JP2018109666A - Electrophotographic carrier, two-component developer and development method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electrophotographic carrier that is able to maintain an excellent charging performance by solving the problem of carrier contamination caused by an external additive used for toner.SOLUTION: Electrophotographic carrier comprises: matrix resin having magnetic particles and a layer coating each magnetic particle, the coating layer containing thermoplastic acrylic resin; a fluorine-containing particles with an average particle diameter of 0.1 to 0.6 μm, dispersed in the matrix resin; and positively-charged fine particles with an average particle diameter of 0.1 to 0.6 μm, dispersed in the matrix resin. Each fluorine-containing particle contains fluorine-containing resin whose content proportion in tetrafluoroethylene unit is 45% by mole based on the entire quantity in monomer unit.SELECTED DRAWING: None

Description

  The present invention relates to an electrophotographic carrier, a two-component developer containing the same, and a developing method using the same.

  In general, image formation using an electrophotographic method includes steps of charging, exposure, development, transfer, and fixing, and is classified into a one-component development method and a two-component development method depending on the development method.

  When the two-component development method is used, the carrier is charged in order to impart appropriate chargeability to the toner and maintain the chargeability for a long period of time in any environment from low temperature and low humidity to high temperature and high humidity. It is necessary to have the imparting performance and maintain the performance. For this reason, the carrier which provided the special coating layer on the surface conventionally is examined (for example, patent documents 1-5).

JP 2011-203690 A JP-A-3-296772 JP 2009-258700 A JP2011-2497A JP-A-2-296256

  In the two-component development method, it is common to coat toner particles (colored particles) with an external additive for the purpose of improving image quality.

  In recent years, image forming apparatuses have been demanded to improve image quality and extend the life of members, and accordingly, toner particle size reduction and diversification of toner external additives have been promoted. The total amount of external additives attached to the surface is relatively large. At this time, the external additive having a small particle size is easily peeled off from the toner surface and is easily embedded in the coating layer of the carrier. Carrier contamination is a problem.

  An object of the present invention is to provide an electrophotographic carrier capable of solving the problem of carrier contamination due to an external additive for toner and maintaining excellent charge imparting performance for a long period of time. Another object of the present invention is to provide a two-component developer and a development method using the electrophotographic carrier.

  One aspect of the present invention relates to an electrophotographic carrier having magnetic particles and a coating layer covering the magnetic particles. In this electrophotographic carrier, the coating layer is dispersed in a matrix resin containing a thermoplastic acrylic resin, fluorine-containing fine particles having an average particle size of 0.1 to 0.6 μm dispersed in the matrix resin, and the matrix resin. Positively-charged fine particles having an average particle size of 0.1 to 0.6 μm, and the fluorine-containing fine particles have a tetrafluoroethylene unit content ratio of 45 mol% or more based on the total amount of monomer units. Containing.

  In this electrophotographic carrier, a carrier for an external additive for toner is prepared by blending a fluorine-containing fine particle containing a predetermined fluorine-containing resin and a positively chargeable fine particle into a coating layer containing a thermoplastic acrylic resin. Adhesion to the surface is suppressed, and even if an external additive for toner adheres to the carrier surface, the surface of the coating layer is scraped little by little, so that the surface of the coating layer without contamination is maintained.

  In one embodiment, the fluororesin is selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and tetrafluoroethylene-ethylene copolymer. It may contain at least one kind. The content of the fluorine-containing fine particles may be 3 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the matrix resin.

  In one embodiment, the positively chargeable fine particles may contain hydrotalcite containing an aluminum element and a magnesium element. The molar ratio of magnesium element to aluminum element may be 0.25 or more and 3.50 or less. Further, the content of the positively chargeable fine particles may be 3 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the matrix resin.

  In one embodiment, the content ratio of the soluble component to tetrahydrofuran in the matrix resin may be 90% by mass or more. Moreover, the weight average molecular weight of the soluble component may be 30,000 or more and 300,000 or less.

In one embodiment, the coating layer may further contain conductive fine particles. In addition, the electrophotographic carrier according to one embodiment may have a carrier resistivity of 1.0 × 10 ⁷ (Ω · cm) or more and 1.0 × 10 ¹² (Ω · cm) or less.

  The electrophotographic carrier according to one embodiment may have an average particle size of 20 μm or more and 60 μm or less.

  Another aspect of the present invention relates to a two-component developer including the above-described electrophotographic carrier and an electrophotographic toner having colored particles and an external additive. Since the two-component developer includes the above-described electrophotographic carrier, the problem of carrier contamination due to the external additive hardly occurs, and excellent toner chargeability is maintained for a long time.

  In one embodiment, the colored particles may contain a binder resin, a colorant, and a release agent. The external additive may contain inorganic fine particles that have been hydrophobized.

  In one embodiment, the release agent may contain at least one selected from the group consisting of paraffin wax and ester wax.

  In one embodiment, the inorganic fine particles may contain spherical silica having an average particle size of 30 to 80 nm and titanium dioxide particles having an average particle size of 10 to 30 nm.

  In one embodiment, the electrophotographic toner may have a weight average molecular weight of 20,000 to 500,000.

  In one embodiment, the average particle diameter of the electrophotographic toner may be 3 μm or more and 9 μm or less.

  In one embodiment, the average circularity of the electrophotographic toner may be 0.940 or more and 0.990 or less.

  Still another aspect of the present invention relates to a developing method including a developing step of developing using the above-described two-component developer. This developing method can maintain a uniform image quality even when developing for a long period of time by using the above-described two-component developer.

  In the development method according to one aspect, in the development step, development may be performed using a development sleeve to which an AC bias voltage having a peak peak value of 300 to 700 V and a frequency of 3 to 8 KHz is applied.

  ADVANTAGE OF THE INVENTION According to this invention, the carrier for electrophotography which can solve the problem of the carrier contamination by the external additive for toners and can maintain the excellent charge imparting performance for a long time is provided. In addition, according to the present invention, a two-component developer and a developing method using the above-described electrophotographic carrier are provided.

1 is a schematic diagram illustrating an example of an image forming apparatus in which a two-component developer according to an embodiment of the present invention is used. It is a figure which shows the evaluation result of the amount of Ti contamination in Example 1 and Comparative Example 1. 6 is a diagram illustrating evaluation results of toner charge amounts in Example 1 and Comparative Example 1. FIG. It is a figure which shows the evaluation result of the toner charge amount in Examples 1-6 and Comparative Examples 1-5.

  Hereinafter, preferred embodiments of the present invention will be described.

  The electrophotographic carrier according to this embodiment includes magnetic particles and a coating layer that covers the magnetic particles. In the present embodiment, the coating layer was dispersed in a matrix resin containing a thermoplastic acrylic resin, fluorine-containing fine particles having an average particle diameter of 0.1 to 0.6 μm dispersed in the matrix resin, and the matrix resin. Positively chargeable fine particles having an average particle size of 0.1 to 0.6 μm. The fluorine-containing fine particles contain a fluorine-containing resin in which the content ratio of tetrafluoroethylene units is 45 mol% or more based on the total amount of monomer units.

  In the present specification, positively chargeable fine particles are fine particles that are charged with a reverse polarity (that is, positively charged) with respect to particles composed of a styrene acrylic copolymer resin having a styrene component of 60% or more. The positively chargeable fine particles are, for example, mixed with 70% styrene acrylic copolymer resin particles having an average particle diameter of 10 μm with a V-type mixer, and then a suction type small charge amount measuring device Model 210HS (Trek). It can be determined by measuring the amount of charge using a product and confirming positive charge.

  In the electrophotographic carrier according to this embodiment, fluorine-containing fine particles containing a predetermined fluorine-containing resin and positively chargeable fine particles are blended in a coating layer containing a thermoplastic acrylic resin. As a result, the electrophotographic carrier according to the present embodiment suppresses the adhesion of the external toner additive to the carrier surface, and even if the external toner additive adheres to the carrier surface, the surface of the coating layer is a little. The surface of the coating layer without contamination can be maintained by scraping each one. For this reason, the carrier for electrophotography according to the present embodiment can maintain excellent charging performance for a long period of time.

  The reason why the above effect is achieved in the electrophotographic carrier according to the present embodiment is considered as follows. First, in the present embodiment, fluorine-containing fine particles are blended in the coating layer, and the fluorine-containing fine particles contain a predetermined fluorine-containing resin. By blending the fluorine-containing fine particles, adhesion preventing property is imparted to the surface of the coating layer, and it becomes difficult for the external additive for toner to adhere to the surface of the coating layer.

  On the other hand, since the fluorine-containing fine particles themselves are negatively charged, the chargeability of the electrophotographic carrier is lowered simply by adding the fluorine-containing fine particles to the coating layer. In this regard, in the present embodiment, positively chargeable fine particles are blended in the coating layer. Since the positively chargeable fine particles have a positive chargeability opposite to that of the fluorine-containing fine particles, the charging of the electrophotographic carrier due to the fluorine-containing fine particles is suppressed by blending the positively chargeable fine particles. For this reason, the carrier for electrophotography according to the present embodiment can maintain excellent charge imparting performance while blending fluorine-containing fine particles in the coating layer.

  Moreover, in this embodiment, the matrix resin which comprises a coating layer contains the thermoplastic acrylic resin. The thermoplastic acrylic resin has a refreshing effect, and the coating layer surface is easily scraped by blending the thermoplastic acrylic resin. For this reason, in this embodiment, even if the toner external additive adheres to the carrier surface, the contaminated coating layer surface is scraped little by little during the development process, and a new coating layer surface free of contamination is formed ( Refresh effect).

  In addition, when positively chargeable fine particles are released in the developer due to peeling of the surface of the coating layer or the like, there is a possibility that the negatively charged toner adheres to the toner and inhibits image formation. However, in this embodiment, positively chargeable fine particles and fluorine-containing fine particles are mixed in the coating layer, and both are considered to be in close contact with each other in the coating layer. For this reason, when the positively chargeable fine particles are released into the developer, the fluorine-containing fine particles are released at the same time in close contact therewith. Due to the presence of the fluorine-containing fine particles, in the present embodiment, the adhesion of the positively chargeable fine particles to the toner is suppressed, and the charge reduction is alleviated.

  The magnetic particles are not particularly limited, and known magnetic particles may be used. For example, the magnetic particles may be magnetite particles, ferrite particles, magnetic material-dispersed resin particles, and the like. As the magnetic particles, magnetic particles having high sphericity are preferable. The 50% particle size (D50) of the magnetic particles based on the volume distribution is preferably 25 μm or more and 53 μm or less, more preferably 30 μm or more and 45 μm or less.

  The coating layer includes a matrix resin containing a thermoplastic acrylic resin, fluorine-containing fine particles having an average particle diameter of 0.1 to 0.6 μm dispersed in the matrix resin, and an average particle diameter of 0.1 μm dispersed in the matrix resin. 1 to 0.6 μm positively chargeable fine particles.

  The thermoplastic acrylic resin is a resin having an acrylic monomer unit, and may be a homopolymer or copolymer of an acrylic monomer. The acrylic monomer is a monomer having an acrylic group or a methacryl group.

  Specific examples of the acrylic monomer include acrylic acid and its ester, methacrylic acid and its ester, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile and the like. The thermoplastic acrylic resin may be a polymer of one or more of these acrylic monomers, or may be a copolymer of these acrylic monomers and other monomers. The other monomer may be any monomer that can be copolymerized with an acrylic monomer, and examples thereof include styrene, vinyl chloride, and vinyl acetate.

  Specific examples of the thermoplastic acrylic resin include polyacrylic acid, polymethacrylic acid, polymethyl acrylate, polymethyl methacrylate, isobutyl acrylate, isobutyl methacrylate, polycyclohexylmethyl acrylate, and styrene copolymers thereof. Among these, methyl methacrylate-styrene copolymer, isobutyl acrylate-styrene copolymer, isobutyl methacrylate-styrene copolymer, and the like are preferable from the viewpoint that the above-described refresh effect can be obtained remarkably.

  The matrix resin may further contain a resin other than the thermoplastic acrylic resin. For example, the matrix resin is a thermoplastic resin such as polystyrene, styrene-butadiene copolymer, ethylene-vinyl acetate copolymer, polyvinyl chloride, polyvinyl acetate, polyvinylidene fluoride resin, fluorocarbon resin, polyvinyl alcohol, silicone resin, It may further contain a thermosetting resin such as a phenol resin.

  The ratio of the thermoplastic acrylic resin in the matrix resin may be, for example, 70% by mass or more, preferably 85% by mass or more, and may be 100% by mass.

  The content ratio of the soluble component (hereinafter also referred to as “THF soluble component”) to tetrahydrofuran (THF) in the matrix resin is preferably 90% by mass or more based on the total amount of the matrix resin, and is 95% by mass. More preferably.

  The weight average molecular weight measured by gel permeation chromatography (GPC) of the THF soluble content is preferably 30,000 or more, and more preferably 50,000 or more. Further, the weight average molecular weight of the THF soluble component is preferably 300,000 or less, and more preferably 200,000 or less.

In addition, in this specification, the content ratio and weight average molecular weight of a THF soluble part are measured with the following method.
<Method for Measuring Content of THF-Soluble Content and Weight Average Molecular Weight>
First, the resin component to be measured is weighed and dissolved / dispersed in THF to obtain a THF treatment solution. The dissolution / dispersion treatment is performed by performing ultrasonic irradiation from the outside for 5 minutes using an ultrasonic bath or the like at room temperature. Next, the obtained THF treatment solution is filtered using a membrane filter (pore size; 0.45 μm, manufactured by Millopore) weighed in advance. After completion of the filtration treatment, the dry mass of the membrane filter is measured, and the mass increase (THF insoluble content) is obtained. This amount of mass increase is subtracted from the amount of resin component used to determine the amount of THF soluble in the resin component and its content ratio.
On the other hand, the filtrate obtained by the filtration treatment is used as a GPC measurement sample by adjusting the concentration so that the resin component concentration in the filtrate is 1 mg / ml. For molecular weight measurement by GPC, HLC-8220 (manufactured by TOSOH) equipped with a differential refractive index detector (RI detector, RI-410, manufactured by Waters) was used as a GPC measuring device, and TSKgarcolumn was used as a measurement column. TSKgelGMHXL (2) and TSKgelG2500HXL (1) are connected and used (all measurement columns are manufactured by TOSOH). As measurement conditions, the column temperature is 23 ° C., the flow rate of THF as an eluent is 1.0 ml / min, and the injection amount of the measurement sample is 200 μl. For the creation of a calibration curve showing “relation between elution time and molecular weight”, TSK standard Polystyrene (manufactured by TOSOH) is appropriately used as standard polystyrene. By this GPC measurement, the weight average molecular weight of the THF soluble matter is determined.

  The matrix resin may further contain other components. For example, the matrix resin may further contain a dispersant and the like. The content of these components is preferably 10% by mass or less, for example, based on the total amount of the matrix resin.

  The fluorine-containing fine particles are fine particles containing a fluorine-containing resin having an average particle size of 0.1 to 0.6 μm. In addition, in this specification, the average particle diameter of a fluorine-containing particle shows the value measured by the following average particle diameter measuring methods. The average particle size of the fluorine-containing fine particles is more preferably 0.2 μm or more, and more preferably 0.5 μm or less.

<Average particle size measurement method>
After dissolving the electrophotographic carrier with methyl ethyl ketone, the magnetic particles are separated from the residue by filtration. Next, 50 or more particles to be measured are randomly extracted from the residue excluding the magnetic particles. For the extracted particles to be measured, after taking an enlarged photo at a magnification of 15,000 times or more with a scanning electron microscope “SU8020” (manufactured by HITACHI), the outline of the image of the particles to be measured in the enlarged photo becomes clear Thus, the image contrast is adjusted to obtain an image for measurement of the number average particle diameter. After appropriately enlarging the obtained measurement image, 50 or more particles to be measured are selected at random, the major axis is measured, and the number average diameter is calculated. This number average diameter is defined as the average particle diameter.

  The fluorine-containing resin is a resin containing a tetrafluoroethylene unit, and may be a homopolymer of tetrafluoroethylene or a copolymer of tetrafluoroethylene and another monomer. The other monomer may be a monomer copolymerizable with tetrafluoroethylene, and examples thereof include ethylene, propylene, hexafluoropropylene, alkyl vinyl ether, perfluoroalkyl vinyl ether and the like.

  In the fluorine-containing resin, the content ratio of tetrafluoroethylene units is 45 mol% or more, preferably 50 mol% or more, based on the total amount of monomer units in the fluorine-containing resin.

  Examples of the fluorine-containing resin include polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer, tetrafluoroethylene-ethylene copolymer, and the like.

  The content ratio of the fluorine-containing resin in the fluorine-containing fine particles may be, for example, 80% by mass or more, preferably 90% by mass or more, and may be 100% by mass, based on the total amount of the fluorine-containing fine particles. That is, the fluorine-containing fine particles may be fine particles composed of a fluorine-containing resin.

  The fluorine-containing fine particles may further contain components other than the fluorine-containing resin. Examples of other components include acrylic resins and epoxy resins. The content of these components is preferably 10% by mass or less based on the total amount of the fluorine-containing fine particles.

  The content of the fluorine-containing fine particles is preferably 3 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of the matrix resin. Moreover, it is preferable that content of a fluorine-containing fine particle is 30 mass parts or less with respect to 100 mass parts of matrix resins, More preferably, it is 17 mass parts or less.

  The positively chargeable fine particles are fine particles having a positive chargeability having an average particle size of 0.1 to 0.6 μm. In the present specification, the average particle diameter of the positively chargeable fine particles indicates a value measured by the above-described average particle diameter measuring method. The average particle diameter of the positively chargeable fine particles is more preferably 0.2 μm or more, and more preferably 0.5 μm or less.

The positively chargeable fine particles preferably contain hydrotalcite containing an aluminum element and a magnesium element. A hydrotalcite is a compound which exhibits the layered double hydroxide represented, for example by a following formula (A). In the formula (A), A ⁿ⁻ represents an n-valent anion, and m ≧ 0.
_{^{[Mg 2+ 1-x Al 3+}} x (OH) 2] [A n- x / n · mH 2 O] ... (A)

  Examples of the n-valent anion of the formula (A) include carbonate ions, sulfate ions, hydroxide ions, chloride ions, and the like, and carbonate ions, hydroxide ions, and chloride ions are preferable.

  In the hydrotalcite, the molar ratio of the magnesium element to the aluminum element is preferably 0.25 or more, and more preferably 1.5 or more. In addition, the molar ratio is preferably 3.50 or less, and more preferably 3.0 or less.

  The content ratio of hydrotalcite in the positively chargeable fine particles may be, for example, 70% by mass or more, preferably 85% by mass or more, and preferably 100% by mass based on the total amount of the positively chargeable fine particles. Good. That is, the positively chargeable fine particles may be fine particles composed of hydrotalcite.

  The positively chargeable fine particles may further contain components other than hydrotalcite. Examples of other components include melamine / formaldehyde condensate, magnesium oxide, magnesium hydroxide and the like. The content of these components is preferably 30% by mass or less, for example, based on the total amount of positively chargeable fine particles.

  The content of the positively chargeable fine particles is preferably 3 parts by mass or more, more preferably 5 parts by mass or more with respect to 100 parts by mass of the matrix resin. Further, the content of the positively chargeable fine particles is preferably 30 parts by mass or less, more preferably 17 parts by mass or less with respect to 100 parts by mass of the matrix resin.

  The coating layer may further contain conductive fine particles. Examples of the conductive fine particles include carbon black fine particles, graphite fine particles, zinc oxide fine particles, and tin oxide fine particles. Carbon black fine particles are particularly preferably used.

  The average particle diameter of the conductive fine particles may be, for example, 0.01 μm or more, and preferably 0.02 μm or more. Further, the average particle diameter of the conductive fine particles may be, for example, 0.12 μm or less, and preferably 0.08 μm or less. In addition, in this specification, the average particle diameter of electroconductive fine particles shows the value measured by the average particle diameter measuring method mentioned above.

  The content of the conductive fine particles is preferably 3 parts by mass or more, more preferably 4 parts by mass or more with respect to 100 parts by mass of the matrix resin. Further, the content of the positively chargeable fine particles is preferably 12 parts by mass or less, more preferably 9 parts by mass or less with respect to 100 parts by mass of the matrix resin.

In the present embodiment, the electrophotographic carrier has a resistivity (carrier resistivity) of 1.0 × 10 ⁷ (Ω · cm) or more (more preferably 1.0 ×) by adding conductive fine particles to the coating layer. 10 ⁸ (Ω · cm) or more is preferable. This tends to prevent the problem that the carrier develops on the photoreceptor. Further, the resistivity (carrier resistivity) of the electrophotographic carrier is adjusted to 1.0 × 10 ¹² (Ω · cm) or less (more preferably 1.0 × 10 ¹¹ (Ω · cm) or less). It is preferable. This tends to prevent image quality deterioration such as missing edges. The carrier resistivity is measured by the following method.

<Measurement method of carrier resistivity>
In an environment with a temperature of 23 ° C. and a humidity of 55%, 0.2 g of carrier is sandwiched in a measurement cell with a gap of 2 mm made of a magnet having a carrier holding area of 1 cm ^2. Using a total of “SM-8220” (manufactured by Hioki Electric Co., Ltd.), the bridge resistance of the carrier is measured.

  The average particle diameter of the electrophotographic carrier according to this embodiment is preferably 20 μm or more, and more preferably 25 μm or more. The average particle size of the electrophotographic carrier is preferably 60 μm or less, and more preferably 45 μm or less. In the present specification, the average particle diameter of the electrophotographic carrier indicates a value of D50 volume diameter measured by a laser diffraction / scattering method using a “Microtrack particle size analyzer” (manufactured by Nikkiso Co., Ltd.).

  The electrophotographic carrier according to this embodiment can be used as a two-component developer in combination with a toner. Hereinafter, the two-component developer according to this embodiment will be described in detail.

(Two-component developer)
The two-component developer according to the exemplary embodiment includes the above-described electrophotographic carrier, and an electrophotographic toner having colored particles and an external additive. Since the two-component developer according to the exemplary embodiment includes the above-described electrophotographic carrier, the problem of carrier contamination due to the external additive hardly occurs, and excellent toner chargeability is maintained for a long time.

  The electrophotographic toner is not particularly limited as long as it is negatively charged and has colored particles and an external additive, and may be a known electrophotographic toner.

  The colored particles may be, for example, particles containing a binder resin and a colorant. Known binder resins and colorants can be used as the binder resin and the colorant. Examples of the binder resin include a styrene copolymer resin, a polyester resin, and a hybrid resin having a polyester unit and a vinyl polymer unit. As the colorant, organic dyes, pigments and the like can be used. In addition, it is preferable that content of the coloring agent in a colored particle is 2-25 mass parts with respect to 100 mass parts of binder resin from a viewpoint of suppressing the influence on charge provision from a carrier.

  The colored particles may further contain a release agent. Examples of the mold release agent include paraffinic wax or derivatives thereof, higher fatty acid alcohols or ester compounds thereof, higher fatty acids or ester compounds thereof. Moreover, as a mold release agent, paraffin type wax and ester type wax (ester of higher fatty acid alcohol, ester of higher fatty acid, etc.) are preferable. The content of the release agent in the colored particles may be, for example, 4 to 12 parts by mass with respect to 100 parts by mass of the binder resin.

  The colored particles may further contain other components other than those described above. For example, the colored particles may further contain a charge control agent. Examples of charge control agents include metal compounds of aromatic carboxylic acids such as salicylic acid, metal salts or metal complexes of azo dyes or azo pigments, polymer compounds having a sulfonic acid or carboxylic acid group in the side chain, boron compounds, A urea compound, a silicon compound, calixarene, etc. are mentioned. The content of the charge control agent in the colored particles may be, for example, 2 to 8 parts by mass with respect to 100 parts by mass of the binder resin.

  The external additive is not particularly limited, and a known external additive can be used. For example, the external additive may be hydrophobized inorganic fine particles (hereinafter also referred to as “hydrophobized inorganic fine particles”).

  Specific examples of the hydrophobized inorganic fine particles include hydrophobized spherical silica (hydrophobized spherical silica), hydrophobized titanium dioxide particles (hydrophobized titanium dioxide particles), zinc oxide (hydrophobized zinc oxide particles), And strontium titanate (hydrophobized strontium titanate particles). The degree of hydrophobicity of the hydrophobized inorganic fine particles is not particularly limited, and may be, for example, 50% or more, preferably 55% or more, more preferably 60% or more. Further, the degree of hydrophobicity of the hydrophobic inorganic fine particles may be, for example, 99.5% or less. In the present specification, the degree of hydrophobicity indicates the degree of hydrophobicity measured by a methanol titration test.

  In a preferred embodiment, the external additive may contain hydrophobized spherical silica. Since the hydrophobized spherical silica is spherical, it generally tends to be detached from the toner surface, and the problem of carrier contamination is likely to occur. For this reason, when the external additive contains hydrophobized spherical silica, the effect of the above-described electrophotographic carrier is remarkably exhibited.

  In the above embodiment, the average particle diameter of the hydrophobized spherical silica may be 30 to 80 nm or 20 to 120 nm. Since such hydrophobic spherical silica has a small particle size, it is generally easily detached from the toner surface and easily embedded in a carrier coating layer. For this reason, when the external additive contains the hydrophobized spherical silica having the above average particle diameter, the effect of the above-described electrophotographic carrier is more remarkably exhibited.

  In a preferred embodiment, the external additive may contain hydrophobized titanium dioxide particles. Hydrophobized titanium dioxide particles are useful as an external additive, but have a large influence on charging inhibition due to adhesion to the carrier surface. For this reason, when the external additive contains hydrophobized titanium dioxide particles, the effect of the above-described electrophotographic carrier is remarkably exhibited.

  In the above embodiment, the average particle diameter of the hydrophobized titanium dioxide particles may be 10 to 30 nm, or 8 to 60 nm. Since such hydrophobized titanium dioxide particles have a small particle size, they are generally easily detached from the toner surface and easily contaminate the carrier surface. For this reason, when the external additive contains the hydrophobized titanium dioxide particles having the above average particle diameter, the effect of the above-described electrophotographic carrier is more remarkably exhibited.

  The external additive is not limited to the above. For example, the external additive may contain hydrophobized silica (having an average particle size smaller than that of the above-mentioned hydrophobized spherical silica) for the purpose of imparting fluidity to the toner. Further, the external additive may contain cerium oxide, alumina, magnetite, etc. for the purpose of polishing deposits on the surface of the photoreceptor.

  The amount of the external additive is not particularly limited, and may be, for example, 2 parts by mass or more, preferably 3 parts by mass or more with respect to 100 parts by mass of the colored particles. Further, the amount of the external additive may be, for example, 8 parts by mass or less, and preferably 6 parts by mass or less with respect to 100 parts by mass of the colored particles.

  The toner for electrophotography preferably has a weight average molecular weight of 20,000 to 500,000 (preferably 25,000 to 300,000). In the present specification, the weight average molecular weight of the electrophotographic toner refers to the THF soluble content obtained by analyzing the tetrahydrofuran (THF) soluble content of the electrophotographic toner by gel permeation chromatography (GPC) method. The weight average molecular weight is shown. The weight average molecular weight of the THF soluble component in the electrophotographic toner is determined by the above-described method for measuring the weight average molecular weight of the THF soluble component using the electrophotographic toner as a measurement target.

  The average particle size of the electrophotographic toner is preferably 3 μm or more, and more preferably 4 μm or more. The average particle size of the electrophotographic toner is preferably 9 μm or less, and more preferably 7 μm or less. By combining with an electrophotographic toner having such an average particle size, the above-described effects of the electrophotographic carrier are remarkably exhibited. In the present specification, the average particle diameter of the electrophotographic toner indicates a value of D50 volume diameter measured using a multisizer III (manufactured by Beckman-Coulter) which is a Coulter counter.

  The average circularity of the electrophotographic toner is preferably 0.940 or more, and more preferably 0.950 or more. The average circularity of the electrophotographic toner may be 0.990 or less and 0.980 or less.

  The content of the electrophotographic toner in the two-component developer according to this embodiment may be, for example, 3% by mass or more, preferably 3.5% by mass or more, and more preferably 4% by mass or more. The toner content in the two-component developer may be, for example, 15% by mass or less, preferably 14% by mass or less, and more preferably 13% by mass or less. This tends to ensure an appropriate charge amount.

  The two-component developer according to the exemplary embodiment can be suitably used for a developing method using an electrophotographic method, an image forming method, and an image forming apparatus. The developing method, the image forming method, and the image forming apparatus are not particularly limited, and may be a known developing method, image forming method, and image forming apparatus.

  As a preferred embodiment, the two-component developer is used in a developing method, an image forming method and an image forming apparatus using a developing sleeve to which an AC bias voltage having a peak peak value of 300 to 700 V and a frequency of 3 to 8 KHz is applied. You can do it.

  FIG. 1 is a schematic diagram illustrating an example of an image forming apparatus in which the two-component developer according to the present embodiment is used. The image forming apparatus 100 includes a first image forming unit (Pa), a second image forming unit (Pb), a third image forming unit (Pc), and a fourth image forming unit (Pd), each having a different color toner. An image is formed on a transfer material through a latent image forming process, a developing process, and a transfer process.

  The configuration of each image forming unit will be described by taking the first image forming unit (Pa) as an example. The first image forming unit (Pa) includes a photoreceptor 11a as an electrostatic latent image carrier, and the photoreceptor 11a rotates in the direction of arrow a. The charging roller 12a is disposed so as to contact the surface of the photoreceptor 11a. In order to form an electrostatic latent image on the photoreceptor 11a whose surface is uniformly charged by the charging roller 12a, exposure light 17a is irradiated from an exposure device (not shown). The developing device 13a holds toner and develops the electrostatic latent image carried on the photoreceptor 11a to form a toner image. The transfer roller 14 a transfers the toner image formed on the surface of the photoconductor 11 a onto the surface of the transfer material conveyed by the belt-shaped transfer material carrier 18.

  In this manner, each toner is sequentially transferred to the transfer material in each image forming unit, and each toner image is superimposed on the same transfer material by one movement of the transfer material. Then, the transfer material is separated from the transfer material carrier 18 and sent to the fixing device 20 by the conveying means. The fixing device 20 includes a fixing roller 21 and a pressure roller 22, and the fixing roller 21 includes heating units 25 and 26 therein. The unfixed toner image transferred onto the transfer material is fixed onto the transfer material by passing through the pressure contact portion between the fixing roller 21 and the pressure roller 22. The image forming apparatus 100 includes a transfer belt cleaning device 29, a belt follower roller 31, a belt static eliminator 32, a registration roller 33, and the like as configurations other than those described above. Further, when the toner is consumed by the development and the toner (mass%) in the developer decreases, the toner concentration detection sensor 35 detects that the replenishment developer is supplied from the replenishment developer container 15a according to the consumed toner amount. To be replenished.

  The preferred embodiment of the present invention has been described above, but the present invention is not limited to the above embodiment.

  EXAMPLES Hereinafter, although an Example demonstrates this invention more concretely, this invention is not limited to an Example.

Example 1
<Preparation of magnetic particles>
The Mn content is 21.0 mol% in terms of MnO, the Mg content is 3.3 mol% in terms of MgO, the Sr content is 0.7 mol% in terms of SrO, and the Fe content is 75.0 mol% in terms of Fe ₂ O _3. Magnetic particles made of the above ferrite were prepared by the following procedure.

Commercially available MnCO ₃ , Mg (OH) ₂ , SrCO ₃ and Fe ₂ O ₃ were appropriately blended so that the respective contents of Mn, Mg, Sr, and Fe would be the values described above, and then water was added to the ball mill ( And then pulverized and mixed for 10 hours. After pulverization and mixing, the calcined ferrite was obtained by firing at 950 ° C. for 4 hours. After coarsely pulverizing the calcined ferrite, water was added again and pulverized with a ball mill for 24 hours to obtain a ferrite slurry. After adding 2 parts by mass of polyvinyl alcohol to 100 parts by mass of the obtained ferrite slurry, and further adding a suitable amount of silica particles and ammonium polycarboxylate as a dispersing agent to stabilize the dispersion state, a spray dryer (manufactured by OHKAWARAKAKOHKI) ) To obtain spherical particles of about 40 μm. The obtained spherical particles were baked at 1100 ° C. for 4 hours in a nitrogen atmosphere, and then the aggregated particles were crushed and coarse particles were removed by sieving to obtain magnetic particles (A-1).

<Preparation of resin solution for coating layer>
20 parts by mass of methyl methacrylate / styrene copolymer (molar ratio 84/16) is dissolved in 2000 parts by mass of toluene, 2 parts by mass of carbon black (manufactured by CABOT), polytetrafluoroethylene particles (average particle size 0.3 μm) 2 parts by mass and 2 parts by mass of hydrotalcite particles (average particle size 0.3 μm) were added and mixed to obtain a resin solution for forming a resin layer (B-1).

<Manufacture of electrophotographic carrier>
Using SPIRA COTA (manufactured by OKADA SEIKO), the resin component for coating layer formation (B-1) was heated to 70 ° C. in a heated atmosphere at 2 parts by mass with respect to 100 parts by mass of the magnetic particles (A-1). It apply | coated so that it might become a mass part, and it heated at 100 degreeC for 5 hours, and removed toluene. Thereafter, using a sieve shaker (manufactured by KOEI SANGYO), coarse particles were removed with a sieve having an opening of 75 μm to obtain an electrophotographic carrier (C-1).

<Manufacture of toner for electrophotography>
For 100 parts by weight of colored particles having an average particle diameter of 6.8 μm, 2.5 parts by weight of hydrophobic spherical silica having an average particle diameter of 70 nm, 1.2 parts by weight of hydrophobic titanium dioxide particles having an average particle diameter of 20 nm, and an average particle diameter 0.6 parts by mass of 12 nm hydrophobized silica (Aerosil RX200, manufactured by Nippon Aerosil Co., Ltd.) and 0.3 parts by mass of cerium oxide were added, dispersed and mixed with a Henschel mixer, and the toner for electrophotography (T-1) was added. Obtained.

<Manufacture of two-component developer>
90 parts by weight of the electrophotographic carrier (C-1) and 10 parts by weight of the electrophotographic toner (T-1) were mixed with a V-type mixer to obtain a two-component developer (D-1).

<Evaluation of actual machine 1. Evaluation of Ti contamination amount>
Using a printer CLX-9201NA manufactured by Samsung, continuous printing was performed by adjusting the printing area so that the toner consumption was 80 g / 1000 sheets (A4) in a high temperature and high humidity environment of 30 degrees and 85%. Only toner was used in the toner cartridge without a carrier.

  After printing a predetermined amount, the toner is separated from the developer, and the intensity of the Ti peak derived from titanium dioxide adhering to the carrier by a loose powder method in a vacuum atmosphere using a fluorescent X-ray analyzer EDXL300 (manufactured by Rigaku Corporation) Was measured. This peak intensity was regarded as the amount of contamination by Ti.

  Printing was performed up to 40 kpv (40000 continuous prints), and the relationship between the print amount and the contamination amount was graphed. The results are shown in FIG. Note that the Ti increase rate in FIG. 1 indicates the increase rate with respect to the analysis value immediately after the start of printing.

<Evaluation of actual machine 2. Evaluation of toner charge amount>
Evaluation of actual machine The continuous printing was performed in the same manner as in the above. For the developer after printing a predetermined amount, the charge amount and the toner under the conditions of applied voltage / application time / rotation number DC-3.0 kv / 30 sec / 2000 rpm using an electric field flight type charge amount measuring device (manufactured by DIT). The concentration was measured to determine the charge amount per unit mass.

  Printing was performed up to 40 kpv (40000 continuous prints), and the relationship between the print amount and the charge amount was graphed. The results are shown in FIG. The charge amount maintenance rate in FIG. 3 indicates the maintenance rate with respect to the analysis value immediately after the start of printing. In Example 1, the charge amount retention rate at the time of 40 kpv was 60.4%.

(Comparative Example 1)
An electrophotographic carrier and a two-component developer were produced in the same manner as in Example 1 except that the polytetrafluoroethylene particles were not added when the coating layer resin solution was prepared.

  The obtained two-component developer was evaluated in the same manner as in Example 1. The results are shown in FIGS. In Comparative Example 1, the charge amount retention rate at the time of 40 kpv was 25.5%.

  As shown in FIGS. 2 and 3, in Comparative Example 1, the carrier surface was gradually contaminated by the printing operation, and the toner charge amount was reduced. On the other hand, in Example 1, contamination of the carrier surface was suppressed and the toner charge amount was maintained at a high rate.

(Example 2)
Example 1 except that tetrafluoroethylene-ethylene copolymer particles (content ratio of tetrafluoroethylene units 90 mol%) were used in place of the polytetrafluoroethylene particles when preparing the resin solution for the coating layer. Similarly, an electrophotographic carrier and a two-component developer were produced.

  About the obtained two-component developer, the same evaluation as in Example 1 The charge amount maintenance rate at 40 kpv was determined. As a result, the charge retention rate at the time of 40 kpv was 60.9%.

(Example 3)
Except that, instead of polytetrafluoroethylene particles, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer particles (tetrafluoroethylene unit content ratio of 80 mol%) were used in the preparation of the resin solution for the coating layer. In the same manner as in Example 1, an electrophotographic carrier and a two-component developer were produced.

  About the obtained two-component developer, the same evaluation as in Example 1 The charge amount maintenance rate at 40 kpv was determined. As a result, the charge retention rate at the time of 40 kpv was 60.9%.

Example 4
Example 1 except that tetrafluoroethylene-ethylene copolymer particles (tetrafluoroethylene unit content ratio 70 mol%) were used in place of the polytetrafluoroethylene particles when preparing the resin solution for the coating layer. Similarly, an electrophotographic carrier and a two-component developer were produced.

  About the obtained two-component developer, the same evaluation as in Example 1 The charge amount maintenance rate at 40 kpv was determined. As a result, the charge amount retention rate at the time of 40 kpv was 60.1%.

(Example 5)
Example except that tetrafluoroethylene-hexafluoropropylene copolymer particles (tetrafluoroethylene unit content ratio 60 mol%) were used instead of polytetrafluoroethylene particles when preparing the resin solution for the coating layer. In the same manner as in Example 1, an electrophotographic carrier and a two-component developer were produced.

  About the obtained two-component developer, the same evaluation as in Example 1 The charge amount maintenance rate at 40 kpv was determined. As a result, the charge amount retention rate at the time of 40 kpv was 61.0%.

(Example 6)
Example 1 except that tetrafluoroethylene-ethylene copolymer particles (content ratio of tetrafluoroethylene units) were used in place of the polytetrafluoroethylene particles when preparing the resin solution for the coating layer. Similarly, an electrophotographic carrier and a two-component developer were produced.

  About the obtained two-component developer, the same evaluation as in Example 1 The charge amount maintenance rate at 40 kpv was determined. As a result, the charge amount retention rate at the time of 40 kpv was 60.2%.

(Comparative Example 2)
Example 1 except that tetrafluoroethylene-ethylene copolymer particles (content ratio of tetrafluoroethylene units) were used in place of the polytetrafluoroethylene particles when preparing the resin solution for the coating layer. Similarly, an electrophotographic carrier and a two-component developer were produced.

  About the obtained two-component developer, the same evaluation as in Example 1 The charge amount maintenance rate at 40 kpv was determined. As a result, the charge amount retention rate at the time of 40 kpv was 53.0%.

(Comparative Example 3)
Example 1 except that tetrafluoroethylene-ethylene copolymer particles (content ratio of tetrafluoroethylene units 30 mol%) were used instead of polytetrafluoroethylene particles when preparing the resin solution for the coating layer. Similarly, an electrophotographic carrier and a two-component developer were produced.

  About the obtained two-component developer, the same evaluation as in Example 1 The charge amount maintenance rate at 40 kpv was determined. As a result, the charge amount retention rate at the time of 40 kpv was 50.0%.

(Comparative Example 4)
Example 1 except that tetrafluoroethylene-ethylene copolymer particles (content ratio of tetrafluoroethylene units 20 mol%) were used instead of polytetrafluoroethylene particles when preparing the resin solution for the coating layer. Similarly, an electrophotographic carrier and a two-component developer were produced.

  About the obtained two-component developer, the same evaluation as in Example 1 The charge amount maintenance rate at 40 kpv was determined. As a result, the charge amount retention rate at the time of 40 kpv was 38.0%.

(Comparative Example 5)
Example 1 except that tetrafluoroethylene-ethylene copolymer particles (content ratio of tetrafluoroethylene units) were used in place of the polytetrafluoroethylene particles when preparing the resin solution for the coating layer. Similarly, an electrophotographic carrier and a two-component developer were produced.

  About the obtained two-component developer, the same evaluation as in Example 1 The charge amount maintenance rate at 40 kpv was determined. As a result, the charge amount retention rate at the time of 40 kpv was 36.0%.

  FIG. 4 is a diagram illustrating evaluation results of toner charge amounts in Examples 1 to 6 and Comparative Examples 1 to 5. In FIG. 4, the TFE component ratio indicates the content ratio of tetrafluoroethylene units in the fluorine-containing resin constituting the fluorine-containing particles.

  DESCRIPTION OF SYMBOLS 100 ... Image forming apparatus, 11a ... Photoconductor, 12a ... Charging roller, 13a ... Developer, 14a ... Transfer roller, 15a ... Developer container, 18 ... Transfer material carrier, 19 ... Separation charger, 20 ... Fixing Device: 21 ... Fixing roller, 22: Pressure roller, 25,26 ... Heating means, 29 ... Transfer belt cleaning device, 31 ... Belt following roller, 32 ... Belt neutralizer, 33 ... Registration roller, 35 ... Toner density detection Sensor.

Claims (15)

Magnetic particles and a coating layer covering the magnetic particles,
The coating layer includes a matrix resin containing a thermoplastic acrylic resin, fluorine-containing fine particles having an average particle size of 0.1 to 0.6 μm dispersed in the matrix resin, and an average particle dispersed in the matrix resin. Positively chargeable fine particles having a diameter of 0.1 to 0.6 μm,
The electrophotographic carrier, wherein the fluorine-containing fine particles contain a fluorine-containing resin having a tetrafluoroethylene unit content ratio of 45 mol% or more based on the total amount of monomer units. The fluororesin is at least selected from the group consisting of polytetrafluoroethylene, tetrafluoroethylene-perfluoroalkyl vinyl ether copolymer, tetrafluoroethylene-hexafluoropropylene copolymer and tetrafluoroethylene-ethylene copolymer. Including one kind,
2. The electrophotographic carrier according to claim 1, wherein the content of the fluorine-containing fine particles is 3 to 30 parts by mass with respect to 100 parts by mass of the matrix resin. The positively chargeable fine particles include hydrotalcite containing an aluminum element and a magnesium element,
The molar ratio of the magnesium element to the aluminum element is 0.25 or more and 3.50 or less,
The electrophotographic carrier according to claim 1, wherein the content of the positively chargeable fine particles is 3 parts by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the matrix resin. The content ratio of the soluble component to tetrahydrofuran in the matrix resin is 90% by mass or more,
The carrier for electrophotography as described in any one of Claims 1-3 whose weight average molecular weights of the said soluble component are 30,000-300,000. The coating layer further contains conductive fine particles,
The carrier for electrophotography according to any one of claims 1 to 4, wherein the carrier resistivity is 1.0 × 10 ⁷ (Ω · cm) or more and 1.0 × 10 ¹² (Ω · cm) or less.   The carrier for electrophotography according to any one of claims 1 to 5, wherein an average particle diameter is 20 µm or more and 60 µm or less. The electrophotographic carrier according to any one of claims 1 to 6,
An electrophotographic toner having colored particles and an external additive;
A two-component developer. The colored particles contain a binder resin, a colorant and a release agent;
The two-component developer according to claim 7, wherein the external additive contains inorganic fine particles subjected to a hydrophobic treatment.   The two-component developer according to claim 8, wherein the release agent contains at least one selected from the group consisting of paraffin wax and ester wax.   The two-component developer according to claim 8 or 9, wherein the inorganic fine particles contain spherical silica having an average particle size of 30 to 80 nm and titanium dioxide particles having an average particle size of 10 to 30 nm.   The two-component developer according to any one of claims 7 to 10, wherein the electrophotographic toner has a weight average molecular weight of 20,000 or more and 500,000 or less.   The two-component developer according to any one of claims 7 to 11, wherein an average particle diameter of the electrophotographic toner is 3 µm or more and 9 µm or less.   The two-component developer according to any one of claims 7 to 12, wherein an average circularity of the electrophotographic toner is 0.940 or more and 0.990 or less.   A development method comprising a development step of developing using the two-component developer according to any one of claims 7 to 13.   The developing method according to claim 14, wherein in the developing step, development is performed using a developing sleeve to which an AC bias voltage having a peak peak value of 300 to 700 V and a frequency of 3 to 8 KHz is applied.

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