JPH1073968A - Carrier for electrophotography, electrostatic latent image developer and picture image formation - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier for electrophotography, an electrostatic latent image developer and a picture image formation method capable of preventing a picture image defect of a brush mark, carrier over, etc., and providing a favourable solid picture image. SOLUTION: Dynamic electric resistance under an electric field of 10<4> V/cm is less than 1Ω.cm in a state where a core material is a magnetic brush and electric resistance of a resin covering layer is within a range of 10 to 1×10<8> Ω.cm on a carrier for electrophotography having the resin covering layer in which electric conductive grain is included on the core material. It is desirable that a contact angle of the resin covering layer against water is more than 90 degrees and film thickness of the resin covering layer is 0.3 to 5μm, desirable that an average grain diameter of the carrier is 10 to 100μm and desirable that the core material is ferrite and that electric resistance of the electric conductive grain is less than 1×10<6> Ω.cm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophotographic carrier used for developing an electrostatic image formed by an electrophotographic method, an electrostatic recording method, etc., and an electrostatic latent image using the electrophotographic carrier. The present invention relates to a developer and an image forming method using the electrostatic latent image developer.

[0002]

2. Description of the Related Art Methods of visualizing image information via an electrostatic image such as electrophotography are currently used in various fields.
In the electrophotographic method, an electrostatic latent image is formed on a photoreceptor in a charging and exposing step, the electrostatic latent image is developed with a developer containing a toner, and visualized through a transfer and fixing step. The developer used here includes a two-component developer composed of a toner and a carrier, and a one-component developer used alone such as a magnetic toner. In the two-component developer, the carrier is used to stir and transport the developer.
It is widely used at present because it shares functions such as electrification and is separated in function as a developer, so that it has good controllability.

As a developing method, a cascade method or the like has been used in the past. At present, however, a magnetic brush method using a magnetic roll as a developer carrier is mainly used. 2
As the component magnetic brush development, a conductive magnetic brush (CMB) development using a conductive carrier and an insulating magnetic brush (IMB) development using an insulating carrier are known. Among them, in CMB development, charges are injected from a development roll due to low carrier resistance, and carriers in the vicinity of a photoreceptor play a role of a development electrode to increase an effective development electric field.
The toner is characterized in that toner transfer is sufficiently performed and solid image reproducibility is excellent. On the other hand, there is a problem that image defects such as a white line called a brush mark and a transfer of a carrier to a photoreceptor called a carrier over which occur due to charge injection from a developing roll or the like easily occur.

In recent years, colorization has rapidly progressed, and the required level of image quality has been increasing more and more. Solid images are particularly important in this color image quality, and there is therefore a strong need for further improvements in CMB carrier performance. Japanese Patent Publication No. Hei 7-120086 discloses a carrier in which a relatively low resistance core is coated with a high resistance resin, whereby the resistance rapidly changes in a certain electric field, the resistance is high in a low electric field, and the resistance is low in a high electric field. Is disclosed.
It is described that since a high electric field is applied to the latent image portion and a low electric field is applied to the non-latent image portion, good black solid printing is obtained and at the same time, no carrier over occurs in the non-latent image portion.
However, from the description of the working example and the operation of Japanese Patent Publication No. 7-120086, it is presumed that the thickness of the coating resin layer is considerably thin and the low-resistance core is partially exposed. Therefore, it is considered that the resistance becomes low in a high electric field. In fact, as in a comparative example described later, in the case of a completely coated resin having a thick coating resin layer, the resistance was high even in a high electric field, and a good solid image could not be obtained. In such a partially coated resin in which a part of the core having a low resistance is exposed, charges easily move through the exposed surface, and therefore, a brush mark is easily generated in the latent image portion.

Further, JP-A-61-107257 and JP-A-61-130959 disclose ferrites having relatively low resistance and having irregularities on the surface based on primary particles. It is described that the presence of such fine irregularities suppresses leakage between charges of different polarities and prevents brush marks. However, since the carrier has fine irregularities on its surface, the contact area with the toner increases, and as a result, the toner tends to adhere, and the charging ability as a carrier deteriorates with time. Japanese Patent Application Laid-Open No. Hei 6-161157 discloses a method in which the resistance, the solid image density, and the fine line reproducibility are simultaneously determined by the ratio of the resistance between the carrier core and the carrier coated with the resin. It has been shown to be satisfactory. However, no sufficient effect has been found particularly in preventing image defects in color images.

[0006]

As described above,
In particular, there has been a strong demand for a durable carrier capable of obtaining a good solid image without causing image defects such as brush marks and carrier over for color images.

[Means for Solving the Problems]

The present inventors have conducted research on the above-mentioned problems. As a result, in order to prevent image defects such as brush marks and carrier over and obtain a good solid image, the resistance of the carrier is within a predetermined range. It has been found that it is important that the resistance of the carrier core is lower than a predetermined value and that the resistance of the coating resin layer falls within a predetermined range.

[0008] That is, the electrophotographic carrier of the present invention has been achieved based on the above findings. The electrophotographic carrier according to the present invention has a core material and a coating resin layer containing conductive powder on the core material. 10 ^{4 when the} material is a magnetic brush
The dynamic electric resistance under an electric field of V / cm is 1 Ω · cm or less, and the electric resistance of the coating resin layer is 10 to 1 × 10
It is in the range of ⁸ Ω · cm. Further, the electrostatic latent image developer of the present invention is an electrostatic latent image developer comprising toner particles comprising a binder resin and a colorant, and a carrier having a coating resin layer provided on a core material, wherein a magnetic brush 10 in state
⁴ Ω · cm dynamic electric resistance under an electric field of ⁴ V / cm
On the following core material, electric resistance is 10 to 1 × 10 ⁸ Ω · c
m, wherein a coating resin layer in the range of m is formed. Further, the image forming method of the present invention, a step of forming a latent image on the latent image carrier, a step of developing the latent image using a developer, a step of transferring the developed toner image to a transfer body,
A fixing step of heating and fixing the toner image on the transfer member, wherein the above-mentioned electrostatic latent image developer is used as the developer.

The electrophotographic carrier of the present invention is a low-resistance core material having a dynamic electric resistance of 1 Ω · cm or less under an electric field of 10 ⁴ V / cm in the state of a magnetic brush (hereinafter also referred to as a carrier core or a core). ), The electric resistance is 10 to 1 × 10
^It has a medium resistance coating resin layer in the range of ⁸ Ω · cm. The reason why it is possible to achieve both the quality of a solid image and the prevention of image defects such as brush marks and carrier over by adopting such a configuration is presumed as follows. Generally, when a conductor is placed in an electric field, electric charges are rearranged along the electric field, that is, polarization occurs. And
The speed of the polarization is related to the resistance of the conductor, and the lower the resistance, the faster the speed of the polarization. It is considered that such a phenomenon occurs also in the core of the carrier placed between the developing roll and the photoreceptor, and the resistance of the core is sufficiently low so that the development takes about 10 ^-3 seconds. When the polarization of the core is completed, it is considered that the development electrode effect due to the polarization of the core itself is added in addition to the charge injection from the developing roll, and as a result, a good solid image is obtained. However, no matter how low the core resistance is, if the resistance of the coating resin layer is too high, the overall resistance increases, and a good solid image cannot be obtained. On the other hand, since the charge injected from the developing roll mainly flows on the carrier surface, if the resistance of the coating resin layer is too low, brush marks and carrier over are likely to occur.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the electrophotographic carrier of the present invention, a low-resistance ferrite is particularly desirable as a carrier core. Iron powder and magnetite are known as carrier cores other than ferrite. However, iron powder has a large specific gravity, so that a toner or an external additive easily adheres to the powder, and therefore has lower stability than ferrite. Further, in the case of magnetite, there is a problem that resistance control is difficult and the latitude of the resistance is narrow. On the other hand, in the case of ferrite, the resistance can be reduced by, for example, reducing at a certain temperature in a hydrogen stream after firing, and various resistances can be obtained by controlling the amount of hydrogen flow, temperature, reduction time, and the like.

The carrier core used in the present invention has a dynamic electric resistance of 10 ⁴ V when measured in the form of a magnetic brush.
/ Cm at an electric field of 1 Ω · cm or less. The reason is that if the resistance exceeds 1 Ω · cm, a carrier having a desired resistance or less cannot be obtained unless the resistance of the coating resin layer is considerably reduced, and image defects occur if the resistance of the coating resin layer is too low. It is because. The electric field of 10 ⁴ V / cm is close to the developing electric field in the actual machine, and is defined by the resistance there.

The dynamic electric resistance of the carrier is as follows.
Ask. About 30cm on the developing roll ^ThreeA career
To form a magnetic brush, area 3cm^Two2. The plate electrode of 2.
They face each other at an interval of 5 mm. At a rotation speed of 120 rpm
While rotating the developing roll, between the developing roll and the plate electrode
A voltage is applied and the current flowing at that time is measured. Get
From the current-voltage characteristics obtained, the resistance was calculated using the Ohm's law equation.
Ask for. In addition, between the applied electric field E and the current density J at this time.
Generally has a relationship of logJ∝E1 / 2
It is well known (for example, Japane Jour
nal of Applied Physics 19
Vol. 12, No. P2413-). Like the carrier of the present invention
10 if the resistance is very low^ThreeHigh voltage over V / cm
In some fields, large currents flow and cannot be measured. This place
In this case, measure three or more points in a low electric field, and
10 by small square method^FourExtrapolated to electric field of V / cm
You.

The average particle size of the carrier core is 10 to 1
00 μm, preferably 20 to 80 μm. If the average particle size is smaller than 10 μm, the developer easily scatters from the developing device, and if it is larger than 100 μm, it is difficult to obtain a sufficient image density. Examples of the coating resin formed on the core include polyolefin resins such as polyethylene and polypropylene; polyvinyl and polyvinylidene resins such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, and polyvinyl carbazole. , Polyvinyl ether and polyvinyl ketone; vinyl chloride-vinyl acetate copolymer; styrene-acrylic acid copolymer; straight silicone resin comprising organosiloxane bond or a modified product thereof; fluororesin such as polytetrafluoroethylene, polyvinyl fluoride, Polyvinylidene fluoride, polychlorotrifluoroethylene; Polyester; Polyurethane; Polycarbonate; Amino resin such as urea-formaldehyde tree ; Epoxy resins. These may be used alone or as a mixture of a plurality of resins.

The thickness of the coating resin layer is from 0.3 to 5 μm, preferably from 0.5 to 3 μm. The thickness of the coating resin layer is 0.
If it is smaller than 3 μm, it is difficult to form a uniform coating resin layer on the core surface, and when a low-resistance core is used as in the present invention, charge transfer occurs through the exposed surface and image defects occur. Likely to happen. On the other hand, if it is larger than 5 μm, granulation of carriers occurs, and a uniform carrier cannot be obtained.

The conductive powder added to the coating resin layer preferably has a resistance of 10 ⁶ Ω · cm or less and an average particle size of 10 to 500 nm. When the particle size of the conductive powder is smaller than 10 nm, the conductive powder is agglomerated and the dispersion of the conductive powder in the layer becomes difficult. When the particle size is larger than 500 nm, it becomes difficult to contain the conductive powder in the coating resin layer, The electric resistance of the coating resin layer cannot be adjusted to a predetermined range. Specific examples of the conductive powder include carbon black, zinc oxide, titanium oxide, tin oxide, iron oxide, and titanium black. The content of the conductive powder is 3 to 40% by volume in the coating resin layer,
Preferably it is 5 to 40% by volume. Content of conductive powder is 3
When the volume is less than% by volume, the resistance of the coating resin layer does not decrease to a desired value, and when the volume is more than 40% by volume, the coating resin layer becomes brittle,
During use, the core is partially exposed to the surface, and the transfer of electric charges tends to cause image defects. When using a water-repellent or low surface energy coating resin having a contact angle to water of 90 degrees or more, the content of the conductive powder is set to 20 to 40.
It is preferable to set the volume%. In this case, since a part of the conductive powder is exposed from the surface of the coating resin layer to form a convex portion and increase the surface area, the coating resin layer becomes more water repellent or the surface energy is further reduced. I do. As a result, the impact of the toner and external additives such as silica, titania, and alumina attached to the toner on the coating resin layer is prevented, and the durability is improved. On the other hand, in the case of a coating resin having a contact angle to water of less than 90 degrees or having a high surface energy, if the content of the conductive powder is too large, the coating resin layer becomes more hydrophilic because of an increase in surface area. Or the surface energy is further increased, which is not preferable. The contact angle of the coating resin with water is measured by forming a coating resin film having a thickness of about several μm on a glass substrate using an applicator or the like and using a normal contact angle meter.

The electric resistance of the coating resin layer is 10 to 1 × 10
^{It is 8} Ω · cm, preferably 10 ^{3 to} 10 ⁷ Ω · cm. The electric resistance of the coating resin layer can be controlled by the type and amount of the conductive powder and the coating resin used.
If the electric resistance of the coating resin layer is smaller than 10 Ω · cm, charges easily move on the carrier surface and image defects occur. If the electric resistance of the coating resin layer is larger than 1 × 10 ⁸ Ω · cm, a good solid image cannot be obtained even if a low-resistance core is used. The electric resistance of the coating resin layer is IT
A coating resin film having a thickness of about several μm is formed on an O conductive glass substrate using an applicator or the like, and a gold electrode is formed on the coating resin film by vapor deposition to obtain a current-voltage characteristic in an electric field of 10 ² V / cm. Ask.

The preferred range of the electric resistance of the carrier whose surface is coated with the resin is 10 to 1 × 10 ⁹ Ω · cm, and the more preferable range is 1 × 10 ^{3 to} 1 × 10 ⁹ Ω · cm. If the resistance of the carrier is smaller than 10 Ω · cm, image defects are likely to occur, and if it is larger than 10 ⁹ Ω · cm, it is difficult to obtain a good solid image.

The method for forming the coating resin layer on the carrier core includes a dipping method in which the carrier core is dipped in a solution for forming the coating resin layer, a spray method in which the solution for forming the coating resin layer is sprayed on the surface of the carrier core, and a carrier method. A fluidized bed method in which a coating resin layer forming solution is sprayed while the core is suspended by flowing air, a kneader coater method in which a carrier core and a coating resin layer forming solution are mixed in a kneader coater to remove the solvent, and the like. .

The solvent used in the coating solution for forming the coating resin layer is not particularly limited as long as it dissolves the resin, and examples thereof include aromatic hydrocarbons such as toluene and xylene, acetone, methyl ethyl ketone and the like. Ketones,
Ethers such as tetrahydrofuran and dioxane can be used. Examples of the method for dispersing the conductive powder include a sand mill and a homomixer.

The electrostatic latent image developer of the present invention comprises the above carrier and toner particles comprising a binder resin and a colorant. Examples of the binder resin used for the toner particles include styrenes such as styrene and chlorostyrene, ethylene,
Monoolefins such as propylene, butylene, and isoprene; vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, and vinyl acetate; methyl acrylate, ethyl acrylate, butyl acrylate, dodecyl acrylate, octyl acrylate, and acrylic acid Phenyl,
Α-methylene aliphatic monocarboxylic acid esters such as methyl methacrylate, ethyl methacrylate, butyl methacrylate, dodecyl methacrylate, vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether, vinyl methyl ketone, vinyl hexyl ketone, vinyl Homopolymers or copolymers of vinyl ketones such as isopropenyl ketone can be exemplified. Particularly typical binder resins include polystyrene, styrene-acrylate copolymers, and styrene-methacrylate copolymers. Copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, styrene-maleic anhydride copolymer, polyethylene and polypropylene. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin, and wax can be used.

Examples of the coloring agent include carbon black, nigrosine, aniline blue, calcoil blue, chrome yellow, ultramarine blue, Dupont oil red, quinoline yellow, methylene blue chloride, phthalocyanine blue, malachite green oxalate, lamp black, and rose bengal. , C.I. I. Pigment Red 48: 1, C.I. I. Pigment Red 1
22, C.I. I. Pigment Red 57: 1, C.I. I.
Pigment Yellow 97, C.I. I. Pigment Yellow 12, C.I. I. Pigment Blue 15: 1, C.I.
I. Pigment Blue 15: 3 and the like can be exemplified.

A known charge control agent may be added to the toner, if desired.
An additive such as a fixing aid may be contained. The average particle size of the toner is 30 μm or less, preferably 4 to 20 μm.
When the developer is prepared by mixing the toner and the carrier, the toner concentration is preferably in the range of 0.3 to 30% by weight.

In the image forming method of the present invention, a latent image is formed on an electrostatic carrier, the latent image is developed using the above-described electrostatic latent image developer, and the developed toner image is transferred to a transfer member. An image can be formed by transferring and heat-fixing the toner image on the transfer body.

[0024]

[Manufacture of carrier]

(Example 1) Magnetite (MX030A, average particle size 50 µm, manufactured by Fuji Electric Chemical Co., Ltd.) 100 parts by weight Toluene 13.5 parts by weight Styrene-methyl methacrylate copolymer (copolymerization ratio 20:80) 1.8 parts by weight Carbon 0.3 parts by weight of black (VXC72, 10 ^-1 Ω · cm particle size 30 nm, manufactured by Cabot Corporation) The above components except magnetite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. Next, the solution for forming a coating resin layer and magnetite were placed in a vacuum degassing type kneader and stirred for 20 minutes while reducing the pressure at a temperature of 60 ° C. to form a coating resin layer. The thickness of the coating resin layer was 0.8 μm. Further, the content of carbon black (VXC72) in the coating resin layer was 8% by volume. When the carrier A was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the resin was uniformly coated. A coating resin layer forming solution was applied to a thickness of 0.8 μm on an ITO conductive glass substrate using an applicator to obtain a coating resin film. FIG. 1 shows the results of resistance measurement of magnetite and carrier A in the form of a magnetic brush. The resistance values when extrapolated to an electric field of 10 ⁴ V / cm are 4 × 10 ⁻⁵ Ω · cm and 1.8 × 10 ⁸ Ω · c, respectively.
m. The resistance value of the coating resin film is 100 V / cm.
The electric field was 3 × 10 ⁵ Ω · cm.

(Example 2) Ferrite (MF-35, average particle size 35 μm, manufactured by Powder Tech Co.) 100 parts by weight Toluene 22 parts by weight Styrene-methyl methacrylate copolymer (copolymerization ratio 20:80) 3 parts by weight Carbon 0.8 parts by weight of black (Monarch 880, 10 ^-1 Ω · cm, particle size 16 nm, manufactured by Cabot) The above components except ferrite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. Next, the coating resin layer forming solution and the ferrite were placed in a vacuum degassing type kneader and stirred for 20 minutes while reducing the pressure at a temperature of 60 ° C. to form a coating resin layer, and a carrier B was obtained. The thickness of the coating resin layer was 0.8 μm. The content of carbon black (Monarch 880) in the coating resin layer was 13% by volume. When this carrier B was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the carrier B was uniformly coated. A coating resin layer forming solution was applied to a thickness of 0.8 μm on an ITO conductive glass substrate using an applicator to obtain a coating resin film. Ferrite and carrier B
Is measured in the form of a magnetic brush, and the resistance value when extrapolated to an electric field of 10 ⁴ V / cm is 5 × 10 ⁻² Ω · c.
m, 4 × 10 ⁷ Ω · cm. The resistance value of the coating resin film was 2 × 10 ³ Ω · cm at an electric field of 100 V / cm.

Example 3 Ferrite (C28-FB, average particle size 50 μm, manufactured by Fuji Electric Chemical Co., Ltd.) 100 parts by weight Toluene 14 parts by weight Styrene-methyl methacrylate copolymer (copolymerization ratio 20:80) 2 parts by weight Tin oxide (Pastran TYPE-IV, 1 Ω · cm, particle size 100 nm, manufactured by Mitsui Kinzoku Co., Ltd.) 2 parts by weight The above components except ferrite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. Next, the coating resin layer forming solution and the ferrite were placed in a vacuum degassing type kneader and stirred for 20 minutes while reducing the pressure at a temperature of 60 ° C. to form a coating resin layer, and a carrier C was obtained. The thickness of the coating resin layer was 0.8 μm. Also, tin oxide (Pastran)
Was 13% by volume in the coating resin layer. When the carrier C was observed with a scanning electron microscope, it was confirmed that the carrier C was uniformly covered without any exposed surface. ITO
The coating resin layer forming solution was applied to a thickness of 0.8 μm on a conductive glass substrate using an applicator to obtain a coating resin film. The resistance of the ferrite and the carrier C was measured in the form of a magnetic brush. The resistance values when extrapolated to an electric field of 10 ⁴ V / cm were 1 × 10 ⁻⁵ Ω · cm and 2 × 10
It was ⁶ Ω · cm. The resistance value of the coating resin film is 100
It was 6 × 10 ⁴ Ω · cm at an electric field of V / cm.

(Example 4) Iron powder (TSV, average particle size 60 μm, manufactured by Powder Tech) 100 parts by weight Toluene 8 parts by weight Styrene-methyl methacrylate copolymer (copolymerization ratio 20:80) 1 part by weight Carbon black (VXC72, 10 ^-1 Ω · cm, particle size 30 nm, manufactured by Cabot Corporation) 0.2 parts by weight The above components except iron powder were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. Next, the solution for forming a coating resin layer and the iron powder were put into a vacuum degassing type kneader, and the temperature was set at 6 ° C.
The mixture was stirred for 20 minutes while reducing the pressure at 0 ° C. to form a coating resin layer, and a carrier D was obtained. 0.8 μm thick coating resin layer
Met. The content of carbon black (VXC72) in the coating resin layer was 10% by volume. When the carrier D was observed with a scanning electron microscope, it was confirmed that the carrier D was uniformly covered without any exposed surface. A coating resin layer forming solution was applied to a thickness of 0.8 μm on an ITO conductive glass substrate using an applicator to obtain a coating resin film. The resistance of the iron powder and the carrier D is measured in the form of a magnetic brush, and the resistance values when extrapolated to an electric field of 10 ⁴ V / cm are 1 × 10 ⁻¹⁴ Ω · cm and 2 × 10 ³ Ω · c, respectively.
m. The resistance value of the coating resin film is 100 V / cm.
The electric field was 8 × 10 ³ Ω · cm.

Comparative Example 1 Ferrite (C28-FB, average particle size 50 μm, manufactured by Fuji Electric Chemical Co., Ltd.) 100 parts by weight Toluene 14.5 parts by weight Styrene-methyl methacrylate copolymer (copolymerization ratio 20:80) 2 A solution for forming a coating resin layer obtained by dissolving a resin in toluene and ferrite are placed in a vacuum degassing kneader, and the temperature is 60 ° C.
The mixture was stirred for 20 minutes while depressurizing to form a coating resin layer, and a carrier E was obtained. The thickness of the coating resin layer was 0.8 μm. When the carrier E was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the resin was uniformly coated. A coating resin layer forming solution was applied to a thickness of 0.8 μm on an ITO conductive glass substrate using an applicator to obtain a coating resin film. As a result of measuring the resistance of the carrier E in the form of a magnetic brush, the value in an electric field of 10 ⁴ V / cm was 6.3 × 10 ¹⁰ Ω · cm. Further 400
The value in an electric field of V / cm is 1.0 × 10 ¹¹ Ω · cm, 40
The value in an electric field of 00 V / cm was 9.8 × 10 ¹⁰ Ω · cm. The resistance value of the coating resin film was 1 × 10 ¹³ Ω · cm at an electric field of 100 V / cm. As can be seen from this comparative example, when the low-resistance core was uniformly coated with the high-resistance resin, no rapid change in resistance due to the electric field was observed.

Example 5 Ferrite (C28-FB, average particle size 50 μm, manufactured by Fuji Electric Chemical Co., Ltd.) 100 parts by weight Toluene 12.3 parts by weight Styrene-methyl methacrylate copolymer (copolymerization ratio 20:80) 0 .43 parts by weight Carbon black (VXC72, 10 ^-1 Ω · cm particle size 30 nm, manufactured by Cabot Corporation) 0.07 parts by weight The above components except ferrite were dispersed in a sand mill for 1 hour to prepare a solution for forming a coating resin layer. did. Next, the coating resin layer forming solution and the ferrite were placed in a vacuum degassing type kneader and stirred for 20 minutes while reducing the pressure at a temperature of 60 ° C. to form a coating resin layer. The thickness of the coating resin layer was 0.2 μm. The content of carbon black (VXC72) in the coating resin layer was 8% by volume, which was the same as in Example 1. When this carrier F was observed with a scanning electron microscope, it was found that an exposed surface was slightly observed. A coating resin layer forming solution was applied to a thickness of 0.8 μm on an ITO conductive glass substrate using an applicator to obtain a coating resin film. The resistance of the carrier F was measured in the form of a magnetic brush, and the resistance value when extrapolated to an electric field of 10 ⁴ V / cm was 4.2 × 10 ⁶ Ω · cm. The resistance value of the coating resin film is 3 × 10 at an electric field of 100 V / cm.
It was ⁵ Ω · cm.

Example 6 Ferrite (C28-FB, average particle size 50 μm, manufactured by Fuji Electric Chemical Co., Ltd.) 100 parts by weight Toluene 14 parts by weight Diethylaminoethyl methacrylate-styrene-methyl methacrylate copolymer (copolymerization ratio 2:20) : 78) 1 part by weight perfluorooctyl methacrylate-methyl methacrylate copolymer (copolymerization ratio 40:60) 1 part by weight tin oxide (Pastran TYPE-IV 6 × 10 ⁴ Ω · cm particle size 100 nm, manufactured by Mitsui Kinzoku Co., Ltd.) 6.1 parts by weight

The above components except ferrite were dispersed in a sand mill for 1 hour to prepare a solution for forming a coating resin layer. Next, the solution for forming a coating resin layer and the ferrite were placed in a vacuum degassing type kneader, and stirred at a temperature of 60 ° C. for 20 minutes while reducing the pressure to form a coating resin layer. The thickness of the coating resin layer was 0.8 μm. The content of tin oxide (Pastran TYPE-IV) in the coating resin layer was 4%.
It was 0% by volume. When this carrier I was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the carrier I was uniformly coated. The coating resin layer forming solution was applied to a thickness of 0.8 μm on an ITO conductive glass substrate using an applicator to obtain a coating resin layer.

The resistance of the ferrite and the carrier I was measured in the form of a magnetic brush, and the resistance values when extrapolated to an electric field of 10 ⁴ V / cm were 1 × 10 ⁻⁵ Ω · cm ^and 4 × 10 ⁶ Ω, respectively.
Cm. The resistance value of the coating resin film is 100 V
/ Cm at an electric field of 7 × 10 ⁴ Ω · cm. Further, the water contact angle of the coating resin film was measured by a contact angle meter CA-A type manufactured by Kyowa Interface Science Co., Ltd., and as a result, it was 111 degrees.

Comparative Example 2 Ferrite (F-300, average particle size: 50 μm, manufactured by Powdertech Co.) 100 parts by weight Toluene 12.3 parts by weight Styrene-methyl methacrylate copolymer (copolymerization ratio: 20:80) 7 parts by weight Carbon black (VXC72, 10 ^-1 Ω · cm particle size 30 nm, manufactured by Cabot Corporation) 0.6 parts by weight The above components except ferrite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. . Next, the coating resin layer forming solution and the ferrite were placed in a vacuum degassing type kneader and stirred for 20 minutes while reducing the pressure at a temperature of 60 ° C. to form a coating resin layer. The thickness of the coating resin layer was 0.8 μm. In addition, carbon black (VX
The content of C72) in the coating resin layer was 16% by volume. When the carrier G was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the resin was uniformly coated. A coating resin layer forming solution was applied to a thickness of 0.8 μm on an ITO conductive glass substrate using an applicator to obtain a coating resin film. When the resistance of the ferrite and the carrier G was measured in the form of a magnetic brush, 10 ⁴ V
/ Cm electric field value is 9.1 × 10 ⁷ Ω · cm.
(Actual value) was 1 × 10 ² Ω · cm (extrapolated value).
The resistance value of the coating resin film is 3 × at an electric field of 100 V / cm.
It was 10 ⁰ Ω · cm.

Comparative Example 3 Ferrite (EFC-50B, average particle size: 50 μm, manufactured by Powder Tech Co.) 100 parts by weight Toluene 12.6 parts by weight Styrene-methyl methacrylate copolymer (copolymerization ratio: 20:80) 7 parts by weight Carbon black (VXC72, 10 ^-1 Ω · cm particle size 30 nm, manufactured by Cabot Corporation) 0.55 parts by weight The above components except ferrite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. . Next, the solution for forming a coating resin layer and ferrite were put into a vacuum degassing type kneader and stirred for 20 minutes while reducing the pressure at a temperature of 60 ° C. to form a coating resin layer, and a carrier H was obtained. The thickness of the coating resin layer was 0.8 μm. In addition, carbon black (VX
The content of C72) in the coating resin layer was 15% by volume. When the carrier H was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the resin was uniformly coated. A coating resin layer forming solution was applied to a thickness of 0.8 μm on an ITO conductive glass substrate using an applicator to obtain a coating resin film. The resistance of the ferrite and the carrier H was measured in the form of a magnetic brush, and was measured at 10 ⁴ V / cm.
The resistance value when extrapolated to the electric field of 1 × 10 ²
Ω · cm and 8 × 10 ⁴ Ω · cm. The resistance value of the coating resin film is 1 × 10 ⁰ Ω · c at an electric field of 100 V / cm.
m.

[Production of Toner] Linear polyester resin 100 parts by weight (linear polyester obtained from terephthalic acid / bisphenol A ethylene oxide adduct / cyclohexane dimethanol; Tg = 62 ° C., Mn = 4,000, Mw) = 12,000, acid value = 12, hydroxyl value = 25) 3 parts by weight of a magenta pigment (CI pigment, red 57) The above mixture was kneaded with an extruder, pulverized with a jet mill, and then an air classifier. D50 = 7 μm
Magenta toner was obtained.

[Evaluation of Image Quality] Examples 1-5 and Comparative Examples 1
100 parts by weight of the carrier obtained in Step 3
It was mixed with parts by weight to prepare developers corresponding to the carriers of Examples 1 to 5 and Comparative Examples 1 to 3. About these developers, an electrophotographic copying machine (A-Co, manufactured by Fuji Xerox Co., Ltd.)
lor630), and the evaluation environment was adjusted to a temperature of 22 ° C. and a humidity of 55% to perform a copy test.

(Image Density) A solid image (20 × 20 mm ² ) having an original density of 1.30 was copied, and the relative reflection density of the output image with respect to white paper was measured with a Macbeth densitometer. Was determined to be. The evaluation was performed for the first copy (initial) and the 50,000th copy.

(Density Unevenness) A limit sample was provided, and the output image was evaluated by visual observation. The symbol “○” indicates uniformity, and the symbol “×” indicates unevenness. The evaluation was performed on the first copy (initial). (Brush mark) The number of white marks included in the output image was evaluated with a microscope for a unit length (5 mm) in a direction perpendicular to the brush direction. The evaluation was performed on the first copy (initial). (Carrier over) The output image was evaluated by visual observation.
The symbol "○" indicates no carrier over, and the symbol "X" indicates carrier over. The evaluation was performed on the first copy (initial). Table 1 shows the above results.
Shown in

[0039]

[Table 1]

As can be seen from the table, when the carrier (A, B, C, D) of the present invention was used, a high solid image density was obtained, and there was no density unevenness. Furthermore, no brush mark or carrier over was seen.
On the other hand, when the low-resistance core was uniformly coated with the high-resistance resin as in the carrier E of the comparative example, brush marks and carrier over were not observed, but the density unevenness was found at the center and the periphery of the solid image. And the image density was low. This is presumably because the resistance of the coating resin layer was too high and the resistance of the carrier also exceeded a desired value, resulting in an IMB-like characteristic. Like the carrier F of the embodiment, the embodiment 1
In comparison with the case where the low-resistance core was coated with the medium-resistance coating resin layer thinly, a slight brush mark was generated. This is probably because although the resistance of the carrier is within the desired range, the presence of the exposed surface causes the electric charge to leak therefrom and a slight brush mark is generated.

When a low-resistance coating resin layer was formed on a high-resistance core like the carrier G of the comparative example, brush marks and carrier over occurred, and the image density was low and density unevenness was observed. Even when a low resistance coating resin layer was formed on a medium resistance core like the carrier H of the comparative example, brush marks and carrier over occurred, and the image density was low and density unevenness was observed. It is considered that, although the resistance of the carrier is within a desired range, the resistance of the coating resin layer is too low and an image defect occurs. The above carriers (A ~
D) has poor stability, whereas carrier I
When the conductive powder is contained in the water-repellent coating resin at 40% by volume as described above, the stability is excellent. As can be seen from the above results, a high-quality color image with no image defects can be obtained by uniformly forming a medium-resistance coating resin layer on a low-resistance core and controlling the resistance of the carrier to a desired range. .

[0042]

By using the carrier of the present invention, a high-quality image with very few image defects such as brush marks and carrier over can be obtained, which has a remarkable effect particularly on a color image.

[Brief description of the drawings]

FIG. 1 is a graph showing a relationship between a current density J and an applied electric field E when a carrier is measured in the form of a magnetic brush in Example 1 and an applied electric field E is extrapolated to an electric field of 10 ⁴ V / cm.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Taku Fukuhara 430 Green Tech Nakai, Nakai-cho, Ashigara-kami, Kanagawa Prefecture Inside Fuji Xerox Co., Ltd. Inside the corporation

Claims (10)

[Claims] 1. An electrophotographic carrier having a coating resin layer containing a conductive powder on a core material, wherein the core material has a dynamic electric resistance under an electric field of 10 ⁴ V / cm in the state of a magnetic brush. An electrophotographic carrier, wherein the carrier is 1 Ω · cm or less, and the electric resistance of the coating resin layer is in the range of 10 to 1 × 10 ⁸ Ω · cm. 2. The electrophotographic carrier according to claim 1, wherein the coating resin layer has a thickness of 0.3 to 5 μm. 3. The carrier has an average particle diameter of 10 to 100.
2. The carrier for electrophotography according to claim 1, wherein the carrier has a thickness of μm. 4. The electrophotographic carrier according to claim 1, wherein the core material is ferrite. 5. The carrier for electrophotography according to claim 1, wherein the electric resistance of the conductive powder is 10 ⁶ Ω · cm or less. 6. The method according to claim 1, wherein the conductive powder is contained in the coating resin layer in an amount of 3 to 40.
The carrier for electrophotography according to claim 1, wherein the carrier is contained by volume%. 7. The method according to claim 1, wherein the contact angle of the coating resin layer with water is 90 degrees or more, and the conductive powder is contained in an amount of 20 to 40% by volume with respect to the coating resin layer.
4. The electrophotographic carrier according to claim 1. 8. The electric resistance of the carrier is 10 to 1 × 10
The electrophotographic carrier according to claim 1, wherein the carrier is in a range of ⁹ Ω · cm. 9. An electrostatic latent image developer comprising toner particles comprising a binder resin and a colorant, and a carrier having a coating resin layer provided on a core material, wherein 10 ⁴ V / V
a coating resin layer having an electric resistance in a range of 10 to 1 × 10 ⁸ Ω · cm on a core material having a dynamic electric resistance of 1 Ω · cm or less under an electric field of 1 cm. Image developer. 10. A step of forming a latent image on a latent image carrier,
Developing the latent image using a developer, transferring the developed toner image to a transfer member, and fixing the toner image on the transfer member by heating. An image forming method using the electrostatic latent image developer according to claim 8 as an agent.