JP2013257464A - Magnetic single component development toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a magnetic single component development toner, which can suppress such problems that an image density decreases than a desired value or an image failure such as fogging occurs in a formed image when images with a low image density are continuously formed for a long period of time or an image is formed in a low temperature and low humidity environment or in a high temperature and high humidity environment, and which can suppress occurrence of disturbance in a toner layer in a low temperature and low humidity environment.SOLUTION: The magnetic single component development toner comprises at least toner base particles containing a binder resin and a magnetic powder, and an external additive adhering to the surfaces of the toner base particles. The toner contains silica as an external additive, which comprises a hydrophobic silica (X) and a positive charging type weak charging silica (Y) that is a wet silica having both polar groups of a positive charging polar group and a fluorine-containing negative charging polar group on the surface thereof. An average aggregation number (a) of the silica on the toner base particle surface and an isolation rate (b) of the silica in the magnetic single component development toner are within predetermined ranges.

Description

  The present invention relates to a magnetic one-component developing toner.

  In general, in electrophotography, 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 formed electrostatic latent image is developed with toner to form a toner image. Further, the formed toner image is transferred to a recording medium to obtain a high quality image. The toner used to form a normal toner image is obtained by mixing a colorant, a charge control agent, a release agent and the like with a binder resin such as a thermoplastic resin, and then kneading, pulverizing, and classifying steps. Toner particles (toner mother particles) having a particle diameter of 5 to 10 μm are used. For the purpose of imparting fluidity to the toner, imparting suitable charging performance to the toner, and improving the cleaning property of the toner from the photosensitive drum, inorganic fine powders such as silica and titanium oxide are used as the toner base. Externally added to the particles.

  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.

  Examples of the toner containing inorganic fine powder having a positively chargeable polar group include, for example, dry silica fine powder having a positively chargeable polar group and a hydrophobic group on the surface, a positively chargeable polar group, and a fluorine-containing polarity. A toner (Patent Document 1) to which a wet silica fine powder containing a group is externally added has been proposed. The toner described in Patent Document 1 is excellent in toner charging stability and image density stability during printing durability.

JP-A-11-143111

  However, in the toner described in Patent Document 1, when an image having a low image density is continuously formed over a long period of time, the toner is subjected to strong stress in the developing device by continuously stirring the toner in the developing device. . For this reason, there is a problem that the charge amount of the toner tends to become unstable, and fog is likely to occur in a formed image using the toner. Further, the toner described in Patent Document 1 tends to be electrically aggregated in a low temperature and low humidity environment. Therefore, in a low temperature and low humidity environment, the thickness of the toner thin layer formed on the developing sleeve is likely to be disturbed (layer disorder), and there is a problem that an image defect due to the layer disorder is likely to occur. Further, the toner of Patent Document 1 has a problem that an image having a desired density cannot always be formed under a high temperature and high humidity environment.

  The present invention has been made in view of the above circumstances, and when image formation is continuously performed at a low image density over a long period of time, or when image formation is performed in a low-temperature and low-humidity environment and a high-temperature and high-humidity environment. Provides a toner for magnetic one-component development that can suppress the occurrence of image defects such as fogging and fogging and other image defects in the formed image, and can suppress the occurrence of layer disturbance in a low-temperature, low-humidity environment. For the purpose.

  The inventors of the present invention are toners for magnetic one-component development in which an external additive is attached to the surface of toner base particles containing at least a binder resin and magnetic powder. The hydrophobic silica (X) subjected to the above-described treatment and the weakly charged silica (Y), the average aggregation number (a) of silica on the surface of the toner base particles, and the silica in the magnetic one-component developing toner The present inventors have found that the above problems can be solved by using a magnetic one-component developing toner having a liberation ratio (b) within a predetermined range, and the present invention has been completed. Specifically, the present invention provides the following.

The present invention is a magnetic one-component developing toner in which an external additive is attached to the surface of toner base particles containing at least a binder resin and magnetic powder,
The external additive includes silica in which at least primary particles form an aggregate,
The silica is hydrophobic silica (X), positively charged polar group, and positively charged weakly charged silica (Y) which is wet silica having a bipolar group of a positively charged polar group and a fluorine-containing negatively charged polar group on the surface; Including
The average aggregation number (a) of the silica on the surface of the toner base particles is 5 to 15,
Magnetic 1 having a liberation rate (b) of 5 to 10% of the silica in the magnetic one-component developing toner measured by classifying free silica in the magnetic one-component developing toner with an airflow classifier. The present invention relates to a toner for component development.

  According to the present invention, when an image is continuously formed at a low image density over a long period of time, or when an image is formed in a low temperature and low humidity environment and a high temperature and high humidity environment, the image density becomes lower than a desired value, It is possible to provide a magnetic one-component developing toner capable of suppressing the occurrence of image defects such as fogging in a formed image and suppressing the occurrence of layer disturbance in a low-temperature and low-humidity environment.

  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 toner for magnetic one-component development (hereinafter also simply referred to as toner) of the present invention, silica is attached as an external additive on the surface of toner base particles containing at least a binder resin and magnetic powder. The silica as the external additive is hydrophobic silica (X), positively charged weakly charged silica (wet silica having a positively charged polar group and a fluorine-containing negatively charged polar group on the surface). Y). Further, the average aggregation number (a) of silica on the surface of the toner base particles and the liberation rate (b) of silica measured by a predetermined method are within a predetermined range. In addition to the binder resin and the magnetic powder, the toner base particles may contain a colorant, a release agent, a charge control agent, and the like as desired.

  Hereinafter, the binder resin, magnetic powder, colorant, charge control agent, release agent, toner base particle manufacturing method, external additive, and external addition treatment will be described in order for the magnetic one-component developing toner of the present invention. .

[Binder resin]
The binder resin contained in the toner base particles is not particularly limited as long as it is a resin conventionally used as a binder resin for toner. Specific examples of the binder resin include styrene resin, acrylic resin, styrene acrylic resin, polyethylene resin, polypropylene resin, vinyl chloride resin, polyester resin, polyamide resin, polyurethane resin, polyvinyl alcohol resin, vinyl ether. And thermoplastic resins such as styrene resins, N-vinyl resins, and styrene-butadiene resins. Among these resins, styrene acrylic resins and polyester resins are preferable from the viewpoints of dispersibility of the colorant in the toner, chargeability of the toner, and fixability to the paper. Hereinafter, the styrene acrylic resin and the polyester resin used in this embodiment will be described.

  The styrene acrylic resin is a copolymer of a styrene monomer and an acrylic monomer. Specific examples of the styrene monomer include styrene, α-methylstyrene, vinyl toluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, p-chlorostyrene, and p-ethylstyrene. Specific examples of the acrylic monomer include methyl acrylate, ethyl acrylate, n-propyl acrylate, iso-propyl acrylate, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, meta Examples include (meth) acrylic acid alkyl esters such as methyl acrylate, ethyl methacrylate, n-butyl methacrylate, and iso-butyl methacrylate.

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

  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-sol Tan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2, Examples include trivalent or higher alcohols such as 4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

  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, alkyl such as isododecenyl succinic acid or alkenyl succinic acid; 1,2,4-benzenetricarboxylic acid (trimellitic acid), 1,2,5- Benzenetricarboxylic 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, trivalent or higher carboxylic acid such as empole trimer acid, and the like. As these divalent or trivalent or higher carboxylic acid components, ester-forming derivatives such as acid halides, acid anhydrides, and lower alkyl esters may be used. 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, and more preferably 90 to 140 ° C.

  As the binder resin, it is preferable to use a thermoplastic resin because of its good fixability, but not only the thermoplastic resin is used alone, but also a crosslinking agent or a thermosetting resin is added to the thermoplastic resin. It is also possible to use one. By introducing a partially crosslinked structure into the binder resin, it is possible to improve the storage stability, shape retention, durability and the like of the toner without deteriorating the toner fixability.

  As the thermosetting resin that can be used together with the thermoplastic resin, 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, and cyanate resins. . 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. When the glass transition point of the binder resin is too low, the toner may be fused inside the developing part of the image forming apparatus or the storage stability of the toner may be reduced, so that the toner container may be transported or stored in a warehouse. In some cases, the toner may be partially fused. In addition, when the glass transition point of the binder resin is too high, the strength of the binder resin is reduced, and the toner is likely to adhere to the latent image carrying portion. Further, when the glass transition point of the binder resin is too high, the toner tends to be difficult to fix well at a low temperature.

  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, the glass transition point of the binder resin is measured as follows. Using a differential scanning calorimeter DSC-6200 manufactured by Seiko Instruments Inc. as a measuring device, the glass transition point of the binder resin is determined by measuring the endothermic curve. 10 mg of binder resin as a measurement sample is put in an aluminum pan, and an empty aluminum pan is used as a reference. The glass transition point of the binder resin can be determined from the endothermic curve of the binder resin obtained by measurement at a measurement temperature range of 25 ° C. to 200 ° C., a temperature increase rate of 10 ° C./min, and normal temperature and humidity.

  The amount of the binder resin used is not particularly limited as long as the object of the present invention is not impaired. Specifically, when the total amount of toner is 100 parts by mass, it is preferably 35 to 55 parts by mass, and more preferably 40 to 50 parts by mass.

[Magnetic powder]
Since the magnetic one-component developing toner of the present invention is a magnetic toner, the binder resin essentially contains magnetic powder. The type of magnetic powder to be blended with the toner is not particularly limited as long as the object of the present invention is not impaired. Examples of suitable magnetic powders include iron oxides such as ferrite and magnetite; ferromagnetic metals such as cobalt and nickel; alloys containing iron and / or ferromagnetic metals; iron and / or ferromagnetic metals. Compounds including: Ferromagnetic alloys subjected to ferromagnetization treatment such as heat treatment; chromium dioxide.

  The particle size of the magnetic powder is not limited as long as the object of the present invention is not impaired. The particle diameter of the specific magnetic powder is preferably 0.1 to 1.0 μm, and more preferably 0.1 to 0.5 μm. When magnetic powder having such a particle size is used, it is easy to uniformly disperse the magnetic powder in the binder resin.

  The magnetic powder can be used that has been surface-treated with a surface treatment agent such as a titanium coupling agent or a silane coupling agent for the purpose of improving dispersibility in the binder resin.

  The usage-amount of magnetic powder is not specifically limited in the range which does not inhibit the objective of this invention. The specific amount of magnetic powder used is preferably 35 to 60 parts by mass, and more preferably 40 to 60 parts by mass when the total amount of toner is 100 parts by mass. If the amount of magnetic powder used is excessive, the image density may be lower than desired when printing continuously at a low image density over a long period of time, or the toner fixability may be extremely reduced. . If the amount of magnetic powder used is too small, fog may occur in the formed image, or the image density may become lower than desired when continuously printing at a low image density over a long period of time. When toner is used as a two-component developer, the amount of magnetic powder used is preferably 20 parts by mass or less, and more preferably 15 parts by mass or less when the total amount of toner is 100 parts by mass.

[Colorant]
The toner for magnetic one-component development of the present invention is usually black because it contains magnetic powder as an essential component. Therefore, the toner is a known dye as a colorant for the purpose of adjusting a formed image formed using the magnetic one-component developer of the present invention to a more preferable black hue within a range that does not impair the object of the present invention. Or it may contain a pigment. Specifically, examples of the pigment include carbon black, and examples of the dye include acid violet.

  The amount of the colorant used is not particularly limited as long as the object of the present invention is not impaired. The specific amount of the colorant used is preferably 1 to 10 parts by mass and more preferably 3 to 7 parts by mass when the total amount of toner is 100 parts by mass.

[Release agent]
The toner for magnetic one-component development of the present invention may contain a release agent for the purpose of improving fixability and offset resistance. The type of release agent added to the toner is not particularly limited as long as the object of the present invention is not impaired. As the release agent, wax is preferable. Specific examples of the wax include polyethylene wax, polypropylene wax, fluororesin wax, Fischer-Tropsch wax, paraffin wax, ester wax, montan wax and rice wax. These release agents can be used in combination of two or more. By adding these release agents to the toner, the occurrence of offset and image smearing (dirt 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. The specific amount of the release agent used is preferably 1 to 10 parts by mass when the total amount of toner is 100 parts by mass. If the amount of release agent used is too small, the desired effect may not be obtained with respect to suppression of 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 of the toner may decrease.

[Charge control agent]
The magnetic one-component developing toner of the present invention may contain a charge control agent in the binder resin. The purpose of the charge control agent is to improve the charge level of the toner and the charge start-up characteristic that is an indicator of whether or not the toner can be charged to a predetermined charge level in a short time, and to obtain a toner having excellent durability and stability. used. When developing with positively charged toner, a positively chargeable charge control agent is used. When developing with negatively charged toner, a negatively chargeable charge control agent is used.

  The type of the 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 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 and quinoxaline; Azin Fast Red FC, Azin Fast Red 12BK, Azine Violet BO, Azine Direct dyes consisting of azine compounds such as Ng Brown 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Deep Black EW, and Azin Deep Black 3RL; Nigrosine such as Nigrosine, Nigrosine Salt, Nigrosine Derivative Compounds; acid dyes composed of nigrosine compounds such as nigrosine BK, nigrosine NB, nigrosine Z; metal salts of naphthenic acid or higher fatty acids; alkoxylated amines; alkylamides; 4 such as benzylmethylhexyldecylammonium and decyltrimethylammonium chloride A class ammonium salt is mentioned. Among these positively chargeable charge control agents, a nigrosine compound is particularly preferable in that a quicker charge rising property can be obtained. These positively chargeable charge control agents can be used in combination of two or more.

  A resin having a quaternary ammonium salt, carboxylate, or 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 having salt, acrylic resin having carboxylate, styrene-acrylic resin having carboxylate, polyester resin having carboxylate, styrene resin having carboxyl group, acrylic having carboxyl group Examples thereof include resins, styrene-acrylic resins having a carboxyl group, and polyester resins having a carboxyl group. 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 resin having a quaternary ammonium salt as a functional group from the viewpoint that the charge amount of the toner can be easily adjusted to a value within a desired range. A copolymer resin is more preferable. Specific examples of preferred acrylic comonomers to be copolymerized with styrene units for styrene-acrylic copolymer resins having a quaternary ammonium salt as a functional group include methyl acrylate, ethyl acrylate, n-propyl acrylate, acrylic acid such as iso-propyl, n-butyl acrylate, iso-butyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, ethyl methacrylate, n-butyl methacrylate, iso-butyl methacrylate (meth ) Acrylic acid alkyl ester.

  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, for example, dimethylaminoethyl (meth) acrylate, diethylaminoethyl (meth) acrylate, dipropylaminoethyl (meth) acrylate, dibutylaminoethyl (meth) acrylate, Specific examples of dialkyl (meth) acrylamide include dimethylmethacrylamide, and specific examples of dialkylaminoalkyl (meth) acrylamide include dimethylaminopropyl methacrylamide. Further, a hydroxy group-containing polymerizable monomer such as hydroxyethyl (meth) acrylate, hydroxypropyl (meth) acrylate, 2-hydroxybutyl (meth) acrylate, or N-methylol (meth) acrylamide can be used in combination during polymerization.

  Specific examples of the negatively chargeable charge control agent include organometallic complexes and chelate compounds. Examples of organometallic complexes and chelate compounds include acetylacetone metal complexes such as aluminum acetylacetonate and iron (II) acetylacetonate, and salicylic acid metal complexes such as chromium 3,5-di-tert-butylsalicylate. A salicylic acid metal salt is preferable, and a salicylic acid metal complex or a salicylic acid metal salt is more preferable. These negatively chargeable charge control agents can be used in combination of two or more.

  The amount of the positively or negatively chargeable charge control agent used is not particularly limited as long as the object of the present invention is not impaired. The amount of the positively or negatively chargeable charge control agent used is typically preferably 1.5 to 15 parts by mass, and 2.0 to 8.0 parts by mass when the total amount of toner is 100 parts by mass. Part is more preferable, and 3.0 to 7.0 parts by weight is particularly preferable. When the amount of the charge control agent used is too small, it is difficult to stably charge the toner to a predetermined polarity. Therefore, the image density of the formed image becomes lower than a desired value, or the image density of the formed image is maintained over a long period of time. May be difficult. In such a case, since the charge control agent is difficult to uniformly disperse in the toner, the formed image is likely to be fogged or the latent image carrier is easily contaminated by the toner component. When the amount of charge control agent used is excessive, image defects due to poor charging of the toner under high temperature and high humidity are likely to occur in the formed image due to deterioration of environmental resistance, or the latent image carrying portion due to the toner component Contamination etc. are likely to occur.

[Method for producing toner mother particles]
The method of producing toner base particles by blending a binder resin with magnetic powder and optional components such as a colorant, a release agent, and a charge control agent can favorably disperse these components in the binder resin. There is no particular limitation. Specific examples of suitable methods for producing toner base particles include a blender of a mixture of a binder resin and magnetic powder, and optional components such as a colorant, a release agent, and a charge control agent, if necessary. And a mixture of the binder resin and the component blended in the binder resin by a kneader such as a single screw or twin screw extruder, and the cooled kneaded material is pulverized and classified. The average particle diameter of the toner base particles is not particularly limited as long as the object of the present invention is not impaired, but generally 5 to 10 μm is preferable.

[External additive]
The toner for magnetic one-component development of the present invention is one in which an external additive is attached to the surface of toner base particles. The external additive contains silica, and the silica is wet silica having a hydrophobic silica (X), a positively chargeable polar group, and a fluorine-containing negatively charged polar group on its surface. And charged silica (Y). The mass ratio (Y / X) of the hydrophobic silica (X) and the weakly charged silica (Y) in the external additive is not particularly limited as long as the object of the present invention is not hindered. 1.5 is preferable, 0.2 to 1.0 is more preferable, and 0.3 to 0.6 is particularly preferable.

  By using an external additive containing hydrophobic silica (X) and weakly charged silica (Y) at such a ratio, the toner base particles are externally added, so that a low image density image can be continuously produced over a long period of time. When the image is formed, or when an image is formed in a low-temperature and low-humidity environment and a high-temperature and high-humidity environment, it is possible to suppress the image density from becoming lower than a desired value and the occurrence of image defects such as fogging in the formed image. In addition, in a low temperature and low humidity environment, it is easy to obtain a toner that can suppress the occurrence of layer disturbance in the toner layer formed on the developer carrier (developing sleeve).

  Hereinafter, silica and other silicas other than silica, including hydrophobic silica (X), weakly charged silica (Y), hydrophobic silica (X), and weakly charged silica (Y), which are included as silica, Other external additives and the amount of the external additive used will be described in order.

[Hydrophobic silica (X)]
Hydrophobic silica (X) is obtained by surface-treating silica with a hydrophobizing agent. When silica hydrophobized is used, a decrease in charge amount under high temperature and high humidity conditions is suppressed, and a toner excellent in fluidity can be easily obtained. As the hydrophobizing agent, for example, a silane coupling agent can be used. In order to supplement the hydrophobizing effect, a silane coupling agent and a hydrophobizing agent other than the silane coupling agent can be used in combination. As the hydrophobizing agent other than the silane coupling agent, hexamethyldisilazane is preferably used because it is excellent in the hydrophobizing effect and the effect of improving the fluidity of the toner.

  Silicone oil can also be used as a hydrophobizing agent for silica. The type of silicone oil is not particularly limited as long as a desired hydrophobizing effect is obtained, and various silicone oils conventionally used as a hydrophobizing agent 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 thereof include silicone oil, alkoxy group-containing silicone oil, acetoxy group-containing silicone oil, amino-modified silicone oil, carboxylic acid-modified silicone oil, and alcohol-modified silicone oil.

  As a method of hydrophobizing silica, a method of dropping or spraying a hydrophobizing agent such as aminosilane or silicone oil while stirring silica at a high speed, or in a stirring hydrophobizing agent in an organic solvent solution The method of adding silica is mentioned. The silica subjected to the hydrophobization treatment is obtained by heating after the hydrophobization treatment. When the hydrophobizing agent is dropped or sprayed, the hydrophobizing agent can be used as it is or diluted with an organic solvent or the like.

[Weakly charged silica (Y)]
The weakly charged silica (Y) is a wet silica having a positively chargeable property and having both a positively chargeable polar group and a fluorine-containing negatively chargeable polar group on the surface. Wet silica is produced by a sol-gel method in which silica fine particles are synthesized in a wet manner by hydrolysis of alkoxysilane, a colloidal method in which silica fine particles are synthesized in a wet manner by hydrolysis of water glass, or the like.

  A method for introducing a positively chargeable polar group and a fluorine-containing negatively chargeable polar group into wet silica is not particularly limited. Suitable methods for introducing a positively chargeable polar group and a fluorine-containing negatively chargeable polar group into wet silica include a positively chargeable surface treatment agent having a positively chargeable polar group, and a fluorine-containing negatively chargeable polar group. A method of treating the surface of wet silica with a negatively chargeable surface treating agent having

(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 chargeable polar group and can introduce the positively chargeable polar group onto the surface of wet silica. Preferable examples of the positively chargeable surface treatment agent include a coupling agent having a positively chargeable polar group such as an amino group.

  Among the positively chargeable surface treatment agents, a coupling agent is preferable because it easily reacts with silanol groups on the wet silica surface and easily introduces positively chargeable polar groups on the wet silica surface. 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. Preferable examples of the silane coupling agent having a positively chargeable polar group include aminosilane coupling agents represented by the following formula (1).

R ¹ —NH—R ² — (NH—R ³ ) _m —SiR ⁴ _a R ⁵ _(3-a) (1)
(In the formula (1), ^{R 1} represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a phenyl group, or benzyl group, ^{R 2} and ^{R 3} are each an alkylene group having 1 to 10 carbon atoms , R ⁴ is an alkyl group having 1 to 10 carbon atoms, R ⁵ is an alkoxy group having 1 to 6 carbon atoms, or a chlorine atom, m is an integer of 0 to 2, and a is an integer of 0 to 2. .)

In formula (1), R ¹ is preferably a hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a phenyl group. R ² and R ³ are each preferably an alkylene group having 1 to 6 carbon atoms, and more preferably an alkylene group having 1 to 4 carbon atoms. R ⁴ is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 4 carbon atoms. R ⁵ is preferably an alkoxy group having 1 to 4 carbon atoms, and more preferably an alkoxy group having 1 to 2 carbon atoms.

Among the compounds represented by the formula (1), suitable compounds include 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 .

(Negatively charged surface treatment agent)
The type of the negatively chargeable surface treating agent is not particularly limited as long as it is a substance having a fluorine-containing negatively chargeable polar group and can introduce a fluorine-containing negatively chargeable polar group onto the surface of wet silica. Preferable examples of such a negatively chargeable surface treatment agent include a coupling agent having a positively chargeable polar group such as a fluoroalkyl group.

  Among the negatively chargeable surface treatment agents, a coupling agent is preferable because it easily reacts with silanol groups on the wet silica surface and easily introduces fluorine-containing negatively chargeable polar groups on the wet silica surface. Specific examples of the coupling agent that can be used as the negatively 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. Preferable examples of the silane coupling agent having a fluorine-containing negatively chargeable polar group include silane coupling agents having a fluoroalkyl group represented by the following formula (2).

R ^6- (AR ⁷ ) _n -SiR ⁸ _b R ⁹ _(3-b) (2)
(In the formula (2), ^{R 6} is a fluoroalkyl having 1 to 20 carbon atoms, ^{R 7} is an alkylene group having 1 to 10 carbon atoms, ^{R 8} is an alkyl group having 1 to 10 carbon atoms, R ⁹ is an alkoxy group having 1 to 6 carbon atoms or a chlorine atom, and A is —COO—, —OCO—, —CONH—, —NHCO—, —SO ₂ NH—, or —NH—SO ₂ —. N is 0 or 1, and b is an integer of 0-2.)

In formula (2), R ⁶ is preferably a fluoroalkyl group having 1 to 15 carbon atoms, and more preferably a fluoroalkyl group having 1 to 10 carbon atoms. R ⁶ may be a fluoroalkyl group in which the hydrogen atom of the alkyl group is partially substituted with a fluorine atom, or a perfluoroalkyl group in which the hydrogen atom of the alkyl group is completely substituted with a fluorine atom. R ⁷ is preferably an alkylene group having 1 to 6 carbon atoms. R ⁸ is preferably an alkyl group having 1 to 6 carbon atoms, and more preferably an alkyl group having 1 to 4 carbon atoms. R ⁹ is preferably an alkoxy group having 1 to 4 carbon atoms or a chlorine atom, and more preferably an alkoxy group having 1 to 2 carbon atoms or a chlorine atom.

Among the compounds represented by the formula (2), suitable compounds include CF ₃ (CH ₂ ) ₂ SiCl ₃ , CF ₃ (CF ₂ ) ₅ SiCl ₃ , CF ₃ (CF ₂ ) ₅ (CH ₂ ) ₂ SiCl. ₃ , CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₂ SiCl ₃ , CF ₃ (CF ₂ ) ₇ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ , CF ₃ (CF ₂ ) ₇ (CH ₃ ) ₂ Si ( CH ₃ ) Cl ₂ , CF ₃ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ , CF ₃ (CH ₂ ) ₂ SiCH ₃ (OCH ₃ ) ₂ , CF ₃ (CF ₂ ) ₃ (CH ₂ ) ₂ Si (OCH) ₃ ) ₃ , CF ₃ (CF ₂ ) ₅ (CH ₂ ) ₂ Si (OCH ₃ ) ₃ , CF ₃ (CF ₂ ) ₅ CONH (CH ₂ ) ₂ Si (OCH ₃ ) ₃ , CF ₃ (CF ₂ ) ₅ COO (CH _{2 2 Si (OCH 3) 3,} CF 3 (CF 2) 7 (CH 2) 3 Si (OCH 3) 3, CF 3 (CF 2) 7 (CH 2) 3 SiCH 3 (OCH 3) 2, CF 3 ( _{CF 2) 7 SO 2 NH (} CH 2) 3 Si (OC 2 H 5) 3, and _{CF 3 (CF 2) 8 (} CH 2) 2 Si (OCH 3) 3 and the like.

  There are various methods for treating the silica surface using a coupling agent having a positively chargeable polar group and a fluorine-containing negatively chargeable polar group as described above. The dry treatment method is similar to the above-described silica hydrophobization treatment. Thus, a positively chargeable polar group and a fluorine-containing negatively chargeable polar group can be introduced on the surface of wet silica. Specifically, first, the coupling agent is mixed and diluted with a solvent such as tetrahydrofuran, toluene, ethyl acetate, methyl ethyl ketone, or acetone to obtain a diluted solution of the coupling agent. While forcibly stirring the silica with a blender or the like, the diluted solution of the coupling agent is dropped or sprayed and mixed thoroughly. Next, the obtained mixture is transferred to a vat or the like, placed in an oven, heated and dried. Thereafter, the mixture is stirred again with a blender and sufficiently pulverized to introduce a positively chargeable polar group and a fluorine-containing negatively polar group into wet silica.

  In addition to such a dry treatment method, a positively chargeable polar group and a fluorine-containing negatively chargeable polar group can be introduced into wet silica by a wet treatment method. As a wet processing method, for example, a method of introducing silica by immersing silica in an organic solvent solution in which the coupling agent dissolves and drying, or an aqueous solution of the coupling agent after dispersing silica in water to form a slurry. Dripping. Then, the method of precipitating silica, heat-drying, crushing, and introduce | transducing into silica is mentioned.

  When preparing weakly charged silica by treating wet silica with a positively chargeable surface treatment agent and a negatively chargeable surface treatment agent, the amount (p) of the positively chargeable surface treatment agent used in the treatment and the negatively chargeable surface treatment The molar ratio (p / n) to the amount (n) of the agent is preferably 1.0 to 2.0, and more preferably 1.2 to 1.8. The charge amount of weakly charged silica (Y) obtained after treating wet silica with a positively chargeable surface treatment agent and a negatively chargeable surface treatment agent is preferably 45 to 65 μC / g.

[Silica other than hydrophobic silica (X) and weakly charged silica (Y)]
The silica may contain silica other than hydrophobic silica (X) and weakly charged silica (Y). Examples of silica other than the hydrophobic silica (X) and the weakly charged silica (Y) include hydrophilic silica that has not been subjected to any surface treatment, and strongly charged silica. The content of hydrophobic silica (X) and weakly charged silica (Y) in the silica used as an external additive is preferably 80% or more, more preferably 90% or more, and 100% with respect to the total mass of silica. Is particularly preferred.

[Other external additives other than silica]
In addition to silica, an external additive other than silica may be attached to the surface of the toner base particles in order to improve the fluidity, storage stability, cleaning properties, etc. of the toner as long as the object of the present invention is not impaired. .

  The external additive other than silica is not particularly limited as long as the object of the present invention is not impaired, and can be appropriately selected from external additives conventionally used for toners. Specific examples of suitable external additives for silica include metal oxides such as 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 average primary particle size of other external additives other than silica is not particularly limited as long as the object of the present invention is not impaired, and typically 0.01 μm or more and 1.0 μm or less is preferable.

  When titanium oxide is used as an external additive other than silica, its volume-specific resistance value is such that a coating layer made of tin oxide and antimony oxide is formed on the surface, the thickness of the coating layer, and the tin oxide and antimony oxide. It can be adjusted by changing the ratio. Further, as the other inorganic fine particles of silica, those which have been subjected to a hydrophobic treatment in the same manner as silica can be used.

[Amount of external additive]
The amount of silica to be externally added to the surface of the toner base particles is preferably 0.8 to 1.5 parts by mass with respect to 100 parts by mass of the toner. When the amount of silica used is too small, the hydrophobicity of the toner is lowered, and the toner is likely to be affected by water molecules in the air in a high temperature and high humidity environment. For this reason, the charge amount of the toner tends to be extremely low, the formed image may be deteriorated, and the fluidity of the toner tends to be lowered. In addition, when the amount of silica used is excessive, the toner tends to be excessively charged, and the image density may be lower than a desired value.

  When external additives other than silica are externally added together with silica, the amount of external additives other than silica is 0.5 to 5.0 parts by mass with respect to the total mass of the toner. Is preferred. When the amount of external additives other than silica is too small, a phenomenon called “image flow” that disturbs the electrostatic latent image tends to occur in a high-temperature and high-humidity environment, and other external additives other than silica. When the amount of the toner used is excessive, the fluidity of the toner tends to deteriorate, and the image density may fall below a desired value, or the durability of the toner may deteriorate.

  In the silica used in the toner of the present invention, primary particles form aggregates. The primary particle diameter of silica is not particularly limited, but is preferably 0.01 to 0.10 μm.

[External processing]
By attaching an external additive to the surface of the toner base particles, a magnetic one-component developing toner is produced. The method of attaching the external additive to the surface of the toner base particles is not particularly limited as long as the externally added silica satisfies the following conditions (1) and (2), and can be appropriately selected from conventionally known methods.
(1) The average aggregation number (a) of silica on the surface of the toner base particles is 5 to 15.
(2) The liberation rate (b) of silica in the toner measured by classifying free silica in the toner with an airflow classifier is 5 to 10%.

Specifically, the processing conditions are adjusted so that the particles of the external additive are not embedded in the toner base particles, and the processing with the external additive is performed by a mixer such as a Henschel mixer or a Nauter mixer. Hereinafter, a method for measuring the average number of aggregates (a) of silica, a method for measuring the liberation rate of silica (b), and conditions for external addition treatment will be described.

In the claims and specification of the present application, the average aggregation number (a) of silica is measured by the following method.
<Method for Measuring Average Aggregation Number (a) of Silica>
First, using a field emission scanning electron microscope (JSM-7401F (manufactured by JEOL Ltd.)), a photograph of the toner base particles is taken at a magnification of 30,000 times or more at a pressure of 0.5 kV. . Next, the photographed electron micrograph is analyzed by image analysis software (WinROOF (manufactured by Mitani Corporation)), and preferably, aggregates are formed on 30 or more silica aggregates adhering to the surface of the toner base particles. The number of primary particles is measured. Next, an average aggregation number is obtained using the number of primary particles contained in the aggregate to be measured.

  The average aggregation number (a) of silica can be adjusted by changing the processing conditions when the toner base particles are processed with the external additive. For example, in the low speed mixing, the average aggregation number (a) tends to decrease as the external additive treatment time increases. Moreover, there exists a tendency for an average aggregation number (a) to become small, so that the usage-amount of an external additive is small.

  When the average aggregation number (a) of silica on the surface of the toner base particles is too small, an image defect due to layer disturbance tends to occur in the formed image in a low temperature and low humidity environment. On the other hand, if the average aggregation number (a) of silica on the surface of the toner base particles is excessive, it is difficult to obtain an image having a desired density when forming an image in a low temperature and low humidity environment.

In the claims and the specification of the present application, the liberation rate (b) of silica is measured by the following method.
<Method for Measuring Silica Free Rate (b)>
The silica release rate (b) is determined by classifying free silica from toner under the following conditions using an airflow classifier (DSX-2 (manufactured by Nippon Pneumatic Industrial Co., Ltd.)). Then, the X-ray fluorescence X-ray intensity of the toner separated from the free silica is measured, and is obtained according to the following formula. As a fluorescent X-ray analyzer, for example, ZSX100e (manufactured by Rigaku Corporation) can be used.
(Free silica separation conditions)
Sample supply rate: 100 g / min Supply section injection pressure: 0.2 MPa
Adjustable string: 80mm
Louver height: 10mm
Louver clearance: 5mm
Distance ring: 0mm
Center navel: 60mm
U damper: 45 °
Cyclone damper: 30 °
Blower total static pressure: -1400 mmAq (-13.73 kPa)
≪Calculation formula of silica liberation rate (b) ≫
(Fluorescence X-ray intensity of Si before separation of free silica−Si fluorescence X-ray intensity of toner after separation of free silica) ÷ Si fluorescence X-ray intensity of toner before separation of free silica × 100

  When the liberation rate (b) of silica is too low, the toners tend to aggregate when images are continuously formed at a low image density over a long period of time or when images are formed in a high temperature and high humidity environment. When the liberation rate of silica (b) is too low, the charge amount of the toner is difficult to stabilize when forming an image in a low temperature and low humidity environment. For this reason, when images are continuously formed at a low image density over a long period of time or when images are formed in a high temperature and high humidity environment, the image density tends to be lower than a desired value.

  On the other hand, when the liberation rate (b) of silica is too high, the developer (developing sleeve) is easily contaminated by the liberated silica when forming an image in a low temperature and low humidity environment. For this reason, when an image is formed in a low-temperature and low-humidity environment, an image defect such as fog is likely to occur in the formed image.

[External treatment conditions]
The average aggregation number (a) of silica and the liberation rate (b) of silica can be adjusted by adjusting the conditions of the mixer used for the external addition treatment. For example, by increasing the number of revolutions of the stirring blade used in a stirrer of a mixer such as a Henschel mixer or a Nauta mixer, the average agglomeration number (a) of silica can be reduced, and the liberation rate of silica (b) Can be lowered. Further, by increasing the treatment time, the average aggregation number (a) of silica can be reduced, and the liberation rate (b) of silica can be lowered. Further, by increasing the temperature in the container of the stirring device, the average aggregation number (a) of silica can be increased, and the liberation rate (b) of silica can be decreased.

  According to the magnetic single-component developing toner of the present invention described above, when an image is continuously formed at a low image density over a long period of time, or when an image is formed in a low-temperature and low-humidity environment and a high-temperature and high-humidity environment. The density can be lower than a desired value, the occurrence of image defects such as fogging can be suppressed, and the occurrence of layer disturbance in a low temperature and low humidity environment can be suppressed. For this reason, the magnetic one-component developing toner of the present invention is suitably used in various image forming apparatuses.

  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.

  A polyester resin used as a binder resin in Examples and Comparative Examples was produced according to Production Example 1 below. Further, weakly charged silica (Y) used in Examples and Comparative Examples was produced according to Production Example 2 below.

[Production Example 1]
(Manufacture of polyester resin)
1960 g of propylene oxide adduct of bisphenol A, 780 g of ethylene oxide adduct of bisphenol A, 257 g of dodecenyl succinic anhydride, 770 g of terephthalic acid, and 4 g of dibutyltin oxide were charged into a reaction vessel. The temperature was raised to 235 ° C. in a nitrogen atmosphere, and the reaction was performed at the same temperature for 8 hours, and then the pressure was reduced to 8.3 kPa and the reaction was performed at the same temperature for 1 hour. Next, after the reaction product was cooled to 180 ° C., trimellitic anhydride was added to adjust the acid value of the polyester resin to about 10 mgKOH / g. Thereafter, the temperature was raised to 210 ° C. at a rate of 10 ° C./hour and the reaction was carried out at the same temperature to obtain a polyester resin.

[Production Example 2]
(Manufacture of weakly charged silica (Y))
Colloidal silica was dissolved in a solution in which 5 g of 7,7,8,8,9,9,9-heptafluorononyltrimethoxysilane and 5 g of N-phenyl-γ-aminopropyltrimethoxysilane were dissolved in 100 ml of toluene. 100 g (Nipsil E-200 (manufactured by Nippon Silica Industry Co., Ltd.)) was immersed, and the mixture was stirred. Next, the mixed solution was heated at 120 ° C. for 24 hours to remove the solvent from the mixed solution, thereby obtaining a dried silica aggregate. The obtained silica aggregate was pulverized using a pin mill (Coroplex 160Z (manufactured by Hadano Sangyo Co., Ltd.)) to obtain weakly charged silica (Y) having an average primary particle size of 24 nm. The average primary particle size was measured according to the following method.

<Average primary particle size measurement method>
Using a field emission scanning electron microscope (JSM-7401F, manufactured by JEOL Ltd.), a photograph of silica at a magnification of 100,000 was taken at a pressurized voltage of 0.5 Kv. The photographed electron micrograph was analyzed by image analysis software (WinROOF (manufactured by Mitani Corporation)), and the primary particle diameter was measured for 100 silica particles. Subsequently, the average primary particle diameter was calculated | required using the primary particle diameter of each primary particle, and the number of the primary particles made into the measuring object.

The charge amount of the obtained weakly charged silica (Y) measured by the following measuring method was 55 μC / g.
<Measurement method of charge amount>
10 g of an uncoated ferrite carrier (F-80 (manufactured by Powdertech)) having an average particle size of 80 μm and 0.3 g of a measurement sample are put into a 20 ml plastic container, and a three-dimensional mixing device (TURBULA MIXER (Willy A. Bachofen AG) is used. Then, the charge amount of the sample was measured with a suction-type charge amount measuring device (210HS-2A (manufactured by TRek)).

[Examples 1-6 and Comparative Examples 1-9]
(Preparation of toner base particles)
45 parts by mass of binder resin (polyester resin obtained in Production Example 1), 5 parts by mass of release agent (Carnauba wax (manufactured by Kato Yoko Co., Ltd.)), positive charge control agent (FCA-207P (Fujikura Kasei Co., Ltd.) 5 parts by mass) and 45 parts by mass of magnetite (TN-15 (Mitsui Metal Mining Co., Ltd.)) were mixed with a Henschel mixer. After the obtained mixture was melt-kneaded with a twin screw extruder, the melt-kneaded product was cooled, and the melt-kneaded product was coarsely pulverized with a hammer mill to obtain a coarsely pulverized product. The coarsely pulverized product was further finely pulverized with a mechanical pulverizer to obtain a finely pulverized product. The resulting finely pulverized product was classified by an airflow classifier to obtain toner base particles having a volume average particle size of 8.0 μm.

(Toner preparation)
100 parts by mass of toner base particles, hydrophobic silica (X) of the amount and type shown in Table 1 or 2, and weakly charged silica (Y) obtained in Production Example 2 in the amount shown in Table 1 or Table 2. , 1.0 part by mass of titanium oxide (ST-100 (manufactured by Titanium Industry Co., Ltd.)) with a Henschel mixer (FM-20B (manufactured by Nihon Coke Kogyo Co., Ltd.)) under the processing conditions described in Table 1 or 2. The toner was mixed and subjected to an external addition process to obtain toners of Examples 1 to 6 and Comparative Examples 1 to 9.

In Examples 1 to 6 and Comparative Examples 1 to 9, the following hydrophobic silicas X-1 and X-2 were used as the hydrophobic silica (X).
Hydrophobic silica (X-1): RA-200 (manufactured by Nippon Aerosil Co., Ltd.), average primary particle size 14 nm, charge amount 150 μC / g
Hydrophobic silica (X-2): NA-50 (manufactured by Nippon Aerosil Co., Ltd.), average primary particle size 30 nm, charge amount 135 μC / g

  The average aggregation number (a) of silica of the toners of Examples 1 to 6 and Comparative Examples 1 to 9 and the liberation rate of silica (b) were measured according to the following methods. Tables 1 and 2 show the average aggregation number (a) of silica and the liberation rate (b) of silica of the toners of Examples 1 to 6 and Comparative Examples 1 to 9.

<Method for Measuring Average Aggregation Number (a) of Silica>
Using a field emission scanning electron microscope (JSM-7401F (manufactured by JEOL Ltd.)), a photograph of the toner base particles was taken at a magnification of 30,000 times or more at a pressure of 0.5 kV. Next, the photographed electron micrograph is analyzed by image analysis software (WinROOF (manufactured by Mitani Corporation)), and about 30 silica aggregates adhering to the surface of the toner base particles, the primary particles forming the aggregates are analyzed. Number was measured. Subsequently, the average number of aggregation was calculated | required using the number of the primary particles contained in the aggregate made into the measuring object.

<Method for Measuring Silica Free Rate (b)>
The silica release rate (b) is determined by classifying free silica from toner under the following conditions using an airflow classifier (DSX-2 (manufactured by Nippon Pneumatic Industrial Co., Ltd.)). The fluorescent X-ray intensity of Si with the toner from which free silica was separated was measured and determined according to the following equation. As the X-ray fluorescence analyzer, ZSX100e (manufactured by Rigaku Corporation) was used.
(Free silica separation conditions)
Sample supply rate: 100 g / min Supply section injection pressure: 0.2 MPa
Adjustable string: 80mm
Louver height: 10mm
Louver clearance: 5mm
Distance ring: 0mm
Center navel: 60mm
U damper: 45 °
Cyclone damper: 30 °
Blower total static pressure: -1400 mmAq (-13.73 kPa)
≪Calculation formula of silica liberation rate (b) ≫
(Fluorescence X-ray intensity of Si before separation of free silica−Si fluorescence X-ray intensity of toner after separation of free silica) ÷ Si fluorescence X-ray intensity of toner before separation of free silica × 100

（※）比較例２では、ヘンシェルミキサーの温度調整は行わなかった。

(*) In Comparative Example 2, the temperature of the Henschel mixer was not adjusted.

[Evaluation]
The toners of Examples 1 to 6 and Comparative Examples 1 to 9 were subjected to the following evaluations in a high temperature and high humidity environment and a low temperature and low humidity environment after initial and continuous image formation. Note that a page printer (FS-4020DN (manufactured by Kyocera Mita Corporation), amorphous silicon drum: film thickness: 14 μm) was used as the evaluation machine.

(After initial and continuous image formation)
The toner charge amount, image density, and fog density after initial and continuous image formation were evaluated according to the following methods. The evaluation results are shown in Tables 3 and 4.
<Charge amount>
The initial toner charge amount was measured in a normal temperature and humidity environment (20 ° C., 65% RH). Subsequently, 100,000 sheets of images were continuously formed at a printing rate of 0.1% in a normal temperature and humidity environment (20 ° C., 65% RH), and the charge amount of the toner after the continuous image formation was measured. The charge amount was measured with a charge amount measuring device (Q / M Meter 210HS (manufactured by TRek)).

<Image density>
With an evaluation machine, an image evaluation pattern was formed on the recording medium in a normal temperature and humidity environment (20 ° C., 65% RH) to obtain an initial image. Thereafter, after continuous printing of 100,000 sheets at a printing rate of 0.1% in a normal temperature and humidity environment (20 ° C., 65% RH), an image evaluation pattern is formed on the recording medium to obtain an image after continuous image formation. It was. The image density of the solid image in the initial image and the image evaluation pattern after the continuous image formation was measured by a reflection densitometer (RD914, manufactured by Gretag Macbeth). The image density was evaluated according to the following criteria.
○ (Pass): 1.15 or more.
X (failure): Less than 1.15.

<Fog density>
The image density of the non-image portion of the recording medium on which the initial image obtained by the image density evaluation and the image evaluation pattern after the continuous image formation was formed was measured with a reflection densitometer (RD914, manufactured by Gretag Macbeth Co.). The fog density was evaluated according to the following criteria.
○ (Pass): 0.010 or less.
X (failure): More than 0.010.

(High temperature and high humidity)
In accordance with the following method, image density and fog density were evaluated for images formed under a high temperature and high humidity environment (30 ° C., 80% RH). The evaluation results are shown in Tables 3 and 4.
<Image density>
An initial evaluation image was obtained by forming an image evaluation pattern on the recording medium with an evaluator in a high temperature and high humidity environment (30 ° C., 80% RH). The image density of the solid image in the image evaluation pattern of the initial image was measured with a reflection densitometer (RD914, manufactured by Gretag Macbeth). The image density was evaluated according to the following criteria.
○ (Pass): 1.15 or more.
X (failure): Less than 1.15.

<Fog density>
The image density of the non-image portion of the recording medium on which the image evaluation pattern of the initial image obtained by the image density evaluation was measured with a reflection densitometer (RD914, manufactured by Gretag Macbeth). The fog density was evaluated according to the following criteria.
○ (Pass): 0.010 or less.
X (failure): More than 0.010.

(At low temperature and low humidity)
According to the following method, the image density and the fog density were evaluated for images formed under a low temperature and low humidity environment (10 ° C., 20% RH). Further, it was evaluated whether or not layer disturbance occurred in the toner layer on the developing roller of the developing device. The evaluation results are shown in Tables 3 and 4. The evaluation results are shown in Tables 3 and 4.
<Image density>
With an evaluation machine, an image evaluation pattern was formed on the recording medium in a low temperature and low humidity environment (10 ° C., 20% RH) to obtain an initial image. The image density of the solid image in the image evaluation pattern of the initial image was measured with a reflection densitometer (RD914, manufactured by Gretag Macbeth). The image density was evaluated according to the following criteria.
○ (Pass): 1.15 or more.
X (failure): Less than 1.15.

<Fog density>
The image density of the non-image portion of the recording medium on which the image evaluation pattern of the initial image obtained by the image density evaluation was measured with a reflection densitometer (RD914, manufactured by Gretag Macbeth). The fog density was evaluated according to the following criteria.
○ (Pass): 0.010 or less.
X (failure): More than 0.010.

<Layer disorder>
The toner and the evaluation machine were allowed to stand for 12 hours in a low-temperature and low-humidity environment (10 ° C., 20% RH). Next, 150 g of toner was filled in the developing device of the evaluation machine and aged for 10 minutes. After aging, a blank recording medium was output, and the output recording medium was observed to evaluate the occurrence of layer disturbance. When the layer disturbance occurs, a thick toner layer is formed on the developing sleeve. In this case, the fog is formed on the recording medium at the period of the developing sleeve due to the thick toner layer. The The occurrence of layer disturbance was evaluated according to the following criteria.
○ (Pass): The fog is not formed on the recording medium.
X (failed): A fog is formed on the recording medium.

  According to Examples 1 to 6, the toner is a magnetic one-component developing toner containing at least a binder resin and magnetic powder, and silica as an external additive attached to the surface of the toner base particles. A hydrophobic silica (X), and a positively charged weakly charged silica (Y) which is a wet silica having a positively charged polar group and a fluorine-containing negatively charged polar group on both surfaces. In addition, silica having an average aggregation number (a) of silica on the surface of the toner base particles of 5 to 15 and a silica liberation rate (b) of 5 to 10% is included as an external additive. In this case, when the image is continuously formed with a low image density for a long time using the toner, or when the image is formed in a low temperature and low humidity environment and a high temperature and high humidity environment, the image density may be lower than a desired value. Suppresses the occurrence of image defects such as fogging in the formed image. And, in the low temperature and low humidity environment, be a layer disturbance to the toner layer on the developing device of the developer carrying member can be prevented from occurring can be seen.

  On the other hand, when the toners of Comparative Examples 1 and 2 in which the liberation rate (b) of silica in the toner is too high are used, image defects such as fogging are likely to occur in the formed image when an image is formed in a low temperature and low humidity environment. I understand that. On the other hand, when the toners of Comparative Examples 3 to 5 in which the liberation rate (b) of silica in the toner is too low are used, images are continuously formed at a low image density over a long period of time, or images are formed in a high temperature and high humidity environment. It is difficult to form an image having a desired image density.

  It can also be seen that when the toners of Comparative Examples 3, 5, 7, and 9 in which the average number of aggregates (a) of silica on the surface of the toner base particles is too small are used, image defects may occur due to layer disturbance. . On the other hand, when the toner of Comparative Example 8 in which the average aggregation number (a) of silica on the toner base particle surface is excessive is used, it is difficult to form an image having a desired image density when forming an image in a low temperature and low humidity environment. I understand.

  In addition, when the toner of Comparative Example 9 that does not use weakly charged silica (Y) is used, image defects such as fogging are likely to occur in the formed image when images are continuously formed at a low image density over a long period of time. I understand that.

Claims (5)

A magnetic one-component developing toner in which an external additive is attached to the surface of toner base particles containing at least a binder resin and magnetic powder,
The external additive includes silica in which at least primary particles form an aggregate,
The silica includes hydrophobic silica (X), positively charged weakly charged silica (Y) which is wet silica having a positively charged polar group and a fluorine-containing negatively charged polar group on both surfaces. Including
The average aggregation number (a) of the silica on the surface of the toner base particles is 5 to 15,
Magnetic 1 having a liberation rate (b) of 5 to 10% of the silica in the magnetic one-component developing toner measured by classifying free silica in the magnetic one-component developing toner with an airflow classifier. Component developing toner.   The magnetic one-component developing toner according to claim 1, wherein the toner base particles further contain magnetic powder.   The magnetic one-component developing toner according to claim 1 or 2, wherein a mass ratio (Y / X) of the hydrophobic silica (X) to the weakly charged silica (Y) is 0.2 to 0.6. . The magnetism according to any one of claims 1 to 3, wherein the weakly charged silica has a positively charged polar group introduced by treatment with a positively charged surface treatment agent represented by the following formula (1). One component developing toner.
R ¹ —NH—R ² — (NH—R ³ ) _m —SiR ⁴ _a R ⁵ _(3-a) (1)
(In the formula (1), ^{R 1} represents a hydrogen atom, an alkyl group having 1 to 10 carbon atoms or a phenyl group, or benzyl group, ^{R 2} and ^{R 3} are each an alkylene group having 1 to 10 carbon atoms , R ⁴ is an alkyl group having 1 to 10 carbon atoms, R ⁵ is an alkoxy group having 1 to 6 carbon atoms, or a chlorine atom, m is an integer of 0 to 2, and a is an integer of 0 to 2. .) 5. The weakly charged silica according to claim 1, wherein a fluorine-containing negatively charged polar group is introduced by treatment with a negatively charged surface treatment agent represented by the following formula (2): Magnetic one-component developing toner.
R ^6- (AR ⁷ ) _n -SiR ⁸ _b R ⁹ _(3-b) (2)
(In the formula (2), ^{R 6} is a fluoroalkyl having 1 to 20 carbon atoms, ^{R 7} is an alkylene group having 1 to 10 carbon atoms, ^{R 8} is an alkyl group having 1 to 10 carbon atoms, R ⁹ is an alkoxy group having 1 to 6 carbon atoms or a chlorine atom, and A is —COO—, —OCO—, —CONH—, —NHCO—, —SO ₂ NH—, or —NH—SO ₂ —. N is 0 or 1, and b is an integer of 0-2.)