JPH0689046A - Production of electrostatic charge image developing magnetic particles - Google Patents

Abstract

PURPOSE:To provide a method for the production of electrostatic charge image developing magnetic particles in which particle distribution is sharp as well as the particles are small in diameter, and which doesn't contain ultrafine particles. CONSTITUTION:A ferrous salt and a ferric salt are allowed to react with each other in an aq. solution to form a magnetite, raw materials consisting of a polymerizable monomer, a polymerization initiator and others are put into the aq. solution containing the magnetite, after the magnetite and the raw material are dispersedly granulated by stirring, the temp. of the aq. solution is raised to 40-80 deg.C to progress a polymerization reaction, and the polymerization product is washed, dehydrated and dried.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing magnetic particles for developing electrostatic images used for developing electrostatic images in electrophotography, electrostatic recording, etc. The present invention relates to a method for producing magnetic particles for developing an electrostatic image for high image quality.

[0002]

2. Description of the Related Art In the conventional electrophotographic method, the surface of an image carrier made of a material such as selenium, zinc oxide, or an organic photoconductor is uniformly charged and then exposed to an electrostatic charge image on the surface of the image carrier. To form. Then, in this electrostatic image, carriers made of magnetic particles such as iron powder and ferrite powder,
Development is performed by bringing a developer mixed with a toner made of an insulating colored resin powder into contact with the toner. Next, a transfer sheet is superposed on the visualized toner image, an electric field is applied from the back surface of the transfer sheet to transfer the toner image to the transfer sheet, and then the toner image is fixed through, for example, a heat fixing unit. The toner remaining on the surface of the photoconductor after the transfer is removed by a cleaning member such as a blade or a fur brush.

A magnetic brush method is generally used for developing the electrostatic charge image formed on the surface of the image carrier. As a developer used in such magnetic brush development, there are many two-component developers in which a magnetic carrier and a non-magnetic or weakly magnetic toner are mixed. On the other hand, there is also a method of using a one-component developer containing a binder resin and magnetic powder as main components as a 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 in that the halftone reproducibility is poor. On the other hand, in the latter method using the one-component developer, the phenomenon of charge aggregation of the toner caused by the increase in the charge amount of the toner,
There is a problem such as insufficient development due to insufficient toner on the sleeve constituting the developing roll.

As a means for solving these problems, for example, a developer prepared by mixing a magnetic carrier and a magnetic toner, as described in JP-A-59-162563 and JP-A-59-216149, is proposed. The conventional two-component type developer and the one-component type developer have both advantages.

[0006]

As the magnetic carrier of the developer, magnetic particles such as iron powder and ferrite powder are used as they are, and those magnetic particles are dispersed in a binder resin. Some of them are used in a closed state. The latter magnetic carrier has a smaller particle size than the former, so that a high quality image is formed and even when carrier adhesion occurs,
It has the advantage of being less likely to damage the surface of the image carrier.

However, since the above-mentioned magnetic particles are generally produced by a pulverization method, fine powder particles, for example, particles having a particle size of 1 μm or less may be mixed in. Therefore, the triboelectric charge amount when used as a magnetic carrier Change and the image quality deteriorates.

In addition, the magnetic carrier is unlikely to be spherical, and the surface often exhibits an uneven state. If the surface is uneven as described above, the surface shape is changed during use, for example, a protrusion is missing, and the amount of triboelectricity is changed to deteriorate the image. Furthermore, if the surface is uneven,
There is a problem that the so-called spent phenomenon of toner adhesion is caused and the image quality is deteriorated.

The present invention solves the above-mentioned problems existing in the prior art, and provides a method for producing magnetic particles for electrostatic image development which have a small particle size and a sharp particle size distribution and do not contain ultrafine particles. The purpose is to do.

[0010]

In order to achieve the above object, in the present invention, a ferrous salt and a ferric salt are reacted in an aqueous solution to produce magnetite, which is present. A raw material composed of a polymerizable monomer, a polymerization initiator and the like is put into an aqueous solution, and the mixture is stirred and dispersed to granulate the magnetite and the raw material.
The technical means of heating the polymerized product by raising the temperature to 0 to 80 ° C. to proceed the polymerization reaction, washing, dehydrating and drying the polymerized product was adopted.

The magnetic particles of the present invention can be used as a magnetic carrier for forming a magnetic developer by mixing with a non-magnetic toner, a weak magnetic toner and a magnetic toner, and also as a one-component magnetic toner.

The content of magnetite contained in the polymerization product in the present invention varies depending on the magnetic characteristics required for the magnetic particles, but in the case of a magnetic carrier, it is preferably 30 to 90% by weight. On the other hand, when used as a magnetic toner, the content of magnetite is
It may be 10 to 80% by weight, preferably 20 to 60
It is good to set it as the weight%.

The polymerizable monomer used in the present invention is a radical-polymerizable one, and one type or a single type may be used so that the produced polymerization product satisfies the characteristics required for magnetic particles as a magnetic carrier or a magnetic toner. Used in combination of two or more. Examples of such monomers include monovinyl aromatic monomers, acrylic monomers, vinyl ester monomers,
Examples thereof include vinyl ether-based monomers, diolefin-based monomers and mono-olefin-based monomers.

Next, as a 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.

In the present invention, in the polymerization step, in addition to the above-mentioned polymerizable monomer and polymerization initiator, a molecular weight modifier and a dispersion stabilizer can be used as a raw material. As the molecular weight modifier, tert-butyl mercaptan can be used. , Tert-dodecyl mercaptan, etc. may be used. As the dispersion stabilizer, gelatin, carboxymethyl cellulose, starch, polyvinyl alcohol, surfactant, etc. 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.

Next, when the magnetic particles are used as a magnetic toner, in addition to colorants (carbon black, aniline blue, lamp lalace, rose bengal, quinoline yellow, malachite green, etc.), if necessary, general Including various additives used in dry developers (charge control agents such as nigrosine dyes and metal-containing azo dyes, mold release agents such as olefin polymers, fluidity modifiers, fillers, etc.) However, the total amount is preferably 15% by weight or less so as not to deteriorate the fixing property. The colorant may be contained in a ratio suitable for forming a visible image with a sufficient concentration (usually 1.2 or more), and is usually contained in the magnetic toner in an amount of 2 to 20% by weight.

[0017]

With the above structure, it is possible to manufacture small particles having no irregularities on the surface and having a uniform particle size for developing electrostatic image particles.

[0018]

Example First, magnetite, which is a ferromagnetic material, is synthesized by an aqueous solution method (wet synthesis method). That is, ferrous sulfate heptahydrate is dissolved in pure water and kept in a constant temperature reaction tank. In this case, the air in the upper space is replaced with nitrogen gas to prevent oxidation. Next, the inside of the constant temperature bath is heated to 60 ° C., 6N aqueous solution of sodium hydroxide is put into the pure water, and FeOOH of iron hydroxide is generated by a neutralization reaction. Further, 10 l / min of air was introduced into the aqueous solution, and the FeOOH was spinelized in 24 hours to obtain magnetite Fe.
Generates ₃ O ₄ .

In the usual means for producing magnetite, the precipitate is extracted at 80 ° C. after completion of the above steps.
Drying is performed for 48 hours. In the present invention,
The process proceeds to the next step without performing this drying. That is, separately by weight as a raw material, 80 parts of styrene, 20 parts of n-butyl methacrylate, 0.5 part of divinylbenzene,
0.5 parts of t-lauryl mercaptan, 2 parts of azobisisobutyronitrile, 1.0 part of polyester-based dispersant (polyhexamethylene adipate) and 2 parts of charge control agent (Bontron E-81 manufactured by Orient Chemical Co., Ltd.) were weighed and mixed, The monomer composition mixed by a ball mill for 2 hours is put into an aqueous solution containing the magnetite and stirred.

For the above stirring work, for example, a homogenizer (Homomixer manufactured by Nippon Tokushu Kika Kogyo Co., Ltd.) is used, and 0.5 part of γ-anilinomethyltriethoxysilane (SZ6083 manufactured by Torre Silicone) is dispersed in 1000 parts of an aqueous solution. , Magnetite 85% by weight, monomer composition 1
It was set to 5% by weight. That is, 10 at 6000 rpm
After dispersion granulation for a minute, the reaction vessel was replaced with nitrogen gas, and the stirring apparatus was changed to a paddle stirring blade. While stirring was continued at 120 rpm, the temperature was raised to 70 ° C. and the reaction was carried out for 10 hours.

The obtained polymerized product was put into cold water, filtered, washed with alkali, washed with water, dehydrated, and then dried at 40 ° C. for 1 hour.
It was dried under reduced pressure for 2 hours to obtain spherical magnetic particles having an average particle size of 10 to 30 μm. The D. C. Electric field 100
The volume resistivity at 0 V / cm was 3 × 10 ¹⁴ Ω-cm.

The magnetic particles produced as described above are used as magnetic carriers, and non-magnetic toner (average particle size: 9.5 μm) is added to the magnetic carrier.
m) was mixed to prepare a magnetic developer having a toner concentration of 4% by weight, and a commercially available two-component copying machine (U-Bi × 300 manufactured by Konica) was used.
According to 0), a copied image was formed and the image was evaluated. As a result, the image density was 1.3 to 1.4, the resolution was 8 to 10 lines / mm, and there was no fog, and an image with good sharpness was obtained. Furthermore, it was confirmed that no flaw was generated on the surface of the image carrier even after copying 50,000 sheets continuously. In the developer containing the conventional magnetic carrier as a constituent material used as a comparative example, flaws were found on the surface of the image carrier at the time of copying 10,000 sheets continuously.

Next, the same image formation was carried out using a magnetic developer having a toner concentration of 30% by weight, which is a mixture of the above magnetic carrier and magnetic toner (average particle size 9.0 μm). In this case, OPC is used as the image carrier, and the surface potential-
650V, peripheral speed 60mm / sec, bias voltage -55
It was set to 0V. Next, the rotation speed of the sleeve made of SUS304 having an outer diameter of 20 mm 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 750G. The developing gap between the image carrier and the sleeve was 0.5 mm, and the doctor gap between the doctor member and the sleeve was 0.4 mm.
The toner image developed under these conditions was transferred onto plain paper and heat-rolled at 180 ° C. and a linear pressure of 1 kg / cm.
The surface of the image carrier was cleaned with a fur brush having a diameter of 30 mm and 100 rpm.

As a result, even after the continuous printing of 500,000 sheets,
It was confirmed that no flaw was generated on the surface of the image carrier. On the other hand, when a conventional developer using a ferrite carrier is used, at the time of copying 15,000 sheets, a flaw is generated on the surface of the image carrier and a vertical line appears on the image,
Image quality deterioration was observed.

[0025]

EFFECTS OF THE INVENTION Since the present invention has the structure and operation as described above, the following effects can be obtained. (1) Magnetic particles having a uniform particle size and a small particle size can be obtained, and the particle size distribution can be sharpened. (2) Since spherical particles with no irregularities on the particle surface can be obtained,
The amount of triboelectricity is stable and high quality images can be obtained. (3) The possibility of scratches on the surface of the image carrier is low
The life of the image carrier can be significantly increased.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location G03G 9/08 381 384

Claims (1)

[Claims] 1. A ferrous salt and a ferric salt are reacted in an aqueous solution to produce magnetite, and a raw material comprising a polymerizable monomer, a polymerization initiator and the like is added to the aqueous solution in which the magnetite is present. Charge and stir to disperse and granulate the magnetite and raw materials, and then add an aqueous solution at 40 to 80 ° C.
A method for producing magnetic particles for developing an electrostatic charge image, the method comprising: heating up to a temperature to proceed a polymerization reaction, washing a polymerization product with water, dehydration, and drying.