JPH0561248A - Magnetic toner for developing electrostatic charge image - Google Patents

Abstract

PURPOSE:To improve a one-component type magnetic toner for use in electrophotographic and electrostatic printing processes. CONSTITUTION:The magnetic toner to be used comprises at least a binder resin, a magnetic material, and an electric charge controller, and the magnetic material is characterized by being coated with a layer of a resin having a weight average molecular weight higher than that of the binder resin, thus permitting the magnetic material of the toner to be prevented from being disclosed to the surface of the toner and the toner to be uniformly charged in a developing section and an image free from deterioration of image quality, such as fog and streaks to be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrostatic charge image developing toner used in electrophotography, electrostatic printing and the like, and more particularly to a magnetic-component developing toner.

[0002]

2. Description of the Related Art Generally, in electrophotography, electrostatic recording, etc., in order to develop an electrostatic latent image formed on a latent image carrier made of a photoconductive photoreceptor or a dielectric,
After developing with a toner, which is made into a thin layer by a blade or the like on a toner supply roller such as a developing sleeve, and appropriately charged, and after transferring the toner image to a transfer material such as paper, It is fixed by heating pressure, solvent vapor, etc. to obtain a copy.

The developing methods applied to these electrophotographic methods and the like are roughly classified into a dry developing method and a wet developing method.
The former is further divided into a method using a two-component developer and a method using a one-component developer. Among the two-component developing methods, there are a magnet brush method using an iron powder carrier, a cascade method using a bead carrier, a fur brush method using a fur, etc., depending on the type of carrier that carries the toner.

The one-component developing methods include:
Powder cloud method that uses toner particles in a spray state, contact development method that develops by directly contacting the toner particles with the electrostatic latent image surface (contact development or toner development), toner particles onto the electrostatic latent image surface A jumping developing method in which toner particles are charged and fly toward the latent image surface by an electric field of the electrostatic latent image without direct contact, and a magnetic conductive toner is brought into contact with the electrostatic latent image surface for development. There are dry methods.

As a method for producing a magnetic toner, there is a crushing method using a crusher such as a jet mill. In this method, a binder resin, a charge control agent, a magnetic material and the like are heated and melted and kneaded, cooled and solidified, and then pulverized by a jet mill or the like and classified to obtain a magnetic toner. But in this way,
Since the magnetic substance is hydrophilic, the wetting with the binder resin is poor, and therefore, during the pulverization, the fracture surface advances to the interface between the magnetic substance and the binder resin and is pulverized. As a result, the magnetic substance is exposed on the surface of the toner or a free magnetic substance is generated. The binder resin in the toner is insulative, while the magnetic material is semi-conductive, and semi-conductive and insulating parts are randomly mixed on the toner surface, complicating the charging behavior of the toner. Is inferred. This causes a problem that image quality is deteriorated due to fog or the like.

As means for improving such problems, there is a technique of attaching a dispersibility improving agent to the surface of a magnetic material (JP-A-54-139554), a titanium coupling agent or a silane coupling agent on the surface of the magnetic material. (Japanese Patent Application Laid-Open No. 55-28019, 58-9153) and the like, for example, by improving the dispersibility of the magnetic substance in the crystalline resin or by increasing the adhesive force between the magnetic substance surface and the binder resin. Although there is a technique for reducing the probability that the magnetic substance is exposed on the toner surface during pulverization, it cannot be said that the desired effect is always obtained.

Further, Japanese Patent Laid-Open Nos. 58-79251 and 62-62
As shown in 75647, attempts have been made to use a resin-coated magnetic material obtained by polymerizing a vinyl monomer or an acrylic resin monomer on the surface of magnetic material particles. By doing so, the adhesive force between the magnetic substance and the coating resin layer is improved, and it is possible to prevent the magnetic substance from being exposed on the toner surface during pulverization. However, the coating resin layer of the magnetic material exposed on the surface of the toner thus obtained does not contain a charge control agent. Therefore, in particular, the higher the content of the magnetic substance in the binder resin is, the larger the portion where the charge control agent does not exist on the surface of the toner particle is, so that uniform triboelectric charging in the developing portion cannot be expected, and fogging and the like can be prevented. However, the image quality will be degraded. In the resin coating on the surface of the magnetic material by such a polymerization method,
It is very difficult to polymerize while dispersing the charge control agent. Therefore, the inventors were able to obtain a good image by using a method of coating the surface of the magnetic particles with a resin in which a charge control agent was dispersed in advance by a spray dry method.
However, the method of coating the magnetic material by the spray dry method has a drawback that the adhesive strength between the resin and the magnetic material is small and the resin is easily detached.

[0008]

DISCLOSURE OF THE INVENTION The present invention uses a magnetic material coated with a resin or a resin in which a charge control agent is dispersed, and prevents desorption of the coated resin from the magnetic material during pulverization,
It realizes stable charging behavior and obtains a good image.

[0009]

The present invention relates to a magnetic toner comprising at least a binder resin, a magnetic material and a charge control agent, wherein the magnetic material is a resin layer or a resin layer in which the charge control agent is dispersed. The present invention relates to a magnetic toner for developing an electrostatic charge image, which is coated and has a weight average molecular weight higher than that of a binder resin.

The details will be described below. First, the purpose of coating the magnetic substance with the resin layer or the resin layer having the charge control agent dispersed therein is to prevent the magnetic substance from being exposed on the surface of the toner particles, as described in the section of the prior art. The reason why the charge control agent is dispersed in the resin is to improve the dispersion of the charge control agent in the toner. However, the adhesive strength between the resin layer coated by the spray drying method and the magnetic substance is not always sufficient, and the resin layer is easily detached from the magnetic substance. Therefore, by making the weight average molecular weight (abbreviated as Mw) of the coating resin layer larger than the Mw of the binder resin, the binder resin portion is preferentially cracked during pulverization to prevent the coating resin layer from detaching. Made possible.

Examples of the binder resin used in the present invention include homopolymers of styrene such as polystyrene, poly-p-chlorostyrene, and polyvinyltoluene and their substitution products; styrene-p-chlorostyrene copolymers, styrene-propylene. Copolymer, styrene-vinyltoluene copolymer, styrene-vinylnaphthalene copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-
Octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-
Acrylonitrile copolymer, styrene-vinyl methyl ether copolymer, styrene-vinyl ethyl ether copolymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile- Indene copolymer,
Styrene-maleic acid copolymers, styrene-based copolymers such as styrene-maleic acid ester copolymers; polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane, polyamide, Epoxy resin, polyvinyl butyral, polyacrylic acid resin, rosin, modified rosin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, etc. Alternatively, they can be mixed and used.

Further, as examples of the binder resin particularly suitable for pressure fixing, the following resins can be used alone or in combination. Polyolefin (low molecular weight polyethylene, low molecular weight polypropylene, oxidized polyethylene polytetrafluoroethylene, etc.), epoxy resin, polyester resin, styrene-butadiene copolymer (monomer ratio 5: 30: 95-
70), olefin copolymer (ethylene-acrylic acid copolymer, ethylene-acrylic acid ester copolymer, ethylene-methacrylic acid copolymer, ethylene-methacrylic acid ester copolymer, ethylene-vinyl chloride copolymer, Ethylene-vinyl acetate copolymer, ionomer resin), polyvinylpyrrolidone, methyl vinyl ether-maleic anhydride copolymer, maleic acid-modified phenol resin, phenol-modified terpene resin.

As the charge control agent used in the toner of the present invention, a quaternary ammonium salt and other basic electron-donating organic substances are used for controlling the positive charge property.
Examples of materials that control the toner to be negatively charged include metal complexes of monoazo dyes and tetraphenylboron derivatives such as sodium and potassium tetraphenylboron.
The amount contained in the toner is 1 to 10 with respect to the binder resin.
Parts by weight. The amount of the charge control agent contained in the coating resin is preferably 1 to 40 parts by weight.

The magnetic material contained in the magnetic toner of the present invention includes iron oxides such as magnetite, hematite and ferrite, metals such as iron, cobalt and nickel, or aluminum, cobalt, copper, lead and magnesium of these metals. Examples thereof include alloys of metals such as tin, zinc, antimony, beryllium, bismuth, cadmium, calcium, manganese, selenium, titanium, tungsten and vanadium, and mixtures thereof. It is desirable that these ferromagnetic materials have an average particle size of about 0.1 to 2 μm. The amount contained in the toner is about 20 to 200 parts by weight, and particularly preferably 100 parts by weight of the resin component.
It is 40 to 150 parts by weight with respect to parts by weight. In addition, it is preferable to pretreat with a silane coupling agent or the like to improve the adhesiveness with the resin.

Further, the toner of the present invention may be mixed with additives as required. Examples of the additives include lubricants such as Teflon and zinc stearate, abrasives such as cerium oxide and silicon carbide, fluidity imparting agents such as colloidal silica and aluminum oxide, anti-caking agents, or carbon black and tin oxide. And the like, or fixing aids such as low molecular weight polyolefins.

As the coating resin for the resin-coated magnetic material, the resins shown as the binder resin can be used, and preferably, a material having a good compatibility with the binder resin is selected, and if possible, the same resin as the binder resin can be selected. It is better to use one. The charge control agent dispersed in the coating resin is the same as that dispersed in the binder resin. The method of dispersing the charge control agent in the coating resin is the same as the method of dispersing the charge control agent in the binder resin,
By kneading using a means such as a hot roll. After kneading, it is pulverized and dissolved in an appropriate amount of toluene solvent to obtain a coating resin solution. The content of the charge control agent in the coating resin may be about the same as the content of the charge control agent in the binder resin.

As a coating method, the above magnetic material was coated with a resin solution by spray drying. The treatment amount of this resin solution is 0.1 to 10 parts by weight, preferably 1 to 5 parts by weight, based on 100 parts by weight of the magnetic material. If the amount is less than 0.1 parts by weight, it is insufficient to cover the magnetic substance, and 10
When it exceeds the weight part, the volatilization of the toluene solvent is likely to be insufficient, which causes a problem that the resin layer peels off.

[0018]

EXAMPLES First, the following four types of resin-coated magnetic materials were prepared. Resin coating example 1 3 parts by weight of a styrene-acrylic resin (Mw = 40000) was dissolved in 1000 parts by weight of a toluene solvent, and a magnetic material was coated by a spray drying method. Resin coating example 2 3 parts by weight of a polyester resin (Mw = 50000) was dissolved in 1000 parts by weight of a toluene solvent, and a magnetic material was coated by a spray dry method.

Resin coating example 3 Styrene-acrylic resin (MW = 40,000) 100 parts by weight Charge control agent (metal-containing complex salt) 3 parts by weight The resin obtained by kneading and pulverizing the above is designated as coating resin 1.

Coating resins 1 and 3 parts by weight were dissolved in a toluene solvent and coated on a magnetic material by a spray drying method. Resin coating example 4 Polyester resin (Mw = 50000) 100 parts by weight Charge control agent (metal-containing complex salt) 3 parts by weight Kneading and pulverizing the above is referred to as coating resin 2.
Two or three parts by weight of the coating resin was dissolved in a toluene solvent and the magnetic material was coated by a spray dry method.

Example 1 Styrene-acrylic resin (Mw = 400,000) 100 parts by weight Release agent (low molecular weight polypropylene) 5 parts by weight Charge control agent (metal-containing complex salt) 5 parts by weight Magnetic substance of resin coating example 1 100 parts by weight The above substances were kneaded with a two-roll mill, pulverized and classified to obtain a toner having an average particle size of 7.5 μm.

When this toner was used to develop an image in a developing device, a good image was obtained and the image remained unchanged after running 10,000 sheets. There was also no toner filming on the developing sleeve or the photoconductor. The charge amount of the toner before and after running is −7.6 (μC / g),
There was almost no change of −7.0 (μC / g). When the surface of the toner was observed with a scanning electron microscope, the exposed portion of the magnetic material was hardly seen.

Comparative Example 1 A toner prepared by using a resin-coated magnetic material having the same formulation as the toner prepared in Example 1 and having the same weight-average molecular weight as the binder resin as the coating resin was used in a developing device. When the image was printed by using the image, fogging occurred in the initial image. Toner charge amount in the early stage of running-
While it was 6.6 (μC / g), it decreased to −4.9 (μC / g) after running. Further, when observed by SEM, it was confirmed that the magnetic substance was exposed on the toner surface.

Example 2 Polyester resin (Mw = 500,000) 100 parts by weight Release agent (low molecular weight polypropylene) 5 parts by weight Charge control agent 5 parts by weight Magnetic substance of resin coating example 1 100 parts by weight Two rolls of the above substances After kneading, the powder was pulverized and classified to obtain a toner having an average particle size of 7.5 μm. When this toner was used to develop an image on a developing device, a good image was obtained, and the image did not change even after running 10,000 sheets. There was also no toner filming on the developing sleeve or the photoconductor. The toner charge amounts before and after running are -6.4 (μC / g) and -5.6 (μC / g), respectively.
And hardly changed.

Example 3 Styrene-acrylic resin (Mw = 400000) 100 parts by weight Release agent (low molecular weight polypropylene) 5 parts by weight Charge control agent (metal-containing complex salt) 5 parts by weight Magnetic substance of resin coating example 2 100 parts by weight The above substances were kneaded with a two-roll mill, pulverized and classified to obtain a toner having an average particle size of 7.5 μm.

When this toner was used to develop an image in a developing device, a good image was obtained and the image remained unchanged after running 10,000 sheets. There was also no toner filming on the developing sleeve or the photoconductor. The charge amount of the toner before and after running is -8.2 (μC / g),
There was almost no change of −8.1 (μC / g). When the surface of the toner was observed with a scanning electron microscope, the exposed portion of the magnetic material was hardly seen.

Example 4 100 parts by weight of styrene-acrylic resin (Mw = 400000) Release agent (low molecular weight polypropylene) 5 parts by weight Charge control agent (metal-containing complex salt) 5 parts by weight Magnetic substance of resin coating example 3 100 parts by weight Department

The above substances were kneaded by a two-roll mill, pulverized and classified to obtain a toner having an average particle size of 7.5 μm. When this toner was used to develop an image on a developing device, a good image was obtained and the image did not change even after running 10,000 sheets. There was also no toner filming on the developing sleeve or the photoconductor. The charge amounts of the toner before and after running are -8.0 (μC / g) and -7.5, respectively.
(ΜC / g) was almost unchanged. When the surface of the toner was observed with a scanning electron microscope, the exposed portion of the magnetic material was hardly seen.

Comparative Example 2 A toner prepared by using a resin-coated magnetic material having the same formulation as the toner prepared in Example 4 and having the same weight average molecular weight as the binder resin as the coating resin was used in a developing device. When the image was printed by using the image, fogging occurred in the initial image. Toner charge amount in the early stage of running-
While it was 5.8 (μC / g), it decreased to −3.9 (μC / g) after running. Further, when observed by SEM, it was confirmed that the magnetic substance was exposed on the toner surface.

Example 5 Polyester resin (Mw = 500,000) 100 parts by weight Release agent (low molecular weight polypropylene) 5 parts by weight Charge control agent (metal-containing complex salt) 5 parts by weight Magnetic substance of resin coating example 4 100 parts by weight or more The substance was kneaded with two rolls, pulverized and classified to obtain a toner having an average particle size of 7.5 μm.

When this toner was used to develop an image on a developing device, a good image was obtained and the image did not change even after running 10,000 sheets. There was also no toner filming on the developing sleeve or the photoconductor. The charge amount of the toner before and after running is −9.2 (μC / g),
There was almost no change at −8.8 (μC / g).

[0032]

As described above, it is possible to prevent the magnetic substance from being exposed on the toner surface by selecting the coating resin and the binder resin of the resin-coated magnetic substance according to the weight average molecular weight,
The toner realizes uniform charging in the developing section, and an image without deterioration in image quality such as fogging and streaks can be obtained.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁵ Identification number Internal reference number FI Technical indication location G03G 9/08 372 (72) Inventor Kunihiko Tomita 1-3-6 Nakamagome, Ota-ku, Tokyo Stocks Within Ricoh Company (72) Inventor Shoichi Sugimoto 1-3-6 Nakamagome, Ota-ku, Tokyo Within Ricoh Company, Ltd.

Claims (2)

[Claims] 1. A magnetic toner comprising at least a binder resin, a magnetic substance and a charge control agent, the magnetic substance being coated with a resin layer, and the weight average molecular weight of the coating resin is the weight average molecular weight of the binder resin. A magnetic toner for developing an electrostatic charge image characterized by being larger than 2. The magnetic toner for developing an electrostatic charge image according to claim 1, wherein the resin layer coating the magnetic material contains a charge control agent.