JPH0683104A - Electrostatic charge image developer - Google Patents

Abstract

PURPOSE:To stabilize a static charge characteristic of a magnetic toner and to enable forming a picture image of high quality even in the high humidity circumstances by mixing a magnetic carrier, a binder consisting of a styrene- acrylic copolymer having a specific acid value and a magnetic toner essentially consisting of magnetic powders subjected to a hydrophobization treatment. CONSTITUTION:As the binder constituting the magnetic toner, the styrene-acrylic copolymer having <5 acid value and high esterification degree is used. As the magnetic powder constituting the magnetic toner, magnetic materials, such as metallic fine powders of iron, manganese, nickel, cobalt, chromium, etc., various kinds of ferrites, alloys or compounds of manganese, etc., and ferromagnetic alloy magnetite, are used. This constitution gives the moisture resistance to the binder and the magnetic powder essentially constituting the magnetic toner, thereby the static charge characteristic of the magnetic toner is stabilized and high quality image is formed even when the toner is used in the high humidity circumstances.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for an electrostatic charge image used for developing an electrostatic charge image formed on the surface of an image carrier, and in particular, a triboelectric charge amount is stabilized and a high quality image can be obtained. The present invention relates to a developer for an electrostatic image.

[0002]

2. Description of the Related Art In conventional electrophotography, 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. And to the electrostatic charge image, a carrier composed of magnetic particles such as iron powder and ferrite powder,
Development is carried out by bringing into contact with a developer (in the case of regular development, the toner is triboelectrically charged in the opposite polarity to the electrostatic charge image) mixed with a toner composed of insulating colored resin powder. 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, for example, by 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. Many developers used in such magnetic brush development are 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 of using a two-component developer, an image having a good image density and resolution can be obtained, but the halftone reproducibility is poor, and in order to maintain a good image, the magnetic property is high. It is necessary to mix and stir the carrier and the toner and control the toner concentration, which is a problem in that the mechanism becomes complicated. 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 of the charge amount of the toner is caused, and the deterioration of the image quality due to the change of the charge amount due to the environment, particularly humidity, etc. There is a problem.

As means for solving these problems, for example, JP-A-59-162563 and 59-216.
A developer prepared by mixing a magnetic carrier and a magnetic toner as described in Japanese Patent No. 149 has been proposed, and has the advantages of both the conventional two-component developer and the one-component developer described above. It is supposed to be.

[0006]

The magnetic toner constituting the above-mentioned developer contains a binder resin and magnetic powder as main components. As the binder resin, for example, in the case of adopting a heat roll fixing method, one or more kinds of styrene-acrylic copolymer, styrene-butadiene copolymer, epoxy resin, polyester resin and the like are mixed. What has been used is being used.

However, many of the conventionally used binder resins have a relatively large acid value due to, for example, improving the charging property or lowering the fixing temperature (for example, JP-B-63-57785). JP-A-2-37
365, etc.). In such a resin having a large acid value, a carboxyl group (—COOH), which is a residue, exists in the polymer skeleton. Since this carboxyl group is hydrophilic, it easily absorbs moisture in the atmosphere. Therefore, in a high humidity environment, there is a problem that the charging property of the developer and / or the magnetic toner is deteriorated, and the developability and the image quality are deteriorated.

Next, the magnetic toner is mainly composed of the binder resin and the magnetic powder, but a part of the magnetic powder is exposed on the surface of the magnetic toner. On the other hand, magnetic powder also has hydrophilic carboxyl groups (-COOH) and hydroxyl groups (-O) as residues in the manufacturing process.
H), an amino group (—NH ₂ ), a nitro group (—NO ₂ ), etc., cause deterioration of the charging characteristics of the magnetic toner in a high humidity environment, similar to the above.

The present invention solves the above problems existing in the prior art, stabilizes the charging characteristics of the magnetic toner, and provides an electrostatic charge image developer capable of forming a high quality image even in a high humidity environment. The purpose is to provide.

[0010]

In order to achieve the above object, in the present invention, a magnetic carrier, a binder made of a styrene-acrylic copolymer having an acid value of less than 5, and a hydrophobically treated magnetic powder. The technical means of mixing with a magnetic toner containing as a main component was adopted.

As the binder constituting the magnetic toner of the present invention, a styrene-acrylic copolymer having a high degree of esterification and an acid value of less than 5 is used. Comonomers can be used.

That is, acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, Monocarboxylic acids having a double bond such as butyl methacrylate, octyl methacrylate, acrylonitrile, methacrylonitrile, acrylamide and the like; or vinyl esters such as vinyl chloride, vinyl acetate, vinyl benzoate, etc .; Ethylene-based olefins such as ethylene, propylene, butylene, etc .; Conjugated diene-based monomers such as butadiene, isoprene, chloroprene, etc. and their derivatives; eg vinyl methyl ketone, vinylhexene Vinyl ketones such as ketone; ethers such as vinyl methyl ether, vinyl ethyl ether, either singly or two or a vinyl monomer such as vinyl ethers such as vinyl isobutyl ether may 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 of chromium, various ferrites, alloys and compounds of 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.
When 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, which causes toner scattering. 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%.

Substances used for the hydrophobic treatment of the above magnetic powder,
That is, as the hydrophobizing agent, silazane such as hexamethyldisilazane, tri-lower alkylalkoxysilane such as dimethyldichlorosilane, octyltrimethoxysilane, trimethylethoxysilane, and commercially available dimethyl silicone oil (KF96 manufactured by Shin-Etsu Chemical, silicone manufactured by Toray) SH200) and the like.

Further, a charge control agent may be contained in order to impart a predetermined charging property 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 carboxyl 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 suitably in the range of 0.1 to 10% by weight based on the total amount of the magnetic toner. Further, the charge amount 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 TB-200 manufactured by Toshiba Chemical). 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, a magnetic powder and a hydrophobizing agent are mixed to form a fluidized bed, and a heat treatment is performed at 300 to 500 ° C. while maintaining an inert gas atmosphere to remove the hydrophilic group and the hydrophobizing agent present on the surface of the magnetic powder. It binds and blocks the hydrophilic groups. The magnetic powder, the binder, and other raw materials that have been hydrophobized in this manner are dry-premixed, heated and kneaded with a kneader or the like, and then cooled and solidified. Next, it is pulverized by a jet mill and classified by a zigzag classifier to obtain a magnetic toner having an average particle size of 3 to 30 μm. When the average particle diameter is less than 3 μm, the developability is deteriorated and the fog of the image is increased, which is not preferable. On the other hand, if the average particle size exceeds 30 μm, the graininess of the image becomes severe, which is inconvenient. The average particle size is preferably 6 to 15 μm.

The developer of the present invention is obtained by mixing a magnetic toner and a magnetic carrier. The magnetic carrier is a known material such as iron powder, magnetite powder, or Ni.
-Zn ferrite, Cu-Zn ferrite, Mn-Z
Ferrite powder such as n-type 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 preferable to set it to 0 ¹³ Ω-cm. In this case, the volume resistivity was determined by filling a magnetic carrier in an insulating cell provided with a pair of electrodes having a gap of 5 mm, and measuring 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 is likely to occur, which is not preferable, while 10 ¹³ Ω-c.
When it exceeds m, it is inconvenient because the developability is lowered and the image density is lowered. The preferred volume resistivity value is 1
It is 0 ⁴ to 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.

[0022]

With the above structure, the binder and the magnetic powder, which are the main components of the magnetic toner, are provided with moisture resistance, the charging characteristics of the magnetic toner are stabilized, and high quality even when used in a high humidity environment. Image can be formed.

[0023]

Example 55 parts by weight of styrene-n-butyl methacrylate copolymer (Mw = 21 × 10 ⁴ , Mn = 1.6 × 10 ⁴ , acid value 3) 40 parts by weight of magnetite (EPT500 manufactured by Toda Kogyo) 3.5 parts by weight of polypropylene (Sanyo) Kasei Co., Ltd. Viscole 550P) Charge control agent 1.5 parts by weight (Orient Chemical Co., Bontron E81) Among the above raw materials, magnetite is 300 to 500 in an inert gas atmosphere in a container in which a fluidized bed is formed by mixing with organosilane in advance. A hydrophobizing treatment is performed by heat treatment at ℃. As a comparative example, a styrene-n-butyl methacrylate copolymer having an acid value of 10 and a magnetite-untreated one were used to prepare a toner as follows.

The raw materials having the above composition were dry preliminarily mixed, kneaded by heating with a kneader, cooled and solidified, pulverized with a jet mill, and classified with a zigzag classifier to obtain a magnetic toner having an average particle diameter of 12 μm. This magnetic toner and ferrite carrier (KBN-100 manufactured by Hitachi Metals, average particle size 74 to 149 μ)
m) was mixed to prepare a developer having a toner concentration of 40% by weight.

Development is carried out by using this developer, and at the time of development, an image carrier made of OPC is used to make -6
It was uniformly charged to 50 V, exposed at a surface moving speed of 60 mm / sec, and exposed, and developed by a developing roll in which a 6-pole symmetrically magnetized permanent magnet member was incorporated in a sleeve of SUS304 having a diameter of 20 mm. The surface magnetic flux density on the sleeve was 650 G, the rotation speed of the sleeve was 160 rpm, and a bias voltage of -550 V was applied to the sleeve. The doctor gap is 0.35 mm and the development gap is 0.30 m.
m. The toner image after development was transferred onto a recording paper and fixed by a heat roll at 180 ° C and a linear pressure of 1 kg / cm.
Shown in.

[0026]

[Table 1]

As is clear from Table 1, the comparative example N
In o.3, since the binder has a high acid value and the magnetite constituting the magnetic toner has not been subjected to the hydrophobic treatment, the charged amount of the magnetic toner in an environment of 20 ° C. and 20% room temperature and normal humidity. Is also large, but at 20 ℃, 8
It becomes small in an environment of 5% room temperature and high humidity. For this reason, it is recognized that the image density at the initial stage is good, but the image density after 10,000 copies are continuously reduced.

Next, in No. 2, the acid value of the binder was lowered, that is, the group (atomic group) having hydrophilicity was reduced to improve the moisture resistance. The charge amount decreases at high humidity, and the image density after 10,000 copies are also significantly decreased. It is considered that this is because the moisture resistance of the magnetic powder exposed on the surface of the magnetic toner is low.

On the other hand, No. 1 shows that the acid value of the binder is lowered and the magnetite which is the magnetic powder is subjected to the hydrophobic treatment, so that the reduction of the charge amount at high humidity is not recognized. At the same time, a high level of image density is maintained even after continuous copying of 10,000 sheets.

[0030]

EFFECTS OF THE INVENTION The present invention has the structure and operation as described above. Therefore, by improving the moisture resistance of the binder and the magnetic powder constituting the magnetic toner, the charging characteristics of the magnetic toner are stabilized. Therefore, there is an effect that a high quality image can be formed even in a high humidity environment.

Claims (1)

[Claims] 1. A static magnetic recording medium comprising a magnetic carrier, a binder made of a styrene-acrylic copolymer having an acid value of less than 5, and a magnetic toner containing a hydrophobically treated magnetic powder as a main component. Charge image developer.