JP2017151255A - Positively chargeable toner - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positively chargeable toner excellent in charging stability (particularly in positive charging property in a high-temperature and high-humidity environment) and capable of continuously suppressing occurrence of fogging for a long period of time to form an image of high picture quality even when the toner is used for continuous printing.SOLUTION: A positively chargeable toner comprises a plurality of toner particles including a toner base particle and an external additive. The external additive comprises a silica powder. A zeta potential of a dispersion liquid of the toner containing the toner by 0.2 mass%, measured at a pH of 5, is 3 mV or more. A zeta potential of a dispersion liquid of the silica powder containing the silica powder before subjected to a stress by 0.03 mass%, measured at a pH of 5, is 15 mV or more and 27 mV or less. A zeta potential of a dispersion liquid of the silica powder containing the silica powder after subjected to a stress by 0.03 mass%, measured at a pH of 5, is 28 mV or more.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a positively chargeable toner, and more particularly to a positively chargeable toner including a plurality of toner particles including an external additive.

  In the toner described in Patent Document 1, hydrophobized silica-alumina composite particles are used as an external additive in order to improve the fluidity and charging stability of the toner. In this toner, the zeta potential of the silica-alumina composite particles before being hydrophobized is from −42.0 mV to −28.0 mV.

JP 2012-123196 A

  The zeta potential (zeta potential) of the silica-alumina composite particles described in Patent Document 1 is low. When such silica-alumina composite particles are applied to a positively chargeable toner, the amount of positive charge of the toner becomes insufficient, and it is considered difficult to form a high-quality image over a long period of time.

  The present invention has been made in view of the above circumstances, has excellent charging stability (especially positive charging in a high-temperature and high-humidity environment), and even when used for continuous printing, the occurrence of fog continuously over a long period of time. An object of the present invention is to provide a positively chargeable toner capable of continuously forming a high-quality image while suppressing the above.

  The positively chargeable toner according to the present invention includes a plurality of toner particles including toner base particles and external additives. The external additive is attached to the surface of the toner base particles. The external additive includes silica powder. The zeta potential measured for the toner dispersion containing 0.2% by mass of the toner under the condition of pH 5 is 3 mV or more. The silica powder dispersion containing 0.03% by mass of the silica powder before being stressed has a zeta potential of 15 mV or more and 27 mV or less measured at pH 5 conditions. The zeta potential measured under a pH of 5 condition for the dispersion of the silica powder containing 0.03% by mass of the silica powder after being stressed is 28 mV or more. The stress application was performed by adding 15 parts by mass of zirconia beads having a diameter of 1 mm to 100 parts by mass of the silica powder dispersion containing 3% by mass of the silica powder, and obtaining an evaluation sample. The evaluation sample is mixed by a tumbler mixer for 30 minutes.

  According to the present invention, charging stability (particularly positive charging in a high-temperature and high-humidity environment) is excellent, and even when used for continuous printing, high-quality images can be produced by continuously suppressing the occurrence of fogging over a long period of time. It becomes possible to provide a positively chargeable toner that can continue to be formed.

It is a graph which shows the relationship between pH of the silica powder used with the positively chargeable toner which concerns on embodiment of this invention, and zeta potential.

  An embodiment of the present invention will be described. Note that the evaluation results (values indicating the shape or physical properties) of the powder (more specifically, the toner core, toner base particles, external additive, toner, etc.) are averaged from the powder unless otherwise specified. This is the number average of the values measured for each of the average particles by selecting a significant number of such particles.

The number average particle diameter of the powder is the number average value of the equivalent circle diameter of primary particles (diameter of a circle having the same area as the projected area of the particles) measured using a microscope unless otherwise specified. . Unless otherwise specified, the volume median diameter (D _v50 ) and the number median diameter (D _n50 ) of the powder are “Coulter Counter Multisizer 3” manufactured by Beckman Coulter, Inc. Is a value measured based on the Coulter principle (pore electrical resistance method). Moreover, the measured value of the volume average particle diameter (MV) of the powder is a laser diffraction / scattering type particle size distribution measuring device (“LA-750” manufactured by Horiba, Ltd.) unless otherwise specified. It is the value measured using. In addition, the measurement value of the circularity (= peripheral length of a circle equal to the projected area of the particle / peripheral length of the particle) is not specified, the flow particle image analyzer (“FPIA (registered trademark)” manufactured by Sysmex Corporation) ) -3000 ") is the number average of the values measured for a substantial number (eg 3000) of particles. The measured value of the BET specific surface area is a value measured by a general BET method (nitrogen adsorption method) unless otherwise specified. Moreover, each measured value of an acid value and a hydroxyl value is a value measured according to "JIS (Japanese Industrial Standard) K0070-1992" unless otherwise specified. Moreover, each measured value of a number average molecular weight (Mn) and a mass average molecular weight (Mw) is the value measured using the gel permeation chromatography, if not prescribed | regulated at all. The glass transition point (Tg) is measured in accordance with “JIS (Japanese Industrial Standard) K7121-2012” using a differential scanning calorimeter (“DSC-6220” manufactured by Seiko Instruments Inc.) unless otherwise specified. It is the value. In the endothermic curve (vertical axis: heat flow (DSC signal), horizontal axis: temperature) at the second temperature rise measured by the differential scanning calorimeter, the change point of the specific heat (outside the extrapolated line of the baseline and the falling line) The temperature (onset temperature) at the intersection with the insertion line corresponds to Tg (glass transition point). Moreover, the softening point (Tm) is a value measured using a Koka type flow tester (“CFT-500D” manufactured by Shimadzu Corporation) unless otherwise specified. In the S curve (horizontal axis: temperature, vertical axis: stroke) measured with the Koka type flow tester, the temperature that becomes "(baseline stroke value + maximum stroke value) / 2" is Tm (softening point). Equivalent to.

  The chargeability means the chargeability in frictional charging unless otherwise specified. The strength of positive chargeability (or strength of negative chargeability) in frictional charging can be confirmed by a known charge train or the like.

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

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

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

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

  The toner according to the exemplary embodiment is a positively chargeable toner having the following configuration (hereinafter referred to as a basic configuration).

(Basic toner configuration)
The positively chargeable toner includes a plurality of toner particles including toner base particles and an external additive. The external additive is attached to the surface of the toner base particles. The external additive includes silica powder. The toner dispersion containing 0.2% by mass of toner has a zeta potential (hereinafter referred to as zeta potential ζT) measured at pH 5 of 3 mV or more. A zeta potential (hereinafter referred to as zeta potential ζS ₁ ) measured at a pH of 5 for a dispersion of silica powder containing 0.03% by mass of silica powder before being stressed is 15 mV or more and 27 mV. It is as follows. A zeta potential (hereinafter referred to as zeta potential ζS ₂ ) measured at a pH of 5 for a dispersion of silica powder containing a stressed silica powder in a proportion of 0.03% by mass is 28 mV or more. is there. For applying stress to the silica powder, an evaluation sample was obtained by adding 15 parts by mass of zirconia beads having a diameter of 1 mm to 100 parts by mass of a dispersion of silica powder containing 3% by mass of silica powder. Thereafter, the evaluation sample is mixed for 30 minutes with a tumbler mixer. A toner dispersion liquid containing 0.2% by mass of toner can be prepared by mixing 99.8 g of a dispersion medium and 0.2 g of toner. The dispersion medium may contain a surfactant.

  In the toner having the above basic configuration, the zeta potential ζT is 3 mV or more. For this reason, the toner having the above basic configuration is easily positively charged and can be suitably used as a positively chargeable toner. In order to prevent the toner from being positively charged excessively, the zeta potential ζT is preferably 25 mV or less.

Further, in the above basic configuration, the zeta potential of the silica powder is higher after applying stress than before applying stress (ζS ₂ > ζS ₁ ). Specifically, the zeta potential ζS ₁ before applying stress is 15 mV or more and 27 mV or less, and the zeta potential ζS ₂ after applying stress is 28 mV or more.

The inventor has found that when the toner having the above-described basic configuration is used for continuous printing, it is possible to continuously form high-quality images while suppressing the occurrence of fog over a long period of time. If the zeta potential ζS ₁ is too low, the toner tends not to be sufficiently positively charged in a high temperature and high humidity environment. When the zeta potential ζS ₁ is too high, the charging stability of the toner is deteriorated, and when the toner in the developing device is stressed by continuous printing, the charging ability of the toner is likely to be lowered. When the toner in the developing device deteriorates due to stress and the charging ability of the toner decreases, the reversely charged toner is caused by friction between the deteriorated toner (toner having low charging ability) and the newly supplied toner in the developing device. This tends to cause fogging. If the zeta potential ζS ₂ is too low, when continuous printing is performed using toner, the charging ability of the toner in the developing device becomes insufficient and fog tends to occur. In order to prevent the toner from being positively charged excessively, the zeta potential ζS ₂ is preferably 35 mV or less.

In order for the toner to have the above basic configuration, the toner preferably has the following configuration (hereinafter referred to as a preferable configuration).
(Preferable configuration of toner)
The silica powder includes a plurality of silica particles (hereinafter referred to as positively charged silica particles) covered with a material having a positive chargeability stronger than silica (hereinafter referred to as positively charged material). Further, the surface of the positively charged silica particles is subjected to a hydrophobic treatment. The surface of the positively charged silica particles may be hydrophobized with one type of hydrophobizing agent, or may be hydrophobized with two or more types of hydrophobizing agents.

Silica (SiO ₂ ) has a relatively strong negative chargeability. In the positively chargeable toner, in order to use silica powder as an external additive, it is preferable to positively charge the silica particles. In order to improve the charging stability of the silica particles, it is preferable to treat the surface of the silica particles with a hydrophobizing agent (for example, a silane coupling agent). It is also conceivable to use a hydrophobizing agent having a strong positive charge for the surface treatment (hydrophobization treatment) of such silica particles. However, it is difficult in terms of cost or technology to obtain an external additive having excellent positive chargeability using such a hydrophobizing agent. When the surface of the silica particles is positively charged using such a hydrophobizing agent, the positively charged silica particles tend to be vulnerable to stress. Specifically, when stress is applied to the particles, the positive chargeability of the particles tends to be weakened. The reason for this is considered to be that the influence of the charging property (negative charging property) of the base (silica) becomes stronger by applying stress to the particles.

On the other hand, in the toner having the above-mentioned preferable configuration, a positively charged material (a material having positive chargeability stronger than silica) is used separately from the hydrophobizing agent. For this reason, it becomes easy to ensure sufficient positive chargeability on the surface of the silica particles, and it becomes easy to satisfy the requirements of the zeta potentials ζT and ζS ₂ defined in the basic configuration. Further, when the toner has the above-described preferable configuration, the zeta potential relationship “ζS ₂ > ζS ₁ ” defined in the basic configuration is easily satisfied. This is considered to be because the influence of the charging property (positive charging property) of the base (positive charging material) is strengthened by applying stress to the positively charged silica particles.

In the above preferred configuration, the BET specific surface area of the silica powder is preferably 110 m ² / g or more. When the BET specific surface area of the silica powder is too small, the zeta potential ζS ₁ and the zeta potential ζS ₂ tend to be substantially the same. If the zeta potential ζS ₁ and the zeta potential ζS ₂ are substantially the same, the effect of suppressing fog as described above cannot be obtained.

FIG. 1 shows the pH measured for an example of a silica powder defined in the above-mentioned preferred configuration (specifically, a silica powder having a BET specific surface area of 130 m ² / g including a plurality of hydrophobically treated positively charged silica particles). And the zeta potential. L1 in FIG. 1 indicates the characteristics of silica particles (silica substrate) that are neither positively charged nor hydrophobized. L2 in FIG. 1 indicates the characteristics of the silica powder before being stressed. L3 in FIG. 1 indicates the characteristics of the silica powder after being stressed.

From the graph of FIG. 1, it can be seen that the zeta potential ζS ₁ (pH 5) is 15 mV or more and 27 mV or less, and the zeta potential ζS ₂ (pH 5) is 28 mV or more.

  Further, it has been confirmed by the inventor that the toner easily has the above-described basic configuration when the number average primary particle diameter of the silica powder is 10 nm or more and 25 nm or less in the above preferable configuration.

  Preferable examples of the toner having the above basic configuration include toners having the following configurations (hereinafter referred to as “preferred examples”).

(Preferred example of toner)
The silica powder includes a plurality of silica particles covered with at least one of alumina (Al ₂ O ₃ ) and aluminum hydroxide (Al (OH) ₃ ). The total amount of alumina and aluminum hydroxide covering the silica particles (hereinafter referred to as Al coating amount) is 10% by mass or more and 25% by mass or less in terms of Al ₂ O _{3 with} respect to the mass of the silica particles. The success or failure of the requirement regarding the Al coating amount is that when the surface of the silica particles is covered with only one of alumina and aluminum hydroxide, the amount of the alumina or aluminum hydroxide is Al relative to the mass of the silica particles. It is judged based on whether it is 10% by mass or more and 25% by mass or less in terms of ₂ O ₃ .

In order to ensure sufficient positive chargeability on the surface of the silica particles, the positively charged silica particles have at least one of alumina (Al ₂ O ₃ ) and aluminum hydroxide (Al (OH) ₃ ) as a positively charged material. It is preferable to include. Further, in order to satisfy the requirements of the zeta potentials ζT, ζS ₁ , and ζS ₂ defined in the basic configuration described above, the coating amount of the positively charged material (Al coating amount) is within the above range (10 mass% or more and 25 It is preferable that it exists in the mass% or less.

  The toner particles contained in the toner may be toner particles not having a shell layer (hereinafter referred to as non-capsule toner particles) or toner particles having a shell layer (hereinafter referred to as capsule toner particles). There may be. However, in order to achieve both the heat resistant storage stability and the low-temperature fixability of the toner, the toner particles contained in the toner are preferably capsule toner particles. Hereinafter, embodiments in which the toner particles contained in the toner are capsule toner particles will be described.

  Toner particles (capsule toner particles) contained in the toner according to the present embodiment include a core (hereinafter referred to as a toner core) and a shell layer (capsule layer) that covers the surface of the toner core. The shell layer is substantially composed of a resin. The external additive adheres to the surface of the shell layer (or the surface area of the toner core not covered with the shell layer). The shell layer may cover the entire surface of the toner core or may partially cover the surface of the toner core. A plurality of shell layers may be laminated on the surface of the toner core. Hereinafter, the toner particles before the external additive adheres are referred to as toner mother particles. In non-capsule toner particles, a toner core in capsule toner particles described later can be used as toner base particles.

  In order to achieve both heat-resistant storage stability and low-temperature fixability of the toner, it is preferable that the shell layer covers an area of 50% to 99% of the surface area of the toner core, and 70% to 95%. It is more preferable to cover the area. In order to achieve both heat-resistant storage stability and low-temperature fixability of the toner, the maximum thickness of the shell layer is preferably 1 nm or more and 100 nm or less.

In order to achieve both the heat-resistant storage stability and the low-temperature fixability of the toner, the volume median diameter (D _v50 ) of the toner is preferably 1 μm or more and less than 10 μm.

  Next, a material for forming the toner core (hereinafter referred to as toner core material) and a material for forming the shell layer (hereinafter referred to as shell material) will be described. Resins suitable for forming toner particles are as follows.

<Preferable thermoplastic resin>
Examples of the thermoplastic resin constituting the toner particles (particularly, the toner core and the shell layer) include, for example, a styrene resin, an acrylic resin (more specifically, an acrylic ester polymer or a methacrylic ester polymer), Olefin resins (more specifically, polyethylene resins or polypropylene resins), vinyl chloride resins, polyvinyl alcohol, vinyl ether resins, N-vinyl resins, polyester resins, polyamide resins, or urethane resins can be suitably used. A copolymer of each of these resins, that is, a copolymer in which an arbitrary repeating unit is introduced into the resin (specifically, a styrene-acrylic acid resin or a styrene-butadiene resin) is also used as a toner. It can be suitably used as a thermoplastic resin constituting the particles.

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

  The styrene-acrylic acid resin is a copolymer of one or more styrene monomers and one or more acrylic monomers. In order to synthesize a styrene-acrylic acid resin, for example, a styrene monomer and an acrylic acid monomer as shown below can be suitably used. By using an acrylic acid monomer having a carboxyl group, a carboxyl group can be introduced into the styrene-acrylic acid resin. Further, by using a monomer having a hydroxyl group (more specifically, p-hydroxystyrene, m-hydroxystyrene, (meth) acrylic acid hydroxyalkyl ester, or the like), the hydroxyl group can be introduced into the styrene-acrylic acid resin. .

  Preferable examples of the styrene monomer include styrene, alkyl styrene (more specifically, α-methyl styrene, p-ethyl styrene, 4-tert-butyl styrene, etc.), p-hydroxy styrene, m-hydroxy styrene. , Vinyl toluene, α-chlorostyrene, o-chlorostyrene, m-chlorostyrene, or p-chlorostyrene.

  Preferable examples of the acrylic acid monomer include (meth) acrylic acid, (meth) acrylic acid alkyl ester, or (meth) acrylic acid hydroxyalkyl ester. Suitable examples of the (meth) acrylic acid alkyl ester include methyl (meth) acrylate, ethyl (meth) acrylate, n-propyl (meth) acrylate, iso-propyl (meth) acrylate, and (meth) acrylic. Examples include n-butyl acid, iso-butyl (meth) acrylate, or 2-ethylhexyl (meth) acrylate. Suitable examples of the (meth) acrylic acid hydroxyalkyl ester include 2-hydroxyethyl (meth) acrylate, 3-hydroxypropyl (meth) acrylate, 2-hydroxypropyl (meth) acrylate, or (meth) acrylic. The acid 4-hydroxybutyl is mentioned.

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

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

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

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

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

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

  Hereinafter, the toner core (binder resin and internal additive), shell layer, and external additive will be described in order. Depending on the use of the toner, unnecessary components (for example, internal additives) may be omitted.

[Toner core]
(Binder resin)
In the toner core, the binder resin generally occupies most of the components (for example, 85% by mass or more). For this reason, it is considered that the properties of the binder resin greatly affect the properties of the entire toner core. By using a combination of a plurality of types of resins as the binder resin, the properties of the binder resin (more specifically, the hydroxyl value, acid value, Tg, Tm, etc.) can be adjusted. For example, when the binder resin has an ester group, a hydroxyl group, an ether group, an acid group, or a methyl group, the toner core tends to become anionic, and the binder resin has an amino group or an amide group. The toner core tends to become cationic. In order to enhance the binding property (reactivity) between the toner core and the shell layer, it is preferable that at least one of the hydroxyl value and the acid value of the binder resin is 10 mgKOH / g or more.

  The binder resin is preferably a resin having one or more groups selected from the group consisting of ester groups, hydroxyl groups, ether groups, acid groups, and methyl groups. The binder resin having such a functional group easily reacts with the shell material and is chemically bonded. When such a chemical bond occurs, the bond between the toner core and the shell layer becomes strong. Further, as the binder resin, a resin having a functional group containing active hydrogen in the molecule is also preferable.

  In order to improve toner fixability during high-speed fixing, the glass transition point (Tg) of the binder resin is preferably 20 ° C. or higher and 55 ° C. or lower. In order to improve the fixability of the toner during high-speed fixing, the softening point (Tm) of the binder resin is more preferably 100 ° C. or lower. The Tg and / or Tm of the resin can be adjusted by changing the type or amount of the resin component (monomer).

  In order to improve the low-temperature fixability of the toner, the toner core preferably contains a thermoplastic resin (more specifically, the above-described suitable thermoplastic resin) as the binder resin. More preferably, the thermoplastic resin is contained in a proportion of 85% by mass or more. In order to improve the dispersibility of the colorant in the toner core, the chargeability of the toner, and the fixability of the toner to the recording medium, it is preferable to use a styrene-acrylic resin or a polyester resin as the binder resin. In order to obtain a toner having excellent low-temperature fixability, 80% by mass or more of the resin contained in the toner core is preferably a polyester resin or a styrene-acrylic acid resin, and 90% by mass or more of the resin. A polyester resin or a styrene-acrylic acid resin is more preferable, and 100% by mass of the resin is more preferably a polyester resin or a styrene-acrylic acid resin.

  When a polyester resin is used as the binder resin for the toner core, the number average molecular weight (Mn) of the polyester resin is preferably 1000 or more and 2000 or less in order to improve the strength of the toner core and the toner fixing property. The molecular weight distribution of the polyester resin (the ratio Mw / Mn of the mass average molecular weight (Mw) to the number average molecular weight (Mn)) is preferably 9 or more and 21 or less.

  When a styrene-acrylic acid resin is used as the binder resin for the toner core, the number average molecular weight (Mn) of the styrene-acrylic acid resin is 2000 or more and 3000 or less in order to improve the strength of the toner core and the toner fixing property. It is preferable that The molecular weight distribution (the ratio Mw / Mn of the mass average molecular weight (Mw) to the number average molecular weight (Mn)) of the styrene-acrylic acid resin is preferably 10 or more and 20 or less.

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

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

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

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

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

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

(Release agent)
The toner core may contain a release agent. The release agent is used, for example, for the purpose of improving the fixing property or offset resistance of the toner. In order to increase the anionicity of the toner core, it is preferable to produce the toner core using an anionic wax. In order to improve the fixing property or offset resistance of the toner, the amount of the release agent is preferably 1 part by mass or more and 30 parts by mass or less with respect to 100 parts by mass of the binder resin.

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

  In order to improve the compatibility between the binder resin and the release agent, a compatibilizer may be added to the toner core.

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

  By adding a negatively chargeable charge control agent (more specifically, an organometallic complex or a chelate compound) to the toner core, the anionicity of the toner core can be enhanced. Further, by adding a positively chargeable charge control agent (more specifically, pyridine, nigrosine, quaternary ammonium salt, or the like) to the toner core, the toner core can be made more cationic. However, if sufficient chargeability is ensured in the toner, it is not necessary to include a charge control agent in the toner core.

(Magnetic powder)
The toner core may contain magnetic powder. Examples of magnetic powder materials include ferromagnetic metals (more specifically, iron, cobalt, nickel, or alloys containing one or more of these metals), ferromagnetic metal oxides (more specifically, Ferrite, magnetite, chromium dioxide, or the like) or a material subjected to ferromagnetization treatment (more specifically, a carbon material or the like imparted with ferromagnetism by heat treatment) can be suitably used. One type of magnetic powder may be used alone, or a plurality of types of magnetic powder may be used in combination.

  In order to suppress elution of metal ions (for example, iron ions) from the magnetic powder, it is preferable to surface-treat the magnetic powder. When a shell layer is formed on the surface of the toner core under acidic conditions, if the metal ions are eluted on the surface of the toner core, the toner cores are easily fixed to each other. It is considered that fixing of the toner cores can be suppressed by suppressing elution of metal ions from the magnetic powder.

[Shell layer]
The shell layer may be a film without graininess or a film with graininess. When resin particles are used as a material for forming the shell layer, if the material (resin particles) is completely melted and cured in a film-like form, it is considered that a film without graininess is formed as the shell layer. It is done. On the other hand, if the material (resin particles) is not completely melted and cured in a film form, a film having a form in which the resin particles are two-dimensionally connected (a film having a granular feeling) is formed as a shell layer. it is conceivable that.

  The shell layer may consist essentially of a thermosetting resin, may consist essentially of a thermoplastic resin, or may contain both a thermosetting resin and a thermoplastic resin. Good. However, in order to improve the low-temperature fixability of the toner, the shell layer preferably contains the above-mentioned suitable thermoplastic resin, and the shell layer is substantially composed of an acrylic resin or a copolymer thereof. It is particularly preferred.

  In order to improve the charging stability of the toner, the shell layer preferably contains a chargeable resin (a resin containing a charge control agent). In order to contain the charge control agent in the shell layer, a repeating unit derived from the charge control agent may be incorporated in the resin constituting the shell layer, or charged particles may be dispersed in the resin constituting the shell layer. Good. However, in order to obtain a toner having excellent chargeability, heat-resistant storage stability, and low-temperature fixability, a thermoplastic resin (more specifically, a shell layer incorporating a repeating unit derived from a positively chargeable charge control agent (more specifically, , Preferably including the above-mentioned suitable thermoplastic resins), and a copolymer of a quaternary ammonium compound (eg, quaternary ammonium salt) monomer and an acrylic acid monomer (eg, acrylate monomer). It is particularly preferable to do this. Preferred examples of the positively chargeable charge control agent used for the synthesis of the chargeable resin are shown below. In addition, you may use the derivative | guide_body or salt of each compound shown below as needed.

  Examples of the positively chargeable charge control agent include pyridazine, pyrimidine, pyrazine, 1,2-oxazine, 1,3-oxazine, 1,4-oxazine, 1,2-thiazine, 1,3-thiazine, 1, 4-thiazine, 1,2,3-triazine, 1,2,4-triazine, 1,3,5-triazine, 1,2,4-oxadiazine, 1,3,4-oxadiazine, 1,2,6- Oxadiazine, 1,3,4-thiadiazine, 1,3,5-thiadiazine, 1,2,3,4-tetrazine, 1,2,4,5-tetrazine, 1,2,3,5-tetrazine, 1, Azine compounds such as 2,4,6-oxatriazine, 1,3,4,5-oxatriazine, phthalazine, quinazoline or quinoxaline; Azin Fast Red FC, Azin Fast Red 12BK, A Direct dyes such as Nioviolet BO, Azin Brown 3G, Azin Light Brown GR, Azin Dark Green BH / C, Azin Dep Black EW, or Azin Dee Black 3RL; Nigrosine (more specifically Nigrosine BK, Acid dyes such as nigrosine NB or nigrosine Z); metal salts of naphthenic acid or higher organic carboxylic acids; alkoxylated amines; alkylamides; benzyldecylhexylmethylammonium chloride, decyltrimethylammonium chloride, or 2- (methacryloyloxy) ) A quaternary ammonium salt such as ethyltrimethylammonium chloride can be preferably used.

[External additive]
The toner particles contained in the toner according to the present embodiment are silica powder that satisfies the requirements of the zeta potentials ζS ₁ and ζS ₂ defined in the basic configuration described above (hereinafter referred to as silica powder according to the present embodiment). Is provided as an external additive. For example, the toner base particles (powder) and the external additive (powder) are agitated together, and the external additive (specifically, a plurality of external additive particles is applied to the surface of the toner base particle by physical force. Adhering (physical bonding). In order to improve the fluidity or handleability of the toner, the amount of the external additive is preferably 0.3 parts by mass or more and 10 parts by mass or less with respect to 100 parts by mass of the toner base particles.

In the above-described preferred configuration, the positively charged material (material having positive chargeability stronger than that of silica) covering the silica particles is preferably a metal oxide and / or metal hydroxide, and alumina (Al ₂ O ₃ ) And / or aluminum hydroxide (Al (OH) ₃ ) is particularly preferred.

In the above preferred configuration, the hydrophobizing agent for hydrophobizing the surface of the positively charged silica particles includes silicone oil (more specifically, dimethyl silicone oil), silazane compound, and silane compound (more Specifically, one or more hydrophobizing agents selected from the group consisting of methyltrimethoxysilane and the like are preferable. In order to suppress charging failure of the toner, the surface of the positively charged silica particles is preferably subjected to a hydrophobic treatment with a silane compound having an alkyl group having 8 or more carbon atoms or a silane compound having an amino group. Both silane compounds having 8 or more alkyl groups (more specifically, n-octyltriethoxysilane and the like) and silane compounds having amino groups (more specifically, 3-aminopropyltriethoxysilane and the like). More preferably, the surface of the positively charged silica particles is hydrophobized. When the surface of the positively charged silica particles is hydrophobized with an alkylsilane having a large number of carbon atoms, the positive chargeability of the silica particles tends to decrease. When the positive charging property of the silica particles is lowered, the zeta potential ζS ₁ is lowered, and the charging failure of the toner tends to be suppressed. In addition, you may remove the hydroxyl group (-OH) on the surface of a silica particle by heat-processing the surface of a silica particle.

[Toner Production Method]
Hereinafter, an example of a method for producing the toner according to the exemplary embodiment having the above configuration will be described.

(Preparation of toner core)
In order to easily obtain a suitable toner core, it is preferable to produce the toner core by an aggregation method or a pulverization method.

  Hereinafter, an example of the pulverization method will be described. First, a binder resin and an internal additive (for example, at least one of a colorant, a release agent, a charge control agent, and magnetic powder) are mixed. Subsequently, the obtained mixture is melt-kneaded. Subsequently, the obtained melt-kneaded product is pulverized and classified. As a result, a toner core having a desired particle size can be obtained.

  Hereinafter, an example of the aggregation method will be described. First, these particles are agglomerated in an aqueous medium containing fine particles of a binder resin, a release agent, and a colorant until a desired particle diameter is obtained. Thereby, aggregated particles containing the binder resin, the release agent, and the colorant are formed. Subsequently, the obtained aggregated particles are heated to unite the components contained in the aggregated particles. As a result, a toner core dispersion is obtained. Thereafter, an unnecessary substance (such as a surfactant) is removed from the dispersion liquid of the toner core to obtain the toner core.

(Formation of shell layer)
First, an aqueous medium (for example, ion exchange water) is prepared. In order to suppress dissolution or elution of the toner core components (particularly the binder resin and the release agent) during the formation of the shell layer, it is preferable to form the shell layer in an aqueous medium. The aqueous medium is a medium containing water as a main component (more specifically, pure water or a mixed liquid of water and a polar medium). The aqueous medium may function as a solvent. A solute may be dissolved in the aqueous medium. The aqueous medium may function as a dispersion medium. The dispersoid may be dispersed in the aqueous medium. As a polar medium in the aqueous medium, for example, alcohol (more specifically, methanol or ethanol) can be used.

  Subsequently, the pH of the aqueous medium is adjusted to a predetermined pH (for example, a pH selected from 3.5 to 5.5) using hydrochloric acid, for example. Subsequently, a toner core and a shell material (for example, a suspension of resin particles) are added to an aqueous medium (for example, an acidic aqueous medium) whose pH is adjusted.

  The shell material adheres to the surface of the toner core in the liquid. In order to uniformly adhere the shell material to the surface of the toner core, it is preferable to highly disperse the toner core in a liquid containing the shell material. In order to highly disperse the toner core in the liquid, a surfactant may be included in the liquid, or the liquid is stirred using a powerful stirring device (for example, “Hibis Disper Mix” manufactured by Primics Co., Ltd.). May be. When the toner core has an anionic property, aggregation of the toner core can be suppressed by using an anionic surfactant having the same polarity. As the surfactant, for example, sulfate ester salt, sulfonate salt, phosphate ester salt, or soap can be used.

  Subsequently, while stirring the liquid containing the toner core and shell material, the liquid temperature is set at a predetermined holding temperature (for example, a speed selected from 0.1 ° C./min to 3 ° C./min). The temperature is selected from 50 ° C to 85 ° C. Furthermore, the temperature of the liquid is maintained at the above holding temperature for a predetermined time (for example, a time selected from 30 minutes to 4 hours) while stirring the liquid. Thereafter, a dispersion of toner base particles is obtained by adding cold water to quench the liquid. While the liquid temperature is kept high, the shell material adheres to the surface of the toner core. The shell material also reacts with the toner core. In addition, it is considered that a film (resin layer) having a granular feeling is formed by two-dimensionally connecting the resin particles on the surface of the toner core.

(Washing process)
The obtained toner base particles may be washed. As a method for cleaning the toner base particles, for example, the dispersion containing the toner base particles is solid-liquid separated to collect the wet cake-like toner base particles, and the collected wet cake-like toner base particles are washed with water. Is preferred. As a method for cleaning the toner base particles, a method is preferred in which the toner base particles in the dispersion containing the toner base particles are settled, the supernatant liquid is replaced with water, and the toner base particles are redispersed in water after the replacement.

(Drying process)
After the cleaning step, the toner base particles may be dried. For example, the toner base particles can be dried using a dryer (more specifically, a spray dryer, a fluidized bed dryer, a vacuum freeze dryer, a vacuum dryer, or the like). In order to suppress aggregation of the toner base particles during drying, it is preferable to dry the toner base particles using a spray dryer. In the case of using a spray dryer, for example, by spraying a dispersion liquid in which an external additive is dispersed onto the toner base particles, the drying step and the external addition step described later can be performed simultaneously.

(External addition process)
An external additive is adhered to the surface of the toner base particles obtained as described above. As the external additive, only the silica powder according to this embodiment may be used, or another external additive (for example, titanium oxide powder) is used together with the silica powder according to this embodiment. Also good. By using a mixer, the toner base particles and the external additive are mixed under conditions that prevent the external additive from being embedded in the toner base particles, thereby allowing the external additive to adhere to the surface of the toner base particles. .

  The contents and order of the toner manufacturing method can be arbitrarily changed according to the required configuration or characteristics of the toner. For example, when reacting a material (for example, a shell material) in a liquid, the material may be reacted in the liquid for a predetermined time after the material is added to the liquid, or the material is added to the liquid over a long period of time. Then, the material may be reacted in the liquid while adding the material to the liquid. Further, the shell material may be added to the liquid at once, or may be added to the liquid in a plurality of times. The toner may be sieved after the external addition step. Further, unnecessary steps may be omitted. For example, when a commercially available product can be used as a material as it is, the step of preparing the material can be omitted by using a commercially available product. Moreover, even if it does not adjust pH of a liquid, when reaction for forming a shell layer advances favorably, you may omit a pH adjustment process. The toner core material and the shell material are not limited to the above-described compounds (such as various monomers for synthesizing the resin). For example, if necessary, a derivative of the aforementioned compound may be used as the toner core material or shell material, or a prepolymer may be used instead of the monomer. Further, in order to obtain the above-mentioned compound, a salt, ester, hydrate, or anhydride of the compound may be used as a raw material. In order to produce the toner efficiently, it is preferable to form a large number of toner particles simultaneously.

  Examples of the present invention will be described. Table 1 shows toners TA-1 to TA-9, TB-1, and TB-2 (each positively chargeable toner) according to Examples or Comparative Examples.

  Hereinafter, a production method, an evaluation method, and an evaluation result of toners TA-1 to TA-9, TB-1, and TB-2 will be described in order. In the evaluation in which an error occurs, a considerable number of measurement values with sufficiently small errors are obtained, and the arithmetic average of the obtained measurement values is used as the evaluation value.

Toner (toners TA-1 to TA-9, TB-1, and TB-2), silica powder before being stressed (hereinafter sometimes simply referred to as silica powder), and stressing The zeta potentials ζT, ζS ₁ , and ζS ₂ were measured for each of the subsequent silica powder (hereinafter sometimes referred to as degraded silica powder). A method for applying stress to the silica powder and a method for measuring the zeta potential are described below.

<Method of applying stress>
3 parts by mass of silica powder is added to 97 parts by mass of a 10% by weight aqueous solution of a nonionic surfactant (“Emulgen (registered trademark) 120” manufactured by Kao Corporation, component: polyoxyethylene lauryl ether), and silica is added. A dispersion of silica powder containing 3% by mass of powder was prepared. Subsequently, 15 parts by mass of zirconia beads having a diameter of 1 mm were added to 100 parts by mass of the obtained dispersion of silica powder to obtain a sample for evaluation. Thereafter, the sample for evaluation was mixed for 30 minutes with a shaker mixer (“Turbler (registered trademark) mixer T2F” manufactured by Willy et Bacofen (WAB)) to give stress to the silica powder in the sample for evaluation. Thus, a deteriorated silica powder was obtained. Thereafter, the degraded silica powder was settled by centrifugation, and the supernatant was removed. Thereafter, the degraded silica powder was dried to obtain a dried degraded silica powder.

<Method for measuring zeta potential>
A predetermined amount of sample (0.2 g of toner, 0.03 g of silica powder or 0.03 g of deteriorated silica powder) and nonionic surfactant (“Emulgen 120” manufactured by Kao Corporation), components, in 98 g of ion-exchanged water : Polyoxyethylene lauryl ether) 2 g of an aqueous solution having a concentration of 10% by mass was added, and a sample (toner, silica powder, or deteriorated silica powder) was dispersed in the liquid. Subsequently, the pH of the obtained sample dispersion was adjusted to 5 to obtain a sample dispersion with adjusted pH. Then, the zeta potential of the sample was measured by electrophoresis (more specifically, laser Doppler electrophoresis) using the dispersion of the sample whose pH was adjusted as a measurement target. Specifically, the zeta potential of a sample (toner, silica powder, or deteriorated silica powder) in a dispersion at a temperature of 23 ° C. and a pH of 5 is measured using a laser Doppler zeta potential meter (“ELSZ-1000” manufactured by Otsuka Electronics Co., Ltd.). ).

[Preparation of materials]
(Preparation of resin dispersion A)
Number average molecular weight (Mn) 2800, mass average molecular weight (Mw) 7000, Mw / Mn (molecular weight distribution) 2.5, Tm (softening point) 94 ° C., Tg (glass transition point) 53 ° C., acid value 13.6 mgKOH / g, A polyester resin having an SP value of 9.8 was prepared. 1000 g of the prepared polyester resin was put into a container of a mixing apparatus (“TK Hibis Disper Mix HM-3D-5” manufactured by PRIMIX Corporation) equipped with a temperature control jacket, and the temperature was 120 ° C. The container contents were melted and kneaded. Subsequently, 80 g of triethanolamine, 20 g of an anionic surfactant (“Emar (registered trademark) 0” manufactured by Kao Corporation, component: sodium lauryl sulfate) and 60 g of ion-exchanged water were added to the container, The contents of the container were mixed for 15 minutes at a Lee rotation speed of 50 rpm. Subsequently, 2870 g of ion-exchanged water having a temperature of 98 ° C. was charged into the container at a rate of 50 g / min to obtain a resin dispersion A containing polyester resin particles. The number average particle diameter of the resin particles contained in the obtained resin dispersion A was 95 nm.

(Preparation of release agent dispersion)
200 g of ester wax (“Nissan Electol (registered trademark) WEP-3” manufactured by NOF Corporation, melting temperature: 73 ° C.) and an anionic surfactant (“Emar 0” manufactured by Kao Corporation, component: sodium lauryl sulfate) 1 g and 800 g of ion-exchanged water were mixed. Subsequently, the obtained mixed solution was heated to 100 ° C. to melt the wax in the mixed solution. Subsequently, the liquid containing the wax was emulsified for 5 minutes using a homogenizer (“Ultra Tarrax T50” manufactured by IKA), and then a gorin type homogenizer (“APV homogenizer 15M-8TA manufactured by SPX). Type | mold)), the emulsification process was performed at the temperature of 70 degreeC, and the dispersion liquid (release agent dispersion liquid) of the release agent particle | grain was obtained. With respect to the obtained release agent dispersion, the solid content concentration was 20% by mass, and the volume average particle size (MV) was 0.15 μm.

(Preparation of colorant dispersion)
20 g of an anionic surfactant (“Emar 0” manufactured by Kao Corporation, component: sodium lauryl sulfate) was dissolved in 410 g of ion exchange water to obtain an aqueous solution of a surfactant. Subsequently, 70 g of a cyan colorant (“CTBX121” manufactured by DIC Corporation, component: copper phthalocyanine) was gradually added to the obtained aqueous solution. After completion of the addition, the liquid containing the colorant was subjected to an emulsification treatment for 5 minutes using a homogenizer (“Ultra Tarrax T50” manufactured by IKA), and then a gorin type homogenizer (“APV homogenizer 15M manufactured by SPX). -8TA type ") was emulsified at a temperature of 100 ° C to obtain a dispersion of colorant particles. With respect to the obtained dispersion of colorant particles, the solid content concentration was 14% by mass, and the volume average particle size (MV) was 0.19 μm.

(Preparation of resin dispersion B)
In a 2 L flask equipped with a thermometer (thermocouple), nitrogen inlet tube, stirrer, and condenser (heat exchanger), 250 g of solvent (isobutanol), 45 g of 2- (diethylamino) ethyl methacrylate, 45 g of methyl p-toluenesulfonate was added. Subsequently, the contents of the flask were reacted for 1 hour (quaternization reaction) at a temperature of 80 ° C. in a nitrogen atmosphere. Subsequently, while flowing nitrogen gas into the flask, 156 g of styrene, 72 g of butyl acrylate, 12 g of a peroxide polymerization initiator (t-butylperoxy-2-ethylhexanoate: manufactured by Arkema Yoshitomi Co., Ltd.) Was further added to the flask. Subsequently, the flask contents were heated to 95 ° C. (polymerization temperature) and stirred for 3 hours. Thereafter, 12 g of a peroxide polymerization initiator (t-butylperoxy-2-ethylhexanoate: Arkema Yoshitomi Co., Ltd.) was further added to the flask, and the flask contents were stirred for 3 hours. Subsequently, the contents of the flask were dried under a high temperature (140 ° C.) and reduced pressure (10 kPa) environment to remove the solvent. Subsequently, the contents of the flask were crushed to obtain a coarsely pulverized product.

  Subsequently, the coarsely pulverized product was further pulverized using a mechanical pulverizer (“Turbomill T250” manufactured by Freund Turbo, Inc.) under the condition of a set particle diameter of 10 μm to obtain a finely pulverized product. Subsequently, 100 g of the finely pulverized product obtained, 1 g of a cationic surfactant (“Cotamine (registered trademark) 24P” manufactured by Kao Corporation, 25% by mass aqueous solution of lauryltrimethylammonium chloride), and 0.1N sodium hydroxide aqueous solution 25 g was mixed to obtain a dispersion. Subsequently, ion-exchanged water was added to the obtained dispersion to prepare a slurry having a total amount of 400 g.

  Subsequently, the obtained slurry was put into a stainless steel pressure-resistant round bottom container. Subsequently, using a high-speed shearing emulsifier (“CLEAMIX (registered trademark) CLM-2.2S” manufactured by M Technique Co., Ltd.), the rotor rotation speed is high temperature (140 ° C.) and high pressure (0.5 MPa). The slurry was sheared and dispersed for 30 minutes under the condition of 20000 rpm. Thereafter, while cooling the slurry at a rate of 5 ° C./min, the slurry was continuously stirred at a rotor rotational speed of 15000 rpm until the temperature in the container reached 50 ° C.

  Subsequently, the obtained slurry at 50 ° C. was put into a 2 L flask, and a mixed liquid (25 g of methyl methacrylate, 25 g of butyl acrylate, 0.2 g of octyl thioglycolate and Coatamine 24P (Kao Corporation) was placed in the flask. (Manufactured) Ion-exchanged water was added to a mixed solution with 1 g to give a total amount of 100 g), which was dropped over 30 minutes. Subsequently, the flask contents were heated to 95 ° C. The flask contents were stirred at a temperature of 95 ° C. for 2 hours and then cooled to obtain a resin particle dispersion (resin dispersion B). With respect to the obtained resin dispersion B, the solid content concentration was 29.8% by mass, and the volume average particle size (MV) was 0.12 μm.

(Preparation of silica powder A)
Silica powder (“Leoro Seal (registered trademark) QS-10” manufactured by Tokuyama Corporation, fumed silica) was repulped with pure water and then heated to adjust the temperature to 40 ° C. Subsequently, while stirring the silica powder at a temperature of 40 ° C., 20% by mass of polyaluminum chloride in terms of alumina (Al ₂ O ₃ ) was added to the silica powder with respect to the mass of the silica powder. Thereafter, the silica powder was stirred for 30 minutes. Subsequently, an aqueous sodium hydroxide solution having a concentration of 200 g / L was added to the silica powder to adjust the pH of the silica powder to 5. Thereafter, the silica powder was stirred for 1 hour. Subsequently, an aqueous sodium hydroxide solution having a concentration of 200 g / L was added to the silica powder to adjust the pH of the silica powder to 7. Subsequently, a dried silica powder was obtained through a washing step (water washing and filtration) and a drying step (temperature 130 ° C., 12 hours) using a dryer. Subsequently, the dried silica powder was baked at a temperature of 600 ° C. in an air atmosphere for 1 hour. As a result, a silica powder containing many silica particles coated with aluminum hydroxide (Al (OH) ₃ ) (hereinafter referred to as coated silica powder) was obtained.

  Subsequently, while stirring the obtained coated silica powder using a small porcelain bowl type crusher (“Ishikawa-type stirring crusher No. 22” manufactured by Ishikawa Factory Co., Ltd.), the mass of the coated silica powder is adjusted. On the other hand, 15 mass% of the first silane coupling agent (3-aminopropyltriethoxysilane) was added to the coated silica powder. Then, the coated silica powder was stirred for 30 minutes using a crusher (Ishikawa-type stirring crusher No. 22). Subsequently, while stirring the coated silica powder using a crusher (Ishikawa-type stirring crusher 22), the mass of the coated silica powder (the mass before applying the first silane coupling agent) 10% by mass of a second silane coupling agent (n-octyltriethoxysilane) was added to the coated silica powder. Then, the coated silica powder was stirred for 30 minutes using a crusher (Ishikawa-type stirring crusher No. 22). Subsequently, the coated silica powder provided with the first and second silane coupling agents was subjected to heat treatment at a temperature of 90 ° C. for 48 hours using a dryer. Thereafter, the heat-treated coated silica powder was crushed. As a result, a coated silica powder (silica powder A) that was hydrophobized was obtained.

(Preparation of silica powder B)
The method for producing silica powder B was the same as the method for producing silica powder A, except that the amount of polyaluminum chloride added was changed from 20% by mass to 25% by mass.

(Preparation of silica powder C)
The production method of the silica powder C was the same as the production method of the silica powder A except that the addition amount of polyaluminum chloride was changed from 20% by mass to 10% by mass.

(Preparation of silica powder D)
The production method of the silica powder D was the same as the production method of the silica powder A except that the firing temperature of the coated silica powder was changed from 600 ° C. to 300 ° C.

(Preparation of silica powder E)
The method for producing silica powder E uses n-butyltriethoxysilane (addition amount: 10% by mass) instead of n-octyltriethoxysilane (addition amount: 10% by mass) as the second silane coupling agent. Except for the above, it was the same as the method for preparing the silica powder A.

(Preparation of silica powder F)
The production method of the silica powder F was the same as the production method of the silica powder A except that the addition amount of n-octyltriethoxysilane was changed from 10% by mass to 25% by mass.

(Preparation of silica powder G)
The method for producing the silica powder G was the same as the method for producing the silica powder A, except that the amount of polyaluminum chloride added was changed from 20% by mass to 9% by mass.

(Preparation of silica powder H)
The method for producing silica powder H was the same as the method for producing silica powder E, except that the amount of n-butyltriethoxysilane added was changed from 10% by mass to 5% by mass.

(Preparation of silica powder I)
The production method of the silica powder I was the same as the production method of the silica powder A except that the amount of n-octyltriethoxysilane added was changed from 10% by mass to 30% by mass.

The BET specific surface area of each of the silica powders A to I was 110 m ² / g or more and 150 m ² / g or less. The number average primary particle diameter of each of the silica powders A to I was 10 nm or more and 25 nm or less.

[Production of Toners TA-1 to TA-9]
(Production of toner core)
Toner core material prepared in the above procedure (specifically, 320 g of resin dispersion A, 90 g of release agent dispersion, and 40 g of colorant dispersion) and an anionic surfactant (“Emar 0” manufactured by Kao Corporation) , Component: sodium lauryl sulfate) 50 g of a 25% by weight aqueous solution and 500 g of distilled water were put into a 2 L stainless round bottom flask. Subsequently, 1 g of 1N sodium hydroxide aqueous solution was added to the flask while stirring the flask contents, and the pH of the flask contents was adjusted to 8. Subsequently, the flask contents were stirred for 10 minutes under the conditions of a temperature of 25 ° C. and a rotation speed of 100 rpm.

Further, 39 g of magnesium chloride hexahydrate (flocculating agent) aqueous solution having a solid content concentration of 50% by mass was dropped into the flask over 5 minutes while stirring the contents of the flask. Subsequently, the contents of the flask were heated at a rate of 0.2 ° C./min to promote particle aggregation in the flask and granulate. The temperature increase was continued until the median diameter (D _n50 ) of the aggregated particles reached 4.5 μm. Specifically, the temperature increase was stopped at about 46 ° C.

  Subsequently, the rotation speed of stirring was increased from 100 rpm to 200 rpm, and the temperature was raised to 55 ° C. at a speed of 0.2 ° C./min while stirring the contents of the flask. Then, the contents of the flask were stirred at a temperature of 55 ° C. for 60 minutes to coalesce the aggregated particles in the flask. As a result, a toner core dispersion having a circularity of 0.953 was obtained.

(Formation of shell layer)
Subsequently, 2 g of a 2N hydrochloric acid aqueous solution was added to the flask containing the toner core dispersion to adjust the pH of the flask contents to 4.5. Subsequently, 160 g of a shell material (resin dispersion B) was placed in the flask, and the flask contents were stirred for 15 minutes (first stirring). Subsequently, 1N-aqueous sodium hydroxide solution was added to the flask to adjust the pH of the flask contents to 7. Subsequently, the flask contents were heated to 60 ° C. at a rate of 0.2 ° C./min. Subsequently, the contents of the flask are stirred at a temperature of 60 ° C. for 120 minutes (second stirring) to cause the shell material (resin particles) to adhere to the surface of the toner core and to form a shell layer on the surface of the toner core. It was. Thereafter, the flask contents were rapidly cooled to 25 ° C. at a rate of −10 ° C./min. As a result, a dispersion of toner base particles was obtained.

(Washing)
The dispersion of toner base particles obtained as described above was filtered (solid-liquid separation) using a Buchner funnel. As a result, toner base particles in the form of wet cake were obtained. Thereafter, the obtained wet cake-like toner base particles were redispersed in ion-exchanged water. Further, dispersion and filtration were repeated 5 times to wash the toner base particles.

(Dry)
Subsequently, the washed wet cake-like toner base particles were dried at a temperature of 35 ° C. for 48 hours. As a result, toner mother particles having a volume median diameter (D _v50 ) of 5.53 μm and a circularity of 0.959 were obtained.

(External)
After the drying, external addition was performed on the toner base particles. Specifically, it is shown in Table 1 determined for each of 100 parts by weight of toner base particles and silica powder (toners TA-1 to TA-9) using an FM mixer having a capacity of 10 L (manufactured by Nippon Coke Kogyo Co., Ltd.). Any one of the silica powders A to I) was mixed with 2 parts by mass for 5 minutes to adhere an external additive (silica powder) to the surface of the toner base particles. Thereafter, the obtained powder was sieved using a 300 mesh (aperture 48 μm) sieve. As a result, toners (toner TA-1 to TA-9) containing a large number of toner particles were obtained.

[Production of Toner TB-1]
The toner TB-1 is produced by changing the amount of shell material (resin dispersion B) added from 160 g to 400 g in the formation of the shell layer, changing the first stirring time from 15 minutes to 30 minutes, Except that the stirring time of No. 2 was changed from 120 minutes to 180 minutes, it was the same as the production method of the toner TA-1.

[Production of Toner TB-2]
The production method of the toner TB-2 was the same as the production method of the toner TB-1, except that in the formation of the shell layer, the amount of the shell material (resin dispersion B) was changed from 400 g to 80 g.

[Evaluation method]
The evaluation method of each sample (toners TA-1 to TA-9, TB-1, and TB-2) is as follows.

(Production of evaluation carrier)
2 L of water was added to 30 g of polyamideimide resin to prepare a resin solution. Subsequently, 120 g of tetrafluoroethylene-6 fluoropropylene copolymer (FEP) and 3 g of silicon oxide were dispersed in the obtained resin solution to obtain a carrier coat solution. Subsequently, 10 kg of a non-coated ferrite core (“EF-35B” manufactured by Powder Tech Co., Ltd., particle size: 35 μm) was coated with the carrier coating solution using a fluidized bed coating apparatus. Thereafter, the ferrite particles coated with the resin were fired at 250 ° C. for 1 hour. As a result, an evaluation carrier was obtained.

(Preparation of developer for evaluation)
A shaker mixer (“Turbler mixer T2F” manufactured by Willy et Bacofen (WAB)) in a state where 30 g of a sample (toner) and 300 g of an evaluation carrier prepared as described above are put in a polyethylene container. Was used for 30 minutes to prepare a developer for evaluation (two-component developer).

(Preparation of evaluation machine)
A color multifunction machine (“TASKalfa 5500ci” manufactured by Kyocera Document Solutions Inc.) was used as an evaluation machine. The evaluation developer prepared as described above was charged into the developing device of the evaluation machine, and the sample (replenishment toner) was charged into the toner container of the evaluation machine. In addition, for the purpose of color image output, a developer and replenishment toner of colors (magenta, yellow, and black) other than the sample are prepared and evaluated using “TASKalfa 5550ci” toner manufactured by Kyocera Document Solutions Co., Ltd. I put it in the machine.

(Fogging density)
In an environment with a temperature of 20 ° C. and a humidity of 65% RH (R / R environment), the above-mentioned evaluation machine is used to perform continuous color image output on 5000 sheets of paper (A4 size plain paper) at a printing rate of 2%. A printing test was conducted. Thereafter, using the evaluation machine, a pattern with a printing rate of 50% (a sample image including a solid portion and a blank portion) is continuously output as a color image on 1000 sheets of paper (evaluation paper) (hereinafter, continuous after a printing test). Described as color image output).

  In continuous color image output after the printing durability test, the reflection density of the blank portion of each evaluation sheet after printing was measured using a reflection densitometer (“SpectroEye (registered trademark)” manufactured by X-Rite), and the fog density The maximum value of (FD) (the highest fog density at 1000 sheets) was determined. The fog density (FD) corresponds to a value obtained by subtracting the reflection density of the base paper (unprinted paper) from the reflection density of the blank portion of the evaluation paper after printing.

The evaluation standard of fog density (FD) is as follows.
A (very good): The fog density (FD) was less than 0.006.
○ (Good): The fog density (FD) was 0.006 or more and less than 0.010.
X (Poor): The fog density (FD) was 0.010 or more.

(Charge amount)
After the developer for evaluation (two-component developer) was prepared by the above-described procedure, it was allowed to stand for 24 hours in a predetermined environment (R / R environment or H / H environment). The R / R environment was an environment having a temperature of 20 ° C. and a humidity of 65% RH. The H / H environment was an environment with a temperature of 32.5 ° C. and a humidity of 80% RH. Thereafter, the charge amount of the toner in the developer was measured.

  In the R / R environment (temperature 20 ° C. and humidity 65% RH), continuous color image output is performed on 100,000 sheets of paper (A4 size plain paper) at a printing rate of 5% using the evaluation machine. A printing durability test was performed. After the printing durability test, the charge amount of the toner in the developing device of the evaluation machine was measured.

The charge amount of the toner in the developer was measured by the following method using a Q / m meter (“MODEL 210HS-1” manufactured by Trek).
<Measurement method of charge amount of toner in developer>
0.10 g of developer (carrier and toner) was charged into a Q / m meter measurement cell, and only the toner out of the charged developer was sucked through a sieve (metal mesh) for 10 seconds. Then, based on the formula “total electric amount of sucked toner (unit: μC) / mass of sucked toner (unit: g)”, the charge amount of toner in the developer (unit: μC / g) is calculated. Calculated.

The evaluation criteria for the charge amount are as follows.
A (very good): The charge amount was 15 μC / g or more.
○ (Good): The charge amount was 10 μC / g or more and less than 15 μC / g.
X (Poor): Charge amount was less than 10 μC / g.

[Evaluation results]
Table 2 summarizes the evaluation results of each sample (toners TA-1 to TA-9, TB-1, and TB-2).

Toners TA-1 to TA-6 and TB-1 (toners according to Examples 1 to 7) each had the above-described basic configuration. Specifically, as shown in Table 1, the zeta potential ζT (the zeta potential measured under the condition of pH 5 for the toner dispersion containing 0.2% by mass of the toner) was 3 mV or more. Further, as shown in Table 1, zeta potential ζS ₁ (the zeta potential measured under the condition of pH 5 for the dispersion of silica powder containing 0.03% by mass of the silica powder before being stressed) ) Was 15 mV or more and 27 mV or less. Also, the zeta potential ζS ₂ (the zeta potential measured under the condition of pH 5 with respect to a dispersion of silica powder containing 0.03% by mass of the silica powder after being stressed) was 28 mV or more. Further, in the toners according to Examples 1 to 7, the Al coating amount was 10% by mass or more and 25% by mass or less in terms of Al ₂ O _{3 with} respect to the mass of the silica particles. Note that the zeta potential of the toner hardly changed even when the toner was stressed.

  As shown in Table 2, each of the toners according to Examples 1 to 7 was excellent in charging stability (particularly positive charging in a high temperature and high humidity environment). In addition, when the toners according to Examples 1 to 7 were used for continuous printing, it was possible to continuously suppress the generation of fog over a long period of time and continue to form high-quality images.

  The positively chargeable toner according to the present invention can be used to form an image in, for example, a copying machine, a printer, or a multifunction machine.

Claims (9)

A positively chargeable toner comprising a plurality of toner particles comprising toner mother particles and an external additive attached to the surface of the toner mother particles,
The external additive includes silica powder,
The zeta potential measured at pH 5 for the toner dispersion containing 0.2% by mass of the toner is 3 mV or more,
The zeta potential measured at a pH of 5 for the dispersion of the silica powder containing the silica powder at a ratio of 0.03% by mass before being stressed is 15 mV or more and 27 mV or less,
The zeta potential measured at a pH of 5 for the dispersion of the silica powder containing the silica powder at a rate of 0.03% by mass after being stressed is 28 mV or more,
The stress application was performed by adding 15 parts by mass of zirconia beads having a diameter of 1 mm to 100 parts by mass of the silica powder dispersion containing 3% by mass of the silica powder, and obtaining an evaluation sample. A positively chargeable toner obtained by mixing the evaluation sample with a tumbler mixer for 30 minutes. The silica powder includes a plurality of silica particles covered with a material having positive chargeability stronger than silica,
The positively chargeable toner according to claim 1, wherein the surface of the silica particles covered with the material having a positive chargeability stronger than that of the silica is subjected to a hydrophobic treatment.   The positively chargeable toner according to claim 2, wherein the material having a positive chargeability stronger than that of silica includes at least one of a metal oxide and a metal hydroxide. As the material having positive chargeability stronger than that of the silica, at least one of alumina and aluminum hydroxide is included,
The total amount of the alumina and the aluminum hydroxide covering the silica particles, the silica mass is in terms of Al ₂ O ₃ at 10 wt% to 25 wt% with respect to the particles, positive claim 2 or 3 Chargeable toner.   The positively chargeable toner according to claim 2, wherein the hydrophobizing treatment includes a hydrophobizing treatment with a silane compound having an alkyl group having 8 or more carbon atoms.   The positively chargeable toner according to claim 2, wherein the hydrophobic treatment includes a hydrophobic treatment with a silane compound having an amino group. The positively chargeable toner according to claim 2, wherein the silica powder has a BET specific surface area of 110 m ² / g or more.   The positively chargeable toner according to claim 2, wherein the silica powder has a number average primary particle diameter of 10 nm or more and 25 nm or less. The toner base particles include a core and a shell layer that covers a surface of the core,
The positively chargeable toner according to claim 1, wherein the shell layer contains a thermoplastic resin having a repeating unit derived from a positively chargeable charge control agent.

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