Toner set for electrostatic image development

Abstract

To provide a toner set for electrostatic charge image development excellent in hot offset resistance and giving a high-gloss printed image, and a method for preparing the toner set.SOLUTION: A toner set for electrostatic charge image development including a yellow toner, a cyan toner, a magenta toner, and a black toner containing a binder resin, a colorant, and a release agent, wherein, in differential scanning calorimetry, the toner is weighed in an aluminum pan and heated from 25°C to 200°C at a temperature rising rate of 10°C / min, when the toner set is cooled from that temperature to 0 °C at a temperature lowering rate of 10 °C / min and then measured while raising the temperature to 180 °C at a temperature raising rate of 10 °C / min, at least one of the yellow toner and the magenta toner has a lower endothermic maximum peak temperature than the cyan toner and the black toner at the time of the second temperature rise, and a difference between the endothermic maximum peak temperature of the cyan toner or the black toner and the lower endothermic maximum peak temperature is 1 °C or more and 40 °C or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a toner set for developing electrostatic images used in developing latent images formed in electrophotography, electrostatic recording, electrostatic printing, etc., and a method for preparing the toner set. [Background technology]

[0002] When performing full-color printing using an electrophotographic image forming apparatus, a toner set consisting of four colors, namely the three primary colors of yellow, cyan, and magenta, plus black toner, is generally used (see Patent Documents 1 to 3).

[0003] On the other hand, with the development of electrophotographic systems, there is a demand for the development of toners for developing electrostatic images that are capable of forming high-gloss printed images in response to ever-higher image quality in color printing. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-71740 [Patent Document 2] Japanese Patent Application Laid-Open No. 2008-249989 [Patent Document 3] Japanese Patent Application Laid-Open No. 2003-295516 Summary of the Invention [Problem to be solved by the invention]

[0005] However, although various efforts have been made to improve the gloss of printed images, it is difficult to achieve both this and hot offset resistance.

[0006] The present invention relates to a toner set for developing electrostatic images that is excellent in hot offset resistance and can produce high-gloss printed images, and a method for preparing the toner set. [Means for solving the problem]

[0007] The present invention provides [1] A toner set for developing electrostatic images, which includes a yellow toner, a cyan toner, a magenta toner, and a black toner, each containing a binder resin, a colorant, and a release agent, and in differential scanning calorimetry, when the toner is weighed in an aluminum pan, heated from 25°C to 200°C at a heating rate of 10°C / min, cooled from that temperature to 0°C at a heating rate of 10°C / min, and then heated to 180°C at a heating rate of 10°C / min, the maximum endothermic peak temperature during the second heating is lower for at least one of the yellow toner and the magenta toner than for the cyan toner and the black toner, and the difference between the maximum endothermic peak temperature of the cyan toner and the black toner and the lower maximum endothermic peak temperature is 1°C or more and 40°C or less; and [2] A method for preparing a toner set for developing electrostatic images by combining at least a yellow toner, a cyan toner, a magenta toner, and a black toner, each containing a binder resin, a colorant, and a release agent, wherein, in differential scanning calorimetry, the toners are weighed into an aluminum pan, heated from 25°C to 200°C at a heating rate of 10°C / min, cooled from that temperature to 0°C at a heating rate of 10°C / min, and then heated to 180°C at a heating rate of 10°C / min, and measured while heating the toners to 180°C at a heating rate of 10°C / min, and the maximum endothermic peak temperature during the second heating is lower for at least one of the yellow toner and the magenta toner than for the cyan toner and the black toner, and the difference between the maximum endothermic peak temperature of the cyan toner and the black toner and the lower maximum endothermic peak temperature is 1°C or more and 40°C or less. Regarding. [Effects of the Invention]

[0008] The toner set for developing electrostatic images of the present invention has excellent hot offset resistance and provides high gloss printed images. DETAILED DESCRIPTION OF THE INVENTION

[0009] The toner set for developing electrostatic images of the present invention is a toner set for developing electrostatic images, which includes a yellow toner, a cyan toner, a magenta toner, and a black toner, each containing a binder resin, a colorant, and a release agent, and is characterized in that at least one of the yellow toner and the magenta toner has a lower maximum endothermic peak temperature than the cyan toner and the black toner. The reason why the method of the present invention can produce a toner set that has excellent hot offset resistance and produces high-gloss printed images is unclear, but is presumed to be as follows. The following mechanism is merely a presumption, and is not intended to be limiting.

[0010] The molecular structures of yellow and magenta colorants have a strong interaction with the binder resin, and yellow and magenta toners containing these colorants do not produce smooth images when fixed. In particular, when printing is performed using a four-color toner set that includes cyan and black toners, the gloss of the printed image tends to be low due to the influence of the yellow and magenta toners. Therefore, the inventors focused on the melting properties of each color toner constituting a toner set and discovered that the gloss of printed images can be improved by lowering the maximum endothermic peak temperature in differential scanning calorimetry, which is an index of toner melting properties, of at least one of the yellow toner and the magenta toner compared to that of the cyan toner and the black toner. Here, if the maximum endothermic peak temperature of the cyan toner and the black toner is also lowered, the hot offset resistance is likely to decrease, possibly due to a decrease in releasability from the fixing device. However, in the present invention, it is believed that it is possible to achieve both high gloss and hot offset resistance by lowering the endothermic peak temperature of at least one of the yellow toner and the magenta toner by a predetermined temperature compared to that of the cyan toner and the black toner.

[0011] As for the maximum endothermic peak temperature, as described above, at least one of the yellow toner and the magenta toner has a lower temperature than the cyan toner and the black toner, and the difference between the cyan toner and the black toner and the lower maximum endothermic peak temperature is 1° C. or more, preferably 3° C. or more, more preferably 5° C. or more, and from the viewpoint of low-temperature fixability, is 40° C. or less, preferably 35° C. or less, more preferably 30° C. or less. Here, the maximum endothermic peak temperature is the maximum endothermic peak temperature during the second temperature rise in differential scanning calorimetry (DSC measurement), when the toner is weighed in an aluminum pan, heated from 25° C. to 200° C. at a heating rate of 10° C. / min (first time), cooled from that temperature to 0° C. at a heating rate of 10° C. / min, and then heated to 180° C. at a heating rate of 10° C. / min (second time) and measured. As time passes after toner production, enthalpy relaxation occurs, and in the first heating, the endothermic peak derived from the glass transition temperature of the resin may become larger than the endothermic peak derived from the melting point of the release agent. On the other hand, in the second measurement, after heating once and resetting the thermal history, the influence of enthalpy relaxation is almost eliminated, and the endothermic peak derived from the melting point of the release agent, which has a large impact on the melting property of the toner, can be detected more accurately.

[0012] The toner set of the present invention is prepared by combining at least a yellow toner, a cyan toner, a magenta toner, and a black toner, and may also include other color toners as needed. Each of the toners included in the toner set of the present invention (hereinafter also referred to as each color toner) contains a binder resin, a colorant, and a release agent. The maximum endothermic peak temperature of the toner is most affected by the melting point of the release agent. In other words, the maximum endothermic peak temperature of the toner can be easily adjusted by the melting point of the release agent blended, and it is preferred that the yellow toner, cyan toner, magenta toner, and black toner are similar except for the types of colorant and release agent used.

[0013] The yellow toner, cyan toner, magenta toner, and black toner, preferably each color toner, may be either a polymerized toner obtained by a suspension polymerization method, an emulsion aggregation method, or the like, or a pulverized toner obtained by a melt-kneading method. In the present invention, however, from the viewpoint of hot offset resistance, a toner obtained by a suspension polymerization method is preferred, and a core-shell type toner in which core particles are coated with a shell layer is also preferred.

[0014] When a toner is obtained by suspension polymerization, for example, a polymerizable monomer composition containing a polymerizable monomer, a colorant, and a release agent is subjected to suspension polymerization in an aqueous medium in the presence of a polymerization initiator, to obtain a toner. Specifically, a preferred method is to granulate the polymerizable monomer composition in an aqueous medium in the presence of a polymerization initiator, and then perform suspension polymerization.

[0015] The polymerizable monomer preferably contains a monovinyl monomer as a main component.

[0016] Examples of monovinyl monomers include styrene; styrene derivatives such as vinyltoluene and α-methylstyrene; (meth)acrylic acid; (meth)acrylic acid esters such as methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, and dimethylaminoethyl (meth)acrylate; (meth)acrylic acid derivatives such as (meth)acrylonitrile and (meth)acrylamide; olefins such as ethylene, propylene, and butylene; vinyl halides and vinylidene halides such as vinyl chloride, vinylidene chloride, and vinyl fluoride; vinyl esters such as vinyl acetate and vinyl propionate; vinyl ethers such as methyl vinyl ether and ethyl vinyl ether; vinyl ketones such as methyl vinyl ketone and methyl isopropenyl ketone; and nitrogen-containing vinyl compounds such as 2-vinylpyridine, 4-vinylpyridine, and N-vinylpyrrolidone. These monovinyl monomers may be used alone or in combination. Among these monovinyl monomers, styrene, styrene derivatives, and (meth)acrylic acid esters are preferred.

[0017] The content of the monovinyl monomer in the polymerizable monomer is preferably 80% by mass or more, more preferably 85% by mass or more, even more preferably 90% by mass or more, and is preferably 100% by mass or less, more preferably 99.5% by mass or less.

[0018] The content of the monovinyl monomer in the polymerizable monomer composition is preferably 60% by mass or more, more preferably 65% ​​by mass or more, even more preferably 70% by mass or more, and preferably 100% by mass or less, more preferably 95% by mass or less, even more preferably 90% by mass or less.

[0019] From the viewpoint of hot offset resistance, the polymerizable monomer preferably contains a crosslinkable polymerizable monomer together with a monovinyl monomer. A crosslinkable polymerizable monomer refers to a monomer having two or more polymerizable functional groups. The crosslinkable polymerizable monomer is preferably a divinyl monomer, and examples thereof include aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, and derivatives thereof; di(meth)acrylic acid esters such as ethylene glycol dimethacrylate and diethylene glycol dimethacrylate; and other divinyl compounds such as N,N-divinylaniline and divinyl ether. These crosslinkable polymerizable monomers can be used alone or in combination of two or more. The content of the crosslinkable polymerizable monomer is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, and preferably 5 parts by mass or less, more preferably 2 parts by mass or less, per 100 parts by mass of the monovinyl monomer.

[0020] In the present invention, from the viewpoints of storage stability and low-temperature fixability, the polymerizable monomer preferably further contains a macromonomer. The macromonomer is a reactive oligomer or reactive polymer having a polymerizable carbon-carbon unsaturated double bond at the end of the molecular chain.

[0021] The number average molecular weight of the macromonomer is preferably 1,000 or more, more preferably 3,000 or more, and preferably 30,000 or less, more preferably 20,000 or less, and even more preferably 10,000 or less.

[0022] The content of the macromonomer is preferably 0.01 part by mass or more, more preferably 0.03 part by mass or more, even more preferably 0.05 part by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 1 part by mass or less, relative to 100 parts by mass of the monovinyl monomer.

[0023] As the colorant, a pigment or a dye is used, and from the viewpoint of further improving the coloring effect, a pigment is preferred. As the pigment, either an inorganic pigment or an organic pigment can be used, but an organic pigment is preferred.

[0024] Examples of colorants for yellow toner include organic pigments such as monoazo compounds, disazo compounds, condensed azo compounds, isoindolinone compounds, isoindoline compounds, benzimidazolone compounds, anthraquinone compounds, azo metal complexes, and methine compounds, as well as azo-based and anthraquinone-based dyes, and specific examples of organic pigments include CI Pigment Yellow 17, 74, 93, 95, 109, 111, 128, 139, 151, 154, 155, 174, 180, 185, and 214. Among these, condensed azo compounds are preferred, and CI Pigment Yellow 93 and CI Pigment Yellow 214 are more preferred.

[0025] Examples of colorants for magenta toners include organic pigments such as monoazo compounds, condensed azo compounds, diketopyrrolopyrrole compounds, anthraquinone compounds, quinacridone compounds, basic dye lake compounds, naphthol compounds, benzimidazolone compounds, thioindigo compounds, and perylene compounds, as well as benzoquinone-based, anthraquinone-based, and indigo-based dyes. Specific examples of organic pigments include CI Pigment Red 2, 3, 5, 6, 7, 23, 48:1, 48:2, 48:3, 48:4, 57:1, 81:1, 122, 144, 146, 150, 166, 169, 177, 184, 185, 202, 206, 220, 221, 238, 254, and 269, and CI Pigment Violet 19. Among these, quinacridone compounds are preferred, and CI Pigment Red 122 and CI Pigment Violet 19 are more preferred.

[0026] Examples of colorants for cyan toners include organic pigments such as copper phthalocyanine compounds and derivatives thereof, anthraquinone compounds, and basic dye lake compounds, as well as benzoquinone-based, anthraquinone-based, indigo-based, and phthalocyanine-based dyes, and specific examples of organic pigments include CI Pigment Blue 1, 7, 15, 15:1, 15:2, 15:3, 15:4, 60, 62, and 66. Among these, copper phthalocyanine compounds are preferred, and CI Pigment Blue 15 is more preferred.

[0027] Examples of colorants for black toner include inorganic pigments such as carbon black and inorganic composite oxides, and dyes such as azine and aniline black.

[0028] From the viewpoint of improving the color development of the toner, the content of the colorant is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 3 parts by mass or more, relative to 100 parts by mass of the binder resin, and is preferably 15 parts by mass or less, more preferably 13 parts by mass or less, and even more preferably 10 parts by mass or less.

[0029] Examples of the release agent include hydrocarbon wax, ester wax, silicone wax, and fatty acid amide wax. Examples of hydrocarbon waxes include mineral or petroleum-based hydrocarbon waxes such as paraffin wax and Fischer-Tropsch wax; and synthetic hydrocarbon waxes such as polyolefin waxes such as polyethylene wax, polypropylene wax and polybutene wax. Examples of ester waxes include mineral or petroleum-based ester waxes such as montan wax; plant-based ester waxes such as carnauba wax, rice wax, and candelilla wax; animal-based ester waxes such as beeswax; and synthetic ester waxes obtained by condensing carboxylic acids such as fatty acids with alcohols such as aliphatic alcohols. Examples of fatty acid amide waxes include oleic acid amide and stearic acid amide. Among these, from the viewpoint of toner releasability, hydrocarbon wax or ester wax is preferred, and ester wax is more preferred.

[0030] Suitable ester waxes include pentaerythritol-based ester waxes, dipentaerythritol-based ester waxes, and aliphatic monoalcohol-based ester waxes.

[0031] The pentaerythritol-based ester wax is preferably an ester of pentaerythritol and an aliphatic monocarboxylic acid, the dipentaerythritol-based ester wax is preferably an ester of dipentaerythritol and an aliphatic monocarboxylic acid, and the aliphatic monoalcohol-based ester wax is preferably an ester of an aliphatic monoalcohol and an aliphatic monocarboxylic acid.

[0032] Examples of the aliphatic monocarboxylic acid include stearic acid, behenic acid, caprylic acid, lauric acid, myristic acid, isostearic acid, palmitic acid, oleic acid, condensed ricinoleic acid, and 12-hydroxystearic acid.

[0033] The aliphatic monocarboxylic acid preferably has 10 or more carbon atoms, more preferably 12 or more carbon atoms, and even more preferably 14 or more carbon atoms, and preferably has 30 or less carbon atoms, more preferably 28 or less carbon atoms, and even more preferably 26 or less carbon atoms.

[0034] Examples of the aliphatic monoalcohols include behenyl alcohol, stearyl alcohol, capryl alcohol, lauryl alcohol, myristyl alcohol, palmityl alcohol, oleyl alcohol, arabinyl alcohol, and ceryl alcohol.

[0035] The aliphatic monoalcohol preferably has 10 or more carbon atoms, more preferably 12 or more carbon atoms, and even more preferably 14 or more carbon atoms, and preferably has 30 or less carbon atoms, more preferably 28 or less carbon atoms, and even more preferably 26 or less carbon atoms.

[0036] Specific examples of pentaerythritol-based ester waxes include pentaerythritol tetrabehenate, pentaerythritol tetrastearate, and pentaerythritol tetrapalmitate.

[0037] Specific examples of dipentaerythritol-based ester waxes include dipentaerythritol hexastearate, dipentaerythritol hexabehenate, and dipentaerythritol stearate.

[0038] Specific examples of the aliphatic monoalcohol ester wax include behenyl behenate, behenyl stearate, stearyl stearate, and stearyl behenate.

[0039] The melting point of the release agent is preferably 60°C or higher, more preferably 65°C or higher, and even more preferably 70°C or higher, from the viewpoint of the releasability of the toner, and is preferably 100°C or lower, more preferably 90°C or lower, even more preferably 85°C or lower, and even more preferably 80°C or lower, from the viewpoint of improving the low-temperature fixability of the toner.

[0040] The content of the release agent is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, even more preferably 7 parts by mass or more, and preferably 15 parts by mass or less, more preferably 13 parts by mass or less, even more preferably 11 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0041] The polymerizable monomer composition may further contain a charge control agent, a chain transfer agent, inorganic fine particles such as silica, aluminum oxide, titanium oxide, zinc oxide, and tin oxide, a magnetic powder, a flowability improver, a conductivity adjuster, a reinforcing filler such as a fibrous substance, an antioxidant, an antiaging agent, a cleaning property improver, and the like.

[0042] The charge control agent may contain either a positively chargeable charge control agent or a negatively chargeable charge control agent.

[0043] Examples of positively chargeable charge control agents include nigrosine dyes such as "Nigrosine Base EX," "Oil Black BS," "Oil Black SO," "Bontron N-01," "Bontron N-04," "Bontron N-07," "Bontron N-09," and "Bontron N-11" (all manufactured by Orient Chemical Industries Co., Ltd.); triphenylmethane dyes containing a tertiary amine as a side chain; quaternary ammonium salt compounds such as "Bontron P-51" (manufactured by Orient Chemical Industries Co., Ltd.); cetyltrimethylammonium bromide; and "COPY CHARGE PX Examples of suitable resins include "VP435" (manufactured by Clariant), etc.; polyamine resins, such as "AFP-B" (manufactured by Orient Chemical Industries Co., Ltd.), etc.; imidazole derivatives, such as "PLZ-2001" and "PLZ-8001" (both manufactured by Shikoku Chemical Industry Co., Ltd.), etc.; and styrene-acrylic resins, such as "FCA-161P," "FCA-201-PS," and "FCA-701PT" (manufactured by Fujikura Chemical Co., Ltd.).

[0044] Examples of negatively chargeable charge control agents include metal-containing azo dyes, such as "Balifast Black 3804," "Bontron S-31," "Bontron S-32," "Bontron S-34," and "Bontron S-36" (all manufactured by Orient Chemical Industries, Ltd.), "Eisenspiron Black TRH," and "T-77" (manufactured by Hodogaya Chemical Industry Co., Ltd.); metal compounds of benzilic acid compounds, such as "LR-147" and "LR-297" (manufactured by Nippon Carlit Co., Ltd.); metal compounds of salicylic acid compounds, such as "Bontron E-81," "Bontron E-84," "Bontron E-88," and "Bontron E-304" (all manufactured by Orient Chemical Industry Co., Ltd.), and "TN-105" (manufactured by Hodogaya Chemical Industry Co., Ltd.); copper phthalocyanine dyes; and quaternary ammonium salts, such as "COPY CHARGE NX VP434 (manufactured by Clariant), nitroimidazole derivatives, etc.; organometallic compounds, etc. These may be used alone or in combination of two or more.

[0045] In the present invention, from the viewpoint of hot offset resistance, it is preferable that the yellow toner, cyan toner, magenta toner, and black toner, preferably each color toner, is a positively charged toner. Therefore, the charge control agent preferably contains a positively charged charge control agent, more preferably contains a polymer-type charge control resin, and even more preferably contains a quaternary ammonium salt-containing resin.

[0046] As the quaternary ammonium salt-containing resin, a quaternary ammonium salt-containing styrene-based resin is preferred.

[0047] The quaternary ammonium salt-containing styrene-based resin is not particularly limited, but is preferably, for example, a copolymer of a styrene monomer (M1) and / or a (meth)acrylic acid alkyl ester monomer (M2) and a quaternary ammonium salt of a (meth)acrylic acid dialkylamino alkyl ester monomer (M3).

[0048] The styrene monomer (M1) is styrene, and does not include derivatives of styrene such as α-methylstyrene, p-methylstyrene, and p-chlorostyrene.

[0049] Examples of the (meth)acrylic acid alkyl ester monomer (M2) include methyl (meth)acrylate, ethyl (meth)acrylate, butyl (meth)acrylate, propyl (meth)acrylate, amyl (meth)acrylate, 2-ethylhexyl (meth)acrylate, cyclohexyl (meth)acrylate, lauryl (meth)acrylate, and stearyl (meth)acrylate. The alkyl group preferably has 4 or more and 12 or less carbon atoms, and among these, butyl (meth)acrylate or 2-ethylhexyl (meth)acrylate is preferred, with butyl (meth)acrylate being more preferred.

[0050] Examples of the quaternary ammonium salt of a (meth)acrylic acid dialkylaminoalkyl ester monomer (M3) include those represented by the formula (I):

[0051] [ka]

[0052] (In the formula, R 1 is a hydrogen atom or a methyl group, R 2 is an alkylene group having 1 to 5 carbon atoms, R 3 ~R 5 each independently represents an alkyl group having 1 to 5 carbon atoms. A compound represented by the following formula is preferred.

[0053] In formula (I), R 1 R is preferably a methyl group. 2 Examples of R include a methylene group, an ethylene group, a propylene group, and a butylene group, and among these, an ethylene group is preferred. 3 ~R 5 Examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an n-butyl group, and a tert-butyl group. Among these, a methyl group or an ethyl group is preferred, and an ethyl group is more preferred.

[0054] Examples of the dialkylaminoalkyl (meth)acrylate include dimethylaminoethyl (meth)acrylate, diethylaminoethyl (meth)acrylate, dipropylaminoethyl (meth)acrylate, and dibutylaminoethyl (meth)acrylate. Among these, diethylaminoethyl (meth)acrylate is preferred because it is inexpensive.

[0055] Examples of methods for producing a quaternary ammonium salt-containing styrene-based resin include a method in which a (meth)acrylic acid dialkylaminoalkyl ester is quaternized using a paratoluenesulfonic acid alkyl ester in a conventional manner to form a quaternary ammonium salt of a (meth)acrylic acid dialkylaminoalkyl ester monomer (M3), which is then mixed with a styrene monomer (M1) and / or a (meth)acrylic acid alkyl ester monomer (M2), and copolymerized in the presence of a polymerization initiator.

[0056] Examples of alkyl paratoluenesulfonates include methyl paratoluenesulfonate, ethyl paratoluenesulfonate, and propyl paratoluenesulfonate. Among these, methyl paratoluenesulfonate is preferred because it can be easily quaternized.

[0057] The amount of the alkyl paratoluenesulfonate used is preferably 0.8 moles or more, more preferably 1 mole or more, and preferably 1.5 moles or less, more preferably 1.2 moles or less, relative to 1 mole of the dialkylamino(meth)acrylate to be reacted with it.

[0058] As the copolymerization method, any method such as solution polymerization, suspension polymerization, bulk polymerization, emulsion polymerization, etc. may be used, but solution polymerization is preferred because it is relatively easy to control the molecular weight of the resulting copolymer and the reaction operation is easy.

[0059] Examples of the solvent used in the solution polymerization include ketone solvents such as methyl ethyl ketone and methyl isobutyl ketone, alcohol solvents such as normal butanol and isobutanol, ester solvents such as ethyl acetate and isobutyl acetate, and aromatic hydrocarbon solvents such as toluene and xylene. Among these, ketone solvents or alcohol solvents are preferred from the viewpoint of the solubility of the copolymer.

[0060] As the polymerization initiator, peroxide initiators such as tert-butylperoxy-2-ethylhexanoate, tert-amylperoxy-2-ethylhexanoate, 1,1-di(tert-butylperoxy)cyclohexane and dibenzoyl peroxide, and azo initiators such as 2,2'-azobis(2-methylbutyronitrile) can be used.

[0061] The amount of the polymerization initiator used is preferably 0.5 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the total of the monomers.

[0062] In the quaternary ammonium salt-containing styrene-based resin, the content of styrene monomer (M1) units in the total amount of styrene monomer (M1) units, (meth)acrylic acid alkyl ester monomer (M2) units, and (meth)acrylic acid dialkylamino alkyl ester quaternary ammonium salt (M3) units is preferably 40 mass% or more, more preferably 50 mass% or more, and preferably 80 mass% or less, more preferably 75 mass% or less.

[0063] In the quaternary ammonium salt-containing styrene-based resin, the content of (meth)acrylic acid alkyl ester monomer (M2) units in the total amount of styrene monomer (M1) units, (meth)acrylic acid alkyl ester monomer (M2) units, and (meth)acrylic acid dialkylamino alkyl ester quaternary ammonium salt (M3) units is preferably 5 mass% or more, more preferably 10 mass% or more, and preferably 40 mass% or less, more preferably 35 mass% or less.

[0064] In the quaternary ammonium salt-containing styrene-based resin, the content of quaternary ammonium salt (M3) units of (meth)acrylic acid dialkylaminoalkyl ester in the total amount of styrene monomer (M1) units, (meth)acrylic acid alkyl ester monomer (M2) units, and (meth)acrylic acid dialkylaminoalkyl ester quaternary ammonium salt (M3) units is preferably 0.5 mass% or more, more preferably 1 mass% or more, and preferably 35 mass% or less, more preferably 30 mass% or less.

[0065] Commercially available quaternary ammonium salt group-containing styrene resins include, for example, "FCA-161P," "FCA-201-PS," and "FCA-701-PT" (all manufactured by Fujikura Kasei Co., Ltd.).

[0066] From the viewpoint of storage stability, the softening point of the quaternary ammonium salt-containing resin is preferably 90°C or higher, more preferably 95°C or higher, and even more preferably 100°C or higher, and from the viewpoint of low-temperature fixability, it is preferably 140°C or lower, more preferably 135°C or lower, and even more preferably 130°C or lower.

[0067] From the viewpoint of storage stability, the glass transition temperature of the quaternary ammonium salt-containing resin is preferably 35°C or higher, more preferably 40°C or higher, and even more preferably 45°C or higher, and from the viewpoint of low-temperature fixability, it is preferably 90°C or lower, more preferably 85°C or lower, and even more preferably 80°C or lower.

[0068] The content of the charge control agent is preferably 0.01 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0069] Examples of the chain transfer agent include mercaptans such as tert-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, 2,2,4,6,6-pentamethylheptane-4-thiol, etc. The chain transfer agent can be added before the start of polymerization or during the polymerization.

[0070] The content of the chain transfer agent is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, relative to 100 parts by mass of the polymerizable monomer.

[0071] A polymerizable monomer composition is obtained by mixing a polymerizable monomer, a colorant, a release agent, and, if necessary, other additives, and dissolving each component.

[0072] The aqueous medium is preferably one containing water as a main component. The water content in the aqueous medium is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 98% by mass or more, and 100% by mass or less. The water is preferably deionized water or distilled water.

[0073] Examples of components other than water that may be contained in the aqueous medium include water-soluble organic solvents such as alkyl alcohols having 1 to 5 carbon atoms; dialkyl ketones having 3 to 5 carbon atoms, such as acetone and methyl ethyl ketone; and cyclic ethers, such as tetrahydrofuran.

[0074] The aqueous medium preferably contains a dispersion stabilizer.

[0075] Examples of dispersion stabilizers include sulfates such as barium sulfate and calcium sulfate; carbonates such as barium carbonate, calcium carbonate, and magnesium carbonate; phosphates such as calcium phosphate; metal oxides such as aluminum oxide and titanium oxide; metal compounds such as metal hydroxides such as aluminum hydroxide, magnesium hydroxide, and ferric hydroxide; water-soluble polymers such as polyvinyl alcohol, methyl cellulose, and gelatin; anionic surfactants; nonionic surfactants; amphoteric surfactants; etc. Dispersion stabilizers can be used alone or in combination of two or more.

[0076] Among the dispersion stabilizers, a dispersion stabilizer containing a colloid of a metal compound, particularly a poorly water-soluble metal hydroxide, is preferred because it can narrow the particle size distribution of the colored polymer particles, and the amount of the dispersion stabilizer remaining after washing is small, allowing for clear reproduction of images and not deteriorating environmental stability.

[0077] The content of the dispersion stabilizer is preferably 0.1 parts by mass or more and 20 parts by mass or less based on 100 parts by mass of the polymerizable monomer.

[0078] Examples of the polymerization initiator used in the polymerization of the polymerizable monomer composition include persulfates such as potassium persulfate and ammonium persulfate; azo compounds 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; di-te Examples of the peroxide include rt-butyl peroxide, benzoyl peroxide, tert-butylperoxy-2-ethylbutanoate, tert-butylperoxy-2-ethylhexanoate, tert-hexylperoxy-2-ethylhexanoate, tert-butylperoxypivalate, diisopropyl peroxydicarbonate, di-tert-butylperoxyisophthalate, and tert-butylperoxyisobutyrate. Alternatively, a redox initiator, which is a combination of the above polymerization initiator and a reducing agent, may be used.

[0079] The amount of the polymerization initiator is preferably 0.1 parts by mass or more, more preferably 0.3 parts by mass or more, even more preferably 0.5 parts by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass or less, even more preferably 10 parts by mass or less, relative to 100 parts by mass of the polymerizable monomer.

[0080] The polymerizable monomer composition can be introduced into an aqueous medium and granulated in the presence of a polymerization initiator. The polymerization initiator may be added to the aqueous medium before granulation after dispersing the polymerizable monomer composition in the aqueous medium, or may be added to the polymerizable monomer composition before dispersing it in the aqueous medium.

[0081] The granulation method is not particularly limited, but it is preferable to use a device capable of strong stirring, such as an (in-line type) emulsifying disperser (trade name "Milder MDN303V" (manufactured by Pacific Machinery Works Co., Ltd.), or "Ebara Milder" (manufactured by Ebara Corporation)), or a high-speed emulsifying / dispersing machine (trade name "TK Homomixer MARK II Type" (manufactured by Primix Corporation)).

[0082] After granulation, the aqueous medium in which the granulated polymerizable monomer composition is dispersed is heated to initiate polymerization.

[0083] The polymerization temperature of the polymerizable monomer composition is preferably 50° C. or higher, more preferably 60° C. or higher, and preferably 95° C. or lower. The polymerization reaction time is preferably 1 hour or higher, more preferably 2 hours or higher, and preferably 20 hours or lower, more preferably 15 hours or lower.

[0084] After the polymerization is completed, the colored polymer particles can be separated as toner particles from the aqueous dispersion of the colored polymer particles by a conventional procedure of filtering, washing to remove the dispersion stabilizer, dehydrating, and drying. The procedures of filtering, washing, dehydrating, and drying are preferably repeated several times as necessary.

[0085] Regarding the washing method, when an inorganic compound such as an inorganic hydroxide is used as the dispersion stabilizer, it is preferable to add an acid or alkali to the aqueous dispersion of toner particles to dissolve and remove the dispersion stabilizer in water. When a colloid of a poorly water-soluble inorganic hydroxide is used as the dispersion stabilizer, it is preferable to add an acid to adjust the pH of the aqueous dispersion of toner particles to 6.5 or less. The acid to be added may be an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, or an organic acid such as formic acid or acetic acid, but sulfuric acid is preferred because of its high removal efficiency and its small burden on production equipment.

[0086] The dehydration and filtration methods may be any of various known methods, and are not particularly limited, including, for example, centrifugal filtration, vacuum filtration, and pressure filtration.

[0087] In the present invention, the colored polymer particles obtained by the suspension polymerization method can be used as a toner as it is, but by using the colored polymer particles as core particles and forming a shell layer on the outside of the core particles, a core-shell toner (capsule toner) can be obtained. For example, by covering core particles containing a resin with a low softening point with a shell layer containing a resin with a higher softening point, it is possible to achieve a balance between lowering the fixing temperature and preventing aggregation during storage.

[0088] The method for producing a core-shell toner using colored polymer particles as core particles is not particularly limited, and the toner can be produced by a conventionally known method. In terms of production efficiency, an in situ polymerization method or a phase separation method is preferred.

[0089] The core-shell toner produced by the in situ polymerization method can be produced, for example, by the following method. A polymerizable monomer (shell polymerizable monomer) for the resin (shell resin) that forms the shell layer, and other shell additives as needed, are dissolved or dispersed in deionized water to obtain an aqueous dispersion of the shell polymerizable monomer. A polymerization initiator for polymerizing the shell polymerizable monomer etc. is added to this aqueous dispersion of the shell polymerizable monomer, and the mixture is placed in an aqueous medium in which colored polymer particles are dispersed, followed by polymerization to obtain a core-shell toner.

[0090] Although the same polymerizable monomers as those described above can be used as the polymerizable monomer for the shell, it is preferable that the shell layer contains polymethyl methacrylate (PMMA) from the viewpoint of storage stability. Therefore, methyl methacrylate is preferred as the polymerizable monomer for the shell.

[0091] The content of methyl methacrylate in the polymerizable monomer for shell is preferably 70 mol % or more, more preferably 80 mol % or more, even more preferably 90 mol % or more, even more preferably 95 mol % or more, and even more preferably 100 mol %.

[0092] Other shell additives may include inorganic fine particles such as silica, aluminum oxide, titanium oxide, zinc oxide, and tin oxide, and crosslinkable polymers having two or more polymerizable functional groups such as urethane acrylate polymers.

[0093] Examples of the polymerization initiator used for polymerizing the polymerizable monomer for the shell include water-soluble polymerization initiators such as metal persulfates, such as potassium persulfate and ammonium persulfate; and azo initiators, such as 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)propionamide] and 2,2'-azobis[2-methyl-N-[1,1-bis(hydroxymethyl)2-hydroxyethyl]propionamide].

[0094] The amount of the polymerization initiator is preferably 0.1 parts by mass or more, more preferably 1 part by mass or more, and preferably 30 parts by mass or less, more preferably 20 parts by mass or less, per 100 parts by mass of the polymerizable monomer for the shell.

[0095] The polymerization temperature for the shell layer is preferably 50° C. or higher, more preferably 60° C. or higher, and preferably 95° C. or lower. The polymerization reaction time is preferably 1 hour or higher, more preferably 2 hours or higher, and preferably 20 hours or lower, more preferably 15 hours or lower.

[0096] After the polymerization is completed, the core-shell toner can be separated from the aqueous dispersion of the core-shell toner in the same manner as the colored polymer particles by filtering, washing to remove the dispersion stabilizer, dehydrating, and drying according to conventional methods.

[0097] The circularity of the toner obtained by the suspension polymerization method is preferably 0.975 or more, more preferably 0.978 or more, even more preferably 0.980 or more, and is preferably 0.995 or less, more preferably 0.992 or less, even more preferably 0.990 or less.

[0098] When producing a pulverized toner by the melt-kneading method, for example, raw materials containing a binder resin, a colorant, and a release agent are uniformly mixed in a mixer such as a Henschel mixer, and then the mixture is melt-kneaded in an internal kneader, a single-screw or twin-screw extruder, an open-roll kneader, or the like, and then cooled, pulverized, and classified to produce the toner.

[0099] Examples of binder resins include polyester resins, vinyl resins such as styrene-acrylic resins, epoxy resins, polycarbonates, polyurethanes, and composite resins containing two or more of these resins. Among these, polyester resins are preferred from the viewpoint of low-temperature fixability.

[0100] The polyester resin is a polycondensation product of an alcohol component and a carboxylic acid component, and the alcohol component preferably contains an alkylene oxide adduct of bisphenol A from the viewpoint of storage stability.

[0101] Examples of alkylene oxide adducts of bisphenol A include polyoxypropylene adducts of 2,2-bis(4-hydroxyphenyl)propane and polyoxyethylene adducts of 2,2-bis(4-hydroxyphenyl)propane, and are represented by the formula (II):

[0102] [ka]

[0103] (In the formula, OR 6 and R 6 O is an oxyalkylene group, and R 6 is an ethylene group and / or a propylene group, x and y are each a positive number and represent the average number of moles of alkylene oxide added, and the sum of x and y is 1 or more, preferably 1.5 or more, and 16 or less, preferably 8 or less, more preferably 6 or less, even more preferably 4 or less, and even more preferably 2.5 or less. A compound represented by the following formula is preferred.

[0104] The content of the alkylene oxide adduct of bisphenol A in the alcohol component is preferably 70 mol % or more, more preferably 80 mol % or more, and even more preferably 90 mol % or more, and 100 mol % or less.

[0105] Examples of other alcohol components include aliphatic diols such as ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, neopentyl glycol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol; and trihydric or higher alcohols such as bisphenol A, hydrogenated bisphenol A, sorbitol, pentaerythritol, glycerin, and trimethylolpropane.

[0106] Examples of the carboxylic acid component include aromatic dicarboxylic acid compounds, aliphatic dicarboxylic acid compounds, and trivalent or higher carboxylic acid compounds.

[0107] Examples of aromatic dicarboxylic acid compounds include phthalic acid, isophthalic acid, terephthalic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

[0108] Examples of the aliphatic dicarboxylic acid compound include fumaric acid, maleic acid, succinic acid, succinic acid derivatives substituted with a hydrocarbon group, glutaric acid, adipic acid, sebacic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

[0109] Examples of the trivalent or higher carboxylic acid compound include trimellitic acid, pyromellitic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

[0110] The alcohol component may contain a monohydric alcohol, and the carboxylic acid component may contain a monocarboxylic acid compound, as appropriate.

[0111] In this specification, macromonomers and hydroxycarboxylic acids are not included in the alcohol component and carboxylic acid component.

[0112] The equivalent ratio of the carboxyl groups of the carboxylic acid component to the hydroxyl groups of the alcohol component (COOH groups / OH groups) is preferably 0.6 or more, more preferably 0.7 or more, even more preferably 0.8 or more, and is preferably 1.3 or less, more preferably 1.2 or less.

[0113] The polyester resin can be produced, for example, by polycondensing an alcohol component and a carboxylic acid component in an inert gas atmosphere, preferably in the presence of an esterification catalyst, and optionally in the presence of a co-catalyst, a polymerization inhibitor, etc., at a temperature of preferably 160°C or higher, more preferably 200°C or higher, and preferably 250°C or lower, more preferably 240°C or lower.

[0114] Examples of the esterification catalyst include tin compounds such as dibutyltin oxide and tin(II) 2-ethylhexanoate, and titanium compounds such as titanium diisopropoxybis(triethanolaminate). The amount of the esterification catalyst used is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and preferably 1.5 parts by mass or less, more preferably 1 part by mass or less, per 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component. Examples of the co-catalyst for the esterification catalyst include gallic acid. The amount of the co-catalyst used is preferably 0.001 parts by mass or more, more preferably 0.01 parts by mass or more, and preferably 0.5 parts by mass or less, more preferably 0.1 parts by mass or less, per 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component. Examples of the polymerization inhibitor include tert-butylcatechol. The amount of the polymerization inhibitor used is preferably 0.001 part by mass or more, more preferably 0.01 part by mass or more, and preferably 0.5 part by mass or less, more preferably 0.1 part by mass or less, relative to 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component.

[0115] In the present invention, the polyester resin may be modified to such an extent that its properties are not substantially impaired. Examples of modified polyester resins include polyester resins grafted or blocked with phenol, urethane, epoxy, or the like, by the methods described in JP-A Nos. 11-133668, 10-239903, and 8-20636. Among the modified polyester resins, urethane-modified polyester resins in which polyester resins are urethane-extended with a polyisocyanate compound are preferred.

[0116] The softening point of the polyester resin is preferably 70°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher from the viewpoint of charging stability, and is preferably 170°C or lower, more preferably 160°C or lower, and even more preferably 150°C or lower from the viewpoint of low-temperature fixability.

[0117] From the viewpoint of low-temperature fixability and fixation width, the polyester resin may be composed of resins with different softening points. The difference in softening point between the two resins is preferably 10°C or more, more preferably 20°C or more, and is preferably 60°C or less, more preferably 40°C or less.

[0118] The polyester resin with the higher softening point (resin AH) has a softening point of preferably 100°C or higher, more preferably 110°C or higher, and even more preferably 120°C or higher, from the viewpoint of fixing width, and preferably 170°C or lower, more preferably 160°C or lower, and even more preferably 150°C or lower, from the viewpoint of low-temperature fixability.

[0119] Furthermore, the softening point of the polyester resin with the lower softening point (resin AL) is preferably 70°C or higher, more preferably 90°C or higher, and even more preferably 100°C or higher, from the viewpoint of charging stability, and is preferably 130°C or lower, more preferably 125°C or lower, and even more preferably 120°C or lower, from the viewpoint of low-temperature fixability.

[0120] The mass ratio of resin AH to resin AL (resin AH / resin AL) is preferably 10 / 90 or more, more preferably 20 / 80 or more, even more preferably 30 / 70 or more, and is preferably 90 / 10 or less, more preferably 80 / 20 or less, even more preferably 75 / 25 or less.

[0121] The glass transition temperature of the polyester resin is preferably 40° C. or higher, more preferably 50° C. or higher, from the viewpoint of storage stability, and is preferably 80° C. or lower, more preferably 70° C. or lower, from the viewpoint of low-temperature fixability.

[0122] The acid value of the polyester resin is preferably 1 mgKOH / g or more, more preferably 3 mgKOH / g or more, from the viewpoint of low-temperature fixability, and is preferably 15 mgKOH / g or less, more preferably 10 mgKOH / g or less, from the viewpoint of charging stability.

[0123] The content of the polyester resin in the binder resin is preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more, and is 100% by mole or less.

[0124] The content of the binder resin in the toner is preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 75% by mass or more, and is preferably 96% by mass or less, more preferably 93% by mass or less, even more preferably 90% by mass or less.

[0125] The types and amounts of the colorant and release agent are the same as those explained for the suspension polymerization method.

[0126] The raw materials to be melt-kneaded may contain additives such as a charge control agent, a magnetic powder, a flowability improver, a conductivity adjuster, a reinforcing filler such as a fibrous substance, an antioxidant, and a cleaning property improver, in addition to the binder resin, the colorant, and the release agent.

[0127] The type of charge control agent is the same as that explained for the suspension polymerization method.

[0128] From the viewpoint of the charge stability of the toner, the content of the charge control agent is preferably 0.01 parts by mass or more, more preferably 0.2 parts by mass or more, and preferably 10 parts by mass or less, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less, and even more preferably 2 parts by mass or less, relative to 100 parts by mass of the binder resin. When the charge control agent is a resin (polymer type), the content is preferably 3 parts by mass or more, more preferably 5 parts by mass or more, and preferably 20 parts by mass or less, more preferably 15 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0129] The circularity of the pulverized toner obtained by the melt-kneading method is preferably 0.920 or more, more preferably 0.925 or more, even more preferably 0.930 or more, and is preferably 0.985 or less, more preferably 0.980 or less, even more preferably 0.975 or less.

[0130] To improve the transferability, it is preferable that an external additive is added to the toner of the present invention. Examples of the external additive include inorganic fine particles such as silica, alumina, titania, zirconia, tin oxide, and zinc oxide, and organic fine particles such as melamine resin fine particles and polytetrafluoroethylene resin fine particles, and two or more of them may be used in combination. Among these, silica is preferred, and from the viewpoint of the transferability of the toner, hydrophobic silica that has been subjected to a hydrophobic treatment is more preferred.

[0131] Examples of hydrophobic treatment agents for hydrophobizing the surfaces of silica particles include hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMDS), cyclic silazanes, silicone oils, aminosilanes, octyltriethoxysilane (OTES), and methyltriethoxysilane.

[0132] From the viewpoint of the chargeability, fluidity and transferability of the toner, the average particle size of the external additive is preferably 5 nm or more, and is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 90 nm or less.

[0133] The external addition treatment by mixing the toner particles with the external additives can be carried out in accordance with a conventional method, and a mixer such as a Henschel mixer can be used.

[0134] From the viewpoint of the chargeability, fluidity, and transferability of the toner, the content of the external additive is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 0.3 parts by mass or more, relative to 100 parts by mass of the toner particles before treatment with the external additive, and is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less.

[0135] Toner volume median particle size (D 50 ) is preferably 3 μm or more, more preferably 4 μm or more, and is preferably 15 μm or less, more preferably 10 μm or less. 50) means the particle size at which the cumulative volume frequency calculated by volume fraction is 50% starting from the smallest particle size. In addition, when the toner is treated with an external additive, the volume median particle size of the toner particles before treatment with the external additive is taken as the volume median particle size of the toner.

[0136] As described above, at least a combination of yellow toner, cyan toner, magenta toner, and black toner can be used as is in an image forming apparatus using a one-component development method, or each color toner can be mixed with a carrier and used in an image forming apparatus using a two-component development method. [Example]

[0137] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples. Physical properties of resins and the like can be measured by the following methods.

[0138] [Number average molecular weight of macromonomer] The number average molecular weight is determined by gel permeation chromatography (GPC) using the following method. (1) Preparation of sample solution The resin is dissolved in tetrahydrofuran to a concentration of 0.5 g / 100 mL, and then filtered through a 2 μm pore size fluororesin filter (manufactured by Sumitomo Electric Industries, Ltd., product name: FP-200) to remove insoluble components, leaving a sample solution. (2) Molecular weight measurement Using the following measurement equipment and analytical column, tetrahydrofuran is used as the eluent at a flow rate of 1 mL per minute, and the column is stabilized in a thermostatic bath at 40°C. 100 μL of sample solution is injected into the column for measurement. The molecular weight of the sample is calculated based on a calibration curve prepared in advance. The calibration curve used here includes several types of monodisperse polystyrene (Tosoh Corporation; 2.63 × 10 3 , 2.06×10 4 , 1.02 × 10 5 , manufactured by GL Sciences Inc.; 2.10 x 10 3 , 7.00 x 10 3 , 5.04×104 ) is used as a standard sample. Measuring device: CO-8010 (product name, manufactured by Tosoh Corporation) Analytical column: GMH XL +G3000H XL (All are product names, manufactured by Tosoh Corporation)

[0139] [Softening point of resin] Using a flow tester "CFT-500D" (Shimadzu Corporation), 1 g of sample is heated at a temperature increase rate of 6°C / min while applying a load of 1.96 MPa with the plunger, and extruding it from a nozzle 1 mm in diameter and 1 mm in length. The plunger depression distance of the flow tester is plotted against the temperature, and the temperature at which half of the sample flows out is taken as the softening point.

[0140] [Glass transition temperature of resin] Using a differential scanning calorimeter "Q-100" (TA Instruments Japan), 0.01-0.02 g of sample is weighed into an aluminum pan, heated to 200°C, and cooled to 0°C at a rate of 10°C / min. The sample is then heated to 150°C at a rate of 10°C / min, and the endothermic peak is measured. The glass transition temperature is the temperature at the intersection of an extension of the baseline below the maximum endothermic peak temperature and a tangent line showing the maximum slope from the rising part of the peak to the peak apex.

[0141] [Acid value of resin] Measurement is performed based on the method of JIS K 0070:1992, except that the measurement solvent is changed from the ethanol and ether mixture specified in JIS K 0070 to a mixture of acetone and toluene (acetone:toluene = 1:1 (volume ratio)).

[0142] [Melting point of release agent] Using a differential scanning calorimeter "Q-100" (TA Instruments Japan), 0.02 g of sample is weighed into an aluminum pan, heated to 200°C, and then cooled from 200°C to 0°C at a rate of 10°C / min. The sample is then heated at a rate of 10°C / min, the calorific value is measured, and the maximum endothermic peak temperature is taken as the melting point.

[0143] [Average particle size of external additives] The average particle size refers to the number-average particle size, and is calculated by measuring the particle sizes (average values ​​of major and minor axes) of 500 particles in a scanning electron microscope (SEM) photograph and averaging these values ​​by number.

[0144] [Maximum peak temperature of toner endothermic heat] Using a differential scanning calorimeter "Q-100" (TA Instruments Japan Co., Ltd.), weigh 0.01-0.02 g of sample into an aluminum pan, heat it from 25°C to 200°C at a heating rate of 10°C / min (first time), and then cool it from that temperature to 0°C at a heating rate of 10°C / min. Next, heat the sample to 180°C at a heating rate of 10°C / min (second time) and measure the endothermic peak. Among the endothermic peaks observed during the second heating, the temperature of the peak with the largest peak area is taken as the maximum endothermic peak temperature.

[0145] [Volume median particle size of toner (D 50 ) Measuring instrument: "Coulter Multisizer (registered trademark) III" (manufactured by Beckman Coulter, Inc.) Aperture diameter: 50 μm Analysis software: "Multisizer (registered trademark) III Version 3.51" (Beckman Coulter, Inc.) Electrolyte: "Isoton (registered trademark) II" (manufactured by Beckman Coulter, Inc.) Dispersion: Polyoxyethylene lauryl ether "Emulgen (registered trademark) 109P" (manufactured by Kao Corporation, HLB (Griffin) = 13.6) dissolved in the electrolyte to adjust the concentration to 5% by mass Dispersion conditions: 10 mg of the measurement sample was added to 5 mL of the dispersion, and the mixture was dispersed for 1 minute using an ultrasonic disperser (machine name: US-1 manufactured by SND Corporation, output: 80 W). 25 mL of electrolyte was then added, and the mixture was further dispersed for 1 minute using the ultrasonic disperser to prepare a sample dispersion. Measurement conditions: The sample dispersion was added to 100 mL of the electrolyte to adjust the concentration so that the particle size of 30,000 particles could be measured in 20 seconds. Then, 30,000 particles were measured, and the volume median particle size (D 50 ) is found.

[0146] [Circularity of Toner Particles] The circularity of the toner particles is measured under the following conditions. Measurement equipment: Flow particle image analyzer "FPIA-3000" (Sysmex Corporation) Dispersion: Polyoxyethylene lauryl ether "Emulgen (registered trademark) 109P" (Kao Corporation, HLB (Griffin) = 13.6) dissolved in deionized water to prepare a 5% by mass dispersion Dispersion conditions: 10 mg of the measurement sample was added to 5 mL of the dispersion, and the mixture was dispersed for 1 minute using an ultrasonic disperser (machine name: US-1, manufactured by SND Corporation, output: 80 W). 25 mL of deionized water was then added, and the mixture was further dispersed for 1 minute using the ultrasonic disperser to prepare a sample dispersion. Measurement mode: HPF measurement mode

[0147] Resin manufacturing example 1 The alcohol component, carboxylic acid components other than trimellitic anhydride, esterification catalyst, and co-catalyst shown in Table 1 were placed in a 5-liter four-neck flask equipped with a nitrogen inlet tube, a downflow condenser with a dehydration tube, a stirrer, and a thermocouple. The mixture was heated to 235°C under a nitrogen atmosphere and then polycondensed at 235°C for 6 hours. The temperature was then lowered to 210°C, and trimellitic anhydride shown in Table 1 was added. The mixture was reacted at 210°C for 1 hour, and then further reacted at 210°C under a reduced pressure of 10 kPa until the softening point shown in Table 1 was reached, yielding a polyester resin (Resin A1). The physical properties are shown in Table 1.

[0148] Resin manufacturing example 2 The alcohol component, carboxylic acid component, esterification catalyst, and co-catalyst shown in Table 1 were placed in a 5-liter four-neck flask equipped with a nitrogen inlet tube, a downflow condenser with a dehydration tube, a stirrer, and a thermocouple, and the temperature was raised to 235°C under a nitrogen atmosphere, followed by polycondensation at 235°C for 6 hours. The reaction was further continued at 235°C under a reduced pressure of 10 kPa until the softening point shown in Table 1 was reached, yielding a polyester resin (Resin A2). The physical properties are shown in Table 1.

[0149] [Table 1]

[0150] Yellow toner production example 1 60 parts by mass of Resin A1 and 40 parts by mass of Resin A2 as binder resins, 7 parts by mass of CI Pigment Yellow 93 (manufactured by BASF, product name: CROMOPHTAL YELLOW 3G) as a colorant, 8 parts by mass of ester wax "WEP-4" (manufactured by NOF Corporation, pentaerythritol tetrapalmitate, melting point: 71°C) as a release agent, and 10 parts by mass of a polymer-type positively charged charge control agent (manufactured by Fujikura Chemical Industries, Ltd., product name: FCA-201-PS, quaternary ammonium salt-containing resin, softening point: 119°C, glass transition temperature: 65°C) were mixed in a Henschel mixer.

[0151] The resulting mixture was melt-kneaded using a co-rotating twin-screw extruder with a kneading section total length of 1560 mm, a screw diameter of 42 mm, and a barrel inner diameter of 43 mm at a screw rotation speed of 200 r / min and a barrel temperature setting of 100°C to obtain a melt-kneaded product. The mixture was fed at a rate of 20 kg / h and had an average residence time of approximately 18 seconds.

[0152] The resulting melt-kneaded product was cooled, coarsely pulverized, and then finely pulverized using a jet mill. The product was then classified using an air classifier (manufactured by Nippon Pneumatic Mfg. Co., Ltd.) to obtain the volume median particle diameter (D 50 The toner particles obtained had a particle diameter of 6.3 μm and a circularity of 0.945.

[0153] To 100 parts by mass of the obtained toner particles, 1 part by mass of hydrophobic silica (manufactured by Cabot Corporation, product name "TG820F", hydrophobic treatment agent: HMDS and cyclic silazane, average particle size: 8 nm) and 1 part by mass of hydrophobic silica (manufactured by Nippon Aerosil Co., Ltd., product name "NA50H", hydrophobic treatment agent: HMDS and aminosilane, average particle size: 30 nm) were added as external additives, and the mixture was mixed using a Henschel mixer at a rotation speed of 3000 r / min (circumferential speed: 32 m / sec) for 3 minutes to obtain a positively charged yellow toner (Y1).

[0154] Yellow toner production example 2 (1) Preparation of polymerizable monomer composition for core 75 parts by mass of styrene and 25 parts by mass of n-butyl acrylate as polymerizable monomers, and 7 parts by mass of CI Pigment Yellow 93 (manufactured by BASF, trade name: CROMOPHTAL YELLOW 3G) as a colorant were dispersed using a media-type emulsifying disperser to obtain a polymerizable monomer mixture. To the obtained polymerizable monomer mixture, 0.75 parts by mass of a polymeric positively charged charge control agent (manufactured by Fujikura Chemical Industries, Ltd., trade name: ACRYBASE FCA-161P, quaternary ammonium salt-containing resin, softening point: 110°C, glass transition temperature: 60°C), 8 parts by mass of an ester wax "WEP-4" (manufactured by NOF Corporation, pentaerythritol tetrapalmitate, melting point: 71°C) as a release agent, 0.3 parts by mass of a polymethacrylic acid ester macromonomer (manufactured by Toagosei Co., Ltd., trade name: AA6, number average molecular weight: 6,000) as a macromonomer, 0.6 parts by mass of divinylbenzene as a crosslinkable polymerizable monomer, and 1.6 parts by mass of tert-dodecyl mercaptan as a chain transfer agent were added, and then mixed and dissolved to prepare a polymerizable monomer composition.

[0155] (2) Preparation of aqueous dispersion medium A magnesium hydroxide colloidal dispersion was prepared by gradually adding, with stirring, an aqueous solution in which 7.3 parts by mass of sodium hydroxide was dissolved in 50 parts by mass of deionized water to an aqueous solution in which 10.4 parts by mass of magnesium chloride was dissolved in 280 parts by mass of deionized water.

[0156] (3) Preparation of polymerizable monomer for shell 2 parts by mass of methyl methacrylate and 130 parts by mass of deionized water were subjected to a fine dispersion treatment using an ultrasonic emulsifier to prepare an aqueous dispersion of the polymerizable monomer for the shell.

[0157] (4) Granulation process The polymerizable monomer composition obtained in (1) was added to the magnesium hydroxide colloidal dispersion obtained in (2) at room temperature, and the mixture was stirred until the droplets stabilized. 4.4 parts by mass of tert-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O) was added as a polymerization initiator. The dispersion containing the added polymerization initiator was stirred with high shear at a rotation speed of 15,000 r / min using an in-line emulsifying disperser (manufactured by Pacific Machinery Works Co., Ltd., trade name: Milder MDN303V) to form droplets of the polymerizable monomer composition.

[0158] (5) Suspension polymerization process: The dispersion containing droplets of the polymerizable monomer composition obtained in (4) was placed in a reactor and heated to 90°C to carry out a polymerization reaction. After the polymerization conversion rate reached nearly 100%, the aqueous dispersion of the shell polymerizable monomer obtained in (3) was dissolved with 0.1 parts by mass of 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., trade name: VA-086, water-soluble initiator) as a shell polymerization initiator, and the resulting solution was added to the reactor. The temperature was then maintained at 95°C for 4 hours to further continue polymerization, after which the reaction was stopped by water cooling to obtain an aqueous dispersion of toner particles.

[0159] (6) Post-processing The aqueous dispersion of toner particles obtained in (5) was washed with acid by adding sulfuric acid dropwise at room temperature while stirring until the pH reached 6.0 or less. Then, the mixture was filtered and separated, and 500 parts by mass of deionized water was added to the obtained solid matter to re-slurry it, and the water washing treatment (washing, filtration, and dehydration) was repeated several times. Then, the mixture was filtered and separated, and the obtained solid matter was placed in a container of a dryer and dried at 40°C for 24 hours, and the volume median particle diameter (D 50 The toner particles obtained had a particle diameter of 6.3 μm and a circularity of 0.984.

[0160] (7) External addition process To 100 parts by mass of the toner particles obtained in (6), 1 part by mass of hydrophobic silica (manufactured by Cabot Corporation, product name "TG820F", hydrophobic treatment agent: HMDS and cyclic silazane, average particle size: 8 nm) and 1 part by mass of hydrophobic silica (manufactured by Nippon Aerosil Co., Ltd., product name "NA50H", hydrophobic treatment agent: HMDS and aminosilane, average particle size: 30 nm) were added, and the mixture was mixed using a Henschel mixer at a rotation speed of 3000 r / min (circumferential speed 32 m / sec) for 3 minutes to obtain a positively charged core-shell type yellow toner (Y2).

[0161] Yellow Toner Production Example 3 Yellow toners (Y3 to Y6) were obtained in the same manner as in Production Example 2, except that the release agents shown in Table 2 were used instead of the ester wax "WEP-4."

[0162] Yellow Toner Production Example 4 (1) Preparation of polymerizable monomer composition 75 parts by mass of styrene and 25 parts by mass of n-butyl acrylate as polymerizable monomers, and 7 parts by mass of CI Pigment Yellow 93 (manufactured by BASF, trade name: CROMOPHTAL YELLOW 3G) as a colorant were dispersed using a media-type emulsifying disperser to obtain a polymerizable monomer mixture. To the obtained polymerizable monomer mixture, 0.75 parts by mass of a polymeric positively charged charge control agent (manufactured by Fujikura Chemical Industries, Ltd., trade name: ACRYBASE FCA-161P, quaternary ammonium salt-containing resin, softening point: 110°C, glass transition temperature: 60°C), 8 parts by mass of an ester wax "WEP-4" (manufactured by NOF Corporation, pentaerythritol tetrapalmitate, melting point: 71°C) as a release agent, 0.3 parts by mass of a polymethacrylic acid ester macromonomer (manufactured by Toagosei Co., Ltd., trade name: AA6, number average molecular weight: 6,000) as a macromonomer, 0.6 parts by mass of divinylbenzene as a crosslinkable polymerizable monomer, and 1.6 parts by mass of tert-dodecyl mercaptan as a chain transfer agent were added, and then mixed and dissolved to prepare a polymerizable monomer composition.

[0163] (2) Preparation of aqueous dispersion medium A magnesium hydroxide colloidal dispersion was prepared by gradually adding, with stirring, an aqueous solution in which 7.3 parts by mass of sodium hydroxide was dissolved in 50 parts by mass of deionized water to an aqueous solution in which 10.4 parts by mass of magnesium chloride was dissolved in 280 parts by mass of deionized water.

[0164] (3) Granulation process The polymerizable monomer composition obtained in (1) was added to the magnesium hydroxide colloidal dispersion obtained in (2) at room temperature, and the mixture was stirred until the droplets stabilized. 4.4 parts by mass of tert-butylperoxy-2-ethylhexanoate (manufactured by NOF Corporation, trade name: Perbutyl O) was added as a polymerization initiator. The dispersion containing the added polymerization initiator was stirred with high shear at a rotation speed of 15,000 r / min using an in-line emulsifying disperser (manufactured by Pacific Machinery Works Co., Ltd., trade name: Milder MDN303V) to form droplets of the polymerizable monomer composition.

[0165] (4) Suspension polymerization process The dispersion containing droplets of the polymerizable monomer composition obtained in (3) was placed in a reactor, and the temperature was raised to 90° C. to carry out a polymerization reaction. Next, the temperature was maintained at 95° C. for 4 hours to further continue the polymerization, and the reaction was stopped by water cooling to obtain an aqueous dispersion of toner particles.

[0166] (5) Post-processing The aqueous dispersion of toner particles obtained in (4) was washed with acid by adding sulfuric acid dropwise at room temperature while stirring until the pH reached 6.0 or less. Then, the mixture was filtered and separated, and 500 parts by mass of deionized water was added to the obtained solid matter to re-slurry it, and the water washing treatment (washing, filtration, and dehydration) was repeated several times. Then, the mixture was filtered and separated, and the obtained solid matter was placed in a container of a dryer and dried at 40°C for 24 hours to determine the volume median particle diameter (D 50 The toner particles obtained had a particle diameter of 6.2 μm and a circularity of 0.984.

[0167] (6) External addition process To 100 parts by mass of the toner particles obtained in (5), 1 part by mass of hydrophobic silica (manufactured by Cabot Corporation, product name "TG820F", hydrophobic treatment agent: HMDS and cyclic silazane, average particle size: 8 nm) and 1 part by mass of hydrophobic silica (manufactured by Nippon Aerosil Co., Ltd., product name "NA50H", hydrophobic treatment agent: HMDS and aminosilane, average particle size: 30 nm) were added, and the mixture was mixed using a Henschel mixer at a rotation speed of 3000 r / min (circumferential speed 32 m / sec) for 3 minutes to obtain a positively charged yellow toner (Y7).

[0168] Yellow Toner Production Example 5 A yellow toner (Y8) was obtained in the same manner as in Yellow Toner Production Example 2, except that 7 parts by mass of CI Pigment Yellow 214 (manufactured by Heubach Color Japan Co., Ltd., product name: PV FAST Yellow H9G) was used instead of CI Pigment Yellow 93 as the colorant.

[0169] Magenta toner production example 1 A magenta toner (M1) was obtained in the same manner as in Yellow Toner Production Example 1, except that 3 parts by mass of CI Pigment Red 122 (manufactured by Clariant, product name: Toner Magenta E) and 3 parts by mass of CI Pigment Violet 19 (manufactured by Clariant, product name: Ink Jet Magenta E5B02) were used instead of CI Pigment Yellow 93 as colorants.

[0170] Magenta toner production example 2 Magenta toners (M2 to M5) were obtained in the same manner as in Yellow Toner Production Example 2, except that 3 parts by mass of CI Pigment Red 122 (manufactured by Clariant, product name: Toner Magenta E) and 3 parts by mass of CI Pigment Violet 19 (manufactured by Clariant, product name: Ink Jet Magenta E5B02) were used as colorants instead of CI Pigment Yellow 93, and the release agents listed in Table 2 were used.

[0171] Magenta toner production example 3 A magenta toner (M6) was obtained in the same manner as in Yellow Toner Production Example 4, except that 3 parts by mass of CI Pigment Red 122 (manufactured by Clariant, product name: Toner Magenta E) and 3 parts by mass of CI Pigment Violet 19 (manufactured by Clariant, product name: Ink Jet Magenta E5B02) were used instead of CI Pigment Yellow 93 as the colorant.

[0172] Cyan toner production example 1 A cyan toner (C1) was obtained in the same manner as in Yellow Toner Production Example 1, except that 5 parts by mass of CI Pigment Blue 15 (manufactured by DIC Corporation, trade name "Fastogen Blue GCTF") was used as the colorant instead of CI Pigment Yellow 93, and ester wax "WE-14" (manufactured by NOF Corporation, dipentaerythritol hexastearate, melting point: 75°C) was used as the release agent instead of ester wax "WEP-4" (manufactured by NOF Corporation, pentaerythritol tetrapalmitate, melting point: 71°C).

[0173] Cyan toner production example 2 Cyan toners (C2 to C5) were obtained in the same manner as in Yellow Toner Production Example 2, except that 5 parts by mass of CI Pigment Blue 15 (manufactured by DIC Corporation, product name "Fastogen Blue GCTF") was used as the colorant instead of CI Pigment Yellow 93, and the release agents listed in Table 2 were used.

[0174] Cyan toner production example 3 A cyan toner (C6) was obtained in the same manner as in Yellow Toner Production Example 4, except that 5 parts by mass of CI Pigment Blue 15 (manufactured by DIC Corporation, trade name "Fastogen Blue GCTF") was used as the colorant instead of CI Pigment Yellow 93, and ester wax "WE-14" (manufactured by NOF Corporation, dipentaerythritol hexastearate, melting point: 75°C) was used as the release agent instead of ester wax "WEP-4" (manufactured by NOF Corporation, pentaerythritol tetrapalmitate, melting point: 71°C).

[0175] Black toner manufacturing example 1 Black toner (K1) was obtained in the same manner as in Yellow Toner Production Example 1, except that 7 parts by mass of carbon black (manufactured by Mitsubishi Chemical Corporation, product name "#25B") was used as the colorant instead of CI Pigment Yellow 93, and ester wax "WE-14" (manufactured by NOF Corporation, dipentaerythritol hexastearate, melting point: 75°C) was used as the release agent instead of ester wax "WEP-4" (manufactured by NOF Corporation, pentaerythritol tetrapalmitate, melting point: 71°C).

[0176] Black toner manufacturing example 2 Black toners (K2 to K5) were obtained in the same manner as in Yellow Toner Production Example 2, except that 7 parts by mass of carbon black (manufactured by Mitsubishi Chemical Corporation, product name "#25B") was used as the colorant instead of CI Pigment Yellow 93, and the release agents listed in Table 2 were used.

[0177] Black toner manufacturing example 3 Black toner (K6) was obtained in the same manner as in Yellow Toner Production Example 4, except that 7 parts by mass of carbon black (manufactured by Mitsubishi Chemical Corporation, product name "#25B") was used as the colorant instead of CI Pigment Yellow 93, and ester wax "WE-14" (manufactured by NOF Corporation, dipentaerythritol hexastearate, melting point: 75°C) was used as the release agent instead of ester wax "WEP-4" (manufactured by NOF Corporation, pentaerythritol tetrapalmitate, melting point: 71°C).

[0178] [Table 2]

[0179] Examples 1 to 9 and Comparative Examples 1 to 3 Yellow toner, magenta toner, cyan toner, and black toner shown in Table 3 were combined to prepare a toner set.

[0180] Test Example 1 [Gross] A commercially available non-magnetic single-component color printer (Brother Industries, Ltd., HL-3240CDW) was modified to enable the extraction of unfixed images. The toner amount was 0.30 mg / cm for black (yellow toner, magenta toner, and cyan toner). 2 ), and brown (yellow toner, magenta toner, black toner all have a toner loading of 0.30 mg / cm 2 ) was printed to obtain an unfixed image with toner superimposed thereon.

[0181] Next, we prepared the same printer with a modified fuser that allowed for variable temperature and variable printing speed. We set the fuser temperature to 180°C and fixed the toner to A4 size paper in portrait orientation at a speed of 2.0 seconds per sheet, resulting in a printed product.

[0182] A piece of cardboard was placed under the image, and the gloss was measured using a gloss meter (manufactured by Horiba, Ltd., product name: "IG-330") under a light irradiation condition of 60°. The results are shown in Table 3. The higher the obtained value, the higher the gloss.

[0183] Test Example 2 [Hot offset resistance (HO resistance)] A commercially available non-magnetic single-component color printer (Brother Industries, Ltd., HL-3240CDW) was modified to enable the extraction of unfixed images. The toner amount was 0.30 mg / cm for black (yellow toner, magenta toner, and cyan toner). 2 ), and brown (yellow toner, magenta toner, black toner all have a toner loading of 0.30 mg / cm 2 ) was printed to obtain an unfixed image with toner superimposed thereon.

[0184] Next, the same printer was prepared with a modified fuser that allowed for variable temperature and variable print speed, and the fuser temperature was raised in 5°C increments from 160°C to 220°C at a rate of 2.0 seconds per sheet in portrait A4 paper orientation, while a fixing test was conducted on unfused prints at each temperature. The resulting printed images were visually observed to confirm the temperature at which hot offset occurred. The results are shown in Table 3. The higher the temperature at which hot offset occurs, the better the hot offset resistance. In the table, ">220" indicates that no hot offset occurred even at 220°C.

[0185] [Table 3]

[0186] From the above results, comparing Examples 2 to 7 and 9 with Comparative Examples 1 to 3, it can be seen that by lowering the maximum endothermic peak temperature of at least one of the yellow toner and magenta toner, it is possible to obtain printed images with excellent hot offset resistance and high gloss. Furthermore, a comparison between Examples 2 and 8 shows that the effect on hot offset resistance is particularly pronounced when the polymerized toner is a core-shell type, and a comparison between Examples 1 and 2 shows that not only polymerized toner but also pulverized toner has good gloss and hot offset resistance. [Industrial Applicability]

[0187] The toner set for developing electrostatic images of the present invention is suitably used for developing latent images formed in electrophotography, electrostatic recording, electrostatic printing and the like.

Claims

1. A toner set for developing electrostatic images, comprising a yellow toner, a cyan toner, a magenta toner, and a black toner, each containing a binder resin, a colorant, and a release agent, wherein, in differential scanning calorimetry (DSC), the toners are weighed into an aluminum pan, heated from 25°C to 200°C at a heating rate of 10°C / min, cooled from that temperature to 0°C at a heating rate of 10°C / min, and then heated to 180°C at a heating rate of 10°C / min, and then measured while heating the toners to 180°C at a heating rate of 10°C / min, the maximum endothermic peak temperature during the second heating is lower for at least one of the yellow toner and the magenta toner than for the cyan toner and the black toner, and the difference between the maximum endothermic peak temperature of the cyan toner and the black toner, whichever is lower, is 1°C or more and 40°C or less.

2. 2. The toner set for developing electrostatic images according to claim 1, wherein the yellow toner, the cyan toner, the magenta toner, and the black toner are positively charged toners.

3. 3. The toner set for developing electrostatic images according to claim 1, wherein the release agent contains an ester wax.

4. 3. The toner set for developing electrostatic images according to claim 1, wherein the yellow toner, cyan toner, magenta toner, and black toner are core-shell toners in which core particles are covered with a shell layer.

5. 5. The toner set for developing electrostatic images according to claim 4, wherein the shell layer contains polymethyl methacrylate.

6. 3. The toner set for developing electrostatic images according to claim 1, wherein the yellow toner, cyan toner, magenta toner, and black toner are obtained by suspension polymerization.

7. A method for preparing a toner set for developing electrostatic images by combining at least a yellow toner, a cyan toner, a magenta toner, and a black toner, each containing a binder resin, a colorant, and a release agent, wherein, in differential scanning calorimetry (DSC), the toners are weighed into an aluminum pan, heated from 25°C to 200°C at a heating rate of 10°C / min, cooled from that temperature to 0°C at a heating rate of 10°C / min, and then heated to 180°C at a heating rate of 10°C / min, and measured while heating the toners to 180°C at a heating rate of 10°C / min, the maximum endothermic peak temperature during the second heating is lower for at least one of the yellow toner and the magenta toner than for the cyan toner and the black toner, and the difference between the maximum endothermic peak temperature of the cyan toner and the black toner and the lower maximum endothermic peak temperature is 1°C or more and 40°C or less.

Images