JP3334735B2 - Magnetic carrier for electrophotography - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a low bulk density, an excellent fluidity, and an appropriate saturation magnetization, especially 30 to 40%.
It has a saturation magnetization of about 80 emu / g and a moderate specific gravity (true specific gravity-the same applies hereinafter), particularly a specific gravity of about 2.5 to 5.2 and a relatively high electric resistance, especially 10 ¹⁰ to 10. ¹²
The present invention relates to a magnetic carrier for electrophotography comprising spherical composite particles having an electric resistance of about Ωcm.

[0002]

2. Description of the Related Art As is well known, in electrophotography, a photoconductive substance such as selenium, OPC (organic semiconductor), α-Si or the like is used as a photosensitive member, and an electrostatic latent image is formed by various means. A method is used in which a toner charged in a direction opposite to the polarity of the latent image is attached to the latent image by electrostatic force using a magnetic brush developing method or the like to visualize the latent image.

In this developing step, carrier particles called carriers are used, and an appropriate amount of positive or negative electricity is applied to the toner by triboelectric charging, and a magnetic force is used to cause the toner to pass through a developing sleeve containing a magnet. Thus, the toner is transported to a developing area near the surface of the photoconductor on which the latent image has been formed.

In recent years, the electrophotographic method has been widely used in copiers and printers, and is required to be able to handle various objects such as fine lines, small letters, photographs, and color originals. Further, higher image quality, higher quality, higher speed, and continuity are also required, and these requirements are expected to increase in the future.

Conventionally, iron powder carriers,
Ferrite carriers or binder type carriers (composite particles in which magnetic fine particles are dispersed in a resin) and the like have been developed and put into practical use.

The iron powder carrier has a flake shape, a sponge shape, and a spherical shape.
A degree, because the bulk density as high as ^{3g / cm 3 ~4g / cm 3} , in order to stir in the developing machine requires a large driving force, many mechanical wear, spent of the toner, It tends to cause deterioration of the chargeability of the carrier itself and damage to the photoreceptor.

The ferrite carrier is spherical, has a specific gravity of about 4.5 to 5.5, and has a bulk density of 2 g / cm ³ to
Since it is about 3 g / cm ³ , the weight, which is a drawback of the iron powder carrier, can be solved to some extent, but it is still not enough.

[0008] The binder type carrier is 2.5 g / cm
^The bulk density is as low as about ³ or less, and the particles have less shape distortion, and the particles have a tendency to have a high particle strength. Since its particle size can be controlled in a wide range, it is most suitable for a high-speed copying machine or a high-speed laser beam printer of a general-purpose computer in which the rotation speed of a developing sleeve or a magnet in the sleeve is large, and is currently most widely used.

The resins used for the binder type carrier are roughly classified into thermoplastic resins such as vinyl-based, styrene-based and acrylic-based resins and thermosetting resins such as phenol-based resins, melamine-based resins and epoxy-based resins. Although a thermosetting resin is known, a thermoplastic resin that can be easily granulated is generally used, and it is said that a thermosetting resin has a practical problem since it is difficult to form a spheroid.

On the other hand, thermosetting resins are superior in durability, impact resistance, and heat resistance as compared with thermoplastic resins. Therefore, a binder type made of inorganic particles and a thermosetting resin taking advantage of these advantages is used. There is a strong demand for a carrier (composite particle powder), and composite particles using a phenol resin as the thermosetting resin and a ferromagnetic powder as the inorganic particles are known (Japanese Patent Application Laid-Open No. 220068/1990, Kaihei 4-10
No. 0850), however, there is no limit to the demand for higher performance of the binder type carrier, and in addition to the above-mentioned characteristics, it is required that the respective characteristics of the magnetization value, the specific gravity, and the electric resistance value are appropriately controlled. ing.

First, the carrier is required to have an appropriate saturation magnetization value, particularly a saturation magnetization value of about 30 to 80 emu / g. That is, a good image can be obtained by setting the value of the saturation magnetization of the carrier in the range of 30 to 80 emu / g. By setting the magnetization value to 30 emu / g or more, the carrier forming the so-called “spike” of the magnet brush on the sleeve separates from the “spike” due to the low magnetic force and flies to the photoconductor, So-called carrier adhesion that adheres to the photoreceptor hardly occurs. In addition, 80 emu /
By setting it to g or less, the mechanical force applied to the magnetic toner can be suppressed, and the crushing of the magnetic toner can be prevented. Therefore, the saturation magnetization of the carrier is required to be in the range of 30 to 80 emu / g.

Second, the carrier is required to charge the toner quickly. That is, it is important to improve the mixing property with the toner, and for that purpose, it is required to have an appropriate specific gravity, particularly, a specific gravity of about 2.5 to 5.2. Although increasing the specific gravity of the carrier is advantageous for the mixing property with the toner itself, it is also required that the toner is not damaged, so that the so-called spent is prevented from occurring, and the developing machine is reduced in size and In order to reduce the weight, the specific gravity of the carrier is desirably small. Accordingly, it is required that the specific gravity is appropriate, particularly, about 2.5 to 5.2.

[0013] The third point required for the carrier is a relatively high electric resistance value, especially 10 ¹⁰ to 10 ¹² Ω.
cm. That is,
When the volume resistivity is as low as 10 ⁶ Ωcm or less as in the case of an iron powder carrier, the charge is injected from the sleeve to cause the carrier to adhere to the image portion of the photoreceptor, or the latent image charge escapes via the carrier, resulting in a latent image. There are problems such as occurrence of disorder and loss of images.

[0014] To solve these problems, a resin coated on the carrier particle surfaces, proposed to increase the electrical resistance of the carrier (JP 47-13954, JP-Sho
57-660 ).

However, since these resins are insulators, the electric resistance of the carrier itself is too high than 10 ¹² Ωcm, so that the carrier charge hardly leaks, and the charge amount of the toner also increases. The resulting image is an image with a sharp edge, but on the other hand, on a large-area image surface, there is a problem that the image density in the central portion becomes extremely low.

From these facts, a relatively high electric resistance value is required, and specifically, a specific volume resistance value of 10 ¹⁰ to 10 is required.
^{About 12} Ωcm is required.

Heretofore, there have been several attempts to make the electrical resistance of a binder type carrier appropriate. For example, at least one of a carrier in which the surface of a core material containing a magnetic material is coated with a conductive layer, and the surface of the conductive layer is further coated with a high-resistance layer (Japanese Patent Laid-Open No. 4-324457), and a magnetic powder-dispersed carrier. The carrier has a volume resistivity of 10 ¹² Ωcm or less on the surface of a carrier in which fine particles of an inorganic oxide are previously added and adhered to the surface of a carrier (Japanese Patent Laid-Open No. 4-124677). Carrier to which conductive fine particles are added (Japanese Unexamined Patent Publication No. 5-27
No. 3789) has been proposed.

[0018]

The bulk density is low, the fluidity is excellent, and a suitable saturation magnetization value, especially 30
Having a saturation magnetization of about ~ 80 emu / g,
Spherical composite particle powders having an appropriate specific gravity, particularly a specific gravity of about 2.5 to 5.2 and a relatively high electric resistance value, particularly an electric resistance value of about 10 ¹⁰ to 10 ¹² Ωcm, are currently the most demanded. However, such a magnetic carrier has not been provided yet.

That is, the spherical phenolic resin-containing composite particles containing ferromagnetic particles described in JP-A-2-220068 and JP-A-4-100850 form a uniform coating layer with the resin. It is not intended to control the electric resistance value.

The above-mentioned Japanese Patent Application Laid-Open Nos. 4-324457, 4-124677 and 5-273.
Similarly, the carrier described in Japanese Patent No. 789 cannot sufficiently satisfy the above-mentioned various properties.

In the carrier described in Japanese Patent Application Laid-Open No. 4-324457, the electric resistance is adjusted by two resin coating layers. For this reason, it is necessary to increase the thickness of each coating layer to some extent. As a result, the content of the magnetic powder is reduced, or a problem occurs in the adhesion between the core particles and the respective coating layers.

The carriers described in JP-A-4-124677 and JP-A-5-273789 are obtained by adhering inorganic oxide fine powder to the surface of composite particles containing ferromagnetic particles. The inorganic oxide fine powder does not have a coating layer uniformly dispersed in a resin matrix,
There is a problem that it is easily peeled off by a mechanical impact.

Accordingly, the present invention is directed to a spherical composite particle powder having a low bulk density and excellent fluidity, which has an appropriate saturation magnetization value, particularly a saturation magnetization value of about 30 to 80 emu / g. A suitable specific gravity, in particular of the order of 2.5 to 5.2 and a relatively high electrical resistance, in particular 10 ¹⁰ to 10 ¹² Ω
An object of the present invention is to provide a magnetic carrier for electrophotography comprising a spherical composite particle powder having an electric resistance of about cm.

[0024]

The above technical object can be achieved by the present invention as described below. That is, the present invention comprises a phenol resin or a non-magnetic iron compound particle and a phenol resin on the surface of a spherical composite core particle obtained by combining a ferromagnetic iron compound particle and a non-magnetic iron compound particle with a phenol resin as a binder. A magnetic carrier for electrophotography comprising spherical composite particles having an average particle diameter of 1 to 1000 μm formed with a coating layer, wherein the ferromagnetic iron compound particles and the nonmagnetic iron compound particles contained in the spherical composite core particles are provided. Is 80 to 99% by weight, and the average particle diameter r _a of the ferromagnetic iron compound particles and the average particle diameter r of the non-magnetic iron compound particles are
The ratio r _a / r _b and _b is an electrophotographic magnetic carrier, characterized in that 1.2 or more.

Hereinafter, the present invention will be described in detail. First, the spherical composite particles according to the present invention will be described.

The spherical composite particles according to the present invention have an average particle diameter of 1 to 1000 μm. Average particle size is 1μm
Particles smaller than 2 μm are liable to secondary agglomeration, and particles larger than 1000 μm have poor mechanical strength, making it impossible to obtain a clearer image. In particular, when high image quality is required, 20 to
The range is preferably 200 μm, more preferably 30 to
The range is 100 μm.

The spherical composite particles according to the present invention contain ferromagnetic iron compound particles and nonmagnetic iron compound particles, and the total amount of ferromagnetic iron compound particles and nonmagnetic iron compound particles is 80 to 99.
% By weight. If the amount is less than 80% by weight, the proportion of the resin increases, so that an appropriate specific gravity cannot be obtained. If the amount exceeds 99% by weight, a binder is insufficient and composite particles having sufficient strength cannot be obtained.

Further, the content of the nonmagnetic iron compound particles is in the range of 20 to 70% by weight based on the total amount of the ferromagnetic iron compound particles and the nonmagnetic iron compound particles. Preferably 30 to
It is in the range of 70% by weight. If less than 20% by weight,
The magnetization value becomes too large. On the other hand, if it exceeds 70% by weight, a sufficient magnetization value cannot be obtained, which is not preferable.

The spherical composite particles according to the present invention preferably have a sphericity represented by the following formula in the range of 1.0 to 1.4.

Sphericity = l / w l: average major axis diameter of spherical composite particles w: average minor axis diameter of spherical composite particles

The spherical composite particles according to the present invention preferably have a bulk density of about 2.5 g / cm ³ or less. More preferably, it is about 2.0 g / cm ³ or less.

The spherical composite particles according to the present invention, the ratio r _a / r _b between the average particle size r _b of the average particle diameter r _a nonmagnetic iron compound particles of the ferromagnetic iron compound particles, 1.2 That is all.
Preferably it is 1.5 or more. If less than 1.2,
The difference between the size of the ferromagnetic iron compound particles and the size of the nonmagnetic iron compound particles disappears, or rather, the size of the nonmagnetic iron compound particles becomes relatively large, so that the ratio of the ferromagnetic iron compound particles occupying the surface decreases. As a result, the electric resistance of the surface of the spherical composite core particles before resin coating becomes high, so that the electric resistance of the spherical composite particles after resin coating exceeds 10 ¹² Ωcm. The ratio r _a / r _b, it is preferred for uniform mixing of 5.0 or less.

The spherical composite particles according to the present invention have a saturation magnetization of 30 to 80 emu / g. Preferably 40
７５75 emu / g. Saturation magnetization value is 80 emu / g
In the case where the value exceeds, the transportability due to the magnetic force of the carrier is increased, and the mechanical force applied to the magnetic toner is increased, so that the magnetic toner may be crushed. When the saturation magnetization value is less than 30 emu / g, the carrier is detached from the surface of the developing sleeve during the transport of the developer, and adheres to the surface of the photoconductor to cause a defect in an image.

The spherical composite particles according to the present invention have a specific gravity of 2.5 to 5.2. Preferably it is 2.5-4.5.

The spherical composite particles according to the present invention have an electric resistance of 10 ¹⁰ to 10 ¹² Ωcm. If it is less than 10 ¹⁰ Ωcm, the charge on the electrostatic latent image flows through the carrier, and the image is disturbed or chipped, which is not preferable. If it exceeds 10 ¹² Ωcm, leakage of carrier charge hardly occurs, the charge amount of the toner increases, and problems such as extremely low image density at the center of the solid black portion occur.

Next, various conditions for implementing the present invention will be described.

The ferromagnetic iron compound particles used in the present invention include ferromagnetic iron oxide particles such as magnetite and maghemite, and metals other than iron (Mn, Ni, Zn, Mg, C).
and the like, spinel ferrite particles containing one or two or more kinds of particles, magnetoplumbite-type ferrite particles such as barium ferrite, and fine particles of iron or iron alloy having an oxide film on the surface. Preferably, it is a ferromagnetic iron oxide particle powder such as magnetite. The particle size of the ferromagnetic iron compound particles is desirably 0.05 to 10 μm, and may be 0.1 to 5 μm in consideration of the dispersion in an aqueous medium and the strength of the resulting spherical composite particles. preferable. The shape may be any of a granular shape, a spherical shape, and a needle shape.

As the nonmagnetic iron compound particles used in the present invention, fine particles such as hematite, goethite and ilmenite can be used. Preferably hematite. The particle size of the non-magnetic iron compound particles is 0.02
To 5 μm, and considering the dispersion in an aqueous medium and the strength of the composite particles to be formed, 0.05
It is preferably about 3 μm. The shape may be any of a granular shape, a spherical shape, and a needle shape.

Examples of the phenol used in the present invention include phenol itself, alkylphenols such as m-cresol, p-tert-butylphenol, o-propylphenol, resorcinol, bisphenol A, and a part of benzene nucleus or alkyl group. Alternatively, compounds having a phenolic hydroxyl group such as halogenated phenols, all of which are substituted with chlorine atoms and bromine atoms, may be mentioned, of which phenol is most preferred. When a substance other than phenols is used, particles may not be easily formed, or even if particles are formed, the particles may have an irregular shape.

Examples of the aldehyde used in the present invention include formaldehyde and furfural in either form of formalin or paraaldehyde, with formaldehyde being particularly preferred.

The molar ratio of the aldehyde to the phenol is preferably from 1 to 2, particularly preferably from 1.1 to 1.
6. If the molar ratio of the aldehydes to the phenols is less than 1, particles are hardly generated, or even if they are formed, the curing of the resin is difficult to progress, so that the strength of the generated particles tends to be weak. If the molar ratio of aldehydes to phenols is greater than 2,
Unreacted aldehydes remaining in the aqueous medium after the reaction tend to increase.

Examples of the basic catalyst used in the present invention include those used in the production of ordinary resole resins, for example, aqueous ammonia, hexamethylenetetramine and alkylamines such as dimethylamine, diethyltriamine and polyethyleneimine. The molar ratio of these basic catalysts to phenols is preferably from 0.02 to 0.3.

When reacting the phenols and aldehydes in the presence of a basic catalyst, the amount of the ferromagnetic iron compound particles and the nonmagnetic iron compound particles to be coexistent is 0.5 parts by weight with respect to the phenols. It is preferably up to 200 times. Further, the strength is more preferably 4 to 100 times in consideration of the strength of the formed spherical composite particles.

The ferromagnetic iron compound particles and nonmagnetic iron compound particles in the present invention can be used as they are without surface treatment, but may be subjected to lipophilic treatment in advance. When using iron compound particles that have not been subjected to lipophilic treatment, a hydrophilic organic compound such as carboxymethyl cellulose or polyvinyl alcohol or a fluorine compound such as calcium fluoride is added as a suspension stabilizer. This facilitates generation of spherical particles.

The lipophilic treatment is carried out by adding a coupling agent such as a silane coupling agent or a titanate coupling agent to a ferromagnetic iron compound particle powder or the like and coating the mixture, or an aqueous solvent containing a surfactant. There is a method in which ferromagnetic iron compound particles and the like are dispersed therein and a surfactant is adsorbed on the surface of the particles. The ferromagnetic iron compound particles and the nonmagnetic iron compound particles may be subjected to lipophilic treatment at the same time, or may be treated separately. Alternatively, only one of the lipophilic treatments may be performed.

Examples of the silane coupling agent include those having a hydrophobic group, an amino group, and an epoxy group. Examples of the silane coupling agent having a hydrophobic group include vinyltrichlorosilane, vinyltriethoxysilane, and vinyl.
Tris (β-methoxy) silane and the like.

Examples of the silane coupling agent having an amino group include γ-aminopropyltriethoxysilane, N
-Β- (aminoethyl) ─γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane and the like.

Examples of the silane coupling agent having an epoxy group include γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) trimethoxysilane and the like. There is.

Examples of the titanate coupling agent include isopropyl triisostearoyl titanate, isopropyl tridodecylbenzenesulfonyl titanate, and isopropyl tris (dioctyl pyrophosphate) titanate.

As the surfactant, a commercially available surfactant can be used. Examples of the surfactant include ferromagnetic iron compound particles, nonmagnetic iron compound particles, and those having a functional group capable of bonding to a hydroxyl group on the particle surface. Desirably, ionic or cationic is preferred.

Although the object of the present invention can be achieved by any of the above-described treatment methods, treatment with a silane coupling agent having an amino group or an epoxy group is preferable in consideration of the adhesiveness to a phenol resin.

The reaction in the present invention is carried out in an aqueous medium. In this case, the amount of water charged is determined by the total solids which is the ratio of the total amount of the ferromagnetic iron compound particles and the non-magnetic iron compound particles to the entire raw material. It is preferable that the partial concentration be 30 to 95% by weight, and particularly preferably 60 to 90% by weight.

In the reaction, first, phenols, formalins, water, ferromagnetic iron compound particles and non-magnetic iron compound particles are charged into a reaction vessel, sufficiently stirred, and then a basic catalyst is added and stirred. While raising the reaction temperature to 70-9.
Adjust to 0 ° C. and cure the phenolic resin. At this time,
In order to obtain spherical composite particles having a high sphericity, it is desirable to gradually raise the temperature. The rate of temperature rise is preferably 0.1.
5 to 1.5 ° C / min, more preferably 0.8 to 1.2 ° C / minute
Minutes.

After the cured reaction product is cooled to 40 ° C. or lower, the obtained aqueous dispersion is separated into solid and liquid by a conventional method such as filtration and centrifugation, and then washed and dried to obtain a ferromagnetic iron. Spherical composite core particles obtained by combining compound particles and nonmagnetic iron compound particles with a phenol resin as a binder are obtained.

The formation of the coating layer made of a phenol resin is as follows.
Phenols, formalins, water, and spherical composite core particle powder were charged into a reaction vessel, and after sufficiently stirring, a basic catalyst was added and the temperature was increased while stirring, and the reaction temperature was reduced to 70 to 9
Adjust to 0 ° C. and cure the phenolic resin. After the cured reaction product is cooled to 40 ° C. or less, the obtained aqueous dispersion is separated into solid and liquid by a conventional method such as filtration, centrifugation, etc., and then washed and dried to remove the phenol resin from the phenol resin on the particle surface Spherical composite particles having a coating layer formed thereon are obtained.

The coating layer composed of the phenol resin and the nonmagnetic iron compound particles was formed in the same manner as the formation of the coating layer composed of the phenol resin except that the nonmagnetic iron compound particles were added together with the phenol. Spherical composite particles having a coating layer formed of nonmagnetic iron compound particles are obtained. The nonmagnetic iron compound particles may have been subjected to a lipophilic treatment.

It should be noted that the object of the present invention is to have a proper saturation magnetization value, especially a saturation magnetization value of about 30 to 80 emu / g, and a proper specific gravity, especially about 2.5 to 5.2. While maintaining a relatively high electric resistance, especially about 10 ¹⁰ to 10 ¹² Ωcm, the surface of the spherical composite particles is epoxy-coated to improve the durability and control the charge amount, which is usually performed. A coating layer made of one or more resins selected from resins, polyester resins, styrene resins, silicon resins, melamine resins, polyamide resins, fluororesins, and the like may be formed. The formation of the coating layer can be performed by a known method.

[0058]

As described above, the characteristics required for the electrophotographic carrier are that the characteristics of the saturation magnetization, specific gravity, and electric resistance are appropriately controlled. Conventionally, carrier particles have been coated with a resin for stabilizing triboelectric charging. However, since the binder-type carrier generally has a high electric resistance value, if the surface is further coated with an insulating resin, the electric resistance value of the carrier is 10 ^12.
Ωcm, the carrier charge hardly leaks, and the charge amount of the toner also increases, resulting in a problem that the resulting image density becomes extremely low.

Further, attempts have been made to control the electric resistance value by, for example, attaching inorganic fine particles to the surface of the composite core particles containing ferromagnetic particles. It is unstable and the contact area between the composite particles is extremely small, which is not preferable for controlling the electric resistance value.

[0060] The present inventors, in the spherical composite particles, the ratio r _a / r _b between the average particle size r _b of the average particle diameter r _a nonmagnetic iron compound particles of the ferromagnetic iron compound particles is 1. By selecting each iron compound particle so as to be 2 or more, the ratio of ferromagnetic iron compound particles having a relatively large particle diameter to the outermost surface on the surface of the composite core particle obtained using a phenol resin as a binder is increased, The electric resistance value of the spherical composite core particle surface before resin coating is kept as low as 10 ⁸ Ωcm or less, and the spherical composite core particle surface has a coating layer made of phenol resin or a phenol resin and nonmagnetic iron compound particles. It was studied to control the electric resistance to a moderately high electric resistance value, that is, 10 ¹⁰ to 10 ¹² Ωcm by forming a coating layer having a thickness of ¹⁰ μm.

[0061] The average of the average particle size r _a nonmagnetic iron compound particles of the ferromagnetic iron compound particles to the electrical resistance of the composite core particles surface before the resin-coated as described above as low as 10 ⁸ [Omega] cm or less it is important that the ratio r _a / r _b of the particle size r _b to select each of the iron compound particles to be 1.2 or more.

[0062] That is, the ratio r _a / r when _b is less than 1.2, the ferromagnetic iron compound particles and the non-magnetic iron compound particles and the little difference in size is eliminated or rather the non-magnetic iron compound particles Is relatively large, the ratio of the ferromagnetic iron compound particles occupying the surface decreases, and the electrical resistance value of the spherical composite core particles before coating with the phenol resin increases,
The electric resistance value of the spherical composite particles coated with the phenol resin exceeds 10 ¹² Ωcm.

The electric resistance of the surface of the spherical composite core particles is 1
By controlling to be as low as 0 ⁸ Ωcm or less, a moderately high electric power can be obtained by forming a coating layer composed of a phenol resin or a coating layer composed of a phenol resin and nonmagnetic iron compound particles on the surface of the spherical composite core particles. Resistance value, ie 1
It can be controlled to 0 ¹⁰ to 10 ¹² Ωcm. Furthermore, when a coating layer composed of a phenolic resin and a nonmagnetic iron compound is formed, in addition to controlling the electric resistance value, the presence of the nonmagnetic iron compound particles contained in the coating layer causes It is possible to provide a carrier having little change in hygroscopicity and excellent in environmental stability of chargeability. Moreover, since there is almost no specific gravity difference between the ferromagnetic iron compound particles and the nonmagnetic iron compound particles, a constant specific gravity can be maintained even when the magnetization value and the electric resistance value are controlled.

[0064]

Next, the present invention will be described with reference to Examples and Comparative Examples. The average particle diameter of the spherical composite particles in the following Examples and Comparative Examples is indicated by a value measured by a laser diffraction type particle size distribution meter (manufactured by Horiba, Ltd.). (Manufactured by S-800)
Observed at

The sphericity was measured by randomly extracting 250 or more spherical composite particles with a scanning electron microscope (S-800, manufactured by Hitachi, Ltd.), and averaging the major axis diameter l and the average minor axis diameter w.
Was calculated by the following equation.

Sphericity = l / wl 1: Average long axis diameter of spherical composite particles w: Average short axis diameter of spherical composite particles

The bulk density was measured according to the method described in JIS K5101.

[0068] The ratio r _a / r _b of the average particle size r _b of the average particle diameter r _a nonmagnetic iron compound particles of the ferromagnetic iron compound particles of spherical composite particles have an average ferromagnetic iron compound particles used Particle size r
It was calculated by calculation from an average particle size r _b of _a nonmagnetic iron compound particles.

The saturation magnetization was measured using a vibrating sample magnetometer VSM-3.
The value was measured using an S-15 (manufactured by Toei Kogyo) under an external magnetic field of 10 kOe.

The true specific gravity was indicated by a value measured with a multi-volume density meter (manufactured by Micromeritics).

The electric resistance is measured by the high resistance meter 4
329A (manufactured by Yokogawa Hewlett-Packard).

Example 1 In a 1-liter four-necked flask, 40 g of phenol, 60 g of 37% formalin, 320 g of spherical magnetite particles (average particle diameter 0.24 μm), 8 g of granular hematite particles (average particle diameter 0.16 μm), fluoride 1.0 g of calcium,
12 g of 28% ammonia water and 40 g of water were added, and the temperature was raised to and maintained at 85 ° C. in 40 minutes while stirring and mixing.
Reaction and curing for minutes. Then, cool down to 30 ° C,
After addition of 0.5 l of water, the supernatant was removed, the precipitate was washed with water and air-dried. Then, this was removed under reduced pressure (5 mmH
g) to obtain spherical composite core particle powder A in which spherical magnetite particles and spherical hematite particles are combined with a phenol resin as a binder.

Further, 2 g of phenol, 2.7 g of 37% formalin, 100 g of spherical composite core particles A, 40 g of water, and 1 g of 28% ammonia water were charged into a 500 ml three-necked flask while stirring, and the temperature was raised to 85 ° C. in 30 minutes. Let
Reaction and curing were performed at the same temperature for 120 minutes.

Next, the content in the flask was cooled to 30 ° C., 0.5 l of water was added, the supernatant was removed, and the precipitate was washed with water and air-dried. Then, this was removed under reduced pressure (5 m
(mHg or less)) and dried at 50 to 60 ° C. to obtain spherical composite particles F coated with a phenol resin. The obtained spherical composite particles F had an average particle diameter of 38 μm, and had a spherical shape close to a true sphere as shown in the scanning electron micrograph (× 1500) of FIG. The content of the nonmagnetic iron compound in the spherical composite particles F was calculated from the measurement of the magnetization value and the specific gravity. As a result, the content was 20.7% by weight based on the total amount of the ferromagnetic iron compound particles and the nonmagnetic iron compound particles. there were. Further, the content of the phenol resin was 11.7% by weight based on the whole. Table 4 shows the properties of the spherical composite particles F.

Example 2 160 g of spherical magnetite particles (average particle diameter 0.24 μm) were charged into a Henschel mixer, stirred well, and then mixed with a silane coupling agent (KBM-602) 1.2.
g was added, the temperature was raised to about 100 ° C., and the mixture was thoroughly stirred and mixed for 30 minutes to obtain spherical magnetite particles coated with a coupling agent.

Separately, granular hematite particles (average particle size 0.10 μm) 24
After charging 0 g and stirring sufficiently, 2.4 g of a silane coupling agent (KBM-403: manufactured by Shin-Etsu Chemical Co., Ltd.) is added, and the mixture is heated to about 100 ° C. and mixed and stirred well for 30 minutes to make it lipophilic. Was performed to obtain granular hematite particles coated with a silane coupling agent.

Next, 42 g of phenol, 63 g of 37% formalin, 160 g of spherical magnetite particles subjected to lipophilic treatment, 240 g of granular hematite particles subjected to lipophilic treatment, and 14 g of 28% aqueous ammonia were placed in a 1-liter four-necked flask. ,
45 g of water was added, the temperature was raised to 85 ° C. for 40 minutes with stirring, and the mixture was reacted and cured at the same temperature for 180 minutes. Next, the content in the flask was cooled to 30 ° C., 0.5 l of water was added, the supernatant was removed, and the lower layer sediment was washed with water and air-dried. Next, this was dried at 50 to 60 ° C. under reduced pressure (5 mmHg or less) to obtain spherical composite core particles B in which spherical magnetite particles and granular hematite particles were bound using a phenol resin as a binder.

Further, in a 500 ml three-necked flask, 2 g of phenol, 2.7 g of 37% formalin, 100 g of spherical composite core particles B, and 0.2 μm spherical hematite particles 1
g, 50 g of water and 1 g of 28% ammonia water were added with stirring, and the temperature was raised to 85 ° C. for 30 minutes.
Reaction and curing for minutes.

Next, the content in the flask was cooled to 30 ° C., 0.5 l of water was added, the supernatant was removed, and the precipitate was washed with water and air-dried. Then, this was removed under reduced pressure (5 m
After drying at 50 to 60 ° C., spherical composite particles G coated with a coating layer composed of granular hematite particles and a phenol resin were obtained. Obtained spherical composite particles G
Had an average particle diameter of 35 μm, and had a spherical shape close to a true sphere as shown in a scanning electron micrograph (× 2000) of FIG. The content of the nonmagnetic iron compound in the spherical composite particles G was calculated from the measurement of the magnetization value and the measurement of the specific gravity. As a result, the content was 58.7% by weight based on the total amount of the ferromagnetic iron compound particles and the nonmagnetic iron compound particles. Met. The content of the phenol resin was 13.9% by weight based on the whole. Table 4 shows properties of the spherical composite particles G.

Examples 3 and 4, Comparative Example 1 Types of spherical magnetite particles and granular hematite particles
Table 1 shows the amount and lipophilicity of the spherical magnetite particles and granular hematite particles separately or simultaneously, and the amounts of phenol, formalin, ammonia water as basic catalyst and water. Reaction and curing were performed in the same manner as in Example 1 except that the composition was changed as shown in Tables 1 to 3 to obtain spherical composite core particles CE. Various properties of the obtained spherical composite core particles CE are shown in Table 2. Further, a coating layer was formed on the particle surface of the spherical composite core particles under the conditions shown in Table 3 to obtain spherical composite particles H to J. Various properties of the obtained spherical composite particles H to J are shown in Table 4.

[0081]

[Table 1]

[0082]

[Table 2]

[0083]

[Table 3]

[0084]

[Table 4]

[0085]

The spherical composite particles according to the present invention have an average particle diameter of the ferromagnetic iron compound particles larger than the average particle diameter of the non-magnetic iron compound particles. The resistance can be controlled to be low, and the resin coating has an appropriate saturation magnetization value, particularly a saturation magnetization value of about 30 to 80 emu / g, and an appropriate specific gravity, particularly 2.5.
~ 5.2 and a moderately high electrical resistance, especially 10
^It has an electrical resistance of about ¹⁰ to 10 ¹² Ωcm, and is most suitable as a magnetic carrier for electrophotography that can realize high image quality, high quality, high speed, and continuity.

Since the spherical composite particles according to the present invention have the above-mentioned various properties, when used as a carrier, they have good mixing properties with the toner, and as a result, the charging speed of the toner can be increased. In addition, spent can be suppressed without damaging the toner, and further, an excessive toner charge amount can be suppressed, and a stable toner charge amount can be maintained even when the carrier is used for a long time.

[Brief description of the drawings]

FIG. 1 is a scanning electron micrograph (× 1500) showing the particle structure of spherical composite particles F obtained in Example 1.

FIG. 2 is a scanning electron micrograph (× 2000) showing the particle structure of a spherical composite particle G obtained in Example 2.

Continuation of front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G03G 9/10

Claims (4)

(57) [Claims] 1. A spherical composite core particle obtained by combining a ferromagnetic iron compound particle and a non-magnetic iron compound particle with a phenol resin as a binder. A magnetic carrier for electrophotography comprising spherical composite particles having a particle diameter of from 1 to 1000 μm, wherein the total amount of ferromagnetic iron compound particles and nonmagnetic iron compound particles contained in the spherical composite core particles is 80 to 99% by weight; and, electrophotographic magnetic, characterized in that the ratio r _a / r _b between the average particle size r _b of the average particle diameter r _a nonmagnetic iron compound particles of the ferromagnetic iron compound particles is 1.2 or more Career. 2. A coating layer comprising nonmagnetic iron compound particles and a phenol resin is formed on the surface of a spherical composite core particle obtained by combining ferromagnetic iron compound particles and nonmagnetic iron compound particles with a phenol resin as a binder. Average particle size 1
A magnetic carrier for electrophotography comprising 1000 μm spherical composite particles, wherein the total amount of ferromagnetic iron compound particles and nonmagnetic iron compound particles contained in the spherical composite core particles is 80%.
A 99% by weight, and, the ratio r _a / r _b between the average particle size r _b of the average particle diameter r _a nonmagnetic iron compound particles of the ferromagnetic iron compound particles is 1.2 or more Characteristic magnetic carrier for electrophotography. The average particle diameter r _a of 3. A ferromagnetic iron compound particles is in the range of 0.05 to 10 [mu] m, and an average particle size r _b of the non-magnetic iron compound particles is in the range of 0.02~5μm The magnetic carrier for electrophotography according to claim 1 or 2. 4. The content of the non-magnetic iron compound particles is 20 to the total amount of the ferromagnetic iron compound particles and the non-magnetic iron compound particles.
4. The magnetic carrier for electrophotography according to claim 1, wherein said magnetic carrier is in the range of from about 70% by weight to about 70% by weight.