JPH0683103A - Magnetic toner for electrostatic charge image - Google Patents

Abstract

PURPOSE:To obtain a picture image having a stable triboelectric charge quantity and a high quality even in the high humidity circumstances by strongly fixing fine particles having the static charge characteristic of the same polarity as a magnetic toner on the surface and weakly fixing fine particles having the static charge characteristic of the reversed polarity to the magnetic toner. CONSTITUTION:In the magnetic toner for electrostatic charge image which is essentially consisting of a binding resin and magnetic powders and constitutes a two-component developer by blending a magnetic carrier therewith, the fine particles having the static charge characteristic of the same polarity as the magnetic toner are strongly fixed on the surface and the fine particles having the static charge characteristic of the reversed polarity to the magnetic toner are weakly fixed. As a strong fixing means, a method where magnetic toners and fine particles are mixed in air flow vortexes using a Henschel mixer is exemplified. A weak fixing means can be done under an ordinary mixing condition. The charge stabilization function of the magnetic toner is secured by the presence of fine particles having the static charge characteristic of the same polarity as the magnetic toner and the flowability of the magnetic toner is secured by the presence of fine particles having the static charge characteristic of the reversed polarity to the magnetic toner.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a magnetic toner for an electrostatic charge image used for developing an electrostatic charge image formed on the surface of an image carrier, and in particular, it has a stable triboelectric charge amount and environmental stability. The present invention relates to a magnetic toner for an electrostatic charge image, which can obtain a high and high-quality image.

[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 carried out by bringing a developer mixed with a toner made of insulating colored resin powder (in the case of regular development, the toner is triboelectrically charged in the opposite polarity to the electrostatic image). 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 the halftone reproducibility is poor, and in order to maintain a good image, Since mixing and stirring of the carrier and the toner and control of the toner concentration are required, there is a problem that the mechanism becomes complicated. On the other hand, in the latter method using the one-component developer, there are problems such as the occurrence of the charge aggregation phenomenon of the toner with the increase of the charge amount of the toner and the deterioration of the image quality due to the change of the charge amount due to the environment, especially humidity. There is.

As means for solving these problems, for example, a developer prepared by mixing a magnetic carrier and a magnetic toner as disclosed 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]

The magnetic toner, which is mixed with the magnetic carrier as described above and constitutes the developer, is a fine powder, so that it usually has low fluidity. Therefore, as a fluidity modifier, for example, in a negatively charged magnetic toner, a means for adding and fixing fine particles of a metal oxide such as silica having a negatively charging characteristic to the surface has been adopted (for example, Japanese Patent Laid-Open Publication No. Sho.
58-185405, 58-216252, 59-137305, JP-A-2-257144, etc.).

However, the fixing state of fine powder of silica or the like on the surface of the magnetic toner is often unstable, so that the fine powder of silica or the like is separated and the triboelectric charge amount is lowered, resulting in the image There is a problem that the concentration is lowered.

Further, as the silica fine powder as the fluidity modifier is separated, the fluidity of the magnetic toner is naturally lowered, and aggregates of the magnetic toner may be generated in the developing device, so that the magnetic toner may reach the developing area. There is a problem that the smooth supply of the magnetic toner is obstructed.

Further, the environmental stability is deteriorated, for example, 3
In a high humidity environment such as 0 ° C. and 80 to 85% RH, there is also a problem that the image density is extremely lowered and the image quality is significantly lowered.

The present invention solves the problems existing in the above-mentioned prior art, and provides a magnetic toner for an electrostatic charge image, which has a stable triboelectric charge amount and can obtain a high quality image even in a high humidity environment. With the goal.

[0011]

In order to achieve the above object, in the present invention, an electrostatic charge image which comprises a binder resin and magnetic powder as main components and is mixed with a magnetic carrier to form a two-component developer In the magnetic toner for use, fine particles having the charging property of the same polarity as the magnetic toner are strongly fixed on the surface,
We adopted the technical means of weakly fixing the particles that have the opposite charging characteristics to the magnetic toner.

In the present invention, as the binder resin, one or more known resins can be appropriately selected and used according to the fixing method. For example, in the case of the heat roll fixing system, one or a mixture of two or more of styrene-acrylic copolymer, styrene-butadiene copolymer, epoxy resin, polyester resin and the like can be used.

Next, as the magnetic powder constituting the magnetic toner of the present invention, for example, iron, manganese, nickel, cobalt,
Materials known as magnetic materials such as fine metal powders such as chromium, various ferrites, alloys and compounds such as manganese, and other ferromagnetic alloy magnetite can be used.

Next, the amount of the magnetic powder to be contained in the magnetic toner is also important for forming a high quality image.
If the content of the magnetic powder is less than 10% by weight, the saturation magnetization of the magnetic toner is significantly reduced, and the magnetic toner is easily separated from the sleeve constituting the developing roll, and toner scattering occurs. On the other hand, if the content of magnetic powder exceeds 75% by weight,
Fixability deteriorates. Therefore, the content of magnetic powder is 10-75
It is preferably set to wt%.

If desired, a coloring agent may be added. Examples of such coloring agents include carbon black,
Aniline blue, chalco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, rose bengal and the like can be mentioned.
These colorants need to be contained in a sufficient amount to form a visible image with a sufficient density, and are usually contained in an amount of 1 to 20% by weight based on the total amount of the magnetic toner.

Further, a charge control agent can be contained in order to add a predetermined chargeability to the magnetic toner. As the charge control agent, a nigrosine dye having a positive charge characteristic,
Based on this, a reaction product with an aliphatic monobasic acid and / or a dibasic acid, a reaction product with a nigrosine dye and a carboxy group-containing resin, a triphenylmethane-based dye, a piperazine-based polymer, and a negative charging property-containing compound. Examples include metal-containing complexes such as Cr azo dyes.

The content of the above charge control agent is appropriately in the range of 0.1 to 10% by weight based on the total amount of the magnetic toner. Further, the amount of charge of this magnetic toner is preferably in the range of 5 to 30 μc / g in absolute value when measured by the blow-off method (using Toshiba Chemical's TB-200 type). Charge amount is 5
If it is less than μc / g, toner scattering and background fog occur, which is not preferable. On the other hand, if it exceeds 30 μc / g, the developability is deteriorated, which is inconvenient.

The magnetic toner of the present invention can be manufactured, for example, as follows. First, raw materials such as a binding resin, magnetic powder, and a coloring agent are dry-preliminarily mixed, heated and kneaded with a kneader, and then cooled and solidified. Next, it is crushed with a jet mill and classified with a zigzag classifier to obtain an average particle size of 3 to 30.
The magnetic toner is μm. When the average particle size is less than 3 μm, the developability is deteriorated and the image fog increases, which is not preferable. On the other hand, if the average particle size exceeds 30 μm,
This is inconvenient because the graininess of the image becomes severe. The average particle size is preferably 6 to 15 μm.

Next, fine particles having the same charging property as that of the magnetic toner are strongly fixed to the surface of the magnetic toner. As such a fixing means, for example, a magnetic toner and fine particles are used with a Henschel mixer. Then, there is a method of mixing in a vortex of the air flow, a method of causing collision using a jet mill, and a method of granulating using a hybridizer.
In this case, the fine particles are strongly fixed to the surface of the magnetic toner by making the conditions of the mixing time and the mixing rotation more strict than the normal conditions.

After the above processing, fine particles having a charging characteristic of the opposite polarity to that of the magnetic toner are weakly fixed. As this means, an ordinary mixing apparatus can be used and can be performed under ordinary mixing conditions. It is preferable that the mixing conditions such as the mixing time and the number of rotations of the mixing are set to be slightly loose.

The fixing strength of the fine particles to be fixed on the surface of the magnetic toner is evaluated as follows, for example. First, a predetermined amount, for example, 10 g of magnetic toner is gently rotated while being magnetically adsorbed on the developing roll. Next, the magnetic toner is blown with air at a pressure not to scatter the magnetic toner (for example, for 15 minutes), and the fine particles on the surface of the magnetic toner are blown off. Then, the amount of fine particles in the magnetic toner before and after the air blowing is quantitatively analyzed by means such as fluorescent X-ray analysis.

In this case, the magnetism before and after air blowing
The amount of fine particles in the toner is W₀, W ₁Then, (W₀
-W₁) / W₀Is 90% or more, the adhesive strength is
"Strong", (W₀-W₁) / W₀Is less than 90%
When the adhesive strength is low, the adhesive strength is evaluated as “weak”.

As the fine particles as described above, metal oxides such as silica, alumina and titania, or at least two kinds of co-oxides of silicon, aluminum and titanium can be used. It is preferable that the surface of these fine particles is treated with a silane coupling agent or a hydrophobizing agent.

The magnetic toner of the present invention is used as a developer mixed with a magnetic carrier. As the magnetic carrier, known materials such as iron powder, magnetite powder, Ni-Zn ferrite, Cu-Zn ferrite, Mn are used.
A ferrite powder such as a Zn-based ferrite can be used.
These powders may be used as they are, or the surface thereof may be coated with a resin material in order to adjust the charge amount.

The volume resistivity of the magnetic carrier is 10 ³ to 1
It is better to set it to 0 ¹³ Ω-cm. In this case, the volume resistivity was measured by filling a magnetic carrier in an insulating cell provided with a pair of electrodes with a gap of 5 mm and setting the D. C. A voltage of 100 V is applied and measurement is performed. If the volume resistivity of the magnetic carrier is less than 10 ³ Ω-cm, carrier adhesion to the image carrier tends to occur, which is not preferable. On the other hand, if it exceeds 10 ¹³ Ω-cm, the developability and the image density decrease. Therefore, it is inconvenient. The preferred volume resistivity value is 10 ⁴ to
It is 10 ¹⁰ Ω-cm.

The mixing ratio of the magnetic toner and the magnetic carrier is
The toner concentration is preferably 10 to 90% by weight.
If the toner concentration is less than 10% by weight, carrier adhesion occurs, while if it exceeds 90% by weight, toner scattering and background fog increase, which is not preferable.

[0027]

With the above structure, the presence of the fine particles having the same polarity charging property strongly fixed to the surface of the magnetic toner ensures the function of stabilizing the charging of the magnetic toner, and
The fluidity of the magnetic toner is ensured by the presence of the weakly fixed particles having the opposite polarity charging characteristics.

[0028]

Examples Styrene-n-butyl methacrylate copolymer 55 parts by weight (Mw = 21 × 10 ⁴ , Mn = 1.6 × 10 ⁴ ) Magnetite 40 parts by weight (Toda Kogyo EPT500) Polypropylene 3.5 parts by weight (Sanyo Kasei VISCOL 550P) ) 1.5 parts by weight of negatively chargeable charge control agent (Bontron E81 manufactured by Orient Chemical Co., Ltd.) The raw materials having the above composition are dry-premixed, kneaded by heating with a kneader, solidified by cooling, pulverized by a jet mill, and classified by a zigzag classifier, A magnetic toner having an average particle diameter of 12 μm was used. Next, 100 parts by weight of this magnetic toner was mixed with 0.5 part by weight of negatively charged hydrophobic silica (R972 manufactured by Nippon Aerosil Co., Ltd.), and the hydrophobic silica was strongly fixed to the surface of the magnetic toner by a Henschel mixer. Further, this magnetic toner 10
0 parts by weight and positively charged silica (RP made by Nippon Aerosil RP-
130) 0.3 part by weight was mixed, and positively charged silica was weakly fixed on the surface of the magnetic toner by a Henschel mixer. As a comparative example, a conventional example lacking fixation of positively charged silica was prepared.

The magnetic toner prepared as described above and a ferrite carrier (KBN-100 manufactured by Hitachi Metals, average particle diameter 74 to 149 .mu.m) were mixed to prepare a developer having a toner concentration of 40% by weight, and development was carried out. When developing,
The image carrier made of PC is uniformly charged to -650V, and exposed at a surface moving speed of 60 mm / sec.
Development was carried out by a developing roll having a 6-pole symmetrically magnetized permanent magnet member in a sleeve having a diameter of 20 mm.
Surface magnetic flux density on the sleeve 650G, sleeve rotation speed 1
A bias voltage of -550V was applied to the sleeve at 60 rpm. The doctor gap was 0.35 mm and the development gap was 0.30 mm. The developed toner image was transferred onto recording paper and fixed with a heat roll at 180 ° C. and a linear pressure of 1 kg / cm. The developing atmosphere was 30 ° C. and 80% RH.

When the above development was continuously carried out, when the comparative example was used, the image density dropped from the initial 1.40 to 1.15 at the time when the number of copies was 20,000, and the image quality deteriorated significantly. Was approved. On the other hand, when the image forming apparatus of the present embodiment is used, even when the number of copies is 20,000, the image density is maintained at 1.36 which is slightly decreased from the initial 1.41 and the image quality is kept at a high level. I was able to keep it. The fluidity of the developer was very good, and no aggregation phenomenon of the magnetic toner was observed.

In this embodiment, the case where the magnetic toner has a negative charging property has been described, but in the positive charging magnetic toner, fine particles having a positive charging characteristic are strongly fixed and particles having a negative charging characteristic are weak. The operation is the same for the magnetic toner having a fixed structure.

[0032]

EFFECTS OF THE INVENTION The present invention, which has the structure and operation as described above, has a stable triboelectric charge amount and has a large humidity resistance even when used in a high humidity environment. There is an effect that copying is possible and a high quality image is obtained.

Claims (1)

[Claims] 1. A magnetic toner for an electrostatic charge image, which comprises a binder resin and magnetic powder as main components and is mixed with a magnetic carrier to form a two-component developer, and has a charging property of the same polarity as that of the magnetic toner on the surface. A magnetic toner for an electrostatic charge image, characterized in that fine particles are strongly fixed, and fine particles having a charging characteristic of a polarity opposite to that of the magnetic toner are weakly fixed.