JPH0434441A - Electrophotographic magnetic carrier and production thereof - Google Patents

Abstract

PURPOSE:To obtain a large satd. magnetization and high electric resistance by uniformly coating the surface of the composite particles which are formed by dispersing ferromagnetic fine particles into a cured phenolic resin matrix, are specified in number average particle size and bulk density and contain a large amt. of these fine particles with a polyamide layer. CONSTITUTION:The composite particles are formed of the ferromagnetic fine particles and the cured phenolic resin by bringing phenols and aldehydes into reaction in an aq. medium and curing the same in the presence of the ferromagnetic fine particles, suspension stabilizer and basic catalyst. The number average particle size is 10 to 100mum and the bulk density is specified to as small as <=2.0g/cm<2>. In addition, the ferromagnetic fine particles are incorporated at a ratio as high as 80 to 99wt.% into these particles. Further, the composite particles are dispersed into lactams, and in the presence of the polymn. catalyst and activator, into an org. solvent and are coated with the polyamide layer over the entire surface thereof by the polyamide obtd. by the anion polymn. of the lactams. The bulk density is reduced in this way and the high magnetization value and high electric resistance are obtd.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is directed to a ferromagnetic material having a small bulk density, large saturation magnetization, and high electrical resistance, the surfaces of which are uniformly coated with a polyamide layer. The present invention relates to a magnetic carrier for electrophotography comprising composite particles of fine particles and a hardened phenol resin, and a method for producing the same.

(Prior art) In electrophotography, selenium, OPC (organic semiconductor)
, α-3i, etc. is used as a photoconductor to form an electrostatic latent image by various means, and then this latent image is charged with a charge opposite to the polarity of the latent image using a magnetic brush development method or the like. Generally, a method is adopted in which dry toner is attached by electrostatic force and visualized.

In this development process, carrier particles called carriers are used to apply an appropriate amount of positive or negative electricity to the toner through triboelectric charging, and to apply magnetic force to the toner through a developing sleeve containing a built-in magnet. The toner is transported to a development area near the surface of the photoreceptor where the image is formed.

In recent years, as copying equipment has become faster, more continuous, and more sophisticated, there has been a strong demand for improved characteristics of carriers used therein.

That is, the characteristics of the carrier are that it has a low bulk density, a large saturation magnetization, and a high electrical resistance.

If the carrier has a large bulk density, a large driving force is required for stirring in the developing machine.

Mechanical wear and tear is large, resulting in so-called spent toner.
Doing so may cause deterioration of the chargeability of the carrier itself and damage to the photoreceptor.
A low bulk density is strongly required.

Furthermore, when the saturation magnetization is small, the magnetic adhesion of the carrier to the developing sleeve becomes weak.

There is a problem that it tends to scatter from the developing sleeve and adhere to the photoreceptor, so it is strongly required to have a large saturation magnetization.

Regarding electrical resistance, since it is necessary to control the triboelectricity of the toner in order to form clear images, the electrical resistance of the magnetic carrier is required to be as high as possible. This fact is shown in Japanese Unexamined Patent Publication No. 60-458.
The role of the carrier during development is to provide the toner with accurate triboelectric charging characteristics and an appropriate charge, and to electrostatically attract and remove the toner adhering to the image area again, forming a clear image. It is in. ” and JP-A-1989-6
Publication No. 3249859, ``...- Because the volume specific electrical resistance of the carrier itself is low at 106 Ω・C or less for boat fishing,
When the toner concentration in the developer decreases due to continuous use.

The charge on the electrostatic latent image carrier escapes through the carrier, and the latent image is disturbed, causing defects in the two images.

There is a problem that the carrier may adhere to the image area of the electrostatic latent image carrier due to charge injected from the developing sleeve. ” is as stated.

Conventionally, iron powder carriers, ferrite carriers, binder type carriers (resin particles in which magnetic fine particles are dispersed), etc. have been developed and put into practical use as magnetic carriers.

(Problems to be Solved by the Invention) Magnetic carriers with low bulk density, large saturation magnetization, and high electrical resistance are currently required in quantity, but magnetic carriers that satisfactorily satisfy these characteristics are not available. Haven't gotten it yet.

That is, some iron powder carriers have flake-like or spongy-9 spherical shapes, but have a true specific gravity of 7 to 8 and a large bulk density of 3 to 4 g/CIa.

Further, the electrical resistance is as low as 102 to 103 Ω·cII+. As mentioned above, to increase electrical resistance.

The particles to be treated are treated in an organic solvent containing resin.

Coating the surface of iron powder with resin is also practiced.

In the case of this method, since the amount that can be coated in one treatment is small, the surface of the iron powder tends to be insufficiently and unevenly coated, and the effect of increasing electrical resistance is not sufficient. Therefore, although the process is repeated several times, it becomes complicated and complicated in one operation, which is not industrially or economically viable. Furthermore, the oxide film on the surface of the iron powder is easily peeled off, and is unstable due to oxidation progressing depending on environmental conditions, so the two resin coatings are likely to peel off and crack, resulting in a part of the iron surface being exposed.

This causes disturbances in charging characteristics.

In addition, the ferrite carrier is spherical and has a true specific gravity of 4.
．． 5 to 5.5, and the bulk density is about 2 to 3 g/d, so the weight, which is a drawback of iron powder carriers, can be solved to some extent, but the rotation speed of the developing sleeve or the magnet in the sleeve is high. It is not yet sufficient to support high-speed copying machines and high-speed laser beam printers for general-purpose computers.

Binder-type carriers have a small bulk density of less than 2 g/ctl1, but as described in Japanese Patent Publication No. 59-24416, after melting and mixing magnetic fine powder and insulating resin, This is because it is manufactured by cooling and pulverizing a mixture.

The content of magnetic fine powder is as low as 80% by weight or less.

It has a low magnetization value. In addition, thermoplastic resins are generally used as insulating resins in the manufacture of binder-type carriers, but their strength is low, and during long-term use, the magnetic carriers break at the magnetic fine powder and become fine particles, causing the developed image to deteriorate. It has been pointed out that this may cause fogging inside the film.

Japanese Patent Application Laid-Open No. 58-136052 proposes the use of a thermosetting resin instead of a thermoplastic resin in order to improve the strength of the magnetic carrier.

Therefore, the technical object of the present invention is to obtain a magnetic carrier having a small bulk density, a large saturation magnetization, and a high electrical resistance.

(Means for Solving the Problems) The present inventors have conducted various studies on methods for obtaining magnetic carriers having low bulk density, large saturation magnetization, and high electrical resistance, and as a result, they have arrived at the present invention.

That is, in the first invention, 1 ferromagnetic fine particles are dispersed in a hardened phenolic resin matrix, the number average particle diameter is lθ ~ 11000a, and the bulk density is 2.0g/CT.
I or less, and the content of the ferromagnetic fine particles is 8
The gist of the present invention is a magnetic carrier for electrophotography, characterized in that the surfaces of composite particles of 0 to 99% by weight are uniformly coated with a polyamide layer.

Further, the second invention is characterized in that the ferromagnetic fine particles are formed by reacting and curing phenols and aldehydes in an aqueous medium in the presence of the ferromagnetic fine particles, a suspension stabilizer, and a basic catalyst. Dispersed in the cured phenolic resin matrix and has a number average particle diameter of 10 to 10,008 m.
, produce composite particles having a bulk density of 2.0 g/cm2 or less and a content of ferromagnetic fine particles of 80 to 99% by weight; 1. Next, the composite particles are treated with lactams and a polymerization catalyst. Magnetism for electrophotography, characterized in that the entire particle surface of the composite particle is coated with a uniform polyamide layer by dispersing the lactam in an organic solvent in the presence of an activator and anionically polymerizing the lactam. The gist is the manufacturing method of the carrier.

(Function) First, the most important point in the present invention is the presence of 9 ferromagnetic fine particles, a suspension stabilizer, and a basic catalyst.

The composite particles obtained by reacting and curing phenols and aldehydes in an aqueous medium are composed of 1 ferromagnetic fine particles and a hardened phenol resin, and have a number average particle diameter of 10 to 10,008 m.

It has a small bulk density of 2.0g10j or less, and contains a large amount of ferromagnetic fine particles of 80 to 99% by weight, so it has a high magnetization value. When the entire particle surface of the composite particles is coated with a polyamide layer using polyamide obtained by anionic polymerization of lactam and dispersed in an organic solvent in the presence of an activator and The coating can be coated in an amount that provides electrical resistance, can form a uniform coating with good adhesion, and has excellent mechanical strength.

Two magnetic carriers according to the present invention will be explained below.

First, the number average particle diameter of the composite particles dispersed in the matrix of ferromagnetic fine particles and hardened phenolic resin in the present invention is 10 to 1000 μm. When the number average particle diameter is less than 10 μm.

It is difficult to eliminate carrier adhesion to the photoreceptor,
On the other hand, if it exceeds too μm, a clear image cannot be obtained. Especially if you are looking for high image quality, 30
The range is preferably 200 μm, more preferably 3
It is in the range of 0 to 100 μm.

Next, what is the bulk density of the composite particles in the present invention?

It is 2.0 g/cm2 or less. Although the lower limit of the bulk density is not particularly limited, it is practically about 1.0 g/cffl.

A carrier having such a low bulk density can be expected to provide higher image quality. The bulk density of the carrier is thought to correspond to the bulk density of the so-called "ears" of the carrier when they are formed along the lines of magnetic force on the developing sleeve, and if the value is low, the "ears" are not formed. It is believed that it is possible to move softly and freely, and as a result, high image quality can be obtained.

Furthermore, the composite particles used in the present invention have curved surfaces, and include those that are monospherical, those that are ellipsoidal, those that are flat, disk-shaped, and those that are distorted with complex curved surfaces. Since both have curved particle surfaces, the contact area between carrier particles is small and they exhibit excellent fluidity. Among these, spherical particles are preferable because they have the best fluidity, cause less distortion in the shape of one particle, and tend to have high two-particle strength.

Furthermore, the content of the ferromagnetic fine particles in the composite particles in the present invention is 80 to 99% by weight. When the content of ferromagnetic fine particles is less than 80% by weight.

If the saturation magnetization value becomes small and exceeds 99% by weight, the binding between the ferromagnetic fine particles by the phenol resin tends to become weak. Considering the strength of the composite particles, the content is preferably 97% by weight or less. Although it is not clear why the content of biferromagnetic fine particles can be increased in this manner in the present invention.

It is presumed that this is because the curing reaction progresses simultaneously with the reaction, so a small amount of phenol resin can firmly bind the ferromagnetic fine particles to each other.

Such composite particles in the present invention have a particle size of about 40 emu.
/g to 150 emu/g. 4
If it is less than 0 emu/g, the carrier tends to adhere to the photoreceptor, while if it is more than 150 emu/g, it is difficult to obtain because no practical biferromagnetic fine powder is known. The saturation magnetization of conventionally well-known ferrite carriers is said to be about 70 emu/g at most (Basics and Applications of Electrophotographic Technology J.
19B8, p. 481) 2 In the case of the composite particles of the present invention, a large saturation magnetization of 70 emu/8 or more can be easily obtained by increasing the content of fine ferrite powder.

Examples of ferromagnetic particles include magnetite, spinel ferrite such as gamma iron oxide, metals other than iron (Mn, Ni
, Zn, Mg, Cu, etc.), magnetoblanbite type ferrite such as spinel ferrite and barium ferrite, and fine particle powder of iron or alloy having an oxide layer on the surface can be used. The shape may be any of 9 grains, 1 sphere, and needle shape. especially,
If high magnetization is required, ferromagnetic fine particles such as iron can be used, but in consideration of chemical stability, magnetite, magnetoblanbite-type ferrite such as spinel ferrite containing gamma iron oxide, barium ferrite, etc. It is preferable to use ferromagnetic fine particle powder. By appropriately selecting the type and content of the ferromagnetic fine particles, composite particles having desired saturation magnetization can be obtained. For example, when trying to obtain magnetization of 40 to 70 e+w/g, magnetoblanbite ferrite such as barium ferrite, spinel ferrite, or the like may be used.

Furthermore, when trying to obtain a high magnetization of about 70 to 10,100 e/g, magnetite or spinel ferrite containing Zn may be used. Furthermore, 100e+
If high magnetization of wu/8 or more is to be obtained, fine particle powder of iron or alloy having oxide layers on two surfaces may be used.

The amount of polyamide coating the surface of the composite particles is preferably 0.05% by weight or more based on the composite particles, and if it is less than 0.05% by weight of O,OS, it may be insufficient and non-uniform. Therefore, the effect of increasing electrical resistance, which is the objective of the present invention, may not be achieved. Also,
If the amount of coating is too large, the content of ferromagnetic fine particles in the composite particles will decrease.

Large magnetization values cannot be obtained. Preferably 0.1-1
It is 0% by weight.

Two methods of manufacturing magnetic carriers according to the present invention will be described below.

First, in the method for producing composite particles in the present invention,
Phenols and aldehydes are reacted in an aqueous medium in the presence of a basic catalyst, ferromagnetic particles, and a suspension stabilizer.

The phenols used here include phenol, 1m-cresol + alkylphenols such as p-tert-butylphenol, O-propylphenol, resorcinol, and bisphenol A, and benzene nuclei or alkyl groups in which part or all of the alkyl group is a chlorine atom. Alternatively, compounds having a phenolic hydroxyl group such as phenols substituted with a bromine atom may be mentioned, and among these, phenol is the most preferred. When a compound other than phenol is used as the phenol, it may be difficult to produce one particle, or even if one particle is produced, it may have an irregular shape, so phenol is most preferable from the viewpoint of shape.

Examples of the aldehydes used in the method for producing composite particles of the present invention include formaldehyde in the form of formalin or paraformaldehyde, and furfural.

Formaldehyde is particularly preferred. The molar ratio of aldehydes to phenol is preferably 1 to 2, particularly preferably 1.1 to 1.6. If the molar ratio of aldehydes to phenols is less than 1, it will be difficult to form a single particle, or even if it is formed, it will be difficult for the resin to harden, so the strength of the formed particles will tend to be weak. When the molar ratio of aldehydes to phenols is greater than 2, the amount of unreacted aldehydes remaining in the aqueous medium after the two reactions tends to increase.

Next, as the basic catalyst used in the method for producing composite particles in the present invention, there is used a basic catalyst commonly used in producing resol resins. For example, ammonia water,
Examples include hexamethylenetetramine and alkylamines such as dimethylamine, diethyltriamine, and polyethyleneimine.

The molar ratio of these basic catalysts to phenols is
0.02-0.3 is preferable.

When the phenols and aldehydes are reacted in the presence of a basic catalyst, the ferromagnetic particles that are allowed to coexist are magnetite, as described above.

Magnetobrambite-type ferrites such as spinel ferrite and nomarium ferrite containing gamma iron oxide, and fine particle powders of iron or alloys having an oxide layer on the surface are preferable.

The amount is 0.5 to 200% by weight based on the phenol.
Double is preferred. Furthermore, as mentioned above, considering the saturation magnetization value of the composite particles to be produced and the strength of the particles, 4 to 1
00 times is more preferable.

Furthermore, the particle diameter of the ferromagnetic fine particles is as follows.

The thickness is preferably 0.01 to 10 μm, and in consideration of the dispersion of the fine particles in an aqueous medium and the strength of the resulting composite particles, the thickness is preferably 0.05 to 5 μm.

Furthermore, the suspension stabilizers used in the method for producing composite particles in the present invention include carboxymethyl cellulose,
Examples include hydrophilic organic compounds such as polyvinyl alcohol, fluorine compounds such as calcium fluoride, and inorganic salts that are substantially insoluble in water such as calcium sulfate.
Calcium fluoride is preferable in consideration of dispersion of the ferromagnetic fine particles inside the phenolic resin matrix. When a suspension stabilizer other than calcium fluoride is used, depending on two conditions, it may be difficult for the ferromagnetic particles mentioned above to disperse inside the phenolic resin matrix, and particles with irregular shapes tend to be produced. .

The amount of such suspension stabilizer added is 0 to phenols.
．． It is preferably 2 to IO% by weight, more preferably 0.5 to 3.5% by weight. If the amount of suspension stabilizer added to the phenol is less than 0.2% by weight, particles with amorphous shapes tend to be produced, while if the amount added exceeds 10% by weight, the composite particle surface The amount of suspension stabilizers such as calcium fluoride remaining in the solution tends to increase.

In addition, to add inorganic salts that are substantially insoluble in water,
Substantially water-insoluble inorganic salts as described above may be added directly, or two or more water-soluble inorganic salts may be added such that such substantially water-insoluble inorganic salts are produced in one reaction. You may.

For example, instead of a fluorine compound of calcium, one of the water-soluble inorganic salts is sodium fluoride, calcium fluoride,
At least one member selected from the group consisting of ammonium fluoride, etc., and at least one member selected from the group consisting of calcium chlorides, sulfates, and nitrates are added to 1.
It is also possible to generate a fluorine compound of calcium during the reaction.

The reaction in the method for producing composite particles of the present invention is carried out in an aqueous medium, and in this case, the amount of water charged is preferably 1, for example, so that the solid content concentration of the carrier is 30 to 95% by weight, especially.

It is desirable that the content be 60 to 90% by weight.

The reaction was carried out at a temperature increase rate of 0.5 to 1.5°C/min under stirring.
Preferably, the temperature is gradually increased at 0.8 to 1.2°C/sin.

6 at a reaction temperature of 70-90°C, preferably 83-87°C.
React for 0-150 minutes, preferably 80-110 minutes. In this reaction, a gelation reaction proceeds simultaneously with one reaction, and a gelled phenolic resin matrix is formed. After reacting and gelling in this manner, when the two reactants are cooled to below 40°C, an aqueous dispersion of spherical composite particles in which ferromagnetic fine particles are uniformly dispersed in a hardened phenolic resin matrix is obtained. .

Next, the aqueous dispersion is separated into solid and liquid by conventional methods such as filtration and centrifugation, and then washed and dried.

The ferromagnetic fine particles are uniformly dispersed in the phenol resin matrix, and composite particles having nine particle surfaces having a curved surface shape are obtained.

For coating with polyamide in the present invention, a known anionic polymerization method can be used. That is, the composite particles are suspended in a polyamide polymerization solution consisting of the composite particles, a lactam, a solvent for the lactam, and an anionic polymerization catalyst, and an activator is added while stirring to effect anionic polymerization of the lactam. The polyamide is produced by ring-opening polymerization of lactams.

The polyamide produced by the progress of the polymerization reaction can cover the entire surface of the composite particles uniformly and densely, making it possible to efficiently improve the electrical resistance of the composite particles and obtain high mechanical strength. be able to.

Lactams include all lactams that produce polyamides, such as caprolactam, enantlactam,
Examples include capryllactam and lauryllactam, among which caprolactam is most preferred.

The ratio of lactams used is 0.0% to the composite particles.
It is preferably 5 to 40% by weight, particularly preferably 5 to 30% by weight. If it is less than 0.5% by weight.

The amount of coverage may be insufficient, while 40% by weight
If it exceeds this amount, the polyamide resin may be produced alone and it may be difficult to separate it from the composite particles.

The solvents used were halogenated with boiling points in the range 80-200°C. Aliphatic hydrocarbons (1), for example paraffinic or cycloaliphatic or aromatic (eg xylene or toluene) solvents. The solvent must be one that dissolves the lactam but not the conjugate particles and does not react with any of the catalysts, activators, lactams, or conjugate particles used in the method of the invention.

The catalyst is sodium or its compound 1, for example.

Examples include sodium hydride and sodium methylate, with sodium hydride being preferred.

The activator is lactam N-carboxyanilide.

Isocyanates, carbodiimides, cyanimides.

Acyl lactam, triazine, urea, N-substituted imide,
Examples include esters.

The reaction in the production method of the present invention is carried out in an organic solvent. In this case, the amount of solvent charged is not particularly limited, but it is desirable that the particle concentration is 10 to 50% by weight.

An example of the polyamide coating reaction in the production method of the present invention will be described below.

In the order of solvent, composite particles, and lactams, under a nitrogen atmosphere,
Add the mixture at room temperature, stir gently, and keep the temperature increasing at a rate of 0.
5~10°(/min, preferably 2~6°C/win
Raise the temperature to 90-150°C2, preferably 100-120°C, and maintain this temperature for 30-120 minutes, preferably 45-75 minutes to dissolve all the lactams and 5-30% of the amount of solvent used. The solvent is distilled off and any water that may be present is distilled off by azeotropic distillation. It is then returned to the atmosphere, the catalyst is added, heated under stirring to 90-150°C, preferably 100-130°C, and the activator pre-dissolved in the solvent is heated at a constant rate for 1-4 hours, preferably After addition at 1.5-3 hours.

Reaction temperature 90~150''C1 preferably 1oO~13o
90 minutes, preferably 20 to 60 minutes. Through this reaction, the surfaces of the 9 particles were uniformly coated with polyamide. After reacting and coating in this manner, the reactant is cooled to 30''C or less to obtain a solvent dispersion of composite particles in which the surfaces of the nine particles are coated with polyamide.

Next, this dispersion liquid is separated into solid and liquid by conventional methods such as filtration and centrifugation, and then washed with a solvent.

The obtained composite particles are dried at a temperature of 80-100°C. Furthermore, after neutralizing the alkaline catalyst residue with an aqueous solution of a weak acid such as phosphoric acid and separating it into solid and liquid, drying it again at a temperature of 80 to 100°C produces composite particles with one surface uniformly coated with a polyamide layer. can get.

The number average particle diameter in the present invention is determined from an optical microscope photograph.
This is the average value of the values measured for 00 particles. Moreover, the bulk density is measured according to the method described in JIS-5101.

(Example) Next, one embodiment of the present invention will be specifically explained using examples.

Note that saturation magnetization is measured using the “vibrating sample magnetometer VSM-3S”.
External magnetic field 10k using -15J (manufactured by Toei Kogyo ■)
The electrical resistance was measured with an OeO material, and the electrical resistance was shown as the value measured with a λ Irresistance Meter 4329AJ (manufactured by Yokogawa Hewlett-Packard). Hitachi production rupture)
This is the result of observation.

<Production of composite particles Examples 1 to 3> Example 1 Into the 11th Mitsulo flask, 50 g of phenol, 65 g of 37% formalin, 400 g of spherical '7 gnetite with an average particle diameter of 0.24 μm, 7.8 g of 28% aqueous ammonia, 1.0 g of calcium fluoride and 50 g of water were added while stirring, heated to 85°C for 40 minutes, and reacted at the same temperature for 180 minutes to produce composite particles consisting of 9 spherical magnetite and hardened phenol resin. I let it happen.

Next, the contents in the flask were cooled to 30°C.

After adding 0.51 g of water, the supernatant liquid was removed, and the spherical particles in the lower layer were further washed with water and air-dried. Next.

This was dried at 50 to 60° C. under reduced pressure (5 wHg or less) to obtain composite particles (hereinafter referred to as composite particles A).

The properties of the obtained composite particles are as shown in Table 2, and the shape was spherical as shown in the scanning electron micrograph (X 1000) in FIG.

Example 2 Reaction, curing and post-treatment were carried out in the same manner as in Example I, except that 4.5 g of hexamethylenetetramine was used instead of 7.8 g of 28% aqueous ammonia as the basic catalyst.
Composite particles (hereinafter referred to as composite particles B) were obtained.

The properties of the obtained composite particles are as shown in Table 2, and the shape was bispherical as a result of scanning electron microscopy observation.

Example 3 Polyhedral magnetite particles 450 as ferromagnetic fine particles
The reaction, curing, and post-treatment were carried out in the same manner as in Example 1, except that g was used.

Composite particles C) were obtained.

The properties of the obtained composite particles are as shown in Table 2, and the shape was bispherical as a result of scanning electron microscopy observation.

<f! Coating with J7 MiF Examples 4-7. Reference example 1>
Example 4 Add 300 xylene to a 500mff1 Mitsuro flask.
d, composite particle A 37.5 g, caprolactam 7.5
Add 20 g of
The temperature was increased to 110'C in minutes and maintained at the same temperature for 60 minutes to dissolve the caprolactam. Next, under reduced pressure (20w
After distilling off 50d of xylene by azeotropic distillation with Hg),
Return to normal pressure and add 64% purity sodium hydride 0.56
g was added thereto, and the temperature was raised to 130° C. for 7 minutes. A solution containing 2.05 g of stearyl inocyasate previously dissolved in 50 d of xylene was added over 1.5 hours, and the mixture was allowed to react at the same temperature for 30 minutes. Subsequently, the contents were cooled to 30°C.

500111! Transfer to a beaker and wash several times with xylene.

After solid-liquid separation, it was dried at a temperature of 80 to 100°C.

This was washed with a 1% aqueous phosphoric acid solution, and after washing with water, the solution was separated and dried at a temperature of 80 to 100°C, thereby coating with a polyamide layer.

The amount of polyamide in the composite particles coated with the obtained polyamide layer was calculated from magnetization measurements of the composite particles, and was 2.5% by weight.

The state of the polyamide coating in the composite particles coated with the polyamide layer obtained in Example 4 was sufficient and uniform, as shown in the scanning electron micrograph (X100O) in FIG. It was recognized that Also.

Its volume electrical resistance was 7.8×1013.

Example 5 A reaction was carried out in the same manner as in Example 4, except that toluene was used instead of xylene as the solvent, and coating with polyamide was performed.

The amount of polyamide in the composite particles coated with the resulting boria-mid layer was 2.2% by weight, as calculated from magnetization measurements of the composite particles.

As a result of scanning electron microscopy, the state of the polyamide coating in the composite particles coated with the polyamide layer obtained in Example 5 was sufficient and uniform, and it was recognized that the particles were coated with polyamide. . Further, its volume electrical resistance was 4xlQI3.

Example 6 The reaction was carried out in the same manner as in Example 4, except that the type of composite particles was B instead of A, and the particles were coated with polyamide.

The amount of polyamide in the composite particles coated with the obtained polyamide layer was calculated from magnetization measurements of the composite particles, and was 2.4% by weight.

As a result of scanning electron microscopy, the state of the polyamide coating in the composite particles coated with the polyamide layer obtained in Example 6 was sufficient and uniform, and it was recognized that the particles were coated with polyamide. . Further, its volume electrical resistance was 2.5×10''.

Example 7 Add xylene 300IR to a 500I11 Mitsuro flask.
fl, composite particles C110g, lauryl lactam 10
g, N.

The reaction was carried out in the same manner as in Example 4, except that 0.13 g of N-ethylene bisstearamide was added under a nitrogen atmosphere, and coating with polyamide was performed.

The amount of polyamide in the composite particles coated with the obtained polyamide layer was calculated from magnetization measurements of the composite particles, and was 1.7% by weight.

As a result of scanning electron microscopy, the state of the polyamide coating in the composite particles coated with the polyamide layer obtained in Example 7 was sufficient and uniform, and it was recognized that the particles were coated with polyamide. . Further, its volume electrical resistance was 1.2×10 10 .

Reference Example 1 Composite particles obtained in Examples 4 to 7 above whose surfaces are coated with a polyamide layer were used as magnetic carriers, and 100 parts by weight of each was mixed with commercially available Toner 3. ,
A magnetic developer was prepared. Next, using this developer,
A copying experiment was conducted on 20,000 sheets of A4 size paper using an electrophotographic copying machine using α-5i as a photoreceptor. In copying experiments using the developers containing the magnetic carriers obtained in Examples 4 to 7, clear images were obtained. On the other hand, for comparison, when a developer was prepared using the composite particles of Examples 1 to 3 which were not coated with polyamide in the same manner as above and a copying experiment was conducted, only unclear images were obtained.

(Effects of the Invention) In the magnetic carrier according to the present invention, which is composed of composite particles of ferromagnetic fine particles and phenol resin whose entire particle surface is uniformly coated with a polyamide layer, the bulk of the composite particles can be reduced as described above. Low density.

Furthermore, due to the high content of ferromagnetic fine particles, it exhibits as high a magnetization value as possible, and also has high electrical resistance due to the coating with a polyamide layer, making it suitable as a magnetic carrier for electrophotography.

In addition, in the composite particles according to the present invention whose entire particle surface is coated with a polyamide layer, the polyamide is strong and friction-resistant.
Since it has excellent abrasion resistance and high mechanical strength, it is possible to obtain the effect of improving the durability of the composite particles.

Furthermore, since the manufacturing method of the present invention has the above-mentioned configuration, it is possible to easily manufacture composite particles of ferromagnetic fine particles and phenolic resin. This is because the electrical resistance can be made sufficiently high through this process.

It is industrially and economically advantageous.

[Brief explanation of the drawing]

FIG. 1 is a scanning electron micrograph (X 1000) showing the particle structure of the composite particles obtained in Example 5, and FIG. Scanning electron micrograph showing the particle structure of composite particles (
X 1000).

Claims (2)

[Claims] (1) Ferromagnetic fine particles are dispersed in a hardened phenolic resin matrix, and the number average particle diameter is 10 to 10
00 μm and a bulk density of 2.0 g/cm^2 or less,
A magnetic carrier for electrophotography, characterized in that the surface of the composite particle having a content of ferromagnetic fine particles of 80 to 99% by weight is uniformly coated with a polyamide layer. (2) The phenol resin in which the ferromagnetic particles are cured by reacting and curing phenols and aldehydes in an aqueous medium in the presence of ferromagnetic particles, a suspension stabilizer, and a basic catalyst. Dispersed in a matrix, with a number average particle diameter of 10 to 1000 μm and a bulk density of 2.
．． Producing composite particles with a particle size of 0 g/cm^2 or less and a content of ferromagnetic fine particles of 80 to 99% by weight,
Next, the composite particles are dispersed in an organic solvent in the presence of a lactam, a polymerization catalyst, and an activator, and the lactam is anionically polymerized to form a uniform polyamide layer over the entire particle surface of the composite particles. 1. A method for producing a magnetic carrier for electrophotography, the method comprising: coating a magnetic carrier with