JP2007148452A - Amorphous ferrite carrier and electrophotographic developer using the ferrite carrier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an amorphous ferrite carrier having lowered resistance, large specific surface area, low specific gravity and extended lifetime, and to provide an electrophotographic developer which prevents toner scattering, gives high image density and can meet the demand for higher speed and full-color image formation by using the ferrite carrier. <P>SOLUTION: The amorphous ferrite carrier is obtained by coating a carrier core material with a resin, wherein the ferrite carrier has indefinite particle shape, includes ≥40% by number of particles of a rock sugar shape and/or an oyster shell shape, has a shape factor (SF-1) of 140-250, its distribution width (δ) of ≤60 and a shape factor (SF-2) of 120-150, and the coating weight of the resin is 0.01-10.0 wt.% based on the amount of the carrier core material. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an amorphous ferrite carrier for a two-component electrophotographic developer used in a copying machine, a printer, and the like, and an electrophotographic developer using the ferrite carrier. Specifically, the resistance is reduced and the specific surface area is high. In addition, the present invention relates to an amorphous ferrite carrier having a low specific gravity and a long life, and to an electrophotographic developer that can prevent toner scattering using the ferrite carrier and can cope with high speed and full color at a high image density.

  The two-component developer used in electrophotography is composed of a toner and a carrier, and the carrier is mixed and stirred with the toner in the developer box to give the toner a desired charge, and the charged toner is removed. A carrier material that carries the electrostatic latent image on the photoreceptor to form a toner image. Even after the toner image is formed, the carrier is held by the magnet and remains on the developing roll. The carrier is returned to the developing box again, mixed and stirred again with new toner particles, and used repeatedly for a certain period.

  Unlike the one-component developer, the two-component developer has a function in which the carrier stirs the toner particles, imparts desired chargeability to the toner particles, and transports the toner. Since it has good controllability in design, it is widely used in the field of full-color machines especially requiring high image quality and high-speed machines requiring image maintenance reliability and durability.

  In such two-component electrophotographic developers, iron powder carriers such as oxide-coated iron powder and resin-coated iron powder have been used as carriers. However, since iron powder carriers have a large true specific gravity, they are developed. There is a lot of stress in the plane and it is difficult to extend its service life.

  Therefore, ferrite carriers such as Cu—Zn ferrite and Ni—Zn ferrite, which have a smaller true specific gravity than iron powder carriers, are used. In addition, these ferrite carriers have many advantageous characteristics for obtaining high-quality images as compared with conventional iron powder carriers.

  As these ferrite carriers, spherical ones are generally used. However, the spherical ferrite carrier has a high resistance, tends to have insufficient developing ability, and cannot cope with the high speed. Further, since the specific surface area is small and toner retention is poor, fogging and toner scattering are likely to occur.

  Therefore, in order to increase the developing ability of the spherical ferrite, it has been proposed to reduce the resistance by coating the surface of the ferrite core with a resin and adding a conductive agent into the resin. However, the resin-coated carrier easily peels off with use over time, and the carrier whose resistance has been lowered by the conductive agent in particular has a large resistance change during the period of use and cannot achieve a sufficiently long life.

  Patent Document 1 (Japanese Patent Application Laid-Open No. 2000-233930) discloses a carrier core consisting essentially of a spinel phase containing manganese oxide and trivalent iron oxide as a ferrite component and containing a certain amount of titanium oxide. A composition is described. Thus, by including titanium oxide, the saturation magnetization can be kept above a certain limit with high conductivity or low resistivity.

  However, by including titanium oxide in the ferrite component in this way, a certain low resistance can be achieved, but since the shape is not controlled, the conductivity of the ferrite particles as the carrier core material is low, and the toner Since the retentivity is not sufficient, the target developing ability cannot be obtained, causing problems such as fogging and toner scattering.

On the other hand, various proposals have been made to use an amorphous ferrite carrier instead of a spherical ferrite carrier. For example, Patent Document 2 (Japanese Patent Application Laid-Open No. 2002-116582) discloses a resistor in which a coating layer formed by dispersing conductive powder in a binder resin is formed on an irregular ferrite core having a shape factor (SF-1) of 130 or more. The use of a carrier of 10 ⁸ to 10 ¹⁰ Ω · cm is described.

  However, only by defining the shape factor (SF-1), the magnetic carrier as the carrier core material is not sufficiently conductive, and the target developing ability cannot be obtained. In addition, since it is necessary to use a large amount of conductive powder in order to improve the developing ability, the color toner is contaminated and the image quality is liable to be deteriorated. Further, when such a large amount of conductive powder is dispersed and contained in the coating layer, the coating layer is easily peeled and detached due to stress in the apparatus, so that the conductivity of the carrier is lost, and it is good for a long time. It is difficult to maintain the characteristics.

  Patent Document 3 (Japanese Patent Application Laid-Open No. 7-261461) describes a magnetic carrier formed with a magnetite particle having a saturation magnetization of 100 emu / g or more in an aspherical shape with an average particle diameter of 10 to 100 μm, thereby improving image quality. In addition, it is described that carrier scattering can be prevented. Examples of the non-spherical shape include a polyhedron shape, a polyhedron shape, a scale shape, a flat shape, and an indefinite shape.

  This Patent Document 3 proposes to form magnetite into non-spherical particles and increase the specific surface area, but since the shape factor and its shape distribution are not controlled, the carrier core material is used. Since a certain magnetic carrier has low conductivity and toner retention is not sufficient, it has been difficult to obtain a high developing ability as the speed increases.

  Patent Document 4 (Japanese Patent Laid-Open No. 2002-182434) describes a flat-shaped magnetic carrier in which a major axis, a minor axis, and a thickness are in a constant relationship, and an easy magnetization axis is in a plane.

  However, when such a magnetic carrier is used, since there are few contact points, conductivity is not sufficient, and toner retention is not sufficient, so that the target developing ability cannot be obtained, and fog and toner are not obtained. Causes problems such as scattering. In addition, the carrier having such a shape tends to be relatively brittle with respect to mechanical impact, and the carrier particles are broken, so that the characteristics may be greatly changed.

JP 2000-233930 A JP 2002-116582 A JP-A-7-261461 JP 2002-182434 A

  In this way, the resistance of the ferrite carrier is reduced, it has a high specific surface area, and it has a low specific gravity and a long service life. When used as a developer, toner scattering is prevented, and high image density, high speed and full color are supported. No attempt has been made.

  Accordingly, an object of the present invention is to prevent toner scattering by using an amorphous ferrite carrier having a low resistance, a high specific surface area, a low specific gravity and a long life, and the use of the ferrite carrier. An object of the present invention is to provide an electrophotographic developer which can cope with high speed and full color in terms of density.

  As a result of intensive studies, the present inventors have found that a ferrite carrier is effective for low specific gravity and long life, and in order to achieve low resistance, it is coated with a resin containing many particles of a specific shape. It is an amorphous ferrite, the shape factor (SF-1) is in a specific range, the distribution width (δ) is below a certain value, and the shape factor (SF-2) is also in a specific range, and the resin The inventors have found that it is effective to use a carrier whose content is in a specific range as a carrier, and reached the present invention.

  That is, the present invention is a ferrite carrier in which the carrier core material is coated with a resin, the particle shape is indefinite, and 40% by number or more is a rock-type rock sugar shape and / or oyster shell shape particles, The shape factor (SF-1) shown by the following equation 3 is 140 to 250, the distribution width (δ) is 60 or less, and the shape factor (SF-2) shown by the following equation 4 is 120 to 150. In addition, the present invention provides an amorphous ferrite carrier characterized in that the coating amount of the resin is 0.01 to 10.0% by weight with respect to the carrier core material.

  Further, in the above-mentioned irregular shaped ferrite carrier, it is desirable that 50% by number or more of the lock-type icing sugar-shaped and / or oyster shell-shaped particles exist.

  Moreover, in the said irregular shaped ferrite carrier, it is desirable that the said shape factor (SF-1) is 145-200.

  In the above irregular shaped ferrite carrier, it is desirable that the ratio of particles having the shape factor (SF-1) of 140 or more is 40% by number or more.

  In the above irregular shaped ferrite carrier, the distribution width (δ) of the shape factor (SF-1) is desirably 55 or less.

  In the above irregular shaped ferrite carrier, the ferrite composition is preferably represented by the following chemical formula 2.

  In the above irregular shaped ferrite carrier, the M is preferably Mn and / or Mg.

  Further, in the above irregular shaped ferrite carrier, a titanium compound may be contained in the ferrite composition.

  Moreover, in the said irregular shaped ferrite carrier, it is preferable that content of the said titanium compound is 0.01-5 weight part converted into titanium with respect to 100 weight part of ferrite components.

Moreover, in the said irregular shaped ferrite carrier, it is desirable that an apparent density is 2.40 g / cm < ³ > or less.

In the above irregular shaped ferrite carrier, the specific surface area is desirably 150 cm ² / g or more.

  Moreover, in the said irregular shaped ferrite carrier, it is desirable that an average particle diameter is 30-120 micrometers.

In addition, in the above irregular shaped ferrite carrier, the saturation magnetization is desirably 75 emu / g (A · m ² / kg) or more.

Moreover, in the said irregular shaped ferrite carrier, it is desirable that resistance is 10 < ² > -10 < ¹⁰ > (omega | ohm).

  The amorphous ferrite carrier is preferably used for color toners.

  The present invention also provides an electrophotographic developer comprising the above ferrite carrier and a toner.

  In the electrophotographic developer, a color toner is preferably used as the toner.

  The amorphous ferrite carrier according to the present invention is obtained by coating a carrier core material with a resin, the shape of which is mainly composed of particles of a rock-type rock sugar shape or an oyster shell shape, and the shape factor (SF-1) is within a specific range. And the distribution width (δ) is below a certain value, the shape factor (SF-2) is also in a specific range, and the resin content is in a specific range, so that the resistance is reduced, and Long life is achieved by having a high specific surface area and a low specific gravity. Therefore, the electrophotographic developer using the amorphous ferrite carrier according to the present invention can prevent toner scattering, has a high image density, and can sufficiently cope with speeding up of the developing machine and full color.

  Hereinafter, the best mode for carrying out the present invention will be described.

<Amorphous ferrite carrier according to the present invention>
The amorphous ferrite carrier according to the present invention is obtained by coating a carrier core material with a resin, and mainly comprises ferrite particles having a rock-type icing sugar shape and / or oyster shell shape. The rock-type rock sugar-shaped and / or oyster shell-shaped ferrite particles are present in the particles in an amount of 40% by number or more, preferably 50% by number or more, and more preferably 60% by number. If the rock-type rock sugar-shaped and / or oyster shell-shaped ferrite particles are less than 40% by number in the particles, a sufficiently low resistance cannot be achieved.

  The lock-type icing sugar shape as used in the present invention means a shape having a generally unequal polygonal shape as shown in the optical electron micrograph of FIG.

  Moreover, the oyster shell shape as used in the field of this invention means what is substantially block-shaped as shown in the optical electron micrograph of FIG.

  The amorphous ferrite carrier according to the present invention has a shape factor (SF-1) represented by the following formula 5 of 140 to 250, preferably 145 to 200, and more preferably 150 to 180. When the shape factor (SF-1) is less than 140, the particle diameter is almost spherical, the contact between the particles is small, the conductivity cannot be increased, and the effect of making the irregular shape is not seen, The toner retainability is lowered. If it exceeds 250, the shape approaches a needle shape and the particles become brittle, so that problems such as breakage of the particles due to stress in the developing machine tend to occur.

  Here, the shape factor (SF-1) is used as a factor expressing the shape of the particle or the like, and it means that the area, length, shape, etc. of the image captured by the scanning electron microscope or the like is quantitatively analyzed with high accuracy. This is based on a statistical method called image analysis, and can be measured by an image analyzer (image analysis software Image-Pro Plus, manufactured by Media Cybernetics). The shape factor (SF-1) is a numerical value obtained by multiplying the value obtained by squaring the maximum carrier length by the carrier projected area, multiplied by π / 4, and multiplied by 100, and the shape of the carrier is spherical. The closer to, the closer to 100. The shape factor (SF-1) was calculated for each particle, and the average value of 50 particles was used as the shape factor of the carrier. The distribution width (δ) represents the standard deviation of the shape factor distribution.

  In the amorphous ferrite carrier according to the present invention, the ratio of particles having the shape factor (SF-1) of 140 or more is preferably 40% by number or more. More desirably, it is 50% by number or more, and most desirably 60% by number or more. If the ratio of the particles having the shape factor (SF-1) of 140 or more is less than 40% by number, the resistance of the carrier cannot be sufficiently lowered.

  Further, the distribution width (δ) of the shape factor (SF-1) is 60 or less, preferably 55 or less, and more preferably 50 or less. When the distribution width (δ) exceeds 60, the particle shape distribution becomes wide, and it becomes difficult to form a magnetic brush uniformly, so that carrier adhesion occurs.

  The shape factor (SF-2) of the ferrite carrier for an electrophotographic developer according to the present invention is preferably 120 to 250. When the shape factor (SF-2) is less than 120, there are few concave portions on the particle surface, and it is difficult to increase the specific surface area. Further, when the shape factor (SF-2) exceeds 250, the surface of the particle has many irregularities and the surface has many vacancies, and the particles are likely to be brittle, so that it is difficult to obtain stable characteristics over a long period of time. Become.

  This shape factor (SF-2) is calculated by the following equation (6).

  The shape factor SF-2 was obtained by photographing the carrier particles using a scanning electron microscope and analyzing the image using image analysis software Image-Pro Plus (Media Cybernetics). These shape factors were calculated for each particle, and the average value of 50 particles was used as the shape factor of the carrier. Here, the shape factor 100 indicates a perfect circle.

  The amorphous ferrite carrier according to the present invention is provided with a resin coating on the surface of the carrier core material for the purpose of improving durability and obtaining stable image characteristics over a long period of time. Various types of conventionally known resins can be used as the coating resin. For example, a fluororesin, an acrylic resin, an epoxy resin, a polyamideimide resin, a polyimide resin, a polyester resin, a fluoroacrylic resin, an acrylic-styrene resin, a silicone resin, or a resin in which at least two kinds of resins selected from these resins are mixed Or modified silicone resins modified with resins such as acrylic resins, polyester resins, epoxy resins, polyamideimide resins, polyimide resins, alkyd resins, urethane resins, and fluororesins.

  The coating amount of the resin is 0.01 to 10.0% by weight with respect to the carrier core material, and preferably 0.3 to 7.0% by weight. More preferably, it is 0.5 to 5.0% by weight. When the coating amount is less than 0.01% by weight, it is difficult to form a uniform coating layer on the carrier surface. When the coating amount exceeds 10.0% by weight, the carriers agglomerate with each other. Along with the decrease, it causes a change in developer characteristics such as fluidity or charge amount in the actual machine.

  The coated resin film is subject to great stress due to agitation in the developing machine and collision with the doctor blade, and thus is easily peeled off and worn. In addition, the spent phenomenon in which the toner adheres to the carrier surface is likely to occur. In order to solve these problems and maintain stable developer characteristics over a long period of time, the abrasion resistance, peel resistance, and spent resistance are good, and the formula (I) and / or A resin containing (II) is preferred. Moreover, it has an effect also with respect to water repellency by including these.

  Examples of the resin containing Formula (I) and / or (II) shown in Chemical Formula 4 include straight silicone resins, organic modified silicone resins, fluorine modified silicone resins and the like as described above.

  In addition, the coating resin can contain a silane coupling agent as a charge control agent. This is because, when the core material exposed area is controlled to be relatively small by coating, the charging ability may decrease, but it can be controlled by adding various silane coupling agents. The type of coupling agent that can be used is not particularly limited, but an aminosilane coupling agent is preferable for a negative toner, and a fluorine-based silane coupling agent is preferable for a positive toner.

  Conductive fine particles can be added to the coating resin. This is because when the coating amount of the resin is controlled to be relatively large by coating, the absolute resistance becomes too high and the developing ability may be lowered. However, since the conductive fine particles have a resistance lower than that of the coating resin or the ferrite as the core material, an excessive amount of the conductive fine particles causes a rapid charge leak. Further, when the content in the coating resin layer is added to 25 to 45% by volume as described in JP-A No. 2002-116582, toner contamination due to the conductive fine particles detached during use is severely undesirable. . Therefore, it is preferable to set the addition amount sufficiently lower than that. Since the shape of the carrier core material according to the present invention is sufficiently controlled, sufficient image characteristics can be obtained with no conductive fine particles added or in a very small amount. The specific addition amount is 0.25 to 20.0% by weight, preferably 0.5 to 15.0% by weight, particularly preferably 1.0 to 10.0%, based on the solid content of the coating resin. % By weight. Examples of the conductive fine particles include conductive carbon, oxides such as titanium oxide and tin oxide, and various organic conductive agents.

  The composition of the amorphous ferrite carrier according to the present invention is not particularly limited as long as it has the above shape, but preferably the ferrite composition is represented by the following general formula (1). Among these, those in which M is Mn and / or Mg are particularly preferable.

  The amorphous ferrite carrier according to the present invention desirably contains a titanium compound in the above-described ferrite composition. By containing a titanium compound, ferritization is promoted and stabilized, and therefore, combined with the shape effect, it is easy to obtain good characteristics with high magnetization and high conductivity over a long period of time. As the titanium compound, titanium oxide, titanium dioxide, titanium carbonate or the like is used. The content of the titanium compound is preferably 0.01 to 5 parts by weight with respect to 100 parts by weight of the ferrite component in terms of titanium. When the content of the titanium compound is more than 5 parts by weight in terms of titanium, the magnetization is likely to decrease, which causes carrier adhesion.

The apparent density of the amorphous ferrite carrier according to the present invention is preferably 2.40 g / cm ³ or less, more preferably 1.50 to 2.30 g / cm ³ . When the apparent density exceeds 2.40 g / cm ³ , stress in the developing machine increases and it is difficult to extend the life.

  The apparent density is measured according to JIS-Z2504 (Apparent density test method for metal powder).

The specific surface area of amorphous ferrite carrier according to the present invention is preferably 150 cm ² / g or more, more preferably 200-600 ² / g. When the specific surface area is less than 150 cm ² / g, the number of contact points between the particles is small, the effect of making the irregular shape is not seen, it is difficult to increase the conductivity, and the toner retainability is low. Become.

  The specific surface area is measured using a powder specific surface area measuring device (model name: SS-100 type) manufactured by Shimadzu Corporation.

  The average particle diameter of the irregular shaped ferrite carrier according to the present invention is preferably 30 to 120 μm, and more preferably 35 to 110 μm. When the average particle size is less than 30 μm, carrier adhesion tends to occur, causing white spots. On the other hand, if it exceeds 120 μm, the image quality becomes coarse and it becomes difficult to obtain a desired resolution. Further, since the specific surface area becomes small, the toner retainability is deteriorated. In addition, the charging ability is low, and it becomes difficult to sufficiently charge the toner.

  The average particle size is measured using a Microtrac particle size analyzer (Model 9320-X100) manufactured by Nikkiso Co., Ltd.

The saturation magnetization of the amorphous ferrite carrier according to the present invention is preferably 75 emu / g (Am ² / kg) or more, more preferably 80 to 97 emu / g (Am ² / kg). When the saturation magnetization is less than 75 emu / g (Am ² / kg), carrier adhesion tends to occur, causing white spots.

  This magnetization was measured using an integral BH tracer BHU-60 type (manufactured by Riken Denshi Co., Ltd.). A magnetic field measuring H coil and a magnetization measuring 4πI coil are placed between the electromagnets. In this case, the sample is placed in a 4πI coil. The outputs of the H coil and the 4πI coil whose magnetic field H is changed by changing the current of the electromagnet are respectively integrated, and the H output is drawn on the X axis, the output of the 4πI coil is drawn on the Y axis, and a hysteresis loop is drawn on the recording paper. Here, the measurement conditions were as follows: sample filling amount: about 1 g, sample filling cell: inner diameter 7 mmφ ± 0.02 mm, height 10 mm ± 0.1, 4πI coil: 30 turns.

Moreover, the resistance of the amorphous ferrite carrier according to the present invention is preferably 10 ² to 10 ¹⁰ Ω, and more preferably 10 ² to 10 ⁹ Ω. If the resistance of the carrier is less than 10 ² Ω, charge leakage tends to occur, causing white spots. On the other hand, when the resistance of the carrier exceeds 10 ¹⁰ Ω, since the resistance becomes too high, problems such as a decrease in developing ability tend to occur.

  The resistance of the irregular ferrite carrier is measured using a measuring jig as shown in FIG. In the figure, 1 is a sample (carrier core material, resin-coated carrier), 2 is a magnet, 3 is an electrode (brass plate), and 4 is an insulator (fluororesin plate). That is, 200 mg of a sample is weighed and inserted into a parallel plate electrode (area 10 × 40 mm) with an interelectrode spacing of 6.5 mm. Next, a magnet (surface magnetic flux density: 1500 gauss, facing magnet area: 10 x 30 mm) is attached to the parallel plate electrodes with the N and S poles facing each other, and the sample is held between the electrodes. Measurements were made using a company SM-8210.

<Method for Producing Ferrite Carrier for Developer According to the Present Invention>
Next, an example of a method for producing a ferrite carrier for developer according to the present invention will be described.

  First, an appropriate amount of ferrite raw material is weighed so as to have a predetermined composition, and further, titanium dioxide, if necessary, additives such as PVA, water, and carbon black are added and mixed in a mixer having a high-speed stirring blade, After granulating with a pressure molding machine, it is calcined. Next, after pulverizing with a roll type pulverizer, the particle size is adjusted using an airflow classifier and a vibration sieve, the calcined product is subjected to main firing, pulverized and classified to obtain amorphous ferrite (carrier core material).

  In addition, as a method of coating the above-mentioned amorphous ferrite (carrier core material) with the above-described coating resin, known methods such as brush coating method, dry method, spray-dry method using fluidized bed, rotary dry method, universal It can coat | cover by the immersion drying method etc. with a stirrer. In order to improve the coverage, a fluidized bed method is preferred.

  When the resin is coated on the carrier core and then baked, either an external heating method or an internal heating method may be used, for example, a fixed or fluid electric furnace, a rotary electric furnace, a burner furnace, or by microwave It can be burned. Although the baking temperature varies depending on the resin to be used, a temperature equal to or higher than the melting point or the glass transition point is necessary. For a thermosetting resin or a condensation-crosslinking resin, it is necessary to raise the temperature to a point where the curing proceeds sufficiently.

<Electrophotographic developer according to the present invention>
The electrophotographic developer according to the present invention will be described.

  The toner particles constituting the developer of the present invention include pulverized toner particles produced by a pulverization method and polymerized toner particles produced by a polymerization method. In the present invention, toner particles obtained by any method can be used.

  The pulverized toner particles are, for example, a binder resin, a charge control agent, and a colorant are sufficiently mixed with a mixer such as a Henschel mixer, then melt-kneaded with a twin screw extruder or the like, cooled, pulverized, classified, After adding the external additive, it can be obtained by mixing with a mixer or the like.

  The binder resin constituting the pulverized toner particles is not particularly limited, but polystyrene, chloropolystyrene, styrene-chlorostyrene copolymer, styrene-acrylic acid ester copolymer, styrene-methacrylic acid copolymer, Furthermore, rosin-modified maleic acid resin, epoxy resin, polyester resin, polyurethane resin and the like can be mentioned. These may be used alone or in combination.

  Any charge control agent can be used. For example, nigrosine dyes and quaternary ammonium salts can be used for positively charged toners, and metal-containing monoazo dyes can be used for negatively charged toners.

  As the colorant (colorant), conventionally known dyes and pigments can be used. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, etc. can be used. In addition, external additives such as silica powder and titania for improving the fluidity and aggregation resistance of the toner can be added according to the toner particles.

  The polymerized toner particles are toner particles produced by a known method such as a suspension polymerization method, an emulsion polymerization method, an emulsion aggregation method, an ester elongation polymerization method, or a phase inversion emulsification method. Such polymerized toner particles are prepared by, for example, mixing and stirring a colored dispersion in which a colorant is dispersed in water using a surfactant, a polymerizable monomer, a surfactant, and a polymerization initiator in an aqueous medium. Then, the polymerizable monomer is emulsified and dispersed in an aqueous medium, polymerized while stirring and mixing, and then a salting-out agent is added to salt out the polymer particles. Polymerized toner particles can be obtained by filtering, washing and drying the particles obtained by salting out. Thereafter, if necessary, an external additive is added to the dried toner particles.

  Further, in producing the polymerized toner particles, in addition to the polymerizable monomer, the surfactant, the polymerization initiator, and the colorant, a fixability improving agent and a charge control agent can be blended and obtained. Various characteristics of the polymerized toner particles can be controlled and improved. A chain transfer agent can be used to improve the dispersibility of the polymerizable monomer in the aqueous medium and adjust the molecular weight of the resulting polymer.

  The polymerizable monomer used for the production of the polymerized toner particles is not particularly limited. For example, styrene and its derivatives, ethylene unsaturated monoolefins such as ethylene and propylene, vinyl halides such as vinyl chloride, Α-methylene aliphatic monocarboxylic acids such as vinyl esters such as vinyl acetate, methyl acrylate, ethyl acrylate, methyl methacrylate, ethyl methacrylate, 2-ethylhexyl methacrylate, dimethylamino acrylate and diethylaminoester methacrylate Examples include esters.

  Conventionally known dyes and pigments can be used as the colorant (coloring material) used in the preparation of the polymerized toner particles. For example, carbon black, phthalocyanine blue, permanent red, chrome yellow, phthalocyanine green, and the like can be used. Moreover, the surface of these colorants may be modified using a silane coupling agent, a titanium coupling agent, or the like.

  As the surfactant used in the production of the polymerized toner particles, an anionic surfactant, a cationic surfactant, an amphoteric surfactant and a nonionic surfactant can be used.

  Here, examples of the anionic surfactant include fatty acid salts such as sodium oleate and castor oil, alkyl sulfates such as sodium lauryl sulfate and ammonium lauryl sulfate, alkyl benzene sulfonates such as sodium dodecyl benzene sulfonate, and alkyl naphthalene sulfonic acids. Salt, alkyl phosphate ester salt, naphthalene sulfonic acid formalin condensate, polyoxyethylene alkyl sulfate ester salt and the like. Examples of the nonionic surfactant include polyoxyethylene alkyl ether, polyoxyethylene fatty acid ester, sorbitan fatty acid ester, polyoxyethylene alkylamine, glycerin, fatty acid ester, and oxyethylene-oxypropylene block polymer. . Furthermore, examples of the cationic surfactant include alkylamine salts such as laurylamine acetate, and quaternary ammonium salts such as lauryltrimethylammonium chloride and stearyltrimethylammonium chloride. Examples of amphoteric surfactants include aminocarboxylates and alkylamino acids.

  The surfactant as described above can be used usually in an amount in the range of 0.01 to 10% by weight with respect to the polymerizable monomer. The amount of such a surfactant used affects the dispersion stability of the monomer and also affects the environmental dependency of the obtained polymerized toner particles. It is preferably used in an amount within the above range that is ensured and does not exert an excessive influence on the environment dependency of the polymerized toner particles.

  For the production of polymerized toner particles, a polymerization initiator is usually used. The polymerization initiator includes a water-soluble polymerization initiator and an oil-soluble polymerization initiator, and any of them can be used in the present invention. Examples of the water-soluble polymerization initiator that can be used in the present invention include persulfates such as potassium persulfate and ammonium persulfate, water-soluble peroxide compounds, and oil-soluble polymerization initiators. Examples thereof include azo compounds such as azobisisobutyronitrile and oil-soluble peroxide compounds.

  When a chain transfer agent is used in the present invention, examples of the chain transfer agent include mercaptans such as octyl mercaptan, dodecyl mercaptan, tert-dodecyl mercaptan, and carbon tetrabromide.

  Further, when the polymerized toner particles used in the present invention contain a fixability improving agent, a natural wax such as carnauba wax, an olefinic wax such as polypropylene or polyethylene can be used as the fixability improving agent. .

  Further, when the polymerized toner particles used in the present invention contain a charge control agent, the charge control agent to be used is not particularly limited, and nigrosine dyes, quaternary ammonium salts, organometallic complexes, metal-containing monoazo dyes, etc. Can be used.

  Examples of the external additive used for improving the fluidity of polymerized toner particles include silica, titanium oxide, barium titanate, fine fluorine particles, and fine acrylic particles. These may be used alone or in combination. Can be used.

  Further, examples of the salting-out agent used for separating the polymer particles from the aqueous medium include metal salts such as magnesium sulfate, aluminum sulfate, barium chloride, magnesium chloride, calcium chloride, and sodium chloride.

  The average particle size of the toner particles produced as described above is in the range of 2 to 15 μm, preferably 3 to 10 μm, and the polymerized toner particles have higher particle uniformity than the pulverized toner particles. If the toner particles are smaller than 2 μm, the charging ability is lowered and fog and toner scattering are likely to occur, and if it exceeds 15 μm, the image quality is deteriorated.

  An electrophotographic developer can be obtained by mixing the carrier and toner produced as described above. The mixing ratio of the carrier and the toner, that is, the toner concentration is preferably set to 3 to 15%. If it is less than 3%, it is difficult to obtain a desired image density, and if it exceeds 15%, toner scattering and fogging tend to occur.

  The developer mixed as described above is a two-component developer having a toner and a carrier while applying a bias electric field to the electrostatic latent image formed on the latent image holding member having the organic photoconductor layer. The present invention can be used in digital copying machines, printers, fax machines, printing machines, etc., which use a developing method that reversely develops with a magnetic brush. Further, the present invention can also be applied to a full color machine using an alternating electric field, which is a method of superimposing an AC bias on a DC bias when a developing bias is applied from the magnetic brush to the electrostatic latent image side.

  Hereinafter, the present invention will be specifically described based on examples and the like.

The raw materials were weighed so that the composition ratio after firing was MnO: 20 mol% and Fe ₂ O ₃ : 80 mol%, and further TiO ₂ : 0.1 parts by weight, carbon black: 0 with respect to 100 parts by weight of the weighed raw materials. .2 parts by weight was added and mixed with a mixer having high-speed stirring blades, granulated with a pressure molding machine, and then held at 950 ° C. for 1 hour for pre-baking. This was pulverized by a roll type pulverizer, and then the particle size was adjusted using an air classifier and a vibrating sieve. This calcined product was held in an electric furnace at a temperature of 1300 ° C. and an oxygen concentration of 0.1% for 4 hours to perform main firing. Thereafter, crushing and classification were performed to obtain a carrier core material.

Next, a resin solution was prepared as follows.
Silicone resin (trade name: SR-2411, solid content 20% by weight, Toray Dow Corning Silicone Co., Ltd.): 500 parts by weight γ-aminopropyltriethoxysilane: 10 parts by weight Toluene: 300 parts by weight

  The resin solution thus prepared was coated on 1000 parts by weight of the ferrite particles using a fluidized bed coater, and further baked at 200 ° C. for 2 hours to obtain a ferrite carrier coated with the resin. The properties of the resin-coated ferrite carrier thus obtained are shown in Table 1. The characteristics are shape factor (SF-1), ratio of shape factor (SF-1) 140 or more, deviation (δ), shape factor (SF-2), apparent density, specific surface area, average particle size, saturation magnetization and The resistance was measured. The measurement method is as described above. Further, FIG. 1 shows an electron micrograph (100 times) of the amorphous ferrite carrier (locked rock sugar shape) thus obtained. As can be seen from this electron micrograph, it can be seen that 80% by number or more of the particles have a rock-type icing sugar shape.

  A developer was prepared by the following method using the obtained resin-coated ferrite carrier, and an actual machine evaluation was performed.

As a toner used with this carrier, a commercially available toner for FANTASIA 200 manufactured by Toshiba Tec Corporation was used, and a developer was prepared so as to have a toner concentration of 5%.
This developer was subjected to printing durability evaluation using a commercially available FANTASIA 200 manufactured by Toshiba Tec Corporation. Image evaluation at that time (image density, image density after 30000 sheet printing, carrier adhesion, toner scattering, color toner color stain) was performed based on the following criteria. The results are shown in Table 2. In addition, in the evaluation of Table 2, Δ or more is a level that causes no practical problem.

  The pulverization conditions were changed depending on the gap between rolls of the roll type pulverizer, and the other conditions were the same as in Example 1 to obtain an amorphous ferrite carrier coated with resin. The properties of the obtained resin-coated ferrite carrier were evaluated according to Example 1, and the results are shown in Table 1. Further, FIG. 2 shows an electron micrograph (100 times) of the amorphous ferrite carrier (oyster shell shape) thus obtained. As can be seen from this electron micrograph, it can be seen that 80% by number or more of the particles have an oyster shell shape. Using the resin-coated ferrite carrier thus obtained, a developer was prepared in the same manner as in Example 1, and the actual machine was evaluated. The results are shown in Table 2.

  After weighing in the same manner as in Example 1, 15% by weight of water was added, and the mixture was mixed and granulated with a Henschel mixer. After calcination, an amorphous ferrite carrier coated with a resin was obtained in the same manner as in Example 1. When this amorphous ferrite carrier was observed with an electron micrograph, 80% by number or more of the particles were oyster shell-shaped. The properties of the obtained resin-coated ferrite carrier were evaluated according to Example 1, and the results are shown in Table 1. Using the resin-coated ferrite carrier thus obtained, a developer was prepared in the same manner as in Example 1, and the actual machine was evaluated. The results are shown in Table 2.

  The calcining temperature was set to 850 ° C., and the pulverization conditions were changed depending on the gap between rolls of the roll type pulverizer. Other conditions were the same as in Example 1, and an amorphous ferrite carrier coated with a resin was obtained. When this amorphous ferrite carrier was observed with an electron micrograph, 60% by number or more of the particles were oyster shell-shaped. The properties of the obtained resin-coated ferrite carrier were evaluated according to Example 1, and the results are shown in Table 1. A developer was prepared from the resin-coated ferrite carrier thus obtained in the same manner as in Example 1, and the actual machine was evaluated. The results are shown in Table 2.

Comparative example

(Comparative Example 1)
The raw materials were weighed so that the composition ratio after firing would be MnO: 20 mol%, Fe ₂ O ₃ : 80 mol%, water was added, pulverized in a wet ball mill for 5 hours, mixed and dried, then 1 at 950 ° C. Temporary firing was performed while maintaining the time. Water was added to the calcined powder, and appropriate amounts of a dispersant and a binder were added to the slurry obtained by pulverizing for 7 hours with a wet ball mill, and then granulated and dried with a spray dryer to obtain a granulated product. The obtained granulated product was held in an electric furnace at a temperature of 1300 ° C. and an oxygen concentration of 0.1% for 4 hours to perform main firing. Thereafter, crushing and classification were performed to obtain a carrier core material. This carrier core material was coated with a resin in the same manner as in Example 1 to obtain a ferrite carrier coated with the resin. When this ferrite carrier was observed with an electron micrograph, almost all of the particles were spherical. The properties of the obtained resin-coated ferrite carrier were evaluated according to Example 1, and the results are shown in Table 1. Using the resin-coated ferrite carrier thus obtained, a developer was prepared in the same manner as in Example 1, and the actual machine was evaluated. The results are shown in Table 2.

(Comparative Example 2)
Spherical iron powder (ASRV-100) manufactured by Powdertech was used as a core material. The core material of the iron powder particles was coated with a resin in the same manner as in Example 1 to obtain an iron powder carrier coated with the resin. When this iron powder carrier was observed with an electron micrograph, almost all of the particles were spherical. The properties of the obtained resin-coated iron powder carrier were evaluated according to Example 1, and the results are shown in Table 1. A developer was prepared from the resin-coated iron powder carrier thus obtained in the same manner as in Example 1, and the actual machine was evaluated. The results are shown in Table 2.

(Comparative Example 3)
Composition ratio after firing CuO: 20mol%, ZnO: 25mol %, Fe 2 O 3: raw material was weighed so that 55 mol%, water was added, 5 hours pulverized in a wet ball mill, and mixed and dried And calcination was performed at 950 ° C. for 1 hour. Water was added to the calcined powder, and appropriate amounts of a dispersant and a binder were added to the slurry obtained by pulverizing for 7 hours with a wet ball mill, and then granulated and dried with a spray dryer to obtain a granulated product. The obtained granulated material was held in a burner furnace at a temperature of 1200 ° C. for 4 hours and subjected to main firing. Thereafter, crushing and classification were performed to obtain a carrier core material.

Next, a resin solution was prepared as follows.
Silicone resin (trade name: SR-2411, solid content 20% by weight, manufactured by Toray Dow Corning Silicone Co., Ltd.): 500 parts by weight γ-aminopropyltriethoxysilane: 10 parts by weight Ketjen Black EC ( Ketjen Black International Co., Ltd.): 30 parts by weightToluene: 300 parts by weight

  The resin solution thus prepared was coated on 1000 parts by weight of the ferrite particles using a fluidized bed coater, and further baked at 200 ° C. for 2 hours to obtain a ferrite carrier coated with the resin. When this ferrite carrier was observed with an electron micrograph, almost all of the particles were spherical. The properties of the obtained resin-coated ferrite carrier were evaluated according to Example 1, and the results are shown in Table 1. Using the resin-coated ferrite carrier thus obtained, a developer was prepared in the same manner as in Example 1, and the actual machine was evaluated. The results are shown in Table 2.

(Comparative Example 4)
“EFY-50BW” (manufactured by Powder Tech) used in the manufacture of carrier A in JP-A No. 2002-116582 was used as an amorphous carrier core material.

Next, a resin solution was prepared as follows.
Silicone resin (trade name: SR-2411, solid content 20% by weight, manufactured by Toray Dow Corning Silicone Co., Ltd.): 500 parts by weight γ-aminopropyltriethoxysilane: 10 parts by weight Ketjen Black EC ( Ketjen Black International Co., Ltd.): 60 parts by weightToluene: 600 parts by weight

  The resin solution thus prepared was coated on 1000 parts by weight of the ferrite particles using a fluidized bed coater, and further baked at 200 ° C. for 2 hours to obtain a ferrite carrier coated with the resin. At this time, the content of the conductive fine particles in the coat resin layer is 60% by weight, which is about 30% by volume in terms of volume. When this amorphous ferrite carrier was observed with an electron micrograph, approximately 70% of the particles were in the shape of rock-type rock sugar. The properties of the obtained resin-coated ferrite carrier were evaluated according to Example 1, and the results are shown in Table 1. Using the resin-coated ferrite carrier thus obtained, a developer was prepared in the same manner as in Example 1, and the actual machine was evaluated. The results are shown in Table 2.

(Image density)
Development was performed under appropriate exposure conditions, and the image density of the solid portion was measured by X-Rite (X-Rite, Inc.) and ranked.
◎: 1.6 or more ○: 1.4 or more and less than 1.6 △: 1.2 or more and less than 1.4 ▲: 1.0 or more and less than 1.2 ×: less than 1.0

(Image density after 30000 sheet printing)
30000 printing press printing was performed under appropriate exposure conditions, and the image density of the solid portion was measured by X-Rite (manufactured by X-Rite, Inc.), and ranking was performed in the same manner as above (image density).

(Carrier adhesion)
Development was performed under appropriate exposure conditions, and the level of vitiligo due to carrier adhesion on the image was visually determined to perform ranking.
A: There are no white spots on 10 sheets of A3 paper. A: 1-5 pieces in 10 sheets of A3 paper. Δ: 6-10 pieces in 10 sheets of A3 paper. ▲: 11-20 pieces in 10 sheets of A3 paper. 21 or more in 10 A3 sheets

(Toner scattering)
The inside of the machine after 30000 sheet printing was observed, visually judged and ranked.
◎: There is no in-flight contamination and the clean state is maintained. ○: The in-flight is slightly contaminated, but it is in a clean state. △: In-flight contamination is at a level that is not a problem. Problems also appear on the paper ×: Cannot withstand use

(Color toner stains)
Development was carried out under appropriate exposure conditions, and visual judgment was made and ranking was performed.
◎: There is no color stains and the image is clean. ○: The image is slightly stained, but the image is clean. △: The image is stained but is at a usable level. ▲: The color stain is severe and usable. X below the level: Unusable for use

(Comprehensive judgment)
◎: Very good in all ○: Good △: Slightly bad, but usable level ▲: Below usable level ×: Unusable

  As is clear from the results in Table 2, Examples 1 to 4 are at practical levels in any of image density, image density after 30000 sheet printing, carrier adhesion, toner scattering, and color toner color stain. In particular, Example 2 is excellent in all items. On the other hand, Comparative Examples 1 to 4 are inferior in image density, toner scattering, and the like after 30000 sheet printing.

  The amorphous ferrite carrier according to the present invention is obtained by coating a carrier core material with a resin, the shape of which is mainly a particle having a rock-type icing sugar shape or an oyster shell shape, and a shape factor (SF-1) within a specific range. And the distribution width (δ) is a certain value or less, the shape factor (SF-2) is also in a specific range, and the content of the resin is in a specific range. Since the specific surface area is low and the specific gravity is low, a long life is achieved. Therefore, the electrophotographic developer using the amorphous ferrite carrier according to the present invention can prevent toner scattering, has a high image density, and can sufficiently cope with speeding up of the developing machine and full color.

FIG. 1 is an electron micrograph (100 ×) of an amorphous ferrite carrier (locked rock sugar shape) obtained from Example 1. FIG. 2 is an electron micrograph (100 times) of the amorphous ferrite carrier (oyster shell shape) obtained from Example 2. FIG. 3 is an explanatory diagram of a measurement jig used for resistance measurement.

Explanation of symbols

1: Sample (carrier core material, resin-coated carrier)
2: Magnet 3: Electrode (brass plate)
4: Insulator (fluororesin plate)

Claims (17)

Ferrite carrier in which the carrier core material is coated with a resin, the particle shape is indeterminate, and 40% by number or more are rock-shaped icing sugar-shaped and / or oyster shell-shaped particles. The shape factor (SF-1) shown is 140 to 250, the distribution width (δ) is 60 or less, the shape factor (SF-2) shown by the following formula 2 is 120 to 150, and the resin An amorphous ferrite carrier, wherein the coating amount is 0.01 to 10.0% by weight with respect to the carrier core material.

The amorphous ferrite carrier according to claim 1, wherein the rock-type rock sugar-shaped and / or oyster shell-shaped particles are present in an amount of 50% by number or more. The amorphous ferrite carrier according to claim 1 or 2, wherein the shape factor (SF-1) is 145 to 200. The amorphous ferrite carrier according to claim 3, wherein the proportion of particles having a shape factor (SF-1) of 140 or more is 40% by number or more. The irregular shaped ferrite carrier according to any one of claims 1 to 4, wherein a distribution width (δ) of the shape factor (SF-1) is 55 or less. The amorphous ferrite carrier according to any one of claims 1 to 5, wherein the ferrite composition is represented by the following chemical formula (1).
The amorphous ferrite carrier according to claim 6, wherein M is Mn and / or Mg. The amorphous ferrite carrier according to claim 6 or 7, wherein the ferrite composition contains a titanium compound. The amorphous ferrite carrier according to claim 8, wherein the content of the titanium compound is 0.01 to 5 parts by weight in terms of titanium with respect to 100 parts by weight of the ferrite component. The amorphous ferrite carrier according to any one of claims 1 to 9, which has an apparent density of 2.40 g / cm ³ or less. A specific surface area is 150 cm < ² > / g or more, The amorphous ferrite carrier in any one of Claims 1-10. The amorphous ferrite carrier according to any one of claims 1 to 11, having an average particle size of 30 to 120 µm. The amorphous ferrite carrier according to any one of claims 1 to 12, wherein a saturation magnetization is 75 emu / g (A · m ² / kg) or more. Resistance is 10 < ² > -10 < ¹⁰ > (omega | ohm), The amorphous ferrite carrier in any one of Claims 1-13. The amorphous ferrite carrier according to any one of claims 1 to 14, which is used for a color toner. An electrophotographic developer comprising the amorphous ferrite carrier according to any one of claims 1 to 15 and a toner. The electrophotographic developer according to claim 16, wherein the toner is a color toner.