JP5504190B2 - Positively chargeable toner - Google Patents

Description

  The present invention relates to a positively chargeable toner.

  In general, in an image forming method such as electrophotography or electrostatic recording, the surface of a photosensitive drum is charged by corona discharge or the like, and then exposed by a laser or the like to form an electrostatic latent image. The image is developed with toner to form a toner image, and the toner image is transferred to a recording medium to obtain a high-quality image. Usually, toners applied to these development methods are mixed with a binder resin such as a thermoplastic resin, a colorant, a charge control agent, a release agent, etc., kneaded, pulverized, and classified to have an average particle size of 5 to 15 μm. Toner particles are used. For the purpose of imparting fluidity to the toner, controlling toner charging, and improving cleaning properties, inorganic fine powders such as silica, titanium oxide, and alumina, and inorganic metal fine powders are externally added to the toner. ing.

  However, these inorganic fine powders generally tend to be negatively charged, and particularly silica has a strong negative chargeability. Therefore, when these inorganic fine powders are used for positively chargeable toners, inorganic fine powders having positively charged polar groups introduced on the surface thereof are used.

  Specifically, a toner (Patent Documents 1 and 2) externally added with silica fine powder surface-treated with an aminosilane coupling agent having a positively chargeable polar group, a positively chargeable charge control agent, Toner with externally added silica fine powder surface-treated with a hydrophobizing agent (Patent Document 3), a silane coupling agent having a functional group containing a nitrogen atom, and a silicone oil having a side chain containing a nitrogen atom Toners (Patent Documents 4 and 5) to which silica fine powder surface-treated by the above method is externally added have been proposed. Since these toners have a positively chargeable polar group such as an amino group on the toner surface (silica fine powder surface), they exhibit a strong positive chargeability.

  In addition, silica fine particles surface-treated with a surface treatment agent having a negatively chargeable polar group such as a fluorine-based silane coupling agent and a surface treatment agent having a positively chargeable polar group such as an amine-based silane coupling agent. A toner to which powder is externally added has been proposed (Patent Document 6). The toner described in Patent Document 6 has a high charge level, is excellent in charge rising property and fluidity, and is useful as a toner for non-magnetic one-component development.

  Further, a toner obtained by externally adding dry silica fine powder having a positively charged polar group introduced therein and hydrophobized using a hydrophobizing agent and wet silica fine powder hydrophobized with silicone oil (Patent Document 7) ), A toner in which a dry silica fine powder having a positively charged polar group and a hydrophobic group and a wet silica fine powder containing a positively charged polar group and a fluorine-containing polar group are externally added (Patent Document 8), and specific A toner (Patent Document 9) has been proposed in which a metal oxide powder such as zirconium oxide treated with a cyclic silazane compound and hydrophobic particles such as silica are externally added. The toners described in Patent Documents 7, 8, and 9 are excellent in charge rising property, durability, and environmental stability.

JP-A-52-135739 JP-A-56-123550 JP 58-216252 A JP 63-072731 A Japanese Patent Laid-Open No. 63-073272 Japanese Patent Laid-Open No. 02-066564 JP-A-11-160907 JP-A-11-143111 JP 2005-121867 A

  However, the toners described in Patent Documents 1 to 8 use silica fine powder as the inorganic fine powder, and even if the silica fine powder is subjected to various surface treatments, the toner has a strong negative charge property exhibited by the silica fine powder. As a result, it was still difficult to maintain positive chargeability. For this reason, in the toners described in Patent Documents 1 to 8, when the toner is subjected to a strong stress in the developing device, the positive chargeability of the toner tends to be lowered, and fogging and toner scattering are likely to occur. In the toner of Patent Document 9, a metal oxide powder such as zirconium oxide is externally added in addition to the silica fine powder. However, such a toner does not solve the problem of the toner described in Patent Documents 1-8. .

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a positively chargeable toner that can maintain good positive chargeability and can suppress image defects such as fogging and toner scattering. .

  The inventors of the present invention have fine particles of zirconium oxide attached to the surface of the toner base particles, and the toner base particles contain at least a binder resin and a colorant. Surface treatment with an agent and silicone oil, and the mass ratio of the positively chargeable surface treatment agent and the silicone oil adhering to the surface of the zirconium oxide fine particles is 6: 4 as a positively chargeable surface treatment agent: silicone oil. The present inventors have found that the above problem can be solved by a positively chargeable toner of ˜2: 8, and have completed the present invention. Specifically, the present invention provides the following.

(1) Zirconium oxide fine particles are attached to the surface of the toner base particles,
The toner base particles contain at least a binder resin and a colorant,
The zirconium oxide fine particles are surface-treated with a positively chargeable surface treatment agent and silicone oil,
A positively chargeable toner having a mass ratio of 6: 4 to 2: 8 of the positively chargeable surface treatment agent and the silicone oil attached to the surface of the zirconium oxide fine particles.

  (2) The positively chargeable toner according to (1), wherein the amount of the positively chargeable surface treating agent is 5 to 30% by mass with respect to the mass of the zirconium oxide fine particles.

  (3) The positively chargeable toner according to (1) or (2), wherein the amount of the silicone oil is 5 to 30% by mass with respect to the mass of the zirconium oxide fine particles.

  (4) The positively chargeable toner according to any one of (1) to (3), wherein the positively chargeable surface treatment agent is a coupling agent.

  According to the present invention, it is possible to provide a positively chargeable toner that can maintain good positive chargeability and can suppress image defects such as fogging and toner scattering.

1 is a schematic configuration diagram illustrating an example of an image forming apparatus.

  Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and can be implemented with appropriate modifications within the scope of the object of the present invention. In addition, although description may be abbreviate | omitted suitably about the location where description overlaps, the summary of invention is not limited.

  In the positively chargeable toner of the present invention (hereinafter also simply referred to as toner), fine particles of zirconium oxide are attached to the surface of toner base particles, and the toner base particles contain at least a binder resin and a colorant. The zirconium oxide fine particles are surface-treated with a positively chargeable surface treatment agent and silicone oil, and the mass ratio of the positively chargeable surface treatment agent and the silicone oil adhering to the surface of the zirconium oxide fine particles is positively charged. Surface treatment agent: 6: 4 to 2: 8 as silicone oil. The positively chargeable toner of the present invention can be mixed with a carrier and used as a two-component developer. Hereinafter, toner base particles and zirconium oxide fine particles constituting the positively chargeable toner of the present invention, a positively chargeable toner manufacturing method, a two-component developer manufacturing method, and an image forming method using the toner of the present invention Will be described in order.

[Toner mother particles]
The toner base particles constituting the positively chargeable toner of the present invention include at least a binder resin and a colorant, and may optionally include a release agent, a charge control agent, and the like. Hereinafter, the binder resin and the colorant, which are essential components of the toner base particles used in the present invention, the optional components, the release agent, the charge control agent, and the method for producing the toner base particles will be described in order. To do.

[Binder resin]
The positively chargeable toner of the present invention is obtained by adhering fine particles of zirconium oxide described later to the surface of toner base particles containing at least a colorant and a binder resin. The binder resin that is a main component of the toner base particles is not particularly limited as long as it is a resin that has been conventionally used as a binder resin for toner. Specific examples of the binder resin include styrene resin, acrylic resin, styrene-acrylic copolymer, polyethylene resin, polypropylene resin, vinyl chloride resin, polyester resin, polyamide resin, polyurethane resin, and polyvinyl alcohol. Examples thereof include thermoplastic resins such as resins, vinyl ether resins, N-vinyl resins, and styrene-butadiene resins. Among these resins, polystyrene resins and polyester resins are preferable from the viewpoints of dispersibility of the colorant in the toner, toner chargeability, and fixing properties to paper. Hereinafter, polystyrene resins and polyester resins will be described.

  The polystyrene resin may be a styrene homopolymer or a copolymer with another copolymerizable monomer copolymerizable with styrene. Specific examples of other copolymerization monomers include p-chlorostyrene; vinyl naphthalene; ethylene unsaturated monoolefins such as ethylene, propylene, butylene, and isobutylene; vinyl halides such as vinyl chloride, vinyl bromide, and vinyl fluoride. Vinyl esters such as vinyl acetate, vinyl propionate, vinyl benzoate, vinyl butyrate; methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, dodecyl acrylate, n-octyl acrylate, acrylic acid (Meth) acrylic esters such as 2-chloroethyl, phenyl acrylate, methyl α-chloroacrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate; other acrylic acids such as acrylonitrile, methacrylonitrile, acrylamide Derivative Vinyl ethers such as vinyl methyl ether and vinyl isobutyl ether; Vinyl ketones such as vinyl methyl ketone, vinyl ethyl ketone and methyl isopropenyl ketone; N-vinyl pyrrole, N-vinyl carbazole, N-vinyl indole, N-vinyl pyrrolidene, etc. N-vinyl compounds and the like. These copolymerizable monomers can be copolymerized with a styrene monomer in combination of two or more.

  As the polyester-based resin, those obtained by condensation polymerization or co-condensation polymerization of an alcohol component and a carboxylic acid component can be used. The components used when synthesizing the polyester resin include the following alcohol components and carboxylic acid components.

  As the alcohol component, a divalent or trivalent or higher alcohol can be used. Specific examples of the divalent or trivalent or higher alcohol component include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1 Diols such as 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, polytetramethylene glycol; bisphenol A, Bisphenols such as hydrogenated bisphenol A, polyoxyethylenated bisphenol A, polyoxypropylenated bisphenol A; sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, Entaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4- Examples include trivalent or higher alcohols such as butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

  As the carboxylic acid component, a divalent or trivalent or higher carboxylic acid component can be used. Specific examples of the divalent or trivalent or higher carboxylic acid component include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, Sebacic acid, azelaic acid, malonic acid, or n-butyl succinic acid, n-butenyl succinic acid, isobutyl succinic acid, isobutenyl succinic acid, n-octyl succinic acid, n-octenyl succinic acid, n-dodecyl succinic acid, n-dodecenyl succinic acid Divalent carboxylic acids such as acids, isododecyl succinic acid, isododecenyl succinic acid and the like or alkyl or alkenyl succinic acid; 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5-benzenetricarboxylic acid Acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphtha Tricarboxylic 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, emporic trimer acid, and other trivalent or higher carboxylic acids. These divalent or trivalent or higher carboxylic acid components may be used as ester-forming derivatives such as acid halides, acid anhydrides, and lower alkyl esters. Here, “lower alkyl” means an alkyl group having 1 to 6 carbon atoms.

  When the binder resin is a polyester resin, the softening point of the polyester resin is preferably 80 to 150 ° C, more preferably 90 to 140 ° C.

  As the binder resin, it is preferable to use a thermoplastic resin because it has good fixability. However, not only the thermoplastic resin alone but also a crosslinking agent or a thermosetting resin should be added to the thermoplastic resin. Can do. By introducing a partially crosslinked structure into the binder resin, it is possible to improve the storage stability, form retention, durability and the like of the toner without deteriorating the fixability.

  As the thermosetting resin that can be used together with the thermoplastic resin, for example, an epoxy resin or a cyanate resin is preferable. Specific examples of suitable thermosetting resins include bisphenol A type epoxy resins, hydrogenated bisphenol A type epoxy resins, novolac type epoxy resins, polyalkylene ether type epoxy resins, cycloaliphatic type epoxy resins, cyanate resins and the like. It is done. These thermosetting resins can be used in combination of two or more.

  The glass transition point (Tg) of the binder resin is preferably 50 to 65 ° C, and more preferably 50 to 60 ° C. If the glass transition point of the binder resin is too low, the toners may be fused inside the developing unit of the image forming apparatus, or the storage stability may be reduced. May be partly fused. On the other hand, when the glass transition point is too low, the strength of the binder resin is lowered, and the toner tends to adhere to the photosensitive drum or the like. When the glass transition point is too high, the low-temperature fixability of the toner tends to decrease.

  In addition, the glass transition point of binder resin can be calculated | required from the change point of specific heat using a differential scanning calorimeter (DSC). More specifically, it can be determined by measuring an endothermic curve using a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. as a measuring device. An endothermic curve obtained by placing 10 mg of a measurement sample in an aluminum pan, using an empty aluminum pan as a reference, and measuring at a measurement temperature range of 25 to 200 ° C. and a temperature increase rate of 10 ° C./min. The glass transition point can be obtained more.

[Colorant]
In the positively chargeable toner of the present invention, zirconium oxide fine particles are attached to the surface of toner base particles containing at least a binder resin and a colorant. As the colorant that can be blended in the toner base particles, known pigments and dyes can be used according to the color of the toner. Specific examples of suitable colorants to be added to the binder resin include black pigments such as carbon black, acetylene black, lamp black and aniline black; yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel Titanium Yellow, Navels Yellow, Naphthol Yellow S, Hansa Yellow G, Hansa Yellow 10G, Benzidine Yellow G, Benzidine Yellow GR, Quinoline Yellow Lake, Permanent Yellow NCG, Tartrazine Lake, C.I. I. Yellow pigments such as CI Pigment Yellow 180; orange pigments such as red mouth yellow lead, molybdenum orange, permanent orange GTR, pyrazolone orange, Vulcan orange, indanthrene brilliant orange GK; Bengala, cadmium red, lead red, mercury cadmium sulfide, permanent red 4R , Resor Red, Pyrazolone Red, Watching Red Calcium Salt, Lake Red D, Brilliant Carmine 6B, Eosin Lake, Rhodamine Lake B, Alizarin Lake, Brilliant Carmine 3B, C.I. I. Red pigments such as CI Pigment Red 238; purple pigments such as manganese purple, fast violet B, and methyl violet lake; bitumen, cobalt blue, alkali blue lake, Victoria blue partially chlorinated, first sky blue, induslen blue BC, I. Blue pigments such as pigment blue 15: 3 (copper phthalocyanine blue pigment); green pigments such as chrome green, chromium oxide, pigment green B, malachite green lake, final yellow green G; zinc white, titanium oxide, antimony white, zinc sulfide And white pigments such as barite powder, barium carbonate, clay, silica, white carbon, talc, and alumina white. These colorants may be used in combination of two or more for the purpose of adjusting the toner to a desired hue.

  Among these colorants, for example, carbon black is preferable as the colorant for black toner, and C.I. I. Pigment Yellow 180 is preferable. Examples of the colorant for cyan toner include C.I. I. Pigment Blue 15: 3 (copper phthalocyanine blue pigment) is preferable, and as a magenta toner colorant, C.I. I. Pigment Red 238 is preferred.

  The content of the colorant in the toner base particles is not particularly limited as long as the object of the present invention is not impaired, and is appropriately determined according to the type of the colorant. The content of the colorant in the toner base particles is preferably 1 to 15 parts by mass, and more preferably 2 to 8 parts by mass with respect to 100 parts by mass of the binder resin from the viewpoint of obtaining a suitable image density.

〔Release agent〕
The positively chargeable toner of the present invention may contain a release agent in the binder resin for the purpose of improving the toner fixability and offset resistance. The type of release agent that can be blended into the binder resin is not particularly limited as long as the object of the present invention is not impaired. The mold release agent is preferably a wax, and examples of the wax include polyethylene wax, polypropylene wax, fluororesin-based wax, Fischer-Tropsch wax, paraffin wax, ester wax, montan wax, rice wax and the like. These waxes can be used in combination of two or more. By adding such a release agent to the toner, the occurrence of offset and image smearing (stain around the image when the image is rubbed) can be more efficiently suppressed.

  The amount of the release agent used is not particularly limited as long as the object of the present invention is not impaired. When the specific amount of the release agent is 100 parts by mass of the binder resin, 0.1 to 20 parts by mass is preferable, and 1 to 8 parts by mass is more preferable. If the amount of release agent used is too small, the desired effect may not be obtained with respect to the suppression of the occurrence of offset and image smearing. If the amount of release agent used is excessive, fusion between toners may occur. Depending on the case, the storage stability may decrease.

(Charge control agent)
The positively chargeable toner of the present invention may contain a positively chargeable charge control agent in the binder resin as long as the object of the present invention is not impaired. The type of the positively chargeable charge control agent is not particularly limited as long as the object of the present invention is not impaired, and can be appropriately selected from positively chargeable charge control agents conventionally used in toners. Specific examples of the positively chargeable charge control agent include pyridazine, pyrimidine, pyrazine, orthooxazine, metaoxazine, paraoxazine, orthothiazine, metathiazine, parathiazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6-oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1, 2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1,2,4,6-oxatriazine, 1,3,4,5-oxatriazine, Azine compounds such as phthalazine, quinazoline, quinoxaline; azine fast red FC, azine fast red 12BK, azine violet BO, azine Direct dyes composed of azine compounds such as Laun 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Dep Black EW, and Azin Dee Black 3RL; Nigrosine Compounds such as Nigrosine, Nigrosine Salts, Nigrosine Derivatives; Nigrosine Acid dyes composed of nigrosine compounds such as BK, nigrosine NB, and nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; quaternary ammonium salts such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride It is done. Among these positively chargeable charge control agents, a nigrosine compound is particularly preferable in that a more rapid start-up property can be obtained. These positively chargeable charge control agents can be used in combination of two or more.

  Quaternary ammonium salts, carboxylates, or resins having a carboxyl group as a functional group can also be used as a positively chargeable charge control agent. More specifically, a styrene resin having a quaternary ammonium salt, an acrylic resin having a quaternary ammonium salt, a styrene-acrylic resin having a quaternary ammonium salt, a polyester resin having a quaternary ammonium salt, a carboxylic acid Styrene resin with salt, acrylic resin with carboxylate, styrene-acrylic resin with carboxylate, polyester resin with carboxylate, polystyrene resin with carboxyl group, acrylic with carboxyl group 1 type, or 2 or more types, such as resin, the styrene-acrylic resin which has a carboxyl group, and the polyester-type resin which has a carboxyl group, are mentioned. The molecular weight of these resins is not particularly limited as long as the object of the present invention is not impaired, and may be an oligomer or a polymer.

  Among resins that can be used as a positively chargeable charge control agent, a styrene-acrylic copolymer having a quaternary ammonium salt as a functional group from the viewpoint that the charge amount can be easily adjusted to a value within a desired range. A resin is more preferable. Specific examples of preferable acrylic comonomers to be copolymerized with styrene units in a styrene-acrylic copolymer resin having a quaternary ammonium salt as a functional group include methyl acrylate, ethyl acrylate, n-propyl acrylate, and acrylic acid. (Meth) such as iso-propyl, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate Examples include alkyl acrylates.

  As the quaternary ammonium salt, a unit derived from a dialkylaminoalkyl (meth) acrylate, dialkyl (meth) acrylamide, or dialkylaminoalkyl (meth) acrylamide through a quaternization step is used. Specific examples of the dialkylaminoalkyl (meth) acrylate include dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, dibutylaminoethyl (meth) acrylate and the like. Specific examples of dialkyl (meth) acrylamide include dimethylmethacrylamide, and specific examples of dialkylaminoalkyl (meth) acrylamide include dimethylaminopropylmethacrylamide. Further, hydroxy group-containing polymerizable monomers such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, and N-methylol (meth) acrylamide can be used in combination during polymerization.

  The amount of the positively chargeable charge control agent is not particularly limited as long as the object of the present invention is not impaired. Typically, the amount of the positively chargeable charge control agent used is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 5 parts by mass with respect to 100 parts by mass of the binder resin. When the amount of the charge control agent used is too small, it is difficult to stably charge the toner to a predetermined polarity, which may make it difficult to maintain the image density over a long period of time. In such a case, the charge control agent is difficult to uniformly disperse, and fogging and contamination of the photoreceptor are likely to occur. When the amount of the charge control agent used is excessive, poor charging at high temperature and high humidity due to deterioration of environmental resistance, image failure, and contamination of the photosensitive member are likely to occur.

[Method for producing toner mother particles]
The method for producing toner mother particles is not particularly limited, and can be appropriately selected from conventionally known methods for producing toner mother particles. As a suitable method for producing toner base particles, for example, a method described below can be cited.

  First, the binder resin and the colorant described above are mixed with optional components such as a release agent and a charge control agent, if necessary, with a mixer or the like. Specific examples of the mixer include Henschel type mixing devices such as a Henschel mixer, a super mixer, and a mechano mill, an ang mill, a hybridization system, and a Cosmo system. Among these, a Henschel mixer is preferable.

  Next, the obtained mixture is melt-kneaded with a kneader or the like. Specific examples of the kneader include an extruder such as a twin-screw extruder, a three-roll mill, a lab blast mill, and the like, and an extruder is preferably used. Moreover, the temperature at the time of melt-kneading is not particularly limited as long as the object of the present invention is not impaired, and a temperature not lower than the softening point of the binder resin and lower than the thermal decomposition temperature of the binder resin is preferable.

  The obtained melt-kneaded product is cooled to be a solid, and then pulverized by a pulverizer or the like. Specific examples of the pulverizer include 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, and an impact pulverizer. An airflow type pulverizer is more preferable.

  The obtained pulverized product is subjected to removal of excessively pulverized product and coarse powder with a classifier or the like to obtain toner mother particles having a desired particle diameter. Specific examples of the classifier include an air classifier such as a swirling wind classifier (rotary wind classifier) such as an elbow jet classifier, a centrifugal classifier, and the like, and an air classifier is more preferable.

  The toner base particles obtained using the materials described above are externally added with zirconium oxide fine particles, which will be described later, to obtain the positively chargeable toner of the present invention.

[Zirconium oxide fine particles]
The positively chargeable toner of the present invention comprises a positively chargeable surface treatment agent and silicone oil in a mass ratio of 6: 4 to 2: 8, more preferably 5: positively chargeable surface treatment agent: silicone oil. Zirconium oxide fine particles that have been surface-treated to adhere to 5 to 3: 7 are adhered to the surface of the toner base particles.

  Zirconium oxide fine particles can be appropriately selected from zirconium oxide having various particle diameters as long as the object of the present invention is not impaired. The primary particle diameter of the zirconium oxide fine particles is preferably 25 to 100 nm and more preferably 30 to 80 nm because a toner having an excellent balance between fluidity and developability can be easily obtained. Hereinafter, the positively chargeable surface treatment agent and silicone oil used for the surface treatment of zirconium oxide and the surface treatment method of zirconium oxide fine particles will be described in order.

[Positively chargeable surface treatment agent]
The type of the positively chargeable surface treating agent is not particularly limited as long as it is a substance having a positively charged polar group and can be attached to the surface of zirconium oxide. Preferable examples of the positively chargeable surface treating agent include a resin material used as a positively chargeable charge control agent and a coupling agent having a positively charged polar group such as an amino group.

  Among these positively chargeable surface treatment agents, a coupling agent is preferable because it is chemically bonded to the surface of the zirconium oxide fine particles and is not easily detached. Specific examples of the coupling agent that can be used as the positively chargeable surface treatment agent include a silane coupling agent, a titanate coupling agent, and an aluminate coupling agent. Of these coupling agents, silane coupling agents are particularly preferred. Examples of the silane coupling agent having a positively charged polar group include aminosilane coupling agents represented by the following formula and mixtures thereof.

_{H 2 N (CH 2) 2} NH (CH 2) 3 Si (OCH 3) 3, H 2 N (CH 2) 2 NH (CH 2) 3 Si (CH 3) (OCH 3) 2, H 2 N ( CH ₂ ) ₂ NH (CH ₂ ) ₃ Si (OCH ₃ ) ₃ , H ₂ N (CH ₂ ) ₂ NH (CH ₂ ) ₂ NH (CH ₂ ) ₃ Si (OCH ₃ ) ₃ , H ₂ N (CH ₂ ) ₃ Si (OCH ₃ ) ₃ and C ₆ H ₅ NH (CH ₂ ) ₃ Si (OCH ₃ ) ₃

  The amount of the positively chargeable surface treating agent used for treating the surface of the zirconium oxide fine particles is preferably 5 to 30% by mass, more preferably 15 to 25% by weight, based on the mass of the zirconium oxide fine particles. If the amount of the positively chargeable surface treatment agent used is too small, the desired positive chargeability may not be obtained. When the amount of the positively charged surface treatment agent used is excessive, or when the toner is stirred for a long time in the developing unit, the positively chargeable surface treatment agent is peeled off from the surface of the zirconium oxide, and the peeled positive surface treatment agent is removed. The chargeable surface treatment agent may adhere to, for example, a developing roller inside the developing device and cause image defects.

  Specific examples of the surface treatment method using a positively chargeable surface treatment agent include untreated zirconium oxide fine particles, or zirconium oxide fine particles surface-treated with a silicone oil described later, and a positively chargeable surface treatment agent by a wet method, or A method of crushing the aggregated zirconium oxide fine particles after mixing by a dry method is mentioned. The positively chargeable surface treating agent may be used as it is, or may be diluted with an organic solvent.

  The amount of the positively chargeable surface treatment agent adhering to the surface of the zirconium oxide fine particles can be measured, for example, by the following method. First, the structure of the positively chargeable surface treatment agent used for the treatment of the zirconium oxide fine particles is specified, and the elemental composition of the positively chargeable surface treatment agent is obtained. Next, the two-component developer is sieved by a sieve that can be separated into a carrier and toner (for example, a sieve having an opening of 23 μm), and the toner is separated from the two-component developer. 0.5 g of the obtained toner is filled in a molding machine and pressurized to 10 MPa to produce a pellet having a diameter of 20 mm. The obtained pellet was used as a sample and analyzed by a fluorescent X-ray analyzer (ZSX (manufactured by Rigaku Corporation)). From the X-ray intensity (kcps), an element derived from the positively chargeable surface treatment agent in the sample ( For example, N, Si, Al, Ti), the amount of Si derived from silicone oil, and the content of Zr derived from zirconium oxide are measured. Next, the mass of the zirconium oxide fine particles is obtained from the measured value of the content of the element derived from the positively chargeable surface treatment agent, the measurement device of the Zr content, and the elemental composition of the positively chargeable surface treatment agent. The mass of the positively chargeable surface treatment agent is calculated.

[Silicone oil]
The type of the silicone oil is not particularly limited as long as the object of the present invention is not impaired, and various silicone oils conventionally used as a processing agent for external additives for toner can be used. As the silicone oil, those having a linear siloxane structure are preferable, and any of non-reactive silicone oil and reactive silicone oil can be used. Specific examples of silicone oils include dimethyl silicone oil, phenylmethyl silicone oil, chlorophenyl silicone oil, alkyl silicone oil, chlorosilicone oil, polyoxyalkylene modified silicone oil, fatty acid ester modified silicone oil, methyl hydrogen silicone oil, silanol group-containing Examples include silicone oil, alkoxy group-containing silicone oil, acetoxy group-containing silicone oil, amino-modified silicone oil, carboxylic acid-modified silicone oil, alcohol-modified silicone oil, and the like. Among these, dimethyl silicone oil is more preferable because it is excellent in hydrophobic effect and silicone oils having various viscosities can be easily obtained.

  The amount of silicone oil used in treating the surface of the zirconium oxide fine particles is preferably 5 to 30% by mass, more preferably 15 to 25% by weight, based on 100% by weight of the zirconium oxide fine particles. When the amount of silicone oil used is too small, it may be difficult to suppress a decrease in charge amount of the toner under high temperature and high humidity conditions, or the fluidity of the toner may be insufficient. If the amount of silicone oil used is excessive, the amount of positively charged polar groups exposed on the surface of the zirconium oxide fine particles may be reduced, making it difficult to obtain the desired positive chargeability.

  Specific examples of the surface treatment method using silicone oil include dripping or spraying silicone oil while stirring untreated zirconium oxide fine particles or zirconium oxide fine particles surface-treated with the aforementioned positively chargeable surface treatment agent at high speed. The method of doing is mentioned. When silicone oil is dropped or sprayed, the silicone oil can be used as it is or diluted with an organic solvent or the like.

  The amount of silicone oil adhering to the surface of the zirconium oxide fine particles can be measured, for example, by the following method. First, if the analysis target is a two-component developer, the two-component developer is sieved by a sieve that can be separated into a carrier and toner (for example, a sieve having an opening of 23 μm), and the toner is separated from the two-component developer. To do. 0.5 g of the obtained toner is filled in a molding machine and pressurized to 10 MPa to produce a pellet having a diameter of 20 mm. The obtained pellet was used as a sample and analyzed by a fluorescent X-ray analyzer (ZSX (manufactured by Rigaku Corporation)). From the X-ray intensity (kcps), an element derived from the positively chargeable surface treatment agent in the sample ( For example, N, Si, Al, Ti), the amount of Si derived from silicone oil, and the content of Zr derived from zirconium oxide are measured. Next, the mass of the silicone oil relative to the mass of the zirconium oxide fine particles is calculated from the content of Si derived from the obtained silicone oil, the content of Zr, and the elemental composition of the silicone oil.

[Method for producing positively chargeable toner]
The positively chargeable toner of the present invention is produced by attaching zirconium oxide fine particles to the surface of the toner base particles described above. The method of attaching the zirconium oxide fine particles to the surface of the toner base particles is not particularly limited. For example, the processing conditions are adjusted so that the zirconium oxide fine particles are not embedded in the toner base particles, and the toner base particles are prepared by various mixers. And a method of mixing zirconium oxide fine particles with each other is preferable. Specific examples of the mixer include a turbine type agitator, a Henschel mixer, a super mixer, and the like, and a Henschel mixer is more preferable.

  The positively chargeable toner of the present invention contains zirconium oxide fine particles and other inorganic fine particles of zirconium oxide for the purpose of improving the fluidity, storage stability, cleaning properties, etc. of the toner within a range not impairing the object of the present invention. You may make it adhere to the surface of a toner mother particle as an external additive.

  The kind of the other inorganic fine particles of the zirconium oxide fine particles used as the external additive is not particularly limited as long as the object of the present invention is not impaired, and can be appropriately selected from the inorganic fine particles conventionally used for toner. Specific examples of suitable external additives include metal oxides such as silica, alumina, titanium oxide, magnesium oxide, zinc oxide, strontium titanate, and barium titanate. These external additives can be used in combination of two or more.

  The amount of the zirconium oxide fine particles used relative to the toner base particles is preferably 0.5 to 8.0 parts by weight, and more preferably 1.5 to 6.0 parts by weight with respect to 100 parts by weight of the toner base particles. When the amount of zirconium oxide fine particles used is too small, it is difficult to obtain the desired positive chargeability, and as a result, it may be difficult to obtain the effect of suppressing image defects such as fogging and toner scattering. When the amount is excessive, zirconium oxide fine particles falling off from the surface of the positively chargeable toner may adhere to, for example, a developing roller inside the developing device and cause an image defect. When other external additives of zirconium oxide fine particles are used together with the zirconium oxide fine particles as the external additive, the total amount of these used amounts is 4.0 parts by mass or less with respect to 100 parts by mass of the toner base particles. Is preferred.

  The average primary particle diameter of the other inorganic fine particles of zirconium oxide is not particularly limited as long as the object of the present invention is not impaired, and typically 0.01 to 1.0 μm is preferable.

  The volume specific resistance value of other inorganic fine particles of zirconium oxide is adjusted by forming a coating layer consisting of tin oxide and antimony oxide on the surface and changing the thickness of the coating layer and the ratio of tin oxide to antimony oxide. it can. Further, as the other inorganic fine particles of zirconium oxide, those treated with a positively chargeable surface treating agent and / or silicone oil can be used in the same manner as zirconium oxide.

[Method for producing two-component developer]
The positively chargeable toner of the present invention can be mixed with a desired carrier and used as a two-component developer. When preparing a two-component developer, it is preferable to use a magnetic carrier.

  Suitable carriers when the positively chargeable toner of the present invention is used as a two-component developer include those in which a carrier core material is coated with a resin. Specific examples of carrier core materials include particles of iron, oxidized iron, reduced iron, magnetite, copper, silicon steel, ferrite, nickel, cobalt, etc., and particles of alloys of these materials with manganese, zinc, aluminum, etc. , Particles such as iron-nickel alloy, iron-cobalt alloy, titanium oxide, aluminum oxide, copper oxide, magnesium oxide, lead oxide, zirconium oxide, silicon carbide, magnesium titanate, barium titanate, lithium titanate, lead titanate , Ceramic particles such as lead zirconate and lithium niobate, particles of high dielectric constant materials such as ammonium dihydrogen phosphate, potassium dihydrogen phosphate, and Rochelle salt, resin carriers in which the above magnetic particles are dispersed in a resin, etc. Is mentioned.

  Specific examples of the resin covering the carrier core material include (meth) acrylic polymers, styrene polymers, styrene- (meth) acrylic copolymers, olefin polymers (polyethylene, chlorinated polyethylene, polypropylene, etc. ), Polyvinyl chloride, polyvinyl acetate, polycarbonate, cellulose resin, polyester resin, unsaturated polyester resin, polyamide resin, polyurethane resin, epoxy resin, silicone resin, fluororesin (tetrafluoroethylene / hexafluoropropylene copolymer) Resin, tetrafluoroethylene / perfluoroalkyl vinyl ether copolymer resin, polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, etc.), phenol resin, xylene resin, diallyl phthalate resin, polyacetal resin, amino resin (Polyamide resin, polyimide resin, polyamide-imide resins, etc.) and the like. These resins can be used in combination of two or more.

  The particle diameter of the carrier is not particularly limited as long as the object of the present invention is not hindered, but is preferably 20 to 200 μm, more preferably 25 to 100 μm, as measured by an electron microscope.

The apparent density of the carrier is not particularly limited as long as the object of the present invention is not impaired. The apparent density varies depending on the composition of the carrier and the surface structure, but typically 2.4 × 10 ^{3 to} 3.0 × 10 ³ kg / m ³ is preferable.

  When the positively chargeable toner of the present invention is used as a two-component developer, the toner content is preferably 1 to 20% by mass, and more preferably 3 to 15% by mass, based on the mass of the two-component developer. By setting the toner content in the two-component developer within such a range, it is possible to maintain an appropriate image density and to suppress contamination of the image forming apparatus and adhesion of toner to transfer paper by suppressing toner scattering.

[Image forming method]
The positively chargeable toner of the present invention can be used in various image forming apparatuses that form images by a one-component development system or a two-component development system. Here, among the two-component development methods, a touch-down development method which is a development method suitable in terms of image quality and life will be described with reference to FIG. In the touch-down development method, fogging and toner scattering are likely to occur due to poor charging of the toner, so that the effect of using the two-component developer containing the toner of the present invention is remarkable.

  In the touch-down development method, a magnetic brush is formed on the surface of the magnetic roller with a two-component developer, and only the toner is transferred from the magnetic brush to the surface of the developing roller that is disposed facing the photoconductor to form a toner layer. In this method, toner is ejected from the toner layer, and the electrostatic latent image on the surface of the photoreceptor is developed as a toner image.

  An image forming apparatus 10 of a touch-down development method illustrated in FIG. 1 includes a drum-shaped photoconductor 11, a charging unit 12 for charging the surface of the photoconductor 11, and an electrostatic latent image by exposing the surface of the photoconductor 11. The toner image is transferred from the photosensitive member 11 to the transfer member that moves on the endless belt 15. The exposure unit 13 forms a toner image by developing the electrostatic latent image with toner. A transfer unit 16 and a cleaning unit 17 for cleaning the surface of the photoreceptor are provided.

  As the photoreceptor 11, an inorganic photoreceptor such as selenium or amorphous silicon; an organic photoreceptor in which a single layer or a laminated photoreceptor layer containing a charge generating agent, a charge transport agent, a binder resin, etc. is formed on a conductive substrate. Etc. Examples of the charging unit 12 include a scorotron system, a charging roller, and a charging brush. As the exposure unit 13, the transfer unit 16, and the cleaning unit 17, known ones may be used.

  The developing unit 14 includes a magnetic roller 18 (developer carrying member) on which a magnetic brush is formed by a two-component developer, and toner transferred from a magnetic brush (not shown) formed on the magnetic roller 18. A developing roller 19 (toner carrier) on which a toner layer (not shown) is formed, a power source 20 for applying a direct current (DC) bias to the magnetic roller 18, and a direct current (DC) bias to the developing roller 19. , A power supply 24 for applying an alternating current (AC) bias to the developing roller 19, a regulation blade 26 for keeping the height of the magnetic brush formed on the magnetic roller 18 constant, and a toner container. Stirring the container 28, the stirring mixer 30 for charging the toner of the two-component developer, and the two-component developer supplied from the stirring mixer 30. A paddle mixer 34 to be supplied to the magnetic roller 18 and a partition plate 32 for partitioning between the stirring mixer 30 and the paddle mixer 34 (the developer is mixed through a flow path (not shown) between the partition plate 32 and a frame 36 described later). 30 to the paddle mixer 34), and a magnetic roller 18, a developing roller 19, a stirring mixer 30, and a frame 36 that houses the paddle mixer 34. The magnetic roller 18 has a plurality of fixed magnets (not shown) disposed therein, and the sleeve-like magnetic roller 18 can rotate around the fixed magnet. Further, the developing roller 19 is disposed on the opposite side of the photoconductor 11.

  In the touch-down development type image forming apparatus shown in FIG. 1, for example, a charging process for charging the surface of the photoconductor 11 by the charging unit 12, and the surface of the photoconductor 11 is exposed by the exposure unit 13. A magnetic brush is formed by a two-component developer composed of a toner and a carrier, and a toner layer is formed by separating only the toner from the magnetic brush. An image is formed by a method including a developing step of attaching the exposed portion of the electrostatic latent image to a toner image.

  A specific image forming method is as follows. First, the charging unit 12 charges the surface of the photoconductor 11, and then the exposure unit 13 exposes the surface of the photoconductor 11 to form an electrostatic latent image. On the other hand, in the developing unit 14, the toner of the two-component developer is charged by the stirring mixer 30, the two-component developer is supplied to the magnetic roller 18 by the paddle mixer 34, and is carried on the surface of the magnetic brush. Then, only the toner is transferred from the magnetic brush to the surface of the developing roller 19 to form a toner layer on the surface of the developing roller 19.

  Then, the toner is ejected from the toner layer of the developing roller 19, and the toner is attached to the exposed portion of the electrostatic latent image of the photoreceptor 11 to develop the electrostatic latent image as a toner image. Next, the toner image is transferred from the photosensitive member 11 to the transfer target moving on the endless belt 15 by the transfer unit 16 to form an image. Separately, the surface of the photoconductor 11 after the transfer process is cleaned using the cleaning unit 17. The above steps are repeated.

  The toner supplied from the container 28 is mixed with a carrier by a stirring mixer 30 to be a two-component developer.

  The positively chargeable toner of the present invention described above can maintain good positive chargeability, and can suppress image defects such as fogging and toner scattering. In particular, when an image is formed at a high printing rate, the amount of toner replenished per unit time is increased, so a higher positive chargeability is required. However, according to the positively chargeable toner of the present invention, an image can be printed at a high printing rate. Even when it is formed, it is possible to suppress the occurrence of image defects such as fogging. In addition, according to the two-component developer using the positively chargeable toner of the present invention, it is possible to satisfactorily suppress the occurrence of fogging and toner scattering even in the touch-down development method.

  Hereinafter, the present invention will be described more specifically with reference to examples. In addition, this invention is not limited at all by the Example.

[Example 1]
(Preparation of external additives)
100 parts by mass of untreated zirconium oxide fine particles (average primary particle size: 40 nm) were placed in a closed Henschel mixer and stirred. Next, 20 parts by mass of a positively chargeable surface treatment agent (KBM-603, aminosilane coupling agent, N-2- (aminoethyl) -3-aminopropyltrimethoxysilane (manufactured by Shin-Etsu Chemical Co., Ltd.)), silicone oil 20 parts by mass (KF-96, dimethyl silicone oil (manufactured by Shin-Etsu Chemical Co., Ltd.)) was sprayed uniformly on the stirred fine particles of zirconium oxide. Thereafter, the zirconium oxide fine particles were held at 110 ° C. for 2 hours with stirring, and the surface treatment of the zirconium oxide fine particles was performed with a positively chargeable surface treating agent and silicone oil. The inside of the Henschel mixer was depressurized to remove by-products generated by the surface treatment, and then heated at 200 ° C. for 1 hour to obtain zirconium oxide fine particles A (ZO-A).

(Preparation of toner base particles)
100 parts by mass of a polyester resin (binder resin, acid value: 5.6 mg KOH / g, melting point 120 ° C.), 4 parts by mass of copper phthalocyanine blue pigment (colorant, CI Pigment Blue 15: 3), wax ( After mixing 5 parts by weight of a mold release agent, Carnauba wax WAX (manufactured by Nippon Seiki Co., Ltd.) and 1 part by mass of a charge control agent (P51 (manufactured by Clariant Japan)) with a Henschel mixer, A melt-kneaded product was obtained by melt-kneading. The obtained melt-kneaded product was cooled and then ground by a hammer mill. Next, the coarsely pulverized product was pulverized with a turbo mill and then classified with an elbow jet classifier to obtain toner base particles having an average particle size of 6.8 μm.

(Preparation of positively chargeable toner)
To 100 parts by mass of the obtained toner base particles, 4.5 parts by mass of zirconium oxide fine particles A are added and mixed for 5 minutes at 2800 rpm in a Henschel mixer 20B (manufactured by Nippon Coke Co., Ltd.). A toner was obtained.

(Preparation of two-component developer)
Positively charged toner and magnetic carrier (carrier used in printer FS-C5300DN (manufactured by Kyocera Mita Corporation), average so that the proportion of positively charged toner in the two-component developer is 12.0% by mass Particle size: 35 μm) was mixed with a rocking mixer (RM-10 (manufactured by Aichi Electric Co., Ltd.)) for 30 minutes under the conditions of 78 rpm, temperature of 20 ° C. and humidity of 60% to obtain a two-component developer.

  The obtained two-component developer was subjected to image formation under a normal temperature and humidity environment at a temperature of 20 ° C. and a relative humidity of 65% using a printer (FS-5300DN) manufactured by Kyocera Mita Corporation as an evaluation machine. Evaluation was performed.

(Image density evaluation)
A two-component developer was set in the printer, and after the printer was turned on and stabilized, samples and images were output. This image was used as the initial image (first image). Next, 5000 sheets of images with a printing rate of 1% were printed while replenishing toner. A sample image for evaluation was output on the 5000th sheet, and this image was used as a low density printed image. Thereafter, 1000 sheets of images with a printing rate of 30% were printed while supplying the replenishing toner. Note that a sample image for evaluation was output on the 1000th sheet (6000th sheet from the initial image). Subsequently, 5000 images with a printing rate of 1% were printed, and then 1000 images with a printing rate of 100% were printed. Note that a sample image for evaluation was output on the 1000th sheet (12000th sheet from the initial image), and this image was used as the high-density print image 2.

  In each of the initial image, the low density print image, the high density print image 1 and the high density print image 2, a solid image of 2 cm × 2 cm is positioned near the left end in the paper transport direction, the center, and the right end. It is formed at three locations in the vicinity of the part.

  About the formed solid image of each image for evaluation, the reflection density was measured using a reflection densitometer (RD-19A: SpectroEyeLT (manufactured by Gretag Macbeth)). The average value of the reflection density was obtained as the image density of the obtained image.

  When the measured image density value is 1.4 or more, it is evaluated as “◎”, 1.3 or more and less than 1.4 is evaluated as “◯”, and 1.2 or more and less than 1.3 is evaluated as “△”. , Less than 1.2 was evaluated as “x”.

(Cover evaluation)
In each evaluation image used for image density evaluation, the value obtained by subtracting the image density value of the base paper (that is, the white paper before image output) from the image density value of the blank paper measured by the reflection densitometer is covered. Concentration. Then, the fog density was measured every predetermined number of sheets, and the fog was evaluated based on the maximum value.

  A maximum fog density value of 0.003 or less was evaluated as “◯”, more than 0.003 and 0.007 or less was evaluated as “Δ”, and more than 0.007 was evaluated as “x”.

(Toner scattering)
The two-component developer was set in the printer, the developer was idled for 2 hours, and then 3.5 g of toner was forcibly supplied to the developer. Thereafter, the developing unit was spun for 5 minutes, during which time the toner (scattered toner) accumulated in the tray installed at the lower part of the developing unit was collected, and the amount (scattered amount) was measured. The scattering amount of 50 mg or less was evaluated as “◯”, the amount exceeding 50 mg was evaluated as “Δ”, and the amount exceeding 200 mg was evaluated as “x”.

(Charge amount)
The developer immediately after printing the initial image, the low-density print image, the high-density print image 1 and the high-density print image 2 is taken out, and the charge amount of each developer obtained is measured by a suction-type charge amount measuring device (MODEL 210HS). (Manufactured by TREK)).

  Table 2 shows evaluation results of image density, fogging, toner scattering, and charge amount of the toner of Example 1.

[Example 2, Example 3, and Comparative Examples 1-6]
(Preparation of zirconium oxide fine particles B to G)
Except for changing the usage amount of the positively chargeable surface treatment agent and the usage amount of the silicone oil to the amounts shown in Table 1 with respect to the mass of the untreated zirconium oxide fine particles, the same manner as the zirconium oxide fine particles A was performed. Zirconium oxide fine particles B to G (ZO-B to ZO-G) were obtained.

(Zirconium oxide fine particles H)
The untreated zirconium oxide fine particles used for the preparation of the zirconium oxide fine particles A were used as the zirconium oxide fine particles H.

(Preparation of silica fine particles A)
Silica fine particles A in the same manner as the zirconium oxide fine particles A except that 100 parts by mass of the untreated zirconium oxide fine particles are changed to 100 parts by mass of untreated silica fine particles (Aerosil 130, manufactured by Nippon Aerosil Co., Ltd.). (SI-A) was obtained.

(Preparation of positively chargeable toner)
The positively chargeable toners of Example 2, Example 3, and Comparative Examples 1 to 6 were obtained in the same manner as Example 1 except that the external additives listed in Table 2 were used.

(Preparation of two-component developer)
Using the positively chargeable toners obtained in Examples 2 to 6 and Comparative Examples 1 to 4, two-component developers were prepared in the same manner as in Example 1. Table 2 shows the evaluation results of image density, fog, toner scattering, and charge amount of the toners of Examples 2 to 6 and Comparative Examples 1 to 4.

  According to Table 2, the surface ratio of the positively chargeable surface treatment agent and the silicone oil that is surface-treated with the positively chargeable surface treatment agent and the silicone oil and adheres to the surface of the zirconium oxide fine particles is positively charged. According to the positively chargeable toners of Examples 1 to 3, which are 6: 4 to 2: 8 as a silicone surface treatment agent, a good image is formed even when printing is performed at a high density, and fogging. In addition, it can be seen that toner scattering hardly occurs and charging can be performed stably over a long period of time.

  According to Comparative Examples 1 and 3, when the usage amount of the positively chargeable surface treatment agent is too much with respect to the usage amount of silicone oil, a sufficient image density may not be obtained in a low density printed image. It can be seen that toner scattering and fogging in a high density printed image are likely to occur, and the charge amount is likely to decrease when printing is performed over a long period.

  According to Comparative Examples 2 and 4, when the amount of silicone oil used is too large relative to the amount of positively charged surface treatment agent used, there is no problem in image density, but in toner scattering and high density printed images. It can be seen that fog is likely to occur, and the amount of charge tends to decrease when printing over a long period of time.

  According to Comparative Example 5, when surface treatment is not performed on the zirconium oxide fine particles, fog is hardly generated, but good image density is not obtained, toner scattering is likely to occur, and charging is performed when printing is performed for a long period of time. It turns out that quantity is easy to fall. Further, according to Comparative Example 6, when silica is used as the external additive, the toner scattering even if the external additive is surface-treated with an appropriate amount of the positively chargeable surface treatment agent and silicone oil. It can be seen that fog is likely to occur in a high-density printed image, and the charge amount is likely to decrease when printing over a long period of time.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 11 Photoconductor 12 Charging part 13 Exposure part 14 Developing part 15 Endless belt 16 Transfer part 17 Cleaning part 18 Magnetic roller 19 Developing roller 20 Power supply 22 Power supply 24 Power supply 26 Regulation blade 28 Container 30 Stirring mixer 32 Partition plate 36 Frame body

Claims (4)

Zirconium oxide fine particles are attached to the surface of the toner base particles,
The toner base particles contain at least a binder resin and a colorant,
The binder resin is a polyester resin;
The zirconium oxide fine particles are surface-treated with a positively chargeable surface treatment agent and silicone oil,
A positively chargeable toner having a mass ratio of 6: 4 to 2: 8 of the positively chargeable surface treatment agent and the silicone oil attached to the surface of the zirconium oxide fine particles. The positively chargeable toner according to claim 1, wherein the amount of the positively chargeable surface treatment agent is 8 to 24 % by mass based on the mass of the zirconium oxide fine particles. The positively chargeable toner according to claim 1, wherein the amount of the silicone oil is 16 to 32 % by mass with respect to the mass of the zirconium oxide fine particles.   The positively chargeable toner according to claim 1, wherein the positively chargeable surface treatment agent is a coupling agent.

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