JP7780930B2 - Toner, electrophotographic developer containing the toner, and image forming apparatus using the toner - Google Patents

Description

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

2. Description of the Related Art In recent years, with the remarkable development of office automation equipment, electrophotographic apparatuses (image forming apparatuses) such as 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 the long life, miniaturization and high speed of electrophotographic devices such as digital copiers and printers, various functions are being demanded of electrophotographic devices and the toners 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 describes that when the number-average equivalent circular diameter of the strontium titanate fine powder is 40 nm or less, its abrasiveness decreases, preventing wear of the carrier surface over time, thereby improving the charge buildup of the toner and preventing the occurrence of fogged images over time in low-temperature, low-humidity environments.

Japanese Patent Application Laid-Open No. 2020-190724

However, in the above prior art, when the particle size (number average circular equivalent diameter) of the strontium titanate microparticles is 40 nm or greater, the abrasiveness of the microparticles causes the carrier coat to peel off, resulting in image defects such as fogging and toner scattering due to reduced charge.

The present invention aims to provide a toner that can achieve a long life for electrophotographic developers and electrophotographic photoreceptors and achieve long-term image stability, an electrophotographic developer containing the toner, and an image forming apparatus that uses the toner.

As a result of extensive research into resolving the above-mentioned problems, the inventors discovered that the above-mentioned problems could be solved by constructing a toner from toner base particles (toner cores), strontium titanate microparticles having silica particles on their surfaces as external additives, and silicone oil-treated silica microparticles, thereby completing the present invention.

Thus, the present invention provides a toner characterized by being composed of at least toner base particles, and strontium titanate microparticles having silica particles on their surfaces and silicone oil-treated silica microparticles externally added to the surfaces of the toner base particles.

The present invention also provides an electrophotographic developer comprising the above-described toner and a carrier.

Furthermore, according to the present invention, there is provided an image forming apparatus that forms an image by forming an electrostatic latent image on the surface of an electrophotographic photosensitive member and transferring the toner developed on the electrostatic latent image to a transfer material, wherein the electrophotographic photosensitive member is a high-hardness drum and the toner is the toner described above.

The present invention makes it possible to provide a toner that can achieve a long life for electrophotographic developers and electrophotographic photoreceptors and achieve long-term image stability, as well as an electrophotographic developer containing the toner and an image forming apparatus that uses the toner.

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 strontium titanate microparticles having silica particles on the surface thereof and silicone oil-treated silica microparticles, which are externally added to the surface of the toner base particles.

In the toner of the present invention, the silicone oil-treated silica microparticles used as an external additive have low free energy and weak adhesive force, which is thought to prevent toner from being spent on the carrier and further prevent the carrier coat from peeling off.
Furthermore, in the toner of the present invention, strontium titanate fine particles having an average primary particle diameter of 40 nm or more can be used in combination with silicone oil-treated silica fine particles as an external additive, and therefore, the abrasive properties of the strontium titanate fine particles do not cause carrier coat peeling, and image defects such as fogging and toner scattering due to reduced charge are not observed, and an appropriate abrasion effect on the surface of the electrophotographic photosensitive member (drum) and, consequently, an anti-filming effect can be obtained. Such an effect is particularly noticeable in high-hardness drums.
The toner of the present invention is also suitable as a toner for low temperature fixing.
Hereinafter, the two types of external additives used in combination, which are a feature of the toner of the present invention, will be described, followed by the toner base particles, which are the basic components of the toner, the physical properties of the toner, a method for producing the toner, an electrophotographic developer containing the toner, and an image forming apparatus to which the toner of the present invention is applied.

[Strontium titanate microparticles having silica particles on the surface]
Strontium titanate microparticles having silica particles on the surface (modified with silica particles) 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 titanate microparticles 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 titanate microparticles are preferably particulate, but may also be spherical, acicular, non-spherical, etc., and may have either a single particle structure or an aggregate structure of several particles.

The degree of modification of strontium titanate microparticles 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 titanate fine particles preferably have an average primary particle size of 30 to 100 nm.
If the average primary particle diameter of the strontium titanate fine particles is less than 30 nm, the adhesion to the toner base particles may increase, and filming may occur easily, whereas if the average primary particle diameter of the strontium titanate fine particles is more than 100 nm, the cleaning ability may deteriorate, and filming may occur easily.
The average primary particle size of the strontium titanate fine particles is preferably 30 to 70 nm, more preferably 30 to 50 nm.
The method for measuring the average primary particle diameter of the strontium titanate fine particles will be described in the Examples.

The strontium titanate fine 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 desulfurized by adding an aqueous solution of sodium hydroxide, and then neutralized 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 for peptization. The resulting solution (Solution 1), an aqueous strontium chloride solution (Solution 2), and an aqueous sodium silicate solution (Solution 3) are mixed in a ratio 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, and the reaction is carried out by stirring for 2 hours while adding an aqueous sodium hydroxide solution.
(4) After the reaction, the mixed solution (slurry) is cooled to 50°C, hydrochloric acid is added, and the mixture is stirred for 2 hours. The resulting precipitate is washed, separated by filtration, and then dried.
(5) The obtained dried product is pulverized in a blender for 1 minute, and the coarse powder is removed using a sieve with 32 μm openings. The resulting fine powder substrate is then surface-coated (surface-modified) with a silane coupling agent.
Methods for coating the surface with a silane coupling agent include surface treatments commonly used in the art with hexamethyldisilazane (HMDS), dimethyldichlorosilane (DDS), octylsilane (OTAS), polydimethylsiloxane (PDMS), and the like.

[Silica particles treated with silicone oil]
The silicone oil-treated silica fine particles contain the untreated silica fine particles (also called "silica base") and silicone oil, and their specific surface area as measured by the BET method is not particularly limited, but is about 30 to 400 m ² /g.
The silica raw material 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 require the use of 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.

Silicone oil-treated silica microparticles can be produced, for example, by directly mixing silica base 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 base material, and then heat-treating the mixture; or by dissolving or dispersing silicone oil in an appropriate solvent, adding and mixing the silica base 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 microparticles can be produced, for example, by the method described in Japanese Patent No. 6849352, and the desired microparticles can be obtained by changing the average primary particle diameter of the silica microparticles serving as the base material and the amount of silicone oil used.

The silicone oil-treated silica fine particles (also referred to as "silica fine particles") preferably have a coverage of 10 to 80% of the toner base particles.
If the coverage of the silica particles is less than 10%, carrier spent may occur when the toner is used in an electrophotographic developer containing a carrier. On the other hand, if the coverage of the silica particles is more than 80%, low-temperature fixability may deteriorate.
The coverage of the silica fine particles is preferably 10 to 50%, more preferably 10 to 30%.
The method for measuring the coverage of the silica fine particles will be described in the Examples.

The silica fine particles preferably have a free carbon content of 1 to 5%.
If the free carbon content of the silica fine particles is less than 1%, the effect of suppressing carrier spent may be reduced when a toner is used in an electrophotographic developer containing a carrier.On the other hand, if the free carbon content of the silica fine particles is more than 5%, fixing inhibition may occur.
The free carbon content of the silica fine particles is preferably 1 to 3%.
The amount of free carbon in the silica fine particles corresponds to the amount of silicone oil on the surface of the silica fine particles that have been surface-treated with silicone oil.
The method for measuring the amount of free carbon in silica fine particles will be described in the Examples.

The silica fine particles preferably have an average primary particle size of 30 to 100 nm.
If the average primary particle diameter of the silica fine particles is less than 30 nm, they may become embedded in the toner base particles and adhere too strongly, making it difficult to maintain the spacer effect.On the other hand, if the average primary particle diameter of the silica fine particles is more than 100 nm, their adhesion to the toner base particles may be weak, making it difficult to obtain the coating effect.
The average primary particle size of the silica fine particles is preferably 30 to 80 nm, and more preferably 30 to 60 nm.
The method for measuring the average primary particle diameter of the silica fine particles will be described in the Examples.

The silica fine particles preferably have an adhesive strength of 40 to 90%.
If the adhesion strength of the silica particles is less than 40%, the silica particles tend to detach from the toner base particles, which may promote the abrasive properties of the strontium titanate particles. On the other hand, if the adhesion strength of the silica particles exceeds 90%, they may become embedded in the toner base particles, and may adhere too strongly, which may result in the spacer effect being lost.
The adhesive strength of the silica fine particles is preferably 40 to 70%, more preferably 50 to 70%.
The method for measuring the adhesion strength of silica fine particles will be described in the Examples.

The silica fine particles used in the present invention can be produced by surface-treating (modifying) silica particles with silicone oil by a known method.
Commercially available silica fine particles, such as those manufactured by Nippon Aerosil Co., Ltd. under the product names NY50 and RY50, can also be used.

In the technical field, silica fine particles treated with a hydrophobizing agent such as silicone oil or a silane compound are used as an external additive for toner base particles, but in the toner of the present invention, the above-mentioned excellent effects are exhibited by using, as an external additive, a combination of strontium titanate fine particles having silica particles on their surfaces and silica fine particles treated with silicone oil.
Here, like other hydrophobizing agents, silicone oil not only imparts hydrophobicity to the silica microparticles, but also imparts releasability to the silica microparticles, which is thought to contribute to improving the developability and cleaning properties of the toner.

[External additive coverage ratio]
The ratio of the coverage CS of the silica fine particles to the coverage CT of the strontium titanate fine particles relative to the toner base particles, CS/CT, is preferably 1-100.
If the coverage ratio CS/CT is less than 1, the toner adhesion increases and filming may occur easily. On the other hand, if the coverage ratio CS/CT exceeds 100, the cleaning ability increases and filming may occur easily.
The coverage ratio CS/CT is preferably 5 to 50, and more preferably 5 to 20.

[Other external additives]
The toner base particles of the present invention may be externally added with 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 fumed silica particles, 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, a wax dispersant, and a grinding aid, if necessary.
[Binder resin]
As the binder resin for the toner base particles of the present invention, resins commonly used in the art can be used, and polyester resins can be suitably used.
The polyester-based resin may be either a non-crystalline polyester-based resin (amorphous polyester-based resin) or a crystalline polyester-based resin, but a non-crystalline polyester-based resin is preferred because it is easier to satisfy the constituent requirements of the present invention and to easily obtain its excellent effects.

Here, amorphous resins and crystalline resins are distinguished by their crystallinity index, with resins with a crystallinity index in the range of 0.6 to 1.5 being crystalline resins, and resins with a crystallinity index of less than 0.6 or more than 1.5 being amorphous resins. That is, resins with a crystallinity index of more than 1.5 are amorphous, while resins with a crystallinity index of less than 0.6 have low crystallinity and a large amount of amorphous portions.
The crystallinity index is a physical property that indicates the degree of crystallization of a resin, and is defined as the ratio of the softening temperature to the highest endothermic peak temperature (softening temperature/highest endothermic peak temperature). Here, the highest endothermic peak temperature refers to the temperature of the highest endothermic peak observed. For crystalline polyester resins, the highest peak temperature is the melting point (Tmp), and for amorphous polyester resins, the highest peak temperature is the glass transition temperature (Tg).
The degree of crystallization can be controlled by adjusting the types and ratios of raw material monomers, as well as production conditions (for example, reaction temperature, reaction time, cooling rate), and the like.

The amorphous polyester resin is not particularly limited, but can be obtained, for example, by a polycondensation reaction between a carboxylic acid monomer containing terephthalic acid or isophthalic acid as a main component and a polyhydric alcohol containing ethylene glycol as a main component.
The reaction conditions are the same as those for producing ordinary polyester resins, and an amorphous polyester resin can be obtained, for example, by reacting a dicarboxylic acid monomer with a polyhydric alcohol in a nitrogen gas atmosphere, optionally in the presence of an esterification catalyst, at a temperature of 190 to 240° C. The reaction ratio of the polyhydric alcohol to the carboxylic acid monomer is preferably 1.3:1 to 1:1.2 in terms of the equivalent ratio of hydroxyl groups to carboxyl groups [OH]:[COOH].

The molar content of terephthalic acid or isophthalic acid in the dicarboxylic acid monomer is preferably 70 to 100%, more preferably 80 to 100%.
The dicarboxylic acid monomer may also include aromatic dicarboxylic acids such as fumaric acid, adipic acid, sebacic acid, succinic acid, and the like, and may also include ester-forming derivatives of terephthalic acid or isophthalic acid, ester-forming derivatives of aromatic dicarboxylic acids, ester-forming derivatives of aliphatic dicarboxylic acids, and acid anhydrides or alkyl esters of these carboxylic acids.
Furthermore, the dicarboxylic acid monomer may be used in combination with a polycarboxylic acid having three or more valences, such as trimellitic acid or pyromellitic acid, or an ester-forming derivative thereof.
The above dicarboxylic acid monomers and polycarboxylic acid monomers may be used alone or in combination of two or more.

The molar content of ethylene glycol in the polyhydric alcohol is preferably 70 to 100%, more preferably 80 to 100%.
The polyhydric alcohol may include other polyhydric alcohols such as 1,3-propylene glycol and 1,4-butanediol.
The above polyhydric alcohols can be used alone or in combination of two or more.

The crystalline polyester resin is not particularly limited, but is preferably composed of a linear saturated aliphatic polyester unit obtained by a polycondensation reaction between a carboxylic acid monomer containing, as a main component, an aliphatic dicarboxylic acid having 9 to 22 carbon atoms and a polyhydric alcohol containing, as a main component, an aliphatic diol having 2 to 10 carbon atoms.
The reaction conditions are the same as those for producing ordinary polyester resins, and for example, a crystalline polyester resin can be obtained by reacting a dicarboxylic acid monomer with a polyhydric alcohol in a nitrogen gas atmosphere, optionally in the presence of an esterification catalyst, at a temperature of 190 to 240° C. From the viewpoint of toner storage stability, the reaction ratio of the polyhydric alcohol to the carboxylic acid monomer is preferably an equivalent ratio of hydroxyl groups to carboxyl groups [OH]:[COOH] of 0.83:1 to 1.3:1.

The molar content of dicarboxylic acid in the carboxylic acid monomer is preferably 90 to 100%. If the molar content of dicarboxylic acid is low, the rate and speed of crystallization may decrease, resulting in insufficient toner aggregation resistance.
Examples of the aliphatic dicarboxylic acid having 9 to 22 carbon atoms include azelaic acid, zebaic acid, 1,10-decanedicarboxylic acid, 1,18-octadecanedicarboxylic acid, etc. The carboxylic acid monomer and polycarboxylic acid monomer may contain an ester-forming derivative of these aliphatic dicarboxylic acids.
Furthermore, the carboxylic acid monomer may be used in combination with a polycarboxylic acid having three or more valences, such as trimellitic acid or pyromellitic acid, or an ester-forming derivative thereof.
The above carboxylic acid monomers may be used alone or in combination of two or more.

The molar content of the aliphatic diol having 2 to 10 carbon atoms in the polyhydric alcohol is preferably 80 to 100%.
Examples of the aliphatic diol having 2 to 10 carbon atoms include ethylene glycol, 1,4-butanediol, and 1,6-hexanediol.
Furthermore, examples of polyhydric alcohols that can be used in combination with the above aliphatic diols include trihydric or higher alcohols such as glycerin and trimethylolpropane.
The above polyhydric alcohols can be used alone or in combination of two or more.

The binder resin is not particularly limited, but preferably has a glass transition temperature Tg of 40 to 70°C.
If the glass transition temperature Tg of the binder resin is lower than 40° C., blocking, in which toner particles thermally aggregate together, is likely to occur inside the image forming apparatus, resulting in image defects (fogging) and reduced storage stability. On the other hand, if the glass transition temperature Tg of the binder resin is higher than 70° C., low-temperature fixability is impaired and image defects (offset) may occur.
The fixing temperature can be adjusted by using, as the binder resin, a resin (H type) having a glass transition temperature Tg of 55 to 75°C and a resin (L type) having a glass transition temperature Tg of 40 to 60°C in combination.

The amount of binder resin in the toner base particles is not particularly limited, but is preferably 80 to 90% by mass.
When the blending amount of the binder resin is within the above range, it is possible to provide a toner that can realize a long life of the electrophotographic developer and the electrophotographic photosensitive member without impairing various physical properties of the toner, and that can realize image stability over a long period of time.

[Colorant]
As the colorant for the toner base particles of the present invention, 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.
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 3 to 15 parts by weight, and particularly preferably 5 to 12 parts by weight, per 100 parts by weight of resin.
When the blending amount of the colorant is within the above range, it is possible to provide a toner that can realize a long life of the electrophotographic developer and the electrophotographic photosensitive member without impairing various physical properties of the toner, and that can realize image stability over a long period of time.

[Release agent]
The release agent for the toner base particles of the present invention may be a release agent commonly used in the technical field, and examples thereof include petroleum-based waxes such as paraffin wax, microcrystalline wax, and derivatives thereof; hydrocarbon-based synthetic waxes such as Fischer-Tropsch wax, polyolefin wax (polyethylene wax, polypropylene wax, etc.), low-molecular-weight polypropylene wax, polyolefin-based polymer wax (low-molecular-weight polyethylene wax, etc.), and derivatives thereof; plant-based waxes such as carnauba wax, rice wax, candelilla wax, and derivatives thereof, and Japan wax; animal-based 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-based 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 release agent is not particularly limited, but preferably has a melting point mp of 80 to 150°C.
If the melting point of the release agent particles is within the above range, it is possible to achieve both low-temperature fixability and hot offset resistance.

The amount of the release agent in the toner base particles is not particularly limited, but is preferably 0.5 to 5.0 parts by mass, and particularly preferably 0.5 to 3.0 parts by mass, per 100 parts by mass 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 realize a long life of the electrophotographic developer and the electrophotographic photosensitive member without impairing various physical properties of the toner, and that can realize image stability over a long period of time.

[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 and negative charges.
As the charge control agent for controlling positive charges, for example, quaternary ammonium salts, pyrimidine compounds, triphenylmethane derivatives, guanidine salts, amidine salts, etc. can be used.
Charge control agents for negative charge control include metal-containing azo compounds, azo complex dyes, metal complexes and metal salts of salicylic acid and its derivatives (metals include chromium, zinc, zirconium, etc.), organic bentonite compounds, and boron compounds.

The amount of the charge control agent in the toner base particles is not particularly limited, but is preferably 0.5 to 3% by mass, and particularly preferably 0.5 to 1.5 parts by mass, based on 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 realize a long life of the electrophotographic developer and the electrophotographic photosensitive member without impairing various physical properties of the toner, and that can realize image stability over a long period of time.

[Wax dispersant]
The toner base particles of the present invention may contain a wax dispersant, if necessary.
The wax dispersant is a component that imparts a dispersing effect to the release agent, and is not particularly limited, but examples thereof include Sanyo Chemical Industries, Ltd., product name: WEP-912.
The amount of wax dispersant blended in the toner base particles is not particularly limited, but is about 0.5 to 2% by mass relative to the releasing agent.

[Grinding aid]
The toner base particles of the present invention may contain a grinding aid, if necessary.
The grinding aid is a component that contributes to the grinding of toner in the grinding step of toner production, and is not particularly limited. For example, an α-methylstyrene copolymer or a styrene-acrylic copolymer can be used, and examples thereof include FTR2120, a product of Mitsui Chemicals, Inc.
The amount of the grinding aid in the toner base particles is not particularly limited, but is preferably 0.5 to 10% by mass, and particularly preferably 2.5 to 5 parts by mass, per 100 parts by mass of the resin.

[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.
The method for measuring the glass transition temperature Tg of the toner will be described in the Examples.

[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 5.0 to 10 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 realize a long life for an electrophotographic developer and an electrophotographic photosensitive member without impairing various physical properties of the toner, and that can realize image stability over a long period of time.
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 account for 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 used in the present invention can be produced by a known method using known devices commonly used in the technical field, for example, a pre-mixing step S1 in which a binder resin, a colorant, a release agent, etc. are mixed to obtain a mixture, a melting and kneading step S2 in which the obtained mixture is melted and kneaded to obtain a molten and kneaded product, a cooling and crushing and classification step S3 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 and classified to obtain toner base particles, and an external addition step S4 in which the obtained toner base particles are mixed with an external additive 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.

For mixing, a known device commonly used in the technical field can be used, for example, a Henschel-type mixer such as 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), or Mechano Mill (trade name, manufactured by Okada Seiko Co., Ltd.), or a mixer such as Ang Mill (trade name, manufactured by Hosokawa Micron Corporation), Hybridization System (trade name, manufactured by Nara Machinery Works, Ltd.), or Cosmo System (trade name, manufactured by Kawasaki Heavy Industries, Ltd.).
The melt-kneading may be performed using known devices commonly used in the technical field, such as general kneaders such as a twin-screw extruder, a three-roll mill, a lab blast mill, etc. Specifically, for example, a single-screw or twin-screw extruder such as TEM-100B (trade name, manufactured by Toshiba Machine Co., Ltd.), PCM-65/87, or PCM-30 (all of which are trade names, manufactured by Ikegai Corporation), or an open-roll type kneader such as Kneadex (trade name, manufactured by Mitsui Mining Co., Ltd.) may be used.

For cooling, a known device commonly used in the art, such as a cooling belt, can be used.
For the coarse grinding, a known device commonly used in the art, such as a speed mill with a screen, 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.
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.

[Electrophotographic Developer]
The electrophotographic developer of the present invention is characterized by containing the toner of the present invention and a carrier.
[Career]
As the carrier, a carrier commonly used in the relevant technical field can be used, and examples thereof include a resin-coated carrier in which the surface of a single or composite ferrite particle made of iron, copper, zinc, nickel, cobalt, manganese, chromium, etc. is coated with a coating substance, and a resin-dispersed carrier in which magnetic particles are dispersed in a resin.

As the coating material, materials commonly used in the art can be used, such as polytetrafluoroethylene, monochlorotrifluoroethylene polymer, polyvinylidene fluoride, silicone resin, polyester resin, metal compound of di-tert-butyl salicylic acid, styrene 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-based 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 particle size of the carrier is not particularly limited, but in consideration of achieving high image quality, it is preferably 10 to 100 μm, and more preferably 20 to 50 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 amount of developer. Furthermore, the coverage of the carrier by the toner is preferably 40 to 80% by mass.

[Image forming apparatus]
The image forming apparatus of the present invention is an image forming apparatus that forms an image by forming an electrostatic latent image on the surface of an electrophotographic photosensitive member and transferring the toner developed on the electrostatic latent image to a transfer material, characterized in that the electrophotographic photosensitive member is a high-hardness drum and the toner is the toner of the present invention.
The toner of the present invention can use strontium titanate fine particles having an average primary particle diameter of 40 nm or more in combination with silicone oil-treated silica fine particles as an external additive, and therefore can obtain an appropriate polishing effect on the surface of an electrophotographic photosensitive member (drum) and, in turn, an inhibitory effect on filming, without causing carrier coat peeling due to abrasive properties and image defects such as fogging and toner scattering due to reduced charge, thereby improving the life of the electrophotographic photosensitive member. Such effects are particularly noticeable in high-hardness drums (silica filler drums).

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 an electrophotographic photosensitive member, a charging means for charging the electrophotographic photosensitive member, an exposure means for exposing the charged electrophotographic 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 electrophotographic photosensitive member, and a discharging means for discharging surface charges remaining on the electrophotographic 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 the photoreceptor 1 of the present invention, 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 used in the art as an electrophotographic 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 having 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 peripheral surface of the photoreceptor 1 (corresponding to the photoreceptor F01 in FIG. 2) 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 apparatus 100 described above is a monochrome image forming apparatus (printer), but it may also be, for example, an intermediate transfer type color image forming apparatus capable of forming color images. Specifically, it may be a so-called tandem type full-color image forming apparatus configured such that multiple electrophotographic 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 apparatus 100 may also be another color image forming apparatus, a copier, a multifunction machine, 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.

[Glass transition temperature Tg of toner base particles]
A differential scanning calorimetry (DSC220, manufactured by Seiko Instruments Inc.) is used to measure a DSC (Differential Scanning Calorimetry) curve by heating 1 g of a sample at a temperature increase rate of 10° C. per minute in accordance with Japanese Industrial Standards (JIS) K7121-1987.
The glass transition point Tg (°C) is determined from the intersection of a straight line extending from the high-temperature side baseline of the endothermic peak corresponding to the glass transition of the obtained DSC curve to the low-temperature side and a tangent line drawn from the rising part of the peak to the apex of the curve at the point where the gradient is maximum.

[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.

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

[Coverage rate CT of strontium titanate nanoparticles]
The coverage CT (%) of the strontium titanate microparticles is calculated from the average primary particle diameter and the surface area of the toner mother particle, assuming that the coverage CT (%) is 100% when the entire surface of the toner mother particle is covered with the external additive in a most dense state, and assuming that the strontium titanate microparticles of the external additive have the same 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.

[Average primary particle diameter of silica fine particles]
The average primary particle diameter of the silica microparticles 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 microparticles.
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 diameter at which the cumulative volume from the small particle diameter side in the cumulative volume distribution became 50% was calculated from the measurement results as the average primary particle diameter (μm) of the resin microparticles.

[Coverage of Silica Fine Particles CS]
The coverage CS (%) of the silica fine 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 fine 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.

[Free carbon content of silica fine particles]
0.7 g of silica microparticles are placed in a cylindrical filter paper with a diameter of 28 mm, and the free silicone oil on the silica microparticles is extracted using a Soxhlet extraction apparatus (manufactured by Buchi, model: B-811) and hexane as the extraction solvent under conditions of an extraction time of 60 minutes and a rinse time of 30 minutes, and the amount of free carbon is measured. The percentage of the carbon amount of the silica microparticles after extraction relative to the carbon amount of the silica microparticles before extraction is calculated, and the amount of carbon lost in the extraction process is taken as the free carbon amount (%). The carbon amount of the silica microparticles is measured using an elemental analyzer ( manufactured by Sumika Chemical Analysis Center, Ltd., model: SUMIGRAPH NX-22F).

[Adhesion strength of silica fine particles]
3 g of toner was weighed into a 100 mL beaker, wetted with 60 mL of a 0.2% aqueous solution of polyoxyethyl phenyl ether, and thoroughly stirred. Then, an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho, Model: US-150E) was used, with the probe inserted so that the liquid level was 70 mL. The ultrasonic energy was adjusted to 150 W, and ultrasonic waves were applied for 3 minutes. After leaving the mixture for several hours, the supernatant was removed, and 50 mL of pure water was added to the precipitate, followed by stirring for 5 minutes. The thoroughly washed precipitate (toner) was then subjected to suction filtration using a membrane filter with a pore size of 1 μm, followed by vacuum drying overnight to thoroughly remove moisture.
Using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation, model: ZSX Primus II), the intensity of the Si element in the external additive of 1 g of toner is analyzed before and after the ultrasonic treatment, and the adhesion strength of the external additive is calculated using the following formula.
Adhesion strength of external additive (%) = [(fluorescent X-ray intensity of Si element after ultrasonic treatment) / (fluorescent X-ray intensity of Si element before ultrasonic treatment)] × 100

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 at a rotation speed of 1500 rpm for 3 minutes to obtain a mixture.
Binder resin: 2500g of amorphous polyester resin (H body, glass transition point around 60°C)
Binder resin: 2000g of amorphous polyester resin (L-form, glass transition point around 55°C)
Colorant: Carbon black (manufactured by Mitsubishi Chemical Corporation, product name: MA-77)
500 g (11.1 parts by weight per 100 parts by weight of binder resin)
Release agent: Polypropylene wax (melting point 150°C, manufactured by Sanyo Chemical Industries, Ltd., product name: Viscol 550P) 150 g (3.3 parts by mass per 100 parts by mass of binder resin)
Charge control agent: Ion conductive material (bis[benzilate(2-)-κ(2)O,O]borate(1-) potassium, manufactured by Nippon Carlit Co., Ltd., product name: LR-147)
50 g (1.1 parts by weight per 100 parts by weight of binder resin)

[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 100°C, a barrel rotation speed of 250 rpm, and a raw material supply rate of 10 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 equipped with a φ1 mm screen to obtain a coarsely pulverized product having a particle size of 1 mm.
The obtained coarsely crushed product was finely pulverized using a fluidized bed opposed jet mill (manufactured by Hosokawa Micron Corporation, model: Counter Jet Mill AFG), and further classified using a rotary (centrifugal airflow) classifier (manufactured by Hosokawa Micron Corporation, model: TSP Separator), thereby obtaining 3,900 g of toner base particles (C-1) to which no external additives had been added.

[External addition process]
The following toner raw materials were introduced into a 20 L air flow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke & Engineering Co., Ltd.), model: FM20C) and mixed at 3000 rpm for 3 minutes to obtain 1000 g of toner.
Toner base particles (C-1) without external additives: 100 parts by mass Strontium titanate fine particles having silica particles on the surface (average primary particle diameter 40 μm: TS-1): 0.2 parts by mass Silicone oil-treated silica fine particles (manufactured by Nippon Aerosil Co., Ltd., product name: RY50:OS-1): 0.5 parts by mass

[Preparation of Electrophotographic 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 5,000 g of an electrophotographic developer.

Example 2
A toner and an electrophotographic developer were obtained in the same manner as in Example 1, except that the toner base particles C-2 prepared as follows were used instead of the toner base particles C-1.
Binder resin: 2500g of amorphous polyester resin (H body, glass transition point around 65°C)
Binder resin: 2000g of amorphous polyester resin (L-form, glass transition point around 60°C)
C-2 was prepared in the same manner as in Example 1 C-1, except that the following was used.

Example 3
A toner and an electrophotographic developer were obtained in the same manner as in Example 1, except that toner base particles C-3 prepared as follows were used instead of toner base particles C-1.
Binder resin: 2500g of amorphous polyester resin (H body, glass transition point around 65°C)
Binder resin: 2000g of amorphous polyester resin (L-form, glass transition point around 55°C)
C-3 was prepared in the same manner as in Example 1, except that C-1 was used.

Examples 2 to 25
Toners and electrophotographic developers were obtained in the same manner as in Example 1, except that strontium titanate microparticles TS-1 having silica particles on their surfaces and the following TS-2 to TS-7, and silicone oil-treated silica microparticles OS-1 and the following OS-2 to OS-11 were used as external additives in the amounts shown in Table 1.

In the following Examples and Comparative Examples, in addition to strontium titanate microparticles TS-1 having silica particles on their surfaces, the following strontium titanate microparticles TS-2 to TS-7 having silica particles on their surfaces and different average primary particle diameters, which were prepared by varying the average primary particle diameter of the strontium titanate microparticles serving as the base material, and strontium titanate microparticles TS-0 not having silica particles on their surfaces, which were prepared without using silica particles, were also used.
The numbers in parentheses indicate the average primary particle size.
TS-2 (30μm)
TS-3 (20μm)
TS-4 (70μm)
TS-5 (100μm)
TS-6 (110μm)
TS-7 (50μm)
TS-0 (40 μm, no silica doping)

In the following examples and comparative examples, in addition to the silicone oil-treated silica fine particles OS-1, the following silicone oil-treated silica fine particles OS-2 to OS-11 were also used, which were prepared by changing the average primary particle diameter of the silica fine particles serving as the base material and the amount of silicone oil used, and had different average primary particle diameters and free carbon amounts.
The values in parentheses indicate the average primary particle size/free carbon content.
OS-2 (30μm, 2%)
OS-3 (20μm, 2%)
OS-4 (60μm, 2%)
OS-5 (80μm, 2%)
OS-6 (100μm, 2%)
OS-7 (110μm, 2%)
OS-8 (40μm, 1%)
OS-9 (40μm, 0.5%)
OS-10 (40μm, 5%)
OS-11 (40μm, 7.5%)

(Comparative Example 1)
A toner and an electrophotographic developer were obtained in the same manner as in Example 1, except that the silicone oil-treated silica fine particles OS-1 were not used as an external additive.
(Comparative Example 2)
A toner and an electrophotographic developer were obtained in the same manner as in Example 1, except that the strontium titanate fine particles TS-0 prepared as above, which did not have silica particles on their surfaces (no silica doping), were used instead of the strontium titanate fine particles TS-1 having silica particles on their surfaces as an external additive.

[evaluation]
Using a test copier obtained by modifying a digital copier (manufactured by Sharp Corporation, model: MX-M6071), the toners and electrophotographic developers prepared in Examples 1 to 25 and Comparative Examples 1 and 2 were evaluated for low-temperature fixability (offset), carrier spent (fogging), drum filming (white streaks), and heat resistance (roughness).

[Low temperature fixability (offset)]
The electrophotographic developer was filled into the developing unit of the above-mentioned commercially available copier, and a sample image including a rectangular solid image measuring 20 mm in length and 50 mm in width was prepared as an unfixed image on recording paper (product name: PPC Paper SF-4AM3, manufactured by Sharp Corporation). At this time, the amount of toner adhesion in the solid image area was adjusted to 0.5 mg/ ^cm2 .
Next, a fixed image was created using an external fixing device that utilized the fixing section of a copier. The fixing process speed was set to 250 mm/sec, and the temperature of the fixing belt was set to 150°C and 160°C to check for low-temperature offset, which was defined as the non-offset temperature. Low-temperature offset refers to the phenomenon in which toner does not fuse to the recording paper during fixing, and the toner re-adheres to the recording paper after the fixing belt has made one revolution while remaining attached to the fixing belt.

In the evaluation of low-temperature fixability (offset), a strength test was also conducted when the temperature at which low-temperature offset occurred was the same as that of a reference toner (*based on the toner of Example 1). In the strength test, a printed recording paper was folded and then unfolded, and the folded printed portion was rubbed with the paper on which a 1 kg weight was placed. If the width of the scraped line did not increase compared to that of the reference toner, the strength was evaluated as unchanged, and if it did increase, the strength was evaluated as decreased.
⊚: Compared with the reference toner, the temperature at which low-temperature offset occurs is the same, and the intensity is also the same.
◯: Compared to the reference toner, the temperature at which low-temperature offset occurs is the same, but the strength is worse.
Δ: The temperature at which low-temperature offset occurs is 5° C. higher than that of the reference toner.
x: The temperature at which low-temperature offset occurs is 10° C. or more higher than that of the reference toner.

Based on the results of the fixing non-offset temperature and fixing strength, the fixing property was evaluated according to the following criteria.
◎: No low-temperature offset on the image sample at 150°C, and fixing strength of 60% or more. ○: No low-temperature offset on the image sample at 150°C, and fixing strength of less than 60%. △: No low-temperature offset on the image sample at 160°C, and fixing strength of less than 60%. ×: Low-temperature offset occurs on the image sample at 160°C.

[Career Spent (Fog)]
The electrophotographic developer was filled into the developing unit of the above-mentioned commercially available copier (monochrome machine), and an original with a printing rate of 25% was printed on A4 size recording paper in 100k sheets at a time up to 1000k sheets. The image density (ID value) in the non-printed areas was measured using a spectrodensitometer (manufactured by X-Rite, model: X-Rite 504) to evaluate the progress of the image.
It should be noted that "k sheets" means "×1000 sheets."
◎: ID value = 2.5 or less up to 1000k sheets, low fogging throughout life ○: ID value = 2.5 or less up to 600k sheets, and ID value = 2.5 or more from 600k to 1000k sheets △: ID value = 2.5 or less up to 400k sheets ×: ID value = 2.5 or more at 200k sheets

[Drum filming (white streaks)]
The electrophotographic developer was filled into the developing unit of the above-mentioned commercially available copier (monochrome machine), and an original with a print rate of 25% was printed on A4-sized recording paper in 100k-sheet increments up to 1000k sheets. The occurrence of white streaks or white spots in the electrophotographic photosensitive member (drum) cycle was visually confirmed to evaluate the progress of the image.
◎: No white streaks or white spots occurred up to 1000k sheets. ◯: No white streaks or white spots occurred up to 600k sheets. △: No white streaks or white spots occurred up to 400k sheets. ×: White streaks or white spots occurred after 200k sheets.

[Heat resistance (roughness)]
The electrophotographic developer was filled into the developing unit of the above-mentioned commercially available copier (monochrome machine), and an evaluation chart (a chart that allows evaluation of solid images) was printed on 10,000 sheets (200 sets of 50 consecutive sheets) of A4-sized recording paper in double-sided printing mode. In the monochrome machine, the heated recording paper is returned to the machine, so heat is easily transferred to the developing tank, making this an accelerated test.
The occurrence of roughness in the solid area was checked, and the heat resistance was evaluated according to the following criteria: Roughness is image unevenness caused by poor transport due to blocking.
◎: No roughness up to 10,000 sheets ○: No roughness up to 6,000 sheets △: No roughness up to 4,000 sheets ×: Roughness occurs up to 2,000 sheets

[comprehensive evaluation]
The above evaluation results were comprehensively evaluated according to the following criteria.
◎: ◎ (very good) in all evaluations
〇: No × or △ in any evaluation, but one or more ○ (good)
△: No × in any evaluation, but one or more △ (suitable for actual use)
×: Any evaluation includes at least one × (unusable)
The main constituent materials and physical properties of the toner, as well as the measurement and evaluation results, are shown in Tables 1 and 2.

@0001

@0002

The following can be seen from Tables 1 and 2.
(1) The toners of the present invention (Examples 1 to 25) suppress carrier spent and the decrease in charge at the time of spent, have good carrier life, suppress fogging and toner scattering, and, compared with conventional toners (Comparative Examples 1 and 2), reduce toner cohesion due to the spacer effect of the strontium titanate fine particles and silica fine particles combined with the hydrophobicity (low adhesive force) of the latter, improve heat-resistant storage stability, and suppress development moko (the occurrence of toner cohesion in the developer) and image roughness. (2) Toner (3) Toners in which silica fine particles have a coverage of 10 to 80% of the toner base particles (Examples 1 to 4, 6, and 8 to 25) have good carrier life and low-temperature fixability. (4) Toners in which silica fine particles have an average primary particle diameter of 30 to 100 nm (Examples 1 to 17, 19 to 20, and 22 to 25) suppress carrier spent and have good carrier life.

(5) Toners in which the silica particles have a free carbon content of 1 to 5% (Examples 1 to 13, 15, and 17 to 25) have good carrier life and low-temperature fixability. (6) Toners in which the silica particles have an adhesion strength of 40 to 90% (Examples 1 to 7, 9 to 11, 13 to 15, and 17 to 25) have a moderate polishing effect due to the strontium titanate particles and a moderate spacer effect due to the silica particles. (7) Toners in which the strontium titanate particles have an average primary particle diameter of 30 to 100 nm (Examples 1 to 7, 9 to 11, and 13 to 25) suppress filming and have good electrophotographic photosensitive member (drum) life. (8) Toners in which the coverage ratio CS/CT of the silica particles to the strontium titanate particles relative to the toner base particles is 1 to 100 have good drum life due to suppressed filming.

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, a fine powder of a core made of strontium titanate to which silica has been added and whose surface has been hydrophobized with a silane compound, and silicone oil-treated silica fine particles , which are externally added to the surface of the toner base particles,
The toner , wherein the silane compound is selected from the group consisting of hexamethyldisilazane, dimethyldichlorosilane, octylsilane, and polydimethylsiloxane . The toner according to claim 1, wherein the toner has a glass transition temperature Tg of 60°C or less. The toner according to claim 1 or 2, wherein the silica microparticles have a coverage of 10 to 80% of the toner base particles. The toner according to any one of claims 1 to 3, wherein the silica fine particles have an average primary particle diameter of 30 to 100 nm. The toner according to any one of claims 1 to 4, wherein the silica fine particles have a free carbon content of 1 to 5%. The toner according to any one of claims 1 to 5, wherein the silica fine particles have an adhesion strength of 40 to 90%. 7. The toner according to claim 1, wherein the fine powder has an average primary particle size of 30 to 100 nm. 8. The toner according to claim 1, wherein a coverage ratio CS/CT of the coverage CS of the silica fine particles to the toner base particles and the coverage CT of the fine powder is 1 to 100. An electrophotographic 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 photosensitive member and transferring the toner developed on the electrostatic latent image to a transfer material, wherein the electrophotographic photosensitive member is a high-hardness drum, and the toner is the toner described in any one of claims 1 to 8.