JP3405384B2 - Electrophotographic developer carrier 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 relates to a carrier for electrophotographic development which has stable triboelectric charging properties and excellent durability, and a method for producing the same.

[0002]

2. Description of the Related Art Selenium and OPC are used in electrophotography.
A photoconductive substance such as (organic semiconductor) or α-Si is used as a photoconductor, an electrostatic latent image is formed by various means, and a magnetic brush developing method or the like is used for this latent image to determine the polarity of the latent image. On the other hand, a method is generally adopted in which charged toner is attached by electrostatic force to visualize the toner.

As is well known, carrier particles called carriers are used in this developing process, and a proper amount of positive or negative electricity is imparted to the toner by frictional charging, and a magnet is incorporated by utilizing magnetic force. The toner is conveyed to the developing area near the surface of the photoreceptor on which the latent image is formed, via the developing sleeve.

In recent years, the electrophotographic method has been widely used in copiers and printers, and it is required to be able to handle various documents such as thin lines, small letters, photographs and color originals. Further, with the increase in speed and continuity, durability as a developer is also required, and it is considered that these demands will be further increased in the future.

Further, as is well known, the developer is required to have durability such that the chargeability of the toner and carrier does not change during use. For example, the toner is strongly adhered to the surface of carrier particles. There is a phenomenon that the chargeability of the original carrier is lost (so-called toner spent) or the coating resin layer on the surface of the carrier particles peels off with time, and as a result, the toner cannot be appropriately charged. It is a problem.

As a measure against the former, a means of coating the surface of the carrier particles with a fluororesin or silicone resin having a low surface energy is adopted, but as a measure against the latter, such a measure is not taken at present. Is.

In particular, carriers such as ferrite and iron powder are
The adhesiveness between the particle surface and the coating resin is not so good, the coating resin is gradually peeled off during use, the chargeability is changed, and as a result, problems such as image disturbance and carrier adhesion are caused.

On the other hand, a so-called binder type carrier in which magnetic powder is dispersed in a resin has been developed in order to solve these problems, but the content of the magnetic powder cannot be increased or the resin is limited. There is a problem such as.

The inventors of the present invention have disclosed in Japanese Patent Laid-Open No. 3-220068.
JP-A-4-100850, JP-A-4-86749
Japanese Patent Application Laid-Open No. 5-237369 and Japanese Patent Application Laid-Open No. 5-237369 disclose inventions aimed at solving the above problems.

The composite particles composed of the magnetic powder and the phenol resin in the inventions described in the above publications have several times better adhesiveness to the coating resin than the above-mentioned ferrite or iron powder, so that they are coated during use. Although the problem of resin peeling hardly occurs, there is a possibility that problems may occur when used in high-speed machines, and there is a demand for a binder-type carrier having better adhesiveness.

At present, as the developer, a two-component developer composed of a toner and a carrier having different charging polarities is used. In a two-component developer that uses a positively chargeable toner and a negatively chargeable carrier in combination, coating with a resin or the like has been performed in order to impart negative chargeability to the carrier, but it is not sufficient. I could not say. Therefore, in order to enhance the positive chargeability of the toner, the carrier is
Higher negative chargeability is required.

Further, the carrier is required to have an electric resistance value above a certain level, and specifically, 10 ¹⁰
An electric resistance value of about 10 ¹⁴ Ωcm is required. That is, when the electric resistance value is as low as 10 ⁶ Ωcm like the iron powder carrier, the carrier is attached to the image portion of the photoconductor by the charge injection from the sleeve, or the latent image charge escapes through the carrier, and There are problems such as image distortion and image loss. On the other hand, if the insulating resin is thickly coated, the electric resistance value becomes too high, the carrier charges are less likely to leak, and the charge amount of the toner also becomes higher, resulting in an edged image. On the other hand, on a large-area image surface, the image density in the central portion becomes very low. Therefore, a moderately high electric resistance 10 ¹⁰ to 1
A carrier having 0 ¹⁴ Ωcm is desired.

For these reasons, a carrier for an electrophotographic developer, which has a high electric resistance value and a negative charging property and is excellent in the peeling durability of the coating resin, is currently most demanded.

Several attempts have heretofore been made with respect to carriers for electrophotographic developers, which are composed of a composite particle powder composed of a phenol resin and iron oxide particle powder. For example, composite particle powder composed of ferromagnetic fine particle powder and hardened phenol resin (Japanese Patent Laid-Open No. 2-220068),
There is a composite particle powder (JP-A-3-192268) in which the particle surface of a composite core particle composed of a ferromagnetic fine particle powder and a hardened phenol resin is coated with a melamine resin.

Attempts have also been made to incorporate inorganic fine powder into the coating resin layer. For example, a carrier coated with a resin containing amorphous silica and conductive fine particles as inorganic fine powder on the surface of carrier core particles (special Kaihei 1-191155
No.), a carrier having a coating resin layer on the surface of carrier core particles and containing an inorganic fine powder selected from silica, titania, alumina, zinc oxide, tin oxide or carbon black in the outermost shell coating layer (JP-A-H06-61206). -202381).

[0016]

A spherical composite particle powder having a high electric resistance value and a negative electrification property and excellent in peeling durability of a coating resin is currently most demanded. It cannot be said that the composite particle powder described in each publication sufficiently satisfies these various characteristics.

That is, since the composite particle powder described in JP-A-2-220068 does not have a coating resin layer,
Sufficient electric resistance and sufficient chargeability cannot be obtained.

Since the composite particle powder described in JP-A-3-192268 has a melamine resin coating, it has a certain degree of electric resistance and positive chargeability, but has a phenolic resin constituting the composite core particles. Since the melamine resin forming the coating layer on the surface of the core particles is different, the adhesion of the resin is weak and the peeling durability of the coating resin is poor.

The carrier described in the above-mentioned JP-A-1-191155 uses iron oxide, ferrite, magnetite or the like as the core particles, while using styrene resin, acrylic resin or the like as the coating resin. However, the adhesiveness of the resin is poor.

The carrier described in JP-A-6-202381 uses a sintered ferrite powder as a core material, the surface of which is coated with styrene acrylic resin, and a styrene acrylic resin in which silica is dispersed in the outermost shell layer. It is inferior in resin adhesion between the core material and the coating resin.

Therefore, the present invention is to provide a carrier for an electrophotographic developer comprising a spherical composite particle powder which has a high electric resistance value and a negative chargeability and is excellent in the peeling durability of the coating resin. Subject.

[0022]

The above technical problems can be achieved by the present invention as follows.

That is, the present invention has an average particle size of 1 to 1000.
A carrier for an electrophotographic developer composed of spherical composite particles of [mu] m, the core particles spherical composite particle, the particle surface of the spherical composite core particles consisting of a phenolic resin and cured with iron oxide particles It has a coating layer composed of silica ((SiO ₂ ) _n · H ₂ O) and a cured phenol resin that is continuous with the resin inside, and the content of iron oxide powder is 80 to 99% by weight. A carrier for an electrophotographic developer characterized by being present and iron oxide particle powder, and a phenol and an aldehyde are reacted in the presence of a basic catalyst in an aqueous medium, from the iron oxide particle powder and the cured phenol resin The spherical composite core particles are formed, and a silicate is added to an aqueous medium containing the spherical composite core particles and the remaining unreacted phenols to react with the unreacted phenols. The phenol resin and the silica ((Si
O ₂ ) _n · H ₂ O) is coated to obtain a spherical composite particle powder, which is a method for producing a carrier for an electrophotographic developer.

The present invention will be described in detail below. First, the spherical composite particle powder according to the present invention will be described.

The spherical composite particle powder according to the present invention has an average particle diameter of 1 to 1000 μm, preferably 10 to 200 μm.
m. If the average particle size is less than 1 μm, secondary agglomeration tends to occur, and if it exceeds 1000 μm, the mechanical strength is weak and a clear image cannot be obtained. The shape of each composite particle constituting the composite particle powder according to the present invention is spherical.

Each spherical composite particle constituting the spherical composite particle powder according to the present invention comprises a spherical composite core particle portion composed of iron oxide particle powder and a hardened phenol resin, and a hardened phenol resin on the surface of the particle. And silica ((SiO ₂ )
_n · H ₂ O). The weight ratio of the spherical composite core particle portion and the coating layer portion,
1000: 1 to 30: 1, preferably 1000: 5 to 3
It is 0: 1. The content of iron oxide particles in the spherical composite particles is 80 to 99% by weight. If it is less than 80% by weight, sufficient specific gravity cannot be obtained. If it exceeds 99% by weight, the resin content becomes insufficient and molding becomes difficult.

Silica ((SiO
_{2) n} · H content ₂ O) is 0.1 to 5.0 wt% with respect to the spherical composite particles in terms of Si, preferably 0.2 to
It is 3.0% by weight. When it is less than 0.1% by weight, the negative chargeability is insufficient. When it exceeds 5.0% by weight, the hygroscopicity of the spherical composite particle powder becomes high, and for example,
This may cause a problem in environmental stability of charging.

The spherical composite particle powder according to the present invention preferably has a bulk density of 2.5 g / cm ³ or less. It is more preferably 2.0 g / cm ³ or less. The specific gravity is 2.5 to 5.2, preferably 2.5 to 4.5.

The spherical composite particle powder according to the present invention has an electric resistance of 10 ¹⁰ to 10 ¹⁴ Ωcm, preferably 10 ¹¹ to 10 10.
It is ¹⁴ Ωcm.

The spherical composite particle powder according to the present invention is excellent in negative chargeability. Specifically, it is as described in the embodiments and examples of the present invention described later.

The spherical composite particle powder according to the present invention has good peeling durability of the coating layer on the particle surface. That is,
The electrification amount and the electric resistance value do not change by the forced durability test described later. Specifically, the rate of change (ΔR / R) in electric resistance value is −10 to + 10%, preferably −
It is 5 to + 5%. Change rate (ΔQ / Q) of charge amount is -1
It is 0 to + 10%, preferably -5 to + 5%.

Next, a method for producing the spherical composite particle powder according to the present invention will be described.

As the phenols used in the present invention, in addition to phenol, alkylphenols such as m-cresol, p-tert-butylphenol, o-propylphenol, resorcinol and bisphenol A, and a part of benzene nucleus or alkyl group or Examples thereof include compounds having a phenolic hydroxyl group such as halogenated phenols, all of which are substituted with chlorine atoms or bromine atoms, and among these, phenol is most preferable. When a compound other than phenol is used as the phenol, particles may be difficult to form, or even if particles are formed, the particles may have an irregular shape. Therefore, phenol is most preferable in consideration of the shape property.

Examples of aldehydes used in the present invention include formaldehyde and furfural in the form of either formalin or paraaldehyde, and formaldehyde is particularly preferable.

The molar ratio of aldehydes to phenols is preferably 1 to 4, particularly preferably 1.2 to 3. The molar ratio of aldehydes to phenols is 1
If it is smaller, the particles are less likely to be formed, or even if they are produced, the curing of the resin is less likely to proceed, so that the strength of the produced particles tends to be weak. On the other hand, the molar ratio of aldehydes to phenols is 4 If it is larger than this, unreacted aldehydes remaining in the aqueous medium after the reaction tends to increase.

As the basic catalyst used in the present invention, a basic catalyst used in ordinary resol resin production can be used. Examples thereof include aqueous ammonia, hexamethylenetetramine, and alkylamines such as dimethylamine, diethyltriamine, and polyethyleneimine. The molar ratio of these basic catalysts to phenols is 0.02 to
0.3 is preferable. When it is less than 0.02, the curing reaction does not proceed sufficiently and granulation is not performed. If it exceeds 0.3, the structure of the phenol resin is affected and the granulation property deteriorates, making it difficult to obtain a large particle size.

The iron oxide particle powder used in the present invention includes:
Magnetic iron oxide particle powder such as magnetite and maghemite,
Spinel ferrite particle powder containing one or more kinds of metals other than iron (Mn, Ni, Zn, Mg, Cu, etc.),
Magnetoplumbite-type ferrite particle powder such as barium ferrite, fine particle powder of iron having an oxide layer on its surface and its alloy, and the like can be used. In addition, non-magnetic iron oxide particles such as hematite, goethite, wustite and the like can be used, and in some cases, they can be used as a mixture with the magnetic iron oxide particles. Preferred are magnetic iron oxide particles such as magnetite and maghemite, and non-magnetic iron oxide particles such as hematite and goethite. More preferred are magnetic iron oxide particles such as magnetite and maghemite. The shape of the particles may be any of granular, spherical and acicular.

The particle size of the iron oxide particle powder is 0.1 to
10 μm is desirable, and considering the dispersion of fine particles in an aqueous medium and the strength of the resulting composite particles,
It is preferably 0.05 to 5 μm.

The iron oxide particle powder used in the present invention is preferably lipophilicized in advance, and when the iron oxide particle powder which has not been lipophilicized is used, a spherical composite is used. It may be difficult to obtain.

The lipophilic treatment is performed by treating the iron oxide particle powder with a coupling agent such as a silane coupling agent or a titanate coupling agent, or by dispersing the iron oxide particle powder in an aqueous solvent containing a surfactant. Then, there is a method of adsorbing a surfactant on the particle surface.

The silane coupling agents include those having a hydrophobic group, an amino group and an epoxy group, and the silane coupling agents having a hydrophobic group include vinyltrichlorosilane, vinyltriethoxysilane and vinyl.
Examples include tris (β-methoxy) silane.

As the silane coupling agent having an amino group, γ-aminopropyltriethoxysilane, N-
There are β- (aminoethyl) -γ-aminopropyltrimethoxysilane, N-β- (aminoethyl) -γ-aminopropylmethyldimethoxysilane, N-phenyl-γ-aminopropyltrimethoxysilane and the like.

As the silane coupling agent having an epoxy group, γ-glycidoxypropylmethyldiethoxysilane, γ-glycidoxypropyltrimethoxysilane, β- (3,4-epoxycyclohexyl) trimethoxysilane, etc. There is.

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

As the surfactant, a commercially available surfactant can be used, and one having a functional group capable of binding to the iron oxide particles or the hydroxyl group on the particle surface is preferable,
Speaking of ionicity, cationic or anionic one is preferable.

The object of the present invention can be achieved by any of the above-mentioned treatment methods, but 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.

When the phenols and the aldehydes are reacted in the presence of a basic catalyst, the amount of iron oxide particle powder to coexist is 75 with respect to the total amount of the phenols, aldehydes and iron oxide particle powders. -99% by weight, preferably 78-99% by weight, and more preferably 80-99% by weight, considering the strength of the composite particles produced.

The reaction in the present invention is carried out in an aqueous medium, and it is preferable that the solid content concentration in the aqueous medium is 30 to 95% by weight, particularly 60 to 90% by weight. Preferably.

In the reaction for producing the spherical composite core particles, phenols, aldehydes, water and iron oxide particle powder are charged into a reaction kettle and sufficiently stirred, then a basic catalyst is added and the temperature is raised with stirring. , The reaction temperature is 70 to 90 ° C., preferably 8
The temperature is adjusted to 3 to 87 ° C. and the curing reaction of the phenol resin is caused. At this time, in order to obtain spherical composite core particles having a high sphericity, it is desirable to raise the temperature gently. The rate of temperature increase is preferably 0.5 to 1.5 ° C / min, more preferably 0.8 to 1.2 ° C / min.

After curing as described above, the reaction mass was heated to 40 ° C.
When cooled below, an aqueous dispersion containing spherical composite core particles in which iron oxide particle powder is uniformly dispersed in a cured phenol resin matrix is obtained.

Then, in an aqueous dispersion containing the spherical composite core particles, the temperature is 70 to 100 ° C. and the pH is 9.0 to 9.7.
While maintaining the silicate added, while reacting unreacted phenols remaining in the aqueous medium to cure and adsorb on the particle surface of the spherical composite core particles, at the same time polymerize silica, Phenolic resin and silica ((SiO ₂ ) _n · H are formed on the surface of the spherical composite core particles.
Spherical composite particles having a coating layer composed of ₂ O) are obtained.

The aqueous dispersion containing the spherical composite particles was separated by filtration and centrifugal separation to obtain a solid-liquid solution, which was washed and dried to obtain a composite in which iron oxide particle powder was uniformly dispersed in the phenol resin matrix. A spherical composite particle powder having a coating layer composed of a phenol resin and silica ((SiO ₂ ) _n · H ₂ O) on the particle surface of the body core particle is obtained.

The reaction temperature is 70 to 100 ° C, preferably 75 to 95 ° C. If the temperature is below 70 ° C,
Since the dehydration reaction during the polymerization of silica ((SiO ₂ ) _n · H ₂ O) does not sufficiently occur, the coating layer contains a hydroxyl group and gelation easily occurs. If the temperature exceeds 100 ° C, a special device such as an autoclave is required, which is not preferable.

The pH is 9.0 to 9.7, preferably 9.1 to 9.5. When the pH is less than 9.0, the rate of precipitation of silicate ions on the particle surface is increased, so that the polymerization of silica does not proceed sufficiently and gelation by silica particles having a low degree of polymerization tends to occur. When the pH exceeds 9.7, it approaches the ionization constant of silicic acid,
Precipitation and elution of silicic acid occur at substantially the same time, which is not preferable.

In order to obtain spherical composite particles having a high sphericity, it is desirable to raise the temperature gently. The rate of temperature increase is preferably 0.5 to 1.5 ° C / min, more preferably 0.8 to 1.2 ° C / min.

The above-mentioned phenol resin and silica ((Si
In the reaction for forming the coating layer composed of O ₂ ) _n · H ₂ O), an aqueous sodium silicate solution, an aqueous potassium silicate solution, or an aqueous calcium silicate solution can be used as the silicate. The amount of silicate added is 0.2 to 10 parts by weight based on 100 parts by weight of the total amount of iron oxide particle powder, phenols and aldehydes added first in the reaction for forming the composite core particles in terms of SiO ₂ . Preferably 0.4-5
Parts by weight. If the amount is less than 0.2 parts by weight, a sufficient effect of imparting electrostatic properties cannot be obtained. If it exceeds 10 parts by weight, the ratio to the phenol resin in the coating layer becomes too large, resulting in poor adhesion.

The silicate may be added as it is or as an aqueous solution, and it is preferable to add it as an aqueous solution from the viewpoint of easy uniform coating. The method of addition may be either addition at once or addition in small portions, but the addition method is preferred. In this case, the dropping rate of the aqueous solution of silicate is 0.05 to 0.30 parts by weight, preferably 0.05 to 0.30 parts by weight in terms of SiO _{2 with} respect to 100 parts by weight of the total amount.
0.20 parts by weight / minute. If it is less than 0.05 parts by weight / minute, the polymerization of silica will be delayed, which is not industrially preferable. If it exceeds 0.30 parts by weight / minute, the concentration of silicate ions in the aqueous suspension becomes too high, and silica may precipitate independently of the core particles, which is not preferable.

The amount of water added together with the silicate is preferably such that the solid content concentration in the aqueous medium after the addition of water is 30 to 30.
It is set to 80% by weight, more preferably 60 to 90% by weight.

As described above, once the reaction temperature was 40 ° C.
It is also possible to add water and silicate directly without cooling below.

In any of the above reactions, spherical particles are easily produced by using a hydrophilic organic compound such as carboxymethyl cellulose or polyvinyl alcohol or a fluorine compound such as calcium fluoride as the suspension stabilizer.

In the production method of the present invention, the unreacted phenols and aldehydes remaining in the wastewater are greatly reduced, so that the COD (chemical oxygen demand) value in the wastewater is also low and the wastewater treatment cost is reduced. It can be significantly reduced.

[0062]

The composite particle powder composed of the ferromagnetic fine particle powder and the hardened phenol resin described in the above-mentioned JP-A-2-220068 does not have a coating layer composed of the phenol resin, and therefore has sufficient electric resistance and positive charging property. Was not obtained, and moreover, a considerable amount of unreacted phenols remained in the aqueous medium after the formation of the composite particles, and there was a problem that the COD value in the waste water became high.

Further, the composite particle powder in which the coating layer made of the melamine resin is formed on the surface of the particle of the composite core particle made of the ferromagnetic fine particle powder and the hardened phenol resin described in the above-mentioned JP-A-3-192268, Sufficient positive charge,
Although the electric resistance value was obtained, the resin constituting the core particles and the resin constituting the coating layer were different, and therefore the adhesion of the resin was insufficient and the peeling durability was insufficient.

Therefore, the coating layer is formed of the same resin, that is, a phenol resin, and in the coating method, the core particles are taken out after the core particles are formed and before the coating layer is formed in the conventional method. By drying the particle surface of the core particles, the coating layer formed thereafter becomes discontinuous, and the peeling durability is not sufficient even if the resin of the core particles and the resin of the coating layer are the same. The method of continuously forming the coating layer was investigated. As described above, a considerable amount of unreacted phenols and aldehydes remain in the aqueous medium after the core particles are prepared, and the pH is 9.
Phenolic resin and silica ((SiO ₂ ) _n · H by adding silicate while adjusting to 0-9.7
_The present inventor has found that a coating layer composed of ₂ O) can be formed.

[0065] by the production method of the present invention, since the coating layer is composed of a phenolic resin and silica _{((SiO 2) n · H} 2 O), a good negative charging property, the electrical resistance value is high,
Moreover, since the core particles and the resin constituting the coating layer are continuous, the peeling durability of the coating resin is improved against stress in the developing machine, and spherical particles exhibiting stable chargeability over time. A composite particle powder is obtained.

The carrier for an electrophotographic developer according to the present invention has good miscibility with the toner, and as a result can accelerate the charging speed of the toner, and on the other hand, has a specific gravity that does not damage the toner. By this, it is possible to suppress spent formation.

[0067]

BEST MODE FOR CARRYING OUT THE INVENTION A typical embodiment of the present invention is as follows.

The average particle diameters in the embodiments and the examples and comparative examples given below are shown by values measured by a laser diffraction type particle size distribution meter (manufactured by Horiba Ltd.), and the particle morphology of the particles is It was observed with a scanning electron microscope (S-800, manufactured by Hitachi, Ltd.).

The content of Si depends on the fluorescent X-ray analyzer MOD.
It was measured by EL3063M (manufactured by Rigaku Denki Kogyo KK).

The saturation magnetization is measured by a vibrating sample magnetometer VSM-3.
External magnetic field of 10k using S-15 (manufactured by Toei Industry Co., Ltd.)
It is shown by the value measured under Oe.

The true specific gravity is shown by a value measured by a multi-volume densitometer (manufactured by Micromeritics).

The electric resistance value (volume specific resistance value) is shown by a value measured by a high resistance meter 4329A (manufactured by Yokogawa Hewlett Packard).

The toner charge amount is 95% of this composite particle powder.
By sufficiently mixing 5 parts by weight of a commercially available toner 4800 (Ricoh) with 4 parts by weight, a blow-off charge amount measuring device TB-200
(Manufactured by Toshiba Chemical Co.).

The peeling durability of the coating resin was examined by the following forced durability test. 50 g of composite particle powder 100
It is put in a cc glass sample bottle, covered with a lid, and then shaken for 10 hours in a paint conditioner (RED DEVIL). For each sample before and after shaking, the rate of change of the charge amount Q and the volume specific resistance value R (Δ
The peeling durability of the coating resin was estimated by the size of (R / R, ΔQ / Q). Here, the larger the rate of change, the more the coating resin was peeled off.

The chemical oxygen demand (COD value) is measured by
Performed in accordance with JIS K0102.17, product 1 kg
Was evaluated as a value (mg / kg).

Average particle size 0.2 in a Henschel mixer
After charging 400 g of spherical magnetite particle powder of 4 μm and stirring well, a silane coupling agent (KBM
-403; Shin-Etsu Chemical Co., Ltd.) 2.0 g was added to about 1
By raising the temperature to 00 ° C. and thoroughly mixing and stirring for 30 minutes, iron oxide particle powder consisting of magnetite particles coated with a coupling agent was obtained.

Separately, in a 1-liter four-necked flask, 50 g of phenol, 70 g of 37% formalin, 400 g of iron oxide particle powder subjected to lipophilic treatment, 10 g of 28% ammonia water,
While stirring 50 g of water, the temperature was raised to 85 ° C. over 40 minutes,
The mixture was reacted and cured at the same temperature for 180 minutes to generate composite core particles composed of iron oxide particle powder and cured phenol resin.

Next, 95 ml of water was added, the pH was adjusted to 9.2 with an aqueous solution of sodium hydroxide, and 8.3 g of water glass No. 3 was added over 3 minutes, and phenol was added to the particle surfaces of the composite core particles. Composite particles coated with resin and silica were obtained. After cooling to 30 ° C., the supernatant was removed, and the lower layer precipitate was washed with water and air dried.

The CO of the wastewater at the end of this process
D (chemical oxygen demand) value is 1k of spherical composite particle powder
It was 3106 mg / kg with respect to g, which was a lower value than the COD value of the waste water at the end of the process shown in Comparative Example 1 below.

Then, this is depressurized (5 mmHg or less).
Then, it was dried at 150 to 160 ° C. to obtain a spherical composite particle powder.

The obtained spherical composite particle powder had an average particle diameter of 33 μm and had a spherical shape close to a true sphere, as shown in the scanning electron micrograph (× 2000) of FIG. The coating resin layer of the phenol resin was continuous and uniform with the resin in the core particles from the scanning electron micrograph (× 15000) of the particle cross section of FIG.

The spherical composite particle powder as a carrier for an electrophotographic developer is excellent in durability and has stable triboelectric chargeability. That is, the specific gravity is 3.56, the volume specific resistance value is 3.0 × 10 ¹² Ωcm, and the toner charge amount is +1.
0 μC / g, the content of silica in the coating resin layer is 0.23% by weight in terms of Si. Further, the peeling durability of the coating resin layer is such that the change rate (ΔR / R) of the volume resistivity value is −2%,
The rate of change in charge amount (ΔQ / Q) is −2%, which is excellent in peeling durability of the coating resin layer.

[0083]

EXAMPLES Next, examples and comparative examples will be given.

Examples 1 to 3, Comparative Examples 1 to 4; Examples 1 to 3 In the reaction for forming the composite core particles, the type and amount of the iron oxide particle powder, the type and amount of the lipophilic treatment agent, and the phenols. , The amount of aldehydes, the amount of basic catalyst and the amount of water,
A spherical composite particle powder was obtained in the same manner as in the embodiment of the present invention, except that the type and amount of silicate added in forming the coating layer were variously changed. The production conditions at this time are shown in Table 1, and various properties of the obtained spherical composite particle powder are shown in Table 2.

Comparative Example 1 Up to formation of the spherical composite core particles was carried out in the same manner as in the embodiment of the present invention, and the subsequent formation reaction of the coating layer was not carried out.
After cooling to 0 ° C., the supernatant was removed, and the lower layer precipitate was washed with water and air-dried.

Next, this is depressurized (5 mmHg or less).
Then, it was dried at 150 to 160 ° C. to obtain a spherical composite particle powder. The COD value of the wastewater at the end of this process is
6400 mg / kg for 1 kg of spherical composite particle powder
Met. Table 2 shows various properties of the obtained spherical composite particle powder.

Comparative Examples 2 to 4 In the reaction of forming the composite core particles, the type and amount of the iron oxide particle powder, the type and amount of the lipophilic treatment agent, the amount of phenols, the amount of aldehydes and the basic catalyst were used. Amount and water were changed in the same manner as in the embodiment of the present invention, except that the amount of water was changed, the subsequent formation reaction of the coating layer was not performed, and the supernatant liquid was cooled to 30 ° C. Was removed, and the precipitate in the lower layer was washed with water and air dried.

Then, this is depressurized (5 mmHg or less).
Then, it was dried at 150 to 160 ° C. to obtain a spherical composite particle powder. The production conditions at this time are shown in Table 1, and various properties of the obtained spherical composite particle powder are shown in Table 2.

[0089]

[Table 1]

[0090]

[Table 2]

[0091]

EFFECTS OF THE INVENTION The spherical composite particle powder according to the present invention has a high electric resistance value and a negative charging property, and moreover is excellent in peeling durability of the coating resin. Since it has the property, it is suitable as a carrier for an electrophotographic developer. Further, in the production method according to the present invention, residual unreacted phenols and aldehydes are reduced, so that COD in wastewater can be reduced.

[Brief description of drawings]

FIG. 1 is a scanning electron micrograph (× 2000) showing a particle structure of spherical composite particles according to an embodiment of the present invention.

FIG. 2 is a scanning electron micrograph (× 1500) showing a particle cross-sectional structure of the spherical composite particles according to the embodiment of the present invention.
0)

Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) G03G 9/107-9/113

Claims (2)

(57) [Claims] 1. A carrier for an electrophotographic developer comprising a spherical composite particle powder having an average particle diameter of 1 to 1000 μm, the spherical composite particle comprising a spherical oxide particle powder and a cured phenol resin. On the surface of the composite core particles
It has a coating layer composed of silica ((SiO ₂ ) _n · H ₂ O) and a cured phenol resin that is continuous with the resin in the core particles, and the content of iron oxide particle powder is 80-
A carrier for an electrophotographic developer, which is 99% by weight. 2. Iron oxide particle powder, phenols and aldehydes are reacted in an aqueous medium in the presence of a basic catalyst to form spherical composite core particles composed of iron oxide particle powder and a hardened phenol resin. Further, by adding a silicate to the aqueous medium containing the spherical composite core particles and the remaining unreacted phenols to react with the unreacted phenols, the spherical composite core particles Phenolic resin and silica ((SiO ₂ ) _n · H on the particle surface
₂ O) and a spherical composite particle powder coated therewith are obtained.