JP2567748B2 - Toner for electrostatic charge development - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic developing toner, and more particularly to an electrostatic developing toner used in a system having a low developing potential.

[0002]

2. Description of the Related Art Generally, in electrophotography, an electric latent image is formed on a photoreceptor, and the latent image is developed with toner.
The toner image is transferred to a transfer material such as paper as required, and then fixed by means such as heating and pressing to obtain a subject. As a developer used in such an electrophotographic method, there are a two-component developer composed of a toner and a carrier and a one-component developer having the functions of a toner and a carrier at the same time.

The one-component developer includes a magnetic one-component developer and a non-magnetic one-component developer. Among them, a magnetic toner containing 10 to 70% by weight of magnetic powder is used as the magnetic one-component developer. Magnetic toners are classified into conductive magnetic toners and insulating magnetic toners. In the former case, electrostatic induction or charge injection serves as a development driving force, and in the latter case, electric charge due to frictional charging serves as a development driving force.

It is known that a one-component developing method using a conductive magnetic toner has an advantage that a uniform image without an edge effect can be obtained because the conductive magnetic toner itself serves as a developing electrode. Further, by suppressing the volume specific resistivity of the toner to about 1 × 10 ⁴ Ω · cm or less, there is an advantage that the toner can be used in a low-potential developing system having a developing potential of 100 V or less.

However, the conductive magnetic toner has a drawback in that the charge of the toner is apt to leak through the transfer paper during electrostatic transfer, which makes it difficult to transfer the toner onto plain paper. Further, since only one layer of toner particles is developed on the photoreceptor, there is a disadvantage that it is difficult to secure image density.

The transferability problem can be solved to some extent by using special paper that has been subjected to high resistance treatment or by using a pressure transfer system using a rubber roller, but ensuring image density is essential. This is a problem and the conventional technology is not yet satisfied.

[0007]

SUMMARY OF THE INVENTION The present invention solves the above problems in the prior art, and provides a sufficient image density in a low potential developing system and a good image characteristic without fog. The purpose is to provide a toner for charge development.

[0008]

The present invention has been made in order to solve the above-mentioned problems, and contains 30 to 70% by weight of magnetic powder and has a volume resistivity of 1 × 10 ³ Ω · cm or less. Certain conductive magnetic toner and volume resistivity of 1 × 10 ⁹
For electrostatic charge development, characterized by mixing an insulating non-magnetic toner having a circularity of 0.5 or more and an insulating non-magnetic toner of 0.5 or more at a weight ratio of 60:40 to 90:10. Toner.

[0009] conductive volume resistivity of the magnetic toner, a main electrode area under a load of 200 g / cm ² and the sample was placed in a cylindrical electrode of 1.00 cm ^2, it was measured under an electric field of 100 V / cm It is a value.

The volume resistivity of the insulating non-magnetic toner is considerably different from that of the conductive magnetic toner, and therefore cannot be measured by the same measuring method. Accordingly, the volume specific resistivity of the insulating non-magnetic toner of the present invention is determined by molding the insulating non-magnetic toner under a pressure of 200 kg / cm ² and setting the SE-70 type solid electrode (manufactured by Ando Electric Co., Ltd.). 2500A
This is a value measured by a capacitance bridge (manufactured by Toyo Technica).

The roundness of the insulating non-magnetic toner particles is measured as follows. First, a toner image is photographed with a SEM (scanning electron microscope), the image is input to the image processing apparatus, and the image is obtained from the following equation. Roundness = (4π × area) / (peripheral length) ^{2 The} roundness is maximum 1 when the object is a perfect circle, and close to 0 when the object is an irregular shape.

The conductive magnetic toner of the present invention is obtained by dispersing magnetic powder and carbon black in a binder resin, mechanically pulverizing them, and then classifying them into a volume average particle diameter of about 7 to 10 μm. Further, after classification, a conductive material such as carbon black may be adhered to the surface of the toner in order to make the conductivity of the toner uniform, and an additive such as silica may be adhered to the surface of the toner particle to improve fluidity.

In the present invention, the binder resin used in the conductive magnetic toner is polystyrene, polyethylene, polypropylene, vinyl resin, polyacrylate, polymethacrylate, polyvinylidene chloride, polyacrylonitrile, polyether, polycarbonate, thermoplastic polyester. In addition to thermoplastic resins such as thermoplastic epoxy resins, cellulosic resins and copolymer resins of those monomers, thermosetting resins such as modified acrylic resins, phenol resins, melamine resins and urea resins can be used. Further, as the magnetic powder, spinel, perovskite, hexagonal, garnet, ferrite having an orthoferrite structure, magnetite, or the like is applied crystallographically.
The composition of ferrite is a sintered body of oxides of nickel, zinc, manganese, magnesium, copper, lithium, barium, vanadium, chromium, calcium and the like and trivalent iron oxides.

In the present invention, the insulating non-magnetic toner is also prepared by dispersing a colorant such as carbon black or a charge amount adjusting agent in a binder resin, pulverizing and classifying the same, and then subjecting it to spheroidizing treatment in a hot air stream. Adjust the roundness to 0.5 or more by applying impact force in a high-speed air stream. Also,
The desired insulating non-magnetic toner can also be obtained by dispersing the toner material in a solvent and spray drying. Further, carbon black or a charge amount adjusting agent may be dispersed during polymerization of the binder resin to directly produce an insulating non-magnetic toner having a desired particle size. As a polymerization method, a suspension polymerization method, an emulsion polymerization method or the like can be preferably used. An additive such as silica may be attached to the surface of the insulating nonmagnetic toner thus obtained in order to improve fluidity.

In the present invention, as the binder resin used for the insulating magnetic toner, those exemplified as the above-mentioned conductive magnetic toner are appropriately used. If necessary, a charge controlling agent such as a monoazo metal dye, a nigrosine dye, or a quaternary ammonium salt may be used.

[0016]

In the conductive magnetic toner constituting the electrostatic charge developing toner of the present invention, the charge is electrostatically induced under the developing electrolysis or injected from the developing sleeve, and the latent image portion on the photoconductor and the conductive magnetic toner are combined. When the electrostatic attraction force of is larger than the magnetic binding force, it adheres to the latent image portion of the image and is developed. On the other hand, the insulating non-magnetic toner is charged in the insulating non-magnetic toner by frictional charging with the height control blade of the developing device, the conductive magnetic toner, or the like, and is developed on the latent image portion of the image. Therefore, a large amount of conductive magnetic toner and insulating non-magnetic toner are mixedly attached to the latent image portion of the image on the photoconductor, so that a sufficient image density can be obtained.

The electrostatic charge developing toner of the present invention is mixed and stirred in the developing device, and the developing three electrostatic charge developing toner is mixed and stirred in the developing device by the magnet roller, and the conductive magnetic toner on the developing sleeve is mixed by the magnet roller. Ears are formed. Therefore, the magnetic powder contained in the conductive magnetic toner needs to be 30 to 70% by weight. When the amount is less than 30% by weight, the magnetic force of the toner for electrostatic charge development becomes small, so that the transportability becomes poor. If the amount exceeds 70% by weight, not only is it difficult to disperse the magnetic powder in the binder resin, but also the amount of the conductive material such as carbon black is reduced, so that the conductivity is secured. Becomes difficult. The insulative non-magnetic toner adheres to the conductive magnetic toner by electrostatic force due to frictional charging, and is conveyed to the image latent image portion in the same manner as the conductive magnetic toner. The mixing ratio of the conductive magnetic toner and the insulating non-magnetic toner is 60:40 to 90:10.
Can be used satisfactorily. The ratio of insulating non-magnetic toner is 40
If the ratio exceeds (the ratio of the conductive magnetic toner is less than 60), the transportability of the conductive magnetic toner becomes poor, and problems such as toner dropping and toner scattering are likely to occur. Also,
When the ratio of the insulating non-magnetic toner is less than 10 (the ratio of the conductive magnetic toner exceeds 90 and is large), it becomes impossible to obtain a sufficient image density.

The volume resistivity of the conductive magnetic toner is 1 ×
If it exceeds 10 ³ Ω · cm, the volume specific resistivity of the toner for electrostatic charge development becomes high, making it difficult to perform development at a low potential. On the other hand, if the volume resistivity of the insulating non-magnetic toner is less than 1 × 10 ⁹ Ω · cm, a sufficient amount of triboelectric charge cannot be obtained due to leakage of electric charges, resulting in a low image density.

When the electrostatic charge developing toner of the present invention is stirred in the developing device, a part of the carbon black exposed or attached to the surface of the conductive magnetic toner is transferred to the surface of the insulating non-magnetic toner. As a result, the charge injection into the conductive magnetic toner becomes defective, and image defects such as fog occur. In the present invention, the circularity of the insulating non-magnetic toner is set to 0.5 or more and the surface area is minimized to limit the migration amount of carbon black from the surface of the conductive magnetic toner and prevent the occurrence of image defects. Is.

[0020]

EXAMPLES Examples of the present invention will be described below. The term "part" means part by weight. Example 1 The materials having the above composition are melt-kneaded with a two-roll kneader, pulverized with a jet mill and classified to have a volume average particle diameter of 9
A conductive magnetic toner of μm was obtained. The volume resistivity of this conductive magnetic toner was 5 × 10 ² Ω · cm. further, The material having the above composition is melt-kneaded by a two-roll kneader, crushed by a jet mill and classified, and then impact force is applied by a Nara hybridization system in a high-speed air stream to obtain a toner having a volume average particle diameter of 9 μm. The particles were obtained. Further, 0.2 part of hydrophobic silica (R-972: manufactured by Nippon Aerosil Co., Ltd.) was mixed with 100 parts of the toner particles to obtain an insulating non-magnetic toner. The volume specific resistivity of this insulating nonmagnetic toner was 7 × 10 ¹⁰ Ω · cm, and the circularity was 0.58. The conductive magnetic toner and the insulating non-magnetic toner were mixed at a ratio of 70:30 parts by weight to obtain the electrostatic charge developing toner of the present invention.

Example 2 After well dispersing the materials of the above formulation, carry out suspension polymerization,
It was dehydrated, washed and dried to obtain toner particles having a volume average particle diameter of 9 μm. Further, with respect to 100 parts of this toner particle, 0.
Two parts of hydrophobic silica (R-972: manufactured by Nippon Aerosil Co., Ltd.) was mixed to obtain an insulating non-magnetic toner. The volume specific resistivity of this insulating non-magnetic toner was 3 × 10 ¹⁰ Ω · cm, and the circularity was 0.78. The conductive magnetic toner of Example 1 and the insulating non-magnetic toner of Example 2 were mixed in a weight ratio of 7
The mixture was mixed at a ratio of 0:30 to obtain the electrostatic charge developing toner of the present invention.

Comparative Example 1 The materials of the above composition are melt-kneaded by a two-roll kneader, pulverized by a jet mill and classified, and the volume average particle diameter is 9 μm.
Was obtained. The volume resistivity of this conductive magnetic toner was 6 × 10 ⁴ Ω · cm. The conductive magnetic toner and the insulating non-magnetic toner of Example 1 are 70:
The mixture was mixed at a ratio of 30 parts by weight to obtain an electrostatic charge developing toner of Comparative Example 1.

Comparative Example 2 After well dispersing the materials of the above formulation, carry out suspension polymerization,
It was dehydrated, washed and dried to obtain toner particles having a volume average particle diameter of 9 μm. Further, with respect to 100 parts of this toner particle, 0.
Two parts of hydrophobic silica (R-972: manufactured by Nippon Aerosil Co., Ltd.) was mixed to obtain an insulating non-magnetic toner. The volume specific resistivity of this insulating nonmagnetic toner was 6 × 10 ⁸ Ω · cm, and the circularity was 0.75. The conductive magnetic toner of Example 1 and the above insulating non-magnetic toner were in a weight ratio of 70:
The mixture was mixed at a ratio of 30 to obtain the electrostatic charge developing toner of Comparative Example 2.

Comparative Example 3 An insulating non-magnetic toner having a volume average particle size of 9 μm was obtained from the insulating non-magnetic toner of Example 1 without applying an impact force in an air stream. The volume specific resistivity of this insulating non-magnetic toner was 7.2 × 10 ¹⁰ Ω · cm, and the circularity was 0.42. Further, the conductive magnetic toner of Example 1 and the insulating non-magnetic toner were mixed at a ratio of 70:30 parts by weight to obtain a toner for electrostatic charge development of Comparative Example 3.

Comparative Example 4 An electrostatic charge developing toner of Comparative Example 4 was obtained using only the conductive magnetic toner of Example 1.

Comparative Example 5 The conductive magnetic toner of Example 1 and the insulating non-magnetic toner of Example 1 were mixed at a weight ratio of 50:50 to obtain a toner for electrostatic charge development of Comparative Example 5. .

The electrostatic charge developing toners of Examples 1 to 2 and Comparative Examples 1 to 5 described above were applied to an LED reversal printer having a developing potential of 40 V and tested. The results shown in Table 1 were obtained.

[0028]

[Table 1]

The image densities in Table 1 are values measured by a Macbeth RD914 reflection densitometer. Also, the fog value is REFL
It is a value measured by ECTOMER TC-6D (manufactured by Tokyo Denshoku Co., Ltd.). As is clear from Table 1, the electrostatic charge developing toner of the present invention had good image density and image resolution, and had very little fog. On the other hand, it was confirmed that Comparative Example 1, Comparative Example 2 and Comparative Example 4 had low image densities, and Comparative Example 2, Comparative Example 3 and Comparative Example 5 had a lot of fog and caused a practical problem.

[0030]

INDUSTRIAL APPLICABILITY The present invention can provide a toner for electrostatic charge development capable of obtaining a sufficient image density in a low potential developing system and obtaining a good image without fog.

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Claims (1)

(57) [Claims] 1. A magnetic powder in an amount of 30 to 70% by weight and carbon powder.
The volume specific resistance including the rack is 1 × 10 ³ Ω ・
The conductive magnetic toner having a volume ratio of cm or less and the insulating non-magnetic toner having a volume resistivity of 1 × 10 ⁹ Ω · cm or more and a circularity of 0.5 or more have a weight ratio of 60:40 to 90. : 1
An electrostatic charge developing toner characterized by being mixed at a ratio of 0.