JP2001183874A - Carrier for development of electrostatic latent image, electrostatic latent image developer and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier for the development of an electrostatic latent image capable of giving a good color image free from image defects such as a brush mark in the formation of an image by an electrostatic latent image developing method and also having high stability to deterioration with the lapse of time, an electrostatic latent image developer and an image forming method. SOLUTION: The carrier has a coating resin layer on a core material and the coating resin layer contains an electrically conductive powder. When the work function of the coating resin is <=5 eV, the hydrogen ion concentration pH of the electrically conductive powder is <=4. When the work function of the coating resin is >5 eV, the hydrogen ion concentration pH of the electrically conductive powder is >=9.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Methods for visualizing image information via an electrostatic latent 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.
They are widely used at present because they share functions such as transport and charging, and have good controllability because they are separated in function as a developer.

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 the CMB development, since the electric resistance of the carrier is low, electric charge is injected from the development roll, and the carrier near the photoreceptor functions as a development electrode, and the effective development electric field increases. As a result, the toner is sufficiently transferred, and the solid image is excellent in reproducibility. On the other hand, there is a problem that image defects such as a white line called a brush mark caused by charge injection from a developing roll and a transfer of a carrier to a photoreceptor called a carrier over are easily generated.

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 in that respect, CMB development is more suitable than IMB development. Therefore, it is strongly desired to further improve the performance of a CMB developing carrier having stability and durability of an output image.

The present inventors have previously proposed a carrier in which a coating resin layer containing a metal oxide-based conductive powder is formed on a core material as a conductive carrier. Thereafter, in the course of further study, even with the same type of metal oxide-based conductive powder, when the conductive powder was dispersed in the resin solution, a problem occurred in that the conductive powder strongly aggregated and the viscosity of the dispersion liquid increased. If conductive powders are strongly agglomerated, brush marks may be generated, or the viscosity of the dispersion liquid may increase, so that the carrier core material may not be uniformly coated. There was a problem that the durability was reduced.

[0006]

Therefore, in the present invention,
When forming an image by the electrostatic latent image developing method, a good color image free from image defects such as brush marks can be obtained, and the electrostatic latent image with high stability against deterioration over time can be obtained. An object is to provide a developing carrier, an electrostatic latent image developer, and an image forming method.

[0007]

Means for Solving the Problems As a result of intensive studies on the above-mentioned problems, the present inventors have found that when the work function of the coating resin is 5 eV or less, the conductive powder having a hydrogen ion concentration (pH) of 4 or less is used. Is selected, and when the work function of the coating resin is greater than 5 eV, a good dispersion of the conductive powder in the coating resin is ensured by selecting a conductive powder having a hydrogen ion concentration (pH) of 9 or more. Can suppress the increase in the viscosity of the conductive powder-containing coating resin solution. As a result, it is possible to form a uniform coating resin layer on the surface of the core material, thereby reducing the chargeability and generating image defects such as brush marks. The inventors have found that it can be suppressed, and completed the present invention. The configuration of the present invention is as follows.

(1) In a carrier for developing an electrostatic latent image having a coating resin layer on a core material, the coating resin layer contains a conductive powder, the work function of the coating resin is 5 eV or less, and A carrier for developing an electrostatic latent image, wherein the carrier has a hydrogen ion concentration (pH) of 4 or less.

(2) In a carrier for developing an electrostatic latent image having a coating resin layer on a core material, the coating resin layer contains a conductive powder, and the work function of the coating resin is greater than 5 eV; A carrier for developing an electrostatic latent image, having a hydrogen ion concentration (pH) of 9 or more.

(3) The content of the conductive powder in the coating resin layer is in the range of 25 to 45% by volume.
The carrier for developing an electrostatic latent image according to (1) or (2). (4) wherein the conductive powder is a metal oxide (1)-
The carrier for developing an electrostatic latent image according to any one of the above (3).

(5) The carrier for developing an electrostatic latent image according to any one of (1) to (4), wherein the conductive powder is acicular conductive powder. (6) The carrier for developing an electrostatic latent image according to (5), wherein the aspect ratio of the major axis to the minor axis of the acicular conductive powder is 3 or more.

(7) The electric resistance of the conductive powder is 1 × 10 to 1
(1) characterized in that it is within the range of × 10 ⁶ Ωcm.
The carrier for developing an electrostatic latent image according to any one of items (1) to (6). (8) The electric resistance of the coating resin layer is in a range of 1 × 10 to 1 × 10 ⁸ Ωcm under an electric field of 10 ² V / cm, any one of the above (1) to (7). The carrier for developing an electrostatic latent image according to claim 1.

(9) The coating resin layer has a thickness of 0.3 to 5 μm.
m, any one of (1) to (8) above.
5. The carrier for developing an electrostatic latent image according to any one of the above. (10) The carrier for developing an electrostatic latent image as described in any one of (1) to (9) above, wherein the average particle size of the carrier core material is in a range of 10 to 100 μm. (11) The carrier according to any one of (1) to (10), wherein the dynamic electric resistance of the carrier is in a range of 1 × 10 to 1 × 10 ⁸ Ωcm under an electric field of 10 ⁴ V / cm. The carrier for developing an electrostatic latent image according to claim 1.

(12) An electrostatic latent image developer comprising a toner containing at least a binder resin and a colorant, and a carrier having a coating resin layer on a core material, wherein any of the above (1) to (11) An electrostatic latent image developer using the carrier according to any one of the above. (13) 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, and a toner image on the transfer body A fixing step of heat-fixing the electrostatic latent image developer, wherein the electrostatic latent image developer according to (12) is used as the developer.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to preferred embodiments. As the material of the carrier core material used in the present invention, any of conventionally known materials can be used, but ferrite and magnetite are particularly preferably selected. As another carrier core material, for example, iron powder is known. However, iron powder has a large specific gravity and thus easily deteriorates the toner, and is inferior in stability to ferrite and magnetite.

The average particle size of the carrier core material of the present invention is preferably 10 to 100 μm, more preferably 20 to 80 μm.
m. 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.

As the conductive powder, carbon black, metal oxide and the like are known. Among them, carbon black is advantageous in that it is inexpensive. However, since the electrical resistance of carbon black itself is considerably low at 10 ^-1 Ωcm or less, C
In the MB developing method, a bias leak is easily caused, which causes image defects such as brush marks. On the other hand, the electrical resistance of the metal oxide of the conductive powder is 10 ⁰ to 10 ⁶ [Omega] cm
Is preferable, since it has a wide selection range.

As the material of the conductive powder used in the present invention, a composite type of fine particles such as titanium oxide, zinc oxide, aluminum borate, potassium titanate and tin oxide coated with a conductive metal oxide is used. Metal oxides doped with antimony or the like (for example, antimony-doped tin oxide) and conductive metal oxides such as oxygen-deficient metal oxides (for example, oxygen-deficient tin oxide). be able to.

The pH of the conductive powder in combination with the coating resin strongly affects the viscosity of the dispersion. Specifically, when a coating resin having a work function of 5 eV or less is used, the pH of the conductive powder is preferably 4 or less, more preferably 3.5 or less.
When using a coating resin having a work function larger than 5 eV, the pH of the conductive powder is preferably 9 or more, more preferably 10.5 or more. When a conductive powder having a pH of more than 4 is dispersed in a coating resin having a work function of 5 eV or less, the dispersibility of the conductive powder is reduced, the conductive powders aggregate, and the viscosity of the dispersion is increased. Coating is hindered. As a result, the chargeability is reduced and causes image defects such as brush marks. When a conductive powder having a pH of less than 9 is dispersed in a coating resin having a work function of more than 5 eV, the dispersibility of the conductive powder is reduced, and the conductive powders are aggregated to increase the viscosity of the dispersion. Uniform coating is hindered. As a result, the chargeability is reduced and causes image defects such as brush marks.

In the present invention, the pH of the conductive powder was measured by suspending the conductive powder in distilled water using a homogenizer and using a pH meter. As the shape of the conductive powder, various shapes such as a needle shape and a spherical shape are used, and the needle shape is particularly suitable for improving environmental stability. "Needles" here
The term "major axis / minor axis" (major axis / minor axis; hereinafter, referred to as "aspect ratio") means 3 or more, preferably 5 or more, and more preferably 10 or more.

The major axis of the acicular conductive powder is 0.05 to 20.
μm is preferred. Even if the aspect ratio is 3 or more, if the major axis is shorter than 0.05 μm, the conductive powder is broken in the process of dispersing in the coating resin, and the effect is easily reduced. When the major axis is longer than 20 μm, the conductive powder is easily separated from the coating resin layer. The minor axis of the acicular conductive powder is 0.01 to 1
μm is preferred. If the ratio is out of this range, the dispersibility deteriorates, and the characteristics of the carrier tend to be non-uniform. The spherical conductive powder preferably has an average particle size of 0.01 to 1 μm.
Outside this range, the dispersibility becomes poor, and the conductive powder tends to separate from the coating resin layer. The electric resistance of the conductive powder of the present invention is suitably in the range of 1 × 10 to 1 × 10 ⁶ Ωcm.

The content of the conductive powder in the coating resin layer is 2
5 to 45 volume% is preferable, and 30 to 40 volume% is more preferable. When hard conductive powder is contained in the coating resin layer, the coating resin layer becomes hard due to the reinforcing effect of the conductive powder, and the impact of external additives such as silica, titania, and alumina attached to the toner on the coating resin layer is reduced. Is prevented and durability is improved. When the content of the conductive powder is less than 25% by volume, the reinforcing effect is not sufficiently exhibited, and when the content is more than 45% by volume, the conductive powder is liable to be detached.

The electric resistance of the coating resin layer is 1 × 10 to 1 × 1
0 ⁸ Ωcm is preferred, and 1 × 10 ³ to 1 × 10 ⁷ Ωcm
Is more preferred. 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. When the electric resistance of the coating resin layer is smaller than 1 × 10 Ωcm, electric charges easily move on the carrier surface, and image defects such as brush marks are easily generated. If the electric resistance of the coating resin layer is larger than 1 × 10 ⁸ Ωcm, a good solid image cannot be obtained. The electric resistance of the coating resin layer is
A coating resin film having a thickness of about several μm is formed on an ITO conductive glass substrate using an applicator or the like, and a gold electrode is formed thereon by vapor deposition to obtain a current-voltage characteristic under an electric field of 10 ² V / cm. Ask.

The dynamic electric resistance of the carrier, that is, the dynamic electric resistance when the carrier whose surface is coated with resin is measured in the form of a magnetic brush, is 1 × 1 at an electric field of 10 ⁴ V / cm.
0 to 1 × 10 ⁸ Ωcm, preferably 1 × 10 ³ to 1 × 1
A range of 0 ⁷ Ωcm is appropriate. If the dynamic electric resistance is less than 1 × 10 Ωcm, image defects such as brush marks tend to occur, and if it is more than 1 × 10 ⁸ Ωcm, it becomes difficult to obtain a good solid image. 10 ⁴ V / cm
Is close to the developing electric field in the actual machine, and the electric resistance is defined by the value under this electric field.

The dynamic electric resistance of the carrier is obtained as follows. A magnetic brush is formed by placing a carrier of about 30 cm ³ on a developing roll, and a plate electrode having an area of 3 cm ² is formed by 2.5 m.
It is made to face a developing roll at intervals of m. A voltage is applied between the developing roll and the plate electrode while rotating the developing roll at a rotation speed of 120 rpm, and the current flowing at that time is measured. From the obtained current-voltage characteristics, the electrical resistance is obtained using the equation of Ohm's law. It is well known that there is generally a relation of In (I / V) ∝V ^1/2 between the applied voltage V and the current I at this time. When the electric resistance is considerably low as in the carrier used in the present invention, 10 ³ V
In a high electric field of / cm or more, a large current may flow and measurement may not be possible. In such a case, measure three or more points in a low electric field,
The value is extrapolated to an electric field of 10 ⁴ V / cm by the least squares method using the above relational expression.

Among the coating resins formed on the carrier core material, examples of the coating resin having a work function of 5 eV or less include polymethyl methacrylate, polystyrene, polyvinyl acetate, polyvinyl alcohol, polyvinyl carbazole, and styrene-acryl copolymer. No. Examples of the coating resin having a work function larger than 5 eV include a fluororesin such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and polychlorotrifluoroethylene. These may be used alone or as a mixture of a plurality of resins. The work function of the coating resin of the present invention was obtained by forming a coating resin film having a thickness of about several μm on a gold-plated metal plate using an applicator or the like, and using the Kelvin contact potential difference method.

The thickness of the coating resin layer is preferably 0.3 to 5
μm, more preferably 0.5 to 3 μm. If the thickness of the coating resin layer is smaller than 0.3 μm, it is difficult to form a uniform and flat coating resin layer on the surface of the carrier core material.
On the other hand, if it is larger than 5 μm, coarse particles are generated due to aggregation of carriers, and a uniform carrier cannot be obtained.

As a method of forming the coating resin layer on the carrier core material, there are a dipping method in which the carrier core material is dipped in a coating resin layer forming solution, that is, a resin solution in which conductive powder is dispersed, a coating resin layer forming solution. Method for spraying the carrier core material on the surface of the carrier core material, fluidized bed method for spraying the solution for forming the coating resin layer while the carrier core material is suspended by flowing air, solution for forming the carrier core material and the coating resin layer in a kneader coater And then kneader coater method of removing the solvent.

The solvent used in the solution for forming the coating resin layer is not particularly limited as long as it can dissolve the above-mentioned coating resin, and examples thereof include aromatic hydrocarbons such as toluene and xylene, acetone, and the like. Ketones such as methyl ethyl ketone and ethers such as tetrahydrofuran and dioxane can be used. As a method for dispersing the conductive powder, a sand mill, a dyno mill, a homomixer, or the like can be used.

The toner of the present invention contains at least a binder resin and a colorant. Examples of the binder resin include styrenes such as styrene and chlorostyrene; monoolefins such as ethylene, 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, phenyl acrylate, methyl methacrylate, and ethyl methacrylate Α-methylene aliphatic monocarboxylic esters such as butyl methacrylate, dodecyl methacrylate; vinyl ethers such as vinyl methyl ether, vinyl ethyl ether and vinyl butyl ether; vinyl methyl ketone, vinyl hexyl ketone,
Homopolymers or copolymers of vinyl ketones such as vinyl isopropenyl ketone can be exemplified. Particularly typical binder resins include polystyrene and styrene-
Acrylic ester copolymers, styrene-methacrylic ester copolymers, styrene-acrylonitrile copolymers, styrene-butadiene copolymers, styrene-maleic anhydride copolymers, polyethylene, polypropylene and the like can be mentioned. Further, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin, waxes and the like can be mentioned. Among these, polyester is particularly suitable as the binder resin. For example, a linear polyester resin composed of a polycondensate containing bisphenol A and a polyvalent aromatic carboxylic acid as main monomer components is preferable.

As the colorant, 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, rose bengal , CI Pigment Red 48: 1, CI Pigment Red 122, CI Pigment Red 57: 1, CI Pigment Yellow 97, C.
I. Pigment Yellow 12, CI Pigment Blue 1
5: 1, CI Pigment Blue 15: 3 and the like can be exemplified.

A known charge controlling 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 ratio of the toner is preferably in the range of 0.3 to 30% by weight of the whole developer. The developer obtained in this way includes a step of forming a latent image on the latent image carrier, a step of developing the latent image using the developer, and a step of transferring the developed toner image to a transfer body. And a fixing step of heating and fixing the toner image on the transfer member.

[0033]

[Example 1]

Ferrite 100 parts by weight (DFC350, average particle size 50 μm, manufactured by Dowa Iron Powder Co., Ltd.) Toluene 8.8 parts by weight Diethylaminoethyl methacrylate-styrene-methyl methacrylate copolymer 1.2 parts by weight (copolymerization ratio 2:20:78) , Weight average molecular weight 50,000, work function 4.5 eV) 3.7 parts by weight of acicular conductive powder (antimony-doped tin oxide coated titanium oxide, manufactured by Ishihara Sangyo)) (pH 3.2, electric resistance 7 × 10 ⁴ Ωcm, long) Shaft 0.3 μm, short axis 0.06 μm, aspect ratio 5) The above components except ferrite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. The viscosity of the solution for forming a coating resin layer was 70 cp. Next, this coating resin layer forming solution and ferrite are put into a vacuum degassing type kneader, and stirred at a temperature of 75 ° C. for 20 minutes while reducing pressure to form a coating resin layer, which is further sieved with a sieve having an opening of 75 μm. Carrier A was obtained. The thickness of the coating resin layer was 0.9 μm. When the content of antimony-doped tin oxide-coated titanium oxide was 40% by volume, the carrier was observed with a scanning electron microscope. As a result, it was confirmed that the carrier was uniformly coated without an exposed surface and the surface was flat. Was.

Further, a coating resin layer forming solution was applied to a thickness of 0.9 μm on an ITO conductive glass substrate using an applicator to obtain a sample for measuring the electric resistance of the coating resin film. The electric resistance of the carrier A was measured in the form of a magnetic brush, and the electric resistance when extrapolated to an electric field of 10 ⁴ V / cm was 3 × 10 ⁵ Ωcm. The electric resistance of the coating resin film was 6 × 10 ⁵ Ωcm at an electric field of 100 V / cm.

Example 2 Ferrite 100 parts by weight (DFC350, average particle size 50 μm, manufactured by Dowa Iron Powder Co., Ltd.) Toluene 10.3 parts by weight Perfluorooctylethyl methacrylate-methyl methacrylate copolymer 1.4 parts by weight ( Copolymerization ratio 40:60, weight average molecular weight 50,000, work function 5.1 eV) 2.76 parts by weight of acicular conductive powder (antimony-doped tin oxide-coated potassium titanate, manufactured by Otsuka Chemical Co., Ltd., pH10, electric resistance 1 × 10 ² Ωcm) The major axis was 15 μm, the minor axis was 0.35 μm, and the aspect ratio was 43) The above components except for ferrite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. The viscosity of the solution for forming a coating resin layer was 85 cp. Next, the solution for forming a coating resin layer and ferrite are put into a vacuum degassing type kneader, and stirred at a temperature of 75 ° C. for 20 minutes while reducing the pressure to form a coating resin layer. Carrier B was obtained. The thickness of the coating resin layer was 0.9 μm. The content of antimony-doped tin oxide-coated potassium titanate was 30% by volume. Observation of this carrier with a scanning electron microscope confirmed that there was no exposed surface, that the carrier was uniformly coated, and that the surface was flat.

Further, a coating resin layer forming solution was applied to a thickness of 0.9 μm on an ITO conductive glass substrate using an applicator to obtain a sample for measuring the electrical resistance of the coating resin film. The electric resistance of the carrier B was measured in the form of a magnetic brush, and the electric resistance was 6 × 10 ⁶ Ωcm when extrapolated to an electric field of 10 ⁴ V / cm. The electric resistance of the coating resin film was 7 × 10 ⁶ Ωcm at an electric field of 100 V / cm.

(Comparative Example 1) Ferrite 100 parts by weight (DFC350, average particle size 50 μm, manufactured by Dowa Iron Powder Co., Ltd.) Toluene 8.8 parts by weight Diethylaminoethyl methacrylate-styrene-methyl methacrylate copolymer 1.2 parts by weight ( Copolymerization ratio 2:20:78, weight average molecular weight 50,000, work function 4.5 eV) 3.7 parts by weight of acicular conductive powder (antimony-doped tin oxide coated titanium oxide, manufactured by Ishihara Sangyo, pH 4.2, electric resistance 7) × 10 ⁴ Ωcm, major axis 0.3 μm, minor axis 0.06 μm, aspect ratio 5) The above components except for ferrite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. The viscosity of the solution for forming a coating resin layer was 450 cp. Next, the solution for forming a coating resin layer and ferrite are put into a vacuum degassing type kneader, and stirred at a temperature of 75 ° C. for 20 minutes while reducing the pressure to form a coating resin layer. Carrier C was obtained. The thickness of the coating resin layer was 0.9 μm. The content of antimony-doped tin oxide-coated titanium oxide was 40% by volume. When this carrier was observed with a scanning electron microscope, a part of the exposed surface was observed.

Further, a coating resin layer forming solution was applied to a thickness of 0.9 μm on an ITO conductive glass substrate using an applicator to obtain a sample for measuring the electrical resistance of the coating resin film. The electric resistance of the carrier C was measured in the form of a magnetic brush, and the electric resistance when extrapolated to an electric field of 10 ⁴ V / cm was 8 × 10 ⁴ Ωcm. The electric resistance value of the coating resin film is 9 × 10 ⁴ Ωcm at an electric field of 100 V / cm.
Met.

(Comparative Example 2) Ferrite 100 parts by weight (DFC350, average particle diameter 50 μm, manufactured by Dowa Iron Powder Co., Ltd.) Toluene 8.8 parts by weight Perfluorooctylethyl methacrylate-methyl methacrylate copolymer 1.2 parts by weight ( Copolymerization ratio 40:60, weight average molecular weight 50,000, work function 5.1 eV) 3.7 parts by weight of spherical conductive powder (oxygen-deficient tin oxide coated barium sulfate, Pastran TYPE-IV, Mitsui Kinzoku Co., Ltd., pH 2.9, electric resistance 6) (× 10 ⁴ Ωcm, average particle size 0.1 μm) The above components except ferrite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. The viscosity of the solution for forming a coating resin layer was 400 cp. Next, this coating resin layer forming solution and ferrite are put into a vacuum degassing type kneader, and stirred at a temperature of 75 ° C. for 20 minutes while reducing pressure to form a coating resin layer, which is further sieved with a sieve having openings of 75 μm. Carrier D was obtained. The thickness of the coating resin layer was 0.9 μm. Further, the content of oxygen-deficient tin oxide-coated barium sulfate was 40% by volume. When this carrier was observed with a scanning electron microscope, a part of the exposed surface was observed.

Further, a coating resin layer forming solution was applied to a thickness of 0.9 μm on an ITO conductive glass substrate using an applicator to obtain a sample for measuring the electrical resistance of the coating resin film. The electric resistance of the carrier D was measured in the form of a magnetic brush, and the electric resistance was 5 × 10 ⁶ Ωcm when extrapolated to an electric field of 10 ⁴ V / cm. The electric resistance of the coating resin film was 6 × 10 ⁶ Ωcm at an electric field of 100 V / cm.

Comparative Example 3 Ferrite 100 parts by weight (DFC350, average particle size 50 μm, manufactured by Dowa Iron Powder Co., Ltd.) Toluene 10.3 parts by weight Perfluorooctylethyl methacrylate-methyl methacrylate copolymer 1.4 parts by weight ( Copolymerization ratio 40:60, weight average molecular weight 50,000, work function 5.1 eV) Needle-like conductive powder 2.76 parts by weight (antimony-doped type tin oxide-coated potassium titanate, pH 8 by Otsuka Chemical Co., Ltd., electric resistance 1 × 10 ²⁾ Ωcm, major axis 15 μm, minor axis 0.35 μm, aspect ratio 43) The above components except for ferrite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. The viscosity of the solution for forming a coating resin layer was 420 cp. Next, the coating resin layer forming solution and the ferrite are put into a vacuum degassing kneader and stirred at a temperature of 75 ° C. for 20 minutes while reducing pressure to form a coating resin layer, which is further sieved with a sieve having an opening of 75 μm. Carrier E was obtained. The thickness of the coating resin layer was 0.9 μm. The content of antimony-doped tin oxide-coated potassium titanate was 30% by volume. When this carrier was observed with a scanning electron microscope, a part of the exposed surface was observed.

Further, a solution for forming a coating resin layer was applied to a thickness of 0.9 μm on an ITO conductive glass substrate using an applicator to obtain a sample for measuring the electrical resistance of the coating resin film. The electric resistance of the carrier E was measured in the form of a magnetic brush, and the electric resistance was 4 × 10 ⁵ Ωcm when extrapolated to an electric field of 10 ⁴ V / cm. The electric resistance of the coating resin film was 7 × 10 ⁶ Ωcm at an electric field of 100 V / cm.

[Production of Toner] Linear polyester resin 100 parts by weight (linear polyester obtained from terephthalic acid / bisphenol A ethylene oxide adduct / cyclohexanedimethanol; Tg = 62 ° C., Mn = 4,000, Mw = 12,000, Acid value = 12, hydroxyl value = 25) Magenta pigment (CI Pigment, Red 57) 3 parts by weight The above mixture was kneaded with an extruder, pulverized with a jet mill, and then dispersed with a wind classifier and d ₅₀ = 7 μm. Magenta colored particles were obtained.

[Evaluation of Image Quality] Examples 1 and 2 and Comparative Examples 1 and 2
100 parts by weight of the carrier obtained in Step 2
The developer was mixed with parts by weight to prepare developers corresponding to the carriers of Examples 1 and 2 and Comparative Examples 1 and 2. For these developers, electrophotographic copiers (Fuji Xerox Co., Ltd., A-Color6
30), and the evaluation environment is normal temperature and normal humidity (22 ° C, 55%)
And a copy test was performed.

(Image Density) A solid image (20 mm × 20 mm) having a document density of 0.50 was copied, and the relative reflection density of the output image on white paper was measured with a Macbeth densitometer.
It was determined that the closer the image density was to 0.50, the better.
The evaluation was performed on the first copy and the 50,000th copy.

(Fog) Toner fog on the image background portion was evaluated by visual observation, and ranked according to the following three grades. The evaluation was performed on the first copy. ：: No fogging Δ: Fog is slightly observed, but there is no practical problem. X: Fogging is remarkable. (Brush mark) The number of white marks included in the output image is determined by a microscope with a unit length (5 mm) perpendicular to the brush direction. Was evaluated. The evaluation was performed on the first copy.

[0047]

[Table 1]

As is evident from Table 1, when the carriers A and B of the present invention were used, no fog or brush marks were obtained, excellent image quality was obtained, and the image was stable against deterioration over time. Was. On the other hand, when the carriers C, D, and E of the comparative examples were used, the image density was high due to the low charge amount, and fog occurred and brush marks were observed.

[0049]

According to the present invention, by adopting the above-mentioned structure, a good color image free from image defects such as brush marks can be obtained with respect to an image obtained by the electrostatic latent image developing method, in particular, a color image. As a result, it has become possible to provide a carrier for an electrostatic latent image developer having high stability against deterioration over time, a developer using the carrier, and an image forming method.

Claims (4)

[Claims] In a carrier for developing an electrostatic latent image having a coating resin layer on a core material, the coating resin layer contains a conductive powder, the work function of the coating resin is 5 eV or less, and the hydrogen of the conductive powder is An electrostatic latent image developing carrier having an ion concentration pH of 4 or less. 2. A carrier for developing an electrostatic latent image having a coating resin layer on a core material, wherein the coating resin layer contains a conductive powder, the work function of the coating resin is greater than 5 eV, and hydrogen of the conductive powder is A carrier for developing an electrostatic latent image, wherein the carrier has an ion concentration pH of 9 or more. 3. An electrostatic latent image developer comprising a toner containing at least a binder resin and a colorant, and a carrier having a coating resin layer on a core material, wherein the carrier according to claim 1 or 2 is used. An electrostatic latent image developer comprising: 4. A step of forming a latent image on a 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, 4. An image forming method comprising: a fixing step of heating and fixing a toner image, wherein the electrostatic latent image developer according to claim 3 is used as the developer.