JP2003167390A - Carrier for electrophotographic developer and developer using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a carrier for electrophotographic developer which is mixed with a polymerized toner and used as electrophotographic developer, which does not impair high image quality at all, which is constituted so that the environment dependency of electrification amount is low, and by which excellent printing characteristic can be obtained at from a low temperature and a low humidity to a high temperature and a high humidity, and a developer using the carrier. <P>SOLUTION: The carrier for electrophotographic developer mixed with the polymerized toner obtained by a suspension polymerization method or an emulsion polymerization method and used as the electrophotographic developer, is characterized in that the surface of the core material of the carrier is coated with resin, and the exposed area ratio of the surface of the core material is 2 to 20%, and further the average area ratio per one spot of the exposed part of the core material is ≤0.03%. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a two-component carrier for an electrophotographic developer, which is used as a mixture with a polymerized toner, and a developer using the carrier.

[0002]

2. Description of the Related Art A two-component electrophotographic developer used in electrophotography is composed of a toner and a carrier, and the carrier is agitated and mixed with the toner in a developing machine. Is a carrier substance that gives a desired charge to the toner and carries the charged toner to the electrostatic latent image on the photoreceptor to form a toner image. Then, the developer is repeatedly used while replenishing the toner consumed by the development.

With the recent widespread use of electrophotographic copying machines, facsimiles, printers and other devices,
Although its usage is diversifying, demands for higher image quality and longer life are increasing especially in the market.

To meet the demand for higher image quality, it has been proposed to reduce the particle size of toner. Since the charging ability of the toner particles tends to decrease as the toner particle size decreases, it is necessary to reduce the particle size of the carrier and increase the specific surface area in order to provide sufficient charging ability. However, the developer using the small particle size toner and the small particle size carrier has poor fluidity and the rise of charging is poor, which causes problems such as toner scattering. To improve this problem, methods such as increasing stirring strength have been considered, but increasing stirring strength increases the stress on the developer and causes toner adhesion to the carrier surface, so-called spent or carrier coat film. There is a problem in that good developer characteristics cannot be maintained for a long period of time because peeling easily occurs and the deterioration of developer characteristics is promoted. If the toner has a smaller particle size,
There is a problem that the yield is low and the cost is high in the manufacturing process.

In order to solve these problems, development of polymerized toner has been advanced in recent years. Since the polymerized toner does not include a crushing step in the manufacturing process, it has an advantage that the yield is small even with a small particle size, and the rounded shape of the polymerized toner has good fluidity even with a small particle size. Further, it can be said that the toner has a sharper particle size distribution than pulverized toner and is suitable for high image quality. However, the polymerized toner is polymerized in an aqueous solvent and uses a large amount of a dispersant having a polar group, so that there is a problem in that the charging characteristics fluctuate greatly with respect to environmental fluctuations as compared with the pulverized toner.

Up to now, several developers have been proposed in order to improve the above environmental dependence.

[0007] Patent Document 1 proposes a carrier coated with a coating agent containing a specific charge control agent for the purpose of improving environmental stability. However, when mixed with a polymerized toner, particularly under high temperature and high humidity conditions. The amount of electrification was lowered below, and it was not sufficient for the requirement for environmental stability. Further, the same publication proposes to increase the coverage of the coating film to a certain level or more for the purpose of reducing carrier adhesion. However, when mixed with a polymerized toner, it improves both environmental stability and carrier adhesion reduction. It was difficult to satisfy the characteristics.

[0008] Further, Patent Document 2 proposes to mix and use two kinds of carriers having different environmental change rates, but by mixing two kinds of carriers, environmental stability is improved. However, in reality, the distribution of the amount of charge becomes wider against environmental changes, which causes fog and toner to be selectively developed.Maintenance of high-quality images was not sufficient. .

In Patent Document 3, the metal atoms present on the surface of the silicone resin-coated carrier particles are 0.1 to 5% by number.
That is, it is said that it is effective for stable charge application and charge rise in each environment. In Patent Document 4,
It is said that the presence of 7 to 20% by number of metal atoms such as iron and alkali metals existing on the surface of the carrier particles prevents the accumulation of electric charges and can obtain a stable image even at low temperature and low humidity. . However, when these carriers are used, there is a problem that electric leakage easily occurs under high temperature and high humidity, and a desired charge amount cannot be obtained, so that toner scattering or fogging easily occurs.

Patent Document 5 proposes a developer comprising a specific polymerized toner and a spherical carrier. And in the invention according to the same publication, by controlling the toner particle diameter and the carrier particle diameter within a certain fixed range by using a spherical carrier,
It is proposed to prevent the toner fusion on the sleeve by reducing the shearing force that the toner particles receive from the carrier particles and avoiding the surface exposure of the low softening point compound due to the destruction of the toner particles. However, it is thought that the fluctuation of the charge amount due to the environment is caused by the interaction between the moisture in the atmosphere and the developer, and it is not possible to stabilize the balance of the leakage and accumulation of the charge in each environment only by making the carrier spherical. I can't
We were not able to fully meet the requirements for environmental stability.

Patent Document 6 proposes controlling the toner concentration, the specific gravity and average particle diameter of the toner, and the specific gravity and average particle diameter of the carrier in order to improve the environmental stability of the polymerized toner. Since the environmental dependence is mainly due to the interaction between the toner, the carrier, and the moisture in the atmosphere, it was not possible to maintain a high-quality image only by such a proposal.

As described above, the polymerized toner is characterized in that it is polymerized in an aqueous solvent during the manufacturing process thereof, but in that case, a large amount of a dispersant having a polar group is used.
After that, although steps such as washing and drying are performed, a trace amount of water or dispersant remains in the toner and / or the toner surface. Probably because they interact with moisture in the atmosphere, the electrical characteristics of the developer fluctuate remarkably compared with the pulverized toner with respect to fluctuations in the environment, that is, temperature and humidity.

In a high temperature and high humidity environment, the amount of charge decreases, which causes problems such as toner scattering and fogging, and also the electrostatic latent image is destroyed due to leakage of charges, and the developer resistance decreases. As a result, problems such as carrier adhesion occur.

Under low temperature and low humidity, the charge amount increases and the image density decreases, and when the charge amount further increases extremely, the carrier is also pulled when the toner is transferred to the photoconductor and carrier adhesion occurs. In addition, the developer resistance also increases,
This lowers the effective bias and causes a decrease in image density and fog.

The cause of the change in the charge amount depending on the environment has not been clarified, but one of them is that the balance between the charge transfer speed between the carrier and the toner, the degree of accumulation and the charge leak is destroyed by water. Is mentioned.

Here, if the resistance of the carrier is excessively increased in order to suppress the leakage of charges under high temperature and high humidity, the developing ability will be lowered and it will be difficult to obtain a sufficient image density, and the charge under low temperature and low humidity will be obtained. It will help up.
Also, in order to suppress excessive charge accumulation under low temperature and low humidity, lowering carrier resistance and toner resistance causes carrier fusing and drum fogging due to charge injection.
This will promote charge leakage under high temperature and high humidity.

Therefore, an object of the present invention is to use it as an electrophotographic developer by mixing it with a polymerized toner, to obtain a good printing characteristic from low temperature and low humidity to high temperature and high humidity, with little environmental dependence of the charge amount. An object of the present invention is to provide a carrier for an electrophotographic developer capable of maintaining a high quality image without adhesion and a developer using the carrier.

[0018]

[Patent Document 1] JP-A-7-301958

[Patent Document 2] Japanese Unexamined Patent Publication No. 8-62899

[Patent Document 3] Japanese Patent Laid-Open No. 7-287422

[Patent Document 4] Japanese Patent Laid-Open No. 11-295934

[Patent Document 5] JP-A-63-243962

[Patent Document 6] Japanese Patent Laid-Open No. 8-76407

[0019]

Means for Solving the Problems The inventors of the present invention have made diligent studies on the stability of the charge amount against environmental fluctuation when using a polymerized toner. It is important that the balance of leaks is stable against environmental fluctuations, and when a carrier core is coated with a specific material and a developer with an exposed area of the core is used, the carrier adheres It has been found that it is possible to achieve environmental stabilization of the charge amount for a long period of time while maintaining high-quality image characteristics without image defects such as.

That is, the present invention is a carrier used as an electrophotographic developer by mixing with a polymerized toner obtained by a suspension polymerization method or an emulsion polymerization method, the surface of a carrier core material being coated with a resin, A carrier for an electrophotographic developer, characterized in that the exposed area ratio of the core material surface is 2 to 20%, and the average area ratio per one exposed portion of the core material is 0.03% or less. Is.

The present invention also provides an electrophotographic developer comprising the above carrier and a polymerized toner obtained by a suspension polymerization method or an emulsion polymerization method.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION The carrier for electrophotographic developer of the present invention and the developer using the carrier are described in more detail below.

In the carrier of the present invention, it is important that the exposed area ratio of the core material surface is 2 to 20%, preferably 3 to 18%, more preferably 3 to 15%. If the exposed area ratio of the core material is less than 2%, the carrier becomes too high in resistance and it becomes difficult to obtain image density. Although it is possible to add a conductive material or the like to reduce the resistance in order to obtain the image density, a large amount of the conductive material is required, and charge leakage easily occurs under high temperature and high humidity. The exposed area ratio of the core material is 20%
If it exceeds, the charge leakage from the core material will have a great adverse effect.

The exposed area ratio of the core material is required to be 0.03% / location or less in average area ratio per location. If this ratio exceeds 0.03%,
Even if the value of the total exposed area ratio is small, since the area of one location is large, it is easily affected by moisture, and charge leakage is likely to occur particularly under high temperature and high humidity.

Further, it is preferable to add a conductive material to the coating resin of the carrier. This is because the exposed area of the core material is controlled to be relatively low by the coating, so that the absolute resistance may be too high and the developing ability may be decreased. However, since the resistance of the conductive material is lower than that of the coating resin or the core material, if the addition amount is too large, a rapid charge leak is caused. It is important to set 0.5 to 30% by weight, preferably 0.5 to 15% by weight,
More preferably, it is 0.5 to 6% by weight. If the addition amount is less than 0.5% by weight, the carrier has high resistance,
It is difficult to obtain a sufficient image density, and if it exceeds 30% by weight, charge leakage is likely to occur, which causes fog particularly under high temperature and high humidity conditions. Examples of the conductive material include conductive carbon and oxides such as titanium oxide and tin oxide. When used as a carrier for black toner, conductive carbon is preferable, and when used as a carrier for color toner, oxidized. Oxides such as titanium are preferred.

The coating resin for the carrier preferably contains a silane coupling agent as a charge control agent. This is because when the exposed area of the core material is controlled to be relatively small by the coating, the charging ability may be lowered, and therefore it can be controlled by adding various silane coupling agents. The type of coupling agent that can be used is not limited, but an aminosilane coupling agent is preferable for the negative polarity toner, and a fluorine-based silane coupling agent is preferable for the positive polarity toner. The addition amount is preferably 2 to 60% by weight based on the solid content of the coating resin.

Various resins can be used as the coating resin for forming the resin coating provided on the surface of the carrier core material. Examples of the resin include fluorine resin, acrylic resin, epoxy resin, polyester resin, Fluorine acrylic resin, acrylic-styrene resin, silicone resin,
Alternatively, a modified silicone resin modified with an acrylic resin, a polyester resin, an epoxy resin, an alkyd resin, a urethane resin, or a cross-linking fluorine-modified silicone resin may, for example, be mentioned.

However, the resin coating coated on the core material is subject to great stress due to agitation in the developing machine or collision with the doctor blade, so that the resin coating is easily peeled off and worn. Further, a spent phenomenon in which toner adheres to the surface of the carrier easily occurs. In order to solve these problems and maintain stable developer properties for a long period of time, the following general formula (I) and / or (II) having good wear resistance, peeling resistance, and spent resistance is used. It is preferable to include. Moreover, these are also effective for water repellency.

[0029]

[Chemical 2] (In the formula, R ₁ , R ₂ and R ₃ are a hydrogen atom, a halogen atom,
Hydroxy atom, methoxy group, alkyl group having 1 to 4 carbon atoms, phenyl group)

Examples of the resin containing the above chemical formula include the above.
Straight silicone resin, organic modified silicone
Examples of the resin include fluorine resin and fluorine-modified silicone resin.
Examples of the fluorine-modified silicone resin include those described above.
Organic silica containing (I), (II) and perfluoroalkyl group
Curable crosslinkable fluorine obtained by hydrolyzing an elementary compound
Examples include modified silicone resins. Perfluoroalki
As an example of an organic silicon compound containing a ruthenium group, CF₃CH
₂CH₂Si (OCH₃)₃, C_FourF₉CH₂CH₂S
i (CH₃) (OCH₃)₂, C₈F₁₇CH₂CH₂S
i (OCH₃) ₃, C₈F₁₇CH₂CH₂Si (OC₂
H_Five)₃, (CF₃)₂CF (CF₂) ₈CH₂CH₂
Si (OCH₃)₃Etc. Among these,
Silicone resin and fluorine-modified silicone resin are especially preferred.
Good

As a method for coating the above-mentioned coating resin on the carrier core material, there are known methods such as a brush coating method, a dry method, a spray dry method using a fluidized bed, a rotary dry method, and a universal stirrer. It can be coated by a liquid immersion drying method or the like. In order to improve the coverage, a fluidized bed method is preferable.

The coating amount of such a resin is preferably 0.3 to 10% by weight with respect to the carrier core material, and is 0.5.
It is more preferably ˜7% by weight. Most preferably 1.2-
It is 4% by weight. If the coating amount is less than 0.3% by weight, it is difficult to form a uniform coating layer on the carrier surface, and
If it exceeds 0% by weight, agglomeration of carriers occurs, which causes variation in developer characteristics.

When the resin is coated on the carrier core material and baked, either an external heating method or an internal heating method may be used, for example, a fixed or fluidized electric furnace, a rotary electric furnace, a burner furnace, or It may be baked by microwave. The baking temperature varies depending on the resin used, but a temperature equal to or higher than the melting point or the glass transition point is necessary, and in the case of a thermosetting resin or a condensation-crosslinking resin, it is necessary to raise the temperature to a level at which curing is sufficiently advanced.

The exposed area ratio of the core material can be controlled by the coating amount described above, but can also be controlled by the coating method, coating conditions, baking conditions and the like. It can also be adjusted by mechanical treatment with a vibro mill or Nauta mixer after baking.

In this manner, the resin is coated on the surface of the carrier core material, baked, cooled, crushed, and subjected to particle size adjustment to obtain a resin-coated carrier.

The average particle size of the carrier is 20 to 1
It is preferably 00 μm, more preferably 25
˜80 μm. If the particle size of the carrier is less than 20 μm, it is effective for obtaining a high image quality, but the magnetization per particle decreases, which causes carrier adhesion. If the average particle size of the carrier is larger than 100 μm, it is difficult to give sufficient charge to the toner because the specific surface area becomes small, which may cause deterioration of image quality.

The carrier core material is not particularly limited, and examples thereof include iron powder, ferrite, magnetite and the like, but ferrite is preferable. Iron powder has a high saturation magnetization and is good for carrier adhesion, but it has high spikes and is too hard, so the toner that has transferred to the photoconductor is scraped off by the spikes of the carrier, and the iron powder has a low resistance, so the charge Is likely to occur, and brush marks are likely to occur due to, for example, damage to the electrostatic latent image on the photoconductor. An example of ferrite is generally represented by the following formula. (MO) _X (Fe ₂ O ₃ ) _Y (In the formula, M is Cu, Zn, Fe, Mg, Mn, Ca,
Li, Ti, Ni, Sn, Sr, Al, Ba, Co, M
at least one selected from the group consisting of o and the like: also X,
Y represents a weight mol ratio and satisfies the condition X + Y = 100)

The above M is Li, Mg, Ca, Mn, S
It is preferable that the ferrite particles are composed of one or several kinds of r and Sn, and the content of other components is 1% by weight or less. By adding Cu, Zn, and Ni elements, the resistance tends to be low, and charge leakage is likely to occur. In addition, it tends to be difficult to coat with a resin, and the dependency on the environment tends to deteriorate. Further, since it is a heavy metal, the stress applied to the carrier may be increased, probably because it is heavy, which may adversely affect the life.

As an example of the method for manufacturing the ferrite core material,
First, an appropriate amount of each oxide is blended, pulverized with a wet ball mill for 10 hours, mixed, dried, and held at 950 ° C. for 4 hours. This is pulverized with a wet ball mill for 24 hours to have a size of 5 μm or less. This slurry is granulated and dried, and the oxygen concentration is controlled for the purpose of adjusting the magnetic properties and resistance.
It can be obtained by holding at 100 to 1300 ° C. for 6 hours, pulverizing, and further classifying to a desired particle size distribution.

The method of controlling the exposed area of the surface of the core material can be controlled by the combination of the oxides and the compounding ratio. It can also be controlled by the temperature during baking, the holding time, and the oxygen concentration.

The electrophotographic developer of the present invention comprises the above carrier and polymerized toner, and has a toner concentration of 1 to 10% by weight.
It is preferably obtained by mixing 2 to 7% by weight.

The polymerized toner used in the present invention can be produced by a known method such as a suspension polymerization method or an emulsion polymerization method. For example, a colorant dispersion in which a colorant is dispersed in water using a surfactant, a polymerizable monomer, a surfactant and a polymerization initiator are mixed and stirred in an aqueous medium to form a polymerizable monomer. The emulsion-dispersed product in an aqueous medium is stirred and mixed, and a salting-out agent is added for salting-out. The particles obtained by salting out are filtered, washed and dried to obtain polymerized toner particles. Then, an external additive is added to the dried toner particles to obtain a polymerized toner.

Polymerizable monomer, surfactant, polymerization initiator,
In addition to the colorant, a fixing property improver and a charge control agent can be used to control and improve various properties of the toner, and to aid emulsion dispersion and adjust the molecular weight of the resulting polymer,
Chain transfer agents can be used.

The polymerizable monomer used in the above-mentioned polymerized toner is not particularly limited, but styrene and its derivatives, ethylene unsaturated monoolefins such as ethylene and propylene, vinyl halides such as vinyl chloride. , Vinyl esters such as vinyl acetate, α-methylene aliphatic monoesters such as methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, 2-ethylhexyl methacrylate, dimethylamino ester acrylic acid, diethylamino ester methacrylic acid, etc. Carboxylic acid esters and the like can be used.

As the colorant used in the polymerized toner, conventionally known dyes and / or pigments can be used. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green and the like can be used. Further, these colorants may be surface-modified by using a silane coupling agent, a titanium coupling agent, or the like.

As the surface active agent used in the above-mentioned polymerized toner, an anionic surface active agent, a cationic surface active agent,
Amphoteric surfactants and nonionic surfactants can be used.

Examples of the anionic surfactant include fatty acid salts such as sodium oleate and potassium castor oil, alkyl sulfates such as sodium lauryl sulfate and ammonium lauryl sulfate, alkylbenzene sulfonates such as sodium dodecylbenzenesulfonate, and alkylnaphthalene. Examples thereof include sulfonate, alkyl phosphate ester salt, naphthalene sulfonate formalin condensate, polyoxyethylene alkyl sulfate ester salt and the like.

As the nonionic surfactant, polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin, fatty acid ester,
An oxyethylene-oxypropylene block polymer etc. are mentioned.

Examples of the cationic surfactant include alkylamine salts such as laurylamine acetate and quaternary ammonium salts such as lauryltrimethylammonium chloride and stearyltrimethylammonium chloride.

Examples of the zwitterionic surfactant include aminocarboxylic acid salts and alkylamino acids.

The amount of the surfactant is based on the polymerizable monomer.
About 0.01 to 10% by weight is preferable. If the amount used is too small, stable emulsion polymerization is difficult to obtain, and if it is too large, the environmental stability of the toner may be adversely affected.

As the polymerization initiator, for example, water-soluble polymerization initiators are persulfates such as potassium persulfate and ammonium persulfate, water-soluble peroxide compounds, and oil-soluble polymerization initiators are azobisisobutyronitrile. And other azo compounds, oil-soluble peroxide compounds and the like.

Examples of the chain transfer agent include mercaptans such as octyl mercaptan, dodecyl mercaptan and tert-dodecyl mercaptan.

As the fixability improver, a natural wax such as carnauba wax, an olefin wax such as polypropylene or polyethylene can be used.

The charge control agent is not particularly limited, and a conventionally used nigrosine dye,
Examples thereof include quaternary ammonium salts, organometallic complexes, metal-containing monoazo dyes and the like.

As the external additive used for improving fluidity, silica, titanium oxide, or those obtained by hydrophobizing them, barium titanate, fine particles of fluororesin, fine particles of acrylic resin, etc. are used alone or in combination. You can also

Examples of the salting-out agent include metal salts such as magnesium sulfate, aluminum sulfate, barium chloride, magnesium chloride, calcium chloride and sodium chloride.

The characteristic values relating to the carrier and the developer described above (the exposed area ratio of the carrier core material, the core material exposed portion 1)
The method for measuring the average area ratio per location, the charge amount, the average particle diameter of the carrier, and the current value of the carrier) will be described.

(Exposure area ratio of carrier core material and average area ratio per exposed core material part) Using an electron microscope (JSM-6100 type) manufactured by JEOL Ltd., an applied voltage of 5
A backscattered electron image is taken at kV. Read it with a scanner, and use the image analysis software "Image-Pro Plus" made by Media Cybernetics to make an image of only the particles, and then binarize the image to obtain white (core exposed) and black parts. (Coated part)
And measure the area of each and the number of white parts. The core material exposed area ratio (%) is calculated by the following calculation formula. Exposed core material area ratio (%) = {area of white portion / (area of white portion + area of black portion)} × 100 Average area ratio per exposed core material portion (% / location) =
Core material exposed area ratio / number of white parts

(Charge amount) 5 g of toner and 95 g of carrier were weighed, and each environment (high temperature and high humidity [HH environment]: 35 ° C., 80 ° C.)
RH%, low temperature and low humidity [LL environment]: 10 ° C, 20RH%)
After exposure for 12 hours to 100 cc plastic bottle under each environment. Then, in each environment, the ball mill is stirred at 100 rpm for 30 minutes. Then, using a blow-off charge amount measuring device (Toshiba Chemical Co., Ltd .: TB-200 type), 0.2 g of the developer was put into a cell in which a stainless steel mesh of 500 mesh was set, and nitrogen gas was set to a pressure of 1 kgf / cm ^2. Blow for 60 seconds. The charge amount (μC / g) per unit toner weight was calculated from the charge after 60 seconds and the set toner concentration (5% by weight).

(Average Particle Size of Carrier) Microtrac Particle Size Analyzer (Model 9320-X, manufactured by Nikkiso Co., Ltd.)
100).

(Current value of carrier) 800 g of carrier
Weighed and exposed to an environment of temperature 20 to 26 ° C. and humidity 50 to 60% RH for 15 minutes or more, and then the magnet roller and the Al tube shown in FIG. 1 were used as electrodes, and the current value was set at a distance of 4.5 mm. The measurement was performed at an applied voltage of 200 V using a measuring device.

[0063]

EXAMPLES The present invention will be specifically described below based on Examples and Comparative Examples.

Example 1 (Production Example of Carrier) 13.3 mol% in terms of Li ₂ O,
76.2 mol% in terms of Fe ₂ O ₃ and 7. in terms of MgO.
Proper amount of each raw material is blended so as to be 7 mol% and 2.8 mol% in terms of CaO, water is added, and 1 with a wet ball mill.
The slurry was crushed for 0 hours, mixed, dried and held at 950 ° C. for 4 hours, crushed with a wet ball mill for 24 hours, granulated and dried, held at 1190 ° C. for 6 hours in the air, and then crushed. The particle size was adjusted to obtain lithium-based ferrite particles (core material). The lithium-based ferrite particles had an average particle diameter of 60 μm and a saturation magnetization of 60 emu / g when the applied magnetic field was 3000 oersted.

Next, a silicone resin (trade name: SR-2
411, Toray Dow Corning Silicone Co., Ltd.) was weighed to 200 g in terms of solid content, and 10 aminosilane coupling agents (trade name: KBE903, Shin-Etsu Chemical Co., Ltd.) were used.
0 g of each was weighed and dissolved in 1000 cc of toluene solvent, and 2% by weight of conductive carbon (trade name: Ketjen Black EC: Ketjen Black International Co., Ltd.) was dispersed in a pearl mill with respect to the resin solid content.

The coating resin solution in which the above conductive carbon was dispersed was sprayed onto 10 kg of the above lithium ferrite particles using a fluidized bed coating apparatus, and the spray amount was adjusted per unit time so that the coating time was 80 minutes. went. afterwards,
The carrier 1 was obtained by baking at 260 ° C. for 1 hour.

The carrier 1 has a current value of 0.45 μA, a charge amount under high temperature and high humidity of 18.4 μC / g, a charge amount under low temperature and low humidity of 22.1 μC / g, and an environmental difference of 3 A very good result of 0.7 μC / g was obtained. Moreover, the exposed area ratio of the core material was 4.5%, and the average area ratio per exposed core material portion was 0.007% / location.

(Toner manufacturing example) Carbon black (trade name: Regal 330R, manufactured by Cabot) as a colorant
After mixing 7 g of sodium dodecyl sulfate and 150 g of ion-exchanged water with 15 g, the mixture was dispersed using a pressure-dispersion homogenizer to prepare a colorant dispersion liquid.

Ion-exchanged water 2000 was added to the colorant dispersion.
g, 280 g of styrene, 50 g of n-butyl acrylate,
Methacrylic acid 20 g and t-dodecyl mercaptan 3 g were added, and the internal temperature was raised to 80 ° C. while stirring. An aqueous solution of a polymerization initiator prepared by dissolving 8 g of potassium persulfate in 600 g of ion-exchanged water was added thereto, and after polymerization for 7 hours,
The mixture was cooled to room temperature to obtain a colorant composite polymer particle dispersion liquid.

An aqueous potassium chloride solution was added while stirring the colorant composite polymer particle dispersion. This mixed solution was allowed to associate at 90 ° C. for 6 hours and then cooled to room temperature.
This was filtered, washed with distilled water and dried, and then 1 wt% of hydrophobic silica powder was added and mixed as a fluidizing agent to obtain polymerized toner particles.

A developer was prepared so that the carrier 1 and the polymerized toner had a toner concentration of 5% by weight. An actual machine test was performed on this developer using a commercially available copying machine AR-S400 manufactured by Sharp Corporation.

The evaluation results are shown in Table 2. As a result, the image density under low temperature and low humidity was measured by the Macbeth densitometer (RD91
4) was 1.30, and the fog under high temperature and high humidity was 0.68 when measured using a color difference meter (Z300A, manufactured by Nippon Denshoku Industries Co., Ltd.). It was possible to obtain a sufficient image density without fogging up to high temperature and high humidity.

Here, the environmental dependence Δ of the charge amount (charge amount under low temperature and low humidity minus charge amount under high temperature and high humidity) and the evaluation criteria by the actual machine test were determined as follows.

(1) Dependence of charge amount on environment (Δ; charge amount under low temperature and low humidity-charge amount under high temperature and high humidity) ⊚: 5.0 or less ○: over 5.0 to 10.0 Δ: 10 Greater than 0.0 to 15.0 x: Greater than 15.0

(2) Image density: Macbeth densitometer (RD9
14) was used for measurement and judgment. A: 1.25 or more O: 1.15 to less than 1.25 C: 1.00 to less than 1.15 X: less than 1.00

(3) Fogging: Measured and evaluated using a color difference meter (Z300A: manufactured by Nippon Denshoku Industries Co., Ltd.). ◎: Less than 0.70 ○: 0.70 to less than 1.00 △: 1.00 to less than 1.50 ×: 1.50 or more

In the following, in Examples and Comparative Examples, only the manufacturing conditions of the carrier are described. The exposed area ratio of the core material surface and the average area ratio per exposed core material part are shown in Table 1, and the current of each carrier is shown. Table 2 shows the values, the charge amount, and the evaluation results by the actual machine.

Example 2 39.7 mol in terms of MnO
%, 9.9 mol% in terms of MgO, 4 in terms of Fe ₂ O ₃
Each raw material was mixed in an appropriate amount so that 9.6 mol% and 0.8 mol% in terms of SrO were added, water was added, and the mixture was pulverized with a wet ball mill for 10 hours, mixed, dried, and held at 950 ° C. for 4 hours, and then wet. The slurry crushed for 24 hours by a ball mill is granulated and dried, and then dried in an atmosphere with an oxygen concentration of 3%.
After holding at 5 ° C. for 6 hours, it was crushed and the particle size was adjusted to obtain manganese ferrite particles (core material). The manganese-based ferrite particles have an average particle size of 60 μm and a saturation magnetization of 65 em when the applied magnetic field is 3000 oersted.
It was u / g.

Next, a silicone resin (trade name: SR-2
411, manufactured by Toray Dow Corning Silicone Co., Ltd.) in solid content of 150 g, and aminosilane coupling agent (trade name: KBE903, manufactured by Shin-Etsu Chemical Co., Ltd.) in an amount of 75 g. Carbon (Product name: Ketjen Black E
C, made by Ketjen Black International)
2% by weight with respect to the resin solid content was dispersed by a pearl mill.

The coating resin solution in which the above conductive carbon was dispersed was applied to 10 kg of the above ferrite particles by using a fluidized bed coating apparatus, and the spray amount was adjusted per unit time so that the coating time was 60 minutes. went. Then 220
The carrier 2 was obtained by baking at 1 ° C. for 1 hour. Using this carrier 2, a test with an actual machine was conducted in the same manner as in Example 1.

[Example 3] Silicone resin (trade name: S
R-2411, Toray Dow Corning Silicone Co., Ltd.) 120 g in terms of solid content, aminosilane coupling agent (trade name: KBE903, Shin-Etsu Chemical Co., Ltd.) 3
6 g of each is weighed and dissolved in 1000 cc of toluene solvent, and conductive carbon (trade name: Ketjen Black EC, Ketjen Black International Co., Ltd.) is dispersed in a pearl mill at 1.5% by weight based on the resin solid content. did.

10 kg of ferrite particles used in Example 2
On the other hand, the coating resin solution in which the above-mentioned conductive carbon was dispersed was coated using a fluidized bed coating apparatus by adjusting the spray amount per unit time so that the coating time was 50 minutes. Then, it baked at 220 degreeC for 1 hour, and obtained the carrier 3. Using this carrier 3, a test with an actual machine was conducted in the same manner as in Example 1.

[Comparative Example 1] Silicone resin (trade name: SR-) was added to 10 kg of the ferrite particles used in Example 1.
2411, manufactured by Toray Dow Corning Silicone Co., Ltd.) was coated with a coating resin solution prepared by dissolving 100 g of the solid content in 500 cc of a toluene solvent using a Henschel mixer. Then, it baked at 220 degreeC for 1 hour, and obtained the carrier 4. Using this carrier 4, a test with an actual machine was conducted in the same manner as in Example 1.

[Comparative Example 2] Silicone resin (trade name: SR-) was added to 10 kg of the ferrite particles used in Example 1.
2411, manufactured by Toray Dow Corning Silicone Co., Ltd.), a coating resin solution prepared by dissolving 30 g of solid content in a 500 cc toluene solvent is sprayed per unit time using a fluidized bed coating device so that the coating time is 30 minutes. Adjust the amount,
The coating was applied. Then, it baked at 220 degreeC for 1 hour, and obtained the carrier 5. Example 1 using this carrier 5
The same test was conducted using the actual machine.

[Comparative Example 3] 14.0 mol in terms of CuO
%, 70.0 mol% in terms of Fe ₂ O ₃ , and 16.0 mol% in terms of ZnO.
After adding water, pulverizing and mixing with a wet ball mill for 10 hours, mixing and drying, and holding at 950 ° C. for 4 hours, pulverizing with a wet ball mill for 24 hours, granulating and drying, and 1040 ° C. for 6 hours in air. After holding, it was crushed and the particle size was adjusted to obtain copper-zinc ferrite particles (core material). The copper-zinc based ferrite particles had an average particle size of 60 μm and a saturation magnetization of 65 emu / g when the applied magnetic field was 3000 oersted.

Next, an acrylic resin (trade name: BR-8
0, manufactured by Mitsubishi Rayon Co., Ltd.) and weighed 80 g in terms of solid content,
Dissolve in 600 cc of toluene solvent and add conductive carbon (trade name: Ketjen Black EC, Ketjen Black International Co., Ltd.) to the resin solid content of 9
Weight% was dispersed with a pearl mill.

10 kg of the above copper-zinc ferrite particles were coated with the above coating resin solution in which the conductive carbon was dispersed using a Henschel mixer. Then 1
The carrier 6 was obtained by baking at 45 ° C. for 1 hour. Using this carrier 6, a test with an actual machine was conducted in the same manner as in Example 1.

[0088]

[Table 1]

[0089]

[Table 2]

[0090]

INDUSTRIAL APPLICABILITY The carrier for an electrophotographic developer of the present invention and the developer using the carrier balance carrier charge leakage under high temperature and high humidity and charge accumulation under low temperature and low humidity to allow carrier adhesion. It is possible to maintain stable charging characteristics against environmental changes for a long period while maintaining high-quality image characteristics free from image defects such as.

[Brief description of drawings]

FIG. 1 is a schematic view schematically showing a carrier current value measuring device.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Ken Naito             Powder Tetsu             Ku Co., Ltd. (72) Inventor Yuji Sato             Powder Tetsu             Ku Co., Ltd. F-term (reference) 2H005 AB06 BA02 BA06 BA07 BA15                       CA12 CA26 CA28 CB04 CB18                       FA02

Claims (6)

[Claims] 1. A carrier used as an electrophotographic developer by mixing with a polymerized toner obtained by a suspension polymerization method or an emulsion polymerization method, the surface of a carrier core material being coated with a resin, A carrier for an electrophotographic developer, which has an exposed area ratio of 2 to 20% and an average area ratio per exposed core material portion of 0.03% or less. 2. The carrier for an electrophotographic developer according to claim 1, wherein the coating resin contains a conductive material in an amount of 0.5 to 30% by weight based on the solid content. 3. The carrier for an electrophotographic developer according to claim 1, wherein the coating resin contains a silane coupling agent. 4. The carrier for electrophotographic developer according to claim 1, wherein the coating resin contains the following formula (I) and / or (II). [Chemical 1] (In the formula, R ₁ , R ₂ and R ₃ are a hydrogen atom, a halogen atom,
Hydroxy atom, methoxy group, alkyl group having 1 to 4 carbon atoms, phenyl group) 5. The magnetic particle core material of the carrier is Li,
A ferrite particle containing at least one selected from Mg, Ca, Mn, Sr and Sn, and Fe and O as main components, and the content of components other than these being 1% by weight or less. The carrier for electrophotographic developer according to any one of claims. 6. An electrophotographic developer comprising the carrier according to claim 1 and a polymerized toner obtained by a suspension polymerization method or an emulsion polymerization method.