Method for producing toner for developing electrostatic images

Abstract

To provide a method for manufacturing a toner for electrostatic charge image development which is excellent in all of glossiness of a printed surface and document offset resistance during storage under high temperature.SOLUTION: A method for manufacturing a toner for electrostatic charge image development includes a step 1 of melting and kneading at least an amorphous resin and a crystalline polyester resin using an open roll type kneader, a step 2 of crushing a kneaded product obtained in the step 1, and then mixing the obtained crushed product with inorganic particles, and a step 3 of crushing the mixture obtained in the step 2, and classifying the mixture, wherein the crystalline polyester resin is a polycondensate of an alcohol component containing aliphatic diol and a carboxylic acid component containing an aliphatic dicarboxylic acid compound, the alcohol component contains short chain aliphatic diol having 2 or more and 6 or less carbon atoms and / or the carboxylic acid component contains a short chain aliphatic dicarboxylic acid compound having 4 or more and 8 or less carbon atoms.SELECTED DRAWING: None

Description

[Technical Field]

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

[0002] With the development of electrophotographic systems, there is a demand for the development of toners for developing electrostatic images (hereinafter simply referred to as "toners") that can accommodate higher image quality and faster speeds. For example, as machine speeds increase, the amount of heat applied to the toner coated on recording paper during fixing decreases, so toners with better low-temperature fixability are required.

[0003] Therefore, it is known that crystalline polyester resins are effective as binder resins for toners in improving the low-temperature fixability of toners, and their combined use with amorphous polyester resins has been investigated (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-159022 [Patent Document 2] Japanese Patent Publication No. 2020-85971 Summary of the Invention [Problem to be solved by the invention]

[0005] Toners containing crystalline polyester resins have excellent gloss on the printed surface because they can be quickly plasticized and deformed during the thermal fixing process. However, when printed materials are stored at high temperatures, if the toner forming the print layer plasticizes, a problem occurs in which part of the toner transfers to the backside of other paper when it is stacked on top of another paper (document offset), staining the other paper.

[0006] The present invention relates to a method for producing a toner for developing electrostatic images that is excellent in both the glossiness of the printed surface and the resistance to document offset during storage at high temperatures. [Means for solving the problem]

[0007] The present invention relates to a method for producing a toner for developing electrostatic images, the method comprising: Step 1: melt-kneading at least an amorphous resin and a crystalline polyester resin using an open-roll kneader; Step 2: pulverizing the kneaded product obtained in Step 1 and then mixing the pulverized product with inorganic fine particles; and Step 3: pulverizing and classifying the mixture obtained in Step 2, wherein the crystalline polyester resin is a polycondensate of an alcohol component containing 80 mol % or more of an aliphatic diol and a carboxylic acid component containing 80 mol % or more of an aliphatic dicarboxylic acid compound, the alcohol component containing a short-chain aliphatic diol having from 2 to 6 carbon atoms and / or the carboxylic acid component containing a short-chain aliphatic dicarboxylic acid compound having from 4 to 8 carbon atoms, and the mass ratio of the crystalline polyester resin to the amorphous resin is from 2 / 98 to 18 / 82. [Effects of the Invention]

[0008] The method of the present invention provides a toner for developing electrostatic images that is excellent in both the glossiness of the printed surface and the resistance to document offset during storage at high temperatures. DETAILED DESCRIPTION OF THE INVENTION

[0009] The present invention provides a method for producing a toner for developing electrostatic images by mixing a coarsely pulverized product of a toner containing an amorphous resin and a crystalline polyester resin with inorganic fine particles and then finely pulverizing the mixture when the toner is produced by a melt-kneading method. The reason why the method of the present invention produces a toner that is excellent in both the gloss of the printed surface and the document offset resistance during storage at high temperatures is unclear, but is presumed to be as follows. The following mechanism is merely a supposition, and the present invention is not limited to this.

[0010] In the present invention, the use of a crystalline polyester resin containing a short-chain aliphatic diol and / or a short-chain aliphatic dicarboxylic acid compound results in closer proximity of ester groups in the resin, improving affinity with the amorphous resin. Furthermore, melt-kneading raw materials containing the amorphous resin and the crystalline polyester resin using an open-roll kneader improves the dispersibility of the crystalline polyester resin in the amorphous resin. As a result, the resulting toner is more easily plasticized during thermal fixation and can be deformed sufficiently with less thermal energy, resulting in a smoother printed surface and improved gloss. However, since the printed toner is still susceptible to thermal plasticization, prints tend to adhere to each other when stored at high temperatures, resulting in color transfer. However, in the method of the present invention, the kneaded material is coarsely pulverized and then further finely pulverized in the presence of inorganic fine particles, allowing the inorganic fine particles to adhere uniformly and firmly to the toner surface. The inorganic fine particles adhered to the toner surface function as spacers even after printing, preventing prints from sticking to each other and suppressing document offset.

[0011] The method for producing the toner of the present invention includes the following steps 1, 2, and 3.

[0012] Step 1 is a step of melt-kneading at least an amorphous resin and a crystalline polyester resin using an open-roll kneader.

[0013] Examples of amorphous resins include amorphous polyester resins, vinyl resins such as styrene-acrylic resins, amorphous epoxy resins, amorphous polycarbonates, amorphous polyurethanes, and composite resins containing two or more of these resins. Of these, amorphous polyester resins are preferred from the viewpoint of low-temperature fixability.

[0014] The amorphous polyester resin is preferably a polycondensate of an alcohol component containing an alkylene oxide adduct of bisphenol A and a carboxylic acid component containing an aromatic dicarboxylic acid compound.

[0015] Examples of the alkylene oxide adduct of bisphenol A include an ethylene oxide adduct of bisphenol A and a propylene oxide adduct of bisphenol A, and are represented by the formula (I):

[0016] [ka]

[0017] (wherein OR and RO are oxyalkylene groups, R is an ethylene group and / or a propylene group, x and y are the average number of moles of alkylene oxide added and are each a positive number, 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, and even more preferably 4 or less.) A compound represented by the following formula is preferred.

[0018] From the viewpoint of low-temperature fixability, 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, even more preferably 90 mol% or more, even more preferably 95 mol% or more, and even more preferably 100 mol%.

[0019] Examples of other alcohol components include aliphatic diols, bisphenol A, hydrogenated bisphenol A, sorbitol, pentaerythritol, glycerin, tri- or higher hydric alcohols such as trimethylolpropane, and the like.

[0020] 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.

[0021] The content of the aromatic dicarboxylic acid compound in the carboxylic acid component is preferably 80 mol % or more, more preferably 90 mol % or more, and even more preferably 95 mol % or more, and 100 mol % or less.

[0022] Examples of other carboxylic acid components include fumaric acid, maleic acid, succinic acid, succinic acid derivatives substituted with a hydrocarbon group, aliphatic dicarboxylic acids such as glutaric acid, adipic acid, and sebacic acid, trivalent or higher carboxylic acids such as trimellitic acid and pyromellitic acid, anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

[0023] The alcohol component may contain a monohydric alcohol, and the carboxylic acid component may contain a monocarboxylic acid compound, as appropriate.

[0024] In this specification, macromonomers and hydroxycarboxylic acids are not included in the alcohol component and carboxylic acid component.

[0025] From the viewpoint of adjusting the softening point of the polyester resin, 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.

[0026] The amorphous 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 cocatalyst, 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.

[0027] Examples of esterification catalysts 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 alcohol component and the carboxylic acid component combined. Examples of promoters for the esterification catalyst include gallic acid. The amount of the promoter 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 alcohol component and the carboxylic acid component combined. Examples of polymerization inhibitors 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, per 100 parts by mass of the total amount of the alcohol component and the carboxylic acid component.

[0028] 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.

[0029] The softening point of the amorphous 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.

[0030] The crystallinity of a resin is expressed by a crystallinity index defined as the ratio of the softening point to the maximum endothermic peak temperature measured by a differential scanning calorimeter, that is, the value of [softening point / maximum endothermic peak temperature]. An amorphous resin is a resin in which no endothermic peak is observed, or if an endothermic peak is observed, the resin has a crystallinity index of more than 1.4, preferably more than 1.5, more preferably 1.6 or more, or less than 0.6, preferably 0.5 or less. On the other hand, the crystallinity index of the crystalline resin is 0.6 or more, preferably 0.7 or more, more preferably 0.9 or more, and 1.4 or less, preferably 1.2 or less, more preferably 1.1 or less. The crystallinity of a resin can be adjusted by the types and ratios of raw material monomers, and production conditions (e.g., reaction temperature, reaction time, cooling rate), etc. The maximum endothermic peak temperature refers to the temperature of the peak with the largest peak area among the observed endothermic peaks. For crystalline resins, the maximum endothermic peak temperature is the melting point.

[0031] The glass transition temperature of the amorphous resin is preferably 40°C or higher, more preferably 50°C or higher, from the viewpoint of charging stability, and is preferably 80°C or lower, more preferably 70°C or lower, from the viewpoint of low-temperature fixability.

[0032] The content of the amorphous resin is preferably 82% by mass or more, more preferably 85% by mass or more, even more preferably 88% by mass or more, and is preferably 98% by mass or less, more preferably 95% by mass or less, even more preferably 93% by mass or less, of the total amount of the amorphous resin and the crystalline polyester resin.

[0033] The crystalline polyester resin is a polycondensation product of an alcohol component containing 80 mol % or more of an aliphatic diol and a carboxylic acid component containing 80 mol % or more of an aliphatic dicarboxylic acid compound, in which the alcohol component contains a short-chain aliphatic diol and / or the carboxylic acid component contains a short-chain aliphatic dicarboxylic acid compound.

[0034] In the alcohol component, examples of the short-chain aliphatic diol include ethylene glycol, 1,2-propanediol, 1,3-propanediol, 1,4-butanediol, 2,3-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-butenediol, and neopentyl glycol.

[0035] The short-chain aliphatic diol has 2 or more and 6 or less carbon atoms, and preferably 2 or more and 4 or less carbon atoms.

[0036] When the alcohol component contains a short-chain aliphatic diol, the content of the short-chain aliphatic diol in the alcohol component is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, and still more preferably 100 mol%.

[0037] Examples of the aliphatic diols other than the short-chain aliphatic diols include 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol.

[0038] The carbon number of the aliphatic diol other than the short-chain aliphatic diol is preferably 8 or more, more preferably 10 or more, and is preferably 16 or less, more preferably 14 or less.

[0039] The content of the aliphatic diol in the alcohol component is 80 mol % or more, preferably 90 mol % or more, more preferably 95 mol % or more, and even more preferably 100 mol %, from the viewpoints of low-temperature fixability and glossiness of the printed surface.

[0040] Examples of alcohol components other than aliphatic diols include alkylene oxide adducts of bisphenol A, aromatic diols such as bisphenol A, hydrogenated bisphenol A, trihydric or higher alcohols such as sorbitol, pentaerythritol, glycerin, and trimethylolpropane.

[0041] Among the carboxylic acid components, examples of short-chain aliphatic dicarboxylic acid compounds include succinic acid (number of carbon atoms: 4), fumaric acid (number of carbon atoms: 4), adipic acid (number of carbon atoms: 6), suberic acid (number of carbon atoms: 8), anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

[0042] The number of carbon atoms in the short-chain aliphatic dicarboxylic acid compound is 4 or more and 8 or less, and preferably 4 or more and 6 or less. When the aliphatic dicarboxylic acid compound is an alkyl ester, the number of carbon atoms in the alkyl group is not included in the above carbon number.

[0043] When the carboxylic acid component contains a short-chain aliphatic dicarboxylic acid compound, the content of the short-chain aliphatic dicarboxylic acid compound in the carboxylic acid component is preferably 80 mol% or more, more preferably 90 mol% or more, even more preferably 95 mol% or more, and even more preferably 100 mol%.

[0044] Examples of aliphatic dicarboxylic acid compounds other than short-chain aliphatic dicarboxylic acid compounds include azelaic acid (number of carbon atoms: 9), sebacic acid (number of carbon atoms: 10), dodecanedioic acid (number of carbon atoms: 12), tetradecanedioic acid (number of carbon atoms: 14), anhydrides of these acids, and alkyl esters of these acids having 1 to 3 carbon atoms.

[0045] The carbon number of the aliphatic dicarboxylic acid compound other than the short-chain aliphatic dicarboxylic acid compound is preferably 9 or more, more preferably 10 or more, and preferably 18 or less, more preferably 16 or less, and even more preferably 14 or less. When the aliphatic dicarboxylic acid compound is an alkyl ester, the carbon number of the alkyl group is not included in the above carbon number.

[0046] The content of the aliphatic dicarboxylic acid compound in the carboxylic acid component is 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 100 mol%, from the viewpoints of durability and glossiness of the printed surface.

[0047] Examples of carboxylic acid components other than aliphatic dicarboxylic acid compounds include aromatic dicarboxylic acid compounds such as phthalic acid, isophthalic acid, and terephthalic acid, and trivalent or higher carboxylic acid compounds such as trimellitic acid and pyromellitic acid.

[0048] The alcohol component may contain a monohydric alcohol, and the carboxylic acid component may contain a monocarboxylic acid compound, as appropriate.

[0049] In the present invention, preferred embodiments of the crystalline polyester resin include: a polycondensate of an alcohol component containing 80 mol % or more of a short-chain aliphatic diol having from 2 to 6 carbon atoms and a carboxylic acid component containing 80 mol % or more of an aliphatic dicarboxylic acid compound having from 9 to 18 carbon atoms; A polycondensate of an alcohol component containing 80 mol% or more of an aliphatic diol having 8 to 16 carbon atoms and a carboxylic acid component containing 80 mol% or more of a short-chain aliphatic dicarboxylic acid compound having 4 to 8 carbon atoms. etc.

[0050] 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 0.8 or more, more preferably 0.9 or more, from the viewpoint of charging stability, and is preferably 1.2 or less, more preferably 1.1 or less, from the viewpoint of low-temperature fixability.

[0051] The polycondensation reaction conditions of the alcohol component and the carboxylic acid component of the crystalline polyester resin are the same as those of the amorphous polyester resin, except that the reaction temperature is preferably 120°C or higher, more preferably 180°C or higher, and 230°C or lower, more preferably 220°C or lower.

[0052] The softening point of the crystalline polyester resin is preferably 50°C or higher, more preferably 65°C or higher, and even more preferably 70°C or higher from the viewpoint of charging stability, and is preferably 120°C or lower, more preferably 110°C or lower, and even more preferably 100°C or lower from the viewpoint of low-temperature fixability.

[0053] From the viewpoint of storage stability, the melting point of the crystalline polyester resin is preferably 60°C or higher, more preferably 65°C or higher, and even more preferably 70°C or higher, and from the viewpoint of low-temperature fixability, it is preferably 105°C or lower, more preferably 100°C or lower, and even more preferably 95°C or lower.

[0054] The content of the crystalline polyester resin is preferably 2% by mass or more, more preferably 5% by mass or more, even more preferably 7% by mass or more, and preferably 18% by mass or less, more preferably 15% by mass or less, even more preferably 12% by mass or less, of the total amount of the amorphous resin and the crystalline polyester resin.

[0055] The mass ratio of the crystalline polyester resin to the amorphous resin (crystalline polyester resin / amorphous resin) is 2 / 98 or more, preferably 5 / 95 or more, and more preferably 7 / 93 or more, from the viewpoints of low-temperature fixability and glossiness of the printed surface, and is 18 / 82 or less, preferably 15 / 85 or less, and more preferably 12 / 88 or less, from the viewpoints of durability and glossiness of the printed surface.

[0056] The content of the amorphous resin and the crystalline polyester resin in the toner is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more, and is preferably less than 100% by mass, more preferably 98% by mass or less, and even more preferably 95% by mass or less.

[0057] In the present invention, the amorphous resin and the crystalline polyester resin are used as binder resins.

[0058] The total content of the amorphous resin and the crystalline polyester resin in the binder resin is preferably 70% by mass or more, more preferably 80% by mass or more, even more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass.

[0059] 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 80% by mass or more, and is preferably less than 100% by mass, more preferably 98% by mass or less, even more preferably 95% by mass or less.

[0060] In step 1, examples of raw materials that can be subjected to melt-kneading together with the amorphous resin and the crystalline polyester resin include colorants, release agents, charge control agents, magnetic powders, flowability improvers, conductivity adjusters, reinforcing fillers such as fibrous substances, antioxidants, and additives such as cleaning improvers.

[0061] As the colorant, dyes, pigments, magnetic materials, etc. used as toner colorants can be used. Examples include carbon black, phthalocyanine blue, permanent brown FG, brilliant fast scarlet, pigment red 122, pigment green B, rhodamine-B base, solvent red 49, solvent red 146, solvent blue 35, quinacridone, carmine 6B, isoindoline, disazo yellow, etc. In the present invention, the toner may be either a black toner or a color toner.

[0062] From the viewpoint of improving the image density and low-temperature fixability of the toner, the amount of colorant used is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and preferably 40 parts by mass or less, more preferably 20 parts by mass or less, and even more preferably 10 parts by mass or less, relative to 100 parts by mass of the binder resin.

[0063] Examples of the release agent include hydrocarbon waxes such as polypropylene wax, polyethylene wax, ethylene-propylene copolymer wax, microcrystalline wax, paraffin wax, and Fischer-Tropsch wax, and oxides thereof; ester waxes such as carnauba wax, montan wax, and deacidified waxes thereof, and fatty acid ester wax; fatty acid amides, fatty acids, higher alcohols, and fatty acid metal salts, and these may be used alone or in combination of two or more.

[0064] The melting point of the release agent is preferably 60°C or higher, more preferably 70°C or higher, from the viewpoint of toner transferability, and is preferably 160°C or lower, more preferably 140°C or lower, even more preferably 120°C or lower, and even more preferably 110°C or lower, from the viewpoint of low-temperature fixability.

[0065] The amount of the release agent used is preferably 0.5 parts by mass or more, more preferably 1 part by mass or more, and even more preferably 1.5 parts by mass or more, relative to 100 parts by mass of the binder resin, from the viewpoints of the low-temperature fixability and offset resistance of the toner and the dispersibility in the binder resin, and is preferably 10 parts by mass or less, more preferably 8 parts by mass or less, and even more preferably 7 parts by mass or less.

[0066] The charge control agent is not particularly limited, and may contain either a positively chargeable charge control agent or a negatively chargeable charge control agent.

[0067] 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," "Bontron N-11," and "Bontron N-79" (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 polyamine resins such as "AFP-B" (manufactured by Orient Chemical Industries Co., Ltd.); imidazole derivatives such as "PLZ-2001" and "PLZ-8001" (both manufactured by Shikoku Chemical Industry Co., Ltd.); and styrene-acrylic resins such as "FCA-701PT" and "FCA-201-PS" (manufactured by Fujikura Chemical Industries Co., Ltd.).

[0068] 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 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 Industries, Ltd.), and "TN-105" (manufactured by Hodogaya Chemical Co., Ltd.); copper phthalocyanine dyes; and quaternary ammonium salts such as "COPY CHARGE NX VP434 (manufactured by Clariant), nitroimidazole derivatives, etc.; organometallic compounds, etc.

[0069] From the viewpoint of the charge stability of the toner, the amount of the charge control agent used 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.

[0070] In step 1, the raw materials to be melt-kneaded are preferably premixed using a Henschel mixer or the like, and then fed to an open-roll kneader.

[0071] An open-roll kneader refers to a kneading machine in which the kneading section is open and not sealed, and the heat of kneading generated during melt kneading can be easily dissipated. The open-roll kneader used in the present invention is provided with a raw material supply port and a kneaded material discharge port provided along the axial direction of the rolls, and from the viewpoint of production efficiency, it is preferably a continuous open-roll kneader.

[0072] The open-roll kneader used in the present invention is preferably a kneader equipped with two rolls with different peripheral speeds, i.e., a roll with a high peripheral speed (high rotation roll) and a roll with a low peripheral speed (low rotation roll). In the present invention, from the viewpoint of dispersibility of the kneaded material, it is preferable that the high rotation roll functions as a heating roll and the low rotation roll functions as a cooling roll, that is, it is preferable that the set temperature of the high rotation roll is higher than that of the low rotation roll. When the set temperatures of the rolls on the raw material input side and the kneaded material discharge side are different, it is preferable that the set temperature of the high rotation roll is higher than that of the low rotation roll at least on the raw material input side, and it is more preferable that the set temperature of the high rotation roll is higher than that of the low rotation roll on both the raw material input side and the kneaded material discharge side.

[0073] The temperature of the rolls can be adjusted, for example, by the temperature of a heat medium passed through the inside of the rolls. The inside of each roll may be divided into two or more sections through which heat mediums of different temperatures are passed.

[0074] The temperature of the raw material inlet side of the high rotation roll is preferably 100° C. or higher, more preferably 120° C. or higher, and preferably 160° C. or lower, more preferably 150° C. or lower, from the viewpoint of reducing the mechanical force during melt-kneading and suppressing heat generation. From the same viewpoint, the temperature of the raw material inlet side of the low rotation roll is preferably 25° C. or higher, more preferably 40° C. or higher, and preferably 90° C. or lower, more preferably 80° C. or lower.

[0075] For both the high-speed rotation roll and the low-speed rotation roll, it is preferable that the temperature on the raw material input side is higher than that on the kneaded material discharge side, and the temperature difference between the raw material input side and the kneaded material discharge side is preferably 20°C or more, more preferably 30°C or more, from the viewpoint of preventing the kneaded material from detaching from the roll, reducing the mechanical force during melt kneading, and suppressing heat generation, and is preferably 60°C or less, more preferably 50°C or less.

[0076] The temperature of the raw material input side of the high rotation roll and the low rotation roll refers to the set temperature at the raw material input end, and the temperature of the kneaded material discharge side refers to the set temperature at the kneaded material discharge end.

[0077] From the viewpoint of reducing mechanical power during kneading and suppressing heat generation, the peripheral speed of the high-speed roll is preferably 2 m / min or more, more preferably 10 m / min or more, even more preferably 25 m / min or more, and preferably 100 m / min or less, more preferably 75 m / min or less, and even more preferably 50 m / min or less. From the same viewpoint, the peripheral speed of the low-speed roll is preferably 1 m / min or more, more preferably 5 m / min or more, even more preferably 15 m / min or more, and preferably 90 m / min or less, more preferably 60 m / min or less, and even more preferably 30 m / min or less. Furthermore, the ratio of the peripheral speeds of the two rolls (low-speed roll / high-speed roll) is preferably 1 / 10 or more, more preferably 3 / 10 or more, and preferably 9.9 / 10 or less, more preferably 8 / 10 or less.

[0078] There are no particular limitations on the structure, size, material, etc. of each roll. The roll surface has grooves used for kneading, and the shape of these grooves may be linear, spiral, wavy, or uneven.

[0079] After step 1, the obtained kneaded product is appropriately cooled until it reaches a pulverizable hardness, and then subjected to the subsequent step 2. Here, cooling means cooling the kneaded product to 0°C to 50°C, or cooling to a temperature equal to or lower than the glass transition temperature of the binder resin in the kneaded product.

[0080] Step 2 is a step of pulverizing the kneaded product obtained in Step 1 and then mixing the pulverized product with inorganic fine particles. In this specification, the pulverization in Step 2 is also referred to as "coarse pulverization," and the pulverized product obtained is also referred to as "coarsely pulverized product."

[0081] Examples of the crusher used for coarse crushing include a hammer mill, an atomizer, and a rotoplex.

[0082] In the coarse pulverization, it is preferable to coarsely pulverize the kneaded material obtained in step 1 until the particle size is approximately 0.1 to 3 mm, and then pass it through a sieve with a mesh size of approximately 2 to 3 mm, and mix the pulverized material that has passed through the sieve with inorganic fine particles as a pulverized material (coarsely pulverized material) with a maximum diameter of 2 to 3 mm or less.

[0083] Examples of inorganic fine particles used in step 2 include silicon dioxide (silica), titanium dioxide, aluminum oxide, zinc oxide, magnesium oxide, cerium oxide, iron oxide, copper oxide, and tin oxide. Among these, from the viewpoint of imparting chargeability, silica or titanium dioxide is preferred, silica is more preferred, and hydrophobic silica that has been subjected to a hydrophobic treatment is even more preferred. These may be used alone or in combination of two or more.

[0084] 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.

[0085] The inorganic fine particles have an average particle size of preferably 5 nm or more, more preferably 7 nm or more, and preferably 40 nm or less, more preferably 20 nm or less, from the viewpoint of the chargeability, fluidity and durability of the toner.

[0086] The amount of inorganic fine particles used in step 2 is preferably 0.3 parts by mass or more, more preferably 0.8 parts by mass or more, and even more preferably 1.2 parts by mass or more, per 100 parts by mass of the coarsely ground material, from the viewpoints of the glossiness of the printed surface and the resistance to document offset during storage at high temperatures, and is preferably 10 parts by mass or less, more preferably 7 parts by mass or less, and more preferably 5 parts by mass or less.

[0087] The coarsely pulverized material and the inorganic fine particles can be mixed using a mixer such as a Henschel mixer. It is preferable to mix them to such an extent that the inorganic fine particles adhere to the surface of the coarsely pulverized material.

[0088] Step 3 is a step of pulverizing and classifying the mixture obtained in step 2. In this specification, the pulverization in step 3 is also referred to as "fine pulverization."

[0089] Examples of mills used for fine pulverization include a fluidized bed counter jet mill, an impact plate jet mill, and a rotary mechanical mill.

[0090] The degree of pulverization is preferably adjusted appropriately depending on the desired toner particle size.

[0091] Examples of classifiers used for classification include air classifiers, inertial classifiers, and sieve classifiers.

[0092] The pulverization and classification may be carried out simultaneously or repeatedly depending on the specifications of the apparatus used and the production efficiency.

[0093] In the present invention, it is preferable to further carry out step 4 in which the classified product obtained in step 3 is mixed with an external additive, from the viewpoint of improving transferability.

[0094] 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-based resin fine particles and polytetrafluoroethylene resin fine particles, and two or more of these may be used in combination. Among these, silica is preferred, and from the viewpoint of toner transferability, hydrophobic silica that has been subjected to a hydrophobic treatment is more preferred.

[0095] 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.

[0096] From the viewpoint of the chargeability, fluidity, and transferability of the toner, the average particle diameter of the external additive is preferably 10 nm or more, more preferably 15 nm or more, and is preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 90 nm or less.

[0097] 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.

[0098] From the viewpoint of the chargeability, fluidity, and transferability of the toner, the amount of external additive used 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 toner particles (classified product) before treatment with the external additive, and is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less.

[0099] The 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.

[0100] The toner obtained by the method of the present invention can be used as a toner for one-component development, or mixed with a carrier to form a two-component developer. [Example]

[0101] The present invention will be described in detail below with reference to examples, but the present invention is not limited to these examples. Physical properties of resins and the like were measured by the following methods.

[0102] [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.

[0103] [Maximum endothermic peak temperature of resin] Using a differential scanning calorimeter "Q-100" (manufactured by TA Instruments Japan), weigh 0.01-0.02 g of sample into an aluminum pan, cool from room temperature (25°C) to 0°C at a rate of 10°C / min, and maintain at 0°C for 1 minute. Then, measure at a rate of 10°C / min. The temperature of the peak with the largest peak area among the observed endothermic peaks is taken as the maximum endothermic peak temperature. For crystalline resins, the maximum endothermic peak temperature is taken as the melting point.

[0104] [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.

[0105] [Melting point of release agent] Using a differential scanning calorimeter "Q-100" (TA Instruments Japan), 0.01 to 0.02 g of sample is weighed into an aluminum pan, heated to 200°C at a rate of 10°C / min, and then cooled from 200°C to -10°C at a rate of 5°C / min. The sample is then heated at a rate of 10°C / min, and the calorific value is measured. The maximum endothermic peak temperature is taken as the melting point.

[0106] [Average particle size of inorganic fine particles and external additives used in fine pulverization] 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.

[0107] [Volume median particle size of toner (D 50 ) Measuring instrument: "Coulter Multisizer (registered trademark) III" (manufactured by Beckman Coulter, Inc.) Aperture diameter: 100 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.

[0108] Resin manufacturing example 1 The alcohol component, carboxylic acid component, and esterification catalyst shown in Table 1 were placed in a 5-liter four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, and a stainless steel stirring rod, and the mixture was heated to 235°C under a nitrogen atmosphere and reacted for 6 hours. The temperature was then lowered to 210°C and the reaction continued at 40 kPa until the softening point shown in Table 1 was reached, yielding an amorphous polyester resin (Resin A1). The physical properties of the resulting resin are shown in Table 1.

[0109] [Table 1]

[0110] Resin manufacturing example 2 A 10 L four-neck flask equipped with a thermometer, stainless steel stirrer, flow condenser, dropping funnel, and nitrogen inlet tube was charged with 2 L of xylene. The dropping funnel contained 880 g of styrene, 220 g of n-butyl acrylate, and 100 g of dibutyl peroxide as a radical polymerization initiator. Under a nitrogen atmosphere, the xylene was heated to 135°C with stirring, and the mixture in the dropping funnel was added dropwise over 1 hour. The temperature was then raised to 200°C and held at 200°C for 2 hours. The pressure in the flask was then reduced to 8 kPa and held for 1 hour. The xylene was then removed to obtain a styrene-acrylic resin (Resin A2). The resulting resin had a glass transition temperature of 54°C and a softening point of 115°C.

[0111] Resin manufacturing example 3 The alcohol and carboxylic acid components shown in Table 2 were placed in a 5-liter four-neck flask equipped with a thermometer, a stainless steel stirring rod, a downflow condenser, and a nitrogen inlet tube, and the temperature was raised to 200°C over 8 hours in a nitrogen atmosphere in a mantle heater. An esterification catalyst was then added, and the reaction was carried out at 8 kPa until the softening point shown in Table 2 was reached, yielding crystalline polyester resins (resins C1 to C7 and C9). The physical properties are shown in Table 2.

[0112] Resin manufacturing example 4 The alcohol component, carboxylic acid component, and polymerization inhibitor shown in Table 2 were placed in a 5-liter four-neck flask equipped with a thermometer, a stainless steel stirring rod, a downflow condenser, and a nitrogen inlet tube, and the temperature was raised to 200°C over 8 hours in a nitrogen atmosphere using a mantle heater. An esterification catalyst was then added, and the reaction was continued at 8 kPa until the softening point shown in Table 2 was reached, yielding a crystalline polyester resin (Resin C8). The physical properties are shown in Table 2.

[0113] Resin manufacturing example 5 The alcohol components, carboxylic acid components other than trimellitic anhydride, and esterification catalyst shown in Table 2 were placed in a 5-liter four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, and a stainless steel stirring rod, and the reaction was carried out under a nitrogen atmosphere at 200°C until a reaction rate of 90% was reached, followed by a reaction at 8 kPa for 1 hour. Trimellitic anhydride was then added, and the reaction was carried out at 200°C under normal pressure for 2 hours to obtain a crystalline polyester resin (Resin C10). The physical properties are shown in Table 2. In this specification, the reaction rate refers to the value calculated by dividing the amount of water produced by reaction (mol) by the theoretical amount of water produced (mol) × 100.

[0114] [Table 2]

[0115] Examples 1 to 14 and Comparative Examples 1 to 4 100 parts by mass of the binder resin shown in Table 3, 5 parts by mass of colorant "ECB-301" (manufactured by Dainichi Seika Chemicals Co., Ltd., phthalocyanine blue (PB15:3)), 3 parts by mass of release agent "HNP-9" (manufactured by Nippon Seiro Co., Ltd., paraffin wax, melting point: 75°C), and 0.5 parts by mass of charge control agent "Bontron E-304" (manufactured by Orient Chemical Industries Co., Ltd.) were mixed for 1 minute using a Henschel mixer, and then melt-kneaded under the conditions shown below.

[0116] The resulting raw material mixture was fed to a continuous twin-open-roll kneader "Kneedex" (manufactured by Mitsui Mining Co., Ltd.) using a table feeder and kneaded to obtain a kneaded product. The continuous twin-open-roll kneader used here had a roll outer diameter of 0.14 m and an effective roll length of 0.8 m. The operating conditions were a rotation speed of the high-speed roll (front roll) of 75 r / min (33 m / min), a rotation speed of the low-speed roll (rear roll) of 50 r / min (22 m / min), and a roll gap of 0.1 mm. The heating and cooling medium temperatures within the rolls were set as follows: the temperature on the raw material inlet side of the high-speed roll was 150°C, the temperature on the kneaded material outlet side was 100°C, the temperature on the raw material inlet side of the low-speed roll was 75°C, and the temperature on the kneaded material outlet side was 30°C. The raw material mixture was fed at a rate of 10 kg / h, and the average residence time was approximately 5 minutes.

[0117] The resulting kneaded product was cooled to about 25°C, then coarsely pulverized in a pulverizer "Rotoplex" (manufactured by Hosokawa Micron Corporation) and passed through a sieve with 2 mm openings to obtain a coarsely pulverized product with a maximum diameter of 2 mm or less. 100 parts by mass of the obtained coarsely pulverized product and the inorganic fine particles shown in Table 3 were mixed in a Henschel mixer for 2 minutes to obtain a coarsely pulverized product with the inorganic fine particles attached.

[0118] The coarsely ground material with the inorganic fine particles attached was finely ground and classified by upper limit (removal of coarse particles) using a counter jet mill "400AFG" (manufactured by Hosokawa Alpine Co., Ltd.). Furthermore, it was classified by lower limit (removal of fine particles) using a classifier "TTSP" (manufactured by Hosokawa Alpine Co., Ltd.) to obtain the volume median particle diameter (D 50 ) yielded toner particles of 6.5 μm.

[0119] 100 parts by mass of the obtained toner particles and 1.0 part by mass of hydrophobic silica "R972" (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: DMDS, average particle size: 16 nm) and 1.0 part by mass of hydrophobic silica "RY-50" (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: silicone oil, average particle size: 40 nm) as external additives were mixed in a Henschel mixer (manufactured by Mitsui Mining Co., Ltd.) at 3000 r / min (circumferential speed: 32 m / sec) for 3 minutes to obtain a toner.

[0120] Comparative Example 5 In the melt-kneading process, instead of a continuous two-open roll kneader, a co-rotating twin-screw extruder "PCM-30" (manufactured by Ikegai Co., Ltd., shaft diameter 2.9 cm, shaft cross-sectional area 7.06 cm) was used. 2 A toner was obtained in the same manner as in Example 1, except that a twin-screw extruder was used. The operating conditions of the twin-screw extruder were a barrel temperature of 100°C, a shaft rotation speed of 200 r / min (a peripheral speed of the shaft rotation of 0.30 m / sec), a mixture supply rate of 10 kg / h (amount of mixture supplied per unit cross-sectional area of ​​the shaft of 1.42 kg / h cm). 2 ) was.

[0121] Comparative Example 6 A toner was obtained in the same manner as in Example 1, except that the coarsely pulverized material was not mixed with inorganic fine particles, but was directly subjected to fine pulverization, upper limit classification (removal of coarse particles) and lower limit classification (removal of fine particles).

[0122] Test Example 1 [Glossiness of printed surface] The toner was loaded into a non-magnetic single-component developing device "OKI MICROLINE 5400" (manufactured by OKI Electric Industry Co., Ltd.), and the toner adhesion amount was measured at 0.40±0.03mg / cm. 2 The density was adjusted to 0.80±0.06 mg / cm, and a 4.1 cm x 4.1 cm solid image was printed on "J Paper" (manufactured by Fujifilm Business Innovation Co., Ltd.). The solid image was removed before passing through the fixing unit to obtain an unfixed image. The paper with the obtained unfixed image was loaded into a non-magnetic one-component developing device "OKI MICROLINE 5400" (manufactured by OKI Electric Industry Co., Ltd.), and a 4.1 cm x 4.1 cm solid image was printed again. The solid image was removed before passing through the fixing unit to obtain an unfixed image with a density of 0.80±0.06 mg / cm. 2 The same procedure was repeated to obtain an unfixed image (two layers) of 1.20±0.09 mg / cm 2 An unfixed image (3 layers) of

[0123] The resulting unfixed three-layer image was fixed in an external fixing machine, an "OKI MICROLINE 3010" (manufactured by Oki Electric Industry Co., Ltd.), with the fixing roll temperature set to 100°C and a fixing speed of 80 mm / sec. The fixing roll temperature was then set to 105°C, and the same procedure was repeated. This was repeated while increasing the temperature in 5°C increments up to 190°C. The gloss of the resulting three-layer fixed image was measured at each fixing temperature, and the maximum value was used to evaluate the gloss. The gloss was measured using a gloss meter "PG-1" (manufactured by Nippon Denshoku Industries Co., Ltd.) with the light source set to 60°. The higher the gloss, the better the gloss. The results are shown in Table 3.

[0124] Test Example 2 [Document offset resistance during storage at high temperatures] The toner was loaded into a non-magnetic single-component developing device "OKI MICROLINE 5400" (manufactured by OKI Electric Industry Co., Ltd.), and 8,000 sheets were printed at a print rate of 1% under conditions of a temperature of 25°C and a relative humidity of 50%. Next, the toner adhesion amount was measured at 0.40±0.03 mg / cm. 2 The print head was adjusted to a value of 1 / 4" and a 4.1 cm x 4.1 cm solid image was printed. The solid image was removed before passing through the fixing unit to obtain an unfixed image. The unfixed image was fixed in an external fixing unit, which was an external fixing unit of an "OKI MICROLINE 3010" (manufactured by Oki Electric Industry Co., Ltd.), with the fixing roll temperature set to 150°C and a fixing speed of 80 mm / sec. J paper (manufactured by Fujifilm Business Innovation Co., Ltd.) was used as the printing medium.

[0125] The resulting fixed image was placed on a blank sheet of paper, and the two sheets of paper were placed together under a surface pressure of 80 g / cm. 2 The sheets were left to stand for one day under a load of 0.05 MPa at a temperature of 50°C. After that, the stacked sheets were removed, and the edge of the sheet was gradually lifted to create a gap between the sheet and the sheet underneath, and a finger was inserted into the gap to peel the sheets off. Ten samples were prepared, and the condition of the fixed image area after peeling was visually inspected, and the document offset resistance was evaluated according to the following evaluation criteria. The results are shown in Table 3.

[0126] [Evaluation criteria] A: There was no sound of peeling for all 10 samples when peeling, and no defects were observed in the images. B: One or two out of ten samples make a sound when peeled, but no image defects are observed. C: When peeled, one or two samples out of ten produced a peeling sound and image defects were observed, or three or more samples produced a peeling sound but no image defects were observed. D: Peeling noise was heard during peeling in 3 or more out of 10 samples, and image defects were observed.

[0127] [Table 3]

[0128] From the above results, it is clear that in Examples 1 to 14, toners excellent in both the glossiness of the printed surface and the document offset resistance during storage at high temperatures can be obtained. On the other hand, in Comparative Example 1, in which no crystalline polyester resin is used, the toner is less likely to deform during thermal fixing and has low smoothness, resulting in a lack of gloss. In Comparative Example 2, in which too much crystalline polyester resin was used, the gloss was high, but the dispersibility of the crystalline polyester resin was poor and the adhesion of the inorganic fine particles used during grinding was uneven, resulting in a lack of document offset resistance. In Comparative Example 3, in which no short-chain monomer is used in the crystalline polyester resin, the compatibility between the crystalline polyester resin and the amorphous resin is low and the dispersibility of the crystalline polyester resin is poor, so the adhesion of the inorganic fine particles used during grinding is uneven, and there is a significant decrease in document offset resistance. In Comparative Example 4, in which the main component of the carboxylic acid component of the crystalline polyester resin is an aromatic dicarboxylic acid compound, the melting point of the crystalline polyester resin is high and the viscosity is also high, so that the toner is difficult to deform during heat fixing and lacks gloss. In Comparative Example 5, in which a twin-screw extruder was used for melt-kneading, the kneading intensity of the kneader was low, so the dispersibility of the crystalline polyester resin was insufficient, and the document offset resistance was poor. In Comparative Example 6, in which inorganic fine particles are not used in the pulverization process, the strength of the toner surface layer is insufficient, and therefore the document offset resistance is poor. [Industrial Applicability]

[0129] The electrostatic image developing toner obtained by the method of the present invention is suitably used for developing latent images formed in electrostatic image developing methods, electrostatic recording methods, electrostatic printing methods and the like.

Claims

1. a process for producing a toner for developing electrostatic images, the process comprising: Step 1: melt-kneading at least an amorphous resin and a crystalline polyester resin using an open-roll kneader; Step 2: pulverizing the kneaded mixture obtained in Step 1, and then mixing the pulverized mixture with inorganic fine particles; and Step 3: pulverizing and classifying the mixture obtained in Step 2; wherein the crystalline polyester resin is a polycondensate of an alcohol component containing 80 mol % or more of an aliphatic diol and a carboxylic acid component containing 80 mol % or more of an aliphatic dicarboxylic acid compound, the alcohol component containing a short-chain aliphatic diol having from 2 to 4 carbon atoms and / or the carboxylic acid component containing a short-chain aliphatic dicarboxylic acid compound having from 4 to 8 carbon atoms; the mass ratio of the crystalline polyester resin to the amorphous resin is from 2 / 98 to 18 / 82; the melting point of the crystalline polyester resin is from 60° C. to 100° C.; and the inorganic fine particles are hydrophobic silica.

2. 2. The method for producing a toner for developing electrostatic images according to claim 1, wherein the amount of the inorganic fine particles used in step 2 is 0.3 parts by mass or more and 10 parts by mass or less per 100 parts by mass of the pulverized product.

3. 2. The method for producing a toner for developing electrostatic images according to claim 1, wherein the amorphous resin comprises an amorphous polyester resin.

4. The amorphous polyester resin is represented by formula (I): 【Chemistry 1】 (In the formula, OR and RO are oxyalkylene groups, R is an ethylene group and / or a propylene group, x and y are positive numbers each representing the average number of moles of alkylene oxide added, and the sum of x and y is 1 or more and 16 or less.) 4. The method for producing a toner for developing electrostatic images according to claim 3, wherein the toner is a polycondensate of an alcohol component containing 70 mol % or more of an alkylene oxide adduct of bisphenol A represented by the formula:

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