JP7825607B2 - Method for producing yellow toner for developing electrostatic images - Google Patents

Description

The present invention relates to a method for producing a yellow toner for developing electrostatic images, which is used to develop latent images formed in electrophotography, electrostatic recording, electrostatic printing, etc.

When producing toner using the melt-kneading method, a method is being considered in which the kneaded material is pulverized in the presence of inorganic fine particles (see Patent Document 1).

Japanese Patent Application Laid-Open No. 2007-328043

Full-color printing demands higher color development. Among the cyan, magenta, and yellow pigments commonly used in full-color toners, yellow, in particular, has a weaker coloring strength than the other colors. Therefore, to achieve the same coloring strength as the other colors, a larger amount of yellow pigment must be added. However, while adding a large amount of yellow pigment increases coloring strength, the pigment in the toner tends to aggregate, resulting in uneven distribution and uneven distribution on the toner surface. As a result, yellow toner is less stable in charge than other color toners, and its fluidity is more likely to deteriorate due to electrostatic aggregation. If the fluidity further decreases due to the detachment of silica from the toner surface during continuous printing, the toner layer formed by the developing roller and regulating blade will have an uneven thickness, making it more prone to smearing than other colors.
As disclosed in Patent Document 1, by carrying out the pulverization process of the kneaded material in the presence of inorganic fine particles in the toner manufacturing process, it is possible to make the inorganic fine particles adhere more firmly to the toner particles than when the inorganic fine particles are added as external additives. However, during continuous printing under low temperature and low humidity conditions, even the inorganic fine particles that have adhered to the toner in the pulverization process tend to detach, resulting in a problem of reduced durability.

The present invention relates to a method for producing a yellow toner for developing electrostatic images that has excellent durability under low-temperature and low-humidity conditions.

The present invention relates to a method for producing a yellow toner for developing electrostatic images, the method including: Step 1 of melt-kneading at least a binder resin and a colorant 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 colorant contains an organic yellow pigment having an NH group amount of 2.7 mmol/g or more, where the NH group amount is defined as the value obtained by dividing the total number of —NH— groups and _—NH2 groups in one molecule by the molecular weight, and the content of the organic yellow pigment is 6 parts by mass or more and 20 parts by mass or less, relative to 100 parts by mass of the binder resin.

The method of the present invention produces a yellow toner for developing electrostatic images that has excellent durability even under low temperature and low humidity conditions.

The present invention relates to a method for producing a yellow toner for developing electrostatic images (hereinafter simply referred to as "toner" or "yellow toner") by using a specific organic yellow pigment as the yellow pigment when producing a yellow toner containing a binder resin and a yellow pigment by a melt-kneading method, and then performing a multi-stage pulverization process, mixing the coarsely pulverized product with inorganic fine particles, followed by fine pulverization. The reason why the method of the present invention produces a yellow toner with excellent durability under low-temperature, low-humidity conditions, even when it contains a high amount of yellow pigment, is unclear, but is presumed to be as follows. Note that the following mechanism is merely a guess and is not limiting.

Under low temperature and low humidity conditions, the toner surface cools and hardens or shrinks, reducing the contact area between the toner and inorganic fine particles. As a result, during continuous printing under low temperature and low humidity conditions, inorganic fine particles that adhere more firmly than inorganic fine particles added as external additives due to mixing with the pulverized material in the pulverization process tend to detach, deteriorating the fluidity and durability of the toner and making it more likely to produce smudges.
However, in the method of the present invention, a large amount of an organic yellow pigment with a large amount of NH groups is used, and the pigment is finely and highly dispersed in the toner, thereby causing a large number of NH groups to be uniformly present on the toner surface. This allows the inorganic fine particles to adhere to the toner surface not only by mechanical force but also more firmly and with a high coverage rate due to the interaction between the functional groups of the inorganic fine particles adhered to the toner surface, such as OH groups on the silica surface, and the NH groups of the pigment, and it is thought that this makes it possible to suppress detachment of the inorganic fine particles even under low temperature and low humidity conditions.

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

Step 1 is a step in which at least the binder resin and colorant are melt-kneaded using an open-roll kneader.

Binder resins include polyester resins, vinyl resins such as styrene-acrylic resins, epoxy resins, polycarbonates, polyurethanes, and composite resins containing two or more of these resins. Of these, polyester resins are preferred from the standpoint of low-temperature fixability.

The polyester resin is a polycondensation product of an alcohol component and a carboxylic acid component, and from the standpoint of charging properties, the alcohol component preferably contains an alkylene oxide adduct of bisphenol A.

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

(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, even more preferably 4 or less, and even more preferably 2.5 or less.)
A compound represented by the following formula is preferred.

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%.

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

From the standpoint of durability, it is preferable that the carboxylic acid component contains an aromatic dicarboxylic acid compound.

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.

The content of the aromatic dicarboxylic acid compound in the carboxylic acid 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%.

Other carboxylic acid components include fumaric acid, maleic acid, succinic acid, succinic acid derivatives substituted with hydrocarbon groups, 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.

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

In this specification, macromonomers and hydroxycarboxylic acids are not included in the alcohol components and carboxylic acid components.

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, and even more preferably 0.8 or more, and is preferably 1.3 or less, and more preferably 1.2 or less.

The polyester resin can be produced, for example, by polycondensing an alcohol component and a carboxylic acid component in an inert gas atmosphere, preferably in the presence of an esterification catalyst, and optionally in the presence of a co-catalyst, 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.

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 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, and 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 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, and 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 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.

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

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

From the viewpoint of heat-resistant storage stability, the glass transition temperature of the polyester resin is preferably 40°C or higher, more preferably 50°C or higher, and from the viewpoint of charge stability, it is preferably 80°C or lower, more preferably 70°C or lower.

The polyester resin is preferably an amorphous resin.
The crystallinity of a resin is represented 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].
The 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 crystalline resin is a resin having a crystallinity index of 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 type and ratio 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.

The content of 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.

Furthermore, the content of polyester resin in the toner is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more, and is preferably 94% by mass or less, and more preferably 92% by mass or less.

The binder resin content in the toner is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 75% by mass or more, and is preferably 94% by mass or less, and more preferably 92% by mass or less.

The colorant includes an organic yellow pigment with a specific amount of NH groups in order to interact with the inorganic fine particles.

The NH group amount of the organic yellow pigment is 2.7 mmol/g or more, preferably 4.0 mmol/g or more, more preferably 7.0 mmol/g or more, and is preferably 15.0 mmol/g or less, more preferably 13.0 mmol/g or less, and even more preferably 12.5 mmol/g or less. Here, the NH group amount is the value obtained by dividing the total number of —NH— groups and _—NH2 groups in one molecule by the molecular weight.

From the viewpoint of achieving the desired NH group content, the organic yellow pigment is preferably at least one selected from the group consisting of benzimidazolone pigments, isoindoline pigments, and condensed disazo pigments.

Examples of benzimidazolone pigments include C.I. Pigment Yellow 180 (total number of —NH— groups and —NH ₂ groups in one molecule=6, molecular weight=733, NH group amount=8.2 mmol/g).

Examples of isoindoline pigments include C.I. Pigment Yellow 185 (total number of —NH— groups and —NH ₂ groups in one molecule=4, molecular weight=337, NH group amount=11.9 mmol/g).

Examples of condensed disazo pigments include C.I. Pigment Yellow 93 (total number of -NH- groups and -NH ₂ groups in one molecule = 4, molecular weight = 937, NH group amount = 4.3 mmol/g), C.I. Pigment Yellow 95 (total number of -NH- groups and -NH ₂ groups in one molecule = 4, molecular weight = 917, NH group amount = 4.4 mmol/g), and C.I. Pigment Yellow 155 (total number of -NH- groups and -NH ₂ groups in one molecule = 2, molecular weight = 717, NH group amount = 2.8 mmol/g).

From the viewpoint of heat-resistant storage stability of the yellow toner, the organic yellow pigment used in the present invention is preferably at least one selected from benzimidazolone pigments and isoindoline pigments, more preferably at least one selected from C.I. Pigment Yellow (PY) 180 and PY185, with PY185 being even more preferred.

The content of the organic yellow pigment is 6 parts by mass or more, preferably 7 parts by mass or more, and more preferably 7.5 parts by mass or more, per 100 parts by mass of binder resin. From the viewpoint of low-temperature fixability, it is preferably 20 parts by mass or less, preferably 17 parts by mass or less, and more preferably 15 parts by mass or less.

The colorant may contain other colorants as long as the effects of the present invention are not impaired. However, the content of the organic yellow pigment in the colorant is preferably 80% by mass or more, more preferably 90% by mass or more, even more preferably 95% by mass or more, and even more preferably 100% by mass. Examples of other colorants 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, and disazo yellow.

The content of colorant is preferably 6 parts by weight or more, more preferably 7 parts by weight or more, and even more preferably 7.5 parts by weight or more, per 100 parts by weight of binder resin. From the viewpoint of low-temperature fixability, it is preferably 20 parts by weight or less, more preferably 17 parts by weight or less, and even more preferably 15 parts by weight or less.

In step 1, raw materials that can be melt-kneaded together with the binder resin and colorant include additives such as release agents, charge control agents, magnetic powders, flowability improvers, conductivity adjusters, reinforcing fillers such as fibrous substances, antioxidants, and cleaning improvers.

Examples of release agents include hydrocarbon waxes such as polypropylene wax, polyethylene wax, ethylene-propylene copolymer wax, microcrystalline wax, paraffin wax, and Fischer-Tropsch wax, as well as their oxides; ester waxes such as carnauba wax, montan wax, and their deoxidized waxes, and fatty acid ester wax; fatty acid amides, fatty acids, higher alcohols, and fatty acid metal salts, which can be used alone or in combination of two or more.

From the viewpoint of toner transferability, the melting point of the release agent is preferably 60°C or higher, more preferably 70°C or higher, and from the viewpoint of low-temperature fixability, it 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 viewpoints of the toner's low-temperature fixability and offset resistance, and its dispersibility in the binder resin, the content of the release agent 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, per 100 parts by mass of 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.

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.

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" VP435 (manufactured by Clariant), etc.; polyamine resins, such as "AFP-B" (manufactured by Orient Chemical Industries, Ltd.), etc.; imidazole derivatives, such as "PLZ-2001" and "PLZ-8001" (both manufactured by Shikoku Chemical Industries, Ltd.), etc.; styrene-acrylic resins, such as "FCA-701PT" and "FCA-201-PS" (manufactured by Fujikura Chemical Industries, Ltd.), etc.

Negatively chargeable charge control agents include metal-containing azo dyes, such as "Barifast Black 3804," "Bontron S-31," "Bontron S-32," "Bontron S-34," and "Bontron S-36" (all manufactured by Orient Chemical Industries, Ltd.), "Eizenspiron Black TRH," and "T-77" (manufactured by Hodogaya Chemical Co., Ltd.); metal compounds of benzilic acid compounds, such as "LR-147" and "LR-297" (both 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 (Clariant), nitroimidazole derivatives, organometallic compounds, etc.

From the viewpoint of toner charging stability, the content of the charge control agent is preferably 0.01 parts by weight or more, more preferably 0.2 parts by weight or more, and preferably 10 parts by weight or less, more preferably 5 parts by weight or less, even more preferably 3 parts by weight or less, and even more preferably 2 parts by weight or less, per 100 parts by weight of the binder resin.

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

An open-roll kneader is one in which the kneading section is open rather than sealed, allowing for easy dissipation of the heat generated during melt-kneading. The open-roll kneader used in the present invention is equipped with a raw material supply port and a kneaded material discharge port located along the axial direction of the rolls, and from the standpoint of production efficiency, it is preferably a continuous open-roll kneader.

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. If 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.

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

From the viewpoint of reducing mechanical force during melt-kneading and suppressing heat generation, the temperature on the raw material inlet side of the high-speed 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 same viewpoint, the temperature on the raw material inlet side of the low-speed 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.

For both the high-speed and low-speed rolls, it is preferable that the temperature on the raw material input side be higher than the temperature on the kneaded material discharge side. 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 rolls, reducing the mechanical force during melt-kneading, and suppressing heat generation, and is preferably 60°C or less, more preferably 50°C or less.

The temperature on the raw material inlet side of the high rotation roll and low rotation roll refers to the set temperature at the raw material inlet end, and the temperature on the kneaded material outlet side refers to the set temperature at the kneaded material outlet end.

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.

Furthermore, 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 can be linear, spiral, wavy, uneven, etc.

After step 1, the resulting kneaded material is cooled appropriately until it reaches a pulverizable hardness, and then subjected to the subsequent step 2. Here, "cooling" refers to cooling the kneaded material to between 0°C and 50°C, or to cooling it to a temperature below the glass transition temperature of the binder resin in the kneaded material.

Step 2 is a step in which the kneaded product obtained in Step 1 is pulverized, and the resulting pulverized product is then mixed with inorganic fine particles. In this specification, the pulverization in Step 2 is also referred to as "coarse pulverization," and the resulting pulverized product is also referred to as "coarsely pulverized product."

Millers used for coarse grinding include hammer mills, atomizers, and rotoplexes.

For coarse pulverization, the kneaded material obtained in step 1 is coarsely pulverized until the particle size is approximately 0.1 to 3 mm, and then passed through a sieve with mesh openings of approximately 2 to 3 mm. The pulverized material that passed through the sieve is preferably mixed with inorganic fine particles as a pulverized material (coarsely pulverized material) with a maximum diameter of 2 to 3 mm or less.

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. Of these, from the standpoint of durability, silica or titanium dioxide is preferred, silica is more preferred, and hydrophobic silica that has been hydrophobized is even more preferred. These can be used alone or in combination of two or more types.

Hydrophobic treatment agents used to hydrophobize the surface of silica particles include hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMDS), cyclic silazanes, silicone oils, aminosilanes, octyltriethoxysilane (OTES), and methyltriethoxysilane.

From the viewpoint of the chargeability, fluidity, and durability of the toner, the average particle diameter of the inorganic fine particles is preferably 5 nm or more, more preferably 7 nm or more, and even more preferably 10 nm or more, and is preferably 40 nm or less, and more preferably 20 nm or less.

The amount of inorganic fine particles used in step 2 is preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 0.7 parts by mass or more, per 100 parts by mass of the coarsely pulverized material, from the viewpoint of the toner's chargeability, fluidity, and durability, 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.

A mixer such as a Henschel mixer can be used to mix the coarsely pulverized material and inorganic fine particles. It is preferable to mix them to the extent that the inorganic fine particles adhere to the surface of the coarsely pulverized material.

Step 3 is a step in which the mixture obtained in Step 2 is pulverized and classified. In this specification, the pulverization in Step 3 is also referred to as "fine pulverization."

Millers used for fine grinding include fluidized bed counter jet mills, collision plate jet mills, and rotary mechanical mills.

It is preferable to adjust the degree of pulverization appropriately depending on the desired toner particle size.

Classifiers used for classification include air classifiers, inertial classifiers, and sieve classifiers.

Fine grinding and classification may be performed simultaneously or repeatedly depending on the specifications of the equipment used and production efficiency.

In the present invention, it is preferable to further perform step 4, in which the classified material obtained in step 3 is mixed with an external additive, in order to improve transferability.

External additives 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 types may be used in combination. Of these, silica is preferred, and from the perspective of toner transferability, hydrophobic silica that has been hydrophobized is even more preferred.

Hydrophobic treatment agents used to hydrophobize the surface of silica particles include hexamethyldisilazane (HMDS), dimethyldichlorosilane (DMDS), cyclic silazanes, silicone oils, aminosilanes, octyltriethoxysilane (OTES), and methyltriethoxysilane.

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 preferably 250 nm or less, more preferably 200 nm or less, and even more preferably 90 nm or less.

External addition processing by mixing toner particles with external additives can be carried out according to conventional methods, and a mixer such as a Henschel mixer can be used.

From the viewpoint of the toner's chargeability, fluidity, and transferability, the amount of external additive used is preferably 0.05 parts by weight or more, more preferably 0.1 parts by weight or more, and even more preferably 0.3 parts by weight or more, per 100 parts by weight of toner particles (classified product) before treatment with the external additive, and is preferably 5 parts by weight or less, and more preferably 3 parts by weight or less.

The volume median particle diameter ( _D50 ) of the yellow toner obtained by the present invention is preferably 3 μm or more, more preferably 4 μm or more, and preferably 15 μm or less, more preferably 10 μm or less. In this specification, the volume median particle diameter ( _D50 ) means the particle diameter at which the cumulative volume frequency calculated by volume fraction is 50% calculated from the smallest particle diameter. In addition, when the toner is treated with an external additive, the volume median particle diameter of the toner particles before treatment with the external additive is taken as the volume median particle diameter of the toner.

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

The present invention will be explained in detail below using examples, but the present invention is not limited to these examples. Physical properties of resins, etc. were measured using the following methods.

[Softening point of resin]
Using a flow tester "CFT-500D" (manufactured by Shimadzu Corporation), 1 g of sample is heated at a temperature increase rate of 6°C/min, while a load of 1.96 MPa is applied by the plunger, and the sample is extruded 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.

[Maximum endothermic peak temperature of resin]
Using a differential scanning calorimeter "Q-100" (manufactured by TA Instruments Japan), 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 temperature decrease rate of 10°C/min, and maintained at 0°C for 1 minute. Thereafter, measurements are performed at a temperature increase rate of 10°C/min. Of the endothermic peaks observed, the temperature of the peak with the largest peak area is taken as the maximum endothermic peak temperature.

[Glass transition 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, heated to 200°C, and cooled from that temperature 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 indicating the maximum slope from the rising part of the peak to the peak apex.

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

[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 determined 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.

[Volume Median Particle Diameter (D ₅₀ ) of Toner]
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) was dissolved in an electrolyte solution to adjust the concentration to 5% by mass. Dispersion conditions: 10 mg of a measurement sample was added to 5 mL of the dispersion solution, and the mixture was dispersed for 1 minute using an ultrasonic disperser (machine name: US-1 manufactured by SND Corporation, output: 80 W). Thereafter, 25 mL of electrolyte was added, and the mixture was further dispersed for 1 minute using the ultrasonic disperser to prepare a sample dispersion.
Measurement conditions: The sample dispersion is added to 100 mL of the electrolyte to adjust the concentration so that the particle diameters of 30,000 particles can be measured in 20 seconds, and then the 30,000 particles are measured and the volume median particle diameter (D ₅₀ ) is determined from the particle diameter distribution.

Resin Production 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.

Resin Production Example 2
A 10 L four-neck flask equipped with a thermometer, stainless steel stirring rod, flow-through 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 further reduced and maintained at 8 kPa for 1 hour, and the xylene was removed to obtain a styrene-acrylic resin (Resin A2). The glass transition temperature of the resulting resin was 54°C and the softening point was 115°C.

Examples 1 to 11 and Comparative Examples 1 and 2
The binder resin and yellow pigment shown in Table 2, 4 parts by mass of a release agent "HNP-9" (paraffin wax, melting point: 75°C, manufactured by Nippon Seiro Co., Ltd.), and 0.5 parts by mass of a 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.

The resulting raw material mixture was fed via a table feeder to a continuous twin-open-roll kneader "Kneedex" (manufactured by Mitsui Mining Co., Ltd.) 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: 150°C on the raw material inlet side of the high-speed roll, 100°C on the kneaded material outlet side, 75°C on the raw material inlet side of the low-speed roll, and 30°C on the kneaded material outlet side. The raw material mixture was fed at a rate of 10 kg/h, with an average residence time of approximately 5 minutes.

The resulting kneaded material was cooled to approximately 25°C and then coarsely pulverized using a Rotoplex pulverizer (manufactured by Hosokawa Micron Corporation). The mixture was then passed through a sieve with 2 mm openings to obtain a coarsely pulverized material with a maximum diameter of 2 mm or less. 100 parts by mass of the resulting coarsely pulverized material and the inorganic microparticles shown in Table 2 were mixed in a Henschel mixer for 2 minutes to obtain a coarsely pulverized material with the inorganic microparticles attached.

The coarsely pulverized material with the inorganic fine particles attached thereto was subjected to fine pulverization and upper limit classification (removal of coarse particles) using a counter jet mill "400AFG" (manufactured by Hosokawa Alpine Co., Ltd.), and further subjected to lower limit classification (removal of fine particles) using a classifier "TTSP" (manufactured by Hosokawa Alpine Co., Ltd.), to obtain toner particles with a volume median particle size ( _D50 ) of 6.5 μm.

100 parts by weight of the resulting toner particles were mixed with 1 part by weight of hydrophobic silica "R972" (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: DMDS, average particle size: 16 nm) and 1 part by weight of hydrophobic silica "RX-50" (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: HMDS, average particle size: 40 nm) as external additives 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 yellow toner.

Comparative Example 3
A yellow toner was obtained in the same manner as in Example 1, except that in the melt-kneading step, a co-rotating twin-screw extruder "PCM-30" (manufactured by Ikegai Corporation, shaft diameter 2.9 cm, shaft cross-sectional area 7.06 cm ² ) was used instead of the continuous two-open roll kneader. The operating conditions of the twin-screw extruder were a barrel setting temperature of 100°C, a shaft rotation speed of 200 r/min (shaft rotation peripheral speed 0.30 m/sec), and a mixture supply rate of 10 kg/h (mixture supply amount per unit cross-sectional area of the shaft 1.42 kg/h·cm ² ).

Comparative Example 4
A yellow 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).

Test example [Image blurring under low temperature and low humidity conditions]
Yellow toner was loaded into a non-magnetic single-component developing device, "OKI MICROLINE 5400" (manufactured by Oki Electric Industry Co., Ltd.), and an A4-sized solid black image was printed in a low-temperature, low-humidity environment (10°C, 20% relative humidity). Next, 500 sheets were printed at a coverage rate of 1%, and then another A4-sized solid black image was printed. J paper (manufactured by Fujifilm Business Innovation) was used as the printing medium. The image density (ID ₁ ) of the initial solid black image at a center portion 5 cm from the bottom and the image density (ID ₂ ) of the central portion 5 cm from the bottom after 500 sheets were printed were measured using a reflection densitometer, "RD-915" (manufactured by Gretag Macbeth), to confirm the difference in image density between the two. If the difference in image density did not exceed 0.4, an additional 500 sheets were printed. Printing was continued until the difference in image density exceeded 0.4. Durability under low-temperature, low-humidity conditions was evaluated based on the number of prints. The results are shown in Table 2. The greater the number of printed sheets, the greater the effect of suppressing image blurring.

These results show that Examples 1 to 11 have good durability under low temperature and low humidity conditions. On the other hand, Comparative Example 1, which contains a small amount of organic yellow pigment, Comparative Example 2, which contains a small amount of NH groups in the organic yellow pigment, Comparative Example 3, which uses a twin-screw extruder instead of an open-roll kneader, and Comparative Example 4, which does not use inorganic fine particles in the grinding process, show early image blurring and insufficient durability compared to the Examples.

The electrostatic image developing yellow toner obtained by the method of the present invention is suitable for use in developing latent images formed in electrostatic image development methods, electrostatic recording methods, electrostatic printing methods, etc.

Claims (2)

1. A method for producing a yellow toner for developing electrostatic images, the method comprising: Step 1: melt-kneading at least a binder resin and a colorant 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 colorant contains an organic yellow pigment having an NH group amount of 2.7 mmol/g or more, where the NH group amount is the value obtained by dividing the total number of -NH- groups and -NH2 groups in _one molecule by the molecular weight, the content of the organic yellow pigment being 6 parts by mass or more and 20 parts by mass or less , relative to 100 parts by mass of the binder resin; the inorganic fine particles are hydrophobic silica, and the number average particle diameter of the inorganic fine particles is 5 nm or more and 40 nm or less . The method for producing a yellow toner for developing electrostatic images according to claim 1, wherein the amount of inorganic fine particles used in step 2 is 0.3 parts by weight or more and 10 parts by weight or less per 100 parts by weight of the pulverized material.