JP2644549B2 - Resin-coated carrier for two-component developer and method for producing the same - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resin-coated carrier for a two-component developer, which constitutes a two-component developer together with a toner, and a method for producing the same.

(Prior art)

U.S. Pat. No. 2,297,691 describes one of the basic methods as electrophotography. Further, this type of system is disclosed, for example, in US Pat. No. 2,277,013, US Pat.
No. 57,809, 2,551,582, 3,220,324, and 3,220,833. Various other electrophotographic methods are described in JP-B-42-23910 and JP-B-43-24748. In each of these methods, an electrostatic latent image is formed by irradiating the photoconductive layer with a light image corresponding to the original, and then the opposite polarity (in the case of the reversal development method, The electrostatic latent image is developed by attaching a toner (colored fine powder) having the same polarity), and a toner image is transferred to a transfer material such as paper as necessary, and then heat, pressure, heat pressure, or solvent vapor is applied. And the like to obtain a copy.

In the step of developing the electrostatic latent image, toner particles charged to a polarity opposite to that of the latent image are attracted by electrostatic attraction and adhered on the electrostatic latent image. As a method of developing an image using toner, there are roughly two methods: a so-called two-component developer in which a small amount of toner is dispersed in a medium called a carrier, and a so-called one-component developer in which the toner is used alone without using the carrier. Is used.

As a developing method using a two-component developer, a cascade developing method described in U.S. Pat.
The magnetic brush development described in 2,895,847 and U.S. Pat. No. 3,590,000 are known.

Carriers used for developing electrostatographic images are broadly classified into conductive carriers and insulating carriers. As the conductive carrier, usually, oxidized or unoxidized iron powder is used, but in a developer containing iron powder carrier as a component,
There is a problem in that the triboelectric charging property with respect to the toner is unstable, and that a visible image formed by the toner is liable to fog. That is, with the use of the developer, toner particles adhere to the surface of the iron powder carrier particles, so that the electrical resistance of the carrier particles increases, the bias current decreases, and the triboelectric charging characteristics become unstable, resulting in formation of the toner. This is because the image density of the visible image decreases and fog increases.

On the other hand, a typical example of the insulating carrier is a carrier in which the surface of a carrier core material made of a ferromagnetic material such as iron, nickel, or ferrite is coated with an insulating resin. As such a carrier coating material, a material having good triboelectric charging characteristics with respect to toner is generally used. Further, the carrier coating has a certain hardness mainly for satisfying the durability, but is preferably a material which does not damage the surface of the photoconductor forming the electrostatic image. In addition, the force on the carrier during recovery must avoid flaking off of the surface and breaking up of the particles leading to undesired results. For example, a carrier should be selected that does not cause the carrier to migrate onto the copy latent image and degrade the quality of the final image (hereinafter referred to as carrier adhesion). That is, a carrier coating material having excellent adhesion and coating properties to the carrier core material should be selected.

Further, as a condition required for the carrier coating material, a material that does not fuse the toner to the carrier surface, that is, a carrier surface having releasability from the toner material is required.

The importance of carrier coatings has been emphasized in various development techniques. A decrease in the carrier coverage results in non-uniformity and instability of the charge application characteristics of the carrier to the toner, and as a result, it is impossible to achieve a good charge state of the toner particles.

In recent years, attempts have been made to reduce the particle size of the toner and the carrier in order to improve the resolution, gradation reproducibility, and high image quality of the image surface obtained with such a two-component developer. That is,
For example, 60μ instead of a large particle size carrier of 80-500μm
m and a small particle size carrier
Although a two-component developer having a particle diameter of 10 μm or less has been studied, carrier adhesion due to the reduction in the particle size of the carrier, toner scattering due to deterioration of the charge imparting ability of the carrier to the toner,
The problem of image fogging is getting closer.

Various studies have been made on the coating properties of the resin on the carrier core material, depending on the coating material. However, in practice, the production stability cannot be obtained, and lottery tends to occur. This is a result of the fact that a coating material with an emphasis on the releasability of the toner is used and the production stability of the carrier core material is not taken into consideration.

The present invention has been developed in order to solve the above problems, by combining a carrier coating material in consideration of the wettability of the carrier core material surface and ultra-fine powder removal of the carrier core material that also causes poor coating, An object of the present invention is to provide a resin-coated carrier in which the carrier coverage is improved, and a lottery in carrier production is avoided or suppressed, and a method for producing the same.

[Object of the invention]

An object of the present invention is to provide a resin-coated carrier for a two-component developer which overcomes the above-mentioned problems.

An object of the present invention is to provide a carrier coated with a carrier coating material for a two-component developer having excellent adhesion to a carrier core material and exhibiting excellent release properties to toner. is there.

SUMMARY OF THE INVENTION An object of the present invention is to provide a carrier for a two-component developer which is excellent in charge imparting characteristics to a toner and has excellent durability without causing carrier adhesion or the like.

It is a further object of the present invention to provide a method for producing a carrier for a two-component developer having the above-mentioned characteristics, being stable in quality, and having little rotting.

[Summary of the Invention]

In the present invention, the magnetic carrier core material has a weight average particle size of 25 to
60% by weight or more of particles having a weight average particle diameter of ± 10 μm having a particle diameter of 100 μm, and containing less than 5% by weight of particles having a particle diameter of not less than the weight average particle diameter + 30 μm; 1 /
The particles having a particle size of less than 10 has a by which particle size distribution containing 2% by weight or less, the magnetic carrier core material, electrically insulating the critical surface tension of less than 30 dyn / cm Resin R ₁ and the critical surface tension But
30 dyn / cm is coated with a more mixed composition of the electrically insulating resin R _2, mixing weight ratio of the resin R ₁ and the resin R ₂ is 5: 5
The present invention relates to a resin-coated carrier for a two-component developer, which has a ratio of 1: 9.

Further, the present invention has a weight average particle diameter of 25 to 100 μm, contains 60% by weight or more of particles having a weight average particle diameter of ± 10 μm, and contains particles having a weight average particle diameter of 30 μm or more. A magnetic carrier core material having a particle size distribution containing less than 5% by weight and containing particles having a particle size of less than 1/10 of the weight average particle size of 2% by weight or less is prepared by classification, and the prepared magnetic carrier core material mixture composition of the electrically insulating critical surface tension of less than 30 dyn / cm resin R ₁ and critical surface tension 30 dyn / cm or more electrically insulating resin R ₂ (weight ratio 5: 5 to 1: 9) The present invention relates to a method for producing a resin-coated carrier for a two-component developer, which is characterized by performing a coating treatment with a resin.

[Specific description of the invention]

The method for producing a carrier of the present invention preferably comprises removing the fine and ultrafine powder of the carrier core by wind classification after ferrite firing-disintegration-sieving (removal of coarse powder and fine powder by mesh filtration) of the carrier core. It is a feature.

That is, according to the study of the present inventors, at the time of ferrite firing-crushing of the carrier core material, the weight average particle diameter aμ is 1 /.
Fine and ultrafine powders having a particle size of 10 or less are produced. These fine powders and ultrafine powders themselves have a high cohesive strength and cannot be completely removed by the usual sieving, and are mixed in 3% by weight or more (usually 3 to 6% by weight) of the total amount. The mixture of the fine powder and the ultrafine powder in the carrier core material causes poor coating of the insulating resin, and further hinders the increase in the resistance of the carrier. That is, the tribo-imparting ability for the toner is reduced, and it is not possible to impart a good charge state to the toner particles.

Further, when a latent image is formed, adverse effects such as the above-described adhesion of the carrier occur.

On the other hand, by removing such ultrafine powder, the resin coat of the carrier core material can be made uniform and the production quality can be stabilized.

As a means for removing ultrafine powder, air classification is the most efficient and can be performed at low cost.

In the present invention, the weight average particle size and the particle size distribution of the carrier core particles refer to values measured using, for example, a microtrack (model 7995) manufactured by Nikkiso Co., Ltd.

Weight average particle size of magnetic carrier core particles is 25-100μ
m, preferably 30 to 80 μm. 25μ weight average particle size
If it is less than m, the carrier easily adheres to the electrostatic image carrier such as the photosensitive drum. When the weight average particle size exceeds 100 μm, it is difficult to uniformly apply a triboelectric charge to the toner, the amount of the toner taken in decreases, the development efficiency decreases, and the image quality (resolution) decreases. In the present invention, the carrier core particles after classification have a weight average particle diameter aμ.
The content of fine or ultrafine core particles having a particle size smaller than 1/10 is 2% by weight or less, preferably 1% by weight
The following is good.

Further, it is preferable that the core material particles have a particle size distribution of 60% by weight or more, preferably 65% by weight or more in a range of ± 10 μm of the weight average particle diameter aμ, and have a sharp particle size distribution. Weight average particle size aμ
When the core material particles are less than 60% by weight in the range of ± 10 μm, the two-component developer prepared by mixing with the toner may not be used for the carrier having a coarse particle size and the carrier having a small particle size. A difference occurs in the ability to apply a triboelectric charge, the charge amount of the toner becomes non-uniform, and the developing characteristics, fine line reproducibility and durability decrease. Further, the content of the carrier core particles having a particle diameter of +30 μm or more of the weight average particle diameter aμ is preferably less than 5% by weight. When the amount of the coarse particles is 5% by weight or more, the ability to impart a triboelectric charge to the toner becomes uneven,
Fogging and carrier adhesion are likely to occur.

As the material of the carrier core material used in the present invention, a substance which is strongly magnetized in its direction by a magnetic field, for example, a ferromagnetic metal such as ferrite, magnetite, iron, cobalt, nickel, or an alloy containing these metals Alternatively, an alloy that does not contain a compound or a ferromagnetic element but becomes ferromagnetic when appropriately heat-treated may be used. The carrier core particles preferably have a spherical shape as shown in the accompanying drawings in view of development characteristics and fluidity.

As a method for removing the ultrafine powder from the carrier core material, an ordinary air classifier can be used after sieving. More preferably, it is preferable to use a DS classifier which has good productivity and can easily change the classification point.

Using the above air classifier, fine powder or ultrafine powder having a weight average particle size of 1/10 or less of the carrier core material is removed until it becomes 2% by weight or less, more preferably 1% by weight or less of the total amount.

The second feature of the present invention is that the insulating resin coating the classified carrier core particles has a critical surface tension.
It consists of a mixture of the insulating resin R ₁ of less than 30 dyn / cm and the insulating resin R ₂ of 30 dyn / cm or more, and the ratio of the resin R ₁ to R ₂ (R ₁ : R ₂ ) is 5: 5.
~ 1: 9. By selecting the above-mentioned carrier coating material, the adhesive strength to the carrier core material, the mechanical strength, the coating property can be increased, and the carrier particles and the toner particles can have releasability.

That is, by the resin R ₁ below critical surface tension 30 dyn / cm is present on the carrier surface, keeping the releasability of the toner, the toner adheres to the carrier surface, the deterioration prevention of the charge-imparting ability to toner carrier plays and a critical surface tension 30 dyn / cm or more resins R ₂ provides a carrier having a mechanical strength having adhesion to the carrier core particles.

Generally, in the process of applying the resin mixture of the present invention to the carrier core particles and removing the solvent, polymer phase separation occurs.In the vicinity of the carrier core, the critical surface tension is large, that is, the carrier core is wettable. there good resin R ₂ is Ritsuchi of, whereas, in the vicinity of carrier surface, the critical surface tension small resin R ₁ is likely to exist in Ritsuchi.

The present invention is characterized by easily providing a resin-coated carrier having the above-described carrier characteristics by selecting a material based on a measure of the wettability of the resin, namely, the critical surface tension of the carrier-coating material.

Resin R ₁ below critical surface tension 30 dyn / cm is reduced adhesion between the carrier core particles exceeds 50 wt%, from defects in the coating property is lowered carrier coating carrier, the frictional charging characteristics of the carrier particles Adversely affect

On the other hand, the resin R ₁ below critical surface tension 30 dyn / cm is 10% by weight
If it is less than 1, the resin-coated carrier surface does not become a low-energy surface, and toner adheres and fuses on the carrier surface,
The ability to impart charge to the toner is reduced, causing a reduction in image density and fogging.

As described above, the present invention is characterized by providing a carrier without rotting and having excellent carrier coverage by combining the removal of ultrafine powder from the carrier core material and the use of a mixture of at least two types of coating resins having different wettability. And

The carrier core particles obtained by removing the fine powder and ultrafine powder obtained as described above are then coated with an insulating resin.

In the present invention, the insulating resin has a volume resistance value of 10 ¹² Ω.
Cm or more, preferably 10 ¹³ Ω · cm or more.

The insulating resin that coats the carrier core particles is
Consist of a mixture of the resin R ₁ and 30 dyn / cm or more resins R ₂ less than the critical surface tension of 30 dyn / cm, more preferably it is preferred critical surface tension of the resin R ₁ is less than 28 dyn / cm. Resin R ₁ with a critical surface tension of less than 30 dyn / cm giving a low energy surface
It is preferable to use a fluorine resin or a silicon resin as shown below.

As the fluorine resin, polyvinyl fluoride (critical surface tension γ
_c = 28 dyn / cm), polyvinylidene fluoride (γ _c = 25 dyn / c)
m), polytrifluoroethylene (γ _c = 22 dyn / cm),
Those having a critical surface tension of 30 dyn / cm or less, such as polytetrafluoroethylene (γ _c = 18 dyn / cm) and polyhexafluoropropylene (γ _c = 16.2 dyn / cm), can be used. In addition, copolymers of vinylidene fluoride and acrylic monomer, copolymers of vinylidene fluoride and vinyl fluoride, copolymers of vinylidene fluoride and tetrafluoroethylene, vinylidene fluoride and hexafluoro Resins having a critical surface tension of less than 30 dyn / cm such as copolymers with propylene, fluoroterpolymers such as terpolymers of tetrafluoroethylene with vinylidene fluoride and non-fluorinated monomers can be used. These resins is less than the critical surface tension of 30 dyn / cm, it can be used as the resin R ₁ individually or in combination.

The resin R ₂ larger than the critical surface tension of 30 dyn / cm combined with the resin R ₁ below critical surface tension 30 dyn / cm, there is a resin synthesized from the following such monomers. For example, styrene, p
Styrene such as chlorostyrene and p-dimethylamino-styrene and substituted products thereof; acrylic acid or methacrylic acid such as methyl acrylate, ethyl acrylate, butyl acrylate, butyl methacrylate, methacrylic acid N, N dimethylaminoethyl ester Esters of maleic acid; half-esters and half-amides of maleic anhydride; nitrogen-containing vinyls such as diesteroid vinylpyridine and N-vinylimidazole; vinyl monomers such as vinyl chloride, acrylonitrile and vinyl acetate; vinylidene monomers such as vinylidene chloride; ethylene and propylene Such as olefin monomers.

To partially exemplify the critical surface tension of a resin comprising the above monomer, polystyrene has γ _c = 33 dyn / cm, polymethyl methacrylate has γ _c = 39 dyn / cm, and polyvinyl chloride has γ _c = 39 dyn / cm, polyvinylidene chloride has γ _c = 40 dyn / cm, and polyethylene has γ _c =
It is 31 dyn / cm.

In addition, polyester, polysulfonate, polyamide, polyurethane, polycarbonate, polyurea, epoxy resin, rosin, modified rosin, terpene resin, phenol resin, fatty acid or alicyclic hydrocarbon resin, aromatic petroleum resin, melamine resin, poly polyether resins such as phenylene oxide or may be used as long as a homopolymer or copolymer or a critical surface tension of the thioether resin 30 dyn / cm or more mixtures thereof as the resin R _2.

Wire carrier ratio of the rear quotes queuing resin R ₁ and the resin R ₂ is preferably 5: 5 to 3: 7 in the range of.

The carrier coating method of the present invention includes an immersion method,
Spray method and fluidized bed method are preferred. Any organic solvent can be used as long as it dissolves the resin, but a mixed solvent of a good solvent and a poor solvent can be used.

The carrier of the present invention is manufactured through a resin coating, followed by a heat drying or curing step.

The coating amount of the insulating resin on the carrier core particles of the present invention is sufficient to form at least a substantially continuous resin film on the surface of the carrier core particles. % By weight, preferably 0.5 to 3% by weight.

As the toner used as a two-component developer in combination with the carrier of the present invention, any triboelectric toner commonly used in electrophotography in which a colorant or a charge control agent is dispersed in a binder resin is used. can do.

Further, other additives (charge control agent, fluidity imparting agent, etc.) can be added to the toner as needed. Examples of the binder resin of the toner used as a two-component developer in combination with the carrier of the present invention include polystyrene, poly p-chlorostyrene, polyvinyl toluene, styrene-p-chlorostyrene copolymer, and styrene-vinyltoluene copolymer. Styrene-vinyl naphthalene copolymer, styrene-ethyl acrylate copolymer, styrene-butyl acrylate copolymer, styrene-octyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate Copolymer, styrene-acryl-
Aminoacrylic copolymer, styrene-aminoacrylic copolymer, styrene-α-chloromethyl methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-vinylmethylether copolymer, styrene-vinylethylether copolymer Polymer, styrene-vinyl methyl ketone copolymer, styrene-butadiene copolymer, styrene-isoprene copolymer, styrene-acrylonitrile-indene copolymer, styrene-maleic acid copolymer, styrene-maleic acid ester copolymer, etc. Styrene copolymer, polymethyl methacrylate, polybutyl methacrylate, polyvinyl chloride, polyvinyl acetate, polyethylene, polypropylene, polyester, polyurethane,
Polyamide, epoxy resin, polyvinyl butyral, polyacrylic acid resin, terpene resin, phenol resin, aliphatic or alicyclic hydrocarbon resin, aromatic petroleum resin, chlorinated paraffin, paraffin wax, etc., alone or as required Can be used in combination of two or more.

In the toner, any appropriate dye or pigment can be used as a colorant. For example, known dyes and pigments such as carbon black, iron black, phthalocyanine blue, ultramarine, and quinacridone benzidine yellow are used.
As charge control agents, amino compounds, quaternary ammonium compounds and organic dyes, especially basic dyes and salts thereof,
Benzylmethyl-hexadecylammonium chloride, decyltrimethylammonium chloride, nigrosine base, nigrosine hydrochloride, safranin γ
And crystal violet, and further, a gold-containing monoazo dye, a gold-containing disazo dye, a metal salicylate chelate, or the like may be added.

As described above, the composition of the toner is a general mixing-
The toner may be used for a toner obtained by a pulverization method, or may be used for a wall material and / or a core material of a microcapsule toner.

〔The invention's effect〕

According to the present invention, the carrier core particles from which fine powder and ultrafine powder have been removed by air classification are used, and the carrier core particle surfaces have different wettability (critical surface tension of 30 dyn / cm or less 30).
(dyn / cm or more) The following various effects can be achieved based on the resin coating.

First, the toner has excellent charge-imparting properties and does not adversely affect images such as carrier adhesion and fog.

Second, since the carrier coating material is excellent in adhesiveness to the carrier core particles and excellent in releasability from the toner and does not cause contamination by the toner, it has excellent durability and long life.

Third, to introduce a very easy and inexpensive process of wind classification of carrier core materials.

Further, by using a coating resin having good wettability with respect to the carrier core particles within a certain range, it is possible to prevent the production blur of the carrier and to stabilize the production.

Hereinafter, the present invention will be described more specifically with reference to Examples, but the present invention is not limited thereto.

Example 1 A ferrite raw material containing Fe ₂ O ₃ and ZnO as main components was granulated, dried and then fired to produce a spherical magnetic ferrite carrier core material. The agglomerates of the carrier core material are crushed and sieved to have a weight average particle size of 52 μm, containing 67% by weight of particles having a weight average particle size of 52 ± 10 μm, and preparing particles having a particle size of 82 μm or more of 1.2%.
A weight of the carrier core material was obtained.

However, as can be seen from the SEM photograph of FIG. 2, ferrite fragments (fine powder and ultrafine powder) having a weight average particle diameter of 1/10 or less were present.

This fine powder and ultrafine powder are 4% by weight of the total amount of the carrier core material.
Existed.

The above carrier core was subjected to air classification using a DS classifier to obtain spherical magnetic ferrite carrier core particles having a weight average particle diameter of 53 μm. The core material particles have a content of particles of less than 5.3 μm of 0.3% by weight, 68% by weight of particles in the range of 43 to 63 μm, and a content of particles of 83 μm or more of 1.1%.
% By weight. The spherical magnetic ferrite carrier core particles obtained by the classification did not substantially contain fine powder and ultrafine powder, as is clear from the SEM photograph shown in FIG.

A critical surface tension of 30 dy is applied to the carrier core material thus obtained.
As a resin R ₁ of less than n / cm, a copolymer of vinylidene fluoride and tetrafluoroethylene (γ _c = 21.5 dyn / cm, volume resistivity = 10 ¹⁶ Ω · cm) and a critical surface tension of 30 dyn / cm or more As the resin, a styrene-methyl methacrylate resin (γ _c =
35.8 dyn / cm, volume resistivity = 10 ¹⁵ Ω · cm) were mixed at a weight ratio of 4: 6, and a coating solution dispersed and dissolved in methyl ethyl ketone was sprayed and coated with the carrier core particles in a fluidized bed state. After coating, at ambient temperature 150 ° C for 3 hours,
Heat treatment was performed to obtain a resin-coated carrier.

On the other hand, a positively chargeable toner having a weight average particle size of 8.7 μm was prepared from 98 parts by weight of a styrene-butyl methacrylate copolymer, 2 parts by weight of nigrosine, and 2 parts by weight of a low molecular weight polyalkylene, and 100 parts by weight of the positively chargeable toner was prepared. 7 parts by weight of 1 part by weight of a hydrophobic positively charged colloidal silica treated with an amino-modified silicone oil and 100 parts by weight of a resin-coated carrier were mixed to prepare a two-component developer. The resulting two-component developer was supplied to a developing machine of a Canon copier NP5000 (having a negatively charged OPC photoreceptor and applying an AC bias in a developing area) to obtain a copied image.

The resulting copied images all had excellent image quality without fogging, and no carrier adhesion was observed on the OPC photoreceptor.

In addition, as a result of observing the surface of the resin-coated carrier after the endurance of 100,000 copies with an electron microscope, no damage to the carrier and no toner adhesion were observed, and the copy image quality was good.

In addition, the variation of the charge amount of the developer due to the durability was small, and it was found that the developer was also excellent in this respect.

Example 2 In order to investigate the carrier production stability, a carrier was prepared five times in the same manner as in Example 1, and the same evaluation was performed.

As a result, the physical properties of this carrier
It almost disappeared, and it became clear that a good image was obtained as in Example 1.

In particular, it has been found that stabilization of the resistance value of the carrier and stabilization of the ability to impart charge to the toner are achieved. The carrier current was measured by the magnet brush method (calculated from the voltage drop due to a 500 V load, see FIG. 3). As a result, the carrier current value was in the range of 11 to 18 μA (see FIG. 4).

Comparative Example 1 A resin-coated carrier was prepared in the same manner as in Example 1 except that fine powder and ultrafine powder (fragment of the carrier core material) were not removed by air classification.

A two-component developer was prepared in the same manner as in Example 1, and an image-drawing test was performed. As a result, carrier adhesion occurred.

Further, the charge amount of the developer was unstable before and after image formation and was unstable.

Comparative Example 2 In order to examine the production stability of the carrier, the carrier was prepared five times in the same manner as in Comparative Example 1, and the same evaluation was performed.

As a result, the production of this carrier (no removal of ultrafine powder)
As for the fluctuation of the physical properties due to the above, the obtained image evaluation also fluctuated greatly.

In particular, the carrier resistance fluctuates greatly in the direction of decreasing,
The result was a lack of stability in carrier manufacturing.

When measured in the same manner as in Example 2, the current value of the carrier increased. That is, the tendency of the resistance value to decrease was measured, which suggested that the carrier coat lacked uniformity (see FIG. 4).

Comparative Example 3 The critical surface tension used as a carrier coat material was 30 dyn /
A resin-coated carrier was prepared in the same manner as in Example 1 except that the ratio of the resin having a size of less than 30 cm to the resin having a size of 30 dyn / cm or more was 6: 4. The resulting carrier had carrier particles having defects in the film, and the coating state was uneven.

The image obtained as a result of image formation also caused fogging. In addition, the carrier after 100,000 sheets had been used, the carrier film was damaged, and the copy image quality and density were reduced.

Comparative Example 4 In order to examine the production stability of the carrier, the same carrier as in Comparative Example 3 was prepared five times, and the same evaluation as in Example 2 was performed.

As a result, the physical properties of the carrier were largely varied, and the obtained image evaluations varied greatly. Particularly, the carrier resistance greatly fluctuated in the decreasing direction, resulting in a lack of stability in carrier production (see FIG. 4).

As is evident from FIG. 4, reduction of carrier rotting by combining removal of fine powder and ultrafine powder (fragment) of the carrier core material by air classification and coating of resin having different wettability at a certain ratio. A possible effect was shown.

Here, a method of measuring a carrier current value by the magnet brush method in the present invention will be described in detail with reference to the drawings.

FIG. 3 is a circuit diagram of a method for specifying a carrier measurement value by the magnet brush method. A carrier magnet brush is formed on the magnetic sleeve 1 and the distance between the aluminum drums 2 is set to 1 mm.
Then, a voltage of 500 V is applied to the circuit of FIG. At this time, the voltage applied to the circuit including the 1 MΩ resistor is measured by the voltmeter 3, and the current value is calculated from the voltage drop at this time.

[Brief description of the drawings]

FIG. 1 shows an electron micrograph showing the metallographic structure surface of the ferrite carrier core material particles after classification in Example 1,
FIG. 2 shows an electron micrograph showing the surface of the metal structure of the ferrite carrier core material before classification. FIG. 3 is a diagram schematically showing an apparatus for measuring the current value of the carrier, and FIG. 4 is a graph showing a change in the current value between the lots of the example and the comparative example.

Claims (4)

(57) [Claims] The magnetic carrier core material has a weight average particle diameter of 25 to 25.
60% by weight or more of particles having a weight average particle diameter of ± 10 μm having a particle diameter of 100 μm, and containing less than 5% by weight of particles having a particle diameter of not less than the weight average particle diameter + 30 μm; 1 /
The particles having a particle size of less than 10 has a by which particle size distribution containing 2% by weight or less, the magnetic carrier core material, electrically insulating the critical surface tension of less than 30 dyn / cm Resin R ₁ and the critical surface tension But
30 dyn / cm is coated with a more mixed composition of the electrically insulating resin R _2, mixing weight ratio of the resin R ₁ and the resin R ₂ is 5: 5
A resin-coated carrier for a two-component developer, wherein the ratio is 1: 9. 2. The magnetic carrier core material having the particle size distribution,
The resin-coated carrier for a two-component developer according to claim 1, wherein the carrier is prepared by air classification. 3. A powder having a weight average particle size of 25 to 100 μm, containing particles having a weight average particle size of ± 10 μm or more by 60% by weight, and particles having a weight average particle size of +30 μm or more. A magnetic carrier core material having a particle size distribution containing less than 2% by weight of particles having a particle size of less than 1/10 of the weight average particle size is prepared by classification. electricity wood critical surface tension of less than 30 dyn / cm insulating resin R ₁
And the critical surface tension of 30 dyn / cm or more mixed composition of the electrically insulating resin R ₂ (weight ratio 5: 5 to 1: 9) in the coating process a resin-coated carrier for two-component developer which is characterized in that Manufacturing method. 4. The magnetic carrier core material having the particle size distribution,
The method for producing a resin-coated carrier for a two-component developer according to claim 3, wherein the resin-coated carrier is prepared by air classification.