toner

Abstract

To provide a toner which is excellent in charging property under a high temperature and high humidity environment, and can suppress fogging.SOLUTION: In a toner in which an external additive is attached to the surface of toner particles, the toner particles contain three kinds of polyester resins, a coloring agent and a release agent. When the three kinds of polyester resins are represented by first to third polyester resins in the order of a decreasing acid value, a difference in the acid value between the first polyester resin and the third polyester resin is 20 mgKOH / g or more and 30 mgKOH / g or less in an absolute value. A difference between a maximum value and a minimum value of a solubility parameter in the three kinds of the polyester resins is 0.5 or more and 1.0 or less in the absolute value. The external additive contains a fine powder body in which the surface of a core obtained by adding silica to strontium titanate is subjected to hydrophobic treatment with a silane compound, and hydrophobic silica particles.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to toner. [Background technology]

[0002] In image forming devices such as copiers, multifunction machines, printers, and facsimile machines that use two-component development, two-component developers are widely used, which are mixtures of toner particles containing binder resin, colorant, and release agent to which external additives are attached, and carrier.

[0003] Polyester resins are widely used as binder resins in toner particles. For example, Patent Document 1 discloses a binder resin composition for polyester toners, which aims to improve chargeability in low-temperature, low-humidity environments and to achieve both low-temperature fixability and heat-resistant storage stability, and which contains Polyester H having a softening temperature of 140°C or more and 170°C or less, Polyester M having a softening temperature of 115°C or more and less than 140°C, and Polyester L having a softening temperature of 80°C or more and less than 115°C, wherein the difference between the softening temperatures of Polyester H and Polyester M is 10°C or more, the difference between the softening temperatures of Polyester M and Polyester L is 20°C or more, and the acid value of the entire binder resin composition is 30 mgKOH / g or more and 80 mgKOH / g or less. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2015-75580 A Summary of the Invention [Problem to be solved by the invention]

[0005] During image formation in high-temperature, high-humidity environments, moisture absorption can cause toner particles to aggregate, leading to poor toner fluidity and poor triboelectric charging between the carrier and toner particles, resulting in fogging (white background fogging) and toner scattering. To prevent toner particle aggregation, a conventional approach has been to add large-sized silica as an external additive. However, this approach poses the problem of filming on the drum (photoconductor drum) due to the large-sized silica particles detaching from the toner particles. To suppress this filming, abrasives such as strontium titanate and magnetite can be added to the toner particle surface. However, this approach has the drawback of degrading image quality due to excessive drum scratches and excessive film loss on the photoconductor, as well as poor developer fluidity due to the adhesion of the external additive to the carrier surface (spent).

[0006] The toner of the present disclosure has been discovered in view of the above circumstances of image formation in a high-temperature, high-humidity environment, and has as its main object to provide a toner that has excellent charging properties in a high-temperature, high-humidity environment and can suppress fogging. [Means for solving the problem]

[0007] The toner of the present disclosure, which has been made to solve the above problems, is a toner having an external additive attached to the surface of a toner particle, the toner particles containing three types of polyester resins, a colorant, and a release agent, and when the three types of polyester resins are designated as first to third polyester resins in order of increasing acid value, the difference in acid value between the first polyester resin and the third polyester resin is 20 mgKOH / g or more and 30 mgKOH / g or less in absolute value, and the solubility parameters (unit: (MPa)) of the three types of polyester resins are 1 / 2 ) has an absolute value of 0.5 or more and 1.0 or less between the maximum and minimum values, and the external additive includes a fine powder in which a core made of strontium titanate to which silica has been added has its surface hydrophobized with a silane compound, and hydrophobic silica particles.

[0008] In the toner, the acid value of the first polyester resin may be 25 mgKOH / g or more and 35 mgKOH / g or less, the acid value of the second polyester resin may be 10 mgKOH / g or more and 20 mgKOH / g or less, and the acid value of the third polyester resin may be 2 mgKOH / g or more and 7 mgKOH / g or less.

[0009] In the toner, the content of the first polyester resin in the toner particles may be 35% by mass or more and 50% by mass or less, the content of the second polyester resin may be 5% by mass or more and 30% by mass or less, and the content of the third polyester resin may be 35% by mass or more and 50% by mass or less.

[0010] In the toner, the coverage of the toner particles with the fine powder may be 3% or more and 10% or less, and the adhesive strength of the fine powder to the toner particles may be 50% or more.

[0011] In the toner, the hydrophobic silica particles may have an average particle size of 7 nm or more and 15 nm or less, and the coverage of the toner particles with the hydrophobic silica particles may be 70% or more and 100% or less.

[0012] In addition, in the above toner, the external additive may contain second hydrophobic silica particles having an average particle size of 30 nm or more and 70 nm or less, and the coverage of the toner particles with the second hydrophobic silica particles may be less than 20%.

[0013] In the above toner, the content of the colorant in the toner particles may be 5% by mass or more and 10% by mass or less, the content of the release agent may be 1% by mass or more and 5% by mass or less, and the toner particles may not contain a charge control agent or may contain less than 1% by mass of a charge control agent. [Effects of the Invention]

[0014] The toner of the present disclosure exhibits excellent effects such as excellent chargeability in a high-temperature, high-humidity environment and suppression of fogging. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 1 is a cross-sectional view schematically illustrating a toner according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0016] The toner of the present disclosure will be described in detail below.

[0017] The toner according to the present embodiment is a toner having external additives attached to the surface of the toner particles. If necessary, the toner may further contain optional components within a range that does not impair the effects of the present disclosure. The volume average particle size of the primary particles of the toner particles can be appropriately selected depending on the purpose, and may be, for example, 5 μm or more and 8 μm or less. FIG. 1 is a cross-sectional view schematically illustrating the toner according to the present embodiment. As shown in FIG. 1, the toner particles contain a binder resin and internal additives (such as a release agent and a colorant), and the internal additives are dispersed in the binder resin.

[0018] <Binder resin> The binder resin in the toner particles according to this embodiment contains three polyester resins with different acid values. In this specification, these three polyester resins are referred to as the first polyester resin, the second polyester resin, and the third polyester resin in descending order of acid value, and in the examples described later, they are also simply referred to as resins 1 to 3.

[0019] The polyester resin used as the binder resin is usually obtained by polycondensation reaction of polybasic acids and polyhydric alcohols by a known method. For example, it can be synthesized by polycondensation reaction, specifically dehydration condensation reaction, of polybasic acids and polyhydric alcohols in the presence of a catalyst in an organic solvent or without a solvent. In this case, a methyl ester of a polybasic acid may be used as part of the polybasic acid, and a demethanol polycondensation reaction may be performed. The polycondensation reaction of polybasic acids and polyhydric alcohols may be terminated when the acid value and softening temperature of the resulting polyester resin reach the desired values ​​(the values ​​to be synthesized). In this polycondensation reaction, by appropriately changing the reaction conditions, such as the compounding ratio and reaction rate of the polybasic acids and polyhydric alcohols, it is possible to adjust, for example, the content of carboxyl groups bonded to the terminals of the resulting polyester resin, and therefore the acid value of the resulting polyester resin, and also to adjust various physical properties (softening temperature, solubility parameter, etc.).

[0020] As the polybasic acid, those known as polyester monomers can be used, for example, aromatic carboxylic acids such as terephthalic acid, isophthalic acid, phthalic anhydride, trimellitic anhydride, pyromellitic acid, and naphthalenedicarboxylic acid; aliphatic carboxylic acids such as maleic anhydride, fumaric acid, succinic acid, alkenylsuccinic anhydride, and adipic acid; and methyl esters of these polybasic acids.

[0021] In the binder resin according to this embodiment, one of the above polybasic acids may be used alone, or two or more of them may be used in combination.

[0022] As the polyhydric alcohol, those known as polyester monomers can be used, for example, aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, and glycerin; alicyclic polyhydric alcohols such as cyclohexanediol, cyclohexanedimethanol, and hydrogenated bisphenol A; and aromatic diols such as ethylene oxide adduct of bisphenol A and propylene oxide adduct of bisphenol A.

[0023] In the binder resin according to this embodiment, one of the polyhydric alcohols may be used alone, or two or more of them may be used in combination.

[0024] In the toner according to the present embodiment, the difference in acid value between the first polyester resin and the third polyester resin is 20 mgKOH / g or more and 30 mgKOH / g or less in absolute value, and the solubility parameters (unit: (MPa)) of the three types of polyester resins are 1 / 2 The difference between the maximum and minimum values ​​of the solubility parameter is preferably 0.5 or more and 1.0 or less in absolute value. It is more preferable that the difference in acid value is 22 mgKOH / g or more and 28 mgKOH / g or less in absolute value, and the difference between the maximum and minimum values ​​of the solubility parameter is more preferably 0.6 or more and 0.9 or less in absolute value.

[0025] The toner according to this embodiment has excellent chargeability and suppresses fogging in a high-temperature, high-humidity environment because the acid values ​​and solubility parameters of the three polyester resins satisfy the above ranges. The reasons for this are considered to be as follows.

[0026] The acid value of a resin affects moisture absorption, coagulation, chargeability, and material dispersibility (dispersibility of internal additives). Toners using resins with high acid values ​​have the following characteristics (1) to (4), while toners using resins with low acid values ​​have the opposite characteristics. (1) Because it is highly hygroscopic, when it is left in a high-temperature, high-humidity environment, it absorbs moisture and its electrostatic charge decreases (it is easily affected by the environment when left standing). (2) The surface free energy increases, which increases the tendency for toner particles to cohere with each other and reduces fluidity, resulting in a decrease in triboelectric charging with the carrier. (3) The binder resin contains many terminal groups (carboxyl groups), so it has high electrostatic properties. (4) The internal additives have high dispersibility in the binder resin.

[0027] In other words, if the binder resin is only one type of polyester resin, it is not possible to satisfy all of the requirements for moisture absorption, cohesiveness, chargeability, and material dispersibility, and it is difficult to exhibit sufficient chargeability in a high-temperature, high-humidity environment.

[0028] For example, resins with a high acid value (e.g., 25 mg KOH / g or higher) have high chargeability and good material dispersibility, but their high hygroscopicity reduces their chargeability when left standing. Furthermore, their high cohesiveness reduces frictional charging with the carrier, resulting in problems such as fogging and toner scattering, especially after leaving the toner in a high-temperature, high-humidity environment. On the other hand, resins with a low acid value (e.g., 2 mg KOH / g to 7 mg KOH / g) have good hygroscopicity and cohesiveness, but have problems such as low chargeability and poor material dispersibility. Poor material dispersibility and the presence of a large amount of colorant and release agent on the toner particle surface reduce chargeability, resulting in fogging and toner scattering.

[0029] The toner of the present disclosure was completed based on the discovery that by using a combination of first to third polyester resins as a binder resin, in which the differences between the maximum and minimum values ​​of the acid value and solubility parameter are within the above-mentioned ranges, it is possible to achieve both the advantages of a resin with a high acid value and a resin with a low acid value, compared to using a single resin with a medium acid value (for example, 8 mg KOH / g to 24 mg KOH / g). This is thought to be because, when the solubility parameters of the first to third polyester resins are within the above-mentioned ranges, the dispersion state of the resins can be controlled to a degree that they are not completely miscible with each other, resulting in a fine dispersion, and the advantages of each resin can be maintained.

[0030] In the toner according to the present embodiment, the acid value of the first polyester resin is preferably 25 mgKOH / g or more and 35 mgKOH / g or less, the acid value of the second polyester resin is preferably 10 mgKOH / g or more and 20 mgKOH / g or less, and the acid value of the third polyester resin is preferably 2 mgKOH / g or more and 7 mgKOH / g or less. By having the acid values ​​of the first to third polyester resins within the above ranges, it becomes easier to achieve both the advantages of a resin with a high acid value and the advantages of a resin with a low acid value, as described above, and the effect of improving chargeability and suppressing fogging in a high-temperature, high-humidity environment is more easily exhibited. The acid value of the first polyester resin is more preferably 28 mgKOH / g or more and 32 mgKOH / g or less, the acid value of the second polyester resin is more preferably 12 mgKOH / g or more and 18 mgKOH / g or less, and the acid value of the third polyester resin is more preferably 3 mgKOH / g or more and 6 mgKOH / g or less.

[0031] In the toner particles according to this embodiment, the content of the first polyester resin is preferably 35% to 50% by mass, the content of the second polyester resin is preferably 5% to 30% by mass, and the content of the third polyester resin is preferably 35% to 50% by mass. By keeping the contents of the first to third polyester resins within the above ranges, it becomes easier to combine the advantages of a resin with a high acid value and a resin with a low acid value, and the effect of improving chargeability and suppressing fogging in high-temperature, high-humidity environments is more easily achieved. If the content of the second polyester resin exceeds the above upper limit, the contents of the first and third polyester resins become too low, which may prevent the effect of combining the advantages of a resin with a high acid value and a resin with a low acid value. The content of the first polyester resin is more preferably 40% to 48% by mass, the content of the second polyester resin is more preferably 7% to 20% by mass, and the content of the third polyester resin is more preferably 40% to 48% by mass.

[0032] The weight-average molecular weight (Mw) of the polyester resin used as the binder resin is preferably 4,000 or more and 100,000 or less. In the present disclosure, the weight-average molecular weight is a value measured by gel permeation chromatography (GPC), using tetrahydrofuran (THF) as the mobile phase and polystyrene as the standard substance.

[0033] Of the first to third polyester resins contained in the toner particles according to this embodiment, the weight average molecular weight of the first polyester resin is preferably 40,000 to 90,000, and more preferably 50,000 to 80,000. The weight average molecular weight of the second polyester resin is preferably 6,500 to 9,000, and more preferably 7,000 to 8,000. The weight average molecular weight of the third polyester resin is preferably 4,000 to 6,500, and more preferably 5,000 to 6,000.

[0034] The polyester resin used as the binder resin preferably has a glass transition temperature of 30°C or higher and 80°C or lower. If the glass transition temperature of the binder resin is lower than the lower limit, blocking, in which the toner thermally aggregates, may occur inside the image forming apparatus, and storage stability may be reduced. If the glass transition temperature of the binder resin is higher than the upper limit, the fixability of the toner to the recording medium may be reduced, and fixing failure may occur.

[0035] Of the first to third polyester resins contained in the toner particles according to this embodiment, the glass transition temperature of the first polyester resin is preferably 50° C. or higher and 70° C. or lower, and more preferably 55° C. or higher and 65° C. or lower. The glass transition temperature of the second polyester resin is preferably 60° C. or higher and 75° C. or lower, and more preferably 65° C. or higher and 70° C. or lower. The glass transition temperature of the third polyester resin is preferably 45° C. or higher and 60° C. or lower, and more preferably 50° C. or higher and 55° C. or lower.

[0036] Of the first to third polyester resins contained in the toner particles according to this embodiment, the softening temperature of the first polyester resin is preferably 125° C. to 150° C., and more preferably 135° C. to 143° C. The softening temperature of the second polyester resin is preferably 95° C. to 115° C., and more preferably 100° C. to 110° C. The softening temperature of the third polyester resin is preferably 80° C. to 98° C., and more preferably 85° C. to 93° C.

[0037] The content of the binder resin in the toner particles is preferably 60% by mass or more and 98% by mass or less, and more preferably 70% by mass or more and 95% by mass or less.

[0038] <Coloring agent> In the toner according to this embodiment, the toner particles may contain a colorant, which may be any of various types and colors of organic or inorganic pigments and dyes commonly used in the field of electrophotography, such as black, white, yellow, orange, red, purple, blue, and green colorants.

[0039] Examples of black colorants include carbon black, copper oxide, manganese dioxide, aniline black, activated carbon, non-magnetic ferrite, magnetic ferrite, and magnetite.

[0040] Examples of white colorants include zinc oxide, titanium oxide, antimony white, and zinc sulfide.

[0041] 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, CI pigment yellow 12, CI pigment yellow 13, CI pigment yellow 14, CI pigment yellow 15, CI pigment yellow 17, CI pigment yellow 93, CI pigment yellow 94, and CI pigment yellow 138.

[0042] 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, CI pigment orange 31, and CI pigment orange 43.

[0043] 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, CI pigment red 2, CI pigment red 3, CI pigment red 5, CI pigment red 6, CI pigment red 7, CI pigment red 8, CI pigment red 9, CI pigment red 10, CI pigment red 11, CI pigment red 12, CI pigment red 13, CI pigment red 14, CI pigment red 15, CI pigment red 16, CI pigment red 17, CI pigment red 18, CI pigment red 19, CI pigment red 20, CI pigment red 21, CI pigment red 22, CI pigment red 23, CI pigment red 24, CI pigment red 25, CI pigment red 26, CI pigment red 27, CI pigment red 28, CI pigment red 29 ... Examples of pigments that can be used include CI Pigment Red 7, CI Pigment Red 15, CI Pigment Red 16, CI Pigment Red 48:1, CI Pigment Red 53:1, CI Pigment Red 57:1, CI Pigment Red 122, CI Pigment Red 123, CI Pigment Red 139, CI Pigment Red 144, CI Pigment Red 149, CI Pigment Red 166, CI Pigment Red 177, CI Pigment Red 178, and CI Pigment Red 222.

[0044] Examples of purple colorants include manganese violet, fast violet B, and methyl violet lake.

[0045] 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, CI pigment blue 15, CI pigment blue 15:2, CI pigment blue 15:3, CI pigment blue 16, and CI pigment blue 60.

[0046] Examples of green colorants include chrome green, chromium oxide, pigment green B, micalite green lake, final yellow green G, and CI pigment green 7.

[0047] In the toner according to the present embodiment, the above colorants may be used alone or in combination of two or more, and the combination may be of different colors or the same color. The content of the colorant in the toner particles is preferably 5% by mass or more and 10% by mass or less, and more preferably 6% by mass or more and 9% by mass or less.

[0048] <Release agent> The toner particles according to this embodiment may contain a release agent. Examples of release agents include waxes commonly used in the electrophotography field. Examples include petroleum-based waxes such as paraffin wax and its derivatives, microcrystalline wax and its derivatives, Fischer-Tropsch wax and its derivatives, polyolefin wax and its derivatives, polypropylene wax and its derivatives, and polyolefin polymer waxes (e.g., low-molecular-weight polyethylene waxes) and their derivatives. Other examples include plant-based waxes such as carnauba wax and its derivatives, rice wax and its derivatives, candelilla wax and its derivatives, and Japan wax. Other examples include animal-based waxes such as beeswax and spermaceti. These may be used alone or in combination. Examples of derivatives include oxides, block copolymers of vinyl monomers and wax, and graft-modified products of vinyl monomers and wax.

[0049] The content of the release agent in the toner particles according to this exemplary embodiment is preferably from 1% by mass to 5% by mass, and more preferably from 1.5% by mass to 4.5% by mass.

[0050] <Other internal additives> The toner according to this embodiment may contain internal additives other than those described above, if necessary. Examples of internal additives other than those described above include charge control agents. Charge control agents are added to impart desirable chargeability to the toner. There are no particular limitations on the charge control agent, and charge control agents used in the field of electrophotography for positive charge control and negative charge control can be used. It is preferable that the toner particles according to this embodiment contain no charge control agent or contain less than 1% by mass of a charge control agent.

[0051] <External additives> The external additive for the toner according to this embodiment includes a fine powder of strontium titanate with silica added thereto, the surface of which has been hydrophobized with a silane compound, and hydrophobic silica particles, as shown in FIG. 1. Hereinafter, the term "fine powder of strontium titanate with silica added thereto, the surface of which has been hydrophobized with a silane compound" will also be referred to simply as "fine powder of strontium titanate modified with silica." By attaching strontium titanate to the toner particle surface in this manner, excessive increase in charge amount can be suppressed in low-temperature, low-humidity environments.

[0052] Strontium titanate as an external additive has a high dielectric constant and a strong leak effect, but the above-mentioned fine powder has silica added to the interior and the surface is hydrophobized with a silane compound, so a moderate leak effect is obtained.

[0053] The toner particles according to this embodiment contain three types of polyester resins that satisfy the above-described acid value and solubility parameter requirements as binder resins, thereby controlling the cohesion of the toner particles. Therefore, in the external addition step of attaching external additives to the toner particles, the external additives (fine powder of silica-modified strontium titanate and hydrophobic silica particles) can be uniformly dispersed on the toner particle surface, maintaining a high adhesion state. Furthermore, the additives are less likely to detach from the toner particle surface, preventing them from adhering to the drum and carrier. Therefore, even when printing is performed over a long period of time (even as the product life progresses), carrier contamination caused by the external additives can be prevented, and stable images can be provided over a long period of time.

[0054] The fine powder obtained by hydrophobizing the surface of a core made of strontium titanate with silica added thereto with a silane compound can be produced, for example, by the following procedures (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 to obtain a washed cake. (2) Water is added to the washed cake to form a slurry, and then hydrochloric acid is added for deflocculation. 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 reaction is completed by stirring for 2 hours while adding an aqueous sodium hydroxide solution. (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 ground in a blender for 1 minute, and the coarse particles are removed with a sieve. 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, such as those using hexamethyldisilazane (HMDS), dimethyldichlorosilane (DDS), octylsilane (OTAS), and polydimethylsiloxane (PDMS).

[0055] In the fine powder according to this embodiment, it is preferable that the coverage of the toner particles with the fine powder is 3% or more and 10% or less, and that the adhesive strength of the fine powder to the toner particles is 50% or more. By having the coverage within the above range, it is possible to more effectively suppress fogging in a high-temperature, high-humidity environment and to suppress an excessive increase in charge amount in a low-temperature, low-humidity environment. Furthermore, by having the adhesive strength within the above range, it is possible to suppress fogging in a high-temperature, high-humidity environment for a long period of time. It is more preferable that the coverage of the toner particles with the fine powder is 5% or more and 8% or less, and that the adhesive strength of the fine powder to the toner particles is 60% or more.

[0056] The hydrophobic silica particles used as an external additive in this embodiment preferably have an average particle size of 7 nm to 15 nm, and the coverage of the toner particles with the hydrophobic silica particles is preferably 70% to 100%. By using small hydrophobic silica particles in this manner, the fluidity of the toner and the dispersibility of the external additive can be improved. The average particle size of the small hydrophobic silica particles is more preferably 8 nm to 12 nm, and the coverage of the toner particles with the small hydrophobic silica particles is more preferably 80% to 100%.

[0057] The external additive according to this embodiment preferably contains second hydrophobic silica particles having a particle size larger than the small hydrophobic silica particles. The second hydrophobic silica particles preferably have an average particle size of 30 nm or more and 70 nm or less, and the coverage of the toner particles with the second hydrophobic silica particles is preferably less than 20%. Adding the second hydrophobic silica particles in an amount that satisfies the coverage range can suppress poor charging, and the effects of the present disclosure, such as improved charging performance and suppression of fogging in high-temperature, high-humidity environments, can be more easily achieved. The average particle size of the second hydrophobic silica particles is more preferably 35 nm or more and 65 nm or less, and the coverage of the toner particles with the second hydrophobic silica particles is more preferably less than 15%. [Example]

[0058] The toner of the present disclosure will be specifically described below based on examples and comparative examples. First, various measurement methods and evaluation methods will be described.

[0059] <Measurement and evaluation methods> [Method for measuring the average particle size of toner particles] 20 mg of sample and 1 mL of sodium alkyl ether sulfate were added to 50 mL of 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 the measurement sample.

[0060] The obtained measurement samples were measured using a particle size distribution analyzer (Beckman Coulter, Inc., Model: Multisizer 3) under the conditions of an aperture diameter of 100 μm and a particle count of 50,000, and the volume average particle size (μm) was calculated from the volume particle size distribution of the sample particles.

[0061] [Method for measuring the average particle size of external additives] The average particle size of the primary particles of the external additive was calculated using a scanning transmission electron microscope (Hitachi High-Technologies Corporation, model: S-4800) at a magnification of 50,000 times, by photographing 100 external additive particles at different fields of view, and measuring the average particle size of each primary particle by image analysis.

[0062] [Calculation method for coverage rate by external additives] The coverage of the toner particles with the external additive represents the ratio of the area of ​​the external additive present on the surface of the toner particles to the surface area of ​​the toner particles, and was calculated using the following formula. f[%]=(√3·D·ρ t ·C) / (2π·d·ρ i ) x 100 In the formula, f is the coverage rate by the external additive, D is the average particle size (μm) of the toner particles, d is the average particle size (μm) of the external additive, ρt is the true specific gravity of the toner particles, ρi is the true specific gravity of the external additive, and C is (mass of the external additive) / (mass of the toner).

[0063] [Method for measuring adhesive strength of external additives] The adhesion strength of the external additive was measured according to the following procedures (1) to (7). (1) 2.0 g of capsule toner is added to 40 mL of a 0.2% by mass aqueous solution of Triton (polyoxyethylene octylphenyl ether) and stirred for 1 minute. (2) The aqueous solution is then irradiated with ultrasound using a homogenizer US-300T (manufactured by Nippon Seiki Seisakusho Co., Ltd.) (output: 40 μA, 4 minutes). (3) After the ultrasonic irradiation, the aqueous solution is left to stand for 3 hours, and the toner and the liberated external additives are separated. (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) with a pore size of 1 μm. (6) The toner remaining on the filter is vacuum dried overnight. (7) Using an X-ray fluorescence analyzer (Rigaku Corporation, model: ZSX Primus II), the intensities of the Ti and Si elements in the external additives of 1 g of toner were analyzed before and after the series of ultrasonic treatments (1) to (6) above, and the adhesion strength of the external additives was calculated using the following formula. Adhesion strength (%) of fine powder in which the surface of a core made of strontium titanate with silica added is hydrophobized with a silane compound = {(Ti strength after treatment) / (Ti strength before treatment)} x 100 Adhesion strength of hydrophobic silica particles (%) = {(Si strength after treatment) / (Si strength before treatment)} × 100

[0064] [Method for measuring the acid value of resin] The acid value of the resin was measured by neutralization titration. 5 g of the sample to be measured was dissolved in 50 mL of tetrahydrofuran (THF), and after adding a few drops of phenolphthalein in ethanol as an indicator, titration was performed with 0.1 mol / L potassium hydroxide (KOH) solution. The point at which the color of the sample solution changed from colorless to purple was set as the endpoint, and the acid value (mgKOH / g) was calculated from the amount of potassium hydroxide solution required to reach the endpoint and the mass of the sample used for titration.

[0065] [How to calculate the solubility parameter of a resin] The solubility parameter (SP value) of the resin was calculated based on the Fedors method, which utilizes the additivity of atomic groups.

[0066] [Method for evaluating toner moisture absorption] The toner to be measured was left for 24 hours in a normal temperature and humidity environment (temperature 25°C, humidity 50%, hereinafter also referred to as "NN environment") and a high temperature and high humidity environment (temperature 35°C, humidity 85%, hereinafter also referred to as "HH environment"), and then the moisture content (%) in each environment was measured to determine the difference in moisture content and evaluated according to the following criteria. The moisture content was measured based on the Karl Fischer method, with the sample heated to 200°C for 15 minutes. ◎ (Excellent): The difference in moisture content is less than 0.05%. ○ (Good): The difference in moisture content is 0.05% or more and less than 0.1%. △ (Acceptable): The difference in moisture content is 0.1% or more and 0.2% or less. × (unacceptable): The difference in moisture content is greater than 0.2%.

[0067] [Method for evaluating toner cohesion] Five grams of the toner to be measured was placed in a 100 mL glass bottle and left in a thermostatic chamber at 50°C for 48 hours. After removing the toner from the thermostatic chamber, the cohesion degree was measured in a room temperature environment using a powder tester (manufactured by Hosokawa Micron Corporation). Specifically, sieves with openings of 250 μm, 150 μm, and 75 μm were set in the powder tester from top to bottom, and vibration was applied at an amplitude of 1.5 mm for 30 seconds. If the weights of the toner on the sieves are W(250), W(150), and W(75), respectively, the cohesion degree was calculated using the following formula: Cohesion degree [%]=(W(250)+W(150)×0.6+W(75)×0.2) / 5×100

[0068] Based on the measured cohesion, the cohesion of the toner was evaluated according to the following criteria. ◎ (Excellent): The cohesion value is less than 5%. ○ (Good): The cohesion value is 5% or more and less than 10%. △ (Fair): The cohesion value is 10% or more and less than 20%. × (Fail): The cohesion value is greater than 20%.

[0069] [Method for evaluating toner charge amount] The toner was sucked through a mesh using a small suction-type charge measurement device (product name: 210HS-2A, manufactured by TREK Corporation), the charge of the separated toner was measured, and the charge amount [-μc / g] was calculated from the measured charge and the weight of the toner separated by suction.

[0070] Based on the calculated charge amount, the charge amount of the toner was evaluated according to the following criteria. ◯ (Good): The charge amount (absolute value) in the HH environment is 20 μc / g or more. △ (Acceptable): The charge amount (absolute value) in the HH environment is 15 μc / g or more and less than 20 μc / g. × (Not acceptable): The amount of charge (absolute value) in the HH environment is less than 15 μc / g.

[0071] [Method for evaluating material dispersibility in toner particles] The toner particles were embedded in a room-temperature curing epoxy resin, and the resulting cured product was subjected to surface polishing using an ultramicrotome equipped with diamond teeth (manufactured by Reichert, product name: Ultracut N). The cross section of the resulting toner particles was observed using a scanning transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, model: S-4800). A number of wax particles (approximately 50) were randomly extracted from the electron micrograph data, and the images were analyzed using image analysis software (product name: A-zo-kun, manufactured by Asahi Kasei Engineering Co., Ltd.). The material dispersibility was evaluated based on the dispersion diameter. The evaluation criteria for material dispersibility are as follows: ◯ (Good): Dispersion diameter is 1.0 μm or less. △ (Acceptable): The dispersion diameter is more than 1.0 μm and 2.0 μm or less. × (unacceptable): Dispersion diameter is greater than 2.0 μm.

[0072] [Method for evaluating the compatibility of resins] The toner particles were embedded in a room-temperature curing epoxy resin to obtain a cured product, which was then surface-polished using an ultramicrotome equipped with diamond teeth (manufactured by Reichert, product name: Ultracut N). The cross-sections of the obtained toner particles were observed using a scanning transmission electron microscope (manufactured by Hitachi High-Technologies Corporation, model: S-4800). The evaluation criteria for the compatibility of the resins were as follows: ◯ (Good): The resins are not completely compatible with each other and are in a finely dispersed state. × (Not acceptable): The resins are completely compatible with each other, or are not compatible with each other.

[0073] [Method for evaluating fogging before and after exposure to high temperature and humidity] In a high temperature and humidity environment (temperature 35°C, humidity 85%), a two-component developer is filled into the development unit of a copier, and the amount of toner adhered to the photoconductor is 0.45 mg / cm 2 The image was formed on an A4 size recording paper by adjusting the whiteness so that the whiteness of the non-image area of ​​the recording medium after image formation was measured using a whiteness meter (manufactured by Nippon Denshoku Industries Co., Ltd., product name: Z-Σ90 COLOR MEASURING SYSTEM). The difference between this whiteness and the whiteness of the recording medium before image formation, which had been measured in advance using the whiteness meter, was calculated and used as the fog density.

[0074] In a high temperature and humidity environment (temperature 35°C, humidity 85%), 5,000 (5K) images with a printing rate of 10% were printed, and the fog density immediately after printing and after leaving overnight were used to evaluate the fog according to the following criteria. ◎ (Excellent): Fog density is 0 or more and 0.5 or less. ◯ (Good): The fog density is more than 0.5 and 1.0 or less. △ (Acceptable): The fog density is more than 1.0 and 2.0 or less. × (unacceptable): The fog density is higher than 2.0.

[0075] [Method for evaluating fog during life in a high-temperature, high-humidity environment] In a high-temperature, high-humidity environment (temperature 35°C, humidity 85%), 5,000 (5K) sheets of an image with a coverage rate of 10% were printed daily, and this was repeated until a total of 50,000 (50K) sheets were printed. Based on the fog density after printing 50,000 (50K) sheets, the fog was evaluated according to the following criteria. The method for measuring the fog density was the same as the "Method for evaluating fog before and after storage in a high-temperature, high-humidity environment" described above. ◎ (Excellent): Fog density is 0 or more and 0.5 or less. ◯ (Good): The fog density is more than 0.5 and 1.0 or less. △ (Acceptable): The fog density is more than 1.0 and 2.0 or less. × (unacceptable): The fog density is higher than 2.0.

[0076] [Evaluation of image density in a low temperature and low humidity environment] In a low-temperature, low-humidity environment (temperature 5°C, humidity 10%), a two-component developer is filled into the development unit of a copier, and the amount of toner adhered to the photoconductor is 0.45 mg / cm 2 After the image was formed on the recording medium, the image density of the solid portion was measured using a reflection densitometer (manufactured by X-Rite, model: RD914).

[0077] Based on the measured image density, the image density was evaluated according to the following criteria. ◎ (Excellent): Image density is 1.4 or more and less than 1.6. ◯ (Good): Image density is 1.2 or more and less than 1.4. △ (Acceptable): Image density is 1.0 or more and less than 1.2. × (unacceptable): Image density is less than 1.0.

[0078] Next, the procedures for producing the toners according to the examples and comparative examples and the results of various evaluations will be described.

[0079] <Preparing toner materials> [Binder resin] The binder resins used to prepare the toner particles according to the examples and comparative examples are listed in the following Tables 1 to 3. Table 1 lists the resins prepared as the first polyester resin (hereinafter also referred to as "resin 1"), Table 2 lists the resins prepared as the second polyester resin (hereinafter also referred to as "resin 2"), and Table 3 lists the resins prepared as the third polyester resin (hereinafter also referred to as "resin 3").

[0080] In Tables 1 to 3, the unit of AV (acid value) is "mgKOH / g" and the unit of SP (solubility parameter) is "(MPa) 1 / 2", Tg (glass transition temperature) and Tm (softening temperature) are in units of "°C", and Mw represents "weight average molecular weight." All of resins 1 to 3 are amorphous polyester resins.

[0081] [Table 1]

[0082] [Table 2]

[0083] [Table 3]

[0084] [Strontium titanate fine powder] (1) Preparation of fine powder A in which strontium titanate is modified with silica Metatitanic acid obtained by the sulfuric acid method was desulfurized and bleached, and then a sodium hydroxide aqueous solution was added to adjust the pH to 9.0, followed by desulfurization. After desulfurization, the mixture was neutralized to pH 5.8 with hydrochloric acid, filtered, and washed with water to obtain a washed cake. Water was added to the washed cake to form a slurry, and then hydrochloric acid was added to adjust the pH to 1.4, followed by peptization. This metatitanic acid was placed in a reaction vessel, and a strontium chloride solution and sodium silicate were added. Next, the mixture was heated to 90°C with stirring, and then a 10N sodium hydroxide aqueous solution was added over 2 hours. The reaction was then completed by continuing stirring at 95°C for 1 hour.

[0085] The reaction-completed slurry was cooled to 50°C, and hydrochloric acid was added until the pH reached 5.0, followed by stirring for 1 hour. The resulting precipitate was decanted and washed, then adjusted to 50°C, and hydrochloric acid was added to adjust the pH to 2.5, followed by hydrophobic treatment. Sodium hydroxide solution was then added to adjust the pH to 6.5, and the mixture was stirred for 1 hour. The resulting cake was then filtered and washed, and dried in air at 120°C for 10 hours to obtain a fine powder (hereinafter referred to as "fine powder A") in which the surface of a core composed of strontium titanate and silica added was hydrophobized with a silane compound. The average particle size of the primary particles was 50 nm.

[0086] (2) Preparation of fine powder B in which strontium titanate is not modified with silica Metatitanic acid obtained by the sulfuric acid method was desulfurized and bleached, and then a sodium hydroxide solution was added to adjust the pH to 9.0, followed by desulfurization. After desulfurization, the mixture was neutralized to pH 5.8 with hydrochloric acid, filtered, and washed with water to obtain a washed cake. Water was added to the washed cake to form a slurry, and then hydrochloric acid was added to adjust the pH to 1.4, followed by peptization. This metatitanic acid was placed in a reaction vessel, and a strontium chloride solution was added. Next, the mixture was heated to 90°C with stirring, and then a 10N sodium hydroxide solution was added over 2 hours. The reaction was then completed by continuing stirring at 95°C for 1 hour.

[0087] The reaction-completed slurry was cooled to 50°C, and hydrochloric acid was added until the pH reached 5.0, followed by stirring for 1 hour. The resulting precipitate was decanted and washed, then adjusted to 50°C, and hydrochloric acid was added to adjust the pH to 2.5, followed by hydrophobic treatment. Sodium hydroxide solution was then added to adjust the pH to 6.5, and the mixture was stirred for 1 hour. The resulting cake was then filtered and washed, and dried in air at 120°C for 10 hours to obtain a fine powder (hereinafter referred to as fine powder B) containing strontium titanate in the core and no silica. The average particle size of the primary particles was 50 nm.

[0088] <Toner Production> [Example 1] Toner particles (toner cores) were prepared by a melt-pulverization method using the following materials. (binder resin) Resins 1-3: Amorphous polyester resin / Total 5000g The types and compounding ratios of resins 1 to 3 are as shown in Table 4 below. (coloring agent) Carbon black (Mitsubishi Chemical Corporation, product name: #44) / 300g (mold release agent) Release agent A: Paraffin wax (melting point 90°C, manufactured by Nippon Seiro Co., Ltd., product name: Fischer-Tropsch Wax FNP0090) / 100g Release agent B: Polypropylene wax (melting point 140°C, manufactured by Mitsui Chemicals, Inc., product name: NP-505) / 50g (Charge control agent) Potassium salt, bis[benzilate(2-)-k(2)O,O]borate(1-) potassium, solubility in water 4.382 g / L (20 °C), manufactured by Nippon Carlit Co., Ltd., product name: Ion Conductor LR-147 / 20 g

[0089] The above materials for the toner particles were pre-mixed for 5 minutes at a rotation speed of 1500 rpm using a high-performance fluid mixer (Henschel mixer, total capacity: 20 L, manufactured by Nippon Coke & Engineering Co., Ltd., model: FM20C).

[0090] 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 material supply rate of 10 kg / h to obtain a melt-kneaded product.

[0091] The obtained molten kneaded material was cooled and solidified on a cooling belt, and then the solidified material was finely pulverized using a fluidized bed opposed jet mill (manufactured by Hosokawa Micron Corporation, model: Counter Jet Mill AFG) and classified (particle size adjusted) using a rotary (centrifugal airflow) classifier (manufactured by Hosokawa Micron Corporation, model: TSP Separator) to produce toner particles with a volume average particle size of 6.0 μm.

[0092] Next, in the external addition step, 100 parts by mass of the produced toner particles, 1.0 part by mass of hydrophobic silica particles having an average primary particle size of 10 nm as external additives, and 0.8 parts by mass of strontium titanate fine powder (fine powder A above) having an average particle size of 50 nm were added to a high-performance fluid mixer (Henschel mixer, total capacity: 20 L, manufactured by Nippon Coke and Engineering Co., Ltd., model: FM20C), and stirred and mixed at a rotation speed of 3000 rpm for 3 minutes to obtain the toner of Example 1 (externally added toner).

[0093] [Examples 2 to 37, Comparative Examples 1 to 7] Toner was obtained in the same manner as in Example 1, except that the types and compounding ratios of Resins 1 to 3 were changed as shown in Tables 4 to 6 below.

[0094] [Examples 38 to 44] A toner was obtained in the same manner as in Example 1, except for changing the external addition step. In the external addition step, 100 parts by mass of the prepared toner particles, 1.0 part by mass of hydrophobic silica particles with an average primary particle size of 10 nm as an external additive, and strontium titanate fine powder with an average particle size of 50 nm (fine powder A described above) were added to a high-performance fluid mixer (Henschel mixer, total capacity: 20 L, manufactured by Nippon Coke & Engineering Co., Ltd., model: FM20C) and stirred and mixed at a rotation speed of 3000 rpm for 3 minutes to obtain a toner (externally added toner). The amount of strontium titanate fine powder added was adjusted to achieve the coverage shown in Table 7. For Examples 43 and 44, the stirring and mixing time in the mixer was adjusted to achieve the adhesion strength shown in Table 7.

[0095] [Comparative Example 8] A toner was obtained in the same manner as in Example 1, except that the strontium titanate fine powder added in the external addition step was changed to a fine powder that was not modified with silica (the above-mentioned fine powder B).

[0096] Comparative Example 9 A toner was obtained in the same manner as in Example 1, except that the strontium titanate fine powder was not added in the external addition step.

[0097] The following Tables 4 to 7 show the types and blending ratios of binder resins in Examples and Comparative Examples. Tables 4 to 6, which relate to Examples and Comparative Examples in which the types and blending ratios of resins were changed, also show the difference ΔAV between the maximum and minimum acid values ​​of the three types of resins, and the difference ΔSP between the maximum and minimum solubility parameters of the three types of resins. The unit of ΔAV is "mgKOH / g", and the unit of ΔSP is "(MPa) 1 / 2 Table 7, which relates to examples and comparative examples in which the strontium titanate fine powder was varied, also shows whether or not strontium titanate fine powder was added, whether or not the strontium titanate fine powder was modified with silica (whether fine powder A or B was used), the coverage by the strontium titanate fine powder, and the adhesive strength of the strontium titanate fine powder.

[0098] [Table 4]

[0099] [Table 5]

[0100] [Table 6]

[0101] [Table 7]

[0102] [Table 8]

[0103] [Table 9]

[0104] [Table 10]

[0105] [Table 11]

[0106] The evaluation results of Examples and Comparative Examples in which ΔAV and ΔSP were changed are shown in Table 8. As is clear from these evaluation results, the toners of Examples 1 to 12, in which ΔAV was 20 mgKOH / g or more and 30 mgKOH / g or less and ΔSP was 0.5 or more and 1.0 or less, had excellent charging properties in a high-temperature, high-humidity environment and were able to suppress fogging.

[0107] In contrast, Comparative Examples 1 and 3, in which ΔAV was outside the range of 20 mgKOH / g or more and 30 mgKOH / g or less, and Comparative Examples 2 and 4, in which ΔSP was outside the range of 0.5 or more and 1.0 or less, were inferior to the Examples in the evaluation of fogging in a high-temperature, high-humidity environment.

[0108] Table 9 shows the evaluation results of examples in which the acid values ​​of Resins 1 to 3 were varied while ΔAV and ΔSP were kept within the above ranges. These evaluation results show that Examples 13 to 16, 19 to 21, and 24 to 27, in which Resin 1 (first polyester resin) had an acid value of 25 mgKOH / g or more and 35 mgKOH / g or less, Resin 2 (second polyester resin) had an acid value of 10 mgKOH / g or more and 20 mgKOH / g or less, and Resin 3 (third polyester resin) had an acid value of 2 mgKOH / g or more and 7 mgKOH / g or less, were superior in evaluation of fogging in a high-temperature, high-humidity environment to Examples 17, 18, 22, 23, 28, and 29, which did not satisfy these requirements.

[0109] In Example 17, where the acid value of Resin 1 was less than 25 mgKOH / g, the evaluations of chargeability and material dispersibility were inferior to the other Examples. In Example 18, where the acid value of Resin 1 was greater than 35 mgKOH / g, the evaluations of hygroscopicity and coagulation were inferior to the other Examples. In Example 22, where the acid value of Resin 2 was less than 10 mgKOH / g and the acid values ​​of Resin 2 and Resin 3 were similar, and in Example 23, where the acid value of Resin 2 was greater than 20 mgKOH / g and the acid values ​​of Resin 2 and Resin 1 were similar, the evaluations of chargeability and material dispersibility were inferior to the other Examples. In Example 28, where the acid value of Resin 3 was less than 2 mgKOH / g, the evaluations of chargeability and material dispersibility were inferior to the other Examples. In Example 29, where the acid value of Resin 3 was greater than 7 mgKOH, the evaluations of hygroscopicity and coagulation were inferior to the other Examples.

[0110] Table 10 shows examples and comparative examples in which the blending ratios of resins 1 to 3 were changed. As is clear from these evaluation results, the toners of Examples 30 to 37, in which the toner particles contained resins 1 to 3 as the three types of polyester resin, had excellent chargeability in a high-temperature, high-humidity environment and were able to suppress fogging.

[0111] In contrast, Comparative Examples 5 to 7, which did not contain any of Resins 1 to 3, were inferior to the Examples in the evaluation of fogging in a high-temperature, high-humidity environment.

[0112] Among the Examples shown in Table 10, Examples 31 to 33, and 36, in which the content of Resin 1 was 35% to 50% by mass, the content of Resin 2 was 5% to 30% by mass, and the content of Resin 3 was 35% to 50% by mass, were found to be superior in the evaluation of fogging in a high-temperature, high-humidity environment. Among the Examples that did not satisfy these content conditions, Example 30, in which the content of Resin 3 exceeded the upper limit of the range, had a large effect of Resin 3; Examples 34 and 35, in which the content of Resin 3 was below the lower limit of the range, had a large effect of Resin 1; and Example 37, in which the content of Resin 2 was below the lower limit of the range, exhibited poor mixing during kneading.

[0113] Table 11 shows examples and comparative examples in which the conditions for the strontium titanate fine powder used as an external additive were varied while the conditions for Resins 1 to 3 were kept constant. As is clear from these evaluation results, the toners of Examples 38 to 44, which contained, as an external additive, fine powder in which silica was added to strontium titanate and the surface of the core was hydrophobized with a silane compound, were able to suppress fogging in high-temperature, high-humidity environments and were excellent in image density in low-temperature, low-humidity environments.

[0114] In contrast, Comparative Examples 8 and 9, which did not satisfy these requirements, were inferior to the Examples in the evaluation of fog in a high-temperature, high-humidity environment or the evaluation of image density in a low-temperature, low-humidity environment.

[0115] Among the examples shown in Table 11, Examples 38 to 40, and 43, in which the coverage of toner particles by fine powder is 3% or more and 10% or less and the adhesion strength of fine powder to toner particles is 50% or more, are superior in the evaluation of fogging in a high-temperature, high-humidity environment and the evaluation of image density in a low-temperature, low-humidity environment.

[0116] In the disclosed embodiment, the coverage of the toner particles with the hydrophobic silica particles is 82%.

[0117] The toner of the disclosed embodiment contains, as external additives, a fine powder of silica-modified strontium titanate and hydrophobic silica particles (small hydrophobic silica particles) with an average particle size of 7 nm to 15 nm. Second hydrophobic silica particles (large hydrophobic silica particles) with an average particle size of 30 nm to 70 nm may also be added. In this case, it is preferable that the coverage of the toner particles with the second hydrophobic silica particles is less than 20%. By adding the second hydrophobic silica particles so that the coverage is within this range, poor charging can be suppressed, and the effects of the present disclosure, such as charging performance and suppression of fogging in high-temperature, high-humidity environments, can be more easily achieved.

[0118] The embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present disclosure should not be interpreted solely by the above-described embodiments, but should be defined based on the claims. Furthermore, all modifications within the scope and meaning equivalent to the claims are included. [Explanation of symbols]

[0119] T Toner 1. Fine powder of strontium titanate modified with silica 2. Hydrophobic silica particles 3. Binder resin 4. Release agent 5. Coloring Agents

Claims

1. A toner having an external additive attached to the surface of a toner particle, the toner particles include three polyester resins, a colorant, and a release agent; When the three polyester resins are designated as first to third polyester resins in descending order of acid value, the difference in acid value between the first polyester resin and the third polyester resin is, in absolute value, 20 mgKOH / g or more and 30 mgKOH / g or less; Solubility parameters for the three polyester resins (unit: (MPa) １／２ ) the difference between the maximum and minimum values ​​is 0.5 or more and 1.0 or less in absolute value, The external additive includes fine powder of strontium titanate, the surface of which is hydrophobized with a silane compound, and hydrophobic silica particles; the hydrophobic silica particles have an average particle size of 7 nm or more and 15 nm or less; The toner is characterized in that the fine powder has an average particle size larger than that of the hydrophobic silica particles.

2. 2. The toner according to claim 1, the acid value of the first polyester resin is 25 mgKOH / g or more and 35 mgKOH / g or less; the acid value of the second polyester resin is 10 mgKOH / g or more and 20 mgKOH / g or less; The toner is characterized in that the acid value of the third polyester resin is 2 mgKOH / g or more and 7 mgKOH / g or less.

3. 3. The toner according to claim 1 or claim 2, In the toner particles, the content of the first polyester resin is 35% by mass or more and 50% by mass or less, the content of the second polyester resin is 5% by mass or more and 30% by mass or less, The toner is characterized in that the content of the third polyester resin is 35% by mass or more and 50% by mass or less.

4. 3. The toner according to claim 1 or claim 2, a coverage of the toner particles with the fine powder is 3% or more and 10% or less; The toner is characterized in that the adhesion strength of the fine powder to the toner particles is 50% or more.

5. The toner according to claim 1 or claim 2, The toner is characterized in that the coverage of the toner particles with the hydrophobic silica particles is 70% or more and 100% or less.

6. The toner according to claim 1 or claim 2, the content of the colorant in the toner particles is 5% by mass or more and 10% by mass or less, and the content of the release agent is 1% by mass or more and 5% by mass or less, The toner, wherein the toner particles do not contain a charge control agent or contain less than 1% by mass of a charge control agent.

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