JPH05216270A - Magnetic developer - Google Patents

Abstract

PURPOSE:To provide a magnetic developer able to obtain highly accurate image, easily removable from the surface of an image carrier after transferring and excellent in cleaning property. CONSTITUTION:In the magnetic developer made by mixing a magnetic carrier with a magnetic toner containing at least a binding resin, a magnetic powder and a charge controlling agent in the weight ratio of (90:10)-(10:90), the magnetic toner is formed by burying the powder of a magnetic body having 0.01-3mum preferably 0.1-1mum average particle diameter into the particle of the toner produced by the polymerization method and having 2-9mum average particle diameter.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic developer containing a mixture of a magnetic carrier and a magnetic toner, which is used for developing an electrostatic charge image formed on the surface of an image carrier by a magnetic brush method. In particular, the present invention relates to a toner for developing an electrostatic charge image, which can obtain a high-definition image and can be easily removed from the image carrier surface after transfer and has good cleaning property.

[0002]

2. Description of the Related Art Conventionally, in an image forming method utilizing electrophotography or electrostatic recording, an electrostatic charge image formed on the surface of an image carrier made of a photoconductor or a dielectric is built in, for example, a permanent magnet member. At the same time, a developing means composed of a sleeve which is inserted into the permanent magnet member so as to be rotatable relative to the permanent magnet member is used, and a toner image is developed by rubbing with a so-called magnetic brush made of a developer. Then, this toner image is directly fixed, or the toner image is transferred onto a transfer sheet such as plain paper and then fixed to obtain a final screen.

Most of the developers used for the above-mentioned magnetic brush development are two-component developers in which a magnetic carrier and a non-magnetic toner are mixed. On the other hand, there is also a method of using a one-component developer composed of a resin and magnetic powder as the developer. In the former method using a two-component developer, an image having good image density and resolution can be obtained, but there is a problem that the reproducibility of halftone is poor.

On the other hand, the latter method using a one-component developer has problems such as the occurrence of charge cohesive development of toner with an increase in toner charge amount, and insufficient development due to insufficient toner on the sleeve. As means for solving these problems, there has been proposed a developer obtained by mixing a magnetic carrier and a magnetic toner as described in JP-A-59-162563 and JP-A-59-216149. It is said to have the advantages of both the two-component developer and the one-component developer.

As a general method for producing the toner constituting the above-mentioned developer, there is known a method in which raw materials are heated, kneaded, cooled and then pulverized and classified. In order to obtain an image with high image density and less background fog, 9 to 13
Generally, the particle size distribution is adjusted so that the average particle size is μm. However, recently, the demand for higher image quality is increasing, and in order to satisfy this demand, the toner tends to have a smaller particle size, and it is necessary to form the average particle size to 2 to 9 μm.

However, the toner having a small particle size produced by the above pulverization method has a disadvantage that the fluidity is low because the shape of the particles is irregular. If a large amount of a fluidity modifier such as finely powdered silica is added to improve the fluidity, the fluidity is improved, but the surface of the photoconductor is damaged, and the charge amount due to humidity is reduced. This causes inconvenience such as large fluctuation.

In order to solve the problems existing in the above kneading-pulverizing method, a method for producing a toner by a suspension polymerization method has been proposed (for example, JP-A-54-84730 and JP-A-56-110947).
No., 59-28165, etc.). In these suspension polymerization methods, a monomer composition in which a polymerizable monomer and a colorant, and optionally a polymerization initiator, a cross-linking agent, a charge control agent, and other additives are dissolved or dispersed, It is added to a dispersion medium containing a suspension stabilizer with stirring, granulated, and polymerized to form a toner.

Since the suspension polymerization method does not include a crushing step at all, the product does not need to be brittle or fragile, and the colorant or the like is not exposed on the fracture surface of the toner generated by the crushing. Therefore, it is a preferable manufacturing method. Further, since the obtained toner has a spherical particle shape, it is said to have advantages such as excellent fluidity.

[0009]

When an image is formed by a magnetic developer formed by mixing the above-mentioned toner with magnetic powder and mixing it with a magnetic carrier,
The one consisting of the steps of development, transfer, fixing, and cleaning has been put into practical use. In order to obtain a high-definition image, it is effective to use the toner having a small particle size as described above, and it is important to completely remove the excess toner adhering to the surface of the image carrier after transfer. Is.

However, it is very difficult to uniformly disperse the magnetic powder in the toner particles of the toner produced by the suspension polymerization method, and a toner which is usually used (average particle diameter of 10 to 11 μm). Since the particle size is smaller (average particle size is 2 to 9 μm), it is difficult to remove from the surface of the image carrier after transfer, and there is a problem that so-called cleaning property is poor. That is, even after cleaning, excess toner remains on the surface of the image carrier, and the remaining toner is transferred to an undesired area in the next image formation, resulting in a problem of deterioration in image quality.

The present invention solves the above problems existing in the prior art, and by making the magnetism of individual toner particles uniform, a high-definition image can be obtained and the toner can be easily removed from the image carrier surface after transfer. It is an object of the present invention to provide a magnetic developer having good cleaning property.

[0012]

In order to achieve the above object, in the present invention, a magnetic carrier and a magnetic toner containing at least a binder resin, magnetic powder and a charge control agent are used at 90:10 to 10 :. In a magnetic developer mixed in a weight ratio of 90, the magnetic toner is produced by a polymerization method, and the average particle diameter is 2-9 μm on the surface of the toner particles.
The technical means of embedding the magnetic substance powder of 0.01 to 3 μm, preferably 0.1 to 1 μm, is adopted.

As a material constituting the magnetic powder in the present invention, an alloy or compound containing an element exhibiting ferromagnetism such as ferrite, magnetite, iron, cobalt, nickel, etc. can be used, but the average particle size is small. If it is too much, the effect of improving the cleaning property cannot be expected, which is not preferable. On the other hand, if the particle size is too large, the embedding of the toner particles on the surface becomes insufficient, and peeling and scattering of the toner particles from the surface occur, which is inconvenient. Therefore, the average particle size is 0.01 to 3 μm, preferably 0.1 to 1 μm. The content of the magnetic powder is 10 to 40% by weight in order to exhibit the function as a coloring agent and to secure the fixing property.

The polymerizable monomer used in the present invention is a radical-polymerizable one and is used alone or in combination of two or more so that the resulting polymer satisfies the characteristics required for the toner. .. Examples of such a monomer include a monovinyl aromatic monomer, an acrylic monomer, a vinyl ester monomer, a vinyl ether monomer, a diolefin monomer, and a monoolefin monomer. Can be mentioned.

As a component to be contained in the toner particles, various additives (charge control agents such as nigrosine dyes and metal-containing azo dyes) used in general dry developers, and release agents such as olefin polymers are used. Agents, fluidity modifiers, fillers, etc.) may be contained, but in order not to lower the fixability, the total content is preferably 15% by weight or less.

The toner having a small particle diameter according to the present invention can be produced by using the above-mentioned materials, for example, JP-A-60-186852 and JP-A-60-186854.
As described in Japanese Patent Publication No. 1993-242, it is possible to use those polymerized using various polymerization methods. That is, not only the polymer that is made into particles by emulsion polymerization, soap-free emulsion polymerization, suspension polymerization, etc., but also by dissolving the polymer obtained by each polymerization method or solution polymerization, bulk polymerization, etc. in a solvent, and then spray drying Granulated products can be used. By such a polymerization method,
It is possible to obtain a toner having an average particle size of 2 to 9 μm and a narrow particle size distribution, that is, a uniform particle size.

That is, in the present invention, materials such as a polymerizable monomer, a colorant, a release agent, a polymerization initiator, a molecular weight modifier, and a dispersion stabilizer are sufficiently mixed and then added into water, and then, for example, Disperse and granulate by stirring at high speed with a homogenizer, and stir at low speed after reaching a predetermined particle size distribution.
The temperature is raised to 80 ° C. and the reaction is allowed to proceed for a predetermined time to complete the polymerization. The obtained polymer is washed with water, filtered, dehydrated and dried to obtain toner particles.

Here, as the polymerization initiator, potassium persulfate, 2-2'-azobisisobutyronitrile, 2,4-
One or more known compounds such as dichloroperoxide and redox type initiator may be used, and the amount thereof is preferably 0.1 to 5% by weight of the monomer composition. As the molecular weight regulator, tert-butyl mercaptan, tert-dodecyl mercaptan, etc. may be used. As the dispersion stabilizer, gelatin, carboxymethyl cellulose, starch, polyvinyl alcohol, surfactant and the like can be used. The dispersion stabilizer is 0.01 to 1 with respect to 100 parts by weight of the monomer.
It is desirable to use it in a ratio of 0 parts by weight.

[0019]

With the above structure, a magnetic developer containing a particle system suitable for high image quality and a magnetic toner having a small particle size with uniform magnetism can be obtained, and the cleaning property can be improved.

[0020]

Example: As a raw material, by weight, styrene 70 parts, n
Butylmethacrylate 30 parts, divinylbenzene 0.5
Parts, t-lauryl mercaptan 0.5 parts, azobisisobutyronitrile 2 parts, polyester dispersant (polyhexamethylene adipate) 1.0 part and charge control agent (Orient Chemical's Bontron E-81) 4 parts are weighed and mixed. And mixed in a ball mill for 2 hours.

Next, 1000 parts of ion-exchanged water and a homogenizer (a homomixer manufactured by Nippon Tokushu Kika Kogyo Co., Ltd.) were stirred in a container, and 0.5 part of γ-anilinomethyltriethoxysilane (SZ6083 manufactured by Toray Silicone Co.) was added. And stirred. Add the above monomer composition mixture into the dispersion medium,
Dispersion granulation was carried out at 00 rpm for 10 minutes. After replacing the reaction vessel with nitrogen, change to a stirrer equipped with a paddle stirrer.
While continuing stirring at 20 rpm, the temperature was raised to 70 ° C. and the reaction was performed for 10 hours.

The polymer obtained was poured into cold water, filtered,
After washing with alkali and washing with water, dehydration and vacuum drying at 40 ° C. for 12 hours were performed to obtain toner particles having a volume average particle diameter of 6 μm (measured value by Coulter counter). Next, 100 parts by weight of the toner particles were mixed with magnetite shown in Table 1 (EPT500 manufactured by Toda Kogyo Co., Ltd., average particle size 0.1 μm) by a dry mixer (Hybridizer manufactured by Nara Kogyo Co., Ltd.), and the magnetite was mixed with the surface of the toner particles. Embedded in a magnetic toner A.

Next, as a comparative example, magnetite (EPT500 manufactured by Toda Kogyo Co., Ltd., average particle size 0.1
(30 μm) was prepared, and this was designated as magnetic toner B. As another comparative example, 68 parts by weight of styrene-n-butyl methacrylate, 25 parts of magnetite (EPT500 manufactured by Toda Kogyo), 2 parts of charge control agent (E-81 manufactured by Orient Chemical Co., Ltd.), polypropylene (Viscor 550P manufactured by Sansei Kasei). A raw material consisting of 5 parts was dry-mixed, kneaded by heating with a kneader, cooled and solidified, and then pulverized and classified to prepare a magnetic toner C having an average particle diameter of 11 μm.

The magnetic toner and ferrite carrier produced as described above (KBN-100 manufactured by Hitachi Metals, particle size 3
7 to 74 μm) in a weight ratio of 40:60 to form a magnetic developer, a copy image is formed under the following conditions, and image evaluation and other results are shown in Table 1.

In this case, the photoconductor is OPC.
With a surface potential of -650 V and a peripheral speed of 60 mm / sec.
The bias voltage was −550V. Next, S with an outer diameter of 20 mm
The rotation speed of the sleeve made of US304 was set to 160 rpm. The permanent magnet member coaxially incorporated in the sleeve was magnetized with 6 poles, and the surface magnetic flux density on the sleeve was 650G. The development gap between the photoconductor and the sleeve is 0.
35 mm, the doctor gap between the doctor member and the sleeve was 0.3 mm. The toner image developed under these conditions was transferred onto plain paper and heat-roll fixed at 180 ° C and a linear pressure of 1 kg / cm. The surface of the photoconductor was cleaned with a urethane blade.

[0026]

[Table 1]

As is clear from Table 1, the magnetic toner B to which the magnetic powder is added during the polymerization gives an image with a lot of background fog. Further, the magnetic toner C produced by the usual pulverization method has a large particle size, and thus has a low resolution.
On the other hand, it can be seen that the magnetic toner A of the present invention has a large image density and resolution, and a high-quality image free of background fog is obtained. Fixing rate (calculated from the image density values before and after peeling with an adhesive tape)
The magnetic powder tends to decrease a little as the content of the magnetic powder increases, but it shows 95% at the content of 40%, which is sufficient for practical use.

[0028]

EFFECTS OF THE INVENTION Since the present invention has the constitution and operation as described above, it is possible to obtain a toner having a small particle diameter with uniform particle diameter and magnetic properties by the polymerization method and to improve the cleaning property. There is an effect that a high-definition, high-quality image can be formed.

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Claims (1)

[Claims] 1. A magnetic carrier and at least a binder resin,
Magnetic toner containing magnetic powder and charge control agent
In a magnetic developer prepared by mixing in a weight ratio of 0:10 to 10:90, a magnetic toner is produced by a polymerization method, and the average particle size of 0.01 to
A magnetic developer characterized by being formed by embedding a magnetic substance powder of 3 μm, preferably 0.1 to 1 μm.