JP7753073B2 - Toner, two-component developer, and method for producing toner - Google Patents

Description

The present invention relates to a toner, a two-component developer, and a method for producing the toner.

Toner (toner for developing electrostatic images) used in electrophotographic image forming devices such as copiers, multifunction machines, printers, and facsimile machines typically has external additives attached to the surface of the toner particles (toner base particles). In the external addition process of the toner manufacturing method, the toner particles and external additives are mixed in a powder mixer such as a Henschel mixer to adhere the external additives to the surface of the toner particles (hereinafter simply referred to as "externally adding").

In recent years, as toner has become more easily fixed at lower temperatures, it has become common to add large amounts of silica with a large particle diameter (approximately 50 nm to 200 nm) (hereinafter simply referred to as "large silica") to toner particles to provide a spacer effect and ensure heat resistance and durability. However, if large silica is weakly attached to the surface of toner particles in order to exert its spacer effect, it tends to become detached, and this detached large silica is difficult to clean, which can cause cleaning problems. Conversely, if large silica is strongly attached to the surface of toner particles, it becomes embedded in the surface of the toner particles, losing its spacer effect. As such, the use of large silica as an external additive is still insufficient.

Fatty acid metal salts are commonly used as external additives to improve cleaning performance, but because they have the opposite polarity to negatively charged toner, adding them as is can reduce the toner's chargeability. Furthermore, fatty acid metal salts can become liberated in the developer tank and accumulate there, accelerating developer degradation and causing image defects such as uneven image density across the printed surface. As such, the use of fatty acid metal salts as external additives is still insufficient.

JP 2018-41038 A

The present invention was made based on the above circumstances, and its purpose is to provide a toner containing large silica and fatty acid metal salts as external additives, which has excellent image density uniformity throughout its life and can suppress drum filming, as well as a two-component developer and a method for producing the toner.

To solve the above problems, the present invention provides the following toner, two-component developer, and toner manufacturing method.

The toner of the present invention, which has been made to solve the above-mentioned problems, is a toner having an external additive adhered to the surface of toner particles, and the external additive contains silica having a volume average particle diameter of 50 nm or more and 200 nm or less, and a fatty acid metal salt having a volume average particle diameter of 1.5 μm or less, and is characterized in that, when measured with a flow-type particle image analyzer having a detection limit of 0.5 μm, the content of ultrafine powder having a particle diameter of 2 μm or less in the toner is 15.0 to 30.0 number % ; and when measured with a flow-type particle image analyzer having a detection limit of 0.5 μm, the content of ultrafine powder having a particle diameter of 2 μm or less in the toner after external additive removal treatment is 0.1 to 10.0 number %.

The present invention described above makes it possible to overcome the challenges inherent in the large silica and fatty acid metal salts used as external additives while leveraging their respective effects. This makes it possible to suppress drum filming throughout the product's life, while also suppressing developer degradation, maintaining good developability, and suppressing image defects such as uneven image density across the printing surface.

The method for removing the external additives is as follows.
(Method of removing external additives)
2.0 g of toner is added to 40 ml of a 0.2% by mass aqueous Triton solution, stirred for 1 minute, and then irradiated with ultrasonic waves at 40 μA for 3 minutes using an ultrasonic homogenizer. After leaving the solution for 3 hours after ultrasonic irradiation, the supernatant is removed, and then approximately 50 ml of pure water is added to the precipitate, which is stirred for 5 minutes and then suction filtered using a membrane filter with a pore size of 1 μm. The residue on the filter is vacuum dried overnight to obtain a toner from which external additives have been removed.

Patent Document 1 discloses a toner for developing electrostatic images in which the ratio of toner particles with a particle diameter of 0.5 μm or more and 2 μm or less, and the ratio of toner particles with a particle diameter of more than 2 μm and 50 μm or less, in the number particle size distribution of the toner particles, are specified. However, it does not disclose or suggest the above-mentioned configuration of the present invention, or the mechanism and effects related to the aggregation of external additives, as described below.

The two-component developer of the present invention, developed to solve the above problems, is characterized by containing the toner of the present invention and a carrier.

The toner manufacturing method of the present invention, which has been devised to solve the above problems, includes a first external addition step in which silica having a volume average particle diameter of 50 nm or more and 200 nm or less is mixed with toner particles to cause the silica to adhere to the surfaces of the toner particles, and a second external addition step in which a fatty acid metal salt is mixed with the toner particles to cause the fatty acid metal salt to adhere to the surfaces of the toner particles, and is characterized in that the second external addition step is performed after the first external addition step.

The present invention provides a toner containing large silica and fatty acid metal salts as external additives, which exhibits excellent uniformity in image density throughout its life and suppresses drum filming, as well as a two-component developer and a method for producing the toner.

The present invention includes a toner, a two-component developer, and a method for producing the toner. These are described in detail below.

1. Toner The toner according to the present invention is a toner having an external additive attached to the surface of the toner particles. If necessary, the toner may further contain optional components within a range that does not impair the effects of the present invention. The volume average particle diameter of the primary particles of the toner particles is not particularly limited, but examples thereof include toner particles having a volume average particle diameter of 4 μm or more and 8 μm or less.

<Binder resin>
Examples of the binder resin in the toner according to the present invention include polyester resins, polystyrene resins such as styrene-acrylic resins, (meth)acrylic acid ester resins, polyolefin resins, polyurethane resins, and epoxy resins, and one of these may be used alone or two or more may be used in combination.

The polyester resin used as the binder resin is typically obtained by polycondensation reaction via an esterification reaction or transesterification reaction using a known method between one or more dihydric alcohol components and trihydric or higher polyhydric alcohol components and one or more dicarboxylic acids and trihydric or higher polycarboxylic acids.

Conditions for the condensation polymerization reaction can be set appropriately depending on the reactivity of the monomer components, and the reaction can be terminated when the polymer reaches the desired physical properties. For example, the reaction temperature is approximately 170 to 250°C, and the reaction pressure is approximately 5 mmHg to atmospheric pressure.

Examples of dihydric alcohol components include alkylene oxide adducts of bisphenol A such as polyoxypropylene (2.2)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene (3.3)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene (2.0)-2,2-bis(4-hydroxyphenyl)propane, polyoxypropylene (2.0)-polyoxyethylene (2.0)-2,2-bis(4-hydroxyphenyl)propane, and polyoxypropylene (6)-2,2-bis(4-hydroxyphenyl)propane; ethylene glycol Examples include diols such as glycol, diethylene glycol, triethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, neopentyl glycol, 1,4-butenediol, 1,5-pentanediol, 1,6-hexanediol, 1,4-cyclohexanedimethanol, dipropylene glycol, polyethylene glycol, polypropylene glycol, and polytetramethylene glycol; bisphenol A; propylene adducts of bisphenol A; ethylene adducts of bisphenol A; hydrogenated bisphenol A, etc.

Examples of trihydric or higher polyhydric alcohol components include sorbitol, 1,2,3,6-hexanetetrol, 1,4-sorbitan, pentaerythritol, dipentaerythritol, tripentaerythritol, sucrose (cane sugar), 1,2,4-butanetriol, 1,2,5-pentanetriol, glycerol, 2-methylpropanetriol, 2-methyl-1,2,4-butanetriol, trimethylolethane, trimethylolpropane, and 1,3,5-trihydroxymethylbenzene.

In the present invention, one of the above dihydric alcohol components and trihydric or higher polyhydric alcohol components may be used alone, or two or more may be used in combination.

Examples of dicarboxylic acids include maleic acid, fumaric acid, citraconic acid, itaconic acid, glutaconic acid, phthalic acid, isophthalic acid, terephthalic acid, cyclohexanedicarboxylic acid, succinic acid, adipic acid, sebacic acid, azelaic acid, malonic acid, n-dodecenylsuccinic acid, n-dodecylsuccinic acid, n-octylsuccinic acid, isooctenylsuccinic acid, isooctylsuccinic acid, and their acid anhydrides and lower alkyl esters.

Examples of trivalent or higher polycarboxylic acids include 1,2,4-benzenetricarboxylic acid, 1,2,5-benzenetricarboxylic acid, 2,5,7-naphthalenetricarboxylic acid, 1,2,4-naphthalenetricarboxylic acid, 1,2,4-butanetricarboxylic acid, 1,2,5-hexanetricarboxylic acid, 1,3-dicarboxyl-2-methyl-2-methylenecarboxypropane, 1,2,4-cyclohexanetricarboxylic acid, tetra(methylenecarboxyl)methane, 1,2,7,8-octanetetracarboxylic acid, pyromellitic acid, empol trimer acid, and their acid anhydrides and lower alkyl esters.

In the present invention, one of the above dicarboxylic acids and tricarboxylic or higher polycarboxylic acids may be used alone, or two or more of them may be used in combination.

The toner particles according to the present invention preferably contain a crystalline polyester resin and an amorphous polyester resin. In this case, the crystalline polyester resin is dispersed in the amorphous polyester resin.

In the present invention, crystalline resins and amorphous resins are distinguished by their crystallinity index. Resins with a crystallinity index in the range of 0.6 to 1.5 are considered crystalline resins, while resins with a crystallinity index of less than 0.6 or greater than 1.5 are considered amorphous resins. Resins with a crystallinity index of more than 1.5 are amorphous, while resins with a crystallinity index of less than 0.6 have low crystallinity and a large amount of amorphous content.

The crystallinity index is a physical property that indicates the degree of crystallization of a resin, and is defined as the ratio of the softening point to the highest endothermic peak temperature (softening point/highest endothermic peak temperature). Here, the highest endothermic peak temperature refers to the temperature of the highest endothermic peak observed. For crystalline polyester resins, the highest peak temperature is the melting point, and for amorphous polyester resins, the highest peak temperature is the glass transition point.

The degree of crystallization can be controlled by adjusting the type and ratio of raw material monomers, as well as production conditions (e.g., reaction temperature, reaction time, cooling rate).

(Crystalline polyester resin)
The crystalline polyester resin is a polyester resin having a crystallinity index of 0.6 to 1.5, preferably a polyester resin having a crystallinity index of 0.8 to 1.2. The crystalline polyester resin can be obtained, for example, by polycondensation of a polybasic acid and a polyhydric alcohol. For example, it can be produced by a known method such as that described in JP-A-2006-113473.

Examples of polyhydric alcohols include ethylene glycol, 1,2-propylene glycol, 1,3-propylene glycol, 1,4-butanediol, 1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol, neopentyl glycol, and 1,4-butenediol. However, it is preferable to use polyhydric alcohols that promote the crystallinity of the resin, such as aliphatic diols having 2 to 8 carbon atoms. These polyhydric alcohols may be used alone or in combination of two or more.

From the perspective of enhancing the crystallinity of the resin, the content of the aliphatic diol having 2 to 8 carbon atoms in the polyhydric alcohol is preferably 80 mol% or more, and when two or more aliphatic diols having 2 to 8 carbon atoms are used, it is desirable that the content of one aliphatic diol having 2 to 8 carbon atoms in the polyhydric alcohol be 70 mol% or more.

Examples of polybasic acids include aliphatic dicarboxylic acids having 2 to 30 carbon atoms, preferably 2 to 8 carbon atoms, such as fumaric acid, adipic acid, oxalic acid, malonic acid, maleic acid, citraconic acid, itaconic acid, glutaconic acid, succinic acid, sebacic acid, azelaic acid, n-dodecylsuccinic acid, and n-dodecenylsuccinic acid; aromatic dicarboxylic acids such as phthalic acid, isophthalic acid, and terephthalic acid; alicyclic dicarboxylic acids such as cyclohexanedicarboxylic acid; and polycarboxylic acids having a valence of 3 or more, such as trimellitic acid and pyromellitic acid. To achieve a high degree of crystallinity (crystallinity index), aliphatic dicarboxylic acids are preferred, and aliphatic dicarboxylic acids having 2 to 8 carbon atoms are even more preferred. These polybasic acids may be used alone or in combination of two or more.

The acid value of the crystalline polyester resin is preferably 5 mgKOH/g or more and 20 mgKOH/g or less. Furthermore, the hydroxyl value of the crystalline polyester resin is preferably 5 mgKOH/g or more and 20 mgKOH/g or less.

The molecular weight of the crystalline polyester resin is preferably such that the weight average molecular weight (Mw) is 5,000 or more and 100,000 or less, and the number average molecular weight (Mn) is 3,000 or more and 20,000 or less. In the present invention, the weight average molecular weight and number average molecular weight are values measured by gel permeation chromatography (GPC), using chloroform as the mobile phase and polystyrene as the standard.

(Amorphous polyester resin)
The amorphous polyester resin is a polyester resin having a crystallinity index of less than 0.6 or more than 1.5, and preferably a polyester resin having a crystallinity index of more than 1.5. The amorphous polyester resin can be obtained, for example, by polycondensation of a polybasic acid and a polyhydric alcohol.

The polybasic acid can be any known monomer used in polyester synthesis. Examples include aromatic carboxylic acids such as terephthalic acid, isophthalic acid, phthalic anhydride, trimellitic acid, trimellitic anhydride, pyromellitic acid, and naphthalenedicarboxylic acid; aliphatic carboxylic acids such as maleic anhydride, fumaric acid, succinic acid, alkenyl succinic anhydride, and adipic acid; and methyl esters of these polybasic acids. These polybasic acids may be used alone or in combination of two or more.

The polyhydric alcohol may also be a known monomer used in polyester synthesis, such as aliphatic polyhydric alcohols such as ethylene glycol, propylene glycol, butanediol, hexanediol, neopentyl glycol, and glycerin; alicyclic polyhydric alcohols such as cyclohexanediol, cyclohexanedimethanol, and hydrogenated bisphenol A; and aromatic diols such as ethylene oxide adducts of bisphenol A and propylene oxide adducts of bisphenol A. These polyhydric alcohols may be used alone or in combination of two or more.

The polycondensation reaction between a polybasic acid and a polyhydric alcohol can be carried out according to conventional methods. For example, the polybasic acid and the polyhydric alcohol are contacted in the presence or absence of an organic solvent and in the presence of a polycondensation catalyst (e.g., tin octoate). The reaction is terminated when the acid value, softening point, etc. of the resulting polyester reach the desired values. This results in an amorphous polyester resin. If a methyl ester of a polybasic acid is used as part of the polybasic acid, a demethanol polycondensation reaction occurs. In this polycondensation reaction, by appropriately changing the blending ratio and reaction rate of the polybasic acid and polyhydric alcohol, for example, the content of carboxyl groups at the polyester terminals can be adjusted, thereby modifying the properties of the resulting amorphous polyester resin. Furthermore, using trimellitic anhydride as the polybasic acid allows for easy introduction of carboxyl groups into the polyester main chain.

The polycondensation reaction between polybasic acids and polyhydric alcohols is typically carried out at temperatures between 150°C and 300°C, preferably between 170°C and 280°C. The polycondensation reaction can be carried out under normal pressure, reduced pressure, or increased pressure. It is desirable to adjust the pressure within the system appropriately while monitoring the progress of the polycondensation reaction by monitoring physical properties (e.g., acid value, melting point, etc.) and the stirring torque or power value of the reactor.

The acid value of the amorphous polyester resin is preferably 10 KOHmg/g or more and 30 KOHmg/g or less, and more preferably 15 KOHmg/g or more and 25 KOHmg/g or less.

The weight average molecular weight (Mw) of the amorphous polyester resin is preferably 5,000 or more and 50,000 or less, and the number average molecular weight (Mn) is preferably 1,000 or more and 10,000 or less. In the present invention, the weight average molecular weight and number average molecular weight are values measured by gel permeation chromatography (GPC), using tetrahydrofuran (THF) as the mobile phase and polystyrene as the standard.

The glass transition temperature (Tg) of the amorphous polyester resin is preferably 55°C or higher and 70°C or lower.

<Wax>
The toner particles according to the present invention contain a wax as a release agent. The wax may be a wax commonly used in the field of electrophotography. For example, synthetic ester wax, paraffin wax, microcrystalline wax, Fischer-Tropsch wax, polyethylene wax, polypropylene wax, carnauba wax, etc. may be used. One of these may be used alone, or two or more may be used in combination. The wax content in the toner particles is not particularly limited, but is preferably 0.5 to 10% by mass.

<Other internal additives>
Furthermore, the toner particles according to the present invention may contain a colorant, a charge control agent, etc. Components other than external additives are collectively referred to as internal additives. As the colorant, organic dyes, organic pigments, inorganic dyes, inorganic pigments, etc. used in the field of electrophotography can be used. As the charge control agent, charge control agents for positive charge control and negative charge control used in the field of electrophotography can be used.

<External additives>
In the present invention, the external additive contains silica having a volume average particle diameter of 50 nm to 200 nm ("large silica" in the present invention) and a fatty acid metal salt having a volume average particle diameter of 1.5 μm or less. When measured using a flow-type particle image analyzer with a detection limit of 0.5 μm , the content of ultrafine powder having a particle diameter of 2 μm or less in the toner of the present invention is 15.0 to 30.0 number %. When measured using a flow-type particle image analyzer with a detection limit of 0.5 μm, the content of ultrafine powder having a particle diameter of 2 μm or less in the toner after external additive removal treatment is 0.1 to 10.0 number %. When measured using a flow-type particle image analyzer with a detection limit of 0.5 μm , "ultrafine powder having a particle diameter of 2 μm or less in the toner" refers not only to ultrafine powder as toner particles but also to aggregates of external additives present in the toner.

The method for removing external additives in the present invention is as follows.
- Method for removing external additives -
2.0 g of toner is added to 40 ml of a 0.2% by mass aqueous Triton solution, stirred for 1 minute, and then irradiated with ultrasonic waves at 40 μA for 3 minutes using an ultrasonic homogenizer. After leaving the solution for 3 hours after ultrasonic irradiation, the supernatant is removed, and then approximately 50 ml of pure water is added to the precipitate, which is stirred for 5 minutes and then suction filtered using a membrane filter with a pore size of 1 μm. The residue on the filter is vacuum dried overnight to obtain a toner from which external additives have been removed.

By configuring the external additive in this way, it is possible to overcome the challenges of each of the large silica and fatty acid metal salts used as external additives while taking advantage of their respective effects. This suppresses drum filming throughout the product's life, while also reducing developer degradation, maintaining good developability, and reducing image defects such as uneven image density across the printed surface.

As described above, the ultrafine powder content in the toner is 15.0 to 30.0 percent by number, and the ultrafine powder content in the toner after external additive removal is 0.1 to 10.0 percent by number. This means that the proportion of large silica aggregates in the toner is relatively high, and the degree of adhesion of the large silica to the toner particle surface is weak. This allows the large silica aggregates to effectively scrape off filming caused by wax or the like on the photoreceptor drum surface. As a result, the toner of the present invention can suppress drum filming throughout its life. From this perspective, it is more preferable that the ultrafine powder content in the toner (before external additive removal) be 18.0 to 25.0 percent by number. Furthermore, it is more preferable that the ultrafine powder content in the toner after external additive removal is 0.1 to 7.0 percent by number.

The toner of the present invention, due to its ultrafine powder composition, produces a large amount of free silica alone. However, by incorporating a fatty acid metal salt with a volume average particle diameter of 1.5 μm or less as an external additive, the charge-generating adhesive force between the fatty acid metal salt and silica allows the fatty acid metal salt to be adsorbed to the silica and cleaned by the cleaning blade moving over the photoreceptor drum surface. Furthermore, when ultrafine powder is present as toner particles (hereinafter simply referred to as toner ultrafine powder) rather than as aggregates of external additives, its large surface area can cause overcharging, making it difficult to selectively develop and resulting in retention in the developer tank. However, in the toner of the present invention, the fatty acid metal salt, which has the opposite charge polarity, appropriately suppresses overcharging of the ultrafine powder, thereby preventing retention of the ultrafine powder in the developer tank. This ultimately suppresses developer degradation, maintaining good developability over the long term and suppressing image defects such as uneven image density across the printed surface.

The fatty acid metal salt in the toner of the present invention preferably has a volume average particle diameter of 0.3 μm or more and 1.5 μm or less, and more preferably 0.5 μm or more and 1.0 μm or less. By keeping the volume average particle diameter of the fatty acid metal salt within the above range, the effects of the fatty acid metal salt described above can be more effectively exerted. If the volume average particle diameter of the fatty acid metal salt is less than 0.3 μm, the effect of adsorbing large silica will be reduced.

Furthermore, from the viewpoint of the effects of the large silica described above, it is preferable that the large silica in the toner of the present invention has a volume average particle diameter of 50 nm or more and 200 nm or less, and more preferably 75 nm or more and 150 nm or less.

In the toner of the present invention, in an external additive adhesion strength test performed by the following method, the non-adhesion rate of the fatty acid metal salt is preferably 40% to 90% and the strong adhesion rate of the fatty acid metal salt is preferably 25% or less, more preferably 50% to 70% and the strong adhesion rate of the fatty acid metal salt is more preferably 5% to 20%.
- Method for testing the adhesion strength of external additives -
The intensity of elements derived from the external additives is measured for 1 g of a toner sample using a fluorescent X-ray analyzer, and the strong adhesion rate and non-adhesion rate are calculated using the following formula (1) and formula (2), respectively.
(Intensity in sample 1)/(Intensity in sample 0)×100 (1)
100 - (Intensity in Sample 2) / (Intensity in Sample 0) × 100 (2)
In the formula, sample 0 represents the toner before the external additive removal treatment, sample 1 represents the toner after the external additive removal treatment, and sample 2 represents the toner that has been subjected to the external additive removal treatment excluding the ultrasonic irradiation step.

Because it is important for the fatty acid metal salt to be present in the nip between the photosensitive drum and the cleaning blade, it must adhere relatively weakly to the toner particles. However, if the adhesion strength is too weak and the non-adhesion rate is extremely high, too much fatty acid metal salt will detach in the developer tank. Therefore, if the fatty acid metal salt detaches from the toner particles in the developer tank at an appropriate level, it will be effective in suppressing overcharging of the ultrafine toner powder, suppressing deterioration of developability due to overcharging of the ultrafine toner powder and preventing deterioration of developability throughout the toner's life. On the other hand, if the amount of fatty acid metal salt detached from the toner particles is too great, it can cause aggregation of the fatty acid metal salt and toner, resulting in poor image quality. Due to this mechanism, in the toner of the present invention, by keeping the non-adhesion rate and strong adhesion rate of the fatty acid metal salt in the above-mentioned external additive adhesion strength test within the above ranges, the toner maximizes the drum filming suppression effect without deteriorating developability. Rather, by suppressing overcharging of the ultrafine toner powder, good developability can be maintained over the long term, and image defects such as uneven image density within the printed surface can be suppressed.

In the toner of the present invention, the content of fatty acid metal salt is preferably 0.05 to 0.50 parts by weight, and more preferably 0.1 to 0.3 parts by weight, per 100 parts by weight of toner particles. If the content of fatty acid metal salt is less than 0.05 parts by weight, the effect of suppressing drum filming may not be sufficient. If the content of fatty acid metal salt exceeds 0.50 parts by weight, the amount of fatty acid metal salt liberated in the developer tank increases, and the toner charge decreases, making it difficult for the toner to mix into the developer. This deteriorates developability and makes image defects such as uneven image density across the printed surface more likely to occur.

In the toner of the present invention, the non-adhesion rate of large silica in the above-mentioned external additive adhesion strength test is preferably 0% to 10% and the strong adhesion rate of large silica is preferably 40% to 73%. It is more preferable that the non-adhesion rate of large silica is 1% to 5% and the strong adhesion rate of large silica is 55% to 70%. By keeping the non-adhesion rate and strong adhesion rate of large silica within the above ranges, the spacer effect that large silica plays can be exerted and good developability can be achieved. If the non-adhesion rate of large silica exceeds 10% or the strong adhesion rate of large silica is less than 40%, the adhesion strength of the external additive to the toner particles is weak, and the large silica is liberated by agitation in the developer tank, accelerating carrier contamination and degrading the developer, resulting in image defects such as uneven image density across the printed surface due to poor toner mixing. If the strong adhesion rate of large silica exceeds 73%, the large silica adheres too strongly to the toner particles and becomes embedded in the surface of the toner particles, preventing the large silica from exerting its inherent spacer effect.

The large silica in the toner of the present invention has a volume average particle diameter of 50 nm or more and 200 nm or less, and more preferably 75 nm or more and 150 nm or less. By ensuring that the volume average particle diameter of the large silica is within the above range, the non-adhesion rate and strong adhesion rate of the large silica can be achieved appropriately to achieve the effects of the present invention.

In the toner of the present invention, the external additive preferably contains, in addition to the large silica and fatty acid metal salt described above, silica having a volume average particle diameter of 15 nm or less (hereinafter also referred to as small silica). By containing small silica in the external additive, the fluidity of the toner particles can be appropriately improved, making it easier to obtain optimal adhesion strength of the external additive.

In the toner of the present invention, the percentage of particles with a diameter of 1 μm or less among the ultrafine powder (particles with a diameter of 2 μm or less as measured by a flow particle image analyzer with a detection limit of 0.5 μm ) contained in the toner is preferably 50% or more, and more preferably 55% to 65%. Since the particle size distribution of a normal toner is generally close to a normal distribution, in the region of particle diameters of 2 μm or less, the number of particles in the range of 1 μm to 2 μm is greater than the number of particles with a diameter of 1 μm or less. However, in the case of a toner in which the external additive state is controlled to produce a relatively large number of large silica aggregates, many of these aggregates are 1 μm or less, and therefore the particle size distribution of the toner also shows a relatively large number of particles with a diameter of 1 μm or less. In other words, a percentage of 1 μm or less among the ultrafine powder contained in the toner is 50% or more, which means that there are a relatively large number of large silica aggregates, thereby further enhancing the effects of the present invention (excellent uniformity of image density throughout the toner's life and suppression of drum filming).

2. Toner Manufacturing Method An example of a toner manufacturing method according to the present invention includes a kneading step S1 of kneading toner raw materials including a binder resin, a wax, and a colorant to produce a kneaded mixture, a pulverizing step S2 of pulverizing the kneaded mixture produced in the kneading step S1 to produce toner particles, a classification step S3 of classifying the toner particles produced in the pulverizing step S2, and an external addition step S4 of adding an external additive to the toner particles classified in the classification step S3.

(Kneading step S1)
In the kneading step S1, the raw materials for the toner particles, namely, a binder resin, a wax, a colorant, and a charge control agent, are mixed in a mixer such as a Henschel mixer, and then kneaded using a kneader to obtain a kneaded mixture. The kneading is performed by heating to a temperature equal to or higher than the softening point of the binder resin and lower than its thermal decomposition temperature. This melts or softens the binder resin, allowing the colorant, wax, charge control agent, and the like to be dispersed in the binder resin. The specific heating temperature during kneading is preferably, for example, 80°C or higher and 200°C or lower, and more preferably 100°C or higher and 150°C or lower. Examples of kneading machines that can be used include a kneader, a twin-screw extruder, a two-roll mill, a three-roll mill, and a lab blast mill. Examples of such kneaders include single- or twin-screw extruders such as TEM-100B (trade name, manufactured by Toshiba Machine Co., Ltd.), PCM-65, PCM-65/87, and PCM-30 (all of which are trade names, manufactured by Ikegai Corporation), and open-roll type kneaders such as Kneadex (trade name, manufactured by Mitsui Mining Co., Ltd.). The kneading step may also be carried out using a plurality of kneaders.

(Crushing process S2)
In the pulverization step S2, the kneaded material obtained in the kneading step S1 is solidified by cooling or the like, and the solidified material is roughly crushed to obtain a coarsely crushed material. A speed mill, a hammer mill, a cutter mill, or the like can be used as a crusher for the coarse crushing. The coarsely crushed material is then finely crushed (fine crushing step). In the fine crushing step, for example, a jet-type crusher that uses a supersonic jet stream to crush the coarsely crushed material, or an impact-type crusher that introduces the coarsely crushed material into a space formed between a rotor and a stator (liner) rotating at high speed can be used. The finely crushed particle group obtained in the pulverization step S2 may be collected as toner particles without performing the classification step S3 described below.

(Classification process S3)
In the classification step S3, the finely pulverized particles obtained in the pulverization step S2 are classified using a classifier to obtain fine particles having a volume average particle size of 4 μm to 8 μm. As the classifier, for example, a rotary air classifier or the like can be used.

(External addition step S4)
In the external addition step S4, the fine particle group (toner particles) obtained in the classification step S3 is mixed with an external additive using a mixer, and the external additive is attached to the surface of each fine particle to obtain a toner particle group, which is then recovered as toner (externally added toner).

The external addition process S4 includes a first external addition process in which silica having a volume average particle diameter of 50 nm or more and 200 nm or less is mixed with the toner particles to cause the silica to adhere to the surfaces of the toner particles, and a second external addition process in which a fatty acid metal salt having a volume average particle diameter of 1.5 μm or less is mixed with the toner particles to cause the fatty acid metal salt to adhere to the surfaces of the toner particles.

In the toner manufacturing method of the present invention, it is preferable to carry out the first external addition step followed by the second external addition step. Adding the external additions in this order makes it easier to obtain optimal adhesion strength. If the fatty acid metal salt is added simultaneously with or before the silica, the silica and fatty acid metal salt tend to form aggregates, making it difficult to obtain optimal adhesion strength, because silica and fatty acid metal salt typically have opposite charge polarities.

3. Two-Component Developer The two-component developer according to the present invention contains the toner according to the present invention and a carrier. The two-component developer can be produced by mixing the toner and the carrier using a known mixer. The mass ratio of the toner to the carrier is not particularly limited, and may be, for example, 3:97 to 12:88.

The carrier is stirred and mixed with the toner in the developer tank, giving the toner the desired charge. The carrier also acts as an electrode between the development device and the photosensitive drum, transporting the charged toner to the electrostatic latent image on the photosensitive drum and forming a toner image. The carrier is held on the development roller of the development device by magnetic force, and after using it for development, it returns to the development tank, where it is stirred and mixed again with new toner and used repeatedly until the end of its life.

The carrier has a carrier core material and a resin coating layer that coats the carrier core material. There are no particular restrictions on the carrier core material, as long as it is used in the electrophotography field. Specific examples of materials for the carrier core material include magnetic metals such as iron, copper, nickel, and cobalt, and magnetic metal oxides such as ferrite and magnetite. There are no particular restrictions on the volume average particle size of the carrier core material, and examples include 30 μm or more and 100 μm or less. The resin coating layer preferably contains a silicone resin or an acrylic resin. Silicone resin can slow the progression of contamination of the carrier coat layer, making it suitable for long-life use.

The present invention will be explained below based on examples and comparative examples, but the present invention is not limited to these examples. First, the measurements used in the examples will be explained.

<Method for measuring the volume average particle diameter of toner particles>
20 mg of sample and 1 ml of sodium alkyl ether sulfate are added to 50 ml of electrolyte (trade name: ISOTON-II, manufactured by Beckman Coulter, Inc.), and the mixture is dispersed at a frequency of 20 kHz for 3 minutes using an ultrasonic disperser (a tabletop dual-frequency ultrasonic cleaner, model: VS-D100, manufactured by AS ONE Corporation) to obtain a measurement sample. The obtained measurement sample is measured using a particle size distribution measuring device (model: Multisizer 3, manufactured by Beckman Coulter, Inc.) under conditions of an aperture diameter of 100 μm and a measurement particle count of 50,000, and the volume average particle diameter is determined from the volume particle size distribution of the sample particles.

<Method for measuring the proportion of ultrafine particles in toner>
A dispersion was prepared by dispersing 5 mg of sample in 10 ml of water containing approximately 0.1 mg of surfactant. The dispersion was then irradiated with ultrasound at 20 kHz and 50 W for 5 minutes to obtain a dispersion with a toner particle concentration of 5,000 to 20,000 particles/μL. Using a flow particle image analyzer (FPIA-3000, manufactured by Sysmex Corporation), the dispersion containing toner particles was passed through a very thin, flat cell. A strobe light was irradiated and images were taken with a CCD (charge-coupled device) camera to measure the particle diameter of each toner particle, and the percentage of particles 2 μm or smaller was calculated (detection limit: 0.5 μm). The ratio of particles 1 μm or smaller to particles 2 μm or smaller was also calculated.

<Method for removing external additives>
The following steps (1) to (6) are carried out in this order to obtain the toner after the external additive removal treatment.
(1) 2.0 g of toner is added to 40 ml of an aqueous solution of Triton (polyoxyethylene octylphenyl ether) with a concentration of 0.2% by mass, and the mixture is stirred for 1 minute.
(2) The aqueous solution is irradiated with ultrasonic waves using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., model: US-300T) (output: 40 μA, 4 minutes).
(3) After the ultrasonic irradiation, the aqueous solution is left to stand for 3 hours to separate the toner from the liberated external additives.
(4) After removing the supernatant, add approximately 50 ml of pure water to the precipitate and stir for 5 minutes.
(5) The solution is subjected to suction filtration using a membrane filter (manufactured by Advantec Co., Ltd.) with a pore size of 1 μm.
(6) The toner remaining on the filter is vacuum dried overnight.

<Method for measuring non-adhesion rate and strong adhesion rate by external additive adhesion strength test>
The toner sample obtained by carrying out the external additive removal treatments shown in (1) to (6) below is referred to as "Sample 1," the toner sample obtained by carrying out the treatments (1) and (3) to (6) below (treatment excluding (2)) is referred to as "Sample 2," and the toner sample before carrying out the external additive removal treatments shown below is referred to as "Sample 0."
(1) 2.0 g of toner is added to 40 ml of an aqueous solution of Triton (polyoxyethylene octylphenyl ether) with a concentration of 0.2% by mass, and the mixture is stirred for 1 minute.
(2) The aqueous solution is irradiated with ultrasonic waves using an ultrasonic homogenizer (manufactured by Nippon Seiki Seisakusho Co., Ltd., model: US-300T) (output: 40 μA, 4 minutes).
(3) After the ultrasonic irradiation, the aqueous solution is left to stand for 3 hours to separate the toner from the liberated external additives.
(4) After removing the supernatant, add approximately 50 ml of pure water to the precipitate and stir for 5 minutes.
(5) The solution is subjected to suction filtration using a membrane filter (manufactured by Advantec Co., Ltd.) with a pore size of 1 μm.
(6) The toner remaining on the filter is vacuum dried overnight.

Next, the intensity of the specific element in the external additive for 1 g of each of Sample 0, Sample 1, and Sample 2 is analyzed using a fluorescent X-ray analyzer (manufactured by Rigaku Corporation, model: ZSX Primus II), and the strong adhesion rate and non-adhesion rate are calculated using the following formula (1) and formula (2), respectively. The specific element is "Si" for silica, "Zn" for zinc stearate, and "Mg" for magnesium stearate.
(Intensity in sample 1)/(Intensity in sample 0)×100 (1)
100 - (Intensity in Sample 2) / (Intensity in Sample 0) × 100 (2)

Next, we will explain various evaluation methods.

<Method for evaluating uniformity of image density>
The prepared developer and toner were loaded into the developing device and toner cartridge of a color multifunction printer (manufactured by Sharp Corporation, model: BP-20C25), respectively. Next, a continuous print test of 50,000 sheets was carried out on A4 paper in an environment with a temperature of 25°C and a humidity of 5%, so that a 10 mm square solid image (ID = 1.45 to 1.50) was formed at three positions: the center and both ends in the axial direction of the developing roller. The image density of the 50,000th print sample was measured at 10 random positions, and the standard deviation was calculated from each image density. A larger standard deviation indicates lower uniformity.

Based on the calculated standard deviation, the evaluation was made according to the following criteria.
◎ (Excellent): Standard deviation is 0.1 or less.
◯ (Good): The standard deviation is more than 0.1 and 0.2 or less.
△ (Acceptable): Standard deviation is greater than 0.2 and equal to or less than 0.4.
× (unacceptable): The standard deviation is more than 0.4.

<Drum filming evaluation method>
The prepared developer and toner were loaded into the developing device and toner cartridge of a color multifunction printer (manufactured by Sharp Corporation, model: BP-20C25), respectively. Next, a continuous print test of 50,000 sheets of A4 paper was conducted in an environment with a temperature of 25°C and a humidity of 5%, so that 10 mm square solid images (ID = 1.45 to 1.50) were formed at three positions: the center and both ends in the axial direction of the developing roller. Then, a solid image (ID: 1.6 to 1.8) and a halftone (HT) image (ID: 0.5 to 0.7) were printed on A3 paper, and the resulting images were visually observed and evaluated for filming resistance according to the following criteria.

⊚ (Excellent): There are no image defects (white streaks, etc.) in both solid images and HT images, and no streaks are observed on the surface of the photoreceptor.
◯ (Good): There are no image defects (white streaks, etc.) in both the solid image and the HT image, but some streaks are observed on the surface of the photoreceptor.
△ (Acceptable): There are no image defects (white streaks, etc.) in the solid image, but slight image defects (white streaks, etc.) can be seen in the HT image, and streaks are partially observed on the photosensitive member surface.
× (unacceptable): Defects (white streaks, etc.) are observed in both the solid image and the HT image, and streaks are observed all over the surface of the photosensitive member.

<Comprehensive evaluation method>
Based on the above evaluation results (evaluation of image density uniformity and evaluation of drum filming), a comprehensive evaluation was made according to the following criteria.

◎ (Excellent): All evaluation items are ◎. Usable.
○ (Good): The lowest rating of the two items is ○. Usable.
△ (Acceptable): The lowest rating of the two items is △. Usable.
× (Not acceptable): The lowest rating of the two items is ×. Cannot be used.

Next, we will explain the process for producing the toner and two-component developer in the examples and comparative examples.

<Preparation of Toner Particles>
[Preparation of amorphous polyester resin A]
A reaction vessel was charged with 440 g (2.7 mol) of terephthalic acid, 235 g (1.4 mol) of isophthalic acid, 7 g (0.05 mol) of adipic acid, 554 g (8.9 mol) of ethylene glycol, and 0.5 g of tetrabutoxy titanate as a polymerization catalyst. The mixture was reacted at 210°C under a nitrogen stream for 5 hours while distilling off the resulting water and ethylene glycol, followed by a 1-hour reaction under a reduced pressure of 5 to 20 mmHg. Next, 103 g (0.54 mol) of trimellitic anhydride was added, and the mixture was reacted for 1 hour under normal pressure, followed by a 1-hour reaction under a reduced pressure of 20 to 40 mmHg. The resin was extracted at the specified softening point. 219 g (3.5 mol) of ethylene glycol was recovered. The resulting resin was cooled to room temperature and then pulverized into particles. This was designated amorphous polyester resin A. The amorphous polyester resin A had a Tg of 56° C., a Tm of 135° C., an SP value of 11.0, an acid value of 37 mgKOH/g, and a hydroxyl value of 50 mgKOH/g.

[Preparation of Crystalline Polyester Resin C]
A reaction vessel was charged with 132 g (1.12 mol) of 1,6-hexanediol, 230 g (1.0 mol) of 1,10-decanedicarboxylic acid, and 3 g of tetrabutoxy titanate as a polymerization catalyst, and the mixture was reacted at 210°C under atmospheric pressure for 5 hours while distilling off the water produced. The reaction was then continued under a reduced pressure of 5 to 20 mmHg, and the resin was removed when the acid value reached 2 mgKOH/g or less. The resulting resin was cooled to room temperature and then pulverized into particles. This resin was designated as crystalline polyester resin C. Crystalline polyester resin C had a Tmp of 80°C, a Tm of 88°C (Tm/Tmp = 1.1), and an SP value of 9.5.

<Preparation of large silica>
[Preparation of Silica Particles Si-A1]
The silica sol obtained by the sol-gel method was subjected to hydrophobic treatment (HMDS treatment) to obtain hydrophobic silica. Nucleus growth was controlled so that the volume average particle diameter was 100 nm.

[Preparation of Silica Particles Si-A2]
In the method for producing the silica particles Si-A1, the nucleus growth was controlled so that the volume average particle size was 200 nm.

[Preparation of Silica Particles Si-A3]
In the method for producing the silica particles Si-A1, the nucleus growth was controlled so that the volume average particle size was 50 nm.

[Preparation of Silica Particles Si-A4]
In the method for producing the silica particles Si-A1, the nucleus growth was controlled so that the volume average particle diameter was 220 nm.

[Preparation of Silica Particles Si-A5]
In the method for producing the silica particles Si-A1, the nucleus growth was controlled so that the volume average particle diameter was 30 nm.

Example 1
[Material mixing, kneading, pulverization, and classification processes]
Binder resin: amorphous polyester resin A 80% by mass
Colorant: Colorant (C.I. Pigment Blue 15:3, manufactured by DIC) 6% by mass
Release agent: Release agent (manufactured by NOF Corporation, product name: WEP3) 5% by mass
Charge control agent: salicylic acid compound (Orient Chemical Industry Co., Ltd., product name: Bontro E84) 1% by mass
Crystalline polyester resin: crystalline polyester resin C 8% by mass

The above materials were premixed for 5 minutes using a Henschel mixer (manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke and Engineering Co., Ltd.), model: FM20C), and then melt-kneaded using an open-roll continuous kneader (product name: MOS320-1800, manufactured by Mitsui Mining Co., Ltd.) [Kneading process].

The open roll settings were: the supply side temperature of the heating roll was 130°C, the discharge side temperature was 100°C, and the supply side temperature of the cooling roll was 40°C, and the discharge side temperature was 25°C. The heating roll and cooling roll both had a diameter of 320 mm and an effective length of 1550 mm, with a roll gap of 0.3 mm on both the supply side and discharge side. The rotation speed of the heating roll was 75 rpm, the rotation speed of the cooling roll was 65 rpm, and the toner raw material supply rate was 5.0 kg/h.

The resulting molten mixture was cooled on a cooling belt and then coarsely pulverized using a speed mill equipped with a φ2 mm screen. The resulting coarsely pulverized material was then finely pulverized using a jet pulverizer (manufactured by Nippon Pneumatic Mfg. Co., Ltd., Model: IDS-2) to obtain a finely pulverized material [Fine-pulverizing process].

The resulting finely pulverized material was then classified using an elbow jet classifier (manufactured by Nittetsu Mining Co., Ltd., model: EJ-LABO) to obtain a classified material [classification process].

The resulting toner particles had a volume average particle diameter of 6.7 μm. The amount of ultrafine powder in the resulting toner particles was 5%.

[External addition process]
To 100 parts by mass of the obtained toner particles, 1.0 part by mass of silica particles "Si-A1" and 1.0 part by mass of silica particles "R976S" (manufactured by Nippon Aerosil Co., Ltd., particle size: 7 nm) were added, and the mixture was stirred for 4 minutes using an air flow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke and Engineering Co., Ltd.), model: FM20C) with the tip speed of the stirring blade set to 40 m/sec. Thereafter, 0.2 parts by mass of zinc stearate particles having a particle size of 0.7 μm (manufactured by NOF Corporation, product name: "MZ-2") were added, and the tip speed of the air flow mixer was set to 40 m/sec and the mixture was stirred for 2 minutes, thereby obtaining an externally added toner.

The amount of ultrafine powder in the resulting externally added toner was 20%, of which 55% was below 1 μm. Furthermore, after the external additive adhesion strength test, the amount of ultrafine powder in the toner was 5%. The non-adhesion rate for zinc stearate particles was 60%, the strong adhesion rate was 10%, and the non-adhesion rate for silica was 3%, and the strong adhesion rate was 65%.

[Resin-coated carrier manufacturing process]
0.375 parts by mass of coating resin 1 (silicone-based, trade name: KR240, manufactured by Shin-Etsu Chemical Co., Ltd.) and 0.375 parts by mass of coating resin 2 (trade name: KR251, manufactured by Shin-Etsu Chemical Co., Ltd.) were dissolved in 12 parts by mass of toluene, and 0.0375 parts by mass of conductive particles (trade name: VULCAN XC-72, manufactured by Cabot Corporation) and 0.0225 parts by mass of a coupling agent (trade name: AY43-059, manufactured by Dow Corning Toray Co., Ltd.) were added and dispersed to prepare a coating resin solution. 12.8 parts by mass of the coating resin solution was used by the immersion method to coat the surface of 100 parts by mass of a ferrite carrier core material having a volume average particle diameter of 40 μm. After that, a curing process was carried out at a curing temperature of 200 ° C. and a curing time of 1 hour, and the resulting mixture was passed through a sieve with a mesh size of 150 μm to prepare a resin-coated carrier.

[Developer manufacturing process]
The obtained toner containing external additives and the resin-coated carrier were mixed so that the concentration of the toner containing external additives relative to the total amount of the two-component developer was 7%, thereby obtaining a two-component developer with a toner concentration of 7%.

<Examples 2, 3, 7 to 9, 14 to 19, Comparative Examples 1, 2, and 6>
The large silica, fatty acid metal salt, and small silica used in the examples and comparative examples are listed in Tables 1 to 3 below, and the types of external additives used in each example and comparative example are listed in Table 4 below. An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the type of large silica, the type and amount of fatty acid metal salt, and the type of small silica were changed as shown in these tables.

Example 4
An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the time for the first external addition was changed to 2 minutes and the time for the second external addition was changed to 2 minutes.

Example 5
An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the time for the first external addition was changed to 6 minutes and the time for the second external addition was changed to 2 minutes.

Example 6 and Comparative Example 5
An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the conditions in the classification step were changed to adjust the amount of ultrafine powder while keeping the volume average particle diameter of the toner at 6.7 μm.

Example 10
An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the time for the first external addition was changed to 5 minutes and the time for the second external addition was changed to 1 minute.

Example 11
An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the time for the first external addition was changed to 3 minutes and the time for the second external addition was changed to 3 minutes.

Example 12
An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the time for the first external addition was changed to 5 minutes 30 seconds and the time for the second external addition was changed to 30 seconds.

Example 13
An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the time for the first external addition was changed to 2 minutes and the time for the second external addition was changed to 4 minutes.

Example 20
Toner particles were obtained by performing the material mixing, kneading, pulverization, and classification steps in the same manner as in Example 1. Next, in the external addition step, 1.0 part by mass of silica particles "R976S" (manufactured by Nippon Aerosil Co., Ltd., particle size: 7 nm) was added to 100 parts by mass of the toner particles, and the mixture was stirred for 4 minutes using an air flow mixer (Henschel mixer, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke & Engineering Co., Ltd.), model: FM20C) with the tip speed of the stirring blade set to 40 m/s. Thereafter, 1.0 part by mass of silica particles "Si-A1" and 0.2 part by mass of zinc stearate particles having a particle size of 0.7 μm (manufactured by NOF Corporation, product name: MZ-2) were added, and the tip speed of the air flow mixer was set to 40 m/s and the mixture was stirred for 2 minutes to obtain an externally added toner. A two-component developer was prepared in the same manner as in Example 1.

<Comparative Example 3>
An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the time for the first external addition was changed to 1 minute and the time for the second external addition was changed to 2 minutes.

<Comparative Example 4>
An externally added toner and a two-component developer were obtained in the same manner as in Example 1, except that the time for the first external addition was changed to 8 minutes and the time for the second external addition was changed to 2 minutes.

The evaluation results for the toners and two-component developers of the examples and comparative examples prepared in this manner are listed in Table 5 below.

As is clear from Table 5, the toners and two-component developers of Examples 1 to 20, which are toners having external additives adhered to the surfaces of toner particles, and which contain silica having a volume average particle diameter of 50 nm to 200 nm and a fatty acid metal salt having a volume average particle diameter of 1.5 μm or less, and in which the content of ultrafine powder having a particle diameter of 2 μm or less in the toner is 15.0 to 30.0 number % when measured with a flow-type particle image analyzer having a detection limit of 0.5 μm, and in which the content of ultrafine powder having a particle diameter of 2 μm or less in the toner after external additive removal treatment is 0.1 to 10.0 number % when measured with a flow-type particle image analyzer having a detection limit of 0.5 μm, were excellent in both the evaluation of image density uniformity and the evaluation of drum filming.

This can be seen particularly from the evaluation results of Examples 1 to 8, which examined the upper and lower limits of the volume average particle diameter of the large silica, the volume average particle diameter of the fatty acid metal salt, and the content of ultrafine powder in the toner before and after external additive removal processing.

In contrast, Comparative Examples 1 to 6, which did not meet these requirements, were inferior to the Examples in at least one of the evaluations of image density uniformity and drum filming.

In the external additive adhesion strength test, Examples 10 and 11, in which the non-adhesion rate of fatty acid metal salt was 40% or more but 90% or less and the strong adhesion rate of fatty acid metal salt was 25% or less, were found to be superior in evaluation of image density uniformity and drum filming compared to Examples 12 and 13, which did not meet these requirements.

It can be seen that Examples 14 and 15, in which the fatty acid metal salt content is 0.05 parts by mass or more and 0.50 parts by mass or less per 100 parts by mass of toner particles, are superior in evaluation of image density uniformity and drum filming to Examples 16 and 17, which do not meet this requirement.

In the external additive adhesion strength test, Example 2, in which the non-adhesion rate of large silica was between 0% and 10% and the strong adhesion rate of large silica was between 40% and 73%, was found to be superior in the evaluation of image density uniformity to Example 4, which did not meet these requirements.

It can be seen that Example 1, which contains silica with a volume average particle diameter of 15 nm or less (small silica) as an external additive, is superior in the evaluation of image density uniformity to Example 19, which contains silica with a volume average particle diameter of 30 nm.

Example 1, in which silica and fatty acid metal salt were added to the toner particles in the external addition process, was superior in overall evaluation to Example 20, in which fatty acid metal salt and silica were added in that order, and was particularly superior in evaluation of image density uniformity.

<Other embodiments>
It should be noted that the embodiments disclosed herein are illustrative in all respects and are not intended to be limiting. Therefore, the technical scope of the present invention should not be interpreted solely by the above-described embodiments, but should be defined by the claims. The technical scope of the present invention also includes all modifications within the scope and meaning equivalent to the claims.

Claims (7)

A toner having an external additive attached to the surface of a toner particle,
the external additive contains silica having a volume average particle diameter of 100 nm or more and 200 nm or less, and a fatty acid metal salt having a volume average particle diameter of 1.5 μm or less,
In an external additive adhesion strength test performed by the following method, the non-adhesion rate of the silica is 0% or more and 10% or less, and the strong adhesion rate of the silica is 40% or more and 73% or less,
the content of ultrafine powder having a particle diameter of 2 μm or less in the toner is 15.0% by number or more and 30.0% by number or less, when measured using a flow particle image analyzer with a detection limit of 0.5 μm ;
A toner characterized in that the content of ultrafine powder having a particle diameter of 2 μm or less in the toner after external additive removal treatment performed by the following method is 0.1% by number or more and 10.0% by number or less, when measured using a flow-type particle image analyzer with a detection limit of 0.5 μm.
<Method for removing external additives>
2.0 g of toner is added to 40 ml of a 0.2% by mass aqueous Triton solution, stirred for 1 minute, and then irradiated with ultrasonic waves at 40 μA for 3 minutes using an ultrasonic homogenizer. After leaving the solution for 3 hours after ultrasonic irradiation, the supernatant is removed, and then approximately 50 ml of pure water is added to the precipitate, which is stirred for 5 minutes and then suction filtered using a membrane filter with a pore size of 1 μm. The residue on the filter is vacuum dried overnight to obtain a toner from which external additives have been removed.
<External additive adhesion strength test method>
The intensity of elements derived from the external additives is measured for 1 g of a toner sample using a fluorescent X-ray analyzer, and the strong adhesion rate and non-adhesion rate are calculated using the following formula (1) and formula (2), respectively.
(Intensity in sample 1)/(Intensity in sample 0)×100 (1)
100 - (Intensity in Sample 2) / (Intensity in Sample 0) × 100 (2)
In the formula, sample 0 represents the toner before the external additive removal treatment, sample 1 represents the toner after the external additive removal treatment, and sample 2 represents the toner that has been subjected to the external additive removal treatment excluding the ultrasonic irradiation step. 2. The toner according to claim 1,
The toner is characterized in that, in the external additive adhesion strength test, the non-adhesion rate of the fatty acid metal salt is 40% or more and 90% or less, and the strong adhesion rate of the fatty acid metal salt is 25% or less. 3. The toner according to claim 1 or claim 2 ,
The toner, wherein the content of the fatty acid metal salt is 0.05 parts by mass or more and 0.50 parts by mass or less with respect to 100 parts by mass of the toner particles. The toner according to any one of claims 1 to 3 ,
The toner is characterized in that the external additive further contains silica having a volume average particle diameter of 15 nm or less. The toner according to any one of claims 1 to 4 ,
The toner is characterized in that, when measured by a flow-type particle image analyzer with a detection limit of 0.5 μm, the proportion of particles having a particle diameter of 1 μm or less in the ultrafine powder is 50% or more. A method for producing the toner according to any one of claims 1 to 5 ,
a first external addition step of mixing silica having a volume average particle diameter of 100 nm or more and 200 nm or less with the toner particles to cause the silica to adhere to the surfaces of the toner particles;
a second external addition step of mixing the fatty acid metal salt with the toner particles to cause the fatty acid metal salt to adhere to the surfaces of the toner particles,
A method for producing a toner, comprising the steps of: performing the first external addition step; and then performing the second external addition step. A two-component developer comprising the toner according to any one of claims 1 to 5 and a carrier.