JP3006657B2 - Magnetic carrier for electrophotography and method for producing the same - 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 50 to 50%.
It has a specific gravity of about 150 emu / g and a relatively high electric resistance of about 2.5 to 5.2, especially about 1 to about 5.2.
The present invention relates to a magnetic carrier for electrophotography comprising a spherical composite particle powder having about 0 ¹⁰ to 10 ¹² Ωcm and a method for producing the same.

[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 generally adopted 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. Then, 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, this electrophotographic method has been widely used in copiers and printers, and is required to be able to handle various documents 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.

[0006] Iron powder carrier has the shape flaky, spongy, there is a spherical, a true specific gravity of 7-8, a bulk density in larger and 3g / cm ³ ~4g / cm ³ In order to stir the toner in the developing machine, a large driving force is required, and mechanical abrasion is large, which tends to cause spent toner, deterioration of chargeability of the carrier itself, and damage of the photoconductor.

The ferrite carrier is spherical, has a true specific gravity of about 4.5 to 5.5, and has a bulk density of 2 g / g.
because it is about cm ³ ~3g / cm ^3, but the weight is a disadvantage of iron powder carrier may to some extent resolved, it is still not enough.

[0008] Further, the binder type carrier is 2.5
g / cm ³ or less, the bulk density is small, and the particles have little shape distortion, and it is easy to make them into spheres that tend to have high particle strength, so that they have excellent fluidity. It is suitable for high-speed copiers and high-speed laser beam printers for general-purpose computers with a large number of rotations of a developing sleeve or a magnet in the sleeve because its particle size can be controlled in a wide range. Is what it is.

Conventionally, resins used in binder type carriers are roughly classified into thermoplastic resins such as vinyl-based, styrene-based, and acrylic-based resins and phenol-based resins, melamine-based resins, and epoxy-based resins. Although a thermosetting resin is known, generally, a thermoplastic resin that is easy to granulate is used, and it is considered that there is a practical problem because the thermosetting resin is difficult to be spherical. I have.

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. You.

First, the carrier is required to have an appropriate saturation magnetization value, particularly, about 50 to 150 emu / g. That is, Japanese Unexamined Patent Publication No. 59-97155 describes that "... the carrier has a saturation magnetization of 50 to 150 em.
If the saturation magnetization is less than 50 emu / g, carrier scattering or carrier adhesion occurs, while 15
If it exceeds 0 emu / g, sweeping and image roughness become severe, and character collapse occurs. It has been proposed that a good image can be obtained by setting the saturation magnetization value of the carrier to 50 emu / g or more as in "...". The carrier that forms the so-called “spike” of the magnet brush on the sleeve by appropriately increasing the magnetization value flies away from the “spike” due to the low magnetic force to the photoreceptor. So-called carrier adhesion that adheres to the surface is less likely to occur. On the other hand, if the magnetization value is too large, the resolution is reduced, such as image roughness. Therefore, the saturation magnetization of the carrier is 50
It is required to be about 150 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 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.
Therefore, it is required that the specific gravity is appropriate, in particular, 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, and the latent image There are problems such as image distortion and image loss.

In order to solve these problems, it has been proposed to coat the surface of the carrier particles with a resin to increase the electrical resistance of the carrier (Japanese Patent Application Laid-Open Nos. 47-13954 and 54-660). Have been.

However, since these resins are insulators, the electric resistance of the carrier itself is too high than 10 ¹² Ωcm, so that leakage of carrier charge is less likely to occur, and the charge amount of the toner also increases. The resulting image is an edged image, but on the other hand, on a large-area image surface, there is a problem that the image density at the center becomes very light.

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.

Conventionally, several attempts have been made to make the binder type carrier more multifunctional, and the carrier is formed into a two-layer structure. For example, a carrier characterized in that a coating containing a resin and hydrophilic inorganic fine particles is applied to the surface of a magnetic material-dispersed carrier core, and the particle diameter of the fine particles is larger than the thickness of the coating layer (Japanese Patent Application Laid-open No. Japanese Unexamined Patent Publication (Kokai) No. 3-111859), wherein at least a part of a magnetic powder-dispersed carrier is one in which an inorganic oxide fine powder is previously added and adhered to the carrier surface. Gazette), the surface of a carrier in which magnetic fine particles are dispersed has a volume resistance of 10 ¹²
Carrier characterized by adding conductive fine particles of Ωcm or less (JP-A-5-273789).
and so on.

[0018]

The bulk density is low, the fluidity is excellent, and an appropriate saturation magnetization, especially 50
１５０150 emu / g and a moderate specific gravity, particularly a relatively high electric resistance of about 2.5 to 5.2.
In particular, spherical composite particles having a particle size of about 10 ¹⁰ to 10 ¹² Ωcm are currently the most required, but such magnetic carriers have not been provided yet.

That is, the phenol resin composite particles containing spherical ferromagnetic particles described in JP-A-2-220068 and JP-A-4-100850 have a ferromagnetic particle content of 80 to 99. % By weight, and a high saturation magnetization can be obtained. On the other hand, when the ratio is increased, the electric resistance usually becomes low, and a high electric resistance of 10 ¹⁰ Ωcm or more cannot be obtained. I can't get it.
Therefore, it is conceivable to add an insulating resin or the like in order to obtain an electric resistance value of 10 ¹⁰ Ωcm or more. However, the added resin or the like usually has a lower specific gravity than the ferromagnetic powder, and a sufficient specific gravity as a whole is obtained. There is a problem that it cannot be obtained.

Further, the above-mentioned Japanese Patent Application Laid-Open Nos. Hei 3-11859, Hei 4-124677 and Hei 5-273 are disclosed.
Similarly, the carrier described in Japanese Patent No. 789 cannot be said to sufficiently satisfy the above-mentioned problem.

The carrier described in the above-mentioned Japanese Patent Application Laid-Open No. 3-11859 has a composite particle containing ferromagnetic particles coated on its surface with a coating material containing hydrophilic inorganic fine particles. It is adjusted so as to be exposed from the surface and is intended to avoid aggregation of the carrier.

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.

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, especially about 50 to 150 emu / g, and an appropriate specific gravity. It is a technical object of the present invention to provide a magnetic carrier for electrophotography characterized by having a relatively high electric resistance value, especially about 2.5 to 5.2, and especially about 10 ¹⁰ to 10 ¹² Ωcm. And

[0024]

The above technical object can be achieved by the present invention as described below. That is, the present invention relates to a ferromagnetic iron compound particle and a non-magnetic iron compound particle which are bonded to each other using a phenol resin as a binder.
A magnetic carrier for electrophotography comprising spherical composite particles having a particle size of from 1 to 1000 μm, wherein the total amount of ferromagnetic iron compound particles and nonmagnetic iron compound particles contained in the composite particles is 80 to 9
9% by weight, and wherein the composite particles comprise a core portion mainly containing the ferromagnetic iron compound particles and a surface layer mainly containing the non-magnetic iron compound particles. The ferromagnetic iron compound particles are mixed with the phenol resin by heating the mixture to 45-60 ° C. while stirring and mixing the ferromagnetic iron compound particles, phenols and aldehydes in an aqueous medium in the presence of a basic catalyst. After generating the gel-like spherical composite core particles dispersed in the aqueous medium, the non-magnetic iron compound particle powder is added to the aqueous medium, and the mixture is stirred and mixed to form a surface of the gel-like spherical composite core particles. Forming a surface layer portion mainly containing nonmagnetic iron compound particles to form gel-like spherical composite particles, and then raising the temperature to 70 to 90 ° C. to form the above-mentioned gel-like spherical composite. Producing a spherical composite particle comprising a core portion mainly containing ferromagnetic iron compound particles and a surface layer mainly containing non-magnetic iron compound particles by curing the particles. It is.

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 it is less than 80% by weight, a sufficiently high saturation magnetization cannot be obtained, and if it exceeds 99% by weight, the binder is insufficient and composite particles having sufficient strength cannot be obtained. Further, the content of the nonmagnetic iron compound particles is preferably in the range of 1 to 33 parts by weight based on 100 parts by weight of the ferromagnetic iron compound particles. When the amount is less than 1 part by weight, the nonmagnetic iron compound particles in the surface layer part are insufficient, so that a moderately high electric resistance value cannot be obtained,
If it exceeds 33 parts by weight, a sufficiently high saturation magnetization cannot be obtained. In addition, it is more preferably in the range of 1 to 25 parts by weight.

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 in the range of about 2.5 g / cm ³ or less. More preferably, it is about 2.0 g / cm ³ or less.

Spherical composite particles according to [0031] the present invention, the ratio r between the average thickness r _b of the surface layer portion containing an average radius r _a and the non-magnetic iron compound particles nuclear unit containing ferromagnetic iron compound particles
_a / r _b is preferably from 10 to 300. 10
If the ratio is less than the above, the ratio of the ferromagnetic iron compound particles to the nonmagnetic iron compound particles decreases, and it is difficult to obtain a sufficiently high saturation magnetization value. If it exceeds 300, the surface layer portion becomes extremely thin, and it becomes difficult to obtain an appropriately high electric resistance value.

The spherical composite particles according to the present invention have a saturation magnetization of 50 to 150 emu / g. 50 emu /
If it is less than g, the magnetic force forming the so-called “spike” is weak, and carrier scattering and carrier adhesion are likely to occur. 1
Magnetization values exceeding 50 emu / g are difficult to obtain using ordinary ferromagnetic iron compound particle powder, and the image tends to be rough, which is not preferable.

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 a volume resistivity of 10 ¹⁰ to 10 ¹² Ωcm. 10 ¹⁰ Ωc
If it is less than m, the charge on the electrostatic latent image flows through the carrier, and the image is disturbed or missing, 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, a method for producing the spherical composite particle powder according to the present invention as described above 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 0.02 to 10 μm, and considering dispersion in an aqueous medium and the strength of the resulting spherical composite particles, 0.05 to 5 μm.
m is 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 10 μm, and considering the dispersion in an aqueous medium and the strength of the formed composite particles, 0.0
It is preferably from 5 to 5 μm. Its shape is granular,
It may be spherical or acicular.

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 aldehydes to phenols 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 resol 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 the phenols and aldehydes are reacted in the presence of a basic catalyst, the amount of the ferromagnetic iron compound particles to be coexisted is preferably 0.5 to 200 times the weight of the phenols. 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 in the present invention can be used without any surface treatment, but may be subjected to lipophilic treatment in advance. When using ferromagnetic 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 non-magnetic iron compound particles can also be used as they are, of course, and may be subjected to a lipophilic treatment in advance.

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.

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, and ferromagnetic iron compound particles are charged into a reaction vessel, sufficiently stirred, and then a basic catalyst is added thereto. Is adjusted to 45-60 ° C. At this point, the reaction of a part of the phenols and formalins proceeds, and gel-like spherical composite core particles in which ferromagnetic iron compound particles are dispersed in a gel-like phenol resin matrix are generated. In order to obtain spherical composite particles having a high sphericity, it is desirable to gradually raise the temperature, but it is also desirable that the curing of the phenolic resin does not progress very much.
The heating rate is preferably 0.5 to 1.5 ° C / min, more preferably 0.8 to 1.2 ° C / min.

The addition of the nonmagnetic iron compound particles is performed after the formation of the gel-like spherical composite core particles. The liquid temperature at the time of addition is between 45 and 60 ° C. Most of the ferromagnetic iron compound particles are incorporated into the gel-like spherical composite particles, and there are almost no ferromagnetic iron compound particles present alone, and the phenol resin as a binder is sufficiently cured. Non-magnetic iron compound particles are added in a gel state that is not in a gel state.

When the non-magnetic iron compound is added after the reaction temperature exceeds 60 ° C. and the phenol resin is sufficiently cured, the resulting spherical composite particles contain no non-magnetic iron compound particles. Alternatively, a product in which only nonmagnetic iron compound particles adhere to the surface of the spherical composite particles is generated.

If the reaction temperature is lower than 45 ° C. and the addition of the nonmagnetic iron compound particles is performed early, composite particles in which the ferromagnetic iron compound particles and the nonmagnetic iron compound particles are uniformly dispersed are formed. However, the desired composite particles having a two-layer structure cannot be obtained.

Next, after adding the nonmagnetic iron compound particle powder,
The mixture is stirred for a while to form a surface layer in which the non-magnetic iron compound particles are dispersed in the phenol resin matrix on the surface of the gel-like spherical composite core particles, thereby producing gel-like spherical composite particles. Thereafter, the temperature was raised while stirring, and the reaction temperature was 70 to 9
Adjust to 0 ° C. and cure the phenolic resin. Also at this time, it is desirable to slowly raise the temperature in order to obtain spherical composite particles having a high sphericity, as described above. The heating rate is preferably 0.5 to 1.5 ° C / min, more preferably 0.8 to 1.5 ° C / min.
1.2 ° C./min.

After the cured reaction product is cooled to 40 ° C. or lower, the resulting 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 phenol resin matrix. A spherical composite particle powder comprising a core in which ferromagnetic iron compound particles are mainly dispersed therein and a surface layer in which nonmagnetic iron compound particles are mainly dispersed in a phenol resin matrix is obtained.

[0059]

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. For example, when the proportion of the ferromagnetic particles is increased to obtain a high magnetization value, the electric resistance value usually decreases, and 10 ¹⁰ Ωc
A high electric resistance value of m or more cannot be obtained. So 10 ¹⁰ Ω
It is conceivable to add an insulating resin or the like in order to obtain an electric resistance value of not less than cm, but the added resin or the like usually has a lower specific gravity than the ferromagnetic powder, so that a sufficient specific gravity cannot be obtained as a whole. .

Conventionally, the electric resistance value has been controlled by, for example, attaching inorganic fine particles to the surface of the composite core particles containing ferromagnetic particles. However, since these are attached, they are structurally unstable. In addition, the contact area between the composite particles is extremely small, which is not preferable for controlling the electric resistance value. Therefore, the present inventors have proposed that, in the spherical composite particles, non-magnetic iron compound particles having a relatively high electric resistance value are mainly formed on the surface of a core portion mainly containing ferromagnetic iron compound particles for obtaining a high magnetization value. It was studied to control the electric resistance value and the specific gravity by forming the containing surface layer.

In order to realize the two-layer structure as described above,
In forming the surface layer mainly containing non-magnetic iron compound particles, the gel-like spherical composite core particles containing ferromagnetic iron compound particles are granulated, and then non-cured at a reaction temperature of 45 to 60 ° C. without being cured. It is important to add magnetic iron compound particles.

That is, when the nonmagnetic iron compound particles are added at a reaction temperature of less than 45 ° C., spherical composite particles in which ferromagnetic iron compound particles and nonmagnetic iron compound particles are uniformly dispersed are formed. Non-magnetic iron compound particle powder was added after the reaction temperature exceeded 60 ° C. and the phenol resin as the binder was sufficiently cured, while the composite particles having the desired two-layer structure could not be obtained. In such a case, non-magnetic iron compound particles are not contained in the formed spherical composite particles, or particles in which only non-magnetic iron compound particles adhere to the surface of the spherical composite particles are generated.

Since the obtained spherical composite particle powder has the two-layer structure, a high magnetization value can be obtained by increasing the content of the ferromagnetic iron compound particles in the nucleus portion, and the surface layer portion can be obtained. Non-magnetic iron compound particles having a high electric resistance value are dispersed in the binder phenolic resin, it can be controlled to a relatively high electric resistance value,
Moreover, since there is almost no difference in specific gravity between the ferromagnetic iron compound particles in the core portion and the nonmagnetic iron compound particles in the surface portion, 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 in the following Examples and Comparative Examples was measured by a scanning electron microscope (S-800 manufactured by Hitachi, Ltd.).
, 250 or more spherical composite particles were extracted at random, and the values were obtained by using an image analyzer. The particle morphology of the spherical composite particles was observed with a scanning electron microscope.

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

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

[0068] and the radius r _a of the core portion containing mainly the ferromagnetic iron compound particles of the spherical composite particles, method for obtaining the thickness r _b of the surface layer portion containing a non-magnetic iron compound particles in the following manner went.

[0069] First, by observing the cross-section photograph of the composite particle by a scanning electron microscope to measure the average value of the thickness r _b of the surface layer portion containing mainly non-magnetic iron compound particles, composite particles previously obtained to from an average particle diameter calculated radius r _a of the core portion containing mainly ferromagnetic iron compound particles.
The ratio from the way the r _a and r _b obtained r _a / r _b
Ask for.

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 densitometer (manufactured by Micromeritics).

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

Example 1 42 g of phenol, 64 g of 37% formalin, spherical magnetite (average particle size: 0.2
4 μm), 392 g, calcium fluoride 1.0 g, 28
13 g of aqueous ammonia and 40 g of water were stirred and mixed.

Next, gel-like spherical composite core particles containing magnetite particles were likely to be formed while occasionally watching the state of the reaction solution while heating at a rate of 0.75 ° C./min. At a time point (48 ° C.), 8 g of granular hematite particles (average particle diameter 0.16 μm) are added, 20 g of water is further added, and the temperature is raised and held at 85 ° C. at a rate of 1.17 ° C./min. After reacting and curing for 180 minutes, spherical composite particles containing magnetite particles in the core and hematite particles in the surface layer were produced.

After cooling to 30 ° C. and addition of 0.5 l of water, the supernatant was removed, and the precipitate containing the composite particles was washed with water and air-dried. Then, this was removed under reduced pressure (5 m
(mHg or less) at 50 to 60 ° C. to obtain spherical composite particle powder A.

The obtained spherical composite particles A have an average particle diameter of 38 μm. The scanning electron micrograph (×
2000) is shown in FIG. As can be seen from FIG. 1, the spherical composite particles had a spherical shape close to a true sphere.

FIG. 2 shows a cross-sectional photograph (× 10000) by a scanning electron microscope. The thickness r _b of the surface layer portion containing hematite particles from 2 averaged 0.7 [mu] m. On the other hand, the average particle diameter of the spherical composite particles since it is 38 [mu] m, the average radius r _a of the core portion containing the magnetite particles was calculated to 18.3Myuemu.

The saturation magnetization is 79 emu / g, the true specific gravity is 3.50, and the electric resistance is 1.3 × 10 ¹⁰ Ωc.
m.

The spherical composite particle powder A has a reddish black color, which indicates that the surface layer mainly contains hematite particles.

Example 2 360 g of spherical magnetite particles having an average particle diameter of 0.24 μm were charged into a Henschel mixer, and the mixture was thoroughly stirred.
2.7 g of a silane coupling agent (KBM-403: manufactured by Shin-Etsu Chemical Co., Ltd.) was added, and the mixture was heated to about 100 ° C. and mixed and stirred well for 30 minutes to obtain spherical magnetite particles coated with the coupling agent. .

Next, 40 g of phenol, 60 g of 37% formalin, 360 g of lipophilic magnetite, 12 g of 28% ammonia water, and 40 g of water were stirred and mixed in a 1-liter four-necked flask.

Next, the gel-like spherical composite core particles containing magnetite particles were likely to be formed while occasionally watching the state of the reaction solution while increasing the temperature at a rate of 0.75 ° C./min. At the time (50 ° C.), 40 g of granular hematite particles (average particle diameter 0.16 μm) were added, and 20 g of water was further added. The temperature was raised to 85 ° C. at a rate of 1.17 ° C./min.
The mixture was held and reacted and cured for 180 minutes to produce spherical composite particles containing magnetite particles in the core and hematite particles in the surface layer.

After cooling to 30 ° C. and addition of 0.5 l of water, the supernatant was removed, and the precipitate containing the composite particles was washed with water and air-dried. Then, this was removed under reduced pressure (5 m
(mHg or less) at 50 to 60 ° C to obtain spherical composite particle powder B.

The obtained spherical composite particles B have an average particle diameter of 34 μm. The scanning electron micrograph (×
2000) is shown in FIG. As can be seen from FIG. 3, the spherical composite particles had a spherical shape close to a true sphere.

FIG. 4 shows a cross-sectional photograph (× 15000) by a scanning electron microscope. The thickness r _b of the surface layer portion containing hematite particles from 4 averaged 1.2 [mu] m. On the other hand, the average particle diameter of the spherical composite particles since it is 34 .mu.m, the average radius r _a of the core portion containing the magnetite particles was calculated to 15.8Myuemu.

The saturation magnetization is 73 emu / g, the true specific gravity is 3.55, and the volume resistivity is 5.2 × 10 ¹¹ Ω.
cm.

The spherical composite particle powder B has a reddish black color, which indicates that the surface layer mainly contains hematite particles.

Examples 3 to 6, Comparative Examples 1 and 2 Amount of ferromagnetic iron compound particles, type and amount of lipophilic treatment agent in lipophilic treatment performed on ferromagnetic iron compound particles, non-magnetic iron Spherical composite particle powders C to H were obtained in the same manner as in Example 1 except that the kind and amount of the compound particles, the amount of phenol, the amount of formalin, the amount of the basic catalyst, the amount of water, and the like were variously changed. .

The production conditions at this time are shown in Table 1, and the characteristics of the obtained spherical composite particles are shown in Table 2.

[0090]

[Table 1]

[0091]

[Table 2]

The spherical composite particles C to F obtained in Examples 3 to 6 were all spherical as a result of observation by a scanning electron microscope.

FIG. 5 is a scanning electron microscope photograph (× 2000) of the spherical composite particles G obtained in Comparative Example 1.
Shown in From FIG. 5, hematite particles were simply attached to the surfaces of the spherical composite particles, and hematite particles detached from the surface were also observed.

[0094]

The spherical composite particles according to the present invention are composed of a core containing ferromagnetic iron compound particles and a surface layer containing non-magnetic iron compound particles, so that they have an appropriate saturation magnetization value, especially Having an appropriate specific gravity, especially about 2.5 to 5.2, and a relatively high electric resistance value, especially about 10 ¹⁰ to 10 ¹² Ωcm. It is suitable as a magnetic carrier for electrophotography capable of realizing 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 miscibility 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 (× 2000) showing the particle structure of spherical composite particles A obtained in Example 1.

FIG. 2 is a scanning electron micrograph (× 10000) showing a part of a cross section of the spherical composite particle A obtained in Example 1.

FIG. 3 is a scanning electron micrograph (× 2000) showing the particle structure of spherical composite particles B obtained in Example 2.

FIG. 4 is a scanning electron micrograph (× 15000) showing a part of a cross section of the spherical composite particle B obtained in Example 2.

FIG. 5 is a scanning electron micrograph (× 2000) showing the particle structure of the spherical composite particles G obtained in Comparative Example 1.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-1-108556 (JP, A) JP-A-1-270061 (JP, A) JP-A 3-111859 (JP, A) JP-A-5-118 94048 (JP, A) JP-A-6-118725 (JP, A) JP-A-3-192268 (JP, A) JP-A-4-95970 (JP, A) JP-A-62-238580 (JP, A) JP-A-2-220068 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G03G 9/10

Claims (4)

(57) [Claims] 1. A magnetic carrier for electrophotography comprising spherical composite particles having an average particle diameter of 1 to 1000 μm obtained by combining ferromagnetic iron compound particles and nonmagnetic iron compound particles with a phenol resin as a binder. The total amount of the ferromagnetic iron compound particles and the non-magnetic iron compound particles contained in the composite particles is 80 to 99% by weight, and the composite particles mainly contain the ferromagnetic iron compound particles and the core. A magnetic carrier for electrophotography, comprising a surface layer mainly containing magnetic iron compound particles. 2. The magnetic carrier for electrophotography according to claim 1, wherein the content of the nonmagnetic iron compound particles is in the range of 1 to 33 parts by weight per 100 parts by weight of the ferromagnetic iron compound particles. Wherein the ratio r _a / r _b between the thickness r _b of the surface layer portion containing mainly the average radius r _a and the non-magnetic iron compound particles nuclear portion containing mainly the ferromagnetic iron compound particles is 10 to 30
The magnetic carrier for electrophotography according to claim 1, wherein the value is 0. 4. A ferromagnetic iron compound obtained by heating a ferromagnetic iron compound particle powder, phenols and aldehydes to 45 to 60 ° C. while stirring and mixing in an aqueous medium in the presence of a basic catalyst. After generating the gel-like spherical composite core particles in which the particles are dispersed in the phenol resin, the non-magnetic iron compound particle powder is added to the aqueous medium and stirred,
By mixing, a surface layer mainly containing non-magnetic iron compound particles is formed on the surface of the gel-like spherical composite core particles to form gel-like spherical composite particles.
The gel-like spherical composite particles are cured by raising the temperature to 0 to 90 ° C. to form a spherical composite comprising a core portion mainly containing ferromagnetic iron compound particles and a surface layer mainly containing nonmagnetic iron compound particles. A method for producing a magnetic carrier for electrophotography, comprising obtaining body particles.