JP5450332B2 - Positively charged dry toner for electrophotography - Google Patents

Description

  The present invention relates to a positively charged dry toner used in an electrophotographic system, a developer containing the positively charged dry toner, and a method for producing the same.

  In an image forming apparatus such as a copying machine, a printer, or a digital multifunction machine that forms an image on paper by electrophotography, an electrostatic charge image (electrostatic latent image) formed on the peripheral surface of a photosensitive drum as an image carrier. ) Is developed with toner by a developing device, and is visualized as a toner image. The toner image on the photosensitive drum is transferred onto a sheet by a transfer device, and then heated and pressed by a fixing device to be fixed on the sheet. The sheet on which the toner image is fixed is finally discharged out of the image forming apparatus.

  The toner used in such an image forming apparatus generally has a configuration in which an external additive or the like is added to core particles in which a colorant or the like is blended with a binder resin.

  As a toner binder resin, polyester resins are known to be particularly suitable for binder resins for color toners because of their excellent transparency, low temperature fixability and secondary color reproducibility. (For example, refer to Patent Document 1).

  In addition, according to the recent demand for higher image quality of formed images, the toner used in the image forming apparatus needs to be designed to have various functions. The structure which coat | covered the surface of the core particle | grain with the resin fine particle is known (for example, refer patent document 2). Furthermore, some toners having a configuration in which the surface of the pulverized toner is coated with resin fine particles have been reported (for example, Patent Documents 3 to 5).

Japanese Patent Laid-Open No. 2002-23424 JP-A-1-257854 Japanese Unexamined Patent Publication No. 57-120942 JP-A-4-3171 JP 2009-14757 A

  First, when a polyester resin is used as the binder resin, since the polyester resin is a resin having a strong negative chargeability, a charge control agent exhibiting a positive chargeability and a charge control resin are used for the positively charged toner. It was necessary to add fine particles dispersed in the resin and having strong positive charge to the toner particles.

  As such fine particles, the surface of fine particles such as silica, titanium oxide, and alumina, which is used for the purpose of improving the fluidity of the toner, has been subjected to a hydrophobic treatment. In most cases, these hydrophobized particles exhibit a negative chargeability. Therefore, in order to obtain fine particles with a strong positive charge, it was necessary to perform a positive charge process in addition to the hydrophobization process.

  However, the toner using the polyester resin and the toner added with fine particles subjected to the positive charging process in addition to the hydrophobizing process have a problem that fog is likely to occur. In particular, fog is particularly likely to occur when new toner is replenished in a state where the toner stays in the developing unit for a long time.

  However, any of the above-described prior art (Patent Documents 2 to 5) in which the surface of the toner core particles is coated with resin fine particles is compatible with both toner storage stability and fixability, and toner spent on the carrier. In order to suppress fogging when a pulverized toner having a polyester resin as a binder resin is used as a positively charged toner, a technique for coating the surface of core particles with resin fine particles is Not yet reported.

  The present invention has been made in view of the circumstances as described above, and covers 70% or more of resin particles (acrylic resin fine particles and / or methacrylic resin fine particles) on the surface of core particles made of polyester resin. Thus, an object is to suppress fogging when a pulverized toner containing a polyester resin is used as a positively charged toner.

  As a result of intensive studies, the present inventors have found that the above problems can be solved by using an electrostatic charge image developing toner having the following configuration, and have completed the present invention by further studying based on such knowledge. .

  That is, one aspect of the present invention is an electrophotographic dry toner including at least a polyester resin, a release agent, a colorant, and resin fine particles, and at least the release agent and the colorant are dispersed in the polyester resin. Thereafter, 70% or more of the surface of the core particle obtained by pulverization and classification is coated with resin fine particles, and the resin fine particles are acrylic resin fine particles or methacrylic resin fine particles, This is a positively chargeable dry toner for electrophotography.

  With such a configuration, it is possible to use a polyester resin that is excellent in transparency and can impart excellent low-temperature fixability and secondary color reproducibility to a color toner as a binder resin for a positively chargeable toner. Further, it is possible to obtain a toner that does not cause fogging even when the additive fine particles are subjected to a positive charging process.

  Although details of the mechanism that can suppress fogging are not clear, acrylic resin and methacrylic resin (acrylic resin, styrene-acrylic resin, etc.) are more positively charged than polyester resin. By covering 70% or more of the core particle surface, the positive chargeability of the toner particle surface could be improved, and the charge distribution state on the toner particle surface should be uniform (that is, not localized). It is thought that it was related to having been able to.

  Furthermore, in the said structure, it is preferable that acrylic resin microparticles | fine-particles and methacrylic resin microparticles | fine-particles are the acrylic resin microparticles | fine-particles and methacrylic resin microparticles which were produced by the emulsion polymerization method using the cationic surfactant.

  This is because resin fine particles (acrylic resin, methacrylic resin, styrene-acrylic resin, etc.) prepared by emulsion polymerization using a cationic surfactant have a higher positive chargeability than polyester resins. This is because the positive chargeability of the toner particles can be greatly enhanced by covering 70% or more of the surface of the toner particles with, for example. For this reason, it is not necessary to add fine positively charged fine particles to the toner particles, and it is possible to use fine particles having almost no positive chargeability, so that it is considered that fogging can be suppressed.

  A developer according to another aspect of the present invention includes the electrophotographic toner and a carrier. According to such a structure, generation | occurrence | production of fog can be suppressed and, therefore, a high quality image can be formed over a long period of time.

  Another aspect of the present invention is a process of obtaining core particles by dispersing and classifying at least a colorant in a polyester resin, and then obtaining the core particles, and selecting the obtained core particles from acrylic resin particles or methacrylic resin particles This is a method for producing a positively chargeable electrophotographic dry toner comprising a step of mechanically mixing with at least one resin fine particle to coat 70% or more of the surface of the core particle with the resin fine particle.

  According to the present invention, a polyester resin that is excellent in transparency and can impart excellent low-temperature fixability and secondary color reproducibility to a color toner can be used as a binder resin for a positively chargeable toner. A toner that does not cause fog in the formed image can be obtained.

[Dry toner for electrophotography]
The electrophotographic dry toner according to the present invention basically includes at least a polyester resin, a release agent, a colorant, acrylic resin fine particles, and / or methacrylic resin fine particles. Then, after dispersing at least a release agent and a colorant in the polyester resin, 70% or more of the surface of the core particle obtained by pulverization and classification is covered with acrylic resin fine particles and / or methacrylic resin fine particles. It is characterized by being.

  Hereinafter, specific embodiments of the core particles and the external additives (resin fine particles, etc.) constituting the toner of the present invention will be described in detail.

<Core particles>
In the present embodiment, the core particle is obtained by blending a binder resin with a colorant, a release agent, or the like. After these materials are dispersed, core particles are obtained by pulverization and classification.

(Binder resin)
In this embodiment, a polyester resin is used as the binder resin. As a result, it is possible to obtain a toner having excellent transparency, low-temperature fixability, secondary color reproducibility, and the like.

  Examples of the polyester resin include those obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component. Moreover, the following are mentioned as a component used when synthesize | combining a polyester-type resin.

  The alcohol component is not particularly limited as long as it can be used as an alcohol for synthesizing a polyester resin. Further, the alcohol component needs to contain an alcohol component (divalent or higher alcohol) having two or more hydroxyl groups in the molecule. Specific examples of the divalent alcohol among those used as the alcohol component include, for example, ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4- Butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol Diols such as bisphenol A, hydrogenated bisphenol A, bisphenols such as polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A, and the like. Further, among the alcohols used as the alcohol component, as the trivalent or higher alcohol, specifically, for example, sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dithiol Pentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, tri Examples include methylolethane, trimethylolpropane, 1,3,5-trihydroxymethylbenzene and the like. Moreover, as said alcohol component, said each component may be used independently and may be used in combination of 2 or more type.

  The carboxylic acid component is not particularly limited as long as it can be used as a carboxylic acid for synthesizing a polyester resin. The carboxylic acid component includes not only carboxylic acids but also acid anhydrides and lower alkyl esters of carboxylic acids. And as said carboxylic acid component, the carboxylic acid (carboxylic acid more than bivalence) which has two or more carboxyl groups in a molecule | numerator needs to be contained. Specific examples of the divalent carboxylic acid used as the carboxylic acid include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, and cyclohexanedicarboxylic acid. Examples include acids, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, alkyl succinic acid, and alkenyl succinic acid. Examples of the alkyl succinic acid include n-butyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid and the like. Examples of the alkenyl succinic acid include n-butenyl succinic acid and isobutyl succinic acid. , Isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, isododecenyl succinic acid and the like. Further, among the carboxylic acids used as the carboxylic acid, the trivalent or higher carboxylic acid specifically includes, for example, 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid. Acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2 -Methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, empole trimer acid, etc. Can be mentioned. Moreover, as said carboxylic acid component, said each component may be used independently and may be used in combination of 2 or more type.

  The glass transition temperature of the polyester resin as the binder resin is, for example, preferably 50 to 70 ° C, and more preferably 55 to 65 ° C. When the glass transition temperature is less than 50 ° C., the toner is fused in the developing device during operation of the image forming apparatus, or the toner is fused in the container during storage or transportation of the toner. There is a tendency for stability to decrease. On the other hand, when the glass transition temperature exceeds 70 ° C., the low-temperature fixability of the toner tends to decrease.

(Coloring agent)
In the present embodiment, as the colorant, those conventionally used as colorants for monochrome toners or color toners can be used without particular limitation. Specific examples thereof include black pigments such as carbon black, yellow pigments such as pigment yellow 180, orange pigments such as molybdenum orange, C.I. I. Examples thereof include red pigments such as Pigment Red 238, purple pigments such as methyl violet lake, blue pigments such as phthalocyanine blue, green pigments such as Pigment Green B, and various dyes.

  In this embodiment, the compounding quantity of a coloring agent is 1-15 mass parts with respect to 100 mass parts of binder resin, for example.

(Release agent)
In the present embodiment, the release agent is blended for the purpose of improving the fixing property of the toner and preventing the deterioration of the offset property. As the release agent, those conventionally used as a release agent for toner base particles can be used without particular limitation. Specific examples thereof include polyethylene wax, polypropylene wax, Teflon (registered trademark) wax, Fischer-Tropsch wax, paraffin wax, ester wax, carbana wax, montan wax, rice wax, and the like. These may be used alone or in combination of two or more.

  In this embodiment, the compounding quantity of a mold release agent is 1-10 mass parts with respect to 100 mass parts of binder resin, for example. When the blending amount of the release agent is less than 1 part by mass, there is a tendency that improvement in toner fixing property and prevention of deterioration in offset property are not satisfactorily achieved. On the other hand, when the compounding amount of the release agent exceeds 10 parts by mass, the toners are fused with each other, and the storage stability of the toner tends to be lowered.

(Charge control agent)
In addition to the above, the toner of this embodiment may contain a charge control agent. The charge control agent is blended for the purpose of maintaining the charge amount of the toner and improving the charge rising characteristic (characteristic of charging to a predetermined charge amount in a short time). Since the toner of this embodiment is positively charged, a positively chargeable charge control agent is used.

  In this embodiment, as the positively chargeable charge control agent, those conventionally used as the positively chargeable charge control agent for the toner base particles can be used without any particular limitation. Specific examples thereof include azine compounds such as pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, and 1,2,3-triazine. These may be used alone or in combination of two or more.

  In the present embodiment, the blending amount when blending the charge control agent is, for example, 0.5 to 15 parts by mass with respect to 100 parts by mass of the binder resin. When the blending amount of the charge control agent is less than 0.5 parts by mass, the image density tends to decrease or the fogging increases. On the other hand, when the blending amount of the charge control agent exceeds 15 parts by mass, there is a tendency that charging failure and image failure are likely to occur under high temperature and high humidity.

(Process for producing core particles)
The method for producing the core particles is not particularly limited, but can be produced, for example, as follows.

  First, the core particle raw materials as described above are mixed with a mixer or the like. As the mixer, a known one can be used, and examples thereof include a Henschel type mixing device such as a Henschel mixer, a super mixer, and a mechano mill, an ang mill, a hybridization system, and a cosmo system.

  Next, the obtained mixture is melt-kneaded with a kneader or the like. A well-known thing can be used as said kneading machine, For example, a twin-screw extruder, a three roll mill, a lab blast mill etc. are mentioned, A twin-screw extruder is used suitably. Further, the temperature at the time of melt kneading is preferably a temperature that is not less than the softening point of the polyester resin and lower than the thermal decomposition temperature of the polyester resin.

  Next, the obtained melt-kneaded product is cooled to form a solid, and the solid is pulverized by a pulverizer or the like. As the pulverizer, known pulverizers can be used. For example, an air pulverizer such as a jet pulverizer (jet mill) that pulverizes using a supersonic jet stream, a mechanical pulverizer such as a turbo mill, or an impact pulverizer. Examples thereof include a pulverizer, and a mechanical pulverizer, particularly a turbo mill, is preferably used.

  Finally, the obtained pulverized product is classified with a classifier or the like. By classifying, excessively pulverized material and coarse powder can be removed, and desired core particles can be obtained. As the classifier, a known one can be used, for example, a wind classifier such as a swirl wind classifier (rotary wind classifier) such as an elbow jet, a centrifugal classifier, etc., In particular, an elbow jet is preferably used.

  The volume average particle diameter of the core particles thus obtained is 5 to 10 μm, more preferably 6 to 8 μm, and further preferably 6 to 8 μm.

<External additive>
(Resin fine particles)
First, one feature of the toner according to the present embodiment is that the surface of the core particle is coated with resin fine particles.

  In this embodiment, the core particle coverage with the resin fine particles is not particularly limited as long as it is 70% or more. For example, the core particles may be 100% coated with the resin fine particles. From the standpoint that the effects of the present invention can be obtained, the higher the covering ratio, the better. However, if the covering ratio is too high, the covering process for that takes time and cost, and the productivity may decrease. Therefore, from the viewpoints of both the effect of the present invention and productivity, the preferable coverage is 70 to 90%, more preferably 75 to 90%.

  The resin fine particles in the present embodiment are at least one selected from acrylic resin fine particles or methacrylic resin fine particles. The acrylic resin fine particles and the methacrylic resin fine particles are not particularly limited as long as they can be used as an external additive of the toner. For example, acrylic resin fine particles mainly containing an acrylic resin, methacrylic resin Methacrylic resin fine particles having a main component, resin fine particles obtained by copolymerizing two or more kinds of acrylic resin monomers and methacrylic resin monomers, acrylic resin monomers or methacrylic resin monomers and styrene, α-methylstyrene, Resin fine particles obtained by copolymerizing two or more kinds of vinyl monomers such as vinyl bromide, vinyl chloride, vinyl acetate, acrylonitrile and methacrylonitrile can be used. More specifically, styrene-methyl acrylate, styrene-ethyl acrylate, styrene-butyl acrylate, styrene-methyl methacrylate, styrene-ethyl methacrylate, and other styrene-acrylic resins, butyl acrylate, methyl methacrylate. Acrylic resins such as butyl methacrylate and butyl acrylate-butyl methacrylate are preferably used.

  Moreover, it is preferable that the average primary particle diameter of resin fine particles exists in the range of 50-1000 nm. More preferably, it exists in the range of 100-500 nm. If the particle diameter is less than 50 nm, the thickness of the resin fine particle layer formed on the surface of the core particle becomes thin, so that it becomes difficult to control, and a uniform resin particle layer cannot be obtained on the core particle surface. On the other hand, if the thickness exceeds 1000 nm, the resin fine particle layer becomes too thick or the resin fine particles are detached from the surface of the core particle, so that a uniform resin fine particle layer cannot be formed. In addition, the average primary particle diameter of the resin fine particles can be measured by, for example, a field emission scanning electron microscope (manufactured by JEOL Ltd., JSM-7700F).

(Production method of resin fine particles)
As a method for producing such resin fine particles, a method of producing the resin fine particles by emulsion polymerization using a surfactant is preferable. More preferably, a cationic surfactant is used.

  Specifically, for example, by using a cationic surfactant, a polymer dispersion is prepared by an emulsion polymerization method as described in the following examples, and freeze-dried and used in this embodiment. Obtained resin fine particles can be obtained.

  Acrylic resin fine particles and methacrylic resin fine particles obtained by this method have a higher positive chargeability than polyester resin, so that the positive chargeability of toner particles is greatly enhanced by coating with these resin fine particles. Can do. As a result, it is not necessary to add fine particles having a strong positive charge to the toner particles as an external additive, and fine particles having almost no positive charge can be used as an external additive, so that fog is effectively suppressed. It becomes possible.

  In this embodiment, examples of the cationic surfactant that can be used for emulsion polymerization include, but are not limited to, alkylamine salts and alkyl quaternary ammonium salts.

  Further, the amount of the resin fine particles added may be appropriately adjusted so that 70% or more of the surface of the core particles is covered with the resin fine particles. The value is preferably within the range of parts. If the addition amount of the resin fine particles is less than 1 part by mass, the coating with the resin fine particles becomes insufficient, and if it exceeds 20 parts by mass, the resin fine particles are aggregated and it is difficult to coat the surface of the core particles.

(Coating method)
The method for coating the core particles with the resin fine particles is not particularly limited as long as 70% or more of the surface of the core particles is covered with the resin fine particles. Specific examples include coating by mechanical impact, thermal fusion, and coating by adhesion. The mechanical impact can be performed by, for example, stirring and mixing, but the stirring and mixing is preferably performed using a Henschel mixer, a turbuler mixer, a super mixer, or the like. More specifically, for example, the coating can be performed by the method described in Examples described later.

(Other)
The toner according to the exemplary embodiment may further include inorganic fine particles as an external additive. By including inorganic fine particles as an external additive, the flowability of the developer can be appropriately adjusted.

  As the usable inorganic fine particles, those conventionally used as external additives added to toner base particles can be used without particular limitation. Specific examples thereof include inorganic fine particles represented by silica, titanium oxide, aluminum oxide, magnetite and the like used as an abrasive.

  In addition, for these inorganic fine particles, depending on the situation, the surface can be changed by using silicone oil, silane coupling agents such as aminosilane, hexamethyldisilazane, etc., or titanate coupling agents. Is preferably hydrophobized. More specifically, for example, the silica fine particles can be subjected to a hydrophobic treatment with an organosilicon compound such as dimethylpolysiloxane.

  Since the fine particles subjected to such a hydrophobic treatment usually exhibit negative chargeability, conventionally, when added to a positively charged toner, it has been necessary to perform a positive charge treatment in addition to the hydrophobic treatment. The toner to which fine particles subjected to a positive charging process in addition to the hydrophobizing process are added has a drawback that fog is likely to occur. However, in the toner according to the present embodiment, since the positive chargeability of the toner particles after adding the resin fine particles is high, it is not necessary to use positively charged fine particles that have been positively charged. It is also possible to use inorganic fine particles or negatively charged inorganic fine particles, which is very useful.

  The average primary particle diameter of the inorganic fine particles used in the present invention is usually 10 to 300 nm, preferably 15 to 200 nm. If the particle size of the inorganic fine particles is less than 10 nm, the change in toner characteristics increases as the inorganic fine particles are embedded in the toner particles with use, and if it exceeds 300 nm, it becomes difficult to fix the inorganic fine particles on the surface of the toner particles. It is.

  Further, the amount of inorganic fine particles added is preferably set to a value within the range of 0.2 to 3 parts by weight with respect to 100 parts by weight of the toner base particles. If the added amount of the inorganic fine particles is less than 0.2 parts by weight, the fluidity of the toner becomes too low and the toner cleaning performance cannot be secured, and if it exceeds 3 parts by weight, the toner particles are easily detached from the toner particles. Therefore, the toner charge amount decreases with use, and the image quality of the image and scattering in the toner occur.

  The process of externally adding the inorganic fine particles to the core particles is performed by, for example, dry stirring and mixing the core particles coated with the resin fine particles and the inorganic fine particles. In that case, the stirring and mixing is preferably performed using a Henschel mixer, a turbuler mixer, a super mixer, or the like so that the inorganic fine particles are not buried in the surface of the core particles.

  Further, in the toner of the present embodiment, in addition to the resin fine particles and the inorganic fine particles, those conventionally used as external additives for the toner can be used in combination without limitation as necessary. it can. The external addition treatment of other components can be performed in the same manner as the external addition treatment of the inorganic fine particles.

[Developer]
The developer containing the toner may be a one-component developer containing the toner and no carrier, or a two-component developer containing the toner and a carrier. A developer is preferably used. Here, the two-component developer will be described. Note that a developer according to another embodiment of the present invention includes the electrophotographic toner and a carrier.

<Career>
In the present invention, any carrier that has been conventionally used as a carrier for two-component developers can be used without any particular limitation. As a specific example, for example, a carrier core material whose surface is coated with a resin can be used.

  Examples of the carrier core material include magnetic metals such as iron, nickel, cobalt, alloys thereof, alloys containing rare earths, hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium. Magnetic particles produced by sintering and atomizing magnetic materials such as soft ferrites such as ferrite and lithium ferrite, iron oxides such as copper-zinc ferrite, and mixtures thereof. .

  Examples of the resin that covers the surface of the carrier core material include polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, tetrafluoroethylene / hexafluoropropylene copolymer (FEP), and tetrafluoroethylene. In addition to fluororesin such as perfluoroalkoxyethylene copolymer (PFA), polyamideimide resin, acrylic resin, straight silicon, etc. can be used.

The particle diameter of the carrier is 15 to 100 μm, more preferably 20 to 70 μm, still more preferably 25 to 50 μm, as measured by electron microscopy. The apparent specific gravity of the carrier varies depending on the composition of the magnetic material, the surface structure, and the like, but is generally preferably in the range of 3000 to 8000 kg / m ³ .

  The two-component developer can be produced by mixing the toner and the carrier in a dry manner using, for example, a ball mill. The toner concentration in the two-component developer is 3 to 20% by weight, more preferably 5 to 15% by weight, and still more preferably 6 to 10% by weight. When the toner density is less than 3% by weight, the image density tends to be excessively thin. On the other hand, when the toner concentration exceeds 20% by weight, the toner is scattered from the developing device during operation of the image forming apparatus, and there is a tendency for fogging and contamination in the image forming apparatus to increase.

  Hereinafter, the present invention will be described in more detail through examples. In addition, this invention is not limited at all by this Example.

[Manufacture of resin fine particles]
・ Resin fine particles A
A 1000 mL reactor equipped with a stirrer, a condenser, and a temperature sensor was charged with 450 mL of distilled water and 0.56 g of sodium dodecyl sulfate, and the mixture was heated to 80 ° C. while stirring under a nitrogen stream. 120 g of aqueous potassium sulfate solution was added. Next, a monomer mixture of 140 g of styrene, 30 g of methyl methacrylate, and 3.6 g of n-octyl mercaptan was added over 1.5 hours, and the mixture was further maintained for 2 hours to complete the polymerization. After completion of the polymerization reaction, the content was cooled to room temperature to obtain a polymer dispersion liquid. Thereafter, it was dried by freeze drying to obtain resin fine particles A.

・ Resin fine particle B
A 1000 mL reactor equipped with a stirrer, a cooling tube, and a temperature sensor was charged with 450 mL of distilled water and 0.52 g of dodecyl ammonium chloride, heated to 80 ° C. with stirring under a nitrogen stream, and 1 wt% excess was added thereto. 120 g of aqueous potassium sulfate solution was added. Next, a monomer mixture of 140 g of styrene, 30 g of methyl methacrylate, and 3.6 g of n-octyl mercaptan was added over 1.5 hours, and the mixture was further maintained for 2 hours to complete the polymerization. After completion of the polymerization reaction, the content was cooled to room temperature to obtain a polymer dispersion liquid. Thereafter, it was dried by freeze drying to obtain resin fine particles B.

・ Resin fine particle C
A 1000 mL reactor equipped with a stirrer, a cooling tube, and a temperature sensor was charged with 450 mL of distilled water and 0.52 g of dodecyl ammonium chloride, heated to 80 ° C. with stirring under a nitrogen stream, and 1 wt% excess was added thereto. 120 g of aqueous potassium sulfate solution was added. Next, a monomer mixed solution of 15 g of butyl acrylate, 165 g of methyl methacrylate, and 3.6 g of n-octyl mercaptan was added over 1.5 hours, and then maintained for another 2 hours to complete the polymerization. After completion of the polymerization reaction, the content was cooled to room temperature to obtain a polymer dispersion liquid. Thereafter, the resin fine particles C were obtained by drying by freeze drying.

［トナーの製造］
（実施例１のトナー）
まず、結着樹脂として、ポリエステル系樹脂（酸価：５．６ｍｇＫＯＨ／ｇ、融点：１２０℃）１００質量部、着色剤として、銅フタロシアニン顔料（クラリアントジャパン株式会社製のＣ．Ｉ．Ｐｉｇｍｅｎｔ Ｂｌｕｅ １５：３）４質量部、ワックスとして、カルナバワックス（融点８２℃）５質量部、電荷制御剤として、４級アンモニウム塩化合物（オリエント化学工業株式会社製のＰ−５１）１質量部を、ヘンシェルミキサ（日本コークス工業株式会社製）で５分間混合した。その後、得られた混合物を２軸押出機（株式会社池貝製のＰＣＭ−３０型）で溶融混練した。そして、混練物を冷却後、得られた溶融混練物を気流式粉砕機（ターボ工業株式会社製のターボミル）で微粉砕し、風力分級機（日鉄鉱業株式会社製のＥＪ−ＬＡＢＯ）で分級処理した。そうすることによって、体積平均径６．７μｍのポリエステルトナー（コア粒子）が得られた。なお、コア粒子の体積平均径は、粒度計（ベックマンコールター株式会社製のマルチサイザー３）によって、測定した。

[Production of toner]
(Toner of Example 1)
First, 100 parts by mass of a polyester resin (acid value: 5.6 mg KOH / g, melting point: 120 ° C.) as a binder resin, and copper phthalocyanine pigment (CI Pigment Blue 15 manufactured by Clariant Japan Co., Ltd.) as a colorant. 3) 4 parts by weight, 5 parts by weight of carnauba wax (melting point 82 ° C.) as wax, 1 part by weight of a quaternary ammonium salt compound (P-51 manufactured by Orient Chemical Co., Ltd.) as a charge control agent, Henschel mixer (Nippon Coke Kogyo Co., Ltd.) for 5 minutes. Then, the obtained mixture was melt-kneaded with a twin-screw extruder (PCM-30 manufactured by Ikegai Co., Ltd.). And after cooling the kneaded product, the obtained melt-kneaded product is finely pulverized with an airflow type pulverizer (turbo mill manufactured by Turbo Industry Co., Ltd.) and classified with an air classifier (EJ-LABO manufactured by Nittetsu Mining Co., Ltd.). Processed. By doing so, a polyester toner (core particles) having a volume average diameter of 6.7 μm was obtained. The volume average diameter of the core particles was measured with a particle size meter (Multisizer 3 manufactured by Beckman Coulter, Inc.).

  1 kg of the polyester toner (core particles) having a volume average particle size of 6.7 μm obtained as described above, the resin fine particles A (styrene-methyl methacrylate copolymer resin fine particles, primary particle size, prepared using an anionic surfactant) 80 g) was mixed for 5 minutes with a Henschel mixer (blade tip speed: 40 m / sec).

  A small amount of the processed toner was sampled, the surface state was photographed with FE-SEM (JSM-7401F manufactured by JEOL Ltd.), and the coverage was calculated by image processing. As a result, the coverage was 85% ( The coverage was calculated in 5% increments).

  Also, the sampled toner is mixed with a ferrite carrier (carrier used in Kyocera Mita printer FS-C5100DN) at a mixing ratio of 8% in a ball mill for 5 minutes (120 rpm), and the charge amount of the toner is measured by a charge amount measuring device. (Model 210HS-2A manufactured by TREK) As a result of measurement, it was 15 μC / g.

  Thereafter, 20 g of positively chargeable silica (Aerosil Silica 90G (primary particle size 20 nm) surface treated with silicone oil and aminosilane) was added, and further mixed with a Henschel mixer for 5 minutes. Example 1 No toner was obtained.

(Toner of Example 2)
1 g of polyester toner (core particles) having a volume average particle diameter of 6.7 μm obtained by the same method as in Example 1 and the resin fine particles B (styrene-methyl methacrylate copolymer resin) prepared using a cationic surfactant 50 g of fine particles (primary particle size 90 nm) were mixed with a Henschel mixer for 5 minutes.

  A small amount of the processed toner was sampled, the surface state was photographed with FE-SEM, and the coverage was calculated by image processing. As a result, the coverage was 85% (the coverage was calculated in increments of 5%). ).

  The sampled toner was mixed for 5 minutes with a ball mill at a mixing ratio of 8% with the ferrite carrier, and the charge amount of the toner was measured. As a result, it was 75 μC / g.

  Thereafter, 20 g of silica (Titanium Oxide T805 manufactured by Aerosil Co., Ltd. (primary particle size: 20 nm)) was added, and further mixed with a Henschel mixer for 5 minutes to obtain a toner of Example 2.

(Toner of Example 3)
1 kg of a polyester toner (core particle) having a volume average particle diameter of 6.7 μm obtained by the same method as in Example 1 and the resin fine particles C (butyl acrylate-methyl methacrylate copolymer) prepared using a cationic surfactant. 80 g of polymer resin fine particles (primary particle size 120 nm) were mixed with a Henschel mixer for 5 minutes.

  A small amount of the processed toner was sampled, and the coverage was calculated by photographing the surface state with FE-SEM and performing image processing. As a result, the coverage was 75% (the coverage was calculated in increments of 5%). ).

  The sampled toner was mixed for 5 minutes with a ball mill at a mixing ratio of 8% with the ferrite carrier, and the charge amount of the toner was measured. As a result, it was 50 μC / g.

  Thereafter, 20 g of silica (Titanium Oxide T805 manufactured by Aerosil Co., Ltd. (primary particle size: 20 nm)) was added, and further mixed with a Henschel mixer for 5 minutes to obtain a toner of Example 3.

(Toner of Example 4)
1 kg of a polyester toner (core particle) having a volume average particle diameter of 6.7 μm obtained by the same method as in Example 1 and the resin fine particles C (butyl acrylate-methyl methacrylate copolymer) prepared using a cationic surfactant. 100 g of polymer resin fine particles (primary particle size 120 nm) were mixed with a Henschel mixer for 5 minutes.

  A small amount of the processed toner was sampled, and the coverage was calculated by photographing the surface state with FE-SEM and performing image processing. As a result, the coverage was 90% (the coverage was calculated in increments of 5%). ).

  The sampled toner was mixed for 5 minutes with a ball mill at a mixing ratio of 8% with the ferrite carrier, and the charge amount of the toner was measured. As a result, it was 52 μC / g.

  Thereafter, 20 g of silica (RY90 (Aerosil particle size: 20 nm)) manufactured by Aerosil Co. was added, and further mixed with a Henschel mixer for 5 minutes to obtain a toner of Example 4.

(Toner of Example 5)
1 g of polyester toner (core particles) having a volume average particle diameter of 6.7 μm obtained by the same method as in Example 1 and the resin fine particles B (styrene-methyl methacrylate copolymer resin) prepared using a cationic surfactant 45 g of fine particles (primary particle size of 90 nm) were mixed with a Henschel mixer for 5 minutes.

  A small amount of the processed toner was sampled, and the coverage was calculated by photographing the surface state with FE-SEM and performing image processing. As a result, the coverage was 70% (the coverage was calculated in increments of 5%). ).

  The sampled toner was mixed for 5 minutes with a ball mill at a mixing ratio of 8% with the ferrite carrier, and the charge amount of the toner was measured. As a result, it was 45 μC / g.

  Then, 20 g of silica (RY90 (Aerosol particle size: 20 nm) manufactured by Aerosil) was added, and further mixed with a Henschel mixer for 5 minutes to obtain a toner of Example 5.

(Toner of Comparative Example 1)
The sampled toner was added to the polyester toner (core particle) having a volume average particle diameter of 6.7 μm obtained by the same method as in Example 1 and the sampled toner was mixed with a ferrite carrier by a ball mill at a mixing ratio of 8%. As a result of mixing for 5 minutes and measuring the charge amount of the toner, it was 26 μC / g.

  Thereafter, 20 g of silica (Titanium oxide T805 manufactured by Aerosil Co., Ltd. (primary particle size 20 nm)) was added, and further mixed for 5 minutes with a Henschel mixer to obtain the toner of Comparative Example 1.

(Toner of Comparative Example 2)
1 g of polyester toner (core particles) having a volume average particle diameter of 6.7 μm obtained by the same method as in Example 1 and the resin fine particles B (styrene-methyl methacrylate copolymer resin) prepared using a cationic surfactant 35 g of fine particles (primary particle size of 90 nm) were mixed with a Henschel mixer for 5 minutes.

  A small amount of the processed toner was sampled, the surface state was photographed with FE-SEM, and the coverage was calculated by performing image processing. As a result, the coverage was 50% (the coverage was calculated in increments of 5%). ).

  The sampled toner was mixed for 5 minutes with a ball mill at a mixing ratio of 8% with the ferrite carrier, and the charge amount of the toner was measured. The result was 32 μC / g.

  Thereafter, 20 g of silica (Titanium Oxide T805 manufactured by Aerosil Co., Ltd. (primary particle size 20 nm)) was added, and further mixed with a Henschel mixer for 5 minutes to obtain a toner of Comparative Example 2.

(Toner of Comparative Example 3)
The resin fine particle A (styrene-methyl methacrylate copolymer resin) prepared by using the same method as in Example 1 and using 1 Kg of a polyester toner (core particle) having a volume average particle diameter of 6.7 μm and an anionic surfactant. 30 g of the fine particles (primary particle size 90 nm) were mixed with a Henschel mixer for 5 minutes.

  A small amount of the processed toner was sampled, the surface state was photographed with FE-SEM, and the coverage was calculated by performing image processing. As a result, the coverage was 50% (the coverage was calculated in increments of 5%). ).

  The sampled toner was mixed for 5 minutes with a ball mill at a mixing ratio of 8% with the ferrite carrier, and the charge amount of the toner was measured. The result was 16 μC / g.

  Thereafter, 20 g of positively-charged silica (Aerosil silica 90G (primary particle size 20 nm) surface treated with silicone oil and aminosilane) was added, and further mixed with a Henschel mixer for 5 minutes. A toner was obtained.

(Development of developer)
The toner obtained in Examples 1 to 5 and Comparative Examples 1 to 3 was mixed with a ferrite carrier (carrier used in Kyocera Mita printer FS-C5100DN) at a mixing ratio of 11% in a ball mill for 30 minutes. Developers using the respective toners were prepared.

[Fog evaluation 1]
After measuring the charge amount of the developer, the developer was put into a FS-C5100DN developer unit made by Kyocera Mita and mounted on the FS-C5100DN, and blank paper printing was performed for 1 hour to evaluate the occurrence of fogging during blank paper printing. . Evaluation was performed according to the following evaluation criteria.
○: No fogging is observed at all. Δ: Although there is fogging, there is no practical problem. ×: There is fogging and there is a practical problem [Fog Evaluation 2]
Next, for the fog evaluation 1 of ◯ or Δ, an equal amount of the developer on which blank paper printing was performed and the unused developer were taken and mixed for 1 minute in a ball mill, and then the mixture was added to FS- It was placed in a C5100DN developer and mounted on the FS-C5100DN, 100 blank pages were printed, and the occurrence of fogging was examined. Evaluation was performed according to the following evaluation criteria.
○: No fogging is observed. △: There is fogging, but there is no problem in practical use. ×: There is fogging, there is a practical problem. did.

[Evaluation results]
The evaluation results are shown in Table 2.

表２より、樹脂微粒子による被覆率が７０％以上のトナーを用いることにより、正帯電性シリカを用いたトナーにおいてもカブリを実用レベルまで抑制することができることが明らかとなった。

From Table 2, it became clear that fogging can be suppressed to a practical level even in a toner using positively chargeable silica by using a toner having a coverage of 70% or more by resin fine particles.

Further, by using a toner in which 70% or more of the surface of the core particle is coated with acrylic resin fine particles prepared by an emulsion polymerization method using a cationic initiator, fogging is generated even when negatively charged fine particles are used. It was found that it can be suppressed to a practical level.

Claims (3)

An electrophotographic dry toner comprising at least a polyester resin, a release agent, a colorant and resin fine particles,
70% or more of the surface of the core particles obtained by pulverizing and classifying after dispersing at least the release agent and the colorant in the polyester resin is coated with resin fine particles ,
The resin fine particles are at least one selected from acrylic resin fine particles or methacrylic resin fine particles ; and
The acrylic resin fine particles or the methacrylic resin fine particles are styrene-methyl methacrylate resin fine particles or butyl acrylate-methyl methacrylate resin fine particles prepared by an emulsion polymerization method using a cationic surfactant. A positively chargeable dry toner for electrophotography. A developer comprising the electrophotographic dry toner according to claim 1 and a carrier. A step of obtaining a core particle by dispersing at least a colorant in a polyester-based resin and then pulverizing and classifying the styrene-made styrene-based polymer using a cationic surfactant. Including mechanically mixing with at least one resin fine particle selected from methyl methacrylate resin fine particles or butyl acrylate-methyl methacrylate resin fine particles, and covering 70% or more of the core particle surface with the resin fine particles,
A method for producing a positively chargeable electrophotographic dry toner.