other hand, a ferrite carrier is chemically stable as compared with an iron powder carrier, has a small change in resistance during use, and has an advantage that the apparent density is about 2/3 that of an iron powder carrier. Therefore, practical use has been promoted.

[0008] The ferrite carrier is composed of a perfect mixture of a suitable metal oxide and iron oxide.
It is a sintered body of an oxide such as n, Mn, Mg, Cu, Li, Ba, V, Cr, Ca and a trivalent iron oxide. As such ferrite carriers, those having various compositions are known, but Ni-Zn ferrite, Mn-Zn ferrite, and Cu-Zn ferrite are generally used.

However, since these ferrite carriers contain elements harmful to the human body such as Zn and Ni, they are subject to legal restrictions when treated as waste. There's a problem. This point Li-Mn
Since ferrite-based carriers are not subject to the above-mentioned legal restrictions, they have attracted attention in recent years, but the optimum development conditions, including the composition, have not been established, and stable formation of high-quality images has been achieved. There is a problem that it is difficult to do.

In the case where the above Li-Mn ferrite carrier is sintered in the atmosphere, for example, 10
The volume resistivity shows a high value even in a high electric field such as kV / cm, and a bias voltage is hard to be applied under a specific developing condition, so that the image density is lowered and it is difficult to obtain a high quality image. Problems also exist.

It is an object of the present invention to solve the above problems existing in the prior art and to provide a method for producing a Li—Mn-based ferrite carrier which does not contain harmful elements and is capable of forming a high quality image. To do.

[0012]

In order to solve the above-mentioned problems, in the first invention, Li ₂ O ₂
After mixing the raw materials so that the basic composition is 15%, MnO 5 to 30%, and Fe ₂ O ₃ 60 to 90%, calcination, pulverization and granulation are performed, and N ₂ gas having an O ₂ concentration of 0 to 15 Vol.% Is used. The technical means of sintering in the atmosphere was adopted.

In the second invention, Li ₂ is used in a molar ratio.
_{O2~15%, MnO5~30%, Fe 2} O 3 60~9
After mixing the raw materials so as to have a basic composition of 0%, calcining, crushing, granulating, sintering in the air, and then heat-treating in an N ₂ gas atmosphere having an O ₂ concentration of 0 to 10 Vol.% Adopted technical means.

The Li-Mn ferrite carrier according to the present invention has a spinel type crystal structure crystallographically. If Li ₂ O is less than 2%, the toner cannot be sufficiently charged, the volume specific electric resistance becomes too high, the image density decreases, and the edge effect becomes too strong, so that the solid black density becomes insufficient. It is not preferable because it becomes uniform.
On the other hand, if the content of Li ₂ O exceeds 15%, the volume specific electric resistance becomes too low, and carrier adhesion is likely to occur, which is inconvenient.

Next, if MnO is less than 5%, the saturation magnetization becomes low and carrier adhesion is likely to occur.
If it exceeds 0%, the saturation magnetization is too high, the rubbing force of the magnetic brush on the image carrier becomes too strong, and brush marks are easily generated, which is not preferable. Further, Fe ₂ O
₃ is less than 60%, the saturation magnetization is low, the image density is low, and carrier adhesion is likely to occur,
On the other hand, if it exceeds 90%, the saturation magnetization becomes too high and brush marks are likely to occur, which is not preferable.

Next, in the Li-Mn type ferrite carrier of the present invention, As, V,
Metal compounds such as Bi, Sb, B, Si and Ca may be added individually or in combination of 0.1 to 1.5% by weight. Thereby, the sintering density is improved and abnormal crystal grain growth is suppressed, and a Li-Mn-based ferrite carrier having a uniform grain surface morphology is obtained.

In this case, as the additive, for example, As ₂ O ₃ , V ₂ O ₅ , Bi ₂ O ₃ , Sb ₂ O ₃ ,
Metal oxides such as B ₂ O ₃ , SiO ₂ , and CaO are applied, and these may be metal compounds (for example, CaCO ₃ ) that can become metal oxides by heating.

In order to improve the sintering density of the Li-Mn-based ferrite carrier and suppress abnormal crystal grain growth, the amount of the metal compound added is preferably 0.5% or less by weight. Even if the addition of 0.5% or more at which the start of generation occurs, up to a weight of about 1.5%, it can be put to practical use without coating the particle surface with resin or the like. The addition amount of the metal compound is most preferably used within the range of 0.1 to 0.5%.

In the present invention, the Li-Mn ferrite carrier particles have an average particle size of 10 (calculated from the weight percentage (particle size distribution) of each particle obtained by the vibration sieving method).
It is desirable that the particle size is within the range of 150 μm to 150 μm, and unless the particle size is less than 10 μm, the carrier easily adheres to the surface of the photoreceptor, except for the case of special electrostatic recording. Is more than 150 μm, the image itself becomes rough, which is not preferable. More preferably 30 to
The range is 100 μm.

In the present invention, the ferrite carrier preferably has a saturation magnetization value of 45 emu / g or more. When the saturation magnetization value is less than 45 emu / g, the adsorbing power to the developer supporting means is lowered, so that carrier adhesion is likely to occur and defects such as white spots occur on the image, which is inconvenient. Furthermore, it is desirable that σ ₁₀₀₀ (value of magnetization measured in a magnetic field of ₁₀₀₀ Oe) is 45 emu / g or more.

In the present invention, the volume specific electric resistance of the above ferrite carrier is determined by D. C. 10 ⁵ to 10 ¹⁰ Ω · cm (preferably 10 ⁷ to 10) in an electric field of 200 V / cm
⁹ Ω · cm), and D. C. It is preferably less than 10 ^{7 in} an electric field of 10 kV / cm. When the value of the volume resistivity is less than the above lower limit value, the magnetic carrier easily separates from the magnetic brush and causes adhesion to the image carrier surface, while when it exceeds the above upper limit value, the edge effect is strengthened,
This is because the solid black development density becomes non-uniform.

In the present invention, when the coercive force of the ferrite carrier exceeds 50 Oe, the particles themselves have the property of a permanent magnet and strongly adhere to the developer supporting means or the like to directly contribute to the development of the toner. As a result, image unevenness occurs and a good image cannot be obtained. Therefore, the coercive force is preferably 50 Oe or less.

The ferrite carrier is required to have wear resistance because it leads to a long life. The fracture strength of the ferrite particles is preferably 5000 g / cm ² or more.

Next, the method of measuring the physical properties described above will be described.
The saturation magnetization value (σ _s ) can be measured with a vibrating sample magnetometer (VSM-3 type manufactured by Toei Industry Co., Ltd.) in a maximum magnetic field of 10 kOe. The volume specific electric resistance (R) was measured by inserting a sample into a cylinder of Teflon (registered trademark) having a diameter of 3.04 mm to a thickness of about 2 mm, applying a load of about 200 g, and applying a load of 20 between both electrodes.
The measurement was performed by applying a DC voltage of 0 V / cm.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION First, raw materials were weighed so as to have a molar ratio in the following () and mixed by a ball mill. The obtained mixed powder is calcined in the atmosphere at a temperature of 900 ° C. for 2 hours,
The calcined sample was crushed with an attritor. The average particle size after pulverization was about 0.7 μm. Then, P.I. V. A (polyvinyl alcohol)
0.5 to 1.0% by weight was added, and the mixture was spray-dried with a spray dryer and granulated.

The obtained granulated powder was placed in an alumina container, sintered under the following sintering conditions, further crushed and classified to obtain a Li-Mn ferrite carrier having an average particle size of 50 μm. It was The volume resistivity of these ferrite carriers and the magnetization value σ in a magnetic field of 1000 Oe.
₁₀₀₀ is shown in Table 1. Note that R ₁ and R ₂ in Table 1 are
Each of D. C. 200 V / cm and D.I. C. 10 kV / cm
The volume specific electric resistance in the electric field of is shown. (A) Li ₂ O (6) + MnO (30) + Fe ₂ O ₃ (64) (B) Li ₂ O (9) + MnO (18) + Fe ₂ O ₃ (73) (C) Li ₂ O (12) + MnO (8) + Fe ₂ O ₃ (80) 1250 ° C. × 2 hours sintering in air 1200 ° C. × 2 hours, N ₂ gas, O ₂ ; 0 to 17 Vo
l.% atmosphere sintering After sintering in air at 1250 ° C. for 2 hours, N ₂
Gas, O ₂ ; 0 to 12 Vol.% Hold at 900 ° C. for 1 hour and then cool.

[0027]

[Table 1]

Next, the toner was prepared in the following manner. That is, 87 parts by weight of bisphenol A type polyester (binder resin; Mw = 19,600, Mn = 2,000), carbon black (colorant: Mitsubishi Kasei # 50) 10 parts, polypropylene (release agent: Sanyo Kasei TP32) 2 parts and 1 part of a charge control agent (Kayacharge T-2N manufactured by Nippon Kayaku) are dry-mixed.

It is melted and kneaded with a twin-screw extruder heated to 150 ° C., then cooled, and the cooled product is roughly crushed by a mechanical crusher to such an extent that it can pass through a wire net having an opening diameter of 1 mm, and then a wind crusher・ Finely pulverized with a jet mill. The powder was classified with a wind-powered classifier (100MZR manufactured by Alpine Co., Ltd.) so that the volume average particle size was about 10 μm, and negatively charged powder was prepared. To this powder, 0.5 part of hydrophobic silica (fluidizing agent; Aerosil R972 manufactured by Nippon Aerosil Co., Ltd.) was added to obtain a toner. The triboelectric charge of this toner is -27.8μ
c / g, volume specific electric resistance was 10 ¹⁴ Ω · cm.

The volume resistivity was measured by inserting a sample with a thickness of about 2 mm into a cylinder made of Teflon (registered trademark) and having a diameter of 3.04 mm, applying a load of about 200 g, and applying a load of 4 between both electrodes.
It was measured by applying a DC voltage of kV / cm. Triboelectric charge amount (Tr
ibo-Electrostatic Charge (TEC) is a value obtained by measuring the triboelectric charge amount of a combination of a ferrite carrier and a toner using a commercially available triboelectric charge amount measuring device (TB-200 manufactured by Toshiba Chemical Co.). . For the measurement of the average particle size (volume basis) of the toner, a Coulter Counter Model TA-II (manufactured by Coulter Counter), which is also commercially available, was used.

The above toner is mixed with the above magnetic carrier to form a two-component magnetic developer having a toner concentration of 5% by weight,
The results of image formation and image evaluation are also shown in Table 1.
In this case, the photosensitive drum was formed by OPC, the surface potential was -650 V, and the peripheral speed was 60 mm / sec. The developing roll is made up of a permanent magnet member (4-pole asymmetric magnetization, surface magnetic flux density of the main magnetic pole for development 800G, surface magnetic flux density of the other magnetic pole 700G),
SUS304 sleeve with an outer diameter of 20mm (150r.p.
m.).

The developing gap is 0.5 mm, the doctor gap is 0.4 mm, the bias voltage from the sleeve is
DC-550V, peak-to-peak voltage 800V,
An image was formed by applying an AC bias voltage having a frequency of 2 kHz. The obtained toner image is transferred to plain paper by corona transfer,
Oilless type heat roll fixing (fixing temperature 180 ℃,
A linear pressure of 1 kg / cm) was applied. Environmental conditions are 20 ℃, 60%
R. H. Met.

In Table 1, the image density is a reflection optical density measured by a Macbeth densitometer, and if it is 1.30 or more, it is recognized as good. The background fog is a density difference between a white portion of an image after printing and white paper before printing, and is a value measured by a colorimetric colorimeter manufactured by Nippon Denshoku Industries. The ground fog is 0.
A value of 10 or less is considered good. In addition, the evaluation symbols for carrier adhesion are as follows: ○: excellent, ×: acceptable.

In Table 1, Nos. 1, 9 and 12 are those sintered in the air, but the magnetic carriers A, B and
In each of C, the volume specific electric resistances R ₁ and R ₂ are large, and the image density appears low.

Next, Nos. 2 to 5 are obtained by subjecting magnetic carrier B to atmospheric sintering and atmospheric heat treatment.
Since No. 5 has a high O ₂ concentration, the value of σ ₁₀₀₀ is low, the image density is low, and the occurrence of background fog and carrier adhesion is recognized. On the other hand, in Nos. 2 to 4, the image density was high, and high-quality images free of background fog and carrier adhesion were obtained.

Nos. 6 to 8 are obtained by subjecting magnetic carrier B to sintering in air and heat treatment in an atmosphere.
Similar to No. 5, No. 8 has a high O ₂ concentration, so that sufficient image quality cannot be obtained. On the other hand, in Nos. 6 and 7, the image density was high, and an image without background fog and carrier adhesion was obtained. From this, it is understood that a good image can be obtained by performing the atmospheric heat treatment even in the air sintering.

As for the magnetic carriers A and C having different compositions, as shown in Nos. 10 and 11 and Nos. 13 and 14, it is found that the atmospheric sintering and the atmospheric heat treatment are effective.

In the case of performing the atmospheric heat treatment, the atmospheric heat treatment may be performed in another heat treatment furnace after the atmospheric sintering, or the atmospheric heat treatment and the atmospheric heat treatment may be continuously performed in the same heat treatment furnace. You can go.

[0039]

EFFECTS OF THE INVENTION Since the present invention has the constitution and operation as described above, it is possible to adjust the volume specific electric resistance of a Li—Mn ferrite carrier containing no harmful element to a desired value, and to obtain a high image quality. There is an effect that the image of can be formed.

Claims (2)

[Claims] 1. Li ₂ O _{2 to} 15% and MnO in molar ratio
After mixing the raw materials so as to have a basic composition of 5 to 30% and Fe ₂ O _{3 of} 60 to 90%, calcination, crushing, and granulation are performed to obtain O ₂
A method for producing a ferrite carrier, comprising sintering in a N ₂ gas atmosphere having a concentration of 0 to 15 Vol.%. 2. Li ₂ O _{2 to} 15% and MnO in molar ratio
After mixing the raw materials so as to have a basic composition of 5 to 30% and Fe ₂ O _{3 of} 60 to 90%, calcination, pulverization, granulation, and sintering in the air, O ₂ concentration of 0 to 10 Vol. % N ₂
A method for manufacturing a ferrite carrier, characterized by performing heat treatment in a gas atmosphere.