JP6390634B2 - Toner for electrostatic latent image development and external additive - Google Patents

Description

  The present invention relates to an electrostatic latent image developing toner and an external additive.

  Patent Document 1 discloses silica-titania composite oxide particles having a sea-island structure (sea: silica, island: titania) as an external additive for toner particles. Further, Patent Document 1 discloses that the silica-titania composite oxide particles are surface-treated with an aminosilane compound.

JP 2009-237338 A

  However, the external additive disclosed in Patent Document 1 is easily detached from the toner particles. Further, in order to use the toner for continuous printing, the durability (and consequently the charging stability) of the external additive is insufficient.

  The present invention has been made in view of the above problems, and an object thereof is to provide an external additive excellent in chargeability and durability, and an electrostatic latent image developing toner including such an external additive. Another object of the present invention is to continuously form high-quality images by continuously suppressing the occurrence of fog when continuous printing is performed using toner.

  The electrostatic latent image developing toner according to the present invention includes a plurality of toner particles including toner base particles containing a binder resin and an external additive attached to the surface of the toner base particles. The external additive includes a plurality of external additive particles including composite particles and a coating layer that covers the surface of the composite particles. The composite particles are composed of a silica core mainly composed of silica and titania particles attached to the surface of the silica core. The coat layer contains a thermosetting nitrogen-containing resin.

  The external additive according to the present invention includes a plurality of external additive particles. The external additive particles include composite particles and a coat layer that covers the surface of the composite particles. The composite particles are composed of a silica core mainly composed of silica and titania particles attached to the surface of the silica core. The coat layer contains a thermosetting nitrogen-containing resin.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to provide the external additive excellent in charging property and durability, and the electrostatic latent image developing toner provided with such an external additive. Further, according to the present invention, in addition to or instead of this effect, when continuous printing is performed using toner, the occurrence of fog is continuously suppressed and high-quality images are continuously formed. The effect that it becomes possible may be produced.

FIG. 4 is a cross-sectional view illustrating an example of a configuration of toner particles contained in a toner according to an exemplary embodiment of the present invention. It is sectional drawing which shows the 1st example of a structure of the external additive particle contained in the external additive which concerns on embodiment of this invention. It is sectional drawing which shows the 2nd example of a structure of the external additive particle contained in the external additive which concerns on embodiment of this invention.

An embodiment of the present invention will be described. Note that the evaluation results (values indicating shape, physical properties, etc.) regarding the powder (more specifically, toner base particles, external additives, toner, etc.) are average values from the powder unless otherwise specified. It is the number average of the values measured for each of these average particles by selecting a significant number of particles. The number average particle diameter of the powder is the number average value of the equivalent circle diameter of primary particles (diameter of a circle having the same area as the projected area of the particles) measured using a microscope unless otherwise specified. It is. Moreover, the measured value of the volume median diameter (D ₅₀ ) of the powder is measured using a laser diffraction / scattering particle size distribution measuring device (“LA-750” manufactured by Horiba, Ltd.) unless otherwise specified. It is the value.

  Hereinafter, a compound and its derivatives may be generically named by adding “system” after the compound name. When the name of a polymer is expressed by adding “system” after the compound name, it means that the repeating unit of the polymer is derived from the compound or a derivative thereof. Acrylic and methacrylic are sometimes collectively referred to as “(meth) acrylic”. The crystalline polyester resin is described as “crystalline polyester resin”, and the non-crystalline polyester resin is simply described as “polyester resin”.

  The toner according to the exemplary embodiment can be suitably used for developing an electrostatic latent image, for example, as a positively chargeable toner. The toner of the present exemplary embodiment is a powder that includes a plurality of toner particles (each having a configuration described later). The toner may be used as a one-component developer. Alternatively, a two-component developer may be prepared by mixing toner and carrier using a mixing device (for example, a ball mill). In order to form a high-quality image, it is preferable to use a ferrite carrier as a carrier. In order to form a high-quality image over a long period of time, it is preferable to use magnetic carrier particles including a carrier core and a resin layer covering the carrier core. In order to impart magnetism to the carrier particles, the carrier core may be formed of a magnetic material (for example, ferrite), or the carrier core may be formed of a resin in which magnetic particles are dispersed. Further, magnetic particles may be dispersed in the resin layer covering the carrier core. In order to form a high-quality image, the amount of toner in the two-component developer is preferably 5 parts by mass or more and 15 parts by mass or less with respect to 100 parts by mass of the carrier. The positively chargeable toner contained in the two-component developer is positively charged by friction with the carrier.

  The toner according to the exemplary embodiment can be used for image formation in, for example, an electrophotographic apparatus (image forming apparatus). Hereinafter, an example of an image forming method using an electrophotographic apparatus will be described.

  First, an electrostatic latent image is formed on a photoconductor (for example, a surface layer portion of a photoconductor drum) based on image data. Next, the formed electrostatic latent image is developed using a developer containing toner. In the developing step, toner (for example, toner charged by friction with a carrier or blade) on a developing sleeve (for example, a surface layer portion of a developing roller in the developing device) is attached to the electrostatic latent image and is applied to the photoreceptor. A toner image is formed. In the subsequent transfer step, the toner image on the photosensitive member is transferred to an intermediate transfer member (for example, a transfer belt), and then the toner image on the intermediate transfer member is further transferred to a recording medium (for example, paper). Thereafter, the toner is heated to fix the toner on the recording medium. As a result, an image is formed on the recording medium. For example, a full color image can be formed by superposing four color toner images of black, yellow, magenta, and cyan.

  The toner according to this embodiment includes a plurality of toner particles. The toner particles include toner base particles containing a binder resin and an external additive. The external additive adheres to the surface of the toner base particles. The toner base particles may contain an internal additive (for example, at least one of a release agent, a colorant, a charge control agent, and a magnetic powder) in addition to the binder resin, if necessary.

  The toner particles contained in the toner according to the present embodiment may be toner particles not having a shell layer (hereinafter referred to as non-capsule toner particles), or toner particles having a shell layer (hereinafter referred to as capsule toner particles). May be described). In the capsule toner particles, the toner base particles include a core containing a binder resin and a shell layer that covers the surface of the core. The shell layer is substantially composed of a resin. For example, by covering a core that melts at a low temperature with a shell layer having excellent heat resistance, it is possible to achieve both heat-resistant storage stability and low-temperature fixability of the toner. Additives may be dispersed in the resin constituting the shell layer. The shell layer may cover the entire surface of the core, or may partially cover the surface of the core. In the capsule toner particles, toner base particles in non-capsule toner particles described later can be used as a core.

  The toner particles contained in the toner according to the exemplary embodiment include an external additive having the following configuration (hereinafter referred to as a basic configuration).

(Basic composition of external additives)
The external additive is an external additive particle (hereinafter, referred to as a silica-titania composite particle) and a coating layer covering the surface of the silica-titania composite particle (hereinafter referred to as a silica-titania composite particle). A plurality of specific external additive particles). Silica-titania composite particles are composite particles composed of a silica core mainly composed of silica and titania particles (externally added titania particles) attached to the surface of the silica core. The silica core may consist only of silica. Further, an additive (internal additive) may be dispersed in silica constituting the silica core. When the silica core contains an internal additive, the amount of the internal additive is preferably 20% by mass or less based on the entire silica core. The coat layer contains a thermosetting nitrogen-containing resin. The nitrogen-containing resin is a resin containing a nitrogen atom in its chemical structure.

  Hereinafter, the configuration of toner particles (particularly, external additive particles) contained in the toner according to the present embodiment will be described with reference to FIGS. FIG. 1 shows an example of toner particles having specific external additive particles. 2 and 3 each show an example of specific external additive particles.

A toner particle 10 shown in FIG. 1 includes toner base particles 11 and a plurality of external additive particles 12. The external additive particles 12 are specific external additive particles. The external additive particles 12 have irregularities on the surface. In the example of FIG. 1, convex portions on the surface of the external additive particles 12 enter the toner base particles 11. The external additive particles 12 contain silica (SiO ₂ ) and titania (TiO ₂ ). Specifically, as shown in FIG. 2, the external additive particle 12 includes a silica core 1, a plurality of titania particles 2, and a coat layer 3. The composite particles of the silica core 1 and the titania particles 2 (externally added titania particles) correspond to silica-titania composite particles. The silica core 1 is, for example, spherical silica particles. Each of the plurality of titania particles 2 is attached to the surface of the silica core 1. The shape of the titania particles 2 is, for example, spherical. However, the shape of the titania particles 2 may be another shape (for example, a needle shape). The coat layer 3 contains a thermosetting nitrogen-containing resin (for example, melamine resin). The coat layer 3 completely covers, for example, silica-titania composite particles (silica core 1 to which titania particles 2 are attached). The volume median diameter (D ₅₀ ) of the external additive particles 12 is, for example, not less than 50 nm and not more than 500 nm. The toner particles 10 may include external additive particles (for example, silica particles and / or titania particles) other than the specific external additive particles.

  In the example of FIG. 2, as a result of the spherical titania particles 2 adhering to the surface of the spherical silica core 1, the external additive particles 12 have a different shape (a shape different from the spherical shape). Specifically, the shape of the external additive particle 12 is a shape in which irregularities are formed on the particle surface by a plurality of protrusions formed on the surface of the spherical particle. Each titania particle 2 protrudes from the surface of the silica core 1. In the example of FIG. 2, a part (bottom part) of each titania particle 2 enters the silica core 1. The protruding amount of each titania particle 2 from the surface of the silica core 1 is not less than half of the shortest diameter of the titania particle 2 and not more than the longest diameter of the titania particle 2 (in the case of the spherical titania particle 2, it is not less than half of the diameter and not more than the diameter). There are many cases.

  The silica core 1 is not limited to silica particles. For example, as shown in FIG. 3, the silica core 1 may be a titania-containing silica particle having a sea-island structure (sea: silica, island: titania) of silica distributed in a sea shape and titania distributed in an island shape. . Although the silica core 1 shown in FIG. 3 is mainly composed of silica, small-diameter titania particles 1a (internally added titania particles) are dispersed in the silica constituting the silica core 1.

  When silica particles are used as an external additive for toner particles, the toner tends to be excessively charged in a low humidity environment due to the high electrical resistance of the silica particles. Silica particles tend to exhibit strong negative chargeability. Therefore, the silica particles are difficult to be positively charged. Silica particles have a high moisture adsorptivity. For this reason, the charge amount of the silica particles tends to decrease in a high humidity environment. In order to improve the positive chargeability and charge stability of the silica particles, it is conceivable to treat the silica particles with aminosilane (positive charge agent) and alkylsilane (hydrophobic agent). However, when continuous printing is performed using toner particle powder (toner) having such silica particles, the surface treatment agent (aminosilane and / or alkylsilane) is peeled off from the silica particles and the toner particles are charged. It becomes unstable and fog is likely to occur. Further, when the surface treatment agent is peeled off in a high humidity environment and the silica particles are exposed, the exposed portion easily absorbs moisture, so that the chargeability of the toner tends to be insufficient.

  The external additive particles (specific external additive particles) contained in the external additive having the above basic configuration include silica-titania composite particles. Silica-titania composite particles are composite particles of a silica core and externally added titania particles. By combining titania having a low electrical resistance with silica having a high electrical resistance, it is possible to suppress excessive charge-up of the toner in a low humidity environment.

  When the external additive particles function as spacers between the toner particles, the fluidity of the toner is improved and aggregation of the toner can be suppressed. It is considered that the heat-resistant storage stability of the toner is improved by suppressing toner aggregation. In order for the external additive particles to function as spacers between the toner particles, the external additive particles need to be somewhat large. However, when the particle diameter of the external additive particles is increased, the external additive particles are easily detached from the toner particles. When an image is formed using toner, if the external additive particles are detached from the toner particles, charging of the toner particles becomes unstable and fogging easily occurs.

  In the external additive having the above basic configuration, the silica-titania composite particle includes a silica core and externally added titania particles. When the titania particles adhere to the surface of the silica core, the shape of the silica-titania composite particles (and thus the shape of the specific external additive particles) tends to be irregular. When irregularly shaped external additive particles and toner base particles are mixed, the protrusions on the surface of the external additive particles stick into the toner base particles, and the external additive particles adhere firmly to the surface of the toner base particles. Tend to. For this reason, irregularly shaped external additive particles are unlikely to be detached from the toner particles. In addition, when irregularly shaped external additive particles are used, the amount of external additive particles entering the surface of the toner base particles (embedding amount) tends to be uniform for a plurality of external additive particles adhering to the toner base particles. . The irregularly shaped external additive particles have abrasiveness. Due to the polishing action of the external additive particles, it is possible to remove foreign substances adhering to the surface of the photosensitive drum (specifically, the surface of the photosensitive layer).

  Furthermore, in the external additive having the above basic configuration, the specific external additive particles include a coat layer that covers the surface of the silica-titania composite particles. By covering the silica core and the titania particles with the coat layer, it is possible to suppress the detachment of the titania particles from the silica core and the burying of the titania particles in the silica core.

  Nitrogen-containing resins have moderately strong positive charging properties and tend to have excellent charging stability with respect to environmental fluctuations and time passages. Thermosetting resins also tend to have excellent durability. In the external additive having the above basic structure, the coat layer contains a thermosetting nitrogen-containing resin. It is considered that toner particle powder (toner) having such an external additive is excellent in positive chargeability and charge stability. When continuous printing is performed using toner particle powder (toner) having an external additive having the above basic configuration, it is possible to continuously suppress the occurrence of fog and continue to form high-quality images. It becomes possible.

In order for the specific external additive particles to function suitably as a spacer between the toner particles, the volume median diameter (D ₅₀ ) of the silica core is 60 nm or more and 100 nm or less, and the volume median diameter of the externally added titania particles ( D ₅₀ ) is preferably 10 nm or more and 25 nm or less. Further, when the silica core and the externally added titania particles have such a particle diameter (D ₅₀ ), sufficient irregularities are formed on the surface of the external additive particles to suppress the detachment of the external additive particles from the toner particles. In order to make the electric resistance of the external additive particles appropriate, the amount of the externally added titania particles is 10 parts by mass or more and 65 parts by mass or less with respect to 100 parts by mass of the silica core. Preferably, it is 20 parts by mass or more and 35 parts by mass or less. If the amount of the externally added titania particles is too large or too small, sufficient irregularities are not formed on the surface of the external additive particles.

  In order to suppress the detachment of titania particles from the silica core and the burying of the titania particles in the silica core, in the above basic configuration, the area ratio of the area covered by the coat layer (hereinafter referred to as the surface area of the silica-titania composite particles) 90% or more is preferable, and 100% is particularly preferable. That the coverage of the coat layer is 100% means that the silica-titania composite particles are completely covered with the coat layer (no exposed portion).

  In order to form sufficient irregularities on the surface of the external additive particles to suppress the detachment of the external additive particles from the toner particles, and to ensure sufficient durability of the external additive particles, a coating layer The thickness is preferably 1 nm or more and 10 nm or less. The thickness of the coating layer can be measured by analyzing a cross-sectional TEM image of the external additive particles using commercially available image analysis software (for example, “WinROOF” manufactured by Mitani Corporation). In addition, when the thickness of the coating layer is not uniform in one external additive particle, four equally spaced locations (specifically, two straight lines that are orthogonal to each other at substantially the center of the cross section of the external additive particle are drawn, The thickness of the coat layer is measured at each of these two straight lines intersecting the coat layer, and the arithmetic average of the four measured values obtained is the evaluation value of the external additive particles (of the coat layer). Thickness).

  Next, the configuration of the non-capsule toner particles will be described. Specifically, the toner base particles (binder resin and internal additive) and the external additive will be described in order.

[Toner mother particles]
The toner base particles contain a binder resin. The toner base particles may contain an internal additive (for example, a colorant, a release agent, a charge control agent, and a magnetic powder).

(Binder resin)
In the toner base particles, generally, the binder resin occupies most of the components (for example, 85% by mass or more). For this reason, it is considered that the properties of the binder resin greatly affect the properties of the entire toner base particles. By using a combination of a plurality of types of resins as the binder resin, the properties of the binder resin (more specifically, the hydroxyl value, acid value, Tg, Tm, etc.) can be adjusted. When the binder resin has an ester group, a hydroxyl group, an ether group, an acid group, or a methyl group, the toner base particles tend to be anionic, and the binder resin has an amino group or an amide group. In other words, the toner base particles tend to be cationic.

  In order to improve the low-temperature fixability of the toner, it is preferable that the toner base particles contain a thermoplastic resin as the binder resin, and contain the thermoplastic resin in a proportion of 85% by mass or more of the entire binder resin. Is more preferable. Examples of the thermoplastic resin contained in the toner base particles include a styrene resin, an acrylic resin (more specifically, an acrylic ester polymer or a methacrylic ester polymer), an olefin resin (more specifically, In particular, polyethylene resin or polypropylene resin), vinyl resin (more specifically, vinyl chloride resin, polyvinyl alcohol, vinyl ether resin, or N-vinyl resin), polyester resin, polyamide resin, or urethane resin are preferable. . A copolymer of each of these resins, that is, a copolymer in which an arbitrary repeating unit is introduced into the resin (specifically, a styrene-acrylic acid resin or a styrene-butadiene resin) is also used as a toner. Preferred as a binder resin for the mother particles.

  In order to improve the low-temperature fixability of the toner, it is particularly preferable that the toner base particles contain a polyester resin as a binder resin. The toner base particles may contain a crystalline polyester resin as a binder resin.

  The thermoplastic resin can be obtained by addition polymerization, copolymerization, or condensation polymerization of one or more thermoplastic monomers. The thermoplastic monomer is a monomer that becomes a thermoplastic resin by homopolymerization (more specifically, an acrylic acid monomer or a styrene monomer), or a monomer that becomes a thermoplastic resin by condensation polymerization (for example, by condensation polymerization). A combination of a polyhydric alcohol and a polyhydric carboxylic acid to be a polyester resin.

  The polyester resin is obtained by polycondensation of one or more polyhydric alcohols and one or more polyhydric carboxylic acids. As the alcohol for synthesizing the polyester resin, for example, dihydric alcohols (more specifically, diols or bisphenols) as shown below or trihydric or higher alcohols can be suitably used. As the carboxylic acid for synthesizing the polyester resin, for example, divalent carboxylic acids or trivalent or higher carboxylic acids as shown below can be suitably used.

  Suitable examples of diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, Examples include 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, di1,2-propanediol, polyethylene glycol, poly1,2-propanediol, or polytetramethylene glycol.

  Preferable examples of the bisphenol include bisphenol A, hydrogenated bisphenol A, bisphenol A ethylene oxide adduct, or bisphenol A propylene oxide adduct.

  Preferable examples of trihydric or higher alcohols include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, 1,2,4-butane. Triol, 1,2,5-pentanetriol, glycerol, diglycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, or 1,3,5- Trihydroxymethylbenzene is mentioned.

  As preferable examples of the divalent carboxylic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, adipic acid, sebacic acid, azelaic acid, malonic acid Succinic acid, alkyl succinic acid (more specifically, n-butyl succinic acid, isobutyl succinic acid, n-octyl succinic acid, n-dodecyl succinic acid, isododecyl succinic acid, etc.), or alkenyl succinic acid (more specific Specifically, n-butenyl succinic acid, isobutenyl succinic acid, n-octenyl succinic acid, n-dodecenyl succinic acid, or isododecenyl succinic acid, etc.) may be mentioned.

  Preferred examples of the trivalent or higher carboxylic acid include 1,2,4-benzenetricarboxylic acid (trimellitic acid), 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra (methylenecarboxyl) Examples include methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, or empole trimer acid.

(Coloring agent)
The toner base particles may contain a colorant. As the colorant, a known pigment or dye can be used according to the color of the toner. In order to form a high-quality image using toner, the amount of the colorant is preferably 1 part by mass or more and 20 parts by mass or less with respect to 100 parts by mass of the binder resin.

  The toner base particles may contain a black colorant. An example of a black colorant is carbon black. The black colorant may be a colorant that is toned to black using a yellow colorant, a magenta colorant, and a cyan colorant.

  The toner base particles may contain a color colorant such as a yellow colorant, a magenta colorant, or a cyan colorant.

  As the yellow colorant, for example, one or more compounds selected from the group consisting of condensed azo compounds, isoindolinone compounds, anthraquinone compounds, azo metal complexes, methine compounds, and arylamide compounds can be used. Examples of the yellow colorant include C.I. I. Pigment Yellow (3, 12, 13, 14, 15, 17, 62, 74, 83, 93, 94, 95, 97, 109, 110, 111, 120, 127, 128, 129, 147, 151, 154, 155 168, 174, 175, 176, 180, 181, 191, or 194), naphthol yellow S, Hansa yellow G, or C.I. I. Vat yellow can be preferably used.

  The magenta colorant is, for example, selected from the group consisting of condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds. One or more compounds can be used. Examples of the magenta colorant include C.I. I. Pigment Red (2, 3, 5, 6, 7, 19, 23, 48: 2, 48: 3, 48: 4, 57: 1, 81: 1, 122, 144, 146, 150, 166, 169, 177 184, 185, 202, 206, 220, 221 or 254) can be preferably used.

  As the cyan colorant, for example, one or more compounds selected from the group consisting of a copper phthalocyanine compound, an anthraquinone compound, and a basic dye lake compound can be used. Examples of cyan colorants include C.I. I. Pigment blue (1, 7, 15, 15: 1, 15: 2, 15: 3, 15: 4, 60, 62, or 66), phthalocyanine blue, C.I. I. Bat Blue, or C.I. I. Acid blue can be preferably used.

(Release agent)
The toner base particles may contain a release agent. The release agent is used, for example, for the purpose of improving the fixing property or offset resistance of the toner. In order to improve the fixing property or offset resistance of the toner, the amount of the release agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

  Examples of the release agent include low molecular weight polyethylene, low molecular weight polypropylene, polyolefin copolymer, polyolefin wax, microcrystalline wax, paraffin wax, or aliphatic hydrocarbon wax such as Fischer-Tropsch wax; oxidized polyethylene wax or a block thereof Oxides of aliphatic hydrocarbon waxes such as copolymers; plant waxes such as candelilla wax, carnauba wax, wood wax, jojoba wax, or rice wax; animal properties such as beeswax, lanolin, or whale wax Waxes; mineral waxes such as ozokerite, ceresin, or petrolatum; waxes based on fatty acid esters such as montanate ester wax or castor wax; fats such as deoxidized carnauba wax The wax portion of the ester or the whole was deoxygenated can be suitably used. One type of release agent may be used alone, or multiple types of release agents may be used in combination.

  When the binder resin is a polyester resin, as the release agent, for example, carnauba wax, ester wax, or polyethylene wax is preferable. When the binder resin is a styrenic resin or a copolymer thereof, as the release agent, for example, paraffin wax or Fischer-Tropsch wax is preferable. In order to improve the compatibility between the binder resin and the release agent, a compatibilizing agent may be added to the toner base particles.

(Charge control agent)
The toner base particles may contain a charge control agent. The charge control agent is used, for example, for the purpose of improving the charge stability or charge rising property of the toner. The charge rising characteristic of the toner is an index as to whether or not the toner can be charged to a predetermined charge level in a short time.

  By adding a negatively chargeable charge control agent to the toner base particles, the anionicity of the toner base particles can be enhanced. Further, by adding a positively chargeable charge control agent to the toner base particles, the cationic property of the toner base particles can be enhanced. However, if sufficient chargeability is ensured in the toner, it is not necessary to add a charge control agent to the toner base particles.

(Magnetic powder)
The toner base particles may contain magnetic powder. Examples of magnetic powder materials include ferromagnetic metals (more specifically, iron, cobalt, nickel, etc.) or alloys thereof, ferromagnetic metal oxides (more specifically, ferrite, magnetite, or chromium dioxide). Etc.) or a material subjected to a ferromagnetization treatment (more specifically, a heat treatment etc.) can be suitably used. One type of magnetic powder may be used alone, or a plurality of types of magnetic powder may be used in combination.

[Production method of toner base particles]
Preferable examples of the method for producing the toner base particles include a pulverization method or an aggregation method. These methods facilitate easy dispersion of the internal additive in the binder resin.

  In an example of the pulverization method, first, a binder resin, a colorant, a charge control agent, and a release agent are mixed. Subsequently, the obtained mixture is melt-kneaded using a melt-kneading apparatus (for example, a single-screw or twin-screw extruder). Subsequently, the obtained melt-kneaded product is pulverized and classified. Thereby, toner mother particles are obtained.

  In an example of the aggregation method, first, these fine particles are aggregated in an aqueous medium containing fine particles of the binder resin, the release agent, and the colorant until a desired particle diameter is obtained. Thereby, aggregated particles containing a binder resin, a release agent, and a colorant are formed. Subsequently, the obtained aggregated particles are heated to unite the components contained in the aggregated particles. Thereby, toner mother particles having a desired particle diameter are obtained.

[External additive]
The toner particles contained in the toner according to the exemplary embodiment include an external additive (and thus a plurality of specific external additive particles) having the above-described basic configuration. For example, when the toner base particles and the external additive are stirred together, the external additive adheres (physically bonds) to the surface of the toner base particles with a physical force. In the above basic configuration, the specific external additive particles include silica-titania composite particles and a coating layer. Silica-titania composite particles are composite particles of a silica core and externally added titania particles.

  In order to improve the fluidity and the like of the toner, it is preferable that the toner particles further include one or more inorganic particles as external additive particles in addition to the specific external additive particles. As inorganic particles, particles of silica particles or metal oxides (more specifically, alumina, titania, magnesium oxide, zinc oxide, strontium titanate, barium titanate, etc.) can be preferably used. Multiple types of inorganic particles may be used in combination. In order to improve the fluidity of the toner, it is preferable to use silica particles as the inorganic particles. In order to improve the abrasiveness of the toner, it is preferable to use titania particles as inorganic particles. In order to improve the fluidity and polishability of the toner, it is particularly preferable that the toner particles further include silica particles and titania particles as external additive particles in addition to the specific external additive particles.

  In order to improve the fluidity or handleability of the toner, the amount of the external additive (when a plurality of types of external additives are used, the total amount of these external additives) is 100 parts by mass of the toner base particles. On the other hand, it is preferable that they are 0.5 mass part or more and 10 mass parts or less. In order to obtain a toner having excellent chargeability and durability, it is preferable that 20% by mass or more of the external additive particles among all the external additive particles are the specific external additive particles. In order to obtain a toner having excellent fluidity, 20% by mass or more of the external additive particles are preferably silica particles among all the external additive particles. In order to obtain a toner having excellent abrasiveness, it is preferable that 20% by mass or more of the external additive particles among all the external additive particles are titania particles.

  From the standpoint of ease of acquisition (specifically, cost or technical ease of acquisition) and the like, the silica core is preferably hydrophilic silica particles (for example, silica particles that have not been surface-treated). More preferably, it is fumed silica particles. In order to adjust the electric resistance of the silica core to a desired magnitude, the silica core is preferably titania-containing silica particles having a sea-island structure (sea: silica, island: titania).

  In the specific external additive particles, the coat layer contains a thermosetting nitrogen-containing resin. In order to impart sufficient positive chargeability and durability to the coating layer, the amount of the thermosetting nitrogen-containing resin contained in the coating layer may be 80% by mass or more based on the entire coating layer. Preferably, it is 90 mass% or more, and it is especially preferable that it is 100 mass%.

  In order to impart sufficient positive chargeability to the coating layer, the thermosetting nitrogen-containing resin contained in the coating layer is a melamine resin, urea resin, sulfonamide resin, guanamine resin, aniline resin. , A polyimide resin (more specifically, a maleimide polymer or a bismaleimide polymer), and one or more resins selected from the group consisting of urethane resins, preferably melamine resins and / or urea resins A resin is particularly preferable.

  When synthesizing a melamine resin or a urea resin, it is considered that, for example, melamine and formaldehyde react or urea and formaldehyde react to produce a compound having a methylol group as an intermediate. When the intermediate of the resin constituting the coating layer has a methylol group, in the polymerization reaction for synthesizing the resin, the intermediate methylol group is bonded to the surface of the silica-titania composite particle (specifically, silica and titania). It is easy to form a bond with each hydroxyl group). For example, a dehydration condensation reaction occurs between a hydroxyl group (HO-) and a methylol group present on the surface of silica-titania composite particles, and a covalent bond tends to be formed between the two. By forming such a covalent bond, it is possible to firmly bond the silica-titania composite particle and the coating layer.

[Production method of external additive]
(Composite process)
The silica-titania composite particles are obtained by mixing the silica core and the titania particles using a mixer (for example, a pin mill) under conditions such that the titania particles are not buried in the silica core. In addition, a commercial item can be used as a silica core. However, you may make your own silica core. Silica particles can be produced by, for example, a known gas phase synthesis method. The titania-containing silica particles can be produced by reacting a raw material gas (for example, SiCl ₄ gas and TiCl ₄ gas) by, for example, combustion.

(Coating process)
Preferable examples of the method of coating the silica-titania composite particles with the coating layer include a coating method or a reaction method. The reaction method is particularly preferable for firmly bonding the silica-titania composite particles and the coating layer. Hereinafter, the material for forming the coating layer is referred to as a coating material.

  In the case of forming a coating layer by a coating method, for example, a solution in which a coating material is dissolved is applied to silica-titania composite particles, and then the solvent is removed. Thereby, a coat layer is formed on the surface of the silica-titania composite particles.

  In an example of the reaction method, first, a coating material (for example, a monomer for synthesizing a thermosetting nitrogen-containing resin) is dissolved in a solvent. By dissolving the coating material in a solvent in advance, the silica-titania composite particles and the coating layer are easily bonded firmly by heating described below. The solvent for the coating material is preferably an aqueous medium. The aqueous medium is a medium containing water as a main component (more specifically, pure water or a mixed liquid of water and a polar medium). The aqueous medium may function as a solvent. A solute may be dissolved in the aqueous medium. The aqueous medium may function as a dispersion medium. The dispersoid may be dispersed in the aqueous medium. As a polar medium in the aqueous medium, for example, alcohol (more specifically, methanol or ethanol) can be used. The boiling point of the aqueous medium is about 100 ° C.

  Subsequently, the silica-titania composite particles are dispersed in the coating material solution to obtain a dispersion of silica-titania composite particles. Further, the pH of the dispersion is adjusted as necessary.

  Subsequently, the dispersion is heated, and the coating material in the dispersion is polymerized on the surface of the silica-titania composite particles. While the temperature of the liquid is kept high, the coating material reacts with the silica-titania composite particles and is immobilized on the surface of the silica-titania composite particles. Thereafter, the dispersion is cooled to room temperature (about 25 ° C.). Thereby, a dispersion of external additive particles is obtained.

  When the thermosetting nitrogen-containing resin contained in the coating layer is a melamine-based resin or a urea-based resin, a silica-titania composite particle dispersion (more preferably, The temperature of the dispersion (pH 2 to 6) is preferably maintained at 60 ° C. or more and 100 ° C. or less by the heating. By maintaining the temperature of the dispersion at an appropriate temperature, the polymerization reaction of the coating material is facilitated. In addition, the polymerization reaction of the coating material is easily promoted by setting the pH of the dispersion to be more acidic than neutral (pH 7).

(Washing process)
The obtained external additive particles may be washed. As a method for cleaning the external additive particles, for example, the dispersion containing the external additive particles is solid-liquid separated to recover the wet cake-like external additive particles, and the recovered wet cake-like external additive particles are collected. A method of washing with water is preferred. As a method for washing the external additive particles, the external additive particles in the dispersion containing the external additive particles are settled, the supernatant liquid is replaced with water, and the external additive particles are redispersed in water after the replacement. The method is preferred.

(Drying process)
After the washing step, the external additive particles may be dried. For example, the external additive particles can be dried using a dryer (more specifically, a spray dryer, a fluidized bed dryer, a vacuum freeze dryer, a vacuum dryer, or the like). Further, when an aggregate of external additive particles is formed after drying, a crushing device (more specifically, a continuous surface reforming device, an airflow crushing device, a mechanical crushing device, or the like) is used. Then, the aggregate may be crushed.

[External addition process]
By using a mixing device, the toner base particles and the external additive are mixed under conditions that prevent the external additive from being embedded in the toner base particles, thereby allowing the external additive to adhere to the surface of the toner base particles. . As the mixing apparatus, for example, a V-type mixer, a Q-type mixer, an FM mixer, a Redige mixer, a multi-purpose mixer, a super mixer, and a hybridization system (registered trademark) can be used. As the external additive, only the external additive having the basic structure described above may be used, or other external additives (for example, silica powder and titania powder) may be used in combination.

  Examples of the present invention will be described. Table 1 shows external additives B1 to B7 used for the production of toners T-1 to T-7 (each of the electrostatic latent image developing toners) according to Examples or Comparative Examples. The amount of externally added titania particles in Table 1 indicates the amount of externally added titania particles (unit: parts by mass) when the amount of silica core is 100 parts by mass.

  Hereinafter, a production method, an evaluation method, and an evaluation result of toners T-1 to T-7 will be described in order. In the evaluation in which an error occurs, a considerable number of measurement values with which the error is sufficiently small are obtained, and the arithmetic average of the obtained measurement values is used as the evaluation value.

[Toner Production Method]
(Preparation of toner base particles)
87 parts by mass of a polyester resin (“Polyester (registered trademark) HP-313” manufactured by Nippon Synthetic Chemical Industry Co., Ltd.), 8 parts by mass of carbon black (“MA100” manufactured by Mitsubishi Chemical Co., Ltd.), and carnauba wax (Toa Kasei Co., Ltd.) 3 parts by mass of the company) and 2 parts by mass of the charge control agent ("BONTRON (registered trademark) N-71" manufactured by Orient Chemical Co., Ltd.), FM mixer ("FM-10B" manufactured by Nippon Coke Industries, Ltd.) And mixed.

Subsequently, the obtained mixture was melt-kneaded using a twin-screw extruder (“TEM-26SS” manufactured by Toshiba Machine Co., Ltd.). Thereafter, the obtained kneaded material was cooled. Subsequently, the cooled kneaded material was coarsely pulverized using a pulverizer (“Rotoplex (registered trademark) 16/8 type” manufactured by Hosokawa Micron Corporation) under the condition of a set particle diameter of 2 mm. Subsequently, the obtained coarsely pulverized product was finely pulverized using a pulverizer (“Turbo Mill RS type” manufactured by Freund Turbo Co., Ltd.). Subsequently, the obtained finely pulverized product was classified using an air classifier (“Elbow Jet EJ-LABO type” manufactured by Nippon Steel Mining Co., Ltd.). As a result, toner mother particles having a volume median diameter (D ₅₀ ) of 7 μm were obtained.

(Preparation of external additive B1)
First, a composite of silica particles and titania particles was performed. Specifically, 100 parts by mass of dry silica powder having a volume median diameter (D ₅₀ ) of 80 nm obtained by a vapor phase synthesis method and titania powder having a volume median diameter (D ₅₀ ) of 15 nm (“AEROXIDE, manufactured by Nippon Aerosil Co., Ltd.) (Registered trademark) NKT90 ", content: titania particle surface-modified with alkylsilyl, titania particle manufacturing method: gas phase method, titania particle crystal structure: anatase type) 25 parts by mass, pin mill (Nara Co., Ltd.) Mixing was performed for 30 seconds under the condition of a rotation speed of 600 rpm using a “sample mill SAM-0 type” manufactured by Kikai Seisakusho. As a result, a plurality of titania particles (externally added titania particles) adhered to the surface of each silica particle contained in the silica powder, and a powder A1 of silica-titania composite particles was obtained.

  Subsequently, a coating layer was formed on the surface of the silica-titania composite particles contained in the powder A1 by the following coating process. In the coating step, first, 50 g of powder of silica-titania composite particles (powder A1 obtained by the above procedure) and 500 g of ion-exchanged water are mixed in an environment of a temperature of 25 ° C. and a humidity of 50% RH. (Primix Co., Ltd. “TK Hibis Disper Mix HM-3D-5 type”) was mixed (stirred) for 30 minutes under the condition of a rotational speed of 30 rpm to obtain a dispersion of composite particles.

  Subsequently, the pH of the dispersion was adjusted to about 3.5 by adding 0.5N dilute hydrochloric acid to the resulting dispersion of composite particles. Subsequently, 50 g of water-soluble methylol melamine (“Nikaresin (registered trademark) S-260” manufactured by Nippon Carbide Industries Co., Ltd.)) was added to the dispersion. Subsequently, the dispersion was stirred for 5 minutes under the conditions of a rotation speed of 30 rpm using the above mixing apparatus (TK Hibis Disper Mix) in an environment of a temperature of 25 ° C. and a humidity of 50% RH. Subsequently, the container contents (dispersion) of the mixing device were transferred to a 1 L separable flask equipped with a thermometer and a stirring device. The stirring device was equipped with a motor and a stirring blade attached to the motor.

  Subsequently, while stirring the flask contents at a rotation speed (stirring blade) of 90 rpm, the temperature of the flask contents was increased from 35 ° C. to 70 ° C. at a rate of 1 ° C./3 minutes.

  Subsequently, while maintaining the temperature of the flask contents at 70 ° C., the flask contents were stirred at a rotation speed (stirring blade) of 90 rpm for 30 minutes. As a result, a coat layer substantially composed of a thermosetting nitrogen-containing resin (melamine resin) was formed on the surface of the silica-titania composite particles. Thereafter, the flask contents were cooled to room temperature (about 25 ° C.).

Subsequently, the obtained dispersion was subjected to suction filtration (solid-liquid separation) using a Buchner funnel to obtain wet cake-like particles (powder). Subsequently, the obtained wet cake-like particles were dispersed in an aqueous ethanol solution having a concentration of 50% by mass to obtain a slurry. Subsequently, using a continuous surface reformer (“Coatmizer (registered trademark)” manufactured by Freund Sangyo Co., Ltd.), the particles in the slurry are dried under conditions of a hot air temperature of 45 ° C. and a blower air volume of 2 m ³ / min. It was.

  Subsequently, the dried particles (powder) are finely pulverized using a collision plate jet pulverizer (“Jet Mill IJT-2” manufactured by Nippon Pneumatic Industry Co., Ltd.) under a pulverization pressure of 0.6 MPa. Additive B1 was obtained. In the fine pulverization, a ceramic flat plate was used as the collision plate. The external additive particles contained in the obtained external additive B1 were provided with silica-titania composite particles and a coat layer covering the surface of the silica-titania composite particles. The silica-titania composite particle was provided with one silica particle and a plurality of titania particles (externally added titania particles) attached to the surface of the silica particle.

(Preparation of external additive B2)
In the coating step, the external additive B2 was produced by using an aqueous solution of methylolated urea ("Milben (registered trademark) Resin SU-100" manufactured by Showa Denko KK) instead of 50 g of water-soluble methylolmelamine (Nicaledin S-260). This was the same as the manufacturing method of the external additive B1 except that 50 g of a solid content concentration of 80% by mass was used. The external additive particles contained in the external additive B2 were provided with a coat layer substantially composed of a thermosetting nitrogen-containing resin (urea resin).

(Preparation of external additive B3)
The external additive B3 was produced by using the additive B1 except that the silica-titania composite particle powder A3-2 produced by the following method was used instead of the silica-titania composite particle powder A1. The manufacturing method was the same.

<Production Method of Powder A3-2>
In the separated two evaporators, silicon tetrachloride (SiCl ₄ ) and titanium tetrachloride (TiCl ₄ ) are vaporized, respectively, and the obtained SiCl ₄ gas and TiCl ₄ gas are burned together with N ₂ (nitrogen) gas. (Burner) was introduced into the combustion chamber. Furthermore, a mixed gas composed of hydrogen and air was introduced into the combustion chamber, and all the introduced gases were burned in the combustion chamber and reacted. As a result, powder of titania-containing silica particles having a sea-island structure (sea: silica, island: titania) (specifically, silica particles containing a plurality of titania particles (internally added titania particles) dispersed therein) as a reaction product. The body was obtained.

Subsequently, the obtained reaction product was cooled, and the titania-containing silica particle powder was collected by a filter. Subsequently, impurities attached to the collected powder were removed using moist air having a temperature of about 600 ° C. As a result, a powder A3-1 of titania-containing silica particles from which impurities were removed was obtained. Regarding the titania-containing silica particles contained in the obtained powder A3-1, the volume median diameter (D ₅₀ ) is 80 nm, and the titania content (= 100 × mass of titania in particles / mass of all particles) is It was 5 mass%. The volume median diameter (D ₅₀ ) and titania content of the titania-containing silica particles were adjusted by the supply amount of raw materials (SiCl ₄ gas and TiCl ₄ gas) and combustion conditions (combustion temperature and combustion time), respectively.

Subsequently, 100 parts by mass of titania-containing silica particles obtained as described above, 20 parts by mass of titania powder having a volume median diameter (D ₅₀ ) of 15 nm (“AEROXIDE NKT90” manufactured by Nippon Aerosil Co., Ltd.) Was mixed using a pin mill (“Sample Mill SAM-0 type” manufactured by Nara Machinery Co., Ltd.) for 30 seconds at a rotational speed of 600 rpm. As a result, a plurality of titania particles (externally added titania particles) adhered to the surface of each titania-containing silica particle, and powder A3-2 of silica-titania composite particles was obtained. The silica-titania composite particle contained in the obtained powder A3-2 includes one titania-containing silica particle and a plurality of titania particles (externally added titania particles) attached to the surface of the titania-containing silica particle. It was.

(Preparation of external additive B4)
The manufacturing method of the external additive B4 was the same as the manufacturing method of the external additive B1 except that the amount of titania powder (AEROXIDE NKT90) was changed from 25 parts by mass to 10 parts by mass in the compounding step.

(Preparation of external additive B5)
As the external additive B5, powder A5 of silica-titania composite particles was used. The powder A5 of silica-titania composite particles was obtained by using the hydrophobizing agent (silicone oil) and the positive charging agent (aminosilane) in the above-described procedure, and the powder A1 (see “Preparation of External Additive B1”). The silica-titania composite particles contained in (1) were surface treated. The external additive particles contained in the external additive B5 did not have a coat layer (resin layer).

(Preparation of external additive B6)
As the external additive B6, a titania-containing silica particle powder A6-2 produced by the following method was used. The external additive particles contained in the external additive B6 were neither provided with externally added titania particles nor a coating layer (resin layer).

<Production Method of Powder A6-2>
In order to adjust the volume median diameter (D ₅₀ ) and titania content of titania-containing silica particles, the supply amount of raw materials (SiCl ₄ gas and TiCl ₄ gas) and combustion conditions (combustion temperature and combustion time) were changed. Except for the above, in the same manner as the above-described method for producing the powder A3-1 (see “Method for producing the powder A3-2”), the titania-containing material having a volume median diameter (D ₅₀ ) of 70 nm and a titania content of 25% by mass. Silica particle powder A6-1 was obtained. Subsequently, the titania-containing silica particles contained in the powder A6-1 are surface-treated using a hydrophobizing agent (silicone oil) and a positive charging agent (aminosilane), and the titania-containing silica particles A6- 2 was obtained.

(Preparation of external additive B7)
The manufacturing method of the external additive B7 was the same as the manufacturing method of the external additive B1, except that the powder A6-1 of titania-containing silica particles was used instead of the powder A1 of silica-titania composite particles. .

(External addition process)
100 parts by mass of toner base particles (toner base particles prepared by the above procedure) and 1 part by mass of first external additive (any of external additives B1 to B7 shown in Table 1 defined for each toner) And 1 part by mass of a second external additive (positively charged silica powder: “AEROSIL (registered trademark) REA200” manufactured by Nippon Aerosil Co., Ltd.) and a third external additive (titania powder: Teika Co., Ltd.) 1 part by mass of “MT-500B”) was mixed for 5 minutes under the condition of a rotational speed of 3500 rpm using an FM mixer (“FM-10B” manufactured by Nippon Coke Industries, Ltd.). As a result, the external additive adhered to the surface of the toner base particles. Thereafter, the obtained powder was sieved using a 300 mesh (aperture 48 μm) sieve. As a result, toners (toners T-1 to T-7) containing a large number of toner particles were obtained.

[Evaluation method]
The evaluation method of each sample (toners T-1 to T-7) is as follows.

(Preparation of developer for evaluation)
2 kg of an epoxy resin (“jER (registered trademark) 1004” manufactured by Mitsubishi Chemical Corporation) was dissolved in 20 L of acetone to obtain a solution. Subsequently, 100 g of diethylenetriamine and 150 g of phthalic anhydride were added to the resulting solution to obtain a mixed solution. Subsequently, the obtained mixed solution and 10 kg of Mn—Mg—Sr ferrite core (“EF-80B2” manufactured by Powder Tech Co., Ltd., particle diameter 80 μm) are mixed with a fluidized bed coating apparatus (“Spiraflow” manufactured by Freund Corporation). (Registered trademark) SFC-5 "). Subsequently, the surface of the ferrite particles (Mn—Mg—Sr ferrite core) was coated with an epoxy resin using a coating device while sending hot air of 80 ° C. into the coating device. The obtained resin-coated particles were heated at 180 ° C. for 1 hour using a dryer. As a result, a developer carrier was obtained.

  100 parts by mass of the obtained developer carrier and 10 parts by mass of a sample (toner) were mixed using a ball mill. As a result, an evaluation developer was obtained.

(Preparation of evaluation machine)
A color printer (“FS-C5016” manufactured by Kyocera Document Solutions Inc.) was used as an evaluation machine. 150 g of the developer for evaluation prepared as described above was charged into the developing device of the evaluation machine, and the sample (replenishment toner) was charged into the toner container of the evaluation machine.

(Print life test)
In an environment of a temperature of 25 ° C. and a humidity of 50% RH, a printing durability test was performed in which continuous printing was performed on 10000 sheets of paper (A4 size plain paper) at a printing rate of 1% using the evaluation machine.

(Specific surface area maintenance rate)
Fully automatic for each of the toner before the printing durability test (toner contained in the developer for evaluation immediately after preparation) and the toner after the printing durability test (toner taken out from the developing device of the evaluation machine after the printing durability test). The BET specific surface area was measured using a BET specific surface area measuring apparatus ("Macsorb (registered trademark) HM MODEL-1208" manufactured by Mountec Co., Ltd.). Based on the BET specific surface area S _A of the toner before the printing durability test and the BET specific surface area S _B of the toner after the printing durability test, it is expressed by the formula “specific surface area retention ratio = 100 × S _B / S _A ”. The specific surface area maintenance rate (unit:%) was determined. In any toner evaluation, the BET specific surface area was larger before the printing test than after the printing test (S _A > S _B ).

  When the specific surface area maintenance ratio was 85% or more, it was evaluated as “good”, and when the specific surface area maintenance ratio was less than 85%, it was evaluated as “poor” (not good).

(Charge amount distribution)
After the printing durability test, nitrogen gas was sprayed onto the developing roller of the evaluator to collect the toner adhering to the surface of the developing sleeve of the evaluator. The collected toner was set in a charge amount / particle size distribution measuring device (“Espert Analyzer (registered trademark)” manufactured by Hosokawa Micron Corporation), and the charge amount distribution of the toner was measured. The Y's Part Analyzer detects the movement of particles due to the influence of an electric field (constant intensity electric field) and acoustic field (constant frequency air vibration) using the laser Doppler method, and simultaneously measures the charge amount and particle diameter of each particle. It is a device to do. Regarding the measured charge amount distribution, the horizontal axis is “Q / d (charge amount / particle diameter)” (unit: fC / μm), and the vertical axis is frequency (number). From the charge amount distribution of the obtained toner, a width having a frequency of 1/4 of the mode value (hereinafter referred to as a 1/4 value width) was obtained. A small ¼ value width of the charge amount distribution indicates that the charge amount distribution is sharp, and a large ¼ value width of the charge amount distribution indicates that the charge amount distribution is broad. Show.

  If the ¼ value width of the charge amount distribution is less than 0.80 fC / μm, it is evaluated as “good”, and if the ¼ value width of the charge amount distribution is 0.80 fC / μm or more, × (not good). evaluated.

(Charge amount)
With respect to the developer for evaluation immediately after the preparation, the charge amount of the toner (toner before the printing durability test) in the developer was measured by the following method. Further, after the printing durability test, the developer was taken out from the developing device of the evaluation machine, and the developer was allowed to stand for 24 hours in a high humidity environment (temperature 32.5 ° C. and humidity 80% RH). Subsequently, the charge amount of the toner (toner after the printing durability test) in the developer was measured by the following method.

<Measurement method of charge amount of toner in developer>
The developer was stirred for 20 seconds using a mixer (“Turbler (registered trademark) mixer T2F” manufactured by Willy et Bacofen (WAB)). Thereafter, 0.10 g of developer is put into a measurement cell of a Q / m meter (“MODEL 210HS-1” manufactured by Trek), and only the toner is sucked through the sieve (metal mesh) for 10 seconds. did. The toner charge amount (unit: μC / g) was calculated based on the formula “total electricity amount of sucked toner (unit: μC) / mass of sucked toner (unit: g)”.

  If the charge amount of the toner before the printing durability test is 15 μC / g or more and 40 μC / g or less and the charge amount of the toner after the printing durability test is 10 μC / g or more and 27 μC / g or less, it is evaluated as “good”. When it did not satisfy any of these requirements, it was evaluated as x (not good).

(Image density and fog density)
After the printing durability test, continuous printing was further performed on 5000 sheets of paper (A4 size plain paper) at a printing rate of 8% using the evaluation machine in an environment of a temperature of 25 ° C. and a humidity of 50% RH. Thereafter, a sample image including a solid portion and a blank portion was printed on a recording medium (evaluation paper). Then, the reflection density (ID: image density) of the solid portion of the sample image on the printed recording medium was measured using a reflection densitometer (“RD914” manufactured by X-Rite). The reflection density meter (RD914) was used to measure the reflection density of each of the blank portion of the sample image on the printed recording medium and the unprinted base paper (unprinted paper). Then, the fog density (FD) was calculated based on the following equation.
FD = (reflection density of blank area) − (reflection density of unprinted paper)

  When the image density (ID) was 1.20 or more, it was evaluated as ◯ (good), and when it was less than 1.20, it was evaluated as x (not good). If the fog density (FD) was 0.007 or less, it was evaluated as ◯ (good), and if it exceeded 0.007, it was evaluated as x (not good).

[Evaluation results]
For each of the toners T-1 to T-7, the results of evaluating the specific surface area maintenance ratio, the charge amount distribution (¼ value width), the charge amount, the image density (ID), and the fog density (FD) are shown in Table 2. Shown in

  Each of the toners T-1 to T-4 (toners according to Examples 1 to 4) was provided with the external additive having the above-described basic configuration. Specifically, in the toners according to Examples 1 to 4, the external additive includes silica-titania composite particles and external additive particles (specific external additive particles) that include a coat layer that covers the surface of the silica-titania composite particles. ). The silica-titania composite particles were composite particles composed of a silica core mainly composed of silica (silica particles or titania-containing silica particles) and titania particles (externally added titania particles) attached to the surface of the silica core. The coat layer contained a thermosetting nitrogen-containing resin (melamine resin or urea resin).

  In each of toners T-1 to T-4 (toners according to Examples 1 to 4), the shape of the specific external additive particles was different, and the externally added titania particles protruded from the surface of the silica core. Moreover, the area ratio of the area | region which a coat layer covers among the surface areas of a silica-titania composite particle was 100%.

  As shown in Table 2, regarding the toners according to Examples 1 to 4, all of the specific surface area maintenance ratio, the charge amount distribution (1/4 value width), the charge amount, the image density (ID), and the fog density (FD) are all included. A good evaluation result was obtained. In addition, the toner according to Examples 1 to 4 is excellent in positive chargeability and durability, and when used in continuous printing, forms a high-quality image by continuously suppressing the occurrence of fogging over a long period of time. I was able to continue.

  Regarding the toner T-5 (toner according to Comparative Example 1), the evaluation results regarding the charge amount and fog density (FD) of the toner after the printing durability test were poor as compared with the toner according to Examples 1 to 4. . This is presumably because the surface treatment agent of the external additive particles was peeled off and the externally added titania particles were detached from the silica-titania composite particles by the continuous printing.

  Regarding toners T-6 and T-7 (toners according to Comparative Examples 2 and 3), compared with the toners according to Examples 1 to 4, the specific surface area maintenance ratio and the charge amount distribution (¼ value width) are related. The evaluation result was bad. This is presumably because the external additive particles are detached from the toner particles.

  The toner for developing an electrostatic latent image according to the present invention can be used for forming an image in, for example, a copying machine, a printer, or a multifunction machine.

1 Silica core 1a Titania particles (internally added titania particles)
2 Titania particles (externally added titania particles)
3 Coating Layer 10 Toner Particles 11 Toner Base Particles 12 External Additive Particles

Claims (9)

A plurality of toner particles comprising a toner base particle containing a binder resin and an external additive attached to the surface of the toner base particle;
The external additive includes a plurality of external additive particles comprising composite particles and a coat layer covering the surface of the composite particles,
The composite particle is composed of a silica core mainly composed of silica, and titania particles attached to the surface of the silica core,
The coating layer is a toner for developing an electrostatic latent image, containing a thermosetting nitrogen-containing resin.   The electrostatic latent image developing toner according to claim 1, wherein the external additive particle has an irregular shape.   The electrostatic latent image developing toner according to claim 1, wherein the titania particles protrude from a surface of the silica core.   4. The electrostatic latent image developing toner according to claim 1, wherein an area ratio of a region covered by the coat layer in a surface region of the composite particle is 100%. The volume median diameter of the silica core is 60 nm or more and 100 nm or less,
The volume median diameter of the titania particles is 10 nm or more and 25 nm or less,
5. The electrostatic latent image developing toner according to claim 1, wherein an amount of the titania particles is 10 parts by mass or more and 65 parts by mass or less with respect to 100 parts by mass of the silica core.   The electrostatic latent image developing toner according to claim 1, wherein the silica core is silica particles.   6. The electrostatic latent image developing toner according to claim 1, wherein the silica core is a titania-containing silica particle having a sea-island structure of silica distributed in a sea shape and titania distributed in an island shape. 6. .   The electrostatic additive image developing toner according to claim 1, wherein the external additive further includes silica particles and titania particles in addition to the external additive particles. Including a plurality of external additive particles,
The external additive particles include composite particles and a coat layer covering the surface of the composite particles,
The composite particle is composed of a silica core mainly composed of silica, and titania particles attached to the surface of the silica core,
The coat layer is an external additive containing a thermosetting nitrogen-containing resin.

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