JP7770872B2 - Toner and two-component developer - Google Patents

Description

The present invention relates to toner and two-component developers.

Toner (toner for developing electrostatic images) used in electrophotographic image forming devices such as copiers, multifunction machines, printers, and facsimile machines typically has external additives attached to the surface of the toner particles. In the external addition process of the toner manufacturing method, the toner particles and external additives are mixed in a powder mixer such as a Henschel mixer, causing the external additives to adhere to the surface of the toner particles.

Conventionally, titanium oxide, a conductive oxide, has been used as an external additive to control the chargeability of toner. However, to create safer toner, a conductive oxide that can replace titanium oxide is needed.

Strontium titanate is an example of a conductive oxide that can replace titanium oxide, but the sharp edges of strontium titanate crystals can cause scratches on the photosensitive drum and lead to over-discharge.

By adding silica microparticles to the surface of strontium titanate microparticles and modifying the surface of the strontium titanate with silica microparticles, these problems are alleviated, and high-charge fogging in low-humidity environments and fogging in high-humidity environments are also suppressed.

Regarding toner that uses such strontium titanate microparticles as an external additive, Patent Document 1 discloses that by using a fine powder of strontium titanate having Si-containing particles with a number-average equivalent circular diameter of 5 nm to 15 nm on the surface as an external additive, it is possible to prevent the occurrence of fogged images over time in low-temperature, low-humidity environments and suppress wear on the photoreceptor.

Fine silica particles have also been used as external additives for some time, and Patent Document 2 discloses that a toner using titanium oxide as a conductive oxide external additive contains two types of fine silica particles with different BET specific surface areas as external additives, and that both types of fine silica particles are treated with silane coupling and silicone oil. This improves transfer efficiency and makes the image uniform when transferring solid images of two or more colors in color, i.e., images in which toners of two or more colors are superimposed, resulting in high-quality color images.

Japanese Patent Application Laid-Open No. 2020-190724 Japanese Patent Application Laid-Open No. 2004-126240

However, toners that use strontium titanate microparticles as an external additive have the problem of variations in image quality across the printed surface when printing on a single sheet of recording paper. Specifically, these issues are as follows:

As shown in Figure 2, during the toner fixing process, as recording paper 21 passes between heating roller 11 and pressure roller 12, the recording paper 21 is heated and pressurized by each roller, and the toner image on the recording paper 21 is heated, melted, and fixed. However, with toner T1, which uses strontium titanate microparticles as an external additive, a discharge charge is generated when recording paper 21 is peeled off from heating roller 11, and the charge remains on heating roller 11. After that, when heating roller 11 makes one rotation, as shown in Figure 3, at a position before normal heating and pressure are applied, the charge remaining on heating roller 11 reacts with toner T1 on recording paper 21, causing electrostatic offset, which creates a problem of disturbance in the fixed image.

Furthermore, there was an issue that the recording paper 21 was difficult to separate from the heating roller 11 during fixing, and even after the leading edge of the recording paper 21 came into contact with the peeling tab 13, the separation did not proceed properly, leaving scratches on the fixed image area due to contact with the peeling tab 13.

The present invention was made based on the above circumstances, and its purpose is to provide a toner and two-component developer that has minimal gloss variation within the printed surface when printed on a single sheet of recording paper, and that has excellent image quality uniformity and image reproducibility.

To solve the above problems, the present invention provides the following toner and two-component developer.

The toner of the present invention, developed to solve the above problems, is a toner in which external additives are adhered to the surfaces of toner particles containing a binder resin and internal additives, the internal additives including a high-melting point wax, a mid-melting point wax, and a colorant, the high-melting point wax having a melting temperature of 133°C or higher, and the mid-melting point wax having a melting temperature that is 30°C or higher lower than the melting temperature of the high-melting point wax, and the external additives including strontium titanate microparticles, oil-treated silica microparticles having an average primary particle diameter of 16 nm or larger, and silica microparticles that have been hydrophobized by a method other than oil treatment and have an average primary particle diameter smaller than the oil-treated silica microparticles.

By containing the high-melting point wax and mid-melting point wax as internal additives, the toner of the present invention maintains its shelf life while allowing the recording paper to begin peeling from the heating roller at a low temperature during the toner fixing process. Furthermore, by containing strontium titanate microparticles as an external additive, localized charge transfer from the toner to the heating roller can be suppressed, thereby suppressing the occurrence of electrostatic offset. Furthermore, by containing the high-melting point wax and mid-melting point wax as internal additives and having the external additives on the surface of the toner particles, a stable glossy image can be obtained across the entire printed surface when printed on a single sheet of recording paper.

The two-component developer of the present invention, developed to solve the above problems, contains the toner of the present invention and a carrier.

This invention makes it possible to provide a toner and two-component developer that exhibits minimal gloss variation within the printed surface when printed on a single sheet of recording paper, and that offers excellent image quality uniformity and image reproducibility.

1 is a cross-sectional view schematically illustrating a toner according to an embodiment of the present invention. 1 is a cross-sectional view of a fixing device, schematically illustrating how discharged charges are generated when the recording paper is separated from the heating roller in the toner fixing process. FIG. 1 is a cross-sectional view of a fixing device, schematically illustrating how electrostatic offset occurs due to charges remaining on a heating roller during a toner fixing process. 1 is a cross-sectional view of a fixing device, schematically illustrating how charge transfer occurs in a heating roller due to discharge from toner during a toner fixing process. FIG. 10 is a cross-sectional view of a fixing device, schematically illustrating how the toner is more easily released from a heating roller and charge transfer is suppressed in the fixing step according to an embodiment of the present invention. FIG.

The present invention includes toner and two-component developers, which are described in detail below.

[toner]
As shown in FIG. 1, the toner according to the present invention is a toner in which an external additive is attached to the surface of toner particles containing a binder resin and an internal additive.

The volume average particle diameter of the primary particles of the toner particles according to the present invention can be selected appropriately depending on the purpose, but is preferably 4 μm or more and 8 μm or less. By reducing the particle diameter so that the volume average particle diameter falls within the above range, high-resolution images can be formed stably over a long period of time, high image density can be obtained even with a small amount of toner adhesion, and toner consumption can be reduced.

If the volume average particle diameter is below the lower limit, the toner will be highly charged and less fluid, making it impossible to stably supply the toner to the photoreceptor, which can result in background fogging and reduced image density. If the volume average particle diameter exceeds the upper limit, the layer thickness of the formed image will be large, resulting in an image with significant graininess and making it difficult to obtain a high-resolution image. In addition, the specific surface area will decrease, reducing the amount of charge on the toner, which can prevent the toner from being stably supplied to the photoreceptor, potentially causing contamination inside the machine due to toner scattering.

The particle size distribution of the toner particles according to the present invention is not particularly limited and can be selected appropriately depending on the purpose, but it is preferable that the number of particles having a volume average particle size of 3 μm or less is 40% or less. The method for measuring the particle size distribution is described below.

The circularity of the toner particles according to the present invention is not particularly limited and can be selected appropriately depending on the purpose, but it is preferably 0.92 or more and 0.97 or less. The method for measuring circularity is described below.

The glass transition temperature (Tg) of the toner particles according to the present invention is preferably 60°C or lower. The method for measuring the glass transition temperature is described below.

<Binder resin>
As the binder resin in the toner according to the present invention, resins commonly used in the field of electrophotography can be used, and examples thereof include polyester resins, polystyrene resins such as styrene-acrylic resins, (meth)acrylic acid ester resins, polyolefin resins, polyurethane resins, and epoxy resins. One of these may be used alone, or two or more may be used in combination.

Among these, amorphous polyester resins are preferred, and it is even more preferred to use a combination of an amorphous polyester resin made of low molecular weight components and an amorphous polyester resin made of medium to high molecular weight components. This improves the productivity, quality, and performance of the toner of the present invention. Note that the terms low molecular weight, medium molecular weight, and high molecular weight used in the present invention are used to relatively compare the molecular weight distribution of polyester resins, and are described below.

In the present invention, crystalline resins and amorphous resins are distinguished by their crystallinity index. Resins with a crystallinity index in the range of 0.6 to 1.5 are considered crystalline resins, while resins with a crystallinity index of less than 0.6 or more than 1.5 are considered amorphous resins. 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 content.

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 point to the highest endothermic peak temperature (softening point/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 temperature (melting point), and for amorphous polyester resins, the highest peak is the glass transition point.

The degree of crystallization can be controlled by adjusting the type and ratio of raw material monomers, as well as production conditions (e.g., reaction temperature, reaction time, cooling rate).

(Amorphous polyester resin)
The amorphous polyester resin is a polyester resin having a crystallinity index of less than 0.6 or more than 1.5, with polyester resins having a crystallinity index of more than 1.5 being preferred.

Amorphous polyester resins are 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 used to produce ordinary polyester resins. For example, amorphous polyester resins 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. 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%, and more preferably 80 to 100%.

The dicarboxylic acid monomer may also include aromatic dicarboxylic acids such as fumaric acid, aliphatic dicarboxylic acids such as adipic acid, sebacic acid, and succinic acid, 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 trivalent or higher polycarboxylic acid such as trimellitic acid or pyromellitic acid, or an ester-forming derivative thereof.

The above dicarboxylic acid monomers and polycarboxylic acid monomers can 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%, and more preferably 80 to 100%. The polyhydric alcohol may contain 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.

(Crystalline polyester resin)
The crystalline polyester resin is a polyester resin having a crystallinity index of 0.6 to 1.5, and preferably a polyester resin having a crystallinity index of 0.8 to 1.2.

The crystalline polyester resin is not particularly limited, but is preferably composed of linear saturated aliphatic polyester units obtained by a polycondensation reaction between a carboxylic acid monomer containing, as its main component, an aliphatic dicarboxylic acid having 9 to 22 carbon atoms and a polyhydric alcohol containing, as its main component, an aliphatic diol having 2 to 10 carbon atoms.

The reaction conditions are the same as those for producing ordinary polyester resins. 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 perspective 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 crystallization rate and speed may decrease, resulting in insufficient toner aggregation resistance.

Examples of aliphatic dicarboxylic acids having 9 to 22 carbon atoms include azelaic acid, zebaic acid, 1,10-decanedicarboxylic acid, and 1,18-octadecanedicarboxylic acid. The carboxylic acid monomer and polycarboxylic acid monomer may also contain ester-forming derivatives of these aliphatic dicarboxylic acids.

Furthermore, the carboxylic acid monomer may be used in combination with a trivalent or higher polycarboxylic acid such as trimellitic acid or pyromellitic acid, or an ester-forming derivative thereof.

The above carboxylic acid monomers can 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 aliphatic diols 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.

(Polyester resin consisting of low to high molecular weight components)
In the following description, a polyester resin made of low molecular weight components will be referred to as resin A, a polyester resin made of medium molecular weight components as resin B, and a polyester resin made of high molecular weight components as resin C.

(Resin A)
Resin A has a molecular weight distribution in which 75% or more of the mass molecular weight is in the range of 1×10 ³ to 1×10 ⁴ , and has a viscosity of 1×10 ⁵ Pa·s or less at 80° C. when measured with a flow tester.

If the molecular weight distribution of a mass molecular weight of less than 1×10 ³ is large, the resin becomes soft and the storage stability of the toner may deteriorate. On the other hand, if the molecular weight distribution of a mass molecular weight of more than 1×10 ⁴ is large, the viscosity of the resin increases and the low-temperature fixability of the toner may deteriorate. The molecular weight distribution in the range of a mass molecular weight of 1×10 ³ to 1×10 ⁴ is preferably 80% or more.

When Resin A has a viscosity of 1×10 ⁵ Pa·s or less at 80°C when measured with a flow tester, good low-temperature fixability suitable for low-temperature fixation such as pad fixation can be obtained. On the other hand, if the viscosity exceeds 1×10 ⁵ Pa·s, the low-temperature fixability of the toner may deteriorate. The viscosity at 80°C when measured with a flow tester is preferably 2×10 ⁴ Pa·s or less. Resin A preferably has a glass transition temperature Tg (°C) of 52 to 56°C and a softening point Tm (°C) of 85 to 100°C.

(Resin B)
Resin B has a molecular weight distribution in which 20% or more of the resin is distributed in the range of mass molecular weight of 1×10 ⁴ to 1×10 ⁵ , and has a main peak in the range of mass molecular weight of 1×10 ³ to 1×10 ^4. Resin B contributes to uniform melt-kneading of resin A and resin C, and if resin B is not blended, not only the low-temperature fixability but also the high-temperature fixability of the toner may not be ensured.

Resin B is adjusted to have a viscosity between that of the low molecular weight component and the high molecular weight component, which allows it to be easily mixed and kneaded with other resins, making it possible to disperse various materials in Resin B in advance.

If Resin B does not have 20% or more of its molecular weight distributed in the range of 1×10 ⁴ to 1×10 ⁵ by mass molecular weight and does not have a main peak in the range of 1×10 ³ to 1×10 ⁴ by mass molecular weight in the molecular weight distribution, it becomes difficult to uniformly melt-knead Resin A and Resin C, and it may become difficult to ensure not only low-temperature fixability but also high-temperature fixability.

Resin B preferably has a glass transition temperature Tg (°C) of 65 to 70°C and a softening point Tm (°C) of 110 to 120°C.

(Resin C)
Resin C has a molecular weight distribution in which 5% or more of the resin is distributed in the range of a mass molecular weight of 1×10 ⁵ or more. Resin A contributes to lowering the viscosity, while resin C contributes to ensuring high-temperature fixability.

If Resin C is not distributed in a range of 1×10 ⁵ or more by 5% or more in the molecular weight distribution, the elasticity of the toner is impaired and high-temperature fixability may not be ensured. Also, if Resin C is distributed in a range of 1×10 ⁵ or more by less than 5% in the molecular weight distribution, the low-temperature region of Pad fixation may not be ensured.

Resin C may contain a gel component. To improve fixing quality on the high-temperature side of the fixable region, it is preferable for the resin to have a gel content of 3 to 20% by mass. If the gel content of Resin C exceeds 20% by mass, grindability may be impaired.

Resin C preferably has a glass transition temperature Tg (°C) of 55 to 65°C and a softening point Tm (°C) of 130 to 150°C.

<Wax>
The toner particles according to the present invention contain a wax as a release agent. Waxes commonly used in the field of electrophotography can be used. Examples of the wax include petroleum-based waxes such as paraffin wax, microcrystalline wax, and their derivatives; hydrocarbon-based 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 their derivatives; vegetable waxes such as carnauba wax, rice wax, candelilla wax, and their derivatives, 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 their derivatives; long-chain alcohols and their derivatives; silicone polymers; and higher fatty acids.

The above derivatives include oxides, block copolymers of vinyl monomers and wax, and graft-modified products of vinyl monomers and wax.

In the present invention, one of the above waxes may be used alone, or two or more may be used in combination.

The toner particles according to the present invention contain a high-melting point wax and a medium-melting point wax, with the high-melting point wax having a melting temperature of 133°C or higher and the medium-melting point wax having a melting temperature that is 30°C or higher lower than the melting temperature of the high-melting point wax.

By including the above two types of wax, a release effect is achieved at low temperatures, and the toner of the present invention improves the releasability of recording paper from the heating roller. Furthermore, the high-melting-point wax seeps out at high temperatures, suppressing high-temperature offset. In particular, as shown by comparing Figures 2 and 5, when a large amount of toner adheres to the recording paper, the recording paper is stably released from the heating roller even at low temperatures. This allows for a stable gloss image across the entire printed surface when printing on a single sheet of recording paper, while also suppressing peeling electrification.

If the difference in melting temperature between the high-melting wax and the mid-melting wax in the toner of the present invention is less than 30°C due to the high-melting wax having a low melting temperature, the heat-resistant storage stability of the toner may deteriorate. Furthermore, if the melting temperature of the mid-melting wax is high and the difference is less than 30°C, poor release may occur on the low-temperature side of the fixable range.

Specifically, the melting temperature of the medium-melting point wax in the toner of the present invention is preferably 70°C or higher and lower than 100°C, and the melting temperature of the high-melting point wax is preferably 133°C or higher and lower than 160°C.

If the melting temperature of the mid-melting point wax exceeds the upper limit specified above, the releasability of the recording paper from the belt or heating roller on the low-temperature side of the fixable area will be impaired, which may result in problems such as poor releasability or curling of the recording paper.

If the melting temperature of the high-melting point wax is below the lower limit above, the fixing quality may deteriorate at the higher temperature end of the fixable range.

The mid-melting wax in the toner of the present invention preferably has a glass transition temperature change ΔTg of 2° C. or less, calculated by the following formula (1).
ΔTg=(glass transition temperature of toner particles containing no mid-melting point wax)−(glass transition temperature of toner particles containing mid-melting point wax) (1)

In other words, ΔTg represents the amount of change in the glass transition temperature of toner particles that occurs when a mid-melting point wax is blended as an internal additive. The glass transition temperature is measured using a differential scanning calorimeter according to the method described below.

When ΔTg is within the above range, it is possible to ensure the storage stability of the toner in high-temperature environments even if the glass transition temperature of the binder resin is not high.

The content of mid-melting point wax in the toner particles according to the present invention is preferably 0.2% by mass or more and 5.0% by mass or less, and more preferably 0.3% by mass or more and 1.5% by mass or less.

By ensuring that the mid-melting point wax content is above the above lower limit, the releasability of the recording paper from the heating roller during the toner fixing process is improved, and the effect of suppressing electrostatic offset due to peeling of the recording paper is enhanced. Furthermore, by ensuring that the mid-melting point wax content is below the above upper limit, it is possible to suppress a decrease in the glass transition temperature (Tg) of the toner caused by blending the mid-melting point wax as an internal additive.

The content of high-melting point wax in the toner particles according to the present invention is preferably 0.4% by mass or more and 5.5% by mass or less, and more preferably 0.7% by mass or more and 5.0% by mass or less.

When the content of high-melting point wax is above the above lower limit, the release effect at high temperatures is improved, and the effect of suppressing high-temperature offset is enhanced. Furthermore, when the content of high-melting point wax is below the above upper limit, there is no impact on the low-temperature fixability of the toner.

The mid-melting point wax in the toner of the present invention is preferably a Fischer-Tropsch wax.

By using a Fischer-Tropsch wax as the mid-melting wax and a polyester resin as the binder resin in the toner of the present invention, it is possible to achieve a combination of a mid-melting wax and a binder resin with a small ΔTg.

<Coloring Agent>
The colorant contained in the toner particles according to the present invention may be any organic or inorganic pigment or dye commonly used in the field of electrophotography, and the type and color are not particularly limited. Examples include 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, zinc sulfide, etc.

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, and C.I. pigment blue 60.

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 with two or more, and the combination may be of different colors or the same color. Two or more colorants may also be used as composite particles. 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 mixture.

Furthermore, to ensure uniform dispersion of the colorant in the binder resin, it may be used in the form of a masterbatch. The composite particles and masterbatch are mixed into the toner composition during dry mixing.

The amount of colorant added can be selected appropriately depending on the purpose, but is preferably 3 to 15 parts by weight, and more preferably 5 to 12 parts by weight, per 100 parts by weight of binder resin.

When the amount of colorant blended is within the above range, it is possible to form images with high image density and excellent image quality without compromising the various physical properties of the toner.

<Other internal additives>
Furthermore, the toner particles according to the present invention may contain, as internal additives, charge control agents, wax dispersants, grinding aids, and the like that are used in the field of electrophotography.

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

The amount of charge control agent added can be selected appropriately depending on the purpose, but it is preferably 0.5 to 3 parts by weight per 100 parts by weight of binder resin.

<External additives>
In the present invention, the external additive comprises strontium titanate microparticles, oil-treated silica microparticles having an average primary particle diameter of 16 nm or more, and silica microparticles that have been hydrophobized by a method other than oil treatment and have an average primary particle diameter smaller than that of the oil-treated silica microparticles. The external additive may contain optional components depending on the purpose, as long as the effects of the present invention are not impaired.

The toner of the present invention contains the above-mentioned high-melting point wax and mid-melting point wax as internal additives, and strontium titanate microparticles as external additives, thereby suppressing local charge transfer from the toner to the heating roller and thereby suppressing the occurrence of electrostatic offset. Furthermore, by containing the above-mentioned high-melting point wax and mid-melting point wax as internal additives and having the above-mentioned external additives on the surface of the toner particles, a stable gloss image can be obtained across the entire printed surface when printed on a single sheet of recording paper.

By using strontium titanate microparticles as an external additive, high charging in low-humidity environments is suppressed, thereby reducing fogging and toner consumption.

By using oil-treated silica fine particles (medium to large particle size silica) with an average primary particle size of 16 nm or more as an external additive, fogging can be suppressed, particularly in high-temperature environments. Furthermore, oil-treated silica fine particles with an average primary particle size of 16 nm or more blend well with molten release agents (wax) with low surface energy, so by using them in conjunction with the high-melting point wax and medium-melting point wax described above, images with minimal gloss variation can be achieved. Furthermore, by using silica fine particles (small particle size silica) with an average primary particle size smaller than the oil-treated silica fine particles that have been hydrophobized by a method other than oil treatment, the low-temperature fixation interference caused by the oil treatment is not present.

The strontium titanate microparticles in the toner of the present invention are preferably strontium titanate microparticles modified with silica microparticles.

By modifying the strontium titanate particles with silica particles, static electricity is removed from the strontium titanate particles stably, suppressing high-charge fogging in low-humidity environments and preventing fogging from worsening in high-humidity environments.

Furthermore, as shown in Figure 4, during the toner fixing process, charge transfer to the heating roller due to discharge from the toner can cause electrostatic offset. However, by modifying the strontium titanate microparticles with silica microparticles, local charge transfer from the toner is suppressed, and electrostatic offset is also suppressed, thereby improving image reproducibility during continuous printing.

Strontium titanate microparticles modified with silica microparticles can be produced, 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 sodium hydroxide solution, and then neutralized with hydrochloric acid, filtered, and washed with water to obtain a washed cake.
(2) Water is added to the washed cake to form a slurry, and then hydrochloric acid is added to perform a peptization treatment. This is called Solution 1, and is mixed with Solution 2, an aqueous solution of strontium chloride, and Solution 3, an aqueous solution of sodium silicate. The mixing ratio of Solutions 1, 2, and 3 is set so that the molar ratio of (Sr+Si)/Ti is 1.2.
(3) The mixed solution is heated to 90° C. under a nitrogen gas atmosphere, and the mixture is stirred for 2 hours while adding an aqueous sodium hydroxide solution to complete the reaction.
(4) After the reaction, the 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 dried product is pulverized in a blender for 1 minute, and the resulting fine powder substrate is then sieved through a 32 μm mesh to remove coarse particles. The resulting fine powder substrate is then surface-coated with a silane coupling agent. Examples of methods for surface coating with a silane coupling agent include surface treatments commonly used in the art using hexamethyldisilazane (HMDS), dimethyldichlorosilane (DDS), octylsilane (OTAS), polydimethylsiloxane (PDMS), etc.

The content of strontium titanate microparticles per 100 parts by mass of toner particles according to the present invention is preferably 0.02 parts by mass or more and 0.6 parts by mass or less, and more preferably 0.05 parts by mass or more and 0.5 parts by mass or less.

By ensuring that the content of strontium titanate microparticles is above the above lower limit, high charge fog in low-humidity environments can be suppressed. Furthermore, by ensuring that the content of strontium titanate microparticles is below the above upper limit, a decrease in toner charge in high-humidity environments can be suppressed.

In the toner of the present invention, the difference ΔD between the average primary particle diameters calculated by the following formula (2), where D _ts is the average primary particle diameter of the strontium titanate fine particles and D _os is the average primary particle diameter of the oil-treated silica fine particles, is preferably −24 nm or more and 70 nm or less, and more preferably 0 nm or more and 70 nm or less.
ΔD=D _os -D _ts ...(2)

By keeping ΔD within the above range, it is possible to suppress discharge occurring solely through the strontium titanate microparticles when the recording paper is peeled off from the heating roller during the toner fixing process. This in turn suppresses excess charge from remaining on the heating roller after peeling, thereby improving image reproducibility during continuous printing.

<Oil-treated silica particles>
The toner of the present invention contains, as an external additive, oil-treated silica fine particles having an average primary particle diameter of 16 nm or more.

Oil-treated silica microparticles with an average primary particle diameter of 16 nm or more have low surface energy and blend well with molten release agents (wax), so by using them in conjunction with the high-melting point wax and medium-melting point wax mentioned above, images with minimal gloss variation can be achieved.

Preferably, the oil-treated silica microparticles are hydrophobic silica microparticles treated with silicone oil. Examples of hydrophobic silica microparticles treated with silicone oil include the hydrophobic silica microparticles described in JP 2012-236752 A. In the toner of the present invention, the free carbon content of the hydrophobic silica microparticles treated with silicone oil is preferably 1.0% by mass or more and 5.0% by mass or less. The method for measuring the free carbon content is described below.

The average primary particle diameter of the oil-treated silica fine particles in the toner of the present invention is preferably 16 nm or more and 110 nm or less, and more preferably 40 nm or more and 110 nm or less.

By not using oil-treated silica microparticles with an average primary particle diameter of less than 16 nm, low-temperature fixability is improved, and more oil-treated silica microparticles with an average primary particle diameter of 16 nm or more can be added, suppressing fogging in high-temperature environments. If oil-treated silica microparticles with an average primary particle diameter exceeding the above upper limit are used as an external additive, the amount added must be increased, and there is a risk of low-temperature fixability being impaired due to the spacer effect.

The content of oil-treated silica fine particles in the toner of the present invention is preferably 0.1 parts by mass or more and 1.8 parts by mass or less, and more preferably 0.3 parts by mass or more and 1.6 parts by mass or less, per 100 parts by mass of toner particles.

By ensuring that the content of oil-treated silica microparticles is above the above lower limit, fogging in high-humidity environments can be suppressed. By ensuring that the content of oil-treated silica microparticles is below the above upper limit, deterioration of low-temperature offset can be suppressed.

Furthermore, the content of oil-treated silica microparticles in the toner of the present invention is preferably such that the coverage of the toner particle surface with the silica microparticles is 10% or more and 80% or less. The method for measuring the coverage is described below.

The adhesion strength of the oil-treated silica microparticles to the toner particles in the toner of the present invention is preferably 40% or more and 90% or less. The method for measuring adhesion strength is described below.

<Silica particles hydrophobized by methods other than oil treatment>
The toner of the present invention contains, as an external additive, fine silica particles that have an average primary particle diameter smaller than that of the above-mentioned oil-treated fine silica particles and that have been hydrophobized by a method other than oil treatment.

By using small particle silica (fine silica particles with an average primary particle size smaller than the above-mentioned oil-treated silica particles) in the external additive that has been hydrophobized by a method other than oil treatment, the low-temperature fixation is not hindered by the oil treatment.

Examples of silica microparticles that have been hydrophobized by methods other than oil treatment include silica microparticles hydrophobized with dimethyldichlorosilane (DDS) (silica microparticles surface-modified with dimethylsilyl groups), silica microparticles hydrophobized with hexamethyldisilazane (HMDS) (silica microparticles surface-modified with trimethylsilyl groups), silica microparticles surface-modified with alkylsilyl groups, and silica microparticles surface-modified with methacrylsilyl groups. Furthermore, since the functional groups that modify the surface of the silica microparticles contain amino groups, which tend to result in a positive charge, it is preferable in the present invention that the functional groups that modify the surface of the silica microparticles do not contain amino groups.

In the toner of the present invention, the average primary particle diameter of the silica fine particles that have been hydrophobized by a method other than oil treatment is preferably 2 nm or more and less than 16 nm.

In the toner of the present invention, the content of silica fine particles that have been hydrophobized by a method other than oil treatment is preferably 0.1 parts by mass or more and 2.0 parts by mass or less per 100 parts by mass of toner particles.

<Other external additives>
The external additive may contain an optional component that improves transportability, chargeability, cleanability, etc., depending on the purpose, within a range that does not impair the effects of the present invention. Examples of the optional component include inorganic fine particles such as fumed silica particles, titanium oxide particles, alumina particles, and magnetite.

[Two-component developer]
The two-component developer according to the present invention contains the toner according to the present invention and a carrier. The two-component developer can be produced by mixing the toner and the carrier using a known mixer. The weight ratio of the toner to the carrier is not particularly limited, and may be, for example, 3:97 to 12:88.

The carrier is stirred and mixed with the toner in the developer tank, giving the toner the desired charge. The carrier also acts as an electrode between the development device and the photosensitive drum, transporting the charged toner to the electrostatic latent image on the photosensitive drum and forming a toner image. The carrier is held on the development roller of the development device by magnetic force, and after using it for development, it returns to the development tank, where it is stirred and mixed again with new toner and used repeatedly until the end of its life.

The carrier has a carrier core material and a resin coating layer that coats the carrier core material. There are no particular restrictions on the carrier core material, as long as it is used in the electrophotography field. Specific examples of materials for the carrier core material include magnetic metals such as iron, copper, nickel, and cobalt, and magnetic metal oxides such as ferrite and magnetite. There are no particular restrictions on the volume average particle size of the carrier core material, and examples include 30 μm or more and 100 μm or less. The resin coating layer preferably contains a silicone resin or an acrylic resin. Silicone resin can slow the progression of contamination of the carrier coat layer, making it suitable for long-life use.

The present invention will be explained below based on examples and comparative examples, but the present invention is not limited to these examples. First, the measurement and evaluation methods used in the examples will be explained.

<Method for measuring the volume average particle diameter of toner 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 was measured using a particle size distribution analyzer (Beckman Coulter, Inc., Model: Multisizer 3) under conditions of aperture diameter: 100 μm, particle count: 50,000 counts, and the volume average particle diameter (μm) was calculated from the volume particle size distribution of the sample particles.

<Method for measuring circularity of toner particles>
Measurement was performed using a flow particle image analyzer "FPIA-3000" (manufactured by Malvern Instruments). Using Particle Sheath (manufactured by Malvern Instruments, product name: PSE-900A) as the sheath liquid, a 5 wt% aqueous dispersion of a commercially available household detergent as the dispersant, and the autosampler device of the analyzer, the sample was dispersed. The resulting dispersion was introduced into the analyzer, and 10,000 toner particles were measured in total count in HPF measurement mode. The binarization threshold for particle analysis was set to 85%, and the average circularity of the toner particles was determined over the entire particle size range.

In this device, the projected area S and perimeter L of the particle image are measured, and the circularity is calculated using the following formula:
Circularity=2×(π×S) ^1/2 /L

<Method for measuring the glass transition temperature of toner particles and resin>
Using a differential scanning calorimeter (manufactured by PerkinElmer Japan Co., Ltd., model: Diamond DSC), approximately 10 mg of the sample was heated at a temperature increase rate of 10°C/min in accordance with Japanese Industrial Standards (JIS) K7121-1987, and a DSC (Differential Scanning Calorimetry) curve was measured.

In the obtained DSC curve, the glass transition temperature (Tg) was determined as the temperature at the intersection of a straight line extending from the high-temperature baseline of the endothermic peak corresponding to the glass transition toward the low-temperature side and a tangent drawn from the rising part of the peak to the point where the slope of the curve is greatest.

<Method for measuring wax melting temperature>
Using a differential scanning calorimeter (manufactured by PerkinElmer Japan Co., Ltd., model: Diamond DSC), about 20 mg of toner particles (or wax) was heated from a temperature of 20°C to 200°C at a heating rate of 10°C/min, and then rapidly cooled from 200°C to 30°C. This operation was repeated twice to measure the DSC curve, and the temperature of the endothermic peak corresponding to melting in the DSC curve measured in the second operation was taken as the melting temperature of the wax.

<Method for measuring the average primary particle size of external additives>
The average primary particle diameter of the external additive was determined by photographing the toner particles using a scanning electron microscope (SEM) (manufactured by Hitachi High-Technologies Corporation, model: S-4800), measuring the particle diameters (major diameters) of 100 particles of the external additive on the toner surface from the obtained image, calculating the average value of the particle diameters of the 100 particles, and using this as the average primary particle diameter.

<Method for measuring the amount of free carbon in hydrophobic silica particles treated with silicone oil>
Using a Buchi Soxhlet extraction apparatus, 0.7 g of hydrophobic silica microparticles were placed in a cylindrical filter paper with a diameter of 28 mm, and hexane was used as the extraction solvent. The extraction time was 60 minutes, and the rinse time was 30 minutes. The free silicone oil on the hydrophobic silica microparticles was extracted and the carbon content was measured. The percentage of the carbon content of the hydrophobic silica microparticles after extraction relative to the carbon content of the hydrophobic silica microparticles before extraction was calculated, and the amount of carbon lost in the extraction process was taken as the free carbon content. The carbon content of the hydrophobic silica microparticles was measured using an elemental analyzer (SUMIGRAPHNC-22F, manufactured by Sumitomo Analysis Center, Ltd.).

<Method for measuring coverage rate by external additives>
The toner was photographed with a scanning electron microscope (SEM) (Model: S-4800, manufactured by Hitachi High-Technologies Corporation). A model calculation was performed using the average primary particle size and specific gravity of the toner particles and the average primary particle size and specific gravity of each external additive, and the coverage rate by each external additive was calculated using the following formula (3).

In the above formula (3), D is the average primary particle diameter of the toner particles, _ρt is the specific gravity of the toner particles, d is the average primary particle diameter of the external additive, _ρi is the specific gravity of the external additive, and C is the number of parts by mass of the external additive added.

<Method for measuring adhesive strength of external additives>
The adhesion strength of the external additive to the toner particles was measured by the following procedure.
(1) 2.0 g of toner is added to 40 ml of an aqueous solution of Triton (polyoxyethylene octylphenyl ether) with a concentration of 0.2% by mass, and the mixture is stirred for 1 minute.
(2) The aqueous solution is irradiated with ultrasonic waves using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., model: US-300T) (output: 40 μA, 4 minutes).
(3) After the ultrasonic irradiation, the aqueous solution is left to stand for 3 hours to separate the toner from the liberated external additives.
(4) After removing the supernatant, add approximately 50 ml of pure water to the precipitate and stir for 5 minutes.
(5) The solution is subjected to suction filtration using a membrane filter (manufactured by Advantec Co., Ltd.) with a pore size of 1 μm.
(6) The toner remaining on the filter is vacuum dried overnight.
(7) Using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation, model: ZSX Primus II), the intensity of the element (Si) in the external additive per 1 g of toner is analyzed before and after the series of processes (1) to (6) above, and the adhesion strength of the external additive is calculated using the following formula.
Adhesion strength (%) = {(Si strength after treatment)/(Si strength before treatment)} × 100

<Evaluation method for printed area (solid area)>
A monochrome multifunction printer (Model: MX-565, manufactured by Sharp Corporation) was used as the evaluation machine. The amount of toner adhesion was adjusted so that the print density was ID = 1.4 approximately 6 cm from the leading edge of the recording paper in the paper feed direction, and the printed area formed by fixing the toner on the recording paper was evaluated for scratches caused by peeling fingernails, gloss variation, and fixing offset. Fixing offset was evaluated by setting the fixing temperature in 5°C increments from 150°C to 220°C and passing the paper, and comparing the temperature at which offset occurred with that of the reference toner (Example B-1) shown in Tables 1 and 8 below.

(Method for evaluating scratches caused by peeling nails)
The damage caused by the peeling nail was evaluated according to the following criteria.

◎ (Excellent): No scratches on the printed area caused by the peeling claws.
Good (Good): There are scratches caused by the peeling nails, but they are not noticeable.
△ (Acceptable): There are noticeable scratches caused by peeling nails.
× (Unacceptable): Residue has been generated due to scratches caused by the peeling claws.

(Gross fluctuation evaluation method)
The gloss values of the leading edge (1 cm from the leading edge), middle (3 cm from the leading edge), and trailing edge (5 cm from the leading edge) of the printed area in the paper feed direction were measured at three points on the FCR (front side, center side, rear side) using a gloss meter (manufactured by Nippon Denshoku Industries Co., Ltd., model: VG2000). The difference from the average value of the three measured values was taken as gloss variation and evaluated according to the following criteria.

A (Excellent): Gloss variation is less than 10%.
◯ (Good): Gloss variation is 10% or more and less than 30%.
△ (Acceptable): The gross variation is 30% or more and less than 60%.
× (unacceptable): noticeable gloss variation before and after the peeled portion.

(Method for evaluating high-temperature offset)
The high-temperature offset was evaluated according to the following criteria.

⊚ (Excellent): The offset occurrence temperature is the same as or 5°C lower than the reference toner.
◯ (Good): The offset occurrence temperature is 10° C. lower than that of the reference toner.
Δ (Acceptable): The offset occurrence temperature is 15° C. lower than that of the reference toner.
x (unacceptable): The offset occurrence temperature is 20° C. or more lower than that of the reference toner.

(Evaluation method for low temperature offset)
In the evaluation of low-temperature offset, a strength test was also conducted when the offset occurrence temperature was the same as that of the reference toner. In the strength test, a printed recording paper was folded and then unfolded, and the folded printed area 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 the reference toner, the strength was evaluated as unchanged, and if it did increase, the strength was evaluated as decreased.

◎ (Excellent): Compared to the reference toner, the offset occurrence temperature is the same and the intensity is also the same.
◯ (Good): Compared to the standard toner, the offset occurrence temperature is the same, but the intensity is worse.
△ (Acceptable): The offset occurrence temperature is 5°C higher than that of the reference toner.
x (unacceptable): The offset occurrence temperature is 10° C. or more higher than that of the reference toner.

(Method for evaluating electrostatic offset)
Ten sheets were printed in succession to check for the occurrence of electrostatic offset, and the occurrence of electrostatic offset was evaluated according to the following criteria: After adjusting the adhesion amount of the solid portion to ID = 1.4 in the same manner as the image for fixing evaluation described above, a paper feed test was carried out using an image pattern in which ID = about 1.4 for the trailing edge 2 cm, ID = about 1.0 for the middle 2 cm, and ID = about 0.6 for the leading edge 2 cm, and electrostatic offset was evaluated.

◎ (Excellent): No electrostatic offset occurs.
◯ (Good): Electrostatic offset occurs (small) at the edge (area where density changes).
△ (Fair): Large electrostatic offset occurs at the edge (area where density changes).
× (unacceptable): Electrostatic offset occurs in the white area.

<Evaluation method for low humidity fogging>
The evaluation machine was operated in an environmental testing room at a temperature of 25°C and a humidity of 5% to print 5,000 A4 sheets of paper with monochrome toner covering 5% of the printable area. The whiteness of the unprinted areas was measured using a whiteness meter (manufactured by Nippon Denshoku Industries Co., Ltd., model: ZE6000). The difference in whiteness between the unprinted and unprinted areas and the whiteness of the recording paper surface before printing was taken as fog and evaluated according to the following criteria.

⊚ (Excellent): The difference in whiteness is 1.0 or less.
◯ (Good): The difference in whiteness is more than 1.0 and 1.5 or less.
△ (Acceptable): The difference in whiteness is more than 1.5 and 2.0 or less.
× (unacceptable): The difference in whiteness exceeds 2.0.

<Method for evaluating high humidity fogging>
The same evaluation method for low-humidity fogging as above was used except that the environment was changed to a temperature of 25°C and a humidity of 80% RH, and the evaluation was based on the following criteria. In addition, the samples that were left in the same environment and measured the next day (fogging after standing) were also evaluated based on the following criteria.

⊚ (Excellent): The difference in whiteness is 1.0 or less.
◯ (Good): The difference in whiteness is more than 1.0 and 1.5 or less.
△ (Acceptable): The difference in whiteness is more than 1.5 and 2.0 or less.
× (unacceptable): The difference in whiteness exceeds 2.0.

<Method for Evaluating Toner Storage Stability>
A container containing 20 g of toner was left to stand in a thermostatic chamber at 50°C for 48 hours, and then 2 g of the toner was taken out and placed on a mesh with a mesh size of 150 μm. The toner on the mesh was vibrated for 10 seconds using a powder tester (Hosokawa Micron Corporation, model: PT-X), and the storage stability was evaluated according to the following criteria.

◎ (Excellent): Not agglomerated and in powder form before vibration is applied.
Good (Good): Softly aggregated, breaks down with vibration and passes through the mesh.
△ (Acceptable): Toner that does not crumble due to vibration can be expelled from the mesh by crushing it with a spatula or the like.
× (unacceptable): The toner aggregates so much that it cannot be removed from the container.

<Evaluation Method Based on Glass Transition Temperature Change ΔTg>
The change in glass transition temperature ΔTg due to the mid-melting point wax was measured and evaluated according to the following criteria: ΔTg was calculated using the following formula (1).
ΔTg=(glass transition temperature of toner particles containing no mid-melting point wax)−(glass transition temperature of toner particles containing mid-melting point wax) (1)
For example, in the examples and comparative examples described later, comparative example A-0 and comparative examples B-2 to B-5 correspond to cases in which no mid-melting point wax is contained, and serve as the reference values for calculating ΔTg as shown in the table below. Note that the object for measuring the glass transition temperature is the "toner particles," in other words, the object for measuring the glass transition temperature is the toner core before the external additive is attached.

◎ (Excellent): ΔTg is 0.5°C or less.
◯ (Good): ΔTg is more than 0.5°C and 1.0°C or less.
△ (Acceptable): ΔTg is greater than 1.0°C and equal to or less than 2.0°C.
× (unacceptable): ΔTg exceeds 2.0°C.

<Toner overall evaluation method>
Based on the above evaluation results, an overall evaluation was made according to the following criteria.

◎ (Excellent): All evaluation items are ◎.
○ (Good): The lowest rating among all evaluation items is ○.
△ (Acceptable): The lowest rating among all evaluation items is △.
× (Fail): The lowest rating among all evaluation items is ×.

Next, we will explain the processes for producing the toner and two-component developer in the examples and comparative examples.

<Preparation of Toner Particles>
The following raw materials for the toner particles were pre-mixed for 5 minutes at 1500 rpm using a Henschel mixer (manufactured by Nippon Coke & Engineering Co., Ltd., model: FM20C) to obtain a mixture [pre-mixing step]. The blending ratios were 8% by mass of colorant, 2% by mass of charge control agent, and the mass % of release agent shown in the table below. The ratio of H-isomer to L-isomer in the binder resin was 5:5.
Binder resin: amorphous polyester resin (H body: high molecular weight component, Tg around 60°C)
Amorphous polyester resin (L-form: low molecular weight component, Tg around 55°C)
Colorant: Carbon black (manufactured by Mitsubishi Chemical Corporation, product name: MA-77)
Release agent: medium-melting point wax (listed in the table below)
High melting point wax (listed in the table below)
Charge control agent: potassium bis[benzilate(2-)-κ(2)O,O]borate(1-) (Japan Carlit Co., Ltd., product name: LR-147)

The mixture obtained in the pre-mixing process 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 feed rate of 10 kg/hour to obtain a melt-kneaded product [melt-kneading process].

The molten mixture obtained in the melt-kneading process was cooled and solidified using a cooling belt, and the solidified material was then finely pulverized using a fluidized bed opposed jet mill (manufactured by Hosokawa Micron Corporation, model: Counter Jet Mill AFG) and classified (particle size adjustment) using a rotary (centrifugal airflow) classifier (manufactured by Hosokawa Micron Corporation, model: TSP Separator) to obtain toner particles. [Cooling and pulverization, classification process].

The resulting finely pulverized material was then classified using an elbow jet classifier (manufactured by Nittetsu Mining Co., Ltd., model: EJ-LABO) to obtain toner particles [classification process].

<External Addition Step (Addition of External Additive to Toner Particles)>
The toner particles and the following external additives were mixed in the ratios shown in the table below using a Henschel mixer (manufactured by Nippon Coke & Engineering Co., Ltd., model: FM20C) at a rotation speed of 3000 rpm for 3 minutes to obtain a toner.
Small particle size silica: fumed silica fine particles (hydrophobic treatment: dimethyldichlorosilane (DDS), manufactured by Nippon Aerosil Co., Ltd., product name: R976s)
Medium to large particle size silica: Hydrophobic silica particles treated with silicone oil (hydrophobic treatment: polydimethylsiloxane (PDMS))
Metal oxide: strontium titanate fine particles (average primary particle diameter 40 nm)

The procedure for producing the strontium titanate microparticles is as follows.
Metatitanic acid obtained by the sulfuric acid method was deironized and bleached, then desulfurized by adding aqueous sodium hydroxide, neutralized with hydrochloric acid, 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 perform a peptization treatment. This was designated Solution 1, and was mixed with Solution 2, an aqueous strontium chloride solution, and Solution 3, an aqueous sodium silicate solution. The mixing ratio of Solutions 1, 2, and 3 was such that the (Sr + Si)/Ti molar ratio was 1.2. The mixed solution was heated to 90°C under a nitrogen gas atmosphere, and stirred for 2 hours while adding aqueous sodium hydroxide to complete the reaction. The slurry after the reaction was cooled to 50°C, hydrochloric acid was added, and the mixture was stirred for 2 hours. The precipitate obtained after stirring was washed, separated by filtration, and then dried. The dried product was pulverized in a blender for 1 minute, and coarse particles were removed using a 32 μm mesh sieve. The resulting fine powder substrate was then surface-coated with a silane coupling agent.

<Preparation of carrier>
A resin liquid was prepared by adding 10 parts by mass of PTFE (manufactured by Daikin Industries, Ltd., product name: LDE-410) as fluororesin fine particles to 100 parts by mass of silicone resin, and a carrier core material was immersed in this resin liquid to obtain a carrier "SC-1."

<Preparation of Two-Component Developer>
The obtained externally added toner and carrier "SC-1" were mixed for 20 minutes in a V-type mixer (manufactured by Tokuju Kogyosho Co., Ltd., product name: V-5) so that the toner concentration was 7% by mass, to prepare a two-component developer.

The types and blending ratios of raw materials in the toners of Examples and Comparative Examples are shown in Tables 1 to 7 below. The evaluation results of the toners and two-component developers of Examples and Comparative Examples are shown in Tables 8 to 14 below. The names of the mid-melting point wax and high-melting point wax in the tables specifically mean the following:
WE-12: Ester wax (manufactured by NOF Corporation, melting temperature 76°C, product name: WE-12)
FNP0090: Fischer-Tropsch wax (manufactured by Nippon Seiro Co., Ltd., melting temperature 97°C, product name: FNP0090)
550P: Polypropylene wax (manufactured by Sanyo Chemical Industries, Ltd., melting temperature 144°C, product name: 550P)
PE130: Polyethylene wax (manufactured by Clariant Chemicals K.K., melting temperature 133°C, product name: LICOWAX PE 130)
L103: Polyethylene wax (manufactured by Clariant Chemicals, melting temperature 106°C, product name: L103)

In addition, RY300, RY200S, NY90L, and RY50 listed as types of oil-treated silica in the table are product names manufactured by Nippon Aerosil Co., Ltd., and their average primary particle sizes are as follows: The oil-treated silicas listed in the table as "changed base" were prepared in the same manner as these oil-treated silicas, but with the size of the base changed.
RY300: 7 nm
RY200S: 16nm
NY90L: 20nm
RY50: 40 nm

As is clear from Tables 1 to 14, the toners and two-component developers of Examples A-1 to H-4, which comprise toner particles containing a binder resin and internal additives to which external additives are adhered, wherein the internal additives comprise a high-melting-point wax, a mid-melting-point wax, and a colorant, wherein the high-melting-point wax has a melting temperature of 133°C or higher and the mid-melting-point wax has a melting temperature at least 30°C lower than that of the high-melting-point wax, and the external additives comprise strontium titanate microparticles, oil-treated silica microparticles having an average primary particle diameter of 16 nm or larger, and silica microparticles hydrophobized by a method other than oil treatment and having an average primary particle diameter smaller than that of the oil-treated silica microparticles, were excellent in the evaluation of scratches caused by peeling fingernails, the evaluation of gloss variation, the evaluation of fixing offset, the evaluation of low-humidity and high-humidity fog, and the evaluation of toner quality.

In contrast, Comparative Examples A-0 to F-5, which did not meet these requirements, were inferior to the Examples in at least one of the following evaluations: damage caused by the peeling claw, gloss variation, fixing offset, low-humidity and high-humidity fog, and toner quality.

Tables 1 and 8 show that Examples A-2 to A-6, in which the mid-melting point wax content in the toner particles is 0.2% by mass or more and 5.0% by mass or less, are superior in various evaluations to Comparative Example A-1, in which the content exceeds that range, and are particularly superior in the evaluation of toner quality. They are also superior in various evaluations to Comparative Example A-0, which does not contain a mid-melting point wax, and are particularly superior in the evaluation of electrostatic offset.

Examples A-2 to A-9, in which the content of high-melting-point wax in the toner particles is 0.4% by mass or more and 5.5% by mass or less, are superior in various evaluations to Comparative Example A-1, which does not contain high-melting-point wax, and are particularly superior in the evaluation of toner quality.

Examples A-2 to A-9 differ from Examples B-1 to B-2 in the type of wax used, and it can be seen that Examples B-1 to B-2, which use a mid-melting point wax as Fischer-Tropsch wax, are superior in various evaluations.

Tables 2 and 9 show that Examples C-1 to C-4, in which the content of strontium titanate microparticles modified with silica microparticles per 100 parts by mass of toner particles is 0.02 parts by mass or more and 0.6 parts by mass or less, are superior in the evaluation of low-humidity fogging to Comparative Example C-5, which does not contain strontium titanate microparticles.

Tables 3 and 10 show that Examples D-1 to D-4, which contain strontium titanate microparticles not modified with silica microparticles, also performed better in the evaluation of low-humidity fogging than Comparative Example C-5, which does not contain strontium titanate microparticles. On the other hand, Examples C-1 to C-4, which contain strontium titanate microparticles modified with silica microparticles, performed better in the evaluation of electrostatic offset and the evaluation of high-humidity fogging after standing than Examples D-1 to D-4.

Tables 4 and 11 show that Examples E-2 to E-6, in which the average primary particle diameter of the oil-treated silica microparticles is 16 nm or more and 110 nm or less, are superior to Comparative Example E-1, in which the average primary particle diameter is outside that range, particularly in the evaluation of gloss variation and low-temperature offset. Furthermore, Tables 5 and 12 show that Comparative Examples F1 to F5, in which the average primary particle diameter of the oil-treated silica microparticles is outside that range, are inferior to the Examples in various evaluations even when the content of the silica microparticles is changed.

Tables 6, 7, 13, and 14 show that Examples G-1 to G-4 and Examples H-1 to H-4, in which the content of oil-treated silica microparticles per 100 parts by weight of toner particles is 0.1 parts by weight or more and 1.8 parts by weight or less, are superior in various evaluations to Comparative Example F-5, which does not contain oil-treated silica microparticles, and are particularly superior in the evaluation of high-humidity fogging. Furthermore, comparing Examples G-1 to G-4 with Examples H-1 to H-4, it is clear that Examples G-1 to G-4, in which the average primary particle diameter of the oil-treated silica microparticles is 40 nm, are superior in the overall evaluation.

<Other embodiments>
It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present invention should not be interpreted solely by the above-described embodiments, but should be defined by the claims. The technical scope of the present invention also includes all modifications within the scope and meaning equivalent to the claims.

T Toner T1 Conventional toner using strontium titanate microparticles as an external additive T2 Toner using strontium titanate microparticles not modified with silica microparticles as an external additive P Toner particles (toner base particles)
REFERENCE SIGNS LIST 1 Strontium titanate microparticles modified with silica microparticles 2 Oil-treated silica microparticles 3 Silica microparticles hydrophobized by a method other than oil treatment 4 Medium-melting point wax 5 High-melting point wax 11 Heating roller 12 Pressure roller 13 Peeling tab 21 Recording paper

Claims (11)

A toner in which an external additive is attached to the surface of toner particles containing a binder resin and an internal additive,
the internal additives include a high-melting point wax, a medium-melting point wax, and a colorant;
The melting temperature of the high-melting point wax is 133°C or higher,
The melting temperature of the medium-melting point wax is lower than the melting temperature of the high-melting point wax by 30°C or more,
The toner is characterized in that the external additive comprises strontium titanate microparticles, oil-treated silica microparticles having an average primary particle diameter of 16 nm or more, and silica microparticles that have been hydrophobized by a method other than oil treatment and have an average primary particle diameter smaller than that of the oil-treated silica microparticles. 2. The toner according to claim 1,
The toner is characterized in that the change in glass transition temperature ΔTg due to the mid-melting point wax, calculated by the following formula (1), is 2° C. or less.
ΔTg=(glass transition temperature of the toner particles when the mid-melting point wax is not contained)−(glass transition temperature of the toner particles) (1) 3. The toner according to claim 1 or claim 2,
The toner, wherein the content of the mid-melting point wax in the toner particles is 0.2% by mass or more and 5.0% by mass or less. The toner according to any one of claims 1 to 3,
The toner, wherein the content of the high-melting-point wax in the toner particles is 0.4% by mass or more and 5.5% by mass or less. The toner according to any one of claims 1 to 4,
the mid-melting point wax is a Fischer-Tropsch wax;
The toner is characterized in that the binder resin is a polyester resin. The toner according to any one of claims 1 to 5,
The toner is characterized in that the strontium titanate fine particles are fine particles in which the surface of a fine powder base containing strontium titanate and silicon element is coated with a silane coupling agent. 7. The toner according to claim 1,
The toner, wherein the content of the strontium titanate fine particles relative to 100 parts by mass of the toner particles is 0.02 parts by mass or more and 0.6 parts by mass or less. The toner according to any one of claims 1 to 7,
The toner is characterized in that the difference ΔD in average primary particle diameter calculated by the following formula (2), where D _ts is the average primary particle diameter of the strontium titanate fine particles and D _os is the average primary particle diameter of the oil-treated silica fine particles, is -24 nm or more and 70 nm or less.
ΔD=D _os -D _ts ...(2) 9. The toner according to claim 1,
The toner is characterized in that the average primary particle diameter of the oil-treated silica fine particles is 16 nm or more and 110 nm or less. 10. The toner according to claim 1,
The toner, wherein the content of the oil-treated silica fine particles relative to 100 parts by mass of the toner particles is 0.1 parts by mass or more and 1.8 parts by mass or less. A two-component developer comprising the toner according to any one of claims 1 to 10 and a carrier.