JP2012063571A - Carrier for electrostatic charge image development, method for manufacturing the same, two-component developer, and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier for electrostatic charge image development suppressing generation of image defect by having high fluidity; and to provide a method for manufacturing the same, a two-component developer, and an image forming method.SOLUTION: This carrier for electrostatic charge image development comprises carrier particles formed by applying a resin coating to the surfaces of core particles comprising porous ferrite particles, and the pore size of the porous ferrite particle is 0.1-0.7 μm. The method for manufacturing the carrier for the electrostatic charge image development includes: a step for mixing and agitating the core particles comprising the porous ferrite particles and resin fine particles to be used for the resin coating at a temperature lower than a glass transition point of resin, sticking the resin fine particles on the surfaces of the core particles and forming carrier intermediates; and a step for agitating the carrier intermediates by a dry method at a temperature of (the glass transition point of the resin-10°C) to (the glass transition point of the resin+20°C) and forming the carrier particles formed by applying the resin coating on the surfaces of the core particles.

Description

  The present invention relates to an electrostatic charge image developing carrier used for developing an electrostatic latent image by electrophotography, a method for producing the same, a two-component developer using the electrostatic charge image developing carrier, and an image forming method.

In recent years, with the increase in the speed of image forming apparatuses, in particular, the speed of color image forming apparatuses, the stirring strength in the developing device has increased, and the stress caused by the stirring received by the developer has increased, causing the problem of toner deterioration. is there.
In order to solve such a problem, the specific gravity of the carrier is reduced, and a magnetic material dispersion type carrier has been proposed (for example, see Patent Document 1). However, depending on such a carrier, there is a problem that the carrier is likely to be crushed and deformed by an impact.

  In addition, it has been proposed to use a carrier containing porous core particles having voids and a resin to reduce the specific gravity of the carrier (see, for example, Patent Document 2). However, the core particles having voids have irregularities on the surface, and even when the surface of the core particles is coated with resin, the resin penetrates into the voids. The smoothness is low, and excellent fluidity cannot be obtained. As a result, image defects such as toner scattering, carrier adhesion, and density unevenness occur. In order to obtain high smoothness on the surface of the carrier particles, a method of increasing the coating amount of the resin applied to the surface of the core particles can be considered. As a result, there is a problem that excellent fluidity cannot be obtained.

JP-A-8-248684 JP 2008-310104 A

  The present invention has been made in consideration of the above circumstances, and an object of the present invention is to provide an electrostatic charge image developing carrier in which generation of image defects is suppressed by having high fluidity, and a method for producing the same. Another object is to provide a two-component developer and an image forming method.

The electrostatic charge image developing carrier of the present invention is an electrostatic charge image developing carrier comprising carrier particles in which the surface of core particles comprising porous ferrite particles is coated with a resin,
The porous ferrite particles have a pore diameter of 0.1 to 0.7 μm.

In the electrostatic image developing carrier of the present invention, the core particle has a shape factor SF-1 of 100 to 125,
It is preferable that the carrier particles have a shape factor SF-1 of 100 to 120.

In the electrostatic charge image developing carrier of the present invention, the core particles have a shape factor SF-2 of 105 to 135,
The carrier particles preferably have a shape factor SF-2 of 105 to 125.

The method for producing an electrostatic charge image developing carrier of the present invention is a method for producing the above-described electrostatic charge image developing carrier,
It has the following step 1 and step 2.
Step 1 Core particles made of porous ferrite particles and resin fine particles used for resin coating are mixed and stirred at a temperature lower than the glass transition point of the resin, and the resin fine particles adhere to the surface of the core particles. Forming a carrier intermediate.
Step 2 The carrier intermediate is agitated at a temperature of −10 ° C. to glass transition point + 20 ° C. of the resin to form carrier particles having a resin coating on the surface of the core particles. Process.

  The two-component developer of the present invention is characterized by comprising the above-mentioned carrier for developing an electrostatic image and a toner for developing an electrostatic image.

  The image forming method of the present invention includes a step of developing an electrostatic latent image using the above two-component developer.

  According to the electrostatic charge image developing carrier of the present invention, the porous ferrite particles as the core particles constituting the carrier particles have a small pore diameter in a specific range, so that the surface of the porous ferrite particles is coated. And the resin particles are prevented from penetrating into the pores of the porous ferrite particles, and the surface of the carrier particles has high smoothness. As a result, the occurrence of image defects is suppressed by having high fluidity. The

  According to the method for producing a carrier for developing an electrostatic charge image of the present invention, the resin coated on the surface of the porous ferrite particles is obtained by performing the step 2 of applying the resin coating on the surface of the core particles by a dry method. Penetration into the pores of the porous ferrite particles is suppressed, and the carrier particles according to the present invention can be obtained reliably.

  According to the two-component developer of the present invention, since the electrostatic charge image developing carrier of the present invention is used, the two-component developer has high fluidity, thereby suppressing the occurrence of image defects.

  According to the image forming method of the present invention, since the electrostatic latent image is developed using the two-component developer of the present invention, the two-component developer has high fluidity, so that image defects are generated. Is suppressed.

It is the schematic which shows an example of the stirring apparatus used for the manufacturing method of the carrier for electrostatic image development of this invention. It is a top view of the horizontal direction rotary body in the stirring apparatus of FIG. It is a front view of the horizontal direction rotary body in the stirring apparatus of FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus used in an image forming method of the present invention.

  Hereinafter, the present invention will be described in detail.

[Electrostatic charge image development carrier]
The carrier for developing an electrostatic charge image (hereinafter also simply referred to as “carrier”) of the present invention comprises carrier particles obtained by coating the surface of core particles made of porous ferrite particles with a resin coating.
The carrier of the present invention may have a form in which a part of the surface of the core particle is covered with the resin as well as a form in which the surface of the core particle is completely covered with the resin.

In the carrier of the present invention, the pore diameter of the porous ferrite particles as the core particles constituting the carrier particles is 0.1 to 0.7 μm, more preferably 0.2 to 0.5 μm.
When the pore diameter of the porous ferrite particles is less than 0.1 μm, it is not possible to achieve a sufficiently low specific gravity. On the other hand, when the pore diameter of the porous ferrite particles exceeds 0.7 μm, the resin coated on the surface of the porous ferrite particles penetrates into the pores of the porous ferrite particles. I can't get it.

In the present invention, the pore diameter of the porous ferrite particles means an average value of pore diameters measured by a mercury intrusion method. Specifically, the pore diameter of the porous ferrite particles is measured as follows.
That is, using a mercury porosimeter “Pascal 140” and “Pascal 240” (above, ThermoFisher Scientific) for a sample (porous ferrite particles 2 cm ³ ), the sample was placed in a commercially available gelatin capsule having a plurality of holes. The capsule is placed in a dilatometer (CD3P (for powder)), degassed using “Pascal 140”, filled with mercury, and the amount of mercury intrusion in the low pressure region (0 to 400 kPa) is set to “ Measured as “1st Run”. Next, deaeration is performed again, and the mercury intrusion amount in the low pressure region (0 to 400 kPa) is measured as “2nd Run”. After measurement of “2nd Run”, the total mass of the dilatometer, mercury, capsule and sample is measured.
Next, the mercury intrusion amount in the high pressure region (0.1 MPa to 200 MPa) is measured using “Pascal 240”. The pore volume, pore diameter, and pore diameter distribution of the porous ferrite particles are determined from the amount of mercury intrusion obtained by the measurement in the high pressure region. The pore diameter is calculated assuming that the surface tension of mercury is 4.80 mN / cm and the contact angle is 141.3 °.

The shape factor SF-1 of the core particle according to the present invention is preferably 100 to 125, more preferably 102 to 115, and the shape factor SF-2 of the core particle is 105 to 135. More preferably, it is 110-130.
When the shape factor SF-1 and the shape factor SF-2 of the core particle are within the above range, the exposed area of the surface of the core particle is reduced, so that the occurrence of image defects is sufficiently suppressed.
When the core particle shape factor SF-1 exceeds 125, since the sphericity of the core particle is low, uniform resin coating is not performed, and the exposed area of the surface of the core particle is increased. There is a possibility that the chargeability of the image becomes uneven and the occurrence of image defects is not sufficiently suppressed.
Further, when the core particle shape factor SF-2 exceeds 135, the smoothness of the surface of the core particle is low, so the uniform resin coating is not applied, and the chargeability of the carrier is uneven, resulting in image defects. There is a risk that the occurrence of is not sufficiently suppressed.

The carrier particle shape factor SF-1 according to the present invention is preferably 100 to 120, more preferably 102 to 115, and the carrier particle shape factor SF-2 is 105 to 125. More preferably, it is 110-120.
When the shape factor SF-1 and the shape factor SF-2 of the carrier particles are within the above range, the carrier has higher fluidity, and thus image defects are sufficiently suppressed.
When the shape factor SF-1 of the carrier particles exceeds 120, the carrier particles may be caught between the carrier particles and between the carrier particles and the toner particles, and high fluidity may not be obtained.
Further, when the shape factor SF-2 of the carrier particles exceeds 125, the carrier particles may be caught between the carrier particles and between the carrier particles and the toner particles, and high fluidity may not be obtained.

  In the present invention, the shape factor SF-1 is an index indicating sphericity. In the case of a true sphere, the shape factor SF-1 is 100. The shape factor SF-2 is an index indicating the degree of unevenness on the surface, and the shape factor SF-2 is 100 in the case of a smooth surface without unevenness.

In the present invention, the shape factor SF-1 and the shape factor SF-2 of the core particles and the carrier particles are average values of the shape factors calculated by the following formulas (SF-1) and (SF-2).
Specifically, using a scanning electron microscope, 100 samples (core particles or carrier particles) were imaged under conditions of a magnification of 150 times, and this captured image was used as an image processing analysis apparatus “Luzex AP” (manufactured by Nireco). The maximum diameter, the projected area, and the perimeter are obtained for each particle, and the shape factor is calculated by the following formula (SF-1) and formula (SF-2). The average value of each shape factor in 100 particles is defined as “shape factor SF-1” and “shape factor SF-2” in the present invention.

Formula (SF-1): SF-1 = {(MXLNG) ² / (AREA)} × (π / 4) × 100
Formula (SF-2): SF-2 = {(PERI) ² / (AREA)} × (1 / 4π) × 100
In the above formulas (SF-1) and (SF-2), “MXLNG” represents the maximum particle diameter, “AREA” represents the projected area of the particle, and “PERI” represents the perimeter of the particle.
Here, the maximum diameter means a width at which the interval between the parallel lines is maximum when the projected image of the particle on the plane is sandwiched between two parallel lines. The projected area refers to the area of the projected image on the plane of the particle.

When obtaining the shape factor of carrier particles, when preparing a sample from a two-component developer, as a preparatory step, a two-component developer, a small amount of neutral detergent and pure water may be added to a beaker. However, discard the supernatant while applying a magnet to the bottom of the beaker, add pure water and discard the supernatant to remove the toner and neutral detergent and separate only the carrier particles, which are dried at 40 ° C. Work to obtain carrier particles alone.
Further, when obtaining the shape factor of the core particles, when trying to obtain a sample from the carrier particles, as a preparation, 2 g of the carrier particles are put into a glass bottle with a capacity of 20 ml, 15 ml of methyl ethyl ketone is added to this glass bottle, And the coating resin is dissolved with a solvent. And a solvent is removed using a magnet, and also it wash | cleans 3 times with 10 ml of methyl ethyl ketone, Then, the operation | work which obtains a core particle single-piece | unit by drying is performed.

As the porous ferrite particles as the core particles according to the present invention, those represented by the following general formula (1) are preferable.
General formula (1): (MO) _X (Fe ₂ O ₃ ) _Y
[In the general formula (1), M represents Fe, Mn, Mg, Sr, Ca, Ti, Cu, Zn, Ni, Li, Al, Si, Zr or Bi. Y is 30 to 95 mol%]

  M in the general formula (1) can be used alone or in combination of two or more. M is preferably one or more selected from Mn, Mg, Sr, Ca, Ti, Li, Al, Si, Zr, Bi from the viewpoint of stabilizing the magnetic properties, and Mn, Mg, Sr, Ca, One or more selected from Li, Zr and Bi are particularly preferred.

The particle diameter of the core particles is preferably 15 to 80 μm, more preferably 20 to 60 μm, in terms of volume-based median diameter (D ₅₀ ).
When the median diameter (D ₅₀ ) on the volume basis is in the above range, the occurrence of carrier adhesion is suppressed.
The particle diameter of the core particles is measured using a laser diffraction particle size distribution measuring apparatus “HELOS” (manufactured by Sympathic) equipped with a wet disperser.

The particle diameter of the carrier particles is preferably 15 to 80 μm, more preferably 20 to 60 μm, in terms of volume-based median diameter (D ₅₀ ).
The particle size of the carrier particles is measured using a laser diffraction particle size distribution measuring apparatus “HELOS” (manufactured by Sympathic) equipped with a wet disperser.

  Examples of the resin coated on the surface of the core particle according to the present invention (hereinafter also referred to as “coating resin”) include polyolefin resins such as polyethylene, polypropylene, chlorinated polyethylene, chlorosulfonated polyethylene; Polyacrylates such as methyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole, polyvinyl ether, and polyvinylidene resins such as polybiliketones; vinyl chloride-vinyl acetate copolymers and styrene- Copolymers such as acrylic acid copolymers; silicone resins composed of organosiloxane bonds or modified resins thereof (eg alkyd resins, polyester resins, epoxy resins, Modified resins with tantalum, etc.); Fluororesin such as polytetrachloroethylene, polyvinyl fluoride, polyvinylidene fluoride, polychlorotrifluoroethylene; polyamide; polyester; polyurethane; polycarbonate; amino resin such as urea-formaldehyde resin; Is mentioned. Of these resins, polyacrylate resins or styrene-acrylic acid copolymer resins are particularly preferable from the viewpoint of preventing spent toner.

  The coating resin preferably has a glass transition point of 60 to 130 ° C, more preferably 100 to 120 ° C.

The glass transition point of the coating resin is measured using a differential scanning calorimeter “DSC-7” (manufactured by Perkin Elmer).
Specifically, 4.5 mg of a measurement sample (coating resin) is precisely weighed to two digits after the decimal point, sealed in an aluminum pan, and set in a sample holder. The reference uses an empty aluminum pan, performs heat-cool-heat temperature control at a measurement temperature of 0 to 200 ° C., a temperature increase rate of 10 ° C./min, and a temperature decrease rate of 10 ° C./min. Analysis is performed based on the data in Heat. The glass transition point is the value of the intersection of the baseline extension before the first endothermic peak rises and the tangent line that shows the maximum slope between the first endothermic peak rising portion and the peak apex.

The resin for coating preferably has a mass average molecular weight (Mw) by gel permeation chromatography (GPC) soluble in tetrahydrofuran (THF) of 100,000 to 900,000, more preferably 200,000 to 700,000. .
When the mass average molecular weight (Mw) of the coating resin is too small, the entanglement of the molecular chains becomes insufficient, so that the coating resin coated on the surface of the core particles may be worn out quickly. There is. On the other hand, when the mass average molecular weight (Mw) of the coating resin is excessive, the coating resin does not have high density, so that the obtained carrier has sufficient stain resistance and wear resistance over a long period of time. May not be obtained.

The molecular weight measurement by GPC is performed as follows.
That is, using an apparatus “HLC-8220” (manufactured by Tosoh Corporation) and a column “TSKguardcolumn + TSKgelSuperHZM-M3 series” (manufactured by Tosoh Corporation), while maintaining the column temperature at 40 ° C., tetrahydrofuran (THF) was used as a carrier solvent at a flow rate of 0. Flow at 2 mL / min, and dissolve the measurement sample in tetrahydrofuran to a concentration of 50 mg / mL under a dissolution condition in which the measurement sample is processed for 5 minutes at room temperature using an ultrasonic disperser, and then processed with a membrane filter having a pore size of 0.2 μm. A sample solution is obtained, and 10 μL of this sample solution is injected into the apparatus together with the above carrier solvent, detected using a refractive index detector (RI detector), and the molecular weight distribution of the measurement sample is determined as a monodisperse polystyrene standard. Calculation is performed using a calibration curve measured using particles. As a standard polystyrene sample for calibration curve measurement, molecular weights manufactured by Pressure Chemical Co., Ltd. are 6 × 10 ² , 2.1 × 10 ³ , 4 × 10 ³ , 1.75 × 10 ⁴ , 5.1 × 10 ⁴ , 1 .1 × 10 ⁵ , 3.9 × 10 ⁵ , 8.6 × 10 ⁵ , 2 × 10 ⁶ , 4.48 × 10 ⁶ , and at least about 10 standard polystyrene samples were measured, and a calibration curve It was created. A refractive index detector was used as the detector.

  The coating amount of the coating resin in the carrier particles according to the present invention is preferably 0.5 to 10 parts by mass, more preferably 1 to 8 parts by mass with respect to 100 parts by mass of the core particles.

[Method for producing core particles]
As a manufacturing method of the core particle used by this invention, the method which has the following process A-process D is mentioned, for example.
Step A: A step of mixing and grinding raw materials (hereinafter also referred to as “ferrite raw materials”) to form a pulverized product.
Step B: A step of pre-baking the pulverized product to form a pre-baked product.
Step C: A step of subjecting the temporarily fired product to main firing to form the final fired product.
Step D: A step of classifying the fired product to form core particles.

(Process A: Grinding process)
The pulverization process in step A can be performed using a pulverizer such as a ball mill or a vibration mill. Moreover, about the grinding | pulverization processing time, 0.5 hour or more is preferable, More preferably, it is 1 to 20 hours. The pulverizer such as the above-mentioned ball mill and vibration mill is not particularly limited, but in order to disperse the ferrite raw material effectively and uniformly, it is preferable to use beads having a particle diameter of 1 mm or less for the medium to be used. Further, the degree of grinding can be controlled by adjusting the diameter, composition and grinding time of the beads used.
Thereafter, in this step A, the pulverized product is processed into a pellet form using, for example, a pressure molding machine, or the slurry is formed by adding water without using a pressure molding machine, and is granulated using a spray dryer. Is done.

(Process B: Temporary firing process)
About the temporary baking process in this process B, it can carry out using a rotary electric furnace, a batch type electric furnace, a tunnel type electric furnace, etc., for example. Moreover, temporary baking temperature is 700-1200 degreeC, for example, and temporary baking time is 0.5 to 5 hours, for example.

(Process C: Main firing process)
In this step C, the calcined product is further pulverized using a pulverizer such as a ball mill or a vibration mill, and then granulated by adjusting the viscosity by adding water and, if necessary, a dispersant, a binder, etc. This is done by controlling the concentration.
The pulverization process in Step C may be performed using a pulverizer such as a wet ball mill or a wet vibration mill with water added.

  The main baking process in the step C can be performed using, for example, a rotary electric furnace, a batch electric furnace, a tunnel electric furnace, or the like. Moreover, this baking temperature is 800-1500 degreeC, for example, and this baking time is 1 to 24 hours, for example.

(Process D: Classification process)
About the classification process in this process D, a well-known wind classification method, a mesh filtration method, a sedimentation method, etc. are employable.

  Moreover, in order to adjust an electrical resistance before the process D, you may perform an oxide film process by heating at low temperature as needed. As this oxide film processing, it can carry out at 300-700 degreeC, for example using a rotary electric furnace, a batch-type electric furnace, etc., for example. The thickness of the oxide film formed by this oxide film treatment is preferably 0.1 nm to 5 μm. Moreover, you may perform a reduction process before an oxide film process as needed.

  The pore diameter of the porous ferrite particles as the core particles can be controlled by adjusting the degree of pulverization of the ferrite raw material in step A, and the amount of binder added, the main firing temperature, and the main firing time in step C. The shape factor SF-1 and the shape factor SF-2 of the core particles can be adjusted by adjusting the degree of pulverization of the ferrite raw material in the step A, the type of furnace used in the step C, the main firing temperature, and the main firing time. Can be controlled.

  According to the carrier of the present invention, since the porous ferrite particles constituting the carrier particles have a small pore diameter in a specific range, it is possible to prevent the coating resin from penetrating into the pores of the porous ferrite particles. The surface of the carrier particles has high smoothness. As a result, the occurrence of image defects is suppressed by having high fluidity.

[Method for producing carrier]
The carrier production method of the present invention is a method having at least the following step 1 and step 2. By such a manufacturing method, the coating resin is prevented from penetrating into the pores of the porous ferrite particles, and the loss of the coating resin is reduced.

Step 1: A raw material (hereinafter also referred to as “carrier raw material”) composed of core particles made of porous ferrite particles and coating resin fine particles (hereinafter also referred to as “coating resin fine particles”) is used for the coating. A step of mixing and stirring at a temperature lower than the glass transition point of the resin to adhere the coating resin fine particles to the surface of the core particle to form a carrier intermediate.
Process 2: The process of forming the carrier particle by which the resin coating is given to the surface of a core particle by stirring a carrier intermediate body at the temperature of the glass transition point vicinity of coating resin by a dry method.

(Step 1: Carrier intermediate forming step)
In this step 1, the mixing / stirring temperature is lower than the glass transition point (Tg) of the coating resin, specifically, (Tg-30 of the coating resin) to (Tg-100 of the coating resin) ° C. It is said.
When the mixing / stirring temperature is in the above range, the coating resin fine particles can be uniformly adhered to the surfaces of the core particles because the coating resin fine particles are mixed and stirred in a solid state.

The particle diameter of the coating resin fine particles in this step 1 is preferably 20 to ₅₀₀ nm, more preferably 50 to 200 nm in terms of volume-based median diameter (D ₅₀ ).
The particle diameter of the coating resin fine particles is measured using “Microtrac UPA150” (manufactured by Nikkiso Co., Ltd.).

  Moreover, in this process 1, it is preferable that it is 0.5-10 mass parts with respect to 100 mass parts of core particles as addition amount of the resin fine particle for coating | cover, More preferably, it is 1-8 mass parts.

(Process 2: Carrier particle formation process)
In this step 2, it is preferable to perform a process of forming carrier particles in which the surface of the core particles is coated with a resin by stirring by applying a mechanical impact force by a dry method.

In this step 2, the stirring temperature is set to a temperature in the vicinity of the glass transition point (Tg) of the coating resin, specifically (Tg-10 of the coating resin) to (Tg + 20 of the coating resin) ° C.
When the stirring temperature is in the above range, the coating resin fine particles attached to the surface of the core particles are in a molten state and the stirring treatment is performed, so that the coating resin is uniformly applied to the surface of the core particles. Carrier particles formed can be formed.

  The shape factor SF-1 and shape factor SF-2 of the carrier particles are controlled by adjusting the amount of coating resin fine particles added in step 1 and the stirring temperature and stirring time in step 1 or step 2. Can do.

As a method for producing the carrier of the present invention, a method using the stirring device shown in FIG. 1 will be specifically described.
As shown in FIG. 1, this agitation apparatus includes a mixing and agitation tank 30, and a top lid 31 is provided with a raw material input port 32 provided with an input valve 33, a filter 34, and an inspection port 35. A horizontal rotating body 38 driven by a motor 42 is provided at the bottom of the mixing and stirring tank 30.

  As shown in FIG. 2, the horizontal rotating body 38 includes a central portion 38d rotated in the direction of the arrow, and three rotary blades 38a made of long pieces provided at equal positions from the central portion 38d. , 38b, 38c, and each of the rotor blades 38a, 38b, 38c is provided with one side of a long piece so that a slope toward the upper lid 31 is formed as shown in FIG. While being close to the bottom 30 a of the mixing and stirring tank 30, the other side is installed at a position rising obliquely upward from the bottom 30 a of the mixing and stirring tank 30, for example, at an angle of 120 °.

In FIG. 1, for example, 37 is a jacket that functions as a heating means when the carrier material is stirred, and 36 is a thermometer that functions as a cooling means after the stirring of the carrier material.
Reference numeral 39 denotes a vertical rotating body composed of two rotating blades, which is provided as needed, and which rotates in the direction of the arrow to promote stirring of the carrier material and prevent its aggregation.
Reference numeral 40 denotes a product discharge port in which a discharge valve 41 is installed.

  In such a stirrer, first, as a preliminary mixing step, a carrier raw material composed of porous ferrite particles and coating resin fine particles is introduced from the raw material introduction port 32 and cooling water of 10 ° C. to 15 ° C. is passed through the jacket 37. The stirring blades 38a, 38b, 38c are rotated at a peripheral speed of 1 m / sec or less, the temperature in the mixing stirring tank 30 is set to be less than Tg of the coating resin, and the charged carrier raw material is mixed and stirred for 1 to 2 minutes. .

  Next, as a carrier intermediate formation step, cooling water of 10 ° C. to 15 ° C. is passed through the jacket 37, the stirring blades 38 a, 38 b, 38 c are rotated at a peripheral speed of 10 m / sec or less, and the temperature in the mixing stirring tank 30 is increased. A carrier intermediate is formed by mixing and stirring the premixed carrier raw material for 10 to 20 minutes so that the coating resin fine particles are adhered to the surface of the porous ferrite particles so that the Tg of the coating resin is less than Tg.

  Then, as the carrier particle forming step, mechanical shock force is generated by rotating the stirring blades 38a, 38b, and 38c at a peripheral speed equal to or higher than the carrier intermediate forming step through warm water or steam through the jacket 37. The carrier intermediate is stirred for 5 to 20 minutes with the temperature in the mixing and stirring tank 20 being equal to or higher than the Tg of the coating resin to form carrier particles in which the surface of the porous ferrite particles is coated with the resin To do.

  Then, the cooling blades 10a to 15 ° C are passed through the jacket 37 and the stirring blades 38a, 38b, and 38c are rotated at a peripheral speed equal to or lower than that of the carrier particle forming step described above. Then, the discharge valve 41 is opened, and the carrier particles formed from the product discharge port 40 are taken out.

  According to the method for producing a carrier of the present invention, the step 2 of applying a resin coating to the surface of the core particle is performed by a dry method, whereby the coating resin is suppressed from penetrating into the pores of the porous ferrite particles, The carrier particles according to the invention can be obtained reliably.

〔toner〕
As the electrostatic image developing toner (hereinafter also simply referred to as “toner”) used in the two-component developer of the present invention, a known toner can be used. Specifically, such toner comprises toner particles containing at least a resin (hereinafter also referred to as “toner resin”) and a colorant. In addition, the toner particles may contain other components such as a release agent and a charge control agent as necessary.

  As the toner resin contained in the toner particles according to the present invention, when the toner particles are produced by a pulverization method, a dissolution suspension method or the like, a styrene resin, a (meth) acrylic resin, a styrene- (meta) ) Vinyl resin such as acrylic acid copolymer resin and olefin resin, polyester resin, polyamide resin, polycarbonate resin, polyether, polyvinyl acetate resin, polysulfone, epoxy resin, polyurethane resin, urea resin, etc. Various known resins can be used. These can be used alone or in combination of two or more.

  When the toner particles are produced by a suspension polymerization method, a miniemulsion polymerization aggregation method, an emulsion polymerization aggregation method, etc., as a polymerizable monomer for obtaining a toner resin, for example, styrene, o-methylstyrene, m -Styrene or styrene derivatives such as methylstyrene, p-methylstyrene, α-methylstyrene, p-phenylstyrene, p-ethylstyrene, 2,4-dimethylstyrene, p-tert-butylstyrene; methyl methacrylate, methacrylic acid Methacrylic acid ester derivatives such as ethyl, n-butyl methacrylate, isopropyl methacrylate, isobutyl methacrylate, t-butyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate and phenyl methacrylate; methyl acrylate, acrylic acid Ethyl, a Acrylic acid ester derivatives such as isopropyl laurate, n-butyl acrylate, t-butyl acrylate, isobutyl acrylate, n-octyl acrylate, 2-ethylhexyl acrylate, phenyl acrylate; acrylonitrile, methacrylonitrile, acrylamide, etc. And vinyl monomers such as acrylic acid or methacrylic acid derivatives. These vinyl monomers can be used alone or in combination of two or more.

Moreover, it is preferable to use combining what has an ionic dissociation group as a polymerizable monomer. The polymerizable monomer having an ionic dissociation group has, for example, a substituent such as a carboxyl group, a sulfonic acid group, and a phosphoric acid group as a constituent group, and specifically includes acrylic acid, methacrylic acid, maleic acid. Acid, itaconic acid, cinnamic acid, fumaric acid, maleic acid monoalkyl ester, itaconic acid monoalkyl ester, styrene sulfonic acid, allyl sulfosuccinic acid, 2-acrylamido-2-methylpropane sulfonic acid, acid phosphooxyethyl methacrylate And 3-chloro-2-acid phosphooxypropyl methacrylate.
Furthermore, as a polymerizable monomer, divinylbenzene, ethylene glycol dimethacrylate, ethylene glycol diacrylate, diethylene glycol dimethacrylate, diethylene glycol diacrylate, triethylene glycol dimethacrylate, triethylene glycol diacrylate, neopentyl glycol dimethacrylate, neopentyl It is also possible to obtain a toner resin having a crosslinked structure using a polyfunctional vinyl such as glycol diacrylate.

  As the colorant contained in the toner particles according to the present invention, a known inorganic or organic colorant can be used. Specific colorants are shown below.

  Examples of the black colorant include carbon black such as furnace black, channel black, acetylene black, thermal black and lamp black, and magnetic powder such as magnetite and ferrite.

  Examples of the colorant for magenta or red include C.I. I. Pigment red 2, C.I. I. Pigment red 3, C.I. I. Pigment red 5, C.I. I. Pigment red 6, C.I. I. Pigment red 7, C.I. I. Pigment red 15, C.I. I. Pigment red 16, C.I. I. Pigment red 48; 1, C.I. I. Pigment red 53: 1, C.I. I. Pigment red 57: 1, C.I. I. Pigment red 122, C.I. I. Pigment red 123, C.I. I. Pigment red 139, C.I. I. Pigment red 144, C.I. I. Pigment red 149, C.I. I. Pigment red 166, C.I. I. Pigment red 177, C.I. I. Pigment red 178, C.I. I. And CI Pigment Red 222.

  Examples of the colorant for orange or yellow include C.I. I. Pigment orange 31, C.I. I. Pigment orange 43, C.I. I. Pigment yellow 12, C.I. I. Pigment yellow 13, C.I. I. Pigment yellow 14, C.I. I. Pigment yellow 15, C.I. I. Pigment yellow 74, C.I. I. Pigment yellow 93, C.I. I. Pigment yellow 94, C.I. I. Pigment yellow 138, and the like.

  Examples of the colorant for green or cyan include C.I. I. Pigment blue 15, C.I. I. Pigment blue 15; 2, C.I. I. Pigment blue 15; 3, C.I. I. Pigment blue 15; 4, C.I. I. Pigment blue 16, C.I. I. Pigment blue 60, C.I. I. Pigment blue 62, C.I. I. Pigment blue 66, C.I. I. And CI Pigment Green 7.

About the above coloring agent, it can be used 1 type or in combination of 2 or more types.
The content of the colorant is preferably 1 to 30% by mass, and more preferably 2 to 20% by mass with respect to the whole toner.

When the toner particles according to the present invention contain a release agent, various known waxes such as paraffin wax and ester wax can be used as the release agent.
The content of the release agent is preferably 1 to 30% by mass, more preferably 5 to 20% by mass with respect to the resin for toner.

  In the case where the toner particles according to the present invention contain a charge control agent, various known compounds can be used as the charge control agent.

The toner particles according to the present invention preferably have a volume-based median diameter (D ₅₀ ) of 3 to 8 μm.
For the volume-based median diameter (D ₅₀ ) of the toner, a measuring device in which a computer system equipped with data processing software “Software V3.51” is connected to “Coulter Multisizer 3” (manufactured by Beckman Coulter). Measured.
Specifically, 0.02 g of toner is added to 20 mL of a surfactant solution (for example, a surfactant solution in which a neutral detergent containing a surfactant component is diluted 10-fold with pure water for the purpose of dispersing the toner). Then, ultrasonic dispersion was performed for 1 minute to prepare a toner dispersion, and this toner dispersion was placed in a beaker containing “ISOTON II” (manufactured by Beckman Coulter) in a sample stand. Pipette until the indicated concentration is 8%. Here, a reproducible measurement value can be obtained by setting the concentration range. In the measurement apparatus, the measurement particle count is 25000, the aperture diameter is 50 μm, the frequency value is calculated by dividing the measurement range of 1 to 30 μm into 256, and the volume integrated fraction is 50 % Particle diameter is defined as the volume-based median diameter (D ₅₀ ).

  The toner particles as described above can constitute the toner of the two-component developer of the present invention as it is, but a known external additive is used for the purpose of improving fluidity, charging property and cleaning property. Furthermore, it can be used by adding. These external additives are not particularly limited, and various inorganic fine particles, organic fine particles and lubricants can be used.

As the inorganic fine particles, it is preferable to use inorganic oxide particles such as silica, titania and alumina, and these inorganic fine particles are preferably subjected to a hydrophobic treatment with a silane coupling agent, a titanium coupling agent or the like. As the organic fine particles, spherical particles having a number average primary particle diameter of about 10 to 2000 nm can be used.
As the organic fine particles, polymers such as polystyrene, polymethyl methacrylate, and styrene-methyl methacrylate copolymer can be used.

  The total amount of external additives added is preferably 0.05 to 5 parts by mass, more preferably 0.1 to 3 parts by mass with respect to 100 parts by mass of the toner.

  The method for producing the toner as described above is not particularly limited, and examples thereof include a pulverization method, a polymerization method such as an emulsion polymerization aggregation method, and a miniemulsion polymerization method.

[Two-component developer]
The two-component developer of the present invention (hereinafter also simply referred to as “developer”) is a mixture of the carrier of the present invention and the toner as described above.
The mixing ratio of the toner and the carrier in the developer of the present invention is such that the toner concentration in the developer is, for example, 3 to 20% by mass, and more preferably 4 to 15% by mass.

  According to the developer of the present invention, since the carrier of the present invention is used, the developer has high fluidity, thereby suppressing the occurrence of image defects.

(Image forming method)
The image forming method of the present invention is a method having a step of developing an electrostatic latent image using the developer as described above. Specific examples include a method having the following steps.
Step (1): A step of charging the surface of the electrostatic latent image carrier.
Step (2): A step of forming an electrostatic latent image on the electrostatic latent image carrier by exposure.
Step (3): A step of developing the electrostatic latent image formed on the electrostatic latent image carrier with a developer composed of a carrier and toner to form a toner image.
Step (4): A step of transferring the toner image formed on the electrostatic latent image carrier to the image support.
Step (5): A step of fixing the toner image transferred onto the image support.
As an image forming method of the present invention, a method using the image forming apparatus shown in FIG. 4 will be specifically described.

  As shown in FIG. 4, the image forming apparatus is a tandem color image forming apparatus, and includes four sets of image forming units 10Y, 10M, 10C, and 10K arranged in a vertical column and transfer units. It has an endless belt-shaped intermediate transfer body unit 7, an endless belt-shaped paper feeding / conveying means 21 for conveying the image support P, and a heat roll type fixing device 24 as a fixing means. A document image reading device SC is disposed on the upper surface of the main body A of the image forming apparatus.

  In FIG. 4, 1Y, 1M, 1C, and 1K are photoreceptors that are electrostatic latent image carriers, and 2Y, 2M, 2C, and 2K give uniform potentials to the surfaces of the photoreceptors 1Y, 1M, 1C, and 1K. The charging means 3Y, 3M, 3C, 3K are exposure means for forming an electrostatic latent image by performing exposure based on image data on the uniformly charged photoreceptors 1Y, 1M, 1C, 1K. 4M, 4C, and 4K are developing units that convey toner onto the photoreceptors 1Y, 1M, 1C, and 1K to visualize the electrostatic latent images, and 5Y, 5M, 5C, and 5K are primary transfer units serving as primary transfer units. The roller, 70 is an intermediate transfer member, and 5A is a secondary transfer roller as a secondary transfer means for transferring the toner image transferred onto the intermediate transfer member 70 by the primary transfer rollers 5Y, 5M, 5C, 5K to the image support P. , 6Y, 6M, 6C, 6K are exposed after primary transfer 1Y, 1M, 1C, and cleaning means for recovering residual toner remaining on the 1K shown.

  As one of the different color toner images formed on each photoconductor, an image forming unit 10Y that forms a yellow image includes a drum-shaped photoconductor 1Y and charging means 2Y disposed around the photoconductor 1Y. , Exposure means 3Y, development means 4Y, primary transfer roller 5Y as primary transfer means, and cleaning means 6Y. An image forming unit 10M that forms a magenta image as another different color toner image includes a drum-shaped photoconductor 1M, a charging unit 2M disposed around the photoconductor 1M, and an exposure unit. 3M, a developing unit 4M, a primary transfer roller 5M as a primary transfer unit, and a cleaning unit 6M. Further, an image forming unit 10C that forms a cyan image as another different color toner image includes a drum-shaped photoconductor 1C, charging means 2C disposed around the photoconductor 1C, and exposure. Means 3C, development means 4C, primary transfer roller 5C as primary transfer means, and cleaning means 6C. Further, as one of other different color toner images, the image forming unit 10K that forms a black image includes a drum-shaped photoconductor 1K, a charging unit 2K disposed around the photoconductor 1K, and an exposure unit 3K. , Developing means 4K, primary transfer roller 5K as primary transfer means, and cleaning means 6K.

  The intermediate transfer body unit 7 is wound around a plurality of rollers 71, 72, 73, 74, and 76, and is supported by an endless belt-like intermediate transfer body 70, and primary transfer rollers 5Y, 5M, 5C, 5K and a cleaning device 6A.

In such an image forming apparatus, in the image forming units 10Y, 10M, 10C, and 10K, the photosensitive members 1Y, 1M, 1C, and 1K are charged and charged by the charging units 2Y, 2M, 2C, and 2K, and the exposing units 3Y and 3M. , 3C, 3K, and developing means 4Y, 4M, 4C, 4K are developed to form toner images of each color, and the primary transfer rollers 5Y, 5M, 5C, 5K form toner images of each color on the intermediate transfer member 70. Sequentially superimposed and transferred. Then, the image support P housed in the paper feed cassette 20 is fed by the paper feed / conveying means 21 and passes through a plurality of intermediate rollers 22A, 22B, 22C, 22D and a registration roller 23, and then the secondary transfer roller 5A. And the color toner images transferred onto the intermediate transfer member 70 are collectively transferred onto the image support P. Thereafter, the color toner image transferred onto the image support P is fixed by pressing and heating in the fixing device 24, and the image support P on which the color toner image is fixed is sandwiched between the paper discharge rollers 25 and out of the apparatus. It is placed on the paper discharge tray 26. The photoreceptors 1Y, 1M, 1C, and 1K after the toner image is transferred to the intermediate transfer body 70 cleans the toner remaining on the photoreceptor during the transfer by the cleaning means 6Y, 6M, 6C, and 6K, and the surface of the photoreceptor. After the fatty acid metal salt is supplied and the supplied fatty acid metal salt is spread to form a film of the fatty acid metal salt on the surface of the photoreceptor, it is used for the next image formation.
On the other hand, after the color toner image is transferred onto the image support P by the secondary transfer roller 5A, the residual toner is removed by the cleaning device 6A from the intermediate transfer body 70 which has separated the curvature of the image support P.

  According to the image forming method of the present invention, since the electrostatic latent image is developed using the developer of the present invention, the occurrence of image defects is suppressed because the developer has high fluidity. .

  Hereinafter, specific examples of the present invention will be described, but the present invention is not limited thereto.

<Toner Production Example 1>
(Preparation of core resin particles)
(1) First-stage polymerization A polymerizable monomer mixture obtained by mixing the following polymerizable monomers in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe and a nitrogen introducing device was prepared.
Styrene 110.9 parts by mass n-Butyl acrylate 52.8 parts by mass Methacrylic acid 12.3 parts by mass After adding 93.8 parts by mass of paraffin wax “HNP-57” (manufactured by Nippon Seiki Co., Ltd.) And dissolved at 80 ° C. to prepare a polymerizable monomer solution.

On the other hand, after preparing a surfactant solution in which 2.9 parts by mass of sodium polyoxyethylene (2) dodecyl ether sulfate was dissolved in 1340 parts by mass of ion-exchanged water, and heating the surfactant solution to 80 ° C., the above The polymerizable monomer solution was added, and the polymerizable monomer solution was mixed and dispersed for 2 hours by a mechanical disperser “CLEAMIX” (manufactured by M Technique) having a circulation path. Then, a dispersion liquid of emulsified particles (oil droplets) having a particle diameter of 245 nm with a volume-based median diameter (D ₅₀ ) was prepared.

  Next, after adding 1460 parts by mass of ion-exchanged water, a polymerization initiator solution in which 6 parts by mass of a polymerization initiator (potassium persulfate) was dissolved in 142 parts by mass of ion-exchanged water and 1.8 parts by mass of n-octyl mercaptan Were added to bring the temperature to 80 ° C. This system was heated and stirred at 80 ° C. for 3 hours to perform polymerization (first stage polymerization) to produce resin particles [C].

(2) Second stage polymerization (formation of outer layer)
A polymerization initiator solution prepared by dissolving 5.1 parts by mass of a polymerization initiator (potassium persulfate) in 197 parts by mass of ion-exchanged water is added to the resin particles [C], and the following polymerization property is obtained at a temperature of 80 ° C. A polymerizable monomer mixture obtained by mixing the monomers was added dropwise over 1 hour.
Styrene 282.2 parts by mass n-butyl acrylate 134.4 parts by weight Methacrylic acid 31.4 parts by mass n-octyl mercaptan 4.93 parts by mass Formation). Then, it cooled to 28 degreeC and obtained resin particle for cores [1]. The resin particle for core [1] had a mass average molecular weight of 21,300, a particle size of 180 nm in volume-based median diameter (D ₅₀ ), and a glass transition point (Tg) of 39 ° C.

(Preparation of resin particles for shell)
Surfactant solution in which 2.0 parts by mass of polyoxyethylene (2) sodium dodecyl ether sulfate is dissolved in 3000 parts by mass of ion-exchanged water in a reaction vessel equipped with a stirrer, a temperature sensor, a cooling pipe, and a nitrogen introduction apparatus. The internal temperature was raised to 80 ° C. while stirring at a stirring speed of 230 rpm under a nitrogen stream.
To this surfactant solution, a polymerization initiator solution in which 10 parts by mass of a polymerization initiator (potassium persulfate) is dissolved in 200 parts by mass of ion-exchanged water is added, and the following polymerizable monomer is mixed. The monomer mixture was added dropwise over 3 hours.
Styrene 528 parts by weight n-butyl acrylate 176 parts by weight Methacrylic acid 120 parts by weight n-octyl mercaptan 22 parts by weight After completion of dropping, the system is heated and stirred at 80 ° C. for 1 hour to polymerize, and resin particles for shells [1] was prepared. The resin particles for shell [1] had a mass average molecular weight of 12,000, a particle size of 120 nm in volume-based median diameter (D ₅₀ ), and a glass transition point (Tg) of 53 ° C.

(Preparation of colorant dispersion)
While stirring 900 parts by weight of an aqueous solution of 10% by weight sodium dodecyl sulfate, 100 parts by weight of a colorant “Regal 330R” (Cabot) was added gradually, and then a mechanical disperser “Clearmix” (M Technique) The colorant dispersion liquid [1] in which the colorant particles are dispersed was prepared by carrying out a dispersion treatment using The average dispersion diameter of the colorant particles in the colorant dispersion liquid [1] was measured using a dynamic light scattering particle size analyzer “Microtrac UPA150” (manufactured by Nikkiso Co., Ltd.).

(Formation of core part)
Resin particles for core [1] 420.7 parts by mass (converted to solid content), 900 parts by mass of ion-exchanged water, and 200 parts by mass of colorant dispersion [1], a temperature sensor, a cooling pipe, a nitrogen introducing device, and a stirring device Was stirred in a reaction vessel equipped with. After adjusting the temperature in the reaction vessel to 30 ° C., 5 mol / L sodium hydroxide aqueous solution was added to this solution to adjust the pH to 9.
Next, an aqueous solution obtained by dissolving 2 parts by mass of magnesium chloride hexahydrate in 1000 parts by mass of ion-exchanged water was added over 10 minutes at 30 ° C. with stirring. After standing for 3 minutes, the temperature was raised and the system was heated to 65 ° C. over 60 minutes. In this state, the particle size of the associated particles was measured with “Coulter Multisizer 3” (manufactured by Coulter Inc.). When the particle size reached 5.5 μm as the volume-based median diameter (D ₅₀ ), sodium chloride 40 .2 parts by mass of an aqueous solution obtained by dissolving 1000 parts by mass of ion-exchanged water was added to stop the growth of the particle size, and the fusion was continued by heating and stirring at a liquid temperature of 70 ° C. for 1 hour as an aging treatment, A core part was formed. When the circularity of the core portion was measured with “FPIA2100” (manufactured by Systex), it was 0.930.

(Formation of shell layer)
Next, at 65 ° C., 50 parts by mass of the resin particles for shell [1] (in terms of solid content) are added, and an aqueous solution in which 2 parts by mass of magnesium chloride hexahydrate is dissolved in 1000 parts by mass of ion-exchanged water is added for 10 minutes. After the addition, the temperature was raised to 70 ° C. (shell formation temperature), and stirring was continued for 1 hour to fuse the resin particles for shell [1] to the surface of the core. Thereafter, an aging treatment is carried out at 75 ° C. for 20 minutes, a shell layer is formed, 40.2 parts by mass of sodium chloride is added, and the mixture is cooled to 30 ° C. under the condition of 8 ° C./min. Prepared.

(Washing, drying)
The colored particle dispersion [1] was subjected to solid-liquid separation with a basket-type centrifuge “MARK III model number 60 × 40” (manufactured by Matsumoto Kikai Co., Ltd.) to form a wet cake of colored particles. This wet cake is washed with water in a basket-type centrifuge until the electric conductivity of the filtrate reaches 5 μS / cm, and then transferred to “flash jet dryer” (manufactured by Seishin Enterprise Co., Ltd.). It dried until it became it, and colored particle [1] was obtained. The colored particles [1] had a particle size of 6.0 μm in terms of volume-based median diameter (D ₅₀ ) and a glass transition point (Tg) of 39.5 ° C.

(Production of toner)
Hydrophobic silica fine particles (number average primary particle size = 80 nm) are 3.5% by mass, and hydrophobic titania fine particles (number average primary particle size = 10 nm) are 0.6% by mass with respect to 100 parts by mass of the colored particles [1]. Then, using a “Henschel mixer” (manufactured by Mitsui Miike Chemical Co., Ltd.), the mixture was mixed at a peripheral speed of 35 m / sec for 25 minutes to prepare toner [1] composed of toner particles [1]. Toner particles [1] had a particle size of 6.0 μm in terms of volume-based median diameter (D ₅₀ ).

[Production example 1 of core particles (porous ferrite particles)]
(A) Milling Step MnO: 35mol%, MgO: 14.5mol %, Fe 2 O 3: 50mol% and SrO: ferrite raw materials were weighed so as to 0.5 mol%, for 5 hours pulverized with a wet ball mill A slurry was obtained. The obtained slurry was dried with a spray dryer to obtain a pulverized product [1] composed of spherical particles. Trimanganese tetraoxide was used as the MnO raw material, magnesium hydroxide was used as the MgO raw material, and strontium carbonate was used as the SrO raw material.

(B) Temporary calcination step After adjusting the particle size of the pulverized product [1], the particles are heated at 950 ° C. for 2 hours using a rotary electric furnace, and subjected to a temporary calcination treatment to obtain a temporary calcination product [1]. It was.

(C) Main calcination step The calcined product [1] is pulverized for 1 hour by a wet ball mill using 1/8 inch diameter stainless steel beads, and further pulverized for 4 hours using 1/16 inch diameter stainless steel beads. went. The primary particle diameter of the particles in this slurry was 2.95 μm in terms of volume-based median diameter (D ₅₀ ). The primary particle size was measured using “Microtrac UPA150” (manufactured by Nikkiso Co., Ltd.). Then, 0.6% by mass of polyvinyl alcohol (20% by mass solution) as a binder is added to the solid content, and then granulated and dried by a spray dryer, and the particle size of the obtained particles is adjusted, and then 650 The organic components such as the dispersant and the binder were removed by heating at 0 ° C. for 2 hours. And using a rotary electric furnace, it hold | maintained at 875 degreeC for 1 hour, this baking process was performed, and this baking product [1] was obtained. At this time, hydrogen gas was charged into the furnace, and the inside of the furnace was placed in a reducing atmosphere.

(D) Classifying step The fired product [1] is crushed, subjected to classification by an air classification method, particle size is adjusted, low-magnetization products are separated by magnetic separation, and porous ferrite particles [1] are separated. Obtained. The porous ferrite particles [1] had a pore diameter of 0.45 μm, a shape factor SF-1 of 110, and a shape factor SF-2 of 125. The pore diameter, shape factor SF-1 and shape factor SF-2 of the porous ferrite particles were measured by the measurement method described above. The same shall apply hereinafter.

[Production Example 2 of Core Particle (Porous Ferrite Particle)]
In the main firing step (C) in the production example 1 of the core particles (porous ferrite particles), a tunnel electric furnace is used and kept at 1050 ° C. for 1 hour in an air atmosphere. The porous ferrite particles [2] were obtained in the same manner except that the main calcination treatment was performed by holding at 1150 ° C. for 1 hour in a nitrogen gas atmosphere. Table 1 shows the pore diameter, shape factor SF-1 and shape factor SF-2 of the porous ferrite particles [2].

[Production Example 3 of Core Particle (Porous Ferrite Particle)]
In the main firing step (C) in the production example 1 of the core particles (porous ferrite particles), as pulverization conditions, pulverization was performed using a 1/8 inch stainless steel bead for 1 hour in a wet ball mill, and then 1 / and pulverized for 12 hours using stainless beads 16 inch diameter primary particle size of the pulverized product in the slurry (D ₅₀₎ and 1 [mu] m, as further conditions for the sintering process, a rotary type electric furnace, the furnace Porous ferrite particles [3] were obtained in the same manner except that hydrogen gas was charged and the inside of the furnace was placed in a reducing atmosphere and maintained at 850 ° C. for 1 hour. Table 1 shows the pore diameter, shape factor SF-1 and shape factor SF-2 of the porous ferrite particles [3].

[Production Example 4 of Core Particles (Porous Ferrite Particles)]
In the main firing step (C) in the production example 1 of the core particles (porous ferrite particles), as pulverization conditions, pulverization was performed using a 1/8 inch stainless steel bead for 1 hour in a wet ball mill, and then 1 / Crushing for 15 hours using 16-inch diameter stainless steel beads, the primary particle size (D ₅₀ ) of the pulverized product in the slurry is 0.8 μm, and the conditions for the main firing treatment are as follows: Porous ferrite particles [4] were obtained in the same manner except that hydrogen gas was charged therein and the furnace was placed in a reducing atmosphere and maintained at 850 ° C. for 1 hour. Table 1 shows the pore diameter, shape factor SF-1 and shape factor SF-2 of the porous ferrite particles [4].

[Production Example 5 of core particles (porous ferrite particles)]
In the main firing step (C) in the production example 1 of the core particles (porous ferrite particles), a tunnel electric furnace is used and kept at 1050 ° C. for 1 hour in an air atmosphere. The porous ferrite particles [5] were obtained in the same manner except that the main calcination treatment was performed by holding at 1200 ° C. for 1 hour in a nitrogen gas atmosphere. Table 1 shows the pore diameter, shape factor SF-1 and shape factor SF-2 of the porous ferrite particles [5].

[Production Example 6 of Core Particle]
In the main firing step (C) in the production example 1 of the core particles (porous ferrite particles), a tunnel electric furnace is used and kept at 1050 ° C. for 1 hour in an air atmosphere. The ferrite particles [6] were obtained in the same manner except that the main baking treatment was performed by holding at 1350 ° C. for 6 hours in a nitrogen gas atmosphere. Table 1 shows the pore diameter, shape factor SF-1 and shape factor SF-2 of the ferrite particles [6].

<Carrier Production Example 1>
A carrier raw material comprising 100 parts by mass of porous ferrite particles [1] and 5 parts by mass of coating fine particles (glass transition point: 115 ° C., particle size (D ₅₀ ): 100 nm) made of a methacrylic ester resin is shown in FIG. Was added to the mixing and stirring tank (30) in the stirring apparatus shown in FIG. 2 and, as a preliminary mixing step, low-speed mixing and stirring were performed at a peripheral speed of 1 m / sec for 2 minutes. Then, as a carrier intermediate forming step, cold water was passed through the jacket (37), and mixed and stirred at 40 ° C. and a peripheral speed of 8 m / sec for 20 minutes to form a carrier intermediate. Thereafter, as a carrier particle forming step, steam was passed through the jacket (37), and the carrier intermediate was stirred at 120 ° C. at a peripheral speed of 8 m / sec for 30 minutes to obtain a carrier [1] composed of carrier particles. Table 2 shows the shape factor SF-1 and the shape factor SF-2 of the carrier particles [1]. In addition, the shape factor SF-1 and the shape factor SF-2 of the carrier particles were measured by the measurement method described above. The same shall apply hereinafter.

<Carrier Production Examples 2 to 6>
In the carrier production example 1, the carrier particles were similarly used except that the porous ferrite particles [2] to [5] and the ferrite particles [6] were used in place of the porous ferrite particles [1] as the carrier raw material. Carriers [2] to [6] comprising [2] to [6] were obtained. Table 2 shows the shape factor SF-1 and the shape factor SF-2 of the carrier particles [2] to [6].

<Carrier Production Example 7>
In Carrier Production Example 1, porous ferrite particles [5] were used instead of porous ferrite particles [1] as a carrier raw material, and the addition amount of methacrylic ester resin fine particles was changed to 10 parts by mass. Other than that, a carrier [7] composed of carrier particles [7] was obtained in the same manner. Table 2 shows the shape factor SF-1 and the shape factor SF-2 of the carrier particles [7].

  Carriers [1] to [4] are carriers according to examples of the present invention, and carriers [5] to [7] are carriers according to comparative examples.

<Developer Production Examples 1 to 7>
The toner [1] and the carriers [1] to [7] are used, the blending ratio is 8 parts by mass of the toner with respect to 100 parts by mass of the carrier, and the toner and the carrier are mixed at room temperature and normal humidity (20 ° C., 50 % RH), blending was carried out at a rotation speed of 20 rpm and a stirring time of 20 minutes, followed by sieving with a 125 μm sieving screen to obtain developers [1] to [7].

[Examples 1-4 and Comparative Examples 1-3]
Digital color MFP “bizhub PRO C6500” (manufactured by Konica Minolta Business Technologies) is filled with developer [1] to [7], respectively, and is subjected to A4 size fine paper in an environment of room temperature 20 ° C. and humidity 50% RH. An image with a pixel rate of 1% (a 7% character image, a human face photo, a solid white image, and a solid black image each equal to 1/4) is formed on 64 g / m ² ), and this is performed 200,000 sheets It was. Table 3 shows the evaluation results obtained by the following evaluation methods.

(1) Transferability A solid image (20 mm × 50 mm) having a pixel density of 1.30 is formed at the initial stage and after printing 200,000 sheets, and the transfer rate is obtained by the following formula (1), and evaluated according to the following evaluation criteria. It was.
Formula (1): Transfer rate (%) = (mass of toner transferred to image support / mass of toner developed on photoreceptor) × 100
-Evaluation criteria-
A: Transfer rate is 96% or more B: Transfer rate is 80% or more and less than 96% (a level that causes no problem in practical use)
C: Transfer rate is less than 80% (a level that causes practical problems)

(2) Carrier adhesion After printing 200,000 sheets, a solid image is printed, the number of carrier particles seen on the solid image is measured visually using a magnifying glass, and evaluated according to the following evaluation criteria. It was.
-Evaluation criteria-
A: No carrier particles adhere on the solid image B: No more than 5 carrier particles adhere to the solid image (a level that causes no problem in practice)
C: More than 5 carrier particles are adhered on the solid image (a level that causes a practical problem).

(3) Toner / carrier scattering After 200,000 sheets were printed, the toner scattering around the developing unit and the contamination inside the apparatus due to carrier scattering were visually observed and evaluated according to the following evaluation criteria.
-Evaluation criteria-
A: No in-machine contamination due to toner / carrier scattering B: In-machine contamination due to slight toner / carrier scattering, but no need for a vacuum cleaner during maintenance (a level that is practically acceptable)
C: Degree of contamination inside the machine due to toner / carrier scattering is severe, and the hand is required to be cleaned with a dirt cleaner during maintenance (practical problem level)

(4) Density unevenness (ghost)
A solid image was printed at the initial stage and after printing 200,000 sheets, and whether or not a ghost was generated was evaluated according to the following evaluation criteria.
Note that ghost refers to a phenomenon in which the image density gradually decreases due to poor replacement of the developer on the developing sleeve.
-Evaluation criteria-
A: No ghost image is generated in the solid image B: A slight ghost image is generated in the solid image (a level at which there is no practical problem)
C: A ghost is generated in the solid image (a level causing a problem in practice).

1Y, 1M, 1C, 1K Photoconductors 2Y, 2M, 2C, 2K Charging means 3Y, 3M, 3C, 3K Exposure means 4Y, 4M, 4C, 4K Developing means 5A Secondary transfer rollers 5Y, 5M, 5C, 5K Primary transfer Roller 6A Cleaning device 6Y, 6M, 6C, 6K Cleaning means 7 Intermediate transfer unit 10Y, 10M, 10C, 10K Image forming unit 20 Paper feed cassette 21 Paper feed conveyance means 22A, 22B, 22C, 22D Intermediate roller 23 Registration roller 24 Fixing device 25 Discharge roller 26 Discharge tray 30 Mixing stirring tank 30a Bottom 31 Upper lid 32 Raw material input port 33 Input valve 34 Filter 35 Inspection port 36 Thermometer 37 Jacket 38 Horizontal direction rotating bodies 38a, 38b, 38c Rotary blade 38d Center Portion 39 Vertical Rotating Body 40 Product Discharge Port 41 Discharge Valve 42 Motor 70 Middle Transfer body 71, 72, 73, 74, 76 Roller A Main body SC Document image reading device P Image support

Claims (6)

A carrier for developing an electrostatic charge image comprising carrier particles formed by coating a resin on the surface of core particles comprising porous ferrite particles,
A carrier for developing an electrostatic charge image, wherein the porous ferrite particles have a pore diameter of 0.1 to 0.7 μm. The core particles have a shape factor SF-1 of 100 to 125;
The carrier for electrostatic image development according to claim 1, wherein the carrier particles have a shape factor SF-1 of 100 to 120. The core particles have a shape factor SF-2 of 105 to 135;
The carrier for electrostatic image development according to claim 1 or 2, wherein the carrier particles have a shape factor SF-2 of 105 to 125. A method for producing a carrier for developing an electrostatic charge image according to any one of claims 1 to 3,
A method for producing an electrostatic charge image developing carrier, comprising the following steps 1 and 2.
Step 1 Core particles made of porous ferrite particles and resin fine particles used for resin coating are mixed and stirred at a temperature lower than the glass transition point of the resin, and the resin fine particles adhere to the surface of the core particles. Forming a carrier intermediate.
Step 2 The carrier intermediate is agitated at a temperature of −10 ° C. to glass transition point + 20 ° C. of the resin to form carrier particles having a resin coating on the surface of the core particles. Process.   A two-component developer comprising the electrostatic image developing carrier according to any one of claims 1 to 3 and an electrostatic image developing toner. An image forming method comprising: developing an electrostatic latent image using the two-component developer according to claim 5.