JP2000221733A - Carrier for electrostatic latent image developer, electrostatic latent image developer and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a carrier for an electrostatic latent image developer having high stability to an environmental change and deterioration with the lapse of time, attaining a high yield ratio in production and capable of forming a good color image. SOLUTION: The carrier for an electrostatic latent image developer has a core material having a sphericity of <=1.220 represented by the equation (sphericity)=(L/2)2.π/S (where L is the maximum diameter of particle projected images and S is the area of particle projected images) and a surface roughness of >=3 represented by the equation (surface roughness)=SBET/S' (where SBET is the BET specific surface area of particles and S' is specific surface area equivalent to spheres) and a coating resin layer containing 25-45 vol.% electrically conductive powder including 20-100 vol. % acicular electrically conductive powder and having 1×10-1×108 Ω.cm electric resistance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier for an electrostatic latent image developer used for developing an electrostatic latent image formed by an electrophotographic method, an electrostatic recording method or the like, and an electrostatic latent image developer. And an image 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. Since the functions such as transport and charging are shared and the functions are separated as a developer, they are widely used at present because of their 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, CMB development involves low electrical resistance of the carrier,
The charge is injected from the developing roll, and the carrier near the photoreceptor acts as a developing electrode to increase the effective developing electric field. As a result, the toner is sufficiently transferred and the solid image is excellent in reproducibility. . Iron powder carriers have long been known as conductive carriers.

[0004] However, iron powder carriers have many disadvantages. For example, the magnetic brush is too hard to damage the photoreceptor due to large saturation magnetization, and the impact force applied to the toner during stirring in the developing device is too large to deteriorate the toner due to the large specific gravity. There is. In order to improve such problems, a carrier has recently been proposed in which ferrite or magnetite is used as a carrier core material, and a coating resin layer containing a conductive powder is formed on the core material (for example, Japanese Patent Application Laid-Open Publication No. H11-163873). JP-A-1-7255, JP-A-4-360156, etc.). As the coating resin, styrene acrylic resin, silicon resin, polyolefin resin, polyester resin, fluorine resin, and the like are used. As the conductive powder, carbon black, graphite, zinc oxide, titanium black, iron oxide, titanium oxide, tin oxide and the like are used.

Further, there is a problem that the carrier provided with the coating resin layer must be improved. One is that during use for a long period of time, the coating resin layer is worn or peeled off due to the contact with the toner or the contact between the carriers, and the chargeability is reduced. In addition, many conductive powders have a hydroxyl group on the surface or are often porous, which makes it easy to adsorb water, and the electrical resistance and chargeability of the carrier fluctuate with changes in humidity. There's a problem. Furthermore, when the surface of a core material having a particle size of several hundreds μm or less is coated with a resin, such as a carrier core material, some carriers adhere to each other,
The yield of carriers falling within a desired particle size distribution may be reduced.

In order to ensure stability against the above-mentioned environmental fluctuations, it is effective to add acicular conductive powder. In addition, it is effective to mix a spherical conductive powder with respect to the stability against aging. It has already been proposed that the acicular conductive powder and the spherical conductive powder are mixed at a predetermined ratio to achieve both stability against environmental fluctuations and deterioration over time (Japanese Patent Application No. 10-5421). However, the above method has a problem that the yield in the process of coating the resin layer on the carrier core material is not sufficient.

[0007]

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems, and has been made capable of forming a good color image on an image obtained by an electrostatic latent image developing method. An object of the present invention is to provide a carrier for an electrostatic latent image developer, a developer, and an image forming method, which have high stability against deterioration and a high production yield.

[0008]

Means for Solving the Problems As a result of research on the above-mentioned problems, the present inventors have used a carrier core material having a specific shape and surface property, and furthermore, have set the content of the conductive powder within a predetermined range. It is found that by mixing conductive powder having a specific shape at a predetermined ratio, it is possible to further improve the stability against aging and environmental fluctuation, and also to improve the production yield. Was.

That is, the configuration of the present invention is as follows. (1) In a carrier for an electrostatic latent image developer having a coating resin layer on a core, the core has a sphericity represented by the formula (I).
1.220 or less, the surface roughness represented by the formula (II) is 1.8 or more, the coating resin layer contains conductive powder, the content of the conductive powder in the coating resin layer is 25 to 45 volume %
The conductive powder contains acicular conductive powder in a volume mixing ratio of 20 to 100%, and the coating resin layer has an electric resistance of 1 × 10 to 1 ×.
A carrier for an electrostatic latent image developer characterized by being in the range of 10 ⁸ Ω · cm. Sphericity = (L / 2) ² · π / S (I) L: Maximum diameter of particle projected image S: Area of particle projected image Surface roughness = S _BET / S ′ (II) S _BET : BET ratio of particle Surface area S ': Spherical equivalent specific surface area

(2) The core material has a magnetization value in a magnetic field of 1 kOe in a range of 60 to 90 emu / g.
The carrier for an electrostatic latent image developer according to (1). (3) The electrostatic latent image developer carrier according to the above (1) or (2), wherein the electrical resistance of the conductive powder is 1 × 10 ⁶ Ω · cm or less. (4) the conductive powder is a metal oxide;
The carrier for an electrostatic latent image developer according to any one of (1) to (3). (5) The carrier for an electrostatic latent image developer according to any one of the above (1) to (4), wherein the conductive powder has a fine particle surface coated with a metal oxide.

(6) The electrostatic latent image developer carrier according to any one of (1) to (5), wherein the coating resin layer has a thickness of 0.3 to 5 μm. (7) The carrier for an electrostatic latent image developer as described in any one of (1) to (6) above, wherein the carrier core material has an average particle size of 10 to 100 μm. (8) wherein the carrier has a dynamic electric resistance in an electric field of 10 ⁴ V / cm in the state of a magnetic brush in a range of 1 × 10 to 1 × 10 ⁸ Ωcm, wherein 7) The electrostatic latent image developer carrier according to any one of the above items.

(9) An electrostatic latent image developer comprising at least toner particles comprising a binder resin and a colorant, and a carrier having a coating resin layer provided on a core material, wherein the carrier is
An electrostatic latent image developer according to any one of (1) to (8).

(10) forming a latent image on the 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 the above (9) as a developer.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be described 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. In the case of iron powder, since the specific gravity is large, the toner is likely to deteriorate, so that ferrite and magnetite are more excellent in stability.

The sphericity of the carrier core material used in the present invention is 1.220 or less and the surface roughness is 1.8 or more,
Preferably, the sphericity is 1.2 or less and the surface roughness is 2 or more. The closer the sphericity is to 1, the closer the shape is to a true sphere, and the higher the surface roughness, the more fine irregularities are present on the surface. In the present invention, by adjusting the sphericity of the core material to 1.220 or less so as to be close to a true sphere, it is possible to improve the fluidity of the carrier, enable uniform coating of the resin layer, and suppress aggregation of the core material particles. The production yield can be improved. The surface roughness of the core material is 3
By adjusting the above to make fine irregularities exist on the surface, the coating resin layer can be firmly fixed by the anchor effect, so that peeling of the coating layer from the carrier can be prevented. Furthermore, by keeping the sphericity and surface roughness of the carrier core material within the above ranges, a flat coating resin layer can be formed, the impact force of the carrier on the toner can be reduced, and the toner is fused to the carrier surface. So-called toner spent can be prevented.

The sphericity of the carrier core material can be determined from the above equation by measuring the maximum diameter and the projected area of the projected image of the core material particles using, for example, an image analyzer (Mitani). Further, the BET specific surface area of the carrier core material can be determined by a normal nitrogen adsorption method. The specific spherical equivalent surface area of the carrier core material can be calculated from the average particle size and the true specific gravity.

The magnetic susceptibility σ of the carrier core material of the present invention is 1 kO
It is measured by the BH tracer method in a magnetic field of e, and its magnetization value σ ₁₀₀₀ is suitably in the range of 60 to 90 emu / g, preferably 70 to 85 emu / g. If σ ₁₀₀₀ is less than 60 emu / g, the magnetic attraction force to the developing roll is weakened, which is not preferable because it adheres to the photoreceptor and causes image defects. Also, σ ₁₀₀₀ is 90em
If the ratio is more than u / g, the magnetic brush becomes too hard, and the photoreceptor is rubbed strongly and is easily damaged, which is not preferable.

The average particle size of the carrier core material of the present invention is 10 to
100 μm, preferably 20-80 μm, is suitable. If the average particle size is smaller than 10 μm, the developer tends to scatter from the developing device, and if the average particle size is larger than 100 μm, it becomes difficult to obtain a sufficient image density.

The conductive powder of the present invention may be of various shapes such as needles and spheres, but the needle-shaped conductive powder is more suitable for improving environmental stability. Spherical conductive powder is suitable for securing stability over time. The term "needle-like" as used herein refers to a material having a ratio of major axis to minor axis (major axis / minor axis: hereinafter referred to as "aspect ratio") of 3 or more, preferably 5 or more, and more preferably 10 or more.

The needle-like conductive powder preferably has a major axis of 0.05 to 20 μm. 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 of the acicular conductive powder is reduced. On the other hand, when the major axis is longer than 20 μm, the conductive powder is easily released from the coating resin layer. Among them, it is preferable that the short axis of the acicular conductive powder is 0.01 to 1 μm. If the ratio is out of this range, the dispersibility may decrease and the characteristics of the carrier may become non-uniform.

The spherical conductive powder preferably has an average particle size of 0.01 to 1 μm. Outside of this range, the dispersibility becomes poor, and the conductive powder tends to separate from the coating resin layer, which is not preferable. The content of the conductive powder in the coating resin layer is suitably in the range of 25 to 45% by volume, preferably 30 to 40% by volume. When hard conductive powder is contained in the coating resin layer, the coating resin layer becomes harder 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 prevented, and the 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 separated, which is not preferable.

Although the mechanism has not been fully elucidated, among the conductive powders in the coating resin layer, acicular conductive powders are mixed in a volume mixing ratio of 20% or more, preferably 50% or more, more preferably 75% or more. %, The environmental stability can be further improved. When the volume mixing ratio of the acicular conductive powder is less than 20%, the effect is not sufficiently exhibited. In the present invention, if the sphericity and the surface roughness of the carrier core material are within a predetermined range, a predetermined effect can be obtained without blending a spherical conductive powder. The electrical resistance of the conductive powder is
It is preferably 1 × 10 ⁶ Ω · cm or less. If this value is exceeded, it becomes difficult to obtain a desired electric resistance of the entire carrier.

The material of the conductive powder of the present invention is not particularly limited as long as it has a desired shape and electric resistance. Examples of the material include titanium oxide, zinc oxide, aluminum borate, potassium titanate, and tin oxide. A composite type in which the surface of the fine particles is coated with a conductive metal oxide or a conductive type metal oxide alone type is preferable. Here, examples of the conductive metal oxide include a metal oxide doped with antimony or the like (for example, antimony-doped tin oxide) and an oxygen-deficient metal oxide (for example, oxygen-deficient tin oxide).

The electric resistance of the coating resin layer is 1 × 10 to 1 × 10 ⁸
Ω · cm, preferably in the range of 1 × 10 ³ to 1 × 10 ⁷ Ω · cm. The electric resistance of the coating resin layer is 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 Ω · cm, electric charges easily move on the carrier surface, and image defects such as brush marks are easily generated. The electric resistance of the coating resin layer is 1 × 10 ⁸
If it is larger than Ω · cm, a good solid image cannot be obtained.
The electric resistance of the coating resin layer was determined by forming a coating resin film having a thickness of about several μm on an ITO conductive glass substrate using an applicator or the like, and forming a gold electrode thereon by vapor deposition at 10 ² V / cm 2.
From the current-voltage characteristics in the electric field.

The dynamic electric resistance of a carrier whose core was coated with resin was measured in the form of a magnetic brush, and the dynamic electric resistance was 10 ⁴ V / cm.
1 × 10 to 1 × 10 ⁸ Ω · cm, preferably 1 ×
A range of 10 ³ to 1 × 10 ⁷ Ω · cm is appropriate. If the dynamic electric resistance is smaller than 1 × 10 Ω · cm, image defects such as brush marks tend to occur, and if it is larger than 1 × 10 ⁸ Ω · cm, it is difficult to obtain a good solid image. The electric field of 10 ⁴ V / cm is close to the developing electric field in an actual machine, and the above dynamic electric resistance is a value under this electric field.

The dynamic electric resistance of the carrier is determined as follows. A carrier of about 30 cm ^{3 is} placed on the developing roll to form a magnetic brush, and flat electrodes having an area of 3 cm ² are opposed to the developing roll at an interval of 2.5 mm. 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, a dynamic electric resistance is obtained using an equation of Ohm's law. It is well known that there is generally a relationship of ln (I / V) lnV ^1/2 between the applied voltage V and the current I at this time. When the dynamic electric resistance is extremely low as in the carrier used in the present invention, a large electric current may flow in a high electric field of 10 ³ V / cm or more, and measurement may not be performed. In such a case, three or more points are measured in a low electric field, and extrapolated to an electric field of 10 ⁴ V / cm by the least squares method using the above relational expression.

Examples of the coating resin formed on the carrier core material include polyolefin resins, for example, polyethylene and polypropylene; polyvinyl and polyvinylidene resins, for example, polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, and polyether. Vinyl chloride, 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, polychlorotri Fluoroethylene; Polyester; Polyurethane; Polycarbonate, amino resin such as urea-formaldehyde resin; Epoxy resin. These may be used alone,
A plurality of resins may be mixed and used.

The thickness of the coating resin layer is suitably in the range of 0.3 to 5 μm, 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. Also, 5μ
If it is larger than m, it is difficult to obtain a uniform carrier due to aggregation of the carriers.

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

The solvent used for the coating resin layer forming solution is
There is no particular limitation as long as it dissolves the coating resin, and examples thereof include aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, and ethers such as tetrahydrofuran and dioxane. . Examples of the method for dispersing the conductive powder include a sand mill, a dyno mill, and a homomixer.

The toner used in the present invention contains 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.

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. , 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 control agent may be added to the toner, if desired.
An additive such as a fixing aid may be contained. The average particle diameter of the toner is suitably 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 suitably in the range of 0.3 to 30% by weight of the whole developer.

In the image forming method of the present invention, a step of forming a latent image on a latent image carrier, a step of developing the latent image using a developer, and a step of transferring the developed toner image to a transfer member And a fixing step of heating and fixing the toner image on the transfer member, wherein the toner image is developed with the above developer.

[0035]

[Manufacture of carrier]

(Example 1) Ferrite 100 parts by weight [manufactured by Dowa Iron Powder Co., Ltd., DFC350, average particle size 50 µm, sphericity 1.198, surface roughness 4.17, magnetization value 76 emu / g (1 kOe)] toluene 8.8 parts by weight diethylaminoethyl methacrylate -Styrene-methyl methacrylate copolymer (copolymerization ratio 2:20:78, weight average molecular weight 50,000) 1.2 parts by weight Needle-like conductive powder (antimony-doped tin oxide-coated titanium oxide) 3.7 parts by weight (HI, manufactured by Ishihara Sangyo Co., Ltd.) -2, electric resistance 5 × 10 ⁴ Ω · cm, fiber length 0.3 μm, fiber diameter 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. . 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 60 ° C. for 20 minutes while reducing the pressure to form a coating resin layer. The carrier A was obtained.

The thickness of the coating resin layer of the obtained carrier A is
It 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, it was confirmed that there was no exposed surface and the carrier was uniformly coated, and the surface was flat. At this time, the production yield was 85%. In addition, ITO
The coating resin layer forming solution was applied to a thickness of 0.9 μm on a 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 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 2 × 10 ⁵ Ω · cm. The electric resistance of the coating resin film was 5 × 10 at an electric field of 100 V / cm.
It was ⁵ Ω · cm.

(Example 2) 100 parts by weight of ferrite [manufactured by Dowa Tekko Kogyo Co., Ltd., DFC350, average particle diameter 50 μm, sphericity 1.198, surface roughness 4.17, magnetization value 76 emu / g (1 kOe)] toluene 10.3 parts by weight Diethylaminoethyl methacrylate-styrene-methyl methacrylate copolymer (copolymerization ratio 2:20:78, weight average molecular weight 50,000) 1.1 parts by weight perfluorooctylethyl methacrylate-methyl methacrylate copolymer (copolymerization ratio 40:60, weight average Molecular weight: 50,000) 0.3 parts by weight Needle-like conductive powder (antimony-doped tin oxide-coated titanium oxide) 2.8 parts by weight (Ishihara Sangyo Co., Ltd., HJ-1, electrical resistance 5 × 10 ⁴ Ω · cm, fiber length 0.08 μm, fiber diameter) 0.02 μm, aspect ratio 4) 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 ferrite are put into 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. Thus, a carrier B was obtained.

The thickness of the coating resin layer of the obtained carrier B is
It was 0.9 μm. The content of antimony-doped tin oxide-coated titanium oxide was 30% by volume. When this carrier was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the carrier was uniformly coated, and the surface was flat. The production yield at this time was 90%. In addition, ITO
The coating resin layer forming solution was applied to a thickness of 0.9 μm on a 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 when extrapolated to an electric field of 10 ⁴ V / cm was 6 × 10 ⁶ Ω · cm. The electric resistance of the coating resin film was 7 × 10 at an electric field of 100 V / cm.
It was ⁶ Ω · cm.

Example 3 Magnetite 100 parts by weight [manufactured by Dowa Tekko Kogyo Co., Ltd., SM350, average particle size 50 μm, sphericity 1.207, surface roughness 3.23, magnetization value 80 emu / g (1 kOe)] toluene 8.8 parts by weight Diethylaminoethyl methacrylate-styrene-methyl methacrylate copolymer (copolymerization ratio 2:20:78, weight average molecular weight 50,000) 1.2 parts by weight Needle-like conductive powder (antimony-doped tin oxide-coated titanium oxide) 2.8 parts by weight (Ishihara Sangyo Co., Ltd.) FT-1000, electric resistance 1 × 10Ω ・ cm, fiber length 1.7 μm, fiber diameter 0.1 μm, aspect ratio 17) Spherical conductive powder (barium sulfate coated with oxygen-deficient tin oxide) 0.9 parts by weight (Mitsui Metals, Pastran TYPE-IV, electric resistance 6 × 10 ⁴ Ω · cm, particle size 0.1 μm) The above components except magnetite 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 magnetite are 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, which is further sieved with a sieve having an opening of 75 μm. Thus, a carrier C was obtained.

The thickness of the coating resin layer of the obtained carrier C is
It was 0.9 μm. The content of antimony-doped tin oxide-coated titanium oxide was 30% by volume, and the content of oxygen-deficient tin oxide-coated barium sulfate was 10% by volume. When this carrier was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the carrier was uniformly coated, and the surface was flat. At this time, the production yield was 75%. Furthermore, IT
A coating resin layer forming solution was applied to an O conductive glass substrate using an applicator to a thickness of 0.9 μm 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 1 × 10 ⁴ Ω · cm. The electric resistance of the coating resin film was 3 × 10 at an electric field of 100 V / cm.
It was ³ Ω · cm.

Example 4 100 parts by weight of magnetite [manufactured by Dowa Tekko Kogyo Co., Ltd., SM350, average particle diameter 50 μm, sphericity 1.207, surface roughness 3.23, magnetization value 80 emu / g (1 kOe)] toluene 8.8 parts by weight Diethylaminoethyl methacrylate-styrene-methyl methacrylate copolymer (copolymerization ratio 2:20:78, weight average molecular weight 50,000) 1.1 parts by weight perfluorooctylethyl methacrylate-methyl methacrylate copolymer (copolymerization ratio 40:60, weight average 0.3 parts by weight Needle-like conductive powder (antimony-doped tin oxide-coated potassium titanate) 0.8 parts by weight (Dentol BK-100, manufactured by Otsuka Chemical Co., Ltd., electric resistance 1 × 10 ⁴ Ω · cm, fiber length 15 μm, fiber Diameter 0.3 μm, aspect ratio 50) Spherical conductive powder (antimony-doped tin oxide-coated titanium oxide) 3.1 parts by weight (Ishihara Sangyo Co., Ltd., ET-500W, electric resistance 2Ω · cm, particle size 0.2 μm) The above components except the Gunetaito to prepare a 1 hour dispersed in the coating resin layer forming solution in a sand mill. Next, the coating resin layer forming solution and magnetite are 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. As a result, a carrier D was obtained.

The thickness of the coating resin layer of the obtained carrier D is
It was 0.9 μm. The content of antimony-doped tin oxide-coated potassium titanate was 10% by volume, and the content of antimony-doped titanium oxide was 30% by volume. When this carrier was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the carrier was uniformly coated, and the surface was flat. At this time, the production yield was 80%. Furthermore, IT
A coating resin layer forming solution was applied to an O conductive glass substrate using an applicator to a thickness of 0.9 μm 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 when extrapolated to an electric field of 10 ⁴ V / cm was 2 × 10 ⁵ Ω · cm. The electric resistance of the coating resin film was 7 × 10 at an electric field of 100 V / cm.
It was ⁵ Ω · cm.

Comparative Example 1 Magnetite 100 parts by weight [manufactured by Fuji Electric Chemical Co., Ltd., MX030A, average particle size 50 μm, sphericity 1.230, surface roughness 1.61, magnetization value 82 emu / g (1 kOe)] toluene 8.8 parts by weight diethylamino Ethyl methacrylate-styrene-methyl methacrylate copolymer (copolymerization ratio 2:20:78, weight average molecular weight 50,000) 1.2 parts by weight Needle-shaped conductive powder (antimony-doped tin oxide-coated titanium oxide) 3.7 parts by weight (manufactured by Ishihara Sangyo Co., Ltd.) , HI-2, electric resistance 5 × 10 ⁴ Ω · cm, fiber length 0.3 μm, fiber diameter 0.06 μm, aspect ratio 5) The above components except magnetite were dispersed in a sand mill for 1 hour to prepare a coating resin layer forming solution. Produced. Next, the coating resin layer forming solution and magnetite are 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. As a result, a carrier E was obtained.

The thickness of the coating resin layer of the obtained carrier E is
It was 0.9 μm. The content of antimony-doped tin oxide-coated potassium titanate was 40% by volume. When this carrier was observed with a scanning electron microscope, it was found that the carrier was uniformly covered without any exposed surface, but many irregularities on the core material surface were observed on the carrier surface. The production yield at this time was 50%. In addition, ITO
The coating resin layer forming solution was applied to a thickness of 0.9 μm on a 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 when extrapolated to an electric field of 10 ⁴ V / cm was 4 × 10 ⁵ Ω · cm. In addition, the electric resistance of the coating resin film was 8 × 10 at an electric field of 100 V / cm.
It was ⁵ Ω · cm.

(Comparative Example 2) Magnetite 100 parts by weight [manufactured by Fuji Electric Chemical Co., Ltd., MO2-FX50-5, average particle size 50 μm, sphericity 1.248, surface roughness 1.58, magnetization value 82 emu / g (1 kOe)] toluene 8.8 parts by weight diethylaminoethyl methacrylate-styrene-methyl methacrylate copolymer (copolymerization ratio 2:20:78, weight average molecular weight 50,000) 1.1 parts by weight perfluorooctylethyl methacrylate-methyl methacrylate copolymer (copolymerization ratio 40:60 , Weight average molecular weight 50,000) 0.3 parts by weight Needle-shaped conductive powder (antimony-doped tin oxide-coated titanium oxide) 2.8 parts by weight (Ishihara Sangyo Co., Ltd., FT-1000, electrical resistance 1 × 10Ωcm, fiber length 1.7 μm, fiber The above components except magnetite 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 magnetite are 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. As a result, a carrier F was obtained.

The thickness of the coating resin layer of the obtained carrier F is
It was 0.9 μm. The content of antimony-doped tin oxide-coated titanium oxide was 30% by volume. When this carrier was observed with a scanning electron microscope, it was found that the carrier was uniformly covered without any exposed surface, but many irregularities on the core material surface were observed on the carrier surface. The production yield at this time was 53%. 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 F 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 5 × 10 ⁴ Ω · cm. The electric resistance of the coating resin film is 8 × 10 ⁴ Ω · at an electric field of 100 V / cm.
cm.

Comparative Example 3 Magnetite 100 parts by weight [Fuji Electric Chemicals Co., Ltd., MX030A, average particle size 50 μm, sphericity 1.230, surface roughness 1.61, magnetization value 82 emu / g (1 kOe)] toluene 8.8 parts by weight diethylamino Ethyl methacrylate-styrene-methyl methacrylate copolymer (copolymerization ratio 2:20:78, weight average molecular weight 50,000) 1.1 parts by weight perfluorooctylethyl methacrylate-methyl methacrylate copolymer (copolymerization ratio 40:60, weight average molecular weight 50,000) 0.1 parts by weight Needle-like conductive powder (antimony-doped tin oxide-coated titanium oxide) 1.85 parts by weight (manufactured by Ishihara Sangyo Co., Ltd., HI-2, electric resistance 5 × 10 ⁴ Ω · cm, fiber length 0.3 μm, fiber Spherical conductive powder (barium sulfate coated with oxygen-deficient tin oxide) 1.85 parts by weight (Pastran TYPE-IV, manufactured by Mitsui Kinzoku Co., Ltd., 6 × 10 ⁴ Ω · cm, particle size 0.1 μm) Magnetite The above-mentioned components except for the above 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 magnetite are 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. As a result, a carrier G was obtained.

The thickness of the coating resin layer of the obtained carrier G is
It was 0.9 μm. The content of antimony-doped tin oxide-coated titanium oxide was 20% by volume, and the content of oxygen-deficient tin oxide-coated barium sulfate was 20% by volume. When this carrier was observed with a scanning electron microscope, it was found that the carrier was uniformly covered without any exposed surface, but many irregularities on the core material surface were observed on the carrier surface. The production yield at this time was 52%. In addition, ITO
The coating resin layer forming solution was applied to a thickness of 0.9 μm on a 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 G 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 5 × 10 ⁵ Ω · cm. In addition, the electric resistance of the coating resin film was 9 × 10 at an electric field of 100 V / cm.
It was ⁵ Ω · cm.

(Comparative Example 4) Ferrite 100 parts by weight [manufactured by Dowa Iron Powder Co., Ltd., DFC350, average particle size 50 μm, sphericity 1.198, surface roughness 4.17, magnetization value 76 emu / g (1 kOe)] toluene 8.8 parts by weight Diethylaminoethyl methacrylate-styrene-methyl methacrylate copolymer (copolymerization ratio 2:20:78, weight average molecular weight 50,000) 1.2 parts by weight Spherical conductive powder (oxygen-deficient tin oxide-coated barium sulfate) 3.7 parts by weight (Mitsui Metals Co., Ltd.) Pastr TYPE-IV, 6 × 10 ⁴ Ω · cm, 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. Next, the coating resin layer forming solution and the ferrite are placed in a vacuum degassing kneader, and the mixture is stirred at a temperature of 60 ° C. for 20 minutes while reducing the pressure to form a coating resin layer. Then, a carrier H was obtained.

The thickness of the coating resin layer of the obtained carrier H is
It was 0.9 μm. The content of oxygen-deficient tin oxide-coated titanium oxide was 40% by volume. When this carrier was observed with a scanning electron microscope, it was confirmed that there was no exposed surface and the carrier was uniformly coated, and the carrier surface was flat. At this time, the production yield was 85%. In addition, ITO
The coating resin layer forming solution was applied to a thickness of 0.9 μm on a 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 H 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 6 × 10 ⁵ Ω · cm. The electric resistance of the coating resin film was 1 × 10 at an electric field of 100 V / cm.
It was ⁶ Ω · cm.

(Production of Toner) 100 parts by weight of linear polyester resin (linear polyester obtained from terephthalic acid / bisphenol A and ethylene oxide adduct / cyclohexanedimethanol: 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 by a jet mill, and dispersed by a wind classifier to obtain d _50. = 7 μm magenta colored particles were obtained.

[Production yield] Examples 1 to 4 and Comparative examples 1 to
Table 1 shows the production yields of the carriers obtained in No. 4. As the production yield, the ratio of the amount of the carrier obtained after sieving to the amount of the carrier core material before coating was calculated. [Evaluation of image quality] 100 parts by weight of the carriers obtained in Examples 1 to 4 and Comparative Examples 1 to 4 were mixed with 5 parts by weight of the above magenta toner, and developed corresponding to the carriers of Examples 1 to 4 and Comparative Examples 1 to 4. An agent was prepared. Using an electrophotographic copying machine (A-Color630, manufactured by Fuji Xerox Co., Ltd.), the evaluation environment was low temperature and low humidity (10 ° C, 15% RH), normal temperature and normal humidity (22 ° C, 55% RH), A copy test was performed by adjusting the temperature and humidity (28 ° C., 85% RH).

(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 against white paper was measured with a Macbeth densitometer.
It was judged that the closer to 50, the better. The evaluation was performed on the first copy and the 50,000th copy under normal temperature and normal humidity, and on the first copy under low temperature and low humidity and high temperature and high humidity. The results are shown in Tables 2 and 3.

(Fog) Toner fog on the image background portion was evaluated by visual observation and ranked in three stages. ○: no fog, Δ: slight fog, but no practical problem, x: severe fog. The evaluation was performed on the first copy and the 50,000th copy under normal temperature and normal humidity, and on the first copy under low temperature and low humidity and high temperature and high humidity. The results are shown in Tables 2 and 3.

[0055]

[Table 1]

[0056]

[Table 2]

[0057]

[Table 3]

(Evaluation) When the carriers of the present invention, A, B, C, and D were used, excellent image quality was obtained, and the image was stable against deterioration over time and environmental fluctuation. Also,
The production yield also showed a high value. On the other hand, the carrier E of Comparative Example 1 and the carrier F of Comparative Example 2 were excellent in stability against environmental fluctuations due to the use of the acicular conductive powder, but did not use a predetermined carrier core material. In addition, even at room temperature and normal humidity, the charge amount was reduced at the 50,000th sheet, the image density was high, and fog was recognized. In particular, the carrier F having a relatively small content of the acicular conductive powder was particularly bad. Also,
The production yields of the carriers E and F both showed low values.

Further, the carrier G of Comparative Example 3 was stable against deterioration over time and environmental fluctuations, since a predetermined amount of the acicular conductive powder and the spherical conductive powder were mixed at a predetermined ratio.
Because we do not use the specified carrier core material,
The production yield was poor. The carrier H of Comparative Example 4 used a predetermined carrier core material, and thus was excellent in stability against aging deterioration and a high production yield. However, since the spherical conductive powder was used, the carrier H was used. Was unstable with respect to environmental fluctuations, and particularly under a high temperature and a high humidity, the charge amount was reduced, the image density was high, and fogging was observed.

[0060]

According to the present invention, a good solid image can be formed on an image obtained by the electrostatic latent image developing method, particularly, a color image by employing the above-mentioned structure, and environmental fluctuations can be obtained. And high stability against deterioration over time,
It has become possible to provide a carrier for an electrostatic latent image developer having a high production yield and a developer using the carrier.

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kazuhiko Yanagita 1600 Takematsu, Minamiashigara-shi, Kanagawa Prefecture Fuji Xerox Co., Ltd. F-term (reference) 2H005 BA02 BA06 BA07 BA15 CB04 DA09 EA01 EA07 EA10 FA01 FB01 2H077 AD02 AD06 DB25 EA03 GA13

Claims (3)

[Claims] 1. A carrier for an electrostatic latent image developer having a coating resin layer on a core material, wherein the core material has a sphericity represented by the formula (I) of 1.220 or less and a sphericity represented by the formula (II): The coating resin layer contains conductive powder, the content of the conductive powder in the coating resin layer is 25 to 45% by volume, and the conductive powder has a volume mixing ratio of In the range of 20 to 100%, the conductive resin powder contains acicular conductive powder, and the electric resistance of the coating resin layer is 1%.
A carrier for an electrostatic latent image developer, wherein the carrier is in the range of × 10 to 1 × 10 ⁸ Ω · cm. Sphericity = (L / 2) ² · π / S (I) L: Maximum diameter of particle projected image S: Area of particle projected image Surface roughness = S _BET / S ′ (II) S _BET : BET ratio of particle Surface area S ': Spherical equivalent specific surface area 2. An electrostatic latent image developer comprising at least toner particles comprising a binder resin and a colorant, and a carrier having a coating resin layer provided on a core material, wherein the carrier is as described in claim 1. An electrostatic latent image developer, characterized in that: 3. 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, 3. An image forming method comprising: a fixing step of heating and fixing a toner image, wherein the electrostatic latent image developer according to claim 2 is used as the developer.