JP4525507B2 - Electrostatic charge image developing carrier, image forming method, and image forming apparatus - Google Patents

Description

  The present invention relates to an electrostatic charge image developing carrier, an image forming method, and an image forming apparatus used for developing an electrostatic latent image in electrophotography, electrostatic recording method, and the like.

A method of visualizing image information through an electrostatic latent image such as electrophotography is currently used in various fields. In electrophotography, an electrostatic latent image formed on a photoreceptor by a charging and exposure process is developed with a developer containing toner, and visualized through a transfer and fixing process. Developers used for development include a two-component developer composed of toner and carrier, and a one-component developer used alone, such as magnetic toner, but the two-component developer includes a carrier whose developer is a developer. Since functions such as agitation, transport, and charging are shared and functions are separated as a developer, it has a feature such as good controllability and is currently widely used. In particular, a developer using a carrier coated with a resin has excellent charge controllability, and is relatively easy to improve environment dependency and stability over time. As a developing method, the cascade method has been used in the past, but at present, the magnetic brush method using a magnetic roll as a developer conveying unit is the mainstream.
In recent years, with the trend toward miniaturization and high speed of copying machines and printers, it has become necessary to reduce the size of developing machines themselves and drive them at high speed, and there has been an increasing demand for improvement in mechanical strength and the like for carriers.
In response to such demands, a technique is disclosed in which carrier dispersion is prevented by using a magnetic material-dispersed carrier to prevent carrier breakage and carrier transfer onto a photoconductor (for example, Patent Documents). 1)), however, the fluidity is not sufficient and carrier destruction cannot be completely prevented.
JP 2002-328493 A

  An object of the present invention is to provide a carrier for developing an electrostatic charge image, an image forming method, and an image forming apparatus that prevent the generation of fine powder due to the destruction of the carrier by increasing fluidity and does not cause white spots on the image due to the fine powder. There is.

  The above-mentioned subject is achieved by the following present invention.

<1> A carrier for developing an electrostatic image having magnetic particles as a core and a coating layer covering the surfaces of the magnetic particles,
In the powder rheometer, the total energy amount from the filling surface of the carrier to the depth of 70 mm at the tip angle of the rotor blade of 100 mm / s and the approach angle of the rotor blade of -5 ° is 1500 to 3000 mJ. Carrier for developing an electrostatic image.

< 2 > a charging step for charging the latent image carrier;
Exposing the charged latent image carrier to form an electrostatic latent image on the latent image carrier; and
A developing step of developing the electrostatic latent image with a developer containing toner and a carrier to form a toner image;
A transfer step of transferring the toner image from the latent image carrier to a recording material,
The carrier includes the electrostatic image developing carrier according to <1 > ,
In the developing step, the developer carrying member carrying the developer on the surface rotates at a peripheral speed of 200 mm / s or more and 600 mm / s or less to face the image carrying member, and the developer is applied to the image carrying member. An image forming method comprising a conveying step.

< 3 > a latent image carrier;
Charging means for charging the latent image carrier;
Exposure means for exposing the charged latent image carrier to form an electrostatic latent image on the latent image carrier;
Developing means for developing the electrostatic latent image with a developer to form a toner image;
Transfer means for transferring the toner image from the latent image carrier to a recording material, and an image forming apparatus comprising:
An image forming apparatus, wherein the developer includes the electrostatic charge image developing carrier according to <1 > .

  According to the present invention, it is possible to provide a carrier for developing an electrostatic image and an image forming method that prevent the generation of fine powder due to the destruction of the carrier by increasing the fluidity of the carrier and does not cause white spots on the image due to the fine powder.

  In general, the core of an electrostatic charge image developing carrier (hereinafter sometimes referred to as “carrier”) is roughly divided into two cases: magnetic particles and magnetic powder-dispersed particles. Exists. Examples of the former include iron powder carrier, ferrite carrier, ferrite / iron powder, and the latter magnetic powder-dispersed particles are obtained by dispersing magnetic powder in a resin.

In the case of the former core composed of the magnetic particles, the specific gravity is large and the saturation magnetization is very large, so that the fluidity and stirrability are liable to be deteriorated. Since the applied impact is large, the toner tends to be spent and the photoconductor is easily damaged.
Accordingly, a coating layer is provided on the surface of magnetic particles to improve fluidity and control charging. The coating layer is generally formed by a solution method using a resin-containing solution, but iron powder / ferrite has low surface energy and insufficient wettability with the resin. The coating layer is easily peeled off by stirring in the machine.

As described above, the problem of the core carrier composed of magnetic particles is deeply related to the fluidity.
Therefore, in the present invention, an electrostatic charge image developing carrier having a core and a coating layer covering the surface of the core is used to improve the fluidity of the carrier and to control charging while further improving the flow. To enhance the nature.

That is, the carrier for developing an electrostatic charge image according to the first aspect of the present invention is a carrier for developing an electrostatic charge image having magnetic particles as nuclei and a coating layer covering the surface of the magnetic particles. In the powder rheometer, the total energy amount from the filling surface of the carrier to the depth of 70 mm when the tip speed of the rotor blade is 100 mm / s and the approach angle of the rotor blade is -5 ° is 1500 to 3000 mJ. the shall be the feature.

Next, fluidity measurement using a powder rheometer will be described.
When measuring the fluidity of particles, it is more influenced by many factors than when measuring the fluidity of liquids, solids, or gases, so in conventional parameters such as particle size and surface roughness, It is difficult to specify the exact fluidity of the particles. In addition, even if a factor to be measured (for example, particle size) is determined to specify fluidity, the factor actually has little effect on fluidity or only in combination with other factors. The significance of measuring the factor may arise, and even determining the measurement factor is difficult.
Furthermore, the fluidity of the powder varies significantly depending on external environmental factors. For example, in the case of a liquid, even if the measurement environment changes, the fluctuation range of the fluidity is not so large, but the fluidity of the particles is greatly influenced by external environmental factors such as humidity and the state of the flowing gas. fluctuate. It is not clear which measurement factors are affected by these external environmental factors, so even if measured under strict measurement conditions, the reproducibility of the measured values obtained is actually poor. is there.

  In addition, as for the fluidity when toner particles are filled in the development tank, the angle of repose and the bulk density have been used as indices, but these physical property values are indirect to the fluidity, and the fluidity is quantified. It was difficult to manage.

On the other hand, since the powder rheometer can measure the total energy amount applied from the carrier to the rotor blade of the measuring machine, it can be obtained as a sum of the factors caused by fluidity. Therefore, in the powder rheometer, as in the past, for the carrier obtained by adjusting the physical property value and particle size distribution of the surface, determine the items to be measured and find and measure the optimum physical property value for each item. The flowability can be measured directly. As a result, it is possible to determine whether it is suitable as a carrier used for developing an electrostatic charge image only by confirming whether it falls within the above numerical range with a powder rheometer. Such carrier production management is a method that is extremely suitable for practical use as compared to the conventional method of managing by indirect values with respect to keeping the carrier fluidity constant. Moreover, it is easy to make measurement conditions constant, and the reproducibility of measured values is high.
That is, the method for specifying the fluidity by the value obtained by the powder rheometer is simple, accurate and highly reliable as compared with the conventional method.

Here, in order to prevent the generation of fine powder due to the destruction of the carrier and prevent the occurrence of white spots on the image due to the fine powder, the inventors measured under the above specific conditions when measured with a powder rheometer. It has been found that it is extremely effective to use an electrostatic charge image developing carrier of 1500 to 3000 mJ when the core is a magnetic fluid. Carriers within this range have fluidity when used for electrostatic image development and can reduce stress due to impact between carriers. As a result, since fine powder due to carrier cracking is not generated, it is possible to prevent image defects such that the fine powder moves onto the photoconductor and white spots occur in an image portion on a transfer material such as a sheet of the transferred portion.

In the case of a carrier whose core is magnetic particles, if the measured value of the powder rheometer is lower than 1500 mJ, the friction effect is low and it is difficult to sufficiently charge the toner. On the other hand, when the value exceeds 3000 mJ, it is difficult to prevent generation of fine powder due to carrier destruction because the stress on the carrier becomes high. More preferably, the measurement value is in the range of 1800～2700MJ, more preferably area by der of 2000～2500MJ.
The structure of the concrete carrier, will be described later.

Next, a measurement method using a powder rheometer will be described.
The powder rheometer is a fluidity measuring device that directly measures fluidity by simultaneously measuring rotational torque and vertical load obtained by rotating a rotating blade spirally in packed particles. By measuring both the rotational torque and the vertical load, the fluidity including the characteristics of the powder itself and the influence of the external environment can be detected with high sensitivity. In addition, since the measurement is performed with the particle filling state kept constant, data with good reproducibility can be obtained.

In the present invention, measurement is performed using FT4 manufactured by freeman technology as a powder rheometer.
First, a container to be measured is filled into a container. As the container, a 160 mL container having an inner diameter of 50 mm and a height of 88 mm is used. The container is filled with a carrier to a height of 88 mm. Before the measurement, the carrier is left at a temperature of 22 ° C. and a humidity of 50% RH for 8 hours or more so that an error does not occur due to external environmental factors at the time of measurement.

  After filling, the filled carrier is conditioned prior to fluidity measurement to eliminate variations in measured values due to fluctuations in filling conditions. In conditioning, gently stir the rotor blades in a rotational direction that is not subject to resistance from the carrier so as not to stress the carrier in the filled state (the direction opposite to the rotational direction at the time of measurement). The stress is removed and the sample is made homogeneous.

After the conditioning is completed, the rotor blades are rotated while entering the filled carrier.
As shown in FIG. 1A, when the rotating blade rotates at a tip speed of 100 mm / s while moving in the particles filled in the container from the filling surface H1 to H2 at an approach angle of -5 °. Measure the rotational torque and vertical load. The reason why the approach angle is set to -5 ° is that the sensitivity is highest in measuring the flow state of the carrier.
In addition, an approach angle means the angle which the axis | shaft of a measurement container and the rotating shaft of a rotary blade make.

The relationship between the rotational torque or the vertical load with respect to the depth H from the filling surface H1 is shown in FIG. 1 (B) and FIG. 1 (C). FIG. 2 shows the energy gradient (mJ / mm) with respect to the depth H obtained from the rotational torque and the vertical load. The area obtained by integrating the energy gradient in FIG. 2 (shaded portion in FIG. 2) is the total energy amount (mJ). In the present invention, H2 is positioned 70 mm deep from the filling surface H1.
In the present invention, in order to reduce the influence of errors, the average value when this operation is performed five times is set as the total energy amount (mJ) defined in the present invention.

  As the rotor blade, a two-blade propeller type φ48 mm diameter blade shown in FIG. 3 manufactured by freeman technology is used.

Next, the structure of the carrier having the total energy amount will be described.
The carrier of the present invention is not particularly limited as long as it corresponds to the above. For realizing such numerical values, the carrier particle size distribution is sufficiently small, or the coating layer on the surface of the carrier core is formed of a material capable of reducing friction, and the carrier shape is spherical. , Those having a sufficiently small carrier shape distribution, those having few aggregates, those having a low specific gravity, and the like, which are applied alone or in combination.

Carrier of the present invention, (the carrier of the first embodiment) the carrier of the nucleus is magnetic particles Ru der.

-Carrier of the first aspect (carrier in which the nucleus is composed of magnetic particles)-
In the carrier of the first aspect, the material of the core is, for example, a magnetic metal such as iron, steel, nickel, or cobalt, or an alloy of these with manganese, chromium, rare earth elements, or the like (for example, nickel-iron alloy, cobalt) -Iron alloys, aluminum-iron alloys, etc.) and magnetic oxides such as ferrite and magnetite can be mentioned, but magnetic particles are desirable from the viewpoint of using a magnetic brush method as a developing method.

The volume average particle size of the core in the carrier of the first aspect is preferably 10 μm to 500 μm, more preferably 30 μm to 150 μm, and still more preferably 30 μm to 100 μm. If the volume average particle size of the carrier core is less than 10 μm, the adhesion between the toner and the carrier becomes high when used for electrostatic charge image development, and the development amount of the toner decreases. On the other hand, if it exceeds 500 μm, the magnetic brush becomes rough and it becomes difficult to form a fine image.
The volume average particle diameter of the core in the carrier of the first aspect refers to a value measured using a laser diffraction / scattering particle size distribution analyzer (LS Particle Size Analyzer: LS13 320, manufactured by BECKMAN COULTER). For the particle size range (channel) obtained by dividing the obtained particle size distribution, the volume cumulative distribution is subtracted from the small particle size side, and the particle size that becomes 50% cumulative is _defined as the volume average particle size D _50v .

The preferred particle size distribution of the nuclei in the carrier of the first embodiment is that volume average particle size D _84v / volume average particle size D _50v is 1.20 or less, number average particle size D _50p / number average particle size D _16p The volume average particle diameter D _84v / volume average particle diameter D _50v is 1.15 or less, and the number average particle diameter D _50p / number average particle diameter D _16p is 1.20 or less. .

In order to obtain a nucleus having such a particle size distribution, it can be adjusted to a desired particle size distribution by a gravity classifier, a centrifugal classifier, an inertia classifier, or by sorting with a sieve. .
In particular, in order to obtain the carrier core having the particle size distribution, it is preferable to use an air classifier method, and it is particularly preferable to remove fine powder / coarse powder at the same time in this method.

  When the particle size distribution of the carrier core is wider than the above range, the total energy amount by the powder rheometer described above deviates from the specified range. On the other hand, if the particle size distribution is to be narrower than the above range, work such as classification becomes excessive and work efficiency becomes extremely poor.

The particle size distribution of the core is determined by dividing the obtained particle size distribution by using a laser diffraction / scattering particle size distribution analyzer (LS Particle Size Analyzer: LS13 320, manufactured by BECKMAN COULTER). ), By subtracting the volume cumulative distribution from the small particle size side to obtain a particle size of 84% cumulative, D _84v , subtracting the number cumulative distribution from the small particle size side to obtain a particle size of 50% cumulative D _50p , When the cumulative particle size of 16% is D _16p , the coarse particle size distribution index is volume average particle size D _84v / volume average particle size D _50v , and the fine particle size particle size distribution index is number average particle size D _50p / number. The value obtained as the average particle diameter D _16p .

The density of nucleus is in the carrier of the first aspect is preferably 3.0~8.0g / cm ^3, more preferably 3.5~7.0g / cm ^3, 4.0~ More preferably, it is 6.0 g / cm ³ . When the density is lighter than 3.0 g / cm ³ , it approaches the fluidity state of the toner, so that the charge imparting ability decreases, and when the density is heavier than 8.0 g / cm ³ , the carrier flow This is not preferable because the total energy amount tends to increase beyond the upper limit.

  The density of the nuclei is measured according to the method described in the density section of “Physical Chemistry Experiment Method (Tokyo Kagaku Dojinsha, 3rd Edition)”. For the measurement, pure water having an electric resistance of 17 MΩ or more is used and the measurement temperature is 25 ° C.

  The carrier of the present invention has a nucleus and a coating layer on the surface thereof. The coating layer is preferably a coating resin layer composed of a matrix resin.

A general matrix resin can be used as the matrix resin. For example, polyolefin resins such as polyethylene and polypropylene; polystyrene and acrylic resins, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, polyvinyl ketone, and other polyvinyl and polyvinylidene resins; Vinyl-vinyl acetate copolymer; styrene-acrylic acid copolymer; straight silicone resin composed of organosiloxane bond or modified product thereof; fluorine such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene, etc. Polyester; Polyurethane; Polycarbonate; Phenol resin; Urea-formaldehyde resin, melamine resin, benzoguanamine resin Silicone resin; urea resin, amino resin such as a polyamide resin and an epoxy resin.
These may be used individually by 1 type and may use 2 or more types together.

In particular, for contamination of the toner component, it is preferable to use a low surface energy resin such as a fluororesin or a silicone resin as a coating resin, and it is more preferable to coat with a fluororesin.
Examples of fluororesins include fluoropolyolefins, fluoroalkyl (meth) acrylate polymers and / or copolymers, vinylidene fluoride polymers and / or copolymers, and mixtures thereof, and form fluororesins. Fluorine-containing monomers containing fluorine such as tetrafluoropropyl methacrylate, pentafluoromethacrylate, octafluoropentyl methacrylate, perfluorooctylethyl methacrylate, trifluoroethyl methacrylate, etc. Is preferred. However, it is not limited to these.

  As the blending amount of the fluorine-containing monomer, it is appropriate to blend in the range of 0.1 to 50.0% by mass with respect to all monomers constituting the coating resin, more preferably 0. The range is from 5 to 40.0% by mass, and more preferably from 1.0 to 30.0% by mass. If the amount is less than 0.1% by mass, it is difficult to ensure contamination resistance. If the amount exceeds 50.0% by mass, the adhesion of the coating resin to the core may be lowered, and the chargeability may be lowered.

  The matrix resin contained in the coating resin layer is preferably 0.5 to 10% by mass, more preferably 1.0 to 5.0% by mass, still more preferably based on the total weight of the carrier. 1.0% by mass to 4.0% by mass. If it is less than 0.5% by mass, the magnetic core particles are likely to be exposed on the surface of the carrier, and the electrical resistance of the carrier tends to be lowered. On the other hand, when it exceeds 10% by mass, the fluidity of the carrier is remarkably lowered, and the toner is difficult to be uniformly charged.

In the coating layer, resin fine particles can be dispersed and contained.
Examples of the resin fine particles include thermoplastic resin particles and thermosetting resin particles. Among these, thermosetting resins that are relatively easy to increase the hardness are suitable, and in order to impart negative chargeability to the toner, it is preferable to use resin particles containing nitrogen atoms. In addition, these resin particles may be used individually by 1 type, and may use 2 or more types together.

  The resin fine particles are preferably dispersed as uniformly as possible in the matrix resin in the thickness direction of the coating resin layer and in the tangential direction to the carrier surface. It is preferable that the resin of the resin fine particles and the matrix resin have high compatibility since the uniformity of dispersion of the resin fine particles in the coating resin layer is improved.

  Examples of the thermoplastic resin include polyolefin resins such as polyethylene and polypropylene; polyvinyl such as polystyrene, acrylic resin, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinyl ketone; Polyvinylidene resin; vinyl chloride-vinyl acetate copolymer; styrene-acrylic acid copolymer; straight silicone resin composed of organosiloxane bond or modified product thereof; polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychloro Fluorine resin such as trifluoroethylene; polyester; polyurethane; polycarbonate and the like.

  Examples of the thermosetting resin used for the resin fine particles include phenol resins; urea-formaldehyde resins, melamine resins, silicone resins, benzoguanamine resins, urea resins, polyamide resins, and other amino resins; epoxy resins; and the like.

  The resin fine resin and the matrix resin may be the same material or different materials. Particularly preferably, the resin of the resin fine particles and the matrix resin are made of different materials.

It is preferable to use thermosetting resin particles as the resin of the resin fine particles because the mechanical strength of the carrier can be improved. A resin having a crosslinked structure is particularly preferable. Further, in order to improve the function of the resin particles as a charging site, it is preferable to use a resin with a fast rise in toner charge. Examples of such resin particles include nylon resin, amino resin, and melamine resin. Nitrogen-containing resin particles are preferred.
The resin fine particles can be granulated while a method of producing granulated resin particles using polymerization such as emulsion polymerization, suspension polymerization, etc., or while a monomer or oligomer is dispersed in a solvent and a crosslinking reaction proceeds. According to a method for producing resin particles, a low molecular component and a crosslinking agent are mixed and reacted by melt kneading, etc., and then pulverized to a predetermined particle size by wind force, mechanical force, etc. Can be manufactured.

  The volume average particle diameter of the resin fine particles is preferably 0.1 to 2.0 μm, more preferably 0.2 to 1.0 μm. If it is smaller than 0.1 μm, the dispersion in the coating resin layer is lowered. On the other hand, if it is larger than 2 μm, the coating resin layer is likely to fall off, and stable chargeability may not be obtained. The method for measuring the volume average particle diameter of the resin fine particles is the same as that for the volume average particle diameter of the core.

  The resin fine particles are preferably contained in the coating layer at 1 to 50% by volume, more preferably 1 to 30% by volume, and even more preferably 1 to 20% by volume. When the content of the resin fine particles in the coating resin layer is less than 1% by volume, the effect of the resin fine particles may not be exhibited. When the content exceeds 50% by volume, the coating resin layer is likely to fall off, and stable charging. This is not preferable because the properties may not be obtained.

The coating layer can further contain conductive fine powder dispersed therein.
Examples of the conductive fine powder include metals such as gold, silver, and copper; carbon black; and titanium oxide, magnesium oxide, zinc oxide, aluminum oxide, calcium carbonate, aluminum borate, potassium titanate, and titanic acid. Metal oxides such as calcium powder; fine powders in which the surface of titanium oxide, zinc oxide, barium sulfate, aluminum borate, potassium titanate powder, etc. is covered with tin oxide, carbon black, or metal; . These may be used alone or in combination of two or more. It is preferable to use a metal oxide as the conductive fine powder because the environmental dependency of the charging property can be further reduced, and titanium oxide is particularly preferable.

Furthermore, it is preferable to treat the fine powder made of the material with a coupling agent. Of these, metal oxides treated with a coupling agent are preferred, and titanium oxide treated with a coupling agent is particularly preferred. The conductive fine powder treated with the coupling agent can be obtained by dispersing the untreated conductive fine powder in a solvent such as toluene, then mixing and treating the coupling agent, and then drying under reduced pressure. it can.
Furthermore, in order to remove the aggregate from the conductive fine powder treated with the obtained coupling agent, it may be crushed by a crusher as necessary. As the crusher, known crushers such as a pin mill, a disk mill, a hammer mill, a centrifugal classification mill, a roller mill, and a jet mill can be used, and a jet mill is particularly preferable. As the coupling agent to be used, known ones such as a silane coupling agent, a titanium coupling agent, an aluminum coupling agent, and a zirconium coupling agent can be used.
Of these, use of a silane coupling agent, particularly conductive fine powder treated with methyltrimethoxysilane, is particularly effective for the environmental stability of charging.

The volume average particle diameter of the conductive fine powder is preferably 0.5 μm or less, more preferably 0.05 μm or more and 0.45 μm or less, and still more preferably 0.05 μm or more and 0.35 μm or less. The method for measuring the volume average particle size of the conductive fine powder is in accordance with the method for measuring the volume average particle size of the core.
When the volume average particle size of the conductive fine powder exceeds 0.5 μm, it is not preferable because it may easily fall off from the coating resin layer and stable chargeability may not be obtained.

The conductive fine powder preferably has a volume electrical resistance of 10 ¹ Ω · cm to 10 ¹¹ Ω · cm, and preferably has a volume electrical resistance of 10 ³ Ω · cm to 10 ⁹ Ω · cm. More preferably. In addition, in this specification, the volume electrical resistance of electroconductive fine powder means the value measured with the following method.
Under normal temperature and humidity, the conductive fine powder is filled into a container having a cross-sectional area of 2 × 10 ⁻⁴ m ² to a thickness of about 1 mm, and then the metal member is placed on the filled conductive fine powder. A load of 1 × 10 ⁴ kg / m ² is applied. A voltage that generates an electric field of 10 ⁶ V / m is applied between the metal member and the bottom electrode of the container, and a value calculated from the current value at that time is defined as a volume electric resistance value.

  The conductive fine powder is usually contained in the coating resin layer in an amount of 1 to 80% by volume, preferably 2 to 20% by volume, more preferably 3 to 10% by volume.

  As a method for forming the coating layer on the surface of the carrier core, the carrier core is prepared by a dipping method in which a solution for forming a coating layer containing the resin, a conductive material and a solvent is immersed in the solution. Spray method in which layer forming solution is sprayed on the surface of carrier core, fluidized bed method in which coating layer forming solution is sprayed in a state where carrier core is suspended by fluidized air, or coating with carrier core in a kneader coater Examples thereof include a kneader coater method in which a solvent is removed by mixing with a layer forming solution.

  The solvent used for preparing the coating layer forming solution is not particularly limited as long as it dissolves the resin. For example, aromatic hydrocarbons such as toluene and xylene, ketones such as acetone and methyl ethyl ketone, and the like. And ethers such as tetrahydrofuran and dioxane can be used.

  The average thickness of the coating layer is preferably 0.1 μm to 10 μm, more preferably 0.1 μm to 3.0 μm, and still more preferably 0.1 μm to 1.0 μm. When the average film thickness of the resin coating layer is less than 0.1 μm, the resistance is reduced due to peeling of the coating layer when used for a long time, and when it exceeds 10 μm, it takes time to reach the saturation charge amount, which is not preferable.

Density of the carrier in this way the first mode in which the surface of the core body coated with a resin or the like is preferably ^{3.0~8.0g / cm 3, 3.5~7.0g / cm} 3 More preferably, it is 4.0-6.0 g / cm < ³ >. When the density is lighter than 3.0 g / cm ³ , the fluidity of the toner is approached, so that the charging ability is reduced. When the density is heavier than 8.0 g / cm ³ , Since fluidity | liquidity fall generate | occur | produces and it becomes the tendency for a total energy amount to become large exceeding an upper limit, it is unpreferable. The method for measuring the carrier density is the same as the method for measuring the density of the carrier nucleus.

In addition, for the carrier of the first aspect, the shape factor SF1 represented by the following formula (1) is preferably SF1130 or less, and more preferably 120 or less.
The shape factor SF1 becomes a true sphere as it approaches 100. The greater the carrier shape factor SF1, the lower the fluidity due to the collision between the carriers due to the shape distortion. Therefore, when the shape factor SF1 exceeds 130, the total energy amount tends to increase beyond the upper limit value.

Formula (1): Shape factor SF1 = (ML ² / A) × (π / 4) × 100
In formula (1), ML represents the absolute maximum length of carrier particles, and A represents the projected area of carrier particles.

  The average value of the shape factor SF1 is obtained by taking 50 or more carrier particles magnified 250 times from an optical microscope into an image analyzer (LUZEX III, manufactured by Nireco), and calculating the above-mentioned individual particles from the maximum length and projected area. The value of SF1 is obtained and averaged.

The saturation magnetization of the carrier of the first aspect is preferably 40 emu / g or more, and more preferably 50 emu / g or more.
As a device for measuring magnetic properties, a vibrating sample type magnetic measuring device VSMP10-15 (manufactured by Toei Kogyo Co., Ltd.) is used. The measurement sample is packed in a cell having an inner diameter of 7 mm and a height of 5 mm and set in the apparatus. The measurement applies an applied magnetic field and sweeps up to 1000 oersted. Next, the applied magnetic field is decreased to create a hysteresis curve on the recording paper. Saturation magnetization, residual magnetization, and coercive force are obtained from the curve data. In the present invention, saturation magnetization refers to magnetization measured in a 1000 oersted field.

Volume resistivity of the carrier is preferably controlled in the range of ^{1 × 10 8 ~1 × 10 14} Ωcm, more preferably in the range of ^{1 × 10 8 ~1 × 10 13} Ωcm, 1 × 10 8 More preferably, it is in the range of ˜1 × 10 ¹² Ωcm.
When the volume electrical resistance of the carrier exceeds 1 × 10 ¹⁴ Ωcm, the resistance becomes high and it becomes difficult to work as a developing electrode at the time of development, so that the solid reproducibility is deteriorated such as an edge effect particularly in a solid image portion. On the other hand, when the density is less than 1 × 10 ⁸ Ωcm, the resistance becomes low, so that when the toner concentration in the developer is lowered, charges are injected from the developing roll into the carrier, and the carrier itself is easily developed.

The volume electric resistance (Ω · cm) of the carrier is measured as follows. The measurement environment is a temperature of 20 ° C. and a humidity of 50% RH.
The carrier to be measured is placed flat on the surface of a circular jig having a 20 cm ² electrode plate so as to have a thickness of about 1 to 3 mm to form a carrier layer. A 20 cm ² electrode plate similar to the above is placed on this and the carrier layer is sandwiched. In order to eliminate the gap between the carriers, the thickness (cm) of the carrier layer is measured after a load of 4 kg is applied on the electrode plate placed on the carrier layer. Both electrodes above and below the carrier layer are connected to an electrometer and a high-voltage power generator. A high voltage is applied to both electrodes so that the electric field is 10 ^3.8 V / cm, and the current value (A) flowing at this time is read to calculate the volume electric resistance (Ω · cm) of the carrier. The calculation formula of the volume electrical resistance (Ω · cm) of the carrier is as shown in the following formula (2).
Formula (2): R = E × 20 / (I−I ₀ ) / L

In the above formula, R is the volume electric resistance (Ω · cm) of the carrier, E is the applied voltage (V), I is the current value (A), I ₀ is the current value (A) at the applied voltage of 0 V, and L is the carrier layer. Represents the thickness (cm). A coefficient of 20 represents the area (cm ² ) of the electrode plate.

<Image forming method>
The image forming method of the present invention comprises at least a charging step for charging a latent image carrier, an exposure step for exposing the charged latent image carrier to form an electrostatic latent image on the latent image carrier, and a toner. Forming a toner image by developing the electrostatic latent image with a developer including a carrier and a carrier, and a transfer step of transferring the toner image from the latent image carrier to a recording material A method is preferred. The carrier used for image formation includes the above-described electrostatic charge image developing carrier.

  The toner contained in the developer is not particularly limited, and generally contains a binder resin and a colorant. A known technique can be applied to the toner used in the present invention.

  In the image forming method of the present invention, known techniques can be appropriately applied to the charging step, the exposure step, the development step, and the transfer step. Further, in addition to these steps, a cleaning step for cleaning the latent image carrier after the transfer step, a fixing step for fixing the transferred toner image on the recording material, and the like may be performed.

The developing step may be a mode in which a developer carrying member (so-called mag roll) carrying the developer on the surface rotates to face the image carrying member and transports the developer to the image carrying member. preferable.
In particular, the developer carrying member is preferably rotated at a peripheral speed of 200 mm / sec to 600 mm / sec, more preferably 300 mm / sec to 500 mm / sec. When the peripheral speed of the mag roll is less than 200 mm / sec, it is not suitable for the recent increase in speed and is not very preferable. Moreover, it is inferior in terms of high density reproducibility. On the other hand, when it exceeds 600 mm / sec, particularly when applied to a small-sized developing machine, trimmer distortion occurs due to insufficient mechanical strength of the developing machine, and density reproducibility is caused by unevenness of the developer on the developer carrier. Since it may be inferior, it is not preferable.

<Image forming apparatus>
The image forming apparatus of the present invention includes at least a latent image carrier, charging means for charging the latent image carrier, and exposing the charged latent image carrier to form an electrostatic latent image on the latent image carrier. An image having exposure means for forming, developing means for developing the electrostatic latent image with a developer to form a toner image, and transfer means for transferring the toner image from the latent image carrier to a recording material. A forming device is preferred.
Each of these components, that is, the electrophotographic photosensitive member, the charging device, the exposure device, the developing device, the transfer device, the cleaning device, and the charge eliminating device are not particularly limited in the present invention, and are conventionally known. Any configuration can be used without problems.
The developing unit preferably includes a stirring unit that stirs the developer and the developer carrier (so-called mag roll) that transports the developer to the image carrier.

  EXAMPLES Hereinafter, although an Example demonstrates this invention, this invention is not limited to these Examples.

<Measuring method of various characteristics>
First, methods for measuring physical properties of carriers and the like used in Examples and Comparative Examples will be described.

-Shape factor-
An optical microscope image of toner dispersed on a nuclear slide glass is taken into an image analyzer (LUZEXIII, manufactured by Nireco) through a video camera, and the equivalent circle diameter of 50 particles is measured. From the maximum length and area, individual particles are measured. SF1 was calculated from the above formula (1), and the average value was obtained.

-Volume average particle size, particle size distribution-
As a measuring apparatus, a laser diffraction / scattering type particle size distribution measuring apparatus (LS Particle Size Analyzer: LS13 320, manufactured by BECKMAN COULTER) was used.
As a measuring method, 10 to 200 mg of a measurement sample was added to 2 ml of a 5% by weight aqueous solution of a surfactant, preferably sodium alkylbenzenesulfonate as a dispersant. This was added to 100 to 150 ml of pure water. The liquid in which the sample is suspended is subjected to dispersion treatment with an ultrasonic disperser for about 1 minute, and the particle size distribution is measured at a pump speed of 80% with the LS Particle Size Analyzer: LS13 320, and the volume average particle size is measured as described above. The diameter, coarse particle size distribution, and fine particle size distribution were determined.

-Measurement of molecular weight distribution-
The molecular weight distribution of the toner resin and the carrier coating resin was performed under the following conditions.
Tosoh Corporation HLC-8120GPC, SC-8020 apparatus was used, TSK gei, SuperHM-H (6.0 mm ID × 15 cm × 2) was used as a column, and THF (tetrahydrofuran) was used as an eluent. The measurement conditions were a sample concentration of 0.5%, a flow rate of 0.6 ml / min, a sample injection amount of 10 μl, and a measurement temperature of 40 ° C. The calibration curve was prepared from 10 samples of A-500, F-1, F-10, F-80, F-380, A-2500, F-4, F-40, F-128, and F-700. The data collection interval in the sample analysis was 300 ms.

-Density measurement-
The density of the carrier nucleus was measured according to the method described above.

[Example 1]
Ferrite particles (Cu—Zn, density: 4.5 g / cm ³ , volume average particle size: 35 μm, shape factor SF1: 125) are cut at 25 μm with an elbow jet (manufactured by Nippon Steel Mining Co., Ltd., product number EJ-LABO). At 45 μm, fine powder and coarse powder were removed to form coating core particles.
The resulting particle size distribution of the coating core particles are coarse powder side particle size distribution index _{(D 84v / D 50v):} 1.18, fine-side particle size distribution index (D _50p / D _16p): Yes 1.20 The volume average particle size was 37 μm and the shape factor SF1 was 124.

  20 parts of toluene solution (solid content 15% by mass) of styrene methyl methacrylate copolymer (weight average molecular weight 80,000) is added to 100 parts of core particles for coating, and inside a 50 L batch kneader equipped with a jacket. The mixture was stirred for 10 minutes, the temperature of the mixture was raised while stirring, stirred for 20 minutes at a temperature of 120 ° C. or higher, cooled and stirred until the temperature of the mixture reached 60 ° C., and the coated carrier was taken out. Thereafter, fine powder / coarse powder removal was repeated 3 times under the above conditions by an elbow jet to obtain a carrier (1).

  The particle size distribution of the obtained carrier (1) was coarse particle size distribution index: 1.15, fine particle size distribution index: 1.16, volume average particle size was 37 μm, and shape factor SF1 was 123. It was.

  The total energy amount of the obtained carrier (1) was measured using a powder rheometer FT4 (manufactured by freeman technology) by the method described above. The specific measurement method is as follows.

First, an auxiliary device was attached to the upper side of the 160 ml container, and the carrier (1) was introduced so as to exceed the upper part of the 160 ml container. Next, a rotating blade (manufactured by freemanology, propeller type φ48 mm diameter blade (diameter 48 mm, width 10 mm) shown in FIG. 3) is set on the upper part of the container packed with the carrier (1) in this measuring apparatus, and −5. Conditioning was performed four times with an approach angle of 0 ° and a tip speed of the rotor blade of 60 mm / s.
Subsequently, the carrier (1) sufficiently deaerated by conditioning is scraped off at the upper end of the 160 ml container, and the impeller is advanced from the lower part of the container to 10 mm at an entry angle of −5.0 ° and the tip speed of the impeller is 100 mm / s. (Entry distance 70 mm), the integrated value of torque at that time was determined as the total energy amount. The total energy amount of the carrier (1) was 2400 mJ.

[Examples 2 to 4]
In the same manner as in Example 1 except that the operation of removing fine powder / coarse powder with an elbow jet in the resin-coated carrier was repeated three times in the same manner except that it was changed between two and five times, respectively, in the same manner as in the carriers (2) to ( 4) was produced. The total energy amount of the carriers (2) to (4) was a value shown in Table 1.

[Example 5]
Ferrite particles (Cu—Zn, density: 4.5 g / cm ³ , volume average particle size: 35 μm, shape factor SF1: 120) are removed by elbow jet at a cut point of 22 μm and 45 μm to remove fine powder and coarse powder. Nucleus particles were formed.
The particle size distribution of the obtained core particles for coating was as follows: coarse particle size distribution index: 1.18, fine particle size distribution index: 1.20, volume average particle size: 37 μm, shape factor SF1: 118 there were.
60 parts of a methyl methacrylate-perfluorohexyl acrylate (80/20) copolymer (weight average molecular weight 50,000, Sanyo Chemical Co., Ltd.) in toluene solution (solid content 5 mass%) is applied to 100 parts of the core particles for coating. 10 parts of a toluene solution (solid content 15% by mass) of a styrene methyl methacrylate copolymer (weight average molecular weight 80000) was added, mixed for 10 minutes in a 50 L batch kneader equipped with a jacket, and the mixture was stirred. After stirring for 20 minutes at a temperature of 120 ° C. or higher, the mixture was cooled and stirred until the temperature of the mixture reached 60 ° C., and coarse powder was removed with a 75 μm sieve to obtain a carrier (5). The total energy amount of the carrier (5) was a value shown in Table 1.

[Comparative Example 1]
Ferrite particles (Cu-Zn, density: 4.5g / cm ^3, a volume average particle diameter: 35 [mu] m, shape factor SF1:. 125) was used without classifying. To 100 parts of the ferrite particles, 20 parts of a toluene solution (solid content 15% by mass) of a styrene-methyl methacrylate copolymer (weight average molecular weight 80,000) was added, and the mixture was placed in a 50 L batch kneader equipped with a jacket. The mixture was mixed for 10 minutes, the temperature of the mixture was raised while stirring, stirred for 20 minutes at a temperature of 120 ° C. or higher, then cooled and stirred until the temperature of the mixture reached 60 ° C., and the coated carrier was taken out. Thereafter, the coarse powder was removed with a 75 μm sieve to obtain a carrier (9).
The total amount of energy of the obtained carrier (9) was 3800 mJ.

[Comparative Examples 2-3]
In Comparative Example 1, coarse powder removal with a 75 μm sieve was similarly performed except that the operation of fine powder / coarse powder removal with an elbow jet was changed to once or twice at the same cut points as in Example 1. Carriers (10) to (11) were produced. The total energy amount of the carriers (10) to (11) was a value shown in Table 1.

[Comparative Example 4]
Ferrite particles (Cu—Zn, density: 4.5 g / cm ³ , volume average particle size: 35 μm, shape factor SF1: 110) were removed with an elbow jet to form core particles for coating. . The particle size distribution of the obtained core particles for coating is as follows: coarse particle size distribution index: 1.18, fine particle size distribution index: 1.20, volume average particle size: 37 μm, shape factor SF1: 109 there were.
60 parts of a toluene solution (solid content 5% by mass) of perfluorohexyl methacrylate / methyl methacrylate copolymer (weight average molecular weight: 50,000, manufactured by Sanyo Chemical Co., Ltd.), 100 parts of styrene Add 10 parts of a toluene solution (solid content 15% by mass) of methyl methacrylate copolymer (weight average molecular weight: 75000), mix for 10 minutes in a 50 L batch kneader equipped with a jacket, and stir the temperature of the mixture After stirring for 20 minutes at a temperature of 120 ° C. or higher, cooling and stirring were performed until the temperature of the mixture reached 60 ° C. to obtain a carrier (12). The total energy amount of the carrier (12) was a value shown in Table 1.

[Comparative Example 5]-Carrier of Example 1 of JP-A-2002-328493-
A carrier of Example 1 of JP 2002-328493 A was produced by the method described in the publication, and a carrier (13) having magnetic powder dispersed particles as a core was obtained.
The total energy amount of the carrier (13) was a value shown in Table 1.

<Preparation of developer>
(Preparation of toner by kneading)
-Manufacture of toner a-
Polyester resin: 100 parts by weight (terephthalic acid / bisphenol A ethylene oxide adduct / linear polyester composed of cyclohexane: weight average molecular weight: 10,000)
Carbon black (Regal 330: manufactured by Cabot): 6 parts by weight

  The above mixture was kneaded with an extruder, pulverized with a jet mill, and classified. Subsequently, it was mixed with an external additive to obtain a black toner (toner a).

-Production of Toner b-
In toner a, carbon black is changed to copper phthalocyanine blue pigment C.I. I. A cyan toner (toner b) was obtained in the same manner as toner a except that the pigment blue was changed to 5 parts by weight of 15: 3.

-Manufacture of toner c-
In toner a, carbon black was changed to C.I. I. Magenta toner (toner c) was obtained in the same manner as toner a except that the pigment red 57: 1 was changed to 5 parts by weight.

-Manufacture of toner d-
In toner a, carbon black was changed to C.I. I. Yellow toner (toner d) was obtained in the same manner as toner d, except that the pigment yellow 180 was changed to 6 parts by weight.

  100 parts by mass of any of the carriers in Examples 1 to 8 and Comparative Examples 1 to 6 are mixed with 6 parts by mass of the toner, and each carrier has four colors of yellow, magenta, cyan, and black. Developer sets (1) to (14) were adjusted.

<Evaluation>
Using the developer sets (1) to (14) thus obtained, the following copy test was performed at a sleeve peripheral speed of 350 mm / sec using a modified machine of DocuPrint C1616 manufactured by Fuji Xerox.
This copy test was performed by copying 10,000 sheets at room temperature and normal humidity (22 ° C., 50% RH) with an area coverage of 0.5%. After 10 copies (initial) and 10000 copies, The evaluation method evaluated image density, fogging, and white spot items.

(Concentration evaluation method)
An image of 2 cm × 5 cm was output, and the image density after printing 10 sheets and the image density after 10000 printing were measured with a reflection densitometer X-rite 938 (manufactured by X-rite). The results are shown in Table 1. From the top, the density of the black image, cyan image, magenta image, and yellow image is represented.
Judgment criteria used for comprehensive evaluation are as follows.
A: Density after 10,000 sheets / 10 density after 10 sheets: 97% or more of all colors ○: Density after 10,000 sheets / Density after 10 sheets: 95% or more of all colors Δ: Density after 10,000 sheets / 10 density after 10 sheets: 90% of all colors X: Concentration after 10,000 sheets / Concentration after ten sheets: Less than 90%

(Cover evaluation method)
For the white background portion of the image, the number of toners per 100 cm ² was counted.
The evaluation criteria used for the comprehensive evaluation are as follows.
◎: No toner ○: Less than 3 △: 3 or more and less than 5 ×: 6 or more

(White point / color point evaluation method)
A full image with an area coverage of 100% was output on A4 paper, and the number of white spots was counted. Also, A4 blank paper was output and the number of color points was counted.
The evaluation criteria used for the comprehensive evaluation are as follows.
◎: No color point / white point ○: Total less than 5 △: Total 5 or more and less than 10 ×: Total 10 or more

(Comprehensive evaluation)
Evaluation items for density, fogging, and color point were evaluated by addition values when ◎ 0 point, ◯ 1 point, △ 2 point, and × 3 point. Judgment criteria are as follows, and ◎ and ○ are practical levels.
◎: Addition value 3 points or less ○: Addition value 4 points to 6 points △: Addition value 7 points to 9 points ×: Addition value 10 points or more

  The obtained evaluation results are shown in Tables 1 and 2.

As shown in Tables 1 and 2, when measured with a powder rheometer under the above conditions, the total energy amount is 1500 mJ to 3000 mJ in the case of an electrostatic charge image developing carrier having a coating layer on the surface of magnetic particles. In some cases , since the fluidity was good, the generation of fog due to the destruction of the carrier was prevented, and no white spots on the image due to the fine powder generated due to the carrier destruction were generated. Further, since the fluidity was good, the transferability was improved and the image density was also good.

It is a figure for demonstrating the measuring method of the total energy amount with a powder rheometer. It is a figure which shows the relationship between the vertical load and energy gradient which were obtained with the powder rheometer. It is a figure for demonstrating the shape of the rotary blade used with a powder rheometer.

Claims (3)

A carrier for developing an electrostatic image having magnetic particles as a core and a coating layer covering the surface of the magnetic particles,
In the powder rheometer, the total energy amount from the filling surface of the carrier to the depth of 70 mm at the tip angle of the rotor blade of 100 mm / s and the approach angle of the rotor blade of -5 ° is 1500 to 3000 mJ. Carrier for developing an electrostatic image. A charging step for charging the latent image carrier;
An exposure step of exposing the charged latent image carrier to form an electrostatic latent image on the latent image carrier, and developing the electrostatic latent image with a developer including toner and a carrier to form a toner image A development step to form;
A transfer step of transferring the toner image from the latent image carrier to a recording material,
The carrier includes the electrostatic image developing carrier according to claim 1 ,
In the developing step, a developer carrying body carrying the developer on the surface rotates at a peripheral speed of 200 mm / s or more and 600 mm / s or less to face the image carrying body, and the developer is applied to the image carrying body. An image forming method comprising a conveying step. A latent image carrier;
Charging means for charging the latent image carrier;
Exposure means for exposing the charged latent image carrier to form an electrostatic latent image on the latent image carrier;
Developing means for developing the electrostatic latent image with a developer to form a toner image;
Transfer means for transferring the toner image from the latent image carrier to a recording material, and an image forming apparatus comprising:
An image forming apparatus, wherein the developer includes the electrostatic image developing carrier according to claim 1 .