JP2012063602A - Positively chargeable dry toner for electrophotography - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress fogging when a pulverization toner containing a polyester resin is used as a positively chargeable toner.SOLUTION: A positively chargeable dry toner for electrophotography is provided, which is a dry toner for electrophotography including at least a polyester resin, a release agent, a colorant and resin fine particles. The toner comprises core particles obtained by dispersing at least the release agent and the colorant in the polyester resin, then pulverizing and classifying, and 70% or more of the surfaces of the core particles are coated with the resin fine particles. The resin fine particles are at least one kind selected from acrylic resin fine particles and methacrylic resin fine particles. When the toner is dispersed in pure water containing 0.2% of a surfactant and irradiated with ultrasonic waves (at a frequency of 50 kHz and 100 W energy) for 10 minutes, a desorption rate of the resin fine particles is less than 5%.

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 is a resin having a strong negative chargeability, a charge control agent exhibiting a positive chargeability and a charge control resin are used in the polyester resin for use in a positively charged toner. It was necessary to add fine particles having a strong positive charge and added 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, a toner using a polyester resin and a toner added with fine particles subjected to a positive charging process in addition to a 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 particles obtained by pulverization and classification is coated with resin fine particles, the resin fine particles are acrylic resin fine particles or methacrylic resin fine particles, and a surfactant. Positively chargeable, characterized in that the desorption rate of resin fine particles after dispersing toner in pure water containing 0.2% and irradiating with ultrasonic waves (50 kHz, 100 W) for 10 minutes is less than 5% This is a 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.

  As described above, when 70% or more of the surface of the core particle is covered with the resin fine particles, it is important that the resin fine particles adhere to the core particle surface with sufficient strength. Specifically, it is necessary that the resin fine particle detachment rate is less than 5% when the toner is dispersed in water and irradiated with ultrasonic waves (50 kHz, 100 W) for 10 minutes. The released acrylic resin fine particles or methacrylic resin fine particles are likely to adhere to the magnet roller, the developing roller and the surface of the photosensitive member in the developing device. If the removal rate of these resin fine particles is 5% or more, the adhesion The image noise resulting from this appears in the formed image. In the present invention, since the desorption rate of the resin fine particles is less than 5%, an image with excellent image quality can be obtained without such image noise appearing in the formed image.

  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 an emulsion polymerization method using a cationic surfactant are more positively charged 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 core particles with resin fine particles or the like. 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 A step of mechanically mixing with at least one resin fine particle to cover 70% or more of the surface of the core particle with the resin fine particle, and in the coating step, pure water containing 0.2% of a surfactant The strength of attaching the resin fine particles to the core particles is adjusted so that the desorption rate of the resin fine particles is less than 5% after the toner is dispersed and ultrasonic waves (50 kHz, 100 W) are irradiated for 10 minutes. This is a method for producing a positively chargeable electrophotographic dry toner.

  According to the present invention, a polyester resin that is excellent in transparency and can impart low-temperature fixability and secondary color reproducibility to a color toner is formed even when used as a binder resin for a positively chargeable toner. A toner that does not cause fog and image noise in the 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. In addition, after the toner is dispersed in pure water containing 0.2% of a surfactant and irradiated with ultrasonic waves (50 kHz, 100 W) for 10 minutes, the desorption rate of the resin fine particles is 5%. It is characterized by being less than.

  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. The core particles are obtained by dispersing these materials and then pulverizing and classifying them.

(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. The alcohol component must 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.

<External additive>
(Resin fine particles)
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%.

  Further, the toner according to the present embodiment has a resin fine particle detachment rate after the toner is dispersed in pure water containing 0.2% of a surfactant and irradiated with ultrasonic waves (50 kHz, 100 W) for 10 minutes. One of the characteristics is that it is less than 5%. When the desorption rate is less than 5%, it is possible to obtain an image with excellent image quality in which image noise does not appear in the formed image. The desorption rate is not particularly limited as long as it is less than 5%, and may be 0%, for example. From the viewpoint that the effect of the present invention can be obtained, the lower the desorption rate, the better. However, the low desorption rate means that the resin fine particles are firmly attached to the core particle, and therefore This process takes time and cost, and productivity may be reduced. Therefore, from the viewpoint of both the effect of the present invention and productivity, the preferable range of the desorption rate is 1% or more and less than 5%, more preferably about 1.5 to 4.5%.

  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. Further, if it 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.

  The resin fine particles are added in an amount of ultrasonic waves (70% or more of the surface of the core particles covered with the resin fine particles and the toner is dispersed in pure water containing 0.2% of a surfactant. (50 kHz, 100 W) may be appropriately adjusted so that the resin fine particle detachment rate after irradiation for 10 minutes is less than 5%. For example, in the range of 1 to 20 parts by mass with respect to 100 parts by mass of the core particles It is preferable to set the value within the range. 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 of coating the core particles with the resin fine particles is a method of coating 70% or more of the surface of the core particles with the resin fine particles, and the toner is in pure water containing 0.2% of a surfactant. The strength of adhesion of the resin fine particles to the surface of the core particles can be adjusted so that the desorption rate of the resin fine particles after irradiation with ultrasonic waves (50 kHz, 100 W) for 10 minutes is less than 5%. If it is a method, it will not specifically limit. 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 the addition of the resin fine particles is high, it is not necessary to use the positively charged inorganic particles that are positively charged. It is possible to use inorganic fine particles which are not present 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 in the range of 0.2 to 3 parts by mass with respect to 100 parts by mass of the toner base particles. If the added amount of the inorganic fine particles is less than 0.2 parts by mass, the fluidity of the toner becomes too low and the toner cleaning performance cannot be secured, and if it exceeds 3 parts by mass, 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. The 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 mass, more preferably 5 to 15% by mass, and still more preferably 6 to 10% by mass. When the toner density is less than 3% by mass, the image density tends to be excessively thin. On the other hand, when the toner concentration exceeds 20% by mass, toner scattering from the developing device occurs 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. Then, it dried by freeze drying and obtained resin fine particle A with a primary particle diameter of 80 nm.

・ 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. Then, it dried by freeze drying and obtained resin fine particle B with a primary particle diameter of 120 nm.

[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 diameter of 6.7 μm and 50 g of the resin fine particles A (styrene-methyl methacrylate copolymer resin fine particles, primary particle size 80 nm) obtained as described above were added to a Henschel mixer (blade tip speed). : 40 m / sec) 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 95% (the coverage was calculated in increments of 5%). ).

  Further, the adhesion strength of the resin fine particles to the core particle surface was determined by an ultrasonic dispersion method. 0.2 g of toner is put in 50 ml of pure water containing 0.2% sodium alkyl ether sulfate as a surfactant, and ultrasonic waves are applied using an ultrasonic cleaner (ASONE Vs-F100, 50 KHz, 100 W). Irradiated for 10 minutes. Next, the liquid was passed through a filter having a diameter of 0.8 μm to obtain a dispersion of released resin fine particles. Measure the turbidity of the dispersion of fine resin particles using a spectral color difference meter SE2000 (Nippon Denshoku Industries Co., Ltd.), and compare the measured L * value of the dispersion with a calibration curve prepared in advance. As a result of calculating the desorption rate of the resin fine particles, the desorption rate was 2.0%.

  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. A toner was obtained.

(Toners of Examples 2 to 5 and Comparative Examples 1 to 3)
The toners of Examples 2 to 5 and Comparative Examples 1 to 3 were treated in the same manner as in Example 1 except that the type and amount of resin fine particles and the treatment conditions when mixed with resin fine particles were changed as shown in Table 2. 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]
The developer obtained above was put in a developing device for FS-C5100DN and mounted on a printer FS-C5100DN manufactured by Kyocera Mita, and blank paper printing was performed for 1 hour. When any toner was used, no fog was observed during white paper printing. After that, after taking an equal amount of the developer on which blank paper printing was performed and the unused developer, the mixture was mixed for 1 minute in a ball mill, and the mixture was placed in the FS-C5100DN developer and mounted on the FS-C5100DN. 100 sheets of blank paper were printed and the occurrence of fogging was examined. Evaluation was performed according to the following evaluation criteria, and ○ and Δ were regarded as acceptable.
◯: No fog is observed Δ: There is fog but there is no problem in practical use ×: There is fog and there is a problem in practical use.

[Print evaluation]
About what passed in the fog evaluation, continuous printing was performed at a printing rate of 10% following the fog evaluation, and evaluation was performed according to the following evaluation criteria.
○: Adherence to the surface of the magnetic roller, development roller, and photoconductor is not recognized. Δ: Adhesion to the surface of the magnet roller, development roller, and photoconductor is recognized but is slight and does not appear in the image. X: Magnet roller, development Adhesion to the roller and the photoreceptor surface appears as noise in the image.

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

  As is apparent from Table 2, by using a toner having a coating ratio of resin fine particles of 70% or more and a resin fine particle detachment ratio of less than 5%, fog, developer member, and drum surface are covered. Adhesion could be suppressed to a practical level.

Claims (4)

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 toner is dispersed in pure water containing 0.2% of a surfactant, and ultrasonic waves (50 kHz, 100 W) A positively chargeable dry toner for electrophotography, wherein the resin fine particles have a desorption rate of less than 5% after being irradiated for 10 minutes.   The dry type for electrophotography according to claim 1, wherein the acrylic resin fine particles and the methacrylic resin fine particles are acrylic resin fine particles and methacrylic resin fine particles prepared by an emulsion polymerization method using a cationic surfactant. toner.   A developer comprising the electrophotographic dry toner according to claim 1 or 2 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; and at least one resin fine particle selected from acrylic resin fine particles or methacrylic resin fine particles. And the step of coating 70% or more of the surface of the core particles with the resin fine particles,
In the coating step, after the toner is dispersed in pure water containing 0.2% of a surfactant and irradiated with ultrasonic waves (50 kHz, 100 W) for 10 minutes, the resin fine particle removal rate is less than 5%. As described above, the strength of attaching the resin fine particles to the core particles is adjusted,
A method for producing a positively chargeable electrophotographic dry toner.