JP7776348B2 - Toner, two-component developer containing the toner, and image forming apparatus using the developer - Google Patents

Description

The present invention relates to toner, a two-component developer containing the toner, and an image forming apparatus using the developer.

2. Description of the Related Art In recent years, with the remarkable development of office automation equipment, image forming apparatuses (electrophotographic apparatuses) such as digital copying machines, printers, and facsimile machines that utilize electrophotographic technology have become widespread.
Furthermore, with the increase in contact charging methods using roller charging and the progress in image forming apparatuses with longer life, smaller size and higher speed, various functions are being demanded of image forming apparatuses and the toner used therein.

For example, Japanese Patent Application Laid-Open No. 2020-190724 (Patent Document 1) proposes a toner containing, as an external additive, strontium titanate fine powder (fine particles) having Si-containing particles with a number-average equivalent circular diameter of 5 nm to 15 nm on the surface, as a technology for preventing the occurrence of fogged images over time in low-temperature, low-humidity environments (temperature 10°C, humidity 15% RH) and providing a toner that can achieve excellent image density. Patent Document 1 also discloses that zinc stearate with a particle size of 0.01 to 1 μm may be used as a "cleaning enhancer" that is a component of the toner base particles.

Japanese Patent Application Laid-Open No. 2020-190724

However, in the above prior art, although zinc stearate is effective in suppressing the occurrence of toner filming, it also significantly reduces the toner charge amount, which causes the problem of fogging (causing poor image quality) in high-temperature, high-humidity environments (temperature 30°C, humidity 80% RH).

The present invention aims to provide a toner that reduces embedding in toner base particles, suppresses the occurrence of toner filming, and suppresses fogging in high-temperature, high-humidity environments, as well as a two-component developer containing the toner, and an image forming apparatus that uses the developer.

As a result of extensive research into resolving the above-mentioned problems, the inventors discovered that by using a combination of strontium silicate titanate particles and disc-shaped zinc stearate particles as external additives to the toner base particles (toner cores), the embedding of particles into the toner base particles is reduced, suppressing the occurrence of toner filming, while also suppressing an increase in the toner charge amount, preventing a decrease in image density, thereby resolving the above-mentioned problems and completing the present invention.

Thus, the present invention provides a toner characterized by being composed of at least toner base particles and, externally added to the surfaces of the toner base particles, silica particles, strontium silica titanate particles, and disc-shaped fatty acid metal salt particles having an average particle diameter of 1.4 μm or less.

The present invention also provides a two-component developer containing the above-described toner and a carrier.

Furthermore, according to the present invention, there is provided an image forming apparatus that forms an electrostatic latent image on the surface of an electrophotographic photoreceptor (hereinafter also referred to as "photoreceptor") and transfers the toner developed on the electrostatic latent image to a transfer material to form an image, wherein the toner is the toner described above.

The present invention provides a toner that reduces embedding in toner base particles, suppresses the occurrence of toner filming, and suppresses fogging in high-temperature, high-humidity environments, as well as a two-component developer containing the toner, and an image forming apparatus that uses the developer.

1 is a schematic side view illustrating a configuration of a main part of an image forming apparatus according to the present invention.

(1) Toner The toner of the present invention is characterized by being composed of at least toner base particles, and silica particles, strontium silica titanate particles, and disc-shaped fatty acid metal salt particles having an average particle diameter of 1.4 μm or less, which are externally added to the surfaces of the toner base particles.
Hereinafter, silica particles, strontium silica titanate particles, and fatty acid metal salt particles as external additives will be described, followed by a description of the toner base particles and a method for producing the toner.

[Silica particles]
The silica particles function as a toner fluidizing agent, and surface-treated silica particles commonly used in the art can be used.
Examples of surface-treated silica particles include silica particles that have been surface-treated with dimethyldichlorosilane (dimethylsilyl: DDS), hexamethyldisilazane (trimethylsilyl: HMDS), silicone oil (dimethylpolysiloxane), etc. Silica particles that have been surface-treated with DDS and silicone oil are preferred, and silica particles that have been surface-treated with silicone oil are particularly preferred because they have an excellent effect of improving fogging in high-temperature, high-humidity environments.

The silica particles (silica raw material) before surface treatment can be produced by known methods such as a dry method (gas phase method), a wet method, or a sol-gel method, with the gas phase method being preferred since it does not use a solvent.
The gas phase method is a method for producing a silica base material by vapor-phase oxidation of a silicon halide compound. For example, a silica base material called dry process (gas phase process) silica or fumed silica is produced by the thermal decomposition oxidation reaction of silicon tetrachloride gas in an oxyhydrogen flame (basic reaction: SiCl ₄ + 2H ₂ + O ₂ → SiO ₂ + 4HCl).
The silica base material may also be a composite of silica and another metal oxide obtained by using a metal halide compound such as aluminum chloride or titanium chloride together with a silicon halide compound in the above-mentioned production process.

Silica particles surface-treated with silicone oil can be produced, for example, by directly mixing silica raw material treated with an organosilicon compound with silicone oil using a mixer such as a Henschel mixer; by diluting the silicone oil with an appropriate solvent such as normal hexane, spraying the silicone oil onto the silica raw material, and then heat-treating the mixture; or by dissolving or dispersing silicone oil in an appropriate solvent, adding and mixing the silica raw material, and then removing the solvent.
The heat treatment after the spraying is preferably carried out in an inert gas atmosphere such as helium, nitrogen, or argon for safety reasons, and nitrogen gas is preferred in consideration of cost, etc. The heat treatment temperature is preferably 200 to 400°C.

Examples of the silicone oil include straight silicone oils such as dimethyl silicone oil, methylphenyl silicone oil, and methylhydrogen silicone oil; epoxy-modified silicone oil, carboxyl-modified silicone oil, carbinol-modified silicone oil, methacrylic-modified silicone oil, mercapto-modified silicone oil, phenol-modified silicone oil, one-end reactive modified silicone oil, heterofunctional group-modified silicone oil, polyether-modified silicone oil, methylstyryl-modified silicone oil, alkyl-modified silicone oil, higher fatty acid ester-modified silicone oil, special hydrophilic modified silicone oil, higher alkoxy-modified silicone oil, higher fatty acid-containing modified silicone oil, and fluorine-modified silicone oil. These may be used alone or in combination of two or more.

Examples of the organosilicon compound include hexamethyldisilazane, trimethylsilane, trimethylethoxysilane, isobutyltrimethoxysilane, trimethylchlorosilane, dimethyldichlorosilane, methyltrichlorosilane, dimethylethoxysilane, dimethyldimethoxysilane, diphenyldiethoxysilane, and hexamethyldisiloxane. These compounds may be used alone or in combination of two or more.
Silicone oil-treated silica particles can be produced, for example, by the method described in Japanese Patent No. 6849352, and desired fine particles can be obtained by changing the average primary particle diameter of the base silica particles and the amount of silicone oil used.
The specific surface area of the corn oil-treated silica particles as measured by the BET method is not particularly limited, but is about 30 to 400 m ² /g.

Silica particles can be produced by known methods such as those described above, but commercially available silica particles, such as those used in the examples and manufactured by Nippon Aerosil Co., Ltd., under the product names RY300, RY200, and RY200S (all silicone oil-treated) and R976S (DDS-treated), can also be used.

<Average primary particle size of silica particles>
The silica particles preferably have an average primary particle size of 7 to 16 nm, which ensures uniform toner fluidity and toner surface coverage.
If the average primary particle diameter of the silica particles is less than 7 nm, they may embed themselves in the toner base particles, adhere too strongly, and the spacer effect may not be maintained. On the other hand, if the average primary particle diameter of the silica particles is more than 12 nm, the adhesion to the toner base particles may be weak, and the coating effect may not be obtained. Furthermore, if the average primary particle diameter of the silica particles is more than 16 nm, the amount of external additives must be increased to ensure the coating rate of the external additives, which is not preferable.
The average primary particle size of the silica particles is more preferably 7 to 12 nm.
The method for measuring the average primary particle diameter of the silica particles will be described in the Examples.

<Silica particle coverage>
The silica particles preferably have a coverage of 94 to 117% of the toner base particles, which allows both suppression of environmental fluctuations in the toner charge amount and fixability.
If the coverage of the silica particles is less than 90%, carrier spent may occur when the toner is used in a two-component developer containing a carrier. On the other hand, if the coverage of the silica particles is more than 117%, low-temperature fixability may deteriorate.
The coverage of the silica particles is more preferably 90 to 117%, and even more preferably 90 to 105%.
The method for measuring the coverage of silica particles will be described in the Examples.

[Strontium silica titanate particles]
Strontium silica titanate particles are strontium titanate particles having silica particles on the surface (modified with silica particles), and are fine powders in which the surface of a core made of strontium titanate to which silica has been added is hydrophobized with a silane compound.

The strontium titanate _SrTiO3 of the strontium silica titanate particles is a perovskite-type titanate compound in which a portion of Sr may be substituted with a third metal component M selected from La, Mg, Ca, Sn, and Si.
Furthermore, the strontium silicate titanate particles are preferably particulate, but may also be spherical, acicular, non-spherical, etc., and may have either a single particle structure or a structure in which several particles are aggregated.

The degree of modification of the strontium silica titanate particles with silica particles can be expressed as the silica content in the fine powder, specifically the molar ratio of Si to Ti (Si/Ti), and is not particularly limited, but is about 0.03 to 10.0. This molar ratio can be measured using X-ray analysis by SEM-EDS from the ratio of the Si peak intensity to the Ti peak intensity, with the carbon peak intensity as the reference.
The molar ratio (Si/Ti) is more preferably 0.03 to 1.0.
If the molar ratio Si/Ti is less than 0.03, the fog value may increase. On the other hand, if the molar ratio Si/Ti exceeds 1.0, the negative chargeability becomes strong, and the increase in charge in a low-humidity environment increases the adhesive force between the toner and the carrier, making it difficult for the toner replenished later to mix, resulting in development without sufficient charging, which may result in increased toner scattering and a high fog value. A more preferable molar ratio Si/Ti is 0.04 to 0.06.

The strontium silica titanate particles preferably have an average primary particle size of 30 to 100 nm.
If the average primary particle diameter of the strontium silicate titanate particles is less than 30 nm, the particles may adhere more strongly to the toner base particles, which may lead to filming. On the other hand, if the average primary particle diameter of the strontium titanate particles is more than 100 nm, the particles may scrape the drum surface, causing abrasive concave scratches, which may deteriorate the cleaning performance and lead to filming.
The average primary particle size of the strontium silicate titanate particles is preferably 30 to 70 nm, more preferably 30 to 50 nm.
The method for measuring the average primary particle size of the strontium silica titanate particles will be described in the Examples.

The strontium silicate titanate particles can be produced by a known method such as a room temperature wet method, for example, by the following steps (1) to (5).
(1) Metatitanic acid obtained by the sulfuric acid method is deironized and bleached, then an aqueous solution of sodium hydroxide is added to adjust the pH to 9.0, desulfurized, and then neutralized to pH 5.8 with hydrochloric acid, filtered, and washed with water to obtain a washed cake.
(2) Water is added to the resulting cake to form a slurry, and then hydrochloric acid is added to adjust the pH to 1.4 for deflocculation. The resulting metatitanic acid solution (Solution 1), an aqueous strontium chloride solution (Solution 2), and an aqueous sodium silicate solution (Solution 3) are mixed in proportions such that the molar ratio of (Sr+Si)/Ti falls within the range of 1.18 to 2.10.
(3) The resulting mixed solution is heated to 90°C under a nitrogen gas atmosphere, stirred for 2 hours while adding a 10N aqueous solution of sodium hydroxide, and then stirred at a temperature of 95°C for 1 hour to allow the reaction to proceed.
(4) After the reaction, the mixed solution (slurry) is cooled to 50°C, hydrochloric acid is added until the pH reaches 5.0, and the mixture is stirred for 1 hour. The resulting precipitate is washed and filtered for solid-liquid separation.
(5) The obtained solid is subjected to a hydrophobic treatment using a silane compound, followed by solid-liquid separation by filtration. The obtained solid is dried at a temperature of 120°C in the air for 10 hours to obtain strontium titanate particles.
Examples of the silane compound (silane coupling agent) include dimethyldichlorosilane (dimethylsilyl: DDS), hexamethyldisilazane (trimethylsilyl: HMDS), octylsilane, and silicone oil (dimethylpolysiloxane).

<External Addition Ratio of Strontium Titanate Particles>
The strontium titanate particles are preferably added externally to the toner base particles in an amount of 0.2 to 0.5% by mass, which allows the excellent fogging-reducing effect of the present invention to be obtained.
If the proportion of strontium titanate particles is less than 0.2% by mass, the increase in the toner charge amount may not be suppressed, whereas if the proportion of strontium titanate particles is more than 0.5% by mass, not only will the toner charge amount drop significantly, but the photoreceptor surface may be scraped and scratched.
The proportion of strontium titanate particles is more preferably 0.2 to 0.4 mass %.

[Fatty metal salt particles]
Since it is important that the fatty acid metal salt be present in the nip between the drum and the cleaning blade, it is necessary to adhere it relatively weakly and control the content of the fatty acid metal salt so that an appropriate amount of fatty acid metal salt is supplied between the photosensitive layer surface and the cleaning blade.
Examples of the fatty metal salt of the fatty metal salt particles include zinc stearate, magnesium stearate, lithium stearate, calcium stearate, and aluminum stearate. Among these, zinc stearate and magnesium stearate are preferred from the viewpoint of filming resistance, with zinc stearate being particularly preferred.

<Shape and average particle size of fatty acid metal salt particles>
The fatty acid metal salt particles are disc-shaped particles having an average particle size of 1.4 μm or less.
It is believed that conventional rod-shaped fatty acid metal salts tend to embed themselves in the toner base particles, making it difficult to obtain the inherent effects of fatty acid metal salts, such as preventing filming and suppressing an increase in charge amount.
On the other hand, the disc-shaped fatty acid metal salt of the present invention is thought to be less embedded in the toner base particles, preventing filming and suppressing an increase in the charge amount, thereby preventing a decrease in image density.

If the average particle diameter of the fatty acid metal salt particles exceeds 1.4 μm, adhesion to the toner base particles is poor, and the fatty acid metal salt particles detach from the toner base particles and migrate to the carrier surface of the two-component developer, which may reduce the toner charge amount and cause fogging. If the average particle diameter of the fatty acid metal salt particles is too small, the fatty acid metal salt particles may not detach from the toner base particles, and the function required for photoreceptor cleaning may not be exerted. Furthermore, if the fatty acid metal salt particles are not present at the contact point between the photoreceptor surface and the cleaning blade, the lubrication performance may not be exerted, and the lower limit thereof is about 0.7 μm.
The method for measuring the average particle size of the fatty acid metal salt particles will be described in the Examples.

In the present invention, "disc-shaped" means that the fatty acid metal salt particles have a thickness of approximately 0.03 to 0.07 μm relative to their average particle diameter. Therefore, the thickness of the fatty acid metal salt particles used in the present invention is preferably approximately 0.05 to 0.1 μm.

Commercially available particles such as zinc stearate molded body manufactured by Nissin Chemical Industry Co., Ltd., and MZ-2 manufactured by NOF Corporation, which are used in the examples, can be used as fatty acid metal salt particles.

<External Addition Ratio of Fatty Acid Metal Salt Particles>
The fatty acid metal salt particles are preferably added externally to the toner base particles in a proportion of 0.1 to 0.3% by mass.
If the proportion of the fatty acid metal salt particles added externally is less than 0.1 mass %, a sufficient amount of fatty acid metal salt particles cannot be supplied to the image forming section, and the effect of stress crack resistance may not be obtained. On the other hand, if the proportion of the fatty acid metal salt particles added externally exceeds 0.3 mass parts, the amount of fatty acid metal salt particles liberated in the developing tank increases, and the toner charge amount decreases, making it difficult for the toner to mix with the developer, resulting in a deterioration in developability and making it more likely that image defects such as roughness will occur.
The proportion of the fatty acid metal salt particles added externally is more preferably 0.1 to 0.2% by mass.

<Adhesion strength of fatty acid metal salt particles>
The fatty acid metal salt particles preferably have an adhesive strength in which they remain on the toner at a ratio of 10% by mass or less when subjected to an external adhesive strength test in which 2.0 g of toner is added to 40 ml of a 0.2% by mass aqueous solution of polyoxyethylene octylphenyl ether and stirred for 1 minute, the resulting aqueous solution is irradiated with ultrasound at an output of 40 μA for 2 minutes, and then left to stand for 3 hours to separate the toner and the liberated external additives. After removing the supernatant, approximately 50 ml of pure water is added to the precipitate and stirred for 5 minutes, and the mixture is suction filtered using a membrane filter with a pore size of 1 μm. The toner remaining on the membrane filter is vacuum dried overnight to obtain a toner after external additive removal treatment.
The external adhesive strength test will be explained in the examples.

If the proportion of fatty acid metal salt particles remaining in the toner exceeds 10% by mass, photoreceptor filming may become more likely to occur. A more preferable proportion of fatty acid metal salt particles remaining in the toner is 7% by mass or less. Furthermore, if the proportion of fatty acid metal salt particles remaining in the toner is too low, the effect of external addition of the fatty acid metal salt particles may not be obtained, so the lower limit is approximately 5% by mass.

[Other external additives]
The toner base particles of the present invention may contain an external additive that improves the transportability, chargeability, cleanability, etc. of the toner, within a range that does not impair the effects of the present invention. Examples of such external additives include inorganic fine particles such as titanium oxide particles, alumina particles, and magnetite.

[Toner base particles]
The toner base particles contain at least a binder resin, a colorant, and a release agent, and may also contain a charge control agent, etc., as required.

<Binder resin>
As the binder resin, resins commonly used in the technical field can be used, such as polyester resins, polystyrene resins such as styrene-acrylic resins, (meth)acrylic acid ester resins, polyolefin resins, polyurethane resins, and epoxy resins, and these can be used alone or in combination of two or more. Among these, polystyrene resins and polyester resins can be preferably used, and polyester resins are particularly preferred.

As the polystyrene resin, a styrene-acrylic resin (styrene-acrylic copolymer resin) is preferred, and examples of styrene monomers that can be used as the resin raw material include styrene derivatives such as styrene, o-methylstyrene, m-methylstyrene, p-methylstyrene, α-methylstyrene, p-ethylstyrene, and 2,4-dimethylstyrene. Examples of acrylic monomers include acrylic acid derivatives and methacrylic acid derivatives such as acrylic acid, methyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate, propyl acrylate, octyl acrylate, 2-chloroethyl acrylate, phenyl acrylate, methacrylic acid, methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, n-octyl methacrylate, 2-ethylhexyl methacrylate, phenyl methacrylate, and dimethylamino methacrylate.
Furthermore, vinyl monomers such as maleic anhydride, maleic acid monomethyl ester, maleic acid monoethyl ester, maleic acid monophenyl ester, maleic acid monoallyl ester, and divinylbenzene may be used as resin raw materials.

The polyester resin is usually obtained by subjecting one or more selected from dihydric alcohol components and trihydric or higher polyhydric alcohol components to a condensation polymerization reaction, esterification, or transesterification reaction using a known method with one or more selected from dicarboxylic acids and trihydric or higher polycarboxylic acids.
The conditions for the condensation polymerization reaction may be appropriately set depending on the reactivity of the monomer components, and the reaction may be terminated when the polymer has reached suitable physical properties. For example, the reaction temperature is about 170 to 250°C, and the reaction pressure is about 5 mmHg to atmospheric pressure.

Examples of dihydric alcohol components include alkylene oxide adducts of bisphenol A such as polyoxypropylene (2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene (3.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene (2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene (2.0)-polyoxyethylene (2.0)-2,2-bis(4-hydroxyphenyl)propane, and polyoxypropylene (6)-2,2-bis(4-hydroxyphenyl)propane; ethylene glycol Examples include diols such as ethanol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; bisphenol A; propylene adducts of bisphenol A; ethylene adducts of bisphenol A; and hydrogenated bisphenol A.

Examples of trihydric or higher polyhydric alcohol components include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose (cane sugar), 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.
In the toner of the present invention, the above dihydric alcohol components and trihydric or higher polyhydric alcohol components may be used alone or in combination of two or more.

Examples of dicarboxylic acids 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, n-dodecenylsuccinic acid, n-dodecylsuccinic acid, n-octylsuccinic acid, isooctenylsuccinic acid, isooctylsuccinic acid, and their acid anhydrides or lower alkyl esters.

Examples of trivalent or higher polyvalent carboxylic acids include 1,2,4-benzenetricarboxylic 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, empol trimer acid, and acid anhydrides or lower alkyl esters thereof.
In the toner of the present invention, the above-mentioned dicarboxylic acids and tricarboxylic or higher polycarboxylic acids may be used alone or in combination of two or more.

The polyester resin preferably has a mass average molecular weight in the range of 3,000 to 50,000. If the weight average molecular weight is less than 3,000, the release properties may be poor on the high temperature side of the fixable region (non-offset region). On the other hand, if the weight average molecular weight exceeds 50,000, the low temperature fixability may be poor.
The polyester resin preferably has an acid value of 5 to 30 mgKOH/g. If the acid value is less than 5 mgKOH/g, the charging characteristics of the polyester resin will be reduced, and the charge control agent will be difficult to disperse in the polyester resin, which may adversely affect the charge buildup and charging stability during continuous use. On the other hand, if the acid value exceeds 30 mgKOH/g, the hygroscopicity will be high and the charging properties may become unstable.

<Coloring Agent>
As the colorant, various types and colors of organic and inorganic pigments and dyes commonly used in the art can be used, including, for example, black, white, yellow, orange, red, purple, blue and green colorants.

Examples of black colorants include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, non-magnetic ferrite, magnetic ferrite, and magnetite.
Carbon black is classified into channel black, roller black, disc black, gas furnace black, oil furnace black, thermal black, acetylene black, etc. depending on the production method, etc., and an appropriate carbon black can be selected from these according to the design properties of the toner to be obtained.
Examples of white colorants include zinc oxide, titanium oxide, antimony white, and zinc sulfide.

Examples of yellow colorants include yellow lead, zinc yellow, cadmium yellow, yellow iron oxide, mineral fast yellow, nickel titanium yellow, navel yellow, naphthol yellow S, Hansa Yellow G, Hansa Yellow 10G, benzidine yellow G, benzidine yellow GR, quinoline yellow lake, permanent yellow NCG, tartrazine lake, C.I. Pigment Yellow 12, C.I. Pigment Yellow 13, C.I. Pigment Yellow 14, C.I. Pigment Yellow 15, C.I. Pigment Yellow 17, C.I. Pigment Yellow 93, C.I. Pigment Yellow 94, and C.I. Pigment Yellow 138.

Examples of orange colorants include red lead yellow, molybdenum orange, permanent orange GTR, pyrazolone orange, vulcan orange, induthrene brilliant orange RK, benzidine orange G, induthrene brilliant orange GK, C.I. Pigment Orange 31, and C.I. Pigment Orange 43.

Examples of red colorants include red iron oxide, cadmium red, red lead, mercury sulfide, cadmium, permanent red 4R, lithol red, pyrazolone red, watching red, calcium salt, lake red C, lake red D, brilliant carmine 6B, eosin lake, rhodamine lake B, alizarin lake, brilliant carmine 3B, C.I. pigment red 2, C.I. pigment red 3, C.I. pigment red 5, C.I. pigment red 6, C.I. pigment red 7, C.I. pigment red 15, C.I. pigment red 16, C.I. pigment red 48:1, C.I. pigment red 53:1, C.I. pigment red 57:1, C.I. Examples of pigments include C.I. Pigment Red 122, C.I. Pigment Red 123, C.I. Pigment Red 139, C.I. Pigment Red 144, C.I. Pigment Red 149, C.I. Pigment Red 166, C.I. Pigment Red 177, C.I. Pigment Red 178, and C.I. Pigment Red 222.

Examples of purple colorants include manganese violet, fast violet B, and methyl violet lake.

Examples of blue colorants include Prussian blue, cobalt blue, alkali blue lake, Victoria blue lake, phthalocyanine blue, metal-free phthalocyanine blue, partially chlorinated phthalocyanine blue, fast sky blue, indanthrene blue BC, C.I. pigment blue 15, C.I. pigment blue 15:2, C.I. pigment blue 15:3, C.I. pigment blue 16, C.I. pigment blue 60, and the like.
Examples of green colorants include chrome green, chromium oxide, pigment green B, micalite green lake, final yellow green G, and C.I. pigment green 7.

In the present invention, the above colorants can be used alone or in combination of two kinds, and the combination may be of different colors or the same color.
Two or more kinds of colorants may be used in the form of composite particles.
The composite particles can be produced, for example, by adding an appropriate amount of water, a lower alcohol, etc. to two or more colorants, granulating the mixture in a general granulator such as a high-speed mill, and drying the granulated mixture.
Furthermore, in order to disperse the colorant uniformly in the binder resin, it may be used in the form of a masterbatch.
The composite particles and masterbatches are incorporated into the toner composition during dry blending.

The amount of colorant blended in the toner base particles is not particularly limited, but is preferably 1 to 10 parts by weight, and particularly preferably 3 to 5 parts by weight, per 100 parts by weight of the binder resin.
When the blending amount of the colorant is within the above range, it is possible to provide a toner that can reduce embedding of the colorant into the toner base particles, suppress the occurrence of toner filming, and suppress fogging under high-temperature and high-humidity environments, without impairing various physical properties of the toner.

<Release Agent>
The release agent may be any release agent commonly used in the technical field, and examples thereof include petroleum waxes such as paraffin wax, microcrystalline wax, and derivatives thereof; hydrocarbon synthetic waxes such as Fischer-Tropsch wax, polyolefin wax (polyethylene wax, polypropylene wax, etc.), low molecular weight polypropylene wax, polyolefin polymer wax (low molecular weight polyethylene wax, etc.), and derivatives thereof; plant waxes such as carnauba wax, rice wax, candelilla wax, and derivatives thereof, and Japan wax; animal waxes such as beeswax and spermaceti; oil-based synthetic waxes such as fatty acid amides and phenol fatty acid esters; long-chain carboxylic acids and derivatives thereof; long-chain alcohols and derivatives thereof; silicone polymers; and higher fatty acids.
The derivatives include oxides, block copolymers of vinyl monomers and wax, and graft modified products of vinyl monomers and wax.
In the present invention, the above-mentioned release agents can be used alone or in combination of two or more.

The amount of the release agent in the toner base particles is not particularly limited, but is preferably 0.5 to 10 parts by weight, and particularly preferably 1.0 to 8.0 parts by weight, per 100 parts by weight of the resin.
When the blending amount of the binder resin is within the above range, it is possible to provide a toner that can reduce embedding of the binder resin in the toner base particles, suppress the occurrence of toner filming, and suppress fogging under high-temperature and high-humidity environments, without impairing various physical properties of the toner.

<Charge Control Agent (Charge Control Agent)>
The toner base particles of the present invention may contain a charge control agent, if necessary. Examples of the charge control agent include charge control agents commonly used in the art for controlling positive charge and negative charge.
Examples of charge control agents for controlling positive charges include nigrosine dyes and derivatives thereof, basic dyes, quaternary ammonium salts, quaternary phosphonium salts, aminopyrine, pyrimidine compounds, polynuclear polyamino compounds, aminosilanes, triphenylmethane derivatives, guanidine salts, and amidine salts.
Examples of charge control agents for negative charge control include oil-soluble dyes such as oil black and Spiron black, metal-containing azo compounds, azo complex dyes, metal naphthenate salts, metal complexes and metal salts of salicylic acid and its derivatives (metals include chromium, zinc, zirconium, etc.), boron compounds, fatty acid soaps, long-chain alkyl carboxylate salts, and resin acid soaps.

The amount of the charge control agent in the toner base particles is not particularly limited, but is preferably 0.1 to 3% by mass, and particularly preferably 0.2 to 2 parts by mass, per 100 parts by mass of the resin.
When the blending amount of the colorant is within the above range, it is possible to provide a toner that can reduce embedding of the colorant into the toner base particles, suppress the occurrence of toner filming, and suppress fogging under high-temperature and high-humidity environments, without impairing various physical properties of the toner.

[Toner Glass Transition Temperature Tg]
The toner of the present invention preferably has a glass transition temperature Tg of 60° C. or less.
The glass transition temperature Tg of the toner can be adjusted by the types and blending ratios of the components of the toner. If the glass transition temperature Tg exceeds 60°C, it may become difficult to achieve both low-temperature fixability and heat-resistant storage stability, and the lower limit thereof is approximately 50°C.

<Volume Average Particle Diameter of Toner Base Particles>
The volume average particle diameter of the toner base particles is not particularly limited and can be set appropriately depending on the purpose, but the toner base particles preferably have a volume average particle diameter of 5 to 8 μm.
When the volume average particle diameter of the toner base particles is within the above range, it is possible to provide a toner that can reduce embedding in the toner base particles, suppress the occurrence of toner filming, and also suppress fogging in a high-temperature, high-humidity environment.
The particle size (particle size) distribution of the toner base particles is not particularly limited and can be set appropriately depending on the purpose, but it is preferable that the toner base particles have a particle size distribution in which particles of 3 μm or less make up 40% or less by number.
Furthermore, the circularity of the toner base particles is not particularly limited and can be set appropriately depending on the purpose, but the toner base particles preferably have a circularity of 0.92 or more and 0.97 or less.

[Toner manufacturing method]
The toner of the present invention can be produced by a known method using a known apparatus commonly used in the art.
Examples of the manufacturing method include a kneading step S1 in which a mixture containing a binder resin, a colorant, a release agent, and, if necessary, a charge control agent is melted and kneaded to obtain a molten and kneaded product, a crushing step S2 in which the obtained molten and kneaded product is cooled and solidified, and coarsely crushed to obtain a coarsely crushed product, and the obtained coarsely crushed product is finely crushed to obtain a finely crushed product, a classification step S3 in which the obtained finely crushed product is classified to obtain toner base particles, and an external addition step S4 in which an external additive is externally added to the obtained toner base particles to obtain a toner.
Dry methods are preferred in that they require fewer steps and require less equipment cost than wet methods, and among these, pulverization is particularly preferred.
The conditions for each step may be appropriately set depending on the target material and the desired physical properties.

<Kneading step (melt kneading) S1>
In the kneading step S1, the toner raw materials are mixed in a mixer and then kneaded in the kneader to obtain a molten mixture. The kneading is performed by heating to a temperature equal to or higher than the softening point of the binder resin and lower than its thermal decomposition temperature. This melts or softens the binder resin, allowing the colorant, release agent, charge control agent, and the like to be dispersed in the binder resin. The specific heating temperature during kneading is preferably, for example, 80 to 200°C, and more preferably 100 to 150°C.

Mixing can be performed using known equipment commonly used in the technical field, such as Henschel-type mixers such as the Henschel Mixer (trade name, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke and Engineering Co., Ltd.)), Super Mixer (trade name, manufactured by Kawata Corporation), and Mechano Mill (trade name, manufactured by Okada Seiko Co., Ltd.), as well as mixers such as the Ang Mill (trade name, manufactured by Hosokawa Micron Corporation), Hybridization System (trade name, manufactured by Nara Machinery Works, Ltd.), and Cosmo System (trade name, manufactured by Kawasaki Heavy Industries, Ltd.).

For melt-kneading, known equipment commonly used in the relevant technical field, such as general kneaders such as twin-screw extruders, three-roll mills, and lab blast mills, can be used. Examples of such kneaders include single- or twin-screw extruders such as TEM-100B (trade name, manufactured by Toshiba Machine Co., Ltd.), PCM-65/87, and PCM-30 (all trade names, manufactured by Ikegai Corporation), and open-roll kneaders such as Kneadex (trade name, manufactured by Mitsui Mining Co., Ltd.). The kneading process may also be carried out using multiple kneaders.

<Crushing process (cooling grinding) S2>
In the pulverization step S2, the molten kneaded product obtained in the kneading step S1 is cooled and solidified, the solidified product is coarsely pulverized to obtain a coarsely pulverized product, and the coarsely pulverized product is finely pulverized to obtain a finely pulverized product.
For cooling, a known device commonly used in the art, such as a cooling belt, can be used.
For the coarse pulverization, known devices commonly used in the art, such as a speed mill with a screen, a hammer mill, or a cutter mill, can be used.
For the fine pulverization, known devices commonly used in the art can be used, such as a jet pulverizer that uses a supersonic jet stream to pulverize, or an impact pulverizer that introduces a solidified material into the space formed between a rotor and a stator (liner) that rotate at high speed, and pulverizes the solidified material.
It is also possible to collect the finely pulverized particles having a desired volume average particle size obtained in the pulverization step S2 as toner base particles without carrying out the classification step S3 described below.

<Classification process S3>
In the classification step S3, the finely pulverized material obtained in the pulverization step S2 is classified using a classifier to obtain toner base particles having a desired volume average particle size.
For classification, a known device commonly used in the art, for example, a classifier capable of removing over-pulverized toner particles by centrifugal force and wind force, such as a rotary wind classifier (rotary wind classifier), can be used.

<External addition step S4>
In the external addition step S4, the toner base particles obtained in the classification step S3 and the external additive are mixed using a mixer to adhere the external additive to the surface of the toner base particles, thereby obtaining a toner (externally-added toner).
For mixing, a known device commonly used in the technical field, for example, the mixing device described in the kneading step S1, can be used.
In the mixing, the toner base particles and the three types of external additives essential components of the present invention, silica particles, strontium titanate particles, and fatty acid metal salt particles, may be mixed simultaneously, or two types of external additives and one type of external additive may be mixed successively with the toner base particles, or each of the three types of external additives may be mixed successively with the toner base particles. In this way, the conditions such as the order of addition of the multiple external additives and the processing time (mixing time) may be appropriately set depending on the target material and the desired physical properties.

In the production of the toner of the present invention, it is preferable to externally add silica particles in the first external addition step, and then externally add strontium silica titanate particles and fatty acid metal salt particles simultaneously in the second external addition step. This prevents the silica particles from causing damage such as scratches to the photoreceptor, and suppresses the occurrence of image defects.

(2) Two-Component Developer The two-component developer of the present invention is characterized by containing the toner of the present invention and a carrier.
[Career]
As the carrier, carriers commonly used in the relevant technical field can be used, and examples thereof include simple or composite ferrite particles made of iron, copper, zinc, nickel, cobalt, manganese, chromium, etc., resin-coated carriers in which the surfaces of carrier core particles are coated with a known coating material, and resin-dispersed carriers in which magnetic particles are dispersed in a resin.

As the coating material, materials commonly used in the technical field can be used, and examples thereof include polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester-based resin, metal compound of di-tert-butylsalicylic acid, styrene-based resin, acrylic resin, polyamide, polyvinyl butyral, nigrosine, aminoacrylate resin, basic dye, lake of basic dye, silica fine powder, alumina fine powder, etc.
The resin used in the resin dispersion type carrier is not particularly limited, but examples thereof include styrene acrylic resin, polyester resin, fluorine resin, and phenol resin.
The above-mentioned coating materials and resins used in the resin dispersion type carrier can be used either alone or in combination of two or more, and are preferably selected according to the toner components.

The shape of the carrier is not particularly limited, but spherical and flat shapes are preferred.
The average particle size of the carrier is not particularly limited, but in consideration of achieving high image quality, it is preferably 30 to 80 μm, and more preferably 40 to 60 μm.

The volume resistivity of the carrier is a value obtained from the current value when carrier particles are placed in a container with a cross-sectional area of 0.50 ^cm2 and tapped, a load of 1 kg/ ^cm2 is applied to the particles packed in the container, and a voltage is applied that generates an electric field of 1000 V/cm between the load and the bottom electrode. If the volume resistivity is low, the carrier becomes charged when a bias voltage is applied to the developing sleeve, making it easier for the carrier particles to adhere to the photoreceptor. Also, breakdown of the bias voltage is more likely to occur. A preferred volume resistivity of the carrier is 1.0 x ¹⁰⁹ to 1.0 x ¹⁰¹³ (Ω·cm).

The carrier's magnetization strength (maximum magnetization) is preferably 10 to 60 emu/g, and more preferably 15 to 40 emu/g. Under typical magnetic flux density conditions of developing rollers, if the magnetization strength is less than 10 emu/g, the magnetic binding force will not work, which may result in carrier scattering. Furthermore, if the magnetization strength exceeds 60 emu/g, in non-contact development, the carrier will become too stiff, making it difficult to maintain a non-contact state between the image carrier and toner, and in contact development, sweeping marks may easily appear in the toner image.

The blending ratio of toner and carrier in a two-component developer is not particularly limited and can be appropriately selected depending on the type of toner and carrier. For example, when mixed with a resin-coated carrier (density 5 to 8 g/cm ² ), the toner content should be 2 to 30% by mass, preferably 2 to 20% by mass, of the total developer weight. Furthermore, the coverage of the carrier by the toner is preferably 40 to 80% by mass.

(3) Image forming device The image forming device of the present invention is an image forming device that forms an image by forming an electrostatic latent image on the surface of a photoreceptor and transferring the toner developed on the electrostatic latent image to a transfer material, and is characterized in that the toner is the toner of the present invention.
The toner of the present invention can provide a toner that can reduce embedding in toner base particles and suppress the occurrence of toner filming without impairing various physical properties of the toner, and can also suppress fogging under high-temperature and high-humidity environments.
Such an effect is particularly pronounced in a silica-added photoreceptor containing silica in the surface layer, and therefore the photoreceptor is preferably a silica-added photoreceptor containing silica in the surface layer.

The image forming apparatus of the present invention is not particularly limited as long as it has the above-mentioned constituent elements, and examples thereof include an image forming apparatus equipped with at least a photosensitive member, a charging means for charging the photosensitive member, an exposure means for exposing the charged photosensitive member to light to form an electrostatic latent image, a developing means for developing the electrostatic latent image formed by exposure to form a toner image, a transfer means for transferring the toner image formed by development onto a recording medium, a fixing means for fixing the transferred toner image on the recording medium to form an image, a cleaning means for removing and recovering toner remaining on the photosensitive member, and a discharging means for discharging surface charges remaining on the photosensitive member.
An example of an image forming apparatus and its operation will be described below with reference to the drawings, but the present invention is not limited to this.

FIG. 1 is a schematic side view showing the configuration of the main part of an image forming apparatus 100 of the present invention.
1 includes a photoreceptor 1, an exposure means (semiconductor laser) 31, a charging means (charger) 32, a developing means (developer) 33, a transfer means (transfer charger) 34, a conveyor belt (not shown), a fixing means (fixer) 35, and a cleaning means (cleaner) 36. Reference numeral 51 denotes a recording medium (recording paper or transfer paper).

Photoreceptor 1 is not particularly limited as long as it is one that is used in the art as a photoreceptor for an image-forming device. Examples include a multilayer photoreceptor in which a charge generation layer containing a charge generation material and a charge transport layer containing a charge transport material are stacked in that order on a substrate, or a photoreceptor that has at least a single-layer photoreceptor containing a charge generation material and a charge transport material.

Photoreceptor 1 is rotatably supported on the main body of image forming apparatus 100 and is driven to rotate around rotation axis 44 in the direction of arrow 41 by a drive means (not shown). The drive means, which may include, for example, an electric motor and a reduction gear, transmits its driving force to the conductive support that forms the core of photoreceptor 1, thereby driving photoreceptor 1 to rotate at a predetermined peripheral speed. Charging means (charger) 32, exposure means 31, developing means (developer) 33, transfer means (transfer charger) 34, and cleaning means (cleaner) 36 are arranged in this order along the outer surface of photoreceptor 1, from upstream to downstream in the direction of rotation of photoreceptor 1, as indicated by arrow 41.

The charger 32 is a charging means for uniformly charging the outer circumferential surface of the photosensitive member 1 to a predetermined potential.
Examples of the charging means include a non-contact charging method such as a corona charging method using a charger, and a contact charging method using a charging roller or a charging brush.
The exposure unit 31 has a semiconductor laser as a light source, and irradiates the surface of the photoreceptor 1 between the charger 32 and the developer 33 with a laser beam light output from the light source, thereby exposing the charged outer peripheral surface of the photoreceptor 1 in accordance with image information. The light is repeatedly scanned in the main scanning direction, that is, the direction of extension of the rotation axis 44 of the photoreceptor 1, and these are focused to sequentially form electrostatic latent images on the surface of the photoreceptor 1. In other words, the amount of charge on the photoreceptor 1, which has been uniformly charged by the charger 32, differs depending on whether it is irradiated with the laser beam or not, thereby forming an electrostatic latent image.

The developing unit 33 is a developing means that uses developer (toner) to develop the electrostatic latent image formed on the surface of the photoreceptor 1 by exposure. It is provided facing the photoreceptor 1 and includes a developing roller 33a that supplies toner to the outer peripheral surface of the photoreceptor 1, and a casing 33b that rotatably supports the developing roller 33a about an axis of rotation parallel to the axis of rotation 44 of the photoreceptor 1 and contains developer containing toner in its internal space.

Transfer charger 34 is a transfer device that transfers the toner image, which is a visible image formed on the outer surface of photoreceptor 1 by development, onto transfer paper 51, a recording medium that is supplied between photoreceptor 1 and transfer charger 34 from the direction of arrow 42 by a transport device (not shown). Transfer charger 34 is, for example, a contact-type transfer device that includes a charging device and transfers the toner image onto transfer paper 51 by applying a charge of the opposite polarity to the toner to transfer the toner image onto transfer paper 51.

The cleaner 36 is a cleaning device that removes and collects toner remaining on the outer surface of the photoreceptor 1 after the transfer operation by the transfer charger 34. It is equipped with a cleaning blade 36a that removes toner remaining on the outer surface of the photoreceptor 1, and a collection casing 36b that contains the toner removed by the cleaning blade 36a. The cleaner 36 is also provided with a static elimination lamp (not shown).

The image forming apparatus 100 is also provided with a fixing device 35, which is a fixing means for fixing the transferred image, downstream of the transport of the transfer paper 51 that has passed between the photoreceptor 1 and the transfer charger 34. The fixing device 35 is provided with a heating roller 35a having a heating means (not shown), and a pressure roller 35b that is provided opposite the heating roller 35a and is pressed against the heating roller 35a to form a contact portion.
Reference numeral 37 denotes a separating means for separating the transfer paper from the photosensitive member, and reference numeral 38 denotes a housing for accommodating the above-mentioned means of the image forming apparatus.

The image forming operation by this image forming apparatus 100 is performed as follows.
First, when the photosensitive member 1 is driven to rotate in the direction of arrow 41 by the driving means, the surface of the photosensitive member 1 is uniformly charged to a predetermined positive potential by the charger 32, which is located upstream of the image-forming point of the light by the exposure means 31 in the direction of rotation of the photosensitive member 1.

Next, light corresponding to image information is irradiated from the exposure means 32 onto the surface of the photoreceptor 1. This exposure removes surface charge from the areas of the photoreceptor 1 that have been irradiated with light, creating a difference in surface potential between the areas that have been irradiated with light and the areas that have not been irradiated with light, forming an electrostatic latent image.
Toner is supplied from a developing device 33, which is located downstream in the rotational direction of the photosensitive member 1 from the point where light is focused by the exposure means 33, to the surface of the photosensitive member 1 on which the electrostatic latent image is formed, thereby developing the electrostatic latent image and forming a toner image.

In synchronization with the exposure of the photosensitive member 1, a transfer paper 51 is supplied between the photosensitive member 1 and the transfer charger 34. The transfer charger 34 imparts a charge of the opposite polarity to that of the toner to the supplied transfer paper 51, and the toner image formed on the surface of the photosensitive member 1 is transferred onto the transfer paper 51.
The transfer paper 51 onto which the toner image has been transferred is transported by the transport means to the fixing device 35, and is heated and pressed as it passes through the contact area between the heating roller 35a and the pressure roller 35b of the fixing device 35, and the toner image is fixed onto the transfer paper 51 to form a solid image. The transfer paper 51 on which the image has been formed in this way is then ejected to the outside of the image forming apparatus 100 by the transport means.

Meanwhile, any toner remaining on the surface of photoreceptor 1 after the toner image has been transferred by transfer charger 34 is removed from the surface of photoreceptor 1 and collected by cleaner 36. The charge on the surface of photoreceptor 1 from which the toner has been removed in this way is removed by light from the discharging lamp, and the electrostatic latent image on the surface of photoreceptor 1 disappears. Photoreceptor 1 is then rotated again, and the series of operations starting with charging are repeated again, forming images continuously.

The image forming device 100 described above is a monochrome image forming device (printer), but it may also be, for example, an intermediate transfer type color image forming device capable of forming color images. Specifically, it may be a so-called tandem type full-color image forming device configured such that multiple photosensitive elements, on which toner images are respectively formed, are arranged side by side in a predetermined direction (for example, the horizontal direction H or approximately the horizontal direction H). The image forming device 100 may also be another color image forming device, a copier, a multifunction device, or a facsimile machine.

The present invention will be specifically explained below with reference to examples and comparative examples, but the present invention is not limited to the following examples as long as it does not depart from the gist of the invention.
The external additives constituting the toner and the physical properties of the toner obtained were measured by the following methods.

[Adhesion strength of fatty acid metal salt particles]
The toner is subjected to an external adhesion strength test according to the following procedure to obtain a toner after the external additive removal treatment.
(1) 2.0 g of toner is added to 40 ml of a 0.2% by weight aqueous solution of polyoxyethylene octylphenyl ether (Rohm & Haas (now Dow Chemical Company), product name: Triton (registered trademark)) and stirred for 1 minute.
(2) Using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., model: US-300T), the resulting aqueous solution is irradiated with ultrasonic waves at an output of 40 μA for 2 minutes.
(3) After that, the mixture is left for 3 hours, and the toner and the free external additives are separated.
(4) After removing the supernatant, add approximately 50 ml of purified water to the precipitate and stir for 5 minutes.
(5) The solution is filtered by suction using a membrane filter (manufactured by Advantec) with a pore size of 1 μm.
(6) The toner remaining on the membrane filter is vacuum dried overnight to obtain the toner after the external additive removal treatment.

The resulting toner after the external additive removal process and the toner before the external additive removal process were analyzed for the intensity of the elements (Zn, Mg) in the external additives of 1 g of toner using a fluorescent X-ray analyzer (Rigaku Corporation, Model: ZSX Primus II), and the mass percentage of the external additives (fatty acid metal salts) that had been detached from the toner in the external adhesion strength test was determined from the difference between these intensities.

[Average particle size of fatty acid metal salt particles]
The average primary particle size of the fatty acid metal salt particles is measured twice using a dynamic light scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., model: Nanotrac wave series), and the average value is used as the average primary particle size (μm) of the fatty acid metal salt particles.
The measurement conditions were a measurement time of 30 seconds, a sample particle refractive index of 1.49, and water as the dispersion medium, with a dispersion medium refractive index of 1.33. The volume particle size distribution of the measurement sample was measured, and the particle size at which the cumulative volume from the small particle size side in the cumulative volume distribution became 50% was calculated from the measurement results as the average primary particle size (μm) of the fatty acid metal salt particles.

[Average primary particle size of strontium silica titanate particles]
Strontium titanate particles are photographed using a scanning electron microscope (SEM) (Hitachi High-Technologies Corporation, model: S-4800), and the particle sizes (major diameters) of 100 particles are randomly selected from the obtained image and the average value of the particle sizes of the 100 particles is calculated, which is the average primary particle size (nm) of the strontium titanate particles.

[Average primary particle size of silica particles]
The average primary particle diameter of the silica particles is measured twice using a dynamic light scattering particle size distribution analyzer (manufactured by Nikkiso Co., Ltd., model: Nanotrac wave series), and the average value is used as the average primary particle diameter (μm) of the silica particles.
The measurement conditions were a measurement time of 30 seconds, a sample particle refractive index of 1.49, and water as the dispersion medium, with a dispersion medium refractive index of 1.33. The volume particle size distribution of the measurement sample was measured, and the particle size at which the cumulative volume from the small particle size side in the cumulative volume distribution became 50% was calculated from the measurement results as the average primary particle size (μm) of the silica particles.

[Silica particle coverage]
The coverage CS (%) of the silica particles is calculated from the average primary particle diameter and the surface area of the toner base particle, assuming that the coverage CS (%) is 100% when the entire surface of the toner base particle is covered with the external additive in a most dense state, and assuming that the silica particles of the external additive have the same particle diameter as the average primary particle diameter.
Specifically, the total projected area of the external additives, determined as follows, is divided by the total surface area of the toner, and the resulting value is taken as the coverage rate of the external additives.
First, the projected area per particle is calculated from the particle size of the external additive using the formula for the area of a circle. Next, the volume of the external additive is calculated using the formula for the volume of a sphere, and this is multiplied by the specific gravity to calculate the weight of the external additive, and then the number of external additives per toner particle is calculated. This is calculated using the number of parts added by weight from the toner weight and the weight of the external additive per particle. The sum of the projected area per particle is calculated from the number of external additives. The total surface area of the toner is calculated from the surface area of one toner particle using the formula for the surface area of a sphere.

[Volume average particle diameter of toner base particles]
20 mg of the sample and 1 mL of sodium alkyl ether sulfate were added to 50 mL of an electrolyte (manufactured by Beckman Coulter, Inc., product name: ISOTON-II), and the mixture was dispersed for 3 minutes at a frequency of 20 kHz using an ultrasonic disperser (manufactured by AS ONE Corporation, model: tabletop dual-frequency ultrasonic cleaner VS-D100) to prepare a measurement sample.
The obtained measurement sample is measured using a particle size distribution measuring device (manufactured by Beckman Coulter, Inc., model: Multisizer 3) under conditions of aperture diameter: 100 μm and number of particles measured: 50,000 counts, and the volume average particle diameter (μm) is determined from the volume particle size distribution of the sample particles.

(Preparation of Strontium Silica Titanate Particles)
Metatitanic acid obtained by the sulfuric acid method was desulfurized and bleached, and then a sodium hydroxide aqueous solution was added to adjust the pH to 9.0, followed by desulfurization. The solution was then neutralized with hydrochloric acid to a pH of 5.8, filtered, and washed to obtain a washed cake. Water was added to the washed cake to form a slurry, and hydrochloric acid was added to adjust the pH to 1.4, followed by peptization. The obtained metatitanic acid was placed in a reaction vessel, and a strontium chloride solution and sodium silicate were added. The mixture was then heated to 90°C with stirring, and a 10N sodium hydroxide aqueous solution was added over 2 hours. The reaction was then completed by continuing stirring at 95°C for 1 hour.
After the reaction was completed, the obtained slurry was cooled to a temperature of 50° C., and hydrochloric acid was added thereto until the pH reached 5.0, followed by stirring for 1 hour. The obtained precipitate was washed by decantation, and then subjected to solid-liquid separation by filtration.
Subsequently, the obtained solid matter was subjected to a hydrophobic treatment using a silane compound, followed by solid-liquid separation by filtration. The solid matter was dried at a temperature of 120°C in the atmosphere for 10 hours to obtain 100 g of an external additive containing strontium titanate as the main component, strontium silica titanate particles having a number-average primary particle diameter of 40 nm.

Example 1
[Pre-mixing process]
The following toner base particle raw materials were introduced into a 20 L capacity air flow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke & Engineering Co., Ltd.), model: FM20C), and pre-mixed for 5 minutes at a rotation speed of 1500 rpm to obtain a mixture.
Binder resin: 100 parts by mass of polyester resin (glass transition point 55°C, softening temperature 105°C) Colorant: 5 parts by mass of carbon black (manufactured by Mitsubishi Chemical Corporation, product name: MA-100) Mold release agent: 4 parts by mass of hydrocarbon-based synthetic wax (melting point 95°C, manufactured by Nippon Seiro Co., Ltd., product name: Fischer-Tropsch Wax FNP0090)

[Melting and kneading process]
The obtained mixture was melt-kneaded using a twin-screw extruder (manufactured by Ikegai Corporation, model: PCM-30) under conditions of a cylinder set temperature of 110°C, a barrel rotation speed of 300 rpm, and a raw material supply rate of 20 kg/hour to obtain a melt-kneaded product.

[Cooling grinding, classification process]
The resulting molten kneaded product was cooled and solidified on a cooling belt, and then coarsely pulverized using a speed mill (New Speed Mill, manufactured by Okada Seiko Co., Ltd., model: ND30) having a φ1 mm screen to obtain a coarsely pulverized product with a particle diameter of 1 mm.
The obtained coarsely crushed material was finely crushed using a fluidized bed opposed jet mill (jet crusher, manufactured by Hosokawa Micron Corporation, model: Counter Jet Mill AFG), and further classified using a pneumatic classifier (manufactured by Hosokawa Micron Corporation, model: TSP Separator), thereby obtaining 3,000 g of unadded toner base particles having a volume average particle diameter of 6.0 μm.

[External addition process]
The obtained toner base particles and silica particles (average primary particle diameter 7 nm, dimethyldichlorosilane treatment, manufactured by Nippon Aerosil Co., Ltd., product name: R976) in an amount corresponding to a coverage rate of 117% on the surface of the toner base particles, i.e., 1.0% by mass relative to the toner base particles, were charged into an air flow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke and Engineering Co., Ltd.), model: FM20C), and the peripheral speed at the outermost periphery of the tip of the stirring blade was set to 40 m/s, and mixing was performed for 1 minute (first external addition step).
Next, strontium silicate titanate particles in an amount equivalent to 0.2% by mass of the toner base particles and disk-shaped zinc stearate particles having an average particle size of 0.7 μm (manufactured by NOF Corporation, product name: Nissan Electol MZ-2) as fatty acid metal salt particles in an amount equivalent to 0.15% by mass of the toner base particles were added to an air flow mixer, and the peripheral speed at the outermost periphery of the tip of the stirring blade was set to 40 m/s, and mixing was performed for 1.5 minutes (second external addition step).
The resulting mixture was sieved using a 270 mesh sieve to obtain about 2000 g of externally added toner.

[Preparation of Two-Component Developer]
The obtained externally added toner and a coated carrier (manufactured by Sharp Corporation, name: genuine carrier for MX-5111FN) were charged into a V-type mixer (manufactured by Tokuju Kosakusho Co., Ltd., product name: V-5) so that the toner concentration was 7% by mass, and mixed for 20 minutes to obtain approximately 400 g of a two-component developer.

Example 2
A toner and a two-component developer were obtained in the same manner as in Example 1, except that disk-shaped zinc stearate particles having an average particle diameter of 1.4 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles.

The disc-shaped zinc stearate particles have a mean particle size of 1.5 μm or less according to the commercial specifications, and those with a mean particle size of up to 1.4 μm are commercially available, but the mean particle size varies depending on the production lot. Therefore, in the examples and comparative examples, disc-shaped zinc stearate particles from a production lot having the desired mean particle size were selected and used.
In addition, in Comparative Example 15, disk-shaped zinc stearate particles having an average particle size of 2.0 μm were used, which were obtained by classifying the fine powder side particles of disk-shaped zinc stearate particles having an average particle size of 1.4 μm (manufactured by NOF Corporation, product name: MZ-2) using an elbow jet classifier (manufactured by Matsubo Corporation, model: EJ-L-3 (LABO) type).

(Examples 3 to 6)
Toners and two-component developers were obtained in the same manner as in Example 1, except that the amount of strontium silicate titanate particles added externally to the toner base particles was changed from 0.2% by mass to 0.1% by mass, that disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as fatty acid metal salt particles, and that the amount of external addition relative to the toner base particles was changed from 0.15% by mass to 0.05%, 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 7 to 10)
Toner and two-component developers were obtained in the same manner as in Example 1, except that disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles, and the amount of external addition to the toner base particles was changed from 0.15% by mass to 0.05%, 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 11 to 13)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that the amount of strontium silicate titanate particles added externally to the toner base particles was changed from 0.2% by mass to 0.4% by mass, that disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles, and that the amount of external addition relative to the toner base particles was changed from 0.15% by mass to 0.10% by mass, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 14 to 16)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that the amount of strontium silicate titanate particles added externally to the toner base particles was changed from 0.2% by mass to 0.5% by mass, that disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles, and that the amount of external addition relative to the toner base particles was changed from 0.15% by mass to 0.10% by mass, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 17 to 19)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that the amount of strontium silicate titanate particles added externally to the toner base particles was changed from 0.2% by mass to 0.6% by mass, that disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles, and that the amount of external addition relative to the toner base particles was changed from 0.15% by mass to 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 20 to 23)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 7 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY300) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of the disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles, and the amount of external addition relative to the toner base particles was changed from 0.15% by mass to 0.05%, 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 24 to 26)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 7 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY300) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 82%, and the corresponding amount of external addition to the toner base particles was changed from 1.0% by mass to 0.7% by mass, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as fatty acid metal salt particles, and the amount of external addition to the toner base particles was changed from 0.15% by mass to 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 27 to 29)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 7 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY300) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 94%, and the corresponding amount of external addition to the toner base particles was changed from 1.0% by mass to 0.8% by mass, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as fatty acid metal salt particles, and the amount of external addition to the toner base particles was changed from 0.15% by mass to 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 30 to 32)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 7 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY300) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 105%, and the corresponding amount of external addition to the toner base particles was changed from 1.0% by mass to 0.9% by mass, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as fatty acid metal salt particles, and the amount of external addition to the toner base particles was changed from 0.15% by mass to 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Example 33)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 7 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY300) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the coverage rate relative to the surface of the toner base particles was changed from 117% to 130%, and the corresponding external addition amount relative to the toner base particles was changed from 1.0% by mass to 1.1% by mass, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles.

(Examples 34 to 36)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 12 nm, silicone oil-treated, manufactured by Nippon Aerosil Co., Ltd., product name: RY200) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 89%, and the corresponding amount of external addition to the toner base particles was changed from 1.0% by mass to 1.3% by mass, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as fatty acid metal salt particles, and the amount of external addition to the toner base particles was changed from 0.15% by mass to 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 37 to 39)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 12 nm, silicone oil-treated, manufactured by Nippon Aerosil Co., Ltd., product name: RY200) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 96%, and the corresponding amount of external addition to the toner base particles was changed from 1.0% by mass to 1.4% by mass, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as fatty acid metal salt particles, and the amount of external addition to the toner base particles was changed from 0.15% by mass to 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 40 to 42)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 12 nm, silicone oil-treated, manufactured by Nippon Aerosil Co., Ltd., product name: RY200) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 102%, and the corresponding amount of external addition to the toner base particles was changed from 1.0% by mass to 1.6% by mass, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as fatty acid metal salt particles, and the amount of external addition to the toner base particles was changed from 0.15% by mass to 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

(Examples 43 to 45)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 12 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY200) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 123%, and the corresponding external addition amount relative to the toner base particles was changed from 1.0% by mass to 1.8% by mass, and disk-shaped zinc stearate particles v having an average particle diameter of 0.9 μm were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as fatty acid metal salt particles, and the external addition amount relative to the toner base particles was changed from 0.15% by mass to 0.10%, 0.15% by mass, and 0.20% by mass, respectively.

Examples 46 and 47
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 16 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY200S) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 97% and 102%, respectively, and the corresponding external addition amount relative to the toner base particles was changed from 1.0% by mass to 1.9% by mass and 2.0% by mass, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles.

Examples 48 and 49
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 7 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY300) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of the disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles, and the treatment time of the second external addition step was changed from 1.5 minutes to 0.5 minutes and 3 minutes, respectively.

(Comparative Examples 1 to 3)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that strontium silicate titanate particles were not externally added, disk-shaped zinc stearate particles having an average particle diameter of 1.0 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles, and the amount of external addition relative to the toner base particles was changed from 0.15% by mass to 0.05%, 0.10%, and 0.15% by mass, respectively.

(Comparative Examples 4 and 5)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that strontium silicate titanate particles were not externally added, disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles, and the amount of external addition relative to the toner base particles was changed from 0.15 mass % to 0.20 mass % and 0.25 mass %, respectively.

(Comparative Examples 6 to 10)
Toner and two-component developers were obtained in the same manner as in Example 1, except that no strontium silicate titanate particles were externally added, rod-shaped zinc stearate particles having an average particle diameter of 0.9 μm and an average length of 2.0 μm (manufactured by Nissin Chemical Industry Co., Ltd., product name: zinc stearate molded body) were used instead of disc-shaped zinc stearate particles having an average particle diameter of 0.7 μm as fatty acid metal salt particles, and the amount of external addition relative to the toner base particles was changed from 0.15 mass% to 0.05 mass%, 0.10 mass%, 0.15 mass%, 0.20 mass%, and 0.25 mass%, respectively.

(Comparative Example 11)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that no strontium silica titanate particles were externally added, silica particles (average primary particle diameter 7 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY300) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of the disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles.

(Comparative Example 12)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that no strontium silica titanate particles were externally added, silica particles (average primary particle diameter 12 nm, silicone oil-treated, manufactured by Nippon Aerosil Co., Ltd., product name: RY200) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 102%, and the corresponding external addition amount relative to the toner base particles was changed from 1.0% by mass to 1.6% by mass, and disk-shaped zinc stearate particles having an average particle diameter of 0.9 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles.

(Comparative Example 13)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 7 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY300) were used instead of the dimethyldichlorosilane-treated silica particles having an average primary particle diameter of 7 nm, and no fatty acid metal salt particles were added externally.

(Comparative Example 14)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that silica particles (average primary particle diameter 12 nm, silicone oil treatment, manufactured by Nippon Aerosil Co., Ltd., product name: RY200) were used instead of the dimethyldichlorosilane-treated silica particles with an average primary particle diameter of 7 nm, the surface coverage of the toner base particles was changed from 117% to 102%, the corresponding amount of external addition to the toner base particles was changed from 1.0% by mass to 1.6% by mass, and no fatty acid metal salt particles were externally added.

(Comparative Example 15)
A toner and a two-component developer were obtained in the same manner as in Example 1, except that disk-shaped zinc stearate particles having an average particle diameter of 2.0 μm (manufactured by NOF Corporation, product name: MZ-2) were used instead of disk-shaped zinc stearate particles having an average particle diameter of 0.7 μm as the fatty acid metal salt particles.

[evaluation]
Using a test copier obtained by modifying a digital copier (manufactured by Sharp Corporation, model: MX-M6071), the toners and two-component developers prepared in Examples 1 to 49 and Comparative Examples 1 to 15 were evaluated for photoreceptor filming, fixability, and fogging (initial, immediately after high-speed printing, and after printing 5,000 (5k) sheets).

[Photoreceptor Filming]
The development unit of the above test copier was filled with a two-component developer, and a 5,000-sheet printing test was carried out using an ISO 19752 standard test chart. Thereafter, a 50% halftone image was printed, and the photoreceptor and the printed image were visually observed to evaluate the photoreceptor filming according to the following criteria.
◎: Excellent (no filming on the photoreceptor)
○: Good (There is filming on the photoreceptor, but the printed image is good and there are no problems with printing)
△: Fair (There is filming in the printed area, but the effect on the print is minor and it is still usable)
×: Unacceptable (there is a problem with the printing section, which has a significant impact on the printing and is not suitable for practical use)

[Fixation]
The development unit of the test copier was filled with a two-component developer, and the temperature was set to -30°C below the standard fixing temperature (180°C), and 10 sheets of paper (JIS A4 size, basis weight 70 g/ ^m2 ) were printed continuously. After fixing, the printed paper was folded, and a peeling width of the toner layer of 0.5 mm or less was judged to have good fixing strength, and a peeling width of more than 0.5 mm was judged to have fair fixing strength. The fixing property was evaluated according to the following criteria, along with the presence or absence of poor fixing.
○: Good (no poor fixing, good fixing strength)
△: Acceptable (no fixing failure, acceptable fixing strength)
×: Unacceptable (faulty fixing occurs)

[Fog]
Using a whiteness meter (manufactured by Nippon Denshoku Industries Co., Ltd., model: ZE6000), the whiteness of the non-image-forming areas after printing (fog when printing 5K) was measured, and the fog was evaluated based on the difference from the whiteness of the paper before printing, which had been measured in advance, according to the following criteria.
The initial fog refers to the fog value after changing the developer and setting up the machine, the 5k fog refers to the fog value immediately after a 5k-sheet printing test was conducted using the ISO 19752 standard test chart, and the fog immediately after high printing refers to the fog value on the 50th sheet when A4 size paper with a printing rate of 25% was run after the 5k fog experiment.
◎: Excellent (whiteness difference is 0.5 or less)
◯: Good (difference in whiteness is greater than 0.5 and less than 1.5)
△: Acceptable (whiteness difference is greater than 1.5 and less than 2.0)
×: Unacceptable (whiteness difference is 2.0)

[comprehensive evaluation]
The above evaluation results were comprehensively evaluated according to the following criteria.
◎: Excellent (filming rating is ◎, and other rating items are also ◎)
◯: Good (filming evaluation is ◎ or ○, and all other evaluation items are ○)
△: Usable (there are no ×s in the evaluation items, but there are △s)
×: Unusable (at least one evaluation item is ×)
The evaluation results obtained are shown in Tables 1 to 4 together with the constituent materials of the external additives of the toner and their physical properties.
In Table 1, "-" means that the corresponding external additive was not added externally.

The following can be seen from Tables 1 to 4.
(1) The toners of the present invention (Examples 1 to 49) are toners that suppress the occurrence of toner filming by reducing embedding in the toner mother particles and can suppress fogging in a high-temperature, high-humidity environment, compared to toners that have disc-shaped fatty acid metal salt particles but no strontium silicate titanate added to the outside (Comparative Examples 1 to 5, 11, and 12), toners that have rod-shaped fatty acid metal salt particles but no strontium silicate titanate added to the outside (Comparative Examples 6 to 10), toners that have strontium silicate titanate but no fatty acid metal salt particles added to the outside (Comparative Examples 13 and 14), and toners that have disc-shaped fatty acid metal salt particles and strontium silicate titanate added to the outside but have an average particle size that is too small (Comparative Example 15).

(2) It can be seen that the fogging values of the toners of the present invention (Examples 1 to 49) differ depending on the small silica surface treatment agent. Even better results were obtained with a silicone oil surface treatment agent. This can be seen by comparing toners containing dimethyldichlorosilane-treated small silica (Examples 1 to 19) with toners containing silicone oil-treated small silica (Examples 20 to 49). This is thought to be because the addition of silicone oil-treated small silica suppresses fluctuations in the toner charge amount even in high-print durability tests. (3) The toners of the present invention (Examples 1 to 49), whether containing externally added disc-shaped fatty acid metal salt particles or externally added strontium silica titanate, are toners that reduce embedding in the toner base particles, suppress the occurrence of toner filming, and can suppress fogging in high-temperature, high-humidity environments, and it can be seen that there is an optimal amount of addition.

1 Electrophotographic photosensitive member 31 Exposure means (semiconductor laser)
32 Charging means (charger)
33 Developing means (developer)
33a Developing roller 33b Casing 34 Transfer means (transfer charger)
35 Fixing means (fixing device)
35a Heating roller 35b Pressure roller 36 Cleaning means (cleaner)
36a Cleaning blade 36b Collection casing 37 Separation means 38 Housing 41, 42 Arrows 44 Rotation axis 51 Recording medium (recording paper or transfer paper)
100 Image forming device (laser printer)

Claims (10)

The toner is composed of at least toner base particles, silica particles externally added to the surface of the toner base particles, fine powder obtained by hydrophobizing the surface of a core made of strontium titanate to which silica has been added with a silane compound, and disc-shaped fatty acid metal salt particles having an average particle diameter of 1.4 μm or less ,
The toner , wherein the silane compound is selected from the group consisting of dimethyldichlorosilane, hexamethyldisilazane, octylsilane, and dimethylpolysiloxane . The toner according to claim 1, wherein the silica particles have an average primary particle diameter of 7 to 16 nm. The toner according to claim 1 or 2, wherein the silica particles have a coverage of 94 to 117% of the surface of the toner base particles. The toner according to any one of claims 1 to 3, wherein the silica particles are surface-treated with silicone oil. 5. The toner according to claim 1, wherein the fine powder is externally added to the toner base particles in an amount of 0.2 to 0.5% by mass. The toner according to any one of claims 1 to 5, wherein the fatty acid metal salt particles are particles of a compound selected from zinc stearate and magnesium stearate. The toner according to any one of claims 1 to 6, wherein the fatty acid metal salt particles are externally added to the toner base particles in an amount of 0.1 to 0.3% by mass. 2.0 g of the toner was added to 40 mL of a 0.2% by mass aqueous solution of polyoxyethylene octylphenyl ether and stirred for 1 minute. The resulting aqueous solution was irradiated with ultrasonic waves at an output of 40 μA for 2 minutes and then left to stand for 3 hours to separate the toner and the liberated external additives. After removing the supernatant, about 50 mL of pure water was added to the precipitate and stirred for 5 minutes. The mixture was suction filtered using a membrane filter with a pore size of 1 μm and the toner remaining on the membrane filter was vacuum dried overnight to obtain a toner after the external additive removal treatment. When subjected to an external adhesion strength test,
8. The toner according to claim 1, wherein the fatty acid metal salt particles have an adhesive strength such that they remain on the toner at a ratio of 10% by mass or less in the toner in an external adhesive strength test. A two-component developer comprising the toner according to any one of claims 1 to 8 and a carrier. An image forming apparatus that forms an image by forming an electrostatic latent image on the surface of an electrophotographic photoreceptor and transferring the toner developed on the electrostatic latent image to a transfer material, wherein the toner is the toner described in any one of claims 1 to 8.