JP2024011110A - Magnetic toner and its manufacturing method - Google Patents

Abstract

To provide a magnetic toner which has excellent low temperature fixability, suppresses existence on the surface of toner particles of a crystalline polyester resin, has good heat-resistant storage property and suppresses member contamination.SOLUTION: There is provided a magnetic toner in which composite body fine particles are bonded onto the surface of toner particles where a crystalline polyester resin and magnetic powder are dispersed in a binder resin, wherein the magnetic powder has a spherical shape, a BET specific surface area of 8.5 m2/g or more and 13.0 m2/g or less and electric resistance of 5×107 Ωcm or more and 1×109 Ωcm or less, the composite body fine particles are oxide titanium fine particles whose surface is coated with silica fine particles, and a difference in a solubility parameter (SP value) between the crystalline polyester resin and the binder resin is within a range of 0.5 or more and 3.0 or less.SELECTED DRAWING: None

Description

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

In recent years, in electrophotographic image forming apparatuses such as copiers, printers, and facsimile machines, improvements in the low-temperature fixing properties of toners have been required in order to meet market demands for energy savings and speed increases. One technique for improving the low-temperature fixability of toner is to include a crystalline polyester resin in a binder resin.

However, when the crystalline polyester resin is present on the surface of the toner particles, the surface of the toner particles becomes soft, and the surface treatment agent attached to the surface of the toner particles is buried in the toner particles, resulting in poor heat-resistant storage properties. The surface treatment agent sometimes detaches from the surface of the toner particles and adheres to the surface of a developing roller, etc., causing contamination. Additionally, the charging stability of the toner deteriorated, resulting in a decrease in image density.

Patent Document 1 discloses a technology in which a binder resin contains a cyclohexane soluble content, thereby improving the dispersion of crystalline polyester and suppressing contamination of a developing member, etc., without deteriorating toner storage stability or pulverizability. Proposed.

Patent Document 2 focuses on the compatibility between a crystalline polyester resin and a hydrocarbon wax, and improves the dispersibility of the crystalline polyester resin within toner particles by mixing them to form a eutectic. Techniques have been proposed for suppressing the phenomenon in which crystalline polyester resin or the like oozes out onto the surface of toner particles. Furthermore, Patent Document 3 proposes a technique for improving the degree of crystallinity of crystalline polyester by using wax to function as a crystal nucleating agent, thereby suppressing deterioration in heat-resistant storage stability and charging stability of toner.

Japanese Patent Application Publication No. 2006-154625 Japanese Patent Application Publication No. 2021-124654 JP 2021-165858 Publication

However, in the above-mentioned proposed technology, for example, Patent Document 1 uses a hybrid resin consisting of a polyester unit and a vinyl polymer unit as the binder resin, and the Examples of Patent Documents 2 and 3 use styrene as the binder resin. - Since acrylic resin is used, the compatibility of the crystalline polyester resin with the binder resin when the toner passes through the fixing device is limited, and there is a possibility that the improvement in low-temperature fixability is not sufficient.

In addition, in some of the examples of Patent Document 1, Patent Document 2, and Patent Document 3, a kneaded and pulverized toner is prepared and used, but heat-resistant storage stability and It is thought that there is still room for improvement regarding issues such as component contamination.

The present invention has been made in view of these conventional problems, and its purpose is to provide excellent low-temperature fixing properties, suppress the presence of crystalline polyester resin on the surface of toner particles, and improve heat-resistant storage stability. It is an object of the present invention to provide a magnetic toner which is good in quality and in which contamination of members by a surface treatment agent is suppressed.

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

A magnetic toner according to the present invention that achieves the above object is 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, and the magnetic powder is , 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 resistance of 5×10 ⁷ Ωcm or more and 1×10 ⁹ Ωcm or less, and the composite fine particles are silica fine particles. It is characterized by being titanium oxide fine particles whose surface is coated with.

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

In the magnetic toner having the above structure, it is preferable that the magnetic powder is 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 a range of 0.5 or more and 3.0 or less.

Further, according to the present invention, there is provided a method for producing a magnetic toner as described above, comprising: a mixing step of mixing a crystalline polyester resin, a magnetic powder, and a binder resin to obtain a mixture; and a step of melt-kneading the mixture. a kneading step to obtain a kneaded product, a coarse pulverization step to coarsely pulverize the kneaded material to obtain a coarsely pulverized product, an annealing step to heat-treat the coarsely pulverized product, and a pulverization step to pulverize the heat-treated coarsely pulverized product to a finely ground product. A pulverization step for obtaining a pulverized product; a classification step for classifying the pulverized product to obtain toner particles of a predetermined particle size; and a step for mixing the toner particles and composite fine particles to form the composite on the surface of the toner particles. The method is characterized by comprising a surface treatment step of attaching fine particles.

In the manufacturing method having the above configuration, the heat treatment temperature in the annealing step is 5° C. or more lower than the melting point of the crystalline polyester resin and higher than the glass transition temperature of the binder resin, and the heat treatment time is 3° C. or more. It is preferable that the time is in the range of not less than 1 hour and not more than 24 hours.

According to the magnetic toner of the present invention, excellent low-temperature fixability is obtained, the presence of crystalline polyester resin on the toner particle surface is suppressed, excellent heat-resistant storage stability is obtained, and component contamination caused by surface treatment agents is achieved. is also suppressed.

According to the manufacturing method of the present invention, it is possible to efficiently manufacture a magnetic toner that has excellent low-temperature fixability and heat-resistant storage stability and can suppress member 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 will be described in detail below, but the present invention is not limited to these embodiments in any way, and may be implemented with appropriate changes within the scope of the purpose of the present invention. be able to.

In this specification, a numerical range indicated using "-" indicates a range that includes the numerical values written before and after "-" as the minimum and maximum values, respectively. In addition, in numerical ranges described step by step in this specification, the upper limit value or lower limit value described in a certain numerical range may be replaced with the upper limit value or lower limit value of another numerical range described step by step. Good too. Moreover, in the numerical ranges described in this specification, the upper limit or lower limit described in a certain numerical range may be replaced with the value shown in the Examples.
In this specification, the term "step" is used not only to refer to an independent step but also to include a step in which the intended purpose of the step is achieved even if the step cannot be clearly distinguished from other steps.

(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 has an electrical resistance. is 5×10 ⁷ Ωcm or more and 1×10 ⁹ Ωcm or less.

The present inventors have conducted extensive studies to see if it is possible to suppress the amount of crystalline polyester resin present on the surface of toner particles, and as a result, in magnetic toner produced by the so-called kneading and pulverizing method, the binder resin is It has been found that the amount of crystalline polyester resin present on the surface of toner particles can be suppressed by making cracks more likely to occur at the interface between the powder and the magnetic powder. In order to promote cracking at the interface between the binder resin and magnetic powder in the pulverization process, the magnetic powder used should be spherical in shape and have a BET specific surface area of 8.5 m ² /g or more and 13.0 m ² /g. We have found that the following can be used. Note that the spherical shape of the magnetic powder includes not only a completely spherical shape but also a shape close to a spherical shape. To determine whether magnetic powder is spherical, for example, use a scanning electron microscope to observe the magnetic powder at a magnification of 30,000 times. You can judge whether a part does not exist or not. Since the magnetic powder is spherical, even if the magnetic powder is exposed on the surface of the toner particles, a decrease in the toner charge amount is suppressed. In addition, 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, that is, if the particle size of the magnetic powder is too large, the interface between the binder resin and the crystalline polyester resin will be smaller than the interface between the binder resin and the magnetic powder. cracking becomes more likely to occur, and the amount of crystalline polyester resin present on the toner particle surface increases, 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, that is, if the particle size of the magnetic powder is too small, the cohesive force between the magnetic powders becomes too strong, making it difficult to disperse them in the binder resin. This causes problems such as a decrease in toner charge amount and an accompanying decrease in image density.

On the other hand, if cracks are likely to occur at the interface between the binder resin and the magnetic powder, the exposure of the magnetic powder on the toner particle surface will increase, the electrical resistance of the magnetic toner will decrease, and there is a risk that an insufficient amount of charge will occur. Therefore, in the present invention, the shape of the magnetic powder used is spherical, and magnetic powder with high electrical resistance is used, and the electrical resistance is set in the 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, there is a risk that the image density will decrease in a high temperature and high humidity environment. If the electrical resistance of the magnetic powder is greater than 1×10 ⁹ Ωcm, the magnetic toner is excessively charged in a low-temperature, low-humidity environment, causing problems such as worsening of the fogging phenomenon in which the magnetic toner adheres to non-image areas.

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

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

The content of magnetic powder in the toner particles is usually preferably in the range of 50 parts by mass to 300 parts by mass, more preferably in the range of 70 parts by mass to 150 parts by mass, based on 100 parts by mass of the binder resin.

(Composite fine particles)
Another major feature of the magnetic toner according to the present invention is that the composite fine particles attached to the surface of the toner particles are titanium oxide fine particles whose surfaces are coated with silica fine particles. The composite fine particles on the surface of the toner particles function as a so-called spacer.

Although it is impossible to completely prevent the composite particles from detaching from the toner particle surface due to the influence of the crystalline polyester resin present on and near the surface of the toner particles, if the composite particles are The electrical resistance of the composite fine particles is about 5×10 ¹³ Ωcm, which is not as high as that of hydrophobic silica, which has been widely used as a surface treatment agent for toner particles. Even if it detaches from the surface of the toner particles and adheres to the surface of the developing roller or charging roller, it is unlikely to have an adverse effect on the toner image.
Further, since the composite fine particles have a higher electrical resistance (approximately 10 ⁸ Ωcm) than ordinary titanium oxide fine particles, they do not reduce the toner charge amount.

The average primary particle size of titanium oxide fine particles is preferably in the range of 80 nm to 300 nm, and the average primary particle size of silica fine particles is preferably in the range of 5 nm to 60 nm. The average primary particle size of the silica fine particles is preferably in the range of 1/60 to 1/5 of the average primary particle size of the titanium oxide fine particles. Further, the blending ratio of titanium oxide fine particles and silica fine particles is preferably in the range of 99/1 to 40/60 in terms of mass ratio. The average primary particle diameter of the composite fine particles is preferably in the range of 80 nm to 300 nm. More preferably, the average primary particle diameter of the composite fine particles is in the range of 200 nm to 300 nm.

The amount of the composite fine particles added is preferably in the range of 0.1 parts by mass to 4.0 parts by mass based on 100 parts by mass of toner particles. More preferably, it is 0.2 parts by mass to 2.0 parts by mass.

Such composite fine particles are produced by, for example, mixing titanium oxide fine particles and silica fine particles 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 organic hydrophobizing agent. It is produced by bonding fine silica particles to the surface of fine titanium oxide particles by reacting the following.

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

Examples of aliphatic dicarboxylic acids include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, suberic acid, azelaic acid, sebacic acid, dodecanedioic acid, and the like.

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, 1,12-dodecanediol and the like.

In terms of crystallinity of the crystalline polyester, the content of linear aliphatic dicarboxylic acid among the carboxylic acid components is preferably 80 mol% or more and 100 mol% or less, more preferably 90 mol% or more and 100 mol% or less. Preferably, it is more preferably 100 mol%.
In terms of crystallinity of the crystalline polyester, the content of 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, More preferably, it is 100 mol%.

The amount of crystalline polyester added is preferably in the range of 1 part by mass to 10 parts by mass based on 100 parts by mass of the binder resin.

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

Here, the difference in solubility parameter (SP value) between the binder resin and the crystalline polyester resin is preferably in a range of 0.5 or more and 3.0 or less. When the difference in solubility parameters is within this range, the dispersibility of the crystalline polyester resin in the binder resin is improved, and excessive plasticization of the binder resin is suppressed.

(Other internal additives)
Conventionally known internal additives such as a charge control agent and a release agent may be added to the toner particles if necessary. As the charge control agent, for example, as a positively chargeable charge control agent, nigrosine dye, fatty acid-modified nigrosine dye, carboxyl group-containing fatty acid-modified nigrosine dye, quaternary ammonium salt, amine compound, organometallic compound, etc. can be used. As the negatively chargeable charge control agent, metal complexes of oxycarboxylic acids, metal complexes of azo compounds, metal complex salt dyes, salicylic acid derivatives, and the like can be used. The amount of the charge control agent added is preferably in the range of 0.1 parts by mass to 10 parts by mass based on 100 parts by mass of the binder resin.

As the mold release agent, for example, various waxes and low molecular weight olefin resins are used. As waxes, for example, polyhydric alcohol esters of fatty acids, higher alcohol esters of fatty acids, alkylene bis fatty acid amide compounds, and natural waxes are used. As the low molecular weight olefin resin, polypropylene, polyethylene, propylene-ethylene copolymer, etc. having a number average molecular weight in the range of 1,000 to 10,000, especially 2,000 to 6,000 are used, and in particular polypropylene is preferably used. The amount of the release agent added is preferably 0.1 parts by mass to 10 parts by mass per 100 parts by mass of the binder resin.

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

The magnetic toner of the present invention can be used as either a one-component developer or a two-component developer. When used as a two-component developer, examples of carriers include magnetic metals such as iron, nickel, and cobalt and alloys thereof, alloys containing rare earth elements, hematite, magnetite, manganese-zinc ferrite, and nickel-zinc ferrite. Magnetic materials manufactured by sintering, atomizing, etc. magnetic materials such as ferrite, soft ferrite such as manganese-magnesium ferrite, lithium-based ferrite, iron-based oxides such as copper-zinc ferrite, and mixtures thereof. Particles and magnetic particles whose surfaces are coated with resin can be used. Furthermore, a magnetic material-dispersed resin can also be used as the carrier. In this case, the magnetic material used can be the magnetic material mentioned above, and the binder resin can be, for example, vinyl resin, polyester resin, epoxy resin, phenol resin, urea resin, polyurethane resin, polyimide resin, cellulose resin, polyester resin, etc. Mention may be made of ether resins or mixtures thereof.

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

The toner concentration in the two-component developer is 1% by mass to 10% by mass, preferably 1% by mass to 7% by mass. If the toner concentration is less than 1% by mass, the image density becomes too thin, while if the toner concentration exceeds 10% by mass, toner scatters in the developing device and toner adheres to dirt inside the machine or to the background area such as transfer paper. This is because there is a risk that problems may occur.

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

(Mixing process)
A binder resin, crystalline polyester resin, magnetic powder, and other additives as necessary are weighed and mixed to obtain a mixture. Examples of additives include charge control agents and mold release agents as described above. A conventionally known mixer can be used to mix each raw material. As the mixer, for example, a Henschel mixer, a V-type mixer, a ball mill, etc. are suitably used.

(kneading process)
Next, the obtained mixture is heated and melted and mixed using a conventionally known heating kneader to form a kneaded product. As the kneading machine, for example, a twin-screw kneading machine, a kneader, an extruder, etc. are suitably used.

(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 product. The particle size of the coarsely ground product is generally preferably in the range of 50 μm to 5000 μm. However, when performing annealing treatment in the post-process, it is better to have the same particle size for more uniform processing, so the upper limit of the particle size of the coarsely ground material is 3000 μm or less by classifying it with a screen with an opening of 3 mm or less. (3 mm or less) is better.

(annealing process)
The coarsely ground material is annealed (heated). The annealing treatment increases the degree of crystallinity of the crystalline polyester resin in the toner particles, improves heat-resistant storage stability and toner durability, and further suppresses surface contamination of the developing roller and charging roller. The heat treatment temperature in the annealing treatment is preferably 5° C. or more lower than the melting point of the crystalline polyester resin and higher than the glass transition temperature of the binder resin. Further, the heat treatment time is preferably in the range of 3 hours to 24 hours. For the annealing treatment, a known dryer such as a temperature-controllable fluidized bed dryer can be used.

(Fine grinding 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 having a predetermined particle size. The average particle size of the toner particles is preferably in the range of 5 μm to 15 μm.

(Surface treatment process)
The produced toner particles, a predetermined amount of composite fine particles, and other surface treatment agents if necessary are put into a stirrer, and the composite fine particles and other surface treatment agents are attached to the surfaces of the toner particles. As the stirrer, for example, a Henschel mixer, a V-type mixer, a Turbula mixer, a hybridizer, etc. are used.

Note that in cases where there is no need to increase the degree of crystallinity of the crystalline polyester resin in the binder resin, the annealing step may be omitted and the kneaded material may be coarsely or finely ground to obtain toner particles of a predetermined particle size. You can.

The raw materials used in the Examples and Comparative Examples described below are as follows.

(Preparation of composite fine particles A)
A hydrophobizing agent solution was prepared by diluting methyl hydrogen silicone oil (“KF-9901” manufactured by Shin-Etsu Chemical Co., Ltd.) to 50% by mass with isopropyl alcohol.
90 parts by mass of titanium oxide fine particles having an average primary particle diameter of 250 nm were placed in an FM mixer, and mixed for 15 minutes while adding the hydrophobizing agent solution by spray.
Next, 30 parts by mass of untreated silica fine particles with an average primary particle diameter of 7 nm were put into an FM mixer, and 10 parts by mass of methyl hydrogen silicone oil (KF-9901, manufactured by Shin-Etsu Chemical Co., Ltd.) was added by spraying. Mixed for an additional minute.
The resulting fine particle mixture was placed in a circulating hot air shelf dryer and heat-treated at 150° C. for 2 hours. Thereafter, the dried material was crushed using an FM mixer to produce composite fine particles A.

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

(Binder resin)
・Amorphous polyester resin A (glass transition point Tg: 59°C, T _1/2 : 122°C, SP value: 11.0, acid value: 9.0mgKOH/g)
・Amorphous polyester resin B (glass transition point Tg: 58°C, T _1/2 : 127°C, SP value: 11.9, acid value: 6.2mgKOH/g)
・Amorphous polyester resin C (glass transition point Tg: 57°C, T _1/2 : 120°C, SP value: 13.1, acid value: 9.0mgKOH/g)

(Crystalline polyester resin)
・Crystalline polyester resin A (T _1/2 : 73°C, SP value: 9.7, acid value 11.0mgKOH/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 x 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 x 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 x 10 ⁶ Ωcm)
・Magnetic powder E (Surface treatment: None, Shape: Octahedral, 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 size 12 nm)
・Silica B: “TG-C390” manufactured by Cabot (surface treated with octylsilane, average primary particle size 65 nm)
・Silica C: “X24-9600A” manufactured by Shin-Etsu Chemical Co., Ltd. (surface treated with hexamethylene disilazane (HMDS), average primary particle size 100 nm)

Example 1
For 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, and a charge control agent (manufactured by Hodogaya Chemical Industry Co., Ltd.) 2.1 parts by mass of paraffin wax ("HNP-9" manufactured by Nippon Seiro Co., Ltd.), 2.1 parts by mass of polypropylene wax ("Viscol 660P" manufactured by Sanyo Chemical Industries, Ltd.) A mass portion was put into a Henschel mixer and mixed for 3 minutes at a circumferential speed of 30 m/s to obtain a mixture.
Next, the obtained mixture was heated and melted and mixed using a twin-screw extruder ("PCM30" manufactured by Ikegai Co., Ltd.) to obtain a kneaded product. The kneaded product was then cooled and solidified.
Thereafter, the cooled and solidified kneaded material was pulverized using a pulverizer ("KTM" manufactured by Earth Technica), and then classified using a classifier ("DSX classifier" manufactured by Nippon Pneumatic Kogyo Co., Ltd.) to obtain an average particle size of 9. Toner particles of .0 μm were obtained.
To 100 parts by mass of the obtained toner particles, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 0.6 parts by mass of composite fine particles B were charged into a Henschel mixer, and the surroundings were mixed. Mixing was carried out for 10 minutes at a speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles B were attached to the surfaces of toner particles.
The obtained magnetic toner was evaluated as follows. The evaluation results are shown in Table 2.

Example 2
To 100 parts by mass of toner particles obtained in the same manner as in Example 1, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 parts by mass of composite fine particles A were added to Henschel. The mixture was placed in a mixer and mixed for 10 minutes at a circumferential speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A were attached to the surface 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 material B was used instead of magnetic material A as the magnetic material. To 100 parts by mass of the obtained toner particles, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 parts by mass of composite fine particles A were charged into a Henschel mixer, and the surroundings were mixed. Mixing was carried out for 10 minutes at a speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A were attached to the surfaces of 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 instead of amorphous polyester resin A as the binder resin. To 100 parts by mass of the obtained toner particles, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 parts by mass of composite fine particles A were charged into a Henschel mixer, and the surroundings were mixed. Mixing was carried out for 10 minutes at a speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A were attached to the surfaces of 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
For 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, and a charge control agent (manufactured by Hodogaya Chemical Industry Co., Ltd.) 2.1 parts by mass of paraffin wax ("HNP-9" manufactured by Nippon Seiro Co., Ltd.), 2.1 parts by mass of polypropylene wax ("Viscol 660P" manufactured by Sanyo Chemical Industries, Ltd.) A mass portion was put into a Henschel mixer and mixed for 3 minutes at a circumferential speed of 30 m/s to obtain a mixture.
Next, the obtained mixture was heated and melted and mixed using a twin screw extruder ("PCM30" manufactured by Ikegai Co., Ltd.) to obtain a kneaded product. After the kneaded material was cooled and solidified, it was coarsely pulverized using a pulverizer ("Rotoplex" manufactured by Hosokawa Micron Corporation) equipped with a screen with an opening of 3 mm to obtain a coarsely pulverized product.
The obtained coarsely pulverized material was heat-treated at a temperature of 62°C for 6 hours (annealing step), then finely pulverized using a pulverizer ("KTM" manufactured by Earth Technica), and then finely pulverized using a classifier ("DSX" manufactured by Nippon Pneumatic Co., Ltd.). Classification was performed using a "classifier") to obtain toner particles with an average particle size of 9.0 μm.
Thereafter, 100 parts by mass of 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 parts by mass of composite fine particles A were put into a Henschel mixer. Mixing was carried out for 10 minutes at a circumferential speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A were attached to the surfaces of 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 material C was used instead of magnetic material A as the magnetic material. To 100 parts by mass of the obtained toner particles, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 parts by mass of composite fine particles A were charged into a Henschel mixer, and the surroundings were mixed. Mixing was carried out for 10 minutes at a speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A were attached to the surfaces of 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 material D was used instead of magnetic material A as the magnetic material. To 100 parts by mass of the obtained toner particles, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 parts by mass of composite fine particles A were charged into a Henschel mixer, and the surroundings were mixed. Mixing was carried out for 10 minutes at a speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A were attached to the surfaces of 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 material E was used instead of magnetic material A as the magnetic material. To 100 parts by mass of the obtained toner particles, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 parts by mass of composite fine particles A were charged into a Henschel mixer, and the surroundings were mixed. Mixing was carried out for 10 minutes at a speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A were attached to the surfaces of 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 instead of amorphous polyester resin A as the binder resin. To 100 parts by mass of the obtained toner particles, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 1.0 parts by mass of composite fine particles A were charged into a Henschel mixer, and the surroundings were mixed. Mixing was carried out for 10 minutes at a speed of 40 m/s to obtain a magnetic toner in which silica A and composite fine particles A were attached to the surfaces of 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
For 100 parts by mass of toner particles obtained in the same manner as in Example 1, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 0.7 parts by mass of silica B ("TG-C390" manufactured by Cabot Corporation) were added. 0.6 parts by mass were placed in a Henschel mixer and mixed for 10 minutes at a circumferential speed of 40 m/s to obtain a magnetic toner in which silica A and silica B were attached to the surfaces of 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
To 100 parts by mass of toner particles obtained in the same manner as in Example 1, 0.7 parts by mass of silica A ("RY200" manufactured by Nippon Aerosil Co., Ltd.) and 0.7 parts by mass of silica C ("X24-9600A" manufactured by Shin-Etsu Chemical Co., Ltd.) were added. ) was placed in a Henschel mixer and mixed for 10 minutes at a circumferential speed of 40 m/s to obtain a magnetic toner in which silica A and silica C were attached to the surface 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)
Output a solid image with a printing rate of 100%, apply mending tape to the solid image, then peel it off, measure the image density before applying the tape and the image density after peeling off the tape, and calculate the fixing rate using the following formula. It was measured.
Fixation rate (%) = (Image density after tape removal) / (Image density before tape application)

(Heat-resistant storage stability)
After 20 g of magnetic toner was placed in a constant temperature bath at a temperature of 50° C. for 24 hours, it was sieved for 15 seconds using a 42 mesh sieve, and the amount of magnetic toner remaining on the sieve was measured.

(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 long axis diameter of the domains was measured. The average long axis diameter of 30 pieces of magnetic toner was calculated and evaluated based on 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)
A magnetic one-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 31, paper P) is schematically shown in FIG. A printer with a printing speed of 60 ppm was filled with the magnetic toners of each example and each comparative example, 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. did.
The state of contamination on the surface of the charging roller after continuous printing was visually observed and evaluated based on the following criteria.
Level 1: There is no contamination on the surface of the charging roller. 2: The surface of the charging roller is 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 is covered with white particles (surface treatment agent). ), the toner image becomes completely white and black spots appear in the white part of the toner image.

(Evaluation of developing roller contamination)
Using the same developing device as used for the charging roller contamination evaluation, 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.
The contamination state of the developing roller surface after continuous printing was observed using a microscope and evaluated based on the following criteria.
Level 1: There is no contamination on the surface of the developing roller, and there is no problem with the toner image. 2: Melted toner is found in some places on the surface of the developing roller, but there is no problem with the toner image. 3: Melted toner is present on the entire surface of the developing roller. Density unevenness is seen in the solid image of the toner image.

(Image density evaluation under high temperature/high humidity (H/H) environment)
Using the same developing device as used for the charging roller contamination evaluation, 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, 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 crystalline polyester resin (C-PES), and the desired heat-resistant storage stability was obtained while maintaining the desired fixation rate. . Further, contamination of the charging roller and developing roller by the surface treatment agent was suppressed to the extent that no defects were caused in the toner image. Furthermore, the solid image density was also sufficient under high temperature and high humidity environments. In addition, the magnetic toner of Example 5, which was subjected to an annealing treatment in the manufacturing process, had excellent dispersibility of the crystalline polyester resin in the binder resin and had a very good heat-resistant storage stability of 0.1 g.

On the other hand, in the magnetic toner of Comparative Example 1 using magnetic powder with a small BET specific surface area, the amount of crystalline polyester resin exposed on the toner particle surface was increased, resulting in a decrease in heat-resistant storage stability. Further, melted toner was observed in some 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, small BET specific surface area, and low electrical resistance, can be used in high-temperature and high-humidity environments. At the bottom, the toner charge amount decreased and the solid image density was low.

In the magnetic toner of Comparative Example 4 in which an amorphous polyester resin with a high SP value was used as the binder resin, the difference in SP value between the crystalline polyester resin and the binder resin was as large as 3.4. The dispersibility of the crystalline polyester resin was low, and both the fixing rate and heat-resistant storage stability were poor. Further, melted toner was observed over the entire surface of the developing roller, and density unevenness was observed in the solid toner image. The solid image density was also low under high temperature and high humidity environments.

In the magnetic toner of Comparative Example 5, which used silica particles surface-treated with octylsilane without using composite particles as a surface treatment agent, melted toner was observed on the entire surface of the developing roller, and the density was low in the solid image of the toner image. Unevenness was observed. In addition, in the magnetic toner of Comparative Example 6, which used silica particles surface-treated with HMDS without using composite particles as a surface treatment agent, the toner charge amount decreased in a high temperature and high humidity environment, and the solid image density decreased. .

According to the magnetic toner of the present invention, excellent low-temperature fixability is obtained, and the presence of the crystalline polyester resin on the toner particle surface is suppressed, resulting in excellent heat-resistant storage stability. Contamination of components is also suppressed.

D Developing device P Paper 11 Developing roller 12 Charging blade 13 Stirring 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 crystalline polyester resin and magnetic powder are dispersed in a binder resin,
The magnetic powder has a spherical shape, 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 x 10 ⁷ Ωcm or more and 1 x 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 fine particles is in the range of 80 nm or more and 300 nm or less. 3. The magnetic toner according to claim 1, wherein the magnetic powder is surface-treated with a silane coupling agent having an alkyl group having 6 to 10 carbon atoms. 3. The magnetic toner according to claim 1, wherein a 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. A method for producing a magnetic toner according to claim 1 or 2, comprising:
a mixing step of mixing crystalline polyester resin, magnetic powder, and binder resin to obtain a mixture;
a kneading step of melt-kneading the mixture to obtain a kneaded product;
a coarse crushing step of coarsely crushing the kneaded material to obtain a coarsely crushed product;
an annealing step of heat-treating the coarsely pulverized material;
A pulverization step of finely pulverizing the heat-treated coarsely pulverized material to obtain a finely pulverized material;
a classification step of classifying the finely pulverized material to obtain toner particles of a predetermined particle size;
A method for producing a magnetic toner, comprising a surface treatment step of mixing the toner particles and composite fine particles and adhering the composite fine particles to the surface of the toner particles. The heat treatment temperature in the annealing step is 5° C. or more lower than the melting point of the crystalline polyester resin 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 a range of 3 hours or more and 24 hours or less.