EP4675362A1

EP4675362A1 - Toner set

Info

Publication number: EP4675362A1
Application number: EP24763812.5A
Authority: EP
Inventors: Kohei Yamada
Original assignee: Zeon Corp
Current assignee: Zeon Corp
Priority date: 2023-02-28
Filing date: 2024-02-26
Publication date: 2026-01-07
Also published as: JPWO2024181332A1; CN120731403A; WO2024181332A1

Abstract

To provide a toner set with excellent higher-order color reproducibility. A toner set comprising positively-chargeable color toners of at least yellow, magenta and cyan, wherein the color toners include an ester wax as a release agent and a styrene-acrylic polymer containing a quaternary ammonium salt-containing (meth)acrylate monomer unit as a positively-chargeable charge control resin; wherein a value of X calculated by the following formula (1) where Fcm is a content of the styrene-acrylic polymer relative to 100 parts by mass of the binder resin; Xa is a copolymerization ratio of the quaternary ammonium salt-containing (meth)acrylate monomer; and Fp is a content of the colorant relative to 100 parts by mass of the binder resin, is more than 0.2 and less than 2.5; and wherein the following formula (2) where X(Y), X(M) and X(C) are the X values of the yellow, magenta and cyan toners, respectively, is satisfied:

X = \{Σ (Fcm \times Xa)\} / Fp

X (M) > X (C) > X (Y)

Description

Technical Field

The present disclosure relates to a toner set comprising a combination of toners for developing electrostatic images (hereinafter may be simply referred to as "toners") which are used to develop an electrostatic latent image in, for example, electrophotography, electrostatic recording, and electrostatic printing.

Background Art

In image forming devices such as an electrophotographic device, an electrostatic recording device and an electrostatic printing device, a method for forming a desired image by forming an electrostatic latent image on a photoconductor and developing the image with a toner for developing electrostatic images, is widely used. This method is applied to a copying machine, a printer, a facsimile machine, multifunctional printers thereof, and so on.
For example, in an electrophotographic device using electrophotography, generally, the surface of its photoconductor comprising a photoconductive material, is uniformly charged by various kinds of methods; by changing a static charge distribution with laser beam irradiation, an electrostatic latent image having a static charge distribution which can form an image required to be reproduced or which can form a negative image corresponding to the required image, is formed on the photoconductor; the electrostatic latent image is developed with a toner to form a toner image; the toner image is transferred onto a recording medium such as print paper directly or through a transfer medium; and the transferred toner image is fixed by heating or the like, thereby obtaining a copy.
In the case of forming a full-color image with toners for developing electrostatic images, first, an original image required to be reproduced, is separated into the three primary color components of yellow (Y), magenta (M) and cyan (C), or the four color components of the three primary colors and black (K). Then, the electrostatic latent images of each of the color components are formed on different photoconductors and developed, thereby forming the primary color toner images of each of the color components. Then, the primary color toner images of each of the color components are aligned on and transferred onto a transfer receptive medium selected from a recording medium or a transfer medium, thereby forming a higher-order color toner image including a higher-order color (such as a secondary color and a tertiary color) which is created by overlapping the primary colors. When the higher-order color toner image is formed on a transfer medium, the image is transferred onto a recording medium. Then, the higher-order color toner image on the recording medium is fixed by heating or the like, thereby obtaining a full-color image including a higher-order color gradation area.
As a full color image forming method which is excellent in both of low-temperature fixability and hot offset resistance, Patent Document 1 discloses a method for forming a full color image by using black, cyan, magenta and yellow toners having apparent viscosities in specific ranges at 105°C and 130°C, wherein, among the four color toners transferred onto a transfer medium, one having the maximum peak or a shoulder peak at a temperature of from 105°C to 130°C in a graph of temperature vs. logarithm molten viscosity, is used as the toner to be arranged on the uppermost layer on the transfer medium, and one having neither the maximum peak nor a shoulder peak at a temperature of from 105°C to 130°C is used as another toner to be arranged on lower layers.
As a toner set having excellent thin line reproducibility and color reproducibility, Patent Document 2 discloses a toner set comprising yellow, magenta and cyan toners, wherein their charge amounts and charge amount variances are within specific ranges, and a difference in the charge amounts between the toners and a difference in the charge amount variances therebetween are equal to or less than specific numerical values.
As a toner set which can print, by electrostatic image development, a full-color image which is superior in gradation and color reproducibility of an image including a higher-order color and which is superior in continuous printing durability, Patent Document 3 discloses a toner set wherein, compared to the internal friction angle θ1 (°) of the first toner, the internal friction angle θ2 (°) of another toner is large, and the difference (θ2 - θ1) between the internal friction angle θ1 (°) of the first toner and the internal friction angle θ2 (°) of another toner is within a specific range.

Citation List

Patent Documents

Patent Document 1: Japanese Patent Application Laid-Open ( JP-A) No. 2008-249989
Patent Document 2: JP-A No. 2019-109536
Patent Document 3: International Publication No. WO2021/172517

Summary

Technical Problem

Further improvement in higher-order color reproducibility is required for full-color image formation using a toner set.
An object of the present disclosure is to provide a toner set with excellent higher-order color reproducibility.

Solution to Problem

According to the present disclosure, the following toner set is provided.

[1] A toner set which is a color toner set comprising positively-chargeable color toners each comprising colored resin particles comprising a binder resin, a colorant, a release agent and a positively-chargeable charge control resin,
- wherein the positively-chargeable color toners comprise at least a yellow toner, a magenta toner and a cyan toner;
- wherein the release agent comprises an ester wax;
- wherein the positively-chargeable charge control resin comprises at least one kind of styrene-acrylic polymer comprising a quaternary ammonium salt-containing (meth)acrylate monomer unit;
- wherein a value of X calculated for the each color toner by the following formula (1) where Fcm is a content (parts by mass) of the styrene-acrylic polymer with respect to 100 parts by mass of the binder resin; Xa is a copolymerization ratio (% by mass) of the quaternary ammonium salt-containing (meth)acrylate monomer; and Fp is a content (parts by mass) of the colorant with respect to 100 parts by mass of the binder resin, is more than 0.2 and less than 2.5: $X = \{Σ (Fcm \times Xa)\} / Fp$ and
- wherein the following formula (2) where X(Y) is the X value of the yellow toner; X(M) is the X value of the magenta toner; and X(C) is the X value of the cyan toner, is satisfied: $X (M) > X (C) > X (Y)$
[2] The toner set according to the above [1], wherein the copolymerization ratio Xa of the quaternary ammonium salt-containing (meth)acrylate monomer in the styrene-acrylic polymer is from 0.1% by mass to 10% by mass.
[3] The toner set according to the above [1] or [2], wherein the ester wax comprises a monoester compound represented by the following formula (A), and a content of the monoester compound is from 10 parts by mass to 25 parts by mass with respect to 100 parts by mass of the binder resin:

R¹-COO-R² Formula (A)

(where R¹ is a linear aliphatic hydrocarbon group containing 15 to 23 carbon atoms, and R² is a linear aliphatic hydrocarbon group containing 16 to 24 carbon atoms).
[4] The toner set according to any one of the above [1] to [3], wherein each of the yellow, magenta and cyan toners further comprises an acidic group-containing copolymer as a polar resin, and a content of the acidic group-containing copolymer is from 0.2 parts by mass to 5 parts by mass with respect to 100 parts by mass of the binder resin.
[5] The toner set according to any one of the above [1] to [4], wherein at least one of the positively-chargeable color toners further comprises a styrene-based thermoplastic elastomer.
[6] The toner set according to any one of the above [1] to [5], wherein the positively-chargeable color toners further comprise a black toner, and the following formula (3) where X(Bk) is the X value of the black toner, is satisfied: $X (C) > X (Bk)$

Advantageous Effects of Invention

According to the toner set of the present disclosure described above, full-color image formation with excellent higher-order color reproducibility can be achieved.

Brief Description of Drawing

[FIG. 1] A schematic view of an example of an image forming device applicable to image formation using the toner set of the present disclosure.

Description of Embodiments

1. Toner set

The toner set of the present disclosure is a color toner set comprising positively-chargeable color toners. The toner set includes at least three color toners of a yellow toner, a cyan toner and a magenta toner. It may further include another color toner. Each of the color toners contains colored resin particles containing a binder resin, a colorant, a release agent and a positively-chargeable charge control resin.
Hereinafter, a method for producing the colored resin particles used in the present disclosure, the colored resin particles obtained by the production method, an additive that may be further contained in the color toners, and an image forming method using the toner set of the present disclosure which is obtained by combining the toners, will be described in order.

1-1. Method for producing colored resin particles

In general, methods for producing colored resin particles are broadly classified into dry methods such as a pulverization method and wet methods such as an emulsion polymerization agglomeration method, a suspension polymerization method and a solution suspension method. The wet methods are preferable since a toner having excellent printing properties such as image reproducibility, can be easily obtained. Among the wet methods, polymerization methods such as the emulsion polymerization agglomeration method and the suspension polymerization method are preferable, since a toner having a relatively small particle size distribution in micron order can be easily obtained. Among the polymerization methods, the suspension polymerization method is more preferable.
The emulsion polymerization agglomeration method is a method for producing colored resin particles by polymerizing emulsified polymerizable monomers to obtain a resin microparticle emulsion, and aggregating the resulting resin microparticles with a colorant dispersion, etc. The solution suspension method is a method for producing colored resin particles by forming a solution into droplets in an aqueous medium, the solution containing toner components (such as a binder resin and a colorant) dissolved or dispersed in an organic solvent, and removing the organic solvent. Both methods can be carried out by known methods.
The colored resin particles used in the present disclosure can be produced by the wet methods or the dry methods. The suspension polymerization method is preferable among the wet methods. When the suspension polymerization method is employed, the colored resin particles are produced by the following steps.

(A) Suspension polymerization method

(A-1) Preparation step of polymerizable monomer composition

First, a polymerizable monomer, a colorant, a release agent, a positively-chargeable charge control resin and, as needed, another additive such as a molecular weight modifier are mixed to prepare a polymerizable monomer composition.
For example, a dispersing machine such as an in-line type emulsifying disperser or a media type emulsifying disperser is used for mixing them in the preparation of the polymerizable monomer composition. The polymerizable monomer composition is preferably prepared by the following method, for example: the polymerizable monomer, the colorant, the molecular weight modifier and so on are mixed and wet-pulverized by the media type disperser, and the charge control resin, the release agent and so on are added to and further mixed with the mixture, thereby preparing the polymerizable monomer composition. By this method, a toner that is excellent in low-temperature fixability and heat-resistant storage stability is easily obtained.

[Polymerizable monomer]

In the present disclosure, the polymerizable monomer means a monomer having a polymerizable functional group, and a binder resin is made by polymerization of the polymerizable monomer. It is preferable to use a monovinyl monomer as a main component of the polymerizable monomer.
As the monovinyl monomer, examples include, but are not limited to, styrene; styrene derivatives such as vinyltoluene and α-methylstyrene; acrylic acid and methacrylic acid; acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate and dimethylaminoethyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate and dimethylaminoethyl methacrylate; nitrile compounds such as acrylonitrile and methacrylonitrile; amide compounds such as acrylamide and methacrylamide; and olefins such as ethylene, propylene and butylene. These monovinyl monomers may be used alone or in combination of two or more. Among them, styrene, the styrene derivatives, and the acrylic or methacrylic esters are preferably used as the monovinyl monomer.
To improve hot offset resistance and storage stability, an optional crosslinkable polymerizable monomer is preferably used in combination with the monovinyl monomer. The crosslinkable polymerizable monomer is a monomer containing two or more polymerizable functional groups.
As the crosslinkable polymerizable monomer, examples include, but are not limited to, aromatic divinyl compounds such as divinyl benzene, divinyl naphthalene and derivatives thereof; ester compounds such as ethylene glycol dimethacrylate and diethylene glycol dimethacrylate, in which two or more carboxylic acids containing a carbon-carbon double bond are esterified to an alcohol containing two or more hydroxyl groups; other divinyl compounds such as N,N-divinylaniline and divinyl ether; and compounds containing three or more vinyl groups. The crosslinkable polymerizable monomers may be used alone or in combination of two or more. Of them, an aromatic divinyl compound is preferably used as the crosslinkable polymerizable monomer, and divinylbenzene is particularly preferably used.
When the polymerizable monomer contains the crosslinkable polymerizable monomer, the content of the crosslinkable polymerizable monomer is not particularly limited. With respect to 100 parts by mass of the monovinyl monomer, the content of the crosslinkable polymerizable monomer is preferably from 0.05 parts by mass to 5 parts by mass, and more preferably from 0.1 parts by mass to 1 part by mass.
It is preferable to use a macromonomer as a part of the polymerizable monomer, since a good balance between the storage stability and low-temperature fixability of the toner is obtained. The macromonomer has a polymerizable carbon-carbon unsaturated double bond at the terminal of the molecular chain and is a reactive oligomer or polymer which usually has a number average molecular weight of from 1,000 to 30,000. As the macromonomer, examples include, but are not limited to, a styrene macromonomer, a styrene-acrylonitrile macromonomer, a polyacrylic ester macromonomer and a polymethacrylic ester macromonomer. Among them, at least one selected from the group consisting of a polyacrylic ester macromonomer or a polymethacrylic ester macromonomer is preferably used. As the acrylic ester used in the polyacrylic ester macromonomer, examples include the above-mentioned acrylic esters usable as the monovinyl monomer. As the methacrylic ester used in the polymethacrylic ester macromonomer, examples include the above-mentioned methacrylic esters usable as the monovinyl monomer. As the macromonomer, it is preferable to appropriately select and use such a macromonomer, that when the polymerizable monomer includes the macromonomer, the glass transition temperature (Tg) of the obtained binder resin is higher than the case where the polymerizable monomer does not include the macromonomer.
As the macromonomer, a commercially-available product may be used. As the commercially-available product of the macromonomer, examples include, but are not limited to, macromonomer series AA-6, AS-6, AN-6S, AB-6 and AW-6S manufactured by Toagosei Co., Ltd.
The macromonomers may be used alone or in combination of two or more.
When the polymerizable monomer includes the macromonomer, the content of the macromonomer is not particularly limited. The content of the macromonomer is preferably from 0.03 parts by mass to 5 parts by mass, and more preferably from 0.05 parts by mass to 1 part by mass, with respect to 100 parts by mass of the monovinyl monomer.

[Colorant]

As the colorant, a colorant conventionally used in toners can be appropriately selected and used without particular limitation.
As the colorant used in the magenta toner, examples include, but are not limited to, magenta pigments such as azo-based pigments (e.g., monoazo pigments, disazo pigments and condensed azo-based pigments) and condensed polycyclic pigments (e.g., quinacridone-based pigments) and magenta dyes. More specifically, examples include, but are not limited to, C.I. Pigment Red 31, 48, 57:1, 58, 60, 63, 64, 68, 81, 83, 87, 88, 89, 90, 112, 114, 122, 123, 144, 146, 149, 150, 163, 170, 184, 185, 187, 202, 206, 207, 209, 237, 238, 251, 254, 255 and 269; C.I. Pigment Violet 19; C.I. Solvent Red 1, 3, 8, 23, 24, 25, 27, 30, 49, 81, 82, 83, 84, 100, 109 and 121; C.I. Disperse Red 9; C.I. Solvent Violet 8, 13, 14, 21 and 27; C.I. Disperse Violet 1; C.I. Basic Red 1, 2, 9, 12, 13, 14, 15, 17, 18, 22, 23, 24, 27, 29, 32, 34, 35, 36, 37, 38, 39 and 40; and C.I. Basic Violet 1, 3, 7, 10, 14, 15, 21, 25, 26, 27 and 28.
As the magenta colorant, a quinacridone-based pigment is preferred, and a mixed crystal of C.I. Pigment Violet 19 and C.I. Pigment Red 122 can be particularly preferably used. The mixed crystal of C.I. Pigment Violet 19 and C.I. Pigment Red 122 can be prepared, for example, by the method described in U.S. Pat. No. 3160510 , in which the mixed crystal components are simultaneously recrystallized from sulfuric acid or another suitable solvent, and treated with a solvent after salt grinding if necessary. The mixed crystal of C.I. Pigment Violet 19 and C.I. Pigment Red 122 can be also prepared, for example, by the method described in German Pat. No. 1217333 , in which the substituted diaminoterephthalic acid mixture is treated with a solvent after cyclization.
In the mixed crystal of C.I. Pigment Violet 19 and C.I. Pigment Red 122, the mass ratio of C.I. Pigment Violet 19 to C.I. Pigment Red 122 used is generally from 80:20 to 20:80, preferably from 70:30 to 30:70, and more preferably from 60:40 to 40:60.
As the colorant used in the yellow toner, examples include, but are not limited to, yellow pigments such as azo-based pigments (e.g., monoazo pigments and disazo pigments) and condensed polycyclic pigments, and yellow dyes. More specifically, examples include, but are not limited to, C.I. Pigment Yellow 3, 12, 13, 14, 15, 17, 62, 65, 73, 74, 83, 93, 97, 120, 138, 155, 180, 181, 185, 186, 213 and 214, and C.I. Solvent Yellow 98 and 162.
In the yellow toner, at least one selected from the group consisting of disazo pigments such as C.I. Pigment Yellow 93, 155, 180, 214 and 219 and yellow dyes such as C.I. Solvent Yellow 98 and 162, is preferably contained as the colorant, since the heat-resistant storage stability of the toner can be easily improved, and a high-quality image can be produced. Of them, at least one selected from the group consisting of C.I. Pigment Yellow 155, C.I. Pigment Yellow 214 and C.I. Solvent Yellow 98 is more preferably contained, and at least one selected from the group consisting of C.I. Pigment Yellow 214 and C.I. Solvent Yellow 98 is more preferably contained.
Also in the yellow toner, a combination of the disazo pigment with the yellow dye is preferably contained as the colorant, since the heat-resistant storage stability of the toner can be easily improved, and a high-quality image can be produced. A combination of at least one selected from the group consisting of C.I. Pigment Yellow 155 and C.I. Pigment Yellow 214 with C.I. Solvent Yellow 98 is more preferred, and a combination of C.I. Pigment Yellow 214 with C.I. Solvent Yellow 98 is more preferred.
Also in the yellow toner, the yellow pigment and dye contained in the yellow colorant is preferably at a mass ratio of from 50:50 to 95:5 (yellow pigment : yellow dye), and more preferably at a mass ratio of from 60:40 to 90:10. The yellow pigment contained in the yellow colorant is preferably the disazo pigment, more preferably at least one selected from the group consisting of C.I. Pigment Yellow 155 and C.I. Pigment Yellow 214, and still more preferably C.I. Pigment Yellow 214. The yellow dye contained in the yellow colorant is preferably C.I. Solvent Yellow 98.
As the colorant used in the cyan toner, examples include, but are not limited to, cyan pigments such as phthalocyanine pigments (e.g., copper phthalocyanine pigments and derivatives thereof) and anthraquinone pigments, and cyan dyes. More specifically, examples include, but are not limited to, C.I. Pigment Blue 2, 3, 6, 15, 15:1, 15:2, 15:3, 15:4, 16, 17:1 and 60, and C.I. Solvent Blue 70. Of them, phthalocyanine pigments (e.g., copper phthalocyanine pigments and derivatives thereof) are preferable.
As the colorant used in the black toner, examples include, but are not limited to, carbon black, titanium black and magnetic powder such as zinc-iron oxide and nickel-iron oxide.
In each of the color toners, the content Fp (parts by mass) of the colorant with respect to 100 parts by mass of the binder resin, is not particularly limited, and it is only required to be controlled so that the X value calculated for the each color toner by the below-described formula (1) is more than 0.2 and less than 2.5, and that the below-described formula (2) is satisfied. From the viewpoint of obtaining sufficient image density, the content Fp is preferably 4 parts by mass or more, more preferably 5 parts by mass or more, and still more preferably 6 parts by mass or more as the lower limit. From the viewpoint of suppressing a decrease in the toner fixability, the content Fp is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, and still more preferably 10 parts by mass or less as the upper limit.
In each color toner, the colorants can be used alone or in combination of two or more.
In the present disclosure, 100 parts by mass of the binder resin is the same as 100 parts by mass of a polymerizable monomer used to obtain the binder resin. In the case of core-shell type colored resin particles, 100 parts by mass of the binder resin is the same as 100 parts by mass of a polymerizable monomer used to obtain the core layer.

[Positively-chargeable charge control resin]

As the positively-chargeable charge control resin, a styrene-acrylic polymer comprising a quaternary ammonium salt-containing (meth)acrylate monomer unit, is used.
In the present disclosure, (meth)acrylate means each of acrylate and methacrylate, and (meth)acryl means each of acryl and methacryl.
Also in the present disclosure, the styrene-acrylic polymer is a copolymer of an aromatic vinyl monomer and a (meth)acrylate monomer. A different monomer from the aromatic vinyl monomer and the (meth)acrylate monomer may be further copolymerized therewith. Also, the (meth)acrylate monomer is at least one kind of monomer selected from the group consisting of an acryloyl group and a methacryloyl group.
The styrene-acrylic polymer comprising the quaternary ammonium salt-containing (meth)acrylate monomer unit is preferred since it has high compatibility with the binder resin and is colorless, and since a toner that is stable in chargeability during high-speed continuous printing can be obtained.
In the present disclosure, as the styrene-acrylic polymer, one kind of styrene-acrylic polymer can be used alone, or a combination of two or more kinds of styrene-acrylic polymers can be used. The term "one kind of styrene-acrylic polymer" means a styrene-acrylic polymer such that the type and copolymerization ratio are the same between the monomers used for the synthesis.
In the present disclosure, the X value calculated for the each color toner by the following formula (1) where Fcm is a content (parts by mass) of the styrene-acrylic polymer with respect to 100 parts by mass of the binder resin; Xa is a copolymerization ratio (% by mass) of the quaternary ammonium salt-containing (meth)acrylate monomer; and Fp is a content (parts by mass) of the colorant with respect to 100 parts by mass of the binder resin, is more than 0.2 and less than 2.5: $X = \{\sum (Fcm \times Xa)\} / Fp$
When one kind of styrene-acrylic polymer is used alone as the styrene-acrylic polymer, "Σ(Fcm × Xa)" in the formula (1) is the product (Fcm × Xa) of Fcm and Xa specified for the styrene-acrylic polymer of one kind. When two or more kinds of styrene-acrylic polymers are used in combination as the styrene-acrylic polymer, "Σ(Fcm × Xa)" in the formula (1) is the sum of the products, each of which is the product of Fcm and Xa (Fcm × Xa), is specified for each of the styrene-acrylic polymers having different functional group amounts.
Since the X value is more than 0.2, the charge amount of the toner is moderate; fogging is suppressed; and a sufficient amount of toner is loaded. Since the X value is less than 2.5, good saturation and image density are obtained, and an improvement image quality is obtained. The X value is preferably 0.25 or more as the lower limit, and it is preferably 2.0 or less, and more preferably 1.6 or less as the upper limit.
The X value (X(M)) of the magenta toner is preferably 0.9 or more, and more preferably 1.2 or more, from the viewpoint of improving the printing durability and suppressing fogging in the high-temperature and high-humidity environment. On the other hand, the X value (X(M)) is preferably 2.0 or less, and more preferably 1.4 or less, from the viewpoint of suppressing fogging in the low-temperature and low-humidity environment.
The X value (X(C)) of the cyan toner is preferably 0.7 or more, and more preferably 0.8 or more, from the viewpoint of improving the printing durability and suppressing fogging in the high-temperature and high-humidity environment. On the other hand, the X value (X(C)) is preferably 1.3 or less, and more preferably 1.0 or less, from the viewpoint of suppressing fogging in the low-temperature and low-humidity environment.
The X value (X(Y)) of the yellow toner is preferably 0.25 or more, from the viewpoint of improving the printing durability and suppressing fogging in the high-temperature and high-humidity environment. On the other hand, the X value (X(Y)) is preferably 0.9 or less, and more preferably 0.7 or less, from the viewpoint of suppressing fogging in the low-temperature and low-humidity environment.
The X value (X(Bk)) of the black toner is preferably 0.25 or more, and more preferably 0.3 or more, from the viewpoint of improving the printing durability and suppressing fogging in the high-temperature and high-humidity environment. On the other hand, the X value (X(Bk)) is preferably 0.9 or less, and more preferably 0.7 or less, from the viewpoint of suppressing fogging in the low-temperature and low-humidity environment.
In the toner set of the present disclosure, the following formula (2) where X(Y) is the X value of the yellow toner; X(M) is the X value of the magenta toner; and X(C) is the X value of the cyan toner, is satisfied: $X (M) > X (C) > X (Y)$
Since the formula (2) is satisfied, the charge amount and the loaded toner amount are almost the same between the color toners, and the higher-order color reproducibility is improved, accordingly.
From the viewpoint of improving the higher-order multidimensional color reproducibility, the difference between X(M) and X(C) (X(M) - X(C)) is preferably from 0.1 to 0.8, more preferably from 0.2 to 0.7, and still more preferably from 0.3 to 0.6. The difference between X(C) and X(Y) (X(C) - X(Y)) is preferably from 0.1 to 0.8, more preferably from 0.2 to 0.7, and still more preferably from 0.3 to 0.6.
When the toner set of the present disclosure further contains the black toner, the following formula (3) is preferably satisfied from the viewpoint of improving the higher-order color reproducibility: $X (C) > X (Bk)$ (wherein X(Bk) is the X value of the black toner).
From the viewpoint of improving the higher-order color reproducibility, the difference between X(C) and X(Bk) (X(C) - X(Bk)) is preferably from 0.1 to 0.7, more preferably from 0.2 to 0.6, and still more preferably from 0.3 to 0.5.
In each color toner of the toner set of the present disclosure, the total of the content (Fcm) (parts by mass) of the styrene-acrylic polymer is preferably from 0.5 parts by mass to 25 parts by mass with respect to 100 parts by mass of the binder resin. When the total of Fcm is equal to or more than the lower limit value, fogging can be suppressed. When the total of Fcm is equal to or less than the upper limit value, print soiling can be suppressed.
In the magenta toner, the total of the content (Fcm) (parts by mass) of the styrene-acrylic polymer is preferably from 1 part by mass to 25 parts by mass, and more preferably 1.5 parts by mass to 23 parts by mass, with respect to 100 parts by mass of the binder resin.
In the cyan toner, the total of the content (Fcm) (parts by mass) of the styrene-acrylic polymer is preferably from 0.5 parts by mass to 15 parts by mass, and more preferably 0.6 parts by mass to 12 parts by mass, with respect to 100 parts by mass of the binder resin.
In the yellow toner, the total of the content (Fcm) (parts by mass) of the styrene-acrylic polymer is preferably from 0.5 parts by mass to 10 parts by mass, and more preferably 0.5 parts by mass to 8 parts by mass, with respect to 100 parts by mass of the binder resin.
In the black toner, the total of the content (Fcm) (parts by mass) of the styrene-acrylic polymer is preferably from 0.5 parts by mass to 20 parts by mass, and more preferably 0.5 parts by mass to 15 parts by mass, with respect to 100 parts by mass of the binder resin.
In the case of using one kind of styrene-acrylic polymer, the total of the content (Fcm) of the styrene-acrylic polymer corresponds to the content of the styrene-acrylic polymer of one kind.
The copolymerization ratio Xa (% by mass) of the quaternary ammonium salt-containing (meth)acrylate monomer in the styrene-acrylic polymer is not particularly limited, and it is controlled so that the X value calculated by the formula (1) is within the above range and the formula (2) is satisfied. From the viewpoint of improving the charge imparting function of the styrene-acrylic polymer, improving the printing durability of the toner and suppressing a printing failure in the high-temperature and high-humidity environment, the copolymerization ratio is preferably 0.1% by mass or more, more preferably 0.4% by mass or more, and still more preferably 0.5% by mass or more as the lower limit. From the viewpoint of improving the chargeability of the toner and the dispersibility of the colorants, improving the higher-order color reproducibility, and suppressing the variance between the particles, it is preferably 10% by mass or less, more preferably 8% by mass or less, still more preferably 5% by mass or less, and even more preferably 2% by mass or less as the upper limit.
For the styrene-acrylic polymer contained in the magenta toner, the Σ(Fcm × Xa) is preferably from 5 to 20, and more preferably from 7 to 15.
For the styrene-acrylic polymer contained in the cyan toner, the Σ(Fcm × Xa) is preferably from 3 to 15, and more preferably from 4 to 10.
For the styrene-acrylic polymer contained in the yellow toner, the Σ(Fcm × Xa) is preferably from 1 to 10, and more preferably from 1.5 to 6.
For the styrene-acrylic polymer contained in the black toner, the Σ(Fcm × Xa) is preferably from 1 to 10, and more preferably from 3 to 6.
When the Σ(Fcm × Xa) of each color toner is within the above range, the formulae (2) and (3) can be easily satisfied, and the higher-order color reproducibility can be easily improved.
The quaternary ammonium salt contained in the styrene-acrylic polymer has an ionic structure represented by -NR₃ ⁺·X^-. In the ionic structure, each R is independently a hydrogen atom or a substituent such as an alkyl group, and it is preferably a hydrogen atom or a linear, branched or cyclic alkyl group containing 1 to 6 carbon atoms. Also in the ionic structure, X^-is a halogen ion, an alkyl group in which one hydrogen atom is substituted with a halogen ion, or a hydrocarbon group which contains -SO₃ ^-, -PO₃ ^- or -BO₃ ^- and in which at least one hydrogen atom is optionally substituted with a halogen atom. As the hydrocarbon group, examples include, but are not limited to, an alkyl group, an aromatic hydrocarbon group and a substituted aromatic hydrocarbon group. From the point of view that the charge amount of the toner is likely to be retained during continuous printing and a print failure is less likely to occur, X^- is preferably a hydrocarbon group which contains -SO₃ ^- and in which at least one hydrogen atom is optionally substituted with a halogen atom, more preferably an aromatic sulfonate anion which optionally contains at least one substituent selected from the group consisting of a halogen atom and a linear, branched or cyclic alkyl group containing 1 to 6 carbon atoms, and still more preferably a benzenesulfonate anion or a para-toluenesulfonate anion.
The quaternary ammonium salt-containing (meth)acrylate monomer unit contained in the styrene-acrylic polymer is preferably a constitutional unit represented by the following formula [I]: (where R¹ is a hydrogen atom or a methyl group; R² is a linear or branched alkylene group containing 1 to 3 carbon atoms, in which at least one hydrogen atom is optionally substituted with a halogen atom; each of R³ to R⁵ is independently a hydrogen atom or a linear, branched or cyclic alkyl group containing 1 to 6 carbon atoms; and X^- is a halogen ion, or a benzene or naphthalene which contains -SO₃ ^-, -PO₃ ^- or -BO₃ ^- and which optionally contains at least one substituent selected from the group consisting of a halogen atom and a linear, branched or cyclic alkyl group containing 1 to 6 carbon atoms.)
As described above, X^- is a halogen ion or a benzene or naphthalene which contains -SO₃ ^-, -PO₃ ^- or -BO₃ ^- and which optionally contains at least one substituent selected from the group consisting of a halogen atom and a linear, branched or cyclic alkyl group containing 1 to 6 carbon atoms. From the point of view that the charge amount of the toner is likely to be retained during continuous printing and a print failure is less likely to occur, X^- is more preferably the above-described aromatic sulfonate anion which optionally contains the substituent. As the aromatic sulfonate anion, examples include, but are not limited to, benzenesulfonate anion and para-toluenesulfonate anion.
As the constitutional unit represented by the formula [I], examples include, but are not limited to, a constitutional unit corresponding to a quaternary ammonium salt-containing (meth)acrylate monomer such as N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium chloride, 2-(methacryloyloxy)ethyltrimethylammonium chloride (DMC: dimethylaminoethyl methacrylate methyl chloride), 2-(methacryloyloxy)-N-benzyl-N,N-dimethylethaneammonium chloride (DML : dimethylaminoethyl methacrylate benzyl chloride), N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium p-toluenesulfonate, 2-(methacryloyloxy)ethyl trimethylammonium p-toluenesulfonate, and 2-(methacryloyloxy)-N-benzyl-N,N-dimethylethaneammonium p-toluenesulfonate. Of them, a constitutional unit corresponding to N,N-diethyl-N-methyl-2-(methacryloyloxy)ethylammonium p-toluenesulfonate is preferred.
The styrene-acrylic polymer is more preferably a copolymer containing the quaternary ammonium salt-containing (meth)acrylate monomer unit, a functional group-free aromatic vinyl monomer unit and a functional group-free (meth)acrylate monomer unit. The term "functional group-free" means that a functional group which can impart positively-chargeable property is not contained. Since such a copolymer has excellent compatibility with the binder resin, the charge amount of the toner is likely to be uniform.
The styrene-acrylic polymer is preferably soluble in the aromatic vinyl monomer, from the viewpoint of dispersibility into the polymerizable monomer composition.
The styrene-acrylic polymer may be, for example, a copolymer obtained by copolymerization of the quaternary ammonium salt-containing (meth)acrylate monomer, the functional group-free aromatic vinyl monomer and the functional group-free (meth)acrylate monomer, or it may be a copolymer obtained by copolymerizing the functional group-free aromatic vinyl monomer and the functional group-free (meth)acrylate monomer and introducing a quaternary ammonium salt-containing group in the copolymer by modification treatment.
The copolymer containing the quaternary ammonium salt-containing (meth)acrylate monomer unit, the functional group-free aromatic vinyl monomer unit and the functional group-free (meth)acrylate monomer unit, which is preferably used as the styrene-acrylic polymer, is not particularly limited. For example, it can be obtained by any of the following methods. In the following methods, the polymerization method is not particularly limited. For example, a known polymerization method such as emulsion polymerization, dispersion polymerization, suspension polymerization and solution polymerization can be employed.
In the description of the following methods, "functional group-free aromatic vinyl monomer" is simply referred to as "aromatic vinyl monomer", and "functional group-free (meth)acrylate monomer" is simply referred to as "(meth)acrylate monomer".

(i) A method in which an aromatic vinyl monomer, a (meth)acrylate monomer and an N,N-disubstituted aminoalkyl (meth)acrylate monomer are copolymerized in the presence of a polymerization initiator, followed by quaternizing the amino group with a quaternizing agent such as a halogenated organic compound and an acid ester compound.
(ii) A method in which an aromatic vinyl monomer, a (meth)acrylate monomer and a monomer in which an N,N-disubstituted aminoalkyl (meth)acrylate monomer is made into a quaternary ammonium salt using a quaternizing agent such as a halogenated organic compound and an acid ester compound, are copolymerized in the presence of a polymerization initiator.

As the aromatic vinyl monomer, examples include, but are not limited to, styrene, α-methylstyrene, 2-methylstyrene, 3-methylstyrene, 4-methylstyrene, 2-ethylstyrene, 3-ethylstyrene, 4-ethylstyrene, 2-propylstyrene, 3-propylstyrene, 4-propylstyrene, 2-isopropylstyrene, 3-isopropylstyrene, 4-isopropylstyrene, 2,4-diisopropylstyrene, 2,4-dimethylstyrene, 4-butylstyrene, 4-t-butylstyrene, 5-t-butyl-2-methylstyrene, 2-chlorostyrene, 3-chlorostyrene, 4-chlorostyrene, 2-methyl-α-methylstyrene, 3-methyl-α-methylstyrene, 4-methyl-α-methylstyrene, 4-bromostyrene, 2-methyl-4,6-dichlorostyrene, 2,4-dibromostyrene and vinylnaphthalene. Of them, styrene and α-methylstyrene are preferred. These aromatic vinyl monomers may be used alone or in combination of two or more.
As the (meth)acrylate monomer, for example, an alkyl (meth)acrylate monomer optionally containing a hydroxyl group is preferably used. As the alkyl (meth)acrylate monomer optionally containing a hydroxyl group, examples include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, n-amyl (meth)acrylate, isoamyl (meth)acrylate, n-hexyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, hydroxypropyl (meth)acrylate and dodecyl (meth)acrylate. They may be used alone or in combination of two or more. In the alkyl (meth)acrylate monomer, the number of the carbon atoms of the alkyl group is not particularly limited. The alkyl group preferably contains 1 to 12 carbon atoms, more preferably 1 to 8 carbon atoms, and still more preferably 1 to 6 carbon atoms. Besides, an alkyl (meth)acrylate monomer containing no substituent is particularly preferred.
As the N,N-disubstituted aminoalkyl (meth)acrylate monomer, examples include, but are not limited to, dimethylaminomethyl (meth)acrylate, diethylaminomethyl (meth)acrylate, dipropylaminomethyl (meth)acrylate, diisopropylaminomethyl (meth)acrylate, ethylmethylaminomethyl (meth)acrylate, methylpropylaminomethyl (meth)acrylate, dimethylamino-1-ethyl (meth)acrylate, diethylamino-1-ethyl (meth)acrylate and dipropylamino-1-ethyl (meth)acrylate. They may be used alone or in combination of two or more. In the N,N-disubstituted aminoalkyl (meth)acrylate monomer, the number of the carbon atoms of the alkyl group is not particularly limited. The alkyl group preferably contains 1 to 3 carbon atoms.
As the halogenated organic compound used as the quaternizing agent, examples include, but are not limited to, a linear, branched or cyclic alkyl halide containing 1 to 6 carbon atoms, such as chloromethane, dichloromethane and trichloromethane, and an aromatic halide such as chlorobenzene, 4-chlorotoluene and 1-chloronaphthalene.
As the acid ester compound used as the quaternizing agent, examples include, but are not limited to, an alkyl sulfonic acid alkyl ester such as methyl methanesulfonate and ethyl methanesulfonate; a benzenesulfonic acid alkyl ester such as methyl benzenesulfonate; a p-toluenesulfonic acid alkyl ester such as methyl p-toluenesulfonate; a phosphoric ester such as trimethyl phosphate; and a boric acid ester such as trimethoxyborane.
These quaternizing agents may be used alone or in combination of two or more.
In the styrene-acrylic polymer containing the quaternary ammonium salt-containing (meth)acrylate monomer unit, the functional group-free aromatic vinyl monomer unit and the functional group-free (meth)acrylate monomer unit, the copolymerization ratio of the functional group-free aromatic vinyl monomer and that of the functional group-free (meth)acrylate monomer are not particularly limited. From the viewpoint of solubility into the polymerizable monomer and dispersibility into the binder resin, the mass ratio of the functional group-free (meth)acrylate monomer unit to the functional group-free aromatic vinyl monomer unit (the (meth)acrylate monomer unit/the aromatic vinyl monomer unit) is preferably from 0.05 to 0.35, more preferably from 0.10 to 0.30, and still more preferably from 0.15 to 0.25.
The glass transition temperature (Tg) of the styrene-acrylic polymer containing the quaternary ammonium salt-containing (meth)acrylate monomer unit, is not particularly limited. It is preferably within a range of 50°C or more and 110°C or less, and more preferably within a range of 60°C or more and 100°C or less. When the glass transition temperature (Tg) is within the above range, the storage stability of the toner can be improved. It is presumed that, since the styrene-acrylic polymer is likely to be localized near the surface of each colorant resin particle, and it functions like the shell (outer shell) of the colored resin particles, when the Tg is within the above range, the storage stability of the toner is improved due to the sufficiently high Tg.
In the present disclosure, the glass transition temperature (Tg) of the charge control resin can be obtained according to ASTM D3418-82, for example. More specifically, using a differential scanning calorimeter (SSC5200 manufactured by Seiko Instruments & Electronics Ltd.) or the like, the temperature of a sample is increased at a temperature increase rate of 10°C/min, thereby obtaining a DSC curve; and the temperature indicating the maximum endothermic peak in the DSC curve can be used as the glass transition temperature.
The weight average molecular weight (Mw) of the styrene-acrylic polymer is not particularly limited, and it is preferably in a range of 5000 or more and 30000 or less, and more preferably in a range of from 10000 or more and 25000 or less. When the weight average molecular weight (Mw) is equal to or more than the lower limit value, a decrease in the storage stability or printing durability of the toner can be suppressed. When the weight average molecular weight (Mw) is equal to or less than the upper limit value, a decrease in the fixability of the toner can be suppressed. In addition, when the weight average molecular weight (Mw) is within the above range, the styrene-acrylic polymer can be appropriately dispersed in the colored resin particles, and the toner having a charge amount that is stable over time, is easily obtained, accordingly.
In the present disclosure, the weight average molecular weight (Mw) is a polystyrene equivalent measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF).
To the extent that does not impair the effects of the present disclosure, the polymerizable monomer composition may further contain a charge control compound having a relatively low molecular weight or another charge control resin different from the styrene-acrylic polymer.
As the different charge control resin, examples include, but are not limited to, a resin containing a positively-chargeable functional group such as a pyridinium group, an amino group and a quaternary ammonium group.
As the charge control compound, examples include, but are not limited to, a nigrosine dye, a quaternary ammonium salt, a triaminotriphenylmethane compound and an imidazole compound.
When the different charge control resin or the charge control compound is contained as the charge control agent, the total content thereof is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, and still more preferably 1 part by mass or less, with respect to 100 parts by mass of the styrene-acrylic polymer.

[Polar resin]

The polymerizable monomer composition may contain a polar resin. Especially, the colored resin particles used in the yellow, magenta and cyan toners preferably contain a polar resin. When the colored resin particles contain a polar resin, the heat-resistant storage stability and printing durability of the toner can be improved. The polar resin tends to be unevenly distributed on the surface side of the colored resin particles, as well as the positively-chargeable charge control resin. The positively-chargeable charge control resin and the polar resin are unevenly distributed on the surface side of the colored resin particles to reinforce the particle surface and function as the shell (outer shell). Accordingly, even when a binder resin and release agent which are high in low-temperature fixability are used, the toner can obtain excellent heat-resistant storage stability. In addition, since the surface of the colored resin particles is less likely to deteriorate, the printing durability of the toner is improved.
The polar resin may be added before or after the wet pulverization using the media type disperser.
As the polar resin, an acidic group-containing copolymer is preferably used, and an acidic group-containing, acrylate-based copolymer is particularly preferred. As the acidic group-containing, acrylate-based copolymer, for example, a copolymer of a (meth)acrylic ester and (meth)acrylic acid is preferably used. The copolymer of a (meth)acrylic ester and (meth)acrylic acid is a copolymer of at least one kind selected from the group consisting of an acrylic ester and a methacrylic ester and at least one kind selected from the group consisting of acrylic acid and methacrylic acid.
As the copolymer, examples include, but are not limited to, a copolymer of an acrylic ester and acrylic acid, a copolymer of an acrylic ester and methacrylic acid, a copolymer of a methacrylic ester and acrylic acid, a copolymer of a methacrylic ester and methacrylic acid, a copolymer of an acrylic ester, a methacrylic ester and acrylic acid, a copolymer of an acrylic ester, a methacrylic ester and methacrylic acid, and a copolymer of an acrylic ester, a methacrylic ester, acrylic acid and methacrylic acid. Of them, preferred is a copolymer of an acrylic ester, a methacrylic ester and acrylic acid.
As the (meth)acrylic ester, examples include, but are not limited to, methyl (meth)acrylate, ethyl (meth)acrylate, n-propyl (meth)acrylate, isopropyl (meth)acrylate, n-butyl (meth)acrylate, isobutyl (meth)acrylate, sec-butyl (meth)acrylate, tert-butyl (meth)acrylate, n-pentyl (meth)acrylate, sec-pentyl (meth)acrylate, isopentyl (meth)acrylate, neopentyl (meth)acrylate, n-hexyl (meth)acrylate, isohexyl (meth)acrylate, neohexyl (meth)acrylate, sec-hexyl (meth)acrylate and tert-hexyl (meth)acrylate.
As the acrylic ester, ethyl acrylate, n-propyl acrylate, isopropyl acrylate and n-butyl acrylate are preferred, and ethyl acrylate and n-butyl methacrylate are more preferred.
As the methacrylic ester, methyl methacrylate, n-propyl methacrylate, isopropyl methacrylate and n-butyl methacrylate are preferred, and methyl methacrylate is more preferred.
The mass ratio of the monomer units of the acrylate-based copolymer is preferably adjusted so that the acid value, weight average molecular weight Mw and glass transition temperature Tg described below are satisfied.
Of 100% by mass of all the monomer units constituting the acrylate-based copolymer, the content of the (meth)acrylic acid unit is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and still more preferably 0.3% by mass or more, as the lower limit. On the other hand, the content is preferably 1.0% by mass or less, more preferably 0.6% by mass or less, and still more preferably 0.5% by mass or less, as the upper limit.
Of 100% by mass of all the monomer units constituting the acrylate-based copolymer, the content of the (meth)acrylic ester unit is preferably 99.0% by mass or more, more preferably 99.4% by mass or more, and still more preferably 99.5% by mass or more, as the lower limit. On the other hand, the content is preferably 99.95% by mass or less, more preferably 99.9% by mass or less, and still more preferably 99.7% by mass or less, as the upper limit.
To the extent that does not impair the effects of the present disclosure, the acrylate-based copolymer may contain another monomer unit different from the (meth)acrylic acid ester unit and the (meth)acrylic acid unit. As the another monomer, examples include, but are not limited to, the styrene derivative, nitrile compound and amide compound exemplified above as the monovinyl monomer constituting the binder resin.
In the acrylate-based copolymer, the content of the another monomer unit is preferably 10 parts by mass or less, more preferably 2 parts by mass or less, and most preferably 0 part by mass, with respect to 100 parts by mass of the (meth)acrylic ester unit.
The acid value of the polar resin is not particularly limited. The acid value of the polar resin is, preferably 0.5 mgKOH/g or more, more preferably 1.0 mgKOH/g or more, and still more preferably 2.0 mgKOH/g or more, as the lower limit. On the other hand, the acid value is preferably 5.0 mgKOH/g or less, more preferably 4.0 mgKOH/g or less, and still more preferably 3.0 mgKOH/g or less, as the upper limit. When the acid value of the polar resin is within the above range, the toner that is excellent in low-temperature fixability, heat-resistant storage stability and printing durability is easily obtained.
In the present disclosure, the acid value of the resin is measured according to JIS K 0070.
The weight average molecular weight (Mw) of the polar resin is not particularly limited. It is preferably 6,000 or more, more preferably 7,000 or more, and still more preferably 9,000 or more, as the lower limit. On the other hand, it is preferably 50,000 or less, more preferably 45,000 or less, and still more preferably 40,000 or less, as the upper limit.
When the weight average molecular weight (Mw) of the polar resin is within the above range, the toner that is excellent in low-temperature fixability, heat-resistant storage stability and printing durability is easily obtained.
The glass transition temperature Tg of the polar resin is not particularly limited. It is preferably 60°C or more, more preferably 65°C or more, and still more preferably 70°C or more, as the lower limit. On the other hand, it is preferably 85°C or less, more preferably 80°C or less, and still more preferably 77°C or less, as the upper limit.
When the glass transition temperature Tg of the polar resin is within the above range, the toner that is excellent in low-temperature fixability, heat-resistant storage stability and printing durability is easily obtained.
In the present disclosure, the glass transition temperature Tg can be obtained according to ASTM D3418-82.
The content of the polar resin with respect to 100 parts by mass of the binder resin is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and still more preferably 1 part by mass or more, as the lower limit. On the other hand, it is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, still more preferably 2 parts by mass or less, and even more preferably 1.5 parts by mass or less, as the upper limit.
When the content of the polar resin is equal to or more than the lower limit value, a decrease in printing durability is suppressed. When the content of the polar resin is equal to or less than the upper limit value, the charge amount of the toner is likely to be appropriate. Especially, a decrease in the charge amount of the toner is suppressed; moreover, a decrease in production stability and a decrease in low-temperature fixability are suppressed.
In the present disclosure, preferably, the content of the acidic group-containing copolymer is within the above range. More preferably, the content of the acidic group-containing, acrylate-based copolymer is within the above range.
A commercially-available product can be used as the polar resin, or the polar resin can be produced by a known polymerization method such as solution polymerization, aqueous solution polymerization, ionic polymerization, high-temperature and high-pressure polymerization and suspension polymerization.
A typical example of the method for producing the polar resin is as described below. Note that the polar resin production method is not limited to the following typical example.
First, a solvent is put in a reaction container as appropriate. After the atmosphere inside the reaction container is replaced by an inert atmosphere, the temperature of the inside of the reaction container is increased, and a raw material monomer is put in the reaction container. At this time, a polymerization initiator is preferably added in combination with the raw material monomer. It is also preferable to put the mixture of the raw material monomer and the polymerization initiator in a dropwise manner in the reaction container. Next, the temperature of the contents of the reaction container is increased to a temperature at which a polymerization reaction is developed, thereby initiating polymerization. After the polymerization is completed, the solvent is removed by distillation as appropriate, thereby obtaining the desired polar resin.

[Styrene-based thermoplastic elastomer]

The polymerizable monomer composition preferably contains the styrene-based thermoplastic elastomer. This results in an improvement of the dispersibility of the release agent, and the low-temperature fixability of the toner can be improved, accordingly. Since a high dispersibility improving effect is exerted by the styrene-based thermoplastic elastomer, the release agent used in combination with the styrene-based thermoplastic elastomer is preferably a monoester compound. In the toner set of the present disclosure, at least one toner of the toner set preferably contains the styrene-based thermoplastic elastomer.
In the case of adding the styrene-based thermoplastic elastomer to the polymerizable monomer composition, the styrene-based thermoplastic elastomer is preferably added in combination with the release agent, and the styrene-based thermoplastic elastomer is more preferably added in combination with the release agent after the wet pulverization using the media type disperser.
In the present disclosure, the styrene-based thermoplastic elastomer is a copolymer of a styrene-based monomer (that is, an aromatic vinyl monomer) and another monomer which is copolymerizable with the aromatic vinyl monomer, such as a random copolymer, a block copolymer and a graft copolymer, and hydrogenated products of such a copolymer, for example.
A thermoplastic elastomer is typically such a material, that when the original volume is considered as 100% by volume, it can be deformed to a volume of 200% by volume by applying small external force at room temperature (20°C), and when the small external force is removed from the material, the material volume returns to less than 130% by volume.
As the styrene-based thermoplastic elastomer, for example, a conjugated diene-aromatic vinyl-based thermoplastic elastomer is preferably used. Particularly preferred is a non-hydrogenated conjugated diene-aromatic vinyl-based thermoplastic elastomer. The conjugated diene-aromatic vinyl-based thermoplastic elastomer is a polymer containing a constitutional unit derived from a conjugated diene monomer and a constitutional unit derived from an aromatic vinyl monomer.
As the conjugated diene-aromatic vinyl-based thermoplastic elastomer, examples include, but are not limited to, a copolymer of a conjugated diene monomer, an aromatic vinyl monomer and, as needed, another monomer which is copolymerizable with them, such as a random copolymer, a block copolymer, a graft copolymer or the like, and hydrogenated products of such copolymer. Of them, a block copolymer containing at least one aromatic vinyl polymer block and at least one conjugated diene polymer block is preferred for better fixability of the toner.
Hereinafter, a representative example of the styrene-based thermoplastic elastomer will be described, which is a block copolymer containing at least one aromatic vinyl polymer block and at least one conjugated diene polymer block (hereinafter, it may be simply referred to as "block copolymer"). The block copolymer contains at least one aromatic vinyl polymer block, which is obtained by polymerizing an aromatic vinyl monomer, and at least one conjugated diene polymer block, which is obtained by polymerizing a conjugated diene monomer.
As the aromatic vinyl monomer used in the aromatic vinyl polymer block, examples include, but are not limited to, those exemplified above as the aromatic vinyl monomer applicable to the charge control resin, and styrene is preferred. In each aromatic vinyl polymer block contained in the block copolymer, the aromatic vinyl monomers may be used alone or in combination of two or more. When the block copolymer contains more than one aromatic vinyl polymer block, it may be composed of the same or different aromatic vinyl monomer units.
The aromatic vinyl polymer block may contain another monomer unit, as long as the aromatic vinyl monomer unit is a main repeating unit. Another monomer applicable to the aromatic vinyl polymer block is, for example, a conjugated diene monomer (such as 1,3-butadiene and isoprene (2-methyl-1,3-butadiene)), an α,β-unsaturated nitrile monomer, an unsaturated carboxylic acid or acid anhydride monomer, an unsaturated carboxylic acid ester monomer and a non-conjugated diene monomer. In the aromatic vinyl polymer block, the content of the monomer units other than the aromatic vinyl monomer unit is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 0% by mass.
As the conjugated diene monomer used in the conjugated diene polymer block, examples include, but are not limited to, 1,3-butadiene, isoprene, 2,3-dimethyl-1,3-butadiene, 2-chloro-1,3-butadiene, 1,3-pentadiene and 1,3-hexadiene. Of them, at least one selected from the group consisting of 1,3-butadiene and isoprene is preferred, and isoprene is particularly preferred, from the point of view that the effect of improving storage stability and low-temperature fixability is high. In each conjugated diene polymer block contained in the block copolymer, these conjugated diene monomers may be used alone or in combination of two or more. When the block copolymer contains more than one conjugated diene polymer block, it may be composed of the same or different conjugated diene monomer units. In addition, a part of the unsaturated bonds of each conjugated diene polymer block may be subjected to a hydrogenation reaction.
The conjugated diene polymer block may contain another monomer unit, as long as the conjugated diene monomer unit is a main repeating unit. Another monomer applicable to the conjugated diene polymer block is, for example, an aromatic vinyl monomer (such as styrene and α-methylstyrene), an α,β-unsaturated nitrile monomer, an unsaturated carboxylic acid monomer, an unsaturated carboxylic anhydride monomer, an unsaturated carboxylic acid ester monomer and a non-conjugated diene monomer. In the conjugated diene polymer block, the content of the monomer units other than the conjugated diene monomer unit is preferably 20% by mass or less, more preferably 10% by mass or less, and particularly preferably 0% by mass.
The content of a vinyl bond in the conjugated diene polymer block (the proportion of a 1,2-vinyl bond unit and a 3,4-vinyl bond unit in all the conjugated diene monomer units of the conjugated diene polymer block) is not particularly limited. It is preferably from 1 mol % to 20 mol %, more preferably from 2 mol % to 15 mol %, and particularly preferably from 3 mol % to 10 mol %.
In the block copolymer, the number and binding form of the polymer blocks are not particularly limited, as long as the block copolymer contains at least one aromatic vinyl polymer block and at least one conjugated diene polymer block. As the block copolymer, examples include, but are not limited to, the following. In the following examples, Ar represents the aromatic vinyl polymer block; D represents the conjugated diene polymer block; X represents the residue of a coupling agent; and n represents an integer of 2 or more.

(a) An aromatic vinyl-conjugated diene block copolymer represented by Ar-D
(b) An aromatic vinyl-conjugated diene-aromatic vinyl block copolymer represented by Ar-D-Ar or (Ar-D)_n-X
(c) A conjugated diene-aromatic vinyl-conjugated diene block copolymer represented by D-Ar-D or (D-Ar)_n-X
(d) An aromatic vinyl-conjugated diene-aromatic vinyl-conjugated diene block copolymer represented by Ar-D-Ar-D
(e) A block copolymer composition that is a combination of any two or more of the above block copolymers (a) to (d)

From the viewpoint of improving the toner fixability, the toner of the present disclosure preferably contains at least the block copolymer (b), and more preferably at least the block copolymers (a) and (b), as the styrene-based thermoplastic elastomer.
When the block copolymer (b) is contained as the styrene-based thermoplastic elastomer, with respect to 100% by mass of the styrene-based thermoplastic elastomer, the content of the block copolymer (b) is preferably 2% by mass or more, and more preferably 5% by mass or more, as the lower limit. On the other hand, the content is preferably 60% by mass or less, and more preferably 50% by mass or less, as the upper limit.
When the block copolymer (a) is contained as the styrene-based thermoplastic elastomer, with respect to 100% by mass of the styrene-based thermoplastic elastomer, the content of the block copolymer (a) is preferably 40% by mass or more, more preferably 50% by mass or more, and still more preferably 55% by mass or more, as the lower limit. On the other hand, the upper limit is not particularly limited, and the content is preferably 98% by mass or less, and more preferably 95% by mass or less.
When the block copolymers (a) and (b) are contained as the styrene-based thermoplastic elastomer, with respect to the total mass (100 parts by mass) of the block copolymers (a) and (b), the content of the block copolymer (b) is preferably from 2 parts by mass to 60 parts by mass, and more preferably from 5 parts by mass to 50 parts by mass.
When the content of the block copolymer (a) and that of the block copolymer (b) are within the above ranges, the fixability of the toner improves, and a decrease in image density is suppressed, accordingly; moreover, the charge amount of the toner is likely to be appropriate, and the bleeding of the release agent is likely to be suppressed.
In the block copolymer (a), the weight average molecular weight (Mw(Ar)) of the aromatic vinyl polymer block Ar is not particularly limited, and it is preferably from 10000 to 50000, and more preferably from 15000 to 30000.
Also in the block copolymer (a), the weight average molecular weight (Mw(D)) of the conjugated diene polymer block D is not particularly limited, and it is preferably from 50000 to 200000, and more preferably from 60000 to 150000.
In the block copolymer (b), the weight average molecular weight (Mw (Ar)) of the aromatic vinyl polymer block Ar is not particularly limited, and it is preferably from 20000 to 70000, and more preferably from 25000 to 50000.
Also in the block copolymer (b), the weight average molecular weight (Mw(D)) of the conjugated diene polymer block D is not particularly limited, and it is preferably from 100000 to 300000, and more preferably from 120000 to 250000.
In the block copolymer, the content rate of the aromatic vinyl monomer unit with respect to all the monomer units is preferably from 10% by mass to 30% by mass, more preferably from 12% by mass to 25% by mass, and still more preferably from 15% by mass to 25% by mass. By adjusting the content rate of the aromatic vinyl monomer unit within the above range, the affinity of the block copolymer for the release agent can be highly balanced with the affinity of the block copolymer for the binder resin, and the toner thus obtained can be a toner having improved storage stability and low-temperature fixability.
When all of the polymer components constituting the block copolymer are only the aromatic vinyl monomer unit and the conjugated diene monomer unit, the content of the aromatic vinyl monomer unit in the block copolymer can be easily measured as follows, according to the method described in Rubber Chem. Technol., 45, 1295(1972). First, the block copolymer is oxidized by ozone. Then, the ozone-oxidized block copolymer is deoxidized with lithium aluminum hydride to decompose the conjugated diene monomer unit moiety, thereby obtaining only the aromatic vinyl monomer unit moiety. Accordingly, the whole content of the aromatic vinyl monomer unit can be easily measured.
In the block copolymer, the weight average molecular weight (Mw) of the aromatic vinyl polymer block is not particularly limited, and it is preferably from 10000 to 50000, and more preferably from 20000 to 40000.
In the block copolymer, the weight average molecular weight (Mw) of the conjugated diene polymer block is not particularly limited, and it is preferably from 50000 to 200000, and more preferably from 60000 to 180000.
The melt index (MI) of the block copolymer is not particularly limited. As a value measured according to ASTM D-1238 (in condition G, 200°C, 5 kg), for example, it is selected in a range of from 1 g/10 min to 1000 g/10 min, and it is preferably from 5 g/10 min to 30 g/10 min.
The block copolymer can be produced by a conventional method. As the block copolymer production method, examples include, but are not limited to, the following method: by anionic living polymerization, the aromatic vinyl monomer and the conjugated diene monomer are sequentially polymerized to form polymer blocks, and they are coupled by reaction with a coupling agent as needed, thereby producing the block copolymer.
A mixture containing at least the block copolymers (a) and (b), which is preferably used as the block copolymer, can be produced by the following method, for example.
First, by anionic living polymerization, the aromatic vinyl monomer is polymerized, and following this, the conjugated diene monomer is added thereto and polymerized, thereby obtaining a diblock copolymer having active terminals. Next, a coupling agent is added thereto, which is in an amount of less than 1 molar equivalent with respect to the active terminals of the diblock copolymer having the active terminals, to initiate a coupling reaction of a part of the diblock copolymer having the active terminals, thereby obtaining an aromatic vinyl-conjugated diene-aromatic vinyl block copolymer represented by (Ar-D)_n-X. Then, by adding a polymerization inhibitor, the residual diblock copolymer having the active terminals is deactivated, thereby obtaining the diblock copolymer represented by Ar-D. At this time, by using a difunctional coupling agent (such as dichlorosilane, monomethyldichlorosilane, dimethyldichlorosilane, diphenyldimethoxysilane, diphenyldiethoxysilane, dichloroethane, dibromoethane, methylene chloride and dibromomethane) as the coupling agent, an aromatic vinyl-conjugated diene-aromatic vinyl block copolymer represented by Ar-D-Ar (D contains the residue of the coupling agent) can be obtained.
As the styrene-based thermoplastic elastomer, instead of the block copolymer described above, the random copolymer of the aromatic vinyl monomer and the conjugated diene monomer can be used. The random copolymer of the aromatic vinyl monomer and the conjugated diene monomer can be produced by, for example, living anionic polymerization using an organic alkali metal compound as a polymerization initiator.
As the organic alkali metal compound, examples include, but are not limited to, an organic lithium compound, an organic sodium compound and an organic potassium compound. More specifically, examples include, but are not limited to, an organic monolithium compound such as n-butyllithium, sec-butyllithium, t-butyllithium, hexyllithium, phenyllithium and stilbene lithium; an organic polylithium compound such as dilithiomethane, 1,4-dilithiobutane, 1,4-dilithio-2-ethylcyclohexane, 1,3,5-trilithiobenzene and 1,3,5-tris(lithiomethyl)benzene; an organic sodium compound such as sodium naphthalene; and an organic potassium compound such as potassium naphthalene. Of these organic metal compounds, n-butyllithium is preferred.
In the random copolymer of the aromatic vinyl monomer and the conjugated diene monomer, the content rate of the aromatic vinyl monomer unit with respect to all the monomer units is not particularly limited, and the content is preferably 50% by mass or less, more preferably 45% by mass or less, and still more preferably 40% by mass or less. By adjusting the content rate of the aromatic vinyl monomer unit to the upper limit value or less, the affinity of the random copolymer for the release agent can be highly balanced with the affinity of the random copolymer for the binder resin, and the toner thus obtained can be a toner having improved storage stability and low-temperature fixability.
The weight average molecular weight (Mw) of the styrene-based thermoplastic elastomer is not particularly limited, and it is preferably from 60,000 to 350,000, and more preferably from 80,000 to 250,000. When the weight average molecular weight (Mw) of the styrene-based thermoplastic elastomer is within the above range, the storage stability and low-temperature fixability of the toner is improved, and the occurrence of a print failure can be suppressed.
With respect to 100 parts by mass of the binder resin, the content of the styrene-based thermoplastic elastomer is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and still more preferably 3 parts by mass or more, as the lower limit. On the other hand, the content is preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, as the upper limit. When the content of the styrene-based thermoplastic elastomer is within the above range, the effect of improving the low-temperature fixability of the toner while suppressing a decrease in the heat-resistant storage stability thereof, is improved.

[Release agent]

The release agent contains at least the ester wax. Accordingly, the low-temperature fixability of the toner can be improved while suppressing a decrease in the storage stability thereof; moreover, the printing durability can be improved. The term "ester wax" means a fatty acid ester compound obtained by an ester reaction of alcohol and fatty acid. The alcohol may be aliphatic alcohol, unsaturated aliphatic alcohol or aromatic alcohol, and it may be monohydric alcohol or polyhydric alcohol. The fatty acid may be saturated fatty acid, unsaturated fatty acid or aromatic carboxylic acid, and it may be monocarboxylic acid or polycarboxylic acid.
Also, the ester wax may be a monoester compound or a polyfunctional ester compound such as diester, triester, tetraester and polyester.
As the monohydric alcohol, examples include, but are not limited to, a monohydric saturated aliphatic alcohol such as methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol, 1-pentanol, 1-hexanol, octanol, 2-ethyl-1-hexanol, nonyl alcohol, lauryl alcohol, cetyl alcohol (hexadecyl alcohol), stearyl alcohol, behenyl alcohol and eicosyl alcohol; a monohydric unsaturated aliphatic alcohol such as allyl alcohol, methallyl alcohol, crotyl alcohol and oleyl alcohol; a monohydric alicyclic alcohol such as cyclohexanol; and a monohydric aromatic alcohol such as phenol, phenylmethanol (benzyl alcohol), methylphenol (cresol), p-ethylphenol, dimethylphenol (xylenol), nonylphenol, dodecylphenol, phenylphenol and naphthol.
As the polyhydric alcohol, examples include, but are not limited to, a dihydric saturated aliphatic alcohol such as ethylene glycol and propylene glycol; a dihydric aromatic alcohol such as catechol and hydroquinone; and a trihydric or higher saturated aliphatic alcohol such as glycerol, pentaerythritol, dipentaerythritol and polyglycerol.
As the monocarboxylic acid, examples include, but are not limited to, a saturated aliphatic monocarboxylic acid such as lauric acid (12 carbon atoms), myristic acid (14 carbon atoms), pentadecylic acid (15 carbon atoms), palmitic acid (16 carbon atoms), margaric acid (17 carbon atoms), stearic acid (18 carbon atoms), arachidic acid (eicosanoic acid) (20 carbon atoms) and behenic acid (22 carbon atoms) and the following unsaturated aliphatic monocarboxylic acids.

Palmitoleic acid (CH₃(CH₂)₅CH=CH(CH₂)₇COOH)
Oleic acid (CH₃(CH₂)₇CH=CH(CH₂)₇COOH)
Vaccenic acid (CH₃(CH₂)₅CH=CH(CH₂)₉COOH)
Linoleic acid (CH₃(CH₂)₃(CH₂CH=CH)₂(CH₂)₇COOH)
(9,12,15)-Linolenic acid (CH₃(CH₂CH=CH)₃(CH₂)₇COOH)
(6,9,12)-Linolenic acid (CH₃(CH₂)₃(CH₂CH=CH)₃(CH₂)₄COOH)
Eleostearic acid (CH₃(CH₂)₃(CH=CH)₃(CH₂)₇COOH)
Arachidonic acid (CH₃(CH₂)₃(CH₂CH=CH)₄(CH₂)₃COOH)

As the polycarboxylic acid, examples include, but are not limited to, an aliphatic dicarboxylic acid such as oxalic acid, malonic acid, maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, alkenyl succinic acid, adipic acid, sebacic acid and cyclohexanedicarboxylic acid; an aromatic dicarboxylic acid such as terephthalic acid, isophthalic acid, phthalic acid and naphthalenedicarboxylic acid; and a trivalent or higher carboxylic acid such as trimellitic acid and pyromellitic acid.
The number of the carbon atoms the alcohol and fatty acid (raw materials for ester wax) have, is preferably 16 or more, more preferably 18 or more as the lower limit value, and it is preferably 24 or less, and more preferably 22 or less as the upper limit value. When the number of the carbon atoms the alcohol and fatty acid (raw materials for ester wax) have is equal to or more than the lower limit value, a decrease in the heat-resistant storage stability of the toner is suppressed. When it is equal to or less than the upper limit value, the low-temperature fixability of the toner is improved.
As the ester wax, a monoester compound is preferred from the viewpoint of improving the low-temperature fixability and heat-resistant storage stability of the toner with balance and improving the printing durability of the toner. Since a monoester compound is low in melt viscosity compared to a polyfunctional ester compound, it can seep well from the toner when fixed; it is effective in plasticizing the binder resin; and it is effective in improving the low-temperature fixability of the toner, accordingly.
As the monoester compound, the monoester compound represented by the following formula (A) is particularly preferred:

R¹-COO-R² Formula (A)

(where R¹ is a linear aliphatic hydrocarbon group containing 15 to 23 carbon atoms, and R² is a linear aliphatic hydrocarbon group containing 16 to 24 carbon atoms).
In the monoester compound represented by the formula (A), R¹ is a linear aliphatic hydrocarbon group derived from a monocarboxylic acid used as a raw material, and R² is a linear aliphatic hydrocarbon group derived from a monohydric alcohol used as a raw material.
The monocarboxylic acid forming R¹ of the formula (A) may be, among the monocarboxylic acids mentioned above, a linear aliphatic monocarboxylic acid containing 16 to 24 carbon atoms, for example. More specifically, examples include, but are not limited to, a linear saturated aliphatic monocarboxylic acid such as palmitic acid, margaric acid, stearic acid, arachidic acid and behenic acid, and a linear unsaturated aliphatic monocarboxylic acid such as palmitoleic acid, oleic acid, vaccenic acid, linoleic acid and linolenic acid.
Of them, a linear saturated aliphatic monocarboxylic acid containing 16 to 24 carbon atoms is preferred; a linear saturated aliphatic monocarboxylic acid containing 18 to 22 carbon atoms is more preferred; behenic acid and stearic acid are more preferred; and stearic acid is particularly preferred.
That is, R¹ of the formula (A) is preferably a linear alkyl group containing 15 to 23 carbon atoms, more preferably a linear alkyl group containing 17 to 21 carbon atoms, still more preferably a behenyl or stearyl group, and particularly preferably a stearyl group.
The monovalent alcohol forming R² of the formula (A) may be, among the monovalent alcohols mentioned above, a monovalent linear aliphatic alcohol containing 16 to 24 carbon atoms, for example. More specifically, examples include, but are not limited to, a monohydric linear saturated aliphatic alcohol such as cetyl alcohol (hexadecyl alcohol), stearyl alcohol, behenyl alcohol and eicosyl alcohol, and a monohydric linear unsaturated aliphatic alcohol such as oleyl alcohol.
Of them, a monovalent linear saturated aliphatic alcohol containing 16 to 24 carbon atoms is preferred; a monovalent linear saturated aliphatic alcohol containing 18 to 22 carbon atoms is more preferred; stearyl alcohol and behenyl alcohol are still more preferred; and behenyl alcohol is particularly preferred.
That is, R² of the formula (A) is preferably a linear alkyl group containing 16 to 24 carbon atoms, more preferably a linear alkyl group containing 18 to 22 carbon atoms, still more preferably a behenyl or stearyl group, and particularly preferably a behenyl group.
In the formula (A), R¹ and R² may be the same groups, or they may be different groups.
In the monoester compound represented by the formula (A), the difference between the number of the carbon atoms contained in the raw material monocarboxylic acid (i.e., the number of carbon atoms obtained by adding 1 to the number of the carbon atoms of R¹) and the number of the carbon atoms contained in the raw material alcohol (i.e., the number of the carbon atoms of R²) is preferably from 0 to 6, and more preferably from 4 to 6, from the viewpoint of improving the low-temperature fixability and heat-resistant storage stability of the toner with balance and improving the printing durability of the toner.
The number of the carbon atoms contained in the monoester compound represented by the formula (A) is preferably from 36 to 48, and more preferably from 40 to 44, from the viewpoint of improving the low-temperature fixability and heat-resistant storage stability of the toner with balance and improving the printing durability of the toner.
As the monoester compound represented by the formula (A), examples include, but are not limited to, behenyl palmitate (C₁₅H₃₁-COO-C₂₂H₄₅), behenyl stearate (C₁₇H₃₅-COO-C₂₂H₄₅), behenyl eicosanoate (C₁₉H₃₉-COO-C₂₂H₄₅), behenyl behenate (C₂₁H₄₃-COO-C₂₂H₄₅), eicosyl palmitate (C₁₅H₃₁-COO-C₂₀H₄₁), eicosyl stearate (C₁₇H₃₅-COO-C₂₀H₄₁), eicosyl eicosanoate (C₁₉H₃₉-COO-C₂₀H₄₁), eicosyl behenate (C₂₁H₄₃-COO-C₂₀H₄₁), stearyl stearate (C₁₇H₃₅-COO-C₁₈H₃₇), stearyl eicosanoate (C₁₉H₃₉-COO-C₁₈H₃₇), stearyl behenate (C₂₁H₄₃-COO-C₁₈H₃₇), hexadecyl eicosanoate (C₁₉H₃₉-COO-C₁₆H₃₃) and hexadecyl behenate (C₂₁H₄₃-COO-C₁₆H₃₃). Of them, behenyl stearate, behenyl palmitate and stearyl behenate are particularly preferred.
As the polyfunctional ester compound, examples include, but are not limited to, a pentaerythritol ester compound such as pentaerythritol tetrabehenate, pentaerythritol tetrapalminate, pentaerythtol tetrastearate, pentaerythritol tetramyristate and pentaerythritol tetralaurate; a glycerin ester compound such as hexaglycerin octabehenate, pentaglycerin heptabehenate, tetraglycerin hexabehenate, triglycerin pentabehenate, diglycerin tetrabehenate and glycerin tribehenate; and a dipentaerythritol ester such as dipentaerythritol hexamyristate, dipentaerythritol hexapalmitate and dipentaerythritol hexalaurate.
The ester wax preferably has an esterification rate of 92% or more, more preferably 95% or more, and still more preferably 97% or more, from the viewpoint of improving the low-temperature fixability of the toner by the sharp meltability of the ester wax.
The esterification rate is the proportion of the number of a hydroxyl group to which fatty acid is esterified, among the total number of hydroxyl groups contained in the raw material alcohol. The esterification rate of the ester wax can be obtained by measuring the saponification value (SV), hydroxyl value (OHV) and acid value (AV) of the ester wax and calculating the esterification rate by the following formula. $\begin{array}{l} Esterificationrate (%) \\ = [(SV - AV) / (SV - AV + OHV)] \times 100 \end{array}$
The saponification value (SV) and acid value (AV) of the ester wax are measured according to JIS K 0070. The hydroxyl value (OHV) of the ester wax is measured according to JIS K 1557.
The molecular weight of the ester wax is preferably 500 or more, and more preferably 550 or more as the lower limit, from the viewpoint of improving the low-temperature fixability of the toner and suppressing the bleeding of the ester wax. On the other hand, the molecular weight of the ester wax is preferably less than 2,000, more preferably 1,500 or less, still more preferably 1,000 or less, and even more preferably 700 or less as the upper limit, from the point of view that the toner is likely to spread when fixed, and a decrease in image density is suppressed.
The melting point of the ester wax is preferably in a range of from 50°C to 90°C, more preferably in a range of from 60°C to 85°C, and still more preferably in a range of from 65°C to 75°C.
As the ester wax, a commercially-available ester wax product can be used, such as WEP2, WEP3, WEP4, WEP5, WE6 and WEll (product names) manufactured by NOF Corporation.
In the present disclosure, another release agent can be used in combination with the ester wax. As another release agent, a release agent that is generally used as a release or softening agent in toners can be used without particular limitation. As the release agent, examples include, but are not limited to, low-molecular-weight polyolefin wax and modified wax thereof; natural plant wax such as jojoba; petroleum wax such as paraffin; mineral wax such as ozokerite; and synthetic wax such as Fischer-Tropsch wax. These release agents may be used alone or in combination of two or more.
With respect to 100 parts by mass of the binder resin, the content of the release agent is preferably 5 parts by mass or more, more preferably 10 parts by mass or more, and still more preferably 15 parts by mass or more, as the lower limit. On the other hand, the content of the release agent is preferably 30 parts by mass or less, and more preferably 25 parts by mass or less, as the upper limit.
When the content of the release agent is equal to or more than the lower limit value, the toner obtains excellent low-temperature fixability, and a decrease in image density is suppressed since the toner is likely to spread when fixed. When the content of the release agent is equal to or less than the upper limit value, a decrease in the production stability and a decrease in the heat-resistant storage stability are suppressed; moreover, the bleeding of the release agent is suppressed.
The content of the ester wax in 100 parts by mass of the release agent is preferably 90 parts by mass or more, more preferably 95 parts by mass or more, and still more preferably 100 parts by mass.
The content of the monoester compound represented by the general formula (A) in 100 parts by mass of the release agent is preferably 90 parts by mass or more, more preferably 95 parts by mass or more, and still more preferably 100 parts by mass.
The content of the monoester compound represented by the general formula (A) is preferably from 5 parts by mass to 25 parts by mass, more preferably from 10 parts by mass to 25 parts by mass, and still more preferably form 15 parts by mass to 25 parts by mass, with respect to 100 parts by mass of the binder resin.

[Molecular weight modifier]

It is preferable to use a molecular weight modifier as another additive, when the polymerizable monomer is polymerized into the binder resin.
The molecular weight modifier is not particularly limited, as long as it is one that is generally used as a molecular weight modifier for toners. As the molecular weight modifier, examples include, but are not limited to, a mercaptan such as t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan and 2,2,4,6,6-pentamethylheptane-4-thiol, and a thiuram disulfide such as tetramethyl thiuram disulfide, tetraethyl thiuram disulfide, tetrabutyl thiuram disulfide, N,N'-dimethyl-N,N'-diphenyl thiuram disulfide and N,N'-dioctadecyl-N,N'-diisopropyl thiuram disulfide. These molecular weight modifiers may be used alone or in combination of two or more.
In the present disclosure, it is desirable that the molecular weight modifier is used in an amount of generally from 0.01 parts by mass to 10 parts by mass, and preferably from 0.1 parts by mass to 5 parts by mass, with respect to 100 parts by mass of the binder resin or 100 parts by mass of the polymerizable (preferably monovinyl) monomer.

(A-2) Suspension step to obtain suspension (droplets forming step)

In the present disclosure, it is preferable that the polymerizable monomer composition is dispersed in an aqueous medium preferably containing a dispersion stabilizer; a polymerization initiator is added therein; and then the polymerizable monomer composition is formed into droplets. The method for forming the droplets is not particularly limited. The droplets are formed, for example, by means of a device that enables strong stirring, such as an (in-line type) emulsifying and dispersing machine (product name: MILDER, manufactured by: Pacific Machinery & Engineering Co., Ltd.) and a high-speed emulsification dispersing machine (product name: T. K. HOMOMIXER MARK II, manufactured by: PRIMIX Corporation).
As the polymerization initiator, examples include, but are not limited to, a persulfate such as potassium persulfate and ammonium persulfate; an azo compound such as 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide), 2,2'-azobis(2-amidinopropane)dihydrochloride, 2,2'-azobis(2,4-dimethylvaleronitrile) and 2,2'-azobisisobutyronitrile; and an organic peroxide such as di-t-butylperoxide, benzoylperoxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxy diethylacetate, t-hexylperoxy-2-ethylbutanoate, diisopropylperoxydicarbonate, dit-butylperoxyisophthalate and t-butylperoxyisobutyrate.
They can be used alone or in combination of two or more. Among them, the organic peroxide is preferably used since it can reduce a residual polymerizable monomer and since the toner with excellent printing durability can be obtained.
Among the organic peroxides, a peroxy ester is preferred, and a non-aromatic peroxy ester (i.e., a peroxy ester having no aromatic ring) is more preferred since they have good initiator efficiency and can reduce a residual polymerizable monomer.
The polymerization initiator may be added after dispersing the polymerizable monomer composition in the aqueous medium and before forming the droplets as described above, or it may be added to the polymerizable monomer composition before dispersing the polymerizable monomer composition in the aqueous medium.
In the present disclosure, the aqueous medium means a medium containing water as a main component. The dispersion stabilizer is preferably added to the aqueous medium. As the dispersion stabilizer, examples include, but are not limited to, the following inorganic and organic compounds: an inorganic compound such as a sulfate (e.g., barium sulfate and calcium sulfate), a carbonate (e.g., barium carbonate, calcium carbonate and magnesium carbonate), a phosphate (e.g., calcium phosphate), a metal oxide (e.g., aluminum oxide and titanium oxide) and a metal hydroxide (e.g., aluminum hydroxide, magnesium hydroxide and iron(II) hydroxide) and an organic compound such as a water-soluble polymer (e.g., polyvinyl alcohol, methyl cellulose and gelatin), an anionic surfactant, a nonionic surfactant and an ampholytic surfactant. These dispersion stabilizers can be used alone or in combination of two or more.
Among the above dispersion stabilizers, the inorganic compound is preferable, and a colloid of a sparingly water-soluble metal hydroxide is particularly preferable. The use of the inorganic compound, particularly the use of the colloid of the sparingly water-soluble metal hydroxide, can narrow the particle size distribution of the colored resin particles and can reduce the amount of the dispersion stabilizer remaining after washing. Accordingly, the toner thus obtained is capable of reproducing clear images and obtains excellent environmental stability.

(A-3) Polymerization step

In the aqueous dispersion medium, as described in the above (A-2), the polymerizable monomer composition is formed into droplets to obtain a suspension, and the obtained suspension is heated to polymerize the polymerizable monomer, thereby obtaining an aqueous dispersion of the colored resin particles.
The polymerization temperature of the polymerizable monomer composition is preferably 50°C or more, and more preferably from 60°C to 95°C. The polymerization reaction time is preferably from 1 hour to 20 hours, and more preferably from 2 hours to 15 hours.
The colored resin particles may be mixed with an external additive, and the mixture may be used as the toner. It is preferable to make the colored resin particles into so-called core-shell type (or "capsule type") colored resin particles which are obtained by using the colored resin particles as the core layer and forming a shell layer, which is different from the core layer, outside the core layer. By covering the core layer, which is made of a substance having a low softening point, with a substance having a higher softening point, the core-shell type colored resin particles can take a balance of lowering the fixing temperature and prevention of aggregation during storage.
The method for producing the core-shell type colored resin particles by using the above-mentioned colored resin particles, is not particularly limited, and they can be produced by any conventional method. The in situ polymerization method and the phase separation method are preferable from the viewpoint of production efficiency.
Hereinafter, the method for producing the core-shell type colored resin particles according to the in situ polymerization method, will be described.
The core-shell type colored resin particles can be obtained by adding a polymerizable monomer for forming a shell layer (a polymerizable monomer for shell) and a polymerization initiator to the aqueous dispersion medium in which the colored resin particles are dispersed, and then polymerizing the monomer.
As the polymerizable monomer for shell, the above-mentioned polymerizable monomers can be similarly used. Among the polymerizable monomers, those that can provide a polymer having a Tg of more than 80°C, such as styrene, acrylonitrile and methyl methacrylate, are preferably used alone or in combination of two or more.
As the polymerization initiator used for polymerization of the polymerizable monomer for shell, examples include, but are not limited to, a water-soluble polymerization initiator such as a metal persulfate (e.g., potassium persulfate and ammonium persulfate) and an azo-type initiator (e.g., 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide) and 2,2'-azobis(2-methyl-N-(1,1-bis (hydroxymethyl)-2-hydroxyethyl)propionamide)). These polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator is preferably from 0.1 parts by mass to 30 parts by mass, and more preferably from 1 part by mass to 20 parts by mass, with respect to 100 parts by mass of the polymerizable monomer for shell.
The polymerization temperature of the shell layer is preferably 50°C or more, and more preferably from 60°C to 95°C. The polymerization reaction time is preferably from 1 hour to 20 hours, and more preferably from 2 hours to 15 hours.

(A-4) Washing, filtering, dehydrating and drying steps

It is preferable that after the polymerization, the aqueous dispersion of the colored resin particles obtained by the polymerization is subjected to operations of washing for removal of the dispersion stabilizer, filtering, dehydrating, and drying repeatedly more than one time as needed, according to any conventional method.
The washing may be carried out as follows: when the inorganic compound is used as the dispersion stabilizer, it is preferable that the dispersion stabilizer is dissolved in water and removed by adding acid or alkali to the aqueous dispersion of the colored resin particles. When the colloid of the sparingly water-soluble inorganic hydroxide is used as the dispersion stabilizer, it is preferable that the pH of the aqueous dispersion of the colored resin particles is adjusted to 6.5 or less by adding acid. As the added acid, examples include inorganic acid such as sulfuric acid, hydrochloric acid and nitric acid, and organic acid such as formic acid and acetic acid. Among them, sulfuric acid is particularly preferable for its high removal efficiency and small impact on production facilities.
The dehydrating and filtering may be carried out by any of various known methods, without particular limitation. For example, a centrifugal filtration method, a vacuum filtration method and a pressure filtration method may be used. Also, the drying step may be carried out by any of various methods, without particular limitation.

(B) Pulverization method

In the case of producing the colored resin particles by employing the pulverization method, the production is carried out by the following steps, for example.
First, the binder resin, the colorant, the release agent, the positively-chargeable charge control resin and, as needed, another additive are mixed by means of a mixer such as a ball mill, a V type mixer, FM MIXER (product name, manufactured by Nippon Coke & Engineering Co., Ltd.), a high-speed dissolver and an internal mixer.
Next, the thus-obtained mixture is kneaded while heating by means of a press kneader, a twin screw kneading machine, a roller or the like. The thus-obtained kneaded product is coarsely pulverized by means of a pulverizer such as a hammer mill, a cutter mill and a roller mill. The coarsely pulverized product is pulverized by finely pulverizing by means of a pulverizer such as a jet mill and a high-speed rotary pulverizer. Then, the finely pulverized product is classified into desired particle diameters by means of a classifier such as an air classifier and an airflow classifier, thereby obtaining colored resin particles produced by the pulverization method.
As the binder resin, the colorant, the release agent, the positively-chargeable charge control resin and another additive added as needed, those mentioned above in "(A) Suspension polymerization method" can be used in the pulverization method. Using the colored resin particles obtained by the pulverization method, core-shell type colored resin particles may be produced by the in situ polymerization method, etc., as with the colored resin particles obtained by the above-mentioned "(A) Suspension polymerization method".
As the binder resin, other resins which are conventionally and broadly used in toners can be used. As the binder resin used in the pulverization method, examples include, but are not limited to, polystyrene, styrene-butyl acrylate copolymers, polyester resins and epoxy resins.

1-2. Colored resin particles

The colored resin particles are obtained by the above production method such as (A) Suspension polymerization method or (B) Pulverization method.
The colored resin particles constituting the toner will be described. The colored resin particles described below encompass both core-shell type colored resin particles and non-core-shell type colored resin particles.
The volume average particle diameter (Dv) of the colored resin particles is preferably from 3 µm to 15 µm, and more preferably from 4 µm to 12 um. When the volume average particle diameter (Dv) is equal to or more than the lower limit value, the flowability of the toner can be improved, and a deterioration in transferability and a decrease in image density can be suppressed. When the volume average particle diameter (Dv) is equal to or less than the upper limit value, a decrease in image resolution can be suppressed.
As for the colored resin particles, the ratio (Dv/Dp) of the volume average particle diameter (Dv) to the number average particle diameter (Dp) is preferably from 1.0 to 1.3, and more preferably from 1.0 to 1.2. When the Dv/Dp ratio is 1.3 or less, a decrease in transferability, image density and resolution can be suppressed. The volume average particle diameter and number average particle diameter of the colored resin particles can be measured by means of a particle diameter distribution measuring device using the Coulter counter method (e.g., product name: MULTISIZER; manufactured by: Beckman Coulter, Inc.), for example.
The average circularity of the colored resin particles is preferably from 0.97 to 1.00, and more preferably from 0.98 to 1.00, from the viewpoint of image reproducibility.
The term "circularity" is defined as a value obtained by dividing the perimeter of a circle having the same area as the projected area of a particle image, by the perimeter of the projected image of the particle.
Also in the present disclosure, the term "average circularity" is used as a simple method for quantitatively representing the shape of the particles and is the index of the degree of the surface roughness of the colored resin particles. The average circularity is 1 when the colored resin particles are perfectly spherical, and it gets smaller as the surface shape of the colored resin particles is more complex.
The average circularity (Ca) is a value obtained by the following average circularity calculation formula:
[Math. 1] $Average circularity (Ca) = (\sum_{i = 1}^{n} (C i \times f i)) / \sum_{i = 1}^{n} (f i)$
In the above formula, n is the number of particles for each of which the circularity Ci is obtained.
In the above formula, Ci is the circularity of each of particles having an equivalent circle diameter of from 0.6 µm to 400 µm and is calculated by the following circularity calculation formula based on the perimeter measured for each particle: $\begin{array}{l} Circularity (Ci) \\ = (\begin{array}{l} Perimeter of a circle having the same area as the \\ projected area of a particle image \end{array}) / (\begin{array}{l} Perimeter of the projected \\ particle image \end{array}) \end{array}$
In the above formula, "fi" is the frequency of the particles having the circularity Ci.
The circularity and the average circularity can be measured by means of flow particle image analyzer "FPIA-3000" (product name, manufactured by: Sysmex Corporation).
The presence or absence of the external additive does not cause a significant difference in the values of the volume average particle diameter (Dv), number average particle diameter (Dp) and average circularity of the toner. Accordingly, the values of the volume average particle diameter (Dv), number average particle diameter (Dp) and average circularity of the toner which contains the external additive, can be deemed identical to those of the colored resin particles which does not contain the external additive.

1-3. External additive

By mixing and stirring the above-mentioned colored resin particles with an external additive, the external additive may be uniformly added (external addition) on the surface of the colored resin particles. The colored resin particles that the external additive is added on the surface, can be used as a one-component toner (a developer). The one-component toner may be further mixed and stirred with carrier particles to make a two-component toner.
As the method of the external addition treatment for adding the external additive on the surface of the colored resin particles, a known external addition treatment method can be employed and is not particularly limited. For example, the external addition treatment can be performed by mixing and stirring the colored resin particles and the external additive using a mixer which is capable of mixing and stirring, such as FM MIXER (product name, manufactured by Nippon Coke & Engineering Co., Ltd.), SUPER MIXER (product name, manufactured by KAWATA Manufacturing Co., Ltd.), Q MIXER (product name, manufactured by Nippon Coke & Engineering Co., Ltd.), MECHANOFUSION SYSTEM (product name, manufactured by Hosokawa Micron Corporation) and MECHANOMILL (product name, manufactured by Okada Seiko Co., Ltd.)
As the external additive, examples include, but are not limited to, inorganic fine particles such as fine particles of silica, titanium oxide, aluminum oxide, zinc oxide, tin oxide, strontium titanate, calcium carbonate, calcium phosphate and cerium oxide; organic fine particles such as fine particles of polymethyl methacrylate resin, silicone resin and melamine resin; and fine particles of metallic soap such as fine particles of zinc stearate and magnesium stearate. Among them, inorganic fine particles are preferred. Among inorganic fine particles, silica fine particles and titanium oxide fine particles are preferred, and silica fine particles are particularly preferred. These external additives may be used alone, and they are preferably used in combination of two or more.
As the external additive, inorganic fine particles A having a number average primary particle diameter of from 5 nm to 14 nm and inorganic fine particles B having a number average primary particle diameter of from 15 nm to 90 nm are preferably contained.
When the inorganic fine particles A and B are contained as the external additive, the mass ratio of the inorganic fine particles A to the inorganic fine particles B (the inorganic fine particles A: the inorganic fine particles B) is not particularly limited, and it may be from 20:80 to 80:20, for example.
The number average primary particle diameter of the external additive particles is measured as follows, for example. First, about 0.1 g of a measurement sample is weighed out and put in a beaker. Next, as a dispersant, 0.1 mL of an alkylbenzene sulfonic acid aqueous solution (product name: DRIWEL, manufactured by Fujifilm Corporation) is added thereto. Next, 10 mL to 30 mL of a diluent (product name: ISOTON II, manufactured by Beckman Coulter, Inc.) is put in the beaker. The mixture is dispersed for 3 minutes with a 20 W (watt) ultrasonic disperser. Then, the number average primary particle diameter is measured with a particle size analyzer (product name: MULTISIZER, manufactured by Beckman Coulter, Inc.) under the following condition: aperture diameter: 100 µm, medium: ISOTON II, and the number of measured particles: 100,000 particles.
The content of the external additive is not particularly limited. It is preferably from 0.05 parts by mass to 6 parts by mass, and more preferably from 0.2 parts by mass to 5 parts by mass, with respect to 100 parts by mass of the colored resin particles. When the content of the external additive is within the above range, a transfer residue and fogging are likely to be suppressed.

2. Image forming method

The toner set of the present disclosure is typically a color toner set for developing electrostatic images, which is used to form full-color images by electrostatic image development.
The method for forming a full-color image by electrostatic image development, is broadly classified into the following two methods, based on differences in transfer steps.

(1) A method in which an original image is subjected to color separation to obtain the data of color components; based on the data of the color components, single toner images of multiple colors are formed; the toner images are sequentially transferred onto one transfer medium to overlap the colors on the transfer medium, thereby forming a full-color image; and then the full-color image is transferred from the transfer medium to a recording medium.
(2) A method in which an original image is subjected to color separation to obtain the data of color components; based on the data of the color components, single toner images of multiple colors are formed; and the toner images are sequentially transferred onto one recording medium to overlap the colors on the recording medium, thereby forming a full-color image.

The toner set of the present disclosure enables the formation of full-color images with excellent higher-order color reproducibility in both of the above methods.
The present disclosure also encompasses the following two image forming methods. One is the method in which the colors are overlapped on the transfer medium, and the other is the method in which the colors are overlapped on the recording medium.
The first method is a method for forming an image by an electrostatic image development type full-color printer using the toner set of the present disclosure,
the method comprising:

developing a first image which is a primary color image formed with the first toner (the first image developing step),
developing second images which are primary color images formed with the second toners (the second images developing step),
forming an image including a higher-order color on a transfer medium by transferring the first image and then the second images onto the transfer medium (the step of overlapping colors on a transfer medium),
transferring the image including the higher-order color formed on the transfer medium onto a recording medium (the higher-order color image transferring step), and
fixing the image including the higher-order color transferred onto the recording medium on the recording medium (the fixing step).

The second method is a method for forming an image by an electrostatic image development type full-color printer using the toner set of the present disclosure,
the method comprising:

developing a first image which is a primary color image formed with the first toner (the first image developing step),
developing second images which are primary color images formed with the second toners (the second images developing step),
forming an image including a higher-order color on a recording medium by transferring the first image and then the second images onto the recording medium (the step of overlapping colors on a recording medium), and
fixing the image including the higher-order color transferred onto the recording medium on the recording medium (the fixing step).

In the present disclosure, the term "primary color" means a color obtained by printing with a single color toner; the term "secondary color" means a color obtained by overlapping primary color toner images of two colors; and the term "higher-order color" means a color obtained by overlapping primary color toner images of multiple colors.
Also in the present disclosure, the term "toner image" literally means an image formed with a toner. In particular, the term is used to emphasize the following: the state that the toner is distributed according to an image required to be reproduced on an image holding surface such as a photoconductor, transfer medium or recording medium, is detected as a visual image.
Also in the present disclosure, the term "initial color" means the color of a primary color toner image which is transferred first onto a transfer receptive medium when a full-color image is formed as follows: primary color toner images of various colors are formed by use of toner developing devices; the toner images are sequentially transferred onto one transfer receptive medium (a recording medium or a transfer medium) to overlap the colors on the transfer receptive medium, thereby forming a full-color image.
Also in the present disclosure, the term "initial developing device" means a developing device used to develop a primary color toner image of the initial color. When toner developing devices are aligned in series along the conveyor path of the transfer receptive medium (recording medium or transfer medium) in a developing system, the developing device that the transfer receptive medium following the conveyor path meets first, is the "initial developing device".
The toner set of the present disclosure is preferably applied to the following printing method: by use of primary color toners such as yellow, cyan and magenta toners, electrostatic latent images corresponding to the primary colors are developed to form primary color toner images on developing devices, and the obtained primary color toner images are sequentially transferred onto one transfer receptive medium selected from the group consisting of a recording medium and a transfer medium to overlap the colors on the transfer receptive medium, thereby forming a full-color image.
In the case of overlapping the colors on the recording medium, the primary color toner images are sequentially transferred from the surfaces having the toner images formed thereon of the developing devices onto the recording medium directly or via an intermediate transfer step of being transferred onto the transfer medium, thereby forming a full-color image including a higher-order color on the recording medium.
In the case of overlapping the colors on the transfer medium, the primary color toner images are sequentially transferred from the surfaces having the toner images formed thereon of the developing devices onto one transfer medium directly or via an intermediate transfer step of being transferred onto another preceding transfer medium, thereby forming a full-color image including a higher-order color on the transfer medium. Then, the full-color image formed on the transfer medium is transferred onto the recording medium directly or via an intermediate transfer step onto another subsequent transfer medium.
The first toner included in the toner set of the present disclosure is the primary color toner which is transferred first onto the transfer receptive medium in the process of overlapping the colors on one transfer receptive medium selected from the group consisting of a recording medium and a transfer medium. The second toners included in the toner set are the primary color toners which are transferred second or later in the process of overlapping the colors on the transfer receptive medium.
The first toner is generally selected from the group consisting of a yellow toner, a cyan toner and a magenta toner.
The second toners are generally selected from the group consisting of the yellow toner, the cyan toner, the magenta toner and the black toner so that the relationship with adjacent overlapped toners satisfies the formula (2) or (3) In the image forming method using the toner set of the present disclosure, in addition to the yellow, cyan and magenta toners which are the reference yellow, cyan and magenta colors, another yellow, cyan or magenta toner or the like, which is different in color parameters (e.g., hue, color density, lightness and chroma) from the toner of the reference yellow, cyan or magenta color, may be used.
As the transfer medium used to overlap the colors thereon, examples include, but are not limited to, an intermediate transfer belt and an intermediate transfer roller.
As the recording medium, examples include, but are not limited to, a coated paper, an art paper, an OHP sheet, as well as a recording paper such as a plain paper.
As the printing device that can execute the above-mentioned process, the following full-color printer may be used, for example: a full-color printer in which developing devices corresponding to the color toners included in the toner set are aligned in series, and primary color images produced by the developing devices (color separation images) are sequentially transferred from the developing devices onto one recording medium directly or via a transfer medium to form an image including a secondary or higher-order color on the recording medium. This is a type of so-called tandem printer.
FIG. 1 is a schematic view of an example of the image forming device to which the toner set of the present disclosure is applicable. The image forming method of the present disclosure is not limited to the one shown in FIG. 1. The structure, size and form of the materials used in the method of the present disclosure are not limited to those of the materials shown in FIG. 1.
An image forming device 100 shown in FIG. 1 is a tandem printer. The image forming device 100 includes the following components: a conveyor path 4 for conveying a recording medium R; four developing devices 1Y, 1M, 1C and 1K corresponding to the four colors of yellow (Y), magenta (M), cyan (C) and black (K), respectively; transfer mediums 2Y, 2M, 2C and 2K and support rollers 3Y, 3M, 3C and 3K corresponding to the four developing devices 1Y, 1M, 1C and 1K, respectively; an exposure device 5 for applying laser light according to primary color image data obtained by color separation of the original image; and a fixing roller 6 and a support roller 7, which are paired with each other. The four developing devices 1Y, 1M, 1C and 1K corresponding to the four colors of yellow (Y), magenta (M), cyan (C) and black (K), respectively, are aligned in series along the conveying direction D of the recording medium R in the image forming device. The four developing devices are aligned in the following order from the upstream side of the conveying direction: the yellow developing device 1Y, the magenta developing device 1M, the cyan developing device 1C, and the black developing device 1K.
The structure of the developing devices will be described with reference to the yellow developing device 1Y as a representative example. The developing device 1Y includes a photoconductor 11Y in a drum form, and the following components are disposed around the photoconductor 11Y: a charging roller 12Y for charging the photoconductor surface to a predetermined voltage; a laser light irradiator 13Y for irradiating the photoconductor 11Y with the laser light produced in the exposure device to form an electrostatic image; a developing section 14Y for developing the electrostatic image by supplying a charged toner to the electrostatic image; the transfer medium 2Y in a roller form for transferring the developed toner image; and a cleaner 15Y for removal of the toner remaining on the photoconductor 11Y after the toner image is transferred onto the transfer medium. The developing section 14Y is connected to a toner storage 16Y through a yellow toner supply path.
As with the yellow developing device 1Y, the remaining developing devices of other colors include a photoconductor (11M, 11C, 11K), a charging roller (12M, 12C, 12K), a laser light irradiator (13M, 13C, 13K), a developing section (14M, 14C, 14K), a cleaner (15M, 15C, 15K) and a toner storage (16M, 16C, 16K). These components and a transfer medium (2M, 2C, 2K) are disposed around the photoconductor.
The method for forming an image by use of the image forming device 100 will be described. In this device, the yellow toner is selected as the first toner and used in the initial developing device 1Y. The magenta (M), cyan (C) and black (K) toners are used in the second and subsequent developing devices as the second toners.
First, in the yellow developing device 1Y, the surface of the photoconductor 11Y is uniformly charged by the charging roller 12Y. A photoconductor generally has high resistance (the resistance of general resin); however, it is characterized in that once irradiated with laser light, the specific resistance of a laser-irradiated part is changed. Accordingly, laser light is produced by the exposure device 5 according to the primary color image data of yellow, and the surface of the charged photoconductor 1Y is irradiated with the laser light by the laser light irradiator 13Y. A photosensitive layer on the surface of the photoconductor 11Y is irradiated with the laser light, thereby forming an electrostatic latent image corresponding to the primary color image of yellow on the surface of the photoconductor 11Y.
The electrostatic latent image is formed by the charge left in a part not irradiated with the laser light. Accordingly, it is a negative latent image.
The electrostatic latent image on the photoconductor 11Y is moved to the position of the developing section 14Y by the rotation of the photoconductor, and the electrostatic latent image is developed there to obtain a primary color toner image of yellow.
The primary color toner image of yellow on the photoconductor is moved to the primary transfer position by the rotation of the photoconductor. At the primary transfer position, the surface of the photoconductor 11Y and the surface of the transfer medium 2Y are brought into contact with each other. Accordingly, the primary color toner image of yellow on the photoconductor undergoes primary transfer to the surface of the transfer medium 2Y.
By the rotation of the transfer medium, the primary color toner image of yellow on the transfer medium 2Y is moved to the position where the primary color toner image of yellow undergoes secondary transfer. At the secondary transfer position, the recording medium R on the conveyor path 4 is sandwiched between the transfer medium 2Y and the support roller 3Y, and the surface of the transfer medium 2Y and the image receptive surface of the recording medium R are brought into contact with each other. Accordingly, the primary color toner image of yellow on the transfer medium 2Y undergoes secondary transfer onto the recording medium R.
Next, in the magenta developing device 1M, the same process as the process of forming the primary color toner image of yellow is executed. That is, in the magenta developing device 1M, a primary color toner image of magenta is formed on the surface of the photoconductor 11M; the formed image undergoes primary transfer to the surface of the transfer medium 2M; and then the transferred image is moved to the position where the primary color toner image of magenta undergoes secondary transfer by the rotation of the transfer medium 2M. Meanwhile, a part having the primary color toner image of yellow formed thereon of the recording medium R is moved from the upstream side of the conveyor path 4 and reaches the position where the primary color toner image of magenta undergoes secondary transfer. The primary color toner image of magenta on the transfer medium 2M is aligned there with the primary color toner image of yellow on the recording medium R and undergoes secondary transfer onto the recording medium R.
Next, in the cyan developing device 1C and the black developing device 1K, the same process as the process of forming the primary color toner image of yellow is executed. Then, the primary color toner images of yellow (Y), magenta (M), cyan (C) and black (K) are overlapped in this order on the recording medium R moved by the conveyor path, thereby obtaining a full-color image including a higher-order color. The recording medium R passes through all of the developing devices, and after the image including the higher-order color is formed, the recording medium R moves to the position where the fixing step is carried out. At that position, the recording medium R is sandwiched between the fixing roller 6 and the support roller 7. Accordingly, the image including the higher-order color is fixed on the recording medium.

Examples

Hereinafter, the present disclosure will be described further in detail, with reference to the following examples and comparative examples. However, the present disclosure is not limited to these examples. Herein, part(s) and % are on a mass basis unless otherwise noted.
The weight average molecular weight Mw of the polymer was determined as a polystyrene equivalent molecular weight measured by GPC. A sample for measurement was obtained as follows: a polymer was dissolved in tetrahydrofuran (THF) so as to have a concentration of 2 mg/mL, and an ultrasonic treatment was carried out thereon for 10 minutes, followed by filtration through a 0.45 µm membrane filter, thereby obtaining the sample for measurement. The measurement conditions were as follows: temperature: 40°C, solvent: tetrahydrofuran, flow rate: 1.0 mL/min, concentration: 0.2 wt. %, and sample input amount: 100 µL. As a column, GPC TSKGEL MULTIPORE HXL-M (30 cm × 2) manufactured by Tosoh Corporation, was used. Also, the measurement was carried out under the condition that the first- order correlation (Log(Mw) - elution time) in a weight average molecular weight (Mw) range of from 1,000 to 300,000, was 0.98 or more.

[Production Example 1: Production of polar resin P1]

First, 200 parts of toluene was put in a reaction container. While stirring the toluene, the gas inside the reaction container was sufficiently replaced with nitrogen. Then, the temperature of the toluene was increased to 90°C. Then, a mixed solution of 97.0 parts of methyl methacrylate, 2.6 parts of ethyl acrylate, 0.4 parts of acrylic acid, and 3 parts of t-butylperoxy-2-ethylhexanoate (product name: PERBUTYL O, manufactured by NOF Corporation) was added dropwise to the reaction container for two hours. Also, the condition of the mixture was maintained for 10 hours under toluene flux, thereby completing polymerization. Then, the solvent was removed by distillation under reduced pressure, thereby obtaining a polar resin P1 (MMA/EA/AA). The polar resin P1 had an acid value of 2.5 mgKOH/g, a Tg of 74°C, and a Mw of 12600.

[Production Example 2: Synthesis of SIS composition]

First, 23.2 kg of cyclohexane, 1.5 mmol of N,N,N',N'-tetramethylethylenediamine and 1.70 kg of styrene were put in a pressure-resistant reactor and stirred at 40°C. While stirring them at 40°C, 99.1 mmol of n-butyllithium was added thereto. With increasing the temperature of the obtained mixture to 50°C, the mixture was polymerized for one hour. The polymerization conversion rate of the styrene was 100% by weight. With controlling the temperature of the mixture at 50°C to 60°C, 6.03 kg of isoprene was continuously added to the reactor for one hour. After the addition of the isoprene was completed, the mixture was further polymerized for one hour, thereby obtaining a styrene-isoprene diblock copolymer (a) (a copolymer (a) represented by Ar-D). The polymerization conversion rate of the isoprene was 100%. Next, 15.0 mmol of dimethyldichlorosilane was added thereto as a coupling agent to initiate a coupling reaction, and the coupling reaction was continued for two hours, thereby obtaining a styrene-isoprene-styrene triblock copolymer (b) (a copolymer (b) represented by Ar-D-Ar). Then, 198 mmol of methanol was added thereto as a polymerization inhibitor, and they were mixed well to stop the reaction, thereby obtaining a reaction solution containing a styrene-isoprene-styrene triblock copolymer (SIS) composition containing the block copolymers (a) and (b). Part of the obtained reaction solution was removed and used to measure the following: the weight average molecular weight Mw of each block, the weight average molecular weight Mw of each block copolymer, the weight average molecular weight Mw of the whole SIS composition, the content rate of each block copolymer, the content of the styrene unit, and the content of the vinyl bond in the conjugated diene block. The results are shown in Table 1.
Then, to 100 parts of the thus-obtained reaction solution (containing 30 parts of a polymer component), 0.3 parts of 2,6-di-tert-butyl-p-cresol was added as an antioxidant. They were mixed to obtain a mixed solution, and the mixed solution was gradually added in a dropwise manner to a hot water at 85°C to 95°C to vaporize the solvent, thereby obtaining precipitates. The precipitates were pulverized and dried by hot air at 85°C, thereby recovering the SIS composition. The melt index of the obtained SIS composition was measured. The result is shown in Table 1.

[Table 1]

Table 1

		SIS composition
Diblock copolymer (a)	Mw of diblock copolymer (a)	109000
	Mw of styrene block	17000
	Mw of conjugated diene block	92000
Triblock copolymer (b)	Mw of triblock copolymer (b)	218000
	Mw of styrene block	17000
	Mw of conjugated diene block	184000
Whole composition	Mw of whole composition	142000
	Styrene unit content (%)	22
	Vinyl bond content (mol %) of conjugated diene block	7
	Content (%) of diblock copolymer (a)	70
	Content (%) of triblock copolymer (b)	30
	Melt index (g/10 min) condition G	10

[Production Example 3: Production of mixed crystal of magenta pigments]

2,5-Di-(4-methylphenylamino)terephthalic acid was cyclized in phosphoric acid to synthesize 2,9-dimethylquinacridone (C.I. Pigment Red 122). Water was added to the obtained phosphoric acid dispersion of 2,9-dimethylquinacridone, and the 2,9-dimethylquinacridone was filtered off by a filter and washed with water. Water was added again to the washed 2,9-dimethylquinacridone to obtain an aqueous dispersion having a solid content of 20%.
Similarly, 2,5-di-phenylaminoterephthalic acid was used to produce an aqueous dispersion of quinacridone (C.I. Pigment Violet 19) with a solid content of 20%.
To 250 parts of an aqueous dispersion of the dimethylquinacridone (C.I. Pigment Red 122) having a solid content of 20% described above and 250 parts of an aqueous dispersion of the quinacridone (C.I. Pigment Violet 19) having a solid content of 20%, 250 parts of ethanol were added to obtain a mixture liquid of pigments. The mixture was transferred to a container equipped with a cooling tube and allowed to react under heating reflux for 5 hours while the pigments were ground. After completion of the reaction, the pigment was filtered off from the reaction solution, washed, dried and then pulverized to obtain a mixed crystal of magenta pigments (that is, a mixed crystal of C.I. Pigment Red 122 and C.I. Pigment Violet 19). The mass ratio of C.I. Pigment Red 122 to C.I. Pigment Violet 19 contained in the mixed crystal was 1:1.

[Production of magenta toner M1]

1. Production of magenta colored resin particles

(1) Preparation of polymerizable monomer composition for core

First, 70 parts of styrene, 30 parts of n-butyl acrylate and 0.2 parts of divinylbenzene as polymerizable monomers, 1.0 part of tetraethylthiuram disulfide as a molecular weight modifier, and 8 parts of the mixed crystal of the magenta pigments obtained in Production Example 3 (the mixed crystal of C.I. Pigment Red 122 and C.I. Pigment Violet 19) as a colorant, were wet-pulverized by means of a media-type disperser (product name: PICOMILL, manufactured by: ASADA IRON WORKS. Co., Ltd.)
To the mixture obtained by the wet pulverization, 10 parts of a charge control resin (CCR1: a styrene-acrylic polymer containing a quaternary ammonium salt-containing (meth)acrylate monomer unit in an amount of 1.0% by mass, "FCA-676P" (product name) manufactured by Fujikura Kasei Co., Ltd., Tg 73°C, Mw 19,500), 20 parts of an ester wax (behenyl stearate, melting point: 70°C), 1 part of the polar resin P1 obtained in Production Example 1 and 5 parts of the SIS composition obtained in Production Example 2 were added, mixed and dissolved to prepare a polymerizable monomer composition for core.

(2) Preparation of aqueous dispersion medium

An aqueous solution in which 7.3 parts of sodium hydroxide was dissolved in 50 parts of deionized water, was gradually added under stirring to an aqueous solution in which 10.4 parts of magnesium chloride was dissolved in 280 parts of deionized water, thereby preparing a magnesium hydroxide colloidal dispersion.

(3) Droplets forming step

At room temperature, the polymerizable monomer composition for core was added to the magnesium hydroxide colloidal dispersion obtained above, and the mixture was stirred until the droplets were stabilized. As a polymerization initiator, 5 parts of t-butylperoxy-2-ethylhexanoate (product name: PERBUTYL O, manufactured by NOF Corporation) was added thereto. Then, the thus-obtained mixture was subjected to high-speed shearing at a rotational frequency of 15,000 rpm by use of an in-line type emulsifying disperser (product name: MILDER, manufactured by Pacific Machinery & Engineering Co., Ltd.) to form the polymerizable monomer composition for core into droplets.

(4) Polymerization step

The thus-obtained suspension in which the droplets of the polymerizable monomer composition for core were dispersed, was put in a reactor equipped with stirring blades, and the temperature thereof was increased to 90°C to initiate a polymerization reaction. When the polymerization conversion rate reached almost 100%, 3.0 parts of methyl methacrylate (a polymerizable monomer for shell) was added to the reactor. The reaction was further continued for 3 hours at 95°C. Then, the reaction was stopped by water-cooling the reactor, thereby obtaining an aqueous dispersion of colored resin particles.

(5) Post-treatment step

The aqueous dispersion of the colored resin particles was subjected to acid washing (25°C, 10 minutes) by adding, while stirring the aqueous dispersion, sulfuric acid to the dispersion until the pH of the dispersion reached 4.5 or less. Then, the colored resin particles were separated by filtration and washed with water. The washing water was filtered. The colored resin particles were repeatedly washed until the electric conductivity of the filtrate at this time was 20 µS/cm. The colored resin particles subjected to the washing and filtering were dehydrated and dried to obtain the colored resin particles in a dry state.

(6) External addition treatment step

To 100 parts of the colored resin particles, the following particles were added.
Silica fine particles A having a number average primary particle diameter 10 nm: 0.7 parts
Silica fine particles B having a number average primary particle diameter of 55 nm (particles hydrophobized with amino-modified silicone oil): 1 part
External addition treatment was performed by mixing the particles by use of a high-speed stirring machine (product name: FM MIXER, manufactured by Nippon Coke & Engineering Co., Ltd.), thereby preparing a magenta toner M1.

[Production of magenta toners M2 to M4]

Magenta toners M2 to M4 were obtained in the same manner as the method for producing the magenta toner M1, except that in "Preparation of polymerizable monomer composition for core", the type and amount of the added charge control resin were changed according to Table 2.
The details of charge control resins CCR2 to CCR4 are as follows.

CCR2: A styrene-acrylic polymer containing a quaternary ammonium salt-containing (meth)acrylate monomer unit in an amount of 2% by mass, "FCA-592P" (product name) manufactured by Fujikura Kasei Co., Ltd., Tg 82°C, Mw 12,000
CCR3: A styrene-acrylic polymer containing a quaternary ammonium salt-containing (meth)acrylate monomer unit in an amount of 0.5% by mass, "FCA-700P" (product name) manufactured by Fujikura Kasei Co., Ltd., Tg 71°C
CCR4: A styrene-acrylic polymer containing a quaternary ammonium salt-containing (meth)acrylate monomer unit in an amount of 8% by mass, "FCA-161P" (product name) manufactured by Fujikura Kasei Co., Ltd., Tg 60°C, Mw 21,000

[Production of magenta toners M5 to M7]

Magenta toners M5 to M7 were obtained in the same manner as the method for producing the magenta toner M1, except that in "Preparation of polymerizable monomer composition for core", the type or amount of the added ester wax was changed according to Table 2, and the SIS composition was not added to the magenta toner M6.

[Production of magenta toners M8 and M9]

Magenta toners M8 and M9 were obtained in the same manner as the method for producing the magenta toner M1, except that in "Preparation of polymerizable monomer composition for core", the amount of the added polar resin P1 was changed according to Table 2.

[Production of magenta toners M10 and M11]

Magenta toners M10 and M11 were obtained in the same manner as the method for producing the magenta toner M1, except that in "Preparation of polymerizable monomer composition for core", the amount of the added SIS composition was changed according to Table 2.

[Production of magenta toners M12 to M15]

Magenta toners M12 to M15 were obtained in the same manner as the method for producing the magenta toner M1, except that in "Preparation of polymerizable monomer composition for core", the amount of the added charge control resin, the amount of the added colorant or both of them were changed according to Table 2.

[Evaluation of the magenta toners]

(1) Heat resistant temperature of the toner

First, 10 g of the toner was placed in a 100 mL polyethylene container, and the container was hermetically sealed. Then, the container was set in a constant temperature water bath at a predetermined temperature. After 8 hours passed, the container was removed from the constant temperature water bath. The toner was transferred from the removed container onto a 42-mesh sieve in a manner preventing vibration as much as possible, and then it was set in a powder characteristic tester (product name: POWDER TESTER (registered trademark) PT-R, manufactured by: Hosokawa Micron Corporation). The amplitude condition of the sieve was set to 1.0 mm, and the sieve was vibrated for 30 seconds. Then, the mass of the toner remaining on the sieve was measured, and the thus-measured mass was determined as an aggregated toner mass.
The maximum temperature at which the aggregated toner mass became 0.5 g or less, was determined as the heat resistant temperature of the toner. As the heat resistant temperature increases, the blocking during toner storage is less likely to occur and the storage stability of the toner improves.

(2) Fixing temperature of the toner

A commercially-available, non-magnetic one-component developing printer (a 30 sheets per minute printer; printing speed: 30 sheets/min) was modified such that the temperature of the fixing roller was able to be changed. While the temperature of the fixing roller of the printer was changed by 5°C, the fixing rate at each changed temperature was measured. The relationship between the temperature and the fixing rate was determined, and the lowest temperature at which the fixing rate of 85% or more was obtained, was defined as the fixing temperature of the toner. The lower the fixing temperature, the better the low-temperature fixability of the toner.
The fixing rate was calculated from the image density ratio before and after a rubbing test operation of a solid area on a test paper sheet printed by the printer. When the image density before the rubbing test is determined as "ID (before)" and the image density after the rubbing test is determined as "ID (after)", the fixing rate is determined as follows. $Fixing rate (%) = [ID (after) / ID (before)] \times 100$
The rubbing test was carried out by attaching the measurement area of the test paper sheet to a fastness tester with an adhesive tape, applying a 500 g load, and carrying out reciprocating rubbing 5 times with a rubbing terminal wrapped with a cotton cloth.

(3) Printing durability

Printing sheets were set in a commercially-available, non-magnetic one-component development printer, and toners were put in the developing devices of the printer. The printer was left for 24 hours in a normal-temperature and normal-humidity (N/N) environment at a temperature of 23°C and a humidity of 50% RH. In the same environment, 20,000 sheets were continuously printed at an image density of 5%. Solid pattern printing (image density 100%) was carried out at every 500th sheets, and the resulting solid pattern images were measured for image density by means of a reflection image densitometer (product name: RD918, manufactured by: Macbeth). Then, white solid pattern printing (image density 0%) was carried out, and the printer was stopped in the middle of the white solid pattern printing. A piece of an adhesive tape (product name: SCOTCH MENDING TAPE 810-3-18, manufactured by: Sumitomo 3M Limited) was attached to a non-image area on the photoconductor of the printer after development to make the toner in the area adhere to the tape piece. Then, the tape piece was attached to a printing sheet. Next, the whiteness degree (B) of the printing sheet on which the tape piece was attached, was measured with a whiteness colorimeter (manufactured by Nippon Denshoku Industries Co., Ltd.) In the same manner, an unused piece of the adhesive tape was attached to the printing sheet, and the whiteness degree (A) was measured. The difference between the whiteness degrees (B) and (A) (B - A) was determined as a fog value. As the fog value gets smaller, fogging decreases and better printing is obtained. The number of continuously printed sheets that maintained an image quality with a fog value of 3 or less, was measured.

(4) Fogging in low-temperature and low-humidity (L/L) environment

Printing sheets were set in a commercially-available, non-magnetic one-component development printer, and toners were put in the developing devices of the printer. The printer was left for 24 hours in a low-temperature and low-humidity (L/L) environment at a temperature of 10°C and a humidity of 20% RH. In the same environment, 3 sheets were continuously printed at an image density of 5%. Then, white solid pattern printing (image density 0%) was carried out, and the printer was stopped in the middle of the white solid pattern printing. A piece of an adhesive tape (product name: SCOTCH MENDING TAPE 810-3-18, manufactured by: Sumitomo 3M Limited) was attached to a non-image area on the photoconductor of the printer after development to make the toner in the area adhere to the tape piece. Then, the tape piece was attached to a printing sheet. Next, the whiteness degree (B) of the printing sheet on which the tape piece was attached, was measured with a whiteness colorimeter (manufactured by Nippon Denshoku Industries Co., Ltd.) In the same manner, an unused piece of the adhesive tape was attached to the printing sheet, and the whiteness degree (A) was measured. The difference between the whiteness degrees (B) and (A) (B - A) was determined as a fog value.

(Evaluation criteria for LL fogging)

A: The fog value was less than 0.5.
B: The fog value was 0.5 or more and less than 1.
C: The fog value was 1 or more and less than 2.
D: The fog value was 2 or more.

(5) Fogging in high-temperature and high-humidity (H/H) environment

Printing sheets were set in a commercially-available, non-magnetic one-component development printer, and toners were put in the developing devices of the printer. The printer was left for 24 hours in a high-temperature and high-humidity (H/H) environment at a temperature of 35°C and a humidity of 80% RH. In the same environment, the fog value was measured in the same manner as the case of the low-temperature and low-humidity (L/L) environment described above.

(Evaluation criteria for HH fogging)

[Table 2]

Table 2

Toner No.		M1	M2	M3	M4	M5	M6	M7	M8	M9	M10	M11	M12	M13	M14	M15
Binder resin	ST (parts)	70	70	70	70	70	70	70	70	70	70	70	70	70	70	70
	BA (parts)	30	30	30	30	30	30	30	30	30	30	30	30	30	30	30
	DVB (parts)	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Charge control resin	Type	CCR1	CCR2	CCR3	CCR4	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1
	Amount (parts)	10	4.5	22	1.5	10	10	10	10	10	10	10	7	10	8	15
	Fcm (parts)	10	4.5	22	1.5	10	10	10	10	10	10	10	7	10	8	15
	Functional group amount Xa (%)	1	2	0.5	8	1	1	1	1	1	1	1	1	1	1	1
Colorant	PR122/PV19 (parts)	8	8	8	8	8	8	8	8	8	8	8	8	10	9	5
Colorant	Fp (parts)	8	8	8	8	8	8	8	8	8	8	8	8	10	9	5
X value	(Fcm × Xa) / Fp	1.25	1.13	1.38	1.50	1.25	1.25	1.25	1.25	1.25	1.25	1.25	0.88	1.00	0.89	3.00
Ester wax	Type	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl behenate	Pentaerythritol tetrastearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate
Ester wax	Amount (parts)	20	20	20	20	20	20	10	20	20	20	20	20	20	20	20
Polar resin P1	Amount (parts)	1	1	1	1	1	1	1	3	0.2	1	1	1	1	1	1
SIS composition	Amount (parts)	5	5	5	5	5	0	5	5	5	10	1	5	5	5	5
Toner evaluation	Heat resistant temperature (°C)	57	58	55	57	59	58	58	59	56	58	57	58	59	58	55
	Fixing temperature (°C)	145	150	140	155	150	165	155	150	140	155	150	145	155	150	140
	Printing durability	>20000	19000	18000	17000	>20000	18000	>20000	>20000	11000	19000	18000	13000	>20000	>20000	>20000
	LL fogging	A	A	A	B	A	A	A	B	B	A	A	A	A	A	D
	HH fogging	A	A	A	A	A	A	A	B	B	A	A	C	B	C	A

[Production of cyan toner C1]

A cyan toner C1 was obtained in the same manner as the method for producing the magenta toner M1, except that in "Preparation of polymerizable monomer composition for core", the amount of the added polymerizable monomer and that of the added charge control resin were changed according to Table 3, and as the colorant, 6 parts of C.I. Pigment Blue 15:3 was used instead of 8 parts of the mixed crystal of the magenta pigments.

[Production of cyan toners C2 to C4]

Cyan toners C2 to C4 were obtained in the same manner as the method for producing the cyan toner C1, except that the type and amount of the added charge control resin were changed according to Table 3.

[Production of cyan toners C5 to C7]

Cyan toners C5 to C7 were obtained in the same manner as the method for producing the cyan toner C1, except that the type or amount of the added ester wax was changed according to Table 3, and the SIS composition was not added to the cyan toner C6.

[Production of cyan toners C8 and C9]

Cyan toners C8 and C9 were obtained in the same manner as the method for producing the cyan toner C1, except that the amount of the added polar resin P1 was changed according to Table 3.

[Production of cyan toners C10 and C11]

Cyan toners C10 and C11 were obtained in the same manner as the method for producing the cyan toner C1, except that the amount of the added SIS composition was changed according to Table 3.

[Production of cyan toners C12 to C16]

Cyan toners C12 to C16 were obtained in the same manner as the method for producing the cyan toner C1, except that the amount of the added charge control resin, the amount of the added colorant or both of them were changed according to Table 3.

[Evaluation of the cyan toners]

In the same manner as the above-described magenta toners, the cyan toners were measured for heat resistant temperature and fixing temperature and then evaluated for printing durability in the normal-temperature and normal-humidity (N/N) environment and fogging in the low-temperature and low-humidity (L/L) environment and the high-temperature and high-humidity (H/H) environment.

[Table 3]

Table 3

Toner No.		C1	C2	C3	C4	C5	C6	C7	C8	C9	C10	C11	C12	C13	C14	C15	C16
Binder resin	ST (parts)	74	74	74	74	74	74	74	74	74	74	74	74	74	74	74	74
	BA (parts)	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26	26
	DVB (parts)	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Charge control resin	Type	CCR1	CCR2	CCR3	CCR4	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1
	Amount (parts)	5	2	11	0.7	5	5	5	5	5	5	5	10	4	5	5	4.5
	Fcm (parts)	5	2	11	0.7	5	5	5	5	5	5	5	10	4	5	5	4.5
	Functional group amount Xa (%)	1	2	0.5	8	1	1	1	1	1	1	1	1	1	1	1	1
Colorant	PB15:3 (parts)	6	6	6	6	6	6	6	6	6	6	6	6	6	5	8	6
Colorant	Fp (parts)	6	6	6	6	6	6	6	6	6	6	6	6	6	5	8	6
X value	(Fcm × Xa) / Fp	0.83	0.67	0.92	0.93	0.83	0.83	0.83	0.83	0.83	0.83	0.83	1.67	0.67	1.00	0.63	0.75
Ester wax	Type	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl behenate	Pentaerythritol tetrastearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate
Ester wax	Amount (parts)	20	20	20	20	20	20	10	20	20	20	20	20	20	20	20	20
Polar resin P1	Amount (parts)	1	1	1	1	1	1	1	3	0.2	1	1	1	1	1	1	1
SIS composition	Amount (parts)	5	5	5	5	5	0	5	5	5	10	1	5	5	5	5	5
Toner evaluation	Heat resistant temperature (°C)	57	58	55	57	59	58	58	59	56	58	57	56	58	56	58	57
	Fixing temperature (°C)	145	150	140	155	150	165	155	150	140	155	150	145	145	140	155	145
	Printing durability	>20000	19000	18000	17000	>20000	18000	>20000	>20000	11000	19000	18000	18000	15000	>20000	>20000	>20000
	LL fogging	A	A	B	A	A	A	A	B	B	A	A	C	A	B	A	B
	HH fogging	A	B	A	A	A	A	A	B	B	A	A	A	C	A	B	B

[Production of yellow toner Y1]

A yellow toner Y1 was obtained in the same manner as the method for producing the magenta toner M1, except that in "Preparation of polymerizable monomer composition for core", the amount of the added polymerizable monomer and that of the added charge control resin were changed according to Table 4, and as the colorant, 6.4 parts of C.I. Pigment Yellow 214 and 1.5 parts of C.I. Solvent Yellow 98 were used instead of 8 parts of the mixed crystal of the magenta pigments.

[Production of yellow toners Y2 to Y4]

Yellow toners Y2 to Y4 were obtained in the same manner as the method for producing the yellow toner Y1, except that the type and amount of the added charge control resin were changed according to Table 4.

[Production of yellow toners Y5 to Y7]

Yellow toners Y5 to Y7 were obtained in the same manner as the method for producing the yellow toner Y1, except that the type or amount of the added ester wax was changed according to Table 4, and the SIS composition was not added to the yellow toner Y6.

[Production of yellow toners Y8 and Y9]

Yellow toners Y8 and Y9 were obtained in the same manner as the method for producing the yellow toner Y1, except that the amount of the added polar resin P1 was changed according to Table 4.

[Production of yellow toners Y10 and Y11]

Yellow toners Y10 and Y11 were obtained in the same manner as the method for producing the yellow toner Y1, except that the amount of the added SIS composition was changed according to Table 4.

[Production of yellow toners Y12 to Y14]

Yellow toners Y12 to Y14 were obtained in the same manner as the method for producing the yellow toner Y1, except that the amount of the added charge control resin, the amount of the added colorant or both of them were changed according to Table 4.

[Evaluation of the yellow toners]

In the same manner as the above-described magenta toners, the yellow toners were measured for heat resistant temperature and fixing temperature and then evaluated for printing durability in the normal-temperature and normal-humidity (N/N) environment and fogging in the low-temperature and low-humidity (L/L) environment and the high-temperature and high-humidity (H/H) environment.

[Table 4]

Table 4

Toner No.		Y1	Y2	Y3	Y4	Y5	Y6	Y7	Y8	Y9	Y10	Y11	Y12	Y13	Y14
Binder resin	ST (parts)	78	78	78	78	78	78	78	78	78	78	78	78	78	78
	BA (parts)	22	22	22	22	22	22	22	22	22	22	22	22	22	22
	DVB (parts)	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Charge control resin	Type	CCR1	CCR2	CCR3	CCR4	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1
	Amount (parts)	2	1	6	0.5	2	2	2	2	2	2	2	6	5	1.5
	Fcm (parts)	2	1	6	0.5	2	2	2	2	2	2	2	6	5	1.5
	Functional group amount Xa (%)	1	2	0.5	8	1	1	1	1	1	1	1	1	1	1
Colorant	PY214 (parts)	6.4	6.4	6.4	6.4	6.4	6.4	6.4	6.4	6.4	6.4	6.4	6.4	5	8
	SY98 (parts)	1.5	1.5	1.5	1.5	1.5	1.5	1.5	1.5	1.5	1.5	1.5	1.5	0.5	1.5
	Fp (parts)	7.9	7.9	7.9	7.9	7.9	7.9	7.9	7.9	7.9	7.9	7.9	7.9	5.5	9.5
X value	(Fcm × Xa) / Fp	0.25	0.25	0.38	0.51	0.25	0.25	0.25	0.25	0.25	0.25	0.25	0.76	0.91	0.16
Ester wax	Type	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl behenate	Pentaerythritol tetrastearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate
Ester wax	Amount (parts)	20	20	20	20	20	20	10	20	20	20	20	20	20	20
Polar resin P1	Amount (parts)	1	1	1	1	1	1	1	3	0.2	1	1	1	1	1
SIS composition	Amount (parts)	5	5	5	5	5	0	5	5	5	10	1	5	5	5
Toner evaluation	Heat resistant temperature (°C)	58	59	56	57	60	59	59	60	57	59	58	57	57	59
	Fixing temperature (°C)	145	150	140	155	150	165	155	150	140	155	150	145	140	150
	Printing durability	>20000	19000	18000	17000	>20000	18000	>20000	>20000	11000	19000	18000	15000	>20000	>20000
	LL fogging	A	A	A	B	A	A	A	B	B	A	A	D	D	A
	HH fogging	A	B	A	A	A	A	A	B	B	A	A	A	A	D

[Production of black toner Bk1]

A black toner Bk1 was obtained in the same manner as the method for producing the magenta toner M1, except that in "Preparation of polymerizable monomer composition for core", the amount of the added polymerizable monomer and that of the added charge control resin were changed according to Table 5; as the colorant, 9 parts of carbon black (CB) (product name: #25B, manufactured by: Mitsubishi Chemical Corporation) was used instead of 8 parts of the mixed crystal of the magenta pigments; and the polar resin P1 was added during the wet pulverization using the media type disperser as well as the polymerizable monomer and so on, and it was not added after the wet pulverization.

[Production of black toners Bk2 to Bk4]

Black toners Bk2 to Bk4 were obtained in the same manner as the method for producing the black toner Bk1, except that the type and amount of the added charge control resin were changed according to Table 5.

[Production of black toners Bk5 to Bk7]

Black toners Bk5 to Bk7 were obtained in the same manner as the method for producing the black toner Bk1, except that the type or amount of the added ester wax was changed according to Table 5, and the SIS composition was not added to the black toner Bk6.

[Production of black toners Bk8 and Bk9]

Black toners Bk8 and Bk9 were obtained in the same manner as the method for producing the black toner Bk1, except that the amount of the added polar resin P1 was changed according to Table 5.

[Production of black toners Bk10 and Bk11]

Black toners Bk10 and Bk11 were obtained in the same manner as the method for producing the black toner Bk1, except that the amount of the added SIS composition was changed according to Table 5.

[Black toner Bk12]

A black toner Bk12 was obtained in the same manner as the method for producing the black toner Bk1, except that the amount of the added charge control resin was changed according to Table 5.

[Evaluation of the black toners]

In the same manner as the above-described magenta toners, the black toners were measured for heat resistant temperature and fixing temperature and then evaluated for printing durability in the normal-temperature and normal-humidity (N/N) environment and fogging in the low-temperature and low-humidity (L/L) environment and the high-temperature and high-humidity (H/H) environment.

[Table 5]

Table 5

Toner No.		Bk1	Bk2	Bk3	Bk4	Bk5	Bk6	Bk7	Bk8	Bk9	Bk10	Bk11	Bk12
Binder resin	ST (parts)	72	72	72	72	72	72	72	72	72	72	72	72
	BA (parts)	28	28	28	28	28	28	28	28	28	28	28	28
	DVB (parts)	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2	0.2
Charge control resin	Type	CCR1	CCR2	CCR3	CCR4	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1	CCR1
	Amount (parts)	4.5	1.5	12	0.5	4.5	4.5	4.5	4.5	4.5	4.5	4.5	5
	Fcm (parts)	4.5	1.5	12	0.5	4.5	4.5	4.5	4.5	4.5	4.5	4.5	5
	Functional group amount Xa (%)	1	2	0.5	8	1	1	1	1	1	1	1	1
Colorant	CB (parts)	9	9	9	9	9	9	9	9	9	9	9	9
Colorant	Fp (parts)	9	9	9	9	9	9	9	9	9	9	9	9
X value	(Fcm × Xa) / Fp	0.50	0.33	0.67	0.44	0.50	0.50	0.50	0.50	0.50	0.50	0.50	0.56
Ester wax	Type	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl behenate	Pentaerythritol tetrastearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate	Behenyl stearate
Ester wax	Amount (parts)	20	20	20	20	20	20	10	20	20	20	20	20
Polar resin P1	Amount (parts)	1	1	1	1	1	1	1	3	0.2	1	1	1
SIS composition	Amount (parts)	5	5	5	5	5	0	5	5	5	10	1	5
Toner evaluation	Heat resistant temperature (°C)	57	58	55	57	59	58	58	59	56	58	57	57
	Fixing temperature (°C)	145	150	140	155	150	165	155	150	140	155	150	145
	Printing durability	>20000	19000	18000	17000	>20000	18000	>20000	>20000	11000	19000	18000	>20000
	LL fogging	A	A	B	A	A	A	A	B	B	A	A	B
	HH fogging	A	B	A	B	A	A	A	B	B	A	A	A

The evaluation results of the color toners showed that the low-temperature fixability of the toner improved when the toner contained the monoester compound represented by the formula (A) in combination with the styrene-based thermoplastic elastomer.
It was also found that, by controlling the content of the polar resin in the toner which contained the charge control resin so that the X value obtained by the formula (1) was within the above-described preferred range, the low-temperature fixability, heat-resistant storage stability and printing durability of the toner improved, and fogging in the low-temperature and low-humidity (L/L) environment and the high-temperature and high-humidity (H/H) environment was suppressed.

[Examples 1 to 12 and Comparative Examples 1 to 6]

The color toners were combined according to Tables 6 to 8, thereby obtaining the toner sets of Examples 1 to 12 and Comparative Examples 1 to 6.

[Secondary color reproducibility]

Printing sheets were set in a commercially-available, non-magnetic one-component development printer (printing speed: 30 sheets/min), and the color toners of the toner set were put in the developing devices of the printer. The printer was left to stand for 24 hours in a normal temperature and normal humidity (N/N) environment of a temperature of 23°C and a humidity of 50% RH. Then, in the same environment, solid pattern printing of a secondary color at a printing density of 100% was carried out by overprinting. In the solid pattern printing of the secondary color, the toner combination of the initial color toner and the secondary transferred toner was as described below. In total, three kinds of solid pattern printing of the secondary color were carried out.

The combination of the magenta toner and the yellow toner
The combination of the magenta toner and the cyan toner
The combination of the cyan toner and the yellow toner

The vertical and horizontal center point of the printed sheet obtained by the solid pattern printing of the secondary color at a printing density of 100%, was used as the reference, and L* (lightness), a* and b* (chromaticity) of three points on the right side of the center point of the printed sheet and those of three points on the left side of the center point of the printed sheet (i.e., a total of 6 points) were measured, as well as those of the reference point (the horizontal and vertical center) of the printed sheet. For each of the 6 points of the printed sheet, a color difference ΔE was obtained by the following formula. Among the ΔE values obtained by the three kinds of solid pattern printing of the secondary color in total, the maximum value was defined as an evaluation value. Then, using the evaluation value, the secondary color reproducibility of the toner set was evaluated based on the following criteria. As ΔE decreases, the secondary color reproducibility of the toner set was evaluated to be higher. ΔE = √((Reference L* - Measured L*)^2 + (Reference a* - Measured a*)^2 + (Reference b* - Measured b*)^2

A: The maximum value of ΔE was less than 2.
B: The maximum value of ΔE was 2 or more and less than 4.
C: The maximum value of ΔE was 4 or more and less than 8.
D: Secondary color unevenness was not visually apparent; however, the maximum value of ΔE was 8 or more.
E: Secondary color unevenness was visually apparent.

[Table 6]

Table 6

	Example 1				Example 2				Example 3				Example 4
Toner No.	M1	C1	Y1	Bk1	M2	C2	Y2	Bk2	M3	C3	Y3	Bk3	M4	C4	Y4	Bk4
Fcm (parts)	10	5	2	4.5	4.5	2	1	1.5	22	11	6	12	1.5	0.7	0.5	0.5
Xa (%)	1	1	1	1	2	2	2	2	0.5	0.5	0.5	0.5	8	8	8	8
Fp (parts)	8	6	7.9	9	8	6	7.9	9	8	6	7.9	9	8	6	7.9	9
X value	1.25	0.83	0.25	0.50	1.13	0.67	0.25	0.33	1.38	0.92	0.38	0.67	1.50	0.93	0.51	0.44
Relationship between magnitudes of X values	X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Y) > X(Bk)
Ester wax type	Behenyl stearate				Behenyl stearate				Behenyl stearate				Behenyl stearate
Ester wax amount (parts)	20				20				20				20
Polar resin P1 (parts)	1				1				1				1
SIS composition (parts)	5				5				5				5
Secondary color reproducibility	A				B				B				B
	Example 5				Example 6				Example 7				Example 8
Toner No.	M5	C5	Y5	Bk5	M6	C6	Y6	Bk6	M7	C7	Y7	Bk7	M8	C8	Y8	Bk8
Fcm (parts)	10	5	2	4.5	10	5	2	4.5	10	5	2	4.5	10	5	2	4.5
Xa (%)	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1	1
Fp (parts)	8	6	7.9	9	8	6	7.9	9	8	6	7.9	9	8	6	7.9	9
X value	1.25	0.83	0.25	0.50	1.25	0.83	0.25	0.50	1.25	0.83	0.25	0.50	1.25	0.83	0.25	0.50
Relationship between magnitudes of X values	X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Bk) > X(Y)
Ester wax type	Behenyl behenate				Pentaerythritol tetrastearate				Behenyl stearate				Behenyl stearate
Ester wax amount (parts)	20				20				10				20
Polar resin P1 (parts)	1				1				1				3
SIS composition (parts)	5				0				5				5
Secondary color reproducibility	B				B				A				B

[Table 7]

Table 7

	Example 9				Example 10				Example 11				Example 12
Toner No.	M9	C9	Y9	Bk9	M10	C10	Y10	Bk10	M11	C11	Y11	Bk11	M1	C3	Y2	Bk4
Fcm (parts)	10	5	2	4.5	10	5	2	4.5	10	5	2	4.5	10	11	1	0.5
Xa (%)	1	1	1	1	1	1	1	1	1	1	1	1	1	0.5	2	8
Fp (parts)	8	6	7.9	9	8	6	7.9	9	8	6	7.9	9	8	6	7.9	9
X value	1.25	0.83	0.25	0.50	1.25	0.83	0.25	0.50	1.25	0.83	0.25	0.50	1.25	0.92	0.25	0.44
Relationship between magnitudes of X values	X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Bk) > X(Y)
Ester wax type	Behenyl stearate				Behenyl stearate				Behenyl stearate				Behenyl stearate
Ester wax amount (parts)	20				20				20				20
Polar resin P1 (parts)	0.2				1				1				1
SIS composition (parts)	5				10				1				5
Secondary color reproducibility	B				B				B				B

[Table 8]

Table 8

	Comparative Example 1				Comparative Example 2				Comparative Example 3
Toner No.	M12	C12	Y1	Bk1	M1	C13	Y12	Bk1	M13	C14	Y1	Bk1
Fcm (parts)	7	10	2	4.5	10	4	6	4.5	10	5	2	4.5
Xa (%)	1	1	1	1	1	1	1	1	1	1	1	1
Fp (parts)	8	6	7.9	9	8	6	7.9	9	10	5	7.9	9
X value	0.88	1.67	0.25	0.50	1.25	0.67	0.76	0.50	1.00	1.00	0.25	0.50
Relationship between magnitudes of X values	X(C) > X(M) > X(Bk) > X(Y)				X(M) > X(Y) > X(C) > X(Bk)				X(M) = X(C) > X(Bk) > X(Y)
Ester wax type	Behenyl stearate				Behenyl stearate				Behenyl stearate
Ester wax amount (parts)	20				20				20
Polar resin P1 (parts)	1				1				1
SIS composition (parts)	5				5				5
Secondary color reproducibility	C				C				D

	Comparative Example 4				Comparative Example 5				Comparative Example 6
Toner No.	M14	C16	Y13	Bk12	M15	C1	Y1	Bk1	M1	C1	Y14	Bk1
Fcm (parts)	8	4.5	5	5	15	5	2	4.5	10	5	1.5	4.5
Xa (%)	1	1	1	1	1	1	1	1	1	1	1	1
Fp (parts)	9	6	5.5	9	5	6	7.9	9	8	6	9.5	9
X value	0.89	0.75	0.91	0.56	3.00	0.83	0.25	0.50	1.25	0.83	0.16	0.50
Relationship between magnitudes of X values	X(Y) > X(M) > X(C) > X(Bk)				X(M) > X(C) > X(Bk) > X(Y)				X(M) > X(C) > X(Bk) > X(Y)
Ester wax type	Behenyl stearate				Behenyl stearate				Behenyl stearate
Ester wax amount (parts)	20				20				20
Polar resin P1 (parts)	1				1				1
SIS composition (parts)	5				5				5
Secondary color reproducibility	E				D				D

In the toner sets of Examples 1 to 12, each color toner contained the ester wax as the release agent; as the positively-chargeable charge control resin, it contained the styrene-acrylic polymer containing the quaternary ammonium salt-containing (meth)acrylate monomer unit; the X value calculated for the each color toner by the formula (1) was more than 0.2 and less than 2.5; and the X values of the yellow, magenta and cyan toners satisfied X(M) > X(C) > X(Y). Accordingly, the color differences ΔE of the printed products in the secondary colors obtained by combining the above-described two colors, were small and were excellent in secondary color reproducibility. In the toner sets of Examples 1 to 12, all of the combinations of the above-described two colors were small in color difference ΔE. Accordingly, it was revealed that a tertiary color obtained by use of the yellow, magenta and cyan toners were also excellent in color reproducibility.
Of them, Examples 1 and 7 were particularly excellent in secondary color reproducibility. The reason is presumed as follows: since the relationship between the magnitudes of the X values of the color toners was well balanced in the toner sets of Examples 1 and 7, the loaded amounts of the color toners were well balanced; since the X values of the color toners were within the preferred ranges, the dispersibility of the pigments in the color toners was good; and due to good seeping of the release agent from the toner, the color toner fixability improved.
Meanwhile, the toner sets of Comparative Examples 1 to 4 did not satisfy X(M) > X(C) > X(Y). In the toner sets of Comparative Examples 5 and 6, since the X value of at least one of the yellow, magenta or cyan toner was 0.2 or less or was 2.5 or more, the secondary color reproducibility was poor. Since the toner sets of Comparative Examples 1 to 6 contained the combination of two color toners having a large color difference ΔE, it was presumed that a tertiary color obtained by use of the yellow, magenta and cyan toners were also poor in color reproducibility.

Reference Signs List

100. Image forming device
R. Recording medium
D. Conveying direction
1. Developing device (1Y, 1M, 1C, 1K)
2. Transfer medium (2Y, 2M, 2C, 2K)
3. Support roller (3Y, 3M, 3C, 3K)
4. Conveyor path
5. Exposure device
6. Fixing roller
7. Support roller
11. Photoconductor (11Y, 11M, 11C, 11K)
12. Charging roller (12Y, 12M, 12C, 12K)
13. Laser light irradiator (13Y, 13M, 13C, 13K)
14. Developing section (14Y, 14M, 14C, 14K)
15. Cleaner (15Y, 15M, 15C, 15K)
16. Toner storage (16Y, 16M, 16C, 16K)

Claims

A toner set which is a color toner set comprising positively-chargeable color toners each comprising colored resin particles comprising a binder resin, a colorant, a release agent and a positively-chargeable charge control resin,
wherein the positively-chargeable color toners comprise at least a yellow toner, a magenta toner and a cyan toner;

wherein the release agent comprises an ester wax;

wherein the positively-chargeable charge control resin comprises at least one kind of styrene-acrylic polymer comprising a quaternary ammonium salt-containing (meth)acrylate monomer unit;

wherein a value of X calculated for the each color toner by the following formula (1) where Fcm is a content (parts by mass) of the styrene-acrylic polymer with respect to 100 parts by mass of the binder resin; Xa is a copolymerization ratio (% by mass) of the quaternary ammonium salt-containing (meth)acrylate monomer; and Fp is a content (parts by mass) of the colorant with respect to 100 parts by mass of the binder resin, is more than 0.2 and less than 2.5: $X = \{\sum (Fcm \times Xa)\} / Fp$ and

wherein the following formula (2) where X(Y) is the X value of the yellow toner; X(M) is the X value of the magenta toner; and X(C) is the X value of the cyan toner, is satisfied: $X (M) > X (C) > X (Y)$
The toner set according to Claim 1, wherein the copolymerization ratio Xa of the quaternary ammonium salt-containing (meth)acrylate monomer in the styrene-acrylic polymer is from 0.1% by mass to 10% by mass.
The toner set according to Claim 1 or 2, wherein the ester wax comprises a monoester compound represented by the following formula (A), and a content of the monoester compound is from 10 parts by mass to 25 parts by mass with respect to 100 parts by mass of the binder resin:

R¹-COO-R² Formula (A)

(where R¹ is a linear aliphatic hydrocarbon group containing 15 to 23 carbon atoms, and R² is a linear aliphatic hydrocarbon group containing 16 to 24 carbon atoms).
The toner set according to Claim 1 or 2, wherein each of the yellow, magenta and cyan toners further comprises an acidic group-containing copolymer as a polar resin, and a content of the acidic group-containing copolymer is from 0.2 parts by mass to 5 parts by mass with respect to 100 parts by mass of the binder resin.
The toner set according to Claim 1 or 2, wherein at least one of the positively-chargeable color toners further comprises a styrene-based thermoplastic elastomer.
The toner set according to Claim 1 or 2, wherein the positively-chargeable color toners further comprise a black toner, and the following formula (3) where X(Bk) is the X value of the black toner, is satisfied: $X (C) > X (Bk)$