JP2002116582A - Electrostatic latent image developer and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrostatic latent image developer with which high image quality may be obtained for a long period and the high image quality may be maintained in a wide toner density range and an image forming method. SOLUTION: The electrostatic latent image developer characterized in that the carriers of the electrostatic latent image developer containing the carriers and toners are formed by providing amorphous ferrite cores of >=130 in the shape coefficient (SF-1=R2/S×π/4×100) obtained by dividing the square of their maximum length (R) by an area (S) with core layers formed by dispersing conductive powder into a binder resin and that the dynamic electric resistance under an electric field of 104 V/cm ranges from 10 to 1×109 Ω.cm and the image forming method.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a developer for developing an electrostatic latent image used for developing an electrostatic latent image formed by an electrophotographic method, an electrostatic recording method, and the like, 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. In the two-component developer, the carrier is agitated and transported by the developer. It is widely used at present because it shares functions such as charging and separates functions 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. In the two-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. The major difference between these developing methods is that the magnitude and shape of the electric field acting on the toner carrier near the photoconductor are different. Depending on the position of the so-called developing electrode from the photoconductor, IMB development and CMB development are different. Are divided. IM
Since the developer of B has a high carrier resistance, the developer becomes insulative, and the developing electrode is covered by a sleeve far from the photoconductor. Therefore, the lines of electric force are concentrated only at the edge of the image, and the electric field at the edge is large, and the electric field at the solid part is weak. Thus, although the reproducibility of the fine line is excellent, the image becomes poorly filled. On the other hand, in the CMB development, since the resistance of the carrier is low, the charge is injected from the development roll to the carrier near the photoreceptor, which serves as a development electrode, and is sufficient at the center and the edge of the solid portion. It is characterized in that a good developing electric field is obtained, the toner is sufficiently transferred, and the solid image is well filled with toner. Such characteristics of the CMB developer are particularly important for reproducibility of a color image. In recent years, a carrier having a resistance in a so-called semi-CMB (SCMB) region having a lower resistance than an IMB carrier is used in a color copying machine. It is supposed to be.

Incidentally, since the developing electrode effect of the developer is related to the electrical time constant of the developer, even if the CMB developer is used, depending on the magnitude of the time constant, the transport conditions of the developer and the image area may be reduced. There are secondary image defects related to the structure and the like. The main ones of these are trail edge deletion in which the image density at the rear end of the high-density patch image (with respect to the traveling direction of the image) is low.
TED) and an image defect called a starvation (STV) in which the density of the rear end of the intermediate density portion having the high density portion becomes lower.

[0005] These image defects are related to the image structure, but the main factor is the electrical time constant of the developer. The lower the time constant of the developer is, the more advantageous it is against these image defects, and the advantage is that the fidelity of solid images is excellent. This becomes increasingly important for the reproducibility of full-color images.

To reduce the time constant of the developer, it is necessary to lower the resistance of the carrier. However, simply lowering the resistance of the carrier is not sufficient. The conductivity of a CMB developer composed of a conductive carrier and an insulating toner is mainly performed through a path in which the carriers are in contact with each other. Therefore, when the toner concentration increases, the carriers are covered with the toner, and the The contact becomes difficult and the resistance of the developer increases. Therefore, in a region where the toner concentration is high, the time constant of the developer becomes large, and the effect of the CMB developer cannot be obtained, and image defects such as TED and STV occur. Therefore, the usable toner concentration is limited. Conversely, when the toner concentration decreases, the resistance of the developer decreases, causing the carrier to move to the photoconductor, which is called carrier over, and white lines, called brush marks, due to electric charge leakage, appearing in the solid image. , There is a lower limit for the toner density that can be used.

By the way, in a developing device which adopts a developing method in which the development weight is determined by the charge amount of the toner while keeping the surface potential of the photosensitive member constant, the charge amount of the toner is adjusted by changing the toner density. In this method, a developer which can be used with a toner concentration as wide as possible is desirable in order to cope with a change in toner charge due to deterioration of the developer, environment, manufacturing fluctuation, and the like. For this purpose, there is a demand for a carrier and toner in which the resistance change of the developer is small with respect to the toner concentration.

There are several factors that determine the resistance of the developer in addition to the toner concentration, such as the particle size of the toner, the fluidity of the toner, the particle size of the carrier, and the shape of the carrier. Among them, the particle size of the carrier and the shape of the carrier show a relatively large contribution. When the particle size of the carrier is reduced, the amount of toner covering the surface becomes relatively small even when the toner concentration is the same (toner carrier coverage), the contact between the carriers increases by that amount, and the resistance decreases. As a result, the toner density can be increased and the upper limit of the toner density can be increased accordingly.

However, the lower limit toner density has image defects such as brush marks related to the toner coverage, and the lower limit toner density also increases, making it difficult to obtain the expected toner density latitude. At present, in many developers, small particles of ferrite or magnetite are granulated and spherical particles of about 30 to 100 μm are used as carriers. Since the carrier is spherical, it excels in fluidity, tends to be uniformly charged, and those having a coating layer on the surface have advantages such as good coatability, but from the viewpoint of developer resistance, they are homogeneous. Due to such a spherical shape, when the surface is covered with the toner, there is a disadvantage that the contact points between the carriers are reduced and the resistance of the developer is increased due to a relatively low coverage. In particular, CM
In the B developer, this property becomes a bottleneck, and even if the resistance of the carrier is reduced, when the developer is used, the resistance rapidly increases as the toner concentration increases.

On the other hand, when the shape of the carrier is made irregular, the toner is easily removed from between the carriers at a portion where the curvature of the carrier is large, and a portion where the carriers are easily in contact with each other is formed. It may happen that the resistance of the agent is hardly increased even when the toner concentration is increased. However, the amorphous carrier that has been used so far is mainly iron powder, and when compared with a spherical ferrite carrier having the same average particle diameter, the toner coverage ratio dependency of the resistance decreases,
Due to the high specific gravity and the strong magnetic force, the pressure between the sleeve and the toner increases, and the pressure on the toner sandwiched between the carriers increases, causing toner carrier contamination and the developer life. Another obstacle of shortening occurs. Further, due to the large magnetization of the iron powder, the ears of the magnetic brush become hard, and unevenness in toner density due to streaks occurs in an image such as a solid, resulting in an image defect.

In the recent color copying machines, the required level of image quality has been increasing more and more, and solid images have become particularly important. for that reason,
There is an increasing need for image quality and CMB developers that can be used with a wide range of toner concentrations.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned conventional problems and achieve the following objects. That is, an object of the present invention is to provide a developer for developing an electrostatic latent image capable of obtaining high image quality over a long period of time and maintaining high image quality in a wider toner density range, and an image forming method. .

[0013]

The above object is achieved by the following means. That is, the present invention provides: <1> a developer for developing an electrostatic latent image including a carrier and a toner, wherein the carrier has a shape factor obtained by dividing a square of a maximum length (R) by an area (S). (SF-1 = R ² / S × π /
4 × 100) to 130 or more irregular shaped ferrite cores,
A coating layer in which conductive powder is dispersed in a binder resin is provided, and a dynamic electric resistance under an electric field of 10 ⁴ V / cm is in a range of 10 to 1 × 10 ⁹ Ω · cm. It is a developer for developing an electrostatic latent image. <2> The relationship between the static electrical resistance (common logarithmic value) of the developer for developing an electrostatic latent image and the toner density (TC) is plotted, and when the relationship is linearly approximated by the least square method, the toner density (T
The electrostatic latent image developing device according to <1>, wherein the gradient of the static electric resistance (common logarithmic value) of the developer for developing an electrostatic latent image with respect to C) is 0.6 / TC or less. Developer. <3> 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 Wherein the developer is the developer for developing an electrostatic latent image according to <1> or <2>. .

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION (Developer for Electrostatic Latent Image Development) The developer for electrostatic latent image development of the present invention comprises a carrier and a toner,
The carrier has an irregular ferrite core (hereinafter referred to as “carrier core”) having a shape factor (SF-1 = R ² / S × π / 4 × 100) obtained by dividing the square of the maximum length by an area of 130 or more. Is provided with a coating layer in which conductive powder is dispersed in a binder resin, and the dynamic electric resistance under an electric field of 10 ⁴ V / cm is in a range of 10 to 1 × 10 ⁹ Ω · cm. It is characterized by. The developer for developing an electrostatic latent image of the present invention can reduce the toner concentration dependency of resistance by using a carrier in which an amorphous ferrite core is coated with a conductive coating layer, and can reduce the impact on toner. The toner density latitude is wide and the developer charging life is long. Further, by setting the electrostatic electric resistance of the carrier within the above range, it is possible to prevent brush marks and carrier over when the toner has a low density. Therefore, high image quality can be obtained over a long period of time, and high image quality can be maintained over a wider toner density range.

The carrier has a dynamic electric resistance in an electric field of 10 ⁴ V / cm in the range of 10 to 1 × 10 ⁹ Ω · cm, preferably 1 × 10 ³ to 1 × 10 ⁷ Ω · cm. is there. If the dynamic electrical resistance is smaller than 10 Ω · cm, image defects such as brush marks are likely to occur and 1 × 10 ⁹ Ω · cm.
If it is larger than cm, a good solid image cannot be obtained. The electric field of 10 ⁴ V / cm is close to the developing electric field in the actual machine, and the dynamic electric resistance is defined by the value under this electric field.
When the carrier falls within the above range, it can be used as a CMB carrier.

Here, the dynamic electric resistance of the carrier is a value obtained as follows. About 30cm on the developing roll
^A magnetic brush is formed with the carrier of ^{3 above} , and the area is 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. still,
Generally, ln is between the applied voltage V and the current I at this time.
It is well known that (I / V) ∝V ^1/2 . When the dynamic electric resistance is very 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.

In the carrier, the amorphous ferrite core has a shape factor (SF-1 = R ² / S × π / 4 × 100) obtained by dividing the square of the maximum length (R) by the area (S) of 130.
Although it is above, it is preferably 140 or more. If the shape factor is less than 130, the toner density dependence of the dynamic electric resistance and the impact on the toner increase, and the toner density latitude becomes narrow.

Here, the shape factor SF-1 is used as a coefficient expressing the form such as the shape of the toner, and quantitatively analyzes the area, length, shape, etc. of the image captured by an optical microscope or the like with high precision. This is based on a statistical technique called image analysis, and can be measured by an image analyzer (for example, Luzex FT; manufactured by Nippon Regulator Co., Ltd.). The shape factor SF-1 is a value obtained by multiplying a value obtained by squaring the maximum length of the diameter of the carrier by the projected area of the carrier, multiplying by π / 4, and further multiplying by 100.
The closer the carrier shape is to a sphere, the closer to 100 the value becomes,
The value becomes larger than 100 as the shape of the carrier is elongated. That is, the difference between the maximum diameter and the minimum diameter of the toner particles, that is, distortion.

In the carrier, various known ferrites can be used as the material of the amorphous ferrite core. Ferrite containing magnetite is preferable as the ferrite, and ferrite containing a metal element other than the iron element is particularly preferably used. The amorphous ferrite core can be produced by granulating ferrite and sintering the ferrite, or sintering the core that has been deformed by applying force during granulation.

In the carrier, the value obtained by dividing the BET specific surface area (cm ² / g) of the amorphous ferrite core by the average particle diameter (μm) of the core is 15 cm ² / μm · g or more. It is preferable from the viewpoint of prevention of marks, and more preferably 25 cm ² / μm · g or more. If it exceeds 80 cm ² / μm · g, the carrier core is likely to be exposed and the coating amount of the coating layer needs to be increased. It is not preferable because it may come out. This value is 15c
If it is less than m ² / μm · g, the adhesion between the coat layer material and the carrier core tends to deteriorate, which is not preferable.

In the carrier, the average particle size of the amorphous ferrite core is preferably from 10 to 100 μm, more preferably from 20 to 80 μm. This average particle size is 1
If it is smaller than 0 μm, the developer tends to scatter from the developing device, whereas if it is larger than 100 μm, it may be difficult to obtain a good image.

In the carrier, an amorphous ferrite core
Is 10^FourDynamic electric resistance under electric field of V / cm is 1
It is preferably 0 Ω · cm or less, more preferably
10 ^-1Ω · cm or less. This dynamic electric resistance is 10Ω
・ If it is less than cm, the resistance of the carrier after coating the coat layer is
It is too high to get the necessary resistance as CMB
It is not preferable because it may become difficult. Also, 10^-FourΩ
If it is less than cm, brush marks are likely to occur.
Not preferred. The dynamic shape of this irregular shaped ferrite core
The electrical resistance is determined in the same way as the dynamic electrical resistance of the carrier.
Value.

In the carrier, the coat layer coated on the irregular shaped ferrite core is formed by dispersing conductive powder in a binder resin. The material of the conductive powder is not particularly limited as long as it has a desired shape and dynamic electric resistance. For example, the surface of fine particles of titanium oxide, zinc oxide, aluminum borate, potassium titanate, barium sulfate, etc. Is preferable, a composite type in which is coated with a conductive metal oxide, or a simple type in which the conductive metal oxide is used. Here, as the conductive metal oxide, a metal oxide doped with antimony or the like (for example, antimony-doped tin oxide),
Oxygen-deficient metal oxide (eg, oxygen-deficient tin oxide)
And the like.

In the carrier, the conductive powder preferably has a needle-like or spherical shape, and more preferably a needle-like shape. The term "needle-like" as used herein refers to the ratio of the major axis (fiber length) to the minor axis (fiber diameter) (major axis / minor axis; hereinafter, referred to as "aspect ratio"), and the aspect ratio is 3 or more. And more preferably 5
That is all. 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 filler may be broken in the process of dispersing in the binder resin and the effect may be reduced, while the major axis may be 20 μm. If the length is longer, the conductive powder may be easily detached from the coat layer. The minor axis of the acicular inorganic powder is preferably 0.01 to 1 μm.
If the ratio is out of this range, the dispersibility becomes poor 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 these ranges, the dispersibility may deteriorate and the conductive powder may be easily separated from the coating layer, which is not preferable.

In the carrier, the static electric resistance of the conductive powder is preferably 1 to 1 × 10 ⁶ Ω · cm. If the static electric resistance is smaller than 1 Ω · cm, brush marks are likely to be generated. On the other hand, if it exceeds 1 × 10 ⁶ Ω · cm, even if the content of the conductive powder is increased (for example, 40% by volume or more is added). ), A predetermined resistance may not be obtained.

In the carrier, the content of the conductive powder in the coating resin layer is preferably from 25 to 45% by volume, and more preferably from 30 to 40% by volume. If the content is less than 25% by volume, it may not be possible to obtain a predetermined resistance. On the other hand, if the content is more than 45% by volume, film formation of the coat layer is poor, and charge leakage is likely to occur, resulting in poor image quality. The brush mark may be more likely to appear.

In the carrier, the binder resin may be a polyolefin resin (for example, polyethylene or polypropylene); a polyvinyl or polyvinylidene resin (for example, polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, Polyvinyl carbazole, polyvinyl ether and polyvinyl ketone); vinyl chloride-vinyl acetate copolymer; styrene
Acrylic acid copolymer; straight silicone resin composed of an organosiloxane bond or a modified product thereof; fluororesin;
For example, polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene; polyester; polyurethane; polycarbonate; amino resin (eg, urea-formaldehyde resin;
Epoxy resin); and the like. These may be used alone or as a mixture of a plurality of resins.

In the carrier, the static electric resistance of the coat layer is preferably 10 to 1 × 10 ⁸ Ω · cm, more preferably 1 × 10 ³ to 1 × 10 ⁶ Ω · cm. The static electric resistance of the coat layer can be controlled by the type and amount of the conductive powder and binder resin used. By controlling this static electric resistance, it can be used as a CMB carrier. Static electric resistance of coat layer is 10Ω
When the diameter is smaller than cm, charges easily move on the carrier surface, and image defects such as brush marks tend to occur. If the static electric resistance of the coat layer is larger than 1 × 10 ⁸ Ω · cm, it may be difficult to obtain a good solid image.

Here, the static electric resistance of the coat layer is IT
A binder 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 thereon by vapor deposition, and a current in an electric field of 10 ² V / cm is applied.
This is a value obtained from the voltage characteristics.

In the carrier, the thickness of the coat layer is 0.1.
It is preferably 3 to 5 μm, more preferably 0.1 μm.
5 to 3 μm. If the thickness of the coat layer is smaller than 0.3 μm, it may be difficult to form a uniform coat layer on the core surface. On the other hand, if it is larger than 5 μm, granulation of carriers occurs, and it may be difficult to obtain a uniform carrier.

In the carrier, the coating layer is formed on the amorphous ferrite core by a dipping method in which the amorphous ferrite core is immersed in a coating layer forming solution, or the coating layer forming solution is applied to the surface of the amorphous ferrite core. Spray method for spraying, fluidized bed method for spraying the coating layer forming solution while the amorphous ferrite core is suspended by flowing air, mixing the amorphous ferrite core and the coating layer forming solution in a kneader coater to remove the solvent And a kneader coater method. The solvent used for the coating layer forming solution is not particularly limited as long as it dissolves the binder resin described above. Examples thereof include aromatic hydrocarbons such as toluene and xylene, and 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 carrier is used as a two-component developer by mixing with the varnish. Hereinafter, the toner will be described in detail.

The toner is not particularly limited, and may be composed of toner particles containing a binder resin, a colorant, and if necessary, other internal additives, and, if necessary, an external additive. Used. The toner particles are formed according to a standard method.
It can be obtained by melt-kneading a colorant and other additives to the binder resin, cooling and pulverizing, and further classifying as necessary. The average particle size of the toner particles is 30 μm or less,
Preferably it is 4 to 20 μm. In the present invention, a toner using a colorant other than black as the colorant is preferably used.

In the toner particles, as the binder resin,
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, 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 are exemplified. Particularly typical binder resins include polystyrene, styrene-acrylate copolymer, styrene-methacrylate copolymer, styrene-acrylonitrile copolymer, styrene-butadiene copolymer, and styrene-maleic anhydride copolymer. Examples include polymers, polyethylene, and polypropylene. Furthermore, polyester, polyurethane, epoxy resin, silicone resin, polyamide, modified rosin, paraffin, and waxes may be mentioned.

In the toner particles, colorants 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, rose bengal, C.I. I. Pigment Red 48: 1, C.I. I. Pigment Red 122, 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 as typical ones.

The toner particles may contain other known additives such as a charge control agent and a fixing aid, if desired. Further, in order to improve the fluidity of the toner particles, a fluidity modifier (external additive) such as silica or titania may be externally added as necessary.

The developer for developing an electrostatic latent image according to the present invention plots the relationship between the static electric resistance (common logarithmic value) of the developer for developing an electrostatic latent image and the toner concentration (TC), and plots the relationship. When a first-order approximation is made by the least-squares method, the gradient of the static electric resistance (common logarithmic value) of the developer for developing an electrostatic latent image with respect to the toner concentration (TC) is preferably 0.6 / TC or less. More preferably, it is 0.5 / (TC) or less. This shows the dependency of the developer resistance on the toner concentration. When the carrier is spherical, the carrier makes one-point contact with the toner, whereas the carrier in the developer for developing an electrostatic latent image of the present invention has an irregular shape. Therefore, the toner comes into surface contact or contact at two or more points, and it is considered that the resistance dependency on the toner density is reduced. Therefore, this value is 0.6 / (TC)
When the value exceeds, the resistance dependency on the toner density increases, and the toner density latitude may become narrow, which is not preferable.

In the developer for developing an electrostatic latent image of the present invention,
The static electric resistance of the developer for developing an electrostatic latent image is obtained by forming a magnetic brush by placing about 30 cm ³ of developer on a developing roll,
A flat electrode having an area of 3 cm ² is opposed to the developing roll at an interval of 2.5 mm, and a fixed voltage is applied between the developing roll and the flat electrode while the developing roll is fixed without rotating, and a current flowing at that time is measured. More required to do. In addition,
This static electric resistance value is a value obtained from a current value in an electric field of 800 V.

In the developer for developing an electrostatic latent image of the present invention,
The toner concentration is a ratio of the toner to the carrier when a developer is prepared by mixing the carrier and the toner. Specifically, the toner concentration is 0.3 to 30 parts by weight with respect to 100 parts by weight of the carrier. And more preferably 3 to 15 parts by weight. Since the image agent for developing an electrostatic latent image of the present invention contains the above-mentioned carrier, high image quality can be maintained for a long time even in the above-mentioned toner concentration range.

(Image Forming Method) 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 And a fixing step of heating and fixing the toner image on the transfer member. The developer is the developer for developing an electrostatic latent image of the present invention. According to the image forming method of the present invention, by using the developer for developing an electrostatic latent image of the present invention, high image quality can be obtained over a long period of time, and high image quality can be maintained in a wide toner density range.

In the image forming method of the present invention, each of the above steps is a general step per se.
-40868 and JP-A-49-91231. The image forming method of the present invention can be carried out using a known image forming apparatus such as a copying machine or a facsimile machine.

The present invention will be specifically described below with reference to examples and comparative examples. In addition, each electrical resistance measurement in an Example was implemented at the temperature of 22 degreeC, and 55% of humidity according to the above.

[Manufacture of Carrier A] -Components- -Ferrite ... 100 parts by weight ("EFY-50BW" manufactured by Powdertech Co., Ltd .: average particle size 51.8 µm, shape factor SF-1 (146)) 13.8 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: Sanyo Chemical; "PX-1A"); antimony-doped tin oxide-coated titanium oxide: 2.76 parts by weight ("HI-2" manufactured by Ishihara Sangyo Co., static electricity) resistor 5 × 10 ⁴ Ω · cm, fiber length 0.3 [mu] m, fiber diameter 0.06 .mu.m, an aspect ratio of 5) oxygen-deficient tin oxide coated barium sulfate ... 0.92 parts by weight (manufactured by Mitsui Mining & Smelting Co., Ltd., "Pastran YPE-IV4350 "static electric resistance 6 × 10 ⁴ Ω · cm, particle size 0.1 [mu] m)

The above components except ferrite were dispersed in a sand mill for one hour to prepare a coating layer forming solution. Next, the coating layer forming solution 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 coat layer. The thickness of the coat layer was 0.9 μm. The content of antimony-doped tin oxide-coated titanium oxide is about 30% by volume, and the content of oxygen-deficient tin oxide-coated barium sulfate is about 10% by volume.
Met.

[Production of Carriers B to E] Carriers B to E were obtained in the same manner as in Carrier A, using the respective components according to Table 1.

Hereinafter, the components of the carriers A and B are shown in Table 1, the shape factor of the carrier, the static electric resistance of the coat layer and the dynamic electric resistance of the carrier are shown in Table 2, and the shape factor of the amorphous ferrite core, RET Table 3 shows the specific surface area, particle diameter, and dynamic electric resistance. Note that the shape factor is “Luzex F
T: manufactured by Nippon Regulator Co., Ltd. ". Also,
The static electric resistance of the coating layer is 0.9 μm using a coating layer forming solution on an ITO conductive glass substrate using an applicator.
To obtain a sample for measuring the static electric resistance of the binder resin film, which was obtained by using this.

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

[Table 3]

Toners to be used in combination with each of the obtained carriers A to E were prepared as follows. [Production of Toner] Linear polyester resin (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) ... 100 parts by weight Magenta pigment (CI pigment, red 57) ... 3 parts by weight

The above mixture is kneaded with an extruder,
After crushing with a jet mill, dispersing with a wind classifier and d
50 = 7 μm magenta toner particles were obtained. 0.8% of external additive MT3103 and 0.81% of RX515H were added to the toner particles to obtain a final toner.

(Production of Developers A to E) Using the carriers A to E, the toners were mixed with the toner to prepare developers A to E, respectively.

(Examples 1 to 3, Comparative Examples 1 and 2) Using the obtained developers A to E, the following evaluations were made according to Table 4. Table 4 shows the results. —Dependency of Static Electric Resistance of Developer on Toner Concentration— The toner concentration of developer A was adjusted to 3, 5, 7, 9, 11, and 13 parts by weight with respect to 100 parts by weight of carrier, respectively. The relationship between the static electrical resistance (common logarithmic value) of the developer and the toner concentration (TC) is plotted, and when the relationship is linearly approximated by the least square method, the static electrical resistance of the developer with respect to the toner concentration (TC) is plotted. The slope of (common logarithmic value) was determined. The same applies to the developing agents B to D. Here, FIG. 1 shows the relationship between the static electric resistance value (common logarithmic value) of the developer A (Example 1) and D (Comparative Example 1) and the toner density, respectively.

-Image Evaluation- The image quality was evaluated using a copying machine (A-Color630, manufactured by Fuji Xerox Co., Ltd.) while changing the toner concentration of each of the developers A to E. The display environment is normal temperature and normal humidity (22 ° C, 55
%), Brush marks, carrier adhesion, rear end chipping and STV were evaluated as image quality. Based on this image quality evaluation, the toner density at the time of occurrence of brush marks and carrier adhesion was defined as the lower limit toner density, and the toner density at which rear end chipping or STV was generated was defined as the upper limit toner density.
The toner density latitude (difference between the upper limit toner density and the lower limit toner density) was determined from the upper limit and the lower limit.

[0054]

[Table 4]

From Table 4, it can be seen that, in the developer using the irregular shaped carrier of the embodiment, the rear end chipping and STV can be suppressed even at a high toner concentration, the upper limit toner concentration is increased, and the carrier adhesion and the generation of brush marks are caused. It can be seen that the determined lower limit toner concentration is similar to the developer using the spherical carrier, and the toner concentration latitude is increased. l

[0056]

As described above, according to the present invention, there are provided an electrostatic latent image developing developer and an image forming method capable of obtaining high image quality over a long period of time and maintaining high image quality in a wider toner density range. can do.

[Brief description of the drawings]

FIG. 1 shows developer A (Example 1) and D used in Examples.
FIG. 6 is a diagram illustrating a relationship between a static electric resistance value (common logarithmic value) and toner density in Comparative Example 1.

Claims (3)

[Claims] 1. A developer for developing an electrostatic latent image comprising a carrier and a toner, wherein the carrier has a shape factor (SF-1) obtained by dividing a square of a maximum length (R) by an area (S). = R ² / S × π / 4 × 100) is provided with a coating layer formed by dispersing conductive powder in a binder resin on an amorphous ferrite core having 130 or more, and
0 ⁴ Dynamic electrical resistance under an electric field of V / cm is 10 to 1
A developer for developing an electrostatic latent image, wherein the developer is in a range of × 10 ⁹ Ω · cm. 2. The relationship between the static electrical resistance (common logarithmic value) of the developer for developing an electrostatic latent image and the toner density (TC) is plotted. 2. The electrostatic latent image developing device according to claim 1, wherein a gradient of static electric resistance (common logarithmic value) of the developer for developing the electrostatic latent image with respect to (TC) is 0.6 / TC or less. 3. Developer. 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 developer is the developer for developing an electrostatic latent image according to claim 1 or 2.