JPH0287167A - Electrostatic image developing carrier and production thereof - Google Patents

Abstract

PURPOSE:To enable a resin for constituting a resin coating to be selected from a wide range and a carrier to be produced in a short time by adding to magnetic particles the resin particles having a particle diameter of <=1/200 of that of the magnetic particles, applying repeated impact forces to this uniform mixture, and coating the magnetic particles with the resin of the resin particles. CONSTITUTION:The magnetic particles are coated with the resin of the resin particles by adding to the magnetic particles having a weight average particle diameter of 10 - 200mum, the resin particles having a weight average particle diameter of <=1/200 of that of the magnetic particles, and applying repeated impact forces on this uniform mixture in a mixer setting the temperature of the mixture to the range of 50 - 110 deg.C, and at that time it is preferred for the magnetic particles to have a sphericity of >=0.7, and for the resin particles to have a BET specific surface area of >=30m<2>/g, thus permitting the carrier to be produced in a short time at high yield, superior in durability, and to exhibit stable high triboelectrifiability.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a carrier for electrostatic image development used in electrophotography, electrostatic recording, electrostatic printing, and the like.

[Background of the invention]

In general, in electrophotography, a uniform electrostatic charge is applied to a latent image carrier, i.e., a photoreceptor, which has a photosensitive layer made of a photoconductive material, and then image exposure is carried out to form an electrostatic latent on the surface of the photoreceptor. An image is formed, and this electrostatic latent image is developed with a developer to form a toner image. The formed toner image is transferred to a transfer material such as paper and fixed by heating or pressure to form a copy image.

Wet developing methods and dry developing methods are known as methods for developing electrostatic latent images. Of these, the developer used in the dry developing method is generally a magnetic toner containing a magnetic material in the toner. Two-component developers are known: a l-component developer consisting of only a magnetic substance, and a two-component developer consisting of a non-magnetic toner containing no magnetic material and a magnetic carrier.

The latter two-component developer triboelectrically charges the toner by mechanically stirring the toner and carrier.
By selecting carrier characteristics, stirring conditions, etc.
It is possible to control the charge polarity and charge amount of the toner to a considerable extent, and the range of colors that can be applied to the toner is wide, and in these respects it is superior to the former one-component developer.

As a carrier used in a two-component developer, a coated carrier in which the surface of magnetic particles is coated with a resin has been praised because it can improve the durability, triboelectric charging properties, etc. of the carrier.

The most commonly used coating carrier is a spray coating carrier obtained by spraying a coating solution in which a coating resin is dissolved in a solvent onto the surface of magnetic particles in a fluidized bed and then drying the coating solution. .

[Problems to be Solved by the Invention] However, in the above-mentioned spray coating technology, since a solvent is used, the carrier particles may fuse with each other.
As a result, the diameter of the carrier increases, and the yield of carrier having a desired particle size distribution decreases significantly. Furthermore, it requires a drying process, takes a considerable amount of time to manufacture the carrier, and has the problem of low productivity. Furthermore, as the resin coverage increases and the diameter of the magnetic particles decreases, productivity further decreases. On the other hand, as a means of improving productivity by shortening the time, it is possible to (1) increase the concentration of the coating resin in the coating solution, or (2) increase the number of spray nozzles.

However, in the case of (2) above, when the coating liquid adheres to the magnetic particles, it does not spread smoothly due to its high viscosity, resulting in an uneven coating, resulting in a decrease in the durability of the carrier. Furthermore, once magnetic particles come into contact with each other, they easily adhere and fuse, resulting in a significant decrease in carrier yield.

In addition, in the case of (2) above, there is a limit to the increase in the number of spray nozzles, and if the amount of coating liquid sprayed at a time increases, the fusion rate of the magnetic particles increases, resulting in the same problem as above. There is. On the other hand, in order to prevent fusion, some technologies include a mechanism called an agitator that applies shear force to the fluidized bed, but if the fused material is forcibly broken up by the agitator, the surface condition becomes rough and uneven. As a result, the durability of the carrier decreases.

Furthermore, spray coating requires a long coating time and requires recovery and incineration of the solvent, making it difficult to manufacture.

Further, the resin forming the coating layer is required to be soluble in a solvent, and the range of resin selection is narrow, which is an obstacle to selecting a resin with good film-forming properties.

Furthermore, when the solvent is evaporated, pores are generated on the carrier surface, making the carrier surface uneven.

In addition, it is easy to fuse, making it difficult to obtain a carrier with a particle size suitable for the purpose, and the yield is also poor.

In addition, some of the sprayed and scattered raw material is not used for layer formation, and the raw material is wasted, and this uncoated material becomes powder and electrostatically adheres to the carrier surface, preventing development. sometimes have a negative impact.

In response to this, a coaching technique that does not rely on spray coating has been developed (Japanese Patent Laid-Open No. 54-35735
No. 55-118047, No. 63-37358,
(See No. 63-37359, No. 63-37360, etc.)
.

The coating disclosed in these documents mechanically mixes a carrier core material and polymer particles, electrostatically encapsulates the surface of the carrier core material with the polymer particles to form a coating layer, and heats the extracted polymer particles. The resin layer is coated on the surface of the carrier core material by melting and fixing with a solvent or by melting and fixing with a solvent.

However, the above coating technology melts the resin included on the core material during immobilization, so the resin particles may adhere to each other, or the core material may adhere and fuse together through the resin particles, resulting in the formation of the desired particles. There is a problem in that the yield deteriorates because carriers with a diameter distribution are obtained.

In addition, since the surface of the core material is coated with a resin layer near or above the melting point, the cooling process takes time, and furthermore, a crushing process is required to loosen the blocked coated carrier and make it into single particles, which reduces production efficiency. Significantly decreased.

Furthermore, the obtained carrier is partially coated with resin, and there is a problem that charging stability at high temperatures is poorer than that of a carrier completely coated with resin.

Furthermore, since the core material is coated with a resin layer at a temperature close to or above the melting point of the resin, the resin may deteriorate, and an inert atmosphere must be created to prevent this from occurring, making the production equipment extremely complicated.

On the other hand, when the resin included on the core material is dissolved with a solvent, the range of resin selection is narrow, as in the case of spray coating described above. There are problems with solvent recovery, incineration, fusion, etc.

[Purpose of the invention]

The present invention solves the various problems mentioned above, and in producing a carrier having a resin coating layer, the first object of the present invention is to:
The resin constituting the resin coating layer can be selected from a wide range, and the resin coating layer can be firmly fixed, with no peeling, and is durable and has stable charge imparting properties over time. An object of the present invention is to provide a carrier for electrophotographic development.

The second object of the present invention is to eliminate the need for treatment such as solvent recovery,
Provides a carrier for electrostatic image development that can be produced in a short time using simple means, and that can obtain a carrier with a desired particle size distribution at a high yield without causing coalescence or pores. It's about doing.

A third object of the present invention is to reduce the occurrence of uncoated materials that do not contribute to coating, and thus to prevent problems caused by uncoated materials being released and electrostatically attached to the carrier surface. The purpose of the present invention is to provide a developing carrier.

A fourth object of the present invention is to provide a carrier for electrostatic image development that does not require a crushing step and can be produced in a short time, by simple means, and at a high yield.

A fifth object of the present invention is to provide a carrier for electrostatic image development that exhibits stable charging performance even at high temperatures and high humidity and is free from environmental dependence.

[Means to solve the problem]

The object of the present invention described above is that the weight average particle size is 10 to 200
The weight average particle size of the μm magnetic particles is 1/1/1 of the magnetic particles.
Less than 200 resin particles were added to form a homogeneous mixture, and impact force was repeatedly applied to the mixture in a mixer whose temperature was set within a range of 50 to 110°C, so that the magnetic particles were mixed with the resin particles. This is achieved by a method for producing a carrier for electrostatic image development coated with a resin material and a carrier for electrostatic image development based on the production method.

In the aspect of the present invention, it is preferable that the circularity of the magnetic particles is 0.7 or more. Furthermore, the resin particles are BE
It is preferable that the T specific surface area is 40 m2/g or more.

[Function and effect of the invention]

According to the carrier for electrostatic image development of the present invention, it can be produced by simple means in a short time and at a high yield, and exhibits excellent durability and stable triboelectric charging properties.

In other words, since the carrier can be obtained by dry coating using magnetic particles and resin particles of a specific particle size, processing such as washing and drying is not necessary, the time required for coating is significantly shortened, and ■ the fusion rate is reduced. As a result, the yield of carriers with a particle size distribution corresponding to the magnetic particles is high. In addition, it eliminates the need for processing equipment such as solvent recovery equipment and solvent combustion equipment, reducing production costs, increases the efficiency of coating magnetic particles with resin particles, and allows for efficient use of raw materials. Since the resin particles are attached and spread on the surface of the body particles, it has excellent peeling resistance and durability, and exhibits stable triboelectric charging properties, making it possible to use resins that are difficult to dissolve in solvents. As a result, the selection range of resins becomes much wider, and coated carriers having various properties can be obtained. ■Since the coating resin completely covers the surface of the carrier, stable triboelectric charging properties are exhibited even at high temperatures and high humidity, making it possible to obtain a coated carrier that is not dependent on the environment.

[Specific structure of the invention]

The present invention will be specifically explained below.

In a preferred embodiment of the present invention, magnetic particles having a weight average particle diameter of 10 to 200 μm and a circularity of 0.7 or more;
Weight average particle size is less than 1/200 of the magnetic particles, BET
By mixing and stirring resin particles with a specific surface area of 40a+''/g or more to obtain a uniform mixed state, and repeatedly applying impact force to this mixture, the resin particles are spread and adhered to the surface of the magnetic particles. Create a coating carrier.

The mixing weight ratio of magnetic particles and resin particles is: magnetic particles 1
The resin particles are used in an amount of 0.1 to 10 parts by weight, preferably 0.5 to 4 parts by weight.

The impact force applied to the mixture of magnetic particles and resin particles may be large enough not to crush the magnetic particles, for example, 115 to 1/2 of the mechanical energy normally required for crushing in toner production. An impact force of approximately 100 liters is sufficient.

If the weight average particle diameter is less than the lower limit of the range of 10 to 200 μm specified for magnetic particles, the coating carrier obtained will have a small diameter, and the carrier will easily adhere to the photoreceptor, resulting in deterioration of image quality.

On the other hand, when the upper limit is exceeded, the resulting coating carrier has a large diameter with a small specific surface area, and in order to impart appropriate triboelectric charging to the toner, strict control of the toner concentration is required, making the toner concentration control system expensive. In addition, it becomes difficult to support the coating carrier uniformly and at a high density on the developer carrier, and as a result, the amount of toner that adheres to the carrier and is transported to the development space becomes unstable, resulting in deterioration of developability and image quality. invite.

Materials for the magnetic particles include substances that are strongly magnetized in the direction of magnetic fields, such as iron, ferrite, magnetite, and other ferromagnetic metals such as iron, nickel, and cobalt, or alloys or compounds containing these metals. It is preferable to use

In addition, ferrite here is a general term for magnetic oxides containing iron, and is a ferrite represented by the chemical formula MO-Fe, 03. In the above chemical formula, M represents a divalent metal, and the specific represents nickel, copper, zinc, manganese, magnesium, lithium, etc.

It is preferable that the magnetic particles have a circularity of 0.7 or more. When such highly circular magnetic particles are used, the obtained coated carrier also has a high circularity and the fluidity of the carrier increases. As a result, it becomes possible to stably convey an appropriate amount of toner to the developing space, and more excellent developing performance is exhibited.

Here, the circularity is defined by the following formula.

Circularity = The circularity of 2 can be measured using, for example, an image analysis device (manufactured by Nippon Avionics).

The weight average particle diameter of the resin particles is based on the magnetic particles,
It is relatively less than 1/200, preferably less than 1/400, but practically 0.001-1 pm, preferably 0.01-0.15. Use resin particles with a BET specific surface area of 40 m"/g or more. When the weight average particle diameter of the resin particles exceeds 1.0 μm or the BET specific surface area does not reach 40 m2/H, the surface of the magnetic particles It is difficult to spread the resin particles, making dry coating processing difficult.Also, if the resin particles are less than 0.01 μm or the BET specific surface area is 6.
If it exceeds QOm''/g, the dispersibility deteriorates, uniform coating may not be achieved, and the yield may also decrease.

The material for the resin particles is not particularly limited, and various resins can be used. That is, in the present invention, non-solvent dry coating is possible, resins that are poorly soluble in solvents can also be used, and the range of resin selection is considerably widened. Specifically, resins such as styrene resin, acrylic resin, styrene-acrylic resin, vinyl resin, ethylene resin, rosin modified resin, polyamide resin, polyester resin, silicone resin, fluorine resin, etc. may be used. Can be done. These resins may be used in combination.

Among these, styrene-acrylic resins and acrylic resins can be particularly preferably used.

This styrene-acrylic resin is a resin obtained by copolymerizing a styrene monomer and an acrylic monomer. Specific examples of styrene monomers include styrene, 0-methylstyrene, l-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-butylstyrene. , p
-t-butylstyrene, p-hexylstyrene, p-octylstyrene, p-nonylstyrene, p-decylstyrene, p-F decylstyrene, p-methoxystyrene,
p-phenylstyrene, p-chlorostyrene, 3.4-
Examples include dichlorostyrene, and these monomers may be used alone or in combination.

Specific examples of acrylic monomers include acrylic acid, methyl acrylate, ethyl acrylate, butyl acrylate, isobutyl acrylate, propyl acrylate, octyl acrylate, dodecyl acrylate, lauryl acrylate, and diacrylic acid. - Acrylic acid or its esters such as ethylhexyl, stearyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, σmethyl chloroacrylate; methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, Methacrylic acid or esters such as isobutyl methacrylate, octyl methacrylate, dodecyl methacrylate, lauryl methacrylate, 2-ethylhexyl methacrylate, stearyl methacrylate, phenyl methacrylate, dimethylaminoethyl methacrylate, diethylaminoethyl methacrylate; others These monomers may be used alone or
A combination of a plurality of them may be used.

When obtaining the styrene-acrylic resin, the composition ratio of the styrene monomer and the acrylic monomer is preferably 9:1-1:9 by weight. The styrene component makes the coating film hard, and the acrylic component makes the coating tough. In addition, by appropriately changing these composition ratios, the amount of charge of the toner during frictional charging between the coating carrier and the toner can be controlled to a considerable extent.

The weight average particle diameter of the carrier is preferably within an appropriate range corresponding to the magnetic particles. That is, when the weight average particle diameter of the carrier is too small, the carrier tends to adhere to the photoreceptor, resulting in deterioration of image quality. On the other hand, when the weight average particle size is too large, the specific surface area becomes small, making it difficult to triboelectrically charge the toner appropriately, and also making it difficult to support the carrier uniformly and at a high density on the developer carrier. As a result, developability deteriorates.

Further, in order to obtain a carrier with uniform properties, it is preferable that the particle size distribution of the carrier is narrow.

The weight average particle diameter (〒W) of the magnetic particles is [Microtrac-Type 7981-OXJ (Leeds)
and Northrup (LEEDS & N0RTII
The weight average particle diameter (7w) of the resin particles was measured using "Coulter mode IN4 series" (manufactured by Coulter Co., Ltd.).

The electrostatic image developing carrier of the present invention can be produced, for example, by the following method.

That is, magnetic particles having a weight average particle diameter of 10 to 200 μI and resin particles having a weight average particle diameter of less than 1/200 of the magnetic particles and a BET specific surface area of 40 m''1 g or more are mixed, for example, with normal stirring. Mix uniformly by stirring using a device, etc., and adjust the temperature of the resulting mixture to 50% depending on the physical properties of the resin.
The surface of the magnetic particles is transferred to, for example, a high-speed stirring type mixer set within a temperature range of ~110°C, and the mixture is repeatedly subjected to impact force for 10 to 60 minutes, preferably 15 to 30 minutes. A coating carrier is obtained by spreading and adhering resin particles to the coating carrier.

At this time, if the product temperature is too high, the adhesiveness of the resin particles will increase, resulting in a phenomenon in which the particles of the resin particle powder agglomerate and become lumps, and magnetic particles may be bonded together and fused by the resin particles. This makes it difficult to uniformly adhere the resin particles to the surface of the magnetic particles.

〔Example〕

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples.

(Manufacture of toner) Polyester resin; 100 parts by weight, Carpon Platter; 10 parts by weight, and low molecular weight polypropylene; 3! ! Amounts of the mixture were mixed using a ball mill, kneaded, pulverized, and classified to obtain a toner having an average particle size of 11 μm.

(Preparation of developer) The carrier prepared in each example and comparative example and the above toner particles were mixed so that the content of toner particles was appropriate for each carrier particle size below, and the electrostatic latent image was formed. A developer was prepared.

(Preparation of carrier) Example 1 Cu-Zn-based ferrite carrier (weight average particle diameter rw 80 μm) 5000 parts by weight Methyl methacrylate/butyl methacrylate (weight composition ratio 8/2) copolymer (rvo, 06 μm) 100
Part by Weight The above materials were mixed for 15 minutes using a high-speed stirring type mixer to prepare an ordered mixture. After that, warm water was circulated through the mixer to bring the product temperature to 70°C, and the main stirring blade was rotated for 1 hour.
Coating was carried out for 5 minutes to obtain a coated carrier.

In addition, in the examples and comparative examples to be summarized, coated carriers were obtained under the same conditions as in Example 1 except for the conditions that are extracted and described.

Example 2 Cu-Zn ferrite carrier (rv 100 μm) 5000 parts by weight* MMA/HMA (8/2) (rvo, 06 μm
) 75 parts by weight (Note) * Methyl methacrylate/butyl methacrylate (8/2) copolymer Example 3 Iron powder carrier (rv100p+a) 5000
Weight part MMA/HMA (8/2XrwO, 06μm) Example 4 Mg-Cu-Zn ferrite carrier (rw45
MMA/HMA (8/2) (rwO, 06, um) Example 5 Cu-Zn ferrite carrier (rw80μm) 60 parts by weight 5000 parts by weight 125 parts by weight 5000 parts by weight MMA/HMA (8/20FvO010μIl)
Too weight part Example 6 Mg-Cu-Zn based ferrite carrier (rv45
μm) 5000 parts by weight MMA/
HMA (8/2XrwO,IO,um) 1
25 parts by weight Example 7 Cu-Zn ferrite carrier (rw 25 μm) 5000 parts by weight MMA/HMA (8/2) (rwO, 06 μm)
175 parts by weight Example 8 Cu-Zn ferrite carrier (rw 80 μm) 5000 parts by weight MMA/ * 5t (6/4) (7wO, 075t
t m) 100 parts by weight (Note) *Styrene Example 9 Cu-Zn ferrite carrier (rw 80 μm) 500
0 parts by weight silicone fine particles (rvO, 1 μm)
100 parts by weight Example 1O Cu-Zn ferrite carrier (rw 80 μm) 500
0 parts by weight Tetrafluoroethylene resin fine particles (rwo, 2 μm) 15
0 parts by weight Example 11 Cu-Zn ferrite carrier (rw 80 μm) 5000 parts by weight Trichloromethyl methacrylate fine particles (rwo,
08 μm) 125 parts by weight Comparative example (1) Cu-Zn ferrite carrier (rw100 μm) 500
0 parts by weight MMA parts by weight (25/75) (rvO, 5μ!
l) 75 parts by weight Comparative example (2) Same composition as Example 1, temperature 120° O1:up Comparative example (3) Mg-Cu-Zn based ferrite carrier (rw44
μm) 5000 parts by weight! i1
MA(rwO,4,um)
150 parts by weight Comparative example (4) Cu-Zn ferrite carrier (rv80.um) 500
0 parts by weight MMA/HMA (8/2XrwO,06,u
m) 100 parts by weight Table 1 shows various matters related to the coated carriers obtained in the above Examples and Comparative Examples.

The conditions and methods for measuring characteristics are as follows.

1. Product Particles obtained by inserting a temperature measurement probe into a particle group in which resin particles are attached to a thermocore material and flowing under an impact force, and randomly bringing the particles into contact with the probe. The approximate average surface temperature of The temperature measurement probe is composed of a thermocouple, a resistance temperature detector, etc., and can measure temperature by electrically measuring its electromotive force, resistance value, etc. Examples of thermocouples include chromel-alumel thermocouples.

In the present invention, the temperature of the product is measured by length lOc+a, diameter 6
．． A chromel-alumel thermocouple (manufactured by Hayashi Denko Co., Ltd.) with a 4+++m stainless steel (SUS304) cover is used, and its end is inserted 5 cm.

2. Method for measuring white powder amount 20 g of coating carrier and 15 mff of methanol were placed in a 20+S12 sample tube, stirred for 10 minutes with a wave rotor (rotation speed 46 rpm), and the supernatant liquid was measured with a photoelectric colorimeter (wavelength 522 ns). The transmittance was determined by placing it in a dedicated cell and measuring its transmittance.

3. Measuring method for (Fe”) 0.2% in 0.001% acetic acid aqueous solution 9IIIQ, 2.2
- A solution containing dipyridyl ethanol coloring reagent 1Il12 and a surfactant and coating carrier Ig at 20%
Put it in a sample bottle and turn it into a wave rotor (rotation speed 46).
rpw+) for 2 minutes. The supernatant liquid is put into a special cell of a photoelectric colorimeter (wavelength: 522 nm), and its transmittance is measured. The absorbance (log〒) is calculated from the transmittance T, and is obtained by multiplying it by the calibration curve 7 actors.

(F e "") -1og T

5. BET specific surface area measurement using Micromeritics F0-Soap ■2300
This was done using a mold (manufactured by Takasu Seisakusho).

6. The fusion rate is 1. It was calculated from the amount of coated carrier that passed through the mesh after sifting Okg of coated carrier using a predetermined sieve.

80 meshes for 100 μm carrier, 100 meshes for 80 μm carrier, 200 meshes for 45 μm carrier (Evaluation of triboelectricity of toner) Using each of the above developers, under high temperature, high humidity environmental conditions and low temperature, low humidity environmental conditions. The amount of triboelectric charge of the toner was measured.

However, the weight average particle diameter of the magnetic particles is 60. For developers that are combined with a carrier that exceeds um, the amount of triboelectric charge of the toner is measured by a known blow-off method, and for a developer that is combined with a carrier that has magnetic particles with a weight average particle size of 60 μm or less, the amount of triboelectric charge of the toner is measured by the actual development process. The triboelectric charging properties of the toner were measured. The results are shown in Table 2.

(Actual photocopying test 1) Using the above developer Examples 1 to 9 and Comparative Examples (2) to (4), an electrophotographic copying machine "υ" equipped with a contact type developer was used.
- A photocopying test was conducted in which a copy image was formed using Bix5500J (Konica Group), and the following items were evaluated. The results are shown in Table 3.

However, the distance between the drum and the sleeve and the distance between the doctor blade and the sleeve in the development conditions were set to appropriate conditions depending on the particle size of each carrier.

In addition, the above Examples to and tt are an electrophotographic copying machine rU-Bix1550J (
A live-action test was conducted and evaluated by the Konica family.

As can be understood from the results of the above examples, this is an example of the present invention! According to No. 11, carriers can be obtained in a short time and with a high yield using simple means, and in live-action tests, it has excellent durability and stable triboelectric charging properties, and does not cause carrier adhesion. It is possible to maintain appropriate toner density and form images of good quality with excellent phenomenon properties.

In addition, since the carrier surface is completely coated with resin, there is no environmental dependence, and a uniform and strong coating layer is obtained, allowing stable performance at high temperatures, high humidity, and low temperatures and low humidity. .

Furthermore, the time required to prepare the coating carrier is short, and even if the coverage changes, the coating time will not become longer just by changing the mixing ratio.

Claims (3)

[Claims] (1) Add resin particles with a weight average particle size of less than 1/200 of the magnetic particles to magnetic particles with a weight average particle size of 10 to 200 μm to form a homogeneous mixture, and adjust the product temperature to a range of 50 to 110°C. A carrier for electrostatic image development, wherein the magnetic particles are coated with the resin material of the resin particles by repeatedly applying impact force to the mixture in a mixer set in the mixer. (2) The carrier for electrostatic image development according to claim 1, wherein the magnetic particles have a circularity of 0.7 or more. (3) Add resin particles with a weight average particle size of less than 1/200 of the magnetic particles to magnetic particles with a weight average particle size of 10 to 200 μm to form a uniform mixture, and keep the product temperature at 50 to 110°C.
A method for producing a carrier for electrostatic image development, comprising repeatedly applying an impact force to the mixture in a mixer set within a width of 10 to 10, to coat the magnetic particles with the resin material of the resin particles.