JP2006053515A - Method of classifying particles for electrophotographic carrier, vibrating sieve for classifying electrophotographic carrier particles, electrophotographic carrier, electrophotographic developer and process cartridge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method of inexpensively manufacturing a carrier for a small-particle-diameter electrophotographic developer giving high image quality (particularly good graininess), less liable to cause carrier adhesion, and having a sharp particle size distribution. <P>SOLUTION: In a method of classifying particles for an electrophotographic carrier using a vibrating sieve including an oscillator with an ultrasonic vibrator, a vibrating sieve in which at least two meshes are layered together and located on the ultrasonic vibrator is used as the vibrating sieve, and a vibration which a lower mesh receives from the ultrasonic vibrator is transmitted to an upper mesh to classify the particles fed on an uppermost mesh. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method of classifying magnetic particles, resin-coated magnetic particles, or electrophotographic carrier particles containing a magnetic material prepared by polymerization or the like, and an electron using the classified particles. The present invention relates to a photographic carrier, an electrophotographic developer using the carrier, a process cartridge containing the developer, and a vibration sieving machine for classification.

Electrophotographic development methods include a one-component development method mainly composed of toner and a two-component development method using a developer obtained by mixing a carrier and toner.
The two-component development method uses a carrier and has a wide frictional charging area for the toner, so the charging characteristics are more stable than the one-component method, which is advantageous for obtaining high image quality over a long period of time. Two-component developers are widely used because of their high toner supply capacity.

In recent years, a development system capable of faithfully developing a latent image has become an important issue in order to cope with resolution enhancement, highlight reproducibility improvement, and colorization. For this reason, various proposals have been made in terms of both process conditions and developer (toner, carrier). In terms of process, it is effective to make the developing gap close, to make the photoconductor thin, and to reduce the writing beam diameter, but there are still significant problems in terms of cost and reliability.
It is known that the reproducibility of dots is greatly improved by using a toner having a small particle diameter as a developer. However, a developer containing a toner having a small particle diameter causes scumming or lack of image density. There remains a problem to be solved.

On the other hand, the use of a small particle size carrier has been proposed in the past and is known to have the following advantages.
That is,
(1) Since the surface area is large, sufficient triboelectric charge can be given to each toner, and the occurrence of low charge amount toner and reverse charge amount toner is small. As a result, the background stains are less likely to occur, the toner around the dots is less dusty and blurred, and the dot reproducibility is improved.
(2) Since the surface area is large and scumming is less likely to occur, the average charge amount of the toner can be reduced, and a sufficient image density can be obtained. Accordingly, the small particle size carrier can make up for the disadvantages when using the small particle size toner, and at the same time is particularly effective in drawing out the advantages of the small particle size toner.
(3) The small particle size carrier has a feature that a dense magnetic brush is formed and an ear mark is hardly generated in an image.
However, the conventional small particle size carrier is liable to cause carrier adhesion, causing damage to the photoreceptor and fixing roller, and has a problem in practicality.

When examining the carrier adhering to the small particle size carrier, the carrier on the small particle size side has an overwhelmingly high ratio. Thus, various methods for sharply classifying the particle size distribution have been proposed. Among them, classification with a sieve can be classified sharply compared with centrifugal force and pneumatic classification methods, and the necessary particles in the particle size distribution can be recovered with high yield.
However, it is known that the classification method using a sieve makes it difficult to classify into a sharp particle size distribution when the particle diameter is small, that is, when the mass per one is small.

  As a method for solving such a problem, a high-quality image is obtained, and it is highly durable and hardly causes carrier adhesion. The weight average particle diameter Dw is 25 to 45 μm, and the particle diameter is 44 μm or less. The content ratio is 70 wt% or more, the content ratio of particles having a particle size of 22 μm or less is 7 wt% or less, and the ratio Dw / Dp of the weight average particle diameter Dw to the number average particle diameter Dp is 1-1. In order to produce an electrophotographic developer carrier in the range of 30, ultrasonic vibration is applied to the wire mesh of the sieving machine, vertical acceleration is applied to the particles, and small diameter particles of less than 22 μm are efficiently and sharply formed. A cutting technique has been proposed (see, for example, Patent Document 1).

According to this method, since vertical acceleration is given to the particles, even particles having the same particle size behave substantially like masses, that is, particles having a large true specific gravity, and can efficiently pass the mesh material. it can. Patent Document 1 further describes the use of an ultrasonic transducer with a resonance ring in order to improve the efficiency of sieving.
However, when using a mesh material with a small mesh opening on the sieve machine, the mesh material is thin and low in strength (the thread is thin). If used for a long time, the edge of the mesh material will be broken by the weight of the carrier, and unclassified There is a problem that the fine particles are mixed in the product as they are, and the fine powder content increases.

Further, when clogging of the mesh material occurs, it is very difficult to remove the carrier because the carrier is buried in the opening, and the mesh material needs to be replaced.
Although some mesh materials are knitted with resin yarn, stainless steel is usually used. This is because in the case of a mesh material knitted with resinous yarn, the rigidity of the yarn is small, so that ultrasonic waves are not effectively transmitted to the mesh material and classification is not possible at all.
On the other hand, when the mesh of the stainless mesh material becomes fine, the manufacturing cost becomes extremely high, resulting in a large problem that the manufacturing cost of the core material and the coat carrier increases.

JP 2001-209215 A

  Therefore, an object of the present invention is to provide a method for producing a carrier for small particle size electrophotographic developer with high image quality (particularly good granularity), hardly causing carrier adhesion and having a sharp particle size distribution at low cost. It is to be.

  According to the present invention, a method for classifying particles for an electrophotographic carrier as shown below, an electrophotographic carrier using the classified particles, an electrophotographic developer using the carrier, and the development A process cartridge containing an agent and a vibration sieving machine for classification are provided.

That is, the said subject is achieved by the classification method of the particle | grains for electrophotographic carriers of the following this invention (1)-(5).
(1) A method of classifying particles for an electrophotographic carrier using a vibrating screen equipped with an oscillator including an ultrasonic vibrator, wherein the vibrating screen serves as at least two meshes on the ultrasonic vibrator. The material supplied in close contact with each other is used to transmit vibration received by the lower mesh material from the ultrasonic vibrator to the upper mesh material, and the electrons supplied on the uppermost mesh material. A method for classifying particles for electrophotographic carrier, characterized by classifying particles for photographic carrier.
(2) As described in (1) above, the mesh material having a small mesh is installed on the upper side and the mesh material having a large mesh is installed on the lower side as the at least two mesh materials. Method for classifying particles for electrophotographic carrier.
(3) The electrophotographic carrier as described in (1) or (2) above, wherein the bending elastic modulus of at least one kind of mesh material having a small mesh installed on the upper side is 1 to 10 GPa. Particle classification method.
(4) As the vibration sieving machine, a resonance member fixed on a mesh material is used, ultrasonic vibration is transmitted to the resonance member to resonate, and then transmitted to the uppermost mesh material surface. The method for classifying particles for an electrophotographic carrier according to any one of (1) to (3).
(5) The method for classifying particles for an electrophotographic carrier according to any one of (1) to (4), wherein both the fine powder side and the coarse powder side of the particle size distribution are classified.

Moreover, the said subject is achieved by the vibration sieve machine for classification of the particle | grains for electrophotographic carriers of the following this invention (6)-(12).
(6) A vibrating screen machine with an oscillator, which is used to classify particles for an electrophotographic carrier and has an ultrasonic vibrator, wherein at least two mesh materials are in close contact with the ultrasonic vibrator. A vibration sieving machine for classifying particles for an electrophotographic carrier, characterized by being laminated.
(7) As described in (6) above, the mesh material having a small mesh opening on the upper side and a mesh material having a large mesh opening on the lower side is used as the at least two mesh materials. Vibrating sieve for classifying particles for electrophotographic carriers.
(8) The electrophotographic carrier according to (6) or (7) above, wherein a bending elastic modulus of at least one kind of mesh material having a small mesh installed on the upper side is 1 to 10 GPa. Vibrating sieve machine for particle classification.
(9) The electrophotography according to any one of (6) to (8), wherein the resonance member is fixedly installed on the mesh material, and the vibration of the ultrasonic vibrator is transmitted to the resonance member to resonate. Vibrating sieve for classifying carrier particles.
(10) The vibration sieving machine for classifying particles for electrophotographic carriers according to any one of (6) to (9), wherein the upper mesh material is a resin.
(11) The vibration sieving machine for classifying particles for electrophotographic carriers as described in (10) above, wherein the resin mesh material is knitted nylon yarn.
(12) The vibration sieving machine for classifying particles for electrophotographic carriers as described in (10) above, wherein the resin mesh material is a knitted polyester yarn.

The above-mentioned problems are achieved by the following methods (13) and (14) for producing a carrier core material for an electrophotographic developer, and a carrier core material for an electrophotographic developer produced by the production method.
(13) The carrier core for an electrophotographic developer, wherein the electrophotographic carrier particles are magnetic particles, and the classification method according to any one of (1) to (9) is used as one of the steps. A method of manufacturing the material.
(14) A carrier core material for an electrophotographic developer obtained by the production method according to (13).

Moreover, the said subject is achieved by the manufacturing method of the carrier for electrophotographic developers of this invention (15)-(19) of the following, and the carrier for electrophotographic developers manufactured by this manufacturing method.
(15) The particles according to any one of (1) to (9) above, wherein the particles for an electrophotographic carrier are particles (referred to as resin-coated magnetic particles) formed by forming a resin film on the surface of magnetic particles. A method for producing a carrier for an electrophotographic developer, characterized in that the method is one of the steps.
(16) The method for producing a carrier for an electrophotographic developer according to (14), further comprising a step of forming a resin coating on the surface of the magnetic particles to obtain the resin coating particles before the classification step. .
(17) A carrier for an electrophotographic developer obtained by the production method according to (15) or (16).
(18) The weight average particle diameter Dw is 30 to 45 μm, the content ratio of particles having a particle diameter smaller than 44 μm is 70% by weight or more, and the content ratio of particles having a particle diameter smaller than 22 μm is 7% by weight or less. And the ratio Dw / Dp of the weight average particle diameter Dw to the number average particle diameter Dp is 1 to 1.30, the carrier for an electrophotographic developer according to (17) above.
(19) The weight average particle diameter Dw is 22 to 32 μm, the content of particles smaller than 36 μm is 90 to 100% by weight, the content of particles having a particle diameter smaller than 20 μm is 7% by weight or less, and the weight average The carrier for electrophotographic development as described in (17) above, wherein the ratio Dw / Dp of the particle diameter Dw to the number average particle diameter Dp is 1 to 1.30.

The above-mentioned subject is achieved by the following electrophotographic developer of the present invention (20) and a process cartridge using the developer of the present invention (21).
(20) An electrophotographic developer comprising a toner and a carrier, wherein the carrier for an electrophotographic developer according to any one of (17) to (19) is used as the carrier. Electrophotographic developer.
(21) At least a photosensitive member, a charging unit for charging the surface of the photosensitive member, a developing unit, and a removing unit for removing the developer remaining on the surface of the photosensitive member. A process cartridge in which the electrophotographic developer described in 1) is accommodated.

  As will be apparent from the following detailed and specific description, according to the present invention, two meshes are closely stacked on the ultrasonic transducer, and each mesh functions to support a load and to function as a sieve. By separating, more preferably, the elastic modulus of the upper mesh is made smaller than the elastic modulus of the lower mesh, whereby it is possible to produce electrophotographic carrier particles having a sharp particle size distribution at a low cost. became.

According to the inventions (1) to (5), a small particle size electrophotographic carrier having a sharp particle size distribution can be efficiently produced.
According to the inventions of the above (6) to (12), a vibration sieving machine for efficiently producing a small particle size electrophotographic carrier having a sharp particle size distribution can be obtained.
According to the invention (13), particles for an electrophotographic carrier having a sharp particle size distribution can be efficiently produced.
According to the invention of (14) or (15), a small particle size electrophotographic carrier having a sharp particle size distribution can be efficiently produced.
According to the invention of (16), it is possible to obtain particles for a small particle size electrophotographic developer carrier having a high image quality, good graininess, hardly causing carrier adhesion and having a sharp particle size distribution.
According to the inventions of (17) to (19), it is possible to obtain a small particle size electrophotographic carrier having a high particle size, good graininess, hardly causing carrier adhesion, and having a sharp particle size distribution.
According to the invention (20), an electrophotographic two-component developer having high image quality, good graininess, and hardly causing carrier adhesion is obtained.
According to the invention (21), a process cartridge using an electrophotographic two-component developer having high image quality, good graininess, and hardly causing carrier adhesion can be obtained.

The particles for an electrophotographic carrier having a sharp particle size distribution in the present invention are classified into the particles for an electrophotographic carrier using an oscillating sieve equipped with an oscillator equipped with an ultrasonic vibrator. On the ultrasonic transducer, at least two meshes are closely stacked and installed, and more preferably, a mesh having a bending elastic modulus of 1 to 10 GPa is installed on the uppermost side, and the ultrasonic vibration It can be manufactured by transmitting the vibration received by the lower mesh from the child to the upper mesh and classifying the particles supplied on the uppermost mesh.
An electrophotographic carrier coated with a resin is prepared by forming a resin film on the surface of the magnetic particles of the core material to produce resin film particles, and then classifying the resin-coated particles with the above vibration sieve. Thus, a sharp particle size distribution can be obtained.

  When there are two mesh materials to be stuck to each other, it is preferable to set the mesh material with a small opening on the upper side and a larger lower side, and the mesh material with a small opening has a classification function and has a large opening. The mesh material receives the vibration directly from the ultrasonic vibrator and transmits the vibration to the upper mesh material, and has the function of substantially supporting the weight of the carrier. When classifying with a vibration sieve, the upper mesh is used. The load on the material is reduced, it can withstand long-term use, and the life can be greatly extended.

As the lower mesh material, it is desirable to use a material having a wire diameter and an opening of, for example, knitted with a thick thread, which efficiently transmits ultrasonic vibrations and is less likely to be worn or cut. Further, the opening is preferably larger than the maximum particle diameter of the particles.
For example, when classifying an electrophotographic carrier having a weight average particle diameter Dw of 22 to 45 μm, it is sufficient that the mesh of the lower mesh material is 62 μm (250 mesh) or more.
On the other hand, since ultrasonic vibration is difficult to be transmitted if the wire diameter of the mesh material becomes too large, in the case of an electrophotographic carrier having a Dw of 22 to 45 μm, an opening of about 104 μm (150 mesh) is particularly preferable.

Further, the material of the lower mesh material is preferably a bending elastic modulus of 50 GPa to 500 GPa having a high strength in order to efficiently transmit the vibration energy of ultrasonic waves, and is particularly preferably metallic.
The mesh material is supported on the lower side and has a classification function on the upper side, and may have a structure of two or more layers. The mesh material on the upper side only needs to have an opening corresponding to the particle size to be classified. Since the lower mesh material is installed, an upper mesh material having a large opening ratio can be used.

In addition, as a vibration sieve machine with an ultrasonic oscillator used in the classification method of the present invention, when a resonance member fixedly installed on a mesh material is used, ultrasonic vibration is transmitted to the entire screen via the resonance ring. Communicating, transmitting uniform vibration to the mesh, and efficiently sieving the material on the mesh.
The ultrasonic vibration that vibrates the mesh material can be obtained by supplying a high-frequency current to the converter and converting it into ultrasonic vibration. The converter in this case consists of a PZT vibrator.
In order to vibrate the mesh material by ultrasonic vibration, the ultrasonic vibration generated by the converter is transmitted to the resonance member fixedly installed on the mesh material, the resonance member resonates by the ultrasonic vibration, and The mesh fixed to the resonance member is vibrated.
In this case, the frequency for vibrating the mesh material is 20 to 50 kHz, preferably 30 to 40 kHz.
The shape of the resonance member may be a shape suitable for vibrating the mesh material, and is usually a ring shape. The vibration direction for vibrating the mesh material is preferably a vertical direction.

FIG. 1 is a conceptual diagram for explaining an example of a vibration sieving machine with an ultrasonic oscillator used in the classification method of the present invention.
In FIG. 1, reference numeral (1) is a vibration sieve, (2) is a cylindrical container, (3) is a spring, (4) is a base (support), and (5) is a mesh material of two or more layers adhered to each other. A mesh with a large opening is installed on the lower side, (6) is a resonance member (in this case, ring-shaped), (7) is a high-frequency current cable, (8) is a converter, and (9) is a ring-shaped frame Indicates.
In order to operate the vibratory sieve with an ultrasonic oscillator (circular sieve) shown in FIG. 1, first, a high frequency current is supplied to the converter (8) via the cable (7). The high-frequency current supplied to the converter (8) is converted into ultrasonic vibration.
The ultrasonic vibration generated in the converter (8) vibrates the resonant member (6) to which the converter (8) is fixed and the ring-shaped frame (9) provided in the vertical direction in the vertical direction. Due to the vibration of the resonance member (6), the mesh member (5) fixed to the resonance member (6) and the frame (9) vibrates in the vertical direction.
A commercial product can be used as the vibration sieve machine equipped with an ultrasonic oscillator, and for example, “Ultrasonic” (product name) manufactured by Sakae Sangyo Co., Ltd. is available.

In addition, the particles to which the classification method of the present invention is applied may be completely unclassified, or those that have been subjected to a pneumatic / mechanical classification treatment. The side, coarse powder side, or both sides can be classified.
In particular, when applied to the classification of the coarse powder side particles, the distribution is sharper than that of a classification method such as a pneumatic method, so that the target particles can be obtained in a high yield, which is preferable.

  The upper mesh can be made by knitting fine lines or by making holes by laser or etching. However, since the carrier has a substantially spherical shape, clogging is likely to occur when the hole shape is circular. Therefore, a fibrous mesh knitted with various materials is more preferable. Furthermore, the material of the upper mesh is preferably a material having an appropriate elastic modulus and a bending elastic modulus in the range of 1 to 10 GPa.

If the elastic modulus of the upper mesh is made smaller than the elastic modulus of the lower mesh, the shape of the upper mesh opening is slightly deformed due to vibration transmitted from the lower mesh, and the mesh is less likely to be clogged. , Can improve the efficiency of classification.
When the flexural modulus of the upper mesh is larger than 10 GPa, the mesh opening is less deformed and clogging is likely to occur, and the classification efficiency is lowered. If the flexural modulus is less than 1 GPa, the upper mesh absorbs the vibration of the lower mesh, and the mesh shape changes greatly, so that the classification efficiency decreases.

The material is not particularly limited as long as the flexural modulus is in the range of 1 to 10 GPa. However, it is preferable to use a resin as a material because of superior manufacturing costs. The cost advantage of the resin mesh is more conspicuous as the mesh has a smaller mesh size. For example, a nylon mesh having a mesh size of about 20 μm has a cost per unit area of about 20 compared to a stainless steel mesh. It only takes about a minute.
The mesh material on the upper side with a small mesh opening and moderate elasticity is not strong enough when the mesh is not installed on the lower side, so the life of the mesh is shortened, and it is used as a mesh material for ultrasonic vibration sieves. Not suitable for use. Therefore, by using a mesh having a sufficient strength with a flexural modulus of 50 GPa to 500 GPa in combination with the lower mesh, the classification accuracy and efficiency are very good.

The mesh material made of resin is not particularly limited in terms of the manufacturing method and material other than the flexural modulus. As long as the mesh material can be produced, a known resin such as a nylon resin, a polyester resin, an acrylic resin, or a fluorine resin can be used.
Among these, nylon resins are excellent mesh materials in terms of durability and chemical resistance, and polyester resins are preferable materials in terms of durability and weather resistance.
Commercially available nylon mesh or polyester mesh may be used, for example, SEFAR (Switzerland) NYTAL series or PETEX series.
Further, when these resins are knitted in a fiber form, they may be used only for either warp or weft.

A mesh made of a material having a flexural modulus of 10 GPa or less may have insufficient strength unless a mesh is installed on the lower side, and may not be suitable for use as a mesh for an ultrasonic vibration sieve. However, it has been confirmed that by using the double sticking method as described above, sufficient strength and durability can be provided, and classification accuracy and efficiency are very good.
The measurement of the flexural modulus of the mesh material can be performed according to ASTM (American Society for Testing and Materials) D790. The value of the flexural modulus in the present invention is also measured according to ASTM D790.

  Further, the magnetic particles (core material) or resin-coated magnetic particles, which are electrophotographic carrier particles classified by the classification method of the present invention, have a sharp particle size distribution and a weight average particle size Dw of 30. The content ratio of particles having a particle size smaller than 44 μm is 70 wt% or more, the content ratio of particles having a particle diameter smaller than 22 μm is 7 wt% or less, and the weight average particle diameter Dw and number average When the ratio Dw / Dp to the particle diameter Dp is 1 to 1.30, preferably 1 to 1.25, excellent characteristics as a carrier for an electrophotographic developer can be obtained. It is good.

The smaller the weight average particle diameter Dw, the better the graininess (highlight image uniformity), but carrier adhesion is likely to occur. When carrier adhesion occurs, the graininess decreases. On the other hand, as the weight average particle diameter Dw is larger, carrier adhesion is less likely to occur. However, if the toner concentration is increased in order to obtain a high image density, scumming tends to increase.
The carrier adhesion here means a phenomenon in which the carrier adheres to the image portion or the background portion of the electrostatic latent image. As the electric field strength increases, the carrier adheres more easily. However, since the electric field strength of the image area is weakened by developing the toner, the carrier adhesion is less likely to occur compared to the background area.

When the carrier content of particles having a particle size smaller than 44 μm and Dw of 30 to 45 μm is less than 44 μm, the particles adhering to the carrier are observed on the photoconductor. I found that there were many.
Therefore, the present inventors evaluated carrier adhesion in a small particle size carrier having a weight average particle size Dw of 30 μm to 45 μm by changing the weight ratio of particles smaller than 22 μm. As a result, particles having a particle size of 22 μm or less were obtained. It was confirmed that carrier adhesion was less likely to occur when the content of 7 was 7 wt% or less, preferably 3 wt% or less.

As the electrophotographic carrier particles, when the weight average particle diameter Dw is 22 to 32 μm, the content of particles smaller than 36 μm is 90 to 100% by weight, and the content of particles having a particle diameter smaller than 20 μm is 7%. %, And the ratio Dw / Dp between the weight average particle diameter Dw and the number average particle diameter Dp needs to be 1 to 1.30.
When the weight average particle diameter Dw is 22 to 30 μm, even if the toner concentration is high, the background is hardly stained and an image with extremely good graininess can be obtained.
The content of particles smaller than 36 μm is 90 to 100% by weight, the content of particles having a particle size smaller than 20 μm is 7% by weight or less, preferably 3% by weight or less, and the weight average particle size Dw and the number average It was found that carrier adhesion is not a problem when the ratio Dw / Dp to the particle size Dp is a sharp particle size distribution of 1 to 1.30, preferably 1 to 1.25.

As the material for the core particles constituting the carrier of the present invention, conventionally known various magnetic materials are used.
The carrier core material particles used in the present invention have a magnetic moment of 50 emu / g or more, preferably 60 emu / g or more when a magnetic field of 1000 oersted (Oe) is applied. The upper limit is not particularly limited, but is usually about 150 emu / g. If the magnetic moment of the carrier core particles is smaller than the above range, carrier adhesion tends to occur, which is not preferable.

The magnetic moment can be measured as follows. A BH tracer (BHU-60 / manufactured by Riken Denshi Co., Ltd.) is used, and 1.0 g of carrier core particles are packed in a cylindrical cell and set in an apparatus. The magnetic field is gradually increased and changed to 3000 Oersted, then gradually reduced to zero, and then the opposite magnetic field is gradually increased to 3000 Oersted.
Furthermore, after gradually reducing the magnetic field to zero, a magnetic field is applied in the same direction as the first. In this way, the BH curve is illustrated, and the magnetic moment of 1000 oersted is calculated from the figure.

Examples of the core particles having a magnetic moment of 50 emu / g or more when a 1000 oersted magnetic field is applied include, for example, ferromagnetic materials such as iron and cobalt, magnetite, hematite, Li-based ferrite, Mn—Zn-based ferrite, Cu -Zn ferrite, Ni-Zn ferrite, Ba ferrite, Mn ferrite and the like.
In this case, the ferrite is a sintered body generally represented by the chemical formula of the following formula (1).
(MO) x (NO) y (Fe ₂ O ₃ ) z (1)
However, x + y + z = 100 mol%, and M and N are metal atoms such as Ni, Cu, Zn, Li, Mg, Mn, Sr, and Ca, respectively. Divalent metal oxide and trivalent iron oxidation It is composed of a complete mixture with the product.

  Examples of the core particles having a magnetic moment of 60 emu / g or more when a 1000 oersted magnetic field more preferably used in the present invention is applied include, for example, magnetic materials such as iron-based, magnetite-based, Mn-Mg-based ferrite, and Mn-based ferrite. Body particles.

Of the particles for an electrophotographic carrier applied as an object of the classification method of the present invention, resin-coated magnetic particles are produced by forming a resin layer on the surface of the core material particles.
As the resin for forming the resin layer, various conventionally known resins used for carrier production can be used. In the present invention, the following resins may be used alone or in combination of two or more.

  Silicone resin, polystyrene, chloropolystyrene, poly-α-methylstyrene, styrene-chlorostyrene copolymer, styrene-propylene copolymer, styrene-butadiene copolymer, styrene-vinyl chloride copolymer, styrene-vinyl acetate copolymer Polymer, styrene-maleic acid copolymer, styrene-acrylic acid ester copolymer (styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-acrylic) Acid octyl copolymer, styrene-phenyl acrylate copolymer, etc.) Styrene-methacrylic acid ester copolymer (styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-butyl methacrylate copolymer) Coalescence, styrene-methacrylic acid phenolic Copolymers, etc.) Styrene resins such as styrene-α-chloroacrylic acid methyl copolymer, styrene-acrylonitrile-acrylic acid ester copolymer, epoxy resin, polyester resin, polyethylene resin, polypropylene resin, ionomer resin, polyurethane resin , Ketone resin, ethylene-ethyl acrylate copolymer, xylene resin, polyamide resin, phenol resin, polycarbonate resin, melamine resin and the like.

  In particular, examples of silicone resins suitable as carrier coating resins include the following. KR271, KR272, KR282, KR252, KR255, KR152 (manufactured by Shin-Etsu Chemical Co., Ltd.), SR2400, SR2406 (manufactured by Toray Dow Corning Silicone), and the like. Suitable modified silicone resins include epoxy-modified silicone, acrylic-modified silicone, phenol-modified silicone, urethane-modified silicone, polyester-modified silicone, and alkyd-modified silicone.

As a method for forming the resin layer on the surface of the carrier core material particles, a known method such as a spray drying method, a dipping method, or a powder coating method can be used. In particular, a method using a fluidized bed type coating apparatus is effective for forming a uniform coated film.
The thickness of the resin layer formed on the surface of the carrier core particles is usually 0.02 to 1 μm, preferably 0.03 to 0.8 μm.

  The carrier of the present invention can be a so-called resin-dispersed carrier having a form in which magnetic powder is dispersed in a known resin such as a phenol resin, an acrylic resin, or a polyester resin.

  In the carrier of the present invention, the resistivity LogR (R: carrier resistance) is 15.0 Ωcm or less, preferably 14.0 Ωcm or less. The lower limit is not particularly limited, but is usually about 10.0 Ωcm. When the carrier resistivity is higher than the above range, carrier adhesion is likely to occur. However, when the carrier resistivity is maintained within the above range, carrier adhesion is less likely to occur, and the developing ability is increased and sufficient image density is obtained. It becomes like this.

The carrier resistivity can be measured by the following method.
As shown in FIG. 2, a cell (11) made of a fluororesin container containing electrodes (12a) and (12b) having a distance between electrodes of 2 mm and a surface area of 2 × 4 cm is filled with a carrier (13), A DC voltage of 100 V is applied, DC resistance is measured by a high resistance meter 4329A (4329A High Resistance Meter; manufactured by Yokogawa Hewlett-Packard Co., Ltd.), and an electrical resistivity LogR (Ωcm) is calculated.
The carrier resistivity can be adjusted by adjusting the resistance of the coating resin on the core particles and controlling the film thickness.

Further, in order to adjust the carrier resistance, the conductive fine powder can be added to the coating resin layer and used.
As the conductive fine particles, conductive ZnO, metal or metal oxide powder such as Al, _SnO 2 doped with SnO ₂ or the various elements that have been prepared in a variety of _{ways, TiB 2, ZnB 2, MoB} 2 , etc. Borides, silicon carbide, polyacetylene, polyparaphenylene, poly (para-phenylene sulfide) polypyrrole, conductive polymers such as polyethylene, carbon black such as furnace black, acetylene black, and channel black.
For these conductive fine powders, use a dispersing machine that uses media such as a ball mill or bead mill, or a stirrer equipped with blades that rotate at high speed after the conductive fine powder has been added to the solvent or coating resin solution used for coating. Can be uniformly dispersed.

Next, the developer is produced by mixing the resin-coated magnetic particles obtained by the classification method of the present invention with a toner. The toner will be described.
The toner used in the present invention contains a colorant, fine particles, a charge control agent, a release agent and the like in a binder resin mainly composed of a thermoplastic resin. Can be used. This toner can be an amorphous or spherical toner prepared by various toner production methods such as a polymerization method and a granulation method. Both magnetic toner and non-magnetic toner can be used.

In the present invention, the weight average particle diameter Dw in the carrier and the carrier core material is calculated based on the particle diameter distribution (relationship between the number frequency and the particle diameter) of the particles measured on the basis of the number. The weight average particle diameter Dw in this case is represented by the following formula (2).
Dw = {1 / Σ (nD ³ )} × {Σ (nD ⁴ )} (2)
In the above formula, D represents the representative particle size (μm) of particles present in each channel, and n represents the total number of particles present in each channel. The channel indicates a length for equally dividing the particle size range in the particle size distribution diagram, and in the case of the carrier of the present invention, a length of 2 μm is adopted. Further, as the representative particle size of the particles existing in each channel, the lower limit value of the particle size stored in each channel was adopted.

In the present invention, the number average particle diameter Dp of the carrier and the carrier core material particles is calculated based on the particle diameter distribution of the particles measured on the basis of the number. The number average particle diameter Dp in this case is represented by the following formula.
Dp = (1 / N) × {ΣnD} (3)
In the above formula, N represents the total number of particles measured, n represents the total number of particles present in each channel, and D represents the lower limit of the particle size present in each channel (2 μm).

As a particle size analyzer for measuring the particle size distribution of the carrier, a Microtrac particle size analyzer (model HRA 9320-X100: manufactured by Honewell) was used. The measurement conditions are as follows.
(1) Particle size range: 100-8 μm
(2) Channel length (channel width): 2 μm
(3) Number of channels: 46
(4) Refractive index: 2.42
A Coulter counter was used for measuring the particle size distribution of the toner.

In the present invention, such sharp electrophotographic carrier particles having a particle size distribution obtained by the classification method of the present invention include both magnetic particle core material and resin-coated magnetic particles. Therefore, the following three cases are included as modes to which the classification method of the present invention is applied.
(1) The carrier core material classified by the classification method of the present invention is coated with a resin to produce an electrophotographic developer carrier having a sharp particle distribution.
(2) After preparing resin-coated magnetic particles formed by coating a carrier core material with a resin, the resin-coated magnetic particles are classified by the classification method of the present invention to provide a developer for electrophotography having a sharp particle distribution. Make a carrier.
(3) The carrier core material classified by the classification method of the present invention is coated with a resin to produce resin-coated magnetic particles, and the resin-coated magnetic particles are further classified by the classification method of the present invention. An electrophotographic developer carrier having a sharp particle distribution is prepared.
In particular, when the resin-coated magnetic particles are used as an electrophotographic carrier, there is an extremely excellent effect that the granularity is good and the carrier adhesion hardly occurs.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples. The present invention is not limited to these examples. Moreover, a part represents a weight part.
(Toner Production Example 1)
Polyester resin 100 parts Carnauba wax No. 1 5 parts Carbon black (Mitsubishi Chemical Corporation: # 44) 9 parts Chromium-containing azo compound (Hodogaya Chemical T-77) 3 parts After thoroughly mixing the above components in a blender It is melt-kneaded with a twin-screw extruder, allowed to cool, then coarsely pulverized with a cutter mill, then finely pulverized with a jet airflow fine pulverizer, and further classified with an air classifier, and a weight average average particle size of 5 Toner base particles of 0.6 μm were obtained.
Furthermore, 1.0 part of hydrophobic silica fine particles (R972: manufactured by Nippon Aerosil Co., Ltd.) was added to 100 parts of the toner base particles, and mixed with a Henschel mixer to obtain toner a.

(Carrier production example 1)
In a silicone resin (SR2411: manufactured by Toray Dow Corning Silicone), 7% of carbon (made by Lion Akzo, Ketjen Black EC-DJ600) is dispersed for 60 minutes using a ball mill. The liquid was diluted to obtain a dispersion having a solid content of 5%.
An aminosilane coupling agent (NH ₂ (CH ₂ ) ₃ Si (OCH ₃ )) was further added to and mixed with this dispersion by 3% with respect to the solid content of the silicone resin to obtain a dispersion.
Using a fluidized bed type coating apparatus, the above dispersion was applied at a rate of about 30 g / min in an atmosphere of 100 ° C. on the particle surface of carrier core particle I: 5 Kg shown in Table 1, and further 200 Heating was performed at 0 ° C. for 2 hours to obtain a resin-coated carrier A having a thickness of 0.31 μm. The film thickness was adjusted depending on the amount of the coating solution.
The particle size distribution of carrier A is shown in Table 2.

(Carrier production example 2)
On the stainless steel mesh, the carrier core material I shown in Table 1 was supplied at a rate of 0.5 kg / min for classification.
The vibration sieve used has the structure shown in FIG. 1, and is directly brought into contact with a 70 cmφ stainless mesh (635 mesh / single affixed) (5) supported by the frame (9) as a resonance member ( 6) is a sieve device (1) provided with a vibrator (8) that oscillates an ultrasonic wave of 36 kHz on the ring (6).
The stainless mesh (5) is disposed in a cylindrical container (2) supported by a base (4) via a spring (3). A vibration motor (not shown) is installed in the base (4), and high-frequency current generated by driving the motor is sent to the vibrator (8) attached to the resonance ring (6) via the cable (7), and ultrasonic waves are generated. It oscillates.
The ultrasonic vibration vibrates the resonance ring (6), and the vibration causes a vibration in the vertical direction of the entire mesh surface (5). Particles on the fine powder side of the carrier core material supplied on the stainless steel mesh (5) in the cylindrical container (2) are subjected to a sieving process and are removed at the lower part of the cylindrical container (2) under the mesh.

This classification operation was repeated to obtain a carrier core material II shown in Table 1 from above the mesh.
As a result of classification, the ratio of particles less than 22 μm in the carrier core material could be greatly reduced. Table 1 shows the particle size distribution of the carrier core material II.
A resin-coated carrier B having a film thickness of 0.30 μm was obtained in the same manner as in Carrier Production Example 1 except that this carrier core material II was used.
The particle size distribution of carrier B is shown in Table 2.
In the above classification treatment, clogging of the mesh was hardly observed in a short time, but clogging gradually increased when used for a long time, and after 1000 kg processing (use for about 30 hours), the mesh needs to be cleaned. It became.
Thereafter, cleaning was performed every 500 kg. However, when the total 2000 kg was used, the mesh was also torn, so it was necessary to replace the mesh.
The classification cost associated with re-stenciling the stainless steel mesh (635 mesh) was 100 yen / kg or more, which was very expensive.

(Carrier production example 3)
In the vibrating screen shown in FIG. 1, two or more meshes represented by reference numeral (5) have the following configuration.
Specifically, a stainless steel mesh having a mesh size of 104 μm (150 mesh) was placed on the lower side, and a nylon mesh having a mesh size of 20 μm was adhered to the stainless steel mesh on the upper side. The material used for the nylon mesh (nylon-66) has a flexural modulus of 2.8 GPa.
The lower stainless steel mesh is directly subjected to vibration from the ultrasonic vibrator, but the nylon mesh is installed in close contact with the stainless steel mesh, so the ultrasonic vibration is transmitted efficiently and the particles to be classified are nylon mesh. Classified.

Using this vibrating screen, the carrier core material I shown in Table 1 was supplied on a nylon mesh at a rate of 0.5 Kg / minute, and subjected to classification treatment in exactly the same manner as in Carrier Production Example 2, thereby carrying the carrier core material. III was obtained.
As a result of classification, the ratio of particles less than 22 μm in the carrier core material could be greatly reduced. Table 1 shows the particle size distribution of the carrier core material III.
A resin-coated carrier C was obtained in exactly the same manner as in Carrier Production Example 1 except that this carrier core material III was used.
The particle size distribution of carrier C is shown in Table 2.
Nylon mesh showed almost no clogging of the mesh in a short time, but clogging gradually increased after long-term use.
After the 1500 kg treatment, it was necessary to clean the mesh. Nylon mesh can be washed and used, but the classification accuracy was lowered, so re-stretching was performed.
The classification cost associated with the replacement of the nylon mesh (no need to replace the lower stainless steel mesh) is one-tenth or less compared to the case of using the stainless steel mesh, and the cost is low.

(Carrier Production Example 4)
Except for using a polyester mesh having a mesh size of 21 μm, the carrier core material I shown in Table 1 is supplied on the polyester mesh at a rate of 0.5 Kg / min. Carrier core material IV was obtained.
As a result of classification, the ratio of particles less than 22 μm in the carrier core material could be greatly reduced. Table 1 shows the particle size distribution of the carrier core material IV.
The material used for the polyester mesh (polyethersulfone) has a flexural modulus of 2.6 GPa.
Further, a resin-coated carrier D was obtained in exactly the same manner as in Carrier Production Example 1 except that the carrier core material IV thus obtained was used. The particle size distribution of carrier D is shown in Table 2.
When this polyester mesh was treated with 2000 kg, it was necessary to clean the mesh.
The classification cost associated with the replacement of the polyester mesh (no need to replace the lower stainless steel mesh) was even lower than when the nylon mesh was used.

(Carrier Production Example 5)
The ultrahigh molecular weight polyethylene mesh having an opening of 20 μm was used as the upper mesh, and the carrier core material I in Table 1 was supplied at a rate of 0.25 kg / min. Classification treatment was performed on a molecular weight polyethylene mesh to obtain a carrier core material V. The reason why the supply speed of the carrier core material is lowered is that the mesh passing rate of the carrier core material (that is, work efficiency with respect to the classification time) is very poor.
The material used for the ultra high molecular weight polyethylene mesh (ultra high molecular weight polyethylene) has a flexural modulus of 0.9 GPa.
As a result of classification, the ratio of particles less than 22 μm in the carrier core material could be greatly reduced. Table 1 shows the particle size distribution of the carrier core material V.
Further, a resin-coated carrier E was obtained by the same method as in Carrier Production Example 1 except that the carrier core material V thus obtained was used.
The particle size distribution of carrier E is shown in Table 2.
This ultra high molecular weight polyethylene mesh was subjected to 2000 Kg, and it was necessary to clean the mesh.
The classification cost associated with the replacement of the ultra high molecular weight polyethylene mesh (no need to replace the lower stainless steel mesh) was higher than when the nylon mesh was used, but was lower than when the stainless steel was used.

(Carrier Production Example 6)
Except for using a 30% reinforced polyester mesh with a glass fiber having a mesh size of 21 μm (hereinafter abbreviated as GF), the carrier core material I shown in Table 1 was added to the GF 30% reinforced polyester mesh in the same manner as in Carrier Production Example 3. Classification was performed by supplying at a rate of 5 kg / min to obtain a carrier core VI.
The flexural modulus of the material used for the GF 30% reinforced polyester mesh (GF 30% reinforced polyethylene terephthalate) is 11.0 GPa.
As a result of classification, the ratio of particles less than 22 μm in the carrier core material could be greatly reduced. Table 1 shows the particle size distribution of the carrier core VI.
Furthermore, a resin-coated carrier F was obtained in exactly the same manner as in Carrier Production Example 1 except that the carrier core material VI thus obtained was used. Table 2 shows the particle size distribution of the carrier F.
This polyester mesh was subjected to 1200 Kg, and therefore it was necessary to clean the mesh.
The classification cost associated with the replacement of the GF 30% reinforced polyester mesh (no need to replace the lower stainless steel mesh) was higher than when the nylon mesh was used, but was lower than when the stainless steel was used.

(Carrier Production Example 7)
Classification treatment was performed in the same manner as in Carrier Production Example 3 except that the resin-coated carrier A prepared in Carrier Production Example 1 was used in place of the carrier core material I in Table 1, and a resin-coated carrier G was obtained.
Table 2 shows the particle size distribution of the carrier G.
Compared with the case of classifying the core material, the fluidity of the particles was better, and the mesh was less clogged than in the case of core material production example 3. However, when the 2000 kg treatment was performed, it was necessary to clean the mesh.

(Carrier Production Example 8)
In the vibrating screen shown in FIG. 1, as two meshes used for the mesh portion of two or more layers represented by reference numeral (5), the mesh is 104 μm (150 mesh) stainless mesh on the lower side, and the mesh is on the upper side. A 41 μm nylon mesh (NITEX41-HC manufactured by SEFAR (Switzerland)) was installed.
The carrier G prepared in Carrier Production Example 7 was classified in the same manner as Carrier Production Example 7 to obtain a resin-coated carrier H. Table 2 shows the particle size distribution of the carrier H.
However, the coarse powder side is the removed carrier, and the resin-coated carrier F is collected under the stainless steel mesh (5) in the cylindrical container (2).

(Carrier production example 9)
A resin-coated carrier I having a film thickness of 0.30 μm was obtained in exactly the same manner as in Carrier Production Example 1 except that the core material VII having an average particle diameter of 26.0 μm in Table 1 was used.
The particle size distribution of Carrier I is shown in Table 2.

(Carrier Production Example 10)
A carrier core material VIII was prepared in exactly the same manner as in Carrier Production Example 3 except that the core material VII in Table 1 was used and the carrier core material was supplied at a rate of 1 kg / min.
As a result of classification, the ratio of particles less than 22 μm in the carrier core material could be greatly reduced. Table 1 shows the particle size distribution of the carrier core material VIII.
Further, a resin-coated carrier J having a film thickness of 0.32 μm was obtained in exactly the same manner as in Carrier Production Example 1. Table 2 shows the particle size distribution of the carrier J.
When the 2000 kg treatment was performed, the mesh had to be cleaned, and therefore, re-stretching (replacement of the lower stainless mesh was unnecessary) was performed.
The classification cost associated with the mesh exchange was as low as one-tenth or lower compared with the case of using a stainless mesh.

(Manufacture and evaluation of developer)
Using 7 parts of toner a obtained in Toner Production Example 1 and 100 parts of Carrier A to Carrier J obtained in Carrier Production Examples 1 to 10, the developer was prepared by stirring for 10 minutes with a mixer.
An image was formed using the obtained developer, and the image quality (granularity) and carrier adhesion margin test were performed.
The image was created using Imagio Color 4000 (Ricoh Digital Color Copier / Printer Combined Machine) under the following development conditions.
Development gap (photosensitive member-developing sleeve): 0.35 mm
Doctor gap (Development sleeve-Doctor): 0.65mm
Photoconductor linear velocity 200mm / sec
(Developing sleeve linear velocity / photosensitive member linear velocity) = 1.80
Writing density: 600 dpi
Charging potential (Vd): -600V
Potential after exposure of the portion corresponding to the image portion (solid document) (V1): -150V
Development bias: DC component -500 V / AC bias component: 2 KHZ, -100 V to -900 V, 50% duty

The test methods employed in the following image forming examples are as follows.
(1) Uniformity of highlight portion: The granularity (brightness range: 50 to 80) defined by the following formula was measured on a transfer paper, and the numerical value was replaced with a rank as shown below.
Granularity = exp (aL + b) ∫ (WS (f)) ^1/2 VTF (f) df
L: Average brightness f: Spatial frequency (cycle / mm)
WS (f): Power spectrum of lightness fluctuation VTF (f): Visual spatial frequency characteristics a, b: Coefficient Rank ◎ (very good): 0 or more and less than 0.1 ○ (good): 0.1 or more and 0.2 Less than △ (usable): 0.2 or more and less than 0.3 × (unusable): 0.3 or more

(2) Carrier adhesion: If carrier adhesion occurs, it may cause damage to the photosensitive drum and the fixing roller, resulting in a decrease in image quality. Even if carrier adhesion occurs, only a part of the carrier is transferred to the paper, and therefore, evaluation was performed by transferring it from the photosensitive drum with an adhesive tape.
Create an image pattern of 2 dot lines (100 lpi / inch) in the sub-scanning direction, apply -400 V as a DC bias component, develop, and adhere to the number of carriers (area 100 cm2) attached between the 2 dot line lines The evaluation was carried out by transferring with a tape and visually observing the number.
The symbols in Table 3 are as follows.
◎: Very good ○: Good ×: Defect (unacceptable)

(3) Carrier manufacturing cost in the classification process ×: Cost comparable to stainless steel mesh ○: Lower cost than stainless steel mesh ◎: Very low cost

(4) Efficiency at the time of classification: Ranking was performed in consideration of both the amount of passage per unit time and the likelihood of clogging.
◎: Very good ○: Good △: Classification is easy but clogging is likely to occur ×: Very poor efficiency Table 3 shows the evaluation results of Examples 1 to 5 and Comparative Examples 1 to 5.

According to the present invention, it is possible to provide a method for efficiently producing a small particle size electrophotographic carrier having high image quality, particularly good granularity, hardly causing carrier adhesion, and having a sharp particle size distribution. An electrophotographic two-component developer can be obtained.

An explanatory structural view of a vibration sieving machine with an ultrasonic oscillator in the present invention is shown. It is a perspective view of the resistance measurement cell used for the measurement of the electrical resistivity of the carrier in this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Vibrating sieve machine 2 Cylindrical container 3 Spring 4 Base 5 Mesh of two or more layers 6 Resonant ring 7 Cable 8 Converter (vibrator)
9 Ring-shaped frame 11 Cell 12 Electrode 13 Carrier

Claims (21)

  A method of classifying particles for an electrophotographic carrier using a vibrating screen equipped with an oscillator including an ultrasonic vibrator, wherein at least two mesh materials are adhered to the ultrasonic vibrator as the vibrating screen. For the electrophotographic carrier supplied on the uppermost mesh material by transmitting the vibration received by the lower mesh material from the ultrasonic transducer to the upper mesh material. A method for classifying particles for an electrophotographic carrier, wherein the particles are classified.   2. The electrophotographic carrier according to claim 1, wherein the at least two mesh materials are one in which a mesh material having a small mesh is installed on the upper side and a mesh material having a large mesh is installed on the lower side. Particle classification method.   The method for classifying particles for an electrophotographic carrier according to claim 1 or 2, wherein a bending elastic modulus of at least one kind of mesh material having a small mesh installed on the upper side is 1 to 10 GPa.   2. The vibration sieving machine, wherein a resonance member is fixedly installed on a mesh material, transmits ultrasonic vibration to the resonance member to resonate, and then transmits it to the uppermost mesh material surface. The method for classifying particles for an electrophotographic carrier according to any one of.   5. The method for classifying particles for an electrophotographic carrier according to claim 1, wherein both the fine powder side and the coarse powder side of the particle size distribution are classified.   A vibratory sieving machine with an oscillator, which is used to classify particles for an electrophotographic carrier and has an ultrasonic vibrator, wherein at least two mesh materials are closely stacked on the ultrasonic vibrator. A vibration sieving machine for classifying particles for an electrophotographic carrier.   7. The electrophotographic carrier according to claim 6, wherein the at least two mesh materials are those having a mesh material with a small mesh on the upper side and a mesh material with a large mesh on the lower side. Vibrating sieve machine for particle classification.   8. The vibrating screen for classifying particles for electrophotographic carriers according to claim 6 or 7, wherein the bending elastic modulus of at least one kind of mesh material having a small mesh installed on the upper side is 1 to 10 GPa. Machine.   9. The electrophotographic carrier particle classification according to claim 6, wherein the resonance member is fixedly installed on the mesh material, and transmits the vibration of the ultrasonic vibrator to the resonance member to resonate. Vibrating sieve machine.   10. The vibration sieving machine for classifying particles for an electrophotographic carrier according to claim 6, wherein the upper mesh material is a resin.   11. The vibration sieving machine for classifying particles for an electrophotographic carrier according to claim 10, wherein the resin mesh material is knitted nylon yarn.   11. The vibration sieving machine for classifying particles for an electrophotographic carrier according to claim 10, wherein the resin mesh material is a knitted polyester yarn.   A method for producing a carrier core material for an electrophotographic developer, wherein the electrophotographic carrier particles are magnetic particles, and the classification method according to claim 1 is used as one of the steps.   A carrier core material for an electrophotographic developer obtained by the production method according to claim 13.   The electrophotographic carrier particle is a particle formed by forming a resin film on the surface of a magnetic particle, and the classification method according to claim 1 is one of the steps. A method for producing a carrier for developer.   The method for producing a carrier for an electrophotographic developer according to claim 14, further comprising a step of forming a resin coating on the surface of the magnetic particles to obtain the resin coating particles before the classification step.   An electrophotographic developer carrier obtained by the production method according to claim 15 or 16.   The weight average particle diameter Dw is 30 to 45 μm, the content ratio of particles having a particle diameter smaller than 44 μm is 70% by weight or more, the content ratio of particles having a particle diameter smaller than 22 μm is 7% by weight or less, and 18. The carrier for an electrophotographic developer according to claim 17, wherein a ratio Dw / Dp between the weight average particle diameter Dw and the number average particle diameter Dp is 1 to 1.30.   The weight average particle diameter Dw is 22 to 32 μm, the content of particles smaller than 36 μm is 90 to 100% by weight, the content of particles having a particle diameter smaller than 20 μm is 7% by weight or less, and the weight average particle diameter Dw The carrier for electrophotographic development according to claim 17, wherein a ratio Dw / Dp between the number average particle diameter Dp and the number average particle diameter Dp is 1-1.30.   An electrophotographic developer comprising a toner and a carrier, wherein the carrier for an electrophotographic developer according to any one of claims 17 to 19 is used as the carrier.   21. The apparatus according to claim 20, further comprising at least a photosensitive member, a charging unit that charges the surface of the photosensitive member, a developing unit, and a removing unit that removes the developer remaining on the surface of the photosensitive member. A process cartridge containing an electrophotographic developer.

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