JP2006267345A - Two component developer, image forming method, and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a two component developer which does not give rise to crack of a carrier and peeling of a coating layer in spite of printing of a number of sheets and with which high quality toner images are stably obtained for a long period. <P>SOLUTION: In the two component developer composed of a toner and carrier, the toner contains at least a binder resin and a colorant and the median diameter (D<SB>50</SB>) in volume standard is 3.0 to 7.0 μm. The carrier has a layer covering the resin on the ferrite particles, and is 20 to 70 μm in number average particle diameter and is 5x10<SP>-5</SP>to 1.0x10<SP>-3</SP>in the ratio (Cl/Fe) between the fluorescent X-ray intensity of an iron element and the fluorescent X-ray intensity of a chlorine element by a fluorescent X-ray analysis. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a two-component developer, an image forming method and an image forming apparatus using the two-component developer.

  As an electrophotographic image forming technique, digital image formation is becoming mainstream in recent years. In digital image formation, fine dot images can be faithfully reproduced. For example, photographic images that have conventionally been difficult to reproduce can be reproduced with toner. As a means for outputting such a high-definition image on a recording medium, a small-diameter toner has attracted attention, and a two-component developer composed of a small-diameter toner and a carrier has been developed.

  By the way, carriers such as iron powder carrier, ferrite carrier, and magnetic material dispersion type carrier have been put to practical use. Among them, light weight and excellent fluidity can be expressed, and magnetic characteristics can be easily controlled. The ferrite carrier having such a property has attracted attention as a carrier for such a small diameter toner. That is, a small-diameter toner has a large surface area per unit volume of toner, and a stable charge imparting performance is required for the carrier. The carrier is also required to exhibit stable fluidity when used as a developer. In response to such needs, since the ferrite carrier can easily control resistance by coating the ferrite particle surface with a resin, it has an advantage that it is easy to design a carrier having a charge imparting performance corresponding to the characteristics of the toner. In addition, since ferrite is produced by firing a magnetic material, it does not contain any material that affects the environment, and therefore attracts attention from the viewpoint of environmental conservation and stability against changes over time.

In addition, various technologies for improving the charge imparting performance have been studied. As one example, the surface of the toner and the carrier are homogenized to improve the charge rising characteristics and sharpen the charge distribution. There is a technique (see, for example, Patent Documents 1, 2, and 3).
JP-A-6-208241 JP-A-8-44103 JP 2004-138644 A

  By the way, the carrier is formed by coating the surface of the magnetic particles as a core with a resin. However, stable durability is required for a long period of time. In addition, since image formation using small-diameter toner is also suitable for creating gravure-specific prints, it has recently been applied to the printing field, and printing is often performed at the level of several hundred thousand sheets. In the field, higher durability of carriers has been demanded.

  However, the load applied to the carrier is large under such use conditions. For example, peeling of the coating layer due to repeated large-scale image formation cannot be avoided. In addition, the problem of carrier destruction that the carrier is applied or broken due to stress on the carrier for a long time has become non-negligible.

  That is, the fine powder generated by the destruction of the carrier and the coating powder generated by the peeling of the coating layer adhere to the surface of the photoconductor during image formation and cause fogging. Further, these fine powders and coating powders cause scratches on the edge portions of the cleaning blade or adhere to the edge portions, causing defective cleaning. When image formation is performed in a poorly cleaned state, black streak-like image defects are generated on the toner image.

  The present invention has been made in view of such circumstances, and is a two-component development capable of forming a stable image with a carrier that does not cause peeling of the coating layer or breakage due to stress even if printing is performed on several hundred thousand sheets. The purpose is to provide an agent. In particular, it is an object of the present invention to provide a two-component developer having performance capable of withstanding a large amount of printing in a printing field where high-definition image formation such as photographic images is required instead of offset printing.

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

(Claim 1)
In a two-component developer comprising a toner and a carrier,
The toner contains at least a binder resin and a colorant, and has a volume-based median diameter (D ₅₀ ) of 3.0 to 7.0 μm.
The carrier has a resin-coated layer on ferrite particles, the number average particle diameter is 20 to 70 μm, and the ratio of the fluorescent X-ray intensity of iron element to the fluorescent X-ray intensity of chlorine element (Cl / Fe) is 5 × 10 ^{−5 to} 1.0 × 10 ⁻³ .

(Claim 2)
The carrier has a ratio (Cl / Fe) of fluorescent X-ray intensity of iron element and fluorescent X-ray intensity of chlorine element by fluorescent X-ray analysis of 1.0 × 10 ^{−4 to} 5 × 10 ^−4. The two-component developer according to claim 1.

(Claim 3)
The two-component developer according to claim 1, wherein the carrier has a shape factor of 1.05 to 1.40 and a standard deviation value of the shape factor of 0.005 to 0.060.

(Claim 4)
The charging process for charging the electrophotographic photosensitive member, the exposure process for exposing the charged electrophotographic photosensitive member to form an electrostatic latent image, and the electrostatic latent image according to any one of claims 1 to 3. An image forming method comprising: a developing step of developing with a component developer to form a toner image; and a transferring step of transferring the toner image to a recording material with or without an intermediate transfer member.

(Claim 5)
A charging means for charging the electrophotographic photosensitive member, an exposure means for exposing the charged electrophotographic photosensitive member to form an electrostatic latent image, and an electrostatic latent image formed on the electrophotographic photosensitive member. 3. Development means for developing with the two-component developer according to any one of 3 to form a toner image, and transfer means for transferring the toner image formed by the development means to a recording material. Image forming apparatus.

  According to the present invention, for example, even when a large number of prints with a level of several hundred thousand are performed, the carrier is not cracked or applied, and the resin coated on the surface may be peeled off. This makes it possible to provide a two-component developer containing a carrier having high durability.

  As a result, high-definition image formation with a small-diameter toner can be stably performed over a long period of time. In particular, in fields such as offset printing where a large amount of high-definition prints such as gravure photographs are used, it is now possible to stably provide high-quality prints without the need to bother printing plates as in the past. Work efficiency has become possible.

  The present invention has been found by paying attention to the presence of trace elements contained in the carrier constituting the two-component developer and its influence. In particular, the present invention pays attention to the fact that the chlorine element in the ferrite particles affects the durability of the carrier, and has found that the effect of the present invention is manifested by controlling this amount. Thus, the reason why the effect of the present invention was expressed by specifying the amount of elemental chlorine contained in the carrier is presumed as follows.

  That is, it is presumed that lattice defects are generated in the molecule by the action of chlorine element present in the structure of the ferrite molecule. And, it is speculated that the ferrite hardness is improved by firmly adhering the ferrite molecules to each other in this lattice defect part, and that the strong durability is expressed without being applied even when subjected to a load. The In addition, the adhesion between the ferrite surface and the resin coating layer is improved by the polar action of the chlorine element, and as a result, it is assumed that the resin coating layer is not easily peeled off.

  In the present invention, the carrier shape factor and its standard deviation are within a specific range so that the carrier surface is uniform and the charge amount distribution does not vary. As a result, stable toner supply can be performed on the photoreceptor, and a good toner image can be stably formed.

  Hereinafter, the two-component developer of the present invention will be described in detail.

The volume-based median particle diameter (D ₅₀ ) of the toner used in the present invention is from 3.0 to 7.0 μm, preferably from 4.0 to 5.0 μm.

The median particle size (D ₅₀ ) on a volume basis is measured and calculated using a device in which a computer system for data processing (manufactured by Beckman Coulter) is connected to “Coulter Multisizer III” (manufactured by Beckman Coulter). be able to.

  As a measurement procedure, 0.02 g of toner is blended with 20 g 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). After that, ultrasonic dispersion is performed for 1 minute to prepare a toner dispersion. This toner dispersion is poured into a beaker containing “ISOTONII” (manufactured by Beckman Coulter) in a sample stand with a pipette until the measured concentration is 5 to 10%, and the measuring machine count is set to 2500 pieces. taking measurement. The aperture diameter of the Coulter Multisizer was 50 μm.

  Next, the carrier used in the present invention will be described.

  First, the size and shape of the carrier used in the present invention are specified as follows. That is, the number average particle diameter of the carrier is 20 to 70 μm, preferably 40 to 60 μm.

  The shape factor is preferably 1.05 to 1.40, more preferably 1.05 to 1.20. Furthermore, the standard deviation of the shape factor is preferably 0.005 to 0.06, and more preferably 0.01 to 0.05.

  By setting it within this range, the uniformity of the surface can be ensured, and there is no problem in terms of technical and productivity in manufacturing, which is preferable.

  When measuring the number average particle diameter of the carrier, the shape factor, and the standard deviation of the shape factor, a developer sample is prepared as follows.

  Add two-component developer, a small amount of neutral detergent and pure water to the beaker and let them get used well. By repeating the above, only the carrier can be separated except for the toner and the neutral detergent in the two-component developer. Next, the separated carrier is dried under the condition of 40 ° C., and the carrier alone is taken out to obtain a measurement sample.

  An image analysis processing device with a built-in program that automatically takes the electron micrograph of the above measurement sample using a scanning electron microscope and automatically calculates the number average particle size, shape factor, and standard deviation Measure by performing the process. The measurement conditions are, for example, measured and calculated by setting the magnification to 150 times, taking 100 particles randomly, taking a photograph, and processing the photograph image captured by the scanner with an image processing analysis apparatus. Here, a commercially available scanning electron microscope is used, and a commercially available image processing analyzer such as “LUZEX AP” (manufactured by Nireco) is also used.

  The number average particle diameter is a value obtained by calculating as the number average value of the ferret diameter.

  The number average value of the ferret diameter is measured by photographing the carrier particles with a transmission electron microscope and measuring and calculating the ferret horizontal diameter with an image analyzer. The ferret horizontal diameter of the carrier particles used in the present invention represents the maximum length in any one direction of each carrier particle in the plurality of carrier particles photographed by the electron microscope. The maximum length means a distance between parallel lines in the case where two parallel lines that are perpendicular to the one arbitrary direction and are in contact with the outer diameter of the particle are drawn.

  In FIG. 1, the conceptual diagram showing the measuring method of the ferret diameter of a carrier particle in this invention is shown.

  For example, in FIG. 1, an arbitrary direction 201 is defined for a photograph 300 of a carrier particle 200 taken with an electron microscope. A distance between two straight lines 202 perpendicular to the arbitrary one direction 201 and in contact with each carrier particle 200 is a ferret diameter 203.

  The shape factor of the carrier is a number average value of values obtained by performing the shape factor value calculated by the following formula (1) on 100 carriers.

Formula (1)
Shape factor = (perimeter of carrier) ² / (actual area of carrier) × (1 / 4π) × 100
The standard deviation of the shape factor is a value calculated by the following equation (2).

Formula (2)
Standard deviation of shape factor = ((measured value of shape factor-number average value of shape factor) ² / number of data) ^1/2
Next, the fluorescent X-ray analysis for the carrier used in the present invention will be described.

  Fluorescence X-ray analysis (XRF) separates the intrinsic X-rays (fluorescent X-rays) generated when X-rays are irradiated onto a substance into individual component wavelengths using a spectroscopic crystal, and performs qualitative analysis from these wavelengths. In addition, quantitative analysis is performed based on the intensity.

  FIG. 2 shows the principle of generation of fluorescent X-rays and a schematic diagram of the analyzer.

The carrier used in the present invention has a ratio (Cl / Fe) between the fluorescent X-ray intensity of iron element and the fluorescent X-ray intensity of chlorine element by fluorescent X-ray analysis, preferably 5 × 10 ⁻⁵ to 1 × 10 ⁻³ , preferably It is 1.0 × 10 ^{−4 to} 5 × 10 ⁻⁴ , particularly preferably 1.0 × 10 ^{−4 to} 2.6 × 10 ⁻⁴ . By setting it within this range, the adhesion point of chlorine in the ferrite particles becomes appropriate, the carrier is not cracked, and the adhesion with the resin coating layer can be ensured.

  The amount of element in the carrier can be measured using an X-ray fluorescence analyzer “XRF-1700” (manufactured by Shimadzu Corporation). An example of a specific method for measuring the carrier used in the present invention is shown below, but the measuring method used in the present invention is not limited to this.

(1) Measurement sample: Pellet measurement sample prepared by pressurizing 3 g of sample (2) X-ray generator
X-ray tube: Rh target
Tube voltage: 40 kV
Tube current: 95 mA
Filter: None (3) Spectral conditions
Wavelength dispersion method (using slits)
(4) Spectral crystal
For iron element: Lithium fluoride (LiF) crystal
For chlorine element: Germanium (Ge) crystal (5) Detector
For iron elements: Scintillation counter (SC)
For chlorine element: Gas flow type proportional counter (F-PC)
(6) Sample stage (goniometer): 2θ
The ratio of the fluorescent X-ray intensity of chlorine to the fluorescent X-ray intensity of iron element is the value of the Net intensity (kcps) from the Kα analytical line from the chlorine element, and the value of the Net intensity (kcps) from the Kα analytical line from the iron element. Calculated as the value divided by.

<< Fabrication of ferrite particles >>
The ferrite particles can be produced by the following steps, but are not limited thereto. The ferrite as used in the present invention is a generic name for magnetic oxides containing iron. For example, the chemical formula of MxOy · Fe ₂ O ₃ (where x = 1 or 2, y = 1-3, A typical example thereof is spinel type ferrite represented by M is a metal having 1 to 3 valences).

  First, the raw material to be used is individually or mixed and pulverized using a pulverizer such as a ball mill. By this pulverization, the raw material is made to have a particle size of about 0.1 to 10 μm. In addition, this particle size is calculated | required with the particle size measuring device of a laser type light-scattering system, for example.

  Next, a slurry is prepared by adding a water-soluble polymer substance and water to the raw material mixture and dispersing the mixture. Then, granulation is performed by spray-drying the slurry to form particles that are bound to the water-soluble polymer substance in a state where necessary raw material substances are dispersed. By controlling the amount of slurry sprayed in this granulation step, ferrite having a desired particle size can be obtained.

Ferritization is performed by heat-treating the granulated raw material powder thus granulated at 1150 to 1300 ° C. and performing firing. In the firing process, as disclosed in JP-A-9-134036 and the like, the heating temperature affects the performance of the generated ferrite. Further, as described in the publication, when the firing treatment is performed under reducing conditions, iron oxide Fe ₂ O ₃ which is one of the main raw materials is partially reduced to produce a FeO structure, Promotes the formation of magnetite phase. Conditions for imparting reducing conditions include coexistence of a dedicated reducing agent such as carbon black in the firing treatment system, or water-soluble polymer materials for preparing firing raw materials burned by firing treatment. Expresses reducing action.

  Since the ferrite produced by the firing treatment is in an agglomerated state, the agglomerated material is pulverized and then sieved to remove large and small particle sizes to obtain ferrite having a predetermined particle size.

  Further, the obtained ferrite is treated with a magnetic separator to remove non-magnetic materials and weak magnetic materials to obtain ferrite having a predetermined particle size.

As the raw material of the ferrite particles, conventionally used metals and metal compounds can be used, but the ratio of the fluorescent X-ray intensity of iron element and the fluorescent X-ray intensity of chlorine element (Cl / Fe) by fluorescent X-ray analysis is 5 ×. It is selected from a chlorine element-containing compound such as 10 ⁻⁵ to 1 × 10 ⁻³ , a metal having a physical property desired to be obtained as a carrier, and a metal compound.

Examples of the chlorine element-containing compound include metals containing chlorine element. Specific examples and the like _{MgCl 2, ZnCl 2, MnCl 2} , FeCl 2, FeCl 3.

  Examples of the raw material for obtaining the physical properties of the carrier include raw materials such as Fe compound, Ni compound, Bi compound, Li compound and the like, and Mg compound, Zn compound, and Mn compound in particular for controlling charging characteristics. Among these, in order to control the resistance value in particular, Cu compounds and Zn compounds are exemplified.

Specific examples of these compounds include, for example, Fe, FeO, Fe ₂ O ₃ , Fe ₃ O ₄ , NiO, Bi ₂ O ₃ , LiO, MgO, Mg (OH) ₂ , MgCO ₃ , Zn, ZnO, Cu _{, CuO, MnO 2, Mn 3} O 4, MnCO 3, CoO, BaCO 3, SrCO 3, Y 2 O 3, CaO, CaCO 3, Al 2 O 3, V 2 O 5, In 2 O 3, Ta 2 O ₅ , ZrO ₂ , B ₂ O ₃ , MoO ₃ , Na ₂ O, SnO ₂ , TiO ₂ , Cr ₂ O _{3 and the} like.

  The binder resin to be added for slurry granulation is not particularly limited, but water-soluble polymer materials such as polyvinyl alcohol polymers and vinyl acetate polymers are preferably used because of the ease of granulation (core) production. be able to.

《Career》
The carrier is obtained by providing a resin coating layer on ferrite particles. The resin composition for coating is not particularly limited, and for example, olefin resin, styrene resin, styrene-acrylic resin, silicon resin, ester resin, fluorine-containing polymer resin, or the like is used.

  Of these, styrene-acrylic resins, polyester resins, fluororesins, and phenol resins are preferably used.

  The method for providing the resin coating layer on the ferrite particles is not particularly limited, and can be performed by a known method.

  Specifically, it can be performed by a dip coating method, a spray coating method, a fluidized bed coating method, etc., but the resin particles are adhered to the ferrite particle surface as a material of the resin coating layer, and the ferrite particles are mechanically impacted. It can also be carried out by a dry mechanical impact method in which resin particles are formed on top.

  The film thickness of the resin coating layer is preferably about 0.1 to 5 μm. By setting the film thickness within this range, it is preferable that a stable charge amount can be obtained and that the phenomenon that the resin coating layer is peeled off hardly occurs.

<Production of toner>
Next, a toner manufacturing method according to the present invention will be described.

  The toner according to the present invention preferably has a small particle size and a uniform distribution. Further, the toner according to the present invention is preferably a chemical toner produced by a chemical method capable of obtaining a toner having a small particle diameter.

  Examples of the method for producing a toner by a chemical method include a suspension polymerization method, an emulsion association method, a dispersion polymerization method, a dissolution suspension method, etc. If a toner having a small particle size and a uniform distribution can be obtained. It is not particularly limited.

  Hereinafter, the emulsion association method will be described.

<Emulsion association method>
The emulsion association method is a method in which resin particles are prepared by salting out / fusion in an aqueous medium. The method is not particularly limited, and examples thereof include methods disclosed in JP-A-5-265252, JP-A-6-329947, and JP-A-9-15904. That is, dispersed particles of constituent materials such as resin particles and a colorant, or a method of salting out, agglomerating and fusing a plurality of particles composed of a resin and a colorant, etc., particularly in water using an emulsifier Then, a coagulant with a critical coagulation concentration or higher is added for salting out, and at the same time, the formed polymer is heated and fused at a temperature higher than the glass transition temperature of the polymer itself to gradually grow the particle size while forming fused particles. When the desired particle size is reached, a large amount of water is added to stop particle size growth, and the shape is controlled by smoothing the particle surface while heating and stirring, and the particles are heated in a fluidized state while containing water. By drying, the toner according to the present invention can be formed.

  In the method for producing a toner according to the present invention, a release agent is dissolved or dispersed in a polymerizable monomer, and then finely dispersed in an aqueous medium, and the polymerizable monomer is polymerized by a miniemulsion polymerization method. A method of salting out / fusion-bonding the composite resin particles formed through the step of causing the colorant particles and the colorant particles is preferably used.

  In addition, as a method for producing the toner according to the present invention, a step of salting out / fusion of composite resin particles and colorant particles obtained by a multistage polymerization method is preferably used.

  Next, an example of a preferable toner production method (emulsion polymerization association method) will be described in detail.

This manufacturing method includes
(1) Dissolution / dispersion step for dissolving or dispersing the release agent in the radical polymerizable monomer (2) Polymerization step for preparing a dispersion of resin particles (3) Resin particles and colorant particles in an aqueous medium (4) Cooling step for cooling the colored particle dispersion (5) Solid-liquid separation of the colored particles from the cooled colored particle dispersion; A washing step for removing the surfactant from the colored particles (6) A drying step for drying the washed colored particles If necessary, (7) a step of adding an external additive to the dried colored particles is included. It may be.

  Hereinafter, each step will be described.

[Dissolution / dispersion process]
This step is a step of preparing a radical polymerizable monomer solution of the release agent by dissolving or dispersing the release agent in the radical polymerizable monomer.

[Polymerization process]
In a preferred example of this polymerization step, a radical polymerizable monomer solution in which the release agent is dissolved or dispersed is added to an aqueous medium containing a surfactant, and mechanical energy is applied to form droplets. Then, the polymerization reaction is allowed to proceed in the droplets by radicals from the water-soluble radical polymerization initiator. In addition, you may add the resin particle as a core particle in the said aqueous medium.

  By this polymerization step, resin particles containing a release agent and a binder resin are obtained. Such resin particles may be colored particles or non-colored particles. The colored resin particles can be obtained by polymerizing a monomer composition containing a colorant. In addition, when using uncolored resin particles, a dispersion of colorant particles is added to a dispersion of resin particles in a fusing step described later, and the resin particles and the colorant particles are fused. It can be set as colored particles.

[Fusion process]
As a method of fusing in the fusing step, a salting out / fusing method using resin particles (colored or non-colored resin particles) obtained in the polymerization step is preferable. In the fusing step, resin particles and colorant particles can be fused together with internal additive particles such as release agent particles and charge control agents.

  The colorant particles can be prepared by dispersing the colorant in an aqueous medium. The dispersion treatment of the colorant is performed in a state where the surfactant concentration is set to a critical micelle concentration (CMC) or more in water. The disperser used for the dispersion treatment of the colorant is not particularly limited, but preferably an ultrasonic disperser, a mechanical homogenizer, a pressure disperser such as a manton gorin or a pressure homogenizer, a sand grinder, a Getzmann mill, a diamond fine mill, or the like. Examples thereof include a medium type disperser.

  The colorant (particles) may be surface-modified. In the surface modification method of the colorant, the colorant is dispersed in a solvent, the surface modifier is added to the molecular weight solution, and the system is reacted by raising the temperature. After completion of the reaction, the colorant is separated by filtration, washed and filtered with the same solvent, and dried to obtain a colorant (pigment) treated with the surface modifier.

  The salting-out / fusion method, which is a preferred fusing method, is a method in which a salting-out agent composed of an alkali metal salt, an alkaline earth metal salt, or the like is added to water having resin particles and colorant particles in excess of the critical aggregation concentration. Adding as a flocculant, and then proceeding to salting out by heating to a temperature above the glass transition point of the resin particles and above the melting peak temperature (° C.) of the release agent, and at the same time, fusing It is a process to be performed.

[Cooling process]
This step is a step of cooling (rapid cooling) the dispersion of colored particles. As a cooling treatment condition, cooling is performed at a cooling rate of 1 to 20 ° C./min. The cooling treatment method is not particularly limited, and examples thereof include a method of cooling by introducing a refrigerant from the outside of the reaction vessel, and a method of cooling by directly introducing cold water into the reaction system.

[Solid-liquid separation and washing process]
In this solid-liquid separation / washing step, a solid-liquid separation process for solid-liquid separation of the colored particles from the dispersion of colored particles cooled to a predetermined temperature in the above-described step, and a solid-liquid separated toner cake (in a wet state) A cleaning treatment for removing deposits such as a surfactant and a salting-out agent from an aggregate obtained by agglomerating certain colored particles into a cake is performed. Here, the filtration method is not particularly limited, such as a centrifugal separation method, a vacuum filtration method using Nutsche or the like, a filtration method using a filter press or the like.

[Drying process]
In this step, the washed toner cake is dried to obtain dried colored particles. Examples of dryers used in this process include spray dryers, vacuum freeze dryers, vacuum dryers, etc., stationary shelf dryers, mobile shelf dryers, fluidized bed dryers, rotary dryers It is preferable to use a stirring dryer or the like. The water content of the dried colored particles is preferably 5% by mass or less, more preferably 2% by mass or less. In addition, when the dried colored particles are aggregated by weak interparticle attractive force, the aggregate may be crushed. Here, as the crushing treatment apparatus, a mechanical crushing apparatus such as a jet mill, a Henschel mixer, a coffee mill, or a food processor can be used.

[External process]
This step is a step of preparing a toner by mixing the dried colored particles with an external additive as necessary.

  As an external additive mixing device, a mechanical mixing device such as a Henschel mixer or a coffee mill can be used.

  Next, the compounds (binder resin, colorant, release agent, charge control agent, external additive, lubricant) constituting the toner will be described.

(Binder resin)
As the polymerizable monomer constituting the binder resin, known monomers can be used. Specifically, it is preferable to use a combination of styrene, acrylic acid or methacrylic acid derivatives, and those having an ionic dissociation group.

(Coloring agent)
As the colorant used in the present invention, a known inorganic or organic colorant can be used. These colorants may be used alone or in combination of two or more as required. The addition amount of the colorant is set in the range of 1 to 30% by mass, preferably 2 to 20% by mass with respect to the whole toner.

(Release agent)
A known compound can be used as the release agent used in the present invention. When the release agent is contained in an amount of 1 to 15% by mass, preferably 3 to 12% by mass, based on the whole toner, good results can be obtained.

(Charge control agent)
A charge control agent can be added to the toner according to the present invention as necessary. A known compound can be used as the charge control agent.

(External additive)
The toner according to the present invention may be used by mixing so-called external additives with colored particles for the purpose of improving fluidity, chargeability and cleaning property. These external additives are not particularly limited, and various inorganic particles, organic particles and lubricants can be used.

  The addition amount of these external additives is preferably 0.1 to 10.0% by mass with respect to the whole toner.

<< Preparation of two-component developer >>
The two-component developer of the present invention is used for mono black toner image formation or color toner image formation.

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

<< Image Forming Method, Image Forming Apparatus >>
A developing step of rotating a developing sleeve carrying a two-component developer having a carrier and toner according to the present invention, and developing an electrostatic latent image formed on the surface of the photoreceptor with the toner of the two-component developer. An image forming method (image forming apparatus).

  Next, an image forming method and an image forming apparatus according to the present invention will be described.

  The image forming method used in the present invention is not particularly limited as long as a developing device using the two-component developer of the present invention can be mounted.

  Specifically, a charging step for charging the photoconductor, an exposure step for exposing the charged photoconductor to form an electrostatic latent image, and developing the electrostatic latent image with a two-component developer containing toner. Examples thereof include an image forming method in which an image is formed via a developing step for forming a toner image and a transfer step for transferring the toner image to a recording material with or without an intermediate transfer member.

  The charging member used in the charging step is preferably a charging roller or a magnetic brush that is charged by contact.

  The image forming apparatus according to the present invention preferably uses the image forming method.

  Further, the process cartridge is formed such that at least one of charging means, exposure means, developing means, transfer means, and cleaning means is coupled with an electrophotographic photosensitive member so that it can be integrated into and removed from the main body of the image forming apparatus. It is preferable.

  FIG. 3 is a cross-sectional configuration diagram illustrating an example of an image forming method according to the present invention.

  In FIG. 3, reference numeral 50 denotes a photosensitive drum (photosensitive member) as an image carrier, which is grounded and rotated clockwise. Reference numeral 52 denotes a scorotron charger (charging process), which uniformly charges the circumferential surface of the photosensitive drum 50 by corona discharge. Prior to the charging by the charger 52, the peripheral surface of the photosensitive member may be discharged by performing exposure by the pre-charging exposure unit 51 using a light emitting diode or the like in order to eliminate the history of the photosensitive member in the previous image formation.

  After uniform charging of the photoreceptor, image exposure based on the image signal is performed by an image exposure unit 53 as an image exposure unit (image exposure process). The image exposure unit 53 in this figure uses a laser diode (not shown) as an exposure light source. Scanning on the photosensitive drum is performed by the light whose optical path is bent by the reflection mirror 532 through the rotating polygon mirror 531 and the fθ lens, and an electrostatic latent image is formed.

  The electrostatic latent image is then developed by a developing device 54 as developing means (developing step). A developing device 54 containing a two-component developer composed of toner and a carrier is provided at the periphery of the photosensitive drum 50, and development is performed by a developing sleeve 541 that contains a magnet and rotates while holding the two-component developer. Is called.

  In general, reversal development is performed in a digital image forming method. Here, reversal development refers to a region where the surface of a photoconductor is uniformly charged by a charger 52 and an image is exposed, that is, an exposed portion of the photoconductor. This is an image forming method in which a potential (exposed area) is visualized by a developing process. On the other hand, the unexposed portion potential is not developed by the developing bias potential applied to the developing sleeve 541.

The inside of the developing device 54 is composed of two-component developer agitating / conveying members 544 and 543, a conveyance amount regulating member, and the like. The two-component developer is agitated and conveyed and supplied to the developing sleeve. It is controlled by the carry amount regulating member. The transport amount of the two-component developer varies depending on the linear velocity of the applied photoreceptor and the specific gravity of the two-component developer, but is generally in the range of ^{20 to} 200 mg / cm ² .

  The two-component developer is transported to the development area after the layer thickness is regulated by the transport amount regulating member, and development is performed. At this time, usually, development is performed by applying a DC bias between the photosensitive drum 50 and the developing sleeve 541 and, if necessary, an AC bias voltage. The two-component developer is developed in contact or non-contact with the photoreceptor. The potential of the photosensitive member is measured by providing a potential sensor 547 above the development position as shown in FIG.

  After the image formation, the recording material P is fed to the transfer area by the rotation operation of the paper feed roller 57 when the transfer timing is ready.

  In the transfer area, a transfer electrode (transfer means: transfer device) 58 operates on the peripheral surface of the photosensitive drum 50 in synchronization with the transfer timing, and the charged recording material P is charged with a polarity opposite to that of the toner. Transfer the toner.

  Next, the recording material P is neutralized by a separation electrode (separator) 59, separated by the peripheral surface of the photosensitive drum 50 and conveyed to the fixing device 60, and the toner is removed by heating and pressurization of the heat roller 601 and the pressure roller 602. After the welding, the sheet is discharged to the outside of the apparatus via the sheet discharge roller 61. The transfer electrode 58 and the separation electrode 59 stop the primary operation after the recording material P passes and prepare for the next toner image formation. In FIG. 3, a transfer band electrode of corotron is used as the transfer electrode 58. The transfer electrode setting conditions vary depending on the process speed (peripheral speed) of the photosensitive member and cannot be specified. For example, the transfer current is set to +100 to +400 μA, and the transfer voltage is set to +500 to +2000 V. can do.

  On the other hand, the photosensitive drum 50 from which the recording material P has been separated removes and cleans residual toner by the pressure contact of the blade 621 of the cleaning device (cleaning means) 62, and again removes the charge by the pre-charge exposure unit 51 and charges by the charger 52. Then, the next image forming process is started.

  Reference numeral 70 denotes a detachable process cartridge in which a photoconductor, a charger, a transfer device, a separator, and a cleaning device are integrated.

  The recording material used in the present invention is a support for holding a toner image, and is usually called an image support, a transfer material or a transfer paper. Specific examples include various types of recording materials such as plain paper from thin paper to thick paper, coated printing paper such as art paper and coated paper, commercially available Japanese paper and postcard paper, plastic film for OHP, and cloth. However, it is not limited to these.

  The present invention will be specifically described below with reference to examples, but the embodiments of the present invention are not limited to these examples.

<< Fabrication of ferrite particles >>
<Preparation of ferrite particles 1>
1. Raw material pulverization step MgCl ₂ was mixed in an amount of 0.01% by mass with a mixture ratio of Fe ₂ O ₃ = 60 mol% and MgO = 40 mol%, and the raw material was pulverized with a pulverizer / mixer.

2. Slurry process and granulation process Adhesive (polyvinyl alcohol) and water were added to the pulverized product pulverized as described above to form a 60% by mass slurry, which was further pulverized by a wet ball mill to prepare a dispersion. The slurry dispersion was sprayed and dried using a spray dryer to produce granulated particles having a number average particle size of about 60 μm.

3. Firing step The above granulated particles were fired at 1150 ° C. in an air atmosphere in a drying furnace to produce ferrite particles.

4). Crushing / Classifying Step The fired ferrite particles were pulverized and sieved to obtain ferrite particles having a number average particle size of about 50 μm, except for those having large and small particle sizes.

5. Magnetic Separation Step The ferrite particles were passed through a magnetic separator to remove non-magnetic or weakly magnetic particles to produce “ferrite particles 1”.

<Preparation of ferrite particles 2-11>
The amount of MgCl ₂ used in the production of “ferrite particles 1” was changed from 0.01% by mass to the amount shown in Table 1, and the amount of spray in the granulation process was adjusted in the same manner as in the case of chlorine. “Ferrite particles 2 to 11” were prepared by changing the element content and the number average particle diameter.

<Production of carrier>
100 parts by mass of each ferrite particle obtained above and 5% by mass of copolymer resin particles of cyclohexyl methacrylate / methyl methacrylate (copolymerization ratio 5/5) were charged into a high-speed agitating mixer equipped with a stirring blade, and 120 A carrier was prepared by stirring and mixing at 30 ° C. for 30 minutes and forming a resin coating layer on the surface of the ferrite particles using the mechanical impact force. The obtained carriers are referred to as “carriers 1 to 11”.

  Table 1 shows the ferrite conditions and carrier properties of “carriers 1 to 11”.

<Production of toner>
<Preparation of Toner A>
(Preparation of colored particles A)
First stage polymerization (mini emulsion polymerization)
175 g of styrene
60 g of n-butyl acrylate
Methacrylic acid 15g
7 g of n-octyl-3-mercaptopropionate
A monomer mixed solution consisting of the above was placed in a reaction vessel equipped with a stirrer, and 100 g of pentaerythritol tetrabehenate was added thereto, heated to 70 ° C. and dissolved to prepare a monomer solution.

  On the other hand, a surfactant solution in which 2 g of polyoxyethylene (2) sodium dodecyl ether sulfate is dissolved in 1350 g of ion-exchanged water is heated to 70 ° C., added to and mixed with the monomer solution, and then a machine having a circulation path. Dispersion was carried out at 70 ° C. for 30 minutes using an expression disperser “Clearmix” (manufactured by M Technique) to prepare an emulsified dispersion.

  Next, an initiator solution prepared by dissolving 7.5 g of potassium persulfate in 150 g of ion-exchanged water was added to this dispersion, and polymerization was performed by heating and stirring the system at 78 ° C. for 1.5 hours. A dispersion of resin particles was obtained. This is referred to as “dispersion of resin particles 1”.

Second stage polymerization (formation of outer layer)
An initiator solution prepared by dissolving 12 g of potassium persulfate in 220 g of ion-exchanged water was added to the “dispersion of resin particles 1” obtained as described above, and 320 g of styrene under a temperature condition of 80 ° C.
n-Butyl acrylate 100g
Methacrylic acid 35g
n-octyl-3-mercaptopropionate 7.5 g
A monomer mixture consisting of was added dropwise over 1 hour. After completion of the dropping, polymerization was carried out by heating and stirring for 2 hours. Then, it cooled to 28 degreeC and obtained "the dispersion liquid of the resin particle 2."

(Colorant particle dispersion)
A solution was prepared by stirring and dissolving 90 g of sodium dodecyl sulfate in 1600 g of ion-exchanged water. While stirring this solution, 400.0 g of carbon black “Regal 330R” (Cabot) is gradually added, and then dispersed using a mechanical disperser “Clearmix” (M Technique). Thus, a colorant particle dispersion was prepared. The particle diameter of the colorant particles in this dispersion was measured using an electrophoretic light scattering photometer “ELS-800” (manufactured by Otsuka Electronics Co., Ltd.) and found to be 110 nm.

((Aggregation / fusion) meeting process)
Resin particle 2 dispersion 2000 g
670 g of ion exchange water
Colorant particle dispersion 400g
The above solution is put into a 5 L reaction vessel equipped with a temperature sensor, a cooling pipe, a nitrogen introducing device, and a stirring device, stirred, and adjusted to a temperature of 30 ° C. Then, a 5N sodium hydroxide aqueous solution is added to this solution The pH was adjusted to 10.

  Next, an aqueous solution in which 60 g of magnesium chloride hexahydrate was dissolved in 60 g of ion-exchanged water was added over 10 minutes at 30 ° C. with stirring. After standing for 3 minutes, the temperature was started to rise, and the temperature of the system was raised to 90 ° C. over 60 minutes to grow the particle size and perform an association reaction. In this state, the particle size of the associated particles was measured with “Coulter Multisizer III” (manufactured by Beckman Coulter), and when the median particle size on the volume basis became 5 μm, 8.5 g of sodium chloride was ion-exchanged. An aqueous solution dissolved in 35 g of water was added to stop particle growth, and then heating and stirring were continued for 3 hours for fusion.

  Then, it cooled to 30 degreeC, hydrochloric acid was added, pH was adjusted to 2.0, and stirring was stopped. The grown associated particles were filtered, washed repeatedly with ion exchange water at 35 ° C., and then dried with hot air at 40 ° C. to obtain “colored particles A”.

Further, in the above association reaction, when the median particle size (D ₅₀ ) on the volume basis becomes 3.0 μm, the particle growth is stopped as “colored particle B”, and the median particle size (D _{50 on the} same volume basis). ) Was 7.0 μm, and the particle growth was stopped when it was “colored particle C”.

(External additive mixing process)
1% by mass of hydrophobic silica (number average primary particle size = 12 nm) and 0.3% by mass of hydrophobic titanium dioxide (number average primary particle size = 20 nm) are added to the “colored particles A” obtained above. Then, “Henschel mixer” (manufactured by Mitsui Miike Chemical Co., Ltd.) was mixed for 10 minutes to prepare “Toner A”. The median particle diameter (D ₅₀ ) on a volume basis was 5.0 μm, the same as “Colored particle A”. In the same procedure, “toner B” was prepared from “colored particle B”, and toner C was prepared from colored particle C. The volume-based median particle diameters (D ₅₀ ) of “Toner B” and “Toner C” were 3.0 μm and 7.0 μm, respectively.

<Preparation of Toner D>
In the production of “Toner A”, when the median particle size (D ₅₀ ) on the volume basis is 5.0 μm, the particle growth is stopped, and the median particle size (D ₅₀ ) on the volume basis is 8.0 μm. “Toner D” was prepared in the same manner except that the particle growth was stopped at the time when the value became. The median particle size (D ₅₀ ) of “toner D” on a volume basis was 8.0 μm.

<< Preparation of two-component developer >>
Each carrier prepared above and each toner were mixed with a low-speed mixer, and mixed so that the toner concentration was 5% by mass to prepare “two-component developers 1 to 14”. The obtained “two-component developers 1 to 9” are referred to as “Examples 1 to 9”, and “two-component developers 10 to 14” are referred to as “Comparative Examples 1 to 5”.

<Evaluation>
For evaluation, “Examples 1 to 9” and “Comparative Examples 1 to 5” produced above were sequentially loaded in “Sitios 7075” (manufactured by Konica Minolta Business Technologies), and 500,000 sheets were printed.

The printing environment is normal temperature and humidity (20 ° C, 60% RH), and the print image is an image with a pixel rate of 10% (7% is a character image, human face image, solid white image, solid black image each 1/4 minutes) A4 high-quality paper (64 g / m ² ) was used as the print paper (transfer material).

  The evaluation was performed on the initial printed image after 500,000 sheets and the cleaning blade edge.

  The evaluation criteria ◎ and ○ are acceptable, and Δ and × are unacceptable.

(Image cover)
For image fogging, the density of unprinted printing paper (white paper) is measured at 20 locations, the image density is measured, the average value is used as the white paper density, and then the white background portion of the printing paper on which the plain image is printed is the same. The image density was measured at 20 locations, the average density was calculated, and the value obtained by subtracting the white paper density from the average density was evaluated as the fog density. The measurement was performed using a reflection densitometer “RD-918” (manufactured by Macbeth).

Evaluation criteria A: Good when the image fog density is 0.003 or less B: Practical problem when the image fog density is 0.006 or less Δ: Practically a little problem when the image fog density is 0.010 or less Level x: Level at which the image fog density is larger than 0.010 and causes a practical problem.

(Reproducibility of photographic images)
The reproducibility of a photographic image is determined by measuring the density of a halftone portion (original (original) reflection image density is 0.70) of a printed photographic image with a reflection densitometer “RD-918” (manufactured by Macbeth). The reproducibility of halftone dots was evaluated by visual observation using a magnifying glass having a magnification of 10 times.

Evaluation criteria A: Reflection density is within 0.80 ± 0.03, and no dot crushing or omission is observed. ○: Reflection density is within 0.80 ± 0.03, and 1 to 3 dot crushing. Occurrence was confirmed, but there was no problem with visual observation. Δ: Reflection density deviated from 0.80 ± 0.03, resulting in a blurry or hard feeling. ×: Halftone dot crushing or missing 3 or more items have been confirmed and the image defects can be confirmed visually.

(Craft of carrier and peeling of coating layer)
The evaluation of the crack of the carrier and the peeling of the coating layer was performed based on the edge scratch attached to the cleaning blade and the state of adhesion of the peeled coating layer.

  Specifically, a solid white image was printed, and the black streaks formed on the print were regarded as image defects due to abnormalities in the cleaning blade (edge scratches or adhesion of a peeled coating layer), and the degree was visually evaluated. .

Evaluation criteria A: Good image defect (black streaks) caused by the cleaning blade is not observed. ○: Image defect (black streaks) attributed to the cleaning blade is faintly observed. X: Image caused by the cleaning blade. Defects (black streaks) are clearly seen and problematic.

(Evaluation of cleaning blade)
The evaluation of the cleaning blade is as follows. Using a 10-times magnifier, the cleaning blade is visually observed for abnormalities in the cleaning blade (edge scratches and peeled coating layer adhesion state). Evaluation was made according to the following evaluation criteria.

Evaluation criteria A: No abnormality was observed on the cleaning blade, and no image defect was observed on the print. O: A slightly peeled coating layer was observed on the cleaning blade, but an image defect was also observed on the print. No: Edge scratches or peeling of the coating layer was observed on the cleaning blade, and image defects were observed on the print.

  Table 2 shows the toner types and carriers used for the preparation of the two-component developer, and the evaluation results.

  As apparent from Table 2, “Examples 1 to 9” of the present invention are excellent in all evaluation items, but “Comparative Examples 1 to 5” outside the present invention have problems in at least any of the items. I understand that.

The conceptual diagram showing the measuring method of the ferret diameter of a carrier particle in this invention is shown. The principle of generation of fluorescent X-rays and a schematic diagram of an analyzer are shown. It is a cross-sectional block diagram which shows an example of the image forming method which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 50 Photosensitive drum 52 Charging device 51 Pre-charge exposure part 53 Image exposure device 531 Polygon mirror 532 Reflection mirror 54 Developing device 541 Developing sleeve 544, 543 Two-component developer stirring and conveying member 547 Potential sensor P Recording material 57 Feed roller 58 Transfer Electrode 59 Separating electrode 60 Fixing device 61 Paper discharge roller

Claims (5)

In a two-component developer comprising a toner and a carrier,
The toner contains at least a binder resin and a colorant, and has a volume-based median diameter (D ₅₀ ) of 3.0 to 7.0 μm.
The carrier has a resin-coated layer on ferrite particles, the number average particle diameter is 20 to 70 μm, and the ratio of the fluorescent X-ray intensity of iron element to the fluorescent X-ray intensity of chlorine element (Cl / Fe) is 5 × 10 ^{−5 to} 1.0 × 10 ⁻³ . The carrier has a ratio (Cl / Fe) of fluorescent X-ray intensity of iron element and fluorescent X-ray intensity of chlorine element by fluorescent X-ray analysis of 1.0 × 10 ^{−4 to} 5 × 10 ^−4. The two-component developer according to claim 1. The two-component developer according to claim 1, wherein the carrier has a shape factor of 1.05 to 1.40 and a standard deviation value of the shape factor of 0.005 to 0.060. The charging process for charging the electrophotographic photosensitive member, the exposure process for exposing the charged electrophotographic photosensitive member to form an electrostatic latent image, and the electrostatic latent image according to any one of claims 1 to 3. An image forming method comprising: a developing step of developing with a component developer to form a toner image; and a transferring step of transferring the toner image to a recording material with or without an intermediate transfer member. A charging means for charging the electrophotographic photosensitive member, an exposure means for exposing the charged electrophotographic photosensitive member to form an electrostatic latent image, and an electrostatic latent image formed on the electrophotographic photosensitive member. 3. Development means for developing with the two-component developer according to any one of 3 to form a toner image, and transfer means for transferring the toner image formed by the development means to a recording material. Image forming apparatus.

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