JP7816766B2 - Magnetic toner and its manufacturing method - Google Patents

Description

The present invention relates to a magnetic toner and a method for producing the same.

In recent years, there has been a demand for improved low-temperature fixability of toner in electrophotographic image forming devices such as copiers, printers, and facsimiles to meet market demands for energy savings and higher speeds. One technique for improving the low-temperature fixability of toner is to incorporate a crystalline polyester resin into the binder resin.

However, when crystalline polyester resin is present on the surface of toner particles, the toner particle surface softens, causing the surface treatment agent attached to the toner particle surface to become embedded in the toner particle, resulting in poor heat-resistant storage stability. The surface treatment agent may also detach from the toner particle surface and adhere to the surface of the developing roller, causing contamination. This can also worsen the toner's charging stability, resulting in reduced image density.

Patent Document 1 proposes a technology in which a binder resin contains a cyclohexane-soluble component, thereby improving the dispersion of the crystalline polyester and suppressing contamination of developing components, etc., without compromising the toner's storage stability or grindability.

Patent Document 2 focuses on the compatibility between crystalline polyester resin and hydrocarbon wax, and proposes a technology in which the two are mixed to form a eutectic, improving the dispersibility of the crystalline polyester resin within toner particles and preventing the crystalline polyester resin from seeping out to the surface of the toner particles. Furthermore, Patent Document 3 proposes a technology in which wax functions as a crystal nucleating agent to improve the crystallinity of the crystalline polyester and prevent a decrease in the heat-resistant storage stability and charging stability of the toner.

Japanese Patent Application Laid-Open No. 2006-154625 Japanese Patent Application Laid-Open No. 2021-124654 Japanese Patent Application Laid-Open No. 2021-165858

However, in the above-proposed technologies, for example, Patent Document 1 uses a hybrid resin consisting of polyester units and vinyl polymer units as the binder resin, while Patent Documents 2 and 3 use a styrene-acrylic resin as the binder resin in the examples. Therefore, when the toner passes through the fixing device, the compatibility of the crystalline polyester resin with the binder resin is limited, and there is a risk that the improvement in low-temperature fixability will not be sufficient.

Furthermore, in the examples of Patent Documents 1, 2, and 3, a kneaded and pulverized toner is produced and used, but it is believed that there is still room for improvement in terms of problems such as heat-resistant storage stability and component contamination caused by the presence of crystalline polyester resin on the surface of the toner particles.

The present invention was made in consideration of these conventional problems, and its purpose is to provide a magnetic toner that has excellent low-temperature fixing properties, minimizes the presence of crystalline polyester resin on the toner particle surface, has good heat-resistant storage stability, and minimizes component contamination by surface treatment agents.

Another object of the present invention is to provide a method for efficiently producing magnetic toner that has excellent low-temperature fixability and heat-resistant storage stability and that can suppress component contamination due to surface treatment agents.

The magnetic toner according to the present invention, which achieves the above-mentioned object, is a magnetic toner in which composite fine particles are adhered to the surfaces of toner particles in which a crystalline polyester resin and a magnetic powder are dispersed in a binder resin, and the magnetic powder is spherical, has a BET specific surface area of 8.5 m ² /g or more and 13.0 m ² /g or less, and an electrical resistance of 5×10 ⁷ Ωcm or more and 1×10 ⁹ Ωcm or less, and the composite fine particles are titanium oxide fine particles whose surfaces are coated with silica fine particles.

In the magnetic toner having the above configuration, it is preferable that the average primary particle diameter of the composite microparticles is in the range of 80 nm or more and 300 nm or less.

In the magnetic toner having the above configuration, it is preferable that the magnetic powder has been surface-treated with a silane coupling agent having an alkyl group having 6 to 10 carbon atoms.

In the magnetic toner having the above configuration, it is preferable that the difference in solubility parameter (SP value) between the crystalline polyester resin and the binder resin is in the range of 0.5 or more and 3.0 or less.

Also according to the present invention, the method for producing the magnetic toner described above is characterized by comprising the following steps: a mixing step of mixing a crystalline polyester resin, a magnetic powder, and a binder resin to obtain a mixture; a kneading step of melting and kneading the mixture to obtain a kneaded product; a coarse pulverization step of coarsely pulverizing the kneaded product to obtain a coarsely pulverized product; an annealing step of heat-treating the coarsely pulverized product; a fine pulverization step of finely pulverizing the heat-treated coarsely pulverized product to obtain a finely pulverized product; a classification step of classifying the finely pulverized product to obtain toner particles of a predetermined particle size; and a surface treatment step of mixing the toner particles with composite fine particles and adhering the composite fine particles to the surfaces of the toner particles.

In the manufacturing method described above, it is preferable that the heat treatment temperature in the annealing step is at least 5°C lower than the melting point of the crystalline polyester resin and higher than the glass transition temperature of the binder resin, and that the heat treatment time is in the range of 3 hours to 24 hours.

The magnetic toner of the present invention provides excellent low-temperature fixability, suppresses the presence of crystalline polyester resin on the toner particle surface, provides excellent heat-resistant storage stability, and suppresses component contamination caused by surface treatment agents.

The manufacturing method of the present invention makes it possible to efficiently produce magnetic toner that has excellent low-temperature fixability and heat-resistant storage stability, and that can suppress component contamination caused by surface treatment agents.

FIG. 2 is a schematic diagram of a developing device used to evaluate magnetic toners of Examples and Comparative Examples.

Specific embodiments of the present invention are described in detail below, but the present invention is not limited to these embodiments and can be modified as appropriate within the scope of the invention.

In this specification, a numerical range indicated using "to" indicates a range that includes the numerical values before and after "to" as the minimum and maximum values, respectively. Furthermore, in the numerical ranges described in stages in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the upper limit or lower limit of another numerical range described in stages. Furthermore, in the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with a value shown in the examples.
In this specification, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.

(Magnetic powder)
One of the major features of the magnetic toner according to the present invention is that the magnetic powder dispersed in the binder resin is spherical, has a BET specific surface area of 8.5 m ² /g or more and 13.0 ^{m 2} /g or less, and an electrical resistivity of 5×10 ⁷ Ωcm or more and 1×10 ⁹ Ωcm or less.

The present inventors have conducted extensive research into whether it is possible to reduce the amount of crystalline polyester resin present on the toner particle surface. As a result, they have discovered that in magnetic toners produced by a so-called kneading and pulverization method, the amount of crystalline polyester resin present on the toner particle surface can be reduced by making it easier for cracks to occur at the interface between the binder resin and the magnetic powder during the pulverization process of the production process. They have also discovered that to promote cracks at the interface between the binder resin and the magnetic powder during the pulverization process, it is sufficient to use magnetic powder that is spherical in shape and has a BET specific surface area of 8.5 m ² /g or more and 13.0 m ² /g or less. Note that "spherical" magnetic powder includes not only perfect spheres but also shapes close to spheres. Whether the magnetic powder is spherical can be determined, for example, by observing the magnetic powder at 30,000x magnification using a scanning electron microscope and determining whether the shape is not hexahedral or octahedral, but rather whether it does not have angular portions characteristic of a polyhedral shape. By using spherical magnetic powder, the decrease in the toner charge amount is suppressed even when the magnetic powder is exposed on the surface of the toner particle, and the dispersibility of the magnetic powder in the binder resin is improved.

If the BET specific surface area of the magnetic powder is smaller than 8.5 m ² /g, i.e., the particle size of the magnetic powder is too large, cracks are more likely to occur at the interface between the binder resin and the crystalline polyester resin than at the interface between the binder resin and the magnetic powder, increasing the amount of crystalline polyester resin present on the toner particle surface and deteriorating the heat-resistant storage stability of the magnetic toner. On the other hand, if the BET specific surface area of the magnetic powder is larger than 13.0 m ² /g, i.e., the particle size of the magnetic powder is too small, the cohesive force between the magnetic powder particles becomes too strong, making it difficult to disperse them in the binder resin, resulting in problems such as a decrease in the toner charge amount and an accompanying decrease in image density.

On the other hand, if cracking at the interface between the binder resin and the magnetic powder is made more likely, the exposed surface of the magnetic powder toner particles increases, reducing the electrical resistance of the magnetic toner and potentially resulting in insufficient charge. Therefore, in the present invention, the magnetic powder used is made spherical and uses magnetic powder with high electrical resistance, with the electrical resistance set to a range of 5×10 ⁷ Ωcm to 1×10 ⁹ Ωcm. If the electrical resistance of the magnetic powder is less than 5×10 ⁷ Ωcm, image density may decrease in high-temperature, high-humidity environments. If the electrical resistance of the magnetic powder is greater than 1×10 ⁹ Ωcm, the magnetic toner may become excessively charged in low-temperature, low-humidity environments, resulting in problems such as worsening of the fogging phenomenon in which the magnetic toner adheres to non-image areas.

Examples of the magnetic powder material used in the present invention include powders of ferromagnetic metals such as iron, cobalt, and nickel, or alloys or compounds such as magnetite, hematite, and ferrite.

The magnetic powder is preferably surface-treated with a silane coupling agent or the like. A suitable silane coupling agent is one having an alkyl group with 6 to 10 carbon atoms. Surface treatment with such a silane coupling agent prevents a decrease in the electrical resistance of the toner when the magnetic powder is exposed to the toner particle surface, and prevents a decrease in image density, particularly in high-temperature, high-humidity environments.

The content of magnetic powder in toner particles is typically preferably in the range of 50 to 300 parts by weight per 100 parts by weight of binder resin, and more preferably in the range of 70 to 150 parts by weight.

(Composite fine particles)
Another major feature of the magnetic toner according to the present invention is that the composite particles attached to the surface of the toner particles are titanium oxide particles coated with silica particles, and the composite particles on the surface of the toner particles function as spacers.

It is impossible to completely prevent the composite fine particles from detaching from the toner particle surface due to the influence of the crystalline polyester resin present on or near the surface of the toner particles. However, if the composite fine particles are titanium oxide fine particles whose surfaces are coated with silica fine particles, the electrical resistance of the composite fine particles is about 5 x 10 ^Ωcm , which is not as high as that of hydrophobic silica, which has been widely used as a surface treatment agent for toner particles until now. Therefore, even if the composite fine particles detach from the toner particle surface and adhere to the surface of the developing roller or charging roller, they are unlikely to have an adverse effect on the toner image.
Furthermore, the composite fine particles have a higher electrical resistance than ordinary titanium oxide fine particles (approximately 10 ⁸ Ωcm), and therefore do not reduce the amount of charge on the toner.

The average primary particle diameter of the titanium oxide microparticles is preferably in the range of 80 nm to 300 nm, and the average primary particle diameter of the silica microparticles is preferably in the range of 5 nm to 60 nm. The average primary particle diameter of the silica microparticles is preferably in the range of 1/60 to 1/5 of the average primary particle diameter of the titanium oxide microparticles. The blending ratio of the titanium oxide microparticles to the silica microparticles is preferably in the range of 99/1 to 40/60 by mass. The average primary particle diameter of the composite microparticles is preferably in the range of 80 nm to 300 nm. A more preferred average primary particle diameter of the composite microparticles is in the range of 200 nm to 300 nm.

The amount of composite microparticles added is preferably in the range of 0.1 to 4.0 parts by weight per 100 parts by weight of toner particles. It is more preferably 0.2 to 2.0 parts by weight.

Such composite microparticles can be produced, for example, by mixing titanium oxide microparticles and silica microparticles in the presence of an organic hydrophobizing agent, such as silicone oil diluted with an organic solvent such as isopropyl alcohol, and then heating the mixture to react with the organic hydrophobizing agent and bond the silica microparticles to the surface of the titanium oxide microparticles.

(Crystalline polyester resin)
The crystalline polyester resin used in the present invention can be a conventionally known one, but is preferably a condensate of an aliphatic dicarboxylic acid and an aliphatic diol. Furthermore, saturated polyester is even more preferable. In this specification, "crystalline" means having a clear endothermic peak (having a melting point Tm) in differential scanning calorimetry (DSC) measurement. "Amorphous" means not having a clear endothermic peak.

Aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, and dodecanedioic acid.

Specific examples of aliphatic diols include ethylene glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, dipropylene glycol, trimethylene glycol, neopentyl glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, 1,9-nonanediol, 1,10-decanediol, 1,11-undecanediol, and 1,12-dodecanediol.

In terms of the crystallinity of the crystalline polyester, the content of linear aliphatic dicarboxylic acid in the carboxylic acid component is preferably 80 mol % or more and 100 mol % or less, more preferably 90 mol % or more and 100 mol % or less, and even more preferably 100 mol %.
In terms of the crystallinity of the crystalline polyester, the content of the linear aliphatic diol in the polyol component is preferably 80 mol % or more and 100 mol % or less, more preferably 90 mol % or more and 100 mol % or less, and even more preferably 100 mol %.

The amount of crystalline polyester added is preferably in the range of 1 to 10 parts by weight per 100 parts by weight of binder resin.

(Binder resin)
The binder resin used in the present invention may be a conventionally known resin. Examples include styrene-based resins, acrylic acid-based resins, olefin-based resins, vinyl resins, amorphous polyester resins, polyamide resins, urethane resins, styrene-acrylic acid-based resins, and styrene-butadiene-based resins. Among these, amorphous polyester resins are preferably used.

Here, it is preferable that the difference in solubility parameters (SP values) between the binder resin and the crystalline polyester resin be in the range of 0.5 or more and 3.0 or less. Having the difference in solubility parameters in this range improves the dispersibility of the crystalline polyester resin in the binder resin and suppresses excessive plasticization of the binder resin.

(Other internal additives)
Conventional internal additives such as charge control agents and release agents may be added to the toner particles as needed. Examples of charge control agents that can be used include positively charged nigrosine dyes, fatty acid-modified nigrosine dyes, carboxyl group-containing fatty acid-modified nigrosine dyes, quaternary ammonium salts, amine compounds, and organometallic compounds. Examples of negatively charged charge control agents that can be used include metal complexes of oxycarboxylic acids, metal complexes of azo compounds, metal complex dyes, and salicylic acid derivatives. The amount of charge control agent added is preferably in the range of 0.1 to 10 parts by mass per 100 parts by mass of the binder resin.

Examples of release agents include various waxes and low-molecular-weight olefin resins. Examples of waxes that can be used include polyhydric alcohol esters of fatty acids, higher alcohol esters of fatty acids, alkylene bis(fatty acid amide) compounds, and natural waxes. Examples of low-molecular-weight olefin resins that can be used include polypropylene, polyethylene, and propylene-ethylene copolymers with number-average molecular weights in the range of 1,000 to 10,000, particularly 2,000 to 6,000, with polypropylene being particularly preferred. The amount of release agent added is preferably 0.1 to 10 parts by weight per 100 parts by weight of binder resin.

(Other surface treatment agents)
In addition to the composite fine particles, a conventionally known surface treatment agent may be adhered to the surface of the toner particles. Examples of such surface treatment agents include inorganic fine powders such as (hydrophobic) silica, alumina, titanium oxide, zinc oxide, magnesium oxide, and calcium carbonate; organic fine powders such as polymethyl methacrylate; and fatty acid metal salts such as zinc stearate, in order to adjust the charge controllability and bulk density (fluidity) of the toner. One or more of these may be used in combination. The amount of the surface treatment agent added is preferably in the range of 0.1 to 2.0 parts by mass per 100 parts by mass of the toner particles. The surface treatment agent and the toner particles can be mixed using, for example, a Henschel mixer, a V-type mixer, a Turbula mixer, a hybridizer, or the like.

The magnetic toner of the present invention can be used in both one-component and two-component developers. When used in two-component developers, the carrier can be magnetic particles produced by sintering and atomizing magnetic materials such as magnetic metals such as iron, nickel, and cobalt, and their alloys, or alloys containing rare earth elements; soft ferrites such as hematite, magnetite, manganese-zinc ferrite, nickel-zinc ferrite, manganese-magnesium ferrite, and lithium ferrite; iron oxides such as copper-zinc ferrite; and mixtures thereof; or magnetic particles whose surfaces are coated with a resin. Magnetic material-dispersed resins can also be used as the carrier. In this case, the magnetic materials used can be the magnetic materials listed above, and the binder resin can be, for example, vinyl resins, polyester resins, epoxy resins, phenolic resins, urea resins, polyurethane resins, polyimide resins, cellulose resins, polyether resins, or mixtures thereof.

The particle size of the carrier, as measured by electron microscopy, is generally 25 μm to 200 μm, and preferably 30 μm to 100 μm. The apparent density of the carrier, when mainly made of a magnetic material, will differ depending on the composition and surface structure of the magnetic material, but is generally preferably in the range of 2.4 g/cm ³ to 3.0 g/cm ³ .

The toner concentration in two-component developers is 1% to 10% by weight, and preferably 1% to 7% by weight. If the toner concentration is less than 1% by weight, the image density will be too low, while if the toner concentration exceeds 10% by weight, toner may scatter within the developing device, causing problems such as contamination inside the device or toner adhering to background areas on transfer paper, etc.

(Method for manufacturing magnetic toner)
Although there is no particular limitation on the method for producing the magnetic toner according to the present invention, it is preferable to produce it as follows: Each step in the production of the magnetic toner will be explained below in order.

(Mixing process)
A binder resin, crystalline polyester resin, magnetic powder, and other additives, if necessary, are weighed and mixed to obtain a mixture. Examples of additives include the charge control agent and release agent, as described above. A conventionally known mixer can be used to mix the raw materials. Suitable mixers include a Henschel mixer, a V-type mixer, and a ball mill.

(Kneading process)
The resulting mixture is then heated, melted, and mixed in a conventionally known heat mixer to form a kneaded product, such as a twin-screw mixer, kneader, or extruder.

(Coarse crushing process)
The kneaded material is cooled and solidified using a drum flaker or the like, and then coarsely pulverized using a pulverizer such as a hammer mill to obtain a coarsely pulverized material. The particle size of the coarsely pulverized material is generally preferably in the range of 50 μm to 5000 μm. However, when performing an annealing treatment in a subsequent process, uniform particle size allows for more uniform treatment, so it is preferable to set the upper limit of the particle size of the coarsely pulverized material to 3000 μm or less (3 mm or less) by, for example, classifying the particles using a screen with a mesh size of 3 mm or less.

(Annealing step)
The coarsely pulverized material is then annealed (heat-treated). The annealing treatment increases the crystallinity of the crystalline polyester resin in the toner particles, improving heat-resistant storage stability and toner durability, and further suppressing surface contamination of the developing roller and charging roller. The heat treatment temperature in the annealing treatment is preferably at least 5°C lower than the melting point of the crystalline polyester resin and higher than the glass transition temperature of the binder resin. The heat treatment time is preferably in the range of 3 to 24 hours. A known dryer, such as a temperature-controllable fluidized bed dryer, can be used for the annealing treatment.

(Fine pulverization process)
The heat-treated coarsely pulverized product is pulverized to a predetermined particle size using a mechanical pulverizer or the like to obtain a finely pulverized product.

(Classification process)
The finely pulverized material is classified using an air classifier or the like to obtain toner particles of a predetermined particle size, with the average particle size of the toner particles preferably being in the range of 5 μm to 15 μm.

(Surface treatment process)
The prepared toner particles, a predetermined amount of composite fine particles, and other surface treatment agents, if necessary, are charged into a mixer to adhere the composite fine particles and other surface treatment agents to the surfaces of the toner particles. Examples of the mixer that can be used include a Henschel mixer, a V-type mixer, a Turbula mixer, and a hybridizer.

In cases where there is no need to increase the crystallinity of the crystalline polyester resin in the binder resin, the annealing step may be omitted and the kneaded material may be coarsely pulverized or finely pulverized to obtain toner particles of the desired particle size.

The raw materials used in the examples and comparative examples described below are as follows:

(Preparation of Composite Microparticles A)
Methyl hydrogen silicone oil (KF-9901 manufactured by Shin-Etsu Chemical Co., Ltd.) was diluted with isopropyl alcohol to 50% by mass to prepare a hydrophobizing agent solution.
90 parts by mass of titanium oxide fine particles having an average primary particle size of 250 nm were charged into an FM mixer, and mixed for 15 minutes while the hydrophobizing agent solution was added by spraying.
Next, 30 parts by mass of untreated silica fine particles having an average primary particle diameter of 7 nm were added to the FM mixer, and 10 parts by mass of methyl hydrogen silicone oil ("KF-9901" manufactured by Shin-Etsu Chemical Co., Ltd.) was further added by spraying, while the mixture was further mixed for 30 minutes.
The resulting fine particle mixture was placed in a circulating hot air shelf dryer and heat-treated for 2 hours at 150° C. Thereafter, the dried product was crushed in an FM mixer to prepare composite fine particles A.

(Preparation of Composite Microparticles B)
Composite particles B were prepared in the same manner as Composite particles A, except that titanium oxide particles having an average primary particle diameter of 100 nm were used.

(Binder resin)
Amorphous polyester resin A (glass transition point Tg: 59°C, T1 _/2 : 122°C, SP value: 11.0, acid value: 9.0 mgKOH/g)
Amorphous polyester resin B (glass transition temperature Tg: 58°C, T1 _/2 : 127°C, SP value: 11.9, acid value: 6.2 mgKOH/g)
Amorphous polyester resin C (glass transition temperature Tg: 57°C, T1 _/2 : 120°C, SP value: 13.1, acid value: 9.0 mgKOH/g)

(Crystalline polyester resin)
Crystalline polyester resin A (T _1/2 : 73° C., SP value: 9.7, acid value: 11.0 mgKOH/g)

(Magnetic powder)
Magnetic powder A (surface treatment: none, shape: spherical, average particle size: 170 nm, BET specific surface area: 9.5 m ² /g, electrical resistance: 1×10 ⁸ Ωcm)
Magnetic powder B (surface treatment: hexyltrimethoxysilane, shape: spherical, average particle size: 170 nm, BET specific surface area: 9.3 m ² /g, electrical resistance: 2×10 ⁸ Ωcm)
Magnetic powder C (surface treatment: none, shape: spherical, average particle size: 210 nm, BET specific surface area: 7.6 m ² /g, electrical resistance: 1×10 ⁸ Ωcm)
Magnetic powder D (surface treatment: none, shape: spherical, average particle size: 200 nm, BET specific surface area: 9.1 m ² /g, electrical resistance: 8×10 ⁶ Ωcm)
Magnetic powder E (surface treatment: none, shape: octahedron, average particle size: 180 nm, BET specific surface area: 7.7 m ² /g, electrical resistance: 2×10 ⁶ Ωcm)

(Silica (surface treatment agent))
Silica A: "RY200" manufactured by Nippon Aerosil Co., Ltd. (surface treated with dimethylpolysiloxane, average primary particle diameter 12 nm)
Silica B: Cabot Corporation's "TG-C390" (surface treated with octylsilane, average primary particle size 65 nm)
Silica C: "X24-9600A" manufactured by Shin-Etsu Chemical Co., Ltd. (surface treated with hexamethylenedisilazane (HMDS), average primary particle diameter 100 nm)

Example 1
100 parts by mass of amorphous polyester resin A (binder resin), 6.4 parts by mass of crystalline polyester resin A, 97.8 parts by mass of magnetic material A, 2.1 parts by mass of charge control agent ("T-77" manufactured by Hodogaya Chemical Co., Ltd.), 4.2 parts by mass of paraffin wax ("HNP-9" manufactured by Nippon Seiro Co., Ltd.), and 2.1 parts by mass of polypropylene wax ("Viscol 660P" manufactured by Sanyo Chemical Industries, Ltd.) were charged into a Henschel mixer and mixed at a peripheral speed of 30 m/s for 3 minutes to obtain a mixture.
Next, the resulting mixture was heated, melted, and mixed in a twin-screw extruder ("PCM30" manufactured by Ikegai Co., Ltd.) to obtain a kneaded mixture, which was then cooled and solidified.
Thereafter, the cooled and solidified kneaded product was pulverized in a pulverizer ("KTM" manufactured by EarthTechnica Co., Ltd.) and then classified using a classifier ("DSX Classifier" manufactured by Nippon Pneumatic Mfg. Co., Ltd.) to obtain toner particles having an average particle size of 9.0 μm.
100 parts by mass of the obtained toner particles were charged into a Henschel mixer with 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 0.6 parts by mass of composite microparticles B, and mixed for 10 minutes at a peripheral speed of 40 m/s to obtain a magnetic toner in which silica A and composite microparticles B adhered to the surface of the toner particles.
The magnetic toner thus obtained was subjected to the following evaluations, and the evaluation results are shown in Table 2.

Example 2
100 parts by mass of the toner particles obtained in the same manner as in Example 1 were charged into a Henschel mixer with 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 part by mass of composite fine particles A, and mixed for 10 minutes at a peripheral speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

Example 3
Toner particles were obtained in the same manner as in Example 1, except that magnetic substance B was used as the magnetic substance instead of magnetic substance A. 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 part by mass of composite fine particles A were added to a Henschel mixer relative to 100 parts by mass of the obtained toner particles, and mixed for 10 minutes at a peripheral speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

Example 4
Toner particles were obtained in the same manner as in Example 1, except that amorphous polyester resin B was used as the binder resin instead of amorphous polyester resin A. 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 part by mass of composite fine particles A were added to a Henschel mixer with 100 parts by mass of the obtained toner particles, and mixed for 10 minutes at a peripheral speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

Example 5
100 parts by mass of amorphous polyester resin A (binder resin), 6.4 parts by mass of crystalline polyester resin A, 97.8 parts by mass of magnetic material B, 2.1 parts by mass of charge control agent ("T-77" manufactured by Hodogaya Chemical Co., Ltd.), 4.2 parts by mass of paraffin wax ("HNP-9" manufactured by Nippon Seiro Co., Ltd.), and 2.1 parts by mass of polypropylene wax ("Viscol 660P" manufactured by Sanyo Chemical Industries, Ltd.) were charged into a Henschel mixer and mixed at a peripheral speed of 30 m/s for 3 minutes to obtain a mixture.
The resulting mixture was then heated, melted, and mixed in a twin-screw extruder (PCM30, manufactured by Ikegai Co., Ltd.) to obtain a kneaded product. The kneaded product was then cooled and solidified, and then coarsely pulverized using a pulverizer (Rotoplex, manufactured by Hosokawa Micron Corporation) equipped with a screen with 3 mm openings to obtain a coarsely pulverized product.
The obtained coarsely pulverized product was subjected to a heat treatment (annealing step) at a temperature of 62°C for 6 hours, and then finely pulverized using a pulverizer ("KTM" manufactured by EarthTechnica Co., Ltd.), and then classified using a classifier ("DSX Classifier" manufactured by Nippon Pneumatic Co., Ltd.) to obtain toner particles having an average particle size of 9.0 μm.
Thereafter, 100 parts by mass of the toner particles, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) as a surface treatment agent, and 1.0 part by mass of the composite microparticles A were added to a Henschel mixer and mixed for 10 minutes at a peripheral speed of 40 m/s to obtain a magnetic toner in which silica A and composite microparticles A adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

Comparative Example 1
Toner particles were obtained in the same manner as in Example 1, except that magnetic substance C was used as the magnetic substance instead of magnetic substance A. 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 part by mass of composite fine particles A were added to a Henschel mixer relative to 100 parts by mass of the obtained toner particles, and mixed for 10 minutes at a peripheral speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

Comparative Example 2
Toner particles were obtained in the same manner as in Example 1, except that magnetic substance D was used as the magnetic substance instead of magnetic substance A. 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 part by mass of composite fine particles A were added to a Henschel mixer relative to 100 parts by mass of the obtained toner particles, and mixed at a peripheral speed of 40 m/s for 10 minutes, thereby obtaining a magnetic toner in which silica A and composite fine particles A adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

Comparative Example 3
Toner particles were obtained in the same manner as in Example 1, except that magnetic substance E was used as the magnetic substance instead of magnetic substance A. 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 part by mass of composite fine particles A were added to a Henschel mixer with 100 parts by mass of the obtained toner particles, and mixed for 10 minutes at a peripheral speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

Comparative Example 4
Toner particles were obtained in the same manner as in Example 1, except that amorphous polyester resin C was used as the binder resin instead of amorphous polyester resin A. 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 part by mass of composite fine particles A were added to a Henschel mixer with 100 parts by mass of the obtained toner particles, and mixed for 10 minutes at a peripheral speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

Comparative Example 5
100 parts by mass of toner particles obtained in the same manner as in Example 1 were charged into a Henschel mixer with 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 0.6 parts by mass of silica B ("TG-C390" manufactured by Cabot Corporation), and mixed at a peripheral speed of 40 m/s for 10 minutes to obtain a magnetic toner in which silica A and silica B adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

Comparative Example 6
100 parts by mass of toner particles obtained in the same manner as in Example 1 were charged into a Henschel mixer with 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 0.6 parts by mass of silica C ("X24-9600A" manufactured by Shin-Etsu Chemical Co., Ltd.), and mixed for 10 minutes at a peripheral speed of 40 m/s to obtain a magnetic toner in which silica A and silica C adhered to the surfaces of the toner particles.
The obtained magnetic toner was evaluated in the same manner as in Example 1. The evaluation results are shown in Table 2.

(Retention rate)
A solid image with a printing rate of 100% was output, mending tape was applied to the solid image, and then peeled off. The image density before and after the tape was applied was measured, and the fixing rate was calculated using the following formula.
Fixation rate (%) = (image density after tape peeling) / (image density before tape application)

(Heat-resistant storage stability)
20 g of magnetic toner was placed in a thermostatic chamber at 50° C. for 24 hours, and then sieved through a 42 mesh sieve for 15 seconds to measure the amount of magnetic toner remaining on the sieve.

(Dispersibility of Crystalline Polyester Resin (C-PES))
The domains of the crystalline polyester resin in the toner particles were observed by TEM observation, and the major axis diameter of the domains was measured. The average major axis diameter of 30 magnetic toner particles was calculated and evaluated according to the following criteria.
Average major axis diameter
○: 0.3μm or less △: More than 0.3μm and 0.6μm or less ×: More than 0.6μm

(Charging roller contamination evaluation)
The magnetic toners of each Example and Comparative Example were filled into a printer having a printing speed of 60 ppm and equipped with a magnetic single-component developing device D (developing roller 11, charging blade 12, stirring blade 13, photosensitive drum 21, charging roller 22, transfer roller 23, cleaning blade 24, exposure device 31, and paper P) as shown in the schematic diagram of FIG. 1, and 2,000 sheets were continuously printed using a text chart with a printing rate of 5% in a low temperature/low humidity (10°C/20%) environment.
After continuous printing, the state of contamination on the surface of the charging roller was visually observed and evaluated according to the following criteria.
Level 1: No contamination at all on the surface of the charging roller. 2: The surface of the charging roller becomes slightly white due to the adhesion of white particles (surface treatment agent), but there is no problem with the toner image. 3: The surface of the charging roller becomes completely white due to the adhesion of white particles (surface treatment agent), and black spots appear in the white parts of the toner image.

(Developing Roller Contamination Evaluation)
Using the same developing device as in the evaluation of charging roller contamination, 2000 sheets were continuously printed using a text chart with a printing rate of 5% in a high temperature/high humidity (30° C./80%) environment.
After continuous printing, the state of contamination on the surface of the developing roller was observed using a microscope and evaluated according to the following criteria.
Level 1: No contamination on the surface of the developing roller, and no defects in the toner image. 2: Melted toner was observed in places on the surface of the developing roller, but no defects in the toner image. 3: Melted toner was observed over the entire surface of the developing roller, and density unevenness was observed in the solid toner image.

(Image density evaluation under high temperature/high humidity (H/H) environment)
Using the same developing device as in the evaluation of charging roller contamination, 2,000 sheets were continuously printed using a text chart with a printing rate of 5% in a high temperature/high humidity environment (30°C/80%). After the continuous printing, a solid image was printed and the toner image density was measured.

As is clear from Table 2, the magnetic toners of Examples 1 to 5 had good dispersibility of the crystalline polyester resin (C-PES), and achieved the desired heat-resistant storage stability while maintaining the desired fixation rate. Contamination of the charging roller and developing roller by the surface treatment agent was also suppressed to a level that did not cause problems in the toner image. Furthermore, solid image density was also sufficient even in high-temperature, high-humidity environments. Additionally, the magnetic toner of Example 5, which underwent annealing treatment during the manufacturing process, had excellent dispersibility of the crystalline polyester resin in the binder resin and very good heat-resistant storage stability of 0.1 g.

In contrast, the magnetic toner of Comparative Example 1, which used magnetic powder with a small BET specific surface area, had more crystalline polyester resin exposed to the toner particle surface, resulting in reduced heat-resistant storage stability. Furthermore, molten toner was observed in places on the surface of the developing roller.

The magnetic toner of Comparative Example 2, which uses magnetic powder with low electrical resistance, and the magnetic toner of Comparative Example 3, which uses magnetic powder with an octahedral shape, a small BET specific surface area, and low electrical resistance, showed a decrease in toner charge amount and low solid image density in high-temperature, high-humidity environments.

In the magnetic toner of Comparative Example 4, which used an amorphous polyester resin with a high SP value as the binder resin, the difference in SP value between the crystalline polyester resin and the binder resin was large at 3.4, the dispersibility of the crystalline polyester resin in the binder resin was low, and both the fixation rate and heat-resistant storage stability were poor. Furthermore, molten toner was observed all over the surface of the developing roller, and density unevenness was observed in solid toner images. Furthermore, the solid image density was low even in high-temperature, high-humidity environments.

In the magnetic toner of Comparative Example 5, which used silica microparticles surface-treated with octylsilane without using composite microparticles as a surface treatment agent, molten toner was observed over the entire surface of the developing roller, and density unevenness was observed in solid toner images. Furthermore, in the magnetic toner of Comparative Example 6, which used silica microparticles surface-treated with HMDS without using composite microparticles as a surface treatment agent, the toner charge amount decreased in a high-temperature, high-humidity environment, resulting in a decrease in solid image density.

The magnetic toner of the present invention provides excellent low-temperature fixability, suppresses the presence of crystalline polyester resin on the toner particle surface, provides excellent heat-resistant storage stability, and also suppresses component contamination caused by surface treatment agents.

D Developing device P Paper 11 Developing roller 12 Charging blade 13 Agitating blade 21 Photosensitive drum 22 Charging roller 23 Transfer roller 24 Cleaning blade 31 Exposure

Claims (6)

A magnetic toner in which composite fine particles are attached to the surface of toner particles in which a crystalline polyester resin and a magnetic powder are dispersed in a binder resin,
the magnetic powder is spherical, has a BET specific surface area of 8.5 m ² /g or more and 13.0 ^{m 2} /g or less, and has an electrical resistivity of 5×10 ⁷ Ωcm or more and 1×10 ⁹ Ωcm or less;
The composite fine particles are titanium oxide fine particles whose surfaces are coated with silica fine particles.
A magnetic toner characterized by: The magnetic toner according to claim 1, wherein the average primary particle diameter of the composite microparticles is in the range of 80 nm or more and 300 nm or less. The magnetic toner according to claim 1 or 2, wherein the magnetic powder has been surface-treated with a silane coupling agent having an alkyl group having 6 to 10 carbon atoms. The magnetic toner according to claim 1 or 2, wherein the difference in solubility parameter (SP value) between the crystalline polyester resin and the binder resin is in the range of 0.5 or more and 3.0 or less. 3. The method for producing the magnetic toner according to claim 1 or 2,
a mixing step of mixing a crystalline polyester resin, a magnetic powder, and a binder resin to obtain a mixture;
a kneading step of melt-kneading the mixture to obtain a kneaded product;
a coarse pulverization step of coarsely pulverizing the kneaded mixture to obtain a coarsely pulverized product;
an annealing step of heat-treating the coarsely pulverized material;
a fine pulverization step of finely pulverizing the heat-treated coarsely pulverized product to obtain a finely pulverized product;
a classification step of classifying the finely pulverized product to obtain toner particles having a predetermined particle size;
a surface treatment step of mixing the toner particles with composite fine particles and adhering the composite fine particles to the surfaces of the toner particles. the heat treatment temperature in the annealing step is lower than the melting point of the crystalline polyester resin by 5°C or more and higher than the glass transition temperature of the binder resin;
6. The method for producing a magnetic toner according to claim 5, wherein the heat treatment time is in the range of 3 hours to 24 hours.