JPH06148946A - Magnetic particle - Google Patents

Abstract

PURPOSE:To obtain magnetic particles which can be suitably used as a carrier or a toner and have uniform diffusivity of magnetic powders in a binding resin and each of which has stable magnetic characteristic and electrostatic chargeability by using magnetic powders surface-treated by specific fine powders. CONSTITUTION:The magnetic particle is composed of a molten kneaded matter containing binding resins and magnetic powders and magnetic powders are surface-treated by fine powders having lower glass transition point than the temp. at the time of melting and kneading. Thus, fine powders stuck to the magnetic powder surface at the time of melting and kneading are melted and are firmly stuck so as to cover the magnetic powder surface. By melting and kneading the binding resin, the binding resin and the molten fine powders on the magnetic powder surface are firmly adhered and the binding resin and the magnetic powder become familiar and are integrated into one body. By mixing fine powders having less particle size than the particle size of the magnetic powder with the magnetic powders, the fine powders are stuck to the magnetic powder surface by van der Waals force or Coulomb force, etc., and mutual aggregation of the magnetic powders by the magnetic force can be prevented due to an obstacle of fine powders stuck to the surface.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier which constitutes a two-component developer together with a chargeable toner in an image forming apparatus utilizing an electrophotographic method, an electrostatic recording method, an electrostatic printing method or the like, The present invention relates to magnetic particles used as a magnetic toner as a one-component developer and also used in magnetic displays and the like.

[0002]

2. Description of the Related Art Heretofore, as the magnetic particles, ferrite particles whose surfaces are coated with a resin are generally used. However, when the above ferrite particles are used in an image forming apparatus as a carrier of a two-component developer, for example, it is the current situation that it is not possible to sufficiently meet the recent demand for higher image quality.

In a developing section of an image forming apparatus using a two-component developer consisting of a carrier and a toner, the developer is first agitated and mixed to charge the toner, and the toner is attached around the carrier particles, and then the magnet is magnetized. A carrier is magnetically attached to the surface of the developing sleeve containing the toner to form a magnetic brush made of the carrier. Then, when the magnetic brush is brought close to or in contact with the surface of the photoconductor on which the electrostatic latent image is formed, the toner in the magnetic brush electrostatically adheres to the electrostatic latent image, and the electrostatic latent image is formed. The toner image is visualized.

However, when ferrite particles are used as the carrier, since the ferrite particles are relatively heavy, the magnetic brush is greatly expanded by the centrifugal force generated when the developing sleeve rotates, and the surface of the photoreceptor is damaged by the inertial force. Alternatively, the image quality of the formed image is deteriorated by scraping off the toner electrostatically adhered to the surface of the photoconductor or shifting the adhesion position.

Another cause of deterioration in the quality of the formed image is that it is difficult to reduce the particle size because the carrier composed of the above-mentioned ferrite particles is manufactured by sintering ferrite powder, and that the carrier has a perfect spherical shape. There is also the fact that it is not possible to form it and the fluidity is poor. Therefore, in recent years, in order to solve the problems of the carrier made of the ferrite particles and to improve the quality of the formed image, a lightweight carrier in which magnetic powder is dispersed in the particles made of a binder resin, that is, a so-called binder type carrier Research and development on careers are actively carried out.

The binder type carrier is manufactured by melt-kneading a binder resin such as styrene-acrylic resin, magnetic powder such as ferrite powder and other additives, and then pulverizing and classifying. Since this binder type carrier is lighter than the above ferrite particles, the magnetic brush does not expand greatly due to centrifugal force, and the inertia force is small, so the surface of the photoconductor is scratched or electrostatically adhered to the surface of the photoconductor. It does not scrape off the deposited toner or shift the adhesion position.

By the way, the charge control of the binder type carrier is carried out by adding a charge control agent such as nigrosine, quaternary ammonium salt, and chrome dye which are usually used in toners, but the weight fraction is more than half. The charging control by the magnetic powder that occupies 10% was not always positively performed. Further, since the magnetic powder is magnetized and easily aggregates, it is often not uniformly dispersed in the binder resin, and it is difficult to obtain a carrier having good magnetic characteristics.

Therefore, by using a magnetic powder surface-treated with a positively chargeable inorganic substance such as magnesium oxide or aluminum oxide or a negatively chargeable inorganic substance such as silica or aluminum silicate, the magnetic powder is dispersed in the binder resin. A carrier having improved magnetic properties, easy charge control, and good magnetic properties has been proposed (JP-A-1-123250,
1-123251).

[0009]

However, in many cases, the inorganic substance for surface-treating the magnetic powder does not have a uniform shape due to secondary aggregation and is not uniformly attached to the magnetic powder, and the inorganic substance is not evenly attached. There is a problem that it is difficult to impart stable magnetic properties to each of the obtained carriers, because the magnetic powder aggregates and the dispersibility in the binder resin becomes insufficient.

Further, the inorganic substance adhered to the surface of the magnetic powder is not so strongly adhered to the magnetic powder even after the binder resin and the magnetic powder are melt-kneaded, and when the magnetic powder is exposed on the surface of the carrier, the magnetic powder is exposed. Therefore, there is a problem in that the chargeability of the carrier is gradually lowered because the inorganic substance is easily lost. further,
The inorganic substance attached to the surface of the magnetic powder is not well compatible with the binder resin, and it is difficult to integrate the magnetic powder and the binder resin, and the carrier easily cracks and the magnetic powder falls off. There is a problem that the property gradually deteriorates and that the dropped magnetic powder contaminates the formed image.

Therefore, in view of the above circumstances, the object of the present invention is that it can be suitably used as a carrier or a toner, the magnetic powder has a uniform dispersibility in the binder resin, and each magnetic particle has a stable magnetic property. It is to provide magnetic particles having characteristics and chargeability.

[0012]

Means and Actions for Solving the Problems The magnetic particles of the present invention for solving the above problems are melt-kneaded products containing a binder resin and magnetic powder, and have a glass transition temperature lower than the temperature during melt-kneading. The magnetic powder is characterized in that it has a point and is surface-treated with a fine powder having a particle size smaller than that of the magnetic powder.

According to the magnetic particles of the present invention having the above-described structure, by mixing fine powder having a particle size smaller than that of the magnetic powder with the magnetic powder, the fine powder is formed on the surface of the magnetic powder by Van der Waals force, Coulomb force, or the like. The fine powder that adheres and adheres to this surface becomes an obstacle, and aggregation due to the magnetic force between the magnetic powders can be prevented. Thereby, the magnetic powder is uniformly dispersed in the binder resin when melt-kneaded with the binder resin, and the magnetic powder is uniformly dispersed in the obtained individual magnetic particles, Magnetic particles having uniform magnetic properties are obtained.

Further, since the fine powder has a glass transition point lower than the temperature at the time of melt-kneading the magnetic powder and the binder resin, the fine powder adhering to the surface of the magnetic powder is melted at the time of melt-kneading, and the surface of the magnetic powder is Attach firmly to cover. Further, when the binder resin is melted and kneaded, the fine powder melt on the surface of the magnetic powder is firmly adhered, and the binder resin and the magnetic powder are well blended and integrated. As a result, the fine powder does not drop from the magnetic powder, and the magnetic particles do not easily break, so that the magnetic particles do not break and the magnetic powder does not fall off. Therefore, each magnetic particle has stable magnetic characteristics and charging characteristics, and when used as a carrier for a two-component developer, it is possible to impart stable charging characteristics to the toner.

That is, according to the magnetic particles of the present invention, since the magnetic powder has fine powder adhered to the surface, it has excellent dispersibility and dispersion stability when dispersed in the binder resin. Since the magnetic particles are not reaggregated, the magnetic particles are almost uniformly dispersed in the generated magnetic particles, and the magnetic particles have excellent magnetic properties. Further, when melt-kneading the binder resin and the magnetic powder,
Since the fine powder having a glass transition point lower than the melt-kneading temperature is uniformly attached to the surface of the magnetic powder, the fine powder attached to the magnetic powder and the binder resin of the magnetic particles are almost even in the magnetic particles. In the mixed state, the magnetic powder and the binder resin are integrated. For this reason, there is no possibility that cracks will occur at the interface between the two and the magnetic powder will not fall off from the magnetic particles, and the manufactured magnetic particles will have excellent durability.

The magnetic particles of the present invention will be described below. As described above, the magnetic particles of the present invention are composed of a melt-kneaded product containing a binder resin and magnetic powder, and the magnetic powder is surface-treated with fine powder having a glass transition point lower than the temperature during melt-kneading. It is characterized by being As the binder resin, various conventionally known resins can be used, for example, polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene- Butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-acrylic Ethyl acid copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-phenyl acrylate copolymer, etc.), styrene-ethyl methacrylate copolymer, (styrene-ethyl methacrylate Copolymer, styrene-butyl methacrylate copolymer,
Styrene-phenyl methacrylate copolymer, etc.), styrene-α-chloromethyl acrylate copolymer, styrene-
Styrene resins such as acrylonitrile-acrylic acid ester copolymers (homopolymers or copolymers containing styrene or styrene substitution products), polyvinyl chloride, low molecular weight polyethylene, low molecular weight polypropylene, ethylene-ethyl acrylate copolymer , Polyvinyl butyral, ethylene-vinyl acetate copolymer, rosin-modified maleic acid resin, phenol resin, epoxy resin, polyester resin, ionomer resin, polyurethane resin, sillcone resin, ketone resin, xylene resin, polyamide resin, and the like. Are used alone or in combination of two or more. Among them, styrene resins, especially styrene-
A (meth) acrylic acid ester copolymer is preferred.

As the magnetic powder, powders of all kinds of magnetic materials known at present, such as a metal exhibiting ferromagnetism, an alloy thereof, various ferrites, or an alloy exhibiting ferromagnetism by being appropriately heat-treated, are used. be able to. Examples of the metal exhibiting ferromagnetism include iron, cobalt, nickel and the like, and an alloy containing these metals as described above can also be used. Examples of the ferrite include ferrosoferric oxide (Fe ₃ O ₄ ) and ferric sesquioxide (γ-Fe).
₂ O ₃ ), zinc iron oxide (ZnFe ₂ O ₄ ), yttrium iron oxide (Y ₃ Fe ₅ O ₁₂ ), cadmium iron oxide (CdFe
₂ O ₄ ), iron gadolinium oxide (Gd ₃ Fe ₅ O ₄ ), iron oxide copper (CuFe ₂ O ₄ ), lead iron oxide (PbFe ₁₂ O ₁₉ ), neodymium iron oxide (NdFeO ₃ ), barium iron oxide (BaFe)
₁₂ O ₁₉ ), magnesium iron oxide (MgFe ₂ O ₄ ), manganese iron oxide (MnFe ₂ O ₄ ), lanthanum iron oxide (LaFeO ₃ ).
Etc. Examples of alloys exhibiting ferromagnetism by heat treatment include Heusler alloys containing manganese and copper, such as manganese-copper-aluminum and manganese-copper-tin. These may be used alone or in combination of two or more.

The particle size of the magnetic powder is not particularly limited, and is preferably about the same as that used for a usual binder type carrier, that is, about 0.01 to 5 μm. If the particle size of the magnetic powder is less than the above range, the saturation magnetization may be lowered, and it may not be possible to obtain magnetic particles having a minute and uniform particle size. If the particle size of the magnetic powder exceeds the above range, dispersibility, even if surface-treated with fine powder,
The dispersion stability may be insufficient, and magnetic particles having uniform magnetic properties may not be obtained.

As the fine powder, various kinds of organic resins can be used, but those having a glass transition point lower than the temperature at the time of melt kneading and having a particle size smaller than the above magnetic powder. If it is, it will not be specifically limited. Specifically, the same binder resin as described above can be used, and an acrylic polymer is preferably used. The glass transition point of the fine powder is limited to a temperature lower than the temperature at the time of melt-kneading the binder resin and the magnetic powder, but is 50 to 170 ° C., preferably 60 to 170 ° C.
A resin having a glass transition point of 130 ° C. is used, and more preferably a glass transition point lower than that of the binder resin.

The particle size of the fine powder is preferably smaller than that of the magnetic powder, and is in the range of about 5 to 75% with respect to the particle size of the magnetic powder, more preferably 25% of the particle size of the magnetic powder. The front and back are used. The mixing ratio of the fine powder and the magnetic powder is 0.1 to 10 parts by weight, preferably 0.3 to 5 parts by weight, based on 100 parts by weight of the magnetic powder.

The surface treatment of the magnetic powder with the fine powder is carried out by dry blending the fine powder and the magnetic powder using a Henschel mixer, a dry blender, a ball mill or the like. The mixing ratio of the magnetic powder surface-treated with the fine powder and the binder resin is 200 to 1000 parts by weight with respect to 100 parts by weight of the binder resin.

The magnetic particles of the present invention are prepared by uniformly pre-kneading the magnetic powder surface-treated with fine powder and a binder resin with a Henschel mixer, a dry blender, a ball mill or the like,
Alternatively, it is produced by directly melt-kneading using a uniaxial or biaxial extrusion kneader, and then pulverizing and classifying. In addition,
The temperature at the time of melt-kneading is appropriately set depending on the kind of the binder resin, but is 80 to 250 ° C., preferably 100 to 20.
Set to a temperature of 0 ° C.

The particle size of the obtained magnetic particles is 20 to 400.
μm, preferably about 30 to 200 μm. The magnetic particles of the present invention can be suitably used as a so-called binder type carrier of a two-component developer, and in addition to the above components, various charge control agents, offset preventing agents (release agents), cross-linking agents and the like can be appropriately used. Additives can be added.

The magnetic particles of the present invention can also be used as a magnetic toner as a one-component developer, and in this case, a colorant can be blended in addition to the above components. There are two types of charge control agents, one for controlling positive charges and the other for controlling negative charges, depending on the charging polarity. As the charge control agent for controlling the positive charge, an organic compound having a basic nitrogen atom, such as a basic dye, an aminopyrine, a pyrimidine compound, a polynuclear polyamino compound, an aminosilane, etc., a filler surface-treated with each of the above compounds, etc. Can be given.

Charge control agents for controlling the negative charge include nigrosine base (CI5045) and oil black (CI26150).
), Oil-soluble dyes such as Bontron S and Spiron Black; charge control resins such as styrene-styrene sulfonic acid copolymers; compounds containing a carboxy group (for example, metal chelate of alkylsalicylic acid), metal complex dyes, fatty acid metals Examples thereof include soap, resin acid soap, and metal salt of naphthenic acid.

The charge control agent is used in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the binder resin. The offset preventing agent is for preventing aggregation of magnetic particles, and examples thereof include aliphatic hydrocarbons, aliphatic metal salts, higher fatty acids, fatty acid esters or partially saponified products thereof, silicone oil, and various waxes. Among them, the weight average molecular weight is 1000 to 10
About 000 aliphatic hydrocarbons are preferred. Specifically, low molecular weight polypropylene, low molecular weight polyethylene,
One or a combination of two or more of paraffin wax, a low molecular weight olefin polymer composed of olefin units having 4 or more carbon atoms, silicone oil and the like is suitable.

The offset preventing agent is 0.1 to 10 parts by weight, preferably 0.5 to 8 parts by weight, based on 100 parts by weight of the binder resin.
Used in parts by weight. The cross-linking agent cross-links the binder resin and the fine powder adhering to the surface of the magnetic powder to improve the mechanical or thermal characteristics of the magnetic particles, and further firmly integrates the magnetic powder and the binder resin. For example, a divinyl compound such as divinylbenzene;
Diallyl compounds such as diallyl phthalate, diallyl isophthalate, diallyl adipate, diallyl glycolate, diallyl maleate and diallyl sebacate; triallyl phosphate, triallyl aconitate, triallyl cyanurate, allyl trimellitic acid, allyl pyromellitic acid Triallyl compounds such as esters; 1,
6-hexanediol diacrylate, neopentyl glycol diacrylate, ethylene glycol diacrylate, diethylene glycol diacrylate, polyethylene glycol diacrylate, polypropylene glycol diacrylate, butylene glycol diacrylate, pentaerythritol diacrylate, 1,4-
Diacrylate compounds such as butanediol diacrylate; triacrylate compounds such as trimethylolpropane triacrylate and pentaerythritol triacrylate; 1,6-hexanediol dimethacrylate,
Dimethacrylate compounds such as neopentyl glycol dimethacrylate, ethylene glycol dimethacrylate, diethylene glycol dimethacrylate, polyethylene glycol dimethacrylate, polypropylene glycol dimethacrylate, butylene glycol dimethacrylate; trimethacrylate compounds such as trimethylolpropane trimethacrylate; dipentaerythritol hexa Acrylate, tetramethylolmethane tetraacrylate, poly (meth) acrylate compounds such as acrylic acid ester of N, N, N ', N'-tetrakis (β-hydroxyethyl) ethylenediamine; allyl-acrylic compounds such as allyl acrylate and allyl methacrylate Compound; N, N'-methylenebisacrylamide, N,
Acrylamide compounds such as N′-methylenebismethacrylamide; prepolymers such as polyurethane acrylate, epoxy acrylate, polyether acrylate, polyester acrylate and the like.

The crosslinking agent is used in an amount of 0.01 to 10 parts by weight, preferably 0.1 to 5 parts by weight, based on 100 parts by weight of the binder resin. When the magnetic particles of the present invention are used as a carrier, the cross-linking agent may be added in a higher proportion. When the magnetic particles of the present invention are used as a magnetic toner, a colorant may be further added.

As the coloring agent, carbon black, aniline blue, chalco oil blue, chrome yellow, ultramarine blue, DuPont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green, rose bengal, etc. Colorants can be used. The colorant is used in an amount of 1 to 15 parts by weight, preferably 5 to 10 parts by weight, based on 100 parts by weight of the binder resin.

When used as a carrier or a magnetic toner, the magnetic particles have an average particle size of 50 to 70 μm or less in the case of a carrier and 5 to 10 μm in the case of a magnetic toner in order to obtain a high resolution image. The following is desirable. As described above, the magnetic particles of the present invention can be used as a carrier constituting a two-component type developer together with a chargeable toner, and in addition to magnetic toners as a one-component type developer and various types of magnetic displays and the like. Can be used in the field of.

[0031]

EXAMPLES The present invention will be described below based on Examples and Comparative Examples. Example As magnetic powder, 100 parts by weight of magnetite (product number BL-100 manufactured by Titanium Industry Co., Ltd.) having an average particle size of 0.5 μm, and as fine powder, acrylic fine powder having an average particle size of 0.1 μm (polymethylmethacrylate, Tg70). ℃) 1 part by weight,
The mixture was mixed with a Henschel mixer to obtain a surface-treated magnetic powder having fine acrylic powder adhered to the surface of the magnetic powder.

100 parts by weight of this surface-treated magnetic powder and styrene-acrylic copolymer 5 as a binder resin
After 0 parts by weight and 2.5 parts by weight of carbon were mixed together in a Henschel mixer, this mixture was melt-kneaded in a twin-screw kneader set to a cylinder temperature of 170 ° C., which is a melt-kneading temperature, and then, Grinding and classifying, average particle size 80μm
Magnetic particles were prepared.

Example 2 The particle size of fine powder is larger than that of magnetic powder, and the average particle size is
Magnetic particles were prepared in the same manner as in Example 1 except that 1 μm of acrylic fine powder was used. Example 3 Magnetic particles were produced in the same manner as in Example 1 except that acrylic fine powder having a glass transition point of 130 ° C., which had a glass transition point higher than that of the binder resin, was used.

Comparative Example 1 Other than using magnetic powder which was not surface-treated with fine powder,
Magnetic particles were prepared in the same manner as in Example 1 above. Comparative Example 2 Magnetic particles were produced in the same manner as in the above-mentioned example except that acrylic fine powder having a glass transition point of 200 ° C. was used as the fine powder.

Comparative Example 3 Magnetic powder was dispersed in water, pH was adjusted to 2.0 with sulfuric acid while heating at 60 ° C., aqueous sodium aluminate solution was gradually added while stirring, and after completion of addition, filtration and heating were performed. By firing, an alumina surface-treated magnetic powder was obtained. Next, magnetic powder was produced in the same manner as in the above-described example except that this alumina surface-treated magnetic powder was used.

The following tests were carried out on the above Examples and Comparative Examples to evaluate the characteristics. Practical Test Using the magnetic particles produced in Examples and Comparative Examples as a binder type carrier, a toner having an average particle size of 10 μm (for DC4585 manufactured by Mita Kogyo Co., Ltd.) and a weight ratio of carrier to toner of 19: 1 were used. A two-component developer was prepared by mixing, and the following measurements were performed to evaluate the characteristics.

Image Density Measurement Each of the developers is treated with a plain paper copying machine (model No. D) manufactured by Mita Kogyo Co., Ltd.
C4585) as a starting developer, and using the same toner as the developer as a replenishing toner, continuous copying of 200,000 black and white originals was performed, and the first image forming sheet (initial), The image densities of the 20,000th and 200,000th formed images were measured using a reflection densitometer (Model No. TC-6D manufactured by Tokyo Denshoku Co., Ltd.).

Measurement of Fogging Density The density of the blank portion of the formed images of the first (initial) 20,000th and 200,000th image formations was measured using the reflection densitometer. Blow-off charge amount measurement The charge amount of the developer before continuous copying of 200,000 sheets (initial stage), after copying 20,000 sheets and after copying 200,000 sheets was measured using a blow-off charge amount measuring device manufactured by Toshiba Chemical Co. .

Table 1 shows the results of these measurements.

[0040]

[Table 1]

From Table 1, in the developers containing the magnetic particles of Comparative Examples 1 to 3 as carriers, the image density and the fog density increased as the number of copies increased, and the blow-off charge amount decreased. In contrast, Examples 1 to 1
In the case of No. 3, even after continuous copying of 200,000 sheets, almost no change was observed in each characteristic, and the formed image was good. Therefore, it was confirmed that the magnetic particles of the examples had excellent durability.

[0042]

As described in detail above, according to the present invention,
Binder type that has good dispersibility and dispersion stability of the magnetic powder in the binder resin, excellent magnetic properties and chargeability of individual magnetic particles, and can give stable chargeability to the toner when used as a carrier. Magnetic particles are obtained.

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Claims (1)

[Claims] 1. A melt-kneaded product containing a binder resin and magnetic powder, wherein the magnetic powder is surface-treated with a fine powder having a glass transition point lower than the temperature at the time of melt-kneading. Characteristic magnetic particles.