JP7824270B2 - Method for producing toner for developing electrostatic images - Google Patents

Description

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

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

Crystalline polyester resins are known to be effective as binder resins for toners in improving their low-temperature fixability, and their use in combination with amorphous polyester resins is being investigated (see Patent Documents 1 and 2).

Japanese Patent Application Laid-Open No. 2019-159022 Japanese Patent Application Laid-Open No. 2020-85971

Toners containing crystalline polyester resins have excellent gloss on the printed surface because they can quickly plasticize and deform during the thermal fixing process. However, if the toner that forms the print layer plasticizes when printed materials are stored at high temperatures, a problem occurs in which part of the toner transfers to the back of other paper when it is placed on top of another paper (document offset), staining the other paper.

The present invention relates to a method for producing a toner for developing electrostatic images that has excellent gloss on the printed surface and excellent resistance to document offset during storage at high temperatures.

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

The method of the present invention produces a toner for developing electrostatic images that has excellent gloss on the printed surface and excellent resistance to document offset during storage at high temperatures.

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

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

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

Step 1 is a step in which at least an amorphous resin and a crystalline polyester resin are melt-kneaded using an open-roll kneader.

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

A preferred amorphous polyester resin is 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.

Examples of alkylene oxide adducts of bisphenol A include ethylene oxide adducts of bisphenol A and propylene oxide adducts of bisphenol A, 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 positive numbers each representing the average number of moles of alkylene oxide added, and the sum of x and y is 1 or more, preferably 1.5 or more, and 16 or less, preferably 8 or less, more preferably 6 or less, and even more preferably 4 or less.)
A compound represented by the following formula is preferred.

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%.

Other alcohol components include aliphatic diols, bisphenol A, hydrogenated bisphenol A, sorbitol, pentaerythritol, glycerin, trimethylolpropane, and other trihydric or higher alcohols.

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 aromatic dicarboxylic acid compounds 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 is 100 mol% or less.

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.

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

Amorphous polyester resins 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 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 low-temperature fixability, the softening point is preferably 170°C or lower, more preferably 160°C or lower, and even more preferably 150°C or lower.

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

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

Crystalline polyester resin is a polycondensation product of an alcohol component containing 80 mol% or more of an aliphatic diol and a carboxylic acid component containing 80 mol% or more of an aliphatic dicarboxylic acid compound, where the alcohol component contains a short-chain aliphatic diol and/or the carboxylic acid component contains a short-chain aliphatic dicarboxylic acid compound.

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

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

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

Aliphatic diols other than short-chain aliphatic diols include 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol.

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

From the viewpoint of low-temperature fixability and glossiness of the printed surface, the content of aliphatic diol in the alcohol component is 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 100 mol%.

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

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

The number of carbon atoms in the short-chain aliphatic dicarboxylic acid compound is 4 to 8, preferably 4 to 6. Note that if the aliphatic dicarboxylic acid compound is an alkyl ester, the number of carbon atoms in the alkyl group is not included in the above carbon number.

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

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

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

From the viewpoint of durability and gloss of the printed surface, the content of the aliphatic dicarboxylic acid compound in the carboxylic acid component is 80 mol% or more, preferably 90 mol% or more, more preferably 95 mol% or more, and even more preferably 100 mol%.

Carboxylic acid components other than aliphatic dicarboxylic acid compounds include aromatic dicarboxylic acid compounds such as phthalic acid, isophthalic acid, and terephthalic acid, and trivalent or higher carboxylic acid compounds such as trimellitic acid and pyromellitic acid.

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

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

The equivalent ratio of the carboxyl groups of the carboxylic acid component to the hydroxyl groups of the alcohol component (COOH groups/OH groups) is preferably 0.8 or more, more preferably 0.9 or more, from the viewpoint of charging stability, and is preferably 1.2 or less, more preferably 1.1 or less, from the viewpoint of low-temperature fixability.

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

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

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

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

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

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

In the present invention, amorphous resins and crystalline polyester resins are used as binder resins.

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

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

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

Colorants that can be used include dyes, pigments, magnetic materials, and the like that are used as toner colorants. 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, and disazo yellow. In the present invention, the toner may be either black toner or color toner.

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 weight or more, more preferably 2 parts by weight or more, and preferably 40 parts by weight or less, more preferably 20 parts by weight or less, and even more preferably 10 parts by weight or less, per 100 parts by weight of binder resin.

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.

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

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 charge stability, the amount of charge control agent used 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 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 viewpoint of imparting chargeability, 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 preferably 40 nm or less, 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 0.8 parts by mass or more, and even more preferably 1.2 parts by mass or more, per 100 parts by mass of the coarsely ground product, 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, 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 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 toner obtained by the method of the present invention can be used as a single-component developer toner, 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 made 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. For crystalline resins, the maximum endothermic peak temperature is taken as the melting point.

[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 then cooled from 200°C to -10°C at a heating rate of 5°C/min. The sample is then heated at a heating rate of 10°C/min to measure the calorific value, 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 to a level that allows the particle diameters of 30,000 particles to 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, and esterification catalyst shown in Table 1 were placed in a 5-liter four-neck flask equipped with a nitrogen inlet tube, a dehydration tube, and a stainless steel stirring rod, and the mixture was heated to 235°C under a nitrogen atmosphere and reacted for 6 hours. The temperature was then lowered to 210°C and the reaction was 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.

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

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

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

Examples 1 to 14 and Comparative Examples 1 to 4
100 parts by mass of the binder resin shown in Table 3, 5 parts by mass of colorant "ECB-301" (manufactured by Dainichiseika Color & Chemicals Co., Ltd., phthalocyanine blue (P.B.15:3)), 3 parts by mass of mold release agent "HNP-9" (manufactured by Nippon Seiro Co., Ltd., paraffin wax, melting point: 75°C), and 0.5 parts by mass of charge control agent "Bontron E-304" (manufactured by Orient Chemical Industries Co., Ltd.) were mixed for 1 minute using a Henschel mixer, and then melt-kneaded under the conditions shown below.

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: the temperature on the raw material inlet side of the high-speed roll was 150°C, the temperature on the kneaded material outlet side was 100°C, the temperature on the raw material inlet side of the low-speed roll was 75°C, and the temperature on the kneaded material outlet side was 30°C. The raw material mixture was fed at a rate of 10 kg/h, and the average residence time was approximately 5 minutes.

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 was mixed with the inorganic microparticles shown in Table 3 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 1.0 part by weight of hydrophobic silica "R972" (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: DMDS, average particle size: 16 nm) and 1.0 part by weight of hydrophobic silica "RY-50" (manufactured by Nippon Aerosil Co., Ltd., hydrophobic treatment agent: silicone oil, 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 toner.

Comparative Example 5
A 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 6
A toner was obtained in the same manner as in Example 1, except that the coarsely pulverized material was not mixed with inorganic fine particles, but was directly subjected to fine pulverization, upper limit classification (removal of coarse particles) and lower limit classification (removal of fine particles).

Test Example 1 [Glossiness of printed surface]
The toner was loaded into a non-magnetic single-component developing device "OKI MICROLINE 5400" (manufactured by OKI Electric Industry Co., Ltd.), and the toner adhesion amount was adjusted to 0.40±0.03 mg/ ^cm² . A 4.1 cm x 4.1 cm solid image was printed on "J Paper" (manufactured by FUJIFILM Business Innovation Co., Ltd.). The solid image was removed before passing through the fixing device to obtain an unfixed image. The paper with the obtained unfixed image was loaded into a non-magnetic single-component developing device "OKI MICROLINE 5400" (manufactured by OKI Electric Industry Co., Ltd.), and another 4.1 cm x 4.1 cm solid image was printed. The solid image was removed before passing through the fixing device to obtain an unfixed image (2 layers) of 0.80±0.06 mg/ ^cm² . The same procedure was repeated to obtain an unfixed image (3 layers) of 1.20±0.09 mg/ ^cm² .

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

Test Example 2 [Document offset resistance during storage at high temperatures]
The toner was loaded into a non-magnetic single-component developing device "OKI MICROLINE 5400" (manufactured by OKI Electric Industry Co., Ltd.), and 8,000 sheets were printed at a print rate of 1% under conditions of 25°C temperature and 50% relative humidity. Next, the toner adhesion amount was adjusted to 0.40±0.03 mg/ ^cm² , and a 4.1 cm x 4.1 cm solid image was printed. The solid image was removed before passing through the fixing unit to obtain an unfixed image. The resulting unfixed image was fixed in an external fixing unit, which was an "OKI MICROLINE 3010" (manufactured by OKI Electric Industry Co., Ltd.), with the fixing roll temperature set to 150°C and a fixing speed of 80 mm/sec. J paper (manufactured by FUJIFILM Business Innovation Co., Ltd.) was used as the printing medium.

The resulting fixed image was placed on a blank J sheet, and the two sheets of paper were placed on top of each other and left to stand for one day under a surface pressure of 80 g/ ^cm² at 50°C. The stacked sheets were then removed, and the edges of the sheets were gradually lifted to create a gap between them and the underlying sheet, which was then peeled off using a finger. Ten samples were prepared, and the condition of the fixed image area after peeling was visually inspected. Document offset resistance was evaluated according to the following evaluation criteria. The results are shown in Table 3.

[Evaluation criteria]
A: No peeling noise was heard during peeling for all 10 samples, and no image defects were observed.
B: One or two samples out of ten make a sound when peeled off, but no image damage is observed.
C: When peeled, one or two samples out of ten produced a peeling sound and image defects were observed, or three or more samples produced a peeling sound but no image defects were observed.
D: Three or more out of ten samples produced a peeling sound when peeled, and image defects were observed.

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

The electrostatic image developing 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 (4)

a process for producing a toner for developing electrostatic images, the process comprising: Step 1: melt-kneading at least an amorphous resin and a crystalline polyester resin using an open-roll kneader; Step 2: pulverizing the kneaded mixture obtained in Step 1, and then mixing the pulverized mixture with inorganic fine particles; and Step 3: pulverizing and classifying the mixture obtained in Step 2; wherein the crystalline polyester resin is a polycondensate of an alcohol component containing 80 mol % or more of an aliphatic diol and a carboxylic acid component containing 80 mol % or more of an aliphatic dicarboxylic acid compound, the alcohol component containing a short-chain aliphatic diol having from 2 to 4 carbon atoms and/or the carboxylic acid component containing a short-chain aliphatic dicarboxylic acid compound having from 4 to 8 carbon atoms; the mass ratio of the crystalline polyester resin to the amorphous resin is from 2/98 to 18/82; the melting point of the crystalline polyester resin is from 60° C. to 100° C.; and the inorganic fine particles are hydrophobic silica . The method for producing a 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. The method for producing a toner for developing electrostatic images according to claim 1, wherein the amorphous resin contains an amorphous polyester resin. The amorphous polyester resin is represented by formula (I):
(In the formula, OR and RO are oxyalkylene groups, R is an ethylene group and/or a propylene group, x and y are positive numbers each representing the average number of moles of alkylene oxide added, and the sum of x and y is 1 or more and 16 or less.)
4. The method for producing a toner for developing electrostatic images according to claim 3, wherein the toner is a polycondensate of an alcohol component containing 70 mol % or more of an alkylene oxide adduct of bisphenol A represented by the formula: