Method for manufacturing toner for developing electrostatic images

Abstract

To provide a method for manufacturing toner for developing electrostatic images, which is excellent in suppressing fogging under low-temperature and low-humidity conditions.SOLUTION: The method for manufacturing toner for developing electrostatic images includes: a first step of melt-kneading an amorphous resin and a release agent using an open-roll type mill; a second step of mixing a crushed product obtained by crushing the kneaded material obtained in the first step with inorganic fine particles; and a third step of crushing and classifying the mixture obtained in the second step, the release agent containing a synthetic ester wax and a hydrocarbon wax.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] Typically, toner for developing electrostatic images is subjected to an external additive treatment to cause inorganic fine particles to adhere to the toner surface. However, in order to prevent the inorganic fine particles from detaching from the toner, a method has been investigated in which a coarsely ground kneaded material is mixed with inorganic fine particles during the toner manufacturing process, and then finely ground to cause the inorganic fine particles to adhere more firmly to the toner surface (see Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [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]

[0004] However, under low temperature and low humidity conditions, the toner surface cools and hardens, or shrinks, reducing the contact area between the toner particles and the inorganic fine particles attached to their surface. Therefore, during continuous printing under low temperature and low humidity conditions, not only inorganic fine particles attached by normal external addition treatment but also inorganic fine particles attached by mixing with the pulverized material in the pulverization process are likely to detach. As a result, the charge amount of the toner decreases, causing fogging.

[0005] The present invention relates to a method for producing a toner for developing electrostatic images, which is excellent in preventing fogging under low temperature and low humidity conditions. [Means for solving the problem]

[0006] The present invention relates to a method for producing a toner for developing electrostatic images, the method comprising: Step 1 of melt-kneading at least an amorphous resin and a release agent using an open-roll kneader; Step 2 of pulverizing the kneaded product obtained in Step 1, and then mixing the pulverized product with inorganic fine particles; and Step 3 of pulverizing and classifying the mixture obtained in Step 2, wherein the release agent contains a synthetic ester wax and a hydrocarbon wax. [Effects of the Invention]

[0007] According to the method of the present invention, a toner for developing electrostatic images that is excellent in preventing fogging under low temperature and low humidity conditions can be obtained. DETAILED DESCRIPTION OF THE INVENTION

[0008] The present invention relates to a method for producing a toner for developing electrostatic images (hereinafter also referred to as toner) containing an amorphous resin and a release agent by a melt-kneading method, using a synthetic ester wax and a hydrocarbon wax as release agents, kneading raw materials using an open-roll kneader, and then mixing the coarsely pulverized product obtained by kneading the raw materials with inorganic fine particles, followed by fine pulverization to obtain a toner. The reason why the method of the present invention produces a toner with excellent fogging suppression under low-temperature and low-humidity conditions is not clear, but is presumed to be as follows. Note that the following mechanism is presumed and is not limited to this.

[0009] In the present invention, toner raw materials containing an amorphous resin, a synthetic ester wax, and a hydrocarbon wax are melt-kneaded using an open-roll kneader with a large kneading shear. This causes the hydrocarbon chains of the synthetic ester wax and the hydrocarbon wax to partially dissolve, moderately disrupting the crystalline structures of both waxes and facilitating dispersion, allowing the waxes to be highly dispersed and uniformly present on the pulverized surface of the kneaded mixture. Furthermore, by mixing the coarsely pulverized mixture with inorganic fine particles and then pulverizing it, the hydrophobic hydrocarbon moieties in the wax molecules interact with the hydrophobic groups on the surfaces of the inorganic fine particles, allowing the inorganic fine particles to adhere firmly to the toner surface. As a result, detachment of the inorganic fine particles from the toner is suppressed even during continuous printing under low temperature and low humidity conditions, stabilizing the toner charge and thus suppressing fogging.

[0010] The method for producing the toner of the present invention includes the following steps 1, 2, and 3.

[0011] Step 1 is a step of melt-kneading at least an amorphous resin and a release agent using an open-roll kneader.

[0012] Examples of amorphous resins include amorphous polyester resins, vinyl resins such as styrene-acrylic resins, amorphous polyamide 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.

[0013] 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.

[0014] 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):

[0015] [ka]

[0016] (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.

[0017] 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%.

[0018] Examples of other alcohol components include diols such as aliphatic diols, bisphenol A, and hydrogenated bisphenol A, and trihydric or higher alcohols such as sorbitol, pentaerythritol, glycerin, and trimethylolpropane.

[0019] 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.

[0020] 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.

[0021] 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.

[0022] The alcohol component may contain a monohydric alcohol, and the carboxylic acid component may contain a monocarboxylic acid compound, as appropriate.

[0023] In this specification, macromonomers and hydroxycarboxylic acids are not included in the alcohol component and carboxylic acid component.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.

[0031] The content of the amorphous 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 98% by mass or less, and more preferably 95% by mass or less.

[0032] In the present invention, the amorphous resin is used as a binder resin.

[0033] The content of the amorphous 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, even more preferably 98% by mass or more, and even more preferably 100% by mass. Examples of binder resins other than amorphous resins include crystalline resins such as crystalline polyester resins.

[0034] The content of the binder 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 98% by mass or less, and more preferably 95% by mass or less.

[0035] The release agent contains a synthetic ester wax and a hydrocarbon wax.

[0036] In the present invention, the "synthetic ester wax" refers to an ester compound obtained by reacting a carboxylic acid with an alcohol. Among them, from the viewpoints of compatibility with hydrocarbon wax and dispersibility in an amorphous resin, an ester obtained by reacting a monohydric aliphatic alcohol having from 14 to 24 carbon atoms with a fatty acid having from 14 to 24 carbon atoms and / or an ester obtained by reacting pentaerythritol with a fatty acid having from 14 to 24 carbon atoms is preferred, and an ester obtained by reacting a monohydric aliphatic alcohol having from 18 to 24 carbon atoms with a fatty acid having from 18 to 24 carbon atoms and / or an ester obtained by reacting pentaerythritol with a fatty acid having from 18 to 24 carbon atoms is more preferred.

[0037] Examples of commercially available synthetic ester waxes include esters obtained by reacting a monohydric aliphatic alcohol having from 14 to 24 carbon atoms with a fatty acid having from 14 to 24 carbon atoms, such as WEP-2, WEP-3, WE-10, and WE-12 (all of which are trade names, manufactured by NOF Corporation), and esters obtained by reacting pentaerythritol with a fatty acid having from 14 to 24 carbon atoms, such as WEP-4, WEP-5, WEP-6, and WEP-8 (all of which are trade names, manufactured by NOF Corporation).

[0038] The synthetic ester wax may contain, as a main component, 80% by mass or more of a component having at least one ester group in the structure.

[0039] The melting point of the synthetic ester wax is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 65°C or higher from the viewpoint of storage stability, and is preferably 120°C or lower, more preferably 100°C or lower, and even more preferably 90°C or lower from the viewpoint of low-temperature fixability.

[0040] Examples of hydrocarbon waxes include paraffin wax, Fischer-Tropsch wax, olefin, microcrystalline wax, polyethylene wax, polypropylene wax, ethylene-propylene copolymer wax, and other polyolefin waxes. Among these, paraffin wax or Fischer-Tropsch wax is preferred from the viewpoint of low-temperature fixability.

[0041] Commercially available paraffin waxes include HNP-11, HNP-9, HNP-10, and HNP-51 (all manufactured by Nippon Seiro Co., Ltd.). Commercially available Fischer-Tropsch waxes include FT-0070 and FNP-0090 (all manufactured by Nippon Seiro Co., Ltd.).

[0042] From the viewpoint of storage stability, the melting point of the hydrocarbon wax is preferably 50°C or higher, more preferably 60°C or higher, and even more preferably 65°C or higher, and from the viewpoint of low-temperature fixability, it is preferably 120°C or lower, more preferably 110°C or lower, and even more preferably 100°C or lower.

[0043] The mass ratio of the synthetic ester wax to the hydrocarbon wax (synthetic ester wax / hydrocarbon wax) is preferably 10 / 90 or more, more preferably 20 / 80 or more, and even more preferably 40 / 60 or more, from the viewpoint of wax dispersibility, and is preferably 90 / 10 or less, more preferably 80 / 20 or less, and even more preferably 60 / 40 or less, from the viewpoint of wax crystallinity.

[0044] The content of the synthetic ester wax and the hydrocarbon wax in the release agent 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.

[0045] Other release agents include natural ester waxes such as carnauba wax, candelilla wax, rice wax, Japan wax, jojoba wax, and derivatives thereof, fatty acid amides, fatty acids, higher alcohols, and fatty acid metal salts.

[0046] The amount of release agent used is preferably 1 part by mass or more, more preferably 2 parts by mass or more, and even more preferably 4 parts by mass or more, relative to 100 parts by mass of the amorphous resin, and from the viewpoint of dispersibility in the amorphous resin, is preferably 15 parts by mass or less, more preferably 12 parts by mass or less, and even more preferably 8 parts by mass or less.

[0047] The content of the release agent in the toner is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less.

[0048] In step 1, examples of raw materials that can be subjected to melt-kneading together with the amorphous resin and the release agent include colorants, charge control agents, magnetic powders, flowability improvers, conductivity adjusters, reinforcing fillers such as fibrous substances, antioxidants, and additives such as cleaning improvers.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] 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.).

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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."

[0066] Examples of the crusher used for coarse crushing include a hammer mill, an atomizer, and a rotoplex.

[0067] 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.

[0068] 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, and silica is more preferred. These may be used alone or in combination of two or more.

[0069] It is preferable that the inorganic fine particles have been subjected to a hydrophobic treatment. For example, examples of hydrophobic treatment agents for hydrophobizing the surface of silica particles include hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMDS), cyclic silazanes, silicone oils, aminosilanes, octyltriethoxysilane (OTES), and methyltriethoxysilane.

[0070] The inorganic fine particles have an average particle size of preferably 5 nm or more, more preferably 10 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.

[0071] 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, even more preferably 1.2 parts by mass or more, per 100 parts by mass of the coarsely ground material, from the viewpoints of glossiness of the printed surface and 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, more preferably 5 parts by mass or less, even more preferably 3 parts by mass or less.

[0072] 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.

[0073] 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."

[0074] Examples of mills used for fine pulverization include a fluidized bed counter jet mill, an impact plate jet mill, and a rotary mechanical mill.

[0075] The degree of pulverization is preferably adjusted appropriately depending on the desired toner particle size.

[0076] Examples of classifiers used for classification include air classifiers, inertial classifiers, and sieve classifiers.

[0077] The pulverization and classification may be carried out simultaneously or repeatedly depending on the specifications of the apparatus used and the production efficiency.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] 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.

[0085] 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]

[0086] 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.

[0087] [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.

[0088] [Maximum endothermic peak temperature of resin] Using a differential scanning calorimeter "Q-100" (manufactured by TA Instruments Japan Co., Ltd.), 0.01 to 0.02 g of sample is weighed into an aluminum pan, cooled from room temperature (25°C) to 0°C at a rate of 10°C / min, and maintained at 0°C for 1 minute. Then, measurements are performed 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.

[0089] [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.

[0090] [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 heating rate of 10°C / min, and then cooled from 200°C to -10°C at a heating rate of 5°C / min. The sample is then heated to 180°C at a heating rate of 10°C / min, and the calorific value is measured. The maximum endothermic peak temperature is taken as the melting point.

[0091] [Average particle size of inorganic fine particles and external additives to be mixed with the coarsely ground material] 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.

[0092] [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.

[0093] Resin manufacturing example 1 The alcohol component, carboxylic acid component, esterification catalyst, and cocatalyst 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.

[0094] [Table 1]

[0095] 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 maintained at 200°C for 2 hours. The pressure in the flask was then reduced to 8 kPa and maintained at 8 kPa for 1 hour. The xylene was then removed to obtain a styrene-acrylic resin (Resin A2). The resulting resin had a softening point of 115°C and a glass transition temperature of 54°C.

[0096] Examples 1 to 10, 13 and Comparative Examples 1 to 3 The amorphous resin and release agent shown in Table 3, 5 parts by mass of colorant "ECB-301" (manufactured by Dainichiseika Color & Chemicals Mfg. Co., Ltd., phthalocyanine blue (PB15:3)), 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.

[0097] The resulting raw material mixture was fed to a continuous twin-open roll kneader "Kneedex" (manufactured by Nippon Coke and Engineering 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 discharge 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 discharge 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.

[0098] The obtained 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.

[0099] 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.

[0100] 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 Nippon Coke and Engineering Co., Ltd.) at 3000 r / min (circumferential speed: 32 m / sec) for 3 minutes to obtain a toner.

[0101] Example 11 A toner was obtained in the same manner as in Example 1, except that 5 parts by mass of "Fastgen Super Magenta R" (manufactured by DIC Corporation, CI Pigment Red 122) was used as the colorant instead of "ECB-301."

[0102] Example 12 A toner was obtained in the same manner as in Example 1, except that 5 parts by mass of "Paliotol Yellow D1155" (manufactured by DIC Corporation, CI Pigment Yellow 185) was used as the colorant instead of "ECB-301."

[0103] Comparative Example 4 In the melt-kneading process, instead of a continuous two-open roll kneader, a co-rotating twin-screw extruder "PCM-30" (manufactured by Ikegai Corporation, 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.

[0104] Comparative Example 5 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).

[0105] Details of the release agents used in the examples and comparative examples are shown in Table 2.

[0106] [Table 2]

[0107] Test example [Fogging under low temperature and low humidity conditions] A non-magnetic single-component developing device, "OKI MICROLINE 5400" (Oki Electric Industry Co., Ltd.), was filled with 50 g of toner, and 5,000 images were printed at a 1% coverage rate with a 20-second break per page at a temperature of 10°C and relative humidity of 20%. J paper (Fujifilm Business Innovation Co., Ltd.) was used as the printing medium. After printing 5,000 images, one solid white image was printed, and the power was turned off midway through the printing process. Then, "Scotch Mending Tape 810" (3M Japan Co., Ltd., width: 18 mm) was cut to a sufficient length along the length of the photoreceptor, and the toner on the photoreceptor surface was attached to the J paper. The color density of the tape was measured at three locations, corresponding to both ends and the center of the photoreceptor, using a reflection densitometer, "RD-915" (Gretag Macbeth). The difference from the color density of the tape itself before the toner was attached was calculated, and the average of the three measurements was calculated. The results are shown in Table 3. A smaller value indicates better fogging suppression.

[0108] [Table 3]

[0109] From the above results, it is clear that in Examples 1 to 13, the occurrence of fogging was suppressed even under low temperature and low humidity conditions. On the other hand, the reason why fog occurs in Comparative Examples 1 to 5 is presumed as follows. In Comparative Example 1, which does not use hydrocarbon wax, the wax remains crystalline in the toner and the molecules do not move easily, making it difficult for the wax to interact with the hydrophobic groups on the surface of the inorganic fine particles, resulting in weak adhesion and easy detachment. In Comparative Example 2, in which carnauba wax, a natural ester wax, was used instead of the synthetic ester wax, the natural ester wax, unlike the synthetic ester wax, has a carbon number distribution and a large carbon number, so it is too compatible with the hydrocarbon wax, plasticizing the toner surface and burying the inorganic fine particles. In Comparative Example 3, which does not use synthetic ester wax, the wax has low affinity with the binder resin and is prone to crystallization, making it difficult for the wax to interact with the hydrophobic groups on the surface of the inorganic fine particles, resulting in weak adhesion strength and easy detachment. In Comparative Example 4, in which a twin-screw extruder was used instead of an open-roll kneader, the twin-screw extruder had a weaker kneading shear than the open-roll kneader, and the wax was insufficiently dispersed, resulting in non-uniform distribution on the toner surface and preventing uniform adhesion of the inorganic fine particles. In addition, the two types of wax were not compatible with each other. In Comparative Example 5, in which the coarsely pulverized material was not mixed with inorganic fine particles, the inorganic fine particles adhered to the toner by the conventional external addition treatment had lower adhesion strength and were more likely to detach than inorganic fine particles that had been mixed with the coarsely pulverized material in advance, and therefore the charge amount of the toner was likely to decrease. [Industrial Applicability]

[0110] 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 method for producing a toner for developing electrostatic images, comprising: step 1 of melt-kneading at least an amorphous resin and a release agent using an open-roll kneader; step 2 of pulverizing the kneaded product obtained in step 1, and then mixing the pulverized product with inorganic fine particles; and step 3 of pulverizing and classifying the mixture obtained in step 2, wherein the release agent contains a synthetic ester wax and a hydrocarbon wax.

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. 3. The method for producing a toner for developing electrostatic images according to claim 1, wherein the mass ratio of the synthetic ester wax to the hydrocarbon wax is 10 / 90 or more and 90 / 10 or less.

Images