JP2011150150A - Resin-coated carrier for developing electrostatic latent image and method for producing the same, and image forming method using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a resin-coated carrier for developing electrostatic latent images, wherein the resistance and the electric charge imparting capacity of which are constantly stabilized, after the start of the use of the carrier and a printed image developed thereby to avoid having carrier adherence, edge effects or fogging, and high quality is obtained continuously, and to provide a method for producing the carrier and an image forming method that uses the carrier. <P>SOLUTION: In the resin-coated carrier for developing the electrostatic latent image is obtained, by forming a coating layer including resin and electroconductive fine particles on the surface of a core material particle, the surface exposure rate which is calculated by using the total amount of the core material particles and the electroconductive fine particles that are exposed to the surface of the coating layer is equal to or higher than 6% and equal to or lower than 12%, when it is measured by an X-ray photoelectron analyzer. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a resin-coated carrier for developing an electrostatic latent image, a method for producing the same, and an image forming method using the same.

  Conventionally, in an image forming method using an electrostatic latent image developing method such as electrophotography, an electrostatic latent image is formed on a photosensitive member or electrostatic recording member using various means, and toner is applied to the electrostatic latent image. In general, a method for developing an electrostatic latent image by attaching particles called “a” is used.

  During this development, the carrier is mixed with the toner, and both are stirred and triboelectrically charged to impart an appropriate amount of positive or negative charge to the toner. Carriers are generally divided into so-called coated carriers having a coating layer of resin or the like on the surface of the core particles and uncoated carriers having no coating layer on the surface. When considered, the coated carrier is superior. Therefore, various types of coated carriers have been developed and put into practical use.

  Although there are various properties required for the carrier, it is required that a proper charge can be stably imparted to the toner and that the proper and stable charge imparting ability can be maintained over a long period of time. For this purpose, the carrier has suitable electrical properties, is resistant to environmental changes such as humidity and temperature, has high impact resistance and friction resistance, and changes its ability to impart charge over the long term. This is important, and various coated carriers have been proposed (see, for example, Patent Document 1).

  The above coated carrier has the advantage that the life of the developer can be extended, but when it is used for a long period of time, the coating layer is worn by friction and impact (stress) in the developing device, and the charge imparting performance to the toner is improved. May decrease. Therefore, in order to stabilize the charge imparting performance over a long period of time, the carrier coating layer is required to have a coating layer that does not cause a decrease in toner charge amount even when subjected to friction or impact.

  Further, in the developing device, external additives and toner fine particles detached from the toner may adhere to the surface of the carrier due to friction with the toner. Since the toner fine particles and the external additive adhering to the carrier hinder contact with new toner, charging efficiency and charging stability are lowered.

  Therefore, a carrier is proposed in which the coating layer of the carrier is scraped by friction with the toner and external additives in the developing unit, and the external additive and toner fine particles adhering to the surface of the coating layer are removed. (For example, see Patent Documents 2 and 3).

  However, the techniques disclosed in these publications can suppress adhesion to the carrier surface and can always form a new surface, so the stability of charging itself is expected to improve. The present situation is that the development stability in the process has not been ensured.

  Further, a technique has been proposed in which low-resistance fine particles (conductive fine particles) are tilted and oriented in the carrier coating layer to maintain chargeability over a long period of time (see, for example, Patent Document 4).

Japanese Patent No. 3912594 Japanese Patent No. 3934514 Japanese Patent No. 3926937 JP 2008-8938 A

  However, it is necessary to improve the performance year by year in response to the demand for higher image quality and higher speed from the market, and high durability is also required to maintain the performance throughout the period of use. From this point of view, even if the conductive fine particles are tilted, the developer does not satisfy both the demands for high image quality and high durability, and a developer that satisfies the demands of the market has not been obtained.

  The reason for this is that when a large amount of conductive fine particles are added, even if the initial carrier resistance is adjusted, the coating layer decreases due to friction and falling off during long-term use, so the carrier resistance decreases. The carrier may gradually change and adhere to the image area. Further, since a large amount of conductive fine particles are present on the carrier surface, it may be very difficult to obtain sufficient chargeability.

  Conversely, when only a small amount of conductive fine particles is added, the edge effect is particularly high in the initial stage. For example, a document having a solid image adjacent to the rear end of the halftone image in the paper feed direction is printed. This will cause white spots in the halftone image area near the boundary with the solid image and carrier adhesion to the edge of the development area during high bias development, so white spots are maintained while maintaining high durability. The present condition is that the carrier which is not generated is not obtained.

  The object of the present invention is that the resistance and charging ability of a resin-coated carrier for developing an electrostatic latent image (hereinafter also simply referred to as a carrier) are always stable from the start of carrier use, and high quality without carrier adhesion, edge effect, and fogging. It is another object of the present invention to provide a carrier capable of continuously obtaining the printed image, a manufacturing method thereof, and an image forming method using the carrier.

  The object of the present invention is solved by adopting the following configuration.

1. In the resin-coated carrier for developing an electrostatic latent image formed by forming a coating layer having resin and conductive fine particles on the surface of the core material particles,
A resin-coated carrier for developing an electrostatic latent image, wherein a surface exposure rate calculated by a total of the core particles and conductive fine particles is 6% or more and 12% or less as measured by an X-ray photoelectron analyzer.

2. The core material particles have a shape factor of 130 or more and 150 or less,
The layer thickness of the coating layer is 0.5 μm or more and 2.0 μm or less,
The conductive fine particles have an average particle size of 0.7 times to 1.5 times the layer thickness of the coating layer,
2. The resin-coated carrier for developing an electrostatic latent image according to 1 above, wherein the content of the conductive fine particles is 2 parts by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the resin.

3. In the method for producing a resin-coated carrier for developing an electrostatic latent image, which forms a coating layer containing resin and conductive fine particles on the surface of the core material particles,
Using a high-speed stirring mixer that can impart mechanical impact force, a mixture of core material particles, resin and conductive fine particles is stirred at high speed without heating or under heating, and the resin is dissolved or softened on the surface of the core material particles. A coating step for forming a coating layer containing a resin and conductive fine particles;
A surface exposure rate adjusting step of exposing the core particles or conductive fine particles to the surface of the coating layer by further applying either heat or impact to the formed coating layer;
The method for producing a resin-coated carrier for developing an electrostatic latent image, wherein the surface exposure rate is 6% or more and 12% or less as measured by an X-ray photoelectron analyzer.

  4). A two-component developer is produced using the resin-coated carrier for developing an electrostatic latent image described in 1 or 2, and a latent image on a photoreceptor is developed with a developing device using the two-component developer. Image forming method.

  The carrier of the present invention, the manufacturing method thereof, and the image forming method using the carrier are stable in the carrier resistance and charge imparting ability from the beginning of use of the carrier, and have high quality printed images without carrier adhesion, edge effect, and fog. Has an excellent effect obtained continuously.

It is an expanded sectional view showing an example of the career of the present invention. It is the schematic which shows an example of the high-speed stirring mixer with a stirring blade. 1 is a schematic cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of an image forming apparatus according to the present invention. FIG. 4 is a cross-sectional configuration diagram illustrating an example of a developing device in FIG. 3.

  Carriers provided with a coating layer on the surface of the core particles have high durability, and have been widely used from the viewpoint of resource saving.

  The present inventors define the above-mentioned problem by defining the surface exposure rate of the core material particles and conductive fine particles of the carrier prepared by providing a coating layer having resin and conductive fine particles on the surface of the core material particles. Various studies were conducted on the belief that this could be solved.

  As a result of various studies, a conductive circuit is formed by exposing a specific amount of core material particles and conductive fine particles to the surface of the coating layer by providing a coating layer containing resin as a main component on the surface of the core material particles. If it is lowered by releasing the charge from the conduction circuit, carrier adhesion, edge effect, and fogging will not occur even if many sheets are printed in low and low humidity and high temperature and high humidity printing environments. It was found that a printed image can be obtained.

  The carrier of the present invention is a core material that is exposed on the surface of the carrier by exposing a specific amount of core material particles and conductive fine particles on the surface of the coating layer having resin and conductive fine particles provided on the surface of the core material particles. By providing a conduction circuit with the exposed portions of the particles and conductive fine particles, the charge imparting ability can be maintained in a preferable range from the initial carrier to the carrier life.

  In the present invention, the initial carrier refers to a carrier in the developer whose number of prints is less than 100, and corresponds to the carrier in the developer used for the initial setting of the image forming apparatus.

  FIG. 1 is an enlarged sectional view showing an example of the carrier of the present invention.

  In FIG. 1, 1 is a carrier, 2 is a core particle, 3 is a conductive fine particle, 4 is a resin, 5 is an exposed portion of the core material particle, 6 is an exposed portion of the conductive fine particle, and 7 is a coating layer.

  As shown in FIG. 1, the carrier of the present invention is one in which part of the core particles and part of the conductive fine particles are exposed on the surface of the carrier.

  First, the surface exposure rate will be described.

<Surface exposure rate>
In the present invention, the surface exposure rate is 6.0% or more and 12.0% or less, preferably 7.0% or more and 11.0% or less.

  By setting the surface exposure rate (%) to 6% or more, the conduction circuit is sufficient, the carrier resistance can be lowered, and the occurrence of the edge effect can be prevented. For example, even when a document having a solid image adjacent to the rear end of the halftone image in the paper feeding direction is printed, it is possible to prevent the halftone image near the boundary with the solid image from being whitened. Further, it is possible to prevent the carrier from adhering to the edge portion of the development area during high bias development.

  On the other hand, by setting the surface exposure rate (%) to 12% or less, the conduction circuit does not become excessive, the charge imparting ability can be maintained, and carrier attachment and landing scattering can be prevented.

  In the present invention, the surface exposure rate (%) means a value obtained by adding the exposure rate of the core particles exposed on the surface of the carrier and the exposure rate of the conductive fine particles.

  Specifically, for 100 carriers, a value obtained by adding the exposure rate of the core particles exposed on the surface of the carrier and the exposure rate of the conductive fine particles is obtained, and the average value is referred to.

(Measurement of exposure rate (F1) of core particle)
The exposure rate of the core particles is measured by the following method using an X-ray photoelectron analyzer (XPS) “ESCA-1000 (manufactured by Shimadzu Corporation)”.

  The X-ray intensity of the analyzer is 10 kV, 30 mA, analysis depth; in the normal mode, assuming that the composition on the surface of the core material particles is uniform, the main elements of the core material particles (for example, carbon, oxygen, iron, manganese, magnesium) The quantitative element is selected from the above, and the exposure rate (%) (F1) of the core particle is calculated from the element peak area intensity of the quantitative element.

(Measurement of exposure rate (F2) of conductive fine particles)
The exposure rate of the conductive fine particles can be measured by the following method using an X-ray photoelectron analyzer (XPS) “ESCA-1000 (manufactured by Shimadzu Corporation)”.

  The X-ray intensity of the analyzer is 10 kV, 30 mA, analysis depth; in the normal mode, the composition on the surface of the conductive fine particles is assumed to be uniform, and the quantitative elements are determined from the main elements (eg, silica, tin, oxygen) of the conductive fine particles. The exposure rate (%) (F2) of the conductive fine particles is calculated from the element peak area intensity of the quantitative element.

(Calculation of surface exposure rate)
The surface exposure rate is obtained for 100 carriers by the following formula, and the average value is calculated.

Surface exposure rate (%) = (F1 + F2) × 100
(Method to adjust the surface exposure rate)
The method for adjusting the surface exposure rate to 6% or more and 12% or less is not particularly limited, but the following methods are preferable.
(1) As the core material particles, those having a shape factor (SF-1) of 130 or more and 150 or less and having an uneven portion on the surface of the core material particles are used.
(2) The average layer thickness (L) of the coating layer is adjusted to 0.5 μm or more and 2.0 μm or less.
(3) The conductive fine particles having an average particle diameter (D) of 0.7 to 1.5 times the average layer thickness (L) of the coating layer are used.
(4) 2 to 8% by mass of conductive fine particles are contained in the coating layer.
(5) After the step of forming the coating layer having the resin and the conductive fine particles on the surface of the core material particles, the step of adjusting the surface exposure rate is performed, and stress is applied in this step, whereby the convex portions of the core material particles and the conductivity The resin covering the conductive fine particles is peeled to expose the core material particles and the conductive fine particles. Alternatively, the core material particles are exposed by moving the resin on the surface of the convex portion to the concave portion side by applying heat and impact.

  In the present invention, a method of producing a carrier by combining (2) to (5) mainly using the above (1) is preferable.

  The reason why the object of the present invention can be achieved by setting the surface exposure rate to 6.0% or more and 12.0% or less is not clear, but is considered as follows.

  Next, items defined in the present invention will be described.

(Shape factor of core particle (SF-1))
As the core particles, those having a shape factor (SF-1) of 130 or more and 150 or less are preferable.

  By using the core material particles having a shape factor (SF-1) of 130 or more and 150 or less, even if the coating layer is worn out over a long period of time, only the convex portions of the core material particles are worn, and the coating layer of the concave portion Is not worn, and the main factor that determines carrier resistance is only the convex part of the core particles exposed on the surface. Therefore, the resistance of the carrier and the charge imparting ability fluctuate greatly from the beginning of use of the carrier to the end of its useful life Can be reduced.

  As a result, by using core material particles having a shape factor (SF-1) of 130 or more and 150 or less, carrier adhesion to the edge, edge effect, fogging, and toner scattering are extremely reduced throughout the entire use period.

  Furthermore, by using new agent particles having a shape factor (SF-1) of 130 or more and 150 or less, the core material particle exposure rate can be easily adjusted.

  In the present invention, the shape factor (SF-1) of the core particles is a numerical value calculated by the following formula 1.

Formula 1
SF-1 = (maximum length of core particle) ² / (projected area of core particle) × (n / 4) × 100
First, in measuring SF-1 of core material particles, core material particles are prepared. However, when the core material particles are not a simple substance but a developer, preparation is performed.
・ Preparation Add developer, a small amount of neutral detergent, and pure water to the beaker and mix well. Discard the supernatant while applying a magnet to the bottom of the beaker. Further, pure water is added, the supernatant liquid is discarded, the toner and neutral detergent are removed, and only the carrier is separated. Thereafter, the coating layer of the carrier obtained by separation is dissolved and removed with a solvent to obtain core particles alone.

Specifically, 2 g of the carrier is put into a 20 ml glass bottle, and then 15 ml of methyl ethyl ketone is put into the glass bottle, stirred for 10 minutes with a wave rotor, and the coating layer is dissolved with a solvent. Using a magnet, only the core material particles are taken out, and the core material particles are washed three times with 10 ml of methyl ethyl ketone. The washed core particles are dried to obtain measurement core particles. In the present invention, the core particle for measurement refers to the particle after the pretreatment.
・ Measurement The measurement of the shape factor of the core particle is performed by taking a photograph of 100 or more core particles randomly with a scanning electron microscope at a magnification of 150 times, and using the image processing analyzer “LUZEX” "AP" (Nireco Corporation).

(Average thickness of coating layer)
The coating layer formed on the surface of the core material particles is a layer having at least a resin and conductive fine particles.

  The average layer thickness of the coating layer is preferably in the range of 0.5 μm to 2.0 μm. The durability can be ensured by setting the average layer thickness of the coating layer to 0.5 μm or more, and the toner can be prevented from being excessively charged by setting the average thickness to 2.0 μm or less.

  The average layer thickness of the coating layer is a value calculated by the following method.

  A surface passing through the center of the carrier is cut using a focused ion beam sample preparation apparatus “SMI2050” (manufactured by SSI Nano Technology Co., Ltd.) to prepare a sample for cross-sectional observation.

  This cross-sectional observation sample was enlarged and photographed with a transmission electron microscope “JEM-2010F” (manufactured by JEOL Ltd.), and the photographed image was captured by a scanner, and an image processing analysis apparatus “LUZEX AP” The average layer thickness of the coating layer is determined by analyzing 50 carriers.

  Preferably, the carrier particles are first sufficiently dispersed in a room temperature curable epoxy resin, then embedded, dispersed in a styrene fine powder having a particle size of about 100 nm, and then pressure-molded. After the necessary blocks were stained with ruthenium tetroxide or osmium tetroxide in combination, a flaky sample was cut out using a microtome with diamond teeth, and a transmission electron microscope (TEM) was used. A photograph is taken at a magnification (approximately 10000 times) in which the cross-section of one carrier particle is within the field of view. A straight line is drawn from the center of the carrier particle toward the carrier particle surface at an interval of 10 °. A point where each straight line is in contact with the core particle surface 3 is A, a point where the straight line is in contact with the coating layer surface is B, and a distance between AB is 36 points. Measurement was made and the average value was taken as the average layer thickness of the coating layer in one carrier particle. The average layer thickness of the coating layer in the present invention is indicated by the average value of the 36-point average layer thickness for 50 carrier particles.

  The average layer thickness of the coating layer is preferably adjusted by the amount of resin and conductive fine particles added to the core particles during carrier production.

(Volume average particle diameter of conductive fine particles)
As the conductive fine particles, those having a volume average particle diameter of 0.7 to 1.5 times the average layer thickness of the coating layer are preferably used.

  When the average particle diameter (D) of the conductive fine particles is within the above range with respect to the average layer thickness (L) of the coating layer, the conductive fine particles and the core material can be in direct contact to form a conduction circuit, The resistance can be lowered with a small amount of conductive fine particles.

  By using conductive fine particles whose volume average particle diameter is 0.7 times or more the number average layer thickness of the coating layer, the conductive fine particles can be exposed to the surface, a conductive circuit can be easily formed, and a desired resistance can be obtained. In order to obtain it, the amount of conductive fine particles added is small. When the addition amount of the conductive fine particles is increased, the charge imparting property is lowered, and a desired toner charge amount cannot be obtained. If the addition amount of the conductive fine particles is decreased to obtain a desired charge amount, the edge effect is enhanced. For example, when a document having a solid image adjacent to the rear end of the halftone image with respect to the paper feeding direction is printed. As a result, white spots occur in the halftone image near the boundary with the solid image.

  On the other hand, by using conductive fine particles having a volume average particle diameter of 1.5 times or less the average layer thickness of the coating layer, the conductive fine particles can be retained in the coating layer, and can be prevented from being detached from the coating layer. It is possible to prevent an image defect due to scattering of fine particles in the apparatus or adhering to an image.

  When the average thickness of the coating layer is 0.5 μm, the number average particle diameter of the conductive fine particles is preferably from 0.35 μm to 0.75 μm. When the average thickness of the coating layer is 2.0 μm, the number average particle diameter of the conductive fine particles is preferably 1.4 μm or more and 3.0 μm or less.

  The number average particle diameter (D) of the conductive fine particles can be measured with a light scattering electrophoretic particle diameter measuring apparatus “ELS-800” (manufactured by Otsuka Electronics Co., Ltd.).

(Amount of conductive fine particles contained in the coating layer)
The amount of the conductive fine particles contained in the coating layer is preferably 2 parts by mass or more and 8 parts by mass or less with respect to 100 parts by mass of the resin. By setting it to 2 parts by mass or more, it is easy to produce a carrier having a surface exposure rate of 6% or more. On the other hand, when the amount is 8 parts by mass or less, a carrier having a surface exposure rate of 12% or less can be easily produced while ensuring the adhesiveness between the core particles and the coating layer.

  Next, members (core material particles, conductive mother particles, resin) constituting the carrier will be described.

<Core particles>
Examples of the core particles used in the present invention include iron powder, magnetite, various ferrite-based particles, or those obtained by dispersing them in a resin. Magnetite and various ferrite particles are preferred. As the ferrite, a ferrite containing a heavy metal such as copper, zinc, nickel and manganese and a light metal ferrite containing an alkaline earth metal such as an alkali metal and / or magnesium are preferable.

  The shape factor (SF-1) of the new agent particles is preferably from 130 to 150. The details are described in the above-mentioned “shape factor of core material particles (SF-1)”.

  The particle diameter of the core particles is preferably 10 μm or more and 100 μm or less, more preferably 20 μm or more and 80 μm or less. Use of core material particles having a volume average particle size in the above range is preferable because the surface exposure rate defined in the present invention can be easily adjusted.

The magnetization characteristics of the core particles are preferably those having a saturation magnetization of 2.5 × 10 ^{−5 to} 15.0 × 10 ⁻⁵ Wb · m / kg.

  The volume average particle size of the core particles is a volume-based average particle size measured by a laser diffraction type particle size distribution measuring device “HELOS” (manufactured by Sympatech) equipped with a wet disperser.

  The saturation magnetization is measured by “DC magnetization characteristic automatic recording device 3257-35” (manufactured by Yokogawa Electric Corporation).

  The core material particles are produced through a process of granulating and drying, for example, ferrite as a raw material, followed by baking by heat treatment, and pulverizing and classifying the obtained core material particles. In the firing step, the granulated and dried particles are placed in a container and placed in a firing furnace for firing.

  The production method of the deformed core material particles having a core material particle shape factor SF-1 of 130 or more and 150 or less is not particularly limited, but in the firing step, the firing temperature is set to 1300 to 1500 ° C., which is higher than before. A production method is preferred.

<Conductive fine particles>
As the conductive fine particles, those having a volume resistance of 1 to 1 × 10 ⁴ Ωcm are preferable. Preferable examples of the conductive fine particles include titanium oxide, tin oxide, magnetite and the like.

  The particle diameter of the conductive fine particles depends on the average film thickness of the coating layer, and those having a volume average particle diameter of 0.35 μm to 3.0 μm are preferably used.

<resin>
As a resin suitable for forming a coating layer, a coating layer can be satisfactorily formed by a coating process in which the surface of the core particle is coated with a resin and conductive fine particles. It is preferable to be able to expose to the preferable range.

  Preferred resins include polyolefin resins such as polyethylene, polypropylene, chlorinated polyethylene and chlorosulfonated polyethylene; polyacrylates such as polystyrene and polymethyl methacrylate, polyacrylonitrile, polyvinyl acetate, polyvinyl alcohol, polyvinyl butyral, polyvinyl chloride, polyvinyl carbazole. Polyvinyl and polyvinylidene resins such as polyvinyl ether and polybiliketones; copolymers such as vinyl chloride-vinyl acetate copolymers and styrene-acrylic acid copolymers; silicone resins composed of organosiloxane bonds or modified resins thereof (for example, alkyds) Resin, polyester resin, epoxy resin, modified resin by polyurethane, etc.): polytetrachloroethylene, polyvinyl fluoride, polyvinyl fluoride Den, poly chloro triflupromazine Lol ethylene and fluorine resins, polyamides, polyesters, polyurethanes, polycarbonates; -; and epoxy resins urea amino resins such as formaldehyde resin. Incidentally, as a resin particularly preferable in terms of preventing spent toner, polyacrylate resin or styrene-acrylic acid copolymer resin can be exemplified.

  Next, the characteristics of the carrier will be described.

(Volume average particle diameter of carrier)
The volume average particle diameter of the carrier provided with a coating layer on the surface of the core particle is preferably 10 μm or more and 100 μm or less, more preferably 20 μm or more and 80 μm or less. Use of a carrier having a volume average particle diameter in the above range is preferable because a high-quality (for example, high resolution, high density) printed image can be obtained.

  The volume average particle diameter of the carrier can be measured by a laser diffraction type particle size distribution measuring apparatus “HELOS” (manufactured by Sympatech) equipped with a wet disperser.

(Carrier SF-1)
The SF-1 of the carrier on which the coating layer is formed is preferably 110 or more and 120 or less. When it is in this range, the fluidity of the carrier is good, which is preferable.

  In measuring SF-1 of carrier particles, when the carrier is not a carrier alone but a developer, the carrier is separated from the developer, and the carrier alone is measured.

  The SF-1 of the carrier can be measured by the same measuring method as that of the core particle SF-1.

(Measurement of carrier resistance)
In the present invention, the resistance of the carrier is a value when the toner is separated from the developer and the carrier is isolated, and the resistance of only the isolated carrier is measured.

The resistance (initial resistance) at the start of use of the carrier is preferably 5 × 10 ^{8 to} 3 × 10 ¹⁰ Ωcm, more preferably 8 × 10 ⁸ to 1 × 10 ¹⁰ Ωcm. When the resistance of the carrier is within the above range, the image effect at the center of the solid image portion is low and the edge effect in which the end portion becomes dark is suppressed in actual shooting at the time of initial use. The effect of suppressing toner scattering can be sufficiently exerted.

  The resistance of the carrier is a resistance that is dynamically measured under developing conditions with a magnetic brush, and can be determined by the following resistance measurement method.

  The carrier resistance is measured by replacing an aluminum electrode drum having the same dimensions as the photosensitive drum with a photosensitive drum, supplying carrier particles on the developing sleeve to form a magnetic brush, and rubbing the magnetic brush against the electrode drum. Then, a voltage (500 V) is applied between the sleeve and the drum, and the current flowing between them is measured. The resistance of the carrier is obtained from the measured value by the following formula 2.

Formula 2
DVR (Ωcm) = (V / I) × (N × L / Dsd)
DVR: Carrier resistance (Ωcm)
V: Voltage between developing sleeve and drum (V)
I: Measurement current value (A)
N: Development nip width (cm)
L: Development sleeve length (cm)
Dsd: Distance between developing sleeve and drum (cm)
In the present invention, the measurement is performed at V = 500 V, N = 1 cm, L = 6 cm, and Dsd = 0.6 mm.

  Next, the manufacturing method of a carrier is demonstrated.

  The surface coverage of the carrier can be adjusted by the shape factor of the core particles, the layer thickness of the coating layer and the average particle diameter of the conductive fine particles, the content of the conductive fine particles, etc. Can be adjusted.

<Carrier manufacturing method>
The carrier production method is particularly limited as long as the coating layer having the resin and the conductive fine particles can be provided on the surface of the core particle so that the surface coverage of the carrier is 6% or more and 12% or less. is not.

  As a preferable method for manufacturing the carrier, a manufacturing method using a wet coating method or a dry coating method can be given.

  Each manufacturing method will be described below.

  <Wet coating method> includes the following.

(1) Fluidized bed type spray coating method A coating solution in which a coating resin is dissolved in a solvent is spray coated on the surface of magnetic particles using a fluidized bed, and then dried to produce a coated layer. (2) Immersion Formula Coating Method A method in which magnetic particles are immersed in a coating solution in which a coating resin is dissolved in a solvent and then coated, and then dried to prepare a coating layer. (3) Polymerization Method A reactive compound is dissolved in a solvent. A method of producing a coating layer by immersing magnetic particles in a coating solution, applying a coating treatment, and then applying heat or the like to conduct a polymerization reaction.

<Dry coat method>
The dry coating method is a particularly preferable method because the surface exposure rate of the carrier defined in the present invention can be easily adjusted.

  Examples of the apparatus that can be used in the dry coating method include stirring and mixing with a high-speed stirring mixer with a stirring blade, a turbuler, a ball mill, a vibration mill, and the like. A high-speed stirring mixer with stirring blades is preferable.

  FIG. 2 is a schematic view showing an example of a high-speed stirring mixer with stirring blades.

  In FIG. 2, reference numeral 11 denotes an upper lid of the main body, and the upper lid 11 is provided with a raw material charging port 12, a charging valve 13, a filter 14 and an inspection port 15. A predetermined amount of core material particles, coating resin particles and conductive fine particles are charged from the raw material charging port 12, and the charged raw materials are stirred by a horizontal rotating body 18 driven by a motor 22. The rotating body 18 has stirring blades 18a, 18b and 18c arranged at an angular interval of 120 ° to each other at the central portion 18d, and these blades are attached with an inclination of about 35 ° with respect to the surface of the bottom portion 10a. It has been. For this reason, when the stirring blades 18a, 18b and 18c are rotated at high speed, the raw material is scraped upward and collides with the upper inner wall of the main body container 10 and falls. Of stirring and pulverization of agglomeration. Reference numeral 17 is a temperature control jacket, 16 is a thermometer, 20 is a product outlet, 21 and 24 are discharge valves, and 23 is an exhaust port in the container.

  As a method for producing a carrier using the high-speed stirring mixer with stirring blades shown in FIG. 2, a method of performing a surface exposure rate adjusting step after a step of forming a coating layer is preferable.

(Step of forming the coating layer)
Core material particles, resin particles and conductive fine particles are mixed, and the resin particles and conductive fine particles are deposited on the surface of the core material particles, and then the applied resin particles are melted or softened by applying mechanical impact force and heat. To adhere to the surface of the core material particles to form a coating layer.

  In the case of heating, the temperature is preferably 80 to 130 ° C., and the rotation speed causing the impact force is preferably 10 m / s or more during heating, and 5 m / s or less in order to suppress aggregation of carrier particles during cooling. The time for applying the impact force is preferably 20 to 60 minutes.

(Process to adjust the surface exposure rate)
After that, an impact force is applied at a low rotational speed, stress is applied to the coated carrier, and the resin covering the convex part resin and conductive fine particles of the core material particles is peeled off to remove the core material particles and conductive fine particles. Expose. Alternatively, the core material particles are exposed by moving the resin on the surface of the convex portion to the concave portion side by applying heat and impact.

  In the step of adjusting the surface exposure rate, the heating temperature is lowered to 60 ° C. or lower, the resin is prevented from peeling by lowering the rotation speed, and the coating layer is on the convex surface by applying heat and weak impact. The amount of surface exposure is adjusted by moving the resin to the concave side or exposing the core particles and conductive fine particles. The time for applying the impact force is preferably 60 to 90 minutes.

  Next, a developer using the carrier of the present invention will be described.

<Developer>
The carrier of the present invention can be mixed with toner and used as a two-component developer.

  The two-component developer is used for mono black toner image formation or color toner image formation.

  The two-component developer according to the present invention can be prepared by mixing the carrier of the present invention and a toner.

  The mixing ratio of the carrier and the toner is preferably carrier: toner = 100: 10 to 100: 2 in terms of mass ratio.

  For mixing the carrier and the toner, various known mixing devices such as a Turbuler mixer, a Henschel mixer, a Nauter mixer, and a V-type mixer can be used.

(toner)
As the toner used in the present invention, those commonly used can be used without particular limitation. For example, a styrene-acrylic resin or a polyester resin can be used as a binder resin, and a conventionally used colorant can also be used as a colorant. Further, a release agent or charge control is used as necessary. Agent is added.

  The production method may be a so-called pulverization method or a polymerization method, and in many cases, external additives such as silica fine particles are added after toner particle formation.

The toner has a volume-based median diameter (D ₅₀ ) of preferably 3.0 μm or more and 8.0 μm or less, and more preferably 4.0 μm or more and 7.0 μm or less.

The measurement of the median diameter (D ₅₀ ) on a volume basis is performed as follows.

  Measurement and calculation are performed using a device in which a computer system for data processing (manufactured by Beckman Coulter) is connected to "Coulter Multisizer 3" (manufactured by Beckman Coulter). As a measuring means, 0.02 g of toner was conditioned with 20 g of a surfactant solution (for example, a surfactant solution obtained by diluting a neutral detergent containing a surfactant 10 times with pure water for the purpose of dispersing the toner). Thereafter, ultrasonic dispersion is performed for 1 minute to prepare a toner dispersion. This toner dispersion is pipetted into a beaker containing ISOTON II (manufactured by Beckman Coulter, Inc.) in a sample stand until the measured concentration is 5 to 10% by mass. By setting this concentration range, a reproducible measurement value can be obtained. In the measuring machine, the measurement particle count is set to 25000, the aperture diameter is set to 50 mm, and the frequency range is calculated by dividing the range of 1 to 30 mm, which is the measurement range, into 256. The particle diameter of 50% from the larger volume integrated fraction is defined as the median diameter on the volume basis.

  Next, an image forming method using the developer prepared above will be described.

(Image forming method)
The carrier of the present invention is more effective in a developing system (forward developing system) in which the moving direction of the photosensitive drum and the developing sleeve is the same in the area where both are closest and face each other (so-called developing area). . In the forward developing system, the toner per unit time to the developing nip portion is compared with a developing system (reverse developing system) in which the moving direction of the photosensitive drum and the moving direction of the developer sleeve in the above region are opposite. This is because the edge effect is more likely to occur because the supply amount is small.

  Hereinafter, an example of an image forming apparatus that is a forward developing system will be described with reference to FIGS.

  FIG. 3 is a schematic cross-sectional configuration diagram of a color image forming apparatus showing an embodiment of the image forming apparatus according to the present invention.

  In FIG. 3, the image forming apparatus GS includes an image forming apparatus main body GH and an image reading apparatus YS.

  The image forming apparatus main body GH is referred to as a tandem color image forming apparatus. It consists of.

  The image forming unit 10Y that forms a yellow (Y) image includes a charging unit 2Y, an exposure unit 3Y, a developing unit 4Y, and a cleaning unit 8Y disposed around a photosensitive drum 1Y as an image carrier. The image forming unit 10M that forms a magenta (M) color image includes a photosensitive drum 1M as an image carrier, a charging unit 2M, an exposure unit 3M, a developing unit 4M, and a cleaning unit 8M. The image forming unit 10C that forms a cyan (C) color image includes a photosensitive drum 1C as an image carrier, a charging unit 2C, an exposure unit 3C, a developing unit 4C, and a cleaning unit 8C. The image forming unit 10K that forms a black (K) image includes a photosensitive drum 1K as an image carrier, a charging unit 2K, an exposure unit 3K, a developing unit 4K, and a cleaning unit 8K. The charging unit 2Y and the exposure unit 3Y, the charging unit 2M and the exposure unit 3M, the charging unit 2C and the exposure unit 3C, and the charging unit 2K and the exposure unit 3K constitute a latent image forming unit.

  The intermediate transfer body 6 is wound around a plurality of rollers and is rotatably supported. Each color image formed by the image forming units 10Y, 10M, 10C, and 10K is sequentially transferred (primary transfer) by the transfer means 7Y, 7M, 7C, and 7K onto the rotating intermediate transfer body 6 and synthesized. A color image is formed. The recording paper P stored in the paper feeding cassette 20 is fed by the paper feeding means 21 and is conveyed to the transfer means 7A via the paper feeding rollers 22A, 22B, 22C, the registration rollers 23, etc. A color image is transferred to (secondary transfer). The recording paper P onto which the color image has been transferred is fixed by the fixing device 24, is sandwiched between the paper discharge rollers 25, and is placed on a paper discharge tray 26 outside the apparatus.

  On the other hand, after the color image is transferred to the recording paper P by the transfer means 7A, the residual toner is removed by the cleaning means 8A from the intermediate transfer body 6 from which the recording paper P is separated by curvature.

  4Y, 4M, 4C, and 4K are developing units that contain a two-component developer composed of a toner having a small particle diameter and a carrier of yellow (Y), magenta (M), cyan (C), and black (K). Reference numerals 5Y, 5M, 5C, and 5K denote toner supply units that supply new toner to the developing devices 4Y, 4M, 4C, and 4K, respectively.

  An image reading device YS including an automatic document feeder 201 and a document image scanning exposure device 202 is installed on the upper part of the image forming apparatus main body GH. The document d placed on the document table of the automatic document feeder 201 is transported by a transport unit, and an image on one or both sides of the document is scanned and exposed by the optical system of the document image scanning exposure device 202, and the line image sensor CCD is scanned. Is read.

  The analog signal photoelectrically converted by the line image sensor CCD is subjected to analog processing, A / D conversion, shading correction, image compression processing, etc. in an image processing unit, and then image writing units (exposure means) 3Y, 3M, 3C. Send a signal to 3K.

  The automatic document feeder 201 includes automatic double-sided document conveying means. The automatic document feeder 201 can continuously read the contents of a large number of documents d fed from the document table and store them in the storage means (electronic RDH function). This is convenient when copying the contents of a large number of originals by the function or when transmitting a large number of originals d by the facsimile function.

  A temperature / humidity sensor TS as an environmental condition detecting means for detecting environmental conditions is provided inside the image forming apparatus main body GH. In addition, a number counter for counting the number of copies connected to the development control unit is provided in the image forming apparatus main body GH.

  Next, the developing devices 4Y, 4M, 4C, and 4K are represented as the developing device 4, and the photosensitive drums 1Y, 1M, 1C, and 1K are represented as the photosensitive drum 1, and FIG. A developing device used in the image forming apparatus will be described below.

  FIG. 4 is a schematic cross-sectional configuration diagram illustrating an example of the developing device in FIG. 3.

  In the following description, the two-component developer is also referred to as a developer. A black arrow indicates the direction of supplying and transporting the two-component developer to the developer carrier, and a white arrow indicates the direction of stripping and collecting the two-component developer from the developer carrier. .

  The developing device 4 is composed of a developing device frame 40, a developing roller 41 as a developer carrying member, a magnetic field generating means (magnet roll) 42, a regulating means 43 made up of a scissor plate, a water wheel type supply means 44, and a screw. A stirring screw 45, 46 for carrying, a peeling roller 47, a peeling plate 48, a collecting means 49 including a screw, a toner concentration detection sensor TD, and the like.

  The electrostatic latent image is developed in the development region DR by the counterclockwise rotation of the peripheral speed Vp indicated by the arrow of the photosensitive drum 1 and the clockwise rotation of the peripheral speed Vs indicated by the arrow of the developing roller 41. A developing bias in which a DC bias having the same polarity as the polarity of the latent image is superimposed on the AC bias is applied to the developing roller 41 by a bias power source BS, and reversal development is performed.

  The developing roller 41 is disposed to face the photosensitive drum 1 carrying the electrostatic latent image, and is rotatably supported. The developing roller 41 rotates as indicated by an arrow to convey the developer to the developing region DR (in the same direction). And a developer layer necessary for development is formed by supporting the developer in the development region DR.

  Hereinafter, the present invention will be described more specifically with reference to the following examples, but the present invention is not limited thereto.

  First, core material particles were produced, and a carrier was produced using the core material particles.

<< Production of core particles >>
(Preparation of core particle 1)
An appropriate amount of each raw material is blended so as to be 21.0 mol% in terms of MnO, 3.3 mol% in terms of MgO, 0.7 mol% in terms of SrO, and 75.0 mol% in terms of Fe ₂ O ₃ , , Pulverized and mixed for 10 hours in a wet ball mill, dried, held at 950 ° C. for 4 hours, granulated and dried for 24 hours in a wet ball mill, and placed in a firing furnace with a built-in stirring device. After adding 50% of the volume and holding it at a peripheral speed of 10 m / s and 1300 ° C. for 4 hours, it was crushed and the particle size was adjusted so that the volume average particle size was 35 μm. Was made. In addition, SF-1 of the core material particle 1 was 130.

(Preparation of core particle 2-5)
In the production of the core material particles 1, “core material particles 2 to 5” were produced in the same manner as the production method of the core material particles 1 except that the firing temperature was changed as shown in Table 1.

  Table 1 shows the firing temperature when preparing the core material particles, the SF-1 of the core material particles, and the volume average particle diameter.

  In addition, SF-1 of a core material particle and a volume average particle diameter are the values measured by the said method.

<< Preparation of conductive fine particles >>
The following were prepared as conductive fine particles.

Conductive fine particles 1: Titanium oxide (volume average particle size = 0.35 μm)
Conductive fine particles 2: Titanium oxide (volume average particle size = 0.50 μm)
Conductive fine particles 3: Titanium oxide (volume average particle size = 0.75 μm)
Conductive fine particles 4: Titanium oxide (volume average particle size = 0.7 μm)
Conductive fine particles 5: Titanium oxide (volume average particle size = 1.0 μm)
Conductive fine particles 6: Titanium oxide (volume average particle size = 1.5 μm)
Conductive fine particles 7: Titanium oxide (volume average particle size = 1.4 μm)
Conductive fine particles 8: Titanium oxide (volume average particle size = 2.0 μm)
Conductive fine particles 9: Titanium oxide (volume average particle size = 3.5 μm)
Conductive fine particles 10: Tin oxide (volume average particle size = 1.0 μm)
<Production of carrier>
(Preparation of carrier 1)
100 parts by weight of the “core particle 1” produced above, 2 parts by weight of “copolymer resin fine particles” of cyclohexyl methacrylate / methyl methacrylate (copolymerization ratio 5/5), and “conductive fine particles 1 (titanium oxide)” "5.0 parts by mass" is put into a "high speed mixer with stirring blades" shown in Fig. 2, heated to 120 ° C, stirred and mixed for 30 minutes at a rotating speed of the stirring blades of 10m / s, and mechanical impact force The coating layer was formed on the surface of the core particle by the action of.

  Then, it cooled to 40 degreeC, stirred and mixed for 60 minutes with the rotational speed of 2 m / s of a stirring blade, gave stress, adjusted the surface exposure rate, and produced "carrier 1" with an average layer thickness of 1.0 micrometer.

(Production of carriers 2 to 18)
“Carriers 2 to 18” are produced in the same manner as the production method for carrier 1 except that the core material particles, the resin, the conductive fine particles, and the amounts thereof used in the production of carrier 1 are changed as shown in Table 2. did.

(Preparation of carrier 19)
In the preparation of Carrier 1, after forming a coating layer on the surface of the core material particles, the carrier whose surface exposure rate was not adjusted was designated as “Carrier 19”.

(Preparation of carrier 20)
In the production of the carrier 1, the step after forming the coating layer on the surface of the core particles is cooled to 30 ° C., stirred and mixed for 120 minutes at a rotating speed of the stirring blade of 4 m / s, and given a stress to expose the surface. “Carrier 20” was prepared in the same manner except that was adjusted.

  Table 2 shows the core material particles, resin, conductive fine particles, carrier surface exposure rate, etc. used in the production of the carriers 1 to 20.

  The surface exposure rate of the carrier is a value obtained by measurement by the above method.

<< Preparation of developer >>
100 parts by mass of each carrier prepared above and 6 parts by mass of black toner for the image forming apparatus “8050 (manufactured by Konica Minolta Business Technologies)” were mixed with a stirrer to prepare “Developers 1 to 20”.

<Performance evaluation>
An image forming apparatus “8050” (manufactured by Konica Minolta Business Technologies, Inc.) was prepared for performance evaluation. The image forming apparatus is sequentially loaded with the developer prepared above, and the image area is 10% in black toner and the image area is 7% (character image is 7%, portrait photo, solid white image, solid black image is 1 each. / 4 original image) was printed on A4 size fine paper (64 g / m ² ).

  Evaluation was performed at the initial stage and after printing 1 million sheets.

(Toner charge)
To measure the toner charge amount, a developer is placed between parallel plate (aluminum) electrodes, the gap between the electrodes is 0.5 mm, the DC bias is 1.0 kV, the AC bias is 4.0 kV, and 2.0 kHz. The development efficiency when the toner was developed was measured. The charge amount and mass of the developed toner were measured, and the charge amount per unit mass Q / m (μC / G) was defined as the charge amount. If the charge amount of the toner is −23 to −43 μC / g, it can be said that there is no problem.

(Carrier adhesion)
The carrier adhesion is developed after developing a non-image chart after printing 1 million sheets. At that time, the number of carriers adhering to the surface of the photoreceptor is observed with a magnifying glass and evaluated by the average number of carriers adhering per 100 cm ^2. did. In the evaluation, “A” and “B” are accepted and “x” is rejected.

Evaluation Criteria A: The number of carriers attached is 20 or less. O: The number of carriers attached is 21 or more and less than 50. X: The number of carriers attached is 50 or more.

(Edge effect)
The edge effect is obtained by printing an image chart in which a solid image having an image density of 1.2 to 1.3 is present at the rear of the printing direction of a solid halftone image having an image density of 0.5 at the initial stage of printing. The degree to which white spots occur at the boundary portion of was visually evaluated. In the evaluation, “A” and “B” are accepted and “x” is rejected.

Evaluation Criteria A: Good without white spots. ○: Some white spots are recognized, but there are no practical problems. X: White spots occur, and there are practical problems.

(Cover)
For the fog, first, the blank image density is measured by averaging the absolute image densities at 20 locations using a reflection densitometer “RD-918” (manufactured by Macbeth Co.). Next, with respect to the white background portion of the 1 millionth evaluation formed image, the absolute image density at 20 locations was similarly measured and averaged, and the value obtained by subtracting the white paper density from this average density was evaluated as the fog density. A fog density of 0.003 or less is acceptable.

  Table 3 shows the evaluation results.

  As apparent from Table 3, in “Developers 1 to 3 and 6 to 16” using “Carriers 1 to 3 and 6 to 16” of the present invention, in all evaluation items, from the initial stage to after long-term use. It can be seen that the object of the present invention has been achieved without problems. On the other hand, “Developer 4, 5, 17-20” using “Carrier 4, 5, 17-20” of Comparative Example has a problem in any of the evaluation items, and the object of the present invention cannot be achieved. I understand that. Since the resistance and chargeability of the liquid crystal display are stable, high-quality images can be obtained continuously for a long period of time.

DESCRIPTION OF SYMBOLS 1 Carrier 2 Core material particle 3 Conductive fine particle 4 Resin 5 Exposed part of core material particle 6 Exposed part of conductive fine particle 7 Coating layer

Claims (4)

In the resin-coated carrier for developing an electrostatic latent image formed by forming a coating layer having resin and conductive fine particles on the surface of the core material particles,
A resin-coated carrier for developing an electrostatic latent image, wherein a surface exposure rate calculated by a total of the core particles and conductive fine particles is 6% or more and 12% or less as measured by an X-ray photoelectron analyzer. The core material particles have a shape factor of 130 or more and 150 or less,
The layer thickness of the coating layer is 0.5 μm or more and 2.0 μm or less,
The conductive fine particles have an average particle size of 0.7 times to 1.5 times the layer thickness of the coating layer,
2. The resin-coated carrier for developing an electrostatic latent image according to claim 1, wherein the content of the conductive fine particles is 2 to 8 parts by mass with respect to 100 parts by mass of the resin. In the method for producing a resin-coated carrier for developing an electrostatic latent image, which forms a coating layer containing resin and conductive fine particles on the surface of the core material particles,
Using a high-speed stirring mixer that can impart mechanical impact force, a mixture of core material particles, resin and conductive fine particles is stirred at high speed without heating or under heating, and the resin is dissolved or softened on the surface of the core material particles. A coating step for forming a coating layer containing a resin and conductive fine particles;
A surface exposure rate adjusting step of exposing the core particles or conductive fine particles to the surface of the coating layer by further applying either heat or impact to the formed coating layer;
The method for producing a resin-coated carrier for developing an electrostatic latent image, wherein the surface exposure rate is 6% or more and 12% or less as measured by an X-ray photoelectron analyzer. A two-component developer is produced using the resin-coated carrier for developing an electrostatic latent image according to claim 1, and the latent image on the photoreceptor is developed by a developing device using the two-component developer. An image forming method.

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